JP4917221B2 - Method for producing polylactic acid foamed particle molded body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a molded article of polylactic acid foamed particles having microbial degradability. More particularly, the present invention relates to a method for producing a polylactic acid foamed particle molded body having excellent mechanical properties between foamed particles, small density variation, and uniform mechanical properties.
[0002]
[Prior art]
Foamed particle molded bodies made of resins such as polystyrene, polyethylene, and polypropylene are widely used for packaging cushioning materials, agricultural boxes, fish boxes, automobile members, building materials, civil engineering materials, and the like. However, since these foamed particle molded bodies are hardly decomposed by microorganisms when left in a natural environment after use, there is a risk of causing environmental destruction problems due to dust scattering.
On the other hand, studies have been made on resins that can be decomposed by microorganisms. To date, for example, a biodegradable resin made of polylactic acid has been put into practical use as a surgical suture, and has been used for many years. In recent years, lactic acid, which is a raw material of polylactic acid, can be produced in large quantities and at low cost by fermentation using corn and the like as raw materials.
Therefore, there has been a demand for a foam made of polylactic acid that has a proven record in practicality, human safety and microbial degradability.
As prior art relating to foams made of polylactic acid, there are extrusions such as JP-T-5-508669, JP-A-4-304244, JP-A-5-139435, JP-A-5-140361, JP-A-9-263651, etc. Examples relating to foams and those relating to expanded particles such as JP-A-5-170965, JP-A-5-170966, JP-A-2000-136261 and the like can be mentioned.
In the prior art related to the above-mentioned polylactic acid foam, particularly those related to foamed particles can obtain a foam having a desired shape without being relatively restricted in shape, and according to purposes such as lightness, shock-absorbing property, and heat insulation. Therefore, it is particularly promising as being practical because it is easy to design physical properties.
[0003]
[Problems to be solved by the invention]
However, the conventional foamed particle molded body made of polylactic acid is one in which foamable resin particles are filled in a mold and the resin particles are foamed by hot air and at the same time the particles are fused together. The variation in the density of the part of the particle molded body was large, the fusion property between the expanded particles was insufficient, and the mechanical properties were inferior. Then, this invention makes it the subject to provide the manufacturing method of the polylactic acid foamed particle molded object which has the small density dispersion | variation of a partial part, is excellent in the meltability of expanded particles, and has a uniform mechanical property.
[0004]
[Means for Solving the Problems]
  In order to solve the above-mentioned problems, the present inventors diligently studied a method for producing a polylactic acid foamed particle molded body, and as a result, the present invention has been completed. That is, according to this invention, the manufacturing method of the polylactic acid foamed particle molding shown below is provided.
(1)Crystallinity with heat of fusion exceeding 0.1 J / gExpanded particles formed from a resin based on polylactic acidA method for producing a foamed particle molded body by in-mold molding,  The apparent density of the expanded particles is 0.015 to 0.3 g / cm ³ In addition, the average cell diameter is 10 to 500 μm, the expanded particles contain 0.7 to 4 mol / (1,000 g expanded particles) of gas, and the expanded particles are placed in the mold.A method for producing a molded body of polylactic acid foamed particles, wherein the foamed particles are heated and fused with a heating medium after filling.
(2)The internal pressure of the expanded particles is 2.2 to 4.5 kgf / cm ² (1) The method for producing a polylactic acid foamed particle molded body according to (1).
(3)The method for producing a molded article of polylactic acid foamed particles according to (1) or (2), wherein the foamed particles are filled into a mold so as to have a compression rate of 5 to 70%.
(4) The method for producing a molded article of polylactic acid expanded particles according to any one of (1) to (3), wherein the polylactic acid is obtained by gelling polylactic acid.
(5) The gas is carbon dioxideAny of (1) to (4)The manufacturing method of the polylactic acid foamed-particle molded object as described in 2.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, foamed particles formed from a resin mainly composed of polylactic acid used as a molding material (hereinafter also simply referred to as foamed particles) are foams produced using a resin based on polylactic acid as a base resin. It is manufactured by foaming resin particles.
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 the monomer to be polymerized. For example, (1) a polymer of lactic acid, (2) a copolymer of lactic acid and another aliphatic hydroxycarboxylic acid, and (3) lactic acid, an aliphatic polyhydric alcohol, and an aliphatic polycarboxylic acid. (4) a copolymer of lactic acid and another aliphatic polyvalent carboxylic acid, (5) a mixture of any one of (1) to (4) above, and the like.
[0006]
In the present invention, a biodegradable aliphatic polyester containing at least 35 mol% of an aliphatic ester component can be mixed with polylactic acid. The aliphatic polyester in this case includes a hydroxy acid polycondensate, a lactone ring-opening polymer, a polycondensate of a polyhydric alcohol component and a polycarboxylic acid component, and the like. Examples of the hydroxy acid polycondensate include a polycondensate of hydroxybutyric acid, and examples of the lactone ring-opening polymer include polycaprolactone, and a polycondensate of a polyhydric alcohol component and a polycarboxylic acid component. Examples thereof include polybutylene succinate, polybutylene succinate adipate, poly (butylene adipate / terephthalate), and the like.
The mixing ratio of the biodegradable aliphatic polyester to the polylactic acid is 50% by weight or less, preferably 5 to 30% by weight, based on the total amount of both.
[0007]
In the present invention, when the polylactic acid foamed molded product is required to have heat resistance, it is preferable to use a polylactic acid having a high glass transition temperature (Tg) or a crystalline material having a high melting point (Tm). preferable.
In the present invention, it is preferable to use those having a glass transition temperature of 50 to 65 ° C, more preferably 55 to 65, or a melting point of 130 to 180 ° C, more preferably 140 to 180.
In the present invention, the melting point and glass transition temperature of the base resin are measured according to JIS K 7121-1987.
The melting point of the base resin is the peak apex temperature 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, a straight line that is equidistant from the extended straight line of each baseline in the vertical axis direction, and a step 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 differential scanning calorimetry of the polylactic acid is that the base resin 1-5 mg is heated up to 200 ° C. at a rate of 10 ° C./min with a differential scanning calorimeter (here Then, the obtained DSC curve is referred to as the first DSC curve.) Then, the temperature is lowered from 200 ° C. to 0 ° C. at a temperature lowering rate of 10 ° C./min. Thereafter, the DSC curve obtained by raising the temperature again to 200 ° C. at a rate of temperature increase of 10 ° C./min is the second DSC curve.
Moreover, when two or more peak peak temperatures appear in the base resin, the higher temperature side is defined as the melting point.
[0008]
Specific examples of the polymer of lactic acid include L-lactic acid, D-lactic acid, DL-lactic acid or a mixture thereof, or L-lactide, D-lactide, DL-lactide, which is a cyclic dimer thereof, or A monomer or a dimer polymer composed of a mixture thereof can be exemplified.
[0009]
Specific examples of the method for producing polylactic acid used in the present invention include, for example, direct dehydration polycondensation using lactic acid or a mixture of lactic acid and aliphatic hydroxycarboxylic acid as a raw material (for example, US Pat. No. 5,310, 865), a ring-opening polymerization method for polymerizing a cyclic dimer (lactide) of lactic acid (for example, a production method disclosed in US Pat. No. 2,758,987), lactic acid and fat Ring-opening polymerization method in which a cyclic dimer of an aromatic hydroxycarboxylic acid such as lactide or glycolide and ε-caprolactone is polymerized in the presence of a catalyst (for example, the production disclosed in US Pat. No. 4,057,537) Process), a process of direct dehydration polycondensation of a mixture of lactic acid, aliphatic dihydric alcohol and aliphatic dibasic acid (for example, the production disclosed in US Pat. No. 5,428,126). Method), a method of condensing polylactic acid, 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 producing a polyester polymer by performing a dehydration polycondensation reaction in the presence of a catalyst, a method of performing solid phase polymerization in at least a part of the steps can be exemplified, but the production method is particularly limited. Not. In addition, a small amount of an aliphatic polyhydric alcohol such as glycerin, an aliphatic polybasic acid such as butanetetracarboxylic acid, a polyhydric alcohol such as a polysaccharide may be coexisted and copolymerized. The molecular weight may be increased by using a binder (polymer chain extender) such as a diisocyanate compound.
[0010]
  PoLilactic acid includes crystalline and non-crystalline ones.In the present invention,From the point of heat resistance of the molded product of the obtained expanded particles, crystallineButuseBe done. In particular, when an amorphous material is used, it is preferable from the viewpoint of in-mold moldability of the obtained foamed particles to use a gelled material in advance. In order to gel the polylactic acid, the polylactic acid or a resin containing the polylactic acid as a main component may be gelled. 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, a polyisocyanate crosslinking method, and the like. In the polylactic acid impregnated with the foaming agent in the present invention, the crystallinity is preferably 20% or less, more preferably 10% or less. The crystallinity is measured with an X-ray diffraction apparatus manufactured by Rigaku Denki Kogyo Co., Ltd., and is determined from the ratio between the crystal peak area and 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%.
[0011]
A conventionally known method can be adopted as a method for producing the expanded particles used in the present invention.
In the present invention, in order to preferably produce expanded particles, first, base resin particles are made. The base resin particles can be produced by a conventionally known method. For example, the base resin is melt-kneaded with an extruder, extruded into a strand, cooled, and then cut into an appropriate length or the strand is cut. It can be obtained by cooling to an appropriate length and then cooling. The weight per base resin particle is 0.05 to 10 mg, preferably 1 to 4 mg. When the particle weight 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 may be various shapes such as a spherical shape and a rod shape in addition to a columnar shape (pellet shape).
[0012]
In the step of melt-kneading the base resin with an extruder and extruding it into a strand, it is preferable to dry the base resin in advance if the base resin is hygroscopic. When a resin containing a large amount of water is introduced into the extruder, the foam resin particles may contain bubbles that adversely affect the uniformity of the bubbles in the foam particles, or the properties of the base resin when melted and kneaded with the extruder There exists a possibility that a fall may occur and melt flow rate (MFR) may become extremely large.
In order to suppress the deterioration of the resin, it is also possible to employ a method of removing moisture from the base resin by vacuum suction using an extruder with a vent port.
The extrusion temperature conditions are also set so that the MFR of the base resin does not become extremely large.
[0013]
Next, the foaming resin particles obtained as described above are impregnated with a foaming agent and then foamed.
In this case, the resin particles are impregnated with a foaming agent and then foamed. The resin particles are impregnated with a foaming agent in a sealed container to obtain expandable resin particles, which are then taken out of the sealed container and the resin A method in which the particles are softened by heating and foamed can be preferably employed. As another method, the resin particles are dispersed in a dispersion medium in the presence of a foaming agent in a sealed container, and the contents are heated to soften the resin particles and impregnate the foaming agent in the particles. Next, one end of the container is opened, and while maintaining the internal pressure of the container at a pressure equal to or higher than the vapor pressure of the foaming agent, the particles and the dispersion medium are simultaneously released into an atmosphere at a lower pressure (usually under atmospheric pressure) than in the container to foam For example, a foaming method to be used, a method in which a decomposable foaming agent is kneaded in advance in resin particles, and the resin particles are heated to a temperature equal to or higher than the decomposition temperature of the foaming agent and foamed can be used.
[0014]
When adopting a method of obtaining expanded particles by an extruder, the base resin is melted by using an extruder, kneaded with a foaming agent to form a foamable melt-kneaded product, and then extruded and foamed into a strand shape. The foamed particles can be produced by cutting to an appropriate length after cooling, or by cooling the strand after cutting to an appropriate length.
[0015]
The base resin may be colored by adding a coloring pigment or dye such as black, gray, brown, blue, or green. If the colored base resin is used, colored foamed particles and molded bodies can be obtained.
Examples of the colorant include organic and inorganic pigments and dyes. As such pigments and dyes, various conventionally known pigments can be used.
Moreover, inorganic substances, such as a talc, a calcium carbonate, a borax, zinc borate, aluminum hydroxide, can be previously added to base resin as a bubble regulator, for example. When additives such as color pigments, dyes or inorganic substances are added to the base resin, the additives can be kneaded into the base resin as they are. It is preferable to make it and knead it with the base resin. Although the addition amount of the color pigment or dye varies depending on the color of the color, it is usually preferably 0.001 to 5 parts by weight with respect to 100 parts by weight of the base resin. By adding an inorganic substance to the base resin, an effect of improving the expansion ratio can be obtained.
In the present invention, additives such as flame retardants, antistatic agents, weathering agents and thickeners can be mixed.
[0016]
Assuming that the product is discarded after use, it is not preferable to add additives such as pigments and bubble regulators.
Moreover, when obtaining expanded particles through the expanded resin particles, the obtained expanded resin particles are preferably stored in an environment in which hydrolysis does not proceed. Similarly, the expanded particles are preferably stored in an environment where hydrolysis does not proceed.
[0017]
As the foaming agent used for obtaining the foamed particles, conventionally known ones such as propane, butane, hexane, cyclobutane, cyclohexane, trichlorofluoromethane, dichlorodifluoromethane, chlorofluoromethane, trifluoromethane, 1,1 Organic physical foaming agents such as 1,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, 1-chloro-1,2,2,2-tetrafluoroethane, Inorganic physical foaming agents such as nitrogen, carbon dioxide, argon, and air are used. Among them, an inorganic physical foaming agent that does not destroy the ozone layer and is inexpensive is preferable, and nitrogen, carbon dioxide, and air are particularly preferable. . In the present invention, carbon dioxide is more preferred from the viewpoint of obtaining foam particles having a smaller apparent density with respect to the amount of foaming agent used.
[0018]
When foaming resin particles are prepared in advance and the foaming resin particles are impregnated with a foaming agent, the resin particles are placed in a sealed container and the foaming agent is added in an amount of 5 to 100 kgf / cm.²What is necessary is just to press-fit in an airtight container so that it may become the pressure range of G. The amount of the foaming agent used is appropriately selected from the relationship between the apparent density of the desired foamed particles and the foaming temperature.
[0019]
Further, in the method of placing the foaming resin particles in a sealed container, bringing the foaming agent into contact with the foaming agent for a predetermined time to impregnate the foam in the particles, and then removing the resin particles from the sealed container to obtain foamable resin particles. The impregnation with the foaming agent is preferably carried out at a temperature lower than the glass transition temperature of the base resin. The impregnation temperature of the foaming agent is preferably 5 to 60 ° C, more preferably 5 to 40 ° C. In addition, the pressure of the foaming agent during the impregnation varies depending on the foaming ratio of the target foamed particles, but is usually 5 to 100 kgf / cm.²G and the impregnation time is 10 minutes to 24 hours. In particular, when carbon dioxide is used for the foaming agent, the carbon dioxide impregnation amount is usually 2.5 to 30% by weight, preferably 3 to 20% by weight.
In this case, the carbon dioxide impregnation amount is expressed by the following equation.
[Expression 1]
Carbon dioxide impregnation amount (% by weight) = A / (A + B) × 100
A: Weight of carbon dioxide impregnated in resin particles
B: Weight of resin particles before carbon dioxide impregnation
[0020]
A in the above formula is obtained by subtracting the weight of the resin particles before impregnation with carbon dioxide from the weight of the carbon dioxide-impregnated resin particles. It should be noted that any of the above weights for calculating the impregnation amount is measured to the order of 0.0001 g.
Examples of the heating medium for heating and foaming the expandable resin particles impregnated with the foaming agent include water vapor, heat-adjusted air, nitrogen, and the like, but usually water vapor is used. As a method of heating and foaming the expandable resin particles, a conventionally known method can be adopted. Usually, the container is filled with expandable resin particles, and steam is introduced to cause foaming. In addition, if the airtight container is provided with an opening valve that slightly leaks the internal pressure, the air in the container can be excluded, and it is easy to obtain expanded particles having a uniform density.
The temperature at which the resin particles impregnated with the foaming agent are heated, 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. −20 ° C.) to (glass transition temperature + 40 ° C.). When the foaming temperature is lower than the above range, sufficient foaming is difficult to occur. When the foaming temperature is higher than the above range, the closed cell ratio of the foamed particles is lowered, and it is difficult to obtain a good molded product.
[0021]
  The expanded particle in the present invention has an apparent density of 0.015 to 0.3 g / cm.³InR0.015-0.2 g / cm³BePreferGood. When the density is larger than the above range, the variation in the density of the expanded particles tends to be large, and the physical properties of the expanded molded particles that can lead to variations in the expandability and fusion properties of the expanded particles when heat-molded in the mold. There is a risk of decline. On the other hand, when the ratio is smaller than the above range, the foaming ratio is relatively high, and thus there is a possibility that the molded article has a large molding shrinkage.
[0022]
In the present specification, the apparent density of the expanded particles is a graduated cylinder containing ethanol at 23 ° C., and more than 500 expanded particles left in the graduated cylinder for 2 days under the conditions of relative humidity 50%, 23 ° C. and 1 atm. Particles (weight W1 of the expanded particle group) are sunk using a wire mesh or the like, and the volume V1 (cm^Three) By dividing the weight W1 (g) of the expanded particle group placed in the graduated cylinder (W1 / V1).
The bulk density of the expanded particles of the present invention is 0.01 to 0.2 g / cm.^ThreePreferably, 0.01 to 0.12 g / cm^ThreeIt is more preferable that
[0023]
In the present specification, the bulk density of the foamed particles is determined by preparing an empty graduated cylinder and leaving it in the graduated cylinder at a relative humidity of 50%, 23 ° C., and 1 atm for 2 days. Volume V2 (cm)^Three) By dividing the weight W2 (g) of the expanded particle group placed in the graduated cylinder (W2 / V2).
[0024]
Furthermore, the average cell diameter of the expanded particles in the present invention is 10 to 500 μm, preferably 30 to 400 μm. When the bubble diameter is smaller than the above range, the film strength is too weak at the time of the heat molding of the present invention, resulting in foam breakage or the like, resulting in a molded article with poor curing recovery. On the other hand, if the bubble diameter is larger than the above range, the film strength is too strong at the time of heating and foaming, so that sufficient expansion does not occur and the molded article has poor surface smoothness.
In the present specification, the average cell diameter of the expanded particles is obtained by dividing the expanded particles into approximately two parts, obtaining the maximum diameter of all the bubbles present in the expanded particle cross section, and performing this operation on 10 or more expanded particles. The arithmetic average value of the maximum diameter is defined as the average bubble diameter.
[0025]
  In order to produce a foamed particle molded body in the present invention, the foamed particles are placed in a mold.Preferably5-70%,ThanPreferably, the filler is filled so as to have a compression rate of 15 to 70%, more preferably 30 to 70%, and then the foamed particles are heated with a heating medium to perform molding. In particular, in the case of foamed particles formed from a resin mainly composed of polylactic acid having a heat of fusion exceeding 0.1 J / g, it is filled in a mold so as to have a compression rate of 15 to 70%, and is heat-molded. It is preferable to do. By this heat forming, the expanded particles are strongly fused to each other, and the integrated density variation is small, giving a foamed molded article having a good appearance. As a mold for molding in this case, a conventional mold or a steel belt used in a continuous molding apparatus described in JP 2000-15708 is used. As the heating means, steam heating is usually used, and the heating temperature may be a temperature at which the surface of the expanded particles melts. In the present invention, at the time of molding, the foamed particles are filled into the mold so that the compression rate is 5 to 70%. In particular, when the polylactic acid is crystalline, if the compression ratio is less than 5%, there is a possibility that the molded body has a poor fusion property and a surface smoothness. On the other hand, if it exceeds 70%, the fusion property inside the molded product tends to be inferior, and it is out of the gist of weight reduction, which is a characteristic of foamed products. In addition, there is a difficulty in equipment installation.
[0026]
The compression rate referred to in the present invention is expressed as follows. The compressibility can be expressed by the relationship between the inner volume of the mold and the bulk volume in the atmosphere of the expanded particles filled in the mold.
[Expression 2]
Compression rate (%) = (A−B) × 100 / A (2)
A: Bulk volume (cm) in the atmosphere of expanded particles filled in the mold^Three)
B: Inner volume of the mold (cm^Three)
A in the above formula represents the weight (g) of the expanded particles filled in the mold, and the bulk density (g / cm) of the expanded particles.^Three).
[0027]
In the present invention, a conventionally known filling method can be employed particularly when the foamed particles are filled in the mold so as to achieve the compression rate. Examples of such a method include 1) cracking method, 2) pressure filling method, and 3) compression filling method.
1) The cracking method is a method in which the raw material beads are mechanically conveyed and filled by an injector in a state where the raw material bead container and the cavity are opened to communicate with atmospheric pressure, and then the mold is clamped. 2) In the pressure filling method, the inside of the raw material bead container is 0.2 to 1.5 kg / cm.²In this method, the cavity is pressurized to about G and released into the atmospheric pressure through the chamber using the differential pressure. 3) In the compression filling method, the pressure p in the raw material bead container is pressurized at a pressure higher than that in the pressure filling method, the inside of one chamber is pressurized, and the difference in the cavity pressure p1 communicated through the vent hole This is a method of conveying and filling the raw material beads by changing the pressure (p-p1). Since the raw material beads are sent in a compressed state, the filling property is excellent.
[0028]
  In the present invention, the foam particles provided in the mold together with the method of filling the foam particles in the mold so as to achieve the above-mentioned compressibility include inorganic gas such as air, nitrogen and carbon dioxide, particularly carbon dioxide as a gas. It is preferable to keep it. An organic gas such as butane can also be used. By using the expanded particles to which gas has been added as the expanded particles for molding, the expandability at the time of forming the expanded particles, the fusion between the particles, the mold shape reproducibility and the dimensional stability of the molded body are improved. The gas is, 0. It is applied within a range of 7 to 4 mol / (1000 g expanded particles).
[0029]
In addition, in this specification, the gas amount (mol / 1000g expanded particle) of an expanded particle is calculated | required as follows.
[Equation 3]
The amount of gas increase (g) in the above formula is determined as follows.
500 or more foamed particles whose internal pressure has been increased by applying a gas filled in the molding machine are taken out and moved to a constant temperature room under an atmospheric pressure of 23% and a relative humidity of 50% within 60 seconds. Place on a balance in the room, take out the foamed particles and read the weight after 120 seconds. The weight at this time is defined as Q (g). Next, the foamed particles are left for 240 hours in the same constant temperature room at a relative humidity of 50% and an atmospheric pressure of 23 ° C. Since the high-pressure gas in the expanded particles permeates the bubble membrane and escapes to the outside as time passes, the weight of the expanded particles decreases accordingly, and after 240 hours, the weight has reached equilibrium. stable. The weight of the expanded particles after 240 hours is measured in the same constant temperature room, and the weight at this time is defined as S (g). Any of the above weights shall be read to the order of 0.0001 g. The difference between Q (g) and S (g) obtained by this measurement is defined as the amount of gas increase (g) in equation (5).
Further, as another method for obtaining a foamed particle molded body in the present invention, foamed particles containing a gas of 0.7 to 4 mol / (1000 g foamed particles) are not compressed or the compression rate is less than 5% in the mold. There is also a method in which the foamed particles are heated and fused by a heating medium after filling by a conventionally known method. When the foamed particles contain a gas of 0.7 to 4 mol / (1000 g foamed particles), the expandability of the foamed particles when the molded product is obtained from the foamed particles, the fusibility between the particles, and the mold shape reproduction of the molded product And dimensional stability are improved. In particular, in the case of expanded particles formed from a resin mainly composed of polylactic acid having a heat of fusion exceeding 0.1 J / g, 1 to 4 mol / (1000 g expanded particles), and further 1.5 to 4 mol / (1000 g expanded particles) It is preferable that gas is included within the range of When the amount of gas is less than 0.7 mol / (1000 g foamed particles), the intended effect of the present invention may not be sufficiently achieved, while when the amount exceeds 4 mol / (1000 g foamed particles). This is accompanied by difficulties in obtaining the foamed particles.
Examples of the gas contained in the expanded particles provided in the mold include air, inorganic gas such as nitrogen and carbon dioxide, or organic gas such as butane, similar to the gas described above, and inorganic gas, particularly carbon dioxide. preferable.
[0030]
In addition, the above-described method of the present invention is extremely effective in molding in-mold polylactic acid expanded particles exhibiting crystallinity, and it is possible to obtain a molded product having good fusion property and appearance. In the present specification, polylactic acid foamed particles exhibiting crystallinity have a heat of fusion of more than 0.1 J / g by differential scanning calorimetry, more preferably 1 J / g or more, particularly 5 J / g or more. Polylactic acid foam particles (the upper limit of the heat of fusion is approximately 100 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, and 1 to 3 mg of foamed particles or resin particles is 10 ° C./min by a differential scanning calorimeter. The DSC curve endotherm obtained when the temperature was increased to 200 ° C. at a temperature increase rate of 10 ° C./minute, the temperature was decreased to 0 ° C. at a temperature decrease rate of 10 ° C./minute, and was again increased to 200 ° C. It is obtained from the peak area.
The shape of the foamed particle molded body according to the present invention is not particularly limited, and the shape may be various shapes such as a container shape, a plate shape, a cylindrical shape, a column shape, a sheet shape, and a block shape. The foamed particle molded body of the present invention preferably has a density of 0.01 to 0.2 g / cm.^ThreeIt is excellent in dimensional stability and surface smoothness.
[0031]
In the present specification, the density (g / cm of the expanded particle molded body)^Three) Is the volume VM (cm^Three) Is a value obtained by dividing the compact weight WM (g) by (WM / VM).
[0032]
【Example】
Next, the present invention will be described in more detail with reference to examples.
[0033]
Examples 1 to 5
Crystalline polylactic acid (Lacty 9030 manufactured by Shimadzu Corporation) and talc are melt-kneaded with an extruder, extruded into a strand, and then the strand is rapidly cooled and solidified in water at about 25 ° C. and then cut. About 1.3 mm in diameter, about 1.9 mm in length, and about 3 mg of resin particles per one piece were obtained. In addition, talc was added so that it might become 2000 ppm.
Next, an autoclave having an internal volume of 5 L was adjusted to 10 ° C., and then 1000 g of the resin particles were added. Carbon dioxide gas was injected into the autoclave through the pressure adjustment valve, and the pressure in the autoclave was adjusted to the pressure shown in Table 1 and maintained for 15 hours. Next, after removing carbon dioxide in the autoclave, resin particles were taken out. Table 1 shows the carbon dioxide impregnation amount of the resin particles.
The resin particles impregnated with the carbon dioxide gas were filled in a sealed container, and then steam was introduced and heated to the temperature shown in Table 1 to obtain expanded and expanded foam particles. Table 1 shows the density of the expanded particles.
The obtained foamed particles were filled in a sealed container, and the foamed particles were pressurized with the gas shown in Table 2 under an atmospheric temperature condition of 20 ° C. to give the gas to the foamed particles. Table 2 shows the gas impregnation amount of the expanded particles. Next, the foamed particles to which the gas was applied were filled in a 200 × 250 × 10 mm mold 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 cured at 30 ° C. for 24 hours. The density of the obtained foamed particle molded body is shown in Table 2.
[0034]
[Table 1]
[0035]
[Table 2]
[0036]
The internal pressure of the expanded particles shown in Table 1 is calculated by the following formula.
[Expression 4]
(However, the increased gas amount indicates the difference between the expanded particle weight at the time of measuring the internal pressure and the expanded particle weight before pressure treatment, which is obtained in the same manner as the increased gas amount in the above formula (3). The gas volume in the expanded particles is a value calculated by the following formula: The gas molecular weight is the same as that of the added gas.₂44 (g / mol) in the case of air and 28.9 (g / mol) in the case of air. )
[Equation 5]
[0037]
Reference examples 1, 2, 4Comparative Example 1
  Non-crystalline polylactic acid (Lacty 9800, manufactured by Shimadzu Corporation, Tg: 53 ° C.), talc, and polyisocyanate compound (Millionate MR-200: manufactured by Nippon Polyurethane Industry Co., Ltd.) are cylinders using a twin screw extruder. After melt-kneading at a temperature of 180 ° C., it is extruded into a strand, and then the strand is quenched and solidified in water at about 20 ° C. and then cut to obtain a diameter of about 1.3 mm, a length of about 1.9 mm, and a length of about 1 per piece. 3 mg of resin particles were obtained. The talc was added at 1% by weight and the polyisocyanate compound was added at 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, an autoclave having an internal volume of 5 L is charged with 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, and heated to 110 ° C. with stirring. The temperature was raised and carbon dioxide was injected and impregnated until the internal pressure of the autoclave reached 4 MPa. Then, after maintaining at the same temperature for 20 minutes, one end of the autoclave is opened, nitrogen gas is introduced into the autoclave, and the contents are released under atmospheric pressure while maintaining the pressure in the autoclave to foam the resin particles. It was. The apparent density of the expanded particles is 0.148 g / cm.³Met. The gel fraction of the expanded particles was 60%. The obtained expanded particles were filled in a sealed container, pressurized with carbon dioxide under an atmospheric temperature condition of 20 ° C., and impregnated with carbon dioxide to obtain expanded particles having a gas impregnation amount shown in Table 2. The foamed particles were filled in a 200 × 250 × 10 mm mold so as to have the compression rate shown in Table 2, and heat molded with steam at 118 ° C. The molded bodies obtained in the examples were cured at 30 ° C. for 24 hours. The obtained foamed particle molded body had good fusion properties, had the density shown in Table 2, and had a gel fraction of 60%.
Reference example 3
  After heating to 120 ° C. with stirring and heating, carbon dioxide was injected and impregnated until the internal pressure of the autoclave reached 4 MPa, so that the carbon dioxide impregnation temperature was 120 ° C. and held at the same temperature for 20 minutes, Except for setting the foaming temperature to 120 ° C by opening one end of the autoclaveReference example 4In the same manner, foamed particles were obtained (the gel fraction of the foamed particles was 60%). The obtained foamed particles were filled into a 200 × 250 × 10 mm mold and heat-molded with water vapor at 118 ° C. The obtained molded body was cured at 30 ° C. for 24 hours. The obtained foamed particle molded article has a good fusion property and has a density of 0.105 g / cm.³The gel fraction was 60%.
  The gel fraction was measured as follows. (Measurement of gel fraction) The measurement of the gel fraction of the resin particles and the expanded particles in the present specification is measured as follows. Using about 1 g of resin particles or expanded particles as a sample, the sample weight W2 is weighed. Next, a weighed sample and 100 ml of chloroform are placed in a 150 ml flask and heated and refluxed at 62 ° C. for 10 hours under atmospheric pressure. Filtration is performed using a suction filtration device having a 200 mesh wire net. The obtained filtered product on the wire mesh is dried in an oven at 80 ° C. under a condition of 30 to 40 Torr for 8 hours. The dry matter weight W1 obtained at this time is measured. The percentage of the weight ratio of the weight W1 to the sample weight W2 (W1 / W2) × 100% is taken as the gel fraction. The measurement of the gel fraction of the foamed particle molded body is the same as that of the foamed particle except that a plurality of rectangular parallelepipeds of 5 mm in length, 5 mm in width and 5 mm in height are cut out so as not to include the surface of the molded body and used as a measurement sample. Measured.
[0038]
【The invention's effect】
According to the production method of the present invention, it is possible to obtain a polylactic acid foamed particle molded body having a small density variation in the partial portion, excellent fusion property between the foamed particles and surface smoothness, and uniform mechanical properties.
The foamed particle molded body obtained by the present invention is excellent in dimensional stability, appearance, cushioning and mechanical strength, and is suitably used as a cushioning material, packaging material, etc. and has biodegradability thereafter. The industrial significance, such as the easy disposal of wastewater, is enormous.

Claims (5)

A method for producing a foamed particle molded body by in-mold molding foamed particles formed from a resin mainly composed of crystalline polylactic acid having a heat of fusion of 5 J / g or more ,
The apparent density of the expanded particles is 0.015 to 0.3 g / cm ³ and the average cell diameter is 10 to 500 μm.
The expanded particles contain 0.7-4 mol / (1,000 g expanded particles) of gas,
A method for producing a molded article of polylactic acid foamed particles , comprising filling the foamed particles in a mold and then heating the foamed particles with a heating medium and fusing them. The internal pressure of the expanded particles is 2.2 to 4.5 kgf / cm ² The method for producing a molded body of polylactic acid expanded particles according to claim 1, wherein: The method for producing a molded body of polylactic acid expanded particles according to claim 1 or 2, wherein the expanded particles are filled in the mold so as to have a compression rate of 5 to 70%.   The method for producing a molded article of polylactic acid expanded particles according to any one of claims 1 to 3, wherein the polylactic acid is obtained by gelling polylactic acid. The method for producing a molded article of polylactic acid expanded particles according to any one of claims 1 to 4 , wherein the gas is carbon dioxide.