JP2021187869A - Polyester film, method for producing polyester film, polyester pellet, and method for producing polyester pellet - Google Patents

Abstract

To provide a polyester film which is less in deposition of a resin derived from a coating layer to a polyester film while the polyester film is obtained by subjecting the coating layer to release treatment, and can be formed into a pellet having the same quality as a pellet of a virgin product when the polyester film is re-melted and formed into a pellet, and a polyester pellet using the same which has the same quality as a virgin polyester pellet.SOLUTION: A polyester film has a polyvinyl alcohol removal index calculated by the following analysis method 1 of 0.10 or less (excluding 0). Analysis method 1: When a solution in which a polyester film is dissolved is filtered, and then a filter medium is analyzed by a total reflection measurement method of infrared spectroscopy, a ratio (a/b) of maximum absorbance a detected in a range of 3,200 to 3,650 cm-1 to maximum absorbance b detected in a range of 2,840 to 3,000 cm-1 is defined as a polyvinyl alcohol removal index.SELECTED DRAWING: Figure 1

Description

The present invention relates to a polyester film, a method for producing a polyester film, a polyester pellet, and a method for producing a polyester pellet.

Polyester films are used, for example, in fields such as electronic parts, optical parts, labels, mold release, and transfer. Polyester films used in these applications often have a coating layer on their surface. Examples of the coating layer include functional layers such as an antistatic layer, a hard coat layer, an antireflection layer, an antiglare layer, a mold release layer, and a printing layer, and ensuring adhesion between the polyester film and the functional layer. An easy-adhesion layer for ensuring the adhesion between the polyester film and the adhesive for laminating can be mentioned. Further, in fields such as mold release and transfer, a mold release layer is provided on the surface of the polyester film or the polyester film, and a functional layer or various thin film layers are laminated on the functional layer, and then the functional layer laminated from the polyester film. The thin film layer may be peeled off, and the peeled functional layer or thin film layer may be utilized in the above-mentioned fields. In the present specification, these functional layers, easy-adhesion layers, and thin film layers may be collectively referred to as a coating layer.

In the process of manufacturing such a polyester film with an easy-adhesion layer and a functional layer, and further in the process of manufacturing a polyester film in which a functional layer and a thin film layer for mold release and transfer are laminated, a coating layer is applied to the surface of the polyester film. It may be out of specification after stacking. Non-standard films are usually discarded, but in order to make effective use of resources, it is desired to peel off (remove) the coating layer from the polyester film and recycle it. Further, even if it is not out of specification, polyester films for mold release and transfer and polyester films used as protective films for processes are discarded after use, but it is also desired to recycle them as well. ..

Techniques for recycling such films are disclosed, for example, in Patent Documents 1 and 2. According to Patent Document 1, 0.1% by mass to 10% by mass of a peroxide is obtained after removing a foreign layer provided on the base material from a base material made of a synthetic resin in an alkaline aqueous solution having a temperature of 105 ° C. or higher. It is described that the foreign layer is removed by treating with an aqueous solution containing. Specifically, a so-called batch method is used in which the base material to be treated is first selected, the entire base material made of the synthetic resin is cut into chips of an appropriate size in advance, crushed, and then subjected to a predetermined alkali treatment. It is adopted. Further, Patent Document 2 describes a method of removing the green sheet residue on the used release film and recycling the release film. Specifically, the green sheet residue on the used release film is removed by contacting it with an adhesive member such as an adhesive roll, and a so-called roll-to-roll method is adopted.

Japanese Patent No. 3270037 Japanese Unexamined Patent Publication No. 2011-104986

In the method of Patent Document 1, it is necessary to crush the base material into chips in advance, and there is a problem that it takes a long time to remove the foreign layer. In addition, the surface area was increased by crushing into chips, and foreign matter was easily mixed. Further, the method of Patent Document 2 has a problem that when the adhesive strength of an adhesive member such as an adhesive roll decreases, the removal rate of green sheet residue decreases.

By the way, various materials are used for the coating layer, and even after the coating layer is peeled off from the polyester film, foreign matter derived from the coating layer may adhere to the surface of the polyester film. On the other hand, when the polyester film is recycled, the recovered polyester film is melted and molded into pellets, and the obtained pellets are melted again to form a film. Therefore, if foreign matter derived from the coating layer adheres to the surface of the polyester film to be recycled, it is considered that the foreign matter derived from the coating layer is mixed in the regenerated polyester film. However, attention has not been paid to these foreign substances mixed in the regenerated polyester film. In addition, it cannot be said that the quality of foreign matter and the like is sufficient for using the regenerated polyester film in the same high-precision application as the raw material polyester film.

Patent Document 1 proposes to peel off the coating layer using an alkaline treatment liquid, but the foreign matter derived from the coating layer cannot be completely removed, and the amount of foreign matter contained in the regenerated polyester film is large. There were many cases.

As the material of the coating layer, for example, polyvinyl alcohol may be used. Since polyvinyl alcohol has a high affinity with water-based compounds, it can be used as an easy-adhesion layer for applying water-based adhesives and coating agents to polyester films, as well as water-based ink receiving layers such as inkjets, release layers, and mold release layers. , Used as an alignment layer for thin film extruders and liquid crystal compounds. When the coating layer contains polyvinyl alcohol in this way, polyvinyl alcohol may be attached to the surface of the polyester film even after the coating layer is peeled off from the polyester film.

The present invention has been made in view of the above circumstances, and an object thereof is to remelt the polyester film because the polyester film from which the coating layer has been peeled off has very little adhesion of the resin derived from the coating layer. It is an object of the present invention to provide a polyester film which can be made into pellets having the same quality as virgin pellets when made into pellets, and polyester pellets having the same quality as virgin polyester pellets using the same. ..

Another object of the present invention is a coating layer laminated polyester film in which a coating layer, particularly a coating layer containing polyvinyl alcohol, is laminated on at least one surface of the polyester film and is wound in a roll shape. It is an object of the present invention to provide a method for producing a polyester film capable of highly removing a kimono, and a method for producing a polyester pellet obtained from the polyester film with a high degree of foreign matter.

The configuration of the present invention is as follows.
[1] A polyester film having a polyvinyl alcohol removal index of 0.10 or less (not including 0) calculated by the following analysis method 1.
(Analysis method 1)
After filtration a solution of a polyester film, when the filter medium was analyzed by a total reflection measurement method of infrared spectroscopy, and the maximum absorbance a detected in the range of 3200~3650cm ^-1, 2840~3000cm ^-1 The ratio (a / b) to the maximum absorbance b detected in the range of is taken as the polyvinyl alcohol removal index.
[2] The polyester film is manufactured from a polyester film having a coating layer containing polyvinyl alcohol laminated on at least one surface and wound in a roll shape [1]. The polyester film described.
[3] An alkaline treatment step in which a coating layer containing polyvinyl alcohol is laminated on at least one surface of the polyester film, and the coated layer laminated polyester film wound in a roll shape is brought into contact with an alkaline treatment liquid, and an alkaline treatment step. The present invention comprises a washing step of bringing the polyester film after the alkali treatment into contact with water.
A method for producing a polyester film having a polyvinyl alcohol removal index of 0.10 or less (not including 0) calculated by the following analysis method 1.
(Analysis method 1)
After filtration a solution of a polyester film, when the filter medium was analyzed by a total reflection measurement method of infrared spectroscopy, and the maximum absorbance a detected in the range of 3200~3650cm ^-1, 2840~3000cm ^-1 The ratio (a / b) to the maximum absorbance b detected in the range of is taken as the polyvinyl alcohol removal index.
[4] The production method according to [3], further comprising a winding step of winding the polyester film after washing with water into a roll shape.
[5] In the alkali treatment step, the coating layer laminated polyester film is brought into contact with a 20 to 60% by mass alkaline treatment liquid at a temperature of 90 to 140 ° C. for 1 to 120 seconds [3] or [4]. The manufacturing method described.
[6] The production method according to any one of [3] to [5], wherein the washing step is to bring the polyester film after the alkali treatment into contact with water at 90 ° C. or lower at least once.
[7] The production method according to any one of [3] to [6], wherein the water washing step is performed by spraying water on the polyester film after the alkali treatment.
[8] A polyester pellet obtained by melt-molding a polyester film obtained by peeling a coating layer from a coating layer laminated polyester film having a coating layer laminated on the surface, and is calculated by the following analysis method 2. Polyester pellets characterized in that the number of foreign substances is 100 / mm ^{2 or less.}
(Analysis method 2)
The polyester pellets are melted and observed with a retardation optical microscope at an observation magnification of 10 times, and the number of foreign substances having a diameter of 3 μm or more and less than 10 μm contained ^{in an observation field area of 1 mm 2 is measured.}
[9] The polyester pellet according to [8], wherein the b value is 13 or less.
[10] An alkali treatment step in which a coating layer is laminated on at least one surface of the polyester film, and the coated layer laminated polyester film wound in a roll shape is brought into contact with an alkaline treatment liquid, after the alkali treatment. It is characterized by including a washing step of bringing the polyester film into contact with water and a pelletizing step of melting and molding the polyester film after washing into pellets.
A method for producing polyester pellets in which the number of foreign substances calculated by the following analysis method 2 is 100 pieces / mm ^{2 or less.}
(Analysis method 2)
The polyester pellets are melted and observed with a retardation optical microscope at an observation magnification of 10 times, and the number of foreign substances having a diameter of 3 μm or more and less than 10 μm contained ^{in an observation field area of 1 mm 2 is measured.}
[11] The coating layer contains polyvinyl alcohol, and the polyester film after washing with water has a polyvinyl alcohol removal index of 0.10 or less (not including 0) calculated by the following analysis method 1 [10]. ] The manufacturing method described in.
(Analysis method 1)
After filtration a solution of a polyester film, when the filter medium was analyzed by a total reflection measurement method of infrared spectroscopy, and the maximum absorbance a detected in the range of 3200~3650cm ^-1, 2840~3000cm ^-1 The ratio (a / b) to the maximum absorbance b detected in the range of is taken as the polyvinyl alcohol removal index.
[12] A coating layer in which a coating layer is laminated on at least one surface of the polyester film An alkali treatment step of bringing the laminated polyester film into contact with an alkaline treatment liquid, and a washing step of bringing the polyester film after the alkali treatment into contact with water. The number of foreign substances is 100, which comprises a step of melting and molding the polyester film after washing with water to form a pellet, and a step of forming a film by melting and molding the pellet into a film. A method for producing a polyester film having a size of / mm ^{2 or less.}

With the above configuration, according to the present invention, it is possible to provide a polyester film having the same quality as a virgin product and a method for producing the same. Further, according to the present invention, it is possible to provide a polyester pellet having the same quality as a virgin product and a method for producing the same.

FIG. 1 is a schematic view of a roll-to-roll device used in one embodiment of the present invention. FIG. 2 is an infrared absorption spectrum of a stripped polyethylene terephthalate film after washing with water. FIG. 3 is an infrared absorption spectrum of a coated layer laminated polyethylene terephthalate film before alkali treatment.

According to the studies by the present inventors, even in the polyester film in which the coating layer is peeled off from the polyester film in which the coating layer is laminated on at least one surface of the polyester film, the components derived from the coating layer are still attached. It was found that when the polyester pellet was molded using the polyester film to which such a component was attached, the pellet became a pellet containing a large amount of foreign matter, which caused the deterioration of the quality. Hereinafter, the film in which the coating layer is laminated may be referred to as a coating layer laminated film, and the film from which the coating layer is peeled off may be referred to as a release-treated film. When the film is a polyester film, the polyester film in which the coating layer is laminated may be referred to as a coating layer laminated polyester film, and the polyester film from which the coating layer has been peeled off may be referred to as a peeling-treated polyester film.

Further, according to the study by the present inventors, when the resin component contained in the coating layer is difficult to be decomposed by the alkaline treatment liquid, for example, the resin component contained in the coating layer is a resin having a carbon-carbon bond as a main chain. When it is a silicone resin, a cellulose resin such as cellol acetate or nitrocellulose, or the resin contained in the coating layer contains a cross-linking agent, this cross-linking agent is a cross-linking agent itself like melamine or an isocyanate compound. When it reacts and easily becomes an agglomerate, these resins are peeled off from the coated layer laminated polyester film, and since they are often present in a suspended state in the alkali treatment liquid, they are reattached to the peeling treatment film, and the alkali treatment conditions are changed. It was found that the amount of foreign matter is difficult to reduce even if it is strict. In particular, when the resin component is polyvinyl alcohol, it swells in an alkaline treatment liquid or water used for washing and becomes a paste, which easily adheres to the film. It was found that when melted and molded, it was easily contained as a foreign substance in the pellets.

Hereinafter, the present invention will be described in detail. Hereinafter, a case where a coating layer containing polyvinyl alcohol is laminated on at least one surface of the polyester film will be described as a representative. In the following, the coating layer containing polyvinyl alcohol may be referred to as a PVA-containing coating layer.

The peel-treated polyester film of the present invention has a polyvinyl alcohol removal index of 0.10 or less (not including 0) calculated by the following analysis method 1.
(Analysis method 1)
After filtering the solution in which the stripping-treated polyester film is dissolved, the maximum absorbance a detected in the range of ^{320 to 3650 cm -1} and 2840 to 3000 cm when the filter medium is analyzed by the total internal reflection measurement method of infrared spectroscopy. The ratio (a / b) to the maximum absorbance b detected in the range of ^{-1 is defined as the polyvinyl alcohol removal index.}

The polyvinyl alcohol removal index (hereinafter, may be referred to as PVA removal index) calculated by the above analysis method 1 indicates the amount of polyvinyl alcohol contained in the peeled polyester film, and the PVA removal index is 0.10 or less. Therefore, the same quality as the virgin product can be realized. The PVA removal index is preferably 0.05 or less, more preferably 0.03 or less. The PVA removal index is preferably as small as possible, but it is peeled off from a polyester film in which a PVA-containing coating layer is laminated on at least one surface of the polyester film (hereinafter, may be referred to as a PVA-containing coating layer laminated polyester film). When producing a treated polyester film, it is not always preferable to set the PVA removal index to 0 in terms of economical industrial production, and usually 0.001 or more is preferable. The PVA removal index may be 0.003 or higher.

The PVA removal index is determined by filtering the solution in which the stripped polyester film is dissolved, and then analyzing the filter medium by the Attenuated Total Reflection (ATR method) of infrared spectroscopy (IR). and the maximum absorbance a detected in the range of 3650 cm ^-1, can be calculated as the ratio (a / b) of the maximum absorbance b detected in the range of 2840~3000cm ^-1. Peaks detected in the range of 3200～3650Cm ^-1 is due to the OH stretching vibration of polyvinyl alcohol, peaks detected in the range of 2840～3000Cm ^-1 is due to the CH stretching vibration of the filter medium ..

As the solvent for dissolving the peeling-treated polyester film, for example, 1,1,1,3,3,3-hexafluoro-2-propanol can be used.

As the filter medium, for example, a membrane filter whose material is polytetrafluoroethylene (PTFE) can be used.

Examples of the polyester film include polyethylene terephthalate (PET) film, polybutylene terephthalate (PBT) film, polyethylene naphthalate (PEN) film, polybutylene naphthalate (PBN) film, polypropylene terephthalate (PPT) film and the like. A PET film is preferable.

The thickness of the polyester film is not particularly limited, but is preferably 5 μm or more and 500 μm or less in consideration of handleability and the like. The thickness is more preferably 7 μm or more, more preferably 400 μm or less, still more preferably 350 μm or less, and particularly preferably 300 μm or less.

The peel-treated polyester film of the present invention is preferably produced from a PVA-containing coated layer laminated polyester film wound in a roll shape. The PVA-containing coating layer may be provided on a part of at least one surface of the polyester film, or may be provided on the entire surface. Further, the PVA-containing coating layer may be attached to at least one surface of the polyester film, or may be attached to both surfaces.

Although the peeled polyester film of the present invention is a recycled product, it has a very low content of foreign substances, and therefore can be used in various fields, and can be particularly preferably used for optical applications.

Next, a method for producing such a peel-treated polyester film will be described.

In the peeling-treated polyester film of the present invention, a PVA-containing coating layer is laminated on at least one surface of the polyester film, and the coating layer laminated polyester film (PVA-containing coating layer laminated polyester) is wound in a roll shape. It can be produced by a method including an alkali treatment step of bringing the film) into contact with an alkaline treatment liquid and a water washing step of bringing the polyester film after the alkali treatment into contact with water. Further, a winding step of winding the peeled polyester film after washing with water obtained by the above into a roll shape may be further included. The production method of the present invention is described in Patent Document 1 in that a coated layer laminated polyester film wound in a roll shape is brought into contact with an alkaline treatment liquid in a long state and then brought into contact with water. It is different from the method of treating the base film crushed into chips with an alkaline treatment liquid.

Hereinafter, each step will be described.

(Alkaline treatment process)
In the alkaline treatment step, a PVA-containing coating layer is laminated on at least one surface of the polyester film, and the coating layer laminated polyester film (PVA-containing coating layer laminated polyester film) wound in a roll shape is made alkaline. Contact with the treatment liquid. "Contacting with an alkaline treatment liquid" means, for example, contacting with an alkaline treatment liquid having a predetermined concentration by a method such as dipping, coating, or spraying. "Contacting with an alkaline treatment liquid" also includes heating the polyester film by contacting with a heated alkaline treatment liquid.

The alkaline treatment liquid contains an alkaline source such as sodium hydroxide and potassium hydroxide. The alkali supply source may be used alone or in combination of two or more. These have the effect of dissolving and swelling the PVA-containing coating layer adhering to the polyester film and peeling (removing) the PVA-containing coating layer from the polyester film. As the alkaline treatment liquid, an aqueous solution such as an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is preferable, and an aqueous solution of potassium hydroxide is more preferable.

The alkaline treatment liquid may further contain an alkaline treatment aid in order to increase the peeling efficiency of the PVA-containing coating layer. As the alkaline treatment aid, those capable of raising the heating temperature of the alkaline treatment liquid, such as a boiling point elevation agent, are preferably used. For example, a surfactant, a water-soluble inorganic compound, a water-soluble organic compound, and a water-soluble solvent are used. And so on. Specifically, for example, 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. Of these, glycols are preferable. These may be used alone or in combination of two or more.

Alkaline treatment conditions can be appropriately and appropriately selected according to the type, thickness, etc. of the polyester film, but high quality with few foreign substances without extending the entire treatment time by using a small and simple facility, which is a preferred embodiment. In order to obtain the peeled polyester film, for example, it is preferable to contact (for example, soak) with a 20 to 60% by mass alkaline treatment liquid heated to a temperature of 90 to 140 ° C. for 1 to 120 seconds.

When the alkaline treatment liquid contains both an alkaline source and an alkaline treatment aid, the treatment liquid in which the concentration of the alkaline treatment liquid containing these is adjusted to 20 to 60% by mass is heated to a temperature of 90 to 140 ° C. and the treatment is performed. It is preferable to bring the liquid into contact with the PVA-containing coated layer laminated polyester film for 1 to 120 seconds.

By setting the heating temperature of the alkaline treatment liquid to 90 ° C. or higher under the above alkaline treatment conditions, the PVA-containing coating layer can be sufficiently removed even with a small and simple facility, which is a preferred embodiment. Further, as described above, since the high-concentration alkaline treatment liquid is preferably used in the present invention, it is possible to prevent the alkaline component from precipitating and solidifying the treatment liquid itself by raising the temperature of the alkaline treatment liquid. .. The heating temperature of the alkaline treatment liquid is more preferably 100 ° C. or higher. On the other hand, by setting the heating temperature of the alkaline treatment liquid to 140 ° C. or lower, it is possible to prevent the peeled polyester film from being deteriorated by contact with the alkaline treatment liquid. The heating temperature of the alkaline treatment liquid is more preferably 135 ° C. or lower.

Under the above alkaline treatment conditions, the concentration of the alkaline treatment liquid (when the alkaline treatment liquid contains an alkaline source and an alkaline treatment aid, the total concentration of these) is 20% by mass or more, so that high quality with less foreign matter is present. Since the PVA-containing coating layer for obtaining the peeling-treated polyester film can be peeled off in a short time, the PVA-containing coating layer can be sufficiently removed even with a small and simple facility, which is a preferred embodiment. The concentration of the alkaline treatment liquid is more preferably 25% by mass or more, further preferably 30% by mass or more, and particularly preferably 35% by mass or more. On the other hand, by setting the concentration of the alkaline treatment liquid to 60% by mass or less, it is possible to prevent the peeled polyester film from being deteriorated by contact with the alkaline treatment liquid. The concentration of the alkaline treatment liquid is more preferably 55% by mass or less, further preferably 50% by mass or less, particularly preferably 47% by mass or less, and most preferably 45% by mass or less.

Under the above alkaline treatment conditions, the PVA-containing coating layer can be sufficiently removed by setting the contact time with the alkaline treatment liquid to 1 second or longer. The contact time is more preferably 3 seconds or longer, still more preferably 5 seconds or longer. On the other hand, by setting the contact time with the alkaline treatment liquid to 120 seconds or less, the treatment can be performed by a compact and simple roll-to-roll type equipment (details will be described later) which is preferably used. Specifically, since the transfer of the polyester film in the alkali treatment tank can be simplified, the alkali treatment tank can be downsized, and the number of alkali treatment tanks can be reduced, so that the entire equipment can be downsized. The contact time is more preferably 90 seconds or less, still more preferably 60 seconds or less, and particularly preferably 40 seconds or less.

The above-mentioned alkaline treatment conditions (particularly concentration and time) are different from the above-mentioned conditions described in Patent Document 1. That is, since the above-mentioned Patent Document 1 employs a batch method in which the base material is crushed in advance and then subjected to alkali treatment, for example, the concentration of the sodium hydroxide aqueous solution is controlled to a low concentration of 0.1 to 20% by mass. , Hydrolysis and dissolution of the base film due to heating are suppressed. Further, in Patent Document 1, in order to effectively exert the peeling effect by the alkali treatment, in the examples, the alkali treatment is carried out for 30 to 60 minutes with a 5% by mass sodium hydroxide aqueous solution for a long time. On the other hand, in the present invention, aiming at the peeling treatment in a short time, the polyester film wound in a roll shape is sent out and directly contacted with the alkaline treatment liquid in a long shape, so that the concentration of the alkaline treatment liquid is high. 20 to 60% by mass, the contact time with the alkaline treatment liquid is 1 to 120 seconds, and the alkaline treatment can be performed at a higher concentration and in a shorter time than in Patent Document 1. As described above, both are different from the above-mentioned Patent Document 1 from the viewpoint of preferable alkaline treatment conditions.

The number of times of alkali treatment is preferably 1 to 5 times, more preferably 1 to 3 times. It should be noted that one alkaline treatment here means the number of times the polyester film is brought into contact with the alkaline treatment liquid, and when the polyester film is immersed in the alkaline treatment liquid, it is one time from the immersion to the pulling up. When performing alkali treatment multiple times using an alkali treatment tank, the same alkali treatment tank may be used, individual alkali treatment tanks may be used, and it is better to use individual alkali treatment tanks. The flexibility is improved, which is also preferable in terms of managing the alkaline treatment liquid in the alkaline treatment tank.

If necessary, physical means such as brush and ultrasonic treatment may be used in combination with the alkaline treatment.

In the alkaline treatment step, since the residue of the PVA-containing coating layer peeled off from the surface of the polyester film is present in the alkaline treatment liquid, the residue of the PVA-containing coating layer is appropriately removed from the alkaline treatment liquid. Is preferable.

(Washing process)
In the water washing step, the polyester film after the alkali treatment is brought into contact with water and washed with water. By contacting with water, the alkaline treatment liquid adhering to the polyester film can be removed, and the residue of the PVA-containing coating layer adhering in the alkali treatment step can be removed.

The method of contacting the polyester film after the alkali treatment with water is not particularly limited, and for example, a method of immersing the polyester film after the alkali treatment in a washing tank, a method of spraying water on the polyester film after the alkali treatment, and the like. However, it is preferable to use these methods together. In the water washing step, it is more preferable to spray water on the polyester film. By spraying water, the alkaline treatment liquid and polyvinyl alcohol adhering to the polyester film can be efficiently removed. The method of spraying water is not particularly limited, and for example, water may be sprayed by spraying water from a nozzle provided toward the polyester film, for example, in a shower shape.

The washing conditions can be appropriately and appropriately selected according to the type and thickness of the polyester film, but by using a small and simple facility, which is a preferred embodiment, high quality with few foreign substances without extending the entire processing time. In order to obtain a peel-treated polyester film, for example, it is preferable to bring it into contact with water at 90 ° C. or lower at least once.

By using water at 90 ° C. or lower, the PVA-containing coating layer can be dissolved without damaging the polyester film. In addition, since boiling of water can be prevented, safe and stable washing with water is possible. The washing temperature is more preferably 80 ° C. or lower, still more preferably 70 ° C. or lower. The lower limit of the temperature of water is not particularly limited, but it is set to more than 0 ° C because water solidifies at 0 ° C or lower. The temperature of water is more preferably 10 ° C. or higher, further preferably room temperature (27 ° C.) or higher, and particularly preferably 40 ° C. or higher.

The number of washings with water is preferably 2 times or more, preferably 5 times or less, and more preferably 3 times or less. In addition, one washing with water here means the number of times that the polyester film is brought into contact with water, and when the polyester film is immersed in water, it is once from the immersion to the pulling up. When water is sprayed on the polyester film, for example, it means the number of times water is sprayed from the nozzles on the polyester film, but when a plurality of nozzles are arranged at intervals in the film transport direction, the water is drained in the middle. Up to once. For example, when two nozzles are arranged at intervals in the film transport direction, the number of washings is counted as one, and for example, a mangle is arranged between the nozzles to remove water adhering to the film. In that case, the number of washings with water is counted as two times. If the water sprayed on the film is to be poured into the water washing tank, the water spraying and the treatment in the water washing tank are combined once.

When the water washing is performed twice or more, the water washing may be performed at the same water temperature each time, or may be performed at different water temperatures. When changing the water washing temperature, the n + 1th water washing temperature may be higher, lower, or lower than the nth water washing temperature. Since PVA is more easily dissolved as the water temperature is higher, the removal rate of PVA is increased by contacting the polyester film after alkali treatment with water having a relatively high temperature and then contacting it with water having a relatively low temperature. Can be done.

A surfactant, a defoaming agent, or the like may be added to the water used in the washing step, but it is preferable that the water used in the final washing step does not contain these.

The contact time with water is not particularly limited, but by setting it to 1 second or longer, the residue of the alkaline treatment liquid and the PVA-containing coating layer can be sufficiently removed. The contact time is more preferably 3 seconds or longer, still more preferably 5 seconds or longer. On the other hand, by setting the contact time to 120 seconds or less, it is possible to wash with water even with a compact and simple roll-to-roll type equipment (details will be described later) which is preferably used. Specifically, since the transfer of the polyester film in the water washing tank can be simplified, the water washing tank can be miniaturized, and the number of water washing tanks can be reduced, so that the entire equipment can be miniaturized. The contact time is more preferably 90 seconds or less, still more preferably 60 seconds or less, and particularly preferably 40 seconds or less.

When the water washing step is performed in a plurality of times, for example, in order to obtain a high quality polyester film with less foreign matter without extending the entire processing time by using a small and simple facility which is a preferable embodiment, for example, washing with water. The processing time of the entire process is preferably 1 to 120 seconds.

When the polyester film treated with alkali is brought into contact with water by immersing it in a washing tank, the residue of the PVA-containing coating layer that adheres to the film and is brought into the washing tank is appropriately removed from the washing tank. It is preferable to be

According to the study by the present inventors, the coating layer containing a resin whose main chain is difficult to be decomposed by an alkali such as polyvinyl alcohol has a residue existing as a fine powder or a thin film solid in the alkaline treatment liquid. It turned out to be more. This residue adheres to the film and is carried from the alkali treatment tank to the washing tank, and the residue of the coating layer increases even inside the washing tank. If the water in the washing tank is not reused, the water used for washing does not contain the residue of the coating layer, but the water for washing is stored in the washing tank and reused for the purpose of reducing waste liquid and for economic reasons. .. For these reasons, it is preferable to perform the treatment while removing the residue of the coating layer from the alkaline treatment liquid or the washing water.

As a method for removing the residue, a method using a filter, a method by centrifugation, a method of scraping off suspended matter with a squid, a method of settling in a settling tank, a method of adding a certain amount of a new alkaline treatment liquid or washing water is added. , A method of extracting the used alkaline treatment liquid or washing water by overflow or the like can be appropriately combined. Further, as will be described later, it is also preferable to have a multi-step washing step, and in the final step, filter with a filter or wash off the peeled polyester film with a shower using fresh water without suspended matter. It is also preferable that the water used for the shower at this time is added to the washing tank and that amount is flushed out by overflow or the like.

According to the method of the present invention, the residue of the coating layer can be removed by a simple method, and a peeling-treated polyester film from which the coating layer has been removed to a low level and a polyester pellet having a small amount of foreign matter obtained from the film can be obtained. be able to.

When the polyester film after the alkali treatment is immersed in a water washing tank and brought into contact with water multiple times, the same water washing tank may be used, individual water washing tanks may be used, or individual water washing tanks may be used. It is preferable to improve the flexibility of the equipment and to manage the water in the washing tank.

After the washing step, it is preferable to dry. The drying temperature is not particularly limited, but is preferably 90 to 140 ° C., for example. By setting the drying temperature to 90 ° C. or higher, the polyester film can be dried in a short time, so that the polyester film can be produced even with a small and simple facility, which is a preferred embodiment. The drying temperature is more preferably 100 ° C. or higher. On the other hand, by setting the drying temperature to 140 ° C. or lower, deterioration of the polyester film can be prevented. The drying temperature is more preferably 135 ° C. or lower.

The drying time is not particularly limited, but is preferably 50 to 150 seconds, for example. 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 film can be prevented. The drying time is more preferably 140 seconds or less.

The dried polyester film may be cut into single leaves or guided to a shredder or the like to be crushed, but it is preferable to lead to a winding step.

(Rolling process)
In the winding step, the peeled polyester film after washing with water is wound into a roll. That is, by sending out the coated layer laminated polyester film wound in a roll shape, contacting it with an alkaline treatment liquid in a long state to peel off the coating layer, contacting it with water, washing it with water, and drying it. , Can be rolled up. The length of the "long shape" varies depending on, for example, the type of device used, but generally means 100 to 20000 m. "In the long state" means that the long coated layer laminated polyester film wound in a roll shape is sent out and brought into contact with the alkaline treatment liquid in the long state as it is, and the alkaline treatment. The purpose is to include both aspects of contacting with an alkaline treatment liquid in a state of being adjusted (treated) so as to be in contact with the liquid. The former "as-is" long state means a mode in which the polyester film is brought into contact with the long coated layer laminated polyester film wound in a roll shape with exactly the same width and length. The latter "adjusted state" means, for example, that a long coated layer laminated polyester film wound into a roll is cut into a width that can be contacted with an alkaline treatment liquid in advance, or has a length that can be contacted. A mode in which the film is rewound into a roll by cutting or the like; when the cut long coating layer laminated film is separately led to an alkaline treatment liquid, if the film is too long, before it is brought into contact with the alkaline treatment liquid. The mode of cutting to a length that can be contacted with the film is included. Further, "contacting with the alkaline treatment liquid in a long state" means that the coated layer laminated polyester film in the above-mentioned state is directly contacted without being crushed. By removing the coating layer in a long shape in this way, the coating layer bites into the cut portion when it is crushed into chips, and the coating layer remains, or the peeled coating layer is between the chips. Problems caused by the conventional method such as being caught in the cut portion and remaining are unlikely to occur, and the coating layer can be effectively removed from the film.

According to the manufacturing method of the present invention, the coated layer laminated polyester film wound into a roll is formed into a long state instead of the batch method in which the base film is crushed in advance as in Patent Document 1 described above. Since it is in direct contact with the alkaline treatment liquid, the coating layer containing polyvinyl alcohol or the like can be efficiently peeled off in a short time. A roll-shaped coating layer laminated polyester film is brought into contact with an alkaline treatment liquid, and after the above contact, a long polyester film from which the coating layer containing polyvinyl alcohol or the like has been peeled off is subjected to the next step (washing and drying). In the roll-to-roll method, which is introduced as it is and wound up in a roll shape, the coated layer laminated polyester film wound in a roll shape is continuously conveyed via a plurality of guide rolls, and a predetermined process is performed. This is a take-up winding type transport method in which the polyester film obtained by winding the polyester film is wound up into a roll state again. According to the roll-to-roll method, a series of peeling steps can be continuously performed in a short time, which is very efficient. Further, when the polyester film from which the coating layer has been peeled off is further cut or melted to be pelletized and moved to the next step, transportation is also efficient.

The coating layer laminated polyester film wound in a roll shape has an easy-adhesion layer provided on at least one surface of the polyester film, and a functional layer is provided on the polyester film directly or via an easy-adhesion layer. Examples thereof include those provided, and those provided with a functional layer for peeling or a thin film layer directly on the polyester film or via an easy-adhesion layer.

In the case of a polyester film in which a functional layer is laminated as a coating layer, or a polyester film in which a functional layer for peeling or a thin film layer is laminated, a functional layer that is a part of the coating layer prior to the alkali treatment step. And the step of removing the thin film layer may be further included. Further, the alkaline treatment step may be performed with the functional layer and the thin film layer laminated.

Examples of the functional layer include an antistatic layer, an adhesive layer, a hard coat layer, an antireflection layer, an antiglare layer, a release layer, a printing layer, a thin film polarizing element, an alignment layer for a liquid crystal compound, an ink receiving layer, and the like. Be done. Examples of the thin film layer include a polyimide precursor, a thin film such as polyarylate and polysulfone, a skin material, a ceramic green sheet, a fuel cell electrode material sheet, and a metal thin film layer. The coating layer such as the easy-adhesion layer, the functional layer, and the thin film layer may be provided on at least one side of the polyester film, or may be provided on both sides. Further, the coating layer may be provided alone or may be formed by laminating two or more kinds of the coating layer. Further, the coating layer may have not only a single function but also a plurality of functions.

Hereinafter, some examples of the easy-adhesion layer and the functional layer will be specifically described.

The easy-adhesive layer is provided on a polyester film, particularly a stretched PET film, and is a layer for improving or adjusting the adhesiveness (adhesive strength) with a functional layer or an adhesive.

Examples of the resin used for the easy-adhesion layer include copolymerized polyester, polyester polyurethane, polyether polyurethane, polycarbonate polyurethane, acrylic resin, urethane-modified acrylic resin, polyvinyl alcohol, and cellulose-based resin. The easy-adhesion layer is preferably crosslinked, and examples of the crosslinking agent include isocyanate compounds, oxazoline compounds, epoxy compounds, and amino resins such as melamine. In addition, organic or inorganic lubricant particles may be added.

The easy-adhesion layer is preferably an in-line method that is applied during the film forming process of the film. The thickness of the easy-adhesion layer is preferably 10 to 200 nm, more preferably 20 to 150 nm.

The resin constituting the antistatic layer is not particularly limited as long as it is a resin generally used for the antistatic layer. The antistatic layer may further contain an antistatic agent. Antistatic agents include, for example, nonionic, cationic, anionic, amphoteric surfactants; polypyrrole, polyaniline, poly (3,4-ethylenedioxythiophene) / poly (4-styrene sulfonate) and the like. Conductive polymers; _{metal oxide fillers such as SnO 2} (Sb dope), In ₂ O ₃ (Sn dope), ZnO (Al dope); carbon-based substances such as carbon black, graphene, carbon nanotubes (CNT), etc. Can be mentioned. These antistatic agents may be used alone or in combination of two or more.

The adhesive layer contains an adhesive commonly used for the adhesive layer. The type of the pressure-sensitive adhesive is not particularly limited, and examples thereof include an acrylic pressure-sensitive adhesive, a rubber-based pressure-sensitive adhesive, a polyurethane-based pressure-sensitive adhesive, and a silicone-based pressure-sensitive adhesive. The adhesive layer may further contain a tack fire (adhesive-imparting resin) or the like.

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

The resin constituting the release layer is not particularly limited as long as it is a resin generally used for the release layer, for example, a silicone resin such as polydimethylsiloxane, an amino resin such as melamine resin or urea resin, an acrylic resin, or an epoxy resin. , Alkid resin and the like. These resins may be used alone or in combination of two or more. The release layer may further contain a release agent such as silicone oil or wax.

The thickness of the functional layer (when a plurality of functional layers are provided, the total thickness thereof) is preferably 0.001 μm or more. In order to effectively exert a predetermined function, the thickness of the functional layer is more preferably 0.005 μm or more, still more preferably 0.01 μm or more. On the other hand, by setting the thickness of the functional layer to 50 μm or less, the functional layer can be removed in a short time. The thickness of the functional layer is more preferably 20 μm or less, further preferably 10 μm or less, and particularly preferably 5 μm or less.

A surface treatment layer may be laminated on the surface of the functional layer for the purpose of enhancing the affinity with the alkaline treatment liquid. As the surface modification treatment used for forming the surface treatment layer, a known method can be adopted, and examples thereof include corona treatment, plasma treatment, and flame treatment.

As described above, the coating layer such as the functional layer may contain a resin whose main chain is difficult to decompose due to alkali, or may be difficult to remove because it is highly crosslinked. In such a case, it is also preferable to surface-treat the surface of the coating layer. The surface treatment means a treatment in which the surface of the coating layer is made hydrophilic to enhance the affinity with the alkaline treatment liquid, or is deteriorated in some way to facilitate decomposition by alkali and permeation of alkali. The surface treatment may be referred to as an oxidation treatment, a decomposition treatment, a deterioration treatment, a hydrophilization treatment, or the like. Further, the surface treatment itself is not intended to peel off the coating layer, but is intended to facilitate the peeling of the coating layer by alkaline treatment.

Examples of the surface treatment include wet treatment, dry treatment, mechanical treatment, and swelling treatment. Examples of the wet treatment include treatment with an aqueous solution of ozone, hydrogen peroxide, nitric acid, perchloric acid, permanganate and the like. Examples of the dry treatment include ozone treatment, hydrogen peroxide gas treatment, corona treatment, plasma treatment, flame treatment and the like. Examples of the mechanical treatment include a treatment for increasing the contact area with the alkaline treatment liquid using a thunder roller, a metal brush, or the like. Examples of the swelling treatment include a treatment of applying a solvent or the like. Among them, dry treatment is preferable, corona treatment, plasma treatment, and flame treatment are more preferable, and corona treatment is more preferable, in terms of safety, handleability, and stability of effect.

The surface treatment is not limited to the roll-shaped treatment method according to the present invention, but even when the surface treatment is performed by the batch method, when the coating layer contains a resin whose main chain is difficult to be decomposed by the alkali as described above, or when the surface treatment is advanced. It is an effective means when it is cross-linked to. However, the surface treatment can be performed in combination with the roll-shaped treatment method according to the present invention in that the removal ability is high by using a high-concentration alkali and the residue of the removed coating layer can be removed. preferable. In the case of the batch method, the concentration of the alkaline treatment liquid is particularly preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less. In the case of the batch method, the contact time with the alkaline treatment liquid becomes long, so that the polyester of the base material may be decomposed when the concentration of the alkaline treatment liquid becomes too high. In the case of the batch method, the contact time with the alkaline treatment liquid is preferably 5 minutes or more, more preferably 10 minutes or more, further preferably 15 minutes or more, preferably 150 minutes or less, and more preferably 120 minutes or less. ..

Next, the method for producing the peel-treated polyester film according to the present invention will be described in more detail with reference to FIG. FIG. 1 illustrates an example of an apparatus 100 preferably used in a so-called roll-to-roll system, but the present invention is not limited to this as long as the operation of the present invention is effectively exhibited. For example, the number of rolls shown in FIG. 1 can be changed as appropriate.

First, a coating layer laminated polyester film 1a in which a PVA-containing coating layer is laminated on at least one surface and wound in a roll shape is prepared, and an alkaline treatment liquid is applied via a plurality of guide rolls 2. It is introduced into the containing alkali treatment tank 3. The details of the treatment method using the alkaline treatment liquid are as described above.

The mode of introduction to the alkaline treatment tank 3 is not particularly limited, and in order to adjust the contact time with the alkaline treatment liquid, for example, a coating layer laminated polyester film is passed to a plurality of guide rolls to form a W-shaped treatment. It may be brought into contact with the liquid. Further, in FIG. 1, a configuration example in which one alkaline treatment tank 3 is arranged is shown, but by arranging a plurality of alkaline treatment tanks 3 and passing through a plurality of alkaline treatment tanks, the contact time with the alkaline treatment liquid can be set. You may adjust. That is, if the polyester film introduced into the alkaline treatment tank 3 is made into a W shape by using a plurality of guide rolls, or if a plurality of alkaline treatment tanks 3 are used, the contact time with the alkaline treatment liquid can be reduced without changing the transport speed. Since it can be lengthened, it can be processed without lengthening the entire processing time.

Next, the polyester film pulled up from the alkali treatment tank 3 is introduced into the water washing tank 4, and the residue of the PVA-containing coating layer once peeled off and removed from the surface of the polyester film by the alkali treatment and then reattached is removed by washing with water. ..

In FIG. 1, two water washing tanks 4 are arranged, hot water of 40 to 90 ° C. is stored in the water washing tank 4a, and water having a temperature lower than that of the hot water stored in the water washing tank 4a is stored in the water washing tank 4b. is doing.

In the water washing tank 4b, the nozzles 5a and the nozzles 5b are arranged on the path of the polyester film introduced from the water washing tank 4a to the water washing tank 4b, and water is sprayed from the nozzles onto the polyester film. 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 on both surfaces of the polyester film as shown in FIG. 1, or may be arranged so as to spray water on only one surface. Further, the nozzle may be arranged in the water washing tank 4a, or may be arranged in both the water washing tank 4a and the water washing tank 4b.

FIG. 1 shows an example in which a polyester film is immersed in water stored in a water washing tank 4, but the present invention is not limited to this, and a shower or the like may be provided as long as the above object is achieved.

As shown in FIG. 1, the mangle 6 may be arranged between the alkali treatment tank 3 and the water washing tank 4a. By squeezing the polyester film obtained by treating in the alkaline treatment tank 3 with a mangle 6 and removing the alkaline treatment liquid adhering to the polyester film, the washing efficiency in the water washing tank 4 can be improved.

FIG. 1 shows an embodiment of introduction into the water washing tank 4 immediately after the alkali treatment tank 3, but the present invention is not limited to this, and for example, an alkali treatment tank is placed between the alkali treatment tank 3 and the water washing tank 4. An auxiliary tank equipped with physical means such as a brush, ultrasonic waves, and a water stream may be arranged for the purpose of removing the residue of the PVA-containing coating layer that remains without being removed in 3.

The peel-treated polyester film washed with water in the water-washing tank 4b is introduced into a drying oven 7, dried, and then wound into a roll to obtain a peel-treated polyester film 1b wound in a roll.

As shown in FIG. 1, a mangle 8 may be arranged in the drying furnace 7. The drying time can be shortened by squeezing the peeled polyester film obtained by washing with water in the water washing tank 4b with a mangle 8 and removing the water adhering to the peeled polyester film.

The peel-treated polyester film thus obtained may be used as it is as a film for various purposes. It is also preferable to melt and mold. When the polyester film is melted and molded, it is preferable to pulverize the peeled polyester film. When crushing, the peeled polyester film after drying may be crushed without being wound, but it is preferable to pulverize the peeled polyester film once wound into a roll and then unwound from the roll with a shredder or the like. .. Further, the crushed peel-treated polyester film may be put into an extruder to form a molded product such as a film, but it is preferable to process the crushed polyester film into pellets once and then use the pellets to form a film or the like. By processing the pellets, supply stability can be ensured when they are put into the extruder, and when they are mixed with virgin pellets and put into the extruder, segregation is unlikely to occur, and a molded product of stable quality can be obtained. be able to.

The method for pelletizing the peel-treated polyester film is not particularly limited, but for example, it is preferable to put the peel-treated polyester film crushed by a shredder or the like into an extruder to melt it and pelletize it. The extruder may be uniaxial or biaxial. The melting temperature is equal to or higher than the melting point of the raw material polyester of the film, preferably "melting point + 10 ° C." or higher, and lower than the decomposition temperature, preferably "decomposition temperature −10 ° C." or lower. Specifically, when the polyester is PET, the melting temperature is preferably 260 ° C. or higher, more preferably 270 ° C. or higher, further preferably 275 ° C. or higher, preferably 300 ° C. or lower, still more preferably 290 ° C. or higher. It is as follows.

The molten polyester is extruded from the die into strands, cooled with water and cut into pellets, or extruded into water and cut into pellets by an underwater cutter provided at the die outlet and cooled. The pellet is then dried.

The shape of the pellet is not particularly limited, and examples thereof include a dice type, a bale type, a flat bale type, a spherical shape, and a rugby ball shape. The size of the pellet is, for example, preferably 1 to 5 mm on each side and diameter (major diameter, minor diameter), and more preferably 2 to 4 mm. The shape and size of the pellets are preferably the same as those of the virgin pellets so that segregation is unlikely to occur when mixed with the virgin pellets.

It is preferable that the extruder, the pipe, and the die are set so that the resin does not easily stay in the extruder so that foreign matter is unlikely to be generated in the pelletization step. Further, it is preferable to use water for cooling the chip, which has a small amount of foreign matter, such as by passing through a filter.

In the polyester pellets obtained by melt-molding the peeled polyester film of the present invention (hereinafter, may be referred to as recycled pellets), the number of foreign substances calculated by the following analysis method 2 ^{is preferably 100 pieces / mm 2} or less.
(Analysis method 2)
The polyester pellets are melted and observed with a retardation optical microscope at an observation magnification of 10 times, and the number of foreign substances having a diameter of 3 μm or more and less than 10 μm contained ^{in an observation field area of 1 mm 2 is measured.} The diameter means the maximum diameter.

By setting the number of foreign substances in the recycled pellets to 100 / mm ² or less, it was used as a polyester film as a base material for a release film for precision thin films such as optical polyester films, ceramic green sheets, and liquid crystal compound thin films. In some cases, the number of defects can be comparable to that of a film made solely from virgin pellets. The number of foreign substances in the recycled pellets ^{is preferably 80 pieces / mm 2} or less, more preferably 60 pieces / mm ² or less, still more preferably 50 pieces / mm ² or less, and particularly preferably 40 pieces / mm ² or less.

It is preferable that the number of foreign substances in the recycled pellets is small, and it is possible to reduce the number of foreign substances by improving the precision of the molten resin filter used in the extruder in addition to the above-mentioned peeling method of the coating layer. However, deterioration of polyester, agglomerates of catalysts and lubricants are also present as foreign substances, it may be difficult to completely eliminate the residue of coating, and it is more than necessary in terms of industrial productivity. Since the pore size of the filter cannot be reduced, the amount of foreign matter in the recycled pellets ^{is preferably 3 / mm 2} or more, more preferably 5 / mm ² or more, still more preferably 8 / mm 2 or more, and particularly preferably 10 ^{/ mm 2.} It is mm ² or more.

The foreign matter in the recycled pellets may contain foreign substances derived from the coating layer for the above reasons, and may be coated with a deteriorated product of polyester, which is a raw material of the film, a polymerization catalyst of polyester, or an agglomerate of lubricant. It may contain substances that are not derived from the layer. Whether or not the foreign matter is derived from the coating layer is determined by dissolving the recycled pellets in a solvent such as HFIP, filtering with a membrane filter such as PTFE, and then measuring the foreign matter on the filter with a microscopic IR or fluorescent X-ray. It can be judged by the presence or absence of characteristic peaks and elements derived from the coating layer.

As for the recycled pellets, foreign matter having a diameter of 10 μm or more ^{is preferably 2 pieces / mm 2} or less, more preferably 1 piece / mm ² or less, and most preferably not observed.

The method of limiting the foreign matter in the recycled pellets to the above range can be performed in the same manner as the above-mentioned peeling method of the coating layer even when the coating layer does not contain polyvinyl alcohol.

Further, the amount of polyvinyl alcohol contained in the peeled polyester film was evaluated by the PVA removal index. Even when the coating layer does not contain polyvinyl alcohol, the peeled polyester film is dissolved in an appropriate solvent. By measuring the residue on the filter filtered with the membrane filter by IR, it is possible to confirm how much the resin derived from the coating layer is removed even at the stage of the release-treated polyester film. Further, it can be confirmed to what extent the resin derived from the coating layer is removed by a method such as measuring the surface of the peeled polyester film by ATR-IR, a fluorescent X-ray method, or ESCA.

The resin used for the coating layer when the coating layer does not contain polyvinyl alcohol is not particularly limited, but as described above, carbon-as a resin that is difficult to be decomposed by an alkaline treatment liquid and easily becomes a foreign substance. Examples thereof include a resin having a carbon bond as a main chain. For example, as a resin often used as a coating agent, various modified acrylic resins such as acrylic resin and silicone-modified acrylic resin, polyvinyl acetal, ethylene-vinyl acetate copolymer, ethylene vinyl alcohol copolymer and the like can be mentioned. In addition to resins having a carbon-carbon bond as a main chain, silicone resins, cellulosic resins such as cellulose acetate and nitrocellulose, and the like can be mentioned.

The recycled pellet of the present invention preferably has a b value of 13 or less in the Hunter Lab color space. The b value indicates yellow / blue coordinates, + b indicates yellow, and −b indicates blue. The b value is considered to be affected by the content of foreign matter derived from the coating layer, including foreign matter in the polyester film that cannot be observed with a microscope, etc., and a b value of 13 or less means that the amount of foreign matter is small. It becomes an index of. By setting the b value to the above or less, not only is it used for various purposes like virgin pellets, but also when a molded product is manufactured by blending with virgin pellets, the ratio of virgin pellets to recycled pellets fluctuates. However, it is possible to obtain a molded product having a certain color tone. The b value is more preferably 12 or less. The lower limit of the b value is preferably -2 or more, and more preferably 0 or more. The method for measuring the b value will be described in the column of Examples.

The polyester pellets (that is, recycled pellets) obtained from the peeled polyester film of the present invention have few foreign substances and can be used as a material for molded products for various purposes. Above all, it is preferable to use it as a polyester film as a base material for a coated layer laminated polyester film, particularly as a polyester film as a base material for an optical polyester film or a release film. By using the recycled pellets in a polyester film for the same purpose as the coated layer laminated polyester film used for peeling, it is possible to produce a stable material balance with little surplus in the production of the film. , Can be a stable and high quality polyester film.

When the recycled pellets are used in a molded product, they may be used only as recycled pellets or may be blended with virgin pellets. The proportion of recycled pellets when blended with virgin pellets is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and even more preferably 15 to 80% by mass. ..

When the recycled pellet is made into a molded product, the manufacturing conditions are the same as when the virgin pellet is used. For example, in the case of a stretched polyethylene terephthalate film, PET pellets containing recycled pellets are melted at 270 to 300 ° C. and extruded into a sheet on a cooling roll, and the obtained sheet is heated to 70 to 130 ° C. After stretching, it can be heat-fixed at 150 to 230 ° C. to obtain a stretched film. The stretching may be uniaxial stretching or biaxial stretching, and roll stretching is preferably used in the flow direction (MD) of film formation, and tenter stretching is preferably used in the width direction (TD) orthogonal to the MD. .. Further, simultaneous biaxial stretching by a tenter may be used.

The thickness of the film produced by using the recycled pellets is preferably 5 μm or more and 500 μm or less. The thickness is more preferably 7 μm or more, more preferably 400 μm or less, still more preferably 350 μm or less, and particularly preferably 300 μm or less.

It is preferable that the film produced by using the recycled pellets is provided with a coating layer. The coating layer of the film may be an in-line method during film formation or an offline method separately performed after film formation. It is also one of the preferable forms that the coating layer is the same coating layer as the coating layer laminated polyester film to be subjected to the peeling treatment.

Foreign matter in the film produced using recycled pellets is melted and observed with a retardation optical microscope at an observation magnification of 10 times, and ^{the number of foreign matter contained in an observation field area of 1 mm 2} with a diameter of 3 μm or more and less than 10 μm. Is preferably 100 pieces / mm ² or less. The number of foreign substances ^{is more preferably 80 pieces / mm 2} or less, further preferably 60 pieces / mm ² or less, particularly preferably 50 pieces / mm ² or less, and most preferably 40 pieces / mm ² or less. The amount of foreign matter in the film ^{is preferably 3 pieces / mm 2} or more, more preferably 5 pieces / mm ² or more, further preferably 8 pieces / mm ² or more, and particularly preferably 10 pieces / mm ² or more. Further, the foreign matter having a diameter of 10 μm or more in the film ^{is preferably 2 pieces / mm 2} or less, more preferably 1 piece / mm ² or less, and most preferably not observed. The foreign matter in the film may be measured in the same manner as in the analysis method 2 except that about 30 mg of the film cut into about 5 mm squares is used instead of the pellets.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples, and may be modified to the extent that it can be adapted to the above or the purpose described below. Yes, they are all within the technical scope of the invention. In the following, unless otherwise specified, "%" means mass%.

(Coating layer laminated polyethylene terephthalate film A)
A polyester film having a PVA-containing coating layer laminated on at least one surface was produced by the following procedure. That is, pellets of polyethylene terephthalate (raw material pellets) as a raw material were put into an extruder, melted at 285 ° C., and extruded onto a cooling roll to prepare a sheet-like material. The sheet-like material was stretched three times in the MD direction at 90 ° C. between rolls having different peripheral speeds, and then a copolymerized polyester: polyvinyl alcohol: blocked isocyanate cross-linking agent was added on both sides of the obtained uniaxially stretched film in terms of solid content ratio. A coating liquid having a ratio of 9: 3: 1 was applied, and the solvent was removed with a dryer. Subsequently, the film was guided to a tenter, stretched 3.3 times at 100 ° C., further heat-fixed at 200 ° C., and the coating layer was crosslinked and cured to produce a coating layer laminated polyethylene terephthalate film A. The thickness of each of the coating layer formed on one surface and the other surface of the laminated polyethylene terephthalate film A was about 60 nm. The obtained coated layer laminated polyethylene terephthalate film A has a thickness of 75 μm, a width of 60 cm, and a length of 3000 m, and is wound around a plastic core in a roll shape.

(No. 1)
Using the apparatus shown in FIG. 1, the prepared coated layer laminated polyethylene terephthalate film A was subjected to alkali treatment, washing with water, drying, winding, and peeling treatment to produce a polyethylene terephthalate film. Specifically, the alkaline treatment liquid stored in the alkali treatment tank 3 contains potassium hydroxide as an alkali supply source, the concentration is 42%, the temperature is 115 ° C., and the alkali treatment step is performed once. .. The contact time between the coated layer laminated polyethylene terephthalate film A and the alkaline treatment liquid was 30 seconds. Further, the polyvinyl alcohol floating on the water surface of the alkali treatment tank 3 was scooped up with a stainless steel mesh and appropriately removed. Hot water having a temperature of 60 ° C. was stored in the water washing tank 4a, and water having a temperature of room temperature (27 ° C.) was stored in the water washing tank 4b. The contact time between the polyethylene terephthalate film and hot water in the water washing tank 4a was 30 seconds, the contact time between the polyethylene terephthalate film and water in the water washing tank 4b was 30 seconds, and the total contact time in the water washing step was 60 seconds. Further, the polyvinyl alcohol floating on the water surface of the washing tank 4a was scooped up with a stainless steel mesh and appropriately removed. In addition, shower nozzles 5a to 5d were arranged in the water washing tank 4b, and fresh water was sprayed on both sides of the polyethylene terephthalate film at a flow rate of 50 L / min. The sprayed water was poured into the washing tank 4b, and the excess water in the washing tank 4b overflowed and was discharged (not shown).

(No. 2)
The above No. No. 1 except that the shower nozzles 5a and 5b were arranged and the shower nozzles 5c and 5d were not arranged. A stripping-treated polyethylene terephthalate film was produced under the same conditions as in 1.

(No. 3)
The above No. No. 1 except that the temperature of the water stored in the water tank 4a was set to room temperature (27 ° C.). A stripping-treated polyethylene terephthalate film was produced under the same conditions as in 1.

(No. 4)
The above No. In No. 1, the polyvinyl alcohol floating on the water surface of the alkali treatment tank 3 was not appropriately removed, the polyvinyl alcohol floating on the water surface of the water washing tank 4a was not appropriately removed, and the shower nozzles 5a to 5a in the water washing tank 4b. No. except the point where 5d was not placed (the point where water was not sprayed). A stripping-treated polyethylene terephthalate film was produced under the same conditions as in 1.

(No. 5)
Approximately 10 kg of the prepared coated layer laminated polyethylene terephthalate film A was prepared, cut into chips corresponding to 0.5 to 3 cm square, and introduced into a tank with a stirring blade in which the alkaline treatment liquid 1 was stored. The alkaline treatment liquid 1 contained 0.7% by mass of potassium hydroxide as an alkali supply source, 0.01% by mass of polyethylene glycol ether as a higher alcohol, and had a temperature of 115 ° C. The contact time between the coating layer laminated polyethylene terephthalate film A and the alkaline treatment liquid 1 was set to 30 seconds, and during this period, after stirring at 105 ° C. and a rotation speed of about 100 rpm for 15 minutes, it was alkaline from the piping provided at the bottom of the tank. The treatment liquid 1 was taken out, water was further supplied to the tank, and the mixture was washed with water by stirring at a rotation speed of about 100 rpm for 5 minutes. Subsequently, the alkaline treatment liquid 2 was charged into the tank, and the mixture was stirred at 120 ° C. and a rotation speed of about 200 rpm for 40 minutes. The alkaline treatment liquid 2 contained 1.0% by mass of potassium hydroxide and 0.05% by mass of polyethylene glycol ether as a higher alcohol. After that, after extracting the alkaline treatment liquid 2 from the pipe provided at the bottom of the tank, water is supplied from the pipe provided at the bottom of the tank, and the mixture is stirred at a rotation speed of about 100 rpm for 10 minutes while overflowing. Washed with water. Then, the chips were taken out from the tank and dried at 100 ° C. for 60 minutes to produce peeled chips.

Next, No. For the peel-treated polyethylene terephthalate films obtained in 1 to 4, the PVA removal index was calculated by the following analysis method 1, and the results are shown in Table 1 below. Specifically, about 200 m was unwound from the surface layer of the wound stripped polyethylene terephthalate film, 5 points were randomly cut out from this part, and the average value of the following a / b ratios measured at these 5 points was calculated. It was used as the PVA removal index. In addition, No. In the peeling treatments 1 to 3, the foreign matter state in the washing tank became stable after the middle stage of the peeling treatment. The samples of the stripping-treated polyethylene terephthalate films 1 to 3 were sampled from the portion treated in a state where the foreign matter state was stable. Specifically, the middle stage of the peeling process means the middle stage of the entire process of the peeling process divided into three equal parts (first half, middle stage, second half). A stable foreign matter state means that the amount of foreign matter to be peeled off is almost the same as the amount of foreign matter removed by scooping or overflowing, and the amount of foreign matter in the alkaline treatment liquid or the washing tank is almost constant. Means.

(Analysis method 1)
A sample (1 cm × 1 cm) cut out from a stripping-treated polyethylene terephthalate film was dissolved in 5 ml of 1,1,1,3,3,3-hexafluoro-2-propanol, and the obtained solution was used as a membrane filter (Membrane Solutions). After filtering using "PTFE025045 (trade name)" manufactured by Limited, pore diameter 0.45 μm), the filter medium was measured by the total reflection measurement method of infrared spectroscopy. As the measuring device by infrared spectroscopy, "FT / IR-4200" manufactured by JASCO Corporation was used. The measured infrared absorption spectrum was calculated and the maximum absorbance a detected in the range of 3200～3650Cm ^-1, the ratio of the maximum absorbance b detected in the range of 2840～3000Cm ^-1 to (a / b).

In addition, No. Five pieces were randomly taken out from the peeling-treated chips obtained in No. 5, and the samples were cut into 1 cm × 1 cm, and the PVA removal index was calculated by the above analysis method 1, and the results are shown in Table 1 below.

Next, No. The infrared absorption spectrum was measured using a stripping-treated polyethylene terephthalate film obtained by alkali-treating and washing with water in 1. The measurement results are shown in FIG. In addition, No. In No. 1, the infrared absorption spectrum was measured using the coated layer laminated polyethylene terephthalate film A before the alkali treatment. The measurement results are shown in FIG. Comparing FIGS. 2 and 3, it can be seen that the peaks detected in the range of ^{320 to 3650 cm -1 were hardly detected by alkaline treatment and washing with water.} It is considered that polyvinyl alcohol was peeled off and removed from the surface of the polyethylene terephthalate film by alkaline treatment and washing with water.

Next, No. The number of foreign substances was calculated by the following analysis method 2 for the recycled pellets obtained by melt-molding the peel-treated polyethylene terephthalate film obtained in 1 to 4. Recycled pellets are No. The peeling-treated polyethylene terephthalate film obtained by alkali treatment and washing with water in steps 1 to 4 is rewound, and while unwinding the rewinding peeling-treated polyethylene terephthalate film, it is cut into chips corresponding to 0.5 to 3 cm square, and sequentially uniaxial extruders are used. I put it in. In the extruder, the resin was melted at a resin temperature of 285 ° C., and the strand-shaped polyethylene terephthalate extruded from the die was cooled in water and then cut into pellets. As the pellets used for the following analysis method 2, those immediately before the completion of pelletization, which corresponds to the latter half of the peeling treatment, were used.

(Analysis method 2)
Peeling treatment One recycled pellet (about 35 mg) obtained from polyethylene terephthalate film is sandwiched between two cover glasses (Matsunami micro cover glass, 25 mm x 25 mm, thickness 0.2 mm) and placed on a hot plate at about 300 ° C. It was heated and melted, pressed to a thickness of 0.8 to 0.9 mm, and immediately quenched to prepare an observation sample. A central portion of the sample thickness was observed using a Nikon phase-difference optical microscope and an objective lens (magnification 10x, aperture 0.5). The image was taken into an image analysis device (“Luzex-FS” manufactured by Nireco) via a CCD camera, and image analysis was performed to measure the number of particles of 3 μm or more and less than 10 μm and the number of particles of 10 μm or more, respectively. The size of the particles was the diameter of the circle corresponding to the area. The same measurement was performed 20 times while changing the field of view, the total number of particles for each was calculated, and the number of particles of 3 μm or more and less than 10 μm or 10 μm or more per 1 square mm of field area was calculated and used as the number of foreign substances in the recycled pellets. ..

In addition, No. Similarly, the number of foreign substances was calculated by the above analysis method 2 for the recycled pellets obtained from the peeling-treated chips obtained in 5. In addition, No. The peeling-treated chips obtained in No. 5 were directly put into a uniaxial extruder and pelletized.

Next, No. Recycled pellets obtained by melt-molding the peel-treated polyethylene terephthalate film obtained in Nos. 1 to 4 and No. The b value was measured for the recycled pellets obtained from the peeling-treated chips obtained in 5. For the b value, a colorimetric color difference meter (ZE6000) manufactured by Nippon Denshoku Kogyo Co., Ltd. was used. The hunter Lab was measured. This operation was repeated 3 times by changing the pellets, and the average value was calculated.

It can be considered from Table 1 as follows. No. Nos. 1 to 3 are examples that satisfy the requirements specified in the present invention, and the obtained recycled pellets can secure the same quality as the raw material pellets used for the coated layer laminated polyethylene terephthalate film A, and are virgin. It is considered that it can be used as a substitute for the product. In addition, No. The b value of the recycled pellets obtained in Nos. 1 to 3 was 13 or less, and the recycled pellets had a high whiteness. On the other hand, No. In No. 4, the PVA removal index exceeded 0.10 because the alkali treatment and washing with water were insufficient. As a result, the number of foreign substances having a particle size of 3 μm or more and less than 10 μm contained in the obtained recycled pellets exceeded 100. In addition, No. The b value of the recycled pellets obtained in 4 was over 13. No. No. 5 is an example of batch-type alkaline treatment and washing with water, and the PVA removal index exceeded 0.10. As a result, the number of foreign substances having a particle size of 3 μm or more and less than 10 μm contained in the obtained peeling-treated pellets exceeded 100. In addition, No. The b value of the pellet obtained in 5 was over 13.

Next, No. Approximately 200 mg of recycled pellets obtained by melt-molding the peel-treated polyethylene terephthalate film obtained in 1 was dissolved in 2 ml of 1,1,1,3,3,3-hexafluoro-2-propanol, and the obtained solution was used as a solution of PTFE. After filtering using a membrane filter (manufactured by Membrane Solutions Limited, pore size 0.5 μm), 10 foreign substances remaining on the filter were collected, and IR measurement of each foreign substance was performed by a micropermeation method. As a result, a ^{broad peak was observed in the range of 320 to 3650 cm -1} in two of these foreign substances, and foreign substances derived from PVA contained in the coating layer were present in these foreign substances. I found out.

(No. 6)
The coating layer in the in-line coating is changed to a coating liquid in which the solid content ratio of the polycarbonate polyurethane: copolymerized polyester: isocyanate compound is 5: 3: 2 and the thickness of the film is changed. The coated layer laminated polyethylene terephthalate film B was manufactured in the same manner as in the manufacture of the laminated polyethylene terephthalate film A. The thickness of each of the coating layer formed on one surface and the other surface of the laminated polyethylene terephthalate film B was about 60 nm. The obtained coated layer laminated polyethylene terephthalate film B has a thickness of 40 μm, a width of 60 cm, and a length of 3000 m, and is wound around a plastic core in a roll shape.

The produced coated layer laminated polyethylene terephthalate film B was subjected to the above No. Under the same conditions as in No. 1, an alkali-treated, washed with water, dried, wound, and peel-treated polyethylene terephthalate film was produced using the apparatus shown in FIG.

(No. 7)
No. except that the coating liquid was not applied. A mold release layer, which is a cured layer of an ultraviolet curable silicone resin having a thickness of 150 nm, is formed on a biaxially stretched polyethylene terephthalate film produced in the same manner as the coating layer laminated polyethylene terephthalate film B used in 6. A layer-laminated polyethylene terephthalate film C was produced.

After the surface of the release layer of the coated layer laminated polyethylene terephthalate film C was subjected to corona treatment (discharge amount 50 w · m ² / min) to modify the surface of the release layer, the above No. In the same manner as in No. 1, an alkali-treated, washed with water, dried, wound, and peel-treated polyethylene terephthalate film was produced using the apparatus shown in FIG. However, the temperature of the alkaline treatment liquid was 100 ° C.

(No. 8)
No. In No. 7, except that the release layer was a cured layer of a heat-addition type silicone resin. In the same manner as in No. 7, a peel-treated polyethylene terephthalate film was produced.

Next, No. The release rate of the release layer was calculated for the peeled polyethylene terephthalate film obtained in 7 and 8. 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 stripped polyethylene terephthalate film using a wavelength dispersive fluorescent X-ray analyzer (Supermini 200 manufactured by Rigaku Co., Ltd.). ..
Release layer removal rate (%) = {(AC)-(BC) / (AC)} x 100
In the formula, A is the Si intensity detected by irradiating the release layer surface of the release layer of the release layer and the laminate of the polyethylene terephthalate base material with X-rays before the release layer is provided, and B is the peeling treatment after the alkali treatment. The Si strength detected by irradiating the surface of the polyethylene terephthalate film with X-rays, and C mean the Si strength detected by irradiating the surface of the base film with X-rays before the release layer is provided. The above formula was designed in consideration of the amount of Si originally contained in the base film (specified by "C" in the formula), and in the formula, (AC) is in the release layer before the alkali treatment. (BC) means the amount of Si contained in the base film, and (BC) means the amount of Si derived from the release layer remaining on the base film after the alkali treatment.

Next, No. 6-8 The obtained peel-treated polyethylene terephthalate film was pelletized, and about 200 mg of each of the obtained recycled pellets was dissolved in 2 ml of 1,1,1,3,3,3-hexafluoro-2-propanol to obtain the obtained product. The solution was filtered using a PTFE membrane filter (Membrane Solutions Limited, pore size 0.5 μm), and then the foreign matter remaining on the filter was recovered in the same manner as described above, and IR measurement was performed by the micropermeation method. As a result, No. From 6 foreign matter from the reaction of an isocyanate compound are observed peak near 1680 cm ^-1 and 1440cm ^-1 were observed, No. From 7, 8, 1260 cm around ^-1, 800 cm around ^-1, 1090 cm around ^-1, observed foreign matters from silicone is observed peak near of 1020 cm ^-1, from coating layer in these foreign substances It turned out that there was a foreign substance.

In addition, No. The peel-treated polyethylene terephthalate film obtained in 6 to 8 was pelletized, and the number of foreign substances was calculated by the above analysis method 2 for each of the obtained recycled pellets. Moreover, the b value was measured. These results are shown in Table 2 below.

Next, No. Recycled pellets obtained from 1, 2, 6, 7, and 8 were blended with virgin pellets (raw material pellets) to produce a biaxially stretched polyethylene terephthalate film. The production of the film is No. The recycled pellets obtained from Nos. 1 and 2 were subjected to the same conditions as the production of the coated layer laminated polyethylene terephthalate film A. The recycled pellets obtained from No. 6 were subjected to the same conditions as the production of the coated layer laminated polyethylene terephthalate film B. For the recycled pellets obtained from Nos. 7 and 8, the same conditions were used for the production of the coated layer laminated polyethylene terephthalate film C. As the recycled pellets, pellets obtained from the latter half of the three equal parts (first half, middle stage, second half) of the entire peeling process were used. No. For the example using the recycled pellets obtained from No. 2, the mixing ratio of the recycled pellets and the virgin pellets was changed as shown in Table 3 below (No. 2-1 and No. 2-2).

For foreign matter in the film using recycled pellets, the above analysis was performed except that the coating layer provided in-line with a razor was removed, the surface of the film was washed away with pure water, and then about 30 mg of a sample cut into about 5 mm square was used. It was done in the same manner as in Law 2. The results are shown in Table 3 below.

Moreover, the color tone of the end face of the obtained film roll was visually evaluated. The case where the end faces of the coated layer laminated polyethylene terephthalate films A and B were equivalent was evaluated as ◯, the case where the yellowness was slightly strong was evaluated as Δ, and the case where the yellowness was clearly strong was evaluated as ×. The results are shown in Table 3 below.

The polyethylene terephthalate film obtained by using recycled pellets has no abnormalities in foreign matter and end face color tone, and has the same quality as the polyethylene terephthalate film using virgin pellets in terms of strength and elongation, so it can be used without problems as a film for the same purpose. I found that I could do it. Furthermore, No. In the film using the recycled pellets obtained from No. 7, No. A release layer was provided in the same manner as in No. 7 to obtain a release film. As a result, it was found that it can be used as a ceramic capacitor release film without any problem.

1a Rolled coating layer laminated polyester film 2 Guide roll 3 Alkaline treatment tank 4, 4a, 4b Washing tank 5a-5d Nozzle 6, 8 Mangle 7 Drying furnace

Claims (12)

A polyester film having a polyvinyl alcohol removal index of 0.10 or less (not including 0) calculated by the following analysis method 1.
(Analysis method 1)
After filtering the solution in which the polyester film was dissolved, when the filter medium was analyzed by the total internal reflection measurement method of infrared spectroscopy,
The maximum absorbance a detected in the range of 320 to 3650 cm ^{-1 and}
The ratio (a / b) to the maximum absorbance b detected in the range of 2840 to 3000 cm ^{-1 is defined as the polyvinyl alcohol removal index.} The polyester according to claim 1, wherein the polyester film is manufactured from a film in which a coating layer containing polyvinyl alcohol is laminated on at least one surface of the polyester film and wound in a roll shape. the film. An alkali treatment step in which a coating layer containing polyvinyl alcohol is laminated on at least one surface of the polyester film, and the coating layer laminated polyester film wound in a roll shape is brought into contact with an alkaline treatment liquid, and the alkali treatment. The washing process of contacting the polyester film with water afterwards,
Characterized by including
A method for producing a polyester film having a polyvinyl alcohol removal index of 0.10 or less (not including 0) calculated by the following analysis method 1.
(Analysis method 1)
After filtering the solution in which the polyester film was dissolved, when the filter medium was analyzed by the total internal reflection measurement method of infrared spectroscopy,
The maximum absorbance a detected in the range of 320 to 3650 cm ^{-1 and}
The ratio (a / b) to the maximum absorbance b detected in the range of 2840 to 3000 cm ^{-1 is defined as the polyvinyl alcohol removal index.} The production method according to claim 3, further comprising a winding step of winding the polyester film after washing with water into a roll shape. The production method according to claim 3 or 4, wherein the alkali treatment step brings the coated layer laminated polyester film into contact with a 20 to 60% by mass alkaline treatment liquid at a temperature of 90 to 140 ° C. for 1 to 120 seconds. The production method according to any one of claims 3 to 5, wherein the washing step is the production method according to any one of claims 3 to 5, wherein the polyester film after the alkali treatment is brought into contact with water at 90 ° C. or lower at least once. The production method according to any one of claims 3 to 6, wherein the washing step is performed by spraying water onto the polyester film after the alkali treatment. It is a polyester pellet obtained by melt-molding a polyester film obtained by peeling a coating layer from a coating layer laminated polyester film having a coating layer laminated on the surface.
A polyester pellet characterized in that the number of foreign substances calculated by the following analysis method 2 is 100 pieces / mm ^{2 or less.}
(Analysis method 2)
The polyester pellets are melted and observed with a retardation optical microscope at an observation magnification of 10 times, and the number of foreign substances having a diameter of 3 μm or more and less than 10 μm contained ^{in an observation field area of 1 mm 2 is measured.} The polyester pellet according to claim 8, wherein the b value is 13 or less. An alkaline treatment step in which a coating layer is laminated on at least one surface of the polyester film, and the coated layer laminated polyester film wound in a roll shape is brought into contact with an alkaline treatment liquid.
A water washing step of bringing the polyester film after the alkali treatment into contact with water, and a pelletizing step of melting and molding the polyester film after the washing with water to form pellets.
Characterized by including
A method for producing polyester pellets in which the number of foreign substances calculated by the following analysis method 2 is 100 pieces / mm ^{2 or less.}
(Analysis method 2)
The polyester pellets are melted and observed with a retardation optical microscope at an observation magnification of 10 times, and the number of foreign substances having a diameter of 3 μm or more and less than 10 μm contained ^{in an observation field area of 1 mm 2 is measured.} The coating layer contains polyvinyl alcohol and
The production method according to claim 10, wherein the polyester film after washing with water has a polyvinyl alcohol removal index of 0.10 or less (not including 0) calculated by the following analysis method 1.
(Analysis method 1)
After filtering the solution in which the polyester film was dissolved, when the filter medium was analyzed by the total internal reflection measurement method of infrared spectroscopy,
The maximum absorbance a detected in the range of 320 to 3650 cm ^{-1 and}
The ratio (a / b) to the maximum absorbance b detected in the range of 2840 to 3000 cm ^{-1 is defined as the polyvinyl alcohol removal index.} An alkaline treatment step in which a coating layer laminated polyester film having a coating layer laminated on at least one surface of the polyester film is brought into contact with an alkaline treatment liquid.
The washing step of bringing the polyester film after the alkali treatment into contact with water,
A pelleting step of melting and molding the polyester film after washing with water to form pellets, and a filming step of melting and molding the pellets to form a film.
Characterized by including
A method for manufacturing a polyester film in which the number of foreign substances is 100 / mm ^{2 or less.}

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