JPH0657029A - Styrenic resin foam - Google Patents

Abstract

PURPOSE:To provide a styrenic resin foam excellent in secondary expansion moldability and strength of moldings. CONSTITUTION:The styrenic resin foam is characterized by comprising a styrenic resin containing a terpenic resin. Furthermore, the styrenic resin foam in a sheetlike form has 0.1-10mm thickness and 0.03-0.5g/cc density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a styrenic resin foam which is excellent in secondary molding by heating and excellent in the strength of a foam molded article. More specifically, the present invention foams a styrene-based resin containing a terpene-based resin in a styrene-based resin to have a specific thickness and heat secondary foaming moldability having a specific density,
The present invention relates to a styrene resin foam having excellent strength of a molded product.

[0002]

2. Description of the Related Art Polystyrene-based resin foam is secondary foamed by heating and can be easily molded into a desired shape, and the resulting molded body is lightweight, has excellent mechanical strength, has a beautiful appearance and is hydrophobic. It is used for food packaging materials such as boxes, trays and cups, and simple containers because of its excellent properties and excellent heat insulation.
Recently, from the viewpoint of improving productivity during secondary molding, reducing molding defects, and improving deep drawability, a styrenic resin foam having good secondary foam moldability and capable of molding at a temperature as low as possible is desired. ing.

Further, in food packaging trays and the like, it is required to improve the strength of foam-molded products so that cracks and the like do not occur during automatic packaging.

[0004]

In the production of a series of heated secondary foam moldings, a sheet-shaped polystyrene foam is heat-treated in a heating furnace to be foamed, then taken out from the heating furnace and molded in a mold. However, because the temperature inside the heating furnace is not uniform or the temperature inside the furnace fluctuates due to outside air temperature, some or all of the sheets become insufficiently heated, causing the sheets to rupture during molding and the mold deciding ability to deteriorate. On the other hand, excessive heating causes conversely keloids on the surface of the molded product, fluctuations in the thickness of the molded product, and the like.

In order to prevent the formation of keloids, there are known methods in which the molecular weight of the styrene foam base material is increased, a film is stuck on the sheet surface, or a layer having a high resin density, that is, a skin layer is formed. However, with such a method, it is difficult to obtain a foam having good moldability, and in the case of a deep-drawing molded product, sheet breakage easily occurs. In addition, a method of adding a plasticizer, a lubricant, etc. to a styrene-based foam base material is known in order to obtain a well-defined foam, but a keloid-like defect that occurs when overheating during secondary molding is known. Phenomena are likely to occur.

It is effective to use a styrene-based resin foam having a wide molecular weight distribution as a method for obtaining a styrene-based foam having a good patterning property while suppressing the formation of keloids. It is described in Japanese Patent Publication No. However, such a molded product of a polystyrene resin foam having a wide molecular weight distribution has a drawback that the strength is essentially weak.

As described above, there is no foam that satisfies all the requirements of the market.

[0008]

Means for Solving the Problems In view of the present situation, the present inventor has conducted diligent studies, and as a result, the styrene-based resin containing a terpene-based resin in the styrene-based resin has a secondary heat moldability and a keloid-like shape. The present invention has been accomplished by finding that a styrenic resin foam which suppresses the generation, has good moldability, and has excellent strength of a foam-molded article can be obtained.

That is, the present invention is a styrene resin foam comprising a styrene resin and a terpene resin, and the foam has a thickness of 0.1 mm to
It is a sheet-shaped styrene resin foam having a diameter of 10 mm and a density of 0.03 to 0.5 g / cc.

The present invention will be described in detail below. The styrene resin referred to in the present invention is a resin obtained by polymerizing a styrene monomer such as styrene, p-methylstyrene, pt-butylstyrene, or α-methylstyrene, or a mixture thereof, a styrene-based monomer. Monomers copolymerizable with the body, for example, acrylonitrile, butyl acrylate, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylic acid, acrylic acid, styrene copolymer resin with maleic anhydride, The above-mentioned styrene-based resin containing a rubber-like elastic material as dispersed particles, styrene-based copolymer resin, and the above-mentioned styrene-based resin, styrene-based copolymer resin and rubber-like elastic material such as styrene-butadiene block copolymer And the like are resins and the like.

The molecular weight of the styrene resin and the styrene copolymer resin is not particularly limited, but is 150,000.
~ 500,000, preferably 180,000-45,000
A styrene resin in the range of 0, more preferably 200,000 to 400,000 is preferably used. When the molecular weight is smaller than this range, the effect of improving the strength is small even if a terpene resin is blended, and the styrene resin and the styrene copolymer resin having a molecular weight higher than this range have poor moldability, Productivity of styrene-based resins and styrene-based copolymer resins themselves is not preferable.

The terpene resin is a Friedel-Crafts type catalyst (for example, aluminum chloride, dipentene and aromatic hydrocarbon obtained by isomerization of d-limonene obtained from citrus cortex or α-pinene obtained from raw pine resin). It can be obtained by carrying out polymerization using boron trifluoride). Styrene, α-methylstyrene and vinyltoluene are preferably used as the aromatic hydrocarbon.

The degree of polymerization of the terpene resin is not particularly limited, but the degree of polymerization is 1000 or less, preferably 500 or less, more preferably 200 or less. If the degree of polymerization exceeds 1000, the compatibility with the styrene resin decreases and the transparency decreases, which is not preferable. Examples of the terpene-based resin include YS resin TO-12 manufactured by Yasuhara Chemical Co., Ltd.
5, TO-115, TO-105, TO-85 and the like can be used.

The terpene-based resin may be added by dissolving in a styrene-based monomer or a monomer mixture copolymerizable with the styrene-based monomer for polymerization, or by adding a styrene-based polymer or a styrene-based copolymer. Melt the terpene resin during the polymerization of the polymer, or add it by dissolving it in a solvent, or add the terpene resin before or after the polymerization is completed and the unreacted styrene monomer is removed. Etc. can be used.

It is also possible to mix a styrene resin and a terpene resin and knead them with an extruder or a molding machine. The mixing ratio of styrene resin and terpene resin is
Terpene resin per 100 parts by weight of styrene resin.
It is 5 to 20 parts by weight, more preferably 0.5 to 15 parts by weight. If it is less than 0.5 parts by weight, no improvement in strength and secondary moldability is observed, and if it exceeds 20 parts by weight, the improvement effect is saturated and the cost of the resin increases, which is not preferable.

The styrene resin foam is a foaming agent of the above styrene resin such as lower hydrocarbons such as propane, butane, pentane and hexane, and halogenated hydrocarbons such as methyl chloride, dichloromethane, trichloromonofluoromethane and dichlorodifluoromethane. Impregnated with, and supplied to the extruder, or after supplying the styrene resin to the extruder, the foaming agent is pressed into the extruder, the foaming agent and the styrene resin are melted and kneaded in the extruder, The thickness is 0.1 to 10 by a known method such as extrusion from a T die or a circular die.
A sheet-shaped styrenic resin foam having a size of mm and a density of 0.03 to 0.5 g / cc is produced.

The thickness of the sheet is preferably 0.1 to 10 mm. If the thickness is less than 0.1 mm, the sheet will be damaged during secondary foam molding, or the molded product will not have sufficient strength. Further, if the thickness exceeds 10 mm, secondary molding becomes difficult, which is not preferable. The density is preferably 0.03 to 0.5 g / cc. If the density is less than 0.03 g / cc, the sheet may be broken during secondary foam molding or the strength of the molded product may not be sufficient, and if it exceeds 0.5 g / cc, the merit as a foamed product may be reduced, which is not preferable.

In obtaining a styrene resin foam by foaming a styrene resin, a nucleating agent such as talc, calcium carbonate or the like, stearic acid, behenic acid, and their metal salts (calcium, magnesium) for controlling the foam cell diameter are used. , Zinc, etc.), a plasticizer such as ethylene bis-stearamide, a lubricant, a pigment, an antistatic agent, a flame retardant, etc. may be mixed and used. Further, in order to change the surface characteristics of the obtained styrene resin foam, a lubricant such as an antistatic agent, silicone or an antibacterial agent may be coated on the surface.

It is also possible to mix the specific styrene resin used in the present invention with another styrene resin within a range not impairing the function of the foam intended in the present invention. To mold the secondary foam by heating the styrene resin foam obtained as described above, the styrene resin foam is placed in a heating furnace, softened and secondary foamed, and then heated. It is common to take out the product and press-mold it immediately to obtain a molded product.

[0020]

EXAMPLES The present invention will be described in more detail below. However,
The invention is in no way limited by these examples. (Production of Styrene Polymer-1) A 10-liter autoclave equipped with a stirrer was charged with 5 kg of styrene, 0.2 kg of ethylbenzene and 1.2 g of 1,1 bis (t-butylperoxy) cyclohexane, and the mixture was kept at 110 ° C. for 3 hours. Thirteen
After polymerization was carried out at 0 ° C. for 3 hours and at 150 ° C. for 2 hours, unreacted styrene and ethylbenzene were recovered by an extruder to obtain a styrene polymer-1. The weight average molecular weight measured by GPC is 34.
It was 6,000.

(Production of Styrene Polymer-2) A 10 liter autoclave equipped with a stirrer was charged with 5 kg of styrene, 0.5 kg of ethylbenzene and 1 g of 1,1 bis (t-butylperoxy) cyclohexane, and the mixture was kept at 120 ° C. for 2 hours. After polymerization at 140 ° C for 2 hours and at 150 ° C for 2 hours, unreacted styrene and ethylbenzene were recovered by an extruder to obtain a styrene polymer-2. The weight average molecular weight measured by GPC was 297,000.

[0022]

Examples 1 to 4 2,5,10,13 parts by weight of terpene resin was mixed with 100 parts by weight of styrene polymer-1 and granulated with a 20 mm twin-screw extruder to obtain styrene resin. It was Table 1 shows the physical properties of the obtained styrene resin. The physical properties were measured according to the following methods.

(1) MFR: In accordance with ISO R1133. (2) VICA softening point: According to ASTM D1525. (3) Tensile strength: According to ASTM D638. The terpene resin used is Yasuhara Chemical Co., Ltd.
YS resin TO-115.

Then, Freon-12 was used as a foaming agent.
The styrene resin was extruded and foamed to obtain a sheet-shaped styrene resin foam having a thickness of 1.2 mm and a density of 0.10 g / cc. The obtained styrene-based resin foam was aged for one month, heated at various temperatures for 10 seconds using an infrared heating furnace, and secondary foamed to obtain a molded lunch box shown in FIG.
Table 2 shows the molding evaluation results and the strength evaluation results of the molded products. In addition, the impact strength is as follows:
A copper ball of 300 g was dropped on the center of (a), and the height (cm) of penetration was measured.

[0025]

[Examples 5 to 7] Other than using the styrene polymer-2,
The same operation as in Examples 1 to 3 was carried out to obtain a styrene resin.
The physical properties are shown in Table 1. A styrene resin foam was obtained by the same operation as in Examples 1 to 3, and secondary foam molding was performed to obtain a lunch box. The evaluation results are shown in Table 2.

[0026]

[Comparative Examples 1 and 2] The same operation as in Example 1 was carried out except that styrene-based polymers-1 and 2 were used as the styrene-based resin to obtain a styrene-based resin foam and a lunch box. The physical properties of the styrene resin are shown in Table 1 and the evaluation results are shown in Table 2.

[0027]

[Comparative Example 3] A styrene resin foam and a lunch box were obtained in the same manner as in Example 1 except that 2 parts of mineral oil was added instead of the terpene resin. The physical properties are shown in Table 1 and the evaluation results are shown in Table 2.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

EFFECT OF THE INVENTION Since the styrene resin foam of the present invention can obtain a uniform softened state at a low temperature, a molded product having no moldoid and good mold reproducibility can be obtained. In addition, the strength of the foam-molded product is significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic view of a lunch box formed in an embodiment of the present invention.

Claims (2)

[Claims] 1. A styrene resin foam comprising a styrene resin and a terpene resin. 2. The foam has a thickness of 0.1 mm to 10 mm,
The styrene-based resin foam according to claim 1, which is a sheet having a density of 0.03 g / cc to 0.5 g / cc.