Laminated film and functional layer removal method

Abstract

To provide a laminate film which enables an easily soluble resin layer provided at least one surface of a base material film to be easily dissolved in both water and alkali aqueous solution, and is excellent in adhesion between the easily soluble resin layer and a functional layer when the functional layer is laminated on the easily soluble resin layer.SOLUTION: A laminate film has an easily soluble resin layer on at least one surface of a base material film, in which the easily soluble resin layer contains a polyester component, the polyester component contains (A) a terephthalic acid, (B) a dicarboxylic acid having a sulfonate group and (C) other dicarboxylic acids as acid components, and a content ratio (mol%) of the component (C) in the total acid components in the easily soluble resin layer is 3.0-8.0 times a content ratio (mol%) of the component (B).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a laminated film and a method for removing a functional layer.

Background Art

[0002] Conventionally, waste plastics have been treated by landfill, ocean dumping, incineration, etc. However, it is becoming difficult to secure landfill sites, and ocean dumping causes environmental problems because plastics do not decompose. Also, although it can be used as heat by incineration, there is a problem that it leads to global warming due to the emission of carbon dioxide gas.

[0003] Therefore, due to the increasing environmental problems in recent years, recycling such as reuse and regeneration of waste plastics is required, and research and development for this purpose are being actively carried out. Moreover, many plastics are produced from fossil fuels, and from the viewpoint of effective use of resources, the construction of recycling methods is required.

[0004] By the way, a polyester film, which is a kind of plastic film, is useful as a base film, and is often used as a laminated film in which various functional layers are laminated on one or both sides thereof. As the functional layer, there are various functional layers such as a hard coat layer, an adhesive layer, a decorative layer, a light shielding layer, a polarizing layer, an ultraviolet shielding layer, etc., and a laminated film in which a material corresponding to the functional layer is laminated on a polyester film is used.

[0005] Such laminated films are hardly reused after use, and are discarded, incinerated, etc.

[0006] Even if a laminated film with a functional layer is recycled by remelting it as it is, since the material constituting the functional layer is mixed into the molten polymer, problems such as the generation of an abnormal odor during extrusion and the cause of breakage during film formation due to a decrease in the melt viscosity of the polymer occur. Furthermore, even if a film can be produced, deterioration in quality due to discoloration or contamination of the resulting film is unavoidable.

[0007] Furthermore, even if the functional layer is physically removed by scraping or other means and then melt-extruded, problems can arise, such as the filter becoming clogged with the remaining functional layer during the filtration process of extrusion, preventing proper film formation.

[0008] As a method for recycling laminated films, for example, there are technologies disclosed in Patent Documents 1 and 2. These technologies involve a laminated film in which an easily soluble resin layer and a surface functional layer are laminated in that order on at least one side of a base film. With this configuration, the plan is to separate and recover the base film from the laminated film by washing it with a solvent that can dissolve only the easily soluble resin layer after use, without dissolving the base film. The separated and recovered material can be remelted, making it possible to regenerate the resin composition that made up the base film. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2004-169005 [Patent Document 2] Japanese Patent Publication No. 2002-265665 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, since the resin constituting the easily soluble resin layer described in Patent Document 1 (hereinafter also simply referred to as the easily soluble resin) is a polyvinyl alcohol resin, the adhesion between the easily soluble resin layer and the surface functional layer may be poor.

[0011] Furthermore, the polyester easily soluble resin layer described in Patent Document 2 has the problem that it dissolves in hot water but does not dissolve in alkaline aqueous solutions, and for functional layers that have particularly high adhesion to the easily soluble resin layer, it is difficult to completely remove the functional layer.

[0012] Therefore, the present invention has been made in view of the above circumstances, and its problem to be solved is to provide a laminated film in which an easily soluble resin layer provided on at least one surface of a base film is easily soluble in both water and an alkaline aqueous solution, and when a functional layer is laminated on the easily soluble resin layer, the adhesion between the easily soluble resin layer and the functional layer is excellent. [Means for solving the problem]

[0013] As a result of diligent research, the inventors have found that a readily soluble resin layer containing a polyester component is provided, wherein the polyester component includes (A) terephthalic acid, (B) a dicarboxylic acid having a sulfonic acid base, and (C) other dicarboxylic acids as acid components, and by adjusting the content ratio (mol%) of component (C) in the total acid components in the readily soluble resin layer to be 3.0 to 8.0 times that of component (B), solubility in water and alkaline aqueous solutions is improved, and adhesion is also excellent when a functional layer is provided. The present invention was completed based on the above findings and has the following aspects.

[0014] [1] A laminated film having a readily soluble resin layer on at least one surface of a base film, wherein the readily soluble resin layer contains a polyester component, the polyester component comprising (A) terephthalic acid, (B) a dicarboxylic acid having a sulfonic acid base, and (C) other dicarboxylic acids as acid components, and the content ratio (mol%) of component (C) in the total acid components in the readily soluble resin layer is 3.0 to 8.0 times the content ratio (mol%) of component (B). [2] The laminated film according to [1], wherein the content of component (B) in the total acid components is 8 mol% or less. [3] The laminated film according to [1] or [2] above, wherein the component (B) is sodium 5-sulfophthalate. [4] The laminated film according to any one of [1] to [3] above, wherein the component (C) contains at least isophthalic acid. [5] The laminated film according to any one of [1] to [4] above, which has a functional layer on the easily soluble resin layer. [6] The laminated film according to [5] above, wherein the functional layer is a silicone release layer. [7] A method for removing a functional layer, which comprises washing the laminated film according to [5] or [6] with a cleaning agent to dissolve the easily soluble resin layer, and removing the functional layer together with the easily soluble resin layer from the base film. [8] The method for removing a functional layer according to [7] above, wherein the cleaning agent is water or an aqueous alkali solution. [Advantages of the Invention]

[0015] The laminated film of the present invention is characterized in that an easily soluble resin layer provided on at least one surface of a base film is easily soluble in both water and an aqueous alkali solution, and when a functional layer is laminated on the easily soluble resin layer, the adhesion between the easily soluble resin layer and the functional layer is excellent. Therefore, for example, before removing the functional layer, it is possible to maintain the same adhesion as that of a normal laminated film with an easy adhesion layer, and yet easily remove the functional layer. Therefore, the laminated film of the present invention can be used in the same manner as a normal polyester film and has excellent recyclability. [Embodiments for Carrying Out the Invention]

[0016] [Laminated Film] The laminated film in the present invention (hereinafter also referred to as "this film") has an easily soluble resin layer on at least one surface of a base film. Further, in the laminated film of the present invention, it is preferable to laminate a functional layer formed from various resin materials on the easily soluble resin layer.

[0017] <Base film> The base film constituting this film may have a single-layer structure or a multilayer structure. In the case of a multilayer structure, it may have a two-layer structure, a three-layer structure, etc., or may be a multilayer of four layers or more, and the number of layers is not particularly limited. Also, the base film may be a stretched film such as a biaxially stretched film or an unstretched film. Among them, it is preferably a stretched film stretched in one axial direction or two axial directions, and more preferably a biaxially stretched film from the viewpoints of balance of mechanical properties, flatness, and thinning.

[0018] Examples of the base film include resin films such as polyester films, polycarbonate films, polyimide films, triacetyl cellulose films, polyolefin films, polyacrylate films, polystyrene films, polyvinyl chloride films, polyvinyl alcohol films, and nylon films. Among them, polyester films are particularly preferred. The polyester constituting the polyester film is not particularly limited, and those commercially available can be appropriately used. Specifically, polyesters obtained by polycondensing dicarboxylic acids and diols can be mentioned. As the above dicarboxylic acid, aromatic dicarboxylic acids are preferred, and as the above diol, aliphatic glycols are preferred. The polyester film preferably has polyester as the main component. Also, when the base film has a multilayer structure, it is preferable that the main component resin of each layer is polyester. Note that the "main component resin" means the resin having the highest content ratio among the resins constituting each layer. For example, it is a resin occupying 50% by mass or more, particularly 70% by mass or more, and especially 80% by mass or more (including 100% by mass) among the resins constituting each layer.

[0019] Examples of the above aromatic dicarboxylic acids include terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, phthalic acid, etc. Examples of the above-mentioned aliphatic glycols include ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, 1,4-cyclohexanedimethanol, and neopentyl glycol.

[0020] Polyester may be either homopolyester or copolymer polyester. Specific examples of polyester include polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, and polybutylene-2,6-naphthalate, with polyethylene terephthalate being preferred among these. Furthermore, polyester may also contain a third component as a copolymer component, other than the main component compounds of the dicarboxylic acid, preferably aromatic dicarboxylic acid, and the main component compounds of the diol, preferably aliphatic glycol. For example, in polyethylene terephthalate, the third component is a component other than terephthalic acid and ethylene glycol. For example, polyethylene terephthalate may have dicarboxylic acid units other than terephthalic acid in an amount of approximately 30 mol% or less of dicarboxylic acid units, and may also have diol units other than ethylene glycol in an amount of approximately 30 mol% or less of diol units.

[0021] There are no particular restrictions on the polymerization catalyst for polyester, and conventionally known compounds can be used, such as titanium compounds, germanium compounds, antimony compounds, manganese compounds, aluminum compounds, magnesium compounds, and calcium compounds.

[0022] To suppress the precipitation of oligomer components, polyester films may be manufactured using polyester with a low oligomer content as the raw material. Various known methods can be used to manufacture polyester with a low oligomer content, such as a method of solid-phase polymerization after polyester production. The polyester film may be constructed with three or more layers, and the outermost layer of the polyester film may be made of a polyester raw material with a low oligomer content to suppress the amount of oligomer component precipitated. Polyester may also be obtained by esterification or transesterification, followed by further increasing the reaction temperature and melt polycondensation under reduced pressure.

[0023] The base film may also contain particles primarily for the purpose of providing slipperiness and preventing scratches during each process. The type of particles is not particularly limited as long as they can provide slipperiness. Specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide, and organic particles such as acrylic resin, styrene resin, urea resin, phenolic resin, epoxy resin, and benzoguanamine resin. Furthermore, during the polyester manufacturing process, precipitated particles obtained by precipitating and finely dispersing a portion of metal compounds such as catalysts can also be used.

[0024] There are no particular limitations on the shape of the particles used; spherical, lumpy, rod-shaped, flattened, or any other shape may be used. Furthermore, there are no particular restrictions on their hardness, specific gravity, color, etc. These particles may be used individually, or two or more may be used in combination as needed.

[0025] The average particle size of the particles used is typically in the range of 0.05 to 5 μm, preferably 0.1 to 4 μm, and more preferably 0.1 to 3.5 μm, considering both the transparency and handling of the film. The average particle size can be measured by the method described in the examples. In the case of non-spherical particles, the average of the longest and shortest diameters is measured as the diameter of each particle.

[0026] If the base film has a multilayer structure and contains particles, the particles should be contained in at least one of the layers. If the base has a surface layer and an intermediate layer, it is preferable to contain the particles in the surface layer. The particles may be contained in one surface layer or in both surface layers. By containing particles in the surface layer, it is possible to effectively impart properties such as slipperiness while reducing the overall particle content of the base film.

[0027] The particle content in the particle-containing layer is typically in the range of 0.010% by mass or more and less than 10% by mass, preferably 0.015 to 5% by mass, and more preferably 0.015 to 3% by mass. If there are no particles or only a small amount, the transparency of the base film increases, resulting in a base film with good transparency. On the other hand, including particles within the above range also improves the slipperiness. Furthermore, if the layer containing particles is a multilayer structure, it is preferably the surface layer, but if the base film has a single-layer structure, it is the entire base film.

[0028] The method for adding particles to the base film is not particularly limited, and conventionally known methods can be employed. For example, the particles can be added at any stage in the production of the resin (e.g., polyester) that constitutes each layer. If the base film is polyester, it is preferable to add the particles after the esterification or transesterification reaction is completed.

[0029] In addition to the particles mentioned above, conventionally known additives such as antioxidants, antistatic agents, ultraviolet absorbers, heat stabilizers, lubricants, dyes, and pigments may be added to the base film as needed. If the base film has a multilayer structure, each additive only needs to be added to at least one of the multiple layers.

[0030] The thickness of the base film is not particularly limited as long as it is within the range that allows for film formation, but is usually in the range of 9 to 100 μm, preferably 12 to 75 μm, and more preferably 25 to 75 μm. If the base film has a multilayer structure, the overall thickness of the base film shall be within the above range.

[0031] <Easily soluble resin layer> The easily soluble resin layer of this film (hereinafter also referred to as "this easily soluble resin layer") is provided on at least one surface of the base film. If this film has a functional layer, it is preferable that the easily soluble resin layer is provided between the base film and the functional layer. By doing so, when the laminated film is washed with a cleaning agent after use, the easily soluble resin is dissolved in the cleaning agent, and the functional layer and any residues or impurities adhering to the functional layer can be completely separated and removed. In other words, the base film can be separated and recovered from the laminated film. Furthermore, the separated and recovered base film can be remelted, making it possible to regenerate the resin that constituted the base film.

[0032] The easily soluble resin layer contains a polyester component, which includes a dicarboxylic acid component, i.e., an acid component, namely (A) terephthalic acid (hereinafter also referred to as "component (A)"), (B) a dicarboxylic acid having a sulfonic acid base (hereinafter also referred to as "component (B)"), and (C) other dicarboxylic acids (hereinafter also referred to as "component (C)"). Furthermore, "polyester component" refers to the constituent components of polyester obtained by polycondensation of at least one dicarboxylic acid component and at least one diol component.

[0033] The components (A) to (C) in the polyester component may be derived from a single polyester constituting the easily soluble resin layer, or from different polyesters. The easily soluble resin layer may be formed, for example, by a copolymer polyester containing component (A) and component (B), or by a copolymer polyester containing component (A), component (B), and component (C). Furthermore, the easily soluble resin layer may be formed using a copolymerized polyester containing at least two of the components (A), (B), and (C), specifically, a copolymerized polyester containing component (A) and component (C), or a copolymerized polyester containing component (B) and component (C).

[0034] Furthermore, multiple polyesters, such as homopolyesters, each consisting of one type of dicarboxylic acid component, may be used in combination so that the easily soluble resin layer contains components (A) to (C). In addition to copolymerized polyesters, polyesters consisting of a single dicarboxylic acid component, such as homopolyesters, may also be used in combination. In any case, the easily soluble resin layer should, as a result, contain components (A) to (C). Furthermore, components (A) to (C) may all be derived from different polyesters (whether homopolyester or copolymerized polyester).

[0035] As described above, the easily soluble resin layer contains a polyester component, and the polyester component contains the acid components (A) to (C) above. However, these do not necessarily have to be included as copolymerized polyesters, and may be a blend of polyesters containing each component. The aforementioned component (B) is preferably included as one of the acid components of the copolymerized polyester. Furthermore, in polyesters consisting of one type of dicarboxylic acid component, such as homopolyester, the dicarboxylic acid component is preferably terephthalic acid, and the homopolyester is preferably polyethylene terephthalate (PET).

[0036] The readily soluble resin layer contains a polyester component, and this polyester component contains component (B) as an acid component, which facilitates water solubility. Examples of component (B) include alkali metal salts, alkaline earth metal salts, and ammonium salts of sulfoterephthalic acid, 5-sulfisophthalic acid, 4-sulfisophthalic acid, and 4-sulfo-2,7-naphthalenedicarboxylic acid, but sodium 5-sulfisophthalate is preferred because it is easier to make it water-soluble. These components (B) may be used individually or in combination of two or more. In this invention, component (A) is terephthalic acid, which is the acid component of the polyester component excluding component (B).

[0037] The aforementioned component (C) may be any dicarboxylic acid other than components (A) and (B), such as isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid. The inclusion of component (C) improves solubility in water, and if the film has a functional layer, it also improves adhesion to the functional layer. These (C) components may be used individually or in combination of two or more, but it is preferable that they contain at least isophthalic acid. Including isophthalic acid as component (C) results in good compatibility with terephthalic acid component (A) and sodium 5-sulfoisophthalate, which is suitable as component (B), and improves the physical properties of the easily soluble resin layer.

[0038] In the present invention, the content ratio (mol%) of component (C) in the total acid components of the easily soluble resin layer must be 3.0 to 8.0 times the content ratio (mol%) of component (B). Within this range, the solubility of the easily soluble resin layer in water and alkaline aqueous solutions will be sufficient. From these perspectives, the content (mol%) of component (C) is more preferably 3.0 to 7.0 times, and most preferably 4.0 to 6.0 times, compared to the content (mol%) of component (B). Furthermore, "total acid components" refers to all the polyester components that make up the easily soluble resin layer, i.e., the dicarboxylic acid components within the polyester components.

[0039] The content (mol%) of component (B) in the total acid components is preferably 8 mol% or less, more preferably 8.0 mol% or less, even more preferably 7 mol% or less, and even more preferably 6.5 mol% or less. Furthermore, while the lower limit is not particularly restricted as long as it is above 0%, it is preferably 1 mol% or more, more preferably 2 mol% or more, and even more preferably 3 mol% or more. The content of component (B) in the total acid components being within the above range ensures sufficient solubility in alkaline aqueous solutions. Furthermore, being below the above upper limit is advantageous in terms of blocking resistance and is effective in applications where it comes into contact with a surface that does not have a functional layer.

[0040] The content (mol%) of component (A) in the total acid components is preferably 50 to 85 mol%, more preferably 55 to 80 mol%, and even more preferably 60 to 75 mol%. If it is above the lower limit, an appropriate amount of component (C) can be secured while ensuring the moldability and strength of the film. If it is below the upper limit, the content of component (B) can be secured. Therefore, sufficient solubility in water and alkaline aqueous solutions is achieved. Furthermore, the content (mol%) of component (C) in the total acid components is preferably 14 to 42 mol%, more preferably 18 to 38 mol%, and even more preferably 20 to 35 mol%. If it is above the lower limit, it is advantageous in terms of solubility in water and adhesion to the functional layer, and if it is below the upper limit, the content of component (B) can be ensured. Therefore, solubility in water and alkaline aqueous solutions is sufficient.

[0041] The diol component in the polyester component can be one or more of the following: ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexanedimethanol, and neopentyl glycol. Here, it is preferable that at least one of the diol components is ethylene glycol. The inclusion of ethylene glycol maintains crystallinity and improves the basic properties of the film, such as heat resistance and strength. The ethylene glycol content is preferably in the range of 40 to 100 mol%, more preferably in the range of 60 to 100 mol%, and even more preferably in the range of 80 to 100 mol% of the total diol components. Normally, when polyester is manufactured (polycondensed) using ethylene glycol as one of the raw materials, diethylene glycol is produced as a by-product from the ethylene glycol. In this specification, this diethylene glycol is referred to as by-product diethylene glycol. The amount of diethylene glycol produced as a by-product from ethylene glycol varies depending on the type of polycondensation, but it is generally about 5 mol% or less of the ethylene glycol. In this invention, by-product diethylene glycol in amounts of 5 mol% or less is also included in ethylene glycol. On the other hand, depending on the content of diethylene glycol, more specifically, if diethylene glycol is contained in amounts exceeding 5 mol%, diethylene glycol is distinguished from ethylene glycol.

[0042] This easily soluble resin layer may contain the aforementioned polyester component, or it may contain other resin components besides the polyester component. As described above, in one embodiment of the present invention, the base film is preferably a polyester film. Therefore, the easily soluble resin layer containing the polyester component and the base film exhibit excellent adhesion. Accordingly, the laminated film of the present invention can be used without any problems, just like a normal laminated polyester film.

[0043] The thickness of the easily soluble resin layer in this film is preferably 0.01 to 10 μm, more preferably 0.05 to 5 μm, and even more preferably 0.1 to 5 μm, from the viewpoint of ease of dissolution in solvents during the recovery process and adhesion to the functional layer described later. Furthermore, the thickness of this film is preferably 9 to 110 μm, more preferably 12 to 85 μm, even more preferably 25 to 85 μm, and particularly preferably 25 to 60 μm.

[0044] Furthermore, the easily soluble resin layer may contain particles. By including particles, the surface of the easily soluble resin layer can be roughened, and if the film has a functional layer, adhesion to the functional layer can be improved. Also, for surfaces without a functional layer, the particles can improve blocking resistance. The particles used can be the same as those contained in the base film, and the particle size, content, etc., can also be the same.

[0045] One example of a method for manufacturing an easily soluble resin layer is to employ a commonly known film manufacturing method. For example, if the main component resin of each layer constituting this film is polyester, and the surface layer of the laminated structure is to be manufactured as an easily soluble resin layer, it can be manufactured as follows. However, the following explanation is just one example of a method for manufacturing a laminated film, and this film is not limited to laminated films manufactured by this method. Furthermore, if this film consists of three layers of three types, A, B, and C, and layer A is an easily soluble resin layer, then layers B and C are the base film, and this film can be described as a laminated film having an easily soluble resin layer on one surface of the base film. In addition, this film (without the functional layer) may be a laminated film of four or more layers, in which case the outermost layer on the side in contact with any functional layer should be an easily soluble resin layer.

[0046] For example, when manufacturing a biaxially oriented film, it is preferable to extrude the polyester raw material, as described above, from a die as a molten sheet using multiple extruders, and then cool and solidify it in a rotating cooling drum (casting drum) to obtain an unstretched laminated sheet. In this case, it is preferable to improve the adhesion between the laminated sheet and the rotating cooling drum in order to improve the flatness of the laminated sheet, and electrostatic application adhesion and / or liquid coating adhesion methods are preferably employed. An unstretched laminated sheet is obtained in this way. The polyester raw material should be supplied to the extruder after being appropriately dried, such as in the form of pellets. Particles, UV absorbers, and other additives may also be blended into the pellets as appropriate.

[0047] Next, the unstretched laminated sheet obtained by the above method is stretched in one direction using a roll or tenter type stretcher. The stretching temperature is usually 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3 to 6 times. Next, the material is stretched in a direction perpendicular to the first stretching direction. In this case, the stretching temperature is usually 70 to 170°C, preferably 80 to 120°C, and the stretching ratio is usually 3 to 7 times, preferably 3.5 to 6 times.

[0048] The film is then heat-treated at a temperature of 180-270°C under tension or under relaxation of 30% or less to obtain a biaxially oriented film. In the above stretching process, a method of performing unidirectional stretching in two or more stages can also be employed. In that case, it is preferable to perform the stretching so that the final stretching ratios in both directions fall within the above ranges.

[0049] Furthermore, simultaneous biaxial stretching can also be used in the manufacture of laminated films. Simultaneous biaxial stretching is a method of simultaneously stretching and oriented the aforementioned unstretched sheet in the longitudinal and width directions while maintaining a temperature controlled to typically 70-120°C, preferably 80-110°C. The stretching ratio is 4-50 times, preferably 7-35 times, and more preferably 10-25 times in terms of area. Next, a heat treatment is performed at a temperature of 170-250°C under tension or under relaxation of 30% or less to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching apparatus employing the above-described stretching method, conventionally known stretching methods such as screw type, pantograph type, and linear drive type can be used.

[0050] The longitudinal direction of the film refers to the direction in which the film progresses during the film manufacturing process, i.e., the winding direction of the film roll. The width direction refers to the direction parallel to the film surface and perpendicular to the longitudinal direction, that is, the direction parallel to the central axis of the roll when the film is in a roll form.

[0051] Furthermore, the easily soluble resin layer may be provided by in-line coating, which treats the film surface during the film manufacturing process, or by off-line coating, which is applied to the manufactured film outside the system. Specifically, the in-line coating method involves coating the polyester at any stage from melt extrusion to stretching, heat fixing, and winding. Typically, the coating is applied to an unstretched sheet obtained by melting and rapid cooling, a stretched uniaxially oriented film, a biaxially oriented film before heat fixing, or a film after heat fixing but before winding. In one embodiment of the present invention, it is preferable to provide the easily soluble resin layer by in-line coating. By providing the easily soluble resin layer by in-line coating, the easily soluble resin layer can be made into a thin film, and as a result, adhesion and blocking resistance can be improved.

[0052] The method for forming the easily soluble resin layer by in-line coating or offline coating is not particularly limited, and conventionally known coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, and curtain coating can be used. The drying and curing conditions are not particularly limited, and for example, when providing the easily soluble resin layer by offline coating, it is generally preferable to perform heat treatment at 80 to 200°C for 3 to 40 seconds, preferably at 100 to 180°C for 3 to 40 seconds. On the other hand, when providing the easily soluble resin layer by in-line coating, it is generally preferable to perform heat treatment at 70 to 280°C for 3 to 200 seconds. Furthermore, regardless of whether it is offline coating or in-line coating, heat treatment and active energy ray irradiation such as ultraviolet irradiation may be used in combination as needed. The base film constituting this film may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

[0053] <Functional Layer> The laminated film of the present invention may include a functional layer. The components of the functional layer are not particularly limited, but from the viewpoint of removal by the functional layer removal method of the present invention, it is preferable that it be composed of a resin. Examples of functional layers include a hard coat layer, an adhesive layer, a release layer, a decorative layer, a light-shielding layer, an ultraviolet-shielding layer, an easy-adhesion layer (primer layer), an antistatic layer, a refractive index adjusting layer, and an oligomer encapsulation layer.

[0054] The hard coat layer is a layer provided to the base film to impart scratch resistance and other properties. The material used to form the hard coat layer is not particularly limited, but examples include monofunctional (meth)acrylates, polyfunctional (meth)acrylates, and cured products of reactive silicon compounds such as tetraethoxysilane.

[0055] The adhesive layer is a layer provided for adhesively adhering to other equipment or devices. The material constituting the adhesive layer is not particularly limited, but for example, known adhesive resins such as acrylic, rubber, or silicone can be used.

[0056] The release layer is a layer provided to impart release properties to the base film, and is used, for example, in release films used in process paper for green sheet molding used in the manufacture of ceramic electronic components, polarizing plates, and adhesive separators for optical components used in the manufacture of flat panel displays such as optical filters. There are no particular restrictions on the material constituting the release layer, and examples include those mainly composed of curable silicone resin, modified silicone resins produced by graft polymerization with urethane resin, epoxy resin, etc., long-chain alkyl group-containing compounds, fluorine compounds, hydrocarbon waxes, olefin polymers, urethane acrylate polymers, etc. Among these, it is preferable that the functional layer is at least one selected from the group consisting of a silicone release layer, an olefin-based release layer, and a urethane acrylate-based release layer. In one embodiment of the present invention, a laminated film having a silicone release layer as a functional layer can be mentioned. In this invention, the functional layer described in the examples is treated as a release layer.

[0057] A decorative layer is a layer added to enhance the design. The materials that make up the decorative layer are not particularly limited, but examples include polyurethane resins, vinyl resins, polyamide resins, polyester resins, acrylic resins, and polyvinyl acetal resins. Pigments, dyes, etc., are added to these resins to create the decoration.

[0058] A light-shielding layer or ultraviolet-shielding layer is a layer provided to protect the contents from ultraviolet light, visible light, etc. The materials constituting the light-shielding layer or ultraviolet-shielding layer are not particularly limited, but examples include the various resins described in the decorative layer section, inorganic fillers such as calcium carbonate, talc, clay, kaolin, silica, diatomaceous earth, and barium sulfate, and organic fillers such as wood flour, pulp flour, and cellulose powder.

[0059] The easy-adhesion layer (primer layer) is a layer provided to adhere other layers or films to the base film, and is not particularly limited, but examples include polyurethane resins, vinyl resins, polyamide resins, polyester resins, acrylic resins, polyvinyl acetal resins, and various crosslinking agents and particles.

[0060] An antistatic layer is a layer provided to prevent static electricity generated by contact with other materials or peeling. While not particularly limited, the antistatic agents used in the antistatic layer include nonionic, cationic, anionic, and amphoteric surfactants, conductive polymers such as polypyrrole, polyaniline, poly(3,4-ethylenedioxythiophene), poly(4-styrene sulfonate), and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate), metal oxide fillers such as SnO2 (Sb-doped), In2O3 (Sn-doped), and ZnO (Al-doped), and carbon compounds such as graphene, carbon black, and carbon nanotubes (CNTs). These may be used individually or in combination of two or more. Furthermore, the antistatic layer may be formed from a resin composition containing the antistatic agent. Examples of resins included in the resin composition include polyester resins, acrylic resins, and urethane resins.

[0061] The refractive index adjustment layer is a layer provided to adjust the refractive index. The materials constituting the refractive index adjustment layer are not particularly limited, but examples include polyester resin, acrylic resin, urethane resin, polycarbonate resin, epoxy resin, alkyd resin, urea resin, fluororesin, and metal oxides such as zirconium oxide and titanium oxide. These may be used individually or in combination of two or more types.

[0062] The oligomer encapsulation layer is a layer provided to prevent film whitening and foreign matter after the heating process. The materials constituting the oligomer encapsulation layer are not particularly limited, but examples include amine compounds, ionic resins, and highly crosslinked coatings.

[0063] These functional layers can be a single layer or consist of two or more layers stacked on top of each other. When two or more layers are laminated, it is preferable that at least one layer is made of resin. In the present invention, the functional layer is laminated on an easily soluble resin layer provided on at least one surface of the base film. That is, if the laminated film of the present invention has a functional layer, the functional layer is provided on the easily soluble resin layer. By interposing the easily soluble resin layer, the easily soluble resin can be dissolved in the solvent by washing with a cleaning agent, and the functional layer on the film surface can be completely removed, allowing only the base film to be recovered.

[0064] [Functional layer removal method] As described above, since this film has an easily soluble resin layer, if the film has a functional layer, the functional layer formed on the easily soluble resin layer can be easily peeled off and removed. A method for removing the functional layer (hereinafter also referred to as "this functional layer removal method") includes a functional layer removal step in which the film is washed with a cleaning agent to dissolve the easily soluble resin layer, and the functional layer is removed from the base film together with the easily soluble resin layer.

[0065] <Cleaning agent> From the viewpoint of enabling recovery of the substrate film without dissolving it, the cleaning agent is preferably water or an alkaline aqueous solution. From the viewpoint of environmental impact, it is preferable to use water. Furthermore, surfactants or other substances may be added to the water to improve wettability with the base film.

[0066] For example, depending on the more specific configuration of the easily soluble resin layer, such as one with improved adhesion to the functional layer, it may be preferable to use an alkaline aqueous solution from the viewpoint of cleaning power. Examples of alkaline aqueous solutions include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and barium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal phosphates such as trisodium phosphate, sodium pyrophosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, tripotassium phosphate, potassium pyrophosphate, and potassium tripolyphosphate; alkali metal silicates such as sodium orthosilicate, sodium metasilicate, and potassium silicate; and ammonia.

[0067] Among alkaline aqueous solutions, alkali metal hydroxides are preferred, and sodium hydroxide and potassium hydroxide are more preferred from the viewpoint of availability and cleaning properties. Furthermore, the alkaline aqueous solution in this cleaning agent can be used individually or in combination of two or more types.

[0068] The content of alkali (earth) metals or ammonia in the entire detergent is preferably 1 to 35% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 25% by mass. Within the above range, sufficient effectiveness as a detergent can be obtained.

[0069] The alkaline aqueous solution may further contain a compound having at least one hydroxyl group in order to enhance its cleaning effect. Examples of compounds having at least one hydroxyl group include alcohols and / or phenols.

[0070] Examples of alcohols include monohydric alcohols such as hexafluoro-2-propanol, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, benzyl alcohol, ethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; dihydric alcohols such as ethylene glycol, diethylene glycol, and propylene glycol; and polyhydric alcohols such as glycerin.

[0071] Examples of phenols include phenol, xylenol, salicylic acid, picric acid, naphthol, catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, dibutylhydroxytoluene, bisphenol A, cresol, estradiol, eugenol, gallic acid, guaiacol, phenolphthalein, serotonin, dopamine, adrenaline, noradrenaline, thymol, tyrosine, and hexahydroxybenzene.

[0072] These can be used individually or in combination of two or more types.

[0073] In addition to the components mentioned above, various other additives can be added to the alkaline aqueous solution. For example, surfactants, antioxidants, rust inhibitors, pH adjusters, preservatives, viscosity modifiers, thickeners, and defoamers can be added.

[0074] <Functional layer removal process> The cleaning method for the film in the functional layer removal process described above includes, for example, immersion in a cleaning tank containing a cleaning agent, application of a cleaning agent in solution, and spraying of a cleaning agent in solution or vaporized. Of these, the immersion method is preferred from the viewpoint of cleaning agent penetration.

[0075] In the immersion method, the temperature of the cleaning agent is preferably room temperature (20°C) or higher. At room temperature (20°C) or higher, the viscosity of the cleaning agent is low, and it penetrates the functional layer easily, resulting in good cleaning performance. From this viewpoint, the temperature of the cleaning agent in the immersion method is more preferably 40°C or higher, even more preferably 50°C or higher, and particularly preferably 60°C or higher. Furthermore, as for the upper limit of the temperature of the detergent, when the detergent is used in solution form, a temperature below the boiling point is preferable. In the case of an aqueous detergent, which is a preferred embodiment of the present invention, a temperature of 100°C or lower is preferable, and 90°C or lower is more preferable. Furthermore, the temperature of the cleaning agent during cleaning is the same as described above, even in methods other than immersion. In addition, microwave irradiation may be performed during cleaning using the immersion method in order to promote the hydrolysis reaction.

[0076] The cleaning time (for example, the immersion time in the case of the immersion method) should preferably be adjusted as appropriate depending on the type of object to be cleaned, as follows:

[0077] When a laminated film having an acrylic adhesive layer as a functional layer is to be cleaned, the cleaning time is preferably 1 second or more and 30 minutes or less. If the exposure time is 1 second or longer, the cleaning agent can sufficiently penetrate the easily soluble resin layer, and cleaning performance can be achieved. On the other hand, if the exposure time is 30 minutes or less, the base film will not dissolve excessively, and the amount of base resin obtained upon recovery, such as polyester, can be secured. From the above perspective, the washing time is more preferably 15 seconds or more and 30 minutes or less, even more preferably 30 seconds or more and 25 minutes or less, and particularly preferably 1 minute or more and 20 minutes or less.

[0078] When a laminated film having an acrylic hard coat layer as a functional layer is to be cleaned, the cleaning time is preferably 1 second or more and 30 minutes or less. If the exposure time is 1 second or longer, the cleaning agent can sufficiently penetrate the easily soluble resin layer, and cleaning performance can be achieved. On the other hand, if the exposure time is 30 minutes or less, the base film will not dissolve excessively, and the amount of base resin obtained upon recovery, such as polyester, can be secured. From the above perspective, the washing time is more preferably 15 seconds or more and 30 minutes or less, even more preferably 30 seconds or more and 25 minutes or less, and particularly preferably 1 minute or more and 20 minutes or less.

[0079] When a laminated film with a silicone release layer as a functional layer is to be cleaned, the cleaning time is preferably 1 second or more and 30 minutes or less. If the exposure time is 1 second or longer, the cleaning agent can sufficiently penetrate the easily soluble resin layer, and cleaning performance can be achieved. On the other hand, if the exposure time is 30 minutes or less, the base film will not dissolve excessively, and the amount of base resin obtained upon recovery, such as polyester, can be secured. From the above perspective, the washing time is more preferably 15 seconds or more and 30 minutes or less, even more preferably 30 seconds or more and 25 minutes or less, and particularly preferably 1 minute or more and 20 minutes or less.

[0080] The specific details of the functional layer removal process are as follows, depending on the shape of the laminated film that is the waste material.

[0081] If the waste laminated film is in roll form, it is preferable to install an unwinding device before the washing tank containing the cleaning agent, unwind the laminated film from the device, and introduce it into the washing tank for washing. It is also preferable to proceed continuously to the next recovery process. Furthermore, in the functional layer removal process, equipment equipped with physical means such as roll brushes, ultrasound, micro / nanobubbles, water jets, and compressed cold air may be provided for the purpose of efficiently removing the functional layer from the laminated film.

[0082] If the waste laminated film is in the form of a lump, it is preferable to install a cutting device before the washing process to break it into flakes before introducing it into the washing tank. Breaking it into flakes increases the contact area between the laminated film and the cleaning agent, allowing the cleaning agent to penetrate more easily and efficiently remove the functional layer. In this embodiment, it is preferable to use a belt conveyor or the like to continuously introduce the flake-shaped laminated film into the washing tank. By adopting this embodiment, washing can be performed with high productivity. In this embodiment, washing can also be performed in a batch manner.

[0083] <Recovery Process> A recovery step may be included after the functional layer removal step to recover the base film. Alternatively, a rinsing step and a drying step may be included prior to the recovery step. The recovery method can be selected according to the shape of the laminated film waste. If the waste laminated film is in roll form, it can be efficiently recovered by continuously processing it using a roll-to-roll method, going through functional layer removal, rinsing, and drying processes, and then winding it up. Furthermore, if the waste laminated film is in the form of a block, as described above, it is preferable to have a cutting step before the functional layer removal step, and to use a belt conveyor or the like to continuously pass the functional layer removal step, rinsing step, and drying step to recover the flake-shaped polyester. As described above, it is advantageous in terms of handling to process the recovered base film into pellets after collection.

[0084] <Rinsing process> In this functional layer removal method, as described above, a rinsing step may be included between the functional layer removal step and the recovery step to wash away the cleaning agent. This step involves washing away the cleaning agent adhering to the substrate film from which the functional layer has been removed using a rinsing solution. Water is preferred as the rinsing solution, but if the cleaning agent is water or otherwise does not need to be washed away, the rinsing step can be omitted.

[0085] <Drying process> A drying step may be included after the rinsing step. The conditions for the drying step are not particularly limited, but are usually 70-150°C for 1-30 minutes. Common drying methods can be used, such as heating and drying with infrared heaters or ovens, hot air drying with hot air dryers, or microwave heating and drying.

[0086] <<Explanation of terms>> In this invention, the term "film" includes "sheets," and the term "sheet" includes "film." In this invention, when "X~Y" (where X and Y are any numbers) is written, unless otherwise specified, it means "X or greater and Y or less," and also includes the meaning of "preferably greater than X" or "preferably less than Y." Furthermore, when "X or greater" (where X is any number) is written, unless otherwise specified, it includes the meaning of "preferably greater than X," and when "Y or less" (where Y is any number) is written, unless otherwise specified, it also includes the meaning of "preferably less than Y." [Examples]

[0087] 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 unless it exceeds the gist of the invention.

[0088] <Evaluation Method> (1) Measurement of the intrinsic viscosity (dl / g) of polyester One g of polyester, from which other polymer components and pigments incompatible with polyester had been removed, was accurately weighed. 100 ml of a phenol / tetrachloroethane mixed solvent (50 / 50 by mass ratio) was added to dissolve it, and the result was measured at 30°C.

[0089] (2) Measurement of average particle size The average particle size was defined as the particle size at 50% of the cumulative volume fraction (d50) in the equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution analyzer (SA-CP3 model) manufactured by Shimadzu Corporation.

[0090] (3) Solubility evaluation From the laminated films obtained in each example and comparative example, the laminated film (3 cm × 4 cm) before the functional layer was added was immersed in 30 mL of water or an alkaline aqueous solution. After immersion, the surface of the laminated film was subjected to qualitative analysis of the element Na using an X-ray fluorescence analyzer (XRF, Shimadzu Corporation "EDX-8000"), and the solubility of the easily soluble resin layer was evaluated according to the following criteria. When using water, the laminated film without the functional layer was immersed at 90°C for 20 minutes. When using an alkaline aqueous solution (2% by mass of NaOH), the film was immersed at 90°C for 20 minutes. ○ (good); Na element is not detected (dissolves). × (poor); Sodium is detected (does not dissolve).

[0091] (4) Adhesion evaluation Two laminated films without functional layers were stacked, with their easily soluble resin layers (layer A or coating layer) overlapping. A 12cm x 10cm test specimen was then prepared at 40°C, 80% RH, and 10kg / cm². 2 The films were then pressed under conditions of 20 hours. Subsequently, the films were separated from each other according to the method specified in ASTM D1893, and the peel load was measured. The heavier the peel load, the better the adhesion of the easily soluble resin layer itself, and therefore the better the adhesion to the functional layer. The evaluation criteria were as follows: ◎(excellent);400g / cm or more ○ (good); 200g / cm or more, less than 400g / cm △(fair); 100g / cm or more, less than 200g / cm × (poor); less than 100g / cm

[0092] (5) Evaluation of blocking resistance Two laminated films obtained in each example and comparative example were prepared before the functional layer was added. The easily soluble resin layer (layer A or coating layer described later) and the base film layer on the opposite side of the easily soluble resin layer (layer C described later) were overlapped, and a 12cm x 10cm test piece was cut out and tested at 40℃, 80%RH, and 10kg / cm². 2 The films were then pressed under conditions of 20 hours. Subsequently, the films were separated from each other using a Shimadzu AUTOGRAPH according to the method specified in ASTM D1893, and the peel load was measured. Materials with lighter peeling loads are less likely to block and therefore have better blocking resistance. The evaluation criteria were as follows: ◎(excellent); less than 50g / cm³ ○ (good); 50g / cm or more, less than 100g / cm △(fair); 100g / cm or more, less than 500g / cm ×(poor); 500g / cm or more, film tears during evaluation, or obvious blocking occurs due to pressing.

[0093] (6) Functional layer removal evaluation (Laminated film with a silicone release layer) In the examples and comparative examples, the laminated films after the silicone release layer was applied were evaluated as follows. A laminated film (3cm x 4cm) with a silicone release layer was cleaned using a cleaning agent. After cleaning, the surface of the laminated film was subjected to quantitative analysis of the Si element using an X-ray fluorescence analyzer (XRF, "EDX-8000" mentioned above). In this evaluation, the Si element content of the laminated film surface before cleaning was set to 100%, and the Si element content of a plain laminated film without a functional layer coating was set to 0%, and the removal rate (%) of the functional layer was calculated.

[0094] The functional layer removal rate calculated using the method described above was evaluated according to the following criteria. The functional layer was removed by immersing the laminated film in a washing tank containing 30 mL of cleaning agent. When using water, the laminated film with the functional layer was washed at 90°C for 20 minutes, and when using an alkaline aqueous solution (2% by mass of NaOH), it was washed at 90°C for 20 minutes. 〇(good); Removal rate 90~100% × (poor); Removal rate less than 0-90%

[0095] <Materials used> [Polyester raw material] Table 1 shows the composition of each polyester raw material used in the examples and comparative examples. In Table 1, TPA is terephthalic acid, IPA is isophthalic acid, 5-SIPA-Na is sodium 5-sulfoisophagate, EG is ethylene glycol, DEG is diethylene glycol, and NPG is neopentyl glycol. Polyester E contains 2% by mass of calcium carbonate with an average particle size of 0.7 μm, and polyester F contains 0.2% by mass of silica particles with an average particle size of 3.2 μm. Furthermore, the intrinsic viscosities of polyesters D, E, and F were 0.64 dl / g, 0.61 dl / g, and 0.65 dl / g, respectively.

[0096] [Table 1]

[0097] (Example 1) The raw materials for each layer were mixed as shown in Table 2. The mixed raw materials for layers A, B, and C were each co-extruded at 280°C in separate melt extruders, and then cooled and solidified on a casting drum cooled to 25°C using an electrostatic application adhesion method to obtain three types of three-layer (layer A / layer B / layer C) unstretched laminated films. Next, the obtained unstretched laminated film was stretched 3.5 times in the longitudinal direction (MD) at 88°C using a roll stretcher. Furthermore, after preheating in a tenter at 100°C, it was stretched 4.4 times in the width direction (TD) at 110°C. After biaxial stretching, it was heat-treated at 220°C to obtain a laminated film with a thickness of 31 μm (layer A: 1.55 μm, layer B: 27.9 μm, layer C: 1.55 μm). As shown in Table 2, the easily soluble resin layer corresponds to layer A. The following functional layers were added to the resulting laminated film. A silicone release agent was applied to the A layer of the resulting laminated film. This agent was prepared by mixing 100 parts by mass of a mixture consisting of 1.6% by mass of curable silicone resin (Shin-Etsu Chemical Co., Ltd., KS847H, 15% diluted), 19.7% by mass of methyl ethyl ketone, 39.4% by mass of toluene, and 39.3% by mass of heptane, with 0.001 parts by mass of addition-type platinum catalyst (Shin-Etsu Chemical Co., Ltd., PL-50T), and the coating amount after drying was 0.1 g / m². 2 The film was coated in this manner and heated in an oven at 150°C for 30 seconds to obtain a laminated film having a silicone release layer. The properties of the obtained laminated film were evaluated using the method described above. The evaluation results are shown in Table 3.

[0098] (Examples 2 and 3 and Comparative Examples 1 and 5) The procedure was the same as in Example 1, except that the composition was as shown in Table 2 below. The evaluation results are shown in Table 3.

[0099] (Example 4) A laminated film having an easily soluble resin layer was obtained by following the same procedure as in Example 1, except that the composition and film formation (thickness) conditions were as described in Table 2 below, and after uniaxial stretching, a 7% by mass aqueous solution of raw material C was applied to the A layer surface of the uniaxially stretched film so that the thickness after drying was 100 nm, before being introduced into a tenter and stretched in the width direction (TD). As shown in Table 2, in Example 4, the easily soluble resin layer corresponds to the coating layer. Subsequently, a functional layer was laminated on the easily soluble resin layer, similar to Example 1. The evaluation results are shown in Table 3.

[0100] (Comparative Examples 2 and 3) The procedure was the same as in Example 1, except that the composition and film formation (thickness) conditions were as described in Table 2 below. The evaluation results are shown in Table 3.

[0101] (Comparative Example 4) After obtaining a laminated film with the composition shown in Table 2 below, a mixed solution of 25% by mass of a 25% by mass aqueous solution of raw material G and 75% by mass of a 25% by mass aqueous solution of raw material H was applied to layer A to a dry film thickness of 1.5 μm. A laminated film having an easily soluble resin layer was obtained by heating in an oven at 100°C for 3 minutes and at 170°C for 15 seconds. As shown in Table 2, the easily soluble resin layer corresponds to the coating layer. Subsequently, a functional layer was laminated on the easily soluble resin layer, similar to Example 1. The evaluation results are shown in Table 3.

[0102] [Table 2]

[0103] [Table 3]

[0104] As shown in Examples 1 to 4, the laminated film of the present invention exhibits excellent solubility, adhesion, blocking resistance, and removal of the functional layer. Therefore, it is clear that the performance as a laminated film is maintained, the functional layer can be peeled off, and the base film can be recovered. Furthermore, it is thought that the differences in adhesion and blocking resistance in Examples 2 and 4 were due to differences in the thickness of the easily soluble resin layer. In Example 4, the thickness of the easily soluble resin layer was very thin, so measurement was not possible using the solubility evaluation described above. However, since the functional layer was removed without any problems in the functional layer removal evaluation, it can be seen that the coating layer corresponding to the easily soluble resin layer dissolves without problems in water and alkaline aqueous solutions. On the other hand, as shown in Comparative Examples 1 and 2, when IPA is not present as the acid component of the easily soluble resin layer, the adhesion between the easily soluble resin layers is insufficient, and it is expected that the adhesion between the easily soluble resin layer and the functional layer will be insufficient when a functional layer is laminated on the easily soluble resin layer. Furthermore, when IPA is not present, the solubility of the easily soluble resin layer will be insufficient with washing with water, so it is necessary to use an alkaline aqueous solution as a cleaning agent. Furthermore, the results from Comparative Examples 3 and 4 show that when the content ratio of component (C) deviates from the range of 3.0 to 8.0 times that of component (B), the solubility of the easily soluble resin layer becomes insufficient when an alkaline aqueous solution is used as a cleaning agent. In addition, the laminated films of Comparative Examples 3 and 4 have poor blocking resistance. Furthermore, the results from Comparative Example 5 show that if the polyester component in the easily soluble resin layer does not contain either component (B) or component (C), the easily soluble resin layer will not dissolve with water or an alkaline aqueous solution, and the functional layer cannot be removed. In addition, it is expected that the adhesion will be poor, resulting in insufficient adhesion between the easily soluble resin layer and the functional layer. [Industrial applicability]

[0105] According to the laminated film of the present invention, the easily soluble resin layer can be dissolved regardless of whether water or an alkaline aqueous solution is used as the cleaning solution. Therefore, if the laminated film of the present invention has a functional layer via the easily soluble resin layer, the functional layer can be easily peeled off after use, and the base film can be recovered. Furthermore, when the laminated film of the present invention has a functional layer, the base film and the functional layer are laminated with high adhesion via an easily soluble resin layer, and it can fully perform its function as a functional film. Therefore, it can be used as various functional films depending on the type of functional layer. Therefore, the laminated film of the present invention is a laminated film having the same functionality as conventional functional films, and the substrate can be recovered and recycled, making it an extremely useful film that combines functionality and environmental performance.

Claims

1. The base film has a functional layer on at least one surface via an easily soluble resin layer, The readily soluble resin layer contains a polyester component, The polyester component comprises, as an acid component, (A) terephthalic acid, (B) a dicarboxylic acid having a sulfonic acid base, and (C) other dicarboxylic acids, and the content ratio (mol%) of component (C) in the total acid component in the easily soluble resin layer is 3.0 to 8.0 times the content ratio (mol%) of component (B). The content of component (B) in the total acid components is 3 to 7 mol%, The functional layer is a silicone release layer. Recyclable laminated film.

2. The recyclable laminated film according to claim 1, wherein the component (B) is sodium 5-sulfoisophthalate.

3. The recyclable laminated film according to claim 1 or 2, wherein the (C) component comprises at least isophthalic acid.

4. The recyclable laminated film according to any one of claims 1 to 3, wherein the easily soluble resin layer is soluble in both water and an alkaline aqueous solution.

5. The recyclable laminated film according to any one of claims 1 to 4, wherein the easily soluble resin layer dissolves by immersion in either of the following solvents (i) or (ii) for 20 minutes. (i) Water at 90°C (ii) 2% by mass aqueous solution of sodium hydroxide at 90°C

6. A method for removing a functional layer, comprising washing a recyclable laminated film according to any one of claims 1 to 5 with a cleaning agent to dissolve the easily soluble resin layer, and removing the functional layer together with the easily soluble resin layer from the base film.

7. The method for removing a functional layer according to claim 6, wherein the cleaning agent is water or an alkaline aqueous solution.

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