JP3946183B2 - White polyester film - Google Patents

Description

  The present invention relates to a white polyester film, and relates to a white polyester film having high reflectance and gloss.

  In the past, a backlight system in which light is applied from the back of the display has been adopted in liquid crystal displays. However, in recent years, the sidelight system as disclosed in JP-A-63-62104 is thin and can be illuminated uniformly. , Has come to be widely used. This sidelight method is a method of illuminating a cold cathode tube or the like from an edge of an acrylic board or the like with a certain thickness. For halftone printing, the illumination light is evenly distributed and has a uniform brightness. A screen is obtained. This method can be made thinner than the backlight method because the lighting is installed not at the back of the screen but at the edge. In this case, it is necessary to install a reflector on the back of the screen in order to prevent the illumination light from escaping to the back of the screen. Adhesion is usually performed in order to fix the reflection plate in the liquid crystal display device. Therefore, the reflection plate is required to have high light reflectivity and high light diffusibility as well as adhesion.

  As a method of obtaining a polyester film suitable for a liquid crystal display reflector that meets this purpose, a method of incorporating titanium oxide is known. This is a method that can be made relatively inexpensive. For example, it is described in Japanese Patent Publication No. 8-16175. However, the reflectance and diffusivity cannot be adjusted sufficiently by simply adding an incompatible resin and titanium oxide. As a result, the LCD display is not bright enough and the surface gloss is adjusted. The reflectance will change, and if there are defects in the light spots on the backlight or the film, it will be noticeable as a defect. Furthermore, the adhesiveness is also changed, and there is a disadvantage that a surface treatment for adhesion is required for installation in the liquid crystal display device.

  In addition, when high concentration of inorganic fine particles such as titanium oxide is added, it can be expected that the reflection efficiency is improved. For example, when 50% by weight is added, the concentration of inert particles is so high that the film breaks frequently and forms a film. It is very difficult to do. As a practical means of reducing the frequency of breakage when the inert particle concentration is very high, a method using a copolymerized polyester can be used, but compared with a case where a polyester that is not substantially copolymerized is used. Only a film with a very high thermal shrinkage and poor thermal dimensional stability can be obtained.

JP-A-4-153232 JP-A-6-322153 JP 63-62104 A Japanese Patent Publication No. 8-16175

  The present invention has an object to solve the problems of the prior art, has a practically sufficient reflection performance in the visible light region, can control the glossiness of the front and back surfaces of the film, and is installed by bonding as it is. Reflective plate for liquid crystal displays and interior lighting signboards that can be stably formed even when inorganic fine particles are added at high concentration, and is stable against dimensional changes due to heat from the light source. An object of the present invention is to provide a white polyester film that can be suitably used as a base material for an automobile.

The inventors of the present invention have arrived at the present invention as a result of intensive studies on a white polyester film. That is, the present invention is a white polyester film that substantially does not contain a resin that is incompatible with the polyester constituting the film, and the average reflectance at a wavelength of 400 to 700 nm is 90% or more for at least one surface of the film. The white polyester film has a difference in glossiness (60 °) between one side and the other side of the film of 5 to 80.

Hereinafter, the present invention will be described in detail.
[polyester]
The white polyester film of the present invention comprises a polyester resin composition containing polyester and inorganic particles.

  As the polyester, a polyester composed of a dicarboxylic acid component and a diol component is used. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, adipic acid, and sebacic acid. Examples of the diol include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and 1,6-hexanediol. Of these polyesters, polyester polyethylene terephthalate is preferred.

  As the polyester, a copolyester is preferable because a stable film can be formed even when high concentration inorganic fine particles are added. As this copolyester, a polyester having a melting point of 250 ° C. or lower, preferably 245 ° C. or lower, more preferably 240 ° C. or lower may be used. As the copolymer component, dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodium sulfoisophthalic acid can be used, and diethylene glycol, neopentyl glycol, poly Diol components such as alkylene glycol can be used. When copolymerized polyethylene terephthalate is used, isophthalic acid, naphthalenedicarboxylic acid, and cyclohexanedimethanol are preferred as the copolymerization component.

  The ratio of the copolymerization component is preferably 1 to 30 mol%, more preferably 3 to 25 mol, further preferably 5 to 20 mol%, and particularly preferably 7 to 15 mol% per total dicarboxylic acid component. If it is less than 1 mol%, the layer containing inorganic fine particles, for example, a film containing 10% by weight or more of inorganic particles has a high stretching stress and may not be formed. If it exceeds 30 mol%, there is a possibility that the film lacks thermal dimensional stability, or even a film cannot be formed, and the roughness for adjusting the surface diffused light may not be adjusted. .

  Various known additives such as an antioxidant, an antistatic agent and an ultraviolet absorber may be added to the polyester.

[Inorganic fine particles]
The white polyester film of the present invention is 10 to 80% by weight, preferably 15 to 70% by weight, more preferably 20 to 60% by weight, particularly preferably 100% by weight of inorganic fine particles per 100% by weight of the resin composition constituting the film. Contains 25 to 55 weights. When the content of the inorganic fine particles is less than 10% by weight, necessary reflected light and whiteness cannot be obtained. If the content of the inorganic fine particles exceeds 80% by weight, cutting is likely to occur during film formation. As the inorganic fine particles, at least one kind of inorganic fine particles selected from the group consisting of titanium oxide, barium sulfate, calcium carbonate, and silicon dioxide is preferable. Of the titanium oxides, the rutile type is preferable because it has less yellowing after being irradiated on the polyester film for a longer time than the anatase type and is suitable for suppressing changes in color difference.

  The average particle size of the inorganic fine particles is preferably 0.1 to 3.0 μm, more preferably 0.2 to 2.5 μm, and further preferably 0.3 to 2.0 μm. When the average particle size is less than 0.1 μm, the dispersibility becomes extremely poor, and the particles are aggregated. Therefore, troubles in the production process are likely to occur, and coarse protrusions are formed on the film, resulting in a film with poor gloss. If it exceeds 3.0 μm, the surface of the film becomes rough and gloss is lowered, and it is difficult to control the gloss to an appropriate range.

  Among inorganic fine particles, rutile titanium oxide, in particular, can improve the glossiness of the film when treated with a fatty acid such as stearic acid and its derivatives in order to improve dispersibility. preferable.

  In addition, when using a rutile type titanium oxide, it is preferable to perform a particle size adjustment and coarse particle removal using a refinement | purification process, before adding to polyester. As industrial means of the purification process, for example, a jet mill or a ball mill can be applied as a pulverizing means, and as a classification means, for example, dry or wet centrifugation can be applied. In addition, these means may combine 2 or more types and refine | purify in steps.

  Moreover, various methods can be used as a method of incorporating inorganic fine particles into polyester. The following method can be mentioned as the typical method. (A) A method of adding before transesterification or esterification reaction at the time of polyester synthesis or adding before the start of polycondensation reaction. (A) A method of adding to polyester and melt-kneading. (C) A method of producing master pellets to which a large amount of inert particles are added in the method (a) or (b) above, and kneading these with a polyester not containing an additive to contain a predetermined amount of additive. (D) A method of using the master pellet of (c) as it is.

In addition, when using the method added at the time of the said polyester synthesis | combination of (a), it is preferable to add to a reaction system as a slurry disperse | distributed to glycol in titanium oxide.
In the present invention, it is particularly preferable to take the above method (c) or (d).

  In general, inorganic fine particles often aggregate to become coarse aggregated particles. In the present invention, in order to reduce the number of coarse agglomerated particles, a non-woven filter having an average opening of 10 to 100 μm, preferably an average opening of 20 to 50 μm, made of a stainless steel fine wire having a wire diameter of 15 μm or less is used as a filter during film formation. It is preferred to filter the molten polymer.

[Additive]
In the polyester composition, as additives, aluminum oxide, magnesium oxide, acrylic resin, urea resin, organic filler such as melamine resin, other resins such as polyethylene, polypropylene, ethylene-propylene terpolymer, olefinic ionomer, Antioxidants, ultraviolet absorbers, fluorescent brighteners, and the like can be mixed as necessary without departing from the scope of the present invention.

  When using a fluorescent brightening agent, the fluorescent brightening agent is preferably added in a range of 0.005 to 0.2% by weight, more preferably 0.01 to 0.1% by weight as a concentration relative to the polyester composition. Then finally. If the addition amount of the fluorescent brightening agent is less than 0.01% by weight, the reflectance in the wavelength region near 350 nm is not sufficient, and the illuminance is not sufficient when the reflector is used. If it exceeds 0.2% by weight, a specific color of the fluorescent whitening agent appears, which is not preferable. As the fluorescent brightening agent, for example, OB-1 (manufactured by Eastman), Uvitex-MD (manufactured by Ciba Geigy), or JP-Conc (manufactured by Nippon Chemical Industry Co., Ltd.) can be used.

  Moreover, it is preferable that the white polyester film of this invention does not contain substantially resin incompatible with the polyester which comprises a film. A white polyester film that contains an incompatible resin and is designed for reflectivity and whiteness with voids at the interface changes the formation of voids when the stretching temperature is changed to provide a difference in glossiness on both sides. May affect reflectivity and whiteness.

[Film formation]
The white polyester film in the present invention may be a single layer film composed of a single layer or a laminated film composed of a plurality of layers. In the case of a plurality of layers, for example, a two-layer configuration of A layer / B layer may be employed, or a three-layer configuration of A layer / B layer / A layer or A layer / B layer / C layer may be employed. Further, a configuration of four or more layers including these configurations may be used.

  Considering the easiness and effect on film formation, the form of single layer or two layers or three layers comprising A layer / B layer / A layer is particularly good. Moreover, in order to provide other functions to one side or both sides of the film, a laminate in which other layers are further laminated may be used. Examples of the other layers include transparent polyester films, metal thin films, hard coat layers, and ink receiving layers.

  An example of the method for producing the film of the present invention will be described. In the case of a single layer film, an unstretched sheet is produced by extruding a molten polymer from a die. In the case of a laminated film, a laminated unstretched sheet is produced by a simultaneous multilayer extrusion method using a feed block. That is, the polymer melt for forming the A layer and the polymer melt for forming the B layer are laminated using a feed block so as to be A layer / B layer / A layer, and then developed on a die and extruded. To do. At this time, the polymer laminated by the feed block maintains the laminated form.

  The unstretched sheet extruded from the die is cooled and solidified by a casting drum to form an unstretched film. This unstretched film is heated by roll heating, infrared heating or the like, and stretched in the longitudinal direction to obtain a longitudinally stretched film. This stretching is preferably performed by utilizing the difference in peripheral speed between two or more rolls. The stretching temperature is preferably a temperature equal to or higher than the glass transition point (Tg) of the polyester, and more preferably a temperature higher by Tg to 70 ° C.

  The higher the stretching temperature on the film surface side to be adjusted, the rougher the film surface of this configuration, and the lower the stretching temperature, the more the film surface goes in the direction of flattening. It is possible to adjust the glossiness on the film surface, that is, the diffused light, and the glossiness range described in this description can be substantially reduced without changing the film color, reflectance, thermal dimensional stability, etc. or the composition of the film. realizable.

  The glossiness of the white polyester film of the present invention is such that the difference in glossiness between one side and the other side of the film is 5 to 80, preferably 7 to 75, more preferably 10 to 70. If the difference between the front and back surfaces exceeds 80, the temperature difference between the front and back surfaces of the film becomes too large, and in the case of stretch spots or severe damage, the film may be broken. If the difference between the front and back sides is less than 5, it deviates from the range that can be commonly used for the receiving sheet and the reflector sheet, and it is not preferable because it does not have sufficiently good adhesiveness.

  The draw ratio is preferably 2.5 to 4.0 times, more preferably 2.8 to both the longitudinal direction and the direction orthogonal to the longitudinal direction (hereinafter referred to as the transverse direction), although depending on the required characteristics of the application. 3.9 times. If it is less than 2.5 times, the thickness unevenness of the film is deteriorated and a good film cannot be obtained, and if it exceeds 4.0 times, breakage tends to occur during film formation, which is not preferable.

  Subsequently, the film after longitudinal stretching is subjected to lateral stretching, heat setting, and thermal relaxation in order to form a biaxially oriented film. These processes are performed while the film is running. The transverse stretching process starts from a temperature higher than the glass transition point (Tg) of the polyester. And it is performed while raising the temperature to (5 to 70) ° C. higher than Tg. Although the temperature rise in the transverse stretching process may be continuous or stepwise (sequential), the temperature is usually raised sequentially. For example, the transverse stretching zone of the tenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium having a predetermined temperature for each zone. As described in the previous longitudinal stretching, the state of the film surface can be adjusted by adjusting the stretching temperature even at the lateral stretching temperature. However, since the film has been stretched in the uniaxial direction first, the second stage (here Since adjustment as transverse stretching is less effective, the adjustment is preferably performed in the first stage (longitudinal stretching here). The transverse stretching ratio is preferably 2.5 to 4.5 times, more preferably 2.8 to 3.9 times, although it depends on the required characteristics of this application. If it is less than 2.5 times, the thickness unevenness of the film is deteriorated and a good film cannot be obtained, and if it exceeds 4.5 times, breakage tends to occur during film formation.

  The film after transverse stretching is preferably heat-treated at a constant width or a width reduction of 10% or less at a temperature (Tm-20 to 80) while holding both ends to reduce the thermal shrinkage. When the temperature is higher than this, the flatness of the film is deteriorated, and the thickness unevenness becomes large, which is not preferable. On the other hand, if the heat treatment temperature is lower than (Tm-80) ° C., the thermal shrinkage rate may increase. Also, in order to adjust the heat shrinkage in the region below (Tm-20-80) ° C in the process of returning the film temperature to room temperature after heat setting, both ends of the film being gripped are cut off and the film is pulled in the vertical direction Can be adjusted and relaxed in the vertical direction. As a means for relaxing, the speed of the roll group on the tenter exit side is adjusted. As the rate of relaxation, the speed of the roll group is reduced with respect to the film line speed of the tenter, and preferably the speed is reduced by 0.1 to 1.2%, that is, relaxation (hereinafter this value is referred to as the relaxation rate). More preferably, a relaxation rate of 0.2 to 1.0%, more preferably a relaxation rate of 0.3 to 0.9% is performed to adjust the heat shrinkage rate in the longitudinal direction. Further, the width of the film in the horizontal direction can be reduced in the process until both ends are cut off, so that a desired heat shrinkage rate can be obtained.

  The white polyester film of the present invention thus obtained has a heat shrinkage rate of 85 ° C. of preferably 0.7% or less, more preferably 0.6% or less, and most preferably 0.5% in both the vertical and horizontal directions. % Or less. The thickness of a film becomes like this. Preferably it is 25-250 micrometers, More preferably, it is 30-220 micrometers, More preferably, it is 40-200 micrometers. If the thickness is 25 μm or less, the reflectance is lowered, and if it exceeds 250 μm, the reflectance cannot be increased even if it is thicker than this, which is not preferable.

  The reflectance of at least one surface of the white polyester film of the present invention is 90% or more, more preferably 92% or more, further preferably 94% or more in terms of the average reflectance at a wavelength of 400 to 700 nm. If it is less than 90%, sufficient reflectance cannot be obtained.

  In the conventional technology, the glossiness of the surface, that is, the light diffusibility on the surface, could not be individually adjusted for the front and back surfaces of the film, and a white polyester film with high reflectance could not be obtained. If the polyester film is used, the glossiness of the front and back surfaces of the film is individually controlled in consideration of the light diffusibility of the film surface to be used, and a film having high reflectance and adhesiveness can be obtained.

  According to the present invention, practically sufficient visible light region reflection performance is provided, the glossiness of each of the front and back surfaces of the film can be controlled, sufficiently good adhesiveness is added, and inorganic fine particles are added at a high concentration A white polyester film that can be stably formed, is stable against dimensional changes due to heat from the light source, and can be suitably used as a substrate for a reflector of a liquid crystal display or an internally illuminated signboard Can be provided.

Hereinafter, the present invention will be described in detail by way of examples.
Each characteristic value was measured by the following method.
(1) Film thickness A film sample was measured for 10-point thickness with an electric micrometer (K-402B manufactured by Anritsu), and the average value was taken as the thickness of the film.

(2) Thickness of each layer A sample is cut into triangles, fixed to an embedded capsule, and then embedded in an epoxy resin. Then, after embedding the sample with a microtome (ULTRACUT-S) into a thin film section having a thickness of 50 nm in parallel with the microtome, the specimen was observed and photographed with a transmission electron microscope at an acceleration voltage of 100 kv. The thickness of each layer was measured and the average thickness was determined.

(3) an integrating sphere attached to the reflectance spectrophotometer (Shimadzu UV-3101PC), the reflectance when BaS0 ₄ white plate was 100% was measured over 400 to 700 nm. The reflectance was read from the obtained chart at intervals of 2 nm. The average value was determined within the above range, and then judged according to the following criteria.
○: Reflectance 90% or more in the entire measurement region Δ: Average reflectance 90% or more in the measurement region and less than 90% in one part ×: Average reflectance in the entire measurement region is less than 90%

(4) Stretchability The film was stretched 2.9 times in the longitudinal direction and 3.6 to 3.7 times in the transverse direction to form a film, and it was observed whether the film could be stably formed. Evaluation was made according to the following criteria.
○: Stable film formation for 1 hour or more ×: Cutting occurs within 1 hour, and stable film formation cannot be performed.

(5) Thermal shrinkage rate The film was held in an oven set at 85 ° C. for 30 minutes in an unstrained state, the distance between the gauge points before and after the heat treatment was measured, and the thermal shrinkage rate (85 ° C. thermal shrinkage rate) according to the following formula: ) Was calculated.
Thermal shrinkage% = ((L0−L) / L0) × 100
L0: Distance between gauge points before heat treatment L: Distance between gauge points after heat treatment

(6) Glass transition point (Tg), melting point (Tm)
Using a differential scanning calorimeter (TA Instruments 2100 DSC), the measurement was performed at a heating rate of 20 m / min.

(7) Glossiness (60 °)
In accordance with JIS standard Z8741, the measurement was performed using a gloss meter “VGS-SENSOR” manufactured by Nippon Denshoku Industries Co., Ltd. N = 5 was measured for each side of the film at an incident angle and a light receiving angle of 60 °, and the average value of each side was used.

(8) Adhesiveness An acrylic hard coat layer with a thickness of 5 μm is formed on the film surface, and a cross cut (100 squares of 1 mm ² ) is applied thereon, and a 24 mm wide cellophane tape (manufactured by Nichiban) is provided thereon. Was peeled off rapidly at a peeling angle of 180 °, and then the peeled surface was observed and evaluated according to the following criteria.
5: Peeling area is less than 10% ············································································ 4・ ・ Adhesive strength is slightly good 2: Peeling area is 30% or more and less than 40% ・ ・ ・ Inadequate adhesion 1: Peeling area is 40% or more ・ ・ ・ ・ ・ ・ ・ ・ Adhesion is extremely poor

[Examples 1 to 8]
The inorganic fine particles shown in Table 1 are added to each copolymerized resin shown in Table 1, and supplied to two extruders each heated to 280 ° C., and the A layer polymer and the B layer polymer are converted into A layer and B The three layers were fed using a three-layer feed block device such that the layers were A / B / A, and formed into a sheet from a die while maintaining the laminated state. Further, the unstretched film obtained by cooling and solidifying the sheet with a cooling drum having a surface temperature of 25 ° C. is heated at the described stretching temperature at each of the film surfaces (herein referred to as A-side and B-side) in the longitudinal direction ( The film was stretched 2.9 times in the longitudinal direction) and cooled with a roll group at 25 ° C. Subsequently, the film was stretched at a magnification of 3.6 in the direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 120 ° C. while being held at both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed in the tenter at the temperature shown in Table 2, longitudinal relaxation and lateral width entered in the temperature range shown in Table 2 were performed, and the resultant was cooled to room temperature to obtain a biaxially stretched film. Table 2 shows the physical properties of the obtained film as a reflector substrate. In any case, the evaluation of adhesiveness was 4 or more (good) on at least one side.

[Examples 9 and 10]
The production methods of Examples 1 to 8 were carried out in the same manner except that they were made into a single layer (that is, the resin was extruded by one extruder) and listed in Tables 1 and 2. In any case, the evaluation of adhesiveness was 4 or more (good) on at least one side.

[Comparative Example 1]
It produced on the conditions described in Table 1,2. Since relaxation in the vertical and horizontal directions is not performed, the heat shrinkage rate is inferior. Moreover, the thing which did not adjust the extending | stretching temperature of front and back was a thing without the difference in the glossiness of front and back. The evaluation of adhesiveness was extremely poor on both sides.

[Comparative Example 2]
Films were formed under the conditions shown in Tables 1 and 2. The content of inorganic fine particles was small and the reflectance was poor. The evaluation of adhesiveness was good or better on both sides, but it had to be used as a film with high glossiness.

[Comparative Example 3]
A film was formed under the conditions shown in Table 1. The film thickness was insufficient and the reflectivity was inferior.

[Comparative Example 4]
A film was formed under the conditions shown in Table 1. Since a non-copolymerized resin was used, the stretchability was extremely low, and the film was frequently cut during film formation, so that a film sample could not be produced.

[Comparative Example 5]
A film was formed under the conditions shown in Table 1. Since the ratio of copolymerization was low and the stretchability was lowered, cutting during film formation occurred frequently. Therefore, it was not possible to measure.

[Comparative Example 6]
Polyethylene terephthalate is used as the resin for the A layer, 14% by weight of calcium carbonate is used as inorganic fine particles in this layer, 10% by weight of the polymethylpentene resin that is incompatible with polyethylene terephthalate is used as the resin for the B layer, and 1% by weight of polyethylene glycol A film was prepared by mixing. As shown in Tables 1 and 2, the reflectance was inferior.

  The polyester film of the present invention has high light reflectivity, excellent thermal dimensional change characteristics, and glossiness is controlled on both sides of the film. Various reflectors, especially reflectors for liquid crystal displays and solar cells. It can be optimally used for the back sheet.

  Paper replacement, ie cards, labels, stickers, delivery slips, video printer paper, ink jet, barcode printer paper, posters, maps, dust-free paper, display boards, white boards, thermal transfer, offset printing, telephone cards, ICs It can be used as a base material for receiving sheets used for various printing records such as cards. Moreover, it can be suitably used for advertising of products and stores, or for internally illuminated signboards used for station information display boards, substrates for reflectors of liquid crystal display devices, and back sheets of solar cells.

Claims (5)

A white polyester film that does not substantially contain a resin that is incompatible with the polyester constituting the film, and has an average reflectance of 90% or more for at least one surface of the film at a wavelength of 400 to 700 nm. A white polyester film having a difference in glossiness (60 °) between the surface and the other surface of 5 to 80. The white polyester film according to claim 1, wherein the heat shrinkage rate at 85 ° C is 0.7% or less in both the longitudinal direction and the transverse direction. The white polyester film according to claim 1, comprising 10 to 80% by weight of at least one inorganic fine particle selected from the group consisting of titanium oxide, barium sulfate, calcium carbonate, and silicon dioxide. White polyester film of claim 1, wherein the thickness of the film is 25～250Myuemu.   The white polyester film according to claim 1, which is used for a reflector.