Copolymer and graft blend each containing acrylonitrile and acrylate components
United States Patent 1 [111 3,880,951  
 Ooya et al. Apr. 29, 1975 COPOLYMER AND GRAFT BLEND EACH 2,123.599 7/1938 Fikcntseher et al 2e0/s5.5 ES  
 CONTAINING ACRYLONITRILE AND ACRYLATE COMPONENTS Inventors: Masaki Ooya; Masayasu Suzuki;  
 Akio Kobayashi, all of lwaki, Japan Kureha Kagaku Kogyo Kabushiki Kaisha, Tokyo-t0, Japan Filed: Mar. 17, 1972 Appl. No.: 235,862  
 Assignee:  
 Foreign Application Priority Data Mar. 18, 1971 Japan 46-15426 Dec. 10, 1971 Japan .1 46-99489 References Cited UNITED STATES PATENTS 5/1938 Hill 260/85.5 ES  
 6/1969 Weitzel et a1. .1 260/876 R Primary ExaminerMurray Tillman Assistant Examiner.l. Ziegler Attorney, Agent, or Firm-Wenderoth, Lind &amp; Ponack [57] ABSTRACT Synthetic resin composition having low gas permeability consisting of a blend of a first resin component which is a copolymer of acrylonitrile or methacrylonitrile and acrylic ester, and a second resin component which is a graft copolymer composed of a monomer mixture of acrylonitrile or methacrylonitrile and acrylic ester grafted upon homopolymer or copolymer of 1,3-butadiene as the trunk polymer for the graft copolymer, the content of the trunk polymer in the entire blend being determined to attain the desired result.  
 4 Claims, N0 Drawings COPOLYMER AND GRAFT BLEND EACH CONTAINING ACRYLONITRILE AND ACRYLATE COMPONENTS BACKGROUND OF THE INVENTION This invention relates to a synthetic resin composition consisting of a blended copolymerized resin component (I) containing acrylonitrile or methacrylonitrile as its principal component, and a graft copolymerized resin component (ll) obtained by graft polymerizing a monomer mixture containing acrylonitrile or metha crylonitrile as its principal component upon a copolymer of 1,3-butadiene and acrylic ester.  
  This resin composition and shaped articles manufactured therefrom possess extremely superior properties as enumerated hereinbelow:  
  i. Since the resin composition is excellent in its heatstability and processability, it can be easily formed into desired articles of various configurations by using the ordinary processing method;  
  ii. The shaped articles to be obtained are substantially of colorless transparency like glass, hence outer appearance of the resulting product is highly attractive;  
  iii. Since the resin composition possesses the least odor, the shaped articles do not issue any disagreeable odor which is scarcely perceived, hence, when the resin composition is used as the packaging material for foodstuff, etc., there does not occur a single problem as to migration of such undesirable odor to the stuffed contents, change in taste of packed foods, etc.;  
  iv. The resin composition exhibits extremely low permeability against carbon dioxide gas, oxygen, water vapor, and others;  
  v. The resin composition possesses extremely high impact strength, particularly it has very small decrease in strength at a low temperature condition and maintains sufficient strength at such circumstance.  
 A blended resin composition of a copolymer of acrylonitrile and acrylate with acrylonitrile as its principal constituent and a copolymer of butadiene and acrylonitrile has heretofore been known. This resin composition, however, is defective in its inferior heat stability and processability. In other words, when this resin composition is hot-melt to be processed into desired articles, its heat stability extremely deteriorates, and the obtained shaped articles assume yellow or yellowish brown in color giving inferior outer appearance of the products. More undesirable defect than this is that, when the resin becomes deteriorated, very disagreeable smell comes off the resin composition. This latter point is liable, when this resin composition is used as the packaging material for foodstuffs, medicines, cosmetics, etc., to cause this odor occurred at the time of shaping to transfer or migrate to the packed contents with the result that commercial value of the packed contents is remarkably impaired. Another deficiency of this known resin composition is that it has considerably lowered impact strength at a low temperature condition, which is not suitable for the packaging material for food stuffs requiring storage in a cool place.  
 SUMMARY OF THE INVENTION It is therefore the primary object of the present ink The above object as well as details of the present invention will become more apparent and readily understandable from the following description thereof when read in conjunction with the preferred examples thereof.  
 DETAILED DESCRIPTION OF THE INVENTION The aforementioned deficiencies with the previously known resin composition stem mainly from the inferior heat stability of the trunk polymer constituting the graft copolymer, i.e., insufficient heat stability of the butadiene-acrylonitrile copolymer constitutes the principal cause for the problem.  
  The present invention is to improve heat stability and processability as well as impact strength and barrier property against gases of the resin composition to a satisfactory degree by the use of a copolymer consisting of polybutadiene or a copolymer of butadiene and one or two kinds of vinyl monomers such as acrylic ester, methylmethacrylate, and styrene.  
  There is known a method for improving the impact strength of the resin composition containing polyacrylonitrile as its principal constituent, wherein the rubber component is dispersed in the resin matrix. In this case, a copolymer of acrylonitrile and diene compound such as butadiene, isoprene, etc. which are regarded as an effective rubber component, and, on which a monomer mixture containing acrylonitrile as its principal component is grafted, is said to be particularly effective.  
  Journal of Applied Polymer Science, Vol. 13, page 2,567, (1969) as well as Belgian Patent No. 746,265 describe that, for the trunk polymer in the graft copolymer, a copolymer of butadiene and acrylonitrile is used, and that, depending on the combined quantity of acrylonitrile in this copolymer, the impact strength of the resin composition is remarkably affected. That is, for the purpose of improving the impact strength of acrylonitrile type resin composition, the trunk polymer for the graft polymer has had to be essentially a copolymer of diene compound and acrylonitrile. However, as already mentioned in the foregoing, the acrylonitrile type resin composition containing this graft copolymer possesses a fatal defect of inferior heat stability, due to which use of the resin composition has been remarkably restricted.  
  The present inventors, as the result of repeated and continuous experiments and researches to obtain a resin composition having no such deficiencies but sufficient impact strength and barrier property against gases, have discovered that, when a polybutadiene or a copolymer consisting of butadiene and one or two kinds of vinyl monomers selected from acrylic ester, styrene, and methylmethacrylate is used as the trunk polymer for the graft copolymer, a resin composition having the desired properties could be obtained.  
  The resin composition according to the present invention consists of a blend of a synthetic resin component (I) and a synthetic resin component (II), in which the content of the trunk polymer in the synthetic resin component (II) of the resin composition ranges from 5 to 20% by weight.  
  The first resin component (I) is a copolymer resin consisting of 50 to by weight of acrylonitrile or methacrylonitrile, and 15 to 50% by weight of acrylic ester represented by the following general formula: CH CHCOOR where R, is alkyl group having 1 to 4 carbon atoms.  
  The second resin component (II) is a graft copolymer prepared by grafting 90 to 25 parts by weight of a monomer mixture composed of 40 to 85% by weight of acrylonitrile or methacrylonitrile and 15 to 60% by weight of acrylic ester represented by the following general formula: CH CHOOR where R is alkyl group having 1 to 4 carbon atoms upon 10 to 75 parts by weight of a homopolymer or copolymer of 1,3- butadiene to be the trunk polymer for the intended graft copolymer and consisting of 50 to 100% by weight of 1,3-butadiene and to 50% by weight of vinyl monomer selected from styrene, acrylic ester, and methylmethacrylate.  
  The first resin component (I) can be manufactured by any of the generally known method such as emulsion polymerization, suspension polymerization, solution polymerization, etc., of which the emulsion polymerization and suspension polymerization are most desirable from the standpoints of economy and ease of operation. The copolymer, as already mentioned above, consists of acrylonitrile or methacrylonitrile and acrylic ester, in which acrylonitrile or methacrylonitrile occupies 50 to 85% by weight with respect to the entire copolymer and the remainder is acrylic ester.  
  For the acrylic ester to be used, there are methylacrylate, ethylacrylate, propylacrylate, and butylacrylate, of which methyl-and ethyl-acrylate are considered preferable from the point of the physical properties of the copolymer.  
  When the content of acrylonitrile in this copolymer exceeds 85% by weight, the thermoplasticity and heat stability of the copolymer becomes lowered with the consequence that shaped articles of colorless transparency can hardly be obtained. Also, when the content of acrylonitrile becomes lower than 50% by weight, mechanical property and barrier property against gases of the shaped articles become lowered, which is not desirable from the standpoint of the intended purpose of use of such shaped articles.  
  The second resin component (II) is prepared by graft copolymerizing a monomer mixture composed of a nitrile group containing monomer such as acrylonitrile or methacrylonitrile, and acrylic ester upon a polybutadiene or a copolymer of 1,3-butadiene and one or two kinds of vinyl monomers selected from acrylic ester, styrene, and methylmethacrylate as the trunk polymer for the grafting,  
  The trunk polymer for the graft copolymer, as mentioned above, is a polybutadiene or a copolymer of 1,3- butadiene and one or two kinds of vinyl monomers selected from acrylic ester, styrene, and methylmethacrylate, of which acrylic ester is one containing therein residual radical of alcohol having 1 to 8 carbon atoms. The content of this vinyl monomer in the copolymer should not exceed 50% by weight, beyond which no sufficient impact strength can be obtained.  
  The monomer mixture to be grafted on the trunk polymer is composed of either one of acrylonitrile or methacrylonitrile having the nitrile group and acrylic ester. Acrylic ester of the same kinds as used in producing the resin component l may be used in this second resin component. In this case, the quantity of the trunk polymer in the graft copolymer ranges from 10 to 75% by weight.  
  In order to obtain sufficient impact strength in the resin composition according to the present invention with a small amount of the graft copolymer, it is desirable that the content of the trunk polymer graft be as large as possible, although, when the content thereof exceeds by weight, the second resin component (ll) loses sufficient compatibility with the first resin component I) with the consequent decrease in the impact strength. Also if the content of the trunk polymer is below 10% by weight, the impact strength does not meet the required standard.  
  The nitrile group containing monomer contained in the graft component is from 40 to by weight. The content beyond 85% by weight would cause decrease in the thermal stability of the resin composition, and the shaped articles assume a yellowish brown color. On the other hand, the content of below 40% by weight does not produce sufficient compatibility between the resin components (I) and (II), hence inferior impact strength.  
  The graft copolymer of the second resin component (II) can be produced by the heretofore known methods such as solution-, bulk-, and emulsion-polymerization. Of these three methods, the emulsion polymerization is the easiest and most preferable method.  
  The blend ratio of this first resin component (I) and the second resin component (ll) for the resin composition is such that the content of the trunk polymer of the second resin component (ll) be maintained within the range of 5 to 20% by weight. Outside this range, no sufficient physical properties of the resin composition can be assured. That is, when the trunk polymer content is less than 5%, the impact strength of the resin composition becomes inferior, and when the content is above 20%, the barrier property against gases as well as the mechanical property of the resin composition become inferior.  
  The first resin component (I) and the second resin component (ll) in the resin composition can be blended by any known method such as in latex form or powder form.  
  In order to enable skilled persons in the art to reduce the present invention into practice, the following preferred examples are given. It should, however, be noted that these examples are illustrative only, and that any change may be made within the ambit of the invention as afforded by the appended claims.  
 EXAMPLE 1 Component Part by Weight Acrylonitrile 75 Methylacrylate 25 n-dodecyl mercapton 1.0 K 8 0, 0.04 NaHSO 001 CT? 1.0 Water 200 (Note: Manufactured and sold by Ku0-Allas (&#39;0.. Japan under a trademark Pclex OTP&#34;. the principal constituent of which is sodium diocryl sull&#39;osuccinate.)  
  Upon completion of the polymerization reaction, the yielded latex was taken out of the autoclave, to which 20 parts by weight of 4% aqueous solution of Al SO0 was added for salting-out, thereby making the latex in slurry form. This latex was further heated to a temperature of 80C, and then filtered, washed with water, and dried. As the result, a copolymer in white powder was emulsified by aqueous solution of OTP was added to the reaction product. Then, the resulting emulsion was taken out of the autoclave and 20 parts by weight of 4% aqueous solution of Al SO was added for salting-out and coagulation. When the coagulated product was Obtained at a rate of yi ld Of 96%. 5 heat-treated at a temperature of 60C, filtered, washed I The copolymer was found to have its reduced VlSCOS- i h water d d i d a g ft copolymer i hi y (&#39;flsP/ 0f 14 2/ at a temperature of der was obtained at a rate of yield of 96%.  
 30C in dimethylformamide solution.  
  preparation of the resin component ([1) Comparatlve Example for Preparation of Resin The following materials were charged into the autocomponent (11&#39;) elave- When the following components were charged into the autoclave and subjected to polymerization reaction by agitating the batch for 16 hours at a temperature of cmnponent pm by Weight 40C, a copolymer latex of butadieneacrylonitrile (B-AN latex) was obtained at a rate of yield of 98%. l ,3-butadienc 40 Methylacrylate l0 Tert-dodecyl mereaptan 0.25 Diisopropylbenzene h d r id Q 1 Component Part by Weight FeSO 7H O 0.002 EDTA 2m salt 0.003 1,3-butadiene 40 Rongalite 0.05 Aerylonitrile l0 Na P- O IOHZO 0.05 Tert-dodecyl mercaptan 0.25 OTP 0.5 Diisopropyl benzene 0.1 Water 1 50 hydroperoxide FeSO 7H2O 0.002 (Now, EDTA 2Na salt 0.003 EDTA Ethylene Diaminc Tetraucctic Acid) Rongalite Na,l ,0,. 101-1 0 0.05 POTP 0.5  
  Upon completion of the polymerization reaction in Water 150 16 hours at a temperature of 40C with agitation, latex was obtained at a rate of yield of 98%. Subsequently,  
 10 parts by weight of water containing therein 0.25 part Next, monomer mixtures of acrylonltrile and ethylaby weight of OTP and 0.25 part by weight of Emulgen Crylate of the various mixing ratios as shown in the fol- 910 (product of Kao-Atlas Co., Japan, the principal l g Table were graftpolymerized on the latex constituent f which i in the same manner as described in Example 1 above.  
 The thus obtained latex was treated for the resin comonent II I was added to the latex and agitated for 1 hour.  
  Thereafter, the following mixture components were MiXlure M1 1 2 3 4 5 6 further added to the latex and reacted for 16 hours at Acrylonimle 35 325 30 49 45.5 42 40C, while agitating. Ethyl acrylate 15 17.5 20 21 24.5 28  
 B-AN latex 50 50 50 50 30 30 30 (solid content) Component Part by Weight The resin components (I) and (II) obtained by Example 1 and Comparative Example were blended by a Diisopmpyl benzene Henschel blender at the mixing ratio shown in the folhydroperoxide lowing Table 1, and homogeneously kneaded by rolls Rongahte 0.05 o water 140 at a rolling temperature of 165 C for 3 minutes to shape the blended resin composition into a sheet form. This sheet was further pressed by a pressing machine Upon completion of the reaction, a benzene solution for l0 minutes at a temperature of 200C under a prescontaining therein 1 part by weight of 3,5-di-tertiarysure of 200 kg/cm to produce test specimens. butyl-4-hydroxy toluene (BHT) and 0.5 part by weight The test specimens were tested for their gas permeaof dilauryl thio-dipropionate (DLTDP) which had been bility, mechanical as well as thermal properties, the results of which are shown in the following Table l.  
 Table 1 Ref. Invenlnvenlnvenlnven- Sample tion tion tion tion Resin component (l)(wt. parts) I00 80 70 60 Resin component (ll)(wt. parts) 0 20 25 30 40 CO gas Permeability 0.15 X 0.5 X 0.6 X 0.8 X 1.0 X (cc.cm/em .sec .cmHg) 10 12 1012 l0 l2 l0 l2 10 12 Moisture permeability (250 microns thick) 5 5 5 5 7 (glm.24 hrs.) Tensile strength at breaking point (kg/cm) 980 940 860 840 S Thermal deformation temp. (C) 82 8| 80 79 76 Parallel light beam transmission(%) 87 84 84 82 76 Table l -Cont1nued Ref. lnvenlnven- Inven- Inven- Sample tion tion tion tion Haze value 4 5 5 6 11 lzod impact strength (v/notch) kg.cm/cm 23C 2.5 68 98 120 130 0.C 2.0 22 28 35 40 l0C 2.0 28 Color tone light light light light light yellow yellow yellow yellow yellow Odor not not not not not sensed sensed sensed sensed sensed Table la Comparative Specimen l 2 3 4 5 6 No. Item Resin component (I) (part by weight) 80 8O 80 70 60 70 Resin component (ll) (part by weight) 20 20 20 3O 30 CO gas permeability 0.5 X 0.5 X 0.6 X 0.5 X 0.5 X 0.6 X (cc.cm/cm .sec.cmHg 10 l0&#34; IO 10&#34; 10* 10&#39; Moisture permeability (g/m 24 hrs.) 6 6 6 6 6 6 Parallel light beam transmission 82 81 78 82 8O 80 Haze value 6 8 l0 6 8 l0 Izod impact strength (v/notch) (kg.cm/cm 23C 65 70 72 81 78 86 0C l0 l4 l5 l0 l2 l5 l0C 5 8 l0 5 6 8 Color tone yellowish brown yellowish brown Odor disagreeable disagreeable smell smell Note:  
 Measurements for the physical properties were conducted in accordance with the following prescribed test methods. a. C0 gas permeability ASTM D-l434-66 b. Moisture permeability ASTM E-96-66 c. Tensile strength at breaking point .llS 14-6734 d. Thermal deformation temp. ASTM D-648-56 e. Parallel light transmission .llS K-67 l4 f. Odor Pressed sheet of the resin compositions having a thickness of 1 mm was cut into a strip of a total surface area of 240 cm. The strips were then immersed for 24 hours in 300 ml of water maintained at a temperature of 60C contained in a glass container with tight stopper. after which the strips were taken out and the water is tested for its smell by organoleptic method.  
 able smell. Lowering of the impact strength at a low temperature condition is also considerable.  
 EXAMPLE 2 Syntheses of the resin components (I) and (II) was It will be understood from the foregoing Tables 1 and la that the resin compositions obtained by Example I of the present invention are extremely superior in their color tone and odor to those of the comparative samples, and, moreover, they show only a small decrease in the impact strength at a low temperature, thereby showing sufficient strength. In contrast to this, the resin compositions of the comparative examples assume a yellowish brown color tone and issue a very disagreefollowed exactly as in Example 1 above, except that the composition of the trunk polymer for the resin component (II) was changed to the ratios as shown in the following table.  
  9 In every case of using the trunk polymers having varying compositional ratio, the graft polymer in white powder form could be obtained. These resin components (II) were blended with the resin component (I) found to be colorless transparent and extremely clear. Almost no odor could be sensed, nor was there recognized any difference in odor between the bottle obtained from the resin component (I) alone and that obing the resin material through an extruder of 50 mm in diameter and then blow-molding the extruded parison.  
  The temperature of the molten resin as extruded was 210C. The outer appearance of the bottle obtained by using any of the abovementioned resin materials was of Exampl 1 above by th Henschel blender at a 5 tained from the resin composition containing the resin ing ratio of 25/75 (resin component (ll)/resin compo- Component (1]) n n and the blended p si i n r m Further, these two bottles were filled with distilled sured for their impact strength, the results of which are water of 60C and tightly closed by a stopper, after as shown in the following Table 2. which they were kept in air bath maintained at a tem- Table 2 A B C D E F G H l lzod impact strength (kgCm/cm&#34;) at 23C 82 71 52 96 58 H 94 58 86 EXAMPLE 3 perature of 60C for 24 hours. Then, the distilled water The Same procedures as in Example 1 above were was examined for its taste and smell. No odor was followed, except that the monomer compositions of the found to have migrated from the bottles into the water, graft component in the resin component (H) were 20 and the water was perfectly odorless and free of any unmade according to the ratios as shown in the following deslraPle taste Table Again, the bottle produced from the resin composition containing 20% by weight of the resin component (II) was filled with 300 ml of water at 23C, and the bottle was dropped from a height of 2 m. No damage Trunk plymer Compomt 25 occurred with the bottle. On the other hand, the bottle Code 1,3- ethylacryloethylbumdicnc acrylmc mile acrylatc produced from the resin component (I alone was damaged at a damage rate of 60%. (J) 40 1() 27.5 22.5 (K) 40 10 30.0 20.0 EXAMPLE (L) 40 32.5 17.5 40 10 a. Preparation of resin component (I) The following materials were charged into an autoclave, and agitated for 24 hours by regulating the reac- O In every case, graft copolymer in white powder form temperature at 60 was obtained at a rate of yield of 96%.  
  Each of these resin components (ll) was blended with the resin component (I) of Example 1 by the Component Part by Weight Henschel blender in such a manner that the blending 8 ratio of the resin component (ll) become 25% by mzmfigg gg g weight. Thereafter, the resin composition thus obtained n-dodecyl mercaptan 0.25 was made into test specimens for measurements of varififfga 8-8; ous physical properties. The results are as shown in the ()TF 5 following Table 3. 300  
 Table 3 J K L M CO2 gas permeability 0.6x 0.6x 0.5 0.5X (ec.cm/cm .sec.cmHg) l0&#34; l0 l0 l0 Moisture permeability (250 microns thick) 5 5 5 5 (g/m .24 hrs.) Tensile strength at breaking point (kg/cm) 940 940 960 960 Thermal deformation temp.(C) 80 8O 80 80 Parallel light beam transmission 82 83 84 84 Haze value 6 5 4 4 lzod impact strength (v/notch) 83 102 97 78 (kg.cm/cm at 23C EXAMPLE 4 Upon completion of the polymerization reaction, re-  
  sulted latex was taken out of the autoclave, to which 20 The resin component (I) in Example 1 and a blend parts by weight of 4% aqueous solution of Al $09 of the resin component (I) and the resin component was added for salting-out, thereby making the latex in (II) in the same Example to contain 20% by weight of slurry form. This latex was further heated to a temperathe latter were respectively made into a bottle of 35 g ture of 80C, and then filtered, washed with water, and in weight and 300 ml in internal volume by first extruddried. As the result, a copolymer in white powder form was obtained at a rate of yield of 94%.  
  The copolymer was found to have a reduced viscosity lsP/C) of 0-093 /8) 8 b. Preparation of resin component (II) The following materials were charged into the auto- 1 l clave, the remaining internal space of which was perfectly substituted for nitrogen, thereafter the charged materials were agitated for 16 hours by regulating the reaction temperature to 40C.  
 Component Part by Weight 1,3-butadiene 40 Ethylacrylate l Tert-dodecyl mercaptan 0.25 Diisopropyl benzene hydroperoxide O. l FeSO .7ll O 0.002 EDTA.2Na salt 0.003 Rongalite 0.05 Na P O l0H O 0.05 OTP 0.05 Emulgen 0.5 Water 150 Component Part by Weight Methacrylonitrile 32.5 Ethylacrylate 17.5 Diisopropyl benzene hydroperoxide 0. 1 Rongalite 0.05 Water 130 Upon completion of the reaction, a benzene solution containing therein 1 part by weight of di-tertiary-butylhydroxy toluene and 0.5 part by weight of nonylphenyl phosphite which had been emulsified by aqueous solution of OTP was added to the reaction product. Then, the resulting emulsion was taken out of the autoclave and 20 parts by weight of 4% aqueous solution of A1 (SO was added to it for salting-out and coagulation. When the coagulated product was further heat-treated at a temperature of 60C, filtered, washed with water, and dried, a graft copolymer in white powder form was obtained at a rate of yield of 96%.  
  The resin components (I) and (11) thus obtained were blended by a Henschel blender at varying mixing ratios as shown in the following Table 4, homogeneously kneaded by rolls at a rolling temperature of 170C for 3 minutes to shape the blended resin composition into sheet form. This sheet was further pressed by a pressing machine for minutes at a temperature of 200C under a pressure of 200 kg/cm to produce test specimens. The measured results of the physical properties of these test specimens are shown in the following Table 4.  
 (v/notch) (kg.cm/cm 23C What we claim is:  
  l. A synthetic resin composition of low gas permeability, consisting essentially of a blend of a first resin component and a second resin component, wherein the first resin component is a copolymer consisting essentially of l. 50 to by weight of a monomer selected from the group consisting of acrylonitrile and methacrylonitrile, and  
 2. 15 to 50% by weight of an acrylic ester represented by the formula CH Cl-ICOOR wherein R is alkyl of 1 to 4 carbon atoms, and the second resin component is a graft copolymer consisting essentially of to 25 parts by weight of a monomer mixture consisting essentially of 1. 40 to 85% by weight of a monomer selected from the group consisting of acrylonitrile and methacrylonitrile, and  
 2. 60 to 15% by weight of an acrylic ester represented by the formula CH CHCOOR wherein R is alkyl of 1 to 4 carbon atoms grafted upon 10 to 75 parts by weight of a polymeric substance to be the trunk polymer for the graft copolymer, which polymeric substance is a copolymer of 3. 50 to 90% by weight of 1,3-butadiene, and  
 4. 10 to 50% by weight of at least one vinyl monomer selected from the group consisting of styrene,  
 methyl methacrylate and esters of acrylic acid wherein the alcohol radical has l-8 carbon atoms, the content of the trunk polymer in the second resin component being from 5 to 20% by weight of the entire blended resin composition.  
  2. The synthetic resin composition according to claim 1, wherein the acrylic ester for the first resin component is selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate and butyl acrylate.  
  3. The synthetic resin composition according to claim 1, wherein the acrylic ester (2) for the second resin component is selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate and butyl acrylate.  
  4. The synthetic resin composition according to claim I, wherein the acrylic ester of the polymeric substance for the trunk polymer is selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and methyl methacrylate.