Method for manufacturing porous body, porous body, and coaster equipped with the same

Abstract

To provide a method for manufacturing a porous body having high water absorption.SOLUTION: A method for manufacturing porous body comprises: a first kneading step of forming a granular kneaded product by kneading a granular material containing pentaerythritol and water-soluble hydrophilic polymer at a prescribed temperature; a second kneading step of forming a kneaded product by kneading the granular kneaded product and a non water-soluble hydrophilic resin such as an urethane resin and a polyacetal resin having hydrophilicity at a prescribed temperature; an injection step of injection molding the kneaded product at a prescribed temperature into a prescribed shape; an immersion step of immersing the injection molded body into liquid containing water of a prescribed temperature to elute the granular kneaded product; and a drying step of drying the molded body from which the granular kneaded product was eluted.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a porous body, a porous body, and a coaster including the porous body. [Background technology]

[0002] Examples of methods for producing porous bodies include the desalination method, which involves adding a powdered pore-forming material such as sodium chloride or magnesium sulfate (hereinafter, such salt pore-forming materials will be referred to as "salt-type pore-forming materials") to a resin base material to form a molding material, forming a solid molded body containing the salt-type pore-forming material, and washing the resulting solid molded body with water to elute the salt-type pore-forming material and form pores in the areas where the salt-type pore-forming material was previously present.

[0003] In this desalination method, as described above, the portions where the salt-type pore-forming material is eluted from the solid molded body become pores. Furthermore, unlike foaming agents, the salt-type pore-forming material itself hardly expands or foams during molding. Therefore, the porosity, which is the proportion of pores in the porous body, can be easily adjusted by adjusting the salt-type pore-forming material content in the solid molded body.

[0004] That is, to produce a porous body with a desired porosity using such a desalination method, it is necessary to incorporate a salt-type pore-forming material corresponding to the desired porosity into the solid molded body. Therefore, when attempting to produce a porous body with a high porosity, for example, 50% by volume, it is necessary to add the salt-type pore-forming material to the resin component so that the content of the salt-type pore-forming material in the solid molded body is 50% by volume or more.

[0005] However, it is difficult to mold a solid molded body with a high porosity, such as one with a salt-type pore-forming material content of 50% by volume or more. This is because the salt-type pore-forming material has a high melting point and typically remains solid (powdered) at the molding temperature of the resin. That is, the higher the salt-type pore-forming material content, the lower the fluidity of the molding material used to mold the solid molded body. Therefore, molding materials for molding solid molded bodies with a salt-type pore-forming material content of 50% by volume or more have low fluidity, making it difficult to achieve the fluidity (MFR value) required for molding.

[0006] In particular, when molding by injection molding or the like, the resin component in a liquid state is injected into a mold, but the powdered salt-type pore-forming material tends to be insufficiently injected, which can result in a solid molded body with a low salt-type pore-forming material content or a non-uniform solid molded body in which the salt-type pore-forming material is contained only inside the molded body, despite the use of a molding material containing a large amount of salt-type pore-forming material.

[0007] A decrease in the content of the salt-type pore-forming material in the solid compact results in a decrease in the porosity of the resulting porous body. Furthermore, a non-uniform solid compact will only result in a non-uniform porous body. Furthermore, a non-uniform solid compact will not only result in a non-uniform porous body, but also insufficient salt-type pore-forming material present on the surface of the compact to be sufficiently eluted during the water washing step, resulting in a porous body with a porosity lower than the desired porosity, or in some areas not becoming porous.

[0008] On the other hand, it is also possible to increase the molding temperature to enhance the fluidity of the resin component. However, even in this case, the salt-type pore-forming material will be present in powder form in the molding material. Therefore, when passing through a die or being injected into a mold, the salt-type pore-forming material is more difficult to inject than the resin. As a result, as in the above case, it is difficult to produce a porous body with a high porosity.

[0009] Furthermore, increasing the porosity requires increasing the content of the salt-type pore-forming material. However, this leads to an increase in the viscosity of the molding material and a decrease in its flowability. Furthermore, increasing the molding temperature to adjust the viscosity can lead to deterioration of the resin. In such cases, the properties of the resulting porous body are degraded.

[0010] For the reasons mentioned above, it has been difficult to mold a solid body for forming a porous body with a high porosity by injection molding or the like.

[0011] In the above-mentioned desalination method, the use of not only salt-type pore-forming materials but also powders of water-soluble organic compounds such as pentaerythritol as pore-forming materials has been investigated.

[0012] Examples of methods for producing such porous bodies include the method described in Patent Document 1. Specifically, Patent Document 1 describes a method for producing a porous polymer body, in which a molding material obtained by dispersing a pore-forming agent containing a water-soluble polymer in a water-insoluble polymer material is molded at a temperature at which the water-insoluble polymer material is thermally melted and part or all of the pore-forming agent is thermally melted, followed by cooling to obtain a solid molded body, and then the pore-forming agent in the solid molded body is eluted with water. This manufacturing method discloses that a porous polymer body having a large pore diameter can be produced while maintaining a high porosity (high porosity).

[0013] However, as a result of investigations by the present inventors, it was found that it was difficult to form a porous body using the manufacturing method described in Patent Document 1. Moreover, even if a porous body could be formed, the obtained porous body was non-uniform and had poor density.

[0014] Therefore, the inventors of the present application have invented and filed a patent application for a method for producing a porous body that can stably produce a porous body with a high porosity (see Patent Document 2).

[0015] The method for producing a porous body disclosed in Patent Document 2 comprises a first kneading step in which a granular pore-forming material is formed by kneading a granular pore-forming material with a water-soluble polymer at a temperature at which at least a portion of the water-soluble polymer melts but the granular pore-forming material does not melt; a second kneading step in which the granular kneaded material is kneaded with a water-insoluble thermoplastic polymer at a temperature at which at least a portion of the water-insoluble thermoplastic polymer melts but the granular kneaded material does not melt; a molding step in which the kneaded material obtained in the second kneading step is molded into a predetermined shape at a temperature at which at least a portion of the water-insoluble thermoplastic polymer melts but the granular kneaded material does not melt; and an elution step in which the solid molded body obtained in the molding step is brought into contact with water to elute the granular kneaded material from the solid molded body into water.

[0016] The present inventors have invented the above technology for the purpose of producing a porous body that can be suitably used for ink-penetrating stamps with ink built into the interior of the stamp or for air filters. Specifically, when a porous body produced by the above production method is used as an ink-penetrating stamp, a clear print can be formed, and an ink-penetrating stamp with good print quality can be obtained. In other words, the above production method can efficiently produce a porous body that can be suitably used for ink-penetrating stamps or air filters. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-257275 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-161639 Summary of the Invention [Problem to be solved by the invention]

[0018] Meanwhile, in order to expand their business, the inventors of the present application have developed products that utilize the porous body of Patent Document 2. The porous body produced by the above-mentioned production method has a relatively high porosity, and the inventors focused on these pores and thought that by using the pores to give the porous body water absorption properties, they could develop the product into a variety of products.

[0019] However, although the porous body produced by the method of Patent Document 2 has a relatively high porosity, it does not have high water absorption. For example, the porous body described in the examples of Patent Document 2 has a porosity of 70%, but its water absorption rate is poor.

[0020] Therefore, the present inventors have conducted extensive research to impart water absorption to this porous body, and have invented a method for manufacturing a porous body with high water absorption, and have completed the present invention. That is, the present invention aims to provide a method for manufacturing a porous body with high water absorption, a porous body with high water absorption, and a coaster using the same. [Means for solving the problem]

[0021] A method for producing a porous body according to one embodiment of the present invention is characterized by comprising: a first kneading step of kneading a granular material containing pentaerythritol with a water-soluble hydrophilic polymer at a predetermined temperature to form a granular kneaded material; a second kneading step of kneading the granular kneaded material with a water-insoluble hydrophilic resin such as a hydrophilic urethane resin or polyacetal resin at a predetermined temperature to form a kneaded material; an injection step of injection-molding the kneaded material into a predetermined shape at a predetermined temperature; an immersion step of immersing the injection-molded molded body in a liquid at a predetermined temperature to dissolve the granular kneaded material; and a drying step of drying the molded body into which the granular kneaded material has been dissolved.

[0022] According to this configuration, a porous body with excellent absorbency can be manufactured by using a hydrophilic resin as the main material of the substrate of the porous body and dissolving the granular kneaded material in a soaking process to form voids. The inventors also conducted tests using various materials, such as water-repellent resins, as the main material of the substrate, but found that when a substrate made of a water-repellent material was used, sufficient absorbency could not be achieved even after subsequent hydrophilic treatment. However, when a hydrophilic resin was used as the main material of the substrate, a porous body with excellent absorbency could be obtained.

[0023] Here, the predetermined temperature in the first kneading step is preferably a temperature at which the hydrophilic polymer melts but the granular material does not melt, but it may also be a temperature at which the hydrophilic polymer melts but only a portion of the granular material melts, as long as it is not a temperature at which the granular material completely melts.

[0024] Furthermore, the predetermined temperature in the second kneading step is preferably a temperature at which the hydrophilic resin softens but the granular kneaded material does not melt, but it may be a temperature at which the hydrophilic resin softens and the granular kneaded material partially melts as long as it does not completely melt the granular kneaded material. The same applies to the predetermined temperature in the injection step.

[0025] Furthermore, this method for producing a porous body is characterized in that the immersion step is carried out multiple times.

[0026] According to this configuration, by performing the immersion process multiple times, more of the granular kneaded material in the molded body can be dissolved, thereby improving the porosity and water absorption. Here, performing the immersion process multiple times means, for example, replacing the liquid in which the molded body is immersed multiple times. This allows a large amount of the granular kneaded material containing pentaerythritol to be dissolved, thereby improving the porosity of the molded body. Desirably, the immersion process is performed until the granular kneaded material is completely dissolved.

[0027] Furthermore, this method for manufacturing a porous body is characterized in that in the immersion step, the liquid is water at a temperature of 50 to 70 degrees, and further includes a second immersion step in which the molded body dried in the drying step after the immersion step is immersed in an aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups, and a second drying step in which the molded body is dried after the second immersion step.

[0028] According to this configuration, after the first immersion step and the first drying step, a second immersion step is performed in which the molded body is immersed in an aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups, followed by a second drying step in which the molded body is dried, thereby forming a layer of the polyhydric alcohol containing two or three hydroxyl groups on the surface of the pores of the porous body.The layer of the polyhydric alcohol containing two or three hydroxyl groups can further improve the absorbency of the porous body and further increase the absorption rate.

[0029] Moreover, this method for producing a porous body is characterized in that in the immersion step, the liquid is an aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups.

[0030] Instead of the above-mentioned first immersion in water, drying, and second immersion in polyhydric alcohol, and drying, a certain level of absorbency can be imparted to the porous body by dissolving the granular kneaded material in an aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups instead of water during the first immersion step, while forming a layer of the polyhydric alcohol in the voids. Note that the most effective method is to perform the above-mentioned first immersion step, drying step, second immersion step, and drying step.

[0031] The method for producing a porous body is also characterized in that the aqueous polyhydric alcohol solution is an aqueous solution containing polyethylene glycol or glycerin. Also, the method for producing a porous body is characterized in that the aqueous polyhydric alcohol solution is an aqueous glycerin solution.

[0032] To improve the absorbency of the porous body, the polyhydric alcohol is preferably an aqueous solution containing polyethylene glycol or glycerin, and most preferably an aqueous glycerin solution.

[0033] Moreover, this method for producing a porous body is characterized in that the volume percent concentration of the pentaerythritol in the kneaded material is 70 to 90%.

[0034] According to this configuration, by using pentaerythritol at a volume percent concentration of 70 to 90% relative to the kneaded material, the water-soluble polymer coats the kneaded material to form a granular kneaded material, so that the porosity of the produced porous body can be made to exceed 70%. In addition, by making the porosity exceed 70%, a porous body with high absorbency can be obtained, in combination with the above configuration.

[0035] Furthermore, this method for producing a porous body is characterized in that the drying step uses a hot air oven at a temperature of 50°C to 70°C.

[0036] The inventors of the present application conducted tests on the drying process, such as rapid drying at high temperatures and slow drying at low temperatures, and found that the absorbency of the porous body improved when the porous body was dried slowly and thoroughly in a hot air oven at a temperature of 50°C to 70°C.

[0037] This method for producing a porous body is characterized in that the drying in the second drying step is performed using a hot air oven at a temperature of 50°C to 70°C.

[0038] In the second drying step, it was also preferable to use a hot air oven at a temperature of 50°C to 70°C.

[0039] A coaster according to one aspect of the present invention is characterized by further comprising a cutting step of cutting the porous body produced by the production method according to claim 8 into a predetermined shape.

[0040] This configuration allows for the production of highly absorbent coasters. Furthermore, the porous sheet can be cut into sheet coasters, and since the porous sheet can be produced in various shapes by injection molding, it is also possible to produce three-dimensional coasters.

[0041] A porous body according to one embodiment of the present invention is characterized in that it comprises a substrate made of a hydrophilic resin such as a hydrophilic urethane resin or a polyacetal resin, having a porosity of 70 to 90%, and a layer containing a polyhydric alcohol having two or three hydroxyl groups is formed on the surface of the pores of the substrate.

[0042] According to this configuration, the porous body is made of a hydrophilic resin with a porosity of 70 to 90% and has a layer containing a polyhydric alcohol having two or three hydroxyl groups formed on the surface of the pores, thereby enabling the porous body to have high absorbency.

[0043] In addition, from the viewpoint of absorbency, it is preferable that the layer containing the polyhydric alcohol in this porous body is a layer containing polyethylene glycol or glycerin, and it is most preferable that the layer containing the polyhydric alcohol is a layer containing glycerin.

[0044] This porous body is characterized in that the porosity of the substrate is 80% or more.

[0045] According to this configuration, by making the porosity 80% or more, the porous body has higher absorbency.

[0046] A coaster according to one aspect of the present invention includes the porous body according to claim 13, and the base material is made of a urethane resin.

[0047] This configuration results in a highly absorbent coaster. [Effects of the Invention]

[0048] According to the present invention, highly absorbent porous bodies, coasters, etc. can be produced. DETAILED DESCRIPTION OF THE INVENTION

[0049] An embodiment of the present invention will be described below, but the present invention is not limited thereto. Furthermore, the blending amounts of each element are merely examples, and the components in the following embodiment include those that are easily replaceable by those skilled in the art, or those that are substantially identical. Furthermore, the configurations described below can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the configurations can be made without departing from the spirit of the present invention.

[0050] <1. Method for manufacturing porous bodies> A method for producing a porous body according to one embodiment of the present invention comprises a first kneading step in which a granular material containing pentaerythritol and a water-soluble hydrophilic polymer are kneaded at a predetermined temperature to form a granular kneaded material, and a second kneading step in which the granular kneaded material is kneaded at a predetermined temperature with a water-insoluble hydrophilic resin such as a hydrophilic urethane resin or polyacetal resin to form a kneaded material.

[0051] The method for producing a porous body of this embodiment includes an injection step in which the kneaded material is injection-molded into a predetermined shape at a predetermined temperature, a first immersion step in which the injection-molded body is immersed in a liquid at a predetermined temperature to elute the granular kneaded material, and a first drying step in which the body from which the granular kneaded material has been eluted is dried. This results in a molded body having voids. The first immersion step is preferably performed multiple times by replacing the liquid. This is to thoroughly elute the granular kneaded material and increase the porosity.

[0052] The method for producing a porous body of this embodiment further includes a second immersion step of immersing the porous molded body in an aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups, followed by a second drying step of drying the molded body. The porous body produced in this way has voids and a polyhydric alcohol layer on the surface of the porous body and on the surface of the voids.

[0053] Pentaerythritol is a water-soluble granular material used as a void-forming material to form voids in a porous body, and by finally dissolving it from the molded product, the voids are formed. Because pentaerythritol has a relatively high melting point, using a granular material containing pentaerythritol as a void-forming material makes it easy to achieve the various temperature conditions in the manufacturing process of the porous body, thereby facilitating the manufacture of the porous body. In addition, molding materials containing granular material containing pentaerythritol solidify quickly after molding, which is also useful in shortening the cooling time of the molded body.

[0054] Furthermore, examples of granular materials containing pentaerythritol include granular materials made of pentaerythritol containing impurities. Industrially produced pentaerythritol contains impurities such as tripentaerythritol and dipentaerythritol, and begins to melt at a temperature lower than the melting point of pentaerythritol, 260°C. The temperature at which granular materials made of pentaerythritol containing impurities begin to melt varies depending on the type and content of the impurities. Preferably, the granular material containing pentaerythritol is a powder that begins to melt at 220 to 240°C.

[0055] The volume average particle size of the granular material containing pentaerythritol is preferably 30 to 63 μm. This allows voids of an appropriate size to be formed. The volume average particle size of the granular material can be measured using a general particle size analyzer.

[0056] The hydrophilic polymer is used by mixing with the granular material containing pentaerythritol, and specifically, is not particularly limited as long as it is a water-soluble hydrophilic polymer having a melting point lower than that of the granular material and higher than that of the hydrophilic resin described below. Examples of this hydrophilic polymer include polyvinyl alcohol, polyethylene oxide, polyvinyl methyl ether, carboxyvinyl polymer, sodium polyacrylate, ethylene oxide, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethylhydroxyethyl cellulose, carboxymethyl cellulose, and methylhydroxypropyl cellulose. The above hydrophilic polymers may be used alone or in combination of two or more.

[0057] Furthermore, polyvinyl alcohol is preferably used as the hydrophilic polymer. This allows for more stable production of porous bodies with high porosity. It is believed that the use of polyvinyl alcohol as the hydrophilic polymer allows the aforementioned effects of the hydrophilic polymer to be favorably exerted. Specifically, a granular kneaded material in which granular materials containing pentaerythritol are coated with a hydrophilic polymer can be uniformly dispersed not only inside the molded body but also near the surface, with the granular materials linked via the hydrophilic polymer coated on the surface.

[0058] The polyvinyl alcohol used as the hydrophilic polymer preferably has a saponification degree of 65 to 90 mol %, more preferably 70 to 80 mol %, and preferably has a polymerization degree of 300 to 1000, more preferably 500 to 700. Examples of polyvinyl alcohol used as the water-soluble polymer include polyvinyl alcohol for hot melt molding.

[0059] A water-insoluble hydrophilic resin such as a hydrophilic urethane resin or polyacetal resin is a resin that serves as the base material for the porous body to be produced, and specifically, it is desirable for the resin to be a hydrophilic resin that has a lower melting point than pentaerythritol or the above-mentioned hydrophilic polymer.

[0060] For example, an aqueous solution containing polyethylene glycol or glycerin can be used as the aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups. Note that glycerin has three hydroxyl groups and is more hydrophilic than an aqueous solution containing two hydroxyl groups, so it is optimal to use an aqueous glycerin solution as the aqueous solution of the polyhydric alcohol. In addition, in this embodiment, as an example, a 20% aqueous glycerin solution is used.

[0061] Next, each manufacturing step will be described in detail. In the method for producing a porous body according to the present embodiment, for example, pentaerythritol was used as the particulate material, polyvinyl alcohol was used as the hydrophilic polymer, and urethane resin was used as the hydrophilic resin. Furthermore, in the first immersion step, water was used, and the immersion was performed multiple times by replacing the water multiple times. In the second immersion step, a 20% aqueous solution of glycerin was used as the aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups.

[0062] First, granular materials containing pentaerythritol and polyvinyl alcohol, a hydrophilic polymer, are kneaded at a temperature at which the polyvinyl alcohol melts and the granular materials containing pentaerythritol do not melt or only partially melt, in this embodiment, a temperature range of 185°C to 200°C, specifically a temperature of 185 to 190°C. This forms a granular kneaded material. The resulting granular kneaded material is in a state where the granular materials are coated with polyvinyl alcohol.

[0063] The blending ratio of the granular material to the polyvinyl alcohol is, for example, preferably 80:20 to 97:3 by mass, more preferably 89:11 to 96:4. If the amount of polyvinyl alcohol is too small relative to the granular material, the effect of mixing with the polyvinyl alcohol is reduced, and a porous body with a high porosity tends to be unable to be suitably formed. This is thought to be because the polyvinyl alcohol is unable to sufficiently coat the granular material.

[0064] On the other hand, if the amount of polyvinyl alcohol is too large relative to the amount of granular material, it tends to be difficult to form a porous body with a high porosity. This is thought to be because the granular mixture, which is a mixture of granular material and polyvinyl alcohol, becomes difficult to disperse uniformly in the molded body.

[0065] Furthermore, when a porous body with high water absorption is to be produced, the blending amount of the granular kneaded material obtained by kneading granular material with polyvinyl alcohol is preferably 65% ​​to 90% by volume percent, and more preferably 80% to 90%. This allows a porous body with a high porosity, and the higher the porosity, the more likely the water absorption is to be improved. In this embodiment, the granular kneaded material was blended to a volume percent concentration of 83% to 87%, and the porosity of the produced molded body was 82%.

[0066] Furthermore, if the amount of granular kneaded material is too high, for example, exceeding 90%, even if the kneaded material of the granular kneaded material and urethane resin described below is melted, it tends to be impossible to ensure fluidity suitable for molding, i.e., it may not be possible to injection mold the porous body.

[0067] The granular material and polyvinyl alcohol are kneaded at a temperature at which at least a portion of the polyvinyl alcohol melts but the granular material does not melt. For example, the temperature range is 185°C to 200°C. For kneading, devices such as an open roll, kneader, intensive mixer, single-screw extruder, and twin-screw extruder can be used. Prior to this, the granular material and polyvinyl alcohol may be premixed using a mixer such as a Henschel mixer, V-shaped mixer, ball mill, ribbon blender, or tumble mixer.

[0068] Next, the granular kneaded material and urethane resin are kneaded at a temperature at which the urethane resin softens and the granular kneaded material does not melt or only partially melts. For example, this is a temperature range of 185°C to 200°C. The kneaded material obtained by this kneading (second kneading step) is used as a molding material and injection molded into a predetermined shape at a temperature at which the urethane resin softens and the granular kneaded material does not melt or only partially melts. In this embodiment, the material is injection molded into a sheet shape.

[0069] It is believed that the molded body obtained by this injection step is one in which adjacent granular kneaded materials are uniformly dispersed, connected via the polyvinyl alcohol coated on the surface. Furthermore, since the granular kneaded material is coated with polyvinyl alcohol, it is believed that it is uniformly dispersed not only inside the obtained molded body but also near the surface.

[0070] Furthermore, the blending amount of urethane resin in this embodiment is set to a volume percent concentration of 10% to 30%, which results in a porous body with a high porosity and improved water absorption.

[0071] As in the first kneading step, this kneading (second kneading step) can be carried out using an apparatus such as an open roll, a kneader, an intensive mixer, a single-screw extruder, or a twin-screw extruder. Prior to this, the granular kneaded material and the urethane resin may be mixed in advance using a mixer such as a Henschel mixer, a V-shaped mixer, a ball mill, a ribbon blender, or a tumble mixer.

[0072] In producing the kneaded product that will become the molding material described above, when the granular mixture and urethane resin are kneaded together, additives such as modifiers such as polymer modifiers, lubricants, antioxidants, plasticizers, heat stabilizers, thickeners, flame retardants, antioxidants (antioxidants), UV absorbers, colorants, antistatic agents, and reinforcing materials may be added as needed.

[0073] The molding using the above-mentioned molding material is performed at a temperature at which the urethane resin softens and the granular kneaded material does not melt or only partially melts. In addition to injection molding, other molding methods such as compression molding, extrusion molding, and blow molding can also be used.

[0074] In addition, in the injection process of this embodiment, an injection molding machine with a 1.5 m long cylinder is used, which is divided into, for example, four equal parts, and the temperature setting for each part is changed to gradually melt the molding material, in order to ensure that the urethane resin and the granular kneaded material are mixed uniformly.

[0075] Next, the molded body obtained by injection molding is immersed in water, thereby dissolving the granular kneaded material from the molded body into the water. As a result, the portions into which the granular kneaded material has dissolved become voids in the molded body. As described above, the granular kneaded material is uniformly dispersed in the molded body while being connected via the polyvinyl alcohol coated on the surface of the granules, and therefore it is believed that voids can be uniformly formed in the molded body. Furthermore, as described above, it is believed that the granular kneaded material has voids uniformly dispersed not only inside the molded body but also near the surface, and therefore it is believed that when it absorbs moisture, the moisture absorption rate is accelerated.

[0076] Furthermore, the water used in the above immersion step is preferably in the temperature range of 50°C to 70°C, and in this embodiment, immersion was performed in water at 60°C as an example. The water temperature is not limited to 60°C, and may be any temperature at which the granular kneaded material melts and is below the melting point of the urethane resin. Furthermore, this immersion step in which the granular kneaded material is dissolved in water is preferably performed multiple times, for example by changing the water multiple times. By performing this immersion step multiple times, the granular kneaded material can be thoroughly dissolved from the molded body, increasing the porosity and improving water absorbency.

[0077] Next, the molded body after immersion in water is subjected to a first drying step in which it is dried at a predetermined temperature to dry the molded body. In this embodiment, as an example, the molded body is dried in a hot air oven at 60°C. If the temperature is too low, the drying speed is slow and sufficient drying is difficult. On the other hand, if the temperature is too high, the drying speed increases, but the urethane resin may be denatured, so drying at a temperature range of 50°C to 70°C is preferable. Furthermore, drying is not limited to a hot air oven, and other drying devices can also be used.

[0078] In this manner, a porous body having voids made from selected materials such as a hydrophilic substrate is completed, and the porous body has a certain degree of absorbency. However, in order to obtain a porous body with the desired water absorption properties, the following steps are further carried out.

[0079] Specifically, a second immersion step is performed in which the molded body after the first drying step is immersed in an aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups. The aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups can be, for example, an aqueous solution containing polyethylene glycol or glycerin. In this embodiment, a glycerin aqueous solution having three hydroxyl groups is used to impart high water absorbency. In this embodiment, a 20% glycerin aqueous solution is used as an example. The temperature of the glycerin aqueous solution is set to the same temperature range of 50°C to 70°C as in the first immersion step, and in this embodiment, immersion is performed using a glycerin aqueous solution at 60°C.

[0080] As a result, the glycerin aqueous solution penetrates into the surface and interior of the compact, contacting and adhering to the surface and voids of the compact.Then, similar to the first drying step, the compact after the second immersion is subjected to a second drying step in which it is dried in a hot air oven at 60°C.

[0081] The molded article thus produced has a glycerin layer formed on its surface and on the surface of the voids. The hydroxyl group-containing glycerin layer improves water absorption and the water absorption rate. For example, a molded article without a glycerin layer required more than 13 seconds to absorb water from a table, whereas a molded article with a glycerin layer could absorb water within 2 seconds.

[0082] Finally, a cutting step is performed in which the sheet-shaped molded product is cut to a predetermined size. For example, by cutting the molded product to a size that can be used as a coaster, coasters with high water absorption can be produced. This cutting step can also be performed after the first drying step. In this case, the molded product cut to a predetermined size may be subjected to a second immersion step and a second drying step.

[0083] Furthermore, the molded product is not limited to a sheet shape, and may be injection molded into other shapes. For example, by injection molding into a three-dimensional shape and cutting it, a three-dimensional coaster with high water absorption can be made. Furthermore, it is not limited to coasters, and other highly absorbent implements can also be made.

[0084] <2. Example> Next, a porous body was produced by the above-described production method, and its effects were compared with those of a comparative example.

[0085] [Example 1] First, 65 parts by mass of pentaerythritol (Neuriser P manufactured by KISCO, melting start temperature: 180°C, melting completion temperature: 240°C) and 5 parts by mass of polyvinyl alcohol (CP1210T05 manufactured by Kuraray Co., Ltd., melting point: 174°C) were mixed in a mixer to form a granular material. The resulting granular mixture was then kneaded at 190°C using a twin-screw extruder. The resulting granular kneaded material was then pelletized using a pelletizer.

[0086] Then, 70 parts by mass of the obtained pellets and 11 parts by mass of a hydrophilic urethane resin (Rezamin P (P-4597) manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., softening point 163°C) were mixed in a mixer. The obtained mixture was kneaded at 185°C using a twin-screw extruder. Thereafter, the obtained kneaded product was pelletized using a pelletizer.

[0087] The pellets were then injection molded at a molding temperature of 185°C to obtain a sheet-like molded product measuring 65mm x 90mm x 2mm. The molded product was immersed in water at 60°C for 24 hours. The water was replaced four times during this period. This allowed most of the granular kneaded material to be dissolved from the molded product. The molded product was then thoroughly dried in a hot air oven at 60°C.

[0088] The dried molded body was then immersed in a 20% glycerin aqueous solution at 60°C for 24 hours. This caused the glycerin aqueous solution to adhere to the surface of the molded body and the surfaces of the pores. The molded body was then thoroughly dried in a hot air oven at 60°C. This resulted in a sheet-like porous body with a porosity of 82%, in which a glycerin layer was formed on the surface of the molded body and the surfaces of the pores.

[0089] [Example 2] First, 27 parts by mass of pentaerythritol (Pentalit manufactured by Koei Chemical Industry Co., Ltd., melting initiation temperature: 232°C) as a granular material and 9 parts by mass of polyvinyl alcohol (CP1210T05 manufactured by Kuraray Co., Ltd., melting point: 174°C) as a water-soluble polymer were mixed in a mixer. The resulting mixture was kneaded at 190°C using a twin-screw extruder. The resulting kneaded product was then pelletized using a pelletizer.

[0090] Then, 36 parts by mass of the obtained pellets and 100 parts by mass of a polyolefin elastomer (Tafmer A-1085S manufactured by Mitsui Chemicals, Inc., melting point 66°C) as a water-insoluble thermoplastic polymer were mixed in a mixer. The obtained mixture was kneaded at 160°C using a twin-screw extruder. The kneaded product was then pelletized using a pelletizer.

[0091] The pellets were then injection molded at a molding temperature of 150°C to obtain a sheet-like solid compact measuring 65 mm x 90 mm x 2 mm. The solid compact was then immersed in warm water at 50°C for 24 hours. This allowed the granular pore-forming material and the water-soluble polymer to elute from the solid compact. The solid compact was then thoroughly dried. This resulted in a porous body with a porosity of 69%.

[0092] [Comparative Example 1] The same procedure as in Example 2 was carried out except that no water-soluble polymer was used. Specifically, first, 360 parts by mass of pentaerythritol (Pentalit manufactured by Koei Chemical Industry Co., Ltd., melting initiation temperature: 232°C) as a granular material and 100 parts by mass of polyolefin elastomer (Tafmer A-1085S manufactured by Mitsui Chemicals, Inc., melting point: 66°C) as a water-insoluble thermoplastic polymer were mixed in a mixer. The resulting mixture was kneaded at 160°C using a twin-screw extruder. The resulting kneaded product was then pelletized using a pelletizer.

[0093] The pellets thus obtained could not be injection molded into a sheet at a molding temperature of 150°C. Furthermore, even when the molding temperature was increased to 210°C, the molding material did not fill the cavity. As a result, a porous body could not be produced.

[0094] Comparative Example 2 The same procedure as in Example 2 was carried out except that the molding temperature was changed to 180°C. However, when the molded body obtained by molding was immersed in water, it dissolved in water, and a porous body could not be produced.

[0095] Comparative Example 3 First, 270 parts by mass of pentaerythritol (Pentalit manufactured by Koei Chemical Industry Co., Ltd., melting onset temperature: 232°C) as a granular material, 90 parts by mass of polyvinyl alcohol (CP1210T05 manufactured by Kuraray Co., Ltd., melting point: 174°C) as a water-soluble polymer, and 100 parts by mass of polyolefin elastomer (Tafmer DF110 manufactured by Mitsui Chemicals, Inc., melting point: 94°C) were mixed in a mixer. The resulting mixture was kneaded at 190°C using a twin-screw extruder. The resulting kneaded product was then pelletized using a pelletizer.

[0096] The pellets were then injection molded at a molding temperature of 150° C. to obtain a sheet-like molded product measuring 65 mm × 90 mm × 2 mm. However, when the molded product was immersed in water, it dissolved in water, and a porous body could not be produced.

[0097] (Comparison of Examples 1 and 2 with Comparative Examples 1, 2, and 3) As described above, porous bodies were produced in Examples 1 and 2, but not in Comparative Examples 1, 2, and 3. This demonstrates that, when producing porous bodies having voids such as those in Examples 1 and 2 according to this embodiment, it is important to knead a granular material containing pentaerythritol with a water-soluble polymer at a temperature at which the water-soluble polymer melts and the granular material does not melt or only partially melts. It also demonstrates that it is important to knead this granular kneaded material with a water-insoluble thermoplastic polymer at a temperature at which the water-insoluble thermoplastic polymer softens and the granular kneaded material does not melt or only partially melts. It also demonstrates that it is important to mold the resulting kneaded material into a predetermined shape at a temperature at which the water-insoluble thermoplastic polymer softens and the granular kneaded material does not melt or only partially melts.

[0098] (Comparison 1 between Example 1 and Example 2) The porous bodies of Examples 1 and 2 were each immersed in water, and the weight of the porous body after immersion was measured, and the weight of the porous body before immersion was measured. The difference between the weights was used to calculate the water content of the porous body. The dimensions of each porous body were then measured, and the volume of the porous body was calculated from the measured dimensions. The water content calculated above was divided by the volume of the porous body to calculate the porosity.

[0099] As a result, the porous body of Example 1 had a porosity of 82%. The porous body of Example 2 had a porosity of 69%. The porous body of Example 2 was similar to the example in the aforementioned Prior Art Document 2, and although Prior Art Document 2 stated that the porosity was 70%, a new measurement revealed that the actual porosity was 69%, which was less than 70%.

[0100] (Comparison 2 between Example 1 and Example 2) Next, the speed at which the porous body of Example 1 and the porous body of Example 2 absorbed water placed in a tray of sufficient size was measured. As a result, the porous body of Example 1 absorbed the water within 2 seconds, while the porous body of Example 2 took more than 13 seconds.

[0101] (Comparison Results Between Example 1 and Example 2) From the results of the above two comparative tests, it is considered that the water absorption rate and the water absorption speed of the porous body of Example 1 were improved by using a hydrophilic urethane resin as the base material of the porous body, by repeating the immersion process multiple times to thoroughly dissolve the granular kneaded material, and by forming a layer of glycerin on the surface of the porous body and the surface of the voids.

[0102] <3. Other embodiments> As described above, a preferred embodiment of the present invention has been described. However, the present invention is not limited to the above-described embodiment, and various modified or altered examples within the scope of the claims also fall within the technical scope of the present invention.

[0103] For example, in the above-described embodiment, as an example, pentaerythritol is used for the granular material, polyvinyl alcohol is used for the water-soluble hydrophilic polymer, a hydrophilic urethane resin is used for the substrate, and a glycerin aqueous solution is used in the second immersion step, but it is believed that a certain level of water absorbency can be obtained even if other hydrophilic resins such as polyacetal resins are used for the substrate.Furthermore, although a glycerin aqueous solution is used in the second immersion step, it is believed that a certain level of water absorbency can be obtained even if other polyhydric alcohol aqueous solutions containing two or three hydroxyl groups, such as polyethylene glycol, are used.

[0104] In addition, although the above embodiment illustrates a coaster using this porous body, this porous body can be used for various products other than coasters. For example, if it is used in products that absorb liquids, such as sanitary products, incontinence prevention pads, absorbent sheets, and absorbent sandbags, it can be made more absorbent than conventional products. Therefore, such products are also included in the technical scope of the present invention.

Claims

1. a first kneading step of kneading a granular material containing pentaerythritol and a water-soluble hydrophilic polymer at a predetermined temperature to form a granular kneaded material; a second kneading step of kneading the granular kneaded material with a water-insoluble hydrophilic resin such as a hydrophilic urethane resin or a polyacetal resin at a predetermined temperature to form a kneaded material; an injection step of injection-molding the kneaded material into a predetermined shape at a predetermined temperature; an immersion step of immersing the injection-molded body in a liquid containing water at a predetermined temperature to dissolve the granular kneaded material; A drying step of drying the molded body into which the granular kneaded material has been eluted. A method for manufacturing a porous body.

2. The immersion step is performed multiple times. A method for producing the porous body according to claim 1.

3. In the immersion step, the liquid is water at a temperature of 50 to 70 degrees, a second immersion step of immersing the molded body dried in the drying step after the immersion step in an aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups; The method further comprises a second drying step of drying the molded body after the second immersion step. A method for producing the porous body according to claim 1.

4. In the immersion step, the liquid is an aqueous solution of a polyhydric alcohol containing two or three hydroxyl groups. A method for producing the porous body according to claim 1.

5. The polyhydric alcohol aqueous solution is an aqueous solution containing polyethylene glycol or glycerin. The method for producing the porous body according to claim 3 or 4.

6. The polyhydric alcohol aqueous solution is a glycerin aqueous solution. The method for producing the porous body according to claim 5.

7. The volume percent concentration of the pentaerythritol in the kneaded product is 65% to 90%. The method for producing the porous body according to claim 6.

8. The drying step is characterized in that a hot air oven having a temperature of 50°C to 70°C is used. The method for producing the porous body according to claim 7.

9. The drying in the second drying step is performed using a hot air oven at a temperature of 50°C to 70°C. The method for producing a porous body according to claim 8 dependent on claim 3.

10. The porous body produced by the method according to claim 9 is a coaster. How to make coasters.

11. The substrate has a porosity of 70% to 90% and is made of a hydrophilic resin such as a hydrophilic urethane resin or a hydrophilic polyacetal resin. a layer containing a polyhydric alcohol having two or three hydroxyl groups formed on the surface of the voids in the base material; Porous material.

12. The layer containing a polyhydric alcohol is a layer containing polyethylene glycol or glycerin. The porous body according to claim 11.

13. The layer containing a polyhydric alcohol is a layer containing glycerin. The porous body according to claim 12.

14. The substrate has a porosity of 80% or more. The porous body according to any one of claims 11 to 13.

15. A porous body according to claim 14, characterized in that the substrate is made of a urethane resin. coaster.