Release film

Abstract

To provide a release film which has more excellent releasability than a conventional release film and can be suitably used in manufacture of an RtoR type flexible circuit board.SOLUTION: A release film has at least one release layer, and the release layer has a softening temperature of a surface measured by nanothermal analysis of 180°C or higher. The softening temperature of the whole release layer is lower than a softening temperature of the surface measured by the nanothermal analysis, and the release layer contains an aromatic polyester resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a release film. [Background technology]

[0002] BACKGROUND 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-press bonded to a flexible circuit board body on which a copper circuit is formed via a thermosetting adhesive or a thermosetting adhesive sheet. At this time, by placing 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 adhesive seeping out and interfering with the plating process of the electrode parts (e.g., Patent Documents 1 and 2).

[0003] In recent years, release films made up 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 uneven surfaces (embedding) in response to the increasingly thin L / S (line / space) of flexible circuit boards. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-283862 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-132806 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, as flexible circuit boards have become thinner, further improvements in the releasability of release films have been required. Furthermore, in recent years, the manufacturing of flexible circuit boards has become increasingly automated, using methods such as the roll-to-roll (RtoR) method. In the RtoR method, the flexible circuit board body and release film are unwound from a roll, transported between heat press plates, heat-press bonded, and then rewound onto the roll. In this RtoR method, the peel angle tends to be low when peeling the release film from the flexible circuit board after heat-press bonding. Therefore, when using conventional release films, a greater force may be required during peeling, which can lead to defects. Therefore, further improvements in the releasability of release films are required.

[0006] An object of the present invention is to provide a release film that has better releasability than conventional films and can be suitably used in the manufacture of flexible circuit boards by the roll-to-roll method. [Means for solving the problem]

[0007] The present invention is a release film having at least one release layer, wherein the release layer has a surface softening temperature of 180° C. or higher as measured by nano-thermal analysis. The present invention will be described in detail below.

[0008] The heat pressing process in the production of flexible circuit boards is sometimes performed at a temperature of 160 to 180°C for the purpose of softening and curing the adhesive. The inventors discovered that if the release film softens in the temperature range corresponding to the softening and curing of the adhesive, the release film and the flexible circuit board tend to adhere to each other, or the adhesive of the coverlay film to be laminated tends to penetrate into the release film, resulting in a decrease in releasability. After further intensive research, they discovered that by setting the softening temperature of the outermost surface of the release layer of the release film to a certain level or higher, it is possible to suppress the penetration of the adhesive into the film and improve releasability, thereby completing the present invention. In this specification, the outermost surface of the release layer typically refers to a region approximately 100 nm deep from the outermost surface of the release layer.

[0009] The release film of the present invention has at least one release layer. The release layer has a surface softening temperature of 180° C. or higher as measured by nano-thermal analysis. It is sufficient that at least one surface of the release layer has such a softening temperature.

[0010] Nano thermal analysis (nanoTA) is a thermal analysis method that uses a tiny thermal probe to measure local (ultra-small area) thermal properties (softening point, glass transition point, melting point, etc.) on the surface of a sample. The softening behavior of the sample is evaluated using a scanning probe microscope (SPM) with a heatable cantilever. Generally, the softening temperature of polymer materials such as thermoplastic resins can be measured by Vicat softening point measurement or a thermomechanical analyzer (TMA), but the softening point in this case reflects the softening temperature of the entire material (bulk), not just the outer surface of the material.

[0011] The softening temperature is preferably measured by nano thermal analysis using the following method. However, other methods may be used as long as they are proven to produce substantially equivalent evaluation results. A thermal probe is placed in contact with the surface of a sample, and the tip of the probe is heated while recording the vertical displacement of the probe, as well as the change in the current flowing through the probe or the voltage applied to the probe. Changes in probe displacement due to thermal changes, such as the thermal expansion or softening of the sample, reflect thermal changes on the sample surface (e.g., glass transition or melting). Specifically, as the temperature of the probe tip increases, the probe displacement increases as the sample expands. When the temperature continues to increase, the probe tip reaches the softening temperature of the sample surface, and the probe tip penetrates the sample surface, causing the probe displacement to decrease. Plotting the displacement versus the surface temperature produces a curve with a maximum value. The temperature at which the displacement reaches its maximum is defined as the softening temperature. While conventional thermal analysis techniques using thermomechanical analyzers (TMA) are focused on bulk samples, nanothermal analysis can evaluate the thermal properties of microscopic regions (microscopic regions with diameters of tens to hundreds of nanometers and depths of approximately 100 nanometers).

[0012] In this specification, nano thermal analysis can be performed using an apparatus such as an AFM5300E / NanoNaviII / Nano-TA2 composite system manufactured by Hitachi High-Tech Science Corporation. For example, an AN2-300 (tip diameter 30 nm) probe can be used, and measurements can be performed in contact mode in air at a temperature rise rate of 5°C / sec. The temperature of the cantilever (thermal probe) is calibrated in advance using three standard resins with known softening temperatures.

[0013] By ensuring that the softening temperature of the release layer surface, measured by nano thermal analysis, is 180°C or higher, the adhesive formed on the coverlay film can be sufficiently prevented from penetrating into the release layer during heat press bonding. This means that the depth to which the adhesive penetrates into the release layer can be reduced, suppressing the anchoring effect of the adhesive, greatly improving the releasability of the release film. In particular, flexible circuit boards manufactured using the roll-to-roll method are heated to high temperatures in a short period of time, subjecting them to strong shear stress and sometimes requiring peeling at a low angle. Even in these cases, the film still exhibits excellent releasability. The softening temperature is preferably 180° C. or higher, and more preferably 200° C. or higher. There is no particular upper limit to the softening temperature, but from the viewpoint of maintaining good embeddability, it is preferably 300° C. or lower, and more preferably 250° C. or lower.

[0014] There are no particular limitations on the method for setting the surface softening temperature of the release layer, measured by nano-thermal analysis, to 180°C or higher, but possible methods include reducing the arithmetic mean roughness Ra of the release layer before surface treatment, or adjusting the surface treatment method and conditions.

[0015] By reducing the arithmetic mean roughness Ra of the release layer before surface treatment, the softening temperature of the surface measured by nano-thermal analysis of the release layer can be increased. The reason for this is unclear, but it can be assumed as follows. For example, when performing surface treatment by friction treatment, if the arithmetic mean roughness Ra is relatively large, the unevenness of the release layer surface inhibits changes in physical properties and uniform treatment, reducing the degree of surface change due to the friction treatment. In contrast, if the arithmetic mean roughness Ra is sufficiently small, it is thought that the unevenness of the release layer surface does not inhibit changes in physical properties and uniform treatment, allowing the surface to be sufficiently changed by the friction treatment. The arithmetic mean roughness Ra of the release layer surface before surface treatment can be, for example, 0.50 μm or less. The arithmetic mean roughness Ra of the release layer before the surface treatment needs only to be small during the surface treatment. After the surface treatment, even if the arithmetic mean roughness Ra increases as a result of embossing the surface of the release layer as described below, this does not significantly affect the softening temperature of the surface measured by nano thermal analysis. The arithmetic mean roughness Ra of the surface of the release layer before the surface treatment is the arithmetic mean roughness Ra in accordance with JIS B 0601:2013, and can be measured using, for example, a Surftest SJ-301 manufactured by Mitutoyo Corporation.

[0016] The arithmetic mean roughness Ra of the surface of the release layer before the surface treatment can be affected by the conditions during film formation. For example, when the resin constituting the release layer is melt-extruded and the molten resin is cooled, the following methods can be used. That is, a method using a cooling roll with a smoother surface to transfer the roll surface shape to the film, or a method adjusting the elongation stress applied to the molten resin during cooling to be large, etc. Also, a treatment such as hot pressing (press annealing) can be added.

[0017] Examples of the surface treatment include friction treatment, heat treatment, uniaxial stretching, biaxial stretching, etc. These surface treatments may be used alone or in combination of two or more. Among them, friction treatment is preferred because it can efficiently treat only the outermost surface of the release layer.

[0018] The method of the friction treatment is not particularly limited, but the friction treatment can be performed 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. The method of the heat treatment is not particularly limited, but may include passing the film between rolls heated to a certain temperature, or heating the film with a heater. 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 certain temperature can be used.

[0019] When friction treatment is performed as the surface treatment, the amount of work energy En (kJ) can be calculated using the following formula (1).

[0020]

number

[0021] In equation (1), Ar is the area (m 2 ), J represents the amount of work per unit time for friction treatment (KJ / min), W represents the width (m) of the film to be friction treated, and LS represents the line speed (m / min), which is the speed at which the film passes through the friction treatment device.

[0022] When friction treatment is performed as the surface treatment, the amount of work energy En (kJ) can be set to, for example, 300 to 900 kJ. When friction treatment is performed as the surface treatment, the friction treatment can be performed in a heated state. By performing the friction treatment at a high temperature, it becomes easier to set the surface softening temperature of the release layer measured by nano thermal analysis to 180°C or higher. The heating temperature in the friction treatment can be, for example, 30 to 70°C.

[0023] The softening temperature of the entire release layer is not particularly limited, but is preferably lower than the softening temperature of the surface of the release layer measured by nano-thermal analysis. The softening temperature of the entire release layer is preferably 150°C, more preferably 160°C, and more preferably 200°C, more preferably 180°C. If the softening temperature of the entire release layer is increased more than necessary, the flexibility of the entire release film will decrease, and its ability to conform to irregularities will decrease, which may result in voids during hot press bonding or an increase in the width of adhesive seepage. By adjusting the softening temperature of the release layer other than the extreme surface, the release layer can have a high softening temperature (e.g., 180°C or higher) at the extreme surface while the entire release layer can have a moderate softening temperature within the above range. By adopting such a configuration, the release film will have even better releasability and ability to conform to irregularities. The softening temperature of the entire release layer can be measured by a thermal analysis method using, for example, a thermomechanical analyzer (TMA). Examples of the thermomechanical analyzer that can be used include a TMA2940 manufactured by TA Instruments. Specifically, the release layer of the release film is peeled off to prepare a sample, which is then heated from 80°C to 250°C at a heating rate of 5°C / min while a force of 0.1 N is applied from above. The displacement of the measuring probe in the vertical direction is measured, and the temperature at which the displacement begins to increase can be determined as the softening temperature.

[0024] The release layer preferably has a low softening temperature region. In this specification, the term "low softening temperature region" refers to a region inside the release layer that has a softening temperature lower than the softening temperature of the surface of the release layer measured by nano-thermal analysis. Here, the "inside of the release layer" means that it is not the very surface of the release layer. By having a low softening temperature region, the release layer can have a high softening temperature at the very surface, while the release layer as a whole can have a moderate softening temperature within the above range. With this configuration, the release film can have even better releasability and conformability to uneven surfaces. Furthermore, even when the release film is peeled at a low angle, the occurrence of defects during peeling can be suppressed, and good releasability can be achieved. The low softening temperature region is preferably present at a position that is 50 nm or more away from the surface of the release layer. In addition, the proportion of the low softening temperature region in the release layer is preferably 50% or more, more preferably 80% or more, even more preferably 95% or more, and particularly preferably 99.5% or more. When the softening temperature of the surface of the release layer measured by nano thermal analysis is Ts and the softening temperature of the low softening temperature region is Tb, the temperature difference Ts-Tb is preferably 3° C. or more, more preferably 5° C. or more, even more preferably 10° C. or more, and particularly preferably 20° C. or more. The lower limit of the softening temperature in the low softening temperature region is preferably 150°C, more preferably 160°C, and the upper limit is preferably 200°C, more preferably 180°C.

[0025] The release layer preferably has a softening temperature higher in the extreme surface region than in the inner region, where the extreme surface region typically refers to a region extending from the surface to a depth of about 100 nm, and the inner region typically refers to a region extending from the surface to a depth of about 100 nm or more. The release layer preferably has a softening temperature in a region from the surface to a depth of 100 nm that is higher than a softening temperature in a region from the surface to a depth of 100 nm or more.

[0026] The softening temperature of the low softening temperature region, the softening temperature of the extreme surface region, and the softening temperature of the internal region can be measured, for example, by preparing a sample with an exposed cross section parallel to the thickness direction of the release film and performing nano thermal analysis on this cross section.

[0027] In nanothermal analysis, even if the maximum value (softening temperature) of the curve showing the probe displacement (displacement curve) is the same, the behavior of the displacement after reaching the maximum value (softening temperature) can differ. That is, the absolute value of the slope of the displacement curve above the softening temperature can be extremely large (e.g., the displacement decreases to half of the maximum value within 3°C of the softening temperature) or relatively gradual (e.g., the displacement does not decrease to half of the maximum value even above 5°C of the softening temperature). A rapid decrease in displacement at temperatures higher than the softening temperature of the very surface suggests that the interior is also softened when the very surface softens, allowing the probe to easily penetrate into the interior of the sample. In other words, the softening temperature of the very surface region is higher than that of the interior region. In such cases, the low-softening-temperature region is likely to exist near the very surface. On the other hand, the fact that the displacement decreases gradually at temperatures higher than the softening temperature of the extreme surface suggests that the interior is not completely softened when the extreme surface softens, and that a certain degree of resistance is encountered when the probe penetrates the interior of the sample, i.e., the softening temperature of the interior region is equivalent to that of the extreme surface region. In such cases, it is believed that the low-softening-temperature region does not exist or exists at a position relatively distant from the extreme surface.

[0028] The resin constituting the release layer is not particularly limited, but polyester, polyolefin or polystyrene is preferred because it improves the releasability of the release film. The polyester preferably contains an aromatic polyester resin. The polyolefin preferably contains poly(4-methyl-1-pentene) or an alicyclic olefin resin. The polystyrene preferably contains a polystyrene resin having a syndiotactic structure. In particular, the release layer more preferably contains an aromatic polyester resin, since this has excellent conformability to irregularities and excellent resistance to bleeding of the adhesive formed on the coverlay film.

[0029] The aromatic polyester resin is not particularly limited, but a crystalline aromatic polyester resin is preferred. Specific examples include polyethylene terephthalate resin, polybutylene terephthalate resin, polyhexamethylene terephthalate resin, polyethylene naphthalate resin, polybutylene naphthalate resin, and butanediol terephthalate polytetramethylene glycol copolymer. 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 a balance of heat resistance, releasability, conformability to uneven surfaces, and the like. Also preferred is a mixed resin of a polybutylene terephthalate resin and a block copolymer of polybutylene terephthalate and an aliphatic polyether. The aliphatic polyether is not particularly limited, and examples thereof include polyethylene glycol, polydiethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0030] From the viewpoint of film forming properties, the aromatic polyester resin has a melt volume flow rate of 30 cm 3 / 10 min or less is preferable, and 20 cm 3 It is more preferable that the melt volume flow rate is 1 / 10 min or less. The melt volume flow rate can be measured in accordance with ISO1133 at a measurement temperature of 250°C and a load of 2.16 kg.

[0031] Among the above aromatic polyester resins, commercially available examples 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).

[0032] The polyolefin containing poly(4-methyl-1-pentene) 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.

[0033] The alicyclic olefin resin is an olefin resin having a cyclic aliphatic hydrocarbon in the main chain or side chain, and from the viewpoints 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 ring-opening copolymer of a norbornene monomer (after, if necessary, modification such as maleic acid addition or cyclopentadiene addition). Other examples include resins obtained by addition polymerization of a norbornene monomer, resins obtained by addition polymerization of a norbornene monomer with an olefinic monomer such as ethylene or an α-olefin, and resins obtained by addition polymerization of a norbornene monomer with a cyclic olefinic monomer such as cyclopentene, cyclooctene, or 5,6-dihydrodicyclopentadiene. Modified versions of these resins are also included.

[0034] 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.

[0035] The polystyrene resin having the syndiotactic structure is not particularly limited. Examples include polystyrene, poly(alkylstyrene), poly(arylstyrene), poly(halogenated styrene), poly(halogenated alkylstyrene), poly(alkoxystyrene), poly(vinyl benzoate ester), etc., having a syndiotacticity of 75% or more in racemic diads or 30% or more in racemic pentads. Other examples include hydrogenated polymers of these, mixtures of these, and copolymers containing these as the main component. The polystyrene resin having the syndiotactic structure may be commercially available, such as XAREC (registered trademark) manufactured by Idemitsu Kosan Co., Ltd.

[0036] The release layer may contain a mixed resin containing a polybutylene terephthalate resin and an elastomer. The elastomer is not particularly limited, and examples thereof include a block copolymer of polybutylene terephthalate and an aliphatic polyether. The aliphatic polyether is not particularly limited, and examples thereof include polyethylene glycol, polydiethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0037] The proportion of the polybutylene terephthalate resin in the resin constituting the release layer is not particularly limited, but is preferably 75% by weight or more. If the proportion of the polybutylene terephthalate resin is 75% by weight or more, the release properties of the release film are improved. A more preferred lower limit of the proportion of the polybutylene terephthalate resin in the resin constituting the release layer is 80% by weight.

[0038] The release layer may contain a rubber component, which improves the ability of the release layer to conform to the irregularities of the release film. 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. Further examples of the rubber component include olefin-based thermoplastic elastomer, styrene-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, ester-based thermoplastic elastomer, amide-based thermoplastic elastomer, etc.

[0039] 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 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 and 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane. 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), and ditridecyl 3,3′-thiodipropionate.

[0040] The release layer may further contain conventionally known additives such as fibers, inorganic fillers, flame retardants, ultraviolet absorbers, antistatic agents, inorganic substances, and salts of higher fatty acids.

[0041] 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 irregularities 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.

[0042] The release film of the present invention may have a single layer structure consisting of only the release layer, or may have a multilayer structure having layers other than the release layer.

[0043] The release film of the present invention preferably further comprises a cushion layer, which improves the ability of the release film to conform to irregularities. 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 or more structure. Among these, a structure having a release layer on both sides of the cushion layer is preferred. In this case, the release layers on both sides may have the softening temperature described above, or only one of the release layers may have the softening temperature described above. Furthermore, the release layers on both sides may have the same resin composition or different resin compositions. Furthermore, the release layers on both sides may have the same thickness or different thicknesses. Furthermore, 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 integrated together, or may have a structure in which the release layer and the cushion layer are integrated together via an adhesive layer.

[0044] The resin constituting the cushion layer is not particularly limited, but it is preferable that the cushion layer contains the resin constituting the release layer. The cushion layer contains the resin that constitutes the release layer, thereby improving the adhesion between the release layer and the cushion layer. The cushion layer more preferably contains the main component resin of the release layer, and even more 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.

[0045] The content of the resin constituting the release layer in the cushion layer is not particularly limited, but a preferred lower limit is 10% by weight and a 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 cushion layer has sufficient flexibility and improves its ability to follow the irregularities of the release film. 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.

[0046] 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, and ethylene-vinyl acetate copolymers. 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 are preferred because they easily achieve both conformability to irregularities and heat resistance.

[0047] The content of the polyolefin resin in the cushion layer is not particularly limited, but a preferred lower limit is 50% by weight and a preferred upper limit is 90% by weight. If the content of the polyolefin resin is 50% by weight or more, the cushion layer will have sufficient flexibility and will have improved ability to conform to the irregularities of the release film. If the content of the polyolefin resin is 90% by weight or less, the adhesion between the release layer and the cushion layer will be 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.

[0048] 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 absorbers, antistatic agents, inorganic substances, and salts of higher fatty acids.

[0049] The cushion layer may have a single layer structure or a multilayer structure including a laminate of multiple layers. When the cushion layer has a multilayer structure, the multiple layers may be laminated together via an adhesive layer.

[0050] 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 irregularities of the release film is improved. If the thickness of the cushion layer is 200 μm or less, exudation of resin from the cushion layer at the film edge 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.

[0051] The method for producing the release film of the present invention is not particularly limited, and examples thereof include a method in which a film is first prepared by a water-cooled or air-cooled co-extrusion inflation method, a co-extrusion T-die film-forming method, a solvent casting method, a hot press molding method, or the like, and then the above-mentioned surface treatment is performed. 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. Alternatively, 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 allows excellent control of the thickness of each layer.

[0052] By subjecting the thus obtained film to the above surface treatment, the softening temperature of the surface of the release layer measured by nano thermal analysis is increased to 180° C. or higher. After the surface treatment, the surface of the release layer may be embossed. Embossing the surface of the release layer can prevent air bubbles from being trapped at the interface when the release film is placed between the coverlay film and the heat press plate, thereby improving wrinkle resistance. When the surface treatment is a friction treatment, it is preferable that the arithmetic mean roughness Ra of the surface of the release layer is small during the surface treatment in order to make the softening temperature of the surface of the release layer measured by nano thermal analysis 180° C. or higher. However, even if the arithmetic mean roughness Ra increases as a result of embossing the surface of the release layer after the surface treatment, this does not significantly affect the softening temperature of the surface measured by nano thermal analysis.

[0053] 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. Since the release film of the present invention has extremely excellent releasability, it can also be suitably used in the production of flexible circuit boards by the roll-to-roll method, which requires high releasability. [Effects of the Invention]

[0054] According to the present invention, it is possible to provide a release film that has better releasability than conventional films and that can be suitably used in the manufacture of flexible circuit boards by the roll-to-roll method. DETAILED DESCRIPTION OF THE INVENTION

[0055] The following examples will explain the present invention in more detail, but the present invention is not limited to these examples.

[0056] Example 1 (1) Preparation of films The resin constituting the release layers (release layer a and release layer b) was polybutylene terephthalate resin (PBT, Novaduran 5026, manufactured by Mitsubishi Engineering-Plastics Corporation).The resin constituting the cushion layer was 75 parts by weight of polypropylene resin (PP) and 25 parts by weight of polybutylene terephthalate resin (PBT) (main component resin of the release layer). The resins constituting the release layer and the resins constituting the cushion layer were co-extruded into a three-layer structure using an extruder (GM Engineering, GM30-28 (screw diameter 30 mm, L / D 28)) at a T-die width of 400 mm, and the extruded molten resin was cooled with a cooling roll (temperature 70 ° C). This resulted in a three-layer film having release layer a (thickness 20 μm) and release layer b (thickness 30 μm) on both sides of the cushion layer (thickness 50 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 with the cooling roll was 300 kPa.

[0057] The above-mentioned extension stress is expressed by the following formula (2).

[0058]

number

[0059] The strain rate and the elongational viscosity of the molten resin are expressed by the following formulas (3) and (4), respectively.

[0060]

number

[0061] In equation (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 contact point of the molten resin with the roll.

[0062] The arithmetic mean roughness Ra of the surface of the release layer a (before friction treatment) of the obtained film was measured in accordance with JIS B 0601:2013 using a Surftest SJ-301 manufactured by Mitutoyo Corporation, and was found to be 0.1 μm.

[0063] (2) Film surface treatment While the obtained film was being fed by a roll, the surface of the release layer a was subjected to friction treatment using a friction treatment device (a polishing treatment device manufactured by Yamagata Kikai Co., Ltd., model YCM-150M) and a woven fabric as the surface material of the friction treatment material, thereby obtaining a release film. During the friction treatment, a surface treatment roll was placed between the feed roll and the take-up roll, and a load was applied to the film by pressing the surface treatment roll against the film. The ratio of the rotation speed of the take-up roll to the rotation speed of the feed roll was adjusted to generate a tension of 400 N / m in the film's unwinding direction. The work energy En applied during the friction treatment was 700 kJ.

[0064] (3) Measurement of the softening temperature of the release layer surface by nano-thermal analysis The surface softening temperature of the obtained film was measured using a Hitachi High-Tech Science AFM5300E / NanoNaviII / Nano-TA2 composite system. Using an AN2-300 (tip diameter 30 nm) as a probe, measurements were performed in contact mode in the atmosphere. First, the surface of the object to be measured was observed over an 8 μm square area, and after confirming the absence of foreign matter, the probe tip was heated at a heating rate of 5°C / sec, and the displacement of the probe tip relative to the temperature increase was recorded. The displacement measurement was performed starting from a temperature of 40°C until a decrease in displacement was observed, and the maximum value of the curve plotting the displacement versus temperature was taken as the softening temperature. Similar measurements were performed three times, and the average value was taken as the softening temperature of the release layer surface (extreme surface). The softening temperature of the release layer of the film obtained in Example 1 was 215°C.

[0065] (4) Measurement of the softening temperature of the entire release layer by thermal analysis The softening temperature of the entire release layer of the obtained film was measured using a TMA2940 manufactured by TA Instruments. Specifically, the release layer of the obtained film was peeled off to prepare a sample, which was then heated from 80°C to 250°C at a temperature increase rate of 5°C / min with a force of 0.1 N applied from above, and the displacement of the measuring probe in the vertical direction was measured. The temperature at which the displacement began to increase was taken as the softening temperature. The softening temperature of the entire release layer of the film obtained in Example 1 was 165°C.

[0066] (Examples 2 to 4, Comparative Example 1) Release films were obtained in the same manner as in Example 1, except that the amount of work energy during the friction treatment was changed.

[0067] (Comparative Example 2) A release film was obtained in the same manner as in Example 1, except that the friction treatment was not carried out.

[0068] (Comparative Example 3) A release film was obtained in the same manner as in Example 1, except that the arithmetic mean roughness Ra of the release layer surface during the rubbing treatment was changed to 3.0 μm.

[0069] Comparative Example 4 A release film was obtained in the same manner as in Comparative Example 3, except that the friction treatment was not carried out.

[0070] (evaluation) The release films obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

[0071] (Evaluation of releasability) The epoxy adhesive surface of a coverlay film (CISV-2535, manufactured by Nikkan Industries Co., Ltd.) cut into a 200 mm square was placed on the release layer a side of the resulting release film. Next, a sliding vacuum heater press (MKP-3000v-MH-ST, manufactured by Mikado Technos Co., Ltd.) was used to press the film at a pressure of 120 kgf, 180°C, and 5 minutes. An evaluation sample measuring 30 mm wide and 150 mm long was then cut out from the sample. The coverlay film side of this evaluation sample was pulled using a Tensilon (STA-1150, manufactured by A&D Co., Ltd.) at a peel speed of 500 mm / min and a peel angle of 180°, and the peel strength (gf / cm) was measured.

[0072] [Table 1] [Industrial Applicability]

[0073] According to the present invention, it is possible to provide a release film that has better releasability than conventional films and that can be suitably used in the manufacture of flexible circuit boards by the roll-to-roll method.

Claims

1. A release film having at least one release layer, the release layer contains a polybutylene terephthalate resin, and the proportion of the polybutylene terephthalate resin in the resin constituting the release layer is 75% by weight or more; the release layer has a surface softening temperature of 180°C or higher and 250°C or lower as measured by nano thermal analysis; A release film, wherein the softening temperature of the surface is measured by the following method using a scanning probe microscope. (Measurement method) A heatable cantilever probe is brought into contact with the surface of a target sample, and the vertical displacement of the probe is recorded while the temperature of the tip of the probe is increased. A curve is created by plotting the recorded vertical displacement of the probe against the temperature of the target sample surface, and the temperature at which the displacement shows a maximum value on this curve is determined to be the surface softening temperature.

2. A release film having at least one release layer, the release layer contains a polybutylene terephthalate resin, and the proportion of the polybutylene terephthalate resin in the resin constituting the release layer is 75% by weight or more; the release layer has a surface softening temperature of 180°C or higher as measured by nano thermal analysis; A release film, wherein the softening temperature of the surface is measured by the following method using a scanning probe microscope. (Measurement method) A heatable cantilever probe is brought into contact with the surface of a target sample, and the vertical displacement of the probe is recorded while the temperature of the tip of the probe is increased. A curve is created by plotting the recorded vertical displacement of the probe against the temperature of the target sample surface, and the temperature at which the displacement shows a maximum value on this curve is determined to be the surface softening temperature.

3. 3. The release film according to claim 1, wherein the softening temperature of the entire release layer measured by the following method is lower than the softening temperature of the surface measured by nano thermal analysis. (Measurement method) Using a thermomechanical analyzer, the release layer is heated from 80°C to 250°C at a temperature increase rate of 5°C / min while applying a force of 0.1 N to the release layer. The temperature at which the displacement of the measuring probe in the vertical direction begins to increase is defined as the softening temperature of the entire release layer.

4. 4. The release film according to claim 1, further comprising a cushion layer, and release layers on both sides of the cushion layer.

5. 5. The release film according to claim 1, 2, 3 or 4, which is used in the production of flexible circuit boards by a roll-to-roll method.

Images