JPH08309847A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE: To provide a polyester film capable of being easily formed without applying a special surface roughening process for increasing the surface roughness of a polyester film and having both of excellent matte properties and transparency in spite of a relatively small surface roughness. CONSTITUTION: A biaxially oriented polyester film based on polyester A is characterized in that the center line average roughness Ra of at least the single surface of the film is 50-3000nm and the glossiness G(%) of the rough surface of the film is 45% or less and G(%) and Ra(nm) satisfy Ra.G<=3000.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polyester film, and more particularly to a biaxially oriented polyester film having fine projections formed on the surface thereof, which requires a relatively large surface roughness and has an appropriate gloss. Applications that require erasability and transparency, such as matte film, tracing applications, labels, stamping films, packaging materials, and light diffusion films for liquid crystal display backlights and lighting equipment that utilize light characteristics, The present invention relates to a biaxially oriented polyester film useful for non-backlight liquid crystal reflectors, anti-string films, overlay applications and the like.

[0002]

2. Description of the Related Art Polyester films are widely used in various applications by utilizing their excellent mechanical properties, thermal properties, optical properties, electrical properties, surface properties, transmission properties, and chemical resistance. It is used. Among them, the roughened polyester film is a label, a stamping film, a drafting film as a tracing film, a second original drawing film, and a packaging by utilizing drawing property, moderate matting property and transparency. It is widely used for materials, light diffusion films for backlights of liquid crystal displays and lighting equipment, and non-backlight liquid crystal reflectors.

Conventionally, these roughened polyester films have been subjected to a sand blasting process (for example, Japanese Patent Publication No. 58-39453) in which sand or the like is sprayed to physically roughen the surface of the biaxially oriented film, and chemicals. A method such as a chemical etching treatment (for example, Japanese Patent Publication No. 38-13784) for applying a treatment, a method for coating a liquid containing fine particles on a smooth film surface to roughen the surface, or a polyester having particles at least on the surface layer (for example, Inactive particles, inorganic particles) are added and stretched to form protrusions on the surface (for example, Japanese Examined Patent Publication No. 52-4308), polyester is melt-extruded and embossed to produce a film having irregularities. A method of forming a film and stretching it (for example,
It was manufactured by Japanese Patent Publication No. 51-28360).

[0004]

However, the polyester film produced by the conventional technique as described above has the following problems, for example.

The sandblast treatment and the chemical etching treatment have problems in that the process is complicated, the cost is high, and the scratch resistance is insufficient, and the transparency is poor. Further, since the surface roughness is made considerably large in order to bring out characteristics such as matteness and drawability, it is difficult to control the roughness, for example, when a moderate surface roughness is required. , It is also the cause of the decrease in transparency. On the other hand, a polyester film having a surface formed by containing particles in at least the surface layer, particles such as inert particles different from the polyester film are added,
Since the surface protrusions are formed by stretching, voids are easily generated around the particles below the protrusions. The voids cause problems that the formed protrusions are easily broken, the film surface is easily scraped off, and the film surface is easily scratched. Further, in order to bring out the characteristics of matteness and drawability, it is necessary to add a large amount of particles, and therefore, for example, problems such as voids and coarse projections in which particles are aggregated increase, and further, There is a problem that transparency is reduced.

The object of the present invention is to subject the polyester film to a complicated treatment for increasing the surface roughness,
Relatively small surface without the need for special equipment and to solve problems such as increase of coarse protrusions and voids and decrease of transparency due to addition of a large amount of particles different from polyester. It is an object of the present invention to provide a biaxially oriented polyester film which is a roughened film having uniform and fine projections, which has excellent roughness, excellent matteness and drawing properties, and good transparency.

[0007]

The polyester film of the present invention for this purpose is a biaxially oriented polyester film containing polyester A as a main component, and the center line average roughness Ra of at least one surface of the film is 50 nm. Above 3
It is a rough surface of 000 nm or less, and the glossiness G (%) of the rough surface is 4
It is 5% or less, and G (%) and Ra (nm) satisfy the following formula.

Ra · G ≦ 3000

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION That is, in the polyester film of the present invention, when the surface glossiness G (%) is 45% or less, preferably 30% or less, more preferably 15% or less, an appropriate gloss is obtained. Erasability can be achieved. If the gloss level G (%) is larger than 45%, specular reflection of light becomes large, and a matte texture cannot be obtained. Further, for example, in applications such as liquid crystal reflectors where aluminum is vapor-deposited,
The field of view becomes narrower, the phenomenon that something looks like a mirror occurs, and in applications such as the diffuser plate of the backlight of liquid crystal displays, the light diffusivity decreases and the brightness decreases, and the light source directly It looks like. In addition, the glossiness is 1% in order to provide appropriate matteness and transparency.
Although the above is preferable, it is not particularly limited.

In order to impart a matte property, a drawing property and a light diffusing property to the film, the center line average roughness Ra of the film is 5
0 nm or more and 3000 nm or less, preferably 70 nm or more and 2000 nm or less, more preferably 100 nm or more 1
It is necessary to be 000 nm or less. When the center line average roughness of the film is less than 50 nm or more than 3000 nm, good matting properties, drawing properties and light diffusibility cannot be imparted.

The center line average roughness R of at least one surface
Relationship between a (nm) and G (%) Ra · G is 3000 or less, preferably 2000 or less, and more preferably 1500 or less, so that, for example, sandblasting treatment, chemical etching treatment, particle addition method, etc. However, superior matting properties can be obtained with a relatively small surface roughness, and coarse protrusions and the like are reduced accordingly.
The film formed by sandblasting, chemical etching, particle addition method, or the like has a matte property, that is, in order to reduce the glossiness G,
The surface roughness Ra must be increased. Therefore, the parameter Ra · G may become larger than 3000. However, increasing the surface roughness is not preferable because, for example, the transparency decreases and the number of coarse projections increases. Ra · G is 50 for good matting properties.
Although the above is preferable, it is not particularly limited.

Further, the total light transmittance at a wavelength of 550 nm is preferably 80% or more, more preferably 83% or more, further preferably 85% or more, and sufficient transparency can be obtained. When the total light transmittance is less than 80%,
Due to the reduced transparency, for example, the use of tracing films, overlays and stamping films makes it difficult to see what is underneath the film, and
In light diffusion applications, the brightness may be reduced.

The film thickness is 10 μm or more, preferably 15 μm or more, more preferably 20 μm or more for tracing applications and light diffusion applications.
Sufficient strength can be obtained. Although the upper limit is not particularly limited, it is preferably 120 μm or less in terms of transportability and the like.

In order to improve the abrasion resistance and transparency of the polyester film, a film in which the projections on the surface are projections mainly caused by fine crystals of polyester A is preferable. Further, in order to control the surface roughness, it is preferable that the protrusions are formed by fine crystals that can form protrusions due to the difference in heat treatment conditions. Crystallization necessary for forming protrusions is achieved by performing no special heat treatment when melt-extruding by a normal method and winding it around a cooling drum, or by performing simple heat retention or gradual cooling with cooling treatment. be able to.

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 a main constituent 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. The crystal nucleating agent effect is enhanced, and the cold crystallization temperature Tcc and the glass transition temperature T
In order to obtain a polyester having a small crystallinity index ΔTcg represented by the difference of g or a low cold crystallization temperature Tcc, lithium acetate, magnesium acetate, potassium acetate, phosphorous acid, phosphonic acid during transesterification and polymerization, The presence of phosphinic acid or its derivatives, antimony oxide, and germanium oxide is effective. A particularly desirable combination is magnesium acetate and phosphonic acid (or a derivative thereof) and antimony oxide, and as the phosphonic acid (or a derivative thereof), phenylphosphonic acid,
Examples include dimethyl phenyl phosphonate.

Further, in order to increase the mobility of the molecule and obtain a polyester having a high crystallization rate, it is effective to add a small amount of a flexible movable component or copolymerize it. Here, the flexible movable component means a component having a long flexible chain in the main chain and having a high affinity with polyester, or a copolymerizable component,
For example, it means a long-chain aliphatic diol, polyalkylene glycol and the like, and it is particularly effective to use polyalkylene glycol such as polyethylene glycol, polypropylene glycol and hexamethylene glycol.
Above all, a polyethylene glycol having a number average molecular weight of 200 or more and 50,000 or less, preferably 1,000 or more and 40,000 or less, more preferably 2,000 or more and 30,000 or less is used in an amount of 0.01% by weight or more and 15% by weight or less, preferably 0. It is preferably used in the range of 1% by weight or more and 13% by weight or less, more preferably 1% by weight or more and 10% by weight or less.

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.

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 no insoluble matter remaining, it can be presumed that the substance that forms the protrusion is a fine protrusion (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 are obtained,
It is preferable that the value of II / (I + II) is 70% or more. However, the method for determining whether or not the surface protrusions are fine protrusions of polyester A is not limited to the above method, and an appropriate method can be selected.

The formation of surface protrusions utilizing the crystallization of the polyester A as described above is carried out, for example, by utilizing the slow cooling from the time of melting as follows. In the process of cooling the melt-extruded film containing polyester A as the main component on the surface of the chill roll, the atmospheric temperature and the temperature of the chill roll can be adjusted without special heat treatment, and cool air or hot air can be applied to the opposite side of the chill roll. By spraying on the surface, crystals grow at least in the surface layer portion on the opposite surface of the cooling roll. Next, 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.

When the rapid crystallized polyester of the present invention is used, the unstretched film has a thickness of 100 to 2000.
If it is in the range of μm, without special heat treatment,
By cooling the film extruded at a temperature 5 to 50 ° C. higher than the melting point of polyester on a cooling roll having a surface temperature of 5 to 50 ° C., crystals grow at least on the opposite surface of the cooling roll, and the center line average after biaxial stretching A film having a roughness of 50 nm or more can be obtained. Further, in a specific unstretched film thickness, in order to obtain a film having a preferable center line average roughness, the film surface on the opposite side of the cooling roll,
The temperature may be controlled by blowing air having a temperature of 10 ° C. or more and 160 ° C. or less and a wind speed of 30 m / min or less.

As the stretching method, sequential biaxial stretching or simultaneous biaxial stretching can be used. However, the method of using the longitudinal method first and then the successive biaxial stretching in which the stretching in the width direction is performed is suitable for obtaining the desired surface morphology and abrasion resistance. However, the method for forming the surface protrusions by utilizing the crystallization of the polyester A is not limited to the above method, and an appropriate method can be selected.

The polyester film of the present invention may be used as a single layer of a biaxially oriented film containing polyester A as a main component, or a laminate in which polyester A is laminated on at least one side of a film containing polyester B as a main component. Although it may be used as a film, it is preferable to use it as a laminated film because there is no possibility that the stretchability is deteriorated such that the film is easily broken during biaxial stretching depending on the degree of crystallization during slow cooling. The laminated thickness when used as a laminated film is not limited, but it is preferable that the laminated thickness is ⅓ or less of the total thickness of the film or 5 μm or less because the influence on the stretchability is particularly small.

The type of polyester B is not particularly limited. When the crystallinity index ΔTcg of the polyester B is larger than the crystallinity index ΔTcg of the polyester A, the influence on the stretchability is reduced, which is preferable. Further, it is preferable that the polyester B does not contain particles, but it may contain particles.

On the other hand, since the surface has dense protrusions, the graphite of the pencil is inserted into the recesses, so that the drawing is excellent. For example, the depth, thickness, sharpness, writing condition, etc. are relatively good. In addition, there is less bleeding of pencil graphite due to light friction. However, when an eraser is used, the eraser can be erased cleanly and the redrawability is excellent. For tracing purposes, the protrusion spacing Sm is preferably 30 μm or less, more preferably 25 μm in order to draw a fine line without bleeding when written with a pencil.
m or less, more preferably 20 μm or less. When the protrusion spacing Sm is larger than 30 μm, it is difficult to draw a fine line without bleeding even if the center line average roughness is sufficiently large.

Further, in the use of a light diffusing plate such as a backlight of a liquid crystal display or a lighting device, in order to obtain a good light diffusing property, the glossiness is preferably 40% or less, more preferably 30% or less, and further preferably. It is 15% or less.
If the glossiness is more than 40%, the light diffusion is insufficient,
You can directly see the light source behind the diffuser,
The uniformity of light is lacking and the brightness is also low. Further, in order to obtain a certain level of brightness, it is preferable that the total light transmittance at a wavelength of 550 nm is 80% or more.

For overlays and the like, the glossiness is preferably 40% or less, more preferably 30% or less, in order to obtain good matte design and antiglare properties.
More preferably, it is 15% or less. When the glossiness is more than 40%, good matteness cannot be obtained and the object is reflected. Further, in order for the undercoat of the film to be visually recognized, the total light transmittance at a wavelength of 550 nm is preferably 80% or more.

The film of the present invention may be used alone, or may be used by laminating it with another material such as glass, paper or metal. Further, a coating layer may be provided on the surface in order to impart easy adhesion, ink receptivity and antistatic property. Further, in order to improve the light diffusion performance, a coating layer containing a high concentration of transparent fine particles may be provided and used.

The use of the present invention is not particularly limited, but particularly for a biaxially oriented polyester film having fine projections formed on the surface, a relatively large surface roughness is required, and an appropriate matteness and transparency are required. Applications that require light, such as matte film, tracing applications, labels, stamping films, packaging materials, and light diffusion films and backlights for liquid crystal displays that utilize light characteristics and non-backlight liquid crystal reflection. It is useful for boards, string films, overlay applications, etc.

[Physical property measuring method and effect evaluating method] The characteristic value measuring method and effect evaluating method of the present invention are as follows.

(1) Centerline average roughness Ra and protrusion spacing Sm The measurement was performed using a high precision thin film step measuring instrument ET-10 manufactured by Kosaka Laboratory. The conditions are as follows, and the average value of 5 measurements was taken as the value.

-Stylus tip radius: 0.5 μm-Stylus load: 5 mg-Measurement length: 1 mm-Cutoff value: 0.08 mm The definitions of Ra, Sm, etc. are given in JIS-B-0601. .

(2) Gloss G According to the method specified in JIS-K-7105,
It measured using the Suga Test Instruments digital variable angle gloss meter UGV-5D. The specular gloss, which is the ratio of the specular reflection light on the surface to the light ray incident at an angle of 60 degrees, was measured. As an index of mattness, ⊚ indicates 15% or less, ∘ indicates greater than 15% and 45% or less, and x indicates greater than 45%.

(3) Light transmittance It was measured using a spectrophotometer U-3410 manufactured by Hitachi Ltd. The total light transmittance in the visible light region in the wavelength range of 300 nm to 700 nm was measured, and in particular, the total light transmittance in the wavelength of 550 nm was taken as the value. As a transparency index, 85% or more is ⊚, 80% or more and less than 85% is ∘, 80%
Less than is represented by x.

(4) Drawability Using a pencil of H manufactured by Mitsubishi Pencil, straight lines were drawn at 1 mm intervals and visually evaluated. What can be written on the film and which does not bleed even if it is rubbed lightly ◎
In addition, a mark that can be written on the film but that bleeds when lightly rubbed on the film is indicated by a circle.

(5) Light diffusing property The device was installed as a diffusing plate in a backlight device of a liquid crystal display plate and evaluated according to the following criteria.

The light source is not visually recognized and has a sufficient brightness: ◎ The light source is slightly visually recognized or the brightness is slightly inferior: ○ The light source is clearly visible or the brightness is significantly inferior: ×

(6) Overlay characteristics As overlay characteristics, not only good matteness but also
It is necessary to visually recognize the base of the film, and the film sample was placed on 1 mm grid paper (e-19) manufactured by KOKUYO Co., Ltd., and whether or not each 1 mm grid line can be discriminated was evaluated based on the following criteria.

Individual lines can be distinguished when eight films are stacked: ◎ Can be distinguished with five films but cannot be distinguished with eight films: ○ Individual lines cannot be distinguished when five films are stacked : ×

(7) Glass transition point Tg, cold crystallization temperature T
cc, crystallization index ΔTcg It was measured using a DSC (Differential Scanning Calorimeter) type II 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 is heated at a rate of 10 ° C./minute to obtain a glass transition point T
g is detected. The temperature was further raised and the crystallization exothermic peak temperature from the glass state was set as the cold crystallization temperature Tcc. The difference between Tcc and Tg (Tcc-Tg) is taken as the crystallization index Δ.
Define as Tcg. 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.

[0040]

EXAMPLES Next, the present invention will be explained based on examples.

Example Polyesters A and B were polyethylene terephthalate polymerized by a conventional method (polymerization catalyst: magnesium acetate,
Antimony trioxide, dimethylphenylphosphonate as a phosphorus compound) was used, or polyethylene glycol was used by copolymerizing ethylene terephthalate as a main repeating unit. When particles were added, polyethylene terephthalate polymerized by a conventional method using ethylene glycol containing particles was used.

Example 1 As polyester A, polyethylene terephthalate polymerized by a conventional method (polymerization catalyst: magnesium acetate 0.1
0% by weight, antimony trioxide 0.03% by weight, dimethylphenylphosphonate 0.35% by weight as a phosphorus compound, and ethylene terephthalate as a main repeating unit, polyethylene glycol (number average molecular weight: 40
00, content: 10% by weight). After drying the pellets of polyester A at 180 ° C. for 3 hours, melt extrusion was performed at 290 ° C. using a known extruder, and wound on a casting drum having a surface temperature of 20 ° C. using an electrostatically applied casting method. Cool, solidify, thickness 60
An unstretched film of 0 μm was made. This unstretched film was stretched at a temperature of 95 ° C. at a stretching speed of 2000% / min in the longitudinal direction by 3.4 times, and further using a known stenter at a stretching speed of 10,000% / min at 95 ° C. The film was stretched 3.4 times in the width direction and further heat-treated at 210 ° C. for 5 seconds under a fixed length to obtain a biaxially oriented film having a thickness of about 50 μm.

Example 2 A laminated film having an A / B two-layer structure was prepared. Polyester A
Polyethylene terephthalate polymerized by a conventional method (polymerization catalyst: 0.10% by weight of magnesium acetate, 0.03% by weight of antimony trioxide, 0.35% by weight of dimethylphenylphosphonate as a phosphorus compound) was used as the main component. Polyethylene glycol (number average molecular weight: 20,000, content:
5% by weight). As the polyester B, polyethylene terephthalate (polymerization catalyst: 0.06% by weight of magnesium acetate, 0.008% by weight of antimony trioxide, 0.02% by weight of dimethylphenylphosphonate as a phosphorus compound) polymerized by a conventional method was used. Pellets of polyesters A and B were dried at 180 ° C for 3 hours and then melted at 290 ° C using two extruders each, and a rectangular confluent block (feed block) for two layers
Then, the B layer is joined and laminated so that the B layer is in contact with the casting drum side, and the surface temperature is 20
It was wound on a casting drum at 0 ° C., cooled and solidified to prepare an unstretched film having a thickness of 700 μm. In the same manner as in Example 1 below, a biaxially oriented film having a thickness of about 60 μm was obtained. The laminated thickness of the stretched film was 2 μm.

Example 3 A laminated film having an A / B / A three-layer structure was prepared. As polyester A, polyethylene terephthalate polymerized by a conventional method (polymerization catalyst: magnesium acetate 0.10% by weight,
0.03% by weight of antimony trioxide and 0.35% by weight of dimethylphenylphosphonate as a phosphorus compound,
Ethylene terephthalate was used as a main repeating unit containing polyethylene glycol (number average molecular weight: 20,000, content: 10% by weight). As the polyester B, polyethylene terephthalate (polymerization catalyst: 0.06% by weight of magnesium acetate, 0.008% by weight of antimony trioxide, 0.02% by weight of dimethylphenylphosphonate as a phosphorus compound) polymerized by a conventional method was used.
Pellets of polyesters A and B were dried at 180 ° C for 3 hours and then melted at 290 ° C by using two extruders each, and a rectangular confluent block (feed block) for three layers.
Are combined and laminated with each other, and are wound on a casting drum having a surface temperature of 20 ° C. by using an electrostatically applied casting method, cooled,
It was solidified to form an unstretched film having a thickness of 760 μm. This unstretched film is stretched at a stretching speed of 200 at a temperature of 95 ° C.
The film was stretched at a rate of 0% / min in the longitudinal direction by 3.0 times, and further, using a known stenter, at a stretching speed of 10,000% / min, 95%.
℃, stretched 3.0 times in the width direction and 210 at a fixed length
Heat treatment was performed at 5 ° C. for 5 seconds to obtain a biaxially oriented film having a thickness of about 85 μm. The laminated thickness is 2μ after stretched film
It was m.

Example 4 A laminated film having an A / B / A three-layer structure was prepared. The same polyesters as in Example 3 were used as the polyesters A and B. After drying the polyester A and B pellets at 180 ° C for 3 hours,
Melted at 290 ° C using 2 extruders each, 3
Layers are joined together by a rectangular joining block (feed block) for layers, and the surface temperature is 40 ° C. using the electrostatically applied casting method.
It was wound on a casting drum of, and cooled and solidified to prepare an unstretched film having a thickness of 670 μm. Then, in the same manner as in Example 3, a biaxially oriented film having a thickness of about 75 μm was obtained. The laminated thickness of the stretched film was 2 μm.

Example 5 A laminated film having an A / B / A three-layer structure was prepared. The same polyesters as in Example 3 were used as the polyesters A and B. After drying the polyester A and B pellets at 180 ° C for 3 hours,
Melted at 290 ° C using 2 extruders each, 3
Layers are joined together by a rectangular joining block (feed block) for layers, and the surface temperature is 40 ° C. using the electrostatically applied casting method.
It was wound on a casting drum of, cooled and solidified to form an unstretched film having a thickness of 600 μm. At this time, the surface of the film that was not in contact with the drum was heated with a warm air of 160 ° C. and 20 m / s by using a known hot air generator and blower. Then, in the same manner as in Example 3, a thickness of about 65 is obtained.
A biaxially oriented film of μm was obtained. The laminated thickness of the stretched film was 2 μm.

Example 6 A laminated film having an A / B / A three-layer structure was prepared. The same polyesters as in Example 3 were used as the polyesters A and B. After drying the polyester A and B pellets at 180 ° C for 3 hours,
Melted at 290 ° C using 2 extruders each, 3
Layers are joined together by a rectangular joining block (feed block) for layers, and the surface temperature is 20 ° C. using an electrostatically applied casting method.
It was wound on a casting drum of, and cooled and solidified to form an unstretched film having a thickness of 950 μm. At this time, the surface of the film that was not in contact with the drum was cooled with a wind of 30 ° C. and 20 m / s using a known blower. In the same manner as in Example 3 below, a biaxially oriented film having a thickness of about 105 μm was obtained. The laminated thickness is 2μ after stretched film
It was m.

Example 7 A laminated film having an A / B / A three-layer structure was prepared. The same polyesters as in Example 3 were used as the polyesters A and B. After drying the polyester A and B pellets at 180 ° C for 3 hours,
Melted at 290 ° C using 2 extruders each, 3
Layers are joined together by a rectangular joining block (feed block) for layers, and the surface temperature is 20 ° C. using an electrostatically applied casting method.
It was wound on a casting drum of, and cooled and solidified to form an unstretched film having a thickness of 840 μm. This unstretched film is stretched at a temperature of 95 ° C. at a stretching rate of 2000%.
At a stretching rate of 10000% / min and a temperature of 95 ° C using a known stenter.
Then, it is stretched 2.25 times in the width direction and then 210 at a fixed length.
Heat treatment was performed at 5 ° C. for 5 seconds to obtain a biaxially oriented film having a thickness of about 125 μm. The laminated thickness is 2 after stretching the film.
μm.

Example 8 A laminated film having an A / B / A three-layer structure was prepared. As polyester A, polyethylene terephthalate polymerized by a conventional method (polymerization catalyst: magnesium acetate 0.10% by weight,
0.03% by weight of antimony trioxide and 0.35% by weight of dimethylphenylphosphonate as a phosphorus compound,
Polyethylene glycol with ethylene terephthalate as the main repeating unit (number average molecular weight: 400, content:
13% by weight) was used. As the polyester B, polyethylene terephthalate (polymerization catalyst: 0.06% by weight of magnesium acetate, 0.008% by weight of antimony trioxide, 0.02% by weight of dimethylphenylphosphonate as a phosphorus compound) polymerized by a conventional method was used. Pellets of polyesters A and B were dried at 180 ° C for 3 hours and then melted at 290 ° C by using two extruders each, and a rectangular confluent block (feed block) for three layers.
Are combined and laminated with each other, and are wound on a casting drum having a surface temperature of 40 ° C. by using an electrostatically applied casting method, cooled,
It was solidified to form an unstretched film having a thickness of 670 μm. Then, in the same manner as in Example 3, a biaxially oriented film having a thickness of about 75 μm was obtained. The laminated thickness is 2 μm for the stretched film
Met.

Comparative Example 1 A laminated film having an A / B / A three-layer structure was prepared. The same polyesters as in Example 3 were used as the polyesters A and B. After drying the polyester A and B pellets at 180 ° C for 3 hours,
Melted at 290 ° C using 2 extruders each, 3
Layers are joined together by a rectangular joining block (feed block) for layers, and the surface temperature is 40 ° C. using the electrostatically applied casting method.
It was wound on a casting drum of, and cooled and solidified to prepare an unstretched film having a thickness of 670 μm. At this time, the surface of the film, which was not in contact with the drum, was heated with warm air of 180 ° C. and 20 m / s using a known hot air generator and blower. Then, in the same manner as in Example 3, a thickness of about 75
A biaxially oriented film of μm was obtained. The laminated thickness of the stretched film was 2 μm.

Comparative Example 2 A laminated film having an A / B / A three-layer structure was prepared. The same polyesters as in Example 3 were used as the polyesters A and B. After drying the polyester A and B pellets at 180 ° C for 3 hours,
Melted at 290 ° C using 2 extruders each, 3
Layers are joined together by a rectangular joining block (feed block) for layers, and the surface temperature is 20 ° C. using an electrostatically applied casting method.
It was wound on a casting drum of, cooled and solidified to prepare an unstretched film having a thickness of 1035 μm. In the same manner as in Example 3 below, a biaxially oriented film having a thickness of about 115 μm was obtained. The laminated thickness is 2 μm for the stretched film
Met.

Comparative Examples 3 and 4 As polyester A, polyethylene terephthalate (polymerization catalyst: magnesium acetate 0.0
6% by weight, 0.008% by weight of antimony trioxide, and 0.02% by weight of dimethylphenylphosphonate as a phosphorus compound, with 1.5% by weight of aggregated silica as external particles in Comparative Examples 3 and 4, respectively. %, 2.5% by weight was used. After drying these polyester pellets at 180 ° C. for 3 hours, using a known extruder,
Melt extrusion was performed at 290 ° C., and the film was wound on a casting drum having a surface temperature of 20 ° C. by an electrostatically applied casting method, cooled and solidified to form an unstretched film having a thickness of 300 μm. This unstretched film at a temperature of 95 ° C.
Stretching is carried out at a stretching rate of 2000% / min in the longitudinal direction by a factor of 3.4, and a known stenter is used to stretch at a stretching rate of 1000.
The film was stretched at 0% / min at 135 ° C. in the width direction by 3.5 times and further heat-treated at 235 ° C. for 5 seconds under a constant length to obtain a biaxially oriented film having a thickness of about 25 μm.

Comparative Example 5 As polyester A, polyethylene terephthalate (polymerization catalyst: magnesium acetate 0.0
6% by weight, 0.008% by weight of antimony trioxide, and 0.02% by weight of dimethylphenylphosphonate as a phosphorus compound were used. After drying the polyester A pellets at 180 ° C. for 3 hours, melt extrusion was performed at 290 ° C. using a known extruder, and a surface temperature of 20 was obtained using an electrostatically applied casting method.
It was wound on a casting drum at 0 ° C., cooled and solidified to form an unstretched film having a thickness of 900 μm. This unstretched film is stretched at a temperature of 95 ° C. at a stretching rate of 2000%.
At a stretching rate of 10000% / min and a temperature of 95 ° C using a known stenter.
And stretched 3.4 times in the width direction, and 210 ° C under a fixed length.
Was heat-treated for 5 seconds to obtain a biaxially oriented film having a thickness of about 75 μm. This film was passed through a sand throwing machine, hitting sand on the film surface to make the film surface uneven, washed with water and dried.

Comparative Example 6 As polyester A, polyethylene terephthalate (polymerization catalyst: magnesium acetate 0.0
6% by weight, 0.008% by weight of antimony trioxide, and 0.02% by weight of dimethylphenylphosphonate as a phosphorus compound were used. After drying the polyester A pellets at 180 ° C. for 3 hours, melt extrusion was performed at 290 ° C. using a known extruder, and a surface temperature of 20 was obtained using an electrostatically applied casting method.
It was wound on a casting drum at 0 ° C., cooled and solidified to form an unstretched film having a thickness of 900 μm. This unstretched film is stretched at a temperature of 95 ° C. at a stretching rate of 2000%.
At a stretching rate of 10000% / min and a temperature of 95 ° C using a known stenter.
And stretched 3.4 times in the width direction, and 210 ° C under a fixed length.
Was heat-treated for 5 seconds to obtain a biaxially oriented film having a thickness of about 75 μm. This film was passed through a treatment bath of 80 ° C. potassium hydroxide aqueous solution (50 mol%) for 2 minutes to roughen the film surface, washed with water and dried.

The characteristics of each film in each of the above Examples and Comparative Examples are shown in Tables 1 and 2. The center line average roughness Ra was measured on the surface not in contact with the casting drum. The polyester film obtained in each of the above examples,
The center line average roughness is 50 nm or more, and it has excellent matteness and transparency, and is excellent in drawability, light diffusivity and overlay characteristics. However, the polyester film obtained in Comparative Example is matte. Some are inferior in sex, and
It was considerably inferior in transparency.

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[Table 1]

[Table 2]

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EFFECT OF THE INVENTION A polyester film can be easily formed without performing a special surface roughening step in order to increase the surface roughness of the polyester film, has a relatively small surface roughness, and has excellent matteness. A polyester film having transparency can be provided.

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Claims (10)

[Claims] 1. A biaxially oriented polyester film containing polyester A as a main component, wherein at least one surface of the film has a center line average roughness Ra of 50 nm or more and 3000 nm or less, and the glossiness of the rough surface. A biaxially oriented polyester film, characterized in that G (%) is 45% or less, and G (%) and Ra (nm) satisfy the following formula. Ra ・ G ≦ 3000 2. A film having a thickness of 10 μm or more and a wavelength of 55
The biaxially oriented polyester film according to claim 1, wherein the total light transmittance at 0 nm is 80% or more. 3. The biaxially oriented polyester film according to claim 1, wherein the rough surface protrusions are protrusions mainly caused by crystals. 4. Polyester A has a flexible movable component of 0.0
The biaxially oriented polyester film according to any one of claims 1 to 3, which is composed of polyester in an amount of 1% by weight or more and 15% by weight or less. 5. The biaxially oriented polyester film according to claim 4, wherein the flexible movable component is a polyalkylene glycol having a number average molecular weight of 200 or more and 50,000 or less. 6. A biaxially oriented polyester film, wherein the polyester film according to claim 1 is laminated on at least one side of a film containing polyester B as a main component. 7. The matte film made of the biaxially oriented polyester film according to claim 1, wherein the glossiness of the rough surface is 40% or less. 8. A tracing film comprising the biaxially oriented polyester film according to claim 1, wherein the protrusion spacing Sm is 30 μm or less. 9. The light diffusing film comprising the biaxially oriented polyester film according to claim 1, wherein the glossiness of the rough surface is 40% or less. 10. The overlay film comprising the biaxially oriented polyester film according to claim 1, wherein the glossiness of the rough surface is 40% or less.