JP2001098088A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-diffusing polyester film which is excellent in light- diffusing properties and has stable qualities, exhibiting a small decrease in total light transmission. SOLUTION: A polyester film is provided which is characterized in that around particles, hollow parts having diameters at least twice that of the particles are present in a number of 50-500,000/mm2 in a film plane and that the total light transmission is 50% or higher. A laminated polyester film is also provided which comprises a film layer substantially containing no particles and the abovementioned polyester film laminated to at least one side thereof.

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 relates to a liquid crystal display and a liquid crystal used in word processors and OA equipment, for applications such as a lighting cover, an illuminated signboard, a window-attached film for a daylighting glass, and the like, in which various light sources are effectively and uniformly illuminated. The present invention relates to a light-diffusing polyester film suitable for a diffusion panel material of a backlight source of a 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. Conventionally used techniques for diffusing light include a method in which particles are contained in a film by using a difference in refractive index between fine particles and a resin, or a mixture in which particles are dispersed in a transparent resin is applied to a film. . 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. Also, 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-7-209502 discloses a method of coating a film with a composition in which calcium carbonate or silica fine particles are dispersed in a resin, and JP-A-9-21.
No. 1207 discloses a method of applying a composition in which polystyrene resin particles are dispersed in a resin to a film. However, when a light diffusion layer is generated by applying a film to a film surface as a secondary processing using a film as a raw material, not only does the production cost rise,
Quality problems such as adhesion of dust, coating streaks, and coating unevenness may occur.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a stable light diffusing property which is excellent in light diffusing property and has little decrease in total light transmission. An object of the present invention is to provide a polyester film.

[0005]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by including a specific cavity in the film, the film has excellent light diffusivity and a reduction in the total light transmission amount. To find that less film is available,
The present invention has been completed. That is, the gist of the present invention is that 50 to 500,000 cavities / m 2 having a diameter of at least twice the particle diameter of the particle are present around the particle in the film plane.
a polyester film characterized by having m ² and a total light transmission of 50% or more, and a laminated polyester film having the polyester film on at least one surface of a film layer substantially containing no particles Exists.

[0006]

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, and naphthalene-2,6-dicarboxylic acid, and ethylene glycol, diethylene glycol, tetramethylene glycol, neopentyl glycol, and 1,4-cyclohexanedicarboxylic acid. It is a polyester containing an ester with a glycol such as methanol as a main component. The polyester is obtained by directly polymerizing an aromatic dicarboxylic acid and a glycol, a method of subjecting an aromatic dicarboxylic acid dialkyl ester and a glycol to a transesterification reaction, followed by polycondensation,
Alternatively, it can be obtained by a method such as polycondensation of a diglycol ester of an aromatic dicarboxylic acid. Representative examples of the polyester used in the present invention include polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate (PEN). 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% of the diol component.
Copolymerized polyester in which less than mol% is a diol component other than the main component may be used.

In the present invention, a specific cavity is present in the film in a specific amount in order to impart light diffusing property to the film. That is, in the film of the present invention, 50 to 500,000 hollow portions having a diameter of not less than twice, preferably not less than 3 times the particle diameter of the particle are present in the film plane.
mm ² , preferably 100 to 50,000 particles / mm ² . If the number of such hollow portions is less than 50 / mm ² , the light diffusivity becomes insufficient, and 500,000 / mm ^2.
If it exceeds 300, it is difficult to maintain the independence of the cavities, and the strength of the film is reduced.

The shape of the particles present in these hollow portions is not particularly limited, but is preferably substantially spherical, and the degree of deformation in the film after film formation (the definition will be described later)
Is preferably 1 to 8. If the degree of deformation is too large, the cavities formed will be small, and the light diffusivity tends to decrease. Further, the particles in the hollow portion of the film of the present invention, when observed by a scanning electron microscope on the cross section and plane of the film, are located at approximately the center of the hollow formed in a lens shape in the film stretching direction, and the particles in the film thickness direction. Has the characteristic of being in contact with the film resin on both sides.

The average particle diameter of the particles present in the hollow portion is not particularly limited, but is usually 0.3 to 10 μm, preferably 0.5 to 5.0 μm. Average particle size 0.3
If the particle size is less than μm, the light diffusivity of the film may be insufficient. If the particle size is more than 10 μm, defects may occur on the film surface. In the present invention, examples of the particles existing in the hollow portion include crosslinked polymer particles and silicone particles.

The crosslinked polymer particles include, for example, polymer particles having an appropriate crosslinked structure in which a cationic functional group is supported on the particle surface. The production method is, for example, as disclosed in Japanese Patent Publication No. 7-17735, in the presence of a modified epoxy group resin having a cationic hydrophilic group at the terminal of the main chain, only one aliphatic amino group in the molecule. It can be produced by emulsion polymerization of a monovinyl compound (A) having a saturated bond and a compound (B) having two or more aliphatic unsaturated bonds in a molecule as a crosslinking agent. Compound (A) which is one component of the copolymer includes acrylic acid, methacrylic acid, and their methyl or glycidyl esters, maleic anhydride and its alkyl derivatives, vinyl glycidyl ether, vinyl acetate, styrene, and alkyl substitution. Examples of styrene and the compound (B) include divinylbenzene and divinylsulfone.

Examples of the silicone particles include silicone rubber elastic particles. For example, (A) an organopolysiloxane having at least two silicon-bonded hydroxy groups in one molecule, as disclosed in JP-A-10-36674;
(B) an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, (C) an organopolysiloxane having at least three silicon-bonded alkoxy groups in one molecule, and (D) a catalyst for a condensation reaction. Can be produced by subjecting a mixture of the above to emulsion polymerization.

When a polyester film having a thickness exceeding 20 μm is required depending on the purpose of use, the polyester film having the above-mentioned specific cavities on at least one surface of a transparent film layer substantially containing no particles is used. What is necessary is just to make the laminated polyester film laminated. A laminated polyester film consisting of a light diffusion layer (cavity-containing layer) and a transparent layer has superior light diffusivity and a reduction in total light transmission compared to a single-layer polyester film with the same thickness and void content. Few.

Although the thickness of the light diffusion layer is not particularly limited, it is usually 2 to 50 μm, preferably 4 to 20 μm. When the thickness of the light diffusion layer is less than 2 μm, the light diffusion property tends to be insufficient. If it exceeds 50 μm, it may be difficult to balance light diffusion and total light transmission. 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 a film having high transparency because it does not contain insoluble particles that absorb or scatter light, or has a small absolute amount even if it does.

The polyester film (light diffusion layer in the case of a laminated film) of the present invention has an average particle size of 0.5 μm.
It is preferred to contain less than inert particles. In the case of inert particles having an average particle size of 0.5 μm or more, the total light transmittance of the film tends to decrease, and the inert particles having a particle size of less than 0.5 μm, preferably less than 0.3 μm are preferably added to the light diffusion layer having a cavity. By containing it, the light diffusion property and the luminance are improved. Examples of the inert particles include silica, silicone particles, crosslinked polymer organic particles, calcium carbonate particles, titanium oxide, calcium phosphate, and the like.

The amount of the inert particles added is not particularly limited, but is usually 0.01 to 10% by weight, preferably 0.2 to 10% by weight.
5% by weight. If the amount is less than 0.01% by weight, the light diffusion effect may not be exhibited. If the amount exceeds 10% by weight, the dispersibility of the particles in the resin tends to deteriorate. The total thickness of the film of the present invention is usually in the range of 2 to 500 μm, regardless of the single-layer structure or the laminated structure. If the total thickness of the film is less than 2 μm, the light diffusivity tends to be insufficient, and if it exceeds 500 μm, mechanical stretching during film formation may be difficult.

In the film of the present invention, the coefficient of friction between the films is preferably 0.5 or less, more preferably 0.4 or less. In a film having a friction coefficient of more than 0.5, air is entangled when the film is wound up during film production, or the film is displaced, wrinkles are generated at the time of slitting,
There is a possibility that the yield may be reduced and the cost may be increased, and scratches and meandering may occur during processing for various uses.

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.
One or both sides of the polyester film of the present invention may be subjected to an anti-reflection treatment. The anti-reflection treatment may be embossing by forming fine irregularities on the surface or utilizing light interference of reflected waves. Thin film formation processing. Furthermore, if necessary, slipperiness, mold release,
A coating treatment for the purpose of imparting antistatic properties, easy adhesion properties, and the like can also be performed.

Next, the method for producing the film of the present invention will be described in detail, but is not particularly limited to the following examples as long as the constitutional requirements of the present invention are satisfied. Raw chips obtained by dispersing solid particles or the like, which induce cavities, in polyester chips by addition or kneading during polymerization, for example, are mixed with other raw chips as they are or by blending with other raw chips to obtain a predetermined concentration.

These polyester chips are dried, extruded from a die at a temperature of from the melting point of the polyester to 320 ° C., and cooled and solidified on a casting drum. At this time, it is preferable to use an electrostatic contact method as a means for holding the film in close contact with the drum. The obtained unstretched film is subjected to the next stretching step. In the stretching step, the film is formed in a temperature range of Tg (glass transition temperature) -10 ° C to Tc (crystallization temperature) -10 ° C in an area magnification of 3 to 50 times, preferably 6 to 30 times. It is stretched in the longitudinal direction (longitudinal direction) and / or the width direction (lateral direction). The stretching method may be uniaxial stretching or biaxial stretching depending on the application. When performing biaxial stretching, any of sequential biaxial orientation stretching, simultaneous biaxial orientation stretching, and a combination thereof may be used. In the case of sequential biaxial stretching, a method of stretching in the longitudinal direction and then stretching in the transverse direction is generally preferably employed. When stretching in the longitudinal and transverse directions, each may be stretched in one step, but may be stretched in multiple steps, or a heat treatment step for relaxing the orientation may be provided between the multiple steps.

In order to impart anti-reflective properties, adhesive properties, antistatic properties, and release properties to the film during or after the above stretching step, a coating layer may be formed on one or both sides of the film, or a corona treatment or the like. A discharge treatment or the like can be performed. In the case of producing a laminated film, a raw material resin containing substantially no particulate lubricant and a polyester containing a predetermined amount of void-inducing particles and the like are melt-extruded from separate extruders, and then a molten polymer flow path is formed. They are bonded and laminated in a pipe or an extrusion die in a laminar flow form, extruded from a die at a temperature of from the melting point of the raw material polymer to 320 ° C., and cooled and solidified on a casting drum. The unstretched laminated film thus obtained is subjected to the above-mentioned stretching step to produce a stretched laminated polyester film.

[0021]

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 the point where the volume fraction of the equivalent particle diameter is 50%. (2) Average particle size, cavity diameter and content of cavity-inducing solid particles The surface in the film stretching direction (the surface of the light diffusion layer in the case of a laminated film) is 0.2 to
After incineration of 0.4 μm, the particle diameter of each particle and the maximum and minimum diameters of cavities formed therearound are observed with a scanning electron microscope, and the average value of the particle diameter and the average value of the cavity diameter are determined. Particles having an average cavity diameter of twice or more the average particle diameter are defined as cavity-derived solid particles. The average value of the particle size and the average value of the cavities were obtained for 100 or more hollow induction solid particles, and the arithmetic mean of each was defined as the average particle size and the cavity diameter of the hollow induction solid particles. In addition, the number of 100 or more hollow induction solid particles was counted from a photograph taken by a scanning electron microscope, and the number of particles per unit area was calculated to be the content. (3) Degree of Particle Deformation A cut surface obtained by cutting a small piece of the film sample in the stretching direction was observed with a scanning electron microscope. The maximum diameter and the minimum diameter were determined for each particle, and the ratio was calculated. This value was determined for at least 100 particles, and the arithmetic mean thereof was defined as the degree of deformation. (4) 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. (5) Color tone of transmitted 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 based on the following criteria.

〇: almost the same as the light of a white fluorescent lamp ×: the color tone has changed (for example, slightly yellowish) Example 1 Crosslinked polymer particles having an average particle size of 1.0 μm 17% of raw material chips of polyethylene terephthalate containing 0% by weight
After drying at 0 ° C. for 3 hours, the mixture is supplied to an extruder and melted at a melting temperature of 280 to 300 ° C., and is passed through a gear pump filter.
The film was drawn through a die onto a casting drum to obtain an unstretched film. At the time of casting, an electrostatic contact method was adopted. The thus-obtained unstretched film is fed to a longitudinal stretching roll, stretched 2.9 times at a film temperature of 83 ° C. (with an IR heater), and further stretched 1.4 times at 87 ° C. (with an IR heater). 130 ℃
The film was stretched 4.4 times in the transverse direction to obtain a biaxially oriented film.
Next, the obtained biaxially oriented film was guided to a heat setting zone and heat set while relaxing 3% in the width direction at 235 ° C. for 5 seconds. The thickness of the obtained light diffusion film was 15 μm, the degree of particle deformation was 2.2, and the diameter of the cavity was 4.5 μm.

Example 2 After drying at 170 ° C. for 3 hours, 1.0% by weight of silicone rubber elastic particles having an average particle size of 2.0 μm and an average particle size of 0.1 μm were used.
The polyethylene terephthalate raw material chips containing 0.2% by weight of fine amorphous silica of m are supplied to a sub-extruder, and the polyethylene terephthalate raw material chips substantially containing no particles are supplied to a main extruder.
It was melted at 0 ° C., and the molten polymer of the sub-extruder was separated from the molten polymer from the main extruder by a feed block via a gear pump filter, and was taken through a die to a casting drum to obtain an unstretched film. At the time of casting, an electrostatic contact method was adopted. The thus-obtained unstretched film is fed to a longitudinal stretching roll, stretched 2.9 times at a film temperature of 83 ° C. (with an IR heater), and further stretched 1.4 times at 87 ° C. (with an IR heater). And stretched 4.4 times in the transverse direction at 130 ° C. to obtain a biaxially oriented film. Next, the obtained biaxially oriented film was guided to a heat setting zone and heat set while relaxing 3% in the width direction at 235 ° C. for 5 seconds. The total thickness of the obtained light diffusion laminated film was 100 μm, and the thickness of the light diffusion layer was 15 μm. The degree of particle deformation is 2.
9. The cavity diameter was 7.8 μm.

Example 3 After drying at 170 ° C. for 3 hours, 1.5% by weight of the crosslinked polymer particles used in Example 1 and 0.2% by weight of fine amorphous silica having an average particle diameter of 0.1 μm were contained. The polyethylene terephthalate raw material chips to be supplied to the sub-extruder, and the polyethylene terephthalate raw material chips containing substantially no particles are supplied to the main extruder and melted at a melting temperature of 280 to 300 ° C.,
The molten polymer from the sub-extruder was separated from the molten polymer from the main extruder by a feed block through a gear pump filter, and was taken through a die to a casting drum to obtain an unstretched film. At the time of casting, an electrostatic contact method was adopted. The unstretched film thus obtained is fed to a longitudinal stretching roll, and the film temperature is set to 8
After being stretched 2.9 times at 3 ° C. (with an IR heater), it is further stretched 1.4 times at 87 ° C. (with an IR heater), guided to a tenter and stretched 4.4 times in the transverse direction at 130 ° C. to be biaxial. An oriented film was obtained. Next, the obtained biaxially oriented film was guided to a heat fixing zone, and 3% in the width direction at 235 ° C. for 5 seconds.
Heat-fixed while relaxing. The total thickness of the obtained light diffusion laminated film is 100 μm, and the thickness of the light diffusion layer is 10 μm.
m. The degree of particle deformation was 2.2 and the cavity diameter was 4.5 μm.

Comparative Example 1 A raw material chip of polyethylene terephthalate containing 1.0% by weight of monodisperse crosslinked polymer particles described in Example 1 of JP-A-4-325532 was used. And the same. The degree of particle deformation in the obtained film was 1.8, and the diameter of the cavity was 1.3 μm.

Comparative Example 2 A film was obtained in the same manner as in Example 1 except that the content of the crosslinked polymer particles in Example 1 was changed to 0.01% by weight. Comparative Example 3 The same procedure as in Example 1 was carried out except that a raw material chip of polyethylene terephthalate containing amorphous silica particles having an average particle size of 3.5 μm and a particle size distribution (R) of 1.6% by weight was used. To obtain a film. The cavity diameter of the obtained film was 3.8 μm.

The physical properties and performances of the obtained films are summarized in Tables 1 to 3 below.

[0028]

[Table 1] Note) The particle content and concentration in Examples 2 and 3 are the particle content and concentration of the light diffusion layer.

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

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, and is easy to manufacture. 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 AA45 AA46 AA67 AB17 AB21 AB25 AB26 AD06 AF29 AF30Y AH12 AH16 BB07 BB08 BC01 BC13 4F100 AK41 AK41A AK41B AT00B BA02 DD21A DE01A DE01H DJ06A EJ38 GB41 JN08 AG18A08A AH33 QA02 QA03 QC06 QD04 QG01 QW05

Claims (3)

[Claims] 1. A hollow portion having a diameter of at least twice as large as the particle size is formed in the film plane around the particle.
A polyester film, wherein there are 00 / mm ² and the total light transmission is 50% or more. 2. A laminated polyester film having the polyester film according to claim 1 on at least one side of a film layer substantially free of particles. 3. The polyester film according to claim 1, which contains inert particles having an average particle size of less than 0.5 μm.