JP2795079B2 - Polystyrene resin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polystyrene resin foam excellent in shock absorption resistance, rigidity and oil resistance, and particularly excellent in foamability and secondary workability.

[0002]

2. Description of the Related Art Polystyrene resins are widely used in molding applications because of their rigidity, good dimensional stability, and low cost. However, lack of impact resistance prevents expansion of applications. I have. In particular, the foamed molded article lacks softness and shock absorption. On the other hand, a foamed molded article made of a polyethylene resin has flexibility but lacks rigidity, and has a narrow melt viscosity region suitable for foaming. Furthermore, a foamed molded article made of a polypropylene-based resin is excellent in flexibility and shock absorption, and has a higher rigidity than a polyethylene-based foamed article. However, the foaming step of the polypropylene-based resin requires a step such as pre-treatment, and the production cost is higher than that of a foam of a polystyrene-based resin or a polyethylene-based resin. In order to compensate for the drawbacks of polyethylene resins, attempts have been made to combine polyethylene resins with polystyrene resins. In bead foam molding, a resin composition, pre-expanded particles, and a foam molded article which have been impregnated with a styrene monomer into a polyethylene resin and then graft-polymerized to form a composite have been proposed. For example, JP-B-52-33156 and JP-B-58-57453 disclose a method of graft polymerization of a styrene monomer of a polyethylene resin and a foam of a styrene-modified polyethylene resin. However, this method requires not only a complicated graft polymerization step for the polyethylene resin, but also requires cross-linking, which increases the production cost. JP-B-63-38058 and JP-B-2-18692 disclose a technique for extrusion foaming of a mixture of a polystyrene resin and a polyethylene resin. However, since the polystyrene-based resin and the polyolefin-based resin have poor compatibility, even if both are mechanically mixed, only those having poor rigidity and impact resistance can be obtained. A composition in which a specific styrene-conjugated diene block copolymer, a hydrogenated block copolymer thereof, or an ethylene-vinyl acetate copolymer is added to a polystyrene resin and a polyolefin resin in order to improve the compatibility between the two. Has been proposed. For example, Japanese Patent Publication No. 62-12
No. 812, JP-B-63-34782 and JP-A-1-174550 disclose a hydrogenated styrene-butadiene-styrene block copolymer or a hydrogenated (styrene-butadiene) n-block copolymer in polystyrene. A technique used as a compatibilizer between a polyolefin resin and a polyolefin resin is disclosed. However, there has not yet been obtained a foamed molded article having the characteristics of a polystyrene resin and a polyolefin resin in a well-balanced manner.

[0003]

In view of such circumstances, an object of the present invention is to solve the problems of the prior art, to provide excellent shock absorption, rigidity and oil resistance, and to improve foaming and Another object of the present invention is to provide a polystyrene resin foam having particularly excellent secondary workability.

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and have reached the present invention. That is, the present invention relates to a polystyrene resin foam obtained by foaming a resin composition comprising the following components (A) to (C). (A) 35 to 75% by weight of a polystyrene resin (B) 10 to 50% by weight of a polyethylene resin (C) 70% of the double bond of the isoprene block portion of the triblock copolymer composed of a styrene block-isoprene block-styrene block % Or more is a hydrogenated triblock copolymer having a number average molecular weight of 10,000 to 400,000 and a weight ratio of a styrene block portion of 40 to 70% by weight. Block copolymer 3 to 35 wt% by weight

The details will be described below. The (A) polystyrene-based resin of the present invention refers to polystyrene (GPPS) obtained by polymerizing a styrene monomer by a bulk polymerization method or a suspension polymerization method, and butadiene rubber or a styrene-butadiene block copolymer dissolved in a styrene monomer. After that, a rubber-modified polystyrene (HIPS) obtained by polymerization by a bulk polymerization method or a bulk-suspension two-stage polymerization method,
GPPS and styrene-butadiene block copolymer
This is a concept including a polystyrene resin composition obtained by heating and kneading using a general-purpose kneader such as a screw or multi-screw extruder or a Banbury mixer. For the polystyrene resin, a plasticizer in which one or two or more of paraffinic, naphthenic, and aromatic hydrocarbons such as mineral oil and liquid paraffin are used to adjust the fluidity is used. Is usually 5% by weight or less, preferably 3% by weight.
It is as follows. If the content exceeds 5% by weight, the fluidity is too high, and the kneadability with the polyethylene resin is deteriorated, so that it may be difficult to obtain a good foam during foaming.

The (B) polyethylene resin of the present invention is:
Ethylene homopolymer, ethylene-α-olefin copolymer
, Ethylene-vinyl acetate copolymer, or a mixture thereof
And low-density polyethylene (L
DPE), high density polyethylene (HDPE), linear low
High density polyethylene (LLDPE), ethylene-propylene
Copolymer, ethylene-vinyl acetate copolymer (EVA)
And the like. Where polyethylene
5% by weight or more of the resin has a density of 0.94 g / cm ^ThreeMore than
Preferably, it is a high density polyethylene resin. this child
With this, the normal foam molding temperature (100 to 130 ° C)
This prevents melt shrinkage and enables high magnification foaming.

The (C) hydrogenated triblock copolymer of the present invention is a triblock copolymer composed of a styrene block-isoprene block-styrene block in which 70% or more of the double bonds in the isoprene block portion of the triblock copolymer are hydrogenated. A hydrogenated triblock copolymer having a number average molecular weight of 10,000 to 400,000 and a weight ratio of a styrene block portion of 40 to 70% by weight. . (C) of the present invention
The components act as compatibilizers.

[0008] The hydrogenation ratio of the double bond in the isoprene block portion of the hydrogenated triblock copolymer is at least 70%, preferably at least 90%. If the proportion is too small, the compatibility is poor and the foaming property is poor. The number average molecular weight of the hydrogenated triblock copolymer is 10,000 to 400,0
00, preferably 12,000 to 350,000. When the molecular weight is too small, the compatibility is poor and the foaming property is poor. On the other hand, when the molecular weight is too large, the foaming property is poor. The weight ratio of the styrene block portion of the hydrogenated triblock copolymer is 40 to 70% by weight, preferably 40 to 65% by weight. When the ratio is too small, the foaming property and the secondary workability are poor. On the other hand, when the ratio is too large, the foamability and the secondary workability are poor. The component (C) of the present invention needs to be a triblock copolymer composed of a styrene block-isoprene block-styrene block. When a diblock copolymer composed of a styrene block and an isoprene block is used without using the present invention, the foamability and the secondary workability are poor.

Even if a hydrogenated block copolymer that does not satisfy the conditions of the present invention is used, the compatibility between the polystyrene resin and the polyethylene resin is not improved, and many bubbles are broken when the resin composition is foamed. Occurs, the open cell rate increases, and further shrinkage is likely to occur, so that a high expansion ratio cannot be obtained. Further, the rigidity and shock absorption of the foam are inferior, and the foam film is easily broken when the foam is compressed.

In order to obtain the hydrogenated block copolymer (C) of the present invention, a known unhydrogenated block copolymer can be prepared by, for example, using JP-B-42-8704 and JP-B-43-66.
Hydrogen may be added by a method described in JP-A-36-36 or the like. As the hydrogenated block copolymer (C), a commercially available product may be used.

The proportion of the components (A) to (C) used in the present invention is (A) 35 to 75% by weight, preferably 40 to 70% by weight of the polystyrene resin, and (B) 10 to 10% by weight of the polyethylene resin. 50% by weight, preferably 15 to 50%
(C) hydrogenated triblock copolymer 3
-25% by weight, preferably 5-20% by weight.
(A) If the amount of the polystyrene resin is too small, the foaming property and the secondary workability are poor. On the other hand, if the amount is too large, the rigidity of the foam becomes too high and the secondary workability is poor. (B) If the amount of the polyethylene resin is too small or too large, the foaming property and the secondary workability are poor. (C) If the amount of the hydrogenated triblock copolymer is too small, the foaming property and the secondary workability are poor, while if it is too large, the mechanical properties such as rigidity are poor.

In the resin composition of the present invention, the polyethylene resin is present in the matrix of the polystyrene resin in the form of fine co-continuous phases or islands. In the case of the co-continuous phase, the width of the polyethylene resin phase is reduced. In the case of islands, the average particle size is 10 μm or less, preferably 5 μm or less.
It is desirable to adjust it to m or less. When the width of the polyethylene-based resin phase exceeds 10 μm or the average particle diameter exceeds 10 μm, the number of breakage of air bubbles in foam molding increases, and the rigidity and shock absorption of the foam sometimes become poor. . As the width or average particle diameter of the resin phase, a value obtained by a transmission electron micrograph of a thin section of the resin composition and an image analyzer is used.

In order to obtain a foam using the resin composition of the present invention, a predetermined amount of (A) a polystyrene resin, (B) a polyethylene resin and (C) a hydrogenated triblock copolymer is added, for example, Melted and kneaded with a melt kneader such as a screw extruder or a twin screw extruder to form pellets ("Plastic Form Handbook", first edition of 1973, edited by Hiroshi Maki and Atsushi Kosakada, published by Nikkan Kogyo Shimbun, pages 158 to 174)
1982; First Edition, "Basics of Plastic Processing," edited by The Society of Polymer Science, published by the Industrial Research Institute, pp. 298-310. ) May be made into a foam by an in-mold foaming method or an extrusion foaming method. As the foaming agent, a volatile solvent type foaming agent such as butane, pentane and freon can be used. The average expansion ratio of the foam is preferably 5 to 60.
It is twice.

When using the resin composition of the present invention, an optional filler such as glass fiber, titanium white, carbon, silica, talc, mica, zinc oxide and the like can be used in combination, if necessary. If necessary, additives such as a flame retardant, an antioxidant, a heat stabilizer, an ultraviolet absorber, a lubricant, and an antistatic agent can be used.

The polystyrene resin foam of the present invention thus obtained has excellent shock absorption resistance, rigidity and oil resistance,
In addition, it is particularly excellent in foaming properties and secondary processing properties, and can be used for home appliances parts, automobile parts, food packaging, and other wide-ranging applications.

[0016]

Examples are shown below. The present invention is not limited to these examples. The data shown in the examples were measured based on the following method. (1) Foamability: Put 5 g of pellets in an autoclave,
After adding 15 g of n-butane, the mixture was allowed to stand at 60 ° C. for 5 hours, and then foamed at 120 ° C. to obtain pre-expanded particles. The evaluation results are shown below. 〇: No foaming, cracking, cracks, etc. 5 to 60 times. ×: Not foamed, cracked or cracked. (2) Secondary formability: 100 mm × 100 of pre-expanded particles
The molded product was placed in a mold having a size of 10 mm and heated at 110 ° C., and the obtained molded product was divided.
The evaluation results are shown below. 〇: A good molded product was obtained, and the fusion rate was 80% or more. Δ: A good molded product was obtained, but the fusion rate was less than 80%. ×: Unfused and shrunk, resulting in no molded product.

Examples 1 to 6 and Comparative Examples 1 to 6 The components shown in Tables 1 and 2 were melt-kneaded at a temperature of 220 ° C. using a twin screw extruder (Model 2S25 manufactured by Toyo Seiki Seisaku-sho, Ltd.). Granulation and foaming were performed. The results are shown in Tables 1 and 2.

The following can be understood from the results. All examples according to the present invention show satisfactory results in all evaluation items. On the other hand, Comparative Example 1 in which the component (C) was not used, Comparative Example 2 in which a hydrogenated triblock copolymer having a low styrene content was used instead of the component (C),
Comparative Example 3 in which the component (A) is too small and the component (B) is too large,
Comparative Example 5 using styrene-butadiene copolymer rubber instead of component (C), and Comparative Example 6 containing too little component (B)
Is inferior in foamability and secondary workability, and Comparative Example 4 containing too much component (A) is inferior in secondary workability.

[0019]

[Table 1]

[0020]

[Table 2]

* 1 GPPS: polystyrene resin (Sumibright E163, manufactured by Sumitomo Chemical Co., Ltd., MI = 7, GPPS having a density of 1.05) * 2 EVA: ethylene having a vinyl acetate content of 5% by weight
Vinyl acetate copolymer (Evatate D manufactured by Sumitomo Chemical Co., Ltd.)
1042, density 0.92, MI = 1.6) * 3 LLDPE: linear low-density polyethylene (Sumikacene-L GA401 manufactured by Sumitomo Chemical Co., Ltd., density 0.9)
* 4 HDPE: high-density polyethylene (UP polyethylene HD 1150-1, manufactured by Union Polymer, density 0.956, MI = 15)

* 5 SEPS1: hydrogenated styrene-isoprene-styrene triblock copolymer (Septon KL2104 manufactured by Kuraray Co., Ltd.) The hydrogenation ratio of the double bond of the isoprene block portion is 97% or more, and the weight ratio of the styrene block portion is 65. Weight%, number average molecular weight 60,
* 6) SEPS2: Hydrogenated styrene-isoprene-styrene triblock copolymer (Septon manufactured by Kuraray Co., Ltd.)
(KL2003, hydrogenation ratio of double bond in isoprene block portion is 97% or more, weight ratio of styrene block portion is 13% by weight, number average molecular weight is 140,000) * 7 SBS: styrene-butadiene copolymer rubber (Shell Chemical) (Kariflex TR1101, Styrene content 30% by weight)

[0023]

As described above, according to the present invention, it is possible to provide a polystyrene resin foam excellent in shock absorption, rigidity and oil resistance, and particularly excellent in foamability and secondary workability. .

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code FI C08L 25:00 (56) References JP-A-1-174550 (JP, A) JP-A-4-89846 (JP, A) No. 62-12812 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08J 9/00-9/42 C08K C08L

Claims (2)

(57) [Claims] 1. A polystyrene resin foam obtained by foaming a resin composition comprising the following components (A) to (C). (A) 35 to 75% by weight of a polystyrene resin (B) 10 to 50% by weight of a polyethylene resin (C) 70% of the double bond of the isoprene block portion of the triblock copolymer composed of a styrene block-isoprene block-styrene block % Or more is a hydrogenated triblock copolymer having a number average molecular weight of 10,000 to 400,000 and a weight ratio of a styrene block portion of 40 to 70% by weight. Block copolymer 3-25 wt% 2. The polystyrene resin foam according to claim 1, wherein 5% by weight or more of (B) the polyethylene resin is a high density polyethylene resin having a density of 0.94 g / cm ³ or more.