JP2018079644A - Multilayer foamed sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer foamed sheet capable of obtaining a molded body which greatly suppresses a lamination amount of a resin layer, secures high surface smoothness, has high surface smoothness by thermoforming, and has good reproductivity of a mold shape.SOLUTION: A multilayer foamed sheet has a polystyrene-based resin foamed layer and a thermoplastic resin film layer laminated and bonded to at least one surface of the foamed layer and has a thickness of 0.5 mm to 2.0 mm, where a thickness of the thermoplastic resin film layer is 10-60 μm, apparent density A of the multilayer foamed sheet is 170-420 kg/m, apparent density B of a surface layer portio being a portion to 200 μm in a thickness direction from the surface of the film layer side of the multilayer foamed sheet is higher than the apparent density A of the multilayer foamed sheet and is 320 kg/mor more, and arithmetic average roughness Ra of the surface of the film layer side of the multilayer foamed sheet is 1.5 μm or less.SELECTED DRAWING: None

Description

  The present invention relates to a multilayer foamed sheet, and more particularly to a multilayer foamed sheet having excellent surface smoothness and excellent thermoformability.

  Multi-layer foam sheets made by laminating non-foamed resin films on foam sheets have better heat insulation, lighter weight, and less resources than non-foamed solid sheets, so food containers processed by thermoforming can be used in supermarkets, etc. Widely used as a disposable container.

  In these multi-layer foam sheets, a high design is achieved by laminating resin films with colored patterns on the foam sheets due to the growing need for food after purchase placed on food containers on the home table. A multi-layer foam sheet that can produce a food container having properties has been developed.

  Under these circumstances, in recent years, food containers having a texture like ceramics and excellent in surface smoothness and design are being demanded. In order to make a food container obtained by thermoforming a multilayer foamed sheet feel like a ceramic, the multilayer foamed sheet is required to have high surface smoothness and reproducibility of mold shape as important physical properties.

  As a method for producing a multilayer foam sheet for producing such a food container, for example, a heat laminating method in which a non-foamed resin film is thermally fused to a resin foam sheet as a base material, a molten resin is applied to the resin foam sheet. For example, an extrusion lamination method in which a non-foamed resin film is laminated is known.

Conventionally, the surface smoothness of multilayer foam sheets and food containers has been studied as required physical properties for printability (see, for example, Patent Documents 1 and 2). In Patent Document 1, surface smoothness is improved by laminating a non-foamed impact-resistant polystyrene resin with a thermal melting of more than 100 g / m ^{2 on a} foamed sheet by extrusion lamination. In Cited Document 2, a non-foamed impact polystyrene having a thickness of 50 μm is laminated on a polystyrene resin foam sheet having a density of 95 kg / m ³ and a thickness of 2.2 mm by extrusion lamination, so that the surface roughness is 0.78 μm. It is described that a multilayer foam sheet can be obtained.

JP 2012-11461 A JP 2001-129939 A

  However, according to the proposal of Patent Document 1, since the amount of the laminated thermoplastic resin is large, the mass of the sheet is heavy, and it is difficult to say that resource saving. Also, when thermoforming into food containers, the laminated surface on which a large amount of resin is laminated requires more heat than non-laminated surfaces, so pay attention to the heating balance of each surface. There is a problem that it is difficult to produce a molded article having a stable quality when the amount of laminated resin is extremely large.

  In addition, in the multilayer foam sheet having a small amount of thermoplastic resin to be laminated, a low density, and a thick thickness as proposed in Patent Document 2, the surface smoothness of the container obtained by thermoforming may be reduced, There was a possibility that the reproducibility of the mold shape was lowered. Further, when obtaining a molded body having a complicated shape such as a partition part, the multilayer foamed sheet is likely to be torn, and there is a possibility that it is likely to be restricted in the design of the container shape.

  The present invention has been made in order to solve such a problem, and while maintaining a high surface smoothness while greatly suppressing the amount of the resin layer laminated, and having a high surface smoothness by thermoforming. An object of the present invention is to provide a multilayer foamed sheet that can obtain a molded article with good reproducibility of the mold shape.

According to the present invention, the following multilayer foam sheet is provided.
<1> A multilayer foamed sheet having a thickness of 0.5 mm to 2.0 mm, comprising a polystyrene-based resin foam layer and a thermoplastic resin film layer laminated and adhered to at least one surface of the foam layer,
The thickness of the thermoplastic resin film layer is 10 to 60 μm, the apparent density A of the multilayer foamed sheet is 170 to 420 kg / m ³ , and the portion from the surface on the film layer side of the multilayer foamed sheet to 200 μm in the thickness direction. The apparent density B of the surface layer is higher than the apparent density A of the multilayer foamed sheet and is 320 kg / m ³ or more, and the arithmetic average roughness Ra of the surface of the multilayer foamed sheet on the film layer side is 1.5 μm or less. A multilayer foam sheet characterized by
<2> The multilayer foamed sheet according to <1>, wherein the content of the foaming agent in the surface layer part is 1% by mass or less.
<3> The multilayer foam sheet has a polystyrene resin foam layer and a thermoplastic resin film layer laminated and bonded only on one side of the foam layer, and the appearance of the foam layer with respect to the apparent density A of the multilayer foam sheet The multilayer foam sheet according to <1> or <2>, wherein the density C ratio (C / A) is 0.75 or more and less than 1.0.
<4> The multilayer foam sheet has a polystyrene resin foam layer and a thermoplastic resin film layer laminated and bonded to both surfaces of the foam layer, and the apparent density of the foam layer with respect to the apparent density A of the multilayer foam sheet The multilayer foamed sheet according to <1> or <2>, wherein the C ratio (C / A) is 0.60 or more and less than 1.0.
<5> The thermoplastic resin film layer X is laminated and bonded to the foamed layer by coextrusion, and heat is laminated and bonded to the surface of the film layer X by thermal lamination or extrusion lamination. The multilayer foamed sheet according to any one of <1> to <4>, wherein the multilayer foamed sheet is composed of a plastic resin film layer Y, and the total thickness of the film layer X and the film layer Y is 10 to 60 μm.

  According to the multilayer foam sheet of the present invention, the thickness and the apparent density of the multilayer foam sheet having the foam layer and the resin film layer laminated and adhered to at least one surface of the foam layer are in a specific range, and the resin of the multilayer foam sheet By setting the surface layer portion on the film layer side to a specific density or higher and the surface roughness to a specific value or lower, a multilayer foam sheet having excellent surface smoothness can be obtained even if the thickness of the thermoplastic resin layer is thin, and While having high surface smoothness by thermoforming, it is possible to obtain a molded body according to the mold shape.

  Hereinafter, the multilayer foamed sheet of the present invention will be described in detail. The multilayer foam sheet of this embodiment includes a polystyrene resin foam layer (hereinafter also referred to as a polystyrene resin foam sheet, a foam sheet, or a foam layer) and a thermoplastic resin that is laminated and bonded to at least one surface of the foam layer. A film layer (also referred to as a resin layer, a film layer, or a non-foamed layer).

  The polystyrene-based resin foam sheet is obtained by adding a foaming agent to a polystyrene-based resin and performing extrusion foam molding. Examples of the polystyrene resin used for the polystyrene resin foam sheet include polystyrene, rubber-modified polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-acrylic acid copolymer, and styrene-methacrylic acid. Copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-maleic anhydride copolymer, polystyrene -Resins such as polyphenylene ether copolymer and a mixture of polystyrene and polyphenylene ether are exemplified. The styrene component content in the polystyrene resin is preferably 50% by mass, more preferably 70% by mass. Among the polystyrene resins, it is preferable to use polystyrene because of its excellent foamability and rigidity when formed into a molded body.

  These resins include polypropylene resins such as propylene homopolymers and ethylene-propylene copolymers, polyethylene resins such as high-density polyethylene and low-density polyethylene, and styrene-conjugated diene blocks, depending on the desired purpose. Those containing other components such as thermoplastic elastomers such as copolymers and hydrogenated products thereof, and rubbers such as ethylene-propylene rubber and butadiene rubber can be used. In this case, the content of other components is preferably approximately 20% by mass or less, more preferably 10% by mass or less, and still more preferably less than 5% by mass.

  As the foaming agent, for example, a volatile foaming agent, an inorganic gas-based foaming agent, a decomposable foaming agent, or the like can be used. Examples of the volatile blowing agent include aliphatic hydrocarbons such as propane, normal butane, isobutane, pentane, and hexane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, 1,2-dichloro-1,1,2,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, 1,1-dichloro-2,2,2-trifluoroethane, Examples thereof include halogenated hydrocarbons such as methyl chloride, ethyl chloride, and ethylene chloride. Examples of the inorganic gas-based foaming agent include inert gases such as carbon dioxide, nitrogen, and air. Examples of the decomposable foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate, and the like. These foaming agents may be used alone or in combination of two or more. In the present invention, it is desirable to use a volatile foaming agent as the main foaming agent from the viewpoint of improving secondary foamability during heating prior to thermoforming of the polystyrene-based foamed sheet. Among these, normal butane, isobutane, or a mixture thereof can be suitably used from the viewpoint of compatibility with polystyrene resin and foaming efficiency.

  The amount of foaming agent added is appropriately adjusted according to the type of foaming agent used, polystyrene resin, the desired expansion ratio, etc., but is usually used for the polystyrene resin for forming the foam sheet. In general, the content is preferably 0.5 to 5.0% by mass, and more preferably 1.0 to 4.0% by mass.

  Moreover, as a component of a polystyrene-type resin foam sheet, in addition to the said component, various additives can be added in the range which does not inhibit the effect of this invention. Examples of the additive include an antioxidant, a heat stabilizer, a weathering agent, an ultraviolet absorber, a flame retardant, an inorganic filler, an antibacterial agent, and a colorant.

The apparent density A of the multilayer foamed sheet of the present invention is in the range of 170 to 420 kg / m ³ . If the apparent density A of the multi-layer foamed sheet is too low, the heat transfer during molding is poor, it becomes difficult to control the heating conditions necessary to improve the reproducibility of the mold shape, the surface smoothness is excellent and the gold There is a possibility that a molded body according to the mold shape (hereinafter also referred to as a sharp molded body) cannot be obtained. On the other hand, when the apparent density A of the multilayer foamed sheet is too high, there is a possibility that the heat retaining properties, light weight, and resource saving characteristics that are the characteristics of the foamed container are insufficient. In view of the above, the apparent density A of the multilayer foam sheet is preferably from 180~400kg / ^{m 3,} more preferably from 210~380kg / ^{m 3} range.

From the same viewpoint, the apparent density C of the polystyrene-based resin foam sheet is generally 150 to 400 kg / m ³ , preferably 170 to 380 kg / m ^{3, and} more preferably 200 to 350 kg / m ³ .

  The apparent density C of the polystyrene-based resin foam sheet (foam layer) in the multilayer foam sheet can be determined as follows. First, a test piece having a predetermined dimension (for example, width 100 mm × length 100 mm) is cut out from the multilayer foamed sheet, the film layer is cut out from the test piece, and the thickness and mass of the test piece excluding the film layer are measured. Next, the apparent density of the test piece is obtained by dividing the mass of the test piece by its volume (width × length × thickness). The said measurement is performed about 10 places of equal intervals in the width direction of a foam sheet, and let those arithmetic mean values be the apparent density C of a foam sheet.

  In addition, when it is difficult to separate the foam sheet (foam layer) and the film layer (non-foam layer) in the multilayer foam sheet, the apparent density C of the foam sheet can be obtained as follows. First, the basis weight of the foam sheet is obtained by subtracting the basis weight of the film layer from the basis weight of the multilayer foam sheet, and the thickness of the foam sheet is obtained by subtracting the thickness of the film layer from the thickness of the multilayer foam sheet. By dividing the basis weight of the foamed sheet obtained by the above method by the thickness of the foamed sheet, the apparent density C of the foamed sheet can be obtained. In addition, when using the polystyrene-type resin foam sheet which has the thermoplastic resin film layer X laminated | stacked and bonded by coextrusion as a base material sheet, the basic weight of a base material sheet, the foaming layer at the time of extrusion, and the film layer X The basis weight of the film layer X is determined from the discharge amount ratio and the thickness of the film layer X is determined by dividing the basis weight by the density of the resin constituting the film layer. The apparent density C of the foam sheet can be determined.

  The thermoplastic resin film layer laminated and adhered to at least one surface of the polystyrene resin foam sheet is not particularly limited as long as the intended object of the present invention can be achieved. A resin film, a polyolefin resin film such as a polyethylene resin or a polypropylene resin, a polyester resin film, a multilayer film of a polystyrene resin and a polyolefin resin, or the like can be used. From the viewpoint of surface smoothness, thermoformability, recyclability, and fusibility with a foamed sheet, it is preferable to use a polystyrene resin film as the thermoplastic resin film, and it is particularly preferable to use a polystyrene film. In addition, as a polystyrene film, the unstretched film manufactured by inflation molding can be used suitably. In addition, from the viewpoints of microwave heating and oil resistance, it is preferable to use a multilayer film of a polystyrene resin and a polyolefin resin or a polyolefin resin film, and these unstretched films can be suitably used. In addition, as a polyolefin resin film, what coated the adhesive agent can be used suitably.

  Any method can be used for laminating and bonding the thermoplastic resin film to the foamed sheet as long as the intended purpose of the present invention can be achieved. For example, the foamed sheet and the thermoplastic resin film are melted by a heated roll or the like. Thermal laminating system to be attached, extrusion laminating system in which a thermoplastic resin film is laminated and bonded to a foamed sheet via a molten resin, and a system in which an adhesive is coated on one side of a thermoplastic resin film and laminated to a foamed sheet. It can be selectively employed. The thermoplastic resin layer may have a multilayer structure by laminating a plurality of layers.

  The thickness of the thermoplastic resin film layer per side of the multilayer foamed sheet is 10 to 60 μm. If the thickness of the thermoplastic resin film layer is too thin, the surface roughness of the multilayer foamed sheet may not be reduced. In addition, due to the secondary foaming of the foamed sheet by thermoforming, the surface roughness of the resulting molded body may increase, and the surface smoothness may decrease. On the other hand, when the thickness of the thermoplastic resin film layer is too thick, the mass of the entire multi-layer foamed sheet increases, which may impair the lightness, resource saving, and cost. From the above viewpoint, the lower limit of the thickness of the thermoplastic resin film layer is preferably 12 μm, more preferably 14 μm, and still more preferably 16 μm. Moreover, it is preferable that the upper limit of the thickness of a thermoplastic resin film layer is 50 micrometers, More preferably, it is 45 micrometers. In addition, when it is difficult to directly measure the thickness of the thermoplastic resin film layer laminated on the multilayer foam sheet by microscopic observation, the basis weight of the film layer, which is the mass per unit area of the film layer, It can be determined by dividing by the density of the resin that constitutes.

  The thickness of the multilayer foamed sheet of the present invention is in the range of 0.5 to 2.0 mm. If the thickness of the multilayer foam sheet is too thin, the strength and heat insulating properties of the molded body obtained by thermoforming may be insufficient. On the other hand, if the thickness of the multilayer foam sheet is too thick, the heat transfer is poor during thermoforming, so that the reproducibility of the mold shape is reduced, the surface smoothness is good, and a sharp molded body is obtained. There is a risk of disappearing. In addition, when obtaining a molded body having a complicated shape such as a partition part or a fitting part, the multi-layer foamed sheet tends to tear at the partition part or the fitting part. There is a risk of receiving. From the above viewpoint, the thickness of the multilayer foam sheet is more preferably in the range of 0.6 to 1.8 mm, and still more preferably 0.6 to 1.6 mm.

In the multilayer foam sheet of the present invention, the apparent density B of the surface layer portion, which is a portion from the surface on the film layer side of the multilayer foam sheet to 200 μm in the thickness direction, is higher than the apparent density A of the multilayer foam sheet and is 320 kg / m. ³ or more. If the above apparent density B is too low, when the resin layer is laminated and bonded to the foamed sheet by thermal lamination or the like, it becomes more susceptible to re-foaming of the foamed sheet surface layer portion due to the heat of the resin layer to be laminated. The surface roughness of the sheet may increase. In addition, at the time of thermoforming, the surface of the foamed sheet surface layer part is easily affected by the secondary foaming, so that the surface roughness of the resulting molded body is increased and the surface smoothness may be lowered. From the above viewpoint, the apparent density B of the surface layer portion of the multilayer foamed sheet is more preferably 340 kg / m ³ or more, and still more preferably 360 kg / m ³ or more. The upper limit is preferably approximately 800 kg / m ³ . Further, from the viewpoint of the balance between mold shape reproducibility and surface smoothness, the ratio of the apparent density B of the surface layer portion of the multilayer foam sheet to the apparent density A of the multilayer foam sheet is 1.1 to 2.3. More preferably, it is 1.2-2.2, More preferably, it is 1.2-2.0.

  Further, in the multilayer foamed sheet, the amount of foaming agent remaining in the surface layer part which is a part from the surface on the film layer side of the multilayer foamed sheet to 200 μm in the thickness direction (content of foaming agent in the surface layer part) is 1% by mass or less. It is preferable that By making the amount of the foaming agent remaining in the above part 1% by mass or less, the influence of secondary foaming in the surface layer part of the foamed sheet by heat molding is reduced, and a molded article with good surface smoothness is more stable. Can be obtained. From the above viewpoint, the amount of the foaming agent remaining in the portion is preferably 0.9% by mass or less. Moreover, it is preferable that the minimum of the quantity of the foaming agent which remain | survives in the said part is about 0.2 mass%.

  On the other hand, the content of the foaming agent in the multilayer foamed sheet is preferably about 0.5 to 3.0% by mass, more preferably 0.5% from the viewpoint of moldability and surface smoothness of the obtained molded body. It is -2.0 mass%. Moreover, it is preferable that content of the foaming agent of a multilayer foamed sheet is larger than content of the foaming agent of the surface layer part of a multilayer foamed sheet.

  In measuring the content (mass%) of the foaming agent in the multilayer foam sheet, first, the measurement sample cut from the multilayer foam sheet is placed in a sample bottle with a lid containing toluene and stirred, After dissolving the foaming agent in toluene, the toluene in which the foaming agent is dissolved is collected with a microsyringe. Thereafter, the content of the blowing agent can be determined by measuring the collected toluene by an internal standard method using gas chromatography.

  In the multilayer foamed sheet of the present invention, the arithmetic average roughness Ra of the surface on the thermoplastic resin film layer side is 1.5 μm or less. If the surface roughness is too large, it becomes difficult to obtain a molded article having excellent surface smoothness by thermoforming. From the above viewpoint, the arithmetic average roughness Ra of the multilayer foamed sheet is preferably 1.2 μm or less, more preferably 1.0 μm or less, and still more preferably 0.9 μm or less.

  The surface roughness in this invention means arithmetic mean roughness Ra, and is the value measured about the multilayer foamed sheet according to JIS-B0601 (1994) using the surface roughness meter. The surface roughness meter may be one generally used, and examples thereof include Surfcoder SE1700α manufactured by Kosaka Laboratory. The arithmetic average roughness is measured five times at a measurement speed of 0.5 mm / second or less at a measurement distance of three times or more of the cut-off value along the extrusion direction of the multilayer foamed sheet, and the arithmetic average value is obtained. The cut-off value is 0.8 mm. The said measurement is performed about 10 places of equal intervals in the width direction of a multilayer foamed sheet, and those arithmetic mean values are made into the surface roughness of a multilayer laminated sheet. Moreover, it measures similarly about the surface roughness of the base material sheet mentioned later.

  In the configuration in which the multilayer foam sheet of the present invention has a foam layer and a thermoplastic resin film layer laminated on one side of the foam layer, the appearance of the polystyrene-based resin foam sheet with respect to the apparent density A of the multilayer foam sheet The ratio of density C is preferably 0.75 or more and less than 1.0. By setting the relationship of these apparent densities within the above range, the amount of the resin layer stacked can be reduced, and a molded article excellent in light weight, resource saving, and cost can be obtained. From the above viewpoint, the lower limit of the ratio of these apparent densities is more preferably 0.80.

  From the same viewpoint, in the configuration in which the multilayer foam sheet of the present invention has a foam layer and a thermoplastic resin film layer laminated and bonded to both surfaces of the foam layer, the foam sheet has an apparent density A of the multilayer foam sheet. The ratio of apparent density C is preferably 0.60 or more and less than 1.0. The lower limit of the apparent density ratio is more preferably 0.70, still more preferably 0.75, and particularly preferably 0.80.

  In the multilayer foam sheet of this invention, it can manufacture using a base material sheet. Here, the base sheet means a polystyrene resin foam sheet or a polystyrene resin foam sheet having a thermoplastic resin film layer X laminated and adhered by coextrusion. When the foamed sheet having the film layer X is used, the thermoplastic resin film laminated and adhered to the surface of the film layer X by thermal lamination or the like is also referred to as a thermoplastic resin film layer Y.

  The multilayer foam sheet of the present invention is preferably produced using a base sheet having a surface roughness of 4 μm or less on the surface to which the film layers are laminated and bonded. By setting the surface roughness of the base sheet within the above range, the surface roughness of the multilayer foamed sheet can be reduced even when thin resin layers are laminated. From the above viewpoint, the surface roughness of the base sheet is preferably 3.5 μm or less.

In the multilayer foam sheet of the present invention, the apparent density of the surface layer portion, which is a portion from the surface of the surface on which the film layer is laminated and bonded to 200 μm in the thickness direction, is higher than the apparent density of the base sheet, and is 300 kg / m. It is preferable to produce using a base sheet that is ³ or more. By setting the apparent density of the surface layer part of the base sheet to a specific range, when the resin layer is laminated and bonded to the base sheet by heat lamination or the like, re-foaming of the base sheet surface layer part by the heat of the resin layer to be laminated The impact can be reduced. In addition, since the influence of secondary foaming on the surface layer portion of the base sheet can be reduced during thermoforming, a molded article having excellent surface smoothness can be obtained even when the resin layer is thin. . From the above viewpoint, the apparent density of the surface layer portion of the base sheet is more preferably 320 kg / m ³ or more. The upper limit is preferably approximately 600 kg / m ³ .

  In the present invention, from the viewpoint of increasing the apparent density of the surface layer portion of the multilayer foam sheet on the surface to which the thermoplastic resin layer is laminated and bonded, and reducing the surface roughness of the multilayer foam sheet, the thermoplastic film layer is formed into the foam layer. The thermoplastic resin film layer X is preferably laminated and adhered by coextrusion, and the thermoplastic resin film layer Y is laminated and adhered to the surface of the film layer X by thermal lamination or extrusion lamination. In this case, the thermoplastic resin film layer X has a thickness of approximately 20 μm or less, and the same raw material as the polystyrene resin used for the polystyrene resin foam sheet can be used as the raw material, but the same kind of polystyrene as the foam sheet. It is preferable to use a resin. In particular, from the viewpoint of reducing the surface roughness of the obtained base sheet, it is preferable that the foam sheet and the thermoplastic resin film layer X are made of polystyrene.

  By using the coextrusion method, the film layer X can be thinly and uniformly laminated on the foam sheet. In addition, by forming the foam sheet and laminating the film layer X at the same time, it is possible to stably obtain a base sheet having a small surface roughness even when the apparent density of the foam sheet is relatively low. it can.

  When the base sheet has the film layer X, the total thickness of the film layer X in the base sheet and the thermoplastic resin film layer Y that is laminated and bonded to the base sheet is the thermoplastic resin film layer in the multilayer foam sheet. Of the thickness. As described above, the thickness of the thermoplastic resin film layer in this case (the total thickness of the film layer X and the film layer Y) is 10 to 60 μm.

  In the present invention, a sheet in which the film layer X is laminated and adhered to at least one surface of the polystyrene resin foam sheet by coextrusion is used as a base sheet, and the film layer Y is further laminated and adhered to the film layer X by thermal lamination or the like. Thus, the influence of re-foaming of the surface portion of the foamed sheet due to the heat of the laminated film layer Y can be reduced, and a multilayer foamed sheet having a small surface roughness can be stably obtained. In addition, compared to the case where a thermoplastic resin film layer is laminated and bonded directly to a polystyrene resin foam sheet, it is less susceptible to the secondary foaming of the foam sheet surface layer, and the surface roughness is small. You can get a body.

  Furthermore, in the base material sheet manufactured by the above-described coextrusion method, the melt flow rate of the polystyrene resin constituting the coextruded film layer X is preferably 10 g / 10 min or more, more preferably 15 g. / 10 min or more. By setting the melt flow rate of the film layer X to be coextruded to the above range, the coextruded polystyrene resin can be uniformly laminated on the foamed sheet without excessively high temperature, While reducing the surface roughness of a base material sheet, the fall of the closed cell rate of a polystyrene-type resin foam sheet can be suppressed. In addition, the upper limit of the melt flow rate of the film layer X is approximately 30 g / 10 min.

  In addition, said melt flow rate means the melt mass flow rate measured by the test method A method of JISK7210 (1999), and the test temperature of 200 degreeC and the load of 5 kg are employ | adopted.

  Next, a preferred embodiment of the method for producing a multilayer foam sheet of the present invention will be described. In the production of the multilayer foam sheet of the present invention, first, a base material sheet is produced by coextruding a polystyrene resin foam sheet or a polystyrene resin foam sheet and a polystyrene resin film layer X. The base sheet can be produced by a conventionally known extrusion foam molding.

  As a method for producing a polystyrene resin foam sheet, first, a raw material polystyrene resin and additives added as necessary are supplied to a tandem extruder and melted at a predetermined temperature in the first stage extruder. After that, a foaming agent is injected, cooled to a predetermined temperature by a second stage extruder, and extruded from a circular die provided at the tip of the extruder to be foamed. And after cooling while taking up the cylindrical foam extruded from the circular die along the cooling cylinder having a cooling function, it is cut into two sheets to obtain a polystyrene-based resin foam sheet of a predetermined size. Can do.

  In the production of polystyrene resin foam sheets, in order to make the apparent density and surface roughness of the surface layer portion of the multilayer foam sheet within a specific range, cooling is performed by applying cooling air to the cylindrical foam immediately after being extruded from the circular die. By doing so, it is preferable to increase the apparent density of the surface layer portion of the polystyrene-based resin foam sheet and to suppress the growth of bubbles in the surface layer portion.

  The obtained polystyrene-based resin foam sheet is cured under predetermined conditions. As the curing conditions, for example, about 20 days at a temperature of 25 ° C. is considered.

  Moreover, as a manufacturing method of the base material sheet which coextruded the polystyrene resin foam sheet and the polystyrene resin film layer X, first, in order to form the polystyrene resin foam sheet (foam layer), the raw polystyrene resin is used. Supply to the tandem extruder, melt at a predetermined temperature in the first stage extruder, press-fit a foaming agent, cool to a predetermined temperature in the second stage extruder, and install at the tip of the extruder Is supplied to a circular die having a coextruded structure. On the other hand, in order to form a polystyrene resin film layer X (non-foamed layer), the raw polystyrene resin is supplied to an extruder, melted at a predetermined temperature, and then supplied to a circular die having a coextrusion structure. To do. Then, the non-foamed layer forming resin melt to be the polystyrene resin film layer X is laminated on at least one surface of the foamed layer forming resin melt to be the polystyrene resin foam sheet in the circular die, and extruded into a cylindrical shape. The resin melt for forming the foam layer is foamed. And after cooling while taking up the cylindrical foam extruded from the circular die along the cooling cylinder provided with the cooling function, a base sheet of a predetermined size can be obtained by cutting it into two sheets. .

  Also in the production of polystyrene resin foam sheet having polystyrene film resin layer X laminated and bonded by coextrusion, in order to make the apparent density and surface roughness of the surface layer part of the multilayer foam sheet into a specific range, it is extruded from a circular die. The apparent density of the foam sheet on the surface layer of the polystyrene resin foam layer, that is, the surface on which the polystyrene resin film layer X is laminated by coextrusion is increased by cooling the cylindrical foam immediately after being applied with cooling air. At the same time, it is preferable to suppress the growth of bubbles in the surface layer portion of the polystyrene-based resin foam layer.

  In addition, the obtained base material sheet is cured on the same conditions as said polystyrene-type resin foam sheet.

The amount of cooling air that cools the cylindrical foam extruded from the annular die is not particularly limited as long as the apparent density of the surface layer portion of the base sheet is within the above range, but one side of the foam sheet On the other hand, it is preferable to set it to about 0.03-0.07 m < ³ > / m < ² > per expansion ratio of a foam sheet. The expansion ratio is a value obtained by dividing the density of the non-foamed resin used for the foam sheet by the apparent density of the foam sheet.

  Moreover, as a method of making the amount of the foaming agent remaining in the surface layer part of the multilayer foamed sheet within the above range, it is possible to adjust by taking a long curing period, etc., but from the viewpoint of improving productivity, foaming is performed. It is preferable that the base sheet is manufactured by setting the amount of the foaming agent added to the polystyrene-based resin for forming the sheet to 2% by mass or less.

In the production of the multilayer foam sheet of the present invention, the thermoplastic resin film layer is laminated and adhered to the polystyrene resin foam sheet or the polystyrene resin foam sheet having the thermoplastic resin film layer X laminated and adhered by coextrusion. At this time, the apparent density of the surface layer portion of the base sheet on the surface on which the film layer is laminated and bonded, specifically, the apparent density of the portion from the surface of the base sheet to 200 μm in the thickness direction is the apparent density of the base sheet. The density is preferably higher than 300 kg / m ³ . Thereby, the apparent density of the surface layer part of a multilayer foamed sheet can be raised. Moreover, it is preferable that the surface roughness of the base material sheet of the surface where the film layers are laminated and bonded is 4 μm or less. Thereby, the surface roughness of a multilayer foamed sheet can be made small.

  The method of laminating and adhering the thermoplastic resin film layer to the base sheet is not particularly limited, and various methods as described above can be adopted. From the viewpoint of reducing the surface roughness of the sheet, it is preferable to use a thermal laminating method.

  The multilayer foamed sheet of the present invention can be obtained by the above production method.

  In addition, thermoforming methods for multilayer foam sheets include vacuum forming and pressure forming, and free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, and reverse drawing. For example, molding, air slip molding, plug assist molding, plug assist reverse draw molding, or a molding method combining these can be used.

  Hereinafter, the multilayer foamed sheet of the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples.

Example 1
Polystyrene resin HH102 (PS Japan melt flow rate 2.6 g / 10 min) was supplied to a tandem extruder, melted at a temperature of 230 ° C. in the first stage extruder, and then the blowing agent butane S (manufactured by Gyxis). 1.4wt% press-fitted, cooled to 170 ° C in the second stage extruder, extruded into a cylindrical shape at a rate of 215kg per hour from a circular die with a slit gap of 0.4mm and a width of 220mm provided at the tip of the extruder And foamed. The cylindrical foam extruded from the circular die is cooled while being taken along a cooling tube having a cooling function of 640 mm in diameter and then cut into two pieces, each having a thickness of 1.0 mm and an apparent density of 350 kg. A polystyrene-based resin foam sheet having a width of / m ³ and a width of 1045 mm was obtained. Immediately after exiting the circular die, air of 1.7 m ³ / min (23 ° C.) from the cooling cylinder side (inside the cylindrical foam) and 1.6 m ³ / min (23 ° C.) from the outside of the cylindrical foam. The cooling of the foamed sheet was promoted. The obtained foamed sheet was cured at a temperature of 25 ° C. for 20 days, and then a 40 μm polystyrene film (manufactured by Towa Kako, unstretched inflation film) was temperature-controlled at 200 ° C. on the surface of the foamed sheet not cooled by the cooling cylinder. Lamination was performed by heat sealing at a rate of 20 m / min with a heating roll to obtain a multilayer foam sheet.

Example 2
Except that a 20 μm polystyrene film (manufactured by Towa Chemical Industries Co., Ltd., unstretched inflation film) was laminated on both sides of the foamed sheet, the same procedure was performed as in Example 1 to obtain a multilayer foamed sheet having a non-foamed layer on both sides.

Example 3
First, in order to form a foam layer, polystyrene resin G9305 (PS Japan melt flow rate 1.5 g / 10 min) was supplied to a tandem extruder, melted at a temperature of 230 ° C. in the first stage extruder, and then foamed. Butane S (manufactured by Gyxis) was injected by 1.5 wt%, cooled to 168 ° C. with a second-stage extruder, and a slit gap of 0.71 mm provided at the tip of the extruder at 306 kg / Hr, width aperture 220 mm To a circular die having a co-extrusion structure. On the other hand, in order to form a non-foamed layer, polystyrene resin 679 (PS Japan melt flow rate 18 g / 10 min) was supplied to an extruder and supplied at 190 ° C. to a circular die having a coextrusion structure at 24 kg / Hr. Then, a non-foamed layer forming resin melt that becomes a polystyrene-based resin layer is laminated on one side of a foamed layer forming resin melt that becomes a foamed sheet in a circular die, and extruded into a cylindrical shape to melt the foamed layer forming resin. The product was foamed. The cylindrical foam extruded from the circular die is cooled while being taken along a cooling tube having a cooling function of 640 mm in diameter, and then cut into two sheets, each having a thickness of 1.1 mm and an apparent density. A polystyrene resin foam sheet (base material sheet) having a polystyrene resin layer (thickness: 17 μm) of 217 kg / m ³ and a width of 1045 mm was obtained. Immediately after leaving the circular die, air of 3.5 m ³ / min (30 ° C.) from the cooling cylinder side (inside the cylindrical foam) and 3.2 m ³ / min (20 ° C.) from the outside of the cylindrical foam. The cooling of the base sheet was promoted by applying. Moreover, the polystyrene-type resin layer was laminated | stacked on the surface which is not cooled with the cooling cylinder of the foam sheet. After heating the obtained base material sheet at a temperature of 25 ° C. for 20 days, a heating roll in which a 20 μm polystyrene film (manufactured by Towa Chemical Industries, unstretched inflation film) was temperature-controlled at 200 ° C. on the surface on which the polystyrene resin layer was laminated. Was laminated by heat fusion at a speed of 20 m / min to obtain a multilayer foam sheet.

Example 4
G9001 (PS Japan Melt Flow Rate 1.5 g / 10 min) was used as the polystyrene resin for forming the foamed layer, and it was cooled to 168 ° C. with a second-stage extruder and laminated with a heating roll. A multilayer foamed sheet was obtained in the same manner as in Example 3 except that a 25 μm polypropylene film (manufactured by Nakamoto Pax) coated with an adhesive was used as the thermoplastic resin film.

Comparative Example 1
Polystyrene resin HH102 (PS Japan melt flow rate 2.6 g / 10 min) was supplied to a tandem extruder, melted at a temperature of 230 ° C. in the first stage extruder, and then the blowing agent butane S (manufactured by Gyxis). 1.4wt% press-fitted, cooled to 166 ° C with a second stage extruder, extruded in a cylindrical shape at a rate of 200kg per hour from a circular die with a slit gap of 0.4mm and a width of 220mm provided at the tip of the extruder. And foamed. The cylindrical foam extruded from the circular die is cooled while being taken along a cooling tube having a cooling function of 640 mm in diameter and then cut into two pieces, each having a thickness of 1.0 mm and an apparent density of 350 kg. A polystyrene-based resin foam sheet having a width of / m ³ and a width of 1045 mm was obtained. Incidentally, immediately after leaving the circular die, an air cooling tube side 1.0m ³ / min (23 ℃) from (tubular foam body ^{side), 1.0m 3 / min (23} ℃) from the outer tubular foam It was applied to promote cooling. The obtained foamed sheet was cured at a temperature of 25 ° C. for 20 days, and then a 40 μm polystyrene film (manufactured by Towa Kako, unstretched inflation film) was temperature-controlled at 200 ° C. on the surface of the foamed sheet not cooled by the cooling cylinder. Lamination was performed by heat sealing at a rate of 20 m / min with a heating roll to obtain a multilayer foam sheet.

Comparative Example 2
Polystyrene resin HH102 (PS Japan melt flow rate 2.6 g / 10 min) was supplied to a tandem extruder, melted at a temperature of 230 ° C. in the first stage extruder, and then the blowing agent butane S (manufactured by Gyxis). 2.4 wt% press-fit, cooled to 158 ° C. with a second stage extruder, extruded into a cylindrical shape at a rate of 195 kg per hour from a circular die with a slit gap of 0.4 mm and a width of 220 mm provided at the end of the extruder. And foamed. The cylindrical foam extruded from the circular die is cooled while being taken along a cooling tube having a cooling function of 640 mm in diameter, and then cut into two pieces, each having a thickness of 1.2 mm and an apparent density of 210 kg. A polystyrene-based resin foam sheet serving as a base material with a width of / m ³ and a width of 1045 mm was obtained. Immediately after leaving the circular die, air of 1.4 m ³ / min (20 ° C.) from the cooling cylinder side (inside the cylindrical foam) and 1.5 m ³ / min (20 ° C.) from the outside of the cylindrical foam. The cooling of the foamed sheet was promoted. The obtained foamed sheet was cured at a temperature of 25 ° C. for 20 days, and then a 40 μm polystyrene film (manufactured by Towa Kako, unstretched inflation film) was temperature-controlled at 200 ° C. on the surface of the foamed sheet not cooled by the cooling cylinder. Lamination was performed by heat sealing at a rate of 20 m / min with a heating roll to obtain a multilayer foam sheet.

Comparative Example 3
Polystyrene resin HH102 (PS Japan melt flow rate 2.6 g / 10 min) was supplied to a tandem extruder, melted at a temperature of 230 ° C. in the first stage extruder, and then the blowing agent butane S (manufactured by Gyxis). 2.4 wt% press-fit, cooled to 158 ° C. with a second stage extruder, extruded into a cylindrical shape at a rate of 195 kg per hour from a circular die with a slit gap of 0.4 mm and a width of 220 mm provided at the end of the extruder. And foamed. The cylindrical foam extruded from the circular die is cooled while being taken along a cooling tube having a cooling function of 640 mm in diameter, and then cut into two pieces, each having a thickness of 1.2 mm and an apparent density of 210 kg. A polystyrene-based resin foam sheet having a width of / m ³ and a width of 1045 mm was obtained. Immediately after leaving the circular die, air of 1.4 m ³ / min (20 ° C.) from the cooling cylinder side (inside the cylindrical foam) and 1.5 m ³ / min (20 ° C.) from the outside of the cylindrical foam. The cooling of the foamed sheet was promoted. After the obtained foamed sheet was cured at a temperature of 25 ° C. for 20 days, a 25 μm polystyrene film (manufactured by Towa Kako, unstretched inflation film) was heated and melted to 250 ° C. on the surface of the foamed sheet not cooled by the cooling cylinder. High impact polystyrene 475D (manufactured by PS Japan, melt flow rate 2.0 g / 10 min) was laminated by performing extrusion lamination at a speed of 20 m / min through 100 μm to obtain a multilayer foam sheet.

  Next, after curing the multilayer foamed sheets obtained in Examples 1 to 4 and Comparative Examples 1 to 3 at a temperature of 25 ° C. for 3 days, a molding machine manufactured by Asano Laboratories (product number FKS-0631-10) was used. Then, thermoforming was performed by match mold vacuum forming to obtain a rectangular container (food tray) in a top view having a flange part and a partition part. As for the external dimensions of the container, the long side of the container × short side (top view) is 21 cm × 15 cm, the height of the container is 3 cm, and the thickness of the container (thickness of the multilayer sheet after molding) is 1.0 mm. The heating conditions were a heater temperature of 330 ° C. and a heating time of 8 seconds ± 1 second.

Table 1 shows properties of the base material sheets of Examples 1 to 4 and Comparative Examples 1 to 3, the obtained multilayer foamed sheet, and the molded body. The physical properties in Table 1 were measured and evaluated as follows.
(Thickness, basis weight, apparent density of base sheet and multilayer foam sheet)
First, the multilayer foamed sheet and the base sheet are cut to a length of 100 mm in the extrusion direction (MD) across the width direction, and further, both ends in the width direction (TD) orthogonal to the extrusion direction are cut off by 25 mm, and the width direction A portion having a central portion of 1000 mm was used as a test piece. This test piece was further divided into 10 equal parts in the width direction, and the thickness near the center was measured with a micrometer. The value obtained by arithmetically averaging the thickness at each measurement point was taken as the thickness of the multilayer foamed sheet or substrate sheet. Further, the mass of the test piece is measured, the mass is divided by the area of the test piece (specifically, 1000 mm × 100 mm), and converted into g / m ² as a unit, and the basis weight of the multilayer foam sheet and the base sheet. The amount. Furthermore, this basic weight was remove | divided by the said thickness, and it was set as kg / cm < ³ > and converted into a unit, and it was set as the apparent density A of the base material sheet and the multilayer foam sheet.
(Surface roughness of the laminated surface of the base sheet, the multilayer foam sheet, and the flange portion of the molded body)
The surface roughness was measured using a surf coder SE1700α manufactured by Kosaka Laboratory Co., Ltd. according to JIS-B0601 (1994). Specifically, a multilayer foam sheet or a base sheet is cut into a size of 20 mm × 20 mm to prepare a test piece, the test piece is left on a horizontal base, and the tip of a stylus having a tip curvature radius of 2 μm. Is brought into contact with the surface of the test piece (the surface on the thermoplastic resin film layer side in the multilayer foam sheet or the surface on which the thermoplastic resin film layer is laminated in the base sheet), and the test piece is adjusted to 0.5 mm / s. Then, the sheet was moved in the extrusion direction of the multilayer foam sheet or the base sheet, and the measurement distance of 8 mm was measured five times, and the arithmetic average value was obtained. The measurement magnification was vertical: 500, horizontal: 2, and the cutoff value was 0.8 mm. The said measurement was performed with respect to the test piece cut out from ten places of equal intervals in the width direction of a test sheet, and those arithmetic mean values were made into surface roughness Ra (micrometer) of a multilayer foam sheet or a base material sheet.

Moreover, in the measurement of the surface roughness of the flange part of a molded object, the test piece of 15 mm x 15 mm was cut out from the flat part of the flange part first. Next, the surface roughness of the test piece was measured with the stylus of the measuring device passing through the center of the test piece. The measurement conditions at this time were the same as the measurement conditions for the multilayer foamed sheet. The above measurement was performed in three directions rotated by 60 ° with respect to the center of the test piece, and the arithmetic average value in the three directions was defined as the surface roughness of the flange portion of the molded body.
(Apparent density of the surface layer portion of the base sheet and multilayer foam sheet)
A 200 μm portion is sliced in the thickness direction from the surface to be laminated of the base sheet and the surface of the multilayer foam sheet on the thermoplastic resin film layer side, and the length (sheet extrusion direction) 20 mm × width (sheet extrusion direction) (Width direction) While cutting out to a 5 mm test piece, the mass and thickness of the test piece were measured with the gauge. The mass of the test piece was divided by the volume (width × length × thickness) of the test piece, and the apparent density of the test piece was determined in terms of units. The above measurement is performed at 10 equally spaced positions in the width direction of the sheet, and the arithmetic average value thereof is calculated based on the apparent density of the surface layer portion of the base sheet and the multilayer foamed sheet (surface layer density of the laminated surface of the base sheet, multilayer). Surface layer density of the laminated surface of the foam sheet).
(Thickness of the foam layer in the multilayer foam sheet)
The thickness of the foamed layer (foamed sheet portion in the multilayer foamed sheet) was determined by reducing the thickness of the non-foamed layer (thermoplastic resin film layer) from the thickness of the multilayer foamed sheet obtained by the above method.
(Basis weight of non-foamed layer in multilayer foamed sheet)
The basis weight of the non-foamed layer was determined by multiplying the thickness of the non-foamed layer by the density of the resin constituting the non-foamed layer and converting the unit. In the case where a polystyrene resin foam sheet having a thermoplastic resin film layer X laminated and adhered by coextrusion is used as the base sheet, the basis weight of the base sheet, the foam layer and the film layer at the time of extrusion The basis weight of the non-foamed layer was determined by adding the basis weight of the film layer Y to the basis weight of the film layer X determined from the discharge amount ratio with X.
(Apparent density C of the foam layer in the multilayer foam sheet)
By dividing the basis weight of the foam layer determined by subtracting the basis weight of the non-foamed layer from the basis weight of the multilayer foam sheet, the apparent density C of the foam layer is obtained by dividing by the thickness of the foam layer obtained by the above method. It was.
(Content of foaming agent in the surface layer of the multilayer foam sheet)
After slicing a 200 μm portion in the thickness direction from the surface of the multilayer foam sheet on the thermoplastic resin film layer side and dissolving the foaming agent contained in the sliced portion by the above method in toluene, Shimadzu Corporation as a measuring machine Using GC-14B manufactured by Seisakusho, the amount of foaming agent remaining in the surface layer portion of the multilayer foamed sheet was measured under the following conditions. In addition, the said operation was performed with respect to the multilayer foamed sheet just before thermoforming to a food tray.
(A) Column: Shimadzu Corporation column Silicone DC550 20% on Chromosorb WA AW-DMCS 60/80 mesh, 4.1 m × 3.2 mm
(B) Column temperature: 40 ° C
(C) Detector temperature: 180 ° C
(D) Inlet temperature: 180 ° C
(E) Detector: FID
(F) Carrier gas: nitrogen 140 ml / min.
(G) Sample volume: 2 μl
(H) Internal standard: cyclopentane (formability)
Formability was visually evaluated according to the following criteria.
○ ... Good formability (good mold shape reproducibility and sharp molded product is obtained)
× ・ ・ ・ There are defects

  The multilayer foamed sheets obtained in the examples have a small surface roughness and a high level of surface smoothness despite the small amount of non-foamed layers. On the other hand, in Comparative Examples 1 and 2, a high amount of non-foamed layer cannot be achieved with a small amount of non-foamed layer, and in Comparative Example 3, a large amount of non-foamed layer needs to be laminated in order to achieve a high surface smoothness. It was confirmed that there was.

  From these results, the multilayer foamed sheet of the present invention has the thickness and apparent density of the multilayer foamed sheet within the range defined by the present invention, and the surface layer portion on the thermoplastic resin film layer side is at or above the specified density, and the multilayer foamed sheet By setting the surface roughness on the thermoplastic resin film layer side to a specified value or less, a laminated foam sheet having excellent surface smoothness can be obtained even when the thickness of the thermoplastic resin film layer is thin, and by thermoforming It was confirmed that a molded article having a high surface smoothness and having a mold shape was obtained.

Claims (5)

A multilayer foam sheet having a thickness of 0.5 mm to 2.0 mm, comprising a polystyrene resin foam layer and a thermoplastic resin film layer laminated and adhered to at least one surface of the foam layer,
The thickness of the thermoplastic resin film layer is 10 to 60 μm, the apparent density A of the multilayer foamed sheet is 170 to 420 kg / m ³ , and the portion from the surface on the film layer side of the multilayer foamed sheet to 200 μm in the thickness direction. The apparent density B of the surface layer is higher than the apparent density A of the multilayer foamed sheet and is 320 kg / m ³ or more, and the arithmetic average roughness Ra of the surface of the multilayer foamed sheet on the film layer side is 1.5 μm or less. A multilayer foam sheet characterized by   The multilayer foamed sheet according to claim 1, wherein the content of the foaming agent in the surface layer portion is 1% by mass or less.   The multilayer foam sheet has a polystyrene-based resin foam layer and a thermoplastic resin film layer laminated and bonded only to one side of the foam layer, and the apparent density C of the foam layer with respect to the apparent density A of the multilayer foam sheet. Ratio (C / A) is 0.75 or more and less than 1.0, The multilayer foamed sheet of Claim 1 or 2 characterized by the above-mentioned. The multilayer foam sheet has a polystyrene-based resin foam layer and a thermoplastic resin film layer laminated and bonded to both surfaces of the foam layer, and the ratio of the apparent density C of the foam layer to the apparent density A of the multilayer foam sheet (C / A) is 0.60 or more and less than 1.0, The multilayer foamed sheet of Claim 1 or 2 characterized by the above-mentioned. The thermoplastic resin film layer is laminated and adhered to the foam layer by coextrusion, and the thermoplastic resin film is laminated and adhered to the surface of the film layer by thermal lamination or extrusion lamination. The multilayer foamed sheet according to any one of claims 1 to 4, wherein the multilayer foamed sheet comprises the layer Y and the total thickness of the film layer X and the film layer Y is 10 to 60 µm.