JP2000178346A - Expandable resin composition having biodegradability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an expandable resin composition which has biodegradability and is excellent in productivity. SOLUTION: The resin composition, whose melt viscosity is 5 or less in terms of a melt index (MI), is prepared by blending 0.5-5 wt.% of a polyisocyanate having 2.0 equivalents/mol or more of isocyanate groups and 5-30 wt.% of particles selected from a substantially spherical metallic oxide or sulfate having an aspect ratio of 1.5 or less and an average particle size of 3 μm or less with a polylactic acid in which the molar ratio of the L to D bodies is 95/5-60/40 or 40/60-5/95, the wt.% being based on the polylactic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a resin composition for a foam used as a cushioning material for packing having biodegradability.

[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. Because
It is difficult to dispose after use, burns high in calories even if incinerated, does not decompose even if incinerator is buried, and does not decompose even if it is landfilled. Is becoming a problem.

[0003] In addition, the effects of natural foams, such as rivers and oceans, caused by foams discarded without being disposed of are no longer ignored. Therefore, resins that decompose in the ecosystem and have less impact on the global environment have been developed. For example, polyhydroxybutyrate-based resins synthesized in the body of microorganisms, polyesters composed of aliphatic glycols and aliphatic carboxylic acids, or polyester-based resins containing caprolactone as a main component have been proposed. Produces low purity, low productivity and limited use.

[0004] 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, the biodegradable resin is used. However, since it is not practically used and the raw materials are petroleum and natural gas, when it is decomposed, carbon dioxide is newly added to the carbon dioxide present on the earth, and does not contribute to suppressing an increase in carbon dioxide. In the long term, oil and natural gas are limited, so that it becomes difficult to obtain them eventually, and they cannot contribute to the real conservation of the global environment.

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 used as medical fibers. The crystallinity has been imparted, and as it is, it has not been used in a large amount as a foam in packaging containers and cushioning materials.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a foamable resin composition having biodegradability and excellent productivity, that is,
An object of the present invention is to provide a foamable resin composition which can be decomposed by microorganisms, has little impact on the global environment even when disposed after use, has high productivity, and can be put to practical use. The present inventors have conducted detailed studies on a base polymer, an additive for increasing the molecular weight of the base polymer, a foaming agent for foaming, and an additive such as a foaming aid. The present inventors have found a biodegradable resin composition having the following, and have already proposed the invention. However, it has been found that the resin composition obtained by the present invention is slightly inferior in the dimensional stability of the molded product (the size of the molded product with respect to the mold size) as compared with polystyrene used as a general-purpose foam molded product. .

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, a specific metal oxide or metal sulfate is added to the polylactic acid resin composition used in the present invention. As a result, they have found that the same level of dimensional stability as that of a polystyrene foam is maintained, and have reached the present invention.

That is, according to the present invention, the molar ratio of L-form to D-form is 95
/ 5 to 64/40, or 40/60 to 5/95, a polyisocyanate having an isocyanate group ≧ 2.0 equivalents / mol is added to the polylactic acid in an amount of 0.5 to 5% by weight based on the polylactic acid.
And 5 to 30% by weight of particles selected from substantially spherical metal oxides or metal sulfates having an aspect ratio of 1.5 or less and an average particle size of 3 μm or less. (MI) is 5 or less.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, it has biodegradability, which is one of the basic conditions, and minimizes the increase in carbon dioxide in nature.
In consideration of productivity and cost that can be put to practical use, a polylactic acid resin starting from lactic acid starting from cereal starch such as corn is preferred. However, those usually used for fibers lack mechanical properties, heat resistance, etc., unless they have crystallinity.
% Is used. On the other hand, in order to form a foam, at least the crystallinity must be as small as possible. The reason is that the crystallization of the crystalline resin proceeds in the step of impregnating the foaming agent, and the resin itself does not stretch during foaming.

Therefore, the polylactic acid referred to in the present invention is a substantially amorphous polylactic acid, and the molar ratio of L-form to D-form is 9%.
Use 5/5 to 60/40 or 40/60 to 5/95 lactic acid. Those having a molar ratio of L-form / D-form of more than 95/5 or less than 5/95 have high crystallinity and cannot be used because the expansion ratio does not increase or the foaming becomes uneven. Those having a ratio of less than 60/40 to more than 40/60 have poor heat resistance and cannot be used. Preferably 90/10 or less to 70/30 or more, or 30/70 or less to 10/90
It is better to be above.

On the other hand, the resin used for the foam is preferably a resin having good gas barrier properties in order to minimize volatilization of the impregnated foaming agent during storage. That is, a resin having a glass transition point (Tg) is used. Among the biodegradable resins, the polylactic acid resin has a higher glass transition point than other biodegradable resins, and thus is suitable for the purpose of the present invention. However, the glass transition point of polylactic acid decreases slightly but slightly according to the ratio of the L-form and the D-form, and reaches a minimum at 50/50. When the glass transition point is reduced, the foaming property is reduced with time for the above-mentioned reason, and the heat resistance of the foam is also undesirably reduced. That is, the glass transition point is preferably 50 ° C. or higher, and therefore, it is necessary that the ratio of the D-form is 40 mol or less or 60 mol% or more, preferably 30 mol or less or 70 mol or more.

Next, it is preferable that the melt viscosity of polylactic acid as the base polymer used in the present invention is higher, and the melt viscosity is JIS K 7210 (load 2.16 kg).
Melt index value (MI) according to f) 1 to 1
It is in the range of 0, more preferably in the range of 1-5.
A resin having a melt viscosity of polylactic acid of less than 1 is difficult to produce by a commonly used method described below.
A resin composition obtained by increasing the viscosity of polylactic acid having a melt viscosity exceeding 0 becomes a foam having a low expansion ratio, and a favorable result cannot be obtained. The reason is that when the same ultrahigh-viscosity resin is obtained by reacting polylactic acid with a low melt viscosity and polylactic acid with a high melt viscosity as a base polymer and reacting with the polyisocyanate described below, the starting material has a low melt viscosity. This is because the resin composition made of polylactic acid has too high a branch density than that of a high melt viscosity, and is likely to have a cross-linked structure, thereby inhibiting foaming.

In general, as means for obtaining polylactic acid having a high melt viscosity, melt polymerization under a high vacuum in a usual reactor, with good stirring efficiency, melt polymerization by a twin-screw kneader, melt polymerization and solidification Although there is a combination with phase polymerization, the reaction is prolonged due to the high viscosity, the productivity is reduced, and it is necessary to pay sufficient attention to the quality deterioration due to thermal decomposition of the resin.

According to this method, the melt viscosity becomes JIS K
Polylactic acid having a melt index value (MI) in the range of 1 to 10 in accordance with 7210 (load 2.16 kgf) can be obtained. Is low and not practical. In order to obtain a high expansion ratio, a resin having a higher melt viscosity is required, and there is a limit in melt polymerization alone.

The present inventors have conducted intensive studies and found that 0.5 to 5% by weight, preferably 1 to 3% by weight, of polyisocyanate having an isocyanate group ≧ 2.0 equivalents / mol relative to the polylactic acid was used. And melted in a molten state to make the melt viscosity JIS K 7210 (load 21.6 kg
A resin composition having a good foaming property having a melt index value (MI) based on f) of 5 or less could be obtained. When the polyisocyanate is less than 5% by weight, the melt viscosity of the resin composition does not increase so much. When the polyisocyanate exceeds 5% by weight, the melt viscosity of the resin composition increases but unreacted polyisocyanate remains or the branch density decreases. It becomes too large and the crosslinking reaction proceeds, so that a large amount of gelled matter is generated and the foaming property is conversely reduced.

Here, as a method of mixing and reacting polylactic acid and polyisocyanate in a molten state to make them ultra-high molecular weight, a usual known method is possible. For example, a method in which a polyisocyanate is added to a pelletized polylactic acid and mixed and melt-mixed with a single-screw or twin-screw kneader, or a method in which polylactic acid is previously melted with a single-screw or a twin-screw kneader or the like, and then the polyisocyanate is added. The target resin composition can be obtained by, for example, producing polylactic acid by melt polymerization using a single-screw or twin-screw kneader or adding a polyisocyanate during the production.

The polyisocyanates used include aromatic, alicyclic and aliphatic polyisocyanates.
For example, as the aromatic polyisocyanate, tolylene,
Diphenylmethane, naphthylene, tolidine, xylene,
A polyisocyanate having a triphenylmethane skeleton,
Examples of alicyclic polyisocyanates include isophorone and polyisocyanates having a skeleton of hydrogenated diphenylmethane, and examples of aliphatic polyisocyanates include polyisocyanates having a skeleton of hexamethylene and lysine. Tolylene, diphenylmethane, especially diphenylmethane is preferably used from the viewpoint of weather resistance and the like.

The polylactic acid resin composition thus obtained is
When a foaming agent and a foaming aid described below are impregnated and subjected to a foaming treatment, a foam having a high expansion ratio is obtained. However, it was found that the molded product molded from the foam had slightly smaller dimensional stability (larger shrinkage allowance) than the polystyrene molded product when removed from the mold. Although the cause is not clear, it is considered that one of the factors is that the glass transition point of polylactic acid is lower than that of polystyrene.

The present inventors have conducted various studies to overcome this problem, and as a result, by adding a metal oxide or metal sulfate having a specific aspect ratio and a specific particle size,
It has been found that dimensional stability is greatly improved.

The average particle size of the metal oxide or metal sulfate used in the present invention is required to be 3 μm or less, more preferably 1 μm or less. If the average particle diameter exceeds 3 μm, the effect of dimensional stabilization is reduced, and this deviates from the object of the present invention. On the other hand, the thickness of the cell of the foam is about 1.5 μm, and particles having a large particle diameter inhibit the formation of the film, and lack the uniformity of the cell size. As a result, the expansion ratio is large. No. When the average particle diameter is 1 μm or less, the obstruction to cell membrane formation is small, the cell size is uniform, the foaming ratio is high, and more preferable results can be obtained.

The metal oxide and metal sulfate particles used in the present invention must have an aspect ratio of 1.5 or less. If the aspect ratio exceeds 1.5, the flowability of the resin composition is impaired, and the foamability is undesirably reduced. When the aspect ratio is 1.5 or less, the fluidity of the resin composition is hardly hindered, and more preferably 1.2 or less.
That is, the metal oxide and metal sulfate particles to be blended must be substantially spherical.

The content of these particles is preferably 5 to 30% by weight, more preferably 10 to 20% by weight, based on the resin composition. If the amount is less than 5% by weight, there is almost no effect on the improvement of dimensional stability. If the amount exceeds 30% by weight, the compounded resin composition becomes hard and the dimensional stability is improved, but the expansion ratio is extremely reduced.

The metal oxide and the metal sulfate to be blended may be any as long as they have the above-mentioned particle diameter and aspect ratio and do not react with the resin. Examples of the metal oxide include aluminum oxide, silicon dioxide, and the like. Titanium oxide is preferably used. Barium sulfate is preferred as the metal sulfate.

The compounding of the metal oxide and the metal sulfate used in the present invention with the resin can be carried out by a known method. As described above, polylactic acid, isocyanate and the metal oxide or the metal sulfate are previously compounded. There are various methods such as a method of melt-kneading with a single or twin screw kneader, a method of adding and kneading an isocyanate and a metal oxide or a metal sulfate to the molten polylactic acid. A method in which a predetermined amount of a substance or a metal sulfate is blended and melt-kneaded by a twin-screw kneader is preferably used because of good dispersibility of the three components.

In order to form uniform and fine foam cells, it is preferable to add a foam nucleating agent. As the foam nucleating agent to be used, solid particulate matter, for example, inorganic particles such as talc, kaolin, zeolite, and mica are suitable. Among them, talc is preferably used for the resin composition of the present invention.

Further, other additives can be appropriately added according to the purpose, and examples thereof include a heat stabilizer, an antioxidant, a flame retardant, an ultraviolet absorber, and a plasticizer. However, the flame retardant or the like is often a halide such as chlorine, and is preferably minimized from the viewpoint of biodegradability and generation of harmful substances during incineration.

The resin composition thus obtained is formed into pellets or bead-shaped particles and then impregnated with a foaming agent and a foaming aid. These particles are usually subjected to primary foaming (preliminary foaming) by heating, and the foaming ratio is temporarily increased from several times to 30 to 30 times.
These are expanded into 50-fold expanded particles, then placed in a mold, and further heated to secondary expansion to form a desired molded body.

Examples of the foaming agent and foaming aid used herein include hydrocarbons such as propane, n-butane, isobutane, n-pentane, sopentane, cyclopentane and hexane, and halogens such as methylene chloride, methyl chloride and dichlorodifluoromethane. Hydrocarbons, dimethyl ether, ethers such as methyl ethyl ether as a foaming agent,
Also, alcohols having 1 to 4 carbon atoms, ketones, ethers,
Benzene, toluene and the like are used as foaming aids.

The combination of a foaming agent and a foaming aid must be appropriately selected depending on the resin used. In the case of the L-form / D-form copolymerized polylactic acid polymer used in the present invention, butane or pentane having a low boiling point is preferably used as a blowing agent. Further, a monohydric alcohol having 1 to 4 carbon atoms is suitable as a foaming aid to be combined therewith. There are various other combinations, and they can be selected in consideration of effects and economics.

The volume ratio of the foaming agent and the foaming assistant can be as follows: foaming agent / foaming assistant = 1/2 to 10/1.
This ratio varies depending on the combination of the foaming agent and the foaming auxiliary, and is generally 1/2 to 2/1. The content (ratio) of the foaming agent and the foaming auxiliary varies depending on the desired expansion ratio and the storage period of the pellets or bead particles, but is usually 5 to 15% by weight as the foaming agent. The content (rate) of the blowing agent can be selected according to the expansion ratio. Generally, the content (ratio) of a low-foamed product may be low, and the content (ratio) of a highly foamed product may be high.

Pellets or bead particles containing a foaming agent and a foaming aid are pre-foamed, then put into a desired mold, further heated to promote foaming, and the cells are fused together to form a strong compact. Shape the body. It is basically the same as the conventional polystyrene (PS) foam molding method. That is, steam having a large heat capacity is preferably used for both prefoaming and foam molding.

The dimensions of the obtained foam molded article are ideally closer to the dimensions of the mold. From a practical point of view, the shrinkage is preferably 2% or less, and the polylactic acid used in the present invention alone has a shrinkage of around 6%, which is a large value compared to polystyrene. However, by incorporating the particles of the present invention, the shrinkage was significantly reduced to 2% or less.

[0033]

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. (Evaluation method) (1) MI of polylactic acid as base polymer: JIS
Measured by a method according to K7210. (Measurement temperature 10
(0 ° C., orifice diameter 2 mm, load of 2.16 kg) (2) MI of the resin composition: Measured by a method in accordance with JIS K 7210. (Measurement temperature 100 ° C, orifice diameter 2
(3) Expansion ratio: The volume of the foaming agent-impregnated pellet before foaming and the volume of the pre-expanded particles were measured using a measuring cylinder, and the expansion ratio was determined as follows. Expansion ratio (times) = volume of pre-expanded particles / volume of pellets impregnated with blowing agent (4) Dimensional stability: 300 × 300 × 30
A mold having a diameter of ² mm was set, and the pre-foamed foam was filled, processed at a steam pressure of 0.2 kgf / cm ² , and molded.
After allowing the obtained molded body to cool at room temperature for 30 minutes, the dimensions were measured, and the dimensional stability was calculated by the following formula. Dimensional stability (% shrinkage) = (1- (dimension of molded product / 30)
0)) × 100 (5) Biodegradability: The pre-expanded particles were put into compost for one month, and the appearance was evaluated as follows. ：: Decomposed to the state where the original shape is not stopped.

Production Example Commercially available L-lactide and D-lactide were each purified by recrystallization using ethyl acetate. Table 1 shows purified L-lactide, D-lactide and tin octylate as a catalyst.
It was charged into an autoclave equipped with a stirrer so as to composition, after vacuum degassing, and ring-opening polymerization in each polymerization conditions under N _2. After completion of the reaction, the polymer was taken out of the autoclave, and the viscosity (ηr) was measured.
A polymer of 3.5 was obtained.

[0035]

[Table 1]

Examples 1 to 11 and Comparative Examples 1 to 6 The isocyanate compound "Millionate MR-200" (isocyanate group 2.7 to
2.8 equivalents / mole, Nippon Polyurethane Industry Co., Ltd.), titanium oxide (aspect ratio 1.2) and talc “LMP-
100 "(Fuji Talc Kogyo) 1.0% by weight
Was kneaded at a cylinder temperature of 180 ° C. with a twin-screw kneader (PCM-30, Ikegai Iron Works, Ltd.) to obtain a pellet-shaped resin composition.

After measuring the MI of these resin compositions,
Into an autoclave were charged 2000 parts each, 1200 parts of isopentane as a foaming agent, and 240 parts of methanol as a foaming aid, sealed, and heated at a rate of 20 ° C./Hr.
C. for 1 hour. Thereafter, the resin was taken out after cooling at 25 ° C., air-dried, weighed, and the impregnation rate was determined. Then, the obtained foaming agent impregnated pellets were steamed (92%).
At 1 ° C. for 1 minute) to evaluate the expansion ratio and biodegradability.

Further, after aging for one day, the pre-expanded particles were filled in a closed mold, and steam pressure was set at 0.2 kg with a steam molding machine.
/ Cm ² , heating for 30 seconds to form
A molded body of 00 × 30 mm was obtained. Put this molded body in the room
After leaving for 0 minutes or more, the respective dimensions were measured, and the dimensional stability (shrinkage ratio) was evaluated. As a control for each evaluation, a commercially available expanded polystyrene “Lyupearl 55KSY-31” was used.
71 "(manufactured by Dainippon Ink Co., Ltd.
7 kg / cm ² ). Table 3 shows the evaluation results.

[0039]

[Table 2]

[0040]

[Table 3]

Evaluation Results The crosslinking agent and the dimensional stability improver were mixed and kneaded with the P1 to P11 resins in which the L / D ratio of polylactic acid was changed so as to have the same composition, and the MI and foaming ratio of the resin composition were kneaded. When P1, P11 have a low expansion ratio, P1 and P11 are not preferable, and P6 has good expansion ratio and decomposability but poor dimensional stability. On the other hand, when the amount of the dimensional stability improver is changed, if the amount is less than 5% by weight, the dimensional stability is poor, and if it exceeds 30% by weight, the expansion ratio is undesirably reduced.

Examples 12 to 18 Comparative Examples 7 to 12 P3 polylactic acid isocyanate compound "Millionate MR-200" (2.7 to 2.8 equivalents / mole of isocyanate group, Nippon Polyurethane Industry Co., Ltd.), dimensionally stable A predetermined amount of silicon dioxide or barium sulfate and 1% by weight of talc were blended so as to have the composition shown in Table 4 as an enhancer, and the mixture was treated in the same kneading machine and kneading conditions as in Examples 1 to 11 and Comparative Examples 1 to 6. Then, a pellet-shaped resin composition was obtained, and subsequently, the same treatment was performed and evaluated. Table 5 shows the results.

[0043]

[Table 4]

[0044]

[Table 5]

Evaluation Results When silicon dioxide was used as the dimensional stability improver, the expansion ratio and the dimensional stability were good in the range of 5% by weight to 30% by weight as in the case of titanium oxide. When the addition amount is less than 5% by weight, the shrinkage ratio is large and the dimensional stability is poor, and when it exceeds 40% by weight, the foaming property is extremely reduced. Aluminum oxide showed almost the same results as silicon dioxide. Further, when the addition amount of barium sulfate was kept constant and the aspect ratio was changed, the expansion ratio was reduced along with the increase in the aspect ratio, and when it exceeded 1.5, the restraint on the resin was increased and the expansion ratio was lowered. When the average particle diameter was changed, when the average particle diameter exceeded 3 μm, the expansion ratio was reduced and the dimensional stability was also reduced.

Examples 19 to 25, Comparative Examples 13 to 15 Titanium oxide (average particle diameter 0.2 μm, aspect ratio 1.2) was used as a dimensional stability improver with a predetermined amount of isocyanate having various functional groups in the polylactic acid of P3. ) Was added and blended, and the composition shown in Table 6 was treated with the same kneading machine and kneading conditions as in Examples 1 to 11 and Comparative Examples 1 to 6, to obtain a pellet-shaped resin composition. The same processing was performed and evaluation was performed. The results are shown in Table 7.

[0047]

[Table 6]

[0048]

[Table 7]

Evaluation Results From Examples 13 to 25 and Comparative Examples 13 to 15, when the amount of isocyanate added was less than 0.5% by weight, the MI of the resin composition obtained by kneading exceeded 5 and the expansion ratio was small. ,
If the amount of the isocyanate exceeds 5% by weight, the MI is in an appropriate range, but the degree of branching and crosslinking is increased, and the expansion ratio is extremely lowered. On the other hand, when the number of functional groups of the isocyanate is less than 2.0,
The MI of the resin composition obtained by kneading exceeds 5 and the expansion ratio is small, deviating from the object of the present invention.

[0050]

As described above, the resin composition of the present invention has foaming properties, heat resistance and mechanical properties comparable to those of the conventionally used expanded polystyrene (PS), and furthermore has excellent antistatic properties. The resin composition has excellent biodegradability and contributes to global environmental protection.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiro Yama, 4-1 Kanebo-cho, Hofu City, Yamaguchi Prefecture Inside (72) Inventor Hiroshi Naito 4-1 Kanebo-cho, Hofu City, Yamaguchi Prefecture, Kanebo God Co., Ltd. (72) Inventor Nakae Tsunahiro 276-516 Osaki, Hofu-shi, Yamaguchi F-term (reference) 4J029 AA02 AB05 AB07 AC01 AD01 AD10 AE18 EA05 JA093 JA203 JA293 JC152 JF163 JF223 JF323 KE05 KE12 KH01 KH08

Claims (5)

[Claims] 1. The molar ratio of L-form to D-form is 95/5 to 64 /
40, or 40/60 to 5/95, a polyisocyanate having an isocyanate group ≧ 2.0 equivalents / mol is added to polylactic acid having a ratio of 0.5 to 5% by weight based on the polylactic acid, and an aspect ratio of 1.5 or less. A particle selected from substantially spherical metal oxides or metal sulfates having an average particle size of 3 μm or less
A resin composition characterized by having a melt viscosity of 5 or less in melt index value (MI), which is blended in an amount of from 30 to 30% by weight. 2. The resin composition according to claim 1, wherein the metal oxide is a compound selected from the group consisting of aluminum oxide, silicon dioxide, and titanium oxide. 3. The resin composition according to claim 1, wherein the metal sulfate is barium sulfate. 4. The resin composition according to claim 1, wherein the aspect ratio of the metal oxide and the metal sulfate is 1.2 or less. 5. The resin composition according to claim 1, wherein the metal oxide and the metal sulfate have an average particle size of 1 μm or less.