JP7624155B2 - Double-sided release film - Google Patents

Description

The present invention relates to a double-sided release film having release layers on both sides of a base film.

In manufacturing processes such as forming double-sided adhesive tape, green sheets for ceramic capacitors, anisotropic conductive films, and insulating resin sheets for circuit boards, a resin film containing each raw material (hereinafter sometimes simply referred to as "resin film") is formed on the surface of a film with release properties and then rolled up, and double-sided release films are widely used as substrates in the manufacturing process. As technological innovation advances in the thinning of functional sheets obtained from resin films, there is a need to improve release films to suit the manufacturing process of thin functional sheets.

For example, an adhesive anisotropic conductive film is widely used as a material for bonding two circuit elements and electrically connecting the terminals between them. This anisotropic conductive film is made of an insulating adhesive with conductive particles dispersed in it, and is sandwiched between the terminals of the elements to be connected and then thermocompressed to simultaneously bond the elements together and electrically connect the terminals.

This anisotropic conductive film is usually manufactured by applying and drying an adhesive varnish, which is made by mixing and dispersing conductive particles in an insulating adhesive made by mixing an insulating resin such as epoxy resin with a hardener, on a carrier film (separator). After applying and drying the varnish, the carrier film is rolled up and cut to an appropriate width for use. Since anisotropic conductive films that have adhesive properties are sticky under normal conditions, it is necessary to provide a release layer on both sides of the carrier film. Furthermore, it is necessary to provide a difference in peel strength when peeling off the anisotropic conductive film between the inner and outer sides of the roll of the carrier film. If both sides of the carrier film are treated with the same release treatment, the anisotropic conductive film may be taken toward the unwinding roll or a gap may occur between the carrier film and the anisotropic conductive film, making it difficult to pull out smoothly.

On the other hand, if the surface irregularities of the polyester film are too large when the anisotropic conductive film is made thinner, the anisotropic conductive film will not be formed uniformly, resulting in problems such as poor conductivity. For this reason, Patent Document 1 discloses a release film for manufacturing anisotropic conductive films, in which the peel strength of both surfaces is within a specified range, and the center line average roughness Ra of the release layers on both surfaces is 0.1 to 1.0 μm.

Patent No. 4495880

However, in recent years, there has been a trend toward thinner resin films, such as anisotropic conductive films, due to the trend toward thinner image display devices. For this reason, the inventors have found that when thinner resin films are formed, the overall unevenness is too large with a release film having a center line average roughness Ra in the range described in Patent Document 1, which makes it easy for higher protrusions to form than the surrounding area, and causes poor surface conditions in the resin film due to paint repellency starting from the high protrusions. In addition, when thinner resin films are formed, it has been found that unless the peeling forces of both surfaces are adequately controlled, the peeling condition is likely to deteriorate when the rear release layer peels off the resin film when unwound from the roll.

The object of the present invention is to provide a double-sided release film that can improve the surface condition of the resulting resin film and the peeling condition of the resin film when unrolled, even when forming a thinner resin film.

As a result of intensive research conducted by the inventors to solve the above problems, they discovered that the above objective could be achieved by controlling not only the surface roughness Ra, which is an index of the overall unevenness of a polyester film, but also the maximum projection height Rp in a specified range of regions, and thus arrived at the present invention.

In other words, the present invention includes the following:

<1> A release layer A, a polyester film, and a release layer B in this order,
A double-sided release film characterized by satisfying the following formulas (1) to (6):
RaA<0.1...(1)
RpA<2.0...(2)
RaB≧0.85×RaA...(3)
RpB≧0.85×RpA...(4)
1.5≦HA/HB≦100...(5)
0.15≦HA+HB≦7...(6)
In the formulas (1) to (6), RaA represents the center surface average roughness (μm) of the surface of release layer A, RaB represents the center surface average roughness (μm) of the surface of release layer B, RpA represents the center surface maximum protrusion height (μm) of the surface of release layer A in an area of 283 μm × 213 μm, RpB represents the center surface maximum protrusion height (μm) of the surface of release layer B in an area of 283 μm × 213 μm, HA represents the peel force (N/25 mm width) of the surface of release layer A, and HB represents the peel force (N/25 mm width) of the surface of release layer B.

<2> The double-sided release film according to <1>, further comprising an antistatic layer between at least one of the release layer A and the release layer B and the polyester film, and the surface resistivity of the surface of the release layer on the side where the antistatic layer is provided is 5×10 ⁴ to 5×10 ¹² Ω/□.

<3> The double-sided release film according to <1> or <2>, wherein the polyester-based film contains inorganic particles having an average particle size of 0.1 to 2.0 μm.

<4> The double-sided release film according to <3>, in which the content of the inorganic particles is 0.05 to 25% by mass.

<5> The double-sided release film according to any one of <1> to <4>, wherein the antistatic layer contains at least one selected from the group consisting of conductive polymers, metal oxide fine particles, and polymers to which a quaternary ammonium salt has been added.

The double-sided release film of the present invention can provide a double-sided release film that can improve the surface condition of the resulting resin film and the peeling condition of the resin film when unrolled, even when forming a thinner resin film. For this reason, it can be suitably used, for example, as a carrier film in the process of forming resin films that are the raw material for various functional sheets, or as a separator during winding.

1A and 1B are cross-sectional views showing the schematic structure of an example of a double-sided release film of the present invention, where FIG. 1A corresponds to Example 1 and FIG. 1B corresponds to Example 4.

The present invention will be described in detail below. For ease of explanation, the film-forming direction of the film may be referred to as the machine axis direction, longitudinal direction, lengthwise direction, or MD direction, and the direction perpendicular to the film-forming direction and thickness direction may be referred to as the width direction, transverse direction, or TD direction.

(Schematic structure of double-sided release film)
The double-sided release film of the present invention contains, in this order, a release layer A, a polyester film, and a release layer B. The term "polyester film" refers to a film containing 50% by mass or more of polyester resin, based on the mass of all resin components, in a single layer when formed as a single layer, or in all layers when formed as multiple layers, and preferably 70% by mass or more.

In the present invention, as shown in Figures 1(a) and 1(b), it is assumed that a resin film 5 is formed on the release layer A2A side, and a release layer B2B is provided on the back side of the polyester film 1.

As shown in FIG. 1(b), an antistatic layer 3 may be interposed between the release layer A2A and the polyester film 1, or between the release layer B2B, or between both the release layer A2A and the polyester film 1. However, from the viewpoints of process simplification and antistatic effect during peeling, it is preferable that the antistatic layer 3 is interposed only between the release layer A2A and the polyester film 1.

The polyester film may have a single layer structure as shown in FIG. 1(a), or may have a three-layer structure of a microparticle-containing layer/microvoid-containing layer/microparticle-containing layer, or a two-layer structure of a microparticle-containing layer/microvoid-containing layer. The polyester film may have another layer laminated on the microparticle-containing layer or the microvoid-containing layer. The polyester film may have a three-layer structure of a microvoid-containing layer/microparticle-containing layer/microvoid-containing layer, or a structure of four or more layers in which the microvoid-containing layer/microparticle-containing layer is repeated. In any laminate structure, it may further have other layers. Examples of layers other than the antistatic layer 3 include an easy-adhesion layer, an easy-slip layer, an anchor layer, an adhesive layer, and a colored layer.

(Characteristics of double-sided release film)
The double-sided release film of the present invention is characterized in that it satisfies the following formulas (1) to (6).
RaA<0.1...(1)
RpA<2.0...(2)
RaB≧0.85×RaA...(3)
RpB≧0.85×RpA...(4)
1.5≦HA/HB≦100...(5)
0.15≦HA+HB≦7...(6)
In the formulas (1) to (6), RaA represents the center surface average roughness (μm) of the surface of release layer A, RaB represents the center surface average roughness (μm) of the surface of release layer B, RpA represents the center surface maximum protrusion height (μm) of the surface of release layer A in an area of 283 μm × 213 μm, RpB represents the center surface maximum protrusion height (μm) of the surface of release layer B in an area of 283 μm × 213 μm, HA represents the peel force (N/25 mm width) of the surface of release layer A, and HB represents the peel force (N/25 mm width) of the surface of release layer B.

Regarding formula (1) and formula (2), if RaA is 0.1 μm or more and RpA is 2.0 μm or more, when a resin film is formed on a double-sided release film (carrier film), the high protruding components may cause repelling on the coated surface of the resin film, or shape transfer to the resin film may occur, causing thickness variations in the resin film layer, and making it easier for defects to occur due to surface defects in the product. From this perspective, the upper limit of RaA is preferably 0.09 μm, more preferably 0.07 μm, and the upper limit of RpA is preferably 1.5 μm, more preferably 1.0 μm.

A release layer with an RaA of less than 0.1 μm can be obtained, for example, by providing a release layer on the surface of a polyester film having a center surface average roughness of 0.01 to 0.1 μm. The RpA can also be controlled, for example, by adjusting the maximum protrusion height on the surface of the polyester film.

The lower limit of RaA is not particularly limited, but from the viewpoint of ease of handling in the manufacturing process, it is preferably 0.01 μm, and more preferably 0.03 μm. The lower limit of RpA is not particularly limited, but from the viewpoint of ease of handling in the manufacturing process, it is preferably 0.1 μm, and more preferably 0.2 μm.

Regarding formula (3) and formula (4), if RaB is less than 0.85×RaA and RpB is less than 0.85×RpA, problems may occur in the handleability of the film during the production process. From this viewpoint, it is preferable to satisfy formula (3′) and/or formula (4′).
RaB≧0.90×RaA...(3')
RpB≧0.90×RpA...(4')
However, from the viewpoint of suppressing the transfer of protruding components on the B-side to the resin film when the resin film is formed and then wound up, the upper limit of RaB is preferably 0.1 μm, more preferably 0.08 μm. From the same viewpoint, the upper limit of RpB is preferably 1.5 μm, more preferably 1.0 μm.

RaB or RpB can also be controlled by adjusting, for example, the center surface average roughness or maximum protrusion height of the polyester film surface.

Formulas (5) and (6) define the relationship between the peel strength HA (N/25 mm) of the release layer A side (heavy peelable side) and the peel strength HB (N/25 mm) of the release layer B side (lightly peelable side) because the double-sided release film is used for forming adhesive resin films and also as a separator when wound into a tape. Formula (5) defines the peel strength ratio between the release layer A side and the release layer B side, and formula (6) defines the peel strength level of both release layer release surfaces.

Regarding the value of HA/HB in formula (5) (hereinafter referred to as the "peeling force ratio"), if the peeling force ratio is 1.5 or more, problems such as the resin film not being able to be pulled out smoothly and remaining on the reel side are less likely to occur. On the other hand, if the peeling force ratio is 100 or less, the peeling force on the release layer A side, i.e., the side on which the resin film remains when pulled out, is not too strong, and the resin film is pressed against the adherend and then the carrier film (separator) is easily peeled off cleanly. From this perspective, it is preferable that the value of HA/HB is in the range of 4 to 70.

Regarding formula (6), if HA+HB is 0.15 or more, the double-sided release film on which the resin film is formed has good handling properties, and the resin film can be unwound in a stable state. Furthermore, if HA+HB is 7 or less, excess stress is unlikely to occur during unwinding, making it easier to prevent deformation during unwinding. From this perspective, it is preferable that the value of HA+HB is in the range of 0.2 to 4.

(polyester)
In the present invention, the polyester constituting the polyester-based film used as the base film is a polyester having an aromatic dicarboxylic acid as the main acid component and an aliphatic glycol as the main glycol component. This polyester is substantially linear and can be formed into a film, and it is particularly preferable that the polyester is a polyester that can be formed into a film by melt molding.

Examples of aromatic dicarboxylic acid components constituting polyesters include terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylketonedicarboxylic acid, and anthracenedicarboxylic acid.

Examples of the aliphatic glycol components constituting the polyester include polymethylene glycols having 2 to 10 carbon atoms, such as ethylene glycol, diethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, and decamethylene glycol, and alicyclic diols, such as 1,4-cyclohexanedimethanol.

In the present invention, the polyester preferably has alkylene terephthalate and/or alkylene-2,6-naphthalate as its main component.

Of these polyesters, in particular, polyethylene terephthalate and polyethylene-2,6-naphthalate are of course preferred, as are copolymers in which, for example, 80 mol % or more of the total dicarboxylic acid components are terephthalic acid and/or 2,6-naphthalenedicarboxylic acid, and 80 mol % or more of the total glycol components are ethylene glycol. In such cases, 20 mol % or less of the total acid components can be the above-mentioned aromatic dicarboxylic acids other than terephthalic acid and/or 2,6-naphthalenedicarboxylic acid, or can be, for example, aliphatic dicarboxylic acids such as adipic acid, sebacic acid, etc.; alicyclic dicarboxylic acids such as cyclohexane-1,4-dicarboxylic acid, etc.

In addition, up to 20 mol% of the total glycol components can be the above glycols other than ethylene glycol, and can also be, for example, aromatic diols such as hydroquinone, resorcin, 2,2-bis(4-hydroxyphenyl)propane, etc.; aliphatic diols having an aromatic ring such as 1,4-dihydroxydimethylbenzene; polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc.

The polyester of the present invention also includes those in which components derived from oxycarboxylic acids, such as aromatic oxyacids such as hydroxybenzoic acid and aliphatic oxyacids such as ω-hydroxycaproic acid, are copolymerized or bonded in an amount of 20 mol % or less based on the total amount of dicarboxylic acid components and oxycarboxylic acid components.

The polyester of the present invention also includes copolymers of trifunctional or higher polycarboxylic acids or polyhydroxy compounds, such as trimellitic acid and pentaerythritol, in amounts that are substantially linear, for example, 2 mol % or less of the total acid components.

The polyester can be produced by a method known per se. The polyester has an intrinsic viscosity, measured as a solution in o-chlorophenol at 35°C, of preferably 0.4 to 0.9 dl/g, more preferably 0.5 to 0.7 dl/g, and particularly preferably 0.55 to 0.65 dl/g.

(Polyester film)
The polyester film serving as the substrate of the double-sided release film preferably has a surface shape similar to the surface shape of the double-sided release film after release layer A and release layer B are formed.

For this reason, it is preferable that the center surface average roughness of the polyester film is 0.01 to 0.10 μm. If the surface roughness exceeds 0.1 μm, it becomes difficult to make the surface roughness RaA of the release layer surface less than 0.1 μm. Furthermore, if the surface roughness falls below 0.01 μm, the surface roughness of the release layer surface will be even lower than the polyester surface roughness, and the handling properties of the film will tend to deteriorate. Note that, depending on the film-forming conditions, RaA does not necessarily equal RaB, so the range of RaB is preferably 0.85 x RaA or more.

In addition, RpA, which is the maximum protrusion of the polyester film, is preferably less than 2.0 μm. If RpA exceeds 2.0 μm, repelling may occur on the resin film coating surface, or the shape may be transferred to the resin film, causing poor resin film uniformity. Since RpA = RpB is not always the case on both sides of the film depending on the film-making conditions, RpB is preferably 0.85 × RpA or more. If RpB is less than 0.85 × RpA, the surface becomes smooth, which may cause problems with handling and winding characteristics.

In addition, it is preferable that the polyester film has optical properties similar to those of the double-sided release film after release layers A and B are formed.

For this reason, the total light transmittance of the polyester film is preferably 0 to 50%, and the haze value is preferably 70% or more. Within this range, the total light transmittance and haze value of the double-sided release film tend to take the values of formulas (7) and (8), making it easier to observe thickness irregularities in the resin film formed on the carrier film. Also, from the viewpoint of confirming that the release film has been reliably peeled off in the process of attaching the resin film to the adherend and then peeling off the double-sided release film, the total light transmittance of the polyester film is preferably 10 to 30%, and the haze value is preferably 80% or more.

(Additives)
In order to simultaneously satisfy the above-mentioned ranges for the center surface average roughness, total light transmittance, and haze value of such a polyester film, there are methods such as incorporating a filler or pigment into the raw polyester material (kneading method), applying a resin paint containing a filler or pigment to the surface of a polyester film, and forming irregularities on the surface by sandblasting, embossing, etching, etc.

In the present invention, any of the above methods may be used, but considering the cost and quality of the double-sided release film of the present invention, the kneading method in which fillers, pigments, etc. are incorporated into the polyester raw material in advance is preferred.

Examples of fillers and pigments to be contained in the polyester include inorganic fillers such as titanium oxide, silicon oxide, barium sulfate, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc, etc.; organic fillers such as polystyrene resin, acrylic resin, urea resin, melamine resin, etc.; and other resin fillers such as polyethylene, polypropylene, ethylene-propylene terpolymer, olefin-based ionomer, etc., and one or more of these may be used. In particular, from the viewpoint of controlling RpA within the range of formula (2), it is preferable to use inorganic fillers (inorganic particles). Furthermore, antioxidants, ultraviolet absorbers, fluorescent whitening agents, etc. may also be contained as necessary.

The filler or pigment contained in the polyester preferably has an average particle size of 0.1 to 2.0 μm, and more preferably 0.1 to 1.0 μm, in order to control the RpA within the range of formula (2).

The content of the filler or pigment is preferably in the range of 0.05 to 25% by mass, more preferably 0.1 to 22.0% by mass, and even more preferably 1 to 20% by mass, based on the entire polyester film. When the fine particle-containing layer is provided as a surface layer, it is preferable that the fine particle-containing layer contains 0.01 to 15% by mass. When the microvoid-containing layer is provided as an intermediate layer, it is not necessary to contain the filler or pigment, but from the viewpoint of controlling the surface unevenness, it is preferable that the fine cavity-containing layer contains 0.01 to 10.0% by mass.

The incompatible thermoplastic resin that serves as the cavity-forming agent is not particularly limited as long as it is incompatible with polyester. Here, "incompatible" refers to a state in which compatibility does not occur at the molecular level at the temperature during melt extrusion of the polyester.

Specific examples of incompatible thermoplastic resins include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, and cellulose resins. In particular, polystyrene resins or polyolefin resins such as polymethylpentene and polypropylene are preferred. These resins may be used alone or in combination of two or more.

When an incompatible thermoplastic resin is contained in the microvoid-containing layer, the total amount of the incompatible thermoplastic resin contained in the microvoid-containing layer is preferably 0.1 to 40 mass %, and more preferably 1 to 25 mass %.

(Thickness of polyester film, etc.)
The polyester film used in the present invention is preferably a biaxially oriented film consisting of a single layer or multiple layers, and preferably has a microvoid-containing layer formed by stretch orientation.

The overall thickness of the polyester film is preferably 10 to 300 μm, more preferably 25 to 200 μm, from the viewpoint of ensuring appropriate handling properties.

When the polyester film has a three-layer structure of a microparticle-containing layer/microvoid-containing layer/microparticle-containing layer, from the viewpoint of controlling the surface shape and optical properties of the polyester film well, the thickness of each microparticle-containing layer is preferably 3-25% of the total, and more preferably 5-15%. When the polyester film has a two-layer structure of a microparticle-containing layer/microvoid-containing layer, from the same viewpoint, the thickness of the microparticle-containing layer is preferably 3-25% of the total, and more preferably 5-15%.

(Production method of polyester film)
The biaxially oriented polyester can be obtained by a conventionally known method.

For example, it is preferable to obtain an unstretched film by melt extruding polyester at a temperature of melting point (Tm: °C) to (Tm + 70) °C, stretch this unstretched film in one axis direction (longitudinal or transverse direction) at a temperature of (Tg - 10) to (Tg + 70) °C (where Tg is the glass transition temperature of the polyester) at a ratio of 2.5 times or more, preferably 3 times or more, and then stretch it in a direction perpendicular to the stretching direction at a temperature of Tg to (Tg + 70) °C at a ratio of 2.5 times or more, preferably 3 times or more. If necessary, it may be further stretched in the longitudinal and/or transverse directions. In this way, the total stretching ratio is preferably 9 times or more in terms of area stretching ratio, more preferably 12 to 35 times, and particularly preferably 15 to 30 times. Furthermore, the biaxially oriented film can be heat-set at a temperature of (Tg + 70) °C to (Tm - 10) °C, and it is preferable to heat-set it at, for example, 180 to 250 °C. The heat setting time is preferably 1 to 60 seconds.

When producing biaxially oriented polyester consisting of two or more layers, the raw materials for each layer are melted and co-extruded to obtain a laminated unstretched film, and then the same process is carried out to produce the film.

When manufacturing a biaxially oriented polyester with a three-layer structure of a microparticle-containing layer/microvoid-containing layer/microparticle-containing layer, a cavity-forming agent can be added to the raw material for the microvoid-containing layer, and microvoids can be formed by stretching the laminated unstretched film.

(Release Layer)
The release layer A and the release layer B (hereinafter collectively referred to as "release layer") in the present invention are not particularly limited as long as their properties satisfy the above formulas (1) to (6). For example, a coating liquid containing a silicone resin, a silicone oil, a fluororesin, a fluorooil, various waxes, or other organic resins such as polyester resin, alkyd, polyurethane, acrylic, melamine, polyvinyl acetal, etc. modified with silicone or fluorine, or a coating liquid containing a silicone oil, a fluorooil, or various waxes added to an organic resin may be used.

Among them, curable silicone resins are preferred in terms of heat resistance, and any reaction type can be used as the curable silicone resin, such as a condensation reaction type, an addition reaction type, or an ultraviolet or electron beam curable type. These curable silicone resins can be used alone or in combination of two or more types.

The curing reactions of various silicone resins can be shown as follows:

The above-mentioned condensation reaction type silicone resin can be exemplified by a condensation reaction between polydimethylsiloxane having terminal -OH groups and polydimethylsiloxane (hydrogensilane) having terminal -H groups using an organotin catalyst (e.g., an organotin acylate catalyst) to form a three-dimensional crosslinked structure.

An example of an addition reaction type silicone resin is one that creates a three-dimensional crosslinking structure by reacting polydimethylsiloxane with vinyl groups at the ends with hydrogen silane, a crosslinking agent, using a platinum catalyst.

Examples of UV-curable silicone resins include the most basic type, which uses the same radical reaction as normal silicone rubber crosslinking, those that introduce acrylic groups and photo-cure, those that use UV light to decompose onium salts to generate strong acids that then cleave epoxy rings to crosslink, and those that crosslink by an addition reaction of thiols to vinyl siloxanes. Electron beams have more energy than UV light, and a radical-based crosslinking reaction occurs without the use of an initiator as in the case of UV curing.

As the curable silicone resin, those having a degree of polymerization of about 500,000 to 200,000, preferably about 1,000 to 100,000 are preferred. Specific examples of these include KS-718, -774, -775, -778, -779H, -830, -835, -837, -838, -839, -841, -843, -847, -847H, X-62-2418, -2422, -2125, -2492, -2494, -470, -2366, -630, X-92-140, -128, KS-723A/B, -705F, -708A, -883, -709, -719 manufactured by Shin-Etsu Chemical Co., Ltd., and TPR-6701 and -6702 manufactured by Toshiba Silicone Co., Ltd. , -6703, -3704, -6705, -6722, -6721, -6700, XSR-7029, YSR-3022, YR-3286, DK-Q3-202, -203, -204, -210, -240, -3003, -205, -3057, SFXF-2560 manufactured by Dow Corning Co., Ltd., Toray Dow Examples of suitable silicone resins include SD-7226, -7320, -7229, BY24-900, -171, -312, -374, SRX-375, SYL-OFF23, SRX-244, and SEX-290 manufactured by Corning Silicone Co., Ltd., and SILCOLEASE 425 manufactured by ICI Japan Co., Ltd. Silicone resins described in JP-A-47-34447 and JP-B-52-40918 can also be used.

When forming the curable silicone resin coating on the surface of a film, a conventionally known coating method such as a bar coating method, a doctor blade method, a reverse roll coating method, or a gravure roll coating method can be used.

Drying and curing of the coating (thermal curing, UV curing, etc.) can be carried out separately or simultaneously. When carried out simultaneously, it is preferable to carry out the drying and curing at 100°C or higher. The drying and curing conditions are preferably 100°C or higher and 30 seconds or more. Drying temperatures below 100°C and curing times below 30 seconds are not preferable because the coating will not be completely cured and will be prone to falling off.

The thickness of the release layer is not particularly limited, but is preferably in the range of 0.005 to 0.5 μm, and more preferably in the range of 0.05 to 0.5 μm. If the thickness is 0.005 μm or more, sufficient release properties are easily obtained, and if it is 0.5 μm or less, the curing time can be shortened, which is convenient in terms of production.

In addition, the method for forming the release layer in the present invention is not particularly limited, but for example, the release layer can be formed in the following manner. That is, an aqueous coating composition obtained by dissolving trialkoxysilane represented by the following general formula (1) and tetraalkoxysilane represented by the following general formula (2) in water through hydrolysis is applied to at least one side of a polyester film, and then dried to produce a release film.

The coating may be carried out in a normal coating process, that is, in a process in which the polyester film is coated separately from the manufacturing process of the film. However, since this process is prone to involving dirt, dust, etc., it is desirable to carry out the coating in a clean atmosphere. From this viewpoint, coating during the polyester film manufacturing process is preferred. In particular, it is preferable to apply the aqueous coating composition to the polyester film before the crystal orientation is completed during this process.

R ¹ -Si(-OR ² ) ₃ (1)
(In the formula, ^R1 represents an alkyl group having 1 to 5 carbon atoms, and ^R2 represents an alkyl group having 1 to 2 carbon atoms.)
Si(-OR ³ ) ₄ (2)
(In the formula, ^R3 represents an alkyl group having 1 to 2 carbon atoms.)
Here, the polyester film before the crystal orientation is completed is an unstretched film in which polyester is thermally melted and made into a film form as it is: the unstretched film is stretched in the machine direction (longitudinal direction) or the transverse direction (width direction). Uniaxially stretched film oriented in one direction; and films oriented in both the longitudinal and transverse directions at low stretch ratios (before finally re-stretching in the longitudinal or transverse direction to complete the orientation crystallization). Biaxially oriented films of the above-mentioned are also included.

Any known coating method can be used as the coating method. For example, kiss coating, bar coating, die coating, reverse coating, offset gravure coating, Mayer bar coating, gravure coating, roll brushing, spray coating, air knife coating, impregnation, and curtain coating can be used alone or in combination.

The polyester film coated with the aqueous coating composition and before completing the crystal orientation is dried and then guided to processes such as stretching and heat setting. For example, a polyester film coated with the aqueous coating composition and uniaxially stretched longitudinally is guided to a stenter and then stretched transversely and heat set. During this time, the aqueous coating composition is dried and thermally crosslinked.

The conditions for orientation crystallization of polyester-based films, such as conditions for stretching, can be those conventionally accumulated in the art, but the heat setting temperature is preferably adjusted so that the melting subpeak temperature (Tsm) of the film is preferably 180° C. or higher, more preferably 200° C. or higher, and even more preferably 210° C. or higher. The melting subpeak temperature (Tsm) here refers to a minute endothermic peak that appears before the crystal melting of polyester in differential scanning calorimetry (DSC), and this melting subpeak (Tsm) is observed as a minute peak at a temperature equivalent to the heat setting temperature of the film, and occurs due to the melting of an incomplete part (pseudocrystal) of the crystal structure formed by the heat setting treatment. If Tsm is below 180°C, the amount of heat required to cure the release layer in the present invention is large, so that sufficient heat is not supplied to cure the coating film, resulting in insufficient crosslinking, and the desired release property may not be achieved. In addition, the adhesive strength of the resin film varies depending on the resin used in the resin film, the degree of cure of the resin, and even the film thickness, so it is necessary to adjust it within a range that satisfies formula (6). In addition to adjusting the combination of the release agent, the amount of curing catalyst, and the coating thickness as described above, at least one of the following four methods can be used for silicone-based release agents to control the peel strength.

(1) A silicone resin having the following D unit, T unit and/or Q unit structures is blended into a polydimethylsiloxane polymer to adjust the concentration of methyl groups in the release layer and increase the surface tension. The blending ratio of this silicone resin is preferably 20 to 60 mass% in terms of solid content concentration. If the blending ratio is less than 20 mass%, the wettability of the release layer may be poor, and if it exceeds 60 mass%, the release layer may become too hard and have poor abrasion resistance, which is not preferable.

However, in the D and T units, R represents an alkyl group such as a methyl group or an aromatic hydrocarbon group such as a phenyl group.

(2) By blending silica filler into polydimethylsiloxane polymer, the concentration of -Si-OH groups in the release layer is adjusted to be high, thereby increasing the surface tension. The silica filler preferably has an average particle size of 1 μm or less. If the average particle size is 1 μm or less, this is preferred because the release layer is less likely to be scraped off when the film is run in the processing step. The blending ratio of silica filler is preferably 0.1 to 1 mass% in terms of solid concentration. If the blending ratio is 0.1 mass% or more, the desired wettability is easily obtained, and if it is 1 mass% or less, this is preferred because the silica filler is less likely to be scraped off from the release layer.

(3) Modified polydimethylsiloxane in which some of the methyl groups in the polydimethylsiloxane polymer are replaced with bulky phenyl groups. Due to the steric hindrance of the phenyl groups, for example, the rotational movement around the -Si-O-Si- bond in the polymer is suppressed, and as a result, the concentration of methyl groups on the surface of the release layer is reduced, which can increase the surface tension. The substitution rate of this phenyl group is preferably 20 to 60 mol %. If this substitution rate is 20 mol % or more, the desired releasability is easily obtained, and if it is 60 mol % or less, the releasability of the release layer between various adhesives and various sheets is good.

(4) Modified polydimethylsiloxane obtained by reacting a polydimethylsiloxane polymer having a relatively high concentration of reactive groups such as silanol groups and methoxy groups with an organic resin having a hydroxyl group in the molecule (e.g., alkyd resin, polyester resin, acrylic resin, etc.). The proportion of dimethylsiloxane in this modified polydimethylsiloxane is preferably 10 to 30% by mass. If this proportion is 10% by mass or more, good releasability is obtained, and if it is 30% by mass or less, the desired releasability is easily obtained.

(Antistatic Layer)
Generally, release films on which a resin film has been formed are prone to generating static electricity when they come into contact with rolls in the process, which can cause fatal damage to electrical and electronic materials.
Specifically, static electricity generated during the friction or contact peeling process between the transport roll and the release film can cause electrostatic patterns, and positional deviations can occur during the attachment or lamination process due to static electricity caused by peeling.

Therefore, in the present invention, an antistatic layer can be provided on at least one side of the polyester film before providing release layers on both sides. This reduces static electricity during unwinding and running, and also makes it less likely to cause static electricity problems when unwinding and using the film as a resin film.

The antistatic layer in the present invention preferably has a surface resistivity of 5×10 ⁴ to 5×10 ¹² Ω/□, more preferably 5×10 ⁵ to 5×10 ¹⁰ Ω/□, after the release layer is provided.

The antistatic layer is not particularly limited, but preferably contains at least one selected from the group consisting of metal oxide fine particles, conductive polymers, and polymers to which a quaternary ammonium salt has been added. There are no particular limitations on the means for forming the antistatic layer, and known methods such as coating, vacuum deposition, and lamination can be used, but from the viewpoint of cost, it is preferable to apply a coating liquid containing an antistatic agent by coating.

Examples of metal oxide fine particles include antimony-doped tin oxide (ATO), ZnO, CeO ₂ , Sb ₂ O ₂ , SnO ₂ , indium tin oxide (often abbreviated as ITO), In ₂ O ₃ , Al ₂ O ₃ , and aluminum-doped zinc oxide (AZO). Fine particles refer to particles of a so-called submicron size, 1 micron or less, and preferably have an average particle size of 0.1 nm to 0.1 μm. According to a preferred embodiment of the present invention, the primary particle size of the conductive fine particles is preferably about 30 to 70 nm, and the secondary particle size is preferably about 200 nm or less.

Examples of conductive polymers include polyacetylene, an aliphatic conjugated system; poly(paraphenylene), an aromatic conjugated system; polypyrrole and polythiophene, a heterocyclic conjugated system; polyaniline, a heteroatom-containing conjugated system; and poly(phenylenevinylene), a mixed conjugated system. Further examples include multi-chain conjugated systems, which are conjugated systems having multiple conjugated chains in the molecule, and conductive composites, which are polymers in which the aforementioned conjugated polymer chains are grafted or block-copolymerized onto a saturated polymer.

As the polymer to which a quaternary ammonium salt is added, a polymerizable compound such as a monomer or oligomer having a quaternary ammonium group and capable of being polymerized by ionizing radiation, or an organometallic compound such as a coupling agent having a functional group capable of being polymerized by ionizing radiation can be used.

Alkoxysilanes or acyloxysilanes may also be added to the antistatic layer in order to improve the strength of the resulting coating film. These silane compounds are hydrolyzed and then present in the coating film in the form of a condensation reaction product.

Examples of these silane compounds include trialkoxysilanes having reactive functional groups other than alkoxy groups, such as methyltriacetoxysilane, dimethyldiacetoxysilane, trimethylacetoxysilane, tetraacetoxysilane, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetraisobutoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, phenyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and vinyltriethoxysilane.

A surfactant may be used in the antistatic layer to improve the appearance. Examples of the surfactant include nonionic surfactants such as polyoxyethylene octylphenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene sorbitan fatty acid ester, and fluorine-based surfactants such as fluoroalkyl carboxylic acid, perfluoroalkyl carboxylic acid, perfluoroalkyl benzene sulfonic acid, perfluoroalkyl quaternary ammonium, and perfluoroalkyl polyoxyethylene ethanol.

The antistatic layer may contain lubricants, dyes, UV absorbers, crosslinking agents, silane coupling agents, etc., as necessary, as long as the purpose of the present invention is not impaired.

Methods for coating and laminating an antistatic layer on the surface of a substrate film include gravure roll coating, reverse roll coating, knife coater, dip coating, and spin coating, but there are no particular limitations on the coating method suitable for the conductive composition. The layer can also be applied by an in-line coating method in which a coating layer is applied during the film manufacturing process, or an offline coating method in which a coating layer is applied after the film is manufactured.

The drying temperature for forming the antistatic layer is usually 60°C or higher and 150°C or lower, and preferably 90°C or higher and 140°C or lower. If the temperature is 60°C or higher, the processing time is short, which is preferable from the viewpoint of improving productivity. On the other hand, if the temperature is 150°C or lower, the flatness of the film is maintained, which is preferable.

The thickness of the antistatic layer is preferably 0.005 μm or more and 5 μm or less. More preferably, it is 0.01 μm or more and 1 μm or less, and even more preferably, it is 0.01 μm or more and 0.2 μm or less. When the thickness of the antistatic layer is 0.005 μm or more, an antistatic effect is obtained, which is preferable. On the other hand, when it is 5 μm or less, there is no risk of impairing the releasability, which is preferable.

(Uses of double-sided release film)
The double-sided release film of the present invention can be used in manufacturing processes such as forming double-sided pressure-sensitive adhesive tapes, forming green sheets for ceramic capacitors, forming anisotropic conductive films, forming insulating resin sheets for circuit boards, etc. Specifically, for example, it can be used as a carrier film in the process of forming resin films that are the raw materials for various functional sheets, or as a separator during winding.

For example, anisotropic conductive films can be manufactured by applying and drying an adhesive varnish made by mixing and dispersing conductive particles in an insulating adhesive made by mixing an insulating resin such as epoxy resin with a coupling agent, a hardener, and a hardening accelerator onto a carrier film (separator).

The present invention will be described in more detail below with reference to examples and comparative examples. In the present invention, the properties were measured and evaluated by the following methods. In the following, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

(a) Film and thickness of each layer The film was cut using a microtome to obtain a cross section perpendicular to the film surface. This cross section was coated with a platinum-palladium alloy by sputtering to obtain an observation sample. The film cross section was observed using a scanning electron microscope (Hitachi, S-510 model) and photographed at an appropriate magnification so that the entire thickness of the film was in one field of view. From this image, the thickness of each layer was measured using a scale. Measurements were performed on three independently prepared cross-sectional samples, and the average value was used as the layer thickness of the laminated film.

(b) Intrinsic viscosity (IV)
The polyester resin was pulverized, dried, and then dissolved in OCP. The intrinsic viscosity (intrinsic viscosity) of the polyester resin was calculated using an automatic viscosity measuring device (Rigosei VMC-252).

(c) Average particle size Particles are measured at a magnification of 10,000 to 100,000 using a scanning electron microscope (S-4700 manufactured by Hitachi, Ltd.), the particle sizes (average value of the major axis and minor axis) of 1,000 particles are read, and the average particle size of the 1,000 particles is calculated.

(1) Center surface roughness (Ra), center surface maximum protrusion height (Rp)
Measurements were taken using a non-contact three-dimensional surface roughness meter (ZYGO: New View 7300) at a measurement magnification of 25 times and a measurement area of 283 μm × 213 μm (=0.0603 mm ² ), and the central surface average roughness (Ra) and central surface maximum protrusion height (Rp) were determined using the surface analysis software Metro Pro built into the roughness meter. At this time, measurements were taken three times at different measurement locations, and the average values were calculated for each.

(2) Peel Strength A polyester adhesive tape (Nitto Denko Corporation, Nit-31B) was attached to the release layer surface of the film and pressed with a 5 kg pressure roller, and then the peel strength (HA, HB) at 180° between the release layer and the adhesive tape was measured with a tensile tester.

(3) Residual Adhesion Rate A polyester adhesive tape (Nitto Denko Corporation, Nit-31B) was pressed onto a cold-rolled stainless steel plate (SUS304) specified in JIS G4305 using a 5 kg pressure roller and maintained for 30 seconds, after which the peel strength was measured at 180° and designated as the basic adhesive strength (f0).

Next, a new polyester adhesive tape was applied to the release layer surface of the sample film with a 5 kg pressure roller, and after maintaining this pressure for 30 seconds, the polyester adhesive tape was peeled off. The peeled polyester adhesive tape was then applied to the stainless steel plate under the same conditions, and the peel strength of the applied portion was measured and taken as the residual adhesive strength (f). The residual adhesion rate was calculated from the obtained basic adhesive strength (f0) and residual adhesive strength (f) using the following formula.

Residual adhesion rate (%) = (f/f0) x 100

(4) Surface Resistivity Value Using a resistivity meter (model number 5451) manufactured by ADC Corporation, the surface resistivity value was measured after 1 minute at an applied voltage of 500 V under the conditions of a measurement temperature of 23° C., measurement humidity of 65% RH and 45% RH, according to the double ring method described in JIS K6271 (2008). The measurement was performed on the release layer surface of the antistatic layer.

(5) Surface condition of resin film (coatability)
A double-sided release film (film width: 1.2 m, length: 500 m) was unwound from a roll, and a resin coating material having the following composition was applied to the release layer A side. The film was then heated at 120°C for 5 minutes to volatilize the solvent and form a resin film having a thickness of 0.5 µm. The surface condition was then observed and evaluated according to the following criteria.

○: No repelling was observed on the resin film surface (resin film surface condition is good).

×: Cracks were observed on the surface of the resin film (poor surface condition of the resin film).
<Resin paint>
An adhesive resin composition having the following composition was adjusted to a solid content concentration of 5% to obtain a resin coating material.

Liquid epoxy resin (Epicoat 828, manufactured by Mitsubishi Chemical Corporation) 1 part by weight Phenoxy resin (PKHH, manufactured by Gabriel Phenoxies) 2 parts by weight Hardener (Amicure PN-23, manufactured by Ajinomoto Fine-Techno Co., Ltd.) 0.3 parts by weight Solvent (MEK / toluene = 1 / 1) 57 parts by weight (6) Peeling state of resin film The above resin paint was applied to the release layer A surface, and then heated at 120 ° C. for 5 minutes to volatilize the solvent, forming a resin film with a thickness of 0.5 μm. Thereafter, the release layer B was layered on top of the resin film so as to be in contact with it, and aged at 50 ° C. for 17 hours under a pressure of 2 kg / cm ^2. After aging, the release layer B was peeled off, and the release layer B surface was observed and evaluated according to the following criteria.
◯: No resin remains on the surface B of the release layer (resin film peeled off well).
×: Resin remains on surface B of release layer (poor peeling of resin film).

[Example 1]
A composition consisting of 90% by mass of polyester (intrinsic viscosity: 0.63 dl/g, Tg: 79°C, Tm: 253°C) made from terephthalic acid and ethylene glycol and 10% by mass of silica (average particle size: 1.7 μm) was melt-extruded onto a rotating cooling drum maintained at 20°C to form an unstretched film, which was then stretched 3.6 times in the machine axis direction and then 3.9 times in the transverse direction to obtain a biaxially stretched polyester film having a thickness of 50 μm.

Release paint A (for release layer A) with the following composition was applied to one side of this film, and then release paint B (for release layer B) was applied to the other side to obtain a double-sided release film. The release paint was cured at 150°C for 30 seconds, and the release layer was applied to both sides to a thickness of 0.2 μm. The properties of this double-sided release film are shown in Table 1.

<Release paint A>
BY24-400 (Dow Corning Toray Silicone Co., Ltd.) 100 parts by weight Solvent (toluene/MEK=1/1) 1400 parts by weight SRX-212 (Dow Corning Toray Silicone Co., Ltd.) 2 parts by weight <Release paint B>
KS-847H (Shin-Etsu Chemical Co., Ltd.) 100 parts by mass Solvent (toluene/MEK=1/1) 1400 parts by mass PL-50T (Shin-Etsu Chemical Co., Ltd.) 2 parts by mass Example 2
A double-sided release film was produced in the same manner as in Example 1, except that release coating C (for release layer A) was used instead of release coating A. The properties of this double-sided release film are shown in Table 1. The release coating C had the following composition.

<Release paint C>
KS-847H (Shin-Etsu Chemical Co., Ltd.) 100 parts by mass KS-3800 (Shin-Etsu Chemical Co., Ltd.) 25 parts by mass Solvent (MEK/toluene=1/1) 1400 parts by mass PL-50T (Shin-Etsu Chemical Co., Ltd.) 2 parts by mass Example 3
A double-sided release film was produced in the same manner as in Example 1, except that release coating D (for release layer A) was used instead of release coating A. The properties of this double-sided release film are shown in Table 1. The release coating D had the following composition.

<Release paint D>
KS-847H (Shin-Etsu Chemical Co., Ltd.) 100 parts by mass KS-3800 (Shin-Etsu Chemical Co., Ltd.) 50 parts by mass Solvent (MEK/toluene=1/1) 1400 parts by mass PL-50T (Shin-Etsu Chemical Co., Ltd.) 2 parts by mass [Example 4]
A double-sided release film was obtained in the same manner as in Example 1, except that an antistatic layer shown below was provided with a thickness of 0.1 μm before applying release coating A, and then release coating B was applied. The properties of this double-sided release film are shown in Table 1.

<Antistatic paint>
Colcoat SP-2014 (Colcoat Co., Ltd., 7% by weight aqueous dispersion of antimony-doped tin oxide) 100 parts by weight Tetraethyl silicate (Wako Pure Chemical Industries, Ltd.) 10 parts by weight Water 100 parts by weight Surfactant (Kao Corporation, Emulgen 1108) 20 parts by weight Example 5
A release film was obtained in the same manner as in Example 1, except that 20% by mass of calcium carbonate particles having an average particle size of 0.5 μm was used instead of 10% by mass of silica (average particle size: 1.7 μm) in Example 1. The properties of this release film are shown in Table 1.

[Example 6]
A release film was obtained in the same manner as in Example 5, except that the antistatic layer used in Example 4 was provided with a thickness of 0.1 μm before applying the release coating A. The properties of this release film are shown in Table 1.

[Example 7]
A release film was obtained in the same manner as in Example 1, except that 15% by mass of silica particles having an average particle size of 0.3 μm was used instead of 10% by mass of silica (average particle size: 1.7 μm) in Example 1. The properties of this release film are shown in Table 1.

[Example 8]
A release film was obtained in the same manner as in Example 7, except that the antistatic layer used in Example 4 was provided to a thickness of 0.1 μm before applying the release coating A. The properties of this release film are shown in Table 1.

[Comparative Example 1]
A double-sided release film was produced in the same manner as in Example 1, except that release coating B (for release layer A) was used instead of release coating A. The performance of this double-sided release film is shown in Table 1.

[Comparative Example 2]
A release film was obtained in the same manner as in Example 1, except that 10% by mass of titanium oxide particles having an average particle size of 3.0 μm was used instead of 10% by mass of silica (average particle size: 1.7 μm) in Example 1. The properties of this release film are shown in Table 1.

[Comparative Example 3]
A release film was obtained in the same manner as in Example 1, except that 0.03 mass% of titanium oxide particles having an average particle size of 6.0 μm were used instead of 10 mass% of silica (average particle size: 1.7 μm) in Example 1. The properties of this release film are shown in Table 1.

In Table 1, the measurement surfaces are shown as side A, which is the surface of release layer A, and side B, which is the surface of release layer B.

As is clear from Table 1, in Examples 1 to 8, which satisfy formulas (1) to (6), the surface condition and peeling condition of the resulting resin film were good even when a thinner resin film was formed.

In contrast, in Comparative Example 1, which does not satisfy formulas (5) and (6), the peeling state of the resulting resin film was poor. In Comparative Example 2, which does not satisfy formulas (1) and (2), and Comparative Example 3, which does not satisfy formula (2), the surface state of the resulting resin film was poor.

The double-sided release film of the present invention can be used, for example, as a carrier film in the process of forming an adhesive resin film, and can also be used as a separator during winding or when using the resin film.

1 Polyester film 2A Release layer A
2B Release layer B
3 Antistatic layer 5 Resin film

Claims (6)

The release layer A includes a polyester film and a release layer B in this order,
A double-sided release film for forming an anisotropic conductive film, characterized in that it satisfies the following formulas (1) to (6):
RaA<0.1...(1)
RpA<2.0...(2)
RaB≧0.85×RaA...(3)
RpB≧0.85×RpA...(4)
1.5≦HA/HB≦100...(5)
0.15≦HA+HB≦7...(6)
In the formulas (1) to (6), RaA represents the center surface average roughness (μm) of the surface of release layer A, RaB represents the center surface average roughness (μm) of the surface of release layer B, RpA represents the center surface maximum protrusion height (μm) of the surface of release layer A in an area of 283 μm × 213 μm, RpB represents the center surface maximum protrusion height (μm) of the surface of release layer B in an area of 283 μm × 213 μm, HA represents the peel force (N/25 mm width) of the surface of release layer A, and HB represents the peel force (N/25 mm width) of the surface of release layer B. The double-sided release film according to claim 1, wherein the release layer A and the release layer B contain a cured product of an addition reaction type silicone resin. 3. The double-sided release film according to claim 1 or 2, further comprising an antistatic layer between at least one of the release layer A and the release layer B and the polyester film, and the surface resistivity of the surface of the release layer on the side on which the antistatic layer is provided is 5×10 ⁴ to 5×10 ¹² Ω/□. The double-sided release film according to any one of claims 1 to 3, wherein the polyester film contains inorganic particles having an average particle size of 0.1 to 2.0 μm. The double-sided release film according to claim 4, wherein the content of the inorganic particles is 0.05 to 25% by mass. 4. The double-sided release film according to claim 3 , wherein the antistatic layer comprises at least one selected from the group consisting of conductive polymers, metal oxide fine particles, and polymers to which a quaternary ammonium salt has been added.