JP2016098367A - Method for freezing pva aqueous solution, method for manufacturing pva gel, and method for manufacturing pva gel laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a PVA gel and a method for manufacturing a PVA gel laminate having higher structural strength than conventional products.SOLUTION: [1] Provided is a method for gradually freezing a PVA aqueous solution 1 from a first side toward a second side, wherein the PVA aqueous solution is gradually cooled from the first side toward the second side such that a normal line to a solidification surface where the freezing of the PVA aqueous solution progresses is parallel to a direction of freezing which proceeds from the first side toward the second side. [2] In the above-mentioned freezing method, a vessel 2 containing the PVA aqueous solution is gradually immersed into a cooling liquid 3 of a temperature below 0°C to gradually freeze the PVA aqueous solution in the vessel upward from the bottom. [3] In the above-mentioned freezing method, the vessel is gradually immersed into the cooling liquid such that the height of the solidification surface of the PVA aqueous solution is positioned in an area of water solidification temperatures at the liquid level of the cooling liquid or directly below the liquid level.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for freezing a PVA aqueous solution, a method for producing a PVA gel, and a method for producing a PVA gel laminate.

  A method for producing a PVA gel in which PVA is physically cross-linked by freezing and thawing a polyvinyl alcohol (PVA) solution is conventionally known.

K. Tamura, O. Ike, S. Hitomi, J. Isobe, Y. Shimizu, M. Nambu, A New Hydrogel and Its Medical Application, ASAIO Trans. 32 (1986) 605-609.

  The structural strength of PVA gel obtained by the conventional freeze-thaw method is not sufficient to be used as a material that substitutes for biological functions in medical applications, and a method for producing PVA gel having excellent structural strength is required. ing.

  This invention is made | formed in view of the said situation, The freezing method of the PVA aqueous solution for manufacturing easily the PVA gel which has the outstanding structural strength, the manufacturing method of PVA gel using the freezing method, and PVA gel It is an object to provide a method for manufacturing a laminate.

[1] A method of gradually freezing the PVA aqueous solution from the first side toward the second side, wherein the normal line of the solidified surface where the freezing of the PVA aqueous solution proceeds is from the first side to the second side. A method for freezing a PVA aqueous solution, characterized in that the PVA aqueous solution is gradually cooled from the first side to the second side so as to be parallel to the freezing direction toward the side.
[2] The above-mentioned [1], wherein the container containing the aqueous PVA solution is gradually inserted into a cooling liquid of less than 0 ° C., whereby the aqueous PVA solution in the container is gradually frozen upward from below. ] The freezing method of the PVA aqueous solution of description.
[3] Gradually put the container in the cooling liquid so that the solidified surface height of the PVA aqueous solution in the container is located in the region of the solidification temperature of the liquid level of the cooling liquid or water just below the liquid level. The method for freezing an aqueous PVA solution as described in [2] above, wherein
[4] The above [3], wherein the container is plate-shaped, and the container is inserted into the cooling liquid at a speed of 0.01 mm / second to 0.10 mm / second in the longitudinal direction. Freezing method of PVA aqueous solution.
[5] The method for freezing a PVA aqueous solution according to [4] above, wherein the thickness of the PVA aqueous solution orthogonal to the longitudinal direction of the container is 0.5 mm to 10 mm.
[6] The method for freezing a PVA aqueous solution according to the above [5], wherein a thickness of the container that separates the PVA aqueous solution from the cooling liquid is 1.0 mm to 10 mm.
[7] The method for freezing a PVA aqueous solution according to [6], wherein the material constituting the container is a synthetic resin having substantially the same thermophysical properties as the PVA aqueous solution.
[8] The first step of freezing the PVA aqueous solution by the method according to any one of [1] to [7] above, and the frozen body of the PVA aqueous solution obtained in the first step in an atmosphere of 0 ° C. or higher And a second step of obtaining a PVA gel by thawing in. A method for producing a PVA gel, comprising:
[9] The method for producing a PVA gel as described in [8] above, wherein in the second step, the obtained PVA gel is frozen again and then freeze-thaw cycle is performed once or more.
[10] The method for producing a PVA gel according to [8] or [9], further including a third step of immersing and swelling the PVA gel obtained in the second step.
[11] A PVA gel laminate is obtained by laminating two or more sheets made of the PVA gel obtained by the production method according to any one of [8] to [10]. A method for producing a PVA gel laminate.
[12] The method for producing a PVA gel laminate according to [11], wherein when stacking a plurality of the sheets, the sheets are stacked in a non-parallel orientation of the fiber structure of each sheet.
[13] In the above [12], when laminating a plurality of the sheets, each sheet is swollen with water in advance, a PVA aqueous solution is applied between the sheets, laminated, and dried. The manufacturing method of the PVA gel laminated body of description.

  According to the PVA aqueous solution freezing method and the PVA gel manufacturing method of the present invention, parallel fiber structures aligned in the direction in which the PVA aqueous solution is frozen (for example, the longitudinal direction of the container containing the PVA aqueous solution) are formed on the surface and inside. The obtained PVA gel having structural anisotropy is easily obtained. Since this PVA gel has a structural strength that does not easily break even when a load is applied in the direction along the fiber structure, it is suitable for applications that require a higher structural strength than conventional PVA gels.

  According to the method for producing a PVA gel laminate of the present invention (hereinafter sometimes simply referred to as “laminate”), any number of sheets required to be used depending on the application can be obtained by stacking sheets made of any number of PVA gels. Can be imparted to the laminate. Moreover, a functional substance can be contained in a predetermined layer constituting the laminate. In this case, the concentration of the functional substance in each layer is gradually changed for each layer to create a concentration gradient of the functional substance contained in the entire laminate (concentration gradient), or to a specific layer in the laminate Only functional materials can be easily carried.

The plate-like container 2 containing the PVA aqueous solution 1 is moved from the first end portion 2a which is the first side to the second end portion 2b which is the second side, at a speed v, in a low temperature water bath at -26 ° C. It is the schematic diagram which showed a mode that it inserts gradually in the ethanol aqueous solution 3 set to (1). It is a schematic diagram which shows the height d of the solidification surface in a container seen from the front of the plate-shaped container 2 of FIG. It is typical sectional drawing which looked at the PVA aqueous solution 1 in the plate-shaped container 2 of FIG. 1 from the thickness direction orthogonal to a height direction. It is a typical perspective view of the PVA gel produced by the freezing method of the PVA aqueous solution which concerns on this invention, and the manufacturing method of PVA gel. The state where the fiber structure is aligned in the X direction is shown. It is typical sectional drawing of the container 12 and the PVA aqueous solution 11 in 2nd embodiment of the freezing method of PVA aqueous solution. It is a graph which shows the relationship between the height d of the solidification surface of PVA aqueous solution on the basis of the liquid level of a cooling solution, and time at the insertion speed v of a predetermined container. It is a graph which shows the relationship between the said height d and the freezing speed (insertion speed of a container) in the state (state in which the solidification speed of PVA aqueous solution corresponded to v) where the solidification surface height d of PVA aqueous solution settled constant. . It is a graph which shows the relationship between temperature and the distance from the said liquid level on the basis of the liquid level of ethanol aqueous solution. In the graph, a positive distance indicates a position above the liquid level, and a negative distance indicates a position in the liquid below the liquid level. The inside of the ethanol aqueous solution is equal to the set temperature of −26 ° C., the liquid level is about 0 ° C., and the temperature rapidly decreases inside the water and reaches below the freezing point (supercooling) of water. (A) It is a perspective view which shows typically the dimension of the dumbbell cutter of JIS K-6251-8 standard. (B) It is a top view of the dumbbell cutter shown to (a). A numerical unit representing a dimension is mm. It is a graph which shows the relationship between the freezing speed (insertion speed of a container) and the maximum stress of the PVA gel produced in the Example. It is a graph which shows the relationship of the freezing speed (insertion speed of a container) and the maximum strain of the PVA gel produced in the Example. It is a graph which shows the freezing speed (insertion speed of a container) of the PVA gel produced in the Example, and the relationship between initial stage elastic modulus. It is a graph which shows the relationship between the freezing speed (insertion speed of a container) of the PVA gel produced in the Example, and mass swelling ratio. It is a SEM photograph of FT4 gel produced by repeating freeze-thaw 4 times by the conventional method. It is a SEM photograph of the anisotropic gel (freezing rate: 0.01 mm / second, gel thickness 2 mm) produced in the Example.

  Hereinafter, the present invention will be described based on preferred embodiments.

≪Freezing method of PVA aqueous solution≫
The method for freezing a PVA aqueous solution according to the first aspect of the present invention is a method of gradually freezing a PVA aqueous solution from a first side toward a second side, and the freezing of the PVA aqueous solution proceeds or is started. In this method, the PVA aqueous solution is gradually cooled from the first side to the second side so that the normal line of the solidified surface is parallel to the freezing direction from the first side to the second side. .

<First embodiment>
As a first embodiment of the method for freezing an aqueous PVA solution, for example, as illustrated in FIG. 1, the plate-like container 2 containing the PVA aqueous solution 1 is gradually inserted into a cooling liquid 3 of less than 0 ° C. There is a method of gradually freezing the PVA aqueous solution 1 inside from the bottom to the top. The manner in which the PVA aqueous solution 1 is gradually frozen from the bottom side to the upper side of the plate-like container 2 is that the cloudy frozen region below the PVA aqueous solution 1 gradually rises to the transparent unfrozen region above. Observed as a state. It is possible to visually observe the interface between the cloudy frozen region and the transparent unfrozen region, and this interface is called a solidified surface (frozen surface).

  Since the container 2 is gradually inserted into the cooling liquid 3 at the time of freezing, the rise of the solidified surface is offset by the lowering of the container 2, and the freezing can proceed so that the solidified surface maintains a constant height. . This will be described with reference to FIG. FIG. 2 is a schematic view of the container 2 of FIG. 1 as viewed from the front. Assuming that the liquid level of the cooling liquid 3 is a reference of height (zero height), when the container 2 is gradually inserted at a relatively slow speed v1, the solid surface height d1 is higher than the liquid level of the cooling liquid 3. Maintained in a high position. This is because the solidification rate of the PVA aqueous solution is larger than v1. On the other hand, when the container 2 is gradually inserted at a relatively fast speed v2, the solidified surface height d2 is maintained at a position lower than the liquid surface of the cooling liquid 3, that is, in the cooling liquid. This is because the solidification rate of the PVA aqueous solution is smaller than v2. Therefore, the height d of the solidified surface can be adjusted by appropriately adjusting the insertion speed v of the container 2 (hereinafter sometimes referred to as the freezing speed).

  In this embodiment, the height d of the solidified surface of the PVA aqueous solution 1 in the container 2 is the liquid surface of the cooling liquid 3 or the region of the solidification temperature (0 ° C.) of water immediately below the liquid surface, or the liquid surface thereof. It is preferable to gradually insert the container 2 into the cooling liquid 3 so as to be located immediately above the lower region. That is, when the temperature of the cooling solution is set in the range of room temperature to −26 ° C., the material and thickness of the container 2 are selected, and the thickness of the sample is set to be approximately the same as the thickness of the material of the container 2, In freezing, it is preferable that the solid surface height d is zero or just below the liquid level.

  Thus, by gradually freezing the PVA aqueous solution from the lower side (first side) to the upper side (second side), the accuracy of the normal of the solidified surface becomes parallel to the freezing direction from the lower side to the upper side. Can be increased. As a result, a fiber structure in which a plurality of submicron fibers are bundled is formed inside the PVA gel obtained later, and the direction of the fiber structure can be aligned in parallel with the freezing direction. A PVA gel in which the orientation of the fiber structure is aligned in parallel has an excellent structural strength with respect to the orientation of the fiber structure.

  With reference to FIG. 3, the relationship between the height d of the solidified surface and the structure of the solidified surface will be considered. FIG. 3 is a schematic cross-sectional view of the PVA aqueous solution in the plate-like container 2 as seen in the thickness direction orthogonal to the height direction.

  When the container 2 is inserted at a relatively slow speed v1, before the liquid level of the cooling liquid 3 is reached, heat is conducted to the already frozen PVA aqueous solution below and the temperature is lowered below the solidification temperature, thereby freezing the upper PVA aqueous solution. Therefore, the height of the solidified surface is located above the liquid level. In this case, since the core portion freezes earlier than the peripheral edge portion of the PVA aqueous solution close to the warm wall surface, the solidified surface tends to be an upwardly convex paraboloid. Therefore, the normal to the solidified surface (arrow in FIG. 3) tends to be non-parallel to the freezing direction (perpendicular to the liquid surface) at the periphery. As a result, the direction of the fiber structure formed according to the direction indicated by the normal line of the solidified surface is different between the core portion and the peripheral portion of the same gel.

  On the contrary, when the container 2 is inserted at a relatively high speed v2, the PVA aqueous solution below the liquid level is obtained by conducting heat from the region that has not been frozen yet after being inserted below the liquid level of the cooling liquid 3. Since the cooling of the liquid is delayed, the height of the solidified surface is located below the liquid level. In this case, since the peripheral portion of the PVA aqueous solution near the wall surface cooled by the cooling liquid 3 freezes before the core portion, the solidified surface tends to be a downwardly convex paraboloid. Therefore, the normal to the solidified surface (arrow in FIG. 3) tends to be non-parallel to the freezing direction (perpendicular to the liquid surface) at the periphery. As a result, the direction of the fiber structure formed according to the direction indicated by the normal line of the solidified surface is different between the core portion and the peripheral portion of the same gel.

  On the other hand, when the container 2 is inserted at a speed v3 at which the height of the solidified surface and the liquid level of the cooling liquid 3 substantially coincide with each other, the low temperature conducted from the already frozen region below and the conduction from the region not yet frozen above. The high temperature is antagonized near the liquid level of the cooling liquid 3. In this case, the peripheral portion of the PVA aqueous solution near the wall surface of the container 2 and the core portion closer to the center are frozen almost simultaneously, so that the solidified surface tends to be a horizontal plane. Therefore, the normal line of the solidified surface (arrow in FIG. 3) tends to be parallel to the freezing direction (perpendicular to the liquid surface) at the peripheral edge and the core. As a result, the direction of the fiber structure formed in accordance with the freezing direction is aligned in the same direction in the core portion and the peripheral portion of the same gel.

As a method for adjusting the relationship between the solidification surface and the height of the cooling liquid 3 to a suitable position as described above, for example, as shown in FIG. 1, using a plate-like container 2 having a plate-like internal space, With the PVA aqueous solution 1 placed in the internal space, the container 2 is placed below 0 ° C. at an insertion speed of 0.01 mm / second to 0.10 mm / second along the longitudinal direction from the bottom side to the top side of the plate-like container 2. There is a method of inserting into the cooling liquid.
The insertion speed is preferably 0.02 mm / second to 0.08 mm / second, more preferably 0.02 mm / second to 0.06 mm / second, and still more preferably 0.02 mm / second to 0.04 mm / second. When the insertion speed is in the above range, a fiber structure aligned in parallel can be easily formed in the PVA gel.

  When the insertion speed is 0.01 mm / second or more and 0.10 mm / second, the structural strength in the fiber orientation direction is high, and the swelling degree is lower than that of the conventional isotropic physical cross-linked PVA gel. The PVA gel having a higher degree of swelling than the high-strength PVA gel can be easily produced. When the freezing rate is 0.08 mm / second or less, the breaking stress in the direction along the fiber structure of the PVA gel can be increased. Here, the breaking stress means the maximum stress that is the limit that the PVA gel can hold without being broken by an external force.

  FIG. 4 shows a schematic perspective view of a PVA gel cut into a rectangular parallelepiped shape. The X direction is a direction along the fiber structure made of PVA, and the Y direction and the Z direction are directions perpendicular to the fiber made of PVA. In this specification, the breaking stress in the direction along the fiber made of PVA refers to the maximum stress that can be held without stretching (stretching) the gel in the X direction. That is, it means the force required to break the fiber structure. The breaking stress in the direction perpendicular to the fiber made of PVA refers to the maximum stress that can be held without being broken by pulling (stretching) the gel in the Y or Z direction. That is, it means the force required to peel off the fibers constituting the fiber structure.

  The shape of the container in which the PVA aqueous solution is put at the time of freezing is not particularly limited. Examples of the container having a length corresponding to the longitudinal direction and the short direction include a plate shape, a cylindrical shape, a rod shape, a box shape, and a spheroid shape. Shaped containers can be mentioned. Here, the shape of the container means the shape of the space that fills the PVA aqueous solution. Therefore, the PVA aqueous solution put in the container and the shape of the PVA gel to be produced follow the shape of the container.

  For example, when a plate-shaped container is used as the container, the thickness direction of the plate is the short direction, and the vertical direction and the horizontal direction of the plate are the longitudinal direction. In this case, inserting the plate-like container containing the PVA aqueous solution into the cooling liquid having a longitudinal direction of less than 0 ° C. means inserting the plate-like container in the vertical direction or the horizontal direction of the plate-like container. In obtaining the effects of the present invention, the insertion direction may be the vertical direction or the horizontal direction. What is important in obtaining the effects of the present invention is that the aqueous PVA solution is gradually cooled from the first end (first side) to the second end (second side) to obtain a solidified surface method. Freezing so that the line is parallel to the freezing direction. An example of this freezing direction is the direction indicated by the normal of the liquid level of the cooling liquid. When frozen as described above, when a PVA gel in which PVA in the PVA aqueous solution is physically cross-linked is formed, along the one direction from the first end to the second end inside the gel, Parallel fiber structures are formed.

The thickness of the plate-like container (that is, the thickness of the PVA aqueous solution that is plate-like when frozen) is preferably 0.5 mm or more, more preferably 0.5 mm to 10 mm, still more preferably 0.5 mm to 5.0 mm. 0.0 mm to 3.0 mm is particularly preferable.
When the thickness is 0.5 mm to 10 mm, the freezing efficiency in one direction from the first end portion to the second end portion during freezing and the freezing efficiency in the thickness direction are increased, and along the one direction. Parallel fiber structures can be easily formed.

  The length and width of the plate-like container are not particularly limited. For example, length × width = 10 cm × 15 cm, length × width = 15 cm × 10 cm, length × width = 50 cm × 50 cm, length × width = 100 cm × 10 cm And the like. These vertical × horizontal sizes can be combined with the preferred thickness sizes described above.

  The wall thickness of the container separating the aqueous PVA solution and the cooling liquid is not particularly limited, but is preferably 1.0 mm to 10 mm, more preferably 1.0 mm to 5.0 mm, and still more preferably 1.0 mm to 3.0 mm. . Within the above range, the heat conduction efficiency between the cooling liquid and the PVA aqueous solution becomes appropriate.

  The material constituting the container is not particularly limited, and synthetic resin, glass, metal, and the like can be applied, but synthetic resin is preferable. When the container is made of a synthetic resin, the heat conduction efficiency on the wall surface of the container becomes appropriate. The kind of the synthetic resin is not particularly limited, and a known resin can be used. Examples thereof include poly (meth) acrylic resin, polyvinyl resin, polyester resin, polyamide resin, and polycarbonate resin. Among these, a transparent resin that allows easy observation of the frozen surface is more preferable.

  If the thermophysical properties of the synthetic resin are similar to the thermophysical properties of the frozen PVA aqueous solution, the heat conduction efficiency during cooling will be moderate, and a fiber structure with even better strength may be formed. This is preferable because it is possible. Here, the thermophysical property means at least one of thermal conductivity and heat capacity.

  The temperature of the cooling liquid is not particularly limited as long as it is a temperature at which the aqueous PVA solution can be frozen. From the viewpoint of easy freezing while growing the fiber structure inside the gel, the temperature of the cooling liquid is not lower than −80 ° C. or higher. It is preferably less than ℃, more preferably from -60 ℃ to less than 0 ℃, and most preferably from -30 ℃ to -10 ℃.

  The kind of the cooling liquid is not particularly limited, and a liquid that can realize the set temperature may be selected as appropriate. In order to obtain the preferable temperature range, it is convenient to use an aqueous solution containing an alcohol-based organic solvent such as methanol, ethanol, or isopropanol.

PVA (polyvinyl alcohol), which is a material of the PVA aqueous solution, preferably has a saponification degree of 95% or more and a polymerization degree of 1000 or more.
The upper limit of the saponification degree of PVA is 100%, but it is preferably less than 100% from the viewpoint of increasing the solubility of PVA.
When the degree of polymerization of PVA is 1000 or more, a high structural strength PVA gel can be obtained. The upper limit of the degree of polymerization is not particularly limited, but is preferably 8000 or less, more preferably 5000 or less, still more preferably 4000 or less, and particularly preferably 3000 or less from the viewpoint of increasing solubility. Usually, the higher the degree of polymerization of the PVA used, the higher the structural strength of the resulting PVA gel. From the viewpoint of increasing the breaking stress of the PVA gel, the polymerization degree of PVA is preferably 1700 or more, more preferably 2400 or more, and further preferably 4000 or more. The PVA having the physical properties exemplified here can be purchased as a commercial product.

The density | concentration of PVA contained in PVA aqueous solution is not specifically limited, Preferably it is 5-25 mass%, More preferably, it is 15-20 mass%.
When the concentration is in the above range, the density of the physical crosslink formed is sufficiently increased, and sufficient structural strength can be imparted to the PVA gel. Moreover, it can prevent that the viscosity of PVA aqueous solution increases and it becomes difficult to inject | pour into a container, and gelatinization of PVA aqueous solution advances during the preservation | save at low temperature.

  The PVA aqueous solution may contain various drugs and functional substances as long as it does not interfere with physical cross-linking of PVA. For example, the functional substance can be supported in the PVA gel to be formed by previously mixing, dispersing, or dissolving the functional substance in the PVA aqueous solution.

Examples of the functional substance include inorganic fine particles such as titanium dioxide, organic molecules such as polysaccharides and proteins, and thermoresponsive polymers such as N-isopropylacrylamide.
The functional substance may be a naturally derived substance or a chemically synthesized substance.
The organic molecule may be a low molecular compound or a high molecular polymer.

  The concentration of the functional substance in the aqueous PVA solution can be, for example, about 1 to 20% by volume, although it depends on the size and physical properties of the functional substance to be used.

<Second embodiment>
As a second embodiment of the PVA aqueous solution freezing method, for example, as illustrated in FIG. 5, a container 12 containing the PVA aqueous solution 11 is placed on a metal base 13 connected to a Peltier element (not shown). A method of gradually cooling the entire bottom surface 12a of the container 12 to about −20 ° C. to −15 ° C. from the bottom to the top of the PVA aqueous solution 11 (in the direction of the arrow in FIG. 5) can be mentioned. At this time, the difference between the water surface 11a of the PVA aqueous solution and the bottom surface 12a of the container is preferably set to about 1 mm to 10 mm. Thus, the PVA aqueous solution 11 that is thinly spread on the bottom surface of the container is not easily affected by the temperature conduction from the side wall of the container 12, and the influence of the temperature conduction due to cooling from the bottom surface of the container 12 acts predominantly. . As a result, the solidified surface F becomes substantially parallel to the bottom surface 12a of the container and the water surface 11a of the PVA aqueous solution, and the normal line of the solidified surface F is in the freezing direction (the direction from the bottom surface of the container 12 toward the water surface of the PVA aqueous solution 11, that is, the PVA aqueous solution. 11 in the direction from the bottom to the top). After freezing the PVA aqueous solution in this way, when the Peltier element is stopped and thawed, a PVA gel in which parallel fiber structures are formed along the thickness direction of the gel (freezing direction, that is, the arrow direction in FIG. 5) is obtained. It is done. Freezing and thawing by the Peltier element can be easily controlled by turning on and off the power source of the Peltier element, so that the freezing and thawing are easily repeated.

≪Method for producing PVA gel≫
The method for producing the PVA gel of the second aspect of the present invention includes the following first to second steps. You may have an auxiliary process other than a 1st process-a 2nd process.

<First step>
The first step is a step of freezing the PVA aqueous solution by the above-described method for freezing a PVA aqueous solution.

<Second step>
The second step is a step of obtaining a PVA gel by thawing the frozen body of the PVA aqueous solution obtained in the first step in an atmosphere of 0 ° C. or higher. For example, a method of thawing the frozen PVA aqueous solution by taking out the container containing the PVA aqueous solution frozen in the first step into an atmosphere of 0 ° C. or higher can be mentioned.
By thawing the PVA aqueous solution frozen in the first step in the second step, a PVA gel in which the PVA in the PVA aqueous solution is physically cross-linked is obtained. The PVA gel thus obtained has an anisotropic network structure.

  The upper limit temperature of the atmosphere of 0 ° C. or higher in the second step is not particularly limited as long as the PVA gel can be stably obtained, and is usually preferably 50 ° C. or lower, more preferably 30 ° C. or lower, and more preferably 10 ° C. or lower. Is more preferable. When the upper limit temperature is 50 ° C. or lower, the target PVA gel can be obtained stably.

  In order to make the shape of the PVA gel conform to the shape of the container, it is preferable that the PVA aqueous solution frozen in the container is not taken out of the container and thawed while being held in the container. The container may be a closed container or an open container (non-covered container).

  Although the PVA aqueous solution thawed in the second step is already gelled, from the viewpoint of further increasing the structural strength by increasing the degree of physical crosslinking (density) in this PVA gel, after the first second step, It is preferable to perform one or more freeze-thaw cycles that freeze again and then thaw. As a specific example, a method of inserting a container containing a PVA gel (thawed body) thawed after the first freezing into the same cooling liquid in the same freezing direction at the same freezing speed in the liquid below 0 ° C again. Is mentioned.

  The total number of freeze-thaw cycles is not particularly limited, but is usually preferably 2 times or more, more preferably 3 times or more, and still more preferably 4 times or more. As the number of repetitions increases, the structural strength of the PVA gel tends to increase. The upper limit of the number of repetitions is not particularly limited, but usually about 10 is appropriate as the upper limit number.

<Third step>
The third step is a step of obtaining a PVA gel by immersing the PVA gel obtained after the second step in water to swell.
When the PVA gel obtained after the second step is immersed in water, the PVA gel absorbs water and swells. By removing from the water after a predetermined time has elapsed, a wet PVA gel sufficiently retaining water (may be referred to as PVA hydrogel) is obtained.

  The time to immerse in water is not specifically limited, It is preferable to immerse until PVA gel reaches equilibrium swelling. Immersion may continue even after the PVA gel reaches equilibrium swelling and the PVA gel no longer swells. The time for the PVA gel to reach equilibrium swelling is usually several hours to several days, although it depends on the shape and volume of the PVA gel.

The water in which the PVA gel is immersed may be purified pure water or an aqueous solution containing arbitrary components depending on the purpose of use.
The temperature of the water in which the PVA gel is immersed is preferably such a temperature that the physical crosslinking of the PVA gel is not released. For example, it is preferably immersed in water at about 4 to 40 ° C.

≪Method for producing PVA gel laminate≫
In the method for producing the PVA gel of the second aspect, a sheet made of PVA gel can be obtained by putting the PVA aqueous solution into a plate-like container. The thickness of the sheet is equivalent to the thickness of the plate-like container. By laminating two or more sheets made of this PVA gel, a PVA gel laminate can be obtained.

The number of sheets to be laminated is not particularly limited, and any number of sheets necessary for the thickness of the laminated body to be manufactured can be stacked.
From the viewpoint of increasing the mechanical strength of the laminate, the thickness of the laminate is preferably 1 mm or more, more preferably 2 mm to 20 mm, and still more preferably 2 mm to 5 mm.

  When laminating and laminating a plurality of the sheets, it is preferable that the fiber structures of the sheets are laminated in a non-parallel direction. The angle formed by the fiber structure direction of the first sheet and the fiber structure direction of the second sheet laminated thereon is, for example, 5 to 90 when viewed from the upper surface (above) of the laminate. In the range of degrees, it can set suitably according to a use purpose and the number of lamination | stacking.

  The structural strength of the PVA gel laminate can be made isotropic by making the fiber structures of the sheets made of a plurality of laminated PVA gels non-parallel to each other, for example, by laminating them so as to be orthogonal to each other. it can. This is because the tensile strength of the PVA gel is strong in the direction along the fiber, and the fiber structure is made non-parallel (non-uniform) between multiple layers, thereby making the tensile strength stronger than that of the conventional FT gel. The direction showing the strength (that is, the direction along the fiber structure) can be achieved by arranging non-parallel or isotropically when all layers are seen through from the upper surface of the laminate. Such a laminate has a structural strength superior to that of a gel made of PVA obtained by a conventional freeze-thaw method, when pulled in any direction.

  When laminating and laminating a plurality of the sheets, it is preferable to swell each sheet in advance with water, apply and laminate a PVA aqueous solution between the sheets, and dry. Thus, by performing swelling, laminating and drying, a network structure composed of PVA (physical cross-linking of PVA in the vicinity of the adhesive surface) can be formed between the layers, and the adhesive strength between the layers can be further increased.

  In the process of forming a network structure composed of PVA between layers, the PVA aqueous solution can be infiltrated into the sheet by applying and laminating the PVA aqueous solution in the gaps between the laminated sheets. The reason why this penetration easily occurs is that, since the microcrystals aggregate in the fiber portion and gel in the sheet, the PVA concentration in the PVA network between the fibers in the sheet is lowered. After the PVA aqueous solution penetrates into the sheet, it is dried to form microcrystals between the PVA in the PVA aqueous solution and between the PVA between the fibers of the sheet, thereby constructing a network. As a result, a PVA gel laminate in which a plurality of sheets are sufficiently bonded is obtained.

  The target PVA gel laminate is obtained by immersing the dried laminate obtained by drying in water and swelling it again.

  The method for swelling the sheet made of PVA gel and the PVA gel laminate is not particularly limited, and may be immersed in water until the equilibrium swelling is reached, for example.

  The method for drying the sheet is not particularly limited, and examples thereof include an air drying method, a method of blowing warm air, and a vacuum drying method.

  The PVA concentration of the aqueous PVA solution applied between the sheets may be the same as or different from the concentration at the time of producing the PVA gel.

The sheet constituting the laminate may carry the above-described functional substance. The position of the sheet carrying the functional substance in the PVA gel laminate can be set to an arbitrary layer.
The sheet carrying the functional substance may form any one of the sheets constituting the PVA gel laminate, or may form any of a plurality of layers.

  According to the method for producing a PVA gel laminate of the present invention, the thickness of the laminate can be arbitrarily controlled by laminating a plurality of sheets made of PVA gel. In addition to this, by changing the composition of the component (for example, the functional substance) in each sheet constituting the laminated body for each layer, the concentration of the component in the laminated body can be gradually inclined.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited by these examples.

≪Preparation of each sample≫
<Preparation of PVA aqueous solution>
PVA powder (model number: PVA117, manufactured by Kuraray Co., Ltd.) having an average degree of polymerization of 1700 and a degree of saponification of 98.00 to 99.00%, and ultrapure water ion-exchanged with a Milli-Q filter after distillation of ion-exchanged water And were used as materials.
By putting this PVA powder and ultrapure water into a screw mouth bottle, preparing to have a PVA concentration of 15.0% by weight, boiling in hot water of 90 ° C. or higher with stirring for 2 hours, and then returning to room temperature, A PVA aqueous solution in which the PVA powder was completely dissolved was obtained.
Using this PVA aqueous solution, a sample was prepared by the following method.

<Preparation of anisotropic gel>
(1) A PVA aqueous solution was poured into a plate-like container prepared by sandwiching a spacer made of silicon rubber having a thickness of 2 mm or 1 mm between two acrylic plates.
(2) As shown in FIG. 1, from the first end 2a (bottom side) of the plate-like container 2 toward the second end 2b (upper side), from v = 0.01 to 0.10 mm / sec. The plate-like container 2 is gradually inserted into the aqueous ethanol solution 3 set at −26 ° C. in the low temperature constant temperature water bath at a selected constant speed, and gradually from the first end to the second end. Frozen. Under the present circumstances, it inserted so that the liquid level of ethanol aqueous solution and the bottom face and water surface of PVA aqueous solution in a container might become horizontal. The plate-like container was completely submerged in an ethanol solution, and after the PVA aqueous solution in the container was frozen, the plate-like container was transferred to a thermostat in an atmosphere of 4 ° C. and kept at 4 ° C. for 6 hours or more to be thawed. This freeze-thaw cycle was repeated 4 times.
(3) The sample prepared in (2) was immersed in ultrapure water for 3 days to obtain an equilibrium swollen PVA gel. Hereinafter, the PVA gel obtained by this production method is referred to as an anisotropic gel.

<Measurement of solidified surface height>
Assuming that the liquid level of the aqueous ethanol solution 3 is a reference of height (zero height), when the container 2 is gradually lowered at a relatively slow speed v1, the height d of the solidified surface of the aqueous PVA solution 1 is It was maintained at a position higher than the liquid level. On the other hand, when the container 2 was gradually lowered at a relatively high speed v2, the height d of the solidified surface was maintained at a position lower than the level of the aqueous ethanol solution 3, that is, in the aqueous ethanol solution. Specific results are shown in FIGS.

  The horizontal axis of the graph of FIG. 6 is set to −26 ° C. in a low-temperature water bath at a constant speed v of 0.01 to 0.10 mm / sec for a plate-like container 2 containing a PVA aqueous solution 1 having a thickness of 2.0 mm. The time during which the ethanol aqueous solution 3 is gradually inserted is shown, and the vertical axis shows the height d of the solidified surface in the plate-like container 2. After 10 minutes from the start of the insertion of the plate-like container 2 (0 minutes), except for the case where the speed was 0.01 mm / second, a stable period in which the height d of the solidified surface was maintained almost constant was entered. . FIG. 7 shows the relationship between the height d and the speed v when the height d becomes substantially constant.

When the thickness of the PVA aqueous solution 1 in the plate-like container 2 is 2.0 mm, when the insertion speed is more than 0.02 and 0.03 mm / second or less, the solid surface height d is in the range of 0 to ± 2 mm. The solidified surface was kept at the same position as the liquid surface of the aqueous ethanol solution 3 (see FIG. 7).
When the thickness of the PVA aqueous solution 1 in the plate-like container 2 is 1.0 mm, when the insertion speed is 0.03 or more and 0.06 mm / second or less, the solid surface height d is in the range of 0 to ± 2 mm. The solidified surface was kept at the same position as the liquid surface of the aqueous ethanol solution 3 (not shown).

  The tip of the temperature sensor is regarded as the bottom surface of the plate-like container 2, the tip is gradually brought closer to the surface of the aqueous ethanol solution 3 at a predetermined speed, and the tip is inserted into the aqueous ethanol solution 3, and the temperature profile at each position is determined. It was measured. This temperature profile is shown in FIG. The vertical axis in FIG. 8 indicates a positive distance away from the liquid surface and a negative distance away from the liquid surface with reference to the liquid surface of the ethanol aqueous solution 3, and the horizontal axis indicates each distance (each position). The temperature at (the temperature at the tip of the sensor) is shown.

  From the result of FIG. 8, at any insertion speed, about 0 ° C. is shown near the liquid surface of the aqueous ethanol solution 3. It shows a temperature much higher than −26 ° C. set in the low temperature water bath. This is due to the fact that the aqueous ethanol solution is not stirred in order to avoid the wave of the liquid surface between the air. In actual measurement, the temperature dropped to −15 ° C. or lower at 3.8 mm below the liquid level. It can be seen that the PVA aqueous solution also has an effect of supercooling and starts freezing not in the interface but in the range of several millimeters immediately below the interface. Therefore, it is considered that the solidified surface height of the PVA aqueous solution should theoretically be 3.8 mm below the liquid surface. However, the tip of the temperature sensor is affected by heat conduction from the upper part of the sensor (sensor body) above, and it is thought that the temperature drop at the tip is slightly delayed, so in fact it is in a range shorter than 3.8 mm. It is considered frozen. On the other hand, when the PVA aqueous solution 1 in the plate-like container 2 is cooled, there is heat conduction (low-temperature conduction) from the previously frozen lower region, so that it is faster than at the tip of the temperature sensor (at a higher position). ) It may be cooled. That is, since the PVA aqueous solution 1 is frozen immediately below the liquid surface of the ethanol aqueous solution 3, it is considered that a cloudy solidified surface of the PVA aqueous solution is observed near the liquid surface.

≪Mechanical test of each sample≫
<Tensile test>
The tensile strength of each sample was measured by the following procedure.
(1) Using a JIS K-6251-8 standard dumbbell cutter (see FIG. 9), a test piece cut out from each sample that was equilibrated and swollen with ultrapure water was prepared. At this time, a test piece was cut out so that the fiber structure of the anisotropic gel was parallel to the tensile direction.
(2) Two test marks were attached to the test piece using food red, and the distance between the test marks was measured with a caliper.
(3) The width and thickness of the test piece were measured using a micrometer.
(4) Using a tensile tester (INSTRON 5965), the test was performed in the air at room temperature while acquiring the image data of the distance between the gauge points.
(5) Based on the image data, the change in distance between the gauge points was measured.
(6) From the obtained data, a relationship diagram between the insertion speed (freezing speed), the maximum stress, the maximum strain, and the initial elastic modulus was created. The initial elastic modulus was obtained from the initial slope of a stress-strain curve (not shown).

As a sample for the tensile test, an anisotropic gel having a thickness of 2.0 mm prepared by the above-described freezing method was used. The results shown in FIGS. 10, 11 and 12 were obtained.
The vertical axis in FIG. 10 represents maximum stress (unit: MPa), and the horizontal axis represents insertion speed (freezing speed). The vertical axis of FIG. 11 represents the maximum strain (unit: none), and the horizontal axis represents the insertion speed (freezing speed). The vertical axis in FIG. 12 represents the initial elastic modulus (Elastic Modulus) (unit: MPa), and the horizontal axis represents the insertion speed (freezing speed).

  From the above results, the anisotropic gel frozen at the insertion speed where the solidified surface height d = 0 ± 2 mm in FIG. 7 is the most excellent structural strength with respect to the maximum stress, the maximum strain, and the initial elastic modulus. showed that. These results reflect that the orientation of the fiber structure formed in the PVA gel is uniformly and substantially parallel along the freezing direction (direction perpendicular to the liquid surface of the ethanol aqueous solution). Conceivable.

  Although the fiber structure observed by the SEM was formed even in the anisotropic gel produced under the condition that the absolute value of the height d of the solidified surface shown in FIG. 7 exceeds 2 mm, the direction of the fiber structure is in the freezing direction. On the other hand, there are some regions with inclinations. It is considered that the structural strength is inferior because there is a region where the fiber structure is uneven.

  The above results were obtained using a test piece cut out so that the fiber structure of the anisotropic gel was parallel to the tensile direction. Instead, an experiment was performed using a test piece cut out so that the fiber structure of the anisotropic gel was perpendicular to the tensile direction. Although detailed experimental results are not shown here, the tensile strength in the parallel direction along the fiber structure of the anisotropic gel is greater than the tensile strength (maximum stress and maximum strain) in the direction perpendicular to the fiber structure of the anisotropic gel. Was found to be much larger.

  The maximum stress of the freeze-thaw gel (FT4 gel) obtained by repeating the freeze-thaw cycle four times by the conventional method described later was measured in the same manner as described above. Although detailed experimental results are not shown here, the results were far inferior to the maximum stress along the direction of the fiber structure of the anisotropic gel. Since no uniform fiber structure is formed in the FT4 gel, a uniform parallel fiber structure formed in one direction in the anisotropic gel is often used to improve the structural strength of the gel. It can be said that it contributes to.

<Mass swelling ratio>
In order to examine the swelling characteristics of each anisotropic gel, the mass swelling ratio was measured. First, an equilibrium swollen gel swollen with ultrapure water was obtained, the water adhering to the surface was wiped off with a paper towel, and the equilibrium swollen mass Wt was measured. This Wt was divided by the mass (dry mass) Wd of the dry film in the dry state before the equilibrium swelling, and the mass swelling ratio Wt / Wd was calculated.

  In a freeze-thaw gel (FT gel) produced by a conventional freeze-thaw method, the degree of crystallinity increases and the mass swelling ratio decreases as the number of freeze-thaw cycles is increased. The mass swelling ratio of the FT4 gel was 6.5. On the other hand, the anisotropic gel produced as described above showed a higher mass swelling ratio than the FT4 gel and a tendency to depend on the insertion speed (freezing speed). The result is shown in FIG. The reason why anisotropic gels exhibit a higher mass swelling ratio than conventional FT gels is that if the insertion speed when freezing in one direction is slowed, the solidified surface height d is in the range from negative to zero, PVA When ice crystals formed when the aqueous solution freezes grow, the aggregation of microcrystals advances, and the crosslink density due to the microcrystals between the fibers decreases, so when a porous structure that easily absorbs water is formed Conceivable. That is, it is considered that the mass swelling ratio is increased because the macro structure of the PVA fiber forms a sparsely packed structure substantially along one direction.

<Production of anisotropic gel (anisotropic D gel) subjected to drying treatment>
In order to further increase the strength of the anisotropic gel, an anisotropic D gel subjected to a drying treatment by the following method was prepared.
(1) In the same manner as in the preparation of the anisotropic gel described above, the outer portion (outer peripheral portion) of the anisotropic gel obtained by repeating the freeze-thaw cycle four times was fixed to the plane of the acrylic plate with an adhesive. . After drying at room temperature until the mass of this anisotropic gel became constant, the outer part to which the adhesive adhered was cut off to obtain a dry film made of PVA.
(2) The dried film prepared in (1) was immersed in ultrapure water for 3 days to obtain a gel that had been swollen in equilibrium. The gel obtained by this production method is hereinafter referred to as anisotropic D gel.

About the produced anisotropic D gel, the maximum stress, the maximum strain, and the initial elastic modulus were evaluated by the tensile test described above. Although detailed test results are not shown here, the structural strength of the anisotropic D gel was significantly improved as compared with the anisotropic gel not subjected to the drying treatment.
As a reason why the anisotropic D gel has such high structural strength, it is considered that a nano-order structural change occurs between the fiber structures.

≪Test with varying number of freeze-thaw cycles in PVA gel production≫
In the method for producing the anisotropic gel and the anisotropic D gel described above, each gel was produced by changing the number of freeze-thaw cycles within a range of 1 to 8. When the physical properties were measured by the measurement methods described above, detailed test results are not shown here, but from the viewpoint of improving the structural strength of anisotropic gel and anisotropic D gel, the freeze-thaw cycle during gel preparation It has been found that the number of times N _FT is preferably 2 times or more, more preferably 4 times or more, and further preferably 6 to 8 times.

≪Test in which PVA concentration of PVA aqueous solution used for preparation of PVA gel was changed≫
By using the material solution in which the PVA concentration of the PVA aqueous solution was changed in the range of 7.5 to 20% by mass, the gel preparation method (the number of freeze-thaw cycles was four) and the anisotropic gel and the different solution An isotropic D gel was prepared. Each physical property was measured by the measurement method described above, and detailed test results are not shown here. However, the structural strength (mechanical strength) is maintained while maintaining the swelling ratio of the anisotropic gel and the anisotropic D gel to some extent. ), The PVA concentration during gel preparation is preferably 10% by mass or more, more preferably 15% by mass or more.

<Preparation of PVA gel laminate and evaluation of structural strength>
(1) A holed petri dish was prepared by hollowing out the central part of a polyethylene petri dish.
(2) Prepare two anisotropic gels that are equilibrated and swollen with water, align the center of the first anisotropic gel with the hole in the petri dish, and It was adhered and fixed to the edge of the hole of the holed petri dish.
(3) A PVA aqueous solution was applied to the upper surface of the fixed first anisotropic gel, and the second anisotropic gel was placed on the upper surface. At this time, the fiber structure direction in the first gel was overlapped with the fiber structure direction in the second gel so as to be orthogonal to each other.
(4) After drying until the mass of the sample became constant at room temperature, the outer part to which the adhesive adhered was cut off to obtain a two-layer dry film.
(5) The dried film produced in (4) was immersed in ultrapure water for 3 days to obtain an equilibrium swollen gel as a PVA laminate.

  Each layer of the obtained PVA gel laminate was sufficiently adhered, and it was difficult to peel off. Moreover, since the fiber structure which each sheet | seat has mutually orthogonally crossed, the PVA gel laminated body showed the tensile strength stronger than the conventional FT4 gel with respect to 2 directions where the fiber structure of each layer is extended.

<Preparation of freeze-thawing gel (FT gel)>
(1) A 15 g PVA aqueous solution was poured into a polyethylene petri dish and sealed.
(2) A cycle in which the petri dish was put into a freezer, frozen at −20 ° C. for 24 hours, and thawed at 4 ° C. for 24 hours was repeated 1 to 4 times.
(3) The sample produced in (2) was immersed in ultrapure water for 3 days to obtain an equilibrium swollen gel (thickness: 2 mm). A gel made of PVA obtained by this production method is referred to as a freeze-thaw (FT) gel in this specification. In addition, according to the number of cycles in which freeze-thaw is repeated, a gel obtained in one cycle is referred to as FT1 gel, and a gel obtained in two cycles is referred to as FT2 gel.

≪Evaluation of physical properties of each sample≫
<Observation of gel structure by SEM>
The difference in the surface structure between the FT4 gel and the anisotropic gel was observed by SEM. The apparatus used was a 3D real surface view microscope VE-8800 (manufactured by Keyence Corporation). Each sample was dried at room temperature and then coated with an Au-Pt alloy. The sample was fixed on the SEM sample stage using a carbon tape, and a vacuum was drawn for observation.

  FIG. 14 is a SEM photograph of FT4 gel (thickness: 2 mm), and FIG. 15 is a SEM photograph of anisotropic gel. This anisotropic gel is an anisotropic gel prepared by freezing in one direction under conditions of a freezing rate v = 0.01 mm / second and a gel thickness of 2.0 mm. A well developed fiber structure was observed inside the gel. Although this fiber structure is generally along the freezing direction, another anisotropy produced under the conditions of a freezing speed of 0.02 to 0.03 mm / sec (that is, a condition where the height d of the solidified surface is almost zero). When the fiber structure of the gel was separately imaged with an SEM, it was observed that the gel was aligned more uniformly and parallel to the freezing direction.

  From the results of the above SEM photograph and the like, it was confirmed that a fiber structure different from the existing FT4 gel was formed on the surface and inside of the anisotropic gel. A network in which individual fibers extend in random directions is formed on the surface and inside of the FT4 gel. On the other hand, on the surface and inside of the anisotropic gel, a bundle structure (fiber bundle structure) in which the fibers are aligned in one direction is formed. Moreover, it can be seen from the SEM photograph that the individual thicknesses of the fiber structure of the anisotropic gel are micrometer size (several micrometers). From this thickness, it is estimated that each fiber is an aggregate of 100 to 1000 microcrystals per unit cross-sectional area.

  The configurations and combinations thereof in the embodiments described above are examples, and the addition, omission, replacement, and other modifications of the configurations can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... PVA aqueous solution, 2 ... Acrylic board, 3 ... Ethanol aqueous solution, 4 ... Silicon rubber spacer, 5 ... Gripper, 11 ... PVA aqueous solution, 12 ... Container, 13 ... Metal base connected to Peltier device, F ... PVA Solidified surface of aqueous solution

Claims (13)

A method of gradually freezing an aqueous PVA solution from a first side toward a second side,
The PVA aqueous solution is moved from the first side to the second side so that the normal line of the solidification surface where the freezing of the PVA aqueous solution proceeds is parallel to the freezing direction from the first side to the second side. A method for freezing an aqueous PVA solution, characterized by gradually cooling the solution.   2. The PVA aqueous solution in the container is gradually frozen from the bottom to the top by gradually inserting the container containing the PVA aqueous solution into a cooling liquid of less than 0 ° C. 2. Freezing method of PVA aqueous solution.   The container is gradually inserted into the cooling liquid so that the solidified surface height of the PVA aqueous solution in the container is located in the region of the solidification temperature of the liquid level of the cooling liquid or water just below the liquid level. The method for freezing a PVA aqueous solution according to claim 2.   The said container is plate shape, The said container is inserted in the said cooling liquid at the speed | rate of 0.01 mm / sec-0.10 mm / sec in the longitudinal direction, The PVA aqueous solution of Claim 3 characterized by the above-mentioned. Freezing method.   The method for freezing a PVA aqueous solution according to claim 4, wherein the thickness of the PVA aqueous solution orthogonal to the longitudinal direction of the container is 0.5 mm to 10 mm.   The method for freezing a PVA aqueous solution according to claim 5, wherein a thickness of the container that separates the PVA aqueous solution from the cooling liquid is 1.0 mm to 10 mm.   The method for freezing a PVA aqueous solution according to claim 6, wherein the material constituting the container is a synthetic resin having substantially the same thermal properties as the PVA aqueous solution. A first step of freezing the PVA aqueous solution by the method according to any one of claims 1 to 7;
And a second step of obtaining a PVA gel by thawing the frozen PVA aqueous solution obtained in the first step in an atmosphere of 0 ° C. or higher.   The method for producing a PVA gel according to claim 8, wherein in the second step, the obtained PVA gel is frozen again and then freeze-thaw cycle is performed once or more.   The method for producing a PVA gel according to claim 8 or 9, further comprising a third step of swelling the PVA gel obtained in the second step by dipping in water.   Production of a PVA gel laminate, wherein a PVA gel laminate is obtained by laminating two or more sheets made of PVA gel obtained by the production method according to any one of claims 8 to 10. Method.   12. The method for producing a PVA gel laminate according to claim 11, wherein when a plurality of the sheets are laminated and laminated, the fiber structures of each sheet are laminated in a non-parallel direction.   13. The PVA gel according to claim 12, wherein when a plurality of the sheets are stacked and laminated, each sheet is previously swollen with water, a PVA aqueous solution is applied between the sheets, stacked, and dried. A manufacturing method of a layered product.