JP2013194146A - Inorganic particle-containing white polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white polyester film having high performance and high productivity.SOLUTION: There is provided a white polyester film which is provided by using polyester and inorganic particles, wherein the polyester comprises polybutylene terephthalate, satisfies formula (1) below and has a ≥97% average reflectance of at least one surface. 1≤a≤0.6×b (1), wherein (a) is the content (wt.%) of inorganic particles based on the total amount of film and b is the content (wt.%) of polybutylene terephthalate based on the total amount of film.

Description

  The present invention relates to a white polyester film, and more particularly to a film containing polybutylene terephthalate with respect to a white polyester film containing inorganic particles.

  As a light source of a liquid crystal display, a backlight system in which light is applied from the back of the display and a light reflection film as disclosed in Patent Document 1 are widely used because of the thin and uniform illumination. In that case, in order to prevent escape of illumination light, it is necessary to install a light reflector on the back of the screen. Since this reflector is required to be thin and have high light reflectivity, as shown in Patent Document 1, a film whitened by containing fine bubbles inside and reflecting light at the bubble interface Etc. are mainly used.

  In order to contain these fine bubbles, there is a method in which a high melting point incompatible polymer or inorganic particles are finely dispersed in a film base material such as polyester and then stretched (for example, biaxially stretched). . During stretching, voids (bubbles) are formed around the incompatible polymer or inorganic particles, and this exerts a light scattering action, resulting in whitening. In recent years, display devices such as a liquid crystal display are also required to have an unprecedented advanced display capability. In particular, backlights are required to have higher brightness and improved white reproducibility.

  In order to achieve high performance and white reproducibility, in the conventional technology, there is an achievement method by adding a large amount of inorganic particles and void nucleating agent, but by adding a large amount, biaxial stretching during film formation Film breaks in the process are induced, resulting in poor productivity. Therefore, improving productivity is an issue. One of the solutions is a method of reducing thickness unevenness in the film width direction in the production process of a biaxially stretched film as disclosed in Patent Document 2. Although a certain level of productivity can be secured by this method, it is insufficient from the viewpoint of maintaining high productivity. As described above, the high performance of the white film and the trade-off in terms of productivity have been problems in the production of light reflecting films.

  Furthermore, in order to produce a film that is stable in terms of process in combination with high productivity, reduction of the generated defects is an indispensable issue. For external defects, a certain effect can be expected by taking measures such as increasing the cleanliness of the film-forming device, but adding a large amount of inorganic particles and void nucleating agent itself is a disadvantage. When it becomes a cause, it is necessary to review those addition methods, so it is addressed as a solution issue.

Japanese Patent No. 2099443 JP 2010-052329 A

  However, the performance improvement of the white film as a light reflector application is always demanded from the market, and in order to solve the problems to be solved, addition of a large amount of inorganic particles and void nucleating agent is indispensable. The present invention makes it possible to maintain and improve productivity in such a multiparticulate white film by examining the structure of the particles and polyester.

  In order to solve this problem, the present invention provides a white polyester film having a large number of bubbles, which is produced by the method described below.

A white polyester film comprising polyester and inorganic particles,
A white polyester film in which the polyester contains polybutylene terephthalate, satisfies the following formula (1), and has an average reflectance of 97% or more on at least one side.
1 ≦ a ≦ 0.6 × b (1)
However, a is content (weight%) of the inorganic particle with respect to the whole film, and b is content (weight%) of polybutylene terephthalate with respect to the whole film.

  By implementing the present invention, a high-performance white film can be provided as a light reflecting film with high productivity.

  The polyester film of the present invention may be either a single layer or a multilayer. The multilayer is a laminated structure using the polyester layers (A) and (B), the polyester layer (A) is a layer containing bubbles, and the polyester layer (B) is laminated on at least one side thereof. It is preferable to have

  In this invention, if it contains the structure of this polyester layer (A) and polyester layer (B), you may be comprised from many layers. For example, a two-layer structure of polyester layer (A) / polyester layer (B) may be used, a three-layer structure of polyester layer (B) / polyester layer (A) / polyester layer (B), or polyester layer (A ) / Polyester layer (B) / polyester layer (A) / polyester layer (B). Furthermore, the structure of five layers or more may be sufficient. By using a multilayer structure, the characteristics of each layer are expressed on the surface of the laminated polyester film, and various characteristics can be controlled.

  Considering the ease and effect on film formation, when the polyester layer (B) is made of a polyester layer having a large number of cells, the polyester layer (B) has a two-layer structure or consists of a polyester layer (B) / polyester layer (A) / polyester layer (B) A three-layer configuration is preferred. That is, the core layer portion is preferably a polyester layer (A), and the surface layer portion on one side or both sides is preferably a polyester layer (B).

  The polyester constituting the present invention is a polymer obtained by condensation polymerization from a diol and a dicarboxylic acid. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, sebacic acid, and the like. The diol is represented by ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol and the like. Specifically, for example, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, etc. It is done. In the case of the present invention, polyethylene terephthalate (hereinafter sometimes abbreviated as PET), polybutylene terephthalate (hereinafter sometimes abbreviated as PBT), and polyethylene naphthalate (hereinafter sometimes abbreviated as PEN) are particularly preferable. .

When polyethylene terephthalate is used as a basic component, from the viewpoint of film formation stability, it is preferably 1 mol% or more and 15 mol% or less, more preferably 3 mol% or more and 14 mol% or less, most preferably 5 mol per total dicarboxylic acid component It is preferable to use a copolymerized polyester containing a copolymer component in an amount of not less than 13% and not more than 13 mol%. If it is less than 1 mol%, film formation may not be possible. Even if it exceeds 15 mol%, film formation may not be possible. Examples of the copolymer component include dicarboxylic acid components such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, adipic acid, sebacic acid, phthalic acid, and 5-sodium sulfoisophthalic acid. Can be mentioned. Examples of the diol include diethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, neopentyl glycol, and polyalkylene glycol. In particular, isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferably used in order to obtain good film forming properties.
From the viewpoint of film formation stability, it is also preferable to include a polyester such as polybutylene terephthalate in the polyethylene terephthalate film. Polybutylene terephthalate is particularly preferable from the viewpoint of easy availability and performance development of the white polyester film.

  In addition, various known additives such as an antioxidant and an antistatic agent may be added to the polyester. As the polyester used in the present invention, polyethylene terephthalate is particularly preferable. Polyethylene terephthalate film is excellent in water resistance, durability, chemical resistance and the like.

  The white polyester film of the present invention needs to have an average reflectance of at least 97% on at least one side. If it is less than 97%, the luminance as a backlight may be insufficient when applied to a liquid crystal display. In the present invention, the average reflectance means that a spectrophotometer (U-3310) manufactured by Hitachi High-Technologies is attached with a 60 mmφ integrating sphere, and a standard white plate of aluminum oxide (part No. 210-0740 manufactured by Hitachi High-Technologies) is 100%. The reflectance is measured over 400 to 700 nm, and the reflectance is read at an interval of 5 nm from the obtained chart, and is an arithmetic average value.

  In order to make the average reflectance 97% or more, it is important that the film is whitened by containing bubbles, and this can improve the average reflectance because it exhibits a light scattering action. . Preferably, the average reflectance is 98% or more, more preferably 100% or more. There is no particular upper limit on the average reflectivity, but in order to increase the average reflectivity, for example, it is necessary to increase the amount of inorganic particles added, and in that case, the film forming property may become unstable. It is preferable that

  The formation of bubbles is achieved by finely dispersing a polymer incompatible with the high melting point polyester in a film base material such as polyester and stretching it. At the time of stretching, bubbles are formed around the incompatible polymer particles, which exert a scattering action on the light, so that it becomes white and high reflectance can be obtained.

  It is preferable that the size of the air bubbles is fine because a large number of air bubbles can be contained while maintaining mechanical properties such as the strength of the film, and a polyester film having high white reproducibility and high reflectance is obtained. I can do it.

  The size of the bubbles is determined by the size of the incompatible polymer particles and the draw ratio at the time of drawing. The size of the incompatible polymer particles is preferably an average particle size of 8 μm or less when the particle size is measured, because the size of the bubbles can be made fine, and more preferably 6 μm or less. When the average particle diameter is larger than 8 μm, it is difficult to obtain a high reflectance, and film breakage is likely to occur during production.

  As a method for stretching the polyester film, a conventionally known stretching technique can be used, but a biaxial stretching method is preferable from the viewpoint of forming fine bubbles. When stretching is performed by the uniaxial stretching method, the formation of fine bubbles becomes insufficient, and the high reflectance required in the present invention may not be obtained. As long as it is a biaxial stretching method, sequential biaxial stretching or simultaneous biaxial stretching may be used. The biaxial stretching ratio is preferably 2.5 to 4.5 times for each of longitudinal stretching and lateral stretching, and the area ratio (longitudinal stretching ratio × lateral stretching ratio) is 9 to 16 times. Is preferred. If the area magnification is less than 9 times, the whiteness of the resulting film may be poor. Conversely, if it exceeds 16 times, the film tends to be broken during stretching and the film forming property tends to be poor.

  When the average particle diameter and area magnification of the incompatible polymer are in the above ranges, the white polyester film in the present invention can contain a large number of fine bubbles and obtain a high reflectance suitable as a liquid crystal display reflector. I can do it.

  As the incompatible polymer, a linear, branched or cyclic polyolefin can be preferably used. Examples of linear and branched polyolefins include poly-3-methylbutene-1, poly-4-methylpentene-1, polyvinyl tert-butane, 1,4-trans-poly-2,3-dimethyl. Butadiene, polyvinylcyclohexane, polystyrene, polymethylstyrene, polydimethylstyrene, polyfluorostyrene, poly-2-methyl-4-fluorostyrene, polyvinyl-t-butyl ether, cellulose triacetate, cellulose tripropionate, polyvinyl fluoride, Examples thereof include a polymer having a melting point of 200 ° C. or higher selected from polychlorotrifluoroethylene. Among them, poly-4-methylpentene is preferable for the polyester base material.

  Cyclic polyolefins include bicyclo [2,2,1] hept-2-ene, 6-methylbicyclo [2,2,1] hept-2-ene, and 5,6-dimethylbicyclo [2,2,1]. Hept-2-ene, 1-methylbicyclo [2,2,1] hept-2-ene, 6-ethylbicyclo [2,2,1] hept-2-ene, 6-n-butylbicyclo [2,2 , 1] hept-2-ene, 6-i-butylbicyclo [2,2,1] hept-2-ene, 7-methylbicyclo [2,2,1] hept-2-ene, tricyclo [4,3 , 0,12.5] -3-decene, 2-methyl-tricyclo [4,3,0,12.5] -3-decene, 5-methyl-tricyclo [4,3,0,12.5]- 3-decene, tricyclo [4,4,0,12.5] -3-decene, 10-methyl- Rishikuro [4,4,0,12.5] -3-decene such as co-polymerized polymer. In addition, those obtained by copolymerizing linear and branched olefins with cyclic polyolefins can also be preferably used. Examples of the linear and branched olefins in this case include ethylene, propylene, Examples include 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and the like. Among these, a copolymer of bicyclo [2,2,1] hept-2-ene and ethylene is preferable.

The addition amount of the incompatible thermoplastic resin is preferably 5% by weight or more and 25% by weight or less when the total weight of the entire polyester film is 100% by weight.
If the content is less than this, the formation of fine bubbles is reduced, making it difficult to obtain high reflectivity. If the content is too high, mechanical properties such as the strength of the film itself may be too low.

  The incompatible thermoplastic resin is more preferably dispersed uniformly in the film. By uniformly dispersing, bubbles are uniformly formed inside the film, and the degree of whitening and thus the reflectance becomes uniform. In order to uniformly disperse the incompatible thermoplastic resin, it is effective to add a low specific gravity agent as a dispersion aid. The low specific gravity agent is a compound having an effect of reducing the specific gravity, and the effect is recognized in a specific compound. For example, for polyester, polyalkylene glycol such as polyethylene glycol, methoxypolyethylene glycol, polytetramethylene glycol, polypropylene glycol, ethylene / propylene oxide copolymer, sodium dodecylbenzenesulfonate, alkylsulfonate It is represented by sodium salt, glycerin monostearate, tetrabutylphosphonium paraaminobenzenesulfonate and the like. In the case of the present invention, polyalkylene glycol, particularly polyethylene glycol is particularly preferable. A copolymer of polybutylene terephthalate and polytetramethylene glycol is also preferably used to improve the dispersibility of the incompatible thermoplastic resin. The addition amount is preferably 3% by weight to 30% by weight, particularly preferably 5% by weight to 25% by weight, based on the total weight of the polyester film. In the polyester film of the present invention, when taking a laminated structure having different compositions from each other, when an incompatible thermoplastic resin is contained in the layer containing fine bubbles, the amount of the low specific gravity agent added is contained in the bubbles. The content is preferably 3% by weight or more and 25% by weight or less, particularly preferably 10% by weight or more and 20% by weight or less, based on the total weight of the polyester layer. If the addition amount of the low specific gravity agent is too small, the effect of the addition is diminished, and if it is too much, the original properties of the film base material may be impaired. Such a low specific gravity agent can be added to the film base polymer in advance and adjusted as a master polymer (master chip).

  By making the white polyester film contain fine bubbles using an incompatible thermoplastic resin, the apparent specific gravity of the polyester film becomes lower than that of a normal polyester film. If a lower specific gravity agent is further added, the specific gravity is further lowered. That is, a white and light film can be obtained. In order to reduce the weight of the white polyester film while maintaining the mechanical properties as a substrate for a liquid crystal display reflector, the specific gravity is preferably 0.3 or more and 1.3 or less. If the specific gravity is less than 0.3, there are too many fine bubbles, which may cause the mechanical properties such as the strength of the film itself to be too low, and the film-forming stability is significantly reduced. When the specific gravity is 1.3 or more, formation of fine bubbles is reduced and it becomes difficult to obtain a high reflectance. When used as a liquid crystal display reflector, the average reflectance and luminance are inferior.

  In order to make the specific gravity 0.3 or more and 1.3 or less, when using a low specific gravity agent as described above, for example, polymethylpentene having a specific gravity of 0.83, 5 to 25% by weight or less based on the whole polyester film. It can be achieved by containing and making the draw ratio 2.5-4.5. When the apparent specific gravity is within the range of the present invention, a large number of fine bubbles can be present while maintaining the film strength, and a high reflectance can be obtained. In other words, when used as a liquid crystal display reflector, the brightness of the screen is remarkably excellent.

  Moreover, the specific gravity of the white polyester film for a liquid crystal display reflector of the present invention is 0.3 or more and 1.3 or less, preferably 0.4 or more and 1.1 or less, when an incompatible thermoplastic resin is used. Preferably it is 0.5 or more and 0.9 or less in order to obtain a higher reflectance.

  In the present invention, the above-described incompatible thermoplastic resin can be suitably used to form fine bubbles, but the use of inorganic particles to form fine bubbles is also preferably exemplified. In this case, it is also preferable to mix the inorganic particles and the incompatible resin so as not to cancel each other out of their performance.

  When using inorganic particles, to obtain high optical properties and stable film-forming properties, the types of particles are titanium dioxide, barium sulfate, calcium sulfate, magnesium sulfate, aluminum oxide, zinc oxide, magnesium oxide, calcium carbonate, carbonic acid. Barium, silica and the like are preferable. Further, they can be used alone or in combination of two or more. Among them, barium sulfate particles and titanium dioxide particles are particularly preferable because film formation stability can be obtained with high optical characteristics.

  When only inorganic particles are used to form fine bubbles, the inorganic particles are preferably contained in an amount of 5% by weight to 35% by weight with respect to the total weight of the polyester film. More preferably, it is 10 to 30 weight%, More preferably, it is 15 to 30 weight%.

  If the content is less than the lower limit of this range, fine bubbles due to inorganic particles may be insufficient and sufficient reflection performance may not be obtained. If the amount is larger than the upper limit of this range, the film-forming stability may be significantly lowered.

  By including fine bubbles in the white polyester film using such inorganic particles, the apparent specific gravity of the polyester film becomes lower than that of a normal polyester film. When using only inorganic particles such as barium sulfate and containing a large number of fine bubbles, the apparent specific gravity is 1.0 or more in order to satisfy the optical characteristics while maintaining the mechanical characteristics as a substrate for a liquid crystal display reflector. It is preferably 1.3 or less, more preferably 1.1 or more and 1.3 or less, in order to obtain a higher reflectance. When the apparent specific gravity is within the range of the present invention, a large number of fine bubbles can be present while maintaining the film strength, and a high reflectance can be obtained. That is, when it is used as a liquid crystal display reflector, it exhibits remarkably excellent reflection performance in terms of screen brightness.

  When inorganic particles are used to contain a large number of fine bubbles, the size of the bubbles is determined by the size of the inorganic particles and the draw ratio during biaxial stretching. The size of the inorganic particles is preferable because when the particle size is measured, the average particle size is 7 μm or less and the size of the bubbles can be made finer, and more preferably 5 μm or less. When the average particle diameter is larger than 7 μm, it is difficult to obtain a high reflectance, and film breakage is likely to occur during production.

  As a stretching method that can be applied to the polyester film in order to contain a large number of fine bubbles, uniaxial stretching and biaxial stretching can be selected. However, in the present invention, when uniaxial stretching is selected, formation of fine bubbles is insufficient. Thus, since it is difficult to obtain the high reflectance required in the present invention, it is necessary to use a biaxial stretching method. As long as it is a biaxial stretching method, sequential biaxial stretching or simultaneous biaxial stretching may be used.

  As described above, if the content of the inorganic particles is sufficient, a large number of fine bubbles are contained, and the reflective performance sufficient for application as a liquid crystal display reflector is exhibited. In addition, it is known that it can have a role of improving white reproducibility and durability as a white polyester film. When inorganic particles are contained in the white polyester film for such purposes, titanium dioxide, barium sulfate, calcium sulfate, magnesium sulfate, aluminum oxide, zinc oxide, magnesium oxide, calcium carbonate, barium carbonate, silica and the like are preferable as the kind of particles. Further, they can be used alone or in combination of two or more. Among them, barium sulfate particles, titanium dioxide particles, and silica particles are particularly preferable because they have good compatibility with polyesters and high optical properties can be obtained.

  When the inorganic particles are contained for this purpose, the content needs to be 1% by weight or more of the whole polyester film. When the amount is less than 1% by weight, white reproducibility and durability as a white polyester film become insufficient, which is not preferable. If the amount is too large, breakage is likely to occur during the formation of the polyester film, and even if no breakage occurs, many film defects due to the inclusion of inorganic particles occur, resulting in poor film formation. There is a case. Preferably, they are 2 weight% or more and 35 weight% or less, More preferably, they are 2 weight% or more and 30 weight% or less.

In the present invention, as described above, polybutylene terephthalate can be suitably used in order to maintain high performance and high productivity as a white polyester film. In the present invention, the content of polybutylene terephthalate needs to be appropriately adjusted in accordance with the content of inorganic particles, and the range must satisfy the following formula.
1 ≦ a ≦ 0.6 × b (1)
However, a is content (weight%) of the inorganic particle with respect to the whole film, and b is content (weight%) of polybutylene terephthalate with respect to the whole film.

  The reason why 1 ≦ a is necessary is that, as described above, if the content of inorganic particles is less than 1% by weight, white reproducibility and durability as a white polyester film become insufficient, which is not preferable.

  The reason why a ≦ 0.6 × b is necessary is that the content b (% by weight) of polybutylene terephthalate with respect to the entire film is a> 0.6 × with respect to the amount of inorganic particles a (% by weight). If it is b, breakage is likely to occur during film formation of the polyester film, and even if no breakage occurs, many film defects due to the inclusion of inorganic particles occur, leading to production loss. This is because the productivity of the polyester film is lowered in any situation.

  The content of polybutylene terephthalate is not particularly limited as long as it satisfies the formula (1), but when producing a white polyester film having a polyethylene terephthalate as a basic component, the high water resistance of polyethylene terephthalate, Durability and chemical resistance may be lost.

When the white polyester film is composed of a plurality of layers, it is preferable that at least one layer thereof contains inorganic particles and polybutylene terephthalate so as to satisfy the following formula (2).
1 ≦ a ′ ≦ 0.6 × b ′ (2)
However, a 'is content (weight%) of an inorganic particle with respect to the layer containing polybutylene terephthalate and an inorganic particle, b' is polybutylene terephthalate with respect to the layer containing polybutylene terephthalate and an inorganic particle. Content (% by weight).

  When the white polyester film is composed of a plurality of layers, the entire white polyester film satisfies the formula (1), and if at least one of the layers satisfies the formula (2), the other polyester layers can be freely designed. It is possible to develop higher performance as a white polyester reflector. Therefore, it is more preferable that the white polyester film in the present invention has a laminated structure of two or more layers, contains inorganic particles and polybutylene terephthalate in at least one layer, and satisfies the formulas (1) and (2). one of.

[Measurement of physical properties and evaluation method of effects]
(1) Film thickness (total thickness of each layer)
The film sample is measured with a calibrated digital micrometer (M-30, manufactured by Sony Precision Technology), and the thickness at 10 points is measured, and the average value is taken as the film thickness.
(2) Thickness of each layer A film is sampled to 5 mm x 1 cm, and the film is cut into a cross section in the direction parallel to the film width direction (hereinafter sometimes referred to as "lateral direction") using a microtome. Using a transmission electron microscope type HU-12 (manufactured by Hitachi, Ltd.), the cross section of the cut polyester layer (A) and the polyester layer (B) was observed and laminated from a cross-sectional photograph magnified 250 times. Calculate the thickness.
(3) Film-forming stability Whether the film can be formed stably is evaluated according to the following criteria.
○: A film can be stably formed for 2 hours or more.
X: Breakage occurs within 2 hours, and stable film formation is not possible.
(4) Average reflectance When a spectrophotometer (U-3310) manufactured by Hitachi High-Technologies is attached with a 60 mmφ integrating sphere and the standard white plate of aluminum oxide (Part No. 210-0740 manufactured by Hitachi High-Technologies) is taken as 100%. Is measured over 400-700 nm. The reflectance is read from the obtained chart at intervals of 5 nm, and the arithmetic average value is calculated to obtain the average reflectance.
(5) Whiteness According to JIS-P8123, using a color meter SM-6 manufactured by Suga Test Instruments Co., Ltd., measuring Lab color tone in the reflection mode with C light and 2 ° field of view, substituting the values of XYZ into the following formula The value is whiteness.
Whiteness = 100 − {(100−L) 2+ (a2 + b2)} 1/2
(6) Specific gravity The film is accurately sampled to 10 cm × 10 cm and accurately weighed to the nearest 0.1 mg with an electronic balance (AC100 manufactured by Mettler). After taking out the weighed sample, the total thickness of each layer of the film is measured using a constant pressure thickness measuring instrument, and the specific gravity is calculated by applying to the following formula.
Specific gravity = (Weighed value (g)) / (Total thickness of each layer (μm)) × 100

  The present invention will be described based on examples.

[Examples 1 to 14]
As the raw material polymer and inorganic particles of the polyester layer (A) and the polyester layer (B), the raw materials shown below were mixed at the mixing ratios shown in Tables 1 and 3. After vacuum drying at 180 ° C. for 3 hours, the extrusion temperature was set to 320 ° C., and the polyester layer (A) was produced by supplying the extruder A heated to 270 to 300 ° C. In parallel, the raw materials shown below were mixed at a compounding ratio different from that of the polyester layer (A) shown in Tables 1 and 3, and vacuum dried at 180 ° C. for 3 hours, and then the extrusion temperature was set to 320 ° C. The polyester layer (B) was produced by supplying to the extruder B heated at 270-300 degreeC. However, about Example 14, the polyester layer (B) was not produced for the structure by the polyester layer (A) single film.
(1) Base resin / polyethylene terephthalate chip (Example: F20S manufactured by Toray Industries, Inc.)
(2) Low specific gravity agent Polyester copolymer obtained by copolymerizing polybutylene terephthalate and polyalkylene glycol in a molar ratio of 7: 3 (eg, “Hytrel” manufactured by Toray DuPont Co., Ltd.)
-Polyester copolymer with polyethylene terephthalate as the main skeleton and copolymerized with 10 mol% isophthalic acid and 5 mol% polyethylene glycol (Example: T794M manufactured by Toray Industries, Inc.)
(3) Incompatible polymer polymethylpentene (Example: Mitsui Chemicals, Inc. TPX)
A cycloolefin copolymer (common name COC) having a glass transition temperature of 180 ° C. (eg, TOPAS manufactured by Polyplastics Co., Ltd.)
(4) Inorganic particles and barium sulfate (purchased as a mixed chip with polyethylene terephthalate)
・ Titanium dioxide (purchased as a mixed chip with polyethylene terephthalate)
・ Calcium carbonate (purchased as a mixed chip with polyethylene terephthalate)
・ Silica (purchased as a mixed chip with polyethylene terephthalate)
On the other hand, a polyethylene terephthalate chip mixed with inorganic particles in the proportions shown in Table 1 was vacuum-dried at 180 ° C. for 3 hours, and then supplied to an extruder B heated to 280 ° C., whereby a polyester layer (B ) Raw material polymer was prepared.

  The raw material polymers of the polyester layers (A) and (B) were laminated through a laminating apparatus so that the layer configuration and the layer thickness were as shown in Tables 1 and 3, and formed into a sheet shape by a T-die. Further, the unstretched sheet obtained by cooling and solidifying the sheet with a cooling drum having a surface temperature of 25 ° C. is led to a group of seven rolls adjusted to a heating temperature of 80 to 98 ° C., and longitudinally increased by 2.5 to 4.5 times. It extended | stretched and cooled with the roll group of 25 degreeC. The film was stretched by 2.5 to 4.5 times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. while being guided by a clip while holding both ends of the film with clips. Thereafter, heat setting was performed at 190 ° C. in a tenter, and after uniform cooling, the film was cooled to room temperature to obtain a film having a winding thickness shown in Tables 1 and 3. The performance of the obtained film as a white polyester film is as shown in Tables 2 and 4, both of which yielded a film having high film forming properties, high average reflectance and whiteness.

[Comparative Examples 1-4]
Using the raw materials shown in Table 5, a film was formed in the same manner and conditions as in Example 1. However, about the comparative example 4, the polyester layer (B) was not produced for the structure by the polyester layer (A) single film. The performance of the obtained film is shown in Table 6, but all of them have good physical properties as a white polyester film, but film formation is frequently broken and is not suitable for production.

[Comparative Example 5]
Using the raw materials shown in Table 5, the same method and conditions as in Example 1 were used to form a film only with the polyester layer (A). The performance of the obtained film is shown in Table 6. Although the film forming property was excellent, the performance as a white polyester film for a reflector was inferior.

The present invention relates to a white polyester film, and more particularly to a film containing polybutylene terephthalate with respect to a white polyester film containing inorganic particles.

Claims (9)

A white polyester film comprising polyester and inorganic particles,
The polyester contains polybutylene terephthalate,
A white polyester film satisfying the following formula (1) and having an average reflectance of at least 97% on at least one side.
1 ≦ a ≦ 0.6 × b (1)
However, a is content (weight%) of the inorganic particle with respect to the whole film, and b is content (weight%) of polybutylene terephthalate with respect to the whole film. The said white polyester film has at least 2 layer or more of a polyester layer (A) and a polyester layer (B), The composition of a polyester layer (A) and the composition of a polyester layer (B) are mutually different. White polyester film. At least one of the polyester layer (A) and the polyester layer (B) contains polybutylene terephthalate and inorganic particles, and the inorganic particle content and polybutylene in the layer (a layer containing polybutylene terephthalate and inorganic particles). The white polyester film according to claim 2, wherein the content of terephthalate satisfies the following formula (2).
1 ≦ a ′ ≦ 0.6 × b ′ (2)
However, a 'is content (weight%) of an inorganic particle with respect to the layer containing polybutylene terephthalate and an inorganic particle, b' is polybutylene terephthalate with respect to the layer containing polybutylene terephthalate and an inorganic particle. Content (% by weight). The white polyester film in any one of Claims 1-3 formed by containing a bubble inside. The white polyester film in any one of Claims 1-4 whose specific gravity is 0.3-1.3. 6. The white polyester film according to claim 4, wherein the air bubbles are formed by containing a resin incompatible with polyester in an amount of 5 wt% to 25 wt% and biaxially stretching. 6. The white polyester film according to claim 4, wherein the air bubbles are formed by biaxially stretching the inorganic particles containing 5 wt% or more and 35 wt% or less of inorganic particles. The polyester layer (A) / polyester layer (B) has a two-layer structure, or the polyester layer (A) / polyester layer (B) / polyester layer (A) has a three-layer structure, and the polyester layer (B) has air bubbles. The white polyester film according to claim 1, which is a layer containing The white polyester film according to claim 1, which is used for a liquid crystal display device.