Sheet and method of manufacturing a sheet

Abstract

A sheet material, wherein the sheet material is a synthetic resin sheet material obtained by cutting processing, and has a surface strength equivalent to the strength of the inside of the sheet material.

Description

Technical Field

[0001] This invention relates to sheets and methods for manufacturing sheets. Background Technology

[0002] Fluororubber is a synthetic resin with excellent heat resistance, electrical insulation, non-stickiness, and weather resistance. When molded into sheets, it is made into fluororesin sheets, which are widely used in chemical materials, electrical and electronic components, semiconductors, automobiles and other industries (e.g., patent documents 1-4).

[0003] For example, polytetrafluoroethylene (PTFE) and the like have significantly high melt viscosity, making it difficult to perform melt molding such as extrusion molding using common thermoplastic resins.

[0004] The method for manufacturing sheets of such resins that are difficult to melt and mold involves compressing raw material powder into a cylindrical block (cast blank), and then cutting the surface of the block into a thin film, a process known as machining.

[0005] For example, in Patent Document 1, a method for manufacturing PTFE sheets is disclosed, which involves suppressing the strain of the block by subjecting it to heat treatment and temperature reduction treatment under specified conditions.

[0006] As an example of the application of synthetic resins such as fluoropolymers, they are known to be used as release sheets due to their non-sticky and excellent release properties. However, if a synthetic resin film obtained through the aforementioned cutting process is used as a release sheet, longitudinal stripes known as cutting marks are sometimes transferred onto the surface of the sheet on the release side.

[0007] As a technique for smoothing the surface of fluoropolymer films, for example, Patent Document 2 discloses a technique for heating and pressing a film obtained by cutting. According to the technique in Patent Document 2, while smoothing the surface of the demolded sheet may reduce some of the longitudinal striations (cutting marks), it cannot substantially remove the longitudinal striations. In addition, if the film after cutting is heated and pressed, thermal deformation will occur due to temperature changes, etc.

[0008] In addition, due to the excellent heat resistance and insulation properties of fluoropolymers, they are also expected to be used as heat-resistant materials such as heat-resistant insulating tapes or printed circuit board materials.

[0009] However, fluoropolymer sheets manufactured by cutting are prone to thermal shrinkage due to heating and other processes, resulting in poor dimensional stability. Therefore, it has been pointed out that they are difficult to process, such as being difficult to bond with other materials.

[0010] Existing technical documents:

[0011] Patent Document 1: Japanese Patent Application Publication No. 2013-027983

[0012] Patent Document 2: Japanese Patent Application Publication No. 2015-189934

[0013] Patent Document 3: Japanese Patent Application Publication No. 2014-231562

[0014] Patent Document 4: Japanese Patent Application Publication No. 2010-201649 Summary of the Invention

[0015] The purpose of this invention is to provide a sheet material that can suppress thermal deformation and has excellent dimensional stability.

[0016] According to the present invention, the following sheets can be provided.

[0017] 1. A sheet material, wherein the sheet material is a synthetic resin sheet obtained by cutting and processing, and has a surface strength equivalent to the internal strength of the sheet material.

[0018] 2. The sheet according to claim 1, wherein the synthetic resin contains a fluoropolymer.

[0019] 3. The sheet according to 1 or 2, wherein, when the erosion rate of the outermost surface of the cut surface obtained by a micro-slurry spray erosion test on the cut surface of the sheet is defined as the surface strength X, and the arithmetic mean of the erosion rates at positions from a depth of 0.5 μm to a depth of 0.8 μm based on the outermost surface of the cut surface is defined as the internal strength Y, the strength ratio expressed by the following formula (a) is 500% or less.

[0020] Strength ratio (%) = (Surface strength X / Internal strength Y) × 100……(a)

[0021] 4. The sheet according to any one of 1 to 3, wherein the adhesive strength of the surface-modified machined surface of the sheet exceeds 0.2 N / mm.

[0022] 5. The sheet according to any one of 1 to 4, wherein the shrinkage rate in the cutting direction after heating at 180°C and then naturally cooling is less than 1.5%.

[0023] 6. The sheet according to any one of 2 to 5, wherein the fluororesin is polytetrafluoroethylene (PTFE) or modified PTFE.

[0024] 7. A material for a printed circuit board, comprising the sheet material described in any one of 1 to 6.

[0025] 8. A method for manufacturing a sheet, wherein the method for manufacturing a sheet is a method for manufacturing the sheet described in any one of 1 to 6, comprising: a step of removing a surface layer comprising the cut surface of a synthetic resin sheet obtained by cutting, wherein the cut surface of the sheet has a surface strength equal to the strength of the sheet interior.

[0026] According to the present invention, it is possible to provide a sheet material that can suppress thermal deformation and has excellent dimensional stability. Attached Figure Description

[0027] Figure 1 This diagram illustrates the cutting process of cutting the outer peripheral surface of the fired shaped body (cast billet) along its length to form a sheet.

[0028] Figure 2 It is a conceptual diagram used to illustrate the internal structure of a molded object.

[0029] Figure 3 It is a scanning electron microscope image of a machined surface with machining marks.

[0030] Figure 4 These are scanning electron microscope images of machined surfaces without machining marks.

[0031] Figure 5 This is a graph showing the relationship between erosion rate and erosion depth obtained through micro-slurry spray erosion tests.

[0032] Figure 6 This is a scanning electron microscope image of the sheet surface obtained in Example 1.

[0033] Figure 7 This is a scanning electron microscope image of the sheet surface obtained in Example 2.

[0034] Figure 8 The image is a scanning electron microscope image of the sheet surface obtained in Comparative Example 1.

[0035] Figure 9 This is a scanning electron microscope image of the sheet surface obtained in Comparative Example 2. Detailed Implementation

[0036] The sheet material and the method for manufacturing the sheet material of the present invention will be described below. In this specification, "x~y" represents a numerical range of "x or more and y or less". Regarding a technical matter, when there are multiple lower limit values ​​such as "x or more", or when there are multiple upper limit values ​​such as "y or less", it is possible to arbitrarily select and combine the upper and lower limit values.

[0037] [Sheet]

[0038] One aspect of the present invention relates to a sheet made of synthetic resin obtained by cutting and machining, which is a sheet having surface strength equal to the internal strength of the sheet.

[0039] Sheets, regardless of thickness, have one flat side and one back side, and can be formed in shapes such as strips and sheets, including films and tapes. Sheets made of synthetic resin refer to sheets containing synthetic resin.

[0040] In addition, in the following description, resin sheets containing synthetic resins will be referred to simply as resin sheets containing synthetic resins.

[0041] So-called cutting processing, such as Figure 1 As shown, this refers to a method of continuously cutting a sheet material thinly by rotating a cast blank 10, which is a compressed molded body of resin powder, while bringing the cutting edge 20 into contact with the surface of the cast blank 10.

[0042] The term "machined surface" refers to the surfaces 30A and 30B cut by the cutting edge in the sheet material produced by machining. Considering that the portion cut off from the outer circumferential surface of the cast billet 10 is typically removed as part of the product, the machined surface typically refers to the two planes of the sheet material. Furthermore, the term "machining direction" refers to... Figure 1 The direction indicated by the middle arrow A. It should be noted that the machined surface includes not only the surface cut by the aforementioned cutting edge, but also the sheet surface after the machining marks or fragile layers described later have been removed from that surface.

[0043] Furthermore, in the following description, "machining marks" refers to stripe-shaped synthetic resin flakes formed on the machined surface. Specifically, machining marks refer to the manner in which synthetic resin flakes are positioned in the gaps described later on the machined surface, meaning the resin flakes on the gaps and the gaps defined by the resin flakes.

[0044] It should be noted that, in detail, when machining marks remain on the sheet surface, the machining direction can be determined as the direction in which those machining marks are formed (specifically, the direction in which the machining marks extend across the aforementioned resin sheet (machining mark) in the sheet surface, or the length direction of the elongated gap partially covered by the resin sheet (machining mark)). In other words, a machining mark refers to a strip-shaped synthetic resin sheet extending along the machining direction on the gap of the machined surface, and the gap defined by the resin sheet.

[0045] On the other hand, if no machining marks (or the fragile layer described later) remain on the sheet surface, the cutting direction can be determined as the shrinkage direction of the sheet after heat treatment. Specifically, when the sheet obtained by cutting is naturally cooled after heat treatment based on the stress characteristics of the cutting process (more specifically, when performing the processing of items 1 to 5 in the "Determination of Heating Dimensional Change Rate" of the embodiments described later), its planar dimensions shrink in the planar direction of the sheet along a predetermined direction that is the cutting direction, and expand in a direction orthogonal to the predetermined direction. That is, when naturally cooled after heat treatment, the direction of shrinkage of the sheet's planar dimensions can be determined as the cutting direction.

[0046] The inventors conducted an in-depth study on the reasons why synthetic resin sheets obtained by cutting are prone to thermal deformation and poor dimensional stability. The results showed that the cutting surface of synthetic resin sheets obtained by cutting is fragile, and the surface characteristics of the sheet are different from the internal characteristics of the sheet, which easily leads to thermal changes in the sheet and deterioration of dimensional stability.

[0047] Because the sheet produced by this method has the same strength on its surface as its interior, it suppresses deformation caused by temperature changes and exhibits excellent dimensional stability.

[0048] Furthermore, since the sheet material of this method has surface strength equal to that of the sheet material itself, when bonding the sheet material to other components (such as metal materials like copper, or other materials), it is easy to obtain surface modification effects such as plasma treatment, thereby improving the bonding strength with other components.

[0049] The difference between the surface strength and internal strength of a sheet can be confirmed, for example, through a micro-slurry spray erosion test.

[0050] In one embodiment, the sheet material has an strength ratio of 500% or less when the surface strength X is defined as the erosion rate of the outermost surface of the cut surface obtained by a micro-slurry spray erosion test on the cut surface, and the internal strength Y is defined as the arithmetic mean of the erosion rates at positions with a depth of 0.5 μm to 0.8 μm based on the outermost surface of the cut surface.

[0051] Strength ratio (%) = (Surface strength X / Internal strength Y) × 100……(a)

[0052] The erosion rate is an indicator of material strength. The higher the erosion rate, the lower the material strength at the particle projection location; the lower the erosion rate, the higher the material strength at the particle projection location.

[0053] For example, a graph plotted with the horizontal axis representing the erosion rate and the vertical axis representing the erosion depth (e.g., refer to...). Figure 5 This indicates the intensity distribution from the outermost layer of the measured object toward the interior of the sheet.

[0054] The erosion rate was specifically determined using the micro-slurry spray erosion test method described in the examples. Furthermore, the surface strength X and internal strength Y were specifically calculated using the methods described in the examples.

[0055] In one embodiment, for example, by having the strength ratio of surface strength X to internal strength Y represented by the above formula (a) be less than 500%, the difference between the surface strength of the sheet surface and the internal strength of the sheet interior becomes smaller, which can simultaneously suppress deformation accompanied by temperature changes and improve dimensional stability; and suppress the breakage of weak parts during surface modification and improve adhesive strength.

[0056] The upper limit of the strength ratio represented by equation (a) can be 450% or less, 300% or less, 250% or less, 245% or less, 220% or less, or 200% or less. Below these upper limits, it is possible to further improve and achieve the aforementioned effects of improving dimensional stability and improving bond strength.

[0057] The lower limit of the strength ratio expressed by equation (a) is not particularly limited, but is usually above 50%.

[0058] In one embodiment, the sheet material substantially does not have the aforementioned processing marks. Here, the layer with processing marks on the machined surface is referred to as the fragile layer. That is, the fragile layer refers to a layer of a certain thickness formed by stretching the surface of the sheet material along the processing direction through a cutting edge during machining. It is presumed that the fragile layer is mechanically brittle and easily affected by thermal changes, etc.

[0059] By essentially eliminating processing marks (fragile layers), deformation caused by temperature changes can be more effectively suppressed, resulting in excellent dimensional stability. Furthermore, the absence of these processing marks (fragile layers) reduces the transfer of processing marks to the demolding side of the sheet when used as a release sheet. Additionally, when bonding the sheet to other components (such as metals like copper or other materials), surface modifications such as plasma treatment can be effectively performed, thereby improving the bond strength with other components.

[0060] As described above, a cast blank (molded body) obtained by firing a compressed molded body of raw material powder is machined. In this case, voids called pores 10a, which exist between the compressed powder particles, are dispersed throughout the cast blank, which is the workpiece (see reference). Figure 2Therefore, on the surface of the sheet material cut by machining, part of the pores inside the cast billet are revealed as recesses.

[0061] In cases where the machined surface has machining marks, at least a portion of the resin sheet extends in the machining direction across the recess (equivalent to the aforementioned gap). Figure 3 Region α in the process. Therefore, the shape of the recesses (equivalent to the aforementioned gaps) identified on the machining surface, part of which is covered by resin sheets, increases the number of elongated shapes (striped shapes) in the machining direction.

[0062] On the other hand, when there are no actual machining marks on the machined surface, the shape of the recesses identified on the machined surface is similar to the shape of the aforementioned pores themselves, thus increasing the number of areas with low elongation in the machining direction (see reference). Figure 4 ).

[0063] Typical machining marks appear as stripes, so their presence or absence can be confirmed using microscopic images. Figure 3 In this application, "substantially free of machining marks" means that machining marks are substantially removed from the machined surface of the sheet, exposing the internal structure.

[0064] Specifically, "substantially lacking processing marks" refers to the following state: First, a carbon ribbon is added to the sample stage of a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, "SU3500"), and the cutting surface of the sample (the 3mm × 3mm area at the center of the sheet) is set up as the observation surface. Next, platinum is deposited on the cutting surface, and the scanning electron microscope (manufactured by Hitachi High-Tech Corporation, "SU3500") is used at an accelerating voltage of 5kV and a magnification of 6000x. In the resulting scanning electron microscope image observed within a range of 20μm horizontally × 15μm vertically, substantially no stripe-shaped portions are observed. This includes cases where the stripe-shaped portions are completely unrecognizable visually in the image, and also cases where, for the purposes of this invention, residual stripe-shaped portions are visually recognizable in the image without violating the essence of this invention.

[0065] (Adhesive strength)

[0066] In one embodiment, the adhesive strength on the machined surface of the sheet material, after surface modification such as plasma treatment, can exceed 0.2 N / mm or be 0.5 N / mm or higher. The adhesive strength is specifically evaluated using the methods described in the embodiments.

[0067] (Heating dimensional change rate)

[0068] In one embodiment, the shrinkage rate (heating dimensional change rate) of the sheet in the cutting direction in the planar direction of the sheet after heat treatment at 180°C and subsequent natural cooling can be less than 1.5%, or less than 1.3% or less, or less than 1.1%. Specifically, the heating dimensional change rate is evaluated using the method described in the examples.

[0069] [Synthetic Resins]

[0070] As the synthetic resin, commonly used synthetic resins can be used without particular limitation, such as polyethylene, polyolefins such as polypropylene, fluoropolymers, polyester resins, polyurethane resins, etc. Among them, fluoropolymers are preferred.

[0071] As a fluoropolymer, commonly used fluoropolymers can be used without particular limitation, but polytetrafluoroethylene (PTFE) is preferred. Polytetrafluoroethylene (PTFE) is a homopolymer of tetrafluoroethylene.

[0072] Alternatively, modified polytetrafluoroethylene (PTFE) can also be used as a fluoropolymer. Modified polytetrafluoroethylene (PTFE) is polytetrafluoroethylene modified with perfluoroalkyl vinyl ethers.

[0073] Examples of perfluoroalkyl vinyl ethers include the perfluoroalkyl vinyl ethers represented by the formula (1) below.

[0074] CF2 = CF-OR f (1)

[0075] (In equation (1), R) f It is a perfluoroalkyl group having 1 to 10 carbon atoms (preferably 1 to 5 carbon atoms), or a perfluoroorganic group represented by formula (2) below.

[0076]

[0077] (In equation (2), n is an integer from 1 to 4.)

[0078] Examples of perfluoroalkyl groups having 1 to 10 carbon atoms in formula (1) include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, and perfluorohexyl, with perfluoropropyl being preferred.

[0079] [Other filling materials]

[0080] In one embodiment, the sheet may further comprise a filler material. Examples of filler materials include alumina, titanium dioxide, silicon dioxide, barium sulfate, silicon carbide, silicon nitride, glass fiber, glass beads, and mica. One or more of these filler materials may be used.

[0081] When the sheet contains one or more filler materials selected from alumina, titanium dioxide, silicon dioxide, barium sulfate, silicon carbide, silicon nitride, glass fiber, glass beads, and mica, the content of such filler is, for example, 0.5 to 50% by mass, preferably 1 to 35% by mass. It should be noted that the sheet may not necessarily contain fillers.

[0082] In one embodiment, the sheet may, for example, be composed of 85% or more, 90% or more, 95% or more, 98% or more, 99% or more, 99.5% or more, 99.9% or more, or 100% by mass of polytetrafluoroethylene or modified polytetrafluoroethylene; and

[0083] It is composed of one or more filler materials selected from alumina, titanium dioxide, silicon dioxide, glass fiber, glass beads and mica.

[0084] [Sheet manufacturing method]

[0085] One aspect of the present invention is a method for manufacturing a sheet, which includes a step of removing a surface layer comprising the cut surface of a synthetic resin sheet obtained by cutting, such that the surface has a surface strength equivalent to the strength of the interior of the sheet.

[0086] One embodiment of the sheet manufacturing method includes the following steps (1) to (4):

[0087] (1) The process of filling a mold with raw material containing synthetic resin and compressing it to form a molded body.

[0088] (2) The process of firing the molded body

[0089] (3) A machining process is performed to cut the surface of the fired molded body to form a sheet.

[0090] (4) The process of removing processing marks (specifically, the surface layer of a certain thickness containing processing marks, i.e., the fragile layer) from the surface of the formed sheet-like molded body.

[0091] As a synthetic resin, the resin described in the aforementioned sheet material project can be used.

[0092] Regarding the raw materials for compression molding, preferred raw materials include synthetic resins containing 80 to 100% by mass of fluoropolymers (e.g., polytetrafluoroethylene or modified polytetrafluoroethylene).

[0093] When the compressed raw material contains one or more fillers selected from alumina, titanium dioxide, silica, glass fiber, glass beads, and mica, the amount of the filler relative to the fluoropolymer (e.g., polytetrafluoroethylene, modified polytetrafluoroethylene, or mixtures thereof) is 1 to 50 by mass.

[0094] The above raw materials are filled into a mold and compressed to form a compression molded body. The surface pressure can be 10-100 MPa, 20-60 MPa, or 30-50 MPa.

[0095] The obtained compressed molded body is fired to obtain a cast billet. The firing temperature can be 100-400℃, 350-370℃, or 360-370℃.

[0096] From the viewpoint of facilitating the cutting process described later, the shape of the cast billet (formed body) is preferably cylindrical. When the cast billet (formed body) is cylindrical, the diameter of the cylinder can be, for example, 100–500 mm or 150–500 mm.

[0097] Next, the surface of the cast blank, which is the shaped body after firing, is cut to form a sheet.

[0098] When the cast billet (molded body) is a cylindrical body, the cutting edge is pressed against the outer peripheral surface of the fired cylindrical body along its length to cut it into a sheet shape.

[0099] When the cast billet (molded body) is a cylindrical body, before performing the process of cutting the outer peripheral surface of the fired cylindrical body in the length direction to form a sheet, the outer peripheral surface, inner peripheral surface and end face of the fired cylindrical body can be removed from the outside of the surface to a thickness of 3 mm.

[0100] The machining process of cutting the outer circumferential surface of the fired cylindrical body along its length to form a sheet can be used. Figure 1 The apparatus shown is used to carry out the operation. The thickness of the sheet obtained by cutting can be, for example, 0.01 to 1 mm or 0.01 to 0.5 mm.

[0101] exist Figure 1 In the process, the fired billet (cylindrical body) 10 is rotated and cut by the cutting edge (machine tool) 20 to form sheet material 30.

[0102] Next, by projecting particles onto the surface of the sheet, the processing marks (specifically, the fragile layer) present on the surface of the sheet are removed. As a result, the surface of the sheet is substantially free of processing marks.

[0103] As a method for removing machining marks by particle projection, any method that can be adjusted to stretch the sheet surface without producing new machining marks (marks different from those based on cutting processes) is acceptable and is not particularly limited. Examples of methods for removing machining marks include dry ice blasting using dry ice as the projecting particles, and treatment involving projecting a slurry containing dispersed particles into water, but these are not limited to these methods.

[0104] The removal of processing marks by particle projection can be achieved by appropriately adjusting the type of projected particles (particle material, shape, particle size) or projection conditions (projection angle, projection distance, projection pressure) to remove processing marks from the sheet surface so that the sheet surface is substantially free of processing marks and does not stretch the sheet surface through particle projection, thus preventing the generation of new processing marks.

[0105] The sheet material described above is suitable for use as, for example, a material for printed circuit boards.

[0106] [Example]

[0107] Example 1

[0108] <Bill Making>

[0109] Powdered polytetrafluoroethylene (PTFE) was filled into a mold and compressed from top to bottom at a pressure of 20 MPa for 0.5 hours to obtain a cylindrical preform (outer diameter 245 mm × inner diameter 75 mm × height 300 mm). The obtained preform was then placed in a firing furnace and fired at 365°C for 5 hours.

[0110] <Cutting Process>

[0111] use Figure 1 The apparatus shown is used to cut the obtained cylindrical sintered body (outer diameter 245mm × inner diameter 75mm × height 300mm) to produce a sheet with a thickness of 0.05mm.

[0112] <Removal of processing marks (specifically, fragile layers)>

[0113] The process of dispersing abrasive particles into a slurry (abrasive fluid) by projecting the abrasive onto the cutting surface of the obtained sheet.

[0114] It should be noted that, in this embodiment, as an example of the process for removing machining marks, the process of projecting abrasive liquid was used. However, in the process for removing machining marks in this invention, any method that can remove machining marks by particle projection can be appropriately adopted.

[0115] The removal of machining marks is carried out under the following conditions.

[0116] (Particle projection conditions)

[0117] • Slurry (grinding fluid):

[0118] Solvent: Pure water

[0119] Abrasive: Alumina (Al2O3), polygonal particles, average particle size (D50) 6.7μm; abrasive content: 1.9% by volume.

[0120] Projection angle: 90°

[0121] • Projection distance: 20mm

[0122] • Air pressure: 0.2 MPa

[0123] Example 2, Comparative Example 2

[0124] Except for the change in the concentration of the abrasive used to remove machining marks as shown in Table 1, the sheets were prepared in the same manner as in Example 1.

[0125] Comparative Example 1

[0126] Except for the absence of a process to remove processing marks, the sheet was prepared in the same manner as in Example 1.

[0127] [Table 1]

[0128] Slurry concentration [vol%] Example 1 1.9 Example 2 15 Comparative Example 1 - Comparative Example 2 0.5

[0129] [Microslurry jet erosion (MSE) test]

[0130] For each sheet obtained in Examples 1-2 and Comparative Examples 1-2, a micro-slurry spray erosion test (hereinafter referred to as the MSE test) was conducted using an MSE testing apparatus (manufactured by Palmeso Co., Ltd., “MSE-A”). The test conditions are shown in Table 2.

[0131] [Table 2]

[0132]

[0133] It should be noted that the “projection force setting” shown in Table 2 refers to the projection conditions that are adjusted by setting the projection pressure and flow rate. In Table 2, “Si wafer: 0.24μm / g” indicates the projection conditions under which the erosion rate is 0.24μm / g when 1g of the polygonal alumina particles shown in Table 2 are projected onto the Si wafer as the reference material, and “PMMA: 1.48μm / g” indicates the projection pressure under which the erosion rate is 1.48μm / g when 1g of the polygonal alumina particles shown in Table 2 are projected onto the PMMA as the reference material.

[0134] The MSE test is conducted as follows.

[0135] First, the cutting surface of each sheet obtained in Examples 1-2 and Comparative Examples 1-2 was placed opposite the jet nozzle and positioned in the MSE test apparatus (Made by Palmeso Co., Ltd., “MSE-A”) with the projection distance shown in Table 2.

[0136] Next, a slurry of a specified concentration obtained by mixing the particles shown in Table 2 with water was projected from a jet nozzle onto the cutting surface of each sheet at the projection force set in Table 2, causing it to collide and thus forming an erosion mark with the area shown in Table 2. Then, the depth of the central portion of the erosion mark was measured using a stylus-type shape measuring machine (PU-EU1) under the measurement conditions shown in Table 2.

[0137] Using the outermost surface of the machined surface as a reference, the formation of the erosion trace based on particle projection and the measurement of the depth of the central part of the erosion trace were repeatedly performed at any depth position between 0.8 μm (in the following description, the depth position inside the sheet with the outermost surface of the machined surface as a reference at the moment of particle projection is referred to as "erosion depth").

[0138] Based on the amount of fine particles projected per unit area at each erosion depth, v(g / mm²). 2 The erosion rate is calculated by taking the depth d (μm) of the central part of the erosion mark and the erosion trace using the following formula (b).

[0139] Erosion rate (μm / g) = d / v……(b)

[0140] The relationship between the erosion rates (μm / g) and erosion depths (μm) obtained as described above is shown in the figure. Figure 5 .

[0141] exist Figure 5 In the figure, the horizontal axis represents the erosion rate (μm / g), and the vertical axis represents the erosion depth (μm).

[0142] For each sheet of Examples 1-2 and Comparative Examples 1-2, in Figure 5 In this study, the erosion rate of the points depicted at an erosion depth of 0 μm (the outermost surface) is set as the surface strength X, and the arithmetic mean of the erosion rates of the points depicted at erosion depths of 0.5 μm to 0.8 μm is set as the internal strength Y. The strength ratio (%) of the surface strength X to the internal strength Y is calculated using the following formula (a).

[0143] Strength ratio (%) = (Surface strength X / Internal strength Y) × 100……(a)

[0144] The results are shown in Table 3.

[0145] [Table 3]

[0146] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Surface strength X [μm / g] 0.089 0.051 0.396 0.343 Internal strength Y [μm / g] 0.037 0.038 0.075 0.043 Strength ratio [%) 240 134 528 797

[0147] [Determination of the rate of dimensional change during heating]

[0148] The dimensional changes (heating dimensional change rate) of the sheets obtained in Example 2 and Comparative Example 1 before and after heating were evaluated using the following steps. The results are shown in Table 4.

[0149] 1. Cut the sheet into 110mm×130mm sizes and let it stand in a constant temperature room at 23℃ for 15 hours.

[0150] 2. Draw a 50mm × 50mm mark on the sheet material after it has been left to stand. Use a digital microscope (KEYENCE CORPORATION, “VHX5000”) to measure the distance between the marks in the cutting direction (hereinafter also called the MD direction) and the direction orthogonal to it (hereinafter also called the CD direction), as the dimension before heating.

[0151] 3. Clamp the two ends of the sheet in the MD direction after the dimensions of 2 are measured with a clamp, and suspend it in a hot air circulating gear oven (manufactured by Tabai ESPEC CORP., "PHH-100").

[0152] 4. Heat the hot air circulating ZIL aging test chamber from room temperature to 180°C, maintain the temperature at 180°C for 1 hour, and then allow it to cool naturally to room temperature.

[0153] After cooling for 5.4 hours, remove the clamps and let it stand in a constant temperature chamber at 23°C for 15 hours.

[0154] After standing for 6.5 seconds, the distance between the marks was measured again using a digital microscope as the dimension after heating.

[0155] 7. Calculate the heating dimension change rate from the dimensions before heating obtained from 2 and the dimensions after heating obtained from 6 using the following formula (i).

[0156] Rate of change of dimensional change after heating = (Dimension after heating - Dimension before heating) / Dimension before heating ... (i)

[0157] [Evaluation of the adhesive properties of the surface-modified sheet]

[0158] The sheets from Example 2 and Comparative Example 1 were cut into 100mm × 100mm pieces, subjected to the plasma treatment described below, and then their adhesion was evaluated as described below. The results are shown in Table 5.

[0159] (Plasma processing)

[0160] A sheet was placed in a vacuum plasma apparatus and evacuated. Plasma treatment was performed for 10 seconds using a 2.45 GHz microwave in a mixed atmosphere of nitrogen and hydrogen.

[0161] (Adhesive strength test)

[0162] A plasma-treated sheet, a halogen-free low-dielectric adhesive (semi-cured) sheet (manufactured by Niganekide Kogyo Co., Ltd., "SAFY", 25 μm thick), and an electrolytic copper foil (manufactured by Mitsui Metals & Mining Co., Ltd., "TQ-M4-VSP", 18 μm thick) were sequentially stacked and pressed together using hot pressing (temperature: 160°C, pressing time: 1 hour, pressing load: 4 MPa) to prepare a specimen for bond strength testing. A 10 mm wide slit was cut into this specimen, and 30 mm of copper foil was peeled off. A 90° peel test was performed on the specimen with the peeled copper foil using a small benchtop testing machine (manufactured by Shimadzu Corporation, "EZ-LX") at a tensile speed of 50 mm / min to determine the bond strength.

[0163] A carbon ribbon was added to the sample stage of a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, "SU3500"), and the cutting surface of the test specimens (the planar area of ​​the central part of the sheet with a size of 3 mm × 3 mm) collected from Examples 1-2 and Comparative Examples 1-2 was set up as the observation surface. Next, platinum was deposited on the cutting surface of the test specimen, and a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, "SU3500") was used with an accelerating voltage of 5 kV and a magnification of 6000x to obtain a scanning electron microscope image observed in an area of ​​20 μm × 15 μm.

[0164] Electron microscope images of the sheets from Examples 1-2 and Comparative Examples 1-2 obtained using the above method are shown below. Figures 6-9 As shown.

[0165] [Table 4]

[0166]

[0167] [Table 5]

[0168] 90° bond strength [N / mm] Example 2 0.8 Comparative Example 1 0.2

[0169] [Potential for industrial applications]

[0170] The sheet material of the present invention is preferably used as a heat-resistant material such as heat-resistant insulating tape, a material for printed circuit boards, or a release sheet, but is not limited thereto.

[0171] The embodiments and / or several examples of the present invention have been described in detail above. However, those skilled in the art can easily make many modifications to these illustrated embodiments and / or examples without departing from the new teachings and effects of the present invention. Therefore, these many modifications are included within the scope of the present invention.

[0172] The entire contents of the documents described in this specification, as well as the contents of the application that forms the basis of this application under the Paris Treaty priority, are hereby cited.

Claims

1. A sheet material, wherein, The sheet is a synthetic resin sheet obtained through cutting and processing. The sheet material does not actually have any processing marks. When the surface strength X is defined as the erosion rate of the outermost surface of the cut surface obtained by a micro-slurry spray erosion test on the cut surface of the sheet, and the internal strength Y is defined as the arithmetic mean of the erosion rates at positions from a depth of 0.5 μm to a depth of 0.8 μm based on the outermost surface of the cut surface, the strength ratio expressed by the following formula (a) is 300% or less. Strength ratio (%) = (Surface strength X / Internal strength Y) × 100……(a).

2. The sheet according to claim 1, wherein, The synthetic resin contains fluorinated resin.

3. The sheet according to claim 1 or 2, wherein, The adhesive strength of the surface-modified machined surface of the sheet exceeds 0.2 N / mm.

4. The sheet according to claim 1 or 2, wherein, The shrinkage rate in the cutting direction after heating at 180°C and then naturally cooling is less than 1.5%.

5. The sheet according to claim 2, wherein, The fluororesin is PTFE or modified PTFE, where PTFE represents polytetrafluoroethylene.

6. A material for a printed circuit board, wherein, The sheet comprising any one of claims 1 to 5.

7. A method for manufacturing a sheet material, wherein, The method for manufacturing the sheet is the same as that for manufacturing the sheet according to any one of claims 1 to 5. include: For at least one side of a synthetic resin sheet obtained by machining, a process is performed to remove the surface layer containing machining marks of the sheet in such a way that the side has the following surface strength. The surface strength is defined as follows: when the erosion rate of the outermost surface of the cut surface obtained by a micro-slurry spray erosion test on the cut surface of the sheet is defined as the surface strength X, and the arithmetic mean of the erosion rates at positions from a depth of 0.5 μm to a depth of 0.8 μm based on the outermost surface of the cut surface is defined as the internal strength Y, the strength ratio expressed by the following formula (a) is 300% or less. Strength ratio (%) = (Surface strength X / Internal strength Y) × 100……(a).

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