JP2017025458A - Method for manufacturing inorganic fiber sheet, fired body, and honeycomb filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an inorganic fiber sheet, capable of manufacturing a filter base material which has sufficient strength, good wavy shaping, and excellent corrugate processing suitability, and including safety to the human body, even when a carrier quantity and a liquid-holding quantity of an absorbent are made large by thinning a thickness, saving a weight, and lowering a density, a fired body of the manufactured inorganic fiber sheet, and a honeycomb filter including the fired body.SOLUTION: A method for manufacturing an inorganic fiber sheet, as a method for manufacturing an inorganic fiber sheet which includes 30-92 mass% of at least one kind of an inorganic fiber selected from the group consisting of a glass fiber and an organism solubility inorganic fiber, and 5-40 mass% of β type sepiolite, includes (i) a step of manufacturing a nonwoven fabric by wet-type paper making raw material slurry containing the inorganic fiber, and (ii) a step of adhering slurry containing β type sepiolite to the nonwoven fabric.SELECTED DRAWING: None

Description

  The present invention relates to an inorganic fiber sheet manufacturing method, a fired body, and a honeycomb filter that are preferably used for manufacturing a filter substrate.

  Since ceramic fibers have characteristics such as high heat resistance, high heat insulation, and non-combustibility, inorganic fiber sheets using ceramic fibers are widely used. For example, the inorganic fiber sheet is used for manufacturing a filter substrate. Specifically, the inorganic fiber sheet is formed into a honeycomb formed body through processing such as corrugation, and then fired to obtain a filter base material. The filter base material carries an adsorbent and a catalyst to form a honeycomb filter used for dehumidification, decomposition or removal of volatile organic compounds (VOC), and the like. In addition, the inorganic fiber sheet is also used as a heat-resistant cushion material.

  A honeycomb rotor is a honeycomb filter. For example, the honeycomb rotor is formed into a cylindrical shape by winding a single-wave molded body in which a corrugated inorganic fiber sheet (core paper) and an inorganic fiber sheet that has not been corrugated are bonded to each other. Is produced by firing and then carrying the adsorbent and then cutting. The honeycomb rotor repeats adsorption and regeneration by rotating in a space partitioned into an adsorption zone for adsorbing an adsorption object such as VOC and a regeneration zone for desorbing the adsorption object.

As a method for producing an inorganic fiber sheet, for example, Patent Documents 1 and 2 describe a method in which a raw material slurry containing ceramic fibers, an organic binder, a mountain bark, and the like is prepared, and the raw material slurry is made into paper to form an inorganic fiber sheet. Has been. Here, the mountain bark is a kind of naturally occurring clay mineral and is hydrous magnesium silicate. The mountain bark is used as an inorganic binder.
Further, in Patent Document 2, an inorganic fiber sheet is corrugated to form a honeycomb formed body and then fired, and an adsorbent or the like is supported on the obtained fired body to form a gas adsorption element (honeycomb filter). Have been described.

However, ceramic fibers are classified as category 2 (suspected of carcinogenesis) in the EU Directive 97 / 69EC for artificial amorphous fibers by the EU (European Union). Therefore, deceramicization is aimed at from the viewpoint of safety to the human body. For example, more than 18% by mass of oxides of alkali metals and alkaline earth metals (Na ₂ O, K ₂ O, CaO, MgO, BaO, etc.). Alternatives to biosoluble fibers contained (category 0, category exemption) and glass fibers are being studied.

Against this background, for example, Patent Document 3 discloses that a non-woven fabric obtained by making a paper made of a slurry containing a biosoluble inorganic fiber as a deceramic fiber and further containing a binder component is formed into a honeycomb formed body and fired at 800 ° C. It is described as a body.
Patent Document 4 discloses a method of obtaining an inorganic fiber sheet by papermaking a slurry containing biosoluble ceramic fiber, glass fiber, organic fiber, cationic inorganic binder and sepiolite which is a kind of mountain bark. It is disclosed.

JP 60-33250 A Japanese Patent No. 2925127 Japanese Patent No. 3880038 Japanese Patent No. 5558518

However, the honeycomb formed body described in Patent Document 3 and the fired body obtained by firing the honeycomb formed body have insufficient strength and are inferior in handling properties. For this reason, if the fired body is processed into the above-described honeycomb rotor, the fired body may be chipped or crushed. In particular, when the fired body is processed into the above-described honeycomb rotor, the fired body is dried and cut after the adsorbent is supported, but the fired body described in Patent Document 3 is subjected to drying and cutting. Easily chipped or crushed.
Further, the fired body obtained from the inorganic fiber sheet described in Patent Document 4 also has insufficient strength.

In addition, filter base materials such as the above-described honeycomb rotors tend to be required to be thin in order to reduce pressure loss. In addition, in order to improve the performance by increasing the amount of adsorbent, such as zeolite, on the filter substrate, it is desirable to increase the amount of liquid retained (in the step of supporting the adsorbent, a large amount of liquid containing the adsorbent). There is also a demand for weight reduction.
In order to reduce the thickness or weight of the filter substrate, it is conceivable to lower the basis weight of the inorganic fiber sheet that is the material of the filter substrate. However, when the basis weight of the inorganic fiber sheet is lowered, the strength of the filter base material (the inorganic fiber sheet after firing) tends to be weak, and the filter carrying the adsorbent on the filter base material may be deformed. is there. Therefore, for example, as described in the examples of Patent Document 4, in the conventional technique, the basis weight of the inorganic fiber sheet is about 80 g / m ² , for example, a lightweight sheet having a basis weight of less than 60 g / m ² is manufactured. It was difficult to do.

In addition, in order to increase the amount of adsorbent such as zeolite and the amount of liquid retained, large diameter fibers are used in the production of the inorganic fiber sheet, the porosity of the filter substrate is increased, and the density of the inorganic fiber sheet is increased. It is possible to lower it. However, as the porosity of the filter base material increases, the strength of the filter base material tends to decrease. In addition, it is difficult to sufficiently support particles having a small particle diameter such as zeolite and catalyst, especially on a filter substrate having a large porosity, and the coating of the filter substrate with these particles becomes insufficient, resulting in voids between fibers. Will remain as holes, making it easier for untreated gas to pass through.
Thus, it has been difficult to produce a filter base material that is thin and lightweight, has a large amount of adsorbent supported and retained, and has sufficient strength.

  The object of the present invention is to have a sufficient strength and a good wavy pattern even when the thickness is reduced to reduce the weight, or the density is decreased to increase the amount of adsorbent supported and the amount of liquid retained. A method for producing an inorganic fiber sheet capable of producing a filter substrate having excellent corrugating suitability and safety to the human body, a fired body of the produced inorganic fiber sheet, and a honeycomb filter provided with the fired body Is to provide.

The present invention has the following configuration.
[1] A method for producing an inorganic fiber sheet containing 30 to 95% 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. There,
A step (i) of producing a nonwoven fabric by wet papermaking the raw material slurry containing the inorganic fiber;
And a step (ii) of attaching a slurry containing β-type sepiolite to the nonwoven fabric.
[2] The method for producing an inorganic fiber sheet according to [1], wherein the raw material slurry contains a non-heat-fusible organic fiber and an organic binder component.
[3] The method for producing an inorganic fiber sheet according to [1] or [2], wherein the raw slurry does not contain sepiolite.
[4] The method for producing an inorganic fiber sheet according to [1] to [3], wherein the β-type sepiolite has an oil absorption of 150% by mass or more.
[5] The inorganic fiber sheet has a tensile strength along the flow direction of the wet papermaking of 300 N / m or more after firing for 2 hours at 500 ° C. in the air, and a wet tensile strength in the flow direction of 100 N. The manufacturing method of the inorganic fiber sheet of [1]-[4] which is / m or more.
[6] The inorganic fiber sheet had a basis weight of 15 to 50 g / ^{m 2,} and liquid retention volume after firing for two hours is 100 g / ^{m 2} or more at 500 ° C. in air, [1] The manufacturing method of the inorganic fiber sheet of [5].
[7] A fired body obtained by firing a honeycomb formed body formed using the inorganic fiber sheet produced by the production method of [1] to [6].
[8] A honeycomb filter in which at least one adsorbent selected from the group consisting of silica gel, zeolite, sepiolite, activated carbon and ion exchange resin is supported on the fired body of [7].

  According to the present invention, even when the thickness is reduced and the weight is reduced, or when the density is decreased and the amount of adsorbent carried or the amount of liquid retained is increased, the strength is sufficient and the wavy mold is good. A method for producing an inorganic fiber sheet capable of producing a filter substrate having excellent corrugating suitability and safety to the human body, a fired body of the produced inorganic fiber sheet, and a honeycomb filter provided with the fired body Can be provided.

Hereinafter, the present invention will be described in detail.
[Method for producing inorganic fiber sheet]
The manufacturing method of the inorganic fiber sheet of this invention contains 30-95 mass% of 1 or more types of inorganic fiber chosen from the group which consists of glass fiber and biosoluble inorganic fiber, and contains beta-40 sepiolite 5-40 mass%. It is a manufacturing method of the inorganic fiber sheet to do. The production method of the present invention includes a step (i) of producing a nonwoven fabric by wet papermaking a raw material slurry containing inorganic fibers, and a slurry containing β-type sepiolite with respect to the nonwoven fabric obtained in step (i). And attaching (ii).
In addition, the inorganic fiber sheet manufactured by this invention does not contain the ceramic fiber classified into the category 2 (suspected of carcinogenesis) in EU directive 97 / 69EC from the point of safety with respect to a human body.

(Process (i))
The raw material slurry used for the manufacture of the nonwoven fabric contains one or more inorganic fibers selected from the group consisting of glass fibers and biosoluble inorganic fibers. The medium usually contains water.
There is no restriction | limiting in particular as a kind of glass fiber, High strength S glass, C glass excellent in acid resistance, etc. other than E glass with much production amount can be used. From the viewpoint of cost, it is preferable to use inexpensive E glass.
Glass fiber may be used individually by 1 type, or may use 2 or more types together.

The biosoluble inorganic fiber used in the present invention is a fiber that does not fall under “WHO inhalable fiber” or, according to the EUQ 97/69 / EC NotaQ “biosoluble fiber determination criteria”, It is a fiber that satisfies any one of the four conditions (1) to (4). Biosoluble inorganic fibers include biosoluble ceramics, biosoluble rock wool, and the like.
“WHO inhalable fiber” is a fibrous substance defined by the World Health Organization (WHO) that is inhaled into the body by breathing and reaches the lungs. The length exceeds 5 μm, the diameter is less than 3 μm, and the aspect ratio exceeds 3 belongs to.
The above four conditions are as follows.
(1) In a short-term inhalation exposure animal experiment, a fiber with a length of more than 20 μm has a half-life of less than 10 days,
(2) A short-term intratracheal infusion animal experiment with a fiber with a length of more than 20 μm and a half-life of less than 40 days,
(3) In the animal experiment of intraperitoneal administration, there is no significant carcinogenicity,
(4) Animal experiments of long-term inhalation exposure that have no pathological findings or tumor formation associated with carcinogenicity (however, the composition is alkali and alkaline earth oxide (Na ₂ O, K ₂ O, CaO, MgO, BaO)) In excess of 18% by mass).

Biologically soluble inorganic fibers usually contain non-fibrous “shots” due to their production method, but when using biosoluble inorganic fibers with a high shot content, the resulting inorganic fibers In some cases, perforations, powder falling, etc. may become a problem in the sheet. Therefore, it is preferable to use a biosoluble inorganic fiber having a shot content of 20% by mass or less.
The biosoluble inorganic fibers may be used alone or in combination of two or more.

The fiber length of the inorganic fiber is not particularly limited, but the length weighted average fiber length of the inorganic fiber 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 equal to or greater than the lower limit of the above range, the strength of the resulting inorganic fiber sheet tends to be more excellent, and if it is equal to or less than the upper limit of the above range, the resulting inorganic fiber sheet has a texture. It tends to be excellent. Inorganic fibers may have different fiber lengths.
The length-weighted average fiber length is calculated by measuring the fiber length of 100 fibers by microscopic observation.

For example, in the case of glass fiber, the average fiber diameter of the inorganic fiber is preferably 3 μm or more. If it is above the lower limit of the above range, it does not fall under the WHO inhalation fiber and is safe for the human body. Moreover, as for the upper limit of the fiber diameter of glass fiber, 8 micrometers is more preferable as an average value. If it is below the upper limit of the said range, both the intensity | strength of an inorganic fiber sheet and the intensity | strength of the filter base material obtained by baking this inorganic fiber sheet will be excellent. Moreover, the opening of the filter base material obtained does not become too large, and the adsorbent can be sufficiently supported. Therefore, the gap between the fibers is left as a through hole, and the raw gas is prevented from passing through, and a filter with excellent performance can be manufactured.
Inorganic fibers having different fiber diameters may be used in combination.
The average value of the fiber diameter is calculated by measuring the fiber diameter of 100 fibers by microscopic observation.

  Content of the inorganic fiber with respect to the inorganic fiber sheet after manufacture is 30-95 mass%, and 50-90 mass% is more preferable. When the inorganic fiber content is less than the lower limit of the above range, when the inorganic sheet is fired to obtain a filter base material, too much organic component is burned off by firing, and the strength of the filter base material obtained after firing May decrease. If the upper limit of the above range is exceeded, the corrugating suitability and handling may be inferior.

The raw material slurry used for manufacturing the nonwoven fabric is not dissolved in water during wet papermaking when manufacturing the inorganic fiber sheet, or melted by the heat applied in the process of manufacturing the inorganic fiber sheet, and the inorganic fiber sheet after manufacture It is preferable to include non-soluble and non-heat-sealable organic fibers that remain in the form of fibers. Examples of the heat applied in the process of manufacturing the inorganic fiber sheet include heat when the nonwoven fabric is dried after the slurry containing β-type sepiolite is adhered. The drying temperature is not particularly limited, but is usually about 100 ° C to 180 ° C. For example, a fiber made of a thermoplastic resin having a melting point of less than 150 ° C. may be melted to form a film and not remain in a fibrous form when dried in such a temperature range.
An inorganic fiber sheet containing non-soluble and non-heat-sealable organic fibers has a good corrugated shape when corrugated, has a good wave shape, and is excellent in corrugating suitability.
Examples of non-soluble and non-heat-sealable organic fibers include natural fibers and non-heat-sealable synthetic fibers, and one or more types can be used. There is no restriction | limiting in the form of a fiber, You may fibrillate.

Examples of natural fibers include cellulose fibers such as wood pulp (conifer pulp, hardwood pulp); natural fibers such as cotton, wool, silk, hemp and the like, and one or more types can be used. The wood pulp may be beaten pulp or unbeaten pulp.
Among these, relatively inexpensive wood pulp is preferable.

  The non-heat-bondable synthetic fiber is a fiber that does not melt by heating during the manufacturing process of the inorganic fiber sheet, and can be selected according to the temperature of the drying temperature set in the manufacturing process of the inorganic fiber sheet. Polypropylene fiber, polybutene fiber, nylon fiber, rayon fiber, cupra fiber, acetate fiber, polyvinyl chloride fiber, acrylic fiber, polyester fiber, polyurethane fiber, polyparaphenylenebenzobisoxazole fiber, polyamideimide fiber, polyimide fiber, polyarylate fiber , Polyetherimide fiber, vinylon fiber, polycarbonate fiber, ethylene-vinyl acetate fiber, polyphenylene sulfide fiber, polyethylene terephthalate fiber, polybutylene terephthalate fiber, polyethylene naphthalate fiber, aramid Chemical fibers such 維等 like. One or more non-heat-sealable synthetic fibers can be used.

The content of non-soluble and non-heat-sealable organic fibers in the manufactured inorganic fiber sheet is preferably 1 to 20% by mass, and more preferably 3 to 15% by mass. When the content of the non-soluble and non-heat-fusible organic fiber is not less than the lower limit of the above range, the effect of improving the corrugating suitability can be sufficiently obtained. When the inorganic fiber sheet is fired to form a filter substrate when the inorganic fiber sheet is not more than the upper limit of the above range, the amount of non-soluble and non-heat-fusible organic fibers burned by firing is small. Accordingly, it is possible to reduce the voids between the fibers formed, and to manufacture a filter with excellent performance in which the passage of untreated gas is suppressed.
When wood pulp is used as the non-soluble and non-heat-sealable organic fiber, the wood pulp content relative to the total amount of non-soluble and non-heat-sealable organic fiber is 30% by mass or more. Preferably, it may be 100% by mass.

It is preferable that the raw material slurry used for manufacturing the nonwoven fabric contains an organic binder component as a component for bonding fibers together.
Examples of the organic binder component include a thermoplastic resin that is at least partially melted by heating during the manufacturing process of the inorganic fiber sheet, and can be selected according to the temperature of the drying temperature set in the manufacturing process of the inorganic fiber sheet. . There is no restriction | limiting in the form of an organic binder component, Any may be fibrous, a particulate form, an emulsion, a liquid form.
Examples of the thermoplastic resin include polyethylene resin, vinyl chloride resin, (meth) acrylic ester resin, styrene-acrylic ester copolymer, vinyl acetate resin, vinyl acetate- (meth) acrylic ester copolymer, ethylene -Vinyl acetate copolymer, polyester resin, polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer and the like. Further, rubber emulsions such as styrene / butadiene rubber (SBR) and nitrile rubber (NBR) may be used. One or more thermoplastic resins can be used.
In addition, as the organic binder component, a composite fiber in which two or more materials having different melting points are combined and a lower melting point portion melts to act as a binder may be used. Examples of the composite fibers include core-sheath fibers and side-by-side fibers. Examples of the core-sheath fiber 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, a thermosetting resin that is cured by heating during the manufacturing process of the inorganic fiber sheet to bond the fibers together can also be used.
Examples of the thermosetting resin include phenol resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, polyurethane resin, thermosetting polyimide resin, and the like. One or more thermosetting resins can be used.

  Although it does not restrict | limit especially as an organic binder component, It is preferable to use PVA, such as PVA fiber, from the point which is excellent in adhesive force. In addition, when it is desired to improve water resistance, it is also preferable to use an acrylic resin emulsion or the like.

It is preferable that content of the organic binder component with respect to the inorganic fiber sheet after manufacture is 1-15 mass%, and 3-10 mass% is more preferable. If the content of the organic binder component is not less than the lower limit of the above range, the fibers can be sufficiently bonded. When the inorganic fiber sheet is fired and used as a filter substrate when the inorganic fiber sheet is below the upper limit of the above range, the amount of the organic binder component that is fired and burned down is small, and between the fibers formed along with such burnout Therefore, it is possible to manufacture a filter with excellent performance in which the passage of untreated gas is suppressed.
When PVA is used as the organic binder component, the content of PVA with respect to the total amount of the organic binder component is preferably 20% by mass or more, and may be 100% by mass. When an acrylic resin emulsion is used as the organic binder component, the content of the acrylic resin (solid content) with respect to the total amount of the organic binder component is preferably 5 to 70% by mass.

  In addition, the organic binder component is added to the raw material slurry for producing the nonwoven fabric, and the liquid containing the organic binder component is spray-coated, curtain-coated, impregnated coated on the nonwoven fabric obtained in step (i), You may make it adhere (external addition application) by methods, such as bar application, roll application, and blade application. The nonwoven fabric to be externally applied may be a dried nonwoven fabric after drying or a wet web before drying.

As described above, the inorganic fiber sheet produced in the present invention contains 5 to 40% by mass of β-type sepiolite. β-type sepiolite acts as an inorganic binder component and imparts strength to the inorganic fiber sheet. In the present invention, a part of β-type sepiolite may be contained in the inorganic fiber sheet by being added to the raw material slurry used for the production of the nonwoven fabric (internal addition). However, in order to obtain an inorganic fiber sheet that can produce a filter substrate having sufficient strength, a slurry containing β-type sepiolite is adhered to the nonwoven fabric in the step (ii) described below in the majority of β-type sepiolite. It is preferable to give to a nonwoven fabric by the method.
Therefore, when the raw material slurry used for the production of the nonwoven fabric contains β-type sepiolite, the content is preferably 9% by mass or less in the total amount of β-type sepiolite contained in the inorganic fiber sheet after production, and 5% by mass. The following is more preferable, and 0% by mass is further preferable.

  Sepiolite has a hydrothermal action at high temperature and high pressure due to the difference in origin, has a high degree of crystallinity, and has a long fiber and a clear fibrous form (formerly called a mountain bark), and shallow seabed. It is caused by sedimentation at the lake bottom and has a low degree of crystallinity and a β-type of short fibers (in the form of lumps or clays). The α-type sepiolite has a large impurity content, and contains about several to tens of mass% of crystalline silica such as quartz classified in the category 1 in the above-mentioned EU Directive 97 / 69EC, which is not preferable for safety to the human body. On the other hand, the β-type has a relatively small impurity content, hardly contains crystalline silica, and is safe for the human body. Therefore, in the present invention, β-type sepiolite is used as sepiolite.

  When using β-type sepiolite, the present inventor has added (internally added) β-type sepiolite to a raw material slurry for producing a nonwoven fabric, and an inorganic fiber sheet capable of producing a filter substrate having sufficient strength is obtained. On the other hand, it was found that an inorganic fiber sheet capable of producing a sufficiently strong filter base material can be obtained by attaching (separate application) β-type sepiolite to the obtained nonwoven fabric. The reason is considered as follows.

As described above, β-type sepiolite has a fine short fiber shape, unlike α-type sepiolite which is a long fiber shape. Therefore, in the step (i), when a raw material slurry containing β-type sepiolite is made by wet papermaking to produce a nonwoven fabric, a flocculant is added to the raw material slurry so that fine β-type sepiolite does not pass through the papermaking wire. To form an aggregate by aggregating β-type sepiolite. By using the aggregate, β-type sepiolite does not pass through the papermaking wire, and the yield of β-type sepiolite is improved. It also has excellent drainage during paper making.
However, when β-type sepiolite is agglomerated during paper making in this way, it becomes a structure in which the aggregate is interrupted between fibers, and the obtained inorganic fiber sheet is scattered with non-uniform β-type sepiolite aggregates, A sparse part of only inorganic fibers and a dense part with many sepiolites are produced. As a result, the obtained inorganic fiber sheet has low strength at the sparse part, and the strength as a whole is insufficient, and in particular, the strength of the filter substrate obtained by firing the inorganic fiber sheet is also insufficient. Moreover, the texture of the inorganic fiber sheet is also inferior.
Further, when β-type sepiolite is scattered in the inorganic fiber sheet as an aggregate, the inorganic fiber sheet is fired to form a filter base material, and the filter base material is impregnated with an impregnating liquid containing an adsorbent to form a filter base material. When the adsorbent is supported, the adsorbent is absorbed together with the moisture of the impregnating solution due to concentration in the portion where the aggregate of β-type sepiolite having water absorption exists. As a result, the adsorbent also exists unevenly in the filter, and the filter performance is poor.
On the other hand, when β-type sepiolite is externally applied to the obtained nonwoven fabric, it is not necessary to use a flocculant. Therefore, β-type sepiolite can be uniformly present in the inorganic fiber sheet, and the strength of the filter base material obtained by firing the inorganic fiber sheet is excellent. Moreover, since the adsorbent can be supported uniformly, the filter performance is also excellent. Further, not only the strength when the filter substrate is dried but also the strength when wet is excellent. Therefore, the water resistance strength is sufficient, and even when the filter base material is impregnated with an impregnating liquid containing an adsorbent and the adsorbent is supported on the filter base material, it is difficult to deform due to its own weight. In addition, since the strength is greatly improved by externally applying β-type sepiolite, the filter base is made thinner and lighter, or the density is lowered to increase the amount of adsorbent loaded and the amount of liquid retained. Even if it is done, sufficient strength is obtained.

For the above reasons, it is most preferable that the raw material slurry used for the production of the nonwoven fabric in the step (i) does not contain β-type sepiolite.
In addition, when it is necessary to add and add β-type sepiolite to the raw slurry, in order to make the aggregate of β-type sepiolite as small as possible and uniformly distribute the β-type sepiolite in the inorganic fiber sheet, It is preferable to add β-type sepiolite to the raw material slurry by the method. That is, first, β-type sepiolite is dispersed with a polyacrylic acid-based anionic dispersant, and then a fine sepiolite aggregate is prepared using an anionic polymer flocculant, and this is mixed with the raw slurry. It is preferable to do.

The raw material slurry used for the production of the nonwoven fabric may contain an inorganic binder component other than β-type sepiolite, such as colloidal silica, water glass, calcium silicate, silica sol, alumina sol, and alkoxysilane, if necessary. More than seeds can be used. However, these inorganic binders may fall off when an external force such as rubbing or bending is applied, resulting in poor handling properties. Therefore, the content of the inorganic binder component other than β-type sepiolite is preferably 5% by mass or less as the content of the inorganic fiber sheet after production.
The inorganic binder component other than β-type sepiolite is added to the raw material slurry for producing the nonwoven fabric, and sprayed with a liquid containing the inorganic binder component on the nonwoven fabric obtained in the step (i). You may make it adhere (external addition application | coating) by methods, such as application | coating, impregnation application | coating, bar application | coating, roll application | coating, and blade application | coating. The nonwoven fabric to be externally applied may be a dried nonwoven fabric after drying or a wet web before drying.

The raw material slurry used for the production of the nonwoven fabric can further contain the following auxiliary agent, additive, filler and the like. Moreover, you may include metal fiber, such as inorganic fibers, such as a carbon fiber, and an alumina fiber, as needed.
Examples of the auxiliary agent include epoxy-based, isocyanate-based, carbodiimide-based, oxazoline-based crosslinking agents, and silane coupling agents having functional groups such as amino groups, epoxy groups, methacryloxy groups, acryloxy groups, and mercaptro groups. One or more can be used. The content of the silane coupling agent is preferably 10 parts by mass or less with respect to 100 parts by mass of the organic binder component.

Additives include antioxidants, light stabilizers, UV absorbers, thickeners, nucleating agents, neutralizing agents, lubricants, antiblocking agents, dispersants, fluidity improvers, mold release agents, flame retardants, Examples include foaming agents, colorants, wetting agents, adhesives, yield improvers, paper strength improvers, filter media, pH adjusters, antifoaming agents, preservatives, pitch control agents, etc. it can. As for content of an additive, 5 mass% or less is preferable with respect to the inorganic fiber sheet after manufacture.
Examples of the filler include calcium silicate, calcium carbonate, kaolin, talc, plastic pigment, glass beads, hollow glass beads, and shirasu balloon. One or more kinds can be used.

The wet papermaking in the step (i) can be performed by a method in which a raw material slurry containing the above-described components and water (medium) is prepared, and the raw material slurry is made with a known paper machine. Examples of the paper machine include a circular paper machine, an inclined paper machine, a long paper machine, and a short paper machine, and multilayer paper making may be performed by combining the same or different types of these paper machines.
There are no particular restrictions on the method of dehydration and drying after papermaking, and 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 about 100 ° C. to 180 ° C. as described above.
In step (i), the process may be transferred to step (ii) without drying. That is, a slurry containing β-type sepiolite may be adhered to the wet web.

(Step (ii))
In step (ii), a slurry containing β-type sepiolite is attached to the nonwoven fabric obtained in step (i) and externally applied. As described above, the nonwoven fabric to be externally applied may be a nonwoven fabric after drying or a wet web before drying. Thus, when externally applied, it is not necessary to use a flocculant as in the case of internal addition. Therefore, β-type sepiolite can be uniformly present in the inorganic fiber sheet, and the strength of the filter base material obtained by firing the inorganic fiber sheet is excellent. Moreover, since the adsorbent can be supported uniformly, the filter performance is also excellent.
By externally applying β-type sepiolite in this way, the strength is greatly improved, so the filter substrate is made thinner and lighter, or the density is lowered to reduce the amount of adsorbent supported and the amount of liquid retained. Even when it is increased, sufficient strength can be obtained.

  As a specific method of external addition coating, spray coating, curtain coating, roll coating, bar coating, blade coating or the like can be employed. After the external application, dehydration and drying are performed using the above-described dryer. The drying temperature is not particularly limited, but is usually about 100 ° C. to 180 ° C. as described above.

The amount of β-type sepiolite to be externally applied in step (ii) is 5 to 40% by mass, and more preferably 8 to 30% by mass with respect to the inorganic fiber sheet after production. If the content of the inorganic fiber is less than the lower limit of the above range, the function as an inorganic binder component does not appear and sufficient strength cannot be obtained. On the other hand, if the upper limit of the above range is exceeded, the inorganic fiber sheet is brittle and easily broken, and is inferior in corrugating suitability, and the inconveniences such as the corrugated wave apex being easily broken are likely to occur.
The β-type sepiolite per unit area of the nonwoven fabric is preferably ^{1~16g / m 2, 2~12g / m} 2 is more preferable.

As β-type sepiolite, it is possible to obtain an inorganic fiber sheet that can produce a filter substrate with sufficient strength (excellent in strength development), and because it is well fixed on inorganic fibers (excellent in covering properties), oil absorption The amount is preferably 80% by mass or more, more preferably 150% by mass or more, and further preferably 180% by mass or more. Although there is no restriction | limiting in particular in the upper limit of oil absorption amount, Usually, it is 300 mass% or less. Since β-type sepiolite having an oil absorption amount equal to or higher than the above lower limit value is well fixed to inorganic fibers, the filter substrate obtained by firing the obtained inorganic fiber sheet does not have an excessively large opening, and adsorbent It can be fully supported. Therefore, the gap between the fibers is left as a through hole, and the raw gas is prevented from passing through, and a filter with excellent performance can be manufactured. Moreover, since the formation of through holes is suppressed, the strength of the filter base material obtained by firing is also excellent.
The oil absorption is a value measured according to JIS K-5101-13-2.

In addition, the β-type sepiolite preferably has a total content of SiO ₂ and MgO of 75% by mass or more with respect to the β-type sepiolite, and more preferably 80% by mass or more from the viewpoint of strength development. Although there is no restriction | limiting in particular in the upper limit of this total content, Usually, it is 90 mass% or less. When the total content of SiO ₂ and MgO is not less than the above lower limit value, there is no influence of impurities and excellent strength development. Examples of components other than SiO ₂ and MgO contained in β-type sepiolite include CaO.

A dispersant, a liquid retention agent, a viscosity modifier, a pH adjuster, an organic binder component, an inorganic binder component, a filler, and the like may be added to the slurry containing β-type sepiolite to be externally applied as necessary.
As the organic binder component and the inorganic binder component, inorganic binder components other than the organic binder component and β-type sepiolite exemplified in the step (i) can be used. As the filler, the filler exemplified in the step (i) can be used.
By using a filler in the slurry containing β-type sepiolite to be externally applied, inorganic fibers can be sufficiently coated. Therefore, it can prevent that the space | gap between fibers remains as a hole and an untreated gas becomes easy to pass through.
Further, instead of adding each of these components to a slurry containing β-type sepiolite, a slurry containing at least one of these components (optional component slurry) may be separately prepared and applied externally. Good. The optional component slurry may be externally applied before, after or simultaneously with the external addition of the slurry containing β-type sepiolite. Further, the non-woven fabric that is the target of the external application of the optional component slurry may be a dry non-woven fabric after drying or a wet web before drying.

  In addition, when using an organic binder component, an inorganic binder component, a filler, etc. here, the usage amount is set so that each content in the finally obtained inorganic fiber sheet is within the above-described range. It is preferable to adjust.

The basis weight of the inorganic fiber sheet produced by the production method of the present invention is not particularly limited, and can be, for example, 10 to 100 g / m ^2. As described above, according to the production method of the present invention, the basis weight An inorganic fiber sheet capable of producing a filter substrate having sufficient strength even when the amount is reduced is obtained. Therefore, when a filter substrate applications, the basis weight of the inorganic fiber sheet is preferably ^{20~60g / m 2, 15~50g / m} 2 is more preferable. If the basis weight is not less than the lower limit of the above range, the strength of the inorganic fiber sheet and the filter substrate obtained from the inorganic fiber sheet is sufficiently obtained, and if the basis weight is not more than the upper limit of the above range, the thickness is suppressed and the pressure is reduced. Loss can be suppressed.
In addition, the inorganic fiber sheet preferably has a liquid retention amount of 100 g / m ² or more, preferably 130 g / m ² or more after firing in air at 500 ° C. for 2 hours. Although there is no restriction | limiting in particular in the upper limit of liquid retention amount, For example, it is 250 g / m < ² > or less. With such a liquid retention amount, the adsorbent can be sufficiently supported when the filter base material is impregnated with the impregnating liquid containing the adsorbent.
The liquid retention amount is a value measured by the method described in Examples described later.

The density of the inorganic fiber sheet produced by the production method of the present invention is not particularly limited. However, according to the production method of the present invention, sufficient strength can be obtained even if the density is reduced. ˜0.4 g / cm ³ is preferred. If the density is equal to or higher than the lower limit of the above range, the voids do not become too large, and both the liquid retention rate, the adsorbent loading amount, and the strength can be achieved. If the density is less than or equal to the upper limit of the above range, sufficient voids are formed, the liquid retention amount is excellent, and a high-performance filter is obtained.
The thickness of the inorganic fiber sheet produced by the production method of the present invention is not particularly limited. However, according to the production method of the present invention, sufficient strength can be obtained even when the thickness is reduced. Is preferable, and 100 to 200 μm is more preferable. If thickness is more than the lower limit of the said range, intensity | strength and liquid retention can be made compatible. If the liquid retention amount is not more than the upper limit of the above range, the pressure loss does not become too large, and a high-performance filter can be obtained.

The inorganic fiber sheet produced by the production method of the present invention preferably has a tensile strength along the flow direction of wet papermaking of 300 N / m or more after firing at 500 ° C. for 2 hours in air, The above is more preferable. When the tensile strength is not less than the lower limit of the above range, sufficient handling properties can be obtained in a filter substrate such as a honeycomb obtained by firing an inorganic fiber sheet. Although there is no restriction | limiting in particular in the upper limit of this tensile strength, Usually, it is 4000 N / m or less.
In addition, the inorganic fiber sheet preferably has a wet tensile strength in the flow direction of 100 N / m or more, more preferably 150 N / m or more after firing in air at 500 ° C. for 2 hours. When the wet tensile strength is not less than the lower limit of the above range, the water resistance strength is sufficient, and when the filter substrate is impregnated with the slurry containing the adsorbent in order to support the adsorbent on the filter substrate, Difficult to deform due to its own weight. Moreover, it is hard to deform | transform with the shrinkage force at the time of drying after impregnation. As will be described later, re-baking may be performed as necessary after impregnation, but if the wet tensile strength is equal to or higher than the lower limit of the above range, it is difficult to be deformed by the shrinkage force at the time of re-baking. Although there is no restriction | limiting in particular in the upper limit of this wet tensile strength, Usually, it is 1000 N / m or less.
The tensile strength and the wet tensile strength are values measured by the methods described in Examples described later.

The air permeability of the inorganic fiber sheet produced by the production method of the present invention is preferably in the range of 0.1 to 250 ml / cm ² / sec. When the aeration is not less than the lower limit of the above range, the liquid retention amount is excellent, and when it is not more than the lower limit of the above range, the strength of the filter substrate obtained by firing the inorganic fiber sheet is sufficient. In addition, it is possible to manufacture a filter with excellent performance by suppressing the gap between the fibers as a through hole and passing through untreated gas. When the adsorbent supported on the filter base is small particles such as zeolite and catalyst, the air permeability is 0.1 to 50 ml / cm ² / sec. It is preferable because it can be supported. The air permeability can be controlled by adjusting the diameter or the like of the inorganic fiber used for the production of the inorganic fiber sheet.
The air permeability is a value measured by a method described in Examples described later.

The inorganic fiber sheet produced by the production method of the present invention preferably has an ash content of 75% by mass or more after being baked in air at 500 ° C. for 2 hours. If the amount of ash is equal to or greater than the lower limit of the above range, the burnout of the organic component is not too large, the gap between the fibers remains as through holes, and the untreated gas is prevented from passing through, and the filter has excellent performance. Can be manufactured.
The amount of ash is a value measured by the method described in the examples described later.

The inorganic fiber sheet thus produced is obtained by externally applying β-type sepiolite, and the inorganic fiber contains at least one of glass fiber and biosoluble inorganic fiber. . Therefore, by using the inorganic fiber sheet, even when the thickness is reduced and the weight is reduced, or even when the density is reduced and the amount of adsorbent supported or the amount of liquid retained is increased, the sheet has sufficient strength and is wavy. Therefore, it is possible to produce a filter base material having good moldability, excellent corrugating suitability, and safety to the human body.
In addition, the inorganic fiber sheet can be used for various reinforcing materials including glass fiber reinforced plastic, gaskets and packing for high temperature parts, and the like.

[Fired body]
The inorganic fiber sheet produced by the production method of the present invention is corrugated to form a honeycomb molded body, and the honeycomb molded body is fired to burn off organic components such as organic binder components and organic fibers. A fired body is obtained.
The firing temperature is preferably 250 ° C. or higher. In particular, when the main component (more than 50% by mass) of the inorganic fiber is at least one of glass fiber and biosoluble rock wool, a firing temperature of about 400 to 600 ° C. is preferable, whereas the main component of the inorganic fiber When is a biosoluble ceramic fiber, a firing temperature of about 600 to 800 ° C. is preferable.

  When manufacturing a honeycomb formed body, a corrugated inorganic fiber sheet (core paper) and a non-corrugated inorganic fiber sheet are usually manufactured. Examples of the adhesive to be used include inorganic pastes such as colloidal silica, water glass, and alumina sol, and one or more of these can be used. Moreover, you may use together organic pastes, such as ethylene-vinyl alcohol, as an adhesive agent.

(Honeycomb filter)
The honeycomb filter of the present invention is obtained by supporting at least one kind of adsorbent on the fired body.
The adsorbent is preferably one or more selected from the group consisting of silica gel, zeolite, sepiolite, activated carbon, and ion exchange resin from the viewpoint of adsorptivity, and various other adsorbents can be used.
Adsorbents used as dehumidifiers include, for example, silica, zeolite, hydrophobic synthetic zeolite, natural zeolite, sepiolite, hydrotalcite, alumina, lime, gypsum, bitter 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, water-absorbing polymer, and the like.
Examples of other adsorbents include carriers capable of adsorbing alkaline compounds (potassium carbonate, sodium carbonate, sodium bicarbonate, calcium hydroxide, calcium carbonate, etc.), such as activated carbon, silica, alumina, allophane, sepiolite, Solid adsorbents supported on cordierite, other clay minerals, and the like; sodium hydroxide, potassium hydroxide, potassium carbonate, calcium hydroxide, ion exchange resin, deodorant and the like. A porous adsorbent in which a catalyst such as titanium is supported on the pores can also be used.

Examples of the adsorbent loading method include a known method of impregnating a fired body with a slurry containing an adsorbent and drying it. After drying, re-baking may be performed as necessary.
The slurry may contain one or more inorganic adhesives such as colloidal silica, water glass, and alumina sol for the purpose of improving adsorbent supportability and honeycomb filter strength.
When the main component of the inorganic fiber is a biosoluble ceramic fiber, the firing temperature when refiring is preferably 600 ° C. or higher because the sintering action of the fiber and sepiolite is obtained. In the case of the inorganic fiber sheet containing, about 400-600 degreeC is preferable.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by a following example.

In the following examples, five types of β-type sepiolite were used.
Any β-type sepiolite is in a clay state.
β-type sepiolite (1): SiO ₂ + MgO content is 85% by mass, oil absorption is 280% by mass
β-type sepiolite (2): SiO ₂ + MgO content is 80% by mass, oil absorption is 190% by mass
β-type sepiolite (3): content of SiO ₂ + MgO is 78% by mass, oil absorption is 150% by mass
β-type sepiolite (4): SiO ₂ + MgO content is 81 mass%, oil absorption is 120 mass%
β-type sepiolite (5): content of SiO ₂ + MgO is 76% by mass, oil absorption is 100% by mass)

<Example 1>
Glass fiber (1) (diameter 3.5 μm, length: 5 mm), glass fiber (2) (diameter 5 μm, length: 5 mm), softwood pulp, and PVA fiber (“VPB105”, manufactured by Kuraray) Glass fiber (1): Glass fiber (2): Softwood pulp: PVA fiber = 55: 30: 7: 8 (mass ratio) added to water and adjusted so that the total concentration of these is 0.2% by mass Thus, a raw material slurry was obtained. Next, the raw material slurry was made by wet paper making to form a randomly arranged web (wet web).
A slurry in which β-type sepiolite (1) is dispersed in water is added to the wet web so that the content of β-type sepiolite (1) in 100% by mass of the obtained inorganic fiber sheet is 25% by mass (unit area). Β-type sepiolite (1) content: 10 g / m ² ) Spray-coated and dried to obtain an inorganic fiber sheet having the basis weight, thickness and density shown in Table 1. Note that the content of β-type sepiolite is determined from the mass difference between the nonwoven fabric before and after the slurry in which β-type sepiolite is dispersed in water is adhered.
Measure the amount of ash, tensile strength in the flow direction of wet papermaking, wet tensile strength in the flow direction, air permeability, and liquid retention for the sheet after firing the obtained inorganic fiber sheet at 500 ° C. for 2 hours in the air. did. The results are shown in Table 1.
The oil absorption of β-type sepiolite is a value measured according to JIS K-5101.

Next, the obtained inorganic fiber sheet was processed into a corrugated paper having a height of 2.5 mm and a pitch of 4 mm to obtain a core paper, and silica sol was mainly applied to a flat sheet-like liner made of the inorganic fiber sheet obtained. It was bonded with an inorganic adhesive as a component and corrugated, and this was wound up to produce a cylindrical honeycomb structure.
This structure was calcined at 500 ° C. for 3 hours, impregnated in a slurry suspension composed of colloidal silica (inorganic binder component) and zeolite, and then subjected to hot air treatment at 300 ° C. for 1 hour to produce a zeolite-supported filter. .
The obtained filter was evaluated for corrugating suitability and filter manufacturability according to the following criteria. The results are shown in Table 1.

<Measurement for inorganic fiber sheet>
(Basis weight)
It measured according to JIS P8124.
(Thickness)
It measured according to JIS P8118.
(density)
It calculated | required by calculation from the said basic weight and the said thickness.

<Measurement about the sheet after firing>
(Ash content)
The measurement was performed according to JIS P8251 except that it burned at 500 ° C. for 2 hours instead of 525 ° C.
(Tensile strength in the flow direction)
After firing the inorganic fiber sheet in the air at 500 ° C. for 2 hours, measurement is performed with a Tensilon type tensile tester (made by ORIENTEC) in accordance with JIS P 8113 along the flow direction in the wet papermaking method. It was.
(Wet tensile strength)
The inorganic fiber sheet was fired in air at 500 ° C. for 2 hours, then immersed in pure water at 30 ° C. for 1 hour, then taken out and suspended by its own weight until the dropping of water droplets stopped. Then, along the flow direction in the wet papermaking method, measurement was performed by a Tensilon type tensile tester (manufactured by ORIENTEC) by a method according to JIS P8113.
(Air permeability)
The measurement was carried out according to method A (Fragile type method) according to JIS L1096.
(Liquid retention amount)
The inorganic fiber sheet (100 mm × 100 mm) was calcined at 500 ° C. for 2 hours in the air according to JIS L1913, and the dry mass A (g / m ² ) was measured. Thereafter, the inorganic fiber sheet was dipped in pure water for 1 minute, then taken out, and the mass B (g / m ² ) after being suspended until the drop of water drops by its own weight was measured. A value obtained by subtracting mass A from mass B was defined as a mass increase amount (liquid retention amount) C with respect to the dry mass of the fired sheet. In addition, the liquid retention amount was converted per 1 m ² and listed in the table.

<Filter performance evaluation>
(Appropriate for corrugating)
○: Wavy shape is good and the wave shape is good.
(Triangle | delta): Wavy patterning is a little bad and the shape of a wave is a little crumbled.
X: Wavy patterning is poor, and there are cracks and tears at the top of the wave.

(Filter productivity (hardness))
○: The filter after supporting zeolite is hard and does not deform at all.
(Triangle | delta): The filter after zeolite carrying hardly deform | transforms.
X: The filter after carrying zeolite is deformed.

<Example 2>
In the same manner as in Example 1, a wet web having a random arrangement was formed. However, in Example 2, an acrylic emulsion was spray-coated on the wet web, and an acrylic resin was adhered to the content shown in Table 1 (adhesion amount: 1 g / m ² ) and dried.
Subsequently, the dry web was made into a slurry obtained by dispersing β-type sepiolite (2) in water instead of the β-type sepiolite (1) used in Example 1, and β-type sepiolite in 100% by mass of the obtained inorganic fiber sheet. Impregnation and drying were performed so that the content of (2) was the value shown in Table 1, and an inorganic fiber sheet having the basis weight, thickness, and density shown in Table 1 was obtained.
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

<Example 3>
An inorganic fiber sheet was obtained in the same manner as in Example 1 except that the slurry of β-type sepiolite (3) was used instead of the slurry of β-type sepiolite (1).
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

<Example 4>
An inorganic fiber sheet was obtained in the same manner as in Example 1 except that the slurry of β-type sepiolite (4) was used instead of the slurry of β-type sepiolite (1).
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

<Example 5>
An inorganic fiber sheet was obtained in the same manner as in Example 1 except that a slurry of β-type sepiolite (5) was used instead of β-type sepiolite (1).
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

<Example 6>
In the following manner, an inorganic fiber sheet containing β-type sepiolite was produced by using both internal and external additives.
First, the same raw material slurry as in Example 1 was obtained.
Separately, 0.5 parts by mass of a dispersant (“Aron T-50”, manufactured by Toagosei Co., Ltd.) and water are added to 100 parts by mass of the β-type sepiolite (1), and the β-type sepiolite (1) is dispersed in water. A prepared slurry was prepared. The raw material slurry, the slurry in which the β-type sepiolite (1) is dispersed in water, and an anionic polymer flocculant (“HH-251” manufactured by Kurita Kogyo Co., Ltd.) are mixed and contain 0.2% concentration of sepiolite. The raw material slurry (A) in Example 6 was obtained.
Next, the raw slurry (A) was made by wet paper making to form a randomly arranged web (wet web).
Inorganic fiber sheet 100 obtained by spraying 6.5 g / m ² per unit area of a slurry obtained by dispersing the same β-type sepiolite (1) spray-coated in Example 1 in water onto a wet web and drying. The total content of β-type sepiolite (1) in mass% was 25 mass%. In this way, an inorganic fiber sheet having a basis weight, thickness, and density having the composition shown in Table 2 was obtained.
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 2.

<Example 7>
Except having changed the usage-amount of each component so that the inorganic fiber sheet of content of each component shown in Table 2 could be obtained (content of (beta) -sepiolite: 3 g / m < ² >), it carried out similarly to Example 1. An inorganic fiber sheet was obtained.
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 2.

<Example 8>
Except having changed the usage-amount of each component so that the inorganic fiber sheet of content of each component shown in Table 2 could be obtained (content of (beta) -sepiolite: 15 g / m < ² >), it carried out similarly to Example 1. An inorganic fiber sheet was obtained.
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 2.

<Example 9>
As shown in Table 2, instead of glass fiber (1), inorganic fiber was used in the same manner as in Example 1 except that biosoluble ceramic fiber (“Super Wool Plus” manufactured by Nippon Thermal Ceramics Co., Ltd.) was used. A sheet was obtained.
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 2.

<Comparative Example 1>
Sepiolite was not applied externally and only internal addition was performed to obtain an inorganic fiber sheet.
Specifically, glass fiber (1): glass fiber (2): conifer pulp: PVA fiber = 55: 30: 7: 8 (mass ratio) was added to water to obtain a slurry. To the slurry, a slurry in which β-type sepiolite (1) is dispersed in water and the same anionic polymer flocculant as used in Example 6 are added, so that the total concentration thereof is 0.2% by mass. The raw material slurry (B) containing sepiolite was obtained. At this time, each fiber, β-type sepiolite (1), and anionic polymer flocculant were mixed so that the mass ratio shown in Table 3 was obtained in the inorganic fiber sheet obtained after the papermaking and drying steps.
Subsequently, the raw slurry (B) was made by wet paper making to form a randomly arranged web (wet web) and dried to obtain an inorganic fiber sheet.
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 3.

<Comparative example 2>
An inorganic fiber sheet was obtained in the same manner as in Comparative Example 1 except that biosoluble ceramic fibers were used in place of the glass fibers (1).
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 3.

<Comparative Example 3>
An inorganic fiber sheet was obtained in the same manner as in Comparative Example 2 except that a cationic polymer flocculant (sulfuric acid band) was used instead of the anionic polymer flocculant.
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 3.

<Comparative Examples 4 and 5>
An inorganic fiber sheet was obtained in the same manner as in Example 1 except that the amount of each component used was changed so that an inorganic fiber sheet having the content of each component shown in Table 3 was obtained.
Thereafter, measurement and evaluation were performed in the same manner as in Example 1. The results are shown in Table 3.

<Discussion>
-From the comparison between Example 1 and Comparative Examples 1 to 3, even if the content of β-type sepiolite is the same, the tensile strength and the wet tensile strength of the fired sheet are excellent by being attached by external application. I understood it. It was also found that a filter having hardness can be obtained by applying the external additive, and the filter can be manufactured with excellent productivity.
The wet tensile strength of Comparative Example 2 was not measurable because the strength was too low.
From the results of Comparative Example 4 and Comparative Example 5, even in the case of external coating, if the amount of β-type sepiolite is small, the filter is insufficiently hard, whereas if the amount of β-type sepiolite is large, it is suitable for corrugating. It was found that the wave shape was poor, and the wave peak was cracked and split.
In addition, from the results of Examples 1 to 5, there is a correlation between the oil absorption amount of β-type sepiolite and the tensile strength and wet tensile strength of the fired sheet, and the more β-type sepiolite is used, the higher the oil absorption amount. It was found that the tensile strength and wet tensile strength of the fired sheet were improved.

Claims (8)

A method for producing an inorganic fiber sheet containing 30 to 95% by mass of one or more inorganic fibers selected from the group consisting of glass fibers and biosoluble inorganic fibers, and containing 5 to 40% by mass of β-type sepiolite,
A step (i) of producing a nonwoven fabric by wet papermaking the raw material slurry containing the inorganic fiber;
And a step (ii) of attaching a slurry containing β-type sepiolite to the nonwoven fabric.   The said raw material slurry is a manufacturing method of the inorganic fiber sheet | seat of Claim 1 containing a non-heat-fusionable organic fiber and an organic binder component.   The said raw material slurry is a manufacturing method of the inorganic fiber sheet of Claim 1 or 2 which does not contain sepiolite.   The manufacturing method of the inorganic fiber sheet as described in any one of Claims 1-3 whose oil absorption amount of the said (beta) -type sepiolite is 150 mass% or more.   The inorganic fiber sheet has a tensile strength along the flow direction of the wet papermaking of 300 N / m or more after firing for 2 hours at 500 ° C. in the air, and a wet tensile strength of 100 N / m or more in the flow direction. The manufacturing method of the inorganic fiber sheet as described in any one of Claims 1-4 which is. The inorganic fiber sheet has a basis weight of 15 to 50 g / m ² , and a liquid retention amount after baking at 500 ° C. for 2 hours in air is 100 g / m ² or more. The manufacturing method of the inorganic fiber sheet as described in any one of Claims.   A fired body obtained by firing a honeycomb formed body formed using the inorganic fiber sheet produced by the production method according to any one of claims 1 to 6.   A honeycomb filter in which the fired body according to claim 7 carries one or more adsorbents selected from the group consisting of silica gel, zeolite, sepiolite, activated carbon, and ion exchange resin.