JP2007328150A - White reflective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a practically sufficient visible light region reflecting performance, stably forming a film, suppressing deterioration due to ultraviolet rays, particularly yellowing, and causing little deformation due to heat, a liquid crystal display or an internal illumination type Provided is a white reflective film that can be suitably used as a reflector substrate for a decorative signboard.
A white reflective film comprising a reflective layer and a support layer supporting the reflective layer, wherein the void volume ratio of the reflective layer is 30 to 80%.
[Selection figure] None

Description

  The present invention relates to a white reflective film, and in particular, relates to a white reflective film having high reflectance and excellent light resistance and heat resistance.

In a liquid crystal display, conventionally, a backlight system that applies light from the back of the display has been adopted, but in recent years, a sidelight system that applies light from the side of the display as disclosed in JP-A-63-62104, Widely used because of its thin and uniform illumination. In this side light system, a reflector is installed on the back as viewed from the display surface. This reflector is required to have high light reflectivity and high diffusibility.
Although a plastic film is used as the substrate for the reflector, in the prior art, the layer responsible for reflection was a reflective layer disposed in the middle.

In general, a cold cathode tube is used as the light applied from the side or the back. Since ultraviolet rays are generated from the cold-cathode tube, when the usage time of the liquid crystal display is extended, the film used as the reflector is deteriorated by the ultraviolet rays, and the brightness of the screen is lowered.
In recent years, there has been a strong demand for an increase in screen size and brightness of a liquid crystal display, and the amount of heat generated from the light source has increased, making it necessary to suppress film deformation due to heat.

JP 63-62104 A Japanese Patent Publication No. 8-16175 JP 2004-50479 A JP 2004-330727 A JP 2005-125700 A

  An object of the present invention is to solve such problems of the prior art, and has a practically sufficient visible light region reflection performance, can be stably formed, and suppresses deterioration (yellowing) due to ultraviolet rays. It is an object of the present invention to provide a white reflective film that can be suitably used as a reflector substrate for a liquid crystal display and is less likely to be deformed by heat.

  That is, the present invention is a white reflective film comprising a reflective layer and a support layer that supports the reflective layer, wherein the void volume ratio of the reflective layer is 30 to 80%.

  According to the present invention, it is possible to stably form a film with a practically sufficient visible light region reflection performance, suppress deterioration (yellowing) due to ultraviolet rays, and reduce deformation due to heat. A white reflective film that can be suitably used as a plate substrate can be provided.

Hereinafter, the present invention will be described in detail.
The white reflective film of the present invention comprises a reflective layer and a support layer that supports the reflective layer.

[Reflective layer]
The reflective layer is composed of a thermoplastic resin composition having a void volume ratio of 30 to 80%, preferably 35 to 75%, and more preferably 38 to 70%. The void volume ratio is achieved, for example, when an incompatible resin or inorganic particle contained in the thermoplastic resin composition and the interface between the thermoplastic resin and the thermoplastic resin are exfoliated to generate voids. Polyester is preferably used as the thermoplastic resin.

[polyester]
As the polyester, known polyesters such as polyethylene terephthalate and polyethylene naphthalate can be used. From the viewpoint of obtaining high heat resistance, a polyester containing a naphthalenedicarboxylic acid component as the dicarboxylic acid component is preferred. Specifically, a copolymerized polyethylene terephthalate containing a naphthalenedicarboxylic acid component in an amount of 3 to 20 mol%, more preferably 4 to 18 mol%, and particularly preferably 8 to 15 mol% is preferable. If the naphthalenedicarboxylic acid component is less than 3 mol%, the film forming property may not be ensured, which is not preferable. If it exceeds 20 mol%, the heat resistance and the film forming property may be deteriorated, which is not preferable.

  The polyester is preferably substantially free of antimony elements. “Substantially not contained” means that the content is 20 ppm or less, preferably 15 ppm or less, more preferably 10 ppm or less. When the antimony element is contained at a substantially low level, the white film is not preferable because it looks black and streaks and the film appearance is remarkably impaired.

  In order to obtain a polyester substantially free of an antimony element, the polyester is polymerized using a catalyst other than the antimony compound. As a catalyst used for polymerization of polyester, it is preferable to use any one of a manganese (Mn) compound, a titanium (Ti) compound, and a germanium (Ge) compound. As the titanium compound, for example, titanium tetrabutoxide and titanium acetate can be used. Examples of germanium compounds include amorphous germanium oxide, fine crystalline germanium oxide, a solution in which germanium oxide is dissolved in glycol in the presence of an alkali metal or alkaline earth metal or a compound thereof, and germanium oxide is dissolved in water. A solution can be used.

[Incompatible resin]
When a polyester and a resin incompatible with polyester are used as the thermoplastic resin composition, examples of the incompatible resin include polyolefin resins and polystyrene resins, specifically, for example, poly-3-methylbutene-1 and poly-4. -Methylpentene-1, polyethylene, polypropylene, polyvinyl-t-butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene, polyfluorostyrene, cellulose acetate cellulose propionate, polychlorotri Fluoroethylene can be used, particularly preferably polypropylene or polymethylpentene. Since these polypropylenes and polymethylpentenes are highly transparent, they are optimal because they can suppress light absorption and improve reflectance.

  The incompatible resin is, for example, 5 to 30% by weight per 100% by weight of the polyester composition of the reflective layer. Preferably it is 8-25 weight%, Most preferably, it is 10-20 weight%. When it exceeds 30% by weight in the reflective layer, the film is very easy to break, and when it is less than 5% by weight, sufficient void formation is not achieved, and the resulting film has low reflectivity, UV light The resistance due to will be inferior.

[Inorganic particles]
When polyester and inorganic particles are used as the thermoplastic resin composition, the inorganic particles have an average particle size of 0.3 to 3.0 μm, preferably 0.4 to 2.5 μm, more preferably 0.5 to 2. 0 μm inorganic particles are used. If the average particle size is less than 0.3 μm, aggregation tends to occur, and if it exceeds 3.0 μm, the film may be broken. Inorganic particles are contained, for example, 31 to 60% by weight, preferably 35 to 55% by weight, and more preferably 37 to 50% by weight per 100% by weight of the polyester composition of the reflective layer. If it is less than 31% by weight, the reflectivity decreases or the deterioration due to ultraviolet rays becomes severe. On the other hand, when it exceeds 60% by weight, the film is easily broken.

  As the inorganic particles, it is preferable to use a white pigment from the viewpoint of obtaining high reflection performance. As the white pigment, for example, titanium oxide, barium sulfate, calcium carbonate, silicon dioxide particles, preferably barium sulfate particles are used. The barium sulfate particles may be either plate-like or spherical. A particularly good reflectance can be obtained by using barium sulfate particles.

  When titanium oxide particles are used as the inorganic particles, rutile titanium oxide particles are preferably used. When the rutile type titanium oxide particles are used, the yellowing after the light is irradiated to the polyester film for a long time is less than that when the anatase type titanium oxide particles are used, and the change of the color difference can be suppressed. When the rutile-type titanium oxide particles are surface-treated with a fatty acid such as stearic acid and / or a derivative thereof, for example, the dispersibility can be improved and a film with particularly high gloss can be obtained. .

  In addition, when using the particle | grains of 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 refining process, for example, a jet mill or a ball mill can be applied as the pulverizing means, and for example, dry or wet centrifugation can be applied as the classification means. Two or more of these means may be combined and purified step by step.

As a method of incorporating the inorganic particles into the polyester, it is preferable to take any of the following methods.
(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 polyester synthesis | combination of said (a), it is preferable to add to a reaction system as a slurry disperse | distributed to glycol in titanium oxide particle.
In particular, it is preferable to take the above method (c) or (d).

  In the present invention, it is preferable to filter the molten polymer by using a nonwoven fabric type 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 as a filter during film formation. . By performing this filtration, it is possible to obtain a film with few coarse foreign matters by suppressing the aggregation of particles that generally tend to agglomerate into coarse agglomerated particles.

[Support layer]
A thermoplastic resin can be used for the support layer. In the case of using a polyester composition for the reflective layer, it is preferable to use a polyester composition for the support layer from the viewpoint of increasing the adhesion to the reflective layer. The polyester composition of the support layer preferably contains 0.5 to 30% by weight, preferably 1 to 27% by weight, more preferably 2 to 25% by weight of inorganic particles. If it is less than 0.5% by weight, sufficient slipperiness cannot be obtained, and if it exceeds 30% by weight, the strength as a support layer for supporting the reflective layer cannot be maintained, which may lead to the breakage of the white reflective film. Absent. The average particle diameter of the inorganic particles is preferably 0.1 to 5.0 μm, preferably 0.5 to 3 μm, and more preferably 0.6 to 2 μm. If the thickness is less than 0.1 μm, the particles are likely to be aggregated, and if it exceeds 5 μm, coarse protrusions are formed and the film may be broken.

[Additive]
You may mix | blend an optical brightener with the white film of this invention. When the fluorescent brightening agent is blended, the concentration of the reflective layer to the polyester composition or the polyester of the support layer is, for example, 0.005 to 0.2% by weight, preferably 0.01 to 0.1% by weight. Then finally. If it is less than 0.005% by weight, the reflectance in the wavelength region near 350 nm is not sufficient, so the meaning of adding is poor. If it exceeds 0.2% by weight, the characteristic color of the fluorescent whitening agent appears. It 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.

  The thickness of the reflective layer is preferably 40 to 90, more preferably 50 to 85 with respect to the total thickness 100 of the reflective layer and the support layer of the white reflective film. If it is less than 40, the reflectance may be inferior, which is not preferable, and if it exceeds 90, it is not preferable from the viewpoint of stretchability.

  The white reflective film of the present invention may be a laminate in which other layers are further laminated in order to impart other functions to one side or both sides. Examples of other layers herein include a transparent polyester resin layer, a metal thin film, a hard coat layer, and an ink receiving layer.

[Production method]
Hereinafter, as an example of a method for producing the white reflective film of the present invention, an example of a method for producing a polyester laminated film having a reflective layer / support layer configuration will be described. A laminated unstretched sheet is produced by a simultaneous multilayer extrusion method using a feed block of polyester melted from a die. That is, the polyester melt constituting the reflective layer and the polyester melt constituting the support layer are laminated to form a reflective layer / support layer using a feed block, and are spread on a die and extruded. 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 draw ratio is preferably 2.2 to 4.0 times, more preferably 2.3 to both the longitudinal direction and the direction orthogonal to the longitudinal direction (hereinafter referred to as the transverse direction), although it depends on the required characteristics of the application. 3.9 times. If it is less than 2.2 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. 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 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. Moreover, in order to adjust the thermal shrinkage in the region of (Tm-20 to 100) ° C. or lower in the process of returning the film temperature to room temperature after heat setting, both ends of the gripped film 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. The film is relaxed by performing a speed reduction of ˜1.0% (this value is referred to as “relaxation rate”), and the longitudinal heat shrinkage rate is adjusted by controlling the relaxation rate. 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.

Here, the case of stretching by the sequential biaxial stretching method has been described in detail as an example, but the laminated film of the present invention may be stretched by either the sequential biaxial stretching method or the simultaneous biaxial stretching method.
The white reflective film of the present invention thus obtained has a heat shrinkage rate of 85 ° C. of 0.5% or less, more preferably 0.4% or less, particularly preferably 0.3% or less in two orthogonal directions. It can be.

  The thickness of the laminated film after biaxial stretching is preferably 25 to 250 μm, more preferably 40 to 250 μm, and particularly preferably 50 to 250 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 white reflective film of the present invention thus obtained has a reflectance of at least one surface of 90% or more, more preferably 92% or more, and particularly preferably 94% or more when viewed with an average reflectance of a wavelength of 400 to 700 nm. It is. 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 The thickness of the film sample was measured at 10 points with an electric micrometer (K-402B manufactured by Anritsu), and the average value thereof was taken as the thickness of the film.

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

(3) Reflectance evaluation An integrating sphere was attached to a spectrophotometer (Shimadzu Corporation UV-3101PC), and the reflectance of the film sample when the BaSO ₄ white plate was 100% was measured over a wavelength range of 400 to 700 nm. The reflectance was read from the obtained reflectance chart at intervals of 2 nm. In addition, when the structure of the film was a reflective layer on one side and a support layer on the other side, the reflectance on the reflective layer side was measured. An average value was determined within the above range. The reflectance was evaluated according to the following criteria.
○: Average reflectivity of 90% or more and reflectivity of 90% or more in the entire measurement region Δ: Average reflectivity of 90% or more, but also in a wavelength range of reflectivity of less than 90%

(4) Evaluation of stretchability The condition of film formation when stretching an unstretched film was observed and evaluated according to the following criteria.
○: Stable film formation over 1 hour ×: Cutting occurs within 1 hour, and stable film formation is not possible

(5) 85 ° C. heat shrinkage rate The film sample was held in an unstrained state for 30 minutes in an oven set at 85 ° C., the distance between the gauge points before and after the heat treatment was measured, and the heat shrinkage rate was calculated by the following formula. .
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) Deterioration due to ultraviolet rays (light resistance evaluation)
The film sample was irradiated with xenon lamp (SUNTEST CPS +) under the conditions of a panel temperature of 60 ° C. and an irradiation time of 300 hours, and the color change before and after the light irradiation was observed. In addition, when the structure of the film was a reflective layer on one side and a support layer on the other side, the measurement was performed by irradiating light from the reflective layer side.
The hue (L ₁ ^* , a ₁ ^* , b ₁ ^* ) of the initial film sample and the hue (L ₂ ^* , a ₂ ^* , b ₂ ^* ) of the film sample after irradiation are measured with a color difference meter (Nippon Denso SZS). -Σ90 COLOR MEASURING SYSTEM), color change dE ^* was calculated by the following formula, and evaluated according to the following criteria.
dE ^* = {(L ₁ ^* −L ₂ ^* ) ² + (a ₁ ^* −a ₂ ^* ) ² + (b ₁ * −b ₂ ^* ) ² } ^1/2
○: dE ^* ≦ 10
Δ: 10 <dE ^* ≦ 15
X: 15 <dE ^*

(8) Deformation due to heat (flexure evaluation)
A film sample was cut into A4 plate, and after processing for 30 minutes in an oven heated to 80 ° C., with the four sides of the film fixed with a metal frame, the deformation (deflection state of the film) was visually observed and the following criteria evaluated.
○: Deflection state is not observed Δ: Minor deflection is observed in part ×: Deflection is present, and unevenness of deflection is observed as a bulge of 5 mm or more

(9) Void volume ratio After isolating only the reflective layer, the density was determined using a vibration digital density meter DMA4500 manufactured by Anton Paar, the film was melted to determine the density, and the following formula was used.
Void volume ratio (%) = 100-100 × (density before melting) / (density after melting)

[Example 1]
132 parts by weight of dimethyl terephthalate, 23 parts by weight of dimethyl 2,6-naphthalenedicarboxylate (12 mol% based on the acid component of the polyester), 96 parts by weight of ethylene glycol, 3.0 parts by weight of diethylene glycol, 0.05 weight of manganese acetate Part and 0.012 part by weight of lithium acetate were charged into a rectification column and a flask equipped with a distillation condenser, and heated to 150 to 235 ° C. with stirring to distill methanol to conduct a transesterification reaction. After the methanol was distilled off, 0.03 part by weight of trimethyl phosphate and 0.04 part by weight of germanium dioxide were added, and the reaction product was transferred to the reactor. Subsequently, while stirring, the pressure in the reactor was gradually reduced to 0.5 mmHg and the temperature was raised to 290 ° C. to carry out a polycondensation reaction. The obtained copolymer polyester had a diethylene glycol component amount of 2.5 wt%, a germanium element amount of 50 ppm, and a lithium element amount of 5 ppm. This polyester resin was used for the polyester of the reflective layer and the support layer, and inert particles shown in Table 1 were added. Supplyed to two extruders each heated to 285 ° C, merged using a two-layer feed block device to form a reflective layer / support layer, and formed into a sheet from a die while maintaining the laminated state did. Further, an unstretched film obtained by cooling and solidifying the sheet with a cooling drum having a surface temperature of 25 ° C. was heated at the described temperature, stretched in the longitudinal direction (longitudinal direction), and cooled by a roll group at 25 ° C. Subsequently, the film was stretched in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 120 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. After that, heat setting is performed in the tenter at the temperature shown in Table 2, and in the conditions shown in Table 2, the film is relaxed in the longitudinal direction and the width is inserted in the transverse direction, cooled to room temperature, and laminated biaxially stretched film of reflective layer / support layer Got. Table 2 shows the physical properties of the obtained laminated film as a reflector substrate.

[Examples 2 to 10]
The reflective layer / support layer composition is the same as in Example 1 except that the composition of the reflective layer and the composition of the support layer are changed as shown in Table 1 and the film forming conditions shown in Table 2 are taken. A laminated film was prepared and evaluated. In Example 4, only dimethyl terephthalate was used without using dimethyl 2,6-naphthalenedicarboxylate.

[Example 11]
Using the copolyester obtained in the same manner as in Example 1 except that 0.05 part by weight of manganese acetate was changed to 0.02 part by weight of titanium acetate, a composition described in Table 1 was prepared. Under the conditions, a two-layer laminated film of a reflective layer / support layer was prepared and evaluated.

[Examples 12 and 13]
Using the copolyester obtained in the same manner as in Example 1 except that 0.05 part by weight of manganese acetate was changed to 0.02 part by weight of titanium acetate, a composition described in Table 1 was prepared. A three-layer laminated film of reflective layer / support layer / reflective layer was prepared and evaluated under the conditions.

[Comparative Examples 1-8]
A reflective layer / support layer bilayer film was prepared and evaluated in the same manner as in Example 1 except that the conditions were changed as shown in Tables 1 and 2. In Comparative Examples 1, 2, 5 and 8, samples could not be collected due to film breakage during film formation.

[Comparative Examples 9 and 10]
A reflective layer / support layer / reflective layer three-layer film was prepared and evaluated in the same manner as in Example 1 except that the conditions were changed as shown in Tables 1 and 2. In either case, samples could not be collected due to film breakage during film formation.

  The white reflective film of the present invention has a high light reflectivity and suppresses deterioration against ultraviolet rays, and various reflectors, especially a reflector for a liquid crystal display, a back sheet for a solar cell, and a reflector for an interior illuminated signboard Can be used optimally. When used as a reflecting plate, it is preferable to use a surface with a high void ratio as the reflecting surface.

  Other applications include paper replacement, ie cards, labels, stickers, home delivery slips, video printer paper, inkjet, barcode printer paper, posters, maps, dust-free paper, display boards, white boards, thermal transfer, offset It can also be used as a base material for receiving sheets used for various printing records such as printing, telephone cards and IC cards.

Claims (6)

  A white reflective film comprising a reflective layer and a support layer supporting the reflective layer, wherein the reflective layer has a void volume ratio of 30 to 80%.   The white reflective film of Claim 1 comprised from the composition which a reflection layer consists of polyester and resin incompatible with this polyester.   The white reflective film of Claim 1 comprised from the composition which a reflection layer consists of polyester and an inorganic particle.   The white reflective film according to claim 1, wherein the support layer is made of polyester.   The white reflective film according to claim 1, wherein the reflective layer is used facing the light source side.   The white reflective film of Claims 1-5 used as a reflecting plate for liquid crystal displays.