Sheets and methods of manufacturing sheets

Abstract

A sheet material made of synthetic resin obtained by cutting and which is substantially free of processing marks.

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.

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

[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 documents:

[0012] Patent Document 1: Japanese Patent Application Publication No. 2013-027983

[0013] Patent Document 2: Japanese Patent Application Publication No. 2015-189934

[0014] Patent Document 3: Japanese Patent Application Publication No. 2014-231562

[0015] Patent Document 4: Japanese Patent Application Publication No. 2010-201649 Summary of the Invention

[0016] The purpose of this invention is to provide a sheet material that can suppress thermal deformation and has excellent dimensional stability.

[0017] According to the present invention, the following sheet is provided.

[0018] 1. A sheet material, wherein the sheet material is a synthetic resin sheet obtained by cutting and machining, and substantially has no machining marks.

[0019] 2. The sheet according to claim 1, wherein the synthetic resin contains a fluoropolymer.

[0020] 3. The sheet according to claim 2, wherein the machined surface has a surface formed by the aggregation of sintered material containing fluororesin powder, the sintered material maintaining a shape substantially the same as the particles of the raw material powder and not producing elongation deformation caused by the machining process.

[0021] 4. The sheet according to any one of 1 to 3, wherein, when a portion of the cutting surface at the center of the sheet with a planar dimension of 3 mm × 3 mm is photographed at a magnification of 6000 using a scanning electron microscope, and a range of 20 μm in width × 15 μm in height is photographed, in any 1280 × 960 pixel area extracted from multiple image data stored with a pixel count of 1280 × 960, no gap elongated in the cutting direction is substantially observed.

[0022] 5. The sheet according to any one of 1 to 4, wherein, after being heated at 180°C and then naturally cooled, the planar dimensions of the sheet shrink in the planar direction of the sheet along a predetermined direction which is the cutting direction, and expand in a direction orthogonal to the predetermined direction.

[0023] 6. The sheet according to any one of 1 to 5, wherein the arithmetic mean of the aspect ratio of the dark portion in the scanning electron microscope image of the machined surface of the sheet exceeds 0.80.

[0024] 7. The sheet according to 6, wherein the arithmetic mean of the aspect ratio of the dark-colored portion is 0.90 or more.

[0025] 8. The sheet according to any one of 1 to 7, wherein the bond strength on the surface of the machined surface that has undergone surface modification exceeds 0.2 N / mm.

[0026] 9. The sheet material according to any one of 1 to 8, wherein the shrinkage rate in the cutting direction during natural cooling after heating at 180°C is less than 1.5%.

[0027] 10. The sheet according to any one of 2 to 9, wherein the fluororesin is polytetrafluoroethylene (PTFE) or modified PTFE.

[0028] 11. A material for a printed circuit board, comprising the sheet material described in any one of 1 to 10.

[0029] 12. A method for manufacturing a sheet, wherein the method for manufacturing a sheet is a method for manufacturing any one of 1 to 10, comprising a step of removing the processing marks from at least one side of a synthetic resin sheet obtained by cutting, such that the side is substantially free of processing marks.

[0030] According to the present invention, a sheet material capable of suppressing thermal deformation and exhibiting excellent dimensional stability can be provided. Attached Figure Description

[0031] 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.

[0032] Figure 2 It is a conceptual diagram used to illustrate the internal structure of a molded object.

[0033] Figure 3 It is a scanning electron microscope image of a machined surface with machining marks.

[0034] Figure 4 These are scanning electron microscope images of machined surfaces without machining marks.

[0035] Figure 5 (a) is a scanning electron microscope image of a machined surface with machining marks. Figure 5 (b) is to Figure 5 A concept diagram representing an extracted dark area shown in (a).

[0036] Figure 6 (a) is a scanning electron microscope image of a machined surface that does not actually have machining marks. Figure 6 (b) is to Figure 6 A concept diagram representing an extracted dark area shown in (a).

[0037] Figure 7 These are scanning electron microscope images of the sheet surfaces obtained in Examples 1-6 and Comparative Examples 1-2.

[0038] Figure 8 yes Figure 4 The image shown is a scanning electron microscope image of the raw material powder of the sheet.

[0039] Figure 9 It is to observe under magnification Figure 8 The β range is shown in the scanning electron microscope image. Detailed Implementation

[0040] The sheet material and its manufacturing method according to 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.

[0041] [Sheet]

[0042] One aspect of this invention relates to a sheet made of synthetic resin obtained through machining, which is a sheet substantially free of machining marks. The sheet, regardless of thickness, has one planar side and another side as its back side, and can be formed in shapes such as strips or sheets, and includes, for example, films or tapes. A sheet made of synthetic resin refers to a sheet containing synthetic resin.

[0043] In addition, in the following description, resin sheets containing synthetic resins will be referred to simply as resin sheets containing synthetic resins.

[0044] So-called cutting processing, such as Figure 1 As shown, this refers to a method of continuously cutting a sheet material thinly by rotating the cast blank 10 of the compressed molded body of sintered resin powder while bringing the cutting edge 20 into contact with the surface of the cast blank 10.

[0045] 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 peripheral 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.

[0046] The term "machining mark" refers to stripe-shaped synthetic resin flakes formed on the machined surface. Specifically, a machining mark refers to the manner in which synthetic resin flakes are positioned in the gaps described later on the machined surface, specifically the resin flakes on the gaps and the gaps defined by the resin flakes.

[0047] 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.

[0048] On the other hand, when no machining marks 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 sheet planar direction 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 planar dimensions can be determined as the cutting direction.

[0049] 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 if processing marks remain on the cutting surface, thermal changes in the sheet are likely to occur, and the dimensional stability will deteriorate.

[0050] Here, the layer with machining marks on the cut surface is called the fragile layer. That is, the fragile layer is the layer formed by stretching the surface of the sheet material along the machining direction through the cutting edge during machining. It is presumed that the fragile layer is mechanically brittle and easily affected by thermal changes, etc.

[0051] The sheet produced by this method does not actually have the aforementioned processing marks (fragile layer), thus suppressing deformation associated with temperature changes and exhibiting excellent dimensional stability.

[0052] In addition, the sheet material of this method does not have the aforementioned processing marks (fragile layer). Therefore, when the sheet material is used as a release sheet material, the transfer of processing marks to the release side of the sheet material can be reduced. Furthermore, when the sheet material is bonded to other components (such as metal materials such as copper, or other materials), surface modification such as plasma treatment can be effectively performed, thereby improving the bonding strength with other components.

[0053] 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 2 Therefore, on the surface of the sheet material cut by machining, part of the pores inside the cast billet are revealed as recesses.

[0054] 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 recess (equivalent to the aforementioned gap) identified on the machining surface, part of which is covered by a resin sheet, results in more elongated portions (striped shapes) in the machining direction.

[0055] 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 ).

[0056] 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.

[0057] 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 using the scanning electron microscope (manufactured by Hitachi High-Tech Corporation, "SU3500") at an accelerating voltage of 5kV and a magnification of 6000x, at a resolution of 1280 × 960 pixels within a 20μm × 15μm area, no stripe-shaped portions are substantially observed in any three points of the image data (1280 × 960 pixel area) from multiple image data stored in the scanning electron microscope image data. This includes not only cases where the stripe-shaped portions are not visually discernible in the image, but also cases where, for the purposes of this invention, residual stripe-shaped portions are visually discernible in the image without violating the essence of this invention.

[0058] In one embodiment, the arithmetic mean of the aspect ratio of the dark regions in a scanning electron microscope image of the machined surface of the sheet material exceeds 0.80. This embodiment provides a method for determining the aforementioned machining marks (striped shapes).

[0059] In this application, the dark areas in the scanning electron microscope image correspond to the depressions (voids) on the surface of the sheet, as determined in the following manner.

[0060] First, the machined surface of the sheet was photographed at 6000x magnification over a range of 20μm x 15μm. Based on multiple image data stored at 1280 x 960 pixels, a defined pixel region (1280 x 960 pixels) was defined and extracted. For this extracted image, a histogram of gray levels (256 levels) was obtained using a multi-value image processing histogram analysis program (e.g., analysis software (Image-Pro 10, manufactured by Media Cybernetics, Inc.)). The obtained histogram was treated as a normal distribution, and the range of mean ± 3σ with a dispersion of σ was extracted and set as 256 levels. Then, the histogram was flattened. Based on the resulting gray-level frequency distribution data, the pixel portions with gray levels of 0–35 in the 256 levels were defined as "dark areas".

[0061] Figure 5 (a) is an example of a scanning electron microscope image of the center of a machined surface with machining marks. For this scanning electron microscope image, the outer edge of the dark part P extracted by image analysis using the method described above is shown surrounded by a line. Figure 5 (b) is to Figure 5 A concept diagram showing an extraction of the darker area shown in (a).

[0062] It should be noted that, in Figure 5 In (a), the direction represented by "a" is the cutting direction. Figure 5 In the example shown in (a), this corresponds to the length direction of the sheet. Figure 5 In (a), the direction represented by "b" is the direction orthogonal to the cutting direction. Figure 5 In the example shown in (a), this corresponds to a direction orthogonal to the length direction of the sheet. It should be noted that... Figure 5 The scale (10 divisions) shown in the lower right of (a) represents 5.00 μm using the entire scale. Regarding this, for Figure 6 The same applies to (a).

[0063] Figure 6(a) is an example of a scanning electron microscope image of the center of a machined surface that does not actually have machining marks. The outer edge of the dark area extracted by the image analysis method described above is shown by using lines to enclose the image. Figure 6 (b) is to Figure 6 A concept diagram showing an extraction of the darker area shown in (a).

[0064] It should be noted that, in Figure 6 In (a), the direction represented by "a" is the cutting direction. Figure 6 In the example shown in (a), this corresponds to the length direction of the sheet. Figure 6 In (a), the direction represented by "b" is the direction orthogonal to the cutting direction. Figure 6 In the example shown in (a), the direction is equivalent to the direction orthogonal to the length direction of the sheet.

[0065] In addition, in this application, "the aspect ratio of the dark part" refers to the diameter of the direction orthogonal to the cutting direction relative to the cutting direction.

[0066] Additionally, "the arithmetic mean of the aspect ratio of the dark areas" refers to the value obtained by taking any three points (1280×960 pixel area) from images observed using a scanning electron microscope on the machined surface of the test sample (the 3mm×3mm planar area at the center of the sheet), calculating the arithmetic mean for the aspect ratio of all dark areas determined in each of these three images, and then further averaging the arithmetic mean obtained from each image. For example, in... Figure 5 In the example shown, since the diameter of the dark part P in the cutting direction is Ra1, and the diameter in the direction orthogonal to the cutting direction is Rb1, the aspect ratio of the dark part P (diameter in the direction orthogonal to the cutting direction / diameter in the cutting direction) is represented by (Rb1 / Ra1). Figure 5 In the example shown, (Rb1 / Ra1) is approximately 0.5.

[0067] Additionally, for example in Figure 6 In the example shown, since the diameter of the dark part P in the cutting direction is Ra2, and the diameter in the direction orthogonal to the cutting direction is Rb2, the aspect ratio of the dark part P is represented by (Rb2 / Ra2). Figure 6 In the example shown, (Rb2 / Ra2) is approximately 1.

[0068] When machining marks are present on the sheet surface, the shape of the recesses in the machined surface is as described above, with more elongated shapes in the cutting direction, therefore... Figure 5As shown, there is a tendency for the aspect ratio to decrease.

[0069] On the other hand, when there are no machining marks on the sheet surface, due to the shape of the recessed portion of the cutting surface as described above, the elongation in the cutting direction becomes lower more frequent, therefore... Figure 6 As shown, there is a tendency for the aspect ratio to be greater than the specified value. Generally speaking, the aspect ratio tends to be greater than the specified lower limit and less than the specified upper limit, that is, it tends to deviate from the value of 1, which is a perfect circle, and therefore can be said to be close to 1.

[0070] In one embodiment, if the arithmetic mean of the aspect ratio of the dark areas in a scanning electron microscope image exceeds 0.80, then there are no substantial traces of processing.

[0071] In addition, the arithmetic mean is a value calculated based on the aspect ratio of all dark areas extracted from the aforementioned pixel region.

[0072] In other embodiments of the present invention, the lower limit of the arithmetic mean of the aspect ratio of the dark portion can also exceed 0.80, and is 0.81 or higher, 0.85 or higher, 0.90 or higher, 0.93 or higher, 0.95 or higher, 1.00 or higher, 1.05 or higher, 1.12 or higher, 1.14 or higher, 1.16 or higher, or 1.20 or higher. In other embodiments of the present invention, the upper limit of the arithmetic mean of the aspect ratio of the dark portion is not particularly limited, and can be configured as 1.5 or lower, 1.35 or lower, 1.33 or lower, 1.26 or lower, 1.23 or lower, or 1.15 or lower. Furthermore, in other embodiments of the present invention, the arithmetic mean of the aspect ratio of the dark portion can be configured by combining the upper and lower limits of the above embodiments; for example, it can be configured as exceeding 0.80 and being 1.5 or lower, or 0.90 or higher and being 1.35 or lower.

[0073] If the arithmetic mean of the aspect ratio of the dark part is within the above range, it can be said that the sheet material has good surface condition, with few machining marks on the cutting surface, and the structure close to the internal structure is exposed on the surface.

[0074] (Haze value)

[0075] In one embodiment, the lower limit of the haze value of the sheet cutting surface can be more than 53%, or more than 55% or more than 60%. In addition, the upper limit of the haze value can be, for example, less than 100%, less than 99%, less than 95%, less than 90%, less than 80%, less than 70%, or less than 65%.

[0076] It should be noted that the haze value is an indicator related to the transparency of the membrane, and is an indicator of turbidity. The haze value is specifically evaluated using the methods described in the examples.

[0077] (Adhesive strength)

[0078] In one embodiment, the adhesive strength of 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.

[0079] (Heating dimensional change rate)

[0080] In one embodiment, the shrinkage rate (heating dimensional change rate) of the sheet material in the cutting direction in the planar direction after heat treatment at 180°C and subsequent natural cooling can be less than 1.5%, or less than 1.3% or 1.1%. Specifically, the heating dimensional change rate is evaluated using the method described in the examples.

[0081] [Synthetic Resins]

[0082] As the synthetic resin, commonly used synthetic resins can be used without particular limitation, such as polyolefins like polyethylene and polypropylene, fluoropolymers, polyester resins, and polyurethane resins. Among these, fluoropolymers are preferred.

[0083] As a fluoropolymer, commonly used fluoropolymers can be used without particular limitation, but polytetrafluoroethylene (PTFE) is preferred. Polytetrafluoroethylene (PTFE) is a homopolymer of tetrafluoroethylene.

[0084] Alternatively, modified polytetrafluoroethylene (PTFE) can also be used as a fluoropolymer. Modified polytetrafluoroethylene (PTFE) is polytetrafluoroethylene modified with perfluoroalkyl vinyl ethers.

[0085] Examples of perfluoroalkyl vinyl ethers include those represented by the formula (1) below.

[0086] CF2 = CF-OR f (1)

[0087] (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.

[0088]

[0089] (In equation (2), n is an integer from 1 to 4.)

[0090] As a perfluoroalkyl group having 1 to 10 carbon atoms in formula (1), examples include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, perfluorohexyl, etc., with perfluoropropyl being preferred.

[0091] [Other filling materials]

[0092] 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.

[0093] 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.

[0094] 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

[0095] It is composed of one or more filler materials selected from alumina, titanium dioxide, silicon dioxide, glass fiber, glass beads and mica.

[0096] [Sheet manufacturing method]

[0097] One aspect of the present invention relates to a method for manufacturing a sheet comprising: a step of removing the processing marks from at least one side of a synthetic resin sheet obtained by cutting, such that the side is substantially free of processing marks.

[0098] One embodiment of the sheet manufacturing method includes the following steps (1) to (4):

[0099] (1) The process of filling a mold with raw material containing synthetic resin and compressing it to form a molded body.

[0100] (2) The process of firing the molded body

[0101] (3) A machining process is performed to cut the surface of the fired molded body to form a sheet.

[0102] (4) The process of removing machining marks from the surface of the formed sheet.

[0103] As a synthetic resin, the resin described in the aforementioned sheet material project can be used.

[0104] 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).

[0105] 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.

[0106] 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.

[0107] The obtained compressed molded body is fired to obtain a cast billet. The firing temperature can be 100-400℃, 350-370℃, or 360-370℃.

[0108] When using raw material powder containing fluorinated resins such as polytetrafluoroethylene as a raw material powder for compression molding, the resulting billet can be obtained as a molded body formed by the agglomeration of the raw material powder sintering material.

[0109] 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.

[0110] Next, the surface of the cast blank, which is the shaped body after firing, is cut to form a sheet.

[0111] 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.

[0112] 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.

[0113] 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 1The 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.

[0114] 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.

[0115] Next, by projecting particles onto the surface of the sheet, the processing marks present on the surface of the sheet are removed. This makes it possible to make the surface of the sheet substantially free of processing marks.

[0116] 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.

[0117] 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.

[0118] In the sheet material obtained by the above method, the structure that is roughly the same as the internal structure of the cast billet is manifested in the surface shape of the machined surface.

[0119] For example, when using raw material powder containing fluororesin, the molded body (cast blank) formed by the agglomeration of the raw material powder is subjected to the above-mentioned cutting and machining mark removal treatment, thereby obtaining a sheet whose machined surface has a surface formed by the agglomeration of the raw material powder. The sintered material maintains a shape that is approximately the same as the particles of the raw material powder, and as a sintered material that does not produce elongation deformation caused by cutting, the machined surface is formed.

[0120] Figure 8 Observation using a scanning electron microscope Figure 4 The image shown is obtained from the raw material powder of the sheet. Figure 9 It is Figure 8 The range represented by β is further magnified and the image is observed using a scanning electron microscope.

[0121] Figure 8The raw material powder (PTFE powder) shown is obtained by granulating primary particles synthesized by suspension polymerization into a powder for compression molding. Within the range shown by β, for example, tiny primary particles (average particle size: about 1 μm) existing at the position shown by Q are aggregated to form secondary particles (e.g., blocky particles occupying the range shown by β) with an average particle size of about 10 to 100 μm.

[0122] Will Figure 8 The compressed molded body obtained by compressing the raw material powder shown is an aggregate of the aforementioned primary particles (average particle size: approximately 1 μm). The machined surface of the sheet material obtained by machining the cast ingot obtained from firing this molded body was observed using a scanning electron microscope. The resulting scanning electron microscope image is shown below. Figure 4 .

[0123] In this casting, primary particles with an average particle size of approximately 1 μm are compressed and formed, and then subjected to a firing process. As a result, some of these primary particles deform into a flattened shape, and others fuse, press, or bond with other primary particles. That is, the casting has a state where the flattened primary particles are interlocked (interlocked), in other words, the primary particles maintain a shape roughly the same as the raw material powder. The machined surface of the sheet obtained by machining this casting is as follows: Figure 4 As shown, the surface is composed of aggregates of particles (calcined raw material powder) with an average particle size of about 1 μm.

[0124] exist Figure 4 In the diagram, for example, the shapes of the regions (calcined products of the raw material powder) shown in c, d, e, and f are similar to... Figure 9 The regions (primary particles of the raw material powder) represented by g, h, i, and j in the figure have approximately the same shape.

[0125] The sheet material described above is suitable for use as, for example, a material for printed circuit boards.

[0126] [Example]

[0127] Example 1

[0128] <Bill Making>

[0129] 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.

[0130] <Cutting Process>

[0131] use Figure 1The 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.

[0132] <Removal of machining marks>

[0133] The process of dispersing abrasive particles into a slurry (abrasive fluid) by projecting the abrasive onto the cutting surface of the obtained sheet.

[0134] 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.

[0135] The removal of machining marks is carried out under the following conditions.

[0136] (Particle projection conditions)

[0137] • Slurry (grinding fluid):

[0138] Solvent: Pure water

[0139] Abrasive: Alumina (Al2O3), polygonal particles, average particle size (D50) 6.7μm, abrasive content: 0.95% by volume

[0140] Projection angle: 90°

[0141] • Projection distance: 20mm

[0142] • Air pressure: 0.2 MPa

[0143] The obtained sheet material is evaluated as follows.

[0144] The results are shown in Table 1.

[0145] [Extracting dark areas and calculating aspect ratio]

[0146] First, a carbon ribbon was attached to the sample stage of a scanning electron microscope (manufactured by Hitachi High-Tech Corporation, "SU3500"), and the cutting surface of the sample (the central plane area of ​​the sheet with a size of 3 mm × 3 mm) was set up as the observation surface. Next, platinum was deposited on the cutting surface of the sample. Using the scanning electron microscope (manufactured by Hitachi High-Tech Corporation, "SU3500") at an accelerating voltage of 5 kV and a magnification of 6000x, images of any three points (1280 × 960 pixel areas) were randomly extracted from multiple image data of scanning electron microscope images observed in an area of ​​20 μm × 15 μm with a pixel count of 1280 × 960 pixels.

[0147] For each extracted image at these three points, a histogram analysis acquisition program (MediaCybernetics.Inc., "Image-Pro 10") was used to obtain a grayscale histogram (256 levels). The obtained histogram was treated as a normal distribution, and the range of the mean ± 3σ with a dispersion of σ was extracted and set as 256 levels. Then, the histogram was flattened. Based on the resulting grayscale frequency distribution data, the pixels with grayscale values ​​of 0–35 in the 256 levels were identified as the "dark areas".

[0148] Next, for all the dark areas identified in each image, the diameter in the cutting direction and the diameter in the direction orthogonal to the cutting direction are measured respectively, and the aspect ratio ((diameter in the direction orthogonal to the cutting direction) / (diameter in the cutting direction)) is calculated. For the aspect ratios of all the condensed areas obtained in this way, the arithmetic mean is calculated for each image, and the arithmetic mean of the aspect ratios of the three images is further arithmetically averaged to calculate the "arithmetic mean of the aspect ratios of the dark areas".

[0149] [Presence or absence of machining marks]

[0150] In the scanning electron microscope images obtained in "extraction of dark areas and calculation of aspect ratio", the presence or absence of processing marks was confirmed. Specifically, in any one of the 1280×960 pixel areas of the three points extracted from the scanning electron microscope images observed under the above conditions, if a strip-shaped resin sheet extending in the cutting direction or a long strip-shaped gap (processing mark) is confirmed on the gap of the sheet cutting surface, it is defined as "processing mark present"; if no processing mark is observed in any of the above three points, it is defined as "no processing mark".

[0151] Examples 2-6, Comparative Example 2

[0152] Except for changing the concentration of the abrasive used to remove machining marks in the slurry (abrasive fluid) as shown in Table 1, sheets were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0153] Comparative Example 1

[0154] Except for the absence of a process to remove processing marks, sheets were prepared in the same manner as in Example 1, and the results were evaluated. The results are shown in Table 1.

[0155] Example 7

[0156] The sheets were prepared and evaluated in the same manner as in Example 6, except that modified polytetrafluoroethylene (PTFE) was used instead of polytetrafluoroethylene. The results are shown in Table 2.

[0157] Comparative Example 3

[0158] Modified polytetrafluoroethylene was used instead of polytetrafluoroethylene. Otherwise, sheets were prepared in the same manner as in Comparative Example 1, and the results were evaluated. The results are shown in Table 2.

[0159] [Determination of the rate of dimensional change during heating]

[0160] The dimensional changes (heating dimensional change rate) of the sheets obtained in Examples 6 and 7 and Comparative Examples 1 and 3 before and after heating were evaluated using the following steps. The results are shown in Table 2.

[0161] 1. Cut the sheet into 110mm×130mm sizes and let it stand in a constant temperature room at 23℃ for 15 hours.

[0162] 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.

[0163] 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").

[0164] 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.

[0165] After cooling for 5.4 hours, remove the clamps and let it stand in a constant temperature chamber at 23°C for 15 hours.

[0166] After standing for 6.5 seconds, the distance between the marks was measured again using a digital microscope as the dimension after heating.

[0167] 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).

[0168] Rate of change of dimensional change after heating = (Dimension after heating - Dimension before heating) / Dimension before heating ... (i)

[0169] [Determination of Haze Value]

[0170] The haze values ​​of the sheets obtained in Example 7 and Comparative Example 3 were measured in the following order.

[0171] According to JIS K7136, a 30mm × 30mm section was cut from the center of the sheet. A haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., "NDH5000") was used to measure the diffuse transmittance and total transmittance. The haze value was calculated using the following formula (ii). The diffuse transmittance and total transmittance were measured at three locations on the sheet (any three points on the cut surface), and the arithmetic mean of the haze values ​​calculated from each measurement was obtained. The results are shown in Table 3.

[0172] Haze value (%) = Diffusion transmittance / Total light transmittance × 100……(ii)

[0173] [Evaluation of the adhesive properties of the surface-modified sheet]

[0174] The sheets from Example 6 and Comparative Example 1 were cut into 100mm × 100mm pieces, subjected to the plasma treatment described below, and then the adhesion was evaluated as described below. The results are shown in Table 4.

[0175] (Plasma processing)

[0176] 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.

[0177] (Adhesive strength test)

[0178] 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 peeled specimen with 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.

[0179] In Examples 1-6 and Comparative Examples 1-2, electron microscope images (6000x magnification, 1280×960 pixel area) obtained by "extraction of dark areas and calculation of aspect ratio" are shown below. Figure 7 .

[0180] [Table 1]

[0181]

[0182] [Table 2]

[0183]

[0184] [Table 3]

[0185]

[0186] [Table 4]

[0187]

[0188] [Potential for Industrial Applications]

[0189] 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.

[0190] 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.

[0191] 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 made of synthetic resin and is obtained through machining. Furthermore, the sheet material does not actually show any processing marks. The arithmetic mean of the aspect ratio of the dark areas in the scanning electron microscope images of the machined surfaces of the sheet exceeds 0.

80. The arithmetic mean of the aspect ratio of the dark area refers to the value obtained by taking a 3mm×3mm area on the cutting surface of the center of the sheet at 6000x magnification using a scanning electron microscope, capturing an area of ​​20μm×15μm in width, and extracting any 3 points from a 1280×960 pixel region of image data stored in multiple image data sets of 1280×960 pixels. The arithmetic mean of the aspect ratio of the dark area is determined for each image, and the arithmetic mean obtained for each image is further arithmetic averaged.

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

3. The sheet according to claim 1 or 2, wherein, Using a scanning electron microscope at 6000x magnification, a 3mm × 3mm area in the cutting surface of the center of the sheet was photographed, covering a range of 20μm horizontally and 15μm vertically. In any 1280 × 960 pixel area extracted from multiple image data stored at 1280 × 960 pixels, no gap elongated in the cutting direction was substantially observed.

4. The sheet according to claim 1 or 2, wherein, When heated to 180°C and then naturally cooled, the planar dimensions of the sheet shrink along a predetermined direction that serves as the cutting direction in the plane of the sheet, and expand along a direction orthogonal to the predetermined direction.

5. The sheet according to claim 1 or 2, wherein, The arithmetic mean of the aspect ratio of the dark-colored area is 0.85 or higher.

6. The sheet according to claim 1 or 2, wherein, The arithmetic mean of the aspect ratio of the dark-colored area is 0.90 or higher.

7. The sheet according to claim 1 or 2, wherein, The bond strength on the surface of the machined surface after surface modification exceeds 0.2 N / mm.

8. 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%.

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

10. A material for a printed circuit board, wherein, The sheet comprising any one of claims 1 to 9.

11. 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 9. The process includes: removing the processing marks from at least one side of a synthetic resin sheet obtained by cutting, in a manner that the side is substantially free of processing marks.

Images