JP2020029513A - Composition for eraser - Google Patents

Abstract

To provide a composition for eraser capable of combining erasing performance with moldability at high level, and a molded body of the same.SOLUTION: The composition for eraser is provided that contains a styrenic thermoplastic elastomer A and contains, with respect to 100 pts.mass of the styrenic thermoplastic elastomer A, 5-100 pts.mass of an ethylene-vinyl acetate copolymer B having a content of a vinyl acetate unit of 20 mass% or less and a melt mass flow rate at 190°C and a load of 21.18 N of 100 g/10 min or less, and 5-150 pts.mass of a softening agent C for non-aromatic rubber. The eraser molded body composed of the composition for eraser is also provided.SELECTED DRAWING: None

Description

  The present invention relates to an eraser composition and a molded article thereof.

  As a composition for an eraser, a composition using natural rubber as a raw material has been known for a long time.In recent years, a composition using polyvinyl chloride as a raw material, which is excellent in erasing properties and unity of eraser scrap, has been used as a plastic eraser. It is called mainstream. However, since the plastic eraser contains a plasticizer, the plastic eraser has an essential disadvantage that the plasticizer migrates to the plastic product in contact with the eraser and attacks the plastic product in contact. For this reason, various types of thermoplastic elastomers other than vinyl chloride as raw materials have been studied.

  Patent Literature 1 discloses an eraser comprising at least an ethylene-vinyl acetate copolymer, a polyolefin-based elastomer, a filler, and a plasticizer.

  Patent Document 2 discloses a styrene-based block copolymer having at least an ABA triblock structure, a polyethylene polymerized by a single-site catalyst or a copolymer mainly composed of the same, An eraser thermoplastic elastomer composition comprising a group rubber softener and an inorganic filler is disclosed.

JP-A-11-334289 JP-A-11-349735

  Patent Literature 1 only describes that ethylene-vinyl acetate copolymers are not bad in terms of erasure properties even if they are hard, and ethylene-vinyl acetate copolymers in which various properties can be selected depending on the vinyl acetate unit content. It is not known what kind of coalescing effect is used as an eraser.

  In Patent Document 2, it is pointed out that when an ethylene-vinyl acetate copolymer is used as a comparative example, the moldability and the cohesiveness of erased scum are inferior. The ethylene-vinyl acetate copolymers Evaflex EV-40X and EV-260 manufactured by DuPont-Mitsui Polychemicals Co., Ltd. used in Comparative Examples have a vinyl acetate unit content of 41% by mass for EV-40X and EV. -260 is 28% by mass, all of which have a high vinyl acetate unit content. When an ethylene-vinyl acetate copolymer having a vinyl acetate unit content of 20% by mass or less is used, a different effect is produced. It is not known.

  On the other hand, while the shape of the conventional eraser is basically a rectangular parallelepiped and there is no major restriction on the molding method, in recent years, a complex shape with many corners and a design eraser such as a super car eraser have been designed. Has become popular, and the demand for moldability of the composition for the eraser has been increased. The easiest way to enhance moldability is to add a large amount of a rubber softener to increase the melt flowability of the composition, but oil bleeding tends to occur and the eraser performance as an eraser Since the decline of the unavoidable is also unavoidable, it has been a reputation that erasers with high designability are not satisfactory in eraser performance, and an eraser composition that simultaneously satisfies moldability and eraser performance is required. .

  An object of the present invention is to provide an eraser composition and a molded article thereof, which can achieve both erase performance and moldability at a high level.

The present invention
[1] Styrene-based thermoplastic elastomer A and a melt mass flow rate at a temperature of 190 ° C. and a load of 21.18 N in which the content of vinyl acetate units is 20% by mass or less based on 100 parts by mass of the styrene-based thermoplastic elastomer A Containing 5 to 100 parts by mass of an ethylene-vinyl acetate copolymer B having a content of 100 g / 10 min or less, and 5 to 150 parts by mass of a softener C for a non-aromatic rubber, and [2] The present invention relates to an eraser molded article comprising the eraser composition according to [1].

  The composition for an eraser of the present invention has an effect of being excellent in moldability and also excellent in eraser performance.

  The composition for an eraser of the present invention contains a styrene-based thermoplastic elastomer A, an ethylene-vinyl acetate copolymer B, and a softener C for a non-aromatic rubber. Polymer B has one feature in that the content of vinyl acetate units (hereinafter, referred to as vinyl acetate content) is as low as 20% by mass or less.

  Ethylene-vinyl acetate copolymer, known as EVA resin, is a copolymer composed of an ethylene monomer unit and a vinyl acetate monomer unit, and has properties that vary greatly depending on the vinyl acetate content. It is. Since those having a high content of vinyl acetate units tend to be excellent in flexibility because of a small number of ethylene monomer units that are likely to exhibit crystallinity, attempts to use an ethylene-vinyl acetate copolymer in the eraser composition have been conducted. In general, an ethylene-vinyl acetate copolymer having a high vinyl acetate content was used, and an ethylene-vinyl acetate copolymer having a low vinyl acetate content was never used. However, an ethylene-vinyl acetate copolymer having a high vinyl acetate content also has an aspect that its affinity with a process oil (softening agent for rubber) is inferior, and as with the composition of the present invention, it is necessary to obtain high moldability. However, a composition which requires a process oil has a problem that oil bleeding is likely to occur.

  Also, as the ethylene-vinyl acetate copolymer, it is known that even though the vinyl acetate content is the same, the melt fluidity of the resin is increased by lowering the molecular weight, but the melt fluidity of the resin alone is high. However, since the compatibility with the styrene-based thermoplastic elastomer A is not good, separation and flow of the components occur during molding, and a skin layer rich in the ethylene-vinyl acetate copolymer component is formed near the mold surface. Problems arise. This skin layer appears as a partial gloss on the surface of the molded product, and not only does the erasability deteriorate partially, but also in a molded product with a design property, the gloss appears in an unintended part. You will lose value.

  Therefore, as a result of investigations by the present inventors, when selecting an ethylene-vinyl acetate copolymer to be used in the composition for the eraser, it was found that the two viewpoints of the vinyl acetate content and the melt fluidity have a synergistic effect. If the ethylene-vinyl acetate copolymer has a vinyl acetate content of 20% by mass or less and a melt mass flow rate at 190 ° C. of 100 g / 10 min or less, the gloss by the skin layer And oil bleed can be suppressed, and the eraser performance is also good.

  The vinyl acetate content in the ethylene-vinyl acetate copolymer B is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, from the viewpoint of flexibility. From the viewpoint of compatibility and affinity with the styrene-based thermoplastic elastomer A and the softener C for non-aromatic rubber, the content is 20% by mass or less, preferably 18% by mass or less, more preferably 15% by mass or less, and still more preferably. Is 13% by mass or less, more preferably 10% by mass or less, further preferably 8% by mass or less.

  The melt mass flow rate of the ethylene-vinyl acetate copolymer B at 190 ° C. and a load of 21.18 N is preferably 1 g / 10 min or more, more preferably 3 g / 10 min or more, from the viewpoint of moldability (mold filling property). And more preferably 5 g / 10 min or more, and from the viewpoint of moldability (prevention of oil bleed and skin layer), it is 100 g / 10 min or less, preferably 80 g / 10 min or less, more preferably 50 g / 10 min. Or less, more preferably 30 g / 10 min or less. Melt mass flow rate (MFR) is also related to the molecular weight. The larger the MFR, the larger the molecular weight, and the smaller the MFR, the smaller the molecular weight.

  The content of the ethylene-vinyl acetate copolymer B is at least 5 parts by mass, preferably at least 10 parts by mass, based on 100 parts by mass of the styrene-based thermoplastic elastomer A, from the viewpoint of melt fluidity and attrition. And more preferably 20 parts by mass or more, and from the viewpoint of flexibility and oil bleed control, it is 100 parts by mass or less, preferably 60 parts by mass or less, more preferably 40 parts by mass or less.

  The content of the ethylene-vinyl acetate copolymer B in the composition of the present invention is preferably 3 to 45% by mass, more preferably 4 to 40% by mass, and still more preferably 5 to 35% by mass.

  The composition of the present invention has a vinyl acetate content of more than 20% by mass and / or a melt mass flow rate of 100 g / 10 min in addition to the ethylene-vinyl acetate copolymer B within a range not impairing the effects of the present invention. It may contain more than ethylene-vinyl acetate copolymer. In particular, an ethylene-vinyl acetate copolymer having a vinyl acetate content of more than 20% by mass is effective for improving the erasure property, but an ethylene-vinyl acetate copolymer other than the ethylene-vinyl acetate copolymer B is used. The content is preferably 2/3 or less, more preferably 1/3 or less, of the ethylene-vinyl acetate copolymer B in terms of mass ratio.

  The styrene-based thermoplastic elastomer A is preferably composed of a hard part (hard segment) and a soft part (soft segment) from the viewpoint of flexibility and moldability, and is composed of a styrene-based monomer as the hard segment. It is more preferable that the block copolymer (Z1) has a polymer block unit (s1) and a polymer block unit (b1) composed of a conjugated diene compound as a soft segment.

  Styrene monomers constituting the block unit (s1) include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, And vinyl anthracene.

  The content of the styrene monomer unit in the block copolymer (Z1) is preferably from 20 to 60% by mass, from the viewpoint of improving flexibility while maintaining compatibility with the ethylene-vinyl acetate copolymer B. More preferably, it is 25 to 50% by mass.

  Examples of the conjugated diene compound constituting the block unit (b1) include butadiene, isoprene, 1,3-pentadiene and the like.

The block copolymer (Z1) may be at least partially hydrogenated. The hydrogenation reduces unsaturated bonds and improves heat resistance and mechanical properties. From the viewpoint of cohesiveness, the lower the hydrogenation rate is, the better, preferably 50% or less, and more preferably, no hydrogenation. In the present invention, the hydrogenation rate, the content of carbon-carbon double bonds derived from the conjugated diene compound in the block copolymer, before and after hydrogenation, measured by ¹ H-NMR spectrum, the measured value Can be obtained from

  In the present invention, the styrene-based thermoplastic elastomer A may be a [block unit (s1) -block unit (b1) -block unit (s1)] type triblock copolymer or [block Unit (s1) -block unit (b1)] A multi-block copolymer of n (n is an integer of 2 or more) or the like is preferable, but from the viewpoint of eraseability and unity of erased scrap, [block unit (s1) -Block unit (b1)] type diblock copolymer.

  The weight average molecular weight of the diblock copolymer is preferably 120,000 or less, more preferably 100,000 or less, from the viewpoints of erasure and cohesion of erased residue. In addition, from the viewpoint of stickiness, it is preferably 30,000 or more, more preferably 50,000 or more.

  The content of the diblock copolymer in the styrene-based thermoplastic elastomer A is preferably 1% by mass or more, more preferably 5% by mass or more, from the viewpoint of erasure and cohesiveness of erased scum, From the viewpoint of heat resistance and stickiness, the content is preferably 60% by mass or less, more preferably 40% by mass or less. The content of the diblock copolymer in the styrene-based thermoplastic elastomer A can be estimated from, for example, a production method. When a diblock is obtained by a method of producing only a diblock and mixed, depending on the mixing amount, most of the block copolymers have hard segments that are sequentially connected to homopolymerized soft segments. It is produced by a method of polymerizing. In that case, the quantitative ratio of the soft segment, diblock form, triblock form, etc. can be estimated from the structural analysis of the intermediate product and the molecular weight measurement of the obtained product.

  The weight average molecular weight of the styrene-based thermoplastic elastomer A is preferably 50,000 or more, more preferably 100,000 or more, and still more preferably 200,000 or more, from the viewpoint of oil bleed resistance, and from the viewpoint of moldability, preferably 600,000. Or less, more preferably 500,000 or less. When it is composed of a plurality of block copolymers, it is preferable that the weighted average value of the weight average molecular weight of each block copolymer falls within the above range.

  The melt mass flow rate of the styrene-based thermoplastic elastomer A at 190 ° C. and a load of 5 kg is preferably 40 g / 10 min or less, more preferably 30 g / 10 min or less, and still more preferably 20 g / 10 min or less, from the viewpoint of erasure. .

  The content of the styrene-based thermoplastic elastomer A in the composition of the present invention is preferably 10 to 70% by mass, more preferably 15 to 60% by mass, and still more preferably 20 to 50% by mass.

  Examples of the non-aromatic rubber softener C include paraffin oil, naphthenic oil, liquid paraffin and the like. Among them, the viewpoint that the affinity with the styrene-based thermoplastic elastomer A is good and bleeding hardly occurs. Therefore, paraffin oil and naphthenic oil are preferred, and paraffin oil is more preferred.

The kinematic viscosity at 40 ° C. of the non-aromatic rubber softener C is preferably 10 mm ² / s or more, more preferably 20 mm ² / s or more, from the viewpoint of preventing volatilization during heating and melting and improving bleed resistance. In addition, it is preferably 500 mm ² / s or less, more preferably 300 mm ² / s or less, more preferably 150 mm ² / s or less, because of easy handling.

It is preferable that the softener C for a non-aromatic rubber contains at least two kinds having different kinematic viscosities at 40 ° C. from the viewpoint of flexibility and prevention of stickiness. These combinations may be paraffin oil or naphthenic oil, or a combination of paraffin oil and naphthenic oil. The difference in kinematic viscosity at 40 ° C. is preferably 10 mm ² / s or more, more preferably 20 to 400 mm ² / s, and still more preferably 40 to 150 mm ² / s.

  When two kinds of non-aromatic rubber softeners having different kinematic viscosities are used in combination, the mass ratio (softener having a lower kinematic viscosity / softener having a higher kinematic viscosity) is preferably 10/90 to 90 / 10, more preferably from 20/80 to 80/20, even more preferably from 30/70 to 70/30.

  The content of the softener C for the non-aromatic rubber is 5 parts by mass or more, based on 100 parts by mass of the styrene-based thermoplastic elastomer A, from the viewpoint of increasing the flexibility of the composition and improving the dispersibility of various components. And preferably at least 20 parts by mass, and from the viewpoint of suppressing stickiness caused by oil bleed, the amount is at most 150 parts by mass, preferably at most 120 parts by mass, more preferably at most 100 parts by mass.

  The content of the softener C for non-aromatic rubber in the composition of the present invention is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and still more preferably 15 to 40% by mass.

  It is preferable that the composition of the present invention further contains a filler D from the viewpoint of erasure.

  As the filler D, an inorganic filler is preferable, and specific examples include calcium carbonate, silica, silica, clay, talc, alumina, zirconia, and glass. Among these, calcium carbonate, talc, and Synthetic silica is preferred, and calcium carbonate is more preferred. As calcium carbonate, light calcium carbonate produced by chemical synthesis, heavy calcium carbonate produced by pulverizing and classifying natural ore, natural calcium carbonate derived from shells and the like, and the like are known. Particularly preferred in the present invention is heavy natural calcium, and those having various particle sizes are commercially available.

The particle size distribution of the filler D can be measured with a centrifugal sedimentation type particle size distribution analyzer, and a volume-based median diameter (D ₅₀ ) can be used as a representative value. The median diameter of the filler D is preferably 100 μm or less, more preferably 50 μm or less, further more preferably 30 μm or less, and still more preferably 10 μm or less, from the viewpoint of erasure and cohesiveness of eraser dust. From the viewpoint of, it is preferably 0.3 μm or more, more preferably 1 μm or more.

  The content of the filler D is preferably at least 30 parts by mass, more preferably at least 50 parts by mass, and still more preferably at least 80 parts by mass, based on 100 parts by mass of the styrene-based thermoplastic elastomer A. It is 300 parts by mass or less, more preferably 250 parts by mass or less, further preferably 200 parts by mass or less.

  The content of the filler D in the composition of the present invention is preferably 10 to 70% by mass, more preferably 20 to 65% by mass, and still more preferably 30 to 60% by mass.

  The thermoplastic elastomer composition of the present invention may contain another thermoplastic resin or a thermoplastic elastomer as long as the effects of the present invention are not impaired.

  Further, the eraser composition of the present invention may be, if necessary, a carbon black, an organic pigment, an inorganic pigment, a dye, an inorganic filler, a heat stabilizer, an antioxidant, and a light as long as the effects of the present invention are not impaired. Various additives such as a stabilizer, an ultraviolet absorber, an anti-blocking agent, and a fragrance may be contained.

  The composition for an eraser of the present invention comprises a styrene-based thermoplastic elastomer A, an ethylene-vinyl acetate copolymer B, and a softener C for a non-aromatic rubber, and, if necessary, a filler D and other additives. Are obtained by mixing and solidifying by cooling.

  The term "mixing" as used in the present invention is not particularly limited as long as various components are satisfactorily mixed, and various components may be dissolved and mixed in a dissolvable organic solvent, or may be melt-kneaded. Although the raw materials may be mixed, the mixing of the raw materials is preferably performed under conditions in which the raw materials are melted.

  In the case of melt-kneading, a general extruder can be used, and it is preferable to use a twin-screw extruder for improving the kneading state. For the supply to the extruder, one obtained by mixing various components in advance using a mixing device such as a Henschel mixer may be supplied from one hopper, or each component is charged to two hoppers and quantitatively determined by a screw below the hopper. You may serve while doing.

  The product obtained by mixing the raw materials constituting the eraser composition can be in the form of a pellet, a sheet, or the like, depending on the use. For example, the mixture is melt-kneaded by an extruder, extruded into strands, and cut into pellets such as columnar or rice grains by a cutter while being cooled in cold water. The obtained pellet is usually formed into a predetermined sheet-like molded product or molded product by injection molding or extrusion molding. Further, the melt-kneaded material can be formed into pellets with a ruder or the like and used as a raw material for forming.

  The A hardness of the eraser composition of the present invention is preferably 90 or less, more preferably 80 or less, even more preferably 70 or less from the viewpoint of flexibility, and from the viewpoint of stickiness suppression and practicality, preferably It is 30 or more, more preferably 40 or more, and still more preferably 50 or more.

  The composition of the present invention can be molded into erasers of various shapes by appropriately heating and molding according to a conventional method. As an apparatus used for producing an eraser using the composition of the present invention, any molding machine capable of melting a molding material can be used. For example, an extrusion molding machine, an injection molding machine, a press molding machine, a blow molding machine, a mixing roll and the like can be mentioned.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples. Various physical properties of the raw materials used in Examples and Comparative Examples were measured by the following methods.

<Component A (styrene-based thermoplastic elastomer A)>
(Content of styrene monomer unit)
Proton NMR measurement is performed using a nuclear magnetic resonance apparatus (manufactured by BRUKER, Germany, DPX-400), and the content of styrene and / or a styrene derivative is determined by quantifying a characteristic group of styrene. The content of other monomer units can also be determined by proton NMR measurement.

[Weight average molecular weight (Mw)]
Under the following measurement conditions, the molecular weight is measured in terms of polystyrene by gel permeation chromatography, and the weight average molecular weight is determined.

Measuring device / pump: JASCO (JASCO Corporation), PU-980
-Column oven: AO-50, manufactured by Showa Denko KK
・ Detector: Hitachi, RI (differential refractometer) detector L-3300
-Column type: K-805L (8.0 x 300 mm) and K-804L (8.0 x 300 mm) each manufactured by Showa Denko KK-Column temperature: 40 ° C
・ Guard column: KG (4.6 × 10mm)
・ Eluent: chloroform ・ Eluent flow rate: 1.0ml / min
・ Sample concentration: about 1mg / ml
・ Sample solution filtration: 0.45 μm pore size disposable filter made of polytetrafluoroethylene ・ Standard sample for calibration curve: Polystyrene manufactured by Showa Denko KK

[Melt mass flow rate (MFR)]
In accordance with ASTM D1238, the value at 190 ° C under a load of 5 kg is indicated in units of g / 10 min.

<Component B (ethylene-vinyl acetate copolymer)>
[Vinyl acetate content and melt mass flow rate (MFR)]
Annex "Ethylene-vinyl acetate resin test" of JIS K6924-2 1997 "Plastics-Ethylene / vinyl acetate (E / VAC) molding and extrusion materials-Part 2: How to prepare test pieces and determine various properties" Method ”, the measurement is performed according to the method described in“ Method ”. The melt mass flow rate is represented by a value at a test temperature of 190 ° C. and a load of 21.18 N in units of g / 10 min.

<Component C (Softener for non-aromatic rubber)>
(Kinematic viscosity)
Measure at a temperature of 40 ° C according to JIS Z 8803.

<Component D (filler)>
[Median diameter (D ₅₀ )]
The volume-based median diameter is measured with a centrifugal sedimentation type particle size distribution analyzer (“SA-CP3” manufactured by Shimadzu Corporation).

Examples 1 to 10 and Comparative Examples 1 to 6
(1) Preparation of Eraser Composition (Pellets) The materials shown in Tables 5 and 6 were dry-blended. Then, the mixture is melt-kneaded with an extruder (continuous kneader) under the following conditions, extruded into strands, and cut into a diameter of about 3 mm and a thickness of about 3 mm with a cutter while cooling in cold water, and pelletize. Manufactured.

(Melting and kneading conditions)
Extruder: KZW32TW-60MG-NH (manufactured by Technovel Corporation)
Cylinder temperature: 180-260 ℃
Screw rotation speed: 200-650r / min

  The details of the raw materials described in Tables 5 and 6 used in Examples and Comparative Examples are as follows.

(2) Production of eraser molded article The pellets were injection molded under the following conditions to produce a sheet having a thickness of 6 mm, a width of 25 mm and a length of 125 mm.

[Injection molding conditions]
Injection molding machine: 100MSIII-10E (trade name, manufactured by Mitsubishi Heavy Industries, Ltd.)
Injection molding temperature: 160 ℃
Injection pressure: 30%
Injection time: 3sec
Mold temperature: 40 ℃

  Using the obtained sheet, measurement of physical properties and evaluation of moldability and eraser performance were performed. The results are shown in Tables 5 and 6. The MFR was measured only in Examples 1 and 2 and Comparative Examples 1 and 3.

[A hardness]
The sheet was allowed to stand in a constant temperature / humidity chamber (temperature 23 ° C., relative humidity 50%) for 24 hours or more to stabilize the state of the sheet. A hardness was measured according to JIS K7215 “Durometer hardness test method for plastics”.

[Spiral flow]
The composition was injection-molded into a spiral mold having a width of 5 mm, a thickness of 3 mm, and a maximum flow length of 1200 mm at 140 ° C., an injection pressure of 70 MPa, and a speed of 10 mm / s, and the maximum flow length (mm) was measured.

(Wear loss)
In the Taber abrasion test, the amount of wear loss was measured. Specifically, using a sheet, in accordance with JIS K 7204, the wear loss (mg) at 23 ° C, wear wheel: H-22, rotation speed: 72r / min, number of rotations: 1,000 times, load: 1000g It was measured. The greater the wear loss, the better the abrasion.

[MFR]
It was measured at 140 ° C. under a load of 2.16 kg by a method in accordance with ASTM D1238.

(Moldability)
(1) Gross The gloss of the sheet surface was measured using a gloss checker (IG-410, manufactured by Horiba, Ltd.).

(2) Stickiness The surface of the sheet was touched with a finger to determine the presence or absence of obvious stickiness, and evaluated according to the following evaluation criteria.
<Evaluation criteria>
：: The surface is smooth and no stickiness is felt.
：: Does not follow the finger, but feels slightly sticky.
×: Level following the finger when touched.

(3) The oil bleed sheet was placed on a drawing paper and allowed to stand at 70 ° C. for 24 hours. Thereafter, it was visually checked whether or not oily bleeding was present on the white drawing paper, and evaluated according to the following evaluation criteria.
<Evaluation criteria>
：: No stain is observed at all.
：: At first glance, no stain was observed, but it was barely discernable by comparing with an unused drawing paper.
×: Stain is clearly observed.

[Erasing performance]
(1) Eraseability Cut the eraser sample into a 5 mm-thick plate and finish the contact area with the test paper in an arc with a radius of 6 mm as a test piece, using the following method in accordance with JIS-S6050, Erasability was evaluated.
Contact the test piece perpendicular to the colored paper and at a right angle to the colored line, and place a weight on the test piece so that the sum of the weight of the weight and the holder becomes 0.5 kg, and 150 ± 10 cm / The colored portion was rubbed back and forth four times at a speed of min. The colored portion after abrasion was visually observed, and the erasure was evaluated according to the following evaluation criteria.
<Evaluation criteria>
A: Coloring has completely disappeared and cannot be distinguished from the non-colored portion.
：: At first glance, coloring was not recognized, but it was barely discernible when uncolored blank test paper was applied to the test pieces and arranged.
Δ: It can be barely determined that coloring remains.
X: Coloring is clearly left.

(2) Group of erased waste
A test piece was prepared by cutting the sheet by a method in accordance with JIS S60504.4, and the test piece was reciprocated 10 times at an erasing load of 500 gf, and the unity rate (%) of erased scrap was calculated from the following equation. The weight of the scraps was measured four times for each composition, and the average value was obtained.

From the above results, it can be seen that the eraser molded articles of Examples 1 to 10 have better moldability and eraser performance as compared with Comparative Examples 1 to 6.
Table 7 shows a comparison between Examples 1 and 2 and Comparative Examples 1 and 3.

From the results of Examples 1 and 2, when the vinyl acetate content of the ethylene-vinyl acetate copolymer is small, even if the MFR is small (high molecular weight), the spiral flow is large, and a moderate abrasion property is obtained due to the high molecular weight. It can be seen that it can be maintained.
In Comparative Example 1, even if the vinyl acetate content of the ethylene-vinyl acetate copolymer was small, those having a too high MFR (low molecular weight) also had a large MFR of the composition, but the spiral flow was so large. Rather, a skin layer rich in the ethylene-vinyl acetate copolymer component is generated, adheres to the composition mold contact surface and stops flowing, and the adhered portion becomes gloss on the surface of the molded product. Further, the oil cannot be retained due to the low molecular weight, and stickiness occurs.
On the other hand, as in Comparative Example 3, when the ethylene-vinyl acetate copolymer has a high vinyl acetate content and a low MFR (high molecular weight), the spiral flow of the composition is low. Further, since the vinyl acetate content is large, the oil cannot be retained and stickiness occurs.
As described above, the unexpected result is that the effect of the composition on the spiral flow tends to be different depending on the vinyl acetate content of the ethylene-vinyl acetate copolymer.

  The composition for an eraser of the present invention is used not only as an eraser as a molded article, but also as an article, stationery, miscellaneous goods and the like by utilizing its moldability.

Claims (7)

  Styrene-based thermoplastic elastomer A and 100 parts by mass of styrene-based thermoplastic elastomer A, the content of vinyl acetate units is 20% by mass or less, and the melt mass flow rate at 190 ° C. and a load of 21.18N is 100 g / A composition for an eraser, comprising 5 to 100 parts by mass of an ethylene-vinyl acetate copolymer B of 10 minutes or less and 5 to 150 parts by mass of a softener C for a non-aromatic rubber.   The composition for an eraser according to claim 1, wherein the styrene-based thermoplastic elastomer A has a weight average molecular weight of 200,000 or more.   The composition for an eraser according to claim 1 or 2, wherein the softener C for non-aromatic rubber contains at least one selected from paraffin oil and naphthenic oil.   The composition for an eraser according to any one of claims 1 to 3, wherein the softener C for a non-aromatic rubber contains at least two kinds having different kinematic viscosities at 40 ° C.   The composition for an eraser according to any one of claims 1 to 4, further comprising 30 to 300 parts by mass of an inorganic filler D based on 100 parts by mass of the styrene-based thermoplastic elastomer A.   The composition for an eraser according to any one of claims 1 to 5, wherein the styrene-based thermoplastic elastomer A contains 1 to 40% by mass of a block copolymer having a diblock structure.   An eraser molded article comprising the eraser composition according to any one of claims 1 to 6.