JP2021054072A - Release film - Google Patents

Abstract

To provide a release film having releasability more excellent than before and appropriately used even in manufacturing a flexible circuit board by a RtoR system.SOLUTION: The release film includes at least one release layer, and a bromine penetrance Z measured by a following bromine containing adhesive permeation test is 4 or less. The bromine containing adhesive permeation test includes performing hot pressing on the conditions of a pressure of 30 kgf, a temperature of 180°C and a period of time of 5 minutes in the state of contacting the adhesive surface of a coverlay film having a bromine compound as an adhesive component to the release layer of the release film; peeling the coverlay film; and calculating the bromine penetrance Z by the following formula (1). Z=Σ{A(i)/B(i)} (1) [where, in the formula (1), A(i) and B(i) show the fragmentation intensity of Br- and the total fragmentation intensity in the i-th measurement of time of flight secondary ion mass spectrometry, respectively, and i represents an integer of 1-100.].SELECTED DRAWING: None

Description

The present invention relates to a release film.

Release films are used in the manufacturing process of printed wiring boards, flexible circuit boards, multilayer printed wiring boards, and the like.
In the process of manufacturing a flexible circuit board, a coverlay film is hot-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 arranging the release film between the coverlay film and the hot press plate, it is possible to prevent the coverlay film and the hot press plate from adhering to each other, and the adhesive exudes. It is possible to prevent problems such as obstruction of the plating process of the electrode portion (for example, Patent Documents 1 and 2).

In recent years, a mold release layer and a cushion layer have been used to ensure performance such as mold releasability and followability to unevenness (embedding) in response to the thinning of L / S (line / space) of a flexible circuit board. A release film composed of multiple layers including and is also used.

Japanese Unexamined Patent Publication No. 5-283862 Japanese Unexamined Patent Publication No. 2009-132806

In recent years, with the thinning of flexible circuit boards, the release film is required to have further improvement in releasability. Further, in recent years, the manufacture of flexible circuit boards has been automated by a roll-to-roll (RtoR) method or the like. In the RtoR method, the flexible circuit board body, the release film, etc., which are unwound from the roll, are conveyed between the hot press plates, bonded by the hot press, and then wound on the roll again. In such an RtoR method, when the release film is peeled from the flexible circuit board after hot press bonding, the peeling angle tends to be low. Therefore, when a conventional release film is used, it may be necessary to apply a larger force at the time of peeling, which may lead to the occurrence of defects or the like. Therefore, the release film is required to have further improvement in releasability.

An object of the present invention is to provide a release film which has excellent releasability as compared with the conventional one and can be suitably used for manufacturing a flexible circuit board by the RtoR method.

The present invention is a release film having at least one release layer and having a bromine permeability Z of 4 or less as measured by the following bromine-containing adhesive penetration test.
(Brominated adhesive penetration test)
After performing hot pressing under the conditions of a pressure of 30 kgf, 180 ° C., and 5 minutes in a state where the adhesive surface of the coverlay film having a bromine compound as an adhesive component and the release layer of the release film are in contact with each other. , The coverlay film is peeled off, and the bromine permeability Z is calculated by the following formula (1).

In the formula (1), A (i) and B (i) indicate the fragment intensity and the total fragment intensity of ^{Br −} in the i-th measurement of the time-of-flight secondary ion mass spectrometry, respectively, and i is 1 to 100. Represents an integer of.
The present invention will be described in detail below.

The heat pressing process in the manufacture of flexible circuit boards may be performed at a temperature of 160 to 180 ° C. for the purpose of softening and curing the adhesive. In the temperature range corresponding to the softening and curing of this adhesive, the present inventors permeate the adhesive component of the laminated coverlay film into the release layer of the release film, and the permeated adhesive component exerts an anchor effect. It has been found that an adhesive force is generated between the adhesive of the release film and the coverlay film to bring about it. As a result of further diligent studies, it was found that the releasability can be improved by controlling the permeation of the adhesive into the releasing layer of the releasing film, and the present invention has been completed.

The release film of the present invention has at least one release layer.
The release film of the present invention has a bromine penetration Z of 4 or less as measured by the following bromine-containing adhesive penetration test. When the value of the bromine penetrance Z is 4 or less, the release film of the present invention can exhibit high releasability. The value of the bromine penetrance Z is preferably 3.5 or less, more preferably 3 or less, further preferably 2.5 or less, and particularly preferably 1.0 or less. The lower limit of the value of the bromine penetrance Z is not particularly limited and may be 0.

Specifically, the bromine-containing adhesive penetration test is carried out as follows. First, a coverlay film having a bromine compound as an adhesive component is prepared. With the adhesive surface of the coverlay film in contact with the release layer of the release film, heat pressing is performed at a pressure of 30 kgf at 180 ° C. for 5 minutes.
As the coverlay film, a coverlay film having a general adhesive layer used in the manufacturing process of a flexible circuit board can be used. Specific examples thereof include commercially available products such as "CISV-1215", "CISV-1225", "CISV-2525" and "CISV-2535" manufactured by Nikkan Kogyo Co., Ltd.
The hot press conditions are the same as those of the hot press conditions in the general manufacturing process of the flexible circuit board.

In the bromine-containing adhesive penetration test, the coverlay film is then peeled off from the release film after hot pressing.
The peeling method is not particularly limited, and examples thereof include a method in which a sample is cut into a length of 125 mm and a width of 25 mm, and then the coverlay film is peeled from the release film at a speed of 500 mm / min by 180 °.

In the bromine-containing adhesive penetration test, the surface of the release layer after the coverlay film is peeled off is then analyzed by a time-of-flight secondary ion mass spectrometry method.
Time-of-flight secondary ion mass spectrometry (TOF-SIMS: Time-of-Flight Second Method Ion Mass Spectrometry) irradiates a solid sample with an ion beam (primary ion) and emits ions (secondary ions) from the surface. Is a method of mass spectrometry using the flight time difference (the flight time is proportional to the square root of the weight). With TOF-SIMS, information on elements and molecular species existing at a depth of 1 nm or less from the sample surface can be obtained with high detection sensitivity.
Examples of the analyzer used for TOF-SIMS include commercially available products such as "TOF-SIMS Type 5" manufactured by ION TOF.
Using a TOF-SIMS analyzer, the fragment strength and total fragment strength ^{of Br −} derived from the adhesive of the coverlay film remaining on the surface of the release layer are measured. In the present invention, etching of the sample surface by sputtering and ^{measurement of Br −} fragment intensity by TOF-SIMS are alternately repeated.

In sputtering, an inert gas such as argon is introduced in a vacuum, a negative voltage is applied to the target to generate a glow discharge, the inert gas atom is ionized, and the gas ion collides with the surface of the target at high speed. The surface of the target can be ground to a depth on the order of nanometer to micrometer.
Specifically, for example, ^{by using C60 +} and adjusting conditions such as voltage to perform sputtering, the surface of the release layer can be dug at a depth of 1 nm / time. Therefore, in this method, the release film can be dug to a depth of 100 nm, for example, by performing 100 times of sputtering.

Below are examples of TOF-SIMS analysis conditions and sputtering conditions in the bromine-containing adhesive penetration test.
Equipment: "TOF-SIMS Type 5" manufactured by ION TOF
Primary ion: 209Bi ^{3 ++}
Primary ion voltage: 25 kV
Primary ion current: 1 pA
Mass range: 1-500 mass
Analysis area: 500 μm x 500 μm □
Charge prevention: Electron irradiation Neutralization Spatter ion: C60 ⁺
Spatter ion voltage: 20 keV
Spatter ion current: 1 nA
Sputtering area: 800 μm x 800 μm □
Spatter count: 99 times

In the bromine-containing adhesive penetration test, the measurement by time-of-flight secondary ion mass spectrometry is performed a plurality of times while etching in the depth direction of the release layer. ^{In the i-th measurement, the fragment strength of Br −} derived from the adhesive of the coverlay film is A (i), and the total fragment strength is B (i). Calculate the value. The value obtained by integrating A (i) / B (i) over all measurement times, that is, the bromine penetrance Z calculated by the above formula (1) is up to the surface layer of the release layer (approximately i × 1 nm depth). , Br ⁻ abundance ratio. The smaller the value of the bromine permeability Z, the more difficult it is for the adhesive of the coverlay film to penetrate into the release film in the hot pressing process in the production of the flexible circuit board.

The method for setting the value of the bromine penetrance Z to 4 or less is not particularly limited, and examples thereof include surface treatment on the surface of the release layer. The surface treatment is not particularly limited, and examples thereof include flame treatment and friction treatment. These surface treatments may be used alone or in combination of both. In particular, a method of applying friction treatment to the surface of the release layer after adjusting to smoothness (reducing the arithmetic mean roughness Ra) or high gloss, or performing flame treatment on the surface of the release layer. The method is effective. Above all, only the surface of the release layer can be efficiently treated, and the treatment can be efficiently performed without being affected by the state of the release layer at the time of treatment (the surface roughness of the release layer at the time of treatment). , Flame treatment is suitable.

The reason why the odor penetrance Z can be reduced by friction or flame treatment is not clear, but it can be estimated as follows. In the release layer, the outermost surface (a region of approximately 0.1 to 1 μm) is considered to be particularly affected by the anchor effect of the adhesive. Friction and flame treatment exert some action on the outermost molecules (for example, increasing the degree of crystallinity), and the molecules on the surface are strongly bound and the free volume of the molecules is reduced, so that the adhesive component is surfaced. It is thought that it will be difficult to invade the inside. The reason why friction against a smooth or highly glossy surface is effective can be estimated as follows. When the arithmetic mean roughness Ra is relatively large, there is a possibility that some physical property change or uniform treatment at the time of friction is hindered by the unevenness of the release layer surface. On the other hand, when the arithmetic mean roughness Ra is sufficiently small, it is considered that the change in physical properties due to the unevenness of the surface of the release layer and the inhibition of uniform treatment are small, and the surface can be sufficiently changed by the friction treatment. Furthermore, since the smooth glossiness is affected by the surface roughness of the target and the size of the crystal grains inside, a large glossiness means that the surface roughness is small and the crystal grains are small (less than a certain size). ) Means that. When the crystal grains are relatively large, a plurality of crystal grains interfere with each other in three dimensions, and the growth of crystals by surface treatment is hindered. On the other hand, when the crystal grains are relatively small, it is considered that the growth of the crystal is promoted without suffering the above-mentioned three-dimensional obstacle, and as a result, the effect of reducing the odor penetration Z is improved. Further, it can be considered that the size of the crystal grains is influenced by the cooling and elongation stress at the time of melt extrusion.
According to the studies by the present inventors, it has been difficult to sufficiently reduce the odor permeability Z even if the surface is neither smooth nor highly glossy is subjected to the friction treatment.

The flame treatment is a treatment in which the surface of the release layer is directly burned with a flame using a gas burner or the like.
The conditions for the flame treatment are not particularly limited, but specifically, for example, a gas burner using propane gas (LPG) as the fuel gas while feeding the film at a constant speed is used, the gas flow velocity is 5 L / min, and air. A method of directly burning the surface of the release layer with a flame from a flow velocity of 125 L / min and a distance of 150 mm between the nozzle and the sample can be mentioned. At this time, the degree of flame treatment can be controlled by adjusting the feed rate of the film.

The method for adjusting the surface of the release layer to be smooth is not particularly limited, but when the resin constituting the release layer is melt-extruded and the molten resin is cooled, for example, the following method can be adopted. preferable. That is, a method of transferring the roll surface shape to the film using a cooling roll having a smoother surface, a method of adjusting the elongation stress applied to the molten resin during cooling, and the like are preferable. The arithmetic mean roughness Ra of the release layer before the friction treatment can be, for example, 0.50 μm or less.
From the viewpoint of reducing the odor permeability Z, the surface of the release layer may be smooth at the time of friction treatment. After the friction treatment, even if the surface of the release layer is embossed to increase the arithmetic mean roughness Ra, the odor penetration Z itself is not significantly affected.

The surface of the release layer preferably has an arithmetic mean roughness Ra of 0.5 μm or more. When the arithmetic mean roughness Ra of the surface of the release layer is 0.5 μm or more, it is possible to prevent air bubbles from being caught in the interface when the release film is placed between the coverlay film and the heat press plate. Therefore, the wrinkle resistance can be improved. The arithmetic mean roughness Ra of the surface of the release layer is more preferably 1 μm or more, further preferably 2 μm or more, and particularly preferably 3 μm or more. The upper limit of the arithmetic mean roughness Ra on the surface of the release layer is not particularly limited, but from the viewpoint of releasability, it is preferably 20 μm or less, and more preferably 15 μm or less.
As described above, when the flame treatment is performed, the bromine penetrance Z can be reduced regardless of the arithmetic mean roughness Ra of the surface of the release layer at the time of the flame treatment. Therefore, it is possible to obtain a release film having excellent wrinkle resistance while exhibiting high releasability.

The method for increasing the arithmetic mean roughness Ra of the release layer is not particularly limited, but when the resin constituting the release layer is melt-extruded and the molten resin is cooled, for example, the following method is adopted. be able to. That is, a method of transferring the roll surface shape to a film using a cooling roll having an uneven surface, a method of adjusting the elongation stress applied to the molten resin during cooling, and the like are preferable. Further, the surface of the film can be embossed by a general method using an embossing roll.

In the release layer, the preferable lower limit of the overall crystallinity is 25%, and the preferable upper limit is 50%.
If the crystallinity of the entire release layer is increased more than necessary, the flexibility of the release film as a whole is reduced, the ability to follow irregularities is reduced, voids are generated during hot press bonding, and an adhesive is used. The exudation width of the film may increase. By adjusting the overall crystallinity of the release layer, the release film of the present invention is excellent in both releasability and followability to unevenness. When the crystallinity of the entire release layer is 25% or more, the heat resistance of the release film is improved. When the crystallinity of the entire release layer is 50% or less, the ability of the release film to follow the unevenness is improved. The lower limit of the crystallinity of the entire release layer is more preferably 30%, still more preferably 35%. The upper limit of the crystallinity of the entire release layer is more preferably 45%, further preferably 40%, and particularly preferably 35%.

The degree of crystallization of the entire release layer is adjusted to the crystalline phase and the amorphous phase by drawing a baseline on the diffraction measurement plot obtained by analyzing the entire release layer by the wide-angle X-ray diffraction method. Can be obtained from the total peak area of the obtained crystalline phase and the total peak area of the amorphous phase by the following formula (2). When the release film is composed of multiple layers, each layer of the release film is peeled off, and the sample consisting of only the release layer is analyzed to evaluate the crystallinity of the entire release layer. be able to.

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

The method for adjusting the crystallinity of the entire release layer to the above range is not particularly limited, but when the resin constituting the release layer is melt-extruded and the molten resin is cooled, for example, the following method is used. It is preferable to adopt it. 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, and the like are preferable. By adjusting the temperature gradient between the surface of the release layer and the inside of the release layer in this way, the rate of crystallization between the surface of the release layer and the inside of the release layer can be adjusted, and the crystals of the entire release layer can be adjusted. The degree of crystallization can be adjusted. The crystallinity of the entire release layer can be adjusted to a value higher than the crystallinity of the polar surface of the release layer.

The release layer preferably contains a polyester resin. This improves the releasability of the releasable film. Among them, the release layer preferably contains an aromatic polyester resin because it has excellent ability to follow irregularities and has excellent ability to prevent the adhesive formed on the coverlay film from seeping out.

The aromatic polyester resin is not particularly limited, but a crystalline aromatic polyester resin is preferable. Specific examples thereof include polyethylene terephthalate resin, polybutylene terephthalate resin, polyhexamethylene terephthalate resin, polyethylene naphthalate resin, polybutylene naphthalate resin, butanediol terephthalate polytetramethylene glycol copolymer and the like. These aromatic polyester resins may be used alone or in combination of two or more. Of these, polybutylene terephthalate resin is preferable from the viewpoint of balance of heat resistance, releasability, followability to unevenness, and the like.
Further, a mixed resin of polybutylene terephthalate resin and a block copolymer of polybutylene terephthalate and an aliphatic polyether is also preferable. The above-mentioned aliphatic polyether is not particularly limited, and examples thereof include polyethylene glycol, polydiethylene glycol, polypropylene glycol, and polytetramethylene glycol.

The aromatic polyester resins, from the viewpoint of film formability, it is preferable that a melt volume flow rate is less than 30 cm ³ / ^10min, more preferably not more than 20 cm 3 / 10min. The melt volume flow rate can be measured at a measurement temperature of 250 ° C. and a load of 2.16 kg according to ISO1133.

Among the above aromatic polyester resins, commercially available ones include, for example, "Perprene (registered trademark)" (manufactured by Toyobo Co., Ltd.), "Hytrel (registered trademark)" (manufactured by Toray DuPont), and "Juranex (registered). "Trademark)" (manufactured by Polyplastics), "Nova DuPont (registered trademark)" (manufactured by Mitsubishi Engineering Plastics), etc.

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 above-mentioned aliphatic polyether is not particularly limited, and examples thereof include polyethylene glycol, polydiethylene glycol, polypropylene glycol, and polytetramethylene glycol.

The ratio of the polybutylene terephthalate resin to the resin constituting the release layer is not particularly limited, but is preferably 75% by weight or more. When the proportion of the polybutylene terephthalate resin is 75% by weight or more, the releasability of the release film is improved. A more preferable lower limit of the ratio of the polybutylene terephthalate resin to the resin constituting the release layer is 80% by weight.

The release layer may contain a rubber component. When the release layer contains a rubber component, the ability of the release film to follow the unevenness is improved.
The rubber component is not particularly limited, and for example, natural rubber, styrene-butadiene copolymer, polybutadiene, polyisoprene, acrylic nitrile-butadiene copolymer, ethylene-propylene copolymer (EPM, EPDM), polychloroprene, butyl rubber. , Acrylic rubber, silicon rubber, urethane rubber and the like. Examples of the rubber component include olefin-based thermoplastic elastomers, styrene-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, ester-based thermoplastic elastomers, and amide-based thermoplastic elastomers.

The release layer may contain a stabilizer.
The stabilizer is not particularly limited, and examples thereof include a hindered phenolic antioxidant, a heat stabilizer, and the like.
The above-mentioned hindered phenolic antioxidant is not particularly limited, and for example, 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-tetraoxa Spiro [5,5] Undecan and the like can be mentioned.
The above heat stabilizer is not particularly limited, and for example, tris (2,4-di-t-butylphenyl) phosphite, trilaurylphosphite, 2-t-butyl-α- (3-t-butyl-4-4). Hydroxyphenyl) -p-cumenylbis (p-nonylphenyl) phosphite, dimyristyl 3,3'-thiodipropionate, disstearyl 3,3'-thiodipropionate, pentaerythtyryl tetrakis (3-laurylthiopropio) Nate), ditridecyl 3,3'-thiodipropionate and the like.

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

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

The release film of the present invention may have a single-layer structure composed of only the release layer, or may have a multilayer structure having a layer other than the release layer.

The release film of the present invention preferably further has a cushion layer. By having the cushion layer, the ability to follow the unevenness of the release film is improved.
When the cushion layer is provided, the release film of the present invention may have at least one release layer and a cushion layer, and may have a two-layer structure or a three-layer or more structure. You may. Above all, it is preferable to have a structure having release layers on both sides of the cushion layer. In this case, the release layers on both sides may have the softening temperature as described above, or only the release layer on one side may have the softening temperature as described above. Further, the release layers on both sides may have the same resin composition or different resin compositions. Further, the release layers on both sides may have the same thickness or may have different thicknesses.
Further, the release film of the present invention may have a structure in which the release layer and the cushion layer are directly contacted and integrated, or the release layer and the cushion layer are integrated via an adhesive layer. It may be a structure.

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.
When the cushion layer contains the resin constituting the release layer, 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 and the polyolefin resin of the release layer. Here, the main component resin of the release layer means the resin having 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 preferable lower limit is 10% by weight and the preferable upper limit is 50% by weight. When 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. When 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 of the release film to follow the unevenness is improved. A more preferable lower limit of the content of the resin constituting the release layer is 20% by weight, and a further preferable lower limit is 25% by weight. A more preferable upper limit of the content of the resin constituting the release layer is 40% by weight, and a more preferable upper limit is 35% by weight.

The polyolefin resin is not particularly limited, and examples thereof include polyethylene resins (for example, high-density polyethylene, low-density polyethylene, linear low-density polyethylene), polypropylene resins, ethylene-vinyl acetate copolymers, and the like. Further, ethylene-acrylic monomer copolymers such as ethylene-methylmethacrylate copolymers, ethylene-ethylacrylate copolymers and ethylene-acrylic acid copolymers can also be mentioned. These polyolefin resins may be used alone or in combination of two or more. Of these, polypropylene resin is preferable because it is easy to achieve both unevenness tracking and heat resistance.

The content of the polyolefin resin in the cushion layer is not particularly limited, but a preferable lower limit is 50% by weight and a preferable upper limit is 90% by weight. When the content of the polyolefin resin is 50% by weight or more, the flexibility of the cushion layer is sufficient, and the ability of the release film to follow the unevenness is improved. When 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 preferable lower limit of the content of the polyolefin resin is 60% by weight, and a more preferable lower limit is 65% by weight. A more preferable upper limit of the content of the polyolefin resin is 80% by weight, and a more preferable 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 absorbers, antistatic agents, inorganic substances, and higher fatty acid salts.

The cushion layer may have a single-layer structure composed of a single layer, or may have a multi-layer structure composed of a laminated body of a plurality of layers. When the cushion layer has a multi-layer structure, a plurality of layers may be laminated and integrated via an adhesive layer.

The thickness of the cushion layer is not particularly limited, but a preferable lower limit is 15 μm and a preferable upper limit is 200 μm. When the thickness of the cushion layer is 15 μm or more, the ability of the release film to follow the unevenness is improved. When the thickness of the cushion layer is 200 μm or less, it is possible to suppress the exudation of the resin from the cushion layer that occurs at the edge of the film during hot press bonding. The more preferable lower limit of the thickness of the cushion layer is 30 μm, and the more preferable upper limit is 150 μm.

The method for producing the release film of the present invention is not particularly limited, and first, for example, a water-cooled or air-cooled coextrusion inflation method, a coextrusion T-die method, a solvent casting method, a heat press molding method, etc. A method of performing the above-mentioned surface treatment after preparing a film according to the above method can be mentioned.
When the structure has the release layers on both sides of the cushion layer, a film to be one of the release layers is prepared, and then the cushion layer is laminated on this film by an extrusion laminating method, and then the other is released. A method of dry lamination the mold layer can be mentioned. Further, a method of dry laminating a film serving as one release layer, a film serving as a cushion layer, and a film serving as the other release layer can be mentioned.
Among them, the method of forming a film by the coextrusion T-die method is preferable because it is excellent in controlling the thickness of each layer.
By subjecting the film thus obtained to the above surface treatment, the value of the bromine penetrance Z can be set to 4 or less.

The application of the release film of the present invention is not particularly limited, but it can be suitably used in the manufacturing process of a printed wiring board, a flexible circuit board, a multilayer printed wiring board, and the like.
Specifically, for example, in the manufacturing process of a flexible circuit board, when a coverlay film is hot-press-bonded to a flexible circuit board body on which a copper circuit is formed via a thermosetting adhesive or a thermosetting adhesive sheet. The release film of the present invention can be used.
Since the release film of the present invention is extremely excellent in releasability, it can be suitably used for manufacturing a flexible circuit board by the RtoR method, which requires high releasability.

According to the present invention, it is possible to provide a release film which has excellent releasability as compared with the conventional one and can be suitably used for manufacturing a flexible circuit board by the RtoR method.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

(Example 1)
(1) Preparation of film Polybutylene terephthalate resin (PBT) was used as the resin constituting the release layer (release layer a and release layer b). As the resin constituting the cushion layer, a mixed resin of 60 parts by weight of low-density polypropylene resin (LDPE) and 40 parts by weight of polybutylene terephthalate resin (PBT) (main component resin of the release layer) was used.
The resin that constitutes the release layer and the resin that constitutes the cushion layer are extruded using an extruder (GM Engineering Co., Ltd., GM30-28 (screw diameter 30 mm, L / D28)) with a T-die width of 400 mm for all three layers. The extruded molten resin was cooled by a cooling roll (temperature 50 ° C.). As a result, a film having a three-layer structure having a release layer a (thickness 25 μm) and a release layer b (thickness 25 μm) on both sides of the cushion layer (thickness 50 μm) was obtained. At the time of cooling, the contact time between the molten resin and the cooling roll was set to 2.5 seconds, and the elongation stress when the molten resin was cooled by the cooling roll was set to 140 kPa.

The elongation stress is represented by the following formula (3).

The strain rate and the extensional viscosity of the molten resin are represented by the following equations (4) and (5), respectively.

In formula (4), V is the roll speed (m / s), V0 is the flow velocity of the molten resin at the mold outlet (m / s), and L is the distance from the mold outlet to the roll contact point of the molten resin (m). Is.

(2) Surface treatment of film While feeding the embossed film with a roll at a speed of 15 m / min, a gas burner using propane gas (LPG) as a fuel gas is used, and the gas flow velocity is 5 L / min and the air flow velocity is 125 L. The surface of the release layer a was directly burned with a flame from a distance of 150 mm between the nozzle and the sample at / min to obtain a release film.

(3) Bromine-containing adhesive penetration test The release layer a of the obtained release film is in contact with the adhesive surface of the coverlay film (“CISV-2535” manufactured by Nikkan Kogyo Co., Ltd.) at a pressure of 30 kgf and 180 ° C. Hot pressing was performed for 5 minutes. Next, the release film after hot pressing was cut into a length of 125 mm and a width of 25 mm, and then the coverlay film was peeled from the release film at a speed of 500 mm / min by 180 °.

The release layer a after peeling of the coverlay film was analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The TOF-SIMS analysis conditions and sputtering conditions were as follows.
Equipment: "TOF-SIMS Type 5" manufactured by ION TOF
Primary ion: 209Bi ^{3 ++}
Primary ion voltage: 25 kV
Primary ion current: 1 pA
Mass range: 1-500 mass
Analysis area: 500 μm x 500 μm □
Charge prevention: Electron irradiation Neutralization Spatter ion: C60 ⁺
Spatter ion voltage: 20 keV
Spatter ion current: 1 nA
Sputtering area: 800 μm x 800 μm □
Number of times of sputtering: 99 times Under the above conditions, TOF-SIMS analysis was performed while performing 100 times of sputtering in the depth direction of the release layer a, and the value of bromine penetrance Z was calculated by the above formula (1).

(4) Measurement of Crystallinity of the entire Release Layer a The release film was peeled off to obtain a sample consisting of only the release layer a. The release layer a was analyzed by wide-angle X-ray diffraction. A linear baseline was drawn on the resulting diffraction measurement plot in the range 2θ = 12.0 to 28.18 °. Fitting was performed on the crystalline phase and the amorphous phase as Gaussian functions, respectively, and the total peak area of the obtained crystalline phase and the total peak area of the amorphous phase were obtained by the above formula (2) for the entire release layer. The crystallinity was determined.

As the wide-angle X-ray diffractometer, a sample horizontal X-ray diffractometer (Smart Lab) for thin film evaluation manufactured by Rigaku Co., Ltd., which was set under the following conditions, was used.
X-ray source CuKα tube voltage 45kV-200mA
Incident optical system Concentrated measurement range 5-80 °
Measurement interval 0.02 °
Scanning speed 5.0 ° / min
Scanning method Out-of-Plane method

(Examples 2 to 7)
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 and elongation stress, and the flame treatment conditions were changed as shown in Table 1. With respect to the obtained release film, the arithmetic average roughness Ra of the surface, the bromine-containing adhesive permeation test, and the degree of crystallization of the entire release layer a were measured in the same manner as in Example 1.

(Example 8)
Polymethylpentene resin (TPX) was used as the resin constituting the release layer (release layer a and release layer b). As the resin constituting the cushion layer, a mixed resin of 50 parts by weight of low-density polypropylene resin (LDPE) and 50 parts by weight of polymethylpentene resin (TPX) (main component resin of the release layer) was used.
The resin that constitutes the release layer and the resin that constitutes the cushion layer are extruded using an extruder (GM Engineering Co., Ltd., GM30-28 (screw diameter 30 mm, L / D28)) with a T-die width of 400 mm for all three layers. The extruded molten resin was cooled by a cooling roll (temperature 70 ° C.). As a result, a film having a three-layer structure having a release layer a (thickness 25 μm) and a release layer b (thickness 25 μm) on both sides of the cushion layer (thickness 50 μm) was obtained. At the time of cooling, the contact time between the molten resin and the cooling roll was set to 1.0 second, and the elongation stress when the molten resin was cooled by the cooling roll was set to 190 kPa.
The obtained film was subjected to flame treatment under the conditions shown in Table 1 in the same manner as in Example 1 to obtain a release film. With respect to the obtained release film, the arithmetic average roughness Ra of the surface, the bromine-containing adhesive permeation test, and the degree of crystallization of the entire release layer a were measured in the same manner as in Example 1.

(Comparative Examples 1 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 and the elongation stress, and the surface treatment method were changed as shown in Table 2. With respect to the obtained release film, the arithmetic average roughness Ra of the surface, the bromine-containing adhesive permeation test, and the degree of crystallization of the entire release layer a were measured in the same manner as in Example 1.
In Comparative Examples 1 and 2, the friction treatment was performed by using a friction treatment device (polishing device manufactured by Yamagata Machinery Co., Ltd., model YCM-150M) on the surface of the release layer a while feeding the obtained film with a roll. This was done by using a woven fabric as the surface material of the friction treatment material. During the friction treatment, a surface-treated roll was provided between the feed-side roll and the take-up-side roll, and the surface-treated roll was pressed against the film to apply a load to the film. The amount of work energy added during the friction treatment was 200 kJ.
Further, in Comparative Example 3, in the stretching treatment, the obtained film was preheated at 75 ° C. for 1 minute using a batch type biaxial stretching machine, and then doubled in the longitudinal direction at a stretching speed of 50 mm / s at 75 ° C. The film was biaxially stretched twice in the lateral direction at the same time, and then heat-set in a hot air oven heated to 190 ° C. for 10 seconds.

(Evaluation)
The release films obtained in Examples and Comparative Examples were evaluated by the following methods.
The results are shown in Tables 1 and 2.

(1) Evaluation of mold release property CVL1 (“CISV-2535” manufactured by Nikkan Kogyo Co., Ltd.) is used as the epoxy adhesive sheet, and the release film is laminated on the epoxy adhesive sheet so that the release layer a is in contact with the epoxy adhesive sheet. , 180 ° C., 30 kgf / cm ² and heat pressed for 5 minutes. After that, the release film spontaneously peeled off in some samples. For samples in which the release film did not spontaneously peel off even after 10 minutes had passed from the hot press, the sample was cut to a width of 30 mm, and a peeling test was performed at a test speed of 500 mm / min and a peeling angle of 30 °. 30 ° peel value) was determined.
Further, in order to compare the releasability under stricter conditions than normally required, the epoxy adhesive sheet CVL1 is replaced with CVL2 (“HXC2525” manufactured by DuPont), which is an epoxy adhesive sheet having stronger adhesive force. Similar measurements were made.
Based on these measurement results, the releasability of the release film was evaluated as follows.
⊚: When the release film spontaneously peels off in the test using CVL1 and the 30 ° peeling strength is 100 gf / cm or less in the test using CVL2 ◯: The release film naturally peels off in the test using CVL1. When the release film is peeled off and the 30 ° peeling strength is greater than 100 gf / cm in the test using CVL2 ×: When the release film is not naturally peeled off in the test using CVL1

The peeling test performed at a peeling angle of 30 ° is generally very difficult to peel because the peeling angle is lower than that of the test performed at a peeling angle of 180 °. That is, it can be said that the release film having a good release test at a release angle of 30 ° has excellent release properties as compared with the conventional release film.

(2) Evaluation of wrinkle resistance A release film, a copper-clad laminate (“NIKAFLEX F-30VC1” manufactured by Nikkan Industries) and a glass cloth (“116AW” manufactured by Yodogawa Hu-Tech) were set in this order on the RtoR tester, and 50 mm. Hot pressing was performed while transporting under the conditions of / sec, 350 mm / set, and 10 N. The hot press conditions were 180 ° C., 100 gf / cm, 80 sec, and the preheat time was 10 sec. After the completion of the hot press, the release film in contact with the polyimide surface was observed, and the number of wrinkles of 2 cm or more along the flow direction was visually confirmed. The case where the number of wrinkles of 2 cm or more was 10 or less was evaluated as “◯”, and the case where the number of wrinkles exceeded 10 was evaluated as “x”.

(3) Evaluation of followability A hole of φ = 1 mm in the copper foil surface of a copper-clad laminate (“NIKAFLEX F-30VC1” manufactured by Nikkan Industries, Ltd.: 12.5 cm × 12.5 cm, polyimide thickness 25 μm, copper foil thickness 35 μm) A coverlay film (12.5 cm × 12.5 cm, polyimide thickness 25 μm, epoxy adhesive layer thickness 35 μm) was laminated so that the epoxy adhesive layer was in contact with each other. Further, the release film was laminated so that the release layer a was in contact with the coverlay film. This laminate was heat pressed for 2 minutes at 180 ° C. and 30 kgf / cm ^2. Then, the release film was peeled off, and the epoxy adhesive flowing out on 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.
Based on the measurement results, the followability of the release film was evaluated as follows.
〇: When the average value of the seepage width of the epoxy adhesive is less than 55 μm ×: When the average value of the seepage width of the epoxy adhesive is 55 μm or more

According to the present invention, it is possible to provide a release film which has excellent releasability as compared with the conventional one and can be suitably used for manufacturing a flexible circuit board by the RtoR method.

Claims (8)

A release film having at least one release layer.
A release film characterized in that the bromine permeability Z measured by the following bromine-containing adhesive penetration test is 4 or less.
(Brominated adhesive penetration test)
After performing hot pressing under the conditions of a pressure of 30 kgf, 180 ° C., and 5 minutes in a state where the adhesive surface of the coverlay film having a bromine compound as an adhesive component and the release layer of the release film are in contact with each other. , The coverlay film is peeled off, and the bromine permeability Z is calculated by the following formula (1).

In the formula (1), A (i) and B (i) indicate the fragment intensity and the total fragment intensity of ^{Br −} in the i-th measurement of the time-of-flight secondary ion mass spectrometry, respectively, and i is 1 to 100. Represents an integer of. The release film according to claim 1, wherein the release layer has an arithmetic mean roughness Ra of the surface of 0.5 μm or more. The release film according to claim 1 or 2, wherein the release layer has an overall crystallinity of 25 to 50%. The release film according to claim 1, 2 or 3, wherein the release layer contains an aromatic polyester resin. The release film according to claim 4, wherein the aromatic polyester resin contains a polybutylene terephthalate resin. The release film according to claim 5, wherein the ratio of the polybutylene terephthalate resin to the resin constituting the release layer is 75% by weight or more. The release film according to claim 1, 2, 3, 4, 5 or 6, further comprising a cushion layer and having release layers on both sides of the cushion layer. The release film according to claim 1, 2, 3, 4, 5, 6 or 7, which is used for manufacturing a flexible circuit board by the RtoR method.