JP7676155B2 - Method for recycling film and recycled film - Google Patents

Description

The present invention relates to a method for recycling film and recycled film.

Films are used in a variety of industrial fields. In recent years, the evolution of the Internet of Things (IoT) has led to a rapid increase in electronic devices such as CPUs installed in computers and smartphones, and as a result, the number of multilayer ceramic capacitors (MLCCs), which are important for driving electronic devices, has also increased explosively. The general method of manufacturing MLCCs is to laminate ceramic green sheets and electrodes on a release film that has a release layer on a base film, dry and harden the laminate, peel the laminate from the release film, stack multiple layers, and sinter. In this process, the release film is discarded as unnecessary material during the process.

In other words, the recent explosive increase in the number of MLCCs has resulted in an increase in the amount of release films discarded as unnecessary material, which is placing a strain on the environment and is becoming an issue. From the standpoint of releasability, the components of the release layer contained in the release film used in the manufacturing process of MLCCs generally have a different composition from the components that make up the film. Therefore, when a release film with a release layer is reused as is, or when a method of remelting a release film with a release layer and reusing it as a molded body containing a film (hereinafter sometimes referred to as material recycling) is carried out, the components of the release layer are present as foreign matter and therefore may not be able to be reused.

In addition, amid the social changes of "living with COVID-19," the demand for tablets, notebook PCs, displays, and other items is growing due to an increase in remote work, and so is the demand for polarizing film, a component of LCD monitors. Polarizing films are generally made of laminates made of polyvinyl alcohol resin and triacetyl cellulose resin. To reduce damage to such laminates during the manufacturing process of LCD monitors, it is common for a protective film to be attached to the laminate.

This method of manufacturing a protective film generally involves a process of using a release film for processing as a step of forming an adhesive on one side of the protective film for laminating it with a polarizing film. That is, the process is such that an adhesive is applied to the release surface of the release film for processing, which is then laminated to one side of the protective film, and the release film for processing is peeled off to transfer the adhesive to one side of the protective film. The release film for processing used in the adhesive formation step, like the release film used in the manufacturing process of MLCCs, may not be able to be reused as it is when the release film with the release layer is reused as is or when material recycling is carried out because the components of the release layer are present as foreign matter.

Patent Document 1 discloses a technique in which wax is kneaded into a film and used as a release film without providing a release layer. Patent Document 2 discloses a method in which a release film having a release layer is cleaned with a metal brush and the film is reused after the release layer is removed. Patent Document 3 discloses a method in which a water-soluble resin layer is provided between the release layer and the polyester film, and the release layer is removed by washing with water, and then the film is reused.

International Publication No. WO 2013/15260 JP 2012-171276 A Patent Publication No. 4284936

However, none of the documents describe a recycling method that includes a step of measuring the amount of impurities, and there is a concern that depending on the amount of impurities contained in the used film, there may be too much foreign matter to reuse the film.

In order to solve the above problems, the present invention has the following configuration.
[I] A method for reusing film, comprising the steps of measuring the amount of impurities in a used film, and performing any one of material recycling, chemical recycling, and thermal recycling.
[II] The method for recycling a film according to [I], wherein the used film is a film that has been used as a base film for release.
[III] The method for recycling a film described in [I] or [II], wherein the used film is a film in which a release layer is provided on at least one side of the film, a releaseable layer is then provided on the release layer of the film having the release layer, the releaseable layer is then released from the film having the release layer and the release layer, and the residue of the releaseable layer and the release layer are then removed from the film having the release layer from which the releaseable layer has been released.
[IV] The method for recycling a film according to any one of [I] to [III], wherein the removal of the residue of the release layer and the release layer is carried out using one or more of light, water, and a solvent.
[V] A method for recycling a film described in [III] or [IV], wherein the step of measuring the amount of impurities in the used film includes a step of measuring the residue of the release layer and the residue of the release layer contained in the used film.
[VI] A method for recycling film described in any one of claims [I] to [V], comprising, after the step of measuring the amount of impurities in the used film, a step of determining whether to perform material recycling, chemical recycling, or thermal recycling based on the amount of impurities.
[VII] A method for recycling film described in any of [I] to [VI], wherein the amount of impurities in the used film is 0.001% by weight or more and 0.2% by weight or less when the total weight of the used film is 100% by weight, and the method includes a step of performing material recycling.
[VIII] A recycled film obtained using raw materials obtained by material recycling used film, wherein the amount of impurities in the used film is 0.001% by weight or more and 0.2% by weight or less when the total weight of the used film is 100% by weight.
[IX] A recycled film obtained using raw materials recycled from used films, in which the amount of barium titanate contained in the recycled film is 0.001% by weight or more and 0.2% by weight or less when the weight of the entire recycled film is 100% by weight.
[X] The recycled film according to [VIII] or [IX], wherein the used film is a film used as a base film for release.
[XI] The recycled film according to [VIII] to [X], wherein the raw material is obtained by material recycling including a process of melting used film at a shear rate of 25 sec ⁻¹ or more and 250 sec ⁻¹ or less.
[XII] The recycled film according to any one of [VIII] to [XI], which is used for release purposes.

According to the present invention, the environmental impact can be reduced by reusing used film.

The present invention will be described in detail below with specific examples.

The present invention is a method for recycling film that includes a step of measuring the amount of impurities in used film and a step of performing either material recycling, chemical recycling, or thermal recycling.

In the present invention, the film is preferably a polyester film from the viewpoint of the diversity of uses and depolymerization properties. A polyester is a material having a dicarboxylic acid component and a diol component. In this specification, the component refers to the smallest unit that can be obtained by hydrolysis of a polyester. Examples of the dicarboxylic acid component that constitutes such a polyester include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid, or ester derivatives thereof.

The diol components constituting such polyesters include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol, alicyclic diols such as cyclohexanedimethanol and spiroglycol, and diols in which multiple units of the above-mentioned diols are linked together. Among these, from the viewpoint of mechanical properties and transparency, polyesters in which polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and PET dicarboxylic acid components are copolymerized with isophthalic acid or naphthalenedicarboxylic acid, and PET diol components are copolymerized with cyclohexanedimethanol, spiroglycol, or diethylene glycol are copolymerized with a portion of the PET diol components are preferably used.

In the present invention, a used film refers to a film that has been used as a product for a specific purpose. By reusing a film that has lost its performance as a result of being used as a product for a specific purpose and would otherwise be discarded, it is possible to reduce the environmental burden. Examples of used films include substrate films for release, such as substrates for used adhesive tapes, release papers for adhesive tapes, and films for product manufacturing processes. Among these, films for product manufacturing processes, particularly release films for MLCC manufacturing processes and polarizing film manufacturing processes, have been used in increasing amounts in recent years, and are therefore preferable because recycling them can reduce the amount of waste and lead to reduced environmental burden. When recycling release films for MLCC manufacturing processes, it is preferable to recycle the substrate film, which is the largest component of the release film, because this can greatly contribute to reducing the environmental burden.

In general, recycling of used films includes the above-mentioned material recycling (a method of reusing used films as they are, or a method of reusing used films as molded bodies after remelting them), as well as a method of burning used films to use them as thermal energy (hereinafter sometimes referred to as thermal recycling), and a method of reusing used films as polymers by purifying the polymer building blocks by depolymerizing the used films and repolymerizing them (hereinafter sometimes referred to as chemical recycling). An example of a chemical recycling method is the method described in JP 2009-167266 A. In the recycling method of the present invention, either method may be used for recycling, but in thermal recycling, there is a concern that carbon dioxide will be generated by combustion, which will have an environmental impact, and in chemical recycling, there is a concern that the number of steps required before recycling will increase, which will reduce the recycling rate. From the viewpoint of reducing the environmental load, it is preferable to recycle used films as materials, but on the other hand, if used films containing a large amount of impurities are recycled as materials, problems such as the generation of foreign matter will occur. Compared to material recycling, chemical recycling can be used even when the used film contains a large amount of impurities, and thermal recycling can be used even when the used film contains even more impurities. When recycling used film, the amount of impurities that may have a negative effect is measured, and the type of recycling to be performed is selected based on the amount of impurities. For used film with an impurity content that is suitable for material recycling, material recycling can be used, which greatly reduces the environmental impact.

The film recycling method of the present invention must include a step of measuring the amount of impurities in the used film. By measuring the amount of impurities in the used film, it is possible to select an appropriate recycling method depending on the amount of impurities, for example, and to recycle the film efficiently. This step may be performed immediately after obtaining the used film, or immediately before a step of material recycling, chemical recycling, or thermal recycling, or both.

In addition, the method for recycling the film of the present invention must include a step of either material recycling, chemical recycling, or thermal recycling. By carrying out any of these recycling methods, it is possible to reuse used film that would otherwise have been discarded, thereby reducing the environmental burden.

In the present invention, the used film is not particularly limited in terms of how it has been used, but if it has been used as a base film for release, it is preferable since it is a film that would otherwise be discarded, and therefore leads to a reduction in the environmental load. A base film for release is used by providing a release layer on at least one side of the base film, then providing a release layer on the release layer of the film having the release layer, and then releasing the release layer from the film having the release layer and the release layer, and the base film with the release layer provided thereon is often discarded after the process of releasing the release layer.

When the used film is a release film for use in the MLCC manufacturing process or polarizing film manufacturing process, the release layer generally uses an alkyd resin-based release agent, a polyolefin-based release agent, a long-chain alkyl group-containing resin-based release agent, a fluorine-based release agent, a silicone-based release agent, or a mixed or copolymer resin-based release agent of an organic system and a silicone system. In this case, when the base film is mainly composed of polyester, the release agent components all have molecular structures significantly different from polyester, so when a base film with a certain amount or more of the release agent component remaining is material recycled, it becomes a foreign matter and adversely affects the properties of the recycled film. In addition, when the used film is a release film for the MLCC manufacturing process, the material to be released is generally a metal such as barium titanate, which is the main component of the green sheet, or titanium, silver, platinum, or copper, which is the main component of the electrode. However, when the base film is mainly composed of polyester, the release agent components all have a molecular structure significantly different from that of polyester, so if the base film with a certain amount or more of the release agent components remaining is material recycled, it will become a foreign matter and adversely affect the properties of the recycled film. On the other hand, as will be described in detail later, when a recycled film recycled from used film as a raw material is used for release purposes, the effect of improving the release properties can be obtained by including a certain amount of such release agent components or release material components in the recycled film. Therefore, when recycling used film as a raw material, it is a preferable embodiment to include the release agent components to an extent that does not form foreign matter in the recycled film.

When the used film of the present invention is a base film for release, as described above, the residue of the release layer and the release layer become impurities in the base film, so it is preferable that the used film is a film from which the residue of the release layer and the release layer have been removed.

The method for removing the residue of the release layer and the release layer is not particularly limited. Examples include a method of removing the layer using one or more of light, water or an aqueous solution, and a solvent, and a method of scraping the layer off using physical force. As described in JP 2001-310970 A, a method of cutting a film having heterogeneous layers laminated thereon and washing the film in an alkaline solution generates an alkaline solution as waste liquid. Therefore, from the perspective of reducing the environmental load, it is preferable to remove the residue of the release layer and the release layer using light or water.

When removing the release layer and the release layer by light irradiation, it is preferable to provide a layer (absorption layer) between the base film and the release layer in advance, which absorbs the energy of the irradiated light and disappears by sublimation or evaporation. The absorption layer can be a combination of a sublimable dye such as vanadium phthalocyanine, a material that absorbs light such as aluminum or carbon black, and a self-decomposing material such as nitrocellulose. From the viewpoint of high energy impartation, a laser beam with an oscillation peak at a specific wavelength is preferably used as the irradiated light. It is also a preferred embodiment to select an oscillation peak in accordance with the absorption layer.

When the release layer and the release layer are removed by washing with water, a method is preferably used in which a layer containing a water-soluble component is provided in advance between the base film and the release layer, or a method is used in which a water-soluble component is included in the release layer. Examples of the water-soluble component include starch and polyvinyl alcohol. Since the used film of the present invention is used as a film for processing, polyvinyl alcohol having heat resistance and solvent resistance is preferably used as the water-soluble component. When polyvinyl alcohol is used as the water-soluble component, it is also effective to use polyvinyl alcohol with low crystallinity in order to improve the solubility in water. Examples of polyvinyl alcohol with low crystallinity include those with a saponification degree of 50 to 80, those with a polymerization degree of 500 or less, those with a bulky side chain group such as an ethanediol group, and combinations thereof.

The used film from which the release layer and the release layer have been removed by the above-mentioned method (hereinafter, sometimes referred to as the used film after cleaning) is preferably subjected to a step of measuring the amount of impurities contained in the film. When the used film is a process release film, the residue of the release material and the release layer are measured as impurities. Furthermore, in view of the characteristics of the above-mentioned recycling method, it is preferable to include a step of determining whether to perform material recycling, chemical recycling, or thermal recycling depending on the amount of impurities contained in the used film. By including this step, it is preferable to be able to reduce the environmental load and to efficiently carry out recycling. In particular, if the amount of impurities in the used film is 0.001% by weight or more and 0.2% by weight or less when the weight of the entire used film is taken as 100% by weight, it is preferable from the viewpoint of recycling efficiency and load reduction to reuse the used film by a recycling method including a step of performing material recycling.

If the amount of impurities exceeds 0.2% by weight when the total weight of the used film is taken as 100% by weight, the recycled film obtained by material recycling will contain a lot of foreign matter, and it may be difficult to obtain the desired characteristics. If material recycling is a method in which used film is used as the recycled film as is, a lot of foreign matter will also be generated on the film surface, and if it is used as, for example, a base material for a release film, the release properties may not be sufficient. Furthermore, if material recycling is a method in which used film is melted again and used as a raw material, the raw material may deteriorate, or other raw materials mixed with the raw material may also deteriorate, making it impossible to form it into a film.

On the other hand, if an attempt is made to reduce the amount of impurities to less than 0.001% by weight when the total weight of the used film is taken as 100% by weight, the damage to the base film caused by the process of removing the impurities will be so great that the mechanical strength of the recycled film may decrease or it may not be able to withstand remelting.

In addition, when the used film is a release film used in the manufacturing process of MLCC, the impurities contained in the film include barium titanate, which is a component of the material to be released, and silicone, which is a component of the release agent. If a recycled film is obtained by material recycling using a used film containing a large amount of such release agent components or material to be released as a raw material, a problem occurs in that a large amount of foreign matter is generated. However, if a used film containing a very small amount of release agent components or material to be released is used as a raw material for material recycling, the releasability of the resulting recycled film is improved. Therefore, it is preferable that the amount of barium titanate contained in the used film is 0.001% by weight or more and 0.2% by weight or less.

In addition, a preferred embodiment of the present invention is a recycled film that is material recycled using used film as a raw material, and the amount of impurities in the used film is 0.001% by weight or more and 0.2% by weight or less when the weight of the entire used film is taken as 100% by weight. In particular, when the recycled film is material recycled using used film that was used as a base film for release, it is preferable to use such a recycled film for release purposes (for example, as a base film for release), because it can maintain mechanical properties and provide good releasability.

In particular, when a used film used as a base film for release in the manufacturing process of MLCC is used as the raw material of the recycled film, the composition contained as impurities includes barium titanate, which is a component to be released, and silicone, which is a releasing component. Since barium titanate is an inorganic substance, when it is present in a small amount in the film, it can be dispersed in the film and play a role as a lubricant. Furthermore, since silicone is present in a film form as a release layer, when it is present in a small amount in the film, the silicone present on the film surface becomes the starting point of surface unevenness, improving the releasability. In particular, when a used film used as a base film for release is used as the raw material of the recycled film and is material recycled by a process of melting the film at a shear rate of 25 sec ^-1 or more and 250 sec ^-1 or less, barium titanate and silicone are dispersed in a uniform and fine shape, which is preferable from the viewpoint of improving the release properties of the recycled film. A more preferable shear rate is 40 sec ^-1 or more and 180 sec ^-1 or less.

The impurities contained in the recycled film are preferably barium titanate and silicone, but it does not matter if the film contains both or just one of them.

In particular, barium titanate is preferably contained since it is an inorganic substance and therefore easily disperses in the film and acts as a lubricant, and its content is preferably 0.001% by weight or more and 0.2% by weight or less.

[Method of evaluating characteristics]
A. Amount of impurities in the film (wt%)
The film is cut into pieces of 1 cm square or less, fed into an extruder with vent holes, melted and extruded at 290°C under reduced pressure of 200 torr or less, and molded into chips. A predetermined amount A (g) of the chips is weighed out, melted again at 290°C, and then filtered through a 400 mesh filter. After the predetermined amount has been poured, the filter is washed with OCP (orthochlorophenol) to dissolve the polymer, and only the components insoluble in OCP are taken out and dried at 100°C for 1 hour, after which the weight B (g) is weighed out, and B is divided by A to obtain a percentage to determine the amount of impurities in the film.

B. Recycling yield (%)
The used film is stored for one week in a warehouse with humidity controlled at 50°C and 30% RH, and then its weight is measured and designated as W1. When the used film is subjected to a process for removing the release object and the release layer, the film after the process (the used film after cleaning) is designated as W1.
Then, the weight of the composition obtained by recycling is measured using the used film. In the case of material recycling in which the used film or the used film after washing is reused as it is, the weight of the film is measured after storing it in a warehouse with humidity controlled at 50°C and 30% RH for one week, and this weight is designated as W2. In the case of material recycling in which the used film or the used film after washing is melted again and molded into a film, the weight of the molded film is measured after storing it in a warehouse with humidity controlled at 50°C and 30% RH for one week, and this weight is designated as W3. The obtained W2 or W3 is divided by W1 to obtain a percentage, which is designated as the recycling yield.
In the case of chemical recycling, the weight of the constituent components (monomer composition) of the obtained polyester is measured, and the weight of the polyester converted from the measured weight is calculated and designated as W4. W4 is then divided by W1 to obtain a percentage, which is the recycling yield.
In the case of thermal recycling, since no usable composition is obtained after recycling, the recycling yield is set to 0%.

C. Release film peel strength (N/m)
A polyester adhesive tape (No. 31B, width 19 mm, manufactured by Nitto Denko Corporation) is attached to the release layer side of the release film, and the 180° peel strength is measured using VPA-H200 manufactured by Kyowa Interface Science Co., Ltd. The obtained value is converted to N/m and evaluated as follows.

A: Peel strength is 0.55 mN/m or less B: Peel strength is more than 0.55 mN/m and 0.70 mN or less C: Peel strength is more than 0.70 mN/m D. Content of barium titanate A sample is weighed out, decomposed under pressure with nitric acid, hydrofluoric acid and perchloric acid, then heated and concentrated, and dissolved by heating in dilute nitric acid to a constant volume. The amount of barium element and titanium element in this solution is measured using an ICP emission spectrometer (Hitachi High-Tech Science PS3520VDDII), the content in the sample is calculated, and converted into the amount of barium titanate.

If the sample is in the form of a film roll, cut it into a rectangle whose long side is the entire length of the film in the width direction to use as the sample.

The present invention will be described below with reference to examples, but the present invention is not necessarily limited to these. In the following, Examples 1 to 6 and 8 to 10 shall be read as Reference Examples 1 to 6 and 8 to 10.

[Production of Coating A] 100 parts by weight of an addition reaction type silicone resin release agent (manufactured by Toray Dow Corning Silicone Co., Ltd. under the trade name LTC750A) and 2 parts by weight of a platinum catalyst (manufactured by Toray Dow Corning Silicone Co., Ltd. under the trade name SRX212) were mixed in toluene as a solvent to obtain a solid content of 5% by weight, to obtain Coating A.

[Production of Coating B] Polyvinyl alcohol "Kuraray Poval (registered trademark)" 5-74 (saponification degree 74, polymerization degree 500) manufactured by Kuraray Co., Ltd. was dissolved in water to a concentration of 2% by weight to obtain Coating B.

[Production of Coating Agent C] Coating Agent C was obtained by mixing 55 parts by weight of "Clear Lacquer (registered trademark)" manufactured by Washin Paint Co., Ltd. as a coating agent containing nitrocellulose, 5 parts by weight of FDN-010 (phthalocyanine vanadium, sublimation temperature 340°C) manufactured by Yamada Chemical Co., Ltd. as a light absorbing material, 20 parts by weight of Epicoat 828 manufactured by Mitsubishi Chemical Corporation as an epoxy resin, 19 parts by weight of melamine resin ("U-Ban (registered trademark)" 2061 manufactured by Mitsui Chemicals, Inc.) as a hardener, and 1 part by weight of catalyst (Light Ester PM manufactured by Kyoei Chemical Co., Ltd.).

[Production of dielectric paste A] 100 parts by weight of barium titanate (manufactured by Fuji Titanium Industries Co., Ltd. under the trade name HPBT-1), 10 parts by weight of polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd. under the trade name BL-1), 5 parts by weight of dibutyl phthalate, and 60 parts by weight of toluene-ethanol (weight ratio 30:30) were mixed with glass beads having a number average particle size of 2 mm, mixed and dispersed in a jet mill for 20 hours, and then filtered to produce a paste-like dielectric paste.

[Production of Coating D] Polyvinyl alcohol "GOHSENOL (registered trademark)" OKS8089 (degree of saponification 88, degree of polymerization 500, ethanediol group introduced into the side chain group) manufactured by Mitsubishi Chemical Corporation was dissolved in water to a concentration of 2% by weight to obtain Coating D.

[Production of Coating E] After adding 97 parts of butyl acrylate, 3 parts of acrylic acid, 0.2 parts of azobisisobutyronitrile as a polymerization initiator, and 233 parts of ethyl acetate, nitrogen gas was introduced and the mixture was substituted with nitrogen for about 1 hour while stirring. The flask was then heated to 60°C and reacted for 7 hours to obtain an acrylic polymer with a weight average molecular weight (Mw) of 1.1 million. To this acrylic polymer solution (solid content of 100 parts by weight), 0.8 parts by weight of trimethylolpropane tolylene diisocyanate (product name "Coronate L", manufactured by Nippon Polyurethane Industry Co., Ltd.) as an isocyanate crosslinking agent and 0.1 parts of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) were added to prepare a pressure-sensitive adhesive composition (Coating E).

[Production of PET-A] Terephthalic acid and ethylene glycol were polymerized in the usual manner using antimony trioxide as a catalyst to obtain melt-polymerized PET. The resulting melt-polymerized PET had a glass transition temperature of 81°C, a melting point of 255°C, an intrinsic viscosity of 0.62, and a terminal carboxyl group content of 20 eq./t.

[Production of PET-1] PET-A was vacuum dried at 160°C for 2 hours, then fed into an extruder, melted at 280°C, and extruded through a die onto a casting drum with a surface temperature of 25°C to produce an unstretched sheet. The sheet was then preheated with a heated roll group, stretched 3.8 times in the longitudinal direction (MD direction) at a temperature of 90°C, and cooled with a roll group at a temperature of 25°C to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it was stretched 4.0 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 110°C in a tenter. It was then heat-set for 10 seconds at a temperature of 230°C in a heat treatment zone in the tenter. It was then uniformly cooled in the cooling zone, wound up, and a film (PET-1) with a thickness of 30 μm was obtained.

[Production of PET-2] PET-A was vacuum dried at 160°C for 2 hours, then fed into an extruder, melted at 280°C, and extruded through a die onto a casting drum with a surface temperature of 25°C to produce an unstretched sheet. The sheet was then preheated with a heated roll group, stretched 3.8 times in the longitudinal direction (MD direction) at a temperature of 90°C, and then cooled with a roll group at a temperature of 25°C to obtain a uniaxially stretched film. The obtained uniaxially stretched film was coated with coating agent B using a Mayer bar so that the thickness after stretching and drying would be 0.1 μm, and then stretched 4.0 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 110°C in a tenter while holding both ends of the film with clips. The film was then heat-set for 10 seconds at a temperature of 230°C in a heat treatment zone in the tenter. The film was then uniformly cooled in the cooling zone and wound up to obtain a film (PET-2) with a thickness of 30 μm.

[Production of PET-3] Coating agent C was applied to one side of PET-1 using a gravure coater so that the coating thickness after drying would be 0.1 μm, and the film was obtained by drying and curing at 100°C for 20 seconds.

[Production of PET-4] PET-A was vacuum dried at 160°C for 2 hours, then fed into an extruder, melted at 280°C, and extruded through a die onto a casting drum with a surface temperature of 25°C to produce an unstretched sheet. The sheet was then preheated with a heated roll group, stretched 3.8 times in the longitudinal direction (MD direction) at a temperature of 90°C, and then cooled with a roll group at a temperature of 25°C to obtain a uniaxially stretched film. The obtained uniaxially stretched film was coated with coating agent D using a Mayer bar so that the thickness after stretching and drying would be 0.1 μm, and then stretched 4.0 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 110°C in a tenter while holding both ends of the film with clips. The film was then heat-set for 10 seconds at a temperature of 230°C in a heat treatment zone in the tenter. The film was then uniformly cooled in the cooling zone and wound up to obtain a film (PET-2) with a thickness of 30 μm.

Example 1
PET-1 was used as the base film, and one side of the PET-1 was coated with coating agent A by gravure coating so that the coating thickness after drying would be 0.1 μm, to obtain a release film roll. Dielectric paste A was applied as the release object to the obtained release film by die coating so that the thickness after drying would be 1.0 μm. Thereafter, the dielectric was released from the obtained laminate, and a used film roll was obtained from which the release object had been peeled off.

The resulting used roll was cut and weighed to measure the amount of impurities. Since the amount of impurities was 0.3% by weight, thermal recycling was selected as the recycling method, and recycling was carried out. The recycling yield was 0%.

Example 2
Chemical recycling was selected as a recycling method for the used film obtained in the same manner as in Example 1, and chemical recycling was performed by the method described in JP 2009-167266 A to obtain terephthalic acid. The yield of the obtained terephthalic acid was 62% based on the amount converted to PET.

Example 3
Material recycling was selected as the recycling method for the used film obtained in the same manner as in Example 1, and the used film was cut and washed with an aqueous sodium hydroxide solution according to the method described in JP-A-2001-310970 to obtain the washed used film, and the amount of impurities in the washed used film was measured. The washed used film was then dried at 160°C for 2 hours under a reduced pressure of 200 torr or less, and then fed into a melt extruder and melt extruded at 280°C. The shear rate during extrusion was 45 sec ^-1 .

The obtained molten material was extruded through a die onto a casting drum with a surface temperature of 25°C to produce an unstretched sheet. The sheet was then preheated with a group of heated rolls, stretched 3.8 times in the longitudinal direction (MD direction) at a temperature of 90°C, and then cooled with a group of rolls at a temperature of 25°C to obtain a uniaxially stretched film. The obtained uniaxially stretched film was stretched 4.0 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 110°C in a tenter while holding both ends with clips. Further, heat fixing was performed for 10 seconds at a temperature of 230°C in a heat treatment zone in the tenter. Next, after uniformly cooling in the cooling zone, it was wound up to obtain a film roll with a thickness of 30 μm. The recycling rate was evaluated from the weight of the obtained film roll. Furthermore, the obtained film roll was coated with coating agent A by a gravure coating method so that the coating thickness after drying was 0.1 μm, and a release film roll was obtained. The physical properties of the obtained release film are shown in Table. The film had slightly poor releasability.

Example 4
The used film roll obtained in the same manner as in Example 1 was introduced into a water washing device equipped with a drying furnace having an unwinding and winding device, and washed while immersed in 100°C water for 2 minutes under a tension of 30 N/m, and then dried at 120°C for 2 minutes to obtain a washed used film roll. The amount of impurities in this washed used film roll was measured, and since the amount of impurities was 0.3% by weight, thermal recycling was selected as the recycling method, and recycling was performed. The recycling yield was 0%.

Example 5
A used film roll was obtained in the same manner as in Example 1, except that PET-2 was used as the base film, and the amount of impurities was measured. Since the amount of impurities was 0.3% by weight, thermal recycling was selected as the recycling method, and recycling was performed. The recycling yield was 0%.

Example 6
A used film roll after washing was obtained in the same manner as in Example 4, except that PET-2 was used as the base film. 1.0 kg of this used film roll after washing was weighed and cut, and the amount of impurities was measured. The amount of impurities was 0.01% by weight. The recycling rate was calculated from the weight of the film roll after washing obtained, and the film was used as a base material and coated by gravure coating so that the coating thickness after drying was 0.1 μm, to obtain a release film roll. The physical properties of the obtained release film are shown in the table. The film had excellent release properties.

(Example 7)
From the used film roll after washing obtained in the same manner as in Example 6, 1.0 kg was weighed and cut, and the amount of impurities was measured. Since the amount of impurities was 0.01% by weight, the used film roll after washing was all cut and dried at 160°C for 2 hours under reduced pressure of 200 torr or less, and then fed into a melt extruder and melt extruded at 280°C. The shear rate during extrusion was 45 sec ^-1 .

The obtained molten material was extruded through a die onto a casting drum with a surface temperature of 25°C to produce an unstretched sheet. The sheet was then preheated with a group of heated rolls, stretched 3.8 times in the longitudinal direction (MD direction) at a temperature of 90°C, and then cooled with a group of rolls at a temperature of 25°C to obtain a uniaxially stretched film. The obtained uniaxially stretched film was stretched 4.0 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 110°C in a tenter while holding both ends with clips. Further, heat fixing was performed for 10 seconds at a temperature of 230°C in a heat treatment zone in the tenter. Next, after uniformly cooling in the cooling zone, it was wound up to obtain a film roll with a thickness of 30 μm. The recycling rate was evaluated from the weight of the obtained film roll. Furthermore, the obtained film roll was coated with coating agent A by a gravure coating method so that the coating thickness after drying was 0.1 μm, and a release film roll was obtained. The physical properties of the obtained release film are shown in Table. The film had excellent release properties.

(Example 8)
A used film roll was obtained in the same manner as in Example 1, except that PET-3 was used as the substrate. The film roll was irradiated with a continuous wave laser beam having a wavelength of 1064 nm and an intensity of 20 W over the entire width of the film from the side having the release layer and the residue of the released material between the unwinding and winding devices, using a laser marker MDX1500 manufactured by Keyence Corporation. The used film roll irradiated with this light was introduced into a water washing device equipped with a drying furnace having an unwinding and winding device, washed while immersed in water at 100°C for 2 minutes under a tension of 30 N/m, and then dried at 120°C for 2 minutes to obtain a used film roll after washing. The amount of impurities in the used film after washing was measured, and since the amount of impurities was 0.08% by weight, the used film roll after washing was all cut, dried at 160°C for 2 hours under a reduced pressure of 200 torr or less, and introduced into a melt extruder and melt extruded at 280°C. The shear rate during extrusion was 45 sec ^-1 .

The obtained molten material was extruded through a die onto a casting drum with a surface temperature of 25°C to produce an unstretched sheet. The sheet was then preheated with a group of heated rolls, stretched 3.8 times in the longitudinal direction (MD direction) at a temperature of 90°C, and then cooled with a group of rolls at a temperature of 25°C to obtain a uniaxially stretched film. The obtained uniaxially stretched film was stretched 4.0 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 110°C in a tenter while holding both ends with clips. Further, heat fixing was performed for 10 seconds at a temperature of 230°C in a heat treatment zone in the tenter. Next, after uniformly cooling in the cooling zone, it was wound up to obtain a film roll with a thickness of 30 μm. The recycling rate was evaluated from the weight of the obtained film roll. Furthermore, the obtained film roll was coated with coating agent A by a gravure coating method so that the coating thickness after drying was 0.1 μm, and a release film roll was obtained. The physical properties of the obtained release film are shown in Table. The film had excellent release properties.

(Example 9)
PET-4 was used as the base film, and one side of the PET-4 was coated with coating agent A by gravure coating so that the coating thickness after drying would be 0.1 μm, to obtain a release film roll. Coating agent E was applied to the obtained release film by die coating so that the thickness after drying would be 20 μm. Thereafter, the obtained laminate was attached to a protective PET film for the polarizing film, and then only the release film was peeled off so that coating agent E was transferred to one side of the protective PET film, to obtain a used film roll.

The obtained used film roll was introduced into a water washing device equipped with a drying furnace having an unwinding and winding device, washed while immersed in 100°C water for 2 minutes under a tension of 30 N/m, and then dried at 120°C for 2 minutes to obtain a washed used film roll. 1.0 kg was weighed from this washed used film roll, cut, and the amount of impurities was measured. Since the amount of impurities was 0.02% by weight, all the washed used film roll was cut, dried at 160°C for 2 hours under a reduced pressure of 200 torr or less, and introduced into a melt extruder and melt extruded at 280°C. The shear rate during extrusion was 45 sec ^-1 .

The obtained molten material was extruded through a die onto a casting drum with a surface temperature of 25°C to produce an unstretched sheet. The sheet was then preheated with a group of heated rolls, stretched 3.8 times in the longitudinal direction (MD direction) at a temperature of 90°C, and then cooled with a group of rolls at a temperature of 25°C to obtain a uniaxially stretched film. The obtained uniaxially stretched film was stretched 4.0 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 110°C in a tenter while holding both ends with clips. Further, heat fixing was performed for 10 seconds at a temperature of 230°C in a heat treatment zone in the tenter. Next, after uniformly cooling in the cooling zone, it was wound up to obtain a film roll with a thickness of 30 μm. The recycling rate was evaluated from the weight of the obtained film roll. Furthermore, the obtained film roll was coated with coating agent A by a gravure coating method so that the coating thickness after drying was 0.1 μm, and a release film roll was obtained. The physical properties of the obtained release film are shown in Table. The film had excellent release properties.

(Example 10)
A used film roll (impurity content: 0.08% by weight) after washing obtained in the same manner as in Example 8 was cut, dried at 160° C. for 2 hours under a reduced pressure of 200 torr or less, and then fed into a melt extruder and melt extruded at 280° C. The shear rate during extrusion was 10 sec ^-1 .

The obtained molten material was extruded through a die onto a casting drum with a surface temperature of 25°C to produce an unstretched sheet. The sheet was then preheated with a group of heated rolls, stretched 3.8 times in the longitudinal direction (MD direction) at a temperature of 90°C, and then cooled with a group of rolls at a temperature of 25°C to obtain a uniaxially stretched film. The obtained uniaxially stretched film was stretched 4.0 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 110°C in a tenter while holding both ends with clips. Further, heat fixing was performed for 10 seconds at a temperature of 230°C in a heat treatment zone in the tenter. Next, after uniformly cooling in the cooling zone, it was wound up to obtain a film roll with a thickness of 30 μm. The recycling rate was evaluated from the weight of the obtained film roll. Furthermore, the obtained film roll was coated with coating agent A by a gravure coating method so that the coating thickness after drying was 0.1 μm, and a release film roll was obtained. The physical properties of the obtained release film are shown in Table. The shear rate during melt extrusion was low, and the film had somewhat poor releasability.

(Comparative Example 1)
The amount of impurities in the used film roll obtained in the same manner as in Example 1 was not measured, and material recycling was selected as the recycling method, and the used film roll was cut into pieces, dried at 160°C for 2 hours under a reduced pressure of 200 torr or less, and then fed into a melt extruder and melt extruded at 280°C. However, the polymer clogged the piping during extrusion, and could not be extruded. Since the amount of impurities was not measured, an appropriate recycling method could not be selected, and recycling was not possible.

Claims (1)

A method for producing a recycled film for use in release applications, obtained by using a raw material obtained by material recycling of used film, the used film being used as a base film for release of an object to be released, the used film containing barium titanate as a component, the used film being a film having a component soluble in water, the base film of the used film being a polyester film, the amount of impurities in the used film after washing being 0.001% by weight or more and 0.2% by weight or less when the weight of the entire used film is taken as 100% by weight, and the raw material being obtained by material recycling having a process including a process of washing the used film with water and a process of melting the used film at a shear rate during extrusion in a melt extruder of 25 sec ^-1 or more and 250 ^sec-1 or less.