Sanitary rubber composition or article
This is a rule 60 divisional of Ser. No. 833,713, filed Feb. 27, 1986. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to sanitary rubber compositions or articles having excellent chemical and physical properties and more particularly, it is concerned with a sanitary rubber composition or article comprising a rubber blended with a finely divided polyethylene powder of a superhigh molecular weight. By the sanitary rubber composition or article, we mean rubber articles in contact with foods, rubber closures or plugs for pharmaceutical vessels, rubber products attached to medical instruments, rubber articles used for human bodies and animals and the like, which have some influences upon human bodies and animals directly or indirectly and which are different from industrial rubber articles, tires and foot wears in chemical and physical properties. That is to say, the sanitary rubber article of the present invention includes rubber articles for foods, drugs, cosmetics, veterinary medicines, feeds and radiation protection, which comes under the administration of the Food and Drug Administration. 
     2. Description of the Prior Art 
     For rubber closures for drugs, for example, about 30 examination and test items must be satisfied. These items include provisions for solving problems such as the following: (1) if an additive used as an essential component for a synthetic rubber is released from the surface of a product, it becomes added to a medical fluid as fine particles, (2) when a rubber closure of a vial is pierced by an injection needle, rubber pieces are broken off and added to a medical fluid and (3) if an opening is formed when the injection needle pierces the rubber closure, a medical fluid may issue and spoil clothes. Thus, sanitary rubber articles must be prepared so as to satisfy these newly added requirements. 
     Up to the present time, it has been proposed to add low molecular weight polyethylene to various rubbers (Japanese Patent Publication No. 5973/1960, Canadian Patent No. 846831/1962) and to produce a rubber plug for an injection fluid by blending a natural rubber or synthetic rubber with a fine powder of polyethylene (Japanese Patent Publication No. 8789/1970). In these techniques, however, a fine powder of polyethylene should be used in a proportion of 1 to 10% by weight with carbon black and lithopone (ZnS+BaSO 4 ) as a reinforcing agent, since the bridging efficiency is low and the physical properties of a bridged product are inferior. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a sanitary rubber composition or article capable of satisfying the quality standard. 
     It is another object of the present invention to provide a rubber closure for an injection, having excellent chemical and physical properties. 
     It is a further object of the present invention to provide a rubber composition for a sanitary article, containing no inorganic filler or reinforcing agent. 
     These objects can be attained by a rubber composition for a sanitary article comprising a synthetic rubber and a fine powder of polyethylene with a mean molecular weight of 1,000,000 to 1,000,000,000. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The inventor has made various efforts over a long time and consequently, has found that a sanitary rubber article which can favorably be compared with rubber articles of the prior art using ordinary additives is obtained by mixing a synthetic rubber prepared by solution polymerization with a fine powder of polyethylene having a mean molecular weight of 1×10 6  to 1×10 9 , bridging with a bridging agent and forming. 
     Accordingly, the present invention provides a rubber composition for a sanitary article, comprising a synthetic rubber, particularly prepared by solution polymerization, and a finely divided powder of polyethylene having a mean molecular weight of 1×10 6  to 1×10 9  (hereinafter referred to as HMWPE) and a sanitary rubber article such as rubber closure for an injection fluid, comprising a blend of a synthetic rubber and HMWPE, which has been bridged and shaped. 
     That is to say, in the present invention, sanitary rubber articles, for example, rubber closures for injectable products such as wads, plugs with or without a skirt or flange and caps, having excellent physical properties (tensile strength, elongation, etc.) and sanitary properties (KMnO 4  consumption, ultraviolet absorption spectrum, etc. of the extraction solution) can be obtained by adding only HMWPE to a synthetic rubber prepared by solution polymerization, followed by bridging and shaping. Generally, HMWPE is added in a proportion of 3 to 50 parts by weight to 100 parts by weight of a synthetic rubber. 
     However, because there are a number of requirements to sanitary rubber products and a number of requirements to be satisfied, addition of only HMWPE is sometimes insufficient. In such cases, other additives such as silicon oxide, aluminum silicates, magnesium silicates, clays and titanium oxides can be added in a proportion of 1 to 30 parts by weight to 100 parts by weight of a synthetic rubber for the purpose of improving the abrasion resistance, flexibility resistance and compression set. If the addition exceeds 30 parts by weight, the bridged rubber product is not suitable as a sanitary rubber article because of increase of the KMnO 4  consumption and residue on evaporation of the extraction solution. 
     When the quantity of HMWPE is more than 50 parts by weight, the bridged rubber product is not suitable as a sanitary rubber article because of the higher hardness, the resinous properties in the quantity of strain and degree of crystallization and the lower viscoelasticity at a high temperature. HMWPE is a polyethylene, for example, prepared by polymerizing ethylene gas at a pressure of 0 to 7 atm in the presence of a Ziegler catalyst consisting of triethylaluminum and carbon tetrachloride in combination and the mean molecular weight is at least 1×10 6  as determined by the viscosity method or at least 3×10 6  as determined by the light scattering method, while an ordinary polyethylene (referred to as PE) has a molecular weight of 2-10×10 4  as determined by the viscosity method or 6-30×10 4  as determined by the light scattering method. 
     Comparison of the properties of HMWPE and PE is tabulated below: 
     
         ______________________________________                                    
Properties   HMWPE     PE       Test Method                               
______________________________________                                    
Density (g/cc)                                                            
             0.93-0.94 0.92-0.94                                          
                                ASTM D 1505                               
Tensile Strength at                                                       
             400-440    90-170  ASTM D 638                                
Breaking Point                                                            
(kg/cm.sup.2)                                                             
Elongation at                                                             
             350-400   150-750  ASTM D 638                                
Breaking Point                                                            
Melting Point (°C.)                                                
             136       105-118  ASTM D 2117                               
Vicat Softening                                                           
             134        76-115  ASTM D 1525                               
Point (°C.)                                                        
Thermal Deformation                                                       
              85       --       ASTM D 648                                
Temperature (°C.)                                                  
______________________________________                                    
 
    
     Preparation of a finely divided powder of HMWPE is carried out by mechanically crushing pellets of high molecular weight polyethylene in the air or water, by dissolving it in a hot solvent such as carbon tetrachloride or trichloroethylene and then cooling rapidly or mixing it with water or alcohol to precipitate it in the form of fine particles. 
     Preferably, HMWPE having a particle size small enough to pass through a sieve of 72μ (200 mesh) is used, but the presence of large amounts of fine particles of less than 1μ is not desirable since scattering takes place due to electrification and dispersion in the rubber is prevented. 
     When small samples of HMWPE are viewed under an electron microscope, a number of cracks can be seen on the surfaces of the particles and a number of heteromorphic particles can be seen. Therefore, it is assumed that a synthetic rubber and HMWPE form a polymer network and thus HMWPE gives more excellent sanitary products than PE in respect of improving the abrasion resistance, impact strength, heat and deformation resistance, chemical and solvent resistance and safety property. In the present invention, accordingly, a sanitary rubber product can be produced without using inorganic reinforcing agents or fillers such as aluminum silicate, magnesium silicate and barium sulfate, and vulcanizing agents. 
     As the synthetic rubber of the present invention, the rubbers used can be prepared by solution polymerization, for example, isobutylene-isoprene rubber (IIR), chlorinated isobutylene-isoprene rubber (CIIR), brominated isobutylene-isoprene (BIIR), isobutylene-isoprene-divinylbenzene copolymer, ethylene-propylene rubber (EPM), ethylene-propylenediene rubber (EPDM), chlorosulfonated polyethylene (CSM), epichlorohydrin rubber (CO, ECO, GCO, GECO), butadiene rubber (BR), isoprene rubber (IR), styrene-butadiene rubber (SBR), isoprene-styrene rubber (SIR) and ethylene-vinyl acetate copolymer (EAM). These rubbers can be used individually or in combination. Thermoplastic rubbers of styrenebutadiene or styrene-isoprene can also be used. Synthetic rubbers by emulsion polymerization and natural rubbers are not suitable for sanitary rubber articles due to the presence of emulsifiers and proteins, respectively. 
     Organic peroxides, which can be used as a vulcanizing agent in the present invention, are for example dicumyl peroxide, 1,4-di-(t-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexyne-3 and the like. 
     In addition, as another bridging agent, there are sulfur- or organosulfur-imparting vulcanizing agents and as a bridging aid, there are vulcanization accelerating agents, vulcanization activating agents, processing aids, vulcanization retarding agents and the like, typical of which are zinc white, stearic acid, magnesium oxide, tetramethyl-thiuram disulfide, tetraethylthiuram disulfide, dipentamethylene tetrasulfide, zinc di-n-butyl-dithiocarbamate, zinc diethyldithiocarbamate, N-cyclohexyl-2-benzothiazolylsulfenamide, N-t-butyl-2-benzothiazolyl-sulfenamide, tetramethylthiuram monosulfide, fatty acid esters and fluorine-containing lubricants. These agents are generally added in a proportion of 0.05 to 10 parts by weight to 100 parts by weight of a synthetic rubber. 
     Furthermore, organosilane compounds such as vinyltriethoxysilane, vinyltriacetylsilane, vinyl-tris(β-methoxyethoxy)silane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, RTV silicone rubbers, silicone oils and the like can also be added in a proportion of 0.05 to 3 parts by weight to 100 parts by weight of a synthetic rubber. 
     The rubber composition of the present invention can be subjected to radiation vulcanization, for example, by the use of an electron beam. 
     As the sanitary rubber product or article of the present invention, for example, there are given rubber parts for rice cookers, sealants for water bottles or cans, rubber closures for vials of medicines or chemicals and medical devices such as parts of artificial kidneys, syringes, etc. 
     The following examples are given in order to illustrate the present invention in detail without limiting the same. 
     EXAMPLES 
     HMWPE (Hizex Million 240 M -commercial name-manufactured by Mitsui Sekiyu Kagaku Kogyo KK. molecular weight=200×10 4  as determined by viscosity method, grain size=capable of passing through a sieve of 105μ, melting point=136° C.) was added to IIR (JSR Butyl 365 -commercial name-, unsaturation degree=2.0 mol %, ML 1+4  (100° C.)=45) in proportions as shown in Table 1, mixed at a temperature of 80° to 120° C. in a pressure kneader (made by Moriyama Seisakujo KK), compounded with bridging systems as shown in Table 1 in a biaxial rubber roll according to ASTM D 3188 (&#39;73) and then subjected to a test using an oscillating disk rheometer (hereinafter referred to as ODR) (made by Toyo Seiki Seisakujo KK) according to ASTM D-2705 (&#39;76), thus obtaining results as shown in Table 2. 
     
                       TABLE 1                                                     
______________________________________                                    
        Examples   Comparative Examples                                   
Components                                                                
          1      2      3    4    3     2    1                            
______________________________________                                    
IIR: JSR 365                                                              
          100    100    100  100  100   100  100                          
HMWPE      43    20.5   5.3                                               
Polyethylene.sup.(1)              5.3   20.5  43                          
Zinc Oxide                                                                
           2      2      2    2    2     2    2                           
Stearic Acid                                                              
          0.5     0.5   0.5  0.5  0.5    0.5 0.5                          
Sulfur     1      1      1    1    1     1    1                           
Vulcanization                                                             
Accelerator                                                               
TRA.sup.(2)                                                               
          0.4     0.4   0.4  0.4  0.4    0.4 0.4                          
BZ.sup.(3)                                                                
          0.7     0.7   0.7  0.7  0.7    0.7 0.7                          
______________________________________                                    
 Note:                                                                    
 .sup.(1) FLOTHENE UF  commercial name  manufactured by Seitetsu Kagaku KK
 grain size = capable of passing through a sieve of ASTM No. 80, melting  
 point = 103-111° C., high density                                 
 .sup.(2) dipentamethylene thiuram hexasulfide                            
 .sup.(3) zinc din-butyl dithiocarbamate                                  
 
    
     
                       TABLE 2                                                     
______________________________________                                    
ODR Test (temp 160° C., amplitude angle 3°)                 
          Examples   Comparative Examples                                 
          1    2      3      4    3    2    1                             
______________________________________                                    
Torque (kg/cm)                                                            
Initial (a) 32.0   26.2   22.0 20.1 22.4 30.8 38.3                        
Minimum (b) 24.5   20.5   16.4 15.8 14.8 12.3 11.2                        
Maximum (c) 48.5   44.0   38.5 36.7 33.6 27.6 22.3                        
(c)-(b)     24.0   23.5   22.1 20.9 18.8 15.3 11.1                        
Cure Time (minute)                                                        
tc (10)      2.9    2.9    2.9  2.9  2.9  3.0  3.1                        
tc (90)      8.6    8.7    8.9  9.9  9.8  9.9  9.9                        
tc (90)-(10)                                                              
             5.7    5.8    6.0  7.0  6.9  6.9  6.8                        
______________________________________                                    
 
    
     As apparent from these results, HMWPE is capable of increasing the torque, while PE decreases the torque, the difference increasing with the larger the quantity of HMWPE. PE acts as a softening agent and as an agent that hinders the vulcanization action of IIR. 
     
                       TABLE 3                                                     
______________________________________                                    
Physical Properties of Vulcanizates.sup.(1)                               
          Examples   Comparative Examples                                 
          1    2      3      4    3    2    1                             
______________________________________                                    
Hardness (Hs)                                                             
            59     45     34   30    36   59   76                         
300% Modulus                                                              
            36     20     13   10    9    15   20                         
(kg/cm.sup.2)                                                             
Tensile Strength                                                          
            76     76     69   76   107  118  115                         
(kg/cm.sup.2)                                                             
Elongation at                                                             
            460    500    750  800  830  820  800                         
Break (%)                                                                 
Permanent Set (%)                                                         
            2.7    2.0    3.2  3.4  5.9  29.6 65.6                        
______________________________________                                    
 Note:                                                                    
 .sup.(1) vulcanization temperature 160° C. × 30 minutes     
 according to JIS K 6301 (1975)                                           
 The vulcanization was carried out according to SRIS3603 and the test of  
 the vulcanizates was carried out according to JIS K6301 (1975).          
 
    
     A sanitation test was carried out by extracting a sample in water at 90° C. for 30 minutes and determining the residue on evaporation and the consumption of potassium permanganate according to JIS 9010 (1982). 
     
                       TABLE 4                                                     
______________________________________                                    
Sanitation Test                                                           
          Examples  Comparative Examples                                  
          1    2     3      4    3    2    1                              
______________________________________                                    
Residue on Evapor-                                                        
            3.2    4.2   6.1  8.3  12.6 23.2 36.8                         
ation (ppm)                                                               
KMnO.sub.4 Reducing                                                       
            4.6    5.2   6.3  7.8   9.6 12.8 15.6                         
Substance (ppm)                                                           
______________________________________                                    
 
    
     As apparent from the results of Tables 3 and 4, HMWPE is capable of improving the modulus, permanent set, residue on evaporation and consumption of KMnO 4 , while PE hinders the curing. 
     It can clearly be understood that HMWPE and PE have the similar physical properties, but show completely different performances when added to IIR and the like. For example, HMWPE and PE have the following physical properties in the form of films: 
     
         ______________________________________                                    
Tensile Strength (kg/cm.sup.2)                                            
                    Elongation at Break (%)                               
______________________________________                                    
HMWPE  236              690                                               
PE     206              880                                               
______________________________________                                    
 
    
     EXAMPLE 4 
     Using the following composition, mixing was carried out in an analogous manner to Examples 1-3: 
     
                       TABLE 5                                                     
______________________________________                                    
CIIR (CHLORO BUTYL 1066.sup.(1))                                          
                    100     parts by weight                               
HMWPE (HIFAX 1900.sup.(2))                                                
                    28                                                    
Zinc Oxide          1                                                     
Magnesium Oxide     2                                                     
Stearic Acid        0.3                                                   
Tetramethylthiuram Disulfide                                              
                    0.6                                                   
Zinc Diethyldithiocarbamate                                               
                    0.6                                                   
______________________________________                                    
 Note:                                                                    
 .sup.(1) commercial name, manufactured by Exxon Chemical                 
 .sup.(2) commercial name, manufactured by Hercules, mean molecular weight
 as determined by viscosity method = 700 × 10.sup.4, density = 0.94,
 grain size = capable of passing through a sieve of ASTM No. 70, tensile  
 strength of film = 239 kg/cm.sup.2                                       
 
    
     Vulcanization of the compound was carried out by pressing at a temperature of 150° C. for 30 minutes according to JIS K 6301. 
     
                       TABLE 6                                                     
______________________________________                                    
Physical Properties of Vulcanizates.sup.(1)                               
______________________________________                                    
Hardness (Hs)       38                                                    
500% Modulus (kg/cm.sup.2)                                                
                    32                                                    
Tensile Strength (kg/cm.sup.2)                                            
                    122                                                   
Elongation at Break (%)                                                   
                    760                                                   
Permanent Set (%)   3.8                                                   
______________________________________                                    
 Note:                                                                    
 .sup.(1) temperature 150° C. × 30 minutes according to JIS K
 6301                                                                     
 
    
     The rubber sample was first washed with a dilute alkali (e.g. NaHCO 3 ) and then extracted with an amount of water 10 times the weight of the rubber at a temperature of 121° C. for 60 minutes according to the test method of rubber closures for aqueous infusions as specified in The Pharmacopoeia of Japan 41. The test results of the extracted liquid and the standard values of The Pharmacopoeia of Japan are shown in Table 7: 
     
                       TABLE 7                                                     
______________________________________                                    
Extraction Test                                                           
                           Standard                                       
                Measured Value                                            
                           Value                                          
______________________________________                                    
Description (%)   99.5         99.0                                       
Foam Test (min)   2            3                                          
pH                0.8          ±1                                      
Zinc (μg/ml)   0.01         0.5                                        
KMnO.sub.4 -reducing Substance (ml)                                       
                  0.8          2.0                                        
Residue on Evaporation (mg)                                               
                  0.8          2.0                                        
Ultraviolet Absorption Spectrum                                           
                  0.08         0.2                                        
______________________________________                                    
 
    
     Specificity tests were also carried out as follows: 
     (1) Insoluble Particulate Matter Test 
     10 rubber closures are placed in a hard glass bottle to which 100 ml of dust-free water is added and which is shaked for 20 seconds, then allowed to stand for 1 hour and subjected to measurement 4 times using a light-shielded type automatic fine particle meter (PC-320, -commercial name- made by HIAC/Royco Co.). The initial data is discarded and a mean value is taken of the next three data. 
     (2) Determination of Fragmentation 
     According to British Standard 3263 (1960), water is charged in a bottle, which is then closed by the rubber closure and fastened by an aluminum cap. A part of the aluminum cap is removed for the ease of penetration by an injection needle and a standard test needle with an outer diameter of 0.72 mm (22 G made by TOP) is penetrated through it 10 times. Then, the bottle is shaken several times and the number of rubber fragments in the water is counted. 
     (3) Determination of Penetrability 
     According to British Standard 3263 (1960), the force of penetration is measured by the use of a SHIMAZU AUTOGRAPH (commercial name, made by Shimazu Seisakujo KK) when a standard test needle with an outer diameter of 0.72 mm is passed through the central part of the rubber closure. 
     (4) Determination of Self-Sealability 
     Water is charged in a bottle of 500 ml, which is then closed by the rubber plug, fastened by an aluminum cap, heated at 121° C. for 30 minutes and cooled. A standard test needle is allowed to penetrate &#34;OUT&#34; part of the rubber closure and the bottle is allowed to stand in an inverted state for 1 hour. Then, an air needle is allowed to penetrate through it to let 400 ml of the water out of the bottle, the test needle is withdrawn and at the same time, the quantity of water flowing out is measured. 
     The results of the above described tests are shown in Table 8: 
     
                       TABLE 8                                                     
______________________________________                                    
                   Measured                                               
                           Standard                                       
                   Value   Value                                          
______________________________________                                    
Insoluble Particulate Matter Test                                         
10 μm (number)     1         10                                        
5 μm (number)      46        100                                       
Determination of Fragmentation                                            
                     no          3                                        
Determination of Penetrability (g)                                        
                     460       1000                                       
Determination of Self-Sealability (ml)                                    
                     0.5                                                  
______________________________________                                    
 
    
     It will be apparent from the results of the specificity test as shown in Table 8 that the rubber sample satisfied all the standard requirements and above all, showed better results in the insoluble particulate matter test than rubber plugs produced by the prior art processes. 
     EXAMPLES 5 TO 8 
     Blending was carried out according to &#34;Test Method of Rubber&#34;, page 108-118, i.e. ASTM standard method: 
     
                       TABLE 9                                                     
______________________________________                                    
            Examples                                                      
            5     6       7        8                                      
______________________________________                                    
Rubber        BIIR.sup.(1)                                                
                      CSM.sup.(2)                                         
                              GECO.sup.(3)                                
                                     BIIR.sup.(1) 100                     
              100     100     100                                         
HMWPE (Example 1)                                                         
              23      23      23     33                                   
Zinc Oxide    1       --      --     1                                    
Magnesium Oxide                                                           
              0.3     10      5      0.3                                  
White Carbon  8       8       8      --                                   
Silane Coupling Agent.sup.(4)                                             
              0.5     0.5     2      0.5                                  
Sulfur        0.3     0.8     --     --                                   
TMTD.sup.(5)  0.2     0.8     .sup.(6) 1.0                                
                                     .sup.(7) 0.6                         
Curing (°C. × min)                                           
              150 × 20                                              
                      160 × 30                                      
                              160 × 30                              
                                     160 × 20                       
______________________________________                                    
 Note:                                                                    
 .sup.(1) POLYSAR BROMO BUTYL X2 commercial name manufactured by Polysar  
 Co., ML.sub.1+4 (125° C.) 53, Br = 1.9 wt %                       
 .sup.(2) Hypalon commercial name manufactured by Du Pont, ML.sub.1+4     
 (100° C.) 55, C1 = 3.5% by weight                                 
 .sup.(3) Gechron 3100 commercial name manufactured by Nippon Zeon Co.,   
 epichlorohydrinethylene oxideallylglycidyl ether ternary copolymer       
 .sup.(4) Mercaptopropyltrimethoxysilane                                  
 .sup.(5) Tetramethy1thiuram disulfide                                    
 .sup.(6) 2,4,6trimercapto-s-triazine                                     
 .sup.(7) 1,1di-(t-butylperoxy)-3,3,5-trimethylcyclohexane                
 
    
     
                       TABLE 10                                                    
______________________________________                                    
Physical Properties of Vulcanizate                                        
              Examples                                                    
              5    6         7      8                                     
______________________________________                                    
Hardness (Hs)    38     39        41  43                                  
Tensile Strength (kg/cm.sup.2)                                            
                106    132       112  86                                  
Elongation at Break (%)                                                   
                620    520       580  500                                 
Compression Set* (%)                                                      
                 37     31        28  23                                  
______________________________________                                    
 Note:                                                                    
  *press 25%, temp 70° C. × 22 hrs, etc. according to JIS K  
 6301                                                                     
 
    
     
                       TABLE 11                                                    
______________________________________                                    
Extraction Test.sup.(1)                                                   
               Examples                                                   
               5    6        7      8                                     
______________________________________                                    
CH.sub.3 COOH 20%                                                         
(90° C. × 30 min)                                            
Residue on Evaporation                                                    
                 0.1    0.1      0.3  0.1                                 
(ppm)                                                                     
KMnO.sub.4 -Reducing                                                      
                 0.3    0.2      0.5  0.3                                 
Substance (ppm)                                                           
UV Spectrum      0.12   0.10     0.15 0.15                                
C.sub.2 H.sub.5 OH 20%                                                    
(90° C. × 30 min)                                            
Residue on Evaporation                                                    
                 0.1    0.1      0.2  0.1                                 
(ppm)                                                                     
KMnO.sub.4 -Reducing                                                      
                 0.2    0.2      0.4  0.2                                 
Substances (ppm)                                                          
UV Spectrum      0.01   0.01     0.02 0.02                                
______________________________________                                    
 Note:                                                                    
 .sup.(1) According to the sanitation test method of rubber products of JI
 T 9010 (1982)                                                            
 
    
     As is evident from the results of Table 11, the rubber products of the present invention are suitable for rubber parts for the preparation of foods. 
     Examples 9 to 10 and Comparative Examples 5 to 7 
     The procedure of blending the composition shown in Table 12 was carried out according to ASTM D 3403. 
     
                       TABLE 12                                                    
______________________________________                                    
           Examples  Comparative Examples                                 
           9     10      5       6     7                                  
______________________________________                                    
IR (Nipol IR 2200).sup.(1)                                                
             100     100     100   100   100                              
Stearic Acid 0.3     0.3     0.3   0.3   0.3                              
Zinc Oxide   2       2       2     2     2                                
Sulfur       2       2       2     2     2                                
TMTS.sup.(2) 0.7     0.7     0.7   0.7   0.7                              
HMWPE.sup.(3)                                                             
             30      15      --    --    --                               
PE.sup.(4)   --      --      --    15    --                               
Dixie Clay   --      --      --    --    30                               
______________________________________                                    
 Note:                                                                    
 .sup.(1) ML.sub.1+4 (100° C.) 83, cis 98%                         
 .sup.(2) Tetramethylthiuram Monosulfide                                  
 .sup.(3) Hizex Million 240M commercial name same as that of Example 1    
 .sup.(4) FLOTHENE UF commercial name same as that of Example 1           
 
    
     An ODR test was carried out in an analogous manner to Example 1 except that the temperature was adjusted to 170° C. The results obtained are shown in Table 13: 
     
                       TABLE 13                                                    
______________________________________                                    
ODR Test                                                                  
           Examples Comparative Examples                                  
           9    10      5       6      7                                  
______________________________________                                    
Torque (kg/cm)                                                            
Initial (a)  23.0   19.2    15.2  15.1   22.2                             
Minimum (b)  19.5   16.8    14.0  11.0   19.8                             
Maximum (c)  48.6   44.1    39.2  20.8   47.9                             
(c) - (b)    29.1   27.3    25.2  9.8    28.1                             
Cure Time (minute)                                                        
t&#39;c (10)     4.8    4.8     4.6   2.4    2.4                              
t&#39;c (90)     22.9   23.0    22.8  20.4   82.0                             
t&#39;c(90)-t&#39;c(10)                                                           
             18.1   18.2    18.2  18.0   79.6                             
______________________________________                                    
 
    
     Comparative Example 5 is a standard pure rubber compound. In Examples 9 and 10 wherein HMWPE is added thereto, the maximum torque and torque (c)-(b) are increased, which implies that extensive vulcanization networks are formed. In Comparative Example 6, wherein PE is added, however, the maximum torque and (c)-(b) are smaller, which implies little vulcanization. HMWPE hardly changes the curing time (t&#39;c (90)), but Dixie Clay lengthens the curing time. 
     
                       TABLE 14                                                    
______________________________________                                    
Physical Properties of Vulcanizates.sup.(1)                               
                      Comparative                                         
            Examples  Examples                                            
            9     10      5       6    7.sup.(3)                          
______________________________________                                    
Hardness (Hs) 46      41      35    no.sup.(2)                            
                                         44                               
300% Modulus (kg/cm.sup.2)                                                
              32      59      25         52                               
Tensi1e Strength                                                          
              141     136     127        102                              
(kg/cm.sup.2)                                                             
Elongation at Break (%)                                                   
              600     520     720        620                              
Tear Resistance (kg/cm)                                                   
              25.3    28.2    24.5       36.2                             
______________________________________                                    
 Note:                                                                    
 .sup.(1) vulcanization condition 160° C. × 40 minutes       
 .sup.(2) No vulcanization test sample was formed.                        
 .sup.(3) vulcanization condition 180° C. × 40 minute        
 
    
     In Comparative Example 6, PE was too soft to obtain a vulcanization test piece for the measurement of physical properties. That is, this comparative example shows that PE hinders the vulcanization. Examples 9 and 10 show that the hardness, modulus, tensile strength and tear resistance are improved. In Comparative Example 7, Dixie Clay retards the vulcanization to such a large extent that a test piece capable of measuring the physical properties can only be obtained by raising the vulcanization temperature: but the physical properties of the vulcanizate, however, are relatively excellent. 
     
                       TABLE 15                                                    
______________________________________                                    
Hygienic Test.sup.(1)                                                     
                        Comparative                                       
               Examples Examples                                          
               9     10     5      6    7                                 
______________________________________                                    
Material Test                                                             
Pb (ppm)         0.05    0.05   0.05 no.sup.(2)                           
                                          2.8                             
Cd (ppm)         0.01    0.01   0.01      0.1                             
Extraction Test.sup.(3)                                                   
Residue on Evaporation (ppm)                                              
                 0.8     0.8    0.8       1.5                             
KMnO.sub.4 -Reducing Substance                                            
                 1.0     1.0    1.8       2.8                             
(ppm)                                                                     
Pb (ppm)         0.01    0.01   0.01      0.5                             
As (ppm)         0.01    0.01   0.01      0.1                             
Zn (ppm)         0.1     0.1    0.1       0.5                             
Formaldehyde     ND.sup.(4)                                               
                         ND     ND        ND                              
Phenol           ND.sup.(4)                                               
                         ND     ND        ND                              
UV Spectrum      0.08    0.10   0.10      0.28                            
______________________________________                                    
 Note:                                                                    
 .sup.(1) according to JIS T 9010                                         
 .sup.(2) No rubber test piece was obtained.                              
 .sup.(3) extracted with water at 120° C. for 30 minutes           
 .sup.(4) no detection                                                    
 
    
     In the material test, Comparative Example 7 shows the presence of considerable amounts of heavy metals such as Pb and Cd from the fillers and zinc oxide, but Examples 9 and 10 show only the presence of Pb and Cd in trace amounts. In Comparative Example 7, heavy metals such as Pb and Zn are also found in the extracted solution. This implies that the rubber product of Comparative Example 7 is unhygienic. 
     Examples 11 to 17 and Comparative Examples 8 and 9 
     Blending of the composition shown in Table 16 was carried out according to ASTM D 3484-76. 
     
                                           TABLE 16                                
__________________________________________________________________________
                                    Comparative                           
        Examples                    Examples                              
        11  12  13  14  15  16  17  8   9                                 
__________________________________________________________________________
BR.sup.(1)                                                                
        100 100 85  100 100 100 100 100 100                               
SBR.sup.(2)                                                               
        --  --  15  --  --  --  --  --  --                                
HMWPE.sup.(3)                                                             
        15  9   15  10  15  15  3   --  --                                
PE.sup.(4)                                                                
        --  6   --  --  --  --  --  6   15                                
Filler.sup.(5)                                                            
        --  --  --  5   2   --  15  15  --                                
Organo  0.25                                                              
            0.25                                                          
                0.25                                                      
                    0.25                                                  
                        0.25                                              
                            0.25                                          
                                0.25                                      
                                    0.25                                  
                                        0.25                              
Peroxide.sup.(6)                                                          
Other Vulcani-                                                            
        --  --  --  --  --  1.0.sup.(7)                                   
                                --  1.0 --                                
zing Agent                                                                
Silane Coupl-                                                             
        --  --  --  --  1   --  0.5 --  --                                
ing agent.sup.(8)                                                         
__________________________________________________________________________
 Note:                                                                    
 .sup.(1) BRO1 commercial name manufactured by JSR, ML.sub.1+4 (100.degree
 C.) 44, quantity of cis 96%                                              
 .sup.(2) SL 552 commercial name manufactured by JSR, ML.sub.1+4          
 (100° C.) 55, bonded styrene 24%, cis 1,4 content 20%             
 .sup.(3) Hifax commercial name manufactured by Hercules Powder Co., mean 
 molecular weight 300 × 10.sup.4 (by viscosity method)              
 .sup.(4) Shorex commercial name manufactured by Showa Denko KK, low      
 density PE, melting point 92° C.                                  
 .sup.(5) Whitex commercial name manufactured by Southern Clay            
 .sup.(6) 1,1di-(t-butylperoxy)-3,3,5-trimethylcyclohexane                
 .sup.(7) 1,2polybutadiene                                                
 .sup.(8) Vinyltrimethoxysilane                                           
 
    
     An ODR test was carried out in an analogous manner to Example 1 except that the temperature was adjusted to 155° C. The results obtained are shown in Table 17: 
     
                                           TABLE 17                                
__________________________________________________________________________
ODR Test                                                                  
                               Comparative                                
          Examples             Examples                                   
          11 12 13 14 15 16 17 8   9                                      
__________________________________________________________________________
Torque (kg/cm.sup.2)                                                      
Initial (a)                                                               
          21.5                                                            
             19.5                                                         
                21.6                                                      
                   19.8                                                   
                      21.2                                                
                         20.5                                             
                            19.8                                          
                               19.5                                       
                                   20.0                                   
Minimum (b)                                                               
          20.4                                                            
             18.1                                                         
                19.5                                                      
                   18.4                                                   
                      19.1                                                
                         18.5                                             
                            18.5                                          
                               14.2                                       
                                   15.0                                   
Maximum (c)                                                               
          50.4                                                            
             51.7                                                         
                50.0                                                      
                   56.4                                                   
                      54.3                                                
                         55.7                                             
                            51.8                                          
                               44.0                                       
                                   42.2                                   
(c)-- (b) 30.0                                                            
             33.6                                                         
                30.5                                                      
                   38.0                                                   
                      35.2                                                
                         37.2                                             
                            33.3                                          
                               29.8                                       
                                   27.2                                   
Cure Time (minute)                                                        
t&#39;c (10)  1.7                                                             
             1.5                                                          
                1.0                                                       
                   1.4                                                    
                      1.5                                                 
                         1.3                                              
                            1.5                                           
                               1.4 1.5                                    
t&#39;c (90)  8.9                                                             
             8.0                                                          
                7.4                                                       
                   7.9                                                    
                      7.8                                                 
                         7.7                                              
                            8.2                                           
                               7.4 7.9                                    
t&#39;c(90)-t&#39;c(10)                                                           
          7.2                                                             
             6.5                                                          
                6.0                                                       
                   6.5                                                    
                      6.3                                                 
                         6.4                                              
                            6.7                                           
                               6.0 6.4                                    
__________________________________________________________________________
 
    
     It is apparent from the results of Table 17 that in comparison of Example 11 and Comparative Example 9, the former is more excellent in respect of the maximum torque and (c)-(b), which shows the difference between HMWPE and PE. Furthermore, the use of PE (Example 12), filler (Example 14) and silane coupling agent (Example 15) with EMWPE results in increase of the torque value (c)-(b). Even when a part of BR is replaced by SBR (Example 13), similar results are obtained to the case when only BR is used. 
     
                                           TABLE 18                                
__________________________________________________________________________
Physical Properties of Vulcanizates.sup.(1)                               
                                     Comparative                          
         Examples                    Examples                             
         11  12  13  14  15  16  17  8   9                                
__________________________________________________________________________
Hardness (Hs)                                                             
         43  45  44  48  44  46  43  43  40                               
200% Modulus                                                              
         18  20  15  23  21  24  19  12  10                               
(kg/cm.sup.2)                                                             
300% Modulus                                                              
         29  31  25  33  31  35  30  23  21                               
(kg/cm.sup.2)                                                             
Tensile  58  60  50  60  58  58  58  43  42                               
Strength(kg/cm.sup.2)                                                     
Elongation at                                                             
         435 430 400 410 425 400 430 390 380                              
Break (%)                                                                 
Tear Resis-                                                               
         15.9                                                             
             16.3                                                         
                 14.9                                                     
                     16.5                                                 
                         16.5                                             
                             16.0                                         
                                 16.0                                     
                                     11.5                                 
                                         10.2                             
tance (kg/cm)                                                             
__________________________________________________________________________
 Note:                                                                    
 .sup.(1) at 140° C. for 25 minutes                                
 
    
     In comparison of Example 11 with Comparative Example 9, it can clearly be appreciated that HMWPE gives a larger modulus, tensile strength and tear resistance than PE. Other Properties are substantially similar to those of the ODR test as shown in Table 17. That is, the joint use of PE (Example 12) or filler (Example 14) with HMWPE results in raising the bridging efficiency. 
     
                                           TABLE 19                                
__________________________________________________________________________
Hygienic Test.sup.(1)                                                     
                                Comparative                               
         Examples               Examples                                  
         11 12 13  14 15  16 17 8   9                                     
__________________________________________________________________________
Residue on                                                                
         0.1                                                              
            0.1                                                           
               0.1 0.1                                                    
                      0.1 0.1                                             
                             0.1                                          
                                0.5 0.5                                   
Evaporation                                                               
(ppm)                                                                     
KMnO.sub.4 -Reduc-                                                        
         0.3                                                              
            0.3                                                           
               0.3 0.3                                                    
                      0.3 0.3                                             
                             0.3                                          
                                0.5 0.5                                   
ing Substance                                                             
(ppm)                                                                     
UV Spectrum                                                               
         0.02                                                             
            0.02                                                          
               0.02                                                       
                   0.02                                                   
                      0.02                                                
                          0.02                                            
                             0.02                                         
                                0.05                                      
                                    0.05                                  
__________________________________________________________________________
 Note:                                                                    
 .sup.(1) extracted at 90° C. for 30 minutes according to JIS T 901
 (1982)                                                                   
 
    
     As is evident from the test results of Table 19, the rubber products of the present invention are satisfactory in their hygienic properties. 
     EXAMPLE 18 AND COMPARATIVE EXAMPLE 10 
     The composition of Table 20 was blended and subjected to tests in an analogous manner to Example 11. 
     
                       TABLE 20                                                    
______________________________________                                    
                    Example 18                                            
______________________________________                                    
BR (BRO2.sup.(1))     92 parts                                            
EPDM (EP25.sup.(2))   8                                                   
White Carbon          3         3                                         
Zinc Oxide            1         1                                         
HMWPE (similar to Example 1)                                              
                      14        14                                        
PE (Shorex M222.sup.(3))                                                  
                      1         1                                         
2,5-dimethyl-2,5-di-(t-butylperoxy)-                                      
                      0.6       0.6                                       
hexyne-3                                                                  
______________________________________                                    
 Note:                                                                    
 .sup.(1) commercial name, manufactured by JSR, ML.sub.1+4 (100° C.
 44, cis 94%                                                              
 .sup.(2) commercial name, manufactured by JSR, ML.sub.1+4 (100° C.
 90, iodine number higher                                                 
 .sup.(3) commercial name, manufactured by Showa Denko KK low density PE  
 
    
     
                       TABLE 21                                                    
______________________________________                                    
Physical Properties of Vulcanizates.sup.(1)                               
______________________________________                                    
Hardness (Hs)       41                                                    
300% Modulus (kg/cm.sup.2)                                                
                    27                                                    
Tensile Strength (kg/cm.sup.2)                                            
                    87                                                    
Elongation at Break (%)                                                   
                    530                                                   
______________________________________                                    
 Note:                                                                    
 .sup.(1) curing at 160° C. for 40 minutes                         
 
    
     
                       TABLE 22                                                    
______________________________________                                    
Material Test                                                             
______________________________________                                    
Cd  (ppm)   0.01     Atomic Absorptiometric Analysis                      
                                       5                                  
Pb  (ppm)   0.05     &#34;                 5                                  
______________________________________                                    
 
    
     The rubber sample was extracted with an amount of water 10 times the weight of the rubber at 121° C. for 60 minutes according to the test method of rubber closures for aqueous infusions as specified in The Pharmacopoeia of Japan 41. The test results of the extracted liquid and the standard values of The Pharmacopoeia of Japan are shown in Table 23: 
     
                       TABLE 23                                                    
______________________________________                                    
Extraction Test                                                           
                           Standard                                       
                Measured Value                                            
                           Value                                          
______________________________________                                    
Description (%)   99.5         99.0                                       
Foam Test (min)   2            3                                          
pH                0.6          ±1.0                                    
Zinc (μg/ml)   0.01         0.5                                        
KMnO.sub.4 -reducing Substance (ml)                                       
                  0.8          2.0                                        
Residue on Evaporation (mg)                                               
                  0.3          2.0                                        
UV Absorption Spectrum                                                    
                  0.07         0.2                                        
______________________________________                                    
 
    
     A specificity test was carried out in an analogous manner to that of example 4. The results obtained are shown in Table 24: 
     
                       TABLE 24                                                    
______________________________________                                    
             Measured Value                                               
                        Standard Value                                    
______________________________________                                    
Particulate Matter Test                                                   
10 μm (number)                                                         
                1            10                                           
 5 μm (number)                                                         
                26           100                                          
Fragmentation  no             3                                           
Penetrability  530          1000                                          
Self-Sealability (ml)                                                     
               no                                                         
______________________________________                                    
 
    
     The rubber closure of the present invention is available for injection of grape sugar, amino acids and electrolyte drugs. 
     
                       TABLE 25                                                    
______________________________________                                    
                       Comparative                                        
               Example 18                                                 
                       Example 10                                         
______________________________________                                    
Rubber           92 parts.sup.(1)                                         
                           92 parts.sup.(2)                               
EPDM.sup.(3)     8         8                                              
White Carbon     3         3                                              
Zinc Oxide       1         1                                              
HMWPE.sup.(4)    14        14                                             
PE.sup.(5)       1         1                                              
2,5-dimethyl-2,5-di-                                                      
                 0.6       0.6                                            
t-butylperoxy)-hexyne-3                                                   
______________________________________                                    
 Note:                                                                    
 .sup.(1) BR: JSR BRO2  commercial name  manufactured by JSR, ML.sub.1+4  
 (100° C.) 44, cis 94%                                             
 .sup.(2) SBR: JSR 1502  commercial name  manufactured by JSR, ML.sub.1+4 
 (100° C.) 52, styrene 23.5% (by cold emulsion polymerization      
 method)                                                                  
 .sup.(3) EPDM: JSR EP 25  commercial name  manufactured by JSR, ML.sub.1+
 (100° C.) 90 iodine number higher                                 
 .sup.(4) HMW: same as in Example 1                                       
 .sup.(5) PE: Shorex M 222  commercial name  manufactured by Showa Denko  
 KK, low density PE                                                       
 
    
     
                       TABLE 26                                                    
______________________________________                                    
Physical Properties of Vulcanizates.sup.(1)                               
                        Comparative                                       
                Example 18                                                
                        Example 10                                        
______________________________________                                    
Hardness (Hs)     41        43                                            
300% Modulus (kg/cm.sup.2)                                                
                  27        25                                            
Tensile Strength (kg/cm.sup.2)                                            
                  87        73                                            
Elongation at Break (%)                                                   
                  530       480                                           
______________________________________                                    
 Note:                                                                    
 .sup.(1) curing at 160° C. for 40 minutes                         
 
    
     
                       TABLE 27                                                    
______________________________________                                    
Material Test                                                             
                    Comparative                                           
            Example 18                                                    
                    Example 10                                            
______________________________________                                    
Cd     (ppm)      0.01      0.1                                           
Pb     (ppm)      0.05      0.5                                           
______________________________________                                    
 
    
     The rubber sample was extracted with an amount of water 10 times the weight of the rubber at 121° C. for 60 minutes according to the test method of rubber closures for aqueous infusions as specified in The Pharmacopoeia of Japan 41. The test results of the extracted liquid and the standard values of The Pharmacopoeia of Japan are shown in Table 28: 
     
                       TABLE 28                                                    
______________________________________                                    
Extraction Test                                                           
                        Comparative                                       
                Example 18                                                
                        Example 10                                        
______________________________________                                    
Description (%)   99.5      98                                            
Foam Test (min)   2         4                                             
pH                +0.6      +1.3                                          
Zinc (μg/ml)   0.01      0.1                                           
KMnO.sub.4 -reducing Substance (ml)                                       
                  0.8       1.5                                           
Residue on Evaporation (mg)                                               
                  0.3       1.8                                           
UV Absorption Spectrum                                                    
                  0.07      0.17                                          
______________________________________                                    
 
    
     
                       TABLE 29                                                    
______________________________________                                    
Specificity Test                                                          
                       Comparative                                        
               Example 18                                                 
                       Example 10                                         
______________________________________                                    
Particulate Matter Test                                                   
10 μm (number)                                                         
                  1         23                                            
 5 μm (number)                                                         
                  26       320                                            
Fragmentation    no         1                                             
Penetrability    530       420                                            
Self-Sealability (ml)                                                     
                 no         5                                             
______________________________________                                    
 
    
     The results of Example 18 imply that the rubber closure of the present invention is available for injection of grape sugar, amino acids, electrolyte drugs, etc. and the result of Comparative Example 10 does not satisfy the requirements in the test of rubber closures for aqueous infusions and the specificity test.