JP2007181950A - Biaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light scattering biaxially oriented polyester film which is not deteriorated by a change in environmental temperature, has a rough surface, is superior in delustering properties, and is easy of adhesion. <P>SOLUTION: In the biaxially oriented polyester film, organic particles are incorporated in a polyester layer constituting one surface layer, the surface roughness (Ra) of the surface layer is at least 0.08 μm, the ratio (L/R) between the thickness (L) of the surface layer and the average particle size (R) of the particles is 4.0 or below, and an easily adhesive coating layer is formed on the surface or back of the film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used by providing an adhesive layer, an ultraviolet curable resin layer or the like on the surface of a polyester film, used for bonding with glass or a molded product requiring matting properties, label use, vapor deposition packaging use, Light-scattering biaxially stretched polyester film with easy adhesion that can be used as a base film for liquid crystal display components, such as diffuser plates and prism sheets for backlight units, and lens sheets for projector screens. About.

  As a biaxially stretched polyester film containing a light diffusing agent, Patent Document 1 or Patent Document 2 proposes a polyester film containing several percent of inorganic particles having an average particle diameter of several μm. There is a problem that the filter pressure rises easily in the line and the productivity is poor. In addition, since inorganic particles have a larger difference in thermal expansion coefficient from the film resin than organic particles, when a film substrate is used at a large environmental temperature change, abnormalities occur in projections on the film surface, and it tends to drop off. Sometimes.

  Moreover, the conventional light-scattering biaxially stretched polyester film is designed to have a light-scattering function due to the difference in refractive index between the light diffusing agent and the film resin. However, since the difference in refractive index is larger at the interface between air and the film resin, the matte effect of the film is greater when the surface is designed to have irregularities. Furthermore, many polyester films may be provided with an adhesive layer or a vapor deposition layer on the surface of the film in order to have various functions depending on the application, and irregularities having various shapes may be formed. In that case, it is desired that the adhesiveness with the surface of the base film is good, but the actual situation is that a film satisfying them is not obtained.

JP 2002-178472 A JP 2004-67853 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is a light-scattering biaxially stretched polyester film having a rough surface that is difficult to change due to changes in environmental temperature, excellent matting properties, and easy adhesion. It is to provide.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by a biaxially stretched polyester film having a specific configuration, and have completed the present invention.

  That is, the gist of the present invention is that the polyester layer constituting one surface layer contains organic particles, the surface layer has a surface roughness (Ra) of 0.08 μm or more, the surface layer thickness (L) and the organic layer. The ratio (L / R) to the average particle size (R) of the particles is 4.0 or less, and the present invention resides in a biaxially stretched polyester film characterized by having an easily adhesive coating layer on any film surface.

Hereinafter, the present invention will be described in detail.
The polyester in the present invention is an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, ethylene glycol, diethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, 1, This polyester is mainly composed of an ester with glycol such as 4-cyclohexanedimethanol. The polyester can be obtained by directly polymerizing an aromatic dicarboxylic acid and a glycol, or by a transesterification reaction between an aromatic dicarboxylic acid dialkyl ester and a glycol, followed by polycondensation, or an aromatic dicarboxylic acid diglycol. It can also be obtained by a method such as polycondensation of an ester. Typical examples of the polyester include polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate (PEN), boribylene terephthalate, and the like. Such a polyester may be a homopolymer that is not copolymerized, 40 mol% or less of the dicarboxylic acid component is a dicarboxylic acid component other than the main component, and 40 mol% or less of the diol component is a diol component other than the main component. It may be a certain copolyester or a mixture thereof.

  In this invention, in order to form the rough surface which scatters light, an organic particle is mix | blended with at least one surface layer. The average particle size of the organic particles used in the present invention is preferably 2 to 40 μm, more preferably 2 to 30 μm, and particularly preferably 3 to 20 μm. When the average particle diameter is less than 2 μm, large protrusions are formed on the film surface, and the light scattering property tends to be inferior. On the other hand, when the average particle diameter exceeds 40 μm, the increase in the pressure of the filter becomes large, so that the productivity tends to be inferior. Moreover, when the filter eyes used are enlarged, foreign matter in the film may increase.

  The content of organic particles in the entire film of the present invention is preferably in the range of 0.02 to 2% by weight, more preferably 0.04 to 1% by weight. If the organic particle content is less than 0.02% by weight, the light scattering property intended by the present invention may not be obtained. On the other hand, even if the content exceeds 2% by weight, the light scattering property is not greatly improved, and useless addition is performed.

  For the organic particles used in the present invention, the 5% pyrolysis temperature under an inert atmosphere as measured by a thermogravimetric analyzer is usually 300 ° C or higher, preferably 310 ° C or higher. When the thermal decomposition temperature is less than 300 ° C., the transmitted light of the film is yellowish due to the generation of a thermally deteriorated product, and the appearance quality may be deteriorated.

  In addition, the organic particles used in the present invention preferably have a hardness that can be deformed under biaxial stretching conditions. Specifically, the degree of deformation is preferably in the range of 1.1 to 5.0. A range of 1.2 to 4.0 is more preferable. In the case of organic particles having a degree of deformation of less than 1.1, the degree of elastic deformation is reduced when subjected to shear stress at a polyester resin dissolution temperature of 250 to 350 ° C., and the life of the filter may be reduced. On the other hand, when the degree of deformation exceeds 5.0, the height of the protrusion is reduced, and the light scattering property tends to be lowered.

  The organic particles used in the present invention preferably have a functional group on the surface. The particles having a functional group are easily charged, and an electrostatic repulsive force between the particles acts to improve dispersibility. If there is no functional group, it tends to aggregate between particles and the filter life tends to be reduced. In addition, the affinity with polyester decreases, forming large voids around the particles, making it easier for the particles to fall off during the film manufacturing process and film processing process, resulting in scratches on the film itself and deterioration in appearance quality. There is a risk of causing. Preferred functional groups are a carboxylic acid group, a hydroxyl group, an epoxy group, and an ester group.

  The organic particles used in the present invention may be a single component, or two or more components may be used simultaneously. Specific examples of organic particles include organic particles such as melamine resin, polystyrene, organic silicone resin, and acrylic-styrene copolymer.

  In the film of the present invention, the ratio (L / R) of the thickness (L) of the surface layer containing organic particles to the average particle size (R) of the organic particles is 4.0 or less, preferably 3.0 or less. Particularly preferably, it is 2.5 or less. If the thickness of the organic particle-containing layer exceeds 4.0 times the average particle diameter of the organic particles used, the ratio of organic particles contributing to the formation of protrusions on the film surface decreases, so the efficiency of light scattering with respect to particle addition decreases. Also, the matte property is reduced. On the other hand, the thickness of the organic particle-containing layer is preferably at least 0.1 times the average particle diameter of the organic particles used. If it is less than 0.1 times, the protrusion density on the surface becomes small and the light scattering property tends to be lowered.

  In the film of the present invention, the organic particle-containing layer has a surface roughness (Ra) of 0.08 μm or more, and needs to be roughened, preferably 0.09 μm or more, particularly preferably 0.10 μm or more. It is. When the surface roughness Ra of the rough surface is less than 0.08 μm, the light scattering property and the matte property are inferior.

  In the present invention, the surface roughness (Ra) of the surface opposite to the rough surface is preferably a flat surface of 0.008 μm or more, more preferably 0.008 μm or more. If Ra is less than 0.008 μm, scratches tend to occur on the smooth surface of the film in the film production process or film processing step. On the other hand, if it exceeds 0.04 μm, the processing characteristics and vapor deposition characteristics may deteriorate depending on the film application. Sometimes. In addition, in order to make Ra of a flat surface 0.008 micrometer or more, it is preferable to contain a trace amount of inert particle in the layer which comprises the surface opposite to a rough surface. The kind of the inert particles may be either inorganic particles or organic particles.

  The gloss of the film of the present invention is preferably 80% or less, more preferably 70% or less, and particularly preferably 60% or less. When the glossiness exceeds 80%, the matte property tends to be inferior.

  The haze of the film of the present invention is preferably 20% or more, more preferably 30% or more, and particularly preferably 35% or more. If the haze is less than 20%, the light scattering property tends to be inferior.

  The film of the present invention may contain additives such as an anti-blocking agent, an ultraviolet absorber, an antistatic agent, an antioxidant, and a fluorescent brightening agent as necessary.

  The film of the present invention is provided with a coating layer on at least one surface in order to improve adhesion with various functional layers present thereon. The easy-adhesion coating layer is usually composed mainly of a polymer and a crosslinking agent. The polymer comprises, for example, at least one of water-based polyurethane, water-based polyester, and water-based acrylic resin, and preferably has a glass transition temperature (Tg) of 0 ° C. or higher, more preferably 40 ° C. or higher, more preferably polyurethane. Among them, a polyester polyurethane has a carboxylic acid residue, and at least a part thereof is made water-based using an amine or ammonia. As the cross-linking agent, melamine-based, epoxy-based, and oxazoline-based resins are generally used, but melamine-based resins are preferable in terms of coating properties and durable adhesiveness.

  As a coating method of the coating agent, for example, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these as shown in Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method” Can be used. The coating layer may be formed only on one side of the polyester film or on both sides. When formed only on one side, other characteristics can be imparted by forming a coating layer different from the above-mentioned coating layer on the opposite surface as necessary. In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  The thickness of the coating layer is usually in the range of 0.02 to 0.5 μm, preferably 0.03 to 0.3 μm, as the final dry thickness. When the thickness of the coating layer is less than 0.02 μm, the adhesion tends to be inferior. On the other hand, when the thickness of the coating layer exceeds 0.5 μm, the films are easily fixed to each other.

  Furthermore, the other surface of the film can be subjected to a coating treatment for the purpose of imparting easy slipping, releasability and antistatic properties.

  The thickness of the film of the present invention is usually in the range of 20 to 300 μm. If the film thickness is less than 20 μm, the workability may be poor. On the other hand, when the film thickness exceeds 300 μm, the weight may increase or the handleability may deteriorate.

  Next, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the structural requirements of this invention are satisfied, it is not specifically limited to the following illustrations.

  When the film of the present invention is produced, the polyester is supplied to at least two extruders, heated to a temperature equal to or higher than the melting point of each polyester, and melted. Next, the molten polymer from each extruder is merged in a feed block through a gear pump and a filter, taken through a die to a casting drum, and extruded as a molten sheet from a T die through a pump and a filter. Subsequently, the molten sheet is rapidly cooled to below the glass transition temperature on a rotary cooling drum to obtain an amorphous unstretched film. At this time, in order to improve the flatness of the unstretched film, the adhesion between the unstretched film and the rotating cooling drum may be improved by an electrostatic application adhesion method, a liquid application adhesion method, or the like. And a uniaxially stretched film is obtained by extending | stretching an unstretched film in the longitudinal direction (longitudinal stretching) using a roll stretching machine. The stretching temperature at this time is stretched in a temperature range of minus 10 ° C. to plus 40 ° C. of the glass transition temperature (Tg) of the raw material resin. The draw ratio is preferably 2.5 to 7.0 times, more preferably 3.0 to 6.0 times. Furthermore, longitudinal stretching may be performed in only one stage, or may be performed in two or more stages. Next, an aqueous coating agent is applied by a coater to provide an easy adhesion layer. Then, it leads to a tenter and a biaxially stretched film is obtained by extending | stretching a uniaxially stretched film in the width direction (lateral stretching) using a tenter stretching machine. The stretching temperature at this time is stretched in a temperature range of + 50 ° C. from the glass transition temperature (Tg) of the raw material resin. The draw ratio is preferably 2.5 to 7.0 times, more preferably 3.5 to 6.0 times. Further, the transverse stretching may be performed only in one stage, or may be performed in two or more stages. Moreover, you may perform simultaneous biaxial stretching which performs vertical and horizontal simultaneously. And a laminated film is manufactured by heat-processing a biaxially stretched film. The heat processing temperature at this time is 130-250 degreeC. When the biaxially stretched film is heat-treated, the biaxially stretched film may be relaxed within 20%.

  ADVANTAGE OF THE INVENTION According to this invention, the easily adhesive light-scattering biaxially stretched polyester film excellent in the matte property which has the rough surface which does not change with environmental temperature changes can be provided, and industrial value of this invention Is expensive.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measurement methods and terms used in the examples and the present invention are defined as follows.

(1) Added particle average particle diameter The particles were observed using an electron microscope to determine the maximum diameter and the minimum diameter, and the average was defined as the particle diameter of one particle. This is done for at least 100 particles in the film. The average particle diameter of the particle group is the weight average diameter of these particles.

(2) Deformation After fixing the film piece with an epoxy resin, it is cut with a microtome so that the cut surface of the film is parallel to the principal axis direction of the molecular chain orientation, and the cut surface is observed with a scanning electron microscope. For at least 50 particles that fall within ± 10% of the average particle size for each particle, the ratio of the maximum diameter to the minimum diameter is calculated, and the arithmetic average is taken as the degree of deformation.

(3) The value is measured using a haze-dividing turbidimeter NDH-300A (manufactured by Nippon Denshoku Industries Co., Ltd.).

(4) Glossiness Measured by incident light in the longitudinal stretching direction of the rough film according to method 3 (60 ° glossiness) of JIS Z-8741-1983.

(5) Surface roughness Ra
It measures according to JIS-B-0601-1982 using the surface roughness measuring machine (SE-3F) by Kosaka Laboratory. However, the cut-off value is 80 μm and the measurement length is 2.5 mm.

(6) Thermal decomposition temperature of organic particles After drying organic particles under reduced pressure at 60 ° C. for 4 hours, measurement was performed using a thermobalance (Rigaku Denki, TAS100 type) under a nitrogen gas atmosphere at a temperature rising rate of 20 ° C./min Measure the temperature at the 5% weight loss.

(7) Light-scattering property Place a paper with MS Gothic font printed with numbers 1 to 9 with 8 points on a desk under fluorescent light, and observe the distance from a distance of 30 cm through the test film to distinguish the numbers. Measure the distance between the missing film and the paper. The light scattering property is evaluated as follows.
○: Distance at which numbers cannot be seen is 5 cm or less, light scattering is good ×: Distance at which numbers cannot be seen exceeds 5 cm, poor light scattering

(8) Adhesiveness with photo-curing resin An acrylic photo-curing resin (KAYANOVA FOP-1700 manufactured by Nippon Kayaku Co., Ltd.) was applied to the surface of the easy-adhesion surface so that the thickness after curing was 6 μm, and 120 W / cm. A surface-cured film is obtained by irradiating at an irradiation distance of 100 mm for about 10 seconds using a high-pressure mercury lamp having the following energy. Immediately after the acrylic photocured layer is formed, a crosscut is made on the layer so that there are 100 grids in a 1-inch width, and a cellotape (registered trademark) rapid peel test is performed three times at the same location. evaluate. The judgment criteria are as follows.
A: Number of cross-cuts = 0
○: 1 ≦ Number of cross cuts ≦ 10
Δ: 11 ≦ number of cross-cuts ≦ 20
×: 21 <Number of cross-cuts peeled

(9) Protruding state of rough surface due to environmental temperature change Place the test film in a container cooled with dry ice for 3 minutes, and then immediately place it in an oven at 60 ° C. for 3 minutes. Then immediately return to a container chilled with dry ice. After repeating this operation 10 times, the protrusion state on the surface of the test film is observed with an electron microscope. Protrusions or a film of resin covering the particles is broken as shown in FIG. 1, projection pieces of the resin covering the protrusions are innumerable observed as (hereinafter referred to as abnormal protrusions) 2 in a range the number of 10 mm ² of Investigate.
○: The number of abnormal projections is 1 / mm ² or less Δ: The number of abnormal projections is 1 to 5 / mm ²
×: The number of abnormal protrusions exceeds 5 / mm ²

(Raw material adjustment)
・ Polyester a
Polyethylene terephthalate synthesized by conventional polycondensation and having an intrinsic viscosity of 0.65 and a melting point of 253 ° C.

・ Polyester b
Crosslinked styrene-acrylic organic particles having a hydroxyl group on the surface of a polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation and having an average particle size of 6 μm and a thermal decomposition temperature of 329 ° C. Kneaded 10% by weight

・ Polyester c
Crosslinked styrene-acrylic organic particles having a glycidyl group on the surface of a polyethylene terephthalate resin synthesized by a conventional polycondensation having an intrinsic viscosity of 0.68 and a melting point of 253 ° C., an average particle size of 10 μm, and a 5% thermal decomposition temperature of 331 ° C. Kneaded with 10% by weight

Polyester d
Crosslinked styrene-acrylic organic particles having a hydroxyl group on the surface of particles having an average particle size of 4 μm and a 5% thermal decomposition temperature of 325 ° C. are synthesized in a polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation Kneaded 10% by weight

・ Polyester e
Cross-linked acrylic organic having an intrinsic viscosity of 0.68 synthesized by a conventional polycondensation, a polyethylene terephthalate resin having a melting point of 253 ° C., an average particle diameter of 1.7 μm, a 5% thermal decomposition temperature of 290 ° C. having a carboxylic acid group on the particle surface Kneaded particles containing 4% by weight

・ Polyester f
A polyethylene terephthalate resin synthesized by a conventional polycondensation with an intrinsic viscosity of 0.68 and a melting point of 253 ° C., kneaded with 10% by weight of amorphous silica particles with an average particle diameter of 4 μm.

・ Polyester g
Mixture in which 10% by weight of polyester d and 90% by weight of polyester a are kneaded

・ Water-based coating agent A
The aqueous coating agent is a mixture in which the following compounds a, b, c and d are mixed at a weight ratio of 47/20/30/3.
a: Polyester aqueous dispersion obtained by reacting terephthalic acid / isophthalic acid / 5-sodiumsulfoisophthalic acid / ethylene glycol / 1.4-butanediol / diethylene glycol in a molar ratio of 28/20/2/35/10/5, respectively Body b: Polymer aqueous dispersion obtained by polymerizing methyl methacrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide in a molar ratio of 45/45/5/5 (emulsifier: anionic surfactant)
c: Melamine-based crosslinking agent (hexamethoxymethyl melamine)
d: An aqueous dispersion of silicon oxide having an average particle size of 0.06 μm

Example 1:
A mixture of 85% by weight of polyester a forming the surface layer (A layer) and 15% by weight of polyester b is supplied to the vented twin-screw extruder (sub), and the polyester a constituting the intermediate layer (B layer) is separated. After being melted at a melt temperature of 280 ° C., the melted polymer from each extruder is merged with a feed block through a gear pump and a filter, and taken up by a casting drum through a die. A three-layer unstretched film was obtained. The unstretched film thus obtained was fed into a longitudinal stretching roll and first stretched 3.7 times at a film temperature of 83 ° C., and then an aqueous coating agent A was applied on one side, led to a tenter, and 4.0 sideways at 95 ° C. The film was stretched twice to obtain a biaxially oriented film. Next, the obtained biaxially oriented film was introduced into a heat setting zone, and heat-set while being relaxed by 3% in the width direction at 230 ° C. for 5 seconds to obtain a polyester film having a thickness described in Table 1 below.

Example 2:
A mixture of 50% by weight of polyester a forming the surface layer (A layer) and 50% by weight of polyester c is supplied to a vented twin screw extruder (sub), and polyester a constituting the intermediate layer (B layer) is separated. After being melted at a melt temperature of 280 ° C., the melted polymer from each extruder is merged with a feed block through a gear pump and a filter, and taken up by a casting drum through a die. A two-layer unstretched film was obtained. Thereafter, as in Example 1, aqueous coating agent A was applied on one side, led to a tenter, stretched, and heat-set to obtain a film having a thickness structure described in Table 1.

Example 3:
A mixture of 50% by weight of polyester a forming the surface layer (A layer) and 50% by weight of polyester d is supplied to a vented twin-screw extruder (sub), and the polyester a constituting the intermediate layer (B layer) is 90%. A mixture of 10% by weight of polyester and 10% by weight of polyester was supplied to another vented twin-screw extruder (main) and melted at a melting temperature of 280 ° C., and then the molten polymer from each extruder was passed through a gear pump and a filter. They were merged in a feed block, taken up on a casting drum through a die, and two types and two layers of unstretched films were obtained. Thereafter, as in Example 1, aqueous coating agent A was applied on one side, led to a tenter, stretched, and heat-set to obtain a film having a thickness structure described in Table 1.

Comparative Example 1:
A mixture of 70% by weight of polyester a forming the surface layer (A layer) and 30% by weight of polyester f is supplied to the vented twin screw extruder (sub), and the polyester a constituting the intermediate layer (B layer) is separated. After being melted at a melt temperature of 280 ° C., the melted polymer from each extruder is merged with a feed block through a gear pump and a filter, and taken up by a casting drum through a die. A seed 2 layer unstretched film was obtained. Thereafter, as in Example 1, aqueous coating agent A was applied on one side, led to a tenter, stretched, and heat-set to obtain a film having a thickness structure described in Table 2 below.

Comparative Example 2:
A mixture of 92% by weight of polyester a constituting the intermediate layer (B layer) and 8% by weight of polyester d is fed to the vented twin-screw extruder (main), and the polyester a forming the surface layer (A layer) is separated. After being melted at a melt temperature of 280 ° C., the melted polymer from each extruder is merged by a feed block through a gear pump and a filter, and taken up by a casting drum through a die. A three-layer unstretched film was obtained. Thereafter, as in Example 1, aqueous coating agent A was applied on one side, led to a tenter, stretched and heat-fixed to obtain a film having a thickness structure described in Table 2.

Comparative Example 3:
A film was obtained under the same conditions as in Example 1 except that the easy adhesion layer was not provided.

Comparative Example 4:
A mixture of 94% by weight of polyester a forming the surface layer (A layer) and 6% by weight of polyester b is fed to a vented twin-screw extruder (sub), and the polyester a constituting the intermediate layer (B layer) is separated. After being melted at a melt temperature of 280 ° C., the melted polymer from each extruder is merged with a feed block through a gear pump and a filter, and taken up by a casting drum through a die. A three-layer unstretched film was obtained. Thereafter, as in Example 1, aqueous coating agent A was applied on one side, led to a tenter, stretched and heat-fixed to obtain a film having a thickness structure described in Table 2.

Comparative Example 5:
A mixture of 50% by weight of polyester a forming the surface layer (A layer) and 50% by weight of polyester e is fed to a vented twin-screw extruder (sub), and polyester a constituting the intermediate layer (B layer) is separated. After being melted at a melt temperature of 280 ° C., the melted polymer from each extruder is merged with a feed block through a gear pump and a filter, and taken up by a casting drum through a die. A three-layer unstretched film was obtained. Thereafter, as in Example 1, aqueous coating agent A was applied on one side, led to a tenter, stretched and heat-fixed to obtain a film having a thickness structure described in Table 2.

  The obtained results are summarized in Tables 1 and 2 below.

  In Examples 1 to 3, there is no abnormality of protrusions due to environmental temperature changes, and an easily adhesive film having excellent matting properties and light scattering properties. In particular, Examples 2 and 3 are excellent in matting properties. On the other hand, in Comparative Example 1, abnormal projections were observed because inorganic particles were used. In Comparative Example 2, the matte property was inferior because no particles were added to the layer forming the surface layer. Since Comparative Example 3 did not have an easy-adhesion coating layer, the adhesiveness with the acrylic photocurable resin was inferior. In Comparative Example 4, since the surface roughness Ra of the rough surface was less than 0.08 μm, the matte property and the light scattering property were inferior. In Comparative Example 5, since the ratio (L / R) of the thickness L of the coextruded layer forming the rough surface to the average particle diameter R of the organic particles exceeded 4.0, the light scattering property and the matte property were inferior.

  The film of the present invention is, for example, an application to be bonded to glass or a molded product that requires matting properties, a label application or a vapor deposition packaging application, or a liquid crystal display component, such as a diffusion plate or prism sheet of a backlight unit, Moreover, it can utilize suitably as base film, such as a lens sheet of the screen for projectors.

It is the electron micrograph which image | photographed the typical thing of the processus | protrusion by which the film | membrane of the resin which covers particle | grains was torn. It is the electron micrograph which image | photographed the typical thing of the processus | protrusion in which countless resin fragments covering a processus | protrusion are observed.

Claims (1)

The polyester layer constituting one surface layer contains organic particles, the surface layer has a surface roughness (Ra) of 0.08 μm or more, the surface layer thickness (L) and the average particle diameter (R) of the organic particles. A biaxially stretched polyester film characterized by having a ratio (L / R) of 4.0 or less and having an easily adhesive coating layer on any film surface.