JP7619272B2 - Glass fiber sheet for filters - Google Patents

Description

The present invention relates to a glass fiber sheet for filters, and more specifically, to a glass fiber sheet for filters that is used as a filter by carrying a functional material inside.

Ceramic fibers have characteristics such as high heat resistance, high insulation, and non-flammability, so inorganic fiber sheets using ceramic fibers are widely used. For example, such inorganic fiber sheets are used as insulation materials, heat-resistant cushion materials, heat-resistant shield materials, separators, and carriers for functional materials such as catalysts. In addition, honeycomb molded bodies obtained by corrugating inorganic fiber sheets are used as honeycomb filters for heat exchange that support functional materials such as adsorbents, or honeycomb filters for gas adsorption.

For example, Patent Documents 1 and 2 describe a method for manufacturing an inorganic fiber sheet, in which a raw material slurry containing ceramic fibers, an organic binder, and bark is prepared, and the raw material slurry is paper-made into an inorganic fiber sheet. Bark here is a type of naturally occurring clay mineral, and is hydrated magnesium silicate. Bark is used as an inorganic binder. Patent Document 2 also describes a method for corrugating an inorganic fiber sheet to form a honeycomb molded body, which is then fired, and an adsorbent or the like is supported on the resulting fired body to form a gas adsorption element (honeycomb filter).

However, ceramic fibers are classified as Category 2 (suspected of being carcinogenic) in the EU (European Union) Directive 97/69EC on artificial amorphous fibers. For this reason, deceramization is being promoted from the perspective of safety for the human body, and replacement with glass fibers or biosoluble fibers, for example, is being considered. The fiber diameter of glass fibers used in deceramization is preferably 3 μm or more.

In light of these circumstances, for example, Patent Document 3 discloses a method of obtaining an inorganic fiber sheet by papermaking a slurry containing mainly biosoluble ceramic fibers, glass fibers, organic fibers, a cationic inorganic binder, and sepiolite, a type of mountain bark. However, there are problems with biosoluble ceramic fibers in that it is difficult to obtain sufficient strength, and it is difficult to make them lightweight and thin.

On the other hand, glass fiber, an alternative to ceramic fiber, has a large fiber diameter and length, so inorganic fiber sheets made from it are hard and difficult to conform to shapes. This makes it difficult to form corrugations, and the fibers tend to break at the crests of the waves, resulting in uneven cell shapes, which creates problems when processing the corrugations.

Patent Document 4 proposes that corrugation processability can be improved by using glass fibers as the main component in combination with organic fibers with an aspect ratio of 300 to 2000. However, it was found that the bonds between the fibers in the inorganic fiber sheet are weak, and that increasing the amount of binder components to improve this tends to impair corrugation processability.

Japanese Unexamined Patent Publication No. 60-33250 Patent No. 2925127 Patent No. 5558518 International Publication No. 2018/079529

The objective of the present invention is to provide a glass fiber sheet for filters which has excellent shape conformability (hereinafter simply referred to as shape conformability) during corrugation processing even when the strength of the inorganic fiber sheet is increased, which prevents powder falling (hereinafter simply referred to as powder falling) during corrugation processing, and which has sufficient functional material support even after the functional material is supported.

The present invention has the following configuration.
(1) A glass fiber sheet for a filter, which contains glass fiber as a main component, further contains wood pulp and a binder, and is formed by wet papermaking,
The glass fiber sheet for a filter functions as a filter by carrying a functional material therein,
51 to 85 mass % of the total fiber content of the glass fiber sheet for filters is the glass fiber,
10 to 49 mass % of the total fiber content of the glass fiber sheet for filters is the wood pulp,
The content of the binder is 1% by mass or more based on the total mass of the glass fiber sheet for filters,
The glass fiber sheet for filters has a basis weight of 15 to 55 g/ ^m2 .
(2) The glass fiber sheet for filters according to (1), wherein the wood pulp has a beating degree of 300 to 750 CSF.
(3) The glass fiber sheet for filters according to (1) or (2), wherein the weighted average fiber diameter of the glass fibers is 4 to 10 μm.
(4) The glass fiber sheet for filters according to any one of (1) to (3), wherein the content of the binder is 25 mass % or less based on the total mass of the glass fiber sheet for filters.
(5) The glass fiber sheet for filters according to any one of (1) to (4), wherein the binder contains polyvinyl alcohol.

According to the present invention, it is possible to provide a fiber sheet for filters that has excellent shape conformability even when the strength of the inorganic fiber sheet is increased. In addition, according to the present invention, it is possible to provide a glass fiber sheet for filters that prevents powder falling during corrugation processing and has sufficient functional material support even after the functional material is supported.

<Glass fiber sheet for filters>
First, an example of the configuration of a glass fiber sheet for filters (hereinafter, simply referred to as a glass fiber sheet) according to one embodiment of the present invention will be described. The glass fiber sheet for filters of this embodiment contains glass fiber as a main component, and wood pulp and a binder as subcomponents, with 51 to 85% by mass of the total fiber content of the glass fiber sheet for filters being glass fiber, and 10 to 49% by mass of the total fiber content being wood pulp. The binder content is 1% by mass or more based on the total mass of the glass fiber sheet for filters.

The glass fiber sheet of this embodiment has a basis weight of 15 to 55 g/ ^m2 . When the basis weight is equal to or more than the lower limit of the above range, the strength of the glass fiber sheet and the glass fiber sheet molded article obtained from the glass fiber sheet can be sufficiently obtained, and when the basis weight is equal to or less than the upper limit of the above range, the thickness can be suppressed and corrugation processing can be easily performed.

(Glass fiber)
The type of glass fiber is not particularly limited, and in addition to E-glass, which is widely produced, high-strength S-glass, C-glass, which has excellent acid resistance, etc. can be used. From the viewpoint of cost, it is preferable to use inexpensive E-glass. In addition, the glass fiber may be used alone or in combination of two or more types.

There are no particular restrictions on the fiber length of the glass fibers, but the length-weighted average fiber length is preferably 1 to 15 mm, and more preferably 1 to 10 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 glass fiber sheet tends to be superior, and if it is equal to or less than the upper limit of the above range, the texture of the resulting glass fiber sheet tends to be superior. The length-weighted average fiber length is calculated by measuring the fiber lengths of 100 fibers by microscopic observation.

The weighted average fiber diameter of the glass fiber is preferably 3 μm or more, and more preferably 4 μm or more. If the weighted average fiber diameter is equal to or greater than the lower limit of the above range, it does not fall under the category of "WHO respirable fiber" and is safe for the human body. This "WHO respirable fiber" is defined by the World Health Organization (WHO) as a fibrous material that is inhaled into the body by breathing and reaches the lungs, and has a length of more than 5 μm, a diameter of less than 3 μm, and an aspect ratio of more than 3.

The weighted average fiber diameter of the glass fibers is preferably 10 μm or less, and more preferably 7 μm or less. If it is equal to or less than the upper limit of the above range, the strength of the glass fiber sheet and the strength of the filter substrate obtained by firing the glass fiber sheet are both improved. The weighted average fiber diameter is calculated by measuring the fiber diameters of 100 fibers by microscopic observation.

51 to 85% by mass of the total fiber content of the glass fiber sheet is glass fiber. The glass fiber content is preferably 55% by mass or more, and more preferably 58% by mass or more, based on the total mass of the fibers contained in the glass fiber sheet. The glass fiber content is preferably 80% by mass or less, and more preferably 68% by mass or less, based on the total mass of the fibers contained in the glass fiber sheet.

(Wood pulp)
As the wood pulp, coniferous pulp and hardwood pulp can be used. Examples of the wood pulp include NBKP, LBKP, NBSP, LBSP, and GP, and the pulping method is not particularly limited. Among them, NBKP is preferable because of its excellent strength.

The wood pulp content in the glass fiber sheet is 10 to 49% by mass of the total fiber content. The wood pulp content is preferably 20% by mass or more, and more preferably 32% by mass or more, based on the total mass of the fiber contained in the glass fiber sheet. The wood pulp content is preferably 45% by mass or less, and more preferably 42% by mass or less, based on the total mass of the fiber contained in the glass fiber sheet.

Wood pulp has superior flexibility compared to other organic fibers, so even if the amount of binder is increased, problems during corrugation processing (e.g., shape conformity) can be solved. The degree of beating of wood pulp is preferably 300 to 750 CSF, and more preferably 450 to 750 CSF. Beating is performed using a beater or the like, and if the degree of beating is within the above range, the flexibility of the glass fiber sheet can be increased due to its softness, and the strength of the glass fiber sheet can be increased by entangling the fibrillated parts of the pulp with the glass fibers. Furthermore, the impregnated functional material, etc. adheres to the fibrillated parts of the pulp present inside the glass fiber sheet, so the functional material, etc. can be efficiently supported.

(Organic Fiber)
In the glass fiber sheet for filters of this embodiment, wood pulp is used as a secondary component, but other organic fibers may be used in combination therewith within a range that does not impair the effect of using the wood pulp.

Examples of organic fibers include natural fibers and synthetic fibers. Examples of natural fibers include natural fibers such as cotton, wool, silk, and hemp. There are no particular limitations on the synthetic fibers, so long as they do not melt when heated during the manufacturing process of the glass fiber sheet, and they can be appropriately selected depending on the drying temperature set in the manufacturing process of the glass fiber sheet. Examples of synthetic fibers include, for example, polyethylene fibers, polypropylene fibers, polybutene fibers, nylon fibers, rayon fibers, cupra fibers, acetate fibers, polyvinyl chloride fibers, acrylic fibers, polyester fibers, polyurethane fibers, polyparaphenylene benzobisoxazole fibers, polyamideimide fibers, polyimide fibers, polyarylate fibers, polyetherimide fibers, vinylon fibers, polycarbonate fibers, ethylene-vinyl acetate fibers, ethylene vinyl alcohol fibers, polyphenylene sulfide fibers, polyethylene terephthalate fibers, polybutylene terephthalate fibers, polyethylene naphthalate fibers, and chemical fibers such as aramid fibers. Any one or more of these may be used in combination.

The length-weighted average fiber length of the organic fibers that can be used in combination is preferably 1 to 15 mm, and more preferably 1 to 10 mm. If the length-weighted average fiber length is equal to or greater than the lower limit of the above range, the yield during papermaking tends to improve, while if it is equal to or less than the upper limit of the above range, the organic fibers tend to be less likely to become entangled and form lumps. The length-weighted average fiber length is calculated by measuring the fiber lengths of 100 fibers by observation under a microscope.

The weighted average fiber diameter of the organic fiber that can be used in combination is not particularly limited, but is preferably 3 times or less, more preferably 2 times or less, the weighted average fiber diameter of the glass fiber. When the weighted average fiber diameter of the organic fiber is 3 times or less than the weighted average fiber diameter of the glass fiber, the effect of reducing the rigidity of the glass fiber sheet and the effect of improving the folding strength by the organic fiber tend to be improved. In particular, since the weighted average fiber diameter of the glass fiber is preferably 3 to 10 μm, the weighted average fiber diameter of the organic fiber is preferably 30 μm or less, more preferably 20 μm or less. There is no particular limit to the lower limit of the weighted average fiber diameter of the organic fiber, but it is preferably 1 μm or more, more preferably 3 μm or more. It is preferable because organic fibers having a weighted average fiber diameter of the above lower limit or more are relatively easy to obtain. The weighted average fiber diameter of the fiber diameter is calculated by measuring the fiber diameter of 100 fibers by microscopic observation. When the cross-sectional shape of the organic fiber is flat, the short diameter and long diameter are measured to calculate the cross-sectional area, and the diameter of a circle equivalent to the cross-sectional area is defined as the fiber diameter.

(binder)
As the binder, an organic binder component or an inorganic binder component can be used. The content of the binder is 1 mass% or more based on the total mass of the glass fiber sheet for filters. The content of the binder is preferably the content of the binder added in the manufacturing process of the glass fiber sheet for filters.

The organic binder component is a component that bonds fibers together. Examples of organic binder components include thermoplastic resins that melt at least in part when heated during the production of the glass fiber sheet, and can be appropriately selected depending on the drying temperature during the production of the glass fiber sheet. There are no limitations on the form of the organic binder component, and it may be any of fibrous, particulate, emulsion, liquid, etc.

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

The organic binder component may be a composite fiber in which two or more materials with different melting points are combined, and the lower melting point part 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 sheath made of polyethylene or the like is formed around a high-melting core made of polyethylene terephthalate, polypropylene, or the like.

As the organic binder component, a thermosetting resin that hardens when heated during the manufacturing process of the glass fiber sheet to bond the fibers together can also be used. Examples of thermosetting resins include phenolic resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, polyurethane resin, and thermosetting polyimide resin. One or more types of thermosetting resins can be used.

Among them, it is preferable to use polyvinyl alcohol (PVA fiber, etc.) as the organic binder component because of its excellent adhesive strength. In addition, when improved water resistance is required for the glass fiber sheet, it is also preferable to use acrylic resin emulsion, etc. The use of these organic binder components is preferable because it improves the strength of the glass fiber sheet and suppresses powder fall of the resulting glass fiber sheet molding.

The content of the organic binder component in the glass fiber sheet is 1% by mass or more, preferably 1 to 25% by mass, and more preferably 3 to 20% by mass, based on the total mass of the glass fiber sheet. The content of the organic binder component is preferably the content of the binder added in the manufacturing process of the glass fiber sheet for filters. When the content of the organic binder component is equal to or more than the lower limit of the above range, the fibers can be sufficiently bonded together. When the content of the organic binder component is equal to or less than the upper limit of the above range, when the glass fiber sheet is fired to form a filter substrate, the amount of the organic binder component that is burned off during firing is small, and the voids between the fibers that are formed as a result of such burning off can be reduced, which is preferable.

When polyvinyl alcohol is used as the organic binder component, the content of polyvinyl alcohol relative to the total mass of the organic binder component is preferably 20% by mass or more, and preferably 40% by mass or more. The content of polyvinyl alcohol relative to the total mass of the organic binder component may be 100% by mass. When an acrylic resin emulsion is used as the organic binder component, the content of acrylic resin (solid content) relative to the total mass of the organic binder component is preferably 5 to 70% by mass.

The inorganic binder component is not particularly limited, but examples thereof include colloidal silica, water glass, calcium silicate, silica sol, alumina sol, sepiolite, and alkoxysilane. One or more of these can be used as the inorganic binder component. However, these inorganic binders may fall off when subjected to external forces such as rubbing and bending, and may have poor handleability. Therefore, the content of the inorganic binder component is preferably 10% by mass or less, and more preferably 7% by mass or less, based on the total mass of the glass fiber sheet.

(Other ingredients)
The glass fiber sheet of the present embodiment may contain, in addition to the glass fiber and wood pulp that are the main fibers described above, and a binder, one or more inorganic fibers other than the glass fiber, and one or more optional components that are added when the glass fiber sheet is produced by wet papermaking, within a range that does not impair the effects of the present invention.

There are no particular limitations on the inorganic fibers other than glass fibers, but considering safety to the human body, it is preferable for them to be biosoluble inorganic fibers.

In this specification, biosoluble inorganic fibers are fibers that do not fall under the category of "WHO respirable fibers" as described above, or fibers that satisfy one of the following four conditions (1) to (4) according to the NotaQ "Biosoluble Fiber Judgment Criteria" of EU Directive 97/69/EC. Biosoluble inorganic fibers include biosoluble ceramics, biosoluble rock wool, etc.

The four conditions are as follows:
(1) In short-term inhalation exposure animal experiments, the half-life of fibers longer than 20 μm is less than 10 days.
(2) In short-term intratracheal instillation animal experiments, the half-life of fibers longer than 20 μm is less than 40 days;
(3) No significant carcinogenicity in animal experiments using intraperitoneal administration.
(4) In long-term inhalation exposure animal experiments, there have been no pathological findings or tumor formation associated with carcinogenicity (however, the composition contains more than 18 mass% alkali and alkaline earth oxides (Na ₂ O, K ₂ O, CaO, MgO, BaO)).

Biosoluble inorganic fibers usually contain non-fibrous "shot" due to their manufacturing process, but if biosoluble inorganic fibers with a high shot content are used, problems such as holes and powder falling off may occur in the resulting glass fiber sheet. For this reason, it is preferable to use biosoluble inorganic fibers with a shot content of 20 mass% or less. Furthermore, biosoluble inorganic fibers may be used alone or in combination of two or more types.

In addition, from the viewpoint of safety for the human body, it is preferable that the glass fiber sheet of this embodiment does not contain ceramic fibers classified as category 2 (suspected of being carcinogenic) in EU Directive 97/69EC. In addition, the proportion of inorganic fibers other than glass fibers in the glass fiber sheet is preferably 45 mass % or less, and more preferably 30 mass % or less, based on the total mass of the glass fiber sheet.

Glass fiber sheets are formed by wet papermaking, but there are no particular restrictions on the optional components added during this process. Examples of optional components include auxiliaries, additives, and fillers.

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

Additives include antioxidants, light stabilizers, UV absorbers, thickeners, nucleating agents, neutralizing agents, lubricants, antiblocking agents, dispersants, flow improvers, release agents, flame retardants, foaming agents, colorants, wetting agents, viscosifiers, retention improvers, paper strength improvers, drainage agents, pH adjusters, defoamers, preservatives, pitch control agents, etc., and one or more of these may be used. The content of the additives is preferably 5% by mass or less based on the total mass of the glass fiber sheet.

Fillers include calcium silicate, calcium carbonate, kaolin, talc, plastic pigments, glass beads, hollow glass beads, etc., and one or more of these can be used.

(Method of manufacturing glass fiber sheet for filters)
Next, an example of a method for producing a glass fiber sheet for filters according to the present embodiment will be described. In the method for producing a glass fiber sheet for filters according to the present embodiment, a raw material slurry containing the above-mentioned glass fibers, wood pulp and binder is wet-laid to produce a glass fiber sheet.

The raw material slurry used to manufacture glass fiber sheets contains glass fibers as the main fiber, as well as wood pulp and a binder. The raw material slurry may also contain fillers and other optional components. The slurry typically contains water as a medium.

Wet papermaking can be carried out by preparing a raw material slurry containing the above-mentioned components and water (medium), and then making paper from the raw material slurry using a known papermaking machine. Examples of papermaking machines include cylinder papermaking machines, inclined papermaking machines, Fourdrinier papermaking machines, and short wire papermaking machines. Multilayer papermaking can be carried out using the same or different types of papermaking machines in combination. However, a single-layer sheet is preferable for corrugation processing. Note that in the case of a multilayer sheet, it is necessary to increase the amount of wood pulp and binder, as delamination is likely to occur during corrugation processing.

There are no particular limitations 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. There are no particular limitations on the drying temperature, but it is usually around 100°C to 200°C.

The organic binder component or inorganic binder component may be added to the raw material slurry for producing the glass fiber sheet, or a liquid containing the organic binder component or inorganic binder component may be applied (external application) to the obtained glass fiber sheet by a method such as spray application, curtain application, impregnation application, bar application, roll application, or blade application. The nonwoven fabric to which the external application is applied may be a dried nonwoven fabric after drying, or a wet web before drying.

<Corrugated processing>
The glass fiber sheet for filters of the present embodiment may be corrugated into a honeycomb shape and used as a filter.

For example, a corrugated (uneven) glass fiber sheet can be obtained by corrugating the above-mentioned glass fiber sheet. A half-wave glass fiber sheet molded body can be obtained by bonding a corrugated glass fiber sheet (core paper) and a non-corrugated glass fiber sheet (liner). A honeycomb molded body can be produced by stacking a plurality of half-wave glass fiber sheet molded bodies.
An adhesive may be used when laminating the glass fiber sheets. Examples of the adhesive include inorganic adhesives such as colloidal silica, water glass, sepiolite, and alumina sol, and one or more of these may be used. In addition, an organic adhesive such as ethylene-vinyl alcohol may be used in combination with the adhesive.

The honeycomb molded body may be used as a filter as is, or may be used as a filter after being fired.

<Functional Materials>
The glass fiber sheet for filters of this embodiment functions as a filter by supporting a functional material inside, and therefore the glass fiber sheet for filters of this embodiment is a sheet for supporting a functional material.

Examples of functional materials include various known adsorbents and dehumidifiers. Examples of adsorbents include porous bodies such as silica gel, zeolite, sepiolite, activated carbon, and silicon oxide; catalysts such as manganese oxide, copper oxide, titanium oxide, chromium oxide, iron oxide, nickel oxide, zinc oxide, and cobalt oxide; and ion exchange resins. These may be used alone or in combination. They may also be used in the form of a composite in which the surface of the porous body is coated with a catalyst. In particular, catalysts such as titanium oxide are preferred as adsorbents for volatile organic compounds (VOCs).

Examples of dehumidifying agents include silica, zeolite, hydrophobic synthetic zeolite, natural zeolite, sepiolite, hydrotalcite, alumina, lime, gypsum, dolomite 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 water-absorbing polymers.

Examples of other functional materials include solid adsorbents in which alkaline compounds are supported on adsorbent carriers (potassium carbonate, sodium carbonate, sodium bicarbonate, calcium hydroxide, calcium carbonate, etc.) or on activated carbon, silica, alumina, allophane, sepiolite, cordierite, and other clay minerals; sodium hydroxide, potassium hydroxide, potassium carbonate, calcium hydroxide, ion exchange resins, deodorants, etc.

One method for supporting the functional material is to impregnate the above-mentioned glass fiber sheet, glass fiber sheet molded body, or honeycomb molded body with a slurry containing the functional material, and then dry it.

As described above, the glass fiber sheet of this embodiment is composed mainly of glass fiber and contains wood pulp and binder in specific ratios, so that the strength of the sheet is maintained while flexibility is imparted. Therefore, the glass fiber sheet of this embodiment has excellent shape conformability and excellent functional material carrying ability. Furthermore, the glass fiber sheet of this embodiment can exhibit sufficient strength even after carrying a functional material.

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
As the fiber component, 60 parts by mass of glass fiber (fiber diameter: 6 μm, fiber length: 6 mm), 40 parts by mass of wood pulp (NBKP) beaten to 500 CSF, and polyvinyl alcohol (Kuraray, Poval K-17U6) as a binder were added to 100 parts by mass of the fiber component in an amount of 16 parts by mass, and a small amount of a dispersant and an antifoaming agent as an auxiliary were added to water, mixed, stirred, and dispersed to prepare a raw material slurry with a concentration of 0.2% by mass. A randomly arranged web was formed by a wet papermaking method, and an acrylic emulsion was spray-coated to 0.2 g/m ² and dried to obtain a single layer of glass fiber sheet.
The basis weight of the obtained glass fiber sheet was measured in accordance with JIS P8124 and was found to be 44 g/ ^m2 .

Example 2
A glass fiber sheet was obtained in the same manner as in Example 1, except that the glass fiber was 70 parts by mass and the wood pulp (NBKP) was 30 parts by mass.

Example 3
A glass fiber sheet was obtained in the same manner as in Example 1, except that the basis weight was changed to 30 g/ ^m2 .

<Comparative Example 1>
A glass fiber sheet was obtained in the same manner as in Example 3, except that the glass fiber was 92 parts by mass and the wood pulp (NBKP) was 8 parts by mass.

<Comparative Example 2>
A glass fiber-containing sheet (hereinafter included in the glass fiber sheet) was obtained in the same manner as in Example 1, except that the glass fiber was 45 parts by mass and the wood pulp (NBKP) was 55 parts by mass.

<Comparative Example 3>
A glass fiber sheet was obtained in the same manner as in Example 1, except that the basis weight was changed to 60 g/ ^m2 .

<Comparative Example 4>
A glass fiber sheet was obtained in the same manner as in Example 1, except that polyvinyl alcohol was not added.

<Evaluation method>
The glass fiber sheet thus obtained was subjected to the following evaluations, and the results are shown in Table 1.

(Strength of glass fiber sheet)
The obtained glass fiber sheet was measured for tensile strength by a Tensilon type tensile tester (manufactured by ORIENTEC Co., Ltd.) in accordance with JIS P 8113 to judge its tensile strength.
○: Strong ×: Weak

(Corrugated processing)
The obtained glass fiber sheet was processed into a corrugated shape with a height of 1.4 mm and a pitch of 2.6 mm to form a core paper, and the core paper was adhered to a flat sheet liner made of the obtained glass fiber sheet with an inorganic adhesive to be corrugated. This was then rolled up to produce a cylindrical honeycomb molded body.

"Evaluation of shape conformity"
When the glass fiber sheet was processed into a corrugated shape, the shape conformability was evaluated based on the following indexes.
◯: The waveform is well shaped and the wave shape is good.
×: The waveform is poorly shaped.

(Powder fall)
The honeycomb portion of the obtained honeycomb formed body was touched with a finger, and powder falling off was evaluated based on the following criteria.
Good: No paper dust on your fingers.
×: Paper dust sticks to fingers.

(Supportability of Functional Materials)
The honeycomb molded body was immersed for 30 minutes in an impregnation solution in which titanium oxide, a VOC adsorbent, was dispersed in water at a high concentration as a functional material. The honeycomb portion of the filter substrate was then sintered to prepare a filter substrate. The functional material support was evaluated using the following indexes by touching the honeycomb portion of the filter substrate with a finger.
○: No powder falling off, excellent support ×: Powder falling off, poor support

As shown in Table 1, Examples 1 to 3 had excellent shape conformability of the glass fiber sheet, had sufficient strength even after firing, and did not fall off.
In Comparative Example 1, the strength and shape conformability of the glass fiber sheet were insufficient, and powder falling occurred in the honeycomb molded body.
In Comparative Example 2, the supportability of the functional material was insufficient.
In Comparative Example 3, the shape conformability of the glass fiber sheet was insufficient.
In Comparative Example 4, the strength of the glass fiber sheet was insufficient, and powder falling occurred in the honeycomb molded body.

Claims (5)

A glass fiber sheet for a filter, which contains glass fiber as a main component, further contains wood pulp and a binder, and is formed by wet papermaking,
The glass fiber sheet for a filter functions as a filter by carrying a functional material therein,
51 to 85 mass % of the total fiber content of the glass fiber sheet for filters is the glass fiber,
the wood pulp accounts for 30 to 49% by mass of the total fiber content of the glass fiber sheet for filters, and the content of the binder is 1% by mass or more based on the total mass of the glass fiber sheet for filters,
The glass fiber sheet for filters has a basis weight of 15 to 55 g/ ^m2 and is for corrugating . The glass fiber sheet for filters according to claim 1, wherein the wood pulp has a degree of beating of 300 to 750 CSF. The glass fiber sheet for filters according to claim 1 or 2, wherein the weighted average fiber diameter of the glass fibers is 4 to 10 μm. The glass fiber sheet for filters according to any one of claims 1 to 3, wherein the content of the binder is 25 mass% or less based on the total mass of the glass fiber sheet for filters. The glass fiber sheet for filters according to any one of claims 1 to 4, wherein the binder comprises polyvinyl alcohol.