JP6919583B2 - Biaxially oriented polyester film - Google Patents

Description

The present invention relates to a polyester film having excellent heat moldability and firmness. Preferably, the present invention relates to a polyester film using a polyester resin raw material recycled from a PET bottle, has excellent heat moldability, and contains oligomers (whitening) during heat molding or in a heating step of coating / drying an adhesive resin or the like. ), And it is possible to produce a molded product, a label, etc. without impairing the quality of the polyester film.

Aromatic polyester typified by polyethylene terephthalate (PET) has excellent mechanical properties, heat resistance, chemical resistance, etc., and is widely used as a molded product for fibers, films, etc. because it is an inexpensive resin. Has been done. Since it is also excellent in hygiene, it is widely used as a food container, especially a container for beverages. In addition, since it is a crystalline resin, it has a high elastic modulus, has an excellent elasticity as a film, and is widely used for various label applications. However, the polyester resin does not always have sufficient followability in heat molding using a mold or the like, and improvement thereof has been desired.

Therefore, in order to improve the moldability while taking advantage of the excellent properties of the polyester resin, for example, a glycol component containing branched aliphatic glycol and alicyclic glycol is copolymerized and introduced into the main chain to introduce the polyester resin. Many studies have been conducted to improve the flexibility and moldability (see, for example, Patent Documents 1 to 3). However, while the moldability is improved, the strength and the firmness are lowered, and it cannot be said that the balance between the two is sufficiently maintained, and there is a drawback that the usage is limited. In addition, it has not been used satisfactorily for applications that require a high degree of elasticity, such as a self-supporting POP label.

Japanese Unexamined Patent Publication No. 2004-07513 Japanese Unexamined Patent Publication No. 2005-068238 Japanese Unexamined Patent Publication No. 2005-186364

An object of the present invention is to solve the above-mentioned problems of the prior art, to achieve both moldability at the time of heat molding and film strength and firmness, and to precipitate oligomers at the time of molding or by heating in a coating process of an adhesive resin or the like. It is an object of the present invention to provide a biaxially oriented polyester film capable of producing a molded product, a label, or the like without impairing the quality by suppressing whitening), and a molding member using the biaxially oriented polyester film.

That is, the present invention has the following configuration.
1. 1. A biaxially oriented polyester film that satisfies the following requirements (1) to (4).
(1) The content of the ester constituent unit derived from the isophthalic acid component with respect to all the ester constituent units in all the polyester resins constituting the biaxially oriented polyester film is 0.5 mol% or more and 5.0 mol% or less (2) 150 ° C. , The amount of change in haze of the film when heated for 30 minutes Δ haze {△ haze = (haze after heating)-(haze before heating)} is 2.0% or less (3) Limit of the entire resin constituting the polyester film The viscosity is 0.59 dl / g or more and 0.65 dl / g or less. storage modulus at 0.99 ° C. when measured at conditions, along the length and width of the average value 5.0 × ¹⁰ 8 of the film ^{[Pa] ~7.6 × 10 8 [} Pa]
2. The biaxially oriented polyester film according to the first aspect, which contains 50% by mass or more and 100% by mass or less of a polyester resin recycled from a PET bottle.
3. 3. The biaxially oriented polyester film according to the first or second above, which has a resin layer containing at least one resin selected from a polyester resin, a polyurethane resin, and an acrylic resin on at least one side of the polyester film.
4. A molded body using the biaxially oriented polyester film according to any one of the first to third.
5. An adhesive label having an adhesive layer on at least one side of the biaxially oriented polyester film according to any one of the first to third aspects.

According to the present invention, in addition to being excellent in heat moldability, oligomer precipitation (whitening) is small even during molding and heating in the coating process of adhesive resin, etc., so that the appearance quality is deteriorated and the productivity is lowered due to mold contamination. It can be suppressed. In addition, since it has an excellent elasticity, it is possible to provide a biaxially oriented polyester film that is suitably used for a molded body that is required to maintain its shape and various POP adhesive labels in which a display portion is erected. can.

Hereinafter, embodiments of the present invention will be described in detail.

(Polyester film)
The polyester film in the present invention may be a single-layer film made of one or more types of polyester resins, or may be a multi-layer film when two or more types of polyester resins are used.

The main component of the polyester resin constituting the film is polyethylene terephthalate, and the dicarboxylic acid component of the polyester is isophthalic acid of 0.5 mol% or more and 5.0 mol% or less with respect to all the ester constituent units in the polyester resin. Those containing an acid component and an ester constituent unit derived from an arbitrary diol component typified by ethylene glycol or diethylene glycol are used. The lower limit of the content of the ester constituent unit derived from the isophthalic acid component is preferably 0.5 mol%, more preferably 0.7 mol%, and further preferably 0.9 mol%. When it is 0.5 mol% or more, the heat moldability is good, which is preferable. The upper limit of the content of the ester constituent unit derived from the isophthalic acid component is preferably 5.0 mol%, more preferably 4.0 mol%, and further preferably 3.5 mol%. When it is 5.0 mol% or less, the decrease in crystallinity is small and the heat shrinkage rate is low, which is preferable.

Further, in the production of the polyester film of the present invention, the ultimate viscosity of at least one kind of resin pellets used is preferably in the range of 0.57 to 1.0 dl / g. When the ultimate viscosity is 0.57 dl / g or more, the obtained film is less likely to break, and it is preferable that the film production can be operated stably. On the other hand, when the ultimate viscosity is 1.0 dl / g or less, the filter pressure increase of the molten fluid does not become too large, and it is preferable that the film production can be operated stably.

In the present invention, it is preferable to use a polyester resin recycled from a PET bottle. The lower limit of the content of the polyester resin recycled from the PET bottle with respect to the polyester film is preferably 50% by mass, more preferably 60% by mass, and further preferably 70% by mass. When it is 50% by mass or more, the moldability is good due to the copolymerization of the isophthalic acid component of the polyester, which is preferable. Furthermore, in terms of utilization of recycled resin, a high content rate is preferable in terms of contributing to environmental protection. The upper limit of the content of the polyester resin recycled from the PET bottle is preferably 100% by mass.

Regardless of whether the film has a single-layer structure or a laminated structure, the ultimate viscosity of the film is preferably 0.59 dl / g or more as a whole. More preferably, it is 0.60 dl / g or more. When the ultimate viscosity of the film is 0.59 dl / g or more as a whole, thermal deterioration during heat molding can be suppressed, and the strength and elastic modulus of the molded body can be maintained, which is preferable. On the other hand, a film having an ultimate viscosity of 0.65 dl / g or less as a whole film is preferable because it can be produced with good operability. Further, it is excellent in heat moldability and is preferable.

The thickness of the polyester film is preferably 38 to 200 μm, more preferably 50 to 190 μm. When the thickness is 38 μm or more, the firmness as a film is improved, the effect of improving the shape retention as a molded body or a label is seen, and when the thickness is 200 μm or less, it is advantageous for weight reduction and flexibility. , Excellent workability and handleability.

The surface of the polyester film of the present invention may be smooth or has irregularities, but it is preferable to form irregularities in order to give a certain degree of slipperiness from the viewpoint of handleability. The haze is preferably 5% or less, more preferably 3% or less, and most preferably 2% or less. When the haze is 5% or less, it is suitable when transparency is required in the molded product or label. The lower limit of the haze is not limited, but may be 0.1% or more, or 0.3% or more.

As a method of forming irregularities on the polyester surface, it can be formed by blending particles in the polyester resin layer of the surface layer or coating a resin solution containing the particles in the middle of film formation.

As a method of blending the particles in the polyester resin, a known method can be adopted. For example, it can be added at any stage in the production of polyester, but is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or at the stage after the completion of the transesterification reaction and before the start of the polycondensation reaction. Then, the polycondensation reaction may proceed. Further, a method of blending a slurry of particles dispersed in ethylene glycol or water with a polyester raw material using a kneading extruder with a vent, or a method of blending dried particles with a polyester raw material using a kneading extruder. It can be done by such as.

Among them, aggregate inorganic particles are homogeneously dispersed in a monomer solution that is a part of the polyester raw material, and then filtered, and the residue of the polyester raw material before the esterification reaction, during the esterification reaction, or after the esterification reaction is used. The method of addition is preferable. According to this method, since the monomer solution has a low viscosity, homogeneous dispersion of particles and high-precision filtration of the slurry can be easily performed, and when added to the rest of the raw material, the dispersibility of the particles is good, which is new. Aggregates are also unlikely to occur. From this point of view, it is particularly preferable to add it to the balance of the raw material in a low temperature state before the esterification reaction.

As the type of particles to be blended, in addition to inorganic lubricants such as silica, calcium carbonate and alumina, heat-resistant organic particles can be preferably used. Of these, silica and calcium carbonate are more preferable. With these, transparency and slipperiness can be exhibited.

In addition, the polyester film may contain various additives within a range that maintains a preferable range of total light transmittance. Examples of the additive include an antistatic agent, a UV absorber, and a stabilizer.

The total light transmittance of the polyester film is preferably 85% or more, more preferably 87% or more. If the transmittance is 85% or more, sufficient visibility can be ensured. It can be said that the higher the total light transmittance of the polyester film, the better, but it may be 99% or less, or 97% or less.

The surface of the polyester film of the present invention can be treated to improve the adhesion to the resin or ink layer forming the hard coat layer.

Examples of the surface treatment method include sandblasting, unevenness treatment by solvent treatment, corona discharge treatment, electron beam irradiation treatment, plasma treatment, ozone / ultraviolet irradiation treatment, flame treatment, chromic acid treatment, hot air treatment, and the like. Oxidation treatment and the like can be mentioned and can be used without particular limitation.

Further, the adhesiveness can be improved by providing the easy-adhesion resin layer on the surface of the polyester film. As the easy-adhesion resin layer, a polyester resin, a polyurethane resin, an acrylic resin, a polyether resin, or the like can be used without particular limitation. Further, a crosslinked structure may be formed in order to improve the adhesion durability of these easy-adhesion layers. By containing a cross-linking agent, it becomes possible to further improve the adhesion under high temperature and high humidity. Specific examples of the cross-linking agent include urea-based, epoxy-based, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based. Further, in order to promote the cross-linking reaction, a catalyst or the like can be appropriately used as needed.

The easy-adhesive resin layer may also contain lubricant particles in order to impart slipperiness to the surface. The particles may be inorganic particles or organic particles, and are not particularly limited. (1) Silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, etc. Barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, zirconium oxide, titanium dioxide, aluminum silicate, silica soil, calcium silicate, aluminum hydroxide, calcium carbonate, magnesium carbonate, calcium phosphate, magnesium hydroxide, barium sulfate, etc. Inorganic particles, (2) Acrylic or methacrylic, vinyl chloride, vinyl acetate, nylon, styrene / acrylic, styrene / butadiene, polystyrene / acrylic, polystyrene / isoprene, polystyrene / isoprene, methyl methacrylate / Butyl methacrylate-based, melamine-based, polycarbonate-based, urea-based, epoxy-based, urethane-based, phenol-based, diallyl phthalate-based, polyester-based, etc. , Silica is particularly preferably used.

The average particle size of the particles is preferably 10 nm or more, more preferably 20 nm or more, still more preferably 30 nm or more. When the average particle size of the particles is 10 nm or more, it is preferable that agglutination is difficult and slipperiness can be ensured.

The average particle size of the particles is preferably 1000 nm or less, more preferably 800 nm or less, still more preferably 600 nm or less. When the average particle size of the particles is 1000 nm or less, transparency is maintained and the particles do not fall off, which is preferable.

(Characteristics of polyester film)
The amount of change in film haze when the polyester film of the present invention is heated at 150 ° C. for 30 minutes Δ haze {△ haze = (haze after heating) − (haze before heating)} is preferably 2.0% or less. It is preferably 1.5% or less, and more preferably 1.0% or less. When the haze is 2.0% or less, oligomer precipitation is suppressed during the heat molding process of the film, the mold is less likely to be contaminated, and the molded body is not whitened and the appearance quality is not deteriorated, which is preferable. Further, when a functional resin such as an adhesive is applied and dried, oligomer precipitation is suppressed, and functionality such as adhesiveness is effectively exhibited, which is preferable. The Δhaze is more preferably small, and the lower limit of the Δhaze is 0%.

When the polyester film of the present invention is measured with a width of 5 mm, a grip interval of 30 mm, a dynamic viscoelasticity measuring device in a tensile mode, a frequency of 10 Hz, and a heating rate of 5 ° C./min, the storage elastic modulus at 150 ° C. is , an average value in the longitudinal direction (MD direction) and the width direction (TD direction) of the film is ^{5.0 × 10 8 [Pa] ~7.6} × 10 8 [Pa]. When the polyester film is within the range of the storage elastic modulus, the polyester film can be appropriately deformed at the time of thermoforming, and the molding followability is improved. If it falls below the lower limit of the storage elastic modulus, deformation occurs during heat molding, and the amount of protrusion tends to increase. Further, when the upper limit value of the storage elastic modulus is exceeded, the heat molding followability is lowered.

(Manufacturing method of polyester film)
Next, the method for producing the polyester film will be described in detail, but the method is not limited thereto. Further, the number of layers is not limited, such as a single-layer structure or a multi-layer structure.

After the polyester resin pellets are mixed and dried at a predetermined ratio, they are supplied to a known hot-dip laminating extruder, extruded into a sheet from a slit-shaped die, and cooled and solidified on a casting drum to form an unstretched film. do. In the case of a single layer, one extruder may be used, but in the case of producing a multi-layer film, two or more extruders, two or more layers of manifolds or a merging block (for example, a merging having a square merging portion). A block) can be used to stack a plurality of film layers constituting each outermost layer, extrude two or more sheets from the base, and cool the film with a casting drum to form an unstretched film.

In this case, it is preferable to perform high-precision filtration in order to remove foreign substances contained in the resin at an arbitrary place where the molten resin is maintained at about 280 ° C. during melt extrusion. The filter medium used for high-precision filtration of the molten resin is not particularly limited, but the filter medium of the stainless sintered body is excellent in the removal performance of aggregates containing Si, Ti, Sb, Ge and Cu as main components and high melting point organic substances. Therefore, it is preferable.

Further, the filtered particle size (initial filtration efficiency 95%) of the filter medium is preferably 50 μm or less, and particularly preferably 20 μm or less. If the filtered particle size (initial filtration efficiency 95%) of the filter medium exceeds 50 μm, foreign matter having a size of 50 μm or more cannot be sufficiently removed. High-precision filtration of the molten resin using a filter medium having a filter medium size (initial filtration efficiency of 95%) of 50 μm or less may reduce productivity, but a film with few protrusions due to coarse particles can be obtained. Preferred above.

More specifically, as described above, PET pellets containing particles for the purpose of imparting slipperiness are sufficiently vacuum-dried, supplied to an extruder, and melt-extruded into a sheet at about 280 ° C. It is cooled and solidified to form an unstretched PET sheet. The obtained unstretched sheet is stretched 2.5 to 5.0 times in the longitudinal direction with a roll heated to 80 to 120 ° C. to obtain a uniaxially oriented PET film.

In the method of providing the easy-adhesive resin layer on the surface of the polyester film, the coating liquid can be applied to at least one surface of the polyester film at any stage of the polyester film manufacturing process to form the easy-adhesive resin layer. For example, after obtaining the uniaxially oriented PET film, the easy-adhesion resin layer may be formed on one side of the polyester film or on both sides. The solid content concentration of the resin composition in the coating liquid is preferably 2 to 35% by mass, and particularly preferably 4 to 15% by mass.

The method of providing the easily adhesive resin layer on the surface of the polyester film can be formed by a coating method of any known method. For example, reverse roll coating method, gravure coating method, kiss coating method, reverse kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, curtain. The coat method, etc. can be mentioned. These methods can also be applied alone or in combination.

Next, the edge of the film is gripped with a clip, guided to a hot air zone heated to 80 to 180 ° C., preheated, and then stretched 2.5 to 5.0 times in the width direction. Subsequently, the heat treatment zone is led to a heat treatment zone of 160 to 240 ° C., and heat treatment is performed for 1 to 60 seconds to complete the crystal orientation. In this heat treatment step, if necessary, a relaxation treatment of 1 to 12% may be performed in the width direction or the longitudinal direction.

The biaxially oriented polyester film according to the present invention is suitably used for heat molding using a mold. When the mold is molded using the biaxially oriented polyester film of the present invention, the appearance quality is deteriorated because the oligomer precipitation (whitening) is small even under heating during molding as compared with the case where the conventional polyester film is used. It is possible to suppress a decrease in productivity due to mold contamination. In addition, it has a remarkable effect that it can be molded at a low molding temperature and the finish of the molded product is improved. Furthermore, the molded product thus molded has excellent elasticity and morphological stability when used in a room temperature atmosphere, and also has a small environmental load. Therefore, the name plate for home appliances, the name plate for automobiles, dummy cans, building materials, and cosmetics It can be suitably used as a molding member for a plate, a decorative steel plate, a transfer sheet and the like.

Since the biaxially oriented polyester film of the present invention has less oligomer precipitation (whitening) even under heating in the coating process of the adhesive resin or the like, the appearance quality does not deteriorate and is attached to articles such as plastic molded products, steel plates and cans. It is useful for adhesive labels that are attached and used, and also has an excellent firmness, so it is particularly useful for POP adhesive labels where a display unit that is required to maintain stable shape is erected. Since it has various good printability and good adhesion to an adhesive, it can provide an adhesive label having excellent appearance and design, and also excellent adhesion and durability between the adhesive layer and an article. Is.

Next, the present invention will be described with reference to Examples and Comparative Examples. First, the evaluation method of the characteristic value used in the present invention is shown below.

(1) Content of ester constituent units derived from terephthalic acid and isophthalic acid contained in the raw material polyester and the polyester constituting the film A sample was dissolved in a mixed solution of heavy chloroform and trifluoroacetic acid (volume ratio 9/1). The sample solution was prepared and the NMR of the proton was measured using NMR (“GEMINI-200”; manufactured by Varian). The peak intensity of a predetermined proton was calculated, and the content (mol%) of the ester constituent unit derived from terephthalic acid and the ester constituent unit derived from isophthalic acid in 100 mol% of the ester constituent units was calculated.

(2) Haze Measured in accordance with JIS K 7136 “How to obtain haze of transparent plastic material”. As a measuring instrument, a haze meter NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. was used.

(3) Evaluation of change in haze (Δhaze) A film was cut into 50 mm squares, and the haze before heating was measured in accordance with JIS K 7136 “How to obtain haze of transparent plastic material”. A haze meter NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. was used as the measuring instrument. After the measurement, the film was set in an oven heated to 150 ° C., the film was taken out after 30 minutes, and the haze of the heated film was measured in the same manner as described above to obtain a haze after heating. The haze difference before and after heating was defined as Δhaze.
△ Haze (%) = (Haze after heating)-(Haze before heating)

(4) Extreme Viscosity The film or polyester resin was pulverized and dried, and then dissolved in a mixed solvent of phenol / tetrachloroethane = 60/40 (mass ratio). After centrifuging this solution to remove inorganic particles, the flow time of the solution at a concentration of 0.4 (g / dl) at 30 ° C. and the flow time of the solvent alone were measured using an Ubbelohde viscometer. From those time ratios, the ultimate viscosity was calculated using the Huggins formula, assuming that the Huggins constant was 0.38. In the case of a laminated film, the ultimate viscosity of each layer was evaluated by scraping off the corresponding polyester layer of the film according to the laminated thickness.

(5) Storage elastic modulus Using a dynamic viscoelasticity measuring device (DVA225 manufactured by IT Measurement Control Co., Ltd.), 150 in the longitudinal direction (MD direction) and the width direction (TD direction) of the film under the following conditions. The storage elastic modulus (E') at ° C was determined. The measurement was performed in tension mode.
(A) Sample width: 5 mm (b) Sample gripping interval: 30 mm
(C) Measurement temperature range: 20 to 250 ° C. (d) Frequency: 10 Hz
(E) Temperature rise rate: 5 ° C./min

(6) Mold Formability After printing on the easy-adhesion resin layer surface of the film, it was heat-pressed with a stainless steel mold at 160 ° C. The press pressure was 5 kgf / cm ^2, and the press pressure was 20 times continuously for 30 seconds each time. The shape of the mold was a cup shape, the opening had a diameter of 50 mm, the bottom part had a diameter of 40 mm, the depth was 10 mm, and all the corners were curved with a diameter of 0.5 mm. .. Molded products were evaluated for moldability, finish, and mold stainability, and ranked according to the following criteria. Here, ○ was regarded as a pass, and Δ and × were regarded as a failure.
◯: The molded product has no tears or wrinkles, and there is no visual stain on the mold after continuous molding. Δ: The molded product has slight wrinkles and the mold is slightly contaminated (visually) after continuous molding. × : Molded product with tears, or wrinkles even if there is no tear, and mold contamination (visual) after continuous molding

(Preparation of polyethylene terephthalate resin (I))
When the temperature of the esterification reaction can reached 200 ° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged, and 0.017 parts by mass of antimony trioxide was used as a catalyst while stirring. 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Then, the pressure was raised and the pressure esterification reaction was carried out under the conditions of a gauge pressure of 0.34 MPa and 240 ° C., the esterification reaction can was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Further, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Then, 15 minutes later, dispersion treatment was performed with a high-pressure disperser, 0.1% by mass of sodium tripolyphosphate aqueous solution was further contained as sodium atoms in the silica particles, and the coarse grain portion was cut by 35% by centrifugation, and the particles were cut. An ethylene glycol slurry of silica particles having an average particle diameter of 2.5 μm, which had been filtered with a metal filter having an opening of 5 μm, was added in an amount of 0.2 parts by mass as a particle content. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can, and a polycondensation reaction was carried out at 280 ° C. under reduced pressure.
After completion of the polycondensation reaction, filtration is performed with a Naslon filter having a 95% cut diameter of 5 μm, extruded into a strand shape from a nozzle, and cooled and solidified using cooling water that has been previously filtered (pore diameter: 1 μm or less). , Cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl / g, an oligomer content of 0.96% by mass, and substantially no inert particles and internally precipitated particles. (Hereafter, it is abbreviated as PET resin (I).)

(Preparation of polyethylene terephthalate resin (II))
In the production of PET (A), a polyethylene terephthalate resin (II) having an intrinsic viscosity of 0.62 dl / g containing no silica particles was obtained. (Hereafter, it is abbreviated as PET resin (II).)

(Adjustment of polyester resin (III) recycled from PET bottles)
After removing the remaining foreign substances such as beverages and labels from the PET bottle for beverages, the flakes obtained by crushing are melted by an extruder, and the filter is changed to a finer one with an opening size in order, and the finer foreign substances are repeated twice. Is filtered, and the third time, the filter is filtered with the smallest opening size filter of 50 μm, extruded into a strand shape from a nozzle, and cooled and solidified using cooling water that has been previously filtered (pore diameter: 1 μm or less). , It was cut into pellets to obtain a polyester resin (III). The ratio of the ester constituent units of the obtained polyester resin (III) is terephthalic acid-derived ester constituent units / isophthalic acid-derived ester constituent units = 98.6 / 1.4 (mol%), and the ultimate viscosity of the resin is It was 0.65 dl / g.

(Preparation of Copolymerized Polyester Resin Water Dispersion Liquid (A))
95 parts by mass of dimethyl terephthalate, 95 parts by mass of dimethyl isophthalate, 35 parts by mass of ethylene glycol, 145 parts by mass of neopentyl glycol, 0.1 parts by mass of zinc acetate and 0.1 parts by mass of antimony trioxide were charged into a reaction vessel at 180 ° C. The transesterification reaction was carried out over 3 hours. Next, 6.0 parts by mass of 5-sodium sulfoisophthalic acid was added, and the esterification reaction was carried out at 240 ° C. for 1 hour, and then at 250 ° C. under reduced pressure (10 to 0.2 mmHg) over 2 hours. A polycondensation reaction was carried out to obtain a copolymerized polyester resin having a number average molecular weight of 19,500 and a softening point of 60 ° C.
300 parts by mass of the obtained copolymer polyester resin and 140 parts by mass of butyl cellosolve are stirred at 160 ° C. for 3 hours to obtain a viscous melt, and 560 parts by mass of water is gradually added to the melt for 1 hour. Later, a uniform pale white copolymerized polyester resin aqueous dispersion (A) having a solid content concentration of 30% was obtained.

(Preparation of polyurethane resin aqueous solution (B))
100 parts by mass of polyester diol (OHV: 2000 eq / ton) composed of adipic acid, 1,6-hexanediol and neopentyl glycol (molar ratio: 4/2/3) and 41.4 parts by mass of xylylene diisocyanate. After mixing and reacting at 80 to 90 ° C. for 1 hour under a nitrogen stream, the mixture was cooled to 60 ° C., and 70 parts by mass of tetrahydrofuran was added to dissolve the mixture. Urethane prepolymer solution (NCO / OH ratio: 2.2, free). Isocyanate group: 3.30% by mass) was obtained. Subsequently, the urethane prepolymer solution was brought to 40 ° C., then 45.5 parts by mass of a 20% by mass sodium bisulfite aqueous solution was added, and the mixture was reacted at 40 to 50 ° C. for 30 minutes with vigorous stirring. After confirming the disappearance of the free isocyanate group content (in terms of solid content), a self-crosslinking polyurethane resin aqueous solution (B) containing an isocyanate group diluted with emulsified water and blocked with sodium disulfide having a solid content of 20% by mass. Got

(Preparation of coating liquid (C) for forming an easy-adhesive resin layer)
7.5 parts by mass of the 30% by mass aqueous dispersion (A) of the copolymerized polyester resin, 11.3 parts by mass of the self-crosslinking polyurethane resin aqueous solution (B), 0.3 parts by mass of the organic tin catalyst, 39.8 parts by mass of water and 37.4 parts by mass of isopropyl alcohol were mixed. Further, a 10% by mass aqueous solution (0.6 parts by mass) of a fluorine-based surfactant (polyoxyethylene-2-perfluorohexyl ethyl ether) and a 20% by mass aqueous dispersion (2) of colloidal silica (average particle size 40 nm). .3 parts by mass) and a 3.5% by mass aqueous dispersion (0.5 parts by mass) of dry silica (average particle size 200 nm, average primary particle size 40 nm) were added. Next, the pH of the mixture is adjusted to 6.2 with a 5 mass% aqueous solution of sodium bicarbonate, and the mixture is precisely filtered with a felt-type polypropylene filter having a filtered particle size (initial filtration efficiency: 95%) of 10 μm to obtain a coating liquid. (C) was prepared.

(Preparation of coating liquid (D) for forming a slippery resin layer)
15 parts by mass of 30% by mass aqueous dispersion (A) of copolymerized polyester resin, 0.4 parts by mass of 50% by mass aqueous solution of sodium dodecyldiphenyloxide disulfonate, 40 parts of polyethylene wax emulsion (molecular weight 4,000) 0.5 parts by mass of a mass% aqueous dispersion, 51 parts by mass of water, and 30 parts by mass of isopropyl alcohol were mixed. Further, a 10% by mass aqueous solution (0.3 parts by mass) of a fluorine-based surfactant (polyoxyethylene-2-perfluorohexyl ethyl ether) and a 20% by mass aqueous dispersion (2) of colloidal silica (average particle size 40 nm). .3 parts by mass) and a 10% by mass aqueous dispersion (0.5 parts by mass) of benzoguanamine-based organic particles (average particle size 2 μm) were added. Next, the above mixture was microfiltered with a felt-type polypropylene filter having a filtered particle size (initial filtration efficiency: 95%) of 10 μm to prepare a coating liquid (D).

(Example 1)
The pellet of the polyester resin (III) was dried under reduced pressure (3 Torr) at 150 ° C. for 8 hours, then supplied to an extruder and melted at 285 ° C. This polymer is filtered through a stainless sintered filter medium (nominal filtration accuracy of 10 μm particles 95% cut), extruded into a sheet from the base, and then contacted with a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method. The film was cooled and solidified to prepare an unstretched film. This unstretched film was uniformly heated to 75 ° C. using a heating roll and heated to 100 ° C. with a non-contact heater to perform 3.3 times roll stretching (longitudinal stretching). Next, the coating liquid (C) was applied to the contact surface side of the casting drum of the uniaxially stretched film, and the coating liquid (D) was applied to the opposite surface by the reverse kiss coating method, so that the thickness of the resin solid content after drying was 0.3 μm. Each was applied so as to be. The uniaxially stretched film having the coating layer is led to a tenter while being dried, heated to 140 ° C., laterally stretched 4.0 times, fixed in width, heat-treated at 240 ° C. for 5 seconds, and further subjected to heat treatment at 210 ° C. in the width direction. A polyester film having a thickness of 188 μm was obtained by relaxing the mixture by 4%.

(Example 2)
A polyester film was obtained in the same manner as in Example 1 above, except that the film thickness after biaxial stretching was changed to 125 μm.

(Examples 3 to 4)
A polyester film having a thickness of 125 μm was obtained in the same manner as in Example 2 above, except that the polyester resin as a raw material was changed to the configuration shown in Table 1.

(Example 5)
The raw material polyester resin was changed to the configuration shown in Table 1. Specifically, in the skin layer formation, the pellets of the PET resin (I) and the pellets of the polyester resin (III) are dried and then mixed at a ratio of polyester resin (III) / PET resin (I) = 85% by mass / 15% by mass. Then, it was melted at 285 ° C. by a melt extruder separate from the core layer forming system. In the core layer forming system, the pellets of the polyester resin (III) were dried and then melted at 285 ° C. by a melt extruder. These polymers are filtered through a stainless steel sintered filter medium (nominal filtration accuracy of 10 μm particles 95% cut), merged in the feed block, extruded into a sheet from the base, and then surfaced using the electrostatic application casting method. It was brought into contact with a casting drum having a temperature of 30 ° C. and cooled and solidified to obtain an unstretched film. The layer ratio of the unstretched film was adjusted so that the discharge amount of each extruder was calculated so that the skin layer / core layer / skin layer = 9/82/9. This unstretched film was uniformly heated to 75 ° C. using a heating roll and heated to 100 ° C. with a non-contact heater to perform 3.3 times roll stretching (longitudinal stretching). Next, the coating liquid (C) was applied to the casting drum contact surface side of the uniaxially stretched film by a reverse kiss coating method so that the thickness of the resin solid content after drying was 0.3 μm. The uniaxially stretched film having the coating layer is led to a tenter while being dried, heated to 140 ° C., laterally stretched 4.0 times, fixed in width, heat-treated at 240 ° C. for 5 seconds, and further subjected to heat treatment at 210 ° C. in the width direction. A laminated polyester film having a thickness of 50 μm was obtained by relaxing the mixture by 4%.

(Example 6)
A laminated polyester film having a thickness of 50 μm was obtained in the same manner as in Example 5 above, except that the polyester resin as a raw material was changed to the configuration shown in Table 1.

(Comparative Example 1)
A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 above, except that the polyester resin as a raw material was changed to the configuration shown in Table 1.

(Comparative Examples 2 and 3)
A polyester film having a thickness of 125 μm was obtained in the same manner as in Example 2 above, except that the polyester resin as a raw material was changed to the configuration shown in Table 1.

(Comparative Example 4)
A laminated polyester film having a thickness of 50 μm was obtained in the same manner as in Example 5 above, except that the polyester resin as a raw material was changed to the configuration shown in Table 1.

According to the polyester film of the present invention, in addition to being excellent in heat moldability, oligomer precipitation (whitening) is small even during molding and heating in the coating process of adhesive resin, etc., so that the appearance quality is deteriorated and the production is caused by mold contamination. It is possible to suppress the decrease in sex. In addition, since it has an excellent elasticity, it is possible to provide a polyester film that is suitably used for a molded body that is required to maintain a stable shape, various POP adhesive labels in which a display portion is erected, and the like.

Claims (5)

A resin layer containing at least one resin selected from polyester-based resin, polyurethane-based resin, and acrylic-based resin is provided on at least one side.
A biaxially oriented polyester film that satisfies the following requirements (1) to (4).
(1) The content of the ester constituent unit derived from the isophthalic acid component with respect to all the ester constituent units in all the polyester resins constituting the biaxially oriented polyester film is 0.5 mol% or more and 5.0 mol% or less (2) 150 ° C. The amount of change in haze of the film when heated for 30 minutes Δ haze {△ haze = (haze after heating)-(haze before heating)} is 2.0% or less (3) Extreme viscosity of the resin constituting the polyester film Is 0.59 dl / g or more and 0.65 dl / g or less. The storage elasticity at 150 ° C. measured in 1) is 5.0 × 108 [Pa] to 7.6 × 108 [Pa], which is the average value in the longitudinal direction and the width direction of the film.
Further, the resin layer contains particles having an average particle size of 10 nm or more and 1000 nm or less.
Biaxially oriented polyester film. The biaxially oriented polyester film according to claim 1, which contains 50% by mass or more and 100% by mass or less of a polyester resin recycled from a PET bottle. The biaxially oriented polyester film according to claim 1 or 2, wherein the resin layer is an easy-adhesion layer containing a copolymerized polyester resin. A molded body using the biaxially oriented polyester film according to any one of claims 1 to 3. An adhesive label having an adhesive layer on at least one side of the biaxially oriented polyester film according to any one of claims 1 to 3.