JP5342437B2 - Polyester film for brightness enhancement members - Google Patents

Description

  The present invention relates to a polyester film suitable for a brightness enhancement member.

  As a brightness enhancement film, BEF (Brightness Enhancement Film: manufactured by 3M), a reflective polarizing film, and DBEF (Dual Brightness Enhancement Film: manufactured by 3M) are known as liquid crystal related members that play a role of improving brightness. Widely used from mobile phones to LCD TVs. According to these films, for example, in a liquid crystal TV, the amount of backlight, the number of lights, and the number of LEDs can be reduced, which has an environmental advantage.

  However, these films have concerns such as high price and supply stability. Although these alternative products have been studied, a film having satisfactory characteristics as a brightness enhancement film has not yet been completed.

  There are several ways to achieve brightness enhancement, such as BEF and DBEF. For example, a method that uses reflection of light by imparting the shape of the polymer surface with a mold (BEF), a method that imparts a super-laminated structure to the film (DBEF), and a recycling of light that is incident and not transmitted as it is There are various methods of applying and aligning various nematic liquid crystals, cholesteric liquid crystals, and the like on polymers.

  The method of applying a liquid crystal to a polymer is advantageous in terms of price and supply stability, but the control of the alignment between the polymer surface and the liquid crystal in contact with the polymer surface is the key.

  Usually, polyimide is generally used as a member for applying alignment liquid crystal such as nematic liquid crystal or cholesteric liquid crystal, and the key is surface treatment performed for alignment control, for example, rubbing treatment. When a polyester film is used as an alternative film, the liquid crystal cannot be well aligned due to the difference in orientation with the polyimide after the surface treatment, for example, after the rubbing treatment, or the appearance of uneven or streaky The occurrence of defects is a problem.

  These problems can be solved by creating a special surface state because the state of the outermost surface of the polyester film as the base material is the key. For example, rubbing by changing the crystallinity by devising the film forming conditions, and changing the surface hardness of the film by devising the type and content of the particles containing the surface hardness The treatment can be performed most effectively, and the liquid crystal can be well aligned.

  However, rubbing treatment at a production site for a polyester film having a high degree of cleanliness causes generation of dust and the like. In addition, the number of processes increases and the productivity is poor, and the rubbing process is very precise and difficult to fine tune, resulting in a poor yield.

JP 2003-26831 A

  The present invention has been made in view of the above-mentioned circumstances, and the problem to be solved is a rubbing treatment method that can control alignment when liquid crystal is applied, does not cause unevenness and streak-like defects, and is a conventional method. It is in providing the polyester film suitable as a film for brightness improvement members with a high yield compared with these.

  As a result of intensive studies in view of the above circumstances, the present inventor has found that the above problem can be easily solved by a polyester film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention resides in a polyester film for a brightness enhancement member, characterized in that 0.15 to 1.20% by weight of azobenzenes is contained in at least one outermost layer of a polyester film having a laminated structure.

  According to the polyester film of the present invention, it is possible to control the orientation at the time of applying the liquid crystal, and to produce a polyester film that can be suitably used as a film for a brightness enhancement member that does not cause unevenness or streak-like defects at low cost and yield. It can be provided well and its industrial value is high.

Hereinafter, the present invention will be described in more detail.
The polyester film constituting the polyester film of the present invention may have a single layer structure or a multilayer structure, and may have four or more layers as long as it does not exceed the gist of the present invention other than a two-layer or three-layer structure. It may be a multilayer, and is not particularly limited.

  The polyester used in the polyester film of the present invention is preferably a homopolyester as a result of pursuing reduction of production costs and ease of process work. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Typical polyester includes polyethylene terephthalate and the like.

  In the polyester film of the present invention, it is preferable to blend particles for the main purpose of imparting slipperiness and preventing scratches in each step. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples of the particles include magnesium, kaolin, aluminum oxide, and titanium oxide. Further, heat-resistant organic particles as described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  Moreover, the average particle diameter of the particle | grains to be used is 0.01-3 micrometers normally, Preferably it is the range of 0.1-2 micrometers. When the average particle size is less than 0.01 μm, the slipperiness may not be sufficiently imparted. On the other hand, when the thickness exceeds 3 μm, transparency may be lowered due to the aggregate of the particles when the film is formed, and it is easy to cause breakage, which causes a problem in terms of productivity. There is.

  Furthermore, the particle content in the polyester film in the present invention is usually in the range of 0.001 to 5% by weight, preferably 0.005 to 3% by weight. When the particle content is less than 0.001% by weight, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 5% by weight, the transparency of the film is insufficient. There is a case.

  The method for adding particles to the polyester film in the present invention is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester constituting each layer, but it is preferably added after completion of esterification or transesterification.

  Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  In addition to the above-mentioned particles, conventionally known antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments, and the like can be added to the polyester film in the present invention as necessary.

  Although the thickness of the polyester film in this invention will not be specifically limited if it can be formed into a film as a film, Usually, 10-350 micrometers, Preferably it is the range of 50-250 micrometers.

  Next, although the manufacture example of the polyester film in this invention is demonstrated concretely, it is not limited to the following manufacture examples at all. That is, a method of using the polyester raw material described above and cooling and solidifying a molten sheet extruded from a die with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, the film is stretched in the direction perpendicular to the first stretching direction. In that case, the stretching temperature is usually 70 to 170 ° C., and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times. is there. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  For the production of the polyester film of the present invention, a simultaneous biaxial stretching method can also be employed. The simultaneous biaxial stretching method is a method in which the above-mentioned unstretched sheet is usually stretched and oriented in the machine direction and the width direction at a temperature controlled normally at 70 to 120 ° C., preferably 80 to 110 ° C. Is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area magnification. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, a conventionally known stretching method such as a screw method, a pantograph method, or a linear driving method can be employed.

  Examples of azobenzenes used in the present invention include azobenzene, 2-methoxyazobenzene, 2-hydroxyazobenzene, 3-methylazobenzene, 3-nitroazobenzene, 3-methoxyazobenzene, 3-hydroxyazobenzene, 4-iodoazobenzene, 4 -Methylazobenzene, 4-carbomethoxyazobenzene, 4-acetylazobenzene, 4-carboxyazobenzene, 4-cyanoazobenzene, 4-ethoxyazobenzene, 4-methoxyazobenzene, 4-nitroazobenzene, 4-acetamidoazobenzene, 4-dimethylaminoazobenzene 4-aminoazobenzene, 4-trimethylammonium azobenzene, 4-dimethylamino-4′-phenylazobenzene, 4-dimethylamino-4′-hydroxyl Zobenzene, 4,4′-bis- (dimethylamino) azobenzene, 4-dimethylamino-4′-p-aminophenylazobenzene, 4-dimethylamino-4′-p-acetamidophenylazobenzene, 4-dimethylamino-4 ′ -P-aminobenzylazobenzene, 4-dimethylamino-4'-mercuric acetate azobenzene, 4-hydroxyazobenzene, 2-methyl-4-hydroxyazobenzene, 4-hydroxy-4'-methylazobenzene, 2,6-dimethyl- 4-hydroxyazobenzene, 2,2′-4 ′, 6,6′-pentamethyl-4-hydroxyazobenzene, 2,6-dimethyl-2 ′, 4 ′, 6′-trichloro-4-hydroxyazobenzene, 4-hydroxy -4'-chloroazobenzene, 2,2 ', 4', 6 '-Tetrachloro-4-hydroxyazobenzene, 3-sulfonate-4-hydroxyazobenzene, 2,2'-dimethoxyazobenzene, 3,3'-dinitroazobenzene, 3,3'-dimethylazobenzene, 4,4'-dimethylazobenzene 4,4′-dimethoxyazobenzene and the like.

  Next, the kneading of azobenzenes into polyester in the present invention will be described. These compounds are preferably used as a masterbatch kneaded into a polyester resin, but may be added directly to the polyester resin. The content of at least one compound selected from the above listed compounds in the film is in the range of 0.15 to 1.20% by weight in at least one outermost layer of the polyester film having a laminated structure. When the content is less than 0.15% by weight, when the alignment liquid crystal is applied, the application is not successful, and unevenness, streaks, etc. are generated, resulting in poor appearance. On the other hand, when the content exceeds 1.50% by weight, the film is considerably yellowish, and a defect such as deterioration or aggregation occurs in the film. In addition, when extruded at a high temperature of 290 ° C. or higher, the boiling point of azobenzene is reached, causing a problem in decomposition or kneading amount.

  Furthermore, about the polyester film of this invention, the layer structure of the kneading | mixing of azobenzene is demonstrated. In order to align the oriented liquid crystal on the polyester film, the design of the surface state of the outermost layer is the key, so azobenzenes must be kneaded into the outermost layer of the polyester film.

  Since the polyester film of the present invention requires alignment liquid crystal coating in a subsequent step, the surface condition for controlling the alignment is an important point. The necessary surface conditions of the present invention include the inclusion of molecules that control the sequence, in this case azobenzenes. As the content method, kneading and coating can be considered. However, coating is not preferable in the polyester film of the present invention. In this brightness enhancement member use polyester film, there is a step of applying a liquid crystal in the subsequent step, and in this step, it is common to use a method by lyotropic and thermotropic, and in the lyotropic method, a solvent is used. After the components of the coating layer are dissolved, there is a high possibility that the components will aggregate and cause surface defects such as unevenness in the film surface. In the present invention, a kneading method is used as a method of incorporating azobenzenes into the polyester.

  With respect to the polyester film of the present invention, in a method of applying an oriented liquid crystal after a rubbing treatment method, which is a conventional method as a film for improving luminance, a yield of about 50% is at most 80%. Therefore, the concept of yield is important when considering productivity, and the method of kneading azobenzenes capable of orientation control of the present invention aims to achieve a yield of 80% or more.

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

(1) Measurement of intrinsic viscosity of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. It was dissolved and measured at 30 ° C.

(2) Measurement of transmittance of polyester film As a reference for transparency, evaluation of transparency by visual observation and transmittance measurement can be mentioned. Judgment is based on the following criteria.
・ Regarding visual observation ○: Almost transparent Δ: Transparent but slightly colored yellow ×: Yellow is strong and cloudy The total light transmittance of the polyester film was measured with a spherical turbidimeter NDH-300A. Judgment is based on the following criteria.
○: Transmittance of 88.7% or more Δ: Transmittance in the range of 88.0-88.6% ×: Transmittance lower than 88.0%

(3) Haze (turbidity) measurement of polyester film The total light transmittance of the polyester film was measured with an integrating sphere turbidimeter NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K7105. Judgment is based on the following criteria.
○: Lower value than 1.8% △: 1.8-2.0%
X: Value is higher than 2.0%

(4) Appearance Evaluation after Applying Liquid Crystal to Polyester Film The polyester film was inspected by using general liquid crystal to determine whether or not the oriented liquid crystal can be aligned. Evaluation was performed according to the following criteria.
○: No irregularities or streaks and clean surface shape Δ: Unevenness or stripes visible ×: Liquid crystal alignment film is not aligned or surface shape is terrible

(5) Yield after application of liquid crystal ○: Yield 80% higher ×: Yield lower than 80%

The polyester used in the examples and comparative examples was prepared as follows.
<Method for producing polyester (A)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 part by weight of ethyl acid phosphate to this reaction mixture, 0.04 part by weight of antimony trioxide was added, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (A) was 0.63.

<Method for producing polyester (B)>
In the method for producing polyester (A), 0.04 part by weight of ethyl acid phosphate was added, and then 0.2 part by weight of silica particles having a Mohs hardness of 5 dispersed in ethylene glycol having an average particle diameter of 2.0 μm, trioxide Polyester (B) was obtained using the same method as the production method of polyester (A), except that 0.04 part by weight of antimony was added and the polycondensation reaction was stopped at a time corresponding to an intrinsic viscosity of 0.65. . The obtained polyester (B) had an intrinsic viscosity of 0.65.

<Polyester (C): 1.5 wt% azobenzene-containing masterbatch (MB) production method>
When producing the polyester (A), 1.5 parts by weight of an azobenzene compound was kneaded at the time of extrusion at 275 ° C. with respect to 98.5 parts by weight of the polyester. The obtained 1.5 wt% MB had an intrinsic viscosity of 0.63.

Example 1:
A mixed raw material in which polyesters (A), (B), and (C) are mixed in proportions of 52%, 8%, and 40%, respectively, is used as a raw material for the outermost layer (surface layer), and polyester (A) is used as a raw material for the intermediate layer. Each was supplied to two extruders, melted at 275 ° C., and then extruded from a die and placed on a cooling roll having a surface temperature set to 40 ° C. by using an electrostatic application adhesion method. A non-stretched sheet was obtained by coextrusion and cooling and solidification in a layer configuration of (intermediate layer / surface layer). Next, the film was stretched 3.7 times in the machine direction at a film temperature of 85 ° C. using the roll peripheral speed difference, led to a tenter, stretched 4.3 times at 120 ° C. in the transverse direction, and heat-treated at a heat setting temperature of 235 ° C. After that, a polyester film having a thickness of 250 μm (surface layer: 12.5 μm, intermediate layer: 225 μm) having an application layer and an intrinsic viscosity of 0.61 was obtained. About the obtained polyester film, scratches and fogging were visually beautiful with no change from before the treatment. Furthermore, about this polyester film, the orientation liquid crystal melt | dissolved in chloroform was apply | coated, and it adjusted so that a liquid-crystal layer might be 0.03 g / m < ² > after drying. When the obtained polyester film after application of the liquid crystal layer was visually evaluated, no streak or unevenness was observed and the polyester film was beautiful. Examples of the compounds constituting the liquid crystal layer are as follows.

(Example compounds)
・ Nematic liquid crystal (ZLI-2293: Merck)
Chiral dopant (MLC-6248: Merk)
Photopolymerizable liquid crystal (RM257: Merck)
QtT (Quarter Thiophene)
cf. K. AMEMIYA et. al. , Applied Physics, Vol. 44, no. 6A, 2005, pp. 3748-3750

Examples 2-4:
In Example 1, it manufactured like Example 1 except changing the compounding quantity of the azobenzene compound of a surface layer, and obtained the polyester film. The produced polyester film was as shown in Table 1 below.

Comparative Examples 1-4:
In Example 1, it manufactured like Example 1 except changing the compounding quantity of the azobenzene compound of a surface layer, and obtained the polyester film. Although the produced polyester film is as showing in Table 2, when the obtained polyester film after liquid crystal layer application | coating was evaluated visually, it was not able to orientate and the surface shape was not good. In Comparative Example 4, the color of the film before applying the liquid crystal was yellowish and the turbidity was not good. However, the appearance after applying the oriented liquid crystal was beautiful without streaks or unevenness.

  The polyester film of the present invention can be suitably used for a brightness enhancement member.

Claims (1)

A polyester film for a brightness enhancement member comprising 0.15 to 1.20% by weight of azobenzene in at least one outermost layer of a polyester film having a laminated structure.