JP7625924B2 - Release film and its manufacturing method - Google Patents

Description

The present invention relates to a release film and a method for producing the same.

A multilayer printed wiring board is a printed wiring board that has conductor patterns on multiple layers (e.g., three or more layers), including a surface conductor layer. Multilayer printed wiring boards are manufactured using the build-up method, in which insulating layers and conductor layers are alternately stacked on an inner layer substrate.

In the build-up method for manufacturing multilayer printed wiring boards, for example, a build-up film having an insulating layer and a release film supporting the insulating layer may be laminated onto an adherend (e.g., a conductor layer), and the insulating layer may be thermally cured (see, for example, Patent Document 1). In the build-up method, a laser may be irradiated onto the insulating layer through the release film in order to form holes (i.e., vias or via holes) in the insulating layer.

Incidentally, Patent Document 2 describes a prepreg protective film. This prepreg protective film comprises a polyethylene naphthalate film and a release layer. This prepreg protective film is attached to the prepreg to prevent foreign matter from adhering to the surface of the prepreg. Note that prepreg is a sheet-like material made by impregnating a reinforcing material such as glass cloth with resin and curing it to the B stage.

The required characteristics for prepreg protective films are not the same as those for release films for the build-up method, because their applications are different. In fact, release films for the build-up method tend to require a higher degree of flatness than prepreg protective films.

JP 2008-37957 A JP 2001-205763 A

Regardless, in the build-up method, the thermal curing of the insulating layer can cause the insulating layer to lift (i.e., the insulating layer becomes partially separated from the release film). It is desirable to prevent this from happening.

In addition, it is desirable that the peeling force used to peel the release film from the insulating layer is not too strong, because if the peeling force is too strong, the insulating layer may break or remain partially on the release layer (specifically, part of the insulating layer may remain on the release layer).

The present invention aims to provide a release film that can suppress the lifting of the insulating layer and can also prevent the peeling force from becoming excessively strong when peeling the release film from the insulating layer, and a method for producing the same.

To solve this problem, the present invention has the following configuration:

Item 1
A polyester film;
A release layer is provided on at least one surface of the polyester film,
The release layer has an arithmetic mean roughness Ra of 20 nm or less, and a ten-point mean roughness Rz of 300 nm or less,
The surface free energy of the release layer is 20 dyne/cm to 32 dyne/cm;
The thermal shrinkage rate is 1.5% or less in the longitudinal direction and 0.0% to 0.5% in the transverse direction.
Release film.
Here, the heat shrinkage rate is the heat shrinkage rate when a release film (which may be a film sample cut out from the release film) is heated at 150° C. for 30 minutes. The heat shrinkage rate is calculated by the following formula.
Heat shrinkage rate = (ΔL/L ₀ ) x 100
Here, _L0 is the gauge length before heating, and ΔL is the amount of dimensional change due to heating. ΔL is calculated by subtracting the gauge length after heating (L) from the gauge length before heating ( _L0 ).

According to item 1, since the release film comprises a polyester film, it can support an insulating layer (specifically, an insulating layer for manufacturing a multilayer printed wiring board). In addition, since it is a polyester film, it has excellent rigidity and heat resistance.

In addition, since the release film has a release layer, the release film can be easily peeled off from the insulating layer.

Furthermore, since the arithmetic mean roughness Ra of the release layer is 20 nm or less and the ten-point mean roughness Rz of the release layer is 300 nm or less, the surface of the insulating layer (specifically, the surface that was in contact with the release layer) can be prevented from becoming excessively rough, making it possible to form wiring (for example, fine wiring) on the insulating layer.

Furthermore, because the surface free energy of the release layer is 32 dyne/cm or less, it is possible to prevent the peeling force from becoming excessively strong when peeling the release film from the insulating layer. This makes it possible to suppress or reduce partial residue of the insulating layer (specifically, partial residue of the insulating layer on the release layer) and breakage of the insulating layer.

Furthermore, since the surface free energy of the release layer is 20 dyne/cm or more, it is possible to prevent the adhesion between the release layer and the insulating layer from becoming excessively weak, and as a result, it is possible to suppress the floating of the insulating layer.

Furthermore, since the thermal shrinkage rate is 0.0% or more in the width direction, there is essentially no thermal expansion of the release film in the width direction when the insulating layer is thermally cured, and as a result, lifting of the insulating layer can be suppressed.

Furthermore, since the thermal shrinkage rate is 1.5% or less in the longitudinal direction and 0.5% or less in the width direction, it is possible to suppress the thermal shrinkage of the release film that may occur when the insulating layer is thermally cured, and as a result, it is possible to suppress the variation in the thickness of the insulating layer.

The present invention preferably further comprises the configurations described in items 2 and onward below.

Item 2
Item 2. The release film according to item 1, wherein the polyester film is a polyethylene naphthalate film.

According to item 2, since the polyester film is a polyethylene naphthalate film, the rigidity and heat resistance of the release film can be increased. As a result, for example, the uniformity of the hole shape can be improved when a laser is irradiated onto the insulating layer through the release film to form a hole.

Item 3
the release layer contains a release agent, the release agent being a compound containing a long-chain alkyl group;
The release layer is cured.
Item 3. The release film according to item 1 or 2.

If the release layer contains a silicone-based release agent as a release agent, the silicone-based release agent may remain on the surface of the insulating layer (specifically, the surface that was in contact with the release layer). Residual silicone-based release agent may cause defects.

In contrast, according to item 3, the release layer contains a long-chain alkyl group-containing compound as the release agent, rather than a silicone-based release agent, so that the silicone-based release agent that may have originated from the release layer does not remain on the surface of the insulating layer. This makes it possible to avoid problems caused by residual silicone-based release agent.

In addition, because the release layer is hardened, the heat resistance of the release layer can be improved.

Item 4
Item 4. The release film according to any one of items 1 to 3, wherein the sum of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction is 11.0 GPa or more.

According to item 4, the sum of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction is 11.0 GPa or more, i.e., the rigidity is excellent, so the uniformity of the hole shape can be improved when a laser is irradiated onto the insulating layer through a release film to form a hole.

Item 5
A method for producing a release film according to any one of items 1 to 4,
applying a coating liquid for forming the release layer onto the polyester film;
and drying the coating liquid on the polyester film at a temperature equal to or lower than the glass transition point of the polyester resin constituting the polyester film.
A method for producing a release film.

According to item 5, the coating liquid is dried at a temperature below the glass transition point of the polyester resin that constitutes the polyester film, so that the occurrence of wrinkles caused by heat applied to the polyester film (hereinafter referred to as "thermal wrinkles") can be suppressed. Therefore, the flatness of the release film can be improved.

Item 6
Item 6. The method for producing a release film according to item 5, further comprising a step of photocuring the coating film formed by the step of drying the coating liquid.

According to item 6, since the coating film is photocured, the heat applied to the polyester film can be reduced compared to heat curing, and as a result, the occurrence of thermal wrinkles can be further suppressed. Therefore, the flatness of the release film can be improved.

Item 7
Item 7. The release film according to any one of items 1 to 6, wherein the release film is a release film for producing a multilayer printed wiring board, and/or the method for producing the release film.
Here, the term "release film for producing a multilayer printed wiring board" refers to a release film for supporting members such as an insulating layer for producing a multilayer printed wiring board.

Item 8
Item 8. The release film according to any one of items 1 to 7, wherein the release film is a release film for producing a ceramic green sheet, and/or the method for producing the release film.

According to item 8, a ceramic green sheet can be manufactured by applying a ceramic slurry for forming a ceramic green sheet to a release film (specifically, a release layer of the release film) and drying the sheet. According to item 8, the problem of replacing the "insulating layer" in the above description of items 1 to 7 with a ceramic green sheet or ceramic slurry can be solved. Also, according to item 8, the effect of replacing the "insulating layer" in the above description of items 1 to 7 with a ceramic green sheet or ceramic slurry can be achieved.

The release film of the present invention can suppress lifting of the insulating layer and also prevent the peeling force from becoming excessively strong when peeling the release film from the insulating layer.

The following describes an embodiment of the present invention.

<1. Release film>
The release film of the present embodiment can be suitably used for producing a multilayer printed wiring board. Specifically, it can be suitably used as a support film for supporting an insulating layer for producing a multilayer printed wiring board. More specifically, the release film of the present embodiment can be suitably used as a support film for supporting an insulating layer when producing a multilayer printed wiring board by a build-up method.

The release film of this embodiment includes a polyester film and a release layer. Specifically, the release film of this embodiment includes a polyester film and a release layer provided on at least one surface of the polyester film.

<1.1. Polyester film>

The polyester film contains a polyester resin. The polyester resin can be composed of a polycarboxylic acid component and a polyalcohol component. In other words, the polyester resin can have a structure in which a polycarboxylic acid and a polyalcohol are dehydrated and condensed. Note that this is merely a description of the structure of the polyester resin, and is not intended to limit the manufacturing method of the polyester resin to dehydration and condensation. Note that a polycarboxylic acid refers to a compound having multiple carboxyl groups. A polyalcohol refers to a compound having multiple alcoholic hydroxyl groups.

The polyester resin can be composed of, for example, a dicarboxylic acid component and a diol component. In other words, the polyester resin can have a structure in which a dicarboxylic acid and a diol are dehydrated and condensed. Note that this is merely a description of the structure of the polyester resin, and is not intended to limit the manufacturing method of the polyester resin to dehydrated and condensed.

Examples of polyester films include polyethylene terephthalate (PET) films and polyethylene naphthalate (PEN) films. Of these, polyethylene naphthalate films are preferred. When the polyester film is a polyethylene naphthalate film, the rigidity and heat resistance of the release film can be increased. As a result, for example, the uniformity of the hole shape can be improved when a laser is irradiated onto the insulating layer through the release film to form a hole.

It is preferable that the main component of the polymer (specifically, polyester resin) constituting the polyethylene naphthalate film is polyethylene-2,6-naphthalate. "The main component is polyethylene-2,6-naphthalate" means that at least 90 mol% of all repeating units of the polymer are ethylene-2,6-naphthalate residues. In other words, it means that 90 mol% or more of all repeating units constituting the polyester resin are ethylene-2,6-naphthalate residues. In this way, the polymer constituting the polyethylene naphthalate film may contain a maximum of 10 mol% of a copolymerization component. Regarding the copolymerization component, examples of dicarboxylic acids include terephthalic acid, isophthalic acid, 2,7-naphthalenedicarboxylic acid, adipic acid, and sebacic acid. Among them, terephthalic acid is preferable. On the other hand, examples of diols include trimethylene glycol, tetramethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol.

It is preferable that 95 mol% or more of all repeating units of the polymer are ethylene-2,6-naphthalate residues. In other words, it is preferable that 95 mol% or more of all repeating units constituting the polyester resin are ethylene-2,6-naphthalate residues. This is because the higher the proportion of ethylene-2,6-naphthalate residues, the higher the glass transition point can be, and the higher the rigidity and heat resistance of the release film can be.

It is more preferable that 100 mol % of all repeating units of the polymer are ethylene-2,6-naphthalate residues. In other words, it is preferable that the polymer constituting the polyethylene naphthalate film is a homopolymer of polyethylene-2,6-naphthalate.

The glass transition point of the polyester resin constituting the polyester film is preferably 100°C or higher, more preferably 105°C or higher, even more preferably 110°C or higher, and even more preferably 115°C or higher. On the other hand, the upper limit of the glass transition point can be, for example, 150°C, 140°C, or 130°C.

It is preferable that the polyester film contains inactive particles. By containing inactive particles in the polyester film, it is possible to improve the handling properties and winding properties during the process.

Examples of inactive particles include inorganic particles such as silica, alumina, kaolin, calcium carbonate, titanium oxide, barium sulfate, and carbon black, and organic particles such as cross-linked acrylic resin, cross-linked polystyrene resin, melamine resin, and cross-linked silicone resin. Of these, spherical silica particles and porous silica particles are preferred.

The spherical silica particles preferably have a ratio of the major axis divided by the minor axis (i.e., major axis/minor axis) of 1.0 to 1.2 and an average particle size of 0.05 μm to 5 μm. The average particle size is preferably 0.1 μm or more, more preferably 0.3 μm or more. On the other hand, the average particle size is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less. It _is described in the Journal of the Chemical Society of Japan ('81, No. 9, p. 1503) that spherical silica particles can be produced, for example, by hydrolyzing ethyl orthosilicate [Si(OC ₂ H ₅ ) ₄ ] to produce monodispersed spheres of hydrated silica [Si(OH) 4 ], and then dehydrating the monodispersed spheres to grow silica bonds [Si-O-Si] three-dimensionally.

Porous silica particles are aggregated particles in the form of aggregates of primary particles. The average particle size of the porous silica particles, specifically the average particle size as aggregated particles, is preferably 0.1 μm to 5 μm, more preferably 0.3 μm to 3 μm. The average particle size of the primary particles constituting the porous silica particles is preferably 0.005 μm to 0.1 μm. If the average particle size of the primary particles is 0.005 μm or more, the disintegration of the porous silica particles at the slurry stage can be reduced, so that reagglomeration (specifically, reagglomeration after disintegration) can be suppressed. If the average particle size of the primary particles is 0.1 μm or less, the porous silica particles have excellent porosity and therefore excellent affinity with polymers. As a result, voids can be reduced, so that the decrease in transparency of the polyester film caused by voids can be suppressed. In addition, the disintegration of the porous silica particles at the slurry stage can be reduced, so that reagglomeration (specifically, reagglomeration after disintegration) can be suppressed. The pore volume of the porous silica particles is preferably 0.5 ml/g to 2.0 ml/g, and more preferably 0.6 ml/g to 1.8 ml/g. If the pore volume is 0.5 ml/g or more, the porous silica particles have excellent porosity and therefore excellent affinity with the polymer (i.e., polyester resin). As a result, voids can be reduced, and the decrease in transparency of the polyester film caused by voids can be suppressed. If the pore volume is 2.0 ml/g or less, the disintegration of the porous silica particles can be reduced, and reagglomeration (specifically, reagglomeration after disintegration) can be suppressed. As a result, the variation in size of the porous silica particles can be prevented from becoming excessively large.

The content of the inactive particles is preferably 0.005% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, when the polyester film is taken as 100% by mass (i.e., when the composition constituting the polyester film is taken as 100% by mass). The content of the inactive particles is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less, when the polyester film is taken as 100% by mass.

The polyester film may contain other additives, such as stabilizers, UV absorbers, flame retardants, antistatic agents, dyes or pigments.

The polyester film may be surface-treated. An example of the surface treatment is corona discharge treatment. Of course, the polyester film does not have to be surface-treated.

The thickness of the polyester film is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. The thickness of the polyester film is preferably 250 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. The polyester film may have a single layer structure or a multilayer structure.

The polyester film is preferably a biaxially stretched polyester film. Such a polyester film can be produced, for example, by cooling the polymer, forming it into granules (e.g., pellets), drying it, feeding it to an extruder, melt-extruding a sheet from a die, then quenching the sheet with a rotating cooling drum, biaxially stretching it, and heat fixing it. The biaxial stretching may be simultaneous longitudinal and transverse biaxial stretching, or may be sequential biaxial stretching. Of these, sequential biaxial stretching is preferred. In sequential biaxial stretching, for example, it is preferred to stretch a sheet that has passed through a rotating cooling drum in the longitudinal direction, i.e., the Machine Direction (hereinafter referred to as "MD") direction, and stretch the sheet after MD stretching in the transverse direction, i.e., the Transverse Direction (hereinafter referred to as "TD") direction. If necessary, a heat relaxation treatment may be performed. The heat relaxation treatment can reduce the dimensional change of the release film due to heating. If necessary, after sequential biaxial stretching, the film may be stretched again in either the longitudinal direction or the transverse direction, or in both directions.

Preferred stretching conditions (e.g. stretching temperature, stretching ratio) are as follows. Regarding the stretching temperature, the first-stage stretching temperature (e.g., the longitudinal stretching temperature, hereinafter referred to as "T1") is preferably (Tg-10)°C to (Tg+45)°C, and the second-stage stretching temperature (e.g., the transverse stretching temperature, hereinafter referred to as "T2") is preferably (T1-15)°C to (T1+40)°C. Tg is the glass transition point of the polyester resin constituting the polyester film. Regarding the stretching ratio, the stretching ratio in one axial direction (i.e., either the longitudinal or transverse direction) is preferably 2.5 times or more, more preferably 3 times to 5 times. The area ratio is preferably 8 times or more, more preferably 10 times to 16 times. The heat setting temperature is preferably 180°C to 250°C, more preferably 230°C to 250°C.

<1.2. Release layer>
The release layer is preferably a layer obtained by curing a composition containing a curable resin. Examples of the curable resin include fluororesin, epoxy resin, melamine resin, alkyd resin, and acrylic resin. Among them, melamine resin and acrylic resin are preferable, and acrylic resin is more preferable.

The curable resin may be, for example, a photocurable resin (e.g., an ultraviolet-curable resin) or a thermosetting resin. Examples of such a resin include a photocurable acrylic resin and a thermosetting melamine resin.

As the curable resin, a photocurable resin is preferable. A photocurable acrylic resin is more preferable, and an ultraviolet-curable acrylic resin is even more preferable.

That is, the release layer is preferably a layer obtained by curing a composition containing a photocurable resin. That is, the release layer is preferably photocured. When the release layer is photocured, the heat resistance of the release layer can be increased. In addition, when the release layer is photocured, the flatness of the release film can be improved. This will be explained. According to the configuration in which the release layer is photocured, when the release layer is formed, it is possible to cure the release layer at a temperature below the glass transition point of the polyester resin constituting the polyester film. In that case (specifically, when the release layer is cured at a temperature below the glass transition point of the polyester resin), it is possible to suppress the occurrence of wrinkles (i.e., heat wrinkles) caused by heat applied to the polyester film. Therefore, the flatness of the release film can be improved. It is more preferable that the release layer is UV cured.

It is preferable that the release layer contains a release agent. That is, it is preferable that the above-mentioned composition (specifically, the composition containing the curable resin) contains a release agent. Examples of the release agent include long-chain alkyl release agents and silicone-based release agents. Among them, long-chain alkyl release agents are preferable. That is, it is preferable that the release layer contains a long-chain alkyl group-containing compound as a release agent. When the release layer contains a long-chain alkyl group-containing compound as a release agent instead of a silicone-based release agent, the silicone-based release agent derived from the release layer does not remain on the surface of the insulating layer. Therefore, it is possible to avoid problems caused by the remaining silicone-based release agent.

For the long-chain alkyl group-containing compound, the long-chain alkyl group is preferably an alkyl group having 8 or more carbon atoms. The number of carbon atoms may be 10 or more, or 12 or more. The long-chain alkyl group is preferably an alkyl group having 30 or less carbon atoms. The number of carbon atoms may be 28 or less, or 26 or less. It is preferable that the long-chain alkyl group-containing compound has a long-chain alkyl group on the side chain.

Examples of compounds containing long-chain alkyl groups include polyvinyl resins containing long-chain alkyl groups, alkyd resins containing long-chain alkyl groups, acrylic resins containing long-chain alkyl groups, and polyester resins containing long-chain alkyl groups. Among these, polyvinyl resins containing long-chain alkyl groups are preferred.

The release layer may contain an additive. That is, the above-mentioned composition (specifically, the composition containing the curable resin) may contain an additive. Examples of additives include a photopolymerization initiator and inactive particles.

The release layer may contain inactive particles as an additive. That is, the above-mentioned composition (specifically, the composition containing the curable resin) may contain inactive particles. By containing inactive particles in the release layer, the handling property and winding property of the release film can be improved. Examples of inactive particles include inorganic particles such as silica, alumina, kaolin, calcium carbonate, titanium oxide, barium sulfate, and carbon black, and organic particles such as crosslinked acrylic resin, crosslinked polystyrene resin, melamine resin, and crosslinked silicone resin. Among them, silica particles are preferable. Considering the surface roughness range described later (specifically, arithmetic mean roughness Ra 20 nm or less and ten-point mean roughness Rz 300 nm or less), fine inactive particles are preferable. Specifically, particles with a particle size of 50 nm or less are preferable.

The arithmetic mean roughness Ra of the release layer is 20 nm or less, and the ten-point mean roughness Rz of the release layer is 300 nm or less. This prevents the surface of the insulating layer (specifically, the surface that was in contact with the release layer) from becoming excessively rough, and as a result, it becomes possible to form wiring (for example, fine wiring) on the insulating layer. The arithmetic mean roughness Ra is preferably 15 nm or less, more preferably 10 nm or less. On the other hand, the ten-point mean roughness Rz is preferably 250 nm or less, more preferably 150 nm or less. These lower limits can be set appropriately. For example, the arithmetic mean roughness Ra may be 1 nm or more, 3 nm or more, or 5 nm or more. On the other hand, the ten-point mean roughness Rz may be 30 nm or more, 50 nm or more, or 75 nm or more. The arithmetic mean roughness Ra and the ten-point mean roughness Rz can be adjusted, for example, by the size of particles (for example, inactive particles) that can be added to the polyester film and the thickness of the release layer. The arithmetic mean roughness Ra and the ten-point mean roughness Rz are values measured and calculated using the method described in the Examples.

The surface free energy of the release layer is 20 dyne/cm to 32 dyne/cm. Because it is 32 dyne/cm or less, it is possible to prevent the peeling force when peeling the release film from the insulating layer from becoming excessively strong. Therefore, it is possible to suppress or reduce partial residue of the insulating layer (specifically, partial residue of the insulating layer on the release layer) and tearing of the insulating layer. Because it is 20 dyne/cm or more, it is possible to prevent the adhesion force between the release layer and the insulating layer from becoming excessively low, and as a result, it is possible to suppress lifting of the insulating layer. The surface free energy is preferably 22 dyne/cm or more, and more preferably 24 dyne/cm or more. The surface free energy is a value measured and calculated by the method described in the examples.

The thickness of the release layer is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. The thickness of the release layer is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less, and even more preferably 2 μm or less.

1.3. Characteristics of release film
The release film of this embodiment has a thermal shrinkage rate of 1.5% or less in the longitudinal direction and 0.5% or less in the width direction. This makes it possible to suppress the thermal shrinkage of the release film that may occur when the insulating layer is thermally cured, and as a result, it is possible to suppress the variation in the thickness of the insulating layer. The length of the release film in the longitudinal direction is greater than the length in the width direction. The longitudinal direction can be rephrased as the Machine Direction (MD) direction. On the other hand, the width direction can be rephrased as the Transverse Direction (TD) direction.

The release film of this embodiment has a thermal shrinkage rate of 0.0% or more in the width direction. This means that there is essentially no thermal expansion of the release film in the width direction when the insulating layer is thermally cured, and as a result, lifting of the insulating layer can be suppressed.

In the release film of this embodiment, the sum of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction is preferably 11.0 GPa or more, and more preferably 11.5 GPa or more. When this sum is 11.0 GPa or more, the rigidity is excellent, and the uniformity of the hole shape can be improved when a laser is irradiated to the insulating layer through the release film to form a hole. This sum may be, for example, 13.0 GPa or less.

When an adhesive tape ("31B tape" manufactured by Nitto Denko Corporation) is attached to the release layer of the release film of this embodiment and the adhesive tape is peeled off from the release film at a peel angle of 180° and a peel speed of 300 mm/min, the peel strength is preferably 3.0 N/25 mm width or less. If it is 3.0 N/25 mm width or less, the adhesive force to the insulating layer does not become excessively large, so partial residue of the insulating layer (specifically, partial residue of the insulating layer on the release layer) and tearing of the insulating layer can be suppressed.

When the thickness of the release film is taken as 100%, the thickness of the release layer is preferably 10% or less, more preferably 8% or less, more preferably 6% or less, and even more preferably 5% or less. The thickness of the release layer is preferably 1% or more, and more preferably 1.5% or more.

The thickness of the release film in this embodiment is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. The thickness of the release film is preferably 250 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less.

2. Method for producing release film
The method for producing a release film of this embodiment includes a step of applying a coating liquid for forming a release layer to a polyester film (hereinafter referred to as "step A"), a step of drying the coating liquid on the polyester film at a temperature below the glass transition point of the polyester resin constituting the polyester film (hereinafter referred to as "step B"), and a step of photocuring the coating film formed by step B (hereinafter referred to as "step C").

In step A, a coating liquid is applied to the polyester film. The coating liquid may contain, for example, a solvent in addition to the components that may be contained in the release layer (for example, the above-mentioned curable resin and release agent). Examples of the solvent include a hydrocarbon solvent and water. Examples of the coating method include a blade coat method, a bar coater method, a gravure coater method, and a reverse gravure coater method.

In step B, the coating liquid is dried at a temperature (hereinafter referred to as the "drying temperature") below the glass transition point of the polyester resin constituting the polyester film. For example, the drying temperature is preferably (Tg-5)°C or lower, more preferably (Tg-10)°C or lower, and even more preferably (Tg-15)°C or lower. If the drying temperature exceeds Tg, the polyester film will shrink in the width direction, causing wrinkles (i.e., thermal wrinkles) extending in the longitudinal direction, resulting in excessively large variations in the thickness of the insulating layer. In contrast, in step B, the coating liquid is dried at a temperature below the glass transition point of the polyester resin constituting the polyester film, so the occurrence of thermal wrinkles can be suppressed. This can improve the flatness of the release film.

In step B, it is preferable to dry the coating liquid while applying tension to the polyester film. This tension can be set appropriately. If this tension is excessively high, the thermal shrinkage of the release film tends to be less than 0.0% (i.e., negative) in the width direction.

In step C, the coating film formed in step B is photocured. This allows the amount of heat applied to the polyester film to be reduced compared to heat curing, and as a result, the occurrence of thermal wrinkles can be suppressed. This improves the flatness of the release film. In step C, it is preferable to cure the coating film at a temperature below the glass transition point of the polyester resin that constitutes the polyester film. It is preferable to cure the coating film with ultraviolet light.

By following this procedure, a cured coating, i.e., a release layer, can be formed on the polyester film.

3. Various modifications can be made to the above-described embodiment.
The above-described embodiment may be modified in various ways. For example, the above-described embodiment may be modified by selecting one or more of the following modifications.

In the above-described embodiment, a configuration has been described in which the insulating layer is thermally cured while being laminated on a release film. However, the above-described embodiment is not limited to this configuration.

In the above-described embodiment, a configuration has been described in which a laser is irradiated onto the insulating layer through a release film to form holes in the insulating layer. However, the above-described embodiment is not limited to this configuration.

In the above embodiment, a configuration has been described in which the release film is used as a support film for supporting an insulating layer when manufacturing a multilayer printed wiring board by a build-up method. However, the above embodiment is not limited to this configuration. For example, the release film may be used for manufacturing a ceramic green sheet. When using a release film for this purpose, a ceramic green sheet can be manufactured by applying a ceramic slurry for forming a ceramic green sheet to the release layer of the release film and drying it.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Note that parts and percentages in the examples refer to parts by mass and percentages by mass, respectively, unless otherwise specified.

<Method of measuring each characteristic>
(1) Surface Free Energy A film sample cut out from a release film was conditioned for 24 hours under conditions of 23°C and 65% RH. For the surface of the release layer of this film sample, an automatic contact angle measuring device (DMo-501 manufactured by Kyowa Interface Science Co., Ltd.) was used to measure the static contact angles of three liquid samples with known surface free energy components, specifically, water, ethylene glycol, and methylene iodide. This measurement was performed five times for each liquid sample. The average value was taken as the contact angle. Then, using the surface tension and surface tension component values of each liquid sample (see Table 1), the surface free energy of the release layer surface was calculated from the Fowkes' extended formula of the following formula 1.
γ _S = γ _S ^d + γ _S ^p + γ _S ^h ... (Formula 1)
In formula 1, γ _S ^d represents a dispersion component, γ _S ^p represents a polar component, and γ _S ^h represents a hydrogen bond component.

(2) Thermal shrinkage rate Two gauge marks were made on a 30 cm square film sample cut out from a release film in the longitudinal direction (specifically, the longitudinal direction of the release film) and the width direction (specifically, the width direction of the release film). The film sample was hung in a gear oven and heated at 150°C for 30 minutes. The gauge length was measured after returning the sample to room temperature (specifically, 23°C). The dimensional change (ΔL) due to heating was calculated by subtracting the gauge length (L) after heating from the gauge length (L ₀ ) before heating for each direction. The thermal shrinkage rate (%) in each direction was then calculated according to Equation 2.
Heat shrinkage rate = (ΔL/L ₀ ) x 100... (Formula 2)
This measurement was carried out on five samples, n = 5. The average value is shown in Table 2 as the heat shrinkage rate.

(3) Arithmetic mean roughness Ra and ten-point mean roughness Rz
Data was acquired using a non-contact three-dimensional surface roughness meter (New View 7300 manufactured by ZYGO Corporation) at a measurement magnification of 25 times and a measurement area of 283 μm × 213 μm (=0.0603 mm ² ). From this data, the arithmetic mean roughness Ra and ten-point mean roughness Rz were calculated using the surface analysis software Metro Pro built into the non-contact three-dimensional surface roughness meter. This was done three times at different measurement locations. The average values are shown in Table 2 as the arithmetic mean roughness Ra and ten-point mean roughness Rz.

(4) Young's modulus A test piece with a width of 10 mm and a length of 15 cm cut out from a release film was pulled with a universal tensile tester (Tensilon manufactured by Toyo Baldwin) at room temperature (specifically 23°C), 100 mm between chucks, a tensile speed of 10 mm/min, and a chart speed of 500 mm/min, and the force and elongation applied to the test piece were measured. The Young's modulus was calculated from the tangent of the rising part of the load-elongation curve obtained by this measurement. The total Young's modulus in the longitudinal direction and the width direction is shown in Table 2.

(5) Flatness A film sample with a width of 1 m and a length of 10 m cut from the center of the width direction of the release film was placed under a three-wavelength fluorescent lamp so that the width direction of the film sample was parallel to the axial direction of the elongated three-wavelength fluorescent lamp, and the reflection of the three-wavelength fluorescent lamp on the film sample was visually inspected. If the film sample had heat wrinkles, the image of the three-wavelength fluorescent lamp reflected on the film sample would be distorted or intermittent. If the image of the three-wavelength fluorescent lamp was almost a straight line, it was judged as ◯, and if the image was distorted and/or intermittent, it was judged as ×.

(6) Hole shape (i.e., laser drillability)
Twenty through holes with a diameter of 100 μm were formed in a film sample cut from a release film using a carbon dioxide laser drilling device (IMPACT-GS500 manufactured by Sumitomo Heavy Industries, Ltd.). The maximum and minimum hole diameters on the laser incident side of each through hole were measured by microscopic observation. The closer the average value of the maximum hole diameters is to the average value of the minimum hole diameters, the higher the uniformity of the hole shape. When the average value of the maximum hole diameters was 1.07 times or less the average value of the minimum hole diameters, it was judged as ◯, and when it was more than 1.07 times, it was judged as ×.

(7) Lifting of the insulating layer An epoxy resin composition was prepared by mixing 100 parts by mass of a bisphenol-type epoxy resin (jER828 manufactured by Mitsubishi Chemical Corporation), 90 parts by mass of an acid anhydride mainly composed of methyl HHPA (RIKACID MH-700 manufactured by New Japan Chemical Co., Ltd.), and 2 parts by mass of a curing accelerator (U-CAT18X manufactured by Acid Apro Co., Ltd.). This epoxy resin composition was applied to the release layer of a film sample cut out from a release film. At this time, the epoxy resin composition was applied so that the thickness of the epoxy resin composition was 20 μm. The film sample was laminated so that the surface of the epoxy resin composition applied to the film sample was in contact with a glass plate, and the two were heated in a dryer at 160° C. for 30 minutes. After this heating, the presence or absence of lifting of the epoxy resin layer (i.e., the insulating layer made of the epoxy resin composition) was visually confirmed. The case where no lifting occurred was judged as ◯, and the case where lifting occurred was judged as ×.

(8) Peel Strength An adhesive tape ("31B tape" manufactured by Nitto Denko Corporation) was attached to the release layer of a test piece cut out from a release film, and the peel strength was measured when the adhesive tape was peeled off from the test piece at a peel angle of 180° and a peel speed of 300 mm/min.

(9) Glass transition temperature (Tg)
The glass transition point (extrapolated onset temperature) of the polymer was measured using a DSC (Thermal Analyst 2100 manufactured by TA Instruments) with a sample weight of 10 mg and a heating rate of 20° C./min.

(10) Intrinsic Viscosity The intrinsic viscosity of a polymer was determined by dissolving the polymer in o-chlorophenol and measuring at 35°C.

Example 1
A polyethylene-2,6-naphthalate homopolymer containing 0.2% by mass of silica particles with an average particle size of 0.5 μm and having an intrinsic viscosity (o-chlorophenol, 35° C.) of 0.6 dl/g was cooled and pelletized, and then dried at 180° C. for 3 hours. The pellets were fed into an extruder, extruded from a die in a molten state, and adhered to a rotating cooling drum maintained at 40° C. by an antistatic adhesion method (i.e., quenched) to obtain an unstretched film. The unstretched film was stretched 3.6 times in the longitudinal direction at 140° C., then 3.8 times in the transverse direction at 130° C., and heat-set at 240° C. to obtain a polyethylene naphthalate film (PEN film) with a thickness of 25 μm.

On the other hand, a coating liquid for forming a release layer was prepared by mixing an ultraviolet-curable resin (HA7975 manufactured by Showa Denko Materials Co., Ltd.) and a long-chain alkyl pendant polymer (Peiroil 1050 manufactured by Lion Specialty Chemicals Co., Ltd.) in a solid content ratio of 85:15. This coating liquid was applied to a PEN film by reverse gravure coating so that the thickness of the release layer (specifically, the thickness after drying) was 1.0 μm. The solvent in the coating liquid was volatilized at 100° C. That is, the coating liquid was dried at 100° C. This drying was performed under a tension of 70 N/m on the PEN film. The coating film after drying was irradiated with ultraviolet light of 1000 mJ/cm ² to harden the coating film. A release film was obtained by such a procedure.

Example 2
A release film was produced in the same manner as in Example 1, except that the coating liquid was applied to the PEN film so that the thickness of the release layer (specifically, the thickness after drying) was 0.5 μm.

Example 3
A release film was prepared in the same manner as in Example 1, except that a coating liquid was prepared by mixing an ultraviolet-curable resin (HA7975 manufactured by Showa Denko Materials Co., Ltd.) and a long-chain alkyl pendant polymer (Peiroil 1050 manufactured by Lion Specialty Chemicals Co., Ltd.) in a solids ratio of 90:10.

<Comparative Example 1>
A release film was prepared in the same manner as in Example 1, except that the coating liquid was prepared without using the long-chain alkyl pendant polymer.

<Comparative Example 2>
A release film was produced in the same manner as in Example 1, except that a thermosetting resin (ACRYDIC 55-467 manufactured by DIC Corporation) was used instead of the ultraviolet-curing resin (HA7975 manufactured by Showa Denko Materials Co., Ltd.), the coating liquid was dried and cured at 150°C while applying a tension of 230 N/m to the PEN film, and ultraviolet light was not irradiated.

The release film of Comparative Example 1, which did not use a release agent (specifically, a long-chain alkyl pendant polymer), had an excessively high surface free energy, and as a result, the peeling force was too strong.

In the release film of Comparative Example 2, in which the coating liquid was dried and cured at 150°C while applying a tension of 230 N/m to the PEN film, thermal wrinkles occurred. In other words, the flatness was poor. In addition, the insulating layer also lifted. This (i.e., the occurrence of the insulating layer lifting) is thought to be due to the thermal expansion of the release film in the width direction when the coating liquid was dried and cured as a result of excessively high tension.

In contrast, the release films of Examples 1 to 3 had an appropriate peeling force, were excellent in planarity, and did not cause lifting of the insulating layer.

Claims (5)

A polyester film;
A release layer is provided on at least one surface of the polyester film,
The release layer has an arithmetic mean roughness Ra of 20 nm or less, and a ten-point mean roughness Rz of 300 nm or less,
The surface free energy of the release layer is 20 dyne/cm to 32 dyne/cm;
The thermal shrinkage rate is 1.5% or less in the longitudinal direction and 0.0% to 0.5% in the transverse direction;
the release layer contains a release agent, the release agent being a compound containing a long-chain alkyl group;
The polyester film is a polyethylene naphthalate film.
A release film for manufacturing multilayer printed wiring boards. The release film according to claim 1 , wherein the release layer comprises a photocurable resin . The release film according to claim 1 or 2, wherein the release layer is cured. A method for producing the release film according to any one of claims 1 to 3,
applying a coating liquid for forming the release layer onto the polyester film;
and drying the coating liquid on the polyester film at a temperature equal to or lower than the glass transition point of the polyester resin constituting the polyester film.
A method for producing a release film. The method for producing a release film according to claim 4, further comprising a step of photocuring the coating film formed by the step of drying the coating liquid.