Inorganic fiber sheet and method for manufacturing the same

Abstract

This invention provides an inorganic fiber sheet that uses bio-soluble fibers while increasing its strength after calcination. [Solution] The method for manufacturing an inorganic fiber sheet includes a step of wet papermaking in which 15 to 50% by weight of bentonite is blended with inorganic fibers and organic fibers. This makes it possible to create a safe inorganic fiber sheet using biosoluble materials. Furthermore, by blending bentonite in the papermaking process without adding it in a later step, the manufacturing process can be simplified.

Description

[Technical Field]

[0001] This invention relates to an inorganic fiber sheet and a method for producing the same. [Background technology]

[0002] Because ceramic fibers possess characteristics such as high heat resistance, high heat insulation, and non-flammability, inorganic fiber sheets using ceramic fibers are widely used. For example, inorganic fiber sheets using refractory ceramic fiber (RCF or fire-resistant ceramic fiber) are used as heat insulation materials, heat-resistant cushioning materials, heat-resistant shielding materials, separators, and supports for functional materials such as catalysts. In addition, honeycomb molded bodies obtained by corrugating inorganic fiber sheets are used as heat exchange honeycomb filters or gas adsorption honeycomb filters that support functional materials such as adsorbents. Furthermore, processes such as calcination, which are performed to burn off organic components in the sheet to improve heat resistance or to suppress outgassing, may be added.

[0003] However, ceramic fibers are classified as Category 2 (suspected carcinogen) in EU Directive 97 / 69EC concerning man-made amorphous fibers. Therefore, for safety reasons, there is a push to eliminate ceramics, and alternatives such as glass fibers and bio-soluble fibers are being considered (see, for example, Patent Documents 1-3). Bio-soluble fibers are new man-made amorphous fibers (Man-Made Vitreous Fiber: MMVF) that have been given the property of dissolving in the body, and are also called Bio-Soluble Fiber. Furthermore, it is considered preferable that the fiber diameter of the glass fibers used in the elimination of ceramics be 3 μm or larger.

[0004] Patent Document 1 discloses a method for obtaining an inorganic fiber sheet by papermaking a slurry mainly composed of biosoluble ceramic fibers, glass fibers, organic fibers, a cationic inorganic binder, and sepiolite, a type of bark.

[0005] However, bio-soluble ceramic fibers have a large fiber diameter, making it difficult to achieve sufficient strength, which leads to problems with their suitability for corrugation processing.

[0006] Furthermore, Patent Document 2 discloses a method for producing an inorganic fiber sheet containing 30 to 92% by mass of one or more inorganic fibers selected from the group consisting of glass fibers and biosoluble inorganic fibers, and 5 to 40% by mass of β-type sepiolite, comprising the steps of (i) producing a nonwoven fabric by wet papermaking of a raw material slurry containing the inorganic fibers, and (ii) attaching the slurry containing β-type sepiolite to the nonwoven fabric. According to the same document, when using β-type sepiolite, if β-type sepiolite is added (internal addition) to the raw material slurry for producing the nonwoven fabric, an inorganic fiber sheet capable of producing a filter substrate with sufficient strength cannot be obtained. For this reason, by attaching β-type sepiolite to the obtained nonwoven fabric (external coating), an inorganic fiber sheet capable of producing a filter substrate with sufficient strength can be obtained. However, in this case, external coating of β-type sepiolite to the nonwoven fabric is required, which increases the number of steps and has the problem of requiring extra manufacturing time and manufacturing costs.

[0007] Furthermore, Patent Document 3 discloses an inorganic fiber sheet containing 3 to 20% by mass of organic fibers with an aspect ratio of 300 to 2000 relative to the total amount of the inorganic fiber sheet mainly composed of glass fibers. However, there was no description regarding the strength when the sheet was calcined and used, and there was a problem that it could not be used in environments above the heat resistance temperature of the organic fibers because it contained organic fibers. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2013-234410 [Patent Document 2] Japanese Patent Publication No. 2017-25458 [Patent Document 3] WO2018 / 079529 issue [Overview of the project] [Problems that the invention aims to solve]

[0009] One of the objectives of the present invention is to provide an inorganic fiber sheet that uses bio-soluble fibers while increasing its strength after calcination. Means for solving the problem and effects of the invention.

[0010] A method for manufacturing an inorganic fiber sheet according to the first embodiment of the present invention includes a step of wet-processing a mixture of inorganic fibers and organic fibers with 15 to 50% by weight of bentonite. This makes it possible to create a safe inorganic fiber sheet using biosoluble materials. Furthermore, by incorporating bentonite during the papermaking process without adding it in a later step, the manufacturing process can be simplified.

[0011] Furthermore, in the second embodiment of the present invention, the method for manufacturing an inorganic fiber sheet is such that the tensile strength after calcination is 200 N / m or more, and the liquid retention capacity is 100 g / m². 2 That's all.

[0012] Furthermore, in the third embodiment of the present invention, the method for producing an inorganic fiber sheet is such that, in any of the above embodiments, the swelling power of the bentonite is 20 ml / 2 g or more.

[0013] Furthermore, a fourth embodiment of the present invention is an inorganic fiber sheet comprising inorganic fibers and organic fibers, further comprising 15 to 50% by weight of bentonite. With the above configuration, the tensile strength after calcination can be improved by incorporating bentonite into the inorganic fiber sheet.

[0014] Furthermore, in the fifth embodiment of the present invention, the inorganic fiber sheet has a swelling capacity of 20 ml / 2 g or more of bentonite.

[0015] Furthermore, the inorganic fiber sheet according to the sixth aspect of the present invention is an inorganic fiber sheet containing inorganic fibers and organic fibers, and further contains bentonite having a swelling power of 20 ml / 2g or more.

[0016] Furthermore, in the inorganic fiber sheet according to the seventh aspect of the present invention, in the above aspect, the tensile strength after calcination is 200 N / m or more, and the liquid retention capacity is 100 g / m 2 or more.

[0017] Furthermore, the inorganic fiber sheet according to the eighth aspect of the present invention contains glass fibers and biosoluble ceramic fibers as the inorganic fibers in any of the above aspects.

[0018] Furthermore, the inorganic fiber sheet according to the ninth aspect of the present invention, in any of the above aspects, is in the form of a sheet obtained by wet papermaking of the inorganic fibers, the organic fibers, and the bentonite. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] [Figure 1] It is a graph showing the relationship between the swelling power of bentonite and the tensile strength after calcination. [Figure 2] It is a graph showing the relationship between the blending amount of bentonite and the tensile strength after calcination. MODES FOR CARRYING OUT THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments shown below are examples for embodying the technical idea of the present invention, and the present invention is not limited to the following. In addition, this specification by no means limits the members recited in the claims to the members of the embodiments. In particular, unless specifically described, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the embodiments are not intended to limit the scope of the present invention only thereto, but are merely illustrative examples. Note that the sizes and positional relationships of members shown in the respective drawings may be exaggerated for clarity of explanation. Furthermore, in the following description, the same names and reference signs denote the same or homogeneous members, and detailed descriptions thereof are omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are formed of the same member, and one member also serves as a plurality of elements; conversely, the function of one member can be shared and realized by a plurality of members. [Embodiment 1]

[0021] The inorganic fiber sheet according to the embodiment of the present invention is used, for example, in the production of filter base materials. Specifically, the inorganic fiber sheet undergoes processing such as corrugation to form a honeycomb molded body, which is then calcined to obtain a filter base material. An adsorbent or a catalyst is supported on such a filter base material to form a honeycomb filter used for dehumidification, decomposition or removal of volatile organic compounds (VOC), and the like. The inorganic fiber sheet is also used as a heat-resistant cushion material and the like. Furthermore, as a honeycomb filter, there is a honeycomb rotor. The honeycomb rotor is produced, for example, by a method comprising: winding a single-corrugated molded body obtained by bonding a corrugated inorganic fiber sheet (core paper) and a non-corrugated inorganic fiber sheet to form a cylindrical shape; calcining this cylindrical honeycomb molded body to allow an adsorbent to be supported thereon, and then cutting the resultant. The honeycomb rotor repeats adsorption and regeneration by rotating in a space partitioned into an adsorption zone for adsorbing an adsorption target such as VOC and a regeneration zone for desorbing the adsorption target.

[0022] The inorganic fiber sheet according to this embodiment does not contain ceramic fibers, which are classified as Category 2 (suspected carcinogen) under EU Directive 97 / 69EC, from the standpoint of safety for the human body. [Method for manufacturing inorganic fiber sheets]

[0023] The present invention relates to a method for producing an inorganic fiber sheet, in which 15 to 50% by weight of bentonite is mixed with inorganic fibers and organic fibers and then wet-processed papermaking. Preferably, the inorganic fibers include glass fibers and biosoluble inorganic fibers.

[0024] Inorganic fibers, organic fibers, and bentonite are wet-processed to obtain a sheet-like nonwoven fabric. Examples of dispersion media for the raw material slurry used in the production of the nonwoven fabric include water, methanol, ethanol, mineral oil, and mixtures thereof, but water is preferred among these.

[0025] Bentonite is a clay mineral whose main component is montmorillonite, with small amounts of quartz, feldspar, etc., as impurities. Its composition varies depending on the mining site, but it can be used without particular limitation in this invention. Refined montmorillonite can also be used in the same way. Furthermore, depending on the type of cations between the crystalline layers, Na-type, Ca-type, and organic bentonite can be used. Among these, Na-type bentonite is preferably used due to its ease of dispersion in water.

[0026] The swelling force when dispersing bentonite in water can be measured according to the Japan Bentonite Industry Association's JBAS104:77 method for testing the swelling of bentonite (powder). Specifically, 2.0 g of a sample adjusted to 8.0% moisture content is added in approximately 10 portions to a 100 ml stoppered graduated cylinder containing 100 ml of distilled water. At this time, the next addition is made only after the previous addition has settled at the bottom of the graduated cylinder. After standing for 24 hours, the apparent volume of the sample mass at the bottom of the graduated cylinder after swelling is read from the scale of the graduated cylinder and expressed as the swelling force Sp (ml / 2g). The swelling force of the bentonite used in the inorganic fiber sheet of the present invention is preferably 20 ml / 2g or more, and more preferably 25 ml / 2g or more. If it is above the lower limit of the above range, the tensile strength after calcination tends to be excellent. There is no particular upper limit to the swelling force, but it is usually 100 ml / 2g or less.

[0027] The bentonite content in the inorganic fiber sheet after manufacturing is 15-50%, with 18-50% being more preferable. If the content is above the lower limit of the above range, the strength after calcination tends to be superior, and if it is below the upper limit of the above range, the liquid retention capacity after calcination tends to be superior.

[0028] There are no particular restrictions on the type of glass fiber used; in addition to E-glass, which is produced in large quantities, high-strength S-glass and C-glass, which has excellent acid resistance, can be used. From a cost perspective, it is preferable to use inexpensive E-glass. Furthermore, one type of glass fiber may be used, or two or more types may be used in combination.

[0029] Biosoluble inorganic fibers are fibers that do not fall under the category of "WHO inhalable fibers," or fibers that satisfy any one of the following four conditions (1) to (4) according to the EU Directive 97 / 69 / EC NotaQ "Criteria for Determining Biosoluble Fibers." Biosoluble inorganic fibers can include biosoluble ceramics and biosoluble rock wool.

[0030] "WHO inhalable fibers" are defined by the World Health Organization (WHO) as fibrous materials that are inhaled into the body through respiration and reach the lungs, with a length greater than 5 μm, a diameter of less than 3 μm, and an aspect ratio greater than 3.

[0031] Furthermore, the four conditions mentioned above are as follows: (1) In animal experiments involving short-term inhalation exposure, fibers with a length of 20 μm or more have a half-life of less than 10 days. (2) In animal experiments involving short-term intratracheal instillation, fibers with a half-life of less than 40 days are those with a length of more than 20 μm. (3) In animal studies using intraperitoneal administration, there is no significant carcinogenicity. (4) Animal studies involving long-term inhalation exposure show no pathological findings or tumor formation linked to carcinogenicity (provided that the composition contains more than 18% by mass of alkali and alkaline earth oxides (Na2O, K2O, CaO, MgO, BaO)).

[0032] Biosoluble inorganic fibers typically contain non-fibrous "shots" due to their manufacturing process. However, using biosoluble inorganic fibers with a high shot content can lead to problems such as holes and powder shedding in the resulting inorganic fiber sheet. Therefore, it is preferable to use biosoluble inorganic fibers with a shot content of 20% by mass or less.

[0033] Biosoluble inorganic fibers may be used individually or in combination of two or more types.

[0034] There are no particular restrictions on the fiber length of the inorganic fibers, but the length-weighted average fiber length of the inorganic fibers is preferably 0.2 to 15 mm, more preferably 1 to 15 mm, and particularly preferably 3 to 13 mm. If the length-weighted average fiber length is above the lower limit of the above range, the strength of the resulting inorganic fiber sheet tends to be superior, and if it is below the upper limit of the above range, the texture of the resulting inorganic fiber sheet tends to be superior. Inorganic fibers of different fiber lengths may be used in combination. The length-weighted average fiber length is calculated by measuring the fiber length of 100 fibers by microscopic observation.

[0035] For inorganic fibers, the fiber diameter is preferably 3 μm or larger on average, for example, in the case of glass fibers. If it is above the lower limit of the above range, it does not fall under the category of WHO inhalable fibers and is safe for the human body. Furthermore, the upper limit of the fiber diameter for glass fibers is more preferably 8 μm on average. If it is below the upper limit of the above range, both the strength of the inorganic fiber sheet and the strength of the filter substrate obtained by calcining the inorganic fiber sheet are excellent. In addition, the mesh opening of the resulting filter substrate does not become too large, and the adsorbent can be sufficiently supported. Therefore, the voids between the fibers remain as through holes, preventing untreated gas from passing through, and a filter with superior performance can be manufactured. Inorganic fibers with different fiber diameters may also be used in combination. The average value of the fiber diameter is calculated by measuring the fiber diameter of 100 fibers by microscopic observation.

[0036] The inorganic fiber content in the inorganic fiber sheet after manufacturing is 30 to 95% by mass, more preferably 50 to 90% by mass, and particularly preferably 50 to 70%. If the inorganic fiber content is below the lower limit of the above range, when the inorganic sheet is calcined to make a filter base material, too much organic matter will be burned off during calcination, which may reduce the strength of the filter base material obtained after calcination. If it exceeds the upper limit of the above range, the suitability for corrugation processing and handling may be inferior.

[0037] The raw material slurry used in the manufacture of nonwoven fabrics preferably contains insoluble and non-heat-fusible organic fibers that do not dissolve in water during wet papermaking when manufacturing inorganic fiber sheets, nor do they melt due to the heat applied during the inorganic fiber sheet manufacturing process, but remain in fibrous form in the inorganic fiber sheet after manufacture. The drying temperature is not particularly limited, but is usually around 100°C to 180°C. For example, fibers made of thermoplastic resins with a melting point of less than 150°C may melt and form a film when dried in this temperature range, and may not remain in fibrous form. Examples of insoluble and non-heat-fusible organic fibers include natural fibers and non-heat-fusible synthetic fibers, and one or more types can be used. There are no restrictions on the form of the fibers, and they may be fibrilized.

[0038] Examples of natural fibers include cellulose fibers such as wood pulp (coniferous pulp, hardwood pulp), cotton, wool, silk, and hemp, and one or more types may be used. The wood pulp may be either beaten or unbeaten. Among these, relatively inexpensive wood pulp is preferred.

[0039] Non-heat-fusible synthetic fibers are those that do not melt when heated during the manufacturing process of inorganic fiber sheets. They can be selected according to the drying temperature set in the manufacturing process of the inorganic fiber sheet, and examples include polypropylene fibers, polybutene fibers, nylon fibers, rayon fibers, cupro fibers, acetate fibers, polyvinyl chloride fibers, acrylic fibers, polyester fibers, polyurethane fibers, poly(p-phenylene)benzobisoxazole fibers, polyamide-imide fibers, polyimide fibers, polyarylate fibers, polyetherimide fibers, vinylon fibers, polycarbonate fibers, ethylene-vinyl acetate fibers, polyphenylene sulfide fibers, polyethylene terephthalate fibers, polybutylene terephthalate fibers, polyethylene naphthalate fibers, aramid fibers, and other chemical fibers. One or more non-heat-fusible synthetic fibers can be used.

[0040] The content of insoluble and non-heat-fusible organic fibers in the inorganic fiber sheet after manufacturing is preferably 1 to 20% by mass, and more preferably 3 to 15% by mass. If the content of insoluble and non-heat-fusible organic fibers is above the lower limit of the above range, a sufficient effect of improving corrugation processing suitability can be obtained. If it is below the upper limit of the above range, when the inorganic fiber sheet is calcined to make a filter base material, the amount of insoluble and non-heat-fusible organic fibers that are burned out by calcination is small, the gaps between fibers that are formed due to such burning can be reduced, and a filter with superior performance that suppresses the passage of untreated gas can be manufactured. When wood pulp is used as the insoluble and non-heat-fusible organic fiber, the content of wood pulp relative to the total amount of insoluble and non-heat-fusible organic fibers is preferably 30% by mass or more, and may be 100% by mass.

[0041] The raw material slurry used in the manufacture of nonwoven fabrics preferably contains an organic binder component as a component that adheres the fibers together. Examples of organic binder components include thermoplastic resins that melt at least partially when heated during the inorganic fiber sheet manufacturing process, and can be selected according to the drying temperature set in the inorganic fiber sheet manufacturing process. There are no restrictions on the form of the organic binder component; it may be fibrous, particulate, emulsion, liquid, or any other form.

[0042] Examples of thermoplastic resins include polyethylene resin, polyvinyl chloride resin, (meth)acrylic acid ester resin, styrene-acrylic acid ester copolymer, vinyl acetate resin, vinyl acetate-(meth)acrylic acid ester copolymer, ethylene-vinyl acetate copolymer, polyester resin, polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer, etc. Rubber emulsions such as styrene-butadiene rubber (SBR) and nitrile rubber (NBR) may also be used. One or more thermoplastic resins can be used.

[0043] Furthermore, as the organic binder component, composite fibers may be used in which two or more materials with different melting points are combined, and the portion with the lower melting point melts and acts as a binder. Examples of composite fibers include core-sheath fibers and side-by-side fibers. Examples of core-sheath fibers include fibers in which a low-melting-point sheath made of polyethylene or the like is formed around a high-melting-point core made of polyethylene terephthalate, polypropylene or the like. As the organic binder component, thermosetting resins that harden by heating during the manufacturing process of inorganic fiber sheets and bond the fibers together can also be used. Examples of thermosetting resins include phenolic resins, epoxy resins, melamine resins, urea resins, unsaturated polyester resins, polyurethane resins, and thermosetting polyimide resins. One or more thermosetting resins can be used.

[0044] While there are no particular restrictions on the organic binder component, it is preferable to use an acrylic resin emulsion because it provides excellent water resistance to the inorganic fiber sheet after manufacturing.

[0045] The content of the organic binder component in the inorganic fiber sheet after manufacturing is preferably 1 to 15% by mass, and more preferably 3 to 10% by mass. If the content of the organic binder component is above the lower limit of the above range, the fibers can be sufficiently bound together. If it is below the upper limit of the above range, when the inorganic fiber sheet is calcined and used as a filter substrate, the amount of organic binder component that is burned off during calcination is small, which reduces the gaps between fibers that are formed due to such burning, and allows for the production of a filter with superior performance that suppresses the passage of untreated gas.

[0046] When using an acrylic resin emulsion as an organic binder component, the content of the acrylic resin emulsion relative to the total amount of the organic binder component is preferably 20% by mass or more, and may also be 100% by mass.

[0047] The raw material slurry used in the manufacture of nonwoven fabrics may, if necessary, contain inorganic binder components other than β-type sepiolite, such as colloidal silica, water glass, calcium silicate, silica sol, alumina sol, and alkoxysilane, and one or more of these may be used. However, these inorganic binders may fall off as powder when subjected to external forces such as friction or bending, resulting in poor handling properties. Therefore, the content of inorganic binder components other than bentonite is preferably 5% by mass or less as the content relative to the inorganic fiber sheet after manufacture.

[0048] The raw material slurry used in the manufacture of nonwoven fabrics may further contain the following auxiliary agents, additives, fillers, etc. Additionally, it may contain inorganic fibers such as carbon fibers, or metallic fibers such as alumina fibers, as needed.

[0049] Examples of auxiliary agents include crosslinking agents such as epoxy, isocyanate, carbodiimide, and oxazoline, and silane coupling agents having functional groups such as amino groups, epoxy groups, methacryloxy groups, acryloxy groups, and mercaptoid groups; one or more of these can be used. The content of the silane coupling agent is preferably in the range of 10 parts by mass or less per 100 parts by mass of the organic binder component.

[0050] Examples of additives include antioxidants, light stabilizers, UV absorbers, thickeners, nucleating agents, neutralizing agents, lubricants, anti-blocking agents, dispersants, flow improvers, release agents, flame retardants, foaming agents, colorants, wetting agents, viscous agents, yield improvers, paper strength improvers, water filter agents, pH adjusters, defoamers, preservatives, and pitch control agents, and one or more of these may be used. The additive content is preferably 5% by mass or less relative to the inorganic fiber sheet after manufacturing.

[0051] Examples of fillers include dry silica, precipitated silica, synthetic silica such as gel silica, calcium silicate, calcium carbonate, kaolin, talc, plastic pigments, glass beads, hollow glass beads, and shirasu balloons, and one or more of these can be used.

[0052] Wet papermaking can be carried out by preparing a raw material slurry containing the above-mentioned components and water (medium), and then making paper using a known papermaking machine. Examples of papermaking machines include cylinder papermaking machines, inclined papermaking machines, long-screen papermaking machines, and short-screen papermaking machines, and multilayer papermaking may be performed by combining the same or different types of these papermaking machines.

[0053] There are no particular restrictions on the dewatering and drying methods after papermaking; known dryers such as Yankee dryers, cylinder dryers, air dryers, and infrared dryers can be used. The drying temperature is not particularly limited, but is usually around 100°C to 180°C.

[0054] When using organic binder components, inorganic binder components, fillers, etc., it is preferable to adjust the amount used so that the content of each component in the final inorganic fiber sheet falls within the range already described above.

[0055] There are no particular limitations on the basis weight of the inorganic fiber sheet according to this embodiment; for example, 10 to 100 g / m². 2While this is possible, as described above, the inorganic fiber sheet manufacturing method according to this embodiment allows for the production of an inorganic fiber sheet with sufficient strength even when the basis weight is reduced. Therefore, for filter substrate applications, the basis weight of the inorganic fiber sheet should be 20 to 80 g / m². 2 Preferably, 25-70 g / m 2 This is more preferable. If the basis weight is above the lower limit of the above range, sufficient strength can be obtained for the inorganic fiber sheet and the filter substrate obtained from the inorganic fiber sheet, and if it is below the upper limit of the above range, the thickness can be reduced and pressure loss can also be suppressed.

[0056] There are no particular limitations on the density of the inorganic fiber sheet according to this embodiment, but with the method for manufacturing the inorganic fiber sheet according to this embodiment, sufficient strength can be obtained even with a low density, for example, 0.20 to 0.45 g / cm³. 3 This is preferable. If the density is above the lower limit of the above range, the voids will not become too large, and it will be possible to achieve a balance between liquid retention rate, adsorbent load capacity, and strength. If the density is below the upper limit of the above range, sufficient voids will be formed, resulting in excellent liquid retention and a high-performance filter.

[0057] There are no particular limitations on the thickness of the inorganic fiber sheet according to this embodiment, but according to the method for manufacturing the inorganic fiber sheet according to this embodiment, sufficient strength can be obtained even if the thickness is small, so for example, 50 to 300 μm is preferred, and 100 to 250 μm is more preferred. If the thickness is above the lower limit of the above range, both strength and liquid retention capacity can be achieved. If the liquid retention capacity is below the upper limit of the above range, the pressure loss will not become too large, and a high-performance filter can be obtained.

[0058] The present inventors discovered that in producing an inorganic fiber sheet that does not use RCF, using 15 to 50% by weight of bentonite, or using bentonite with a swelling power of 20 ml / 2 g or more, eliminates the need for external additives to increase strength, and allows the production of an inorganic fiber sheet that can be produced in a short time by blending inorganic fibers and organic fibers all at once in the wet papermaking process. Although the reason for this has not been confirmed, it is presumed that when the extremely thin tabular crystal particles present in bentonite and their laminated structure are dried during the wet papermaking process, they lose water molecules between the layers along with the evaporation of water, and align and aggregate between the particles and on the fiber surfaces, thereby exerting the effect of reinforcing the fiber intersections in the inorganic fiber sheet. In addition, the improved strength makes it possible to obtain sufficient strength even when the filter base material is made thinner and lighter, or when the density is lowered to increase the adsorbent loading amount or liquid retention amount. [Characteristics after calcination]

[0059] Further, the inorganic fiber sheet has a liquid retention after calcination of 100 g / m 2 or more, preferably 130 g / m 2 or more. There is no particular limitation on the upper limit of the liquid retention, but it is, for example, 250 g / m 2 or less. With such a liquid retention, when the filter base material is impregnated with an impregnation liquid containing an adsorbent, the adsorbent can be sufficiently supported. The liquid retention is a value measured by the method described in the examples below.

[0060] Here, the calcination conditions are, for example, calcination at 500°C for 2 hours in air. In general, inorganic fiber sheets are subjected to calcination in the process of being used as filter base materials, so it is common practice to define characteristics based on conditions after calcination. Calcination conditions vary depending on the application and purpose of the filter base material and are not standardized, so the above-mentioned calcination at 500°C for 2 hours in air is used as a tentative standard.

[0061] Furthermore, the inorganic fiber sheet is preferably 200 N / m or more, more preferably 300 N / m or more, and particularly preferably 450 N / m or more, along the flow direction of the wet papermaking process, after calcination at 500°C in air for 2 hours. If the tensile strength is above the lower limit of the above range, sufficient handling properties can be obtained in the honeycomb-shaped or other filter substrate obtained by calcining the inorganic fiber sheet. There is no particular limit to the upper limit of the tensile strength, but it is usually 4000 N / m or less.

[0062] By using inorganic fiber sheets manufactured in this manner, it is possible to produce filter substrates that possess sufficient strength even when the thickness is reduced to reduce weight or the density is lowered to increase the amount of adsorbent that can be carried or the amount of liquid that can be retained. These substrates also have good corrugation properties and suitability for corrugation processing, and are safe for human use. Furthermore, these inorganic fiber sheets can be used for various reinforcing materials, including glass fiber reinforced plastics, as well as for gaskets and packings in high-temperature areas.

[0063] In this embodiment, an inorganic fiber sheet is subjected to corrugation processing to form a honeycomb molded body, and the honeycomb molded body is calcined to burn off organic components such as organic binder components and organic fibers, thereby obtaining a calcined body. The calcination temperature is preferably 250°C or higher. In particular, when the main component of the inorganic fiber (more than 50% by mass) is at least one of glass fiber and biosoluble rock wool, a calcination temperature of about 400 to 600°C is preferred, while when the main component of the inorganic fiber is biosoluble ceramic fiber, a calcination temperature of about 600 to 800°C is preferred. When manufacturing a honeycomb molded body, a single-wave molded body is usually manufactured by bonding a corrugated inorganic fiber sheet (core paper) and an uncorrugated inorganic fiber sheet. Examples of adhesives used in this process include inorganic adhesives such as colloidal silica, water glass, and alumina sol, and one or more of these can be used. In addition, organic adhesives such as ethylene-vinyl alcohol may be used in combination as an adhesive.

[0064] Furthermore, a honeycomb filter can be obtained by supporting at least one type of adsorbent on the calcined body described above. As the adsorbent, one or more selected from the group consisting of silica gel, zeolite, sepiolite, activated carbon, and ion exchange resin are preferred in terms of adsorption properties, but various other adsorbents can also be used. Examples of adsorbents used as dehumidifiers include silica, zeolite, hydrophobic synthetic zeolite, natural zeolite, sepiolite, hydrotalcite, alumina, lime, gypsum, dolomitic lime, magnesium hydroxide, perlite, diatomaceous earth, lithium chloride, calcium chloride, Portland cement, alumina cement, palygorskite, aluminum silicate, activated clay, activated alumina, bentonite, talc, kaolin, mica, activated carbon, and superabsorbent polymers. Other examples of adsorbents include solid adsorbents in which alkaline compounds are supported on carriers with adsorption capacity (potassium carbonate, sodium carbonate, sodium bicarbonate, calcium hydroxide, calcium carbonate, etc.), or on activated carbon, silica, alumina, allophane, sepiolite, cordierite, or other clay minerals; sodium hydroxide, potassium hydroxide, potassium carbonate, calcium hydroxide, ion exchange resins, deodorants, etc. Porous adsorbents in which catalysts such as titanium are supported in the pores can also be used.

[0065] A known method for supporting the adsorbent involves impregnating a calcined body with a slurry containing the adsorbent and then drying it. After drying, firing may be performed as needed. This slurry may contain one or more inorganic adhesives such as colloidal silica, water glass, or alumina sol to improve the adsorbent's support and the strength of the honeycomb filter. When firing is performed, the firing temperature is preferably 600°C or higher if the main component of the inorganic fibers is biosoluble ceramic fibers, as this allows for sintering between the fibers and bentonite. In the case of an inorganic fiber sheet containing glass fibers, a temperature of around 400-600°C is preferred. [Examples 1-3, Comparative Example 1]

[0066] Next, inorganic fiber sheets according to Examples 1 to 3 and an inorganic fiber sheet according to Comparative Example 1 were prepared using glass fibers with a fiber diameter of 6.5 μm and a length of 3 mm and biosoluble rock wool with a fiber diameter of 6.0 μm and a length of 0.65 mm as inorganic fibers, coniferous pulp as organic fibers, and precipitated silica with an average particle diameter of 11.5 μm and bentonite with an average particle diameter of 70 μm and different swelling strengths as fillers. The blending ratios of the inorganic fiber sheets used in each example and comparative example are shown in Table 1. Here, inorganic fibers, organic fibers, and bentonite were dispersed and mixed in water at various blending ratios, and the raw material concentration was adjusted to 0.2% by weight to obtain a raw material slurry. An inorganic fiber sheet was obtained from this slurry by wet papermaking using a long-wire paper machine. The results of the following test measurements performed on the obtained inorganic fiber sheets are shown in Table 1. (Basic weight)

[0067] The basis weight of the obtained inorganic fiber sheet was measured in accordance with JIS P 8124 (2011). (Thickness, density)

[0068] The thickness and density of the obtained inorganic fiber sheets were measured in accordance with JIS P 8118 (2014). (ash)

[0069] The ash content of the obtained inorganic fiber sheets was measured in accordance with JIS P 8251 (2003), except that it was heat-treated at 500°C for 2 hours. (Tensile strength after calcination)

[0070] The tensile strength in the flow direction of the obtained inorganic fiber sheet after calcination was measured in accordance with JIS P 8113 (2006) using a Tensilon type universal tester (manufactured by A&L Co., Ltd.) in the flow direction of a wet paper machine after heat treatment at a temperature of 500°C for 2 hours. (Liquid retention volume after calcination)

[0071] The obtained inorganic fiber sheet was heat-treated at 500°C for 2 hours in accordance with JIS L1913 (2010) for measuring water retention, and the dry mass A (g) of the inorganic fiber sheet (100 mm × 100 mm) was measured. Then, the inorganic fiber sheet was immersed in pure water for 15 minutes, then removed with tweezers, and held for 5 minutes until the water droplets stopped falling due to its own weight, and its mass B (g) was measured. The mass of the water held was calculated by subtracting mass A from mass B, and the sample area (0.01 m²) was then measured. 2 Divide by ) to get 1m 2 The liquid retention capacity was calculated by converting it to a per-unit rate.

[0072] Table 1 shows the blending ratio of the inorganic fiber sheet samples, the physical properties of the inorganic fiber sheet, and the physical properties of the sheet after calcination for each example and comparative example. Figure 1 shows the relationship between the expansion force of bentonite and the tensile strength after calcination. As shown in this figure, it was found that the tensile strength after calcination stabilizes when the expansion force of bentonite is in the range of 20 ml / 2g or more.

[0073] [Table 1] [Examples 4-8, Comparative Example 2]

[0074] Next, inorganic fiber sheets according to Examples 4-8 and the inorganic fiber sheet according to Comparative Example 2 were prepared using glass fibers with a fiber diameter of 6.5 μm and a length of 3 mm and biosoluble rock wool with a fiber diameter of 6.0 μm and a length of 0.65 mm as inorganic fibers, and coniferous pulp and bentonite with an average particle size of 70 μm and a swelling force of 21 ml / 2 g as organic fibers. The blending ratio of the inorganic fiber sheets used in each example and comparative example, the physical properties of the inorganic fiber sheets, and the physical properties of the sheets after calcination are shown in Table 2.

[0075] [Table 2]

[0076] Furthermore, the relationship between the amount of bentonite added and the tensile strength after calcination of the obtained inorganic fiber sheet is shown in the graph in Figure 2. As shown in this figure, it was confirmed that the tensile strength after calcination tended to improve as the amount of bentonite added increased. Therefore, it is preferable to add 15 to 50% by weight of bentonite. However, the tensile strength after calcination decreased above a bentonite content of 45% by weight. In addition, a linear decrease in liquid retention was observed when the bentonite content was within the range of 6 to 50% by weight. Within this range, the strength improves with increasing bentonite content, so the appropriate tensile strength and liquid retention can be set according to the application, and the amount added can be determined accordingly. In other words, the tensile strength and liquid retention of the inorganic fiber sheet can be appropriately changed by changing the amount of bentonite added. Furthermore, by finding that the upper limit of the bentonite content is 50% by weight, or in other words, the upper limit at which the tensile strength after calcination decreases, it is possible to avoid adding unnecessary bentonite and determine an appropriate amount to use within a range that is effective in improving tensile strength. On the other hand, as strength increases, the amount of liquid retention decreases, so in this respect as well, the appropriate amount of bentonite to be added according to the required amount of liquid retention is determined. [Industrial applicability]

[0077] The inorganic fiber sheet of the present invention and the inorganic fiber sheet obtained by the method for producing the same can be suitably used as base paper for the manufacture of filter substrates.

Claims

1. A method for manufacturing an inorganic fiber sheet, A process of wet papermaking using inorganic and organic fibers with 15-50% by weight of bentonite, A method for manufacturing an inorganic fiber sheet containing [the specified material].

2. A method for manufacturing an inorganic fiber sheet according to claim 1, A method for producing an inorganic fiber sheet in which the swelling power of the bentonite is 20 ml / 2 g or more.

3. An inorganic fiber sheet containing inorganic fibers and organic fibers, further, An inorganic fiber sheet containing 15-50% by weight of bentonite.

4. The inorganic fiber sheet according to claim 3, An inorganic fiber sheet in which the swelling power of the bentonite is 20 ml / 2 g or more.

5. An inorganic fiber sheet containing inorganic fibers and organic fibers, further, An inorganic fiber sheet containing bentonite with a swelling capacity of 20 ml / 2 g or more.

6. An inorganic fiber sheet according to any one of claims 3 to 5, An inorganic fiber sheet in the form of a sheet obtained by wet-processing the inorganic fibers, the organic fibers, and the bentonite.

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