JP2009068021A - Polylactic acid-based resin foam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid-based resin foam, having excellent heat resistance. <P>SOLUTION: The polylactic acid-based resin foam is a foamed molded product prepared by thermoforming a foamed sheet that makes a ploylactic acid-based resin a major component of the base material resin. The difference (ΔH<SB>endo</SB>:2°C/min-ΔH<SB>exo</SB>:2°C/min) of the endotherm (ΔH<SB>endo</SB>:2°C/min) and the exotherm (ΔH<SB>exo</SB>:2°C/min) of the foamed molding, determined by heat flux differential scanning calorimetry at the heating rate of 2°C/min, is ≥10 J/g. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polylactic acid resin foamed molded article.

  Conventionally, a foam made of a general-purpose resin such as a polyethylene resin, a polypropylene resin, or a polystyrene resin has been used in many fields because it is excellent in lightness, heat insulation, and buffering property. However, foams made of these general-purpose resins, when left in a natural environment after use, are hardly decomposed by microorganisms in the soil, which may cause environmental pollution problems.

  In order to solve such a problem, biodegradable resins that can be decomposed by microorganisms in the soil have been developed. One example is a biodegradable polylactic acid resin. The polylactic acid-based resin has microbial degradability and is excellent in safety to the human body, and thus has been put into practical use as, for example, a surgical suture and has a long track record. Moreover, in recent years, lactic acid, which is a raw material for polylactic acid-based resins, has been produced in large quantities and at low cost by fermentation methods using corn and the like as raw materials. The development of foams, especially foam sheets, made from selenium has been underway.

  However, since the conventional polylactic acid resin foamed sheet (Patent Document 1) is mainly composed of amorphous polylactic acid, it is excellent in moldability but has a problem in heat resistance, and is deformed at room temperature. It was. On the other hand, although crystalline polylactic acid is excellent in heat resistance, it has problems in moldability and foamability, and it has been difficult to obtain a high-quality foam sheet. Even if a foamed sheet was produced, the crystalline polylactic acid resin foamed sheets (Patent Documents 2 and 3) were excellent in heat resistance but poor in thermoformability. Moreover, since the apparent density is large, the bubble shape is non-uniform, and the closed cell ratio is low, it is not easy to thermo-mold.

JP 2002-322309 A [Claims] JP 2002-3709 A [Claims] JP 2000-136259 A [Claims]

  This invention makes it a subject to provide the polylactic acid-type resin foam molded object which is excellent in heat resistance.

According to the present invention, the following polylactic acid resin foamed molded article is provided.
[1] A foam-molded article obtained by thermoforming a foam sheet comprising a polylactic acid-based resin as a main component of a base resin, by heat flux differential scanning calorimetry at a heating rate of 2 ° C./min. The difference (ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) between the endothermic amount (ΔH _{endo: 2 ° C./min} ) and the calorific value (ΔH _{exo: 2 ° C./min} ) required is 10 J / g. A polylactic acid resin foamed molded product characterized by the above.

The polylactic acid resin foam molded article of the present invention has a difference (ΔH _{endo: 2 °} C./min−ΔH) between a specific endothermic amount (ΔH _{endo: 2 ° C./min} ) and a calorific value (ΔH _{exo: 2 ° C./min} ). _{exo: 2 ° C./min} ), it is a biodegradable foamed molded article having excellent rigidity and heat resistance.

It is a foam sheet longitudinal cross-sectional view for demonstrating the measuring method of the bubble diameter of a foam sheet. It is explanatory drawing of the DSC curve which shows _(DELTA) H _{endo: row} of the polylactic acid calculated | required by heat flux differential scanning calorimetry. It is another explanatory drawing of the DSC curve which shows _(DELTA) H _{endo: row} of the polylactic acid calculated | required by heat flux differential scanning calorimetry. It is a graph for demonstrating the measuring method of the melt tension of base resin or a foam sheet. It is explanatory drawing of the DSC curve which shows (DELTA) _{H exo: 2 degree-C / min} and (DELTA) _{H endo: 2 degree-C / min} of the foam sheet calculated | required by heat flux differential scanning calorimetry. It is other explanatory drawing of the DSC curve which shows _(DELTA) H _{exo: Bead} and _(DELTA) H _{endo: 2 degree-C / min} of the foam sheet calculated | required by heat flux differential scanning calorimetry. It is further explanatory drawing of the DSC curve which shows _{(DELTA) Hexo: Bead} and (DELTA) _{Hendo: Bead} of a foam sheet calculated | required by heat flux differential scanning calorimetry. It is a graph for demonstrating the measuring method of the half crystallization time of a foam sheet.

  The polylactic acid resin foam sheet for thermoforming in the present invention (hereinafter also simply referred to as a foam sheet) comprises a polylactic acid resin as a main component of the base resin. The polylactic acid resin refers to a polymer containing 50 mol% or more of lactic acid component units. These include (1) a polymer of lactic acid, (2) a copolymer of lactic acid and another aliphatic hydroxycarboxylic acid, and (3) a lactic acid, an aliphatic polyhydric alcohol, and an aliphatic polycarboxylic acid. A copolymer, (4) a copolymer of lactic acid and an aliphatic polyhydric carboxylic acid, (5) a copolymer of lactic acid and an aliphatic polyhydric alcohol, (6) a mixture of any combination of the above (1) to (5), etc. Is included. Specific examples of the lactic acid include L-lactic acid, D-lactic acid, DL-lactic acid or their cyclic dimer L-lactide, D-lactide, DL-lactide, or a mixture thereof. .

The polylactic acid resin used in the present invention has an endothermic amount (ΔH _{endo: row} ) of 10 J / g or more, preferably 20 J / g among the polylactic acid resins described above, which is determined by the following heat flux differential scanning calorimetry. As mentioned above, More preferably, it is 30 J / g or more. The upper limit of the endothermic amount (ΔH _{endo: row} ) of the polylactic acid resin used in the present invention is not particularly limited, but is generally 60 J / g. The polylactic acid resin having an endothermic amount (ΔH _{endo: row} ) of 10 J / g or more used in the present invention is a crystalline polylactic acid resin, or a crystalline polylactic acid resin and an amorphous polylactic acid. Those having an endothermic amount (ΔH _{endo: row} ) of 10 J / g or more are selected from a mixture with a resin.
In the present specification, crystalline polylactic acid has an endothermic amount (ΔH _{endo: row} ) of the above-mentioned polylactic acid exceeding 2 J / g.
The endothermic amount (ΔH _{endo: row} ) of the crystalline polylactic acid is usually 20 to 65 J / g. Further, in this specification, the amorphous polylactic acid means that an endothermic peak having an endothermic amount (ΔH _{endo: row} ) of the above-mentioned polylactic acid of 2 J / g or less appears or no endothermic peak appears.

The endothermic amount (ΔH _{endo: row} ) of the polylactic acid resin is a value obtained by heat flux differential scanning calorimetry described in JIS K7122-1987. However, 1 to 4 mg of a polylactic acid resin is used as a test piece, and the condition adjustment of the test piece and the measurement of the DSC curve are performed according to the following procedure. The test piece was put in a container of a DSC apparatus, heated and melted to 200 ° C., kept at that temperature for 10 minutes, then cooled to 125 ° C. at a cooling rate of 2 ° C./minute, and kept at that temperature for 120 minutes. A DSC curve is obtained when heat-melting to a temperature approximately 30 ° C. higher than the end of the melting peak at a heating rate of 2 ° C./min after the heat treatment cooling to 40 ° C. at a cooling rate of 2 ° C./min.
As shown in FIG. 2, the endothermic amount of the polylactic acid resin (ΔH _{endo: row} ) is defined as a point a where the endothermic peak departs from the low temperature side baseline of the endothermic peak of the DSC curve, and the endothermic peak is A point that returns to the high temperature side base line is a point b, and a value obtained from the straight line connecting the points a and b and the area of the portion surrounded by the DSC curve. Also, the device should be adjusted so that the baseline is as straight as possible, and if the baseline is inevitably curved, as shown in FIG. Point a, and point b where the endothermic peak returns to the curved high-temperature baseline.
In the measurement of the endothermic amount (ΔH _{endo: row} ), the condition of the test piece and the measurement conditions of the DSC curve were as _follows: 120 ° C. holding for 120 minutes, 2 ° C./min cooling rate and 2 ° C./min The reason for adopting the heating rate is that the crystallization of the polylactic acid-based resin test piece is advanced as much as possible, and the endothermic amount (ΔH _{endo: row} ) of the fully crystallized state or a state close thereto is adjusted. This is because it is intended to be obtained by measurement.

  In the present invention, the polylactic acid resin as a main component of the base resin means 100% by weight of the polylactic acid resin, or 50% by weight or more and less than 100% by weight of the polylactic acid resin and 0% by weight. This means that a mixture with a thermoplastic resin other than the above-mentioned polylactic acid-based resin in excess of 50% by weight is used as the base resin. That is, in the present invention, a thermoplastic resin other than the polylactic acid resin can be mixed in the base resin at a ratio of 50% by weight or less within a range in which the object and effect of the present invention can be achieved. When a thermoplastic resin other than the polylactic acid resin is mixed in the base resin, the polylactic acid resin is contained in the base resin in a proportion of 70% by weight or more, and further 90% by weight or more. Is preferably included. Examples of thermoplastic resins other than polylactic acid resins include polyethylene resins, polypropylene resins, polystyrene resins, polyester resins, and the like. Among them, biodegradable fats containing at least 35 mol% of aliphatic ester component units. A group polyester resin is preferred. In this case, the aliphatic polyester resins include hydroxy acid polycondensates other than the above polylactic acid resins, ring-opening polymers of lactones such as polycaprolactone, polybutylene succinate, polybutylene adipate, polybutylene succinate adipate , Polycondensates of aliphatic polyhydric alcohols such as poly (butylene adipate / terephthalate) and aliphatic polycarboxylic acids, and the like are included.

  Specific examples of the method for producing the polylactic acid-based resin include, for example, a method of direct dehydration polycondensation using lactic acid or a mixture of lactic acid and aliphatic hydroxycarboxylic acid as a raw material (see, for example, US Pat. No. 5,310,865). Production method shown), ring-opening polymerization method for polymerizing cyclic dimer (lactide) of lactic acid (eg, production method disclosed in US Pat. No. 2,758,987), lactic acid and aliphatic hydroxycarboxylic acid A ring-opening polymerization method in which an acid cyclic dimer, for example, lactide or glycolide and ε-caprolactone are polymerized in the presence of a catalyst (for example, a production method disclosed in US Pat. No. 4,057,537), lactic acid , A method of directly dehydrating polycondensation of a mixture of an aliphatic dihydric alcohol and an aliphatic dibasic acid (for example, a production method disclosed in US Pat. No. 5,428,126), lactic acid polymerization , Aliphatic dihydric alcohol, aliphatic dibasic acid and polymer in the presence of an organic solvent (for example, the production method disclosed in European Patent Publication No. 071880 A2), lactic acid in the presence of a catalyst, In producing a polyester polymer by performing a dehydration polycondensation reaction, a method of performing solid phase polymerization in at least a part of the steps can be exemplified, but the production method is not particularly limited. Further, a small amount of an aliphatic polyhydric alcohol such as glycerin, an aliphatic polybasic acid such as butanetetracarboxylic acid, or a polyhydric alcohol such as polysaccharide may be copolymerized.

  In the foam sheet of the present invention, the base resin mainly composed of the above-mentioned polylactic acid resin and the air conditioner are supplied to the extruder, heated and melt-kneaded, and then the physical foaming agent is pressed into the extruder and kneaded. It can be obtained by adjusting the resin temperature to an appropriate foaming temperature, extruding from a die and foaming, and rapidly cooling the surface of the obtained foam by blowing air or mist immediately after extrusion. Examples of the die used for extrusion foaming include an annular die and a T die, and the annular die is preferable in order to obtain the foam sheet having the apparent density and the uniform thickness. When extrusion foaming is performed using an annular die, a cylindrical foam is obtained. If the foam is taken along the side of the cylindrical cooling device and cut in the extrusion direction, a wide foam sheet can be obtained. .

The amorphous polylactic acid resin foam sheet corresponding to one of the comparative examples of the foam sheet in the present invention uses an amorphous polylactic acid resin as a base resin and has a low apparent density by a well-known extrusion foaming method. A sheet can be obtained. However, the amorphous polylactic acid foam sheet is excellent in thermoformability, but when the glass transition point is exceeded, the rigidity suddenly decreases, and the resulting molded product cannot maintain a certain shape, There is no practical heat resistance. Therefore, the amorphous polylactic acid resin foamed sheet has good thermoformability but insufficient heat resistance. On the other hand, the foamed sheet in the present invention has a heat absorption amount (ΔH _{endo: row} ) determined by heat flux differential scanning calorimetry as described above as a polylactic acid resin constituting the main component of the base resin of the foamed sheet. By adjusting the crystal state by using 10 J / g or more, it is possible to solve the problems of thermoformability and heat resistance of the molded polylactic acid-based resin foam.

Unlike the case where amorphous polylactic acid is used as the base resin, when the polylactic acid-based resin having the endothermic amount (ΔH _{endo: row} ) of 10 J / g or more is the main component of the base resin, It is difficult to adjust the viscoelasticity of the foamable molten resin when obtaining a foam sheet having an apparent density of 63 to 630 kg / m ³ and a thickness of 0.5 to 7 mm, and the melt tension of the base resin at 190 ° C. is 5 cN or more. Is preferably used, more preferably 8 cN or more, and even more preferably 10 cN or more. If the melt tension is less than 5 cN, sufficient melt tension cannot be obtained at the time of foaming, and there is a possibility that a good foam sheet having a small apparent density and a sufficient thickness excellent in mechanical properties may not be obtained. The polylactic acid resin foam sheet obtained from the base resin having a melt tension of 5 cN or more becomes a polylactic acid resin foam sheet having a melt tension at 190 ° C. of 5 cN or more.

The melt tension can be measured with a melt tension tester type II manufactured by Toyo Seiki Seisakusho. Specifically, a melt tension tester having an orifice with an inner diameter of 2.095 mm and a length of 8 mm is used, and the orifice is heated to 190 ° C. in advance, and a base resin or a polylactic acid resin foam sheet is contained therein. About 4 g of a measurement sample consisting of crushed pieces is placed and left for 5 minutes, and then the molten resin at 190 ° C. is extruded from an orifice into a string with a piston speed of 10 mm / min. This string is used for detecting a tension of 45 mm in diameter. A 50 mm diameter scraping roller while gradually increasing the scraping speed at a rate of 5 rpm / second (stretching acceleration of the string-like object: 1.3 × 10 ⁻² m / sec ² ) after being put on the pulley. Take it off with. When the molten resin is extruded from the orifice into a string shape, air bubbles are prevented from being mixed in the string object as much as possible.

In order to obtain the melt tension, first, the scooping speed is increased until the string-like material hung on the tension detecting pulley is cut, and the scooping speed when the cord-like material is cut: R (rpm) is obtained. Next, the string-like material is scraped at a constant tearing speed of R × 0.7 (rpm), and the melt tension of the string-like material detected by the detector connected to the tension detection pulley is measured over time. When the vertical axis indicates the melt tension and the horizontal axis indicates the time, a graph having an amplitude as shown in FIG. 4 is obtained.
As the melt tension in this specification, the median value (X) of the amplitude of the stable portion in FIG. 4 is adopted. However, if the string-like material is not cut even when the reeling speed reaches 500 rpm, the melt tension of the string-like material is obtained from the graph obtained by winding the string-like material with the reeling speed set to 500 rpm. It should be noted that a unique amplitude value may be detected in rare cases during the measurement of the melt tension over time, but such a unique amplitude value is ignored.

   Further, the melt flow rate (MFR) of the base resin is 0.1 to 10 g / 10 min (provided that the test condition of the method A of JIS K7210-1976 is MFR measured by a temperature of 190 ° C. and a load of 21.2 N). It is preferably 0.1 to 5 g / 10 min, more preferably 0.3 to 3 g / 10 min. If the MFR is too small, the viscosity becomes too high, and bubbles cannot grow, and there is a possibility that a practical foam cannot be obtained. If the MFR is too large, the viscosity will be too low, and dripping will occur immediately after extrusion from the die, which may deteriorate the molding processability.

  As described above, the base resin constituting the foamed sheet in the present invention preferably has a melt tension at 190 ° C. of 5 cN or more and an MFR of 0.1 to 10 g / 10 minutes. As a method for obtaining such a polylactic acid resin, for example, an organic peroxide is added to a polylactic acid resin having a melt tension of less than 5 cN (not including 0) and an MFR of 2 to 12 g / 10 min. A method of making a modified polylactic acid resin by fine cross-linking (gel fraction is substantially 0%), a polylactic acid resin and an isocyanate, an epoxy compound, a metal complex, a polyvalent carboxylic acid, or a mixture thereof Examples thereof include a method of increasing the molecular weight by reacting with such a high molecular weight agent to obtain a modified polylactic acid resin.

The organic peroxide used in the method for finely crosslinking the polylactic acid-based resin described above has a half-life temperature of 1 minute (when the organic oxide is decomposed at a constant temperature, the amount of active oxygen is half of the original in 1 minute. It is desirable that the constant temperature is higher than the temperature lower by 10 ° C. than the melting point of the polylactic acid resin to be modified. If the one-minute half-life temperature is 10 ° C. or more lower than the melting point of the polylactic acid-based resin, the organic peroxide and the polylactic acid-based resin may not be uniformly mixed during the heating and kneading. Since the oxide is decomposed and reacted, the modification effect may be non-uniform. Further, in order to obtain a sufficient modification effect, it is necessary to add a larger amount than an organic peroxide having a one-minute half-life temperature of 1 minute higher than a temperature 10 ° C. lower than the melting point of the resin. As a result, in the subsequent extrusion foaming process, the crosslinking reaction proceeds more than necessary, and a gel content may be generated in the molten resin, which may make it difficult to obtain a satisfactory foam.
On the other hand, when the one-minute half-life temperature of the organic peroxide is significantly higher than the melting point of the resin, the reforming reaction is carried out at a high temperature. May decrease, and further, a foam may not be obtained. Therefore, it is desirable that the 1 minute half-life temperature of the organic peroxide does not exceed a temperature 20 ° C. higher than the melting point of the polylactic acid resin.

Examples of organic peroxides preferably used include various conventionally known ones such as isobutyl peroxide [85 ° C.], cumyl peroxyneodecanoate [94 ° C.], α, α′-bis (neodeca Noylperoxy) diisopropylbenzene [82 ° C.], di-n-propyl peroxydicarbonate [94 ° C.], diisopropyl peroxydicarbonate [88 ° C.], 1-cyclohexyl-1-methylethylperoxyneodecanoate [ 94 ° C], 1,1,3,3-tetramethylbutylperoxyneodecanoate [92 ° C], bis (4-t-butylcyclohexyl) peroxydicarbonate [92 ° C], di-2-ethoxyethyl Peroxydicarbonate [92 ° C], di (2-ethylhexylperoxy) dicarbonate [91 ° C] t-Hexylperoxyneodecanoate [101 ° C], dimethoxybutylperoxydicarbonate [102 ° C], di (3-methyl-3-methoxybutylperoxy) dicarbonate [103 ° C], t-butylperoxy Neodecanoate [104 ° C], 2,4-dichlorobenzoyl peroxide [119 ° C], t-hexylperoxypivalate [109 ° C], t-butylperoxypivalate [110 ° C], 3, 5, 5-trimethylhexanoyl peroxide [113 ° C], octanoyl peroxide [117 ° C], lauroyl peroxide [116 ° C], stearoyl peroxide [117 ° C], 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate [124 ° C], succinic peroxide [132 ° C], 2 , 5-dimethyl-2,5-di (2-ethylhexanoylperoxy) hexane [119 ° C.], 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate [138 ° C.], t-hexyl Peroxy-2-ethylhexanoate [133 ° C.], t-butyl peroxy-2-ethylhexanoate [134 ° C.], m-toluoyl benzoyl peroxide [131 ° C.], benzoyl peroxide [130 ° C.] , T-butylperoxyisobutyrate [136 ° C.], 1,1-bis (t-butylperoxy) -2-methylcyclohexane [142 ° C.], 1,1-bis (t-hexylperoxy) -3 , 3,5-trimethylcyclohexane [147 ° C.], 1,1-bis (t-hexylperoxy) cyclohexane [149 ° C.], 1,1- (T-butylperoxy) -3,3,5-trimethylcyclohexane [149 ° C.], 1,1-bis (t-butylperoxy) cyclohexane [154 ° C.], 2,2-bis (4,4- Dibutylperoxycyclohexyl) propane [154 ° C.], 1,1-bis (t-butylperoxy) cyclododecane [153 ° C.], t-hexylperoxyisopropyl monocarbonate [155 ° C.], t-butylperoxymaleic acid [168 ° C], t-butylperoxy-3,5,5-trimethylhexanoate [166 ° C], t-butylperoxylaurate [159 ° C], 2,5-dimethyl-2,5-di ( m-toluoyl peroxy) hexane [156 ° C.], t-butyl peroxyisopropyl monocarbonate [159 ° C.], t-butyl pero Si-2-ethylhexyl monocarbonate [161 ° C.], t-hexyl peroxybenzoate [160 ° C.], 2,5-dimethyl-2,5-di (benzoylperoxy) hexane [158 ° C.], dicumyl peroxide [ 175 ° C.] and the like. Of the above organic peroxides, dicumyl peroxide is particularly preferable.
In addition, the temperature in [] immediately behind each said organic peroxide is a 1 minute half-life temperature of each organic peroxide. The organic peroxide is used alone or in combination of two or more, and is usually added in an amount of 0.3 to 0.7 parts by weight, preferably 0.4 to 0.6 parts by weight per 100 parts by weight of the base resin. Used.

  In the present specification, the one-minute half-life temperature of the organic peroxide is determined using an organic peroxide having a concentration of 0.1 mol / L using a solution that is relatively inert to radicals (for example, benzene and mineral spirits). The oxide solution is prepared, sealed in a glass tube subjected to nitrogen substitution, immersed in a thermostat set at a predetermined temperature, and pyrolyzed for measurement.

Further, as described above, the modified polylactic acid resin has a gel fraction of substantially 0%. In addition, this gel fraction is calculated | required as follows.
A sample of weight W1 obtained by accurately weighing about 1 g of a polylactic acid-based resin and 100 ml of chloroform are placed in a 150 ml flask, and heated and refluxed in boiling chloroform at about 61 ° C. for 10 hours. Filtration is performed using a suction filtration apparatus having a mesh wire mesh. The obtained filtered product on the wire mesh is dried in an oven at 20 ° C. under a condition of 30 to 40 Torr for 24 hours. The dry matter weight W2 obtained at this time is measured. The weight percentage [(W2 / W1) × 100] (%) of the weight W2 with respect to the sample weight W1 is defined as a gel fraction.
And the gel fraction substantially 0% means that the gel fraction of the polymer obtained by the above formula is 2% or less, preferably 0.5% or less.

  As a foaming agent used in the production of the foamed sheet in the present invention, an aliphatic hydrocarbon such as a lower alkane such as propane, normal butane, isobutane, normal pentane, isopentane and hexane is used to obtain a foam sheet having a low apparent density. And physical foaming agents such as halogenated aliphatic hydrocarbons such as methyl chloride and ethyl chloride, and inorganic gases such as carbon dioxide. Among these, normal butane, isobutane, and carbon dioxide are preferable. In addition, as a foaming agent for obtaining the foamed sheet in the present invention, in addition to the above physical foaming agent, a chemical foaming agent, or a physical foaming agent and a chemical foaming agent can be used in combination, but the apparent density is small. In order to obtain a foamed sheet, it is preferable to use a physical foaming agent as a foaming agent or a combination of a physical foaming agent and a chemical foaming agent.

  For example, inorganic foam regulators such as talc and silica and organic foam regulators such as calcium stearate are added to the foam sheet in the present invention. Various additives such as a colorant and an antioxidant can be added to the base resin depending on the purpose.

The apparent density of the foamed sheet which is the reference invention of the present invention is 63 to 630 kg / m ³ , preferably 84 to 504 kg / m ³ . If the apparent density is too small, the strength of the resulting molded product may be reduced, and the thermoformability may be deteriorated, resulting in failure to obtain a molded product having a shape according to the mold. On the other hand, when the apparent density is too large, characteristics as a foam such as lightness, heat insulation, and buffering property may be lost.

  In the present specification, the apparent density of the foam sheet is a value obtained by cutting a sample having a length of 10 cm, a width of 10 cm, and a thickness of the entire thickness of the foam sheet from the foam sheet, and dividing the weight of the sample by the volume of the sample.

  The thickness of the foamed sheet of the reference invention is 0.5 to 7 mm, preferably 0.5 to 5 mm, more preferably 0.7 to 3 mm. If the thickness is too thin, the strength of the molded product obtained by thermoforming may be too low, and if the thickness is too thick, the thermoformability may be deteriorated and uneven thickness may occur in the molded product.

  In the present specification, the thickness of the foam sheet is measured at intervals of 10 mm along the entire width of the foam sheet, and is the arithmetic average of the obtained measured values.

In the foam sheet of the reference invention, the bubble shape satisfies the following formulas (1) to (3). In addition, this bubble shape is measured about the center layer of a foam sheet so that it may mention later.
0.05 <Z <0.8 (1)
0.2 <Z / X <0.8 (2)
0.2 <Z / Y <0.65 (3)
However, in the formulas (1) to (3), X, Y, and Z are average cell diameters in the extrusion direction (MD direction), width direction (TD direction), and thickness direction of the foamed sheet, respectively, and the unit is mm. It is.

When at least one of the above Z / X and Z / Y is 0.2 or less, the bubble shape is flat, and the rigidity of the sheet becomes insufficient. Moreover, there exists a possibility that the thermoforming property of a foamed sheet, especially deep drawability may worsen, and the mechanical strength of the molded object obtained may fall. On the other hand, when Z / X is 0.8 or more and / or Z / Y is 0.65 or more, the drawdown at the time of heat forming tends to be large, and the thermoformability may be deteriorated. On the other hand, when Z is 0.05 mm or less, thermoformability and mechanical properties are deteriorated. When Z is 0.8 mm or more, the appearance may be poor, and the flexibility may be insufficient, so that buckling is likely to occur when force is applied from the outside. Therefore, the foam sheet having a cell shape that satisfies the above range is excellent in mechanical strength and thermoformability, and the mechanical strength of the polylactic acid resin foam molded article obtained by thermoforming the foam sheet. It will also be excellent.
Z / X is 0.3 to 0.7, Z / Y is 0.25 to 0.60, and Z is 0.1 to 0.5 mm in terms of mechanical strength and thermoformability. preferable.

  In addition, the bubble shape represented by said (1)-(3) is measured about the center layer of a foam sheet. Here, the central layer means a layer that includes the center in the thickness direction and does not include the range from the both surfaces to the total thickness of the foamed sheet of 10%. That is, as shown in FIG. 1, it is the center part of the thickness direction of the foam sheet which occupies 80% of the sheet total thickness.

In this specification, the average cell diameters X, Y, and Z are measured as follows. The average cell diameter (X: mm) in the extrusion direction (MD direction) of the central layer of the foam sheet, the average cell diameter (Y: mm) in the width direction (TD direction), and the average cell diameter (Z: mm) in the thickness direction are The vertical cross-section in the extrusion direction of the foam sheet and the vertical cross-section in the width direction are magnified with a microscope and measured based on the obtained micrograph, and the average cell diameter X and average cell diameter obtained by the measurement are measured. Z / X and Z / Y are determined from Y and average bubble diameter Z.
More specifically, a microscopic magnified photograph of the thickness direction cross section in the direction along the MD direction of the foam sheet is obtained, and 0.1 × (foam sheet total thickness: from the foam sheet both surfaces S based on the obtained photograph) A line is drawn at a position corresponding to the position of T) to divide into bubbles of the surface layer and the center layer, and the bubble diameters in the MD direction and the thickness direction are shown in FIG. 1A for all the bubbles present in the center layer on the photograph. The value of x and z of each bubble 2 is obtained for each bubble by measuring with a vernier caliper, and each of x1, x2, x3... Xn and z1, z2, z3. The arithmetic average values X and Z are obtained, and the value of Z / X is obtained from the values of X and Z. As a matter of course, the values of X and Z are converted based on the enlargement ratios of the above photographs to obtain the true average bubble diameter.

  The value of Y is 0.1 × (foamed sheet total thickness: from the foam both surfaces S based on the photograph obtained by obtaining a microscopic enlarged photograph of the thickness direction cross section in the direction along the TD direction of the foamed sheet. A line is drawn at a position corresponding to the position of T), and it is divided into bubbles of the surface layer and the center layer, and the bubble diameter in the TD direction for all the bubbles present in the center layer on the photograph is measured with a caliper as shown in FIG. The y value of each bubble 2 is measured and obtained for each bubble, and the arithmetic average value Y is obtained from the values of y1, y2, y3... Yn thus obtained. The Z / Y value is obtained from the obtained Z value. As a matter of course, the value of Y is converted based on the magnification of the above photograph to obtain the true average bubble diameter. Further, in the measurement of Z, X, and Y, bubbles 2a on the line of 0.1 × (foamed sheet total thickness: T) from both surface layer portions S are excluded from measurement.

The bubble diameter ratio and the bubble diameter can be adjusted as follows.
As a method for adjusting the bubble diameters X, Y, Z, 0.1 to 3 parts by weight of an inorganic or organic bubble regulator such as talc or sodium bicarbonate is added to 100 parts by weight of the base resin, or extrusion. It can be adjusted by adjusting the pressure of the die during foaming. That is, within a range where a foam sheet having a good appearance, a desired apparent density and thickness can be obtained, the bubble diameter can be reduced by increasing the amount of the bubble regulator, and the bubble diameter can be increased by increasing the pressure of the die. Can be reduced.
The bubble diameter ratio Z / X can be adjusted by adjusting the take-up speed of the foam sheet after extrusion foaming, and the bubble diameter ratio Z / Y can be adjusted by adjusting the expansion ratio of the foam sheet after extrusion foaming. Can be adjusted.

  The closed cell ratio of the foamed sheet in the present invention is preferably 50 to 100%, more preferably 70 to 100%, still more preferably 80 to 100%. When the closed cell ratio is within the above range, the mechanical strength and the secondary foamability during thermoforming are particularly excellent, and the polylactic acid resin foam molding obtained by thermoforming the foamed sheet The appearance of the body such as mechanical strength and mold reproducibility is also excellent.

In this specification, the closed cell ratio (%) of the foam sheet is based on the procedure C described in ASTM D2856-70 (1976 recertification), and the air comparison type hydrometer 930 type manufactured by Toshiba Beckman Co., Ltd. is used. It is a value calculated from the following equation (4) from the true volume Vx of the test piece measured using.
Closed cell ratio (%) = (Vx−W / ρ) × 100 / (Va−W / ρ) (4)
However, in the above equation (4), Vx is the true volume (cm ³ ) of the test piece measured by the above-described method, and the volume of the resin constituting the test piece and all the bubbles in the closed cell portion in the test piece. It corresponds to the sum of the volume.
In addition, Va, W, and ρ in the above equation (4) are as follows.
Va: Apparent volume of the test piece calculated from the outer dimensions of the test piece used for measurement (cm ³ )
W: Total weight of the test piece used for measurement (g)
ρ: Density of base resin constituting the test piece (g / cm ³ )
In addition, since the test piece must be stored in a non-compressed state in the sample cup attached to the air comparison hydrometer, the test piece is cut out from the foam sheet so that the length and width are 2.5 cm each (the thickness is the same as that of the foam sheet). The thickness is kept as it is), and a plurality of sheets are overlapped and used so that the apparent volume is closest to 15 cm ³ .

The foamed sheet of the reference invention solves the problems of thermoformability and heat resistance improvement of the polylactic acid-based resin foamed molded article at the time of molding or after molding by adjusting the crystal state of the foamed sheet. That is, the difference between the endothermic amount (ΔH _{endo: 2 ° C./min} ) and the calorific value (ΔH _{exo: 2 ° C./min} ) determined by heat flux differential scanning calorimetry at a heating rate of 2 ° C./min of the foam sheet ( ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) is less than 20 J / g, and the endothermic amount (ΔH _{endo: 2 ° C./min} ) is 10 J / g or more as described above. The foam surface obtained by the extrusion foaming method is adjusted by quenching immediately after extrusion, for example, by blowing air or mist.

Here, the calorific value (ΔH _{exo: 2 ° C./min} ) refers to the amount of heat released by the crystallization accelerated by the heat flux differential scanning calorimetry at a heating rate of 2 ° C./min. A larger value of the amount (ΔH _{exo: 2 ° C./min} ) means that the crystallization of the foam sheet has not progressed. The endothermic amount (ΔH _{endo: 2 ° C./min} ) means the heat of fusion when the crystal of the test piece melts by heat flux differential scanning calorimetry at a heating rate of 2 ° C./min. The endothermic amount (ΔH _{endo: A} foam sheet having a larger value of ( _{2 ° C./min} ) means that rigidity and heat resistance are improved as crystallization progresses. The difference between the endothermic amount and the exothermic amount (ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) is determined by setting a test piece used for heat flux differential scanning calorimetry in the measuring device. This corresponds to the amount of heat of fusion required for melting the amount of crystals that had been present at the time, and the smaller the value, the less the crystallization of the foam sheet.
Therefore, (ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) is less than 20 J / g, which means that the foamed sheet is not greatly crystallized and has excellent thermoformability. Means that (ΔH _{endo: 2 ° C./min} ) is 10 J / g or more, the foam sheet becomes excellent in rigidity and heat resistance when crystallization proceeds by heat treatment in the subsequent process. Means.

In the reference invention, the value of (ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) is less than 20 J / g (including 0), preferably 1 to 20 J / g, more preferably 2 ~ 18 J / g. When (ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) is 20 J / g or more, the thermoformability of the foamed sheet, particularly the expansion ratio (the area of the molding part (A), The ratio of (B) to (A): (B) / (A)) when the area after molding of the portion corresponding to the area (A) is (B) is 1.5 or more, particularly 1.8. The above deep-drawing thermoformability deteriorates.

Further, in the reference invention, the endothermic amount (ΔH _{endo: 2 ° C./min} ) of the foamed sheet is 10 J / g or more, preferably 20 J / g or more, more preferably 25 J / g or more. When the endothermic amount of the foam sheet (ΔH _{endo: 2 ° C./min} ) is less than 10 J / g, the rigidity and heat resistance desired in the reference invention can be obtained even if the foam sheet obtained is crystallized by a heat treatment in a subsequent process. I can't. The upper limit of the endothermic amount (ΔH _{endo: 2 ° C./min} ) of the reference invention foamed sheet is not particularly limited, but is generally 60 J / g. In the reference invention, the value of ΔH _{exo: 2 ° C./min} of the foamed sheet may be 0.

The calorific value (ΔH _{exo: 2 ° C./min} ) and the endothermic amount (ΔH _{endo: 2 ° C./min} ) of the foam sheet are values determined by heat flux differential scanning calorimetry described in JIS K7122-1987. However, 1-4 mg foam pieces cut out from the foamed sheet are used as test pieces, and the condition adjustment and DSC curve measurement of the test pieces are performed according to the following procedure. A test piece is put in a container of a DSC apparatus, and a DSC curve is obtained when the sample is heated and melted to a temperature about 30 ° C. higher than the end of the melting peak at a heating rate of 2 ° C./min without heat treatment. The exothermic amount of the foam sheet (ΔH _{exo: 2 ° C./min} ) is defined as a point c where the exothermic peak is separated from the low temperature side baseline of the exothermic peak of the DSC curve, and the exothermic peak returns to the high temperature side baseline. Let a point be a point d, and a value obtained from the area of a portion surrounded by a straight line connecting the points c and d and the DSC curve. The endothermic amount of the foam sheet (ΔH _{endo: 2 ° C./min} ) is defined as a point e where the endothermic peak departs from the low-temperature base line of the endothermic peak of the DSC curve, and the endothermic peak reaches the high-temperature base line. The return point is defined as a point f, and a value obtained from the area of the portion surrounded by the straight line connecting the point e and the point f and the DSC curve. The apparatus is adjusted so that the baseline in the DSC curve is as straight as possible. In addition, when the baseline is inevitably curved, a point where the exothermic peak is separated from the curved low temperature side baseline is a point c, and a point where the exothermic peak returns to the curved high temperature side baseline is a point d, or Point e is the point at which the endothermic peak leaves the curved low-temperature side baseline, and point f is the point at which the endothermic peak returns to the curved high-temperature side baseline.

For example, in the case shown in FIG. 5, the heat generation amount of the foamed sheet (ΔH _{exo: 2 ° C./min} ) is obtained from the area surrounded by the straight line connecting the points c and d determined as described above and the DSC curve. The endothermic amount of the foamed sheet (ΔH _{endo: 2 ° C./min} ) is determined from the area surrounded by the straight line connecting the points e and f determined as described above and the DSC curve. In the case shown in FIG. 6, since it is difficult to determine the point d and the point e by the above method, the intersection of the straight line connecting the point c and the point f determined as described above and the DSC curve. _Is determined as a point d (point e) to determine the calorific value (ΔH _{exo: 2 ° C./min} ) and the endothermic amount (ΔH _{endo: 2 ° C./min} ) of the foam sheet. Further, as shown in FIG. 7, when a small exothermic peak occurs on the low temperature side of the endothermic peak, the heat generation amount (ΔH _{exo: 2 ° C./min} ) of the foam sheet is the first exothermic in FIG. It is obtained from the sum of the area A of the peak and the area B of the second exothermic peak. That is, the area A is defined as a point c where the exothermic peak moves away from the low temperature side baseline of the first exothermic peak, and a point d where the first exothermic peak returns to the high temperature side baseline. It is assumed that the area A is a portion surrounded by a straight line connecting the point d and the DSC curve. The area B is defined as a point g where the second exothermic peak is separated from the low temperature side baseline of the second exothermic peak, a point f where the endothermic peak returns to the high temperature side baseline, and a point g. An intersection of the straight line connecting the point f and the DSC curve is defined as a point e, and an area B of a portion surrounded by the straight line connecting the point g and the point e and the DSC curve. On the other hand, in FIG. 7, the endothermic amount (ΔH _{endo: 2 ° C./min} ) of the foam sheet is a value obtained from the area of the portion surrounded by the straight line connecting point e and point f and the DSC curve.

In addition, in the measurement of the calorific value (ΔH _{exo: 2 ° C./min} ) and the endothermic amount (ΔH _{endo: 2 ° C./min} ), the reason for adopting the heating rate of 2 ° C./min as the measurement condition of the DSC curve is as follows: The exothermic peak and the endothermic peak are separated as much as possible, and an accurate endothermic amount (ΔH _{endo: 2 ° C./min} ) and (ΔH _{endo: 2 °} C./min-ΔH _{exo: 2 ° C./min} ) are used for heat flux differential scanning calorimetry. Is based on the inventors' knowledge that a heating rate of 2 ° C./min is suitable.

  Moreover, it is preferable that the heat-sag value measured by JISK7195-1993 is 10 mm or more as for the foamed sheet of reference invention. When the heat zag value is less than 10 mm, the crystallization of the foamed sheet may have progressed too much, and the thermoformability may be insufficient. In addition, the measurement of the heat zag value is a test of a width of 10 mm, a length of 125 mm, and a thickness of 3 mm so as to leave at least one surface layer from the foamed sheet (if the foamed sheet has a thickness of 3 mm or less, the thickness is as it is). A piece is cut out, the test piece is fixed to the test piece holder so that the surface layer of at least one side of the test piece becomes the upper surface, and measurement is performed at a test temperature of 75 ° C.

In the foam sheet of the reference invention, the calorific value (ΔH _{exo: 10 ° C./min} ) determined by heat flux differential scanning calorimetry at a cooling rate of 10 ° C./min of the foam sheet is preferably 20 to 45 J / g. More preferably, it is 25-40 J / g, More preferably, it is 30-38 J / g. When the endothermic amount (ΔH _{exo: 10 ° C./min} ) is too small, even if an attempt is made to crystallize the resulting foamed sheet by a heat treatment in a subsequent step, the heat treatment takes too much time, so polylactic acid having excellent heat resistance Even if a resin-based foamed molded article can be obtained, the foamed sheet may be inferior in productivity. On the other hand, if the endothermic amount (ΔH _{exo: 10 ° C./min} ) is too large, the crystallization speed is too high and crystallization proceeds too much at the time of foam sheet production. There is a possibility of becoming an inferior foam sheet.

In the reference invention, when the calorific value (ΔH _{exo: 10 ° C./min} ) is 20 to 45 J / g, the crystallization rate is neither too fast nor too slow, and foaming is in a state of low crystallinity. It means having a crystallization rate suitable for both the production of a sheet and the production of a polylactic acid-based resin foam molded body having high crystallinity in a heat treatment in a subsequent process. In heat flux differential scanning calorimetry under conditions where the cooling rate is slow, such as 2 ° C./min, crystallization is accelerated by the measurement even for a foam sheet made of a base resin with a slow crystallization rate. A clear exothermic peak is confirmed. On the other hand, in the heat flux differential scanning calorimetry under the fast cooling rate of 10 ° C./min, the foam sheet made of the base resin having a slow crystallization rate is not accelerated by the measurement, Little or no exothermic peak is confirmed, or crystallization is hardly promoted and no clear exothermic peak is confirmed. Thus, in the heat flux differential scanning calorimetry of the foam sheet, the crystallization proceeds at a cooling rate of 2 ° C./min, but the crystallization proceeds little or not at a cooling rate of 10 ° C./min. Although thermoforming is easy, since the time required for the heat treatment in the subsequent process becomes long, the productivity of the polylactic acid-based resin foam molded article may be insufficient. Therefore, a foamed sheet whose crystallization progresses even in heat flux differential scanning calorimetry under the condition of a cooling rate of 10 ° C./min is a polylactic acid resin with excellent heat resistance because crystallization progresses early in the heat treatment in the subsequent process. It is excellent in the productivity of the foam molded article.

In addition, the calorific value (ΔH _{exo: 10 ° C./min} ) of the foam sheet is a value determined by heat flux differential scanning calorimetry described in JIS K7122-1987. However, 1-4 mg foam pieces cut out from the foamed sheet are used as test pieces, and the condition adjustment and DSC curve measurement of the test pieces are performed according to the following procedure. A test piece is put in a container of a DSC apparatus, heated and melted to 200 ° C., kept at that temperature for 10 minutes, and then a DSC curve is obtained when cooling to 10 ° C. at a cooling rate of 10 ° C./min. The exothermic amount of the foam sheet (ΔH _{exo: 10 ° C./min} ) is defined as a point h where the exothermic peak departs from the high-temperature base line of the DSC curve, and the exothermic peak returns to the low-temperature base line. A point is a point i, and a value obtained from a straight line connecting the point h and the point i and an area of a portion surrounded by the DSC curve. The device should be adjusted so that the baseline is as straight as possible. If the baseline is inevitably curved, the point where the exothermic peak departs from the curved high-temperature side is point h, the curved low-temperature side. The point at which the exothermic peak returns to the baseline is point i.

  In addition, the crystallization speed of the foamed sheet of the reference invention is preferably an appropriate speed as described above, and specifically, the half crystallization time of the foamed sheet at 110 ° C. is 2 to 200 seconds. It is preferably 10 to 150 seconds, more preferably 20 to 120 seconds. If the semi-crystallization time is too long, even if an attempt is made to crystallize the resulting foamed sheet by a heat treatment in a subsequent step, the heat treatment takes too much time, and thus a polylactic acid resin foam molded article having excellent heat resistance is obtained. Even if it is possible, there is a possibility that the foam sheet is inferior in productivity. On the other hand, if the half crystallization time is too short, the crystallization speed is too high, and crystallization proceeds too much during the production of the foamed sheet, which may result in a foam sheet having poor thermoformability, particularly deep drawability.

  The half crystallization time at 110 ° C. in this specification is a resin sample heated to 200 ° C. in advance using a crystallization rate measuring instrument (MK-801 type manufactured by Metron Co., Ltd. (former Kotaki Shoji Co., Ltd.)). , And put into a crystal bath set at 110 ° C. for measurement. A resin sample for measurement is prepared by defoaming a foam sheet into a film. In this case, the thickness of the film is 0.1 ± 0.02 mm, and the dimensions of the film are 15 × 15 mm squares. A sample sandwiched between the microscope cover glass is used as a measurement sample. Further, the luminance value of the light source lamp is set to 3V as an instruction value.

  The Metron Co., Ltd. crystallization rate measuring instrument is an apparatus for determining the degree of crystallization from the relationship between crystallization of a sample and birefringence of light. A value A in which the amount of light due to birefringence is constant is read from the vertical axis on the graph from the curve on the graph shown in FIG. 8 and corresponds to a value B on the vertical axis on the graph obtained by multiplying the value by 0.5. This is a value obtained as the value C of the curve on the graph.

A preferable foamed sheet satisfying the requirements of the heat generation amount of the foamed sheet (ΔH _{exo: 10 ° C./min} ) and / or the half crystallization time at 110 ° C. of the foamed sheet is a polylactic acid-based resin which is a main component of the base resin. In addition, as a crystallization speed improver, inorganic substances such as talc, silica, zeolite, kaolin, bentonite, clay, magnesium carbonate, aluminum oxide, and calcium sulfate are 0.2 parts by weight or more and 100% by weight with respect to 100 parts by weight of the polylactic acid resin. It can be obtained by using less than 1 part, more preferably 1 to 3.5 parts by weight. Of the inorganic substances, talc is particularly preferable. When the amount of the inorganic substance added to the polylactic acid-based resin exceeds the above range, the closed cell ratio of the obtained foamed sheet is reduced, and the mechanical strength and thermoformability of the thermoformed foamed sheet are insufficient. It will be a thing. On the other hand, when the addition amount is less than the above range, the effect of improving the crystallization speed is insufficient.

  In addition, the foamed sheet of the reference invention can be provided with a thermoplastic resin layer on at least one side of the foamed sheet by a method such as adhesion with a film adhesive, thermal adhesion of the film, co-extrusion, or extrusion lamination of a molten resin. Examples of the resin constituting the thermoplastic resin layer include a polyethylene resin, a polypropylene resin, a polyester resin, a polystyrene resin, a polyamide resin, and the like, and among them, the same as the base resin of the foam sheet in the present invention. And biodegradable thermoplastic resins such as polyester resins containing at least 35 mol% of aliphatic ester component units are preferred.

  The foam sheet in the present invention is used as a foam sheet for thermoforming. Hereinafter, a polylactic acid resin foam molded body obtained by thermoforming the foam sheet will be described.

The polylactic acid-based resin foamed molded product of the present invention (hereinafter also simply referred to as a foamed molded product) is a foamed molded product obtained by thermoforming a foamed sheet containing a polylactic acid-based resin as a main component of a base resin. The difference between the calorific value (ΔH _{exo: 2 ° C./min} ) and the endothermic amount (ΔH _{endo: 2 ° C./min} ) determined by heat flux differential scanning calorimetry at a heating rate of 2 ° C./min of the foamed molded product ( ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) is 10 J / g or more, preferably 15 J / g or more, more preferably 20 J / g or more, and particularly preferably 25 J / g or more. It is sufficiently advanced and has particularly excellent rigidity and heat resistance. When the value of (ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) is too small, it means that crystallization is insufficient, and foaming molding in which desired rigidity and heat resistance cannot be obtained. Is the body. That is, the value of (ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) of the foamed molded product is the melting when the crystals of the foamed molded product melt at the time of heat flux differential scanning calorimetry. It corresponds to the amount of heat, and the larger the value, the more crystallization of the foamed molded product is advanced. The upper limit of (ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) is not particularly limited, but is generally 60 J / g. In the present invention, the value of ΔH _{exo: 2 ° C./min} of the foamed molded product may be 0.

The calorific value (ΔH _{exo: 2 ° C./min} ) and endothermic amount (ΔH _{endo: 2 ° C./min} ) heat flux differential scanning calorimetry in the foam molded product of the present invention is 1 to 4 mg cut out from the foam molded product. Except that the foam piece is a test piece, the heat flux differential scanning calorimetry of the heat generation amount (ΔH _{exo: 2 ° C./min} ) and the endothermic amount (ΔH _{endo: 2 ° C./min} ) of the foam sheet is the same It is.

  The foamed sheet in the present invention is heat-softened, and is subjected to vacuum forming and / or pressure forming using a mold, and thermoforming such as a matched mold forming method and a plug assist forming method using them. Therefore, it can be mainly molded into trays, cups, bowls, lunch boxes and the like.

  The foamed molded product of the present invention is, for example, the same or different from the molding die for promoting crystallization, which has been temperature-controlled at a temperature of preferably 80 to 130 ° C., more preferably 90 to 120 ° C. after thermoforming of the foamed sheet. It is preferably obtained by holding for 10 to 60 seconds with the provided mold. If the temperature of the mold for promoting crystallization is too low, it takes time to crystallize sufficiently and the productivity may be inferior. On the other hand, if the temperature of the mold is too high, not only is it difficult to crystallize sufficiently, but the strength of the foamed molded product after mold release is lowered, and the shape of the foamed molded product may not be maintained.

  The foamed molded article of the present invention is cured, for example, for 6 to 36 hours in an atmosphere of about 60 to 80 ° C. above the glass transition temperature of the polylactic acid resin after thermoforming the foamed sheet. Can also be obtained.

As described above, the foamed sheet of the reference invention has a low degree of crystallinity. Therefore, by heating to near the glass transition temperature of the polylactic acid-based resin at the time of thermoforming, it becomes a good indication such as deep drawing, and the appearance of the resulting foamed molded article is also good. The foamed molded article of the present invention has been crystallized at the same time as the thermoforming of the foamed sheet, or after the thermoforming, by maintaining the temperature above the glass transition temperature of the polylactic acid resin as described above. Excellent heat resistance. In particular, the foam sheet of the reference invention having a calorific value (ΔH _{exo: 10 ° C./min} ) determined by heat flux differential scanning calorimetry at a cooling rate of 10 ° C./min is 20 to 45 J / g, A foamed molded article having sufficiently high heat resistance can be obtained by a method of promoting crystallization with a mold that is the same as or different from a molding mold for promoting crystallization.

  In the present specification, the measurement of the glass transition temperature is a value determined as the midpoint glass transition temperature of the DSC curve obtained by heat flux differential scanning calorimetry according to JIS K7121 (1987). In addition, the test piece for calculating | requiring a glass transition temperature is 3 of JISK7121 (1987). Conditioning of test piece In accordance with “When measuring glass transition temperature after performing a certain heat treatment” described in (3), put the test piece into a DSC apparatus container at 10 ° C./min up to 200 ° C. A test piece is prepared by heating and dissolving by heating and immediately adjusting to 0 ° C. at 10 ° C./min.

  The foamed molded article of the present invention thus obtained is biodegradable and is preferably used as a food packaging container such as a lunch box, cup noodle container, fruit container, vegetable container, precision equipment, buffer packaging container for electrical products, etc. Is done.

  Hereinafter, the present invention will be described with reference to examples and comparative examples.

The polylactic acid resins A to D used in the reference examples and reference comparative examples are as follows.
Polylactic acid-type resin AD was manufactured as follows using the twin-screw extruder with an internal diameter of 47 mm.
Crystalline polylactic acid resin H-100 (density: 1260 kg / m ³ , endothermic amount (ΔH _{endo: row} ): 49 J / g) manufactured by Mitsui Chemicals, Inc. and peroxides (DCP) in the amounts shown in Table 1 : Dicumyl peroxide) is supplied to a twin-screw extruder, heated to a temperature at which the resin is sufficiently melted and melt-kneaded, adjusted to a resin temperature of 215 ° C., and then extruded into a strand. After cooling the shaped extrudate in water at about 25 ° C., polylactic acid resins A to D were obtained by cutting into pellets. Table 1 shows the physical properties of the polylactic acid resins A to D.

  As the polylactic acid resin E, crystalline polylactic acid resin H-100 was used. Table 2 shows the physical properties of the polylactic acid resin E.

Reference Example 1
Using a tandem type extruder in which a first extruder having an inner diameter of 90 mm and a second extruder having an inner diameter of 120 mm were connected, a foam sheet was produced as follows.
After supplying the polylactic acid-based resin A and the type and amount of the air conditioner shown in Table 3 to the first extruder and heat-melting and kneading, the type and amount of the foaming agent shown in Table 3 are placed in the first extruder. The mixture was pressed and kneaded. Next, the foamable melt-kneaded product is cooled in a second extruder connected to the first extruder, and after adjusting the resin temperature to 171 ° C., it has a cylindrical slit having a diameter of 110 mm and a slit interval of 0.5 mm. It was extruded from an annular die and foamed into a cylindrical shape. Next, this cylindrical foam was taken out while cooling and cut in the extrusion direction to obtain a foam sheet. As specific cooling conditions for the cylindrical foam, air was blown into the cylindrical foam immediately after extrusion under the condition of 0.4 m ³ / min (23 ° C., 1 atm) and 0.9 m ³ was externally applied. Per minute (23 ° C., 1 atm) and blowing the cylindrical foam along the side of the cylindrical cooling device with a diameter of 333 mm adjusted to 5 ° C., thereby forming the cylindrical foam Cooled.

Reference Example 2
Except having used the foaming agent of the kind and amount shown in Table 3, adjusting the resin temperature to 172 ° C., and then extruding from a circular die having a cylindrical slit with a diameter of 135 mm and a slit interval of 0.5 mm, A foamed sheet was obtained in the same manner as in Reference Example 1.

Reference Example 3
The resin C was used in place of the resin A, the type and amount of the foaming agent shown in Table 3 was used, and the resin temperature was adjusted to 167 ° C. A foamed sheet was obtained in the same manner as in Reference Example 1 except that extrusion was performed from an annular die having a gap.

Reference Example 4
The resin E was used in place of the resin A, the type and amount of foaming agent shown in Table 3 were used, and the resin temperature was adjusted to 183 ° C. A foamed sheet was obtained in the same manner as in Reference Example 1 except that extrusion was performed from an annular die having a gap.

Reference Example 5
The resin B was used in place of the resin A, the type and amount of the foaming agent shown in Table 3 were used, and the resin temperature was adjusted to 180 ° C. A foamed sheet was obtained in the same manner as in Reference Example 1 except that extrusion was performed from an annular die having a gap.

Reference Example 6
Resin E was used in place of Resin A, and 0.4 parts by weight of DC with respect to 100 parts by weight of Resin E and E was supplied to the first extruder, and the types and amounts of foams shown in Table 3 The foamed sheet was the same as in Reference Example 1 except that the agent was used and the resin temperature was adjusted to 170 ° C. and then extruded from an annular die having a cylindrical slit having a diameter of 135 mm and a slit interval of 0.5 mm. Got.

Reference Example 7
Except that the foaming agent of the type and amount shown in Table 3 was used, the resin temperature was adjusted to 170 ° C., and then extruded from an annular die having a cylindrical slit having a diameter of 135 mm and a slit interval of 0.5 mm. A foamed sheet was obtained in the same manner as in Reference Example 1.

Reference Example 8
The resin D was used in place of the resin A, the type and amount of the foaming agent shown in Table 3 were used, and the resin temperature was adjusted to 170 ° C. A foamed sheet was obtained in the same manner as in Reference Example 1 except that extrusion was performed from an annular die having a gap.

Reference Comparative Example 1
Except that the foaming agent of the type and amount shown in Table 4 was used, the resin temperature was adjusted to 174 ° C., and then extruded from an annular die having a cylindrical slit having a diameter of 135 mm and a slit interval of 0.5 mm. A foamed sheet was obtained in the same manner as in Reference Example 1.

Reference Comparative Example 2
The resin C was used in place of the resin A, the type and amount of the foaming agent shown in Table 4 were used, and the resin temperature was adjusted to 167 ° C. A foamed sheet was obtained in the same manner as in Reference Example 1 except that extrusion was performed from an annular die having a gap.

Reference Comparative Example 3
The resin C was used in place of the resin A, the type and amount of the foaming agent shown in Table 4 were used, and the resin temperature was adjusted to 171 ° C., and then a cylindrical thin tube with a diameter of 135 mm and a slit interval of 0.5 mm was used. Except that it was extruded from an annular die having a gap, no air was blown outside the cylindrical foam, and the temperature of the cylindrical cooling device was adjusted to 110 ° C., the foam sheet was the same as in Reference Example 1. Obtained.

Reference Comparative Example 4
The resin C was used in place of the resin A, the type and amount of the foaming agent shown in Table 4 were used, and the resin temperature was adjusted to 181 ° C., and then a cylindrical thin tube with a diameter of 135 mm and a slit interval of 0.5 mm was used. A foamed sheet was obtained in the same manner as in Reference Example 1 except that extrusion was performed from an annular die having a gap.

Heat flux differential scanning calorimetry at the apparent density, thickness, closed cell ratio, bubble shape (Z, Z / X, Z / Y), heating rate 2 ° C./min of the foam sheets obtained in Reference Examples 1-8. Exothermic amount (ΔH _{exo: 2 ° C./min} ), endothermic amount (ΔH _{endo: 2 ° C./min} ), endothermic amount (ΔH _{endo: 2 ° C./min} ) and endothermic amount (ΔH _{endo: 2 ° C./min} ) ) Difference (ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ), calorific value when heat flux differential scanning calorimetry is performed at a cooling rate of 10 ° C./min (ΔH _{exo: 10 ° C./min} ) Table 3 shows the measurement results of semi-crystallization time, evaluation of moldability, appearance, and heat resistance improvement, and Table 4 shows the measurement results and evaluation results of the foamed sheets obtained in Reference Comparative Examples 1 to 4.
In addition, the heat absorption amount and heat generation amount of polylactic acid resin and polylactic acid resin foam sheet are measured using the product name “DSC-50” manufactured by Shimadzu Corporation as the measuring device, and the analysis software is “Shimadzu Thermal Analysis Workstation”. The partial area analysis program version 1.52 for TA-60WS was used.

表中、ｎブタンはノルマルブタン、ｉブタンはイソブタンを表す。また、表中、重量部は基材樹脂１００重量部に対する値である。

In the table, n-butane represents normal butane and i-butane represents isobutane. In the table, parts by weight are values relative to 100 parts by weight of the base resin.

表中、ｎブタンはノルマルブタン、ｉブタンはイソブタンを表す。また、表中、重量部は基材樹脂１００重量部に対する値である。

In the table, n-butane represents normal butane and i-butane represents isobutane. In the table, parts by weight are values relative to 100 parts by weight of the base resin.

In Tables 3 and 4, evaluation of foam sheet forming property, appearance, and heat resistance improvement was performed as follows.
Evaluation of moldability of foamed sheet Each of the foamed sheets obtained in each of the reference examples and the comparative examples was subjected to a thermoforming test using a pressure vacuum forming machine for FKS type test manufactured by Asano Laboratories. And evaluated. Specifically, using the molding machine, after heating both surfaces of the foamed sheet clamped on all sides to a surface temperature of 40 ° C. with a heater, the mold has an opening diameter of 125 mm, a lower diameter of 110 mm, and a depth of 50 mm. The following evaluation was performed about the behavior of the foam sheet in the heating furnace when molding a frustoconical container (deployment ratio: 2.3) having a circular storage portion and molding the foam sheet, and the obtained molded product. .
○: Drawdown (sagging) of the foamed sheet in the heating furnace is not observed or is somewhat observed, but the thickness of the molded product is uniform.
X: Drawdown in the heating furnace is large, resulting in uneven thickness of the molded product. Alternatively, cracks are generated on the inner wall surface or the outer wall surface of the molded product.

Appearance Evaluation The following evaluation was performed by visual observation of the appearance of the foam sheet.
○: The surface gloss of the foam sheet is uniform.
X: Air bubbles are conspicuous in the portion of the surface of the foam sheet.

Evaluation of heat resistance improvement The following evaluation was performed based _on the calorific value (ΔH _{exo: 10 ° C./min} ) of the foamed sheets obtained in each of the examples and comparative examples.
O ... The calorific value (ΔH _{exo: 10 ° C / min} ) is 20 J / g or more.
Δ _{: The} calorific value (ΔH _{exo: 10 ° C./min} ) is more than 5 J / g and less than 20 J / g.
X ... calorific value (ΔH _{exo: 10 ° C / min} ) is 5 J / g or less.

  The foamed sheets obtained in Reference Examples 1, 2, 6, and 8 were designated as foamed sheets A, B, C, and D, respectively, and the following Examples 1 to 5 and Comparative Example 1 were performed.

Example 1
Using a pressure air vacuum forming machine for testing FKS type manufactured by Asano Laboratories Co., Ltd., both surfaces of foam sheet A clamped on all sides were heated to a surface temperature of 40 ° C. with a heater, and then the opening diameter was 125 mm with a mold. A frustoconical container (development magnification: 2.3) having a circular storage part with a diameter of 110 mm and a depth of 50 mm was molded. Thereafter, heat treatment was performed by holding the container for 30 seconds in a mold heated to 90 ° C.

Example 2
Using the foam sheet B, a frustoconical container was molded in the same manner as in Example 1, and then heat-treated by holding the container in a mold heated to 110 ° C. for 30 seconds.

Example 3
Using the foam sheet C, a frustoconical container was molded in the same manner as in Example 1, and then heat-treated by holding the container for 30 seconds in a mold heated to 110 ° C.

Example 4
Using the foam sheet D, a frustoconical container was molded in the same manner as in Example 1, and then heat-treated by holding the container in a mold heated to 90 ° C. for 15 seconds.

Example 5
Using the foam sheet D, a frustoconical container was formed in the same manner as in Example 1, and then heat-treated by holding the container for 30 seconds in a mold heated to 90 ° C.

Comparative Example 1
Using the foam sheet A, a frustoconical container was molded in the same manner as in Example 1 except that heat treatment was not performed.

  Table 5 shows various physical properties of the foam molded articles obtained in Examples 1 to 5 and Comparative Example 1.

The evaluation of heat resistance of foam formability in Table 5 was performed as follows.
Evaluation of heat resistance The foamed molded articles obtained in each of the Examples and Comparative Examples were heated in an oven for 5 minutes to examine deformation before and after heating.
◎ ・ ・ ・ No deformation up to 90 ℃.
○ ・ ・ ・ No deformation up to 70 ℃.
X: Deforms severely up to 70 ° C.

Claims (1)

A foamed molded article obtained by thermoforming a foamed sheet comprising a polylactic acid-based resin as a main component of a base resin, and is obtained by heat flux differential scanning calorimetry at a heating rate of 2 ° C / min of the foamed molded article. The difference (ΔH _{endo: 2 °} C./min−ΔH _{exo: 2 ° C./min} ) between the endothermic amount (ΔH _{endo: 2 ° C./min} ) and the calorific value (ΔH _{exo: 2 ° C./min} ) is 10 J / g or more. A polylactic acid resin foamed molded product characterized by the above.

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