JP6917032B2 - Resin molded products and their manufacturing methods - Google Patents

Description

The present invention relates to a resin molded product having a continuous porous structure and a method for producing the same.

Resin molded products having a continuous porous structure are used in a wide range of applications such as industrial water-absorbing rolls, various sanitary materials, stamping materials, stationery brush pens, painting material brush pens, and decorative brush pens. In such a resin molded product having a continuous porous structure, various improvements in water absorption are required. Specifically, for example, industrial water absorption rolls are required to improve the water absorption rate, and pen tip members such as stationery brush pen tips, painting material brush pen tips, and makeup brush pen tips are water-based ink or water-based. There is a demand for improved water absorption capacity and water retention of the water-based ink and water-based cosmetics when the cosmetics are applied to painting materials and skin.

For example, as a raw material resin for a resin molded product that constitutes a pen tip member of a brush pen to which water-based ink or water-based cosmetics are applied, a thermoplastic resin such as an olefin-based thermoplastic resin is often used because of its ease of molding. However, since thermoplastic resins generally show hydrophobicity and have poor compatibility with water, water absorption is exhibited only by the capillary phenomenon effect due to the continuous porous structure in such a pen tip member. .. Therefore, such a pen tip member does not have sufficient water absorption capacity and stable water retention, and as a result, when water-based ink or water-based cosmetics are applied to an art material or skin, the water-based ink or water-based cosmetics are squeezed. There are problems such as dropping and blurring of the applied coating image.

In Patent Document 1 and Patent Document 2, a resin composition containing a pore-forming material is formed into a shape suitable for an application, and then the pore-forming material is removed by an appropriate treatment to obtain a continuous porous material exhibiting hydrophilicity. A manufacturing method for manufacturing a resin molded product having a structure is disclosed. In the production methods described in Patent Documents 1 and 2, the moldability of the resin molded product is improved by changing various compounding agents in the resin composition, changing the temperature conditions at the time of compounding, and the like. It suppresses the formation of a skin layer (dense layer) on the surface of the obtained resin molded product, and controls the shape of the pores formed inside the resin molded product and its continuity. By increasing the communication of pores in the entire resin molded product in this way, the water absorption of the resin molded product is improved.

However, in the resin molded product as described above, since the raw material resin used in the resin composition for forming the resin molded product is hydrophobic, it is said that sufficient performance in terms of water absorption rate and water retention can be obtained. I can not say.

On the other hand, in Patent Document 3, as a technique for imparting hydrophilicity to a synthetic resin used as a raw material resin for a resin molded product, a hydrophilic resin is kneaded with a thermoplastic resin for a matrix together with a thermoplastic resin-coated pulp fiber. By doing so, a technique for imparting hydrophilicity to the thermoplastic resin for a matrix is disclosed.

However, since the hydrophilic resin generally has low heat resistance, it cannot be said that the resin composition to which the hydrophilic resin is added is suitable as a raw material resin for melt molding through a heating step. Even if melt molding can be performed using a resin composition containing a hydrophilic resin, a pore-forming material to be blended in the resin composition when a resin molded product having a continuous porous structure is to be molded. Is often removed by water extraction treatment after molding, but this water extraction step cannot be used.

Further, as a technique for imparting hydrophilicity to the resin molded product itself, there are examples of treating the molded resin molded product with a surfactant and plasma processing the surface of the molded resin molded product. A resin molded product treated with a surfactant has a problem of being inferior in long-term durability of hydrophilicity, and further, a resin molded product treated with plasma shows hydrophilicity only on the surface of the resin molded product, and as a result, the resin molded product exhibits hydrophilicity. There is a problem that sufficient water absorption capacity cannot be obtained.

In addition, the resin molded product having a continuous porous structure is flexible and does not easily give discomfort due to the feeling of hardness and coldness when it comes into contact with the human body. Therefore, if good water absorption can be imparted to the resin molded product, it is considered that it can be used as a sanitary material that absorbs a liquid such as blood. However, since conventional resin molded products lack conductivity, they cannot be used as members that require conductivity even if they are provided with hydrophilicity (for example, electrocardiogram pads for measuring electrical signals from living organisms, electrodes for electroencephalograms, etc.). difficult.

For this reason, a resin molded product having a continuous porous structure has not been conventionally used as a member for measuring an electrocardiogram or an electroencephalogram, and a hard plate-shaped or columnar member is used as a biological electrode. Such conventional biological electrodes are used with a conductive paste interposed between the skin and the electrodes. However, the conductive paste is sticky, and when applied to the skin, it causes discomfort such as coldness and stickiness. Further, it is necessary to remove the paste after removing the electrodes, and it is complicated to remove the paste applied to a certain thickness to the extent that it is not sticky.

Therefore, a dry electrode capable of measuring biological signals such as brain waves without using a conductive paste has been proposed. Conventionally, the dry electrode is made of a hard member such as metal, and the burden of discomfort at the time of wearing is large. Therefore, a dry electrode has been proposed in which an elastic body is used as a base material and a structure containing a nanocarbon material is fixed on the surface of the tip of the base material that comes into contact with the human body (Patent Document 4).

However, the electrode of Patent Document 4 may be separated from the base material and the structure. In addition, there is also a problem that the manufacturing cost is high because a step of fixing the base material and the structure is required.

Japanese Unexamined Patent Publication No. 2008-24899 Japanese Unexamined Patent Publication No. 2011-161639 Japanese Unexamined Patent Publication No. 2011-201964 Japanese Unexamined Patent Publication No. 2017-073370

The present invention has been made based on the above circumstances, and an object of the present invention is to produce a resin molded product having a continuous porous structure having excellent water absorption rate, large water absorption capacity and high water retention for a long period of time. To provide a method.

The present invention also provides a resin molded product that can be used as a human body mounting member, specifically, a sanitary material or a biological electrode by improving not only water absorption but also conductivity of a resin molded product having a continuous porous structure. do. The biological electrode according to the present invention can reduce the discomfort caused when it comes into contact with the human body, and can be easily manufactured by integral molding.

The present invention provides a resin molded product obtained by molding a resin composition in which cellulose fibers are contained in a thermoplastic resin. According to the present invention, by molding the resin composition into a columnar or plate shape depending on the intended use, a resin molded product having flexibility, hydrophilicity and good water absorption characteristics can be obtained. The resin molded product according to the present invention also has conductivity in a state of absorbing the electrolyte liquid.

The resin composition is a molded product having a thickness of about 0.5 to 25 mm, preferably 1 to 15 mm, which is molded into a plate shape such as a circle or a substantially quadrangle. The molded product may be used as it is, or the surface may be cut as necessary to obtain a resin molded product used as a liquid absorbing pad or an electrode pad for an electrocardiogram. Alternatively, the resin composition is molded into a pillar having a length of about 5 to 30 mm, specifically, a substantially cylindrical shape or a polygonal columnar shape, and the molded product is directly cut or the surface is cut as needed to perform various pen tips and living organisms. Obtain a resin molded product used as an electrode for use. By cutting the surface of the molded product, the surface and the inside of the resin molded product can have the same continuous porous structure, and a more homogeneous structure can be obtained.

The molded product to be cut is a solid molded product obtained by melt-molding a kneaded resin composition, which is subjected to water extraction treatment, and the solid molded product can be washed and dried after being water-extracted and then cut. preferable.

In the present specification, the substantially columnar shape includes a cylinder, a polygonal prism, a cone, and a polygonal pyramid. In addition, "protruding one end" means that one end is narrowed down compared to the other end, and not only one end is sharp like a pen tip, but the tip is rounded. Including the case where there is.

The resin molded product of the present invention is a resin molded product having a continuous porous structure.
It is characterized by comprising a resin composition containing a thermoplastic resin and cellulose fibers.

In the resin molded product of the present invention, the content ratio of the cellulose fiber in the resin composition is preferably 0.1 to 30% by mass.

In the resin molded product of the present invention, the thermoplastic resin is preferably an olefin elastomer.

In the resin molded product of the present invention, the average pore diameter of the pores constituting the continuous porous structure is preferably in the range of 1 to 120 μm, the porosity is preferably 60 to 85% by volume, and the continuous porous structure is further formed. It is more preferable that the average pore diameter of the constituent pores is in the range of 1 to 60 μm and the porosity is 65 to 75% by volume.

The resin molded product of the present invention is a resin molded product that uses an elastomer resin such as an olefin elastomer as the thermoplastic resin, has a continuous porous structure, and can be used as a flexible and water-absorbable artificial sponge. Is preferable.

The resin molded product of the present invention can be used as a pen tip member.

The method for producing a resin molded product of the present invention is the method for producing the above-mentioned resin molded product.
A step of chipping a raw material resin composition obtained by kneading a thermoplastic resin, a cellulose fiber, and a pore-forming material, and a water extraction treatment after melt-molding the chipped raw material resin composition to obtain the pore-forming material. It is characterized in that a resin molded product having a continuous porous structure containing cellulose fibers is obtained through a step of forming pores by removing the pores.

The resin molded product of the present invention has a continuous porous structure composed of a resin composition containing a thermoplastic resin and cellulose fibers. Therefore, it basically has water absorption due to the capillarity effect of the continuous porous structure, and further, due to the extremely high hydrophilicity of the cellulose fiber, an excellent water absorption rate and a large water absorption capacity can be obtained, and water is absorbed by the resin molded product. Since the moisture retention property of the water is obtained and the cellulose fiber is stably present in the thermoplastic resin as a material constituting the resin molded product, these effects can be obtained with high reproducibility over a long period of time.

In addition to having improved water absorption, the resin molded product of the present invention also has conductivity when it holds the electrolyte solution, so that it can be used as a biological electrode by containing the electrolyte solution. Since the biological electrode according to the present invention is flexible, it is possible to reduce the discomfort given when it comes into contact with the human body. Here, "flexible" and "flexible" mean that the sponge hardness based on the Japan Rubber Association standard (SRIS / 0101) is 90 or less, preferably 75 or less.

The biological electrode according to the present invention does not require a conductive paste that is sticky and complicated to remove as an auxiliary agent for energization. As the biological electrode according to the present invention, non-greasy and cheaper salt water or the like can be used as the conductive auxiliary agent, so that the labor and cost involved in mounting can be reduced. If an electrolyte such as sodium chloride (salt) is supported on the resin molded product as a conductive auxiliary agent, the resin molded product can exhibit conductivity simply by spraying water or the like to absorb water. Further, since the biological electrode according to the present invention is obtained by integrally molding the resin composition, it is easy to manufacture and there is no concern about separation of members. Moreover, since the structure is simple and easy to manufacture, the manufacturing cost is low and it can be disposable.

It is an SEM photograph of the surface of the test piece [1] manufactured in Example 1. It is a FIB photograph of the surface of the test piece [4] manufactured in Example 3. It is a FIB photograph of the cross section of the test piece [4] manufactured in Example 3.

Hereinafter, the present invention will be described in detail.

[Resin molded product]
The resin molded product of the present invention is a resin molded product having a continuous porous structure, particularly a resin molded product having a hydrophilic continuous porous structure, which is composed of a resin composition containing a thermoplastic resin and cellulose fibers. Is.
The continuous porous structure refers to a structure having a large number of pores communicating with each other inside a resin complex in which a thermoplastic resin and a cellulose fiber are mixed.
In the resin molded product of the present invention, both the thermoplastic resin and the cellulose fiber are exposed on the surface of the resin composite, that is, the outer surface and the pore surface (inner surface) of the resin composite that can be seen from the outside. ..

〔Thermoplastic resin〕
As the thermoplastic resin contained in the resin composition, it is preferable to use a resin suitable for extrusion molding or injection molding, and specifically, polyethylene resin, polypropylene resin, polybutylene resin, ethylene vinyl acetate copolymer and the like. Olefin-based thermoplastic resins; thermoplastic elastomers such as styrene-based elastomers, olefin-based elastomers, vinyl chloride-based elastomers, and urethane-based elastomers; and mixtures thereof can be used. Among these, it is particularly preferable to use an olefin-based elastomer. These can be used alone or in combination of two or more.

[Cellulose fiber]
The cellulose fiber used in the resin molded product of the present invention remains as a constituent material of the resin composite without being eluted in the water extraction step of eluting the pore-forming material in order to form a continuous porous structure in the production method described later. Anything that can be done will do.
Examples of such cellulose fibers include fibers composed of cellulose molecules, for example, cellulose fibers obtained by decomposing wood pulp and bamboo. Specifically, it is possible to use microfibrillated cellulose obtained by defibrating wood pulp with a high-pressure homogenizer or the like, lignocellulose nanofibers obtained by further subjecting it to hot water treatment, or cellulose nanofibers from which lignin has been removed. can.

The content ratio of the cellulose fiber in the resin composition is preferably 0.1 to 30% by mass, more preferably 0.4 to 10% by mass.
When the content of cellulose fibers in the resin composition is excessive, dispersion spots of cellulose fibers are likely to appear on the surface of the resin molded product, and the moldability may be inferior. On the other hand, when the content of the cellulose fibers in the resin composition is too small, the exposed state of the cellulose fibers on the surface of the resin composite of the resin molded product (the outer surface of the resin composite and the surface of the pores) becomes insufficient. Therefore, the hydrophilicity required for the intended use may not be obtained, and the obtained resin molded product may have low water absorption.

[Average pore size of pores constituting the continuous porous structure]
The average pore diameter of the pores constituting the continuous porous structure is preferably in the range of 1 to 120 μm, more preferably in the range of 1 to 60 μm. The average pore diameter of the pores constituting the continuous porous structure can be controlled by the average particle size of the pore-forming material used in the method for producing a resin molded product described later.
When the average pore diameter of the pores constituting the continuous porous structure is within the above range, an excellent water absorption rate can be surely obtained due to the effect of the capillary phenomenon. When the average pore diameter is excessively large, for example, when the resin molded product is a pen tip member, the ink flow of the pen tip member becomes excessive, and when the average pore diameter of the pores exceeds 120 μm, the effect of the capillary phenomenon cannot be obtained. As a result, there is a possibility that problems such as dropping of the retained ink may occur. On the other hand, when the average pore diameter is less than 1 μm and is excessively small, the effect of the capillary phenomenon is too strong and the discharge of the liquid absorbed by the resin molded product is restricted. For example, when the resin molded product is a pen tip member. The ink flow is poor and there is a risk of fading.

The average pore diameter of the pores that make up the continuous porous structure is determined by taking an SEM (scanning electron microscope) photograph of the cross section of the resin molded product, and using an automatic image processing analyzer for the photographic image captured by the scanner. The pores constituting the continuous porous structure in the cross section of the resin molded product were subjected to binarization treatment, and the maximum diameter of each of 50 arbitrary pores was calculated and used as the average value. Here, the maximum diameter means the maximum distance when the image of the pores is sandwiched between two parallel lines. Pore is a concept assuming a hole through which a pore-forming material is removed in a manufacturing method described later, and refers to a hole that is approximately a circular approximation.

[Porosity of resin molded products]
The porosity of the resin molded product is preferably in the range of 60 to 85% by volume, more preferably in the range of 65 to 75% by volume. The porosity can be controlled by the amount of the pore-forming material used in the method for producing a resin molded product described later.
When the porosity of the resin molded product is within the above range, a large water absorption capacity can be reliably obtained. If the porosity of the resin molded product is excessively high and the average pore diameter of the pores exceeds 120 μm, for example, if the resin molded product is a pen tip member, there may be a problem such as ink dripping on the pen tip member. May occur. On the other hand, if the porosity of the resin molded product is excessively low and the density of the pores is excessively low, for example, when the resin molded product is a pen tip member, there is a risk that the ink discharge from the pen tip member may be blurred. be.

The porosity of the resin molded product is calculated by the formula: [1- (mass of the resin molded product / true specific gravity of the resin molded product) / (apparent volume of the resin molded product)] × 100.

[Arbitrary component]
The resin composition constituting the resin molded product may contain an arbitrary component other than the thermoplastic resin and the cellulose fiber.
Optional ingredients include pigments, colorants, antioxidants, antistatic agents, conductivity-imparting agents, UV deterioration inhibitors, reinforcing agents, crystallization accelerators, clearing agents, bubble inhibitors, processing aids, lubricants, etc. Plasticizers, photocatalysts and the like can be used. These optional components may be used alone or in combination of two or more.

The resin molded product may contain a conductive auxiliary agent. As the conductive auxiliary agent, an electrolyte salt that does not irritate the skin, such as sodium chloride, potassium chloride, and magnesium chloride, is preferable. The conductive auxiliary agent may be supported on the resin molded product by subjecting the solid molded product obtained by melt molding the kneaded resin composition to water extraction treatment, further washing the molded product, immersing it in an electrolyte solution and drying it. The electrolyte concentration of the electrolyte solution is preferably 10% by mass or less, particularly preferably 1 to 5% by mass. When cutting a resin molded product, it is preferable before the conductive auxiliary agent is supported. The conductive auxiliary agent is preferably 0.05 to 0.5 g / cm ³ , particularly 0.1 to 0.2 g / cm ³ , in terms of the volume ratio of the resin molded product.

The resin molded product of the present invention preferably has a water absorption time of 10 seconds or less, particularly preferably 7 seconds or less, according to the JIS L1907 dropping method. Since the resin molded product of the present invention has such water absorption characteristics, when it is used as a biological electrode by absorbing water, the presence of an electrolytic solution such as saline solution between the resin molded product and the human body reduces the electrical resistance. can. Since the resin molded product of the present invention is flexible, it easily fits the unevenness of the human body when it is used as a biological electrode, but if it contains a liquid, the contact with the human body can be further stabilized. Therefore, the stability of sending and receiving electrical signals to and from the living body can be improved, the efficiency of receiving electrical signals from the living body, the efficiency of applying electrical stimulation to the living body are improved, and the electrical loss is reduced. can.

The shape of the resin molded product of the present invention is not particularly limited as long as it exhibits its performance, and can be configured to have an appropriate shape according to various uses.

The resin molded product of the present invention is suitably used as a product that absorbs water, water-soluble ink, water-soluble cosmetics, water-based paint, physiological saline, alcohol such as ethanol and isopropanol, and the like. It can be suitably used as a water-absorbing roll; a water-absorbing sheet; a cleaning cloth; a filter; a stamping material such as a penetrating mark; a pen tip member such as a stationery brush pen tip, an art material brush pen tip, or a decorative brush pen tip.

[Manufacturing method of resin molded products]
The method for producing a resin molded product of the present invention is a method for producing a resin molded product having the above-mentioned continuous porous structure.
Specifically, it has the following steps.
(1) A kneading step of kneading a raw material containing at least a thermoplastic resin, a cellulose fiber and a pore-forming material to obtain a raw material resin composition (2) A chipping step of converting the raw material resin composition into chips (3) Chipping Molding step of obtaining a solid molded product by melt molding using the raw material resin composition as a molding material (4) Water extraction step of obtaining a resin molded product by removing the pore-forming material from the solid molded product by water extraction treatment.

[Kneading process]
In the kneading step, a raw material containing at least a thermoplastic resin, a cellulose fiber, and a pore-forming material is kneaded.
As the kneading device, for example, an open roll, a kneader, an intensive mixer, a single-screw screw extruder, a twin-screw screw extruder and the like can be used.

The kneading temperature in the kneading step is not particularly limited as long as the thermoplastic resin is softened or melted and the pore-forming material is not softened, and is, for example, 80 to 150 ° C.

The content ratio of the cellulose fiber in the raw material resin composition may be adjusted according to the content ratio of the cellulose fiber in the resin composition forming the desired resin molded product, and may be, for example, 0.1 to 30% by mass.

[Pore forming material]
The pore-forming material is insoluble in the thermoplastic resin contained in the resin composition constituting the resin molded product, and has fluidity when a particulate matter dissolved in an aqueous solvent or an aqueous solvent is added. Particles in a state can be used, and for example, inorganic fine particles and organic fine particles can be used.
Examples of the inorganic fine particles include alkaline earth metal salts such as calcium carbonate; alkali metal salts such as potassium chloride, sodium chloride, sodium sulfate, potassium sulfate, sodium nitrate and potassium nitrate.
Examples of the organic fine particles include starches such as cornstarch, wheat starch and potato starch; sugars such as sugar; pentaerythritol, tetramethylolmethane, pentaglycerin, hexitol, glycitol and peptitol.
These can be used alone or in combination of two or more.

Since the portion where the pore-forming material is eluted from the solid molded product in the water extraction step becomes the pores of the resin molded product, the average particle size of the pore-forming material is the pores constituting the continuous porous structure in the desired resin molded product. The average particle size may be any one corresponding to the average pore size of the above, and is set to, for example, 1 to 120 μm.

The blending ratio of the pore-forming material in the raw material resin composition is a ratio according to the porosity constituting the continuous porous structure in the desired resin molded product, and varies depending on the average particle size of the pore-forming material, but is, for example, thermoplastic. It is 250 to 600 parts by mass with respect to 100 parts by mass of the resin.

The raw material resin composition may contain a pore-forming agent together with a pore-forming material. The pore aid is hydrophilic and contributes to the removal of the pore-forming material in the water extraction step.
Specific examples of the pore aid include polyhydric alcohol monomers such as ethylene glycol, glycerin, propylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, pentaerythritol, erythritol, and pinacol; diethylene glycol and triethylene. Examples thereof include polyhydric alcohol polymers such as glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and polyethylene glycol.
These can be used alone or in combination of two or more.

The blending ratio of the shape pore aid in the raw material resin composition is, for example, 10 to 60 parts by mass with respect to 100 parts by mass of the thermoplastic resin.

In the resin molded product, pores may be formed by using a known decomposition type foaming agent or evaporative foaming agent instead of the pore forming material that requires washing with water.

The raw material resin composition may contain a surfactant.
The surfactant is not particularly limited, and a nonionic surfactant, a cationic surfactant, an anionic surfactant, and an amphoteric surfactant can be used.
The blending ratio of the surfactant in the raw material resin composition is, for example, 5 to 30 parts by mass with respect to 100 parts by mass of the thermoplastic resin.

[Chip making process]
In the chipping step, the raw material resin composition obtained in the kneading step is chipped.

[Molding process]
In the molding step, the chipped raw material resin composition obtained by the kneading step is used as a molding material, and this is melt-molded into a desired shape.
The molding method is not particularly limited, and a method suitable for a desired shape can be adopted from methods such as an injection molding method, a compression molding method, an extrusion molding method, and a calendar molding method.

When molding is performed by an injection molding method, specifically, when the raw material resin composition (molding material) is put into the mold from the cylinder of the injection molding machine, the surface of the mold is made of a thermoplastic resin glass. The thermoplastic resin cooled to less than the transition point and rapidly increased in viscosity is cooled and solidified with the cellulose fibers and the pore-forming material dispersed therein, whereby a solid molded product is obtained.
The molding temperature may be any temperature as long as the thermoplastic resin is softened or melted and the pore-forming material is not softened. For example, the cylinder temperature is preferably 80 to 200 ° C. and the mold temperature is preferably 20 to 100 ° C.

[Water extraction process]
In the water extraction step, the pore-forming material in the solid molded body obtained in the molding step is removed by water extraction treatment and outflow or elution to obtain a resin molded product having a continuous porous structure.
Through the water extraction step, a resin composite composed of components that are not removed by the water extraction treatment in the raw material resin composition, which constitutes the solid molded product, remains, and the pore-forming material in the solid molded product is continuously present. The former portion becomes hollow, which forms a continuous porous structure. The portion of the solid molded body in which the pore-forming materials are continuously present is a portion in which the pore-forming materials are in contact with each other and a portion in which the separated pore-forming materials are filled with a shape-forming agent. say.
In the water extraction step, most of the components removed by the water extraction treatment in the raw material resin composition are pore-forming materials, pore aids and surfactants, and some cellulose fibers may also be removed. be. Then, at least the thermoplastic resin and many cellulose fibers remain in the resin complex without being removed by the water extraction treatment. In addition, a very small amount of pore-forming material may remain in the resin complex.

The specific method for performing the water extraction treatment of the pore-forming material is not particularly limited as long as the pore-forming material can be removed using an aqueous solvent. Specifically, for example, a method of immersing the solid molded body in an aqueous solvent and leaving it for a predetermined time, a method of spraying the solid molded body with the aqueous solvent, a method of washing the solid molded body with the aqueous solvent, and the like can be adopted. can. The temperature of the aqueous solvent in the water extraction treatment may be less than the glass transition point of the thermoplastic resin, and is, for example, 30 to 80 ° C.
The aqueous solvent may be any solvent as long as it can flow out or elute the pore-forming material and does not dissolve the cellulose fibers, such as water, water-soluble lower fatty alcohol, dilute acid water such as hydrochloric acid water, and rare alkaline water. Can be mentioned.

When dilute acid water or rare alkaline water is used as the aqueous solvent, it is preferable to carry out the neutralization treatment after performing the water extraction step.

The resin molded product obtained in the water extraction step is preferably washed and dried.

The resin molded product of the present invention has a continuous porous structure composed of a resin composition containing a thermoplastic resin and cellulose fibers. Therefore, it basically has water absorption due to the capillarity effect of the continuous porous structure, and further, due to the extremely high hydrophilicity of the cellulose fiber, an excellent water absorption rate and a large water absorption capacity can be obtained, and water is absorbed by the resin molded product. Since the moisture retention property of the water is obtained and the cellulose fiber is stably present in the thermoplastic resin as a material constituting the resin molded product, these effects can be obtained with high reproducibility over a long period of time.
Further, according to the method for producing a resin molded product as described above, the resin molded product as described above can be reliably obtained.

Although the embodiments of the present invention have been specifically described above, the embodiments of the present invention are not limited to the above examples, and various modifications can be made.

Specific examples of the present invention will be described below, but the present invention is not limited thereto.

<Example 1>
Olefin-based elastomer ("Engage ENR8440" manufactured by DuPont); calcium carbonate (average particle size 20 μm) as a pore-forming material; 438 parts by mass, pentaerythritol as a pore aid; 30 parts by mass, pores with respect to 100 parts by mass. PEG (polyethylene glycol) (PEG2000) with an average molecular weight of 2000 as an auxiliary agent; 44 parts by mass, PEG (polyethylene glycol) (PEG1500) with an average molecular weight of 1500 as a pore aid; 13 parts by mass, surfactant (Sanyo Kasei Co., Ltd.) "Emalmin 110"); 5 parts by mass, wood pulp fiber as cellulose fiber; 6 parts by mass were blended, and these were placed in a kneader heated to 150 ° C., stirred and kneaded to obtain a raw material resin composition. After that, it was pelletized using a pelletizer.

This pelletized raw material resin composition is molded into a cylindrical shape having an outer diameter of 3 mm, an inner diameter of 1.5 mm, and a length of 10 mm at a temperature of 100 to 160 ° C. using an injection molding machine, and then treated with hydrochloric acid to carbonate. Calcium was removed, neutralized, washed, and dried to prepare a resin molded product having a continuous porous structure. Hereinafter, this will be referred to as a test piece [1].
The porosity of this test piece [1] was 70% by volume, and the average pore diameter of the pores was 20 μm.

<Example 2>
In Example 1, the filter paper made of natural pulp was cut into strips instead of wood pulp fibers, and the natural pulp fibers crushed into fibers by a mill were added. A resin molded product having a porous structure was produced. Hereinafter, this will be referred to as a test piece [2].
The porosity of this test piece [2] was 70% by volume, and the average pore diameter of the pores was 20 μm.

<Comparative example 1>
A resin molded product having a continuous porous structure was produced in the same manner as in Example 1 except that wood pulp fibers were not added in Example 1. Hereinafter, this will be referred to as a test piece [3].
The porosity of this test piece [3] was 70% by volume, and the average pore diameter of the pores was 20 μm.

<Example 3>
Styrene-based elastomer (“TPE-SB2710” manufactured by Sumitomo Chemical Co., Ltd.); calcium carbonate (average particle size 10 μm) as a pore-forming material; PEG (polyethylene glycol) (PEG2000) with an average molecular weight of 2000 as a pore aid; 38 parts by mass, PEG (polyethylene glycol) (PEG1500) with an average molecular weight of 1500 as a pore aid; 12 parts by mass, surfactant (Sanyo Kasei) "Sannonic TN"); 5 parts by mass, "Seroxan" (hydrophobicized cellulose nanofiber) manufactured by Seeds React Co., Ltd .: 5 parts by mass, and put them in a kneader heated to 150 ° C. The raw material resin composition was obtained by stirring and kneading, and then pelletized using a pelletizer.
After that, a resin molded product was produced in the same manner as in Example 1. Hereinafter, this will be referred to as a test piece [4].
The porosity of this test piece [4] was 72% by volume, and the average pore diameter of the pores was 20 μm.

The following water absorption test was performed using these test pieces [1] to [4].
[Water absorption test A: Water absorption rate]
Hold the upper end of each of the test pieces [1] to [4] in a vertically extending posture, and the lower end 3 mm is the water-based carbon black ink for eyeliner "WD-3 / V1" (RIKEN CHEMICAL INDUSTRIES). It was immersed in (manufactured by the same company), and the penetration time of the ink into the entire test piece was measured.
As a result, it was confirmed that in the test piece [1] containing the wood pulp fiber, the ink permeated 100% of the portion in 55 seconds. Further, in the test piece [2], it was confirmed that the ink permeated 100% of the portion in 40 seconds. Further, in the test piece [4], it was confirmed that the ink permeated 100% of the portion in 19 seconds. On the other hand, in the test piece [3] containing no wood pulp fiber, it was confirmed that the dyed portion of the test piece [3] was about 70% after 10 minutes had passed.

[Water absorption test B: Water absorption capacity]
Each of the test pieces [1] to [4] is placed on the surface of water in which the water-based carbon black ink for eyeliner "WD-3 / V1" (manufactured by RIKEN CHEMICAL INDUSTRIES) is dissolved, and floats and sinks after 30 minutes. The condition was observed.
As a result, 70% of the test pieces [1], [2], and [4] containing cellulose fibers (wood pulp fibers, natural pulp fibers or cellulose nanofibers) may be immersed under the water surface. confirmed. On the other hand, it was confirmed that the test piece [3] containing no cellulose fiber was not immersed under the water surface at all.

[Water absorption test C: Water absorption characteristics by JIS L1907 dropping method]
A disk test piece having a radius of 5 cm and a thickness of 10 mm was prepared by the same preparation procedure as the test piece [4] of Example 3. When the water absorption characteristics of this test piece were measured by the JIS L1907 dropping method, the time from dropping water to completely absorbing water was 5 seconds.

A disk test piece having a radius of 5 cm and a thickness of 10 mm was prepared by the same preparation procedure as the test piece [3] of Comparative Example 1. When the water absorption characteristics of the test piece of this comparative example were measured by the JIS L1907 dropping method, the time from dropping water to completely absorbing water was 90 seconds.

From the results of these water absorption tests, it can be seen that a certain degree of water absorption can be exhibited by using an olefin-based elastomer that does not have water absorption by itself into a molded product having a continuous porous structure. On top of that, by further blending cellulose fibers (wood pulp fibers, natural pulp fibers or cellulose nanofibers) with the resin composition for forming a molded product having a continuous porous structure, water absorption is significantly improved. At the same time, it was confirmed that the water retention once absorbed was also excellent. When SEM photographs of the surfaces of the test pieces [1] and [4] were taken and observed, it was found that the ends of the cellulose fibers (wood pulp fibers, natural pulp fibers) were clearly exposed on the surface. From this, it is presumed that the water absorption is improved by exposing the end portion of the cellulose fiber (wood pulp fiber, natural pulp fiber or cellulose nanofiber) on the surface of the resin molded product or the surface of the pores. NS.
An SEM photograph of the surface of the test piece [1] is shown in FIG. In FIG. 1, there is a resin composite (gray part and white streaks) around the pores composed of black parts, and in the resin composite, cellulose fibers (divided from wood pulp fibers) (white streaks) are thermoplastic. It can be observed that the cellulose fibers are buried in the resin (gray part) and the bundles of cellulose fibers are exposed from the thermoplastic resin in some places. An example of a portion where cellulose fibers appear as a bundle is indicated by a white arrow in the SEM photograph of FIG.
Further, the electron micrographs of the cross section of the test piece [4] by the FIB method are shown in FIGS. 2A and 2B. It can be seen that cellulose nanofibers having a size of 200 to 300 nmΦ protrude from the surface of the pores.

<Measurement of sponge hardness>
The same test piece used in the water absorption test C was measured with a sponge durometer TYPE FO (trade name: TECLOCK, GS-744G). The measured hardness of the test piece was 74.

<Measurement of impedance>
The impedance of the test piece [4] of Example 3 was measured using an impedance measuring device (trade name: CHECKTRODE, model 1089mkIII) manufactured by UFI. Specifically, a pair of substantially columnar test pieces were immersed in a saline solution having a concentration of 2% by mass, dehydrated by centrifugation, and dried (test piece [5]). This test piece [5] supported ^{salt at 0.1 g / cm 3.} This test piece carrying salt was absorbed by water and sandwiched between two-terminal probes, and the impedance was measured. The average impedance of this test piece [5] carrying the electrolyte was 12 kΩ.

The impedance of the test piece [3] of Comparative Example 1 was measured by the same method. The test piece [3] was unmeasurable because the average impedance value exceeded the maximum measurable value of 50 kΩ.

Regarding continuous porous resin molded products that can be used for water-absorbing rolls, various sanitary materials, stamping materials, various pen tips, etc., in particular, continuous porous resin that has excellent water absorption, can impart conductivity, and has good contact with the human body. Related to molded products.

Claims (6)

A resin molded product having a continuous porous structure.
The resin composition comprises a thermoplastic resin and a cellulose fiber, and the resin molded product is a resin molded product which is a pen tip member . A resin molded product having a continuous porous structure.
A resin molded product comprising a resin composition containing a thermoplastic resin and cellulose fibers, wherein the resin molded product is a biological electrode that gives an electrical stimulus to a living body or measures an electrical signal of the living body . The resin molded product according to claim 2, wherein the resin molded product further contains a conductive auxiliary agent. A resin molded product having a continuous porous structure.
A resin molded product comprising a resin composition containing a thermoplastic resin and a cellulose fiber, the resin molded product having a plate shape and being a sanitary member in contact with the biological epidermis . The resin molded product according to claim 4, wherein the sanitary member is a liquid absorbing pad that covers the skin. A biological electrode unit in which a plurality of the resin molded products according to claim 2 or 3 are supported on a support.

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