Method for manufacturing composite sheet, method for manufacturing laminate, composite sheet, and laminate

Abstract

The manufacturing method of the composite sheet of the present invention is a manufacturing method of a composite sheet in which an operation of disposing a dispersion liquid containing polytetrafluoroethylene particles on the surface of a glass cloth and heating is performed two or more times, wherein, in the case where the operation is performed two times, the dispersion liquid further containing a polymer having a carbonyl group or the like is used only in the first operation or only in the last operation, and, in the case where the operation is performed three or more times, the dispersion liquid further containing a polymer having a carbonyl group or the like is used only in the first operation, only in the last operation, or only in the first and last operations.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing composite sheets, a method for manufacturing laminates, composite sheets, and laminates. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is used in various industrial applications due to its excellent properties, including good mold release properties, electrical properties, water and oil repellency, chemical resistance, weather resistance, and heat resistance. PTFE-glass cloth composite sheets (hereinafter referred to as "composite sheets"), which are made by loading PTFE onto glass cloth, and laminates of composite sheets and substrates are widely used as conveyor belts in food manufacturing. In addition, laminates of composite sheets and metal substrates are used as substrates for printed circuit boards. As one embodiment of the manufacturing method of composite sheets, a method is known to impregnate a dispersion of PTFE particles in glass cloth and perform heating operations multiple times (see Japanese Patent Publication No. 2020-513437 and International Publication No. 2020 / 004339).

[0003] However, due to the inherently low surface tension and weak interaction with other materials, PTFE tends to have difficulty adhering firmly to the substrate surface. Therefore, delamination of the composite sheet from the substrate and PTFE from the composite sheet are likely to occur due to the linear expansion of the composite sheet. In particular, the aforementioned delamination is likely to be more pronounced in composite sheets used in conveyor belts during food manufacturing due to repeated heating and cooling processes. Summary of the Invention The technical problem that the invention aims to solve

[0004] Therefore, the technical problem to be solved by the present invention is to provide a composite sheet capable of suppressing at least one of the peeling of the composite sheet from the substrate and the peeling of PTFE from the composite sheet in a laminate and having excellent heat resistance, a laminate having the composite sheet, a method for manufacturing the composite sheet, and a method for manufacturing a laminate using the composite sheet. means of solving technical problems

[0005] The means to solve the above-mentioned technical problems include the following methods. <1> A method for manufacturing a composite sheet, wherein the operation of distributing a dispersion of polytetrafluoroethylene particles on the surface of a glass cloth and heating it is performed two or more times; when the operation is performed twice, the dispersion containing at least one of a polymer having a carbonyl group and its precursor is used only in the first operation or only in the last operation; when the operation is performed three or more times, the dispersion containing at least one of a polymer having a carbonyl group and its precursor is used only in the first operation, only in the last operation, or only in the first and last operations. <2> As mentioned above <1> The method for manufacturing the composite sheet, wherein the operation is performed more than three times, and the dispersion containing the polytetrafluoroethylene particles and at least one of the polymer having a carbonyl group and its precursor is used only in the first and last operations. <3> As mentioned above <1> or <2> The method for manufacturing the composite sheet, wherein the polymer containing carbonyl groups is a thermoplastic tetrafluoroethylene-based polymer. <4> As mentioned above <1> ~ <3> The method for manufacturing the composite sheet according to any one of the following methods, wherein the polymer having carbonyl groups is a thermoplastic polymer with a melting temperature of 200°C or higher. <5> As mentioned above <1> ~ <4> The method for manufacturing the composite sheet according to any one of the following, wherein heating the dispersion comprises heating for calcining at least one of the polytetrafluoroethylene particles, the polymer having a carbonyl group, and the precursor of the polymer having a carbonyl group. <6> As mentioned above <1> ~ <5> The method for manufacturing the composite sheet according to any one of the claims, wherein the polymer having carbonyl groups is contained in the form of particles with an average particle size (D50) of 0.03 μm to 200 μm. <7> A method for manufacturing a laminate, wherein the above-mentioned <1> ~ <6> The composite sheet manufactured by any one of the methods described herein is laminated with a substrate. <8> A composite sheet comprising a glass cloth and polytetrafluoroethylene supported on the glass cloth, further comprising a polymer having carbonyl groups, wherein the polymer having carbonyl groups is concentrated on at least one of the surfaces of the glass cloth and the composite sheet. <9> A laminated body having the above-mentioned features <8> The composite sheet and the substrate disposed on the surface of the composite sheet. <10> As mentioned above <9> The laminated body wherein the peel strength of the composite sheet from the substrate is above 10 N / cm. Invention Effects

[0006] According to one embodiment of the present disclosure, a composite sheet capable of suppressing at least one of the peeling of the composite sheet from the substrate and the peeling of PTFE from the composite sheet in a laminate and having excellent heat resistance, a laminate having the composite sheet, a method for manufacturing the composite sheet, and a method for manufacturing a laminate using the composite sheet can be provided. Detailed Implementation

[0007] The specific embodiments of this disclosure will be described in detail below. However, the embodiments of this disclosure are not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps, etc.) are not essential unless specifically stated otherwise. The same applies to numerical values ​​and their ranges; they do not limit the embodiments of this disclosure.

[0008] The numerical range represented by “~” in this disclosure includes the ranges where the values ​​recorded before and after “~” are the minimum and maximum values, respectively. In this disclosure, each component may contain multiple corresponding substances. Where multiple substances corresponding to each component are present in the composition, unless otherwise specified, the content or percentage of each component refers to the total content or percentage of the multiple substances present in the composition. In this disclosure, the particles corresponding to each component may be multiple. In the case where multiple particles corresponding to each component are present in the composition, unless otherwise specified, the particle size of each component refers to the value of a mixture of the multiple particles present in the composition. In this disclosure, the term "stacked" means stacking layers together, which can be two or more layers combined together, or two or more layers that can be detached. In this disclosure, the "average particle size (D50)" is the cumulative 50% diameter of the particle volume as determined by laser diffraction and scattering. That is, the particle size distribution is determined by laser diffraction and scattering, and a cumulative curve is obtained with the total volume of the particle group as 100%. The particle size at the point on the cumulative curve where the cumulative volume reaches 50% is the particle size. The D50 of the particles was determined by analyzing the powder dispersed in water using laser diffraction and scattering analysis with a laser diffraction and scattering particle size distribution measuring device (manufactured by Horiba Manufacturing Co., Ltd., LA-920 measuring instrument). In this disclosure, "the melting temperature of the polymer" is the temperature corresponding to the maximum value of the polymer's melting peak as determined by differential scanning calorimetry (DSC). In this disclosure, "melt flow rate" refers to the melt flow rate of polymers as specified in JIS K 7210-1:2014 (ISO 1133-1:2011). In this disclosure, the "glass transition temperature (Tg)" is a value determined by analyzing polymers using the dynamic viscoelasticity assay (DMA). In this disclosure, "viscosity" refers to the value obtained by measuring the dispersion using a type B viscometer at 25°C and 30 rpm. The measurement was repeated three times, and the average of the three measurements was taken. In this disclosure, "thixotropic ratio" refers to the value (η1 / η2) calculated by dividing the viscosity η1 measured at 25°C and 30 rpm by the viscosity η2 measured at 60 rpm. Each viscosity measurement was repeated three times, and the average of the three measurements was taken. In this disclosure, "polymer" is a compound formed by the polymerization of monomers. That is, a "polymer" has multiple monomer-based units. In this disclosure, a "unit" in a polymer refers to a group of atoms based on a monomer formed by polymerization of the monomer. A unit can be formed directly through a polymerization reaction, or a unit can be formed by treating the polymer to transform a portion of the unit into a unit of another structure. In this disclosure, "(meth)acrylic acid" is a term used to encompass both the concepts of acrylic acid and methacrylic acid.

[0009] The method for manufacturing the composite sheet of the present invention is a method for manufacturing a composite sheet by disposing a dispersion of polytetrafluoroethylene particles (hereinafter also referred to as "PTFE particles") on the surface of glass cloth and heating it more than twice. When the operation is performed twice, the dispersion containing at least one of polymers having carbonyl groups and their precursors is used only in the first operation or only in the last operation. When the operation is performed three or more times, the dispersion containing at least one of polymers having carbonyl groups and their precursors is used only in the first operation, only in the last operation, or only in the first and last operations. According to the method for manufacturing the composite sheet disclosed herein, a composite sheet capable of suppressing at least one of the following—the delamination of the composite sheet from the substrate in a laminate and the delamination of PTFE from the composite sheet—and possessing excellent heat resistance can be manufactured. While the mechanism of action is uncertain, it is roughly presumed as follows. In the first operation, by using a dispersion containing PTFE particles and a polymer with carbonyl groups, a composite sheet can be manufactured in which the polymer with carbonyl groups is concentrated on the surface of the glass cloth, thus suppressing the peeling of PTFE from the composite sheet. This is presumably because the carbonyl groups in the polymer form a dense matrix, making it easy for the polymer chains of the polymer and PTFE to entangle with each other. In particular, if the polymer with carbonyl groups is a thermoplastic tetrafluoroethylene-based polymer, the PTFE loading is promoted starting from the molten tetrafluoroethylene-based polymer adhering to the glass cloth, thus making it easier to highly load PTFE. In the last operation described, by using a dispersion containing PTFE particles and a polymer with carbonyl groups, a composite sheet in which the polymer with carbonyl groups is concentrated on the surface of the composite sheet can be manufactured, which can suppress delamination in the laminate formed by stacking the composite sheet of this disclosure with a substrate. This is presumably because the carbonyl groups of the polymer form a dense matrix and improve adhesion through interaction with other materials. In particular, if the polymer with carbonyl groups is a thermoplastic tetrafluoroethylene-based polymer, adhesion to other substrates is more easily improved while highly loading PTFE. Furthermore, compared to using the dispersion containing at least one of polymers having carbonyl groups and their precursors in all operations, the heat resistance of the composite sheet is improved by using the dispersion containing at least one of polymers having carbonyl groups and their precursors only in the first operation, only in the last operation, or only in the first and last operations. This is presumably because the increased proportion of PTFE in the composite sheet makes its high heat resistance more readily apparent.

[0010] First, the dispersion used in the manufacturing method of the composite sheet disclosed herein will be described as follows. The dispersion contains PTFE particles. One type of PTFE particle can be used, or two or more types can be used. PTFE can be a homopolymer of tetrafluoroethylene (hereinafter also referred to as "TFE"), or a copolymer of TFE with trace amounts of perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), hexafluoropropylene (hereinafter also referred to as "HFP"), fluoroalkyl vinyl ether, etc., i.e., so-called modified PTFE. The proportion of TFE units in PTFE is preferably 99.5 mol% or more, more preferably 99.9 mol% or more of all units. Furthermore, the PTFE particles are preferably composed primarily of PTFE. Relative to the total mass of the PTFE particles, it is preferable to contain 90% by mass or more of PTFE, and more preferably 100% by mass of PTFE. In addition, PTFE is preferably non-thermally fusible. "Non-thermally fusible" means it cannot be melted and molded, i.e., it does not exhibit melt flowability. Specifically, it is defined as a melt flow rate of less than 0.5 g / 10 minutes, measured according to ASTM D3307 at a test temperature of 372°C and a load of 49 N. In addition, in this disclosure, PTFE does not include the F polymer described later.

[0011] PTFE is preferred based on the following formula (1), where the number average molecular weight Mn is above 200,000. Mn = 2.1 × 1010 ×ΔHc -5.16 …(1) In equation (1), Mn represents the number-average molecular weight of PTFE, and ΔHc represents the heat of crystallization of PTFE (cal / g) determined by differential scanning calorimetry.

[0012] The D50 of PTFE particles is preferably 0.1 μm or more, more preferably 0.2 μm or more. The D50 of PTFE particles is preferably 3 μm or less, more preferably 0.5 μm or less. The content of PTFE particles relative to the total mass of the dispersion is preferably 5 to 70% by mass, more preferably 10 to 65% by mass, and even more preferably 20 to 60% by mass. Dispersions containing PTFE particles can be commercially available dispersions. For example, AD-915E manufactured by AGC Corporation can be used as an aqueous dispersion of PTFE particles.

[0013] In the method for manufacturing the composite sheet disclosed herein, the operation of preparing the dispersion and heating is performed twice or more. In at least one of the first and last operations, the dispersion contains at least one of a polymer having a carbonyl group and its precursor. One or more of the polymer having a carbonyl group and its precursor may be used. Furthermore, in the operations other than the first and last operations, the dispersion used can be used without particular restriction as long as it contains PTFE particles and does not contain at least one of a polymer having a carbonyl group and its precursor. The polymer having carbonyl groups is preferably selected from one or more of tetrafluoroethylene polymers having carbonyl groups (hereinafter also referred to as "F polymers"), polyimide resins (hereinafter also referred to as "PI"), and polyamide-imide resins (hereinafter also referred to as "PAI"). From the viewpoint of more effectively suppressing the peeling of the composite sheet from the substrate and the peeling of PTFE from the composite sheet in the laminate, F polymers are more preferred. Polymers containing carbonyl groups can be in particulate or non-particulate form, but from the viewpoint of dispersibility in a dispersion, particulate form is preferred. In addition, in this disclosure, "precursor" refers to a compound that reacts to become a polymer having a carbonyl group, such as polyamic acids (polyamic acid, polyamic ester, etc.) that are imidized to become PI, PAI, etc.

[0014] The melting temperature of the polymer containing carbonyl groups is preferably above 200°C, more preferably above 260°C. The melting temperature of the polymer containing carbonyl groups is preferably below 325°C, more preferably below 320°C. By keeping the melting temperature of the polymer containing carbonyl groups within the above range, the heat resistance, low linear expansion, and processability of the composite sheet can be improved. Furthermore, when a composite sheet manufactured by using a dispersion of a polymer containing carbonyl groups with a melting temperature of 200°C or higher in the final step of the above-described operation is used in a conveyor belt during food manufacturing, the demolding durability of the food from the composite sheet tends to improve. This is presumably because the PTFE particles concentrated on the surface of the composite sheet generate stress concentration during food peeling. Additionally, polymers containing carbonyl groups with a melting temperature of 200°C or higher do not melt under normal food manufacturing conditions, and it is presumed that they can exert a better effect on improving peel durability than on improving the adhesive strength of the composite sheet surface. From the viewpoint of further improving the heat resistance of the composite sheet, the glass transition temperature of the polymer containing carbonyl groups is preferably above 50°C, more preferably above 75°C. There is no particular upper limit to the glass transition temperature of the polymer containing carbonyl groups, but it is preferably below 150°C, more preferably below 125°C.

[0015] Polymer F is a polymer containing TFE-based units (hereinafter also referred to as "TFE units"). From the viewpoint of appropriately presenting the properties produced by the TFE units, the content of TFE units in polymer F is preferably 90 to 98 mol% relative to the total number of units in polymer F. Polymer F preferably has thermal fusibility. Thermal fusibility refers to the property of having a melt flow rate of 1 to 1000 g / 10 minutes under a load of 49 N. In order to facilitate interaction with PTFE, further suppress the peeling of PTFE from the composite sheet, and further improve the heat resistance of the composite sheet, the fluorine content of the F polymer is preferably 70-76% by mass.

[0016] The carbonyl group is preferably a carboxyl group, alkoxycarbonyl group, amide group, isocyanate group, urethane group (-OC(O)NH2), acid anhydride residue (-C(O)OC(O)-), imide residue (-C(O)NHC(O)-, etc.) and carbonate group (-OC(O)O-), more preferably an acid anhydride residue. The polymer may also have oxygen-containing polar groups other than carbonyl groups. Examples of such oxygen-containing polar groups include hydroxyl groups and phosphonoyl groups.

[0017] The preferred number of carbonyl groups in polymer F is 1 × 10⁻⁶. 6The number of carbon atoms in the main chain ranges from 10 to 5000, more preferably from 100 to 3000. Furthermore, the number of carbonyl groups can be quantified according to the polymer composition or the method described in International Publication No. 2020 / 145133. The carbonyl group can be contained in the monomer-based unit of the F polymer or in the terminal group of the F polymer backbone, with the former being preferred. Examples of the latter include tetrafluoroethylene polymers having carbonyl groups as terminal groups derived from polymerization initiators, chain transfer agents, etc., and polymers obtained by plasma treatment or ionizing radiation treatment of tetrafluoroethylene polymers.

[0018] As monomers containing carbonyl groups, itaconic anhydride, citraconic anhydride and 5-norbornene-2,3-dicarboxylic anhydride (hereinafter also referred to as NAH) are preferred, and NAH is more preferred from the viewpoint of excellent adhesion of glass cloth.

[0019] The polymer F is preferably polytetrafluoroethylene (PTFE), a polymer containing TFE units and ethylene-based units (ETFE), a polymer containing TFE units and propylene-based units, a polymer containing TFE units and perfluoro(alkyl vinyl ether) (PAVE)-based units (PAVE units) (PFA), or a polymer containing TFE units and hexafluoropropylene-based units (FEP), more preferably PFA or FEP having carbonyl groups, and even more preferably PFA having carbonyl groups. These polymers may also contain units based on other comonomers.

[0020] The F polymer is preferably a polymer containing TFE units and PAVE units, having a carbonyl group; more preferably, it is a polymer containing TFE units, PAVE units, and units based on monomers having carbonyl groups; even more preferably, it is a polymer containing TFE units, PAVE units, and units based on monomers having carbonyl groups, and comprising, with respect to all units, 90-99 mol%, 0.99-9.97 mol%, and 0.01-3 mol% of these units in sequence. Specific examples of such an F polymer include the polymer described in International Publication No. 2018 / 16644.

[0021] In the dispersion, the polymer containing carbonyl groups is preferably contained in the form of particles with an average particle size (D50) of 0.03 μm to 200 μm, more preferably in the form of particles with an average particle size (D50) of 0.1 μm to 200 μm, and particularly preferably in the form of particles with an average particle size of 0.1 μm to 30 μm. Particles with the above-mentioned D50 exhibit excellent flowability and are easily and uniformly distributed on the surface of the glass cloth. Furthermore, they readily exhibit high levels of heat resistance and electrical properties.

[0022] When using F polymer particles (hereinafter also referred to as "F particles") as the carbonyl-containing polymer, the F particles are preferably composed mainly of F polymer. The content of F polymer in the F particles is preferably 80% by mass or more, more preferably 100% by mass.

[0023] When the dispersion contains a polymer having carbonyl groups, from the viewpoint of more effectively suppressing the peeling of the composite sheet from the substrate and the peeling of PTFE from the composite sheet, the content of the polymer having carbonyl groups relative to the total mass of the dispersion is preferably 1 to 30% by mass, more preferably 3 to 20% by mass, and even more preferably 5 to 15% by mass. When the dispersion contains a polymer having carbonyl groups, the ratio of the percentage of the polymer having carbonyl groups to the percentage of PTFE particles in the dispersion (percentage of the polymer having carbonyl groups / percentage of PTFE particles) is preferably 50 / 50 to 5 / 95 by mass, more preferably 40 / 60 to 10 / 90, and particularly preferably 30 / 70 to 15 / 85. When the dispersion contains a polymer with carbonyl groups, from the viewpoint of more effectively suppressing the peeling of the composite sheet from the substrate and the peeling of PTFE from the composite sheet, the ratio of the content of the polymer with carbonyl groups in the dispersion to the sum of the contents of PTFE particles and the polymer with carbonyl groups (content of polymer with carbonyl groups / sum of the contents of PTFE particles and the polymer with carbonyl groups) is preferably 1 / 100 to 100 to 100 by mass. Furthermore, from the viewpoint of more effectively suppressing the delamination of the composite sheet from the substrate and the delamination of PTFE from the composite sheet in the laminate, the sum of the contents of PTFE particles and polymers having carbonyl groups is preferably 10 to 65% by mass relative to the total mass of the dispersion, more preferably 20 to 60% by mass, and even more preferably 30 to 60% by mass.

[0024] The dispersion may contain a surfactant, thereby improving its dispersibility and workability. The surfactant is preferably a nonionic surfactant. The hydrophilic portion of the surfactant preferably has an alkylene group or an alcohol hydroxyl group. The hydrophobic portion of the surfactant preferably has an acetylene group, a polysiloxane group, or a fluorinated organic group (such as a perfluoroalkyl group). In other words, the surfactant is preferably an acetylene-based surfactant, a silicone-based surfactant, or a fluorinated surfactant, with silicone-based surfactants being more preferred. Examples of silicone-based surfactants include “BYK-347”, “BYK-349”, “BYK-378”, “BYK-3450”, “BYK-3451”, “BYK-3455”, “BYK-3456” (manufactured by BYK Chemicals Japan), “KF-6011”, and “KF-6043” (manufactured by Shin-Etsu Chemical Co., Ltd.). When the dispersion contains a surfactant, its content relative to the total mass of the dispersion is preferably 1 to 15% by mass.

[0025] The dispersion contains a liquid dispersion medium. In other words, the dispersion is a dispersion formed by dispersing PTFE particles in a liquid dispersion medium. A dispersion containing both PTFE particles and F particles can also be considered as a dispersion formed by dispersing PTFE particles and F particles in a liquid dispersion medium. In this dispersion, because the PTFE particles and F particles are highly and uniformly dispersed in the liquid, the above-mentioned mechanism of action is easily and clearly manifested. The boiling point of the liquid dispersion medium is preferably in the range of 50–240°C. One type of dispersion medium can be used alone, or two or more can be used in combination. When using two or more liquid dispersion media, it is preferable that the two or more liquid dispersion media are miscible with each other. Examples of suitable dispersion media include water, N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, N-methyl-2-pyrrolidone, γ-butyrolactone, cyclohexanone, cyclopentanone, butyl acetate, methyl isopropanone, methyl ethyl ketone, etc., with water being the preferred medium. The content of the liquid dispersion medium relative to the total mass of the dispersion is preferably 30-95% by mass, more preferably 35-90% by mass.

[0026] The dispersion may also contain polymers different from PTFE and polymers with carbonyl groups (hereinafter also referred to as "different polymers"). Different polymers may be thermosetting or thermoplastic. One or more different polymers may be used. As for different polymers, any polymer other than PTFE and polymers containing carbonyl groups is acceptable, without particular limitation. Examples include tetrafluoroethylene polymers, polyester resins (such as liquid crystal aromatic polyesters), polyimide resins, epoxy resins, maleimide resins, polyurethane resins, polyphenylene ether resins, polyphenylene ether resins, and polyphenylene sulfide resins. When the dispersion contains different polymers, the content of the polymer relative to the total mass of the dispersion is preferably 0.1 to 5% by mass.

[0027] In addition to the above-mentioned components, the dispersion may also contain thixotropic agents, pH adjusters, pH buffers, viscosity modifiers, defoamers, silane coupling agents, dehydrating agents, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, conductive agents, release agents, surface treatment agents, flame retardants, various inorganic fillers, various organic fillers, and other components, without impairing the effect of the manufacturing method of the composite sheet disclosed herein.

[0028] The viscosity of the dispersion is more preferably 75–10000 mPa·s. In this case, not only is the dispersibility excellent, but the workability and homogeneity of the dispersion on glass cloth are also easily improved. Moreover, the dispersion exhibits excellent miscibility with varnishes made from different types of resin materials. The thixotropic ratio of the dispersion is preferably 1.0 to 2.2, more preferably 1.5 to 2.0. In this case, the dispersibility is excellent, the workability is good, and the homogeneity of the dispersion on glass cloth is easily improved. Moreover, the dispersion has excellent miscibility with varnishes made from different types of resin materials. From the viewpoint of adjusting the viscosity or thixotropic ratio within the above range, the dispersion may contain viscosity modifiers or thixotropic modifiers, specifically vinyl alcohol polymers and cellulose ethers. Specific examples of vinyl alcohol polymers include the "S-LEC (registered trademark) B" series, the "S-LEC (registered trademark) K (KS)" series, the "S-LEC (registered trademark) SV" series (all manufactured by Sekisui Chemicals Co., Ltd.), and the "Mowital (registered trademark)" series (manufactured by Kuraray Co., Ltd.). Specific examples of cellulose ethers include the "SUNROSE (registered trademark)" series (manufactured by Nippon Paper Co., Ltd.), the "METOLOSE (registered trademark)" series (manufactured by Shin-Etsu Chemical Co., Ltd.), and "HEC CF grade" (manufactured by Sumitomo Seika Co., Ltd.). When the dispersion contains a viscosity modifier or a thixotropic modifier, its content relative to the total mass of the dispersion is preferably 0.01 to 5% by mass.

[0029] The dispersion can be manufactured by mixing PTFE, a polymer containing carbonyl groups, and a liquid dispersion medium. When the dispersion contains a liquid dispersion medium, the above mixing can be performed by adding each component together to the liquid dispersion medium or by adding each component sequentially. The mixing can be carried out in batches or continuously. Examples of devices that can be used for the above-mentioned mixing include agitators with blades (Henschel mixers, pressure kneaders, Banbury mixers, planetary mixers, etc.), pulverizers with media (ball mills, pulverizers, basket mills, sand mills, sand grinders, DYNO mills, DISPERMAT dispersers, SC mills, Spike mills, or stirred mills, etc.), and dispersion devices with other mechanisms (microfluidizers, nano-dispersers, Ultimaizer dispersers, ultrasonic homogenizers, dissolvers, dispersers, high-speed impeller dispersers, thin-film gyratory high-speed mixers, etc.).

[0030] In the method for manufacturing the composite sheet disclosed herein, the preparation of the dispersion on the glass cloth and the heating operation are performed more than twice, but from the viewpoint of further improving heat resistance, it is preferable to perform the operation 3 to 10 times, and more preferably 4 to 7 times. Examples of methods for preparing a dispersion on glass cloth include: a roller application method in which a portion of a roller is immersed in the dispersion to adhere it to the roller surface, and then the glass cloth is brought into contact with the roller to adhere the dispersion; a roller impregnation method in which the glass cloth is directly immersed in the dispersion, and then the amount of dispersion adhered is controlled by passing it through a clamping roller as needed; and a spraying method in which the dispersion is atomized and blown onto the glass cloth. Among the above methods, the roller impregnation method is preferred because it easily and uniformly imparts the dispersion. Furthermore, the roller impregnation method is also preferred because the amount of dispersion adhered to the glass cloth can be easily adjusted by using clamping rollers or similar devices. The preparation of the dispersion on the glass cloth can be carried out in batches or continuously, but from the viewpoint of easily suppressing uneven preparation of the dispersion on the glass cloth and improving productivity, continuous preparation is preferred.

[0031] From the viewpoint of suppressing the peeling of the composite sheet from the substrate and the peeling of PTFE from the composite sheet in the laminate, and improving heat resistance, it is preferable to perform the operation three or more times and to use the dispersion containing the above-mentioned polytetrafluoroethylene particles and at least one of the polymers having carbonyl groups and their precursors only in the first and last operations.

[0032] The amount of dispersion adhering to the glass cloth is preferably adjusted to be 0.1 to 10 parts by mass of the polymer containing carbonyl groups relative to 100 parts by mass of the heat-treated glass cloth, more preferably 0.2 to 5 parts by mass.

[0033] Heating of the dispersion disposed on the glass cloth preferably includes heating for sintering at least one of PTFE particles, a polymer having a carbonyl group, and a precursor of a polymer having a carbonyl group. Additionally, heating of the dispersion disposed on the glass cloth preferably includes heating for evaporating the liquid dispersion medium contained in the dispersion. The heat treatment for evaporating the liquid dispersion medium can be performed simply by keeping the glass cloth containing the dispersion above the evaporation temperature of the liquid dispersion medium to dry the liquid film disposed on the glass cloth. In the above heat treatment, it is not necessary to completely evaporate the liquid dispersion medium. Specifically, the amount of liquid dispersion medium to be evaporated is preferably 50% or more by mass of the liquid dispersion medium contained in the dispersion.

[0034] The heating treatment for evaporating liquid dispersion media can be carried out in one stage at a certain temperature, or in two or more stages at different temperatures. The preferred heating temperature is 50–280°C. The preferred heating time is 0.1–30 minutes.

[0035] Heating treatments used for firing can include methods such as using an oven, using a ventilated drying furnace, or irradiating with heat rays such as infrared rays. Alternatively, a combination of infrared heating and hot air heating can be used. Firing can be carried out under either atmospheric or reduced pressure. Furthermore, the firing atmosphere can be any of the following: an oxidizing gas atmosphere, a reducing gas atmosphere, or an inert gas atmosphere. When the dispersion contains a polymer with carbonyl groups, the firing temperature is preferably 300–350°C, more preferably 310–340°C. When the dispersion does not contain a polymer with carbonyl groups, the firing temperature is preferably 340–390°C, more preferably 350–380°C. The firing time is preferably 30 seconds to 30 minutes, more preferably 1 to 15 minutes. Herein, the firing temperature generally refers to the temperature of the drying atmosphere.

[0036] The preparation and heating of the dispersion on the glass cloth can be achieved using a device equipped with a dip-coating machine and a firing furnace. A vertical firing furnace can be used as an example. Alternatively, a glass cloth coating apparatus manufactured by Tabata Machinery Industry Co., Ltd. can be used as an example.

[0037] To improve affinity with polymers containing carbonyl groups, the glass cloth used in the manufacturing method of the composite sheet disclosed herein is preferably a glass cloth treated with a silane coupling agent. Examples of glass cloth materials include E-glass, C-glass, A-glass, S-glass, D-glass, NE-glass, L-glass, and low dielectric constant glass, but from the viewpoint of easy availability, E-glass, S-glass, and NE-glass are preferred. Glass cloth typically contains sizing agents; therefore, from the viewpoint of improving heat resistance, it is preferable to reduce the amount of sizing agent by heating before applying the dispersion to the glass cloth. Examples of sizing agents include: starches such as starch, processed starch, dextrin, and amylose; synthetic polymers such as carboxymethyl cellulose, polyvinyl alcohol, and acrylamide-vinyl acetate copolymer; and silane coupling agents.

[0038] The composite sheet can be used as antenna components, printed circuit boards, aircraft components, automotive components, sports equipment, food industry supplies, coatings, cosmetics, etc. Specifically, it can be used as wire coating materials (aircraft wires, etc.), electrical insulating tape, oil drilling insulating tape, printed circuit board materials, separation membranes (precision filtration membranes, ultrafiltration membranes, reverse osmosis membranes, ion exchange membranes, dialysis membranes, gas separation membranes, etc.), electrode adhesives (for lithium secondary batteries, fuel cells, etc.), photocopier rollers, covers for furniture, automotive dashboards, and household appliances, sliding parts (load bearings, sliding shafts, valves, bearings, gears, cams, belt conveyors, food conveyor belts, etc.), tools (shovels, files, chisels, saws, etc.), boilers, hoppers, pipes, ovens, baking molds, chutes, plastic molds, toilets, container coating materials, etc.

[0039] The method for manufacturing a laminate disclosed herein includes laminating a composite sheet manufactured by the method for manufacturing the composite sheet with a substrate. The laminate may comprise multiple composite sheets or multiple substrates. Examples of substrate materials include metal substrates (metal foils made of copper, nickel, aluminum, titanium, and their alloys), resin films (films made of polyimide, polyarylate, polysulfone, polyallyl sulfone, polyamide, polyetheramide, polyphenylene sulfide, polyallyl ether ketone, polyamide-imide, liquid crystal polyester, liquid crystal polyesteramide, etc.), and prepregs (precursors to fiber-reinforced resin substrates). Examples of substrate shapes include planar, curved, and uneven surfaces; furthermore, they can be any of the following: foil, plate, film, and fibrous.

[0040] The lamination of the composite sheet and the substrate can be performed by hot pressing them together, or by using conventional adhesives, but hot pressing is preferred. The hot pressing conditions are preferably varied according to the thickness of the laminate being manufactured, for example, a temperature of 170–450°C, a pressure of 1.5–5 MPa, and a time of 60–150 minutes.

[0041] The composite sheet of the present invention comprises a glass cloth and polytetrafluoroethylene supported on the glass cloth, and further comprises a polymer having carbonyl groups, wherein the polymer having carbonyl groups is concentrated on at least one of the surfaces of the glass cloth and the composite sheet. The composite sheet of this disclosure can be manufactured, for example, by the method for manufacturing the composite sheet. In the method for manufacturing the composite sheet, in at least one of the first and last operations, a dispersion containing a polymer having carbonyl groups is used for surface preparation and heating of the glass cloth, thus the polymer having carbonyl groups is concentrated on at least one of the surfaces of the glass cloth and the composite sheet. Details of glass cloth, polytetrafluoroethylene, polymers containing carbonyl groups, etc., are as described above, and therefore will not be described here.

[0042] The laminate disclosed herein comprises the aforementioned composite sheet and a substrate disposed on the surface of the composite sheet. The laminate disclosed herein may comprise two or more composite sheets, or two or more substrates. Details of the composite sheet and substrate are as described above, and therefore will not be elaborated upon here.

[0043] In the laminate disclosed herein, the peel strength of the composite sheet from the substrate is preferably 5 N / cm or more, and more preferably 10 N / cm or more. The peel strength was determined using the following method. First, the composite sheet was overlapped with an 18 μm thick copper foil and heat-pressed under vacuum at 380°C to create a laminate. The laminate was then cut into test pieces with a length of 100 mm and a width of 10 mm. The test piece was fixed at a position 50 mm away from one end along its length. Under a tensile speed of 50 mm / min and a peel angle of 90°, the composite sheet was peeled from the copper foil from the other end of the test piece. The maximum load (N / cm) during peeling was measured and taken as the peel strength. In the method for manufacturing the composite sheet, if a dispersion containing no carbonyl groups is used in the final step of applying the dispersion to the surface of the glass cloth and heating it, the resulting composite sheet will have a peel strength from the substrate of approximately 1 to 5 N / cm. When the peel strength of the composite sheet from the substrate is greater than 5 N / cm, it can be inferred that the polymer containing carbonyl groups is at least concentrated on the surface of the composite sheet. Example

[0044] The embodiments of this disclosure are described in detail below, but the embodiments of this disclosure are not limited thereto. <F particle> F particle 1: composed of 1 × 10⁻⁶ TFE units, NAH units, and PPVE units, respectively, containing 97.9 mol%, 0.1 mol%, and 2.0 mol% of TFE units, NAH units, and PPVE units. 6Particles composed of a polymer with 1000 carbon atoms in its main chain and carbonyl groups (melting temperature: 300℃) (D50: 2.1μm) F particle 2: Particles (D50: 2.0 μm) consisting of a polymer (melting temperature: 300 °C) containing 97.5 mol% and 2.5 mol% TFE units and PPVE units, without oxygen-containing polar groups. <Dispersion> Dispersion 1: An aqueous dispersion containing 60% by mass of non-thermally fusible PTFE particles (D50: 0.3 μm) (manufactured by AGC Corporation, “Product No. AD-915E”) <surfactants> Surfactant 1: Organosilicon surfactant <Glass cloth> Glass cloth 1: Manufactured by Nitto Boshoku Co., Ltd., E-glass IPC specification 1080 <Preparation of Dispersions> F particles 1, surfactant 1, and water were mixed to obtain a dispersion (40 parts by mass of F particles, 2.5 parts by mass of surfactant, and 57.5 parts by mass of water). Dispersion 1 was mixed with this dispersion to obtain dispersion A containing PTFE particles and F particles 1 at a ratio of 85:15 (mass basis, PTFE particles: F particles 1). F particles 2, surfactant 1, and water were mixed to obtain a dispersion (40 parts by mass of F particles, 2.5 parts by mass of surfactant, and 57.5 parts by mass of water). This dispersion 1 was then mixed with the dispersion to obtain dispersion B containing PTFE particles and F particles 2 at a ratio of 85:15 (mass basis, PTFE particles:F particles 2).

[0045] <Example 1> Glass cloth 1 was impregnated in dispersion A and dried in a drying oven at 120°C for 5 minutes. Then, it was fired in a far-infrared furnace at 340°C for 10 minutes. Next, the sintered glass cloth 1 is impregnated in dispersion 1 and dried in a drying oven at 120°C for 5 minutes. Then, it is sintered in a far-infrared furnace at 380°C for 10 minutes. The impregnation and heating in the dispersion 1 above were repeated a total of 5 times to prepare a composite sheet.

[0046] <Example 2> Glass cloth 1 is impregnated in dispersion 1 and dried in a drying oven at 120°C for 5 minutes. Then, it is fired in a far-infrared oven at 380°C for 10 minutes. The impregnation and heating of the above dispersion 1 were repeated a total of 5 times. Next, dispersion A is coated onto the surface of the glass cloth 1, which has been coated with dispersion 1 and heated, and then dried in a drying oven at 120°C for 5 minutes. Then, it is fired in a far-infrared furnace at 380°C for 10 minutes to produce a composite sheet.

[0047] <Example 3> Dispersion A is coated on one surface of glass cloth 1 and dried in a drying oven at 120°C for 5 minutes. Then, it is fired in a far-infrared oven at 340°C for 10 minutes. Next, the sintered glass cloth 1 is impregnated in dispersion 1 and dried in a drying oven at 120°C for 5 minutes. Then, it is sintered in a far-infrared oven at 380°C for 10 minutes. The impregnation and heating in the above dispersion 1 were repeated a total of 4 times. Next, the sintered glass cloth 1 is impregnated in dispersion A and dried in a drying oven at 120°C for 5 minutes. Then, it is sintered in a far-infrared furnace at 380°C for 10 minutes to produce a composite sheet.

[0048] <Example 4> Glass cloth 1 is impregnated in dispersion 1 and dried in a drying oven at 120°C for 5 minutes. Then, it is fired in a far-infrared furnace at 380°C for 10 minutes. The impregnation and heating in the above dispersion 1 were repeated a total of 6 times to prepare a composite sheet.

[0049] <Example 5> Glass cloth 1 was impregnated in dispersion A and dried in a drying oven at 120°C for 5 minutes. Then, it was fired in a far-infrared furnace at 340°C for 10 minutes. The impregnation and heating of the above dispersion A were repeated a total of 6 times to prepare a composite sheet.

[0050] <Example 6> Except for changing dispersion A to dispersion B, the composite tablets were prepared in the same manner as in Example 3.

[0051] <Evaluation of PTFE's exfoliation inhibition>> The composite sheets manufactured in Examples 1, 3 to 6 were placed in a furnace at 260°C for 10 seconds, left to stand, and then removed and cooled to 20°C. The above heating and cooling process was repeated 5 times. The surface of the composite sheet was then ground, and the surface of the composite sheet was visually observed. The evaluation was carried out according to the following evaluation criteria and summarized in Table 1. (Evaluation Criteria) A: No PTFE peeling from the composite sheet was observed. B: PTFE was observed to peel off from the composite sheet.

[0052] <Heat Resistance Evaluation> The composite sheets manufactured in Examples 1 to 6 were ground while being heated to 250°C. The surface of the ground composite sheets was visually observed, and the evaluation was carried out according to the following evaluation criteria, which are summarized in Table 1. In Table 1, "-" indicates that no evaluation was performed. The same applies to the following evaluations. (Evaluation Criteria) A: No scratches were observed or almost no scratches were observed on the surface of the composite sheet. B: Scratches were observed on the surface of the composite sheet.

[0053] <Evaluation of substrate peel resistance>> The composite sheets manufactured in Examples 2 to 6 were overlapped with copper foil with a thickness of 18 μm and hot-pressed under vacuum at 380°C to form a laminate. The laminate was cut into test pieces 100 mm long and 10 mm wide. The test pieces were fixed at a distance of 50 mm from one end along their length. Under a tensile speed of 50 mm / min and a peel angle of 90°, the composite sheet was peeled from the copper foil from the other end of the test piece. The maximum load (N / cm) during peeling was measured and evaluated according to the following criteria, summarized in Table 1. The maximum load is also summarized in Table 1. (Evaluation Criteria) A: The maximum load is above 10 N / cm. B: Maximum load is less than 10 N / cm.

[0054] <Peel Durability Test> Sugar was placed on the surface of the composite sheets manufactured in Examples 2 to 6, heated to 180°C, and then the heated sugar was peeled off. The heating and peeling of the sugar were repeated, and the number of times the sugar could no longer be peeled off was determined. The results were evaluated according to the following evaluation criteria and summarized in Table 1. (Evaluation Criteria) A: The heating and stripping of sugar can be repeated more than 10 times. B: The heating and stripping of sugar cannot be repeated 10 times.

[0055] Table 1

[0056] The entire publication of Japanese Patent Application 2022-013144, filed on January 31, 2022, is incorporated herein by reference. All documents, patent applications, and technical specifications described herein are incorporated by reference to the extent that each document, patent application, and technical specification is specifically and separately described as incorporated by reference.

Claims

1. A method for manufacturing a composite sheet, wherein, The process of preparing a dispersion of polytetrafluoroethylene particles on the surface of glass cloth and heating it is repeated 3 to 10 times. The dispersion containing at least one of a polymer having a carbonyl group and its precursor is used only in the first operation, only in the last operation, or only in the first and last operations, wherein the ratio of the content of the polymer in the dispersion to the sum of the content of the polytetrafluoroethylene particles and the polymer is 5 / 100 to 20 / 100 by mass.

2. The method for manufacturing the composite sheet as described in claim 1, wherein, The dispersion containing the polytetrafluoroethylene particles and at least one of the polymers having carbonyl groups and their precursors is used only in the first and last operations.

3. The method for manufacturing the composite sheet as described in claim 1 or claim 2, wherein, The polymer containing carbonyl groups is a thermomeltable tetrafluoroethylene-based polymer.

4. The method for manufacturing the composite sheet as described in claim 1 or claim 2, wherein, The polymer containing carbonyl groups is a thermomeltable polymer with a melting temperature above 200°C.

5. The method for manufacturing the composite sheet as described in claim 1 or claim 2, wherein, Heating of the dispersion includes heating for calcining at least one of the polytetrafluoroethylene particles, the polymer having carbonyl groups, and the precursor of the polymer having carbonyl groups.

6. The method for manufacturing the composite sheet as described in claim 1 or claim 2, wherein, The polymer containing carbonyl groups is contained in particles with an average particle size D50 of 0.03 μm to 200 μm.

7. A method for manufacturing a laminated body, wherein, The composite sheet manufactured by the method of manufacturing the composite sheet according to claim 1 or claim 2 is laminated with a substrate.

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