JP2001322218A - Coextrusion laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coextrusion laminated polyester film excellent in light diffusibility, reduced in the reduction of the total light transmission quantity and having stable quality. SOLUTION: The coextrusion laminated polyester film is an oriented polyester film comprising at least two layers and the thickness of one outermost layer is 0.2 μm or more and 1.0-10.0 wt.% of particles with a mean particle size of 1.5-50 μm are added to the outermost layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film which has no change in the color tone of transmitted scattered light, has excellent light diffusivity, has a small decrease in the total amount of transmitted light, and is easy to produce. More specifically, the present invention is used for applications such as lighting covers, illuminated signboards, window-attached films for daylighting glass, etc., in which it is required to ensure effective and uniform brightness of various light sources, word processors and OA equipment. The present invention relates to a light-diffusing polyester film suitable for a liquid crystal display or a diffusion panel material for a backlight source of a liquid crystal color television.

[0002]

2. Description of the Related Art In order to effectively use light from a light source, a light diffusing film has been used for a lighting cover, a liquid crystal display device and the like.

[0003] As a technique conventionally used as a method of diffusing light, the difference in refractive index between the fine particles and the resin is reduced by blending particles into a film or applying a resin in which particles are dispersed to the film. There is a way to use it.
For example, Japanese Patent Application Laid-Open No. 3-78701 discloses an example using calcium carbonate particles. However, when a large amount of inorganic particles having a large particle diameter is used as a light diffusing agent, the total light transmission In some cases, the film strength may be reduced. Further, depending on the type of inorganic particles used, light in a specific wavelength region of white light may be absorbed and the color tone of the transmitted and scattered light may change. Further, JP-A-7-20
No. 9502 discloses a method of coating a film with a composition in which calcium carbonate or silica fine particles are dispersed in a resin, and Japanese Unexamined Patent Publication No. 9-211207 discloses a method of coating a composition in which polystyrene resin particles are dispersed in a resin. The method of applying to each is disclosed. However, when using a film as a raw material and applying a light diffusion layer to the film surface as a secondary process, not only increases the manufacturing cost, but also quality problems such as adhesion of dust, coating streaks, and coating unevenness. May occur.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object to solve the above problems. To provide a polyester film.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that by adopting a specific structure, there are few surface defects, excellent surface flatness and excellent light diffusion, and The inventors have found that a film with a small decrease in the total light transmission can be obtained, and have completed the present invention.

That is, the gist of the present invention is at least
An oriented polyester film comprising at least one layer,
One outermost layer has a thickness of 0.2 μm or more, and particles having an average particle diameter of 1.5 to 50 μm are contained in the outermost layer in an amount of 1.0 to 1 μm.
Co-extruded laminated polyester film characterized by containing 0.0% by weight.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The polyester in the present invention includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid and ethylene glycol, diethylene glycol, tetramethylene glycol, neopentyl glycol, 1,4 -A polyester having an ester with a glycol such as cyclohexanedimethanol as a main component. The polyester can be obtained by directly polymerizing an aromatic dicarboxylic acid and a glycol, or by subjecting a transalkylation reaction of an aromatic dicarboxylic acid dialkyl ester and a glycol to a polycondensation method, or a diglycol of an aromatic dicarboxylic acid. It can also be obtained by a method such as polycondensation of an ester. Representative examples of the polyester used in the present invention include polyethylene terephthalate, polyethylene-2,
6-naphthalenedicarboxylate (PEN) and the like are exemplified. Such a polyester may be a homopolymer that is not copolymerized, and 10 mol% or less of the dicarboxylic acid component is a dicarboxylic acid component other than the main component, or 10 mol% or less of the diol component is a diol component other than the main component. Such a copolymerized polyester may be used.

The film of the present invention is a co-extruded laminated film having a structure of at least two layers, and requires a layer containing a specific amount of specific particles and having a light diffusion function.

In order to impart light diffusion characteristics, the present invention incorporates a large amount of large particles in a biaxially oriented polyester film, which has not been conventionally incorporated, but sacrifices film formation stability. There is a problem. In order to solve such a problem, in the present invention, the film has a structure of two or more layers. In order to form a film having two or more layers, it is preferable to co-extrude a layer imparting film forming continuity.

The layer imparting light diffusivity has an average particle diameter of 1.5 in order to achieve a high balance between the total light transmission and the diffusion transmittance.
To 50 μm, preferably 2.0 to 30 μm, more preferably 3.0 to 20 μm. If the average particle size is less than 1.5 μm, the diffuse transmittance is undesirably low. When the average particle size exceeds 50 μm,
Particles serve as a starting point to easily break the film, which is a problem both in the production stage and after the production, and that the surface roughness of the film is undesirably too large.

The content of the particles used in the present invention in the light diffusion layer is 1.0 to 10.0% by weight, preferably 1.5 to 8.
0% by weight, and more preferably 2.0 to 6.0% by weight. If the content of the particles is less than 1.0% by weight, the diffusion transmittance is undesirably low. On the other hand, if the content exceeds 10.0% by weight, the film is apt to be broken, and the surface roughness of the film becomes too large to impair the flatness, which is not preferable.

Examples of such fine particles include silicon oxide, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, lithium phosphate, magnesium phosphate, lithium fluoride, aluminum oxide, titanium oxide, kaolin, talc, and carbon black. , Silicon nitride, boron nitride, and crosslinked polymer fine powders as described in JP-B-59-5216, but are not limited thereto as long as they satisfy the present invention. However, spherical silica particles are particularly preferred. The particle shape of the spherical silica is preferably closer to a spherical shape in terms of the total light transmittance and the diffuse transmittance, and the spherical ratio is usually 0.90 to 1.0, preferably 0.93 to 1.0, and more preferably. 0.96 to 1.0. Spherical ratio 0.9
If it is less than 0, the diffuse transmittance tends to decrease.

At this time, the fine particles to be blended may be a single component, or two or more components may be used simultaneously. When two or more components are used, the average particle diameter and the content of the particles of at least one component may be within the above-mentioned ranges.

The thickness of the light diffusion layer is at least 0.2 μm, preferably at least 1.0 μm. Light diffusion layer thickness is 0.2
If it is less than μm, the diffuse transmittance cannot be increased, which is not preferable.

The layers other than the light diffusion layer may be made of a polyester substantially free of particles. Usually, a polyester film is formed with projections on the film surface for the purpose of improving film formability and workability, and imparts lubricity to the film.In the present invention, the particles used for the light diffusion layer are Since protrusions are formed on the surface, lubricity can be obtained even if particles are not compounded in layers other than the light diffusion layer.

The thickness of the layers other than the light diffusing layer is not particularly limited, but a certain thickness is required in order to impart appropriate film strength, continuous film forming property and the like. The required thickness varies depending on the particle diameter and the amount of particles incorporated in the light diffusion layer, but in the present invention, the thickness is preferably 0.2 times or more the particle diameter incorporated in the light diffusion layer. 0.2 of particle diameter blended in light diffusion layer
If the ratio is less than twice, there may be a problem in terms of film strength and continuous film forming property.

In the present invention, the substantially particle-free polyester is synthesized without particles added for purposes other than the purpose of the polymerization catalyst. This polyester is
Contains no insoluble particles that absorb or scatter light,
Even if it is contained, its absolute amount is small, so that it has high transparency when formed into a film.

The total thickness of the laminated film of the present invention is usually 2
５００500 μm. When the total thickness of the film is less than 2 μm, the light diffusion property tends to be insufficient,
If it exceeds m, stretching during film formation may be difficult due to limitations of the film forming machine.

The film of the present invention has a total light transmittance of usually 60% or more, preferably 65% or more, more preferably 70% or more, and a diffuse transmittance of usually 50% or more, preferably 55% or more, and more preferably. Is 60% or more. If the total light transmission is less than 60% or the diffusion transmittance is less than 50%, the performance as a light diffusion film tends to be insufficient. In this case, it is necessary to form a light diffusion layer by coating or the like. Applications may be limited.

The polyester film of the present invention may contain, if necessary, an antistatic agent, a coloring agent, an antioxidant, an antifoaming agent,
Additives such as a fluorescent whitening agent and flame retardancy may be blended.

Further, one or both sides of the polyester film of the present invention may be subjected to an antireflection treatment before use.
Examples of the antireflection treatment include an embossing treatment by forming minute irregularities on the surface, a thin film forming treatment utilizing light interference of reflected waves, and the like. Further, if necessary, a coating treatment for the purpose of imparting lubricity, releasability, antistatic property, easy adhesion, and the like can be performed.

The laminated film of the present invention is preferably a film obtained by extruding a biaxially stretched and heat-set film by a co-extrusion method in which all layers are co-melt extruded from a die.
As a co-extrusion method, any of a feed block type and a multi-manifold type may be used.

The method for producing a laminated film of the present invention will be described more specifically. However, the present invention is not particularly limited to the following examples as long as the constitutional requirements of the present invention are satisfied.

A polyester containing a predetermined amount of specific particles (layer A) and a polyester substantially containing no particles (B
) Are supplied to separate melt-extrusion devices, and heated and melted to a temperature equal to or higher than the melting point of the polymer. Next, the melted polymer is joined and laminated in a laminar flow form in an extrusion die, extruded from a slit-shaped die, and quenched and solidified on a rotary cooling drum to a temperature of a glass transition temperature or less, substantially amorphous. An unoriented sheet in a state is obtained. In this case, in order to improve the flatness of the sheet, it is preferable to increase the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid application adhesion method are preferably employed.

In the present invention, the sheet thus obtained is biaxially stretched to form a film. The stretching conditions are specifically described as follows. Preferably, the unstretched sheet is stretched 2 to 6 times at 70 to 145 ° C in the machine direction to form a longitudinally uniaxially stretched film, and then at 90 to 160 ° C in the transverse direction.
It is preferred that the film be stretched up to 6 times and heat-treated at 150 to 250 ° C for 1 to 600 seconds. Further, at this time, in the maximum temperature zone of the heat treatment and / or the cooling zone at the outlet of the heat treatment, 0.1% in the longitudinal direction and / or the transverse direction.
A method of relaxing by about 20% is preferred. Further, re-longitudinal stretching and re-lateral stretching can be added as necessary.

The laminated film of the present invention may be subjected to transverse stretching after completion of longitudinal stretching, if necessary, in order to improve necessary properties according to the required properties, for example, adhesion, antistatic properties, weather resistance and surface hardness. A so-called in-line coating in which the coating is performed before the tenter entrance and the drying is performed in the tenter may be performed. In addition, various coatings may be performed by offline coating after the production of the laminated film. Such a coat may be on one side or both sides. As the material for the coating, any of an aqueous system and / or a solvent system may be used in the case of off-line coating, but an aqueous system or an aqueous dispersion system is preferable in the case of in-line coating.

[0028]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. The measurement methods and the definitions of terms used in the present invention are as follows. (1) Average particle diameter of particles The particles in the film were observed with a scanning electron microscope, the maximum diameter and the minimum diameter were determined for each particle, and the arithmetic mean was defined as the particle diameter (diameter) of one particle. The average particle diameter of the particle group refers to the particle diameter (diameter) at a point at a volume fraction of 50% of the equivalent particle diameter of the particle diameter. (2) Diffused light amount and total light transmission amount The diffused light amount and total light transmission amount of the film were measured using a spectroscopic turbidimeter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. (3) Film Lamination Thickness A small film piece was fixed and molded with an epoxy resin, cut with a microtome, and the cross section of the film was observed with a transmission electron microscope photograph. Of the cross sections, two are substantially parallel to the film surface, and the interface is observed by light and dark. The distance between the two interfaces and the film surface was measured from ten photographs, and the average value was defined as the lamination thickness. (4) Color tone of transmitted and scattered light The color tone of the transmitted and scattered light was visually observed by holding the film over a white fluorescent lamp, and evaluated according to the following criteria.

〇: almost the same as the light of a white fluorescent lamp ×: the color tone has changed (for example, slightly yellowish) (5) Continuous film-forming properties Continuous film-forming properties are classified into the following ranks. Was evaluated.

：: Continuous film formation is possible without breakage Δ: Occasionally breakage occurs and film formation cannot be continuously performed in some cases X: Breakage occurs frequently and film formation cannot be continuously performed The method for producing the polyester used in the examples and comparative examples will be described. (Production of Polyester-A) Dimethyl terephthalate 10
0 parts by weight and 60 parts by weight of ethylene glycol were used as starting materials, 0.09 part by weight of magnesium acetate tetrahydrate was placed in a reactor as a catalyst, the reaction start temperature was set to 150 ° C., and the reaction temperature was gradually increased with the distillation of methanol. The temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially completed. To this reaction mixture, 0.04 part of ethyl acid phosphate and 0.04 part of antimony trioxide were added, and a polycondensation reaction was performed for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from the normal pressure, and finally was 0.3 mmHg. After 4 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure. The viscosity of the obtained polyester was 0.65. (Production of Polyester-B) After drying Polyester-A, spherical silica particles having an average particle size of 4.2 μm and a sphericity ratio of 0.98 were extruded with a vented twin-screw extruder so as to be 3.0% by weight. Polyester-B was obtained. (Production of polyester-C) Polyester-C was produced in the same manner as polyester-B except that the particle size of spherical silica was changed to 10 µm.

Example 1 Polyester-B as Layer A was dried at 180 ° C. for 4 hours and fed to a main extruder set at 285 ° C. and polyester-A as Layer B to a sub-extruder set at 285 ° C. It is.

The polymer of the main extruder and the polymer of the sub-extruder are merged by a feed block via a gear pump and a filter and extruded into a sheet.
The mixture was rapidly cooled and solidified by a rotating cooling drum set at a temperature of 0 ° C. using an electrostatic application cooling method to obtain a substantially amorphous sheet having a thickness of 260 μm.

Next, the obtained amorphous sheet is stretched 3.5 times at 83 ° C. in the sheet flow direction and 3.7 times at 87 ° C. in a direction perpendicular to the sheet flow, and then stretched at 235 ° C. by 3 times.
After a heat treatment for 2 seconds, it is cooled and the layer A / layer B = 5 μm
A biaxially oriented film having a thickness of 15 μm and a thickness of / 10 μm was produced.

Comparative Example 1 Polyester C was dried at 180 ° C. for 4 hours, and then dried at 285 ° C.
Through a gear pump and a filter, extrude a sheet into a casting drum from a die, and quench and solidify using a rotating cooling drum with a surface temperature of 30 ° C. using an electrostatic application cooling method. , Thickness 260μm
A substantially amorphous sheet was obtained.

The obtained amorphous sheet was stretched 3.6 times in the longitudinal direction at 83 ° C., and then stretched in the width direction at 230 ° C. for 10 seconds.
%, And a heat treatment was applied to produce a single-layer biaxially oriented film having a thickness of 38 μm. However, the film was frequently broken and no film was obtained.

Examples 2 to 8 and Comparative Examples 2 to 6 In Example 1, the types, particle diameters, amounts and film thickness of the added particles to be blended in the inner layer are shown in Tables 1 and 2 below.
A biaxially oriented film was produced in the same manner as in Example 1 except that the film was changed as shown in Example 1.

The physical properties and performance of the obtained film are summarized in Tables 1 and 2 below.

[0038] In Comparative Examples 1 and 2, the continuous film-forming property was poor, and a film for evaluation could not be obtained.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

Industrial Applicability The polyester film of the present invention has excellent light diffusing properties, has a small decrease in the total amount of transmitted light, is easy to manufacture, and can be used for various applications such as lighting covers, illuminated signboards, window-attached films for daylighting glass and the like. It can be advantageously used as a light source to ensure effective and uniform brightness, and as a diffusion panel material for a backlight source of a liquid crystal display or a liquid crystal color television used in a word processor or OA equipment, and has a high industrial value.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4F071 AA43 AA46 AA88 AB26 AD06 AE17 AF30 AH12 BA01 BB06 BB08 BC01 BC12 4F100 AA20A AA20C AA20H AK41A AK41B AK41C BA02 BA03 BA06 BA16 DE01A DE01C DE01HEJN20 JA01 JE20 YY00A YY00C YY00H 4J002 CF051 CF061 CF071 CF081 CF091 DD036 DE136 DE146 DE236 DE246 DG056 DH046 DJ016 DJ036 FA086 GQ00

Claims (3)

[Claims] 1. An oriented polyester film comprising at least two or more layers, wherein one of the outermost layers has a thickness of 0.1.
2 μm or more, and the average particle size in the outermost layer is 1.5 to
A co-extruded laminated polyester film containing 50 μm particles in an amount of 1.0 to 10.0% by weight. 2. The co-extruded laminated polyester film according to claim 1, wherein the total light transmittance is 60% or more and the diffuse transmittance is 50% or more. 3. Particles having an average particle size of 1.5 to 50 μm,
The co-extruded laminated polyester film according to claim 1 or 2, which is spherical silica having a sphere ratio of 0.90 to 1.0.