JP4583160B2 - Biodegradable laminated foam sheet and molded body thereof - Google Patents

Description

  The present invention relates to a biodegradable laminated foam sheet and a molded product thereof. Specifically, the biodegradability used when a molded product such as a container or a lid used in the field of packaging materials is manufactured by thermoforming. The present invention relates to a biodegradable laminated foam sheet having excellent lightness and thermoformability, and excellent mechanical properties such as rigidity and impact resistance, and a molded product thereof.

Conventionally, polyolefin-based resins and polystyrene-based resins have been used as foamed sheets and have characteristics such as lightness, buffering properties, and heat insulation properties, and are mainly used as food packaging containers and cushioning materials. Most of these have no biodegradability and are used in a large amount, so that in recent years they have become a problem of waste disposal and also from the viewpoint of environmental load. Along with these growing environmental problems, packaging materials suitable for the protection, storage, and transportation of food and other contents during use, and practical properties as packaging containers are not impaired, and after use, soil surfaces, soil, compost, and activity There has been a demand for the development of packaging materials that can be quickly decomposed into raw materials in natural environments such as sludge and water.
On the other hand, recently, aliphatic polyesters, polysaccharides, and many other biodegradable resins have been put into practical use, and examinations as foamed sheets have been attempted, but aliphatics have been put to practical use. Polyesters generally have a low melting point and are inferior in heat resistance and foamability to polyolefin resins and polystyrene resins, and therefore need to be improved from materials or molding.

  As a method for improving the foamability of the aliphatic polyester material, a high molecular weight degradable copolymer of polyvalent carboxylic acid and hydroxycarboxylic acid is used (for example, see Patent Document 1), and has a long chain branch. From the viewpoint of polymerization such as using an aliphatic polyester (for example, see Patent Document 2), and by adding an acid anhydride such as succinic anhydride to a polyhydroxycarboxylic acid resin to increase the melt viscosity, foaming is performed. A polyhydroxycarboxylic acid resin composition that has been easily converted to an aliphatic acid (see, for example, Patent Document 3), and a resin composition in which an isocyanate compound is reacted with polylactic acid (for example, see Patent Document 4). Polyester resin is cross-linked with organic peroxide, gelled and foamed (for example, see Patent Document 5), aliphatic polyester and meta Examination of crosslinking with peroxides or reactive compounds such as cross-linking foaming of crylic acid ester in the presence of lactide (see, for example, Patent Document 6), and biodegradable linear polyester resin Separate from aliphatic polyesters such as using a mixture of polycaprolactone (for example, see Patent Document 7), using a resin composition of aliphatic polyester, polycaprolactone and polyolefin resin (for example, see Patent Document 8). Studies have been made on blend modification by adding a biodegradable resin or the like.

However, each method is an obstacle to practical use because it leads to stability in quality and performance, complexity of the manufacturing process and cost increase. Furthermore, it has thermoformability similar to polyolefin resin and polystyrene resin foam sheets and practical physical properties of thermoformed products, and also has biodegradability that is required at the disposal stage after use. The sheet has not yet been reported.
Japanese Patent Laid-Open No. 10-7778 JP 2003-286360 A Japanese Patent Laid-Open No. 11-60928 JP 2000-07037 A JP-A-10-324766 JP 2003-28360 A JP-A-8-188706 JP 2003-335881 A

  In view of the above problems, the present invention is excellent in biodegradability after use, excellent in lightness and thermoformability, and has biodegradability having practical properties comparable to polyolefin resin and polystyrene resin foam sheets. It is an object of the present invention to provide a laminated foam sheet and a molded body comprising the same.

  As a result of intensive studies to solve the above problems, the present inventors have identified a specific intermediate layer in a biodegradable foamed laminated sheet having two surface layers, a front surface and a back surface layer, and an intermediate layer disposed between the surface layers. By using a biodegradable resin foam layer with an expansion ratio and a specific average cell diameter, it has excellent light weight and thermoformability, and has biodegradability that has practical properties comparable to polyolefin resin and polystyrene resin foam sheets. The present inventors have found that a laminated foam sheet can be obtained and have completed the present invention.

That is, according to the first invention of the present invention, the laminate is composed of a biodegradable resin composed of two surface layers, a front and back surface layer, and an intermediate layer disposed between the surface layers. The biodegradable resin is a layer composed of a biodegradable resin composition containing 5 to 400 parts by weight of a filler with respect to 100 parts by weight of the biodegradable resin, and the intermediate layer has an expansion ratio of 1.1 to 30 times and an average cell diameter. A biodegradable laminated foam sheet characterized by comprising a biodegradable resin foam layer having a thickness of 30 to 300 μm.

According to the second invention of the present invention, in the first invention, the biodegradable resin used for the surface layer and the intermediate layer is an aliphatic polyester. Is provided.

According to a third invention of the present invention, in the second invention, the aliphatic polyester has an aliphatic or alicyclic diol unit having a molecular structural unit represented by the following general formula (1), and A biodegradable laminated foam sheet comprising an aliphatic or alicyclic dicarboxylic acid unit having a molecular structural unit represented by the following general formula (2) as an essential component is provided.
—O—R ¹ —O— (1)
(In formula (1), R ¹ represents a divalent chain aliphatic hydrocarbon group or alicyclic hydrocarbon group which may have an oxygen atom in the chain.)
—OC— (R ² ) _n —CO— (2)
(In Formula (2), R ² represents an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, and n represents 0 or 1)

According to a fourth invention of the present invention, in the third invention, the aliphatic polyester or the alicyclic diol unit of the aliphatic polyester is a 1,4-butanediol unit, an aliphatic or alicyclic dicarboxylic acid unit. A biodegradable laminated foam sheet is provided in which is a succinic acid unit.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the thickness ratio of each surface layer is 5% or more of the total thickness of the biodegradable laminated foam sheet, and 30 % Or less, a biodegradable laminated foam sheet is provided.

According to a sixth invention of the present invention, in any one of the first to fifth inventions, a skin layer having a thickness ratio of 10% or less of the total thickness is provided outside the surface layer. A biodegradable laminated foam sheet is provided.

Moreover, according to the 7th invention of this invention, the molded object which uses the biodegradable laminated foam sheet of the invention in any one of the 1st- 6th is provided.

  According to the present invention, in the biodegradable laminated foam sheet having the surface layer of the front and back two layers and the intermediate layer disposed between the surface layers, the expansion ratio of the biodegradable resin of the intermediate layer is present there By specifying the cell diameter, the biodegradation has practical properties comparable to polyolefin resin and polystyrene resin foam sheets, and has excellent biodegradability, light weight, thermoformability, rigidity, and impact resistance. Can be obtained.

  The present invention is made of a biodegradable resin, a front and back two surface layers made of a composition containing a filler, and an intermediate layer made of a foam of a biodegradable resin disposed between the surface layers, and further necessary Accordingly, a biodegradable laminated foam sheet composed of a skin layer and the like, and a molded body thereof. This will be described in detail below.

1. Each layer of biodegradable laminated foam sheet (1) Constituent component of surface layer (i) Biodegradable resin The type of biodegradable resin used for the surface layer of the biodegradable laminated foam sheet of the present invention is not particularly limited. Are polycaprolactone, polybutylene succinate, polybutylene succinate adipate, polyethylene succinate, polyethylene adipate, polybutylene adipate, polyhydroxybutyrate, polyhydroxyvalylate and other aliphatic polyesters and derivatives thereof, polycyclohexylene dimethyl adipate And alicyclic polyesters and derivatives thereof, fatty acid ester copolymers such as hydroxybutyrate-hydroxyvalerate copolymers, polylactic acid, and the like, and a plurality of types of resins may be used.
Among these, aliphatic polyesters are preferable, and in particular, the following general formula (1)
—O—R ¹ —O— (1)
(In formula (1), R ¹ represents a divalent chain aliphatic hydrocarbon group or alicyclic hydrocarbon group which may have an oxygen atom in the chain.)
An aliphatic or alicyclic diol unit having a molecular structure represented by the following general formula (2)
—OC— (R ² ) _n —CO— (2)
(In Formula (2), R ² represents an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, and n represents 0 or 1)
Any of a homopolymer and a copolymer (random copolymer, block copolymer, alternating copolymer, etc.) having an aliphatic or alicyclic dicarboxylic acid unit having a molecular structural unit represented by

As the compound that gives an aliphatic or alicyclic diol unit, the following general formula (4)
HO—R ¹ —OH (4)
(In the formula (4), R ¹ represents a divalent chain aliphatic hydrocarbon group or alicyclic hydrocarbon group which may have an oxygen atom in the chain.)
The diol compound represented by these is mentioned. The carbon number of the chain aliphatic hydrocarbon group in R ¹ is usually 2 to 10, preferably 2 to 6. Further, the number of carbon atoms in the alicyclic hydrocarbon group in ^{R 1} is usually 3-10, preferably 4-8. Specific examples of the chain aliphatic or alicyclic diol include ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6- Examples include hexanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol. Among these, 1,4-butanediol is preferable from the viewpoint of the physical properties of the obtained polymer.

  In addition to the above, specific examples of the diol compound having an oxygen atom in the chain include diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, co-polymerization of polyethylene glycol and polypropylene glycol. Examples include coalesce, dibutanediol, polytetramethylene glycol and the like. Among these, polyethylene glycol having a molecular weight of 1 to 2 million, polypropylene glycol, a copolymer of polyethylene glycol and polypropylene glycol, and a dihydroxyalkylene glycol condensate such as polytetramethylene glycol are preferable.

Examples of those which give aliphatic or alicyclic dicarboxylic acid units include the following general formula (5)
_{^{HOOC- (R 2) n -COOH ...}} (5)
(In Formula (5), R ² represents an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, and n represents 0 or 1)
Or a derivative thereof. Among these, in the above general formula (5), n is 0 or 1, and R ² is — (CH ₂ ) _m — (m represents an integer of 1 to 10). The dicarboxylic acid which is an aliphatic hydrocarbon group or a C3-C10 bivalent alicyclic hydrocarbon group, its lower alkyl ester, or an acid anhydride is preferable. In particular, in the above general formula (5), n is 0 or 1, and R ² is represented by — (CH ₂ ) _m — (m represents an integer of 1 to 6). The dicarboxylic acid which is a hydrogen group or a C4-C8 bivalent alicyclic hydrocarbon group, its C1-C4 lower alkyl ester, or an acid anhydride is preferable. Specific examples of the dicarboxylic acid or its derivative include oxalic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedioic acid, 1,4-cyclohexanedicarboxylic acid, and lower alkyl esters thereof (for example, dimethyl ester , Diethyl esters, etc.) and acid anhydrides thereof (for example, succinic anhydride, adipic anhydride, etc.). From the viewpoint of the physical properties of the resulting copolymer, succinic acid, adipic acid, sebacic acid, their lower alkyl esters, and acid anhydrides thereof are preferred, and succinic acid, succinic anhydride, or mixtures thereof are particularly preferred.

The aliphatic polyester is represented by the following general formula (3).
—O—R ³ —CO— (3)
(In formula (3), R ³ represents a divalent aliphatic hydrocarbon group.)
An aliphatic oxycarboxylic acid unit having a molecular structure represented by Specific examples of providing aliphatic oxycarboxylic acid units include lactic acid, glycolic acid, 2-hydroxy-n-butyric acid, 2-hydroxycaproic acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methyl. Examples include butyric acid, 2-hydroxyisocaproic acid, 4-hydroxycyclohexanecarboxylic acid, and 4-hydroxymethylcyclohexanecarboxylic acid. Furthermore, derivatives of these lower alkyl esters (for example, methyl ester, ethyl ester, etc.) and intramolecular esters may be used. These oxycarboxylic acids or derivatives thereof may be used alone or in a mixture. Further, when optical isomers exist in these, any of D-form, L-form and racemic form may be used, and the use form may be any of solid, liquid and aqueous solution. Of these, lactic acid or glycolic acid is preferred. In particular, lactic acid is preferred because it has a high polymerization rate and is easily available. Lactic acid can be easily obtained as an aqueous solution having a concentration of 30 to 95% by weight.

  As for the amount of the aliphatic oxycarboxylic acid, the lower limit is usually 0 mol%, preferably 0.01 mol%, and the upper limit is usually 30 mol%, preferably, among all the components constituting the aliphatic polyester. 20 mol%.

  The aliphatic polyester used in the present invention is an aliphatic and / or alicyclic polyhydric alcohol, aliphatic or alicyclic having three or more functional groups different from the diol and dicarboxylic acid in addition to the diol and dicarboxylic acid. Copolymerization of the formula polyvalent carboxylic acid or its anhydride, or aliphatic polyvalent oxycarboxylic acid is preferred because it can increase the melt viscosity of the resulting aliphatic polyester. Specific examples of the aliphatic or alicyclic polyhydric alcohol having 3 functional groups include trimethylolpropane, glycerin or its anhydride, and the aliphatic or alicyclic polyhydric alcohol having 4 functional groups. A specific example is pentaerythritol.

  Specific examples of the aliphatic or alicyclic polyvalent carboxylic acid having 3 functional groups or an anhydride thereof include propanetricarboxylic acid or an anhydride thereof, and the aliphatic or alicyclic polycarboxylic acid having 4 functional groups. Specific examples of the monovalent carboxylic acid or its anhydride include cyclopentanetetracarboxylic acid or its anhydride.

  In addition, the aliphatic oxycarboxylic acid component having three functional groups includes (a) a type having two carboxyl groups and one hydroxyl group in the same molecule, and (a) one carboxyl group and a hydroxyl group. Are divided into two types, and either type can be used. Specifically, malic acid of the type (a) is mentioned. In addition, the aliphatic oxycarboxylic acid component having four functional groups is (a) a type having three carboxyl groups and one hydroxyl group in the same molecule, (ii) two carboxyl groups and two These types are divided into a type having the same hydroxyl group in the same molecule and (c) a type having three hydroxyl groups and one carboxyl group in the same molecule, and any type can be used. Specific examples include citric acid and tartaric acid. These may be used alone or in combination of two or more.

  The amount of the compound having three or more functional groups is generally 0 mol%, preferably 0.01 mol%, and the upper limit is usually lower in all the constituent components constituting the aliphatic polyester resin. 5 mol%, preferably 2.5 mol%.

  In addition, aliphatic polyesters that are obtained by copolymerizing aromatic compounds such as aromatic oxycarboxylic acids, aromatic polyhydric alcohols, and aromatic polycarboxylic acids within a range that does not impair the requirements of biodegradability and melting point range are also used. it can. Specific examples of the aromatic compound used for the copolymerization are as follows. That is, specific examples of the aromatic oxycarboxylic acid include hydroxybenzoic acid and the like, and specific examples of the aromatic polyhydric alcohol include bisphenol A, 1,4-benzenedimethanol and the like. Specific examples of the divalent carboxylic acid include terephthalic acid, isophthalic acid, trimellitic acid, pyromellitic acid, benzophenone tetracarboxylic acid, phenylsuccinic acid, 1,4-phenylenediacetic acid, and anhydrides thereof. The amount of these aromatic compounds introduced is usually 50 mol% or less, preferably 30 mol% or less, based on the total aliphatic compounds.

  The aliphatic polyester used in the present invention can be produced by a known method. For example, melt polymerization in which after the esterification reaction and / or transesterification reaction between the aliphatic or alicyclic dicarboxylic acid component and the aliphatic or alicyclic diol component is performed, a polycondensation reaction is performed under reduced pressure. However, from the viewpoint of economy and simplicity of the production process, the polyester can be produced by melt polymerization in the absence of a solvent. The manufacturing method is preferred. The polycondensation reaction is preferably performed in the presence of a polymerization catalyst. The addition timing of the polymerization catalyst is not particularly limited as long as it is before the polycondensation reaction, and it may be added when the raw materials are charged, or may be added at the start of pressure reduction.

The polymerization catalyst is generally a compound containing a group 1 to group 14 metal element excluding hydrogen and carbon in the periodic table. Specifically, at least one metal selected from the group consisting of titanium, zirconium, tin, antimony, cerium, germanium, zinc, cobalt, manganese, iron, aluminum, magnesium, calcium, strontium, sodium and potassium Examples thereof include compounds containing an organic group such as carboxylate, alkoxy salt, organic sulfonate, or β-diketonate salt, and inorganic compounds such as metal oxides and halides described above and mixtures thereof.
Among these, metal compounds containing titanium, zirconium, germanium, zinc, aluminum, magnesium and calcium, and mixtures thereof are preferable, and among these, titanium compounds and germanium compounds are particularly preferable. In addition, the catalyst is preferably a compound that is liquid at the time of polymerization or that dissolves in an ester low polymer or polyester because the polymerization rate increases when it is melted or dissolved at the time of polymerization.

  The amount of catalyst added in the case of using a metal compound as the polymerization catalyst is such that the lower limit is usually 5 ppm, preferably 10 ppm, and the upper limit is usually 30000 ppm, preferably 1000 ppm, more preferably as the amount of metal to the polyester to be produced. Is 250 ppm, particularly preferably 130 ppm. If too much catalyst is used, it is not only economically disadvantageous but also lowers the thermal stability of the polymer. Conversely, if it is too little, the polymerization activity is lowered, and as a result, the polymer decomposes during polymer production. Is more likely to be triggered.

  The lower limit of the reaction temperature of the esterification reaction and / or transesterification reaction between the dicarboxylic acid component and the diol component is usually 150 ° C., preferably 180 ° C., and the upper limit is usually 260 ° C., preferably 250 ° C. The reaction atmosphere is usually an inert gas atmosphere such as nitrogen or argon. The reaction pressure is usually normal pressure to 10 kPa, but normal pressure is preferred. The reaction time is usually 1 hour or longer, and the upper limit is usually 10 hours, preferably 4 hours.

In the subsequent polycondensation reaction, the lower limit of the pressure is usually 0.01 × 10 ³ Pa, preferably 0.01 × 10 ³ Pa, and the upper limit is usually 1.4 × 10 ³ Pa, preferably 0.4 ×. The process is performed under a vacuum of 10 ³ Pa. At this time, the lower limit of the reaction temperature is usually 150 ° C., preferably 180 ° C., and the upper limit is usually 260 ° C., preferably 250 ° C. The lower limit of the reaction time is usually 2 hours, and the upper limit is usually 15 hours, preferably 10 hours.

  In the present invention, a known vertical or horizontal stirred tank reactor can be used as a reactor for producing the aliphatic polyester. For example, melt polymerization is performed in two stages of esterification and / or transesterification and reduced pressure polycondensation using the same or different reactors, and a vacuum pump and a reactor are used as the reduced pressure polycondensation reactor. A method of using a stirred tank reactor equipped with a evacuation pipe for decompression to be connected can be mentioned. In addition, a condenser is connected between the vacuum exhaust pipe connecting the vacuum pump and the reactor, and the volatile components and unreacted monomers generated during the condensation polymerization reaction are recovered by the condenser. Is preferred.

  In the present invention, the molar ratio of the diol unit and the dicarboxylic acid unit to become an aliphatic polyester having the target melting point is such that the lower limit of the amount of the diol unit to 1 mol of the dicarboxylic acid unit is usually 0.8 mol, preferably 0.9 mol, and the upper limit is usually 1.5 mol, preferably 1.3 mol, particularly preferably 1.2 mol.

  In the present invention, for example, an isocyanate compound, an epoxy compound, an oxazoline, an acid anhydride, a carbodiimide compound, and a peroxide are allowed to act on the aliphatic polyester to the extent that the biodegradability is not affected, thereby increasing the molecular weight. Or what was bridge | crosslinked can also be used.

  The molecular weight and molecular weight distribution of the aliphatic polyester used in the present invention are not particularly limited as long as they have substantially sufficient mechanical properties and can be molded, but the melt flow of the aliphatic polyester used in the present invention is not limited. When the index (MFR) is measured at 190 ° C. and 2.16 kg, the lower limit is usually 0.1 g / 10 minutes, and the upper limit is usually 100 g / 10 minutes, preferably 50 g / 10 minutes, particularly preferably 30 g. / 10 minutes.

(Ii) Filler The surface layer of the biodegradable laminated foam sheet of the present invention is a layer from a composition in which a filler is blended with a biodegradable resin from the effect of improving the rigidity of the sheet and improving the thermoformability. be able to. Fillers are roughly classified into inorganic fillers and organic fillers.
Inorganic fillers include talc, calcium carbonate, silica, diatomaceous earth, zeolite, bentonite, calcined perlite, kaolin, kaolinite, glass, limestone, calcium silicate, sodium silicate and other silicates, aluminum oxide, magnesium carbonate, calcium hydroxide And hydroxides such as ferric carbonate, zinc oxide, titanium oxide, iron oxide, aluminum phosphate, and barium sulfate.
Examples of organic fillers include wood flour, starch, cellulose, and cellulose derivatives.
These fillers can be used alone or in combination of two or more, regardless of whether they are inorganic or organic. Among these, talc and calcium carbonate are preferable from the viewpoint of performance and price. Talc is more preferred.
The particle size of the filler is not particularly limited, but preferably the average particle size is 0.1 to 50 μm. Particularly preferred are talc and calcium carbonate having an average particle size of 0.1 to 20 μm, and most preferred is talc having an average particle size of 0.1 to 20 μm.

  The blending amount of the filler is preferably 400 parts by weight or less, more preferably 5 to 400 parts by weight, and further preferably 5 to 150 parts by weight with respect to 100 parts by weight of the biodegradable resin. When the blending amount of the filler exceeds 400 parts by weight, the extrudability of the laminated foamed sheet and conversely the extensibility of thermoforming deteriorates, which is not preferable.

(Iii) Optional component In the surface layer of the biodegradable laminated foam sheet of the present invention, various conventionally known additives can be blended as long as the object of the present invention is not impaired. Additives include, for example, crystal nucleating agents, antioxidants, ultraviolet absorbers, light resistance agents, heat stabilizers, colorants, flame retardants, mold release agents, antistatic agents, antifogging agents, surface wetting improvers, incineration Resin additives such as adjuvants, pigments, lubricants and various surfactants can be mentioned.

(2) Constituent component of intermediate layer (i) Biodegradable resin As the type of biodegradable resin used for the intermediate layer of the biodegradable laminated foam sheet of the present invention, the biodegradable resin used for the surface layer should be used. Can do. The biodegradable resin of the intermediate layer may be a biodegradable resin different from the surface layer, but it is preferable to use the same biodegradable resin.
(Ii) Foaming The biodegradable resin layer of the intermediate layer needs to be foamed, and the foaming ratio is 1.1 to 30 times, preferably 3 to 20 times. If the expansion ratio is less than 1.1 times, substantial effects such as weight reduction due to foaming are not exhibited, and if the expansion ratio exceeds 30 times, open cells increase and the drawdown property at the time of container molding and the container The formability of the will be reduced.
Moreover, the average cell diameter of the intermediate | middle foamed layer of this invention is 30-300 micrometers, Preferably it is 50-100 micrometers. When the average bubble diameter exceeds 300 μm, the bubble film is easily broken during container molding, and it is difficult to obtain the shape of the container.
The average cell diameter is controlled by a known method, for example, the particle size and blending amount of the foam core material, the pressure until the air is released from the die, the distance until the foam is solidified, and the resin temperature. Can be done.

As a method for forming the intermediate layer of the present invention into a foam layer, a foaming agent is mixed in advance with the biodegradable resin forming the intermediate layer, or the biodegradable resin is injected at the stage of plasticizing with an extruder. There is a method of foaming at the time of extrusion.
As the foaming agent used here, a known decomposable foaming agent or a gas or volatile foaming agent can be used.

  Examples of the decomposable foaming agent include inorganic decomposable foaming agents such as ammonium carbonate, sodium bicarbonate, ammonium bicarbonate, and ammonium nitrite, azo compounds such as azodicarbonamide, azobisisobutyronitrile, diazoaminobenzene, Nitroso compounds such as N, N′-dinitrosopentanemethylenetetramine, N, N′-dimethyl-N, N′-dinitrosoterephthalamide, benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, p, p′-oxybis Examples thereof include benzenesulfonyl semicarbazide, p-toluenesulfonyl semicarbazide, trihydrazinotriazine, barium azodicarboxylate, citric acid, and the like, and these can be used alone or in combination of two or more. The use ratio of these degradable foaming agents is preferably 0.1 to 8 parts by weight with respect to 100 parts by weight of the biodegradable resin.

Examples of gaseous blowing agents include nitrogen, carbon dioxide, propane, neopentane, methyl ether, dichloromethane difluoride, n-butane, isobutane, and various chlorofluorocarbons. In addition, gas means here that it is gas at normal temperature.
On the other hand, examples of the volatile blowing agent include water, ether, petroleum ether, acetone, pentane, hexane, isohexane, heptane, isoheptane, benzene, toluene, various alcohols, halogenated hydrocarbons (for example, methyl chloride), and the like. It is done.
The use ratio of the gas or volatile foaming agent is preferably 0.5 to 20 parts by weight with respect to 100 parts by weight of the biodegradable resin. As the blowing agent, nitrogen, carbon dioxide gas, or water is preferably contained alone or as a mixture thereof in a proportion of 5% by weight based on the total amount of the blowing agent. If it is less than 5% by weight, the dispersion of the foaming agent varies, and the stability of the resulting foam is poor. Moreover, you may mix | blend as a decomposable foaming agent which can decompose | disassemble by the heating in an extrusion process and can generate | occur | produce nitrogen, a carbon dioxide gas, or water.

  In the present invention, it is preferable to use at least one foaming agent selected from baking soda, citric acid, carbon dioxide, or butane gas and at least one foaming agent selected from a gas foaming agent from the viewpoint of appearance and cell density. These foaming agents may be used in combination with other known foaming aids in order to adjust the decomposition temperature, generated gas and decomposition rate.

  In addition to the foaming agent, the biodegradable resin of the intermediate layer includes, as a foam control agent, an inorganic powder such as talc and silica, an acidic salt such as a polyvalent carboxylic acid, a polyvalent carboxylic acid and sodium carbonate or sodium bicarbonate. You may mix | blend a reaction mixture etc. Moreover, other additives, such as a ultraviolet absorber, antioxidant, a nucleating agent, and a coloring agent, can also be mix | blended.

2. Layer structure and production of biodegradable laminated foam sheet The layer structure of the laminated foam sheet of the present invention includes at least two front and back surface layers and an intermediate layer disposed between the surface layers. The sandwich structure in which the layers are sandwiched between the surface layers is the gas retention of the foam layer, which is the intermediate layer, the effect of inhibiting cell breakage and open cell formation, the rigidity and thermoformability of the laminated foam sheet, and the surface smoothness This is because the effect of maintaining the sex is extremely large.
As long as the layer structure of the laminated foam sheet of the present invention has at least the above-mentioned sandwich structure, the type, number, arrangement, etc. of the layer are not particularly limited. For example, it may be a two-kind three-layer structure consisting of only the two surface layers and the intermediate layer, or a three-kind five-layer structure in which a new layer is further provided outside the surface layer, or the surface layer. Various structures such as a three-kind five-layer structure or a four-kind seven-layer structure in which a new layer is provided between the intermediate layer and the intermediate layer can also be employed.

  As a new layer further provided outside the surface layer in the present invention, or a new layer provided between the surface layer and the intermediate layer, for example, according to demands such as prevention of sprinkling eyes, imparting decorativeness, etc. Examples thereof include a skin layer provided on the outer side of the surface layer (outermost layer of the sheet). Here, by setting the thickness of the skin layer to 10% or less of the total thickness, the skin layer according to the purpose can be obtained without impairing the purpose of the laminated foam sheet.

The thickness ratio of each surface layer is preferably 5% or more and 30% or less of the total thickness of the laminated foam sheet. When the thickness ratio of each surface layer is less than 5% of the total thickness of the laminated foamed sheet, the smoothness of the laminated foamed sheet surface is lowered, and the surface layer is easily broken due to the extension of thermoforming, so that the shaping tends to be impaired. On the other hand, if it exceeds 30%, effects such as lightness and heat insulation due to foaming of the laminated sheet are lowered.
The total thickness of the laminated foam sheet is not particularly limited and may be adjusted according to the purpose of use, etc., but is usually 0.4 to 3.0 mm, particularly 0.5 to 2 for general food containers. 0.5 mm is preferred.

As a method for producing the biodegradable resin laminate sheet of the present invention, using the above-described resin or composition for each layer, a known molding method such as a single screw extruder, a multi-screw extruder, a tandem extruder, etc. Co-extrusion using an extruder including a T-die and a circular die, for example, a co-extruder having a part or a die laminated by a joining part of an extruder for forming an intermediate layer and an extruder for forming a surface layer It can be produced by a foaming method.
For the intermediate layer, a composition containing a foaming agent is used, and the temperature is 250 to 100 ° C., preferably 230 to 80 ° C., the pressure is 35 to 3 MPa, and preferably 15 to 10 MPa (hereinafter referred to as P1). The molten mixture obtained is extruded from the T die into a process region having a pressure lower than P1, and then the molten mixture extruded from the T die or the circular die is cooled by a cooling roll or a cooling cylinder.
The distance from when the molten mixture melt-mixed in the extruder is extruded from the die outlet to contact the cooling roll or the cooling cylinder eliminates the corrugated mark due to volume expansion due to foaming when the molten mixture is extruded from the die. For the purpose, it is preferably 0.05 to 5 mm, more preferably 0.05 to 3 mm. In addition, the surface temperature of the cooling roll or the cooling cylinder is 120 ° C. or less, preferably 90 ° C. or less for the purpose of forming a bubble shape that is dense and has no directionality in the foam. Preferably it is done.

3. Formed body of biodegradable laminated foam sheet The biodegradable laminated foam sheet obtained as described above is shaped into various containers, cups and trays by thermoforming. Container molding is generally vacuum molding in which a plastic sheet is heated and softened and pressed against a desired mold, the air in the gap between the mold and the material is removed and closely adhered to the mold by atmospheric pressure, and compression above atmospheric pressure is performed. It is a generic term for pressure forming or the like that uses air or vacuum together, and as a method, vacuum or pressure is used, and if necessary, a method of forming into a mold shape using a plug together (straight method, Drape method, air slip method, snapback method, plug assist method, plug assist reverse draw molding method, match mold molding method, etc.), solid phase press molding, and stamping molding. If it is a shaping | molding method by the combination etc. of these thermoforming methods, it will not specifically limit. Various conditions such as the thermoforming temperature, the degree of vacuum, the pressure of compressed air, and the forming speed are appropriately set depending on the plug shape, the die shape, the properties of the raw material sheet, and the like.

  The biodegradable laminated foam sheet of the present invention is significantly improved in sheet physical properties and sagging property when heated compared to a single foam sheet of a conventional biodegradable resin. By using it for secondary molding, molded articles such as containers, cups, trays and the like close to polyolefin-based resins and polystyrene-based resin sheets can be obtained.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. In addition, the measuring methods, such as a physical-property value of each item in an Example, and the manufacture example of the used biodegradable resin are shown below.

1. Measurement method (1) Sheet density (g / cm ³ ): The laminated foamed sheet was cut into 10 cm squares, and the density of the entire sheet was determined from its weight and thickness.
(2) Expansion ratio of the intermediate layer (times): The intermediate layer density was calculated based on the total density of the laminated foam sheet, and calculated according to the following formula.
Intermediate layer expansion ratio = (intermediate layer density when foaming) ÷ (intermediate layer density when not foamed)
(3) Average cell diameter (μm) of the intermediate layer: A cross section is cut out in the extrusion direction of the laminated foam sheet, and the cross section is enlarged and projected using a microscope or the like according to ASTM-D3576. On the projected image, a straight line is drawn in a direction corresponding to each of the thickness direction of the sheet, the extrusion direction of the sheet, and the direction orthogonal thereto, and the number of bubbles intersecting the straight line is counted. The value obtained by dividing the true length of the straight line by the number of bubbles is the average cell diameter in the sheet thickness direction, the sheet extrusion direction, and the direction perpendicular thereto, and this is the arithmetic average. The value obtained by doing this was taken as the average cell diameter of the foamed layer.
(4) Bubble state of the intermediate layer: The cross-section of the laminated foamed sheet (direction perpendicular to the flow direction) was sliced to about 10 to 20 μm with a microtome, observed with an optical microscope, photographed, and evaluated according to the following criteria.
A: The closed cells are uniform and fine.
○: Closed cells Δ: Some open cells are present ×: Most are open cells (5) Sheet appearance: The surface of the laminated foam sheet was observed visually and evaluated according to the following criteria.
◎: Smooth ○: Almost smooth ×: Concavities and convexities (6) Container moldability: The obtained laminated foamed sheet was used by using an indirectly heated pressure forming machine (manufactured by Asano Laboratory, Cosmic Molding Machine). The upper and lower heaters at a position 20 cm away from the sheet were heated at 325 ° C. The sheet was molded into a ribbed lunch container having a length of 24 cm, a width of 18 cm, and a depth of 4 cm under the conditions of a heating time of 12 seconds and a pneumatic pressure of 2 kg / cm ² . The shape and appearance of the obtained container were visually observed and judged according to the following evaluation criteria.
(Double-circle): The surface state of a container is favorable and shaping has been completed in detail.
○: The surface condition of the container is good, and the rib-shaped part and the bottom corner part are slightly shaped, but there is no practical problem.
X: The surface of the container flutters, cloudes, etc., the gloss is impaired, or the shaping is not completed in detail.
(7) Biodegradability test: A field using a 1: 1 mixture of humus and compost was set outdoors, and JIS No. 2 dumbbell pieces punched from the obtained sheets were embedded at a depth of about 7 cm. did. After leaving in the field for a predetermined period from the start of burying, the test piece was taken out, the attached soil was removed, the weight was measured, and the weight residual ratio was measured. The water given to the field during the test was only natural rain, and no artificial water was supplied.

2. Production of biodegradable resin (Production Example 1)
In a reaction vessel having a capacity of 1 m ³ equipped with a stirrer, a nitrogen introducing tube, a heating device, a thermometer, and an auxiliary agent addition port, 134 kg of succinic acid, 121 L of 1,4-butanediol, and germanium oxide were dissolved in advance by 1 wt%. 7.21 kg of 90% DL lactic acid aqueous solution was charged. Nitrogen gas was introduced under stirring, and the reaction was started at 120 ° C. in a nitrogen gas atmosphere, and the temperature was raised to 200 ° C. over 1 hour and 40 minutes. Subsequently, the temperature was raised to 230 ° C. over 1 hour and 25 minutes, and at the same time, the pressure was reduced to 1 mmHg, and polymerization was performed at 230 ° C. and 1 mmHg for 4 hours and 20 minutes to obtain an aliphatic polyester (A1). The melt flow rate (JIS-K7210, temperature 190 ° C., load 2.16 kgf) of the obtained aliphatic polyester (A1) was 4.2 g / 10 minutes.

(Production Example 2)
In a reaction vessel having a capacity of 1 m ³ equipped with a stirrer, a nitrogen introducing tube, a heating device, a thermometer and an auxiliary agent addition port, 134 kg of succinic acid, 116 L of 1,4-butanediol, 0.24 kg of DL malic acid, and germanium oxide were added. 7.21 kg of 90% DL lactic acid aqueous solution dissolved 1% by weight in advance was charged. Nitrogen gas was introduced under stirring, and the reaction was started at 120 ° C. in a nitrogen gas atmosphere, and the temperature was raised to 200 ° C. over 1 hour and 40 minutes. Subsequently, the temperature was raised to 230 ° C. over 1 hour and 25 minutes, and at the same time, the pressure was reduced to 1 mmHg, and polymerization was performed at 230 ° C. and 1 mmHg for 4 hours and 20 minutes to obtain an aliphatic polyester (A2). The resulting aliphatic polyester (A2) had a melt flow rate (JIS-K7210, temperature 190 ° C., load 2.16 kgf) of 3.8 g / 10 min.

(Production Example 3)
In a reaction vessel having a capacity of 1 m ³ equipped with a stirrer, a nitrogen introduction tube, a heating device, a thermometer, and an auxiliary agent addition port, 122 kg of succinic acid, 22.2 kg of adipic acid, 115 L of 1,4-butanediol, DL malic acid 0 .23 kg and 7.21 kg of 90% DL lactic acid aqueous solution in which 1 wt% of germanium oxide was dissolved in advance were charged. Nitrogen gas was introduced under stirring, and the reaction was started at 120 ° C. in a nitrogen gas atmosphere, and the temperature was raised to 200 ° C. over 1 hour and 40 minutes. Subsequently, the temperature was raised to 230 ° C. over 1 hour and 25 minutes, and at the same time, the pressure was reduced to 1 mmHg, and polymerization was performed at 230 ° C. and 1 mmHg for 4 hours to obtain an aliphatic polyester (A3). The melt flow rate (JIS-K7210, temperature 190 ° C., load 2.16 kgf) of the obtained aliphatic polyester (A3) was 4.0 g / 10 min.

(Examples 1-7)
Aliphatic polyesters (A1) to (A3) obtained in Production Examples 1 to 3 as biodegradable resins (A4: polybutylene succinate (“Bionore 1001” manufactured by Showa Polymer Co., Ltd.), melt flow rate 1.5 g / 10 minutes)) and polylactic acid (PLA: manufactured by Mitsui Chemicals, trade name Lacia “H400”). The surface layer material was previously blended with a biodegradable resin and a predetermined amount of filler (talc: manufactured by Fuji Talc Co., Ltd., particle size 10 μm), and kneaded at 200 ° C. with a twin-screw kneader to obtain pellets.
As the foaming agent for the intermediate layer, an inorganic decomposable foaming agent of a 1: 1 mixture of monosodium citrate and sodium bicarbonate was used.
Next, in each layer formulation shown in Table 1 for each example, the surface layer and the intermediate layer were each melted in an extruder with a diameter of 40 mmφ, co-extruded by a feed block method, and then the intermediate layer foamed from the T die. Two types and three layers of laminated foam sheets were melt-extruded. The molten sheet that came out of the die was cooled and corrugated with a small-diameter roll in which cooling water having a temperature adjusted to 40 ° C. was flown to produce a biodegradable laminated foam sheet having a width of 400 mm and a total thickness of 900 μm. The sheet physical properties, container moldability, and biodegradability of each laminated sheet thus obtained were measured. The results are shown in Table 1.

(Comparative Examples 1 and 2)
In Example 1 in Table 1, a sheet having the same full thickness without providing a surface layer and a sheet having no filler talc from the surface layer were used as Comparative Examples 1 and 2, respectively. Molding and measurement were performed. The results are shown in Table 1.

(Examples 8 and 9)
In the laminated foam sheet configuration of Examples 1 and 2, a foamed layer was formed with an extruder having a diameter of 65 mm using a gas foaming agent (n-butane gas) as a foaming agent for an intermediate layer and monomonosodium citrate as a foam regulator. A two-type three-layer laminated foam sheet having an intermediate layer foamed was obtained by a foam sheet apparatus equipped with a coextrusion circular die and a cooling cylinder. About the obtained laminated foam sheet, sheet physical property, container moldability, and biodegradability were measured, respectively. The results are shown in Table 1.

(Comparative Example 3)
In the laminated foamed sheet structure of Comparative Example 2, a laminated foamed sheet similar to that in Example 8 was produced using a gas foaming agent (n-butane gas) as the foaming agent and monosodium citrate as the bubble regulator. For the expansion rate of the foaming agent, the surface layer does not contain a filler, so the melt tension against the expansion force of the gas foaming agent in the intermediate layer of the surface layer material is insufficient, and the gas in the intermediate layer penetrates the surface layer. Thus, a foam could not be obtained.

  By using a specific biodegradable laminated foam sheet having two surface layers of the front and back surfaces of the present invention and an intermediate layer disposed between the surface layers, it is excellent in biodegradability after use and is lightweight. Biodegradable resin raw materials used for thermoformed products such as various containers, cups, and trays that are environmentally friendly, because of its excellent physical properties such as rigidity and impact resistance. Industrial value as an anti-sheet is extremely high.

Claims (7)

A laminate comprising a biodegradable resin composed of two surface layers, front and back, and an intermediate layer disposed between the surface layers , wherein the surface layer is a filler with respect to 100 parts by weight of the biodegradable resin. It is a layer composed of a biodegradable resin composition containing 5 to 400 parts by weight, and the intermediate layer is composed of a biodegradable resin foam layer having an expansion ratio of 1.1 to 30 times and an average cell diameter of 30 to 300 μm. A biodegradable laminated foam sheet characterized by   The biodegradable laminated foam sheet according to claim 1, wherein the biodegradable resin used for the surface layer and the intermediate layer is an aliphatic polyester. The aliphatic polyester has an aliphatic or alicyclic diol unit having a molecular structural unit represented by the following general formula (1), and an aliphatic or fat having a molecular structural unit represented by the following general formula (2) The biodegradable laminated foam sheet according to claim 2 , comprising a cyclic dicarboxylic acid unit as an essential component.
—O—R ¹ —O— (1)
(In formula (1), R ¹ represents a divalent chain aliphatic hydrocarbon group or alicyclic hydrocarbon group which may have an oxygen atom in the chain.)
—OC— (R ² ) _n —CO— (2)
(In Formula (2), R ² represents an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, and n represents 0 or 1) The raw material according to claim 3 , characterized in that the aliphatic or alicyclic diol unit of the aliphatic polyester is a 1,4-butanediol unit and the aliphatic or alicyclic dicarboxylic acid unit is a succinic acid unit. Degradable laminated foam sheet. The thickness ratio of the surface layer each layer, the biodegradable laminated foam sheet total thickness of more than 5% of, and is equal to or less than 30%, the raw according to any one of claims 1-4 Degradable laminated foam sheet. The biodegradable laminated foam sheet according to any one of claims 1 to 5 , wherein a skin layer having a thickness ratio of 10% or less of the total thickness is provided outside the surface layer. . The molded object which uses the biodegradable laminated foam sheet of any one of Claims 1-6 .