JP2000044697A - Synthetic resin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide synthetic resin formed sheet hardly deformed even when heated in a microwave oven. SOLUTION: This synthetic resin foamed sheet is one made of polystyrene and polypropylene, and satisfies the following heat-distortion property when the foamed sheet is molded into a container having 0.6 mm thickness and receiving 100 g edible oil and is heated in a 500-watt microwave oven for 5 min: h/h0=0.5-1.3 (h0 and h are the depth in the center of the bottom of the container before and after heating respectively).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin sheet, a synthetic resin foam sheet, and a container obtained therefrom, which are suitable as molding materials for various food containers.

[0002]

2. Description of the Related Art Styrene resins are widely used as container materials for various foods such as side dishes because of their excellent moldability and rigidity.
It is also common to eat various prepared dishes as they are heated in a microwave oven. However, the styrene-based resin has poor heat resistance, so that when a dish or the like is heated together with a microwave in a container, there is a problem that the container is deformed. Such deformation due to heating is particularly remarkable in a container containing a food containing a large amount of edible oil, and tends to be larger at the bottom of the container. Therefore, if a container containing a side dish such as fried food or a stew, or a container containing a liquid such as curry is heated in a microwave oven, the container will be greatly deformed and it will be difficult to eat as it is, or the stew due to deformation of the container Etc. spills out and stains the inside of the microwave oven.

[0003] The present invention provides a synthetic resin sheet and a synthetic resin foam sheet capable of suppressing deformation when heated in a microwave oven as much as possible and improving user-friendliness when made into a food container such as a food container. The purpose is to: Another object of the present invention is to provide a container obtained from a synthetic resin sheet or a synthetic resin foam sheet.

[0004]

According to the present invention, (A) 10 to 90% by weight of a styrene resin and (B) a melting point of 100 to 3 are used.
A sheet obtained from a resin composition containing 90 to 10% by weight of a thermoplastic resin at 00 ° C., wherein the sheet has a shape and dimensions shown in FIG. 1 obtained by molding the sheet,
When 100 g of edible oil is placed in a tray type container having a thickness in the range of 0.3 to 2.0 mm and heated in a microwave oven of 500 W for 5 minutes, the following formula (1): h / h ₀ = 0.5 to 1. 3 (1) [where h ₀ denotes the depth at the center of the container bottom before heating, and h denotes the depth at the center of the container bottom after heating. ]
A synthetic resin sheet characterized by satisfying the heat deformability represented by the following formula: Further, the present invention provides (A)
10 to 90% by weight of styrene resin and (B) melting point of 10
A foamed sheet obtained from a resin composition containing 90 to 10% by weight of a thermoplastic resin at 0 to 300 ° C., wherein the foamed sheet has a shape and dimensions shown in FIG. 1 obtained by molding the foamed sheet. When 100 g of edible oil is put in a tray type container having a thickness of 0.3 to 2.0 mm and heated in a microwave oven of 500 W for 5 minutes, the following formula (1): h / h ₀ = 0.5 to 1 0.3 (1) [wherein, h ₀ denotes a depth at the center of the container bottom before heating, and h denotes a depth at the center of the container bottom after heating. ]
A synthetic resin foam sheet characterized by satisfying the heat deformability represented by the formula: Furthermore, the present invention
A container comprising the synthetic resin sheet or the synthetic resin foam sheet is provided.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The synthetic resin sheet (meaning non-foamed, the same applies hereinafter) and the synthetic resin foamed sheet of the present invention are composed of a styrene resin (A) and a styrene resin (B).
It can be obtained by molding a resin composition containing a thermoplastic resin whose component has a melting point of 100 to 300 ° C.

Examples of the styrene resin as the component (A) used in the resin composition include a styrene monomer polymer and a copolymer of a styrene monomer and another monomer copolymerizable therewith.

Styrene monomers include styrene,
Alkyl-substituted styrene such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4-t-butylstyrene, 2,4-dimethylstyrene, α-methylstyrene, α-methyl-4- One or more selected from α-alkyl-substituted styrene such as methylstyrene, halogenated styrene such as 2-chlorostyrene and 4-chlorostyrene, and the like can be given.

Other monomers copolymerizable with the styrene monomer include acrylic acid or methacrylic acid, methyl acrylate or methyl methacrylate, ethyl acrylate or ethyl methacrylate, butyl acrylate or butyl methacrylate, acrylic acid 2 Acrylic acid such as -ethylhexyl or 2-ethylhexyl methacrylate (C _1-
C ₈₎ esters or methacrylic acid (C ₁ ~C ₈₎ esters, acrylonitrile, maleic anhydride, maleimide,
One or more types selected from maleic acid or derivatives thereof such as N-substituted maleimide such as N-methylmaleimide and N-ethylmaleimide can be mentioned.

The styrene resin as the component (A) may be a rubber-modified styrene resin. Examples of the rubber used in the production of the rubber-modified styrene resin include non-styrene rubbers such as butadiene rubber, butadiene-isoprene rubber, butadiene-acrylonitrile rubber, ethylene-propylene rubber, isoprene rubber, acrylic rubber, and ethylene-vinyl acetate rubber; At least one selected from styrene rubbers such as butadiene rubber and styrene-isoprene rubber can be used. The butadiene rubber may be a high cis type having a high content of cis-1,4 structure or a low cis type having a low content of cis-1,4 structure. When the rubber-modified styrenic resin is used, the content of the rubber component in the resin is 1 to 2
It is preferably 0% by weight.

[0010] When the component (A) is formed into a copolymer, the polymerization form is not particularly limited.
It may be a random copolymer or a copolymer having a tapered block structure.

The content of the component (A) in the resin composition is from 10 to 90% by weight, preferably from 40 to 90% by weight, particularly preferably from 60 to 90% by weight.

The melting point of the component (B) used in the resin composition is 1
As the thermoplastic resin of 00 to 300 ° C., polyolefin resin, crystalline polystyrene, polyester resin,
One or more types selected from a polyamide resin, a polycarbonate resin, a polysulfone resin, a polyether resin, a polyketone resin, and a polyacetal resin can be given. As the component (B), a polyolefin resin, particularly, polypropylene is preferable.

The content of the component (B) in the resin composition is from 90 to 10% by weight, preferably from 10 to 60% by weight, particularly preferably from 10 to 40% by weight.

The resin composition may further contain one or more compatibilizers selected from the following (C-1) to (C-4) as component (C). When a component that also acts as a compatibilizing agent with the component (B) is used as the component (A), the compatibilizing can be sufficiently performed only by the action alone. There is no.

(C-1) A copolymer comprising a vinyl aromatic compound and a conjugated diene compound or a hydrogenated product thereof. Examples of the vinyl aromatic compound include monomers used in the component (A) described above, and examples of the conjugated diene compound include butadiene, chloroprene, and isoprene.

(C-2) An epoxidized copolymer of a vinyl aromatic compound and a conjugated diene compound or a hydrogenated product thereof. Examples of the copolymer comprising a vinyl aromatic compound and a conjugated diene compound include a copolymer (C-1).

(C-3) A copolymer of a styrene monomer as a constituent unit of the component (A) and a monomer as a constituent unit of the component (B).

(C-4) A copolymer of a vinyl aromatic compound and a compound having a carboxyl group or an acid anhydride. Examples of the vinyl aromatic compound include the styrene-based monomer used in the component (A) described above, and examples of the compound having a carboxyl group and the acid anhydride are copolymerizable with the styrene-based monomer used in the component (A). Other monomers can be mentioned.

The content of the component (C) in the resin composition is 0.1 to 2 with respect to the total amount of the components (A) and (B).
0 parts by weight, preferably 1 to 10 parts by weight.

If necessary, a colorant such as a pigment, a dispersant such as a higher fatty acid salt, an inorganic filler such as talc, a conductivity-imparting agent, an antistatic agent, and silicone are added to the resin composition. be able to.

The synthetic resin sheet of the present invention is prepared by, for example, melting and kneading a pellet (resin pellet) made of the above resin composition with a usual extruder, and then using a circular die.
It can be obtained by extrusion molding through a T-die or the like.

The synthetic resin foam sheet of the present invention can be obtained by extrusion foam molding according to the method of molding a synthetic resin sheet. Examples of the foam molding method include a method of adding a chemical foaming agent and performing extrusion molding, a method of performing extrusion molding while injecting a foaming gas raw material, and a method of extruding a liquid foam gas raw material impregnated with a resin composition. Etc. can be applied. Examples of the chemical foaming agent and foam gas raw material include hydrocarbons such as sodium hydrogen carbonate, ammonium hydrogen carbonate, azodicarbonamide, azobisisobutyronitrile, liquid propane, and butane.

The synthetic resin foam sheet of the present invention preferably has at least one selected from the following requirements (a) to (c). Any one of these requirements may be provided, but it is particularly preferable that two requirements are provided, and it is more preferable that all three requirements are provided.

(A) The surface gloss is preferably at least 10%, particularly preferably at least 15%. If the surface gloss is 10% or more, even when stretched during molding,
Surface appearance does not deteriorate. The surface gloss is measured according to JIS
It is a value measured at an incident angle of 60 ° according to K7105.

(B) The expansion ratio is preferably from 1.1 to
3.0 times, and particularly preferably 1.4 to 2.2 times. When the expansion ratio is 1.1 times or more, the heat retention, heat insulation, and appearance are good, and when the expansion ratio is 3 times or less, the container has good stacking properties and is not bulky.

(C) The average number of cell membranes per unit thickness is
It is preferably 1 to 50 / mm, particularly preferably 5 to 40 / mm. When the average number of cell membranes is 1 / mm or more, heat retention, heat insulation and appearance are good, and when the number is 50 / mm or less, the container has good stiffness and impact resistance. The average number of cell membranes is obtained by collecting ultrathin sections from the width direction of the synthetic resin foam sheet, counting the number of cell membranes observable with an optical microscope in the thickness direction, and converting the number per mm.

In the synthetic resin sheet and the synthetic resin foam sheet of the present invention, it is preferable that the component (A) and the component (B) form a bicontinuous phase structure in order to enhance heat resistance and oil resistance. Here, "the component (A) and the component (B) form a bicontinuous phase structure" means that the sheet substrate has a MD direction (sheet substrate flow direction) and a TD direction (a direction orthogonal to the MD direction). In any of the directions, the styrene resin phase of the component (A) and the polyolefin resin phase of the component (B) do not exist in an independent state like particles or fibrous, but rather both phases. Means that a mixed phase structure is formed in a state of being connected to each other in a mesh shape.
When the synthetic resin sheet and the synthetic resin foam sheet have such a bicontinuous phase structure, the relationship between the volume change rate represented by the following formula (I) and the weight loss rate represented by the following formula (II) is satisfied. Things.

V ′ / V = 0.5 to 2.5 (I) [wherein, V ′ represents the volume (cm ³ ) of the sheet after immersion in tetrahydrofuran at 25 ° C. for 24 hours, and V represents the volume before immersion. Indicates the volume (cm ³ ) of the sheet. (W−W ′) / W × n _PS ≧ 0.7 (II) wherein W ′ represents the weight (g) of the sheet after immersion in tetrahydrofuran at 25 ° C. for 24 hours, and W represents the weight before immersion. The sheet weight (g) is shown, and n _PS is the styrene resin content ratio (% by weight) of the sheet before immersion. In the formula (I), V ′ / V is preferably 0.6 to 2.V.
0, particularly preferably 0.7 to 1.8. In the formula (II), (W−W ′) / W × n _PS is preferably from 0.75 to 1.0, particularly preferably from 0.8 to 1.
0.

The synthetic resin sheet and the synthetic resin foam sheet of the present invention have the shape and dimensions shown in FIG. 1 obtained by molding those sheets and have a thickness of 0.3 to 2.0 mm. When 100 g of edible oil is put into the oven and heated in a microwave oven of 500 W for 5 minutes, the following formula (1): h / h
₀ = 0.5 to 1.3 (1) [wherein, h ₀ denotes the depth at the center of the container bottom before heating, and h denotes the depth at the center of the container bottom after heating. ]
This satisfies the thermal deformability represented by When the numerical value of the formula (1) is less than 1, it means that the bottom of the tray-type container has mainly deformed in a convex shape, and when it exceeds 1, it means that the bottom of the tray-type container has mainly deformed in a concave shape. I do. The change in the numerical value of the equation (1) in the test is as follows.
It is not limited to the one due to the deformation of the bottom, but also includes the one due to the deformation of the side surface. A preferred numerical range in the formula (1) is 0.7 to 1.2, and particularly preferably substantially 1.

Further, the synthetic resin sheet and the synthetic resin foam sheet of the present invention satisfy the thermal deformability represented by the formula (1), and have no practical problem when applied as a side dish container after heating. So that preferably the diameter is 0.5
The pinhole having a diameter of 0.3 mm or more, particularly preferably 0.3 mm or more, is not formed.

The synthetic resin sheet and the synthetic resin foam sheet of the present invention can be laminated into two or more layers by laminating resin non-foam sheets made of the same or different materials on one or both surfaces. The resin non-foamed sheet used in this case can be appropriately selected from desired materials in accordance with the intended use and properties to be imparted, for example, heat resistance, abrasion resistance, improvement in surface appearance, printability, and the like. . Known methods such as a co-extrusion method and a dry lamination method can be applied as a method for manufacturing the laminate.

The container of the present invention is obtained by molding the above-described synthetic resin sheet or synthetic resin foam sheet into a desired shape. The term “container” as used in the present invention includes a main body and a lid. For example, a container for a side dish includes a tray and a lid. The container of the present invention is suitable as a food container, particularly a food container containing a large amount of oil, but is not limited thereto, and is heated in various types of instant food containers of a type in which boiling water is poured, paper cups, microwave ovens, and the like. It can also be applied to containers that are heat-sterilized at the time of manufacture and use, various non-heated containers, and the like.

[0033]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. In addition, each test below was performed by the following method.

(1) Heat resistance of microwave oven (h / h ₀ value) 100 g of edible salad oil (manufactured by Nisshin Oil Co., Ltd.) was placed in a tray type container having the shape and dimensions shown in FIG.
The h / h ₀ value represented by the formula (1) when heated in a 500 W microwave oven for 5 minutes was determined.

(2) Existence of Pinholes After the microwave heat resistance test, the tray type container is visually inspected for pinholes (colored portions of salad oil). 0.5
mm or more was measured using a foreign matter measurement chart (manufactured by the Ministry of Finance, Printing Bureau). ：: No pinhole with an area of 0.2 mm ² or more. ×: There is a pinhole with an area of 0.2 mm ² or more.

(3) Stackability 100 tray-type containers having the shape and dimensions shown in FIG. 1 were formed, and the height (stack height) when all of them were overlapped was measured to evaluate the stackability. This shows that the smaller the value of the stack height is, the better the moldability is, and a thinner, sharper molded product can be obtained.

Examples 1 to 12 and Comparative Examples 1 to 2 Using a resin composition comprising the components (A), (B) and (C) having the compositions shown in Table 1, a synthetic resin sheet was prepared by the following method. A synthetic resin foam sheet was manufactured. In Table 1,
The components (A) and (B) are expressed in weight%, and the component (C) is expressed in parts by weight based on the total amount of the components (A) and (B). The details of the component (A), the component (B), and the component (C) are as follows.

(A) Component GPPS: Styrene resin ("Daicel Styrol 51" manufactured by Daicel Chemical Industries, Ltd.) HIPS: High impact polystyrene resin ("Daicel Styrol S85" manufactured by Daicel Chemical Industries, Ltd.); rubber content: 8 weight %) SBS: Styrene-butadiene block copolymer ("Tafprene 126" rubber content 60% by weight, manufactured by Asahi Chemical Industry Co., Ltd.) (B) Component PP-1: Polypropylene ("F109D" manufactured by Grand Polymer Co., Ltd.) PP -2: polypropylene ("F219D" manufactured by Grand Polymer Co., Ltd.) PP-3: polypropylene ("F769" manufactured by Grand Polymer Co., Ltd.) (C) component (compatibilizer) (C-3a): styrene-ethylene- Propylene-styrene copolymer ("Septon 2104" manufactured by Kuraray Co., Ltd.) (C-3b) : Styrene-ethylene-butylene-styrene copolymer (“Clayton G165” manufactured by Shell Co., Ltd.)
0 ") (C-2): hydrogenated epoxy-modified styrene-butadiene copolymer (JP-A-7-25984, page 2, column 2, 31)
To 43 lines, according to Daicel Chemical Industries, Ltd.
Obtained by hydrogenating Epo Friend A1020 manufactured by Nihon Kabushiki Kaisha).

After melt-kneading such a resin composition with a twin-screw extruder (PCM30 / 2-28.5-2V, manufactured by Ikegai Co., Ltd.),
The extruded strand was cut to obtain a resin pellet. In Example 12 and Comparative Example 1, resin pellets were supplied to an extruder (φ65 mm, L / D = 32), melt-kneaded, extruded from a T-die, and quenched to obtain a synthetic resin sheet. The extruder and T-die exit temperatures were adjusted according to the Vicat softening point of the resin pellets. Example 1
11. In Comparative Example 2, first, with respect to the resin pellet,
One part by weight of mineral oil was spread, and a mixture of sodium bicarbonate and sodium citrate (manufactured by Sankyo Chemical Co., Ltd .; CellMic 623) as a foaming agent was blended in the amount shown in Table 1, and a composition for foam molding was prepared. I got Next, these compositions were supplied to an extruder (φ6 mm, L / D = 32), melt-kneaded, extruded from a T-die, foamed, and rapidly cooled to obtain a synthetic resin foam sheet. The extruder and T-die exit temperatures were adjusted according to the Vicat softening point of the resin pellets. The containers shown in FIG. 1 were molded from these resin sheets using a single-shot vacuum molding machine manufactured by Asano Laboratories, and the above-described tests were performed. Table 1 shows the results.

[0040]

[Table 1]

The containers obtained from the sheets of Examples 1 to 12 had a small thermal deformation and were of no practical problem. Also, no pinholes were produced at all, including those with a diameter of 0.5 mm or less. Furthermore, as is clear from the good stackability, the moldability was also excellent. The sheets of Examples 1 to 12 had a bicontinuous phase structure, and satisfied the relationship between the volume change rate represented by the above formula (I) and the weight loss rate represented by the formula (II).

[0042]

The synthetic resin sheet and the synthetic resin foam sheet of the present invention have excellent heat resistance in a microwave oven. Therefore, when molded into a food container such as a side dish, the deformation is small even when the container is heated. For this reason, even if the food is eaten as it is after heating, it is not difficult to eat and the contents do not spill out, so that the user's ease of use is improved.

[Brief description of the drawings]

FIG. 1 is a front view and a plan view of a container used for a microwave heat resistance test.

Claims (11)

[Claims] (A) 10 to 90% by weight of a styrene resin
And (B) a thermoplastic resin 90 having a melting point of 100 to 300 ° C.
A sheet obtained from a resin composition containing 10 to 10% by weight, wherein the sheet has a shape and dimensions shown in FIG. 1 obtained by molding the sheet, and has a thickness of 0.3 to 2.0 mm. tray-type container was charged with cooking oil 100 g, the following equation in the case of heating for 5 minutes at 500W microwave oven _{(1): h / h 0} = 0.5~1.3 (1) [ wherein, h ₀ is The depth at the center of the container bottom before heating is shown, and the h is the depth at the center of the container bottom after heating. ]
A synthetic resin sheet that satisfies the heat deformability represented by: 2. The synthetic resin according to claim 1, wherein the content of the styrenic resin (A) is 60 to 90% by weight, and the content of the thermoplastic resin (B) is 40 to 10% by weight. Sheet. 3. The synthetic resin sheet according to claim 1, which satisfies the thermal deformability represented by the formula (1) and does not generate a pinhole having a diameter of 0.5 mm or more after heating. A synthetic resin sheet. 4. The resin composition according to claim 1, further comprising at least one compatibilizer selected from the following (C-1) to (C-4) as a component (C). 3. The synthetic resin sheet according to 3. (C-1) a copolymer of a vinyl aromatic compound and a conjugated diene compound or a hydrogenated product thereof; (C-2) an epoxidized product of a copolymer of a vinyl aromatic compound and a conjugated diene compound; or (C-3) a copolymer of a styrene monomer serving as a constituent unit of the component (A) and a monomer serving as a constituent unit of the component (B), and (C-4) a vinyl aromatic compound. , A copolymer with a compound having a carboxyl group or an acid anhydride. 5. A container comprising the synthetic resin sheet according to any one of claims 1 to 4. 6. (A) 10 to 90% by weight of a styrene resin
And (B) a thermoplastic resin 90 having a melting point of 100 to 300 ° C.
A foamed sheet obtained from a resin composition containing from 10 to 10% by weight, wherein the foamed sheet has a shape and dimensions shown in FIG. 100 g of edible oil is placed in a tray type container having a range of 0 mm, and 500 W
H / h ₀ = 0.5 to 1.3 when heating in a microwave oven for 5 minutes: h / h ₀ = 0.5 to 1.3 (1) wherein h ₀ represents the depth at the center of the bottom of the container before heating, h indicates the depth at the center of the bottom of the container after heating. ]
A synthetic resin foam sheet characterized by satisfying the heat deformability represented by: 7. The synthetic resin according to claim 6, wherein the content of the styrene resin (A) is 60 to 90% by weight, and the content of the thermoplastic resin (B) is 40 to 10% by weight. Foam sheet. 8. The synthetic resin foam sheet according to claim 6, which satisfies the thermal deformability represented by the formula (1) and does not generate a pinhole having a diameter of 0.5 mm or more after heating. A synthetic resin foam sheet, characterized in that: 9. The resin composition further comprises at least one compatibilizer selected from (C-1) to (C-4) according to claim 3 as the component (C). 9. The synthetic resin foam sheet according to 7, 8 or 9. 10. The synthetic resin foam sheet according to claim 6, which has one or more requirements selected from the following (a), (b) and (c). (A) The surface gloss of the foam sheet substrate is 10% or more. (B) The expansion ratio is 1.1 to 3.0 times. (C) The average number of cell membranes per unit thickness is 1 to 50. Pieces / mm
Being 11. A container comprising the synthetic resin foam sheet according to any one of claims 6 to 10.