JP6149507B2 - Polyester film - Google Patents

Description

  The present invention is a polyester film that exhibits good releasability that hardly changes even in a high temperature environment, such as ink or adhesive, and has a small dimensional change in a high temperature environment. For example, a process paper or a release paper for transfer The present invention relates to a film useful for such applications.

  A plastic film such as a polyester film is not easily torn compared to paper, and is less likely to lose strength due to water or the like, and thus is used as a process paper for transfer or a release paper. In such an application, after an ink or an adhesive is applied to the film, the film is dried to remove the solvent contained in the ink or the adhesive, and in some cases, an aging treatment is further performed. As a film for transfer or peeling, it is necessary that the adhesiveness between the ink and the adhesive and the film is appropriately controlled (in other words, excellent peelability). The adhesiveness (peelability) is kept constant even when the aging conditions change (peeling stability), and the dimensional change of the film due to heat during drying and aging is difficult to occur (dimensional stability). Required.

  As a polyester film for transfer or peeling, a releasable film (Patent Document 1) in which a specific resin that does not easily change its peeling force due to heat or the like is applied to the surface layer of the polyester film, A laminated film (Patent Document 2) is known in which a specific resin composition that easily undergoes cohesive failure is interposed between a heat-bondable resin layer.

Japanese Patent Laid-Open No. 57-133058 Japanese Patent Laid-Open No. 01-202449

However, each of the films of Patent Documents 1 and 2 is obtained by laminating a surface layer made of a predetermined resin on a polyester film as a base material, and is formed using a polyester resin and other resin components (surface layer components). ing. Therefore, there are problems that the surface layer components are mixed when recovering the polyester after use, and that the manufacturing process is complicated and it is difficult to stably manufacture the product.
Therefore, it is not a laminated film in which a predetermined layer is required to be laminated on a polyester film as in Patent Documents 1 and 2, but it is formed from only a polyester resin in consideration of recovery, and the complexity and stability of the manufacturing process. Even if it is formed as a single layer in consideration of the above, a new polyester film for transfer or peeling that can have peeling stability and dimensional stability is demanded.

  The present invention has been made against the background of such prior art problems. That is, an object of the present invention is to provide a polyester film that exhibits good releasability that hardly changes due to heat with respect to ink, adhesive, and the like, and that has little dimensional change due to heat.

The polyester film of the present invention that can achieve the above-mentioned object is a stretched polyester film having a thickness of 3 to 50 μm, the film having a heat shrinkage in the longitudinal direction of 1 to 8%, and at least one surface of the film is The present invention has a gist in that the following conditions (i) to (iii) are satisfied.
(I) The crystallinity obtained by the total reflection infrared absorption method (ATR-IR method) is 1.25 or more. (Ii) The plane orientation coefficient obtained by the total reflection infrared absorption method (ATR-IR method). 0.2 to 0.25 (iii) The polar force component in the surface free energy is 10 to 16 mJ / m ²

  In the present invention, since the degree of crystallinity and the plane orientation coefficient of the film surface are controlled within a predetermined range larger than usual, it becomes possible to suppress the change in peelability due to heat, and the polarity in the surface free energy Since the force component is controlled within a predetermined range smaller than usual, it is possible to realize good peelability.

  The polyester film of the present invention is preferably a biaxially stretched film.

  According to the present invention, heat can be applied to ink, adhesive, etc. without laminating another resin layer (such as a resin that does not easily cause a change in peeling force due to heat or a resin that easily causes cohesive failure) on the polyester film surface. Thus, it is possible to provide a polyester film that exhibits good peelability that hardly changes, and that has little dimensional change due to heat. Such a polyester film of the present invention does not require a surface layer laminating step, and thus can be manufactured simply and stably. Moreover, when the polyester is recovered after being used for a transfer application or a peeling application, the surface resin is not used. There is an advantage that it is not mixed and is easily collected and used.

1. Characteristics of the polyester film The polyester film of the present invention has a thickness of 3 to 50 µm. If thickness is this range, it can be used conveniently for uses, such as a process paper for transfer, and a release paper. The lower limit of the film thickness is preferably 5 μm, more preferably 10 μm. On the other hand, the upper limit of the film thickness is preferably 45 μm, more preferably 40 μm. If the film thickness is too thin or conversely too thick, for example, the workability may be reduced in the above applications.

  The stretched polyester film of the present invention has a heat shrinkage rate of 1 to 8% in the longitudinal direction of the film. If the heat shrinkage rate in the longitudinal direction of the film is within this range, it is possible to prevent dimensional changes from occurring due to drying or aging when used as a transfer or peeling film. The lower limit of the heat shrinkage rate in the longitudinal direction of the film is preferably 1.1%, more preferably 1.2%. On the other hand, the upper limit of the heat shrinkage rate in the longitudinal direction of the film is preferably 7.5%, more preferably 7%. If the thermal shrinkage rate in the longitudinal direction of the film is too larger than the above range, a pitch shift or the like may occur in various processing steps, and the appearance may be deteriorated. The smaller the heat shrinkage rate in the longitudinal direction of the film, the better. However, even if it is smaller than the above range, no further dimensional stability improvement effect can be expected. In the present invention, the “heat shrinkage rate in the longitudinal direction of the film” is a value measured under heating conditions of 150 ° C. for 15 minutes.

  In order to control the heat shrinkage rate in the longitudinal direction of the stretched polyester film of the present invention within the above range, it is important to sufficiently heat-fix the film (especially heat-fixing in the central portion in the thickness direction). What is necessary is just to perform magnification (especially draw ratio of 1st axis | shaft extending | stretching), heat setting temperature, and a relaxation rate in the range mentioned later.

  The stretched polyester film of the present invention preferably has a value of [thermal shrinkage in the longitudinal direction] − [thermal shrinkage in the width direction] of 8% or less, more preferably 7% or less, and even more preferably 6% or less. It is. If this value (difference in heat shrinkage) is within the above range, it becomes easier to suppress the change in the peeling force due to heat.

In the stretched polyester film of the present invention, at least one surface satisfies all the following conditions (i) to (iii). When all of the following (i) to (iii) are satisfied, it is possible to express good peelability and to suppress a change in peel force due to heat.
(I) The crystallinity obtained by the total reflection infrared absorption method (ATR-IR method) is 1.25 or more. (Ii) The plane orientation coefficient obtained by the total reflection infrared absorption method (ATR-IR method). 0.2 to 0.25 (iii) The polar force component in the surface free energy is 10 to 16 mJ / m ²

  The lower limit of the crystallinity of (i) is preferably 1.255, more preferably 1.26, and the upper limit is preferably 1.4, more preferably 1.395, and still more preferably 1.39. When the crystallinity is less than 1.25, the crystallized state of the film surface tends to change at high temperatures, and the peeling force becomes unstable. On the other hand, even if the degree of crystallinity exceeds 1.4, a further effect of stabilizing the peeling force cannot be expected, but it may be rather brittle and the productivity may be reduced. In addition, the crystallinity degree of said (i) can be measured by the method mentioned later in an Example, for example.

  The lower limit of the plane orientation coefficient (ii) is preferably 0.201, more preferably 0.202, and the upper limit is preferably 0.249, more preferably 0.248. When the plane orientation coefficient is less than 0.200, the crystallization state of the film surface easily changes at high temperatures, and the peeling force becomes unstable. On the other hand, when the plane orientation coefficient exceeds 0.250, the peeling force tends to decrease, and the peeling force tends to change particularly due to heat. The plane orientation coefficient (ii) can be measured by, for example, a method described later in Examples.

  When a film is produced, a heat setting treatment for imparting thermal stability is usually performed after stretching, but at this time, a large amount of heat is applied to the surface portion when compared with the surface of the film and the central portion in the thickness direction. It will be. If the amount of heat applied to the central part in the film thickness direction is small, the crystallization inside the film will be insufficient and the heat shrinkability will increase, so that the heat setting process will also give sufficient heat to the central part in the film thickness direction. To be done. However, if so, excessive heat is applied to the film surface, so the degree of crystallinity and plane orientation on the film surface tend to decrease, and the range tends to be out of range. Therefore, in order to increase the crystallinity of the above (i) and the plane orientation coefficient of the above (ii) and keep it within the above range, for example, by setting the draw ratio in the range described later, The amount of heat in the heat setting process may be reduced after devising to crystallize with a smaller amount of heat.

The lower limit of the polar force component of the surface free energy (iii) is preferably 10.5 mJ / m ² , more preferably 11 mJ / m ² , and the upper limit is preferably 15.5 mJ / m ² , more preferably 15 mJ / m ² . When the polar force component of the surface free energy exceeds 16 mJ / m ² , the adhesiveness increases due to the interaction between polar groups on the film surface, resulting in a decrease in peelability. On the other hand, if the polar force component of the surface free energy is less than 10 mJ / m ² , the peelability becomes too high, and the adhesion between the film and the ink, adhesive, etc. is insufficient, It may not be suitable for use in applications such as process paper or release paper. In addition, the polar force component of the surface free energy of (iii) can be measured, for example, by the method described later in Examples.

  In order to control the polar force component of the surface free energy in the above (iii) within the above range, for example, the processing time in the heat setting process may be adjusted. If the heat setting time is shortened, the polarity of the surface free energy The force component tends to be small. Moreover, when the heat setting temperature is lowered, the polar force component of the surface free energy tends to be reduced. However, if heat fixation is performed at a low temperature and in a short time to keep the surface free energy small, problems such as excessive heat shrinkage may occur due to the degree of crystallization of the film becoming too small. As described later, it is preferable to carry out the stretching of the first axis at a relatively high magnification.

  The peelability of the stretched polyester film of the present invention can be evaluated by, for example, the initial peel rate in Examples described later. This initial peel rate is preferably at least 50% or more, more preferably 55% or more, further preferably 60% or more, further preferably 90% or more, particularly preferably 95% or more, and most preferably 100%. is there. If the initial peeling rate is less than 50%, the transferability and releasability are insufficient and there is a possibility that it is not suitable for practical use.

  The peel stability of the stretched polyester film of the present invention can be evaluated by, for example, the peelability change rate in the examples described later. The absolute value of the peelability change rate is preferably at least 50% or less, more preferably 45% or less, further preferably 40% or less, further preferably 10% or less, particularly preferably 5% or less, Most preferably, it is 0%. If the peelability change rate exceeds 50%, transferability and releasability may be insufficient and may not be suitable for practical use.

  The stretched polyester film of the present invention preferably has a haze value of 0.5% or more and 20% or less, more preferably 0.7% or more and 19% or less, still more preferably 0.8% or more, 18% or less. If the haze value is too small, scratches and the like may be conspicuous and the productivity may be reduced. On the other hand, if the haze value is too large, the transparency is lowered and the use in applications where transparency is required is restricted. There is.

  The polyester film of the present invention may be a single layer film or a laminated film, but it is desirable that at least all of the resins constituting the film (single layer or laminated layer) are polyester resins. Thus, if it is a film consisting only of a polyester resin, even if it is a single layer film or a laminated film, the resin on the surface may be mixed when recovering the polyester after it is used for transfer or peeling applications. It is easy to collect and use. In particular, it is more preferable that the polyester film of the present invention is a single layer film because a lamination process is not required, and thus simple and stable production is possible.

  In addition, as an example of the laminated film formed only from the polyester resin, for example, a base material layer formed of the first polyester resin and a second polyester resin (first polyester so as to sandwich the base material layer) And a laminated film composed of two surface layers formed of (different from resin). Such a laminated film can be manufactured simply and stably by, for example, a co-extrusion method because each layer is made of a polyester resin.

2. Polyester film forming material The polyester resin used as a raw material of the polyester film of the present invention is not particularly limited. For example, terephthalic acid such as polyethylene terephthalate (PET), polypropylene terephthalate (PPT), and polybutylene terephthalate (PBT) is used as a raw material. A polyester resin made from naphthalenedicarboxylic acid such as polyethylene resin, polyethylene naphthalate (PEN), polypropylene naphthalate (PPN), polybutylene naphthalate (PBN), and other components (for example, isophthalic acid, Polycarboxylic acids such as adipic acid, sebacic acid, dimer acid, hydrogenated dimer acid, cyclohexanedicarboxylic acid; diethylene glycol, propanediol, neopentyl glycol, cyclohexane And various polyester resins obtained by copolymerizing polyhydric alcohols such as xanthodimethanol, dimer diol, hydrogenated dimer diol, polyethylene glycol and polytetramethylene glycol; Among these, PET, PBT, PEN, and a polyester resin obtained by copolymerizing these with other components are preferable, PET and PBT are more preferable, and PET is more preferable.

  The melting point of the polyester resin is preferably 200 ° C. or higher, more preferably 250 ° C. or higher, and further preferably 260 ° C. or higher in consideration of general use temperature. When the melting point of the polyester resin is less than 200 ° C., the thermal stability is lowered, and there is a possibility that shrinkage or sagging may occur due to a thermal history in various processes.

  The raw material composition for forming the stretched polyester film of the present invention may contain other resins together with the polyester resin in order to impart various functions. As other resins, for example, polyamide resins, polyolefin resins, polyurethane resins, polycarbonate resins, acrylic resins, vinyl resins, and the like are preferable. It is preferable that content of other resin is the range of 0.5-50 mass% with respect to 100 mass% of raw material compositions containing a polyester resin. If it is less than 0.5% by mass, the effect for the purpose is small, and if it exceeds 50% by mass, the original properties of the polyester resin may be impaired.

  In addition, it is also a preferable aspect to recycle the resin collected from a portion that does not become a product generated during film formation as the above-described various resins used as the raw material of the stretched polyester film of the present invention.

The raw material composition for forming the stretched polyester film of the present invention can contain a lubricant for the purpose of imparting slipperiness.
The lubricant is not particularly limited, and a conventionally known inorganic lubricant or organic lubricant can be used. Among them, inorganic lubricants such as silica, calcium carbonate, and alumina are preferable, and silica and calcium carbonate are more preferable. Silica is more preferred. The lower limit of the particle size of the lubricant is preferably 0.1 μm, more preferably 0.5 μm, and the upper limit is preferably 20 μm, more preferably 15 μm, and even more preferably 10 μm. If the particle size of the lubricant is too small, the effect of imparting slipperiness may be difficult to obtain. On the other hand, if the particle size is too large, the slipperiness is improved, but the transparency of the film tends to decrease. The lubricant may be indeterminate, or may have any shape such as a sphere, an oval sphere, a confetti shape, a thin plate shape, or a needle shape.

  The content of the lubricant is preferably 10 ppm (mass basis, the same shall apply hereinafter) or more, more preferably 20 ppm or more, and further preferably 30 ppm or more in the raw material composition forming the film. When the content of the lubricant is too small, the slipperiness cannot be sufficiently obtained, and the practicality of the film may be lowered. On the other hand, the upper limit of the content of the lubricant is preferably 10,000 ppm, more preferably 8000 ppm, and further preferably 5000 ppm. When there is too much content of a lubricant, the transparency of a film may fall.

3. Production Method Hereinafter, preferred production methods for the stretched polyester film of the present invention will be described. However, these are merely examples, and the stretched polyester film of the present invention is not limited to those obtained by the following production method.

  The stretched polyester film of the present invention is prepared by, for example, melting a raw material composition containing a polyester resin, then extruding the sheet from a die onto a cooling roll to form an unstretched film, and then stretching the unstretched film, Obtained by fixed processing.

3.1 Production of Unstretched Film The resin melting temperature for melting the raw material composition may be appropriately set according to the resin melting point and the like, but the lower limit is preferably 220 ° C, more preferably 230 ° C, and even more preferably. The upper limit is preferably 320 ° C, more preferably 315 ° C, still more preferably 310 ° C, and particularly preferably 300 ° C. If the resin melting temperature is too low, the melt viscosity becomes high and ejection (extrusion) may be difficult. On the other hand, if the resin melting temperature is too high, the polyester resin may be thermally decomposed to cause a decrease in molecular weight.

  The lower limit of the set temperature of the die (die temperature) is preferably 250 ° C., more preferably 255 ° C., further preferably 260 ° C., and the upper limit is preferably 350 ° C., more preferably 340 ° C., further preferably 330 ° C. . If the die temperature is too low, the melt viscosity becomes high and discharge (extrusion) may be difficult. On the other hand, if the die temperature is too high, the polyester resin may be thermally decomposed to cause a decrease in molecular weight.

  The lower limit of the set temperature of the cooling roll (cooling roll temperature) is preferably 2 ° C., more preferably 5 ° C., further preferably 10 ° C., and the upper limit is preferably 80 ° C., more preferably 50 ° C., further preferably 40 ° C. It is. If the chill roll temperature is too low, condensation may occur and cause dirt in the process. On the other hand, if it is too high, cooling will be insufficient and crystallization will progress, resulting in poor stretchability and poor thickness. There is a risk of becoming.

  The lower limit of the casting speed when producing an unstretched film is preferably 2 m / min, more preferably 5 m / min, and the upper limit is preferably 120 m / min, more preferably 110 m / min, even more preferably 100 m / min. is there. If the casting speed is too slow, productivity tends to decrease, while if it is too fast, casting tends to become unstable.

  The lower limit of the thickness (cast thickness) of the unstretched film thus obtained is preferably 45 μm, more preferably 50 μm, still more preferably 60 μm, and the upper limit is preferably 1250 μm, more preferably 1000 μm, still more preferably 800 μm. If the unstretched film is too thin, it may be difficult to perform subsequent stretching biaxially. On the other hand, if it is too thick, the inside of the film (center in the thickness direction) will be insufficiently cooled, and the heat shrinkage rate Inconveniences such as an increase in

3.2 Stretching The polyester film of the present invention is preferably a biaxially stretched film. Therefore, the unstretched film is usually stretched by biaxial stretching. The stretching method may be either simultaneous biaxial stretching or sequential biaxial stretching. In the case of sequential biaxial stretching, it may be stretched in the width direction (TD direction) after stretching in the longitudinal direction (MD direction) of the film, or in the longitudinal direction (MD direction) after stretching in the width direction (TD direction). You may extend | stretch. In the present invention, the first stretching performed in sequential biaxial stretching may be referred to as “first-axis stretching”, and the subsequent stretching in the direction perpendicular to the first axis may be referred to as “biaxial stretching”.
In the present invention, after the simultaneous or sequential biaxial stretching, the stretching may be further performed in the longitudinal direction or the width direction (in the case of sequential stretching, preferably the direction perpendicular to the direction of the biaxial stretching). If stretching is performed in multiple stages, such as sequential biaxial stretching or simultaneous or sequential biaxial stretching followed by further stretching, for example, the uniaxial orientation becomes uniform in the direction of the first axis stretching, and the direction of the first axis stretching Therefore, the peelability is further improved and the change at the high temperature can be more easily suppressed.

  The stretching conditions (preheating temperature, stretching temperature, stretching ratio, etc.) may be appropriately set according to whether the first-axis stretching or the second-axis stretching. Detailed conditions for the first-axis stretching and the second-axis stretching will be described below. In addition, the heating method at the time of extending | stretching can employ | adopt conventionally well-known means, such as a hot-air heating system, a roll heating system, and an infrared heating system, irrespective of 1st axis | shaft extending | stretching and 2nd axis | shaft stretching.

3.2.1 Uniaxial stretching The lower limit of the preheating temperature of the first axial stretching is preferably 30 ° C, more preferably 40 ° C, and the upper limit is preferably 200 ° C, more preferably 150 ° C. If the preheating temperature for the first-axis stretching is too low, preheating may be insufficient and stretching may be difficult. On the other hand, if it is too high, crystallization may occur and stretching may be difficult.

  The lower limit of the stretching temperature of the first-axis stretching is preferably 50 ° C., more preferably 55 ° C., still more preferably 60 ° C., and the upper limit is preferably 150 ° C., more preferably 145 ° C., further preferably 140 ° C. If the stretching temperature for the first-axis stretching is too low, the resin may not be softened and stretching may be difficult. On the other hand, if it is too high, crystallization may occur and stretching may be difficult.

  The lower limit of the stretching speed of the first-axis stretching is preferably 100% / min, more preferably 200% / min, and the upper limit is preferably 100,000% / min, more preferably 90000% / min, even more preferably 80000% / min. It is. If the stretching speed of the first-axis stretching is too slow, the productivity tends to decrease, while if too high, the film-forming stability tends to decrease.

  The lower limit of the draw ratio of the first-axis stretching is preferably 3.8 times, more preferably 3.85 times, still more preferably 3.9 times, and the upper limit is preferably 4.5 times, more preferably 4.4 times. More preferably, it is 4.35 times. Thus, when the first-axis stretching is performed at a relatively high magnification, the central part in the thickness direction of the film can be crystallized with a smaller amount of heat. It is possible to sufficiently crystallize the film without breaking the crystallization on the surface. If the draw ratio of the first-axis stretching is too low, the crystallinity of the central part in the film thickness direction tends to decrease, and the film surface can be crystallized even if the stretching conditions after the second-axis stretching and the heat setting temperature are adjusted. As a result, it becomes difficult to control the degree, and the change in peelability may become large, especially when drying or aging conditions are changed. On the other hand, if the draw ratio of the first-axis stretching is too high, the film tends to break, and the productivity during film formation may be reduced.

3.2.2 Biaxial stretching The lower limit of the preheating temperature of the biaxial stretching is preferably 30 ° C, more preferably 40 ° C, still more preferably 50 ° C, and the upper limit is preferably 150 ° C, more preferably 145 ° C. More preferably, it is 140 ° C. If the preheating temperature for the biaxial stretching is too low, the temperature rise is insufficient and stretching may be difficult. On the other hand, if it is too high, crystallization may occur and stretching may be difficult.

  The lower limit of the stretching temperature of the biaxial stretching is preferably 50 ° C., more preferably 55 ° C., still more preferably 60 ° C., and the upper limit is preferably 180 ° C., more preferably 175 ° C., further preferably 170 ° C. If the stretching temperature for biaxial stretching is too low, the resin may not be softened and stretching may be difficult. On the other hand, if it is too high, crystallization may occur and stretching may be difficult.

  The lower limit of the stretching speed of the biaxial stretching is preferably 10% / min, more preferably 20% / min, and the upper limit is preferably 100,000% / min, more preferably 90000% / min, still more preferably 80000% / min. Minutes. If the stretching speed of the biaxial stretching is too slow, the productivity tends to decrease, while if too high, the film forming stability tends to decrease.

  The lower limit of the draw ratio of the biaxial stretching is preferably 3.5 times, more preferably 3.6 times, still more preferably 3.7 times, and the upper limit is preferably 5 times, more preferably 4.8 times, More preferably, it is 4.5 times. If the draw ratio of the biaxial stretching is too low, productivity at the time of film formation is lowered, and there is a possibility that unevenness occurs in the thickness of the film, while if too high, the orientation of the first axis is destroyed. The crystallinity of the surface becomes low, and the change in peelability may increase when drying or aging conditions are changed.

3.3 Heat setting treatment The stretched film is usually subjected to heat setting treatment.
The lower limit of the temperature during the heat setting treatment (heat setting temperature) is preferably 130 ° C, more preferably 140 ° C, still more preferably 150 ° C, and the upper limit is preferably 230 ° C, more preferably 220 ° C, still more preferably. 200 ° C. If the heat setting temperature is too low, the heat shrinkage rate tends to increase, so that it is difficult to control the temperature within the above range, and as a result, there is a risk of causing dimensional stability defects in various processing steps. On the other hand, if the heat setting temperature is too high, the crystal on the film surface is melted / collapsed by heat, and the crystallinity and the plane orientation coefficient of the film surface tend to be small, so that it is difficult to control the above range. There is a risk that the change in peelability will increase when drying or aging conditions are changed.

  The strength of heat fixation is determined by the heat fixation temperature, heat fixation treatment time, and heating means (wind speed for hot air heating, irradiation intensity for infrared heating, etc.). It is not determined by. Therefore, it is preferable to appropriately adjust, for example, the film forming speed and the heating zone length together with the heat setting temperature. From the viewpoint of productivity, it is also preferable to shorten the heat fixing treatment time while setting the heat fixing temperature relatively high within the allowable range.

  When performing the heat setting treatment, the film can be relaxed during or before the heating. The relaxation direction may be the width direction of the film or the longitudinal direction, but is preferably the width direction. The lower limit of the relaxation rate is preferably 0%, more preferably 0.5%, still more preferably 1.0%, and the upper limit is preferably 20%, more preferably 10%. If the relaxation rate is too high, sagging may occur during relaxation, and the thickness accuracy may be impaired. Therefore, the relaxation rate is considered together with the heat shrinkage rate.

As described above, the polyester film of the present invention can be a laminated film in which each layer is made of a polyester resin, if necessary. In the case of a laminated film, a layer disposed on a surface different from the surface intended for easy peeling can be a functional film that imparts antistatic properties, adhesiveness, scratch resistance, and the like.
When a single layer polyester film as a base material is laminated with a polyester film as a surface layer (for example, the above functional film) to form a laminated film, for example, a coating liquid according to a predetermined purpose is stretched after stretching is completed. What is necessary is just to apply to a polyester film or the unstretched polyester film before completion | finish of extending | stretching. In terms of simplifying the production process, it is advantageous to coat the unstretched film. As the coating method, for example, various methods such as bar coating, roll coating, and spray coating can be employed. The thickness during coating (coating thickness) may be such that the final thickness (thickness after biaxial stretching) is preferably 1 nm to 100 nm, more preferably 2 nm to 80 nm. If the final thickness of the various films is too thin, the purpose of providing the film is difficult to achieve, while if too thick, problems such as the formed film being easily scraped may occur.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited by the following examples and the like, and is appropriately within a range that can meet the above and the following purposes. Of course, it is possible to carry out with modifications, and these are all included in the technical scope of the present invention.
In addition, the measurement of the various physical properties in the following examples and comparative examples and the evaluation of the obtained film were performed by the following measurements.

(Intrinsic viscosity of polyester)
0.1 g of polyester was dissolved in 25 mL of a mixed solvent of phenol / tetrachloroethane (volume ratio: 3/2) and measured at 30 ° C. using an Ostwald viscometer.

(Thickness of unstretched film or stretched film)
It measured by the method based on JIS-Z-1702.

(Heat shrinkage)
Except that the test temperature was 150 ° C. and the heating time was 10 minutes, the heat in the longitudinal direction (MD direction) and the width direction (TD) of the film was measured according to the dimensional stability test method at elevated temperature described in JIS-C-2318. Shrinkage was measured.

(Crystallinity / plane orientation coefficient)
A total reflection infrared absorption measurement (FT-IR ATR measurement) is performed under the following conditions on one side of the stretched film (if any one side of the film is corona-treated, the non-corona-treated surface) It was.
vFT-IR apparatus: “FTS-60A / 896” manufactured by Bio Rad DIGILAB
Single reflection ATR attachment: "golden gate MKII" manufactured by SPECAC
Internal reflection element: Diamond incident angle: 45 °
Resolution: 4cm ^-1
Integration count: 128 times

Crystallinity, the absorption appears near 1340 cm ^-1, was calculated by the intensity ratio of the absorption appears near ^{1410cm -1 (1340cm -1 / 1410cm -1} ). Here, 1340 cm ⁻¹ is absorption due to the bending vibration of CH ₂ (trans structure) of ethylene glycol, and 1410 cm ⁻¹ is absorption independent of crystal and orientation.

The plane orientation coefficient indicates the degree of relaxation of the surface layer orientation, and in each direction in the absorption (the bending vibration of CH ₂ (trans structure) of ethylene glycol) that appears in the vicinity of 1340 cm ⁻¹ in the spectrum obtained by the above measurement. Absorption coefficients (Kx, Ky, Kz) were determined and calculated based on the formula: 2 Kz / (Kx + Ky). Here, Kx is the MD direction, Ky is the TD direction, and Kz is the absorption coefficient in the thickness direction. In addition, since absorption (identification unknown) which appears in the vicinity of 1410 cm ⁻¹ does not change regardless of the orientation state, the absorption at 1340 cm ⁻¹ was repeated and normalized.

  As for the plane orientation coefficient (relaxation degree of surface layer orientation) in the present invention, the smaller the value, the smaller the extinction coefficient in the thickness direction or the greater the extinction coefficient in the plane direction. This means that the degree of molecular chain orientation relative to the film surface is strong. Conversely, the larger the value of the plane orientation coefficient, the weaker the degree of plane orientation, or the more relaxed plane orientation.

(Polar force component in surface free energy)
Contact angle meter ("Surface Energy Analyzer CA-X" manufactured by Kyowa Interface Science Co., Ltd.) for one side of the stretched film (if any one side of the film is corona-treated) ) To measure the contact angle θw of water in contact with the measurement surface and the contact angle θy of methylene diiodide in contact with the measurement surface under the conditions of 20 ° C. and 65% RH. Based on the Wu equation, the polar force component (mJ / m ² ) of the surface free energy was calculated. For calculation (analysis), the Wu method in the analysis software of the surface energy analysis apparatus was used.

(Haze)
About three different places of the obtained stretched film, the haze (%) was measured by using a haze meter (“NDH2000” manufactured by Nippon Denshoku Co., Ltd.) according to JIS-K-7105, and the average value thereof. Was the haze value of the stretched film.

(Initial peeling rate / peeling rate after heating)
For the initial peel rate, the obtained stretched film was used, and for the peel rate after heating, the stretched film after heating at 120 ° C. for 1 hour was used as a test sample, and a copolymer polyester resin (Toyobo Co., Ltd.) was placed on each test sample. “Byron (registered trademark) resin 200SS”) was applied so that the thickness after drying was 5 μm, and dried in an oven at 100 ° C. for 5 minutes. After that, cuts were made on the coated surface of the copolyester resin to produce 100 1 mm × 1 mm grids, and cellophane adhesive tape (“Cello Tape (registered trademark)” manufactured by Nichiban Co., Ltd.)) was strongly pressure-bonded to the grids. Then, a cross-cut peel test was conducted to peel off the end of the tape at a 90 ° angle, and the peel rate (the number of peeled cross-cuts out of 100 cross-cuts) was defined as the peel rate (%).

(Peelability change rate)
The peelability change rate was calculated based on the following formula from the initial peel rate and the peel rate after heating.
Change rate of peelability (%) = [(initial peel rate−peel rate after heating) / initial peel rate] × 100

Example 1
Polyethylene terephthalate (intrinsic viscosity: 0.63 dl / g, silica (“Silicia” manufactured by Fuji Silysia Chemical Co., Ltd .; grade: 310P, shape: amorphous, average particle size: 2.7 μm) as a lubricant contains 600 ppm), 120 After being dried under reduced pressure (1.3 hPa) at 24 ° C. for 24 hours, it was melted at a resin temperature of 285 ° C. using a single-screw extruder, and this was cooled at a die temperature of 285 ° C. and a 25 ° C. cooling roll (peripheral speed). 50 m / min), cast at a speed of 8 m / min, and apply a voltage of 7.2 kV from a tungsten wire electrode with a diameter of 30 μm placed so as to face the circumferential surface of the cooling roll to pass a current of 0.2 mA. Thus, an unstretched film having a thickness (center portion) of 200 μm was obtained by electrostatically adhering to the cooling roll.

Next, the obtained unstretched film was longitudinally stretched in the longitudinal direction (MD direction) and then laterally stretched in the width direction (TD direction) to produce a stretched polyester film. Specifically, after preheating an unstretched film at a preheating temperature (roll temperature) of 120 ° C., the film is stretched 4.3 times in the longitudinal direction at a stretching temperature of 110 ° C., and then 4 in the width direction at a stretching temperature of 100 ° C. Then, the film was stretched by a factor of 0.0, and then heat-fixed at 200 ° C. with a relaxation rate in the width direction of 2.0% to obtain a stretched polyester film.
The properties of the obtained film are shown in Table 1.

(Examples 2 and 3)
A stretched polyester film was obtained in the same manner as in Example 1, except that the temperature of the heat setting treatment after stretching (heat setting temperature) was changed as shown in Table 1.
The properties of the obtained film are shown in Table 1.

Example 4
Polyethylene terephthalate (Intrinsic viscosity: 0.63 dl / g, Silica (“Silysia” manufactured by Fuji Silysia Chemical Co., Ltd .; grade: 310P, shape: amorphous, average particle size: 2.7 μm) as a lubricant contains 1000 ppm), 120 After being dried under reduced pressure (1.3 hPa) at 24 ° C. for 24 hours, it was melted at a resin temperature of 280 ° C. using a single-screw extruder, and this was cooled at a die temperature of 280 ° C. by a 25 ° C. cooling roll (peripheral speed). 50 m / min) is cast at a speed of 5.5 m / min, and a voltage of 7.2 kV is applied from a 30 μm diameter tungsten wire electrode placed so as to face the circumferential surface of the cooling roll, and a current of 0.2 mA is applied. By flowing, the film was electrostatically adhered to the cooling roll to obtain an unstretched film having a thickness (center portion) of 200 μm.

Next, the obtained unstretched film was stretched in the width direction (TD direction) and then stretched in the longitudinal direction (MD direction) to prepare a stretched polyester film. Specifically, after preheating the unstretched film at a preheating temperature (roll temperature) of 100 ° C., it is transversely stretched 3.8 times in the width direction at a stretching temperature of 90 ° C., and then 3 in the longitudinal direction at a stretching temperature of 100 ° C. Then, the film was stretched 9 times longitudinally, and then heat-fixed at 180 ° C. with a relaxation rate in the width direction of 1.6% to obtain a stretched polyester film.
The properties of the obtained film are shown in Table 1.

(Example 5)
A stretched polyester film was obtained in the same manner as in Example 4 except that the production conditions, stretching conditions, and heat setting treatment conditions of the unstretched film were changed as shown in Table 1. In addition, as calcium carbonate (lubricant), synthetic calcium carbonate having an average particle size of 0.88 μm (“Brilliant (registered trademark) 1500” manufactured by Shiraishi Calcium Co., Ltd.) was used.
The properties of the obtained film are shown in Table 1.

(Example 6)
Polyethylene terephthalate (intrinsic viscosity: 0.63 dl / g, silica (“Silicia” manufactured by Fuji Silysia Chemical Co., Ltd .; grade: 310P, shape: amorphous, average particle size: 2.7 μm) as a lubricant contains 700 ppm), 120 After being dried under reduced pressure (1.3 hPa) at 24 ° C. for 24 hours, it was melted at a resin temperature of 280 ° C. using a single screw extruder, and this was cooled by a 20 ° C. cooling roll (peripheral speed) from a 38 cm wide T die at a die temperature of 285 ° C. 50 m / min), cast at a speed of 10 m / min, and apply a voltage of 7.2 kV from a 30 μm diameter tungsten wire electrode placed so as to face the circumferential surface of the cooling roll to pass a current of 0.2 mA. Thus, an unstretched film having a thickness (center portion) of 220 μm was obtained by electrostatically adhering to the cooling roll.

Next, the obtained unstretched film is horizontally stretched in the width direction (TD direction), then vertically stretched in the longitudinal direction (MD direction), and further stretched in the width direction (TD direction), and then stretched polyester. A film was prepared. Specifically, after preheating an unstretched film at a preheating temperature (roll temperature) of 100 ° C., the film is stretched 3.9 times in the width direction at a stretching temperature of 95 ° C., and the relaxation rate in the width direction is set to 5%. Then, the film was longitudinally stretched 3.8 times in the longitudinal direction at a stretching temperature of 100 ° C., then stretched 1.2 times in the width direction again at a stretching temperature of 120 ° C., and then relaxed in the width direction. A heat setting treatment was performed at 220 ° C. with a rate of 3.0% to obtain a stretched polyester film.
The properties of the obtained film are shown in Table 1.

(Comparative Examples 1-9)
A stretched polyester film was obtained in the same manner as in Example 1 except that the production conditions, stretching conditions, and heat setting treatment conditions of the unstretched film were changed as shown in Table 2.
The properties of the obtained film are shown in Table 2.

(Comparative Examples 10-14)
A stretched polyester film was obtained in the same manner as in Example 4 except that the production conditions, stretching conditions, and heat setting treatment conditions of the unstretched film were changed as shown in Table 3.
The properties of the obtained film are shown in Table 3.

  The polyester film of the present invention exhibits good releasability that is difficult to change due to heat with respect to inks, adhesives, etc., and since the dimensional change due to heat is small, it can be dried or aged when used as a film for transfer or peeling. Even when the conditions of the time change, or even when heat is applied during storage or the like, good peeling stability and dimensional stability can be maintained, which is suitable as a transfer process paper or a release paper.

Claims (2)

A stretched polyester film having a thickness of 3 to 50 μm,
The heat shrinkage rate measured at 150 ° C. for 15 minutes in the longitudinal direction of the film is 1 to 8%,
A polyester film characterized in that at least one surface of the film satisfies the following conditions (i) to (iii):
(I) The crystallinity obtained by the total reflection infrared absorption method (ATR-IR method) is 1.25 or more. (Ii) The plane orientation coefficient obtained by the total reflection infrared absorption method (ATR-IR method). 0.2 to 0.25 (iii) The polar force component in the surface free energy is 10 to 16 mJ / m ²   The polyester film according to claim 1, which is a biaxially stretched film.