KR102714296B1 - Biaxially oriented polyester film - Google Patents

Abstract

The present invention provides a biaxially oriented polyester film which is suitable as a support film, which can impart a good gloss-removing appearance to the surface when transferring a transfer film such as an electromagnetic shielding film to a member such as an FPC or a module, and which has excellent peelability of the support film after transfer. That is, the present invention is achieved by a biaxially oriented polyester film, which is a laminated polyester film having a substrate layer and a particle-containing gloss-removing layer, wherein the centerline average roughness of the surface of the gloss-removing layer is 400 to 1000 nm, the 10-point average roughness is 4000 to 8000 nm, and the gloss ( _G60 ) on the surface is 6 to 20, and further, the void rupture rate of protrusions on the surface is 20% or less.

Description

BIAXIALLY ORIENTED POLYESTER FILM

The present invention relates to a biaxially oriented polyester film, which is particularly preferable as a support film used when transferring an electromagnetic shielding film to a flexible printed circuit or module, and more specifically, to a matte-free biaxially oriented polyester film which is preferable for transferring the uneven shape of the surface of the support film simultaneously with the transfer, thereby providing a non-glossy surface to the surface of the electromagnetic shielding film.

Conventionally, it has been known to cover electronic devices including office equipment such as PCs, communication devices such as mobile phones, and medical devices, and various devices incorporating such devices with an electromagnetic shielding film in order to absorb electromagnetic waves generated from a nearby area and suppress interference such as malfunctions, incorrect contacts at contact points, and noise. Recently, a method has been practiced in which an electromagnetic shielding film is formed on a support film (for example, an electromagnetic shielding film in which a protective layer and an electromagnetic shielding layer are laminated in this order), and this is pressed at high temperature onto the surface of various devices to transfer the electromagnetic shielding film (for example, Patent Documents 1 and 2).

In addition, in the case of conventional transfer-type electromagnetic shielding films, a flat support film was used to obtain a clear product appearance, but recently, attempts have been made to use a transfer method to provide a surface appearance of a product with a matte-free appearance. Accordingly, a support film with excellent matte-free appearance transferability and a matte-free layer has been demanded.

Meanwhile, regarding a film having a gloss removal layer, Patent Document 3 discloses a gloss removal laminated polyester film for molding which has excellent moldability, thickness variation, and heat resistance. However, it has not been examined as a support film for use in transferring electromagnetic shielding films, etc., and therefore, although it is sufficient for general molding processing, it is insufficient as a support film for transfer.

In addition, Patent Document 4 discloses a two-axis oriented coextruded matte polyester film having good matte removal properties and transparency, and discloses adding 1 to 10 wt% of particles having a particle size of 2 to 5 ㎛ to one side of a laminated film. However, the gloss (G ₆₀ ) of the film specifically exemplified is about 50 to 70, and further, no examination has been conducted on its use as a support film for transfer processing.

Japanese Patent Publication No. 2004-95566 Japanese Patent Publication No. 2009-38278 Japanese Patent Publication No. 4-110147 Japanese Patent Publication No. 2002-200723

Recently, in order to increase production efficiency when transferring electromagnetic shielding films to flexible printed circuits (FPCs) or modules, transfer processing at higher temperatures and higher speeds has been performed. However, under such transfer conditions, in the case of the conventional support film described above, if the film gloss is lowered, the problem of peelability in which the support film breaks during peeling easily occurs. In addition, if the support film is colored white to improve visibility, the base film becomes more prone to breakage.

The present invention has been made in consideration of the above, and its purpose is to provide a biaxially oriented polyester film which is particularly preferable as a support film for transferring an electromagnetic shielding film, which can impart a more excellent gloss-removing appearance to the surface than conventionally possible when transferring an electromagnetic shielding film to a member such as an FPC or a module, and which is less likely to cause problems such as breakage even when the support film is peeled off after transfer. Furthermore, it is preferable to provide a biaxially oriented polyester film which has good visibility.

The present inventors, as a result of careful examination to solve the above problems, have found that when imparting a matte appearance to an electromagnetic shielding film by a transfer method, if the particle size in the support film is increased or the particle content is increased in order to impart a more matte matte appearance than before, a problem occurs in the peelability of the support film after the transfer, and that this problem can be improved by suppressing the exposure of the particles used in the matte layer to the surface of the film matte layer, and as a result of further examination, have completed the present invention.

Thus, according to the present invention,

"1. A biaxially oriented polyester film having a base layer and a particle-containing gloss removal layer on at least one surface, wherein the centerline average roughness (Ra) of the surface of the gloss removal layer is 400 to 1000 nm, the 10-point average roughness (Rz) is 4000 to 8000 nm, the gloss ( _G60 ) of the surface is 6 to 20, and the void rupture rate of protrusions on the surface is 20% or less.

2. A biaxially oriented polyester film as described in 1 above, wherein the color L value of the substrate layer is 60 to 80.

3. A biaxially oriented polyester film as described in 1 or 2 above, wherein the apparent surface energy of the gloss removal layer surface is 60 dyn/cm or less.

4. A biaxially oriented polyester film according to any one of the above 1 to 3, wherein the polyester constituting the gloss removal layer contains polyethylene terephthalate as a main component and at least one selected from the group consisting of polytrimethylene terephthalate, polybutylene terephthalate, and poly(cyclohexylenedimethylene) terephthalate.

5. A biaxially oriented polyester film according to any one of 1 to 4 above, wherein the average particle size of the particles in the gloss removal layer is 2.5 to 5.5 ㎛ and the content is 5 to 18 mass%.

6. A biaxially oriented polyester film according to any one of the above 1 to 5, wherein the particles in the gloss removal layer are amorphous silica or synthetic zeolite.

7. A biaxially oriented polyester film according to any one of the above 1 to 6, wherein the main component of the polyester constituting the substrate layer is polyethylene terephthalate.

8. A biaxially oriented polyester film as described in 7 above, wherein the intrinsic viscosity of the polyester constituting the substrate layer is 0.56 to 0.70 ㎗/g.

9. A biaxially oriented polyester film according to any one of 1 to 8 above, wherein the particle content of the substrate layer is 3.0 mass% or less based on the mass of the substrate layer.

10. A biaxially oriented polyester film according to any one of the above 1 to 9, which is used as a support film for transferring an electromagnetic shielding film.

This is provided.

According to the present invention, when a transfer film such as an electromagnetic shielding film formed on the surface of a gloss removal layer is transferred to a member such as an FPC or a module, a biaxially oriented polyester film can be provided which imparts a good gloss removal appearance to the surface of the member, and which is less likely to suffer from a decrease in peelability such as breakage when the support film is peeled off after the transfer. In addition, a biaxially oriented polyester film which preferably has good visibility can be provided.

Hereinafter, the present invention will be described in detail.

＜2-axis oriented polyester film＞

The biaxially oriented polyester of the present invention is a laminated polyester film having a substrate layer and a particle-containing gloss removal layer on at least one surface. By having the gloss removal layer and the substrate layer, the surface roughness and gloss described later can be obtained under stable film forming properties. If there is no substrate layer and only a particle-containing single layer is used, it becomes difficult to simultaneously satisfy surface roughness and gloss and stable film forming properties.

(gloss removal layer)

The gloss removing layer occupying at least one surface of the laminated polyester film is made of polyester containing particles for forming unevenness on the surface (unevenness-forming particles). In terms of a void rupture rate of the surface protrusions described later being 20% or less, a copolymerized polyester having good stretchability of the particle-containing polyester or a polyester composition obtained by melt-blending a plurality of polyesters is preferable, and in particular, it is preferable that the polyester used in the substrate layer described later has the same main component as that of the polyester. That is, for example, when the main component of the polyester of the substrate layer is ethylene terephthalate, the polyester of the gloss removing layer is preferably a polyethylene terephthalate-based copolymerized polyester or a polyester composition containing polyethylene terephthalate as the main component. Among these, as a secondary component of the polyester composition, it is preferable that at least one member be selected from the group consisting of polytrimethylene terephthalate, polytetramethylene terephthalate, and poly(cyclohexylenedimethylene) terephthalate.

In addition, the average particle size of the particles in the gloss removal layer is preferably 2.5 to 5.5 ㎛, and the content thereof is preferably 5 to 18 mass% based on the mass of the gloss removal layer. In addition, it is preferable that the maximum particle size of the particles contained in the gloss removal layer be 16 ㎛ or less. By adopting such an aspect, it becomes easy to obtain a sufficient gloss removal appearance while also making it excellent in peelability in the transfer process.

When the particle content in the gloss removal layer is below the lower limit, it tends to be difficult to obtain the gloss described above, and on the other hand, when it exceeds the upper limit, not only does the effect of improving peelability after high-temperature pressing in the transfer process tend to be low, but also the film forming property deteriorates and tearing easily occurs, so that the film forming itself tends to become difficult. From this viewpoint, the particle content is preferably 7 mass% or more, more preferably 10 mass% or more, and further preferably 16 mass% or less, and further preferably 14 mass% or less.

The average particle size of the particles is more preferably 3.0 to 5.5 ㎛, and even more preferably 3.0 to 5.3 ㎛. When the average particle size of the particles is less than the lower limit, the effect of lowering the gloss is reduced, so that the amount of particles added is further increased to lower the gloss, and the effect of improving peelability in the transfer process tends to be reduced. On the other hand, when the average particle size of the particles exceeds the upper limit, not only the effect of improving peelability tends to be reduced, but also the film forming property tends to be reduced.

In addition, the maximum particle diameter of the particles is preferably 15 ㎛ or less, more preferably 12 ㎛ or less. In addition, the maximum particle diameter referred to here is the particle diameter at 98% of the cumulative particle diameter distribution curve (d ₉₈ ).

The particles used in the gloss removal layer preferably have a weight change of 3.0% or less at 300°C as measured by the TG-DTA method, and more preferably 1.5 to 3.0%. In addition, the weight change of the particles referred to here is specifically the weight change at 300°C measured when the temperature is increased from 30°C to 500°C at a heating rate of 10°C/min using a TG-DTA device. If the weight change exceeds the upper limit, foaming may occur in the polyester film manufacturing process or the electromagnetic shielding film transfer process, or the molecular weight may be reduced, thereby lowering the film-forming properties or heat resistance of the film. In particular, when the particles are contained in a large amount, the film-forming properties or heat resistance of the film may be significantly reduced.

The type of particles may be either inorganic or organic, and examples thereof include amorphous silica (colloidal silica), silica, talc, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, alumina, carbon black, titanium dioxide, kaolin, synthetic zeolite, cross-linked polystyrene particles, and cross-linked acrylate particles. Among these particles, amorphous silica or synthetic zeolite is preferable, and either one of these may be used alone or in combination. Also, a mixture of particles of the same type but having different particle sizes may be used. In addition, in the case of amorphous silica, it is more preferable that the surface is treated with a silane coupling agent to reduce moisture adsorption.

Particularly preferable particles are synthetic zeolites, and in order to reduce the adsorptivity of the synthetic zeolite, particularly the moisture adsorption, it is preferable that the particles are treated with an acid having a pH of 5 or higher to a degree that does not destroy the particle shape, and further, it is preferable that the particles are heat-treated at a temperature of 300°C or higher.

The shape of the particles is not specifically specified, but if it is irregular, the particle size distribution becomes wider, coarse protrusions are likely to occur due to agglomeration, the peelability improvement effect is lowered, or the film forming property of the film may deteriorate. Therefore, the shape of the particles is preferably spherical or polyhedral. Examples of preferable particles include spherical or polyhedral synthetic zeolites. In particular, in the case of polyhedral particles, a matting effect is easily obtained. Among polyhedral particles, cubic particles are particularly preferable.

The method of adding these particles is not particularly limited, but examples thereof include adding them as a glycol dispersion during polycondensation of polyester, and adding them to a gloss removal layer via a master batch during extrusion.

The thickness of this gloss removal layer is suitably in the range of 3 to 10 ㎛, preferably 4 to 9 ㎛, for a two-layer configuration, and in the range of 2 to 5 ㎛ for a three-layer configuration.

(base layer)

The polyester constituting the base layer of the present invention is a linear saturated polyester synthesized from an aromatic dibasic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof. Specific examples of such polyesters include polyethylene terephthalate, polybutylene terephthalate, poly(cyclohexylenedimethylene) terephthalate, polyethylene-2,6-naphthalenedicarboxylate, and the like, and a copolymer obtained by copolymerizing a small amount of a precursor component with these, or a blend of these with a small proportion of another resin, etc. Of these, polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate are preferable from the viewpoint of heat resistance, and polyethylene terephthalate is particularly preferable because it has a good balance between heat resistance and moldability.

The particle content of the substrate layer is preferably 3.0 mass% or less, more preferably 2.5 mass% or less, and even more preferably 2.0 mass% or less, based on the mass of the substrate layer. By adopting such an aspect, it becomes easy to obtain excellent film forming properties.

The type of particles used in the substrate layer is not particularly limited as long as they are particles that are usually added to the film, and may be either inorganic particles or organic particles. Specific examples thereof include amorphous silica (colloidal silica), silica, talc, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, alumina, carbon black, titanium dioxide, kaolin, synthetic zeolite, cross-linked polystyrene particles, and cross-linked acrylate particles. One type or two or more types of different particles among these particles may be contained, and a mixture of particles of the same type but having different particle sizes may also be used. Among these particles, in order to improve visibility, it is preferable to contain 0.5 to 2.0 mass% of titanium dioxide. If it is less than this range, visibility may deteriorate, and in many cases, it may cause breakage or embrittlement during peeling.

The substrate layer may contain, as necessary, other resins than polyester, colorants, antistatic agents, stabilizers, antioxidants, ultraviolet absorbers, fluorescent whitening agents, etc., as long as they do not impede the purpose of the present invention.

The thickness of the substrate layer is preferably 10 to 140 ㎛, more preferably 20 to 100 ㎛, and particularly preferably 40 to 60 ㎛.

(surface roughness)

The centerline average roughness (Ra) of the surface of the gloss removal layer of the present invention must be 400 to 1000 nm, and the 10-point average roughness (Rz) must be 4000 to 8000 nm. When Ra and Rz are within these ranges, the surface gloss removal appearance of the electromagnetic shielding film or the like after transfer becomes a good basis. When at least one of Ra or Rz is below the lower limit, the effect of improving the gloss removal appearance becomes insufficient. On the other hand, when at least one of Ra or Rz exceeds the upper limit, although the gloss removal appearance is good, since the surface unevenness is too severe, problems such as particle detachment during film forming or delamination in the transfer process easily occur. From this viewpoint, the lower limit of Ra is preferably 500 nm, more preferably 600 nm, and the upper limit of Ra is preferably 800 nm, more preferably 750 nm. Also, the lower limit of Rz is preferably 5000 nm, more preferably 6000 nm, and the upper limit of Rz is preferably 7500 nm, more preferably 7000 nm.

Additionally, Ra and Rz can be obtained by adjusting the content in the gloss removal layer, for example, by using particles having the above-mentioned average particle diameter and maximum particle diameter.

(Gloss: G ₆₀ )

The biaxially oriented polyester film of the present invention requires that the gloss (G ₆₀ ) of the gloss removal layer surface be 6 to 20, preferably 9 to 15. In addition, the gloss (G ₆₀ ) referred to here is a value measured at an incident angle and a reception angle of 60° both in accordance with JIS standard Z 8741. When the gloss is within this range, the gloss removal surface appearance can be preferably provided to the surface of a transfer film such as an electromagnetic shielding film. If the gloss is less than the lower limit, the amount of particles added increases, which deteriorates the film forming properties, and it becomes difficult to keep the rupture rate of surface protrusions to 20% or less, which causes heavy peeling, so this is not preferable. On the other hand, if the gloss exceeds the upper limit, it becomes impossible to provide a sufficient gloss removal appearance to the surface of an electromagnetic shielding film, so this is not preferable.

(Void burst rate)

The void rupture rate of the protrusion on the surface of the gloss removal layer of the present invention must be 20% or less, and if this value exceeds 20%, when the support film is peeled off after transfer, the protrusion where the void rupture occurred becomes the starting point of the rupture at the time of peeling, which is not preferable. From this viewpoint, the void rupture rate is preferably 15% or less, and more preferably 10% or less. There is no need to specifically limit the lower limit, and the lower the better, but from the viewpoint of actual manufacturing, it is about 5%.

In addition, the void rupture rate of the surface protrusion can be easily achieved by, as described above, using a polyester composition in which the polyester used in the gloss removal layer is a copolymerized polyester or a polyester composition in which other types of polyester are melt-blended to increase the stretchability of the particle-containing polyester, or further, by slightly increasing the intrinsic viscosity of the polyester to increase the stretchability of the particle-containing polyester.

In addition, the void rupture rate of the protrusion was calculated by taking a photograph of the surface of the gloss removal layer with FE-SEM, counting the total number of protrusions and the number of protrusions with cavities around the protrusions (void rupture of protrusions) among them, and calculating the ratio (%) of the number of ruptures to the total number.

(surface energy)

In addition, the gloss removal layer surface of the present invention preferably has an apparent surface tension of 60 dyn/cm or less, more preferably 58 dyn/cm or less, in terms of peelability. Such surface tension can be achieved by using a copolymerized polyester or polyester composition containing a more hydrophobic diol component as the diol component of the polyester used in the gloss removal layer, while reducing the void rupture rate of the protrusions.

＜Film manufacturing method＞

The polyester film of the present invention, when the main component of the polyester is polyethylene terephthalate, can be manufactured, for example, by the following method. That is, a deglazing layer and a substrate layer are laminated and extruded by a coextrusion method, cooled and solidified by a casting drum to form a non-stretched film, and then stretched in the longitudinal direction (meaning the film forming machine axis direction. Hereinafter, it is sometimes called the machine axis direction, continuous film forming direction, longitudinal direction, or MD) and the transverse direction (meaning the direction perpendicular to the continuous machine axis direction and the thickness direction. Hereinafter, it is sometimes called the width direction, TD).

Longitudinal stretching is performed, for example, at a temperature of 60 to 130°C, preferably 90 to 125°C, and elongates by a factor of 2.0 to 3.5, preferably 2.5 to 3.0. Transverse stretching is performed, for example, at a temperature of 100 to 130°C, preferably 90 to 125°C, and elongates by a factor of 2.0 to 4.0, preferably 3.0 to 4.0. In addition, one-directional stretching can also be performed in two or more stages, but it is preferable that the final stretching ratio be within the above-mentioned range.

Next, heat setting treatment is performed as desired. For example, when the gloss removal layer and the substrate layer are composed of polyethylene terephthalate, heat setting is performed at a temperature of 220 to 240°C, preferably 220 to 235°C, for a time of 2 to 30 seconds, preferably 2 to 20 seconds, and more preferably 3 to 10 seconds. At that time, in order to reduce the heat shrinkage rate, it may be performed under limited shrinkage or elongation of less than 20%, or under constant length, or it may be performed in two or more stages.

＜Other film characteristics＞

(Intrinsic viscosity)

The intrinsic viscosity (IV) of the base polyester layer constituting the biaxially oriented polyester film of the present invention is preferably in the range of 0.50 to 0.70 ㎗/g. This intrinsic viscosity is expressed as a measurement value in an o-chlorophenol solution at 25 ℃. The lower limit of this intrinsic viscosity is preferably 0.56 ㎗/g, particularly preferably 0.60 ㎗/g, because peelability becomes better. In addition, the upper limit of this intrinsic viscosity is preferably 0.67 ㎗/g, and more preferably 0.65 ㎗/g. When the intrinsic viscosity of the film does not reach the lower limit, the mechanical performance tends to deteriorate and handling becomes difficult. On the other hand, when the intrinsic viscosity of the film exceeds the upper limit, the viscosity becomes excessively high, the load in the film manufacturing process increases, and productivity decreases.

Meanwhile, the gloss removal layer contains a considerable amount of particles having a large average particle size as described above in order to satisfy requirements related to the gloss removal layer surface roughness, gloss (G ₆₀ ) and surface protrusion void rupture rate. Therefore, in terms of handling properties such as peelability, the intrinsic viscosity of polyester is preferably higher, but if it becomes too high, the film forming property deteriorates along with the high particle content, so it is preferable to adjust the intrinsic viscosity depending on the type and content of the contained particles.

(film thickness)

The two-axis oriented polyester film of the present invention may have a thickness that is usable as a support film for use in electromagnetic shielding film transfer, etc., and is preferably 10 to 150 µm, more preferably 20 to 100 µm, and particularly preferably 45 to 70 µm.

Example

Hereinafter, the present invention will be further described by examples. In addition, each characteristic value was measured by the following method.

1. Gloss (G ₆₀ )

In accordance with JIS standard (Z 8741), measurements were made using a glossmeter "VGS-SENSOR" manufactured by Nippon Denshoku Kogyo Co., Ltd. Measurements were made at both an incident angle and a reception angle of 60° (N = 5), and the average value was used.

2. Average particle size

The particles were stirred in a mixer to a concentration of 3% in ethylene glycol, and measurement was performed using a laser scattering particle size distribution measuring device SALD-7000 manufactured by Shimadzu Corporation. From the particle size distribution measurement results, the 50% volume particle size ( _D50 ) was obtained, and this was used as the average particle size.

3. Particle content

A sample is cut from a layer of a film sample from which the particle content is to be measured, and a solvent is selected that dissolves polyester but does not dissolve the particles, and the particles are then centrifuged from the solution, and the ratio (mass%) to the total mass of the particles is used as the particle content.

4. Thickness of each layer of film

The sample was cut into a triangle, fixed in a capsule, and embedded in epoxy resin. Then, the embedded sample was sectioned into 50 nm thick thin sections parallel to the longitudinal direction using a microtome (ULTRACUT-S), and then observed and photographed using a transmission electron microscope at an acceleration voltage of 100 kV, and the thickness of each layer was measured at 10 points from the photographs, and the average thickness was obtained for each layer. For the gloss removal layer, measurements were made on a portion where no particles existed.

5. Center line average roughness Ra and 10 point average roughness Rz

According to JIS-B 0601, B 0651, using a three-dimensional surface roughness meter (manufactured by Kosaka Laboratory, product name: SURF CORDER SE-3CK), the center line average roughness Ra and the 10-point average roughness Rz were measured under the conditions of a stylus tip R of 2 µm, a scan pitch of 2 µm, a scan length of 1 mm, a number of scans of 100, a cutoff of 0.25 mm, and a magnification of 5000 times.

6. Film specific viscosity

It was measured under an atmosphere of 25℃ with orthochlorophenol. In addition, the intrinsic viscosity of the substrate layer was measured by cutting out a portion of the substrate layer from a biaxially oriented polyester film.

7. Void burst rate of the protrusion

The surface of the gloss removal layer of the sample film was photographed using FE-SEM, and the number of protrusions present in an area of 0.5 ㎟ (10 fields of view of 200 ㎛ × 250 ㎛) and the number of void ruptures among them were counted, and the number of ruptures was calculated as a ratio (%) to the total number.

Additionally, in the surface photograph, a protrusion with a void around it was judged to be a protrusion where a void rupture occurred.

8. Color L value

Using a spectrophotometer SE6000 manufactured by Nippon Denshoku Kogyo, the color L value of the substrate layer side of the sample film was measured by blackboard reflection.

9. Apparent surface tension

In accordance with JIS K 6768, a wetting index liquid was applied to the surface of the gloss removal layer of the sample film and the apparent surface tension was measured.

10. Peelability

A methylmelamine release layer (ATOM BOND RP-30-30 manufactured by Mitsuwa Laboratory) having a thickness of 0.1 ㎛ was formed on the surface of a sample film, and a UV-curable acrylic resin (Seikabeam EXF-3005 (NS) manufactured by Dainichi Purification Industries, Ltd.) was coated and cured thereon to form an insulating protective layer having a thickness of 5 ㎛, and a conductive layer having a thickness of 15 ㎛ was formed by coating a conductive paste having the following composition, thereby manufacturing a transfer film having an electromagnetic shielding film on a support film.

Dainichi Purification Industry Co., Ltd., Urethane Resin UD1357: 60 parts by mass

Silver powder (average thickness 100 nm, average particle size 5 ㎛): 20 parts by mass

Dendritic silver-coated copper powder (average particle size 5 μm): 20 parts by mass

Next, the transfer film obtained above was bonded to the surface of a flexible print substrate (a four-layer structure in which a polyimide layer (12.5 μm), an adhesive layer (15 μm), a copper foil layer (12 μm), and a polyimide layer (12.5 μm) are laminated in this order from top to bottom) with the conductive layer facing the covering surface side, and pressed under the conditions of a temperature of 200°C, a pressure of 1 MPa, and 1 hour. After releasing the pressure, the sample was cooled to 25°C at room temperature, the support film was peeled off by hand, and the surface of the transferred insulating protective layer was observed with the naked eye. The following indices were evaluated.

○: Peeling: Peeled cleanly.

△: Warrior: White foreign matter remains on the electromagnetic shield film side.

×: Breakage: The transfer film breaks during peeling.

11. Product gloss removal ability

In the same manner as the gloss of the above 1, the gloss (G ₆₀ ) of the surface of the insulating protective layer was measured for the sample after the insulating protective layer transfer obtained in the above 9, and the results were evaluated by the following indices.

◎: 15 or less… The product has very good gloss removal properties

○: Over 15, under 20… Good gloss removal ability of the product

×: Over 20… Poor gloss removal ability of the product

12. Evaluation of the visibility of film samples

A few drops of water were dropped on a black acrylic plate, and a sample film was placed on top of it with the gloss removal layer in contact with the acrylic plate. The air between the sample film and the acrylic plate was removed, and the appearance of the sample film was checked and evaluated using the following indices.

◎ : White… Good visibility

○: Translucent… Lack of visibility

× : Transparent… Poor visibility

[Example 1]

The particles and resin shown in Table 1 are added to polyethylene terephthalate (inherent viscosity 0.63 ㎗/g) to form an A layer polymer for forming a gloss removal layer (A layer), and further, particles and resin are added in the same amount as in the A layer in the amount shown in Table 1 to form a B layer polymer for forming a substrate layer (B layer), and each is supplied to an extruder heated to 280°C, and the A layer polymer and the B layer polymer are joined using a two-layer feed block device having an A/B laminated configuration, and while maintaining the laminated state, the sheet is melt-extruded from the die onto a rotary cooling drum maintained at 20°C to form an unstretched film, and then the unstretched film is stretched 3.2 times in the longitudinal direction, and then stretched 3.4 times in the transverse direction at 140°C, and heat-set at 235°C to form a biaxially oriented polyester film (thickness 50 ㎛) was obtained. The evaluation results of the obtained film are shown in Table 1.

[Example 2]

A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the contents of the resin added to the A layer polymer and the B layer polymer were as described in Table 1. The evaluation results of the obtained film are shown in Table 1.

[Example 3]

A biaxially oriented polyester film was obtained in the same manner as in Example 2, except that two types of polyethylene terephthalate having intrinsic viscosities of 0.63 ㎗/g and 0.68 ㎗/g were used for the B layer polymer, and the mixing ratio was set to 7 parts by mass of the former and 2 parts by mass of the latter. The evaluation results of the obtained film are shown in Table 1.

[Examples 4 to 9, Comparative Examples 1 to 2]

A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the types and amounts of particles and resins added to the A layer polymer and the B layer polymer were changed as described in Table 1. The evaluation results of the obtained film are shown in Table 1.

[Example 10]

The particles and resin shown in Table 2 were added to polyethylene terephthalate (inherent viscosity 0.63 ㎗/g) to form an A layer polymer for forming a gloss removal layer (A layer), and further, particles and resin were added in the same amount as in the A layer in the amount shown in Table 2 to form a B layer polymer for forming a substrate layer (B layer), and each was supplied to an extruder heated to 280°C, and the A layer polymer and the B layer polymer were joined using a two-layer feed block device having an A/B laminated configuration, and while maintaining the laminated state, the sheet was melt-extruded from the die onto a rotary cooling drum maintained at 20°C to form an unstretched film, and then the unstretched film was stretched 3.2 times in the longitudinal direction, and then stretched 3.4 times in the transverse direction at 140°C, and heat-set at 230°C to form a biaxially oriented polyester film (thickness 50 ㎛) was obtained. The evaluation results of the obtained film are shown in Table 2.

[Examples 11, 13 to 15, Comparative Examples 3 and 4]

A biaxially oriented polyester film was obtained in the same manner as in Example 10, except that the particles, resins and their contents added to the A layer polymer and the B layer polymer were as described in Table 2. The evaluation results of the obtained film are shown in Table 2.

[Example 12]

Except that two types of polyethylene terephthalate having intrinsic viscosities of 0.63 ㎗/g and 0.68 ㎗/g were used for the B layer polymer, the mixing ratio being 7 parts by mass of the former and 2 parts by mass of the latter, and that the particles, resins and their contents added to the A layer polymer and the B layer polymer were as described in Table 2, the same procedure as in Example 11 was conducted to obtain a biaxially oriented polyester film. The evaluation results of the obtained film are shown in Table 2.

In Table 1 and Table 2, PBT stands for polybutylene terephthalate, PTMT stands for polytrimethylene terephthalate, and PCHT stands for poly(cyclohexylenedimethylene) terephthalate.

Industrial applicability

The two-axis orientation film of the present invention, when used as a support film for transfer of an electromagnetic shielding film or the like, can provide a good matte finish to the surface of the electromagnetic shielding film or the like after transfer, and furthermore, since the support film peelability after transfer in the transfer process is excellent, its industrial utility value is very high.

Claims (7)

A laminated polyester film having a base layer and a particle-containing gloss removal layer on at least one surface, wherein the centerline average roughness (Ra) of the surface of the gloss removal layer is 400 to 1000 nm, the 10-point average roughness (Rz) is 4000 to 8000 nm, the gloss ( _G60 ) on the surface is 6 to 20, and the void rupture rate of protrusions on the surface is 20% or less.
The apparent surface tension of the surface of the above-mentioned gloss removal layer is 60 dyn/cm or less,
The polyester constituting the gloss removal layer contains polyethylene terephthalate as a main component and at least one secondary component selected from the group consisting of polytrimethylene terephthalate, polybutylene terephthalate and poly(cyclohexylenedimethylene) terephthalate, and the content of the secondary component in the gloss removal layer is 10 to 40 mass% based on the mass of the gloss removal layer.
The color L value of the substrate layer is 60 to 80,
A two-axis oriented polyester film used as a support film for transferring electromagnetic shielding films. In paragraph 1,
A biaxially oriented polyester film having an average particle size of 2.5 to 5.5 ㎛ and a particle content of 5 to 18 mass% in the gloss removal layer. In paragraph 1,
A biaxially oriented polyester film, wherein the particles in the gloss removal layer are amorphous silica or synthetic zeolite. In the first paragraph,
A biaxially oriented polyester film, the main component of which is polyethylene terephthalate, forming the base layer. In paragraph 4,
A biaxially oriented polyester film having an intrinsic viscosity of 0.56 to 0.70 ㎗/g of polyester constituting the substrate layer. In any one of claims 1 to 5,
A biaxially oriented polyester film having a particle content of the substrate layer of 3.0 mass% or less based on the mass of the substrate layer. delete