JP2005068306A - Expandable polylactic acid-based resin composition and method for producing the same resin composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition enabling avoidance of conglutination in an impregnation process when producing an expandable polylactic acid-based resin composition. <P>SOLUTION: The expandable polylactic acid-based resin composition comprises an polyoxyethylene (POE) derivative. The POE derivative is preferably one of POE fatty acid ester, POE alkyl ether and POE sorbitan fatty acid ester. Aggregation, conglutination, etc., in the impregnation process can be avoided while ensuring desired physical property (foaming property) by including the POE derivative into the expandable polylactic acid-based resin composition. As a result, conglutination problem in the impregnation process in the method for producing the expandable polylactic acid-based resin composition is solved and the resin composition can stably be produced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a foamable polylactic acid-based resin composition and a production method that enables stable production of the resin composition.

  As an alternative to expanded polyethylene (EPE) and polystyrene (EPS) that use fossil resources as raw materials, Patent Document 1 proposes an expanded molded body mainly composed of polylactic acid. This polylactic acid uses starch, which is a non-petroleum resource, as a starting material, and it can be said that the foamed molded product is very desirable from the viewpoints of protection of earth resources and environmental conservation.

  In Patent Document 1, first, a foamable polylactic acid-based resin composition is produced, pre-foamed, and then molded into a foamed molded product. Furthermore, in Patent Document 2, when producing the foamable polylactic acid resin composition, in order to obtain stable physical properties, the kneaded polylactic acid resin composition is subjected to heat treatment under a certain humidity condition to be crosslinked and thickened. It is said that it is necessary to impregnate the foaming agent after increasing the melt viscosity.

  On the other hand, the present inventors used a polylactic acid-based resin composition having latent cross-linking and thickening as a method for producing a foamable polylactic acid-based resin composition, and impregnated with a foaming agent with a crosslinking reaction in an aqueous system. And a highly productive method for obtaining a foamable polylactic acid resin composition has been proposed (Japanese Patent Application No. 2002-315403).

  Further, in order to obtain a highly foamed product of a foamable resin composition typified by EPS, it is necessary to impregnate a certain amount or more of a foaming agent, and a method of impregnating at a high temperature for the purpose of promoting impregnation is generally employed. Therefore, a highly foamed product can be obtained by the same method as a method for producing a foamable polylactic acid resin composition.

  However, when impregnation is performed at a high temperature, the polylactic acid resin composition having a low softening temperature is plasticized, so that the particles of the resin composition may be aggregated and stuck in the impregnation tank. Considering production, it was a very big problem.

International Publication No. 99/21915 Pamphlet JP 2000-17037 A

  In view of the circumstances as described above, an object of the present invention is to provide a resin composition capable of avoiding sticking in the impregnation step when producing a foamable polylactic acid resin composition.

  As a result of intensive studies to solve such problems, the present inventors have completed the present invention. That is, by including a polyoxyethylene derivative in the foamable polylactic acid-based resin composition, aggregation, sticking, and the like in the impregnation step can be avoided while ensuring desired physical properties (foamability).

  As a method of including the polyoxyethylene derivative in the foamable polylactic acid-based resin composition, it can be handled by adding the polyoxyethylene derivative in the impregnation step. It has been revealed that almost all of the added polyoxyethylene derivative is contained in the foamable polylactic acid resin composition.

  According to the present invention, the problem of sticking in the impregnation step in the method for producing a foamable polylactic acid resin composition is eliminated, and the resin composition can be stably produced.

Hereinafter, the present invention will be described in detail.
The polylactic acid resin composition of the present invention is not particularly limited as long as it contains 51% or more of a resin containing 60 mol% or more of lactic acid as a monomer unit. If the ratio of D-form or L-form is extremely small, it will easily crystallize and cause poor foaming. Therefore, the D / L ratio of the polylactic acid resin is preferably 5/95 to 95/5. More preferably, it is 8/92 to 92/8.

  This polylactic acid-based resin composition needs to have an appropriate viscosity in a foaming temperature range of 70 ° C. to 90 ° C., thickening by cross-linking reaction using various cross-linking agents, and adjusting viscosity by blending with other compounds. And so on.

  Among them, particularly when polyisocyanate is used as a cross-linking agent, an excess cross-linking agent is added to the amount of polylactic acid end groups, and after kneading, heat treatment is performed in the presence of water, thereby removing unreacted isocyanate groups as water. Viscosity can be further increased by reacting to form allophanate bonds or urea bonds. Therefore, this polyisocyanate is suitably used as a cross-linking agent because a highly viscous resin composition can be obtained without applying an excessive load to the kneader table.

  Examples of the polyisocyanate compound used in the present invention include aromatic and aliphatic polyisocyanates. For example, aromatic polyisocyanates include polyisocyanate compounds having a skeleton of tolylene, diphenylmethane, naphthylene, and triphenylmethane. Moreover, as alicyclic polyisocyanate, there exists a polyisocyanate compound which makes isophorone and diphenylmethane hydroxide frame | skeleton. Examples of the aliphatic polyisocyanate include polyisocyanate compounds having hexamethylene and lysine as a skeleton. Any of these can be used, but tolylene and diphenylmethane-based polyisocyanates are preferable, and diphenylmethane-based polyisocyanate is particularly preferable because of versatility and handling properties. The polylactic acid-based resin composition of the present invention is obtained by adding an isocyanate compound to a polylactic acid-based resin. As the isocyanate compound, polyisocyanates having an isocyanate group of 2.0 equivalent / mol or more are preferably used. . Moreover, it is preferable that the addition amount of an isocyanate compound is 0.1 to 6% with respect to resin, More preferably, it is 1 to 3%.

  This resin composition to which an isocyanate compound has been added has a latent cross-linking thickening property. By performing the post-impregnation in a system in which water is present, the viscosity becomes suitable for foaming after the impregnation step. Prescription design.

  If desired resin physical properties can be obtained, crosslinking agents other than polyisocyanates can be used, and organic peroxides and polyfunctional epoxy compounds can be used alone or in combination. In addition, various plasticizers may be added for the purpose of improving physical properties, but those that do not significantly inhibit the crosslinking reaction and do not bleed out during the subsequent impregnation are preferred.

  To the polylactic acid resin composition of the present invention, a bubble preparation agent (foaming nucleating agent) such as inorganic powder may be added for the purpose of uniformizing the foamed cells and making the pores. Specifically, talc, mica, clay mineral, calcium carbonate, sodium hydrogen carbonate / citric acid and the like can be used, but are not particularly limited thereto.

  As a method for preparing the polylactic acid-based resin composition as described above, any method used for preparing a general resin compound can be used, but a twin screw extruder is particularly preferably used.

Next, the manufacturing method of the foamable polylactic acid-type resin composition of this invention is demonstrated.
In order to avoid aggregation and sticking of the resin composition particles in the impregnation tank when impregnating the foaming agent at a high temperature using the polylactic acid resin composition described above as a raw material, the produced foamable polylactic acid resin composition Must contain a polyoxyethylene derivative.

  The polyoxyethylene derivatives in the present invention correspond to O / W nonionic surfactants, and are classified into polyoxyethylene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl ethers, and the like.

  Examples of polyoxyethylene fatty acid esters include polyethylene glycol monostearate, polyethylene glycol monooleate, polyethylene glycol distearate, polyethylene glycol dioleate, and the like. Polyoxyethylene sorbitan fatty acid esters include polyoxyethylene sorbitan monostearate, Examples of the polyoxyethylene alkyl ether include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, and polyoxyethylene oleyl cetyl ether.

  As a method of incorporating the polyoxyethylene derivative into the resin, a method such as kneading at the time of kneading or coating the resin particle surface before impregnation with the foaming agent is possible. It has been found that if a polyoxyethylene derivative is added, almost all of the added amount penetrates into the foamable polylactic acid resin composition.

  That is, when considering productivity, the method of adding a polyoxyethylene derivative in the impregnation step is the simplest and most practical, and can be handled by adding 0.1% or more of the polyoxyethylene derivative to the resin at the time of impregnation. .

  In the present invention, since the foaming agent is impregnated while proceeding with the crosslinking reaction by the reaction of the isocyanate groups in the polylactic acid resin composition and water, water is indispensable, and the required amount is 5% with respect to the resin. That's it. When water is used as the dispersion medium, 60% or more of the resin is required in consideration of dispersibility in the impregnation tank.

  As the foaming agent to be impregnated into the polylactic acid resin composition, inorganic gases such as nitrogen and carbon dioxide, hydrocarbons such as propane, butane, isobutane, pentane and isopentane, and mixtures thereof are used. Fluorocarbons are also suitable as the foaming gas, but it is preferable to avoid them when environmental considerations are required. In particular, isobutane, normal butane, isopentane, and normal pentane are preferable.

  The required impregnation amount of the foaming agent is 4% by weight or more in order to obtain a highly foamed product (expansion ratio of 30 times or more), but it can be handled by high temperature impregnation at 90 ° C. or more. The impregnation conditions are adjusted and determined according to the resin composition of the desired polylactic acid resin composition. Taking the case of an impregnation temperature of 90 ° C. as an example, the impregnation time is appropriately 60 minutes to 150 minutes.

  In the present invention, by using an aprotic solvent such as acetone or ethyl acetate as an impregnation aid during the impregnation step, the amount of foaming agent impregnation is further increased to stabilize the foamable resin composition with a foaming ratio of 50 times or more. Can also be obtained.

  Moreover, you may impregnate the component which provides a coloring component and functionality at the time of an impregnation. For example, antistatic agents, fragrances, deodorants, antiseptics, antibacterial agents, various colorants and the like can be mentioned.

  The foamable polylactic acid-based resin composition of the present invention can be foamed by steam, hot air, high frequency, etc., as in the method disclosed in Patent Document 2, but a method using a pre-foaming machine for foamed polystyrene. The simplest and most common.

  Similarly, the pre-foamed polylactic acid-based resin composition is most easily and generally performed using a molding machine used for molding foamed polystyrene, foamed polyethylene, foamed polypropylene, or the like. Alternatively, foaming and molding can be performed simultaneously in the mold.

Hereinafter, it demonstrates in detail using an Example.
(Production example)
Isocyanate compound “Millionate MR-200” (isocyanate group 2.7-2) to polylactic acid having a weight% isomer ratio (L / D) = 90/10, a solution viscosity (RV) of 1 wt% chloroform solution = 3.7 .8 equivalent / mol, 1.5% by weight of Nippon Polyurethane Industry Co., Ltd.) was added and kneaded at a cylinder temperature of 185 ° C. with a twin screw extruder (PCM70, Ikegai Co., Ltd.), and using an underwater cutter. The average particle size was 1.3 mm.

(Examples 1-4)
100 parts by weight of polylactic acid-based resin composition particles obtained in Production Example, 100 parts by weight of water, 20 parts by weight of isobutane as a foaming agent, polyoxyethylene fatty acid diester “Ionet DO-1000” (Sanyo Kasei) 0.15 1.8 parts by weight were charged into a pressure vessel and held at 90 ° C. for 2 hours. After sufficiently cooling, the product was taken out and dried to obtain expandable polylactic acid resin composition particles A to D.

(Comparative Example 1)
100 parts by weight of the polylactic acid-based resin composition particles obtained in the production example, 100 parts by weight of water, and 20 parts by weight of isobutane as a blowing agent were charged in a pressure vessel and held at 90 ° C. for 2 hours. After sufficiently cooling, the product was taken out and dried to obtain expandable polylactic acid resin composition particles.

(Comparative Example 2)
100 parts by weight of the polylactic acid-based resin composition particles obtained in the production example, 100 parts by weight of water, and 20 parts by weight of isobutane as a foaming agent were charged in a pressure vessel and kept at 80 ° C. for 2 hours. After sufficiently cooling, the product was taken out and dried to obtain expandable polylactic acid resin composition particles.

<Quantitative determination of polyoxyethylene fatty acid diester>
The amount of polyoxyethylene fatty acid diester contained in the foamable polylactic acid resin composition was determined by the following method.
The ester group of the polyoxyethylene fatty acid diester is alkali-decomposed and converted into a fatty acid, converted into a methyl ester, and methyl palmitate derived from the polyoxyethylene fatty acid diester is obtained from the relative ratio of the internal standard (methyl heptadecanoate). The quantity of polyoxyethylene fatty acid diester was determined by gas chromatography analysis.

(Example 5)
100 parts by weight of the polylactic acid-based resin composition particles obtained in the production example, 100 parts by weight of water, 20 parts by weight of isobutane as a foaming agent, and 0.3 parts by weight of polyoxyethylene lauryl ether (equivalent to IHI Co., Ltd. Briji 35) The pressure vessel was charged and held at 90 ° C. for 2 hours. After sufficiently cooling, the product was taken out and dried to obtain expandable polylactic acid resin composition particles.

(Example 6)
100 parts by weight of polylactic acid-based resin composition particles obtained in the production example, 100 parts by weight of water, 20 parts by weight of isobutane as a foaming agent, and 0.3 parts by weight of polyoxyethylene sorbitan fatty acid ester (trademark of IHI Co., Ltd., TWEEN 40) Was put in a pressure vessel and kept at 90 ° C. for 2 hours. After sufficiently cooling, the product was taken out and dried to obtain expandable polylactic acid resin composition particles.

(Example 7)
100 parts by weight of polylactic acid-based resin composition particles obtained in the production example, 100 parts by weight of water, 20 parts by weight of isobutane as a foaming agent, 15 parts by weight of acetone, polyoxyethylene fatty acid diester “Ionette DO-1000” (Sanyo Kasei) ) 0.3 part by weight was charged into a pressure vessel and held at 90 ° C. for 2 hours. After sufficiently cooling, the product was taken out and dried to obtain expandable polylactic acid resin composition particles.

(Comparative Example 3)
100 parts by weight of the polylactic acid-based resin composition particles obtained in the production example, 100 parts by weight of water, 20 parts by weight of isobutane as a foaming agent, and 0.3 parts by weight of sorbitan monolaurate (trademark equivalent to IHI Corporation Span 20) The container was charged and kept at 90 ° C. for 2 hours. After sufficiently cooling, the product was taken out and dried to obtain expandable polylactic acid resin composition particles.

(Comparative Example 4)
100 parts by weight of the polylactic acid-based resin composition particles obtained in the production example, 100 parts by weight of water, 20 parts by weight of isobutane as a blowing agent, and 0.3 parts by weight of polyethylene glycol having a molecular weight of 1000 are charged in a pressure-resistant container at 90 ° C. Hold for 2 hours. After sufficiently cooling, the product was taken out and dried to obtain expandable polylactic acid resin composition particles.

(Example 7)
100 parts by weight of polylactic acid-based resin composition particles obtained in the production example, 100 parts by weight of water, 20 parts by weight of isobutane as a foaming agent, 15 parts by weight of acetone, polyoxyethylene fatty acid diester “Ionette DO-1000” (Sanyo Kasei) ) 0.3 part by weight was charged into a pressure vessel and held at 90 ° C. for 2 hours. After sufficiently cooling, the product was taken out and dried to obtain expandable polylactic acid resin composition particles.

(Comparative Example 5)
100 parts by weight of the polylactic acid-based resin composition particles obtained in the production example, 100 parts by weight of water, 20 parts by weight of isobutane as a blowing agent, and 15 parts by weight of acetone were charged in a pressure vessel and held at 90 ° C. for 2 hours. After sufficiently cooling, the product was taken out and dried to obtain expandable polylactic acid resin composition particles.
Subsequently, the impregnation rate and expansion ratio of the resin particles obtained in the above-described Examples and Comparative Examples are obtained by the following methods.

<Impregnation rate of foamable polylactic acid-based resin composition>
The impregnation rate is obtained from the weight of the resin particles before and after the impregnation by the following formula.
Impregnation rate (%) = 100 × (weight after impregnation−weight before impregnation) / weight before impregnation

<Expansion ratio of expanded particles>
The obtained resin particles are foamed by being exposed to steam at 85 ° C. for 1 minute, and then the foamed particles are scraped into a polyethylene cup having an internal volume of 2000 ml, and the weight is measured, and the weight of the foamed particles is subtracted from the tare weight. Seek. The expansion ratio is obtained from the apparent volume (2000 ml) and the weight of the expanded particles by the following formula.
Expansion ratio = apparent volume (2000 ml) / weight of expanded particles (g)

Table 1 shows the influence of the amount of POE fatty acid diester added during the impregnation step. When the addition amount is 0% by weight and impregnated at 80 ° C., no agglutination occurs. However, the amount of the foaming agent impregnated is insufficient and sufficient foaming property cannot be obtained. . However, for those added with 0.1% by weight or more of POE fatty acid diester, no sticking is observed at any concentration, and the foaming property is very good. Moreover, since the amount of impregnation increases as the amount of addition of the POE fatty acid diester increases, it is considered that there is also an effect of promoting foaming agent impregnation. When the resin particles after impregnation are analyzed, it is found that almost all of the added POE fatty acid diester is contained in the resin.

  Table 2 shows the effects of additives other than the POE fatty acid diester. Like POE fatty acid diesters, POE lauryl ether and POE sorbitan monolaurate corresponding to O / W type nonionic surfactants do not cause sticking and are effective in stabilizing the impregnation process. On the other hand, when sorbitan monolaurate which is a W / O type nonionic surfactant is used, sticking occurs. Further, only polyethylene glycol which is the main component of the POE derivative is not effective in avoiding sticking.

  In Table 3, acetone is used as an auxiliary agent for the purpose of promoting foaming agent impregnation. In a system to which acetone, which is a good solvent for polylactic acid, is added, there is a condition that it is very easy to agglutinate, but if POE fatty acid diester is added, no agglutination occurs and the expansion ratio exceeds 50 times. When the POE fatty acid diester is not added, the agglomeration is intense and the whole lump is formed.

  The biodegradable foam that can be stably produced according to the present invention can be replaced by all uses of non-biodegradable foam, but is difficult to recover and reuse, such as a fish box, It is particularly preferably used for vegetable boxes and the like.

Claims (7)

A foamable polylactic acid-based resin composition containing a polyoxyethylene derivative. The resin composition according to claim 1, wherein the polyoxyethylene (POE) derivative is any one of POE fatty acid ester, POE alkyl ether, and POE sorbitan fatty acid ester. The resin composition according to claim 1 or 2, wherein the lactic acid component isomer composition (L-form / D-form) of the polylactic acid resin is 95/5 to 5/95. The resin composition according to any one of claims 1 to 3, comprising 4% by weight or more of a blowing agent. The resin composition according to any one of claims 1 to 4, wherein the blowing agent is a hydrocarbon containing at least one of isobutane, normal butane, isopentane, and normal pentane. 6. The method for producing a foamable polylactic acid resin composition according to claim 1, wherein a POE derivative is added in the step of impregnating the foaming agent. The method for producing the resin composition according to claim 6, wherein the step of impregnating the foaming agent is carried out in an aqueous system.