JP4611117B2 - Thermoplastic resin foam sheet and method for producing the sheet container - Google Patents

Description

  The present invention relates to a foamed sheet made of a thermoplastic resin and a method for producing the foamed sheet container. More specifically, it is preferably used for manufacturing various packaging containers, and is a foam sheet made of a thermoplastic resin, particularly excellent in cold resistance, heat insulation, oil resistance, heat resistance, rigidity, etc., and excellent in biodegradability. Thermoplastic resin foam sheet suitable for manufacturing trays, cups, bowls, dishes, containers, boxes (hereinafter collectively referred to as containers) by the next molding method, and better heat resistance than this foam sheet The present invention relates to a manufacturing method for a container.

  Depending on the type, commercially available food is stored in a resin container, refrigerated and frozen at a low temperature of 10 to -30 ° C., stored and transported, and when eaten, the temperature of 100 to 120 ° C. with a microwave oven is used for each container. Some are cooked in These food containers are required to have heat resistance so that they do not deform when cooked to the above temperature range with a microwave oven, and also have oil resistance that is not easily eroded by oils, seasonings, etc. contained in food. Is done. Also, cold resistance and impact resistance are required so that the container containing the food is not damaged even if it is shocked from the outside in a state where it is refrigerated and frozen at a low temperature.

  As a container for storing food to be cooked by a microwave oven, a container made by molding (molding) a polypropylene resin sheet by a thermoforming method has been conventionally used. Since polypropylene resin is excellent in heat resistance, the container is less deformed when heated in a microwave oven. However, since polypropylene resin is inferior in cold resistance, food is stored in this container and stored in a refrigerator / freezer at a low temperature of 10 to −30 ° C. or during cargo handling work in the transportation process by a frozen vehicle. There is a disadvantage that cracks and cracks occur due to external impacts such as dropping, collision, vibration, etc., and it is unbearable for cooking with a microwave oven. In order to improve this defect, a thermoforming sheet made of a resin composition in which a polyethylene resin and an inorganic filler are blended with a polypropylene resin has been proposed (Patent Document 1). However, the container obtained from this sheet is still insufficient in cold resistance and heat resistance.

  Foamed sheets made from high-density polyethylene resin are excellent in heat insulation, impact resistance, rigidity, and the like, and are used as containers, cardboard materials, and the like. Foamed sheets made from ordinary high-density polyethylene resins have the disadvantage that uniform foam cells are difficult to form, and a method using a polyethylene resin with a high melt viscosity has been proposed as a method to remedy this defect. ing. When the melt viscosity is high, a large load is applied to the extruder motor when the foamed sheet is produced by the extruder, making it difficult to produce the foamed sheet. As a technique for solving this problem, there has been proposed a foam sheet made of a resin composition in which two types of polypropylene resins are blended with a high-density polyethylene resin (Patent Document 2). However, according to experiments by the inventors, it has been found that the container obtained from the foamed sheet is still insufficient in cold resistance and heat resistance.

The containers are discarded after use, and in many cases, the discarded items are incinerated or crushed and landfilled in a landfill. Since the incineration heat is high when the resin is incinerated, there is a drawback of damaging the incinerator. Therefore, a method of reducing the amount of resin used by foaming is employed. When landfilled in a landfill, the resin is difficult to corrode and decompose, so there is a disadvantage that it remains semipermanently, so photodegradable resins and biodegradable resins have been proposed and partially put into practical use. It has the disadvantage of high cost and the usage is much less than expected.
Japanese Patent Laid-Open No. 2-80454 JP 2001-213989 A Japanese Patent No. 3029612 JP 2004-189833 A

  In view of the above situation, the present inventors have developed a resin sheet excellent in cold resistance, heat insulation, oil resistance, heat resistance, rigidity, etc., excluding conventional defects, and excellent in biodegradability, and heat resistance from this resin sheet. As a result of intensive studies aimed at providing a method for producing a container having excellent properties, the present invention has been completed. That is, the object of the present invention is to provide a thermoplastic resin foam sheet having excellent extrusion characteristics during foam sheet production, excellent cold resistance, heat insulation, oil resistance, heat resistance, rigidity, etc., and excellent biodegradability, particularly two An object of the present invention is to provide a thermoplastic resin foam sheet suitable for producing dishes, containers, trays, boxes, and the like by the next molding method, and a method for producing a container having excellent heat resistance.

In order to solve the above problems, in the first invention, a polylactic acid (A) having a weight average molecular weight of 50,000 or more is 20 to 90% by weight, and a polystyrene resin (B) 5 having a weight average molecular weight of 200,000 to 400,000 is used. 65 wt%, and a density is 0.90 to 0.96, with respect to MFR of 3 to 20 g / 10 min of the polypropylene resin (C) ternary total 100 weight consisting 5 to 40 wt%, ( a) styrene-butadiene-styrene block copolymer, (b) hydrogenated product of styrene-butadiene-styrene block copolymer, (c) styrene-isoprene-styrene block copolymer, (d) styrene-isoprene-styrene. 1 to 20 parts by weight of a compatibilizer (D) selected from the group consisting of a hydrogenated block copolymer and (e) a styrene-ethylene-propylene-styrene copolymer The resin fat composition is a raw material, the expansion ratio is 1.1 to 5.0 times, and the thickness is 0.5 to 3.0 mm. A foam sheet is provided.

In the second invention, the polylactic acid (A) having a weight average molecular weight of 50,000 or more is 20 to 90% by weight, the polystyrene resin (B) having a weight average molecular weight of 200,000 to 400,000 , and 5 to 65% by weight, and (A) Styrene-butadiene- with respect to 100 weights of a total of three components consisting of 5 to 40% by weight of a polypropylene resin (C) having a density of 0.90 to 0.96 and an MFR of 3 to 20 g / 10 min. Styrene block copolymer, (b) Hydrogenated styrene-butadiene-styrene block copolymer, (c) Styrene-isoprene-styrene block copolymer, (d) Hydrogen of styrene-isoprene-styrene block copolymer additives, and (e) a styrene - ethylene - propylene - styrene copolymer from consisting compatibilizing agent selected from the group (D) 1 to 20 parts by weight formed by mixing resin fat pairs The material is a raw material, the expansion ratio is 1.1 to 5.0 times, the thickness is 0.5 to 3.0 mm, the mold temperature when thermoforming is set to a temperature range of 105 to 115 ° C, Provided is a method for producing a foamed sheet container made of a thermoplastic resin, characterized by annealing for 10 to 20 seconds after container molding.

The present invention is as described in detail above, and has the following particularly excellent effects, and its industrial utility value is extremely great.
1. The foamed sheet made of thermoplastic resin according to the present invention is excellent in extrusion characteristics when producing a foamed sheet because a raw material resin is obtained by blending polylactic acid with a polystyrene resin and a polypropylene resin at a specific ratio.
2. Since the thermoplastic resin foam sheet according to the present invention contains an appropriate amount of a compatibilizing agent, even if polylactic acid, an incompatible polystyrene-based resin, and a polypropylene-based resin are blended, fluff is formed on the surface of the foamed sheet. The foamed sheet has a beautiful appearance and is excellent in moldability, cold resistance, heat insulation, impact resistance and the like.
3. The foamed sheet made of the thermoplastic resin according to the present invention is excellent in chemical resistance because it is blended with a polypropylene resin, and is hardly eroded by oils, seasonings and the like contained in food.
4). The foamed sheet made of thermoplastic resin according to the present invention is easily biodegradable because it contains polylactic acid, and since the polylactic acid resin is blended with a polystyrene resin and a polypropylene resin that are cheaper than the polylactic acid resin, Cost is cheap.
5. The thermoplastic resin foam sheet according to the present invention is excellent in cold resistance and rigidity, so it can be stored in a refrigerator / freezer at a low temperature or during a cargo handling operation in the transportation process by a freezer vehicle. Cracks and cracks are less likely to occur due to external impacts such as dropping, collision, and vibration.
6). The foamed sheet made of the thermoplastic resin according to the present invention has a foaming ratio in the range of 1.1 to 5 times, and the amount of the material resin used can be reduced, so that the cost of the product can be reduced.
7). The container manufactured from the thermoplastic resin foam sheet according to the present invention may be any container that can be formed into a film and has physical properties that can withstand practical use. Since the amount of material resin used is small, when incineration is carried out after recovery, there are few calories burned per volume, making it difficult to damage the incinerator, and there is little black smoke per volume generated during incineration and less air pollution. it can.
8). The container made of a thermoplastic resin foam sheet produced by the method according to the second invention of the present invention is particularly excellent in heat resistance, and is therefore suitable as a container for storing various foods that are heated and cooked with a microwave oven.

Hereinafter, the present invention will be described in detail.
The raw material resin of the thermoplastic resin foam sheet according to the present invention is polylactic acid (A) {hereinafter sometimes referred to as resin (A)}, polystyrene resin (B) {hereinafter referred to as resin (B). And three components of polypropylene resin (C) {hereinafter sometimes referred to as resin (C)}.

  In the present invention, the polylactic acid (A) refers to a resin having a monomer unit derived from L-lactic acid and / or D-lactic acid as a main component. Here, the “main component” means that these monomer units are contained in an amount of 75 mol% or more and contain other monomer units of less than 25 mol%. Examples of other monomer units include glycol compounds, dicarboxylic acids, hydroxycarboxylic acids, and lactones. Examples of glycol compounds include ethylene glycol, propylene glycol, butanediol, heptanediol, hexanediol, octanediol, nonanediol, decanediol, 1,4-cyclohexanemimethanol, neopentylglycol, glycerin, pentaerythritol, and bisphenol A. Polyethylene glycol, polypropylene glycol and polytetramethylene glycol. Dicarboxylic acids include oxalic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonic acid, glutaric acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, bis (p-carboxyphenyl) ) Methane, anthracene dicarboxylic acid, 4,4, -diphenyl ether dicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-tetrabutylphosphonium isophthalic acid and the like. Examples of the hydroxycarboxylic acids include glycolic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxybenzoic acid, and the lactones include caprolactone, valerolactone, propiolactone, undecalactone, 1,5-oxepan-2-one and the like can be mentioned. The proportion of other monomer units is particularly preferably 0 to 10 mol%.

  In order to obtain a foam sheet exhibiting particularly high heat resistance, it is preferable to use a polylactic acid (A) having a high optical purity of the lactic acid component. Among the total lactic acid components of the polylactic acid resin, those containing 80% or more of L-form are preferable. If the proportion of D-form is large, it becomes amorphous and is difficult to crystallize during product annealing, and heat resistance is not improved. A more preferable ratio of the L isomer ratio is 90% or more, and particularly preferable is 95% or more.

  The polylactic acid (A) is not particularly limited as long as it can be formed into a film and has physical properties enough to withstand practical use. The melting point is preferably 120 ° C. or higher, and more preferably 150 ° C. or higher. The melting point of polylactic acid (A) can be measured with a differential scanning calorimeter. The polylactic acid (A) has a molecular weight of preferably 50,000 or more, more preferably 100,000 or more, and particularly preferably 200,000 or more. Here, the weight average molecular weight refers to a molecular weight measured by gel permeation chromatography (GPC).

  Polylactic acid (A) can be produced by a conventionally known production method. A typical method is a method of ring-opening polymerization of lactide, which is an anhydrous cyclic dimer of lactic acid (lactide method), but a direct polymerization method of lactic acid may also be used.

In the present invention, the polystyrene resin (B) is a polymer of a styrene monomer, a copolymer of a styrene monomer as a main component, and other monomers copolymerizable therewith, rubber modified This refers to styrene resin. Examples of the styrene monomer include alkyl-substituted styrenes such as styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4-t-butylstyrene, 2,4-dimethylstyrene, Examples include α-alkyl-substituted styrenes such as α-methylstyrene and α-methyl-4-methylstyrene, and halogenated styrenes such as 2-chlorostyrene and 4-chlorostyrene. These styrenic monomers may be one kind or a mixture of two or more kinds.

Other monomers copolymerizable with styrenic monomers include acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, acrylic acid Maleic acid such as 2-ethylhexyl, acrylic acid (C ₁ -C ₈ ) ester such as 2-ethylhexyl methacrylate, acrylonitrile, maleic anhydride, maleimide, N-substituted maleimide such as N-methylmaleimide, N-ethylmaleimide Or a derivative thereof. These other monomers may be one kind or a mixture of two or more kinds.

As rubber used for rubber modified styrene resin production, polybutadiene,
Styrene-butadiene copolymer rubber, styrene-isoprene copolymer rubber, butadiene-isobrene copolymer rubber, butadiene-acrylonitrile copolymer rubber, ethylene-propylene copolymer rubber, polyisoprene, acrylic rubber, ethylene-vinyl acetate copolymer rubber Etc. The content of the rubber component in the rubber-modified styrenic resin is selected in the range of 1 to 20% by weight.

  The polystyrene resin (B) has a heat distortion temperature (according to JIS K7207) of 70 ° C. or higher, preferably 80 ° C. or higher, more preferably 85 ° C. or higher. The polystyrene resin (B) preferably has a weight average molecular weight in the range of 200,000 to 400,000. Here, the weight average molecular weight refers to a molecular weight measured by gel permeation chromatography (GPC).

  The polystyrene resin (B) can be produced by a conventionally known production method. Examples thereof include a bulk polymerization method, a suspension polymerization method, an emulsion polymerization method, and a bulk-suspension polymerization method.

The polypropylene resin (C) preferably has a density of 0.90 to 0.96 and an MFR (measured according to JIS K7210) of 3 to 20 g / 10 min. When the MFR is less than 3 g / 10 minutes, the fluidity is poor and it is difficult to produce a foamed sheet. When the MFR exceeds 20 g / 10 minutes, when a container is produced from the foamed sheet by a thermoforming method, the drawdown becomes large, which is not preferable. . The polypropylene resin (C) can be easily produced by a conventionally known production method. For example, propylene gas is purified to a purity of 95% or more, for example, propylene is blown into a solvent to which a triethylaluminum and titanium trichloride-based Ziegler-Natta catalyst is added at a temperature of 30 to 70 ° C., and the pressure is from atmospheric pressure to 5 kg / cm 2. Polymerization is started as a range of ² . The ratio of the stereoregular components (isotactic and atactic) of the resin can be adjusted by the type and concentration of the catalyst, the molar ratio of triethylaluminum to titanium trichloride, the reaction temperature, the reaction time, and the like.

  The foamed sheet made of thermoplastic resin according to the present invention is made from a resin composition containing the above three components of resin (A), resin (B) and resin (C). The blending ratio of the three components is 20 to 90% by weight of the resin (A), 5 to 65% by weight of the resin (B), and 5 to 40% by weight of the resin (C) (the total amount of the three components is 100% by weight). ). When the proportion of the resin (A) is less than 20% by weight, the biodegradability of the foamed sheet becomes poor, and when the proportion of the resin (A) exceeds 90% by weight, the strength, heat resistance, moldability, etc. of the foamed sheet Is not preferable. In the above range, the resin (A) is preferably 30 to 80% by weight, the resin (B) is 20 to 60% by weight, and the resin (C) is 20 to 35% by weight.

The compatibilizing agent (D) is a component for improving the mutual solubility of the three components of the insoluble resin (A), the resin (B) and the resin (C). Specifically, (a) styrene-butadiene-styrene block copolymer (manufactured by Asahi Kasei Co., Ltd., trade name: Toughprene), (b) (a) hydrogenated product of styrene-butadiene-styrene block copolymer (Asahi Kasei Co., Ltd.) Product name: Tuftec P2000, and product name: Tuftech H1043 ), (c) styrene-isoprene-styrene block copolymer (trade name: Hybler 5127 , manufactured by Kuraray Co., Ltd. ), (d) (c) styrene-isoprene- Hydrogenated product of styrene block copolymer (Kuraray Co., Ltd., trade name: Hibler 7125), (e) Styrene-ethylene-propylene-styrene copolymer (Kuraray Co., Ltd., trade names: Septon 2063, Septon 2104), etc. Can be mentioned.

The compounding amount of the compatibilizing agent (D) is in the range of 1 to 20 parts by weight with respect to 100 parts by weight of the resin component containing three kinds of resins. When the blending amount is less than 1 part by weight, the function as a compatibilizing agent is not exhibited, and when it exceeds 20 parts by weight, the strength, heat resistance, etc. of the foamed sheet are lowered, which is not preferable. In the above range, 2 to 10 parts by weight is particularly preferable, and 3 to 6 parts by weight is particularly preferable.

In the raw material resin composition, the crystallization accelerator (E), the nucleating agent (F), the antioxidant, the metal deactivator, and the phosphorus stabilizer are added to the raw material resin composition as necessary. , UV absorbers, light stabilizers, fluorescent brighteners, metal soaps, antacid adsorbent stabilizers, crosslinking agents, chain transfer agents, nucleating agents, lubricants, plasticizers, fillers (other than crystallization accelerators) Various resin additives such as reinforcing agents, pigments, dyes, flame retardants, and antistatic agents.

  The crystallization accelerator (E) functions to increase the crystallization speed of the foam sheet. Examples of the crystallization accelerator (E) include talc, sodium bicarbonate, a mixture of talc and titanium dioxide. The crystallization accelerator (E) exhibits a granular form having an average particle size of 0.3 to 10.0 μm, and is in the range of 1 to 10 parts by weight with respect to 100 parts by weight of the resin component containing three kinds of resins. And When the blending amount is less than 1 part by weight, the function as a crystallization accelerator is not exhibited, and when it exceeds 10 parts by weight, the fluidity of the raw resin component is lowered, which is not preferable. Particularly preferred in the above range is 2 to 8 parts by weight.

The nucleating agent (F) creates a bubble start part and makes it easy to control the size of the bubbles in the foam sheet. Preferred nucleating agents include citric acid, a mixture of citric acid and sodium bicarbonate, and the like. Similarly to the crystallization accelerator (E), the nucleating agent (F) is in the form of granules having an average particle size of 0.3 to 10.0 μm, and the blending amount is 100 parts by weight of a resin component containing three kinds of resins. On the other hand, it is preferable to select in the range of 0.01-1 part by weight. The crystallization accelerator (E) and the nucleating agent (F) are mixed together with the above various resin additives and melt kneaded to be granulated, or dry blended with the obtained granular raw material resin mixture. preferable.

  The method for blending the crystallization accelerator (E), the nucleating agent (F), the above resin additive and the like into the raw material resin composition containing the three kinds of resins and the compatibilizer (D) is based on the melt kneading method. However, the mixing / melting sequence and the method thereof are not particularly limited. The heating temperature at the time of melt-kneading varies depending on the type of the raw material resin, but if selected in the range of 150 to 300 ° C., the raw material resin composition is sufficiently melted and is not thermally decomposed and sufficiently foamable. Is preferable in that it can be obtained. Examples of the apparatus for melt kneading the raw material resin composition include a kneader, a Banbury mixer, a Brabender, a single screw extruder, a twin screw extruder, and the like.

  Next, a method for producing the foamed sheet according to the present invention from the raw material resin composition will be described. The foam sheet is obtained by mixing a granular thermoplastic resin with a crystallization accelerator (E), a nucleating agent (F) and the above resin additive, a step of plasticizing the mixture in an extruder, and a plasticized mixture. Each step of mixing (introducing or press-fitting) a foaming agent to prepare a foamable mixture, plasticizing the foamable mixture in an extruder, foaming and extruding from an extruder die, and continuously producing a foamed sheet It is manufactured by the method containing.

  The foaming agent is a material that is mixed with a raw material resin composition in a molten state in a melt-kneader and changes in phase from solid to gas, liquid to gas, or gas itself. Used to control). As for the foaming agent dissolved in the raw material resin composition, those that are liquid at room temperature undergo a phase change into a gas depending on the resin temperature and dissolve in the molten resin, and those that are a gas at room temperature dissolve in the molten resin without any phase change. The foaming agent dispersed and dissolved in the molten resin expands inside the sheet when the molten resin is extruded from the extrusion die into a sheet shape, so that it expands inside the sheet, forming a large number of fine closed cells in the sheet. A foam sheet is obtained. The foaming agent acts as a plasticizer that lowers the melt viscosity of the raw resin composition as a secondary effect, and lowers the temperature for bringing the raw resin composition into a plasticized state.

  Examples of the blowing agent include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; alicyclic hydrocarbons such as cyclobutane, cyclopentane, and cyclohexane; chlorodifluoromethane, difluoromethane, trifluoromethane, and trichlorofluoro Methane, dichloromethane, dichlorofluoromethane, dichlorodifluoromethane, chloromethane, chloroethane, dichlorotrifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, dichlorotetrafluoroethane, trichlorotrifluoroethane Halogenated hydrocarbons such as tetrachlorodifluoroethane and perfluorocyclobutane; inorganic gases such as carbon dioxide, nitrogen and air; And the like. These foaming agents may be one kind or a mixture of two or more kinds.

  The amount of the foaming agent to be added varies depending on the type of foaming agent, the target foaming ratio of the foamed sheet, etc., but is preferably selected in the range of 1 to 20% by weight with respect to the raw material resin composition. The higher the amount of foaming agent mixed, the larger the foam will become, due to the combined effect of the higher pressure in the foam and the lower resistance of the foam wall against the plasticizing action of the foam. The magnification also increases. A preferable mixing amount of the blowing agent is 2 to 15% by weight.

  The step of preparing the foamable mixture and the step of foaming the foamable mixture can be performed in an extruder. That is, the thermoplastic resin composition blended with the crystallization accelerator (E) and the nucleating agent (F) is melted with an extruder and mixed (introduced or pressed) from the middle of the extruder cylinder. The extruder may be either a single screw extruder or a twin screw extruder. The extruder die may be a T die or a circular (circular) die.

The thermoplastic resin foam sheet produced by the above method has an expansion ratio of 1.1 to 5.0 times and a thickness of 0.5 to 3.0 mm.
The range. When the foaming ratio of the foamed sheet is less than 1.1, the secondary processed product is inferior in heat insulating properties, cold resistance, buffering properties, etc., and when the foaming ratio exceeds 5.0 times, the rigidity is inferior, which is not preferable. . Particularly preferred in the above range is 1.5 to 4.0 times. In addition, if the thickness of the foam sheet is less than 0.5 mm, the secondary processed product is inferior in rigidity, impact strength, elastic modulus, heat insulation, etc. If the thickness exceeds 3 mm, the foam cell is uniform. In addition to making it difficult to produce a foam sheet, the amount of raw material resin used is increased, and the secondary processability is inferior. Particularly preferred within the above range is 0.7 to 2.8 mm.

  The thermoplastic resin foam sheet according to the present invention may be obtained by laminating a non-foamed layer (film) made of a thermoplastic resin on one or both surfaces of the foam sheet for the purpose of improving surface properties, rigidity, thermoformability and the like. it can. Laminate (film) thermoplastic resins include polylactic acid, polystyrene resin, modified polyphenylene ether resin, polyethylene resin, polypropylene resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyamide resin, acrylic resin , Polyvinyl chloride resin, polycarbonate resin and the like. The method for laminating the non-foamed layer on the foamed sheet is not particularly limited. (A) After the foamed sheet is produced, a separately produced non-foamed film is laminated by a heating method or a method using an adhesive. And (b) a method of extruding a non-foamed film directly from a T-die onto the foamed sheet surface and laminating. Particularly preferred is a method in which the non-foamed resin is polylactic acid and laminated by the method (b).

  The thermoplastic resin foam sheet according to the present invention provides secondary processability, that is, a plug molding method or vacuum molding, by defining the ratio of the three raw material resins, the ratio of the compatibilizer (D), and the characteristics of the foam sheet. It is excellent in processability when obtaining a final product by a thermoforming method such as a pressure forming method or a pressure forming method, and a molded product free from thickness unevenness can be obtained. Examples of thermoforming methods include plug molding, matched mold molding, straight molding, drape molding, plug assist molding, plug assist reverse draw molding, air slip molding, snapback molding, reverse Examples thereof include a draw molding method, a plug and ridge molding method, and a ridge molding method.

  Next, a container can be manufactured from the thermoplastic resin foam sheet according to the first invention of the present invention described above by the thermoforming method described above. According to the study by the present inventors, it has been found that the heat resistance of a container produced from a thermoplastic resin foam sheet by a thermoforming method depends on the crystallinity of the molded container. Moreover, it turned out that the crystallinity degree of a container is dependent on the metal mold | die (surface) temperature at the time of manufacturing a container by a thermoforming method, and annealing conditions (temperature, time). Hereinafter, the manufacturing method of a container is demonstrated according to the method which concerns on 2nd invention.

  It was found that the preferable mold (surface) temperature and annealing conditions were a mold temperature in the range of 105 to 115 ° C., and the annealing time after container forming was preferably 10 to 20 seconds. If the mold (surface) temperature is less than 105 ° C, it depends on the annealing time, but the molded product is difficult to crystallize, the heat resistance of the product container is not improved, and if the mold temperature exceeds 115 ° C, the product container Tends to be in a softened state, both of which are not preferred. A particularly preferable range of the mold temperature is 108 to 113 ° C. Also, if the annealing time is less than 10 seconds, depending on the mold surface temperature, the molded product is difficult to crystallize, and the heat resistance of the product container is not improved. In addition to welding, the molding cycle is lengthened, both of which are undesirable. The annealing of the product container refers to maintaining the state where the product container after thermoforming with the molding die is not released from the molding die for a predetermined time.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to the following description examples. In the following description examples, evaluation of various physical properties of the raw material resin composition and various properties of the thermoplastic resin foam sheet were performed by the methods described below.

<Raw resin, auxiliary material>
A: Polylactic acid (made by Mitsui Chemicals, trade name: Lacia H-400, having a weight average molecular weight of 200,000).
B: Polystyrene (PS Japan, brand name: G9305, weight average molecular weight of 340,000).
C: Polypropylene (manufactured by Nippon Polypro Co., Ltd., brand name: FY4), having a density of 0.9 g / cm ³ and MFR of 5 g / 10 min.
D: Styrene-butadiene-styrene block copolymer (manufactured by Asahi Kasei Co., Ltd., trade name: Toughprene).
E: Talc (manufactured by Dainichi Seika Co., Ltd., brand name: OK4070-70-N, average particle diameter is 3 μm).
F: Baking soda-citric acid (manufactured by Eiwa Kasei Co., Ltd., trade name: Cerbon SC / K).

(A) Extrusion characteristics: 40 mmφ, L / D = 36 twin screw extruder, cylinder temperature set to 200 ° C., extruder motor load and screw tip resin temperature when extruded at 40 rpm It was evaluated by. In a relative comparison, a case where the load on the extruder motor was low was indicated as ◯, a case where the load on the extruder motor was high was indicated as x, and an intermediate between ○ and x was indicated as △.
(B) Foaming ratio: Measured according to JIS K6767.
(C) Appearance of the sheet: Visual observation of the thermoplastic resin foam sheet, ○ in which wrinkles parallel to the extrusion direction (corrugated line) and wrinkles are not recognized, ○ wrinkles parallel to the extrusion direction (corrugated line) Are recognized as x, and those between ◯ and x as Δ.

(D) Drawdown property: Using a batch type differential pressure molding machine (manufactured by Kansai Automatic Molding Machine, model: PK450V), the thermoplastic resin foam sheet is fixed by a clamp having a size of 50 cm × 50 cm, and the thickness is It heated for 15 seconds with the heater preset temperature of 300 degreeC with the heater from the upper and lower sides of a 1.0 mm foam sheet, and the drawdown property was evaluated with the visible light laser displacement sensor (the Keyence company make, model: BL-300). When the amount of sag in the center of the foamed sheet is less than 20 mm, ◯ is indicated, when the amount of sag is 20 mm or more, ×, and between ◯ and X are indicated as Δ.

(E) Moldability: A thermoplastic resin foam sheet is fixed with a clamp having a size of 50 cm × 50 cm using a batch type differential pressure molding machine (manufactured by Kansai Automatic Molding Machine Co., Ltd., model: PK450V), and the thickness is 1 Heated for 15 seconds with a heater set temperature of 300 ° C from above and below the foam sheet of 0mm, and took a 20cm x 25cm x 3cm lunch box type container using a test die and differential pressure molding method (from the male side) The pressure was reduced by a method. About the obtained container, the appearances, such as the presence or absence of uneven thickness, the type-determined situation, were visually observed, and “good” as a whole, “poor” as poor, and “mid” between “good” and “good” as “△”.
( F ) Heat-resistant temperature: Commercially available salad oil (Nissin Oil Co., Ltd., trade name: Nisshin Salad Oil) was put in an oil bath, the temperature was increased from 50 ° C. to 5 ° C., and the container was immersed for 1 minute at each temperature. After removal, the appearance was visually observed. The maximum temperature (° C.) at which no deformation was observed in any part of the container was defined as the heat resistant temperature.
( G ) Comprehensive evaluation: A case where all of the evaluation items (a) and (c) to (f) are good, ○, any inferior one is ×, and an intermediate between ○ and × is Δ , Respectively.

[Example 1 to Example 14, Comparative Example 1 to Comparative Example 4]
<Manufacture of foam sheet>
The raw material resin components A, B, C, auxiliary raw materials D (compatibilizer) and E (crystallization accelerator) are weighed in the proportions shown in Table 1, and mixed uniformly with a ribbon blender to obtain a mixture. It was. To this mixture, 0.5 part by weight of auxiliary material F (nucleating agent) was weighed and added, and uniformly mixed with a ribbon blender to obtain a blend. This blend was supplied to a hopper of a twin screw extruder having a diameter of 40 mmφ, L / D = 36, and a cylinder temperature set to 200 ° C., and carbon dioxide as a blowing agent was added to 1 part by weight of 100 parts by weight of the plasticized mixture. 5% by weight, pressed and mixed from the middle cylinder of the extruder, extruded into atmospheric pressure from a circular die (75mmφ), while taking over the mandrel, stretching and cooling by blowing air at 0.15 m ³ / min in the interior of the mandrel Then, a cylindrical foam sheet was obtained, and the foam sheet having a width of 700 mm was obtained by cutting it with a cutter.

<Production of raw material mixture, foam sheet, evaluation test of foam sheet>
By the above-described method, the raw material mixture, the production of the foamed sheet, and the foamed sheet were subjected to the evaluation test by the method described above, and the evaluation results are shown in Table-1.

From Table 1 above, the following becomes clear.
(1) The raw material of which the blending ratio of the polylactic acid resin (A), the polystyrene resin (B), the polypropylene resin (C) and the compatibilizer (D) satisfies the requirements defined in claim 1 In addition, the extrusion characteristics at the time of foam sheet production are excellent (see Examples 1 to 14).
(2) Further, the foaming ratio of the polylactic acid resin (A), the polystyrene resin (B), the polypropylene resin (C) and the compatibilizer (D), the foaming ratio, etc. satisfy the requirements specified in claim 1 The sheet has a beautiful appearance, has little draw down when producing a container by a secondary molding method, and is excellent in moldability (see Examples 1 to 14).
(3) On the other hand, even if the blending ratio of the polylactic acid resin (A), the polystyrene resin (B) , and the polypropylene resin (C) satisfies the requirements specified in claim 1, the compatibilizer (D )) Does not satisfy the requirements specified in claim 1, it is inferior in the extrusion characteristics at the time of foam sheet production, the appearance of the sheet, the drawdown property, the moldability at the time of secondary molding, etc. (see Comparative Example 1) .
(4) Even if the blending ratio of the compatibilizer (D) satisfies the requirements specified in claim 1, the blending ratio of the polylactic acid resin (A), the polystyrene resin (B), and the polypropylene resin (C). However, those that do not satisfy the requirements specified in claim 1 are also inferior in extrusion characteristics, sheet appearance, draw-down property, moldability in secondary molding, and the like (see Comparative Example 2 ).
(5) Further, the mixing ratio of the polystyrene-based resin (B), also the mixing ratio of the polypropylene resin (C) and the compatibilizer (D) is satisfied the requirements defined in claim 1, polylactic acid resin (A) However, those that do not satisfy the requirements specified in claim 1 are inferior in extrusion characteristics, inferior in sheet appearance, formability in secondary molding, and the like (see Comparative Examples 3 and 4).

[Examples 15 to 28, Comparative Examples 5 to 7]
The thermoplastic resin foam sheets obtained in Examples 1 to 14 and Comparative Examples 2 to 4 were used in a batch type differential pressure molding machine (manufactured by Kansai Automatic Molding Machine Co., Ltd., model: PK450V). And fixed with a clamp of 50cm x 50cm dimensions, heated from above and below the foam sheet with a thickness of 1.0mm for 15 seconds with a heater set temperature of 300 ° C, and a lunch box container of 20cm x 25cm x 3cm Molding was performed by a differential pressure molding method (a method of depressurizing from the male mold side) using a single die test mold. Molded products (containers) were obtained by changing the mold surface temperature, the annealing time of the molded products after differential pressure molding, and the like as described in Table-2.

The details of the molding conditions of the containers and the evaluation test results for the obtained containers are shown in Table 2. The evaluation items in Table-2 were as follows.
(I) Heat-resistant temperature (° C.): A commercially available salad oil (Nisshin Oil Industries, trade name: Nisshin Salad Oil) is put in an oil bath, and the temperature is raised by 5 ° C. in the range of 90 ° C. to 130 ° C. The container was taken out after being immersed for 1 minute at a temperature, and the appearance was visually observed. The maximum temperature (° C.) at which no deformation was observed in any part of the container was defined as the heat resistant temperature.

(J) Microwave oven heating test: The contents of the inner lunch box of the curtain (rice and side dish) are placed in the container storage part, a lid made of biaxially oriented polystyrene is covered, and the inside of the microwave oven (Sharp, model: RE-6000) And set to 1400 W and heated for 50 seconds. After heating, it was taken out from the microwave oven, and the presence or absence of deformation of the container was visually observed. A case where no deformation was observed in any part of the container was indicated as ◯, and a case where deformation was observed was indicated as △.
(K) Cold resistance: Tap water was stored in the container housing, and placed in a freezer of a freezer set to −20 ° C. (model: CR-221BSE) and left for 24 hours to freeze the tap water. . The container was taken out from the freezer, dropped from a height of 80 cm onto the concrete floor, and the presence or absence of cracking of the container was visually observed. A sample in which no cracks were observed was indicated as ◯, and a sample in which cracks were observed was indicated as ×.

From Table 2 above, the following becomes clear.
(1) The blending ratio of the polylactic acid resin (A), the polystyrene resin (B), the polypropylene resin (C), and the compatibilizer (D) satisfies the requirements specified in claim 1, and in claim 4. A container manufactured and molded under the specified conditions has a heat resistance temperature of 5 to 20 ° C. higher than that of the comparative example, and is excellent in mold releasability, microwave heating test, and cold resistance (Example 15). To Example 28).
(2) On the other hand, even if the blending ratio of the compatibilizer (D) satisfies the requirements defined in claim 1, the blending ratio of the polylactic acid resin (A) is more than the range defined in claim 1 , When the mixing ratio of the polystyrene resin (B) and the polypropylene resin (C) is less than the range specified in claim 1 , the container was welded to the mold when the container was released from the mold. The mold release was difficult, and the microwave heating test and the cold resistance evaluation test could not be performed (see Comparative Example 5).
(3) Even if the blending ratio of the polystyrene-based resin (B), the polypropylene-based resin (C) and the compatibilizing agent (D) satisfies the requirements specified in claim 1, the blending ratio of the polylactic acid resin (A) is claimed. Even if the foamed sheets of Comparative Example 3 and Comparative Example 4 that do not satisfy the requirements specified in Item 1 are annealed under the same conditions as in Example 15 and the like, the heat resistant temperature does not improve, and the microwave oven heating test, cold resistance, etc. (See Comparative Examples 6 and 7).

[Example 29 to Example 37, Comparative Example 8 to Comparative Example 11]
The thermoplastic resin foam sheet obtained in the example described in Example 8 above is fixed by a clamp having a size of 50 cm × 50 cm using a batch type differential pressure molding machine (manufactured by Kansai Automatic Molding Machine Co., Ltd., model: PK450V). Then, a foam set sheet with a thickness of 1.0 mm is heated by a heater from the top and bottom at a heater set temperature of 300 ° C. for 15 seconds, and a 20 cm × 25 cm × 3 cm lunch box type container is taken with a single die test die. It was molded by (Method of depressurization from the male mold side). Molded products were obtained by variously changing the mold surface temperature, the molded product (container) annealing time after differential pressure molding, as described in Table-3. The obtained molded product was subjected to an evaluation test ( heat resistance temperature , microwave heating test, cold resistance), and the evaluation results are shown in Table-3 .

From Table 3 above, the following becomes clear.
(1) When the mold surface temperature is in the range of 105 to 115 ° C. and the annealing time is 10 seconds to 20 seconds, the crystallinity of the container is increased or the heat resistance is excellent (Examples 29 to See Example 37).
(2) On the other hand, when the mold surface temperature is set to 120 ° C., even if the annealing time is set to 20 seconds, the crystallinity is not increased and the container is softened so that it is difficult to release from the mold. (See Comparative Example 8).
(3) Further, when the mold temperature is set to 100 ° C. or lower, the crystallinity of the container does not increase even when the annealing time is set to 30 seconds, and the heat resistance is inferior to that of the examples (Comparative Example 9 and Comparative Example). 10).
(4) In addition, when the mold temperature is around room temperature, the heat resistance is not improved at all (see Comparative Example 11).

  The foamed sheet made of thermoplastic resin according to the present invention is lightweight, excellent in cold resistance, heat insulation, oil resistance, heat resistance, rigidity, etc., and also excellent in biodegradability, by a thermoforming method such as vacuum forming or pressure forming. Many secondary molded articles (containers) can be obtained. Containers include trays, cups, bowls, dishes, containers, boxes and the like. In particular, since containers manufactured under specific molding conditions are excellent in heat resistance, they store pre-cooked foods, and are stored, transported and refrigerated / frozen at a low temperature of 0 to −30 ° C. It is suitable as a container for frozen cooked food that is cooked by a microwave oven at a temperature of 100 to 120 ° C.

Claims (5)

Polylactic acid (A) having a weight average molecular weight of 50,000 or more and 20 to 90% by weight, polystyrene resin (B) having a weight average molecular weight of 200,000 to 400,000 , and a density of 0.90 to 0 96, and (a) styrene-butadiene-styrene block copolymer (100) with respect to 100 weights of a ternary component consisting of 5 to 40% by weight of a polypropylene resin (C) having an MFR of 3 to 20 g / 10 min. b) hydrogenated styrene-butadiene-styrene block copolymer, (c) styrene-isoprene-styrene block copolymer, (d) hydrogenated styrene-isoprene-styrene block copolymer, and (e) styrene - ethylene - propylene - styrene copolymer from consisting compatibilizing agent selected from the group (D) is 1 to 20 parts by weight blended become resin fat composition as a raw material, originating Ratio is 1.1 to 5.0 times, the thickness is characterized by comprising been a 0.5 to 3.0 mm, thermoplastic resin foam sheet. The foamed sheet made of a thermoplastic resin according to claim 1, wherein the raw material resin composition is further blended with a crystallization accelerator (E) and a nucleating agent (F). A container made of a foamed sheet made of a thermoplastic resin, which is obtained by thermoforming the foamed sheet made of a thermoplastic resin according to claim 1 or 2. Polylactic acid (A) having a weight average molecular weight of 50,000 or more and 20 to 90% by weight, polystyrene resin (B) having a weight average molecular weight of 200,000 to 400,000 , and a density of 0.90 to 0 96, and the total amount of three components consisting of 5 to 40% by weight of a polypropylene resin (C) having an MFR of 3 to 20 g / 10 min , (a) a styrene-butadiene-styrene block copolymer, ( b) hydrogenated styrene-butadiene-styrene block copolymer, (c) styrene-isoprene-styrene block copolymer, (d) hydrogenated styrene-isoprene-styrene block copolymer, and (e) A resin fat composition containing 1 to 20 parts by weight of a compatibilizer (D) selected from the group consisting of styrene-ethylene-propylene-styrene copolymers is used as a raw material. The foam magnification is 1.1 to 5.0 times, the thickness is 0.5 to 3.0 mm, the mold temperature during thermoforming is set to a temperature range of 105 to 115 ° C., and 10 to 10 after container molding. A method for producing a thermoplastic resin foam sheet container, characterized by annealing for 20 seconds.   The method for producing a thermoplastic resin foam sheet container according to claim 4, wherein the raw material resin composition is further blended with a crystallization accelerator (E) and a nucleating agent (F).