JP4868773B2 - Polyurethane porous body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyurethane porous body which has very uniform porous structure in all area of layer and has very fine open pores even if it was a thick porous body, which is superior in water absorbing speed, and of which the dimentional stability is good. <P>SOLUTION: The polyurethane porous body is obtained by crosslinking-reacting a polyurethane resin emulsion using 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro[5,5]undecene or 1,4-bis(3-aminopropyl)piperazine as a crosslinking agent to a water-soluble urethane prepolymer in the presence of a water-soluble polymer compound, then by gelling it; and is characterised in that the water-soluble urethane polymer is the water-soluble urethane prepolymer of which the end isocyanate group is masked by sodium bisulfite. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a urethane porous body having completely continuous voids, such as a water absorbent roll, a cosmetic puff, a polishing pad for various semiconductors or optical materials, an ink retaining material, a liquid absorbing pad for board laver production, artificial leather, synthetic leather, etc. The present invention relates to a porous polyurethane material that can be suitably used in various product fields utilizing the properties of the material.

  Conventionally, a polyurethane porous body has been subjected to heat-sensitive gelation of a polyurethane resin emulsion in the presence of a water-soluble polymer such as carboxymethyl cellulose, hydroxyethyl cellulose, carboxyethyl cellulose, carboxypropyl cellulose or starch. Thereafter, it is produced by crosslinking reaction with a crosslinking agent, insolubilization, and washing with water.

  In this production method, after completion of the crosslinking reaction, the water-soluble polymer that is no longer necessary must be washed with water and completely removed, which requires a considerable amount of time and is extremely inefficient. It was also a cause of loss of productivity.

  Therefore, in order to increase the productivity of polyurethane porous bodies, it is necessary to improve the reactivity of the polyurethane resin emulsion to thermal gelation and to develop a technology to completely remove the water-soluble polymer from the porous body after the crosslinking reaction. Although it has been sought after, it has not yet been fully resolved.

  As a method for producing a polyurethane porous body that solves such problems, a so-called forced emulsification type polyurethane resin emulsion is used, and a water-soluble polymer compound is added as a viscosity modifier as necessary, and the forced emulsification type polyurethane resin emulsion is added. There is a method for producing a polyurethane porous body using a water-soluble polyisocyanate compound as a crosslinking agent.

  The water-soluble polyisocyanate compound used as a crosslinking agent in this case is a water-soluble or water-dispersible polyisocyanate compound in which a prepolymer having an isocyanate group at the terminal is masked with sodium bisulfite, methyl ethyl ketone oxime, phenol or the like. The moisture content in the polyurethane resin emulsion dissociates the masked isocyanate group, and this free terminal isocyanate group reacts with the polyurethane resin, forming a strong molecular structure and insolubilizing the water-resistant open cell. It is considered that the polyurethane porous body having

  However, at the stage where the terminal isocyanate group masked with sodium bisulfite, methyl ethyl ketone oxime, phenol or the like in the water-soluble or water-dispersible polyisocyanate compound is dissociated, the liberated isocyanate group is separated from water molecules which are low molecular compounds in the emulsion. There is a strong tendency to react preferentially, and the cross-linking reaction with a polyurethane resin coated with an emulsifier is not preferred. In addition, the reaction between water molecules and isocyanate groups always generates carbon dioxide (carbon dioxide) and releases it into the water, which accumulates in the center of the porous body and causes the formation of coarse cells. The resulting polyurethane porous body becomes a coarse cell or a large cell, or causes cracking, and it is difficult to obtain a polyurethane porous body having uniform fine pores.

  In order to avoid such inconveniences, for example, oxazoline compounds, epoxy compounds, carbodiimide compounds, and the like have been studied as crosslinking agents other than isocyanate compounds, but all of them have reactivity with urethane resins in the presence of moisture. The gelling effect on the polyurethane resin emulsion of the main agent accompanying the crosslinking reaction is extremely low, and it was difficult to obtain a polyurethane porous body having the desired fine pores.

  In order to suppress this phenomenon, a formulation that makes the block structure of polyurethane emulsion particles strong in the heat-sensitive gelation stage of polyurethane resin emulsion has been studied, and polyvinyl methyl ether, polyacrylamide, polyethylene glycol, polyethylene glycol / polypropylene have been studied. Studies have been conducted on a method for producing a polyurethane porous body by using an organic compound such as glycol-modified silicone oil and an inorganic compound such as sodium sulfate, sodium carbonate and calcium chloride.

  For example, there is a method in which a high-viscosity compounded solution obtained by adding a water-soluble inorganic salt such as sodium carbonate or calcium chloride to a dimethylformamide (DMF) solution of a polyurethane resin is gelled in water. It was difficult to completely remove the holes, and it took a long time of 24 to 48 hours for complete gelation.

  Generally, when a polyurethane porous body is obtained by heat-sensitive gelation of a polyurethane resin emulsion and then crosslinking reaction with a cross-linking agent, the polyurethane resin emulsion particles form a strong block structure at the stage of heat-sensitive gelation. While maintaining the structure, the polyurethane resin is linked and gelled by heating, and in this process, a cross-linking agent such as a water-soluble polyisocyanate compound reacts with the polyurethane resin to form an even stronger molecular structure and insolubilizes. It is considered to be a polyurethane porous body having open cells excellent in water resistance.

  Therefore, an important factor in producing a dense porous body is the formation of a strong block structure between polyurethane resin emulsion particles and the connection / gel of polyurethane resin by heating while maintaining the block structure. It can be said that it is chemical fusion.

Based on this viewpoint, the present inventor previously examined the composition of the water-soluble polyisocyanate compound, which is a crosslinking agent for the polyurethane resin in the polyurethane resin emulsion, and the amount of the water-soluble polyisocyanate compound. It has been proposed to obtain a dense polyurethane porous body by thermal-gelling a polyurethane resin emulsion while chain-extending with a diamine compound as a crosslinking agent (Patent Document 1). However, although the obtained polyurethane porous body has a uniform cell structure, it has a disadvantage that the water absorption rate is slightly low and the dimensional stability is slightly lacking, and further improvement is required. is the current situation.
JP 2003-48940 A

  Therefore, in view of the above situation, the present invention has a porous structure that is extremely uniform throughout the layer, has fine continuous pores, has excellent water absorption speed, and has dimensional stability, even if it is a thick porous body. It is an object to provide a good polyurethane porous body.

The present invention for solving such problems has, as a basic aspect, polyurethane resin emulsion as 3,9-bis (3-aminopropyl) -2,4,8,10- as a crosslinking agent for water-soluble urethane prepolymer. Using tetraoxaspiro [5.5] undecane or 1,4-bis (3-aminopropyl) piperazine, a basic skeletal structure of the porous body is obtained by crosslinking reaction in the presence of a water-soluble polymer compound. After the formation, the polyurethane porous body is obtained by gelling the polyurethane emulsion by heating to be integrated with the skeleton structure.

  In a specific embodiment of the present invention, the polyurethane porous body is characterized in that the water-soluble urethane prepolymer is a water-soluble urethane prepolymer in which a terminal isocyanate group is masked with sodium bisulfite.

  Furthermore, this invention is a polyurethane porous body whose water-soluble high molecular compound is sodium alginate as a specific aspect.

  As a more specific embodiment, the present invention is a polyurethane porous body characterized in that the gelation step is performed in the presence of triethylenediamine, triethylamine, tripropylamine or tributylamine.

  That is, the present invention increases the cohesive force in water by using an amine compound having a specific heterocyclic group in the gelation reaction system as a crosslinking agent for the water-soluble urethane prepolymer in the polyurethane resin emulsion. One feature is to obtain a polyurethane porous body having continuous pores.

The polyurethane porous material provided by the present invention is a 3,9-bis (3-aminopropyl) -2,4,8,10-, which has not been studied at all as a crosslinking agent for a water-soluble urethane prepolymer. Tetraoxaspiro [5.5] undecane or 1,4-bis (3-aminopropyl) piperazine is used. By using such a crosslinking agent, the obtained polyurethane porous body is excellent in dimensional stability when wet, has good water absorption, is extremely dense, and has continuous pores.

  That is, the present invention forms a continuous porous skeletal structure by causing a polyurethane resin emulsion to undergo a crosslinking reaction in the presence of a specific amine compound as a cross-linking agent for a water-soluble polyurethane prepolymer, and in or on the surface of the skeletal structure. By fixing the polyurethane emulsion particles, the urethane emulsion particles gelled by heating lose the emulsified state and are completely taken into the skeletal structure to form a porous body excellent in dimensional stability. The generation of giant cells observed when using conventional water-soluble polyisocyanate compounds can be avoided, and even in the case of thick porous bodies, the porous structure throughout the layer is extremely uniform and dense, and dimensional stability This has the advantage that a good polyurethane porous body can be obtained.

  Therefore, the polyurethane porous body provided by the present invention has extremely fine continuous pores, has a good touch, and has a water absorbing roll, a cosmetic puff, a polishing pad such as various semiconductors or optical materials, and an ink. It has the advantage that it can be suitably used for a holding material, a liquid absorbing pad for producing plate seaweed, an artificial leather base material, a synthetic leather base material and the like.

As described above, the basic aspect of the present invention is 3,9-bis (3-aminopropyl) -2,4,8,10-tetraoxaspiro [5.5] as a cross-linking agent for a water-soluble urethane prepolymer . A polyurethane porous material obtained by gelling a polyurethane emulsion after crosslinking reaction in the presence of a water-soluble polymer compound using undecane or 1,4-bis (3-aminopropyl) piperazine Is the body.

  As the polyurethane resin emulsion that can be used in the present invention, basically, either a forced emulsification type polyurethane resin emulsion or a self-emulsification type polyurethane resin emulsion can be used. It is good to do. The self-emulsifying polyurethane resin emulsion means any polyurethane resin resin having a carboxylic acid group. For example, dimethylolpropionic acid, dimethylolbutanoic acid and the like have a carboxylic acid group in the molecule. It can be obtained by copolymerizing a polyhydroxy compound.

  On the other hand, the forced emulsification type polyurethane resin emulsion means a forcibly emulsified polyurethane resin emulsion having no carboxylic acid group. Further, it has a self-emulsifying polyurethane resin emulsion structure, and a surfactant may be used in combination in order to improve the emulsion stability.

  The polyurethane resin emulsion is composed of a polyol component and a polyisocyanate component. Examples of the polyol component include polypropylene glycol, polytetramethylene glycol, poly-2-methyltetramethylene glycol, polybutanediol adipate, poly- 3-methylpentanediol adipate, poly-1,6-hexanediol adipate, polyneopentyl glycol adipate, poly-3-methylpentanediol carbonate, polynonanediol carbonate, polyethylene glycol adipate, polycaprolactone, poly-β-methylvalero Lactone and the like can be used alone or in combination.

  Furthermore, as the short-chain diol compound as the polyol component, 1,3-butanediol, 1,4-butanediol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, 3-methylpentanediol, nonane Diols, octanediols, glycols such as dimethylolheptane and the above-mentioned dimethylolpropionic acid and dimethylolbutanoic acid can be used.

  Moreover, a short chain diamine compound can also be used as a chain extender. Examples of such short-chain diamine compounds include hexamethylene diamine, ethylene diamine, isophorone diamine, norbornene diamine, bis (p-aminophenyl) methane, bis (4-aminocyclohexyl) methane, hydrazine, piperazine, and tetraethylenepentamine. Can be used.

  As described above, the self-emulsifying polyurethane resin emulsion is obtained by emulsifying and dispersing under alkaline conditions such as triethylamine using, for example, dimethylolpropionic acid or dimethylolbutanoic acid as part of the chain extender, The particle diameter is as extremely fine as about 0.01 to 0.1 μm.

  On the other hand, the forced emulsification type polyurethane resin emulsion mainly uses a nonionic surfactant or a combination of a nonionic surfactant and an anionic surfactant in an amount of about 3 to 5% by mass based on the urethane resin. It is emulsified, and its particle size is about 0.1 to 1 μm, about 10 times larger than that of the self-emulsifying type, and the surfactant is not completely removed even after washing with water after gelation. When the heat fusion at the time of drying is insufficient, the dimensional stability is impaired.

  For this reason, a method for producing a polyurethane porous body by using a water-soluble urethane polymer in a polyurethane resin emulsion has been studied. However, in the case of a self-emulsifying polyurethane resin emulsion, the diamine compound used as a crosslinking agent can be used under alkaline conditions. Thus, the triethylamine used for emulsifying and dispersing the resin was substituted and could not react with the regenerated isocyanate group of the water-soluble urethane prepolymer, and the intended polyurethane porous body could not be obtained.

  Therefore, further studies were conducted to examine various diamine compounds that act as a crosslinking agent for the regenerated isocyanate group (dissociated isocyanate group) of the water-soluble urethane prepolymer, and the diamine compound having a specific heterocyclic structure was converted to both amino groups. The present invention was completed by confirming that the cohesive force between them was high and that good results were obtained.

  That is, in the self-emulsifying type polyurethane resin emulsion, due to its ultrafine particle size, the regenerated isocyanate group in the water-soluble urethane prepolymer reacts with the diamine compound as a crosslinking agent and precipitates, along the water-soluble polymer chain. When the porous body is formed, it is considered that the self-emulsifying polyurethane resin emulsion is completely taken in, and an extremely dense porous body is formed.

In this case, the water-soluble urethane prepolymer is a water-soluble polyisocyanate compound used as a raw material for forming a continuous porous skeleton structure for a polyurethane resin emulsion. Sodium bisulfite (NaHSO ₃₎ is added to the prepolymer having a terminal isocyanate group. ) Is most preferably used because it can easily dissociate the isocyanate group under temperature conditions close to room temperature, suppresses the heat flow inside the mold during heating, and forms a uniform cell.

  In this case, the components of the urethane prepolymer include polyethylene glycol, polypropylene glycol, polyethylene glycol / polypropylene glycol block copolymer, polytetramethylene glycol, tetrahydrofuran / 2-methyltetrahydrofuran random copolymer, polybutanediol adipate, Addition reaction of dihydroxy compounds such as polyethylene glycol adipate, polyhexanediol adipate, polyneopentyl glycol adipate, and poly-3-methylpentanediol adipate with diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, and toluene diisocyanate A prepolymer having an isocyanate group at the end. After, sodium bisulfite isocyanate group of the terminal is obtained by masking (block) in methyl ethyl ketone oxime, compound such as phenol. In addition, the preferable range of the reproduction | regeneration density | concentration of a terminal isocyanate group is 1.5-7.5 mass%.

  The blending ratio of the urethane resin solid content in the polyurethane resin emulsion and the urethane resin component in the water-soluble urethane prepolymer is converted into the content ratio of dissociated isocyanate groups (regenerated isocyanate groups) in the prepolymer, and is 100/150 to It is in the range of 100/250, more preferably in the range of 100/170 to 100/230. That is, the content ratio of the dissociated isocyanate group in the water-soluble urethane prepolymer is preferably in the range of 1.5 to 7.5% by mass. The amount of the water-soluble urethane prepolymer used is 150 with respect to the polyurethane resin emulsion. It is in the range of -250% by mass, preferably 150-250% by mass.

As a diamine compound used as a crosslinking agent for the water-soluble urethane prepolymer in the present invention, 3,9-bis (3-aminopropyl) -2,4,8 as a chain extender excellent in dimensional stability when wet is used. , 10-tetraoxaspiro [5.5] undecane or 1,4-bis (3-aminopropyl) piperazine.

  The diamine compound is a chain extender excellent in dimensional stability when wet, and it is presumed that the heterocyclic ring in the skeleton increases the cohesive strength of the gel. The amount used is preferably in the stoichiometric range of 0.8 to 1.0 with respect to the regenerated isocyanate group of the urethane prepolymer. If it is less than 0.8, the generation of carbon dioxide due to the reaction with moisture becomes remarkable, and it becomes difficult to form fine cells.

Among the diamine compounds previously proposed by the present inventor (Patent Document 1), methyliminobispropylamine preferably used is not only symmetric in chemical structure but also has a flexible structure. It has been considered that the polyurethane porous body to be produced has a large elongation, and as a result, the tear strength can be increased. However, the water absorption rate and dimensional stability are not so favorable. On the other hand, the diamine compound used in the present invention is water-soluble because it is a heterocyclic structure having an oxygen atom and a nitrogen atom, unlike an aromatic diamine, and has a strong skeletal structure. In particular, it has been found that a polyurethane porous body having a very fine microstructure is produced with a small water swelling ratio, and a good water absorption rate and dimensional stability.

  In the gelation / crosslinking of the polyurethane resin emulsion of the present invention, a water-soluble polymer compound may be further added in addition to the above-described polyurethane resin emulsion, water-soluble urethane prepolymer and diamine compound.

  Such a water-soluble polymer compound is considered to adsorb a polyurethane resin emulsion and a water-soluble urethane prepolymer to form a porous body precursor skeleton structure. For this reason, the properties required for this water-soluble polymer compound are preferably those capable of forming hydrogen bonds with the urethane emulsion particles and acting as a thickener for the polyurethane resin emulsion.

  In the present invention, generally usable as a water-soluble polymer compound, for example, polyvinyl pyrrolidone, polyvinyl methyl ether, carboxymethyl cellulose, ammonium polyacrylate, sodium polyacrylate, polyacrylamide, polyethylene glycol, diisocyanate-modified polyethylene glycol Etc. were found to be undesirable. That is, for example, diisocyanate-modified polyethylene glycol is presumed to have an amino group in the terminal or skeleton structure in the production process, and is considered to inhibit the polymerization of the water-soluble urethane prepolymer.

  Therefore, in the present invention, sodium alginate is preferable as the water-soluble polymer compound to be used. The addition amount of the water-soluble polymer compound is preferably in the range of 0.1 to 3% by mass, more preferably in the range of 0.5 to 1.5% by mass with respect to the total urethane resin amount. In addition, it is preferable to add what was previously prepared as aqueous solution for a water-soluble polymer compound.

  In the present invention, in order for the water-soluble urethane prepolymer added with sodium bisulfite to efficiently react with the diamine compound serving as a cross-linking agent to form a porous body, initial solidification near room temperature is important. For this purpose, an alkalinity imparting agent as a catalyst for promoting the reaction between isocyanate and amine is required.

  Examples of such alkalinity imparting agents include tertiary amine compounds that do not react with dissociated isocyanate groups (regenerated isocyanate groups) in water-soluble urethane prepolymers, and specifically include triethylenediamine, triethylamine, and tripropyl. Examples thereof include amines and tributylamine.

  In this invention, the preferable range of the total solid content concentration in the compounding liquid of resin which prepares a polyurethane porous body is 15-30 mass%, More preferably, it is the range of 18-26 mass%. If it is less than 15% by mass, the solid content is insufficient, a uniform cell cannot be formed, and a density difference occurs vertically in the mold, resulting in non-uniformity. Moreover, when it exceeds 30 mass%, the viscosity is high, the contained air cannot be removed, and pinholes are easily generated.

  In order to form the polyurethane porous material provided by the present invention, it is important to perform the gelation step in two stages. That is, first, near the room temperature, for example, at 10 to 25 ° C., the regenerated isocyanate compound in the water-soluble urethane prepolymer and the diamine compound as a cross-linking agent are reacted with each other, so that the heat flow does not occur. Form the body.

  Next, the gelation of the emulsion particles is promoted by heating, and the emulsion particles are completely fixed in the gelled structure, whereby the formation of the porous body is completed. This heating gelation step is preferably achieved by heating to 80 to 95 ° C. When gelation is completed by heating, the skeletal structure is smaller than the initial mold size, and the water-soluble polymer compound added in the initial stage is ejected as foreign matter from the porous body structure, and its removal can be performed very easily. Become.

  In the gelation and crosslinking reaction in the present invention, other components commonly used in polymer chemistry such as a colorant, an antibacterial agent, an antifoaming agent, and a thickener are used in combination as necessary. It goes without saying that you can do it.

The polyurethane porous body of the present invention formed under these conditions is greatly improved from the conventional polyurethane porous body in which the water absorption rate is 60 seconds or more, and the crystallinity and cohesion between urea bonds are improved. As a result of the improvement, the water swelling rate also decreased, and the swelling rate that can be used in the field of water-absorbing rolls was achieved.

  Therefore, the porous polyurethane material provided by the present invention is, for example, as a sheet-like material, a bed as a care medical product, a health and welfare product, a puff for cosmetics, an abrasive sheet, an agricultural material, an electronic device manufacturing related material, an air cleaner It can be used for various products such as equipment filters and artificial leather substrates.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in more detail, it cannot be overemphasized that this invention is not what is limited to these Examples.

Examples 1-5 :
Each component was uniformly mixed with a stirrer according to the formulation shown in Table 1 below. Next, this mixture was placed in a container made of sus304, sealed, and allowed to stand at room temperature for 30 minutes, and then immersed in a heating medium at 60 ° C. and kept in that state for 2 hours. After completion of the reaction, it was washed with water and dried to obtain a polyurethane porous body of the present invention.

  The water absorption rate, swelling rate, and cell size of the obtained polyurethane porous body were measured, the results were comprehensively evaluated, and the results were shown together in the table.

* 1: E4500: Daiichi Kogyo Seiyaku Co., Ltd., forced emulsification type non-yellowing urethane resin emulsion * 2: AP12: Nikka Chemical Co., Ltd., forced emulsification type non-yellowing urethane resin emulsion * 3: AL45: Nikka Chemical Co., Ltd. Made of water-soluble urethane polymer (sodium bisulfite block type)
* 4: APP: 1,4-bis (3-aminopropyl) piperazine * 5: ATOU: 3,9-bis (3-aminopropyl) -2,4,8,10-tetraoxaspiro [5.5] Undecane * 6: B943: manufactured by Asahi Denka Co., Ltd., mineral oil-based antifoaming agent * 7: F-SSL: sodium alginate * 8: TEA: triethylamine * 9: TBA: tributylamine

* 10: Evaluation of water absorption (seconds) was performed as follows.
About 0.1 mL of water droplets were gently dropped with a dropper on the surface of the polyurethane porous body washed and dried, and the time (seconds) until the dropped water droplets were absorbed by the polyurethane porous body and completely disappeared.

* 11: Swellability (%) was evaluated as follows.
Two marked lines were drawn at intervals of 10 cm on the surface of the polyurethane porous body washed and dried, and the porous body was immersed in water, and the dimensional change rate of the marked line width after 60 minutes was measured. .

* 12: The overall evaluation was based on the following criteria by comprehensively evaluating the results of water absorption and swelling described above and the cell size.
○: Good ×: Bad

Comparative Examples 1-5 :
Each component was uniformly mixed with a stirrer according to the formulation shown in Table 2 below. Next, this mixture was placed in a container made of sus304, sealed, and allowed to stand at room temperature for 30 minutes, and then immersed in a heating medium at 60 ° C. and kept in that state for 2 hours. After completion of the reaction, it was washed with water and dried to obtain a polyurethane porous body of a comparative example.

  About the obtained polyurethane porous body, the water absorption speed | rate, swelling rate, and cell size were measured similarly to the said Example, the result was comprehensively evaluated, and those results were shown together in the table | surface.

(Note) The notes in the table are the same as in Table 1 except for the following.
* 13: MIBPA: methyl iminobispropylamine * 14: TEDA: triethylenediamine

As is clear from the results of Examples 1 to 5 and Comparative Examples 1 to 5, the polyurethane porous body of the present invention has good dimensional stability when wet, excellent water absorption, and an extremely dense cell. It has a structure. This is a 3,9-bis (3-aminopropyl) -2,4,8, having a specific heterocyclic skeleton as a diamine compound that links and connects isocyanate groups regenerated from a water-soluble urethane prepolymer. This is due to the use of 10-tetraoxaspiro [5.5] undecane or 1,4-bis (3-aminopropyl) piperazine, and is specific to the polyurethane porous material of the present invention. Prove.

As described above, according to the present invention, a polyurethane porous body having good dimensional stability when wet, excellent water absorption, and a very dense cell structure is provided. These polyurethane porous bodies include water-absorbing rolls, cosmetic puffs, polishing pads such as various semiconductors or optical materials, ink retaining materials, liquid-absorbing pads for plate laver production, artificial leather base materials, synthetic leather base materials, etc. It can be suitably used in various product fields utilizing the properties of a urethane porous body having completely continuous voids, and its industrial effects are enormous.

Claims (3)

Polyurethane resin emulsion as a crosslinking agent for water-soluble urethane prepolymers as 3,9-bis (3-aminopropyl) -2,4,8,10-tetraoxaspiro [5.5] undecane or 1,4-bis (3 A polyurethane porous body obtained by cross-linking reaction in the presence of sodium alginate using aminopropyl) piperazine followed by gelation.   The polyurethane porous body according to claim 1, wherein the water-soluble urethane prepolymer is a water-soluble urethane prepolymer in which a terminal isocyanate group is masked with sodium bisulfite. The polyurethane porous body according to claim 1 or 2 , wherein the gelation step is performed in the presence of triethylenediamine, triethylamine, tripropylamine or tributylamine.