JPH0621179B2 - Method for producing porous polymeric material for artificial muscle - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a material for artificial muscle, and can be used as a small actuator that is a drive source for robots, medical equipment, artificial limbs, and the like.

[Prior Art] Certain polymeric materials have the property of reversibly expanding and contracting when the environment solution to be immersed is replaced with acid-alkali, water-alcohol, water-acetone, or the like. Such a polymer material is called a mechanochemical material, and is expected to be applied as a small and highly efficient actuator that is soft and light. For example, Japanese Patent Application No. 60-254042 (Japanese Patent Publication No.
3-10192) and Japanese Patent Application No. 60-254043 (Japanese Patent Publication No. 63-10193).

[Problems to be Solved by the Invention] With respect to mechanochemical materials, it has been a major problem to improve responsiveness and output density (output per unit volume).

Regarding the responsiveness, the material is formed into a fine fiber shape or a thin film shape in order to increase the contact area with the environmental solution,
When these materials are bundled and used as an artificial muscle, the materials come into close contact with each other, the permeability of the solution when the environmental solution is exchanged is poor, and the responsiveness is still insufficient.

In order to solve this responsiveness problem, it is considered that not only the mechanochemical material is formed into a fine fiber shape or a thin film shape, but also a large number of through holes are uniformly dispersed and formed on almost the entire surface of the material. . This allows the environmental solution to penetrate to the inner layers of the bundled material.

On the other hand, however, if a large number of through holes are formed, the strength of the material may be reduced and the output density may be reduced.

The present invention has been made in view of the circumstances as described above, and a through-hole having a pore size large enough to enhance the permeation effect of the solution when the environmental solution is exchanged is formed into a fine fibrous or thin film mechanochemical. It can be formed by being almost evenly distributed in the material, so the response speed can be made sufficiently fast to be applied as an artificial muscle, and the size of the pore diameter and the mechanics of the pore wall part can be changed depending on the purpose of use of the artificial muscle. It is an object of the present invention to provide a method for producing a porous polymer material for artificial muscle, which is capable of controlling the physical properties and retaining the required elasticity and strength.

[Means for Solving the Problems] To solve this problem, the method for producing a porous polymeric material for artificial muscle of the present invention is a method in which a mixed aqueous solution of polyvinyl alcohol and a polymer electrolyte is frozen at room temperature. In the method for producing a porous polymer material for artificial muscle, which comprises repeating the freeze / thaw process for thawing twice or more, the temperature drop rate of the frozen object immediately before freezing is formed in the porous polymer material for artificial muscle. It is characterized in that the larger the hole diameter, the slower it is adjusted according to the size of the macro hole.

[Operation] In the method for producing the porous polymer material for artificial muscle configured as described above, the mixed solution is repeatedly frozen and thawed twice or more. When it freezes, phase separation occurs, and an aggregation region where water is aggregated is formed, while the concentration of the polymer compound increases around it. When this is thawed and frozen again, phase separation proceeds further, the aggregation region of water expands, and the concentration of the polymer compound further increases around it. When the freezing / thawing process is repeated twice or more, preferably about ten times or more, the water agglomeration region becomes pores, and pore walls are formed around the pores.

What is important here is that in each freezing / thawing process, the rate of temperature decrease immediately before freezing is adjusted depending on the purpose of use of the porous polymer material for artificial muscle to be formed.

That is, when used for the purpose of driving a load or the like by contracting under a load, a large contracting force, that is, mechanical strength, and a good initial responsiveness are desired. The temperature drop rate is slowed down (decreased).

This is because as the freezing rate slows down, the phase separation in the material after freezing progresses better and the aggregation region of each water expands better, and at the same time, the portion containing macromolecules around the aggregation region. It is considered that because the concentration is higher, the cross-linking is easily promoted, and the foamed shape of the communicating cells gradually forms a dense wall. Therefore, when the frozen material is thawed, the water agglomeration region becomes pores, and the pore diameter becomes larger as the temperature decrease rate becomes smaller, and a denser pore wall is formed around the pores as the temperature decrease rate becomes smaller. . As a result, good initial responsiveness, high contraction rate when a load is applied,
A strong mechanochemical porous polymer material for artificial muscle is formed.

The more you want the shrinkage rate to be high when there is no load, and the shorter it takes to complete the operation (sensors, display materials, etc. may be considered for such applications), The temperature drop rate is increased (increased).

In this case, by repeating freezing and thawing, a large number of pores are formed, but phase separation does not proceed so much and each pore has a small pore diameter. Also, since the hole wall does not become a very dense layer,
There is no slow penetration of the environmental solution in the resulting material, the time to reach equilibrium is relatively short, and the operation is completed faster than with larger pore sizes. In addition, the shrinkability under no load is better than that when the pore size is large.

[Embodiment] Hereinafter, details of the present invention will be described with reference to the drawings illustrating an embodiment.

FIG. 1 is an explanatory view showing a method for producing a porous polymer material for artificial muscle of the present invention.

First, the mixed aqueous solution 2 as a raw material is prepared. The mixed aqueous solution 2 is a mixed aqueous solution of polyvinyl alcohol and a polyelectrolyte, and here, as the polyelectrolyte, one of (I) an acidic polyelectrolyte and a basic polyelectrolyte (II) an acidic polyelectrolyte Two types of basic polyelectrolytes are considered, and in each case they are mixed at a predetermined molar ratio (the above-mentioned Japanese Patent Application Nos. 60-254042 and 60-60).
254043).

As the mixed aqueous solution 2, a well-stirred, preferably well-stirred one that has been further cured is used, and the mixture is sealed in a mold for thin film formation. As a method of realizing such a mold, for example, a method of casting between two glass plates via a spacer having a height (for example, 110 μm) corresponding to the thickness of the thin film to be molded can be adopted. .

The freeze / thaw process is repeated twice or more, preferably about 10 times. At this time, freezing has a temperature decrease rate of −0.
10 ° C below zero so that 001 ° C / sec to -100 ° C / sec
Or, it is performed by leaving it in an environment of 270 ° C. below zero. But -1
It is considered that it can be used even at 000 ° C / sec. To obtain such a decrease, for example, liquid nitrogen, liquid helium or the like can be used. The thawing is performed, for example, by leaving it at room temperature and then drying to obtain a porous material for artificial muscle.

Here, an important point of the present invention is that the slow / fast temperature drop rate of the frozen object immediately before freezing of each time is determined by the macropores having large diameters among the pores to be formed in the porous material for artificial muscle. It is to adjust according to the size of the pore size, and the larger the pore size, the slower the temperature drop rate immediately before each freezing.

According to the experiment described below, the slower the temperature drop rate of the frozen object immediately before freezing, the larger the pore size of the macropores formed in the porous material for artificial muscle as a result, which improves the initial responsiveness. It is known that the larger the hole diameter of the macropores, the denser the pore wall and the greater the contraction force under load, that is, the greater the mechanical strength. It is known that the faster the temperature drop rate of, the better the stretchability of the porous material for artificial muscle when no load is applied, and the faster the completion of the operation. Accordingly, the temperature decrease rate immediately before freezing is selected.

[Experimental example] (1) Composition of mixed aqueous solution 2 Polyvinyl alcohol (product name Kuraray 117H, molecular weight 74,800, saponification degree 99.6% or more) and polyacrylic acid (product name SP2, molecular weight about 170,000) , Polyallylamine hydrochloride (Nitto Boseki, molecular weight about 60,000
0) are mixed in a base molar ratio of 1.74: 0.245: 0.26, respectively, and stirred well.

(2) Curing condition Curing refers to a process of keeping the temperature within a predetermined temperature range for a predetermined time. Here, the curing temperature is 25
The temperature and the curing time were 11 days. The reason for selecting this curing condition is that, as shown in FIG. 6, the output density of the produced gel is maximum under this curing condition. 6th here
The figure shows the results of an experiment in which the material was uniaxially stretched during gelation and the elasticity was increased in one direction. The restraining direction is the case where a load is applied in the stretching direction, and the vertical direction is the stretching direction. This is the characteristic when a load is applied perpendicularly to the direction.

(3) A mixed aqueous solution 2 satisfying the above (1) and (2) sandwiched between two 0.8 mm-thick glass plates through a 110-μm-thick spacer and sealed with a 10 μm-thick polyvinylidene chloride film. The freezing and thawing process is carried out for the following. In order to change the temperature drop rate immediately before freezing, the following A,
Three freezing methods of B and C were used.

A: Put it in a polyethylene bag with a thickness of 40 μm and freeze it in ethanol cooled to 50 ° C below zero. B: Make a 2 mm thick silicon rubber plate into a 60 mm × 35 mm × 95 mm box and freeze it in a freezer at -50 ° C. C: embedded in a gel of the same material having a thickness of 4 mm and frozen in a freezer at 50 ° C. below zero, and frozen by each of the above methods, and thawed at room temperature. The freeze-thaw process was repeated 10 times to prepare a gel. . The reason that 10 times was selected as the number of times of freezing and thawing was originally intended to be stronger if the number of times was further increased, but this number that was considered to be the minimum necessary for comparing each production method was selected (No. (See Fig. 7). At this time, when a thermocouple (copper-constantan 50 μm diameter) was inserted into each undiluted solution and the temperature was measured, the temperature drop rate immediately before freezing was: A: −3.78 [° C./sec] B: −7.66 × 10 ^{− 2} [° C./sec] C; −3.29 × 10 ⁻² [° C./sec] (see FIG. 8).

To investigate the microstructure of these gels, the gel film pieces were placed in liquid nitrogen slush and rapidly frozen, kept at -15 ° C and depressurized with a vacuum pump.
The water was sublimated and dried overnight. At this time, the size of the gel shrank to 72%, 65% and 70% of the original sizes of A, B and C, respectively.

In the SEM photograph obtained by depositing this on gold, the macropores of A, B, and C each have a pore diameter of A of approximately 1 μm or less, B of approximately 1 to 2 μm, and C of approximately 2 μm or more. It was found that the size of the macropores corresponded to the slow and fast temperature drop, and the slower the temperature drop rate immediately before freezing, the larger the pore size.

The characteristics of the gel caused by these differences in macropore structure are shown in FIGS. 2, 3, 4, and 5.

Fig. 2 shows the change over time in the contraction rate until the equilibrium contraction rate is reached when a load of 1 kg / cm ² is applied. FIG. 3 shows the case of changing.

According to FIG. 3, when no load is applied, the shrinkage rate increases as the temperature drop rate immediately before freezing increases, and the tendency reverses when a load is applied, and the shrinkage rate increases as the temperature drop rate immediately before freezing decreases. Therefore, it can be seen that C, which has the slowest temperature drop rate immediately before freezing, has a small decrease in shrinkage rate with an increase in load.

FIG. 4 shows the relationship between tensile stress applied to the gel film and strain. According to FIG. 4, it can be seen that the slower the temperature drop rate immediately before freezing, the smaller the strain and the better the elasticity, that is, the higher elastic modulus.

It can be seen from FIGS. 3 and 4 that the slower the temperature drop rate immediately before freezing is, the stiffer the gel becomes and the larger the elastic modulus is.

Further, FIG. 5 shows the time change of the contraction process after the injection of acetone. This is the time response without loading.

The responsiveness of C is good at the beginning of the contraction process.

This shows that the large initial pore size of C improves the initial response.

On the other hand, in FIG. 5, the responsiveness of C deteriorates at the end of the contraction process. It is considered that this is because the response of the dense portion of C was slow. It is considered that the responsiveness at the final stage of the contraction process is improved when the uneven distribution of the dense parts is small.

[Effects of the Invention] As is clear from the above description, according to the present invention, through-holes having a pore size large enough to enhance the permeation effect of the solution when the environmental solution is exchanged are formed into a fine fiber shape or a thin film shape. It can be formed in a mechanochemical material by being almost evenly distributed, and therefore the response speed (initial and final) can be made sufficiently fast to be applied as an artificial muscle, and depending on the purpose of using the artificial muscle, Controlling the size of the hole diameter and the mechanical properties of the wall of the hole depending on whether the contraction under load or the contraction under no load is intended to ensure the necessary elasticity and strength. It is possible to obtain a method for producing a porous polymer material for artificial muscle which is capable of

[Brief description of drawings]

FIG. 1 is an explanatory view showing a method for producing a porous polymer material for artificial muscle according to an embodiment of the present invention, and FIG. 2 is 1 kg / cm.
Graph showing while applying a ^second load to the specimen of the artificial muscle for porous polymer material the relation between time and shrinkage from immersed in acetone, to FIG. 3 the relationship of the load and the equilibrium shrinkage ratio obtained by multiplying the sample The graph shown in FIG. 4, FIG. 4 is a graph showing the relationship between stress and strain applied to the sample, FIG. 5 is a graph showing the time change of the contraction process of the sample, and FIG. 6 is the constraint on the relationship between the load applied to the sample and the output density. Direction and vertical direction, FIG. 7 is a graph showing the relationship between load and shrinkage ratio by the number of freeze / thaw processes, and FIG. 8 shows the relationship between time and temperature during freezing of A, B and C. It is a figure.

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Claims (3)

[Claims] 1. A method for producing a porous polymer material for artificial muscle, which comprises freezing a mixed aqueous solution of polyvinyl alcohol and a polyelectrolyte and thawing at room temperature, and repeating the freezing / thawing process twice or more. The artificially characterized in that the temperature drop rate of the immediately preceding frozen object is adjusted to be slower as the pore size is larger, depending on the size of the macropores to be formed in the porous polymer material for artificial muscle. Method for producing porous polymeric material for muscle 2. The artificial body according to claim 1, wherein the temperature decrease rate of the frozen object immediately before freezing is −0.01 ° C./sec or less and −100 ° C./sec or more. Method for producing porous polymeric material for muscle 3. The porosity for artificial muscle according to claim 1, further comprising a curing step of keeping the mixed aqueous solution at room temperature in a sealed state before the first freeze / thaw step. Method for producing polymer material