JP3108472B2 - Biodegradable resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biodegradable resin composition comprising a saponified ethylene-vinyl acetate copolymer and a starch-based polymer and capable of giving a molded article having excellent moldability and physical properties. It is about.

[0002]

2. Description of the Related Art Plastics molded products such as plastics films and containers as packaging materials, plastics films and bundling tapes as agricultural materials may be discarded by other than regular processing routes. is there.
In this case, the molding maintains its shape for many years, causing serious waste pollution. Therefore, it is desired that a molded article which may be disposed of in the field, in a field, in a river, or the like is promptly decomposed by microorganisms in soil or water after the purpose of use is achieved.

[0003] From such a background, research and development of a biodegradable composition for obtaining a biodegradable molded product have been actively conducted. Among these research and developments, the following application was filed for a biodegradable or disintegrable composition comprising a saponified ethylene-vinyl acetate copolymer (that is, an ethylene-vinyl alcohol copolymer) and a starch-based polymer. It has been done.

JP-A-3-31333 discloses a polymer composition for producing a biodegradable plastic article comprising an ethylene / vinyl alcohol copolymer and a modified starch. Polymer compositions having an ethylene content of 10-90% by weight and a melt flow index (measured at 230 ° C., 2.16 kg) of 2-50 are indicated.

The publication states that the more preferable properties of the ethylene / vinyl alcohol copolymer are as follows. -Intrinsic viscosity [η] (30 in dimethyl sulfoxide)
° C): 0.5 to 0.9, preferably 0.65 to 0.80. Molecular weight distribution _Mw / _Mn (GP in tetrahydrofuran
C): 1.3-4. Melting point: less than 180C, preferably 160-170C. Degree of hydrolysis 90-99.9%.

This publication also describes a high-boiling plasticizer. In claim 4, the high-boiling plasticizer is contained in a concentration of 0.05 to 100% by weight based on the starch component. Item 5 indicates that the high boiling point plasticizer is contained at a concentration of 20 to 100% by weight based on the starch component. In Example 1, 50 parts by weight of an extruded mixture containing 15% by weight of glycerin based on an ethylene / vinyl alcohol copolymer was mixed with 70 parts by weight of starch, 50 parts by weight of water, and 15 parts by weight of urea. An example in which a pellet is formed by an extruder and then formed into a film by an extruder equipped with an inflation head is described in Example 2. In Example 2, 63% by weight of starch having a moisture content of 11% by weight, 25% by weight of glycerin, and 7% of urea were used. % By weight and 5% by weight of an ethylene-acrylic acid copolymer were extruded into pellets, and then the obtained pellets were 60% by weight.
Examples 3 to 8 show examples of mixing and extruding with 40% by weight of ethylene-vinyl alcohol copolymer, and Examples 3 to 8 show 39% by weight of starch having a moisture content of 11% by weight and 37% by weight of ethylene / vinyl alcohol copolymer. %, Glycerin 12.8% by weight, water
An example is shown in which 3.2% by weight, 3% by weight of an ethylene-acrylic acid copolymer and 5% by weight of urea were pelletized and formed into a film in the same manner as in Example 1. It is considered that the ethylene-vinyl alcohol copolymer is substantially anhydrous.

JP-A-3-24101 discloses that starch is mixed with a high-boiling plasticizer and a modifier selected from urea, alkaline earth or alkali metal hydroxides and mixtures thereof at a temperature below the boiling point of the plasticizer. It discloses a process for preparing a modified starch composition for producing a biodegradable plastic article, which comprises mixing at a temperature of 120 to 170 ° C. for a time sufficient to modify the starch. States that this modified starch composition is suitable for mixing with an ethylene / vinyl alcohol copolymer.

[0008] Claim 2 of this publication discloses that the high boiling plasticizer is added in an amount of 0.05 to 100% by weight based on the weight of the starch. -100% by weight is indicated. In Examples 1 to 4, 63% by weight of starch having a moisture content of 11% by weight was used.
And 25% by weight of glycerin, and extrusion molding to obtain modified starch.
An example is shown in which the mixture is extruded by mixing 40% by weight of the ethylene / vinyl alcohol copolymer with 40% by weight.

JP-A-2-14228 discloses a blended polymer material obtained from a melt containing decomposed starch containing water and at least one synthetic thermoplastic polymer which is substantially insoluble in water. Claim 4 of the claims of the application of this publication contains, as thermoplastic polymers, ethylene / vinyl acetate copolymers, ethylene / vinyl alcohol copolymers, ethylene / acrylic acid copolymers, ethylene / ethyl acrylate copolymers, Ethylene / methyl acrylate copolymers, ABS copolymers, styrene / acrylonitrile copolymers, polyacetals are mentioned as being used, and although ethylene / vinyl alcohol copolymers are mentioned, ethylene / vinyl alcohol copolymers are used. No examples are given.

This publication also describes a plasticizer. Claim 14 of the claims describes that about 0.5 to about 0.5 of all components.
15% by weight of plasticizer is added, and claim 16 shows that the total content of plasticizer and water is not more than 25% by weight of all components.

According to the present invention, a starch having a water content of 5 to 30% by weight, based on the starch / water component, has a sufficient length of time to form a melt in a closed vessel at an elevated temperature. In producing the polymer material by heating, it is described that the starch / water material is mixed with a substantially water-insoluble synthetic thermoplastic polymer before or during the formation of a melt. In columns 8-12,
"As a" substantially water-insoluble synthetic thermoplastic polymer ", the polymer is preferably polymer 10 at room temperature.
It is understood that water is dissolved at a rate of up to 5% per 0g, more preferably at a rate of up to about 2%. "It is stated.

[0012]

The biodegradable composition comprising an ethylene-vinyl alcohol copolymer and a starch-based polymer contains a large amount of a starch-based polymer which is easily decomposed during melt molding and has a high ethylene-based content. The vinyl alcohol copolymer itself is one of the most difficult thermoplastic resins among general-purpose thermoplastic resins. There is. Therefore, in industrial production, it is indispensable to mix a considerable amount of high-boiling point plasticizers such as polyhydric alcohols and urea and provide them for melt molding. (Eg, stickiness due to transfer of the plasticizer to the surface of the molded product, deterioration of the basic physical properties of the molded product), and may cause hygiene problems. In order to prevent such troubles, the amount of the plasticizer to be used must be reduced, but in that case, the melt moldability deteriorates as described above.

JP-A-3-31333 and JP-A-3-31.
Although the use of a wide range of high-boiling plasticizers is disclosed in Japanese Patent No. 24101, the reason why the high-boiling plasticizer is blended in a large amount in the examples is that the blending amount of the high-boiling plasticizer is large. Otherwise, the moldability itself may be impaired. In JP-A-2-14228, there is no practical example using an ethylene-vinyl alcohol copolymer, and no study has been made on a blending system of the copolymer and a starch-based polymer.

In these publications, the water used for blending is derived from water contained in undried starch-based polymer or water newly added from outside the system. The method is a method for melt-molding a composition comprising a conventional ethylene-vinyl alcohol copolymer / starch-based polymer.

After all, the above-cited Japanese Patent Application Laid-Open No. 3-33333
JP, JP-A-2-14228 and JP-A-3-142228
Japanese Patent No. 24101 discloses a technique as a background regarding a biodegradable or disintegrable composition comprising a saponified ethylene-vinyl acetate copolymer (ethylene-vinyl alcohol copolymer) and a starch-based polymer. It is still unsolved to secure the properties required for molded products (prevention of plasticizer migration, favorable basic physical properties, and favorable biodegradability) while maintaining good moldability sufficient for industrial use. Matters.

Under the above-mentioned circumstances, the present invention is intended to provide an industrially employable good moldability while using a combination of a saponified ethylene-vinyl acetate copolymer and a starch-based polymer. At the same time, it is an object of the present invention to provide a biodegradable resin composition capable of providing a molded article having a plasticizer migration-preventing property, preferable basic physical properties, and a desired biodegradability or disintegration property.

[0017]

The biodegradable resin composition of the present invention has a composition having an ethylene content of 20 to 60 mol%, a saponification degree of a vinyl acetate unit of 90 mol% or more, and a water content. It comprises 20 to 60% by weight of a saponified hydrated ethylene-vinyl acetate copolymer (A) and a starch-based polymer (B).

Hereinafter, the present invention will be described in detail.

In the present invention, the hydrous ethylene-vinyl acetate copolymer saponified product (A) has an ethylene content of 20%.
60 mol%, saponification degree of vinyl acetate unit is 90 mol%
The one having the above composition is used. When the ethylene content and the degree of saponification are out of this range, the mechanical properties and gas barrier properties become insufficient.

The water content of the water-containing saponified ethylene-vinyl acetate copolymer (A) is set to 20 to 60% by weight. When the water content is less than 20% by weight, the starch-based polymer (B)
And the melt dispersibility is inferior and smooth melt moldability cannot be achieved, and the combined use of a plasticizer becomes unavoidable. On the other hand, the water content is 6
If the content exceeds 0% by weight, foaming occurs during melt molding, making smooth molding difficult, and the surface properties of the obtained molded product deteriorate. The peak temperature (corresponding to the melting point) by DSC of the hydrous ethylene-vinyl acetate copolymer saponified product (A) having the above specified water content is 110 ° C. or lower, particularly 90 ° C.
１０５105 ° C.).

The saponified ethylene-vinyl acetate copolymer having the above copolymer composition may be used in combination with other copolymerizable monomers, for example, other α-olefins, ethylenically unsaturated monomers, as long as the spirit of the present invention is not impaired. Carboxylic acid compounds (acids, anhydrides, salts, esters, amides, nitriles, etc.), vinyl ethers, vinyl esters other than vinyl acetate, ethylenically unsaturated sulfonic acid compounds (acids, salts, etc.), oxyalkylene group-containing monomers, etc. And may be “post-modified” such as oxyalkylene etherification, cyanoethylation, acetalization, and urethane formation.

The above-mentioned saponified hydrated ethylene-vinyl acetate copolymer (A) is typically prepared by subjecting an ethylene-vinyl acetate copolymer to alkali saponification and then methanolic saponified ethylene-vinyl acetate copolymer. Water is added to the solution to form a water-methanol mixed solvent solution, the solution is introduced into water to coagulate, and the coagulated product is pelletized or pulverized, followed by washing and purification. In the washing and purification, an acid, particularly an aqueous solution of a weak acid or a diluted strong acid or an aqueous solution of an acidic salt thereof, is sufficiently washed, and if necessary, after the acid attached to the resin is removed by washing with water, a desired water content is obtained. It is desirable to dry under appropriate drying conditions.

Here, the weak acids include acetic acid, propionic acid, glycolic acid, lactic acid, adipic acid, azelaic acid,
Glutaric acid, succinic acid, benzoic acid, isophthalic acid, terephthalic acid, and those having a pKa (25 ° C.) of 3.5 or more are usually used. Examples of strong acids include oxalic acid, maleic acid, and other organic acids having a pKa (25 ° C.) of 2.5 or less, phosphoric acid, and the like.
Examples thereof include inorganic acids such as sulfuric acid, nitric acid, and hydrochloric acid, and acidic salts of these strong acids can also be used. The treatment with a strong acid (or an acid salt thereof) is usually performed after the treatment with a weak acid and before or after washing with water.

Examples of the starch-based polymer (B) include raw starch (corn starch, potato starch, sweet potato starch, wheat starch, kissava starch, sago starch, tapioca starch, sorghum starch, rice starch, mame starch, kudzu starch, Physically modified starch (α-starch, fractionated amylose, wet heat-treated starch, etc.); enzyme-modified starch (hydrolyzed dextrin, enzyme-decomposed dextrin, amylose, etc.); chemically degraded starch (acid-treated starch, Hypochlorite oxidized starch, dialdehyde starch, etc.); chemically modified starch derivatives (esterified starch, etherified starch, cationized starch, crosslinked starch, etc.) and the like are used. Among the chemically modified starch derivatives, the esterified starch includes acetate esterified starch, succinic esterified starch, nitrated esterified starch, phosphorylated esterified starch, urea phosphorylated esterified starch, xanthated esterified starch, and acetoacetated starch. Examples of etherified starch such as acetic acid-esterified starch include allyl etherified starch, methyl etherified starch, carboxymethyl etherified starch, hydroxyethyl etherified starch, and hydroxypropyl etherified starch. Formaldehyde cross-linked starch such as a reaction product of diethylaminoethyl chloride, a reaction product of starch and 2,3-epoxypropyltrimethylammonium chloride, etc. , Epichlorohydrin crosslinked starch, phosphoric acid crosslinked starch, acrolein-crosslinked starch and the like.

The starch-based polymer (B) can also be used as a hydrate with a hydrous ethylene-vinyl acetate copolymer saponified product (A).

The compounding ratio of the saponified hydrated ethylene-vinyl acetate copolymer (A) and the starch-based polymer (B) is 80:20 to 20:80, especially 70:30, by weight on a dry basis.
~ 30: 70, preferably a starch-based polymer
When the proportion of (B) is too small, the biodegradability or disintegration is impaired, while when the proportion is too large, the mechanical properties of the molded product become insufficient. However, depending on the application, the amount may slightly deviate from the above mixing ratio.

The resin composition of the present invention further comprises a polyhydric alcohol (glycerin, trimethylolpropane, pentaerythritol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol,
Although an appropriate amount of a plasticizer such as polypropylene glycol, mannitol, and sorbitol) and urea can be blended, a feature of the present invention is that smooth melt molding can be performed even without or with a small amount of a plasticizer.

In addition, if necessary, resin components other than those described above (polyvinyl alcohol and derivatives thereof, ethylene copolymers and other polyolefins, hydrogenated styrene-butadiene rubber, polyurethane, polyamide, polyhydroxybutyrate, etc.), starch-based high Natural polymers other than molecules (polysaccharide polymers, cellulose polymers, protein polymers, etc.), heat stabilizers, autoxidizers, fillers, coloring agents,
A water-proofing agent or the like may be added.

As the melt molding method, an extrusion molding method (including a blow molding method) and an injection molding method are employed, but a calender molding method and other molding methods can also be employed. At the time of melt molding, the hydrous ethylene-vinyl acetate copolymer saponified product (A) and the starch-based polymer (B) are separately or simultaneously supplied to an extruder, melt-kneaded, and once pelletized. A method of supplying the material to a molding machine according to the purpose and molding it into an intended shape is suitably adopted. The former extruder is usually an extruder with a vent. The melt molding temperature in the latter stage is often set to 150 ° C. or lower.

The molded product obtained by the biodegradable resin composition of the present invention, packaging materials (films, sheets, bottles,
It can be used for various purposes, including agricultural materials (agricultural films, binding tapes, etc.); consumer materials (diaper backsheets, shopping bags, garbage bags, etc.).

[0031]

In the present invention, since the water-containing ethylene-vinyl acetate copolymer saponified product (A) having a water content of 20 to 60% by weight is used, the molded product has various properties and hygiene. Good moldability is ensured even if the disadvantageous plasticizer is omitted or greatly reduced.

[0032]

The present invention will be further described with reference to the following examples.

Examples 1 to 5, Comparative Examples 1 to 4 <Production of water- or water-free saponified ethylene-vinyl acetate copolymer> Ethylene-acetic acid having an ethylene content of 29.0 mol%, 38.0 mol% or 44.0 mol% A methanol solution of sodium hydroxide as a catalyst was added to a methanol solution of a vinyl copolymer, and a continuous saponification reaction was carried out in a tower.Water was added to a methanol solution of the obtained saponified product to form a methanol-water mixed solvent solution. After that, it was discharged from the nozzle into water at 20 ° C. or lower. As a result, the solution was solidified into a strand having a diameter of about 3 mm, and the solidified product was pulled out of water and cut.

The strand-like solidified product is pelletized by a pelletizer, the sodium acetate contained in the polymer is removed by washing with water, and the polymer is washed with a dilute aqueous solution of acetic acid and then with a dilute aqueous solution of phosphoric acid. It dried under drying conditions and adjusted to target moisture content.

The composition, water content and melting point (DSC) of the obtained hydrous or hydrous ethylene-vinyl acetate copolymer saponified product
Is shown in Table 1.

Table 1 A-1 A-1a A-2 A-3 A'-1 A'-2 A'-3 Ethylene content (mol%) 44.0 44.0 38.0 29.0 44.0 38.0 29.0 Degree of saponification (mol%) 99.5 99.5 99.5 99.5 99.5 99.5 99.5 Water content (% by weight) 53 26 30 55 0.5 1.0 0.5 Melting point (° C) 96 100 98 93 164 172 186

<Pelletization of Compound> The pellets of the water-containing or water-free saponified ethylene-vinyl acetate copolymer prepared above and raw starch (water content: 12
% By weight of corn starch) and glycerin, if necessary, in a ratio and combination shown in Table 2 below into a Henschel mixer and mixed, and then supplied to a vented twin-screw extruder to melt-extrude in a strand form, and a pelletizer. And pelletized. The twin screw extrusion conditions were as follows.

Screw diameter 30 mm L / D 30 Screw rotation speed 150 rpm Vent Open vent Dice Two nozzles with a diameter of 3.0 mm

<Melting Molding> The compound pellets obtained above were supplied to an injection molding machine having a mold clamping pressure of 100 TON, and injection molding was performed under the following conditions to obtain a size of 100 mm × 100 m.
m, 1.5mm thick sheet (flat plate), JIS K-71
No. 1 tensile test piece and JIS K-2703 based on No. 13
A bending test piece was prepared based on the above.

Injection pressure 1200 kg / cm ² Injection speed High speed mold
Side gate No. 1 mold for tensile test and mold for bending test Mold temperature 40 ℃

<Results> The results are shown in Table 2 together with the conditions.

[0042]Table 2 Example Comparative example 1 2 3 4 5 1 2 3 4 EVOH used A-1 A-1 A-1a A-2 A-3 A'-1 A'-2 A'-3 A'-1 Moisture content (% by weight) 53 53 26 30 55 0.5 1.0 1.0 0.5 Mixing ratio (parts by weight) EVOH 150 100 100 100 160 70 70 70 70 Raw starch 100 100 100 100 100 100 100 100 100 Glycerin--------35 Pellet workability Good Good Good Good Good Good Not possible Not possible Not possible Good Composition of processed pellets (% by weight) EVOH 33 26 40 38 34---34 Raw starch 42 50 47 48 41---44 Water 25 24 13 14 25---5 Glycerin--------17 Good for processing pellets Good Good Good Good Good---Good Injection moldability Mechanical strength Tensile strength (kg / cm^Two) 240 300 350 360 260---250 Elongation (%) 50 40 40 35 40---40 Bending strength (kg / cm ² ) 220 280 350 350 250---250 With or without bleed No No No No No---Yes Biodegradability (disintegration) 6 months b b b b b---c 1 year aaaaa---b (Note) EVOH stands for ethylene-vinyl acetate copolymer
monster. In the section of pellet workability, “good” means miscibility.
Good, good strand take-off, "impossible" is miscible
Because it does not become a strand due to failure and cannot be pelletized
No injection molding. Mechanical strength is JIS K-711
3 (tensile test method), JIS K-2703 (bending test)
Method) at 20 ° C.

Regarding biodegradability (disintegration), the flat sample pieces obtained above were buried in compost mixed soil, excavated after 6 months and 1 year, and the state of the sample pieces was visually observed. And the following three levels. Comparative Examples 1 to
No. 3 was not evaluated because of poor moldability. a: 50% or more of the volume of the sample piece is deformed. b: Irregularities are seen on the entire surface of the sample piece, and the four sides of the sample also have irregularities, and collapse is in progress. c: Concave spots are partially observed on the surface and the end of the sample piece.

[0044]

Industrial Applicability The biodegradable resin composition of the present invention has good melting properties which can be industrially adopted, despite being a combined system of a saponified ethylene-vinyl acetate copolymer and a starch-based polymer. Has moldability. Moreover, the compounding of the plasticizer, which is disadvantageous in terms of the physical properties and hygiene of the molded product, can be omitted or greatly reduced, so that the desired biodegradability or disintegration can be exhibited while securing the basic physical properties. be able to.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 3/00-3/20 C08L 29/04 C08J 3/14

Claims (3)

(57) [Claims] 1. A water-containing ethylene-vinyl acetate copolymer having a composition having an ethylene content of 20 to 60 mol%, a degree of saponification of vinyl acetate units of 90 mol% or more, and a water content of 20 to 60% by weight. A biodegradable resin composition comprising a saponified product (A) and a starch-based polymer (B). 2. A saponified hydrated ethylene-vinyl acetate copolymer (A) is coagulated by introducing a water-methanol mixed solvent solution of the saponified ethylene-vinyl acetate copolymer into water.
The water content is adjusted after the washing and purification treatment.
The biodegradable resin composition according to the above. 3. The biodegradable resin composition according to claim 1, wherein the mixing ratio of the hydrous ethylene-vinyl acetate copolymer saponified product and the starch-based polymer is 80:20 to 20:80 by weight on a dry basis. Stuff.