JP7712741B2 - Release Film - Google Patents

Description

The present invention relates to a release film.

2. Description of the Related Art Release films are used in the manufacturing processes of printed wiring boards, flexible circuit boards, multilayer printed wiring boards, and the like.
In the manufacturing process of a flexible circuit board, a coverlay film is heat-pressed to a flexible circuit board body having a copper circuit formed thereon via a thermosetting adhesive or a thermosetting adhesive sheet. At this time, by disposing a release film between the coverlay film and the heat-press plate, it is possible to prevent the coverlay film and the heat-press plate from adhering to each other, and also to prevent problems such as the adhesive seeping out and interfering with the plating process of the electrode portion.
In recent years, release films made of multiple layers including a release layer and a cushion layer have also been used to ensure performance such as releasability and ability to conform to irregularities (embedding ability) in response to the thinning of L/S (line/space) of flexible circuit boards.

Release films are required to have releasability that allows easy peeling after heat press bonding. In order to improve releasability, for example, the polarity of the release film surface has been adjusted. The crystallinity of the release film has also been adjusted. Patent Document 1 describes a release film having a surface layer containing a polyester resin, in which the proportion of carbonyl groups oriented parallel to the surface among the carbonyl groups contained in the polyester resin in a region from the surface of the surface layer to a thickness of 1 μm is 45% or more. Patent Document 2 describes a release film having a release layer containing a polyester resin on at least one surface, in which the crystallinity of the release layer is 10% or more and 50% or less.

JP 2015-083379 A JP 2016-2730 A

In recent years, as flexible circuit boards become thinner, further improvement in the releasability of the release film is required. In addition, in recent years, the manufacturing of flexible circuit boards has also been automated by the roll-to-roll (RtoR) method and the like. In the RtoR method, the flexible circuit board body and the release film, etc., unwound from the roll are transported between heat press plates, heat press bonded, and then wound up on the roll again. In such an RtoR method, when the release film is peeled off from the flexible circuit board after heat press bonding, the peel angle tends to be low. Therefore, when a conventional release film is used, a larger force may have to be applied during peeling, which may lead to the occurrence of defects. Therefore, further improvement in the releasability of the release film is required.
In order to improve the releasability, it is conceivable to adjust the molecular orientation in the crystalline phase on the surface of the release film. However, as described in Patent Document 1, it has been difficult to obtain the high releasability that has been required in recent years by simply adjusting the orientation of carbonyl groups in the region from the surface of the surface layer to a thickness of 1 μm.

The present invention aims to provide a release film that has excellent releasability and conformability to uneven surfaces, and can be suitably used in the manufacture of flexible circuit boards using the roll-to-roll method.

The present invention provides a release film having at least one release layer containing an aromatic polyester resin, wherein the release layer satisfies X/Y>0.7, where X is the area derived from (010) and Y is the area derived from (100) in a profile obtained by oblique incidence wide-angle X-ray diffraction with an incidence angle of 0.06°.
The present invention will be described in detail below.

The present inventors have found that in a release film having at least one release layer containing an aromatic polyester resin, the orientation of carbonyl groups in an extremely thin region (extreme surface) of the surface region of the release layer is particularly important for improving the release properties. The present inventors have found that by adjusting the orientation of carbonyl groups in an extremely thin region (extreme surface) of the surface of the release layer, the release properties can be dramatically improved without impairing the ability to conform to unevenness, and have completed the present invention.

The release film of the present invention has at least one release layer containing an aromatic polyester resin.
The release layer satisfies X/Y>0.7, where X is the area derived from (010) and Y is the area derived from (100) in a profile obtained by oblique incidence wide-angle X-ray diffraction method (in-plane method) with an incidence angle of 0.06°.
By setting the incidence angle to 0.06° in the oblique incidence wide-angle X-ray diffraction method, it is possible to obtain a profile of only the extreme surface of the release layer, rather than a profile of the entire release layer or a relatively thick surface region of the release layer. The extreme surface refers to an extremely thin region of the surface, more specifically, a region from the surface to a thickness of about 4 nm.

The area X derived from the (010) indicates the amount of carbonyl groups oriented (parallel to the surface) so as to penetrate into the surface of the release layer, and the area Y derived from the (100) indicates the amount of carbonyl groups oriented (perpendicular to the surface) so as to face the surface of the release layer.Therefore, the value of X/Y indicates the relative ratio of the amount of carbonyl groups oriented (parallel to the surface) so as to penetrate into the surface of the release layer to the amount of carbonyl groups oriented (perpendicular to the surface) so as to face the surface of the release layer.The carbonyl groups are mainly derived from the aromatic polyester resin contained in the release layer.
When the value of X/Y at the extreme surface of the release layer is greater than 0.7, the proportion of carbonyl groups oriented (parallel to the surface) so as to penetrate into the surface of the release layer increases, and the polarity of the extreme surface of the release layer decreases. Therefore, the adhesive (epoxy adhesive) formed on the coverlay film during hot press bonding can be sufficiently suppressed from penetrating into the release layer, and the electrostatic interaction between the adhesive (epoxy adhesive) and the release film can be suppressed, so that the releasability of the release film is greatly improved. It is sufficient that at least one surface of the release layer has such a value of X/Y at the extreme surface. On the other hand, even if the release layer has such a value of X/Y at the extreme surface, the flexibility of the release film as a whole is maintained, and the ability to follow unevenness is not reduced. The value of X/Y at the extreme surface of the release layer is preferably greater than 1.0, more preferably greater than 2.0.

The upper limit of the value of X/Y at the extreme surface of the release layer is not particularly limited, but a preferred upper limit is 10.0. If the value of X/Y at the extreme surface of the release layer is 10.0 or less, contamination of the flexible circuit board caused by the components of the release layer can be prevented. A more preferred upper limit of the value of X/Y at the extreme surface of the release layer is 8.0.

The value of X/Y at the extreme surface of the release layer can be determined as follows. That is, the surface of the release layer is analyzed by oblique incidence wide-angle X-ray diffraction with an X-ray incidence angle of 0.06°, a baseline is drawn on the diffraction measurement plot obtained, and fitting is performed for the crystalline phase and the amorphous phase, respectively. Furthermore, by performing fitting, the area X originating from (010) and the area Y originating from (100) in the crystalline phase are determined, and the value of X/Y can be determined from the obtained X and Y.

As an X-ray diffraction apparatus for determining the value of X/Y at the outermost surface of the release layer, for example, a multi-function X-ray diffraction apparatus for surface structure evaluation (ATX-G type) manufactured by Rigaku Corporation set under the following conditions can be used.
X-ray source CuKα tube voltage-tube current 50kV-300mA
Incidence optical system Concentration method incidence angle (ω) 0.06°
Measurement range: 5-70°
Measurement interval: 0.02°
Scanning speed: 1.0°/min
Scanning method: In-Plane method

The method for adjusting the value of X/Y at the extreme surface of the release layer to the above range is not particularly limited, but a method is preferable in which the arithmetic mean roughness Ra of the release layer before the surface treatment is adjusted to be small and/or the glossiness of the release layer before the surface treatment is adjusted to be large, and then the surface of the release layer is subjected to surface treatment. By adjusting the arithmetic mean roughness Ra of the release layer before the surface treatment to be small and/or the glossiness of the release layer before the surface treatment to be large, the effect of carbonyl groups penetrating into the surface is greatly improved when the surface treatment is performed on the surface of the release layer, and the value of X/Y at the extreme surface of the release layer can be adjusted to the above range.

The method for reducing the arithmetic mean roughness Ra of the release layer before surface treatment and/or increasing the gloss of the release layer before surface treatment is not particularly limited, but when melt-extruding the resin constituting the release layer and cooling the molten resin, it is preferable to adopt, for example, the following method. That is, a method of using a cooling roll with a smoother surface to transfer the shape of the roll surface to the film, or a method of adjusting the elongation stress applied to the molten resin during cooling to be large, etc. are preferable.

The reason why the effect of the carbonyl group infiltrating into the surface by adjusting the arithmetic mean roughness Ra and glossiness before the surface treatment is improved by the surface treatment is not clear, but it can be assumed as follows. When the arithmetic mean roughness Ra is relatively large, the effect of the surface treatment on the extreme surface may vary, but when the arithmetic mean roughness Ra is relatively small, the effect of the surface treatment on the extreme surface becomes uniform, and it is considered that the probability and amount of the carbonyl group on the extreme surface infiltrating into the surface is improved. In addition, since the glossiness is affected by the surface roughness of the target and the size of the crystal grains inside, a high glossiness means that the surface roughness is small and the crystal grains are small (below a certain size). When the crystal grains before the surface treatment are relatively large, multiple crystal grains become three-dimensional obstacles to each other, preventing the orientation of the extreme surface by the surface treatment. On the other hand, if the crystal grains before surface treatment are relatively small, the orientation of the extreme surface is promoted by the surface treatment without the above-mentioned three-dimensional hindrance, and as a result, it is thought that the effect of the carbonyl groups on the extreme surface penetrating into the plane is improved. It is also thought that the size of the crystal grains is affected by the cooling and elongation stress during melt extrusion. The crystal grain size of the extreme surface can be calculated using the Scherrer formula from the results of measurement of oblique incidence wide-angle X-ray diffraction.

The arithmetic mean roughness Ra of the surface of the release layer is not particularly limited, but the preferred lower limit is 0.01 μm, the preferred upper limit is 0.50 μm, the more preferred lower limit is 0.02 μm, and the more preferred upper limit is 0.40 μm. When the arithmetic mean roughness Ra of the surface of the release layer is in the above range, the releasability of the release film is easily improved.
The arithmetic mean roughness Ra of the surface of the release layer is an arithmetic mean roughness Ra in accordance with JIS B 0601:2013, and can be measured, for example, using a Surftest SJ-301 manufactured by Mitutoyo Corporation.
In addition, even if a surface treatment is performed after film formation during the production process of the release film, the arithmetic mean roughness Ra of the surface of the release layer is usually relatively little affected by the surface treatment after film formation, and the value does not change significantly before and after the surface treatment.
The arithmetic mean roughness Ra of the surface of the release layer is mainly affected by the conditions during film formation. However, when a process such as hot pressing (press annealing) is performed, the surface irregularities are flattened, and the value of the arithmetic mean roughness Ra generally becomes smaller.

The surface gloss of the release layer is not particularly limited, but the lower limit is preferably 100%, the upper limit is preferably 200%, the lower limit is more preferably 120%, and the upper limit is more preferably 180%. When the surface gloss of the release layer is in the above range, it becomes easy to adjust the value of X/Y at the extreme surface of the release layer to the above range, and the releasability of the release film is easily improved.
The surface gloss of the release layer is measured in accordance with JIS Z8741 at an incident angle of 60°, and can be measured, for example, by using a gloss meter VG-1D manufactured by Nippon Denshoku Industries Co., Ltd.
In addition, even if a surface treatment is performed after film formation during the production process of the release film, the surface gloss of the above-mentioned release layer is usually relatively little affected by the surface treatment after film formation, and the value does not change significantly before and after the surface treatment.
The surface gloss of the release layer is mainly influenced by the conditions during film formation.

The surface treatment is not particularly limited, and examples thereof include friction treatment, heat treatment, uniaxial stretching or biaxial stretching, etc. These surface treatments may be used alone or in combination of two or more kinds.
The method of the friction treatment is not particularly limited, but a method of performing the friction treatment using a friction treatment device (for example, a polishing treatment device manufactured by Yamagata Kikai Co., Ltd., model YCM-150M) and using a woven fabric as the surface material of the friction treatment material is preferred.
The method of the heat treatment is not particularly limited, but a method in which the film is passed between rolls heated to a certain temperature, a method in which the film is heated by a heater, and the like are preferable.
The method for the uniaxial or biaxial stretching treatment is not particularly limited, but a method in which the formed film is stretched at a constant temperature is preferred.

The degree of crystallinity of the entire release layer is not particularly limited, but the preferred lower limit is 25% and the preferred upper limit is 50%.
The release layer has the above-mentioned X/Y value at the extreme surface, and the release layer as a whole has a moderate degree of crystallinity in the above range, so that the release film has better releasability and conformability to unevenness. If the crystallinity of the entire release layer is 25% or more, the heat resistance of the release film is improved. If the crystallinity of the entire release layer is 50% or less, the conformability of the release film to unevenness is improved. The more preferable lower limit of the crystallinity of the entire release layer is 30%, and the even more preferable lower limit is 35%. The more preferable upper limit of the crystallinity of the entire release layer is 45%, the even more preferable upper limit is 40%, and the particularly preferable upper limit is 35%.

The crystallinity of the entire release layer can be calculated by plotting a baseline on a diffraction measurement plot obtained by analyzing the entire release layer by wide-angle X-ray diffraction, fitting the crystalline phase and the amorphous phase, and calculating the crystallinity of the entire release layer from the total peak area of the crystalline phase and the total peak area of the amorphous phase according to the following formula (1). When the release film is made of multiple layers, each layer of the release film is peeled off, and a sample consisting of only the release layer is analyzed, thereby evaluating the crystallinity of the entire release layer.
Crystallinity (%) = total peak area of crystalline phase / (total peak area of crystalline phase + total peak area of amorphous phase) × 100 (1)

As an X-ray diffraction apparatus for determining the crystallinity of the entire release layer, for example, a horizontal sample X-ray diffraction apparatus for thin film evaluation (Smart Lab) manufactured by Rigaku Corporation set under the following conditions can be used.
X-ray source CuKα tube voltage-tube current 45kV-200mA
Incident optical system: Concentration method Measurement range: 5-80°
Measurement interval: 0.02°
Scanning speed: 5.0°/min
Scanning method Out-of-plane method

The method for adjusting the degree of crystallinity of the entire release layer to the above range is not particularly limited, but when melt-extruding the resin constituting the release layer and cooling the molten resin, it is preferable to adopt, for example, the following method. That is, a method of adjusting the contact time between the molten resin and the cooling roll, a method of adjusting the cooling roll temperature, etc. are preferable.

The release layer contains an aromatic polyester resin.
Since the release layer contains the aromatic polyester resin, the release film of the present invention has excellent releasability and conformability to irregularities, and also has excellent resistance to bleeding of the adhesive formed on the coverlay film.

The aromatic polyester resin is not particularly limited, but crystalline aromatic polyester resin is preferred.Specific examples include polyethylene terephthalate resin, polybutylene terephthalate resin, polyhexamethylene terephthalate resin, polyethylene naphthalate resin, polybutylene naphthalate resin, terephthalic acid butanediol polytetramethylene glycol copolymer, etc.These aromatic polyester resins may be used alone or in combination of two or more.Among them, polybutylene terephthalate resin is preferred from the viewpoint of balance of heat resistance, releasability, conformability to unevenness, etc.
Also preferred is a mixed resin obtained by mixing a block copolymer of polybutylene terephthalate and an aliphatic polyether with a polybutylene terephthalate resin. The aliphatic polyether is not particularly limited, and examples thereof include polyethylene glycol, polydiethylene glycol, polypropylene glycol, and polytetramethylene glycol.

From the viewpoint of film formability, the aromatic polyester resin preferably has a melt volume flow rate of 30 cm ³ /10 min or less, more preferably 20 cm ³ /10 min or less. The melt volume flow rate can be measured in accordance with ISO 1133 at a measurement temperature of 250° C. and a load of 2.16 kg.

Commercially available examples of the aromatic polyester resins include "Pelprene (registered trademark)" (manufactured by Toyobo Co., Ltd.), "Hytrel (registered trademark)" (manufactured by DuPont-Toray Co., Ltd.), "Duranex (registered trademark)" (manufactured by Polyplastics Co., Ltd.), and "NovaDuran (registered trademark)" (manufactured by Mitsubishi Engineering Plastics Corporation).

The release layer may further contain other resins. The other resins are not particularly limited, and examples thereof include polyolefins and polystyrenes. The polyolefins preferably contain poly(4-methyl-1-pentene) or alicyclic olefin-based resins. The polystyrenes preferably contain polystyrene-based resins having a syndiotactic structure.

The poly(4-methyl-1-pentene)-containing polyolefin preferably contains 90% by weight or more of poly(4-methyl-1-pentene) resin.
As the poly(4-methyl-1-pentene) resin, for example, a commercially available product such as TPX (registered trademark) manufactured by Mitsui Chemicals, Inc. can be used.

The alicyclic olefin resin is an olefin resin having a cyclic aliphatic hydrocarbon in the main chain or side chain, and from the standpoint of heat resistance, strength, etc., thermoplastic saturated norbornene resin is preferred.
Examples of the thermoplastic saturated norbornene resin include resins obtained by hydrogenating a ring-opening polymer or a ring-opening copolymer of a norbornene monomer (after performing modification such as addition of maleic acid or addition of cyclopentadiene as necessary). Other examples include resins obtained by addition polymerization of a norbornene monomer, resins obtained by addition polymerization of a norbornene monomer and an olefin monomer such as ethylene or an α-olefin, and resins obtained by addition polymerization of a norbornene monomer and a cyclic olefin monomer such as cyclopentene, cyclooctene, or 5,6-dihydrodicyclopentadiene. Modified products of these resins are also included.

The polystyrene containing the polystyrene resin having a syndiotactic structure preferably contains 70% by weight or more and 90% by weight or less of the polystyrene resin having a syndiotactic structure.
The polystyrene resin having a syndiotactic structure is a resin having a stereoregular structure in which phenyl groups and substituted phenyl groups, which are side chains, are alternately positioned in opposite directions relative to the main chain formed from carbon-carbon sigma bonds.

The polystyrene resin having the syndiotactic structure is not particularly limited. For example, polystyrene having a syndiotacticity of 75% or more in racemic diads or 30% or more in racemic pentads, poly(alkylstyrene), poly(arylstyrene), poly(halogenated styrene), poly(halogenated alkylstyrene), poly(alkoxystyrene), poly(vinyl benzoate ester), etc. may be mentioned. In addition, hydrogenated polymers of these, mixtures of these, copolymers containing these as main components, etc. may be mentioned. As the polystyrene resin having the syndiotactic structure, for example, commercially available products such as XAREC (registered trademark) manufactured by Idemitsu Kosan Co., Ltd. may be used.

The release layer may contain a rubber component. When the release layer contains a rubber component, the ability to conform to the irregularities of the release film is improved.
The rubber component is not particularly limited, and examples thereof include natural rubber, styrene-butadiene copolymer, polybutadiene, polyisoprene, acrylonitrile-butadiene copolymer, ethylene-propylene copolymer (EPM, EPDM), polychloroprene, butyl rubber, acrylic rubber, silicone rubber, urethane rubber, etc. Examples of the rubber component include olefin-based thermoplastic elastomers, styrene-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, ester-based thermoplastic elastomers, amide-based thermoplastic elastomers, etc.

The release layer may contain a stabilizer.
The stabilizer is not particularly limited, and examples thereof include hindered phenol-based antioxidants and heat stabilizers.
The hindered phenol-based antioxidant is not particularly limited, and examples thereof include 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane, and the like. The heat stabilizer is not particularly limited, and examples thereof include tris(2,4-di-t-butylphenyl)phosphite, trilauryl phosphite, 2-t-butyl-α-(3-t-butyl-4-hydroxyphenyl)-p-cumenylbis(p-nonylphenyl)phosphite, dimyristyl 3,3'-thiodipropionate, distearyl 3,3'-thiodipropionate, pentaerythryl tetrakis(3-laurylthiopropionate), ditridecyl 3,3'-thiodipropionate, and the like.

The release layer may further contain conventional additives such as fibers, inorganic fillers, flame retardants, ultraviolet absorbers, antistatic agents, inorganic substances, and salts of higher fatty acids.

The thickness of the release layer is not particularly limited, but a preferred lower limit is 10 μm and a preferred upper limit is 40 μm. If the thickness of the release layer is 10 μm or more, the heat resistance of the release film is improved. If the thickness of the release layer is 40 μm or less, the ability of the release film to conform to unevenness is improved. A more preferred lower limit of the thickness of the release layer is 15 μm and a more preferred upper limit is 30 μm.

The release film of the present invention preferably further comprises a cushion layer, which improves the ability of the release film to conform to unevenness.
When the release film of the present invention has the cushion layer, it is sufficient that the release film has at least one release layer and a cushion layer, and may have a two-layer structure or a three-layer structure or more. In particular, it is preferable that the release film has a structure in which the release layer is provided on both sides of the cushion layer. In this case, the release layers on both sides may have the above-mentioned X/Y value at the extreme surface, or only the release layer on one side may have the above-mentioned X/Y value at the extreme surface. In addition, the release layers on both sides may have the same resin composition or different resin compositions. In addition, the release layers on both sides may have the same thickness or different thicknesses.
In addition, the release film of the present invention may have a structure in which the release layer and the cushion layer are in direct contact with each other and laminated together, or may have a structure in which the release layer and the cushion layer are laminated together via an adhesive layer.

The resin constituting the cushion layer is not particularly limited, but a polyolefin resin is preferred.
The polyolefin resin is not particularly limited, and examples thereof include polyethylene resins (e.g., high-density polyethylene, low-density polyethylene, linear low-density polyethylene), polypropylene resins, ethylene-vinyl acetate copolymers, and the like. Other examples include ethylene-acrylic monomer copolymers such as ethylene-methyl methacrylate copolymers, ethylene-ethyl acrylate copolymers, and ethylene-acrylic acid copolymers. These polyolefin resins may be used alone, or two or more types may be used in combination. Among these, polypropylene resins and polyethylene resins are preferred because they easily achieve both conformability to irregularities and heat resistance, and it is more preferred to use polypropylene resin and polyethylene resin in combination.

The cushion layer preferably contains the resin that constitutes the release layer.
The cushion layer contains the resin constituting the release layer, so that the adhesion between the release layer and the cushion layer is improved. The cushion layer more preferably contains the main component resin of the release layer, and further preferably contains the main component resin of the release layer and a polyolefin resin. Here, the main component resin of the release layer means the resin with the highest content among the resins contained in the release layer.

The content of the resin constituting the release layer in the cushion layer is not particularly limited, but the preferred lower limit is 10% by weight, and the preferred upper limit is 50% by weight. If the content of the resin constituting the release layer is 10% by weight or more, the adhesion between the release layer and the cushion layer is improved. If the content of the resin constituting the release layer is 50% by weight or less, the flexibility of the cushion layer is sufficient, and the ability to follow the unevenness of the release film is improved. A more preferred lower limit of the content of the resin constituting the release layer is 20% by weight, and an even more preferred lower limit is 25% by weight. A more preferred upper limit of the content of the resin constituting the release layer is 40% by weight, and an even more preferred upper limit is 35% by weight.

The content of the polyolefin resin in the cushion layer is not particularly limited, but the preferred lower limit is 50% by weight, and the preferred upper limit is 90% by weight. If the content of the polyolefin resin is 50% by weight or more, the flexibility of the cushion layer is sufficient, and the ability to follow the unevenness of the release film is improved. If the content of the polyolefin resin is 90% by weight or less, the adhesion between the release layer and the cushion layer is improved. A more preferred lower limit of the content of the polyolefin resin is 60% by weight, and an even more preferred lower limit is 65% by weight. A more preferred upper limit of the content of the polyolefin resin is 80% by weight, and an even more preferred upper limit is 75% by weight.

The cushion layer may further contain a resin such as polystyrene, polyvinyl chloride, polyamide, polycarbonate, polysulfone, or polyester.
The cushion layer may further contain additives such as fibers, inorganic fillers, flame retardants, ultraviolet absorbing agents, antistatic agents, inorganic substances, and salts of higher fatty acids.

The cushion layer may be a single-layer structure consisting of a single layer, or a multi-layer structure consisting of a laminate of multiple layers. When the cushion layer has a multi-layer structure, the multiple layers may be laminated together via an adhesive layer.

The thickness of the cushion layer is not particularly limited, but a preferred lower limit is 15 μm and a preferred upper limit is 200 μm. If the thickness of the cushion layer is 15 μm or more, the ability to conform to the unevenness of the release film is improved. If the thickness of the cushion layer is 200 μm or less, the exudation of resin from the cushion layer that occurs at the end of the film during heat press bonding can be suppressed. A more preferred lower limit of the thickness of the cushion layer is 30 μm and a more preferred upper limit is 150 μm.

The method for producing the release film of the present invention is not particularly limited, and examples thereof include a water-cooled or air-cooled coextrusion inflation method, a coextrusion T-die film formation method, a solvent casting method, and a hot press molding method.
In the case of a structure having the release layers on both sides of the cushion layer, a method of preparing a film to be one of the release layers, laminating the cushion layer on this film by extrusion lamination, and then dry laminating the other release layer can be used. Also, a method of dry laminating the film to be one of the release layers, the film to be the cushion layer, and the film to be the other release layer can be used.
Among these, the co-extrusion T-die method is preferred because it provides excellent control over the thickness of each layer.

The use of the release film of the present invention is not particularly limited, but it can be suitably used in the production processes of printed wiring boards, flexible circuit boards, multilayer printed wiring boards, and the like.
Specifically, for example, in the manufacturing process of a flexible circuit board, the release film of the present invention can be used when hot press bonding a coverlay film to a flexible circuit board main body having a copper circuit formed thereon via a thermosetting adhesive or a thermosetting adhesive sheet.
The release film of the present invention is excellent in both releasability and conformability to unevenness, and in particular has extremely excellent releasability, and therefore can be suitably used in the production of flexible circuit boards by the roll-to-roll method, which requires high releasability.

The present invention provides a release film that has excellent releasability and conformability to uneven surfaces, and can be suitably used in the manufacture of flexible circuit boards using the roll-to-roll method.

The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples.

Example 1
(1) Production of release film: A polybutylene terephthalate resin (PBT) was used as the resin constituting the release layer. 60 parts by weight of a polypropylene resin (PP) and 40 parts by weight of a high density polyethylene (HDPE) were used as the resin constituting the cushion layer.
The resin constituting the release layer and the resin constituting the cushion layer were three-layer co-extruded at a T-die width of 400 mm using an extruder (GM Engineering, GM30-28 (screw diameter 30 mm, L/D 28)), and the extruded molten resin was cooled by a cooling roll (temperature 70°C). This resulted in a three-layer film having a release layer (thickness 20 μm) on each side of a cushion layer (thickness 60 μm). During cooling, the contact time between the molten resin and the cooling roll was 1.0 second, and the elongation stress when cooling the molten resin by the cooling roll was 450 kPa.

The tensile stress is expressed by the following formula (2).
Elongational stress (Pa) = strain rate (1/s) × elongational viscosity of molten resin (Pa s) (2)
The strain rate and the elongational viscosity of the molten resin are expressed by the following formulas (3) and (4), respectively.
Strain rate (1/s) = 9 × V × {(V/V0)^(1/9)-1}/L (3)
Elongational viscosity of molten resin (Pa s) = zero shear viscosity (Pa s) × strain rate (1/s)^(-0.1) (4)
In formula (3), V is the roll speed (m/s), V0 is the flow velocity of the molten resin at the die outlet (m/s), and L is the distance (m) from the die outlet to the point where the molten resin contacts the roll.

The surface of one of the release layers of the obtained film was subjected to friction treatment using a friction treatment device (Yamagata Kikai Co., Ltd. polishing treatment device, model YCM-150M) and a woven fabric as the surface material of the friction treatment material, to obtain a release film. The amount of work energy applied during the friction treatment was 350 kJ. Furthermore, the crystal grain size of the (010) crystal on the extreme surface before the friction treatment was 60 Å, the arithmetic mean roughness Ra was 0.05 μm, and the glossiness was 188%.

(2) Measurement of arithmetic mean roughness Ra The arithmetic mean roughness Ra of the surface of the release layer after the friction treatment was measured in accordance with JIS B 0601:2013 using a Surftest SJ-301 manufactured by Mitutoyo Corporation. The results are shown in Table 1.

(3) Measurement of Glossiness The glossiness of the surface of the release layer after the rubbing treatment was measured in accordance with JIS Z8741 at an incident angle of 60° using a glossmeter VG-1D manufactured by Nippon Denshoku Industries Co., Ltd. The results are shown in Table 1.

(4) Calculation of the value of X/Y at the extreme surface The surface of the release layer after friction treatment was analyzed by oblique incidence wide-angle X-ray diffraction with an X-ray incidence angle of 0.06°. The X-ray incidence direction was measured by matching it with the flow direction (MD: Machine Direction) of the film. A linear baseline was drawn in the range of 2θ = 9.5 to 35° on the obtained diffraction measurement plot. Fitting was performed as a Gaussian function for each of the crystalline phase and the amorphous phase, and the area X derived from (010) and the area Y derived from (100) in the crystalline phase were obtained, and the value of X/Y was calculated from the obtained X and Y. The results are shown in Table 1.

As the grazing incidence wide-angle X-ray diffraction device, a multi-function X-ray diffraction device for surface structure evaluation (ATX-G type) manufactured by Rigaku Corporation was used, which was set under the following conditions.
X-ray source CuKα tube voltage-tube current 50kV-300mA
Incidence optical system Concentration method incidence angle (ω) 0.06°
Measurement range: 5-70°
Measurement interval: 0.02°
Scanning speed: 1.0°/min
Scanning method: In-Plane method

(5) Analysis of the orientation of carbonyl groups in the region from the surface to a thickness of 1 μm The surface of the release layer was analyzed by oblique incidence X-ray diffraction with an X-ray incidence angle of 0.19°. The X-ray incidence direction was measured by matching it with the flow direction (MD: Machine Direction) of the film. A linear baseline was drawn in the range of 2θ = 9.5 to 35° on the obtained diffraction measurement plot, and fitting was performed as a Gaussian function for each of the crystalline phase and the amorphous phase. Furthermore, by performing fitting, the relative ratio of the amount of carbonyl groups oriented parallel to the surface to the total amount of carbonyl groups oriented parallel to the surface and carbonyl groups oriented perpendicular to the surface was obtained. The results are shown in Table 1.

As the grazing incidence wide-angle X-ray diffraction device, a multi-function X-ray diffraction device for surface structure evaluation (ATX-G type) manufactured by Rigaku Corporation was used, which was set under the following conditions.
X-ray source CuKα tube voltage-tube current 50kV-300mA
Incidence optical system Concentration method incidence angle (ω) 0.19°
Measurement range: 5-70°
Measurement interval: 0.02°
Scanning speed: 1.0°/min
Scanning method: In-Plane method

(6) Measurement of crystallinity of entire release layer Each layer of the release film was peeled off to obtain a sample consisting of only the release layer after friction treatment. The release layer after friction treatment was analyzed by wide-angle X-ray diffraction. A baseline was drawn on the obtained diffraction measurement plot. Fitting was performed as a Gaussian function for each of the crystalline phase and the amorphous phase, and the crystallinity of the entire release layer was calculated from the obtained total peak area of the crystalline phase and the total peak area of the amorphous phase by the following formula (1). The results are shown in Table 1.
Crystallinity (%) = total peak area of crystalline phase / (total peak area of crystalline phase + total peak area of amorphous phase) × 100 (1)

As the wide-angle X-ray diffraction device, a horizontal type X-ray diffraction device for thin film evaluation (Smart Lab) manufactured by Rigaku Corporation was used, which was set under the following conditions.
X-ray source CuKα tube voltage-tube current 45kV-200mA
Incident optical system: Concentration method Measurement range: 5-80°
Measurement interval: 0.02°
Scanning speed: 5.0°/min
Scanning method Out-of-plane method

Example 2
A release film was obtained in the same manner as in Example 1, except that polybutylene terephthalate resin (PBT) and PBT-polytetramethylene glycol copolymer were used in a weight ratio of 85:15 as the resin constituting the release layer, and the contact time between the molten resin and the cooling roll, the cooling roll temperature, the elongation stress, and the amount of work energy during friction treatment were changed as shown in Table 1. The physical properties of the obtained release film were determined in the same manner as in Example 1.

(Examples 3 to 4, Comparative Examples 1, 3 to 4)
A release film was obtained in the same manner as in Example 1, except that the contact time between the molten resin and the cooling roll, the cooling roll temperature, the elongation stress, and the amount of work energy during the friction treatment were changed as shown in Table 1. The physical properties of the obtained release film were determined in the same manner as in Example 1.

(Comparative Example 2)
A release film was obtained in the same manner as in Example 2, except that the cooling roll temperature, the elongation stress, and the amount of work energy during the friction treatment were changed as shown in Table 1. The physical properties of the obtained release film were determined in the same manner as in Example 1.

<Evaluation>
The release films obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

(1) Evaluation of releasability The release film was placed on an epoxy adhesive sheet (manufactured by Nikkan Kogyo Co., Ltd., CISV2535) so that the release layer after friction treatment was in contact with the epoxy adhesive sheet, and the sheet was heat-pressed for 5 minutes under conditions of 180°C and 30 kgf/ ^cm2 . After that, the release film naturally peeled off in some samples. For samples in which the release film did not naturally peel off even after 10 minutes had passed from the heat press, the sample was cut to a width of 30 mm, and a peel test was performed at a test speed of 500 mm/min and a peel angle of 30° to determine the 30° peel strength (30° peel value). The case in which the release film naturally peeled off was marked as ○, and the case in which it did not naturally peel off was marked as ×.

(2) Evaluation of conformability A coverlay film (12.5 cm x 12.5 cm, polyimide thickness 25 μm, epoxy adhesive layer thickness 35 μm) with a hole of φ = 1 mm was laminated on the copper foil surface of a copper clad laminate (CCL) (12.5 cm x 12.5 cm, polyimide thickness 25 μm, copper foil thickness 35 μm) so that the epoxy adhesive layer was in contact with the coverlay film. Furthermore, a release film was laminated so that the release layer after friction treatment was in contact with the coverlay film. This laminate was hot pressed for 2 minutes under conditions of 180 ° C. and 30 kgf / cm ^2. Thereafter, the release film was peeled off, and the epoxy adhesive that flowed out onto the copper clad laminate (CCL) was observed with an optical microscope. The exudation width of the epoxy adhesive was measured at 12 points and the average value was calculated to evaluate the conformability of the release film. When the average value of the exudation width of the epoxy adhesive was less than 55 μm, it was marked as ○, and when it was 55 μm or more, it was marked as ×.

The present invention provides a release film that has excellent releasability and conformability to uneven surfaces, and can be suitably used in the manufacture of flexible circuit boards using the roll-to-roll method.

Claims (7)

A release film having at least one release layer containing an aromatic polyester resin,
The release layer is a release film characterized in that, in a profile obtained by oblique incidence wide-angle X-ray diffraction at an incidence angle of 0.06°, when an area derived from (010) is X and an area derived from (100) is Y, the relationship X/Y>0.7 is satisfied. The release film according to claim 1, characterized in that the crystallinity of the entire release layer is 25 to 50%. The release film according to claim 1 or 2, characterized in that the release layer has an arithmetic mean surface roughness Ra of 0.50 μm or less. The release film according to claim 1, 2 or 3, characterized in that the release layer has a surface gloss of 100% or more. The release film according to claim 1, 2, 3 or 4, further comprising a cushion layer and a release layer on both sides of the cushion layer. The release film according to claim 1, 2, 3, 4 or 5, characterized in that the aromatic polyester resin contains polybutylene terephthalate resin. The release film according to claim 1, 2, 3, 4, 5 or 6, characterized in that it is used in the manufacture of flexible circuit boards by the roll-to-roll method.