JPH04359951A - Hydrogel molding having controllable disintegrating time and its preparation - Google Patents

Abstract

PURPOSE:To prepare the title molding which has strength high enough to firmly retain its shape for a certain period of time for its use and spontaneously disintegrates after the period by such a simple operation as similar to the production of a general-purpose plastic. CONSTITUTION:The title molding is prepd. by thermally dissolving 50-60 pts.wt. polyvinyl alcohol-based polymer having an average degree of polymn. of 100-3500 and a degree of saponification of at least 95mol% in a mixed solvent consisting of 5-60 pts.wt. polyol such as ethylene glycol and 10-60 pts.wt. water and allowing the soln. to gel in a mold at room temp. The molding may be prepd. by thermally melting a gel formed as above and allowing the resulting soln. to gel again at room temp.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is capable of controlling the shape collapse time so that the hydrogel has high strength and firmly maintains its shape during a certain period of use, and naturally disintegrates after a certain period of use. The present invention relates to a hydrogel molded article and a method for producing a hydrogel molded article whose shape collapse time can be controlled and which allows such a hydrogel molded article to be manufactured by simple operations similar to general-purpose plastics. Such hydrogel molded bodies are particularly useful for disposable agricultural sheets,
It can be effectively used for agricultural materials such as binding tape or pots for seedlings.

0002

BACKGROUND OF THE INVENTION In recent years, the problem of environmental pollution caused by plastic waste has attracted much attention, and there has been an increasing demand for plastics that naturally disintegrate or decompose in the natural environment.

[0003] As naturally disintegrating resins, starch/polyethylene resin compositions are used in the United States and other countries for connecting rings for beverage can packs and the like because they are inexpensive. The polyethylene used here is a photodegradable polymer obtained by copolymerizing ethylene and carbon monoxide, but it does not decompose in soil. Furthermore, even if the shape collapses due to direct sunlight, there are doubts as to whether it will ultimately biodegrade, and there is a risk of secondary contamination due to decaying materials.

[0004] Furthermore, polycaprolactone, which is a type of aliphatic polyester, and a mixture of polycaprolactone and starch are known as naturally degradable resins, but the resins are very expensive, and they do not require the use of specific enzymes. No decomposition occurred in a system without the presence of , and it was almost impossible to control the shape collapse time and decomposition time.

Furthermore, Japanese Patent Publication No. 54-15820 discloses that cellulose chips or powder and thermoplastic resins such as ethylene-vinyl acetate copolymer, polyethylene and polypropylene, epoxy resins, polyester resins, acrylic resins, etc. A molded article (flower pot) is disclosed in which a thermosetting resin is mixed with cellulose powder and melt-molded. However, in this invention, since the resin used as the binder is hydrophobic, it has almost no water permeability, and only the cellulosic material present on the surface of the molded object undergoes biodegradation, and the entire molded object is completely destroyed. It doesn't reach the point of collapse.

Furthermore, Japanese Utility Model Application Publication No. 48-61045 discloses a molded article (flower pot) that disintegrates over time, which is made by molding inorganic and organic materials such as soil and starch using polyvinyl alcohol (hereinafter referred to as PVA) resin as a binder. Disclosed. PVA resin is decomposed by microorganisms in the natural world and ultimately becomes water and carbon dioxide, so there is no secondary pollution and there is no risk of causing pollution problems. Therefore, it is very preferable as a base material for degradable resin compositions. Unfortunately, however, since PVA itself is a water-soluble resin, it softens, swells, or dissolves in systems where water is present, such as in water or soil, making it almost impossible to maintain its shape. Furthermore, since it cannot be heat-melted and molded like general-purpose plastics, it is extremely expensive and impractical.

[0007] In addition, the PVA/starch film disclosed in JP-A-2-252744 takes advantage of the inherent degradability of PVA, and also improves water resistance by mixing a crosslinking agent with PVA and stretching the film. The aim is to control the disintegrability of PVA by improving its properties. However, since a crosslinking agent is used, hot melt molding is impossible, and extremely complicated steps such as casting an aqueous solution, stretching, drying, and heat treatment are required. Furthermore, since a stretching operation is required, the molded product is limited to a film. Furthermore, PVA made water resistant with a crosslinking agent
It is difficult to control the decay time, and it is also difficult to decompose in nature.

By the way, as a hydrogel, alginic acid, sodium alginate, potassium alginate, ammonium alginate, alginate propylene glycol ester, carrageenan, hydrophilic carboxyvinyl polymer, agar, gelatin, glue, konjac, etc. are mixed in several percent to several percent in water. It is known to add 10% and heat to dissolve it to make an aqueous solution, which is then cooled and gelled. but,
It takes a very long time to heat, melt, gel, and obtain a molded product, and the temperature also needs to be extremely low, resulting in extremely poor productivity. Furthermore, these hydrogels had poor elasticity and were extremely brittle, so they could not be used as general molded products.

[0009] Japanese Patent Publication No. 47-12854 describes PVA
A method for obtaining a PVA hydrogel by freezing an aqueous solution is disclosed. This PVA hydrogel has more elasticity and strength than gels such as agar, but it dries out significantly when placed in the air, so it cannot be used as a general molded product. In addition, productivity was also extremely poor since PVA hydrogel could not be obtained unless it was left at a low temperature of -5°C or lower, preferably -15 to -50°C, for a long period of time.

[0010] Furthermore, it has been known for a long time that when boric acid or borax is added to a PVA aqueous solution, it immediately gels (Japanese Patent Publication No. 11210/1983, Japanese Patent Publication No. 46-196).
Publication No. 02). However, the hydrogel obtained in this way is fluid, weak, and has hydrorepellent properties (separates the water it contains).
Therefore, the gel is weak and lacks stability, making it unusable as a normal molded product.

[0011] Furthermore, Japanese Patent Application Laid-Open No. 58-37076,
Japanese Patent Application Publication No. 58-195558, Japanese Patent Publication No. 3-1617
No. 5 discloses that PVA with an average polymerization degree of 800 or 1500 or more and a saponification degree of 95 mol% or more is dissolved in a mixed solution of water-soluble polyhydric alcohol such as glycerin and water, and after cooling and solidifying at -5°C or lower, P obtained by vacuum dehydration
VA hydrogels are disclosed. PVA hydrogels such as those disclosed in these publications have excellent elasticity and flexibility, and are therefore suitable for use in cold insulation materials and the like. In addition, this PVA hydrogel is a new material that has been attracting attention in recent years because it contains water, has good biocompatibility, and has excellent strength. However, in order to develop sufficient strength as a molded product, it must be molded using a melt-freeze method or cross-linked by irradiation with ultraviolet rays or gamma rays, making the manufacturing process extremely complicated and reducing productivity. It was extremely poor and could not be used as a general purpose molded product. Therefore, as a molded article, its use has only been considered for limited applications, such as contact lenses, artificial bones, and artificial muscles, taking advantage of its biocompatibility.

0012

[Problems to be Solved by the Invention] In view of this situation, the problem of the present invention is to ensure that the hydrogel has high strength and firmly maintains its shape during a certain period of use, and that it collapses naturally after a certain period of use. The object of the present invention is to provide a hydrogel molded article whose shape collapse time can be controlled so that the shape disintegration time can be controlled, and a method for producing a hydrogel molded body whose shape collapse time can be controlled and which can be manufactured by simple operations similar to general-purpose plastics.

[0013]

[Means for Solving the Problems] As a result of various studies regarding the above-mentioned problems, the present inventors have found that by mixing a specific PVA, polyol, and water at a specific mixing ratio and heating and dissolving the mixture, a melt with good fluidity can be obtained. The melt gels easily in a short time at a temperature around room temperature, and the melt and hydrogel are reversible, so hydrogels can be easily formed using an injection molding machine or an extrusion molding machine, just like general-purpose plastics. We obtained the knowledge that a molded body can be obtained, and this hydrogel molded body has high strength for a certain period of time, is difficult to shrink during drying, and maintains its shape well, and after a certain period of time, it easily disintegrates in a water-based system. Based on this knowledge, we have arrived at the present invention.

That is, the gist of the present invention is (A) a polyvinyl alcohol polymer having an average degree of polymerization of 100 to 3,500 and a degree of saponification of 95 mol% or more, (B) a polyol, and (C
) Water is the main component, and the weight composition ratio of these main components (A)/
(B)/(C) is 5 to 60/5 to 60/10 to 60, and is a hydrogel molded article with a controllable shape collapse time. The molded article has (A) an average degree of polymerization of 100 to 350
0 and a polyvinyl alcohol-based polymer having a saponification degree of 95 mol% or more, (B) a polyol and (C) water as the main components,
The weight composition ratio (A)/(B)/(C) of these main components is 5
Mix to give a ratio of ~60/5 to 60/10 to 60, heat and melt the resulting mixture, and then gel it at room temperature, or further heat and melt the gel molded product and gel it at room temperature. It can be manufactured by molding. Note that in the present invention, room temperature refers to -5 to 40°C.

The present invention will be explained in more detail below. The average degree of polymerization of PVA used in the present invention is 100 to
3,500, preferably 200 to 2,000. If the average degree of polymerization exceeds 3500, the viscosity of the solution will become extremely high, so PVA
The concentration of the hydrogel must be kept below 5% by weight, and it is difficult to obtain a hydrogel by simply curing it at room temperature for a short time, and even if it is obtained, it will be soft, sticky, and brittle. . On the other hand, PVA with an average degree of polymerization of less than 100
In this case, the cohesive force of the hydrogel is small, and the strength of the hydrogel is weak, so when it is molded into a molded product, it becomes brittle and easily broken. The average degree of polymerization of PVA is related to the degree of saponification and the mixing ratio of components, which will be described later, but it is also a factor related to the viscosity of the solution when dissolved, the gelation time, and the shape retention of the hydrogel, so the average degree of polymerization is 100. The viscosity of the solution, the gelation time, and the shape retention of the hydrogel can be controlled by adjusting the molecular weight within the range of ~3,500 or by using a mixture of polymers with different degrees of polymerization within this range.

[0016] It is necessary that the degree of saponification is 95 mol% or more. If the degree of saponification is less than 95 mol%, the gel shape retention is extremely low, and not only does it take a long time to gel at a temperature around room temperature, but the resulting hydrogel is soft and brittle. Such hydrogels have almost no water resistance, and if placed in water or in a water-based system such as soil, they immediately soften and dissolve. On the other hand, hydrogels made using completely saponified PVA with a degree of saponification of 99 mol% or more hardly swell or dissolve in water. Therefore, the shape collapse time in a water-present system can be controlled by adjusting the degree of saponification of PVA or by blending one or more types of partially saponified PVA with different degrees of saponification into fully saponified PVA.

Considering the above, the viscosity of the solution,
In order to control gelation time, shape retention of hydrogels, and shape collapse time in water-present systems, PVA
The average degree of polymerization is 100 to 3500, and the degree of saponification is 95 mol%.
By adjusting within the above range, a PVA component suitable for the purpose can be obtained. In addition, the average degree of polymerization is 100 to 800, and the degree of saponification is 9.
Even if one or more types of partially saponified PVA with an average degree of polymerization of 1000 to 3500 and a degree of saponification of 95 mol% or more are mixed with a completely saponified PVA having a content of 9 mol% or more, a PVA component suitable for the purpose can be obtained. It will be done.

The amount of PVA blended in the hydrogel molded article of the present invention is 5 to 60 parts by weight, preferably 20 to 5 parts by weight.
0 parts by weight. If the amount is less than 5 parts by weight, the gelation rate is extremely slow, resulting in a soft hydrogel and significant drying shrinkage. Moreover, if it exceeds 60 parts by weight, the melting temperature becomes extremely high, making it difficult to dissolve. Basically, when using PVA with a low degree of polymerization, it is preferable to increase the PVA content relatively, and when using PVA with a high degree of polymerization, it is preferable to decrease the PVA content.

[0019] The blending amount of polyols is 5 to 60 parts by weight,
Preferably it is 15 to 40 parts by weight. If the amount is less than 5 parts by weight, the gel not only has poor flexibility and is brittle, but also has a slow gelation rate and gels in a short time, making it impossible to obtain a hydrogel with high gel strength and shape retention. Furthermore, because the drying rate of the hydrogel is not moderated, when exposed to air, its properties change significantly due to volatilization of water, resulting in surface cracks, loss of flexibility, and hardening. Moreover, if it exceeds 60 parts by weight, the viscosity when dissolved is not only difficult to mold, but it also becomes a sticky sol-like substance that is more like an adhesive than a gel, and if left unattended, it will bleed violently and fail as a molded product. Lacks stability.

The amount of water added is 10 to 60 parts by weight, preferably 15 to 40 parts by weight. If the amount is less than 10 parts by weight, swelling and softening in water will be significant, resulting in insufficient water resistance. This requires at least 1 to form a hydrogel.
This is believed to be because hydrogen bonding between PVA molecules does not occur sufficiently unless 0 parts by weight, preferably 15 parts by weight or more of water is present. Moreover, if it exceeds 60 parts by weight, the gelation time becomes long, the drying shrinkage and stickiness of the hydrogel are large, and a stable hydrogel with a fast gelation rate cannot be obtained.

Average degree of polymerization used in the present invention: 10
0 to 3500 and a saponification degree of 95 mol% or more, the vinyl ester is solution polymerized, emulsion polymerized,
Examples include a method of saponifying polyvinyl ester obtained by suspension polymerization. Methods for saponifying vinyl esters include direct saponification methods such as alkali saponification and acid saponification, or conventional saponification methods using alcoholysis.

Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate,
Vinyl laurate, vinyl trifluoroacetate, vinyl bivalate, etc. may be used, and these may be used alone or in a mixture of two or more. Among these, vinyl acetate is particularly preferred industrially. Furthermore, a vinyl ester copolymer obtained by copolymerizing vinyl bivalate has remarkable syndiotactic properties and is easily gelled, so it can be suitably used.

[0023] Furthermore, those partially modified with α-olefins such as ethylene and propylene, alkyl vinyl ethers, vinyl versatate, acrylamide, etc. that can be copolymerized with these vinyl esters, and those obtained by acetalizing these vinyl esters, There is no problem in using it as long as it does not impair the effects of the present invention.

[0024] Polyols include ethylene glycol (hereinafter referred to as EG), 1,2-propylene glycol (hereinafter referred to as PG), 1,3-propylene glycol, diethylene glycol, polyethylene glycol, glycerin, D-sorbitol, Examples include glucose, pentanediol, etc., and one type or a mixture of two or more of these can be used. Among these polyols, EG, PG, glycerin, etc. can be suitably used because they are inexpensive, have little bleeding, are nontoxic, and are naturally degradable.

[0025] Furthermore, by mixing a filler in addition to the above-mentioned components, the gelation time can be accelerated and the hardness of the gel can be increased. Fillers used in the present invention include clay or talc such as kaolin, hallosite, pyroferite, and sericite, silica, heavy, light, or surface-treated calcium carbonate, aluminum hydroxide, aluminum oxide, titanium oxide, and diatom. Earth, barium sulfate, calcium sulfate, zeolite, zinc oxide, silicic acid, silicate,
Examples include inorganic substances such as mica and magnesium carbonate, and starches such as cornstarch can be used as organic substances. Among these fillers, clay, calcium carbonate, talc, etc. are cheap and safe;
Since the gelation rate is also extremely high, it can be suitably used.

[0026] Also, high polymerization degree PV with a polymerization degree of 3500 or more
A. Appropriate amounts of glass fiber, gelatin, glue, agar, foaming agents, starch, crosslinking agents, plasticizers, mold release agents, antifoaming agents, pigments, dyes, etc. may be mixed within the range that does not impair the effects of the present invention. It is possible.

[0027] In producing the hydrogel molded body, (
A) A polyvinyl alcohol polymer with an average degree of polymerization of 100 to 3500 and a degree of saponification of 95 mol% or more, (B) polyol, and (C) water as the main components, and the weight composition ratio of these main components (A) / (B) /(C) is 5~60/5~60/10
The resulting mixture is heated and melted and then gelled at room temperature, or the gelled mixture is further heated and melted and gelled at room temperature.

[0028] The heating dissolution temperature of the mixture is preferably as low as possible, as long as the mixture dissolves. This is because foaming of the hydrogel can be prevented, hydrogen bonds between PVA molecules are more likely to occur, and the curing speed is increased. The melt obtained by heating and melting a mixture having the above-mentioned component composition easily gels at room temperature, so if it is poured into molds of various shapes or by using various molding methods, it can be molded into various shapes. A molded body is obtained.

[0029] In obtaining the molded article, various molding methods can be employed since the melt and the hydrogel are reversible. In other words, it can be treated in the same way as general-purpose thermoplastic resins such as polyethylene, polypropylene, polyester, and vinyl chloride.For example, it can be used in extrusion molding, injection molding, cast molding, inflation molding, hot processing molding, vacuum molding, etc. Molding methods can be used.

[0030] Alternatively, it is also possible to extrude the heated and melted product and process it into chips, and then heat and melt the chips to form a molded product as described above. This is preferable because it is easy to handle. When processing into chips, the hydrogel strands extruded from the extruder can be easily turned into chips after cooling in air or water.

[0031]Also, if the heated and melted product is packed in a retort pack or tube while it is still fluid and sealed, it can be used at home, outdoors, at construction sites, etc.
When you want to use it, you can put it in boiling water or put it in a microwave to return it to a solution, and then pour it into a mold to easily obtain a hydrogel mold, making it very easy to handle.

[0032] The hydrogel molded article of the present invention can be shaped into a shape suitable for its intended use by taking advantage of its gel strength, gel shape retention, natural disintegration properties, and ease of molding. It can be used as: For example, sheets (films), various containers, binding tapes, pots for seedlings, sustained release base materials for fertilizers and drugs such as insect repellents and herbicides, cold storage materials, cold insulation materials, sealing materials that can be used underwater,
Examples include fishing bait (artificial bait, etc.), disposable fishing and agricultural materials, etc. In particular, the hydrogel molded article of the present invention has high gel strength and maintains its shape well within a certain period of use.
It is not damaged by rainwater or groundwater, and after a certain period of use, it disintegrates mechanically or naturally in a water-based system, and furthermore, it is decomposed by microorganisms in the soil, so these characteristics can be utilized. Therefore, it does not cause pollution problems even if it is used as disposable agricultural materials such as agricultural sheets or pots for seedlings and left in fields.

[0033]

EXAMPLES The present invention will be explained in detail below using Examples, but the present invention is not limited to these in any way.

Example 1 25 g of low polymerization degree PVA with a polymerization degree of 230 and a saponification degree of 99.0 mol%, a polymerization degree of 1750 and a saponification degree of 98.7
mol% of PVA 5g, light calcium carbonate 65g,
A suspension consisting of 33 g of PG and 37 g of water was heated and stirred at 95° C. to uniformly dissolve it. The fluidity of the solution at this time was good. This 95°C solution was placed in a concave mold at room temperature (1
Approximately 5 g was poured at 8°C), immediately covered with a convex mold, and pressed by hand. When the mold was removed after being left in this state for 3 seconds, it was completely gelled. The pot-shaped hydrogel molded body thus formed was not sticky, very flexible, and had properties similar to tough silicone rubber. When this hydrogel molded article was left indoors (20° C., 65% RH) for 72 hours, the weight decreased by 7%, and the change in shape was hardly visible. Furthermore, when the hydrogel molded body was left in water (20° C.) for one month, there was almost no change in shape or strength. However, 3 more
When left in water for a month, the shape completely collapsed and it was dissolved and dispersed in water.

Example 2 A suspension consisting of 30 g of low polymerization degree PVA with a degree of polymerization of 480 and a degree of saponification of 98.0 mol %, 15 g of EG, and 55 g of water was heated and stirred at 95° C. to uniformly dissolve it. The fluidity of this solution at 95°C was good. Approximately 5 g of this solution was poured into a concave mold at room temperature (18° C.), immediately covered with a convex mold, and pressed by hand. When the mold was removed after being left in this state for 10 seconds, it was completely gelled. The pot-shaped hydrogel molded product thus formed was somewhat soft, but not sticky, and had very flexible, tough rubber-like properties. When this hydrogel molded article was left indoors (20° C., 65% RH) for 72 hours, the weight decreased by 9% and almost no change in shape was visible. In addition, the hydrogel molded body was placed in water (at 20°C).
) When it was left for 20 days, there was almost no change in shape or strength. However, when it was left in water for another month, its shape completely collapsed and it was dissolved and dispersed in water.

Example 3 PVA with a degree of polymerization of 560 and a degree of saponification of 98.9 mol%
300g, kaolin (soil) 450g, EG35
A suspension consisting of 0 g and 350 g of water was heated and stirred at 95°C to uniformly dissolve it. The fluidity of this solution at 95°C was good. This 95°C solution was filled into a retort pack, sealed, and left to cool at room temperature (18°C), resulting in complete gelation in 10 minutes. The properties of this hydrogel are rubber-like, and when the pack is immersed in boiling water, it returns to its original fluid solution state within 5 minutes, and after opening the pack,
When poured into a spherical mold with a diameter of cm and left at room temperature for 10 minutes, the ball became extremely tough and had excellent repulsion. In addition, if the packs were frozen in the freezer, they could be used as a flexible cold insulation material in place of ice packs. When this cold insulation material was buried in soil for six months, it completely collapsed and was almost impossible to distinguish from soil.

Example 4 The hydrogel molded product of Example 3 was crushed into chips with a diameter of 2 to 3 mm using a crusher, the chips and an aromatic agent (liquid) were mixed, and the mixture was molded into 1 mm pieces at 97°C using an extruder. When molded into a thick sheet, an extremely flexible, tough, and stretchable sustained-release aromatic sheet was obtained. When this sheet was left in seawater for two months, its shape completely collapsed and it was dispersed and dissolved in seawater.

Example 5 The hydrogel molded body of Example 3 was crushed into chips with a diameter of 2 to 3 mm using a crusher, and chemical fertilizer (fine powder) was mixed with the mixture, and the mixture was molded into chips with a diameter of 4 cm (0.2 mm) at 97°C using an injection molding machine. When molded into pots for raising seedlings with a thickness of .6 mm, the pots were extremely flexible, tough, and stretchable, and had the performance of a slow-release fertilizer. After planting 20-day radish seeds in this pot and allowing them to germinate, the pots were then transplanted to a field and the seedlings were raised.The roots broke through the wall of the pot 17 days after germination and grew smoothly. After 30 days, I harvested the daikon radish and observed the condition of the pot.
The pots had completely collapsed and dispersed, so much so that they were almost indistinguishable from soil.

Comparative Example 1 10 g of high polymerization degree PVA with a polymerization degree of 4000 and a saponification degree of 98.7 mol%, 10 g of soft calcium carbonate, PG2
A suspension consisting of 0 g and 70 g of water was heated and stirred at 95° C., but the viscosity was so high that it could not be cast. Therefore, in order to improve fluidity, PG and water were further added to adjust the weight composition ratio of PVA:PG:water to 4:20:76, and the process was carried out in the same manner as in Example 1. When removed from the mold, the hydrogel did not harden and was sticky and very weak.

Examples 6 to 13, Comparative Examples 2 to 8 Suspensions of PVA having various degrees of polymerization and saponification, various polyols, water, and various fillers were heated and stirred in the same manner as in Example 1. A hydrogel molded body was obtained by melting, casting, and demolding. The performance of this hydrogel molded article is shown in Table 1. The evaluation method is as follows. Note that Comparative Examples 5 and 7 did not cure at room temperature, so -35
It was frozen at ℃ for 40 hours to gel, and its strength, water resistance, and shrinkability were evaluated. Comparative Example 8 was prepared using gelatin and treated in the same manner.

(1) Fluidity Fluidity at 95°C ◎: Very good ○: Good △: Slightly bad
×; Almost no liquidity

(2) Gelation (gelation time) Time when gelation starts and demolding becomes possible ◎: Within 5 seconds ○: 5 to 60 seconds △: 1 to 10 minutes
×；More than 10 minutes

(3) Condition of hydrogel during strong demolding (compared to silicone rubber)
◎; Same level ○; Slightly soft △; Soft and slightly sticky ×; Soft and sticky

(4) Disintegrability Number of days required for the hydrogel molded body to completely collapse in shape when immersed in water at 20° C. ◎; 6 months to 1 year ○; 3 to 6 months △; 1 to 3 months ×; less than 1 day

(5) Shrinkage Change in shape of hydrogel molded product when left at 20°C and 65% RH for 72 hours ◎; Almost no change ○;
Slightly hardened △; Slightly hardened and deformed ×; Significantly hardened and deformed

[0046]

[Table 1]

[0047]

[Effects of the Invention] As configured as described above, the hydrogel molded article of the present invention whose shape collapse time can be controlled has high hydrogel strength and maintains its shape well for a certain period of use. After this time, it will collapse naturally. Further, according to the manufacturing method of the present invention, a hydrogel molded article whose shape collapse time can be controlled can be obtained with simple operations similar to those of general-purpose plastics.

Claims (2)

[Claims] Claim 1: The main components are (A) a polyvinyl alcohol polymer with an average degree of polymerization of 100 to 3,500 and a degree of saponification of 95 mol% or more, (B) a polyol, and (C) water, and the weight composition ratio of these main components ( A)/(B)/(C) is 5-6
A hydrogel molded article having a controllable shape collapse time, characterized in that the shape collapse time is 0/5 to 60/10 to 60. 2. The main components are (A) a polyvinyl alcohol polymer with an average degree of polymerization of 100 to 3,500 and a degree of saponification of 95 mol% or more, (B) a polyol, and (C) water, and the weight composition ratio of these main components ( A)/(B)/(C) is 5-6
Mix it so that the ratio is 0/5 to 60/10 to 60, heat and melt the resulting mixture, and then gel it at room temperature, or
A method for producing a hydrogel molded article whose shape collapse time can be controlled, which comprises further heat-melting the gel-molded product and gelling it at room temperature.