JPH034248B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a hydrogel, and in particular provides a method for producing a cold-retaining gel from polyvinyl alcohol with excellent properties not found in conventional hydrogels.

Various cooling gels have already been proposed under the names of cooling gels, cold storage gels, cold storage thermal media, colloidal refrigerants, cold storage devices, cold storage compositions, and ice pillows that do not require ice. It is put into practical use. However, as exemplified below, all of them have problems in product properties or manufacturing methods.

(1) The production of agar gel is well-known as a simple method for producing hydrogel for cold storage. That is,
After dissolving agar equivalent to 0.1 wt% or more, for example 1 to 10 wt%, in hot or boiling water at 80 to 94 °C,
Moisture content 90-99wt by cooling to room temperature
% of water-containing gel (hydro gel) can be easily obtained. However, when this gel is cooled in the ice compartment of a refrigerator and then used as a cold preservation gel, for example as an ice pillow or ice bag substitute,
Agar gel has poor elasticity and is extremely brittle, giving the human body the sensation of a foreign body, and the gel disintegrates during use, making it far from providing a comfortable feel. In addition, it often freezes and hardens in the ice compartment of a refrigerator, making it inconvenient to use as an ice pillow or ice bag substitute.

In this case, the freezing temperature can be lowered by immersing agar in an antifreeze solution such as ethylene glycol or propylene glycol, or by cooling a heated aqueous solution containing both agar and antifreeze solution. The gel is also brittle and easily disintegrates, making it unsuitable for use in pillows and other cold storage gels.

(2) It has long been well known that when boric acid (or boric acid aqueous solution) or borax (or borax aqueous solution) is added to polyvinyl alcohol aqueous solution, gelation occurs immediately. However, the resulting gel is fluid, soft, and readily shreds by simply pinching it with the fingertips. Additionally, there is the problem of syneresis (separation of water content) during repeated use.
−11210).

By cooling polyvinyl alcohol/borax gel in an ice chamber of a refrigerator (freezer), the water inside the gel freezes, and in order to prevent the gel from becoming hard, monohydric alcohol and polyhydric alcohol are added to the polyvinyl alcohol aqueous solution. A method of gelling with borax after adding alcohol, glucose, or sucrose has also been proposed, but in this case, the strength of the gel decreases and there is also the problem of syneresis during repeated use (Tokuko Sho 46−19602).

Another method for lowering the freezing point of polyvinyl alcohol/borax gel is to immerse the gel in an antifreeze solution such as ethylene glycol or propylene glycol, but this gel is also made softer by ethylene glycol, propylene glycol, etc. In addition to becoming distorted and losing its shape,
The gel also has the disadvantage of collapsing even with antifreeze solutions such as methanol, ethanol, and acetone.

The present inventor conducted research to develop a method for inexpensively and stably producing a water-insoluble gel with excellent mechanical properties that does not easily freeze in refrigerators (freezers) and ice chambers, using polyvinyl alcohol. , the knowledge that by cooling, solidifying, and vacuum dehydrating (drying) an aqueous solution or suspended aqueous solution containing polyvinyl alcohol and water-soluble polyhydric alcohol, a solid gel that is highly elastic, highly flexible, and difficult to freeze can be obtained. A method for producing a cooling gel (Patent application 1982-134311) and a head cooling gel for preventing hair loss due to side effects of anticancer drugs (Patent application 1982-77502)
Submitted as.

That is, in these, polyvinyl alcohol with a saponification degree of 95 mol% or more and an average degree of polymerization of 1500 or more, and a carbon number 2 having 2 to 6 hydroxyl groups in the molecule.
-6 water-soluble polyhydric alcohol, and the concentrations of the polyvinyl alcohol and the water-soluble polyhydric alcohol are 2.5 to 10 wt% and 20 to 80 wt%, respectively.
The aqueous solution adjusted to
The present invention provides a method for producing a gel for cold storage, which is characterized by performing vacuum dehydration to a weight loss rate of solidified material of 5 wt% or more and 95 wt% or less.

According to these, by gelling an aqueous solution or suspended aqueous solution containing polyvinyl alcohol and the water-soluble polyhydric alcohol, a gel that is rich in elasticity and flexibility and does not freeze even in a freezer icebox was obtained.

Further, this gel is completely different from the gel of an aqueous polyvinyl alcohol solution in that it is insoluble in water or hot water and exhibits no stickiness.
That is, a new gel has been provided that is completely different from the knowledge regarding the conventional gelling of an aqueous polyvinyl alcohol solution by cooling, or the gelling of a conventionally known aqueous polyvinyl alcohol solution by chemical treatment.

Because the gel itself has a feel similar to living tissue, it can be used as a highly elastic ice pack, such as an ice pillow or an ice bag substitute. Therefore, in order to prevent hair loss due to the side effects of anticancer drugs, we molded it into the shape of a helmet to keep the head cool and used it directly (filling it into a vinyl chloride bag, etc.).
It can be worn and attached closely to the head (without being encapsulated).

As a result of further research into the method for producing this gel, the present inventor has determined that a mixed aqueous solution of polyvinyl alcohol and water-soluble polyhydric alcohol should be heated at a temperature of at least 50°C.
This is poured into a container of the desired shape while maintaining the high temperature above, and is then cooled, solidified, vacuumed and
By performing partial dehydration, even high-concentration aqueous solutions with polyvinyl alcohol concentrations exceeding 10wt% can be removed.
The present invention has been completed based on the discovery that a hydrogel having a desired shape can be obtained, thereby producing a hydrogel that is more durable than that in the case of the above-mentioned application.

That is, in the present invention, the polyvinyl alcohol concentration of the polyvinyl alcohol aqueous solution is 10 wt%.
It is characterized by exceeding. The fact that such a highly concentrated polyvinyl alcohol aqueous solution is viscous;
Therefore, it is well known that as the concentration of polyvinyl alcohol increases, it becomes difficult to handle. For example, the viscosity of a 15wt% aqueous solution of polyvinyl alcohol (degree of polymerization 2400) is 55000cP.
(25℃), and the coexistence of water-soluble polyhydric alcohol further increases its viscosity.
Therefore, it takes a long time to handle the viscous liquid, that is, to pour it into a mold, and there are also disadvantages in that air bubbles are mixed in during the injection process, and the bubbles are difficult to eliminate. However, according to the present invention, even when the polyvinyl alcohol concentration exceeds 10 wt%, the above-mentioned difficulties can be avoided and a hydrogel with a desired shape can be obtained. That is, the viscosity of a 15 wt% aqueous solution of the polyvinyl alcohol (degree of polymerization 2400) is 19000 cP at 50°C, 10000 cP at 70°C, and only 6000 cP at 90°C. Even if 1 to 40 wt% coexist, the viscosity remains at 20,000 to 6,100 (50 to 90°C), and the 25%
The temperature decreases to 1/9 to 1/2 of that at ℃. Therefore, if a polyvinyl alcohol aqueous solution maintained at such a high temperature is injected into a mold, this injection operation will be speeded up, and the inclusion of air bubbles will be reduced. Even if it gets mixed in,
This can be made to float and disappear relatively quickly.

The degree of saponification of the polyvinyl alcohol used in the present invention needs to be 95 mol% or more, preferably 97 mol% or more.

The average degree of polymerization of the polyvinyl alcohol used in the present invention is required to be 1500 or more. In the present invention, for example, polyvinyl alcohol having an average degree of polymerization of about 1,500 to 3,300 can be used, but it is preferable to use commercially available products with a high degree of polymerization (average degree of polymerization of 1,500 to 2,600) as they are.

In the present invention, first, an aqueous solution containing polyvinyl alcohol and a water-soluble polyhydric alcohol is prepared. The concentration of polyvinyl alcohol can be more than 10 wt% and less than 25 wt%, preferably less than 20 wt%.

In the present invention, prior to forming a gel, a water-soluble polyhydric alcohol as a freezing point depressant is dissolved in the polyvinyl alcohol aqueous solution. This means that when the hydrogel of the present invention is left in the ice maker of a household refrigerator, it easily (quickly) freezes and freezes.
Useful to prevent stiffness.

The water-soluble polyhydric alcohol having 2 to 6 hydroxyl groups in the molecule used in the present invention includes:
Polyhydric alcohols having about 2 to 6 carbon atoms are usually used. Examples of the deicing agent include ethylene glycol. The freezing point of pure ethylene glycol is -16℃, but for example, the freezing point of an aqueous solution with a concentration of 10wt% and 19wt% is -3℃, respectively.
and -8℃. This freezing point lowering effect is not limited to ethylene glycol, but also 1,2-propylene glycol (propylene glycol) (10wt% substitution,
-3℃), 1,3-propylene glycol (10wt
% substitution, -3℃), glycerin (10wt% substitution, -1
It is also found in water-soluble polyhydric alcohols such as 2-methyl-2,4-pentanediol (10 wt% substitution, -2°C), and these lower the curing temperature of the gel to below -0°C.

Furthermore, the freezing points of a 0.8 to 1.8 wt% aqueous solution of glucose and a 0.1 to 1 wt% aqueous solution of sutucarose are -0.1 to -0.2°C and -0.01 to -0.06°C, respectively. However, since the effect of lowering the freezing point of the aqueous solution can be obtained to some extent,
In the present invention, the amount of polyhydric alcohol used as a freezing point depressant is adjusted to 1% depending on the usage conditions (storage temperature in the refrigerator, storage time) of the hydrogel of the present invention.
It can be selected as appropriate within the range of ~40wt%.

The above-mentioned various water-soluble polyhydric alcohols are embedded in the hydrogel of the present invention and contribute to preventing air drying and stiffening of the gel. As mentioned above, the usage amount is as follows:
Depending on the pre-cooling temperature of the hydrogel, an arbitrary value of 40wt% or less can be selected, taking into account the freezing point lowering effect of the water-soluble polyhydric alcohol. However, if the amount of polyhydric alcohol used is small, that is, 10 wt% or less, the air-drying prevention effect of the hydrogel of the present invention will be significantly reduced, but in this case, if necessary, the hydrogel of the present invention may be It can be used by being sealed or packaged in a film or bag made of vinyl or polyethylene, or it can be used as it is (without packaging) for about 1 hour during the administration of anticancer drugs, which will be described later. It is a good idea to take precautions such as storing it in a bag.

To prepare an aqueous solution containing polyvinyl alcohol and water-soluble polyhydric alcohol, you can add and dissolve polyvinyl alcohol and water-soluble polyhydric alcohol in water, or, for example, dissolve polyvinyl alcohol in water in advance and then , a method can be adopted in which polyhydric alcohol (or its aqueous solution) is mixed therein, and in any case, the final polyvinyl alcohol concentration exceeds 10 wt%, and the polyhydric alcohol concentration is 1 to 40 wt%.
Adjust to. In these cases, since polyvinyl alcohol is poorly soluble in solvents other than water, it often takes a state in which transparent microgel particles are dispersed in an aqueous solution containing a water-soluble polyhydric alcohol (transparent suspended aqueous solution state). However, this does not pose any problem in implementing the present invention.

In the present invention, an aqueous solution or suspended aqueous solution containing polyvinyl alcohol and a water-soluble polyhydric alcohol is injected into a desired mold while maintaining the temperature at a high temperature of 50°C or higher, and then cooled, solidified, and molded. Features. As mentioned above, when the concentration of polyvinyl alcohol with an average degree of polymerization of 1500 or more exceeds 10 wt%, its viscosity increases significantly, and it is usually difficult to speed up the injection operation. To further supplement and illustrate, the viscosity of an aqueous solution containing 16 wt% of polyvinyl alcohol with an average degree of polymerization of 2600 is:
80000cP at 20℃, 36000cP at 40℃
reach. However, according to the present invention, if this is maintained at a high temperature of 50°C or higher, the viscosity decreases significantly, and can be limited to 10,000 cP at 90°C, for example. In the present invention, in this way,
After injecting the polyvinyl alcohol-containing aqueous solution into the mold, a freezing operation is applied to it.

In this case, the aqueous solution (or suspended aqueous solution) is cooled to a temperature below the whitening, opaqueness, and (freezing) temperature.
For example, the freezing (unfrozen white) temperature of a 16 wt% aqueous solution of polyvinyl alcohol with an average degree of polymerization of 2600 is -3°C, but it often leads to a supercooled state and -
It does not freeze or harden even at 4 to -5 degrees Celsius and remains transparent, but even in such cases, by leaving it in this supercooled state (-3 to -5 degrees Celsius), it will become normal within 30 minutes. Freezing conditions (-3°C) develop. Polyvinyl alcohol with a degree of polymerization of 2400
A freezing temperature of -2°C (-4 to -5°C when supercooled) is also observed for the 15 wt% aqueous solution. The coexistence of polyhydric alcohols in these aqueous solutions further lowers the freezing temperature, for example, when the glycerin concentration
19wt%, polyvinyl alcohol (degree of polymerization 2400)
The freezing temperature of an aqueous solution with a concentration of 11 wt% is -6°C (-10°C when supercooled). As described above, the freezing temperature of the aqueous solution in the present invention depends on the degree of polymerization and concentration of polyvinyl alcohol, the type and coexistence concentration of polyhydric alcohol, but in any case, in the present invention, the freezing temperature of the aqueous solution containing polyvinyl alcohol must be cooled to a temperature sufficient to freeze.

In the present invention, after the above-mentioned cooling treatment, the material is vacuum dehydrated without being melted. Dehydration rate (cooling/
As the weight loss rate of the solidified gel increases, the mechanical strength of the gel also improves, but if we consider its normal use as a hydrogel, it is necessary to increase the dehydration rate to obtain a strong gel. In view of the flexibility of the gel, it is preferred that the dehydration rate be 5 to 95 wt%, preferably 10 to 80 wt%, and more preferably 15 to 40 wt%. The vacuum dehydration referred to here is
By dehydrating under reduced pressure, the degree of reduced pressure is not particularly limited, but can be carried out at, for example, 2 mmHg or less, preferably 1 mmHg or less, and even 0.1 mmHg or less.
This dehydration step cannot be omitted. That is,
Unless this is carried out, the elasticity of the present invention
Moreover, a gel with excellent mechanical strength cannot be obtained, and as dehydration progresses, the gel strength increases and various properties such as non-adhesiveness and water resistance are significantly improved. It is essential for However, in the present invention, there is no need to carry out sufficient dehydration (drying) treatment as seen in freeze-drying of injectable liquids or freeze-drying of water-containing foods such as coffee, milk, fruit juice, and noodles. , the object of the present invention is fully achieved, and as described above, the gel strength increases as dehydration progresses, so the amount of dehydration can be selected depending on the desired gel strength. In any case, this partial dehydration treatment is indispensable to the present invention and has extremely important significance, so if it is omitted, the non-flowable, non-adhesive, highly water-containing and Hydrogels with excellent mechanical strength cannot be obtained.

The gel of the present invention has a feel similar to that of living tissue, so it can be used as a highly elastic ice pack, such as an ice pillow or an ice bag substitute, and it has a fresh feel and a crispy... - Demonstrates similar elasticity.

The gel of the present invention can be used as an ice pillow or ice bag substitute as described above, and can also be used as a head cooling gel used to prevent alopecia as a side effect of cancer chemotherapy. This head cooling gel is suitable for use in preventing hair loss caused by administering anticancer drugs to cancer patients.
−mycin) i.e. Daunorubicin
Or Adriamycin, i.e.
14-hydroxy daunorubicin (doxorubicin)
It can be of great utility in preventing and inhibiting severe hair loss as a side effect. Among these, adriamycin is often noted as an important anticancer agent because it exhibits particularly excellent therapeutic effects against a wide range of cancers, but it is also well known that its toxicity is extremely severe. For example, when adriamycin is administered every 25 days, more than 90% of patients suffer from alopecia, and this loss of hair causes great psychological distress to the patients and is difficult to understand in modern times. In some cases, this can lead to serious problems that can lead to a lack of trust in medical care.

The cause of this hair loss appears to be that antibiotics administered into the body are absorbed into the hair cell tissue, and with the intention of suppressing this absorption rate, the metabolism of living cells is significantly reduced (around 25 degrees Celsius). , efforts have been made to cool the hair cells. Administered antibiotics reach the head after a few minutes, leave the head within 30 to 40 minutes, and are hardly detected in the bloodstream of the head after that. Specific methods for cooling have been explored. In other words, an ice pack is wrapped around the head, a sponge helmet is impregnated with a large amount of cold water, and jelly, agar, polyvinyl alcohol, etc. Attempts were made to encapsulate borax gel. However, with the ice pack method, gravity causes the water and ice to flow down to the bottom of the bag wrapped around the head and become unevenly distributed, making it difficult to cool the entire head uniformly. There are practical difficulties, such as poor performance and large amounts of cold water leaking and dripping. In the method of enclosing a high water content gel as a cooling medium into the hollow part of a hollow cap made of a polyvinyl chloride bag, conventionally known high water content hydrogels are all fluid (polyvinyl alcohol borax gel, carboxymethylcellulose gel). Alternatively, since it is a soft or brittle solid (agar, jelly, carrageenan, alginate gel), it is difficult to maintain its shape (helmet shape), and furthermore, it has poor elasticity, making it difficult to fit tightly onto the head. In order to prevent the cooling medium from becoming misshapen and unevenly distributed, perforations were made vertically and horizontally over the entire surface of the hollow bag type helmet (many small sections were created) to prevent the internal filling from moving. An attempt was also proposed to provide a large number of independent vesicles (small inner chambers) and seal a cooling medium in each (Japanese Patent Application Laid-Open No. 140107/1983), but
Since this helmet itself lacks elasticity, it does not fit tightly over the entire head, creating a gap, so it lacks practical value.

As a measure to prevent hair loss as a side effect of adriamycin, a method has been proposed in which the scalp is tightened with a rubber band and administered, but if consideration is given to the cruel pain caused to the patient by applying external pressure to the head, this attempt is also recommended. , is by no means desirable.

The problem with the above-mentioned head cooling method is that it is necessary to obtain a cooling material with appropriate properties, that is, a high water content gel (hydro gel) that has rubber-like elasticity and mechanical strength that can maintain the shape of the helmet. I attribute it to not being able to do it.

According to the present invention, a head cooling gel can be created by injecting an aqueous solution or suspended aqueous solution containing the polyvinyl alcohol and water-soluble polyhydric alcohol into a mold for molding a helmet, cooling, solidifying, and molding.

In this case, it is desirable that the shape of the helmet covers not only the entire head hair, but also the mandible (that is, the hair on the left and right sides of the head) and even the eyebrows. helmets etc. are inappropriate, but
A helmet made of the gel of the present invention can be easily manufactured by making desired modifications to a mold for molding a helmet used for driving a motorcycle, ice hockey, etc.

In the present invention, the helmet-shaped gel thus obtained can be used as it is (that is, without being packaged or enclosed in a bag made of polyvinyl chloride, polyethylene, polypropylene, etc.) as a helmet for keeping the head cool. , the feel of the hydrogel of the present invention can be directly transmitted to the head,
Since this hydrogel is highly stretchable (elastic), sufficient adhesion is always achieved over a wide range of head sizes and shapes. In other words, compared to the case where jelly, paste-like synthetic gel, etc. are sealed in a bag made of polyvinyl chloride or rubber, etc., as described above,
It is clear that the present invention, which directly covers the head with a hydrogel that has a konnyaku-like (or kuzumochi-like) feel, is much more compatible with the ergonomic treatment philosophy.

According to the present invention, the polyvinyl alcohol concentration of the raw material for hydrogel production exceeds 10 wt%,
It can be increased up to 25wt%. This results in
The strength (elastic modulus) of the obtained hydrogel can be increased, and it has the advantage of being able to withstand repeated use over a long period of time, accidental mechanical shock, rough handling, storage, etc.

Examples of the present invention will be described below.

Example 1 Polyvinyl alcohol with a saponification degree of 99.5 mol%, an average degree of polymerization of 2600, and a 4% aqueous solution viscosity (20°C) of 67 cP
A suspended aqueous solution consisting of 430 g (water content 7 wt%), 175 g of glycerin, 0.35 g of n-butyl para-hydroxybenzoate, 17.5 g of colistin sulfate powder, and 2800 g of water was subjected to pressure steel sterilization at 120°C for 25 minutes.
Subsequently, by stirring in a sterile room and uniformly dissolving, polyvinyl alcohol 12wt%,
Glycerin 5wt%, para-hydroxybenzoic acid n
- An aqueous solution containing 100 ppm of butyl and 5000 ppm of colistin sulfate was obtained. This aqueous solution is 6000cP at 40℃
The viscosity at 90℃ is 1000cP.
It declined to . 3400g of this aqueous solution at 70℃ (2000cP)
While maintaining the temperature at ~90℃ (1000cP), stainless steel
Pour into a steel helmet mold (helmet depth: approx. 26 cm, outer diameter: approx. 22 cm, thickness: approx. 2 cm), cool at -25°C for 8 hours, and immediately vacuum dehydrate.
325 g of water was removed (dehydration rate 9.5 wt%), and then the mixture was allowed to stand at room temperature to melt.

The helmet obtained through this process is highly elastic and flexible, and has sufficient mechanical strength to be repeatedly put on and taken off as a helmet, and will not freeze or become stiff even if left in the icemaker of a refrigerator for one hour. , the original flexibility and elasticity were retained. This was left at room temperature, and when the temperature reached 0℃, it was placed on the head of an adult and the head was placed in a supine position. After 8 minutes, the scalp temperature reached 21-23℃, and after that, the scalp temperature reached 21 to 23℃ for 38 minutes. ~25℃
was maintained.

Example 2 Polyvinyl alcohol (saponification degree 99.1 mol%,
Average degree of polymerization 2400, viscosity of 4% aqueous solution (20℃)
60cP) powder 340g (moisture content 7wt%), glycerin
A mixed suspension aqueous solution of 500g and 1160g of water was heated at 120℃
By applying pressure steam sterilization for 35 minutes and then stirring in a sterile room, an aqueous solution of 16 wt% polyvinyl alcohol and 25 wt% glycerin was obtained.
Here, butyl para-hydroxybenzoate 100mg
(equivalent to 50ppm) and 10g of fradiomycin sulfate powder
(equivalent to 5000ppm) was dissolved.

While maintaining this aqueous solution at 70 to 90°C, mold a stainless steel helmet mold (helmet depth approximately 23 cm, outer diameter approximately 20 cm, thickness approximately 2 cm).
After cooling at −45° C. for 9 hours, the mixture was immediately subjected to vacuum dehydration to remove 210 g of water (dehydration rate: 10 wt%), and then allowed to stand at room temperature to melt.

The helmet thus obtained was highly elastic and flexible, and had sufficient mechanical strength to allow it to be attached and detached as a helmet.Also, when it was left in a refrigerator ice compartment for one hour, no freezing or hardening was observed. The flexibility and elasticity were maintained. Leave this at room temperature, 0℃
When this temperature was reached, it was placed on the head of an adult and the scalp was placed in a horizontal supine position. After 9 minutes, the scalp temperature was 21 to 23.
°C was reached and then maintained at 21-25 °C for 37 min.

Example 3 Polyvinyl alcohol with a saponification degree of 99.5 mol%, an average degree of polymerization of 2600, and a 4% aqueous solution viscosity (20°C) of 67 cP
200g was dissolved in 1260g of water, and 44g of propylene glycol was mixed thereto to give a polyvinyl alcohol concentration of 13wt% and a propylene glycol concentration of 3wt%. This viscosity is 10000cP at 40℃ and at 25℃
It was 20000cP, 4000cP at 60℃, and 2000cP at 90℃. 1500g of this aqueous solution was poured into a helmet mold while maintaining it at 60-90℃, and then kept at -20℃ for 8 hours.
After being left to cool, it was immediately subjected to vacuum dehydration to remove 200 g of water (dehydration rate: 13 wt%), and then allowed to stand at room temperature to melt.

The helmet thus obtained was highly elastic and flexible, and also had sufficient mechanical strength to be repeatedly put on and taken off as a helmet.

This is stored in an ice storage room, and when it reaches 0℃,
As a result of wearing it on the head of an adult and having them take a supine position,
After 8min, the scalp temperature reaches 20-22℃, and then
The temperature was maintained at 20-25°C for 33 min.

Example 4 Polyvinyl alcohol with a saponification degree of 99.5 mol%, an average degree of polymerization of 1800, and a 4% aqueous solution viscosity (20°C) of 28 cP
270g (moisture content 7wt%), propylene glycol
A suspension consisting of 500 g and 1250 g of water (polyvinyl alcohol concentration 13 wt%, propylene glycol concentration 25 wt%) was subjected to pressure steam sterilization at 120° C. for 30 minutes, and then stirred in a sterile room to uniformly dissolve it. Its viscosity is 4500cP (20℃),
The viscosity was 2500cP (at 40°C), but by maintaining it at 50°C, the viscosity decreased to 1700cP.
2 kg of this aqueous solution was poured into a helmet mold while maintaining the temperature at 50 to 60°C, and after cooling at -40°C for 6 hours, it was immediately subjected to vacuum dehydration to remove 230 g of water (dehydration rate: 12 wt%), and then It was allowed to melt by standing at room temperature.

The helmet thus obtained was highly elastic and flexible, and had sufficient mechanical strength to be repeatedly put on and taken off as a helmet. Store this in the refrigerator, and when it reaches 0 degrees Celsius, put it on the head of an adult.
After 9 minutes, the scalp temperature was 20.
~22°C was reached and then maintained at 20-25°C for 38 min.

Example 5 A suspension consisting of 238 g of polyvinyl alcohol (7 wt% water content), 300 g of glycerin (8 wt% water content), and 1460 g of water with a saponification degree of 97.5 mol%, an average degree of polymerization of 2200, and a viscosity of 4% aqueous solution (20°C) 56 cP. 120 in aqueous solution
The mixture was subjected to pressure steam sterilization at 35 minutes at ℃ and then stirred in a sterile room to uniformly dissolve it, thereby obtaining an aqueous solution containing 12 wt% polyvinyl alcohol and 15 wt% glycerin.

The viscosity of this aqueous solution is 6000cP (20℃), 2500cP
(40℃) and 1300cP (60℃). This aqueous solution
1900g was placed in a stainless steel helmet molding mold (helmet depth approx. 21cm, outer diameter approx.
cm, thickness approximately 2 cm), and after cooling at -40℃ for 9 hours,
It was immediately subjected to vacuum dehydration to remove 220 g of water (dehydration rate 12 wt%), and then allowed to stand at room temperature to melt.

The helmet thus obtained was highly elastic and flexible, and had sufficient mechanical strength to be repeatedly put on and taken off as a helmet. I put this in the refrigerator, and when it reached 0℃, I put it on the head of a child (8 years old) and had him lie on his back. After 8 minutes, the scalp temperature reached 20 to 22℃, and then for 38 minutes. 20-25
maintained at ℃.

Example 6 Saponification degree 97.5 mol%, average degree of polymerization 2200, 4% aqueous solution viscosity (20°C) 56 cP, pyrivinyl alcohol 350 g (water content 7 wt%), glycerin 160 g, water
2685g, paromomycin sulfate
Suspension mixture of 16g of powder (sulfate) powder in an aqueous solution at 120℃
By applying pressure steam sterilization for 25 minutes and then stirring in a sterile room to uniformly dissolve polyvinyl alcohol 11wt% and glycerin.
An aqueous solution containing 5 wt% and 5000 ppm of paromomycin sulfate was obtained. The viscosity of this aqueous solution is 4000cP (20℃),
They were 1500cP (40℃) and 700cP (60℃). Part 3.1
Kg was poured into a helmet molding mold (helmet depth: approx. 25 cm, outer diameter: approx. 22 cm, thickness: approx. 2 cm) while maintaining the temperature at 60 to 70°C, and after cooling at -40°C for 6 hours, vacuum dehydration was immediately performed. , excluding 200g of water (dehydration rate: 6.5wt
%) and then allowed to stand at room temperature to melt.

The helmet thus obtained was highly elastic and flexible, and had sufficient mechanical strength to be repeatedly put on and taken off as a helmet.Also, no freezing or hardening was observed after it was left in the icemaker of a refrigerator for one hour. , the original flexibility and elasticity was retained. This was left at room temperature, and when the temperature reached 0℃, it was placed on the head of an adult and the adult was placed in a semi-prone position. After 9 minutes, the scalp temperature reached 21-23℃, and after that, the scalp temperature reached 21-23℃ for 39 minutes. ~twenty five
maintained at ℃.

Comparative Example 1 In Example 5, to the helmet molding mold,
Aqueous solution of polyvinyl alcohol and glycerin 1900
After injecting g, the mixture was allowed to cool at -40°C for 24 hours, and then allowed to stand and melt at room temperature without performing the partial dehydration operation of the present invention.

When the molded body was taken out of the mold, it was so soft that it was impossible to stand it upright on a desk.
In addition, it was found that the adhesive was extremely sticky, making it extremely uncomfortable to wear when forced to wear it, and that it easily slipped from the hand when put on and taken off, and was easily damaged. That is, the usefulness of the cooling and vacuum/partial dehydration operations of the present invention is obvious.

Comparative Example 2 350 g of polyvinyl alcohol with a saponification degree of 95 mol% and a polymerization degree of 100 (water content 7 wt%), glycerin 160
A mixed solution of 2,685 g of water, 16 g of paromomycin sulfate was heated at 120° C. for 25 minutes to obtain an aqueous solution containing 11 wt% polyvinyl alcohol and 5 wt% glycerin. Pour 3.1Kg of this aqueous solution into the mold and store at -40℃ for 6 hours.
After cooling, vacuum dehydration is performed to remove 200g of moisture (dehydration rate
6.5%) and then melted at room temperature. After dismantling the mold,
When the molded product (helmet) was removed and placed on the head, a crack appeared from the front of the helmet to the head. That is, although the degree of saponification is 95 mol%, which is within the range of the present invention, it was inconvenient to use polyvinyl alcohol whose degree of polymerization was as low as 1000.

Comparative Example 3 175 g of polyvinyl alcohol with a saponification degree of 98 mol% and a polymerization degree of 2200 (water content 7 wt%), glycerin 160
A mixed solution of 5.5 wt % polyvinyl alcohol and 5 wt % glycerin was obtained by heating a mixture of 120° C. and 2860 g water for 25 minutes. This 3.1Kg (60~70℃)
was poured into a mold, left to cool at -40°C for 6 hours, and then vacuum dehydrated to remove 2000 g of water (dehydration rate 6.5 wt%), and then left in a chamber to melt. When the molded product (helmet) was removed from the mold, it could not stand upright on the desk and fell immediately. Store folded in half overnight (sealed)
As a result, creases (hikyu distortion) occurred, and even when the tape was attached to the head, the difference in level (crease) was not resolved, and the intended purpose of applying the tape to the entire head could not be achieved.
When the concentration of polyvinyl alcohol was low, the resulting gel was only soft, which was disadvantageous to the present invention.

Comparative Example 4 350 g of polyvinyl alcohol with a degree of saponification of 94 mol% and a degree of polymerization of 2200 (water content 7 wt%), glycerin 160
A mixed solution of 2,685 g of polyvinyl alcohol and 2,685 g of water was heated at 120° C. for 25 minutes to obtain an aqueous solution containing 11 wt% polyvinyl alcohol and 5 wt% glycerin. This 3.1Kg was poured into a mold, left to cool at -40℃ for 6 hours, and immediately vacuum dehydrated.
After removing 200 g of water (dehydration rate: 6.5 wt%), the mixture was allowed to stand at room temperature to melt. The molded product (helmet) had a viscous paste-like appearance, and even if the mold was deliberately dismantled, deformation, cracks, and damage occurred during the process of removing it. Therefore, it is inconvenient to use polyvinyl alcohol with a low degree of saponification.

Comparative Example 5 350 g of polyvinyl alcohol with a degree of polymerization of 2200 and a degree of saponification of 97.5 mol% (water content 7 wt%), glycerin
A mixed solution of 160 g and 2685 g of water was heated at 120° C. for 25 minutes to obtain an aqueous solution containing 11 wt% polyvinyl alcohol and 5 wt% glycerin. This 3.1 kg was poured into a mold, and after being left to cool at -40°C for 6 hours, it was immediately subjected to vacuum dehydration to remove 67 g of water (dehydration rate: 2.2 wt%), and then allowed to stand at room temperature to melt. After dismantling the mold, the molded product (helmet) was taken out, but it could not be placed upright on the desk and fell immediately. When the helmet was kept folded in half (sealed) overnight, creases appeared, and even after the helmet was placed on the head, the steps (creases) did not go away, making it difficult to apply the helmet tightly to the entire head. I couldn't do it. Therefore, it is disadvantageous if the dehydration rate of the polyvinyl alcohol aqueous solution is low.

Claims (1)

[Claims] 1 A polyvinyl alcohol containing polyvinyl alcohol with a saponification degree of 95 mol% or more and an average polymerization degree of 1500 or more, and a water-soluble polyhydric alcohol having 2 to 6 carbon atoms and having 2 to 6 hydroxyl groups in the molecule, and the polyvinyl alcohol and the concentration of the water-soluble polyhydric alcohol, respectively, 10
more than 25wt% and less than 1wt% and 40wt
While maintaining the adjusted aqueous solution at a high temperature of 50°C or higher, pour it into a container of the desired shape, and then,
A method for producing a hydrogel, which comprises cooling and solidifying this at a temperature lower than -5°C, and then subjecting it to vacuum dehydration at a dehydration rate of 5 wt% or more and 95 wt% or less.