JP5046610B2 - Resin composition comprising styrene resin and polylactic acid - Google Patents

Description

  The present invention relates to a styrene resin composition containing polylactic acid. By blending polylactic acid, which is a plant-derived material, the amount of petroleum-derived styrene resin can be reduced, the original properties of styrene resin are not impaired, and fluidity is further improved A composition is provided, and the resin composition can be preferably used for a molded body such as a casing.

Styrenic resins are used in many industrial fields such as foams, sheets, and casings, taking advantage of their ease of molding and light weight.
On the other hand, in recent years, non-petroleum resins that do not use petroleum as a raw material have attracted attention from the viewpoint of environmental problems such as global warming associated with the problem of depletion of petroleum resources and carbon dioxide emissions.
Under these circumstances, resins using plant-derived raw materials as monomers have been developed. Starch obtained from corn and potatoes has already been saccharified, further lactic acid bacteria to lactic acid, and then lactic acid cyclized to lactide, A polylactic acid resin has been produced by ring-opening polymerization of this.

The carbon in the plant-derived raw material resin thus obtained is fixed by photosynthesis of carbon dioxide in the atmosphere, so that even if incinerated, it increases the total amount of carbon dioxide. It can be said that there is no so-called “carbon neutral” material. In other words, it is a circulation type material that can maintain the environment.
By using such a plant-derived material capable of maintaining the environment in a petroleum resin, the amount of petroleum resin used can be reduced, and various studies have been conducted (Patent Documents). 1). If the above materials can be blended and used in a styrene resin, which is a typical petroleum resin, the amount of styrene resin used is large, and the amount of reduction is expected to be great. Reducing the amount of styrene resin used is to reduce the amount of oil used and the total amount of carbon dioxide gas, leading to a reduction in environmental burden.

JP 2005-048067 A

  The present invention achieves the above-mentioned problems, and can reduce the environmental burden by blending a plant-derived resin with a styrene resin, and can be put into practical use without losing the original moldability of the styrene resin. It combines the rigidity, impact strength and excellent fluidity.

As a result of diligent studies by the present inventor to achieve this problem, a styrene resin, a block copolymer comprising a styrene monomer and a (meth) acrylic acid ester monomer, and a resin composition comprising polylactic acid are obtained. The present inventors have found that it has fluidity and various mechanical properties that can be applied to various molding methods, and has reached the present invention.
That is, the present invention is as follows.
(1) Rubber-modified polystyrene, or a mixture of rubber-modified polystyrene and polystyrene (A) 80 to 30% by weight, a block copolymer (B) consisting of a styrene monomer and a (meth) acrylic acid ester monomer 10 A resin composition comprising -30 wt% and polylactic acid (C) 10-40 wt%, wherein a block copolymer (B) comprising a styrene monomer and a (meth) acrylate monomer an ab type block copolymer, wherein the a segment is formed from a styrene monomer, and the b segment is formed from a (meth) acrylic acid ester monomer having an alkyl chain having 1 to 4 carbon atoms. And the ratio of the a segment and the b segment is 40/60 to 95/5 in weight ratio.
(2) A molded article comprising the resin composition according to (1).

  According to the present invention, environmental load can be reduced by blending plant-derived resin with styrenic resin, and practical rigidity and impact strength and excellent without losing the original moldability of styrenic resin. A resin composition having excellent fluidity can be provided.

Hereinafter, the present invention will be described in detail.
The styrene resin (A) used in the present invention is a polymer mainly composed of styrene.
Examples of the styrene resin (A) include polystyrene, rubber-modified polystyrene, styrene resin obtained by copolymerizing styrene and other vinyl monomers, and the like.
Polystyrene is a homopolymer of styrene, and generally available ones can be appropriately selected and used. Generally available polystyrenes are provided with different flowability by adjusting the degree of polymerization of styrene, molecular weight distribution, and the amount of plasticizer and lubricant. As for the fluidity of the polystyrene used in the present invention, the melt flow rate measured in accordance with ISO 1133 is preferably in the range of 1 to 10 g / 10 min. When the flowability of polystyrene is lower than the above range, the moldability of the resin composition of the present invention, particularly the mold filling property in injection molding, is not preferable. On the other hand, when the flowability of polystyrene exceeds the above range, the moldability of the resin composition of the present invention, particularly the thickness uniformity in extrusion molding, vacuum molding, and blow molding, is unfavorable.

Rubber-modified polystyrene is a molding material in which a rubber-like polymer is graft-polymerized and dispersed in a continuous phase composed of a polymer of styrene alone, and generally available materials can be appropriately selected and used. Examples of the rubber used for the rubber-modified polystyrene include polybutadiene, styrene-butadiene copolymer, polyisoprene, butadiene-isoprene copolymer, natural rubber, and ethylene-propylene copolymer. In particular, polybutadiene and styrene-butadiene copolymer are preferable.
As for the fluidity of rubber-modified polystyrene, the melt flow rate measured according to ISO 1133 is preferably in the range of 1 to 10 g / 10 min. When the fluidity of the rubber-modified polystyrene is below the above range, the moldability of the resin composition of the present invention, particularly the mold filling property in the injection molding, is not preferable. On the other hand, when the fluidity of the rubber-modified polystyrene exceeds the above range, the moldability of the resin composition of the present invention, particularly the thickness uniformity in extrusion molding, vacuum molding, and blow molding, is unfavorable.
Examples of the styrene resin obtained by copolymerizing styrene and another vinyl monomer include a copolymer of styrene and (meth) acrylic acid, a copolymer of styrene and maleic anhydride, and the like.

The block copolymer (B) comprising a styrene monomer and a (meth) acrylic acid ester monomer used in the present invention is an ab block copolymer, and the a segment is a styrene monomer. The b segment is formed from a (meth) acrylic acid ester monomer having an alkyl chain having 1 to 4 carbon atoms. The ab type block copolymer can be produced by using, for example, polymeric peroxide by a known production process such as bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization.
Specific examples of the (meth) acrylic acid ester monomer having an alkyl chain having 1 to 4 carbon atoms include (meth) acrylic acid methyl ester, (meth) acrylic acid ethyl ester, ester (meth) acrylic acid isopropyl ester, Examples include butyl acrylate, and the most easily available monomer is methacrylic acid methyl ester.

The ratio of the a segment made of a styrene monomer and the b segment made of a (meth) acrylic acid ester monomer is 40/60 to 95/5 by weight, preferably 45/55 to 93/7. It is. When the weight ratio of the b segment composed of a (meth) acrylate monomer is outside the above range, a block copolymer (B) composed of a styrene monomer and a (meth) acrylate monomer is blended. It is not preferable because the tensile fracture strain and the Charpy impact strength are not improved or may be lowered.
A commercially available block copolymer (B) composed of the above preferred styrene monomer and (meth) acrylic acid ester monomer may be used. Examples include “Modiper MS10B” manufactured by Nippon Oil & Fats Co., Ltd.

The polylactic acid (C) used in the present invention is obtained by saccharifying starch obtained from corn, potatoes, etc., further obtaining lactic acid by lactic acid bacteria, and then cyclizing the lactic acid into lactide, which is subjected to ring-opening polymerization. Then, polylactic acid (C) obtained by the method can be used. Also, polylactic acid obtained by synthesizing lactide from petroleum and ring-opening polymerization thereof, or polylactic acid obtained by obtaining lactic acid from petroleum and directly dehydrating and condensing it may be used.
Further, the ratio of L-lactic acid and D-lactic acid constituting the polylactic acid (C) can be used without any particular limitation. However, when it is necessary to increase the heat resistance by crystallizing polylactic acid, the ratio of L-lactic acid to D-lactic acid is 100: 0 to 90:10, preferably the ratio of L-lactic acid to D-lactic acid. Polylactic acid having a ratio of 100: 0 to 95: 5 is used.

Furthermore, other components may be copolymerized with polylactic acid (C) in addition to D-lactic acid and L-lactic acid which are main constituent monomers. Examples of other copolymer components include ethylene glycol, propylene glycol, butanediol, oxalic acid, adipic acid, and sebacic acid. Such a copolymer component is preferably contained in an amount of usually 0 to 30 mol%, more preferably 0 to 10 mol%, in all monomer components.
The molecular weight and molecular weight distribution of polylactic acid (C) are not particularly limited as long as it can be substantially molded, but the weight average molecular weight is preferably 10,000 to 400,000, more preferably 40,000 to 300,000. It is.

The total of the styrene resin (A), the block copolymer (B) composed of the styrene monomer and the (meth) acrylic acid ester monomer, and the polylactic acid (C) is 100% by weight, and the styrene resin ( A) 90 to 10% by weight, 5 to 40% by weight of a block copolymer (B) composed of a styrene monomer and a (meth) acrylic acid ester monomer, and 5 to 50% by weight of polylactic acid (C) is there. Preferably, the styrene resin (A) is 80 to 30% by weight, the block copolymer (B) consisting of a styrene monomer and a (meth) acrylic acid ester monomer and 10 to 30% by weight, and polylactic acid (C ) 10 to 40% by weight. The total of the block copolymer (B) composed of the styrene resin (A), the styrene monomer, and the (meth) acrylic acid ester monomer is less than 50% by weight, that is, the polylactic acid (C) is 50% by weight. If it exceeds 50%, the Vicat softening temperature and heat distortion temperature of the resin composition will be significantly lowered compared to polystyrene and rubber-modified polystyrene, which is not preferable. On the other hand, the total of the block copolymer (B) composed of the styrene resin (A), the styrene monomer, and the (meth) acrylic acid ester monomer exceeds 95% by weight, that is, polylactic acid (C). If it is less than 5% by weight, the physical properties of the resin composition are not substantially different from those when polylactic acid (C) is not added, and the effect of adding polylactic acid (C) is not manifested.
In addition, when the block copolymer (B) composed of a styrene monomer and a (meth) acrylic acid ester monomer is less than 5% by weight, the tensile fracture strain, Charpy impact strength, etc. are improved. Is almost unacceptable. On the other hand, when the addition amount of the block copolymer (B) composed of the styrene monomer and the (meth) acrylic acid ester monomer exceeds 40% by weight, the improvement of the Charpy impact strength or the like is peaked or It may be slightly lowered, which is not preferable.

A method of blending, melting, kneading, and granulating a styrene resin (A), a block copolymer (B) composed of a styrene monomer and a (meth) acrylic acid ester monomer, and polylactic acid (C) It does not specifically limit, The method currently used by manufacture of the resin composition can be used. For example, the above ingredients blended with a drum tumbler, Henschel mixer, etc. are melted and kneaded using a Banbury mixer, single screw extruder, twin screw extruder, kneader, etc., and granulated with a rotary cutter, fan cutter, etc. A composition can be obtained. The resin temperature in melting and kneading is preferably 180 to 240 ° C. In order to achieve the target resin temperature, the cylinder temperature of the extruder or the like should be set to a temperature 10 to 20 ° C. lower than the resin temperature. When the resin temperature is less than 180 ° C., the flowability of the styrene resin (A) and the block copolymer (B) composed of the styrene monomer and the (meth) acrylic acid ester monomer is insufficient, and the polylactic acid (C ) Is insufficient and is not preferable. On the other hand, when the resin temperature exceeds 240 ° C., polylactic acid (C) is thermally decomposed, which is not preferable.
Furthermore, the resin composition of the present invention comprises a styrene resin (A), a block copolymer (B) composed of a styrene monomer and a (meth) acrylic acid ester monomer, and polylactic acid (C). When melting, kneading, and granulating, additives such as antioxidants, lubricants, colorants, ultraviolet absorbers, and light stabilizers can be added.
The resin composition of the present invention is molded into a resin product by a method such as injection molding, sheet extrusion molding, vacuum molding, profile extrusion molding, or blow molding.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further, this invention is not limited to a following example, unless the summary is exceeded.
<Styrene resin (A) -1>
(A) -1; Rubber-modified polystyrene “H8117” manufactured by PS Japan Co., Ltd.
The basic physical properties are shown in (Table-1).
<Styrene resin (A) -2>
(A) -2; Polystyrene “685” manufactured by PS Japan Co., Ltd.
The basic physical properties are shown in (Table-1).

<Block copolymer (B) -1 comprising styrene monomer and (meth) acrylic acid ester monomer>
(B) -1; “Modiper MS10B” manufactured by NOF Corporation
It is a block copolymer of styrene and methyl methacrylate, and the composition ratio is styrene / methyl methacrylate = 90/10. Moreover, the viscosity of the solution which melt | dissolved the said block copolymer in the styrene monomer at 30 weight% was 2.0 Pa.s.
<Polylactic acid (C)>
(C) -1; “4032D” manufactured by Nature Works LLC
The melt flow rate measured according to ISO 1133 (200 ° C., 5 kgf) was 14.2 g / 10 min.

<Manufacture of resin composition>
Styrenic resin (A), block copolymer (B) comprising styrene monomer and (meth) acrylic acid ester monomer, and polylactic acid (C) (Table-2) to (Table-4) Weighed as shown in the upper row.
Weighed raw materials are mixed with a drum tumbler, and the same direction twin screw extruder (WERNER & PF)
The mixture was melt kneaded at a cylinder setting temperature of 200 ° C. and a screw rotation speed of 200 rpm with a LEIDEER ZSK25) and extracted as a molten strand. The molten strand was cooled with water and the strand was cut with a rotary cutter to obtain a pellet-shaped resin composition.

<Measurement of physical properties> Measurement of melt flow rate and mechanical properties The melt flow rate of the resin composition produced above was measured in accordance with ISO 1133. Also, the resin composition produced above is injection molded into an ISO type A test piece, tensile strength and tensile fracture strain according to ISO 527-1, bending elastic modulus according to ISO 178, Charpy impact strength according to ISO 179, and ISO 306 according to ISO 306. Vicat softening temperature was measured.
The above measurement results are shown in the lower part of (Table-2) to (Table-4).

<Table-2>
In Example 1, 10 parts by weight of a block copolymer (B) -1 composed of a styrene monomer and a (meth) acrylic acid ester monomer was blended. In contrast, in Comparative Example 1, 10 parts by weight of polystyrene-based styrene resin (A) -2 was blended, and the amount of HIPS rubber and the content of polylactic acid were the same as those in Example 1. In Example 1, the Charpy impact strength is higher.
Similarly, in comparison with Examples 2 to 4 and Reference Example 5, Comparative Examples 2 to 5 are styrene block copolymers (B) -1 comprising styrene monomers and (meth) acrylate monomers. System resin (A) -2. The examples generally have higher tensile fracture strain and Charpy impact strength.

<Table-3>
When the blending amount of polylactic acid (C) exceeds 50% by weight (Comparative Example 6), the Vicat softening temperature, which is an index of heat resistance, is greatly reduced to 50 ° C. or less, which is not preferable.
Further, as can be seen by comparing Example 6 and Comparative Example 7, the blending amount of the block copolymer (B) composed of the styrene monomer and the (meth) acrylate monomer is 40% by weight. Beyond that, the improvement in tensile rupture strain and Charpy impact strength is at its peak. In addition, when the amount of the block copolymer (B) composed of the (meth) acrylic acid ester monomer is less than 5% by weight (Comparative Example 8), improvement in tensile breaking strain and Charpy impact strength is not recognized. .

<Table-4>
Styrene resin (A) is a rubber-modified polystyrene (styrene resin (A) -1) and polystyrene (styrene resin (A) -2) mixed system. Improvement in tensile fracture strain and Charpy impact strength is recognized by blending the block copolymer (B) composed of the monomer. (Example 7 vs. Comparative Example 10, Example 8 vs. Comparative Example 11)

  The resin composition of the present invention is preferably used in many industrial fields such as foams, sheets and housings, which are uses of polystyrene.

Claims (2)

Rubber-modified polystyrene or a mixture of rubber-modified polystyrene and polystyrene (A) 80 to 30% by weight, block copolymer (B) consisting of styrene monomer and (meth) acrylate monomer 10 to 30 % by weight % And polylactic acid (C) 10 to 40 % by weight of a block copolymer (B) comprising a styrene monomer and a (meth) acrylic acid ester monomer, ab A block copolymer, a segment is formed from a styrene monomer, b segment is formed from a (meth) acrylic acid ester monomer having an alkyl chain having 1 to 4 carbon atoms, and The resin composition characterized by the ratio of a segment and b segment being 40/60 to 95/5 by weight ratio.   The molded object which consists of a resin composition of Claim 1.