JP5694260B2 - Laminated polyester film - Google Patents

Description

  The present invention relates to a laminated polyester film. More specifically, the present invention relates to a laminated polyester film having a coating layer formed from a coating solution containing a polymer having a cation in the side chain on one side of a multilayer polyester film containing a colorant.

  Polyester films are excellent in heat resistance, water resistance, chemical resistance, mechanical strength, dimensional stability, etc., and have been used in various industrial applications, and their applications are expanding and diversifying. In such diversification, the required characteristics have become more and more stringent, but the current situation is that they have not been fully satisfied.

  For example, in the use of a film containing a colorant such as an automobile window pasting film, an X-ray bluing film, and a display application, even if a good colorant such as color preparation, heat resistance and dispersibility is selected, it is severe. Under such heating conditions, the colorant bleeds out from the film containing the colorant, and there is a need for improvement.

  In order to solve the above problems, Patent Documents 1 and 2 propose a coextruded laminated film comprising three or more layers containing a colorant in an intermediate layer in order to prevent bleeding out of the colorant. However, the film described in the above patent document still has insufficient colorant sealing performance under severe heating conditions.

Japanese Patent Laid-Open No. 10-157040 JP 2002-52675 A

  This invention is made | formed in view of the said situation, Comprising: The solution subject is providing the polyester film which has the outstanding colorant sealing performance also on severe heating conditions.

  As a result of intensive studies in view of the above circumstances, the present inventors have found that the use of a polyester film having a specific configuration can easily solve the above-described problems, and have completed the present invention.

That is, the gist of the present invention is that at least one layer of a multilayer polyester film having at least three layers containing a colorant in the intermediate layer has a polymer having a cation in the side chain as a proportion of 85% by weight or more based on the total nonvolatile components in the coating solution. A film having a coating layer formed from a coating solution containing the solution, and after heating the film at 180 ° C. for 10 minutes, the coating layer surface (250 cm ² ) is extracted with 10 mL of dimethylformamide, and the dimethylformamide In the laminated polyester film, the color difference ΔE * ab value of the liquid before extraction is 10 or less.

  According to the polyester film of the present invention, a colorant film excellent in colorant sealing performance can be provided, and its industrial value is high.

  The present invention is a multilayer polyester film having at least three layers, and examples of the polymer constituting each layer of the multilayer film include polyesters obtained using aromatic dicarboxylic acid or its ester and glycol as main starting materials, and repeating structural units. A polyester having 80% or more of ethylene terephthalate units or ethylene-2,6-naphthalate units is preferred. If it is in said range, you may contain the other 3rd component.

  As an aromatic dicarboxylic acid component, in addition to terephthalic acid and 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxyethoxybenzoic acid, etc.), etc. Can be used. As the glycol component, in addition to ethylene glycol, for example, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be used. In the film of the present invention, the outermost layer is a layer constituting two exposed surfaces, and the other layers are called intermediate layers. The intrinsic viscosity (IV) of the polyester composition constituting the outermost layer and the intermediate layer is usually 0.30 to 0.90, preferably 0.40 to 0.80, more preferably 0.50 to 0.80. is there. If the IV value is less than 0.3, the heat resistance, mechanical strength, etc. when used as a film tend to be inferior. On the other hand, if the IV value exceeds 0.90, the load becomes excessive in the extrusion process during the production of the polyester film, and as a result, the productivity may be lowered.

  The laminated polyester film of the present invention contains a colorant. In this invention, the structure which contains the coloring agent in the intermediate | middle layer of a multilayer film from a viewpoint of reducing the bleeding out of a coloring agent is preferable.

  As the colorant contained in the intermediate layer of the present invention, it is preferable to consider the heat resistance during the production of the polyester and the dispersibility in the polyester. In terms of chemical structure, anthraquinone dyes, phthalocyanine pigments, etc. Are preferably used, and disperse dyes and oil-soluble dyes are suitable for dyeing. These dyes are generally used by appropriately selecting several types and mixing them, and the content in the raw material polyester constituting each layer is preferably in the range of 0.01 to 10% by weight.

  In the outermost layer of the laminated film of the present invention, the surface is roughened to improve the workability of the winding process at the time of film production and the coating and the laminating process at the time of manufacturing the film for pasting automobile windows. It is preferable to impart slipperiness, and for this purpose, addition of fine inert particles to the film can be mentioned.

  The fine inert particles used in the present invention preferably have an average particle size of 0.5 to 3 μm, and more preferably 0.8 to 2 μm. When the average particle size is less than 0.5 μm, workability tends to be inferior. Moreover, in the particle | grains with an average particle diameter exceeding 3 micrometers, the planarity of the film surface may be impaired or transparency may be impaired. Furthermore, the addition amount of the inert particles is usually 0.001 to 1.0% by weight, preferably 0.005 to 0.7% by weight. When the addition amount of the inert particles is less than 0.001% by weight, the winding property of the film tends to be inferior. Moreover, when the addition amount of an inert particle exceeds 1.0 weight%, the degree of the roughening of a film surface will become large too much, and there exists a tendency for film transparency to be impaired.

  Examples of inert particles that can be used in the present invention include silicon oxide, titanium oxide, zeolite, silicon nitride, boron nitride, celite, alumina, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, calcium phosphate, Examples include, but are not limited to, lithium phosphate, magnesium phosphate, lithium fluoride, aluminum oxide, silicon oxide, titanium oxide, kaolin, talc, carbon black, silicon nitride, boron nitride, and crosslinked polymer fine powder. It is not something. In the present invention, the inert particles to be blended may be a single component, or two or more components may be used simultaneously. In the present invention, the method of incorporating the inert particles and the dye into the polyester is not particularly limited, but the method of adding to the polymerization step, the method of kneading the particles and the dye using an extruder to obtain a master batch. Etc.

  In the present invention, it is an essential requirement to have a coating layer formed from a coating solution containing a polymer having a cation in the side chain on at least one side of the multilayer polyester film.

  In the present invention, the polymer having a cation in the side chain refers to a polymer containing a cation in the side chain structure in the molecular structure of the polymer.

  Specific examples of the side chain structure containing a cation include those represented by the following formulas (1) and (2).

（１）

(1)

（２）

(2)

In the above formulas (1) and (2), the number of carbon atoms of R ^{1 to} R ⁵ is not limited as long as it can be synthesized. For example, R ¹ is hydrogen, a phenyl group, or an alkyl group having 1 to 8 carbon atoms. R ² is an alkylene group having 1 to 8 carbon atoms, and R ³ , R ⁴ and R ⁵ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms. X ⁻ represents an anion.

  In addition to the above, examples include structures formed by polymerizing vinylbenzyltrimethylammonium salt, 2-hydroxy3-methacryloxypropyltrimethylammonium salt, and the like.

  In addition, examples of the anion serving as a counter ion of these quaternary ammonium salts include ions such as halogen ions, sulfonates, phosphates, nitrates, alkylsulfonates, and carboxylates.

  In the present invention, the polymer having a cation in the side chain includes a polymer having a zwitterion in the side chain.

  The polymer having zwitterion in the side chain refers to a polymer containing both a cation and an anion in the side chain structure in the molecular structure of the polymer.

Examples of the side chain structure containing a cation include the side chain structure as described above, and examples of the side chain structure containing an anion include various anions such as carboxylate, sulfonate, phosphate, and nitrate. Side chain structure.
Specific examples of the side chain structure containing an anion include those represented by the following formula (3).

In the above formula (3), the carbon number of R ¹ is not limited as long as it can be synthesized. For example, R ¹ is hydrogen, a phenyl group, or an alkyl group having 1 to 8 carbon atoms. M ⁺ represents a hydrogen ion or a metal ion.

  In addition, the polymer having an amphoteric ion in the side chain in the present invention includes a polymer having a cation and an anion within the same molecular structural unit, such as the following formulas (4) and (5).

（４）

(4)

（５）

(5)

In the above formulas (4) and (5), the number of carbon atoms of R ^{1 to} R ⁵ is not limited as long as synthesis is possible. For example, R ₁ is hydrogen, a phenyl group, or an alkyl group having 1 to 8 carbon atoms. R ₂ is an alkylene group having 1 to 8 carbon atoms, R ³ and R ⁴ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and R ⁵ is an alkylene group having 1 to 4 carbon atoms. Is mentioned. X ⁻ represents an anion, and M ⁺ represents a hydrogen ion or a metal ion.

  In the present invention, from the viewpoint of the coloring material sealing effect, it is more preferable to use a polymer having a side chain structural unit exhibiting a cationic property and an anionic property within the same structural unit.

  As a ratio with respect to all the non-volatile components in the coating solution for forming the coating layer, the polymer having a cation in the side chain is usually in the range of 10% by weight or more, preferably in the range of 30% by weight or more, more preferably in the range of 85% by weight. is there.

  If it is less than 10% by weight, the effect of suppressing bleeding out of the color material from the laminated film may be reduced.

  In this invention, you may contain a crosslinking agent in the said coating liquid. Crosslinking agents include melamine compounds, guanamines, alkylamides, polyamides, epoxy compounds, oxazoline compounds, aziridine compounds, block isocyanate compounds, silane coupling agents, dialcohol aluminate coupling agents, zircoaluminate A coupling agent, a peroxide, a heat or photoreactive vinyl compound, a photosensitive resin, and the like can be mentioned. From the viewpoint of improving mechanical strength, the use of a melamine compound is particularly preferable.

  In the present invention, the coating solution may contain one or more water-soluble or water-dispersible polymers for the purpose of improving the coating strength. Examples of such polymers include polyester resins and polyurethanes. Examples thereof include resins, acrylic resins, vinyl resins, epoxy resins, amide resins, and the like.

  In addition, these skeleton structures may have a composite structure substantially by copolymerization or the like, and examples of the polymer having a composite structure include acrylic resin graft polyester, acrylic resin graft polyurethane, and vinyl resin graft. Examples thereof include polyester and vinyl resin graft polyurethane.

  Among the above polymers, from the viewpoint of compatibility with other substances in the coating liquid, it is preferable to use polyvinyl alcohol classified as a vinyl resin as the polymer.

  In the present invention, particles may be contained in the coating solution for improving the slipperiness of the coating layer. Examples of the particles include inert inorganic particles such as colloidal silica, alumina, calcium carbonate, and titanium dioxide, fine particles obtained from polystyrene resins, polyacrylic resins, polyvinyl resins, or organic particles represented by these crosslinked particles. The

  The coating solution used to obtain the coating layer contains an antifoaming agent, coating improver, thickener, antistatic agent, mold release agent, antioxidant, ultraviolet absorber, foaming agent, etc. as necessary. You may contain.

  Further, the coating solution preferably contains water as a main medium, and may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film forming performance. When the organic solvent is used by being mixed with water, which is the main medium, it is desirable to use it in a range that dissolves in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol and methyl alcohol, glycols such as ethylene glycol, propylene glycol and diethylene glycol, and n-butyl. Cellosolve, ethyl cellosolve, methyl cellosolve, glycol derivatives such as propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, N-methylpyrrolidone Amides such as, but not limited to. These organic solvents may be used alone or in combination of two or more as required.

  When the coating layer is provided on the film of the present invention, the thickness is usually 0.001 to 0.5 μm, preferably 0.005 to 0.3 μm, more preferably 0.01 to the thickness after final drying. 0.2 μm. When the thickness of the coating layer exceeds 0.5 μm, the films are likely to block each other, and particularly when the stretched coated film is re-stretched for the purpose of increasing the strength of the film, it tends to stick to the roll during the process. May be. If the thickness of the coating layer is less than 0.001 μm, the colorant sealing effect may be reduced.

  In addition, in order to improve the applicability | paintability to the film of a coating agent and adhesiveness, you may give a chemical process and an electrical discharge process to a film before application | coating. Moreover, in order to improve the surface characteristics of the coating layer of the biaxially stretched film of the present invention, the coating layer surface may be subjected to a discharge treatment after the coating layer is formed. As a method of forming the coating layer, there are a method of forming a biaxially stretched film (inline coating) and a method of forming after biaxial stretching (offline coating). As a specific example of the former, for example, a thin film forming liquid is applied to the surface of an unstretched film and then stretched in a biaxial method. Or the method of extending | stretching, after apply | coating a thin film formation liquid to the surface of a uniaxially stretched film is mentioned, The method of using these together is also suitable.

  When the stretching treatment is not performed after coating, the adhesion between the formed coating layer and the base film tends to be weak, and a coating layer suitable for practical use may not be obtained. In order to achieve these industrially advantageously, it is preferable to apply within the production process of the biaxially stretched film, but it is not limited thereto. A reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or the like can be used as a method for applying the above-described coating solution to a polyester film. Although the manufacturing method of the laminated | multilayer film of this invention is demonstrated concretely, as long as the structural requirements of this invention are satisfied, it is not specifically limited to the following illustrations.

  Polyester containing a predetermined amount of colorant (for intermediate layer) and, if necessary, polyester containing a predetermined amount of inert particles (for outermost layer) are supplied to separate melt-extrusion devices, and the melting point of each polymer is exceeded. It is heated to the temperature of and melted. Next, the molten polymer is bonded and laminated in a laminar flow in an extrusion die, extruded from a slit die, rapidly cooled and solidified on a rotating cooling drum to a temperature below the glass transition temperature, and substantially amorphous. An unoriented sheet in a state is obtained. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  Specifically describing the stretching conditions in the present invention, the unstretched sheet is preferably stretched 2 to 6 times in the longitudinal direction at 70 to 120 ° C. to form a longitudinal uniaxially stretched film, and then in the lateral direction 90 to 160 ° C. The film is preferably stretched 2 to 6 times at 150 to 250 ° C. for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 15% in the vertical direction and / or the horizontal direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  When processing the laminated film of the present invention, on the opposite side of the above-mentioned coating layer surface of the laminated film of the present invention, the properties required according to the required properties, such as adhesion, antistatic properties, weather resistance and surface hardness are improved. Therefore, in-line coating may be performed. Moreover, you may perform various coats with an offline coat | cover on the opposite surface of the above-mentioned coating layer surface after manufacture of a laminated film.

In the present invention, ΔE ^* ab is used for evaluating the bleeding out of the colorant on the surface of the laminated film. The ΔE ^* ab value is obtained by heating the laminated film, extracting the coated surface of the film with dimethylformamide, and obtaining the L ^* value, a ^* value, and b ^* value of the extract and reference dimethylformamide with a spectrophotometer. The difference ΔL ^* , Δa ^* , Δb ^* is substituted into the following equation 1 for calculation.

ΔE ^* ab = [(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² )] ^1/2
The lower the value of ΔE ^* ab, the higher the transparency of the extract, and it can be said that the colorant bleed-out to the surface of the laminated film is suppressed.

In the present invention, from the viewpoint of practicality, the value of ΔE ^* ab needs to be 10 or less, and is preferably 4 or less.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The physical property measurement method used in the present invention is shown below.

(1) Intrinsic viscosity IV (dl / g)
A mixed solvent of phenol / tetrachloroethane: 50/50 (weight ratio) was added to 1 g of polyester at a ratio of 100 ml, and the mixture was measured at 30 ° C.

(2) Average particle diameter of added particles (μm)
Using a centrifugal sedimentation type particle size distribution analyzer SA-CP3 manufactured by Shimadzu Corporation, the particle size was measured by a sedimentation method based on Stokes' resistance law. The average particle diameter was determined by using a value of 50% of integration (volume basis) in the equivalent spherical distribution of particles obtained by measurement.

(3) Method for measuring film thickness of coating layer The surface of the coating layer was dyed with RuO ₄ and embedded in an epoxy resin. Thereafter, the section prepared by ultramicrotomy stained with RuO _4, a coating layer cross-section was measured by using a TEM (Hitachi High Technologies Corporation H-7650, accelerating voltage 100 V).

(4) Colorant sealing performance evaluation (ΔE ^* ab value evaluation)
The films prepared in the examples and comparative examples are heated in an oven at 180 degrees for 10 minutes. Thereafter, the heat-treated film is folded so that the surface of the coating layer is inside the box, and a box shape having a length of 20 cm, a width of 12.5 cm, and a height of 5 cm is formed.
Next, 10 mL of dimethylformamide is put in contact with the bottom surface (250 cm ² ) of the box prepared by the above method and left for 3 minutes, and then dimethylformamide is recovered in a 20 mL vial. The collected dimethylformamide is placed in a quartz liquid cell having a length of 12.5 mm, a width of 12.5 mm, and a height of 45 mm. -3100 PC ", the transmittance was measured, and the values of L ^* value, a ^* value, and b ^* value at 2 ° field of view and standard D65 light source were obtained. Similarly, the L ^* value, a ^* value, and b ^* value of dimethylformamide as a reference are obtained, and the differences ΔL ^* , Δa ^* , and Δb ^* are substituted into Equation 1 below, and ΔE ^* ab with respect to the dimethylformamide as a reference The value was calculated.

ΔE ^* ab = [(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² )] ^1/2

(5) Colorant sealing performance evaluation (visual evaluation)
The film is heated in a 180 degree oven for 10 minutes. Thereafter, the heat-treated film is folded so that the surface of the coating layer is inside the box, and the upper part is opened to form a box shape having a length of 20 cm, a width of 12.5 cm, and a height of 5 cm. 10 mL of dimethylformamide is put in contact with the bottom (250 cm ² ) of the box prepared in step 3 and left for 3 minutes, and then dimethylformamide is collected in a 20 mL vial. The recovered dimethylformamide was visually judged under a fluorescent lamp to determine the degree of colorant extraction, and evaluated according to the following criteria.

A: Almost no outflow of colorant is observed. O: Excessive outflow of colorant is observed. Δ: The outflow of colorant can be clearly confirmed. X: The outflow degree of the colorant is severe.

  The composition component which comprises the coating layer used by the Example and the comparative example is as showing below.

  The ionic polymer used below is a general term for polymers having a cation and / or an anion in the molecular structure of the polymer. In addition, the weight% used in Examples and Comparative Examples means weight% in a nonvolatile content.

[Compositional components constituting the coating layer]
(A) Ionic polymer Ionic polymer (A1): R ¹ , R ³ , and R ⁴ in the formula (4) are methyl groups, R ² is an ethylene group, and R ⁵ is a methylene group. , X ⁻ is a chlorine ion, and M ⁺ is a sodium ion. A polymer having a zwitterion in the side chain as a main component. Ionic polymer (A2): a side chain composed of a structural unit of the following formula (6) Polymer with cation

（６）

(6)

  Ionic polymer (A3): a polystyrenesulfonic acid having a weight average molecular weight of about 70,000, which is a polymer having an anion

  Ionic polymer (A4): copolymerizing the structural unit of the following formula (7), the structural unit of the following formula (8), and the structural unit of the following formula (9) at a ratio of 90/5/5 by weight ratio. Polymer having a cation in the main chain, the number average quantity being 20000

（７）

(7)

（８）

(8)

（９）

(9)

(B) Polymer Polymer (B1): Polyvinyl alcohol having a saponification degree of about 88% Polymer (B2): Acrylic acid having a glass transition temperature (Tg) of about 50 ° C. copolymerized with acrylic acid alkyl ester and methacrylic acid alkyl ester resin

(C) Crosslinking agent Crosslinking agent (C1): Crosslinkable resin of hexamethoxymethylol melamine Crosslinking agent (C2): 3-glycidoxypropyltrimethoxysilane Crosslinking agent (C3): Crosslinking of hexamethoxymethylolmelamine / urea professor Resin

(D) Particles Particles (D1): Alumina surface-modified silica sol aqueous dispersion having an average particle size of 0.02 μm

≪Production of polyester-A≫
100% by weight of dimethyl terephthalate and 60% by weight of ethylene glycol are used as starting materials, 0.09% by weight of magnesium acetate tetrahydrate as a catalyst is placed in a reactor, the reaction start temperature is set to 150 ° C. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially completed. To this reaction mixture, 0.04% by weight of ethyl acid phosphate, 0.04% by weight of antimony trioxide and 0.05% by weight of silica particles having an average particle size of 1.9 μm were added, and a polycondensation reaction was performed for 4 hours. . That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After 4 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure. The intrinsic viscosity (IV) of the obtained polyester was 0.65.

<< Production of Polyester-B and Polyester-B1 >>
In the production of Polyester-A, Polyester-B was prepared in the same manner as Polyester-A except that 0.05% by weight of silica particles having an average particle size of 1.9 μm was not added and the polycondensation reaction was made 3 hours and 15 minutes. Obtained. The intrinsic viscosity (IV) of the obtained polyester was 0.53. Polyester-B was subjected to solid state polymerization at 225 ° C.-0.3 mmHg for 15 hours. The obtained polyester-B1 had an intrinsic viscosity (IV) of 0.78.

≪Production of polyester-C≫
After drying 100% by weight of polyester-B1, 0.4% by weight of Mitsubishi Res. Diresin Red HS, 0.8% by weight of Blue H3G, and 0.3% by weight of Yellow F were vented twin-screw extruder. And kneaded to obtain polyester-C. The intrinsic viscosity (IV) of the obtained polyester was 0.61.

Example 1:
Polyester-C was dried at 180 ° C. for 4 hours and fed to a main extruder set at 285 ° C. and polyester-A was fed into a sub-extruder set at 285 ° C. The polymer of the sub-extruder is branched into two layers (outermost layer) on the front and back sides of the film, and then merged with a feed block. The thickness composition ratio is A / C / A = 3/19 / 3 was co-extruded to obtain a substantially amorphous sheet having a thickness of 366 μm by rapid cooling and solidification using an electrostatic cooling method with a rotary cooling drum set at a surface temperature of 30 ° C. The obtained amorphous sheet was stretched 3.4 times in the longitudinal direction at 83 ° C., and then an aqueous coating composed of 100% by weight of A1 was applied to one side of the film with a film thickness of 0. 0 in the final dry coating state. The film was applied to a thickness of 05 μm and stretched 4.3 times in the transverse direction at 93 ° C., and then heat treated at 225 ° C. for 3 seconds to obtain a polyester film having a total layer thickness of 25 μm. When the obtained polyester film was evaluated, the colorant sealing performance was good. The characteristics of this film are shown in Table 1 below.

Comparative Example 1 :
In Example 1, the film was stretched 3.4 times in the longitudinal direction at 83 ° C., and then an aqueous coating composed of 80% by weight of A2g, 10% by weight of B1 and 10% by weight of D1 was formed on one side of the film. A polyester film was obtained in the same manner as in Example 1 except that the coating film was used with a use of 0.02 μm. The obtained polyester film had good colorant sealing performance as shown in Table 1 below.

Comparative Example 2 :
In Example 1, the film was stretched 3.4 times in the longitudinal direction at 83 ° C., and then, on one side of the film, A2 was 36% by weight, B1 was 14% by weight, C1 was 40% by weight, and D1 was 10% by weight. A polyester film was obtained in the same manner as in Example 1 except that the coating was applied so that the film thickness was 0.02 μm in the state of the final dry coating film. The obtained polyester film had good colorant sealing performance as shown in Table 1 below.

Comparative Example 3 :
In Example 1, the film was stretched 3.4 times in the longitudinal direction at 83 ° C., and then an aqueous coating comprising 65% by weight of A3 and 35% by weight of C2 was formed on one side of the film with the film thickness in the state of the final dry coating film. A polyester film was obtained in the same manner as in Example 1 except that the coating was applied to 0.02 μm. As shown in Table 1 below, the obtained polyester film had poor color material sealing performance.

Comparative Example 4 :
In Example 1, the film was stretched 3.4 times in the longitudinal direction at 83 ° C., and then an aqueous coating composed of 40% by weight of A4, 40% by weight of B2, and 20% by weight of C3 was formed on one side of the film. A polyester film was obtained in the same manner as in Example 1 except that the coating film was applied to a final dry coating film thickness of 0.03 μm. As shown in Table 1 below, the obtained polyester film had poor color material sealing performance.

Comparative Example 5 :
In Example 1, the film was stretched 3.4 times in the longitudinal direction at 83 ° C., and then a water-based paint composed of 90% by weight of B1 and 10% by weight of D1 was formed on one side of the film. A polyester film was obtained in the same manner as in Example 1 except that the coating was applied to 0.02 μm.
As shown in Table 1 below, the obtained polyester film had poor colorant sealing performance.

  In addition, the numerical value of the ratio described in the compounding component column of Table 1 represents the weight ratio of the nonvolatile content in the coating solution.

  The film of the present invention can be suitably used in the use of a film containing a colorant, such as an automobile window pasting film, an X-ray bluing film, and a display application.

Claims (3)

Coating formed from a coating solution containing 85% by weight or more of a polymer having a cation in the side chain as a proportion of all non-volatile components in the coating solution on at least one side of a multilayer polyester film containing at least three layers containing a colorant in the intermediate layer A color difference ΔE between the liquid after heating the surface of the coating layer (250 cm ² ) with 10 mL of dimethylformamide and the liquid before extraction of the dimethylformamide after heating the film at 180 ° C. for 10 minutes. * A laminated polyester film having an ab value of 10 or less. The laminated polyester film according to claim 1, wherein the polymer having a cation in a side chain is a polymer having a side chain structure showing a cation and an anion in the same molecular structural unit. After heating the film at 180 ° C. for 10 minutes, the surface of the coating layer (250 cm ² 3) The laminated polyester film according to claim 1 or 2, wherein the color difference ΔE * ab value between the liquid after extraction with 10 mL of dimethylformamide and the liquid before extraction of the dimethylformamide is 4 or less.