JPH05295210A - Molded form controllable in shape degradation time and its production - Google Patents

Abstract

PURPOSE:To provide the subject molded form high in mechanical strength and water resistance during being in service in systems containing microorganisms at a low concentrations such as in the air, while being degradable in systems containing microorganisms at higher concentrations such as in the soil or water, and to obtain this form by melt forming similarly to the case with general-purpose plastics. CONSTITUTION:The objective molded form produced from (A) a polyvinyl alcohol-based polymer >=90mol% of mean saponification degree, (B) water, and (C) a water-soluble natural high-molecular compound and/or derivative therefrom with the weight ratios A/B of (10:90) to (80:20) and (A+B)/C of (100:0.5) to (100:500).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded product whose shape collapse time can be controlled and a method for producing the molded product.

[0002]

2. Description of the Related Art In recent years, the problem of environmental pollution of plastic waste has been greatly closed up, and there is an increasing demand for plastics that naturally decompose or disintegrate in the natural environment.

As a naturally disintegrating resin, since a starch / polyethylene resin composition is inexpensive, it is used as a connecting ring for beverage can packs in the United States. Polyethylene used here is a photodegradable polymer obtained by copolymerizing ethylene and carbon monoxide, but it does not decompose in soil. Moreover, even if the shape is destroyed by direct sunlight, it is doubted whether or not it will be finally biodegraded, and there is a risk of secondary pollution due to the collapsed material.

As the naturally degradable resin, polycaprolactone which is one of aliphatic polyesters and a mixture of polycaprolactone and starch are known, but the price of the resin is very high. In addition, the decomposition time changes depending on the amount of specific microorganisms present in the system, and since only starch dispersed in large islands decomposes rapidly, it is almost impossible to control the decomposition time and the shape disintegration time.

Further, Japanese Patent Publication No. 54-15820 discloses a cellulosic chip or powder and a thermoplastic resin such as ethylene-vinyl acetate copolymer, polyethylene or polypropylene, an epoxy resin, a polyester resin or an acrylic resin. Of the thermosetting resin is mixed with a cellulosic powder, and the mixture is melt-molded (plant pot). However, since the resin used as the binder in the present invention is hydrophobic, it has almost no water permeability, and only the cellulosic material present on the surface of the molded body undergoes biodegradation, and the entire molded body is completely destroyed. It won't collapse.

Further, Japanese Utility Model Publication No. 48-61045 discloses a time-disintegrating molded article (plant pot) obtained by molding an inorganic or organic material such as soil or starch with a polyvinyl alcohol (hereinafter referred to as PVA) resin. It is disclosed. It has been confirmed that PVA-based resins are decomposed by microorganisms in the natural world, and finally they become water and carbon dioxide gas, so there is no secondary pollution and there is no risk of causing pollution problems. Therefore, it is a very preferable base material for the decomposable resin composition. However, unfortunately, since PVA is a water-soluble resin itself, it softens and swells or dissolves in a system in which water is present, such as in water or soil, so that it can hardly retain its shape. Furthermore, since it cannot be hot-melt molded like a general-purpose plastic, it is very expensive in terms of molding cost and is not in practical use at present.

The PVA / starch film disclosed in JP-A-2-252744 makes use of PVA's original decomposability, mixes a crosslinking agent with PVA, and further stretches the film to obtain water resistance. To improve the disintegration property of PVA. However, since a cross-linking agent is used, hot melt molding is impossible, and a very complicated process of casting an aqueous solution and drying-stretching-heat-treating is required. Further, since the stretching operation is required, the molded product is limited to the film. Furthermore, PV made water resistant by a crosslinking agent
In A, it is difficult to control the disintegration time and it is difficult to decompose in nature.

[0008]

In view of the above situation, the object of the present invention is to provide a molded article having high strength and high water resistance and a good shape during the period of use in a system containing a small amount of microorganisms such as air. However, when it is placed in a system with a relatively large amount of microorganisms such as soil or water, it is decomposed by microorganisms and disintegrates, and a molded article whose shape disintegration time is controllable, and such molded article are generally used. Another object of the present invention is to provide a manufacturing method capable of being heat-melted and molded similarly to plastics.

[0009]

Means for Solving the Problems As a result of various studies on the above problems, the present inventors have found that a specific PVA polymer, water and a natural water-soluble polymer and / or a natural water-soluble polymer derivative are contained in a specific mixing ratio. The molded product mixed with is strong and resistant to water and retains its shape well within the period of use in a system with few microorganisms such as in the air, but it is placed in a system with relatively many microorganisms such as soil and water. We obtained the knowledge that if it is broken, it will be decomposed and decomposed by microorganisms, and molded products of such composition can be melt-molded, and can be easily operated using injection molding machines and extrusion molding machines like general-purpose plastics. The present invention has been achieved by finding that a molded product can be obtained.

That is, the gist of the present invention is as follows:
The composition comprises (A) a polyvinyl alcohol polymer having an average saponification degree of 90 mol% or more, (B) water and (C) a natural water-soluble polymer and / or a natural water-soluble polymer derivative, and their weight composition ratio is ( A) / (B) is 10/90 to 80/20
And (A + B) / (C) is 100 / 0.5-100
/ 500 is a molded article whose shape disintegration time is controllable, and secondly, (A) a polyvinyl alcohol polymer having an average saponification degree of 90 mol% or more, (B) water and (C) a natural water-soluble polymer. And / or a natural water-soluble polymer derivative (A)
/ (B) is 10/90 to 80/20, and (A + B)
/ (C) is blended so as to be 100 / 0.5 to 100/500, and is heat-melted and molded, which is a method for producing a molded body.

The present invention will be described in more detail below. The average degree of saponification of the PVA polymer used in the present invention is 90 mol%.
As described above, those having an average saponification degree of 95 mol% or more are preferably used. If the average degree of saponification is less than 90 mol%, the shape retention is extremely low, the curing rate is extremely slow in hot melt molding such as injection molding, and the resulting molded article becomes very soft and brittle. It has almost no water resistance, and if it is interposed in a system in which water exists, such as water or soil, it immediately softens and dissolves. Therefore, PVA having an average saponification degree of 90 mol% or more is used. In addition, two or more kinds of PVA-based polymers having different average saponification degrees are mixed and the average saponification degree is adjusted to 90 mol% or more to obtain good moldability and improve water resistance of the molded article. You may.

The average degree of polymerization of the PVA polymer used in the present invention is not particularly limited, but it is 100 to 1000.
Those of 0, particularly 500 to 5000 are preferably used. If the average degree of polymerization is less than 100, the resulting molded article tends to be brittle, and if it exceeds 10,000, the production method of PVA becomes complicated and not only expensive, but also the viscosity when mixed and melted with water becomes extremely high. Therefore, molding becomes difficult, which is not preferable. Although the average degree of polymerization of the PVA-based polymer is related to the blending of the components, it is a factor related to the viscosity at the time of heat melting, the strength of the molded product, etc., so the average degree of polymerization is 1
By adjusting the average degree of polymerization to 100 to 10,000 by adjusting the average degree of polymerization to 100 to 10,000 by adjusting two or more types of PVA-based polymers having different degrees of polymerization, the viscosity at the time of heat melting and the strength of the molded body can be controlled. can do.

The PVA polymer / water weight ratio in the molded product of the present invention is 10/90 to 80/20, preferably 30/70 to 70/30. Basically, when a PVA-based polymer having a low degree of polymerization is used, the PVA-based polymer content is relatively increased, and when a PVA-based polymer having a high degree of polymerization is used, the PVA-based polymer content is increased. It is preferable to reduce the amount. PVA-based polymer / water weight ratio of 10/90
When the compounding ratio of the PVA-based polymer is smaller than the above, not only the curing rate at the time of hot melt molding becomes extremely slow, but also a soft and brittle molded body and the shrinkage due to drying are remarkable. Also, PVA
When the PVA polymer blending ratio is more than 80/20 by weight, the heat melting temperature and the heat melting viscosity become extremely high, and not only molding becomes difficult but also the molded body becomes water. In contrast, it swells and softens significantly, resulting in insufficient water resistance.
This is presumably because hydrogen bonds are not sufficiently formed between PVA polymer molecules unless water is present to some extent. However, this hydrogen bond is thermoreversible, and it is easily broken by heat and produced by cooling. For this reason, it becomes possible to perform molding by heat melting as described later.

The blending amount of the natural water-soluble polymer and / or the natural water-soluble polymer derivative (hereinafter referred to as natural polymer) is P
0.5 to 500, based on the weight of VA polymer / water as 100
Parts by weight, preferably 10 to 100 parts by weight. 0.5
If it is less than 1 part by weight, even if the molded product is placed in a system containing a large amount of microorganisms such as soil or water, it takes a very long time to decompose and disintegrate by the microorganisms, and the decomposition time can hardly be controlled. .. Further, the more the natural polymer is blended, the faster the disintegration and decomposition rate by microorganisms becomes. However, when it exceeds 500 parts by weight, not only the viscosity at the time of heat melting is high and it is difficult to mold, but the molded body itself is soft. It becomes fragile.

By the way, it is said that PVA itself is degraded by some specific bacteria such as Pseudomonas genus bacteria and Xanthomonas genus, but the existence of these bacteria is not universal. However, since microorganisms and bacteria that decompose natural polymers such as starch exist in a large number and are universally present, it is considered that the decomposition rate of a natural polymer having a constant content is almost constant. .. However, when these natural polymers and the like are not microscopically dispersed in PVA, that is, when the dispersed particle size of the natural polymer in the PVA-based polymer is dispersed in large islands of about 40 μm or more, the microorganisms are Since only natural polymers are selectively decomposed and assimilated, it is considered difficult to uniformly control the decomposition and disintegration of the entire molded body.

In the present invention, water not only imparts thermoreversibility (thermoplasticity and cooling hardening), but also has a function of microdispersing or compatibilizing the PVA polymer and the natural polymer. .. When the PVA-based polymer and the natural water-soluble polymer are microdispersed or when they are compatible with each other, the microorganisms are the same as the natural product without distinction between the PVA-based polymer and the natural polymer-derived one. It is considered that the disintegration time can be controlled because it exhibits microbial degradability. That is, the molded product of the present invention is not merely a plasticized PVA polymer, but the presence of water has a very important meaning. From the viewpoint of controlling the degradability and disintegration property of the molded product, the dispersed particle size of the natural polymer in the molded product is 5 μm or less, particularly preferably 2 μm.
It is preferably m or less.

The average degree of saponification used in the present invention is 90.
Examples of the method for producing a PVA-based polymer having a mol% or more include a method of saponifying a polyvinyl ester obtained by solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization of a vinyl ester. Examples of the method for saponifying a vinyl ester include direct saponification such as alkali saponification and acid saponification, or a conventional saponification method by alcoholysis.

Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate,
Examples thereof include vinyl laurate, vinyl trifluoroacetate, vinyl pivalate, and the like, and these may be used alone or as a mixture of two or more kinds. Of these, vinyl acetate is industrially preferable. PV obtained by saponifying vinyl pivalate alone or a copolymer of vinyl pivalate and other vinyl ester.
The A-based polymer can be preferably used because it has a remarkable syndiotactic property, a high water resistance, and a molded product having high hardness can be obtained.

Further, α-olefins such as ethylene and propylene which can be copolymerized with these vinyl esters, alkyl vinyl ethers, vinyl versatate, dicarboxylic acids such as monomethyl maleate, acrylamide and the like within a range not impairing the effect of the present invention. There may be used any of those obtained by partially copolymerizing and saponifying the above, or those obtained by acetalizing these saponified products within a range not impairing the effects of the present invention.

As the natural polymer, raw starch such as corn starch, wheat flour and rice starch, α-starch, dextrin, oxidized starch, dialdehyde starch, esterified starch, etherified starch, cationized starch, cross-linked starch and the like. Modified starches such as starch and starch derivatives, sugars such as glucose, sugar, glucose and sorbitol, water-soluble cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose and hydroxypropyl cellulose, glycerin, alginic acid, guar gum, gum arabic, tragacanth gum Natural polymers such as chitin, chitin, chitosan, gelatin, glue, and agar are exemplified, and one kind or a mixture of two or more kinds thereof can be used. Among them, starches are inexpensive and have good shape-retaining effect and microbial degradability of the molded product, and thus can be suitably used. As described above, these natural polymers are believed to be very microscopically dispersed or evenly compatible with the PVA-based polymer by interposing water, which is advantageous for decomposition by microorganisms.

If a filler is mixed in addition to the above components, the curing rate at the time of molding can be increased and the hardness of the molded article can be increased. The filler used in the present invention includes kaolin, halosite, pyroferrite, clay or talc such as sericite, carbon black, silica, heavy, light or surface-treated calcium carbonate, aluminum hydroxide, aluminum oxide, and oxidation. Inorganic substances such as titanium, diatomaceous earth, barium sulfate, calcium sulfate, zeolite, zinc oxide, silicic acid, silicates, mica and magnesium carbonate can be mentioned. As the organic substance, water-insoluble natural polymers such as wood powder and pulp powder, and synthetic polymers such as polyethylene, ethylene-vinyl acetate copolymer and polypropylene can be used. Among these fillers, clay, talc and the like are inexpensive and safe and can be preferably used. Further, glass fibers, lubricants, foaming agents, cross-linking agents, plasticizers, release agents, defoamers, pigments, dyes and the like can be mixed in appropriate amounts within a range that does not impair the effects of the present invention.

In producing the molded article, (A) a polyvinyl alcohol polymer having an average saponification degree of 90 mol% or more,
(B) water and (C) natural water-soluble polymer and / or natural water-soluble polymer derivative, (A) / (B) 10 / 90-8
0/20 and (A + B) / (C) is 100 / 0.5
It is blended so as to be 100/500, and heat-melted to be molded.

In producing a molded body, since the molten state and the cured state are thermoreversible, various molding methods can be adopted. That is, it can be molded by heat melting like a general-purpose thermoplastic resin such as polyethylene, polypropylene, polyester, or polyvinyl chloride.
That is, the molding method such as extrusion molding, injection molding, cast molding, inflation molding, hot working molding, vacuum molding, etc.
It can be molded by heat melting at 0 to 160 ° C, preferably 70 to 130 ° C.

Alternatively, the heat-melted material may be extrusion-molded and processed into a chip shape, and the chip may be re-melted to obtain a molded body. This is preferable because it is easy to handle. When processed into a chip shape, the strands extruded from the extruder can be easily made into chips after air cooling or water cooling.

If the heat-melted product is packed in a pack such as a retort pack or a tube while it is fluid and sealed, hot water with the pack can be used at home, outdoors, or at a construction site. If it is put into a mold or put in a microwave oven, it will return to a fluid state, so if this is poured into a mold, a molded body can be easily obtained.

The molded product of the present invention is formed into a shape suitable for its intended purpose by utilizing its properties such as strength, shape-retaining property, microbial degradability and natural disintegration property, and also by utilizing the ease of molding. It can be used as the following. For example, sheets, films, various containers, binding tapes, seedling pots,
Fertilizers and sustained-release base materials for drugs such as insect repellents and herbicides, cold storage materials,
Cooling materials, sealing materials that can be used in water, fishing baits (simulated baits, etc.), and disposable fishing and agricultural materials are included. In particular, the molded article of the present invention has high strength within a certain period of use,
It retains its shape well, is not damaged by rainwater or groundwater, and if left in a system with a relatively large amount of microorganisms after a certain period of use, decomposition proceeds by microorganisms,
Since it disintegrates, it can be used as a disposable agricultural material such as an agricultural sheet or a seedling pot by utilizing such characteristics.

[0027]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The performance characteristics were measured as in the following (1) to (5).

(1) Thermal meltability (melt moldability) Melt extrusion state at 95 ° C. (fluidity) ⊚: very good ∘: good ∘ △; somewhat bad ×; almost no fluidity

(2) Curing time The time at which curing begins and the mold can be released.

(3) Strength State of molded body (sheet) at the time of releasing (compared to silicone rubber) ⊙; comparable ○: somewhat soft Δ: soft and slightly adhesive
×: Soft and sticky

(4) Water resistance Swelling ratio (length relative to the original sample) of the molded product when immersed in water at 20 ° C. for 1 day ◎; 1 to 1.2 ○; 1.3 to 1.5 △; 1.6 to 1.9 ×; 2 or more

(5) Disintegration time Period until soil is buried outdoors and the original shape cannot be determined A; within 1 month B; 1-3 months C; 3 months-1 year
D; 1 year or more

Examples 1 to 9 Comparative Examples 1 to 5 The components shown in Table 1 were mixed by a blender to obtain a granular material or a paste material, and the granular material or the paste material was prepared using an extruder. Sheets were melt-extruded at 95 ° C., cooled and solidified by a drum-type cooler to produce molded articles (sheet thickness: 1 mm), and the performance characteristics of the obtained molded articles were measured. The results are shown in Table 2.

[0034]

[Table 1]

[0035]

[Table 2]

As is clear from Table 1, the molded product of the present invention is excellent in strength and water resistance, and the disintegration time can be controlled by adjusting the components and leaving it in a system containing a relatively large amount of microorganisms. .. In addition, it can be seen that the extrudability is good because the heat melting property is good and the curing time is short.

[0037]

EFFECTS OF THE INVENTION As described above, the molded article of the present invention whose shape disintegration time is controllable has strength and water resistance within a certain period of use in a system containing few microorganisms such as air. It keeps its shape high and firm, and after a certain period of use, it will be decomposed and disintegrated by microorganisms if left in a system with relatively many microorganisms. Further, according to the manufacturing method of the present invention, a molded body can be manufactured by a simple operation as in a general-purpose plastic. Further, such a molded product whose shape collapse time can be controlled can be effectively used as an agricultural material such as a disposable agricultural sheet, a binding tape or a seedling pot.

Claims (2)

[Claims] 1. A composition comprising (A) a polyvinyl alcohol polymer having an average saponification degree of 90 mol% or more, (B) water and (C) a natural water-soluble polymer and / or a natural water-soluble polymer derivative, and their weight. The composition ratio is (A) / (B) 10/9
0 to 80/20, and (A + B) / (C) is 100 /
A molded product having a controllable shape collapse time of 0.5 to 100/500. 2. A polyvinyl alcohol polymer having an average saponification degree of 90 mol% or more, (B) water and (C) a natural water-soluble polymer and / or a natural water-soluble polymer derivative,
(A) / (B) is 10/90 to 80/20, and (A
+ B) / (C) is mixed so that it may become 100 / 0.5-100 / 500, and it heat-melts and shape | molds, The manufacturing method of the molded object of Claim 1 characterized by the above-mentioned.