JPH0848793A - Polyester film - Google Patents

Abstract

PURPOSE: To obtain a polyester film excellent in printability, hiding power, a degree of whiteness, etc., by using a biaxially oriented polyester film produced by adding rutile titanium dioxide having a specified particle diameter to a specified polyester resin.

CONSTITUTION: The biaxially oriented polyester film is made from an ethylene terephthalate polyester resin containing at least 60 wt.% main repeating units and having an inherent viscosity of 0.4-0.9 dl/g and contains 5-30 wt.%, based on the weight of the film, rutile titanium dioxide having a mean particle diameter of 0.05-5 μm. The film is desirably the one in which the titanium dioxide is coated with 0.1-1 wt.% aluminum. It is desirably the one further containing 0.005-0.1 wt.%, based on the titanium dioxide, cobalt acetate. It is further desirably the one containing 0.05-0.30 wt.%, based on the weight of the film, organic fluorescent whitener.

COPYRIGHT: (C)1996,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film, and more particularly, it has various surface characteristics, whiteness, hiding power, antistatic property and printability, and is used for various cards, label articles and printings. The present invention relates to a polyester film useful for producing paper, business cards, printing materials and industrial substrates, especially magnetic cards.

[0002]

2. Description of the Related Art Generally, a communication card such as a telephone card,
Pre-paid magnetic cards (prepaid cards) such as credit cards such as bank cards, fixed-rate cards such as department store cards, and transportation cards such as subway cards and highway traffic cards are mainly made of polyvinyl chloride and paper. It has been. However, a card manufactured using polyvinyl chloride as a basic raw material is too thick and is inconvenient when carrying several cards at the same time, and is weak in impact strength, flexibility, heat resistance, etc. Fragile,
There is a drawback that the film is easily deformed by heat generated during printing or during use. On the other hand, cards made from paper have poor water resistance, durability, and high grade, so
There is a limit to wide application to real life.

In order to solve such problems, the efforts to use a polyester film having excellent mechanical properties and being easy to carry for various magnetic cards have been increasing recently.

Polyester, particularly polyethylene terephthalate, is chemically and physically stable, has a high mechanical strength especially when biaxially stretched, and is excellent in heat resistance, durability, chemical resistance, electric insulation, etc. Instruments, magnetic recording media,
It is widely used not only in capacitors, photographic films, industrial products, packaging materials and label products, but also in the manufacture of various molded products.

[0005] Polyester film basically has high transparency and glossiness and is widely used for packaging and industrial applications. It is used for various magnetic cards such as credit cards and telephone cards. In order to use it is necessary to control the transparency and gloss,
In particular, not only the hiding property of the film itself, but also the physical properties suitable for the coating process of the magnetic layer, the hiding layer and the printing layer, the antistatic property and the smoothness must be excellent.

Various studies have been conducted in order to give the polyester film suitable physical properties for magnetic cards and the like, but recently, an inorganic filler having a high refractive index for controlling transparency and white The method of producing a white polyester film by using a whitening agent for enhancing the degree is evaluated to be the most appropriate.

To date, various methods have been developed for controlling the transparency and gloss while taking advantage of the excellent properties of polyester films. For example, JP-A-62-24
In JP 3120 and 65-206622, inorganic particles are added to polyester, and JP-A-65-185532 is used.
In Japanese Patent Laid-Open No. 66-66, barium sulfate is used alone.
In Japanese Patent No. 50241, after blending a polyester with a polyolefin resin, barium sulfate and calcium carbonate are added, and JP-A-63-161029 and 63-1379 are incorporated.
No. 27 discloses the use of fine particle calcium carbonate, and JP-A No. 62-241928 discloses an attempt to solve the above-mentioned drawbacks by using titanium and silica together.

[0008]

However, the white polyester film produced by such a method is easily discolored when exposed to high temperature or sunlight for a long time, and is not suitable for use as a high-quality card. .
In addition, since static electricity is easily generated due to the characteristics of the polyester film, not only problems such as non-uniform printing and defective ink adhesion occur in the printing process, but in particular, various information recorded on the magnetic card is lost. There have been many difficulties in widespread use because of fear.

Further, the calcium carbonate used for controlling the refractive index causes the surface glossiness of the film to be too high and causes eye fatigue, and barium sulfate added to maintain the hiding property of the film is Since the hiding property is not so good, it should be added in a larger amount than the existing titanium compounds, and as a result, it becomes bluish and has the drawback of lowering the high-class appearance.

Not only that, the productivity is lowered due to the aggregation phenomenon of the additives generated in the polymerization process and the filter clogging phenomenon generated in the film manufacturing process, and it is difficult to mass-produce. In particular, a large amount of inorganic substances are directly added to the polymerization process. If you do
Problems such as generation of bubbles, discoloration, generation of by-products, and increase in residence time occur.

The present inventors have conducted research to solve the above-mentioned problems and improve the whiteness, mechanical properties, antistatic properties, printability, etc. of polyester films.
By adding a rutile type titanium dioxide having a particle size in a predetermined range to polyester in an appropriate amount, and optionally adding cobalt acetate or a fluorescent organic whitening agent, excellent mechanical properties and antistatic properties, printability, It has been found that a polyester film having improved hiding power and whiteness can be produced, and the present invention has been completed. The present invention has been made based on such findings.

Accordingly, it is an object of the present invention to provide a white polyester film having improved whiteness, mechanical properties, printability, hiding power and antistatic property.

[0013]

In order to achieve the above object, the present invention has an intrinsic viscosity of 0.4 to 0.9 dl in which 60% by weight or more of main repeating unit is ethylene terephthalate.
A polyester film characterized by containing rutile type titanium dioxide having an average particle size of 0.05 to 5 μm in an amount of 5 to 30% by weight based on the weight of the film.

In addition to the titanium dioxide, the polyester film according to the present invention may further contain cobalt acetate in an amount of 0.005 to 0.1% by weight based on the weight of titanium dioxide, or may contain light in the short wavelength region of visible light. A fluorescent organic brightener having divergent properties is added to the film weight of 0.05 to 0.30.
A quaternary ammonium salt represented by the following formula (1) may be further included in an amount of 0.01% by weight on the film surface.
It is preferably applied in an amount of 0.1 g / m ² .

[0015]

Embedded image (In the formula, R ₁ is an alkyl group having 10 to 20 carbon atoms,
R ₂ is a hydrocarbon having a chain structure having less than 4 carbon atoms, R ₃ and R ₄ are each independently an alkyl group having less than 5 carbon atoms, and X ₋ is a counter anion.) The polyester of the present invention is 0.4-when measured at a concentration of 0.3 g per 25 ml of orthochlorophenol at 35 ° C.
It has an intrinsic viscosity of 0.9 dl / g, preferably 0.5-0.8 dl / g. When the intrinsic viscosity is less than 0.4 dl / g, stretching and breaking are frequent in the film manufacturing process, and not only the productivity is greatly decreased, but also the physical properties such as mechanical strength of the final film are deteriorated. Intrinsic viscosity is 0.9 dl / g
If it exceeds, the melt viscosity is excessively increased and the extrusion process becomes unstable in the film forming process, which causes difficulty in the manufacturing process, resulting in a large decrease in productivity in the subsequent process.

The polyester of the present invention can be obtained by polycondensing a polyvalent organic acid component and a polyhydric alcohol component. The organic acid is preferably a carboxylic acid, particularly an aromatic dicarboxylic acid, and the alcohol is a glycol,
Particularly preferred is alkylene glycol.

Specific examples of the aromatic dicarboxylic acid include dimethyl terephthalic acid, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, cyclohexane dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ether dicarboxylic acid, anthracene dicarboxylic acid and α, β. -Bis (2-chlorophenoxy) ethane-4,
4'-dicarboxylic acids are mentioned, of which dimethyl terephthalic acid and terephthalic acid are particularly preferred.

Specific examples of the alkylene glycol include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol,
Hexamethylene glycol and hexylene glycol are mentioned, of which ethylene glycol is particularly preferred.

In the polyester of the present invention, 60% by weight or more is a homopolyester of polyethylene terephthalate, and the remaining 40% by weight or less is another repeating unit,
That is, it is a copolymer component. As the copolymer component, diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylene glycol, 1,4-cyclohexanedimethanol, sodium 5-diol compound such as 5-sulforesorcin, adipic acid, sodium 5- Included are dicarboxylic acids such as sulfoisophthalic acid and the like, and polyfunctional carboxylic acids such as trimetric acid and pyromellitic acid.

Titanium dioxide is classified into rutile type and anatase type according to its crystal structure. Anatase type titanium dioxide having a cubic crystal structure has a high water adsorbing property and causes aggregation during the compounding process. However, there is a problem that not only the optical properties of the film surface are deteriorated, but also the film is easily deteriorated by the external environment, particularly temperature, sunlight and moisture. On the other hand, rutile type titanium dioxide having a hexagonal crystal structure used as an inorganic filler in the present invention effectively absorbs ultraviolet rays, which are harmful to the film, and converts energy into a form of heat, thereby forming an organic compound. It has a function of preventing the combined body from being deteriorated by ultraviolet rays.

Titanium dioxide has the effect of hiding the final film,
It affects whiteness and light transmittance. In order to improve the hiding power of the film, it is important to maximize the light scattering effect, but the light scattering degree can be adjusted by the average particle size and the interval of the inorganic particles. If the inorganic particles are too large or the spacing is too narrow, almost no diffraction occurs, while if the inorganic particles are too small, light passes through the inorganic particles as they are, so the particle size of the titanium dioxide used is that of the light to be scattered. It is preferably slightly smaller than ½ of the wavelength.

The whiteness of the film is adjusted to a level of 80 to 110%, preferably 85 to 105%.
If it is less than 0%, the film becomes yellow and the quality of the film is deteriorated at the time of printing. On the other hand, if it exceeds 110%, the surface of the film is bluish, which also deteriorates the quality of the film. The light transmittance of the film is 0.5 to 2.0.
%, Preferably 0.6-1.5%, more preferably 0.1.
Although it is adjusted to 8 to 1.0%, when the light transmittance exceeds 2.0%, the back surface of the film becomes visible because the hiding property of the film is small, and when the light transmittance is less than 0.5%. ,
Since it contains a large amount of fine bubbles, the strength of the film becomes weak.

In order to satisfy the above conditions,
The average particle size of rutile titanium dioxide is 0.05-5.0μ
m, preferably 0.1 to 3.0 μm, and the addition amount is 5 to 30% by weight of the polyester film, preferably 10 to
It is 25% by weight. The average particle size and the addition amount can be adjusted depending on the thickness of the final film and the application. If the amount of titanium dioxide added is more than 30% by weight,
The mechanical properties such as strength and flexibility of the film are deteriorated, and the whiteness and the transmittance are almost constant due to the increase of the addition amount, so that the addition of a large amount has no effect. On the other hand, 5
If it is less than wt%, the optical properties of the film will be poor.

Titanium dioxide has a characteristic that it has a high water adsorption property, and an adhesion phenomenon occurs. In some cases, the supply port may be blocked. In this case, when the surface of the titanium dioxide particles is coated with 0.01 to 1% by weight of aluminum metal ions based on the weight of the titanium dioxide particles, the surface water content is remarkably reduced and water vapor is generated during extrusion molding and other melting steps. Is hardly released, improving the aggregation phenomenon and dispersibility,
It is possible to manufacture a polyester film having excellent yellowing resistance, weather resistance, dispersibility and coloring power.

The polyester film of the present invention also includes
In order to enhance the whitening effect, cobalt acetate, which is an inorganic pigment, is added in an amount of 0.005 to 0.1 based on the weight of titanium dioxide.
It can be added in an amount of% by weight, preferably 0.01 to 0.05% by weight. If the cobalt acetate is added in an amount of less than 0.005% by weight, the effect of improving whiteness cannot be expected, and if it is used in an amount of more than 0.1% by weight, a yellowing phenomenon occurs.

The polyester film of the present invention also includes
A fluorescent organic whitening agent can be further added. For example, a bisbenzoazole-based pigment absorbs light energy in the ultraviolet region to transfer the energy to the short wavelength region of visible light and diverge the light. It improves the reduction in the reflectance of visible light in the short wavelength of the film, which is a phenomenon that occurs when only an inorganic substance is added. The reflectance at 440 nm, which is a short wavelength region of visible light, is preferably 75% or more. For this purpose, the amount of the pigment added is set to 0.05 to 0.30% by weight based on the polyester film. Good to do. If the addition amount is less than 0.05% by weight, 4
Almost no increase in reflectance was observed at 40 nm,
If added in excess of wt.%, The reflectance at 440 nm will be too high and the film will appear bluish white.

In addition to the titanium dioxide, cobalt acetate and fluorescent organic brighteners mentioned above, the polyesters of the present invention also include one or more other known additives such as UV absorbers, heat stabilizers, polycondensation catalysts, dispersions. An agent, an antistatic agent, a crystallization accelerator, a nucleating agent, an antiblocking agent and the like can be contained within a range that does not impair the effects of the present invention.

In the production of the polyester film according to the present invention, the addition of the above-mentioned additives or the like produces a polyester polycondensate in which a part of the additives is added at a high concentration, and the additives are not added separately or the rest is left. After manufacturing polyester polycondensate in which some additives are added in high concentration, these are mixed with each other and extruded into a final film. Master patch chips (high concentration chips, masterbatc)
h chip) production method, but this method has an advantage that contamination of the polymerization reactor can be reduced and dispersibility of the additive can be enhanced. The master chip is preferably melt-mixed by using a compounding machine having two rotating shafts.

The method for producing the polyester film of the present invention is not particularly limited, but a polyester containing the titanium dioxide and the fluorescent organic brightener and other additives may be used.
A biaxially oriented polyester film can be produced by melt-extruding by a usual method such as a T-die method or an inflation method, forming an unstretched sheet, and then biaxially stretching the sheet.

The polyester film of the present invention also includes
A quaternary ammonium salt represented by the following formula (1) can be externally applied as an antistatic agent. The external coating agent is easy to control the thickness of the coating layer and impart slip property,
It is applied to a polyester sheet or film to provide an antistatic effect.

[0031]

[Chemical 3] (In the formula, R ₁ is an alkyl group having 10 to 20 carbon atoms,
R ₂ is a hydrocarbon having a chain structure having less than 4 carbon atoms, R ₃ and R ₄ are each independently an alkyl group having less than 5 carbon atoms, and X ₋ is a counter anion.) The quaternary ammonium salt Typical examples thereof include, but are not limited to, butyloxyethyl hydroxyethyl orthodecyloxyammonium salt, bishydroxydecylpropylammonium salt, and hydroxybutyldodecyloxybutylethylammonium salt.

The quaternary ammonium salt is dissolved in water or alcohol and is 0.1 to 10% by weight, preferably 2 to
It is used as an aqueous solution having a concentration of 5% by weight and applied so that the solid active ingredient is present on the film surface in an amount of 0.01 to 0.1 g / m ² . If the concentration of the aqueous solution is less than 0.1% by weight, not only sufficient antistatic properties cannot be imparted to the film, but also uncoated parts may occur, resulting in deviation of physical properties between parts. When it is used at a high concentration, undissolved particles are present and the appearance of the film becomes poor, resulting in a problem that the adhesive strength after printing is lowered.

The ammonium salt aqueous solution can be externally applied on the unstretched sheet or on the surface of the film after uniaxial or biaxial stretching, depending on the film production conditions. The stretching process is carried out by a conventional stretching process of a polyester film at a stretching temperature of 60 to 150 ° C. and a stretching ratio of 2.5 to 6.0 times in each of the longitudinal direction and the transverse direction to maximize the static elimination property of the film. In order to achieve this, it is desirable to thermally cure the film for a predetermined time at a high temperature of 250 ° C. or higher after stretching, within a range in which the characteristics of the film are not deteriorated.

The polyester film of the present invention manufactured as described above continuously maintains a surface resistance of 10 ⁹ Ω or less, which prevents foreign substances from adhering to the surface and is excellent in antistatic property, and 45 dyn / Excellent adhesion to ink and various coating solutions under film surface tension of cm or more.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples of the present invention, various performance evaluations of the produced films were performed by the following methods.

(1) Surface glossiness The surface glossiness of the film was measured by the method of ASTM D523 using a black mirror as a reference mirror at a measurement angle of 60 °.

(2) Light transmittance The light transmittance of the film is 25 mm at a scattering angle of 2.5 °.
ASTM D1003 with a sample having a particle size of
It was measured by the method of.

(3) Color b value and reflectance Light source color difference meter (model: SZS-
Σ80) is used to determine the reflectance by measuring the% of the light reflected in the visible region wavelength of 440 nm, and the color b
The values were measured at a measuring angle of 2 ° using the C light source as the measuring light source.

(4) Whiteness The whiteness of the film was determined by the following formula by calculating the reflectance% (B) at 450 nm and the reflectance% (G) at 550 nm by the method of JIS-L-1015.

Whiteness = 4B-3G (5) Antistatic Property The antistatic property of the film is Hewlett Pac in the United States.
It was determined by measuring the surface resistance of the film under a voltage application of 500 V at 23 ° C. and 60% relative humidity using a Kard insulation resistance measuring machine. The smaller the surface resistance, the better the antistatic property of the film.

(6) Receptivity to ink / coating composition-printability The degree of aggregation of the Reule index standard liquid of Nippon Wako Shinyaku Co., Ltd. was measured on the surface of the film, and the printability of the film was measured according to the following criteria. Was evaluated.

◯: No aggregation occurs Δ: 2 to 4 aggregations per unit area (10 cm × 10 cm) ×: 5 or more aggregations per unit area (10 cm × 10 cm) (7) Dispersibility When a resin of 30 kg per hour was discharged using a pilot extruder, a change (ΔP) in filter pressure applied to a 200 mesh filter after a predetermined time elapsed was measured and compared.

Example 1 7500 g of dimethyl terephthalate and 4780 g of ethylene glycol were mixed, and 0.368 g of a magnesium compound was added as a transesterification reaction catalyst to react them, and a polyethylene terephthalate monomer, that is, bis-2-hydroxyethyl terephthalate was added. Manufactured. Sodium 3,5-dicarboethoxybenzenesulfonate and potassium octylbenzenesulfonate are added in an amount of 0.15% by weight and 0.15% by weight of antimony trioxide as a polycondensation catalyst to carry out a polycondensation reaction to obtain an intrinsic viscosity of 0. .62 dl /
g of polyester polymer was prepared.

To the obtained polymer was added 60 wt% of rutile type hexagonal titanium dioxide coated with 0.05 wt% of aluminum based on the weight of titanium dioxide, based on the weight of the polymer. Then, 0.03% by weight of cobalt acetate was added and blended based on the weight of the titanium dioxide to manufacture a high-concentration master chip. The operating conditions of the compounding machine at this time are as follows.
0 to 250 rpm, the temperature of the molten resin 280 to 2
Maintained at 90 ° C.

The master chip prepared as described above was dry-mixed with ordinary polyester chips to contain 18% by weight of titanium dioxide, dried, melted and extruded into a sheet, and then prepared by a usual method. Each of them was stretched in the longitudinal direction and the transverse direction at a stretching ratio of 3: 1 and a thickness of 188.
A biaxially stretched white polyester film having a thickness of μm was manufactured, and each property of the film was measured. The results are shown in Table 1.

As shown in Table 1, the films produced as described above were generally excellent in various properties and the like.

Examples 2 to 8 Polyester films were produced by repeating the procedure of Example 1 while changing the final concentration of the additive as shown in Table 1. The physical properties of the film thus manufactured are shown in Table 1.
It was generally good as shown in.

Comparative Examples 1 to 8 Polyester films were produced by repeating the procedure of Example 1 while changing the final concentration of the additives as shown in Tables 1 and 2. The physical properties of the film thus manufactured are shown in Table 2.

[0049]

[Table 1]

[Table 2] In Tables 1 and 2, the coating amounts of cobalt acetate and aluminum are based on the weight of titanium dioxide.

Example 9 7500 g of dimethyl terephthalate and 4780 g of ethylene glycol were blended, 0.368 g of a magnesium compound was added as a transesterification reaction catalyst, and the mixture was reacted to produce a polyethylene terephthalate monomer, that is, bis-2-hydroxyethyl terephthalate. did.

Next, 0.15% by weight of antimony trioxide was added as a polycondensation catalyst to carry out a polycondensation reaction to produce a polyester resin having an intrinsic viscosity of 0.620 dl / g. Then, 40% by weight of rutile type titanium dioxide having an average particle size of 0.4 μm and 0.30% by weight of a fluorescent organic brightener were added to the polyester resin obtained above under the conditions of a compound rotation speed of 350 rpm and a discharge resin temperature of 285 ° C. Was mixed and kneaded to produce a high-concentration master chip. The operating condition of the compounding machine at this time is that the screw rotation speed is 350 rp.
m, the temperature of the molten resin was 285 ° C.

The master chip prepared as described above was dry-mixed with a normal polyester chip in a mixing ratio of 1: 1 and extruded to obtain 20% by weight and 0.15% by weight of titanium dioxide and a fluorescent organic brightener, respectively. After forming the sheet containing the same, the film was longitudinally and laterally stretched at a stretching ratio of 2.5 by a usual method to produce a biaxially stretched film having a thickness of 188 μm.

Then, a 2% aqueous solution of butyloxyethyl hydroxyethyl orthodecyloxyammonium sulfate was externally coated on the surface of the film so that 0.09 g / m ² of the solid active ingredient was present, and then the temperature of 250 ° C. was applied. And dried for 5 seconds. The films produced in this way were generally excellent in physical properties, antistatic properties, printability, etc., as shown in Table 3 below.

Examples 10 to 16 Polyester films were prepared by repeating the procedure of Example 9 while changing the final concentrations of the additives and the surface coating agent as shown in Table 3. As shown in Table 3, the physical properties of the film thus produced were generally good.

Comparative Examples 9 to 16 Polyester films were produced by repeating the procedure of Example 1 while changing the final concentrations of the additives and the surface coating agent as shown in Table 4 below. The physical properties of the film thus produced are shown in Table 4.

[0056]

[Table 3]

[Table 4] As described above, a polyester film produced by adding titanium dioxide to a polyester resin according to the present invention, optionally adding an inorganic pigment and a fluorescent organic whitening agent, and externally applying a quaternary ammonium salt to the surface is white. Excellent in mechanical strength, mechanical properties, printability and antistatic property,
It can be suitably used for various magnetic cards and the like.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B29L 7:00

Claims (8)

[Claims] 1. An intrinsic viscosity of from 0.4 to 0.9 d in which 60% by weight or more of the main repeating unit is ethylene terephthalate.
In a film made of 1 / g of polyester resin,
A biaxially oriented polyester film comprising 5 to 30% by weight of rutile titanium dioxide having an average particle diameter of 0.05 to 5 μm based on the weight of the film. 2. The polyester film according to claim 1, wherein the titanium dioxide is coated with 0.1 to 1% by weight of aluminum. 3. 0.00 based on said titanium dioxide
The polyester film according to claim 1, further comprising 5 to 0.1% by weight of cobalt acetate. 4. From 0.05 to 0.05 based on the weight of the film.
The polyester film of claim 1, further comprising 0.30% by weight of a fluorescent organic brightener. 5. The polyester film according to claim 1, wherein the quaternary ammonium salt of the following formula (1) is applied on the film surface in an amount of 0.01 to 0.1 g / m ² . Embedded image (In the formula, R ₁ is an alkyl group having 10 to 20 carbon atoms,
R ₂ is a hydrocarbon having a chain structure having less than 4 carbon atoms, R ₃ and R ₄ are each independently an alkyl group having less than 5 carbon atoms, and X ₋ is a counter anion.) 6. The quaternary ammonium salt of formula (1) is selected from the group consisting of butyloxyethylhydroxyethylorthodecyloxyammonium salt, bishydroxydecylpropylammonium salt, and hydroxybutyldodecyloxybutylethylammonium salt. It is at least 1 type, The polyester film of Claim 5 characterized by the above-mentioned. 7. The polyester film according to claim 1, wherein titanium dioxide having a particle size of 0.1 to 3 μm is contained in an amount of 10 to 25% by weight of the polyester film. 8. The film has a surface resistivity of 10 ₉ Ω or less, a whiteness of 80 to 110%, a light transmittance of 0.5 to 2.0%, and a 440 nm reflectance of 75% or more. The polyester film according to claim 1.