JP2008063538A - Polyester film for mold release film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film which is excellent in an optical property, being an important property for a liquid crystal display and the like, and exhibits high degree precision in the detection of a drawback in the film test, and thus practically realizes a polyester film for mold release with high precision capable to easily detect drawback in the test by an important test Cross-Nicol method, in the production process of polarizing plate. <P>SOLUTION: The polyester film for release from mold is characterized by containing particles with an average diameter in a range of 0.2-1.5 μm and a particle size distribution value (d25/d75) of 1.0-2.0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a polyester film that is an important property in films for liquid crystal display applications, etc., is excellent in optical properties, and can obtain a high degree of accuracy in defect detection in film inspection, particularly a release film for polarizing plates It is related with the polyester film used suitably for.

  Polyester films represented by polyethylene terephthalate and polyethylene naphthalate have excellent mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, etc. It is used in applications. However, as the application diversifies, the processing conditions and usage conditions of the film diversify, and the particle component in the release film becomes a bright spot when inspecting the foreign material of the polarizing plate, and the accuracy of the inspection decreases. Has occurred.

  In recent years, with the rapid spread of mobile phones and personal computers, the demand for liquid crystal displays (LCDs) that are thinner, lighter, consume less power, and have higher image quality than the conventional display CRT is growing significantly. There is also a remarkable growth in the technology for increasing the screen size of LCDs. As an example of increasing the screen size of LCD, recently, LCD is used for large TV applications of, for example, 30 inches or more. In a large-screen LCD, a bright LCD with a large screen is often obtained by increasing the luminance of a backlight incorporated in the LCD or incorporating a film for improving the luminance in a liquid crystal unit.

  Recently, there is a tendency to increase the brightness of the display screen for the purpose of improving the visibility of the LCD, and in such a so-called high brightness type LCD, a small bright spot existing in the display often becomes a problem. In a component such as a polarizing plate, a retardation plate or a retardation polarizing plate incorporated in a display, a foreign material having a minute size that has not been a problem in conventional low-brightness LCDs has become a problem. Yes. For this reason, while preventing the entry of foreign matter in the manufacturing process, it is also important to improve the inspection accuracy so that even if foreign matter is mixed, it can be recognized as a defect.

  As a defect inspection of a polarizing plate, a visual inspection by a crossed Nicol method is generally used. Further, for example, in a polarizing plate used for a large-sized TV having a size of 40 inches or more, an inspection by an automatic foreign substance inspection device using the crossed Nicol method is also possible. The crossed Nicols method that is being implemented is a method in which two polarizing plates are put in a quenching state with their orientation main axes orthogonal to each other, and if there are foreign objects or defects, they appear as bright spots, so that visual defect inspection can be performed. is there.

  Conventionally, the particles in the polyester film are usually used to ensure the slipperiness and winding characteristics of the film, and if the appropriate particle size and blending amount are not satisfied, the desired slipperiness cannot be ensured. As a result, the winding characteristics deteriorate, resulting in a deterioration in productivity. However, when the particle size and blending amount are within the normally used range, as described above, when used as a release film for a polarizing plate, the added particles become bright spots in the foreign substance inspection process, which hinders inspection. Is a problem.

  In addition, a pressure-sensitive adhesive layer is usually provided on the polarizing plate, and a polyester film provided with a release layer is used as a release film therefor. When a product having such a configuration is inspected, a crossed Nicols inspection is performed in a state where a release polyester film is sandwiched between two polarizing plates. In general, when a release polyester film is used for this, foreign matter and defects are difficult to see in the crossed Nicols inspection, and it may be easy to miss them.

Regarding these, it is disclosed that when a polyester film is sandwiched between two polarizing plates, the inspection value is improved when the retardation value is within a certain range (see Patent Document 1). However, there may be a problem when an inspection for surely finding defects is performed.
JP 2000-338327 A

  The present invention is intended to solve such a conventional problem, and the problem to be solved is to provide a polyester film for a release film capable of realizing a high degree of accuracy in the inspection of a polarizing plate by the crossed Nicols method. There is.

  As a result of intensive studies in view of the above problems, the present inventor can provide a polyester film that is particularly suitable for a polyester film for a release film, without impairing excellent film properties, according to a polyester film having a specific configuration. As a result, the present invention has been completed.

That is, the gist of the present invention is to contain particles having an average particle size in the range of 0.2 to 1.5 μm and a particle size distribution value (d25 / d75) in the range of 1.0 to 2.0. It exists in the polyester film for release films characterized by these.
Hereinafter, the present invention will be described in detail.
The polyester film referred to in the present invention is a film which is melt-extruded from an extrusion die, and is subjected to stretching and heat treatment as necessary after cooling a molten polyester sheet extruded by a so-called extrusion method.

  The polyester constituting the film of the present invention is obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. The polyester used may be a homopolyester or a copolyester. In the case of a copolyester, it may be a copolymer containing 30 mol% or less of the third component.

  The dicarboxylic acid component of the copolymerized polyester is selected from isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid and oxycarboxylic acid (for example, P-oxybenzoic acid). The glycol component includes one or more selected from ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

  The polyester may be converted into chips after melt polymerization, and further subjected to solid phase polymerization as necessary under heating under reduced pressure or in an inert gas stream such as nitrogen. The intrinsic viscosity of the obtained polyester is preferably 0.40 dl / g or more, and preferably 0.40 to 0.90 dl / g.

  In the present invention, it may be a film having a structure obtained by coextrusion laminating a polyester having a low oligomer content on the surface of at least one side of a layer composed of a polyester having a normal oligomer content. In the polyester film for release film obtained in the present invention, the effect of preventing bright spots due to oligomer precipitation is obtained, which is particularly preferable.

  In the polyester obtained by the present invention, a weathering agent, a light-proofing agent, an antistatic agent, a lubricant, a light-shielding agent, an antioxidant, a fluorescent whitening agent, a matting agent, and a heat-stabilizing agent as long as the gist of the present invention is not impaired. You may mix | blend an agent and coloring agents, such as dye and a pigment.

  Examples of the particles to be blended in the film include silicon oxide, alumina, calcium carbonate, kaolin, titanium oxide, and crosslinked polymer fine powder as described in JP-B-59-5216. These particles may be used alone or in combination of two or more components. And the content is 1 weight% or less normally, Preferably it is 0.01 to 1 weight%, More preferably, it is the range of 0.02 to 0.6 weight%. When the content of the particles is small, the film surface is flattened, and there is a tendency that scratches on the surface in the film production process are likely to occur or the winding properties are inferior. Further, when the content of the particles exceeds 1% by weight, the degree of roughening of the film surface becomes too large, and the transparency may be impaired.

  The average particle size of the particles contained in the polyester film needs to be in the range of 0.2 to 1.5 μm. When the particle size is less than 0.02 μm, the film surface is flattened, and the film manufacturing process There is a tendency that the winding characteristics in are inferior. When the particle diameter exceeds 5 μm, when used as a polarizing plate release film, it may become a bright spot and hinder foreign matter inspection.

  Further, the particle size distribution of the particles used must be sharp. Specifically, the particle size distribution value, which is an index representing the sharpness of the particle size distribution, needs to be 1.0 to 2.0, and more preferably 1.1 to 1.8. Here, the particle size distribution value is the particle size distribution value d25 / d75 (d25 and d75 are calculated by calculating the accumulated accumulation of the particle group from the large particle side, and the particle size (μm corresponding to 25% and 75% of the total volume, respectively) Is a value defined by When the particle size distribution value exceeds 2.0, coarse particles become bright spots, which similarly impedes foreign matter inspection.

  On the other hand, in order to improve the transparency of the film, when a laminated film of two or more layers is used, a method of blending particles only in the surface layer is also preferably employed. The surface layer in this case is at least one of the front and back layers, and of course, particles can be blended in both the front and back layers.

  In the present invention, the method of blending the particles with the polyester is not particularly limited, and a known method can be adopted. For example, it can be added at any stage for producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or before the start of the polycondensation reaction after completion of the transesterification reaction. The condensation reaction may proceed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a method of blending dried particles and a polyester raw material using a kneading extruder Etc.

  The polyester film in the present invention preferably has a variation in orientation angle of 3 degrees / 500 mm or less, more preferably 2 degrees / 500 mm or less, in the measurement method described in the examples. When the variation in the orientation angle exceeds 3 degrees / 500 mm, the transmitted light intensity varies depending on the position of the polarizing plate when inspecting the polarizing plate, which is an undesirable obstacle to stable inspection of the polarizing plate.

  The polyester film in the present invention preferably has a refractive index (nβ) in the direction perpendicular to the film in-plane direction of 1.6400 or less with respect to the main orientation axis. There is a tendency to increase the fluctuation of the angle, which not only becomes an obstacle to stable inspection of the polarizing plate, but also the formation of voids in the particles becomes prominent and easily visible as a bright spot during the inspection of the polarizing plate. There is a case.

  The thickness of the film of the present invention is not particularly limited as long as it can be formed as a film, but is usually 4 to 100 μm, preferably 9 to 50 μm.

  Next, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the summary of this invention is satisfied, this invention is not specifically limited to the following illustrations.

  First, the preferable example of the manufacturing method of polyester used by this invention is demonstrated. Here, an example in which polyethylene terephthalate is used as the polyester is shown, but the production conditions differ depending on the polyester used. According to a conventional method, esterification from terephthalic acid and ethylene glycol or transesterification of dimethyl terephthalate and ethylene glycol is carried out, the product is transferred to a polymerization tank, the temperature is increased while reducing the pressure, and finally The polymerization reaction is advanced by heating to 280 ° C. under vacuum to obtain a polyester.

  The intrinsic viscosity of the polyester used in the present invention is usually in the range of 0.40 to 0.90, preferably 0.45 to 0.80, more preferably 0.50 to 0.70. When the intrinsic viscosity is less than 0.40, the mechanical strength of the film tends to be weakened. When the intrinsic viscosity is more than 0.90, the melt viscosity becomes high, the load on the extruder is increased, and the production cost is increased. Problems may occur.

  Next, for example, the polyester chip obtained as described above and dried by a known method is supplied to a melt-extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer and melted. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed. In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 2 to 90 to 160 ° C. in the lateral direction. It is preferable to perform ~ 6 times stretching and heat treatment at 150 to 240 ° C for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary. Furthermore, it is also possible to perform simultaneous biaxial stretching of the unstretched sheet so that the area magnification is 10 to 40 times.

  The polyester film of the present invention can be subjected to so-called in-line coating for treating the film surface during the stretching step as long as the effects of the present invention are not impaired. Although it is not limited to the following, for example, after the first stage of stretching is completed, before the second stage of stretching, improvement of antistatic property, slipperiness, adhesion, etc., secondary workability improvement, weather resistance, etc. In order to improve the property and surface hardness, a coating treatment with an aqueous solution, an aqueous emulsion, an aqueous slurry, or the like can be performed. Various coatings may be performed by offline coating after film production. Such a coat may be either single-sided or double-sided. The coating material may be either water-based and / or solvent-based for off-line coating, but is preferably water-based or water-dispersed for in-line coating.

  When a release layer is installed on the polyester film of the present invention, the material constituting the release layer is not particularly limited as long as it has releasability, and a type mainly composed of a curable silicone resin may be used. Alternatively, a modified silicone type obtained by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin may be used. Among these, when a curable silicone resin is used as a main component, good releasability is sufficient.

  Types of curable silicone resins include solvent addition type, solvent condensation type, solvent ultraviolet curable type, solventless addition type, solventless condensation type, solventless ultraviolet curable type, solventless electron beam curable type, etc. But it can also be used.

  ADVANTAGE OF THE INVENTION According to this invention, the polyester film which can be used for release films, such as a polarizing plate and a phase difference plate, can reduce the luminescent spot of a film as much as possible, and can raise a foreign material inspection precision is provided. Value is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. In the examples and comparative examples, “parts” means “parts by weight”. The measuring method used in the present invention is as follows.

(1) Measurement of Intrinsic Viscosity of Polyester 1 g of polyester was precisely weighed, 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) was added and dissolved, and measurement was performed at 30 ° C.

(2) Average particle size (d50) and particle size uniformity (d25 / d75)
The average particle size d50 was defined as the particle size having an integrated volume fraction of 50% in an equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution analyzer (SA-CP3 type) manufactured by Shimadzu Corporation. In addition, the ratio d25 / d75 of the diameter of the point having a weight fraction of 25% and the diameter of the point having a weight fraction of 75%, integrated from the large particle side, was used as the particle size distribution value.

(3) Measurement of variation in orientation angle in the film In the width direction of the polyester film, from the center position toward the both ends in the width direction, the sample at every 500 mm and the samples at the extreme ends are cut out, respectively, Oji measuring instruments Using an automatic birefringence meter (KOBRA-21ADH) manufactured by the company, the change in the orientation angle for every 500 mm in the film width direction was determined. When calculating the change in the orientation angle including the positions at the extreme ends, if the distance between the sample positions is less than 500 mm, the change in the orientation angle every 500 mm is calculated by proportional calculation. Subsequently, a 3 m length was cut out in the longitudinal direction of the film, and a sample was cut out from a total of 7 positions every 500 mm (including both ends) in the longitudinal direction from the center in the film width direction, and the orientation angle was determined. Thus, the variation of the orientation angle for every 500 mm in the width direction and the longitudinal direction was obtained, and the maximum variation value was set as the variation of the orientation angle of the film. Further, in the measurement, it is important to make the reference axis of the orientation angle the same in all samples, and the reference axis can be arbitrarily determined.

(4) Refractive index of film (nβ)
In the width direction of the polyester film, from the center position, the position at every 500 mm toward the both ends in the width direction and the sample at the extreme ends are cut out, and the main surface in the film plane is obtained using an Abbe refractometer manufactured by Atago Optical Co. The refractive index in the direction perpendicular to the orientation axis was measured at each position, and the average value was obtained to obtain nβ.

(5) Visual inspection property under crossed Nicols 100 parts of curable silicone resin (“KS-779H” manufactured by Shin-Etsu Chemical), 1 part of curing agent (“CAT-PL-8” manufactured by Shin-Etsu Chemical) on one side of the polyester film Then, a release agent composed of 2200 parts of methyl ethyl ketone (MEK) / toluene mixed solvent system was applied so that the coating amount was 0.1 g / mm ² and dried at 170 ° C. for 10 seconds to obtain a release film. After that, the release film is brought into close contact with the polarizing film via an adhesive so that the width direction of the release film is parallel to the orientation axis of the polarizing film, and oriented on the tightly attached release film. The inspection polarizing plate is overlapped so that the axis is orthogonal to the film width direction, white light is irradiated from the polarizing plate side, and 10 inspectors are visually observed from the inspection polarizing plate, and crossed Nicols. Under A visual inspection of was evaluated according to the following criteria. In the measurement, samples of A4 size were cut out from locations corresponding to positions of 10, 50, and 90% of the film width in the film width direction from the end of the obtained polyester film, respectively. .
<Criteria for visual inspection under crossed Nicols>
(Good inspection) ◎>○>△>×> XX (Inspection failure)
Among the above criteria, those above Δ are levels that can be used without any problem in actual use.

(6) Foreign substance recognition 100 parts of curable silicone resin (“KS-779H” manufactured by Shin-Etsu Chemical), 1 part of curing agent (“CAT-PL-8” manufactured by Shin-Etsu Chemical), methyl ethyl ketone (MEK) / toluene mixed solvent system 2200 A release agent comprising a part is applied to one side of a polyester so that the coating amount is 0.1 g / mm ² and dried at 170 ° C. for 10 seconds to obtain a release film. A release film was adhered to the polarizing film via a known acrylic pressure-sensitive adhesive so that the width direction was parallel to the orientation axis of the polarizing film, thereby producing a polarizing plate with the release film. Here, when the polarizing plate was prepared, black metal powder (foreign matter) having a size of 50 μm or more was mixed between the pressure-sensitive adhesive and the polarizing film so as to be 50 / m ² . A polarizing plate for inspection is superimposed on the polarizing plate release film mixed with the foreign matter thus obtained so that the orientation axis is orthogonal to the width direction of the release film, and white light is irradiated from the polarizing plate side. Ten inspectors visually observed from the polarizing plate for inspection, and evaluated whether the foreign matter mixed between the adhesive and the polarizing film could be found by the following classification. In the measurement, the film was evaluated using a total of three films at the center and both ends of the obtained film, and the result of the point where the visual inspection property was the best was obtained. It was cognitive.
<Foreign substance recognition classification criteria>
(Good foreign body recognition) ◎ ＞ ○ ＞ △ ＞ × (foreign body poor recognition)
Among the above criteria, those above ○ are levels that can be used without any problem in actual use.

Examples 1-4 and Comparative Examples 1-2:
<Manufacture of polyester (A)>
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, magnesium acetate tetrahydrate is added as a catalyst to the reactor, the reaction start temperature is 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. The temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. Ethyl acid phosphate was added to the reaction mixture, which was then transferred to a polycondensation tank, and 0.04 part of antimony trioxide was added to carry out a polycondensation reaction for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure to obtain a polyester chip (A). The intrinsic viscosity of this polyester was 0.63.

<Manufacture of polyester (B)>
In the method for producing polyester (A), after adding ethyl acid phosphate, the content of synthetic calcium carbonate particles having an average particle size of 0.8 μm and a particle size distribution value of 1.6 in an amount of 1 wt. The polyester (B) was obtained using the same method as the production method of the polyester (A) except that the addition was made so as to be%. The obtained polyester (B) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (C)>
In the production method of the polyester (B), the additive particles are synthetic calcium carbonate particles having an average particle size of 0.5 μm and a particle size distribution value of 1.7, and the content with respect to the polyester is 1 wt%. A polyester (C) was obtained using a method similar to the production method of B). The obtained polyester (C) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (D)>
In the method for producing polyester (B), the additive particles are synthetic calcium carbonate particles having an average particle size of 1.4 μm and a particle size distribution value of 1.9, and the content of the polyester is 1% by weight. Polyester (D) was obtained using the same method as the production method of B). The obtained polyester (D) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (E)>
In the production method of the polyester (B), the additive particles are silica particles having an average particle size of 2.5 μm and a particle size distribution value of 1.3, and the content of the polyester is 0.6% by weight. A polyester (E) was obtained using a method similar to the production method of B). The obtained polyester (E) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (F)>
In the method for producing polyester (B), the additive particles are natural calcium carbonate particles having an average particle diameter of 0.8 μm and a particle size distribution value of 2.5, and the content of the polyester is 1% by weight. A polyester (F) was obtained using a method similar to the production method of B). The obtained polyester (F) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (G)>
In the method for producing polyester (B), polyester (B) is used except that the additive particles are silica particles having an average particle size of 0.12 μm and a particle size distribution value of 2.0, and the content with respect to the polyester is 0.3% by weight. A polyester (G) was obtained using a method similar to the production method of B). The obtained polyester (G) had an intrinsic viscosity of 0.63.

<Manufacture of film>
A mixed raw material obtained by mixing the polyester (A) chip and the polyester (B), (C), (D), (E), and (F) chips in the ratios shown in Tables 1 and 2 is used for the A layer. As raw material, 100% polyester (A) chip raw material is supplied to the two extruders as the raw material for B layer, melt-extruded at 290 ° C, A layer is the outermost layer (surface layer), and B layer is the middle The layer was cooled and solidified on a cooling roll having a surface temperature set to 40 ° C. using an electrostatic application adhesion method to obtain an unstretched sheet. Next, a polyester film having a width of 3000 mm was obtained under the conditions shown in Tables 1 and 2 for the longitudinal stretching ratio, the longitudinal stretching temperature, the transverse stretching ratio, the transverse stretching temperature, and the heat treatment temperature (main crystal temperature). The total thickness of the obtained film was 40 μm, and the thickness of each layer was 4 μm / 32 μm / 4 μm (A / B / A). In Comparative Example 3, the film using the polyester (A) and (G) chips as the film surface layer became extremely flat in surface shape and deteriorated in slipperiness. Therefore, the film after stretching and heat treatment was wound into a roll. When it was taken, it could not be wound up well, and scratches were generated on the entire surface of the film, making it impossible to produce a product.

  The film of the present invention can be suitably used as a polyether film for a release film that can realize a high degree of accuracy in, for example, inspection of a polarizing plate by the crossed Nicols method.

Claims (2)

For a release film comprising particles having an average particle size in the range of 0.2 to 1.5 μm and a particle size distribution value (d25 / d75) in the range of 1.0 to 2.0 Polyester film. 2. The polyester film for a release film according to claim 1, wherein a refractive index (nβ) in a direction perpendicular to the main orientation axis is 1.6400 or less in the in-plane direction of the film.