JP4933737B2 - Laminated polyester film - Google Patents

Description

  The present invention relates to a laminated polyester film, and relates to a laminated polyester film having a high reflectance in the visible region.

  A sidelight system as disclosed in Japanese Patent Laid-Open No. 63-62104 is widely known for liquid crystal displays because of its merit of being thin and uniform. This sidelight system is a system that illuminates a cold cathode tube or the like from the edge of a transparent plate such as an acrylic plate with a certain thickness, and the illumination light is uniform for halftone printing on the transparent plate. A screen with uniform brightness can be obtained.

  On the other hand, in displays such as liquid crystal televisions that require higher brightness than the sidelight method, illumination light such as cold-cathode tubes is placed on the back of the screen so as to cover the entire screen. A direct type system in which illumination is applied from behind the screen through a high sheet has been adopted.

  In any of the systems, a light source having a higher light intensity is used as the luminance is higher, and the influence of ultraviolet rays from the light source on the member cannot be neglected. In such applications, a film having a reflective performance is used to return light from the light source in the direction opposite to the screen side to the screen side. Tolerance to deterioration is also required. Resistance to deterioration by ultraviolet rays in a liquid crystal display is particularly problematic in terms of discoloration caused by ultraviolet rays and a decrease in reflectance. As a solution to these problems, a technique described in JP-A-2001-226501 is known. However, both of them have insufficient brightness as reflective films for high-brightness displays, UV absorption performance is insufficient, UV absorbers bleed out of the film, and there are great problems in the film manufacturing process. There were problems such as the occurrence or bleed out with time after the film was formed, resulting in a decrease in UV absorption performance.

JP 63-62104 A JP 2001-226501 A

  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, and has a rutile type having barium sulfate or ultraviolet absorption performance in order to provide sufficient reflection performance. Even if titanium dioxide is added at a high concentration, it can be stably formed, has high reflection performance, prevents deterioration from ultraviolet rays contained in the light source, and does not substantially cause bleeding out of ultraviolet absorbers, It aims at providing the laminated polyester film which can be used suitably as a film for reflection of a liquid crystal display or an interior illumination type electrical signboard.

That is, the present invention relates to a polyester composition comprising 21 to 60% by weight of barium sulfate particles having an average particle size of 0.1 to 10 μm and 1 to 40% by weight of rutile titanium dioxide particles having an average particle size of 0.1 to 5.0 μm. Layer A, 0.1 to 15% by weight of barium sulfate particles having an average particle size of 0.1 to 10 μm adjacent to this layer, and 1 to 15% by weight of rutile titanium dioxide particles having an average particle size of 0.1 to 5.0 μm only containing the content and the rutile total biaxially oriented laminated polyester composed of a layer B of the polyester composition is 16 wt% or less 11% or more by weight of the content of titanium dioxide particles of the barium sulfate particles It is a film.

  According to the present invention, practically sufficient visible light region reflection performance, stable film formation, high reflection performance, preventing deterioration from ultraviolet rays contained in the light source, such as ultraviolet absorbers It is possible to provide a laminated polyester film that can be suitably used as a surface light source reflector of a liquid crystal display or an internally illuminated signboard that does not substantially cause bleed out.

Hereinafter, the present invention will be described in detail.
[polyester]
The laminated polyester film of the present invention comprises a layer A of a polyester composition containing barium sulfate particles and rutile type titanium dioxide particles, and a layer B of a polyester composition containing barium sulfate particles and rutile type titanium dioxide particles adjacent to this layer. Composed.

  As the polyester of the polyester composition, 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, polyethylene terephthalate is particularly preferred.

  When polyethylene terephthalate is used, it is preferable to use a copolyester containing 1 to 15 mol%, more preferably 3 to 14 mol%, and most preferably 5 to 13 mol% of a copolymer component per total dicarboxylic acid component. . If it is less than 1 mol%, a layer containing inert particles, for example, 31 wt% or more of barium sulfate or rutile type titanium dioxide particles may not be formed, which is not preferable. If it exceeds 15 mol%, it is not preferable because a film lacking thermal dimensional stability may be formed or even a film cannot be formed.

  As the copolymer component, examples of the dicarboxylic acid component include 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. In particular, it is preferable to use isophthalic acid or 2,6-naphthalenedicarboxylic acid as a copolymerization component of the polyester used for the layer A in order to obtain good film forming properties.

[Barium sulfate particles]
The polyester composition of layer A contains 21-60% by weight of barium sulfate particles, preferably 23-55% by weight, more preferably 25-50% by weight. And the polyester composition of the layer B contains 0.1-15 weight% of barium sulfate particles, Preferably it is 0.2-14 weight%, More preferably, it contains 0.5-13 weight%. By containing in this range, good film forming property can be obtained while obtaining sufficient reflection performance.

  In any layer, the average particle diameter of barium sulfate is 0.1 to 10 μm, preferably 0.3 to 8 μm, and more preferably 0.5 to 5 μm. By using a material having an average particle diameter in this range, good dispersibility and film forming property can be obtained. The barium sulfate may be plate-shaped or spherical.

[Rutyl type titanium dioxide particles]
The polyester composition of layer A contains 1 to 40% by weight, preferably 1.5 to 35% by weight, and more preferably 2 to 30% by weight of rutile-type titanium dioxide particles. By containing in this range, sufficient reflection performance and ultraviolet absorption effect can be obtained.

  The polyester composition of layer B contains 1 to 15% by weight, preferably 2 to 14% by weight, more preferably 3 to 13% by weight of rutile-type titanium dioxide particles. By containing in this range, while protecting the whole protective film from an ultraviolet-ray, favorable film forming property can be maintained.

  In any of the layers, the average particle diameter of the rutile type titanium dioxide particles is 0.1 to 5.0 μm, preferably 0.2 to 4.0 μm, and more preferably 0.3 to 3.0 μm. By using a material having an average particle diameter in this range, dispersibility and film-forming property can be obtained.

  In order to further improve dispersibility, rutile-type titanium dioxide particles are preferably used after being treated with a fatty acid such as stearic acid or a derivative thereof, because the glossiness of the film can be further improved.

  In addition, before mix | blending a rutile type titanium dioxide with a polyester composition, it is preferable to perform a particle size adjustment and coarse particle removal using a refinement | purification process. 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, you may refine | purify these means combining 2 or more types in steps.

[Method of blending particles]
Various methods can be used as a method of blending the barium sulfate particles and the rutile-type titanium dioxide into the polyester composition. The following method can be mentioned as the typical method. (A) A method of adding particles before the end of the ester exchange reaction or esterification reaction during polyester synthesis, or a method of adding particles before the start of the polycondensation reaction. (A) A method in which particles are added to polyester and melt kneaded. (C) A method of producing master pellets in which a large amount of particles are added in the above method (a) or (b) and kneading these with a polyester not containing additives to contain a predetermined amount of additives. (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 a titanium dioxide particle to a reaction system as a slurry disperse | distributed to glycol.

As a blending method of the barium sulfate particles and the slightly rutile type titanium dioxide, it is particularly preferable to take the above method (c) or (d).
The barium sulfate particles and the rutile type titanium dioxide particles are formed by using a nonwoven fabric type filter having an average opening of 10 to 100 μm, preferably an average opening of 15 to 50 μm made of stainless steel fine wire having a wire diameter of 20 μm or less as a filter during film formation. It is preferred to filter the molten polymer just before it is extruded from. By doing in this way, the number of coarse aggregated particles can be reduced.

[Fluorescent brightener]
It is preferable to add a fluorescent brightening agent to the polyester composition. In this case, the fluorescent brightening agent may be added in a concentration of preferably from 0.01 to 0.2% by weight, more preferably from 0.05 to 0.1% by weight, based on the polyester composition. If the blending amount of the fluorescent whitening 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.

  Examples of fluorescent whitening agents include OB-1 (manufactured by Eastman), Uvitex-MD (manufactured by Ciba Geigy), JP-Conc (manufactured by Nippon Chemical Industry Co., Ltd.), TBO (manufactured by Sumitomo Seika Co., Ltd.) Can be used.

[Layer structure]
The laminated polyester film of the present invention comprises a layer A and a layer B adjacent thereto. As long as the structure of the layer A and the layer B is included, it may be composed of a large number of layers. For example, it may be a two-layer configuration of layer A / layer B, a three-layer configuration of layer B / layer A / layer B, or a four-layer configuration of layer A / layer B / layer A / layer B. Good. Furthermore, the structure of five layers or more may be sufficient.

  In view of the ease and effect on film formation, a two-layer structure or a three-layer structure composed of layer B / layer A / layer B is preferable. In particular, a mode in which the layer A is protected by the layer B, that is, a three-layer configuration of layer B / layer A / layer B is preferable.

It is good also as a laminated body which further laminated | stacked the other layer in order to provide another function to the single side | surface or both surfaces of a film. Examples of the other layers include a transparent polyester resin layer, a metal thin film, a hard coat layer, an ink receiving layer, and a coating layer.
Examples of the coating layer include a coating layer containing an antioxidant, an antistatic agent, and a fluorescent brightening agent.

[Film forming method]
Hereinafter, an example of the method for producing the film of the present invention will be described.
First, a laminated unstretched sheet is produced by simultaneous multilayer extrusion using a feed block of a polyester composition melted from a die. That is, the polyester composition melt for forming layer A and the polyester composition melt for forming layer B are laminated using a feed block so as to be, for example, layer B / layer A / layer B. Expand and extrude. At this time, the polyester composition laminated | stacked so that it may become layer B / layer A / layer B with a feed block is maintaining the laminated | stacked form. Although a multi-manifold die can also be manufactured, it is preferable to use a feed block from the viewpoint of adhesion at the interface of the laminated film and manufacturing simplicity.

  The polyester composition extruded from the die is cooled and solidified on a casting drum to form an unstretched laminated film. This unstretched laminated film is heated by a heating means such as roll heating or infrared heating, and is first stretched in the longitudinal direction to obtain a longitudinally stretched film. This stretching is preferably performed by utilizing a difference in peripheral speed between two or more rolls. The stretching temperature is set to a temperature equal to or higher than the glass transition point (Tg) of the polyester, and particularly preferably a temperature higher by Tg to 70 ° C. The draw ratio is preferably 2.5 to 4.0 times, more preferably 2.8 to 3.9 times in both the longitudinal direction and the direction orthogonal to the longitudinal direction (hereinafter referred to as the transverse direction). If the ratio is less than 2.5 times, the thickness unevenness of the film is deteriorated and a good film cannot be obtained. If the ratio exceeds 4.0 times, breakage is likely 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. 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-10 to 100) 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 amount of thermal shrinkage in the region of (Tm-20 to 100) ° C. or lower during 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 take-up speed in the film 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, preferably 0.1 to 1.5%, more preferably 0.2 to 1.2%, particularly preferably 0.3. A speed reduction or relaxation of ˜1.0% is performed (hereinafter this value is referred to as relaxation rate). This relaxation makes it possible 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.

[Physical properties]
The heat shrinkage rate at 85 ° C. of the laminated polyester film of the present invention thus obtained is 0.7% or less, more preferably 0.6% or less, particularly preferably 0.5% or less in both two orthogonal directions. It can be achieved. The thickness of the film after biaxial stretching is preferably 25 to 250 μm, more preferably 30 to 220 μm, and particularly preferably 40 to 200 μm. If it is 25 μm or less, the reflectivity is undesirably lowered, and if it exceeds 250 μm, it is not preferable because an increase in reflectivity cannot be expected even if it is thicker than this.

  The reflectance of at least one surface of the laminated polyester film of the present invention is preferably 90% or more, more preferably 92% or more, and particularly preferably 94% or more, with an average reflectance of a wavelength of 400 to 700 nm. If it is less than 90%, it is not preferable because sufficient screen brightness cannot be obtained.

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 300 to 800 nm. The reflectance was measured at intervals of 2 nm.

(4) Stretchability Whether the film can be stably formed was evaluated according to the following criteria.
○: A film can be stably formed for 1 hour or more.
X: Cutting occurs within 1 hour, and stable film formation is not possible.

(5) Heat shrinkage rate The film was held in an oven set at 85 ° C. for 30 minutes in an unstrained state, and the distance between the gauge points before and after the heat treatment was measured. ) Was calculated.
Thermal contraction rate (%) = ((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) Average particle size Using a S-4700 field emission scanning electron microscope manufactured by Hitachi, Ltd., arbitrarily measure 100 particles before being added to the resin (film) at a magnification of 10,000 times (elliptical) In the case of (obtained by major axis + minor axis) / 2), the average particle size was determined.

(8) Bleed-out One film was sandwiched between two slide glasses, held at 200 ° C. for 15 minutes, and both sides of the slide glass and both sides of the film were visually evaluated for bleed-out according to the following criteria.
○: Bleed-out is not substantially observed.
X: Bleed-out is observed on the glass or film surface, and discoloration is also observed visually.

(9) Evaluation by ultraviolet irradiation A xenon lamp irradiator (SUNTEST + manufactured by ATLAS) was used as a lamp with strong ultraviolet rays, and irradiated for 300 hours at a black panel temperature of 60 ° C., and the hue before irradiation (L1 *, a1 *, b1) *) And the hue (L2 *, a2 *, b2 *) after irradiation were measured with a color difference meter (Nippon Denshoku SZS-Σ90 COLOR MEASURING SYSTEM).
ΔE * was determined by the following equation.
ΔE * = {(L1 * -L2 *) 2 + (a1 * -a2 *) 2 + (b1 * -b2 *) 2} 1/2

[Example 1]
The barium sulfate and rutile type titanium dioxide described in Table 1 and Table 2 are added to the copolymer polymers described in Table 1 and Table 2, and are supplied to two extruders heated to 280 ° C., respectively. The polymer of layer B was merged using a three-layer feed block device in which layers A and B were B / A / B, and formed into a sheet from a die while maintaining the laminated state. Further, the unstretched film obtained by cooling and solidifying this sheet with a cooling drum having a surface temperature of 25 ° C. was heated at the stretching temperature shown in Table 1 and stretched 2.8 to 3.4 times in the longitudinal direction (longitudinal direction). Cooled with a roll group. Subsequently, the film was stretched at a magnification of 3.5 to 3.7 in a 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 under the conditions shown in Table 3, longitudinal relaxation and lateral width insertion, and cooling to room temperature to obtain a biaxially stretched film. The properties of the obtained film were as shown in Table 4.

In Table 1 and Table 2, the abbreviations are as follows.
Tg: Glass transition point Tm: Melting point PET: Polyethylene terephthalate IPA: Isophthalic acid NDC: 2,6-Naphthalenedicarboxylic acid PMX: Polymethylpentene All the titanium dioxide used was a rutile crystal particle.

[Examples 2 , 4, 5, 7, 8 and Comparative Examples 8, 9 ]
A film was formed in the same manner as in Example 1 except that the conditions were as described in Table 1, Table 2, and Table 3. The properties of the obtained film were as shown in Table 4.

[Comparative Example 1]
A film was formed in the same manner as in Example 1 except that the conditions were as described in Table 1, Table 2, and Table 3. The obtained film had a small amount of rutile titanium dioxide added and was inferior in resistance to ultraviolet rays.

[Comparative Example 2]
A film was formed in the same manner as in Example 1 except that the conditions were as described in Table 1, Table 2, and Table 3. The characteristics of the obtained film were as shown in Table 4, and the addition amount of barium sulfate was small and the reflectance was poor.

[Comparative Example 3]
Except for carrying out under the conditions described in Table 1, Table 2 and Table 3, an attempt was made to form a film in the same manner as in Example 1, but because the copolymer polyethylene terephthalate was not used, the stretchability was low, The film could not be made,

[Comparative Example 4]
Except for carrying out under the conditions described in Table 1, Table 2 and Table 3, film formation was attempted in the same manner as in Example 1, but the addition amount of barium sulfate and rutile titanium dioxide was large, and the stretchability was high. Since it was low, a film could not be produced.

[Comparative Example 5]
A film was prepared in the same manner as in Comparative Example 1, and a polyurethane emulsion liquid (AP-40 manufactured by Dainippon Ink, Inc.) was applied on one side to a thickness of 0.3 μm after drying and dried in an oven at 110 ° C. Further, this surface was used with Udouble UV6010 (manufactured by Nippon Shokubai Co., Ltd., solution concentration 20% state), dried in an oven at 150 ° C. so that the thickness after drying was 5 μm, and reflected performance, UV resistance, Bleed out was assessed. The characteristics of the obtained film are as shown in Table 4, and although the reflection performance and ultraviolet resistance were excellent, bleeding out was observed.

[Comparative Example 6]
A sample was prepared and evaluated in the same manner as in Comparative Example 5 except that the uvable UV6010 of Comparative Example 5 was replaced with the following coating solution and the thickness after drying was changed to 4 μm.

The composition of the coating liquid is as follows.
U double UV714 (manufactured by Nippon Shokubai Co., Ltd.) 10 parts by weight Sumidur N3200 (manufactured by Sumitomo Bayern Urethane Co., Ltd.) 0.5 parts by weight Ethyl acetate / toluene (weight ratio 1/1) 12 parts by weight

  Reflection performance, UV resistance, and bleed out were evaluated from the coated surface side of the obtained sample. The characteristics of the obtained sample are as shown in Table 4, and although the reflection performance and the ultraviolet resistance were excellent, bleed out was observed.

[Comparative Example 7]
Polyethylene terephthalate is used as the resin of layer A, 14% by weight of calcium carbonate as inorganic fine particles, 10% by weight of polymethylpentene resin that is incompatible with polyethylene terephthalate is used as the resin of layer B, and 1% by weight of polyethylene glycol After mixing, a film was formed according to Example 1. The characteristics of the obtained film were as shown in Table 4, and were inferior in reflectance and ultraviolet resistance.

  The laminated polyester film of the present invention has a high reflectance in the visible light region, and various reflections including internally illuminated signboards and liquid crystal display devices used for information display boards at stations, etc. for the promotion of products and stores. Especially as a board | substrate base material, it can use optimally for the reflection base material of a flat type information display apparatus (liquid crystal display etc.) especially, and the back seat | sheet of a solar cell.

  Also, paper replacement, that is, cards, labels, stickers, home delivery slips, video printer image paper, inkjet, barcode printer image paper, posters, maps, dust-free paper, display boards, white boards, thermal transfer, offset printing, telephone cards, It can also be used as a substrate for various printing and recording applications such as IC cards.

Claims (3)

Layer A of a polyester composition comprising 21 to 60% by weight of barium sulfate particles having an average particle size of 0.1 to 10 μm and 1 to 40% by weight of rutile titanium dioxide particles having an average particle size of 0.1 to 5.0 μm, and < An amount of 0.1 to 15% by weight of barium sulfate particles having an average particle diameter of 0.1 to 10 μm and 1 to 15% by weight of rutile titanium dioxide particles having an average particle diameter of 0.1 to 5.0 μm are adjacent to this layer. unrealized, layers of content and the polyester composition total is 16 wt% or less 11% or more by weight of the content of the rutile titanium dioxide particles of the barium sulfate particles B
A biaxially stretched laminated polyester film composed of   The biaxially stretched laminated polyester film according to claim 1, wherein the polyester of layer A is polyethylene terephthalate containing 1 to 15 mol% of a copolymer component per total dicarboxylic acid component.   The biaxially stretched laminated polyester film according to claim 1, which is used as a surface light source reflector.