Method for removing a functional layer from a substrate film having a functional layer, and method for recovering the substrate film

Abstract

To provide a method for efficiently removing a functional layer from a base film having a functional layer in a short time.SOLUTION: There is provided a method for removing a functional layer provided on at least one surface of a base film, the method comprises a step of bringing the base film wound into a roll into contact with an alkaline treatment liquid in a long-body state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for removing a functional layer from a substrate film having the functional layer, and a method for recovering the substrate film. [Background technology]

[0002] Films in which functional layers having various functions are coated on the surface of a base film such as a synthetic resin are used in fields such as electronic components, optical components, labels, and release agents. Among the above-mentioned films, used films, films that do not meet specifications, and films that have been damaged during distribution are usually discarded (hereinafter, such films may be referred to as films to be discarded). However, for the sake of effective use of resources, it is preferable to recycle the base film by removing (peeling off) the functional layers.

[0003] An example of such a technique is Patent Document 1. In Patent Document 1, a foreign layer formed on a synthetic resin substrate is removed in an alkaline aqueous solution at 105°C or higher, and then the foreign layer is removed by treating with an aqueous solution containing 0.1% by mass to 10% by mass of peroxide. Specifically, a so-called batch method is adopted in which the substrate to be treated is first selected, and the entire synthetic resin substrate is pre-cut into chips of appropriate size and crushed, and then subjected to a predetermined alkaline treatment.

[0004] Patent Document 2 also discloses a method for producing a release film for ceramic sheet production by simultaneously biaxially stretching a raw sheet made of syndiotactic polystyrene, and a method for recycling the release film by removing green sheet residue from the used release film. In this method, the green sheet residue is removed by a so-called roll-to-roll method. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3270037 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-104986 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method of Patent Document 1 requires the substrate to be crushed into chips in advance, and there is a problem in that it takes a long time to remove the heterogeneous layer.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for efficiently removing a functional layer from a substrate film having the functional layer in a short period of time. Another object of the present invention is to provide a method for more efficiently removing functional layers from films to be discarded, such as used films, films that do not meet specifications, and films that have been damaged during distribution, thereby recovering high-quality base films with few impurities. [Means for solving the problem]

[0008] The present invention is configured as follows. 1. A method for removing a functional layer on at least one surface of a substrate film, comprising: A method for removing a functional layer, comprising a step of bringing the substrate film wound into a roll into contact with an alkaline processing liquid in a long state. 2. The removal method according to the above item 1, wherein the step comprises a step of contacting the alkaline treatment liquid with a 20 to 60 mass % alkaline treatment liquid heated to a temperature of 90 to 140°C for 1 to 120 seconds. 3. The removal method according to 1 or 2 above, further comprising a step of winding up the film from which the functional layer has been removed into a roll. 4. A method for recovering a base film by removing a functional layer on at least one surface of the base film, comprising: A method for recovering a substrate film, comprising a step of removing the functional layer by the removal method according to any one of 1 to 3 above. [Effects of the Invention]

[0009] According to the removal method of the present invention, a functional layer can be efficiently removed from a substrate film having a functional layer in a short period of time. Furthermore, according to the recovery method of the present invention, the functional layer can be efficiently removed from the above-mentioned base film that would otherwise be discarded, such as used film, and a high-quality base film with few impurities can be recovered. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a roll-to-roll apparatus used in one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the desired object can be achieved by bringing the above-mentioned base film wound into a roll into contact with an alkaline processing solution in a long state, thereby completing the present invention.

[0012] The method of the present invention will be described in detail below. In the following, in order to distinguish between a substrate film and a substrate film having a functional layer, the latter film may be specifically referred to as a "substrate film coated with a functional layer."

[0013] (1) Method for Removing a Functional Layer from a Substrate Film Having a Functional Layer As described above, the removal method of the present invention is a method for removing a functional layer on at least one surface of a substrate film, and is characterized by the step of bringing the substrate film wound into a roll into contact with an alkaline treatment liquid in a long state. The present invention differs from the method of Patent Document 1 in that the substrate film ground into chips is treated with an alkaline treatment liquid in that the substrate film wound into a roll is brought into contact with an alkaline treatment liquid in a long state.

[0014] (1-1) Base film Examples of resins constituting the substrate film used in the present invention include synthetic resins. Synthetic resins may be either thermoplastic or thermosetting resins. Examples of the synthetic resins include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polypropylene terephthalate (PPT); polyamide resins such as polycaproamide (6-nylon) and polyhexamethylene adipamide (6,6-nylon); polyimide resins; polyamide-imide resins; polyolefin resins such as polyethylene, polybutene, polypropylene, polymethylpentene, polystyrene, and cyclic olefins; acrylic resins; polycarbonate resins; polyvinyl chloride resins; polyvinylidene chloride resins; polyphenylene sulfide resins; polyphenylene oxide resins; phenolic resins; and cellulose-based resins. Polyester resins are preferred, and PET is more preferred.

[0015] Considering ease of handling, the thickness of the substrate film is preferably 5 μm or more and 500 μm or less. A more preferred lower limit is 7 μm. A more preferred upper limit is 400 μm, even more preferably 350 μm, and particularly preferably 300 μm.

[0016] (1-2) Functional layer At least one surface of the substrate film has a functional layer. Here, the functional layer is a layer that can impart various functions to the substrate film, and examples thereof include an easy-adhesion layer, a release layer, an antistatic layer, an adhesive layer, and a hard coat layer. These functional layers may be present on at least one surface of the substrate film, or may be present on both surfaces. The functional layer may be present alone, or two or more types may be laminated. The functional layer may have not only a single function but also multiple functions.

[0017] The resin constituting the easy-adhesion layer is not particularly limited as long as it is a resin generally used for easy-adhesion layers, and examples thereof include polyester resins, acrylic resins, polycarbonate resins, polyurethane resins, polyvinyl alcohol resins, polyamide resins, polyvinyl acetate resins, etc. These resins may be used alone or in combination of two or more.

[0018] The resin constituting the release layer is not particularly limited as long as it is a resin commonly used in release layers, and examples thereof include silicone resins such as polydimethylsiloxane, amino resins such as melamine resins and urea resins, acrylic resins, epoxy resins, and alkyd resins. These resins may be used alone or in combination of two or more. The release layer may also contain a release agent such as silicone oil or wax.

[0019] The resin constituting the antistatic layer is not particularly limited as long as it is a resin commonly used in antistatic layers. The antistatic layer preferably further contains an antistatic agent. Examples of the antistatic agent include nonionic, cationic, anionic, and amphoteric surfactants; conductive polymers such as polypyrrole, polyaniline, and poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate); SnO2 (Sb-doped), In2O3 (S Examples of the antistatic agent include metal oxide fillers such as ZnO (doped with ZnO) and ZnO (doped with Al); and carbon-based materials such as carbon black, graphene, and carbon nanotubes (CNT). These antistatic agents may be used alone or in combination of two or more.

[0020] The adhesive layer contains an adhesive commonly used for adhesive layers. The type of adhesive is not particularly limited, and examples thereof include acrylic adhesives, rubber adhesives, polyurethane adhesives, and silicone adhesives. The adhesive layer may further contain a tackifier (tackifier resin).

[0021] The resin constituting the hard coat layer is not particularly limited as long as it is a resin generally used for hard coat layers, and examples thereof include acrylic resins, urethane resins, epoxy resins, etc. These resins may be used alone or in combination of two or more.

[0022] The thickness of the functional layer (if there are multiple functional layers, the total thickness of these layers) is preferably 0.001 μm or more and 50 μm or less. To effectively exert the predetermined function, it is more preferably 0.005 μm or more, and even more preferably 0.01 μm or more. On the other hand, if it exceeds 50 μm, it may take a long time to remove the functional layer. It is more preferably 20 μm or less, even more preferably 10 μm or less, and particularly preferably 5 μm or less.

[0023] For the purpose of increasing the affinity with the alkaline processing solution described below, the surface of the functional layer may be subjected to a surface treatment layer. The surface modification treatment used to form the surface treatment layer may be performed by a known method. Examples of such treatments include corona treatment, plasma treatment, and flame treatment.

[0024] (1-3) Contact with alkaline processing solution The present invention is characterized in that the substrate film having the functional layer and wound into a roll is brought into contact with an alkaline processing solution in a long state. The present invention is characterized in that the substrate film is brought into contact with an alkaline processing solution, and from the viewpoint of achieving the object of the present invention, it is not intended to strictly control the conditions of the alkaline processing solution (e.g., temperature, concentration, contact time). As will be described later, by employing the method of the present invention, a high-quality substrate film with few impurities can be efficiently recovered without extending the overall processing time, even when the alkaline processing solution is outside the preferred range, as in Example 8, for example.

[0025] First, the alkaline treatment used in the present invention will be described in detail.

[0026] The alkaline processing liquid used in the present invention contains an alkali source such as sodium hydroxide or potassium hydroxide. The alkali sources may be used alone or in combination of two or more. These alkali sources have the effect of dissolving and swelling the functional layer, weakening the bond at the interface between the substrate film and the functional layer, and peeling (removing) the functional layer from the substrate film. The alkaline processing liquid is preferably an aqueous solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution, and more preferably an aqueous potassium hydroxide solution.

[0027] The alkaline processing solution may further contain an alkaline processing aid to improve the peeling efficiency of the functional layer. Examples of alkaline processing aids that are preferred include those capable of increasing the heating temperature of the alkaline processing solution, such as boiling point elevating agents. Examples include surfactants, water-soluble inorganic compounds, water-soluble organic compounds, and water-soluble solvents. Specific examples include nonionic surfactants, water-soluble polymers, inorganic salts, organic salts, alcohols, glycols (ethylene glycol, diethylene glycol, propylene glycol, etc.), water-soluble organic solvents (dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethylene glycol ethers (various cellosolves)), and polysaccharides. Among these, glycols are preferred. These may be used alone or in combination.

[0028] Here, "contacting with an alkaline processing solution" includes, for example, a step of contacting (e.g., immersing, applying, spraying, etc.) with an alkaline processing solution of a predetermined concentration and then heating. The above conditions can be appropriately selected depending on the type and thickness of the substrate film and functional layer. However, to obtain a high-quality substrate film with few impurities using a small, simple facility, which is a preferred embodiment, without extending the overall processing time, it is preferable to contact (immerse) the substrate film for 1 to 120 seconds in a 20 to 60 mass % alkaline processing solution heated to a temperature of 90 to 140°C. For example, when the alkaline processing solution contains both an alkali source and an alkaline processing aid, it is preferable to heat the alkaline processing solution containing these to a concentration of 20 to 60 mass % to 90 to 140°C and contact the functional layer-coated substrate film with the above processing solution for 1 to 120 seconds.

[0029] The above-mentioned preferred alkaline treatment conditions (particularly concentration and time) differ from those described in Patent Document 1. Patent Document 1 employs a batch process in which the substrate is crushed beforehand and then subjected to alkaline treatment, and therefore, for example, the concentration of the aqueous sodium hydroxide solution is controlled to a low concentration of 0.1 to 20 mass % to prevent hydrolysis and dissolution of the substrate film due to heating. Furthermore, in Patent Document 1, in order to effectively exert the peeling effect of the alkaline treatment, in the examples, washing is performed for a long period of time, for 30 to 60 minutes, with a 5 mass % aqueous sodium hydroxide solution. In contrast, in the present invention, the substrate is brought into direct contact with the alkaline treatment solution in a rolled state in order to achieve a short peeling process, and therefore the concentration of the alkaline treatment solution is The alkaline treatment solution has a concentration of 20 to 60 mass % and a contact time of 1 to 120 seconds, which allows for alkaline treatment at a higher concentration and for a shorter period of time than in Patent Document 1. In this way, both patents are further different from Patent Document 1 in terms of the preferred alkaline treatment conditions.

[0030] Under the above-mentioned preferred conditions, if the heating temperature of the alkaline processing solution is less than 90°C, it will take a long time to peel off the functional layer in order to obtain a high-quality substrate film with few impurities, and there is a risk that the functional layer will not be sufficiently removed using the small, simple equipment of the preferred embodiment. Furthermore, as described above, a high-concentration alkaline processing solution is preferably used in the present invention, and if the temperature of the alkaline processing solution is low, there is a risk that the alkaline component will precipitate and the processing solution itself will solidify. On the other hand, if the heating temperature exceeds 140°C, there is a risk that the substrate film will be altered by contact with the alkaline processing solution. A more preferred temperature is 100°C or higher and 135°C or lower.

[0031] If the concentration of the alkaline processing liquid (if the alkaline processing liquid contains an alkali source and an alkaline processing aid, the total concentration of these) is less than 20% by mass, it will take a long time to peel off the functional layer to obtain a high-quality substrate film with few impurities, and there is a risk that the functional layer cannot be sufficiently removed using the small, simple equipment that is a preferred embodiment. On the other hand, if the concentration of the alkaline processing liquid exceeds 60% by mass, there is a risk that the substrate film will be deteriorated by contact with the alkaline processing liquid. The concentration of the alkaline processing liquid is more preferably 25% by mass or more, even more preferably 30% by mass or more, and particularly preferably 35% by mass or more. It is also more preferably 55% by mass or less, even more preferably 50% by mass or less, particularly preferably 47% by mass or less, and most preferably 45% by mass or less.

[0032] If the contact time with the alkaline treatment solution is less than 1 second, the functional layer may not be sufficiently removed. On the other hand, if the contact time exceeds 120 seconds, the film may not be suitable for use in a small, convenient roll-to-roll system (details of which will be described later). Specifically, the transfer of the functional layer-coated substrate film in the alkaline treatment tank may become complicated, requiring a larger alkaline treatment tank, or multiple alkaline treatment tanks may be required, resulting in an increase in the overall equipment size. The contact time is more preferably 3 seconds or more, even more preferably 5 seconds or more. It is also more preferably 90 seconds or less, even more preferably 60 seconds or less, and particularly preferably 40 seconds or less.

[0033] The alkaline treatment is preferably carried out 1 to 5 times, more preferably 1 to 3 times. Here, one alkaline treatment refers to the period from immersing a substrate film having a functional layer in an alkaline treatment solution until it is removed. When alkaline treatment is carried out multiple times, the same alkaline treatment tank or separate alkaline treatment tanks may be used, but using separate alkaline treatment tanks is preferred in terms of facility flexibility and management of the alkaline treatment solution.

[0034] In the present invention, it is important that the functional layer-coated substrate film wound into a roll be brought into contact with the alkaline processing liquid in a long state in the above-mentioned contact step with the alkaline processing liquid.

[0035] Here, the length of "long" varies depending on the type of device used, but generally means 100 to 20,000 m.

[0036] The term "in a long length" includes both an embodiment in which a long functional layer-coated substrate film wound into a roll is unwound and brought into contact with an alkaline processing liquid as it is in a long length state, and an embodiment in which the film is brought into contact with an alkaline processing liquid after being adjusted (treated) to a state in which it can be contacted with an alkaline processing liquid. The former "in a long length state" refers to an embodiment in which the film is brought into contact with the alkaline processing liquid while maintaining the same width and length as the long film wound into a roll. The latter "adjusted state" refers to, for example, an embodiment in which the film is brought into contact with an alkaline processing liquid after being adjusted (treated) to a state in which it can be contacted with an alkaline processing liquid. and a mode in which the film is previously slit into a width that allows contact with the alkaline processing liquid or cut into a length that allows contact and then rewound into a roll; and a mode in which, when the slit long film is to be introduced separately into the alkaline processing liquid, if the film is too long, the film is cut into a length that allows contact before being brought into contact with the alkaline processing liquid.

[0037] Furthermore, "contacting the film in a long state with the alkaline processing liquid" means that the film in the above-mentioned state is directly contacted without being crushed or the like. According to the method of the present invention, unlike the batch method in which the substrate film is pre-pulverized as described in Patent Document 1, the functional layer-coated substrate film wound into a roll is directly contacted with the alkaline treatment solution in a long state, thereby enabling efficient peeling of the functional layer in a short time. Preferably, the roll-shaped functional layer-coated substrate film is contacted with the alkaline treatment solution, and after the contact, the roll-shaped substrate film from which the functional layer has been peeled is directly introduced into the next process (water washing, drying) and wound up in roll form, i.e., a roll-to-roll method is recommended. The roll-to-roll method is a winding-and-rewinding type transport method in which a roll-shaped film is continuously transported via multiple guide rolls, and the film that has undergone the specified treatment is wound up again into a roll. The roll-to-roll method allows a series of functional layer peeling processes to be carried out continuously in a short time, making it very efficient.

[0038] (1-4) Other After the alkaline treatment, it is preferable to wash with water and dry.

[0039] The water washing is carried out to remove trace amounts of the functional layer remaining on the substrate film after the above treatment and to remove the alkaline processing solution remaining on the substrate film after the above treatment. In this case, if the water washing is carried out with warm water at, for example, about 40 to 90°C, the above effects are more effectively exhibited.

[0040] The drying time is preferably 50 to 150 seconds. If the drying time is less than 50 seconds, the drying will be insufficient, which may cause blocking. It is more preferably 60 seconds or more. On the other hand, if the drying time exceeds 150 seconds, the substrate film may be deformed. It is more preferably 140 seconds or less.

[0041] Next, the functional layer removal method of the present invention will be described in more detail with reference to Fig. 1. Fig. 1 illustrates an example of an apparatus preferably used in a so-called roll-to-roll method, but the present invention is not limited to this as long as the effects of the present invention are effectively exhibited. For example, the number of rolls shown in Fig. 1 can be changed as appropriate.

[0042] First, a long functional layer-coated substrate film wound into a roll is prepared and introduced into an alkaline treatment tank containing an alkaline treatment liquid via multiple rolls. The details of the treatment method using the alkaline treatment liquid are as described above. The manner of introduction into the alkaline treatment tank is not particularly limited. To adjust the contact time with the alkaline treatment liquid, for example, the functional layer-coated substrate film may be passed between multiple guide rolls to form a W-shape and then contacted with the alkaline treatment liquid. Alternatively, multiple alkaline treatment tanks may be used to adjust the contact time with the alkaline treatment liquid. For example, by using multiple guide rolls to form a W-shape for the functional layer-coated substrate film introduced into the alkaline treatment tank, or by using multiple alkaline treatment tanks, the contact time with the alkaline treatment liquid can be extended without changing the conveying speed, thereby enabling treatment without extending the overall treatment time.

[0043] Next, the film treated in the alkaline treatment tank is introduced into a water washing tank, where any remaining functional layer and other components that were not removed by the alkaline treatment are washed away. While Fig. 1 shows immersion in a water washing tank, this is not limiting as long as the above-mentioned objective is achieved; for example, showering may also be used. Furthermore, multiple water washing tanks may be provided to enhance the effectiveness of water washing and removal.

[0044] Although FIG. 1 shows an embodiment in which the substrate is introduced into the water rinsing tank immediately after the alkaline treatment tank, the present invention is not limited to this. For example, an auxiliary tank equipped with a physical means such as a brush, ultrasonic waves, or water flow may be provided between the alkaline treatment tank and the water rinsing tank in order to remove any remaining functional layer that has not been removed.

[0045] After washing with water, the substrate film is introduced into a drying oven, and the functional layer is removed and wound up into a roll. Figure 1 shows a roll-to-roll system in which the rolled up film is treated in a specified tank and then wound up into a roll, but this is not limited to this. It is also possible to use a rolled film only for transport to the alkali treatment tank, and to cut the film after passing through the drying oven without winding it into a roll, for example.

[0046] (1-5) Usefulness of the removal method of the present invention The usefulness of the functional layer removal method according to the present invention can be expressed by the ability to remove the functional layer.

[0047] Specifically, the removability of the functional layer can be evaluated by calculating the elements (e.g., Si) contained in the functional layer, for example, by fluorescent X-ray analysis. The method for calculating the element removal rate will be described in detail in the Examples section. In the Examples, the removability of the functional layer was evaluated based on the removal rate of Si in the functional layer, but this is not limited thereto, and it is sufficient to calculate the removal rate of the elements mainly contained in the functional layer.

[0048] According to the present invention, the functional layer can be removed with a removal rate of preferably 90% or more, more preferably 95% or more, even more preferably 98% or more, and most preferably 100%. A removal rate of more than 100% is undesirable, since it means that not only the functional layer but also the base film layer will decompose. If the functional layer can be removed with a removal rate approaching 100%, as in the present invention, the performance of the recycled base film will be essentially the same as that of a virgin base film (base film before the functional layer is coated), resulting in a high-quality base film with few impurities. In particular, the method of the present invention is extremely useful in that it can remove silicone-based resins used as release layers, which are difficult to remove using the method of Patent Document 1, with a removal rate of 99% (see Example 2 below).

[0049] (2) A method of recovering a substrate film by removing a functional layer from the substrate film having the functional layer. The method for recovering a substrate film according to the present invention includes a step of removing the functional layer by the above-described removal method. According to the present invention, by applying the above-described removal method to a used or other functional layer-coated substrate film, the functional layer can be efficiently removed, thereby enabling the recovery of a high-quality substrate film with few impurities.

[0050] The usefulness of the substrate film recovery method according to the present invention can be evaluated by the thickness retention rate of the original roll (substrate film). Here, the thickness retention rate of the original roll is evaluated by observing the cross section of the substrate film before and after the removal method using SEM photographs and measuring the change in thickness. A higher thickness retention rate indicates a higher recovery rate of the original roll. According to the present invention, the thickness of the original roll can be retained at a retention rate of preferably 90%, more preferably 95% or more, and particularly preferably 100%.

[0051] The impurity content of the substrate film recovered by the method of the present invention is very low, for example, 5% or less, and therefore the method of the present invention is extremely useful in that it allows high-quality substrate film to be recycled efficiently. [Example]

[0052] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and modifications can be made within the scope of the above and below-described aims. All of these are included in the technical scope of the present invention. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass."

[0053] Using various functional layer-coated substrate films shown in Table 1 and the roll-to-roll type device shown in Figure 1, the functional layer was peeled off by changing the alkaline treatment conditions as shown in Table 1, and the removal rate of the functional layer and the thickness retention rate of the original sheet (substrate film) were measured.

[0054] In the roll-to-roll type apparatus shown in FIG. 1, the alkaline treatment tank has two guide rolls (shown) at the bottom and one guide roll (not shown) at the top. In Examples 1 to 5, Example 7, and Reference Examples 1 to 3, the film was passed over the two lower guide rolls as shown in Fig. 1. In Example 6, the film was passed over only the upper guide roll without using the two lower guide rolls. In Example 8, the film was passed over the two lower guide rolls and the upper guide roll in a W-shape and passed over the upper guide roll. The processing time was adjusted by the film transport speed.

[0055] In Example 2 of Table 1, the surface of the functional layer (release layer) was subjected to corona treatment (discharge amount 50 W m 2 / min) to modify the surface of the release layer.

[0056] The functional layer-coated substrate films shown in Table 1 were prepared as follows.

[0057] (1) Preparation of Adhesion Layer-Coated Substrate Films of Examples 1, 3, 4, 5, 6, and 8, and Reference Examples 1 to 3 Here, Vylonal MD-16 manufactured by Toyobo Co., Ltd., which is a water-dispersible high molecular weight copolymer polyester resin, was used as the resin constituting the easy-adhesion layer. Specifically, 5.5 g of the above Vylonal MD-16, 8 g of blocked isocyanate-containing polyurethane resin, 0.2 g of dibutyltin laurate catalyst, 0.3 g of a 20% dispersion of colloidal silica with a particle size of 50 nm, and 1 g of a fluorine-based surfactant leveling agent were mixed with 85 g of an aqueous solution of water:isophthalic acid (IPA) = 6:4 (mass ratio) to obtain a coating solution for an easy-adhesion layer. Next, a wet coating amount of 6 g / m was applied to one side of a 75 μm-thick polyethylene terephthalate film. 2 The coating solution was applied to the surface, and the surface was heated in an oven at 170°C. The film was dried in a vacuum oven to obtain a polyester film having an easily adhesive layer.

[0058] (2) Preparation of release layer-coated substrate film of Example 2 Here, KS-847T manufactured by Shin-Etsu Chemical Co., Ltd., which is a thermosetting dimethyl silicone resin, was used as the resin constituting the release layer. Specifically, 5 g of the above KS-847T was dissolved in 94 g of a mixed solution of methyl ethyl ketone and toluene at a ratio of 6:4 (mass ratio), and 1 g of a platinum catalyst was added to obtain a coating solution for a release layer. Next, a wet coating amount of 6 g / m was applied to one side of a 30 μm-thick polyethylene terephthalate film. 2 The coating solution was applied to the surface, and then dried in an oven at 160°C. A polyester film having a release layer was obtained.

[0059] (3) Preparation of the adhesive layer-coated substrate film of Example 7 Here, an acrylic graft polyester resin having the following composition was used as the resin constituting the easy-adhesion layer. Aqueous dispersion of a reaction product of 75 parts of a polyester resin (terephthalic acid / isophthalic acid / fumaric acid / ethylene glycol / neopentyl glycol = 48 / 48 / 4 / 50 / 50 (mol%)), 17.5 parts of methacrylic acid, and 7.5 parts of ethyl acrylate, neutralized with triethylamine. Specifically, the above aqueous dispersion was prepared according to the description in Example 1 of JP-A-2008-87349. A 5% by mass aqueous dispersion of this was used as a coating solution for the easy-adhesion layer. Next, a 6-nylon film having a thickness of 75 μm was wet-coated with a coating amount of 6 g / m 2 The above coat The liquid was coated onto the nylon film and dried in an oven at 120°C to obtain a nylon film having an easy-adhesion layer.

[0060] The removal rate of the functional layer was calculated by measuring the amount of Si element contained in the functional layer using a wavelength dispersive X-ray fluorescence analyzer (Supermini200 manufactured by Rigaku Corporation) and using the following formula: The formula was calculated taking into account the amount of Si originally contained in the substrate film (defined as "C" in the formula), where (AC) represents the amount of Si contained in the functional layer-containing substrate film before alkaline treatment, and (BC) represents the amount of Si derived from the functional layer remaining in the substrate film after alkaline treatment. Functional layer removal rate (%) ={(AC)-(BC) / (AC)}×100 A: Si intensity in the functional layer coated substrate film before the alkaline treatment method B: Si intensity in the functional layer-coated substrate film after alkaline treatment C: Si intensity in the substrate film before coating with the functional layer

[0061] These results are also shown in Table 1.

[0062] [Table 1A]

[0063] [Table 1B]

[0064] From Table 1, the following can be considered: First, Examples 1 to 7 are examples in which the functional layer was peeled off by employing the method of the present invention, in which a substrate film wound into a roll is brought into contact with an alkaline processing solution in a long state. In all cases, the functional layer was efficiently removed with a very high removal rate of 92% or more after a short contact time with the alkaline processing solution of only 5 to 90 seconds. In addition, the thickness retention rate of the raw roll (substrate film) was also very high, so that the peeling method of the present invention allows for the recovery of high-quality substrate films with few impurities.

[0065] In Example 8, the alkaline treatment concentration and temperature were the same as in Reference Example 3, but the film was passed over three guide rolls in a W-shape in the alkaline treatment tank, allowing for a longer contact time with the alkaline treatment solution. In Example 8, by creating a W-shape for the film path through the alkaline treatment tank, the total treatment time required from unwinding one roll to peeling off the functional layer and winding it up was essentially the same as in Reference Example 3. In Example 8, by extending the contact time with the alkaline treatment solution to 240 seconds, a high functional layer removal rate of 95% was achieved. Note that by ensuring a sufficient contact distance between the alkaline treatment solution and the film, such as by providing multiple rolls in the alkaline treatment tank to create a path in which the film folds multiple times or by providing multiple alkaline treatment tanks, the film transport speed can be increased and the overall treatment time can be shortened.

[0066] In contrast, Reference Examples 1 to 3 all show the alkaline processing solution conditions preferred in the present invention. More specifically, the removal rate of the functional layer decreased in Reference Example 1, in which the concentration of the alkaline processing liquid was low, Reference Example 2, in which the temperature of the alkaline processing liquid was low, and Reference Example 3, in which the concentration of the alkaline processing liquid was low and the temperature of the alkaline processing liquid was also low.

[0067] In the cases of Reference Examples 1 to 3, the alkaline treatment time must be further extended to increase the removal rate of the functional layer. Although this may require a larger and more complex device, as described above, it is possible to increase the removal rate by increasing only the alkaline treatment time without substantially increasing the overall treatment time, for example, by increasing the number of guide rolls in the alkaline treatment tank of the device shown in Figure 1 to suspend the film therebetween or by adding an additional alkaline treatment layer.

[0068] Therefore, the method of the present invention is extremely useful in that it enables the recovery of a high-quality substrate film with few impurities without extending the overall treatment time depending on the conditions of the alkaline treatment solution, and is also extremely useful in that it enables the recovery of a high-quality substrate film with few impurities even using a small, simple device by setting the conditions of the alkaline treatment within a specific range.

Claims

1. A method for removing a functional layer on at least one surface of a substrate film, comprising: the functional layer is at least one layer selected from the group consisting of an easy-adhesion layer, a release layer, an antistatic layer, and a hard coat layer; A method for removing a functional layer, comprising the step of contacting the substrate film wound into a roll in a long state with a 20 to 60 mass % alkaline treatment liquid heated to a temperature of 95 to 140°C for 60 seconds or less, thereby removing 90% or more of the functional layer.

2. A method for removing a functional layer on at least one surface of a substrate film, comprising: the functional layer is at least one layer selected from the group consisting of an easy-adhesion layer, a release layer, an antistatic layer, and a hard coat layer; A method for removing a functional layer, comprising a step of contacting the substrate film wound into a roll in a long state with a 20 to 60 mass % alkaline processing liquid that contains a boiling point elevating agent and is heated to a temperature of 95 to 140°C.

3. 3. The method for removing a functional layer according to claim 2, wherein the boiling point elevating agent is at least one selected from the group consisting of ethylene glycol, diethylene glycol, and propylene glycol.

4. The removal method according to any one of claims 1 to 3, further comprising a step of winding up the film from which the functional layer has been removed into a roll.

5. 5. The removal method according to claim 1, wherein the functional layer is made of at least one resin selected from the group consisting of polyester resin, silicone resin, and acrylic resin.

6. A method for recovering a substrate film by removing a functional layer on at least one surface of the substrate film, comprising: A method for recovering a substrate film, comprising a step of removing the functional layer by the removal method according to any one of claims 1 to 5.

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