JP5697379B2 - Water-resistant cellulose sheet - Google Patents

Description

  The present invention relates to a water-resistant cellulose sheet composed of fine cellulose fibers.

A nonwoven fabric composed of so-called nanofibers with a fiber diameter of 1 μm or less has many fine voids formed by the network structure formed by the nanofibers, so fine particles contained in gas or liquid can be filtered out with low pressure loss. It is expected to be used as a filter medium that can be used.
Moreover, since the nonwoven fabric comprised from a nanofiber can hold | grip fine abrasive grain efficiently between nanofibers, it is utilized as a polishing tape for smoothing the texture surface of a hard disk.

  Examples of the nanofiber material constituting the nonwoven fabric include polyester fiber, polyamide fiber, polyolefin fiber, cellulose fiber, and the like. In particular, microfibers obtained from natural cellulose such as bacterial cellulose (hereinafter abbreviated as BC) and pulp as raw materials. Non-woven fabrics made of so-called fine cellulose fibers, such as fibrous cellulose (microfibrated cellulose, hereinafter abbreviated as MFC), are filtered with high adsorption performance derived from heat resistance, chemical resistance and high surface activity. High properties as a material can be expected. Further, since the nonwoven fabric made of fine cellulose fibers has high crystallinity and high elastic modulus, it can be expected to be used as an abrasive.

As a non-woven fabric composed of fine cellulose fibers, BC film forming technology is introduced in the following Patent Document 1. Patent Document 1 discloses that a hybrid film obtained by hybridizing an epoxy resin or an acrylic resin to a BC film obtained by pressing and drying a BC gel obtained by stationary culture has a low linear expansion coefficient. At the same time, since it has high transparency, it is disclosed that it is effective as an optical film or an optical substrate.
However, according to Patent Document 1, the BC membrane obtained by stationary culture is a membrane having a very dense structure, and the porosity (opening rate) is at most about 30%. A membrane with a small porosity cannot be used as a filter medium from the viewpoint of filtration efficiency (that is, the filtration rate must be slowed because the pressure loss is too high). Furthermore, since cellulose has a high affinity for water and swells in a solution system containing water, if the nonwoven fabric of Patent Document 1 is used as a solution-based filter medium containing water or a blood separation membrane, the time-lapse occurs. However, there is a problem that the average pore diameter is changed and the collection efficiency or the separation efficiency is lowered. Similarly, when polishing is performed with a solution system containing water, there is a problem that the shape changes with time and the life as an abrasive is very short.

On the other hand, the present inventors have proposed a nonwoven fabric composed of cellulose fibers having a maximum fiber diameter of 1500 nm or less and having a high porosity and a fine network structure (refer to Patent Document 2 below). The cellulose nonwoven fabric described in Patent Document 2 has excellent film quality uniformity with little variation in physical properties depending on the measurement site.
However, the cellulose nonwoven fabric described in Patent Document 2 also has a problem of low resistance to water, like the BC film of Patent Document 1.
As described above, a nonwoven fabric composed of fine cellulose fibers having high porosity and high durability against water has not been proposed so far.

JP 2005-60680 A International Publication No. 2006-004012

  The problems to be solved by the present invention are the heat resistance, chemical resistance, high adsorption performance derived from high elasticity and surface activity, and high porosity and high durability against water. It is providing the water-resistant cellulose sheet which consists of a fine cellulose fiber which has.

As a result of intensive studies and experiments to solve the above problems, the present inventors have unexpectedly found that the above problems can be solved by the following solution means, and have completed the present invention.
That is, the present invention is as follows.

[1] A water-resistant cellulose sheet comprising a nonwoven fabric composed of fine cellulose fibers having a number average fiber diameter of 500 nm or less, wherein the fine cellulose fibers are divinyl sulfone, carbodiimide, dihydrazine, dihydrazide, epichlorohydrin, polyfunctional epoxy It is bridge | crosslinked by the at least 1 sort (s) of crosslinking agent chosen from the group which consists of a compound and an isocyanate compound, and the following (1)-(4) requirements:
(1) Weight ratio of fine cellulose fiber: 96.6 % by weight or more and 99% by weight or less (2) Porosity: 50% or more (3) Tensile strength equivalent to 10 g / m ² per unit area: 6N / 15mm or more (4) A water-resistant cellulose sheet satisfying all of the wet / dry strength ratio of tensile strength: 50% or more.

  [2] The water-resistant cellulose sheet according to [1], wherein an average pore diameter change rate after water permeation is 40% or less.

[ 3 ] A filter medium comprising the water-resistant cellulose sheet according to [1] or [2] .

[ 4 ] A filter cartridge including the filter medium according to [ 3 ].

[ 5 ] A blood separation membrane comprising the water-resistant cellulose sheet according to any one of [1] to [ 3 ].

[ 6 ] A polishing tape comprising the water-resistant cellulose sheet according to any one of [1] to [ 3 ].

  The water-resistant cellulose sheet of the present invention has high adsorption performance derived from heat resistance, chemical resistance, high elastic modulus and high surface activity specific to cellulose, and has high porosity and high durability against water. Therefore, it can be used as a filter medium in a wide solvent range from aqueous to organic solvent, and at the same time, it can be effectively used as a blood separation membrane / adsorption membrane. The water-resistant cellulose sheet of the present invention can be used as a polishing tape in a semiconductor production line.

The water-resistant cellulose sheet of the present invention is composed of a cellulose nonwoven fabric composed of fine cellulose fibers having a number average fiber diameter of 500 nm or less.
Here, the number average fiber diameter of the fine cellulose fiber defined in the present invention is calculated by the following method.
(Calculation method of number average fiber diameter)
With respect to the surface of the sheet, when the observation with a scanning electron microscope (SEM) was performed at 3 times at random at a magnification equivalent to 10,000 times, the obtained SEM image was lined in the horizontal and vertical directions with respect to the screen. Then, the fiber diameter of the fiber that intersects the line is measured from the enlarged image, and the number of intersecting fibers and the fiber diameter of each fiber are counted. In this way, the number average fiber diameter is calculated using two series of measurement results for one image. Further, the number average fiber diameter is calculated in the same manner for the other two extracted SEM images, and the results for a total of three images are averaged to obtain the number average fiber diameter of the target sample.

  When the number average fiber diameter of the fine cellulose fibers is 500 nm or less, the tensile strength tends to increase due to an increase in the entanglement points between the fine fibers, and the wet / dry strength ratio increases. When the number average fiber diameter of the fine cellulose fibers is larger than 500 nm, a cellulose sheet having a tensile / dry strength ratio of 50% or more cannot be obtained. Although the reason is not clear, for example, there is a treatment with a crosslinking agent as one of the resistance imparting methods. However, when the fiber diameter is large, it is assumed that only a very small part of the fiber surface has an effect of the crosslinking treatment. The number average fiber diameter of the fine cellulose fiber is 10 nm or more and 350 nm or less, more preferably 30 nm or more and 300 nm or less from the viewpoint of strength development and improvement of the wet / wet strength ratio. The fine cellulose fiber of the present invention is a short fiber (staple-like) fine fiber and does not include an endless long fiber (filament-like) fiber.

  It is preferable that the water-resistant cellulose sheet of the present invention does not contain cellulose fibers exceeding the maximum fiber diameter of 1500 nm. In the present invention, the fact that the cellulose fiber having the above-mentioned large fiber diameter is not included is obtained when the surface of the sheet is randomly observed at three places with a scanning electron microscope (SEM) at a magnification equivalent to 10,000 times. It means that the average number of fibers having a fiber diameter exceeding 1500 nm is less than 2 in all SEM images. When cellulose fibers having a maximum fiber diameter exceeding 1500 nm are contained, mechanical properties such as high elongation may partially fluctuate. The maximum fiber diameter of the cellulose fiber is more preferably 1200 nm or less, and still more preferably 1000 nm or less.

  In the water-resistant cellulose sheet of the present invention, the weight ratio of fine cellulose fibers is 1% by weight or more and 99% by weight or less. When the weight ratio of the fine cellulose fibers is less than 1% by weight, it is difficult to form a uniform fine pore diameter, so that a large number of coarse pinholes are formed and the specific surface area is reduced. Collection efficiency is greatly reduced. On the other hand, when the weight ratio of the cellulose fiber exceeds 99% by weight, the mechanical strength is lowered and the handleability is poor. The weight ratio of the fine cellulose fibers in the water-resistant cellulose sheet of the present invention is preferably 3% by weight to 95% by weight, and more preferably 5% by weight to 90% by weight.

  The water-resistant cellulose sheet of the present invention has a porosity of 50% or more. When the water-resistant cellulose sheet of the present invention has a porosity of 50% or more, it can exhibit high collection efficiency when used as a filter medium or a separation membrane. Furthermore, the polishing tape is manufactured by applying a kneaded abrasive abrasive and a binder resin to a nonwoven fabric as a base material, but the water-resistant cellulose sheet of the present invention has a high porosity. In addition, the abrasive grains can be efficiently gripped, and the integrity with the binder resin is improved, and troubles such as peeling in the polishing process do not occur. A preferable porosity range is 60% or more, and more preferably 70% or more. The upper limit value of the porosity is not particularly limited, but the controllable range is 98% or less, preferably 95% or less.

The tensile strength corresponding to a basis weight of 10 g / m ² of the water-resistant cellulose sheet of the present invention is 6 N / 15 mm or more. The tensile strength of the sheet is affected by the basis weight, but if the tensile strength corresponding to a basis weight of 10 g / m ² is less than 6 N / 15 mm, the sheet will be damaged during handling. Preferably, it is 7 N / 15 mm or more, more preferably 8 N / 15 mm or more (both are equivalent to a basis weight of 10 g / m ² ). On the other hand, the upper limit of the tensile strength of the water-resistant cellulose sheet of the present invention is not particularly limited, but it is substantially impossible to exceed 100 N / 15 mm per 10 g / m ² . The tensile strength in the present invention is measured after drying for 6 hours in a dryer controlled at 105 ° C. and after storing for 30 minutes or more in a desiccator.

The water-resistant cellulose sheet of the present invention needs to have a tensile / dry strength ratio of 50% or more. The wet / dry strength ratio defined in the present invention means that the tensile strength of the dry sheet is defined as the dry strength under the above-mentioned predetermined conditions, and the dry sheet is immersed for 5 minutes in a container with sufficient water to immerse the sheet. The measured tensile strength is defined as wet strength, and the following formula (1):
Dry / wet strength ratio (%) = (wet strength) / (dry strength) × 100 Formula (1)
The one calculated by. Here, it is not necessary to convert the dry strength and wet strength to the equivalent of 10 g / m ² per unit area.

The water-resistant cellulose sheet of the present invention has a tensile / wet strength ratio of 50% or more. Therefore, when used as a solution-based filter medium containing water or a blood separation membrane, the average pore diameter does not change with time. In addition, the collection effect can be stably maintained for a long period of time, and the service life can be extended when used as an abrasive. The wet / dry strength ratio of the water-resistant cellulose sheet of the present invention is preferably 60% or more from the advantage of use (longer life as a filtering material or an abrasive), more preferably 70% or more. In addition, the water-resistant cellulose sheet of the present invention preferably has an average pore diameter change rate of 40% or less after water permeation from the viewpoint of extending the life as a filtering material or an abrasive, more preferably 30% or less, and most preferably Is 20% or less. The average pore diameter is evaluated in a pore diameter distribution measurement test using a palm porometer (CFE-1200AEX manufactured by Seika Sangyo). The average pore diameter change rate after water permeation is expressed by the following formula (2):
Average pore diameter change rate after water permeation (%) = (average pore diameter after water permeation−average pore diameter before water permeation) / average pore diameter before water permeation × 100 formula (2)
Is calculated by

Here, the average pore diameter after water permeation is set such that the sheet is not leaked, and the ultrapure water is fed at a pressure of 1 kg / cm ² for 60 minutes using a liquid feed pump. Evaluation is performed using a sample completely substituted with ethanol.

  The fine cellulose fiber constituting the water resistance of the present invention is preferably crosslinked with a crosslinking agent. As the cross-linking agent, at least one cross-linking agent selected from the group consisting of divinyl sulfone, carbodiimide, dihydrazine, dihydrazide, epichlorohydrin, polyfunctional epoxy compound, and isocyanate compound is selected because of its reactivity with cellulose.

  Polyfunctional epoxy compounds include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol diglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythridine ether. Examples include cytosyl, diglycidyl ether, trimethylolpropane polyglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether.

Examples of the isocyanate compound include water-dispersible polyisocyanates. Specific examples of water-dispersible polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and 4,4′-. Diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4′-diisocyanate, 2,2′-diphenylpropane-4,4′-diisocyanate, 3,3 ′ -Dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate Aromatic isocyanates such as 3,3′-dimethoxydiphenyl-4,4′-diisocyanate, aliphatic isocyanates such as 1,6-hexamethylene diisocyanate, 1,4-tetramethylene diisocyanate, lysine diisocyanate, xylylene-1,4 ′ Aromatic diisocyanates such as diisocyanate, xylylene-1,3′-diisocyanate, isophorone diisocyanate, water-added tolylene diisocyanate, water-added xylylene diisocyanate, water-added diphenylmethane diisocyanate, water-added tetramethylxylylene diisocyanate, alicyclic diisocyanate And NCO group-terminated compounds obtained by reacting these compounds with active hydrogen group-containing compounds.
Also, as a water-dispersible polyisocyanate, a polyol is added to an organic isocyanate and an isocyanurate-forming catalyst is added, and instead of a polyisocyanate having an isocyanurate ring structure introduced, a polymer of diisocyanate, a bifunctional or higher functional polyol, etc. You may use the prepolymer-like isocyanate compound obtained by reaction with a diisocyanate or a polymetric body. These polyisocyanates can be used alone or in a mixture of two or more.

  Among the cross-linking agents listed above, divinyl sulfone, ethylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol poly (polyglycerol) are used from the viewpoint of safety, high reactivity with cellulose, stability of the cross-linking agent, and suppression of coloring. Glycidyl ethers, aliphatic or alicyclic polyisocyanates are preferred.

  Moreover, the fine cellulose fiber which comprises the water resistance of this invention may be chemically modified within the range which does not inhibit the objective of this invention. For example, some or most of the hydroxyl groups present on the surface of fine cellulose fibers (fine cellulose fibers) are esterified containing acetate ester, nitrate ester, sulfate ester, alkyl ethers such as methyl ether, carboxymethyl It may include etherified carboxy ethers, etherified ones containing cyanoethyl ether, and those in which the hydroxyl group at the 6-position is oxidized by a TEMPO oxidation catalyst to form carboxyl groups (including acid and salt forms). it can. In addition, when used as a protein removal filter, an antibody may be immobilized on these chemically modified cellulose fibers, or alkyl ethers such as polyethylene glycol may be grafted on the cellulose surface, which is expected. It can be appropriately selected depending on the characteristics.

In order for the water-resistant cellulose sheet of the present invention to function suitably, it is important to have a fine network structure and a certain air permeability, and the basis weight is 5 g / m ² or more and 200 g / m ² or less. The air permeability resistance needs to be controlled with a balance of 10 s / 100 ml or more and 2000 s / 100 ml or less. A sheet having a basis weight of less than 5 g / m ² is too thin and the handleability is remarkably deteriorated. On the other hand, when the basis weight is greater than 200 g / m ² , the porosity is reduced.

Air permeability resistance is an index of the ease of flow of fluids such as gas and liquid. The lower the value of air resistance, the easier the fluid flows, and vice versa. . The air permeation resistance in the present invention is obtained by dividing a 25 cm square filter medium into 10 equal areas, and using the Gurley type densometer (model G-B2C, manufactured by Toyo Seiki Co., Ltd.) for the 10 sections, 100 ml of air. The average value of the measured values of the permeation time is excluded from the air resistance specified in the present invention if there is a portion below 10 s / 100 ml or a portion exceeding 2000 s / 100 ml even at one location. This is because it suggests poor film quality uniformity. When the air resistance evaluated by the method according to the definition of the present invention is less than 10 s / 100 ml, the trapping efficiency as a filter medium / separation membrane is remarkably lowered. I can't. On the other hand, when the air resistance exceeds 2000 s / 100 ml, when it is used as a filter medium / separation membrane, the filtration rate is remarkably reduced and the pressure loss is large in the filtration step, causing the membrane to burst. The basis weight of the filter medium of the present invention is preferably 8 g / m ² or more and 180 g / m ² or less from the viewpoint of handling and low pressure loss, and most preferably 10 g / m ² or more and 150 g / m ² or less. The air resistance is preferably in the range of 20 s / 100 ml to 1500 s / 100 ml from the viewpoint of collection efficiency and prevention of membrane breakage during filtration.

The cellulose nonwoven fabric composed of fine cellulose fibers in the filter medium of the present invention may contain one or more water-soluble compounds selected from the group consisting of sugars, polyhydric alcohols, alcohol derivatives, and water-soluble polymers.
Here, as sugar, glucose, mannose, galactose, fructose, xylose, trehalose, cellobiose and maltose, as polyhydric alcohol, ethylene glycol, propylene glycol, diethylene glycol and glycerin, as alcohol derivative, ethylene glycol monomethyl ether , Ethylene glycol monoethyl ether, ethylene glycol mono n-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol dimethyl ether, water-soluble polymers include polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, polypropylene glycol, polyacrylic acid, Polymethacrylic acid, water-soluble polysaccharides, and Soluble polysaccharide derivatives, and the like, but not limited thereto.

  Here, the water-soluble polysaccharide means a water-soluble polysaccharide, and various compounds exist as natural products. For example, α-1,4-glucan represented by starch, solubilized starch, amylose and pullulan, α-1,6-glucan represented by dextran, curdlan and β-1,3-glucan represented by lentinan Examples include glucan, amylopectin, branched sugars typified by glycogen, xylan, galactan, mannan, glucomannan, glucomannoglycan, galactoglucomannoglycan, and heteroglycans typified by guaran. It is not something.

  The water-soluble polysaccharide derivative includes the above-described water-soluble polysaccharide derivatives, for example, alkylated products, hydroxyalkylated products, and acetylated products, which are water-soluble. Alternatively, even if the polysaccharide before derivatization is insoluble in water such as cellulose, starch, etc., the water-solubilized one by derivatization, for example, hydroxyalkylation, alkylation, carboxyalkylation is also said water-soluble Included in polysaccharide derivatives. Specifically, hydroxyalkyl celluloses such as hydroxyethyl cellulose and hydroxypropyl cellulose, hydroxyalkyl starches such as hydroxyethyl starch and hydroxypropyl starch, methylcellulose, carboxymethylcellulose, carboxyethylcellulose, and hydroxyethylmethylcellulose and hydroxypropylmethylcellulose. In addition, water-soluble polysaccharide derivatives derivatized with two or more kinds of functional groups are also included, but are not limited thereto.

  Among the water-soluble compounds described above, water-soluble polysaccharides and water-soluble polysaccharide derivatives, which are water-soluble polymers, are often highly heat-resistant and have a large effect of improving the strength of cellulose nonwoven fabrics. When the water-soluble polysaccharide and the water-soluble polysaccharide derivative are used, the cellulose nonwoven fabric obtained is particularly preferable because it has a high strength that does not impair the heat resistance inherent in cellulose.

  When the water-soluble cellulose sheet contains the water-soluble compound, the water-soluble compound functions as a binder that reinforces the contact point strength between fine cellulose fibers. The content of the water-soluble compound is preferably 0.5% by weight or more and 20% by weight or less, more preferably 0.8% by weight or more and 15% by weight or less, and further preferably 1.0% by weight or more with respect to the weight of the filter medium. 10% by weight or less. The water-soluble compound described above preferably has a 2% aqueous solution viscosity (B-type viscometer) of 500 to 6,000 mPa · s in order to exhibit the binder effect, and a sheet described later. It is preferable that the solution viscosity of the water-soluble compound is within this range also for the dispersion stability of the emulsion paper dispersion in the production process.

  The water-resistant cellulose sheet of the present invention is less than 10% by weight based on the weight of the sheet, and is a polypropylene short fiber, a composite fiber of polypropylene (core) and polyethylene (sheath) as long as the object of the present invention is not impaired Binder fibers such as a composite fiber of polypropylene (core) and ethylene vinyl alcohol (sheath), a composite fiber of high-melting polyester (core) and low-melting polyester (sheath) can be contained. Further, the water-resistant cellulose sheet of the present invention is less than 10% by weight with respect to the sheet weight and does not impair the effects of the present invention, so that silica particles, alumina particles, diamond particles, boron nitride, silicon carbide, titanium oxide Inorganic particulate compounds such as particles and calcium carbonate particles, and organic fine particles such as crosslinked acrylic resin, crosslinked polystyrene, melamine resin, phenol resin, epoxy resin, urea resin, and polycarbonate resin can be contained.

  In the water-resistant cellulose sheet of the present invention, a layer composed of organic fibers having a number average fiber diameter of 0.5 μm or more and 30 μm or less can be disposed at a weight ratio of 1% by weight to 95% by weight with respect to the weight of the filter medium.

  By combining the layer made of organic fibers and the non-woven fabric made of fine cellulose fibers specified in the present invention, the handleability as a sheet is improved. May be improved (perhaps because the organic fiber layer is used to filter out those having a large particle size). The number average fiber diameter of the organic fibers is preferably 0.5 μm or more and 30 μm or less for the purpose of improving the strength of the sheet, maintaining flexibility, and uniformity of the film quality. Moreover, when the number average fiber diameter of the organic fibers is within this range, the organic fiber layer forms pores of several μm to several tens of μm, and acts as a filter material for coarse particles. The weight ratio of the organic fiber to the water-resistant cellulose sheet is preferably 1% by weight or more and 95% by weight or less, and the strength of the sheet is improved by being 1% by weight or more. When the weight ratio of the organic fibers exceeds 95% by weight, the features of the fine cellulose fibers (high adsorption performance due to the high specific surface area) are hindered. The fiber diameter of the organic fiber is preferably 1 μm or more and 25 μm or less, more preferably 1.5 μm or more and 20 μm or less, and the weight ratio of the preferable organic fiber layer is 5% by weight or more and 90% by weight or less, more preferably 10% by weight or more and 80% or less. % By weight or less.

  Here, organic fibers include polyamide fibers such as 6-nylon and 6,6-nylon, polyester fibers such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate, polyethylene fibers, polypropylene fibers, wood pulp, and cotton linters. It is at least one selected from the group consisting of natural cellulose fibers, regenerated cellulose fibers such as viscose rayon and copper ammonia rayon, and purified cellulose fibers such as lyocell and tencel. The layer made of organic fibers may be either a short fiber nonwoven fabric or a long fiber nonwoven fabric, but a long fiber nonwoven fabric is preferable from the viewpoint of improving handleability.

  The fine cellulose fibers enter the thickness direction with respect to the layer made of the organic fibers, and the penetration depth is the surface layer portion of the layer made of the organic fibers when the thickness of the layer made of the organic fibers is 100%. To 5% or more. When the fine cellulose fibers are contained in the organic fiber layer by 5% or more, peeling between the fine cellulose fiber nonwoven fabric layer and the organic fiber layer is prevented. Moreover, sliding off of the fine cellulose fiber from the filter medium is prevented. Furthermore, the pore size size distribution of the filter medium is formed from the surface layer portion to the deep layer portion of the organic fiber layer, and it can function as a high performance filter medium capable of efficiently filtering and separating particles having a wide particle size distribution from coarse particles to fine particles. The penetration depth of fine cellulose fibers with respect to the organic fiber layer is more preferably 10% or more, and further preferably 15% or more, when the thickness of the layer made of the organic fibers is 100%.

  In addition, even if the structure of the sheet | seat which consists of a fine cellulose fiber nonwoven fabric and an organic fiber layer is a two-layer structure by which the fine cellulose fiber was laminated | stacked on the support body of the organic fiber layer, it is this cellulose on both surfaces of the organic fiber layer. It may have a three-layer structure in which a nonwoven fabric is arranged. Further, a fine cellulose fiber nonwoven fabric may be arranged on one side or both sides of the multilayered nonwoven fabric composed of different organic fibers, and an organic fiber layer may be further arranged on one side or both sides of the multilayer structure, In this case, the penetration depth of fine cellulose fibers into the organic fiber layer should be determined by the penetration depth of the multilayered nonwoven fabric made of different organic fibers, and the weight ratio of the organic fiber layer to the sheet weight is determined by the organic Judge by the weight of all fiber layers.

  The water-resistant cellulose sheet of the present invention has high adsorption performance derived from heat resistance, chemical resistance, high elastic modulus and high surface activity specific to cellulose, and has high porosity and high durability against water. Therefore, it can be effectively used as a solution-based filter medium containing water, a blood separation membrane, or a base material for a polishing tape.

Hereinafter, although the example of the manufacturing method of the water-resistant cellulose sheet of this invention is demonstrated, it does not specifically limit to this method.
The cellulose nonwoven fabric used in the present invention is obtained by first preparing an aqueous dispersion of fine cellulose fibers (fine cellulose fibers) and forming a film by the method described below using the dispersion.
The fine cellulose fiber means a cellulose fiber having a fiber diameter of 2 nm to 200 nm called microfibril or a bundle thereof. More specifically, cellulose produced by acetic acid bacteria and bacteria called bacterial cellulose, or cellulose derived from plants such as pulp called microfibrillated cellulose, or cellulose derived from animals such as squirt cellulose is used as a high-pressure homogenizer, Independent microfibrils peeled off from the fiber surface, or fine fibers converged by them, obtained by refining with a highly shearing device such as an ultra-high pressure homogenizer or grinder (Non-patent Document 1; AFTurbak, FWSnyder and KRSandberg, “Microfibrillated Cellulose, A New Cellulose Product: Properties, Uses, and Commercial Potential” J. Appl. Polym. Sci .: Appl. Polym. Symp., 37, 815 (1983)). Among these, in the present invention, it is more preferable to use microfibrillated cellulose as a raw material from the viewpoint of cost and quality control.

  As the microfibrillated cellulose raw material, so-called wood pulp and non-wood pulp such as softwood pulp and hardwood pulp can be used. Examples of non-wood pulp include cotton-derived pulp including cotton linter pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp. Cotton-derived pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp are respectively cotton lint, cotton linter, and hemp-based abaca (for example, many from Ecuador or the Philippines) It means a refined pulp obtained through a refining process such as delignification or bleaching process by digesting raw materials such as Zaisal, bagasse, kenaf, bamboo, and straw. In addition, purified seaweed-derived cellulose and sea squirt cellulose can also be used as raw materials for microfibrillated cellulose.

Next, a method for refining cellulose fibers will be described.
It is preferable that the cellulose fiber is refined through a pretreatment process, a beating process, and a refinement process.
In the pretreatment step, it is effective to make the raw material pulp easy to be refined by autoclaving under water impregnation at a temperature of 100 to 150 ° C., enzyme treatment, or a combination thereof. These pretreatments not only reduce the load of the micronization process, but also discharge impurity components such as lignin and hemicellulose present on the surface and gaps of the microfibrils that make up the cellulose fibers to the aqueous phase, resulting in a finer process. Since there is also an effect of increasing the α-cellulose purity of the formed fiber, it may be very effective in improving the heat resistance of the cellulose nonwoven fabric.

  In the beating treatment step, the raw material pulp is 0.5 wt% or more and 4 wt% or less, preferably 0.8 wt% or more and 3 wt% or less, more preferably 1.0 wt% or more and 2.5 wt% or less. Disperse in water to a partial concentration and highly promote fibrillation with a beating device such as a beater or disc refiner (double disc refiner). When using a disc refiner, if the clearance between the discs is set as narrow as possible (for example, 0.1 mm or less) and processing is performed, extremely advanced beating (fibrillation) proceeds. It may be effective because the conditions for the conversion process can be relaxed.

A preferable degree of beating processing is determined as follows.
In our study, as the beating process was performed, the CSF value (indicating the degree of beating of the cellulose. Evaluated by the Canadian standard freeness test method for pulp as defined in JIS P 8121) decreased over time. After becoming close to zero, a tendency to increase again after further beating treatment was confirmed, and the microfibrillated cellulose used for adjusting the aqueous dispersion was once the CSF value was close to zero. Further, it was found that it is preferable to continue the beating process and beat until the CSF value increases. In the present invention, the CSF value in the process of decreasing the CSF value from unbeaten is expressed as *** ↓, and the CSF value in a tendency to increase after becoming zero is expressed as *** ↑. In the beating process, the CSF value preferably has at least zero or a value of *** ↑ that increases thereafter, and more preferably CSF50 ↑. In an aqueous dispersion (hereinafter also referred to as “slurry”) prepared to such a beating degree, fibrillation is advanced to a high degree, and fine cellulose fibers having a number average fiber diameter of 500 nm or less can be easily provided. The water-resistant cellulose sheet made of a cellulose nonwoven fabric obtained from the above tends to have improved tensile strength due to an increase in the adhesion point between fine cellulose fibers. In addition, a highly beaten slurry with a CSF value of at least zero or a *** ↑ value that increases thereafter increases in homogeneity and can reduce clogging in the subsequent refinement process by a high-pressure homogenizer or the like. There are the above advantages.

  A high-pressure homogenizer, an ultrahigh-pressure homogenizer, a grinder, or the like can be used for refining cellulose fibers. In this case, the solid content concentration in the aqueous dispersion is 0.5% by weight or more and 4% by weight or less, preferably 0.8% by weight or more and 3% by weight or less, more preferably 1.0%, in accordance with the beating treatment described above. If the solid content concentration is in the range of not less than 2.5% by weight, clogging does not occur and an efficient miniaturization process can be achieved.

  Examples of high-pressure homogenizers used include NS type high-pressure homogenizers from Niro Soabi (Italy), SMT's Lanier type (R model) pressure-type homogenizers, and Sanwa Kikai Co., Ltd. high-pressure homogenizers. Any device other than these devices may be used as long as the device performs miniaturization by a mechanism substantially similar to those of these devices. Ultra-high pressure homogenizers mean high-pressure collision type miniaturizers such as Mizuho Kogyo Co., Ltd. microfluidizer, Yoshida Kikai Kogyo Co., Ltd. Nanomizer, and Suginoma Machine Co., Ltd. Any device other than these devices may be used as long as the device performs miniaturization with a substantially similar mechanism. Examples of the grinder-type miniaturization device include the pure fine mill of Kurita Machinery Co., Ltd. and the stone mill type milling die represented by Masuyuki Sangyo Co., Ltd. Any device other than these may be used as long as the device performs miniaturization by this mechanism.

The fiber diameter of the fine cellulose fiber is determined based on the conditions of the miniaturization process (selection of equipment and operating pressure and the number of passes) by a high-pressure homogenizer or the like, or the pre-treatment conditions (for example, autoclave treatment, enzyme treatment, and beating treatment). Etc.).
In addition, fine cellulose fibers having a number average fiber diameter of 500 nm or less can be easily prepared by the following method without going through the above pretreatment step, beating treatment step, and refinement step. That is, as a pretreatment, the raw pulp is oxidized with a hydroxyl group at the 6-position by a TEMPO oxidation catalyst, and carboxyl groups (including acid type and salt type) are introduced (carboxyl group amount ≧ 0.3 mmol / g), homogenizer, mixer, etc. Thus, fine cellulose fibers having a number average fiber diameter of 500 nm or less can be prepared very easily by stirring in water. This method is also extremely effective for preparing fine cellulose fibers excellent in fiber diameter uniformity.

Next, the manufacturing method of a water-resistant cellulose sheet is demonstrated.
The water-resistant cellulose sheet is manufactured by first producing a cellulose nonwoven fabric composed of high-porosity fine cellulose fibers, followed by a post-treatment method for imparting water resistance in post-processing, and manufacturing the cellulose nonwoven fabric with water resistance. There are two types of “convenient methods” for simultaneously imparting sex. Hereinafter, each method will be described in detail.

First, the “post-processing method” will be described.
The “post-treatment method” is an emulsion paper-making process of (a) to (c) and (d) a post-treatment process using a crosslinking agent.
The emulsion papermaking process comprises (a) an aqueous dispersion preparation process, (b) a papermaking process, and (c) a drying process.
(A) The aqueous dispersion (emulsion) used in the preparation step has a fine cellulose fiber content prepared in the micronization step of 0.05% by weight to 0.5% by weight and a boiling point range of 50 ° C. to 200 ° C. under atmospheric pressure. An aqueous dispersion containing 0.5% by weight or more and 10% by weight or less of an oily compound having a temperature of 0 ° C. or less and 85% by weight or more and 99.5% by weight or less of water is preferable.

  When the concentration of the fine cellulose fibers in the aqueous dispersion is 0.05 wt% or more and 0.5 wt% or less, more preferably 0.08 wt% or more and 0.35 wt% or less, a stable papermaking is suitably performed. can do. When the concentration of fine cellulose fibers in the aqueous dispersion is lower than 0.05% by weight, the drainage time becomes very long, the productivity is remarkably lowered, and the film quality uniformity is remarkably deteriorated. On the other hand, if the fine cellulose fiber concentration is higher than 0.5% by weight, the viscosity of the dispersion is excessively increased, which makes it difficult to form a uniform film.

Next, in the aqueous dispersion prepared in the preparation step, an oily compound having a boiling point range of 50 ° C. or more and 200 ° C. or less at atmospheric pressure of 0.15 wt% or more and 10 wt% or less is used as an emulsion. It is preferably dispersed in an aqueous phase composed of water of not less than 9% and not more than 99.5% by weight.
The concentration of the oily compound in the aqueous dispersion for papermaking is preferably 0.15% by weight or more and 10% by weight or less, more preferably 0.3% by weight or more and 5% by weight or less, and further preferably 0.5% by weight. Above 3% by weight. Even if the concentration of the oily compound exceeds 10% by weight, the cellulose nonwoven fabric of the present invention can be obtained. However, the amount of the oily compound used as a production process increases, and accordingly, the necessity of safety measures and cost increase. This is not preferable because of the restrictions. Further, if the concentration of the oily compound is less than 0.15% by weight, it is not preferable because only a sheet having an air resistance higher than a predetermined air resistance range can be obtained. In the emulsion papermaking method, in the emulsion formed under the above-described conditions, the oily compound does not move to the filtrate side by the papermaking process, which means filtration in a papermaking machine, compared to water, and is highly water-insoluble and highly hydrophilic. It is characterized by efficiently remaining in the vicinity of cellulose as a molecule and substantially concentrating oily compounds. That is, when reaching the drying step, the water-insoluble hydrophilic polymer is surrounded by an oily compound having a lower surface tension than water, which prevents fusion between the polymers during drying and has air permeability. It becomes a driving force for forming a cellulose nonwoven fabric (in principle, the same as the above-described replacement method using an organic solvent). In addition, a water-soluble polymer can be suitably added to the aqueous dispersion used in the present invention, but an emulsion formed under the above-mentioned conditions localizes the water-soluble polymer on the surface of the oil droplets. As a result, the water-soluble polymer efficiently remains on the cellulose surface and acts effectively as a binder.

  Since the air-permeable nonwoven fabric cannot be obtained unless the oily compound is removed during drying, the oily compound to be used must be removable in the drying step. Therefore, in the present invention, the oily compound contained as an emulsion in the aqueous dispersion must be in a certain boiling range, and specifically, the boiling point under atmospheric pressure is 50 ° C. or more and 200 ° C. or less. It is preferable. More preferably, when the temperature is 60 ° C. or higher and 190 ° C. or lower, the aqueous dispersion can be easily operated as an industrial production process, and can be removed by heating relatively efficiently. If the boiling point of the oily compound under atmospheric pressure is less than 50 ° C., it is necessary to handle it under low temperature control in order to stably handle the aqueous dispersion, which is not preferable in terms of efficiency, and the oily compound under atmospheric pressure. If the boiling point exceeds 200 ° C., too much energy is required to heat and remove the oily compound in the drying step, which is also not preferable.

Furthermore, the solubility of the oily compound in water at 25 ° C. is 5% by weight or less, preferably 2% by weight or less, and more preferably 1% by weight or less for efficient formation of the necessary structure of the oily compound. It is desirable from the viewpoint of making a contribution. Specific examples of the oily compound are shown below.
For example, hydrocarbons having 6 to 14 carbon atoms, specifically n-hexane, n-heptane, n-octane, n-decane, n-undecane and isomers thereof (for example, isohexane, isooctane , Isodecane), chain saturated hydrocarbons such as cyclohexane and cyclohexene, chain or cyclic unsaturated hydrocarbons such as diisobutylene and cyclohexene, benzene, toluene and xylene. Aromatic hydrocarbons having a range of 5 to 9 carbon atoms and monovalent and primary alcohols such as n-pentanol, n-hexanol, n-heptanol, n-octanol, isohexanol, Isoheptanol, (Z) -3-hexen-1-ol, 2-methyl-1-pentanol, 2-ethyl-1-butano 4-methyl-1-pentanol, 3,3-dimethyl-1-butanol, (2E, 4E) -2,4-hexadien-1-ol, 2-methyl-2-hexanol, isoheptanol, 2 -Ethyl-1-hexanol, isooctanol, 1,3-benzodioxole-5-methanol and the like can be mentioned, but are not limited thereto.
Although not a primary alcohol, 4-methyl-2-pentanol, 3-methyl-3-pentanol, 2-methyl-2-hexanol, 2-heptanol, cycloheptanol, 4-heptanol, 1-methylcyclohexanol 1-ethynylcyclopentanol, 2-octanol, (S) -2-octanol, cyclooctanol, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynylcyclohexanol, 1-octin-3-ol Monohydric alcohols having a carbon number in the range of 5 to 9 can also be suitably used as the oily compound.

  Among the oily compounds described above, in particular, the oily compound is in the range of 5 to 9 carbon atoms, and is preferably at least one compound selected from monovalent and primary alcohols, more preferably 1 of the alcohols. The cellulose nonwoven fabric of the present invention can be particularly preferably produced by using at least one compound selected from pentanol, 1-hexanol, and 1-heptanol. This is considered to be suitable for the production of a nonwoven fabric having a high porosity and a fine porous structure because the oil droplet size of the emulsion is extremely small (1 μm or less under normal emulsification conditions).

  These oil compounds may be blended as a simple substance, or a plurality of mixtures may be blended. Furthermore, in order to control the emulsion characteristics to an appropriate state, a specific water-soluble compound contained in the cellulose nonwoven fabric used in the present invention may be dissolved in these oily compounds. However, the mixing amount of the specific water-soluble compound at this time is preferably 25% by weight or less based on the oily compound. If the amount is more than this, the ability to form an emulsion of an oily compound is lowered, which is not preferable.

It is important that the oily compound described above is dispersed as an emulsion in the aqueous dispersion in the preparation process. In this case, it is an O / W type emulsion in which oil droplets are dispersed in an aqueous phase. Since the network structure corresponding to the oil droplet size is reflected in the structure after drying, the oil droplet size is preferably small and stably dispersed.
Here, the specific water-soluble compound described above may be dissolved in the aqueous phase in the aqueous dispersion. These water-soluble polymers are localized near the surface of the oil droplet particles, contribute to the stabilization of the slurry, and are incorporated into the mechanism of the emulsion paper making, that is, the oil droplets in the loose aggregate formed by fine cellulose fibers. Since it remains in the wet paper during the paper making process, it remains in the wet paper with a high residual rate, which is preferable in order to form uniform and fine holes at a high ratio.
In the emulsion papermaking method, by using a specific water-soluble compound, the specific water-soluble compound remains in the wet paper, that is, in the cellulose nonwoven fabric after drying with high efficiency. In this respect, the emulsion paper making method is a more preferable method for producing the cellulose nonwoven fabric used in the present invention.

  In the aqueous dispersion for emulsion papermaking, it is preferable that the specific water-soluble compound described above is dissolved in the aqueous phase. The concentration of the specific water-soluble polymer is 0.003% to 0.3% by weight, more preferably 0.005% to 0.08% by weight, and still more preferably 0.006% by weight. The amount is 0.07% by weight or less, and this range is preferable because the cellulose nonwoven fabric used in the present invention can be easily obtained and the state of the aqueous dispersion is often stabilized. If the concentration is lower than 0.003% by weight, the effect of adding the specific water-soluble compound is hardly exhibited, and it is not preferable, and if the concentration exceeds 0.3% by weight, the amount of addition such as foaming increases. Since a negative effect tends to appear, it is not preferable. For the purpose of stabilizing the emulsion, a surfactant may be contained in the aqueous dispersion in addition to the specific water-soluble compound, and the total amount of the surfactant and the specific water-soluble polymer may be included in the concentration range.

  As the surfactant in this case, an anionic surfactant such as alkyl sulfate ester salt, polyoxyethylene alkyl sulfate ester salt, alkylbenzene sulfonate, α-olefin sulfonate, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, Examples include cationic surfactants such as benzalkonium chloride, amphoteric surfactants such as alkyldimethylaminoacetic acid betaines and alkylamidodimethylaminoacetic acid betaines, and nonionic surfactants such as alkylpolyoxyethylene ethers and fatty acid glycerol esters. However, it is not limited to these.

  In addition, various additives may be added to the aqueous dispersion according to the purpose. For example, inorganic particulate compounds such as silica particles, alumina particles, diamond particles, boron nitride, silicon carbide, titanium oxide particles, calcium carbonate particles, crosslinked acrylic resins, crosslinked polystyrene, melamine resins, phenol resins, epoxy resins In addition, organic fine particles such as urea resin and polycarbonate resin, and various salts and organic solvents that do not inhibit the stability of the emulsion are in a range that does not adversely affect the production of the high porosity structure of the present invention (of various types It may be added by selection or selection of composition).

  In the aqueous dispersion, the components other than water have a composition of 85% to 99.5% by weight, preferably 90% to 99.4% by weight, more preferably 92% to 99.2%. It is preferably dispersed or dissolved in water. When the composition of water in the aqueous dispersion is lower than 85% by weight, the viscosity increases in many cases, making it difficult to uniformly disperse the emulsion in the dispersion, and a cellulose nonwoven fabric having a uniform structure and high porosity is obtained. Since it becomes difficult to obtain, it is not preferable. On the other hand, when the composition of water in the aqueous dispersion exceeds 99.5% by weight, the content of the emulsion is reduced as a blended composition, the concentration of the oily compound in the concentrated composition is lowered, and the breathable structure Is also not preferable because it is difficult to obtain.

The average dispersion diameter of fine cellulose fibers in the papermaking aqueous dispersion is preferably 3 μm or more and 200 μm or less.
Dispersion average diameter of the fine cellulose fibers for papermaking aqueous dispersion (hereinafter. Referred to R _v), the permeability of water, more than 3μm in view of efficiency of the paper making is preferably not more than 200μm from the viewpoint of uniformity of the nonwoven fabric. The dispersion average diameter (R _v ) means that the dispersion for papermaking is a laser scattering particle size distribution measuring device (manufactured by Horiba, Ltd., laser diffraction / scattering particle size distribution measuring device LA-920, the lower limit detection value is 0.02 μm). ), And means the arithmetic average diameter of the volume average obtained by measurement at room temperature. In this measurement, the volume distribution is based on Mie's scattering theory (M. Kerker, “The Scattering of Light”, USA, Academic Press, New York, NY, 1969, Cap. 5.). The arithmetic average diameter is used, and the relative refractive index of the cellulose used in this case with respect to the refractive index of water is 1.20.
R _v of aqueous dispersion (slurry), more preferably 5μm or 150μm or less, and more preferably in the range of 10μm or 120μm or less, it is possible to provide a more uniform excellent in cellulose nonwoven fabric.

The aqueous dispersion prepared in the preparation step is an emulsion composition composed of the above-described compound group, but any method of emulsification can be employed in forming the emulsion. That is, an O / W emulsion is prepared by a method such as mechanical emulsification, phase inversion emulsification, liquid crystal emulsification, phase inversion temperature emulsification, D phase emulsification, or ultrafine emulsification (microemulsion emulsification) using a solubilized region.
The aqueous dispersion is prepared by mixing all additives into water and preparing an aqueous emulsion dispersion by an appropriate emulsification method, or by preparing an aqueous emulsion previously composed of an oily compound and an emulsifier by an appropriate emulsification method as described above. It may be prepared and mixed with an aqueous dispersion composed of separately prepared fine cellulose fibers and other additives to form an aqueous dispersion. In this case, the blender is adjusted so that the average dispersion diameter is 1 μm or more and 300 μm or less. It is preferable that the blades having such a cutting function are controlled and adjusted with a disperser or a high-pressure homogenizer that rotates at high speed.

  Next, (b) a papermaking process in which the fine cellulose fiber is filtered and the emulsion concentration is concentrated by dehydrating the aqueous dispersion prepared in the first process with a papermaking machine. The papermaking process is basically an operation using a filter or filter cloth (also called a wire in the technical field of papermaking) that dehydrates water from a water-containing dispersion and retains a water-insoluble hydrophilic polymer. Any apparatus may be used as long as it is present. As described above, the oil droplets in the emulsion are incorporated in the aggregate (soft agglomerate) composed of fine cellulose fibers and having a dispersion average diameter of 3 μm or more and 200 μm or less. Even if it is discharged, it remains on the filter or filter cloth, and the concentration of the emulsion component substantially proceeds.

As the paper machine, if a device such as an inclined wire type paper machine, a long net type paper machine, or a circular net type paper machine is used, a sheet-like cellulose nonwoven fabric with few defects can be suitably obtained. Whether the paper machine is a continuous type or a batch type, it may be properly used according to the purpose.
Paper making is performed using the above paper machine, and paper making is a process of filtering soft agglomerates such as fine cellulose dispersed in an aqueous dispersion using a wire or filter cloth. The size of is important. In the present invention, essentially, a water-based dispersion for papermaking prepared under the above-described conditions, the yield ratio of water-insoluble components including cellulose and the like contained in the dispersion is 70% by weight or more, preferably Any wire or filter cloth that can make paper at 95% by weight or more, more preferably 99% by weight or more can be used.

However, even if the yield ratio of cellulose or the like is 70% by weight or more, if the drainage is not high, it takes a long time to make paper and the production efficiency is remarkably deteriorated. When the amount is preferably 0.005 ml / cm ² · s or more, and more preferably 0.01 ml / cm ² · s or more, suitable papermaking can be performed from the viewpoint of productivity. When the yield ratio of the water-insoluble component is lower than 70% by weight, not only the productivity is remarkably reduced, but also the water-insoluble component such as cellulose is clogged in the wire or filter cloth to be used. The peelability of the subsequent cellulose non-woven fabric is also significantly deteriorated.

Here, the water permeation amount of the wire or the filter cloth at 25 ° C. under atmospheric pressure shall be evaluated as follows.
When installing a wire or filter cloth to be evaluated on a batch type paper machine (for example, an automatic square sheet machine manufactured by Kumagai Riki Kogyo Co., Ltd.), 80 to 120 mesh in the case of a wire or as a filter cloth. A filter cloth is placed on a metal mesh (assuming that there is almost no drainage resistance), a sufficient amount (yml) of water is poured into a paper machine having a papermaking area of xcm ² , and filtered under atmospheric pressure. Measure time. The amount of water permeation when the drainage time is zs (seconds) is defined as y / (xz) (ml / cm ² · s).

Examples of filters or filter cloths that can be used even for extremely fine cellulose fibers include TETEXMONDLW07-8435-SK010 (PET) manufactured by SEFAR (Switzerland), NT20 (PET / nylon blend) manufactured by Shikishima Canvas. However, it is not limited to these.
The sheet of the present invention can be provided with an organic fiber layer such as polyamide fiber, polyester fiber, or cellulose fiber. In this case, it is preferable to perform paper making using the organic fiber layer as a support. In this case, it is sufficient to select a material that can satisfy the requirements regarding the yield ratio and the water permeation amount in combination with the support for the wire or filter cloth of the paper machine.

  In the dehydration by the papermaking process, high solid differentiation proceeds simultaneously with the concentration of the emulsion, and a wet paper which is a concentrated composition in which the concentration of fine cellulose fibers and the concentration of oily compound are increased from the aqueous dispersion is obtained. The solid content ratio of the wet paper is controlled by the degree of dehydration by the suction pressure (wet suction or dry suction) of the papermaking or pressing process, preferably the solid content concentration is 6 wt% or more and 25 wt% or less, more preferably the solid content. The concentration is adjusted in the range of 8 wt% to 20 wt%. If the solid content of the wet paper is lower than 6% by weight, there is no self-supporting property as the wet paper and problems in the process are likely to occur. Moreover, when the solid content of the wet paper is dehydrated to a concentration exceeding 25% by weight, not only the aqueous phase but also the concentrated emulsion is discharged out of the system. Since the density | concentration of this will fall, it becomes impossible to form a cellulose nonwoven fabric with a high porosity, and is not suitable. As described above, in the emulsion papermaking method, the emulsion is concentrated by the papermaking process, and the concentration of the oily compound in the wet paper after the dehydration process is preferably about 5 times or more compared to the oily compound concentration in the aqueous dispersion before the dehydration. In such a case, it is concentrated 10 times or more.

  In addition, when using the support body which is an organic fiber layer, the said support body is mounted on the paper machine which set the wire or the filter cloth, and a part of water which comprises aqueous dispersion liquid is spin-dry | dehydrated on this support body (papermaking). A multilayered sheet composed of a multilayer structure of at least two layers can be produced by laminating and integrating wet paper of cellulose nonwoven fabric composed of fine cellulose fibers on the support. In order to produce a multilayer sheet having three or more layers, a support having a multilayer structure having two or more layers may be used. Moreover, it is good also as a multilayer sheet | seat of three or more layers by performing the multistage papermaking of the cellulose nonwoven fabric of this invention of two or more layers on a support body.

  The wet paper obtained in the paper making process becomes a cellulose nonwoven fabric by evaporating the oily compound and water in the drying process (c) by heating. The drying process is a constant-length drying type that can dry water and an oily compound (hereinafter referred to as “dispersion medium” together with water and an oily compound) in a state where the width is constant as in a drum dryer. Use of a dryer is preferable because a cellulose nonwoven fabric having a higher porosity can be stably obtained. The drying temperature may be appropriately selected according to the conditions, but it is preferably 45 ° C. or higher and 180 ° C. or lower, and more preferably 60 ° C. or higher and 150 ° C. or lower. Can be manufactured. When the drying temperature is less than 45 ° C, the volatilization rate of the dispersion medium is slow in many cases, and thus high productivity cannot be secured, which is not preferable. When the drying temperature is higher than 180 ° C, the hydrophilic polymer constituting the structure is In some cases, heat denaturation may occur, and energy efficiency affecting the cost is also reduced, which is not preferable. In some cases, it is also effective to obtain a cellulose nonwoven fabric excellent in pore diameter uniformity by preparing a composition at a low temperature drying of 100 ° C. or lower and performing a multi-stage drying in which drying is performed at a temperature of 100 ° C. or higher in the next stage. Sometimes.

Subsequent to the emulsion papermaking process, (d) a post-treatment process using a crosslinking agent will be described.
The cellulose nonwoven fabric obtained by emulsion papermaking is immersed in a solvent in which various crosslinking agents are dispersed or dissolved, washed with water, and dried to impart water resistance to the cellulose nonwoven fabric.
Examples of the crosslinking agent used here include divinyl sulfone, carbodiimide, dihydrazine, dihydrazide, epichlorohydrin, a polyfunctional epoxy compound, and an isocyanate compound.
The solvent includes petroleum ether, hexane, benzene, toluene, xylene, mesitylene and other hydrocarbon solvents, diethyl ether, tetrahydrofuran, diethylene glycol dimethyl ether and other ether solvents; acetone, methyl ethyl ketone, methyl isobutyl ketone and other ketone solvents. , Ester solvents such as ethyl acetate, butyl acetate, amyl acetate, chlorine-containing solvents such as methylene chloride, chloroform, chlorobenzene, dichlorobenzene, N, N-dimethylformamide, N, N-dimethylacetamide, N, N -Aprotic polar solvents such as dimethylimidazolidinone and dimethyl sulfoxide. These solvents may contain water, but the concentration thereof needs to be controlled within a range in which the cellulose nonwoven fabric does not swell / disintegrate.

Various crosslinking agents are dispersed or dissolved in the solvent. In this case, the concentration of the crosslinking agent is preferably 0.1 to 15% by weight. When the concentration of the cross-linking agent is less than 0.1%, a cellulose sheet having a desired wet / dry strength ratio cannot be obtained. When the concentration of the crosslinking agent exceeds 15% by weight, the wet / dry strength ratio increases, but the dry strength tends to decrease. More preferably, it is 0.2 to 10 weight%, More preferably, it is 0.3 to 5 weight%.
The temperature and time of the post-treatment are not particularly limited and may be set in consideration of the dry / wet strength ratio of the final sheet and the safety (flammability and explosiveness) of various solvents. If the treatment temperature exceeds 200 ° C., cellulose Since the nonwoven fabric is thermally deteriorated and the tensile strength is lowered, the temperature is preferably 100 ° C. or lower, and more preferably 80 ° C. or lower. Further, since the treatment takes a long time when the treatment temperature is low, it is preferably 15 ° C. or higher, more preferably 25 ° C. or higher. The appropriate range of the treatment time varies depending on the temperature, but is 30 seconds to 24 hours.

The cellulose nonwoven fabric that has been dipped at a predetermined temperature and time is washed with running water for 30 to 60 minutes and then dried. The drying temperature in this case conforms to (c) drying process conditions in the emulsion papermaking process.
The above is the method for producing the water-resistant cellulose sheet of the present invention by the “post-treatment method”.

Next, a “simple method” for simultaneously producing a paper making of cellulose nonwoven fabric and imparting water resistance will be described.
There are two types of “simple methods”: (I) a method using a crosslinking agent and (II) a method using a binder fiber.
First, (I) a method using a crosslinking agent will be described.
“Simple method” — (I) When using a crosslinking agent, in the preparation step of (a) aqueous dispersion of the emulsion papermaking method described above, various crosslinking agents having a concentration of 0.01 to 10% by weight are added to the aqueous dispersion. Added. Examples of the crosslinking agent include vinyl sulfone, carbodiimide, dihydrazine, dihydrazide, epichlorohydrin, polyfunctional epoxy compound, and isocyanate compound. In this case, it is preferable to prepare using a pH adjuster according to the reactivity of the cross-linking agent using the pH of the solution. However, in a strongly acidic or strongly alkaline region, the cellulose nonwoven fabric is hydrolyzed in the drying step, and is marked. A decrease in strength occurs. The pH range of the preferred aqueous dispersion is pH 5.0 to 9.0, more preferably pH 5.5 to 8.5.

  Subsequently, the wet paper produced in accordance with the above-mentioned emulsion paper making method (b) paper making process is heated (drying process promoted) at the same time as the oily compound and water are evaporated in the drying process (c), thereby providing water resistance. It becomes a cellulose sheet. The drying temperature may be appropriately selected according to the conditions, but is preferably 45 ° C. or higher and 180 ° C. or lower, and more preferably 60 ° C. or higher and 160 ° C. or lower from the viewpoint of crosslinking reactivity. When the drying temperature is less than 45 ° C, the crosslinking reaction rate is slow, and when it is higher than 180 ° C, the strength may be lowered. The drying time may be selected in consideration of the drying temperature and the wet / dry strength ratio of the final sheet, but is preferably in the range of 30 seconds to 30 minutes. When a dryer such as a drum dryer is used, adjustment of the feed rate or roll The diameter can be adjusted.

Next, (II) a method using a binder fiber will be described.
"Simple method"-(II) When using the binder fiber, the binder fiber is added to the aqueous dispersion in the step (a) of preparing the aqueous dispersion in the above-mentioned emulsion papermaking method. Examples of binder fibers include polypropylene short fibers, polypropylene (core) and polyethylene (sheath) composite fibers, polypropylene (core) and ethylene vinyl alcohol (sheath) composite fibers, high melting point polyester (core) and low melting point polyester. Examples thereof include melt-type binder fibers such as (sheath). The addition amount of the binder fiber is preferably in the range of 0.01 to 0.5% by weight, and if it is 0.01% by weight or less, the fine cellulose fibers cannot be effectively bonded to each other, and if it exceeds 0.5% by weight, it continues. (C) In the drying step, the binder fiber is stretched into a film shape and closes the fine pores formed by the fine cellulose fibers (reduction in porosity). A preferable binder fiber concentration is 0.02 to 0.2% by weight, and more preferably 0.03 to 0.1% by weight. The number average fiber diameter of the binder fibers is preferably in the range of 0.5 to 20 μm from the viewpoint of not closing fine pores, more preferably 1 to 15 μm, and most preferably 2 to 12 μm.

Subsequently, the wet paper made in accordance with the above-mentioned emulsion papermaking method (b) papermaking step may be heat-treated (fused with binder fibers) at the same time as the oily compound and water are evaporated in the drying step (c). In addition, after the oily compound and water are once evaporated, a separate heat treatment may be performed. What is necessary is just to select a drying temperature or heat processing temperature suitably according to the binder fiber to be used.
You may provide the smoothing process which performs a smoothing process with the calendar apparatus to the water-resistant cellulose sheet obtained by each method mentioned above. As the calendar device, in addition to a normal calendar device using a single press roll, a super calendar device having a structure in which these are installed in a multistage manner may be used. By selecting the materials (material hardness) and linear pressures on both sides of the roll during the calendar treatment, these devices can be used to obtain a water-resistant cellulose sheet having various physical property balances.
By satisfying the above conditions, it has high adsorption performance derived from heat resistance, chemical resistance, high elastic modulus and high surface activity unique to cellulose, and has high porosity and high durability against water. A water-resistant cellulose sheet can be provided.

Hereinafter, the present invention will be described specifically by way of examples.
The main measured values of physical properties were measured by the following methods.
(1) Number average fiber diameter of fine cellulose fibers The surface of a sheet made of fine cellulose fibers is randomly observed at three locations with a scanning electron microscope (SEM) at a magnification equivalent to 10,000 times. With respect to the obtained SEM image, a line is drawn in the horizontal direction and the vertical direction with respect to the screen, and the fiber diameter of the fiber intersecting the line is measured from the enlarged image, and the number of intersecting fibers and the fiber diameter of each fiber are counted. In this way, the number average fiber diameter is calculated using two series of measurement results for one image. Further, the number average fiber diameter is calculated in the same manner for the other two extracted SEM images, and the results for a total of three images are averaged to obtain the number average fiber diameter of the target sample.

(2) Number average fiber diameter of organic fibers Except for observation with a scanning electron microscope (SEM) at a magnification equivalent to 1000 times, the number average fiber diameter of fine cellulose fibers is evaluated in the same manner.

(3) Maximum fiber diameter of fine cellulose fiber It is confirmed by an SEM image that the maximum fiber diameter of the fine cellulose fiber is 1500 nm or less.
With respect to the surface of the non-woven filter medium composed of fine cellulose fibers, the fiber diameter 1500 nm in all the obtained SEM images was obtained when the observation with a scanning electron microscope (SEM) was performed at three magnifications at a magnification equivalent to 10,000 times. Count the number of fibers that exceed and take the average value. However, in the image, when it can be clearly confirmed that several fine fibers are bundled to have a fiber diameter of 1500 nm or more, it is not regarded as a fiber having a maximum fiber diameter of 1500 nm or more.

(4) Weight ratio of fine cellulose fibers in sheet (P)
The sheet is dried for 6 hours in a drier whose temperature is controlled at 105 ° C. in advance, and after cooling in a desiccator for 30 minutes, the weight is determined (W ₁ ).
The sheet is stirred (30 minutes) in a solvent that does not dissolve cellulose in an amount 10 times the weight of the sheet, filtered (sieved with a pore size of 2 mm), washed, and then the same operation is performed with 20 times the amount of solvent used Repeat twice and filter the remaining cellulose. After drying at a temperature not lower than the boiling point of the solvent for 6 hours and cooling in a desiccator for 30 minutes, the weight is determined (total amount of container and fine cellulose fibers; W ₃ ). The weight ratio (P) of fine cellulose fibers is expressed by the following formula (3):
Weight ratio of fine cellulose fibers (P) = (W ₃ −W ₂ ) / W ₁ × 100 Formula (3)
Ask for.

(5) Weight per unit area The weight per unit area of the filter medium is calculated according to P-8124.

(6) Air permeability resistance A 25 cm square sheet is divided into 10 equal parts, and permeation of 100 ml of air using the Gurley type densometer (model G-B2C, manufactured by Toyo Seiki Co., Ltd.) for the 10 sections. Measure the time and take the average of 10 points. Here, even if there is a part that is less than 10 s / 100 ml or a part that exceeds 2000 s / 100 ml even at one place, it does not fall within the air permeability resistance range of the present invention.

(7) Tensile strength / elongation The tensile strength was evaluated according to the method defined in JIS P 8113, using a tabletop horizontal tensile tester (No. 2000) manufactured by Kumagaya Riki Kogyo Co., Ltd. Ten points were measured, and the average value was taken as the tensile strength and elongation. Considering the difference in basis weight, the strength is evaluated by a value equivalent to 10 g / m ² basis weight.

(8) Tensile strength to wet strength ratio The tensile strength evaluated in (7) is defined as dry strength, and the tensile strength measured after dipping for 5 minutes in a container filled with water sufficient to immerse the sheet is defined as wet strength. Following formula (1):
Dry / wet strength ratio (%) = (wet strength) / (dry strength) × 100 Formula (1)
Calculate with Here, neither dry strength nor wet strength is converted to an equivalent weight per unit area of 10 g / m ² .

(9) Porosity The porosity Pr (%) of the sheet is expressed by the following formula (4) from a 10 cm square film thickness d (μm) and its weight W (g):
Pr = (d−W × 67.14) × 100 / d (4)
Calculate using.

(10) Average pore diameter In the pore diameter distribution measurement test using a palm porometer (manufactured by Seika Sangyo CFE-1200AEX), the average pore diameter was increased by increasing the air pressure at 5 cc / min for a sample completely wetted with ethanol. evaluate. The average pore diameter change rate after water permeation is expressed by the following formula (2):
Average pore diameter change rate after water permeation (%) = (average pore diameter after water permeation−average pore diameter before water permeation) / average pore diameter before water permeation × 100 formula (2)
Calculate with
Here, the average pore diameter after water permeation is set such that the sheet is not leaked in a filter, and ultrapure water is fed at a pressure of 1 kg / cm ² for 60 minutes using a feed pump, and then the moisture is ethanol. Evaluation is performed using a sample completely substituted with.

[Example 1]
A cotton linter raw cotton having a polymerization degree (DP) of 1750 is immersed in water so as to be 10% by weight, heat-treated in an autoclave at 130 ° C. for 4 hours, and the resulting swollen pulp is washed with water many times, A swollen pulp in an impregnated state was obtained.
The swollen pulp is dispersed in water to a solid content of 1.5% by weight to form a water dispersion (400 L). As a disk refiner device, SDR14 type laboratory refiner (pressure type DISK type) manufactured by Aikawa Tekko Co., Ltd. is used. The beating process was continued for 20 minutes on the 400 L water dispersion with a disc clearance of 1 mm, and then the beating process was continued under conditions where the clearance was reduced to almost zero. . Sampling was carried out over time, and the CSF value of the Canadian standard freeness test method (hereinafter referred to as CSF method) of pulp defined by JIS P 8121 was evaluated for the sampling slurry. Then, once it was close to zero, if the beating process continued further, a tendency to increase was confirmed. The beating treatment was continued under the above conditions for 10 minutes after the clearance was reduced to near zero, and a beating slurry with a CSF value of 73 ml ↑ was obtained. The obtained beating slurry was subjected to micronization treatment 5 times under an operating pressure of 100 MPa using a high-pressure homogenizer (NS015H manufactured by Niro Soabi (Italy)) as it was, and an aqueous dispersion M1 of microfibrillated cellulose (solid) Minor concentration: 1.5% by weight).

Next, this M1 and oily compound were added as shown in Table 1 below, and emulsified and dispersed for 4 minutes with a home mixer. The aqueous dispersion had a dispersion average diameter Rv of 168 μm.
A plain fabric made of PET / nylon blend (Shikishima Kanbus Co., Ltd., NT20: water permeation at 25 ° C. in the atmosphere: 0.03 ml / cm ² · s, filtration of microfibrillated cellulose at 25 ° C. under atmospheric pressure. The above adjustment is based on a cellulose non-woven fabric with a basis weight of 10 g / m2 on a batch type paper machine (made by Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine 25 cm x 25 cm, 80 mesh) set with 99% or more of ability to filter. 312.5 g of the water-based dispersion liquid was added, and then papermaking (dehydration) was performed at a reduced pressure with respect to atmospheric pressure of 4 KPa.

The wet paper made of the concentrated composition in a wet state on the obtained filter cloth is peeled off from the wire and pressed at a pressure of 1 kg / cm ² for 1 minute, and then the wet paper surface is brought into contact with the drum surface. In the two layers of wet paper / filter cloth, the wet paper is dried for about 120 seconds with the drum dryer having a surface temperature set to 130 ° C. so that the wet paper is in contact with the drum surface. Then, the filter cloth was peeled from the cellulose sheet-like structure to obtain a cellulose sheet composed of white uniform fine cellulose fibers.
A cellulose sheet is immersed in a toluene solution in which 1,6′-hexamethylene diisocyanate is dissolved in toluene at a concentration of 2% by weight as a crosslinking agent, and the surface temperature is set to 130 ° C. after washing with running water for 30 minutes. The wet paper was also dried for about 120 seconds so that the wet paper was in contact with the drum surface, and S1 was obtained.
When SEM image analysis was performed on the surface of S1 at a magnification of 10,000, no fine cellulose fibers on the surface of S1 exceeding 1500 nm were found, and the number average fiber diameter was 158 nm.
Moreover, as shown in Table 2 below, S1 had a high porosity and a high strength and wet / dry strength ratio.

[Example 2]
Refinement, slurry preparation, papermaking drying and post-processing as in Example 1 except that hydroxypropylmethylcellulose (60SH-4000 manufactured by Shin-Etsu Chemical Co., Ltd.) is added to the aqueous dispersion with the composition shown in Table 1 below. And S2 was obtained. As shown in Table 2 below, S2 was in the physical property range defined in the present invention, and had high porosity and resistance to water.

[Example 3]
Except that the post-treatment time with the cross-linking agent was 12 hours, refinement, slurry preparation, papermaking drying and post-processing were performed in the same manner as in Example 2 to obtain S3. As shown in Table 2 below, S3 was in the physical property range defined in the present invention, and had high porosity and resistance to water.

[Examples 4 to 6]
Except for using 4,4′-diphenylmethane diisocyanate as the cross-linking agent and carrying out the cross-linking agent concentration under the conditions shown in Table 1 below, the same refinement, slurry preparation, paper-making and post-processing as in Example 3 were performed. , S4 to S6 were obtained. The physical properties of S4 to S6 are shown in Table 2 below.

[Example 7] Difference in treatment method Except that block diisocyanate was used as a crosslinking agent, refinement, slurry preparation, papermaking drying and post-processing were performed in the same manner as in Example 3 to obtain S7. The physical properties of S7 are shown in Table 2 below.

[Comparative Example 1]
Except not performing the post-processing by a crosslinking agent, refinement | miniaturization, slurry preparation, and papermaking drying were performed similarly to Example 2, and C1 was obtained. Although C1 has a high porosity and dry strength, it has low durability against water, disintegrates when immersed in water, and the wet strength cannot be evaluated.

[Comparative Example 2]
C2 was obtained by carrying out refinement, slurry preparation, papermaking drying and post-processing as in Example 4 except that the concentration of the crosslinking agent was 0.05% by weight. C2 has high porosity and dry strength, but has low durability against water, a low wet-wet strength ratio, and a large average pore diameter change rate after water permeation.

[Comparative Example 3]
Except that an aqueous dispersion was prepared under the conditions shown in Table 1 below, C3 was obtained by carrying out refining, papermaking and post-processing as in Example 4. C3 had a low porosity and a dry / wet strength ratio of less than 50%. Since C3 is a dense film, it seems that the effect of the crosslinking treatment did not penetrate into the film.

[Comparative Example 4]
Papermaking and post-processing were performed in the same manner as in Example 4 except that the number average fiber diameter of the cellulose fibers was carried out under the conditions shown in Table 1 below, to obtain C4. In C4, the wet and dry strength ratio was less than 50%, and the average pore diameter change rate after water permeation was also large. Since C3 has a large fiber diameter, it seems that the effect of the crosslinking treatment could not be sufficiently exhibited.

[Examples 8 to 13]
Examples 8 to 13 are the same as in Example 4 except that the process according to (I) is carried out under the conditions shown in Table 3 below. Processing was performed to obtain S8 to S13. As shown in Table 4 below, S8 to S13 all had high porosity and dry strength, and water resistance was also improved.

[Comparative Examples 5 and 6]
Except for carrying out under the conditions shown in Table 3 below, papermaking and post-processing were performed in the same manner as in Example 8 to obtain C5 and C6. C5 has high porosity and dry strength, but has low durability against water, a low wet-wet strength ratio, and a large average pore diameter change rate after water permeation. C6 has low durability against water, disintegrates when immersed in water, and the wet strength could not be evaluated. Moreover, C6 was damaged by the water permeation test, and the average pore diameter evaluation after water permeation could not be performed.

[ Reference Examples 14 to 16]
In Reference Examples 14 to 16, the simple method of simultaneously imparting water resistance performance by papermaking and binder fibers- (II) was performed under the conditions shown in Table 5 below, and a linear pressure of 16 kg / cm × 185 ° C. with a 200φ flat roll. Except having been heat-treated in the same manner as in Example 4, papermaking and post-processing were performed to obtain S14 to S16. As shown in Table 6 below, S14 to S16 all had high porosity and dry strength, and water resistance was also improved.

[Comparative Examples 7 and 8]
Except for carrying out under the conditions shown in Table 5 below, papermaking and post-processing were performed in the same manner as in Reference Example 14 to obtain C7 and C8. In C7, polypropylene fiber covered the cellulose fiber surface by hot press treatment, and a dense film was formed. Therefore, the porosity of C7 was low. Since C8 used a polypropylene fiber having a large fiber diameter, the cellulose fiber surface was partially covered, and the variation in air resistance was very large. Also, the dry strength produced 4 points that were less than 6 N / 15 mm out of 10 measurements, and the variation was large. The wet strength and average pore diameter evaluation were also highly variable.

  The water-resistant cellulose sheet of the present invention has high adsorption performance derived from heat resistance, chemical resistance, high elastic modulus and high surface activity specific to cellulose, and has high porosity and high durability against water. Therefore, it can be used as a filter medium in a wide solvent range from aqueous to organic solvent, and at the same time, it can be effectively used as a blood separation membrane / adsorption membrane. The water-resistant cellulose sheet of the present invention can be used as a polishing tape in a semiconductor production line.

Claims (6)

A water-resistant cellulose sheet comprising a nonwoven fabric composed of fine cellulose fibers having a number average fiber diameter of 500 nm or less, the fine cellulose fibers comprising divinyl sulfone, carbodiimide, dihydrazine, dihydrazide, epichlorohydrin, a polyfunctional epoxy compound, and It is crosslinked by at least one crosslinking agent selected from the group consisting of isocyanate compounds, and the following requirements (1) to (4):
(1) Weight ratio of fine cellulose fiber: 96.6 % by weight or more and 99% by weight or less (2) Porosity: 50% or more (3) Tensile strength equivalent to 10 g / m ² per unit area: 6N / 15mm or more (4) A water-resistant cellulose sheet satisfying all of the wet / dry strength ratio of tensile strength: 50% or more.   The water-resistant cellulose sheet according to claim 1, wherein the average pore diameter change rate after water permeation is 40% or less. Filtering material comprising a water-soluble cellulose sheet according to claim 1 or 2.   A filter cartridge comprising the filter medium according to claim 3. The blood separation membrane containing the water-resistant cellulose sheet of any one of Claims 1-3 . The polishing tape containing the water-resistant cellulose sheet of any one of Claims 1-3 .