JP7693202B2 - Plastic eraser - Google Patents

Description

The present invention relates to a plastic eraser.

Erasers (rubbers) have excellent erasing properties and are widely used as an indispensable tool for erasing written lines.

The mechanism by which an eraser erases written lines is that the eraser is brought into close contact with the written lines on the paper and rubbed to cause the written lines to adhere to the eraser, while the surface portion of the eraser that has attracted the written lines (the portion that was in contact with the paper) is detached from the eraser as eraser dust, and the eraser surface is renewed, making it possible to attract the written lines again. Therefore, the generation of eraser dust is essential for an eraser, and erasers that do not produce eraser dust or eraser dust that is difficult to produce have insufficient erasability because the eraser surface is not renewed. For this reason, erasers are required to be able to attract written lines well and to be able to detach eraser dust well from the eraser.

For example, Patent Documents 1 and 2 disclose that by containing two or more types of thermoplastic elastomers including an acrylic thermoplastic elastomer as a base resin and a softener, the eraser can penetrate to the bottom of the paper surface that is recessed by writing, resulting in excellent erasability and good eraser dust production.
As the performance of erasers has improved, various additional features have been required, such as better erasability, a lighter erasing feel, and the degree of collection of eraser dust.

For example, Patent Document 3 discloses an eraser that uses a thermoplastic elastomer as a base resin and further contains a 1-butene homopolymer or a copolymer mainly composed of 1-butene, which makes it easy to produce eraser dust, has excellent erasability, and provides a very good erasing feel.
However, an eraser with excellent erasing feeling can be obtained by increasing the hardness of the eraser and reducing the frictional resistance between the eraser and the paper surface when the writing line is erased with the eraser, but in this case, it is known that the degree of collection of eraser dust detached from the eraser becomes significantly poor. If the degree of collection of eraser dust is poor, the generated eraser dust scatters in the vicinity, soiling the surroundings and the paper surface, and there is a problem that the writing property is significantly reduced.
On the other hand, if the hardness of the eraser is reduced and the frictional resistance is increased in order to improve the degree of eraser dust collection, the erasing feel becomes heavy.

When it comes to character erasers, there is a trade-off between the ease of erasing and the degree to which the eraser dust gathers; improving one aspect impairs the other, and no character eraser has yet been proposed that satisfies both the ease of erasing and the degree to which the eraser dust gathers.

JP 2013-091230 A JP 2012-131163 A JP 2017-114068 A

The objective of the present invention is to provide a plastic eraser that not only has excellent erasing properties and easily generates eraser dust, but also excels in both the light erasing feel and the degree to which eraser dust accumulates, two properties that have been difficult to achieve together.

As a result of extensive research into solving the above problems, the inventors discovered that a plastic eraser containing at least a vinyl chloride resin as a base resin, a plasticizer, spherical particles, and an acrylic thermoplastic elastomer can solve the problem of achieving both a light erasing feel and the degree of collection of eraser dust, thus arriving at the present invention.

That is, the present invention is as follows.
(1) A plastic eraser comprising at least a vinyl chloride resin as a base resin, a plasticizer, spherical particles and an acrylic thermoplastic elastomer.
(2) The plastic eraser according to (1) above, wherein the spherical particles have an average particle size of 1 to 50 μm.
(3) The plastic eraser according to (1) or (2) above, wherein the content of the spherical particles is 1 to 5% by mass based on the total amount of the plastic eraser.
(4) The plastic eraser according to any one of (1) to (3) above, wherein the content of the acrylic thermoplastic elastomer is 0.1 to 5 mass % based on the total amount of the plastic eraser.
(5) The plastic eraser according to any one of (1) to (4) above, wherein the acrylic thermoplastic elastomer is a block copolymer composed of a hard segment having methyl methacrylate as a main constituent monomer and a soft segment having butyl acrylate or butyl acrylate and 2-ethylhexyl acrylate as main constituent monomers.

The present invention provides an eraser that not only has good erasability, which is the inherent performance of an eraser, and good generation of eraser dust when erasing written lines, but also has a light erasing feel and good eraser dust collection.

FIG. 1 is a schematic diagram showing a method for measuring the dynamic friction coefficient, in which (a) shows a side view of the entire friction tester, and (b) shows a bottom view of the metal plate with a test piece attached.

The present invention will be described in detail below.

The present invention is characterized by containing at least a vinyl chloride resin and a plasticizer as the base resin, which are widely used in plastic erasers, as well as spherical particles and an acrylic thermoplastic elastomer.

[Base resin]
In the present invention, a vinyl chloride resin is used as the base resin, which is preferable because it can provide an eraser with a light erasing feel.

As the vinyl chloride resin, any vinyl chloride resin that has been conventionally used can be used. Examples include polyvinyl chloride with a degree of polymerization of about 400 to 4,000, as well as vinyl chloride-vinyl acetate copolymer, vinylidene chloride, vinyl chloride-methyl acrylate copolymer, vinyl chloride-methyl methacrylate copolymer, and vinyl chloride-octyl acrylate copolymer. These may be used alone or in combination of two or more types as necessary. As the vinyl chloride resin, paste resin is preferred because it is easy to mix with plasticizers and to process.

The content of the vinyl chloride resin is preferably 15 to 40% by mass based on the total amount of the composition constituting the plastic eraser. If it is within this range, the erasing feeling of the eraser will not be too heavy (light). It is more preferably 20 to 35% by mass, and particularly preferably 20 to 30% by mass.
Hereinafter, "mass %" will be abbreviated to "%".

[Plasticizer]
In the present invention, any known plasticizer can be used without any particular limitation, and a plasticizer having excellent miscibility with vinyl chloride resins is preferably used.

Specific examples of preferred plasticizers include, for example,
Phthalate plasticizers such as di-2-ethylhexyl phthalate (DOP), di-n-octyl phthalate (n-DOP), diisononyl phthalate (DINP), dinonyl phthalate (DNP), diisodecyl phthalate (DIDP), ditridecyl phthalate (DTDP), and diundecyl phthalate (DUP);
Trimellitic acid-based plasticizers such as tri-2-ethylhexyl trimellitate (TOTM), triisodecyl trimellitate (TIDTM), triisooctyl trimellitate (TIOTM), and triisononyl trimellitate;
Pyromellitic acid-based plasticizers such as trioctyl pyromellitic acid (TOPM);
polyester plasticizers such as polyesters obtained by condensing a dibasic acid (e.g., adipic acid), at least one polyhydric alcohol (e.g., an aliphatic glycol having 2 to 18 carbon atoms, and a polyalkylene glycol such as diethylene glycol or dipropylene glycol), and at least one selected from a monohydric alcohol having 9 to 18 carbon atoms or a monocarboxylic acid having 9 to 18 carbon atoms (including liquid polyester plasticizers);
Epoxy plasticizers such as epoxidized fats and oils, and epoxidized fatty acid esters;
adipic acid plasticizers such as di-2-ethylhexyl adipate (DOA), diisononyl adipate (DINA), and diisodecyl adipate (DIDA);
Sebacic acid plasticizers such as di-2-ethylhexyl sebacate (DOS) and dibutyl sebacate (DBS);
Azelaic acid plasticizers such as di-2-ethylhexyl azelate (DOZ);
Phosphate-based plasticizers such as tricresyl phosphate (TCP) and tri-2-ethylhexyl phosphate (TOP);
Citric acid-based plasticizers such as triethyl citrate, acetyl tri-n-butyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, and acetyl tri-(2-ethylhexyl) citrate;
Benzoic acid-based plasticizers such as PN-6120, PN-6122 (both trade names, ADEKA Corporation, glycol diester), Benzoflex 9-88 (dipropylene glycol dibenzoate), Benzoflex 50 (a mixture of diethylene glycol dibenzoate and dipropylene glycol dibenzoate), Benzoflex 2088 (a mixture of diethylene glycol dibenzoate, dipropylene glycol dibenzoate, and triethylene glycol dibenzoate) (all trade names, EASTMAN Corporation), PB-3A, and W-83 (all trade names, DIC Corporation);
Alkyl sulfonic acid phenyl esters such as Mezamol and Mezamol II (both trade names, LANXESS);
Cyclohexanedicarboxylic acid esters such as DINCH (trade name, BASF Corporation);
The above plasticizers may be used alone or in combination of two or more kinds, if necessary.

The alkylsulfonic acid phenyl ester is represented by the following chemical formula:

Among the above plasticizers, non-phthalic acid plasticizers are preferred due to their high environmental adaptability. Among non-phthalic acid plasticizers, alkylsulfonic acid phenyl esters and benzoic acid glycol diesters are more preferred, as they are plasticizers with excellent erasability and low stickiness. These plasticizers are highly compatible with vinyl chloride resins, can be easily mixed or kneaded, are less likely to migrate, and are excellent in heat resistance and processability.
It is also preferable to use the above plasticizers in combination with liquid acrylic polymers or liquid polyesters that are liquid at room temperature. By using liquid acrylic polymers or liquid polyesters in combination with other ester-based plasticizers, the migration resistance of the other plasticizers (the migration of the plasticizer to the eraser surface can be improved), and an eraser with a non-sticky surface and high erasability can be obtained.

The plasticizer content is preferably 30-70% of the total amount of the composition constituting the plastic eraser. Within this range, the eraser will not become too soft (hard), so there is no risk of the erasing properties decreasing, and there is no risk of it affecting the erasing feel or the amount of eraser dust that accumulates. A content of 40-65% is more preferable, and 45-60% is particularly preferable.

[Spherical particles]
In the present invention, at least one type of spherical particles selected from inorganic particles or organic particles is blended as a filler with good friction, in addition to the fillers described below. By blending spherical particles, the friction resistance between the eraser and the paper surface can be reduced, and a good erasing feeling can be obtained.
Examples of the inorganic spherical particles include shirasu balloons, fly ash balloons, glass beads, glass bubbles, titanium oxide, and spherical silica.
Examples of the organic spherical particles include spherical acrylic polymers, spherical urethane polymers, spherical styrene polymer particles, spherical nylon polymers, and spherical fluororesin polymers.
The above-mentioned spherical particles may be used alone or in combination of two or more kinds as required. Among these, glass beads and spherical silica are preferred because they can reduce frictional resistance and provide a light erasing feel.

The spherical particles preferably have an average particle diameter of 1 to 50 μm. If the average particle diameter is 1 μm or more, the eraser can be easily erased without causing eraser dust and has a light erasing feel, and if the average particle diameter is 50 μm or less, there is no risk of the erasing property being reduced due to the eraser being too light. More preferably, the average particle diameter is 5 to 45 μm.
The average particle size can be measured by a laser diffraction method.

The content of spherical particles is preferably 1-5% of the total amount of the composition constituting the plastic eraser. If the amount of spherical particles is 1% or more, the erasing feel can be sufficiently lightened, and if it is 5% or less, there is no risk of the frictional resistance becoming too small, which will impair erasing properties and eraser dust collection. It is more preferably 1-4%, and particularly preferably 1.5-3.5%.

The compounding ratio of the spherical particles to the acrylic thermoplastic elastomer described below is preferably 50/50 to 90/10 (spherical particles/acrylic thermoplastic elastomer). Within this range, an eraser with a light erasing feel and good eraser dust collection is obtained. More preferably, it is 50/50 to 80/20.

[Acrylic thermoplastic elastomer]
In the present invention, the acrylic thermoplastic elastomer is used for the purpose of imparting adhesiveness, and mainly contributes to the degree of collection of eraser dust.

A thermoplastic elastomer is a material that exhibits rubber elasticity at room temperature similar to that of crosslinked rubber, and exhibits plasticity similar to that of thermoplastic resins when heated, making it possible to perform thermoforming.
Known thermoplastic elastomers include styrene-based, olefin-based, acrylic-based, PVC-based, polyester-based, polyurethane-based, polyamide-based, and chlorinated polyethylene copolymer crosslinked alloys. Of these, acrylic thermoplastic elastomers are preferred because they improve the collection of eraser dust and suppress an increase in the frictional resistance of the eraser (making the erasing feel heavier).

The acrylic thermoplastic elastomer may be one that is composed of a hard segment A whose main constituent monomer is a methacrylic acid ester that prevents plastic deformation, and a soft segment B whose main constituent monomer is an elastic acrylic acid ester. The bonding form of the hard segment A and the soft segment B may be an AB type two-block copolymer, an ABA type three-block copolymer, a star block copolymer, etc., but a three-block copolymer is preferred because it is easy to form a thread-like network in the vinyl chloride base resin.

Examples of the methacrylic acid ester, which is the main constituent monomer of the hard segment A, include esters of methacrylic acid and fatty acids having 1 to 18 carbon atoms. Among these, from the viewpoint of adhesive properties, monomers such as esters of methacrylic acid and alcohols having 3 or less carbon atoms, such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, and isopropyl methacrylate, are preferred, and methyl methacrylate is particularly preferred.
Examples of the acrylic acid ester, which is the main constituent monomer of the soft segment B, include esters of acrylic acid and fatty acids having 1 to 12 carbon atoms. Among these, n-butyl acrylate or a combination of n-butyl acrylate and 2-ethylhexyl acrylate is preferred from the viewpoint of adhesive properties.

The content of hard segment A in the acrylic thermoplastic elastomer is preferably 5 to 30%, more preferably 10 to 30%, and even more preferably 10 to 25%, based on the total amount of the triblock copolymer. Within this range, good eraser dust collection and a light erasing feel can be obtained.

If the weight-average molecular weight of the acrylic thermoplastic elastomer is in the range of 60,000 to 400,000, it can provide the eraser with good eraser dust collection and good moldability. If the weight-average molecular weight is small, the cohesive strength decreases, while if the weight-average molecular weight is large, the melt moldability of the eraser tends to deteriorate. The weight-average molecular weight is a value calculated from the polystyrene-equivalent molecular weight measured by gel permeation chromatography (GPC).

Commercially available triblock copolymers can also be used. Examples of triblock copolymers of methyl methacrylate and n-butyl acrylate include Kuraly LA2140, LA2250, LA2270, LA2330, LA3320, and LA4285, and examples of triblock copolymers of methacrylic acid and n-butyl acrylate/2-ethylhexyl acrylate include Kuraly LK9243 (all trade names, manufactured by Kuraray Co., Ltd.). These may be used alone or in combination of two or more types as necessary.

The acrylic thermoplastic elastomer is preferably contained in the range of 0.1 to 5% of the total amount of the composition constituting the plastic eraser. If the content is 0.1% or more, the degree of eraser dust collection can be improved. If the content is 5% or less, there is no risk of the erasing feeling becoming heavy. The content is more preferably 0.1 to 4%, and particularly preferably 0.2 to 3%.

In the present invention, the reason why the incorporation of an acrylic thermoplastic elastomer results in an eraser that has a light erasing feel and good eraser dust collection is unclear, but is speculated as follows. In other words, generally, when the hardness of the eraser is reduced to increase the eraser dust collection, the frictional resistance between the eraser and the paper surface increases, resulting in a heavy erasing feel. However, it is speculated that the reason is that the acrylic thermoplastic elastomer forms a thread-like network inside the eraser, and the spherical particles and filler are arranged within this network, so that the acrylic thermoplastic elastomer does not inhibit the behavior of the materials that impart lightness (spherical particles and filler).

[Filler]
The eraser of the present invention can be blended with a filler to adjust the hardness and erasing feeling. As the filler, silica powder (main component: silicon dioxide) or limestone powder (heavy calcium carbonate) is generally used, and these inorganic powders are used in a fine powder form so as not to damage the writing surface. Other than that, diatomaceous earth, talc, shirasu powder, magnesium carbonate, inorganic and organic hollow particles, etc. can be used. Limestone powder is preferred because it provides a good erasing feeling.

The amount of filler blended is preferably 15-40% of the total amount of the composition that makes up the plastic eraser. If the blended amount is 15% or more, the erasing feeling is not heavy and eraser dust is easily produced, so erasability does not decrease. If the blended amount is 40% or less, the area of the base resin that comes into contact with the paper surface is sufficiently secured, so erasability does not decrease. More preferably, it is 20-35%, and particularly preferably, 20-30%.

[Stabilizer]
In order to prevent the base resin from deteriorating at high temperatures during molding, a stabilizer may be used as necessary in the eraser of the present invention, and a light stabilizer such as an ultraviolet absorber may be blended to improve light stability. In addition, additives such as a viscosity adjuster, a lubricant, a solvent, a colorant, a preservative, an antifungal agent, and a fragrance may also be blended. The amount of these additives to be blended is not particularly limited as long as it is within a range that does not impair the effects of the present invention.

＜Erasing feeling＞
In the present invention, the erasing feeling can be expressed by the dynamic friction coefficient between the eraser and the paper surface, and the smaller the value, the lighter the erasing feeling when erasing.
The coefficient of dynamic friction is preferably 0.60 or more and less than 0.90. In actual use, if the coefficient of dynamic friction is too small, the written lines will stretch and the eraser surface will be difficult to scrape off, so the lines will not be erased as you are erasing. If the coefficient of dynamic friction is 0.60 or more, the eraser will firmly bite into the paper and the written lines can be erased. On the other hand, if the coefficient of dynamic friction is less than 0.90, a good erasing feeling can be obtained. It is more preferably 0.60 to 0.85, and particularly preferably 0.60 to 0.80.

<Manufacturing method>
The eraser of the present invention can be manufactured by kneading the base resin, plasticizer, spherical particles, acrylic thermoplastic elastomer, filler, stabilizer, and various additives in predetermined amounts as required by a conventional method, and then molding the mixture by a known method such as press molding, injection molding, or extrusion molding. The molding temperature is 90 to 150°C. The molded product is cut to a predetermined size to produce a finished product. There are no particular limitations on the manufacturing method, and it is sufficient to select a manufacturing method that provides a light erasing feel and eraser dust collection.

The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.
The dynamic friction coefficient and eraser dust accumulation of the eraser were measured and evaluated by the following methods.

[Kinematic friction coefficient]
The method for measuring the dynamic friction coefficient will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the method for measuring the dynamic friction coefficient, where (a) is a side view of the entire friction tester, and (b) is a view from below (bottom side) of a metal plate 2 to which four test pieces 1 and wires 6 are attached. Note that, since Fig. 1 is a schematic diagram, the size ratios and shapes of the various parts are not accurate.
(1) Test piece 1 was prepared by forming the lower tip (the part that came into contact with test paper 4) of a rectangular eraser having a width of 12 mm, a height of 8 mm, and a thickness (vertical) of 5 mm into an arc with a radius of 6 mm. Four identical pieces were prepared in total.
(2) The test pieces 1 were attached one by one to each of the four corners of the underside of a square metal plate 2 (60 mm long x 60 mm wide) with a thickness (height) of 6 mm, with the arc facing downward and oriented in the same direction (see FIG. 1(b)).
(3) The friction tester 5, which is installed horizontally to the ground, includes a test stand 5b that can move horizontally on a main body 5a, and a load cell 5c. A test paper 4, which is PPC paper with a whiteness of 90% or more, is attached to the test stand 5b.
(4) The metal plate (2) was placed on top of the test paper 4 with the test pieces 1 facing downward and the direction of movement of the test table 5b was the tangent to the apex of the arc of the test piece 1 (perpendicular to the thickness direction of the test piece 1), and the four test pieces 1 were brought into contact with the test paper 4 perpendicularly.
(5) A weight 3 was placed on the center of the upper surface of the metal plate 2 so that the total weight together with the metal plate 2 was 0.5 kg.
(6) The metal plate 2 was connected to the load cell 5c via a wire 6, and the test table 5b (and the test paper 4) was moved 50 mm in the direction opposite to the load cell 5c (the direction of the arrow in FIG. 1(a)) at a speed of 200 mm/min to measure the dynamic friction coefficient between the four test pieces 1 and the test paper 4. The median value of three measurements was taken as the measured value.

[Collection level]
(1) The eraser was cut into a plate having a thickness of 5 mm, and the tip portion that came into contact with the test paper was shaped into an arc having a radius of 6 mm to prepare a test piece.
(2) The above test piece was fixed to a test piece holder used in the test of JIS S6050:2002 6.4 erasability (character erasure rate).
(3) The above test piece was reciprocated 20 times (erasing distance: ¹⁶⁰ cm, speed: 150 cm/s) under a constant load (erasing load: 500 gf) on a non-colored test paper (basis weight: 90 g/m2 or more, whiteness: 75% or more) and the number of eraser chips generated was visually counted and evaluated. The evaluation criteria are as shown in Table 1.

(Examples 1 to 14, Comparative Examples 1 to 5)
The compositions shown in Table 2 were mixed in the mixing ratios (numbers indicate parts by mass) shown in the same table, kneaded in a pressure kneader, and then heated and extruded at 110° C. to obtain erasers (test specimens).

The coefficient of dynamic friction of the resulting erasers (test specimens) was measured and the degree of eraser dust accumulation was evaluated. The results are shown in Table 2.

From the results in Table 2, it can be seen that the plastic erasers of the present invention (Examples 1 to 14) can improve the degree of collection of eraser dust by using the acrylic thermoplastic elastomer and spherical particles, while keeping the dynamic friction coefficient low. In other words, it is possible to erase written lines with a light erasing feel, and to provide an eraser in which detached eraser dust is collected without scattering. On the other hand, in Comparative Examples 2 to 4, which contain polymer components other than the acrylic thermoplastic elastomer, the degree of collection of eraser dust is improved, but the dynamic friction coefficient is also high, and a light erasing feel is not obtained. The same is true for Comparative Example 5, which does not contain spherical particles. In Examples 1 to 14, it is presumed that the spherical particles and filler are arranged between the thread-like network formed by the acrylic thermoplastic elastomer, and do not inhibit the behavior (lightness of erasing) that they impart.

The plastic eraser of the present invention can be suitably used for erasing lines drawn with pencils, mechanical pencils, etc.

1 Test piece (eraser)
2 Metal plate 3 Weight 4 Test paper 5 Friction tester 5a Body 5b Test stand 5c Load cell 6 Wire

Claims (5)

A plastic eraser characterized by containing at least a vinyl chloride resin as a base resin, a plasticizer, spherical particles, and an acrylic thermoplastic elastomer. The plastic eraser according to claim 1, wherein the average particle size of the spherical particles is 1 to 50 μm. The plastic eraser according to claim 1 or 2, wherein the content of the spherical particles is 1 to 5% by mass based on the total mass of the plastic eraser. The plastic eraser according to any one of claims 1 to 3, wherein the content of the acrylic thermoplastic elastomer is 0.1 to 5 mass% based on the total weight of the plastic eraser. The plastic eraser according to any one of claims 1 to 4, wherein the acrylic thermoplastic elastomer is a block copolymer composed of a hard segment whose main constituent monomer is methyl methacrylate and a soft segment whose main constituent monomers are butyl acrylate or butyl acrylate and 2-ethylhexyl acrylate.

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