JPH11349735A - Thermoplastic elastomer eraser composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic elastomer composition having excellent moldability, processability, usability, erasability and the cohesivity of erasing residues, and used for erasing characters. SOLUTION: This thermoplastic elastomer for erasing characters comprises (a) 100 pts.wt. of a block copolymer comprising at least two polymer blocks A consisting mainly of a vinylaromatic compound and at least one polymer block consisting mainly of a conjugated diene compound, and/or a hydrogenated block copolymer obtained by hydrogenating the block copolymer, (b) 5-200 pts.wt. of polyethylene or a copolymer consisting mainly of ethylene, which are (co)polymerized in the presence of a single site catalyst, (c) 20-250 pts.wt. of a non-aromatic softener for rubbers, and (d) 0-400 pts.wt. of an inorganic filler.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic elastomer eraser composition which, when used as an eraser, is excellent in eraseability, erases scraps by a small amount of frictional heat, and the eraser scraps are easily separated from the eraser body. It is about things.

[0002]

2. Description of the Related Art In recent years, many erasers using thermoplastic elastomers have been developed in place of the mainstream erasers of polyvinyl chloride. The thermoplastic elastomer combines a styrene resin elastomer and an olefin resin. For example, as an olefin resin,
Polyolefin resins having a melting point or softening point of 100 ° C. or more, such as polypropylene, polyethylene, and ethylene-vinyl acetate copolymer, are used. In order to form erasers from these resins, it is necessary to increase the molding temperature. In addition to the moldability and workability, the eraser, the cohesiveness of the eraser scrap, and the ease of removal of the eraser scraps caused by friction from the eraser body are the same as those of the conventional PVC eraser. Inferior to.

[0003]

Means for Solving the Problems By blending a block copolymer mainly composed of a vinyl aromatic / conjugated diene compound with a polyethylene resin polymerized with a single-site catalyst, it is possible to reduce the erasure and eraser residue. It has been found that a thermoplastic elastomer eraser composition which is excellent in unity and can be molded at low temperature and low pressure can be obtained.

That is, the present invention relates to (a) a block copolymer comprising at least two polymer blocks A mainly composed of vinyl aromatic and at least one polymer block B mainly composed of a conjugated diene compound. 100 parts by weight of a hydrogenated block copolymer obtained by hydrogenation of the coalesced polymer and / or (b) polyethylene or a copolymer mainly composed of polyethylene polymerized with a single-site catalyst 5 to 200 parts by weight (C) 20 to 250 parts by weight of a softening agent for non-aromatic rubber (d) 0 to 400 parts by weight of an inorganic filler.
A composition is provided.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Each component of the present invention will be described.

The essential component (a) of the present invention is a block comprising at least two polymer blocks A mainly composed of a vinyl aromatic compound and at least one polymer block B mainly composed of a conjugated diene compound. A copolymer or a product obtained by hydrogenating the copolymer, or a mixture thereof, for example, ABA, BABA, AB-
Examples thereof include a vinyl aromatic compound-conjugated diene compound block copolymer having a structure such as ABA and / or a hydrogenated product thereof.

[0007] The (hydrogenated) block copolymer (here, the (hydrogenated) block copolymer means a block copolymer and / or a hydrogenated block copolymer) is a vinyl aromatic compound. From 5 to 60% by weight, preferably from 20 to 5% by weight.
0% by weight.

The polymer block A mainly composed of a vinyl aromatic compound is preferably composed of only a vinyl aromatic compound or a copolymer of a conjugated diene compound with 50% by weight or more, preferably 70% by weight or more of a vinyl aromatic compound. It is a copolymer block or a hydrogenated product thereof.

The polymer block B mainly composed of a conjugated diene compound is preferably composed of only a conjugated diene compound or a copolymer of a vinyl aromatic compound with 50% by weight or more, preferably 70% by weight or more of a conjugated diene compound. It is a united block or its hydrogenated product.

In each of the polymer block A mainly composed of the vinyl aromatic compound and the polymer block B mainly composed of the conjugated diene compound, the distribution of the vinyl compound or the conjugated diene compound in the molecular chain is random or tapered. (In which the monomer component increases or decreases along the molecular chain), may be partially blocked, or may be in any combination thereof.

When there are two or more polymer blocks A mainly composed of a vinyl aromatic compound or two or more polymer blocks B mainly composed of a conjugated diene compound, they may have the same structure or different structures. Good.

As the vinyl aromatic compound constituting the (hydrogenated) block copolymer, for example, one or more selected from styrene, α-methylstyrene, vinyltoluene, p-tert-butylstyrene and the like are selected. Of which styrene is preferred. As the conjugated diene compound,
For example, one or more kinds are selected from butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and the like.
Isoprene and combinations thereof are preferred.

The micro bond in the polymer block B mainly composed of a conjugated diene compound can be arbitrarily selected.

In the butadiene block, 1,2-
The micro-bonding is preferably 20 to 50%, particularly preferably 25 to 45%.

In the polyisoprene block, 70 to 100% by weight of the isoprene compound is 1,4%.
Those having micro-bonds and wherein at least 90% of the aliphatic double bonds based on the isoprene compound are hydrogenated;

The weight average molecular weight of the (hydrogenated) block copolymer of the present invention having the above-mentioned structure is preferably from 5,000 to 1,500,000, more preferably from 10,000 to 550,000, More preferably, 1
It is in the range of from 00,000 to 550,000, particularly preferably from 10,000 to 400,000. The molecular weight distribution (ratio (Mw / Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn)) is preferably 10 or less, more preferably 5 or less, and more preferably 2 or less. (Hydrogenated)
The molecular structure of the block copolymer may be linear, branched, radial, or any combination thereof.

Numerous methods have been proposed as methods for producing these block copolymers. Representative methods include, for example, the method described in Japanese Patent Publication No. It can be obtained by performing block polymerization in an inert solvent using a Ziegler type catalyst. By hydrogenating the block copolymer obtained by the above method in the presence of a hydrogenation catalyst in an inert solvent, a hydrogenated block copolymer is obtained.

Specific examples of the (hydrogenated) block copolymer include styrene / butadiene / styrene copolymer, styrene / isoprene / styrene copolymer, styrene / ethylene / butadiene / styrene copolymer, styrene / ethylene A propylene / styrene copolymer;

Preferred are styrene / butadiene / styrene copolymers and styrene / isoprene / styrene copolymers, and more preferred are styrene / butadiene / styrene copolymers.
It is a styrene copolymer.

The essential components (b) include high-density polyethylene (low-pressure polyethylene), low-density polyethylene (high-pressure polyethylene), and linear low-density polyethylene (ethylene and ethylene) polymerized with a metallocene catalyst (single-site catalyst). A small amount, preferably 1 to 10 mol% of butene
One or two selected from polyethylene, ethylene-propylene copolymer, and the like, such as 1, copolymers with α-olefins such as hexene-1 and octene-1;
More than one species is preferably used.

Preferably, the specific gravity is 0.90 or less, and the melting point is 95.
℃ or lower, metallocene catalyst (single site catalyst)
Is an ethylene octene copolymer produced by using These generally have a temperature of 190 ° C. and a load of 2.16 k.
The MFR in g is preferably 1.0 g / 10 min or more, more preferably 20 g / 10 min or more. These can be used alone, but it is preferable to combine the two within the above ranges of the specific gravity, melting point and MFR.

The amount of the component (b) is 100 parts (a)
It is 5 to 200 parts by weight based on parts by weight. If it is less than 5 parts by weight or more than 200 parts by weight, the erasing power is lost. A preferred amount is 10 to 150 parts by weight.

Component (c) The rubber softener used in the present invention is preferably a paraffinic one, and more preferably a paraffinic one having no aromatic ring component. The amount of the component (c) is from 20 to 250 parts by weight based on 100 parts by weight of the component (a).
Parts by weight, preferably 30 to 100 parts by weight. If the upper limit is exceeded, the hardness of the elastomer composition becomes too low, and the moldability and the required hardness are lost. If the lower limit is exceeded, the hardness of the elastomer composition becomes too high, and the usability is lost.

Component (d) The inorganic filler is blended if necessary. Inorganic fillers have an economic advantage by increasing the amount, in addition to improving the moldability and improving the erasing power as a eraser molded article. Examples of the inorganic filler include calcium carbonate, talc, magnesium hydroxide, mica, clay, barium sulfate, natural silicic acid, synthetic silicic acid (white carbon), titanium oxide, and carbon black. Preferably, calcium carbonate and talc are used. The amount of component (d) is 400 parts by weight or less, preferably 200 parts by weight or less, based on 100 parts by weight of component (a). If the amount exceeds 400 parts by weight, the mechanical strength of the obtained elastomer composition will be remarkably reduced, and the hardness will be increased, the flexibility will be lost, and the strength as a eraser molded article will be lost.

The composition of the present invention may contain, in addition to the above components, an antiblocking agent, a heat stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, a coloring agent, and the like, depending on the intended use. is there.

[0026]

EXAMPLES The evaluation methods used in the examples and comparative examples are as follows. 1) Hardness According to JIS K 7215, a 6.3 mm-thick press sheet was used as a test piece. 2) Injection molding machine with mold clamping pressure of 120 tons, 6.4 × 1
A 3 × 127 (mm) square bar was molded under the following conditions to obtain a test sample. Molding temperature 100 ° C Mold temperature 30 ° C Injection speed 15mm / sec Injection pressure 300kg / cm2 Holding pressure 200kg / cm2 Injection time 3sec Cooling time 20sec 2-1) Usability Pencil specified in JIS S 6006, JIS P The test paper specified in 3201 was used. The character was erased by holding a place 2 cm from the tip of the test sample.

：: Neither bending nor stickiness nor unnaturalness (feeling, etc.) as eraser. Δ: One of the above is missing. X: Two or more of the above are missing.

2-2) Eraseability Measured according to JIS S 6004. ○: Erase rate of 98% or more △: Erase rate of 90% or more ×: Erase rate of less than 90% 2-3) Group of erased scraps 3 cm on paper
Rubbing was performed five times with the width, and the lump of the scum was compared. ：: 80% or more of the entire waste is collected into one waste having a length of 1 cm or more. Δ: 40% or more of the entire residue is collected into one residue having a length of 1 cm or more. ×: Less than 40% of the entire residue is collected into one residue having a length of 1 cm or more. 2-4) Transferability of plasticizer The sample was placed on a PS plate, an ABS plate, and paper, and was placed at 60 ° C for 72 hours.
Then, a load of 80 g / cm2 was applied, and the transfer of the oil was visually observed. ：: No transition in all cases. X: There is a transition when any one or more. 2-5) Moldability Deformation, flow mark, breakage of gate, presence / absence of spool breakage, and spontaneous fall of the molded product were compared. ：: Can be molded without any problem. Δ: Moldable, but any one of deformation, flow mark, gate cut, spool cut, etc., or not falling naturally. ×: Cannot be molded. The following substances were used as each component. Component (a) (a-1) Asahi Kasei Industries Co., Ltd. SBS oil exhibition 50p
hr Sorprene T-475 (a-2) Asahi Kasei Industries Co., Ltd. SBS No oil exhibition
Sorprene T-431 Component (b) (b-1) Metallocene catalyst LLDPE elastomer Engage EG840 manufactured by Dow Chemical Japan Co., Ltd.
0 Specific gravity 0.870 Melt flow rate (190
° C, load 2.16 kg): 30.0 g / 10 min Melting point 60 ° C (b-2) Metallocene catalyst LLDPE elastomer Engage EG844 manufactured by Dow Chemical Japan Co., Ltd.
0 Specific gravity 0.895 Melt flow rate (190
° C, load 2.16 kg): 1.6 g / 10 min Melting point 95 ° C (b-3) For comparison, EVA Evaflex EV-40X manufactured by DuPont Mitsui Polychemicals, Inc.
Melt flow rate (190 ° C, load 2.16k
g): 65 g / 10 min Melting point 40 ° C. (b-4) For comparison, EVA Evaflex EV-260 manufactured by DuPont-Mitsui Polychemicals, Inc.
Melt flow rate (190 ° C, load 2.16k
g): 6 g / 10 min Melting point 72 ° C. (b-5) For comparison, Ziegler-Natta catalyst LLDPE Mirason 403P manufactured by Mitsui Chemicals, Inc. Specific gravity 0.920 Melt flow rate (190 ° C., load 2.16 kg): 7. 0g / 10min melting point 12
3 ° C Component (c) Idemitsu Kosan Co., Ltd. Paraffin Oil Diana Process Oil PW-90 Component (d) Nitto Powder Chemical Industry Co., Ltd. Calcium Carbonate NS400

[0029]

EXAMPLES 1 TO 7 The parts by weight of component (a) shown in the table
(B), (c) and (d) and 0.5 parts by weight of stearic acid (ST-AC) as a component (e) lubricant were charged into a pressure kneader. The vapor pressure was set to a gauge pressure of 1.0 kg / cm 2, and kneading was performed for 3 minutes until the resin temperature reached 100 ° C. Thereafter, the mixture was pelletized with a twin-screw extruder at an L / D of 20, a kneading temperature of 60 ° C, and a screw rotation speed of 80 rpm.

From the obtained pellets, a square bar of 6.4 × 13 × 127 (mm) was prepared using an injection molding machine with a mold clamping pressure of 120 tons, and was molded under the same conditions as in the evaluation method 2). Example results

[0031]

[Table 1] In Example 1, when EG8400 is used as the component (b-1), the erasure property and the lump of scum are good. However, usability and moldability are slightly insufficient. Therefore, Examples 2 and 3
As shown in (2), when component (b-2) EG8440 having a high melting point is used in combination and component (c) is reduced, usability and moldability are improved.

In Example 4, component (a-1) T-475
When the component (a) T-431, which is not an oil-extended product, is used in place of the above, the moldability is good. However, the usability and erasing properties are slightly insufficient. (B-2) EG8 in Example 5 based on Example 3
Although 440 was increased, usability, erasability, and unity of eraser dust were slightly insufficient. In the sixth embodiment, the (b-1) EG8400 is replaced with the (b-2) EG
By setting the number to be greater than 8440, the usability and the lump of the scraps are improved as compared with the fifth embodiment. In Example 7, the erasure is improved by adding the component (c) to the composition of Example 6.

Comparative Examples 1-2 In place of component (b), EVA having a melting point of 95 ° C. or less (EV
-40X) and (EV-260) and molded under the same conditions as in the evaluation method 2). In Comparative Example 1, the erasability was satisfactory, but the usability and the consistency of the scum were slightly insufficient, and the moldability was poor. Comparative Example 2 shows two types of EVA
Although the useability and the moldability could be improved by using in combination, erased scum is not collected.

Comparative Example 3 In place of component (b), Ziegler-Natta catalyst LLD
PE 403P was used. Since a resin having a melting point of 120 ° C. is used, it is necessary to set the molding temperature to 150 ° C. Parts (a), (b), (c) and (d) of parts by weight shown in the table
And component (e) stearic acid (ST-AC) as a lubricant
0.5 part by weight is put into a pressure kneader, the vapor pressure is set to a gauge pressure of 3.0 kg / cm 2, and the resin temperature is 140 ° C.
And then kneaded for 6 minutes. Thereafter, the mixture was pelletized with a twin-screw extruder at an L / D of 20, a kneading temperature of 60 ° C, and a screw rotation speed of 80 rpm. From the obtained pellets, square bars of 6.4 × 13 × 127 (mm) were formed by injection molding, and were molded under the following conditions. Molding temperature 150 ° C Mold temperature 30 ° C Injection speed 15mm / sec Injection pressure 800kg / cm2 Holding pressure 200kg / cm2 Injection time 3sec Cooling time 20sec Hardness is hard, and usability is somewhat poor. In addition, erasure is poor,
Erasers are not collected.

Claims (1)

[Claims] 1. A block copolymer comprising (a) at least two polymer blocks A mainly composed of vinyl aromatic and at least one polymer block B mainly composed of a conjugated diene compound, and / or Or 100 parts by weight of a hydrogenated block copolymer obtained by hydrogenation thereof (b) 5-200 parts by weight of polyethylene or a copolymer composed mainly of polyethylene polymerized with a single-site catalyst (c) A thermoplastic elastomer composition for eraser, comprising 20 to 250 parts by weight of a softener for aromatic rubber (d) 0 to 400 parts by weight of an inorganic filler.