WO2000018588A1

WO2000018588A1 - Composition for eraser rubber

Info

Publication number: WO2000018588A1
Application number: PCT/JP1999/005225
Authority: WO
Inventors: Noboru Sakamaki; Kyoko Kobayashi; Akira Uchiyama
Original assignee: Mitsui Chemicals, Inc.
Priority date: 1998-09-25
Filing date: 1999-09-24
Publication date: 2000-04-06

Abstract

A composition for eraser rubbers which comprises a thermoplastic olefin elastomer comprising 50 to 5 parts by weight of a crystalline polyolefin (a) and 50 to 95 parts by weight of an olefin copolymer rubber (b) (provided that the sum of components (a) and (b) is 100 parts by weight), wherein the rubber (b) has been wholly or partly crosslinked.

Description

Description Eraser composition Technical field

The present invention relates to an olefin-based thermoplastic elastomer composition for an eraser which has excellent erasing performance, has no migration property, and is reusable. Background art

One type of eraser known at present is a natural rubber-based eraser, which is made by mixing natural rubber as a base material with a filler, adjusting the vulcanization state using sulfur, and finishing. The natural rubber-based eraser can freely adjust the hardness of the eraser by adjusting the mixing ratio of the natural rubber and the filler and the vulcanization state, and can obtain a strong one against bending and breaking. The vulcanization reaction proceeds easily under the influence of sunlight and temperature, and becomes hard or brittle.

In addition, polyvinyl chloride-based erasers are made by mixing vinyl chloride resin with plasticizers and fillers, then heat-treating and molding. There was a problem that a part of the plasticizer used was liberated, bleeded to the product surface, transferred to a paint such as a pencil, and eroded the surface to make it sticky.

On the other hand, elastomer-based synthetic rubber-based erasers deal with the problem that some plasticizers used in polyvinyl chloride-based erasers migrate to paints such as pencils due to release of part of the plasticizer and attack the surface. Therefore, it is considered as an eraser that does not require the use of a plasticizer. These include low-crystalline polyolefin-based thermoplastic elastomers, fillers such as rubber (substrate), and, if necessary, chlorinated polyethylene (Japanese Patent Publication No. 58-4). No. 72) or a copolymer of polyethylene and polypropylene, ethylene propylene rubber, white sub and glycerin or a derivative thereof, and a filler (Japanese Patent Publication No. 58-54004) Publication). In all of these, white sub was an essential component in order to achieve erasure performance, but it was easily deteriorated over time and the eraser performance was insufficient. Among the fillers, white subice (white factice), amesub (semi-trans lucent factic e), black sub (brown factice) and the like contain free sulfur. If the molding temperature rises to 180 ° C or higher, the molded product will become brownish-colored and have an irritating odor when mixed with olefin-based elastomer mixed with polypropylene resin and processed. Therefore, the eraser performance is not satisfied. Disclosure of the invention

An object of the present invention is to solve the problems of the conventional eraser as described above, and is excellent in erasing performance, has no migration property, does not deteriorate with time, and is reusable. An object of the present invention is to provide a composition for an eraser that does not require a sulfuric acid reaction step, can be streamlined in molding and manufacturing a product, and has no discoloration and no pungent odor even by high-temperature molding.

The present invention includes the following inventions.

(1) A thermoplastic thermoplastic elastomer containing 50 to 5 parts by weight of a crystalline polyolefin (a) and 50 to 95 parts by weight of an olefin copolymer rubber (b) [where component (a) and The total amount of (b) is 100 parts by weight. ] The composition for an eraser according to claim 1, wherein the olefin copolymer rubber (b) is completely or partially crosslinked.

(2) Olefin copolymer rubber (b) Strength \ 100 parts by weight of fully or partially cross-linked thermoplastic elastomer, containing 5 to 300 parts by weight of filler (c) The composition according to the above (1).

(3) The composition according to (2), wherein the filler (c) is a sulfur-free sub.

(4) The composition according to (1), wherein the crystalline polyolefin (a) is a polypropylene resin.

(5) The composition according to (2), wherein the crystalline polyolefin (a) is a polypropylene resin. (6) The composition according to the above (1), wherein the olefin copolymer rubber (b) is dispersed in the olefin thermoplastic elastomer with a particle size of 50 μm or less.

(7) The composition according to (2), wherein the olefin copolymer rubber (b) is dispersed in the olefin thermoplastic elastomer with a particle size of 50 μπι or less.

The composition for an eraser of the present invention is a olefin-based thermoplastic elastomer containing 50 to 5 parts by weight of a crystalline polyolefin (a) and 50 to 95 parts by weight of an olefin copolymer rubber (b). The total amount of (a) and (b) is 100 parts by weight. ] The composition for an eraser according to claim 1, wherein the olefin copolymer rubber (b) is completely or partially crosslinked. In the composition, the crystalline polyolefin (a) is desirably a polypropylene resin, and the olefin copolymer rubber (b) is dispersed in the olefin thermoplastic elastomer with a particle size of 50 or less. Is desirable.

Further, the composition may contain, if necessary, a filler (c) such as calcium carbonate or a sulfur-free sub-substrate in an amount of 5 to 300 parts by weight based on 100 parts by weight of the completely or partially cross-linked thermoplastic elastomer. It may be contained in parts by weight.

The eraser composition of the present invention preferably does not contain a chlorine-based material such as polyvinyl chloride.

Hereinafter, the eraser composition of the present invention will be described in detail.

The olefin thermoplastic elastomer used as the base material for the eraser used in the present invention comprises a crystalline polyolefin (a) and an olefin copolymer rubber (b), and the weight ratio (aZb) is It is in the range of 50 50-595, preferably 2575-10Z90. If the compounding ratio of the crystalline polyolefin (a) is too high, the thermoplastic elastomer becomes too hard, the feel of the rubber of the eraser disappears, the handwriting of pencils and mechanical pencils worsens, and eraser residue is generated. As it gets worse, the erasing performance decreases.

Examples of the crystalline polyolefin (a) used in the present invention include a homopolymer or a copolymer of α-olefin having 2 to 20 carbon atoms.

Specific examples of the crystalline polyolefin (a) include the following (co) polymers. (1) Ethylene homopolymer (manufacturing method may be either low pressure method or high pressure method)

(2) Copolymer of ethylene with 10% or less by mol of other α-olefin or vinyl monomer such as vinyl acetate or ethyl acrylate

(3) Propylene homopolymer (polypropylene resin)

(4) Random copolymer of propylene and 10 mol% or less of other "monoolefin"

(5) Block copolymer of propylene and 30% or less of other α-olefins

(6) 1-butene homopolymer

(7) Random copolymer of 1-butene and 10 mol% or less of other α-olefin

(8) 4-methyl-pentene homopolymer

(9) Random copolymer of 4-methyl-1-pentene and up to 20 mol% of other α-olefin

Specific examples of the α-olefin include ethylene, propylene, 1-butene, toppentene, 1-hexene, 1-octene, 1-decene, 2-methyl-propene, and 3-methyl- Examples include 1-pentene and 4-methylpentene.

The olefin copolymer rubber (b) used in the present invention is an amorphous random elastic copolymer containing α-olefins having 2 to 20 carbon atoms as a main component, and two or more α-olefins. And α-olefins comprising two or more types of α-olefins and non-conjugated gens, and the like.

Specific examples of such an olefin copolymer rubber (b) include the following rubbers.

(1) Ethylene 'α-olefin copolymer rubber

[Ethylene-olefin (molar ratio) = about 90 10-50-50]

(2) Ethylene .α-olefin 'non-conjugated gen copolymer rubber

[Ethylene // «-olefin (molar ratio) = about 90Z1 0-50 050]

(3) Propylene / monoolefin copolymer rubber

[Propylene / α-olefin (molar ratio) = Approx. 90/10 50-50]

(4) Butene-α-olefin copolymer rubber

[Butene-olefin (molar ratio) = about 90 10-50 / 50] Specific examples of the α-olefin include the same α-olefins as the specific examples of the one-year-old refin constituting the above-mentioned crystalline polyolefin. Specific examples of the non-conjugated diene include dicyclopentadiene, 1,4-hexadiene, cyclooctadiene, methylenenorbornene, and ethylidene norbornene.

These copolymer rubbers generally have a viscosity of ML 1 + 4 (100 ° C.) of 10 to 250, preferably 40 to 150. The iodine value when the non-conjugated diene is copolymerized is preferably 25 or less from the viewpoint of fluidity and moldability.

The above-mentioned olefin copolymer rubber is present in the thermoplastic elastomer in a crosslinked state such as partially crosslinked or completely crosslinked, and is particularly preferably present in a partially crosslinked state. When the rubber component is cross-linked, the rubber itself becomes less elongated and the elasticity of the rubber also increases. Therefore, when the rubber component is used by pressing it lightly as an eraser, the erasure surface can be moderately pressed and the erasure performance improves. Further, the eraser scraps are easily cut, and the erasing performance can be improved. If the rubber component is non-crosslinked, the eraser will have a large elongation, the eraser will stick, and the erasure performance will be extremely poor.

As a crosslinking agent for crosslinking such an olefin copolymer rubber, an organic peroxide-phenol crosslinking agent or the like is used.

Specific examples of the organic peroxide include dicumylperoxide, di-tert-butylperoxide, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, and 2,5. -Dimethyl-2,5-di (tert-butylperoxy) hexine-3,1,3-bis (tert-butylperoxyisopropyl) benzene, 1,1-bis (tert-butylperoxy) -3,3 , 5-Trimethylcyclohexane, n-butyl-4,4_bis (tert-butylperoxy) valerate, benzoylperoxide, p-chlorobenzoylperoxide, 2,4-dichlorobenzoylperoxide, tert-butylperoxy benzoate, tert-butylperoxyisopropyl carbonate, diacetyl peroxide, lauroyl beloxide, tert-butylcumylperoxide and the like. It is.

Specific examples of the phenolic crosslinking agent include a phenolic resin. The rubber other than the copolymer rubber (b) can be blended with the thermoplastic thermoplastic elastomer used in the present invention. Examples of such other rubbers include, for example, styrene rubbers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), natural rubber (NR), butyl rubber (IIR), SEBS, and polybutylene. Of these, butyl rubber is preferably used. The eraser performance of the composition in which the crosslinked olefin rubber and the above-mentioned rubber are blended is good, and the erasure performance is good because the scraps are easily generated.

When the olefin copolymer rubber and the other rubber are used in combination with the olefin thermoplastic elastomer, the other rubber is a total of 100% by weight of the crystalline polyolefin and the olefin copolymer rubber. The amount is usually 40 parts by weight or less, preferably 5 to 30 parts by weight with respect to parts by weight. In the case of a component in which the olefin copolymer rubber is blended more than the other rubbers, one that has little change over time can be obtained by bridging by dynamic heat treatment.

Furthermore, additives such as mineral oil-based softeners, heat stabilizers, antistatic agents, weather stabilizers, anti-aging agents, coloring agents, lubricants, and fragrances may be added to the olefin thermoplastic elastomers as necessary. It can be blended in a range that does not impair the object of the present invention.

The olefinic thermoplastic elastomer preferably used in the present invention comprises crystalline polypropylene and ethylene'α-olefin copolymer rubber or ethylene'α-olefin.non-conjugated gen copolymer rubber. In the plastic elastomer, these rubbers are present in a partially cross-linked state, and the weight ratio of the crystalline polypropylene to the olefin copolymer rubber is preferably 5Ο / δΟδΖθδ. Is in the range of 25Ζ75 to 10Ζ90.

More specific examples of the thermoplastic elastomer preferably used in the present invention include (0) 50 to 5 parts by weight of crystalline polypropylene (a-1), and (ii) ethylene 'propylene copolymer rubber or ethylene. 50 to 95 parts by weight of rubber (b-1) composed of propylene / non-conjugated gen copolymer rubber [the total amount of components (a-1) and (b-1) is 100 parts by weight]; (Hi) A mixture of the rubber (d-1) other than the rubber (b-1) and 5 to 100 parts by weight of a rubber or a mineral oil-based softener (d-2) is prepared in the presence of an organic peroxide. The rubber (b-1) obtained by dynamic heat treatment is cross-linked Thermoplastic elastomers.

Mineral oil-based softeners soften the rubber component and reduce its hardness even when crosslinked, and when fillers are mixed, increase the dispersibility of the fillers and the resulting thermoplasticity. The molding processability of the elastomer can be improved.

Further, the eraser performance of the composition to which such a mineral oil-based softening agent is added is suitable for appropriately removing shavings and improving the erasing performance.

Examples of the mineral oil-based softener include process oil, lubricating oil, paraffin oil, liquid paraffin, petroleum asphalt, and petrolatum.

In the present invention, when an organic peroxide is used as the cross-linking agent, it is usually 0.05 to 3 parts by weight, preferably 0.1 to 3 parts by weight, based on 100 parts by weight of the total amount of crystalline polyolefin and rubber. Used in a proportion of 1 part by weight.

In the partial cross-linking treatment with the above-mentioned organic peroxide, io, P-quinone dioxime, ρ, ρ'-dibenzoyl quinone dioxime, Ν-methyl-Ν-4-dinitrosaniline, nitrosobenzene, diphenyldananidin, trimethylol Peroxide cross-linking aids such as propane-N, N, -m-phenylenediimide, or divinylbenzene, triarylcyanurate, ethylene glycol dimethacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate And polyfunctional methacrylate monomers such as trimethylolpropane trimethacrylate and aryl methacrylate; and polyfunctional vinyl monomers such as vinyl butylate and vinyl stearate. By using such a compound, a uniform and mild crosslinking reaction can be expected. Particularly, in the present invention, divinylbenzene is most preferred. Divinylbenzene is easy to handle, has good compatibility with the crystalline polyolefin and rubber, which are the main components of the crosslinked product, has the action of solubilizing the organic peroxide, and has a function of dispersing the organic peroxide. Since it acts as an agent, a thermoplastic elastomer having a uniform cross-linking effect due to heat treatment and a good balance between fluidity and physical properties can be obtained.

The crosslinking aid or the polyfunctional vinyl monomer as described above is used in a proportion of usually 0.1 to 2% by weight, preferably 0.2 to 2% by weight, based on the whole to-be-crosslinked product. The thermoplastic elastomer of the present invention is obtained by dynamically heat treating a crystalline polyolefin and a rubber in the presence of a crosslinking agent. The thermoplastic elastomer thus obtained has a phase structure in which crosslinked rubber is dispersed in the form of islands using crystalline polyolefin as a matrix. The particle size of the crosslinked rubber particles thus dispersed is preferably 50 zm or less. In this way, by dispersing the olefin copolymer rubber to a particle size of 50 im or less, a uniform component is obtained, and as an eraser, eraser scraps appear properly and the erasing performance is improved. If the amount of the crosslinking agent is too large, or if the balance with the crosslinking aid or the polyfunctional vinyl monomer is poor, the crosslinking reaction of the rubber and the dispersion balance with the crystalline polyolefin will be lost, and the crosslinking reaction of only the rubber component will proceed too much and the rubber The particle size exceeds 50 μπι due to the dispersion of the polyolefin, which causes poor dispersion with the crystalline polyolefin, so that it cannot be provided as a uniform component. On the other hand, if the amount of the crosslinking agent is extremely small, the crosslinking reaction will be insufficient, so that appropriate rubber elasticity will not be exhibited, and the softness and rubber feeling peculiar to the eraser will be lost. Would.

The above-mentioned “dynamically heat-treating” refers to kneading the above components in a molten state.

As the kneading device, a conventionally known kneading device, for example, an open-type mixing roll, a non-open-type Banbury mixer, an extruder, a kneader, a continuous mixer, or the like is used. Among these, a non-open type kneading device, for example, a twin screw extruder is preferable, and the kneading is preferably performed in an atmosphere of an inert gas such as nitrogen gas or carbon dioxide gas. The kneading is preferably performed at a temperature at which the half-life of the organic peroxide used is less than 1 minute. The kneading temperature is usually from 150 to 280 ° C, preferably from 170 to 240 ° C, and the kneading time is usually from 1 to 20 minutes, preferably from 3 to 10 minutes. Further, the shear force applied is, 1 0 0 sec one ¹ or more as shear rate, preferably 5 0 0 ~ 1 0, 0 0 0 sec - is determined within ^1.

The thermoplastic elastomer particularly preferably used in the present invention is partially crosslinked. The term “partially crosslinked” means that the gel content measured by the following method is 20 to 98% by weight. "Completely crosslinked" means that the gel content is 98% by weight or more. In the present invention, the gel content is 40 to 9 It is preferably in the range of 8% by weight.

[Method for measuring gel content]

A 100 mg sample of the thermoplastic elastomer was sampled and cut into 0.5 mm x 0.5 mm x 0.5 mm strips. After immersion for 48 hours in, remove the sample onto filter paper and dry at room temperature for at least 72 hours until the weight becomes constant. From the weight of the dried residue, the weight of all cyclohexane-insoluble components (fibrous filler, filler, pigment, etc.) other than the polymer component, and the crystalline polyolefin (a) in the sample before cyclohexane immersion The value obtained by subtracting the weight of the final weight is referred to as “corrected final weight (Y)”.

On the other hand, the weight of the olefin copolymer rubber (b) in the sample is referred to as “corrected initial weight (X)”.

Here, the gel content is obtained by the following equation.

Gel content [wt%]

= [Final weight captured (Y) initial weight corrected (X)] X 100

In the eraser composition of the present invention, when a filler is blended with the olefin thermoplastic elastomer, the filler may be, for example, calcium silicate, calcium carbonate, kaolin, clay, or sulfur-free. And the like. These fillers can be used alone or in combination of two or more. Among these fillers, sulfur-free sub and calcium carbonate are preferably used. The sulfur-free sub is a sub that does not contain a free sulfur component and does not contain a toxic sulfur component, so it is safe and has little deterioration over time. Among the fillers, the white sub contains free sulfur, but in the sample containing this white sub, brownish discoloration is seen, and a nose-like irritating odor is generated. Not deserve to be satisfied.

Sulfur-free property sub is, for example, sulfur-free from Tenma Sub Kako Co., Ltd. of Osaka, Japan U - are commercially available under the trade name 8 ^TM or sulfur-free U- 1 0 ^TM, this can be used. Sulfur-free U- 8 ^TM and sulfur-free U- 1 0 ^TM does not contain sulfur and chlorine content, ash content is less than 2 wt% 0., specific gravity (JIS K7 1 1 2 A method) 1. 0 1 ± 0.02.

The filler is a fully or partially cross-linked olefin thermoplastic elastomer. It is usually used in an amount of 5 to 300 parts by weight, preferably 10 to 250 parts by weight, per 100 parts by weight. By using the filler in such a range, the eraser performance is good. Erasers are easy to appear, the eraser feels a little heavy when held, and a good eraser that requires less force when erasing. A feeling is obtained.

These fillers may be used as they are in powder form, or they may be mixed with crystalline polyolefin polyethylene resin, polypropylene resin, or ethylene-propylene copolymer in order to suppress scattering of the powder and facilitate mixing. It may be kneaded into united rubber or the like and used as a batch of filler master.

When molding an eraser, the olefin-based thermoplastic elastomer is composed of crystalline polyolefin and rubber and has excellent fluidity, so it has been used in compression molding, transfer molding, injection molding, extrusion molding, etc. It can be molded using a molding device.

This description includes part or all of the contents as disclosed in the description of Japanese Patent Application No. 10-270409, which is a priority document of the present application. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

(Example 1)

MFR (ASTM D 1 238—65 T, 230 ° C) 24 gZl 0 min, density 0.91 1 gZcm ³ polypropylene (a-1) 10 parts by weight, ethylene content 67 mol%, iodine value 1 3 、 Methylene viscosity ML 1 + 4 (100 ° C) 74 Ethylene propylene .5-ethylidene-2-norbornene copolymer rubber (b-1) 90 parts by weight and Banbury mixer After kneading at 180 ° C. for 5 minutes in a nitrogen atmosphere, the kneaded material was passed through a roll to form a sheet, which was cut with a sheet cutter to produce a square pellet.

Next, the angular pellets, 2,5-dimethyl-2,5-di- (tert-butylperoxy) hexyne-30.8 parts by weight as a crosslinking agent, and divinylbenzene (DVB) as a polyfunctional vinyl monomer 0.8 parts by weight with a Henschel mixer. Was.

Next, this mixture was extruded at 220 ° C. in a nitrogen atmosphere using a twin screw extruder having an LZD = 40 and a screw diameter of 50 mm to obtain an olefin thermoplastic elastomer.

The gel content of the obtained olefin thermoplastic elastomer was 91% by weight as determined by the above method.

Next, a sheet having a thickness of 1 mm was prepared by compression molding, and a hardness and tensile test were performed according to JIS K6301.

Further, a sample having a thickness of 10 mm and a width of 30 mm was formed by extrusion using a 500 mm single screw extruder. The prepared sample was cut into a suitable length, the appearance was observed, and evaluated according to the following criteria.

〇 · · · White, odorless.

△ · · 'Slight discoloration power Odorless.

X-· 'Brown discoloration is observed, with an irritating odor.

In addition, a erasure performance test was performed according to JIS S6004. The erasure performance is shown by erasure rate (%).

Table 1 shows the results.

(Example 2)

The olefin was prepared in the same manner as in Example 1 except that 25 parts by weight of polypropylene (a-1) and 75 parts by weight of ethylene 'propylene' 5-ethylidene-2-norbornene copolymer rubber (b-1) were used. A thermoplastic elastomer was obtained.

The gel content of the obtained olefin thermoplastic elastomer was 88% by weight.

Then, in the same manner as in Example 1, a hardness, a tensile test, an appearance observation of the molded sample, and a erasure performance test were performed.

Table 1 shows the results.

(Example 3)

25 parts by weight of polypropylene (a-1), 55 parts by weight of ethylene / propylene '5-ethylidene-2-norbornene copolymer rubber (b-1), and 0.6 g of MFR A olefin thermoplastic elastomer was obtained in the same manner as in Example 1 except that 20 parts by weight of butyl rubber (d-1) for 10 minutes was used.

The gel content of the obtained olefin thermoplastic elastomer was 83% by weight.

Table 1 shows the results.

(Example 4)

25 parts by weight of polypropylene (a-1), 75 parts by weight of ethylene / propylene '5-ethylidene-2-norbornene copolymer rubber (b-1), and paraffinic oil (d — 2) (PW-380, manufactured by Idemitsu Kosan Co., Ltd.) An olefin thermoplastic elastomer was obtained in the same manner as in Example 1 except that 40 parts by weight was used.

The gel content of the obtained olefin thermoplastic elastomer was 86% by weight.

Table 1 shows the results.

(Example 5)

25 parts by weight of polypropylene (a-1), 75 parts by weight of ethylene 'propylene' 5-ethylidene-2-norbornene copolymer rubber (b-1), and heavy calcium carbonate (c-1) ( An olefin thermoplastic elastomer was obtained in the same manner as in Example 1 except that 50 parts by weight of Whiten SB (Shiraishi Calcium Co., Ltd.) was used.

The gel content of the obtained olefin thermoplastic elastomer was 85% by weight.

Table 1 shows the results. (Example 6)

25 parts by weight of polypropylene (a-1), 75 parts by weight of ethylene 'propylene' 5-ethylidene-2-norbornene copolymer rubber (b-1), and sulfur-free yellow sub (c-2 ) An olefin thermoplastic elastomer was obtained in the same manner as in Example 1 except that 50 parts by weight of sulfur-free U-8 (manufactured by Tenma Sub Chemical Co., Ltd.) was used.

Table 1 shows the results.

(Example 7)

25 parts by weight of polypropylene (a_ 1), 75 parts by weight of ethylene 'propylene' 5-ethylidene-2-norbornene copolymer rubber (b-1), and white sub (c-13) as a filler (Olefin Thermoplastic Elastomer) was obtained in the same manner as in Example 1 except that 50 parts by weight (manufactured by Tenma Sabuko Kako Co., Ltd.) was used.

The gel content of the obtained olefin thermoplastic elastomer was 87% by weight.

Table 1 shows the results.

(Comparative Example 1)

A Banbury mixer was used in the same manner as in Example 1 using 25 parts by weight of polypropylene (a_1) and 75 parts by weight of ethylene 'propylene' 5-ethylidene-2-norbornene copolymer rubber (b-1). A square pellet was manufactured using a sheet, a roll and a sheet cutter.

Further, extruding with a twin-screw extruder was performed in the same manner as in Example 1 except that 2,5-dimethyl-2,5-di- (tert-butylperoxy) hexyne-3 and vinylbenzene were not used. An olefinic thermoplastic elastomer was obtained.

Next, the same procedure as in Example 1 was performed using the obtained olefin thermoplastic elastomer. The hardness, tensile test, appearance observation of the molded sample, and erasure performance test were performed in the same manner.

Table 1 shows the results.

(Comparative Example 2)

The procedure of Example 1 was repeated, except that 60 parts by weight of polypropylene (a-1) and 40 parts by weight of ethylene / propylene '5-ethylidene-2-norbornene copolymer rubber (b-1) were used. A thermoplastic elastomer was obtained.

The gel content of the obtained olefin thermoplastic elastomer was 90% by weight.

Table 1 shows the results.

table 1

All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety. Industrial applicability

Since the eraser composition of the present invention uses an olefin-based thermoplastic elastomer as a base material, it has no migration property, does not deteriorate with time, and has burrs generated during molding and a raw material remaining after the product is collected. It is possible to reuse such as crushing and re-forming. Furthermore, since the rubber-based thermoplastic elastomer is in a cross-linked state, the rubber component has less adhesiveness than a non-cross-linked state, and is easily exfoliated and has excellent erasing performance.

In addition, since the vulcanization reaction step is not required for the formation of the eraser, it is possible to streamline the molding and manufacturing of the product.

Claims

The scope of the claims

1. Olefin-based thermoplastic elastomer containing 50 to 5 parts by weight of crystalline polyolefin (a) and 50 to 95 parts by weight of olefin copolymer rubber (b) [However, components (a) and (b) ) Is 100 parts by weight. ] The composition for an eraser according to claim 1, wherein the olefin copolymer rubber (b) is completely or partially crosslinked.

2. The claim that the filler (c) contains 5 to 300 parts by weight with respect to 100 parts by weight of the fully-partially or partially cross-linked thermoplastic elastomer (b). 2. The composition according to claim 1, wherein

3. The composition according to claim 2, wherein the filler (c) is a sulfur-free sub.

4. The composition according to claim 1, wherein the crystalline polyolefin (a) is a polypropylene resin.

5. The composition according to claim 2, wherein the crystalline polyolefin (a) is a polypropylene resin.

6. The composition according to claim 1, wherein the olefin copolymer rubber (b) is dispersed in the olefin thermoplastic elastomer with a particle size of not more than 50 ^ η.

7. The composition according to claim 2, wherein the olefin-based copolymer rubber (b) is dispersed in the olefin-based thermoplastic elastomer with a particle size of 50 im or less.