JPH05140361A - Cushioning material - Google Patents

Abstract

(57) [Abstract] [Purpose] A cushioning material made of a foam of a thermoplastic polymer composition containing polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid as a main component. [Effect] When it is buried in the ground as waste or dumped in the sea or river, it becomes harmless water and carbon dioxide gas in a relatively short period in the natural environment like natural products such as paper and trees. Disassemble.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cushioning material. More specifically, the present invention relates to a cushioning material which is composed of a thermoplastic polymer composition mainly containing lactic acid polymer and has degradability in a natural environment.

[0002]

2. Description of the Related Art Conventionally, polystyrene and polyolefin foam sheets have been used for the corners and partitions of cardboard boxes, and net foams have been used for the packaging of fragile items such as fruits and vegetables and fresh foods. Widely used as a partition plate or directly covered. In particular, these foamable cushioning materials are molded with a small amount of resin, and after achieving the purpose,
However, the cushioning material molded from such a resin is bulky and increases the amount of dust when discarded, and the conventional material has a very slow decomposition rate in the natural environment. Therefore, if buried, it will remain in the ground semipermanently. In addition, the discarded plastics have caused problems such as damage to the landscape and the living environment of marine life. However, hitherto, there is no known cushioning material that easily decomposes in a natural environment.

On the other hand, polylactic acid or a copolymer of lactic acid is known as a degradable thermoplastic polymer.
This lactic acid-based polymer is degradable in a natural environment, and when placed in soil or seawater, it begins to decompose in a few weeks and disappears in about a year. The decomposition products are lactic acid, carbon dioxide and water, all of which are harmless. Lactic acid as a raw material is obtained from inexpensive fermentation such as corn starch and corn syrup, and is easily produced from petrochemical raw materials such as ethylene.

The preparation of polylactic acid or a copolymer of lactic acid is disclosed in US Pat. No. 1,995,970 and is synthesized from a cyclic dimer of lactic acid commonly referred to as lactide. Because of its biocompatibility and degradability, this lactic acid-based polymer is used as a surgical suture and a medical sustained-release material, but its use as a cushioning material has not yet been known.

[0005]

SUMMARY OF THE INVENTION The present invention is to provide a cushioning material which can be decomposed in a natural environment.

[0006]

The present inventors have focused their attention on lactic acid-based polymers for the purpose of obtaining a cushioning material that can be decomposed in a natural environment. It was found that a foam having a cushioning property can be obtained without impairing the decomposability by obtaining a foam and using it alone or laminating it with paper or the like, and completed the present invention. That is, the present invention relates to a buffer material composed of a thermoplastic polymer composition containing polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid as a main component.

The polylactic acid or the copolymer of lactic acid and hydroxycarboxylic acid used in the present invention uses lactic acid or lactide, which is a cyclic dimer of lactic acid, and hydroxycarboxylic acid as a raw material, or optionally other monomers as appropriate. Can be used. When lactic acid is used, dehydration condensation is used, but to obtain a high molecular weight product, ring-opening polymerization of lactide is preferable. As the lactide used in the ring-opening polymerization, L-lactide, D-lactide, meso lactide, or a mixture thereof is used, but a compound in which D and L-lactide have opposite optical activities is preferable. The mixing ratio is preferably D or L-lactide / optical antipode = 95/5 to 50/50.

The degree of polymerization of the lactic acid type polymer is 150 to 2
It is 10,000. If the degree of polymerization is lower than this, the strength of a molded product such as a film is small and it is not suitable for practical use. On the other hand, if the degree of polymerization is too high, the viscosity in the molten state during heating is high and the moldability is poor. The polymerization method may be a method using a solvent or a method not using a solvent, but in view of the problem of solvent recovery, industrially bulk polymerization without a solvent is preferable.
As the ring-opening polymerization catalyst, zinc, tin chloride, carboxylate or the like is generally used, but the catalyst is not particularly limited. Toxicities should be considered when used in biocompatible materials and food products. The lactic acid-based polymer according to the present invention may contain a plasticizer, a modifier and the like.

The cushioning material according to the present invention is manufactured from a thermoplastic polymer composition containing a lactic acid-based polymer as a main component.
Usually, a foamed sheet or a foamed body is produced using the above-mentioned thermoplastic polymer, and this is formed into an arbitrary shape and used as a cushioning material. The production of the foamed sheet or foam can be carried out by using a usual method. That is, it can be produced by using a so-called extrusion foaming method in which foaming is simultaneously performed by extruding from an extruder using a foaming agent, and the shape of the foam can be obtained by selecting a mold attached to the tip of the extruder. Be done. Examples of the foaming agent include evaporative foaming agents that are foamed by evaporation, such as hydrocarbons such as ethane, butane, pentane, hexane, heptane, ethylene, propylene, petroleum ether, methyl chloride, monochlorotrifluoromethane, dichlorodifluoromethane, dichlorotetramethane. Examples thereof include halogenated hydrocarbons such as fluoroethane, carbon dioxide gas, nitrogen gas, and water. The amount of these foaming agents added is 0.1 to 30% by weight, particularly 0.5 to 30% by weight, based on the thermoplastic polymer composition.
10% by weight is preferred.

If necessary, a decomposition-type foaming agent which decomposes to generate gas when heated, for example, an inorganic foaming agent such as sodium bicarbonate, azodicarbonamide, N, N'-dinitropetamethylenetetramine, p, p'- Organic foaming agents such as oxybis (benzenesulfonylcarbazide), azobisisobutyronitrile, benzenesulfonylhydrazide, foaming aids or nucleating agents such as stearic acid, oxalic acid, salicylic acid, phthalic acid, benzoic acid, citric acid, tartaric acid An appropriate amount of an inorganic acid such as the above, a salt of the organic acid or the inorganic acid, a carbonate such as sodium carbonate, zinc oxide, calcium oxide, titanium oxide, silica, alumina, clay, kaolin, diatomaceous earth and the like may be added. For coloring or other modification of the foamed molded product, it is also possible to add an appropriate amount of pigment, flame retardant, filler or the like.

The extrusion temperature of the foam varies depending on the composition of the polymer, but the melt viscosity is usually 10,000 to 100,
Perform at a temperature of 000 poise. If it is lower than this, the viscosity of the melted polymer is high, the formation of bubbles is slow, and the expansion ratio does not increase. On the other hand, if the viscosity of the polymer is too low at a temperature higher than this, bubbles cannot be retained, and a foamed sheet of uniform quality cannot be obtained. The expansion ratio depends on the performance of the cushioning material, but is preferably 5 to 25 times. If it is less than 5 times, the buffer performance is insufficient and the packaged item is damaged. On the other hand, when it exceeds 25 times, the surface of the foam becomes brittle. The bubble size of the foam is preferably 0.1 to 5 mmΦ. 0.1 mm
If it is less than Φ, there are many losses during the production of the foam. Also, 5m
If it exceeds mΦ, the surface becomes brittle. For foam sheets,
After the sheet is reheated to be softened, it can be formed into a desired shape by thermoforming such as vacuum or pressure forming. Preferably, it is preferable that the sheet has a large number of end faces by partially providing holes. The foam having a net shape is used by bringing it into a predetermined length so as to be brought into contact with an object to be packaged, or by being bonded to paper to be used as an intermediate partition plate or an underlay plate.

[0012]

The present invention will be described in detail below with reference to examples. Examples 1 to 3 0.5% by weight of talc was added as a cell regulator to a mixture of poly D, L-lactide and poly L-lactide having a molecular weight of about 100,000 shown in Table-I, and the temperature was 200 ° C. in an extruder of 50 mmΦ.
After melt-kneading at the temperature of, butane was injected under pressure at a ratio of 0.065 mol to 100 g of the resin. After press fitting, the cylinder temperature of the extruder is set to 140 to 175 ° C. to cool the resin mixture, and the resin mixture is discharged into the atmosphere through the slit to have a thickness of 2 to 3 m.
A foamed sheet having a width of m and a width of 650 mm was obtained. Apparent density and cushioning performance of the obtained foamed sheet (46 cm for 5/8 steel balls)
Judgment from the height of the object and judgment by the height at which it bounces; JIS K
(Corresponding to -6382) are shown in Table-I. This foam was embedded in a soil having a temperature of 35 ° C. and a water content of 30% to perform a decomposition test. The degradability was evaluated by the weight reduction rate. The results are also shown in Table-I.

Examples 4 to 6 Foam sheets were molded in the same manner as in Example 1 except that the copolymer of L-lactide and oxycarboxylic acid shown in Table II was used.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

INDUSTRIAL APPLICABILITY The buffer material of the present invention, which is mainly composed of a polymer containing lactic acid as a main component, is the same as a natural product such as paper or wood when it is buried in the ground as waste or dumped in the sea or river. It decomposes into harmless water and carbon dioxide within a relatively short period of time in the natural environment.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masanobu Amioka 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] 1. A buffer material comprising a thermoplastic polymer composition containing polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid as a main component. 2. The cushioning material according to claim 1, wherein the lactic acid is L-lactic acid, D-lactic acid or a mixture thereof. 3. The cushioning material according to claim 1, wherein the hydroxycarboxylic acid is glycolic acid.