JPH04132748A - Production of bio-decomposable sheet - Google Patents

Abstract

PURPOSE:To obtain the subject sheet having improved appearance and transparency by melting and kneading a composition composed mainly of a saponified ethylene-vinyl acetate copolymer and a hydrated starch-based polymer in two stages and forming the composition in the form of a sheet under specific condition. CONSTITUTION:A composition composed mainly of a hydrated starch-based polymer and a saponified ethylene-vinyl acetate copolymer preferably having an ethylene content of 20-60mol% and a saponification degree of the vinyl acetate unit of >=60mol% is supplied to a vented extruder to perform the 1st stage melting and kneading and the kneaded product is supplied to an extruder to perform the 2nd stage melting and kneading. The kneaded molten mixture is extruded in the form of a sheet and immediately calendered or the mixture is compounded and then formed in the form of a sheet by calendering to obtain the objective bio-decomposable sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing biodegradable sheets with improved appearance and transparency.

Traditional technology Plastic films and containers as packaging materials,
Plastic molded products such as plastic films and binding tapes used as agricultural materials are often discarded through non-regular disposal routes.In this case, the molded products maintain their shape for many years. It is causing serious waste pollution. Therefore, it is desirable that molded products that are likely to be discarded outdoors, in fields, in rivers, etc., be quickly decomposed by microorganisms in the soil or water after the purpose of use is achieved.

Against this background, development of biodegradable molded products has recently become active.

It is known that blending starch-based polymers is effective in making molded products biodegradable.

For example, JP-A-2-14228 discloses a blended polymeric material obtained from a melt containing decomposed starch containing water and a small amount of one substantially water-insoluble synthetic thermoplastic polymer. Thermoplastic polymers synthesized with include polyethylene, polyisobutylene, polypropylene, polyvinyl chloride, polyvinyl acetate, polystyrene, polyacrylonitrile, polyvinylcarbazole, polyamide, polyacrylic ester, polymethacrylic ester, ethylene-vinyl acetate copolymer, ethylene - Vinyl alcohol copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ABS copolymer, styrene-acrylonitrile copolymer polyacetal, etc. Molding methods include injection molding, There is also a description that blow molding, extrusion and coextrusion molding, compression molding, and vacuum molding are employed.

U.S. Patent No. 3,949,145 describes saponification degree of 85
~100 mol% polyvinyl alcohol 1 to 4 parts by weight,
A film consisting of 8 parts by weight of starch, 1 to 5 parts by weight of glycerin, and 0.1 to 0.1 to 0.1 to 0.5 parts of polyol-toluene diisocyanate brepolymer containing free neuisocyanate groups.
A degradable agricultural mulch film coated with a water-resistant coating composition consisting of a mixture of 0.2 parts by weight and 1 part by weight of polyvinylidene chloride-acrylonitrile copolymer or 1 part by weight of plasticizer-containing polyvinyl chloride is provided. It is shown.

The present applicant has also filed a patent application for a polyvinyl alcohol/starch film containing polyvinyl alcohol and starch with a degree of saponification of 93 mol% or more and stretched in at least one axis (Japanese Patent Application Laid-Open No.
-151639).

Problems to be Solved by the Invention A molded product obtained by melt-molding a thermoplastic resin blended with a starch-based polymer exhibits biodegradability, so it can be used as a waste countermeasure. However, since starch-based polymers tend to thermally decompose during melt molding, molded products tend to be discolored, discolored, scorched, and smeared (foreign substances). In order to suppress thermal decomposition, when starch-based polymers are blended in the form of hydrous materials and subjected to low-temperature molding, compatibility or dispersibility may be insufficient, such as secondary agglomerated particles of starch-based polymers mixed in in the form of lumps. , the appearance of the molded product becomes inferior. This problem is a fatal drawback, especially for thin sheets.

The present inventor discovered that while conducting research on obtaining a biodegradable sheet by melt-molding a composition containing a saponified ethylene-vinyl acetate copolymer and a hydrated starch-based polymer as the main components, In order to improve the compatibility or dispersibility of the composition, the composition is fed to a vented extruder for first stage melt kneading, and then further fed to an extruder equipped with a T-die for second stage melt kneading. As a result of trying to melt-knead and extrude it into a sheet, we succeeded in improving the compatibility or dispersibility of the starch-based polymer, but the evaporation of the water contained in the second-stage melt-kneaded product As a result, the surface of the sheet became uneven at the T-Gui outlet, and the product sheet was faced with a situation where the transparency could not be ensured.

The present invention has been made to further develop such attempts and to obtain a biodegradable sheet with improved transparency.

Means for Solving the Problems The method for producing a biodegradable sheet of the present invention involves feeding a composition whose main components are a saponified ethylene-vinyl acetate copolymer and a hydrated starch polymer to an extruder equipped with a vent. First
After performing the melt kneading in the stage, it is further fed to the extruder and the second stage is melt-kneaded.
After performing melt-kneading in the second stage and extruding the melt-kneaded product in the second stage into a sheet shape, immediately calender processing is performed, or after the melt-kneaded product in the second stage is once bound, it is converted into a sheet shape by calender processing. It is characterized by being molded.

Note that the term "sheet" in the present invention includes a film.

The present invention will be explained in detail below.

The saponified ethylene-vinyl acetate copolymer has an ethylene content of 20 to 60 mol% and a degree of saponification of vinyl acetate units of 60 mol% or more (especially 80 mol% or more, and even 9 mol% or more).
0 mol % or more) is preferably used, and if the composition deviates from the above, it will be disadvantageous in terms of compatibility with starch-based polymers. The saponified copolymer may contain other α-olefins, ethylenically unsaturated carboxylic acids, their salts, anhydrides, esters, amides, nitriles, vinyl ethers, vinyl esters other than vinyl acetate, ethylenically unsaturated sulfonic acids, The saponified copolymer may contain a small amount of a comonomer such as an alkylene group-containing monomer.
As long as the purpose of the present invention is not impaired, urethanization,
It may be "post-modified" such as acetalization, cyanoethylation, or oxyalkylene etherification.

Starch-based polymers Examples of starch-based polymers in the hydrated material include corn starch, potato starch, sweet potato starch, rice starch, kissaba starch, sago starch, kubioka starch, sorghum starch, rice starch, bean starch, arrowroot starch, bracken starch, lotus starch, and water chestnut starch. Physically modified starch (α-starch, fractionated amylose, heat-treated starch, etc.), enzymatically modified starch (hydrolyzed dextrin, enzymatically decomposed dextrin, amylose, etc.), chemically modified starch (acid-treated starch, chlorate oxidized starch, dialdehyde starch, etc.), chemically modified starch derivatives (esterified starch, etherified starch, cationized starch, crosslinked starch, etc.), etc. Of the chemically modified starch derivatives, esterified starch includes: Etherified starches include allyl ether, such as acetate esterified starch, succinate esterified starch, nitrate esterified starch, phosphate esterified starch, urea esterified starch, xanthate esterified starch, acetoacetated starch Examples of cationized starches include reaction products of starch and 2-diethylaminoethyl chloride, starch and 2,3- Examples of the crosslinked starch, such as a reaction product of epoxyprobyl trimethylammonium chloride, include formaldehyde crosslinked starch, epichlorohydrin crosslinked starch, phosphoric acid crosslinked starch, acrolein crosslinked starch, and the like.

The water content of the hydrated starch polymer is suitably 8 to 30% by weight. If the water content is too low, the starch-based polymer will decompose during molding, causing problems such as coloring, discoloration, burnt spots, and foreign matter contamination. -If the blade-kin-sui rate is too high,
Smooth molding becomes difficult, and even if molding is possible, the smoothness of the molded product is impaired.

The blending ratio of the saponified ethylene-vinyl acetate copolymer and the hydrated starch polymer is 80:20 to 20 by weight.
It is desirable to set the ratio to 20:80, especially 70:30 to 30 near 0. If the proportion of starch-based polymer hydrate is too small, the biodegradability will be impaired, while if the proportion is too large, the molded product will deteriorate. Mechanical properties are insufficient. However, depending on the application, it may be acceptable to deviate slightly from the above blending ratio.

The composition of the present invention mainly contains the above-mentioned saponified ethylene-vinyl acetate copolymer and hydrated starch polymer, but also contains a plasticizer (polyhydric alcohol, etc.),
It may contain stabilizers, fillers, colorants, waterproofing agents, cellulose polymers, other polysaccharide polymers, protein polymers, polyvinyl alcohol, other general-purpose thermoplastic resins, etc. , glycerin, trimethylolpropane, pentaerythritol, ethylene glycol,
Blending polyhydric alcohols such as diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, mannitol, and sorbitol is useful, and the total amount of saponified ethylene-vinyl acetate copolymer and starch polymer hydrate It is preferable to add about 1 to 30 parts by weight per 100 parts by weight.

In the present invention, the composition containing the above-mentioned saponified ethylene-vinyl acetate copolymer and hydrated starch polymer as main components is fed to a vented extruder and subjected to the first stage of melt-kneading, and then Further, the mixture is supplied to an extruder and subjected to second-stage melt-kneading.

The melt kneading in the first stage is 190'C or less (especially 160 to 19
It is desirable that the water content in the first stage extrudate be 5% by weight or less (particularly 4% by weight or less). If the temperature during melt-kneading exceeds 190°C, it may lead to thermal decomposition of the starch-based polymer. If the moisture content in the extrudate exceeds 5% by weight, the second stage of melt molding and Even if calendering is performed, there is a risk that the resulting sheet will be contaminated with foam, and quality deterioration may occur, such as foaming of the sheet and perforation due to evaporation of water.

The second stage melt-kneading is carried out at 160°C or lower (especially 130 to 160°C).
If the temperature exceeds 160°C, the starch-based polymer will thermally decompose, resulting in thermal discoloration of the sheet, discoloration, burning, scorching, foaming of the sheet due to evaporation of water, and reduction in sheet thickness. Fluctuations are likely to occur.

In the present invention, either (1) the second-stage melt-kneaded product is extruded into a sheet and immediately calendered, or (2) the second-stage melt-kneaded product is once made into a compound and then calendered into a sheet. Shape.

When the molding method (2) is employed, a second stage extrusion molding machine equipped with a T-die is used to extrude the sheet into a sheet and simultaneously calender it. Calendering is performed at a roll temperature of 130-160"C and a roll rotation ratio of 1.0-1.
It is particularly preferable to carry out the test under the conditions of 0.05.

When using the molding method (2), the extrudate from the second stage extruder is once compounded into granules or pellets,
This compound is fed to calender rolls and calendered. It is particularly preferable that the calendering process in this case is also carried out under the conditions of a roll temperature of 130 to 160°C and a roll rotation ratio of 1.0 to 1.05.

The calender rolls used in the above calendering process can be of various types, including a Z-shaped 4-roll roll, an inverted 4-roll roll, an L-shaped 4-roll roll, an upright 4-roll roll, and an upright 3-roll roll. .

The biodegradable sheet obtained by the method of the present invention can be used for foods (
Packaging materials for pharmaceuticals, industrial chemicals, fertilizers, fragrances, construction materials, etc. (including beverages and seasonings); Vacuum compression molded cups and trays for foods, drugs, various industrial materials, parts, etc.; Agricultural films, binding tapes, etc. Agricultural materials: Can be used for a variety of purposes, including bags such as shopping bags and garbage bags.

Actions and Effects of the Invention Since the biodegradable sheet obtained by the method of the present invention mainly consists of a saponified ethylene-vinyl acetate copolymer and a hydrated starch-based polymer, it has sufficient strength and strength during use.
Although it has other properties (e.g., fragrance retention, oil resistance, chemical resistance, antistatic properties, heat retention, etc.), it is quickly decomposed by microorganisms in soil and water after the purpose of use is achieved. .

In addition, because we have adopted a unique molding method, the resulting sheet is There is hardly any discoloration, discoloration, burnt spots, bumps, fish eyes, etc., making it extremely desirable in terms of appearance and transparency.

Example Next, the present invention will be further explained with reference to Examples.

Example 1 Ethylene content 44 mol%, saponification degree of vinyl acetate unit 9
45 parts by weight of a saponified ethylene-vinyl acetate copolymer having a content of 9.0 mol%, 55 parts by weight of cornstarch having a moisture content of 13% by weight, and 20 parts by weight of glycerin were mixed in a Henschel mixer, and then supplied to a vented extruder. The first stage melt-kneading was performed under the following conditions and extruded into a linear shape.

Extruder: 30mm diameter, twin screw extruder with co-rotating vent, L/D
=30 Cylinder maximum temperature: 170°C Die temperature: 170°C Moisture content of extrudate: 3.1% by weight The extruded linear product was immediately fed as it was to an extruder equipped with a T-die, and was processed under the following conditions. A second stage of melt-kneading was performed and extruded into a sheet.

Extruder: 40mm diameter, single screw extruder, full flight type screw L/D=28, compression ratio 3.0 Cylinder maximum temperature: 145℃ T-gui temperature: 145℃ Immediately transfer the extruded sheet material to Z type The material was supplied to four rolls, calendered under the following conditions, and then passed through a cooling roll to obtain a sheet with a thickness of 110 C1u.

Roll condition 1 Yu 1 pi 1-7 Yu 2 = zydan 10th-ru 140 1.0 20th-ru
145 1.0 No. 30-Rule 150
1.0 No. 40-Rule 155 1.
0 Cooling roll temperature: 30°C Rolling speed: 4.8 m/min The appearance of the obtained sheet was observed, the haze was measured, and it was buried in the soil, and after 3 months, 6 months, and 1 year had elapsed. I checked the condition.

Comparative Example 1 Example 1 was repeated except that the first stage of melt-kneading was omitted. That is, after mixing in a Henschel mixer, the mixture was directly supplied to an extruder equipped with a T-die for second-stage melt molding, and further subjected to calender processing.

Comparative Example 2 Example 1 was repeated except that the calendering was omitted. That is, after the first stage of melt-kneading, the second stage of melt-kneading was performed and extruded into a sheet, which was immediately passed through a cooling roll.

The results of the above-mentioned Example 1 and Comparative Examples 1 and 2 are shown in Table 1.

Table 1 Note 1. In the tank for the appearance of the sheet, ○ means no grains mixed in, △ means there are some grains mixed in, and X means there are countless grains mixed in.

Note 2. The meanings of the symbols in the biodegradable tank are as follows.

A: Cracks B: Many cracks C: Numerous holes and cracks Example 2 Ethylene content 38 mol%, saponification degree of vinyl acetate unit 9
9.0 mol% ethylene-vinyl acetate copolymer saponified product 40 parts by weight, water content 15 weight% tapioca starch 60
Parts by weight and 20 parts by weight of glycerin were mixed in a Henschel mixer, then supplied to a vented extruder, subjected to first-stage melt kneading under the following conditions, and extruded into a linear shape.

Extruder: 30++v+ diameter, twin-screw extruder with co-rotating vent Schilling-Maximum temperature: 180°C Gui temperature: 180°C Moisture content of extrudate: 2.8% by weight The extruded linear product is immediately transferred to the extruder as it is. supply to,
A second stage of melt-kneading was performed under the following conditions to extrude into a linear shape and form compound pellets.

Extruder: 40 mm diameter, single screw extruder, full-flight screw L/D = 28, compression ratio 3.0 Maximum cylinder temperature: 145°C T-guid temperature: 145°C This compound pellet was passed through a strainer (similar to barrel extruder) ), heated to a temperature of 150°C, and fed to three upright rolls, calendered under the following conditions, and then passed through a cooling roll to obtain a sheet with a thickness of 150 μm.

Roll condition temperature L! 145 1.0 20th Rule
150 1.02 No. 30-Rule 155
1.02 Cooling roll temperature 30°C Rolling speed 3, (l m/min) Observe the appearance of the obtained sheet, measure the haze, and bury it in the soil for 3 months, 6 months, and 1 year. The condition after the passage of time was investigated.

Example 3 Example 2 was repeated except that potato starch was used in place of tapioca starch and the moisture content of the first stage extrudate was 2.8% by weight.

Comparative Example 3 Example 2 was repeated except that the first stage of melt-kneading was omitted. That is, after mixing in a Henschel mixer, the mixture was directly fed to an extruder for second-stage melt molding, and then passed through a strainer before calendering.

The results of Examples 2 to 3 and Comparative Example 3 described above are shown in Table 2.

Part 2 table B: There are many cracks. C: There are countless holes and cracks.

Claims (1)

[Claims] 1. After a composition containing a saponified ethylene-vinyl acetate copolymer and a hydrated starch polymer as main components is fed to a vented extruder and subjected to first-stage melt-kneading. , and then fed to an extruder to perform second-stage melt-kneading, extrude the second-stage melt-kneaded material into a sheet, and immediately calender, or once compound the second-stage melt-kneaded material. A method for producing a biodegradable sheet, which is characterized by forming the sheet into a sheet by calendering. 2. The first stage melt-kneading is carried out at 190°C or lower, the moisture content of the extrudate is set to 5% by weight or lower, and the second stage melt-kneading is carried out at 160°C or lower. manufacturing method. 3. Calendering, roll temperature 130-160℃,
2. The manufacturing method according to claim 1, wherein the manufacturing method is carried out under conditions of a roll rotation ratio of 1.0 to 1.05. 4. The production method according to claim 1, wherein the water content of the hydrated starch polymer in the composition subjected to the first stage melt-kneading is 8 to 30% by weight. 5. The weight ratio of the saponified ethylene-vinyl acetate copolymer and the hydrated starch polymer in the composition to be subjected to the first stage melt-kneading is 80:20 to 20:80. Manufacturing method described. 6. The manufacturing method according to claim 1, wherein the composition subjected to the first stage melt-kneading further contains a polyhydric alcohol. 7. The production method according to claim 1, wherein the saponified ethylene-vinyl acetate copolymer has an ethylene content of 20 to 60 mol% and a degree of saponification of vinyl acetate units of 60 mol% or more.