JPH0976340A - High gloss food container lid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high gloss food container lid composed of a rubber modified styrenic resin having high glooss, high impact strength, high rigidity and high surface hardness and especially used as yoghurt. SOLUTION: In a rubber modified styrenic resin containing a rubbery elastomer as dispersing particles, a resin phase is a polymer consisting of 30-70wt.% of a styrenic monomer (a) and 70-30wt.% of an acrylic ester monomer (b) and the average particle size of rubber particles of a dispersion phase is 0.3-2.0μm. A sheet obtained from the rubber modified styrenlc resin containing 5-15wt.% of the rubbery elastomer is thermoformed to obtain a food container.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a food container comprising a sheet obtained from a rubber-modified styrene resin. More specifically, the present invention relates to a high-gloss food container lid, which is a sheet made of a rubber-modified styrene resin having a surface gloss of 85% or more and excellent in gloss.

[0002]

2. Description of the Related Art Resin products for food container lids are rapidly becoming widespread because of their workability, printability and strength. Hard PVC is the mainstream for lid materials that require high gloss. However, alternative materials are required due to waste disposal problems, recycling problems, and the like. The use of rubber-modified polystyrene resin as a typical alternative material has been examined, but the gloss of the thermoformed product is not sufficient. Further, a mixture of polystyrene and a styrene-butadiene block copolymer has been studied, but there are problems such as insufficient gloss, low impact strength, low rigidity, and low surface hardness. It has not been put to practical use. In addition, this styrene-butadiene block copolymer is a practicable PVC substitute material because a gel-like substance is generated in the extruder during blending, which adversely affects the appearance of the molded product and the defective ink ejection during printing. Poor.

[0003]

The present invention has a high gloss, a high impact strength, a high rigidity, and a food container made of a rubber-modified styrenic resin having a high surface hardness, particularly a high gloss used for a yogurt container. A sheet suitable for a food container lid is provided.

[0004]

That is, the present invention relates to a rubber-modified styrene resin containing a rubber-like elastic material as dispersed particles, wherein the resin phase (mother phase) is (a) styrene monomer 30. To 70% by weight and 70% to 30% by weight of (b) acrylic acid ester-based monomer, the dispersed phase has a rubber particle average particle size in the range of 0.3 to 2.0 μm, and has a rubber-like shape. A food container is characterized in that a sheet made of a rubber-modified styrene resin containing 5 to 15% by weight of an elastic body is thermoformed.

A sheet formed by thermoforming the rubber-modified styrenic resin of the present invention has a surface gloss of 85% or more,
A sheet made of rubber-modified styrenic resin with excellent gloss, suitable for high-gloss food container lids. The details of the present invention will be described below. In the present invention, styrene, α-methylstyrene, t-butylstyrene, p-methylstyrene and the like can be used as the styrene monomer constituting the rubber-modified styrene resin. These styrene monomers can be used alone or in combination. As the acrylic acid ester-based monomer, methyl methacrylate, butyl acrylate, butyl methacrylate, ethyl acrylate, etc. can be used. These acrylate monomers can be used alone or in combination.

The composition ratio of the styrene-based monomer and the acrylate-based monomer is required to be a polymer in which the styrene-based monomer is 30 to 70% by weight. If the styrene-based monomer content is less than 30%, the processability, which is a characteristic of the rubber-modified styrene-based resin, is significantly reduced, which is not preferable, and 70%
If it exceeds, the glossiness becomes insufficient. Polybutadiene rubber and styrene-butadiene rubber can be used as the rubber component serving as the dispersed phase of the rubber-modified styrenic resin of the present invention. The rubber particle diameter of the dispersed phase is 0.3 to 2.0 μm
It is. If the particle size is less than 0.3, the impact strength is significantly reduced, which is not preferable. When the particle size is 2.0 μm or more, the gloss of the thermoformed product is lowered, which is not preferable.

The amount of the rubber-like elastic material used in the rubber-modified styrenic resin is important for developing impact strength, and it is necessary that the styrene-based resin be contained in an amount of 5 to 15% by weight. It is preferably 8 to 15% by weight. If the amount of the rubber-like elastic material is less than 5%, the strength reinforcing effect is not sufficient. If it exceeds 15% by weight, the productivity in the polymerization step is lowered, which is not preferable. The average particle diameter of the rubber particles of the present invention was measured by a laser light scattering measurement method using rubber-modified styrene resin pellets with dimethylformamide as a solvent.

A thermoplastic elastomer can be added to the rubber-modified styrenic resin of the present invention. As the elastomer that can be added, SBR type thermoplastic rubber is preferable,
For example, TR-2000 manufactured by Nippon Synthetic Rubber Co., Ltd. and Toughprene 125 or 126 manufactured by Asahi Kasei Kogyo Co., Ltd. are preferable. The amount of the thermoplastic elastomer added is preferably 10% by weight or less, more preferably 8% by weight or less, based on 100% by weight of the rubber-modified styrene resin. If it exceeds 10% by weight, a gel-like substance is generated in the extruder, and there is a possibility that the appearance of the molded product or the phenomenon of defective ink ejection during printing may occur.

The terpene resin used in the present invention is preferably contained in an amount of 1 to 15 parts by weight based on 100 parts by weight of the rubber-modified styrene resin. The terpene resin is synthesized by cation copolymerization of an aromatic vinyl hydrocarbon and a terpene by Friedel-Crafts polymerization using a strong Lewis acid represented by aluminum chloride as a catalyst in an anhydrous state under an inert atmosphere. The terpenes referred to here are d-limonene obtained from citrus cortex and α obtained from raw pine resin.
-Pentene and the like obtained by isomerization of pinene. The terpene resin in the present invention also includes a partially hydrogenated terpene resin obtained by hydrogenating the terpene resin. The hydrogenation amount is not particularly limited, but it is necessary to leave 10 mol% or more of the aromatic ring. This is the compatibility with the dispersed phase with the styrene phase (matrix) which is the mother phase at the polymerization stage when the aromatic ring of the terpene resin disappears,
Alternatively, the adhesiveness deteriorates and the mechanical strength decreases.

Examples of the terpene-based resin include YS resin, T 125 and T 11 manufactured by Yasuhara Chemical Co., Ltd.
5, T105 and T85 are, for example, CLEARON M10 manufactured by Yasuhara Chemical Co., Ltd. as a partial hydrogenation system.
5, M115 is used. The addition of terpene resin is
It can be obtained by blending with a rubber-modified styrene resin after polymerization with an extruder. It is also possible to carry out polymerization by mixing a mixture obtained by extruding and kneading into a rubber component in advance with a kneading extruder or dissolving in a volatile organic solvent such as ethylbenzene in a polymerization solution.

The styrene-based resin of the present invention can be produced by a conventional method for producing high-impact polystyrene.
That is, an uncrosslinked rubber is dissolved in a polymerization liquid, and this raw material liquid is supplied to a reactor equipped with a stirrer to perform polymerization. The control of the rubber particle diameter can be achieved by a well-known general method, that is, by the molecular weight of the resin component (matrix) PS, or by increasing or decreasing the rotation speed of the stirrer.

In the polymerization, it is possible to use a solvent such as ethylbenzene, toluene or xylene for the polymerization raw material liquid. To increase the polymerization efficiency, an organic peroxide such as benzoyl peroxide or a radical generator such as azobisbutyronitrile can be added at the beginning of the polymerization or during the polymerization. The unreacted material is preferably distilled off by using a flash tank system used for general polystyrene or an extruder equipped with a multi-vented system. At this time, it is more effective to inject water or an inert gas into the molten resin. Unreacted monomers and polymerization solvent are removed and pelletized.

The terpene resin used in the present invention is dissolved in a raw material solution in which a rubbery polymer is dissolved, or
During the polymerization, it is added in the molten state under heating or dissolved in a solvent, or after leaving the recovery system, it is added in the molten state under heating, or a rubber-modified styrene resin and a terpene resin are blended and extruded. It can be added by a method of melt-mixing with a machine.

The thermoplastic elastomer used in the present invention can be added by blending it with a rubber-modified styrene resin and melt-mixing with an extruder. The sheet forming machine in the present invention may be a machine used for ordinary styrenic resins, but if a belt type sheet extruder manufactured by United Mold Co. is used, a sheet having excellent gloss can be obtained. Can be done. As the sheet forming conditions, the resin temperature is 190 to 230 ° C. and the cooling roll temperature is 5
It is preferable to select the range of 0 to 65 ° C.

As the secondary thermoforming method for the sheet, vacuum forming, pressure forming, hot plate heating type pressure forming or the like can be selected. As molding conditions, it is preferable to set the ambient temperature in the hitter zone to 180 to 240 ° C. and the heating time to 5 to 6 seconds. The gloss of the sheet can be sufficiently increased by using a roll touch or a belt type extruder at the time of sheeting, but the sheet that expresses the gloss originally not possessed by the resin under the processing conditions is the secondary thermoforming. Then, due to the so-called luster restoration phenomenon, the gloss is lost and the original gloss is restored.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

[0017]

Example 1 Two reactors equipped with a stirrer were connected in series, and 42.5% by weight of styrene and butyl acrylate were used.
1% by weight and 38.2% by weight of methyl methacrylate were mixed, and 2.7% by weight of ethylbenzene was further added. 7.5% by weight of a rubber-like elastic material is dispersed and melted in this mixture.
Thereafter, the polymerization reaction was carried out in a continuous polymerization tank in which the inlet temperature was set at 100 ° C. and the outlet temperature was set at 150 ° C. Vacuum degassing was carried out to distill off unreacted monomer, and residual volatile matter was reduced to 5
It was made less than 00 ppm.

With respect to 100 parts by weight of the rubber-modified styrenic polymer obtained by the above operation, 5.0 parts by weight of the thermoplastic elastomer (Tuffprene 126) and 6.5 parts by weight of the terpene resin (Clearlon M115) are added. Rubber-modified styrenic resin composition shown in Table 1 obtained by granulating with a single-screw extruder-
1 was obtained. Processed titanium 3 to 100 parts by weight of this composition
A weight of 0.35 mm was obtained with a sheet extruder. After that, a lid having a width of 110 mm, a length of 85 mm, and a depth of 20 mm was formed by pressure molding.

The proportion of the constituent units was quantified by pyrolysis gas chromatography. Table 2 shows the DuPont impact strength and gloss of the obtained sheet, and the gloss of the thermoformed lid. The glossiness was measured according to ASTM: D523-67.

[0020]

Example 2 A rubber-modified styrene resin composition-2 shown in Table 1 was obtained in the same manner as in Example 1 except that the terpene resin was not added, and the physical properties shown in Table 2 were obtained.

[0021]

Comparative Example 1 The procedure of Example 1 was repeated except that the rubber-like elastic material was changed to 2.0 parts by weight to obtain the rubber-modified styrene resin composition-3 shown in Table 1, and Table 2 The physical properties shown were obtained.

[0022]

Comparative Example 2 Except for increasing the rotation speed of the stirrer during polymerization,
By operating in the same manner as in Example 1, a rubber-modified styrenic resin composition-4 shown in Table 1 was obtained, and physical properties shown in Table 2 were obtained.

[0023]

[Comparative Example 3] The same operation as in Example 1 was carried out except that butyl acrylate and methyl methacrylate were not used,
The rubber-modified styrene resin composition-5 shown in Table 1 was obtained,
The physical properties shown in Table 2 were obtained.

[0024]

[Comparative Example 4] Except that 21.6% by weight of styrene, 10.2% by weight of butyl acrylate, 54.2% by weight of methyl methacrylate, 10.3% by weight of ethylbenzene, and 3.7% by weight of rubber-like elastic material. Operate as in Example 1,
The rubber-modified styrene resin composition-6 shown in Table 1 was obtained,
The physical properties shown in Table 2 were obtained.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

EFFECTS OF THE INVENTION It can be seen that the food container lid formed from the sheet obtained from the rubber-modified styrene resin composition of the present invention is excellent in high gloss and impact strength. The lid thermoformed from the rubber-modified styrenic resin composition of the present invention is most suitable for a lid material such as a yogurt container that requires high designability.

Claims (3)

[Claims] 1. A rubber-modified styrenic resin containing a rubber-like elastic material as dispersed particles, wherein the resin phase (mother phase) is (a) styrene-based monomer 30 to 70% by weight, and (b) acrylic acid. It is a polymer composed of 70 to 30% by weight of an ester monomer, and the average particle size of rubber particles in the dispersed phase is 0.3 to 2.
A food container characterized by thermoforming a sheet obtained from a rubber-modified styrenic resin having a rubber-like elastic body in an amount of 0 μm in an amount of 5 to 15% by weight. 2. The food container according to claim 1, wherein 1 to 10 parts by weight of the thermoplastic elastomer is added to 100 parts by weight of the rubber-modified styrene resin. 3. The food container according to claim 1, wherein 1 to 15 parts by weight of the terpene resin is added to 100 parts by weight of the rubber-modified styrene resin.