WO2022131261A1

WO2022131261A1 - Sheet and method for producing sheet

Info

Publication number: WO2022131261A1
Application number: PCT/JP2021/046082
Authority: WO
Inventors: 智和渡邉; 優吉田; 友乃宇梶; 昌史関口
Original assignee: ニチアス株式会社
Priority date: 2020-12-16
Filing date: 2021-12-14
Publication date: 2022-06-23
Also published as: TW202235503A; CN116635223A; JPWO2022131261A1; CN116648349A; JPWO2022131263A1; JP7487340B2; TW202241714A; WO2022131263A1; TWI807541B

Abstract

Provided is a sheet that is made of a synthetic resin and that is obtained by skiving processing, wherein the sheet has substantially no processing marks.

Description

Sheets and sheet manufacturing methods

The present invention relates to a sheet and a method for manufacturing the sheet.

Fluororesin is a synthetic resin with excellent heat resistance, electrical insulation, non-adhesiveness, and weather resistance, and fluororesin sheets formed into sheets are chemical materials, electrical and electronic parts, semiconductors, and automobiles. It is widely used in industrial fields such as (for example, Patent Documents 1 to 4).

For example, since polytetrafluoroethylene (hereinafter referred to as PTFE) has a remarkably high melt viscosity, it is difficult to perform melt molding such as extrusion molding as is performed with general thermoplastic resins. ..
As a method for producing a resin sheet that is difficult to melt-mold, a method called skiving, in which a raw material powder is compression-molded to form a cylindrical block (billet) and then the block surface is carved into a thin film. Has been adopted.

For example, Patent Document 1 discloses, regarding a method for producing a PTFE sheet, a technique for suppressing distortion of a block body by heat-treating and lowering the temperature of the block body before skiving processing under predetermined conditions.

As an application example of a synthetic resin such as a fluororesin, it is known to be used as a mold release sheet, for example, taking advantage of its non-adhesive property and excellent mold release property. However, when the synthetic resin film obtained through the skiving process described above is used as a release sheet, vertical streaks called skive marks may be transferred to the surface of the sheet on the release side.
As a technique for smoothing the surface of a fluororesin film, for example, Patent Document 2 discloses a technique for heat-pressing a film obtained by a skive method. According to the technique of Patent Document 2, the surface of the release sheet is smoothed, but some vertical streaks (skiving marks) may be reduced, but the vertical streaks cannot be substantially removed. Further, when the film after skiving is heat-pressed, thermal deformation due to a temperature change or the like may occur.

Further, since fluororesin has excellent heat resistance and insulating properties, it is expected to be applied as a heat resistant material such as a heat resistant insulating tape or a printed circuit board material.
However, it has been pointed out that the fluororesin sheet produced by skiving is easily heat-shrinked by heating or the like and has poor dimensional stability, so that it is difficult to perform processing such as joining with other materials.

Japanese Unexamined Patent Publication No. 2013-027983 JP-A-2015-189934 Japanese Unexamined Patent Publication No. 2014-231562 JP-A-2010-201649

An object of the present invention is to provide a sheet capable of suppressing thermal deformation and having excellent dimensional stability.

According to the present invention, the following sheets are provided.
1. 1. A sheet made of synthetic resin obtained by skiving processing and having substantially no processing marks.
2. 2. The sheet according to 1, wherein the synthetic resin contains a fluororesin.
3. 3. The skived surface has a surface on which calcined products of raw material powder containing fluororesin powder are accumulated, and the calcined product retains substantially the same shape as the particles of the raw material powder and is stretched and deformed by skiving processing. The sheet according to 2 in which is not generated.
4. A portion of the skived surface in the center of the sheet having a plane dimension of 3 mm × 3 mm was photographed in a range of 20 μm in width × 15 μm in length at a magnification of 6000 times using a scanning electron microscope, and stored in 1280 × 960 pixels. The sheet according to any one of 1 to 3, wherein the voids extending in the skiving processing direction are not substantially visible in the arbitrary 1280 × 960 pixel region extracted from the plurality of image data.
5. When the sheet is allowed to cool after heating at 180 ° C., the plane dimension of the sheet contracts along a predetermined direction which is a skiving processing direction in the sheet plane direction, and expands along a direction orthogonal to the predetermined direction. The sheet according to any one of 1 to 4.
6. The sheet according to any one of 1 to 5, wherein the arithmetic mean value of the aspect ratio of the dark-colored portion in the scanning electron microscope image of the skived surface of the sheet exceeds 0.80.
7. The sheet according to 6, wherein the arithmetic mean value of the aspect ratio of the dark-colored portion is 0.90 or more.
8. The sheet according to any one of 1 to 7, wherein the surface-modified surface has an adhesive strength of more than 0.2 N / mm on the skived surface.
9. The sheet according to any one of 1 to 8, wherein the shrinkage in the skiving direction when allowed to cool after heating at 180 ° C. is less than 1.5%.
10. The sheet according to any one of 2 to 9, wherein the fluororesin is polytetrafluoroethylene (PTFE) or modified PTFE.
A material for a printed circuit board, which comprises the sheet according to any one of 11.1 to 10.
12. The method for producing a sheet according to any one of 12.1 to 10, wherein the one surface of the synthetic resin sheet obtained by skiving has substantially no processing marks on at least one surface thereof. A method for manufacturing a sheet, which comprises a step of removing the processing marks.

According to the present invention, it is possible to provide a sheet that can suppress thermal deformation and has excellent dimensional stability.

It is a figure which shows the skive process which cuts the outer peripheral surface in the longitudinal direction of a fired molded body (billet) into a sheet shape. It is a conceptual diagram for demonstrating the internal structure of a molded body. It is a scanning electron microscope image of a skiving machined surface which has a work mark. It is a scanning electron microscope image of a skiving machined surface having no processing mark. FIG. 5A is a scanning electron microscope image of a skiving machined surface having processing marks, and FIG. 5B is a conceptual diagram showing one of the dark-colored portions shown in FIG. 5A by extracting it. Is. FIG. 6A is a scanning electron microscope image of a skived surface having substantially no processing marks, and FIG. 6B is an extraction of one of the dark-colored portions shown in FIG. 6A. It is a conceptual diagram shown by. 6 is a scanning electron microscope image of the sheet surface obtained in Examples 1 to 6 and Comparative Examples 1 and 2. It is a scanning electron microscope image of the raw material powder of the sheet shown in FIG. It is a scanning electron microscope image which observed by magnifying the range shown by β of FIG.

Hereinafter, the sheet and the method for manufacturing the sheet according to the present invention will be described. In the present specification, "x to y" represents a numerical range of "x or more and y or less". Regarding one 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", the upper limit value and the lower limit value can be arbitrarily selected and combined. It shall be possible.

[Sheet]
The sheet according to one aspect of the present invention is a sheet made of synthetic resin obtained by skiving processing and has substantially no processing marks. The sheet has one surface forming a flat surface and the other surface which is the back surface thereof, regardless of the thickness, and can be formed in a band shape, a flat plate shape, or the like, and includes, for example, a film or a tape. The sheet made of synthetic resin means a sheet containing synthetic resin.
Further, in the following description, a resin piece containing a synthetic resin is simply referred to as a resin piece of a synthetic resin.

As shown in FIG. 1, skiving refers to a method of continuously cutting a sheet thinly by applying a cutting blade 20 to the surface of the billet 10 while rotating the billet 10 obtained by firing a compression molded product of resin powder. ..
The skived surface refers to the

surfaces

30A and 30B cut by the cutting blade in the sheet machined by skiving. The skived surface typically refers to both planes of the sheet, in view of the fact that the portion cut out having the outer peripheral surface of the billet 10 on one surface is usually excluded as a product. The skiving direction is the direction indicated by the arrow A in FIG.
The machined mark is a streak-shaped synthetic resin piece formed on the skived surface. Specifically, the processing mark refers to an embodiment in which a resin piece of synthetic resin is erected in a gap described later on the skiving surface, and refers to a resin piece on the gap and a gap defined by the resin piece. ..
In addition, when the skiving processing direction is described in detail, when the processing marks remain on the sheet plane, the skiving processing direction is the formation direction of the processing marks (specifically, the resin piece described above on the voids in the sheet plane (specifically, the resin piece described above (specifically, on the sheet plane). It can be specified as the direction in which the processing mark) extends over, or the longitudinal direction of the void that is partially covered with the resin piece (processing mark) to form an elongated shape). In other words, the machining mark means a resin piece of a streak-shaped synthetic resin extending in the machining direction on a void on the skiving processed surface, and a void defined by the resin piece.
On the other hand, when no processing marks remain on the sheet plane, the skiving processing direction can be specified as the shrinkage direction after the heat treatment of the sheet. Specifically, the sheet obtained by skiving is subjected to heat treatment and then allowed to cool due to the stress characteristics of skiving (more specifically, item 1 in "Measurement of heating dimension change rate" of the embodiment described later. (When the processing of item 5 is performed), the plane dimension contracts along a predetermined direction which is a skiving processing direction in the sheet plane direction, and expands along a direction orthogonal to the predetermined direction. That is, the direction in which the plane dimension of the sheet shrinks when it is allowed to cool after heat treatment can be specified as the skiving direction.

As a result of diligent research on the cause of the fact that the synthetic resin sheet obtained through skiving is easily thermally deformed and inferior in dimensional stability, the present inventors have found that processing marks remain on the skiving surface. It was found that the thermal change is likely to occur and the dimensional stability is deteriorated.
Here, a layer having processing marks on the skive processed surface is referred to as a fragile layer. That is, the fragile layer means a layer formed by stretching the surface layer of the sheet by the cutting blade in the processing direction by skiving. It is presumed that the fragile layer is mechanically fragile and susceptible to thermal changes and the like.

Since the sheet of this embodiment does not substantially have the above-mentioned processing marks (fragile layer), deformation due to temperature changes is suppressed, and the sheet is excellent in dimensional stability.
In addition, since the sheet of this embodiment does not substantially have the above-mentioned processing marks (fragile layer), when the sheet is used as a mold release sheet, the processing marks on the sheet to be released are left. Transfer can be reduced, and when the sheet is adhered to another member (for example, a metal material such as copper or another material), surface modification such as plasma treatment can be effectively performed, so that the other member can be effectively bonded. The adhesive strength with and can be improved.

As described above, skiving is performed on a billet (molded body) obtained by firing a compression molded body of raw material powder. In this case, voids called voids 10a existing between the compressed powders are dispersed and exist inside the billet which is the workpiece (see FIG. 2). For this reason, a part of the void inside the billet appears as a depressed portion on the surface of the sheet carved by skiving.
When the skiving surface has processing marks, at least a part of the resin piece extends over the depressed portion (corresponding to the above-mentioned void) and extends in the skiving processing direction (region α in FIG. 3). For this reason, the shape of the depressed portion (corresponding to the above-mentioned void) identified on the skiving surface is a portion that is elongated in the skiving processing direction by covering a part of the recessed portion (corresponding to the above-mentioned void) (streak-shaped portion). Will increase.
On the other hand, when there are substantially no machining marks on the skiving surface, the shape of the recessed portion identified on the skiving surface is close to the shape of the void itself described above, so that the degree of elongation in the skiving direction is low in many cases. (See Fig. 4).
Since a typical processing mark looks like a streak, the presence or absence of the processing mark can be confirmed by a microscope image (FIG. 3). In the present application, "substantially having no machining marks" means that the machining marks are substantially removed on the skiving surface of the sheet and the internal structure is exposed.
Specifically, "substantially having no processing marks" means the following states. First, a carbon tape is attached to the sample table of a scanning electron microscope (Hitachi High-Tech Co., Ltd., "SU3500"), and the skived surface of the measurement sample (planar dimension 3 mm x 3 mm in the center of the sheet) becomes the observation surface. To install. Next, platinum was vapor-deposited on the skive-processed surface, and a scanning electron microscope (manufactured by Hitachi High-Tech Co., Ltd., "SU3500") was used to observe an acceleration voltage of 5 kV at a magnification of 6000 times in a range of 20 μm in width and 15 μm in length. It means that the streak-shaped portion is not substantially visually recognized in an arbitrary three-point image (1280 × 960 pixel region) in a plurality of image data in which an electron microscope image is stored with a number of 1280 × 960 pixels. This includes not only the case where the streak-shaped portion is not visually recognized on the image at all, but also the case where the streak-shaped portion remaining within a range not contrary to the essence of the present invention is visually recognized on the image in light of the object of the present invention.

In the sheet according to one embodiment, the arithmetic mean value of the aspect ratio of the dark-colored portion in the scanning electron microscope image of the skived surface exceeds 0.80. The present embodiment provides one method for specifying the above-mentioned processing marks (streak-shaped portions).
Here, in the present application, the dark-colored portion in the scanning electron microscope image corresponds to the depressed portion (void) on the sheet surface, and is specified as follows.

First, the skived surface of the sheet was photographed with a scanning electron microscope at a magnification of 6000 times in a range of 20 μm in width × 15 μm in length, and from a plurality of image data saved in 1280 × 960 pixels, a predetermined pixel area (1280 ×). 960 pixel area) is set and extracted. For this extracted image, a gray scale (256 gradations) using a histogram analysis acquisition program for multi-valued image processing (for example, analysis software (for example, "Image-Pro 10" manufactured by Media Cybernetics. Inc.)). A histogram is acquired, the acquired histogram is used as a normal distribution, and the range of the average value ± 3σ when the dispersion amount is σ is extracted and used as 256 gradations. Further, the histogram is flattened, and the pixel portion of 0 to 35 gradations in 256 gradations is defined as a "dark color portion" based on the grayscale frequency distribution data obtained by the flattening process.

FIG. 5A is an example of a scanning electron microscope image of the central portion of the skive machined surface having processing marks, and the dark color portion P extracted by image analysis of the scanning electron microscope image by the above-mentioned method. The outer edge of is surrounded by a line. FIG. 5B is a conceptual diagram showing one of the dark-colored portions shown in FIG. 5A by extracting it.
In FIG. 5A, the direction indicated by "a" is the skiving direction, and in the example shown in FIG. 5A, it corresponds to the longitudinal direction of the sheet. In FIG. 5A, the direction indicated by "b" is a direction orthogonal to the skiving processing direction, and in the example shown in FIG. 5A, it corresponds to a direction orthogonal to the longitudinal direction of the sheet. The scale (10 scales) shown in the lower right of FIG. 5A shows 5.00 μm in the entire scale. This point is the same for FIG. 6A.

FIG. 6A is an example of a scanning electron microscope image of the central portion of the skive machined surface having substantially no processing marks, and the scanning electron microscope image was extracted by image analysis by the above-mentioned method. The outer edge of the dark part is surrounded by a line. FIG. 6B is a conceptual diagram showing one of the dark-colored portions shown in FIG. 6A by extracting it.
In FIG. 6A, the direction indicated by “a” is the skiving direction, and in the example shown in FIG. 6A, it corresponds to the longitudinal direction of the sheet. In FIG. 6A, the direction indicated by “b” is a direction orthogonal to the skiving processing direction, and in the example shown in FIG. 6A, it corresponds to a direction orthogonal to the longitudinal direction of the sheet.

Further, in the present application, the "aspect ratio of the dark color portion" is a diameter in a direction orthogonal to the skiving processing direction with respect to the diameter in the skiving processing direction.
The "arithmetic mean value of the aspect ratio of the dark color portion" is arbitrary from the image observed using a scanning electron microscope on the skived surface of the measurement sample (planar dimension 3 mm × 3 mm portion in the center of the sheet). 3 points of image (1280 × 960 pixel area) are extracted, and the arithmetic mean value is calculated for each image for the aspect ratio of the total dark color part specified in each of these 3 points of images, and obtained for each image. It is a value obtained by further arithmetically averaging the obtained arithmetic mean value. For example, in the example shown in FIG. 5, since the diameter of the dark color portion P in the skiving processing direction is Ra1 and the diameter in the direction orthogonal to the skiving processing direction is Rb1, the aspect ratio of the dark color portion P (in the skiving processing direction). The diameter in the orthogonal direction / the diameter in the skiving direction) is represented by (Rb1 / Ra1). In the example shown in FIG. 5, (Rb1 / Ra1) is approximately 0.5.
Further, for example, in the example shown in FIG. 6, the diameter of the dark color portion P in the skiving processing direction is Ra2, and the diameter in the direction orthogonal to the skiving processing direction is Rb2, so that the aspect ratio of the dark color portion P is (Rb2). It is represented by / Ra2). In the example shown in FIG. 6, (Rb2 / Ra2) is approximately 1.

When there are processing marks on the sheet surface, the shape of the depressed portion on the skiving surface tends to be smaller in the aspect ratio as shown in FIG. 5 because most of the shapes are elongated in the skiving direction as described above. There is.
On the other hand, when there are no machining marks on the sheet surface, the shape of the depressed portion on the skiving surface is often low in the degree of elongation in the skiving direction as described above, so that the aspect ratio is as shown in FIG. It tends to be larger than the predetermined value. In the big picture, the aspect ratio tends to be larger than a predetermined lower limit value and smaller than a predetermined upper limit value, that is, it tends to have a variation in the vicinity of 1 which is a perfect circle, and thus can be said to be close to 1.

In one embodiment, if the arithmetic mean value of the aspect ratio of the dark-colored portion in the scanning electron microscope image exceeds 0.80, it is assumed that there are substantially no processing marks.
The arithmetic mean value is a value calculated from the aspect ratio of all dark color portions extracted from the pixel area described above.

As another embodiment of the present invention, the lower limit of the arithmetic mean value of the aspect ratio of the dark color portion exceeds 0.80, 0.81 or more, 0.85 or more, 0.90 or more, 0.93 or more, It may be 0.95 or more, 1.00 or more, 1.05 or more, 1.12 or more, 1.14 or more, 1.16 or more, or 1.20 or more. As another embodiment of the present invention, the upper limit of the arithmetic mean value of the aspect ratio of the dark color portion is not particularly limited, but is, for example, 1.5 or less, 1.35 or less, 1.33 or less, 1 It can be composed of .26 or less, 1.23 or less, or 1.15 or less. Further, in another embodiment of the present invention, the arithmetic mean value of the aspect ratio of the dark color portion can be configured by combining the upper limit value and the lower limit value of the above embodiment, for example, exceeding 0.80 and 1.5. It can also be composed of the following, or 0.90 or more and 1.35 or less.
If the arithmetic mean value of the aspect ratio of the dark-colored portion is within the above range, it can be said that the sheet has a good surface condition with few processing marks on the skived surface and a structure close to the internal structure exposed on the surface.

(Haze value)
In one embodiment, the lower limit of the haze value of the sheet skived surface may be more than 53%, 55% or more, or 60% or more. The upper limit of the haze value may be, for example, 100% or less, 99% or less, 95% or less, 90% or less, 80% or less, 70% or less, or 65% or less.
The haze value is an index relating to the transparency of the film and is an index representing turbidity (turbidity). The haze value is specifically evaluated by the method described in Examples.

(Adhesive strength)
In one embodiment, the adhesive strength on the skived surface of the sheet after surface modification such as plasma treatment may be more than 0.2 N / mm, 0.5 N / mm. It may be the above. The adhesive strength is specifically evaluated by the method described in Examples.

(Heating dimensional change rate)
The sheet according to one embodiment may have a shrinkage rate (heat dimensional change rate) of less than 1.5% in the skiving direction in the sheet plane direction when allowed to cool after heat treatment at 180 ° C. It may be 1.3% or less, or 1.1% or less. The heating dimensional change rate is specifically evaluated by the method described in Examples.

[Synthetic resin]
As the synthetic resin, generally used ones can be used without particular limitation, and examples thereof include polyolefins such as polyethylene and polypropylene, fluororesins, polyester resins, and urethane resins. Among these, fluororesin can be preferably used.

As the fluororesin, generally used ones can be used without particular limitation, but polytetrafluoroethylene (PTFE) is preferable. Polytetrafluoroethylene (PTFE) is a homopolymer of tetrafluoroethylene.

Further, as the fluororesin, modified polytetrafluoroethylene (modified PTFE) may be used. Modified polytetrafluoroethylene (modified PTFE) is polytetrafluoroethylene modified with perfluoroalkyl vinyl ether.
Examples of the perfluoroalkyl vinyl ether include perfluoroalkyl vinyl ether represented by the following formula (1).
CF ₂ = CF-OR _f (1)
(In the 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)).

(In equation (2), n is an integer of 1 to 4.)

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, a perfluorohexyl group and the like. It is preferably a perfluoropropyl group.

[Other fillers]
In one embodiment, the sheet may further contain a filler. Examples of the filler include alumina, titanium oxide, silica, barium sulfate, silicon carbide, silicon nitride, glass fiber, glass beads, and mica. As these fillers, one kind or two or more kinds can be used.

When the sheet contains one or more fillers selected from alumina, titanium oxide, silica, barium sulfate, silicon carbide, silicon nitride, glass fiber, glass beads and mica, the content thereof is, for example, 0.5 to 0.5. It is 50% by mass, preferably 1 to 35% by mass. The sheet does not necessarily have to contain a filler.

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

[Sheet manufacturing method]
In the method for producing a sheet according to one aspect of the present invention, the processing marks are removed from at least one surface of the synthetic resin sheet obtained by skiving processing so that the one surface does not substantially have processing marks. Includes the process of performing the processing.

The method for manufacturing a sheet according to an embodiment includes the following steps (1) to (4):
(1) A step of filling a mold with a raw material containing a synthetic resin and compression molding to form a molded body (2) A step of firing a molded body (3) A step of cutting the surface of the fired molded body into a sheet shape. Step of performing skive processing (4) Step of removing processing marks from the surface of the sheet-shaped molded product

As the synthetic resin, the resin described in the above-mentioned sheet item can be used.
As the raw material to be compression-molded, a raw material containing 80 to 100% by mass of a fluororesin (for example, polytetrafluoroethylene or modified polytetrafluoroethylene) as a synthetic resin is preferable.
When the raw material to be compressed contains one or more kinds of fillers selected from alumina, titanium oxide, silica, glass fiber, glass beads, and mica, the blending amount of the filler is fluororesin (for example, polytetrafluoroethylene, modified). 1 to 50% by mass based on polytetrafluoroethylene or a mixture thereof).

The above raw materials are filled in a mold and compression molded to form a compression molded product. The surface pressure may be 10 to 100 MPa, 20 to 60 MPa, or 30 to 50 MPa.

The obtained compression molded product is fired to obtain a billet. The firing temperature may be 100 to 400 ° C, 350 to 370 ° C, or 360 to 370 ° C.
When a raw material powder containing a fluororesin such as polytetrafluoroethylene is used as the raw material powder of the compression molded body, the obtained billet is obtained as a molded body obtained by accumulating the calcined product of the raw material powder.

The shape of the billet (molded body) is preferably cylindrical from the viewpoint of ease of skiving processing described later. When the billet (molded body) is a cylindrical body, the diameter of the cylindrical body may be, for example, 100 to 500 mm or 150 to 500 mm.

Next, skiving processing is performed to cut the surface of the billet, which is a fired molded product, into a sheet.
When the billet (molded body) is a cylindrical body, a cutting blade is applied to the outer peripheral surface of the fired cylindrical body in the longitudinal direction to cut it into a sheet shape.

When the billet (molded body) is a cylinder, the outer peripheral surface, inner peripheral surface, and end face surface of the fired cylinder are before the step of cutting the longitudinal outer peripheral surface of the fired cylinder into a sheet shape. May be removed from the outside of the surface to a thickness of 3 mm, respectively.

The skiving step of cutting the outer peripheral surface of the fired cylinder in the longitudinal direction into a sheet can be carried out by using the apparatus shown in FIG. The thickness of the sheet obtained by cutting may be, for example, 0.01 to 1 mm, or 0.01 to 0.5 mm.
In FIG. 1, the fired billet (cylindrical body) 10 is rotated and cut with a cutting blade (bite) 20 to obtain a sheet 30.

Then, by projecting the particles onto the surface of the sheet, the processing marks existing on the surface of the sheet are removed. As a result, the surface of the sheet can be prevented from having substantially no processing marks.
As a method of removing processing marks by particle projection, particularly if the method can be adjusted so that the sheet surface is stretched by the particle projection and new processing marks (marks different from the processing marks by skiving processing) are not generated. Not limited. Examples of the method for removing the processing marks include, but are not limited to, a dry ice blast treatment using dry ice as the projection particles and a treatment of projecting a slurry in which the particles are dispersed in water.

The removal of the processing marks by particle projection is new so that the processing marks on the sheet surface can be removed so that the sheet surface has substantially no processing marks, and the sheet surface is stretched by particle projection. This can be done by appropriately adjusting the type of projection particles (particle material, shape, particle size) and projection conditions (projection angle, projection distance, projection pressure) so as not to generate processing marks. ..

In the sheet obtained by the above-mentioned method, substantially the same structure as the structure inside the billet appears as the surface shape of the skived surface.
For example, when a raw material powder containing a fluororesin is used as the raw material powder, the molded body (billet) formed by accumulating the fired products of the raw material powder is subjected to the above-mentioned skiving processing and processing marks removal processing. The finally obtained sheet has a skived surface having a surface on which the calcined product of the raw material powder is accumulated. The fired product retains substantially the same shape as the particles of the raw material powder, and constitutes the skived surface on the assumption that the stretch deformation due to skiving does not occur.

FIG. 8 is an image obtained by observing the raw material powder of the sheet shown in FIG. 4 with a scanning electron microscope, and FIG. 9 is an image observed with a scanning electron microscope with the range indicated by β in FIG. 8 further enlarged. Is.
The raw material powder (PTFE powder) shown in FIG. 8 is obtained by granulating primary particles synthesized by suspension polymerization for compression molding, and is a minute primary particle existing at a position indicated by, for example, Q in the range shown in β. The particles (average particle size: about 1 μm) are aggregated to form secondary particles having an average particle size of about 10 to 100 μm (for example, agglomerate particles occupying the range shown in β).
The compression molded body obtained by compression molding the raw material powder shown in FIG. 8 is an aggregate of the above-mentioned primary particles (average particle diameter: about 1 μm), and the billet obtained by firing the molded body is skived. A scanning electron microscope image obtained by observing the skived surface of the obtained sheet with a scanning electron microscope is shown in FIG.
Since the billet is formed by compression molding primary particles having an average particle diameter of about 1 μm and undergoing a firing process, a part of the primary particles is deformed into a flat shape, and a part is fused and crimped with other primary particles. Or it is glued. That is, the billet has a state in which the flat primary particles are bonded (engaged) with each other, in other words, the primary particles hold substantially the same shape as the particles of the raw material powder, and the billet is skived. As shown in FIG. 4, the skived surface of the obtained sheet has a surface in which particles (baked product of raw material powder) having an average particle diameter of about 1 μm are accumulated.
In FIG. 4, for example, the shape of each region (baked product of raw material powder) shown in c, d, e, and f is the shape of each region (primary particles of raw material powder) shown in g, h, i, and j in FIG. Each has substantially the same shape as the shape.

The sheet of this embodiment described above is suitably used, for example, as a material for a printed circuit board.

Example 1
<Making billets>
A mold is filled with polytetrafluoroethylene (PTFE) powder and compression-molded from above and below at a press pressure of 20 MPa for 0.5 hours to form a cylindrical preformed body (outer diameter 245 mm x inner diameter 75 mm x height 300 mm). Obtained. The obtained preformed body was put into a firing furnace and fired at 365 ° C. for 5 hours.

<Skiving>
The obtained cylindrical fired body (outer diameter 245 mm × inner diameter 75 mm × height 300 mm) was skived with the apparatus shown in FIG. 1 to produce a sheet having a thickness of 0.05 mm.

<Removal of processing marks>
A treatment was performed in which a slurry (polishing liquid) in which an abrasive was dispersed as projection particles was projected onto the skived surface of the obtained sheet.
In this embodiment, the process of projecting the polishing liquid is adopted as an example of the process of removing the processing marks, but in the process of removing the processing marks in the present invention, for example, a method capable of removing the processing marks by particle projection may be used. For example, different methods can be adopted as appropriate.
The processing marks were removed under the following conditions.
(Particle projection conditions)
・ Slurry (polishing liquid):
Solvent: Pure water Abrasive: Aluminium (Al ₂ O ₃ ), polygonal particles, average particle size (D50) 6.7 μm,
Abrasive content: 0.95% by volume
・ Projection angle: 90 °
・ Projection distance: 20 mm
・ Air pressure: 0.2MPa

The obtained sheets were evaluated as follows.
The results are shown in Table 1.

[Extraction of dark areas and calculation of aspect ratio]
First, a carbon tape is attached to the sample table of a scanning electron microscope (Hitachi High-Tech Co., Ltd., "SU3500"), and the skived surface of the measurement sample (planar dimension 3 mm x 3 mm in the center of the sheet) becomes the observation surface. I installed it like this. Next, platinum was deposited on the skive-processed surface of the measurement sample, and observed using a scanning electron microscope (manufactured by Hitachi High-Tech Co., Ltd., "SU3500") at an acceleration voltage of 5 kV and a magnification of 6000 times in a range of 20 μm in width × 15 μm in length. From a plurality of image data obtained by storing the scanned electron microscope image with the number of 1280 × 960 pixels, an image of a 1280 × 960 pixel region is optionally extracted from an arbitrary three-point image (1280 × 960 pixel region). did.
For each of these three extracted images, a gray scale (256 gradations) histogram was created using a histogram analysis acquisition program (“Image-Pro 10” manufactured by Media Cybernetics. Inc.) for multi-value image processing. The acquired histogram was used as a normal distribution, and the range of the average value ± 3σ when the dispersion amount was σ was extracted and used as 256 gradations. Further, a histogram flattening process was performed, and based on the grayscale frequency distribution data obtained by this, the pixel portion of 0 to 35 gradations in 256 gradations was specified as a “dark color portion”.
Next, for all the dark colored parts specified in each image, the diameter in the skiving processing direction and the diameter in the direction orthogonal to the skiving processing direction are measured, and the aspect ratio ((diameter in the direction orthogonal to the skiving processing direction) / ( The diameter in the skiving direction))) was calculated. Arithmetic mean values were calculated for each image for the aspect ratio of the total enrichment portion thus obtained, and the arithmetic mean values obtained for each of the three images were further arithmetically averaged to "dark-colored portions". "Arithmetic mean value of aspect ratio" was calculated.

[Presence / absence of processing marks]
The presence or absence of processing marks was confirmed in the scanning electron microscope image obtained in "Extraction of dark color portion and calculation of aspect ratio". Specifically, any of the three 1280 × 960 pixel region images extracted from the scanning electron microscope image observed under the above conditions extends in the skiving direction on the voids on the skiving surface of the sheet. If a streak-shaped resin piece or a gap (machining mark) forming a long shape in the same direction is found, it is regarded as "having a machining mark", and no machining mark is found in any of the above-mentioned three images. In the case, it was set as "no processing marks".

Examples 2 to 6, Comparative Example 2
A sheet was prepared and evaluated in the same manner as in Example 1 except that the polishing agent concentration of the slurry (polishing liquid) used for removing the processing marks was changed as shown in Table 1. The results are shown in Table 1.

Comparative Example 1
A sheet was prepared and evaluated in the same manner as in Example 1 except that the step of removing the processing marks was not performed. The results are shown in Table 1.

Example 7
Sheets were prepared and evaluated in the same manner as in Example 6 except that modified polytetrafluoroethylene (modified PTFE) was used instead of polytetrafluoroethylene. The results are shown in Table 2.

Comparative Example 3
Sheets were prepared and evaluated in the same manner as in Comparative Example 1 except that modified polytetrafluoroethylene was used instead of polytetrafluoroethylene. The results are shown in Table 2.

[Measurement of heating dimension change rate]
The dimensional changes (heated dimensional change rate) of the sheets obtained in Examples 6 and 7 and Comparative Examples 1 and 3 before and after heating were evaluated by the following procedure. The results are shown in Table 2.
1. 1. The sheet was cut to a size of 110 mm × 130 mm and allowed to stand in a constant temperature room at 23 ° C. for 15 hours.
2. 2. 1. 1. A 50 mm x 50 mm marked line is drawn on the sheet after standing still, and the distance between the marked lines in the skiving direction (hereinafter, also referred to as MD direction) and its orthogonal direction (hereinafter, also referred to as CD direction) is digital. It was measured with a microscope (manufactured by Keyence Co., Ltd., "VHX5000") and used as the pre-heating dimension.
3. 3. 2. 2. After measuring the dimensions of the sheet, both ends in the MD direction were clipped and hung in a hot air circulation type gear oven (manufactured by Tabie Spec Co., Ltd., "PHH-100").
4. 3. 3. The hot air circulation type gear oven was heated from room temperature to 180 ° C., held for 1 hour after reaching 180 ° C., and allowed to cool to room temperature.
5. 4. After allowing to cool, the clip was removed and the mixture was allowed to stand in a constant temperature room at 23 ° C. for 15 hours.
6. 5. After standing still, the distance between the marked lines was measured again with a digital microscope, and the dimensions were determined after heating.
7. 2. 2. Pre-heating dimensions and 6. From the post-heating dimensions obtained in 1), the heating dimension change rate was calculated by the following formula (i).
Heating dimension change rate = (post-heating dimension-pre-heating dimension) / pre-heating dimension ... (i)

[Measurement of haze value]
The haze values of the sheets obtained in Example 7 and Comparative Example 3 were measured by the following procedure.
In accordance with JIS K7136, a part with a plane dimension of 30 mm x 30 mm is cut out from the center of the sheet, and the diffusion transmittance and total light transmittance are measured using a haze meter (Nippon Denshoku Industries Co., Ltd., "NDH5000"). Then, the haze value was calculated from the following equation (ii). The diffusion transmittance and the total light transmittance were measured at three points on the sheet (arbitrary three points on the skived surface), and the arithmetic mean value of the haze value calculated from each measured value was calculated. The results are shown in Table 3.
Haze value (%) = diffuse transmittance / total light transmittance × 100 ... (ii)

[Evaluation of sheet adhesiveness after surface modification]
The sheets of Example 6 and Comparative Example 1 were cut into 100 mm × 100 mm, subjected to the plasma treatment shown below, and then the adhesiveness evaluation shown below was performed. The results are shown in Table 4.

(Plasma processing)
A sheet was placed in a vacuum plasma apparatus to evacuate, and plasma treatment was performed for 10 seconds using a 2.45 GHz microwave in a mixed gas atmosphere of nitrogen gas and hydrogen gas.

(Adhesive strength measurement)
Plasma-treated sheet, halogen-free low-dielectric adhesive (semi-curing) sheet (manufactured by Nikkan Kogyo Co., Ltd., "SAFY", thickness 25 μm), and electrolytic copper foil (manufactured by Mitsui Mining & Smelting Co., Ltd., "TQ-M4-""VSP" (thickness 18 μm) was superposed in this order and crimped with a hot press (temperature: 160 ° C., press time: 1 hour, press load: 4 MPa) to prepare a sample for adhesive strength measurement. A notch was made in this sample to a width of 10 mm, and the copper foil was peeled off by 30 mm. The peeled sample with the copper foil was subjected to a 90 ° peeling test at a tensile speed of 50 mm / min using a small tabletop tester (manufactured by Shimadzu Corporation, "EZ-LX"), and the adhesive strength was measured.

FIG. 7 shows an electron microscope image (magnification 6000 times, 1280 × 960 pixel region) acquired in “Extraction of dark color portion and calculation of aspect ratio” in Examples 1 to 6 and Comparative Examples 1 to 2.

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

Although some embodiments and / or embodiments of the present invention have been described above in detail, those skilled in the art will appreciate these exemplary embodiments and / or embodiments without substantial departure from the novel teachings and effects of the present invention. It is easy to make many changes to the examples. Therefore, many of these modifications are within the scope of the invention.
All the documents described in this specification and the contents of the application underlying the priority under the Paris Convention of the present application are incorporated.

Claims

A synthetic resin sheet obtained by skiving.
A sheet that has virtually no processing marks.
The sheet according to claim 1, wherein the synthetic resin contains a fluororesin.
The skived surface has a surface on which calcined products of raw material powder containing fluororesin powder are accumulated.
The sheet according to claim 2, wherein the fired product retains substantially the same shape as the particles of the raw material powder and is not stretched and deformed by skiving.
A portion of the skived surface in the center of the sheet having a plane size of 3 mm × 3 mm was photographed in a range of 20 μm in width × 15 μm in length at a magnification of 6000 times using a scanning electron microscope, and stored in 1280 × 960 pixels. The sheet according to any one of claims 1 to 3, wherein the void extending in the skiving processing direction is substantially invisible in the arbitrary 1280 × 960 pixel region extracted from the plurality of image data.
After heating at 180 ° C. and then allowed to cool, the plane dimension of the sheet contracts along a predetermined direction which is the skiving direction in the sheet plane direction and expands along a direction orthogonal to the predetermined direction. The sheet according to any one of claims 1 to 4.
The sheet according to any one of claims 1 to 5, wherein the arithmetic mean value of the aspect ratio of the dark-colored portion in the scanning electron microscope image of the skived surface of the sheet exceeds 0.80.
The sheet according to claim 6, wherein the arithmetic mean value of the aspect ratio of the dark color portion is 0.90 or more.
The sheet according to any one of claims 1 to 7, wherein the surface-modified adhesive strength on the skived surface exceeds 0.2 N / mm.
The sheet according to any one of claims 1 to 8, wherein the shrinkage rate in the skiving processing direction when allowed to cool after heating at 180 ° C. is less than 1.5%.
The sheet according to any one of claims 2 to 9, wherein the fluororesin is polytetrafluoroethylene (PTFE) or modified PTFE.
A material for a printed circuit board, including the sheet according to any one of claims 1 to 10.
The method for manufacturing the sheet according to any one of claims 1 to 10.
A method for manufacturing a sheet, comprising a step of removing at least one surface of a synthetic resin sheet obtained by skiving so that the one surface does not substantially have processing marks.