JP3133415B2 - 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 starch polymer, a saponified ethylene-vinyl acetate copolymer and a plasticizer.

[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.

[0005] In this publication, polyethylene glycol, polypropylene glycol, polyethylene-
Plasticizers including low molecular weight polyalkylene oxides such as propylene glycol: low molecular weight organic plasticizers such as glycerol, glycerol monoacetate, diacetate or triacetate: propylene glycol, sorbitol, sodium diethylsulfosuccinate, citrate Triethyl citrate, tributyl citrate and the like are described.

Japanese Patent Application Laid-Open No. 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 a mixture 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. In Example 5, Clarane R20 (registered trademark) ethylene / vinyl alcohol copolymer was used. Examples are given, but the ethylene content is not specifically described.

JP-A-2-14228 discloses a blended polymer material obtained from a melt containing degraded 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 reference is also made to ethylene / vinyl alcohol copolymers, but the ethylene content of the ethylene / vinyl alcohol copolymers is mentioned. Are not described, and no examples using the copolymer are given.

In each of these publications, polyols such as polyethylene glycol, ethylene glycol, propylene glycol, sorbitol and preferably glycerin having a molecular weight of 200 to 4000 are described as plasticizers.

[Problems to be solved by the invention]

[0009] Starch-based polymers are polymers that are easily decomposed by heat, and when they are blended with resin and subjected to melt molding,
Above a temperature of about 180 ° C., thermal decomposition occurs. On the other hand, saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH) is one of the thermoplastic resins which is difficult to melt-mold. For example, the melting point of EVOH having a high degree of saponification is 180 ° C. or more when the ethylene content is about 30 mol% or less. Therefore, there is a problem that a molding trouble or a defect easily occurs in a molded product in a mixed system of both. Therefore, in industrial production, it is indispensable to mix various plasticizers as described above and provide them for melt molding. However, in such a case, even if a plasticizer as described above is simply used, in the mixed system of the above-mentioned starch-based polymer and EVOH,
Compatibility is poor, transparency and flexibility when processed into films and sheets are not sufficient, and changes in physical properties and contamination due to plasticizer bleed also occur. Further improvements are required to be satisfactory.

[0010]

The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems. As a result, when a specific polyhydric alcohol is blended as a plasticizer, the compatibility is good, and the film and the like are excellent. It has been found that the molded product of the present invention is excellent in transparency and flexibility, and furthermore, it is possible to prevent a change in physical properties and contamination due to bleeding, and completed the present invention. That is, the present invention provides: (A) a starch-based polymer, (B) an ethylene content of 20 to 60 mol%, a saponification degree of vinyl acetate units of 90 mol% or more , and a melt flow index.
(Measured at 210 ° C. under a load of 2160 g) 1 to 60 g / 1
0 min ethylene - vinyl acetate copolymer saponification product has three 2 hydroxyl groups in (C) molecules, Ri consists polyhydric alcohol having a molecular weight of 600 or less with a melting point of 40 ° C. or higher, and
(C) is 100% by weight of the total amount of (A) and (B)
5-50 parts by weight der Ru biodegradable resin composition with respect to part. ".

[0011] The starch-based polymer (A) of the present invention includes raw starch (corn starch, potato starch, sweet potato starch, wheat starch, kissava starch, sago starch, tapioca starch, sorghum starch, rice starch, mame starch, kuzu 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 starches include 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 esterified starch include allyl etherified starch, methyl etherified starch, carboxymethyl etherified starch, hydroxyethyl etherified starch, and hydroxypropyl etherified starch. Cross-linked starch such as a reaction product of diethylaminoethyl chloride, a reaction product of starch and 2,3-epoxypropyltrimethylammonium chloride, and the like. , Epichlorohydrin crosslinked starch, phosphate crosslinked starch, acrolein crosslinked starch and the like. The starch-based polymer (A) can also be used as a hydrate with the following EVOH (B).

The EVOH (B) of the present invention has an ethylene content of 20 to 60 mol%, preferably 25 to 50 mol%, and a saponification degree of vinyl acetate units of 90 mol% or more, preferably 95 mol% or more. Can be used. If the ethylene content is less than 20 mol%, the melt moldability decreases, and the
Exceeding the range impairs the mechanical strength and gas barrier properties and is not practical. If the saponification degree is less than 90 mol%, the mechanical strength is insufficient. The melt flow index of the above EVOH (B) was measured at 210 ° C. under a load of 2160 g,
60g / 10 minutes, preferably those of 2~30g / 10 minutes
There you can use.

[0013] EVOH having the above copolymer composition
(B) is, for example, another α-olefin, an ethylenically unsaturated carboxylic acid-based compound (acid, anhydride, salt, ester,
Amide, nitrile, etc.), vinyl ethers, vinyl esters other than vinyl acetate, ethylenically unsaturated sulfonic acid compounds (acids, salts, etc.), oxyalkylene ethers, and the like. , Cyanoethylation, acetalization, urethanization and the like, and may be "post-modified".

EVOH (B) is typically a powder, particles or saponified ethylene-vinyl acetate copolymer after alkali-saponification of an ethylene-vinyl acetate copolymer having the above-defined ethylene content. Obtained by washing and purifying the pellet. For washing and purification, an aqueous solution of an acid, particularly a weak acid, or a dilute strong acid (or an acid salt thereof)
The resin is sufficiently washed with an aqueous solution of, and if necessary, the acid attached to the resin is removed by washing with water, followed by drying.

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 the strong acid include organic acids having a pKa (25 ° C.) of 2.5 or less, such as oxalic acid and maleic acid, and inorganic acids such as phosphoric acid, sulfuric acid, nitric acid, and hydrochloric acid. it can. Treatment with a strong acid (or its acid salt) is performed after treatment with a weak acid,
Usually, before or after washing with water.

[0016] Starch polymer (A) and EVOH (B)
Is preferably 80:20 to 20:80, particularly 70:30 to 30:70 by weight, and if the ratio of the starch-based polymer (A) is too small, it may be biodegradable or The disintegration is impaired, while if the proportion is too high, the mechanical properties of the molded article become insufficient.
However, depending on the application, the amount may slightly deviate from the above mixing ratio.

The polyhydric alcohol of the present invention has 2 to 3 hydroxyl groups in the molecule and has a melting point of 40 ° C. or higher, preferably 40 to 150 ° C., and a molecular weight of 600 or lower, preferably 100
~ 300 is used. Examples of such polyhydric alcohols include 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, hydrobenzoin, 1,
2-cyclohexanediol, 1,4-cyclohexanediol, 2,4-cyclohexanedimethanol, etc.
Trihydric alcohols such as trihydric alcohol, trimethylolpropane and trimethylolethane, and preferably 1,6 hexanediol, neopentyl glycol,
4-cyclohexanedimethanol, trimethylolpropane and the like are practical.

The amount of the polyhydric alcohol is 5 to 50 parts by weight, preferably 10 to 40 parts by weight, based on 100 parts by weight of the total of the starch-based polymer (A) and the EVOH (B). If the amount is less than 5 parts by weight, the effect is insufficient.
If the amount exceeds the weight part, not only the effect is not exhibited in proportion to the compounding amount, but also the mechanical strength becomes insufficient and the like, which makes it impractical. In addition, if necessary, resin components other than the above (ethylene copolymer and other polyolefins, hydrogenated styrene-butadiene rubber, polyurethane, polyamide, polyhydroxybutyrate, etc.), natural polymers other than starch-based polymers (polysaccharides) Polymers, cellulosic polymers, protein polymers, etc.), heat stabilizers, extenders, fillers, lubricants, coloring agents, flame retardants, water resistant agents, autoxidants, ultraviolet stabilizers, crosslinkers, antibacterial Agents, herbicides, antioxidants and the like, and urea, alkaline earths, alkali metal hydroxides and mixtures thereof can also be added as starch modifiers.

As the melt molding method, an extrusion molding method (including a blow molding method) is mainly employed, but a calender molding method, an injection molding method, or the like can also be employed. At the time of extrusion molding, the starch-based polymer (A) and EVOH
(B) is separately or simultaneously supplied to an extruder, melt-kneaded and pelletized once, and then the pellets are supplied to an extruder and formed into a predetermined shape. The melt molding temperature is desirably set to about 160 ° C. or lower in order to suppress the decomposition of the starch-based polymer (A). When the starch-based polymer (A) is a hydrate or when water is added for molding, the water content in the extrudate is reduced to about 5% by weight or less using an extruder with a vent, and then the subsequent step is performed. It is desirable to provide for melt molding.

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

[0021]

The specific polyhydric alcohol of the present invention, when used as a plasticizer in a mixture of a starch polymer (A) and EVOH (B), has good compatibility at the time of molding, transparency and flexibility. It is possible to form an excellent film and to prevent bleeding.

[0022]

EXAMPLES The present invention will be described below more specifically with reference to examples. Examples 1 to 4 <Production of EVOH (B)> The ethylene content was 29.0 mol%, 38.0 mol%, 44.4 mol%.
The ethylene-vinyl acetate copolymer of 0 mol% or 49.0 mol% is saponified by a conventional method, and then washed with water, washed with a dilute aqueous solution of acetic acid, and washed with a dilute aqueous solution of phosphoric acid, and further washed with water. Go and dry. Table 1 shows the composition and melt flow index (MFI) of the obtained EVOH (B). The melt flow index was measured using a melt indexer.
It was measured under the conditions of 0 mm, a load of 2160 g, and a temperature of 210 ° C.

Table 1 B-1 B-2 B-3 B-4 Ethylene content (mol%) 44.2 49.0 38.2 28.9 Degree of saponification (mol%) 99.5 99.2 99. 4 99.3 MFI (g / 10 min) 12.0 15 25 8

<Compound Pelletization> Raw starch (A) (corn starch having a water content of 12% by weight) as an example of a starch-based polymer, and the above EVOH (B) pellets and plasticizer are shown in Table 2 below. The ratio and combination were put into a Henschel mixer and mixed, then supplied to a vented twin-screw extruder, melt-extruded into strands, and pelletized with a pelletizer to obtain a resin composition. The twin screw extrusion conditions were as follows. Screw diameter 30 mm L / D 30 screw speed of 150 rpm (co-rotating) vent open vent die diameter 5mm nozzle two temperature conditions _{C 1 C 2 C 3 C 4} C 5 H D 100 ℃ 140 ℃ 160 ℃ 160 ℃ 160 ℃ 160 ℃ 160 ℃

<Evaluation of transparency>
Hot pressed under the conditions of ^{0 ℃ × 50kgf / cm 2 ×} 5 minutes, 1m
Form an m-thick plate. Evaluation of transparency is based on JIS K710
According to 5, the total light transmittance of the hot press plate was measured. <Evaluation of flexibility> Similarly, AS
According to TM D638, the tensile modulus at 20 ° C. was measured.

<Film Processing> The compound pellets obtained above were supplied to a single-screw extruder equipped with a T-die, and a
It was formed into a 0 μm film. The film forming conditions using a single screw extruder were as follows. Screw diameter 40 mm L / D 28 screw speed of 50rpm screw shape full-flight type compression ratio 3.0 T die Coat hanger type Die width 450mm die lip opening 0.5mm temperature _{C 1 C 2 C 3 C 4} H D 140 ℃ 160 160 ℃ 160 ℃ 160 ℃ 160 ℃

<Bleed test> The above film is sandwiched between filter papers and left for 1 week at 20 ° C. and 65 RH%.
The contamination of the filter paper by the bleed of the plasticizer was examined by washing the filter paper after standing with methyl alcohol and measuring the infrared absorption of the concentrate obtained from the washing liquid. <Biodegradability> The film obtained above was treated with B5 size (2
After being cut into a size of 5.8 mm x 18.2 mm), it was buried in a mixed fertilizer soil, excavated after 6 months, visually observed for the state of the film, and evaluated in the following three stages. a: The film shape was hardly maintained, to the extent that residual fragments could be confirmed. b: Shape remains, but many cracks and holes are observed on the entire surface.

[Results] The results are shown in Table 2 together with the composition. Table 2 Example 1 2 3 4 Use EVOH (B) B-1 B-2 B-3 B-4 Use plasticizer (C) (Note) C-1 C-2 C-3 C-4 Molecular weight 104 144 118 134 melting point (° C.) 128-130 45-50 43 59 mixing ratio (parts by weight) raw starch (A) 60 65 55 50 EVOH (B) 40 35 45 50 plasticizer (C) 20 15 25 30 pellet workability good good Good Good Total light transmittance (%) 75 78 82 76 Tensile modulus (kgf / cm ² ) 6300 4800 5100 6600 Film workability Good Good Good Good Bleed None None None None Biodegradability a aa a (Note) C- 1: neopentyl glycol C-2: 1,4-cyclohexanedimethanol C-3: 1,6-hexanediol C-4: trimethylolpropane

Comparative Examples 1 to 4 Experiments were carried out in the same manner as in Example 1 except that the plasticizer (C) was changed to the compounds shown in Table 3, and the results are shown in Table 3.

[Table 3] Table 3 Comparative Example 1 2 3 4 Plasticizer used (Note 1) D-1 D-2 D-3 D-4 Molecular weight 92 300 4000 182 Melting point (° C) 18 -15 to 6 53 ■ 56 97 pellets Workability (Note 2) Good Good Bad Bad Total light transmittance (%) 80 780 0 80 Tensile modulus (kgf / cm ² ) 5600 5200 12000 30000 Film workability (Note 2) Good Good Bad Bad Bleed (Note 2) Yes Yes-- Biodegradable (Note 2) bb-- (Note 1) D-1: Glycerin D-2: Low molecular weight polyethylene glycol. Here, the molecular weight is shown by the average molecular weight. D-3: high molecular weight polyethylene glycol. Here, the molecular weight is shown by the average molecular weight. D-4: D-sorbitol (Note 2) In the section of pellet workability, “poor” means that strand take-up is difficult. In the section of film workability, "defective" means that film formation is difficult. Therefore, the bleed and biodegradability of Comparative Examples 3 and 4 were not measured.

[0030]

The biodegradable resin composition of the present invention has a transparency by blending a specific polyhydric alcohol having good compatibility as a plasticizer with the starch-based polymer (A) and EVOH (B). In addition, a film having excellent flexibility can be obtained, and since there is no bleeding, there is an effect that there is no change in physical properties or contamination.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 3/00-3/20 C08K 5/053 C08L 23/26 C08L 29/04

Claims (1)

(57) [Claims] 1. A starch-based polymer, (B) an ethylene content of 20 to 60 mol%, a saponification degree of vinyl acetate units of 90 mol% or more , and a melt flow index.
(Measured at 210 ° C. under a load of 2160 g) 1 to 60 g / 1
0 min ethylene - vinyl acetate copolymer saponification product has three 2 hydroxyl groups in (C) molecules, Ri consists polyhydric alcohol having a molecular weight of 600 or less with a melting point of 40 ° C. or higher, and
(C) is 100% by weight of the total amount of (A) and (B)
5-50 parts by weight der Ru biodegradable resin composition with respect to part.