Method for producing polyester base material

Abstract

To provide a method for producing a polyester base material that is less in deposition of a resin derived from a release layer while the release layer and a peeling layer are subjected to removal treatment, and can be formed into a pellet having the same quality as a pellet of a virgin product when the polyester base material is re-melted and formed into a pellet.SOLUTION: A method for producing a polyester base material includes: an alkali treatment step of bringing a laminate in which a release layer is laminated on at least one surface of a polyester base material through a release layer containing Si into contact with an alkaline treatment liquid, and thereby peeling the release layer and the peeling layer from the polyester base material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a polyester substrate by peeling off a release layer and a release layer from a laminate in which a release layer is laminated on at least one surface of a polyester substrate via a release layer. [Background technology]

[0002] In recent years, transfer printing and in-mold molding methods have been widely used as methods for decorating or modifying the surface of molded products and the like. In particular, a method has been proposed in which a porous layer is formed on a release substrate to impart not only a design but also a change in texture, and then the porous layer is transferred to an object to give the object not only a different appearance but also a leather-like feel. This method can be used, for example, in home appliances, mobile phones, mobile devices, building materials, furniture, stationery, and vehicle interior parts. For example, in Patent Document 1, the present inventors disclose a method in which a porous layer is formed on a release substrate by a wet coagulation method, and then the layer is peeled off to form an in-mold molding sheet.

[0003] In the process of manufacturing laminated polyester films for transfer or peeling, the film may not meet specifications after laminating a release layer and a layer to be peeled or transferred (hereinafter referred to as the release layer) onto the surface of the polyester substrate. Films that do not meet specifications are usually discarded, but for the sake of efficient resource utilization, it is desirable to remove the release layer and release layer from the polyester substrate and recycle the polyester substrate.

[0004] Patent Document 2 describes a method of removing a foreign layer formed on a synthetic resin substrate in an alkaline aqueous solution at 105°C or higher, and then treating the substrate with an aqueous solution containing 0.1% to 10% by mass of peroxide to remove the foreign layer. Specifically, a so-called batch method is adopted in which the substrate to be treated is first selected, and the entire synthetic resin substrate is pre-cut into chips of appropriate size and crushed, and then subjected to a predetermined alkaline treatment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-291089 [Patent Document 2] Patent No. 3270037 Summary of the Invention [Problem to be solved by the invention]

[0006] When peeling off the release layer from such a laminate in which the release layer is provided on the polyester substrate, the release layer is physically removed and then alkali-treated, which causes a problem of complicated processes. Furthermore, the release layer is usually made of a resin such as a silicone-based resin or an acrylic resin that is difficult to decompose, and is usually firmly adhered to the polyester film through easy adhesion, so that part of the release layer may remain attached to the surface of the polyester substrate. In particular, when a Si-based water repellent agent is used in the release layer, it is difficult to remove the release layer.

[0007] On the other hand, when recycling polyester substrates, the recovered polyester substrate is melted and molded into pellets, and the resulting pellets are then melted again to form a film. Therefore, if a release layer is attached to the surface of the polyester substrate to be recycled, it is thought that foreign matter from the release layer will be mixed into the recycled polyester substrate. However, no attention has been paid to these foreign matter mixed into the recycled polyester substrate. Furthermore, the quality of the recycled polyester substrate, such as the amount of foreign matter, has not been sufficient for use in the same high-precision applications as the raw polyester film.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a polyester base material, which is a polyester base material from which the release layer and peeling layer have been removed, but which has very little adhesion of resin originating from the release layer, and which can be remelted and pelletized to produce pellets having the same quality as virgin pellets. [Means for solving the problem]

[0009] The present invention is configured as follows. [1] A method for producing a polyester substrate, comprising: an alkaline treatment step of contacting a laminate having a release layer laminated on at least one surface of a polyester substrate via a release layer with an alkaline treatment liquid, thereby peeling the release layer and the release layer from the polyester substrate. [2] The method according to [1], further comprising a water-washing step of contacting the alkali-treated polyester substrate with water. [3] The manufacturing method according to [1], wherein the laminate is wound into a roll, further comprising a water-washing step of contacting the alkali-treated polyester substrate with water, and a winding step of winding the water-washed polyester substrate into a roll. [4] The method according to any one of [1] to [3], wherein the alkaline treatment step involves contacting the substrate with a 0.5 to 60 mass % alkaline treatment solution at a temperature of 70 to 150°C for 1 second to 180 minutes. [Effects of the Invention]

[0010] With the above-described configuration, according to the present invention, a polyester substrate can be produced from a laminate in which a release layer is laminated on at least one surface of a polyester substrate via a release layer. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of a roll-to-roll apparatus used in one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] When producing a polyester base material by peeling off the release layer and the release layer from a laminate in which a release layer is laminated on at least one surface of the polyester base material via a release layer, the release layer is first removed by mechanical means or the like, and then the release layer is removed by contacting the polyester base material to which the release layer is attached with an alkaline treatment solution, etc. However, the inventors of the present invention have investigated and found that even if the release layer is removed and then the polyester base material is subjected to alkaline treatment, the resin derived from the release layer still adheres to the polyester base material, and when polyester pellets are molded using a polyester base material with such resin attached, the pellets contain a lot of foreign matter, which causes a decrease in quality.

[0013] Therefore, the present inventors have conducted extensive research to ensure the release layer attached to the polyester substrate is reliably peeled off and removed. As a result, it has been found that, rather than removing the release layer and then carrying out an alkaline treatment, the release layer is peeled off from the polyester substrate by contacting the laminate with the release layer as it is with an alkaline treatment solution, and at this time, surprisingly, it has also been found that the release layer interposed between the polyester substrate and the release layer is easily removed together. Note that the reason why the release layer is easily removed by treating the laminate with the release layer as it is is not clear, but it is speculated that when the release layer is removed, the release layer is removed together with the laminate by a physical action.

[0014] The present invention will be described in detail below. Hereinafter, a polyester substrate having a release layer laminated on at least one surface thereof via a release layer will be referred to as a laminate, and a polyester substrate from which the release layer and the release layer have been peeled will be referred to as a removal-treated polyester substrate.

[0015] The method for producing a polyester substrate according to the present invention is characterized by including an alkaline treatment step in which a laminate having a release layer laminated on at least one surface of a polyester substrate via a release layer is brought into contact with an alkaline treatment liquid, thereby peeling the release layer and the release layer from the polyester substrate.

[0016] Examples of polyester substrates include polyethylene terephthalate (PET) film, polybutylene terephthalate (PBT) film, polyethylene naphthalate (PEN) film, polybutylene naphthalate (PBN) film, and polypropylene terephthalate (PPT) film, with PET film being preferred.

[0017] The thickness of the polyester substrate is not particularly limited, but is preferably 5 μm or more and 500 μm or less in consideration of handling, etc. The thickness is more preferably 7 μm or more, more preferably 400 μm or less, even more preferably 350 μm or less, and particularly preferably 300 μm or less.

[0018] Examples of the release layer include those commonly used as release layers, such as silicone resin, acrylic resin, polyolefin resin, and alkyd resin. Among them, a release layer formed using a water repellent agent containing silicone resin is preferred in the present invention. The thickness of the release layer is preferably 0.01 to 50 μm, more preferably 0.05 μm or more, and even more preferably 20 μm or less.

[0019] The release layer is provided on the release layer and is not particularly limited as long as it is peeled off for use. "Peeled and used" may mean either that the release layer is attached to the transfer target and then peeled off from the release layer on the polyester substrate, or that the release layer is peeled off separately from the release layer on the polyester substrate.

[0020] When an alkaline treatment is performed with the release layer laminated, the alkaline treatment solution penetrates through the release layer and acts on the release layer, promoting the removal of the entire release layer. Therefore, the release layer is preferably a porous layer. The porous layer referred to here is a layer having continuous through-holes. Examples of porous layers include those formed from resins or inorganic materials. Examples of porous layers include those manufactured using the following methods and materials. For example, if the purpose is surface modification, the porous layer can be appropriately selected to suit the intended texture and feel. Examples include those in which a resin is dissolved in a solvent and applied, followed by layer separation to form a porous layer, those in which fibrous fillers are bonded using a binder such as a resin, and those in which organic particles or inorganic particles are bonded using a binder such as a resin. Examples of resins include polyester resins, polyamide resins, polyurethane resins, styrene resins, acrylic resins, vinyl chloride resins, chlorinated polyethylene, polyolefin resins, vinyl acetate resins, butyral resins, and cellulose resins. Examples of fibrous fillers include polyester, acrylic, polyamide, polyurethane, cotton, hemp, palm, coconut fiber, wool, and silk. Examples of organic particles include styrene resin, acrylic resin, and melamine resin, as well as wood flour, cork powder, and charcoal particles. Examples of inorganic particles include silica, alumina, titanium oxide, talc, diatomaceous earth, sand, pumice powder, and oyster shell powder.

[0021] The thickness of the release layer (when there are multiple release layers, the total thickness of these layers) is preferably 0.001 μm or more. In order to effectively exert the predetermined function, the thickness of the release layer is more preferably 0.005 μm or more, and even more preferably 0.01 μm or more. On the other hand, by setting the thickness of the release layer to 50 μm or less, the release layer can be removed in a short time. The thickness of the release layer is more preferably 20 μm or less, even more preferably 10 μm or less, and particularly preferably 5 μm or less.

[0022] The above description concerns a laminate for surface modification, which is a suitable example to which the present invention can be applied. However, the present invention is not limited to this, and can be applied to laminates used for industrial purposes after peeling off the release layer, such as laminates used in the production of membranes, the production of thin electrode films for fuel cells and solid-state batteries, and the production of thin-film resin films or thin-film inorganic oxide sheets that serve as insulators for capacitors and laminated circuits.

[0023] A surface treatment layer may be laminated on the surface of the release layer in order to enhance affinity with the alkaline treatment solution. The surface modification treatment used to form the surface treatment layer can be a known method, such as corona treatment, plasma treatment, or flame treatment.

[0024] The term "contacting with an alkaline processing liquid" means, for example, contacting with an alkaline processing liquid of a predetermined concentration by methods such as immersion, coating, spraying, etc. "Contacting with an alkaline processing liquid" also includes heating the laminate by contacting it with a heated alkaline processing liquid.

[0025] The alkaline processing liquid contains an alkali source such as sodium hydroxide or potassium hydroxide. The alkali sources may be used alone or in combination of two or more. These alkali sources permeate from the release layer side, dissolve and swell the release layer, and have the effect of peeling (removing) the release layer from the polyester substrate. As the alkaline processing liquid, an aqueous solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferred, and an aqueous potassium hydroxide solution is more preferred.

[0026] The alkaline processing liquid may further contain an alkaline processing aid to improve the peeling efficiency of the release layer and the peeling layer. Examples of alkaline processing aids that are preferably used include those capable of increasing the heating temperature of the alkaline processing liquid, such as boiling point elevating agents. Examples include surfactants, water-soluble inorganic compounds, water-soluble organic compounds, and water-soluble solvents. Specific examples include nonionic surfactants, water-soluble inorganic salts, water-soluble organic salts, water-soluble polymers, polysaccharides, alcohols, glycols (ethylene glycol, diethylene glycol, propylene glycol, etc.), water-soluble organic solvents (dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethylene glycol ethers (various cellosolves)), and the like. Among these, glycols are preferred. These may be used alone or in combination.

[0027] The alkaline treatment conditions can be appropriately selected depending on the type, thickness, etc. of the polyester substrate, but for example, it is preferable to contact (e.g., immerse) the laminate in an alkaline treatment liquid of 0.5 to 60 mass % heated to a temperature of 70 to 150° C. for 1 second to 180 minutes. When the alkaline treatment liquid contains both an alkali source and an alkaline treatment aid, it is preferable to heat the alkaline treatment liquid containing these, the concentration of which is adjusted to 0.5 to 60 mass %, to a temperature of 70 to 150° C., and contact the laminate with this treatment liquid for 1 second to 180 minutes.

[0028] Under the alkaline treatment conditions described above, the release layer and peel layer can be sufficiently removed by setting the heating temperature of the alkaline treatment liquid to 70°C or higher. Furthermore, in the present invention, even if the alkaline treatment liquid has a high concentration within the above range, by increasing the temperature of the alkaline treatment liquid, it is possible to prevent the alkaline component from precipitating and the treatment liquid itself from solidifying. The heating temperature of the alkaline treatment liquid is more preferably 80°C or higher, even more preferably 90°C or higher, and particularly preferably 100°C or higher. On the other hand, by setting the heating temperature of the alkaline treatment liquid to 150°C or lower, it is possible to prevent deterioration of the release-treated polyester substrate due to contact with the alkaline treatment liquid. The heating temperature of the alkaline treatment liquid is more preferably 135°C or lower.

[0029] Under the above alkaline treatment conditions, the concentration of the alkaline treatment liquid (when the alkaline treatment liquid contains an alkali source and an alkaline treatment aid, the total concentration of these) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more. On the other hand, by setting the concentration of the alkaline treatment liquid to 60% by mass or less, deterioration of the release-treated polyester substrate can be prevented. The concentration of the alkaline treatment liquid is more preferably 55% by mass or less, even more preferably 50% by mass or less, particularly preferably 47% by mass or less, and most preferably 45% by mass or less.

[0030] Under the above alkaline treatment conditions, the peeling layer and the release layer can be sufficiently removed by contacting the alkaline treatment liquid for 1 second or more. The contact time is preferably 3 seconds or more, and more preferably 5 seconds or more. On the other hand, the contact time with the alkaline treatment liquid is preferably 180 minutes or less.

[0031] Among these alkaline treatment conditions, the concentration of the alkaline treatment solution and the contact time with the alkaline treatment solution may be appropriately selected depending on the alkaline treatment method, etc. Examples of alkaline treatment methods include a batch method in which the laminate is first cut into chips and then placed in a tank equipped with a stirring blade for alkaline treatment, and a roll-to-roll method in which a rolled laminate is unwound and then alkaline treatment is performed while still in the long form.

[0032] (batch method) In the case of a batch process, the concentration of the alkaline processing liquid is particularly preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. In the case of a batch process, the contact time with the alkaline processing liquid is long, and if the concentration of the alkaline processing liquid becomes too high, the polyester of the substrate may be decomposed. In the case of a batch process, the contact time with the alkaline processing liquid is particularly preferably 5 minutes or more, more preferably 10 minutes or more, even more preferably 15 minutes or more, and more preferably 150 minutes or less, even more preferably 120 minutes or less. In the case of a batch process, if the alkaline treatment is carried out multiple times, the total time is preferably within the above range. In the case of a batch process, the temperature of the alkaline treatment is as described above, but if the concentration of the alkaline processing liquid is low and the temperature cannot be increased, the temperature may be increased by applying pressure.

[0033] (Roll-to-roll method) In the case of the roll-to-roll system, the concentration of the alkaline treatment liquid is preferably 20% by mass or more, since this allows the release layer and the release layer to be peeled off in a short time to obtain a high-quality release-treated polyester substrate with little foreign matter. The concentration of the alkaline treatment liquid is more preferably 25% by mass or more, even more preferably 30% by mass or more, and particularly preferably 35% by mass or more. In the case of the roll-to-roll system, the contact time with the alkaline treatment liquid is preferably 120 seconds or less, which enables treatment using small, simple equipment (details will be described later). Specifically, this simplifies the transfer of the polyester substrate in the alkaline treatment tank, allowing the alkaline treatment tank to be made smaller, and the number of alkaline treatment tanks can be reduced, thereby enabling the overall equipment to be made smaller. The contact time is more preferably 90 seconds or less, even more preferably 60 seconds or less, and particularly preferably 40 seconds or less.

[0034] The number of alkali treatments is preferably 1 to 5 times, and more preferably 1 to 3 times. Here, one alkali treatment refers to the number of times the laminate is brought into contact with the alkaline treatment solution. When the laminate is immersed in the alkaline treatment solution, one treatment is counted as the period from immersion to removal from the alkaline treatment solution. When alkaline treatments are carried out multiple times using an alkaline treatment tank, the same alkaline treatment tank may be used, or separate alkaline treatment tanks may be used. Using separate alkaline treatment tanks provides greater flexibility in terms of equipment and is also preferred in terms of managing the alkaline treatment solution in the alkaline treatment tanks.

[0035] The alkali treatment may be carried out in combination with physical means such as brushing or ultrasonic treatment, if necessary.

[0036] In the alkaline treatment step, the release layer and peel layer peeled from the surface of the polyester substrate are present in the alkaline treatment liquid, and therefore it is preferable to carry out the alkaline treatment step while appropriately removing the release layer and peel layer from the alkaline treatment liquid.

[0037] The production method of the present invention preferably further comprises a water-washing step of bringing the alkali-treated polyester substrate into contact with water, which can remove the alkaline treatment solution adhering to the polyester substrate and the release layer and peel layer adhering in the alkali treatment step.

[0038] In the batch process, the chips after alkali treatment may be added to a separate tank equipped with an agitator for water washing, or the alkaline treatment solution may be extracted from the tank in which the alkali treatment was performed and water may be added. The contact time with water in the water washing step is the same as the preferred time for the alkali treatment. The water temperature and number of washes in the water washing step are in accordance with the batch process described below.

[0039] In the case of the roll-to-roll method, the method of contacting the alkali-treated polyester substrate with water is not particularly limited, and examples thereof include a method of immersing the alkali-treated polyester substrate in a water washing tank and a method of spraying water onto the alkali-treated polyester substrate, and it is preferable to use these methods in combination. In the water washing step, it is more preferable to spray water onto the polyester substrate. By spraying water, the alkaline treatment solution, release layer, and peel layer adhering to the polyester substrate can be efficiently removed. The method of spraying water is not particularly limited, and for example, water may be sprayed in a shower-like manner from a nozzle provided toward the polyester substrate.

[0040] The water washing conditions can be appropriately selected depending on the type and thickness of the polyester substrate. However, to obtain a high-quality release-treated polyester substrate with minimal foreign matter without extending the overall treatment time, it is preferable to contact the substrate with water at 90°C or below at least once. Using water at 90°C or below allows the release layer and peel layer to be washed and removed without damaging the polyester substrate. Furthermore, boiling of water can be prevented, allowing for safe and stable washing. The water washing temperature is more preferably 80°C or below, even more preferably 70°C or below. There is no particular lower limit for the water temperature, but it should be above 0°C because water solidifies below 0°C. The water temperature is more preferably 10°C or above, even more preferably room temperature (27°C) or above, and particularly preferably 40°C or above.

[0041] The number of water washes is preferably two or more, preferably five or less, and more preferably three or less. Here, one water wash refers to the number of times the polyester substrate is brought into contact with water. When the polyester substrate is immersed in water, one wash is counted from the time the substrate is immersed until it is removed. When spraying water onto the polyester substrate, for example, it refers to the number of times water is sprayed onto the polyester substrate from a nozzle. When multiple nozzles are arranged at intervals in the substrate transport direction, one wash is counted until the water is drained halfway. For example, when two nozzles are arranged at intervals in the substrate transport direction, the number of water washes is counted as one. When, for example, a mangle or the like is arranged between the nozzles to remove water adhering to the substrate, the number of water washes is counted as two. Furthermore, if the water sprayed onto the substrate is poured off into a water washing tank, the combination of the water spraying and the treatment in the water washing tank is counted as one wash.

[0042] When washing with water is performed two or more times, the water temperature may be the same or different for each wash. When the water washing temperature is changed, the water temperature for the (n+1)th wash may be higher or lower than the water temperature for the nth wash, and a lower temperature is preferred. Since the release layer and peel layer are easier to remove the higher the water temperature, the removal rate of the release layer and peel layer can be increased by contacting the alkali-treated polyester substrate with water at a relatively high temperature and then with water at a relatively low temperature.

[0043] The water used in the washing steps may contain a surfactant, an antifoaming agent, etc., but it is preferable that these agents not be added to the water used in the final washing step.

[0044] Although the contact time with water is not particularly limited, by setting it to 1 second or more, the alkaline processing solution, the release layer, and the peel layer can be sufficiently removed. The contact time is more preferably 3 seconds or more, and even more preferably 5 seconds or more. On the other hand, by setting the contact time to 120 seconds or less, washing can be performed even with a small and simple roll-to-roll system that is preferably used. Specifically, since the transfer of the polyester substrate in the water washing tank can be simplified, the water washing tank can be made smaller, and the number of water washing tanks can be reduced, thereby making the entire equipment more compact. The contact time is more preferably 90 seconds or less, even more preferably 60 seconds or less, and particularly preferably 40 seconds or less.

[0045] When the water washing step is carried out in multiple steps, it is preferable to set the total treatment time of the water washing step to 1 to 120 seconds, for example, in order to obtain a high-quality polyester base material with little foreign matter without extending the total treatment time.

[0046] When the alkali-treated polyester substrate is brought into contact with water by immersing it in a water washing tank, it is preferable to carry out the contact while appropriately removing the release layer and peel layer that have adhered to the polyester substrate and been brought into the water washing tank from the water washing tank.

[0047] The method for removing the residue can be a suitable combination of methods such as using a filter, centrifugal separation, scraping off suspended matter with a squeegee or the like, settling in a settling tank, adding a certain amount of fresh alkaline processing solution or washing water and removing the corresponding amount of used alkaline processing solution or washing water by overflow or the like. As will be described later, it is also preferable to use a multi-stage washing step, and in the final stage to filter the solution or to rinse the release-treated polyester substrate with a shower using fresh water free of suspended matter. It is also preferable to add the water used in the shower to the washing tank and then flush it out by overflow or the like.

[0048] The method of the present invention makes it possible to remove the release layer and peel layer in a simple manner, and to obtain a release-treated polyester substrate from which the release layer and peel layer have been removed to a low level, and polyester pellets obtained therefrom containing little foreign matter.

[0049] When the alkali-treated polyester substrate is brought into contact with water multiple times by immersing it in a water-washing tank, the same water-washing tank may be used, or separate water-washing tanks may be used. Using separate water-washing tanks improves the flexibility of the equipment and is also preferred in terms of managing the water in the water-washing tanks.

[0050] Next, after the water washing step, it is preferable to dry the film. The drying temperature is not particularly limited, but is preferably, for example, 90 to 150°C. By setting the drying temperature to 90°C or higher, drying can be completed in a short time. The drying temperature is more preferably 100°C or higher. On the other hand, by setting the drying temperature to 150°C or lower, deterioration of the polyester base material can be prevented. The drying temperature is more preferably 135°C or lower.

[0051] The drying time is not particularly limited, but is preferably, for example, 50 seconds or more and 120 minutes or less. In the case of a batch method, drying can be performed using a blender dryer or the like. The drying time is particularly preferably 10 to 120 minutes, and more preferably 15 to 90 minutes. In the case of a roll-to-roll method, it is preferable to pass the long film through an oven dryer while it is still long and dry it. In the case of a roll-to-roll method, the drying time is preferably, for example, 50 to 150 seconds. By setting the drying time to 50 seconds or more, uneven drying can be reduced. The drying time is more preferably 60 seconds or more. On the other hand, by setting the drying time to 150 seconds or less, deformation of the polyester substrate can be prevented. The drying time is more preferably 140 seconds or less.

[0052] When the dried polyester substrate is in a long form, it may be cut into sheets or shredded in a shredder or the like, but it is preferable to send it to a winding process.

[0053] In the production method of the present invention, the laminate is wound into a roll, and the method may further include a water-washing step of bringing the alkali-treated polyester base material into contact with water, and a winding step of winding the water-washed polyester base material into a roll.

[0054] The laminate wound into a roll has a release layer and a peel layer provided on at least one surface of the laminate.

[0055] The laminate wound into a roll is fed out, and in a long state, it is brought into contact with an alkaline processing solution to peel off the release layer and peel layer, and then brought into contact with water to wash, and then dried, whereby it can be wound into a roll. The length of "long" varies depending on, for example, the type of equipment used, but generally means 100 to 20,000 m. "In a long state" includes both an embodiment in which the long laminate wound into a roll is fed out and contacted with the alkaline processing solution as is, and an embodiment in which the laminate is contacted with the alkaline processing solution after being adjusted (treated) to a state that allows contact with the alkaline processing solution. The former "long state as is" refers to an embodiment in which the laminate is contacted while maintaining the same width and length as the long polyester substrate wound into a roll. The latter "adjusted state" includes, for example, an embodiment in which a long polyester base material wound into a roll is cut into a width or length that allows contact with the alkaline treatment liquid beforehand and then rewound into a roll; an embodiment in which, when the cut long laminate pieces are to be introduced separately into the alkaline treatment liquid, if the laminate pieces are too long, they are cut into a length that allows contact before being brought into contact with the alkaline treatment liquid; and the like.

[0056] Furthermore, "contacting the laminate in a long state with the alkaline treatment liquid" means that the laminate in the above-mentioned state is directly contacted without crushing, etc. By removing the release layer and peeling layer in a long state in this way, problems associated with conventional methods, such as the release layer biting into the cut portions when crushing into chips and leaving the release layer, or the peeled release layer getting caught between chips or in the cut portions and remaining, are less likely to occur, and the release layer and peeling layer can be effectively removed from the polyester substrate.

[0057] Next, the method for producing a release-treated polyester substrate according to the present invention will be described in more detail with reference to Fig. 1. Fig. 1 shows an example of an apparatus 100 that uses a roll-shaped laminate and is preferably used in a so-called roll-to-roll system, but is not limited to this as long as the effects of the present invention are effectively exhibited. For example, the number of rolls shown in Fig. 1 can be changed as appropriate.

[0058] First, a laminate 1a having a release layer and a peel layer laminated on at least one surface and wound into a roll is prepared, and introduced into an alkaline treatment tank 3 containing an alkaline treatment liquid via a plurality of guide rolls 2. The details of the treatment method using the alkaline treatment liquid are as described above.

[0059] The manner of introduction into the alkaline treatment tank 3 is not particularly limited. To adjust the contact time with the alkaline treatment solution, the laminate may be passed over multiple guide rolls in a W-shape, for example, and then brought into contact with the alkaline treatment solution. While FIG. 1 shows an example of a configuration in which one alkaline treatment tank 3 is provided, multiple alkaline treatment tanks 3 may be provided and the contact time with the alkaline treatment solution may be adjusted by passing the laminate through multiple alkaline treatment tanks. That is, by using multiple guide rolls to form the laminate introduced into the alkaline treatment tank 3 in a W-shape or by using multiple alkaline treatment tanks 3, the contact time with the alkaline treatment solution can be extended without changing the conveying speed, allowing treatment to be performed without extending the overall treatment time.

[0060] Next, the polyester substrate is pulled out of the alkaline treatment tank 3 and introduced into a water washing tank 4, where the release layer and peeling layer that were once peeled off and removed from the surface of the polyester substrate by the alkaline treatment and then reattached are removed by washing with water.

[0061] In FIG. 1, two washing tanks 4 are arranged, washing tank 4a stores hot water at 40 to 90° C., and washing tank 4b stores water at a lower temperature than the hot water stored in washing tank 4a.

[0062] In the water washing tank 4b, nozzles 5a and 5b are arranged on the path of the polyester substrate introduced from the water washing tank 4a into the water washing tank 4b, and water is sprayed from the nozzles onto the polyester substrate. The number of nozzles is not limited to two, and may be one, or three or more. The nozzles may be arranged so as to spray water onto both sides of the polyester substrate as shown in FIG. 1, or so as to spray water onto only one side. Furthermore, the nozzles may be arranged in the water washing tank 4a, or in both the water washing tank 4a and the water washing tank 4b.

[0063] FIG. 1 shows an example in which the polyester substrate is immersed in water stored in a water washing tank 4, but the present invention is not limited to this as long as the above-mentioned object is achieved, and for example, showering may also be performed.

[0064] As shown in Fig. 1, a mangle 6 may be disposed between the alkaline treatment tank 3 and the washing tank 4a. The polyester substrate obtained after treatment in the alkaline treatment tank 3 is squeezed with the mangle 6 to remove the alkaline treatment solution adhering to the polyester substrate, thereby improving the washing efficiency in the washing tank 4.

[0065] FIG. 1 shows an embodiment in which the substrate is introduced into the water washing tank 4 immediately after the alkaline treatment tank 3, but this is not limiting. For example, an auxiliary tank equipped with a physical means such as a brush, ultrasonic waves, or water flow may be placed between the alkaline treatment tank 3 and the water washing tank 4 in order to remove any remaining release layer or peeling layer that was not removed in the alkaline treatment tank 3.

[0066] The release-treated polyester substrate washed in the water washing tank 4b is introduced into a drying furnace 7, dried, and then wound up in a roll, to obtain a release-treated polyester substrate 1b wound up in a roll.

[0067] As shown in Fig. 1, a mangle 8 may be placed inside the drying furnace 7. The release-treated polyester substrate obtained after washing in the water washing tank 4b is squeezed with the mangle 8 to remove water adhering to the release-treated polyester substrate, thereby shortening the drying time.

[0068] The release-treated polyester substrate thus obtained may be used for various applications. It is also preferable to melt and mold it. When melting and molding it, it is preferable to pulverize the release-treated polyester substrate. When pulverizing, the release-treated polyester substrate after drying may be pulverized without being wound up, but it is preferable to first wind it up into a roll and then pulverize the release-treated polyester substrate unwound from the roll using a shredder or the like. The pulverized release-treated polyester substrate may be fed into an extruder to form a molded product such as a film, but it is preferable to first process it into pellets and use these pellets to form a film or the like. By processing it into pellets, supply stability can be ensured when it is fed into an extruder, and when it is mixed with virgin pellets and fed into an extruder, segregation is less likely to occur, and molded products of stable quality can be obtained.

[0069] The method for pelletizing the release-treated polyester substrate is not particularly limited. For example, it is preferable to feed the release-treated polyester substrate, which has been pulverized using a shredder or the like, into an extruder, melt it, and pelletize it. The extruder may be a single-screw or twin-screw extruder. The melting temperature is equal to or higher than the melting point of the polyester raw material of the film, preferably "melting point + 10°C" or higher, and equal to or lower than the decomposition temperature, preferably "decomposition temperature - 10°C" or lower. Specifically, when the polyester is PET, the melting temperature is preferably equal to or higher than 260°C, more preferably equal to or higher than 270°C, even more preferably equal to or higher than 275°C, and is preferably equal to or lower than 300°C, even more preferably equal to or lower than 290°C.

[0070] The molten polyester is extruded through a die in the form of a strand, cooled with water, and cut into pellets, or extruded into water and cut into pellets by an underwater cutter installed at the die outlet, where it is cooled. The pellets are then dried.

[0071] The shape of the pellets is not particularly limited, and examples thereof include dice-shaped, bale-shaped, flat bale-shaped, spherical, and rugby ball-shaped. The size of the pellets is preferably, for example, 1 to 5 mm in each side or diameter (longer diameter, shorter diameter), more preferably 2 to 4 mm. The shape and size of the pellets are preferably the same as those of virgin pellets so that segregation is less likely to occur when mixed with virgin pellets.

[0072] To prevent the pelletization process from producing foreign matter, it is preferable to prevent resin retention in the extruder, piping, and die. It is also preferable to use water for cooling the chips that contains as little foreign matter as possible by passing it through a filter.

[0073] The polyester pellets obtained from the release-treated polyester substrate of the present invention contain little foreign matter and can be used for various applications, among which it is preferable to use them as a raw polyester substrate that serves as the substrate for the above-mentioned laminate, particularly as a polyester substrate that serves as a polyester substrate for optical applications or a polyester substrate that serves as the substrate for a release film. [Example]

[0074] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and modifications can be made within the scope of the above or below-described purpose, and all such modifications are included in the technical scope of the present invention.

[0075] Example 1 A polyester film (laminate) having a release layer laminated on at least one side via a Si-containing release layer was prepared as follows: A 0.2 μm-thick release layer of a polydimethylsiloxane-based water repellent containing Si was formed on both sides of a 50 μm-thick polyethylene terephthalate substrate. The following release layer material was then applied to each side with a bar coater at a coating weight of 200 g per square meter. The film was then immersed in 25°C water for 4 minutes, then in 40°C warm water for 15 minutes. The film was then squeezed with a mangle at 0.4 MPa and dried in a 140°C oven to form a release layer and produce a laminate. The release layer material was formulated as follows: 100 parts Resamine CU8614 (Dainichiseika Chemicals, polyurethane), 70 parts dimethylformamide (Dainichiseika Chemicals, pigment), and 15 parts Seika Seven BS780S (Dainichiseika Chemicals, pigment). The release layers formed on both sides of the polyethylene terephthalate substrate can be used, for example, as exterior components for home appliances. The release layers were porous and 50 μm thick, and the resulting laminate was 60 cm wide and 2000 m long, wound into a roll around a plastic core.

[0076] The prepared laminate was subjected to an alkali treatment, water washing, drying, and winding using the apparatus shown in Figure 1 to produce a release-treated polyethylene terephthalate substrate. Specifically, the alkaline treatment solution stored in the alkaline treatment tank 3 contained potassium hydroxide as an alkali supply source, had a concentration of 42%, and was heated to 100°C. The alkaline treatment process was performed once. The contact time between the laminate and the alkaline treatment solution was 10 seconds. Residues of the release layer and the peel layer floating on the water surface of the alkaline treatment tank 3 were removed appropriately by scooping them up with a stainless steel mesh. The water washing tank 4a contained warm water at a temperature of 60°C, and the water washing tank 4b contained water at room temperature (27°C). The contact time between the polyethylene terephthalate substrate and the warm water in the water washing tank 4a was 30 seconds, and the contact time between the polyethylene terephthalate substrate and the water in the water washing tank 4b was 30 seconds. The total contact time in the water washing process was 60 seconds. Residues of the release layer and peel layer floating on the water surface of the water washing tank 4a were scooped up with a stainless steel mesh and appropriately removed. Shower nozzles 5a to 5d were placed in the water washing tank 4b, and water was sprayed onto both sides of the polyethylene terephthalate substrate at a flow rate of 50 L / min. The sprayed water flowed into the water washing tank 4b, and excess water from the water washing tank 4b was allowed to overflow and be discharged (not shown).

[0077] (Comparative Example 1) The release layer was peeled from the laminate produced in Example 1 to obtain a laminate of a polyethylene terephthalate substrate and a release layer, which was then wound up into a roll. To peel the release layer, two paper tubes with double-sided tape attached to their surfaces were prepared, and the double-sided tape surfaces of the paper tubes were brought into contact with the release layer surfaces on both sides of the laminate to peel off the release layer. While unrolling the roll of laminate, the release layer was wound up around the paper tube. The resulting laminate of a polyethylene terephthalate substrate and a release layer was washed with water, dried, and wound up in the same manner as in Example 1 to produce a release-treated polyethylene terephthalate substrate.

[0078] Next, the removal rate of the release layer of the obtained release-treated polyethylene terephthalate substrate was calculated.

[0079] (Measurement of release layer removal rate) The removal rate of the release layer was calculated based on the following formula by measuring the amount of Si element on the surface of the release-treated polyethylene terephthalate substrate using a wavelength dispersive X-ray fluorescence analyzer (Supermini200 manufactured by Rigaku Corporation). Release layer removal rate (%) = {(AC) - (BC) / (AC)} × 100

[0080] In the formula, A represents the Si intensity detected by irradiating the release layer surface of a laminate of a release layer and a polyethylene terephthalate substrate with X-rays before the release layer is provided, B represents the Si intensity detected by irradiating the release-treated polyethylene terephthalate substrate surface with X-rays after alkali treatment, and C represents the Si intensity detected by irradiating the raw polyethylene terephthalate substrate surface with X-rays before the release layer is provided. The above formula was calculated taking into account the amount of Si originally contained in the raw polyethylene terephthalate substrate (defined as "C" in the formula), and in the formula, (AC) represents the amount of Si contained in the release layer before alkali treatment, and (BC) represents the amount of Si derived from the release layer remaining in the polyethylene terephthalate substrate after alkali treatment.

[0081] As a result, the removal rate of the release layer in Example 1 was 99.7%, and the removal rate of the release layer in Comparative Example 1 was 50.9%. [Explanation of symbols]

[0082] 1a Laminate wound in a roll 2 guide rolls 3. Alkaline treatment tank 4, 4a, 4b washing tank 5a~5d Nozzles 6, 8 Mangle 7 Drying oven

Claims

1. an alkaline treatment step of contacting a laminate in which a release layer is laminated on at least one surface of a polyester substrate via a release layer with an alkaline treatment liquid to peel off the release layer and the release layer from the polyester substrate; A method for producing a polyester substrate, comprising:

2. a water washing step of contacting the alkali-treated polyester substrate with water; The method of claim 1 further comprising:

3. The laminate is wound into a roll, a water washing step of contacting the alkali-treated polyester substrate with water; and a winding step of winding up the polyester base material after washing into a roll; The method of claim 1 further comprising:

4. The alkaline treatment step is carried out by contacting the substrate with an alkaline treatment solution having a concentration of 0.5 to 60% by mass at a temperature of 70 to 150° C. for 1 second to 180 minutes. The method according to any one of claims 1 to 3, wherein

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