Method for removing coating layer

Abstract

Provided is a method for removing a coating layer, the method comprising: a step in which a stack (501) obtained by superposing layers of one sheet of a release film (50) including, for example, a substrate film and a coating layer is prepared or a stack obtained by superposing layers of a plurality of sheets of the release film (50) is prepared; a step in which the stack (501) is immersed in treatment water (W1); a step in which after the immersion in the treatment water (W1), the release film (50) is released from the stack (501); and a step in which the coating layer is removed from the released release film (50). The coating layer includes an interlayer and a releasant layer, the interlayer being interposed between the substrate film and the releasant layer.

Description

Coating layer removal method

[0001] The present invention relates to a method for removing a coating layer.

[0002] In recent years, from the perspectives of global resource conservation and environmental protection, there has been an increasing movement in various fields to build a recycling-oriented society through efforts such as reducing waste generation, reusing, and recycling. For example, Patent Document 1 discloses a method for removing a coating on a resin substrate, which includes a coating removal step of placing a resin substrate having a coating on its surface in a cleaning container and stirring the resin substrate together with an alkaline aqueous solution in an amount such that the liquid level is higher than the top of the resin substrate deposited in the cleaning container at 80 to 180°C and at a rotation speed of the tip of a stirring blade of 2 to 100 m / sec. Furthermore, Patent Document 2 discloses a method for recovering a release film, which is a release film having a release layer formed on at least one side of the base film via a soluble resin layer, and which includes immersing the used release film in a solvent capable of dissolving the soluble resin to dissolve the soluble resin in the solvent, thereby separating and removing the release layer on the film surface and recovering only the base film.

[0003] JP 2004-027072 A JP 2002-265665 A

[0004] The method described in Patent Document 1 is a technique for removing a coating from a resin substrate using an alkaline aqueous solution. The used alkaline aqueous solution contains components of the coating (e.g., a release agent), which reduces its cleaning ability when reused. Purifying the alkaline aqueous solution is also problematic because it requires a lot of effort. The release film described in Patent Document 2 has a release layer laminated on at least one side of a substrate film via a readily soluble resin layer (water-soluble resin or water-dispersible resin). The method described in Patent Document 2 utilizes the property of the readily soluble resin layer to be easily dissolved in a solvent, thereby peeling the release layer from the release film. However, if the layer formed on the substrate film is a water-insoluble resin layer, it is difficult to remove the release layer from the release film using the method described in Patent Document 2. Furthermore, the method described in Patent Document 2 has the risk of the readily soluble resin layer dissolved in the solvent re-adhering to the release film. Furthermore, the readily soluble resin layer may contaminate the solvent. Furthermore, in release films consisting of a base film and a coating layer, the adhesive strength required between the base film and the coating layer differs, and depending on the release film, it may be difficult to maintain the adhesive state between the base film and the coating layer, which is required for product quality.

[0005] An object of the present invention is to provide a method for removing a coating layer, which can easily remove the coating layer from a release film.

[0006] [1] A method for removing a coating layer, comprising the steps of: preparing a laminate in which a single release film having a base film and a coating layer is stacked, or a laminate in which multiple release films are stacked; immersing the laminate in treatment water; releasing the release film from the laminate after immersion in the treatment water; and removing the coating layer from the released release film, wherein the coating layer includes an intermediate layer and a release agent layer, and the intermediate layer is disposed between the base film and the release agent layer.

[0007] [2] The method for removing a coating layer according to [1], wherein the laminate is a roll of one long piece of the release film wound up, and the release film is wound up so that a first surface of the coating layer opposite to the base film and a second surface of the base film opposite to the coating layer face each other directly or indirectly, and the removing step is performed by roll-to-roll.

[0008] [3] The method for removing a coating layer according to [2], wherein the releasing step is a step of removing the stack from the treatment water and making the release film capable of being unwound from the stack, and the removing step is a step of passing the release film unwound from the stack through cleaning water while scraping off the coating layer from the base film.

[0009] [4] The method for removing a coating layer according to any one of [1] to [3], wherein the release film is a release film with a ceramic green sheet attached, and a ceramic green sheet is attached to the opposite side of the coating layer from the base film.

[0010] [5] The method for removing a coating layer according to any one of [1] to [4], wherein the immersion step is a step of placing the stack and the treated water in a pressure vessel, heating the treated water, and pressurizing the pressure in the pressure vessel to a pressure higher than 1 atmosphere.

[0011] According to one aspect of the present invention, a method for removing a coating layer can be provided that allows the coating layer to be easily removed from a release film.

[0012] Fig. 1 is a cross-sectional view of a release film used in the removal method according to the present embodiment. Fig. 2 is a view showing an example of a roll-shaped stack used in the removal method according to the present embodiment. Fig. 3 is a view showing an example of a folded stack used in the removal method according to the present embodiment. Fig. 4 is a view showing an example of a sheet-like stack used in the removal method according to the present embodiment. Fig. 5 is a view showing an example of a roll-shaped stack immersed in treatment water in the immersion step according to the present embodiment. Fig. 6 is a view for explaining the release step and the removal step according to the present embodiment. Fig. 7 is another view for explaining the release step and the removal step according to the present embodiment. Fig. 8 is another view for explaining the release step and the removal step according to the present embodiment.

[0013] [First embodiment] (Method for removing a coating layer) The method for removing a coating layer according to this embodiment (hereinafter also referred to as the removal method according to this embodiment) includes the steps of preparing a laminate comprising a single layer of a release film having a base film and a coating layer, or a laminate comprising multiple layers of the release film, immersing the laminate in treated water, releasing the release film from the laminate after immersion in the treated water, and removing the coating layer from the released release film. The coating layer includes an intermediate layer and a release agent layer, and the intermediate layer is disposed between the base film and the release agent layer. Hereinafter, the preparing step, immersing step, releasing step, and removing step may be referred to as the preparing step, immersing step, releasing step, and removing step, respectively.

[0014] In this embodiment, the term "treated water" refers to water used to immerse the laminate in the immersion step. The treated water is preferably ordinary water, i.e., industrial water, and may be purified water or distilled water. It may also be water recycled from wastewater used in various industrial production processes, or water recycled from wastewater used in the implementation of this embodiment. When wastewater is reused, it may be recycled wastewater, as appropriate. From the perspective of improving work efficiency, the treated water may contain, but is preferably free of, additives that impart functionality. Examples of additives include surfactants and water-soluble organic solvents. When the treated water contains an additive, the concentration of the active ingredient of the additive in the treated water is preferably 0.2% by mass or less, more preferably 0.1% by mass or less, relative to the total amount of the treated water. Furthermore, the treated water is preferably not water to which an additive has been intentionally added. Furthermore, the treated water is preferably not an alkaline aqueous solution prepared by intentionally adding a basic substance, and is preferably not an acidic aqueous solution prepared by intentionally adding an acidic substance. Since the wastewater may be able to be recycled simply, the treated water may contain basic substances and acidic substances as additives. In this case, it is preferable that the pH of the treated water is 5.8 or higher and 8.6 or lower, so as to comply with the uniform effluent standards (other items) based on the Water Pollution Control Act.

[0015] The inventors discovered that when a laminate including one or more release films is immersed in treatment water, even in the state (form) of the laminate (e.g., even when the release films are stacked with almost no gaps in the thickness direction), the treatment water penetrates into the interface between the base film and the intermediate layer from the edge of the release film in the planar direction, resulting in a weakened adhesion between the base film and the coating layer. The "edge of the release film in the planar direction" refers to, for example, the position of the roll side indicated by symbol E4 in the case of the roll-shaped laminate 501 in FIG. 3 , the position of the roll side indicated by symbol E1 in the case of the roll-shaped laminate 504 in FIG. 2A , the position of the side indicated by symbol E2 in the case of the folded laminate 502 in FIG. 2B , and the position of the side indicated by symbol E3 in the case of the sheet-like laminate 503 in FIG. 2C . According to the removal method of this embodiment, the adhesion between the base film and the coating layer is weakened in advance in the immersion step, and then the coating layer is removed from the release film in the removal step, thereby facilitating removal of the coating layer. Furthermore, according to the removal method of this embodiment, the release film is immersed in the treatment water while in a stacked state, which makes it possible to treat a large amount of release film compared to immersing multiple release film sheets in the treatment water with the release film surfaces exposed (open state). Furthermore, the amount of treatment water can be reduced. The state in which the release film surfaces are exposed (open state) refers to a state in which the multiple release film sheets are not in contact with each other.

[0016] (Release Film) FIG. 1 is a cross-sectional view of a release film used in the removal method of this embodiment. The release film 50 has a base film 51 and a coating layer 52. The coating layer 52 includes an intermediate layer 521 and a release agent layer 522, with the intermediate layer 521 being disposed between the base film 51 and the release agent layer 522. In FIG. 1, a indicates the surface of the intermediate layer 521 facing the base film, b indicates the surface of the intermediate layer 521 facing the release agent layer, d indicates the surface of the release agent layer, and c indicates the surface of the release agent layer 522 facing the intermediate layer. e indicates the surface of the base film. In the release film according to this embodiment, it is preferable that the base film and the intermediate layer are in direct contact. In the case of FIG. 1, the base film 51 and the intermediate layer 521 are in direct contact, and the intermediate layer 521 and the release agent layer 522 are in direct contact.

[0017] The release film 50 may be used in the production of a ceramic green sheet and may be the release film remaining after the ceramic green sheet has been peeled off. Residue from the ceramic green sheet may be attached to the release film. The ceramic green sheet is preferably used in the production of a multilayer ceramic capacitor (MLCC). The release film 50 is a release film with a ceramic green sheet attached, and a ceramic green sheet may be attached to the surface of the coating layer 52 opposite the substrate film 51 (reference symbol d in FIG. 1). FIG. 2A is a diagram of a roll in which a release film 50G with a ceramic green sheet is wound around a winding core 1G. FIG. 2A shows the state in which the release film 50G with a ceramic green sheet has been unwound from the roll. The roll shown in FIG. 2A is an example of a laminate in which a single release film is stacked, and is referred to as a roll laminate 504. The roll laminate 504 will be described in the preparation process section. In FIG. 2A, residue 920 from the ceramic green sheet is attached to the surface of the coating layer 52. After the ceramic green sheet is peeled off, recesses 910 are formed, and the coating layer 52 is exposed from the recesses 910.

[0018] In the release film used in the removal method of this embodiment, the intermediate layer is preferably hydrophilic and water-insoluble. When the intermediate layer is hydrophilic, the coating layer can be more easily removed from the release film. The reason for this is explained with reference to FIG. 1 . The intermediate layer 521 in the release film 50 adheres to the base film 51 mainly through hydrogen bonding and the anchoring effect ( FIG. 1 ). If the intermediate layer 521 is hydrophilic, when the release film is immersed in treatment water while still in a laminated state in the immersion step, treatment water is more likely to penetrate from the edge of the release film 50 in the plane direction to the interface between the base film 51 and the intermediate layer 521, weakening the hydrogen bonding and anchoring effect between the intermediate layer 521 and the base film 51. As a result, when the coating layer 52 is removed from the release film 50 in the removal step, the intermediate layer 521 is more likely to peel off from the base film 51 together with the release agent layer 522.

[0019] When the intermediate layer is water-insoluble, the components of the intermediate layer 521 are prevented from eluting into the treatment water during the immersion step. Therefore, the water-insoluble intermediate layer 521 can prevent contamination of the treatment water, making it easier to reuse the treatment water after use. Furthermore, in the removal step of this embodiment, it is preferable to remove the coating layer from the release film while passing the release film through cleaning water. When the intermediate layer is water-insoluble, even when cleaning water is used in the removal step, the components of the intermediate layer 521 are prevented from eluting into the cleaning water. Furthermore, passing the release film through cleaning water prevents the removed coating layer from reattaching to the substrate film. The cleaning water used in the removal step of this embodiment is preferably ordinary water, i.e., industrial water, and preferably water of the same quality as the treatment water used in the above-mentioned immersion step.

[0020] In this specification, whether an intermediate layer is "hydrophilic" or not is determined to be hydrophilic if the water contact angle of the surface of the intermediate layer facing the substrate film is 55 degrees or less. In the case of the release film 50 shown in FIG. 1 , if the water contact angle of the surface of the intermediate layer 521 facing the substrate film (symbol a in FIG. 1 ) is 55 degrees or less, the intermediate layer 521 is hydrophilic. From the viewpoint of promoting the separability of the substrate film, the contact angle is preferably 50 degrees or less, more preferably 45 degrees or less. The contact angle is a value obtained by measuring the water contact angle of the surface of the intermediate layer that was in contact with the substrate film (the peeled surface) after separating the substrate film from the release film, i.e., after contacting the intermediate layer with water and peeling the interface between the intermediate layer and the substrate film. Purified water is used as the water that comes into contact with the intermediate layer when measuring the water contact angle.

[0021] Specifically, the intermediate layer is separated from the substrate film by the following method, and the water contact angle of the surface of the intermediate layer facing the substrate film is measured. The obtained value is the water contact angle of the surface of the intermediate layer facing the substrate film. A 50 mm wide adhesive tape (manufactured by Nitto Denko Corporation, product name "Polyester Adhesive Tape No. 31B") is attached to the release agent layer surface of the release film, and then cut to a size of 50 mm x 50 mm to prepare a test piece. 2 L of purified water is placed in a 5 L pressure vessel, and the purified water is boiled to 100 °C using a heater. The test piece (cut to a size of 50 mm x 50 mm) is then immersed in boiling water (purified water) at 100 °C. The lid of the pressure vessel is then closed, and heating is resumed until the pressure inside the pressure vessel reaches 2 atmospheres. Boiling (fume) is confirmed to confirm that the pressure inside the pressure vessel has reached 2 atmospheres, and after 15 minutes have passed (held) in this state, the pressure vessel is returned to normal pressure. Thereafter, it is confirmed that the test piece has been separated into a laminate in which the release agent layer and the intermediate layer are integrally supported on the pressure-sensitive adhesive tape, and the base film in the pressure vessel, and the pressure-sensitive adhesive tape supporting the release agent layer and the intermediate layer is removed from the purified water and dried at room temperature for 24 hours. Thereafter, the water contact angle is measured for the surface of the intermediate layer supported on the pressure-sensitive adhesive tape (the surface of the intermediate layer that was in contact with the surface of the base film).

[0022] In this specification, whether an intermediate layer is "water-insoluble" or not is determined when the difference between the water contact angle of the release agent layer surface (symbol d in Figure 1 ) and the water contact angle of the intermediate layer on the substrate film side (symbol a in Figure 1 ), measured using the following method, is 30 degrees or more. The difference in contact angles is preferably 40 degrees or more, more preferably 50 degrees or more. A small difference indicates that the components constituting the intermediate layer have dissolved in water, resulting in the measurement of a release agent layer that is partially exposed. The water contact angle of the release agent layer surface is not particularly limited, but is usually 80 degrees or more, preferably 85 degrees or more, and more preferably 90 degrees or more. The upper limit of the water contact angle of the release agent layer surface is usually 150 degrees, preferably 140 degrees, and more preferably 130 degrees. The water contact angle of the release agent layer surface is measured using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name "DM-701") by the sessile drop method in accordance with JIS R3257: 1999. Distilled water is used as the droplet.

[0023] The water contact angle may be a value measured by the following method. The test piece (cut into a size of 50 mm x 50 mm) is prepared. Next, 300 mL of purified water is filled into a 500 mL glass beaker, and the entire test piece is immersed in purified water heated to 90°C and left for 3 hours. Thereafter, it is confirmed that the test piece has been separated into a laminate in which the release agent layer and the intermediate layer are integrally supported on the adhesive tape, and the substrate film. The adhesive tape carrying the release agent layer and the intermediate layer is removed from the heated purified water and dried at room temperature for 24 hours. The water contact angle is then measured for the surface of the intermediate layer supported on the adhesive tape (the surface of the intermediate layer that was in contact with the surface of the substrate film). The contact angle is measured by the sessile drop method in accordance with JIS R3257:1999 using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name "DM-701"). Distilled water is used for the droplet.

[0024] Each step of the removal method according to this embodiment will be described.

[0025] <Preparation Step> The preparation step is a step of preparing a laminate in which a base film and a release film having a coating layer are laminated together, or a laminate in which a plurality of such release films are laminated together.

[0026] (Roll-shaped laminate, folded laminate) In the preparation step, examples of the laminate in which a single release film is laminated include a roll-shaped product in which a single long release film is wound into a roll and laminated (hereinafter, this may be referred to as a roll-shaped laminate), and a laminate in which a single sheet-shaped release film is folded and laminated (hereinafter, this may be referred to as a folded laminate).

[0027] The roll-shaped laminate is, for example, a roll-shaped product in which a release film is wound around a winding core. The winding core of the roll-shaped laminate is preferably made of a heat-resistant and water-resistant material, from the viewpoint of being immersed in treatment water in the immersion step. The dimensions of the roll-shaped laminate are, for example, a width (dimension perpendicular to the winding direction) of 100 mm or more and 1000 mm or less, preferably 200 mm or more and 600 mm or less. The winding diameter of the roll-shaped laminate (diameter of the roll including the winding core) is, for example, 100 mm or more and 1500 mm or less, preferably 150 mm or more and 1000 mm or less. The release film constituting the roll-shaped laminate is preferably wound so that a first surface of the coating layer opposite the substrate film (in the case of FIG. 1, the release agent layer surface (symbol d)) and a second surface of the substrate film opposite the coating layer (in the case of FIG. 1, the substrate film surface (symbol e)) directly or indirectly face each other. "Directly facing" means that the first surface of the coating layer and the second surface of the base film face each other without any other material interposed therebetween, whereas "indirectly facing" means that the first surface of the coating layer and the second surface of the base film face each other with another material (e.g., a ceramic green sheet) interposed therebetween (see FIG. 2A ).

[0028] 2A is a diagram showing an example of a roll-shaped laminate 504. The roll-shaped laminate 504 shown in FIG. 2A has a ceramic green sheet-attached release film 50G wound around a winding core 1G. An insertion hole 2G is formed in the center of the winding core 1G.

[0029] The folded laminate is, for example, a laminate in which a single sheet-like release film is folded by any folding method. The folding method is not particularly limited, but examples include a method of folding the folded laminate in a zigzag manner so that the edges of the folded portions are aligned (overlapping at the top and bottom) when viewed in a plane (see FIG. 2B ), and a method of folding in a zigzag manner so that the edges of the folded portions do not overlap at the top and bottom. FIG. 2B is a diagram showing an example of a folded laminate. In the folded laminate 502 shown in FIG. 2B , a single sheet-like release film 50 is folded in a zigzag manner so that the edges of the folded portions are aligned when viewed in a plane.

[0030] For example, when a release film unwound from a normal roll is folded to form a folded laminate, the size of the folded laminate (width x length x thickness (height)) is preferably within the following range. By folding the release film, the folded laminate can be formed into a rectangular parallelepiped block, making it easier to load and transport than a roll-shaped laminate. The width of the folded laminate depends on the width of the roll before unwound, but is usually 100 mm or more and 1000 mm or less, and preferably 200 mm or more and 600 mm or less. The length of the folded laminate is preferably 100 mm or more and 1000 mm or less, and more preferably 200 mm or more and 600 mm or less. The thickness (height) of the folded laminate is preferably 100 mm or more and 1000 mm or less, and more preferably 200 mm or more and 600 mm or less.

[0031] (Layered Sheet) In the preparation process, a layered structure (hereinafter sometimes referred to as a layered sheet) in which multiple release films are stacked in the thickness direction can be exemplified by a layered structure in which multiple release films are stacked in the thickness direction. The shape of the release films is not particularly limited, but examples include rectangular and polygonal shapes. The shape of the release films may also be irregular. The multiple release films may be stacked in the same direction, or the release films may be stacked so that the base films and coating layers face each other between each release film. The release films may be stacked in any direction. "Stacked in the same direction" refers to stacking the release films so that the base films and coating layers face each other between each release film. Figure 2C is a diagram showing an example of a layered sheet. The layered sheet 503 shown in Figure 2C has multiple rectangular release films 50 stacked in the same direction.

[0032] When the release film constituting the sheet stack is rectangular, the dimensions of the release film are, for example, 100 mm or more and 1000 mm or less, preferably 200 mm or more and 600 mm or less, and the thickness (height) of the sheet stack is preferably 100 mm or more and 1000 mm or less, more preferably 200 mm or more and 600 mm or less.

[0033] Hereinafter, the term "layered body" will be used to collectively represent the rolled layered body, the folded layered body, and the sheet layered body.

[0034] <Immersion Step> The immersion step is a step of immersing the laminate in treated water. When the treated water is warm, the immersion step may be a step of immersing the laminate in treated water contained in a container, a step of pouring the treated water into a container containing the laminate, or a step of heating the water to a predetermined temperature after pouring the water and the laminate into a container. A known heater can be used to heat the water. In the immersion step, the container that contains the treated water and in which the laminate is immersed may be referred to as an immersion container. In the immersion step, when cold or warm treated water is used under normal pressure, the immersion container is, for example, a water tank. In the case where the treated water is used as superheated water, the immersion container is a pressure vessel. When the treated water is used as warm water, the temperature of the treated water is preferably 80°C or higher and 100°C or lower, more preferably 90°C or higher and 100°C or lower. In the immersion step, after the water temperature reaches a target temperature, the laminate is held in the treatment water at this temperature for a predetermined time. In this specification, the holding time of the laminate in the treatment water from the time the target temperature is reached is defined as the immersion time of the laminate. The immersion time of the laminate is, for example, 5 minutes or more and 120 minutes or less, preferably 10 minutes or more and 30 minutes or less.

[0035] When superheated water is used as the treated water, the immersion step is a step of placing the laminate and the treated water in a pressure vessel, heating the placed treated water, and pressurizing the pressure in the pressure vessel to a pressure higher than 1 atmosphere. Superheated treated water is obtained by heating water under pressure. In the immersion step, the pressure in the pressure vessel and the temperature of the heated treated water (superheated water) are each determined by Boyle's law and are preferably within the following ranges. The pressure in the pressure vessel is preferably 1.2 atmospheres or more, more preferably 1.4 atmospheres or more, from the viewpoint of facilitating infiltration of the superheated water into the interface between the base film and the intermediate layer. The pressure in the pressure vessel is preferably 9.9 atmospheres or less, more preferably 4.7 atmospheres or less, from the viewpoint of suppressing melting of the resin component contained in the release film. The pressure in the pressure vessel is adjusted using a pressure regulating valve or the like. The temperature of the superheated water is preferably 105°C or more, more preferably 110°C or more, from the viewpoint of facilitating infiltration of the superheated water into the interface between the base film and the intermediate layer. The temperature of the superheated water is preferably 180°C or less, more preferably 150°C or less, from the viewpoint of suppressing melting of the resin component contained in the release film. In the immersion step, the holding time of the laminate in the superheated water after the water temperature reaches the target temperature (immersion time of the laminate) is, for example, preferably 5 minutes or more, more preferably 10 minutes or more. Furthermore, the immersion time of the laminate in the superheated water is preferably 60 minutes or less, more preferably 40 minutes or less.

[0036] In the immersion step, the laminate may be immersed in the treatment water as is, or may be immersed in the treatment water while being contained in a holding container with a release film to facilitate maintaining the shape of the laminate. Alternatively, the laminate may be immersed in the treatment water while being fixed (held) using a jig. Examples of holding containers include containers with multiple holes (e.g., baskets, sieves, metal mesh, etc.). The method for holding the laminate using a jig is not particularly limited. For example, in the case of a roll-shaped laminate, the end of the roll is fastened with a jig (e.g., adhesive tape or a rubber band), in the case of a folded laminate, the end of the folding is fastened with a jig, and in the case of a sheet-like laminate, the laminate is fastened with a jig (e.g., a clip) so as to press the laminate from both sides in the stacking direction of the release film.

[0037] Figure 3 shows a state in which the roll-shaped laminate 501 is immersed directly in treated water (immersion step). In Figure 3, the treated water W1 is warm water and is contained in an immersion container 20. The roll-shaped laminate 501 is a roll-shaped product in which a release film 50 is wound around a winding core 5A. An insertion hole 5B is formed in the center of the winding core 5A. As shown in Figure 3, by immersing the roll-shaped laminate 501 directly in the warm treated water W1, the treated water W1 penetrates into the interface between the base film and the intermediate layer from the end in the surface direction of the release film (the position on the side of the roll indicated by symbol E4 in Figure 3), and therefore the coating layer can be easily removed from the release film in the subsequent removal step.

[0038] <Release Process> The release process is a process of releasing the release film from the laminate after immersing the laminate in treated water for a predetermined time. Releasing the release film from the laminate refers to, for example, exposing the coating layer of the release film or the surface of the ceramic green sheet so that it faces the removal means described below (wire brush 34 in the cases of Figures 4 to 6). When the laminate is a roll-shaped laminate, releasing the release film from the laminate is performed by unwinding the release film from the roll-shaped laminate. When the laminate is a folded laminate, releasing the release film from the laminate refers to unfolding the folded laminate to return it to a single sheet-like release film. When the laminate is a sheet-like laminate, releasing the release film from the laminate refers to unfolding the sheet-like laminate to return it to individual individual release films. When the stack is a sheet-like stack and the subsequent removal step involves removing the coating layer with cleaning water contained in a cleaning container, the release step may include cutting the release film of each stack to a predetermined size before placing it in the cleaning container so that it can be easily stirred in the cleaning container. A size that is easy to stir is preferably, for example, a side length of 5 mm or more and 150 mm or less, and more preferably 10 mm or more and 100 mm or less. It is preferable that the surface exposed when the stack is released is not dry. In other words, when the stack is released, it is preferably performed while the stack is maintained in a wet state. This makes it easier to remove the coating layer from the release film.

[0039] <Removing Step> The removing step is a step of removing the coating layer from the released release film. The removing step is preferably carried out while passing the released release film through cleaning water. This allows the removed coating layer to be washed off so that it does not re-adhere to the base film. When the laminate is a roll-like laminate (a roll-like object in which one long release film is wound), the removing step is preferably carried out roll-to-roll. When the laminate is a roll-like laminate, the releasing step is a step of removing the roll-like laminate from the treatment water and making the release film ready to be unwound from the roll-like laminate, and the removing step is preferably a step of passing the release film unwound from the roll-like laminate through cleaning water to scrape the coating layer off the base film. Examples of scraping means include blades and wire brushes. Known components can be used for the blades and wire brushes. The number and arrangement of the scraping means are not particularly limited. Another scraping means includes a high-pressure water jet. Hereinafter, the container used in the removal step may be referred to as a cleaning container. The cleaning container is, for example, a water tank. In the removal step, it is preferable to pass the release film unwound from the roll-shaped laminate through cleaning water contained in the cleaning container while winding it around a guide roller. The temperature of the cleaning water used in the removal step may be any temperature. Room-temperature cleaning water can reduce energy consumption. Furthermore, warm cleaning water can weaken the interfacial bond between the substrate film and the coating layer in the removal step, even if the immersion step does not sufficiently weaken the bond, thereby reliably removing the coating layer. When high-temperature cleaning water is used, the temperature of the cleaning water is, for example, preferably 40°C or higher, more preferably 60°C or higher. Furthermore, it is preferably less than 100°C, more preferably 98°C or lower. The removal step of this embodiment aims to prevent the removed coating layer from re-adhering to the substrate film, and therefore the objective can be achieved in a short passage time. The time required for passage through the washing water is usually from 0.01 seconds to 10 minutes, preferably from 0.1 seconds to 5 minutes.The immersion container used in the immersion step and the washing container used in the removal step may be the same or different.

[0040] When the laminate is a sheet-like laminate, the removing step is a step of removing the coating layer from the release film released from the laminate, for example, with cleaning water contained in a cleaning container. The removing step is preferably a step of stirring the release film together with the cleaning water. When the laminate is a sheet-like laminate, the removing step may be a step of barrel polishing the release film released from the laminate together with cleaning water and media (abrasives). By barrel polishing the release film, the coating layer can be efficiently removed from the release film. When cleaning water is used in the removing step, the removing step is preferably a step of submerging the substrate film separated from the release film in water and floating the removed coating layer on the water. After the removing step, the substrate film separated from the coating layer is taken out of the cleaning water and recovered.

[0041] (Specific Examples of the Releasing Step and the Removing Step) In the removing method according to the present embodiment, when a roll-shaped laminate is used as the laminate and warm treated water is used, for example, the immersion step is performed using an immersion container 20 shown in FIG. 3, and the release step and the removal step are performed using a roll-to-roll type removing device 100 shown in FIG. 4. The removing device 100 shown in FIG. 4 includes a payout means 10, a removing means 30, a winding means 40, and a plurality of guide rollers GR1, GR2, and GR3. The payout means 10 is a means for paying out the release film 50 from the roll-shaped laminate 501, and includes a support member 10A that rotatably supports the winding core 5A of the roll-shaped laminate 501. The removing means 30 includes a guide roller GR2 and a wire brush 34 (an example of a scraping means) that scrapes off the coating layer 52 from the base film 51. In the case of FIG. 4, the removing means 30 includes a cleaning container 32. The cleaning container 32 contains cleaning water W2. The wire brush 34 is disposed opposite the guide roller GR2 and is disposed so as to abut against the surface of the release film 50 facing the coating layer 52. The winding means 40 is a means for winding the base film 51 into a roll after the coating layer 52 has been removed, and includes a support member 40A that engages and supports a winding core 6A for the base film 51. The support member 40A is connected to a drive device (not shown), which rotates the winding core 6A together with the support member 40A, allowing the release film 50 and base film 51 to travel from the feeding means 10 to the winding means 40.

[0042] As described above, the immersion process is performed using the immersion container 20 shown in FIG. 3 . After the immersion process, the roll-shaped laminate 501 is removed from the treated water W1, and the core 5A of the roll-shaped laminate 501 is attached to the support member 10A of the unwinding means 10, allowing the release film 50 to be unwound from the roll-shaped laminate 501 (releasing process). The release film 50 unwound from the roll-shaped laminate 501 by the unwinding means 10 is wound around a guide roller GR1 and then passes through cleaning water W2 in a cleaning container 32. Thereafter, as the release film 50 is wound around a guide roller GR2 provided in the cleaning water W2, the coating layer 52 is scraped off from the substrate film 51 by a wire brush 34 provided opposite the guide roller GR2 (removing process, scraping process). After the removing process, the substrate film 51 separated from the coating layer is removed from the cleaning container 32 and separated from the coating layer removed in the cleaning water W2. Thereafter, the base film 51 is wound around a guide roller GR3, and is wound into a roll by the winding means 40 and collected.

[0043] [Specific Example 2] When a folded laminate is used instead of the roll-shaped laminate 501 in the immersion step described in Specific Example 1, the removal step is carried out using, for example, a removal device 100B shown in Figure 5. The removal device 100B shown in Figure 5 includes a folded laminate payout means 11A, a removal means 30A, a folding and collecting means 41A, and a plurality of guide rollers GR2, GR4, and GR5. The folded laminate payout means 11A is a means for paying out the release film 50 from an end of the folded laminate 502A shown in Figure 5 (the end or start of the folding of the release film 50). The folding and collecting means 41A is a means for automatically folding the base film 51 from which the coating layer has been removed along the folds of the original folded laminate 502A. The folded stack feeding means 11A and the folding and collecting means 41A can both be publicly known means.

[0044] The immersion step is performed using the immersion container 20 shown in FIG. 3 , as in Example 1. After the immersion step, the folded and stacked body 502A is removed from the immersion container 20 and loaded into the folded and stacked body payout means 11A. The release film 50 constituting the folded and stacked body 502A is paid out by the folded and stacked body payout means 11A shown in FIG. 5 , wound around a plurality of guide rollers GR4 and GR5, and then passed through the cleaning water W2, as in Example 1. Thereafter, as the film is wound around the guide roller GR2 provided in the cleaning water W2, the coating layer 52 is scraped off from the substrate film 51 by a wire brush 34 provided opposite the guide roller GR2 (removing step, scraping step). After the removing step, the substrate film 51 separated from the coating layer is removed from the cleaning container 32 and separated from the coating layer removed in the cleaning water W2. Thereafter, the base film 51 is wound around a plurality of guide rollers GR4 and GR5, and is folded and collected by the folding and collecting means 41 A. Note that the base film 51 may be wound into a roll by a known winding means and collected instead of the folding and collecting means 41 A.

[0045] [Modifications of the Embodiments] The present invention is not limited to the above-described embodiments, and can include modifications and improvements within the scope of achieving the object of the present invention.

[0046] [Variation 1] The removal step may be performed using a removal device 100A shown in Figure 6 instead of the removal device 100 shown in Figure 4. The removal device 100A shown in Figure 6 has the same configuration as the removal device 100 shown in Figure 4, except that it includes a circulation means 300. The circulation means 300 is a means for returning cleaning water W2 to the cleaning container 32 after filtering it with a filter 35. The circulation means 300 includes a drain outlet 32A provided in the cleaning container 32, a filter 35 that filters the cleaning water W2, a storage section 36 that stores the filtered cleaning water W2, an inlet 38 provided at the opening of the cleaning container 32, and a circulation path 37 that connects the bottom drain outlet 36A of the storage section 36 and the inlet 38.

[0047] 6 , the coating layer (residue of the coating layer) removed from the release film 50 is discharged together with cleaning water W2 from drain outlet 32A of cleaning container 32 and filtered by filter 35. Cleaning water W2 filtered by filter 35 is stored in storage section 36, then discharged from drain outlet 36A at the bottom of storage section 36, circulates through circulation path 37, and is supplied again into cleaning container 32 from inlet 38.

[0048] [Variation 2] In the immersion process described with reference to FIG. 3 , the water tank serving as the immersion vessel 20 may be replaced with a pressure vessel (not shown) for carrying out the immersion process. In this case, superheated treated water is used. The stack may be a rolled stack, a folded stack, or a sheet stack. The shape of the stack to be immersed in the superheated treated water in the pressure vessel is not particularly limited as long as it does not float in the treated water and does not become loose. The stack may be held by a jig or the like and immersed in the treated water so that it does not float in the water and does not become loose. The pressure vessel may, for example, include a pressure vessel body, a pressure lid that seals the pressure vessel body, and a pressurizing means for pressurizing the interior of the pressure vessel. The pressurizing means includes a heating means for heating water to obtain superheated treated water and a pressure control means for controlling the air pressure inside the pressure vessel to a pressure higher than 1 atmosphere. A known heater may be used as the heating means. Examples of the pressure control means include a pressure adjustment valve (e.g., a safety valve), a pressure adjustment valve (e.g., a relief valve), and a pressure adjustment valve used in a pressure cooker (e.g., a weight type and a spring type), etc. The pressure control means may have a pressure sensor that measures the pressure inside the pressure vessel.

[0049] In the case of Modification 2, the immersion process is carried out as follows: The stack and treated water are placed in a pressure vessel. The placed treated water is heated, and the pressure inside the pressure vessel is pressurized to a pressure higher than 1 atmosphere. After the pressure inside the pressure vessel reaches the target temperature, the water is maintained at this temperature for a predetermined time (immersion process). The pressure inside the pressure vessel is then returned to normal pressure, the pressure lid is opened, and the stack is removed from the treated water. The release process and removal process after the immersion process are carried out, for example, using the removal device 100 shown in Figure 4 in a manner similar to the "Specific example of the release process and removal process" described above.

[0050] [Other Modifications] In the removal devices described in Figures 4 to 6, the number of guide rollers is not particularly limited. In the removal devices described in Figures 4 and 6, a foreign matter removal means may be provided at any location between the downstream side of the cleaning container 32 (the location where the base film 51 is removed from the cleaning water W2 after the removal step) and the winding means 40. In the case of Figure 5, the foreign matter removal means may be provided at any location between the downstream side of the cleaning container 32 and the folding and collecting means 41A. The foreign matter removal means is a means for removing foreign matter adhering to the base film 51. Examples of foreign matter include a coating layer remaining on the base film 51 and water droplets adhering to the base film 51. The foreign matter removal means is not particularly limited, and examples thereof include an air knife and a dryer.

[0051] The configuration of the release film used in the above embodiment and modified examples will be described.

[0052] [Release Film] The release film used in the above embodiment has a base film and a coating layer. The coating layer includes an intermediate layer and a release agent layer. The intermediate layer is disposed between the base film and the release agent layer. The intermediate layer may be a single layer, or a multi-layer consisting of two or more intermediate layers of the same or different types. The release agent layer may be a single layer, or a multi-layer consisting of two or more release agent layers of the same or different types. From the viewpoint of facilitating removal of the coating layer from the release film and recovery of the remaining base film, the release film preferably has a configuration in which the base film and the intermediate layer are directly laminated. Here, "direct lamination" refers to, for example, a configuration in which the respective layers are in direct contact with each other without any other layer between the base film and the intermediate layer. Furthermore, in one embodiment of the release film, the base film, the intermediate layer, and the release agent layer may be directly laminated in this order. That is, the respective layers may be in direct contact with each other without any other layer between the base film, the intermediate layer, and the release agent layer.

[0053] <Base film> The base film is a resin film formed from a resin component to be recovered. Examples of resin films that can be used include polyester films such as polyethylene terephthalate film, polybutylene terephthalate, and polyethylene naphthalate; polyolefin films such as polyethylene film and polypropylene film; polyimide film; polyamide film; polycarbonate film; polyacetate film; ethylene-vinyl acetate copolymer (EVA) film; ethylene-(meth)acrylic acid copolymer film; ethylene-(meth)acrylic acid ester copolymer film; cycloolefin polymer film; polyurethane film; polyphenylene sulfide film; and cellophane. The density of the base film is preferably greater than the density of water at 40°C, and is 1.0 g / cm. ３or more is more preferable. This makes it easier for the base film to sink in the cleaning water, and therefore, for example, when a removal process is carried out while stirring the release film released from the sheet stack in the cleaning water, the base film can be easily recovered from the bottom side of the cleaning container. Among base films, polyester film is preferred because it has a density greater than that of water at 40°C and has excellent heat resistance and strength. As the polyester film, polyester films whose main component is polyethylene terephthalate, polybutylene terephthalate, or polyethylene naphthalate are preferred from the viewpoint of easy resin recovery and recycling. In this specification, the term "main component" or "principal component" means that the proportion of the main component to the total mass of the material is 50% by mass or more. The resin film may also contain known fillers, colorants, antistatic agents, antioxidants, organic lubricants, catalysts, etc. The resin film may be transparent or may be colored as desired. Furthermore, at least one surface of the substrate film may be subjected in advance to a surface treatment such as sputtering, corona discharge, flame, ultraviolet irradiation, electron beam irradiation, or etching such as oxidation, as required.

[0054] The thickness of the substrate film is not particularly limited, but from the viewpoint of strength, rigidity, etc., it is preferably 10 μm or more and 500 μm or less, more preferably 15 μm or more and 300 μm or less, and even more preferably 20 μm or more and 200 μm or less.

[0055] <Release Agent Layer> The release agent layer is preferably a layer formed from a release agent composition. The release agent composition used to form the release agent layer is not particularly limited as long as it has releasability, and for example, a release agent composition containing as a main component a silicone-based compound; a fluorine compound; a long-chain alkyl group-containing compound; or a thermoplastic resin material such as an olefin-based resin or a diene-based resin; or the like can be used. It is also preferable to use a release agent composition containing as a main component an energy ray-curable or thermosetting resin. These release agent compositions may be used alone or in combination of two or more.

[0056] In the release agent composition containing a silicone compound as a main component, examples of the silicone compound include silicone compounds having an organopolysiloxane as a basic skeleton. Examples of the silicone compound include heat-curable silicone compounds such as addition reaction type and condensation reaction type; and energy beam-curable silicone compounds such as ultraviolet-curable and electron beam-curable types.

[0057] In the release agent composition containing a fluorine compound as a main component, examples of the fluorine compound include fluorine silicone compounds, fluorine boron compounds, and poly(perfluoroalkylene ether) chain-containing compounds.

[0058] In the release agent composition containing a long-chain alkyl group-containing compound as a main component, examples of the long-chain alkyl group-containing compound include polyvinyl carbamate obtained by reacting a polyvinyl alcohol polymer with a long-chain alkyl isocyanate, alkyl urea derivatives obtained by reacting a polyethyleneimine with a long-chain alkyl isocyanate, and copolymers of long-chain alkyl (meth)acrylates. Furthermore, a long-chain alkyl-modified alkyd resin may be used, which is an alkyd resin obtained by the condensation reaction of a polyhydric alcohol and a polybasic acid and which is modified with a long-chain fatty acid as a modifier.

[0059] As a release agent composition mainly composed of an energy ray-curable resin, for example, one containing an energy ray-curable compound having a reactive functional group selected from a (meth)acryloyl group, an alkenyl group, and a maleimide group, and a polyorganosiloxane is preferred. In the release agent layer formed from this release agent composition, an energy ray-curable compound and a polyorganosiloxane having different molecular structures, polarities, and molecular weights are used, so that before curing, components derived from the polyorganosiloxane are segregated near the outer surface of the release agent layer, and then cured by energy rays, and the segregation is fixed. This improves the releasability of the release agent layer. The release agent composition mainly composed of an energy ray-curable resin may further contain a photopolymerization initiator.

[0060] Examples of release agent compositions containing a thermosetting resin as a primary component include release agent compositions containing a melamine resin as a primary component and release agent compositions containing an epoxy resin as a primary component. Release agent compositions containing a melamine resin as a primary component include compositions containing a melamine resin as a primary component, an acid catalyst for thermally curing the melamine resin, and a polyorganosiloxane that imparts release properties to the release agent layer. Furthermore, release agent compositions containing an epoxy resin as a primary component include compositions containing an epoxy resin as a primary component, an acid or basic thermosetting catalyst for thermally curing the epoxy resin, and a polyorganosiloxane that imparts release properties to the release agent layer. Before curing, components derived from the polyorganosiloxane segregate near the outer surface of the release agent layer, and then cure to solidify the segregation. This improves the release properties of the release agent layer.

[0061] The release agent layer may contain other additives in addition to the resin component, such as an antioxidant, a light stabilizer, a flame retardant, a conductive agent, an antistatic agent, and a plasticizer.

[0062] The thickness of the release agent layer can be appropriately selected and is not particularly limited, but is, for example, preferably 0.02 μm or more and 5 μm or less, more preferably 0.03 μm or more and 2 μm or less, and even more preferably 0.05 μm or more and 1.5 μm or less.

[0063] <Intermediate Layer> The intermediate layer is preferably a layer made of a silane-based compound that is hydrophilic and water-insoluble and exhibits polycondensability upon hydrolysis, from the viewpoint of easier removal of the coating layer from the surface of the intermediate layer facing the substrate film.

[0064] The silane-based compound preferably contains, as a main component, at least one selected from tetrafunctional silane-based compounds represented by the following general formula (a) and oligomers thereof: Si(OR) ｐ (X) ４－ｐ(a) [In general formula (a), R represents an alkyl group, and X represents a halogen atom. When multiple Rs are present, the multiple Rs may be the same or different. When multiple Xs are present, the multiple Xs may be the same or different. p represents an integer of 0 to 4.] The number of carbon atoms in the alkyl group is preferably 1 to 4. The silane-based compounds represented by general formula (a) may be used alone or in combination of two or more.

[0065] Furthermore, the silane compound represented by the general formula (a) preferably includes a silane compound in which p in the general formula (a) is 4. The silane compound in which p in the general formula (a) is 4 (i.e., a tetrafunctional silane compound) is preferably a tetraalkoxysilane. More preferred examples of the tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane. Among these, from the viewpoints of ease of availability and reactivity in the hydrolysis reaction, at least one of tetramethoxysilane and tetraethoxysilane, or a mixture of tetramethoxysilane and tetraethoxysilane, is preferred.

[0066] Commercially available products can also be used as the hydrolysis polycondensate of the silane compound, and suitable examples of such commercially available products include "Colcoat (registered trademark) N-103X," "Colcoat (registered trademark) PX," "Methyl silicate 51" which is an average tetramer oligomer of tetramethoxysilane, "Methyl silicate 53A" which is an average heptamer oligomer of tetramethoxysilane, "Ethyl silicate 40" which is an average pentamer oligomer of tetraethoxysilane, "Ethyl silicate 48" which is an average decamer oligomer of tetraethoxysilane, and "EMS-485" which is a mixture of an average decamer oligomer of tetramethoxysilane and an average decamer oligomer of tetraethoxysilane (all manufactured by Colcoat Co., Ltd.).

[0067] The release film used in each embodiment is preferably a release film after use for a specific application. The release film used for a specific application (in practical use) may have a configuration in which a water-insoluble resin component is blended into the intermediate layer together with the silane compound to improve adhesion between the substrate film and the coating layer (intermediate layer and release agent layer) during use, within a range that does not impair the effects of this embodiment. The intermediate layer may be configured by applying and curing a composition containing a water-insoluble resin component. Examples of water-insoluble resin components include energy ray-curable resins, epoxy resins, and melamine resins. It is preferable that the water-insoluble resin component maintains its water-insolubility even after curing.

[0068] The "water-insoluble resin component" is preferably an energy ray-curable resin, and examples thereof include polyfunctional (meth)acrylates such as dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate. When the intermediate layer contains a hydrophilic and water-insoluble resin (preferably the silane-based compound), the content of the hydrophilic and water-insoluble resin is preferably 30% by mass or more and 90% by mass or less, and more preferably 40% by mass or more and 80% by mass or less, relative to the total mass of the intermediate layer. The upper limit of the content of the hydrophilic and water-insoluble resin in the intermediate layer is 100% by mass. When the intermediate layer contains a hydrophilic, water-insoluble resin (preferably the silane-based compound) and a "water-insoluble resin component," the content of the hydrophilic, water-insoluble resin is preferably 30% by mass or more and 90% by mass or less, and more preferably 40% by mass or more and 80% by mass or less, relative to the total mass of the intermediate layer. The content of the "water-insoluble resin component" is preferably 10% by mass or more and 70% by mass or less, and more preferably 20% by mass or more and 60% by mass or less, relative to the total mass of the intermediate layer. The upper limit of the total content of the hydrophilic, water-insoluble resin and the "water-insoluble resin component" in the intermediate layer is 100% by mass.

[0069] Furthermore, when an energy ray-curable resin is blended in the intermediate layer, it is preferable that the intermediate layer further contains a photopolymerization initiator. Examples of the photopolymerization initiator include 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, and 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone. When the intermediate layer contains a photopolymerization initiator, the content of the photopolymerization initiator is preferably 20 parts by mass or less, and more preferably 10% by mass or less, based on 100 parts by mass of the "water-insoluble resin component."

[0070] The thickness of the intermediate layer is preferably 0.01 μm or more and 1 μm or less, more preferably 0.03 μm or more and 0.5 μm or less, and even more preferably 0.05 μm or more and 0.3 μm or less, from the viewpoint of facilitating water penetration when the intermediate layer comes into contact with water.

[0071] Because the release film used in each embodiment of the present invention has a hydrophilic, water-insoluble intermediate layer, the removed coating layer residue has a configuration in which it has both a release agent layer surface and a hydrophilic intermediate layer surface. When this configuration of residue is immersed in cleaning water, the release agent layer surface faces the air due to surface tension, and the intermediate layer surface faces the water, resulting in stability. In other words, this configuration of residue is more likely to exist at the water-air interface than in water. Here, because the coating layer residue is an extremely thin film, even if it has a slightly higher density, the buoyancy due to surface tension is greater, and it is thought that the water-insoluble intermediate layer allows it to continue floating on the water surface.

[0072] The release film used in each embodiment is generally used for the purpose of protecting the surfaces of other functional sheets or various parts used for specific purposes during the production, transportation, storage, etc. of these functional sheets or parts. In fact, after fulfilling its role of protecting these parts, it is often peeled off from the surface and discarded. Therefore, by using the release film, the coating layer and the base film can be easily separated from the release film, which is an application that greatly contributes from the viewpoints of resource conservation and environmental protection.

[0073] The present invention is not limited to the above-described embodiment, and may include modifications and improvements within the scope of achieving the object of the present invention.

[0074] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0075] [Example 1] (Preparation of Release Film) A biaxially stretched polyethylene terephthalate film (thickness: 31 μm) was prepared as a substrate film. Next, a hydrolysis polycondensation product of alkoxysilane (manufactured by Colcoat Co., Ltd., product name "Colcoat (registered trademark) N-103X") was prepared and mixed with isopropyl alcohol to obtain a composition for forming an intermediate layer with a solids concentration of 1.5 mass %. Next, the obtained composition for forming an intermediate layer was uniformly applied to one side of the substrate film using a bar coater so that the thickness of the intermediate layer after drying was 0.1 μm, thereby forming a coating layer. The coating layer was cured by thermal heating at 130°C for 1 minute, thereby forming an intermediate layer. Next, 94 parts by mass of dipentaerythritol hexaacrylate (solid content 100% by mass), which is a polyfunctional acrylate, 1 part by mass of acrylic-modified polydimethylsiloxane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "X-22-164A", solid content 100% by mass), and 5 parts by mass of a photopolymerization initiator (manufactured by IGM Resins B.V., product name "Omnirad (registered trademark) 907" (2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one, solid content 100% by mass) were diluted with a mixed solvent of isopropyl alcohol and methyl ethyl ketone to obtain a release agent composition with a solid content concentration of 20% by mass. The mixing ratio of the mixed solvent of isopropyl alcohol and methyl ethyl ketone was isopropyl alcohol:methyl ethyl ketone = 3:1 (mass ratio). Dipentaerythritol hexaacrylate corresponds to a water-insoluble resin component.

[0076] The obtained release agent composition was applied onto the intermediate layer formed on the substrate film using a bar coater and dried at 80°C for 1 minute to obtain a coating layer. Next, the coating layer was irradiated with ultraviolet light (integrated light amount: 250 mJ / cm ２) to form a release agent layer (thickness: 1 μm), thereby obtaining a release film (substrate film / intermediate layer / release agent layer) in which the substrate film, intermediate layer, and release agent layer were laminated in this order. The layer consisting of the intermediate layer and the release agent layer (intermediate layer / release agent layer) constitutes a coating layer. In the release film of Example 1 (substrate film / intermediate layer / release agent layer), the water contact angle of the surface of the intermediate layer facing the substrate film was 39 degrees. The water contact angle of the surface of the release agent layer was 93 degrees. From this, the difference between the water contact angle of the surface of the release agent layer and the water contact angle of the surface of the intermediate layer facing the substrate film was calculated to be 54 degrees.

[0077] Next, 20 sheets of the resulting release film were cut into 5 cm squares and prepared. The 20 release films were stacked in the same direction to obtain a laminated sheet (preparation process). Two 75 mm square (3 mm thick) float glass sheets were placed on both end surfaces (top and bottom) of the laminated sheet, and the laminated sheet was sandwiched between the two float glass sheets. Next, the edges of the top and bottom float glass sheets were fastened with two clips. This resulted in an evaluation sample in which the shape of the laminated sheet was maintained. Next, the evaluation sample was immersed in hot water (treated water) at 100°C for 15 minutes (immersion process). After immersion for 15 minutes, the evaluation sample was removed from the hot water. Next, the clips and float glass were removed from the evaluation sample, and the laminated sheet was returned to the 20 release films (release process). Thereafter, the 20 release films were placed in 100 mL of purified water (washing water) at room temperature (25° C.) and stirred for 10 seconds using tweezers (removal step).

[0078] [Example 2] A release film (substrate film / intermediate layer / release agent layer) of Example 2 was obtained in the same manner as in Example 1. Next, using the release film of Example 2, a preparation step was carried out in the same manner as in Example 1, and then an evaluation sample in which the shape of the sheet stack was maintained was obtained. Next, an immersion step was carried out in the following manner. After the immersion step, a release step and a removal step were carried out in this order in the same manner as in Example 1.

[0079] (Immersion process (pressure vessel)) A cylindrical stainless steel pressure vessel with a capacity of 5 L was used as the pressure vessel. A flange-mounted lid on the top of this pressure vessel was equipped with a pressure gauge and a relief valve as pressure control means. 2 L of water (treated water) was placed in this pressure vessel, and the water was boiled to 100°C using an induction heating (IH) heater. The evaluation sample was then immersed in the boiling water at 100°C (accommodation process), the lid was closed, the relief valve was set to 2 atmospheres, and heating was resumed. After confirming boiling (fume), the pressure inside the pressure vessel reached 2 atmospheres and the temperature of the superheated water was confirmed to be 120°C. After 15 minutes had passed (maintained) in this state, the pressure inside the pressure vessel was returned to normal pressure (immersion process).

[0080] Example 3 An intermediate layer-forming composition A was prepared by the following method. A release film of Example 3 (substrate film / intermediate layer / release agent layer) was obtained in the same manner as in Example 1, except that an intermediate layer was formed using the obtained intermediate layer-forming composition A. The water contact angle of the surface of the intermediate layer facing the substrate film in the release film of Example 3 (substrate film / intermediate layer / release agent layer) was 43 degrees. The water contact angle of the surface of the release agent layer was 93 degrees. From these results, the difference between the water contact angle of the surface of the release agent layer and the water contact angle of the surface of the intermediate layer facing the substrate film was calculated to be 50 degrees.

[0081] Next, using the release film of Example 3, a preparation process was carried out in the same manner as in Example 2, and an evaluation sample in which the shape of the sheet stack was maintained was obtained. After that, an immersion process, a release process, and a removal process were carried out in this order.

[0082] (Preparation of intermediate layer-forming composition A) An alkoxysilane hydrolysis polycondensate S1 (manufactured by Colcoat Co., Ltd., product name "Colcoat (registered trademark) N-103X") and a polyfunctional acrylate, dipentaerythritol hexaacrylate A1 (manufactured by Toagosei Co., Ltd., product name "Aronix M-400"), were mixed in a solids ratio (mass ratio) of 60:40 (S1:A1) to obtain a mixture. A photopolymerization initiator (manufactured by IGM Resins B.V., product name "Omnirad 907") and 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one (solids content 100% by mass) were added to the mixture. Finally, methyl ethyl ketone (MEK) and isopropyl alcohol were mixed in a volume ratio of 3:7 to obtain an intermediate layer-forming composition with a solids content of 1.0% by mass. The mixing ratio of the photopolymerization initiator, 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one to the mixture was as follows: Photopolymerization initiator: 10% by mass relative to Aronix M-400 (solid content 100% by mass) 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one: 10% by mass relative to Aronix M-400 (solid content 100% by mass)

[0083] (Formation of Intermediate Layer) Next, the composition for forming an intermediate layer was applied onto the substrate film using a bar coater, and the applied composition was passed through a drying oven at 130°C for 1 minute, and then irradiated with ultraviolet light (integrated light amount: 250 mJ / cm ２ ) to obtain a film with an intermediate layer (thickness: 0.04 μm).

[0084] Comparative Example 1 A release film (substrate film / release agent layer) of Comparative Example 1 was obtained in the same manner as in Example 1, except that no intermediate layer was formed. In the case of Comparative Example 1, the release agent layer constitutes the coating layer. The water contact angle of the release agent layer surface in the release film (substrate film / release agent layer) of Comparative Example 1 was 93 degrees. However, since the release film of Comparative Example 1 did not have an intermediate layer and the release agent layer was not separated from the substrate film, the water contact angle of the release agent layer surface on the substrate film side could not be measured using the measurement method described below.

[0085] Next, using the release film of Comparative Example 1, a preparation process was carried out in the same manner as in Example 1, and an evaluation sample in which the shape of the sheet stack was maintained was obtained. After that, an immersion process, a release process, and a removal process were carried out in this order.

[0086] [Comparative Example 2] A release film (substrate film / intermediate layer / release agent layer) of Comparative Example 2 was obtained in the same manner as in Example 3. Next, 20 sheets of the obtained release film were cut into 5 cm squares. Thereafter, the 20 release films were placed in 100 mL of purified water (cleaning water) at room temperature (25°C) and stirred with tweezers for 10 seconds to perform a removal step. In Comparative Example 2, the immersion step was not performed.

[0087] [Coating Layer Removability] The coating layer removability of the release films after the removal step in Examples 1 to 3 and Comparative Examples 1 and 2 was evaluated according to the following criteria. The results are shown in Table 1. (Evaluation Criteria) A: By immersing in a beaker and gently stirring, most of the coating layer was removed within 5 minutes. B: Under condition A, no coating layer removal occurred, but most of the coating layer was removed within 120 minutes. C: Under conditions A and B, no coating layer removal occurred, but by lightly scraping the surface of the release agent layer with steel wool before immersion in the beaker, and then immersing in a 500 mL beaker containing 300 mL of purified water at 30°C and gently stirring, most of the coating layer was removed within 120 minutes. D: No coating layer removal occurred under any of conditions A, B, or C.

[0088]

[0089] The results of Examples 1 to 3 demonstrated that a coating layer can be easily removed from a release film by sequentially performing an immersion step, a release step, and a removal step using a sheet-leaf stack of 20 release films (substrate film / intermediate layer / release agent layer). The results of Comparative Example 1 demonstrated that a coating layer cannot be removed from a release film even when a sheet-leaf stack of 20 release films (substrate film / release agent layer) without an intermediate layer is used and the immersion step, the release step, and the removal step are sequentially performed. The results of Comparative Example 2 demonstrated that a coating layer cannot be removed from a release film even when a sheet-leaf stack similar to that of Example 3 is used and only the removal step is performed. Among Examples 1 to 3, the release film of Example 3 contains a water-insoluble resin as the intermediate layer, thereby enhancing adhesion between the substrate film and the coating layer (intermediate layer and release agent layer). Even when a sheet-leaf stack of 20 release films is used, the coating layer can be easily removed from the release film by sequentially performing an immersion step, a release step, and a removal step.

[0090] [Evaluation of Intermediate Layer] (Hydrophilicity of Intermediate Layer) Using the release films (substrate film / intermediate layer / release agent layer) obtained in Examples 1 and 3, the water contact angle of the surface of the intermediate layer facing the substrate film was measured by the following method. The results are as described above. First, a 50 mm wide adhesive tape (manufactured by Nitto Denko Corporation, product name "Polyester Adhesive Tape No. 31B") was attached to the release agent layer surface of the release film. The release film with the adhesive tape attached was then cut to a size of 50 mm x 50 mm, and this was used as a test specimen. Next, 300 mL of purified water was filled into a 500 mL glass beaker, and the entire test specimen was immersed in purified water heated to 90°C and left for 3 hours. Thereafter, it was confirmed that the test specimen was separated into a laminate in which the release agent layer and intermediate layer were integrally supported on the adhesive tape, and the substrate film. The adhesive tape carrying the release agent layer and intermediate layer was then removed from the heated purified water and dried at room temperature for 24 hours. Thereafter, the contact angle of water on the surface of the intermediate layer carried on the adhesive tape (the surface of the intermediate layer that had been in contact with the surface of the base film) was measured using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name "DM-701") by the sessile drop method in accordance with JIS R3257:1999. Distilled water was used as the droplet.

[0091] (Water-insoluble nature of intermediate layer) Using the release films of Example 1, Example 3, and Comparative Example 1, the water contact angle of the surface of the release agent layer was measured by the method described above. The results are as described above. For Examples 1 and 3, the difference between the water contact angle of the measured release agent layer surface and the water contact angle of the surface of the intermediate layer facing the substrate film, measured by the method described above, was calculated.

[0092] The release film used in Example 2 has the same configuration as the release film in Example 1, and the release film used in Comparative Example 2 has the same configuration as the release film in Example 3. Therefore, the intermediate layers in Example 2 and Comparative Example 2 are also hydrophilic and water-insoluble.

[0093] 5A, 6A, 1G... Winding core, 5B, 2G... Insertion hole, 10... Feeding means, 10A... Support member, 11A... Feeding means for folded stack, 20... Immersion container, 30, 30A... Removal means, 32... Cleaning container, 32A... Drainage port, 34... Wire brush, 35... Filter, 36... Storage section, 36A... Bottom drainage port, 37... Circulation path, 38... Inlet, 40... Winding means, 40 A...support member, 41A...folding and collecting means, 50, 50G...release film, 51...substrate film, 52...coating layer, 100, 100A, 100B...removal device, 300...circulation means, 501, 504...roll-shaped stack, 502, 502A...folded stack, 503...sheet-leaf stack, 521...intermediate layer, 522...release agent layer, 910...recess, 920...residue.

Claims

1. A method for removing a coating layer, comprising the steps of: preparing a laminate comprising a single sheet of release film having a base film and a coating layer, or a laminate comprising a plurality of such release films; immersing the laminate in treatment water; releasing the release film from the laminate after immersion in the treatment water; and removing the coating layer from the released release film, wherein the coating layer includes an intermediate layer and a release agent layer, and the intermediate layer is disposed between the base film and the release agent layer.

2. The method for removing a coating layer according to claim 1, wherein the laminate is a roll of a single long piece of the release film, the release film is wound up so that a first side of the coating layer opposite the base film and a second side of the base film opposite the coating layer directly or indirectly face each other, and the removing step is performed by roll-to-roll.

3. A method for removing a coating layer as described in claim 2, wherein the releasing step is a step of removing the laminate from the treatment water and making the release film capable of being unwound from the laminate, and the removing step is a step of passing the release film unwound from the laminate through cleaning water while scraping off the coating layer from the base film.

4. A method for removing a coating layer described in any one of claims 1 to 3, wherein the release film is a release film with a ceramic green sheet, and a ceramic green sheet is attached to the side of the coating layer opposite the base film.

5. A method for removing a coating layer described in any one of claims 1 to 3, wherein the immersion step is a step of containing the stack and the treatment water in a pressure vessel, heating the treatment water, and pressurizing the pressure in the pressure vessel to a pressure higher than 1 atmosphere.

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