JP4829136B2 - Laminated foam sheet, method for producing the same, and tray for fruits and vegetables - Google Patents

Description

  The present invention relates to a laminated foam sheet having a particularly excellent buffering property as a buffer material, a method for producing the same, and a tray for fruits and vegetables obtained by thermoforming the sheet.

  Conventionally, thermoplastic resin foam sheets such as polystyrene resin foam sheets, cross-linked polyethylene resin foam sheets, polypropylene resin foam sheets, etc. are thermoformed, and multiple storage recesses for buffer packaging of fruits, such as apples, pears, peaches, and tomatoes A tray having a molded product or a tray molded product using a pulp mold is used. These trays have different advantages and disadvantages depending on the type of fruits and vegetables to be stored and the storage form. For example, trays made of polystyrene resin foam sheets are often used to store pears that have a certain amount of weight and have a hard surface, and trays made of crosslinked polyethylene resin foam sheets are used to store peaches that are soft and easily damaged. used. Furthermore, trays with pulp molds are used to store apples and tomatoes. Thus, a wide variety of fruit and vegetable trays are required.

  On the other hand, when using a variety of different trays depending on the type of fruit and vegetables, it is necessary to have inventory in anticipation of the required quantity at an earlier stage than the harvest time of fruit and vegetables. When there were few or many, it was difficult to interchange trays of different materials. Furthermore, the fruit and vegetable tray made of a polystyrene resin foam sheet has a problem that its impact resistance is low due to its resin characteristics and it is easy to break. Also, fruit and vegetable trays made of polypropylene resin foam sheets are difficult to obtain for specific purposes unless specific polypropylene resins are used. Since the resin is expensive, we supply cheap fruit and vegetable trays. There is a difficult problem. Furthermore, the fruit and vegetable tray made of a crosslinked polyethylene resin foam sheet has a problem that it is difficult to recycle because it has a crosslinked structure, and the manufacturing process is complicated and the cost is increased. Moreover, the tray which consists of pulp molds has the problem that intensity | strength falls remarkably at the time of water absorption.

  Therefore, the fruits and vegetables trays have been unified and the fruits and vegetables trays that can solve the problems of each material are being developed. Polystyrene resin foam sheets are preferred as this type of tray material because they are excellent in terms of recycling and cost, and the development of fruit and vegetable trays is aimed at improving the problems of polystyrene resin foam sheets, For example, in order to improve the impact properties of ordinary polystyrene, attempts have been made to use rubber-modified impact resistant polystyrene. However, the effect of improving the flexibility of foam by impact-resistant polystyrene alone is not so great. If the amount of impact-resistant polystyrene increases, problems such as foaming and deterioration of moldability also occur. It is insufficient as a tray.

Various techniques have been proposed so far to provide a higher-performance polystyrene-based resin foam sheet and a molded product thereof. For example, a fruit and vegetable tray formed from a foamed sheet of a mixed resin of a polystyrene-based resin and an ethylene-styrene copolymer has been proposed (see Patent Document 1).
Moreover, the tray for fruit and vegetables shape | molded from the foamed sheet | seat of the mixed resin of polystyrene-type resin, ethylene-styrene copolymer, and polyethylene-type resin is proposed (refer patent document 2).
Furthermore, a specific resin obtained from a polystyrene resin, a polyethylene resin, a copolymer of styrene and a conjugated diene having a specific hardness, or a resin composition containing hydrogen, which has improved the problem of fusibility of the foam sheet. A hard extruded foam layer has been proposed (see Patent Document 3).
JP 2000-22620 A JP 2001-151220 A JP 2004-238413 A

However, the conventional techniques disclosed in Patent Documents 1 to 3 have the following problems.
Although the fruit and vegetable trays disclosed in Patent Documents 1 and 2 are excellent in flexibility and buffering properties, they contain an ethylene-styrene copolymer and thus have low heat resistance and are exposed to a high temperature state during storage of the fruit and vegetable tray. If this occurs, there is a problem that the stacked trays are fused and difficult to peel off.
Although the fruit and vegetable tray disclosed in Patent Document 3 has an improvement effect on the fusion of the tray as compared with the fruit and vegetable trays disclosed in Patent Documents 1 and 2, the glass transition temperature is lower than that of the styrene resin. Since it contains a low resin, depending on the storage conditions, the fruit and vegetable trays may be fused together, and the problem has not been completely overcome.
Furthermore, although all the fruit and vegetable trays disclosed in Patent Documents 1 to 3 have excellent surface buffering properties, the fruit and vegetable trays for storing heavy fruits are insufficient in terms of strength.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laminated foamed sheet that can prevent fusion during storage of a molded product and is excellent in the strength of the molded product, a manufacturing method thereof, and a tray for fruits and vegetables.

In order to achieve the above object, the present invention provides a polystyrene resin (a), a polyethylene resin (b) having a density of 0.87 to 0.92 g / cm ^3, a copolymer of styrene and a conjugated diene, or hydrogenation thereof. An extruded foam layer of a resin composition (i) containing a product (c), wherein a copolymer of styrene and conjugated diene or a hydrogenated product thereof (c) has a durometer type A hardness value HDA of 90 or less. A laminated foamed sheet in which a first foamed layer having a density of an extruded foamed layer of 0.03 to 0.2 g / cm ³ and a polystyrene resin foamed layer are laminated, and the laminated foamed sheet is heated and deformed. value in the extrusion direction from 90 to 103, Ri 97-117 der in the extrusion direction and perpendicular,
The resin composition (i) is a polystyrene resin (a) 50 to 90% by mass, a polyethylene resin (b) 3 to 20% by mass, a copolymer of styrene and conjugated diene or a hydrogenated product (c) 3 thereof. Having a composition of ˜47 mass% (however, a polyethylene resin (b) + copolymer of styrene and conjugated diene or a hydrogenated product thereof (c) = range of 10 to 50 mass%),
The thickness of the laminated sheet is in the range of 1.0 mm to 5.0 mm, the basis weight is in the range of 80 to 400 g / m ² , and the thickness ratio of the first foam layer to the polystyrene resin foam layer is 10: Provided is a laminated foam sheet having a range of 1-1: 2 .

  The present invention also provides a fruit and vegetable tray obtained by thermoforming the laminated foam sheet according to the present invention.

  The present invention also provides a method for producing a laminated foamed sheet, wherein the first foamed layer and the polystyrene-based resin foamed layer are produced by coextrusion to obtain the laminated foamed sheet according to the present invention.

  According to the present invention, the foam sheet and its molded product have high flexibility, can further improve the peelability between the foam sheet and the molded product, have sufficient weather resistance, and can be used for a wide variety of products, such as flexibility, cushioning and A high-strength laminated foam sheet and fruit and vegetable tray can be provided.

FIG. 1 is a schematic cross-sectional view showing an embodiment of the laminated foam sheet of the present invention. The laminated foam sheet 1 of the present embodiment includes a polystyrene resin (a), a polyethylene resin (b) having a density of 0.87 to 0.92 g / cm ^3, a copolymer of styrene and a conjugated diene, or a hydrogenated product thereof. (C) an extruded foam layer of a resin composition (i), wherein a copolymer of styrene and conjugated diene or a hydrogenated product thereof (c) has a durometer type A hardness value HDA of 90 or less. The first foamed layer 2 having an extruded foam layer density of 0.03 to 0.2 g / cm ³ and a polystyrene resin foam layer 3 (hereinafter referred to as a PSP layer) are laminated. The heat-deformed value of the laminated foamed sheet 1 is in the range of 90 to 103 in the extrusion direction (hereinafter referred to as MD direction), and 97 in the direction orthogonal to the MD direction (hereinafter referred to as TD direction). It is in the range of ~ 117 It is set to.

  The laminated foam sheet 1 of the present embodiment shown in FIG. 1 exemplifies a structure in which a first foam layer 2 and a PSP layer 3 are laminated, but the laminated foam sheet 1 of the present invention is It is not limited only to the embodiment, and a non-foamed resin film can be laminated on the surface of the laminated foamed sheet to constitute a laminated foamed sheet.

[First foam layer]
The first foam layer 2 in the laminated foam sheet 1 of the present invention comprises a polystyrene resin (a), a polyethylene resin (b) having a density of 0.87 to 0.92 g / cm ³ , and a copolymer of styrene and a conjugated diene. Or an extruded foam layer of the resin composition (i) containing the hydrogenated product (c) thereof, wherein the copolymer of styrene and conjugated diene or the hydrogenated product (c) thereof has a durometer type A hardness value HDA. Is 90 or less, and the density of the extruded foamed layer is 0.03 to 0.2 g / cm ³ .

  The polystyrene resin (a) used for the first foamed layer 2 is a polystyrene resin or a polystyrene resin mixture containing polystyrene resin as a main component, particularly a polystyrene homopolymer alone or a polystyrene homopolymer 50- A resin composed of 90% by mass and impact resistant polystyrene or 10-50% by mass of a styrene-acrylic acid ester copolymer is preferable. Adding impact-resistant polystyrene to polystyrene homopolymer is effective in improving flexibility, but if the amount of impact-resistant polystyrene increases, the retention of foaming agent gas decreases and moldability deteriorates. The weather resistance decreases due to the rubber component contained therein, and problems such as a decrease in flexibility and cracking of the molded product are likely to occur when the molded product is stored for a long period of time. For this reason, it is preferable that the compounding quantity of an impact-resistant polystyrene shall be 50 mass% or less of the whole polystyrene resin (a), it is more preferable to set it as 40 mass% or less, and it is further more preferable to set it as 30 mass% or less. .

  Examples of the styrene-acrylate ester copolymer include a copolymer of a styrene monomer and an acrylate ester. As the acrylate ester, acrylic acid such as ethyl acrylate and butyl acrylate, and a carbon number of 1 to 1 is used. 10 esters with alcohols are preferred. As such a copolymer, styrene-butyl acrylate is preferable in terms of an effect of improving flexibility. In the styrene-acrylic acid ester copolymer used in the present invention, the acrylic acid ester content is 1 to 40% by mass, preferably 1 to 30% by mass. Since the heat resistance of the resin decreases depending on the content of the acrylate ester in the styrene-acrylate ester copolymer, when a large amount of the styrene-acrylate ester copolymer is blended as a raw material, In some cases, the heat resistance may be excessively reduced, and in such a case, problems such as fusibility between the laminated foam sheets 1 and thermal deformation of the molded product are likely to occur. Therefore, when the styrene-acrylic acid ester copolymer is blended as a whole, the blending amount is preferably 50% by mass or less, more preferably 40% by mass or less of the entire polystyrene resin (a), More preferably, it is 30 mass% or less.

The polyethylene resin (b) used for the first foam layer 2 is a polyethylene resin having a density of 0.87 to 0.92 g / cm ³ . If the density of the polyethylene resin (b) is lower than 0.87 g / cm ^3, it is not preferable because the problem of fusing property is increased as compared with the effect of improving flexibility. A polyethylene-based resin having a density exceeding 0.92 g / cm ³ is not preferable, except for an ethylene-vinyl acetate copolymer, which has a small effect of improving flexibility and must be blended in a large amount. Density of the polyethylene resin (b) used in the present invention is preferably in the range of 0.88~0.92g / cm ^3, a range of 0.88~0.91g / cm ³ is more preferable. Preferred polyethylene resins in the present invention include, for example, low density polyethylene, linear low density polyethylene, ultra low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-α olefin copolymer, ethylene-methyl methacrylate copolymer. Examples thereof include copolymers, ethylene-ethyl acrylate copolymers, etc., or other vinyl monomers copolymerizable with ethylene and ethylene. Of these, the ethylene-vinyl acetate copolymer increases the flexibility and increases the resin density as the vinyl acetate content increases. A resin having a vinyl acetate content exceeding 15% by mass has a high effect of improving flexibility, but it is not preferable because an odor problem and a fusing problem are likely to occur. Therefore, the ethylene-vinyl acetate copolymer preferably has a vinyl acetate content of 15% by mass or less.

  The copolymer of styrene and conjugated diene or the hydrogenated product (c) thereof used for the first foam layer 2 has a durometer type A hardness value HDA of 90 or less. The type of copolymer may be a block copolymer or a random copolymer. Examples of the conjugated diene include conjugated dienes having 4 to 10 carbon atoms such as butadiene, isoprene, and 2-ethylbutadiene. A preferable styrene-conjugated diene copolymer or a hydrogenated copolymer thereof is a styrene-isoprene block copolymer or a hydrogenated product thereof, a styrene-butadiene block copolymer or a hydrogenated product thereof. The fully saturated structure of these copolymers includes, for example, styrene-ethylene / butylene copolymer, styrene-ethylene / butylene / styrene block copolymer, styrene / ethylene / propylene copolymer, and styrene / ethylene / propylene / styrene block. Such as a copolymer. In order to prevent deterioration of the weather resistance of the laminated foamed sheet 1 and its molded product, a copolymer that is particularly hydrogenated and has a smaller number of double bonds in the molecular chain is preferable. . In the laminated foam sheet 1 of the present invention, the copolymer of styrene and conjugated diene or the hydrogenated product thereof may be used alone or in combination of two or more.

  Furthermore, in the present invention, the copolymer of styrene and conjugated diene or its hydrogenated product (c) has a durometer type A hardness value HDA of 90 or less, preferably 20 to 80, more preferably 20 to 70. Use things. When the value of HDA is higher than 90, the effect of improving the flexibility is small, and in order to satisfy the flexibility of the first foam layer 2, it must be blended in a large amount, resulting in problems of foamability and fusibility. Or the cost increases. When the HDA is less than 20, the resin viscosity is too low and the foamability may be lowered, or the heat resistance of the foam may be lowered.

  The first foamed layer 2 includes a resin composition (i) containing the polystyrene resin (a), a polyethylene resin (b), a copolymer of styrene and a conjugated diene, or a hydrogenated product (c) thereof. ) And a foaming agent (ii) are obtained by extrusion foaming, and the resin composition (i) comprises 50 to 90% by mass of a polystyrene resin (a), a polyethylene resin (b) 3 ~ 20% by mass, copolymer of styrene and conjugated diene or hydrogenated product thereof (c) 3 to 47% by mass (provided that polyethylene resin (b) + copolymer of styrene and conjugated diene or hydrogenated thereof) It is preferable to have a composition of a thing (c) = 10-50 mass%.

  The blending amount of the polyethylene resin (b) in the resin composition (i) is in the range of 3 to 20% by mass, preferably in the range of 4 to 20% by mass, and in the range of 4 to 15% by mass. More preferably. When the blending amount of the polyethylene resin (b) is 3% by mass or less, the effect of improving the flexibility by the polyethylene resin (b) becomes insufficient, and the flexibility of the laminated foamed sheet molded product such as the fruit and vegetable tray becomes insufficient. There is a case. On the other hand, if the blending amount of the polyethylene resin (b) exceeds 20% by mass, the foaming agent gas remaining in the laminated foamed sheet is quickly dissipated into the atmosphere. Is worse, and as a result, the moldability is unfavorable.

  The blending amount of the copolymer of styrene and conjugated diene or its hydrogenated product (c) in the resin composition (i) is in the range of 3 to 47% by mass, preferably in the range of 5 to 35% by mass. The range of 5-25 mass% is more preferable. When the blending amount of the copolymer of styrene and conjugated diene or its hydrogenated product (c) is less than 3% by mass, the compatibility between the polystyrene resin (a) and the polyethylene resin (b) is reduced. The flexibility improvement effect by the copolymer of styrene and conjugated diene or its hydrogenated product (c) is also small, which is not preferable. On the other hand, when the blending amount of the copolymer of styrene and conjugated diene or its hydrogenated product (c) exceeds 47% by mass, the open cell ratio increases due to the decrease in resin viscosity, the moldability deteriorates, and the laminated foam sheet. This is not preferable because problems such as lowering of heat resistance and deterioration of peelability occur.

  In a preferred embodiment, the polyethylene resin (b), a copolymer of styrene and conjugated diene or a hydrogenated product thereof (c) has a total amount of (b) and (c) of 10 to 50% by mass. Is preferably blended in the resin composition (i) so as to be in the range of 20 to 40% by mass, more preferably 25 to 35% by mass. When the total amount of the polyethylene resin (b), the copolymer of styrene and conjugated diene or the hydrogenated product (c) thereof is less than 10% by mass, the flexibility improving effect is reduced, which is not preferable. On the other hand, if the total amount exceeds 50% by mass, the foamability and thermoformability deteriorate, and the peelability deteriorates, which is not preferable.

When the density of the first foamed layer 2 is high, the flexibility is insufficient, and the flexibility of the laminated foamed sheet 1 can be improved by lowering the density. However, since the thermoforming characteristics are different for each of polystyrene-based resin and polyethylene-based resin, and further, a copolymer of styrene and conjugated diene or a hydrogenated product thereof, when the first foamed layer 2 has a low density, molding at the time of thermoforming Since the property deteriorates, the density of the first foamed layer 2 is set in the range of 0.03 to 0.2 g / cm ³ . The density of the first foam layer 2 is more preferably in the range of 0.04 to 0.1 g / cm ^{3 in} terms of moldability, flexibility, and strength of the molded product.

[PSP layer]
The polystyrene resin used for the PSP layer 3 constituting the laminated foamed sheet 1 of the present invention is a polystyrene resin or a polystyrene resin mixture containing polystyrene resin as a main component, particularly a polystyrene homopolymer alone, Or it is preferable that it is resin which consists of 50-90 mass% of polystyrene homopolymers and 10-50 mass% of impact-resistant polystyrene or a styrene-acrylic acid ester copolymer.

  The polystyrene homopolymer PSP layer 3 is brittle and may break when the laminated foam sheet 1 is used. Since adding a rubber component to the polystyrene homopolymer has an effect of improving brittleness, it is preferable to use as the PSP layer 3 a polystyrene resin in which the rubber component is blended with the polystyrene homopolymer. The rubber content of the polystyrene resin constituting the PSP layer 3 is preferably in the range of 1 to 6% by mass. When the rubber content is less than the above range, the brittleness improvement effect of the polystyrene resin cannot be sufficiently obtained. On the other hand, if the rubber content exceeds the above range, the foaming agent gas retainability decreases and the moldability deteriorates, or the weather resistance decreases due to the rubber component contained in the resin, and the molded product is stored for a long time. In such a case, problems such as a decrease in flexibility and cracking of the molded product are likely to occur. In addition, it is preferable to perform addition of the rubber component to the polystyrene resin which comprises the PSP layer 3 in the form which adds a suitable amount of a styrene-butadiene-type copolymer to a polystyrene homopolymer.

The density of the PSP layer 3 is preferably in the range of 0.03 to 0.2 g / cm ^{3 in} terms of moldability, flexibility, and strength of the molded product, and is preferably 0.04 to 0.1 g / cm 3. A range of ³ is more preferable.

[Laminated foam sheet]
The laminated foamed sheet 1 of the present invention is formed by laminating the first foamed layer 2 obtained by foaming the resin composition (i) and the PSP layer 3, and the heat deformation value of the laminated foamed sheet 1 (measurement method is Will be described in detail later.) Is in the range of 90 to 103 in the MD direction and 97 to 117 in the TD direction. By setting the heat deformation value of the laminated foamed sheet 1 in the above range, the foamed layers having greatly different properties are laminated, so that the laminated foamed sheet 1 is excellent in thermoforming and is difficult to thermoform. Is formed into a molded product such as a fruit and vegetable tray, a high-strength molded product having a good appearance with no cracks on the surface can be obtained.
A more preferable range of the heat deformation value is a range of 93 to 100 in the MD direction and a range of 99 to 111 in the TD direction. Further, the MD / TD value is preferably 0.84 to 0.95, and more preferably 0.86 to 0.92, while the values in the respective directions satisfy the above values.

  Here, the adjustment method of the heat deformation value in the laminated foam sheet 1 will be described. The heating deformation value can be adjusted by changing each extrusion condition when the laminated foamed sheet 1 is extruded and foamed. That is, it can be adjusted by changing the ratio between the outlet diameter of the resin of the extrusion die and the diameter of the cooling mandrel, or by changing the gap (slit) dimension of the outlet of the resin of the extrusion die.

  The total thickness of the laminated foam sheet 1 of the present invention is preferably in the range of 1.0 mm to 5.0 mm, and more preferably in the range of 1.5 mm to 3.0 mm. If the total thickness of the laminated foamed sheet 1 is thinner than the above range, the buffering properties and strength are lowered. On the other hand, if the total thickness is thicker than the above range, the moldability is lowered.

  In the laminated foam sheet 1 of the present invention, the thickness ratio between the first foam layer 2 and the PSP layer 3 is preferably in the range of first foam layer: PSP layer = 10: 1 to 1: 2. When there are few 1st foam layers 2, there exists a possibility that buffer property may be insufficient. If the thickness of the PSP layer 3 is 0.2 mm or more, the effect of improving the fusion property is sufficiently obtained. The thickness ratio of each of these layers may be adjusted in the required quality of buffer properties and strength.

The basis weight of the laminated foam sheet 1 of the present invention is preferably in the range of 80 - 400 g / ^{m 2,} the range of 100 to 300 g / ^{m 2} is more preferable. If the basis weight of the laminated foamed sheet 1 is less than the above range, the strength is insufficient. On the other hand, if the basis weight exceeds the above range, the cost increases, which is not preferable.

  The basis weight ratio of each layer of the first foam layer 2 and the PSP layer 3 is preferably in the range of first foam layer: PSP layer = 90: 10 to 50:50. The basis weight of each layer is not particularly limited as long as the required quality of the buffer property and strength is adjusted. However, if the basis weight of the first foam layer 2 is small, the buffer property is lowered.

  Note that the thickness of the molded product is increased by thermoforming the laminated foam sheet 1.

[Method for producing laminated foam sheet]
The laminated foamed sheet 1 of the present invention is laminated by thermally bonding foamed sheets obtained by individually extruding the foamed sheets to be the first foamed layer 2 and the PSP layer 3 or using an adhesive. However, since it is excellent in productivity and it is easy to adjust the heat deformation value of the laminated foamed sheet 1, it is preferable to manufacture by coextrusion.

  FIG. 2 is a configuration diagram showing an example of a manufacturing apparatus used in the method for manufacturing a laminated foam sheet according to the present invention. In FIG. 2, reference numeral 11 denotes a first extruder, 12 denotes a hopper, and 13 denotes a foaming agent supply port. , 14 is a second extruder, 15 is a single extruder, 16 is a hopper, 17 is a blowing agent supply port, 18 is a confluence mold, 19 is a die, 20 is a plug, 21 is a roller, and 22 is a take-up roller. .

  In order to manufacture the laminated foam sheet 1 by coextrusion using this manufacturing apparatus, first, the resin material of the first foam layer 2 is introduced from the hopper 12 of the first extruder 11 and the hopper 16 of the single extruder 15 is used. The PSP layer 3 is charged with the resin material, and the resin is heated to a temperature equal to or higher than its melting temperature in each extruder to be melted and mixed. At this time, various additives can be added together with the resin materials as necessary.

  The resin material melted in each of the first extruder 11 and the single extruder 15 is press-fitted with a foaming agent from the foaming agent supply ports 13 and 17, and in each of the extruders 11 and 15, Mix. The resin material of the first foam layer 2 mixed with the foaming agent in the first extruder 11 is sent to the second extruder to be an appropriate extruded foam resin temperature, and then sent to the confluence mold 18. On the other hand, the resin material of the PSP layer 3 mixed with the foaming agent in the single extruder 15 is sent from the other flow path of the converging mold 18 after being set to an appropriate extrusion foamed resin temperature. The respective foaming agent mixed resins joined in the joining mold 18 are extruded from an annular slit provided in the die 19 and foamed, and immediately after that, led to a cooling plug 20 to form a cylindrical foam. It becomes.

  The cylindrical foam is cut at two places by a cutter provided behind the plug 20, and is wound around the take-up roller 22 as a laminated foam sheet 1 through a plurality of rollers 21. In this example, two cylindrical foams are cut into two laminated foam sheets to form two laminated foam sheets. However, the present invention is not limited to this, and one cylindrical foam is cut into one laminated foam sheet 1. May be manufactured. When the obtained laminated foamed sheet 1 is wound up in a roll shape, it is desirable to wind it up with as little tension as possible in order to prevent winding tightness.

  As the foaming agent used in the production method of the present invention, any of known chemical foaming agents and physical foaming agents can be used. Examples of the chemical foaming agent include decomposition types such as azodicarbonamide and decomposition types such as sodium bicarbonate-citric acid. Examples of the physical blowing agent include hydrocarbons such as propane, butane and pentane, inert gases such as nitrogen and carbon dioxide, ethers such as dimethyl ether and diethyl ether, halogenated hydrocarbons such as tetrafluoroethane, chlorodifluoroethane and difluoroethane. Etc.

  In the production method of the present invention, one or both of the resin material of the first foam layer 2 and the resin material of the PSP layer 3 are known, such as a bubble regulator, a colorant, a shrinkage inhibitor, a flame retardant, a lubricant, and a deterioration inhibitor. These additives can be added as appropriate. Examples of the air conditioner include inorganic fillers such as talc, mica, mica and montmorillonite, organic fine particles such as fluororesin, decomposition chemical foaming agents such as azodicarbonamide, reactive chemical foaming agents such as sodium bicarbonate-citric acid, nitrogen An inert gas such as carbon dioxide can be used. Examples of the shrinkage-preventing agent include ester compounds of fatty acid and polyhydric alcohol such as stearic acid monoglyceride, and foaming agents for the polyethylene resin component, the copolymer of styrene and conjugated diene, or the hydrogenated component thereof. Since the effect of suppressing the gas escape rate can be expected, it is preferable.

  The open cell ratio of the laminated foamed sheet 1 obtained by the production method of the present invention is preferably 20% by volume or less, and more preferably 15% by volume or less. A content exceeding 20% by volume is not preferable because the secondary foamability at the time of thermoforming of the laminated foam sheet 1 is deteriorated and the moldability is inferior.

  The bubble diameter of the foamed sheet obtained by the method of the present invention is preferably in the range of 0.05 to 1.0 mm. When the bubble diameter is less than 0.05 mm, the open cell ratio of the foamed sheet tends to increase and the moldability also deteriorates, which is not preferable. When the bubble diameter exceeds 1.0 mm, the flexibility of the foam sheet is deteriorated, which is not preferable.

  The laminated foamed sheet 1 obtained by the method of the present invention has good releasability between sheets and molded articles. When a laminated foamed sheet is taken from a raw roll at the time of molding a laminated foamed sheet, a plurality of molded articles are stacked. Even after storage, the workability is good because it is easy to remove one by one.

[Sheet molded products, fruit and vegetable trays]
The laminated foam sheet 1 obtained by the production method of the present invention can be thermoformed by a known molding method to form a molded article such as a tray. In particular, since the laminated foam sheet 1 according to the present invention has good cushioning properties due to its flexibility, it can be suitably used for a fruit and vegetable tray having a plurality of storage recesses.

  3 and 4 are views showing an example of the fruit and vegetable tray according to the present invention. FIG. 3 is a plan view of the fruit and vegetable tray 30 and FIG. 4 is a cross-sectional view taken along the line II in FIG. The fruit and vegetable tray 30 is formed by thermoforming the laminated foamed sheet 1 shown in FIG. 1 to form a plurality of storage recesses 31 for storing fruits and vegetables and cutting it into a predetermined dimension. The plurality of storage recesses 31 of the fruit and vegetable tray 30 can accommodate fruits and vegetables such as apples, pears, peaches, and tomatoes.

Example 1
Formulation A (VLDPE “Excellen VL100” (density 0.90 g / cm ³ ) manufactured by Sumitomo Mitsui Polyolefin Co., Ltd.) 8% by mass, styrene-butadiene copolymer hydrogenated product “SS9000” manufactured by Asahi Kasei Chemicals Co., Ltd., 18% by mass, Toyo Styrene Co., Ltd. GPPS “HRM12” manufactured by 74 mass%) 100 parts by mass is supplied with 0.6 parts by mass of talc as a cell nucleating agent to a φ115 mm-first extruder of φ115 mm-φ150 mm tandem extruder and melted. 5.8 parts by mass of isobutane / normal butane = 65/35 as a blowing agent was injected from the middle of the extruder, kneaded, cooled to 139 ° C. with a second extruder having a diameter of 150 mm, and a combined mold at a rate of 165 kg / hr. Supplied to. On the other hand, blending B (polystyrene resin (“HRM12” manufactured by Toyo Styrene Co., Ltd.) 93 mass% and “Tufprene 125” (manufactured by Asahi Kasei Chemicals Co., Ltd., styrene-butylene copolymer, styrene component: butadiene component = 40: 60) as a rubber component. ) 7% by mass) Based on 100 parts by mass, 1.0 part by mass of talc as a cell nucleating agent was supplied to a single extruder having a diameter of 115 mm and melted. Then, isobutane / normal butane = 65 / Then, 4.3 parts by mass of 35 was injected, kneaded, cooled to 148 ° C., and supplied to the confluence mold at a rate of 71 kg / hr. The two kinds of resins supplied to the confluence mold are merged and laminated in the confluence mold, and then supplied to an annular die having a diameter of 190 mm, and the outer side is composed of compound A through the die slit (0.30 mm). Immediately after being extruded into a cylindrical shape so that the foamed layer is a polystyrene-based resin foamed layer of compounding B, the inside and outside are cooled by air and cooled along a 670 mm diameter plug. Then, the cooled cylindrical foam was cut open to produce a laminated foam sheet. The physical properties of the laminated foam sheet are shown in Tables 1 and 2.
The laminated foam sheet that had been stored and aged was heated in a heating furnace, and then sandwiched and pressed between a male mold and a female mold, and thermoformed into a fruit and vegetable tray.

(Example 2)
A foamed sheet was obtained in the same manner as in Example 1 except that the blend B was blended C (polystyrene resin (“HRM12” manufactured by Toyo Styrene Co., Ltd.) 100 mass%) and the cell nucleating agent was changed to 1.0 part by mass of talc. . The physical properties of the laminated foam sheet are shown in Tables 1 and 2.
The laminated foam sheet that had been stored and aged was heated in a heating furnace, and then sandwiched and pressed between a male mold and a female mold, and thermoformed into a fruit and vegetable tray.

(Comparative Example 1)
75 mass% of GPPS “HRM26” manufactured by Toyo Styrene Co., Ltd. as a polystyrene resin, 10 mass% of “Excellen VL100” as a polyethylene resin, “SS9000” as a copolymer of styrene and conjugated diene or a hydrogenated product thereof The resin composition material added with 0.6 parts by mass of talc as a cell nucleating agent to 100 parts by mass of 15% by mass of the resin raw material is supplied to a φ115 mm-φ150 mm tandem extruder with a φ115 mm first extruder. After melting, 5.8 parts by mass of isobutane / normal butane = 65/35 as a blowing agent was injected from the middle of the extruder, kneaded, cooled to 139 ° C. with a φ150 mm second extruder, and calibrated at 205 kg / hr. It was fed to a 175 mm annular die and extruded into a cylindrical shape through a die slit (0.40 mm). Later, while cooling over air to its inside and outside diameter is cooled molded along a on the plug of 670 mm, were produced foam sheet monolayer leading the cooled cylindrical foam. The physical properties of this foam sheet are shown in Tables 1 and 2.
The foamed sheet that had been stored and aged was heated in a heating furnace, and then sandwiched between a male mold and a female mold and pressed to form a fruit and vegetable tray.

(Comparative Example 2)
To 100 parts by mass of Formulation A, 0.6 part of talc as a cell nucleating agent is supplied to a φ115 mm first extruder of a φ115 mm-φ150 mm tandem extruder, melted, and then isobutane as a blowing agent from the middle of the extruder 5.9 parts by mass of / normal butane = 68/32 was press-fitted and kneaded, and then cooled to 139 ° C. with a second extruder having a diameter of 150 mm and supplied to the confluence mold at a rate of 165 kg / hr. On the other hand, with respect to 100 parts by mass of the blend B, 1.0 part of talc as a cell nucleating agent was supplied to a single extruder having a diameter of 115 mm and melted, and then isobutane / normal butane = 65/35 as a blowing agent from the middle of the extruder. After 4.1 parts by mass injection and kneading, the mixture was cooled to 148 ° C. and supplied to the confluence mold at a rate of 71 kg / hr. The two types of resins supplied to the confluence mold are merged and laminated in the confluence mold, and then supplied to an annular die having a diameter of 175 mm, and the outer side is composed of compound A through a slit (0.40 mm) in the die. Immediately after the foamed layer was extruded into a cylindrical shape so that the inside became a polystyrene-based resin foamed layer of Formulation B, the inside and the outside were cooled with air.
And the cylinder after cooling was cut open and the laminated foam sheet was manufactured. The physical properties of the laminated foam sheet are shown in Tables 1 and 2. The laminated foam sheet produced in this example had a heat deformation value that was outside the specified range of the present invention.
The laminated foam sheet that had been stored and aged was heated in a heating furnace, and then sandwiched and pressed between a male mold and a female mold, and thermoformed into a fruit and vegetable tray.

(Comparative Example 3)
A foamed sheet was obtained in the same manner as in Example 1 except that the diameter of the annular die was changed to 200 mm and the slit of the die was changed to 0.34 mm.
The physical properties of the laminated foam sheet are shown in Tables 1 and 2. The laminated foam sheet produced in this example had a heat deformation value that was outside the specified range of the present invention.
The laminated foam sheet that had been stored and aged was heated in a heating furnace, and then sandwiched and pressed between a male mold and a female mold, and thermoformed into a fruit and vegetable tray.

  About the foamed sheet manufactured in Examples 1-2 and Comparative Examples 1-3 described above, the heat deformation value, the foamed sheet peelability and the moldability were examined. The measurement method and evaluation criteria for each of these items were as follows.

<Heating deformation value measuring method>
The heating deformation value is measured in the following manner. First, five test pieces on a plane square having a side of 10 cm are cut out from a sample (laminated) foam sheet so that each side is parallel to the MD direction or the TD direction of the foam sheet.
Thereafter, on the front and back surfaces of each test piece, two straight lines connecting the center portions of the sides facing each other are drawn in a cross shape. Next, after each test side is left and heated in an atmosphere of 125 ° C. for 90 seconds, the test piece is left to cool at room temperature for 5 minutes.
Next, the length of the straight line drawn on the front and back surfaces of the test piece is measured, and the average value of the front and back in each direction is set as the heat deformation value in the MD direction and the TD direction of the test piece. The arithmetic average value of the five test pieces is defined as the heat deformation value of the (laminated) foamed sheet.
Heat deformation value = length after heating / length before heating × 100

<Foamed sheet peelability>
First, in the oven set to 70 ° C, put 5 kg of weight from the top of the sample foamed sheet 10cm x 10cm, stacked with about 5 sheets, and sandwiched by the same size aluminum plate about 1mm thick Allow to stand horizontally. After heating in that state for 12 hours, the temperature was once lowered and allowed to stand at room temperature for 1 hour, and further heated at 70 ° C. for 12 hours. Then, after taking out from oven and leaving to stand at normal temperature for 1 hour, the peelability between foam sheets was investigated. The stacked foam sheets were peeled off one by one, and evaluated according to five levels of ◎, ○, ×, and XX according to the degree of peeling when the four sheets were peeled off. Three sets of this were performed.
A: All four sheets make almost no sound and no power.
○: One or more sounds like crispy sounds, but not very powerful.
Δ: All four sound like crispy sounds, but not very powerful.
X: It does not peel off if it does not apply a crunchy sound with 1-2 sheets.
XX: All four pieces do not come off unless crisp sound is applied.

<Moldability>
In a single heating molding machine, the temperature inside the heating furnace is set to 180 ° C., and the resulting foam sheet is molded using a mold having 16 holes with an opening of 100 mm and a depth of 40 mm. Was observed. “X” indicates that only a cracked or cracked product can be obtained, and “◯” indicates that these defects are not observed.

From the results of Tables 1 and 2, the laminated foam sheets of Examples 1 and 2 according to the present invention have the MD and TD heat deformation values within the specified range of the present invention (90 to 103 in the MD direction and 97 in the TD direction). ˜117) and both the peelability and moldability were good.
On the other hand, Comparative Example 1 in which the first foamed layer was a single layer had poor peelability.
In Comparative Example 2 and Comparative Example 3, the heat deformation value was outside the specified range of the present invention, and the moldability was poor.

It is a schematic sectional drawing which shows one Embodiment of the laminated foam sheet of this invention. It is a block diagram which illustrates the manufacturing apparatus of a laminated foam sheet. It is a top view which shows an example of the tray for fruit and vegetables of this invention. It is the II sectional view taken on the line of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laminated foam sheet, 2 ... 1st foam layer, 3 ... Polystyrene-type resin foam layer, 11 ... 1st extruder, 12, 16 ... Hopper, 13, 17 ... Foam supply port, 14 ... 2nd extruder, DESCRIPTION OF SYMBOLS 15 ... Single extruder, 18 ... Merge die, 19 ... Die, 20 ... Plug, 21 ... Roller, 22 ... Winding roller, 30 ... Fruit and vegetable tray, 31 ... Containing recess

Claims (3)

A resin composition (i) comprising a polystyrene resin (a), a polyethylene resin (b) having a density of 0.87 to 0.92 g / cm ³ and a copolymer of styrene and conjugated diene or a hydrogenated product thereof (c) ) And a hydrogenated product (c) thereof having a durometer type A hardness value HDA of 90 or less, and the density of the extruded foam layer is 0.03. a first foam layer is ~0.2g / cm ^3, a laminated foam sheet is a polystyrene resin foamed layer are laminated, 90-103, extrusion direction in heat deformation values extrusion direction of the laminated foam sheet 97-117 der in the direction perpendicular to the is,
The resin composition (i) is a polystyrene resin (a) 50 to 90% by mass, a polyethylene resin (b) 3 to 20% by mass, a copolymer of styrene and conjugated diene or a hydrogenated product (c) 3 thereof. Having a composition of ˜47 mass% (however, a polyethylene resin (b) + copolymer of styrene and conjugated diene or a hydrogenated product thereof (c) = range of 10 to 50 mass%),
The thickness of the laminated sheet is in the range of 1.0 mm to 5.0 mm, the basis weight is in the range of 80 to 400 g / m ² , and the thickness ratio of the first foam layer to the polystyrene resin foam layer is 10: A laminated foam sheet having a range of 1-1: 2 . Seika tray obtained by thermoforming the laminated foam sheet as claimed in claim 1. The method for producing a laminated foamed sheet according to claim 1 , wherein the first foamed layer and the polystyrene-based resin foamed layer are produced by coextrusion to obtain the laminated foamed sheet according to claim 1.

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