JP2013091230A - Eraser - Google Patents

Abstract

[PROBLEMS] To provide an eraser made of polyvinyl chloride resin, which is soft and deformable in accordance with a dent in a handwritten portion on paper, such as a polyvinyl chloride eraser, and has a good abrasion property capable of generating debris with a light load. Providing erasers that do not use vinyl chloride resin, which produces harmful substances during incineration, or plasticizers that are likely to be endocrine disruptors.
A three-block copolymer or a star-shaped block copolymer having a molecular structure in which a molecular constraint component for preventing plastic deformation is provided at an end and a rubber component having elasticity is sandwiched between molecular constraint components, An eraser containing at least two or more thermoplastic elastomers and softening agents including an acrylic thermoplastic elastomer whose molecular constraint component is a methacrylic ester polymer block and whose rubber component is an acrylate polymer block.
[Selection figure] None

Description

  The present invention relates to an eraser containing at least two or more types of thermoplastic elastomers and softening agents, including acrylic thermoplastic elastomers.

Conventionally, as an eraser for erasing the handwriting on a pencil lead or a mechanical pencil lead, polyvinyl chloride is made into a semi-gel state by thermoforming the temperature of a plastisol of a mixture consisting of a plasticizer and a filler based on polyvinyl chloride. There was an elastomer eraser made of a white sub, a softening agent and a filler, and kneaded and heat-molded with an elastomer such as an eraser rubber and an elastomer such as natural rubber, synthetic rubber and thermoplastic elastomer as a base material. Of these erasers, polyvinyl chloride erasers dominate the market because of their good erasability and stability over time.
The principle of erasing pencils with erasers and pencils is that the pencils that adhere to the ridges of paper fibers and the graphite that forms the core of the mechanical pencils adhere to the surface of the eraser, It is taken into the swarf by being twisted and removed from the paper surface, and erasure is performed, and it is necessary that the swarf is easily generated. Moreover, since the paper surface of a handwriting part is crushed by the core, it is dented with respect to the paper surface which is not a handwriting part. The eraser must enter the dent portion of the handwriting, but soft rubber elasticity is necessary for the eraser to enter the dent portion of the handwriting. Since the polyvinyl chloride eraser is worn as a semi-gelled state with a light rubbing force by adjusting the heating temperature, it is easy to make off chips. In addition, polyvinyl chloride eraser has a sufficiently soft rubber elasticity by adding a large amount of plasticizer to polyvinyl chloride (6.2 hardness of JIS S6050 (2002) “Plastic Eraser”). However, the hardness of commercially available polyvinyl chloride erasers was in the range of 50 to 80), and occupied the mainstream of the eraser market.
However, in recent years, proposals have been made to substitute polyvinyl chloride with another material for the purpose of avoiding harmful substances such as dioxin produced during incineration of polyvinyl chloride.

In Japanese Patent No. 2675192 (Patent Document 1), instead of polyvinyl chloride, a polyalkyl methacrylate is used, and a plasticizer such as phthalic acid diester, which is also used in a polyvinyl chloride eraser, and calcium carbonate, etc. An eraser using a filler is disclosed.
However, plasticizers such as phthalic acid diesters and aliphatic dibasic acid esters used in polyvinyl chloride erasers are concerned with endocrine disrupting substances (so-called environmental hormones). For this reason, there has been further proposed an eraser that does not use polyvinyl chloride and does not use a plasticizer. The main of these proposals relates to improvements in elastomeric erasers based on thermoplastic elastomers.
Since natural rubber and synthetic rubber are solidified through a vulcanization process and a crosslinking process, recycling after molding is difficult and energy efficiency is low, whereas thermoplastic elastomers can be repeatedly heat-molded and recycled during the manufacturing process. It is easy and has been selected as a base material for elastomer erasers.
Further, the eraser needs to be weakened because it needs to be worn away by rubbing to generate erase chips. In the case of elastomer erasers, white sub-substance (sulfur chloride polymer of vegetable oil called sub-stitut or factist), which is compatible with elastomer and weak in strength, is added in large quantities so that scraps are generated by rubbing on the paper surface. The strength was weakened. However, the white sub is easily deteriorated due to deterioration such as oxidation due to energy such as temperature and ultraviolet rays, and since it contains chlorine, the generation of harmful substances at the time of incineration is the same as the eraser made of polyvinyl chloride. Combining thermoplastic elastomers that are incompatible with each other, or combining thermoplastic elastomers with uncrosslinked rubber or crosslinked rubber, as a method of reducing strength so that swarf is generated by rubbing on paper without using This is the main proposal for the eraser.

  For example, in the Japanese Patent No. 2671319 (Patent Document 2), the present applicant has disclosed that an eraser composition comprising at least a polyolefin-based thermoplastic elastomer, a polystyrene-based thermoplastic elastomer, and a filler, in which a rubber component is partially crosslinked, has a strength. It is disclosed that there is good erasability and no use of a sub, so that stability over time is good.

  Japanese Patent Publication No. 7-73958 (Patent Document 3) discloses an olefin-based thermoplastic elastomer component in which completely crosslinked rubber particles composed of ethylene-propylene-nonconjugated diene are embedded in polypropylene, a filler, and a styrene-based polymer. An eraser comprising a thermoplastic elastomer and other additives is disclosed.

  Japanese Patent No. 3913030 (Patent Document 4) discloses an eraser having a well-organized scrap containing styrene-based thermoplastic elastomer or olefin-based thermoplastic elastomer and uncrosslinked butyl rubber.

  Also, in Japanese Patent No. 4517168 (Patent Document 5), non-polyvinyl chloride eraser is generally inferior in erasability compared to polyvinyl chloride eraser. To improve this, acrylic rubber And an eraser containing a thermoplastic elastomer, particularly an eraser containing an acrylic rubber having a core-shell structure and a styrenic thermoplastic elastomer. By using an acrylic rubber having a core-shell structure, the eraser has a smooth erase surface and a good erase feeling.

Japanese Patent No. 2675192 Japanese Patent No. 2671319 Japanese Patent Publication No. 7-73958 Japanese Patent No. 3913030 Japanese Patent No. 4517168

  In order not to produce harmful substances such as dioxins during incineration, do not use materials containing chlorine in ingredients such as polyvinyl chloride resin or white sub, but phthalic acid diesters and aliphatics that are a concern for endocrine disruptors It is to obtain an eraser having the same erasability as a polyvinyl chloride eraser without using a plasticizer such as a dibasic acid ester.

As a combination of incompatible thermoplastic elastomers, those using a polystyrene-based thermoplastic elastomer and a polyolefin-based thermoplastic elastomer (Patent Documents 2 and 3) become an eraser having rubber elasticity because of the combination of the elastomers. However, although polystyrene, which is a molecular constraint component of styrene thermoplastic elastomer, and polypropylene, which is a molecular constraint component of olefin thermoplastic elastomer, are incompatible, rubber component of styrene thermoplastic elastomer and rubber of olefin thermoplastic elastomer The degree of incompatibility of the components is insufficient, the wearability is weak, and the generation of swarf is insufficient.
Butadiene and isoprene, which are structural units of the rubber component of the styrenic thermoplastic elastomer, have a little polarity because they have carbon-carbon double bonds, but ethylene, propylene, and butylene have no carbon-carbon double bonds and no polarity. Ethylene and propylene, which are rubber components of olefinic thermoplastic elastomers, are not polar, and nonconjugated dienes have carbon-carbon double bonds, but the residual amount of carbon-carbon double bonds in the thermoplastic elastomer is small due to crosslinking. . For this reason, the rubber phase of the styrene-based thermoplastic elastomer and the polyolefin-based thermoplastic elastomer has no polarity and is very similar, so that the degree of incompatibility is insufficient. Moreover, the soft rubber elasticity of the polyvinyl chloride eraser to which a large amount of plasticizer is added cannot be obtained because the amount of softener added is small.

  Styrenic thermoplastic elastomers or olefinic thermoplastic elastomers combined with uncrosslinked butyl rubber (Patent Document 4) are cohesive because the butyl rubber component is non-crosslinked and thus sticky, but butyl rubber is styrene based Since it resembles a rubber component of a thermoplastic elastomer or an olefin-based thermoplastic elastomer, phase separation is insufficient and generation of swarf is insufficient. In addition, when a large amount of a softening agent is added to the uncrosslinked butyl rubber, it dissolves in the softening agent and plasticizes, and the rubber elasticity is lost. Therefore, the addition amount of the softening agent is small. Therefore, it cannot have a soft rubber elasticity like a polyvinyl chloride eraser with a large amount of plasticizer added.

The acrylic rubber or the acrylic rubber having a core-shell structure and the styrene thermoplastic elastomer are used in combination (Patent Document 5), and since the acrylic rubber has a strong polarity, it is not compatible with the styrene thermoplastic elastomer, and thus easily wears. Although the erased surface becomes smooth, a large amount of softening agent cannot be added, so that it cannot have a soft rubber elasticity like a polyvinyl chloride eraser with a large amount of plasticizer added.
Not only acrylic rubber, but cross-linked rubber has molecules fixed by cross-linking points, so it cannot contain a large amount of softening agent inside, and uncross-linked rubber has no molecular constraints due to cross-linking points, so a large amount of When a softener is added, it dissolves and plastically deforms against external force, so a large amount of softener cannot be blended.
In addition, since acrylic rubber itself is a copolymer of 2-chloroethyl vinyl ether, which is a cross-linking point with alkyl acrylate, which is the main component, it contains chlorine and is a substitute for polyvinyl chloride resin for chlorine-free. As inappropriate.

  An object of the present invention is to provide an elastomer-made eraser that avoids harmful substances such as dioxins during incineration, and that can be sufficiently erased without fear of endocrine disrupting substances.

  The gist of the present invention is an eraser containing at least two or more kinds of thermoplastic elastomers including an acrylic thermoplastic elastomer and a softening agent.

The acrylic thermoplastic elastomer has a polymer block composed of a single methacrylic acid ester monomer having a monomer Tg of 25 ° C. or higher at the end, and is sandwiched between the end polymer blocks at 20 ° C. A block copolymer having a molecular structure of three blocks or a star block having a polymer block composed of a single acrylate monomer having the following monomer Tg.
A polymer block consisting of a single methacrylic acid ester monomer having a monomer Tg of 25 ° C. or higher is called a molecular constraining component (soft segment). The ingredients gather to form a strong domain.
A polymer block composed of a single acrylate monomer having a monomer Tg of 20 ° C. or lower is called a rubber component (soft segment), and plays a role of deforming a cross-linked rubber. A soft rubber phase is formed. At this time, since both the molecular constraint component and the rubber component are polymer blocks made of a single monomer, the phase is separated into the molecular constraint component domain and the rubber phase.
Acrylic thermoplastic elastomer has a polymer block made of methacrylic acid ester and a polymer block made of acrylate ester, both of which have strong polarities due to ester bonds, so they are not compatible with other thermoplastic elastomers and A mixture of a thermoplastic elastomer and other thermoplastic elastomers tends to wear due to its low strength.
The acrylic thermoplastic elastomer can be further softened while maintaining rubber elasticity by using a large amount of a softening agent. Acrylic thermoplastic elastomer has a molecular constraint component domain that melts when heated, so there is no intermolecular constraint during heating and plastic deformation occurs due to external force, but when it cools, the domain of the molecular constraint component is re-formed. . At this time, since the rubber phase containing the softening agent is rearranged at an optimum position, a large amount of the softening agent can be added, and a bleed that exudes the softening agent without containing a small amount of the softening agent like a crosslinked rubber. There is no phenomenon such as bloom and bloom, and the elasticity is lost unlike uncrosslinked rubber and plasticization does not occur at room temperature.
Acrylic resin, which is a random copolymer obtained by combining a plurality of conventional methacrylic acid esters and / or acrylic acid esters, does not phase-separate due to random copolymerization and contains a large amount of softening agent because there is no rubber phase. In contrast, acrylic thermoplastic elastomers have a molecular constraining component at the end and a three-block copolymer or star block copolymer having a rubber component sandwiched between the molecular constraining components. Since it is a coalescence, it can contain a large amount of softener.
For this reason, erasers containing at least two or more types of thermoplastic elastomers including acrylic thermoplastic elastomers and softeners tend to generate swarf, like polyvinyl chloride erasers, and they are dented by writing due to soft rubber elasticity. Since it penetrates to the bottom of the surface of the paper, it does not contain chlorine and plasticizers such as phthalic acid diesters and aliphatic dibasic acid esters while obtaining the same erasability as a polyvinyl chloride eraser.

The acrylic thermoplastic elastomer used in the present invention has a polymer block composed of a single methacrylic acid ester monomer having a monomer Tg of 25 ° C. or higher at the end, and is sandwiched between the end polymer blocks. In other words, it is a block copolymer having a molecular structure of three blocks or a star block having a polymer block composed of a single acrylate monomer having a monomer Tg of 20 ° C. or lower.
The methacrylic acid ester constituting the molecular constraint component has a monomer Tg of 25 ° C. or higher, more preferably 70 ° C. or higher and 130 ° C. or lower. When the temperature is less than 25 ° C., the molecular constraint component may be softened at room temperature, and when the temperature is less than 70 ° C., the molecular constraint component domain is softened due to heat generated by abrasion during eraser erase, and the eraser is easily plastically deformed. If it exceeds 130 ° C., the thermoplasticity becomes poor, and it is necessary to raise the temperature at the time of molding the eraser, which wastes energy.
Examples of the methacrylic acid ester having a monomer Tg of 25 ° C. or higher include methyl methacrylate (Tg about 105 ° C.), ethyl methacrylate (Tg about 65 ° C.), n-propyl methacrylate (Tg about 35 ° C.), methacrylic acid. Isopropyl (Tg about 81 ° C), isobutyl methacrylate (Tg about 48 ° C), sec-butyl methacrylate (Tg about 60 ° C), cyclohexyl methacrylate (Tg about 66 ° C), benzyl methacrylate (Tg about 54 ° C), etc. There is.
As an acrylic ester which comprises a rubber component, it has a monomer Tg of 20 degrees C or less, More preferably, it is 0 degrees C or less. In the rubber phase, the Tg as a rubber phase is reduced by adding a large amount of a softening agent, but even if it exceeds 20 ° C, rubber elasticity may not be obtained at room temperature. In some cold conditions, rubber elasticity may not be obtained.
Examples of the acrylate ester having a monomer Tg of 20 ° C. or less include methyl acrylate (Tg about 8 ° C.), ethyl acrylate (Tg about −20 ° C.), n-butyl acrylate (Tg about −55 ° C.), acrylic Examples include cyclohexyl acid (Tg about 15 ° C.), benzyl acrylate (Tg about 6 ° C.), and the like.
The number-average molecular weight of the polymer-constrained component of the acrylic thermoplastic elastomer and the polymer block of the rubber component is not necessarily limited, but the range of the number-average molecular weight of the methacrylate polymer block is 1,000 to 450, 000 is known, and 8,000 to 900,000 is known as the range of the number average molecular weight of the acrylate polymer block.
The monomer Tg is the Tg (glass transition temperature) of a homopolymer of the monomer, and is used when calculating the Tg of a copolymer composed of a plurality of monomers using the Fox equation. For example, the value is described in Polymer Handbook Third Edition (Wiley-Interscience, 1989).
Such an acrylic thermoplastic elastomer is disclosed in Japanese Patent Publication No. 7-25859, and in Japanese Patent No. 3828447, this acrylic thermoplastic elastomer production method and an acrylic resin are used in combination. Thus, it is disclosed that flexibility and mechanical strength can be balanced. Furthermore, Japanese Patent Application Laid-Open No. 2004-2844 discloses a methyl methacrylate-butyl acrylate-methyl methacrylate triblock copolymer as an acrylic thermoplastic elastomer. JP-A-6-287395 discloses a method of copolymerizing or graft polymerizing an unsaturated carboxylic acid or the like with an acrylic thermoplastic elastomer, and an acrylic thermoplastic elastomer modified by such a method. Improves the adhesion to the filler. Commercially available acrylic thermoplastic elastomers include a mixture of methyl methacrylate-nbutyl acrylate-methyl methacrylate copolymer and methyl methacrylate-n butyl acrylate diblock copolymer, Clarity LA4285, LA2250, LA2140e (above) , Manufactured by Kuraray Co., Ltd.).
The amount of the acrylic thermoplastic elastomer used is preferably in the range of 0.20 to 0.75, where the weight of the total thermoplastic elastomer is 1.

  Thermoplastic elastomer is a material that exhibits rubber elasticity at room temperature in the same way as crosslinked rubber, and exhibits plasticity when heated and can be thermoformed in the same manner as a thermoplastic resin. In the current market, acrylic thermoplastic elastomers are used. In addition, there are styrene thermoplastic elastomer, olefin thermoplastic elastomer, vinyl chloride thermoplastic elastomer, polyester thermoplastic elastomer, polyurethane thermoplastic elastomer, nylon thermoplastic elastomer, chlorinated polyethylene copolymer crosslinked alloy, etc. . As the thermoplastic elastomer used together with the acrylic thermoplastic elastomer in the present invention, those other than the vinyl chloride-based thermoplastic elastomer containing chlorine and the chlorinated polyethylene copolymer cross-linked alloy can be used, and especially the styrene-based thermoplastic which is soft. Elastomers and olefinic thermoplastic elastomers are suitable.

Styrenic thermoplastic elastomer is a three-block copolymer or star shape having a molecular structure in which a polystyrene block, which is a molecular constraining component that prevents plastic deformation, is sandwiched between polystyrene blocks. It is a block copolymer. As rubber components, polybutadiene and polyisoprene and those saturated by hydrogenation are known. Styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, styrene-isoprenebutadiene-styrene block Copolymer, Styrene-Butadiene Butylene-Styrene Block Copolymer, Styrene-Ethylene Butylene-Styrene Block Copolymer, Styrene-Ethylene Propylene-Styrene Block Copolymer, Styrene-Ethylene Ethylene Propylene-Styrene Block Copolymer, Styrene -Vinyl polyisoprene-styrene block copolymer, styrene-hydrogenated vinyl polyisoprene-styrene block copolymer and the like are known.
Examples of commercially available styrenic thermoplastic elastomers include styrene-butadiene-styrene block copolymers such as Tufprene A, 125, 126S, Asaprene T-411, T-432, T-437, T- 438, T-439 (above, manufactured by Asahi Kasei Chemicals Corporation), Kraton D1101E, D1155B (above, manufactured by Kraton Polymer, USA) and the like. Examples of the styrene-isoprene-styrene block copolymer include Kraton D1114P, D1160E, and D1164P (above, manufactured by Kraton Polymer, USA). Examples of the styrene-butadiene butylene-styrene block copolymer include Tuftec P1500 and P2000 (manufactured by Asahi Kasei Chemicals Corporation). As styrene-ethylene butylene-styrene copolymers, Tuftec H1221, H1052, H1062, H1053, H1041, H1051, H1041, H1043, H1272 (above, manufactured by Asahi Kasei Chemicals Corporation), Septon 8076, 8007 8004, 8104, 8006 (manufactured by Kuraray Co., Ltd.), Kraton G1643M, G1645M, G1652H, G1660H (manufactured by Kraton Polymer, USA), Espolex SB2400, SB2610, SB2710 (The above is manufactured by Sumitomo Chemical Co., Ltd.). Examples of the styrene-ethylenepropylene-styrene block copolymer include Septon 2005, 2063, 2004, 2002, 2007, 2006, 2043, 2104 (manufactured by Kuraray Co., Ltd.). Examples of the styrene-ethyleneethylenepropylene-styrene block copolymer include Septon 4033, 4044, 4055, 4077, and 4099 (above, manufactured by Kuraray Co., Ltd.). Examples of the styrene-vinylpolyisoprene-styrene block copolymer include Hibler 5127 and 5125 (manufactured by Kuraray Co., Ltd.). Examples of the styrene-hydrogenated vinyl polyisoprene-styrene block copolymer include Hibler 7125 and 7311 (manufactured by Kuraray Co., Ltd.).
In addition to these, JSR TR, JSR SIS (manufactured by JSR Corporation), elastomer AR (manufactured by Aron Kasei Co., Ltd.), Maxilon ZAK (manufactured by Showa Kasei Kogyo Co., Ltd.), tribrene, super tribune (above, There are styrene-based thermoplastic elastomers marketed under trade names such as Shinsei Kasei Co., Ltd. and Lavalon (Mitsubishi Chemical Co., Ltd.).

  Further, as those which give these styrene-based thermoplastic elastomers a function of improving the adhesion to the filler, Tuftec M1911, M1913, M1943 (above, acid-modified styrene-ethylenebutylene-styrene copolymer) Asahi Kasei Chemicals Co., Ltd.), Kraton FG1901G and FG1924G (Made by Kraton Polymer, USA) grafted with maleic anhydride, and amine-modified Tuftec MP10 (Asahi Kasei Chemicals Co., Ltd.), styrene block Is a reactive cross-linked styrene-ethylene ethylene propylene-styrene block copolymer, Septon V9461 and V9475 (above, manufactured by Kuraray Co., Ltd.), styrene block is a reactive cross-linked styrene-ethylene butylene-styrene block copolymer There is Septon V9827 ((Ltd.) manufactured by Kuraray Co.) as a.

In contrast to the styrene-based thermoplastic elastomer of the three-block copolymer, there are a two-block copolymer that does not have one end of the polystyrene block at the end, and a polystyrene block that replaces the polystyrene block at one or both ends with a crystalline polyolefin block.
As the diblock copolymer, Asaflex 805, 810, 825, 815 (with wax), 830, 835 (with wax), 840, 845 are used as styrene-butadiene diblock copolymers. (With wax) (as above, manufactured by Asahi Kasei Chemicals Co., Ltd.), etc. As a mixture of styrene-butadiene-styrene block copolymer and styrene-butadiene diblock copolymer, Kraton D1101A (containing 2% 16 blocks) ), D1133K (contains 34% of 2 blocks), D1118K (contains 78% of 2 blocks) (above, manufactured by Kraton Polymer, USA), and the like. As a mixture of a styrene-isoprene-styrene block copolymer and a styrene-isoprene diblock copolymer, Kraton D111K (containing 2 blocks 18%), D1113P (containing 2 blocks 56%), D1124P (containing 2 blocks 29) % Content) (above, manufactured by Kraton Polymer, USA). As a mixture of styrene-isoprene butadiene-styrene block copolymer and styrene-isoprene butadiene diblock copolymer, Kraton D1170B (containing 2 blocks 26%), D1171P (containing 2 blocks 26%) (the above, Kraton polymer) Company, USA). Examples of the styrene-ethylenepropylene diblock copolymer include Septon 1001, 1020 (above, Kuraray Co., Ltd.), Kraton G1701M, G1702H (above, Kraton Polymer, USA), and the like.
As one in which one end is replaced with a crystalline polyolefin block, there is DYNARON 4600P (manufactured by JSR Corporation) as a styrene-ethylene butylene-crystalline olefin copolymer, and both ends are replaced with a crystalline polyolefin block. Examples of the crystalline olefin-ethylenebutylene-crystalline olefin copolymer include DYNARON 6100P, 6200P, and 6201B (manufactured by JSR Corporation).

The olefinic thermoplastic elastomer is a mixed (blended) material in which a rubber component having elasticity is dispersed in a polyolefin, which is a molecular constraint component that prevents plastic deformation. The rubber component may be uncrosslinked, partially crosslinked, or completely crosslinked. In addition, there is a type of cross-linking in which dynamic cross-linking is performed in which the rubber component is cross-linked when the molecular constraint component and the rubber component are mixed. In some cases, the molecular constraint component and the rubber component are partially graft-polymerized.
As the molecular constraint component, polyethylene and polypropylene are known as polyolefins. As the rubber component, ethylene propylene rubber and acrylonitrile butadiene rubber (NBR) such as ethylene-propylene copolymer (EPM) and ethylene-propylene-diene terpolymer (EPDM) are known.
Among these, those dynamically crosslinked using polypropylene as a molecular constraint component and ethylene-propylene-diene terpolymer (EPDM) crosslinked as a rubber component are preferable. Commercially available products include Miralastomer 5030N, 6030N, 7030N, 8032N, 8030N, 8020N, 9020N (Mitsui Chemicals Co., Ltd.), Espolex TPE3675, 3785, 3775, 3485, 3255, 4675, 4785, 4855, 820, 822 (manufactured by Sumitomo Chemical Co., Ltd.), Thermorun 3555N, 3655N, 3705N, 3755N, 3855N, 3981N, QT60MB, QTTA0628 , QT70MA, QT80MA (manufactured by Mitsubishi Chemical Corporation).
In addition to this, Santoprene, Geolast (exxonmobile, USA), EXCELLINK (manufactured by JSR Corporation), ENGAGE (manufactured by Dow Chemical Japan Co., Ltd.), PANDEX, Desmopan, Texin (above, DIC Bayer) Polymer Co., Ltd.), Sirlink (Toyobo Co., Ltd.), Amzel (Plus Tech Co., Ltd.), Zelas (Mitsubishi Chemical Co., Ltd.), etc. There is a thermoplastic elastomer.

  The polyester-based thermoplastic elastomer is an ester-ether type or ester-ester type multi-block copolymer comprising an aromatic polyester as a molecular constraint component and an aliphatic polyether or aliphatic polyester as a rubber component. Polyester-based thermoplastic elastomers are commercially available under the trade names of Perprene (manufactured by Toyobo Co., Ltd.), Hytrel (manufactured by Toray DuPont Co., Ltd.), and Primalloy (manufactured by Mitsubishi Chemical Corporation).

  The urethane-based thermoplastic elastomer is a copolymer having a molecular constrained component composed of diisocyanate and short chain glycol and a rubber component composed of diisocyanate and polyol. Elastolan (BASF Japan Co., Ltd.), Clamiron U (Kuraray Co., Ltd.), Maxilon GFU (Showa Kasei Kogyo Co., Ltd.), Resamine (Daiichi Seika Kogyo Co., Ltd.) , Pellehtane (manufactured by Dow Chemical Japan Co., Ltd.), and milactolan (manufactured by Nippon Milactolan Co., Ltd.).

  The nylon-based thermoplastic elastomer is a block copolymer of a molecular constraining component made of nylon and a rubber component made of polyester or polyol. Nylon thermoplastic elastomers are commercially available under trade names such as Pebax (ARKEMA, France), UBESTA XPA (manufactured by Ube Industries, Ltd.), Daiamide, Vestamide (above, Daicel Eponic) .

The softener used in the present invention is added in order to make the eraser easily enter the bottom of the dent of the handwriting by softening the hardness of the thermoplastic elastomer. Examples of semi-solid synthetic polymer materials and synthetic oils include polybutadiene, polyisoprene, polybutene (polyisobutylene), and olefin oligomers.
Rubber compounded oils include mineral oil softeners and vegetable oil softeners. Mineral oil softeners are also called petroleum softeners, extender oils and process oils. According to the method of Kurtz, the mineral oil softener is a paraffin oil having a paraffin chain carbon number of 50% or more of the total carbon number, a naphthene oil having a naphthene ring carbon number of 30 to 45%, and an aromatic ring carbon number of 35. % Or more aromatic oil. According to this classification, liquid paraffin can be regarded as paraffin oil having 100% paraffin chain carbon number.
There is also a classification of safe oils with no carcinogenicity that is less than 3% by weight of PCA (polycyclic aromatic compound), which is a DMSO (dimethyl sulfoxide) extract according to test method IP346 of the British Petroleum Institute.
Commercially available paraffin oil softeners include Daphne Oil CP12N, CP15N, CP32N, KP8, KP15, KP32, KP68, KP100 (above, liquid paraffin, 0% aromatic ring carbon number), Diana Process Oil PW32 (aromatic ring carbon number 0%), PW90 (aromatic ring carbon number 0%), PW150 (aromatic ring carbon number 0%), Diana Fresia P32 (less than 3% by weight of PCA), P90 (Less than 3% by weight of PCA), P150 (less than 3% by weight of PCA), W8 (less than 3% by weight of PCA), K8 (less than 3% by weight of PCA), and S10 (less than 3% by weight of PCA) (Idemitsu Kosan Co., Ltd.) Manufactured), JOMO process P200 (less than 3% by weight of PCA), P300 (less than 3% by weight of PCA), P400 (less than 3% by weight of PCA) , The P 500 (less than PCA3 wt%) (or, JX manufactured Nippon Oil & Energy Corporation), and the like.
Commercially available naphthenic oil softeners include Diana Process Oil NP24, NS90S, 100, NR26, NR68, NM280, Diana Fresia G6, G9, F9, NR9, N28, N90, N90, N150. U46, U56, U68, U130 (above, manufactured by Idemitsu Kosan Co., Ltd.), JOMO Process R (above, manufactured by JX Nippon Mining & Energy Corporation), and the like.
Examples of commercially available aromatic oil softeners include Diana Process Oil AC12, 460, AH16, and 24 (above, manufactured by Idemitsu Kosan Co., Ltd.).
Examples of vegetable oil softeners include castor oil, cottonseed oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut oil, pine oil, tall oil and the like.
Examples of commercially available liquid polybutadiene include Poly bd R-45HT and R-15HT (manufactured by Idemitsu Kosan Co., Ltd.).
Commercially available liquid polyisoprene is Claprene LIR-30, LIR-50 (above, Kuraray Co., Ltd.), Poly ip (Idemitsu Kosan Co., Ltd.), and hydrogenated polyisoprene is Claprene LIR. -290, LIR-200, and LIR-230 (manufactured by Kuraray Co., Ltd.).
Examples of commercially available liquid polybutenes include Nisseki Polybutene LV-7, LV-50, LV-100, HV-35, and HV-50 (above, manufactured by JX Nippon Mining & Energy Corporation). Examples of semi-solid polybutene (polyisobutylene) include Tetrax 3T, 4T, 5T, 6T, Hymor 4H, 5H, and 6H (above, manufactured by JX Nippon Oil & Energy Corporation).
Examples of commercially available olefin oligomers include Lucant HC-40, HC-100, HC-600, and HC-2000 (above, Mitsui Petrochemical Co., Ltd.), which are ethylene / α olefin oligomers.
Mineral oils marketed as lubricating oils can also be used as softeners if they have the same components as the mineral oil softener.
These softening agents are those that are compatible with the rubber component of the thermoplastic elastomer and soften the thermoplastic elastomer. However, when they are compatible with the molecular constraint component, the molecular constraint component phase dissolves and the rubber elasticity is lost. It is. For this reason, it selects suitably by the combination of the thermoplastic elastomer used together with an acrylic thermoplastic elastomer.
However, in view of the current situation that the plasticizer used for polyvinyl chloride eraser is limited in the range of use due to concerns about endocrine disrupting substances, in the highly polar acrylic thermoplastic elastomer does not dissolve the molecular constraint component A non-polar, non-carcinogenic PCA content of less than 3% by weight and / or a paraffin oil softener that does not contain an aromatic ring is more preferred as a softener.
These softeners are added in large amounts to impart soft rubber elasticity such as a polyvinyl chloride eraser, and are preferably 0.5 to 2 times the total amount of thermoplastic elastomer by weight. Acrylic thermoplastic elastomer can contain a larger amount of softener than cross-linked rubber, but when blended more than twice, the so-called bloom or bleed phenomenon occurs when the softener exudes to the surface of the eraser. Not only the surface becomes sticky, but also dust adheres or slips on the paper surface, so that no erasure is generated and the erasability is significantly lowered. Moreover, if it is less than 0.5 times, it cannot be said that the softness of the eraser is sufficient.

In addition to these, those conventionally added to erasers and rubber products such as fillers, stabilizers, colorants, gelling agents and the like can be added as necessary.
The filler used in the present invention may be added for the purpose of facilitating generation of swarf or reducing the frictional resistance with the paper surface, and may be added for the purpose of improving the tear strength or bending strength. . Most of the fillers are inorganic particles, but the effect of facilitating the generation of debris and reducing the frictional resistance with the paper surface is often obtained when the particle diameter is 2 μm or more, and the tear strength The effect of improving the bending strength is often obtained when the particle diameter is 0.1 μm or less. Particles having a particle size of 2 to 0.1 μm have the effect of balancing both. On the other hand, if the particle diameter exceeds 10 μm, the traces of the fillers touch the paper surface, and the erase marks become fluffy and rewriting becomes easy to get dirty. For this reason, as the main filler, lumps or spherical heavy calcium carbonate, light calcium carbonate, synthetic calcium carbonate, magnesium carbonate, kaolin, clay having an average particle diameter of 2 μm or more and 8 μm or less that does not damage the paper surface because it tends to generate chips. , Cinnabar and the like are preferably used.
In addition, a filler for obtaining an effect of a unique shape such as a needle-shaped particle, a plate-shaped particle, a spherical particle, a porous particle, or a particle having a complicated shape formed by combining fine particles can be used.
The acicular particles include magnesium oxysulfate fiber, acicular calcium carbonate, natural mineral fiber that replaces asbestos, the plate particles include talc, mica, sericite, and the like, and the spherical particles include shirasu balloon and fly ash. Examples include balloons, glass beads, glass bubbles, and titanium oxide. Examples of porous particles include diatomaceous earth, porous silica, and porous graphite carbon.
These fillers are preferably used in an amount of 0.5 to 3 times the total amount of the thermoplastic elastomer by weight. When blended more than 3 times, not only the eraser becomes hard, but also there are many fillers to which the graphite of the handwriting does not adhere, and the thermoplastic elastomer to which the handwriting of graphite adheres decreases, so the erasability deteriorates. . If it is less than 0.5 times, the frictional resistance between the eraser and the paper surface is large, and the feeling of erasure becomes heavy.

As the stabilizer used in the present invention, those used for thermoplastic elastomers, plastics, rubbers and the like can be used. “Polymer additive handbook” (Toru Haruna, CMC Publishing Co., Ltd., November 2010) 7th edition issued) As the commercially available antioxidants, Table 1, “Representative phenolic antioxidants” on page 28 of the same book, Res. Hindered phenolic antioxidants, semi-hindered phenolic antioxidants, hindered phenolic antioxidants. Examples of the antioxidants are shown in Table 1, “List of Phosphorous Antioxidants” on page 40 of the same book. Phosphorous antioxidants are exemplified in Table 2, “Table 2. ”Illustrates sulfur-based antioxidants. As commercially available UV absorbers, benzotriazoles are disclosed in Table 1, “Structure, molecular weight, and trade names of typical benzotriazole UV absorbers” on page 52 of the same book. “Structure, molecular weight, and trade name of typical triazine-based UV absorbers” discloses triazines, and Table 3, “Structure, molecular weight, and trade name of typical benzophenone-based UV absorbers” on page 56 of the same book. Benzophenone series is disclosed in Table 4, page 58, "Structure, molecular weight, and trade name of other UV absorbers" in the same book, cyanoacrylate UV absorber, salicylate UV absorber, oxanilide UV absorber. Is illustrated. As a commercially available light stabilizer, as a hindered amine light stabilizer (HALS), Table 2 on page 61 of the same book, “Structure, molecular weight, and trade name of typical N—H HALS” shows a hindered amine type of N—H skeleton. Light stabilizers are disclosed. Table 3 on page 63, "Structure, molecular weight, and trade name of typical N-Me HALS" discloses hindered amine light stabilizers having an N-Me skeleton. No. 64, Table 4, “Structure, molecular weight and trade name of typical N-OR HALS” discloses hindered amine light stabilizers of NO-Alkyl (alkoxyamino group) HALS skeleton. As commercially available metal deactivators, oxalic acid derivatives, salicylic acid derivatives, hydrazine derivatives, and other derivatives are disclosed in Table 1, “Representative copper damage inhibitors” on page 68 of the same document.
The antioxidant is effective for preventing oxidative degradation of the thermoplastic elastomer when the eraser material is heat-kneaded and heat-molded. UV absorbers and light stabilizers are effective in preventing deterioration due to UV rays in sunlight. Especially when rubber components of styrenic thermoplastic elastomer contain double bonds, UV bonds are deteriorated due to these double bonds. It is particularly effective because it is easy.

As the colorant used in the present invention, a colorant conventionally used for thermoplastic elastomers, rubbers, plastics, etc. can be used, inorganic pigments such as titanium oxide and carbon black, azo series, phthalocyanine series, selenium series and dioxazine. Organic pigments, dyes, etc., such as those based on isoindoline and lakes, can be used. Further, easily dispersible pigments processed so as to be easily colored on thermoplastic elastomers, rubbers, plastics, etc., and processed pigments such as color chips can also be used.
Gelling agents that can be used in the present invention include organic gelling agents such as dibenzylidene sorbitol, tribenzylidene sorbitol, dextrin fatty acid ester, acyl fatty acid amide, castor oil derivative, and inorganic gelling such as bentonite, hectorite, and silica. The agent can be used.

  The eraser containing the above components becomes an eraser by being heat-kneaded and molded. Heat kneading is a process in which different types of thermoplastic elastomers are mixed by applying mechanical force in a state where the thermoplastic elastomer is plasticized by heating, and at the same time, a softener, a filler, a stabilizer, a colorant, a gel. An agent and the like are also added and kneaded. As the kneader, an open roll for rubber kneading with a heating device, a Banbury mixer, a pressure kneader, a twin screw extruder, or the like can be used. As the molding machine, a conventionally known plastic molding machine can be used, and specifically, a press molding machine, an injection molding machine, an extrusion molding machine, or the like can be used.

  Examples and Comparative Examples are shown below, but the present invention is not limited at all.

Example 1
Clarity LA2250 (acrylic thermoplastic elastomer, manufactured by Kuraray Co., Ltd.)
14.0 parts by weight Septon 4055 (styrene-based thermoplastic elastomer, manufactured by Kuraray Co., Ltd.)
14.0 parts by weight Diana Process Oil PW32 (paraffin oil softener, manufactured by Idemitsu Kosan Co., Ltd.)
31.0 parts by weight Heavy calcium carbonate (average particle size 3.6 μm) 40.9 parts by weight Irganox 1010 (hindered phenol antioxidant, manufactured by BASF Japan Ltd.) 0.1 part by weight Preheat to 130 ° C. A pressure kneader is charged with all of the above components, Clarity LA2250, Septon 4055, heavy calcium carbonate, Irganox 1010 and 1/3 of Diana Process Oil PW32, and kneading while pressing the pressure lid and pressing. Went for a minute. After confirming that Septon 4055 and clarity LA2250 did not remain in the pellet state, the remaining Diana process oil PW32 was added in four portions, and kneaded for 5 minutes each time. The above mixture kneaded with a pressure kneader was formed into a sheet having a thickness of 3 mm with a calender roll preheated to 80 ° C., and cut into a square pellet of about 4 mm square with a square pelletizer.
The square pellets cooled to room temperature were thermoformed by a single screw extruder equipped with a full flight type screw having a compression ratio of 3 and L / D = 24 to obtain an eraser. The molding temperature of the extruder was set to increase the temperature from the feed zone 70 ° C. to the metering zone 130 ° C., and the screw temperature control was 50 ° C. The molded eraser was cooled with water and then cut into a predetermined length to obtain a block-shaped eraser.

Example 2
Clarity LA2140e (acrylic thermoplastic elastomer, manufactured by Kuraray Co., Ltd.)
16.0 parts by weight Septon 4033 (styrene-based thermoplastic elastomer, manufactured by Kuraray Co., Ltd.)
7.0 parts by weight Daphne Oil KP68 (paraffin oil softener, manufactured by Idemitsu Kosan Co., Ltd.)
31.4 parts by weight Heavy calcium carbonate (average particle size 5.0 μm) 45.5 parts by weight Irganox 1010 (described above) 0.1 parts by weight An eraser was obtained in the same manner as in Example 1.

Example 3
Clarity LA4285 (acrylic thermoplastic elastomer, manufactured by Kuraray Co., Ltd.)
6.0 parts by weight Septon 2004 (styrene thermoplastic elastomer, manufactured by Kuraray Co., Ltd.)
14.0 parts by weight Lucant HC-40 (ethylene / α-olefin oligomer, manufactured by Mitsui Petrochemical Co., Ltd.)
40.0 parts by weight Heavy calcium carbonate (average particle size 1.0 μm) 39.9 parts by weight Irganox 1010 (described above) 0.1 parts by weight An eraser was obtained in the same manner as in Example 1.

Example 4
Clarity LA2250 (previously described) 10.0 parts by weight Septon 4055 (previously described) 1.5 parts by weight Miralastomer 7030N (olefin-based thermoplastic elastomer, manufactured by Mitsui Chemicals, Inc.)
18.0 parts by weight Diana Process Oil PW90 (paraffin oil softener, manufactured by Idemitsu Kosan Co., Ltd.)
20.5 parts by weight Heavy calcium carbonate (average particle size 4.8 μm) 50.0 parts by weight An eraser was obtained in the same manner as in Example 1 except that the preheating temperature of the pressure kneader was changed to 150 ° C.

Example 5
Clarity LA2250 (previously described) 11.0 parts by weight Mirastomer 7030N (previously described) 18.0 parts by weight Diana process oil PW90 (previously described) 8.0 parts by weight Diana process oil PW150 (paraffin oil softener, manufactured by Idemitsu Kosan Co., Ltd.)
16.0 parts by weight Heavy calcium carbonate (average particle size 3.6 μm) 47.0 parts by weight First, the whole amount of Diana process oil PW90 is added, and after 20 minutes of kneading, Diana process oil PW150 is divided into four times and kneaded. Except for the above, an eraser was obtained in the same manner as in Example 4.

Example 6
Clarity LA2250 (previously described) 5.0 parts by weight Septon 4055 (previously described) 2.5 parts by weight Miralastomer 6030N (olefin-based thermoplastic elastomer, manufactured by Mitsui Chemicals, Inc.)
13.0 parts by weight DYNARON6201B (crystalline olefin-ethylenebutylene-crystalline olefin copolymer, manufactured by JSR Corporation) 2.5 parts by weight Diana Process Oil PW90 (described above) 22.0 parts by weight Heavy calcium carbonate (average Particle size 9.7 μm) 55.0 parts by weight An eraser was obtained in the same manner as in Example 4.

Comparative Example 1
Tuftec H1062 (Styrenic thermoplastic elastomer, manufactured by Asahi Kasei Chemicals Corporation)
8.0 parts by weight Thermolane 3755N (olefin-based thermoplastic elastomer, manufactured by Mitsubishi Chemical Corporation)
16.0 parts by weight Poly bd R-45HT (liquid polybutadiene, manufactured by Idemitsu Kosan Co., Ltd.)
13.0 parts by weight Calcium carbonate (average particle size 1.0 μm) 62.9 parts by weight Irganox 1010 (described above) 0.1 parts by weight An eraser was obtained in the same manner as in Example 1.

Comparative Example 2
Septon 2043 (Styrenic thermoplastic elastomer, manufactured by Kuraray Co., Ltd.)
18.0 parts by weight Parapet SA-FW001 (acrylic rubber-containing acrylic resin, manufactured by Kuraray Co., Ltd.)
18.0 parts by weight Diana Process Oil PW32 (previously described) 20.0 parts by weight Calcium carbonate (average particle size 1.7 μm) 43.9 parts by weight Irganox 1010 (previously described) 0.1 parts by weight The eraser was applied in the same manner as in Example 1. Obtained.

Erasure rate 1
The erasure rate was measured according to the test method of 6.4 erasing ability (erasure rate) of JIS S6050 (2002) “Plastic Eraser”.

Erasure rate 2 (strong writing)
Mechanical pencils do not change the thickness of the lead in writing compared to pencils, so the pressing force per unit area during writing is larger than pencils, and the dents in the paper are larger. For this reason, when writing strongly with a mechanical pencil, the erasability is particularly bad with an eraser having insufficient softness. Therefore, in the test method described in the test method of 6.4 erase ability (erasure rate) of JIS S6050 (2002) “Plastic eraser”, the pencil HB specified in JIS S6006 is 0.5 mm HB sharp core ( High polymer Ain0.5HB, manufactured by Pentel Co., Ltd.), weight 0.3 kg changed to 0.5 kg, and the tip shape of the shin is perpendicular to the cone shape with a tip diameter of 0.6 mm. The erasure rate was measured in the same manner as the erasure rate 1 except that the end face was changed.

Quench rate 3 (light erasure)
When the load applied to the eraser is light, it is difficult to wear and the generation of erase chips is poor. For this reason, the erasability is particularly bad with an eraser with poor wear. Therefore, in the test method described in the test method of 6.4 erasing ability (erasing rate) of JIS S6050 (2002) “Plastic Eraser”, 0.5 kg of the sum of the weight of the weight and the holder is set to 0. Except for changing to 3 kg, the erasure rate was measured in the same manner as the erasure rate of 1.

Hardness The hardness of the eraser was measured according to the 6.2 hardness test method of JIS S6050 (2002) “Plastic Eraser”.

  Table 1 shows the results of measuring the erasure rate 1, the erasure rate 2, the erasure rate 3, and the hardness of Examples 1 to 6 and Comparative Examples 1 and 2.

In Examples 1 to 6, the hardness was sufficiently soft and good erasability was achieved even with an erasure rate of 2 (strong writing) and an erasure rate of 3 (light erasure). Example 3 is an eraser that has a slightly finer filler particle size than the other examples, is somewhat hard because the softener is not paraffin oil, and has a slightly lower erasure rate 3 (light erasure) but good erasability. .
Comparative Example 1 did not contain an acrylic thermoplastic elastomer and used an olefinic thermoplastic elastomer in which a styrene thermoplastic elastomer and a rubber component were cross-linked, but it was slightly hard and had a erasure rate of 2 (strong writing). Since it is inferior and wear is inferior, the erasure rate is 3 (light erasure) and the generation of swarf is insufficient and hardly disappears.
Comparative Example 2 did not contain an acrylic thermoplastic elastomer and used an acrylic resin mainly composed of a styrene thermoplastic elastomer and acrylic rubber, but was hard and inferior in the erasure rate 2 (strong writing) and inferior in wear. For this reason, at the erasure rate of 3 (light erasure), almost no swarf is generated, so the erased surface is soiled and does not disappear.

  As described above in detail, the eraser containing at least two or more types of thermoplastic elastomers and softeners including the acrylic thermoplastic elastomers of Examples 1 to 6 has an eraser hardness of 50 to 80, which is similar to a polyvinyl chloride eraser. Because it has soft rubber elasticity and wear resistance equivalent to that of a polyvinyl chloride eraser, it can erase not only the erasure rate (erasure rate 1) in JIS S6050 (2002) “Plastic eraser” but also strong handwriting erasure. Even with an erasing rate of 2 and an erasing rate of 3 which is erasing with a light load, erasability equivalent to that of an eraser made of polyvinyl chloride is obtained.

Claims (5)

An eraser containing at least two or more kinds of thermoplastic elastomers including an acrylic thermoplastic elastomer and a softening agent. The eraser according to claim 1, wherein the thermoplastic elastomer used in combination with the acrylic thermoplastic elastomer is at least a styrene thermoplastic elastomer. 2. The eraser according to claim 1, wherein the thermoplastic elastomer used in combination with the acrylic thermoplastic elastomer is at least an olefinic thermoplastic elastomer. The eraser according to any one of claims 1 to 3, wherein the amount of the acrylic thermoplastic elastomer is 0.20 to 0.75, where the weight of the total thermoplastic elastomer is 1. The eraser according to claims 1 to 4, wherein the softening agent is a paraffin oil softening agent having a PCA content of less than 3% by weight and / or containing no aromatic ring.