JP3218066B2 - Heat shrinkable foam composite sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable foamed composite sheet. More specifically, the present invention relates to a heat-shrinkable composite foamed sheet made of a thermoplastic polymer composition mainly composed of a lactic acid polymer and having degradability in a natural environment.

[0002]

2. Description of the Related Art Conventionally, as a heat-shrinkable foamed composite sheet used as a label for a one-way glass bottle, a foamed polystyrene resin or a foamed polypropylene resin is mainly used. However, heat-shrinkable foamed composite sheets made from such a resin increase the amount of garbage when discarded.In addition, conventional products have a very low decomposition rate in the natural environment. , Remains in the ground semi-permanently. There is also a problem that the dumped plastics damage the landscape and destroy the living environment of marine life. However, a heat-shrinkable foamed composite sheet that is easily decomposed in a natural environment has not been known.

On the other hand, polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid is known as a thermoplastic and biodegradable polymer. This lactic acid polymer is 100% biodegradable in the body of an animal within a few months to a year. When left in soil or seawater, it starts to decompose in a few weeks in a humid environment and disappears in about one year. The decomposition products are lactic acid, carbon dioxide and water, all harmless.

[0004] The raw material lactic acid is obtained from fermentation of inexpensive materials such as corn starch and corn syrup, and also from petrochemical raw materials such as ethylene. The preparation of polylactic acid or copolymers with lactic acid is disclosed in U.S. Pat. No. 1,995,970, which is synthesized from a cyclic dimer of lactic acid commonly called lactide. This lactic acid-based polymer is used as a surgical suture or a sustained-release material for medicine because of its biocompatibility and degradability.
Use as a heat-shrinkable foamed composite sheet has not yet been known.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a composite sheet in which a foamed polylactic acid-based sheet and a polylactic acid-based film, which are decomposable in a natural environment and have heat shrinkability, are bonded to each other.

[0006]

Means for Solving the Problems The inventors of the present invention aimed at obtaining a heat-shrinkable foamed composite sheet which can be decomposed in a natural environment.
Heat without paying attention to lactic acid-based polymer over, lactate polymer obtained the bonded composite sheet film comprising a heat-shrinkable foamed sheet and the resin made of a resin mainly composed of, impairing degradability have further the polymer It has been found that a shrinkable foamed composite sheet can be obtained, and the present invention has been completed. That is, the present invention is characterized in that it is constituted by a film made of a heat-shrinkable foamed sheet and a thermoplastic polymer composition comprising a thermoplastic polymer composition comprising a copolymer of polylactic acid or lactic acid and hydroxycarboxylic acid It is a heat-shrinkable foamed composite sheet.

[0007] The polymer used in the present invention is a mixture of polylactic acid and a polymer of another hydroxycarboxylic acid, or a copolymer of lactic acid and another hydroxycarboxylic acid. As other hydroxycarboxylic acids, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid and the like are used.

[0008] These polymers may be those synthesized by direct dehydration polycondensation from lactic acid or other hydroxycarboxylic acids, or ring-opening polymerization of lactide, or glycolide or ε-caprolactone, or a mixture thereof. A product obtained by doing so may be used. Alternatively, a copolymer synthesized by subjecting a polymer of polylactic acid and another hydroxycarboxylic acid to a transesterification reaction at a high temperature may be used. The lactic acid constituting the polymer may be L-lactic acid, D-lactic acid or a mixture thereof.

The average molecular weight of the polymer is between 10,000 and 100
10,000 is preferred. If the molecular weight is lower than this, the strength of a molded article such as a film is small and is not suitable for practical use. Also,
If the molecular weight is higher than this, the viscosity in a thermally molten state is high and the moldability is poor. Further, the polymer composition of the present invention may contain a plasticizer, a modifier and the like.

The heat-shrinkable foam sheet according to the present invention has a thickness of
Is 0.1 to 1.0 mm, preferably 0.15 to 0.5
mm, when heated to 160 ° C., shrinks greatly in the winding direction of the sheet, and preferably shrinks by 30% or more in one direction, and the direction perpendicular to the direction is 1% or more.
It has the property of shrinking less than 0%. When the shrinkage is less than 30% in one direction, the composite sheet laminated with the polylactic acid-based film is cut into a rectangular shape, and the end surface is sealed to form a cylindrical body. Does not adhere to In addition, if the cylindrical body in close contact with the container has a shrinkage performance in which the height direction exceeds 10%, the mounting position after shrinkage is shifted and the commercial value is impaired. The heat-shrinkable foam sheet can be implemented using any method. Usually, it is preferable to use what is called extrusion foaming, in which foaming is performed simultaneously with extrusion from an extruder using a foaming agent.

Examples of the foaming agent include evaporative foaming agents that foam by evaporation, for example, hydrocarbons such as butane, petane and propane, methyl chloride, monochlorotrifluoromethane,
Examples thereof include halogen compounds such as dichlorodifluoromethane and dichlorotetrafluoroethane, carbon dioxide gas, and nitrogen gas. The addition amount of these blowing agents is preferably 0.1 to 30% by weight, particularly preferably 0.5 to 10% by weight , based on the polymer composition.

If necessary, a decomposition-type blowing agent that decomposes to generate a gas upon heating, for example, an inorganic blowing agent such as sodium bicarbonate, azodicarbonamide, N, N'-dinitrosopentamethylenetetramine, p, p ' Organic blowing agents such as oxybis (benzenesulfonyl hydrazide), foaming aids or nucleating agents such as stearic acid, oxalic acid, salicylic acid, phthalic acid, benzoic acid, citric acid, tartaric acid, etc .; Salts, carbonates such as sodium carbonate, zinc oxide, calcium oxide, titanium oxide, silica, clay and the like may be added in appropriate amounts.

The extrusion temperature of the heat-shrinkable foam sheet varies depending on the composition of the polymer.
Performed at a temperature of 0-100,000 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. Conversely, if the viscosity of the polymer is too low at a temperature higher than this, bubbles cannot be retained, and a uniform quality foam sheet cannot be obtained. Foaming ratio is 1.5 ~
10 times is preferred.

The shrinkage performance of the heat-shrinkable foamed sheet is imparted in a step of heating and mixing the raw materials in an extruder and then releasing the raw materials into the atmosphere to take out the sheet.

The polylactic acid-based film has a thickness of 0.01 to
It is 0.05 mm, preferably 0.015 to 0.03 mm, and is obtained by stretching a film made of a polylactic acid-based polymer without using a foaming agent and a nucleating agent in one direction. Incidentally, the polylactic acid-based film preferably has a heat shrinkage performance similar to that of the heat shrinkable foam sheet .

In the heat-shrinkable foamed sheet , a two-layer coextruded foamed sheet having a non-foamed layer of 0.005 to 0.05 mm of a polylactic acid resin on one side is provided with the non-foamed layer disposed on an adhesive surface. This is suitable for maintaining the smoothness with the polylactic acid-based film and increasing the adhesive strength with the polylactic acid-based film. On the other hand, printing is performed on heat-shrinkable foam
Applied to the back side of the bets or polylactic acid film, heat-shrinkable
It is sandwiched between a foam sheet and a polylactic acid-based film.
Preferably, printing is performed on the polylactic acid-based film.

The lamination of the heat-shrinkable foam sheet and the polylactic acid-based film can be carried out by a usual method. That is, a desired product can be obtained by heating the film and directly welding it to the heat-shrinkable foamed sheet , or by using an adhesive thermoplastic resin as a binder.

[0018]

The present invention will be described below in detail with reference to examples. Examples 1 to 3 Heat-shrinkable foam sheet 0.5 parts by weight of talc (Microace; manufactured by Nippon Talc) was added to 100 parts by weight of a mixture of poly D, L-lactide and poly L-lactide having a molecular weight of about 100,000 shown in Table 1. And Freon 22
5 parts by weight (manufactured by Mitsui DuPont Fluorochemicals) was used as a raw material for the foaming layer, while 100 parts by weight of a mixture of poly D, L-lactide and poly L-lactide having a molecular weight of about 100,000 was used as a raw material for the non-foaming layer. The heat-shrinkable foamed sheet having a two-layer structure obtained as described above, wherein the foamed sheet has a thickness of 0.20 mm in the foamed layer, 0.019 mm in the non-foamed layer, and a thickness of 16 mm.
A sheet having a shrinkage ratio of 50% in the extrusion direction when heated to 0 ° C. and 4% in a direction perpendicular thereto.

Polylactic acid-based film A film formed by inflation molding of 100 parts by weight of a mixture of poly D, L-lactide and poly L-lactide having a molecular weight of about 100,000 shown in Table 1. The film having a thickness of 0.020 mm having a shrinkage of 35% and a shrinkage of 8% in a direction perpendicular thereto. The polylactic acid-based film was printed so that characters and designs could be read through the film.

The above-mentioned heat-shrinkable foam sheet and the polylactic acid-based film were bonded together by heating the film with a hot roll at 190 ° C. to directly adhere to the foam sheet. The polylactic acid film was smooth and glossy without impairing the surface properties. This composite sheet was slit into a ring having a width of 100 mm and tested by a wrapping machine so as to be wound around a glass bottle. The label was cut stably, with high dimensional accuracy and low loss. When the glass bottle with the label was passed through a 200 ° C. shrink tunnel, it shrunk until it adhered to the shoulder and lower part of the bottle.

The composite sheet was subjected to a decomposition test by burying the coated bottle in soil at a temperature of 35 ° C. and a water content of 30%. Degradability was evaluated based on the change in appearance and the rate of weight loss. Table-Results
Also described in 1. Comparative Example 1 A composite sheet was obtained in the same manner as in Example 1 except that the heat-shrinkable foamed sheet had a performance of 25% in one direction and 3% in a direction perpendicular thereto. The obtained composite sheet was wound around a bottle and did not shrink sufficiently even through a shrink tunnel, resulting in uneven shrinkage.

[0022]

[Table 1] Examples 4 to 6 Heat-shrinkable foamed composite sheets were produced in the same manner as in Example 1 except that copolymers of L-lactide and oxycarboxylic acid shown in Table 2 were used. The results are also shown in Table 2.

[0023]

[Table 2]

[0024]

The heat-shrinkable foamed composite sheet comprising a thermoplastic polymer composition comprising polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid according to the present invention has excellent buffering properties and heat resistance, and has good gloss and beautiful appearance. Bottle cover labels and, when buried underground as waste or dumped into the sea or rivers, can be used for a relatively short period of time in the natural environment, similar to natural products such as paper and wood. Decomposes into harmless water and carbon dioxide.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B32B 5/18 B32B 27/36 C08J 9/04

Claims (4)

(57) [Claims] 1. A heat-shrinkable foamed sheet comprising a thermoplastic polymer composition comprising polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid, and a film comprising the thermoplastic polymer composition. Shrinkable foam composite sheet. Wherein lactic acid is L- lactate, D- lactic acid or heat-shrinkable foamed composite sheet of claim 1, wherein the mixtures thereof. 3. The heat-shrinkable foamed composite sheet according to claim 1, wherein the hydroxycarboxylic acid is glycolic acid. 4. The heat-shrinkable polylactic acid-based foamed sheet has a heat-shrinking property in that when heated to 160 ° C., it shrinks by 30% or more in one direction and shrinks by less than 10% in a direction perpendicular thereto.
Heat-shrinkable foamed composite sheet of the mounting according to claim 1, wherein, characterized in that the shall.