JP2006346899A - Release film and adhesive film using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a release film which makes it possible to manufacture an adhesive film more accurately controlled in its thickness than before by a method for forming the adhesive film by coating the mold release layer of the release film with a coating agent and solidifying the coating layer of the release film, and the adhesive film formed using the release film. <P>SOLUTION: The base material of the release film is formed of a porous polyester film with a thickness irregularity of 5% or below and a void ratio of 5-50 vol.%. Further, the radiation absorbance of the polyester film is preferably set to 85% or below of a non-porous state by making the polyester film porous. Furthermore, the polyester film preferably contains 0.2-20 vol.% of an inorganic filler. The adhesive film is formed by coating the mold release layer of the release film with the coating agent and subsequently solidifying the coating layer on the release film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention particularly relates to a release film suitably used as a support for an adhesive film, such as an anisotropic conductive film used for mounting electronic components, and an adhesive film using this release film.

  For example, an adhesive film mainly composed of a resin having a heat-sensitive adhesive property or a pressure-sensitive adhesive property, such as an anisotropic conductive film used for mounting an electronic component on a wiring board or the like, is usually difficult to handle by itself. As such, it is supplied in a state of being laminated on one side of a release film that does not have adhesiveness and has releasability with respect to the adhesive film. Moreover, as a release film, what has the laminated structure which formed the release layer in the single side | surface of a film-form base material, and provided the release property with respect to an adhesive film is used.

  For example, Patent Document 1 describes a release film having a release layer mainly composed of a fluorine compound. The release layer mainly composed of a fluorine compound can improve the adhesion to the base material compared to the silicone oil layer. Therefore, when releasing the adhesive film, the release layer is attached to the adhesive film. Thus, release from the substrate can be prevented. Therefore, it is possible to prevent the release layer attached to the adhesive film from inhibiting the adhesiveness of the adhesive film and improve the reliability of the adhesive film.

  The adhesive film usually has a constant thickness on the surface of the release film on which the release layer has been formed while feeding the liquid coating material that is the basis of the long release film at a constant speed. It is continuously produced by, for example, continuously applying to the substrate and then drying through a dryer.

In an adhesive film for electronic use such as an anisotropic conductive film, it is required to strictly control its thickness. Therefore, when continuously manufacturing an adhesive film by the above manufacturing method, as a non-destructive, non-contact inline film thickness meter, for example, a film thickness using radiation such as X-ray, β-ray, γ-ray, etc. with a total of such, a change in thickness T ₁ of the adhesive film was continuously formed on a release film was measured in real time in accordance with the feeding of the release film, and feeds back the measurement result to the coating step of coating material In general, the thickness T ₁ of the adhesive film is always managed to be constant by adjusting the coating thickness.

In the film thickness meter using radiation, the intensity I of the radiation transmitted through the laminate of the peeling film and the adhesive film, which is the object of measurement, is continuously measured according to the feeding of the peeling film. From the measured values that change every moment, the change in the thickness T ₁ of the adhesive film continuously formed on the release film is continuously obtained by the following formula (1).

In the above formula (1), I ₀ is the initial value of the radiation intensity when not passing through the laminate, A ₁ is the radiation absorption coefficient in the adhesive film, A ₂ is the radiation absorption coefficient in the substrate, T ₂ is the average thickness of the substrate. In addition, since a mold release layer is remarkably small compared with a base material and an adhesive film, it can be disregarded.
JP 2002-370315 A Japanese Patent No. 3309918

  Paper or stretched polypropylene film may be used as the base material for the release film. However, the release film on which heat resistance, rigidity, dimensional stability, and adhesive film are laminated is continuously applied to a predetermined width. Polyester films such as polyethylene terephthalate (PET) are generally used in terms of ease of processing when slitting into a tape shape and good finish of the slit processed surface. In particular, in order to improve the dimensional stability of the substrate and the ease of slitting, for example, a so-called white PET film containing an inorganic filler such as titanium oxide powder is often used.

However, since the base material blended with an inorganic filler, such as the above white PET film, has a radiation absorption coefficient A _{2 that} is significantly larger than the radiation absorption coefficient A ₁ in the adhesive film, the film thickness meter was used. In measuring the thickness, the variation in the thickness of the base material is amplified, and the measurement accuracy is lowered. Therefore, the reliability of the calculation result of the adhesive film thickness T ₁ obtained by the above formula (1) is lowered, and the variation in the thickness T ₁ of the adhesive film formed by feeding back the calculation result is rather large. There is a problem that arises.

  An object of the present invention is to provide a release film capable of producing an adhesive film whose thickness is more accurately controlled than in the prior art by the above forming method, and an adhesive film formed using the release film. There is to do.

  The invention according to claim 1 is a release film comprising a film-like substrate and a release layer provided on the surface of the substrate, wherein the substrate has a thickness variation of 5% or less and a porosity. Is a release film characterized by being formed of a porous polyester film of 5 to 50% by volume.

  The invention according to claim 2 is the release film according to claim 1, wherein the radiation absorption rate of the polyester film as the substrate is made 85% or less of the non-porous state by making it porous.

  Invention of Claim 3 is a peeling film of Claim 1 in which the polyester film as a base material contains 0.2-20 volume% inorganic filler.

  Invention of Claim 4 is a peeling film of Claim 1 in which the polyester film as a base material has a nonporous skin layer on both front and back.

  The invention described in claim 5 is an adhesive film having heat-sensitive adhesiveness or pressure-sensitive adhesiveness, and after applying the coating agent on which the film is based on the release layer of the release film according to claim 1, It is an adhesive film characterized by being solidified.

  Invention of Claim 6 is an adhesive film of Claim 5 which is an anisotropic conductive film.

In the invention described in claim 1, since the base material is formed of a porous polyester film having a porosity of 5 to 50% by volume, the amount of polyester or the like per unit volume is reduced. The absorption coefficient A _{2 of} radiation can be reduced. Therefore, coupled with managing the variation in the thickness of the polyester film to 5% or less, in particular, when measuring the thickness using a film thickness meter using radiation can improve the accuracy of the measurement, It is possible to improve the reliability of the calculation result of the thickness T ₁ of the adhesive film obtained by the equation (1). Therefore, according to the first aspect of the present invention, the thickness T _{1 of the} adhesive film formed by feeding back the calculation result can be managed more accurately than before.

According to the second aspect of the present invention, the radiation absorptivity A ₂ of the polyester film as a substrate, by porous, because you are more than 85% of the non-porous state, the accuracy of the thickness measurement, This can be further improved.

According to invention of Claim 3, the rigidity of a polyester film can be improved by making the polyester film as a base material contain 0.2-20 volume% inorganic filler, and the porosity is enlarged. Thus, the radiation absorption rate A ₂ of the polyester film can be further reduced. Therefore, despite containing an inorganic filler to increase the radiation absorptivity A _2, the radiation absorptance A ₂ of the polyester film, can be reduced to equal approximately to those containing no inorganic filler.

  According to invention of Claim 4, since the polyester film as a base material has a non-porous skin layer on both front and back surfaces, the rigidity of the polyester film is further improved, and the base film for the adhesive film is applied. The thickness of the adhesive film can be more accurately managed by making the coating thickness uniform when applying the agent. Moreover, when the laminated body after forming the adhesive film is wound into, for example, a roll, it is possible to reduce the occurrence of defects such as wrinkles and to improve the ease of slit processing. .

In the invention described in claim 5, the adhesive film having heat-sensitive adhesiveness or pressure-sensitive adhesiveness is formed by applying the coating agent on which the adhesive film is based on the release layer of the release film and then solidifying it. Is done. Therefore, according to the invention of claim 5, wherein the thickness T ₁ of the adhesive film can be assumed to have been correctly managed than ever.

  The structure of the adhesive film can be applied to an anisotropic conductive film as described in claim 6.

  The release film of the present invention includes a film-like base material and a release layer provided on the surface of the base material, and the base material has a thickness variation of 5% or less and a porosity of 5 to 50. It is characterized by being formed of a volume% porous polyester film.

  As the polyester that forms the porous polyester film, the PET is preferably used, and other polyesters that can be formed into a film, such as polyethylene naphthalate (PEN), can also be used.

  In order to make the polyester film porous, after melting and kneading the polyester that is the base of the film and a resin that is incompatible with polyester, such as polystyrene, extrusion molding, A method of producing voids around the fine particles by producing a sheet in which fine particles are dispersed and stretching the sheet is suitably employed.

  In order to adjust the porosity of the porous polyester film formed by this method, the content of other resins such as polystyrene and the stretching amount of the sheet may be adjusted. The content of the other resin is preferably 1 to 40% by weight in the total amount of the other resin and the polyester. If the content is less than 1% by weight, a porous polyester film having a porosity of 5% by volume or more may not be obtained by the above-described method. Therefore, the heat resistance and strength of the film may be reduced.

  The polyester film can contain an inorganic filler such as titanium oxide powder as in the conventional case. The content is preferably 0.2 to 20% by volume of the total volume of the molding material that is the basis of the polyester film, including polyester, the other resin, and an inorganic filler. If the content is less than 0.2% by volume, the effect of improving the dimensional stability of the base material and the ease of slitting due to the inclusion of the inorganic filler may not be sufficiently obtained, and 20% by volume. In the case where it exceeds 1, the content of polyester is relatively reduced, so that the heat resistance and strength of the film may be lowered.

In the present invention, the porosity of the porous polyester film is limited to 5 to 50% by volume for the following reason. That is, when the porosity of the polyester film is less than 5% by volume, the amount of the polyester or the like per unit volume described above is reduced by making the polyester film porous, and the radiation absorption coefficient A ₂ The effect of reducing cannot be obtained. Therefore, the accuracy of measurement and the reliability of the calculation result of the thickness T ₁ of the adhesive film obtained by the above formula (1) cannot be improved, and the thickness T _{1 of the} adhesive film can be managed accurately. Can not. In addition, a polyester film having a porosity of more than 50% by volume tends to bend due to a decrease in rigidity, and cannot sufficiently function as a support for an adhesive film.

On the other hand, if the porosity is in the range of 5 to 50% by volume, the amount of polyester and the like per unit volume is reduced while maintaining the rigidity of the polyester film in a favorable range, and the radiation absorption coefficient. A ₂ can be reduced. Specifically, by making the polyester film porous, the radiation absorption rate A ₂ can be reduced to 85% or less of the non-porous state.

The porosity of the polyester film is determined by taking into consideration that the amount of polyester and the like per unit volume is reduced and the radiation absorption coefficient A ₂ is reduced as much as possible while maintaining the rigidity within a favorable range. When a film does not contain an inorganic filler, it is preferable that it is 10-20 volume% especially also in said range. This allows the radiation absorptivity A ₂ of the polyester film, reduced to about 60-82% of the non-porous state.

Moreover, when the polyester film contains an inorganic filler, the rigidity of the polyester film can be improved by the filler, so that the porosity can be increased, particularly 20 to 30% by volume. Is preferred. This allows the radiation absorptivity A ₂ of the polyester film, reduced to about 40-65% of the non-porous state. Therefore, despite containing an inorganic filler to increase the radiation absorptivity A _2, the radiation absorptance A ₂ of the polyester film, can be reduced to equal approximately to those containing no inorganic filler.

In the present invention, the variation in the thickness of the polyester film is limited to 5% or less. If the variation in the thickness exceeds 5%, even if the porosity is within the above range, the radiation absorption is limited. Even if the coefficient A ₂ is reduced, the accuracy of measurement and the reliability of the calculation result of the thickness T ₁ of the adhesive film, which is obtained by the above equation (1), cannot be improved due to the influence of the variation in thickness. This is because the thickness T _{1 of the} adhesive film cannot be accurately managed.

In addition, the variation in the thickness of the polyester film is considered to improve the accuracy of measurement and the reliability of the calculation result of the thickness T ₁ of the adhesive film, and to manage the thickness T _{1 of the} adhesive film as accurately as possible. Ideally it is 0%. However, it is not easy and practical to manufacture a large amount of polyester film having no thickness variation at a low cost. Considering the balance between the productivity of the polyester film and managing the thickness T _{1 of the} adhesive film as accurately as possible, the variation in the thickness of the polyester film is particularly 1 to 3% even within the above range. Is preferred.

  In order to make the dispersion of the thickness of the polyester film within the above range, the polyester film has a thickness dispersion within the above range from the raw film having a width wider than that of the polyester film and a long length. It is only necessary to select and cut out an area that matches the width and length of the image. A polyester film is usually produced by biaxially stretching a sheet that is the basis of the polyester film. Since the thickness of the central portion in the width direction is small, for example, from a raw film having a width of 2 m and a length of 10,000 m, A plurality of polyester films having variations within the above range and having a width of about 300 mm × a length of about 500 m can be cut out in the width direction and a large number in the length direction.

In addition, the dispersion | variation in the thickness of the polyester film said by this invention is continuous in-line, using the film thickness meter etc. which used radiation, etc. which were demonstrated previously, sending a long polyester film at a fixed speed. Among the data of the distribution of the thickness t ₂ of the polyester film obtained by measuring the following, from the standard deviation σ of the thickness and the average value T _{2 of the} thickness, the following formula (2):
C _V2 = σ / T ₂ (2)
Means a value twice as large as the coefficient of variation C _V2 calculated by. Therefore, the variation in the thickness of the polyester film of 5% or less means that 2 × C _V2 is 5% or less.

In the film thickness meter using radiation, the intensity i of the radiation transmitted through the polyester film to be measured is continuously measured in accordance with the feeding of the polyester film, and the measured value of the intensity i changes every moment. From the following equation (3), the distribution of the thickness t ₂ of the polyester film is obtained.

〔式(3)中のｉ₀は、ポリエステルフィルムを透過しない場合の、放射線強度の初期値、ａ₁は、ポリエステルフィルムにおける放射線の吸収係数である。〕

[I ₀ in the formula (3) is an initial value of the radiation intensity when not passing through the polyester film, and a ₁ is an absorption coefficient of radiation in the polyester film. ]

The average value T ₂ of the distribution of the thickness t ₂ of the polyester film obtained as described above is preferably about 25 to 100 μm as in the conventional case.

  For example, a non-porous skin layer made of a resin such as polyester, polyurethane, or acrylic may be provided on both front and back surfaces of the porous polyester film. As a result, the rigidity of the polyester film can be further improved, and the thickness of the adhesive film can be more accurately managed by making the coating thickness uniform when applying the coating agent that is the basis of the adhesive film. Become. Moreover, when the laminated body after forming the adhesive film is wound into, for example, a roll, it is possible to reduce the occurrence of defects such as wrinkles and to improve the ease of slit processing. .

The thickness of the skin layer is preferably 1/100 to 1/4 of the thickness of the polyester film. If thickness is less than this range, there exists a possibility that the effect which improves the rigidity of the polyester film by providing a skin layer may not fully be acquired. Further, when the thickness exceeds the above range is by the polyester film and the porous, there is a possibility that the effect of reducing the absorption coefficient A ₂ of a radiation is insufficient. For example, when extruding a sheet that becomes the basis of a polyester film, the skin layer may be laminated while being extruded at the same time, or laminated on an extruded sheet or a stretched polyester film later. May be. Furthermore, it can also be formed by applying a coating liquid that becomes the basis of the skin layer on both the front and back surfaces of the stretched polyester film and then solidifying it.

  As the release layer provided on the surface of the polyester film (when the polyester film has a skin layer, the surface of the skin layer), a layer of a release agent such as a fluorine-based material or a silicone-based material can be used as in the conventional case. The thickness of the release layer is preferably 0.1 to 1 μm in consideration of releasing the adhesive film more reliably without causing variations in the thickness affecting the thickness of the adhesive film. .

  The adhesive film of the present invention is characterized in that it is formed by applying the base coating agent on the release layer of the release film of the present invention and then solidifying it. Examples of the adhesive film include various adhesive films mainly composed of a resin having heat-sensitive adhesiveness or pressure-sensitive adhesiveness, and an anisotropic conductive film whose thickness needs to be strictly controlled is particularly preferable.

  An anisotropic conductive film generally has a structure in which a conductive component such as a metal powder is dispersed in a resin film having heat-sensitive adhesiveness. In addition, the filling rate of the conductive component of the anisotropic conductive film is adjusted so that the conductive resistance in the surface direction of the film (referred to as “insulation resistance”) becomes high.

  The anisotropic conductive film is thermally bonded in a state where a plurality of electrodes are arranged at a predetermined pitch, for example, sandwiched between a connection part of an electronic component and a connection part of a wiring board. When the anisotropic conductive film is compressed in the thickness direction by heating and pressurization at that time, the filling rate of the conductive components in the thickness direction is increased, and the conductive components are close to or in contact with each other to form the conductive network. As a result of the formation, the conductive resistance in the thickness direction (referred to as “connection resistance”) is lowered. However, at this time, since the filling rate of the conductive component in the plane direction of the anisotropic conductive film does not increase, the plane direction maintains an initial state where the insulation resistance is high and the conductivity is low.

Therefore, the anisotropic conductive film has an anisotropic conductive characteristic with a low connection resistance in the thickness direction and a high insulation resistance in the plane direction, and based on this anisotropic conductive characteristic,
While preventing the occurrence of a short circuit between the electrodes adjacent to each other in the surface direction of the film in each connection portion, while maintaining an electrically independent state,
The conductive connection between the electrodes facing each other in both connection portions is excellent.
It becomes possible. In addition, the anisotropic conductive film can fix the electronic component on the wiring board by thermal bonding due to the heat-sensitive adhesive property of the film itself. Therefore, if an anisotropic conductive film is used, the operation | work of electronics mounting becomes easy.

  In order to form an anisotropic conductive film using the release film of the present invention, first, a coating material containing a resin having a heat-sensitive adhesive property and a conductive component in a predetermined ratio (a ratio corresponding to the filling rate). Adjust. Then, while feeding the long release film fed from the raw roll at a constant speed, the coating agent is fixed on the surface of the release film on which the release layer is formed, for example, using a die coater or the like. The anisotropic conductive film is continuously formed on the release film when the resin is thermosetting and then semi-cured when the resin is thermosetting. .

At this time, using a film thickness meter using radiation, etc., the change in the thickness T ₁ of the adhesive film continuously formed on the release film is measured in real time in accordance with the feed of the release film. By feeding back the measurement result to the coating agent coating step and adjusting the coating film thickness, the thickness T ₁ of the adhesive film can be managed so as to be always constant.

  The release film on which the anisotropic conductive film is continuously formed is laminated on the surface of the formed anisotropic conductive film with a cover material having a release treatment on the surface to be laminated and wound on a roll, or Directly sent to the slit process, which is the next process, and slitted to a predetermined width to be commercialized. A cover layer may be omitted by forming a release layer on the surface of the polyester film that is the basis of the release film on the side opposite to the side on which the anisotropic conductive film is formed.

  Any of various resins having a heat-sensitive adhesive property or a pressure-sensitive adhesive property can be used as a resin that is the basis of an adhesive film such as an anisotropic conductive film. Among these, examples of the heat-sensitive adhesive resin used for the anisotropic conductive film include thermosetting resins such as epoxy resins, urea resins, melamine resins, and phenol resins, acrylic resins, and polyimide resins. Moreover, although the thickness of an adhesive film can be suitably set according to the use, generally it is preferable that it is about 10-1000 micrometers.

Example 1:
As the polyester film, a porous PET film containing no inorganic filler and having an average thickness T ₂ of 50 μm and a porosity of 10% by volume was used. The PET film had an X-ray absorption coefficient A ₂ of 0.0021% and a thickness variation of 2%. A coating solution containing C ₈ H ₁₆ O and C ₈ F ₁₈ in a weight ratio of 75:25 is applied to one side of this polyester film, and dried to form a release layer, which has a width of 300 mm × A release film of Example 1 having a length of 500 m was produced.

Example 2:
As the polyester film, a width of 300 mm × length was obtained in the same manner as in Example 1 except that a porous PET film containing no inorganic filler, having an average thickness T ₂ of 50 μm, and a porosity of 20% by volume was used. A release film of Example 2 having a thickness of 500 m was produced. The PET film had an X-ray absorption coefficient A ₂ of 0.0016% and a thickness variation of 2%.

Comparative Example 1:
Comparative example having a width of 300 mm and a length of 500 m in the same manner as in Example 1 except that a non-porous PET film containing no inorganic filler and having an average thickness T ₂ of 50 μm was used as the polyester film. A release film of 1 was produced. The PET film had an X-ray absorption coefficient A ₂ of 0.0026% and a thickness variation of 2%.

Example 3:
As a polyester film, the same as Example 1 except that a porous PET film containing 2% by volume of titanium oxide powder and having an average thickness T ₂ of 50 μm and a porosity of 20% by volume was used. A release film of Example 3 having a width of 300 mm and a length of 500 m was produced. The PET film had an X-ray absorption coefficient A ₂ of 0.0034% and a thickness variation of 2%.

Example 4:
As a polyester film, the same as in Example 1 except that a porous PET film containing 2% by volume of titanium oxide powder and having an average thickness T ₂ of 50 μm and a porosity of 30% by volume was used. A release film of Example 4 having a width of 300 mm and a length of 500 m was produced. The PET film had an X-ray absorption coefficient A ₂ of 0.0023% and a thickness variation of 2%.

Comparative Example 2:
As a polyester film, a non-porous PET film containing 2% by volume of titanium oxide powder and having an average thickness T ₂ of 50 μm was used in the same manner as in Example 1, and the width was 300 mm × the length was 500 m. A release film of Comparative Example 2 was produced. The PET film had an X-ray absorption coefficient A ₂ of 0.0057% and a thickness variation of 2%.

Example 5:
As the polyester film, the same as used in Example 2, containing no inorganic filler, both on the front and back surfaces of a porous PET film having an average thickness T ₂ of 50 μm and a porosity of 20% by volume, respectively. Except for applying a water dispersion of polymerized polyester resin (registered trademark Vironal manufactured by Toyobo Co., Ltd.) and then drying to use a laminate having a non-porous skin layer with a thickness of 0.5 μm Produced the release film of Example 5 having a width of 300 mm and a length of 500 m in the same manner as in Example 1. The X-ray absorption coefficient A ₂ of the laminate was 0.0017%, and the thickness variation was 2%.

While feeding the release films of the examples and comparative examples prepared above at a constant speed, the surface of the release film on which the release layer was formed was coated with a coating agent used as the adhesive film, using a die coater, Mainly a resin having a heat-sensitive adhesive property, which is continuously applied so as to have a constant thickness and then continuously dried through a dryer, and has a target thickness of 25 μm and an X-ray absorption coefficient A ₁ of 0.0020. The adhesive film to be formed was continuously formed.

In manufacturing, the change of the thickness T ₁ of the adhesive film continuously formed on the release film is adjusted to the release film using a film thickness meter using X-rays after leaving the dryer. The measurement result was fed back to the coating process of the coating agent, and the coating thickness was adjusted to manage the target thickness.

As described above, both sides of the release film on which the adhesive film was continuously formed were cut and cut in the length direction to produce an adhesive film with a release film having a width of 240 mm and a length of 100 m. Then, after continuously slitting this adhesive film with a release film to a width of 3 mm, one slit at the center in the width direction and one at a position 60 mm away from the left and right, a total of three The thickness t ₃ of the adhesive film with a release film and the thickness of the release film after the adhesive film is peeled at the same position (≈the thickness t ₂ of the PET film or laminate) are every 1 m in the length direction. And a micrometer [trade name Laser Hollow Gauge LGH-1010 manufactured by Mitutoyo Corporation].

For each measurement point, the thickness of the release film (≈t ₂ ) is subtracted from the thickness t ₃ of the adhesive film with the release film to calculate the thickness t _{1 of the} adhesive film, and the distribution is obtained. Among the distribution data of the thickness t ₁ , from the standard deviation σ of the thickness and the average value T _{1 of the} thickness, the following formula (4):
C _V1 = σ / T ₁ (4)
A value twice as large as the coefficient of variation C _V1 calculated by the above was obtained as the variation in the thickness of the adhesive film.

In Examples, the flexural modulus of the release film of Comparative Example was measured in accordance with the Japanese Industrial Standard JIS K7106 _-1995 "stiffness test method bending of the plastic by cantilever". The results are shown in Table 1.

  From the results of Examples 1 and 2 and Comparative Example 1 in the table, the polyester film is made porous, the porosity is increased, and the X-ray absorption coefficient is decreased, so that the variation in the thickness of the adhesive film is reduced. I knew it was possible. Further, from the results of Examples 3 and 4 and Comparative Example 2, in the system in which the polyester film contains titanium oxide powder, the polyester film is similarly made porous and the porosity is increased. It was found that the variation in the thickness of the adhesive film can be reduced as the linear absorption coefficient is reduced.

  Moreover, from the results of Examples 1 to 4, it was found that when the polyester film contains titanium oxide powder, the porosity can be improved while maintaining rigidity. Furthermore, from the results of Example 5, it was found that even when the skin layers were formed on both the front and back surfaces of the polyester film, the porosity could be improved while maintaining the rigidity.

Claims (6)

  A release film including a film-like base material and a release layer provided on the surface of the base material, wherein the base material has a thickness variation of 5% or less and a porosity of 5 to 50% by volume. A release film characterized by being formed of a porous polyester film.   The release film according to claim 1, wherein the radiation absorption rate of the polyester film as the substrate is made to be 85% or less of the non-porous state by making it porous.   The release film according to claim 1, wherein the polyester film as a substrate contains 0.2 to 20% by volume of an inorganic filler.   The release film according to claim 1, wherein the polyester film as a substrate has non-porous skin layers on both front and back surfaces.   An adhesive film having heat-sensitive adhesiveness or pressure-sensitive adhesiveness, which is formed by applying the coating agent on which the adhesive film is formed on the release layer of the release film according to claim 1 and then solidifying it. Features an adhesive film.   The adhesive film according to claim 5, which is an anisotropic conductive film.