JPH0776628A - Cushioning sheet and composite sheet therefrom - Google Patents

Abstract

PURPOSE:To provide a cushioning sheet made from a thermoplastic polymer composition comprising poly(lactic acid) or a copolymer thereof with other hydroxycarboxylic acids and a composite sheet therefrom. CONSTITUTION:Lactic acid polymer is prepared by directly dehydrative polycondensation reaction of lactic acid and other hydroxycarboxylic acid or by ring-opening polymerization of the lactic acid dimeric lactide and a cyclic ester intermediate of hydroxycarboxylic acids, for example, a dimeric glycolide of glycolic acid and epsilon-caprolactone as a cyclic ester of 6-hydroxycaproic acid. The lactic acid polymer is mixed with usually known plasticizers, a variety of modifiers to provide a thermoplastic polymer composition through mixing and kneading them. The cushioning sheet mainly composed of lactic acid polymer has high compression strength, compressive resistance, scratch resistance, water resistance and fungiresistant properties, further the composition is suitable for a cushioning sheet, since it is degradable under natural environments causing no environmental pollution. The composite sheet comprising the cushioning sheet and kraft paper is suitably used as a transportation material such as cardboards or envelops.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a thermoplastic polymer composition containing polylactic acid or a copolymer of lactic acid and other hydroxycarboxylic acid (hereinafter, polylactic acid and the copolymer are collectively referred to as lactic acid-based polymer) as a main component. The present invention relates to a composite sheet produced by laminating a buffer sheet, which has degradability in a natural environment, and kraft paper.

[0002]

2. Description of the Related Art A cushioning sheet in which a large number of bubbles are formed by laminating an embossing film having a large number of embosses and a base film, and a composite sheet obtained by laminating kraft paper or the like on one or both sides of the cushioning sheet. Conventionally, it has been widely used as a cushioning material and a packaging material for transporting items such as electric parts, glass, pottery, foods, arts and the like. A general-purpose resin such as polyethylene resin is generally used for the cushioning sheet and the composite sheet. However, the cushioning sheet made from such general-purpose resin,
Some have excellent impact resistance, light weight, heat absorption resistance, and flexibility, but when they are disposed of, they increase the amount of dust and they do not decompose in the natural environment, so even if they are buried, they are semi-permanent. Remains in the ground. In addition, the discarded plastics have caused problems such as damage to the landscape and destruction of the living environment of marine life.

Degradable polymers include copolymers of hydroxybutyrate and hydroxyvalerate and starch-based plastics, but these have weak physical strength when used as a buffer sheet. Is not practical. Furthermore, there were problems that molds tended to grow under the normal environment and that the mice got bite. On the other hand, a lactic acid-based polymer has been attracting attention as a biodegradable thermoplastic polymer. These polymers are 100% biodegradable in the body of animals within a few months to a year, and when placed in soil or seawater, they start to degrade in a few weeks in a moist environment for about a year to a few years. It has the property that it disappears over the years, and the decomposition products become lactic acid, carbon dioxide, and water that are harmless to the human body.

Polylactic acid in a lactic acid-based polymer is usually synthesized from a cyclic dimer of lactic acid called lactide, and its production method is described in USPI, 995,970, USP.
2,511, USP 2,683,136. A copolymer of lactic acid and other hydroxycarboxylic acid is usually synthesized from lactide which is a cyclic dimer of lactic acid and a cyclic ester intermediate of hydroxycarboxylic acid (usually glycolic acid dimer glycolide). Is USP 3,636,956 and USP 3,
797,499. However, a cushioning sheet using the above lactic acid-based polymer has not been developed, and at present, it satisfies the cushioning performance such as impact resistance and flexibility, and has a cushioning property that easily decomposes in a natural environment. There are no sheets and composite sheets consisting of them.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a cushioning sheet having a practical cushioning property, easily decomposed in a natural environment, and having good antifungal properties, and a composite sheet comprising the same. To do.

[0006]

Means for Solving the Problems The present inventors have arrived at the present invention as a result of extensive studies to solve the above problems. That is, the present invention is a cushioning sheet made of a thermoplastic polymer composition containing a lactic acid-based polymer as a main component, and is also a composite sheet obtained by laminating kraft paper or the like on one side or both sides of the cushioning sheet.

In addition to L-lactic acid, D-lactic acid or a mixture thereof or lactide which is a cyclic dimer of L-lactic acid can be used as a raw material for the lactic acid-based polymer in the present invention. Other hydroxycarboxylic acids that can be used in combination with lactic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5
-Hydroxyvaleric acid, 6-hydroxycaproic acid, etc., and further a cyclic ester intermediate of hydroxycarboxylic acid, for example, glycolide which is a dimer of glycolic acid or ε- which is a cyclic ester of 6-hydroxycaproic acid.
Caprolactone can also be used.

The lactic acid-based polymer can be produced by direct dehydration polycondensation of lactic acid or lactic acid and other hydroxycarboxylic acid, or lactide which is a cyclic dimer of lactic acid or a cyclic ester intermediate of hydroxycarboxylic acid. For example, it can be obtained by ring-opening polymerization using glycolide, which is a dimer of glycolic acid, or ε-caprolactone, which is a cyclic ester of 6-hydroxycaproic acid.

The polymer produced by direct dehydration polycondensation is azeotropic dehydration condensation of lactic acid or lactic acid as a raw material and other hydroxycaproic acid, preferably in the presence of an organic solvent, particularly a phenyl ether type solvent. Polymerization is preferably carried out by a method of removing water from the solvent distilled by azeotropic distillation and returning the solvent in a substantially anhydrous state to the reaction system to obtain a high molecular weight polylactic acid having a strength suitable for the present invention. .

If the molecular weight of the lactic acid-based polymer is 20,000 or more, a high molecular weight polymer can be used within the range where moldability is possible. If the molecular weight is less than 20,000, the strength of the molded product becomes small, which is not suitable for practical use. Further, even if it is one million or more, the present invention can be used, but some ingenuity is required for moldability. The lactic acid-based polymer is mixed and kneaded with a known plasticizer and various modifiers to obtain a thermoplastic polymer composition. The lactic acid-based polymer or composition is used in the form of pellets, rods, powder or the like, and any known kneading technique can be applied to its production.

Cushioning sheet according to the present invention and more
The composite sheet consisting of
A base film made of a thermoplastic polymer composition
It is manufactured by the method described below. Buffer sea
Is a thermostat with a base film with a thickness of 15-300μ
Hold in or heat at 50-100 ° C by hot roll
Heat and soften every time. Then emboss roll (eg
Hole depth 5 mm, hole diameter 9.5 mm, number of holes 9,720
/ M ²Each hole has a vacuum hole that allows vacuum forming.
), Wrap the film softened by heating to
10 to 400 mmHg, preferably 20 to 100 mmHg
g to form an embossed film (in this case,
Lum is wrapped around a temperature-controlled embossing roll,
An embossed flap that has a recess on the entire surface by vacuum forming.
The film is molded, and then the base film is
It is generally heat-welded to the flat portion of the frame. ). this
Separately embossed film by heat roll 100-130
15-300μ thick base softened by heating to ℃
It is manufactured by welding a film and cooling.

The thickness of the cushioning sheet is determined by the thickness of the base film or the shape of the emboss, but is usually 1 to 1.
It is 8 mm, and generally about 3 to 13 mm. The convex projections of the cushioning sheet have a shape such as a semicircular shape, a cylindrical shape, and an elliptical shape, and the convex projections have a height of 1 to 18 mm, generally about 3.3 to 13 mm, and a diameter. Is 2-45m
m, mostly 3 to 37 mm, and the number of protrusions is 60 to 85% per unit m ² , but other than that may be used depending on the purpose of use.

In the production of the cushioning sheet of the present invention, the base film used as a raw material is a conventional polyethylene resin film at a temperature of about 100 to 120 ° C.
Embossing is possible in the temperature range of 50 to 100 ° C., and the welding temperature of the formed embossing film and the base film is 120 to 150 ° C. for polyethylene resin.
In contrast, it has a wide welding temperature range of 100 to 170 ° C. and is excellent in moldability. Also, when a composite sheet is manufactured by laminating kraft paper or the like on one or both sides of a cushioning sheet, polyethylene resin is extruded from the T-die of the extruder at a temperature of 300 ° C. or more in the case of polyethylene resin and is laminated with the kraft paper. Match or emboss roll temperature 280 ℃
It is general that the kraft paper is preheated at a temperature of about 60 ° C. in advance and heat-bonded by pressure bonding, but the base film of the raw material and the kraft paper are directly heated at a temperature of 130 to 160 ° C. and a pressure of 0. Welding is possible under the condition of 1 to 0.5 kg / cm ² . The lamination process is performed at a low temperature and can be obtained by easily adhering in a wide temperature range, so that a processable and stable composite sheet can be produced.
Hereinafter, the present invention will be described in more detail with reference to Examples.

[0014]

【Example】

Production Example 1 90% L-lactic acid 10.0 kg After distilling water while stirring at 150 ° C./50 mmHg for 3 hours, 6.2 g of tin powder was added, and the mixture was further stirred at 150 ° C./50 mmHg for 2 hours to oligomerize. . 28.8 g of tin powder and 21.1 kg of diphenyl ether were added to this oligomer, and the temperature was changed to 150 ° C / 3.
The azeotropic dehydration reaction was carried out at 5 mmHg, and the distilled water and the solvent were separated by a water separator, and only the solvent was returned to the reactor. Two hours later,
The organic solvent returned to the reactor was passed through a column packed with 4.6 kg of molecular sieve 3A and then returned to the reactor to carry out a reaction at 150 ° C./35 mmHg for 40 hours, and an average molecular weight was Mw = 110,000 polylactic acid solution. Got
After adding 44 kg of dehydrated diphenyl ether to this solution and diluting it, it was cooled to 40 ° C. to precipitate, and the crystals were filtered, washed with 10 kg of n-hexane three times, and 60 ° C./5.
After drying at 0 mmHg, 6.1 kg (yield 85%) of polylactic acid powder was obtained. This powder was processed in a pelletizer to be pelletized and used in the following tests. The average molecular weight of the obtained polymer was Mw = 110,000.

The average molecular weight (weight average molecular weight) of the polymer was measured by gene permeation chromatography using polystyrene as a standard under the following conditions. Equipment; Shimadzu LC-10AD detector; Shimadzu RID-6A column; Hitachi Chemical GL-S350DT-5, GL-S3
70DT-5 solvent; chloroform concentration; 1% injection volume; 20 μl flow rate; 1.0 ml / min

Production Example 2 DL-lactic acid polymer was obtained by pelletizing in the same manner as in Production Example 1 except that 100 parts of L-lactic acid was changed to 100 parts of DL-lactic acid. The average molecular weight of this polymer was about 110,000. Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 Using the polymer obtained in Production Example 1 as a raw material, a pressure of 40 mm
Extruder temperature is 200 ° C by connecting a 75mmφ die to the extruder.
Inflation molding gives a thickness of 5 under the condition of BUR = 2
I got a 0μ film (cut both ends of the film
And used). The film was controlled at a temperature of 80 ° C
Wrap it on a roll to soften it by heating, then emboss throw
(Hole depth 5mm, hole diameter 9.5mm, number of holes 9,7
20 / m ²Wrap it around and emboss at a reduced pressure of 50 mmHg.
And then heat it to a temperature range of 120 ° C.
Wind another 40 μm thick base film on another smooth roll.
The embossed film is hung and pressed onto the embossing roll.
On the flat surface of the
5mm cushioning sheet (69 protrusions per unit area
%) Was obtained.

The performance of the cushioning sheet was determined by the following test method. (1) In the degradability test, the weight loss rate after 3 months was 15%, and the shape was easily broken.
(2) In the mold resistance test, mold growth was not observed even after 3 months. (3) The compressive strength was good with no rupture of bubbles in the cushioning sheet. (1) Degradability test: A test piece was embedded in soil at a temperature of 35 ° C. and a water content of 30%, and the appearance and the weight loss rate after 3 months were obtained. (2) Mold resistance test: In accordance with JIS Z-2911, place a test piece on an inorganic agar medium, spray inoculate a spore suspension of 5 kinds of test bacteria, incubate at 30 ° C, and mold over time. Was observed. (3) Compressive strength: 120 × 120m in accordance with the Defense Agency's standard (draft) test method for aerated plastic film cushioning material
The m cushioning sheet was compressed to half the initial thickness and kept in this state for 1 minute, and the bursting of bubbles was observed.

Example 2 Using the polymer obtained in Production Example 1 as a raw material, a T-die was connected to a 40 mmφ extruder, and two kinds of films having a thickness of 100 μ and 200 μ were obtained by T-die molding under the conditions of an extrusion temperature of 200 ° C. It was The embossing roll has a hole depth of 13 m
m, hole diameter 31 mm, hole number 990 / m ² , using a roll of 200 μ, embossing conditions are 100 ° C., the formed embossed film and the 100 μm film.
Smoothing roll temperature 120 for welding μ base film
The thickness was about 13 mm in the same manner as in Example 1 except that the temperature was changed to
To obtain a buffer sheet (the number of protrusions is 70% per unit area). The performance of the cushioning sheet is (1) 3 in the degradability test.
The weight reduction rate after 10 months was 10%, and the shape was easily broken. (2) In the mold resistance test, mold growth was not observed even after 3 months. (3) The compressive strength was good with no rupture of bubbles in the cushioning sheet.

Example 3 Using the polymer obtained in Production Example 2 as a raw material, a 50 μm film was obtained under the conditions of Example 1. The film is wound on a roll controlled at 80 ° C. to be softened by heating, and then the temperature is set to 1
It is wrapped around an embossing roll (hole depth 5 mm, hole diameter 9.5 mm, number of holes 9720 / m ² ) controlled at 50 ° C to form an embossed film at a pressure reduction degree of 40 mmHg, and a thickness is applied to another smooth roll. A 50 μ base film and kraft paper are simultaneously wound around, pressed onto the embossing roll to be welded to the flat surface of the embossing film, and then cooled with a cooling roll to form a composite sheet having a thickness of about 5 mm (the number of protrusions per unit area is 69%). The performance of the composite sheet is
(1) In the degradability test, the shape was easily broken after 3 months.
(3) In the compressive strength test, no bubbles burst.

Comparative Example 1 The polymer used in Example 1 was a low density polyethylene 50.
The film was changed to a μ film and embossed in the same manner as in Example 1. However, since the pore shape could not be sharply obtained, the roll temperature was increased by 40 ° C. and the welding temperature was increased by 30 ° C.
A buffer sheet was obtained in the same manner as in. In the (1) degradability test of the obtained buffer sheet, there was no weight change for 3 months. Comparative Example 2 A film made of the polymer used in Example 1 was prepared from a copolymer of hydroxybutyrate and hydroxyvalerate with 5%.
The film was changed to a 0 μ film and embossed in the same manner as in Example 1, but since the pore shape could not be sharply obtained, the roll temperature was increased by 40 ° C. and the welding temperature was increased by 25 ° C. To obtain a buffer sheet. In the degradability test (1) of the obtained cushioning sheet, the shape was distorted after 3 months. (2) In the mold resistance test, mold formation was recognized from 1 week onward, and the growth area of mold reached 2/3 or more after 2 to 3 weeks.

[0022]

EFFECTS OF THE INVENTION The buffer sheet mainly composed of lactic acid type polymer according to the present invention is excellent in compressive strength, compression resistance, scratch resistance, waterproofness and mold resistance and can be decomposed in a natural environment. It is suitable as a cushioning material without the problem of environmental pollution. Further, a composite sheet composed of a cushioning sheet and kraft paper is suitable as a transportation material such as a cardboard and an envelope.

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

Claims (4)

[Claims] 1. A buffer sheet comprising a thermoplastic polymer composition containing polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid as a main component. 2. The buffer sheet according to claim 1, wherein the lactic acid is L-lactic acid, D-lactic acid or a mixture thereof. 3. The buffer sheet according to claim 1, wherein the hydroxycarboxylic acid is glycolic acid. 4. A composite sheet obtained by laminating kraft paper or the like on one side or both sides of the cushioning sheet according to claim 1.