JPH1180401A - Thermoplastic resin foamed sheet and container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet and a container which possess excellent volume reduction disposability after use, has pearlescent appearance and can cope with heating in microwave ovens. SOLUTION: A container prepd. by forming of a thermoplastic resin foamed sheet comprising 40 to 60 pts.wt. polypropylene resin, 10 to 30 pts.wt. polystyrene resin, 10 to 40 pts.wt. inorg. filler, and 3 to 20 pts.wt. hydrogenation product of a block copolymer of styrene with isobutylene or 2 to 20 pts.wt. block copolymer of styrene with butadiene, the sheet having been stretched by 1.05 to 3 times, and, when used as a container for side dishes or packed lunches, has excellent resistance to heating in microwave ovens and, after use, has excellent volume reduction disposability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamed thermoplastic resin sheet having heat resistance in a microwave oven, excellent in volume reduction and disposal after use, and having a pearl-like appearance, and a molded container thereof.

[0002]

2. Description of the Related Art In recent years, many cooked foods or bento have been sold to convenience stores, supermarkets and the like in accordance with changes in lifestyle. These foods are often used after being reheated in a microwave oven, and thus it is essential that the containers have microwave heat resistance. 2. Description of the Related Art Conventionally, as a food packaging container capable of heating in a microwave oven, a sheet (hereinafter referred to as PP / F) in which talc, which is an inorganic substance, is filled in a polypropylene-based resin in an amount of 30 to 40% by weight with respect to the total composition
(Referred to as a sheet) is used. This molded article is widely used as a container which is not deformed even when heated in a microwave oven in a state in which the food is filled, and is not deformed by heat generated by the food inside.

[0003] However, this container has a problem that it is difficult to hold it with bare hands immediately after heating since the heat of the content easily passes when the content is heated in a microwave oven. Further, there is a problem in that when the container is discarded after use, the container is tough and hard to tear and hard to be crushed, so that the container has to be discarded in the same shape and the capacity of the waste increases.

[0004] In order to solve this problem, foaming PP / F can be considered. However, simply foaming significantly reduces the rigidity. If the thickness of the molded body is increased to compensate for the decrease in rigidity, the cost increases. As a method for increasing the rigidity of a thin foamed polypropylene-based sheet, a method of adding a polystyrene resin in Japanese Patent Application Laid-Open No. 1-278439 and a method of forming a multilayered structure in Japanese Patent Application Laid-Open No. 1-166942 are known. However, Japanese Patent Application Laid-Open No. 1-278439 cannot provide sufficient rigidity, and Japanese Patent Application Laid-Open No. 1-166942 has a problem that it is expensive due to the multi-layer structure.

[0005]

DISCLOSURE OF THE INVENTION The present invention has a heat resistance of 130 ° C. in a microwave oven and retains practical strength, but also has a reduced volume disposal property, that is, a container can be easily crushed at the time of disposal. Therefore, it is possible to provide a thermoplastic resin foam sheet and a container having a beautiful pearl-like appearance, which can reduce the apparent capacity of a container which becomes garbage, and which is not present in conventional PP / F containers. As an issue.

[0006]

Means for Solving the Problems The present inventors have conducted various studies to solve the above-mentioned problems, and as a result, have found that a resin composition comprising a polypropylene resin, a polystyrene resin and an inorganic filler has a specific phase. Sheets and molded bodies foamed with the use of a solubilizing agent are relatively inexpensive and rigid, while having excellent heat resistance and volume reduction and disposal properties compatible with microwave oven heating at 130 ° C, and environmental suitability (low burning calories). The present invention has been found to have high characteristics and to have a pearl-like appearance, and has completed the present invention.

The first invention of the present invention comprises (A) 40 to 60 parts by weight of a polypropylene resin, (B) 10 to 30 parts by weight of a polystyrene resin, (C) 10 to 40 parts by weight of an inorganic filler, and (D) ) Foaming ratio containing 3 to 20 parts by weight of hydrogenated styrene and isoprene block copolymer is 1.05.
It is a thermoplastic resin foam sheet of up to three times.

The second invention comprises (A) 40 to 60 parts by weight of a polypropylene resin, and (B) 10 to 3 parts of a polystyrene resin.
0 parts by weight, (C) 10 to 40 parts by weight of an inorganic filler, and
(D) an expansion ratio containing 2 to 20 parts by weight of a block copolymer composed of styrene and a conjugated diene hydrocarbon is 1.0
5 to 3 times the thermoplastic resin foam sheet.

According to a third aspect of the present invention, there is provided a molded container comprising the thermoplastic resin foam sheet according to the first or second aspect of the present invention, which can be heated in a microwave oven.

A fourth invention is the molded container according to the third invention, which is filled with food.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The term "polypropylene resin" as used in the present invention refers to a propylene homopolymer (hereinafter referred to as PP homopolymer) obtained by homopolymerizing propylene, or a copolymer such as ethylene, acrylate or maleic acid having a content of 20% by weight or less. Saturated organic acid and its anhydride, having 4 to 4 carbon atoms
Copolymers obtained by copolymerizing 12 monomer units such as α-olefin with propylene are exemplified. The copolymer may be a random copolymer, a block copolymer, or a graft copolymer. Further, there may be mentioned those obtained by introducing a long-chain polypropylene as a branched chain into a polypropylene-based resin main chain by a method such as irradiation with radiation. Alternatively, modified products such as oxidation and chlorination of these polymers may be used. In carrying out the present invention, these polypropylene resins may be used alone or in combination of two or more.

The polystyrene resin of the present invention may be a polystyrene homopolymer (hereinafter referred to as GP-PS), or styrene and one or more other comonomers, for example, α-
Copolymers with methylstyrene, acrylonitrile, butadiene, methyl methacrylate, acrylic acid, methacrylic acid, maleic anhydride and the like can be mentioned. Further, a rubber-reinforced polystyrene generally called HI-PS obtained by graft-polymerizing a styrene-butadiene copolymer component with polystyrene can also be used. These can be used in combination. Of these, GP-PS is preferable as the polystyrene resin, particularly from the viewpoint of economy.

The inorganic filler of the present invention includes talc, clay, mica, calcium silicate, montmorillonite, bentonite, silica, alumina, titanium oxide, iron oxide,
Zinc oxide, magnesium oxide, pumice, aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, aluminum phosphate, calcium carbonate, dolomite, calcium sulfate, calcium sulfite, barium sulfate, carbon black, white carbon, zeolite, glass powder, Oya stone, shirasu balloon, glass balloon and the like can be mentioned, and among them, talc is particularly preferably used in terms of acid stability, handling and economy.

In the present invention, the thermoplastic resin is preferably in the range of 40 to 60 parts by weight of the polypropylene resin and 10 to 30 parts by weight of the polystyrene resin from the viewpoint of the appearance of the foamed sheet and the molded article and the physical properties of the molded article. preferable. If the amount of the polypropylene-based resin is too small, the heat resistance of the microwave oven cannot be obtained. If the amount of the polystyrene-based resin is too small, the rigidity of the sheet or the molded product cannot be improved.

The mixing ratio of the resin composition of the present invention is as follows: sheet,
The inorganic filler is preferably in the range of 10 to 40 parts by weight from the viewpoints of the rigidity of the molded body, environmental suitability, and moldability from the sheet to the molded body. If the amount of the inorganic filler is less than 10 parts by weight, rigidity and environmental suitability cannot be obtained, and if it exceeds 40 parts by weight, the moldability from a sheet to a formed body is significantly reduced.

The expansion ratio of the resin composition of the present invention is as follows:
1.05 from the viewpoint of rigidity and economical efficiency as a sheet or molded body
The range is preferably from 3 to 3 times, more preferably from 1.1 to 1.5 times. If the expansion ratio is too small, the effect of improving economic efficiency is poor, and if it is too large, to obtain a predetermined rigidity, it is necessary to increase the sheet thickness more,
Poor in economics.

In the present invention, a method using a foaming agent is suitably used for foaming the working composition. In this case, the foaming agent is not particularly limited, and various chemical foaming agents and physical foaming agents can be used. Specifically, examples of the chemical foaming agent include organic ones such as azodicarbonamide, azobisisobutyronitrile, and p-toluenesulfonyl hydrazide, and inorganic blowing agents such as sodium hydrogencarbonate and sodium citrate. Examples of the physical foaming agent include propane, butane, pentane, water, carbon dioxide, and nitrogen. In addition, the powdery material as the foaming agent may be a material that is made into a masterbatch with a resin or various additives, or a material in which a physical foaming agent is impregnated in a base resin. More preferably, the foaming agent is preferably an inorganic foaming agent from the viewpoint of surface appearance.

In the present invention, a colorant generally used, a lubricant such as ethylene bisamide, a hindered phenol-based or phosphorus-based antioxidant may be added as a resin additive, if necessary.

The hydrogenated styrene-isoprene block copolymer (hereinafter referred to as SEPS) used in the present invention is composed of at least one polymer block A composed of styrene and at least one polymer block B composed of isoprene. The total number average molecular weight is from 5,000 to 50
A block copolymer having a content of the entire polymer block A of 10 to 70% by weight, and (AB) n or A- (BA) n (n is an integer of 1
The hydrogen block copolymer has a block form of (5 or less) and is obtained by hydrogenating at least 70% or more of the aliphatic double bond of the entire block B. The block copolymer (hereinafter referred to as STR) composed of styrene and conjugated diene hydrocarbon is composed of one or more polymer blocks A composed of styrene and one or more polymer blocks B composed of conjugated dienes (butadiene, isoprene). The total number average molecular weight is in the range of 5,000 to 500,000, and the content of the entire polymer block A is 10 to 80.
% By weight of the block copolymer, and (AB)
It is a block copolymer having a block form of n or A- (BA) n (n is an integer of 1 to 5).

The added amount of SEPS is preferably 3 to 20 parts by weight, and the added amount of STR is preferably 2 to 20 parts by weight. In this range, physical properties such as tearing strength that enable the container to be crushed when the container is crushed are balanced, and the container can be discarded with reduced volume while having a practically appropriate strength. In other words, in practice, the container is not damaged even if the prepared food is put into the container and transported, and the apparent volume can be reduced by crushing or tearing the container when disposing the container. . If the amount of SEPS or STR is too small, the strength of the sheet, particularly the tear strength, is undesirably low in any case. Conversely, if the addition amount is too large, the strength decreases and the material becomes flexible. Therefore, when the contents are put into the container, the shape of the container is deformed by the weight, which is not preferable, and the heat resistance of the microwave oven is also reduced.

The resin composition used in the production of a foamed sheet may be prepared by melt-mixing with a single-screw or twin-screw extruder prior to sheet extrusion, excluding the foaming agent, without using a melt-kneading process. Alternatively, a dry-blended product may be used. As a method of mixing the inorganic filler, a material obtained by melt-mixing an inorganic substance with polypropylene at a high concentration in advance and forming a master batch may be used.

For the foamed sheet of the present invention, a commonly used extrusion method can be applied.
Any of a circular die and a modified die may be used.
In addition, for decoration or the like, a non-foamed layer may be laminated on a foamed sheet by a method such as co-extrusion or heat lamination of a previously formed film.

As the molded article of the present invention, the foamed sheet obtained by the present invention is used for ordinary thermoforming such as vacuum forming.
Products formed by pressure molding, vacuum pressure molding, plug assist molding, press molding, and the like can be given.

The container thus obtained is suitably used as a container for foods, prepared foods and the like, or as a lunch box container.
Particularly, a food containing a lot of oil is used, and even if it is heated by microwave oven, it has sufficient heat resistance, so that it is not deformed or punctured.

[0025]

The molded container using the thermoplastic resin foam sheet according to the present invention can be microwaved and is suitably used as a food, prepared food or lunch box container.

[0026]

The present invention will be described in more detail with reference to the following examples. (Example 1) A polypropylene resin having a melt index of 9 and a random copolymer (F manufactured by Grand Polymer Co., Ltd.)
229D) 50 parts by weight, talc (manufactured by Shiraishi Calcium Co., Ltd.)
30 parts by weight of talc FVS), 20 parts by weight of a polystyrene resin (manufactured by Denki Kagaku Kogyo Co., HRM-5), 0.25 parts by weight of a blowing agent (manufactured by Eiwa Chemical Co., SC-K), 0.2 part by weight of liquid paraffin, After dry blending SEPS (1) (Kuraray Co., Ltd., Septon 2104, hydrogenated product of triblock copolymer of styrene and isoprene, styrene content 65% by weight), the resin temperature was 236 with a single screw extruder of 65 mmφ.
° C, resin pressure 153kg / cm3, extrusion rate 77.9kg /
A sheet having a thickness of 0.6 mm was manufactured under the condition of h.

The expansion ratio of the sheet was 1.22 times, and the maximum diameters of the foam cells in the direction parallel to and perpendicular to the sheet extrusion direction were 237 μm and 100 μm, respectively. The following evaluation was performed on this sheet.

(1) DuPont Impact Using a DuPont impact tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.), 50% of the sheet with a tip diameter of 1/2 inch and a weight of 100 g was used.
The breaking energy was measured.

(2) Feeling of hand folding A sheet is cut into a width of 25 mm and a length of 50 mm, both ends are bent in the length direction, and it is observed whether or not the sheet is broken when the crease is formed in the width direction. 、, a substance having a trigger for cracking was rated as △, and a cracked one was rated as ×.

(3) Tear strength: Based on JIS K-6772. That is, width 40mm
Three test pieces each having a length of 150 mm are taken from the vertical and horizontal directions of the sample, and a cut is made into the inside of each test piece to a length of about 75 mm from the center of the short side to the inside in parallel with the long side. The test piece is attached to a gripper of a tensile tester such that both sides of the cut side are turned upside down, and the test piece is torn in parallel with the cut direction at a pulling speed of 200 ± 20 mm / min to determine a maximum load. The direction indicates the direction of the cut.

A lunch box having a shape as shown in FIG. 1 was prepared from the sheet by vacuum forming, and the following test was conducted. (1) Drop strength A 300 g weight was fixed to the lunch container so as to be uniform, and dropped from 50 cm in a direction in which the edge in the short direction became vertical to see if the lunch container was broken. Note that no lid was used. (2) Oven heat resistance The lunch container was left in a 130 ° C. gear oven for 10 minutes to check for deformation of the container. (3) Heat resistance of microwave oven The edible salad oil was put into a lunch box for 8 minutes (about 300 g), heated in a microwave oven without a lid for 5 minutes, and the deformation of the container, the presence or absence of oil leakage and the like were examined. Table 1 shows the composition of Example 1 and Table 2 shows the evaluation results.

[0032]

[Table 1]

[0033]

[Table 2]

(Example 2) The same procedure as in Example 1 was carried out except that the raw materials shown in the form 1 were previously kneaded by a single screw extruder.

Example 3 The same procedure as in Example 1 was carried out except that the raw materials shown in Table 1 were previously kneaded with a twin-screw extruder.

Example 4 The procedure of Example 1 was repeated except that SEPS (1) was changed to 10 parts by weight as shown in Table 1.

Example 5 The same operation as in Example 1 was carried out except that 5 parts by weight of SEPS (1) and 10 parts by weight of PS were mixed, and then mixed with 10 parts by weight of PS.

(Embodiment 6) S instead of SEPS (1)
The procedure was performed in the same manner as in Example 1 except that EPS (2) (manufactured by Kuraray Co., Ltd., Septon 2043, hydrogenated product of a triblock copolymer of styrene and isoprene, styrene content: 13% by weight) was used.

(Embodiment 7) S instead of SEPS (1)
The same procedure was performed as in Example 1 except that 2.5 parts by weight of TR (STR-1602, manufactured by Denki Kagaku Kogyo KK, triblock copolymer of styrene and butadiene) was used.

(Embodiment 8) S instead of SEPS (1)
The same operation as in Example 1 was performed except that TR (STR-1602, manufactured by Denki Kagaku Kogyo KK, triblock copolymer of styrene and butadiene) was used in an amount of 5 parts by weight.

Comparative Example 1 50 parts by weight of a polypropylene resin, 30 parts by weight of talc, 20 parts by weight of a polystyrene resin,
After dry blending 0.25 parts by weight of a foaming agent and 0.2 parts by weight of liquid paraffin, the resin temperature was 228 ° C., the resin pressure was 140 kg / cm 3, and the throughput was 7 using a 65 mmφ single screw extruder.
A sheet having a thickness of 0.6 mm was manufactured under the condition of 7.4 kg / h. Table 3 shows the composition.

[0042]

[Table 3]

The expansion ratio of the sheet was 1.19 times, and the maximum diameters of the foam cells in the direction parallel to and perpendicular to the sheet extrusion direction were 208 μm and 78 μm, respectively. The same evaluation as in the example was performed for the sheet and the lunch container formed from the sheet. Table 4 shows the evaluation results.

[0044]

[Table 4]

Comparative Example 2 As in Table 3, the same procedure as in Example 1 was carried out except that 5 parts by weight of SEBS (Taftec H1041, manufactured by Asahi Kasei Corporation, a hydrogenated product of a triblock copolymer of styrene and butadiene) was added. went.

Comparative Example 3 SEBC (Dynallon 4600P, hydrogenated product of styrene-butadiene-olefin crystal block copolymer, manufactured by Nippon Synthetic Rubber Co.)
The procedure was performed in the same manner as in Example 1 except that parts by weight were added.

(Comparative Example 4) The same operation as in Example 1 was carried out except that 2.5 parts by weight of SEPS was added.

The procedure was performed in the same manner as in Example 1 except that 25 parts by weight of SEPS (1) was added.

Table 3 shows the composition of the commercially available PP / F, and Table 4 shows the evaluation results.

[Brief description of the drawings]

FIG. 1 is a shape diagram of a container used when measuring physical properties of the container in Examples.

Claims (4)

[Claims] (A) Polypropylene resin 40 to 60
Parts by weight, (B) 10 to 30 parts by weight of a polystyrene resin,
A thermoplastic resin foam sheet containing (C) 10 to 40 parts by weight of an inorganic filler and (D) 3 to 20 parts by weight of a hydrogenated styrene-isoprene block copolymer and having an expansion ratio of 1.05 to 3 times. 2. (A) Polypropylene resin 40 to 60
Parts by weight, (B) 10 to 30 parts by weight of a polystyrene resin,
(C) 10 to 40 parts by weight of an inorganic filler and (D) a block copolymer 2 composed of styrene and a conjugated diene hydrocarbon
A foamed thermoplastic resin sheet having a foaming ratio of 1.05 to 3 times containing 〜20 parts by weight. 3. A molded container comprising the thermoplastic resin foam sheet according to claim 1 and capable of being heated in a microwave oven. 4. The molded container according to claim 3, which is filled with food.