Inorganic fiber sheet

Abstract

The present invention addresses the problem of providing an inorganic fiber sheet capable of achieving both moldability and processability during corrugation processing. The inorganic fiber sheet according to the present invention comprises glass fibers, an organic binder, and organic fibers, and is characterized in that the content of the organic binder is 8-20 mass%, and the organic binder is composed of two or more organic binders having different heating peak temperatures as determined by differential thermal analysis.

Description

TECHNICAL FIELD

[0001] The present application relates to an inorganic fiber sheet. BACKGROUND

[0002] Conventionally, a technique is known in which, in order to produce a filter having inorganic fibers as a main component, a honeycomb structure is formed by corrugating an inorganic fiber sheet. For example, Patent Literature 1 describes an inorganic fiber sheet having a corrugated shape obtained using a corrugating device having a gear. Further, Patent Literature 1 describes that an inorganic fiber sheet having a corrugated shape and an inorganic fiber sheet having a flat shape are stacked to form a skeleton having a honeycomb shape.

[0003] Patent Literature 1: Japanese Patent Application Publication No. 2010-13773

[0004] When an inorganic fiber sheet is processed using a corrugating device having a gear, moldability (anti-sticking property after processing, which makes it easy to peel the inorganic fiber sheet from the gear) and processability (processing suitability of the corrugated shape) are sought. In a situation in which the temperature, pressure, and time during corrugating greatly vary, if the moldability or processability decreases, the yield of the material deteriorates, and the productivity decreases. SUMMARY

[0005] The present application relates to an inorganic fiber sheet.

[0006] A first aspect of the present application is an inorganic fiber sheet characterized by comprising glass fibers, an organic binder, and organic fibers, the content of the organic binder being 8 to 20 mass%, and the organic binder being composed of two or more kinds of organic binders having different heat generation peak temperatures in differential thermal analysis.

[0007] On the basis of the first aspect, a second aspect is characterized in that each of the two or more kinds of organic binders has a heat generation peak temperature in differential thermal analysis in the range of 300 to 440°C, and when the highest heat generation peak temperature is set as T1 and the lowest heat generation peak temperature is set as T2, the organic binder having the heat generation peak temperature of T1 is different from the organic binder having the heat generation peak temperature of T2, and the absolute value of the difference |T1-T2| is 50 to 110°C.

[0008] On the basis of the second aspect, a third aspect is characterized in that the content of the organic binder having the heat generation peak temperature of T1 is 5 to 16 mass%, the content of the organic binder having the heat generation peak temperature of T2 is 1 to 8 mass%, and the content of the organic binder having the heat generation peak temperature of T1 is more than the content of the organic binder having the heat generation peak temperature of T2.

[0009] Based on any one of the first to third methods, the fourth method is characterized in that the content of the aforementioned organic fiber is more than 20% by mass and less than 30% by mass.

[0010] Based on any of the first to fourth methods, the fifth method is characterized in that the aforementioned organic fiber is a polyester fiber.

[0011] Based on any of the first to fifth methods, the sixth method is characterized in that, for the aforementioned inorganic fiber sheet, the ratio of tensile strength in the length direction to tensile strength in the width direction (tensile strength in the length direction / tensile strength in the width direction) is 2 to 8.

[0012] Based on any of the first to sixth methods, the seventh method is characterized in that, for the aforementioned glass fibers, the average fiber diameter is 6 to 8 (μm) and the fiber diameter deviation is less than the standard deviation of 3 (μm).

[0013] Based on any of the first to seventh methods, the eighth method is characterized in that the aforementioned inorganic fiber sheet does not contain acrylic resin.

[0014] Based on any of the first to eighth methods, the ninth method is characterized in that the aforementioned inorganic fiber sheet is used for a honeycomb filter.

[0015] According to the present invention, an inorganic fiber sheet that can achieve both formability and processability during corrugation processing can be provided. Detailed Implementation

[0016] The present invention will now be described based on preferred embodiments.

[0017] The inorganic fiber sheet of the embodiment includes glass fiber, organic adhesive and organic fiber.

[0018] The inorganic fiber sheet of the embodiment is mainly composed of glass fiber. The glass fiber content of the inorganic fiber sheet of the embodiment is preferably 50% by mass or more, more preferably less than 72% by mass.

[0019] There are no particular limitations on the materials used for glass fiber, but examples include: E glass with low alkali content, high-strength S glass, C glass with excellent acid resistance, and ECR glass with excellent corrosion resistance.

[0020] The inorganic fiber sheet of the embodiment contains an organic binder. Preferably, the organic binder melts below 250°C. Thus, the organic binder can function as a binder for the inorganic fiber sheet. Preferably, the lower limit of the melting point of the organic binder is appropriately set according to the purpose, but it is preferably a substance that is solid at least at room temperature (5~35°C).

[0021] Alternatively, the organic adhesive may be composed of thermoplastic materials such as thermoplastic resins. If the organic adhesive is fibrous, it is easier to combine with other fibrous materials such as glass fibers, and is therefore preferred.

[0022] The content of the organic binder in the inorganic fiber sheet of the embodiment is preferably 8 to 20% by mass, more preferably 8 to 17% by mass. If the content of the organic binder is above the lower limit mentioned above, it is preferable to ensure sufficient tensile strength required for corrugation processing. If the content of the organic binder is below the upper limit mentioned above, it is preferable to be able to form a good waveform during corrugation processing.

[0023] The aforementioned organic adhesives consist of two or more organic adhesives with different peak heating temperatures determined by differential calorimetry. When only one type of organic adhesive is used, it is difficult to balance formability (anti-sticking properties that allow for easy peeling from the gear after processing) and processability (processability of the corrugated pattern). By appropriately combining two or more organic adhesives, it is possible to achieve a balance between formability and processability during corrugated processing.

[0024] The aforementioned organic adhesive softens during corrugation processing, enabling the formation of a good corrugated waveform. Furthermore, the organic adhesive forms a film on the fibers during inorganic fiber sheet fabrication, thereby bonding the interlacing points of the fibers. This prevents fiber shedding and avoids fiber adhesion to the gears during corrugation processing.

[0025] Preferably, each of the two or more organic binders mentioned above has a peak heating temperature in differential thermal analysis within the range of 300 to 440°C. Each of these peak heating temperatures is above the lower limit, resulting in excellent thermal stability during corrugation processing. Each of these peak heating temperatures is below the upper limit, thereby suppressing the vaporization of organic components during the firing process after corrugation processing.

[0026] More specifically, for the two or more organic adhesives mentioned above, when the highest heating peak temperature is designated as T1 and the lowest heating peak temperature is designated as T2, the organic adhesive having a heating peak temperature of T1 is different from the organic adhesive having a heating peak temperature of T2. Furthermore, it is preferable that the absolute value of the difference |T1-T2| is 50~110°C, and more preferably |T1-T2| is 80~100°C.

[0027] The two or more organic adhesives mentioned above include organic adhesives having a heating peak temperature of T2, whereby at least a portion of the organic adhesive melts and is able to bond the interlacing points of the fibers.

[0028] Furthermore, in the inorganic fiber sheet of the embodiment, it is preferable that the content of the organic binder having a heating peak temperature of T1 is 5 to 16% by mass, the content of the organic binder having a heating peak temperature of T2 is 1 to 8% by mass, and the content of the organic binder having a heating peak temperature of T1 is greater than the content of the organic binder having a heating peak temperature of T2.

[0029] If the content of the organic adhesive having a heating peak temperature of T2 is above the lower limit mentioned above, an appropriate amount of film can be formed at the interlacing points of the fibers, bonding the interlacing points together. This prevents fiber shedding and adhesion of fibers to the gears during corrugation processing. If the content of the organic adhesive having a heating peak temperature of T2 is below the upper limit mentioned above, excessive resin film formation will not occur, thus allowing for proper waveform formation during corrugation processing.

[0030] There are no particular limitations on the materials used as organic adhesives, but at least two organic adhesives belonging to each of the following groups can be cited: polyvinyl alcohol (PVA) resins, polyethylene resins, polypropylene resins, acrylic resins, polyvinyl chloride resins, nylon resins, starch, etc.

[0031] In the case where the inorganic fiber sheet of the embodiment contains two or more organic adhesives, it is possible that any two or more of them belong to the same group of materials, or that all organic adhesives belong to the same group of materials. Alternatively, at least one of the two or more organic adhesives may belong to a different group of materials relative to any of the others, or they may each belong to a different group of materials.

[0032] Among two or more organic adhesives belonging to the same group, it is preferable that at least their heating peak temperatures are different. Examples of phenomena that contribute to the manifestation of heating peaks in differential thermal analysis include combustion, oxidation, and crystallization. Additionally, examples of phenomena that contribute to the manifestation of endothermic peaks in differential thermal analysis include evaporation, sublimation, melting, and phase change.

[0033] The inorganic fiber sheet of the embodiment contains organic fibers. Preferably, the organic fibers are different from the organic adhesives described above and do not melt below 250°C.

[0034] There are no particular limitations on the materials used for organic fibers. Examples include polyethylene fiber, polypropylene fiber, polybutene fiber, nylon fiber, rayon fiber, cuprammonium fiber, acetate fiber, polyvinyl chloride fiber, polyurethane fiber, polybenzobisoxazole terephthalate fiber, polyamide-imide fiber, polyimide fiber, polyaryl ester fiber, polyether-imide fiber, vinylon fiber, polycarbonate fiber, ethylene vinyl acetate fiber, ethylene vinyl alcohol fiber, polyphenylene sulfide fiber, polyester fiber (polyethylene terephthalate fiber, polybutylene terephthalate fiber, polyethylene naphthalate fiber, etc.), cellulose fibers such as wood pulp, and aramid fiber. One or more of these organic fibers can be selected.

[0035] The content of organic fibers in the inorganic fiber sheet of the embodiment is preferably more than 20% by mass and less than 30% by mass, more preferably 22 to 28% by mass. If the content of organic fibers exceeds the above lower limit, the retention and adsorption of the functional material impregnated after corrugation is also better after firing. If the content of organic fibers is less than the above upper limit, the ash content after firing is lower.

[0036] As the organic fiber, polyester fibers such as polyethylene terephthalate (PET) resin are preferred. This ensures that the organic fibers do not melt during papermaking of the inorganic fiber sheet, and also do not melt during corrugation forming at temperatures below 200°C. Furthermore, PET fibers are preferred considering ease of firing, price, and availability. At least a portion of the PET fiber may also be modified PET fiber or recycled PET fiber.

[0037] The polycarboxylic acid residues contained in PET fibers are not limited to 100% by mass of terephthalic acid residues (terephthaloyl). They can also be mainly composed of terephthalic acid residues and contain other polycarboxylic acid residues. There are no particular limitations on other polycarboxylic acid residues, but examples include aromatic polycarboxylic acid residues such as isophthalic acid residues (isophthaloyl) and naphthalenedicarboxylic acid residues (naphthaloyl), and aliphatic polycarboxylic acid residues such as adipic acid residues (adipyl) and sebacic acid residues (sebacyl).

[0038] The polyol residues contained in PET fibers are not limited to 100% by mass of ethylene glycol residues (ethylene). They can also be mainly composed of ethylene glycol residues, but also include other polyol residues. Examples of other polyol residues include propylene glycol residues (propyleneene), butanediol residues (butylene), 1,4-cyclohexanediethanol residues, and diethylene glycol residues.

[0039] In the preferred embodiment, the inorganic fiber sheet exhibits fiber orientation along both the length and width directions. Here, the length direction is MD (Machine Direction), and the width direction is CD (Cross Direction). However, in this embodiment, the direction in which the waveform is formed during corrugation processing is designated as the length direction, and the direction orthogonal to it is designated as the width direction. Furthermore, when manufacturing the inorganic fiber sheet of this embodiment using a known papermaking machine, it is preferable that the MD and CD directions of the papermaking machine align with the aforementioned length and width directions during corrugation processing, respectively.

[0040] Specifically, the ratio of the tensile strength in the length direction to the tensile strength in the width direction of the inorganic fiber sheet in the embodiment is preferably 2 to 8, more preferably 2.5 to 5.0. By making the above-mentioned tensile strength ratio above or above the lower limit value, sufficient tensile strength required for corrugation processing can be ensured. By making the above-mentioned tensile strength ratio below or above the upper limit value, a good waveform can be formed during corrugation processing.

[0041] In the inorganic fiber sheet of the embodiment, the glass fiber preferably has a fiber diameter distribution suitable for corrugation processing.

[0042] Preferably, the average fiber diameter of the glass fibers is 6 to 8 μm. If the average fiber diameter of the glass fibers is above the lower limit, the adsorption functional material can be properly retained during impregnation after corrugation. If the average fiber diameter of the glass fibers is below the upper limit, it is beneficial to prevent air leakage when passing through the filter of the final product.

[0043] The fiber diameter deviation of the aforementioned glass fibers is preferably set to a standard deviation of 3 μm or less. By setting the standard deviation below the upper limit, the gaps between the fibers are reduced, which helps prevent air leakage through the filter of the final product.

[0044] The inorganic fiber sheet of the preferred embodiment does not contain acrylic resin. For example, acrylic fibers may also not be used in the organic adhesive.

[0045] The preferred basis weight of the inorganic fiber sheet in this embodiment is 20.0~25.0 g / m³. 2 More preferably, it is 21.2~24.2 g / m 2 If the above-mentioned basis weight is above the lower limit, the tensile strength required to withstand handling during corrugated processing can be sufficiently ensured. If the above-mentioned basis weight is below the upper limit, machinability (machinability of the processed waveform) can be easily ensured during corrugated processing.

[0046] The density of the inorganic fiber sheet in this embodiment is preferably 0.130~0.160 g / cm³.3 If the density is above the lower limit, the inorganic fiber sheet does not need to be excessively thick, making it easier to ensure the flow path of the honeycomb through the final product filter and reducing pressure loss during filtration. If the density is below the upper limit, processability (the suitability of the processed waveform) is easily ensured during corrugated processing.

[0047] The inorganic fiber sheet used in this embodiment is preferably for use in a honeycomb filter. In addition to inorganic fibers (glass fibers), organic fibers, and organic adhesives, it may also include inorganic adhesives, fillers, etc., as optional components.

[0048] The inorganic fiber sheet of the embodiments can be made of inorganic fibers, or it can be made of glass fibers alone, or it can be made of inorganic fibers other than glass fibers. The inorganic fiber sheet of the embodiments can be made of inorganic fibers as an adhesive, or it can be made of organic adhesives and inorganic adhesives together.

[0049] There is no particular limitation on the method for manufacturing inorganic fiber sheets. Inorganic fiber sheets can be manufactured by dewatering and drying the resulting wet sheets after the raw material pulp has been papered using a known papermaking machine. Preferably, the raw material pulp contains the aforementioned fibers and various materials including binders, with water included as the medium. Additives may also be appropriately added to the raw material pulp.

[0050] There are no particular limitations on specific examples of papermaking machines, but cylinder papermaking machines, inclined papermaking machines, long-wire papermaking machines, and short-wire papermaking machines can also be used individually. Combined papermaking machines, which combine the same or different types of papermaking machines, can also be used.

[0051] There are no particular limitations on the drying method for wet sheets, but well-known dryers such as Yankee dryers, drum dryers, airflow dryers, and infrared dryers can be used. A drying temperature of around 100-200°C can be cited as an example.

[0052] The size of the inorganic fiber sheet in this embodiment is not particularly limited, but it can also be wound into a roll. Furthermore, the inorganic fiber sheet can be cut to a predetermined size or processed into a predetermined shape for use.

[0053] The inorganic fiber sheet of the embodiment is suitable for corrugated applications due to its excellent formability and processability during corrugation. A honeycomb filter manufactured using the inorganic fiber sheet of the embodiment comprises a corrugated sheet obtained by corrugating the inorganic fiber sheet. In the honeycomb filter, the combination of inorganic fiber sheets arranged in a honeycomb pattern is not particularly limited, and any suitable structure can be used.

[0054] Honeycomb-shaped inorganic fiber sheets can also be formed by combining two or more corrugated sheets, or by combining one or more corrugated sheets and one or more flat sheets. Here, the flat sheet is an inorganic fiber sheet that has not been corrugated, and it can be a straight sheet, a planar sheet, a curved sheet, or a curved surface sheet.

[0055] When a honeycomb sheet is composed of inorganic fiber sheets, multiple corrugated sheets can be overlapped, for example. Alternatively, one or more corrugated sheets can be sandwiched between multiple flat sheets. Different corrugated sheets can be overlapped on both sides of a flat sheet. Multiple corrugated sheets can also be alternately overlapped with multiple flat sheets. When using multiple corrugated sheets, the shape, height, spacing, etc., of the waveform can be the same. Corrugated sheets with different waveform shapes, heights, spacing, etc., can also be combined.

[0056] The inorganic fiber sheet in the embodiment can be a flat sheet or a roll before corrugation, or a corrugated sheet or a honeycomb sheet after corrugation. The honeycomb sheet can compactly house and arrange the corrugated sheet with a large surface area, and therefore can also be used in applications other than filters, such as adsorption sheets, dehumidification sheets, and deodorization sheets.

[0057] The inorganic fiber sheet of the embodiment can retain the adsorption of functional materials such as silica gel, zeolite, activated carbon, and metal oxides. The functional materials may also possess one or more functions selected from catalysts, adsorbents, dehumidifiers, deodorizers, etc. The retention and adsorption of functional materials in the inorganic fiber sheet can be implemented either before or after corrugation of the inorganic fiber sheet.

[0058] Alternatively, the inorganic fiber sheet of the embodiment may be fired before being used in the product. The purpose of firing is not particularly limited, but examples include: modification of functional materials, reduction of organic components, etc. The reduction of organic components may be suppressed during firing, or organic components may be removed to make it suitable for use at high temperatures. The firing process of the inorganic fiber sheet may be performed at the stage of the inorganic fiber sheet before corrugation, or after corrugation.

[0059] The present invention has been described above based on preferred embodiments, but the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention. As changes, additions, substitutions, omissions, and other modifications of structural elements in each embodiment can be cited.

[0060] Example

[0061] The present invention will now be described in detail with reference to the embodiments.

[0062] The raw material pulp was prepared according to the composition (mass %) shown in Tables 1 to 3, and inorganic fiber sheets were produced by wet papermaking.

[0063] In the compositions shown in Tables 1 to 3, the following abbreviations are used to represent raw materials for organic adhesives and organic fibers.

[0064] "PVA452" refers to PVA fiber (peak heating temperature 452℃).

[0065] "PVA430" refers to PVA fiber (peak heating temperature 430℃).

[0066] "PVA400" refers to PVA fiber (peak heating temperature 400℃).

[0067] "PP342" is polypropylene fiber (peak heating temperature 342℃).

[0068] "PVA360" refers to PVA fiber (peak heating temperature 360℃).

[0069] "PVA300" refers to PVA fiber (peak heating temperature 300℃).

[0070] "PVA289" is PVA fiber (peak heating temperature 289℃).

[0071] “PE469” is polyethylene fiber (peak heating temperature 469℃).

[0072] "PVA380" refers to PVA fiber (peak heating temperature 380℃).

[0073] "AC320" is acrylic resin (peak heating temperature 320℃).

[0074] “PET542” is PET fiber (peak heating temperature 542℃).

[0075] "AR553" is aramid fiber (peak heating temperature 553℃).

[0076] In the compositions shown in Tables 1 to 3, glass fibers with an average fiber diameter of 7 μm and a standard deviation of 2 μm were used as glass fibers.

[0077] The “orientation” in Tables 1-3 refers to the ratio of the tensile strength in the length direction to the tensile strength in the width direction of the inorganic fiber sheet (tensile strength in the length direction / tensile strength in the width direction).

[0078] In the corrugation process of inorganic fiber sheets, a corrugation with a height of 5.0 mm and a spacing of 25.0 mm was formed by processing at 180°C. The formability and processability of the obtained corrugated sheets were evaluated.

[0079] "Formability" was evaluated based on the following criteria for assessing the resistance to sticking during corrugation processing.

[0080] Excellent (A): The inorganic fiber sheet is completely separated from the gear.

[0081] Good (B): Part of the inorganic fiber sheet was adhered but peeled off.

[0082] (C) No: The inorganic fiber sheet was not peeled off from the gear.

[0083] "Machinability" was evaluated based on the following criteria for assessing the machinability of corrugated parts.

[0084] Advantage (A): The waveform is completely formed on the inorganic fiber sheet through corrugation processing.

[0085] Good (B): There are parts of the inorganic fiber sheet that cannot be corrugated by corrugation processing.

[0086] (C) No: There are many parts of inorganic fiber sheets that cannot be corrugated by corrugation.

[0087] The “Comprehensive Evaluation” was conducted using the following evaluation criteria.

[0088] The overall rating is 5: both formability and processability are excellent (A).

[0089] The overall evaluation score is 4: good formability (B) and excellent processability (A).

[0090] The overall evaluation is 3: excellent formability (A) and good processability (B).

[0091] The overall rating is 2: both formability and processability are good (B).

[0092] The overall evaluation is 1: Both formability and processability are unacceptable (C).

[0093]

[0094]

[0095]

[0096] In Examples 1-23, both formability and processability were rated as excellent (A) or good (B), with an overall evaluation of 2 or higher. In Comparative Examples 1-3, the overall evaluation was 1.

[0097] Industrial availability

[0098] According to the present invention, an inorganic fiber sheet that can achieve both formability and processability during corrugation processing can be provided.

Claims

1. An inorganic fiber sheet, characterized in that, Including glass fiber, organic adhesives, and organic fibers, The content of the organic adhesive is 8-20% by mass. The organic binder is composed of two or more organic binders with different peak heating temperatures as determined by differential thermal analysis.

2. The inorganic fiber sheet according to claim 1, characterized in that, The two or more organic adhesives each have a peak heating temperature in differential thermal analysis within the range of 300~440℃. When the highest peak heating temperature is set as T1 and the lowest peak heating temperature is set as T2, the organic adhesive with a peak heating temperature of T1 is different from the organic adhesive with a peak heating temperature of T2, and the absolute value of the difference |T1-T2| is 50~110℃.

3. The inorganic fiber sheet according to claim 2, characterized in that, The content of the organic adhesive with a heating peak temperature of T1 is 5-16% by mass, the content of the organic adhesive with a heating peak temperature of T2 is 1-8% by mass, and the content of the organic adhesive with a heating peak temperature of T1 is greater than the content of the organic adhesive with a heating peak temperature of T2.

4. The inorganic fiber sheet according to claim 1, characterized in that, The content of the organic fiber is more than 20% by mass and less than 30% by mass.

5. The inorganic fiber sheet according to claim 1, characterized in that, The organic fiber is polyester fiber.

6. The inorganic fiber sheet according to claim 1, characterized in that, The ratio of the tensile strength in the length direction to the tensile strength in the width direction of the inorganic fiber sheet, i.e., the tensile strength in the length direction / the tensile strength in the width direction, is 2 to 8.

7. The inorganic fiber sheet according to claim 1, characterized in that, The average fiber diameter of the glass fiber is 6μm to 8μm, and the standard deviation of the fiber diameter is less than 3μm.

8. The inorganic fiber sheet according to claim 1, characterized in that, The inorganic fiber sheet does not contain acrylic resin.

9. The inorganic fiber sheet according to any one of claims 1 to 8, characterized in that, The inorganic fiber sheet is used for honeycomb filters.

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