JP2001098044A - Biodegradable and foamable polylactic acid resin composition - Google Patents

Abstract

(57) [Problem] To provide a biodegradable polylactic acid composition excellent in foaming property, having high productivity and low cost. A polylactic acid resin composition comprising a polylactic acid and a polyisocyanate, wherein the polylactic acid has a molar ratio between L-form and D-form of 95/5 to 60/40, and has a weight average Biodegradable foaming characterized by having a molecular weight and a number average molecular weight of 200,000 or more and 40,000 or more and a polydispersity (ratio of weight average molecular weight to number average molecular weight) of 6 or less. Polylactic acid resin composition having properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biodegradable composition,
The present invention relates to a biodegradable resin composition having excellent foamability, which is mainly used for foamable packaging materials, mainly containing lactic acid that contributes to global environmental protection.

[0002]

2. Description of the Related Art Plastic foams utilizing light weight, cushioning properties, and moldability are widely used as packaging and packing materials, and are made of petroleum-based chemical products such as polystyrene (PS) and polyolefin. It is difficult to dispose after use, and even if it is incinerated, it has a high calorie burn,
It has become a major social problem that it does not decompose even if it is damaged by incinerators or landfilled, and because it has a large volume, it occupies the space of the disposal site.

[0003] In addition, the effects of the foams that have been dumped without being disposed on natural systems such as rivers and oceans are not negligible. Therefore, resins that decompose in the ecosystem and have less impact on the global environment have been developed. For example, a polyhydroxybutyrate resin synthesized in the body of a microorganism, a polyester composed of an aliphatic glycol and an aliphatic carboxylic acid, or a polyester resin containing caprolactone as a main component, etc., have been announced. Due to the production of microorganisms, the purity is low, the productivity is extremely low, and the use is limited.

The latter is certainly good in productivity because the raw material is inexpensive and available in large quantities such as petroleum and natural gas. However, since it is a crystalline resin and has a low glass transition point, it is biodegradable. The practical use of packaging materials is limited in terms of practicality, and petroleum and natural gas are used as raw materials.When decomposed, carbon dioxide is added to the existing carbon dioxide on the earth, so it is necessary to control the increase in carbon dioxide. Does not contribute. In the long term, since the raw material source is limited, it becomes difficult to obtain the material source soon, and it cannot contribute to global environmental protection in the true sense.

Further, as a biodegradable material, glycolic acid, lactic acid and the like can be obtained as a polymer by ring-opening polymerization of glycolide or lactide, and are used as a sustained-release agent for medical use or as a fiber for medical use. However, as it is, it has not been used in a large amount as a foam, as a packaging container or as a cushioning material.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a biodegradable polylactic acid composition having excellent foaming properties with high productivity and at low cost. More specifically, it can be conveyed to a subsequent processor in the state of expandable particles such as expandable polystyrene particles, and the expandable particles are pre-expanded on the side of the trader, and the obtained expanded particles are molded in a mold. An object of the present invention is to provide a biodegradable resin composition mainly composed of polylactic acid, which is excellent in foaming properties and has high productivity and is inexpensive.

[0007] Regarding the expandable particles and expanded particles of the polylactic acid composition, Japanese Patent Laid-Open Nos. 5-17965 and 5-1 have already been disclosed.
7966. However, as a result of a detailed examination by the present inventors, none of the proposals was expected to be effective.

Japanese Patent Application Laid-Open No. Hei 5-17965 proposes foamed particles. Even if the method detailed in the specification is faithfully reproduced, highly expanded foamed particles can be stably produced in large quantities. I couldn't do it. The cause is that when the polylactic acid composition treated in a water dispersion system under high temperature and high pressure is spouted into the atmosphere at high temperature, it becomes flocculent and does not become particles. Pre-expanding expandable beads such as expandable polystyrene beads and forming the expanded particles into a form requires spherical particles close to a true sphere, and it is impossible to form the form with a cotton-like material. Also,
When the treated polylactic acid composition is cooled to around 100 ° C. and jetted, only deformed foamed particles having a low expansion ratio are obtained, which is not one that can withstand mold forming. Further, when the foamed particles are transported to a user, the bulky bulkiness is extremely low in transport efficiency and disadvantageous in cost. Further, Japanese Unexamined Patent Publication No.
No other manufacturing method is described in 17965,
With this proposal, it cannot be expected to obtain expanded particles having excellent flexibility and cushioning properties.

On the other hand, Japanese Patent Application Laid-Open No. Hei 5-17966 proposes expandable particles mainly composed of polylactic acid or hydroxycarboxylic acid. Can obtain only very small expanded particles. The reason is that in order to obtain highly expanded particles, it is necessary that the molecular weight of the resin composition is at least 300,000 or more in weight average molecular weight. According to the content of the proposal, such a high molecular weight polylactic acid or hydroxycarboxylic acid is used. It is impractical to produce a resin composition containing as a main component, and it is also difficult to produce expandable particles. Even if it can be manufactured, the production efficiency is poor and it is far from practical use.
Further, the fact that the low-boiling organic compound impregnated during the production is more easily volatilized than the particles is one of the reasons why a high expansion ratio cannot be obtained.

The present inventors have proposed a base polymer, which is an essential condition as a biodegradable resin having a high foaming property.
As a result of detailed studies on an additive for increasing the molecular weight, an additive for foaming, and the like, a biodegradable resin composition having sufficient productivity was found, and an invention was proposed (Japanese Patent Application Laid-Open No. HEI 9-205). However, although the resin composition obtained by the present invention can obtain expanded particles having a high expansion ratio, the expansion ratio varies, and the expansion properties such as expanded cell diameter and expanded particle diameter are unstable. Contains. Solving this problem is indispensable for production of foamed particles mainly composed of polylactic acid and molded products thereof, and for market entry.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies on polylactic acid compositions having excellent foaming properties.
Crystallinity, weight average molecular weight, number average molecular weight, and polydispersity of polylactic acid, which is a starting material of the resin composition, are very important factors. By controlling these within a specific range, the resin and polylactic acid can be used. It has been found that foamed particles having a high expansion ratio can be obtained extremely stably from a polylactic acid resin composition obtained by blending an isocyanate.

That is, the present invention relates to a polylactic acid resin composition comprising polylactic acid and a polyisocyanate, wherein the polylactic acid has a molar ratio between L-form and D-form of 95/5 to 60/4.
0, the weight average molecular weight and the number average molecular weight are 200,
A biodegradable and foamable polylactic acid resin composition having a polydispersity (ratio of weight average molecular weight to number average molecular weight) of 6 or more and 40,000 or more. It is.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Polylactic acid composed of D-form and L-form used in the present invention includes polylactic acid having a melting point but a small heat of fusion. That is, the polylactic acid has a heat of fusion (2nd scan @ H) of 0.1 J / g or less as measured by DSC, and corresponds to a D-copolymerization ratio of 5 mol% or more. The copolymerization ratio of the D-form and the L-form of the polylactic acid used in the present invention needs to be 5 to 40 mol% for the D-form. In particular, when expanded particles having a high expansion ratio are required, the heat of fusion (2
The D-form without nd scan (H) is preferably 8 to 20 mol%. If the molar ratio of the D-form is less than this range, the polylactic acid has high crystallinity, and cannot be used from a resin composition using this resin because the expansion ratio does not increase or the foaming becomes uneven. On the other hand, if the D-form exceeds 40 mol%, heat resistance is inferior, so that it is not suitable.

The polylactic acid used in the present invention must have a weight average molecular weight and a number average molecular weight of 200,000 or more and 40,000 or more, respectively. The weight average molecular weight is preferably 200,000 or more, particularly preferably 220,000 or more. The resin composition obtained by using polylactic acid in this range stably provides expanded particles having a high expansion ratio. On the other hand, the weight average molecular weight of polylactic acid is 200,
If it is less than 000, the expansion ratio will fluctuate from the resin composition obtained therefrom, and it will not be possible to stably obtain expanded particles having a high expansion ratio. For the same reason, the number average molecular weight is preferably 40,000 or more, particularly preferably 50,000 or more. If it is less than 40,000, the same result as the weight average molecular weight can be obtained.

However, it is not possible to obtain a resin composition which stably provides expanded particles having a high expansion ratio, which is the object of the present invention, by merely controlling either the weight average molecular weight or the number average molecular weight. . The present inventors have found that, in addition to these constituent requirements, the ratio between them, that is, the polydispersity is an important requirement, and found that the value is preferably 6 or less, particularly preferably 5 or less. That is, by using polylactic acid whose weight average molecular weight, number average molecular weight and polydispersity are controlled within a predetermined range, the resin composition obtained therefrom can provide stable and highly expandable foamed particles. You can. When the polydispersity exceeds 6, an extreme decrease in the expansion ratio occurs.

The polylactic acid used in the present invention may be a polylactic acid branched by adding a small amount of a polyhydric alcohol, polycarboxylic acid, polyepoxy compound or the like having three or more functions. Blend or copolymerize other resins within a range that does not impair excellent properties such as biodegradability, foaming properties, morphological stability of foamed molded articles, storage properties of foamed particles, mechanical properties, chemical resistance, etc. Can be done. The proportion of the resin to be blended or copolymerized depends on the nature of the resin, but is generally within 5% by weight.

With the polylactic acid of the present invention thus obtained alone, even if a foaming agent, a foaming aid, a foam nucleating agent, etc. are blended or added, the foaming ratio is extremely small at several times or less. Is difficult to use. In order to obtain a highly foamable resin, it is necessary to further increase the molecular weight of the polylactic acid used in the present invention.
It has been found that it is effective to add a predetermined amount of polyisocyanate to the polylactic acid to increase the viscosity.

The polyisocyanate used in the present invention may be any of aromatic, alicyclic and aliphatic polyisocyanates. Examples of the aromatic polyisocyanate include trisphenylphenylmethane, naphthylene, tolidine, xylene and xylene. Triphenylmethane-based polyisocyanates, alicyclic polyisocyanates include isophorone, hydrogenated diphenylmethane-based polyisocyanates, and aliphatic polyisocyanates include hexamethylene and lysine-based polyisocyanates. From the viewpoint of general versatility, handleability, weather resistance, etc., triresiphenylmethane, particularly diphenylmethane, is preferably used.

The number of functional groups of these polyisocyanates is
It is preferable that the amount is 2 equivalents or more from the viewpoint of increasing the melt viscosity of the polylactic acid composition. A more preferred number of functional groups is 2.
3 equivalents or more, especially 2.7 equivalents or more are good. The mixing amount of the polyisocyanate is preferably 0.5 to 3% by weight, and the particularly preferable mixing amount of the polyisocyanate is 0.8 to 2% by weight. When the mixing amount is in this range, the melt viscosity is likely to increase, the branch density and the crosslink density will be appropriate, and the foamability will be good.

Next, in the present invention, the number of foam cells is increased,
A foam nucleating agent is used according to a conventional method for the purpose of making it uniform and small. As a foaming nucleating agent to be mixed and dispersed in polylactic acid, talc, diatomaceous earth, silica, kaolin, zeolite, mica, alumina, bentonite, asbestos and the like can be used. The compounding amount is preferably 0.5 to 20% by weight based on the polylactic acid, and more preferably 2 to 10% by weight.
It is.

Among these foam nucleating agents, talc is particularly preferably used in view of the number of foam cells, the uniformity of the cells and the size thereof. The average particle size of the foam nucleating agent such as talc used in the present invention is preferably 10 μm or less, more preferably 5 μm or less.

The method of adding and dispersing a foam nucleating agent such as polyisocyanate and talc to the polylactic acid used in the present invention is a polymerization step of obtaining polylactic acid from lactide, kneading the polylactic acid with a thickener and a foam nucleating agent. Any method of melt-kneading with a mixer or the like may be used. For example, in order to add and disperse a foam nucleating agent having a high concentration of 2% by weight or more, a method of melt-kneading using a twin-screw kneader is preferable. The method of melt kneading using a twin-screw kneader is also preferable due to its strong reactivity.

The polylactic acid resin composition thus obtained is impregnated with a foaming agent and a foaming aid by a usual method, and foamed particles having a high foaming ratio and a molded product thereof can be obtained by a foaming treatment. The blowing agent used in the present invention is a hydrocarbon compound having 2 to 6 carbon atoms, which is a homolog or an isomer such as ethane, propane, butane, pentane or hexane, or methyl chloride, dichloromethane, chloroform, fluoromethane, difluoro. Halogen or hydrogen compounds such as methane and trifluoromethane are mainly used. Among these, butane, pentane or a mixture thereof is particularly preferably used.

In the present invention, it is preferable to use a foaming aid in addition to these foaming agents. When using foaming aids,
It is preferable because the polylactic acid resin composition is sufficiently impregnated with the hydrocarbon compound as a foaming agent and foamed particles having a high foaming ratio can be obtained.

As the foaming aid, a low molecular weight aromatic compound such as benzene, toluene, or xylene is generally used, but no effect is observed in the polylactic acid composition of the present invention. The foaming aid used in the present invention is preferably an aliphatic alcohol having 1 to 4 carbon atoms, or a lower aliphatic ketone such as acetone, methyl ethyl ketone or diethyl ketone. Among these foaming aids, methyl alcohol, ethyl alcohol,
Acetone is particularly preferably used.

The polylactic acid resin composition of the present invention comprises a foaming agent,
The impregnation of the foaming aid can be carried out in an aqueous dispersion or non-aqueous system, which is a usual method, under heating and under high pressure. For example, a predetermined amount of the polylactic acid composition of the present invention, a foaming agent, and a foaming assistant are charged into an autoclave, and the foamed particles can be easily obtained by heating for several hours while maintaining the internal temperature at 80 to 90 ° C.

The expandable particles obtained in the present invention can be treated under the conditions of, for example, a steam temperature of 50 to 105 ° C. and a processing time of 10 to 300 seconds to obtain expanded particles having a high expansion ratio, which is the object of the treatment. A similar molded article can be obtained from the expanded particles.

Further, the polylactic acid resin composition of the present invention comprises:
Depending on the purpose, other additives such as a heat stabilizer, an antioxidant, an antistatic agent, a conductive agent, a flame retardant, an ultraviolet absorber, and a plasticizer can be appropriately added. However, flame retardants and the like are often halides such as chlorine, and are preferably kept to a minimum from the viewpoint of biodegradability and the generation of harmful substances during incineration.

The highly expandable foamed particles and the molded product obtained by using the polylactic acid resin composition of the present invention can be used for, for example, foam containers for foods, It can be used for various purposes such as food containers, foam sheets, loose cushioning materials, molded cushioning materials, porous sheets or molded articles, and has a very high economic value.

[0030]

The present invention will be described more specifically with reference to the following examples and comparative examples. In addition, evaluation was performed by the following method.

ΔH: DSC7 manufactured by PerkinElmer was used. After the first scan of 10 mg of the sample heated to 200 ° C. at 10 ° C./min, it was quenched and brought to 0 ° C., and the second scan heated to 200 ° C. at 10 ° C./min.
Measured with n.

Weight average molecular weight, number average molecular weight, polydispersity: evaluation by GPC Sample preparation: About 100 mg of resin is completely dissolved in 50 ml of chloroform. This was filtered through a 0.45 μm membrane filter to obtain a test solution. GPC measurement conditions: Pump Hitachi L-6000A column GMH _XL (7.8 mm ID × 30 cm) Eluent chloroform Flow rate 1.0 ml / min Temperature 35 ° C. Detector RI (Tosoh) Injection volume 100 μl (Hitachi Autosampler L-7200)
Use) Molecular weight calibration curve: Prepared based on standard polystyrene

Melt viscosity: Measuring instrument: Koka type flow tester (C manufactured by Shimadzu Corporation)
TF-500) Measurement conditions: Measurement temperature 190 ° C. Orifice diameter 2 mm Load 130 kg

Impregnation rate: calculated from the weight of particles obtained according to the method of Production Example 3 by the following equation. Impregnation rate (%) = ((weight of impregnated particles−1000) / 1
000) × 100

Expansion ratio: The volume of the expandable particles before expansion and the volume of the expandable particles were measured using a measuring cylinder, and the expansion ratio was determined from the ratio between the two.

Evaluation of molded article Tensile strength: Measured according to JIS K-6767. Sample: Prepared by cutting out a molded product of 300 × 300 × 30 mm.

Flexibility: Measure compressive stress Measured according to JIS K-7220. Specimen: 300 × 300 × 60 mm molded product to length 10
It is made by cutting out a shape object of 0 mm, width 100 mm and height 50 mm. Measurement: Using a Tensilon tester, compression was performed at a compression speed of 10 mm / min, and a 10% strain stress (kgf / cm ² ) was measured.

Buffering property: The dynamic buffering coefficient was measured. Specimen: 300 × 300 × 60 mm molded product to length 10
It is made by cutting out a shape object of 0 mm, width 100 mm and thickness 50 mm. Measurement: Using a Yoshida Seiki CST320 type tester, the impact load, thickness displacement, and maximum acceleration were measured while changing the falling weight with a falling height of 35 cm and the minimum acceleration was obtained from the load-maximum acceleration diagram. The dynamic buffer coefficient was calculated by the following equation. Buffer coefficient = minimum acceleration × ｛(fall height + compression displacement) /
Sample thickness｝

Production Example 1: Production Example of Polylactic Acid Commercially available L-lactide and D-lactide were each purified by recrystallization using ethyl acetate. Purified L-lactide, D-lactide and tin octylate as a catalyst were added at 10 ppm as tin, D-lactide was charged into an autoclave with a stirrer so as to have the composition shown in Table 1, and after deaeration under reduced pressure, under N2 atmosphere 170-210 ° C, 0.5-
The mixture was heated for 3 hours to effect ring-opening polymerization. After completion of the reaction, the polymer was taken out of the autoclave, and the weight average molecular weight, the number average molecular weight, and the polydispersity were measured. Table 1 shows the results.
It was shown to.

[0040]

[Table 1]

Production Example 2: Production Example of Polylactic Acid Composition Next, the polymer was dried until the water content became 1000 ppm or less, and then 3% by weight of talc based on the polymer was used.
After blending 1% by weight of diphenylmethane polyisocyanate and 2.8 equivalents / mol of functional groups, the mixture was fed to a twin-screw kneader, and the number of rotations was 100 rpm and the melting temperature was 18
The reaction was kneaded under the conditions of 0 ° C., residence time of 3 to 5 minutes, and discharge rate of 10 kg / hour. After cutting the obtained polylactic acid composition, aging treatment was performed to obtain particles having a diameter of about 1.5 mm.

Production Example 3: Production Example of Expanded Particles 1000 parts of the polylactic acid composition exemplified in Production Example 2, 300 parts of isopentane as a foaming agent, and 50 parts of methanol as a foaming aid were charged into a rotary autoclave at a temperature of 80-9.
After maintaining at 0 ° C. and a rotation speed of 3 rpm for 2 hours, the mixture was cooled to obtain expandable particles having an impregnation ratio of 3 to 13%. Then, 500 ppm of zinc stearate was blended with the expandable particles, and about 3 kg was added to a pre-expanding machine (DYHL-300, Daisen Industries Co., Ltd.).
It was charged and kept at a temperature of 85 ° C. for 1 minute with steam.
After the obtained expanded particles were air-dried, the expansion ratio was measured.

Production Example 4: Production Example of Molded Product A foam molding machine (DS-300L-M, Daisen Industries Co., Ltd.)
C) 300x300x30mm or 300x300x
A mold having a size of 60 mm was installed, and the foamed particles exemplified in Production Example 3 were aged for 24 hours and then filled, and then steam pressure was 0.5
The mixture was treated at a rate of 10 kg / cm ² for 10 to 30 seconds and molded to obtain a molded product. The molded article was evaluated for density, flexibility and cushioning property.

Examples 1 to 4 and Comparative Examples 1 to 3 Polylactic acid compositions produced by the methods exemplified in Production Examples 1 and 2 (Examples 1 to 4 and Comparative Examples 1 to 2 (P1 to P6))
And polystyrene particles as a control (Comparative Example 3) were impregnated by the method exemplified in Production Example 3 to obtain expandable particles having an impregnation ratio of 2 to 12% by weight, and magnesium stearate was blended with the expandable particles. Then, the mixture was treated by the method and conditions exemplified in Production Example 3 to obtain expanded particles. The control polystyrene particles (Comparative Example 3) used the same amount of isopentane as a foaming agent, and the foaming treatment was performed at a steam temperature of 95 ° C. for 1 minute. After measuring the expansion ratio of the obtained expanded particles, molding was performed by the method exemplified in Production Example 4 to obtain each molded product, and the physical properties of these molded products were evaluated.

[0045]

[Table 2]

Evaluation Results From the results shown in Table 2, Comparative Example 1 (P1) has good crystallinity and crystallinity despite satisfying the weight average molecular weight, number average molecular weight and polydispersity required for the present invention. Due to the high degree of conversion, the expansion ratio is extremely small and cannot be used as a foam.
In Examples 1 to 4 (P2 to P5), the expansion ratio of the expanded particles, which is the object of the present invention, is high.
4) was at the same level as the expansion ratio of polystyrene as a control, and a favorable result was obtained. In Comparative Example 2 (P6), the expansion ratio was high, but the heat resistance of the molded product obtained by molding the expanded particles was poor. Examples 2 to 4 (P3 to P
The mechanical properties such as tensile strength, compressive stress and buffer coefficient of the molded product obtained by molding the expanded particles of 5) were equivalent to those of the control polystyrene.

Examples 5-7, Comparative Examples 3, 4-8 Polylactic acid compositions (Examples 2, 5-7 and Comparative Examples 3-8 (P3, P7
To P14)) and polystyrene particles as a control (Comparative Example 3) were impregnated by the method exemplified in Production Example 3 to obtain expandable particles having an impregnation ratio of 2 to 12% by weight. Production Example 3 was prepared by blending 0.05% by weight of zinc stearate with the expandable particles.
And foamed particles were obtained. The control polystyrene particles were treated at a steam temperature of 95 ° C. for 1 minute. After measuring the expansion ratio of the obtained expanded particles, molding was performed by the method exemplified in Production Example 4 to obtain each molded product, and the physical properties of these molded products were evaluated.

[0048]

[Table 3]

Evaluation Results Regarding the relationship between the weight average molecular weight and the expansion ratio, as apparent from the comparison between Comparative Example 4, Examples 5 and 2 (P7, P8, P3), when the weight average molecular weight falls below 200,000, Magnification drops extremely. Examples 5 and 2 (P
8, P3) has a weight average molecular weight of 20 within the scope of the present invention.
The expansion ratio was good at 000 or more, which was comparable to the control polystyrene (Comparative Example 3). Furthermore,
The mechanical properties of a molded product obtained by molding these expanded particles were almost the same as those of expanded styrene. Regarding the relationship between the number average molecular weight and the expansion ratio, the expansion ratio was good except for Comparative Example 5 (P9) as apparent from the comparison of Comparative Example 5, Examples 6, 7 and 2 (P9 to P11, P3). Met. Comparative Example 5 (P9) had a weight average molecular weight of 2
Although the number average molecular weight was less than 40,000, the foaming ratio was low even though it exceeded 00,000. In Examples 6, 7, and 2 (P10, P11, and P3), the number average molecular weight was 40,000 or more, and the expansion ratio was good. Number average molecular weight 40,0
00 is the critical point of foaming. Furthermore, if the number average molecular weight is 50,000 or more, the expansion ratio is further improved. Regarding the relationship between polydispersity and expansion ratio, Comparative Examples 6 to 8 (P12 to P14), Examples 2 and 6
As is clear from (P3 and P10), Comparative Examples 6 to 8 (P12 to P14) having a polydispersity degree of more than 6 had foaming ratios higher than 200,000 despite the weight average exceeding 200,000. Extremely low, greatly deviating from the object of the present invention. One of the causes of an increase in polydispersity is the molecular weight and number of oligomers in polylactic acid. The polydispersity increases as the molecular weight decreases and the number of molecules increases.
Therefore, as is apparent from the present invention, in order to obtain a polylactic acid composition having a large expansion ratio, it is necessary to use a polylactic acid having a weight-average molecular weight, a number-average molecular weight, and a polydispersity within a comprehensively determined range. is necessary.

Examples 8-11, Comparative Examples 9-11 Polylactic acid P3 produced by the method exemplified in Production Example 1
Then, a predetermined amount of a diphenylmethane polyisocyanate having a functional group of 8 equivalents / mole was blended by the method exemplified in Production Example 2 to obtain a polylactic acid resin composition. The resin composition was impregnated by the method exemplified in Production Example 3 to obtain expandable particles having an impregnation ratio of 1 to 12% by weight. 0.05% by weight of zinc stearate was blended with the expandable particles and treated by the method exemplified in Production Example 3 to obtain expanded particles. The control polystyrene particles were treated at a steam temperature of 95 ° C. for 1 minute. After measuring the expansion ratio of the obtained expanded particles, molding was performed by the method exemplified in Production Example 4 to obtain each molded product, and the physical properties of these molded products were evaluated.

[0051]

[Table 4]

Evaluation Results In Comparative Examples 1 and 2 in which no polyisocyanate was added and the blend amount was less than 0.5%, only the results that the melt viscosity of the resin composition was low and the expansion ratio was low were obtained. When the blended amount of the polyisocyanate was 0.5% or more, the melt viscosity of the resin composition increased with the added amount of the blended amount of the polyisocyanate, and the expansion ratio also improved, and was at the same level as the expanded polystyrene. However, when the blend amount of the polyisocyanate exceeded 3%, the melt viscosity increased but the expansion ratio rapidly decreased. It is considered that the cause is that the crosslinking reaction by the polyisocyanate excessively proceeded, the molecules were strongly restrained by the crosslinked structure, and foaming was inhibited. 0.5% by weight of polyisocyanate
It can be said that ２2% by weight is particularly preferable.

[0053]

As described above, the biodegradable polylactic acid resin composition obtained by the present invention can produce expanded particles having a high expansion ratio and molded products thereof, and these are required for packaging materials. It has a sufficient function, and can be obtained at the same level as the conventionally used expanded polystyrene (PS) with good production efficiency and at low cost, contributing to global environmental conservation.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoshi Yoshimoto 4-1 Kanebo-cho, Hofu-shi, Yamaguchi Prefecture Inside Kanebo Goden Co., Ltd. (72) Inventor Masahiro 4-1 4-1 Kanebo-cho, Hofu City, Yamaguchi Prefecture Kanebo God Co., Ltd. (72) Inventor Tsunadai Nakae 276 F. Osaki, Hofu-shi, Yamaguchi 516 F term (reference) 4F074 AA68 AA81 AB00 AB01 AB02 AB05 AF00 BA35 BA36 BA37 BA39 BA40 BA44 BA45 BA46 BA53 BA73 BA95 BC15 CA24 CC04X CC05X CC10X CC22X CC25X CC28X DA02 DA03 DA33 DA34 4J034 BA03 DA01 DA05 DB04 DB08 DC50 DF01 DF24 HA01 HA07 HA11 HC03 HC12 HC13 HC17 HC46 HC52 HC61 HC65 HC67 HC71 HC73 NA01 NA02 NA03 NA05 NA06 NA08 QA03 QA05 QB19 QC01 RA06

Claims (6)

[Claims] 1. A polylactic acid resin composition comprising a polylactic acid and a polyisocyanate, wherein the polylactic acid comprises L
The molar ratio of the isomer to the D-isomer is 95/5 to 60/40, the weight average molecular weight and the number average molecular weight are 200,000 or more and 40,000 or more, and the polydispersity (weight average molecular weight and A biodegradable and foamable polylactic acid resin composition having a number average molecular weight of 6 or less. 2. The polylactic acid has a molar ratio of L-form to D-form of 9
The polylactic acid resin composition according to claim 1, which is in the range of 2/8 to 80/20. 3. The polylactic acid has a weight average molecular weight of 220,0.
The polylactic acid resin composition according to claim 1, which is at least 00. 4. The polylactic acid has a number average molecular weight of 50,000.
The polylactic acid resin composition according to claim 1, which is the above. 5. The polylactic acid resin composition according to claim 1, wherein the polydispersity (the ratio of the weight average molecular weight to the number average molecular weight) is 5 or less. 6. The compounding amount of the polyisocyanate is 0.5 to
The polylactic acid resin composition according to claim 1, which is 2% by weight.