JP3311371B2 - Cushioning material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cushioning material. More specifically, the present invention relates to a buffer material having a decomposable property in a natural environment, comprising a thermoplastic polymer composition mainly composed of a lactic acid polymer.

[0002]

2. Description of the Related Art Conventionally, for packaging of easily fragile items such as fruits and vegetables, fresh foods, foamed sheets of polystyrene or polyolefin have been used for corners and partitions of cardboard boxes, and foams in net form have been used. Widely used as a partition plate or directly overlaid. In particular, these foamable cushioning materials are molded with a small amount of resin, and after achieving the purpose,
However, these materials are disposable, but the cushioning material molded from such a resin increases the amount of bulk and garbage when discarded, and the conventional material has a very low decomposition rate in the natural environment. Therefore, when buried, it remains semi-permanently in the ground. Discarded plastics also cause problems such as spoiling the landscape and destroying the living environment of marine life. However, hitherto, there is no known cushioning material that is easily decomposed in a natural environment.

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

The preparation of polylactic acid or copolymers of lactic acid is disclosed in US Pat. No. 1,995,970, which is synthesized from a cyclic dimer of lactic acid, commonly called lactide. This lactic acid-based polymer has been used as a surgical suture or a sustained-release material for medicine because of its biocompatibility and degradability, but it has not been known as a buffer material yet.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a buffer material which can be decomposed in a natural environment.

[0006]

Means for Solving the Problems The inventors of the present invention focused on a lactic acid-based polymer for the purpose of obtaining a buffer material that can be decomposed in a natural environment. It has been found that a foam having a cushioning property can be obtained without losing the decomposability by obtaining a foam and using it alone or by laminating it with paper or the like, and completed the present invention. The present invention provides a a buffer material made of foamed thermoplastic polymer composition a copolymer of polylactic acid or lactic acid and hydroxycarboxylic acid ing
The foam has an expansion ratio of more than 10 times and not more than 25 times
Cushioning material characterized by the following (however,
Foaming with hydrofluorocarbon foaming agent
Excludes body cushioning material. ) .

The polylactic acid or the copolymer of lactic acid and hydroxycarboxylic acid used in the present invention may be prepared by using lactic acid or lactide, which is a cyclic dimer of lactic acid, or hydroxycarboxylic acid as a raw material, or optionally adding other monomers. 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 for the ring-opening polymerization, L-lactide, D-lactide, meso lactide, or a mixture thereof is used, but a mixture of D or L-lactide and the opposite optical activity is preferable. The mixing ratio is preferably D or L-lactide / optical enantiomer = 95/5 to 50/50.

The degree of polymerization of the lactic acid-based polymer is from 150 to 2
It is 0000. If the degree of polymerization is lower than this, the strength when formed into a molded product such as a film is small and is not suitable for practical use. On the other hand, if the degree of polymerization is too high, the viscosity in a molten state when heated is high, and the moldability is poor. As the polymerization method, a method using a solvent or a method not using a solvent may be used, but bulk polymerization without using a solvent is industrially preferable from the problem of solvent recovery.
As a catalyst for ring-opening polymerization, zinc chloride, tin chloride or carboxylate is generally used, but is not particularly limited. When used for biocompatible materials and foods, toxicity must be considered. Further, the lactic acid-based polymer according to the present invention may contain a plasticizer, a modifier and the like.

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

[0010] If necessary, a decomposition-type foaming agent which decomposes to generate a 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, and foaming aids or nucleating agents such as stearic acid, oxalic acid, salicylic acid, phthalic acid, benzoic acid, citric acid, and tartaric acid And the like, inorganic acids such as the above, salts of the above organic acids or inorganic acids, carbonates such as sodium carbonate, zinc oxide, calcium oxide, titanium oxide, silica, alumina, clay, kaolin, diatomaceous earth and the like may be added in appropriate amounts. An appropriate amount of a pigment, a flame retardant, a filler or the like may be added for coloring or other denaturation of the foam molded article.

The extrusion temperature of the foam varies depending on the composition of the polymer, but usually the melt viscosity is from 10,000 to 100,
Perform at a temperature of 000 poise. If it is lower than this, the viscosity of the molten polymer is high and the generation 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 higher temperature, the air bubbles cannot be retained, and a foam sheet of uniform quality cannot be obtained. The expansion ratio varies depending on the performance of the cushioning material, but is preferably 5 to 25 times. If it is less than 5 times, the cushioning performance will be insufficient, and the package will be damaged. On the other hand, if it exceeds 25 times, the surface of the foam becomes brittle. The size of the foam cells is preferably 0.1 to 5 mmΦ. 0.1mm
If it is less than Φ, the loss during the production of the foam is large. Also, 5m
If it exceeds mΦ, the surface becomes brittle. For foam sheets,
After the sheet is reheated and softened, it can be formed into a desired shape by thermoforming such as vacuum or pressure forming. Preferably, it is preferable to partially provide a hole and have many end faces of the sheet. When the foam is in a net shape, the foam is used in a predetermined length so as to be in contact with an article to be packaged, or is bonded to paper to be used as a partition board or an underlay board.

[0012]

The present invention will be described below in detail with reference to examples. Examples 1 to 3 0.5% by weight of talc as a cell regulator was added 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 mixture was heated to 200 ° C. with an extruder of 50 mmφ.
After melt-kneading at a temperature of 0.15 g, butane was injected at a rate of 0.065 mol per 100 g of the resin. The resin mixture is cooled by setting the cylinder temperature of the extruder after press-fitting to 140 to 175 ° C., and is discharged into the atmosphere through a slit to have a thickness of 2 to 3 m
m, a foamed sheet having a width of 650 mm was obtained. Apparent density and cushioning performance of the obtained foamed sheet (5/8 steel ball is 46 cm
Drop from the height of the object and judge by the rebound height; JIS K
-6382) are shown in Table I. The foam was buried in soil at a temperature of 35 ° C. and a water content of 30% to perform a decomposition test. The evaluation of the degradability was determined based on the weight reduction rate. The results are shown in Table-I.

Examples 4 to 6 A foam sheet was formed in the same manner as in Example 1 except that the copolymer was changed to the copolymer of L-lactide and hydroxycarboxylic acid shown in Table II.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

EFFECT OF THE INVENTION A cushioning material made of foam of a polylactic acid or lactic acid and the thermoplastic polymer composition ing a copolymer of a hydroxycarboxylic acid of the present invention, the foam,
Having an expansion ratio of more than 10 times and not more than 25 times
That, cushioning material, characterized in that (however, hydrofluoroether
A cushioning material made of a foam foamed with a carbon foaming agent
except for. ) Can be converted into harmless water and carbon dioxide within a relatively short period of time in the natural environment, like natural products such as paper and wood, when buried underground or dumped into the sea or river as waste. Decompose.

Continuation of the front page (56) References JP-A-4-304244 (JP, A) JP-A-5-508669 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9 / 14 CFD

Claims (3)

(57) [Claims] Calling of claim 1 polylactic acid or thermoplastic polymer compositions ing a copolymer of lactic acid and hydroxycarboxylic acid
A cushioning material comprising a foam , wherein the foam has an expansion ratio of more than 10 times and 25 times or less.
That, cushioning material, characterized in that (however, hydrofluorocarbons car
The cushioning material made of the foam foamed with the foaming agent is removed.
Good. ). 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.