JP2018048278A - Polystyrenic resin foam sheet, polystyrenic resin laminated foam sheet, and polystyrenic resin laminated foam molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-resistant foam sheet capable of obtaining a molded body which has adequately improved brittleness and thermal moldability, has such heat resistance as to suppress deformation of a container even when cooked by a microwave oven, is excellent in adhesiveness with a polyolefin-based resin film, and has an adhesive strength enough to suppress delamination of a laminated film by heating with the microwave oven.SOLUTION: A polystyrenic resin foam sheet contains a polystyrenic resin being a mixture of a styrene-(meth)acrylic acid copolymer, polystyrene, and impact resistant polystyrene containing a rubber with a particle diameter of 0.8 μm or more and less than 1.8 μm and a gel content, as a base material resin, where a weight ratio of the styrene-(meth)acrylic acid copolymer in the polystyrenic resin and a weight ratio of the polystyrene and a weight ratio of the impact resistant polystyrene are in a specific range, and a content of a gel derived from the impact resistant polystyrene in the polystyrenic resin is in a specific range.SELECTED DRAWING: None

Description

  The present invention relates to a polystyrene-based resin foam sheet, and more particularly to a polystyrene-based resin foam sheet for thermoforming a food container for microwave heating, and further a polystyrene-based resin film laminated with a polyolefin-based resin film. The present invention relates to a resin-laminated foam sheet and a laminated foam-molded body thereof.

  Since the polystyrene foam sheet is excellent in light weight, heat insulation, and rigidity, a molded body obtained by thermoforming is widely used for food containers and the like. However, since the polystyrene resin constituting the polystyrene foam sheet is insufficient in heat resistance, the heat resistant foam mainly composed of a styrene- (meth) acrylic acid copolymer is used for food containers for cooking by heating in a microwave oven. Sheet molded bodies have been widely used (for example, Patent Document 1).

  However, the heat-resistant foam sheet mainly composed of a styrene- (meth) acrylic acid copolymer is more brittle than a general polystyrene foam sheet, and is easily cracked when applied with an external force, resulting in poor impact resistance. there were. As a solution, there is a technique of adding high impact polystyrene (impact polystyrene) to a polystyrene- (meth) acrylic acid copolymer (for example, Patent Document 2). However, impact-resistant polystyrene has a problem that the brittleness improvement effect is low when added in a small amount, and heat resistance is impaired when added in a large amount, and foamability decreases. Therefore, a technique of adding a styrene-butadiene thermoplastic elastomer (hereinafter also referred to as SBS) has been generally used (for example, Patent Document 3).

  In addition, the heat-resistant foam sheet mainly composed of a styrene- (meth) acrylic acid copolymer has a problem that it is inferior in thermoformability as compared with a polystyrene foam sheet. In order to improve adhesiveness with a polystyrene (impact polystyrene) resin layer, polystyrene is added (for example, Patent Document 4).

JP 62-94539 A JP-A 63-264335 Japanese Patent Laid-Open No. 3-109441 JP 2014-79940 A

  However, the styrene-butadiene-based thermoplastic elastomer is excellent in the brittleness improvement effect of the foamed sheet and can improve the brittleness by adding a small amount, but it is easy to reduce the heat resistance of the foamed sheet, and is the original purpose by blending SBS. Heat resistance is sacrificed.

  Moreover, since a styrene- (meth) acrylic acid copolymer is inferior in oil resistance, when using for a microwave oven use, it is necessary to laminate | stack polyolefin films, such as a polypropylene excellent in oil resistance, on the surface of a heat resistant foam sheet. . As a means of laminating polyolefin films, a method of heat-sealing a polyolefin-polystyrene multilayer film to a heat-resistant foamed sheet, a method of heat-sealing a polyolefin film coated with an adhesive, these films and a heat-resistant foamed sheet A method of laminating with a resin layer of impact-resistant polystyrene is used. However, these films and resin layers are bonded to the heat-resistant foamed sheet mainly composed of a styrene- (meth) acrylic acid copolymer described in Patent Documents 1 to 3, compared to a normal polystyrene foamed sheet. There is a problem that it is difficult to do. In addition, in order to bond these films to the heat-resistant foam sheet, it is necessary to give more heat than a normal foam sheet, and it is possible to transfer the foam sheet surface to a temperature suitable for heat fusion. Since it is not easy, there also exists a problem that the difficulty in an adhesion process is high.

  Further, after thermoforming the laminated foamed sheet obtained by the laminating means, when food is put into a stored molded body and heated in a microwave oven, the gas inside the bubbles is released with softening of the heat-resistant foamed sheet. In some cases, problems such as peeling of the laminated film (hereinafter referred to as delamination) may occur. As a result of investigating the cause, the present inventors have laminated a polyolefin film on a heat-resistant foamed sheet containing a styrene- (meth) acrylic acid copolymer as a main component and a styrene-butadiene-based thermoplastic elastomer added thereto. It has been found that the laminated foam sheet thus obtained has a decrease in the adhesive strength of the film over time depending on the lamination conditions, and delamination may occur due to insufficient adhesive strength.

  In the laminated foam sheet described in Patent Document 4, the problem of delamination has been solved, but when high impact resistance is required, it is necessary to add a styrene-butadiene-based thermoplastic elastomer to the base resin. There was room for improvement in terms of achieving both high impact resistance and heat resistance.

  As described above, the heat resistant foam sheet has a problem of lacking oil resistance. In order to impart oil resistance to the heat-resistant foamed sheet, it is necessary to laminate a polyolefin film on the surface thereof, and the heat-resistant foamed sheet has a problem of poor adhesion to the polyolefin film. Furthermore, the heat-resistant foamed sheet has a problem that it is brittle. When a styrene-butadiene-based thermoplastic elastomer is used to improve brittleness, the adhesiveness tends to be insufficient depending on the bonding conditions. There is a problem that the inherent heat resistance of the polymer cannot be exhibited. Furthermore, the heat-resistant foam sheet also has a problem that thermoforming is difficult.

  The present invention has improved brittleness and thermoformability, has heat resistance capable of suppressing deformation of the container even when cooked in a microwave oven, and adheres to polyolefin resin films such as polypropylene film A heat-resistant foam sheet comprising a styrene- (meth) acrylic acid copolymer as a main component, which is capable of obtaining a molded article having excellent adhesive strength that is excellent in suppressing delamination of a laminated film due to microwave heating The purpose is to provide. Furthermore, the present invention is a heat-resistant polystyrene-based resin laminated foam sheet having excellent oil resistance in which a polyolefin-based resin film is laminated on the heat-resistant foam sheet, and a molded product obtained by thermoforming the laminated foam sheet. Thus, an object of the present invention is to provide a polystyrene-based resin laminated foamed molded product in which the occurrence of delamination during heating in a microwave oven is prevented.

According to the present invention, the following polystyrene resin foam sheet, polystyrene resin laminate foam sheet, and polystyrene resin laminate foam molded article are provided.

[1] In a foam sheet using a polystyrene resin as a base resin,
The polystyrene-based resin is a mixture of a styrene- (meth) acrylic acid copolymer, polystyrene, and high-impact polystyrene containing a gel content and containing rubber having a particle size of 0.8 μm or more and less than 1.8 μm,
The weight ratio of the styrene- (meth) acrylic acid copolymer in the polystyrene resin is 45 to 74% by weight, the weight ratio of polystyrene is 5 to 40% by weight, and the weight ratio of impact-resistant polystyrene is 5%. -25% by weight (however, the total of the three is 100% by weight),
A polystyrene-based resin foam sheet characterized in that the gel content derived from the high-impact polystyrene in the polystyrene-based resin is 3 to 6% by weight.
[2] The polystyrene-based resin foam sheet as described in 1 above, wherein the weight ratio of the polystyrene to the impact-resistant polystyrene is 75:25 to 30:70.
[3] A polystyrene resin laminated foam sheet, wherein a polyolefin resin film is laminated and adhered to at least one side of the polystyrene resin foam sheet according to 1 or 2.
[4] The polystyrene resin laminated foam sheet as described in 3 above, wherein a peel strength between the polystyrene resin foam sheet and the polyolefin resin film is 4.0 N / 25 mm or more.
[5] A polystyrene-based resin laminated foam molded article obtained by thermoforming the polystyrene-based resin laminated foam sheet according to 3 or 4 above.

  The polystyrene-based resin foam sheet of the present invention uses a mixture of a styrene- (meth) acrylic acid copolymer, polystyrene, and specific impact-resistant polystyrene as a base resin, and the styrene-methacrylic acid copolymer and the When the weight ratio of polystyrene and the impact-resistant polystyrene is within a specific range, and the gel content in the mixture is within a specific range, the heat resistance and impact resistance are excellent, and the thermoformability is excellent. Excellent adhesion to polyolefin resin film.

FIG. 1 is an explanatory diagram of a method for measuring impact fracture strength. FIG. 2 is a DSC curve graph obtained by the heat flux differential scanning calorimetry method for the base resin of the foam sheet of the present invention.

Hereinafter, the polystyrene-based resin foam sheet, the polystyrene-based resin laminate foam sheet, and the polystyrene-based resin laminate foam molded body of the present invention will be described in detail.
The base resin constituting the polystyrene resin foam sheet (hereinafter also referred to as a foam sheet or a heat-resistant foam sheet) of the present invention is a polystyrene resin, and the polystyrene resin is a styrene- (meth) acrylic acid copolymer. A blend of polystyrene, polystyrene, and impact-resistant polystyrene containing a rubber having a particle size of 0.8 μm or more and less than 1.8 μm and containing a gel component.

  Since impact-resistant polystyrene mainly composed of styrene- (meth) acrylic acid copolymer and polystyrene component has poor compatibility, there is a concern about material characteristics such as a material in which they are mixed and mechanical strength becomes weak. However, in the present invention, by using a mixed resin obtained by mixing polystyrene and specific impact-resistant polystyrene with a styrene- (meth) acrylic acid copolymer as a base resin, heat resistance having sufficiently practical mechanical strength. An expandable foam sheet could be obtained.

  The styrene- (meth) acrylic acid copolymer is a copolymer of styrene and (meth) acrylic acid, and is generally referred to as heat resistant polystyrene. The Vicat softening temperature is preferably 110 ° C. or higher, more preferably 116 ° C. or higher. The content of the (meth) acrylic acid component in a general styrene- (meth) acrylic acid copolymer as heat-resistant polystyrene is about 5 to 25% by weight in the copolymer, preferably 5 to 15 % By weight. In order to improve moldability and the like, a small amount of a methacrylic acid alkyl ester such as methyl methacrylate and butyl acrylate and / or an alkyl acrylate ester may be copolymerized in a small amount as a third component. In this specification, styrene-methacrylic acid copolymer, styrene-acrylic acid copolymer, styrene-acrylic acid-methacrylic acid copolymer, and a mixture of two or more thereof are collectively referred to as styrene- ( It is called a (meth) acrylic acid copolymer.

  As said polystyrene, what is called general purpose polystyrene (GPPS) can be used. General-purpose polystyrene is generally a homopolymer of styrene, but it may contain a branching agent such as divinylbenzene or a polyfunctional macromonomer in its molecular chain. The Vicat softening temperature is usually about 90 to 105 ° C.

  As the impact-resistant polystyrene, a rubber-modified polystyrene resin containing a gel content is used. Such a rubber-modified polystyrene resin is usually obtained by radical polymerization of a styrene monomer in the presence of a rubber-like polymer such as polybutadiene, and rubber-like polymer particles in which polystyrene chains are graft-polymerized. Forms a dispersed phase, and a morphology in which polystyrene forms a continuous layer is formed, and includes a gel component.

  The Vicat softening temperature of the high impact polystyrene is preferably 90 ° C or higher. When the Vicat softening temperature is 90 ° C. or higher, the foam sheet has sufficient heat resistance. The upper limit of the Vicat softening temperature of impact-resistant polystyrene is approximately 97 ° C.

  The Vicat softening temperature is a value measured by the A50 method based on JIS K7206: 1999.

  The rubber-modified polystyrene resin may contain a component derived from a monomer other than styrene such as α-methylstyrene, o-methylstyrene, m-methylstyrene, and p-methylstyrene, in addition to the styrene component.

  Examples of the rubbery polymer constituting the high impact polystyrene include polybutadiene, styrene-butadiene random or block copolymer, polyisoprene, styrene-isoprene random or block copolymer, ethylene-propylene rubber, and ethylene-propylene. -Butadiene rubber etc. are mentioned, In particular, a random or block copolymer of polybutadiene and styrene-butadiene is preferably used. These may be partially hydrogenated.

  In the present invention, among the impact-resistant polystyrene, impact-resistant polystyrene having a rubber particle size of 0.8 μm or more and 1.8 μm or less is used. If the rubber particle size is less than 0.8 μm, the impact resistance of the foamed sheet may be too low. On the other hand, if the rubber particle size exceeds 1.8 μm, the heat resistance inherent in the styrene-methacrylic acid copolymer may be impaired, and the adhesiveness with the polyolefin resin film may be reduced, and the film may be damaged during microwave heating. There is a risk of lamination. From this viewpoint, the lower limit of the rubber particle size is preferably 0.9 μm. The upper limit of the rubber particle size is preferably 1.6 μm, more preferably 1.4 μm.

  The reason why the foam sheet blended with the specific impact-resistant polystyrene is excellent in heat resistance is that the rubber region having a specific range of rubber particle diameter is dispersed in a domain shape in the base resin, Since the softening of the foam sheet is suppressed, it is considered that the heat resistance of the styrene- (meth) acrylic acid copolymer is sufficiently developed. On the other hand, in the styrene-butadiene copolymer conventionally used for improving brittleness, since the butadiene segment is evenly dispersed in the microphase dispersion structure, softening of the foam sheet during heating occurs rapidly. It is considered that the heat resistance of the styrene- (meth) acrylic acid copolymer cannot be expressed.

  Further, the impact-resistant polystyrene used in the present invention contains a gel component. The amount of the gel is evaluated as the gel content in the polystyrene resin, and the gel content is required to be 3 to 6% by weight. If the gel content is less than 3% by weight, the brittleness improving effect may be insufficient. Moreover, when this gel content exceeds 6 weight%, there exists a possibility that heat resistance may fall.

The rubber particle size in the present specification is obtained by taking a transmission electron micrograph of an ultrathin section of impact-resistant polystyrene, and measuring the particle size of 500 dispersed rubber particles in the obtained photograph, and the following formula (1) The value calculated by In the case where the rubber particles are oriented, the average value of the minor axis and the major axis is taken as the particle size.
Rubber particle size = ΣniDi ² / ΣniDi (1)
In the above formula (1), ni is the number of rubber particles having a particle diameter Di.

In this specification, gel content is measured as follows.
First, weigh accurately about 1.5 g of the sample, put it into a 100 mL conical flask with a stopper, add 30 mL of methyl ethyl ketone (MEK), leave it for a whole day and night, and confirm that the sample is dissolved in MEK for 10 minutes. Shake. This is put into a precisely weighed centrifuge tube and centrifuged at 4000 rpm for 40 minutes. The supernatant liquid centrifuged by decantation is discarded, and the inner wall of the centrifuge tube is washed with a small amount of MEK. The centrifuge tube is pre-dried in a fume hood for 1 day, and then dried in a vacuum dryer at 70 ° C. for 15 hours or more. After drying, after cooling to normal temperature in a desiccator, the centrifuge tube is precisely weighed, and the gel content is determined by the following equation (2). In addition, when measuring the gel content in the polystyrene resin constituting the foam sheet, using a test piece cut out from the foam sheet as a sample, when measuring the gel content of the impact polystyrene material, Use pellets of high impact polystyrene.
Gel content (% by weight) = (ba) / S × 100 (2)
Where S: weight of sample, a: weight of centrifuge tube, b: total weight of dried gel and centrifuge tube

  In the present invention, in the polystyrene resin, a morphology is formed in which the styrene- (meth) acrylic acid copolymer forms a continuous phase, and a mixture of the polystyrene and the high-impact polystyrene forms a continuous phase. It is preferable. Since the styrene- (meth) acrylic acid copolymer forms a continuous phase, the heat resistance is improved, and because the mixture of polystyrene and impact polystyrene forms a continuous phase, the thermoformability is improved. As a result, these resins, particularly polystyrene, appear on the surface of the foamed sheet, thereby improving the adhesion.

The weight ratio of the styrene- (meth) acrylic acid copolymer in the polystyrene resin is 45 to 74% by weight, the weight ratio of polystyrene is 5 to 40% by weight, and the weight ratio of impact-resistant polystyrene is 5%. -25% by weight (however, the total of the three members is 100% by weight).
If the weight ratio of the styrene- (meth) acrylic acid copolymer is too small, the heat resistance of the foamed sheet may be too low. On the other hand, if the weight ratio of the styrene- (meth) acrylic acid copolymer is too large, the impact resistance, thermoformability, and adhesion may not be improved. If the weight ratio of polystyrene is too small, the thermoformability may be reduced, and the adhesiveness when the films are laminated may be reduced. On the other hand, if the weight ratio of polystyrene is too large, the heat resistance may be too low. If the weight ratio of the impact resistant polystyrene is too small, the impact resistance of the foam sheet may be insufficient. On the other hand, if the weight ratio of the impact-resistant polystyrene is too large, the heat resistance may be too low.
From this viewpoint, the lower limit of the weight ratio of the styrene- (meth) acrylic acid copolymer in the polystyrene resin is preferably 50% by weight, and the upper limit is preferably 70% by weight.
Moreover, it is preferable that the minimum of the weight ratio of a polystyrene is 15 weight%, and it is preferable that the upper limit is 35 weight%.
Further, the lower limit of the weight ratio of the impact resistant polystyrene is preferably 10% by weight, and the upper limit thereof is preferably 20% by weight.

  The weight ratio of polystyrene to impact-resistant polystyrene in the polystyrene resin is preferably 75:25 to 30:70. When the weight ratio of polystyrene and impact-resistant polystyrene is within the above range, the foamed sheet is particularly excellent in the balance between impact resistance and thermoformability, and particularly excellent in adhesion to the resin film. It will be a thing. From this viewpoint, the weight ratio of polystyrene to high-impact polystyrene is more preferably 75:25 to 40:60, and further preferably 70:30 to 50:50.

  In the present invention, a styrene-acrylonitrile copolymer, a styrene-methyl methacrylate copolymer, a styrene-ethyl methacrylate copolymer, a styrene-polymer are added to the base resin to such an extent that the intended purpose of the present invention is not impaired. Other polystyrene resins such as maleic anhydride copolymer and polyphenylene ether resins can be added. However, the blending amount is preferably 20% by weight or less, more preferably 10% by weight or less, based on the entire base resin. Moreover, it is preferable that base-material resin does not contain thermoplastic elastomer components, such as a styrene-butadiene copolymer and a methyl methacrylate-butadiene-styrene copolymer.

  In addition, various additives such as an antioxidant, a heat stabilizer, an inorganic filler, a colorant, and the like can be added to the base resin as necessary.

In the present invention, the overall apparent density of the foam sheet is preferably 50 to 210 kg / m ³ . If the overall apparent density is too small, the molded product obtained because the mechanical strength is too low may not be used as a food container. On the other hand, if the overall apparent density is too large, the lightness may be lost and the cost may increase. From this point of view,該全body apparent density is more preferably from 65~210kg / ^{m 3,} more preferably from 70~210kg / ^{m 3.}

In this invention, it is preferable that ratio (density ratio) of the apparent density of the surface layer part of a foam sheet with respect to the whole apparent density is 1.1-2.5. When the density ratio is in the above range, the impact resistance of the foamed sheet can be further improved. Moreover, when laminating a polyolefin resin film, it is more preferable to set the density ratio on the laminated surface side to 1.1 to 1.6.
In addition, the said surface layer part means the part to 200 micrometers in the thickness direction from the surface of a foam sheet. The density ratio may be different on both sides of the foam sheet.

The apparent density of the surface layer portion is measured as follows.
A 200 μm portion is sliced in the thickness direction from the surface of the foamed sheet and cut into test pieces having a width of 5 mm × length of 20 mm, and the weight and thickness of the test piece are measured with a gauge. The weight of the test piece is divided by the volume (width × length × thickness) of the test piece, and converted to a unit to determine the apparent density of the surface layer portion (hereinafter also referred to as surface layer density).
The said measurement is performed about 10 places of equal intervals over the width direction of a foamed sheet, and those arithmetic mean values are made into the surface layer density of a foamed sheet.

  In the foamed sheet of the present invention, the average cell diameter is preferably 0.02 to 0.4 mm, more preferably 0.04 to 0.2 mm. When the average cell diameter is within the above range, the balance between the thermoformability of the foamed sheet and the laminated foamed sheet and the physical properties such as strength, appearance, and printability of the obtained container is particularly excellent. The average cell diameter of the foamed sheet is mainly adjusted by adjusting the amount of the cell regulator, adjusting the widening ratio and take-up speed of the heat-resistant foamed sheet, and blowing air to the foaming foam immediately after extrusion. Fine adjustment can be made, for example, by rapidly cooling the surface of the foam.

  The average bubble diameter is determined as follows. A cross section perpendicular to the extrusion direction is photographed with a microscope at 10 positions at equal intervals in the width direction of the laminated foam sheet, and the thickness t of the foam sheet is measured for each cross-sectional photograph. Next, a straight line 1 is drawn in the thickness direction of each cross-sectional photograph, and the number n of all bubbles in the foamed sheet that intersects the straight line 1 is counted. The bubble diameter (t / n) is calculated for each cross-sectional photograph from t and n thus obtained, and the average of 10 (t / n) is taken as the average bubble diameter of the foam sheet.

Next, the polystyrene resin laminated foam sheet of the present invention (hereinafter also simply referred to as a laminated foam sheet) will be described.
The laminated foam sheet is obtained by bonding and laminating a polyolefin resin film on one side of the polystyrene resin foam sheet. However, a polyolefin resin film may be bonded and laminated on both sides.

  Examples of the polyolefin resin constituting the polyolefin resin film include polyethylene resins such as high density polyethylene, low density polyethylene, linear low density polyethylene, and ethylene-vinyl acetate copolymer, and polypropylene, propylene-ethylene random copolymer. Examples thereof include polypropylene resins such as polymers and block polypropylene.

  Usually, a polyolefin resin film (PO film) is provided with an adhesive layer for adhering to a foamed sheet. Examples of the adhesive constituting the adhesive layer include conventionally known adhesives such as commonly used acrylic adhesives, urethane adhesives, and ethyl acetate, and conventionally known adhesive resins such as ethylene-vinyl acetate. It is done. In addition, a so-called PO / PS dry film in which a polyolefin resin film and a polystyrene resin film are bonded in advance can also be used.

  The thickness of the polyolefin resin film is preferably 10 to 50 μm, more preferably 20 to 30 μm. Oil resistance can be provided, maintaining the thermoformability of a foam sheet as this thickness is in the said range.

When the laminated foam sheet is used in a container that requires particularly high heat resistance, such as a container for foodstuffs with a high oil content, the polyolefin resin film is adhered and laminated to the foam sheet via an impact-resistant polystyrene layer. It is preferable. In this case, the basis weight of high impact polystyrene layer is preferably in the 70~200g / ^{m 2,} more preferably from 90~180g / ^{m 2.}

  The peel strength between the foamed sheet and the polyolefin resin film is preferably 4.0 N / 25 mm or more. When the peel strength is within the above range, delamination during heating by a microwave oven can be more effectively suppressed. From this viewpoint, the peel strength is more preferably 5.0 N / 25 mm or more. The upper limit of the peel strength is approximately 12 N / 25 mm.

  The peel strength is measured as follows. A test piece having a width of 25 mm is cut out from the laminated foamed sheet along the extrusion direction, and the resin film or the resin layer is peeled from the laminated foamed sheet in a 90 ° peel test in accordance with JIS Z0237: 2009 at a peeling speed condition of 300 mm / min. Then, the peel strength at that time is measured.

  The closed cell ratio of the foamed sheet of the present invention is preferably 70% or more, more preferably 80% or more, from the viewpoints of secondary foamability during thermoforming and the strength of the resulting molded article.

The closed cell ratio of the foam sheet in the present specification was measured using an air comparison type hydrometer 930 type manufactured by Toshiba Beckman Co., Ltd. according to the procedure C of ASTM-D2856-70 (randomly 25 mm × 25 mm × from the laminated sheet A laminated foamed sheet obtained by stacking a plurality of cut samples cut into a sheet thickness so that the total thickness of the samples approaches 20 mm (but not exceeding 20 mm) and storing them in a sample cup. Using the true volume Vx of (cut sample), the closed cell ratio S (%) is calculated by the following formula (3), and is obtained as an average value of n = 5.
S (%) = (Vx−W / ρ) × 100 / (Va−W / ρ) (3)

Vx: the true volume (cm ³ ) of the cut sample measured by the above method, which corresponds to the sum of the volume of the resin constituting the foamed sheet and the total cell volume of the closed cell portion in the cut sample.
Va: Apparent volume (cm ³ ) of the cut sample calculated from the outer dimensions of the cut sample used for measurement.
W: Total weight of cut sample used for measurement (g)
ρ: Density of resin constituting the foam sheet (g / cm ³ )

Next, the manufacturing method of the foam sheet of this invention is demonstrated.
The foamed sheet of the present invention can be obtained by conventionally known so-called extrusion foaming. That is, using an extruder, the base resin and various additives such as a bubble adjusting agent added as necessary are heated, melted, kneaded, pressed with a physical foaming agent, and further kneaded. It is formed by foaming a foamable molten resin adjusted to the resin temperature to be extruded through a die under atmospheric pressure.

  A physical foaming agent can be used as the foaming agent. Examples of the physical blowing agent include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane, halogenated hydrocarbons such as methyl chloride, ethyl chloride, and methylene chloride, dimethyl ether, diethyl ether, methyl ethyl ether, and the like. Examples include ethers, carbon dioxide, nitrogen, and water. Of these, butane is preferred because it is easy to produce a foam sheet and the foam sheet has excellent thermoformability.

  The addition amount of the foaming agent and the addition amount of the cell regulator can be appropriately selected depending on the type of the base resin, the type of the foaming agent, the type of the foam regulator, and the density of the target foamed sheet. A foaming agent is 0.5-10 weight part with respect to 100 weight part of resin, and a bubble regulator is 0.1-3 weight part. The resin temperature of the foamable molten resin at the time of foaming can be appropriately selected depending on the type of base resin, the type of foaming agent, the type of cell regulator, and the density of the desired foamed layer, but is usually 120 to 180 ° C.

  As a method of adjusting the apparent density of the surface layer portion, a method of adjusting the amount of air blown for cooling immediately after extrusion foaming can be mentioned.

In the foamed sheet of the present invention, as described above, a polyolefin resin film can be laminated on the surface.
As a method of laminating a polyolefin resin film to a foam sheet through an adhesive layer, (1) a multilayer film in which an adhesive layer is laminated on a polyolefin resin film is heat-sealed with the adhesive layer surface side facing the foam sheet surface. (2) A film (PO / PS dry laminated film) in which a polyolefin resin film and a polystyrene resin film are laminated and bonded in advance through an adhesive layer, and the polystyrene resin film surface side is the foam sheet surface. (3) A multilayer film in which an impact-resistant polystyrene layer is formed by extrusion lamination on a foamed sheet and an adhesive layer is provided on the polyolefin-based resin film is formed on the adhesive layer surface side. (4) Impact-resistant polystyrene on foam sheet The emission layer is formed by extrusion lamination, a PO / PS dry lamination film thereon, a method for pressing the adhesive, and the like toward the polystyrene resin film surface to a high impact polystyrene layer.

  When the laminated foam sheet is used in a container that requires particularly high heat resistance, such as a container for foodstuffs with a high oil content, it is preferable to employ the method (3) or (4).

The laminated foam sheet of the present invention is excellent in thermoformability, and a molded product obtained by thermoforming is suitably used as a container for a microwave oven heated food.
Thermoforming methods include vacuum forming and pressure forming, as well as free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, air slip forming, Examples thereof include plug-assist molding, plug-assist reverse draw molding, and a molding method combining these. Such a thermoforming method is a preferable method because a container can be obtained continuously in a short time. In addition, when thermoforming a laminated foam sheet, it is preferable to shape | mold so that the polyolefin resin film excellent in oil resistance may be located inside the molded object obtained.

  The molded body obtained by thermoforming can be used as containers such as trays, cups, bowls, lunch boxes and the like mainly used for microwave oven heating.

  Next, the polystyrene resin foam sheet of the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples.

[Manufacture of foam sheet]
As a production apparatus, a tandem extruder having a first extruder (screw diameter 115 mm), a second extruder (screw diameter 150 mm), and an annular die having a diameter of 180 mm attached to the outlet of the second extruder was used.

(Styrene- (meth) acrylic acid copolymer)
The following styrene- (meth) acrylic acid copolymer was used.
(1) Styrene-methacrylic acid copolymer manufactured by PS Japan Co., Ltd .: Product name “G-9001” (abbreviation G9001, Vicat softening temperature 118 ° C.)
(2) Styrene-methacrylic acid copolymer manufactured by Toyo Styrene Co., Ltd .: Product name “T080” (abbreviation T080, Vicat softening temperature 117 ° C.)

(Impact polystyrene)
The following impact resistant polystyrene was used.
(1) Impact-resistant polystyrene manufactured by PS Japan Co., Ltd .: Product name “H8117” (abbreviation H8117, rubber particle size 1.3 μm, gel content 30% by weight, Vicat softening temperature 95 ° C.)
(2) Impact-resistant polystyrene manufactured by Toyo Styrene Co., Ltd .: Product name “XL4” (abbreviation XL4, rubber particle size 0.9 μm, gel content 21% by weight, Vicat softening temperature 94 ° C.)
(3) Impact-resistant polystyrene manufactured by Toyo Styrene Co., Ltd .: Product name “475D” (abbreviation 475D, rubber particle size 2.3 μm, gel content 21% by weight, Vicat softening temperature 93 ° C.)
The Vicat softening temperature is a value measured by the A50 method based on JIS K7206: 1999.

The following polystyrene was used.
(1) Polystyrene manufactured by PS Japan Co., Ltd .: Product name “GX154” (abbreviation GX154, Vicat softening temperature 103 ° C.)
(2) Polystyrene manufactured by DIC Corporation: Product name “HRM26B” (abbreviation HRM26B, Vicat softening temperature 103 ° C.)

Examples 1-6, Comparative Examples 1-4
The type and amount of styrene- (meth) acrylic acid copolymer shown in Table 1, the type and amount of impact-resistant polystyrene shown in Table 1, the type and amount of polystyrene shown in Table 1, and the formulation shown in Table 1 An amount of talc (bubble adjusting agent: High Filler # 12 manufactured by Matsumura Sangyo Co., Ltd.) was uniformly mixed in a batch type continuous mixing apparatus set on the hopper of the first extruder, and then supplied to the first extruder. The cylinder temperature of the extruder is set to a maximum temperature of 240 ° C., the mixed resin is heated and melted, and mixed butane in an amount shown in Table 1 with respect to 100 parts by weight of the mixed resin (normal butane 35% by weight and isobutane 65% by weight). The mixture is pressed into a foaming agent and further kneaded, and then cooled to the extrusion resin temperature shown in Table 1 by a second extruder, then supplied to the annular die, and 300 kg / hour through the slit of the die. Extruded into a cylindrical shape with a discharge amount of 1, and immediately after that, air in the amount shown in Table 1 was blown on the inside and outside of the cylindrical foam to cool. Thereafter, the sheet was taken along the outer surface of a cooling device (mandrel) having a diameter of 670 mm while further cooling, and further cut into two along the extrusion direction to obtain a foam sheet having a width of 1050 mm. Table 2 shows the physical properties of the obtained foamed sheet.

[Lamination of polyolefin resin film]
A film “CPP / PS 45 μm plain” in which CPP 25 μm (Santox KT) and CPS 20 μm (Oishi Sangyo SPH) are laminated by dry lamination and the heat-resistant foam sheet are passed between a heat roll and a backup roll at 190 ° C. The film was pressure-bonded to the foamed sheet to obtain a laminated foamed sheet. At this time, the line speed was set to 17 m / min, and the gap between the heat roll and the backup roll was set to 0.5 mm.
Table 2 shows the evaluation of impact resistance, polyolefin resin film adhesion, and heat resistance of the obtained laminated foam sheet.

[Impact resistance (impact fracture strength)]
The impact resistance of the laminated foamed sheets obtained in Examples and Comparative Examples was evaluated by the following criteria by the following test.
A test piece 11 having a size of 60 mm × 60 mm is cut out from the laminated foam sheet, and as shown in FIG. 1, the test piece 11 is placed on the cylindrical support base 12 having a circular measurement hole 12a having an inner diameter of 40 mm on the side of the resin film laminated surface. The rod 14 having a hemisphere with a diameter of 20 mm at the tip and a load cell connected thereto is fixed at a lowering speed of 500 m / min from above. The test piece 11 was pierced by, and the load and displacement at the time of destruction were recorded (n = 5). The arithmetic average value of the measured values obtained was evaluated according to the following criteria.

◎: Load at break 30N or more ○: Load at break 20N or more and less than 30N ×: Load at break less than 20N

[Evaluation of adhesion of polyolefin resin film]
The adhesion between the foam sheet and the polyolefin resin film was evaluated as follows. From the laminated foam sheet, test pieces having a length of 300 mm × width of 25 mm are cut out from the five locations along the extrusion direction at equal intervals in the width direction of the sheet, and each test piece is peeled off by a method in accordance with JIS Z0237. The peel strength was determined by measuring the strength and arithmetically averaging the measured values (n = 5), and evaluated according to the following criteria.

A: Peel strength is 5.0 N / 25 mm or more B: Peel strength is 4.0 N / 25 mm or more and less than 5.0 N / 25 mm X: Peel strength is less than 4.0 N / 25 mm

[Heat resistance (deformation)]
The laminated foamed sheet was thermoformed to obtain a tray-shaped molded body having a long side of 190 mm, a short side of 140 mm, and a depth of 25 mm, and a microwave oven test was performed using the obtained molded body. Specifically, 90 g of a commercially available retort curry was put into the molded product, and the lid was covered and heated at 600 W for 1 minute and 30 seconds. In addition, the lid | cover made from the thermoformed polystyrene which can be fitted with a flange and was provided with the steam escape was used. Measure the long side dimension and short side dimension of the molded product before and after heating, respectively, the absolute value of the difference between the long side dimension before heating and the long side dimension after heating (long side dimension difference), and the short side before heating The absolute value of the difference between the dimension and the short side dimension after heating (short side dimension difference) was determined. The larger value of the long-side dimensional difference and the short-side dimensional difference was defined as the heating dimensional difference, and evaluation was performed according to the following criteria.

A: Heating dimensional difference is less than 2 mm ○: Heating dimensional difference is 2 mm or more and less than 4 mm X: Heating dimensional difference is 4 mm or more

[Heat resistance (delamination test)]
In the deformation evaluation test, the heated compact was observed and evaluated according to the following criteria.
A: No delamination occurs. ○: A delamination level that cannot be recognized without careful observation occurs. ×: A delamination level that can be easily recognized occurs.

(Heat flux differential scanning calorimetry)
A test was cut out from each foamed sheet, and “when measuring the glass transition temperature after performing a certain heat treatment” as a condition adjustment of the test piece by a heat flux differential scanning calorimetry based on JIS K7121-1987 (heating rate and The DSC curve was obtained by heating at a heating rate of 10 ° C./min.
In the mixture of styrene- (meth) acrylic acid copolymer, high-impact polystyrene and polystyrene, two stages of a low temperature side and a high temperature side appear as shown in FIG. The low-temperature stage appears based on the glass transition of impact-resistant polystyrene and polystyrene, and the high-temperature stage appears based on the glass transition of the styrene- (meth) acrylic acid copolymer. The stage appears when the styrene-methacrylic acid copolymer constituting the base resin is incompatible with the high-impact polystyrene and polystyrene.

  The ratio of the low temperature side stage (C) and the high temperature side stage (D) is plotted as shown in FIG. 1, and the height of the low temperature side stage (C) and the height of the high temperature side stage (D) are measured. / (C + D)) × 100 was the ratio of the low temperature side stage (C), and (D / (C + D)) × 100 was the ratio of the high temperature side stage (D).

The ratio of these stages is determined in correlation with the blending ratio of styrene- (meth) acrylic acid copolymer, high impact polystyrene and polystyrene. That is, since the weight ratio of the styrene- (meth) acrylic acid copolymer in the base resin is 45 to 74% by weight, the ratio of the high temperature side stage to the entire stage is approximately 45 to 74%.

A Low glass transition temperature B High glass transition temperature
C Low-temperature stage D High-temperature stage 11 Test piece 12 Cylindrical support 12a Circular measurement hole 13 Fixing tool 13b Circular measurement hole

Claims (5)

In the foam sheet using a polystyrene resin as a base resin,
The polystyrene-based resin is a mixture of a styrene- (meth) acrylic acid copolymer, polystyrene, and high-impact polystyrene containing a gel content and containing rubber having a particle size of 0.8 μm or more and less than 1.8 μm,
The weight ratio of the styrene- (meth) acrylic acid copolymer in the polystyrene resin is 45 to 74% by weight, the weight ratio of polystyrene is 5 to 40% by weight, and the weight ratio of impact-resistant polystyrene is 5%. -25% by weight (however, the total of the three is 100% by weight),
A polystyrene-based resin foam sheet characterized in that the gel content derived from the high-impact polystyrene in the polystyrene-based resin is 3 to 6% by weight.
2. The polystyrene-based resin foam sheet according to claim 1, wherein a weight ratio of the polystyrene to the impact-resistant polystyrene is 75:25 to 30:70.
A polystyrene-based resin laminated foam sheet, wherein a polyolefin-based resin film is laminated and adhered to at least one side of the polystyrene-based resin foam sheet according to claim 1.
4. The polystyrene-based resin laminated foam sheet according to claim 3, wherein a peel strength between the polystyrene-based resin foam sheet and the polyolefin-based resin film is 4.0 N / 25 mm or more.
A polystyrene-based resin laminate foam molded article obtained by thermoforming the polystyrene-based resin laminate foam sheet according to claim 3 or 4.