TWI697698B - White reflective film and backlight for liquid crystal display - Google Patents

Abstract

The problem is to provide a backlight at a low cost by using a white reflective film with excellent economic efficiency, film forming properties, whiteness, reflectivity, light weight, and excellent surface shape, which has excellent brightness characteristics and compatibility with other components.

The solution to the problem is a white reflective film for edge-lit backlights, which satisfies the following (i)~(iii), (i) is at least two layers including a surface layer (A) and a substrate layer (B) containing bubbles (Ii) The surface layer (A) has an average surface roughness (SRa) of 90nm or more but less than 300nm, and (iii) the surface layer (A) is composed of a polymer that is different from the polymer constituting the matrix The domain (domain).

Description

White reflective film and backlight for LCD

The present invention relates to a white reflective film that seeks to improve the brightness unevenness of a liquid crystal backlight. In more detail, a white reflective film is suitable for use in backlights for edge-lit liquid crystal displays and surface light sources for lighting such as advertisements and vending machines.

The backlight that illuminates the liquid crystal tank is used in the liquid crystal display, which can be divided into direct type and edge type. In the case of direct type, multiple cold cathode tubes or light-emitting diodes (LEDs) are arranged as light sources directly under the screen, which can be mainly used for TV applications that require high brightness. On the other hand, in the side-light type In the case, the light source is arranged at the end of the screen, and the surface light source is made by using a light guide plate. Therefore, it can be thinned and can be used for tablet computers, notebook computers, desktop displays, and TV applications that require thinning. These reflective films for backlights generally use porous white films made of bubbles (Patent Document 1). Of course, the reflective film used in the side-light type needs high reflection performance, especially compatibility with the light guide plate. At present, in order to solve the problem of uneven white spots caused by the contact between the light guide plate and the white film (bright dot-like parts are observed) or the uneven brightness caused by vibration scratches on the printed part of the light guide plate, coating is used Spherical particles with appropriate hardness to improve the rigidity and reflection characteristics of the white film of the substrate It is sought to improve brightness unevenness on the screen (Patent Documents 2 and 3).

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 8-262208

[Patent Document 2] JP 2003-92018 A

[Patent Document 3] Japanese Patent No. 5578177

However, in recent years, the requirements for long-term durability and impact durability of tablet computers or notebook computers have increased, and there is a need for reflective films that can withstand the durability test of the so-called high-load dot test. With this localized impact test, because the uneven surface of the reflective film is in strong contact with the light guide plate, scratches will be generated on the surface of the light guide plate, resulting in uneven brightness.

In the prior art described in Patent Documents 2 and 3, it is possible to suppress uneven white dots (bright dot-like portions are observed) or scratches on the printed layer on the light guide plate due to vibration. However, it cannot fully meet the recent requirements of tablet PCs or The impact durability of notebook computers.

Therefore, the subject of the present invention is to provide, at a low cost, a film having impact durability, excellent reflectivity, and surface shape that could not be achieved by the above-mentioned conventional reviews.

In order to solve the above problems, the present invention adopts the following (1)~ (9) Any means.

(1) A white reflective film for edge-lit backlights, which satisfies the following (i) to (iii), (i) is at least two layers including a surface layer (A) and a substrate layer containing bubbles (B) Laminated film, (ii) the surface layer (A) has an average surface roughness (SRa) of 90nm or more but less than 300nm, and (iii) the surface layer (A) is composed of a polymer different from the polymer constituting the matrix Domain.

(2) The white reflective film for edge-lit backlights as described in (1), wherein the interface thickness of the aforementioned regions is 20 nm or more and 1,000 nm or less.

(3) The white reflective film for edge-lit backlights as described in (1) or (2), wherein the shape of the area described in (1) or (2), when the cross section of the surface layer (A) is observed, The ratio of the length in the thickness direction: the length in the longitudinal direction is 1:3 or more and 1:50 or less.

(4) The white reflective film for edge-lit backlight according to any one of (1) to (3), wherein the surface layer (A) contains particles, and the content of the particles is less than 5% by mass.

(5) The white reflective film for side-light backlight as in any one of (1) to (4), wherein the gloss difference between 20° and 85° of the surface layer (A) is more than 50%.

(6) The white reflective film for edge-lit backlights according to any one of (1) to (5), wherein the surface layer (A) contains at least polyester or polyolefin having an alicyclic structure.

(7) The white reflective film for edge-lit backlights as in any one of (1) to (6), wherein the surface layer (A) is composed of two or more polymers, and its cooling crystallization temperature (Tmc) is lower than The difference is 10°C or more but less than 40°C.

(8) A backlight for a liquid crystal display, which is composed of the film described in any one of (1) to (7).

(9) The backlight for liquid crystal displays as described in (8), wherein the light source is a light-emitting diode.

According to the present invention, particles are not added to the surface layer (A) on the side where the white reflective film is in contact with the light guide plate (the side of the reflective surface when in use, the side opposite to the light guide plate), but a polymer with a special structure is selected and controlled The surface roughness in a specific range can provide a white reflective film that can suppress scratches on the light guide plate in the impact test of the backlight. When the white reflective film obtained by the present invention is used in an edge-lit backlight and a surface light source for lighting equipped with an LED light source, the light guide plate can be prevented from being scratched, so that uneven brightness can be reduced to a level higher than the previous level. For fit.

The present invention aims at the aforementioned problem, namely, the white reflective film that suppresses the scratching of the light guide plate in the impact test of the side-lit backlight, and found that when it is not in contact with the side of the light guide plate of the white reflective film (the reflective surface when in use) When particles are added to the surface layer (A) on the side facing the light guide plate, and a polymer with a special structure is selected, and the surface roughness is in a specific range, the aforementioned problems can be solved in one fell swoop.

In addition, brightness unevenness means the following unevenness which is visually observed when the backlight is turned on.

(i) Uneven strips

(ii) Uneven water droplets

(iii) Unevenness that becomes dark part is observed

In addition, the white spot unevenness means that when the backlight is turned on, an elliptical spot unevenness with a major diameter of less than 5 cm is visually observed.

The white reflective film related to the present invention will be described in detail below.

[Basic composition of white reflective film]

The white reflective film of the present invention is composed of a surface layer (A) and a substrate layer (B) containing air bubbles. If the difficulty and effect of film formation are considered, it must have a two-layer structure, and a three-layer structure is preferable . In particular, a form in which the surface layer (A) protects the substrate layer (B), that is, a three-layer structure of surface layer (A)/substrate layer (B)/surface layer (A) is preferable. In addition, in the case of further forming a multilayer, the core layer is preferably the base layer (B), and the surface layer on one or both sides is preferably the surface layer (A).

[Substrate layer containing air bubbles (B)]

For whiteness and reflective properties, the white reflective film of the present invention must have bubbles inside the base layer (B), and by making it contain components that are incompatible with the polyester or polypropylene constituting the base layer (B) And for biaxial extension, bubbles can be formed.

Regarding examples of its production method, there are known examples of polyesters with barium sulfate as an incompatible component described in Japanese Patent No. 3731172 or titanium oxide as an incompatible component described in JP 2012-158167. As the component polypropylene, among the organic-based immiscible resins, specific examples of organic substances include straight-chain forms such as polyethylene, polypropylene, polybutene, polymethylpentene, and cyclopentadiene. , Branched or cyclic polyolefin. This polyolefin can be a single polymer or copolymer, or even Two or more types can be used in combination. Among these, from the viewpoint of excellent transparency and excellent heat resistance, polypropylene, polymethylpentene, etc. are suitable for crystalline olefins, and cycloolefin copolymers and the like are suitable for amorphous polyolefins.

In the present invention, when the total mass of the bubble-containing substrate layer (B) is 100% by mass, the addition amount of incompatible components is preferably 5-50% by mass, and 5-30% by mass. For better. If the content of incompatible components is less than 5% by mass, sufficient bubbles cannot be generated inside the film, and whiteness or light reflection properties may be poor. On the other hand, if the content of incompatible components exceeds 50% by mass, the strength of the film is reduced, the film is easily broken during stretching, and problems such as dust may be generated during post-processing. By setting the content within this range, sufficient whiteness, reflectivity, and lightness can be expressed.

[Surface roughness of surface layer (A)]

In the white reflective film of the present invention, the average roughness (SRa) of the center surface of the surface layer (A) must be above 90nm and less than 300nm, preferably 120~300nm, most preferably 120~250nm. In the case of less than 90nm, the glossiness becomes high, and it is easy to observe the adhesion of dust on the surface. In addition, the edge-light type backlight is likely to cause uneven brightness, especially white spots. On the other hand, in the case of 300 nm or more, when the vibration test is performed together with the light guide plate, the surface of the surface layer (A) will be cut, and the problem of transfer to the light guide point of the light guide plate is likely to occur.

The average roughness of the center surface of the surface of the surface layer (A) is a value measured by the following method.

According to JIS B0601 (2001), a probe-type surface roughness meter (model: ET 4000A) manufactured by Kosaka Laboratory is used to measure the average roughness of the center surface (SRa). The conditions are as follows, and the average value of 5 measurements is taken as the measured value.

‧Probe tip radius: 0.1μm

‧Probe load: 100μN

‧Measuring length: 1.0mm

‧Cut-off value: 0.25mm

[The surface layer (A) has a region composed of a polymer different from the polymer constituting the matrix]

In order to prevent the unevenness of brightness when it comes into contact with the light guide plate or the unevenness of brightness after impact test, the surface layer (A) must have a region composed of a polymer different from the polymer constituting the matrix. The area can be easily observed by comparing the cross-sectional SEM of the surface layer (A).

If there is no area formed by a polymer, for example, if inorganic particles are used to achieve the center surface average roughness (SRa) of the invention, the light guide plate will be scratched during the impact test, resulting in uneven brightness. In addition, when organic particles are used to achieve the center surface average roughness (SRa), the organic particles fall off in the impact test and adhere to the light guide plate, resulting in uneven brightness.

In the present invention, the interface thickness of the region is preferably 20 nm or more and 1,000 nm or less. In the case of less than 20nm, gaps are likely to occur between the substrate and the area, and the substrate will be rolled up and attached to the light guide plate during the impact test, which may cause uneven brightness. In addition, if it is larger than 1,000 nm, it will be excessively dissolved, and a sufficient surface roughness may not be obtained. The region thickness is preferably in the range of 50 nm to 1,000 nm, and more preferably 50 nm to 500 nm.

The transesterification reaction can be controlled by using the transesterification reaction inhibitor The corresponding method and the method of using a compatibilizer to control the compatibility are controlled so as to achieve the range of the aforementioned area thickness.

In the present invention, the shape of the region is preferably a slightly flattened shape coextensive with the substrate. Specifically, when observing the cross section of the surface layer (A), the ratio of the length in the thickness direction: the length in the longitudinal direction is preferably 1:3 or more 1:50 or less. In the case of less than 1:3, the area is not co-extensive, and voids are easily generated. During the impact test, the substrate will be rolled up and attached to the light guide plate, which may cause uneven brightness. In addition, if it is greater than 1:50, it will be excessively coextensive with the substrate, and unevenness may not be formed. The more preferable range of the area shape is 1:5 or more and 1:50 or less, and even more preferably 1:10 or more and 1:50 or less.

In order to achieve the shape of the aforementioned region, for example, a method of controlling the difference in Tg of the polymer constituting the matrix and the region can be cited. Specifically, the difference in Tg between the polymers constituting the matrix and the domains is preferably controlled to be 10°C or more and less than 40°C.

The surface roughness formed by the area formed by the polymer different from the polymer constituting the matrix is not sharp protrusions formed by particles, etc., but gentle protrusions, so the attack on the light guide plate is low , It can greatly suppress the uneven brightness or the uneven brightness after impact test.

The thickness of the surface layer (A) is preferably 4 μm or more and 12 μm or less. If the thickness is less than 4 μm, there are many cases where cracks occur during film formation, the workability is reduced, or sufficient surface irregularities cannot be formed. In addition, if it is higher than 12 μm, the brightness may decrease. It is preferably 6 μm or more and 12 μm or less.

[Cooling crystallization temperature (Tmc)]

In order to prevent uneven brightness after the impact test, in the present invention, the main protrusion of the surface layer (A) preferably has a polymer as the core. In order to form a protrusion with a polymer as a core, it is preferably composed of two or more types of polymers, and these are not compatible with each other during the extruder or film forming process and form a state of layer (A).

The criteria of incompatibility include, for example, observing the difference in the cooling crystallization temperature (Tmc) of the surface layer (A). Specifically, the cooling crystallization temperature (Tmc) is preferably 10°C or more and 40°C or less. If it exceeds 40°C, cold crystallization will be promoted, resulting in hard surface irregularities, and a problem of cutting into the light guide plate may occur. Preferably, it is 15°C or higher but less than 35°C.

In the case of a polyester, a method of suppressing compatibility may include a method of adding a so-called transesterification inhibitor that suppresses the activity of a polymer polymerization catalyst, or a method of suppressing the thermal history during film formation.

[Polyester or polyolefin with alicyclic structure]

In the present invention, among the two or more polymers, it is preferable to contain at least one polyester or polyolefin having an alicyclic structure. In particular, if polyester or polyolefin having an alicyclic structure with different compatibility is used, it is easy to form appropriate surface irregularities. Such alicyclic structure is preferably a cyclopropane ring, a cyclobutane ring, a cyclopentane ring, and a cyclohexane ring. Make dimethyl terephthalate as the acid component and 1,3-cyclopropanediol, 1,3-cyclobutanediol, 1,3-cyclopentanediol, and 1,4-cyclohexane as the diol component Dimethanol, polycondensation reaction is carried out in the presence of 200 ppm of butyl tin ginseng (2-ethylhexanoate) to obtain polyester particles or polyolefin particles with alicyclic structure.

For the polyester having a cyclobutane ring, "TRITAN" (registered trademark) (manufactured by Eastman Chemical Company) is suitably used, and the polyester having a ring For the hexane ring polyester, "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) is suitable, and "ZEONOR" (registered trademark) (registered trademark) (manufactured by Zeon Co., Ltd.) is suitable for the polyolefin having a cyclopentane ring.

The addition amount of the polyester (B) having an alicyclic structure is not particularly limited, but relative to the total mass of the surface layer (A) 100% by mass, it is preferably 10% by mass to 40% by mass, and particularly preferably 15 The mass% is above 35 mass%. If it is less than 10% by mass, the edge-lit backlight is prone to uneven brightness, especially white spots.

In the present invention, among the two or more polymers, polymers other than polyesters or polyolefins having an alicyclic structure can use glycols such as ethylene glycol or butylene glycol and terephthalic acid or isophthalic acid. A polyester copolymerized with dicarboxylic acid components such as formic acid. Among them, it is preferable to use polyethylene terephthalate (PET) which is a polymer of ethylene glycol and terephthalic acid. In addition to the aforementioned PET, in order to impart film stability or make it easier to form surface irregularities, a copolymerized PET (PET-I) of ethylene glycol, isophthalic acid and terephthalic acid can also be used. When the addition amount of PET-I is set to 100% by weight for the surface layer (A), it is preferably 20% by weight or more and less than 50% by weight. If it is less than 20% by weight, the effect of film formation stability may be low, or the effect of surface unevenness may be low. In addition, if it is 50% by weight or more, the heat resistance may decrease.

[Particle content]

In a range that does not impair the effect of the present invention, particles less than 5 mass% may be contained. If the particles are more than 5% by mass, the light guide plate will be scratched, the polymer will peel off from the particles, or the particles themselves will fall off, which will contaminate the guide. The light board situation. The preferable range of the particle content is 4% by mass or less, and more preferably 3% by mass or less.

The particles of the present invention refer to inorganic particles or organic particles. Examples of the inorganic particles include titanium dioxide, calcium carbonate, barium sulfate, and silicon dioxide. Examples of organic particles include acrylic, polystyrene, nylon and the like.

[Poor gloss]

In the present invention, the difference in gloss between 20° and 85° of the surface layer (A) is preferably 50% or more. Because of the large difference in gloss, the light reflective film can efficiently return light to the front of the display. It is preferably 65% or more, more preferably 80% or more.

[Method of Making Film]

An example of the manufacturing method of the biaxially stretched film of the present invention will be described, but the present invention is not limited to this example.

Regarding the surface layer (A), a mixture containing polyester (B) having a polyester or polypropylene and alicyclic structure and various additives as necessary is sufficiently vacuum-dried and supplied to the heated extruder. For the addition of the polyester (B) having an alicyclic structure, a masterbatch prepared by uniform melt kneading in advance may be used, or it may be directly supplied to a kneading extruder.

Regarding the bubble-containing substrate layer (B), a mixture containing components incompatible with polyester or polypropylene and a dispersant as necessary is sufficiently vacuum dried and supplied to the heated extruder. For the addition of incompatible components, a master batch prepared by uniformly melt-kneading in advance can be used, or it can be directly supplied to a kneading extruder.

In addition, in the case of melt extrusion, it is preferable to filter with a filter with a pore diameter of 40 μm or less, and then introduce it into the metal nozzle of the T-die, and form the A molten flake is obtained.

The molten sheet is adhered to a roller whose surface temperature is cooled to 10-60°C by static electricity, and cooled and solidified to produce an unstretched A/B/A3 layer film. Guide the unstretched three-layer film to a group of rollers heated to 70~120°C, preferably 70~100°C, and extend it 2.5~4 times in the longitudinal direction (longitudinal direction, that is, the film advancing direction), and Cool with rolls at a temperature of 20-50°C.

Next, both ends of the film are clamped with clamps and guided to the tenter at the same time. In a gas environment heated to a temperature of 90 to 150°C, the film is stretched in the direction perpendicular to the longitudinal direction (width direction) to 2.5~ 4 times.

The stretch magnification is set at 2.5 to 4 times in the long side direction and the width direction respectively. The area magnification (longitudinal stretch magnification × transverse stretch magnification) must be 9 to 16 times, more preferably 10 to 12 times. If the area magnification is less than 9 times, the resulting white reflective film will have insufficient formation of bubbles or unevenness and film strength, and if the area magnification exceeds 16 times, it will easily break during stretching.

After the crystal orientation of the obtained biaxially stretched film is completed, in order to impart dimensional stability, heat treatment is continued in the tenter at a temperature of 150 to 240°C for 1 to 30 seconds, and then cooled to room temperature after uniform cooling. , And then perform corona discharge treatment as necessary to further improve the adhesion to other materials, and wind the white reflective film of the present invention. In the above heat treatment step, it is preferable to perform a relaxation treatment of 3-12% in the width direction or the longitudinal direction.

[Edge-lit backlight]

The white reflective film of the present invention is suitable for edge-light type backlight. side The light-type backlight, for example, is formed by sequentially assembling the white reflective film and the light guide plate of the present invention on a frame with unevenness. The white film is assembled so that one side of the surface layer (A) faces the light guide plate. In addition, a light source such as an LED is installed on the side of the light guide plate. In addition, a diffuser, a porridge, etc. can also be provided on the front of the light guide plate (on the side opposite to the white reflective film).

[Use of white reflective film]

The white reflective film of the present invention can be used for backlights, and is particularly suitable for use in backlights for edge-lit liquid crystal displays, and surface light sources for lighting such as advertisements or vending machines.

It is also suitable for use as a reflecting plate constituting various surface light sources, or a sealing film or a sealing sheet of a solar cell module requiring reflection characteristics. Others can also be used as paper substitutes, that is, cards, labels, stickers, home delivery sheets, photo paper for video printers, inkjet paper, photo paper for bar code printing, posters, maps, dust-free paper, signs, whiteboards, Thermal transfer printing, offset printing, telephone cards, IC cards, etc., used in various printing records such as letter paper base materials, wallpaper and other building materials, lighting fixtures or indirect lighting fixtures used inside and outside the house, mounted on automobiles, railways, airplanes, etc. Electronic components such as components, circuit materials, etc.

[Measurement of physical properties and evaluation method of effect]

test methods

The evaluation method of the physical property value and the evaluation method of the effect of the present invention are as follows.

A. Surface roughness

According to JIS B0601 (2001), use the probe type surface roughness meter (model: ET 4000A) manufactured by Kosaka Laboratory to measure the average roughness of the center surface Degree (SRa). The conditions are as follows, and the average value of 5 measurements is taken as the measured value.

‧Probe tip radius: 0.1μm

‧Probe load: 100μN

‧Measuring length: 1.0mm

‧Cut-off value: 0.25mm

B. Area

Cut out the cross section of the white reflective film sample and use the electric field emission scanning electron microscope "JSM-6700F" (manufactured by JEOL Co., Ltd.) to observe the surface layer (A) at a magnification of 2,000 to 10,000 times. Observe the cross section photographs taken area. The case where it does not have a clear interface, is a coextensive, slightly flattened shape, and has a shaded portion is judged to have a region composed of a polymer different from the polymer constituting the matrix. On the other hand, those with voids formed around them are judged to be particles.

Next, in the case of an area made of polymer, an ultrathin section of the surface layer (A) was made, and after staining with OsO ₄ , the shape of the area and the interface thickness of the area were observed with a transmission electron microscope TEM.

The shape of the area can be calculated by measuring the length in the thickness direction: the length in the longitudinal direction with the distance between two points. Similarly, the interface of the area (the width of the shaded part) is measured by the distance between two points, and the interface thickness is defined. The shape of the area and the thickness of the area at the interface are the average values measured at 5 locations.

C. Particle content

A small piece cut from the surface of the white reflective film with an awl was used as a sample, and the ash content was measured in accordance with JIS K7250-1:2006. With the same The operation measures the other 5 white reflective films and takes the average value of these 5 as the particle content.

D. Cooling crystallization temperature (Tmc)

Weigh 5 mg of small pieces cut from the surface of the white reflective film with an awl to the sample pan, according to JIS K7122 (1987), using the differential scanning calorimetry device "Robotic DSC-RDC220" manufactured by SEIKO Electronics Co., Ltd., and use it for data analysis Disk session "SSC/5200" is measured according to the following procedures. Incidentally, the temperatures listed below are average values measured using 5 film samples.

It is heated from 25°C to 300°C at a temperature increase rate of 20°C/min, kept in this state for 5 minutes, and then rapidly cooled to 25°C or less. Immediately continue to raise the temperature from room temperature to 300°C again at a rate of 20°C/min, keep it in this state for 5 minutes, and then lower the temperature from 300°C to 25°C at a rate of 20°C/min, except for the rapid cooling process. In addition, during each heating and cooling process, the endothermic/exothermic peak is measured.

The temperature of the exothermic peak in the process of cooling from 300°C to 25°C at a rate of 20°C/min was defined as the cooling crystallization temperature (Tmc).

In the cooling crystallization temperature, the high heat generation peak temperature is set as Tmc1 and the low heat generation peak temperature is set as Tmc2, and the difference between the cooling crystallization temperature (Tmc) is obtained according to the following formula.

Difference of cooling crystallization temperature (Tmc) = Tmc1-Tmc2

E. Compatibility with light guide plate

(i) Light guide plate contamination

A 40-inch LCD TV (manufactured by Sony, KDL-40EX700) was disassembled, and an edge-light type backlight using LED as the light source was taken out. The size of the light-emitting surface It is 89cm×50cm, and the diagonal length is 102.2cm. From this, take out the light guide plate from the backlight, cut the light guide plate into a square with a side length of 5 cm, overlap the uneven portion of the light guide plate with the surface layer (A) of the white reflective film of the present invention, and place 500 g on the opposite side of the surface layer (A) With a weight of 3cm×5 times, rub the surface layer (A) of the white reflective film of the present invention. Then, the surface (A) surface of the 5 cm square light guide plate in contact with the surface of the white reflective film of the present invention was observed with a microscope, and the following evaluation results were obtained.

A: Excellent (no attachments are observed)

B: Good (If you observe carefully, you can observe attachments)

F: Poor (attachment is observed)

The above A and B are deemed qualified.

(ii) High load spot test

The light guide plate taken out from the above backlight is cut into a square with a side length of 5 cm, and the uneven part of the light guide plate is overlapped with the surface layer (A) of the white reflective film of the present invention, and the surface layer (A) is made of SUS with a diameter of 1 mm on the opposite side The cylindrical rod weighs 200g and performs 1000 dotting tests. Then, the side of the light guide plate contacting the surface layer (A) of the white reflective film was observed with a microscope, and the following evaluation results were obtained.

A: Excellent (no scar is observed)

B: Good (If you observe carefully, a scar is observed)

F: Bad (scars observed)

The above A and B are deemed qualified.

(iii) Uneven brightness

The reflective film in the backlight of the 32-type liquid crystal TV LHD32K15JP manufactured by Hisense Japan Co., Ltd. is changed to the one of the present invention. White reflective film and light it up. After standing by for 1 hour in this state and stabilizing the light source, under a 500Lx lighting environment or in a dark environment, visually recognizable brightness unevenness was observed, and the following evaluation results were obtained. In addition, the so-called uneven brightness here refers to the unevenness of the bright spots caused by the contact between the reflective film and the light guide plate.

A: Excellent (no uneven brightness is observed under 500Lx lighting environment and dark environment)

B: Good (uneven brightness was observed in a dark environment of 500Lx, but no uneven brightness was observed in a lighting environment)

F: Poor (uneven brightness is observed in both a 500Lx lighting environment and a dark environment)

The above A and B are deemed qualified.

F. Film production

In the Examples and Comparative Examples, when the film was formed, the film rupture only occurred once per day or less, and the case where there was no step contamination caused by particles falling off was regarded as A, and the film rupture only occurred once per day or less. It can be confirmed by naked eyes that contaminants accumulate on the surface of the roller are classified as B, and when film breakage occurs 2 times/day or more and 3 times/day or less, it is classified as F. Mass production must have film forming properties above B. If it is above A , There is further cost reduction effect.

G. Gloss

A digital variable angle gloss meter UGV-5B (manufactured by SUGA Tester Co., Ltd.) was used to measure from the surface layer (A) side of the white reflective film in accordance with JIS Z-8741 (1997). In addition, regarding the measurement conditions, 60° gloss is the value when the measurement conditions are set as incident angle=60° and light receiving angle=60°. Similarly, 20° gloss is incident angle=20° and light receiving angle=20° Time The value, 85° gloss is the value when the incident angle=85° and the light receiving angle=85°.

[Example]

The present invention will be further specifically illustrated by the following examples and the like, but the present invention is not limited thereto.

(raw material)

‧Surface (A)

Terephthalic acid is used as the acid component, ethylene glycol is used as the diol component, and antimony trioxide (polymerization catalyst) is added so that it becomes 300 ppm in terms of antimony atom relative to the obtained polyester particles, and the polycondensation reaction is carried out. Thus, polyethylene terephthalate particles (PET) with an ultimate viscosity of 0.63 dl/g and a carboxyl end group weight of 40 equivalents/ton were obtained.

Isophthalic acid was added in the same way to obtain a polyethylene terephthalate/isophthalate copolymer (PET-I).

In the same way, butylene glycol was added to obtain polybutylene terephthalate (PBT).

‧Polyester with alicyclic structure

The acid component uses dimethyl terephthalate, the diol component uses CHDM (cyclohexane dimethanol), and the polycondensation reaction is carried out in the presence of 200 ppm of butyl tin ginseng (2-ethylhexanoate) to obtain copolymerization Polyester.

In addition, commercially available products (for example, alicyclic structure a uses "TRITAN" (manufactured by Eastman Chemical Company), alicyclic structure b uses "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company)), alicyclic structure c Adopt "ZEONOR" (registered trademark) (made by Zeon Co., Ltd.)).

These products are characterized by the copolymerization component constituting the diol component. For example, EASTAR has a cyclohexane ring and TRITAN has a cyclobutane ring component.

(Examples 1~8) (Examples 1 and 2 are reference examples)

57 parts by mass of PET, 5 parts by mass of (PBT/PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (trade name: Hytrel manufactured by Toray Dupont), and 1,4- 8 parts by mass of copolymerized polyethylene terephthalate (33mol% CHDM copolymerized PET) formed by the copolymerization of 33 mol% of cyclohexanedimethanol relative to ethylene glycol, poly(5-methyl)norbornene 20 parts by mass and 10 parts by weight of rutile titanium oxide were prepared and mixed, dried at 180°C for 3 hours, and then supplied to extruder B (layer B) heated to 270 to 300°C.

On the other hand, layer (A) adopts PET, PET-I, alicyclic structure a adopts "TRITAN" (manufactured by Eastman Chemical Company), and alicyclic structure b adopts "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company) ), particle a uses silica with a particle size of 0.6μm, particle b uses a silica with a particle size of 3.5μm, and particle c uses a barium sulfate with a particle size of 0.6μm, mixed in the ratio shown in Table 1, and vacuum dried at 180°C After 3 hours, they were supplied to extruder A heated to 280°C, and these polymers were layered through a layering device such that layer A/layer B/layer A (8μm/137μm/8μm) were formed by T-die. For flakes. Furthermore, the unstretched film formed by cooling and solidifying the film with a cooling drum with a surface temperature of 25°C is guided to a group of rolls heated to 85-98°C, stretched 3.4 times in the longitudinal direction, and cooled with a group of rolls of 21°C. Next, the two ends of the longitudinally stretched film are clamped with clamps and guided to the tenter at the same time, and stretched 3.6 times in the transverse direction perpendicular to the long sides in a gas environment heated to 120°C. Then, it was heat-fixed at 200°C in a tenter, and then cooled to room temperature after uniformly slow cooling to obtain a biaxially stretched laminated film. The physical properties of the substrate for light reflection are shown in Table 1.

In this way, the white reflective film of the present invention can be formed stably, and exhibits excellent characteristics of the surface shape (high-load dot test, light guide plate contamination, and reduced brightness unevenness).

(Example 9)

(Surface (A))

The amorphous cycloolefin resin A (produced by Zeon Co., Ltd., trade name "ZEONOR 1430R", density (ASTMD792): 1.01g/cm ³ , glass transition temperature Tg (JIS K7121): 133 ℃ pellets and The pellets of propylene resin (manufactured by Japan Polypro Co., Ltd., trade name "Novatec PPEA9") were mixed in a mass ratio of 30:70, and the mixture was supplied to the extruder A according to the above-mentioned method.

(Substrate layer containing air bubbles (B))

The particles of polypropylene resin (manufactured by Japan Polypro Co., Ltd., trade name "Novatec PP FY6HA") and titanium oxide (manufactured by KRONOS company, trade name "KRONOS2230", rutile titanium oxide, Al, Si surface treatment, TiO ₂ content 96.0%, production method: chlorine method) was mixed in a mass ratio of 50:50, and the mixture was supplied to the extruder B according to the above-mentioned method.

(Production of white reflective film)

In each extruder, after melting and kneading at 200°C and 230°C, they are merged in the T die for the three layers of the two raw materials to form layer (A)/layer (B)/layer (A) 3 The layer structure is extruded into a sheet shape, and cooled and solidified to form a laminated sheet. The resulting laminated sheet was stretched twice to MD with a roller at a temperature of 130°C, and then stretched by a tenter at 130°C. It was stretched 3 times to TD and biaxially stretched to obtain a white reflective film having a thickness of 150 μm (resin layer (A): 8 μm, resin layer (B): 134 μm). The physical properties of the substrate for light reflection are shown in Table 1.

In this way, the white reflective film of the present invention can be stably formed, and exhibits excellent characteristics of the surface shape (high-load dot test, light guide plate contamination, and reduced brightness unevenness).

(Example 10~12)

57 parts by mass of PET, 5 parts by mass of (PBT/PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (trade name: Hytrel manufactured by Toray Dupont), and 1,4- 8 parts by mass of copolymerized polyethylene terephthalate (33mol% CHDM copolymerized PET) formed by the copolymerization of 33 mol% of cyclohexanedimethanol relative to ethylene glycol, poly(5-methyl)norbornene 20 parts by mass and 10 parts by weight of rutile titanium oxide were prepared and mixed, dried at 180°C for 3 hours, and then supplied to extruder B (layer B) heated to 270 to 300°C.

On the other hand, layer (A) uses PET, PET-I, and alicyclic structure b uses "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company), mixed in the ratio shown in Table 1, and vacuumed at 180°C After drying for 3 hours, it was supplied to an extruder A heated to 280°C, and these polymers were layered through a layering device so as to become layer A/layer B/layer A, and formed into a sheet shape by a T die. Furthermore, the unstretched film formed by cooling and solidifying the film with a cooling drum with a surface temperature of 25°C is guided to a group of rolls heated to 85-98°C, stretched 3.4 times in the longitudinal direction, and cooled with a group of rolls of 21°C. Next, clamp the two ends of the longitudinally extending film with clamps, and guide them to the tenter at the same time, and heat it to 120℃ in a gas environment. In the middle, it extends 3.6 times in the direction perpendicular to the long side. Then, it was heat-fixed at 200°C in a tenter, cooled to room temperature after uniformly slow cooling, to obtain a biaxially stretched laminate film with a thickness of 150 μm. In addition, by adjusting the discharge rates of the extruder A and the extruder B, the thickness of the surface layer was adjusted to 8 μm to 12 μm in a state where the overall thickness was 150 μm.

The physical properties of the obtained laminated film as a substrate for light reflection are shown in Table 1. In this way, the white reflective film of the present invention can be stably formed, and exhibits excellent characteristics of the surface shape (high-load dot test, light guide plate contamination, and reduced brightness unevenness).

(Comparative Examples 1~6)

In a composite film forming apparatus having a main extruder and a sub-extruder, the formula shown in Table 2 was changed to form a film.

In Comparative Examples 1 and 6, the main protrusions were particles, so the light guide plate was scratched. In Comparative Examples 3 to 6, the alicyclic structure a adopts "TRITAN" (manufactured by Eastman Chemical Company), the alicyclic structure b adopts "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company), and the alicyclic structure d adopts " ECOZEN" (manufactured by SK chemicals)) was mixed in the ratio shown in Table 2, and supplied to the extruder A under the same raw materials and conditions as in Example 1 to produce a white reflective film. As a result, in Comparative Examples 2 and 3 In 5, SRa is small, causing uneven brightness, and in Comparative Example 4, SRa is large, causing light guide plate contamination.

(Comparative Examples 7 and 8)

57 parts by mass of PET, 5 parts by mass of (PBT/PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (trade name: Hytrel manufactured by Toray Dupont), 1,4-ring Hexane dimethanol vs. ethylene glycol 8 parts by mass of copolymerized polyethylene terephthalate (33mol% CHDM copolymerized PET), 20 parts by mass of poly(5-methyl)norbornene, and 10 parts by mass of rutile titanium oxide Parts by weight were prepared and mixed, dried at 180°C for 3 hours, and then supplied to extruder B (layer B) heated to 270 to 300°C.

On the other hand, layer (A) uses PET, PET-I, and alicyclic structure b uses "EASTAR" (registered trademark) (manufactured by Eastman Chemical Company), mixed in the ratio shown in Table 1, and vacuumed at 180°C After drying for 3 hours, it was supplied to an extruder A heated to 280°C, and these polymers were layered through a layering device so as to become layer A/layer B/layer A, and formed into a sheet shape by a T die. Furthermore, the unstretched film formed by cooling and solidifying the film with a cooling drum with a surface temperature of 25°C is guided to a group of rolls heated to 85-98°C, stretched 3.4 times in the longitudinal direction, and cooled by a group of rolls at 21°C . Next, the two ends of the longitudinally stretched film are clamped with clamps and guided to the tenter at the same time, and stretched 3.6 times in the transverse direction perpendicular to the long sides in a gas environment heated to 120°C. Then, it was heat-fixed at 200°C in a tenter, cooled to room temperature after uniformly slow cooling, to obtain a biaxially stretched laminate film with a thickness of 150 μm. In addition, by adjusting the discharge rates of the extruder A and the extruder B, the thickness of the surface layer was adjusted to 3 μm with the overall thickness of 150 μm.

Table 2 shows the physical properties of the obtained laminated film as a substrate for light reflection. SRa is small, and uneven brightness occurs.

(Comparative Examples 9-10)

In a composite film forming apparatus having a main extruder and a sub-extruder, the formula shown in Table 2 was changed to form a film.

The main protrusions are particles c, so the light guide plate is scratched.

[Industrial availability]

The white reflective film of the present invention can be used for backlights, and is particularly suitable for use in backlights for edge-lit liquid crystal displays, and surface light sources for lighting such as advertisements or vending machines. It is also suitable for use as a reflecting plate constituting various surface light sources, or a sealing film or a sealing sheet of a solar cell module requiring reflection characteristics. Others can also be used as paper substitutes, that is, cards, labels, stickers, home delivery sheets, photo paper for video printers, inkjet paper, photo paper for bar code printing, posters, maps, dust-free paper, signs, whiteboards, Thermal transfer printing, offset printing, telephone cards, IC cards, etc., used in various printing records such as letter paper base materials, wallpaper and other building materials, lighting fixtures or indirect lighting fixtures used inside and outside the house, mounted on automobiles, railways, airplanes, etc. Electronic components such as components, circuit materials, etc.

Claims (9)

A white reflective film for edge-lit backlights, which satisfies the following (i) to (iii), (i) is a two-layer laminate film containing at least a surface layer (A) and a substrate layer containing bubbles (B), (ii) The center surface average roughness (SRa) of the surface of the surface layer (A) is 120 nm or more but less than 300 nm, and (iii) the surface layer (A) has a region composed of a polymer different from the polymer constituting the matrix. According to claim 1, the white reflective film for edge-lit backlights, wherein the interface thickness of the aforementioned area is 20 nm or more and 1,000 nm or less. Such as claim 1 or 2 of the white reflective film for edge-lit backlight, where the shape of the area of claim 1 or 2, when the cross-section of the surface layer (A) is observed, the length in the thickness direction: in the longitudinal direction The length ratio is 1:3 or more and 1:50 or less. Such as claim 1 or 2 of the white reflective film for side-light backlight, wherein the surface layer (A) contains particles, and the content of the particles is less than 5% by mass. For example, the white reflective film for edge-light type backlight of claim 1, wherein the gloss difference between 20° and 85° of the surface layer (A) is more than 50%. According to claim 1, the white reflective film for side-light backlight, wherein the surface layer (A) contains at least polyester or polyolefin having an alicyclic structure. The white reflective film for edge type backlight of claim 1, wherein the surface layer (A) is composed of two or more kinds of polymers, and the difference in the cooling crystallization temperature (Tmc) is 10°C or more but less than 40°C. A backlight for liquid crystal displays, which uses the film of claim 1 constitute. For example, the backlight for liquid crystal display of claim 8, wherein the light source is a light emitting diode.