JP3490241B2 - Degradable films or sheets, molded articles made of these, and methods for decomposing them - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an unstretched degradable film / sheet of a polylactic acid-based polymer having a mixing ratio of L-lactic acid or D- lactic acid of 94% or more, or a molding comprising the film / sheet. Products and these films
The present invention relates to a method for disassembling a sheet or a molded product .

[0002]

2. Description of the Related Art Among biodegradable resins, aliphatic polyesters have come to the market due to the fact that alcohols and carboxylic acids formed upon decomposition have extremely low toxicity. Typical examples include polycaprolactone, polyhydroxybutyrate, polyhydroxybutyrate-valerate copolymer, polyethylene succinate, and polybutylene succinate. However, these resins have a problem that the glass transition point is as low as −60 ° C. to 10 ° C.

[0003]

On the other hand, among aliphatic polyesters, polylactic acid-based polymers also have a high glass transition point, exhibit properties similar to those of polyethylene terephthalate, have crystallinity, and are oriented by biaxial stretching. Moreover, although it is extrudable and castable and has good transparency, it has been a problem that biodegradability is extremely poor.

[0004]

Means for Solving the Problems As a result of detailed examination of the decomposition mechanism of the polylactic acid polymer, the present inventor found that the polylactic acid polymer is first hydrolyzed by water and then biodegraded by microorganisms. Biodegradation by microorganisms is extremely slow at low temperatures, but it is sufficiently fast at high temperatures, and hydrolysis by water causes initial disintegration of molded articles, such as on the surface of film sheets. It was found to be accelerated by the resulting cracks.
Moreover, it has been found that the compounding of inorganic particles is effective in causing this initial disintegration.

That is, according to the present invention, 100 parts by weight of a polylactic acid polymer having a mixing ratio of L-lactic acid or D- lactic acid of 94% or more and 1 to 120 parts by weight of inorganic particles are blended to obtain an unstretched decomposed material. Film or sheet, or a molded product formed from the unstretched degradable film or sheet, and a method for disassembling the film, sheet or molded product .

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The polylactic acid-based polymer used in the present invention is a homopolymer of lactic acid (referred to as "polylactic acid").
Alternatively, it is a copolymer of lactic acid and another hydroxycarboxylic acid, or a mixture thereof. As lactic acid, L-
Lactic acid and D-lactic acid are mentioned, and other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid and the like. To be
Therefore, in order to improve the crystallinity of the polylactic acid-based polymer, the mixing ratio of L-lactic acid or D-lactic acid is preferably 94% or more.

The weight average molecular weight of these polymers is preferably in the range of 50,000 to 100,000,
If it falls below such a range, there arises a problem that practical physical properties are hardly exhibited. On the other hand, if it exceeds, the melt viscosity becomes too high and the moldability becomes poor. Further, in order to improve the thermal stability, it is preferable that the residual monomer and the catalyst are small. For the production of such a polymer, any known method such as condensation polymerization method and ring-opening polymerization method can be adopted. For the purpose of increasing the molecular weight, a small amount of a chain extender, for example, a diisocyanate compound, diepoxy is used. Compounds, acid anhydrides, acid chlorides and the like may be used.

In the present invention, inorganic particles are blended with the polylactic acid polymer. Examples of the inorganic particles used include particles of silica, titania, talc, alumina, clay, calcium carbonate, magnesium carbonate, glass powder and the like. The size and shape of the particles are not particularly limited, but a larger specific surface area is preferable because the disintegration effect is enhanced. The blending ratio is 100% polylactic acid-based polymer.
1 to 120 parts by weight of inorganic particles, preferably 3 to 1 part by weight
If the amount of the inorganic particles is less than 1 part by weight, the decomposability cannot be improved, and if the amount is more than 120 parts by weight, the physical properties of the molded product, for example, the tensile strength, are reduced and the practicality is lost.

In the above formulation, other polymer materials may be added as long as the effects of the present invention are not impaired. Also,
Additives and modifiers such as plasticizers, lubricants, reinforcing agents, UV absorbers, light stabilizers, fungicides, pigments, fluorescent agents, etc. for the purpose of adjusting molding processability and other physical properties of films and sheets. It is also possible to do so. Of course, the above-mentioned polymeric materials, additives, modifiers and other auxiliary materials can also be added in advance to the polylactic acid polymer or inorganic particles before compounding.

The blending of the polylactic acid polymer and the inorganic particles and the addition of the above-mentioned auxiliary materials in the present invention may be carried out simultaneously at the time of film / sheet extrusion described later, but usually,
Prior to the film / sheet extrusion, it is preferable to melt-extrude in a strand form using another extruder and pelletize. Therefore, in order to prevent the hydrolysis of the polylactic acid polymer in the extruder at the melting temperature, it is desirable to sufficiently dry the raw materials in advance.

Next, the pelletized polylactic acid-based polymer is usually melt-extruded from a die using an extruder and formed into a film or sheet. As a special case, pellet press molding or calender molding may be performed as long as it is in a molten state.

As the extruder used for the above pelletization or film / sheet formation, any known form such as a single-screw, same-direction twin-screw, or different-direction twin-screw extruder can be used. For pelletizing, it is general to use a same-direction twin-screw extruder having a high kneading effect. The set temperature of the extruder is appropriately determined depending on the chemical composition and molecular weight of the polylactic acid polymer, but is preferably in the range of 170 to 230 ° C. That is, at 170 ° C or lower, polylactic acid having a high melting point does not melt, and at 230 ° C or higher, thermal decomposition becomes remarkable.

When a film is to be obtained, a flat product or a cylindrical product melt-extruded from a T-die, an I-die, a round die, etc. is rapidly cooled by a cooling cast roll, water, compressed air, etc. Uniaxially or biaxially by a roll method, a tenter method, a tubular method or the like.
Further, a so-called inflation method in which melt extrusion is performed from a round die and air is blown into a cylindrical object which is still in a molten state to reduce the thickness can be desirably used.

Further, by using the film stretching / heat setting technique as disclosed in Japanese Patent Publication No. 5-508819 and Japanese Patent Laid-Open No. 6-23836, transparency, mechanical strength, rigidity and thermal dimensional stability can be obtained. It is possible to obtain a polylactic acid-based film having excellent properties. The thickness of the film is determined in the range of 10 to 250 μm depending on the application.

The most preferable method for obtaining the sheet is a method of extruding the sheet in a plane using a T-die and quenching it with a metal cast roll equipped with a temperature control device, and separating the sheet from the cast roll if necessary. By nipping with the metal roll of No. 3, it is possible to obtain a polylactic acid-based sheet having excellent transparency and smoothness. The thickness of the sheet is determined in the range of approximately 250 μm to 1 mm depending on the application.

The present invention is also directed to the degradable film sheet obtained as described above and a molded article made of the film sheet. Examples of the method for obtaining a molded article from a film or sheet include a thermoforming method such as a vacuum forming method and a pressure forming method, which can be used for blister processed products, food cups, trays and the like. Also,
It can also be used as a box-type package by putting a folding ruled line on the sheet. In addition, paper and metal foil,
It is also used for sheets laminated with other plastic films and molded products thereof.

[0017]

EXAMPLES Examples will be shown below, but the present invention is not limited thereto. The measurements and evaluations shown in the examples were carried out under the following conditions.

(1) Tensile strength Using a Toyo Seiki Tensilon II type machine, JIS K712
It measured based on 7. Tensile speed during measurement is 10
It was set to 0 mm / min.

(2) Degradability test Simple composting test In a commercially available household composter, 10 kg of horticultural leaf soil and 5 kg of commercially available dog food
And then add 500 ml of water to give a thickness of 20
The buried soil was 0 mm. Sample is 40m from the film
The sample was cut out into m × 100 mm, inserted into a sample holder composed of two 60 mm × 150 mm wire meshes (3 mm size), and a thin wire was passed through the mesh to bind the sample. The contact of the sample with the outside and the collapse and scattering of the sample were suppressed as much as possible. The sample is one embodiment or one
Six sheets were prepared for each of the comparative examples and were embedded together with the sample holder so that the six sheets were vertically aligned in the soil of the composter. The bottom of each holder is 25mm from the bottom of the soil
Was placed at a height of 25 mm and the upper base was at a depth of 25 mm from the surface of the soil. One holder was taken out every one week after embedding, and the state of the surface of the sample was observed to confirm the presence or absence of disintegration. In addition, for the sample for the first week after burying, the amount of weight loss was examined and used as an index of the decomposition rate. From the weight reduction amount, the reduction amount of the polylactic acid polymer itself was calculated by the following formula. Reduction amount of polylactic acid polymer (mg) = weight reduction amount (mg)
× Ratio Ratio = [parts of polylactic acid polymer] / [parts of polylactic acid polymer + parts of inorganic particles]

Immersion in water degradability test Immersion in water in field test of Biodegradable Plastics Study Group ("Field test of biodegradable plastics" Biodegradable Plastics Study Group Technical Committee Report 1st Report (September 1992) ), And the test was performed.
That is, a film sheet was cut out into 120 mm × 30 mm and sandwiched in the center of three stainless steel sample holders. A window with the same shape as the sheet sample is opened in the center of the sample holder, and two stainless steel wire nets (40 mesh) are chewed so that the sheet does not flow out as it is and good contact with water I was in a state. The appearance of the sample after immersing in fresh water for 2 years was observed.

Comparative Example 1 and Example 1 The ratio of the structural unit composed of L-lactic acid to the structural unit composed of D-lactic acid was approximately 98: 2, the glass transition point was 58 ° C., and the melting point was 175.
C., with respect to 100 parts by weight of polylactic acid pellets having a weight average molecular weight of 180,000, anatase type crystalline titanium dioxide A-170 (average particle size 0.15 μm) manufactured by Sakai Chemical Industry Co., Ltd.
0.5 parts by weight (Comparative Example 1) and 5 parts by weight (Example 1) were mixed, respectively, and extruded into a strand shape at 220 ° C. with a 26 mmΦ biaxial kneading extruder to prepare two types of pellets. The two types of pellets containing titanium dioxide were extruded from a T-die at 210 ° C. in a 30 mmΦ uniaxial extruder and rapidly cooled by a casting roll to obtain a white unstretched sheet having a thickness of about 0.4 mm. Table 1 shows the results of the measurement of tensile strength and the decomposability test (simple compost test).

[Comparative Example 2] A transparent unstretched sheet having a thickness of about 0.4 mm was obtained in the same manner as in Example 1 except that titanium dioxide was not added. Table 1 shows each measured value and the evaluation result.

[Examples 2 and 3 and Comparative Example 3] Example 1
In place of titanium dioxide, 10 parts by weight of fine powder silicon dioxide Sylysia 310 (average particle size 1.4 μm) manufactured by Fuji Silysia Chemical Ltd. (average particle size 1.4 μm) (Example 2), 100
Except for the use of parts by weight (Example 3) and 150 parts by weight (Comparative Example 3), the thickness was about 0.4, in the same manner as in the same example.
A transparent unstretched sheet of mm was obtained. Table 1 shows each measured value and the evaluation result.

[Example 4 and Comparative Example 4] The unstretched sheets obtained in Example 1 and Comparative Example 2 were immediately roll-stretched 2.3 times in the longitudinal direction at 70 ° C, and then in the width direction at 75 ° C. Was stretched 2.6 times by a tenter, the sheet was introduced into a heat treatment zone, and heat-set at 130 ° C. for 20 seconds. The thickness of the obtained stretched sheet is 0.2 mm. Table 1 shows each measured value and the evaluation result.

[0025]

[Table 1]

From the results shown in Table 1, the following facts were confirmed. In the unstretched film, Example 1 is compared to Comparative Examples 1-2, and Examples 2-3 are Comparative Example 2
Compared with, the initial amount of weight loss is large, and there is a tendency for disintegration to begin earlier. In Comparative Example 3, the decomposition is remarkable, but in comparison with Examples 2 to 3, the tensile strength is significantly decreased and the practicality is poor. Further, also in the stretched heat-fixing film, in Example 4 in which the inorganic particles are blended, the decomposition is faster than in Comparative Example 4 in which no blending is performed.

[Example 5 and Comparative Example 5] The unstretched sheets obtained in Example 1 and Comparative Example 2 were subjected to a water immersion degradability test. The results are shown in Table 2.

[0028]

[Table 2]

Table 2 shows that the decomposition was accelerated by the addition of the inorganic particles even in the natural environment.

[0030]

According to the present invention, by incorporating a specific amount of inorganic particles, the degradability of the polylactic acid polymer can be increased while maintaining practical strength. Therefore, the degradable film / sheet of the present invention or a molded article comprising the film / sheet is used in applications where rapid degradation is desired in a natural environment, such as seedling pots and spruce tapes used in a one-year cycle, and It is suitable for fishing tackles and packaging materials such as food that are accidentally scattered in the environment.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C08L 67/04

Claims (4)

(57) [Claims] 1. An unstretched degradable film or sheet prepared by mixing 1 to 120 parts by weight of inorganic particles with 100 parts by weight of a polylactic acid polymer having a mixing ratio of L-lactic acid or D- lactic acid of 94% or more. . 2. A molded product molded from the unstretched degradable film or sheet according to claim 1. 3. An unstretched film or sheet prepared by mixing 1 to 120 parts by weight of inorganic particles with 100 parts by weight of a polylactic acid-based polymer having a mixing ratio of L-lactic acid or D-lactic acid of 94% or more is hydrolyzed. After disintegration, further, a method for decomposing an unstretched film or sheet that undergoes biodegradation by microorganisms, in which the disintegration by hydrolysis is promoted by cracks (cracks) generated on the surface of the film or sheet by inorganic particles, A method for decomposing a degradable film or sheet, which comprises shifting to biodegradation by microorganisms. 4. A molded article comprising an unstretched film or sheet in which 1 to 120 parts by weight of inorganic particles are mixed with 100 parts by weight of a polylactic acid-based polymer having a mixing ratio of L-lactic acid or D-lactic acid of 94% or more. After being disintegrated by hydrolysis,
Furthermore, a method for decomposing a molded article composed of an unstretched film or sheet that undergoes biodegradation by microorganisms, wherein the hydrolysis-induced disintegration begins with cracks caused by inorganic particles on the surface of the molded article , and A method for disassembling a molded article composed of a degradable film or sheet, characterized by shifting to disassembly.