Method for Suppressing Generation of Surface Blisters during Extrusion Molding of Polystyrene Resin Composition

Abstract

To provide a method for suppressing occurrence of eye mucus in extrusion molding of a polystyrene-based resin composition.SOLUTION: A method for suppressing occurrence of eye mucus in extrusion molding of a polystyrene-based resin composition is obtained by blending a polystyrene-based resin with a polypropylene wax having a weight average molecular weight of 27,000-45,000.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for suppressing the generation of surface resin during the extrusion molding of a polystyrene-based resin composition.

Background Art

[0002] Among thermoplastic resins, polystyrene-based resins are inexpensive and have high processability, and are used in a wide range of fields such as food packaging materials, CD cases, and housings of household appliances.

[0003] Polystyrene-based resins are generally extrusion-molded after being blended with various additives such as impact modifiers, lubricants, and fillers. Due to these additives, deposits called "surface resin" may accumulate at the die opening of the extruder during extrusion molding. When the amount of generation is large, there is a problem that defective products are generated due to adhesion as foreign substances to the molded product.

[0004] As a conventional technique for suppressing the generation of surface resin during the extrusion molding of a polystyrene-based resin composition, there are pellets made of a rubber-modified polystyrene-based resin with a pellet moisture content of 150 ppm or less, and a melt extrusion method of the rubber-modified polystyrene-based resin using the same (Patent Document 1), and a die for a resin foam sheet manufacturing apparatus characterized by having the resin flow path formed by coating the surface of the portion facing the resin flow path with either titanium nitride or tungsten carbide, or an outer ring having the surface of the portion facing the resin flow path nitrided (Patent Document 2), etc. are disclosed.

[0005] However, it is difficult to control the moisture content of the raw materials depending on the type of raw materials and the production time, and the design of a die with a special coating requires designing a die for each molded product type, which is complicated. Therefore, a more excellent technique for suppressing the generation of surface resin during the extrusion molding of a polystyrene-based resin composition has been demanded.

Prior Art Documents

Patent Documents

[0006] Patent Document 1 Japanese Unexamined Patent Application Publication No. 11-236422 Patent Document 2 Japanese Unexamined Patent Application Publication No. 2000-246782 Summary of the Invention Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a method capable of suppressing the generation of surface fisheyes during the extrusion molding of a polystyrene resin composition. Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by blending a polypropylene wax having a specific molecular weight with a polystyrene resin. Based on these findings, the present inventors have further conducted studies and completed the present invention. That is, the present invention comprises a method for suppressing the generation of surface fisheyes during the extrusion molding of a polystyrene resin composition, which comprises blending a polypropylene wax having a weight average molecular weight of 27,000 to 45,000 with a polystyrene resin. Effects of the Invention

[0009] By using the present invention, the generation of surface fisheyes during the extrusion molding of a polystyrene resin composition can be suppressed. Modes for Carrying Out the Invention

[0010] As the polystyrene resin used in the present invention, there is no particular limitation as long as it is a polystyrene resin generally used for molded articles of polystyrene resins. For example, a homopolymer of one type of styrene monomer (e.g., styrene, methylstyrene, chlorostyrene, etc.) (e.g., polystyrene, polymethylstyrene, polychlorostyrene, etc.), a copolymer of two or more types of styrene monomers, a copolymer of a styrene monomer and another monomer, a copolymer of a styrene monomer and an elastomer, etc. may be mentioned. Further, a mixture of two or more types of these polystyrene resins, or a mixture of these polystyrene resins and other thermoplastic resins may also be acceptable.

[0011] Examples of the other monomers constituting the above-mentioned "copolymer of a styrene monomer and another monomer" include acrylonitriles such as acrylonitrile and methacrylonitrile, unsaturated carboxylic acids such as acrylic acid and methacrylic acid, unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate, dienes such as chloroprene, butadiene, and isoprene, olefins such as 1-butene and 1-pentene, α,β-unsaturated carboxylic acids (e.g., maleic anhydride, etc.) or their anhydrides, etc.

[0012] Examples of the elastomers constituting the above-mentioned "copolymer of a styrene monomer and an elastomer" include polydiene rubbers such as butadiene rubber, chloroprene rubber, and isoprene rubber, styrene-diene elastomers such as styrene-butadiene rubber, and block copolymer elastomers having a polydiene block in their molecular structure such as styrene-butadiene-styrene rubber, etc.

[0013] The polypropylene wax used in the present invention (hereinafter also simply referred to as "polypropylene wax") is a polypropylene obtained by polymerizing propylene or depolymerizing high-molecular-weight polypropylene, and has a weight-average molecular weight of 27,000 to 45,000, preferably 35,000 to 45,000. There is no particular limitation on the method for measuring the weight-average molecular weight. For example, the weight-average molecular weight in terms of polystyrene measured under the following measurement conditions by GPC (gel permeation chromatography) can be adopted. [Measurement Conditions] Column: TSKgel column (manufactured by Tosoh Corporation) × 4 Temperature: 140 °C Eluent: o-dichlorobenzene Flow rate: 1.0 mL / min Sample concentration: 0.15 mg / mL Conversion standard: Polystyrene

[0014] Examples of polypropylene wax include Biscole 330P (trade name; weight-average molecular weight 40,000; manufactured by Sanyo Chemical Industries, Ltd.), Hiwax NP805 (trade name; weight-average molecular weight 32,600; manufactured by Mitsui Chemicals, Inc.), Biscole 440P (trade name; weight-average molecular weight 30,000; manufactured by Sanyo Chemical Industries, Ltd.), LICOCENE PP2602 (trade name; weight-average molecular weight 29,700; metallocene-based polypropylene wax; manufactured by Clariant Chemicals, Ltd.), etc., which are commercially manufactured and sold, and these can be used in the present invention.

[0015] In the present invention, as a method for blending polypropylene wax with a polystyrene resin, there is no particular limitation as long as the polypropylene wax can be uniformly dispersed in the polystyrene resin. However, it is preferable to heat and knead the polystyrene resin and the polypropylene wax using an extruder. When using an extruder, the blending of the polypropylene wax with the polystyrene resin by heat kneading and the extrusion molding of the polystyrene resin composition after blending can be carried out simultaneously. As a specific method for blending and extrusion molding using an extruder, the polystyrene resin and the polypropylene wax are put into the extruder, and a polystyrene resin composition blended with the polypropylene wax is obtained by heat kneading, and then the polystyrene resin composition is extrusion molded. Examples of the extruder to be used include a single-screw extruder, a twin-screw extruder, etc. From the viewpoints of kneading power and productivity, it is preferable to use a twin-screw extruder. Examples of the types of twin-screw extruders include a twin-screw non-intermeshing type with different directions, a twin-screw intermeshing type with different directions, a twin-screw non-intermeshing type with the same direction, a twin-screw intermeshing type with the same direction, etc.

[0016] In the present invention, as the blending temperature of the polypropylene wax with the polystyrene resin, when using an extruder, the temperature for heat kneading (the barrel temperature of the extruder) is not particularly limited as long as it is equal to or higher than the temperature at which the polystyrene resin and the polypropylene wax melt and within the range where these components do not deteriorate too much, but a temperature of 120 to 230 °C is preferable.

[0017] In the present invention, when blending the polypropylene wax with the polystyrene resin, a method of preparing a masterbatch in which the polypropylene wax is previously blended with the polystyrene resin and blending the masterbatch with the polystyrene resin is preferable. This method is effective for effectively dispersing the polypropylene wax in the polystyrene resin. The blending amount of the polypropylene wax in 100% by mass of the masterbatch is usually 5 to 40% by mass, preferably 10 to 30% by mass.

[0018] In the present invention, the compounding amount of polypropylene wax with respect to the polystyrene resin is usually 0.1 to 20% by mass, preferably 1 to 5% by mass, in 100% by mass of the polystyrene resin composition after compounding polypropylene wax or the like.

[0019] In the present invention, components other than polypropylene wax may be compounded with the polystyrene resin. The components are not particularly limited as long as they are components usually compounded with the polystyrene resin. Examples thereof include impact resistance improvers, lubricants, fillers, antistatic agents, antioxidants, heat stabilizers, ultraviolet absorbers, neutralizing agents, plasticizers, pigments, dyes, and conductive agents.

[0020] The present invention will be described below with reference to examples, but this is merely for explaining the present invention and does not limit the present invention.

Examples

[0021] [Production of masterbatch containing wax component] (1) Raw materials 1) Polystyrene resin (trade name: Toyo Styrol HRM-12; general-purpose polystyrene; manufactured by Toyo Styrene Co., Ltd.) 2) Polypropylene wax 1 (trade name: Biskol 330P; weight-average molecular weight 40,000; manufactured by Sanyo Chemical Industries, Ltd.) 3) Polypropylene wax 2 (trade name: Hiwax NP805; weight-average molecular weight 32,600; manufactured by Mitsui Chemicals, Inc.) 4) Polypropylene wax 3 (trade name: Biskol 440P; weight-average molecular weight 30,000; manufactured by Sanyo Chemical Industries, Ltd.) 5) Polypropylene wax 4 (trade name: Licocene PP 2602; metallocene-based polypropylene wax; weight-average molecular weight 29,700; manufactured by Clariant Chemicals) 6) Polypropylene wax 5 (trade name: Hiwax NP505; weight-average molecular weight 25,700; manufactured by Mitsui Chemicals, Inc.) 7) Polypropylene wax 6 (trade name: Hiwax NP105; weight-average molecular weight 11,200; manufactured by Mitsui Chemicals, Inc.)

[0022] (2) Formulation The formulation of the masterbatch prepared using the above raw materials is shown in Table 1.

[0023]

Table 1

[0024] (3) Manufacturing method Weighed the raw materials described in Table 1 so that the total was 1000 g, and used a co-rotating twin-screw extruder (Model: KZW15TW-45MG-NH; Screw diameter = 15 mm; L / D = 45; manufactured by TechnoBel) to heat and knead at a barrel (C1~C6, H / D) temperature of 140~220 °C (C1 = 140 °C, C2~C6 = 220 °C) and a screw rotation speed of 300 rpm to extrude and mold a polystyrene resin composition containing a wax component. The polystyrene resin composition extruded in a strand shape was cut with a pelletizer to produce masterbatches 1~6 in a cylindrical shape (diameter 3 mm, length 3 mm).

[0025] [Evaluation test for suppressing the occurrence of eye varnish] Polystyrene resin (trade name: Toyo Styrene HRM-12; general-purpose polystyrene; manufactured by Toyo Styrene Co., Ltd.), elastomer (trade name: JSR-RB810; 1,2-polybutadiene; manufactured by JSR Corporation), and any one of masterbatches 1 to 6 were weighed so that the total amount would be 2000 g according to the formulation in Table 2. These raw materials were put into a plastic bag and held by hand, and mixed uniformly for 30 seconds. The obtained mixture was heat-kneaded for 20 minutes under the conditions of a barrel (C1 to C6, H / D) temperature of 140 to 220 °C (C1 = 140 °C, C2 to C6 = 220 °C), a screw rotation speed of 300 rpm, and an extrusion rate of 3 kg / h using a twin-screw co-rotating intermeshing type extruder (model: MFU15TW-60HG-NH; screw diameter = 15 mm; L / D = 60; manufactured by Techno bel) to perform extrusion molding of the polystyrene resin composition. At the time when 20 minutes had elapsed, all the surface gloss generated near the die opening was removed with a spatula, and further heat-kneaded for 20 minutes to perform extrusion molding of the polystyrene resin composition, obtaining test sections 1 to 11. For each test section, the surface gloss generated near the die opening was collected with tweezers and the mass was measured, and evaluated according to the evaluation criteria in Table 3 below. The results are shown in Table 4.

[0026] In each test section, the compounding amounts of the polystyrene resin (including the polystyrene resin contained in the masterbatch) and the elastomer in the polystyrene resin composition were adjusted so as to always be the same amount. In each test section, the elastomer was compounded with the polystyrene resin as an impact resistance improver. Test sections 1 to 8 are examples of the present invention, test sections 9 and 10 are comparative examples of the present invention, and test section 11 is a reference example of the present invention.

[0027]

Table 2

[0028]

Table 3

[0029]

Table 4

[0030] As is clear from the results, Test Sections 1 to 8 had results of "〇" or above, and an excellent effect of suppressing eye mucus generation was obtained. On the other hand, Test Sections 9 and 10 had results of "△" or "×", and there was no effect of suppressing eye mucus generation.

Claims

【Claim 1】A masterbatch is prepared by blending a polypropylene wax having a weight average molecular weight of 27,000 to 45,000 with a polystyrene resin in advance. A method for suppressing the generation of surface fisheyes during the extrusion molding of a polystyrene resin composition, characterized by blending the masterbatch with a polystyrene resin, wherein the blending amount of the polypropylene wax in 100% by mass of the masterbatch is 5 to 40% by mass.

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