JP4070337B2 - Method for producing cellulose porous body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a porous cellulose material using hydrogel particles as a porogen.
[0002]
[Prior art]
Conventionally, as a sponge used in various fields such as window glass, cleaning of automobiles, cleaning of tableware, bathing, etc., a sponge made of polyurethane has been often used from the viewpoint of performance. However, a polyurethane sponge has a problem that a toxic gas such as cyan gas is produced as a by-product during incineration. In addition, there is a problem that even if this is disposed of in landfill, it remains without being biodegraded. Therefore, recently, from the viewpoint of environmental protection, cellulose sponges such as viscose sponges having high biodegradability have attracted attention. Since this has high water absorption, it can be used in the above-mentioned fields.
[0003]
Various methods for producing viscose as a raw material are known as methods for producing the cellulose sponge. For example, a method of producing a cellulose sponge by adding reinforcing fibers and crystalline mirabilite to viscose, putting it in a mold, solidifying by heating, and then completely regenerating using acid, washing the mirabilite with water or warm water, is a special method. This is disclosed in Japanese Patent Publication No. 36-10992 and Japanese Patent Publication No. 36-11982.
[0004]
In addition, a method of using calcium carbonate as a porosifying agent instead of the above-mentioned crystal mirabilite, that is, mixing calcium carbonate with viscose, coagulating the viscose, removing the calcium carbonate by acid decomposition, and making it from cellulose A method for producing a sponge is disclosed in JP-A-63-92602.
[0005]
In this case, unlike the case where crystal mirabilite is used, calcium carbonate is an inorganic salt that is sparingly soluble in water, so it does not dissolve during viscose mixing and does not cause salting out and solidification of the viscose. There is no need to carry out the step, and the amount of voids depends on the amount of calcium carbonate used.
[0006]
Furthermore, as another porous means, a method using foaming of carbon dioxide gas by reaction of calcium carbonate and acid is disclosed in Japanese Patent Laid-Open No. 3-231942. In this method, calcium carbonate as a foaming agent is mixed in viscose and immersed in a coagulation regeneration solution containing an acid, thereby simultaneously coagulating the viscose and making it porous by the generation of carbon dioxide gas. Reproduction is performed. This is not a method of forming voids by the shape of the inorganic crystal particles themselves, but is made porous by carbon dioxide gas generated by the reaction between calcium carbonate and acid. Since it is gas foaming, the calcium carbonate is very small in quantity, and it does not clog the T-die or the like and can be continuously extruded. Further, the decomposition and removal of calcium carbonate can be performed quickly, and the manufacturing time can be shortened.
[0007]
[Problems to be solved by the invention]
However, in the above method using crystalline mirabilite as a porogen, the mirabilite itself is water-soluble, so that the crystalline mirabilite begins to dissolve during dispersion into viscose, and finally the viscose is salted out and solidified. . Therefore, in practice, in order to minimize the dissolution of the crystalline salt cake, it is necessary to mix while cooling to the lowest possible temperature and promptly move to the next step. Furthermore, it is necessary to use the crystal mirabilite in excess of the target void amount in anticipation of dissolution during raw material preparation.
[0008]
Furthermore, in order to obtain a high porosity, it is necessary to use a large excess of crystalline mirabilite, and viscose mixed with a large amount of crystalline mirabilite is not itself fluid but also has hard crystalline particles. Therefore, for example, when extrusion molding is performed with a T die or the like, particles are caught in a narrow gap inside the die, and the flow path is immediately closed, making it impossible to form a continuous sheet.
[0009]
For these reasons, the above-mentioned method using crystalline mirabilite as a porosifying agent is a mixture of viscose and crystalline mirabilite once placed in a mold, heated and solidified, then cooled and taken out of the molded body from the mold, An acid treatment process and a water washing process will be performed, and it will become a batch type process as a whole. Moreover, even if heating temperature is 90-100 degreeC and high temperature, 3 to 4 hours are required for an acid treatment process. Furthermore, since the crystalline sodium sulfate remaining in the regenerated cellulose does not elute immediately, it takes a considerable amount of time in the water washing step to completely remove it. That is, although this method can obtain a porous porous body having a high porosity, it has a drawback that it takes a lot of labor and time for production.
[0010]
In addition, the above-mentioned method of adding calcium carbonate as a porosifying agent to viscose, heating and coagulating, and acid decomposition to remove calcium carbonate consumes a large amount of acid for complete decomposition of calcium carbonate. In addition, since calcium carbonate is not removed unless it comes into contact with an acid, when the solidification of the viscose proceeds, it becomes difficult for the acid to penetrate inside, and the decomposition of calcium carbonate is delayed. For this reason, the undecomposed product of calcium carbonate tends to remain. Therefore, even in this method, it takes time to completely remove the porous agent.
[0011]
Furthermore, the above-mentioned method in which calcium carbonate and acid are brought into contact with each other and made porous by gas foaming is such that when calcium carbonate and acid react, solidification of viscose has already progressed to some extent from the surface, and once solidified However, since pore formation with carbon dioxide gas no longer proceeds, the formation of voids is naturally limited, and it is difficult to obtain a high porosity. On the other hand, even if the amount of calcium carbonate is increased in order to obtain a high porosity, part of the carbon dioxide gas that actually contributes to the formation of voids is only gradually leaking out of the porous body. is there. This is the same even if the acid temperature is raised to increase the amount of carbon dioxide generated. In addition, if the viscose is diluted with water to delay the coagulation, the foaming efficiency is improved, but the cellulose concentration in the viscose actually decreases, so the shrinkage due to drying becomes more severe and the high porosity is increased. You can't get anything. Furthermore, the strength is significantly reduced.
[0012]
Accordingly, an object of the present invention is to provide a method capable of overcoming the drawbacks of the prior art and producing a porous cellulose body having a high porosity in a shorter time.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention is characterized in that the hydrogel particles are mixed with an alkaline cellulose solution, molded and coagulated, the cellulose is regenerated and heated to elute the hydrogel particles. To do.
[0014]
Since water-containing gel particles are used as the porosifying agent, it is possible to prevent salting out and coagulation of the alkaline cellulose by dissolving into the alkaline cellulose solution as in the case of crystal mirabilite. Moreover, when elastic hydrous gel particles are used, the extruding can be performed without crushing the porous agent or closing the die or the like during extrusion. For this reason, it is possible to shape | mold a porous cellulose sheet | seat by continuously extruding the alkaline-type cellulose solution which added the hydrogel particle | grains as a porous agent, for example from T-die etc.
[0015]
In addition, the size and amount of voids formed inside the porous cellulose body can be controlled by the size and amount of water-containing gel, and the porosity is not limited as in the case of calcium carbonate. It is possible to obtain a high porosity corresponding to the above.
[0016]
Furthermore, when using a large amount of water-containing gel as the porosifying agent, the water-containing gel is quickly heated to its melting point or more so that the porosifying agent quickly enters a solution state and flows out to the outside. There is no need for an operation for dissolving the crystals with running water over a long period of time as in the case of crystal mirabilite or an acid decomposition treatment as in the case of calcium carbonate, and the operation can be performed in a short time.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0018]
In the method for producing a porous cellulose material according to the present invention, hydrous gel particles are used as a porous agent, mixed with an alkaline cellulose solution, molded and coagulated, regenerated cellulose, and heated to produce the hydrogel particles. This is an elution method.
[0019]
The alkali-type cellulose solution is obtained by reacting raw material cellulose under alkaline conditions and dissolving it. The origin of the cellulose of the above raw material is not particularly limited, and for example, pulp, cotton, hemp and the like can be used. Examples of the alkaline cellulose solution include viscose, cellulose copper ammonia solution, and cellulose carbamate solution. Among these, viscose, particularly viscose for cellophane production is preferable. Further, when viscose is used as the alkaline cellulose, the concentration of cellulose contained is preferably 3 to 15% by weight, and preferably 4 to 10% by weight. If it is lower than 3% by weight, the mechanical strength of the regenerated cellulose is low, and crushing or cutting may occur during production.
[0020]
On the other hand, when the content is higher than 15% by weight, the viscosity is remarkably increased although the degree of polymerization is entangled, and it becomes difficult to uniformly disperse and extrude the porous agent or the like.
[0021]
Furthermore, the alkali concentration in the viscose is preferably 2 to 15% by weight, preferably 5 to 13% by weight in terms of sodium hydroxide. Furthermore, the ammonium chloride value in the viscose is preferably from 3 to 12, and preferably from 4 to 9.
[0022]
The water-containing gel particles are not particularly limited as long as they have gelling ability and thermally reversibly undergo sol-gel transition and are water-soluble in a sol state. By using the water-containing gel particles, it is possible to quickly obtain a cellulose porous body having a high porosity. Examples of such water-containing gel particles include water-containing gel particles such as agar, κ-carrageenan, ι-carrageenan, galactomannan, xanthan gum, gelatin, and collagen.
[0023]
Among these, it forms an elastic gel, can exist stably in an alkaline cellulose solution, and has a feature that its melting point, that is, the temperature at which the gel transitions to the sol is relatively low. Gelatin is most preferred. The type of gelatin may be either alkali-treated gelatin or acid-treated gelatin.
[0024]
When gelatin hydrogel particles are used as the hydrogel particles, the molecular weight of gelatin is preferably 15,000 to 250,000, and preferably 60,000 to 100,000. This molecular weight affects the strength of a gel at a predetermined concentration, so-called jelly strength (JIS K 6503). As gelatin jelly strength to be used, 100 to 300 bloom is generally preferable, and 150 to 200 bloom is preferable. If the jelly strength is lower than 100 bloom, the gelatin gel is likely to be broken during mixing with the alkaline cellulose solution. If it is higher than 300 bloom, the gel is not easily deformed. There is a case.
[0025]
As a method for obtaining the above-mentioned gelatin-containing hydrogel particles, powdery gelatin may be directly added to water or an alkaline cellulose solution to swell, and used as a particulate gel, or once with hot water. A solution may be used and then cooled to below the gelation temperature to obtain a gel, which may be crushed. For the method of obtaining hydrous gel particles other than gelatin, a gelling agent may be required. Usually, however, the solution is once heated with hot water, and then cooled to below the gelation temperature to obtain a gel. A grinding method is employed. In addition, although melting | fusing point of gelatin gel is dependent on gel concentration, generally it is 20-36 degreeC. For this reason, it is necessary to keep the temperature below the melting point of the gelatin gel so as not to be transferred to the sol when mixed into the alkaline cellulose solution. The same applies to other hydrogel particles.
[0026]
The gel concentration of the hydrous gel particles is preferably 1 to 40%, and preferably 10 to 20%. When the gel concentration is lower than 1%, the strength of the gel may become extremely low, and it may be finely broken during mixing and stirring of the raw materials, thereby impairing the effect as a porous agent. On the other hand, if it is higher than 40%, the water-containing gel particles may absorb the water in the alkaline cellulose solution, and mixing and stirring may not be possible.
[0027]
Since the size of the void formed in the porous cellulose body depends on the particle size of the hydrogel to be added, the particle size of the hydrogel to be added may be selected according to the size of the void to be formed.
[0028]
The porosity of the cellulose porous body can be increased with the addition amount of the water-containing gel particles, but the addition amount of the water-containing gel particles is 0.05 to 100 times the cellulose content in the alkaline cellulose solution. Well, 0.8 to 50 times is preferable. If it is less than 0.05 times, voids are hardly formed, so it is difficult to form a porous body. On the other hand, if it exceeds 100 times, the mechanical strength of the molded product is significantly reduced and continuous production becomes difficult. There is.
[0029]
Since the cellulose porous body obtained by the above production method is porous, there are cases where sufficient wet strength cannot be obtained. In this case, reinforcing fibers may be added to the mixture of the alkaline cellulose solution and the hydrogel particles (hereinafter referred to as “molding mixture”) for the purpose of giving the cellulose porous body strength. The type of the reinforcing fiber is not particularly limited as long as it does not hinder mixing and dispersion in the alkaline cellulose solution and extrusion molding. Examples of this include natural fibers such as hemp, cotton and pulp, regenerated fibers such as rayon, semi-synthetic fibers such as acetate, inorganic fibers such as carbon fibers and glass fibers, or a mixture of two or more of them. Can do. These fibers may be modified by physical, chemical, or biological techniques.
[0030]
The length of the reinforcing fiber is 0.5 to 10 mm, preferably 2 to 6 mm, although it depends on the type of fiber. When the thickness is less than 0.5 mm, the reinforcing effect by the fibers is difficult to appear, and when the thickness exceeds 10 mm, the fibers are easily tangled with each other during dispersion mixing, and a pill-like shape is easily formed and the die is easily clogged.
[0031]
The addition amount of the reinforcing fiber is adjusted according to the degree of reinforcement and the purpose, but is preferably 5 to 200% by weight with respect to the cellulose content in the alkaline cellulose solution. If it is less than 5% by weight, the reinforcing effect due to the fibers hardly appears, and if it exceeds 200% by weight, the molding mixture becomes hard and loses its fluidity, or depending on the fibers, it tends to clog the dies during extrusion molding.
[0032]
There is no particular limitation on the order and method of mixing the hydrogel particles and the reinforcing fibers with the alkaline cellulose solution. In some cases, it can be used in combination with other porosifying agents.
[0033]
The method for molding the alkaline cellulose solution and the hydrogel particles and the molding mixture in which the reinforcing fibers are mixed as necessary may be either a batch type or a continuous type. Moreover, each process of coagulation | solidification after a shaping | molding, a reproduction | regeneration, and the elution of a water-containing gel particle can be performed by either a batch type or a continuous type.
[0034]
Examples of a method for continuously forming, coagulating, regenerating and elution of the water-containing gel particles of the molding mixture include a method using an apparatus as shown in FIG. That is, the molding mixture 1 is stored in the liquid storage tank 2, and the molding mixture 1 is sent from here to the die 4 by the supply pump 3. By the die 4, the molding mixture 1 is extruded to form a continuous molded body 5. The extrusion method is not particularly limited, and any die can be used as the die 4. The die type to be used can be selected according to the flow characteristics of the molding mixture 1 and the shape and size of the target molded body. By using an annular die or the like, a molded body such as a prismatic shape, a columnar shape, or a cylindrical shape can be obtained.
[0035]
The type of the supply pump 3 is not limited as long as it can perform smooth and quantitative liquid feeding, can be stably pushed out from the die, and does not destroy the hydrogel particles. An example is a screw pump. Further, instead of the supply pump 3, a mechanism for feeding liquid from the liquid reservoir 2 to the die 4 by air pressure may be employed. This air pressure can be generated by using a compressor or the like.
[0036]
The formed body 5 formed by the die 4 is solidified by being immersed in a coagulating liquid 7 in the coagulating tank 6. If a coagulating liquid containing an acid is used, it can be regenerated into cellulose simultaneously with coagulation. As the coagulation liquid 7, there are various concentrated salt solutions, organic solvents, and the like. In order to regenerate cellulose simultaneously with coagulation of the alkaline cellulose solution, inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, benzoic acid, etc. The organic acid is preferred. Among these, sulfuric acid is more preferable in that coagulation regeneration proceeds rapidly and the acid is relatively difficult to volatilize.
[0037]
When sulfuric acid is used as the coagulating liquid 7, the concentration is preferably 1 to 20% by weight, and preferably 5 to 10% by weight. If it is less than 1% by weight, it takes time to coagulate the alkali-type cellulose solution. If it exceeds 20% by weight, the coagulation regeneration is abruptly caused, resulting in non-uniform shrinkage and significant deformation of the molded body.
[0038]
In the coagulation liquid 7, inorganic neutral salts such as sodium chloride, potassium chloride, ammonium chloride, sodium sulfate and magnesium sulfate may be mixed singly or in combination for the purpose of promoting coagulation of the alkaline cellulose solution. it can.
[0039]
In addition, the coagulating liquid 7 is heated to the melting point or higher of the water-containing gel particles, and elution is performed by solification of the water-containing gel particles simultaneously with the coagulation regeneration, thereby speeding up the formation time of the cellulose porous body.
[0040]
The molded body 5 fed from the die 4 is solidified while being moved by the guide roller in the solidified liquid 7 and is sent to the regenerated liquid 10 in the regenerating tank 9 by the driving roller 8. The regeneration tank 9 is a tank provided for completely regenerating alkali-type cellulose into cellulose and at the same time eluting hydrogel particles. As the regenerating solution 10, the acids shown in the coagulating solution 7 can be used. Further, the temperature of the regenerating liquid 10 is set to be equal to or higher than the melting point of the water-containing gel particles. Thereby, the water-containing gel particles in the molded body 5 are eluted in the regenerating liquid 10.
[0041]
The regenerating liquid 10 may have the same acid concentration as the coagulating liquid 7, but may have an acid concentration higher than that of the coagulating liquid 7 for the purpose of shortening the regenerating time. Furthermore, the regeneration time can be shortened by setting the temperature of the regenerating liquid 10 higher than the temperature of the coagulating liquid 7.
[0042]
The coagulating liquid 7 and the regenerating liquid 10 can be prevented from becoming nonuniform in temperature and concentration of each liquid by circulating with the circulation pump 11. In addition, the regenerated solution 10 contains a hydrated gel particle lysate. By replenishing the regenerated solution as appropriate, it is possible to always carry out the regeneration reaction under certain conditions.
[0043]
After the gap formation and cellulose regeneration are performed, the molded body 5 is squeezed by the driving roller 12 and the nip roller 13, and the gelatin solution remaining inside the molded body 5 is squeezed out and sent to the washing tank 14. Therefore, the molded body 5 is washed with water or warm water 15 to obtain a porous cellulose body.
[0044]
In the production of this porous cellulose body, if necessary, a step of bleaching treatment with sodium hypochlorite or the like and a step of softening treatment with glycerin, diethylene glycol, triethylene glycol or the like are inserted, and the cellulose porous body after drying is inserted. It is possible to improve the texture and feel of the body. In particular, when viscose is used as the alkaline cellulose solution, a desulfurization process using sodium sulfide or the like may be inserted after the regeneration process.
[0045]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
[0046]
In the following, “%” indicates “% by weight”. As for the porosity, first, the bulk specific gravity (g / cm 2) is calculated from the weight and volume of the dried sample cut into 10 cm square.^Three), And then the true specific gravity (g / cm) using a pycnometer by the water displacement method^Three) And the porosity was calculated from the following equation. However, samples were collected at random, and the average value of n = 10 was used as the porosity of each example and each comparative example.
[0047]
Porosity (%) = (true specific gravity−bulk specific gravity) / true specific gravity × 100
Further, the wet tensile strength was measured by using a universal testing machine under a tensile speed of 50 mm / min as a JIS K7113 No. 1-1 / 2 dumbbell-shaped test piece after the dried sample was dipped and wetted again in water. (N = 10). In addition, MD in wet tensile strength shows that it was pulled along the flow direction of the machine, and CD shows that it was pulled along the direction perpendicular to the flow direction of the machine.
[0048]
Example 1
Viscose for cellophane production (cellulose concentration 9.5%, ammonium chloride number 7, alkali concentration 5.6%, viscosity 5,500 centipoise) 10kg and hemp fiber (length 6mm, thickness 5d) 570g in a kneader After stirring and mixing, 20 kg of gelatinous hydrogel particles (average particle size 2.5 mm) were added as a porosifying agent, and the mixture was stirred and mixed at a temperature of 20 ° C. or lower to prepare a molding mixture for molding. In addition, the gelatin-containing gel particles described above were prepared by adding 4 kg of dried gelatin powder (Nitta Gelatin Co., Ltd. # 150, jelly strength 150-180 bloom) to 16 kg of water at 20 ° C. or lower and stirring the gelatin completely. Swelled in water and pulverized to an average particle size of 2 to 3 mm.
[0049]
This molding mixture was cast on a 30 cm × 50 cm glass plate so as to have a thickness of 4 mm, and immersed in a coagulating solution of 6.8% sulfuric acid containing 180 g / l sodium sulfate for 5 minutes to solidify.
[0050]
Next, the solidified molded body was separated from the glass plate and immersed in a regenerated solution of 9.1% sulfuric acid for 15 minutes. Since this regenerated solution is heated to 40 ° C., the gelatin gel particles as a porogen are eluted to form voids, and further, the acid penetrates into the molded body to completely regenerate the cellulose. did. Next, the gelatin solution remaining inside was squeezed out with a mangle, and the compact was washed with warm water of 40 ° C.
[0051]
Further, this molded body was desulfurized with a 3 g / l sodium sulfate aqueous solution heated to 70 ° C., and then bleached with a 0.3% sodium hypochlorite aqueous solution. Next, the molded body was sufficiently washed with water, and then dried with hot air at 120 ° C. until the water content became about 10% to obtain a sheet-like cellulose porous body.
[0052]
The thickness of this sheet is 3.2 mm, the porosity is 94.8%, and the wet strength is 3.5 kgf / cm.²Met. When the cross section was observed with a scanning electron microscope, it was confirmed that a very porous structure was formed.
[0053]
(Example 2)
A molding mixture was produced as in Example 1. Cellulose porous bodies were continuously produced from this molding mixture using the apparatus shown in FIG. Specifically, a screw pump was used as the supply pump 3, and the molding mixture 1 was supplied at 500 ml / min to a coat hanger die (lip width 30 cm, gap 4 mm) as a kind of die 4. Since this coat hanger die is installed in the upper part of the coagulation tank 6 having a 6.8% sulfuric acid coagulation liquid 7 containing 180 g / l sodium sulfate, it is formed into a sheet extruded by the coat hanger die. The molded body 5 is immersed in the coagulating liquid 7 and solidified.
[0054]
Next, the solidified sheet-like molded body 5 was fed into a regenerated solution of 9.1% sulfuric acid. Since the regenerated solution 10 is heated to 40 ° C., the gelatin gel particles used as the porosifying agent are eluted to form voids, and further, the acid penetrates into the inside of the sheet 5 and the cellulose Completed playback. Then, the gelatin solution remaining inside the sheet 5 was squeezed out by the nip roller 13, sent to the water washing tank 14, and washed with warm water 15 at 40 ° C.
[0055]
Further, the sheet 5 was desulfurized with a 3 g / l sodium sulfate aqueous solution (not shown) heated to 70 ° C., and then bleached with a 0.3% sodium hypochlorite aqueous solution (not shown). And after washing | cleaning the sheet | seat 5 sufficiently, it dried with the hot air of 120 degreeC until the moisture content became about 10%, and obtained the continuous cellulose sheet.
[0056]
The sheet 5 has a thickness of 2.9 mm, a porosity of 94.2%, and a wet tensile strength of MD 6.1 kgf / cm.²CD 3.1 kgf / cm²Met. Moreover, when the cross section was observed with the scanning electron microscope, as shown in FIG. 2, it was confirmed that it is a very porous structure.
[0057]
(Example 3)
A continuous cellulose sheet was obtained in the same manner as in Example 2 except that hydrous gel particles of agar were used as the porogen and that the regenerated solution 10 and the warm water 15 in the washing tank 14 were set to 95 ° C. . The gel particles of agar were dissolved by adding 4 kg of agar powder (manufactured by Nacalai Tesque Co., Ltd .; reagent) to 16 kg of hot water at 95 ° C., cooled to 20 ° C., and gelled. It was obtained by pulverizing to 2 to 3 mm.
[0058]
The thickness of this sheet is 2.3 mm, the porosity is 92.8%, and the wet tensile strength is MD 2.7 kgf / cm.²CD1.5kgf / cm²Met. Moreover, when the cross section was observed with the scanning electron microscope, it was confirmed that it was a very porous structure.
[0059]
Example 4
Example 2 except that a cellulose copper ammonia solution (copper concentration 4.0%, ammonia concentration 9.8%, cellulose concentration 5.7%) was used instead of viscose, and desulfurization treatment was not performed. In the same manner, a continuous cellulose sheet was obtained.
[0060]
The thickness of this sheet is 2.8 mm, the porosity is 93.3%, and the wet tensile strength is MD 2.9 kgf / cm.²CD1.4kgf / cm²Met. Moreover, when the cross section was observed with the scanning electron microscope, it was confirmed that it was a very porous structure.
[0061]
(Example 5)
Viscose for cellophane production (cellulose concentration 9.5%, ammonium chloride number 7, alkali concentration 5.6%, viscosity 5,500 centipoise) 10kg, hemp fiber (length 6mm, thickness 5d) 570g, and water 16kg After stirring and mixing in a kneader, 4 kg of gelatin dry powder (Nitta Gelatin Co., Ltd. # 150, jelly strength 150 to 180 bloom) is directly added while maintaining the temperature at 20 ° C. or lower. Was completely swollen with water to obtain hydrogel particles, thereby preparing a molding mixture. The following operations were performed in the same manner as in Example 2 to obtain a continuous cellulose sheet.
[0062]
This sheet has a thickness of 2.8 mm, a porosity of 94.1%, and a wet tensile strength of MD 5.9 kgf / cm.²CD 2.9kgf / cm²Met. Moreover, when the cross section was observed with the scanning electron microscope, it was confirmed that it was a very porous structure.
[0063]
(Comparative Example 1)
Instead of using gelatin gel particles as the porosifying agent, 30 kg of crystal mirabilite having an average particle diameter of 2.5 mm was used, and the mixture was stirred and mixed at 10 ° C. in order to avoid dissolution of the crystal mirabilite as much as possible. Similarly, preparation of a porous cellulose was attempted. However, the coagulation liquid and the regenerated liquid hardly permeate the inside of the molded body, and therefore, the regeneration of cellulose did not progress easily. Therefore, the coagulation liquid and the regeneration liquid were heated to 95 ° C. Still, it took 1 hour to regenerate cellulose. Thereafter, washing with water was performed to completely remove the crystalline mirabilite, which is a porous agent, but it took 1 hour.
[0064]
The thickness of this sheet is 2.8 mm, the porosity is 92.1%, and the wet tensile strength is MD 3.9 kgf / cm.²CD 2.9kgf / cm²Met. Moreover, when the cross section was observed with the scanning electron microscope, it was confirmed that it was a very porous structure.
[0065]
(Comparative Example 2)
Example 2 is the same as Example 2 except that 30 kg of crystal mirabilite having an average particle diameter of 2.5 mm was used instead of gelatin gel particles as a porosifying agent, and stirring and mixing was performed at 10 ° C. in order to avoid dissolution of the crystal mirabilite as much as possible. Similarly, continuous extrusion was attempted. However, the die was immediately closed and a continuous molded product could not be obtained.
[0066]
(Comparative Example 3)
Instead of using gelatin gel particles as a porous agent, 2.85 kg of calcium carbonate as a foaming agent (SS # 30, average particle size 7.4 μm, manufactured by Nippon Flour & Chemical Co., Ltd.) is used at room temperature. Continuous molding was attempted in the same manner as in Example 2 except that the mixture for stirring was mixed to form a molding mixture, and the coagulating liquid 7 and the regenerating liquid 10 were both 7.1% hydrochloric acid at 60 ° C. A typical cellulose sheet was obtained. However, due to the low mechanical strength of the sheet when wet immediately after coagulation regeneration, the sheet was often cut during the continuous operation. The thickness of this sheet is 1.7 mm, the porosity is 88.0%, and the wet tensile strength is MD1.4 kgf / cm.²CD 0.9kgf / cm²Met. Further, when the cross section was observed with a scanning electron microscope, as shown in FIG. 3, it was porous, but the porosity was low and there were many dense portions.
[0067]
result
In Example 1, a porous cellulose material was obtained by a batch-type treatment, but the porosity was very high, and a similar cellulose porous material could be obtained even when continuously produced using the same molding mixture. It was. Moreover, in any case of Examples 2-4, the mixture for shaping | molding can be continuously extruded in a favorable state, without obstruct | occluding a die | dye, Moreover, in any case, a water-containing gel is promptly in a reproduction | regeneration tank. The eluted voids were formed. As a result, the permeation of the acid into the molded body was accelerated, and the cellulose porous body having a uniform void structure with a high void ratio was obtained.
[0068]
On the other hand, in Comparative Example 1, since the porosifying agent did not elute quickly, the acid could not permeate and it took time for coagulation regeneration. Furthermore, it took time to completely remove the porous agent by washing with water. Further, in Comparative Example 2, crystal mirabilite, which is a water-soluble salt and hard particles, was used, so that the die was clogged and could not be continuously extruded into a sheet shape. Further, as in Comparative Example 3, when calcium carbonate was used, the temperature of the acid was increased for the purpose of increasing the porosity, and a large amount of calcium carbonate was used. Not only was not obtained, but also the strength was low.
[0069]
【The invention's effect】
According to the present invention, since the hydrogel particles are used as the porosifying agent, the porosifying agent quickly flows out as a solution when heated to a temperature higher than the melting point of the hydrous gel. Can do. Thereby, the penetration of the acid into the molded body is fast, and the regeneration of the cellulose is also performed quickly.
[0070]
Further, since the hydrogel particles do not block the extrusion port such as the T-die or the flow path, it is advantageous for continuous extrusion molding.
[0071]
Furthermore, when the hydrous gel particles having elasticity are used, the porous agent can be extruded without being crushed or clogging dies during extrusion molding.
[0072]
In the present invention, since it is possible to obtain a porous body having a high porosity according to the amount of hydrous gel that is a porous agent, for example, continuous production of a porous cellulose body having excellent liquid absorbency is performed. It is possible.
[0073]
In addition, the size and amount of voids formed inside the porous cellulose body can be controlled by the size and amount of water-containing gel, and the porosity is not limited as in the case of calcium carbonate. It is possible to obtain a high porosity corresponding to the above.
[0074]
Furthermore, when the communicating holes are formed with a porous agent, the hydrogel quickly becomes a solution and flows out to the outside just by heating the hydrous gel above its melting point. The operation of dissolving the crystals with running water and the time for the acid decomposition treatment as in the case of calcium carbonate are not required, and the operation can be performed in a short time.
[Brief description of the drawings]
FIG. 1 is a schematic process diagram showing an example of a method for producing a porous cellulose material according to the present invention.
FIG. 2 is a cross-sectional photograph of a sheet-like cellulose porous material obtained in Example 2 using a scanning electron microscope.
FIG. 3 is a cross-sectional photograph of a sheet-like cellulose porous material obtained in Comparative Example 3 using a scanning electron microscope.
[Explanation of symbols]
1 Molding mixture
2 Liquid reservoir
3 Supply pump
4 dice
5 Molded body
6 Coagulation tank
7 Coagulation liquid
8 Drive roller
9 Regeneration tank
10 Regenerating solution
11 Circulation pump
12 Driving roller
13 Nip roller
14 Flush tank
15 Hot water

Claims (1)

A method for producing a porous cellulose body, comprising mixing hydrogel particles in an alkaline cellulose solution, shaping and coagulating, regenerating cellulose, and eluting the hydrogel particles by heating.

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