KR20110054990A - Biaxially Stretched Polyester Film for Release Film and Release Film Using the Same - Google Patents

Abstract

The present invention relates to a biaxially stretched polyester film for a release film and a release film using the same. The present invention provides a biaxially oriented polyester film for a release film having a birefringence of at least 3 ° and a birefringence of 0.05 or more in a width direction of 2 m within a width direction, and a release film using the same. The biaxially stretched polyester film for a release film according to the present invention has a large birefringence and an excellent orientation angle due to a reduction in the bowing phenomenon caused by stretching, so that light leakage or glossiness can be controlled during defect inspection using a polarizing plate. .

Release film, biaxially stretched polyester film, birefringence, orientation angle, light leakage

Description

Biaxially stretched polyester film for release film and release film using same {BIAXIALLY ORIENTED POLYESTER FILM AND RELEASE FILM USING THE SAME}

The present invention relates to a biaxially stretched polyester film for a release film and a release film using the same. More particularly, the birefringence is large, and the orientation angle is excellent due to the reduction of the bowing phenomenon caused by the stretching. The present invention relates to a biaxially stretched polyester film for a release film capable of controlling light leakage or gloss and a release film using the same.

In general, the demand for liquid crystal displays (hereinafter referred to as "LCDs"), which has advantages of light weight, low power consumption, thinness, and high quality, is rapidly increasing, compared to conventional CRT (Cathode Ray Tube). In recent years, such LCDs often use a functional film that increases the brightness of the backlight or improves the brightness of the backlight. In the LCD of such a high-brightness type, the brightness of the LCD is high. As a result, activities to prevent foreign substances from entering into the manufacturing process of each component are being strengthened, and even if foreign substances are mixed, standards for process inspection, quality inspection, and shipment inspection are becoming more stringent so that the corresponding products do not leak. In this case, the defect inspection method used is a visual inspection by the cross-cinnic method in which the alignment axes of the polarizing plates are orthogonal using two polarizing plates, and the product to be inspected is inserted between the polarizing plates. If present, it will appear as a bright point.

In particular, biaxially stretched polyester films are widely used due to excellent mechanical, thermal, and optical properties as members of polarizing plate films, but light leaks in polarizing plate cross nicol inspection due to optical anisotropy of polyester films by biaxial stretching process. This creates a phenomenon, which makes it difficult to inspect small foreign objects or defects present in polarizer-related products. In addition, in recent years, the cross nicol inspection method has been strengthened. In addition to inspecting the two polarizers from the front in an orthogonal state, in addition to the inclination angle from the left and right sides, the inspector can easily examine the eyes due to the glare caused by the glossy phenomenon. Fatigue and obstacles in testing defects and foreign objects.

As an example of the member for a polarizing plate, Japanese Unexamined-Japanese-Patent No. 7-101026 uses the release film which made the base film the biaxially-oriented aromatic polyester film, and uses the biaxially-oriented polyester film in the direction of the orientation main axis and the polarizing plate A laminate and a release film therefor are described, which are positioned so that the direction of the retardation polarizer or the orientation axis of the retardation plate is substantially the same. However, in order to align the direction of the orientation major axis of the biaxially oriented polyester film and the direction of the orientation axis of the polarizing plate, the retardation polarizing plate or the retardation plate substantially, the orientation major axis of the biaxially oriented polyester film is checked and the direction and the polarizing plate are Although it is necessary to make the direction of the orientation axis of a retardation polarizing plate or a retardation plate substantially correspond, it is extremely difficult from a productive point of view. In addition, when using only the part in which the main orientation axis | shaft of a biaxially-oriented polyester film exists in the width direction (direction orthogonal to a machine direction), although the effort which confirms the above-mentioned orientation main axis will disappear, the produced biaxially-oriented poly Part of the central portion of the ester film, other portions are likewise unusable and disadvantageous in terms of productivity and cost, resulting in commercial difficulties.

In general, biaxially oriented polyester film is a balance between the mechanical and thermal characteristics by the stretching process in the longitudinal direction and the width direction in the film forming process, the direction of the molecular orientation major axis of the film is the stretching ratio in the width or longitudinal direction The central portion in the width direction is oriented in the width direction but gradually inclines in the longitudinal direction from the center portion to the end portion.

An orientation angle means the angle between the width direction or the longitudinal direction of a film, and a molecular orientation main axis, and means the angle which molecular orientation makes with respect to the width direction of a film in this invention. In other words, the difference in the orientation angle occurs depending on the position in the width direction, the main cause of the bowing phenomenon is difficult to control the stress in the film longitudinal direction due to the high temperature heat treatment process for securing mechanical properties in the tenter stretching process Because this happens. By this phenomenon, the orientation angle becomes larger toward both ends than the center portion of the film. At this time, when the polyester film used to protect the polarizing substrate is larger than a certain level, when the laminated film is laminated on the uniaxially oriented polarizing substrate, light interference due to optical isotropy occurs when visual inspection by the cross nicol method is performed. This makes light leak from the perfect black mode state at the time of inspection, making it difficult to inspect foreign objects or defects. Since the degree of interference becomes more severe toward both ends than the center part, if only a specific (particularly, the center part) position part using an orientation angle satisfying a value below a certain level is used as a release film, there is a problem in that productivity is greatly reduced.

Therefore, in order to use the full-length polyester film produced as a suitable use for the polarizing substrate protection purpose, it is necessary to attempt to minimize the bowing phenomenon. In order to minimize the bowing phenomenon, in the polyester manufacturing process, the method of orienting strongly in either direction by making large difference in the draw ratio of the longitudinal direction and the width direction has been proposed. In particular, a method of decreasing the variation in the orientation angle in the width direction by increasing the draw ratio in the width direction relative to the longitudinal direction is common. In order to realize this, when the stretching in the width direction is excessive, the film is often torn during the stretching process, which adversely affects the productivity. Therefore, as the draw ratio in the width direction is fixed within the film's tear-free range and the draw ratio in the longitudinal direction is lowered, the orientation angle in the width direction gradually approaches 0 ° and the variation in the orientation angles in each width direction decreases. Stretching mura by the stretching of the direction occurs, and when visual inspection by the cross nicol method, it appears as a defect or interfere with the inspection. On the other hand, when the draw ratio in the longitudinal direction is increased in order to improve the draw mura problem, the orientation angle in the width direction is increased, which makes it unsuitable as a protective film for polarizing plates. In addition, in the case of biaxially stretched polyester film, if the thermal stability is poor, thermal wrinkles of the film may occur in the post-coating process, so the post-processing temperature is usually 150 ° C. or lower, and thus heat shrinkage management is required. Not only causes problems with dimensional stability but also causes problems with adhesive coating.

An object of the present invention is to provide a biaxially stretched polyester film for a release film that can control light leakage or gloss during defect inspection using a polarizing plate.

An object of the present invention is to provide a release film using the biaxially stretched polyester film.

The biaxially stretched polyester film for release films of the present invention for achieving the above object has an orientation angle range of 2 m or less in the width direction within 3 °, and a birefringence is 0.05 or more.

On the other hand, in the biaxially stretched polyester film for release films of this invention, it is preferable that the refractive index values of a longitudinal direction and a width direction are 0.05 or more.

On the other hand, it is preferable that the shrinkage rate of the biaxially stretched polyester film for release film of the present invention is each within 5% of the heat shrinkage in the width direction and in the longitudinal direction, more preferably within 4%.

It is preferable that the haze of the biaxially stretched polyester film for release films of this invention is less than 6%.

Biaxially stretched polyester film for a release film of the present invention must satisfy the following formula (1):

[Equation 1]

A ≤ B x 30

In the above formula, A is a luminance value measured in a state where the biaxially stretched polyester film is placed between two polarizing plates having an orthogonal alignment axis and the longitudinal direction is coincident with one of the polarizing plates, and B is an alignment axis of the two polarizing plates. It is the luminance value measured in the orthogonal state.

The biaxially stretched polyester film for a release film of the present invention may be used as a release film by further forming a silicone coating layer on either side.

The biaxially stretched polyester film for a release film according to the present invention has a large birefringence and an excellent orientation angle due to a reduction in the bowing phenomenon caused by stretching, so that light leakage or gloss can be controlled during defect inspection using a polarizing plate. . As a result, the release film of the present invention can facilitate visual inspection of foreign matters and defects by the cross nicol method, and in particular, when used in a large screen LCD, the accuracy of visual inspection can be reduced by reducing the possibility of defects and foreign substances. It is possible to drastically reduce the defective rate of the product.

The biaxially stretched polyester film for release films of the present invention has an orientation angle range of 2 m or less in the width direction of the film within 3 °, and a birefringence is 0.05 or more.

As for the biaxially stretched polyester film for release films of this invention, the orientation angle with respect to the width direction is less than 3 degrees in 2 m width. If it is less than 3 ° within 2m width, the two polarizer cross nicol inspections will not leak light and maintain the black mode environment, making it easy to inspect foreign materials and defects while improving productivity and cost aspects. When it exceeds 3 ° in 2m width, the light leaks due to the misalignment of the alignment axis with the alignment axis of the polarizer.

On the other hand, the birefringence in the present invention is the absolute value of the difference between the width direction and the longitudinal refractive index value in the present invention, because the stretch ratio in the width direction is large, the refractive index value in the longitudinal direction from the refractive index value in the width direction is referred to as birefringence . In the biaxially stretched polyester film for release film of this invention, it is preferable that birefringence value is 0.05 or more. If less than 0.05, two polarizer cross nicol test is so glossy that it may cause a failure of the inspection, and foreign matters or defects may be omitted.

The polyester used for the biaxially oriented film for release film of this invention points out the polyester obtained by polycondensing aromatic dicarboxylic acid and aliphatic glycol, and there is no restriction | limiting in particular in the kind. General polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and the like may be used, but are not limited thereto. As aromatic dicarboxylic acid, terephthalic acid, 2, 6- naphthalenedicarboxylic acid, etc. are mentioned, As aliphatic glycol, ethylene glycol, diethylene glycol, 1, 4- cyclohexane dimethanol, etc. are mentioned. Typical polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. The said polyester can also be a copolymer containing a 3rd component. Examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (for example, P-oxybenzoic acid). Examples thereof include ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentylglycol, and the like. These dicarboxylic acid components and glycol components may use 2 or more types together.

On the other hand, the heat shrinkage of the biaxially stretched polyester film for release film of the present invention is measured under a drying condition of 150 ℃, 30 minutes It is preferable that the thermal contraction rates in the width direction and the longitudinal direction are each within 5%, more preferably within 4%. When it exceeds 5%, thermal wrinkles generated in the film in the post-processing process may cause inspection failure or problems in coating appearance such as adhesive. The heat shrinkage rate is for maintaining the thermal stability, the smaller the better.

It is preferable that the haze of the biaxially stretched polyester film for release films of this invention is less than 6%. If the haze value exceeds 6%, the water defects existing on the surface and inside of the film may be missed during inspection, and may cause defects such as bright spots caused by foreign matter when the polarizer is attached. Low haze transparent films are required to enhance the management of product defects and optical properties, which are becoming increasingly difficult to measure. When the haze exceeds 6%, there is a problem in that optical properties such as color are degraded.

The haze depends on the type and content of particles present in the polyester film. If the amount of particles used is too small, problems such as scratching and winding projections may occur due to unfavorable winding of the product. It is preferable not to lower | hang. As the type of particles used, inorganic particles such as silica, calcium carbonate, aluminum and titanium dioxide, organic particles such as crosslinked polystyrene resin particles and crosslinked acrylic resins are preferable, and one or more kinds can be selected and used, and the average particle size is used. Is preferably between 0.05 and 3.5 μm. If the particle diameter is too low, less than 0.05㎛, the surface roughness of the film surface is excessively low, causing scratches and adhesion defects on the surface of the film during the manufacturing process of the polyester film, if exceeding 3.5㎛ scratch and adhesion of the film surface It is beneficial for defects, but the haze is so high that there is a possibility of missing defects in product defect inspection and can cause surface crete defects.

Biaxially stretched polyester film for a release film of the present invention must satisfy the following formula (1):

[Equation 1]

A ≤ B x 30

Where A is a biaxially stretched polyester film between two polarizing plates having an orthogonal alignment axis, and the length of the biaxially stretched polyester film is aligned with one alignment axis of the polarizing plate, and the brightness of the light passing through the two polarizing plates from the lower light source is measured. It is the measured luminance value and B is the luminance value which measured the brightness of the light which passed the two polarizing plates from the lower light source in the state orthogonal to the orientation axis of two polarizing plates.

The B value is a state in which the alignment axes of the two polarizers are orthogonal to each other, so that the light passed from the bottom is at a minimum, which is easy to inspect the foreign matter. When the light is refracted by the polyester film and passed through the two polarizing plates is increased, the measured A value is increased. If the value of A exceeds 30 times of the value of B, the inspection of the orthogonal polarizer does not facilitate the inspection of foreign matters or defects inside the polarizer by light leakage. Will cause.

In the biaxially stretched polyester film for a release film of the present invention, a silicone coating layer is additionally formed on one side thereof and may be used as a release pen. The silicone coating layer applied to one side of the polyester film is used to protect the adhesive layer until it is laminated with the adhesive layer attached to the film surface having a specific function and the adhesive layer is attached to the other substrate. The compound for the silicone coating layer used for this purpose is preferably a curable silicone resin for stable release force management, and for example, a resin containing a curable silicone resin as a main component, or a urethane resin, an epoxy resin or an alkyd. Silicone resins obtained by graft polymerization of organic resins such as resins may be used.

The biaxially stretched polyester film of the present invention is melted by an extruder after vacuum drying the polyester resin of the above-described configuration, extruded into a sheet through a T-die and adhered to the casting drum by pinning to a cooling roll Cooling and solidifying to obtain an unstretched polyester sheet, and in a roll heated above the glass transition temperature of the polyester resin, uniaxial stretching in the longitudinal direction of the circumferential speed ratio between the rolls and the rolls was performed in the range of 2.5 to 4.0 times. Prepare ester film.

A biaxially stretched polyester film is further stretched in the range of 3.5 to 6 times in the width direction to prepare a biaxially stretched polyester film. It passes the stretching process in the width direction at 95 ℃ or higher and then undergoes the heat treatment process at 180 ~ 240 ℃ high temperature to adjust the mechanical strength, elongation and crystallinity, and finally the film length in the width direction to relieve stress caused by high temperature stretching. A biaxially stretched polyester film is prepared through a stress relaxation process to reduce the thickness, and the thickness is usually 5 to 300 μm, preferably 10 to 250 μm.

Hereinafter, the present invention will be described in detail with reference to examples of the present invention. These examples are only presented by way of example only to more specifically describe the present invention, it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples. .

[Examples 1 to 3]

Polyethylene terephthalate resin containing 400 ppm of silica particles having an average particle diameter of 2.3 mu m was dried under reduced pressure at 160 DEG C for 6 hours. The dried resin was melted and extruded in an 280 ° C. extruder, filtered through an 8 μm size filter, and then the melt was extruded through a T-die, followed by cold forming into sheets on a cooling roll at 20 to 25 ° C. through electrostatic application. To prepare an unstretched sheet. After passing the unstretched sheet through the heated rolls, it is stretched 2.8 times in the longitudinal direction using the peripheral speed ratio between the infrared heater and the rolls, and then stretched 4.7 to 5.0 times in the width direction by passing through a tenter stretching section of 90 to 110 °. I was. Finally, a biaxially stretched polyester film for a transparent release film having a thickness of 38 μm was produced by passing a heat treatment process at 195 to 205 ° C. (stress relaxation rate 4.7 to 5.0%). The obtained results are shown in Table 1.

[Comparative Examples 1 to 3]

Biaxially stretched polyester in the same manner as in the examples except that the film was stretched 2.8 to 3.4 times in the longitudinal direction and 4.7 times in the width direction, and the heat treatment temperature was changed to 205 to 230 ° C. and the stress relaxation rate was changed to 4.5 to 5.0%. A film was prepared.

The biaxially stretched polyester films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to the following experiments in order to find out the properties required as protective films under the polarizing plate inspection environment.

Experimental Example 1: Birefringence Measurement

The refractive index of the biaxially stretched polyester films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured using a refractometer (ATAGO ABBE, KS-SYSTEM). The birefringence was obtained by the following formula and the results are shown in Table 1.

Birefringence = widthwise refractive index-lengthwise refractive index

Experimental Example 2: Heat Shrinkage Measurement

After sampling the specimen of 150 mm in width and 150 mm in length, the biaxially stretched polyester film prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was enlarged by 10 times with a magnifying glass (Mitutoyo's PROfile project PJ-H3000F). Check the size The sample was heated for 30 minutes in a hot-air circulating high temperature dryer set at 150 ° C., taken out, and the actual size was confirmed by a magnifying glass, and calculated from the following equation, and the results are shown in Table 1.

Thermal contraction rate (%) = (length before heating-length after heating) / length before heating

Experimental Example 3 Light Leaping Phenomena

The films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were each 10 cm in size, and sandwiched between two polarizing plates orthogonal to each other such that the alignment axes were 90 °. In the state in which the longitudinal direction of the biaxially stretched polyester film was aligned with the alignment axis of any one polarizer, the luminance in the cross nicol state was measured in a sample at nine intervals within a sample using a luminance meter (CA2000, manufactured by Konica Minolta). The average value (A) was obtained. The light leakage phenomenon was evaluated based on the luminance average value (B) measured while the two polarizers were orthogonal.

   ○: A ≤ B x 30

   △: B x 30 <A ≤ 60

   ×: A> 60

Experimental Example 4 Gloss

The biaxially stretched polyester film of A4 size prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was uniaxially stretched and adhered between two polarizing plates orthogonal to each other. Visually check the gloss phenomenon according to the generation of strong rainbow colors at the position between the sample for inspection and the naked eye at about 30 ° with the length direction of the biaxially stretched polyester film coincident with the alignment axis of the polarizing plate. Observe. The occurrence degree of gloss was evaluated based on the following criteria.

   ○: The color of the entire sample consists of only bluish and reddish areas, and there is no yellow or white color, so it is not glossy.

   (Triangle | delta): The bluish and reddish area | region which the color which makes up the whole sample shows that a yellow phase is pale in a part or some edge part.

   ×: Yellow and white light appear strongly in many areas of the sample, and glare is strong, so that defect inspection is difficult

Experimental Example 5 Haze Measurement

In accordance with JIS K7105, a biaxially stretched polyester film sample cut into dimensions of 4 cm in the film length and 4 cm in the width direction was measured three times at different locations using a haze meter (AUTOMATIC DIGITAL HAZEMETER, Nippon Densoku, Japan). The average value was applied and the results are shown in Table 1.

Experimental Example 6: End Orientation Angle Measurement

For the biaxially stretched polyester film full width products prepared in Examples 1 to 3 and Comparative Examples 1 to 3, samples of A4 size for orientation angle measurement were taken at both end positions in the width direction, and thereafter, every 2 m inward positions. Samples were taken in A4 size for orientation angle measurement at. The samples at each position were measured for orientation angles using a molecular orientation system (MOA), and the results are shown in Table 1. Here, the orientation angle is an angle at which the main axis of molecular orientation is in the width direction.

 Table 1

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3

Condition
Length stretch ratio 2.8 2.8 2.8 3.4 3.4 2.8 Width draw ratio 4.7 4.7 5.0 4.7 4.7 4.7 Heat treatment temperature (℃) 195 205 205 205 220 230 Stress relaxation rate (%) 6.5 4.5 4.6 4.5 4.5 5.0


result



Birefringence 0.059 0.060 0.063 0.038 0.039 0.058 Heat shrink Longitudinal direction (%) 4.2 3.7 3.8 3.9 2.2 1.8 Width direction (%) 3.5 2.8 3.0 2.9 2.2 0.6 Light leakage ○ ○ ○ △ △ X Luster ○ ○ ○ △ X ○ Haze 3.2 3.3 3.5 3.3 3.4 3.3 End orientation angle (°) 4.4 5.5 4.9 7.7 9.5 13.5 Between 2m width
Difference in Orientation Angle (°) 2.1 2.5 2.3 3.3 4.1 5.5

As shown in the results of Table 1 for Examples 1 to 3 and Comparative Examples 1 to 3, the lower the longitudinal draw ratio, the higher the width draw ratio, and the lower the heat treatment temperature, the lower the orientation angle and pass through the two polarizing films. It can be seen that the light is lowered, and at the same time the birefringence is increased to produce less bi-color polyester film excellent in the inspection of the film surface or the foreign matter with the effect that less gloss occurs.

While the invention has been described in detail only with respect to the described embodiments, it will be apparent to those skilled in the art that various modifications and variations are possible within the spirit of the invention, and such modifications and variations belong to the appended claims.

Claims (7)

The biaxially stretched polyester film for release films whose orientation angle range between 2 m in a width direction of a film is less than 3 degrees, and whose birefringence is 0.05 or more. The biaxially stretched polyester film for release film according to claim 1, wherein the heat shrinkage in the width direction and the longitudinal direction is each within 5% at 150 ° C and 30 minutes in dry conditions. The release film of claim 1, wherein the polyester film further comprises one or more particles selected from the group consisting of silica, calcium carbonate, aluminum, titanium dioxide, crosslinked polystyrene resin, and crosslinked acrylic resin particles. Biaxially stretched polyester film. The biaxially stretched polyester film for a release film of claim 3, wherein the particles have an average particle diameter of 0.05 to 3.5 μm. The biaxially stretched polyester film for a release film according to claim 1, wherein the haze is within 6%. Biaxially stretched polyester film for release film that satisfies Equation 1 below: [Equation 1] A ≤ B x 30 In the above formula, A is a luminance value passed from the lower light source while a biaxially stretched polyester film is placed between two polarizing plates having an orthogonal alignment axis and the longitudinal direction is coincident with one alignment axis of the polarizing plate, and B is two polarizing plates. It is the luminance value passed from the lower light source in the state where the alignment axis of is orthogonal. A release film having a silicon coating layer formed on one side of the biaxially stretched polyester film according to any one of claims 1 to 6.