Treating method for giving hydrophilic property to the surface of hydrophobic polymer substrate
This is a continuation application Ser. No. 802,010, filed May 31, 1977 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a treating method for imparting hydrophilic property to the surfaces of hydrophobic polymer substrates having carbon atoms bonded with a single hydrogen atom in their molecules. 
     As the treating methods for imparting hydrophilic property to the surfaces of hydrophobic polymer substrates, there are several known methods such as corona discharge treatment and surface grafting treatment using radioactive rays. In the former corona discharge treatment, however, the hydrophilic property is insufficient so that the use of the method is restricted. In the latter method applying radioactive rays, the treatment becomes expensive since it be indispensable to employ safety measures. In addition, the polymer substrates themselves are subjected to some influences and their properties are causes to vary, and therefore, the disadvantage of narrow utility cannot be avoided. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the above, the present inventors have carried out eager and extensive studies on the treating method for imparting hydrophilic property to the surfaces of the above-mentioned hydrophobic polymer substrates having carbon atoms bonded with a single hydrogen atom in the molecule, which method is free from the disadvantages of the conventional art methods. As the result, the method of the present invention has been accomplished. 
     It is, therefore, the primary object of the present invention to provide an improved method for imparting hydrophilic property to the surfaces of hydrophobic polymer substrates which is free from the above disadvantages in the conventional art. 
     Another object of the present invention is to provide a treating method for imparting hydrophilic property to the surfaces of hydrophobic polymer substrates which is quite effective in operation but easy to be carried out. 
     In accordance with the method of the present invention, (A) a radically polymerizable compound, the homopolymer of which is soluble and/or swellable in water or in electrolytic solutions (hereinafter referred to as &#34;polymerizable compound&#34;) is applied to the surface of (B) a hydrophobic polymer substrate having, in its molecules, carbon atoms bonded with a single hydrogen atom (hereinafter simply referred to as &#34;hydrophobic polymer substrate&#34; or &#34;polymer substrate&#34;), and then actinic rays are irradiated to the hydrophobic polymer substrate that is applied with the polymerizable compound. 
     In a further aspect of the invention, a triplet state sensitizer of 50 Kcal/mol or more in triplet state energy or a photosensitizer that produces free radicals by irradiation (hereinafter referred both sensitizers to as &#34;sensitizer&#34;) can be added to the polymerizable compound before the latter is applied to the hydrophobic polymer substrate. 
     It is assumed that the treatment method of the present invention depends upon the addition reaction of a polymerizable compound to a hydrophobic polymer substrate caused by the free radical polymerization with the absorption of photo-energy. Further, in the method of the present invention, the selectivity to the wavelength of light rays is utilized and the addition reaction can be performed without causing any change in the hydrophobic polymer substrate. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The hydrophobic polymer substrates referred to in the present invention are linear or cross-linked polymers having, in their molecules, 0.05 mol/kg or more carbon atoms bonded to a single hydrogen atom, and having a fixed form at room temperature. It is undesirable that the polymer substrates have carbon atoms bonded to a single hydrogen atom in conjugated double bonds since the velocity of addition of the polymerizable compound is too slow to those carbon atoms. Exemplified as these polymers are polystyrene, polypropylene, polyvinyl chloride, polyvinyl carbazole, polyacrylonitrile, polyacrylic esters, polyvinyl acetate, copolymers obtained with copolymerizing two or more of the monomers used for preparing the above polymers, double- or multiple-component copolymers obtained with copolymerizing one or more of the above monomers with the comonomers such as methacrylic esters, methacrylonitrile, butadiene, isoprene and ethylene, the internally cross-linked products of the above polymers, and branched polymers of ethylene, epoxy resin, unsaturated polyester, polyurethane comprising branched glycol as a part of alcohol component, and polyester comprising branched glycol as a part of alcohol component. 
     When the hydrophobic property of the surface is distinct, the effect of imparting hydrophilic property becomes large. In practice, it is preferred that a substrate having a contact angle of 60 degrees or more with water is used. Further, when carbon atoms having a single hydrogen atom are less than 0.05 mol/kg in the polymer molecules, the quantity of addition of the polymerizable compound becomes insufficient, so that the surface of the substrate is insufficiently imparted with a hydrophilic property. 
     Furthermore, in the present invention, the homopolymers of the above polymerizable compounds are soluble in water or in electrolytic solutions, and/or swellable by at least 10% by volume in water or in electrolytic solutions. Still further, the polymerizable compounds solely or together with sensitizers, causes a radical addition reaction when they are applied with radiation in the range of absorption wavelength. Exemplified as such compounds are one or the mixture of maleic anhydride, acrylamide, methacrylamide, N-methyl acrylamide and methacrylamide, N-ethyl acrylamide and methacrylamide, N-propyl acrylamide and methacrylamide, N-butyl acrylamide and methacrylamide, N-2-hydroxyethyl acrylamide and methacrylamide, N,N-methylene bisacrylamide and bismethacrylamide, N-methylol acrylamide, acryl morpholine, methacryl morpholine, N-propyloxy acrylamide, N,N-dimethyl acrylamide and methacrylamide, N,N-diethyl acrylamide and methacrylamide, diacetone acrylamide, acrylic acid and methacrylic acid, 2-hydroxyethyl acrylate and methacrylate, diethylene glycol monoacrylate and monomethacrylate, triethylene glycol monoacrylate and monomethacrylate, polyethylene glycol monoacrylate and monomethacrylate (molecular weight of polyethylene glycol is from 194 to about 9,000) 2-hydroxypropyl acrylate and methacrylate, 3-hydroxypropyl acrylate and methacrylate, glycerol monoacrylate and monomethacrylate, polyethylene glycol diacrylate and dimethacrylate (molecular weight of polyethylene glycol is from 194 to about 9,000) N-vinylimidazole, vinylpyridine, N-vinylpiperidone, N-vinylcaprolactam, N-vinylpyrolidone, 2-dimethylaminoethyl acrylate and methacrylate, 2-diethylaminoethyl acrylate and methacrylate, 2-sulfoethyl acrylate and methacrylate, 3-sulfopropyl acrylate and methacrylate, p-styrene sulfonic acid, 2-phosphoric ethyl acrylate and methacrylate, and 2-phosphoric-1-chloromethylethyl acrylate and methacrylate. The above polymerizable compounds can be combined with not more than 50% by weight of radically polymerizable vinyl monomers commonly used. 
     As the sensitizers used for the method of the present invention, conventionally known ones may be employed. For example, there are compounds that produce independently free radicals by the application of actinic rays such as benzoin ethers, azobisisobutyronitrile, and thiuram compounds; those which produce free radicals by depriving other molecules of their active hydrogen atoms such as benzophenone and acetophenone, photo-redox system such as ferric chloride, and dye-reduction system such as riboflavin and ascorbic acid. 
     For bringing the hydrophobic polymer substrate into contact with the polymerizable compound, the commonly known method can be used. For example, a hydrophobic polymer substrate is immersed into a polymerizable compound or its solution, or a polymerizable compound or its solution is applied to the surface of a hydrophobic polymer substrate, or it is further dried after the application. Further, a polymerizable compound may be melted over the hydrophobic polymer substrate. In another method, a hydrophobic polymer substrate may be placed in the vapor of a polymerizable compound. It is to be noted, however, that the polymerizable compound or its solution must not dissolve the hydrophobic polymer substrate. That is, in the non-mixing contact surface between the polymer substrate in solid phase and the polymerizable compound in gaseous or liquid phase, the energy transfer caused by actinic rays and the mass transfer of active sites are brought about to impart hydrophilic property to the polymer substrate, which is the characteristic feature of the present invention. 
     In the above-described application of polymerizable compound, one or the mixture of thickeners or tackifiers such as water-soluble polymers and surface active agents can be previously added as catalyst promoters into the polymerizable compound. 
     The preferable range of the wavelength of actinic rays as the energy source for the reaction is 300 nm to 700 nm, and a further desirable fact is that the actinic rays do not cause the deterioration and/or crosslinkage of the polymer substrate. As for such irradiation sources, for example, a low pressure mercury lamp, high pressure mercury lamp, fluorescent lamp, xenon lamp, carbon arc lamp, tungsten incandescent lamp and sunlight can be used. The radiation may be applied through the hydrophobic polymer substrate, or through the photopolymerizable compound, or directly from both sides, or further through the light-permeable wall of a container. Though the irradiation time is different according to the degree of desired hydrophilic property and the kind of irradiation source, it is generally in the range of several seconds to 24 hours. 
     After the treatment to give hydrophilic property, the treated polymer substrate is rinsed with a non-solvent such as water or methanol so as to remove unreacted polymerizable compound and/or the polymer which has not joined to the polymer substrate. 
     Furthermore, it is possible to improve the hydrophilic property without the releasing of the adduct of polymerizable compound by extending the contact time with water or the electrolytic solution. 
     In the hydrophobic polymer substrate which is treated by the method of the present invention to impart hydrophilic property, the surface of the substrate is made completely hydrophilic which is understood from the notable lowering of the contact angle with water. Further, even when the treated polymer substrate is rubbed in boiled water, the contact angle is not reduced. 
     In accordance with the method of the present invention, the treatment for imparting hydrophilic property to the surface of hydrophobic polymer substrate can be carried out quite easily as compared with the methods in the conventional art. The polymer substrate which is treated through the method of the present invention is excellent in its antistatic property, dyeing property and so forth. In addition, the treated polymer substrate has advantageous and wide utilities such as for membranes, printing materials with the imparted hydrophilic property and laminating materials with the improved affinity to adhesive. 
    
    
     In order that those skilled in the art may better understand the present invention and the manner in which it may be practised, the following specific examples are given. It should be understood, however, that these are only illustrative and in no way restrictive of the invention. 
     EXAMPLE 1 
     A 10% solution of polystyrene (average molecular weight: ca. 20,000) in toluene was prepared and 2 g of this solution was fed in a high flat petri dish of 10 cm in inner diameter. The petri dish was left to stand still so as to obtain a cast film of polystyrene. A solution of maleic anhydride in acetone (1 mol/lit) was coated to cover the upper surface of the thus obtained film and radiation was applied for 10  minutes through the maleic anhydride layer by using a high pressure mercury lamp (100 W) which was placed 4 cm above. After the irradiation, the maleic anhydride solution was removed and the film was immersed in running water for 64 hours, dried and the contact angle with water was measured. The result of this test is shown in the following Table 1. 
     EXAMPLE 2 
     40 g of acrylamide and 2 g of benzophenone were dissolved in 60 g of methanol and the solution was applied over a film which was prepared in like manner as Example 1. The coated film was then irradiated for 5 minutes through the upper acrylamide layer by using a low pressure mercury lamp (40 W) which was placed 5 cm above. After the irradiation, the film was rinsed with water and dried. The contact angle with water of the treated surface was measured, the result of which is shown in the following Table 1. 
     EXAMPLE 3 
     A polyvinyl chloride film (trademark: &#34;Vinyl Foil&#34; made by Mitsubishi Plastics Industries Limited, in Japan) was applied with the same acrylamide solution as that of Example 2 and treated and tested in like manner as the former Example 2. The result of measurement on the contact angle with water is shown in the following Table 1. 
     EXAMPLE 4 
     A 10% solution of acrylonitrile-styrene copolymer (acrylonitrile: styrene =55:45, number average molecular weight: 100,000) in toluene was prepared and it was applied to the surface of a glass plate. The resulting dried cast film was applied with the same acrylamide solution as that of Example 2, treated in like manner as Example 2 and the contact angles with water were measured, the results of which are shown in the following Table 1. 
     EXAMPLE 5 
     A solution was prepared by dissolving 40 g of acrylamide and 2 g of benzoin propyl ether into 60 g of methanol. This solution was applied to the surface of the same substrate as that in Example 3 and it was treated in like manner as Example 2. The result of measurement of contact angle with water is shown in the following Table 1. 
     EXAMPLE 6 
     A solution was prepared by dissolving 40 g of acrylamide and 2 g of benzophenone into 60 g of acetone. This solution was applied to the surface of a polypropylene film (trademark: &#34;Polypro F600&#34; made by Mitsui Petrochemical Industries, Ltd., in Japan) and it was then treated in like manner as Example 2. The contact angle with water was measured, the result of which is shown in the following Table 1. Further, it was confirmed by infrared absorption spectrum that the added acrylamide is not released when the treated film is immersed into boiling water for 24 hours. 
     EXAMPLE 7 
     The same substrate as that of Example 3 was applied with 2-hydroxyethyl methacrylate containing 5% of benzophenone. Irradiation was then carried out for 20 minutes through the layer of 2-hydroxyethyl methacrylate by using a low pressure mercury lamp (50 W) which was placed at 5 cm distance apart. After the irradiation, it was immersed in running water for 64 hours and dried. The contact angle with water was then measured, the result of which is shown in Table 1. 
     EXAMPLE 8 
     A solution was prepared by dissolving 10 g of 2-hydroxyethyl methacrylate, 1 g of maleic anhydride and 0.5 g of benzophenone in 9 g of methyl isobutyl ketone, and the solution was applied to the surface of the same substrate as that in Example 3. Then it was treated in like manner as Example 7 and the contact angle with water was measured, the result of which is shown in the following Table 1. 
     EXAMPLE 9 
     A solution was prepared by dissolving 40 g of N-methylol acrylamide and 2 g of benzophenone in 60 g of ethanol, and this solution was applied to the surface of the same substrate as that in Example 3. It was then irradiated for 5 minutes in like manner as Example 2. After the irradiation, it was rinsed with water and dried. The contact angle with water of the treated surface was measured, the result of which is shown in the following Table 1. 
     EXAMPLE 10 
     A 20μ film of low density polyethylene (trademark: &#34;Petrosen&#34; made by Japan Polychemical Co., Ltd. in Japan: branched polymer of ethylene) was applied with the same acrylamide solution as that of Example 2 and treated and tested in like manner as the former Example 2. The result of measurement on the contact angle with water is shown in the following Table 1. 
     EXAMPLE 11 
     A solution was prepared by dissolving 20 g of Epikote #1004, and 1 g of 2-ethyl 4-methyl imidazole in 60 g of methyl ethyl ketone. The solution was applied to the surface of a glass plate, and dried for 10 minutes at 160° C. Further, the dried cast film (thickness: 30μ) of epoxy resin was applied with acryl amide solution as that of Example 2. Then they were treated in like manner as Example 2 and the contact angles with water were measured, the results of which are shown in the following Table 1. 
     EXAMPLE 12 
     A polyester resin (MW: 10,000) was prepared by condensation reaction of phthalic anhydride/1,2-propylene glycol (148/76) in 3-methoxy butyl acetate for 4 hrs at 180° C. The polyester resin solution was applied to the surface of a glass plate, and dried for 30 minutes at 60° C. 
     Further, the dried cast film (thickness: 15μ) of polyester resin was applied with acrylamide solution as that of Example 2. Then, they were treated in like manner as Example 2 and the contact angles with water were measured, the results of which are shown in the following Table 1. 
     EXAMPLE 13 
     A solution was prepared by dissolving 63 g of hexamethylene diisocyanate and 38 g 1,2-propylene glycol in 200 g of acetone. The solution was applied to the surface of a glass plate, and dried for 30 minutes at 80° C. 
     Further, the dried cast film (thickness: 30μ) of epoxy resin was applied with acryl amide solution as that of Example 2. Then, they were treated in like manner as Example 2 and the contact angles with water were measured, the results of which are shown in the following Table 1. 
     EXAMPLE 14 
     An unsaturated polyester resin (MW: about 12,000) was prepared by condensation reaction of tetrahydrophthalic anhydride/ethylene glycol (152/62) in 3-methoxy butyl acetate for 4 hrs at 180° C. The polyester resin solution was applied to the surface of a glass plate, and dried for 30 minutes at 60° C. Further, the dried cast film (thickness: 15μ) of polyester resin was applied with acrylamide solution as that of Example 2. Then, they were treated in like manner as Example 2 and the contact angles with water were measured, the results of which are shown in the following Table 1. 
     
                       TABLE 1                                                     
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         Contact Angle between                                            
                         Contact Angle between                            
         Water and       Water and                                        
Example No.                                                               
         Untreated Substrate                                              
                         Treated Substrate                                
______________________________________                                    
Example 1                                                                 
         90       degrees    62     degrees                               
Example 2                                                                 
         90       &#34;          57     &#34;                                     
Example 3                                                                 
         88       &#34;          31     &#34;                                     
Example 4                                                                 
         98       &#34;          41     &#34;                                     
Example 5                                                                 
         88       &#34;          36     &#34;                                     
Example 6                                                                 
         105      &#34;          80     &#34;                                     
Example 7                                                                 
         88       &#34;          40     &#34;                                     
Example 8                                                                 
         88       &#34;          39     &#34;                                     
Example 9                                                                 
         88       &#34;          31     &#34;                                     
Example 10                                                                
         101      &#34;          36     &#34;                                     
Example 11                                                                
         85       &#34;          18     &#34;                                     
Example 12                                                                
         77       &#34;          21     &#34;                                     
Example 13                                                                
         95       &#34;          12     &#34;                                     
Example 14                                                                
         92       &#34;          16     &#34;                                     
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     Remarks: 
     (i) Measurement of Contact Angle: 10μ liter of distilled water was dropped on the substrate and after 1 minute, the angle between the water surface and the substrate surface was measured by using a telescope (Precision measurement device for contact angle: Model CA-D made by kyowa Kagaku K.K., in Japan). 
     (2) After the application of polymerizable compounds, when they were rinsed without irradiation, the lowering of contact angles was not observed in any examples. 
     Although the present invention has been described in connection with preferred examples thereof, many variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.