Sheet, substrate for printed circuit boards, and method for producing sheet

Abstract

To provide a sheet that exhibits superior thermal stability (low thermal expandability), and also demonstrates superior elongation properties.SOLUTION: A sheet includes the following components (A)-(B), the sheet having an elongation rate at break exceeding 150%: (A) a fluororesin; and (B) a filler having an average particle size of 20% or less relative to a predetermined thickness of the sheet.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a sheet, a base material for printed circuit boards, and a method for producing the sheet. [Background technology]

[0002] Fluorine resins are synthetic resins that have excellent heat resistance, electrical insulation, non-stickiness, and weather resistance. Fluorine resin sheets formed into sheets are widely used in industrial fields such as chemical materials, electrical and electronic parts, semiconductors, and automobiles. In relation to these applications, various properties such as electrical properties and thermal properties of fluororesin sheets may be insufficient, and therefore, in order to improve these properties, fluororesin is mixed with a filler and used (Patent Documents 1 to 4).

[0003] As an application example of synthetic resins such as fluororesins, for example, their use as release sheets taking advantage of their non-adhesive and excellent releasability properties is known. However, since commonly used fluororesins (such as polytetrafluoroethylene (hereinafter referred to as PTFE)) have a relatively large thermal expansion coefficient, when used as release sheets, they have poor thermal stability and may cause problems such as dimensional differences with the object to be released during heating. For this reason, in order to suppress the thermal expansion of fluororesin sheets such as PTFE, a filler is blended into the sheet. For example, Patent Document 2 shows that the thermal expansion coefficient of the sheet obtained after molding is reduced by using a PTFE composition obtained by mixing PTFE resin and ceramic powder in a specified manner.

[0004] On the other hand, in a fluororesin sheet in which a filler is blended with a fluororesin, if the thickness of the sheet is small, through holes (pinholes) tend to easily occur, and the elongation properties of the sheet tend to be easily reduced. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 031071 [Patent Document 2] Special Publication No. 2022-510017 [Patent Document 3] Patent No. 2557248 [Patent Document 4] Japanese Patent Application Publication No. 10-17838 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to solve the above problems, the inventors attempted to suppress the occurrence of pinholes and the deterioration of elongation properties by using a filler with a smaller particle size to be mixed into the fluororesin sheet, but were unable to solve these problems.

[0007] An object of the present invention is to provide a sheet having excellent thermal stability (low thermal expansion) and excellent elongation properties. [Means for solving the problem]

[0008] According to the present invention, the following sheets etc. are provided. 1. A sheet comprising the following components (A) and (B), the sheet having a breaking elongation of more than 150%: (A) Fluorine resin (B) a filler having an average particle size of 20% or less of the predetermined thickness of the sheet; 2. The sheet according to 1, wherein the predetermined thickness of the sheet is 25 to 300 μm. 3. The sheet according to 1 or 2, wherein the average particle size of the filler is 0.1 to 10 μm. 4. The sheet according to any one of 1 to 3, wherein the blending ratio of the filler is 20 to 50 volume %. 5. The sheet according to any one of 1 to 4, wherein the fluororesin is polytetrafluoroethylene (PTFE) or modified PTFE. 6. The sheet according to any one of 1 to 5, wherein the filler is one or more selected from the group consisting of alumina, titanium oxide, silica, barium sulfate, silicon carbide, boron nitride, silicon nitride, glass fiber, glass beads, and mica. 7. The sheet according to any one of 1 to 6, wherein the sheet has a thermal expansion coefficient of less than 100 ppm / °C. 8. The number of through holes with a diameter of 50 μm or more present in the sheet is 2 8. The sheet according to any one of 1 to 7, wherein the number of particles per unit area is 25 or less. 9. A substrate for printed circuit boards comprising the sheet according to any one of 1 to 8. 10. A step of preparing a raw material composition by mixing the following components (A') to (B): A step of forming a cylindrical compact from the raw material composition; sintering the molded body; and skiving the surface of the fired molded body to form it into a sheet. (A') a fluororesin having an average particle size of 50% or less of the predetermined thickness of the sheet; (B) a filler having an average particle size of 20% or less of the predetermined thickness of the sheet; 11. The method for producing a sheet according to 10, wherein the sheet has a predetermined thickness of 25 to 300 μm. 12. The method for producing a sheet according to 10 or 11, wherein the average particle diameter of the fluororesin particles is 0.1 to 10 μm. 13. The method for producing a sheet according to any one of 10 to 12, wherein the average particle size of the filler is 0.1 to 10 μm. 14. The method for producing a sheet according to any one of 10 to 13, wherein the mixing ratio of the filler is 20 to 50 volume %. 15. A method for producing a sheet according to any one of 10 to 14, wherein the step of preparing the raw material composition comprises removing the solvent from a raw material-containing solution in which (A') a fluororesin having an average particle size of 50% or less of the specified thickness of the sheet and (B) a filler having an average particle size of 20% or less of the specified thickness of the sheet are dispersed in a solvent. 16. A method for producing a sheet according to any one of 10 to 14, wherein the step of preparing the raw material composition is a step of dry-mixing (A') a fluororesin having an average particle size of 50% or less of the specified thickness of the sheet, and (B) a filler having an average particle size of 20% or less of the specified thickness of the sheet. 17. A sheet obtained by the manufacturing method according to any one of 10 to 16. Effect of the Invention

[0009] According to the present invention, a sheet having excellent thermal stability (low thermal expansion) and excellent elongation properties can be provided. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic diagram illustrating a method for preparing a raw material composition in a conventional sheet manufacturing method. [Diagram 2] FIG. 2 is a schematic diagram illustrating a method for preparing a raw material composition in the sheet manufacturing method of the present invention. [Diagram 3] FIG. 2 is a diagram showing a skiving process in which the outer peripheral surface in the longitudinal direction of a sintered compact (billet) is cut into a sheet shape. [Figure 4] FIG. 13 is a diagram showing the results of elemental mapping analysis of the sheet of Example 2. [Diagram 5] FIG. 2 is a diagram showing the results of elemental mapping analysis of the sheet of Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The sheet and the method for manufacturing the sheet according to the present invention will be described below. In this specification, "x to y" represents a numerical range of "not less than x and not more than y". When there are multiple lower limit values ​​such as "not less than x" for one technical matter, or multiple upper limit values ​​such as "not more than y" for one technical matter, any combination of the upper limit values ​​and the lower limit values ​​may be selected.

[0012] Sheet A sheet according to one aspect of the present invention is a sheet containing the following components (A) and (B), and the sheet has a breaking elongation of more than 150%. (A) Fluorine resin (B) a filler having an average particle size of 20% or less of the predetermined thickness of the sheet; A sheet has one flat surface and the other flat surface, regardless of thickness, and can be configured in a belt-like, flat plate-like shape, etc., and includes, for example, a film and a tape.

[0013] The present inventors have found that, when a filler is blended into a sheet containing a fluororesin, the thermal expansion coefficient of the sheet is kept low. However, when coarse particles having a particle diameter close to the desired thickness of the sheet are present in the raw material composition, when a molded product made from the raw material composition is skived into a thin sheet of about 100 μm, through holes (pinholes) are generated in the sheet, making it prone to breakage due to the through holes and reducing the elongation properties. The present inventors have also found the following. That is, if there is a large difference between the particle size of the filler 51 in the raw material composition for producing the sheet and the particle size of the raw material fluororesin particles 50 (see FIG. 1(a)), as the amount of the filler 51 increases, the small particle size filler 51 penetrates into the gaps between the large particle size fluororesin particles 50 in the raw material composition, and the filler 51 aggregates between the fluororesin particles 50, and aggregates of the filler 51 having a particle size increased to a size close to the thickness of the target sheet are easily generated (see FIG. 1(b)). When the raw material composition containing this aggregate is fired, the fluororesin particles 50 melt and become an integrated matrix, but the aggregates of the filler 51 remain as they are. As a result, it was found that when the fired molded body is skived and molded into a thin sheet of about 100 μm, the presence of the aggregates of the filler 51 in the molded body causes through holes (pinholes) to occur in the sheet. Skiving refers to a method of cutting out a thin, continuous sheet 30 by applying a cutting blade 20 to the surface of a billet 10, which is a sintered compression molded body of resin powder, while rotating the billet 10, as shown in FIG. 3.

[0014] The sheet of this embodiment contains a filler, so that the thermal expansion coefficient is kept low and the sheet has excellent thermal stability. In addition, the sheet of this embodiment has excellent elongation characteristics because the breaking elongation percentage is more than 150%. As a result, the sheet of this embodiment has high thermal stability (low thermal expansion) and high elongation characteristics. The sheet of this embodiment can be obtained by mixing the filler 51 having the above-mentioned predetermined particle diameter and the fluororesin particles 50' reduced in size to the same extent as the particle diameter of the filler 51 as a raw material, and using a raw material composition (see FIG. 2(b)) in which the fluororesin particles 50' and the filler 51 are uniformly dispersed. Since the fluororesin particles 50' and the filler 51 are uniformly dispersed in the raw material composition, even if the amount of the filler is increased, the phenomenon in which the filler 51 penetrates into the gaps between the fluororesin particles 50' and aggregates are generated (state of FIG. 1(b)) can be suppressed. By suppressing the generation of aggregates, the generation of through holes (pinholes) is suppressed in a thin sheet obtained by skiving a molded body obtained by sintering the raw material composition. Therefore, the sheet obtained by skiving has high thermal stability (low thermal expansion) and high elongation properties. A method for reducing the particle size of the fluororesin particles 50' to approximately the same as the particle size of the filler 51 will be described in detail in the sheet manufacturing method.

[0015] (Fluorine resin) As the fluororesin, any commonly used fluororesin can be used without any particular limitation, but polytetrafluoroethylene (PTFE) is preferred. Polytetrafluoroethylene (PTFE) is a homopolymer of tetrafluoroethylene.

[0016] Furthermore, modified polytetrafluoroethylene (modified PTFE) may be used as the fluororesin. Modified polytetrafluoroethylene (modified PTFE) is polytetrafluoroethylene modified with perfluoroalkyl vinyl ether. The perfluoroalkyl vinyl ether may be represented by the following formula (1). CF2=CF-OR f (1) (In formula (1), R f is a perfluoroalkyl group having 1 to 10 carbon atoms (preferably 1 to 5 carbon atoms), or a perfluoroorganic group represented by the following formula (2): [ka]

[0017] (In formula (2), n is an integer of 1 to 4.)

[0018] Examples of the perfluoroalkyl group having 1 to 10 carbon atoms in the formula (1) include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group, and preferably a perfluoropropyl group.

[0019] The content of the fluororesin in the sheet may be 50 vol% or more, 60 vol% or more, or 70 vol% or more, and may be 80 vol% or less, 70 vol% or less, or 60 vol% or less. When the content of the fluororesin is equal to or greater than the lower limit, the sheet has good strength. Furthermore, if the content of the fluororesin is equal to or less than the upper limit, the filler contained in the sheet keeps the coefficient of thermal expansion low, and excellent thermal stability is obtained.

[0020] (filling material) The sheet of this embodiment contains a filler, such as alumina, titanium oxide, silica, barium sulfate, silicon carbide, boron nitride, silicon nitride, glass fiber, glass beads, or mica. As the filler, silica, boron nitride, and alumina can be suitably used from the viewpoint of imparting high thermal stability (low thermal expansion) to the sheet. These fillers can be used alone or in combination of two or more.

[0021] The content of the filler in the sheet is preferably 20% by volume or more, and may be 25% by mass or more, or may be 30% by mass or more. In addition, the content of the filler in the sheet is preferably 50% by volume or less, and may be 48% by mass or less, 45% by mass or less, 40% by mass or less, or 30% by mass or less. When the content of the filler in the sheet is equal to or more than the lower limit, the thermal expansion coefficient of the sheet is suppressed to a small value, for example, equal to or less than 100 ppm / ° C., and the sheet has excellent thermal stability. When the content of the filler in the sheet is equal to or less than the upper limit, the sheet can maintain sufficient strength and has good handleability.

[0022] The average particle size of the filler is 20% or less of the predetermined thickness of the sheet. If the average particle size of the filler particles is within the above range, it can contribute to suppressing the occurrence of pinholes. The average particle size of the filler may be 18% or less, 15% or less, 12% or less, 10% or less, 8% or less, or 5% or less of the predetermined thickness of the sheet. The specific thickness of the sheet will be described later.

[0023] The average particle size of the filler may be appropriately selected depending on the desired sheet thickness, and is preferably 0.1 μm or more, and may be 0.2 μm or more, 0.3 μm or more, 0.5 μm or more, or 1 μm or more. The average particle size of the filler is preferably 10 μm or less, and may be 9 μm or less, 8 μm or less, 5 μm or less, or 3 μm or less. The average particle size of the filler is preferably 0.1 μm or more and 10 μm or less. By having the average particle size of the filler within the above range, aggregation between the filler particles can be suppressed and the proportion of coarse particles can be reduced, thereby suppressing the occurrence of through holes (pinholes) in the sheet and obtaining excellent elongation properties.

[0024] In this specification, the average particle diameter of the filler contained in the sheet is determined by measuring the particle diameter (diameter or longest diameter) of each of 100 arbitrarily selected filler particles in a scanning electron microscope image obtained by observing the surface of the sheet over an area of ​​100 μm horizontal × 100 μm vertical with a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, “SU8220”) at an acceleration voltage of 5 kV and a magnification of 1000 times, and taking the arithmetic mean value thereof.

[0025] (optional ingredient) In one embodiment, the sheet may further include optional components, including, but not limited to, a flame retardant, a flame retardant assistant, a pigment, an antioxidant, a reflecting agent, an opacifying agent, a lubricant, a processing stabilizer, a plasticizer, a foaming agent, and the like. In this case, the total content of the optional components in the sheet may be 20% by mass or less, 10% by mass or less, or 5% by mass or less.

[0026] In one embodiment, the sheet is, for example, 85% by weight or more, 90% by weight or more, 95% by weight or more, 98% by weight or more, 99% by weight or more, 99.5% by weight or more, 99.9% by weight or more, or 100% by weight Polytetrafluoroethylene or modified polytetrafluoroethylene; and one or more fillers selected from alumina, titanium oxide, silica, glass fibers, glass beads, and mica.

[0027] (Sheet characteristics) The sheet according to one aspect of the present invention has a predetermined thickness, and the thickness is preferably in the range of 25 to 300 μm. A method capable of producing a sheet having such a thickness and mainly composed of a fluororesin and a filler is skive processing. Details of the skive processing and the method of producing the sheet according to one aspect of the present invention will be described later. Known methods for manufacturing a single sheet whose main components are fluororesin and filler include coating, extrusion molding, rolling, etc. However, when manufacturing a sheet by coating, for example, the sheet thickness is generally limited to 25 μm, and if it is attempted to make the sheet thicker than that, multiple coats are required, which makes the process complicated. Furthermore, when a sheet is produced by a method using extrusion molding or rolling, the thickness of the obtained sheet is usually as large as 1 mm, and it is difficult to obtain a sheet having a thickness of 25 to 300 μm by the method using extrusion molding or rolling.

[0028] The thickness of the sheet is preferably 25 μm or more, and may be 30 μm or more, 50 μm or more, 70 μm or more, or 100 μm or more, and the thickness of the sheet is preferably 300 μm or less, and may be 200 μm or less, 150 μm or less, or 100 μm or less. When the sheet has a thickness of 25 μm or more, the sheet can maintain sufficient strength and has good handleability. Furthermore, when the sheet has a thickness of 300 μm or less, sufficient flexibility is obtained. In this specification, the "thickness of a sheet" means the average value of thicknesses measured at any ten points on the sheet.

[0029] In one embodiment, the sheet has an elongation at break of greater than 150%, optionally 152% or more, optionally 200% or more, optionally 300% or more, optionally 350% or more, or optionally 380% or more. The breaking elongation is measured by the method described in the Examples.

[0030] In one embodiment, the thermal expansion coefficient of the sheet may be less than 100 ppm / °C, may be 40 ppm / °C or more and 90 ppm / °C or less, may be 50 ppm / °C or more and 80 ppm / °C or less, or may be 60 ppm / °C or more and 70 ppm / °C or less. The thermal expansion coefficient is measured by the method described in the examples.

[0031] In one embodiment, the number of through holes (pinholes) with a diameter of 50 μm or more present in the sheet is 2 Preferably, there are 25 or less per unit area, more preferably 20 or less, even more preferably 15 or less, 10 or less, even more preferably 5 or less, and desirably 0. The number of through holes (pinholes) is measured by the method described in the Examples.

[0032] [Printed circuit board substrates] A substrate for printed circuit boards according to an embodiment of the present invention includes the sheet according to the embodiment of the present invention. Because fluororesin has excellent heat resistance and insulation properties, it is expected to be used as a heat-resistant material such as heat-resistant insulating tape and as a material for printed circuit boards. However, conventional fluororesin sheets manufactured by skiving are prone to thermal shrinkage when heated and have poor dimensional stability, which makes them difficult to process, for example, by joining with other materials. In contrast, a sheet according to one embodiment of the present invention has filler particles uniformly dispersed in a fluororesin matrix, thereby suppressing thermal shrinkage and improving dimensional stability, and has the advantage of being easier to process, such as by bonding with other materials, than conventional fluororesin sheets. An example of a substrate for a printed circuit board using the sheet according to one embodiment of the present invention is one in which a metal foil such as a copper foil is laminated on the sheet.

[0033] [Sheet manufacturing method] A method for producing a sheet according to one embodiment of the present invention includes the following steps (1) to (4): (1) The following components (A') to (B) (A') a fluororesin having an average particle size of 50% or less of the predetermined thickness of the sheet; (B) a filler having an average particle size of 20% or less of the predetermined thickness of the sheet; A step of preparing a raw material composition by mixing the above. (2) A step of forming a cylindrical compact from the raw material composition (3) Firing the molded body (4) A process of performing a skiving process in which the surface of the sintered compact is cut to form a sheet.

[0034] (Step (1) Preparation of raw material composition) As the fluororesin of component (A'), the fluororesin of component (A) explained in the section on the sheet above can be used.

[0035] The fluororesin used as a raw material has a particulate shape, and its average particle size is 50% or less of the predetermined thickness of the sheet, and may be appropriately selected according to the desired sheet thickness. The average particle size of the fluororesin particles is preferably 0.1 to 10 μm. By using fluororesin particles having an average particle size within the above range, a raw material composition in which the filler particles and fluororesin particles are uniformly dispersed can be obtained. The average particle size of the fluororesin particles may be 0.1 μm or more, 0.2 μm or more, 1 μm or more, or 5 μm or more. The average particle size of the fluororesin particles may be 10 μm or less, or may be 5 μm or less.

[0036] Examples of methods for making the average particle size of the fluororesin particles 50% or less of the predetermined thickness of the sheet, preferably within the range of 0.1 to 10 μm, include a method using a commercially available fluororesin particle dispersion (generally having an average particle size in the range of 0.1 to 0.5 μm) in which fluororesin particles are dispersed in a solvent, and a method in which commercially available powder-shaped fluororesin particles (generally having an average particle size in the range of 200 to 600 μm) are pulverized to the above average particle size. Details of the process using the fluororesin particles obtained by the above two methods will be described later.

[0037] In this specification, the average particle size of the fluororesin particles used to prepare the raw material composition can be measured using a particle size distribution measuring device (manufactured by Spectris Inc., "MS-3000") under the condition of a measurement air pressure of 1 Bar.

[0038] As the filler of component (B), the fillers explained in the above section on sheets can be used. The filler has a particle shape, and the preferred range of the average particle size and the reasons therefor are the same as those explained in the section on the sheet above for the preferred range of the average particle size of the filler particles and the reasons therefor. The average particle size of the filler particles used in preparing the raw material composition can be measured by the same method as for the average particle size of the fluororesin particles.

[0039] One embodiment of the method for obtaining a raw material composition by mixing component (A') and component (B) includes a method in which the solvent is removed from a raw material-containing solution in which component (A') and component (B) are dispersed in a solvent, and the resulting mixed powder is stirred and mixed with a bladed stirrer or the like.

[0040] An example of the raw material-containing solution is a dispersion in which particles of a fluororesin (e.g., PTFE) are produced in a solvent by emulsion polymerization or the like and dispersed in the solvent, and component (B) is added thereto, followed by stirring and mixing with a stirrer or the like. In this case, the fluororesin particles dispersed in the dispersion medium correspond to component (A') (fluororesin particles having an average particle size of 50% or less of the predetermined thickness of the sheet).

[0041] The raw material-containing solution is not limited to those described above, and may be, for example, a dispersion obtained by separating fluororesin particles (component (A')) produced by emulsion polymerization or the like from the solvent used in the polymerization, dispersing the particles in a different solvent, and then adding component (B) to the dispersion.

[0042] The solvent used in the dispersion is not particularly limited, but examples thereof include methyl ethyl ketone, water, and the like.

[0043] The amount of component (B) to be mixed in the dispersion is mixed so that the content of component (A') and the content of component (B) contained in the raw material composition obtained from the raw material-containing solution are each in the desired ratio. The preferred range of the content of component (A') contained in the raw material composition is the same as the preferred range of the content of component (A) explained in the above-mentioned sheet section. In addition, the preferred range of the content of component (B) contained in the raw material composition is the same as the preferred range of the content of component (B) explained in the above-mentioned sheet section.

[0044] The stirring speed of the dispersion to which component (B) has been added is not particularly limited, and may be, for example, 100 to 800 rpm, or 200 to 600 rpm. The stirring time for the dispersion to which component (B) has been added is not particularly limited, but may be, for example, 1 to 20 minutes, or 2 to 18 minutes.

[0045] The method for removing the solvent from the raw material-containing solution is not particularly limited. For example, the solvent can be removed by precipitating component (A') and component (B) contained in the raw material-containing solution by coprecipitation or the like to separate them from the raw material-containing solution, and then drying them in a drying oven or the like to volatilize and remove the solvent component contained in the precipitate.

[0046] When the precipitate is dried in a drying oven or the like, the drying temperature may be, for example, 60 to 400°C, or 80 to 300°C.

[0047] The stirring speed when the mixed powder of component (A') and component (B) obtained after drying is stirred and mixed using a bladed stirrer or the like is not particularly limited, and may be, for example, 1000 to 6000 rpm or 2000 to 5000 rpm. The stirring time for the mixed powder obtained after drying is not particularly limited, but may be, for example, 1 to 15 minutes, or 2 to 10 minutes.

[0048] As one embodiment of the method for obtaining a raw material composition by mixing component (A') (fluororesin particles having an average particle size of 50% or less of the predetermined thickness of the sheet) and component (B) (filler particles having an average particle size of 20% or less of the predetermined thickness of the sheet), for example, a method of dry mixing component (A') and component (B) may be used.

[0049] Examples of the method for mixing component (A') and component (B) include a method in which secondary particles formed by agglomeration of primary particles of a fluororesin are crushed to obtain a fluororesin (component (A')) having an average particle size of 0.1 to 10 μm, and then component (A') and component (B) are stirred and mixed using a bladed stirrer or the like.

[0050] The particle size of the secondary particles of the fluororesin is not particularly limited, and may be, for example, 100 to 800 μm, 130 to 700 μm, or 150 to 600 μm. The method for crushing the secondary particles is not particularly limited, but examples thereof include a method using a crusher such as a mixer crusher, an airflow crusher, or a freeze crusher.

[0051] The components (A') and (B) are mixed so that the content of the component (A') and the content of the component (B) contained in the raw material composition are in the desired ratio. The preferred range of the content of the component (A') contained in the raw material composition is the same as the preferred range of the content of the component (A) explained in the above-mentioned sheet section. The preferred range of the content of the component (B) contained in the raw material composition is the same as the preferred range of the content of the component (B) explained in the above-mentioned sheet section.

[0052] The stirring speed of component (A') and component (B) in dry mixing is not particularly limited, and may be, for example, 1000 to 6000 rpm, or 2000 to 5000 rpm. The stirring time for component (A') and component (B) in the dry mixing is not particularly limited, but may be, for example, 1 to 15 minutes, or may be 2 to 10 minutes.

[0053] In addition to the component (A') and the component (B), the raw material composition may contain optional components. As the optional components, the optional components described in the above-mentioned sheet section can be used. The preferred range of the amount of the optional components to be blended can be the same as the preferred range of the content of the optional components described above in the section on the sheet.

[0054] (Step (2) Formation of Molded Body) The raw material composition is molded into a cylindrical shape to form a molded body. Examples of a method for forming a molded body include a method in which the raw material composition is filled into a mold and compression molded to form a cylindrical compression molded body. The surface pressure may be 10 to 100 MPa, 20 to 60 MPa, or 30 to 50 MPa. By compression molding the raw material composition obtained by mixing component (A') and component (B), a compression molded product in which the fluororesin particles and filler are uniformly dispersed can be obtained (see FIG. 2(b)).

[0055] (Step (3) Firing of the molded body) The compression molded body thus obtained is sintered to obtain a billet. The sintering temperature may be 100 to 400°C, 350 to 370°C, or 360 to 370°C. The resulting billet is a compact formed by accumulating the sintered raw material powder. By firing the molded body, the individual fluororesin particles in the molded body are melted and integrated into a matrix in which the filler particles are uniformly dispersed. By sintering a compression-molded body of a raw material composition obtained by mixing component (A') and component (B), it is possible to suppress the generation of agglomerates of the filler, and to obtain a good billet with few coarse particles.

[0056] From the viewpoint of ease of carrying out the skiving process described later, the billet (molded body) is preferably cylindrical in shape. When the billet (molded body) is a cylinder, the diameter of the cylinder may be, for example, 100 to 500 mm, or 150 to 500 mm.

[0057] (Step (4) Sheet formation by skiving) Next, a skiving process is performed in which the surface of the billet, which is the sintered compact, is cut into a sheet shape. As shown in FIG. 3, when the billet (formed body) is a cylinder, a cutting blade is applied to the outer circumferential surface in the longitudinal direction of the sintered cylinder to cut it into a sheet.

[0058] As described above, the billet obtained using the raw material composition obtained by mixing component (A') and component (B) is a good billet with few coarse particles formed by agglomeration of filler particles. Therefore, by skiving the billet, the occurrence of through holes (pinholes) is suppressed, and a sheet with excellent elongation properties is obtained.

[0059] When the billet (molded body) is a cylinder, before carrying out the process of cutting the longitudinal outer peripheral surface of the sintered cylinder into a sheet, the outer peripheral surface, inner peripheral surface and end surface of the sintered cylinder may each be removed to a thickness of up to 3 mm from the outside of the surface.

[0060] The skiving process, in which the longitudinal outer peripheral surface of the fired cylinder is cut into a sheet, can be carried out using an apparatus as shown in Fig. 3. The thickness of the sheet obtained by cutting may be appropriately selected according to the intended use of the sheet, and may be, for example, 25 µm or more, 30 µm or more, 50 µm or more, 70 µm or more, or 100 µm or more. The thickness of the sheet obtained by cutting may be, for example, 300 µm or less, 200 µm or less, 150 µm or less, or 100 µm or less. In FIG. 3, a sintered billet (cylinder) 10 is rotated and cut into a sheet 30 by a cutting blade (bite) 20 .

[0061] The billet obtained through the above-mentioned steps (1) to (3) is skived to obtain a sheet having a thickness of 25 to 300 μm.

[0062] The sheet of this embodiment described above is suitably used, for example, as a heat-resistant material such as a heat-resistant insulating tape, a substrate for a printed circuit board, a printed circuit board, or a release sheet. EXAMPLES

[0063] (Preparation of raw material composition) Manufacturing Example 1 A PTFE dispersion (a dispersion liquid in which PTFE particles are dispersed in a solvent) and spherical silica (average particle diameter 1 μm) as a filler were mixed so that the volume ratio of the PTFE particles and spherical silica contained in the PTFE dispersion was PTFE particles:spherical silica = 6:4, and the mixture was stirred and mixed using a stirrer at a rotation speed of 300 to 500 rpm for 5 to 15 minutes to obtain a raw material-containing solution.

[0064] While stirring the raw material-containing solution with a stirrer, ethanol was further added to the raw material-containing solution to co-precipitate the PTFE particles and spherical silica. The coprecipitate was dried in a drying oven at 100°C to 200°C to volatilize and remove the solvent, thereby obtaining a dry powder.

[0065] The obtained dry powder was mixed for 0.5 to 1 minute at a rotation speed of 3000 to 4000 rpm using a stirrer with rotating blades to obtain raw material composition 1 containing PTFE powder (average particle size: 0.25 μm) and spherical silica (average particle size: 1 μm).

[0066] Manufacturing Example 2 Polytetrafluoroethylene (PTFE) powder (average particle size: 400 μm) was crushed to obtain PTFE powder with an average particle size of 5 μm.

[0067] The PTFE powder having an average particle diameter of 5 μm obtained above and spherical silica (average particle diameter: 3 μm) as a filler were mixed in a volume ratio of PTFE powder:spherical silica = 6:4, and mixed for 3 to 7 minutes at a rotation speed of 3000 to 4000 rpm using a rotary blade mixer to obtain raw material composition 2 containing PTFE powder (average particle diameter: 5 μm) and spherical silica (average particle diameter: 3 μm).

[0068] Production Example 3 PTFE powder (average particle diameter: 400 μm) and spherical silica (average particle diameter: 1 μm) as a filler were mixed in a volume ratio of PTFE powder:spherical silica = 6:4, and mixed for 3 to 7 minutes at a rotation speed of 3000 to 4000 rpm using a rotor blade mixer to obtain raw material composition 3 containing PTFE powder (average particle diameter: 400 μm) and spherical silica (average particle diameter: 1 μm).

[0069] Example 1 <Billet Production> 600 g of the raw material composition 1 was filled into a cylindrical mold and compression molded from above at a pressure of 30 MPa for 3 minutes to obtain a cylindrical preform (outer diameter 67 mm × inner diameter 33 mm). The obtained preform was placed in a firing furnace and fired at 365°C for 6 hours.

[0070] <Skib processing> The obtained cylindrical fired body (outer diameter 67 mm × inner diameter 33 mm) was skived with the device shown in Figure 3 at a cutting speed of 8 m / min and a target thickness of 100 μm to produce a 100 μm thick sheet.

[0071] Example 2 A sheet was produced in the same manner as in Example 1, except that raw material composition 2 was used instead of raw material composition 1.

[0072] Comparative Example 1 A sheet was produced in the same manner as in Example 1, except that raw material composition 3 was used instead of raw material composition 1.

[0073] Reference example 1 A PTFE sheet containing no filler ("TOMBONo9001", manufactured by Nichias Corporation) was prepared.

[0074] [Evaluation method] (Dispersion state of filler) Elemental mapping analysis was performed on arbitrary surface regions of the sheets obtained in Example 2 and Comparative Example 1 using an energy dispersive X-ray analyzer (manufactured by Horiba, Ltd., "E-Max N") at an acceleration voltage of 15 kV. The results of elemental mapping analysis of the sheets of Example 2 and Comparative Example 1 are shown in FIG. 4 and FIG. 5, respectively.

[0075] From the results of elemental mapping analysis shown in FIG. 4, it was confirmed that the sheet obtained in Example 2 had spherical silica Si (black parts) uniformly dispersed in the PTFE resin (gray parts). On the other hand, from the results of the elemental mapping analysis shown in FIG. 5, it was confirmed that the sheet obtained in Comparative Example 1 contained aggregates Si (black parts) in which spherical silica Si (black parts) aggregated in the PTFE resin (gray parts), and that through holes (pinholes) (parts surrounded by dashed lines) were generated during the skive processing.

[0076] (Number of through holes (pinholes)) The sheets obtained in Examples 1 and 2 and Comparative Example 1 were each measured from an arbitrary position (for example, a middle position in the short direction of a long sheet excluding the ends in the long direction, or a central portion of the sheet) with a surface area of ​​100 cm 2 The samples were collected for counting the through holes (pinholes), and were observed under magnification using a microscope (Keyence Corporation, "VHX-5000") to count the number of through holes (pinholes) with a maximum diameter of 50 μm or more. The results are shown in Table 1.

[0077] (Elongation at break) From the sheets obtained in Examples 1 and 2 and Comparative Example 1, samples for measuring elongation at break were taken so that the width of the measurement site was 10 mm, and the distance between chucks (distance between gauge marks) L0 was 22.25 mm. Using a tensile tester (manufactured by Shimadzu Corporation, "Ez-LX"), the sheets were pulled at a pulling speed of 200 mm / min until breakage in an environment of 23°C and 50% RHn, and the elongation at break was calculated from the distance between the gauge marks at breakage, L1 (mm), according to the following formula (3). The results are shown in Table 1. Breaking elongation = (L1 - L0) / L0 × 100% … (3)

[0078] (Thermal expansion coefficient) Raw material compositions 1 to 3 were each filled into a mold of 5 mm length x 5 mm width, and compression molded for 1 minute at a molding surface pressure (press pressure) of 30 MPa to obtain a cubic molded body with a side length of 5 mm. This molded body was sintered at 360 degrees for 6 hours, and the thermal expansion coefficient of the obtained sintered body (test body for measuring thermal expansion coefficient) was measured using a thermomechanical measuring device (TMA) (manufactured by TA Instruments Japan, Inc., "Q400"). The thermal expansion coefficient was measured with a follow-up load of 0.05 N, a measurement temperature from room temperature to 200°C, and a temperature rise rate of 5°C / min. The thermal expansion coefficient was calculated from the amount of thermal expansion in the range of 50 to 150°C in the measurement performed from room temperature to 200°C.

[0079] [Table 1] [Industrial Applicability]

[0080] The sheet of the present invention is suitably used as a heat-resistant material such as heat-resistant insulating tape, a base material for printed circuit boards, a printed circuit board, and a release sheet, but is not limited thereto. [Explanation of symbols]

[0081] 10 Billet 20 cutting blade 30 sheets 50, 50' Fluoroplastic particles 51 Filler particles

Claims

1. A substrate for printed circuit boards comprising a sheet containing the following components (A) and (B): The sheet has a breaking elongation percentage of more than 150%. (A) Fluorine resin (B) a filler having an average particle size of 20% or less of the predetermined thickness of the sheet;

2. 2. The substrate for printed circuit boards according to claim 1, wherein the predetermined thickness of the sheet is 25 to 300 μm.

3. 3. The substrate for printed circuit boards according to claim 1, wherein the filler has an average particle size of 0.1 to 10 μm.

4. 3. The substrate for printed circuit boards according to claim 1, wherein the blending ratio of the filler is 20 to 50% by volume.

5. 3. The substrate for printed circuit boards according to claim 1, wherein the fluororesin is polytetrafluoroethylene (PTFE) or modified PTFE.

6. 3. The substrate for printed circuit boards according to claim 1, wherein the filler is at least one selected from the group consisting of alumina, titanium oxide, silica, barium sulfate, silicon carbide, boron nitride, silicon nitride, glass fiber, glass beads, and mica.

7. The substrate for a printed circuit board according to claim 1 or 2, wherein the sheet has a thermal expansion coefficient of less than 100 ppm / °C.

8. The number of through holes with a diameter of 50 μm or more present in the sheet is 100 cm ２ The substrate for printed circuit boards according to claim 1 or 2, wherein the number of particles is 25 or less per one particle.

9. a step of preparing a raw material composition by mixing the following components (A') to (B); a step of forming a cylindrical compact from the raw material composition; sintering the compact; and skiving the surface of the fired molded body to form it into a sheet. (A') a fluororesin having an average particle size of 50% or less of the predetermined thickness of the sheet; (B) a filler having an average particle size of 20% or less of the predetermined thickness of the sheet;

10. The method for manufacturing a substrate for a printed circuit board according to claim 9, wherein the predetermined thickness of the sheet is 25 to 300 μm.

11. The method for producing a substrate for a printed circuit board according to claim 9 or 10, wherein the average particle diameter of the fluororesin particles is 0.1 to 10 μm.

12. The method for producing a substrate for a printed circuit board according to claim 9 or 10, wherein the filler has an average particle size of 0.1 to 10 μm.

13. The method for producing a substrate for a printed circuit board according to claim 9 or 10, wherein the blending ratio of the filler is 20 to 50% by volume.

14. 11. The method for producing a substrate for a printed circuit board according to claim 9 or 10, wherein the step of preparing the raw material composition comprises removing the solvent from a raw material-containing solution in which the (A′) fluororesin having an average particle size of 50% or less of the predetermined thickness of the sheet and the (B) filler having an average particle size of 20% or less of the predetermined thickness of the sheet are dispersed in a solvent.

15. 11. The method for producing a substrate for a printed circuit board according to claim 9 or 10, wherein the step of preparing the raw material composition is a step of dry-mixing the (A′) fluororesin having an average particle size of 50% or less of the predetermined thickness of the sheet and the (B) filler having an average particle size of 20% or less of the predetermined thickness of the sheet.

16. A substrate for a printed circuit board obtained by the manufacturing method according to claim 9 or 10.

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