JP2003082150A - Polylactic acid expandable resin particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic acid expandable particle not restricting the kind of a usable foaming agent, and the foaming agent being impregnated to the polylactic acid resin particle in a water suspension system or in a mixed system with water, and capable of obtaining the expanded particle having a proper cell size after the expansion molding without using a foaming core agent. SOLUTION: This polylactic acid expandable resin particle is obtained in the water suspension system or in the mixed system of 100 pts.wt. polylactic acid resin composition and 1-50 pts.wt. water, by impregnating not less than 3 wt.% foaming agent to the polylactic acid resin composition, then by drying, and the polylactic acid expandable resin particle with a residual water content of not greater than 0.5% has 5,000-30,000 minute pores of 1 μm-10 μm diameter per 1 mm<2> of its cross section.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to polylactic acid-based expandable resin particles. More specifically, the type of foaming agent used is not limited, and impregnation of the polylactic acid-based resin composition with the foaming agent is performed in a water suspension system or a mixed system in which water is mixed, and foaming is performed. The present invention relates to a polylactic acid-based expandable resin particle capable of obtaining a foamed molded article having a fine and highly uniform cell size after foaming without adding a nucleating agent.

[0002]

2. Description of the Related Art A large amount of plastic foams, which are lightweight, cushioning and molding processable, are used in many applications such as packing materials for home appliances, construction boards and heat insulation blocks, fish boxes, etc. There are various types such as heat-insulating containers, cups for instant food, and buried blocks in civil engineering works such as roads.
However, the material is a chemical product mainly made of petroleum such as polystyrene and polyolefin, and when burned, it burns a lot of calories and damages the incinerator. Disposal after use is extremely difficult, such as difficulty in securing it, which is a major social problem. In addition, the impact on natural systems such as pollution of rivers and oceans caused by foamed moldings that are not disposed of is beginning to stand out. Therefore, polyhydroxybutyrate-based resins synthesized in the body of microorganisms, polyesters composed of aliphatic glycol and aliphatic carboxylic acids or polyester-based resins containing caprolactone as the main component decompose in the ecosystem and A biodegradable resin has been developed that has few adverse effects. However, the former has a low purity and is extremely poor in productivity because it is produced by microorganisms, and its use is limited. And the latter has good productivity because raw materials such as oil and natural gas are cheap and available in large quantities.
Since it is a crystalline resin and has a low glass transition point, it is not practical as a biodegradable foamed resin. Furthermore, because it uses petroleum and natural gas as raw materials, it generates carbon dioxide gas after decomposition,
It has many environmental impacts. From such a viewpoint, in recent years, expandable resin particles mainly composed of polylactic acid and foams thereof have been attracting attention. This polylactic acid-based foam is mostly decomposed by microorganisms, has very little adverse effect on the environment even after disposal after use, and is inexpensive and has high productivity and practicality. Conventional foams such as the foams can be conveyed to a processor in the form of expandable particles, the expanders can pre-expand the foamed particles, and the resulting expanded particles can be molded into a frame. It also has the advantage of.

The following techniques are known for polylactic acid-based expandable particles or polylactic acid-based expandable resin compositions. For example, in Japanese Patent Laid-Open No. 2000-17039, the molar ratio of L-form to D-form is 95/5 to 60/40, or 40/60 to 5/95, and the melt viscosity is in the range of 1 to 10 in melt index value. In the linear polylactic acid in Table 1, 0.7 to 5% by weight of a polyisocyanate compound having an isocyanate group of ≧ 2.3 equivalents / mole is blended with respect to the polylactic acid, and the melting temperature of the reacted resin composition is Disclosed is a biodegradable foamable resin composition having a melt index value (MI) of 3 or less. Among them, L body and D body are 90/10 to 70/30, or 30 /
It has a molar ratio of 70 to 10/90 and a linear polylactic acid of 1
It is preferable that the compound has an MI of from 5 to 5, and that the isocyanate compound has an isocyanate group ≧ 2.7 equivalents / mole, and the compounding amount thereof is 1 to 3% by weight. A further preferred embodiment describes that the biodegradable foamable resin composition has an MI of 0.5 or less. As described above, the publication describes the composition of a resin composition capable of forming a foamable resin composition, and further, in Examples, impregnation of a foaming agent into a polylactic acid resin composition is performed in a non-aqueous system. It is being appreciated. It is also preferable to add a foaming nucleating agent in order to form an appropriate cell. Further, JP-A-8-253617 discloses that a lactic acid-based polyester copolymer having a weight average molecular weight of 20,000 to 400,000 and containing a lactic acid component, a dicarboxylic acid component and a diol component as structural units absorbs a volatile compound. Expandable particles of lactic acid-based polyester are disclosed.
Among them, it is preferable that a lactic acid-based polyester copolymer having a weight average molecular weight of 20,000 to 400,000 and containing a lactic acid component, a dicarboxylic acid component and a polyoxyalkylene ether diol component as a structural unit absorbs a volatile compound. The expandable particles of lactic acid-based polyester are preferable, wherein the weight ratio of the lactic acid component in the lactic acid-based polyester is 50 to 98% of that of the lactic acid-based polyester. Furthermore, the volatile compounds used are preferably pentane, butane and propane, or mixtures thereof. As the method for producing expandable particles of lactic acid-based polyester, particles are obtained by cooling lactic acid-based polyester dissolved in an organic solvent, and further absorbing volatile compounds, or crushing lactic acid-based polyester. The method is characterized in that particles are obtained by the above method, and the volatile compound is further absorbed, the lactic acid-based polyester and the volatile compound are kneaded in an extruder, then extruded, and then cut. Alternatively, a method in which a lactic acid-based polyester and a volatile compound are kneaded and then extruded into a pressurized liquid through an extrusion hole of a die head, immediately cut, and then cooled is also mentioned. More specifically, the lactic acid-based polyester, the volatile compound, and 1.5 parts by weight or less of the inorganic powder with respect to 100 parts by weight of the lactic acid-based polyester are kneaded and then mixed in a pressurized liquid through an extrusion hole of a die head. Extruded into
One of the preferred embodiments is a method of immediately cutting and then cooling. As another preferable method for producing the expandable particles of lactic acid-based polyester, the lactic acid-based polyester, a volatile compound, and optionally an inorganic powder are kneaded, and then the lactic acid-based polyester is extruded through an extrusion hole of a die head to obtain an expandable lactic acid-based polyester. Examples include a method of extruding into a heated and pressurized liquid having a glass transition temperature of −5 ° C. or higher and cutting and gradually cooling particles obtained in the heated and pressurized liquid, or holding the particles at the same temperature or higher and then cooling. There is. As described above, this publication describes the composition of the expandable particles of lactic acid-based polyester and the method for producing the expandable particles.

The process in which a polylactic acid resin composition is impregnated with a foaming agent to form expandable resin particles and then pre-expanded to form a foamed molded article is greatly different from that of the polystyrene resin composition in the following points. There is. Usually, in the case of forming polystyrene-based expanded particles, in order to obtain fine and highly appropriate cells, a polystyrene resin composition is impregnated with a foaming agent to form expandable resin particles, and then aged. It is important to do. When a polystyrene resin composition is impregnated with a foaming agent to form expandable resin particles, and then foamed after aging at room temperature or at a temperature of 20 ° C. or less for several days or more, good expansion of several hundred μm or less in the expanded particles is achieved. The cells are formed, and it becomes a good expanded particle which is expanded to a ratio according to the amount of the foaming agent added. On the other hand, in the case of a polylactic acid-based resin composition, the cell size is hardly changed even if it is aged after being impregnated with a foaming agent, and its homogenization is not achieved. For example, at room temperature or at a temperature of 20 ° C. or lower. It is difficult to form fine and proper cells with high uniformity even when foaming is performed after long-term aging for 10 days or more. Further, the glass transition temperature of the polylactic acid-based resin composition is the glass transition temperature of the polystyrene-based resin composition (100 to 110).
40 ° C. or more (50 to 60 ° C.) lower than (° C.), and when the foaming agent is further impregnated, the temperature drops to near room temperature. When the polylactic acid-based expandable resin particles having a low glass transition temperature are foamed with water vapor as described above, foaming occurs in an extremely short time, but the inside of the resin particles becomes hollow, and the expanded particles have an extremely distorted shape. It causes problems such as significant shrinkage after completion. As a result, fine and highly uniform cells are hardly formed, and it is completely impractical as a foam product. Further, even if water is present in the system of impregnating the polystyrene resin composition with a foaming agent, the obtained polystyrene expandable resin particles have no hindrance to the foaming process,
A good foam is formed. However, when water is present in the step of impregnating the polylactic acid-based resin composition with the foaming agent, the polylactic acid-based expandable resin particles after the impregnation have little or no change even if the temperature or heating condition in the foaming step is changed. No foaming occurred and it was virtually impossible to obtain a foam. In order to solve such a problem, when a polylactic acid-based resin composition is used, the method of impregnating the resin composition with a foaming agent is a non-aqueous method to further form a highly uniform and proper cell. In order to achieve a high expansion ratio and to form cells with high uniformity, use of a specific foaming agent / foaming auxiliary agent has been devised so far. It was

Due to such a technical background, the above-mentioned Japanese Unexamined Patent Publication No. 2
000-17039 and JP-A-8-253617, as well as JP-A-2000-17038 and JP-A-2
000-17039, JP 2001-98104.
Also in the technique disclosed in the publication, the method of impregnating the foaming agent with the polylactic acid resin composition is non-aqueous. Further, a butane compound, for example, a hydrocarbon compound having 3 to 4 carbon atoms such as n-butane and isobutane disclosed in JP 2001-164027 A is used as a foaming agent, and together with this, a foaming aid is an essential component. The technique for producing expandable particles by impregnating a biodegradable resin composition specifies the type of foaming agent / foaming aid to be used. Further, these publications mentioned above make it essential or preferable to add a cell forming agent (nucleating agent) in order to form a proper cell.

[0006]

However, when the method of impregnating the polylactic acid resin composition with the foaming agent is a non-aqueous method,
There are the following problems. The polylactic acid-based resin composition is directly impregnated with a foaming agent or the like. However, in order to carry out the impregnation efficiently, the temperature is raised to the glass transition temperature of the polylactic acid-based resin composition or higher. Needs to be softened so that the foaming agent can easily impregnate the resin composition. However, when the temperature during impregnation is set to be equal to or higher than the glass transition temperature, the polylactic acid-based resin composition is softened and at the same time, the foaming agent is easily mixed with the resin composition and easily swells. The resin compositions tend to adhere to each other again and become so-called agglomerates. Some of these agglomerates may cause troubles such as clogging of the pipeline during granulation in the process from foaming to molding, and when these agglomerates increase, the foaming agent During the impregnation, the polylactic acid resin composition may be completely solidified. Further, if high foaming efficiency and miniaturization / uniformity of cells after foaming are required in the foaming process, usable foaming agents are limited to hydrocarbons having 3 to 4 carbon atoms, such as butane, and there is room for selection. Is virtually eliminated, and the addition of a foaming auxiliary is indispensable. In the case of butane, etc., it is a gas at room temperature, so there is a problem in handling, and since the pressure increases during heating during impregnation, a more pressure-resistant impregnation tank is required. However, it is not preferable. Furthermore, in order to obtain a proper cell, it is necessary to add a large amount of nucleating agent such as talc, which deteriorates the surface appearance of the foamed molded product, and further, the fusion property between cells inside the molded product is significantly reduced. Let In addition, the manufacturing process is also complicated, and the productivity is not satisfactory.
Thus, the means for obtaining a foam by impregnating a polylactic acid-based resin composition with a foaming agent in a non-aqueous system leaves many problems, and is a foamed particle having good cells with fine and high uniformity,
In addition, it is difficult to say that it is sufficient to efficiently form a foam-molded article having a beautiful surface appearance.

On the other hand, as an example of impregnating a resin composition with a foaming agent in an aqueous system, JP-A-9-124 by the present inventors is known.
No. 831, the number and size of the micropores present in the cut surface of the expandable styrenic resin particles are within a certain range, and the resin particles are contained in a glass cell having a thickness of 10 mm together with water as a medium. There is a relationship between the absorbance measured for light that is transmitted and scattered through the sample using a filled sample and a transmission integrating sphere, and the average particle size of the resin particles, expressed by a certain equation. It is disclosed that, when established, the pre-expanded particles obtained therefrom can form a uniform and good cell structure without addition of a special cell-forming agent and without further aging treatment.
However, the technique disclosed in the above publication is intended for the polystyrene resin composition as described above, and the disclosed technique is not always applied to the polylactic acid resin composition as it is. . Then, Japanese Unexamined Patent Publication No. 2000
JP-A-17038, JP 2001-98104 A, JP 2001-164027 A disclose a resin composition or foamed particles that can be used as a foamable resin composition, a foamed molded article formed of them, or a method for producing them. The above-mentioned Japanese Patent Laid-Open No. 8-2536
No. 17, JP-A-2000-17039 discloses the composition of the resin or foaming agent in the polylactic acid-based expandable resin composition or the polylactic acid-based expandable resin particles, but the inside of the expandable resin particles The structure is not described or suggested at all. The present invention has been made in view of the above circumstances, and the subject is to impregnate a polylactic acid resin composition with a foaming agent in an aqueous suspension system or a mixed system in which water is mixed. And the subsequent foaming is performed without any limitation on the type of the foaming agent used, and a highly practical foamed molded product having fine and highly uniform cells after foam molding is used as a nucleating agent. It is to provide polylactic acid-based expandable resin particles that can be obtained without addition.

[0008]

[Means for Solving the Problems]
As a result of various studies, in a water suspension system or a mixed system in which water is mixed, a polylactic acid-based resin composition is impregnated with a foaming agent, and water contained in a trace amount in the polylactic acid-based expandable resin particles obtained thereafter, Specifically, by appropriately removing the water filled in the fine pores in the resin particles, it is possible to obtain expandable resin particles that can solve the above problems, and after foaming, it is fine and uniform. It was found that the foamed particles had a proper cell with a high value. Specifically, in foaming the above-mentioned polylactic acid-based expandable resin particles, good expanded particles can be formed regardless of the type of the foaming agent,
Furthermore, they succeeded in obtaining fine and highly expanded foamed particles having an appropriate cell size without adding a nucleating agent such as talc, and reached the present invention.

That is, according to the present invention, the cut surface of the polylactic acid-based expandable resin particles containing the foaming agent in an amount of 3% by weight or more based on the polylactic acid-based resin composition has 5,000 to 30,000 fine pores per 1 mm ^{2 in} sectional area. The present invention relates to a polylactic acid-based expandable resin particle characterized by being present individually. A preferred embodiment of the present invention is a mixed system of a polylactic acid resin composition and water, wherein 1 part of water is added to 100 parts by weight of the polylactic acid resin composition.
Polylactic acid-based expandable resin particles obtained by impregnating the polylactic acid-based resin composition with a foaming agent in an amount of 3 parts by weight or more in an amount of 3 parts by weight or more, and then drying, and having a residual water content of 0.5. % Or less, the cut surface of the polylactic acid-based expandable resin particles is characterized by having 5,000 to 30,000 fine pores per 1 mm ^{2 in} cross-sectional area. Furthermore, the micropores are characterized by having an average diameter of 1 μm to 10 μm. Another preferable aspect of the present invention is that the polylactic acid-based resin composition comprises polylactic acid having a molar ratio of L-form and D-form of 95/5 to 60/40, or 40/60 to 5/95, and an isocyanate. A polyisocyanate compound having a group of ≧ 2.0 equivalents / mole is added to the polylactic acid in an amount of 0.
It is characterized in that 5 to 5% by weight is mixed and reacted. The present invention also relates to a foam-molded article obtained by pre-foaming the above polylactic acid-based expandable resin particles and then foam-molding the same.

In the present invention, in order to form expanded particles having fine cells with high uniformity and highness, a foaming agent is added to a polylactic acid-based resin composition in an aqueous suspension system or a mixed system in which water is mixed. With respect to the cut surface of the expandable resin particles formed by impregnating with, the micropores have an average diameter of 1 μm to 10 μm, and 5000 to 30,000 per 1 mm ² in cross-sectional area.
It is desirable to exist individually. As a result, when foaming is performed, the fine pores serve as the starting points for foaming, and fine and highly uniform foamed particles are formed without the addition of a cell-forming agent (nucleating agent). When the number of fine pores is 5000 or less per 1 mm ^{2 in} cross-sectional area, the obtained expanded particles have a coarse cell structure, and when the foamed molded product is cut, the properties of the cut surface are poor and the appearance is bad. The heat insulation performance of the molded product deteriorates. On the other hand, the micropores are 300 per 1 mm ^{2 in} cross section.
If the number is 00 or more, shrinkage is likely to occur during foam molding, and it becomes difficult to accurately mold into a desired mold, and the practicability decreases.

If the diameter of the fine pores is 1 μm or less, the obtained cells tend to have a fine structure, and if it exceeds 10 μm, the obtained cells have a coarse structure. Therefore, it is preferable that the average particle size is in the range of 1 μm to 10 μm because the practicality of the product is deteriorated. More preferable diameter of the micropores is
The average is 2 to 5 μm.

In the process of impregnating the polylactic acid resin composition with the foaming agent, it is sufficient that the foaming agent is contained in an amount of 3% by weight or more based on the polylactic acid resin composition. When the content of the foaming agent is less than 3% by weight based on the polylactic acid-based resin composition, the subsequent foaming becomes insufficient and the magnification of the molded product becomes low, so that the practicability as a product decreases.

Examples of blowing agents include propane, butane,
Aliphatic hydrocarbons such as pentane, cyclopentane and hexane, or halogenated hydrocarbons such as methyl chloride and freon are included. These foaming agents may be used alone or in combination of two or more kinds. Among them, butane or pentane is more preferable because the foaming agent is less likely to escape when water contained in the polylactic acid-based resin composition impregnated with the foaming agent is removed. The content of these foaming agents in the resin composition is preferably 3 to 25% by weight, more preferably 5 to 15% by weight, depending on the relationship with the expansion ratio.

In the present invention, the process of impregnating the polylactic acid resin composition with the foaming agent is performed in a mixed system in which water is mixed with the polylactic acid resin composition. Here, the water-mixed mixed system referred to in the present invention includes a system in which water is present in general, and a system in which water is added to a polylactic acid-based resin composition to homogenize it, or a polylactic acid-based system in water. An aqueous suspension system in which the resin composition is dispersed is included.
In the mixed system in which water is mixed, it is preferable to mix 1 part by weight or more of water with 100 parts by weight of the polylactic acid resin composition. When the amount of water mixed is 1 part by weight or less, the number of micropores in the polylactic acid-based expandable resin particles cannot reach a predetermined value as described above. On the other hand, the admixture of water is 1
The number of micropores formed tends to increase as the amount increases from the weight part, and the number of micropores can be adjusted to a desired level. When the amount of water mixed exceeds 50 parts by weight, the number of micropores formed hardly increases. Further, when the amount of water admixed exceeds 300 parts by weight, the number and size of the micropores formed are not so affected, but the concentration of the polylactic acid-based resin composition in the mixed system becomes considerably low, The workability in the impregnation process of the foaming agent is deteriorated and the productivity is reduced. Therefore, the upper limit of the admixture amount of water should be determined from the viewpoint of productivity, and may be any admixture amount of water that causes an extreme decrease. Preferred is a system in which 3 to 200 parts by weight of water is mixed with 100 parts by weight of the polylactic acid resin composition.

FIG. 1 is a cut surface of polylactic acid-based expandable resin particles obtained by impregnating a foaming agent in a mixed system in which 50 parts by weight of water is mixed with 100 parts by weight of the polylactic acid-based resin composition. However, it can be seen that many micropores are formed. Further, a cut surface of polylactic acid-based expandable resin particles obtained by impregnating a foaming agent in a mixed system in which 5 parts by weight of water is mixed with 100 parts by weight of the polylactic acid-based resin composition is shown in FIG. Although the number of micropores was slightly reduced as compared with the case of the mixed system in which 50 parts by weight of water was mixed, the size was good. On the other hand, in the impregnation of the foaming agent,
Micropores were hardly observed on the cut surface of the polylactic acid-based expandable resin particles obtained when the non-aqueous system was used. From these facts, the presence of water is indispensable for impregnating the polylactic acid-based resin composition with the foaming agent for the formation of the micropores, which is the focus of the present invention. You can see that it is an important point.

When a polylactic acid-based resin composition is impregnated with a foaming agent in a water suspension system or in a mixed system in which water is mixed, the polylactic acid-based expandable resin particles contain a large number of fine particles as described above. The pores are formed, but at this point, the micropores are filled with water. When the resin composition in which the fine pores are filled with water is directly foamed with steam or the like, it is not foamed or hardly foamed. It is considered that this is because the water in the micropores having a large latent heat has a kind of endothermic action against the heating required for foaming, and thus inhibits the foaming.
Before foaming, in order to allow foaming and to obtain expanded particles with fine cells with high uniformity after foaming,
It is necessary to appropriately remove water in the micropores so that the residual water content in the polylactic acid-based expandable resin particles is 0.5% or less. Therefore, the micropores filled with water also have a cross-sectional area of 1 with respect to the cut surface of the expandable resin particles, like the micropores after the water removal.
It is desirable that there are 5000 to 30,000 pieces per mm ² .

The number of micropores in the polylactic acid-based expandable resin particles impregnated with the foaming agent is closely related to the cell size of the expanded particles formed by pre-expanding the polylactic acid-based expandable resin particles. I have a relationship. That is, the larger the number of fine pores, the finer the cells of the expanded particles, and the smaller the number of fine pores, the larger the cells of the expanded particles. The number of micropores in the polylactic acid-based expandable resin particles depends on various conditions in the impregnation step of the foaming agent in the presence of water (amount of added water,
Addition amount of foaming agent, type and amount of dispersant, impregnation temperature,
It depends on the impregnation time, temperature rising rate and cooling rate, etc., but in the present invention, the temperature in the step of dissipating the internal moisture of the polylactic acid-based expandable resin particles after the impregnation of the foaming agent is extremely important. I found that.

In the present invention, a drying step is required in order to dissipate the internal water content of the polylactic acid-based expandable resin particles after the impregnation with the foaming agent. At this time, if the drying is carried out at a temperature considerably higher than the glass transition temperature (50 to 60 ° C.) of the polylactic acid resin composition, foaming will partially start, which is not preferable. When drying is performed at a temperature slightly higher than the glass transition temperature, the number of micropores in the polylactic acid-based expandable resin particles that have been present up to that point is greatly reduced, and it is formed by prefoaming after the completion of the drying step. In addition to the extremely large cell diameter of the foamed particles, the amount of the foaming agent also increases, resulting in insufficient foaming thereafter. To avoid this problem,
The drying temperature needs to be not higher than the glass transition temperature of the polylactic acid resin composition, preferably not higher than 40 ° C. Further, when the drying temperature is 5 ° C. or lower, the dissipation of the internal water content of the polylactic acid-based expandable resin particles is extremely slow and the efficiency is very poor. That is, the drying of the polylactic acid-based expandable resin particles after the impregnation with the blowing agent to dissipate the internal water is performed at 5 ° C. or higher and at the glass transition temperature of the polylactic acid-based resin composition or lower, preferably 40 ° C. or lower. Done. More preferably, it is 5 ° C to 35 ° C. When the water content in the polylactic acid-based expandable resin particles is allowed to escape in the range of 5 ° C. to 35 ° C. or less and foaming is performed, a cell having a particularly good size and number can be obtained.

Since the cell size of the expanded particles is closely related to the drying temperature, it is possible to obtain a cell having a desired size by changing the drying temperature. When the drying temperature is high, the number of micropores in the polylactic acid-based expandable resin particles existing before the drying step decreases, so when the expandable resin particles are expanded, the cells of the foam to be formed become large. .
On the other hand, if the drying temperature is low, the number of fine pores in the polylactic acid-based expandable resin particles does not decrease, so that the cells of the foam to be formed become small. The change in the number of micropores in the polylactic acid-based expandable resin particles is affected by the drying temperature, and specifically, the rate of water escape in the polylactic acid-based expandable resin particles and the polylactic acid-based resin composition are described. It is presumed that the softness of is directly involved. That is, when the drying temperature is relatively high and the polylactic acid-based expandable resin particles are dried in a soft state, the water in the micropores is likely to be rapidly removed, and the inside of the micropores is depressurized. Therefore, it is considered that the number of the micropores decreases because the micropores cannot retain their shape and are crushed. On the contrary, when the drying temperature is relatively low and the polylactic acid-based expandable resin particles are dried in a slightly hard state, the water in the micropores in the polylactic acid-based expandable resin particles is rapidly removed. Since it does not occur, the inside of the micropores is not decompressed and crushed, so it is considered that the number of micropores does not decrease.

A method for removing the water from the micropores filled with water to form micropores having a residual water content of 0.5% or less in the polylactic acid-based expandable resin particles is not particularly determined. However, it does not matter as long as it does not have an unfavorable effect such as breaking the micropores or increasing or decreasing the number thereof. For example, the polylactic acid-based expandable particles whose surface water content has been dehydrated in a centrifugation step or the like are dried by exposing them to a dry air at 5 ° C to 40 ° C for 5 to 48 hours in a ventilated state, or by vacuum drying. It is also possible to dry by using a dehydrating agent such as silica gel in a desiccator.

As described above, in the process of removing water from the fine pores in the polylactic acid-based expandable resin particles by drying or the like, finally, the amount of water remaining in the polylactic acid-based expandable resin particles is , 0.5% or less is preferable, and 0.1% or less is more preferable. Water content in the expandable resin particles is 0.
When 5% or more remains, the foaming hardly occurs at all even if the temperature of steam, the heating condition, etc. are changed at the time of foaming.

The amount of water remaining in the expandable resin particles after the operation of removing the water in the polylactic acid-based expandable resin particles depends not only on the conditions for the removal, but also on the amount of water at the time of impregnation of the foaming agent, Water-soluble polymers represented by surfactants, sparingly water-soluble inorganic dispersants, polyvinyl alcohol, etc., which are added as dispersion stabilizers necessary to prevent aggregation and fusion of particles during impregnation with a foaming agent. It can also be adjusted by the type and amount of the system stabilizer.

A further preferred embodiment of the present invention is L
The molar ratio of the body to the D body is 95/5 to 60/40, or 40 /
Polylactic acid of 60 to 5/95 has an isocyanate group ≧
It is the use of a polylactic acid-based resin composition obtained by mixing 2.0 equivalents / mole of a polyisocyanate compound with respect to the polylactic acid in an amount of 0.5 to 5% by weight and reacting the polylactic acid. By impregnating the resin composition with a foaming agent, expandable resin particles having excellent foamability can be obtained. The molar ratio of L-form to D-form is 95/5
Those exceeding 5 or less than 5/95 cannot be used because the crystallinity is high and the expansion ratio does not increase, or the foaming becomes uneven. Further, when the resin composition is used, the addition amount of the isocyanate compound that affects the melt index value (MI) that determines the quality of foamability is less than 0.5% by weight based on the polylactic acid. ,
The MI of the polylactic acid resin composition does not increase so much and is 5% by weight.
If it exceeds, the foaming property is deteriorated.

As described above, in the cut surface of the polylactic acid-based expandable resin particles, the fine pores have a diameter of 1 to 10 μm, 1
Under the condition that there are 5,000 to 30,000 particles per mm ² , the type of the foaming agent is not limited, and fine and highly uniform foamed particles can be obtained.

The polylactic acid-based expandable resin particles of the present invention include
If necessary, it contains a foaming aid such as toluene, xylene, methanol or acetone, a plasticizer such as DOP, DOA, DBP, coconut oil or palm oil, a flame retardant such as hexabromocyclododecane or tetrabromobisphenol A, etc. be able to.

The resin composition can be impregnated with these foaming agent, foaming auxiliary agent and the like in an aqueous system or a water suspension system by heating under high pressure. That is, since an impregnation temperature higher than the glass transition temperature of the resin is selected, it is usually 70 to 11
It can be impregnated at 0 ° C. for 0.5 to 3 hours.

The present invention has an advantage that the addition of a cell-forming agent (nucleating agent) which has been conventionally used is not necessary, but it is safe to add such a cell-forming agent. Although not present, it is desirable to add in an amount such that the surface appearance is not deteriorated and the fusion between the cells inside the molded product is not significantly reduced. Suitable cell forming agents include, for example, talc, sodium citrate, ethylene bisstearic acid amide, and the like.

The steps from the thus-obtained expandable resin particles of the present invention to a molded article may be carried out by a conventional method and are not particularly limited. It is foamed or made into pre-expandable particles by hot air of 60 to 120 ° C., and then these pre-expandable particles are filled in a mold of a closed mold having small holes and slits, and steam or hot air is further added. A method of forming a molded body in which individual particles are fusion-bonded and integrated by heating and re-foaming by using

The "micropores" in the present invention refer to the small pores having an average diameter of about 1 to 10 μm existing inside the polylactic acid-based expandable resin particles. The micropores may contain substances other than polylactic acid-based resin, that is, additives such as water, a foaming agent, a solvent, and a plasticizer.

[0030]

EXAMPLES The present invention will be described in more detail with reference to the following examples and comparative examples. The evaluation was carried out by the following method.

1. Melt index (MI) value of polylactic acid-based composition was measured by a method according to JIS K7210 (measurement temperature 190 ° C., orifice diameter 2 mm, load 2.16 Kg).

2. Of micropores in polylactic acid-based expandable resin particles
Observation and counting Sample polylactic acid-based expandable particles are immersed in liquid nitrogen and frozen.
Tie and then use a sharp blade to freeze polylactic acid
Cut the expandable particles and observe the cut surface with an electron microscope.
I took a picture with it and the obtained electron micrograph
Cross section 1 mm ²Per diameter of 1 to 10 μm
The number of micropores was calculated.

3. After precisely weighing about 1 gram of a water content measurement sample of polylactic acid-based expandable resin particles, in a water vaporizer,
The sample is heated at 190 ° C. for 15 minutes, and the amount of water generated during that time is measured by the Karl Fischer moisture meter (MKC-210
It was measured using Kyoto Electronics Manufacturing Co., Ltd.).

4. About 1 gram of a sample for measuring a foaming agent of polylactic acid-based expandable resin particles was precisely weighed, dissolved in toluene, and quantified using a gas chromatograph.

5. Pre-expansion and Expansion Ratio Polylactic acid-based expandable resin particles were heated for 30 seconds with steam at 85 ° C. to 95 ° C. to give pre-expanded particles. Further, in the case of expanded polystyrene, it was heated with steam at 100 ° C. for 2 minutes to obtain pre-expanded particles. The volume of the obtained pre-expanded particles was measured using a measuring cylinder, and the bulk magnification was determined.

Production of Polylactic Acid Resin Composition Polylactic acid resin composition (1) Production: Commercially available L-lactide and D-lactide were recrystallized using ethyl acetate for purification. Purified L-lactide, D-lactide and tin octylate as a catalyst of 10 ppm as tin
The mixture was added, charged into an autoclave equipped with a stirrer so that the D-form ratio was 10 mol%, deaerated under reduced pressure, and then subjected to ring-opening polymerization in an N ₂ atmosphere. After completion of the reaction, the polymer was taken out from the autoclave. The polymer is then treated with 100% water.
After drying to 0 ppm or less, after blending 1% by weight of the polymer with 2.8 equivalents of diphenylmethane polyisocyanate having a functional group as a viscosity increasing agent,
Supply to a twin-screw kneader, rotation speed 100 rpm, melting temperature 1
After reaction kneading under conditions of 80 ° C., residence time of 3 to 5 minutes, and discharge rate of 10 kg / hour, the mixture was extruded and cut from a die to obtain particles having a diameter of about 1 mm. The obtained polylactic acid resin composition had an MI value of 0.2.

Production of polylactic acid resin composition (2): Commercially available L-lactide and D-lactide were recrystallized from ethyl acetate for purification. Purified L-lactide,
D-lactide and tin octylate as a catalyst (10 ppm as tin) were added, charged in an autoclave with a stirrer so that the D-form ratio was 10 mol%, deaerated under reduced pressure, and then subjected to ring-opening polymerization in an N ₂ atmosphere. After completion of the reaction, the polymer was taken out from the autoclave. Then, after drying the polymer until the water content is 1000 ppm or less,
Add 3% by weight of talc with a particle size of about 2.5 to 3 μm,
As a viscosity increasing agent, diphenylmethane polyisocyanate having a functional group of 2.8 equivalents was blended in an amount of 1% by weight with respect to the polymer, and then the mixture was fed to a twin-screw kneader at a rotation speed of 100 rp.
m, melting temperature 180 ° C., residence time 3 to 5 minutes, discharge rate 10 kg / hour, reaction kneading was performed, and extrusion cutting was performed from a die to obtain particles having a diameter of about 1 mm. The obtained polylactic acid resin composition had an MI value of 0.2.

Production of Polylactic Acid-based Expandable Resin Particles 100 parts of each of the polylactic acid-based resin compositions (1) and (2) obtained above are added with water in the addition amount shown in Table-1. In a mixed system of a lactic acid resin composition and water, 100 parts of each of the polylactic acid resin compositions (1) and (2) was impregnated with a foaming agent according to the formulation shown in Table-1.
The impregnation was carried out by holding in an autoclave equipped with a stirrer at 90 ° C. for about 1 hour.

[Table 1] Note) The styrene beads of Reference-1 are beads obtained by suspension polymerization of styrene and impregnated with a foaming agent (n-pentane) in an aqueous suspension system. It is impregnated for 4 hours at ℃.

The polylactic acid-based expandable resin particles impregnated with the foaming agent in the formulation shown in Table 1 were dried under the following conditions. Drying condition (1): The bag was sealed in a polyethylene bag and stored at a temperature of 15 ° C for 10 days. Drying condition (2): Dry air at 25 ° C. was blown at a rate of 2 L / min for 1 kg of the polylactic acid-based expandable resin particles to perform drying for 12 hours. Drying condition (3): Dry air at 30 ° C. was blown at a rate of 2 L / min per 1 kg of the polylactic acid-based expandable resin particles to perform drying for 12 hours. Drying condition (4): Dry air at 35 ° C. was blown at a rate of 2 L / min per 1 kg of the polylactic acid-based expandable resin particles to perform drying for 12 hours. Drying condition (5): Dry air at 40 ° C. was blown at a rate of 2 L / min per 1 kg of the polylactic acid-based expandable resin particles to perform drying for 12 hours. Drying condition (6): Dry air at 45 ° C. was blown at a rate of 2 L / min per 1 kg of polylactic acid-based expandable resin particles to perform drying for 12 hours. Then, after drying under each of the above conditions, the polylactic acid-based expandable resin particles were pre-expanded with steam. The number of micropores at this time, the expansion ratio, and the cell size are shown in Table 2.

[Table 2]

[0040] Results Example No. -1: polylactic acid composition without the addition of talc, but the water was added 50 parts by weight isopentane is impregnated system as a blowing agent, in Example No. 1-1, the number of microporous Is 1900
The number was 0 / mm ² . The dried particles had an internal water content of 0.08%, which was reduced to 0.1% or less. However, when pre-expanded, good expanded particles having an expansion ratio of 35 and a cell size of 70 μm were obtained. became. Furthermore, example number 1
-2, 1-3, 1-4, 1-5 and the temperature of dry air is 3
As the temperature increased to 0 ° C, 35 ° C, 40 ° C, and 45 ° C, the number of micropores formed was 15,000, 11,000, and 600.
In Example No. 1-5, the number of cells in the expanded beads after pre-expansion became slightly coarse with a diameter of 600 μm, and the shape of the expanded beads also became slightly distorted. Example number-2, 3, 4: The amount of water is 100, 200, 300
It is an example of impregnating according to Example No. -1 in parts by weight,
Compared with the results of Example No.-1, the number of micropores was slightly increased, and the cell size and the shape of the foamed particles were not significantly changed. Example No. -5: This is an example in which the amount of water was 30 parts and impregnation was carried out according to Example No. 1, but the drying was performed in a sealed state 5-1.
, The internal water content exceeded 0.5%, the cells were extremely coarse, and the cells contracted after foaming into a distorted shape, and the expansion ratio was as low as 9 times. On the other hand, drying was performed in an open state 5
In -2, the particles having a low internal water content of 0.06% foamed well. Example No. -6: This is an example in which a predetermined amount of talc was added. The product dried in a sealed state as in 6-1 had an extremely large internal water content of 2.4% and was in a state of not foaming at all. It was On the other hand, in 6-2 dried in the open state, the internal water content was reduced to 0.28%, so that foaming was possible, but the cell size was different between the central part and the outside, and it was in a non-uniform state. Example Nos. -7 and 8: n-pentane instead of isopentane,
This is an example of using isobutane as a foaming agent. In all cases, the number of micropores was in the range of 5000 to 30,000 / mm ² , and the amount of water was reduced by performing drying in an open state, resulting in good cells and in a foamed state. Example Nos. -9 and 10: In this example, the amount of water added is 5 parts and 2 parts, but the amount of water immediately after impregnation decreases and the number of micropores also decreases. Along with that, the size of the cell is also increasing. Example No. 11: This is an example in which the amount of water was further reduced, but the number of micropores was reduced, the cell became 1000 μm or more in size, and the particles after foaming contracted to strain, and an appropriate magnification was obtained. I couldn't get it. Example Nos. 12 and 13: A system in which water was not added during impregnation, but in the absence of water, no micropores were formed in the polylactic acid-based expandable resin particles. This did not change depending on the drying conditions and the type of foaming agent, and proper foaming was not performed. Example number -14: This is an example in which a nucleating agent was added, but the cell diameter was large and proper foaming could not be performed.

The polylactic acid-based expandable resin particles of the present invention described above are the cut surfaces of the polylactic acid-based expandable resin particles containing the foaming agent in an amount of 3% by weight or more based on the polylactic acid-based resin composition. The present invention is characterized in that there are 5,000 to 30,000 micropores having a residual water content of 0.5% or less per 1 mm ^{2 of} cross-sectional area. By using the polylactic acid-based expandable resin particles, it becomes possible to impregnate the polylactic acid-based resin composition with the foaming agent in an aqueous or water-suspended system instead of the non-aqueous system having the above-mentioned problems. It was Furthermore, it is not necessary to add a nucleating agent such as talc, and at the same time, the foaming agent can be used without limitation in its type, and it is possible to form a foam having fine cells with high uniformity after foaming. Becomes

[Brief description of drawings]

FIG. 1 shows an electron micrograph taken at a magnification of 500 times near the outer surface of the inside of polylactic acid-based expandable resin particles when 50 parts of water was added.

Claims (5)

[Claims] 1. A foaming agent is added to a polylactic acid resin composition in an amount of 3
Polylactic acid-based expandable resin particles, characterized in that the cut surface of the polylactic acid-based expandable resin particles contained in an amount of not less than 5% by weight has 5,000 to 30,000 micropores per 1 mm ^{2 in} cross-sectional area. 2. A mixed system of a polylactic acid resin composition and water, wherein 1 part of water is added to 100 parts by weight of the polylactic acid resin composition.
Polylactic acid-based expandable resin particles obtained by impregnating the polylactic acid-based resin composition with a foaming agent in an amount of 3 parts by weight or more in an amount of 3 parts by weight or more, and then drying, and having a residual water content of 0.5. % Or less, the cut surface of the polylactic acid-based expandable resin particle has 5000 to 30,000 micropores per 1 mm ^{2 in} cross-sectional area. 3. The polylactic acid-based expandable resin particle according to claim 1, wherein the micropores have an average diameter of 1 μm to 10 μm. 4. The polylactic acid-based resin composition has a molar ratio of L-form to D-form of 95/5 to 60/40, or 40 / 60-5.
A resin composition obtained by mixing polylactic acid of 95/95 with a polyisocyanate compound having an isocyanate group ≧ 2.0 equivalents / mol based on 0.5 to 5% by weight of the polylactic acid. The polylactic acid-based expandable resin particles according to claim 1 or 2. 5. A foam-molded article obtained by pre-foaming the polylactic acid-based expandable resin particles according to any one of claims 1 to 4 and then foam-molding them.