WO2015125644A1

WO2015125644A1 - Polyester film

Info

Publication number: WO2015125644A1
Application number: PCT/JP2015/053503
Authority: WO
Inventors: 井澤雅俊; 石田洋一; 長谷川正大
Original assignee: 東レ株式会社
Priority date: 2014-02-24
Filing date: 2015-02-09
Publication date: 2015-08-27
Also published as: TW201538329A; JP6489012B2; JP2019116099A; JP6756387B2; JPWO2015125644A1

Abstract

Provided, at a low cost, is a surface light source having an excellent luminance characteristic and affinity to other members by using this polyester film which is excellent with regard to economic efficiency, a film-forming property, whiteness, reflectivity, lightness of weight, and surface shape. The biaxially-stretched polyester film contains (1) 10-90 mass% of polyester (a) having a glass transition temperature (Tg) of at least 50°C and less than 80°C, and 10-90 mass% of polyester (b) having a glass transition temperature (Tg) of 100-120°C inclusive. The difference between the glass transition temperatures (Tg) of polyester (a) and polyester (b) is 50°C or less. The biaxially-stretched polyester film has: layer (A) which does not substantially contain inorganic or organic particles; polyester (c); and layer (B) which contains at least one component (d) that is incompatible with polyester (c). Layer (A) forms at least one surface, and this surface has a centre line average roughness (Ra) of 300 nm or more and a 10-point average roughness (Rz) of 3000 nm or more.

Description

Polyester film

The present invention relates to a polyester film, and more particularly to a film used as a reflector for a liquid crystal display.

Liquid crystal displays, which are widely used in various electronic devices such as TVs, personal computers, and tablet terminals, have a light source called a backlight at the rear of the display for screen display. Moreover, the backlight needs to irradiate the whole screen uniformly. As a system satisfying this characteristic, there are surface light source structures called a side light type and a direct type. In particular, a thin type display employs a side-light type backlight, that is, a type of backlight that emits light from the side of the screen. In general, in the side light type, a sheet called a light guide plate, which has been subjected to various treatments such as halftone printing or embossing on one side of a transparent substrate such as an acrylic plate having a certain thickness, is used. By applying light from the light source on the side to the edge of the light guide plate, the illumination light is evenly distributed upward, and a screen having uniform brightness is obtained. Moreover, since illumination is installed only at the edge portion, the number of light sources can be reduced, the cost and weight can be reduced, and the thickness can be made thinner than the direct type. Furthermore, in order to prevent the illumination light from escaping to the back of the screen, a reflecting plate is provided below the light guide plate, thereby reducing the loss of light from the light source and brightening the liquid crystal screen.

Such a surface light source for a liquid crystal screen, particularly a reflector used in a side light type, is required to be compatible with a light guide plate as well as a thin film and light weight as well as high reflection performance. Conventionally, as a reflector, white pigment is added to the film, fine bubbles are contained inside, and high reflection performance is achieved by this interface reflection, and particles such as inorganic particles are added to the surface layer. An uneven shape has been imparted by processing or coating to prevent close contact with the light guide plate (Patent Documents 1, 2, 3, 4, 5, 6, 7).

It has also been proposed to select a material having a high strength and not easily deteriorated, such as inorganic particles and resin particles, in particular, as the material used for the surface layer (Patent Documents 8 and 9).

JP 2009-98660 A JP 2009-173015 A Japanese Patent Laid-Open No. 2002-98808 JP 2004-126345 A International Publication 2011/105294 Japanese Patent No. 5218931 JP 2009-285912 A Special table 2009-513800 gazette JP 2009-96999 A

However, in the reflective film provided with the concavo-convex shape by the methods described in Patent Documents 1, 2, 3, 4, 5, 6 and 7, depending on the material of the light guide plate, there are various types such as halftone printing and embossing of the light guide plate. The treated surface is likely to be scratched, and the scratch or shavings may cause screen unevenness. Moreover, the coating of a reflective film may peel off by the vibration at the time of conveyance. Furthermore, the above-mentioned coating and embossing are often applied independently after film formation, which requires a multi-step and special process, which is expensive and increases the number of processes exposed to high temperatures. When the bubbles are crushed or the constituent resin is deteriorated, the light reflection performance is lowered.

In addition, in recent years, customer requirements have become stricter, and in particular, in sidelight type backlights, it has been required to form unevenness with less height difference and height difference, which is proposed in Patent Documents 8 and 9. Such existing designs are becoming difficult to meet this requirement.

Therefore, an object of the present invention is to provide a film or a reflective member having excellent reflectivity and surface shape that could not be achieved by the above-described conventional studies at low cost without separate processes other than the film forming process such as coating. .

In order to solve the above problems, the present invention has the following configuration.
(1) 10 to 90% by mass of a polyester (a) having a glass transition temperature (Tg) of 50 ° C. or more and less than 80 ° C. and 10 to 90% by mass of a polyester (b) having a Tg of 100 ° C. or more and 120 ° C. or less A layer (A) in which the difference in Tg between the polyester (a) and the polyester (b) is 50 ° C. or less and substantially free of inorganic and organic particles;
Having a layer (B) comprising polyester (c) and at least one component (d) incompatible with the polyester (c);
A biaxially stretched polyester film in which the layer (A) is at least one surface, the centerline average roughness (Ra) of this surface is 300 nm or more, and the ten-point average roughness (Rz) is 3000 nm or more.
(2) The polyester film according to (1), wherein the polyester (a) is polyethylene terephthalate.
(3) The polyester film according to (1) or (2), wherein the polyester (b) uses a diol having a cyclic skeleton as a diol component.
(4) The polyester film according to any one of (1) to (3), wherein the polyester (b) uses 2,2,4,4-tetramethyl-1,3-cyclobutanediol as a diol component. .
(5) The layer (A) is a polyester (a) having a glass transition temperature (Tg) of 50 to 80 ° C. and a polyester (b) having a Tg of 100 to 120 ° C. A biaxially stretched polyester film comprising 10 to 90% by mass.
(6) A reflector for a liquid crystal display using the biaxially stretched polyester film according to any one of (1) to (5).

According to the present invention, it is possible to provide a polyester film having both high reflectivity and an excellent surface shape, and particularly when this polyester film is used as a reflector or reflector in a surface light source, the liquid crystal screen is brightly illuminated, It is possible to make the liquid crystal image clearer and easier to see, and further, it is possible to suppress adhesion and scraping with the light guide plate, which are problems with a backlight using a sidelight type light source.

Hereinafter, the present invention will be described in detail.
[Configuration of polyester film]
The polyester film of the present invention is a film having a layer (A) and a layer (B). In the present invention, considering the ease of film formation and effects, a structure of two or more layers is required, and a three-layer structure is preferable. In the present invention, the layer (A) needs to be configured to be at least one surface. In particular, a mode in which the layer (B) is protected by the layer (A), that is, a three-layer structure of layer (A) / layer (B) / layer (A) is preferable. Moreover, when it becomes a multilayer, it is preferable that a core layer part is a layer (B), and the surface layer part of one side or both sides is a layer (A). Moreover, it is preferable that the polyester film of this invention consists of a layer (A) and a layer (B).

The thickness of the layer (A) of the polyester film of the present invention is preferably 2 to 20 μm. When the thickness of the layer (A) is less than 2 μm, the center line average roughness (Ra) is 300 nm or more and the ten-point average even when the polyester (a) and the polyester (b) are blended within the range described later. The surface shape with a roughness (Rz) of 3000 nm or more is difficult to be obtained, and it is extremely easy to break due to the influence of the layer (B) containing a large number of bubbles having the incompatible component (d) as a core, and stable film formation cannot be performed. This is not preferable. When the thickness of the layer (A) exceeds 20 μm, when the polyester film is used as a reflecting plate, it becomes difficult for light to reach the layer (B), and air bubbles and polyester having an incompatible component (d) as a core This is not preferable because the components reflected at the interface with the surface may decrease and optical characteristics such as reflectance and luminance may deteriorate.

[Layer (A)]
In the polyester film of the present invention, the layer (A) needs to contain polyester (a) and polyester (b). In the present invention, the layer (A) is more preferably composed of polyester (a) and polyester (b). By blending the polyester (a) and the polyester (b) within the range described later, a surface shape having a center line average roughness (Ra) of 300 nm or more and a ten-point average roughness (Rz) of 3000 nm or more is obtained. Obtainable.

In the polyester film of the present invention, it is necessary that the glass transition temperature (Tg) of the polyester (a) is 50 ° C. or more and less than 80 ° C., and the Tg of the polyester (b) is 100 ° C. or more and 120 ° C. or less. As described above, a polyester having a Tg difference of 20 ° C. or more is melt-kneaded, extruded, and biaxially stretched to produce a portion that is not easily stretched. Thereby, continuous and minute stretching unevenness occurs, and as a result, an uneven shape is formed on the surface of the film. When the polyester film having such a concavo-convex shape formed on the surface is used as a reflector or reflector in a surface light source, adhesion to the light guide plate can be prevented particularly in a type using a sidelight type light source.

If the Tg of the polyester (a) constituting the layer (A) is 80 ° C. or higher, the Tg of the entire polyester film will increase, so that it cannot be stretched under normal stretching conditions. When the Tg of the polyester (b) is less than 100 ° C., it is difficult to separate the stretched portion from the easily stretched portion, and the desired surface irregularities are not formed. When the Tg of the polyester (b) is 120 ° C. or higher, the Tg difference from the polyester (a) is too large, and the stretching unevenness increases and tears, so that the film cannot be formed. Similarly, no film can be formed even if the difference in Tg between polyester (a) and polyester (b) exceeds 50 ° C. Therefore, in the present invention, the difference in Tg between polyester (a) and polyester (b) needs to be 50 ° C. or less.

In the polyester film of the present invention, the center line average roughness (Ra) of the surface of the layer (A) needs to be 300 nm or more. Preferably, it is 400 nm or more. The upper limit is preferably less than 800 nm, more preferably less than 750 nm.

The ten-point average roughness (Rz) of the surface of the layer (A) needs to be 3000 nm or more. Preferably, it is 4000 nm or more. The upper limit is preferably less than 8000 nm. The numerical values of Ra and Rz are related to the unevenness of the film surface. By providing irregularities on the film surface, the specular reflection component of the light reflection on the film surface is reduced, and the glossiness of the film can be lowered, and the light from the illumination light source is evenly distributed to the liquid crystal cell. It is a film that reflects and hardly adheres to the light guide plate. Even if Ra is in the above range, if Rz is less than 3000 nm, the glossiness of the film surface increases, and uneven brightness tends to occur when incorporated in a liquid crystal display backlight. Even if Rz is in the above range, when Ra is less than 300 nm, the portions other than the protrusions on the film surface become smooth and highly glossy, and more easily come into close contact with the light guide plate, resulting in uneven brightness. When both the Ra value and the Rz value are within the above ranges, the film becomes low gloss, the handling property in the subsequent process such as incorporation into the backlight housing is improved, and the compatibility with the light guide plate is also achieved. Get better. That is, luminance unevenness can be significantly suppressed. In addition, when it is going to obtain the surface from which Ra becomes 800 nm or more, or the surface from which Rz becomes 8000 nm or more, film forming property may deteriorate.

The polyester film of the present invention has an uneven shape in the layer (A). The uneven shape preferably has a maximum height of 5 to 30 μm, more preferably 5 to 20 μm, and most preferably 5 to 15 μm. When the thickness is less than 5 μm, the luminance unevenness in the edge light type backlight may increase. On the other hand, when larger than 30 micrometers, the bubble in a layer (B) may be crushed, reflective performance may fall and a brightness | luminance may fall.

The measuring method of the maximum height of the convex part is as follows. (I) A white reflective film is cut into a 5 cm square to obtain a sample. (Ii) Using a laser microscope VK-9700 manufactured by Keyence Co., Ltd., observing the sample with the magnification of the objective lens set to 20 times, the portion detected at a height of 1 μm or more is defined as a convex portion, To do. (Iii) In an arbitrary range (2 cm × 2 cm) on the convex side surface of the sample, the height is calculated from the profile function of the attached analysis software, and the maximum value is selected therefrom. (Iv) The above measurement is carried out on 5 samples collected at random, and the number average is defined as “the maximum height of the convex portion”.

Further, the layer (A) needs to be substantially free of inorganic and organic particles. Here, being substantially free means that there is no intentional addition of inorganic particles or organic particles. More specifically, the layer (A) is cut in the thickness direction using a microtome, and the obtained cross section is observed with a transmission electron microscope (HU-12, manufactured by Hitachi, Ltd.). To do. The observation magnification is 250 times, and the observation range (the cross-sectional range of the layer (A) to be observed) is 1000 [(μm) ² ]. In the observation range, when the ratio of the area of the inorganic particles and the organic particles to the observation range (1000 [(μm) ² ]) is 0.3% or less, the layer (A) is substantially inorganic particles and organic particles. Is determined not to be substantially included. The ratio of the area of the inorganic particles and the organic particles to the observation range (1000 [(μm) ² ]) is preferably 0.1% or less, more preferably 0.05% or less, and most preferably inorganic particles. And no organic particles are observed.
When the layer (A) contains inorganic and organic particles, even if an attempt is made to provide unevenness on the film surface by the above-described method, the film may not be formed because of tearing. Moreover, even if it can form into a film, these particle | grains will enter into a recessed part, and the value of Ra and Rz will be less than 300 nm and less than 3000 nm, respectively.

[Polyester (a) and polyester (b)]
The polyester (a) and the polyester (b) constituting the layer (A) are: 1) the weight of a dicarboxylic acid component or an ester-forming derivative thereof (hereinafter sometimes collectively referred to as “dicarboxylic acid component”) and a diol component. It can be obtained by condensation, 2) polycondensation of a compound having a carboxylic acid or carboxylic acid derivative skeleton and a hydroxyl group in one molecule, and a combination of 1) and 2).

Examples of the dicarboxylic acid component constituting the polyester (a) include aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, methylmalonic acid, and ethylmalonic acid, terephthalic acid, and isophthalic acid. , Phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, dicarboxylic acid such as 2,6-naphthalenedicarboxylic acid, and the like, but are not limited thereto, for example, polyfunctional acid. Trimellitic acid, pyromellitic acid and the like can also be suitably used. Moreover, these may be used independently or may be used in multiple types as needed.

Examples of the diol component constituting the polyester resin include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol. And the like, and diols such as aromatic diols such as 1,3-benzenedimethanol and 1,4-benzenedimethanol, but are not limited thereto. Moreover, these may be used independently or may be used in multiple types as needed.

The polyester (a) can be obtained by polycondensation by appropriately combining the above compounds.

The polyester (a) may be crystalline or non-crystalline, but it is preferable to contain at least one non-crystalline polyester for forming the surface shape described later. As used herein, non-crystalline refers to a resin having a heat of crystal fusion of less than 1 cal / g.

Examples of the polyester suitably used for the polyester (a) include polyethylene terephthalate (hereinafter sometimes abbreviated as PET), polypropylene terephthalate, polybutylene terephthalate, and the like.

By using the above-mentioned resin as the polyester (a), high mechanical strength can be imparted when a film is formed while maintaining no coloration. More preferably, PET is preferable because it is inexpensive and has excellent water resistance, durability, and chemical resistance.

Examples of the dicarboxylic acid component constituting the polyester (b) include aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, methylmalonic acid, and ethylmalonic acid, terephthalic acid, and isophthalic acid. , Phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, dicarboxylic acid such as 2,6-naphthalenedicarboxylic acid, and the like, but are not limited thereto, for example, polyfunctional acid. Trimellitic acid, pyromellitic acid and the like can also be suitably used. Moreover, these may be used independently or may be used in multiple types as needed.

Also, examples of the diol component constituting such a polyester resin include linear aliphatic diols and diols having a rigid skeleton, that is, cycloaliphatic diols (diols having a cyclic skeleton).

Examples of the linear aliphatic diol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol and the like.

Cycloaliphatic diols (diols having a cyclic skeleton) include cyclobutanediol, cyclopentanediol, cyclohexanediol, cycloheptanediol, cyclooctanediol, cyclopropanedimethanol, cyclobutanedimethanol, cyclopentanedimethanol, cyclohexane Hexanedimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, isosorbide, 3,9-bis (1,1-dimethyl-2-hydroxyethyl) -2,4,8,10 -Tetraoxaspiro [5.5] undecane, 5-methylol-5-ethyl-2- (1,1-dimethyl-2-hydroxyethyl) -1,3-dioxane and the like.

In the present invention, a polyester having at least one of these diols as a diol component is preferably used. Further, the polyester (b) preferably has two or more different diol components selected from the above, and particularly preferably has three or more components. However, since it is difficult to adjust the copolymerization ratio when the component is five or more. It may not be preferable.

In the present invention, it is preferable that the polyester (b) comprises at least one diol having the above cyclic skeleton as the diol component. By using the diol component having such a cyclic skeleton, the Tg of the polyester (b) can be increased. Particularly in the present invention, the polyester (b) is preferably formed using 2,2,4,4-tetramethyl-1,3-cyclobutanediol as the diol component.

As an example of the polyester (b), it is preferable to have ethylene glycol and 1,4-cyclohexanedimethanol as an example of two or more different diol components described above. More preferably, it has ethylene glycol and 1,4-cyclohexanedimethanol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol, isosorbide, 3,9-bis (1,1 -Dimethyl-2-hydroxyethyl) -2,4,8,10-tetraoxaspiro [5.5] undecane and 5-methylol-5-ethyl-2- (1,1-dimethyl-2-hydroxyethyl) A total of three components having one diol component selected from the group consisting of -1,3-dioxane. Among them, it is particularly preferable to have ethylene glycol, 1,4-cyclohexanedimethanol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol.

In the case where ethylene glycol, 1,4-cyclohexanedimethanol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol are used as the diol component of the polyester (b), the respective ratios are the total of the diol components. When mol% is 100 mol%, ethylene glycol is 0 to 15 mol%, 1,4-cyclohexanedimethanol is 60 to 75 mol%, 2,2,4,4-tetramethyl-1,3-cyclobutanediol. Is preferably 25 to 40 mol%.

By using the above-mentioned resin as the polyester (b), high mechanical strength can be imparted when the film is formed while maintaining the non-coloring property, and the surface shape as described later as the layer (A) is used. Can be formed.

The Tg of the polyester (a) and the polyester (b) can be appropriately adjusted by the combination of the dicarboxylic acid component and the diol component and the copolymerization ratio thereof. Examples of the polyester (a) include PET using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component, and polyester using terephthalic acid and isophthalic acid as the dicarboxylic acid component (hereinafter sometimes abbreviated as PETI). Can be mentioned. In addition, the polyester (b) is a polyester (for example, “2”) using a combination of terephthalic acid as the dicarboxylic acid component and 1,4-cyclohexanedimethanol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol as the diol component. TRITAN "(manufactured by Eastman Chemical Company)).

The polyester (a) and the polyester (b) may each be a combination of two or more, and the polyester (a) is particularly preferably a combination of PET and PETI.

In the present invention, the layer (A) comprises 10 to 90% by mass of a polyester (a) having a glass transition temperature (Tg) of 50 ° C. or more and less than 80 ° C., and a polyester (b) having a Tg of 100 ° C. or more and 120 ° C. or less. ) It is necessary to contain 10 to 90% by mass. In the present invention, the layer (A) has a glass transition temperature (Tg) of 50 to 80 ° C. and a polyester (a) of 10 to 90% by mass, and Tg is 100 to 120 ° C. The polyester (b) is preferably composed of 10 to 90% by mass.

In the polyester film of the present invention, the content of the polyester (a) needs to be 10 to 90% by mass with respect to the layer (A). More preferably, it is 20 to 80% by mass, and most preferably 30 to 70% by mass. If the content of the polyester (a) is less than 10% by weight, the content of the polyester (b) having a high Tg is too high, and stretching may not be possible under normal stretching conditions. On the other hand, if it exceeds 90% by weight, a surface shape as described later cannot be obtained.

In the polyester film of the present invention, the polyester (b) content needs to be 10 to 90% by mass with respect to the layer (A). More preferably, it is 20 to 80% by mass, and most preferably 30 to 70% by mass. If the content of the polyester (b) is less than 10% by weight, a surface shape as described later cannot be obtained. On the other hand, when the content exceeds 90% by weight, the content of the polyester (b) having a high Tg is too large, so that the film cannot be stretched under normal stretching conditions, and film-breaking often occurs.

[Layer (B)]
The layer (B) of the polyester film of the present invention is a layer comprising at least one component (d) that is incompatible with the polyester (c) and the polyester (c). By using the polyester (c) and the incompatible component (d), it is possible to easily contain bubbles having the incompatible component (d) as a core by a method as described later, It becomes possible to produce a polyester film having high reflection characteristics. Therefore, the layer (B) of the polyester film of the present invention contains polyester (c), a component (d) that is incompatible with the polyester (c), and bubbles, so that optical properties such as luminance and reflectance are improved. This is preferable.

The polyester film of the present invention has the above-mentioned configuration, controls the light diffusibility of reflected light, imparts high mechanical strength to the film, imparts film-forming properties, imparts antistatic properties, etc. Further, a layer having light resistance or other functions having an accompanying function may be laminated. Various characteristics can be controlled by using a multilayer structure.

[Polyester (c)]
Polyester (c) is: 1) polycondensation of a dicarboxylic acid component or an ester-forming derivative thereof (hereinafter sometimes referred to as “dicarboxylic acid component”) and a diol component, and 2) carboxylic acid or carboxylic acid within one molecule. It can be obtained by polycondensation of a compound having an acid derivative skeleton and a hydroxyl group, and a combination of 1) and 2).

In the polyester film of the present invention, one or more polyester resins can be used as the polyester (c), but it is preferable to include the polyester (c1) and the polyester (c2) described later. By using polyester (c1) and polyester (c2), a white polyester film having high optical properties can be obtained stably.

Polyester (c1) is composed of 1) polycondensation of a dicarboxylic acid component or an ester-forming derivative thereof (hereinafter sometimes collectively referred to as “dicarboxylic acid component”) and a diol component, and 2) carboxylic acid or carboxylic acid within one molecule. It can be obtained by polycondensation of a compound having an acid derivative skeleton and a hydroxyl group, and a combination of 1) and 2).

In 1), as the dicarboxylic acid component constituting such polyester resin, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelain Acids, aliphatic dicarboxylic acids such as methylmalonic acid, ethylmalonic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1 , 8-Naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, 5-sodium sulfoisophthalic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, 9,9′-bis (4-carboxyl) Aromatic diphenyl such as phenyl) fluorenic acid Representative examples include dicarboxylic acids such as rubonic acid, or ester derivatives thereof, but are not limited thereto. For example, polymellitic acids such as trimellitic acid, pyromellitic acid, and ester derivatives thereof are also preferably used. Can do. Moreover, these may be used independently or may be used in multiple types as needed.

Also, dicarboxy compounds obtained by adding oxyacids such as l-lactide, d-lactide, hydroxybenzoic acid and the like, and a combination of a plurality of the oxyacids to the carboxy terminus of the dicarboxylic acid component described above. Preferably used.

The diol component constituting the polyester resin in 1) includes ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3 -Aliphatic diols such as butanediol, aromatic diols such as bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis (4-hydroxyphenyl) fluorene, etc. Examples of such diols include, but are not limited to, diols. Moreover, these may be used independently or may be used in multiple types as needed.

In 2), examples of the compound having a carboxylic acid or carboxylic acid derivative skeleton and a hydroxyl group in one molecule include oxyacids such as l-lactide, d-lactide, and hydroxybenzoic acid, and derivatives thereof, and oxyacids thereof. And a dicarboxy compound to which a plurality of is added.

The polyester (c1) can be obtained by polycondensation by appropriately combining the above compounds. Polyesters suitably used for the polyester (c1) include polyethylene terephthalate (hereinafter abbreviated as PET), polyethylene-2,6-naphthalenedicarboxylate (hereinafter abbreviated as PEN), and polypropylene. Examples include terephthalate (hereinafter sometimes abbreviated as PPT) and polybutylene terephthalate (hereinafter sometimes abbreviated as PBT).

As the polyester (c1), the same polyester as the polyester (a) of the layer (A) can be used.

By using the above-mentioned resin as the polyester (c1) used in the present invention, high mechanical strength can be imparted when a film is formed while maintaining no coloration. More preferably, PET is preferable because it is inexpensive and has excellent water resistance, durability, and chemical resistance. In addition, various known additives such as an antioxidant and an antistatic agent may be added to the polyester.

Here, in the polyester film of the present invention, the polyester (c) preferably has a polyester (c2), and the polyester resin component (c2) preferably contains an alicyclic diol component having 4 to 8 carbon atoms. . Here, the alicyclic group having 4 to 8 carbon atoms in the present invention is a cycloalkane, and is a cyclic aliphatic represented by the general formula C _n H _2n (where 4 ≦ n ≦ 8). A general term for hydrocarbons.

An alicyclic diol having 4 to 8 carbon atoms refers to a substance having both the structure of a cyclic aliphatic hydrocarbon part having 4 to 8 carbon atoms and a diol part. That is, specific examples of the alicyclic diol having 4 to 8 carbon atoms include cyclobutanediol, cyclopentanediol, cyclohexanediol, cycloheptanediol, cyclooctanediol, cyclopropanedimethanol, cyclobutanedimethanol, cyclopentane. Examples include dimethanol, cyclohexane dimethanol, cycloheptane dimethanol, and cyclooctane dimethanol.

The diol component bonded to the cycloaliphatic hydrocarbon moiety having 4 to 8 carbon atoms may be bonded to any carbon atom of the cycloaliphatic hydrocarbon moiety. For example, the cycloaliphatic hydrocarbon moiety When is a cyclohexane, it is preferable that a diol component is bonded to positions 1 and 4.

Of the alicyclic diols having 4 to 8 carbon atoms, 1,4-cyclohexanedimethanol (CHDM) is particularly preferable because it is easy to mix with a monomer price and a polyester resin (particularly PET). Used for.

The diol component in the present invention is not limited to a component existing as a diol, and includes a case where it is contained as a constituent component of a polyester, for example, a copolymer, or a mixture of these resins.

In the polyester film of the present invention, the content of the polyester (c2) is preferably 1.2 to 36% by mass with respect to the layer (B). More preferably, it is 1.9 to 30% by mass, still more preferably 2.4 to 26% by mass, and most preferably 3.3 to 20% by mass. If the content of the polyester (c2) is less than 1.2% by mass, the fine dispersion effect of the incompatible component (d) is lowered and the reflection performance is lowered, which is not preferable. On the other hand, if it exceeds 36% by mass, the heat resistance of the polyester film is lowered, and the dimensional change may be increased when exposed to high temperatures, which is not preferable. In the white polyester film of the present invention, when the content of the polyester (c2) is 1.2 to 36% by mass, a polyester film having film forming stability, reflectivity, and dimensional stability can be obtained.

[Incompatible component (d)]
The polyester film of the present invention needs to have air bubbles inside the layer (B) for whiteness and reflection properties, but is incompatible with the polyester (c) constituting the layer (B) (d ) And biaxially stretching, bubbles can be formed around the incompatible component (d). The bubbles formed in this manner exhibit a light scattering action, and a large number of bubbles exist throughout the polyester film, whereby the polyester film is whitened and high reflectance can be obtained.

In the present invention, the incompatible component (d) may be organic or inorganic, and both crystalline and amorphous are preferably used. Specific examples of the organic material include linear, branched, or cyclic polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, and cyclopentadiene. The polyolefin may be a homopolymer or a copolymer, and may be used in combination of two or more. Among these, polypropylene and polymethylpentene are preferably used as the crystalline polyolefin, and cycloolefin copolymer is preferably used as the amorphous polyolefin in terms of excellent transparency and heat resistance.

As specific examples of the inorganic substance, calcium carbonate, magnesium carbonate, titanium oxide, antimony oxide, magnesium oxide, barium carbonate, zinc carbonate, barium sulfate, calcium sulfate, aluminum oxide, silicon oxide (silica), and the like can be used. Among these, calcium carbonate, titanium oxide, barium sulfate, and silica are preferable from the viewpoints of long-term film-forming stability and improved reflection characteristics. These may be used alone or in combination of two or more. Further, it may be in the form of a porous or hollow porous material, and may be subjected to a surface treatment in order to improve the dispersibility with respect to the polyester within a range not impairing the effects of the present invention.

In the polyester film of the present invention, when an amorphous polyolefin is used as the incompatible component (d), a cycloolefin copolymer can be particularly preferably used. The cycloolefin copolymer is composed of at least one cycloolefin selected from the group consisting of cycloalkene, bicycloalkene, tricycloalkene, tetracycloalkene and pentacycloalkene, and linear olefin such as ethylene and propylene. It is a copolymer. The amorphous resin as used herein refers to a resin having a heat of crystal fusion of less than 1 cal / g.

Typical examples of the cyclic olefin in the cycloolefin copolymer include bicyclo [2,2,1] hept-2-ene, 6-methylbicyclo [2,2,1] hept-2-ene, and 5,6-dimethyl. Bicyclo [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 -There are en.

Also, representative examples of linear olefins in the cycloolefin copolymer include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene and the like.

In the present invention, the incompatible component (d) preferably has a glass transition temperature Tg of 170 ° C. or higher. More preferably, it is 180 degreeC or more. It is because it can disperse | distribute more finely in polyester (c) at the time of kneading | mixing by setting it as 170 degreeC or more, a bubble is formed in an extending process, and the loss | disappearance of the bubble in a heat treatment process can be suppressed more. The upper limit is preferably 250 ° C. If it exceeds 250 ° C., the extrusion temperature at the time of film formation becomes high and the processability may be inferior. In addition, if the glass transition temperature Tg of the incompatible component (d) is less than 170 ° C., the incompatible component (d) is deformed when the film is heat-treated to impart dimensional stability. In some cases, bubbles formed using the core as a nucleus are reduced or disappeared, and the reflection characteristics are deteriorated. In addition, if the heat treatment temperature is lowered to maintain the reflection characteristics, the dimensional stability of the film may be lowered in that case.

Further, when a cyclic olefin copolymer resin is used as the incompatible component (d), the linear olefin component is preferably an ethylene component from the viewpoint of reactivity.

Furthermore, as the cyclic olefin component, bicyclo [2,2,1] hept-2-ene (norbornene) and its derivatives are preferable from the viewpoint of productivity, transparency, and high Tg.

Also, when a cyclic olefin copolymer resin is used as the incompatible component (d), it is effective to add a dispersant to uniformly disperse the resin. Examples of the dispersant include, for polyester, polyalkylene glycol such as polyethylene glycol, methoxy polyethylene glycol, polytetramethylene glycol, and polypropylene glycol, ethylene oxide / propylene oxide copolymer, sodium dodecylbenzenesulfonate, and alkyl sulfonate. 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. Also, a copolymer of polybutylene terephthalate and polytetramethylene glycol is preferably used for improving the dispersibility of the incompatible component (d). The addition amount is preferably 3% by mass or more and 20% by mass or less, and particularly preferably 5% by mass or more and 15% by mass or less with respect to the total mass of the layer (B). If the amount of the dispersant added is too small, the effect of the addition is diminished, and if it is too large, the original properties of the film base material may be impaired. Such a dispersant can be added to the polymer constituting the layer (B) in advance to prepare a master polymer (master chip).

Therefore, in the present invention, when the polyester film layer (B) has the polyester resin (c) and the incompatible component (d), and the incompatible component (d) is an organic substance, the glass transition temperature Is preferably 170 ° C. or higher and 250 ° C. or lower. Furthermore, the incompatible component (d) is preferably amorphous, and more preferably (amorphous) cycloolefin copolymer.

In the present invention, the amount of the incompatible component (d) added is preferably 5 to 50% by mass when the total mass of the layer (B) is 100% by mass, and 5 to 30% by mass. It is more preferable. If the content of the incompatible component (d) is less than 5% by mass, sufficient bubbles are not generated inside the film, and the whiteness and light reflection characteristics may be inferior. On the other hand, when the content of the incompatible component (d) exceeds 50% by mass, the strength of the film is lowered, breakage during stretching tends to occur, and inconvenience such as generation of powder during post-processing occurs. There is a case. By setting the content within this range, sufficient whiteness, reflectivity, and lightness can be exhibited.

[Relative reflectance]
The polyester film of the present invention preferably has a relative reflectance of 102% or more. More preferably, it is 102.5% or more, More preferably, it is 103% or more. There is no particular upper limit for the relative reflectance, but in order to increase the reflectance, it is sufficient to increase the amount of the incompatible component (d) that becomes the bubble-forming nucleating agent, but the film forming property becomes unstable. Therefore, it is preferably 110% or less. Here, the relative reflectance means that an integrating sphere made of barium sulfate on the inner surface, a spectrophotometer equipped with a 10 ° inclined spacer, aluminum oxide as a standard white plate, and light incident at an incident angle of 10 °. Is a reflectance obtained by averaging the relative reflectance at a wavelength of 560 nm when the reflectance of the standard white plate is 100%. In the polyester film of the present invention, by setting the relative reflectance to 100% or more, a biaxially stretched film excellent in whiteness and reflection characteristics can be obtained, and particularly when used for a liquid crystal display device, a high luminance improvement is achieved. An effect can be obtained.

[Bubble formation]
Here, in order to adjust the relative reflectance of the polyester film of the present invention to the above-described range, it is preferable that the film is whitened by containing bubbles. Thereby, since the light scattering action is exhibited, the reflectance can be improved.

Formation of bubbles is achieved by finely dispersing the incompatible component (d) in the layer (B) and biaxially stretching it. During stretching, bubbles are formed around the incompatible component (d), and the number of interfaces between the bubbles and the substrate in the film thickness direction is preferably 15 or more per 10 μm film thickness, more preferably 20 or more, more preferably 25 or more. When the number of the interfaces is 15 or more, this exhibits light reflection and scattering action, so that it is whitened and high reflectance can be obtained. If the number of interfaces is less than 15, the light reflection and scattering actions are insufficient, and it is difficult to achieve whitening and high reflectivity.

[Film forming method]
As an example, the method for obtaining the polyester (a) will be described, but it is not limited to this example. Using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component, antimony trioxide (polymerization catalyst) was added to the resulting polyester pellets to 300 ppm in terms of antimony atoms, and a polycondensation reaction was performed. Polyethylene terephthalate pellets (polyester (a)) can be obtained. The Tg of the polyester (a) can be appropriately adjusted by the combination of the dicarboxylic acid component and the diol component described above and the copolymerization ratio thereof.

Next, as an example, a method for obtaining the polyester (b) will be described, but it is not limited to this example. Dimethyl terephthalate as the acid component, CHDM (cyclohexanedimethanol) and 2,2,4,4-tetramethyl-1,3-cyclobutanediol as the diol component, and 200 ppm of butyltin tris (2-ethylhexanoate) A polycondensation reaction can be carried out in the presence of Tg copolymerized polyester pellets (polyester (b)) at 116 ° C. The Tg of the polyester (b) can be appropriately adjusted by the combination of the dicarboxylic acid component and the diol component described above and the copolymerization ratio thereof. Specifically, it is polymerized by a known method (for example, see JP-T-2013-504650, JP-A-2012-219129, JP-T 2009-513801), or a commercial product (for example, , “ECOZEN” (manufactured by SK chemicals), “TRITAN” (manufactured by Eastman Chemical Company), “ALTERSTER” (manufactured by Mitsubishi Gas Chemical Co., Ltd.)) is obtained to obtain a polyester (b) having a desired Tg. be able to.

Next, as an example, a method for obtaining the polyester (c1) will be described, but it is not limited to this example. Using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component, antimony trioxide (polymerization catalyst) was added to the resulting polyester pellets to 300 ppm in terms of antimony atoms, and a polycondensation reaction was performed. Polyethylene terephthalate pellets (polyester (c1)) can be obtained.

Next, as an example, a method for obtaining the polyester (c2) will be described, but it is not limited to this example. Add terephthalic acid as the dicarboxylic acid component, alicyclic diol having 4 to 8 carbon atoms as the diol component, and magnesium acetate, antimony trioxide, phosphorous acid as the catalyst to add 300 ppm in terms of antimony atoms A polyester (c2) obtained by copolymerizing an alicyclic diol having 4 to 8 carbon atoms and terephthalic acid can be obtained by performing a polycondensation reaction.

Next, as an example, a method for obtaining the incompatible component (d) will be described, but the present invention is not limited to this example. The incompatible component (d) is obtained by polymerizing the above-described cycloolefin and olefin by a known method (for example, see JP-A No. 61-271308, International Publication No. 2007/060723) or being marketed. For example, “TOPAS” (manufactured by Polyplastics Co., Ltd.). Moreover, master pellets, such as polyester (a) containing the inorganic substance mentioned above, can be used.

Next, as an example, a method for obtaining a dispersant will be described, but the present invention is not limited to this example. The dispersant is a block copolymer of PBT (polybutylene terephthalate) and PAG (mainly polytetramethylene glycol), and has a melt index (MI) of 14 (2.160 g, 240 ° C.). The copolymerization ratio is butylene terephthalate: alkylene glycol = 70 mol%: 30 mol (for example, “Hytrel” (manufactured by Toray DuPont Co., Ltd.)).

Next, an example of the method for producing a biaxially stretched film of the present invention will be described, but the present invention is not limited to such an example.

For layer (A), polyester (a) and polyester (b), and a mixture containing various additives as necessary, are sufficiently vacuum dried and supplied to a heated extruder. The addition of the polyester (b) may be performed using a master chip prepared by uniform melt-kneading in advance, or may be directly supplied to a kneading extruder.

For the layer (B), the mixture containing the component (d) incompatible with the polyester (c) and a dispersant as necessary is sufficiently vacuum-dried and supplied to a heated extruder. The addition of the incompatible component (d) may be performed using a master chip prepared by melt-kneading uniformly in advance, or may be directly supplied to a kneading extruder.

In addition, it is preferable to melt-extrude, after filtering through a filter having a mesh of 40 μm or less, to introduce into a T-die die and obtain a molten sheet by extrusion molding.

The melted sheet is closely cooled and solidified by static electricity on a drum cooled to a surface temperature of 10 to 60 ° C. to produce an unstretched A / B / A three-layer film. The unstretched three-layer film is led to a group of rolls heated to 70 to 120 ° C., preferably 70 to 100 ° C., and the longitudinal direction (that is, the traveling direction of the film, sometimes referred to as “longitudinal direction”). Then, the film is stretched 2.5 to 4 times and cooled by a roll group having a temperature of 20 to 50 ° C.

Subsequently, the film is guided to a tenter while holding both ends of the film with clips, and in an atmosphere heated to a temperature of 90 to 150 ° C., a direction perpendicular to the longitudinal direction (referred to as “width direction” or “lateral direction”). May be stretched 2.5 to 4 times.

The draw ratio is 2.5 to 4 times in each of the longitudinal direction and the width direction, but the area ratio (stretch ratio in the longitudinal direction × stretch ratio in the width direction) must be 9 to 16 times. More preferably, it is ˜12 times. When the area magnification is less than 9 times, formation of bubbles and irregularities in the resulting polyester film and film strength are insufficient, and when the area magnification exceeds 16 times, tearing tends to occur during stretching.

In order to complete the crystal orientation of the obtained biaxially stretched film and impart dimensional stability, heat treatment is subsequently performed in a tenter at a temperature of 150 to 240 ° C. for 1 to 30 seconds, and after uniform cooling, The polyester film of the present invention can be obtained by cooling to room temperature, and then, if necessary, performing corona discharge treatment or the like in order to further improve the adhesion to other materials and winding. During the heat treatment step, it is preferable to perform a 3 to 12% relaxation treatment in the width direction or longitudinal direction.

In general, the higher the heat treatment temperature, the higher the thermal dimensional stability. Therefore, it is preferable that the film is formed at a high temperature (190 ° C. or higher). This is because the polyester film of the present invention may be used as a reflective film for a surface light source (backlight) mounted on a liquid crystal display or the like, and thus it is desired to have a certain thermal dimensional stability. Depending on the backlight, the internal atmospheric temperature may rise to about 100 ° C.

Further, the biaxial stretching method may be either sequential or simultaneous. Further, after biaxial stretching, the film may be re-stretched in either the longitudinal direction or the width direction.

The biaxially stretched film thus obtained preferably has a heat shrinkage measured by a method described later of 0.5% or less under the condition of treating at 80 ° C. for 30 minutes. When the thermal shrinkage rate exceeds 0.5% at 80 ° C., the film shrinks greatly when used as a reflector for a liquid crystal display, and the entire surface of the housing display cannot be covered. Since a dark part may arise in a part, it may be unpreferable.

The polyester film of the present invention preferably has a specific gravity of less than 1.2. When the specific gravity is within this range, 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 outstanding performance in terms of screen brightness. Moreover, it is preferable that it is 0.3 or more and less than 1.0, since it can reduce in weight, maintaining a mechanical characteristic.

The polyester film of the present invention has a concavo-convex shape that does not include particles such as inorganic substances in the layer (A) that forms the surface layer on at least one side, and does not use any post-process such as coating or embossing. In addition, when bubbles are formed inside the film, it has high reflectivity, is lightweight, and is used as a reflector for liquid crystal displays, particularly as a reflector for edge light type displays, it is compatible with other members, particularly light guide plates. And high luminance can be obtained. In particular, the layer (A) is preferably used in such a manner that the surface of the layer (A) faces the light guide plate. When used in such a manner, particularly high luminance can be obtained while suppressing unevenness in luminance.

The effect of the polyester film of the present invention is more effectively manifested when a concave or convex portion having a height of 5 μm or more is provided on the surface of the light guide plate in the edge light type backlight. Furthermore, when a concave portion or a convex portion having a size of 10 μm or more is provided, the effect is exhibited more significantly. The upper limit of the height of the concave and convex portions on the surface of the light guide plate is not particularly limited, but is preferably 100 μm or less because the effect is remarkably exhibited. More preferably, it is 60 μm or less.
[Measurement of physical properties and evaluation method of effects]
Measurement Method The physical property value evaluation method and effect evaluation method of the present invention are as follows.

A. Based on JIS B0601 (2001), the surface roughness layer (A) has a center line average roughness (Ra) and a ten-point average roughness (Rz) of Kosaka Laboratory, stylus type surface roughness meter ( Model No .: SE-3FA). The conditions were as follows, and the average value of five measurements was taken as the value.
・ Tip tip radius: 0.5μm
-Stylus load: 5mg
・ Measurement length: 0.8mm
Cut-off value: 0.08 mm.

B. Reflectance A spectrophotometer (U-3310) manufactured by Hitachi High-Technologies Co., Ltd. is attached with an integrating sphere, and the spectral reflectance on the surface of the polyester film layer (A) when the standard white plate (aluminum oxide) is 100% is 400 to 700 nm. Measure over. The reflectance is read from the obtained chart at intervals of 5 nm, and the average value is calculated to obtain the average reflectance.

C. Specific gravity of film A polyester film was cut into a size of 5 cm × 5 cm and measured using an electronic hydrometer SD-120L (Mirage Trading Co., Ltd.) based on JIS K7112 (1980). In addition, five sheets were prepared for each polyester film, each was measured, and the average value was used as the specific gravity of the polyester film.

D. Thermal shrinkage The polyester film is cut into a length (long side) 300 mm × width (short side) 20 mm with the direction to be measured as the length (long side) direction, and a test piece is formed at the center of the test piece at room temperature. A mark is attached at a distance of 200 mm (= L0). Here, the straight line connecting the two mark points is parallel to the long side. Next, the test piece is suspended vertically in a thermostat kept at 80 ° C. with one short side sandwiched between clips, and left for 30 minutes. Then, after cooling to the same room temperature, the distance (= L) between the test marks of a test piece is measured. The thermal contraction rate was calculated from the following formula from L and L0.
Thermal contraction rate (%) = {(L0−L) / L0} × 100.

E. Film-forming properties When the film is formed in Examples / Comparative Examples, film breakage occurs only once / day or less, and “AA” indicates that there is no process contamination due to particle dropping, etc., and film breakage occurs only once / day or less. “A” indicates that the accumulation of dirt on the roll surface can be confirmed with the naked eye, “B” indicates that film breakage occurs 2 times / day to 3 times / day, and “B” indicates that film breakage occurs 4 times / day. What occurred above was designated as “C”. For mass production, a film-forming property of “B” or more is necessary, and if it is “A” or more, there is a further cost reduction effect.

F. Glass transition temperature (Tg) of polyester
Using a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. according to JIS K7122 (1987), a disk session “SSC / 5200” was used for data analysis. The measurement was carried out as follows.

After peeling the polyester film into each layer using an adhesive tape or the like, 5 mg of the layer (A) is weighed in a sample pan and heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min. It was kept for a minute and then rapidly cooled to 25 ° C. or lower. Immediately thereafter, the temperature was increased again from room temperature to 300 ° C. at a rate of temperature increase of 20 ° C./min, and measurement was performed to obtain a differential scanning calorimetry chart.
Based on JIS K7121 (1987), the glass transition temperature of polyester (b) was determined according to the method for determining the midpoint glass transition temperature described in 9.3 (1) of JIS K7121 (1987). In other words, in the obtained differential scanning calorimetry chart, the glass transition temperature is the same as the step of the glass transition and the straight line equidistant in the vertical axis direction from the extended straight line of each base line in the stepwise change portion of the glass transition. It was obtained from the point where the curve of the change part intersects. When two or more of these points are observed, the point observed at 50 ° C. or higher and lower than 80 ° C. is the glass transition temperature of polyester (a), and the point observed at 100 ° C. or higher and 120 ° C. or lower is the glass of polyester (b). The transition temperature was used.

G. Compatibility with light guide plate (i) Scraping A 40-inch liquid crystal television (KDL-40EX700, manufactured by Sony Corporation) was disassembled, and an edge light type backlight using an LED as a light source was taken out. The size of the light emitting surface was 89 cm × 50 cm, and the diagonal length was 102.2 cm. The light guide plate was taken out from the backlight, and the light guide plate was cut into 5 cm square. A polyester film was stacked on the light guide plate so that the surface of the layer (A) of the polyester film was in contact with (opposed to) the light guide plate. Further, 500 g of a weight is placed thereon, and is reciprocated 3 cm × 5 so as to rub the surface of the polyester film of the present invention. Thereafter, the surface of the 5 cm square light guide plate that was in contact with the surface of the polyester film of the present invention was observed with a microscope, and the evaluation results were as follows.
“AA”: Excellent (no scratches visible)
“A”: Good (scratches are visible when observed closely)
“B”: Inferior (scratches are visible)
“C”: very inferior (strong scratches are visible)
The above “AA” and “A” were accepted.

(Ii) Luminance unevenness A new Hisense Japan Co., Ltd. 32-inch LCD TV LHD32K15JP The reflective film attached to the backlight was removed, changed to a polyester film, and turned on (here, the surface of the polyester film layer (A)) Was installed to face the light guide plate).
In this state, after waiting for 1 hour to stabilize the light source, what can be visually recognized as luminance unevenness in a 500 lx illumination environment or a dark environment was observed, and the following evaluation results were obtained. Note that the luminance unevenness referred to here is due to bright spots caused by contact between the reflective film and the light guide plate.
“AA”: Excellent (Uneven brightness in 500 lx lighting environment and dark environment)
“A”: Good (Uneven brightness in a dark environment of 500 lx is visible, but uneven brightness is not visible in a lighting environment.)
“B”: Inferior (Brightness unevenness is visible both in a 500 lx lighting environment and in a dark environment.)
“C”: Very inferior (A very strong uneven brightness can be seen both in a 500 lx lighting environment and in a dark environment.)
The above "AA" and "A" were accepted.

Hereinafter, the present invention will be described in more detail with reference to examples and the like, but the present invention is not limited thereto.

(material)
・ Polyester (a)
Using terephthalic acid as the acid component and ethylene glycol as the diol component, adding to the polyester pellets to obtain antimony trioxide (polymerization catalyst) to 300 ppm in terms of antimony atoms, conducting a polycondensation reaction, limiting viscosity Polyethylene terephthalate pellets (PET) having 0.63 dl / g and carboxyl end group amount of 40 equivalents / ton were obtained.

A polyethylene terephthalate / isophthalate copolymer (PETI) was obtained by adding isophthalic acid in the same manner.

Polybutylene terephthalate (PBT) was obtained by adding butanediol in the same manner.

Also, commercial products (for example, “VYLON” (Toyobo Co., Ltd.)) were used.

These Tg were 78 ° C for PET, 75 ° C for PETI, 60 ° C for PBT, and 47 ° C for VYLON.

・ Polyester (b)
Dimethyl terephthalate as the acid component, CHDM (cyclohexanedimethanol) and 2,2,4,4-tetramethyl-1,3-cyclobutanediol as the diol component, and 200 ppm of butyltin tris (2-ethylhexanoate) A polycondensation reaction was carried out in the presence to obtain a copolyester having a Tg of 116 ° C.

Commercially available products (for example, “ECOZEN” (manufactured by SK chemicals), “TRITAN” (manufactured by Eastman Chemical Company), “ALTERSTER” (manufactured by Mitsubishi Gas Chemical Company)) were used. These are characterized by a copolymer component constituting the diol component, for example, ECOZEN is an isosorbide component, TRITRAN is a 2,2,4,4-tetramethyl-1,3-cyclobutanediol component, and ALTERSTER is 3,9 -Bis (1,1-dimethyl-2-hydroxyethyl) -2,4,8,10-tetraoxaspiro [5.5] undecane component, each of which is a diol component having a cyclic skeleton Since it is bulky, it is considered that polyester has a high Tg. (In the table, ECOZEN is abbreviated as “ECZ”, TRITAN as “TRT”, and ALTERSTER as “AST”)
In the following examples and comparative examples, either “TRITA having a Tg of 108 ° C.” or “TRITAN having a Tg of 116 ° C.” was used as “TRITAN”. As “ECOZEN”, any one of “ECOZEN having a Tg of 100 ° C.”, “ECOZEN having a Tg of 120 ° C.”, and “ECOZEN having a Tg of 95 ° C.” was used. In addition, as “ALTERSTER”, any one of “ALTERSTER having a Tg of 100 ° C.”, “ALTERSTER having a Tg of 110 ° C.”, and “ALTERSTER having a Tg of 95 ° C.” was used.

・ Polyester (c)
Using terephthalic acid as the acid component and ethylene glycol as the glycol component, adding to the polyester pellets that can obtain antimony trioxide (polymerization catalyst) to 300 ppm in terms of antimony atoms, performing a polycondensation reaction, limiting viscosity Polyethylene terephthalate pellets (PET) having 0.63 dl / g and carboxyl end group amount of 40 equivalents / ton were obtained.

Also, CHDM (cyclohexanedimethanol) copolymerized PET was used in combination with PET. This is PET obtained by copolymerizing 60 mol% of cyclohexanedimethanol with the above-described method with respect to the glycol component (denoted as TPA / EG / CHDM in the table).

In some comparative examples, the copolymerized PET (TPA / EG / CHDM) was also used as polyester (a) or polyester (b).

Incompatible component (d)
A cycloolefin copolymer “TOPAS” (manufactured by Polyplastics Co., Ltd.) having a glass transition temperature of 180 ° C. was used (described as COC in the table).

For titanium oxide and barium sulfate, titanium oxide master pellets sold by DIC Corporation or the like were used (the base resin is polyester (c) PET).

-Dispersant PBT-PAG (polybutylene terephthalate-polyalkylene glycol) copolymer was used (product name: Hytrel, manufactured by Toray DuPont Co., Ltd.). The resin is a block copolymer of PBT (polybutylene terephthalate) and PTMG (mainly polytetramethylene glycol), and has a melt index (MI) of 14 (2.160 g, 240 ° C.). The copolymerization ratio is butylene terephthalate: alkylene glycol = 70 mol%: 30 mol% (described as PBT / PTMG in the table).

(Examples 1 to 19, 21, 23 to 26)
In a composite film forming apparatus having a main extruder and a sub-extruder, the raw material mixture shown as the layer (B) in Table 1 was vacuum-dried at a temperature of 180 ° C. for 3 hours, and then supplied to the main extruder side. After melt extrusion at a temperature of 0 ° C., the mixture was filtered through a 30 μm cut filter and then introduced into a T-die composite die. On the other hand, the raw material mixture shown as layer (A) in Table 1 was vacuum-dried at a temperature of 180 ° C. for 3 hours, then supplied to a sub-extruder, melt-extruded at a temperature of 280 ° C., and filtered through a 30 μm cut filter. After that, it was introduced into a T-die composite die. Next, in the T-die composite die, the layers (A) extruded from the sub-extruder were joined so as to be laminated (A / B / A) on both sides of the layer (B) extruded from the main extruder. Thereafter, it was co-extruded into a sheet to obtain a molten laminated sheet, and the molten laminated sheet was closely cooled and solidified by an electrostatic charge method on a drum maintained at a surface temperature of 20 ° C. to obtain an unstretched laminated film. Subsequently, the unstretched laminated film is preheated with a group of rolls heated to 85 ° C. according to a conventional method, and then stretched so that the area ratio is as shown in Table 1 in the longitudinal direction (longitudinal direction) using a 90 ° C. heated roll. And cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film.

While holding both ends of the obtained uniaxially stretched film with clips, it is led to a preheating zone at a temperature of 95 ° C. in the tenter, and continuously in a heating zone at a temperature of 105 ° C. in a direction perpendicular to the longitudinal direction (width direction). The film was stretched so that the area ratio was as shown in Table 1. Subsequently, a heat treatment was performed at 125 ° C. for 20 seconds in a heat treatment zone in the tenter, and further a relaxation treatment (relaxation rate: 4%) was performed at a temperature of 180 ° C., and then at a temperature of 140 ° C. Relaxation treatment (relaxation rate: 1%) was performed in the width direction. Then, after uniform cooling, it was wound up to obtain a polyester film. The various characteristics are shown in Table 1. As described above, the polyester film of the present invention was able to be stably formed, and exhibited excellent properties such as reflectivity, lightness, surface shape (reduction in luminance unevenness, good compatibility with the light guide plate), and thermal dimensional stability.

(Examples 20 and 22)
A polyester film was obtained in the same manner as in Examples 1 to 19 except that the layer (A) extruded from the sub-extruder was laminated (B / A) to the layer (B) extruded from the main extruder. It was. The various characteristics are shown in Table 1. As described above, the polyester film of the present invention was able to be stably formed, and exhibited excellent properties such as reflectivity, lightness, surface shape (reduction in luminance unevenness, good compatibility with the light guide plate), and thermal dimensional stability.

(Comparative Examples 1 to 16)
In a composite film-forming apparatus having a main extruder and a sub-extruder, an attempt was made to form a polyester film in the same manner as in Example 1 using the mixture and conditions of the raw materials shown in Table 2. Comparative Examples 2, 7, and 9 , 13 could not be formed into a film. Various characteristics are shown in Table 2. For the examples other than Comparative Examples 2, 7, 9, and 13 (except for Comparative Example 16), the surface shape was flat compared to the examples, and Ra and Rz were within the scope of the present invention. It was outside. When the compatibility with the light guide plate was examined, it was not scraped, but the unevenness was insufficient, the polyester film and the light guide plate were in close contact, and uneven brightness occurred. In Comparative Example 16, no luminance unevenness occurred, but the luminance was remarkably low due to the low reflectance, which was not practical at all.

The polyester film of the present invention is economical, film-forming, white, reflective, lightweight, and has a surface shape. By using this polyester film, a surface light source excellent in luminance characteristics and compatibility with other members is inexpensive. Can be provided.

The polyester film of the present invention can be applied to uses that require whiteness, reflectivity, concealment, and thermal dimensional stability, but as a particularly preferred use, a plate-like material incorporated in a surface light source for light reflection Can be given. Specifically, it is preferably used for an edge light reflector for a liquid crystal screen, a reflector for a direct type light, and a cold cathode ray tube or a reflector around LED illumination.

Claims

A polyester (a) having a glass transition temperature (Tg) of 50 ° C. or more and less than 80 ° C. and 10 to 90% by mass; and a polyester (b) having a Tg of 100 ° C. or more and 120 ° C. or less and 10 to 90% by mass. a difference in Tg between a) and polyester (b) is 50 ° C. or less, and a layer (A) substantially free of inorganic and organic particles;
Having a layer (B) comprising polyester (c) and at least one component (d) incompatible with the polyester (c);
A biaxially stretched polyester film in which the layer (A) is at least one surface, the centerline average roughness (Ra) of this surface is 300 nm or more, and the ten-point average roughness (Rz) is 3000 nm or more.
The biaxially stretched polyester film according to claim 1, wherein the polyester (a) is polyethylene terephthalate.
The biaxially stretched polyester film according to claim 1 or 2, wherein the polyester (b) comprises a diol having a cyclic skeleton as a diol component.
The biaxially stretched polyester film according to any one of claims 1 to 3, wherein the polyester (b) uses 2,2,4,4-tetramethyl-1,3-cyclobutanediol as a diol component.
A reflector for a liquid crystal display using the biaxially stretched polyester film according to any one of claims 1 to 4.