JPH0687978A - Pressure-sensitive adhesive composition for masking tape - Google Patents

Abstract

PURPOSE:To obtain a pressure-sensitive adhesive composition, capable of suppressing the formation of bubbles in a parting line part of the tape edge without any remaining pressure-sensitive adhesive on a peeled surface after baking and drying when used as a pressure-sensitive adhesive for masking tapes. CONSTITUTION:The pressure-sensitive adhesive composition for masking tapes is obtained by including 0-100 pts.wt. zinc oxide, 20-150 pts.wt. tackifier resin, 0.05-7 pts.wt. thiuram-based compound and 0.05-10 pts.wt. at least one compound selected from the group consisting of dithiocarbamate-based compounds, xanthate-based compounds and thiazole-based compounds in 100 pts.wt. base polymer containing 40-97wt.% natural rubber, 3-60wt.% styrene-butadiene copolymer rubber and 0-32wt.% polyisobutylene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-sensitive adhesive composition for a masking tape used for coating automobile bumpers, outer panels and the like.

[0002]

2. Description of the Related Art In order to enhance the appearance and appearance of automobile bodies, various coating methods are applied to bumpers, vehicle body skins and the like. Bumpers are made plastic and color-finished as automobiles become lighter.

Various masking tapes are used for separately coating bumpers and outer panels of automobiles.
As the level of demand for coating film quality has increased and technological development of coating methods has progressed, the demand for higher performance and diversification of masking tapes has increased.

Specific performance requirements for the masking tape are, for example, (1) having sufficient adhesive strength at room temperature (adhesiveness), (2) not peeling off during baking and drying of paint at high temperature (heat resistance). ), (3) The adhesive does not remain on the tape peeling surface after baking and drying, (4) The parting line of the coating film of the masking part can be clearly displayed (parting property), (5) The adherend is not contaminated. (Non-polluting), etc.

By the way, since the adherend to be masked is usually a curved surface having irregularities, the tape support is required to have a certain elongation or more. Therefore, conventionally, a crepe tape using a crepe paper as a support has been mainly used for two-tone painting of a car body outer panel or a bumper. A rubber-based pressure-sensitive adhesive is mainly used as an adhesive for the masking tape. However, the crepe tape has a problem that the parting line is not finished clearly. Moreover, the crepe tape cannot sufficiently follow the expansion of the bumper during heating and the contraction of the bumper during cooling in the baking / drying process after coating the plastic bumper, which may cause warpage in the bumper. is there.

Therefore, recently, a masking tape using a plastic film has come to be used as a support which can follow the expansion and contraction of the plastic bumper in the baking and drying process.

However, when a masking tape using a plastic film as a support is used for coating,
At the parting line portion of the tape edge, there is a problem that air bubbles (so-called cracks) are likely to occur in the coating film. With a masking tape using crepe paper as a support, even if gas is generated due to an organic solvent or low-boiling substance contained in the pressure-sensitive adhesive (adhesive) layer or adherend, the crepe paper will not Although it is discharged through fine holes, in the case of a plastic film masking tape, since such fine holes are not provided, the gas accumulated under the tape is discharged from the tape edge, and therefore the parting line part of the tape edge. Bubbles are formed in the coating film applied to the.

After the masking tape is peeled off, these air bubbles remain as voids in the coating film, which impairs the appearance of the coating film, and when further overcoating is performed, these voids cause the generation of new air bubbles, which causes overcoating. Bubbles are generated in the film.

[0009] Conventionally, in order to prevent the deterioration of the aesthetic appearance due to such bubbles, after separately coating with a masking tape, a two-component acrylic / isocyanate clear coating is applied to the entire surface or only the parting line portion of the coating film to be separately coated. A method of baking and hardening has been proposed (Japanese Patent Laid-Open No. 1-203 / 1990).
079, JP-A 1-203085). However, in the present situation, a masking tape using a plastic film as a support has not been found an effective means for preventing or suppressing the formation of bubbles themselves.

[0010]

The object of the present invention is to suppress the formation of bubbles in the parting line portion of the tape edge when used as a pressure-sensitive adhesive for masking tape, and to prevent the release surface after baking and drying. Another object of the present invention is to provide a pressure-sensitive adhesive composition having no residual pressure-sensitive adhesive. Another object of the present invention is to provide a pressure-sensitive adhesive composition for a masking tape which uses a plastic film as a support.

As a result of intensive studies to solve the above-mentioned problems of the prior art, the present inventors have found that a rubber-based pressure-sensitive adhesive will have residual pressure-sensitive adhesive unless it is cross-linked by a cross-linking agent. On the contrary, it was found that when the degree of crosslinking is too high, the residue disappears but the adhesiveness at high temperature decreases and the parting property decreases.

Further, as a result of research, as a base polymer of a rubber-based pressure-sensitive adhesive for masking tape, a specific elastomer was used in combination in a specific amount ratio, and
By appropriately crosslinking with a specific amount of a specific cross-linking agent, even when a plastic film is used as a support, the generation of bubbles at the tape edge is prevented or suppressed, resulting in a clear parting line. It was found that Further, in the masking tape using this pressure-sensitive adhesive composition, the adhesive does not remain on the tape peeling surface after baking and drying.

When the pressure-sensitive adhesive composition of the present invention is used as a pressure-sensitive adhesive for a masking tape, the reason why the generation of bubbles is prevented or suppressed is that an organic solvent or other low-boiling substance which normally evaporates upon heating. It is presumed that this is because the gas caused by is temporarily suppressed from being discharged to the outside of the system that has been sorbed by the pressure-sensitive adhesive composition. The present invention has been completed based on these findings.

[0014]

According to the present invention, therefore, a base containing (A) 40 to 97% by weight of natural rubber, 3 to 60% by weight of styrene-butadiene copolymer rubber and 0 to 32% by weight of polyisobutylene. 0 to 100 parts by weight of (B) zinc oxide, relative to 100 parts by weight of polymer,
(C) 20 to 150 parts by weight of tackifying resin, (D) 0.05 to 7 parts by weight of thiuram compound, and (E) selected from the group consisting of dithiocarbamate compound, xanthogenate compound and thiazole compound. There is provided a pressure-sensitive adhesive composition for a masking tape, which comprises 0.05 to 10 parts by weight of at least one compound described above.

The present invention will be described in detail below. (Base Polymer) In the present invention, as the base polymer of the pressure-sensitive adhesive, natural rubber and styrene-butadiene copolymer rubber are used as essential components, and polyisobutylene rubber is optionally used in combination.

As the natural rubber used in the present invention,
Commonly used ribbed smoked sheets, air dry sheets, pale crepes and the like are used. Natural rubber is usually masticated so as to have an appropriate molecular weight.

The proportion of natural rubber used is 40 to 97% by weight, preferably 45 to 95% by weight, based on the base polymer. If the proportion of natural rubber used is less than 40% by weight, good tack cannot be obtained, and if it exceeds 97% by weight, the apparent viscosity at 90 ° C. of the pressure-sensitive adhesive composition does not decrease and the parting property during coating decreases. To do.

The styrene-butadiene copolymer rubber used in the present invention is a random copolymer, a block copolymer,
Although any graft copolymer may be used, a random copolymer is preferable from the viewpoint of adhesive properties. These may be synthesized, but commercially available products can be used.

The random copolymers are Nipol 1500 and Nipol 150 manufactured by Nippon Zeon Co., Ltd.
2, Nipol 1507, Nipol 1006, Nipol 1
009, Nipol 2000; trade name JSR1500, JSR1502, JSR150 manufactured by Nippon Synthetic Rubber Co., Ltd.
3, JSR1013N, JSR0202 and the like.

The block copolymers are trade names TR1101, TR1118 and TR4122 manufactured by Shell Chemical Co.
S, TRKX138S; trade name Tuftec H manufactured by Asahi Kasei Co., Ltd., and the like. As the graft copolymer, trade names TR1122, TR1116, and T manufactured by Shell Chemical Co., Ltd.
R4205S etc. are mentioned.

The ratio of styrene-butadiene copolymer rubber used is 3 to 60% by weight, preferably 5% by weight in the pace polymer.
˜55 wt%. If this usage ratio is less than 3% by weight, the apparent viscosity of the pressure-sensitive adhesive composition at 90 ° C. does not decrease, and the parting property during coating decreases. If it exceeds 60% by weight, good tack cannot be obtained.

When polyisobutylene is added to the base polymer, it has the effects of improving the durability of the pressure-sensitive adhesive composition and suppressing the floating of the masking tape (particularly the floating of the tape edges) at high temperatures. Polyisobutylene is used in the base polymer in an amount of 0 to 32% by weight, preferably 0 to 30% by weight. This usage rate is 32
If the content exceeds 100% by weight, the pressure-sensitive adhesive composition undergoes phase separation,
A uniform composition cannot be obtained.

As the polyisobutylene, commercially available products can be used, and specifically, the product names Vistanex LM-MH and Vistanex MM-L-80 manufactured by Exxon Co.,
Vistanex MM-L-100, Vistanex MM
-L120, Vistanex MM-L-140; trade name Opanol B-10, Opanol B-80 by Basuf Company,
Opanol B-120 etc. are mentioned.

A preferred combination of the base polymers is (1) a blend of 40 to 97% by weight of natural rubber and 3 to 60% by weight of styrene-butadiene copolymer rubber, and (2) 40 to 97% by weight of natural rubber. , Styrene-butadiene copolymer rubber in excess of 25% by weight and 60% by weight or less, and polyisobutylene in 5 to 32% by weight.

(Zinc Oxide) Zinc oxide (zinc white) is not necessarily used, but since it acts as an activating aid in sulfur-free vulcanization, its incorporation accelerates the crosslinking reaction. The proportion of zinc oxide used is 0 to 100 parts by weight, preferably 1 based on 100 parts by weight of the base polymer.
-80 parts by weight, more preferably 2-50 parts by weight. If the usage ratio exceeds 100 parts by weight, the kneading operation becomes difficult, and the tack of the pressure-sensitive adhesive tape decreases. Zinc oxide is usually used by kneading it with a base polymer using an open roll, a pressure kneader, a Banbury mixer or the like.

(Tackifying Resin) The tackifying resin is used in a proportion of 20 to 150 parts by weight, preferably 30 to 100 parts by weight, based on 100 parts by weight of the base polymer. If this usage ratio is less than 20 parts by weight, sufficient tackiness cannot be obtained, and conversely, if it exceeds 150 parts by weight, the tack will decrease.

Examples of the tackifying resin include natural products such as rosin resin and terpene resin and their derivatives; aliphatic petroleum resin, alicyclic petroleum resin, aromatic petroleum resin, coumarone indene resin, Examples thereof include synthetic resins such as styrene-based resins, phenol resins, and xylene resins; these may be used alone or in combination of two or more kinds.

Examples of the rosin resin include rosin, polymerized rosin, hydrogenated rosin, rosin ester, hydrogenated rosin ester and rosin phenol resin. As a rosin,
Gum rosin, tall oil rosin, wood rosin (manufactured by Hercules, USA) and the like can be mentioned. Examples of the polymerized rosin include polypeel resin and Daimalex resin (manufactured by Rika Hercules). Examples of the hydrogenated rosin include steberite and Foral AX (manufactured by Rika Hercules). As rosin ester, ester gum A, ester gum AAV (manufactured by Arakawa Chemical Co., Ltd.), Harrier Star T, Harrier Star S (manufactured by Harima Kasei Co.), ester gum 8L, pentaline A (manufactured by Rika Hercules Co., Ltd.)
Etc. Examples of the hydrogenated rosin ester include ester gum H, ester gum HP (manufactured by Arakawa Chemical Co., Ltd.), pentaline H, Foral 85, Foral 105 (manufactured by Rika Hercules) and the like. Examples of the rosin phenol resin include Sumilite resin PR12603 (manufactured by Sumitomo Durez Co., Ltd.) and Tamanor 803 (manufactured by Arakawa Chemical Co., Ltd.).

As the terpene resin, a terpene resin,
There are terpene phenol resin, aromatic modified terpene resin and the like. Examples of the terpene resin include YS resin Px (produced by Yasuhara Yushi Co., Ltd.) and Piccolite A (produced by Hercules Co., Ltd.). Examples of the terpene phenol resin include YS Polystar T and Schenectady SP566 (manufactured by Schenectady, USA). Examples of the aromatic modified terpene resin include YS resin TO (produced by Yasuhara Yushi Co., Ltd.).

Examples of the aliphatic petroleum resin include Picco Pail (manufactured by Hercules), Escorets (manufactured by Esso Kagaku), Wing Tack 95 (manufactured by Goodyear, USA), Hilets (Mitsui Petrochemicals), Quinton A
(Manufactured by Nippon Zeon Co., Ltd.), Marcarets (manufactured by Maruzen Petrochemical Co., Ltd.), Coporex (manufactured by Toho Petroleum Resin Co., Ltd.) and the like. Examples of the alicyclic petroleum resin include Alcon P and Alcon M (manufactured by Arakawa Chemical Co., Ltd.). Examples of the aromatic petroleum resin include petrozine (manufactured by Mitsui Petrochemical Co., Ltd.) and high resin (manufactured by Toho Petroleum Resin Co., Ltd.).

Examples of the coumarone indene resin include coumarone NG (Nippon Steel Chemical). Examples of the styrene resin include piccolastic A (manufactured by Hercules). Examples of the phenol resin include hitanol (manufactured by Hitachi Chemical Co., Ltd.), tacky roll (manufactured by Sumitomo Chemical Co., Ltd.), and resin top (manufactured by Gunei Chemical Industry Co., Ltd.). Examples of the xylene resin include Nikanol (manufactured by Mitsubishi Gas Chemical Co., Inc.) and the like.

(Crosslinking Agent) In the present invention, a crosslinking agent (vulcanization accelerator) such as a thiuram compound is used to crosslink the base polymer by sulfur-free vulcanization. The thiuram compound is a component that crosslinks the pressure-sensitive adhesive and is used in a proportion of 0.05 to 7 parts by weight with respect to 100 parts by weight of the base polymer. If the usage ratio is less than 0.05 parts by weight, solvent resistance and heat resistance are deteriorated and the pressure-sensitive adhesive tends to remain. Further, if it exceeds 7 parts by weight, the crosslink density becomes high, so that the solvent resistance and the heat resistance are improved, but the tackiness at a high temperature and the sorption property of the solvent become low, and the parting property is deteriorated.

Examples of the thiuram compounds include tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram monosulfide, tetrabutylthiuram disulfide, tetramethylthiuram monosulfide, N, N'-dimethyl-N, N'-diphenylthiuram disulfide. , Dipentamethylene thiuram monosulfide, dipentamethylene thiuram disulfide, dipentamethylene thiuram tetrasulfide, dipentamethylene thiuram hexasulfide, dicyclopentamethylene thiuram disulfide, and the like.

The dithiocarbamate-based compound, the xanthogenate-based compound and the thiazole-based compound have the action of promoting the crosslinking reaction, and they are used alone or in combination of two or more kinds. The use ratio of these components is 0.05 to 10 parts by weight based on 100 parts by weight of the base polymer. This usage rate is 0.
If it is less than 05 parts by weight, the effect is low, and if it exceeds 10 parts by weight, the adherend is contaminated, which is not preferable.

As the dithiocarbamate compound,
Pentamethylenedithiocarbamic acid piperidine salt, pipecolyldithiocarbamic acid pipecoline salt, lead dimethyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, zinc dimethylpentamethylenedithiocarbamate, lead ethylphenyldithiocarbamate, potassium dimethyldithiocarbamate, potassium dibutyldithiocarbamate , Selenium dimethyldithiocarbamate, selenium diethyldithiocarbamate, bismuth dimethyldithiocarbamate, zinc dimethyldithiocarbamate,
Zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, zinc dibenzyldithiocarbamate, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, sodium dibutyldithiocarbamate, Examples thereof include copper dimethyldithiocarbamate, ferric dimethyldithiocarbamate, and tellurium diethyldithiocarbamate.

Examples of the xanthate-based compound include zinc butylxanthate, zinc isopropylxanthate, sodium isopropylxanthate, zinc ethylxanthate, dibutylxanthogen disulfide and the like.

Examples of thiazole compounds include 2-mercaptobenzothiazole, 2-mercaptothiazoline, dibenzothiazyl disulfide, 2-mercaptobenzothiazole zinc salt, 2-mercaptobenzothiazole copper salt, 2-mercaptobenzothiazole sodium salt, and 2 −
(2 ′, 4′-Dinitrophenylthio) benzothiazole, 2-mercaptobenzothiazolecyclohexylamine salt, 2- (N, N-diethylthiocarbamoylthio) benzothiazole, 2- (2,6-dimethyl-4-)
Examples thereof include morpholinothio) benzothiazole and 2- (4'-morpholinodithio) benzothiazole.

(Pressure Sensitive Adhesive Composition) The pressure sensitive adhesive composition of the present invention contains the above-mentioned components. In addition to the above, for example, phenol-based, amine-based, thioether-based Anti-aging agents such as fighting agents, softeners, plasticizers,
Fillers other than zinc white, colorants and the like can be added as required.

The pressure-sensitive adhesive composition is dissolved in one or more organic solvents such as toluene, hexane, heptane, methyl ethyl ketone, acetone, methanol, isopropanol, ethyl acetate, butyl acetate, etc., and the obtained solution is supported. Apply it on your body's plastic film and dry
Crosslink.

Examples of the plastic film include polyester film, polyethylene film, polypropylene film and the like. When the solvent resistance of these films is poor, an organic solvent solution of the pressure-sensitive adhesive composition is previously coated on a release paper to form a pressure-sensitive adhesive composition layer, and then the layer is formed on the plastic film. May be transferred to.

The crosslinking of the base polymer is carried out simultaneously with the drying of the pressure-sensitive adhesive composition layer. This drying / crosslinking is usually
It is carried out by heating at 80 to 150 ° C for 1 to 5 minutes. When the crosslinking is insufficient, the tape may be wound into a roll and then post-crosslinked at 40 to 150 ° C. for 1 hour to 1 week.

The masking tape thus obtained is used when the apparent viscosity of the pressure-sensitive adhesive is measured under the conditions according to the measuring method of the holding force specified in JIS-Z-0237 item 11. The apparent viscosity at 90 ° C. calculated by the formula [I] is preferably in the range of 0.5 × 10 ⁷ to 1 × 10 ⁸ poise. If the apparent viscosity at 90 ° C. is less than 0.5 × 10 ⁷ poises, when peeled after baking and drying, the residual pressure sensitive adhesive to the adherend member surface occurs, the paint to exceed 1 × 10 ⁸ poise in the opposite The close-off property becomes poor.

Η = [W / S × 980] · h / D [I] η: Apparent viscosity (poise) S: Application area (cm ² ) W: Load (stress) (g) h: Pressure-sensitive adhesive layer Thickness (cm) D: Flow rate (cm / sec) [W / S × 980] is shear stress (dyne / cm ² ).
Indicates. Further, the flow velocity D is calculated by reading the deviation distance Δx at every predetermined time interval t and calculating the average value thereof.

Specifically, cleaned stainless steel (SU
S304) The test plate is attached so that the area of 25 × 25 mm of the test piece is in contact, and the non-attached portion is folded over with the inner surface facing inward. The test piece is pressed back and forth once with a roller at a pressure-bonding speed of about 300 mm / min. The test piece is heated to the measurement temperature of 90 ° C. Make the test piece hang vertically and put 100
Attach a weight of 0 g and apply the load. Then 5
After a second, the start point is read, the deviation distance (Δx) of the test piece is read at predetermined time intervals (60 seconds), and the flow velocity D is calculated from the average value of the five points.

[0045]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The blending amount is parts by weight unless otherwise specified.

The methods for measuring the physical properties are as follows. <Viscosity> Apparent viscosity at 90 ° C. (×
10 ⁷ poise) was measured. <Solvent resistance> Test piece of adhesive tape (15 mm x 30 m
m) was immersed in toluene, the dissolved state was observed after 5 minutes, and the evaluation was performed according to the following three stages. ×: dissolved, Δ: partially dissolved, ◯: not dissolved.

<Discontinuity> A polypropylene plate was washed with trichloroethane, an adhesive tape was attached, and then a urethane-based paint was sprayed so that the thickness after drying was 30 μm. After drying at 120 ° C. for 20 minutes, the generation state of bubbles in the coating film at the tape edge portion was visually observed and evaluated in the following three stages. ×: There are many bubbles, Δ: There are some bubbles, ◯: No bubbles.

<Pasted trace> After washing the polypropylene plate with trichloroethane, a urethane-based paint is sprayed so that the thickness after drying is 30 μm, and then the temperature is 120 ° C. for 20 minutes.
A test plate was prepared by drying for a minute. An adhesive tape was attached to this, and after heating at 120 ° C. for 20 minutes, the adhesive tape was peeled off, and the state of the peeled marks on the peeled surface was visually observed,
The following three grades were used for the evaluation. X: A large amount of adhesive residue, Δ: a little adhesive residue, ◯: no adhesive residue.

<Tack> Measured by the ball rolling method of JIS Z-0237, 12 and evaluated by the following criteria by ball number. ×: less than ball nubber 5, ◯: ball number 5 or more.

[Examples 1 to 3 and Comparative Examples 1 to 3] Natural rubber was kneaded with zinc white by an open roll and masticated. Then, each component shown in Table 1 was added and dissolved in toluene with stirring. Let The obtained solution was applied to a polypropylene film (thickness 40 μm), dried at 80 ° C. for 5 minutes and crosslinked. Then, the tape was wound on a roll and left at 60 ° C. for 24 hours for post-crosslinking. The dry thickness of the pressure sensitive adhesive layer was 32 μm. The results are shown in Table 1.

[0051]

[Table 1]

The components in Table 1 are as follows. <NR> Natural rubber; Natural rubber was prepared by previously kneading zinc white with an open roll. Zinc white was blended in an amount of 10 parts with respect to 100 parts of the base polymer. However, in Table 1, only the NR component is shown. <SBR> Styrene-butadiene copolymer rubber; Nippon Zeon Co., Ltd.
Nipol 1006 <PIB>Polyisobutylene; Exxon, Vistanex MM
-L-100 <Escoletts> Aliphatic petroleum tree; manufactured by Esso Chemical Co., Ltd. <TBT> Tetrabutylthiuram disulfide (thiuram compound) <ZBX> Zinc butylxanthogenate (xanthogenic acid compound) <M> 2-Mercaptobenzothiazole (Thiazole-based compound) In Comparative Example 3, the pressure-sensitive adhesive solution was phase-separated and the test piece could not be prepared.

[Examples 4 to 5 and Comparative Examples 4 to 6] Adhesive tapes were prepared in the same manner as in Examples 1 to 3 except that pressure sensitive adhesive compositions were prepared according to the formulations shown in Table 2. , And evaluated in the same manner. The results are shown in Table 2.

[0054]

[Table 2] In the test piece of Comparative Example 4, a part of the pressure-sensitive adhesive remained in the parting test.

[0055]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a good pressure-sensitive adhesive composition for a masking tape, which has an excellent parting property for coating masking and has no residual (sticking mark) of the pressure-sensitive adhesive.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location C09J 107/00 JDW 8218-4J 109/06 JDX 8218-4J 123/22 JBZ 7107-4J // B05D 1/32 8720-4D C09J 7/02 JJX 6770-4J (72) Inventor Shigeyuki Hayashi 2-4, Kudanminami 2-4, Chiyoda-ku, Tokyo Nichiban Co., Ltd.

Claims (3)

[Claims] 1. (A) 40 to 97% by weight of natural rubber,
Based on 100 parts by weight of a base polymer containing 3 to 60% by weight of styrene-butadiene copolymer rubber and 0 to 32% by weight of polyisobutylene, (B) 0 to 10 zinc oxide.
0 parts by weight, 20 to 150 parts by weight of (C) tackifying resin,
(D) 0.05 to 7 parts by weight of thiuram compound, and 0.05 to 10 parts by weight of at least one compound selected from the group consisting of (E) dithiocarbamate compound, xanthogenate compound and thiazole compound. A pressure-sensitive adhesive composition for a masking tape, which comprises: 2. The base polymer is natural rubber 40-97.
The composition according to claim 1, which comprises 3% to 60% by weight of styrene-butadiene copolymer rubber. 3. The base polymer is natural rubber 40-97.
The composition according to claim 1, wherein the composition comprises, by weight, more than 25% by weight of styrene-butadiene copolymer rubber and 60% by weight or less, and 5 to 32% by weight of polyisobutylene.