JPH08245822A - Expandable polystyrene resin bead and foam made using the bead - Google Patents

Abstract

PURPOSE: To obtain expandable high-impact PS resin beads which give a foam having excellent falling ball impact strength by using a PS resin matrix having a specific weight-average mol.wt. CONSTITUTION: A high-impact PS resin having a weight-average mol.wt. of 200,000 or higher, preferably 260,000 or higher, is used as a matrix. The expandable beads preferably contain a nucleator (e.g. ethylenebisstearylamide) in an amount of 0.03-1 pt.wt. per 100 pts.wt. the resin. The resin preferably contains polybutadiene rubber having a salami-like structure. The beads are molded to obtain a high-quality foam which has a cell diameter of 50-300μm and which, when having an expansion ratio of 40, has a 50% failure height of 22cm or more in a falling ball impact test.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expandable polystyrene-based resin particles and a foam using the particles, and is particularly composed of expandable polystyrene-based resin particles having rubber-like elasticity and the particles useful for buffer packaging applications. Regarding foams.

[0002]

2. Description of the Related Art It has been well known that molded articles obtained by molding expandable polystyrene resin particles have a drawback that they are easily broken. In order to improve this fragility, Japanese Patent Publication No. 47-17465 and Japanese Unexamined Patent Publication No. 54-1.
Japanese Patent No. 58467 discloses a method of mechanically mixing a block copolymer of styrene and butadiene with a polystyrene resin. Japanese Patent Publication No. 47-18428 discloses a method of using a high impact polystyrene resin. However, the expandable high-impact polystyrene-based resin particles produced by the conventional method have a drawback that the falling ball impact strength is low because the aging is slow at room temperature storage and the cell diameter is large.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, expands quickly even at room temperature storage, has a small cell diameter, and provides a foamed polystyrene type foam having good falling ball impact strength. The present invention provides a resin particle and a foam using the particle.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that expandable high-impact polystyrene-based resin particles in which the polystyrene-based resin of the matrix has a weight average molecular weight of 200,000 or more. The inventors have found that a high-impact polystyrene foam excellent in falling ball impact strength can be obtained by using it and further controlling the cell diameter of the foam to a specific size, and completed the present invention.

That is, the first aspect of the present invention is the expandable high-impact polystyrene resin particles, wherein the polystyrene-based resin of the matrix has a weight average molecular weight of 200,000 or more, and the second aspect of the present invention is the matrix. The high-impact polystyrene-based foams, wherein the polystyrene-based resin has a weight average molecular weight of 200,000 or more, and the molded body has a cell diameter of 50 to 300 μm.

The weight average molecular weight of the polystyrene resin of the high impact polystyrene resin matrix used in the present invention is 200,000 or more, preferably 260,000 or more. If it is less than 200,000, the falling ball impact strength will be low, and a good foam object of the present invention cannot be obtained. Further, when the weight average molecular weight is 260,000 or more, the falling ball impact strength is further increased, which is preferable. As the rubber form, any of a salami structure, a core shell structure, and a combination of both may be used, but the salami structure rubber is preferable because of high falling ball impact strength. As the structure of the rubber, it is possible to use either one having many cis structures or many structures having trans structures in the double bond portion, and both can be used in combination. The polystyrene resin portion of the high-impact polystyrene resin is a polymer of styrene, but one or more kinds of other monomers such as α-methylstyrene, methyl methacrylate and methyl acrylate may be copolymerized.

Examples of the nucleating agent used in the present invention include organic substances such as ethylenebisstearylamide, methylenebisstearylamide and polyethylene wax, salts such as calcium stearate, and inorganic substances such as talc, which may be used alone or in combination of two kinds. The above can be used in combination. The amount of the nucleating agent used is preferably 0.03 to 1 part by weight, and more preferably 0.05 to 0.5 part by weight, relative to 100 parts by weight of the high-impact polystyrene resin. If it is less than 0.03 part by weight, room temperature aging is slow, and if it exceeds 1 part by weight, the cell diameter tends to be too fine and moldability tends to be poor.

As a method of mixing the nucleating agent, it is general to dry-blend with a high-impact polystyrene resin at the time of pelletizing and then melt-mix in an extruder. When it is desired to improve the dispersion of the nucleating agent, it is desirable to use a twin-screw extruder, and in that case, the amount of the nucleating agent used can be reduced.

The blowing agent used in the present invention is preferably pentane. There is no particular limitation on the ratio of normal pentane and isopentane. Also, a small amount of butane, cyclopentane, hexane or the like may be used in combination. From the standpoint of the volatile dissipative property, pentane is preferred as the blowing agent over butane.

Examples of the dispersant used in the present invention include partially saponified polyvinyl alcohol, polyacrylate, polyvinylpyrrolidone, carboxymethyl cellulose,
In addition to organic compounds such as methyl cellulose, calcium pyrophosphate, calcium phosphate, calcium carbonate, magnesium carbonate, magnesium phosphate, magnesium pyrophosphate, inorganic compounds made of fine powder hardly soluble in water such as magnesium oxide, these are independent. Alternatively, two or more kinds can be used in combination. When using an inorganic compound as a suspending agent, it is desirable to use a surfactant together.

A solvent may be used to promote the penetration of the foaming agent into the resin when the expandable polystyrene resin particles are produced. As such a solvent, cyclohexane and aromatic hydrocarbons such as toluene, xylene, and ethylbenzene are suitable, and these can be used alone or in combination of two or more kinds.

As a method of impregnating resin particles with a foaming agent, for example, a high-impact polystyrene resin is dry-blended with a nucleating agent, heated and melted in an extruder, extruded in a strand form from a die, cooled and cut. To obtain pellets, which are dispersed in an aqueous medium using a dispersant and impregnated with pentane as a foaming agent. In addition, dry blending a high-impact polystyrene-based resin with a nucleating agent, heating and melting with an extruder, press-fitting a foaming agent, and then extruding in a strand form from a die,
There is also a method of obtaining expandable high-impact polystyrene resin particles by cooling and cutting immediately after leaving the die and before foaming.

The expandable polystyrene resin particles of the present invention may contain, if necessary, a filler, a plasticizer, a flame retardant, a lubricant,
One kind or two or more kinds of additives such as a colorant, an ultraviolet absorber and an antioxidant can be contained.

By molding the expandable polystyrene resin particles obtained as described above, the cell diameter is 50 to 3
In the range of 00 μm, a high-quality molded product having a half fracture height of 22 cm or more in a falling ball impact test at 40 times can be easily obtained.

[0015]

The present invention will be described below with reference to examples.
The invention is not limited to the examples. In the following description, "parts" and "%" represent "parts by weight" and "% by weight", respectively, unless otherwise specified. The weight average molecular weight (Mw), cell diameter, surface property and falling ball impact strength were measured or evaluated by the following methods.

Weight average molecular weight (Mw) After dissolving a high-impact polystyrene resin in tetrahydrofuran and centrifuging the insoluble matter, the soluble matter is analyzed by GPC.
The molecular weight was measured at. The GPC and column used were as follows. GPC: Tosoh Corporation HLC-8020 Column: TSK gel GMHXL 30 cm x 2

Cell Diameter A molded body was sliced and the cell diameter of about 30 cells was measured under a microscope, and the average was taken to obtain the cell diameter.

Surface property The surface of the molded product was visually observed, and in particular, it was evaluated on a scale of 5 according to the state of grain boundaries. A score of 3 or more was considered good.

Falling ball impact strength (half the breaking height) According to JIS K 7211. Molded body 200 x 2
It was cut into 0 × 40 mm, and a 321 g steel ball was dropped on it.

Examples 1 to 3 High-impact polystyrene-based resin (Mw = 240,000 of polystyrene-based resin of matrix) containing 7% of high-cis rubber having a salami structure having an average rubber particle diameter of 1.8 μm 10
1 part of ethylenebisstearylamide (EBS) was dry blended with 0 part to obtain a master pellet with a twin-screw extruder. Next, this master pellet and a pellet of the same high-impact polystyrene resin as a total of 75 parts, and a high-impact polystyrene resin containing 9% of middle cis rubber having an average rubber particle diameter of 2.5 μm (Mw = 200 of the polystyrene resin of the matrix). 2,000) and 25 parts of ethylenebisstearylamide are dry blended so that the amount of ethylenebisstearylamide is the amount shown in Table 1, and the mixture is mixed with a single-screw extruder NEX-050 (L / D = 22) manufactured by Nakamura Industrial Co., Ltd. , Diameter 0.9
mm, length 1.6 mm, average particle weight 1 mg pellets were obtained.

Next, 140 parts of water as an aqueous suspension, 0.015 part of sodium alpha-olefinsulfonate, 1 part of calcium phosphate and 100 parts of the above pellets were charged into a reactor having an internal volume of 3 liters and equipped with a stirrer, and the reaction was carried out. The vessel was sealed. Then, with stirring, pentane (normal pentane /
8 parts of isopentane = 75/25) were press-fitted. 105 ° C
After being impregnated for 4 hours, it was cooled to 30 ° C., taken out from the reactor, dehydrated and dried to obtain expandable polystyrene resin particles of the present invention. Six days later, the resin particles were pre-expanded about 40 times, and the next day, molding machine TH manufactured by Toyo Kikai Metal Co., Ltd.
The foam was molded with 90VMII. Table 1 shows the EBS amount, cell diameter, and half-ball impact strength at break.

Example 4 The same operation as in Example 1 was carried out except that the expandable polystyrene resin particles containing 0.01 part of ethylenebisstearylamide were dehydrated and dried and then prefoamed 20 days later.

Comparative Examples 1 to 3 The same operations as in Example 1 were carried out except that ethylene bisstearyl amide was dry blended in the amounts shown in Table 1 and pelletized with a single screw extruder.

[0024]

[Table 1] * No molded product was obtained.

Examples 5 to 8 High-impact polystyrene resin (Mw is shown in Table 2) containing 9% of rubber having an average rubber particle diameter of 1.8 microns 100
1 part of ethylenebisstearylamide was dry blended to obtain a master pellet with a twin-screw extruder. next,
The same high-impact polystyrene resin as this master pellet was mixed with ethylenebisstearylamide in an amount of 0.
Dry blending was performed so as to be 1 part, and pellets having a diameter of 0.9 mm, a length of 1.6 mm and an average particle weight of 1 mg were obtained by a single-screw extruder. The impregnation with the foaming agent and the prefoaming and molding were carried out in
It carried out by the method similar to.

Comparative Example 4 The procedure of Example 5 was repeated except that a high impact polystyrene resin having an Mw shown in Table 2 was used.

[0027]

[Table 2]

From the results shown in Tables 1 and 2 above, the foam obtained from the high-impact polystyrene resin particles of the present invention exhibits excellent falling ball impact strength. On the other hand, in Comparative Examples 1 and 2, the aging is not sufficient, the cell diameter is large, and the falling ball impact strength is small. In Comparative Example 3, the cell diameter is too small to obtain a molded body. In Comparative Example 4, the polystyrene-based resin of the matrix has a small weight average molecular weight, and the high-impact polystyrene-based foam has a small falling ball impact strength.

[0029]

As described above, as the expandable polystyrene resin particles of the present invention, by using the polystyrene resin of the matrix having a weight average molecular weight of 200,000 or more,
Furthermore, by controlling the cell diameter of the foam within a specific range, a foam having a significantly improved falling ball impact strength is provided.

Claims (8)

[Claims] 1. Expandable high-impact polystyrene resin particles, wherein the polystyrene resin of the matrix has a weight average molecular weight of 200,000 or more. 2. Expandable high-impact polystyrene resin particles, wherein the polystyrene resin of the matrix has a weight average molecular weight of 260,000 or more. 3. The expandable high-impact polystyrene-based resin particles according to claim 1, wherein the nucleating agent is contained in an amount of 0.03 to 1 part by weight based on 100 parts by weight of the high-impact polystyrene-based resin. 4. The expandable high-impact polystyrene resin particles according to claim 1, 2 or 3, wherein the polybutadiene rubber contained in the high-impact polystyrene resin has a salami structure. 5. The polystyrene-based resin of the matrix has a weight average molecular weight of 200,000 or more, and the molded product has a cell diameter of 50 to 50.
High-impact polystyrene foam characterized by having a size of 300 μm. 6. The high-impact polystyrene foam according to claim 5, wherein the polystyrene resin of the matrix has a weight average molecular weight of 260,000 or more. 7. The polybutadiene rubber contained in the high-impact polystyrene resin has a salami structure.
Alternatively, the high-impact polystyrene foam according to item 6. 8. The high-impact polystyrene-based foam according to claim 5, 6 or 7, which has a half breaking height of 22 cm or more in a falling ball impact test at 40 times.