JP2003064213A - Method for manufacturing molding from poly(lactic acid) foam particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a molding from poly(lactic acid) foam particles which molding is low in the fluctuation of the density between portions, which excels in the fusion between foam particles, and which gives uniform mechanical properties. SOLUTION: The foam particles formed from a resin having poly(lactic acid) as the major component are charged into a mold so as for the compression ratio to be 5-70% and then the foam particles are heated by a heating medium and fused together.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polylactic acid expanded particle molded article having biodegradability. More specifically, the present invention relates to a method for producing a foamed polylactic acid molded article which has excellent fusion-bonding properties between expanded particles, has a small density variation, and has uniform mechanical properties.

[0002]

Foamed particle moldings made of resins such as polystyrene, polyethylene and polypropylene are widely used as cushioning materials for packaging, agricultural production boxes, fish boxes, automobile parts, building materials, civil engineering materials and the like. However, since these foamed particle molded bodies are hardly decomposed by microorganisms when they are left in a natural environment after use, they may cause a problem of environmental destruction due to dust scattering. On the other hand, research on resins that are decomposed by microorganisms has also been made, and for example, microbially decomposable resins made of polylactic acid as surgical sutures have been put into practical use so far, and have achieved many years of achievements. Further, in recent years, lactic acid, which is a raw material of polylactic acid, can be produced in large quantities at low cost by a fermentation method using corn or the like as a raw material. Therefore, a foam made of polylactic acid, which has a proven track record in practicality, human safety and biodegradability, has been desired. As a prior art relating to a foam made of polylactic acid, Japanese Patent Publication No. 5-508669,
JP-A-4-304244, JP-A-5-139435
Japanese Patent Application Laid-Open No. 5-140361, Japanese Patent Application Laid-Open No. 9-26365.
No. 1, etc. relating to extruded foams, JP-A-5-1709
No. 65, JP-A-5-170966, JP-A 2000-1
36261 and the like related to expanded particles.
In the prior art related to the above polylactic acid foam, in particular those related to expanded particles, a foam having a desired shape can be obtained without being relatively restricted in shape, and depending on the purpose such as lightness, cushioning and heat insulating properties. It is especially promising because it has practical properties because it can be easily designed.

[0003]

However, in the conventional foamed particle molded article made of polylactic acid, the expandable resin particles are filled in a mold, and the resin particles are foamed by hot air, and at the same time, the particles are mutually reciprocated. Since they were fused, there was a large variation in the density of the part of the expanded particle molded article, the fusibility of the expanded particles to each other was insufficient, and the mechanical properties were poor. Therefore, it is an object of the present invention to provide a method for producing a polylactic acid foamed particle molded article which has a small density variation in a partial portion, is excellent in fusion bonding between expanded particles, and has uniform mechanical properties.

[0004]

Means for Solving the Problems The present inventors have completed the present invention as a result of extensive studies on a method for producing a polylactic acid expanded particle molded article in order to solve the above problems.
That is, according to the present invention, the following method for producing a polylactic acid expanded particle molded article is provided. (1) Filling a foamed particle formed of a resin containing polylactic acid as a main component in a mold so as to have a compression ratio of 5 to 70%, and then heating the foamed particle with a heating medium to fuse the particles. A method for producing a polylactic acid foamed particle molded article, which is characterized. (2) The apparent density of the expanded beads is 0.015 to 0.3 g
/ Cm ^{3 The} method for producing a polylactic acid expanded particle molded article according to (1) above. (3) The expanded particles are 0.3 to 4 mol / (1,000 g
The method for producing a polylactic acid expanded particle molded article according to (1) or (2) above, which contains a gas of expanded particles). (4) Expanded particles formed of a resin containing polylactic acid as a main component include a gas of 0.7 to 4 mol / (1000 g expanded particles), and the expanded particles are filled with a heating medium after filling the expanded particles in a mold. A method for producing a polylactic acid expanded particle molded article, which comprises heating and fusing. (5) The method for producing a foamed polylactic acid molded article according to any one of (1) to (4), wherein the polylactic acid is a gelled polylactic acid. (6) The heat of fusion of the polylactic acid as measured by differential scanning calorimetry exceeds 0.1 J / g.
The method for producing a polylactic acid expanded particle molded article according to any one of (5). (7) The above (3) or (4), wherein the gas is carbon dioxide
The method for producing a foamed product of polylactic acid expanded particles according to 1.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, expanded particles (hereinafter also simply referred to as expanded particles) formed from a resin containing polylactic acid as a main component used as a molding material are based on a resin containing polylactic acid as a main component. It is manufactured by foaming resin particles for foaming produced as a material resin. The polylactic acid, which is the main component of the base resin, refers to a polymer containing 50% by weight or more of a lactic acid component in terms of the weight of monomers used for polymerization. Examples thereof include (1) a polymer of lactic acid, (2) a copolymer of lactic acid and another aliphatic hydroxycarboxylic acid, (3) lactic acid, an aliphatic polyhydric alcohol and an aliphatic polycarboxylic acid. And (4) a copolymer of lactic acid and another aliphatic polycarboxylic acid, (5) a mixture of any of the above (1) to (4), and the like.

In the present invention, a biodegradable aliphatic polyester containing at least 35 mol% of an aliphatic ester component can be mixed with polylactic acid. In this case, the aliphatic polyester includes a hydroxy acid polycondensate, a lactone ring-opening polymer, a polycondensate of a polyhydric alcohol component and a polyvalent carboxylic acid component, and the like. Examples of the hydroxy acid polycondensate include a polycondensate of hydroxybutyric acid, and examples of the ring-opening polymer of a lactone include polycaprolactone and the like, and a polycondensate of a polyhydric alcohol component and a polyvalent carboxylic acid component. Examples thereof include polybutylene succinate, polybutylene succinate adipate, and poly (butylene adipate / terephthalate). The mixing ratio of the biodegradable aliphatic polyester to polylactic acid is 50% by weight or less, preferably 5 to 30% by weight, based on the total amount of both.

In the present invention, when the polylactic acid foamed molded article is required to have heat resistance, polylactic acid having a high glass transition temperature (Tg) or a crystalline polylactic acid having a high melting point (Tm) is used. It is preferably used. In the present invention, its glass transition temperature is 50 to 65 ° C, further 55 to 65, or its melting point is 130 to 180 ° C, further 140 to
The use of 180 is preferred. In the present invention, the melting point and glass transition temperature of the base resin are JIS K 712.
It measures according to 1-187. The melting point of the base resin is
It is the temperature at the peak apex obtained from the second DSC curve obtained by differential scanning calorimetry. The glass transition temperature of the base resin is obtained from the second DSC curve obtained by differential scanning calorimetry, and is a straight line that is equidistant in the vertical axis direction from the extended straight line of each baseline and the stepwise shape of the glass transition. The midpoint glass transition temperature at the point where the curve of the changing portion intersects. The second DSC curve obtained by the differential scanning calorimetry of the polylactic acid means that 1 to 5 mg of the base resin is heated to 200 ° C. at a heating rate of 10 ° C./min by a differential scanning calorimeter (here. Then, the DSC obtained
The curve is called the first DSC curve. ), Then 20
The temperature is lowered from 0 ° C. to 0 ° C. at a rate of 10 ° C./min. After that, the DSC curve obtained by raising the temperature to 200 ° C. again at a heating rate of 10 ° C./min is referred to as the second DSC curve.
When two or more peak peak temperatures appear in the base resin, the high temperature side is the melting point.

Specific examples of the lactic acid polymer include L-
Lactic acid, D-lactic acid, DL-lactic acid or a mixture thereof, or a monomer or dimer of L-lactide, D-lactide, DL-lactide which is a cyclic dimer thereof, or a mixture thereof. A polymer can be mentioned.

Specific examples of the method for producing the polylactic acid used in the present invention include, for example, a method of direct dehydration polycondensation using lactic acid or a mixture of lactic acid and an aliphatic hydroxycarboxylic acid as a raw material (for example, US Pat. No. 5 , 310, 86
5), a ring-opening polymerization method for polymerizing a cyclic dimer (lactide) of lactic acid (for example, US Pat.
No. 758,987), a ring-opening polymerization method in which a cyclic dimer of lactic acid and an aliphatic hydroxycarboxylic acid, for example, lactide or glycolide and ε-caprolactone are polymerized in the presence of a catalyst ( For example, US Pat.
57,537), a method of direct dehydration polycondensation of a mixture of lactic acid, an aliphatic dihydric alcohol and an aliphatic dibasic acid (for example, US Pat. No. 5,428,
No. 126), a method of condensing polylactic acid, an aliphatic dihydric alcohol, an aliphatic dibasic acid and a polymer in the presence of an organic solvent (for example, European Patent Publication No. 0).
No. 71280 A2), a method of performing solid phase polymerization in at least some steps in producing a polyester polymer by performing dehydration polycondensation reaction of lactic acid in the presence of a catalyst, etc. However, the manufacturing 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 a polysaccharide may be allowed to coexist and be copolymerized. The molecular weight may be increased by using a binder (polymer chain extender) such as a diisocyanate compound.

The polylactic acid used in the present invention includes crystalline and non-crystalline ones, but it is preferable to use crystalline one from the viewpoint of heat resistance of the obtained expanded particle molded article. In particular, when an amorphous material is used, it is preferable to use a material which has been subjected to gelation treatment in advance from the viewpoint of in-mold moldability of the obtained expanded particles. To gel the polylactic acid,
The polylactic acid or the resin containing the polylactic acid as a main component may be subjected to gelation treatment. The gelation treatment in this case includes various conventionally known methods such as a method using an organic peroxide, an electron beam crosslinking method, a silane crosslinking method, and a polyisocyanate crosslinking method. In the polylactic acid impregnated with the foaming agent in the present invention, its crystallinity is preferably 20% or less,
More preferably, it is 10% or less. The crystallinity is measured by an X-ray diffractometer manufactured by Rigaku Denki Kogyo Co., Ltd., and is calculated from the ratio of the crystal peak area to the total peak area of the obtained chart. In the gelled polylactic acid used in the present invention, the gel fraction is 5 to 100%, preferably 10 to 90%, more preferably 20 to 80%.

As a method for producing the expanded beads used in the present invention, a conventionally known method can be adopted. In the present invention, in order to preferably produce expanded beads, first, base resin particles are prepared. The base resin particles can be produced by a conventionally known method. For example, after melt-kneading the base resin with an extruder, the base resin is extruded in a strand shape, and after cooling, cut into an appropriate length or the strand is cut. It can be obtained by cutting to an appropriate length and then cooling. The weight of each base resin particle is 0.05 to 10 mg, preferably 1 to 4 mg
It is better to If the weight of the particles is smaller than the above range, it becomes difficult to produce the resin particles. The shape of the resin particles is not particularly limited, and in addition to the columnar shape (pellet shape), the spherical shape,
It may have various shapes such as a rod shape.

In the step of melt-kneading the base resin with an extruder and extruding it into a strand, if the base resin has hygroscopicity, it is preferable to dry the base resin in advance. When a resin containing a large amount of water is put into the extruder, bubbles that adversely affect the uniformity of the bubbles in the expanded resin particles are mixed into the resin particles for expansion, and the physical properties of the base resin when melt-kneading with an extruder There is a possibility that the melt flow rate (MFR) may be extremely increased due to the decrease. In order to suppress the deterioration of the resin, a method of using a extruder with a vent and vacuum suction to remove water from the base resin can also be adopted. Also, the extrusion temperature conditions are set so that the MFR of the base resin does not become extremely large.

Next, the foaming resin particles obtained as described above are impregnated with a foaming agent and then foamed. In this case, as a method of foaming after impregnating the resin particles with the foaming agent, the resin particles are impregnated with the foaming agent in the closed container to obtain expandable resin particles, and then these are taken out from the closed container, and the resin A method of heating and softening the particles to foam them can be preferably adopted. Further, as another method, while dispersing the resin particles in the dispersion medium in the presence of a foaming agent in a closed container, the contents are heated to soften the resin particles to impregnate the foaming agent in the particles, Next, open one end of the container, and while maintaining the pressure inside the container at a pressure equal to or higher than the vapor pressure of the foaming agent, simultaneously release the particles and the dispersion medium into an atmosphere at a pressure lower than that in the container (usually under atmospheric pressure) to foam. It is also possible to use a foaming method in which the decomposition-type foaming agent is kneaded into the resin particles in advance, and the resin particles are heated to a temperature above the decomposition temperature of the foaming agent to foam.

When the method of obtaining expanded particles by an extruder is adopted, the base resin is melted by using an extruder and kneaded with a foaming agent to obtain an expandable melt-kneaded product, and then extruded in a strand form. The foamed particles can be produced by foaming and cutting the material to an appropriate length after cooling or cutting the strand to an appropriate length and then cooling.

The base resin may be colored by adding a coloring pigment or dye such as black, gray, brown, blue or green. If you use a colored base resin,
It is possible to obtain colored expanded particles and a molded body. Examples of the colorant include organic and inorganic pigments and dyes. As such pigments and dyes, various conventionally known pigments can be used. Further, an inorganic substance such as talc, calcium carbonate, borax, zinc borate, aluminum hydroxide or the like can be added to the base resin in advance as a cell regulator. When an additive such as a coloring pigment, a dye or an inorganic substance is added to the base resin, the additive can be kneaded into the base resin as it is, but usually a master batch of the additive is taken into consideration in consideration of dispersibility and the like. It is preferable to make it and knead it with the base resin. The amount of coloring pigment or dye added varies depending on the color of coloring,
Usually, 0.001 to 5 parts by weight is preferable with respect to 100 parts by weight of the base resin. By adding an inorganic substance to the base resin, the effect of improving the expansion ratio can be obtained.
Further, in the present invention, it is possible to mix additives such as a flame retardant, an antistatic agent, a weathering agent and a thickener.

It should be noted that it is not preferable to add a high concentration of an additive such as a pigment and a cell regulator, assuming that the product is discarded after use. When the expanded resin particles are obtained through the expanded resin particles, the obtained expanded resin particles are preferably stored in an environment in which hydrolysis does not proceed. Similarly, it is preferable to store the foamed particles in an environment in which hydrolysis does not proceed.

The foaming agent used for obtaining the expanded beads is a conventionally known one, for example, propane, butane, hexane, cyclobutane, cyclohexane, trichlorofluoromethane, dichlorodifluoromethane, chlorofluoromethane, trifluoromethane, 1,1,1,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, 1-chloro-1,2,
Organic physical foaming agents such as 2,2-tetrafluoroethane and inorganic physical foaming agents such as nitrogen, carbon dioxide, argon, and air are used. Among them, inorganic layers that do not destroy the ozone layer and are inexpensive The physical foaming agents of the system are preferable, and nitrogen, carbon dioxide and air are particularly preferable. In the present invention,
Carbon dioxide is more preferable from the viewpoint that foamed particles having a smaller apparent density can be obtained with respect to the amount of the foaming agent used.

When foaming resin particles are prepared in advance and the foaming resin particles are impregnated with the foaming agent, the resin particles are placed in a closed container and the foaming agent is in a pressure range of 5 to 100 kgf / cm ² G. It may be press-fitted into the closed container. The amount of the foaming agent used is appropriately selected from the relationship between the desired apparent density of the foamed particles and the foaming temperature.

Further, the resin particles for foaming are put in a closed container,
In this method, the foaming agent is contacted with the foaming agent for a predetermined time to impregnate the particles with the foaming agent, and then the resin particles are taken out from the closed container to obtain expandable resin particles. It is preferable to carry out at a temperature below the temperature. The impregnation temperature of the foaming agent is preferably 5 to 60 ° C,
More preferably, it is 5-40 degreeC. The pressure of the foaming agent during the impregnation varies depending on the expansion ratio of the target foamed particles, but is usually 5 to 100 kgf / cm ^2.
G, and the impregnation time is 10 minutes to 24 hours. In particular, when carbon dioxide is used as the foaming agent, it is preferable that the impregnation amount of carbon dioxide is usually 2.5 to 30% by weight, preferably 3 to 20% by weight. The impregnated amount of carbon dioxide in this case is represented by the following equation.

[Equation 1] Carbon dioxide impregnation amount (wt%) = A / (A + B) × 100 A: Weight of carbon dioxide impregnated in resin particles B: Weight of resin particles before carbon dioxide impregnation

A in the above equation is obtained by subtracting the weight of resin particles before carbon dioxide impregnation from the weight of carbon dioxide impregnated resin particles. It should be noted that any of the above weights for calculating the impregnated amount is measured up to the order of 0.0001 g. As a heating medium for heating and foaming the expandable resin particles impregnated with the foaming agent, steam, heat-adjusted air, nitrogen and the like can be mentioned, but steam is usually used. As a method for heating the foamable resin particles to foam them, a conventionally known method can be adopted, but normally, the foamable resin particles are filled in a container and steam is introduced to foam them.
If the closed container is provided with an opening valve that slightly leaks the internal pressure, the air in the container can be removed, and expanded particles having a uniform density can be easily obtained. The temperature when heating the resin particles impregnated with the foaming agent, that is, the foaming temperature is usually (glass transition temperature −30 ° C.) to (glass transition temperature + 60 ° C.), preferably (glass transition temperature) of the base resin. -2
0 ° C) to (glass transition temperature + 40 ° C). When the foaming temperature is lower than the above range, sufficient foaming is unlikely to occur, and when the foaming temperature is higher than the range, the closed cell ratio of the foamed particles is lowered, and it is difficult to obtain a good molded product.

The foamed particles of the present invention preferably has an apparent density of 0.015~0.3g / cm ^3, further preferably 0.015~0.2g / cm ^3. When the density is larger than the above range, the variation in the density of the expanded particles is likely to be large, and the physical properties of the expanded particle molded body can be obtained, which leads to the expansion of the expanded particles during the heat molding in the mold and the variation in the fusion property. There is a risk of deterioration. On the other hand, when it is smaller than the above range, the expansion ratio is relatively high,
There is a risk that the molded product will have a large molding shrinkage.

In the present specification, the apparent density of the expanded particles is 23 ° C., and a graduated cylinder containing ethanol is prepared. The graduated cylinder has a relative humidity of 50%, 23 ° C., and 1 a.
At least 500 expanded particles (weight W1 of expanded particle group) left for 2 days under the condition of tm were sunk using a metal net or the like, and the volume V1 (cm ³ ), The weight W1 (g) of the expanded particle group placed in the graduated cylinder is divided (W1 / V1). The expanded particles of the present invention preferably have a bulk density of 0.01 to 0.2 g / cm ³ ,
It is more preferably 0.01 to 0.12 g / cm ³ .

In the present specification, as for the bulk density of the expanded particles, an empty graduated cylinder is prepared, and the graduated cylinder is left to stand for 2 days under the conditions of relative humidity 50%, 23 ° C. and 1 atm.
The volume V2 (c) indicated by the scale of the graduated cylinder when 00 or more expanded particles (weight W2 of the expanded particle group) are put in
m ³ ) Weight W of the expanded particle group put in the graduated cylinder
Calculate by dividing 2 (g) (W2 / V
2).

Further, the foamed particles in the present invention have an average cell diameter of 10 to 500 μm, preferably 30 to 40.
It is 0 μm. When the cell diameter is smaller than the above range, the film strength is too weak at the time of the heat molding of the present invention, so that the cells are broken and the curing recovery property becomes poor. On the other hand, if the cell diameter is larger than the above range, the film strength will be too strong at the time of foaming by heating, so that sufficient expansion does not occur, resulting in a molded product having poor surface smoothness. In the present specification, the average cell diameter of the foamed particles is obtained by dividing the foamed particles into approximately two parts, determining the maximum diameters of all the cells present in the cross section of the foamed particles, and performing this operation for 10 or more foamed particles. The arithmetic mean value of the maximum diameter is defined as the average bubble diameter.

In the present invention, in order to produce a molded product of expanded particles, expanded particles are contained in the mold in an amount of 5 to 70%, preferably 15 to 70%.
After filling so as to have a compression ratio of 70%, more preferably 30 to 70%, the expanded particles are heated by a heating medium to carry out molding. In particular, in the case of expanded particles formed from a resin containing polylactic acid as a main component having a heat of fusion of more than 0.1 J / g, it is filled in a mold so as to have a compression rate of 15 to 70%, and heat-molded. Preferably. By this heat-molding, the foamed particles are strongly fused to each other, and there is little variation in the integrated density, and a foamed molded article having a good appearance is provided. As a molding die in this case, a conventional die or JP-A-2000-15 is used.
A steel belt used in the continuous forming apparatus described in No. 708 is used. As the heating means, steam heating is usually used, and the heating temperature may be any temperature at which the surface of the expanded beads melts. In the present invention, at the time of molding, the expanded particles are filled in the mold so as to have a compression rate of 5 to 70%. Especially when polylactic acid is crystalline, the compressibility is 5
If it is less than%, the fusion property of the molded article may be poor and the molded article may have poor surface smoothness. On the other hand, if it exceeds 70%, the fusion property inside the molded article tends to be poor, and the purpose of weight reduction, which is a characteristic of the foamed product, tends to be lost. Also,
Compressor equipment is difficult.

The compression ratio referred to in the present invention is expressed as follows. The compressibility can be expressed by the relationship between the internal volume of the mold and the bulk volume of the expanded particles filled in the mold in the atmosphere.

## EQU00002 ## Compressibility (%) = (A−B) × 100 / A (2) A: Bulk volume (c) of the expanded particles filled in the mold in the atmosphere.
m ³ ) B: Inner volume of the mold (cm ³ ) A in the above formula is obtained by dividing the weight (g) of the expanded particles filled in the mold by the bulk density (g / cm ³ ) of the expanded particles. Desired.

In the present invention, a conventionally known filling method can be adopted particularly when the expanded particles are filled in the mold so as to have the compression ratio. Examples of such a method include 1) a cracking method, 2) a pressure filling method, and 3) a compression filling method. 1) The cracking method is a method in which raw material beads are mechanically transported and filled by an injector in a state where the raw material bead container and the cavity are communicated with atmospheric pressure and opened, and then the mold is clamped. 2) The pressure filling method is 0.2 to 1.5 kg / cm in the raw material bead container.
^This is a method in which the cavity is pressurized to about ² G and is opened to the atmospheric pressure through the chamber, and is transported and filled by utilizing the differential pressure. 3) In the compression filling method, the pressure p in the raw material bead container is increased at a pressure higher than that in the pressure filling method, the pressure in one chamber is increased, and the difference in the cavity internal pressure p1 communicating through the vent hole. In this method, the pressure (p-p1) is changed to convey and fill the raw material beads,
Since the raw material beads are sent in a compressed state, the filling property is excellent.

In the present invention, in combination with the method of filling the foamed particles into the mold so that the above compression ratio is obtained, the foamed particles to be provided in the mold are previously filled with an inorganic gas such as air, nitrogen, carbon dioxide, etc., especially carbon dioxide. It is preferably contained as a gas.
Also, an organic gas such as butane can be used. By using the expanded particles to which a gas has been added as the expanded particles for molding, the expandability of the expanded particles at the time of molding, the mutual fusion property of the particles, the mold shape reproducibility of the molded product, and the dimensional stability are improved. The gas is
Preferably 0.3 to 4 mol / (1000 g expanded particles), more preferably 0.7 to 4 mol / (1000 g).
(Expanded particles).

In the present specification, the gas amount of the expanded particles (mol / 1000 g expanded particles) is obtained as follows.

[Equation 3] The gas increase amount (g) in the above equation is determined as follows. Taking out 500 or more expanded particles whose internal pressure has been increased by applying gas to the molding machine, move them to a temperature-controlled room at a relative humidity of 50% and atmospheric pressure of 23 ° C. within 60 seconds, and then keep the temperature constant. The weight is put on an indoor scale, the expanded particles are taken out, and the weight after 120 seconds is read. Q at this time
(G). Next, the foamed particles are treated with a relative humidity of 50% and 2
It is left for 240 hours in the same constant temperature room under the atmospheric pressure of 3 ° C.
The high-pressure gas in the expanded particles permeates the bubble film and escapes to the outside with the lapse of time, so the weight of the expanded particles decreases accordingly, and after 240 hours, the equilibrium has been reached, so that the weight is substantially stable. The weight of the expanded particles after 240 hours is measured in the same thermostatic chamber, and the weight at this time is defined as S (g). The weight of any of the above is 0.0
It shall be read to the nearest 001 g. The difference between Q (g) and S (g) obtained by this measurement is defined as the gas increase amount (g) in the equation (5). Further, in the present invention, as another method for obtaining a foamed particle molded body, 0.7 to 4 mol / (100
(0 g foamed particles) A method in which expanded particles containing a gas of 0 g are not compressed or are filled in a mold by a compression ratio of less than 5% by a conventionally known method, and then the expanded particles are heated and fused by a heating medium is also included. To be Expanded particles are 0.7-4 mol /
By containing a gas of (1000 g foamed particles), the expandability of the foamed particles when obtaining a molded product from the expanded particles, the fusion property between the particles, the reproducibility of the mold shape of the molded product, and the dimensional stability are improved. Particularly in the case of expanded particles formed from a resin whose main component is polylactic acid having a heat of fusion of more than 0.1 J / g,
1-4 mol / (1000 g expanded particles), further 1.5-
It is preferable to contain a gas within the range of 4 mol / (1000 g expanded particles). The amount of gas is 0.7 mol / (100
If the amount is less than 0 g expanded particles), the intended effect of the present invention may not be sufficiently achieved, while 4 mol
If it exceeds / (1000 g expanded particles), there is a difficulty in equipment for obtaining the expanded particles. As the gas contained in the foamed particles to be provided in the mold, air, nitrogen, an inorganic gas such as carbon dioxide, or an organic gas such as butane can be used as the gas described above. preferable.

Further, the above-mentioned method of the present invention is extremely effective in in-mold molding of polylactic acid expanded particles exhibiting crystallinity, and a molded product having good fusion property and good appearance can be obtained. In the present specification, the foamed polylactic acid particles exhibiting crystallinity include polylactic acid as a main component having a heat of fusion of more than 0.1 J / g as measured by differential scanning calorimetry, further 1 J / g or more, especially 5 J / g or more. Polylactic acid foam particles (The upper limit of heat of fusion is about 1
00 J / g). Further, in the present specification, the heat of fusion by differential scanning calorimetry: ΔH (J / g)
Is measured in accordance with JIS K7122-1987,
After heating 1 to 3 mg of the foamed particles or the resin particles to 200 ° C. at a temperature rising rate of 10 ° C./min by a differential scanning calorimeter,
DS obtained when the temperature is lowered to 0 ° C. at a rate of 10 ° C./min and is again raised to 200 ° C. at a rate of 10 ° C./min.
It is determined from the endothermic peak area of the C curve. The shape of the expanded particle molded article according to the present invention is not particularly limited, and its shape is
For example, various shapes such as a container shape, a plate shape, a cylinder shape, a column shape, a sheet shape, and a block shape can be used. The expanded particle molded article of the present invention preferably has a density of 0.01 to 0.2 g /
cm ³ and is excellent in dimensional stability and surface smoothness.

In the present specification, the density (g / cm ³ ) of the foamed particle molded body is obtained by dividing the molded body weight WM (g) by the volume VM (cm ³ ) obtained from the outer dimension of the molded body (WM / VM).

[0032]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Examples 1 to 5 Crystalline polylactic acid (Lacty 903 manufactured by Shimadzu Corporation)
0) and talc are melted and kneaded by an extruder, then extruded into a strand shape, and then this strand is rapidly solidified in water at about 25 ° C. and then cut to have a diameter of about 1.3 mm and a length of about 1. 9 mm, and about 3 mg of resin particles were obtained. The talc was added so as to be 2000 ppm. Then, an autoclave having an internal volume of 5 L is
After adjusting to ° C, 1000 g of the resin particles were added.
Carbon dioxide gas was press-fitted into the autoclave through the pressure control valve, the pressure inside the autoclave was adjusted to the pressure shown in Table 1, and the pressure was maintained for 15 hours. Next, the carbon dioxide gas in the autoclave was extracted, and then the resin particles were extracted. Table 1 shows the carbon dioxide impregnation amount of the resin particles. The resin particles impregnated with carbon dioxide gas were filled in a closed container, and then steam was introduced to heat the particles to a temperature shown in Table 1 to obtain expanded and expanded foamed particles. Table 1 shows the density of the expanded beads. The obtained expanded particles were filled in a closed container, and the expanded particles were pressurized with the gas shown in Table 2 under an atmospheric temperature condition of 20 ° C. to give the gas to the expanded particles. The gas impregnation amount of the expanded particles is shown in Table 2. Next, the foamed particles to which the gas was applied were filled in a mold of 200 × 250 × 10 mm so as to have a compression rate shown in Table 2, and heat-molded with steam having a temperature shown in Table 2. The obtained molded body was aged at 30 ° C. for 24 hours. Table 2 shows the densities of the obtained expanded particle molded products.

[0034]

[Table 1]

[0035]

[Table 2]

The internal pressure of the expanded particles shown in Table 1 is calculated by the following formula.

[Equation 4] (However, the increased gas amount indicates the difference between the weight of the expanded particles at the time of measuring the internal pressure and the weight of the expanded particles before the pressure treatment, which is obtained in the same manner as the increased gas amount in the above formula (3), and T is the absolute temperature of the atmosphere. The volume of gas in the expanded particles is a value calculated by the following formula: The gas molecular weight is 44 (g / mol) when the applied gas is CO ₂ and 28.9 (g / mol) when it is air.
And )

[Equation 5]

Examples 6, 7, 9 and Comparative Example 1 Amorphous polylactic acid (Lacty 980 manufactured by Shimadzu Corporation)
0, Tg: 53 ° C.), talc, and a polyisocyanate compound (Millionate MR-200: manufactured by Nippon Polyurethane Industry Co., Ltd.) using a twin-screw extruder at a cylinder temperature of 18
After melt-kneading at 0 ° C, it is extruded into a strand, and then this strand is rapidly cooled and solidified in water at about 20 ° C and then cut to have a diameter of about 1.3 mm, a length of about 1.9 mm, and about 3 mg per piece. Resin particles of The talc was added in an amount of 1% by weight and the polyisocyanate compound was added in an amount of 3% by weight. The polyisocyanate in this case is the compound name polymethylene polyphenyl polyisocyanate. The obtained resin particles were stored for 30 days in an atmosphere of about 30 ° C. and a relative humidity of about 50%. The gel fraction of the resin particles after the storage was 53%. Next, 100 parts by weight of resin particles, 300 parts by weight of water, 0.5 parts by weight of aluminum oxide, and 0.06 parts by weight of sodium dodecylbenzenesulfonate are charged into an autoclave having an internal volume of 5 L, and heated to 110 ° C. with stirring. Then, the temperature was raised, and carbon dioxide was injected and impregnated until the internal pressure of the autoclave reached 4 MPa. Then, after holding at the same temperature for 20 minutes, one end of the autoclave is opened and nitrogen gas is introduced into the autoclave to release the contents under atmospheric pressure while maintaining the pressure inside the autoclave to foam the resin particles. It was The apparent density of the expanded beads was 0.148 g / cm ³ .
The gel fraction of the expanded beads was 60%. The obtained foamed particles were filled in a closed container, pressurized with carbon dioxide under an atmospheric temperature condition of 20 ° C., and impregnated with carbon dioxide to obtain gas-impregnated amounts of the foamed particles shown in Table 2. The foamed particles were filled in a mold of 200 × 250 × 10 mm so as to have the compressibility shown in Table 2, and heat-molded with steam at 118 ° C.
The molded bodies obtained in the examples were aged at 30 ° C. for 24 hours. The obtained expanded particle molded article has a good fusion property,
It had a density shown in Table 2 and a gel fraction of 60%. Example 8 The temperature of carbon dioxide impregnation is 120 ° C. by heating to 120 ° C. with stirring and raising the temperature to inject and impregnate carbon dioxide until the internal pressure of the autoclave becomes 4 MPa.
Then, after holding at the same temperature for 20 minutes, expanded beads were obtained in the same manner as in Example 7 except that the foaming temperature was 120 ° C. by opening one end of the autoclave (gel fraction of expanded particles 60%). . 200 × 250 of the obtained expanded particles
It was filled in a mold of × 10 mm and heat-molded with steam at 118 ° C. The obtained molded body was aged at 30 ° C. for 24 hours.
The obtained expanded bead molded product had a good fusion property, a density of 0.105 g / cm ³ , and a gel fraction of 60%. The gel fraction is measured as follows. (Measurement of Gel Fraction) The gel fraction of the resin particles and the expanded particles in the present specification is measured as follows. About 1 g of resin particles or expanded particles is used as a sample, and the sample weight W2 is weighed. Next, the weighed sample and 100 ml of chloroform were placed in a 150 ml flask and heated to reflux under atmospheric pressure for 10 hours at 62 ° C., and the resulting heat-treated product was sufficiently hot at 50 ° C. or higher. 2 at home
Filtration is performed using a suction filtration device having a 00 mesh wire mesh. The obtained filtered product on the wire net is dried in an oven at 80 ° C. under the condition of 30 to 40 Torr for 8 hours. The dried product weight W1 obtained at this time is measured. The percentage (W1 / W2) × 100% of the weight ratio of the weight W1 to the sample weight W2 is the gel fraction. The measurement of the gel fraction of the foamed particle molded body was performed in the same manner as in the case of the foamed particles except that a rectangular parallelepiped having a length of 5 mm × a width of 5 mm × a height of 5 mm was cut out so as not to include the surface of the molded body and used as a sample for measurement. Measured.

[0038]

According to the production method of the present invention, there is provided a polylactic acid foamed particle molded article having a small density variation in a partial portion, excellent fusion bonding between foamed particles, excellent surface smoothness, and uniform mechanical properties. can get. The expanded particle molded product obtained by the present invention has excellent dimensional stability, appearance, cushioning property and mechanical strength, and is suitably used as a cushioning material, packaging material, etc., and has biodegradability. Its industrial significance is great, such as the easy disposal of

Continued front page    (72) Inventor Masakazu Sakaguchi             10-3 Satsukicho, Kanuma City, Tochigi Prefecture             KSP Kanuma Research Institute (72) Inventor Toshio Tokoro             10-3 Satsukicho, Kanuma City, Tochigi Prefecture             KSP Kanuma Research Institute F-term (reference) 4F074 AA68 BA32 BA33 BA53 BA54                       CA51 CC03X CC04Y DA02

Claims (7)

[Claims] 1. A foamed particle formed of a resin containing polylactic acid as a main component is filled in a mold so as to have a compression ratio of 5 to 70%, and then the foamed particle is heated and fused by a heating medium. A method for producing a polylactic acid expanded particle molded article, which is characterized by the following. 2. The apparent density of the expanded beads is 0.015 to 0.015.
The method for producing a polylactic acid expanded particle molded article according to claim 1, wherein the method is 0.3 g / cm ³ . 3. The expanded particles are 0.3 to 4 mol / (1,
000 g foamed particles). 4. The expanded particles formed from a resin containing polylactic acid as a main component contain 0.7 to 4 mol / (1000 g expanded particles) of gas, and the expanded particles are filled in a mold and then heated by a heating medium. A method for producing a polylactic acid expanded particle molded article, which comprises heating the expanded particles to fuse them. 5. The method for producing a polylactic acid expanded particle molded article according to claim 1, wherein the polylactic acid is obtained by gelling polylactic acid. 6. The method for producing a polylactic acid expanded particle molded article according to claim 1, wherein a heat of fusion of the polylactic acid measured by differential scanning calorimetry exceeds 0.1 J / g. 7. The method for producing a foamed polylactic acid molded article according to claim 3, wherein the gas is carbon dioxide.