JPH11129369A - Synthetic resin foam sheet and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a synthetic resin foam sheet having excellent moldability (particularly deep drawing moldability), surface uniformity of molding and hygienic qualities, by effectively utilizing recovered resin. SOLUTION: The synthetic resin foam sheet comprises a base foam layer formed of a recycled resin or virgin resin, and a surface layer of a virgin resin formed on at least one surface of the foam layer. In the foam sheet, the surface layer may be a foam layer. The foam layer and the surface layer can be formed of a styrene resin such as a rubber modified styrene resin or the like. A foaming magnification of each of the base foam layer and the surface foam layer is 1.3 to 2.5 times. A ratio of the base foam layer is 0 to 99% of the overall foam sheet. The number of mean foam films per unit thickness in each of the base foam layer and the surface foam layer is 20 to 50 pieces/mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a synthetic resin foam sheet suitable as a molding material for food trays and the like, a method for producing the same, and a molded container.

[0002]

2. Description of the Related Art As containers for storing foods, containers formed from synthetic resin foam sheets are widely used. For example, Japanese Patent Application Laid-Open No. Hei 5-96676 discloses a styrene resin foam sheet having a two-layer structure in which a high foam layer and a low foam layer are laminated. However, since this sheet contains a highly foamed layer, the sheet or molded product becomes bulky,
As transport costs increase, stack heights increase, requiring large inventory or storage space. further,
Because of the bulkiness, the collection process of the container-formed skeleton becomes complicated. Japanese Patent Publication No. 54-40266 discloses that a sheet is produced in an unfoamed or low-foamed state, and is heated and foamed into a two-layer structure at the time of molding separately and stretched to produce a raw material of a molded article, and the raw material is subjected to molding. A method for forming a laminated styrene resin foam sheet is disclosed. Although this method can reduce the transportation cost and the inventory space, the operation during molding is complicated and the total cost is increased.

[0003] JP-A-6-182948 discloses a sheet having a two-layer structure in which a foamed layer and an unfoamed layer are laminated. Japanese Patent Publication No. 5-54810, JP-A-3-6
Japanese Patent No. 1042 discloses a three-layer styrene-based foam sheet having a foamed layer as a central layer and non-foamed layers laminated on both sides of the central layer. A styrene foam sheet having a three-layer structure in which a foam layer is used as a center layer and a foam layer is laminated on both sides of the center layer is disclosed. JP-A-4-191038, JP-A-4-1938
JP-A-364920 discloses a three-layer structure comprising a central layer, which is extruded and foamed from a circular die into a tubular shape, and a surface layer laminated on both sides of the central layer and having bubbles of a specific shape having a small average cell diameter. A foamed sheet of structure is disclosed. However, when these foamed sheets are subjected to deep drawing, bubbles are stretched by stretching stress, and the surface uniformity and appearance of the molded product are impaired.

Japanese Patent Publication No. 61-3820 discloses that the rubber content is 20% or less, the expansion ratio is 1.5 to 7.0, and the thickness is 0.
An extruded polystyrene sheet for heat molding of a thin-walled molded product having a thickness of 3 to 1.0 mm, a number of cell membranes in a thickness direction of 5 to 20, and a residual gas amount of 0.3 mol / kg or less is disclosed. Although the balance of bulkiness and strength of the molded product obtained from this expanded polystyrene sheet is at a practical level, not only is the sheet's concealing power small, but when stretched by the stress during molding, bubbles are noticeable, and the molded product The surface uniformity and appearance are deteriorated. Furthermore, in recent years, recycling of molding materials has been desired in order to protect the environment, effectively use resources, and reduce costs. However, from the viewpoint of food hygiene and the like, molded sheets for containers that store the collected resin in foods, etc. It is difficult to effectively recycle.

[0005]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a synthetic resin foam sheet having excellent moldability (particularly, deep drawability) and excellent surface uniformity of a molded article, and a method for producing the same. Another object of the present invention is to provide a synthetic resin foam sheet capable of improving economic efficiency by effectively reusing a recovered resin and ensuring high hygiene even when reusing a resin, and a method for producing the same. Is to provide. Still another object of the present invention is to provide a synthetic resin foam sheet which has high transportation efficiency and can accommodate many foam sheets or foam molded articles in a small storage or storage space, and a method for producing the same.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and have found that at least one surface of a base foamed layer made of recycled resin or virgin resin has a surface of virgin resin. Using a synthetic resin foam sheet having a low foaming ratio with a layer formed thereon, it has been found that a molded article having high deep drawability and surface uniformity can be obtained, and the present invention has been completed.

That is, the present invention provides (1) a synthetic resin foam sheet comprising a base foam layer containing a recycled resin and a virgin resin surface layer formed on at least one surface of the base foam layer. (2) A synthetic resin foam sheet comprising a virgin resin base foam layer and a virgin resin surface layer formed on at least one surface of the base foam layer. In this foam sheet, the surface layer may be a non-foam layer or a foam layer. Further, the base foamed layer and the surface layer of the present invention can be formed of a styrene resin such as a rubber-modified styrene resin. Further, the foamed synthetic resin sheet of the present invention has a surface foamed layer or a non-foamed layer formed on at least one surface of the base foamed layer, and when the surface layer is a foamed layer, the base foamed layer and the surface foamed layer The expansion ratio is 1.3 to 2.5 times, and the ratio of the base foam layer is 40 to 99 of the entire synthetic resin foam sheet.
In weight%, the average number of cell membranes per unit thickness in the base foam layer and the surface foam layer may be 20 to 50 cells / mm. Further, the synthetic resin foam sheet of the present invention has a base foam layer formed of a styrene resin containing a rubber-modified styrene resin, and a styrene foam formed on both sides of the base foam layer and containing a rubber-modified styrene resin. A synthetic resin foam sheet having a thickness of 0.5 to 1.5 mm constituted by a surface foamed layer or a non-foamed layer formed of a resin,
The base foam layer accounts for 55 to 70% by weight of the entire sheet and is colored, and the average number of cell membranes per unit thickness of the sheet in the base foam layer and the surface foam layer is 23 to 48 / mm, respectively. You may. The synthetic resin foam sheet melt-kneads a first resin composition for forming a base foam layer and a second resin composition for a surface layer formed on at least one surface of the base foam layer. And extruded and foamed in a die. In the present specification, the “average number of cell membranes” means that when a cross section in the thickness direction of the foamed sheet is observed with a microscope, air bubbles existing in the thickness direction at least at five places except for the skin layer of each foamed layer. Mean the number of partition walls.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The synthetic resin foam sheet of the present invention comprises:
A base foam layer, and a surface layer formed on at least one surface of the base foam layer; (1) the base foam layer is formed of a resin containing a recycled resin, and the surface layer is made of a virgin resin And (2) the base foamed layer is formed of a resin containing a virgin resin, and the surface layer is formed of a virgin resin. In the first and second embodiments, examples of the synthetic resin forming the center layer and the surface layer include acrylic resins such as styrene-based resins, polyester-based resins, polyvinyl chloride and poly (meth) acrylate, and acetic acid. Cellulose derivatives such as cellulose, olefinic resins such as polyethylene and polypropylene, polycarbonates, polyamides, polyesteramides, polyphenylene ethers, polyimides, polyamideimides, polyetheresters and the like are mentioned. The synthetic resin contains a unit containing these resin units. It may be a polymer or a modified product.
These synthetic resins can be selected from resins of the same system or different systems, and used alone or in combination of two or more. Further, the same or different synthetic resins can be used in an appropriate combination in the base foam layer and the surface layer. Preferred synthetic resins include resins having high extrudability and processability, such as styrene-based resins, modified phenylene ethers (eg, polystyrene-modified polyphenylene ether by mixing or grafting with styrene-based resins) and olefin-based resins. In particular, in order to enhance the deep drawability, a combination of (a) a styrene resin and (b) a combination of a styrene resin and modified polyphenylene ether is included.

Examples of the styrene resin include a homopolymer of a styrene monomer, a copolymer of a styrene monomer and a copolymerizable vinyl monomer, and a rubber-modified styrene resin (such as a styrene thermoplastic elastomer). And the like). Styrene-based monomers include, for example, styrene, styrene derivatives (e.g., p-methylstyrene, p-ethylstyrene, p-isopropylstyrene, butylstyrene,
t-butylstyrene, α-methylstyrene, alkylstyrene such as vinyltoluene, etc.). Preferred styrene monomers include styrene and α-methylstyrene. Examples of the copolymerizable vinyl monomer include a vinyl cyanide monomer (eg, acrylonitrile, methacrylonitrile) and a (meth) acrylate monomer (eg, (meth) acrylic acid such as methyl methacrylate). Hydroxyl group-containing (meth) acrylates and glycidyl (meth) acrylates such as C _1-10 alkyl esters, 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate; and carboxyl group-containing monomers ((Meth) acrylic acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, etc.), and maleimide monomers (maleimide, N-methylmaleimide, N-butylmaleimide, N-phenylmaleimide, etc.). . Preferred copolymerizable vinyl monomers include (meth) acrylic esters such as methyl methacrylate, (meth) acrylic acid, maleic anhydride, and maleimide monomers such as N-phenylmaleimide.

The homopolymer of the styrene monomer includes polystyrene, and the copolymer using the styrene monomer includes a styrene-acrylonitrile copolymer (AS).
Resins), styrene-methyl methacrylate copolymer, styrene- (meth) acrylic acid copolymer, styrene-maleic anhydride copolymer, and the like.

[0011] The rubber-modified styrenic resin is an impact-resistant styrenic resin (mixture of a rubber component and a styrene-based resin which may be rubber-modified, at least a styrene-based monomer in the presence of the rubber component). Graft copolymer obtained by polymerizing a polymer) or an ABA type block copolymer. Usually, a graft copolymer or a block copolymer is often used, and the block copolymer often forms a thermoplastic elastomer. This graft copolymer may be a random copolymer, and the structure of the graft copolymer or the block copolymer may be linear or star (star).
It may be. Examples of the rubber component include conjugated diene rubber (polybutadiene, polyisoprene, 2-chloro-1-1,3-butadiene, 1-chloro-1,3-butadiene, butadiene-styrene copolymer, etc.), ethylene- Examples thereof include propylene rubber (EPDM rubber), acrylic rubber, ethylene-vinyl acetate copolymer, and chlorinated polyethylene. These rubber components can be used alone or in combination of two or more. As a preferable rubber component, a conjugated diene rubber is often used. In the graft polymer, at least a styrene monomer may be used, but the styrene monomer is often used in combination with a vinyl cyanide monomer, and if necessary, the copolymerizable vinyl monomer may be used. The body may be used in combination. The ratio between the styrene monomer and the vinyl cyanide monomer is, for example, styrene monomer monomer / vinyl cyanide monomer = 10/90
To 90/10 (% by weight), preferably 20/80 to 80
/ 20 (% by weight), more preferably 30/70 to 70
/ 30 (% by weight). The ratio between the styrene monomer and the copolymerizable vinyl monomer is, for example, styrene monomer / copolymerizable vinyl monomer = 10/90 to 100
/ 0 (% by weight), especially about 30/70 to 70/30 (% by weight). The content of the rubber component in the rubber-modified styrenic resin is, for example, 5 to 50% by weight, and preferably 6 to 50% by weight.
About 40% by weight, more preferably about 6 to 30% by weight. The rubber-modified styrenic resins can be used alone or in combination of two or more.

Preferred rubber-modified styrenic resins include graft polymers [especially high-impact (HI) polystyrene, for example, styrene-butadiene copolymer (SB).
Resin), butadiene-styrene-maleic anhydride copolymer (rubber-modified styrene-maleic anhydride copolymer), styrene-acrylonitrile-butadiene copolymer (AB
S resin), AXS resin (where A is acrylonitrile,
X is at least one rubber component selected from ethylene-propylene rubber (EPDM rubber), acrylic rubber, ethylene-vinyl acetate copolymer, chlorinated polyethylene, and S represents styrene)], styrene block copolymer (For example, thermoplastic elastomers such as styrene-butadiene-styrene (SBS) copolymer and styrene-isoprene-styrene (SIS) copolymer). These rubber-modified styrene resins are hydrogenated products. You may. Particularly preferred rubber-modified styrenic resins include SB
Resin, rubber-modified styrene-maleic anhydride copolymer, styrene-acrylonitrile-butadiene copolymer (AB
S resin), styrene-butadiene-styrene (SBS)
Block copolymers, styrene-isoprene-styrene (SIS) block copolymers, and hydrogenated products thereof are included.

The styrenic resin includes a plurality of different styrenic resins, for example, a homopolymer or a copolymer of a styrenic monomer (eg, polystyrene), a styrenic monomer and a copolymerizable vinyl monomer. And a copolymer (eg,
AS resin, styrene-maleic anhydride copolymer, etc.),
Rubber-modified styrene resin (for example, SB resin, ABS
Or a combination of two or more resins selected from impact-resistant styrene resins such as resins, thermoplastic elastomers such as SBS block copolymers and SIS block copolymers). In particular, in order to impart a high level of rigidity, strength and impact resistance to a foamed sheet or molded article in a well-balanced manner, it is necessary to use styrene with at least one kind of rubber-modified styrene resin (particularly impact-resistant polystyrene or thermoplastic elastomer). It is preferable that the styrene resin composition is composed of a plurality of styrene resins including at least a rubber-modified styrene resin. Such a styrenic resin or a styrenic resin composition includes (1)
A homo- or copolymer of a styrene monomer (particularly, polystyrene which is a homopolymer of styrene) and a rubber-modified styrene resin (particularly, SB resin, ABS resin, rubber-modified styrene-maleic anhydride copolymer, etc.) (A thermoplastic elastomer such as impact-resistant polystyrene or SBS block copolymer) and, if necessary, a copolymer of a styrene monomer and a copolymerizable vinyl monomer (for example, AS resin) And (2) one or more rubber-modified styrene-based resins, and, if necessary, a homo- or copolymer of styrene-based monomers and a styrene-based monomer and a copolymerizable vinyl monomer. In combination with a copolymer of the above.

In such a styrene resin or styrene resin composition, the rubber content is, for example, 5 to 20.
%, Preferably about 6 to 15% by weight, more preferably about 6 to 10% by weight (for example, 7 to 10% by weight), and often about 5 to 10% by weight. If the rubber content exceeds 20% by weight, the waist strength of the foamed sheet decreases,
If it is less than 5% by weight, the impact resistance will be reduced. Further, in order to impart deep drawing formability and impact resistance, the styrene content in the styrene resin or the styrene resin composition is, for example, 20 to 80% by weight, preferably 25 to 75% by weight.
(For example, 30 to 60% by weight).

The styrenic resin composition can be prepared according to the rubber content and styrene content of each component. For example, (1) 100 parts by weight of a styrene monomer alone (particularly polystyrene) A copolymer of a styrene monomer and a copolymerizable vinyl monomer (eg, an AS resin) in an amount of 0 to 100 parts by weight (preferably about 0 to 50 parts by weight); 100 parts by weight (preferably 20 to 80 parts by weight, more preferably 30 parts by weight
To 70 parts by weight) of a styrenic resin composition, (2)
One or more rubber-modified styrene-based resins are used in an amount of 100 parts by weight, and the styrene-based monomer homo- or copolymer 0
A styrene resin composition of about 50 to 50 parts by weight, about 0 to 50 parts by weight of a copolymer of a styrene monomer and a copolymerizable vinyl monomer may be used.

In the present invention, the base foam layer can be formed of recycled resin (recycled resin) or virgin resin (new material resin), and the surface layer can be formed of virgin resin (new material resin). Recycled resin refers to waste material generated by primary processing or secondary processing of a synthetic resin such as a sheet (for example, slit scrap at the end of a styrene resin sheet which may be foamed,
Dust after container molding, re-pelleted product, off-spec product of non-standard generated in the process of changing rubber content in the production of rubber-modified styrenic resin, etc.), distributed as a product on the market, and used by consumers after use It refers to discarded waste (waste products) and regenerated products such as pellets obtained by collecting and repelling waste. The virgin resin (new material resin) means an unprocessed resin other than the recycled resin.

A preferred recycled resin is a synthetic resin which has a low molecular weight, a small amount of decomposition, gelling and coloring even after a plurality of heat histories. For example, the styrene resin and the non-styrene resin (for example, the modified polyphenylene ether) And the like. As the styrene resin, particularly, a homopolymer or copolymer of a styrene monomer (such as polystyrene), a copolymer of a styrene monomer and a vinyl monomer (such as an AS resin), a rubber-modified styrene resin ( Impact-resistant styrenic resins and thermoplastic elastomers) are preferred. When a styrene-based resin composition is formed by combining a styrene-based resin and a non-styrene-based resin (such as a modified polyphenylene ether), the ratio of the two is, for example, the former / the latter = 60/40 to 100/0 (weight). %), Preferably in the range of about 70/30 to 100/0 (% by weight). In the base foam layer containing the recycled resin, the ratio between the recycled resin and the virgin resin is, for example, the former / the latter = 20/80 to 100/0.
(% By weight), preferably in the range of about 30/70 to 100/0 (% by weight), and more preferably in the range of about 40/60 to 100/0 (% by weight).

The base foam layer formed of a recycled resin or a virgin resin may be colored. This coloring is often caused by the recycled resin. That is, the recycled resin is often colored due to heat history, contamination or coloring accompanying the primary or secondary processing. For example, if scraps after forming a container are re-pelletized and repeatedly used for extrusion, hygiene is impaired. However, even if the base foam layer is colored, by laminating the virgin resin surface layer (especially the surface foam layer) covering the base foam layer,
High hygiene can be secured. Therefore, by using recycled resin such as waste material, the commercial value of foamed sheets and foamed molded products can be increased. The colored base foam layer may be formed by using a resin composition containing a coloring agent in addition to the recycled resin. In addition, also when forming a base foaming layer using a virgin resin, the base foaming layer may be colored by using a resin composition containing a coloring agent. The coloring degree and hue of the base foam layer are not particularly limited, and may be yellow, orange, red, purple, blue, gray, black, or the like. When coloring the base foam layer with a coloring agent, the amount of the coloring agent used is, for example,
0.0 to 100 parts by weight of the resin component for the base foam layer
It can be selected from the range of about 1 to 30% by weight, preferably about 0.1 to 10% by weight.

The synthetic resin foam sheet may have a two-layer structure in which a surface layer (an unfoamed surface layer and a foamed surface layer) is formed on one side of the base foamed layer. It may have a three-layer structure in which an unfoamed surface layer and a foamed surface layer are formed. In the case of a sheet having a three-layer structure in which a surface layer is formed on both surfaces of the base foam layer, a surface foam layer is formed on one surface of the base foam layer, and a non-foam surface layer is formed on the other surface. Is also good. A preferred surface layer is a foam layer. Further, the surface layer may be a non-foamed layer, and the non-foamed layer may be a skin layer formed on the surface of the foamed layer (particularly a skin layer formed of a virgin resin).

In the foamed sheet composed of the base foamed layer and the surface layer, the expansion ratio of the base foamed layer can be selected according to the intended use, desired characteristics, and the like. In order to enhance the deep drawing formability, for example, it is about 1.3 to 2.5 times, preferably about 1.5 to 2.4 times, more preferably about 1.7 to 2.3 times, and about 1.4 to 1.4 times. It may be about 2.0 times. When the surface layer is a foamed layer, the base foamed layer and the surface foamed layer may have different foaming ratios, but often have substantially the same foaming ratio, and the foaming ratio of the foamed sheet is often large. Is, for example, a magnification similar to the above, that is, 1.
3 to 2.5 times, preferably 1.5 to 2.4 times, more preferably 1.7 to 2.3 times, and 1.4 to 2.0 times.
It may be about twice. When the expansion ratio exceeds 2.5 times, the deep drawability deteriorates, the surface of the molded product becomes rough, and the aesthetic appearance is easily impaired. When the expansion ratio is less than 1.3 times, the sheet becomes hard and bubbles are conspicuous at the time of molding. Is easily damaged. The expansion ratio can be adjusted by the type and amount of the foaming agent.

The proportion of the base foam layer in the entire synthetic resin foam sheet varies depending on the structure of the foam sheet, the presence or absence of foaming of the surface layer, and the like. % By weight (for example, 50 to
75% by weight), preferably 40 to 80% by weight (for example,
55-70% by weight), more preferably about 40-70% by weight (for example, 60-70% by weight). If the proportion of the base foamed layer is less than 40% by weight, the recovery ratio of the recovered material is reduced, which is disadvantageous in terms of cost and 99%.
If the amount exceeds 10% by weight, the utilization rate of the recovered material increases, which is not preferable from the viewpoint of food hygiene. When a non-foamed surface layer or a surface foamed layer is formed on both surfaces of the base foamed layer, the thickness of each surface layer may be the same or different.

The foamed sheet of the present invention comprising a base foamed layer containing a recycled resin (or a base foamed layer of a virgin resin) and a surface layer of a virgin resin has a base foamed layer (when the surface layer is a foamed layer). Is characterized in that the average number of cell membranes per unit thickness is large. A foamed sheet having such a foamed layer has high deep drawability and surface uniformity of a molded container. That is, two layers or three
The average number of cell membranes per unit thickness of the base foam layer, particularly the entire foam layer (base foam layer and surface foam layer) constituting the layered foam sheet is, for example, 20 to 50 / cell.
mm, preferably 23 to 48 pieces / mm, more preferably 25 to 45 pieces / mm (for example, 25 to 40 pieces / mm)
It is about. In a foamed sheet having a thickness of about 0.3 to 2 mm, the average number of cell membranes in the thickness direction is 20 to 50 (preferably 23 to 48, more preferably 25 to 4).
5). When the average number of cell membranes exceeds 50 / mm, the ductility of the sheet is impaired, and the deep drawability tends to decrease. When the average cell number is less than 20 / mm, the concealing power of the sheet is small and bubbles are noticeable due to stretching during molding. The appearance is impaired.
When the surface layer is composed of a foamed layer, the average number of cell membranes per unit thickness of the base foamed layer and the surface layer may be different from each other within the above range. Often it is. The average number of bubble films is, for example,
It can be adjusted by the production conditions such as the amount of the nucleating agent added, the extrusion temperature, and the cooling conditions. When the surface layer is a non-foamed layer, the proportion of the base foamed layer is about 80 to 99%, preferably about 90 to 99%, of the total thickness of the synthetic resin foam sheet. When the proportion of the base foamed layer is less than 80%, the thickness of the non-foamed layer becomes large, and the appearance, heat insulating properties, and container strength are reduced.
If it exceeds 9%, the impact resistance is reduced, or the appearance is deteriorated due to foam breaking. The resin composition of the non-foamed surface layer may be the same as the base foamed layer, or may be a virgin resin. In a synthetic resin foam sheet whose surface layer is a non-foam layer, the average number of cells in the thickness direction is about 20 to 50 / mm.

The thickness of the foamed sheet can be selected according to the intended use, desired physical properties, etc., and is, for example, 0.3 to 2.0 mm, preferably 0.5 to 1.5 mm, more preferably 0.7 to 1.5 mm.
About 1.2 mm, and often about 0.7 to 1.5 mm. If the thickness of the foamed sheet is less than 0.3 mm, the stiffness decreases, and if it exceeds 2.0 mm, the stack height of the molded article increases, and a large storage space is required. In addition, the sheet thickness is the expansion ratio, the discharge amount of the extruder,
It can be adjusted by the take-up speed of the take-up machine.

The foamed sheet of the present invention only needs to have a two-layer or three-layer structure composed of at least a base foam layer and a surface layer. In addition, another coating layer (for example, a laminate layer of polypropylene or the like) that does not impair sanitary properties or deep drawability may be laminated.

[Manufacturing Method] The foamed synthetic resin sheet of the present invention is prepared in advance by preparing one of a foamed sheet constituting the base foamed layer and a sheet constituting the surface layer, and then forming one of the foamed sheets by means of an adhesive or heat fusion. It can be manufactured by laminating the other sheet on the other sheet, but the productivity and economy is to manufacture using an extruder equipped with a plurality of extruders and a joining die such as a crosshead die. This is advantageous from the point of view. The die has a lip opening (for example, 0.1 to 1.5) corresponding to the thickness of the synthetic resin foam sheet.
mm, preferably about 0.3 to 1 mm), and may be flat, T-shaped (T die), cylindrical (ring die), or the like. A preferred die is a T die (a multi-manifold die or the like).
Layer or three-layer T-die) and ring die (two-layer or three-
Layer inflation dies, etc.). A first resin composition for forming a base foam layer and a second resin composition for a surface layer formed on at least one surface of the base foam layer are supplied to the extruder through a hopper. Then, each resin composition is melt-kneaded by an extruder, combined in a die, extruded and foamed, thereby obtaining a foamed sheet. In addition, as a method of increasing the number of cell membranes and the expansion ratio, the shape of the screw is changed to a shape having high kneading properties (for example, a screw with a mixing function such as a full-flat screw with a mixing pin having a plurality of protrusions). (Plastics AG Co., Ltd., “Extrusion molding”, supervised by Kenkichi Murakami, p. 154), a method of cooling with a T-die having a coolable structure, and the like.

As described above, a styrene resin or a modified polyphenylene ether is often used as the first resin composition and the second resin composition. In particular, a rubber-modified styrene resin and, if necessary, In many cases, a styrene-based resin composition containing a modified polyphenylene ether [particularly, a styrene-based resin composition having a rubber component content of about 5 to 20% by weight (for example, 5 to 10% by weight)] is used. The first resin composition for forming the base foam layer may be a resin composition containing a recycled resin as described above,
It may be a resin composition composed of a virgin resin. As the recycled resin, a waste material or a waste product generated by primary processing or secondary processing of the sheet can be used, and the ratio between the recycled resin and the virgin resin is as described above.

The first resin composition contains a foaming agent.
When the surface layer is a non-foamed layer, the second resin composition does not need to contain a foaming agent, but when the surface layer is a foamed layer, the second resin composition also contains a foaming agent. . As the foaming agent, conventional compounds, for example, volatile foaming agents such as propane, butane, pentane and hexane, ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, sodium citrate, azo compounds (azobisisobutyronitrile, Azodicarbonamide, diazoaminobenzene, etc.), sulfonylhydrazide compounds (benzenesulfonylhydrazide, p-toluenesulfonylhydrazide, diphenyloxy-4,4'-bissulfonylhydrazide, etc.), nitroso compounds (N, N'-dinitrosopentamethylene) Examples thereof include a chemical foaming agent (decomposition type foaming agent) such as tetramine, carbon dioxide, nitrogen gas, and water.
These blowing agents may be used in combination. The content of the foaming agent is, for example, 0.1 to 5 parts by weight, preferably 0.3 to 5 parts by weight based on 100 parts by weight of the resin component of the resin composition.
2.5 parts by weight, more preferably about 0.5 to 1.5 parts by weight. The blowing agent may be impregnated into the resin component.

In order to adjust the average number of cell membranes, it is advantageous that the first resin composition (and, if necessary, the second resin composition) contains a nucleating agent. As a nucleating agent, inorganic fine powder,
For example, talc, silica, diatomaceous earth, clay, alumina, calcium carbonate, barium sulfate and the like can be mentioned.
The amount of the nucleating agent can be selected according to the desired average number of cell membranes and the like. For example, 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, per 100 parts by weight of the resin component of the resin composition.
It can be selected from a range of about parts by weight. Further, the first or second resin composition may contain other additives, for example, an antioxidant,
Stabilizers such as ultraviolet absorbers, plasticizers, flame retardants, antistatic agents, fillers, spreading agents (eg, polyethylene glycol, mineral oil, etc.) may be added.

The sheet extruded and foamed from the die of the extruder is uniaxially or biaxially stretched as required, and rapidly cooled to obtain a foamed sheet. When a ring die is used, the foamed sheet can be obtained by folding the cylindrical sheet with a pinch roll and cutting open the sheet by trimming. In order to improve the appearance and the like, the synthetic resin foam sheet is formed by extrusion lamination or dry lamination using an adhesive (vinyl acetate adhesive, ethylene, vinyl acetate adhesive, urethane adhesive, etc.). (Polyethylene, polypropylene,
Polystyrene). Further, a release agent (polysiloxane in the form of an emulsion or the like) may be applied to the synthetic resin foam sheet.

The synthetic resin foam sheet thus obtained is usually wound up by a winding roll or the like, and is subjected to a molding process such as a container molding with the surface layer being an inner surface. Usually, the container can be constituted by an accommodation recess for accommodating an object to be accommodated, and a flange portion extending from an upper end of the accommodation recess.

[0031]

According to the present invention, since the foamed sheet is composed of the intermediate foamed layer and the surface layer of the virgin resin, the moldability (particularly, deep drawing moldability) and the surface uniformity of the molded article are high. In addition, since the base foam layer can be formed from the resin containing the recovered recycled resin, the recycled resin can be effectively reused to increase the economic efficiency, and even if the resin is reused, the surface layer has higher sanitation. Can be secured. Further, the synthetic resin foam sheet having a low expansion ratio has a high transportation efficiency and can accommodate many foam sheets or foam molded articles in a small storage or storage space.

[0032]

EXAMPLES The present invention will be described below in more detail with reference to Examples, but the present invention is not limited to these Examples. The following virgin resins were used in Examples and Comparative Examples. General-purpose polystyrene GPPS; Daicel Chemical Industries, Ltd.
Manufactured by Daicel Styrol 51; impact-resistant polystyrene HIPS; manufactured by Daicel Chemical Industries, Ltd .; trade name: Daicel Styrol S81; rubber content: 7% by weight Styrene-butadiene block copolymer SBS; Asahi Kasei Corporation ), Trade name "Tufprene 126", styrene content 40% by weight The tensile modulus, elongation at break and appearance of the container are as follows:
Evaluation was made by the following method. 1. Tensile modulus and elongation at break; JIS K712
7 2. Appearance: Evaluated visually with the following criteria. ◎: High concealing property, no coloration of the intermediate layer is observed. ：: Low concealing property, disturbing coloring of the intermediate layer. ×: Internal bubbles can be clearly confirmed.

Examples 1 and 2 Virgin resin pellets were used in the proportions shown in Table 1. A mixture of sodium bicarbonate and monosodium citrate (Serkyo Chemical Co., Ltd., CellMike 623) was used as a foaming agent, and the mixture was spread on the pellets with mineral oil.

The foamable resin composition thus prepared is supplied to a φ65 / φ50 mm multilayer extruder (manufactured by Pla Giken Co., Ltd.), heated by an extruder, melt-kneaded, and extruded at the tip of the extruder. It was extruded and foamed into a sheet shape from a T-die to produce a foamed sheet having a three-layer structure.

Examples 3 and 4 The resin compositions for the base foamed layer in the proportions shown in Table 1 were:
The foamed sheet recovered from the foamed sheet obtained in Example 1 was supplied to an extruder having a diameter of 40 mm to be pelletized, and pellets of a recycled resin were prepared. Virgin resin pellets having a composition ratio as shown in the table were used as the resin composition for the surface foam layer. The resin composition thus prepared was extruded and foamed in the same manner as in Example 1 to produce a foamed sheet having a three-layer structure.

Examples 5 to 7 Using virgin resin pellets at the ratios shown in Table 1, foamed sheets having a three-layer structure having different expansion ratios and different surface layer thicknesses were prepared.

Example 8 A foaming agent was added to the resin composition for the base foamed layer to obtain a resin composition having a diameter of φ65.
The extruder was supplied to a 50 mm extruder without adding a foaming agent to the resin composition for the surface foamed layer to obtain a foamed sheet having a three-layer structure in which both surface layers were non-foamed layers.

Comparative Examples 1 and 2 In the same manner as in Examples 1 and 4, except that virgin resin pellets were used in the proportions shown in the table and the number of bubbles was changed by lowering the kneading properties using a full flat screw. A layered foam sheet was obtained.

Table 1 shows the evaluation results.

[0040]

[Table 1] In Examples 3 and 4, even when the recovery material is used, the air bubbles are in a very small state, and the sheet has an excellent appearance. Also,
No decrease in strength was observed in all layers as compared with Examples 1 and 2 using a new material.

Further, the foamed sheets of Examples 1 to 8
When the container was molded into a cup of 0 mm and a depth of 48 mm,
In each case, a hygienic container with an excellent appearance was obtained.

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Claims (16)

[Claims] 1. A foam base layer containing a recycled resin,
A synthetic resin foam sheet comprising a virgin resin surface layer formed on at least one surface of the base foam layer. 2. A synthetic resin foam sheet comprising a virgin resin base foam layer and a virgin resin surface layer formed on at least one surface of the base foam layer. 3. The synthetic resin foam sheet according to claim 1, wherein the surface layer is a foamed layer or a non-foamed layer. 4. The synthetic resin foam sheet according to claim 1, wherein the base foam layer is formed of a styrene resin. 5. The synthetic resin foam sheet according to claim 1, wherein the surface layer is formed of a styrene resin. 6. The synthetic resin foam sheet according to claim 4, wherein the styrene-based resin contains at least a rubber-modified styrene-based resin having a rubber content of 5 to 20% by weight. 7. A base foam layer and a surface foam layer formed on at least one surface of the base foam layer are each formed of a styrene resin composition containing a rubber-modified styrene resin, The synthetic resin foam sheet according to any one of claims 1 to 6, wherein the base foam layer and the surface foam layer have substantially the same expansion ratio of 1.3 to 2.5 times. 8. The average number of cell membranes per unit thickness in the base foam layer and the surface foam layer is 20 to 5 respectively.
The synthetic resin foam sheet according to any one of claims 1 to 7, wherein the number is 0 / mm. 9. The synthetic resin foam sheet according to claim 1, which has a thickness of 0.3 to 2 mm and an average number of cell membranes in the thickness direction of 20 to 50. 10. A foamed surface layer is formed on at least one surface of the foamed base layer, the foaming ratio of the foamed base layer and the foamed surface layer is 1.3 to 2.5 times, and the ratio of the foamed base layer is synthetic. The average number of cell membranes per unit thickness in the base foam layer and the surface foam layer is 40 to 99% by weight of the total thickness of the resin foam sheet, and each is 20 to 50 / mm. Item 7. The synthetic resin foamed sheet according to item 1. 11. A base foam layer formed of a styrene resin containing a rubber-modified styrene resin, and a surface formed on both sides of the base foam layer and formed of a styrene resin containing the rubber-modified styrene resin. A synthetic resin foam sheet having a thickness of 0.5 to 1.5 mm and a foam layer, wherein the base foam layer accounts for 55 to 70% by weight of the entire sheet and is colored, and the base foam layer and the surface foam A synthetic resin foam sheet wherein the average number of cell membranes per unit thickness of the sheet in the layer is 23 to 48 / mm, respectively. 12. A first resin composition for forming a foamed base layer and a second resin composition for a surface layer formed on at least one surface of the foamed base layer are melt-kneaded, respectively. A method for producing the synthetic resin foam sheet according to any one of claims 1 to 11, wherein the synthetic resin foam sheet is joined and extruded and foamed in a die. 13. The method for producing a synthetic resin foam sheet according to claim 12, wherein the first resin composition includes a waste material or a waste product generated by primary processing or secondary processing of the sheet. 14. The method for producing a synthetic resin foam sheet according to claim 12, wherein an expandable styrene resin composition containing a rubber-modified styrene resin is used as the first resin composition and the second resin composition. . 15. The method according to claim 12, wherein a styrene resin composition containing 5 to 10% by weight of a rubber component is used as the first resin composition and the second resin composition. A method for producing a synthetic resin foam sheet. 16. A container formed of the synthetic resin foam sheet according to claim 1.