JPH09141797A - Biaxially oriented laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably supply a highly abrasion-resistant polyester film with superior optical properties and image drawing characteristic through the range of ordinary steps to manufacture a polyester film. SOLUTION: This biaxially oriented laminated polyester film consists of a polyester A layer laminated at least, on one of the faces of a polyester B layer. The central line surface roughness of the polyester A layer is at least, 50nm and the content of particles on the surface layer of the polyester A layer is 5wt.% or less. In addition, the total light beam permeability Ti(%) and the diffusion permeability Td(%) satisfy expression Ti>=80, Ti×Td>=4000.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a biaxially oriented laminated polyester film, and more particularly to a biaxially oriented laminated polyester film having fine projections formed on its surface and having excellent optical characteristics.

[0002]

2. Description of the Related Art Polyester films are widely used for various purposes. Among them, especially in packaging materials, labels, tracing applications, etc., printability and writability are required, and in applications such as cover films and transfer films, it is necessary to have matteness and texture. Therefore, in a light diffusing film for a backlight of a liquid crystal display panel or the like, a polyester film having a large surface roughness is used because it is necessary to have a good light diffusing property.

Conventionally, silica particles, calcium carbonate particles, crosslinked polystyrene particles and silicone have been used as a method for roughening the surface of a polyester film in order to impart printability, writing ability, matteness, texture and light diffusion. A method of stretching a polyester film in which particles insoluble in polyester, such as particles, are added in a high concentration, a method of embedding inert particles as a post-treatment in the polyester film after film formation, or a method of attaching it with a binder, a surface of the polyester film as a solvent There is known a method of treating the resin with a chemical that decomposes the resin.

Further, a film is known in which the surface projections are formed by utilizing the crystallization of the polyester itself for the purpose of imparting a high degree of abrasion resistance to the polyester film (for example, JP-A-7-1575). This film has excellent abrasion resistance compared to conventional polyester films that have projections formed by containing particles, for example, less powder is generated when running on a plastic guide, and scratch resistance. It is also known that, for example, it has a feature that the scratch depth when a scratch test is performed with a sapphire scratching needle is shallow.

[0005]

However, the conventional film as described above has the following problems. That is, in a polyester film in which particles insoluble in polyester are added, when a film having a large surface roughness is to be obtained, the particles must be added in a high concentration, the stretchability is lowered, and total light transmission is obtained. There are problems such as lower rates. In addition, in the case where inorganic particles are embedded in the polyester film after film formation as a post-treatment, or a film adhered with a binder or the surface of the polyester film is treated with a chemical that decomposes a solvent or resin, Since a treatment process different from the film process is required, there arises a problem that the production speed cannot be increased or the cost is increased.

Further, as the processing speed of the film increases, there arises a problem that the film is easily scratched when it travels on a traveling means such as a metal guide.

The present invention solves the above problems and stabilizes a film having a large surface roughness, excellent abrasion resistance and a large total light transmittance in the usual polyester film forming process. The purpose is to provide at low cost.

[0008]

To this end, the biaxially oriented laminated polyester film of the present invention is polyester B
A biaxially oriented laminated polyester film obtained by laminating a layer made of Polyester A on at least one side of a layer made of
nm or more, the content of particles in the surface layer of the surface is 0.5 wt%
Below, total light transmittance Ti (%) and diffuse transmittance Td
(%) Is made of a biaxially oriented laminated polyester film which satisfies Ti ≧ 80 Ti × Td ≧ 4000.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION That is, by setting the center line average surface roughness Ra of a layer made of polyester A to 50 nm or more, preferably 100 nm or more, more preferably 150 nm or more, the surface when light is reflected or transmitted. In this case, diffusion can easily occur, and the film can have a diffusing ability when used as a diffusion plate, and glare and electric lights can be prevented from being reflected when used as a cover fill. In addition, the film can be provided with writability when used as a tracing sheet. When the center line average roughness Ra is less than 50 nm, preferable light diffusing ability and writability cannot be obtained.

The total light transmittance Ti is 80% or more, preferably 83% or more, more preferably 85% or more, and at the same time, the product Ti × Td of the total light transmittance and the diffuse transmittance is 400.
0 or more, preferably 5000 or more, more preferably 6
By setting it to be 000 or more, when it is used as a cover sheet or a tracing sheet, it is visible on the surface of other members and the visibility of the background pattern can be clearly seen, and the matte property due to the diffusion of light on the surface. It is possible to obtain a film having good antiglare property, texture and writing property at the same time. When used as a diffusion sheet, a film having a large amount of diffused light can be obtained. Total light transmittance Ti is 80%
If it is smaller or the product of total light transmittance and diffuse transmittance, Ti × Td, is less than 4000, the visibility of the substrate when superposed with other members is good, and at the same time, the matteness, the reflection preventing property, and the writing property are improved. No good film can be obtained. Further, when used as a diffusion sheet, only a film having a small amount of diffused light can be obtained.

Further, when the content of the particles of the surface layer in the laminated portion is 0.5% by weight or less, preferably 0.4% by weight or less, more preferably 0.3% by weight or less, excellent wear resistance is obtained. You can get a film. When the content of particles in the surface layer in the laminated portion is larger than 0.5% by weight,
Voids are generated around the particles and the projections are easily destroyed, and when traveling on a hard guide means such as a metal guide, the projections are scraped on the film surface and the film surface is easily scratched, or the powder generated by scraping is generated. It may adhere to the traveling means or the surface of the film.

When the protrusion spacing Sm on the surface of the layer made of polyester A is 30 μm or less, preferably 20 μm or less, a film having more excellent light diffusing property and writability can be obtained, which is preferable.

When the ratio of the maximum height Rt of the surface of the layer made of polyester A to the center line average roughness Ra, Rt / Ra, is 10 or less, preferably 9 or less, the friction coefficient becomes particularly stable, which is preferable.

As a film having the above-mentioned surface roughness and light transmittance and a small content of surface layer particles in the laminated portion, it is preferable that the surface protrusions are caused by the polyester A crystals. However, even if the method described in Japanese Patent Application Laid-Open No. 5-1575 is simply used, the product Ti of the total light transmittance and the diffuse transmittance is 50 nm or more when the surface roughness is 50 nm or more.
A film having × Td of 4000 or more cannot be obtained. In order to form a protrusion due to crystals and obtain a large film of surface roughness, product of total light transmittance and diffuse transmittance in a normal polyester film forming process, the crystallization rate is increased by the nucleating agent effect. It is effective to use a polyester which is large and has high mobility of the polyester molecular chain. As such a polyester having high molecular mobility, a polyester having a crystallization index ΔTcc ′ of 80 ° C. or higher, preferably 90 ° C. or higher is preferable.

Of the surface protrusions, the proportion of protrusions caused by crystals is preferably 80% or more, more preferably 90% or more. If the proportion of the protrusions caused by crystals is less than 80%, there is a problem that the film is easily scratched or powder is easily generated when traveling on a hard guide means such as a metal guide.

Whether or not the surface protrusions are caused by the crystals of polyester A is the reason why the protrusions are formed by etching below the target protrusion in the film thickness direction with an appropriate solvent. When the substance remains as an insoluble substance, it is treated as particles added from the outside or particles precipitated internally (I). When there is substantially nothing that remains as an insoluble matter, it can be presumed that the substance that forms the protrusion is fine crystals (II). Examples of the solvent include phenol / carbon tetrachloride (weight ratio: 6 /
The mixed solvent of 4) is preferably used. By this method, the frequency of I and the frequency of II when the field of view is set to 1 mm ² is obtained, and the value of II / (I + II) can be used as the ratio of protrusions due to crystals. However, the method for determining whether or not the surface protrusions are made of fine crystals of polyester A is not limited to the above method, and an appropriate method can be selected.

In the present invention, the type of polyester A is not particularly limited, but ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-
It is particularly preferable when at least one structural unit selected from 4,4'-dicarboxylate and ethylene naphthalate units is the main constituent. Of these, polyesters containing ethylene terephthalate as the main repeating unit are particularly preferable. Further, in order to form a large number of protrusions in a short heat treatment time, polyethylene terephthalate having a high crystallization rate due to the effect of a crystal nucleating agent is particularly preferable. In order to enhance the effect of the crystal nucleating agent, it is desirable that lithium acetate, magnesium acetate, potassium acetate, phosphorous acid, phosphonic acid, phosphinic acid or their derivatives, antimony oxide, or germanium oxide be present during transesterification or polymerization. A particularly desirable combination is magnesium acetate and phosphonic acid (or a derivative thereof) and antimony oxide, and examples of the phosphonic acid (or a derivative thereof) include phenylphosphonic acid and dimethylphenylphosphonate. Further, in order to increase the mobility of the molecule and obtain a polyester having a large crystallization index ΔTcc ′, the flexible movable component is 0.01% by weight or more and 15% by weight or less, preferably 0.1% by weight or more and 13% by weight or less. , And more preferably in the range of 1% by weight or more and 10% by weight or less. Here, the flexible movable component means a long-chain aliphatic dicarboxylic acid, a long-chain aliphatic diol, a polyalkylene glycol, or the like, which has a long flexible chain in the main chain and has high affinity with or copolymerizable with polyester. In particular, polyalkylene glycol having a number average molecular weight of 1,000 or more and 50,000 or less, preferably 3,000 or more and 30,000 or less, more preferably 5,000 or more and 25,000 or less is preferable, and among them, polyethylene glycol, polypropylene glycol, and hexamethylene glycol are particularly preferable. Here, the polyester A containing a flexible movable component may be one in which the flexible movable component is added after the polymerization of the polyester A is completed, but the flexible movable component is added before or during the polymerization of the polyester A, Part or all of the flexible movable component is polyester A
It may be copolymerized with. However, the method for producing the polyester A is not limited to the above. It should be noted that two or more kinds of polyesters may be mixed within a range that does not impair the object of the present invention. Further, it is desirable that the polyester A contains substantially no particles.

The type of polyester B is not particularly limited. It is preferable that the crystallization index ΔTcc ′ of the polyester B is smaller than the crystallization index ΔTcc ′ of the polyester A because the influence on the stretchability is reduced. Further, it is desirable that the polyester B does not contain particles, but it may contain particles. However, in order to obtain a film having a high total light transmittance, the particle concentration of polyester B is 0.
It is preferably at most 5%.

The polyester film of the present invention may be a film obtained by laminating polyester A on one side of a film made of polyester B, or a film obtained by laminating polyester A on both sides of a film made of polyester B. It may be. When polyester A is laminated on one side of a film made of polyester B,
When the polyester A is laminated on the surface not in contact with the cooling drum, the cooling rate during extrusion casting becomes slow, and crystallization of the polyester A easily occurs, and at this time,
This is preferable because it is possible to obtain a preferable film by controlling the temperature change of the polyester A by blowing hot air or cold air.

The layer thickness of the polyester A layer is not particularly limited, but a particularly preferable surface morphology is obtained when the layer thickness is 0.5 μm or more and 5 μm or less, and the influence on the stretchability during film formation is small. Therefore, it is preferable.
Further, a coating layer may be provided on at least one surface in order to impart easy adhesion and antistatic properties.

Next, a method for producing the film of the present invention will be described.

The melt-extruded film in which polyester A is laminated on at least one side of polyester B is cooled on the surface of a chilled metal roll by an electrostatic cast method to obtain an unstretched film. At this time, depending on the crystallization rate of the polyester A, the thickness of the unstretched film, and the temperature of the cooling drum, the polyester A on the side not in contact with the drum is crystallized to obtain a film having a preferable surface morphology and optical characteristics. You can Next, if crystallization during casting is not sufficient, heat treatment is applied to at least one side of the unstretched film, if necessary. Here, the unstretched film refers to a state immediately after being extruded from the die and before being cooled and solidified, to a film that is slightly solidified (up to about 2 times) in the uniaxial direction after being cooled and solidified. The purpose of this heat treatment is to increase the crystallinity of the film surface before stretching to a preferable crystallinity, and as a treatment method, a method in which a film having a high temperature immediately after extrusion is gradually cooled to be crystallized, There are a method of re-heating a film which has been cooled and solidified to crystallize it, and a method of heat-treating it in a state of being slightly stretched in the uniaxial direction. One of these methods can be performed in the film forming process to obtain the target surface morphology, but two or more of these methods can be used in combination in the film forming process. You may.

In order to obtain the surface morphology in accordance with this purpose,
Although the method (1) is preferred, the method (1) or (2) can be used to obtain a desired surface morphology by adopting appropriate conditions. The treatment method of is not particularly limited, but it is a method of heat treatment by winding it around a heating roll, a method of hot air treatment from the opposite surface that comes into contact with the roll in a state of being wound around the roll, or contacting with a roll in a state of being wrapped around the roll There is a method of heat treatment with an infrared heater from the opposite surface, a method of heat treatment with an infrared heater between rolls / rolls, a method of heating with a stenter, and the like, but the method is not particularly limited to these. As processing conditions, it is desirable to perform heat treatment at a temperature of 100 to 240 ° C. for 0.5 to 100 seconds. More preferably, 120 to 2
The heat treatment condition of 20 ° C. for 1 to 50 seconds is a desirable condition for efficiently obtaining the target surface morphology in the film forming process.

Further, this unstretched film is biaxially stretched and heat-set by a known method to obtain a biaxially oriented polyester film. During this stretching, the crystals formed near the surface of the film are harder than the amorphous part and are less likely to be deformed, so that protrusions are formed on the surface. Here, in order to improve dimensional stability, relaxation heat treatment may be performed in the width direction during heat setting.

As a stretching method, it is effective to use a longitudinal method first and then a sequential biaxial stretching in which widthwise stretching is performed. Stretching in the longitudinal direction depends on the glass transition temperature T of polyester.
5000 to 50,000% at high temperature higher than 10g
It is effective to carry out the stretching at a stretching speed of 1 / min at once or in several times in a range of 3 to 6 times. The stretching in the width direction is preferably performed at a temperature of 80 to 160 ° C. and a stretching speed of 1000 to 20000% / min in a range of 3 to 7 times. The biaxially stretched film may be further stretched in at least one direction, but the constant length heat treatment after stretching is 1
It is preferable to carry out at 70 to 240 ° C. for 0.5 to 60 seconds. Furthermore, in order to obtain a film having excellent dimensional stability, 170% while relaxing in the width direction by 5 to 15% after the constant length heat treatment.
It is effective to perform a relaxation heat treatment at ˜240 ° C. for 0.5 to 60 seconds.

A preferred method for producing a laminated film is to produce a melt-extruded film as described above by melting and supplying polyesters A and B from two extruders, respectively, and supplying the two- or three-layer manifold. Alternatively, it is a method of laminating polyester A on one side or both sides of polyester B using a merging block and melt-extruding from a slit-shaped die, but a method of laminating using a merging block having a rectangular merging portion is a stable surface. Are particularly preferred.

The use of the present invention is not particularly limited, but it is required to have large surface roughness, large total light transmittance, matteness, texture, anti-glare property, writability, light diffusibility and abrasion resistance. It is suitable for such applications such as packaging materials, labels, cover films, tracing films, and reflection sheets. Among them, especially, a tracing film that is written on with a pencil, etc.
Diffusion sheet used for diffusing light in liquid crystal backlights and lighting equipment, anti-reflective sheet that overlaps with other glossy members and suppresses glare and glare of lighting etc. without changing the pattern of the underlying member It is very effective in terms of transmittance and surface morphology in the use of a cover film which is superposed on the above to protect the surface and gives a moist texture.

[0028]

[Method for measuring physical properties and method for evaluating effects] The method for measuring characteristic values and the method for evaluating effects according to the present invention are as follows.

(1) Center line average roughness Ra and maximum height R
t, protrusion interval Sm Using a high-precision thin film step measuring instrument ET-10 manufactured by Kosaka Laboratory, center line average roughness Ra, maximum height Rt, protrusion interval Sm
Was measured. The conditions are as follows, and the average value obtained by measuring 20 times by scanning the film in the width direction was used as the value.

-Stylus tip radius: 0.5 μm-Stylus load: 5 mg-Measurement length: 1 mm-Cutoff value: 0.08 mm Note that the definitions of Ra, Rt, Sm, etc. are, for example, written by Jiro Nara "Surface". Roughness measurement / evaluation method "(General Technology Center, 1983).

(2) Content of particles A composition analysis was carried out by a microscopic FT-IR method (Fourier transform microscopic infrared spectroscopy), and a ratio of a peak due to a carbonyl group of polyester to a peak due to a substance other than polyester. I asked from. In order to convert the peak height ratio into a weight ratio, a calibration curve was prepared in advance using a sample with a known weight ratio, and the polyester ratio with respect to the total amount of polyester and other substances was determined. In addition, an X-ray microanalyzer was also used as needed. If a solvent that can dissolve the polyester and not the particles can be selected, dissolve the polyester and centrifuge the particles from the polyester.
The weight percentage of particles was determined.

(3) Particle content in the surface layer of the film A film slit into a tape having a width of 1/2 inch was used, and a single-edged blade was vertically pressed against the surface on which the polyester A was laminated. It is run for 20 cm while being pushed in by 0.5 mm (running tension: 500 g, running speed: 6.7 cm / sec). At this time, the particle content of the scraped material on the surface of the film attached to the tip of the single-edged blade was determined according to the method for measuring the particle content.

(4) Average Particle Size of Particles Polyester is removed from the film by a plasma ashing method to expose the particles. The processing conditions are selected so that the polymer is ashed but the particles are not damaged as much as possible. The particles are observed with a scanning electron microscope (SEM), and the particle image is processed with an image analyzer. The magnification of SEM is approximately 2000 to 10,000 times, and the visual field in one measurement is appropriately selected from approximately 10 to 50 μm on each side. The volume average diameter d is obtained by the following formula from the volume fraction with the particle diameter when the number of particles is 5000 or more by changing the observation location.

D = .SIGMA.di.multidot.Nvi where di is the particle size and Nvi is the volume fraction thereof.

When the particles are organic particles or the like and are significantly damaged by the plasma low temperature ashing method, the following method may be used.

The cross section of the film was examined with a transmission electron microscope.
Observe at 3,000 to 100,000 times. The section thickness of the TEM is set to about 100 nm, the location is changed and 500 or more visual fields are measured, and the volume average diameter d is calculated from the above formula.

(5) Proportion of Crystal-Dependent Protrusions Phenol / under the target protrusion in the film thickness direction
When etching is performed with a mixed solvent of carbon tetrachloride (weight ratio: 6/4) and the substances that form the protrusions remain as insoluble substances, particles added from the outside or particles precipitated inside Yes (I). When there is substantially nothing that remains as an insoluble matter, it can be presumed that the substance that forms the protrusion is fine crystals (II). By this method, the frequency of I and the frequency of II when the visual field was set to 1 mm ² were obtained, and the value of II / (I + II) was taken as the ratio of protrusions due to crystals.

(6) Laminate Thickness Using a transmission electron microscope (H-600 manufactured by Hitachi) at an accelerating voltage of 100 kV, the cross section of the film was subjected to an ultrathin section method (R
uO ₄ staining), the interface is captured, and the laminated thickness is determined. The magnification is usually selected according to the laminated thickness to be judged, and is not particularly limited, but 10,000 to 100,000 times is suitable.

(7) Crystallization index ΔTcc 'The crystallization index was measured using a DSC (Differential Scanning Calorimeter) II type manufactured by Parking Elma. The measurement conditions of DSC are as follows. That is, 10 mg of a sample is set in a DSC device,
After melting at a temperature of 300 ° C. for 5 minutes, it is quenched in liquid nitrogen. This sample was heated at a rate of 10 ° C./min, and the crystallization exothermic peak temperature from the glass state was applied to the cold crystallization temperature Tcc,
The endothermic peak temperature based on crystal melting is defined as the melting temperature Tm. Further, after the feed reached 300 ° C. again, it was kept at this temperature for 5 minutes and then cooled at 10 ° C./minute, and the crystallization exothermic peak temperature at the time of temperature decrease was defined as the temperature-down crystallization temperature Tmc. Here, the difference between Tmc and Tcc (Tmc-Tcc) is defined as the crystallization index ΔTcc ′.

As the sample, raw material pellets before film formation may be used, or 10 mg of powder obtained by scraping off the surface layer of the film after film formation with a razor blade may be used.

(8) Intrinsic viscosity [η] (unit: dl / g) The value calculated from the following formula was used from the solution viscosity measured at 25 ° C. in polyester orthochlorophenol.

Η _sp / C = [η] + K [η] ² · C where η _sp = (solution viscosity / solvent viscosity) -1 C is the weight of dissolved polymer per 100 ml of solvent (g / 10)
0 ml, usually 1.2), K is the Huggins constant (0.343
And).

The solution viscosity and solvent viscosity were measured using an Ostwald viscometer.

(9) Total light transmittance Ti (%), diffuse transmittance Td
(%) Hitachi spectrophotometer U-3410 with total light transmittance Ti at a wavelength of 550 nm using dedicated detectors.
(%) And diffuse transmittance Td (%) were measured.

(10) Underground visibility A film sample was placed on a 1 mm grid paper (e-19) manufactured by KOKUYO Co., Ltd., and it was evaluated whether each 1 mm grid line could be discriminated.
Evaluation was made according to the following criteria.

Individual lines cannot be distinguished when 5 films are stacked: × Can be distinguished by stacking 5 films but cannot be distinguished when 8 films are stacked: ○ Individual lines can be distinguished when 8 films are stacked : ◎

(11) Anti-glare function Using a digital variable angle gloss meter UGV-5D manufactured by Suga Test Instruments Co., Ltd. according to the method defined in JIS-K-7105,
The 60 ° specular gloss is measured. When the gloss is 20% or less, it is ⊚, and when it is more than 20% and 30% or less, it is ∘, 30.
Those larger than% were defined as x.

(12) Using a pencil of H on the writable film, straight lines were drawn at 1 mm intervals and the following evaluations were made visually.

⊚: Individual straight lines can be identified, and the color of the lines is dark. ◯: Individual straight lines can be identified, but the color of the lines is slightly light. B: Dark lines can be drawn, but individual lines cannot be distinguished due to blurring. X: A clear line cannot be drawn.

(13) Abrasion resistance A film obtained by slitting a film into a tape having a width of 1/2 inch is loaded with a load of 100 g using a tape low-speed running tester, and a commercially available razor single-edged blade (FA Feather Safety Razor Co., Ltd. FA
S-10) is pressed against the running surface for 1 mm to run (running speed 250 m / min, running distance 100 mm, running times 1
Times). At this time, the adhesion width of the shavings adhering to the razor one-sided blade is observed with a microscope. When the adhesion width of the shavings is 40 μm or less, it is ⊚, when it is more than 40 μm and 60 μm or less, it is ◯,
When it was larger than 60 μm, the abrasion resistance was evaluated as ×. The model test using the single-edged razor well reflects the abrasion resistance when traveling on a traveling means harder than a polyester film such as a metal guide in the processing step, and the property of polluting the step due to generation of powder.

[0051]

Next, the present invention will be described based on embodiments.

Examples, Comparative Examples Using the catalysts having the compositions shown in Tables 1 and 2, polyethylene terephthalate polymerized by a conventional method or a copolyester having ethylene terephthalate as a main repeating unit was used. When particles were added, polyethylene terephthalate polymerized by a conventional method using ethylene glycol containing particles was used.

Pellets of polyesters A and B listed in Table 3 were each dried at 180 ° C. for 3 hours, and then melt-extruded at 290 ° C. by using two known extruders, for two layers or three. A rectangular confluent block (feed block) for layers is confluently laminated so as to have a laminated constitution shown in Table 2, and is wound around a metal casting drum having a surface temperature of 20 ° C. by an electrostatically applied casting method and cooled. Then, it was solidified to obtain an unstretched film. At this time, in Example 3, the surface of the unstretched film, which was not in contact with the cooling drum, was subjected to heat treatment with a wind of 100 ° C. and 20 m / min using a hot air heater and a nozzle.

When this unstretched film is heat-treated, it is heat-treated on a known silicone rubber roll under the conditions shown in Table 3, and then 90 ° C. between the rolls and a stretching rate of 2000% / min. After stretching 3.4 times in the machine direction in the machine direction, it was stretched 3.4 times in the width direction at 10,000% / min using a known stenter, and heat-treated at 200 ° C. for 3 seconds under a fixed length.
A biaxially oriented laminated film having the thickness described in 1. was obtained.

Table 4 shows the characteristics of each film in each of the above Examples and Comparative Examples. In the case of a film having a two-layer structure, the center line average roughness Ra of the surface on which the polyester A is laminated, the maximum height Rt, the particle concentration of the surface layer, and the ratio of protrusions due to crystals were measured.

In Examples 1 to 7, the preferable particle concentration is
Centerline average roughness Ra, surface particle concentration, total light transmittance T
i, a film having a diffused transmittance Td was obtained, which was a film excellent in underlayer visibility, anti-glare ability, writability, and abrasion resistance, but the polyester films obtained in Comparative Examples 1 to 5 were: The film was inferior in any of the visibility of the base, the ability to prevent reflection, the writing property, and the abrasion resistance.

[0057]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[0058]

INDUSTRIAL APPLICABILITY A polyester film having excellent abrasion resistance, excellent optical characteristics and drawing properties can be stably provided in a usual polyester film forming process.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29L 9:00

Claims (12)

[Claims] 1. A laminated biaxially oriented polyester film obtained by laminating a layer made of polyester A on at least one side of a layer made of polyester B, wherein the center line surface roughness of the surface of the layer made of polyester A is 50 nm. that's all,
Biaxially oriented laminate, characterized in that the content of particles in the surface layer of the surface is 0.5% by weight or less, and the total light transmittance Ti (%) and the diffuse transmittance Td (%) satisfy the following formulas. Polyester film. Ti ≧ 80 Ti × Td ≧ 4000 2. The biaxially oriented laminated polyester film according to claim 1, wherein the protrusion spacing Sm on the surface is 30 μm or less. 3. The ratio of the maximum height Rt of the surface to Ra, R
The biaxially oriented laminated polyester film according to claim 1 or 2, wherein t / Ra is 10 or less. 4. The biaxially oriented laminated polyester film according to claim 1, wherein 80% or more of the protrusions on the surface are formed by polyester A crystals. 5. A crystallization index ΔTcc ′ of polyester A.
Is 80 ° C. or higher, and the biaxially oriented laminated polyester film according to any one of claims 1 to 4. 6. Polyester A comprises a flexible movable component of 0.
The biaxially oriented laminated polyester film according to any one of claims 1 to 5, wherein the biaxially oriented laminated polyester film is composed of polyester in an amount of 01% by weight or more and 15% by weight or less. 7. The polyester A has a number average molecular weight of 10
The biaxially oriented laminated polyester film according to any one of claims 1 to 6, which comprises a polyester containing 0.01 to 15% by weight of a polyalkylene glycol of 00 to less than 50,000. 8. The biaxially oriented laminated polyester film according to claim 1, wherein the thickness of the laminated portion made of the polyester A is 0.5 μm or more and 5 μm or less. 9. A tracing film comprising the biaxially oriented laminated polyester film according to any one of claims 1 to 8. 10. A diffusion sheet comprising the biaxially oriented laminated polyester film according to any one of claims 1 to 8. 11. An antireflection sheet comprising the biaxially oriented laminated polyester film according to any one of claims 1 to 8. 12. A cover film comprising the biaxially oriented laminated polyester film according to claim 1.