JP2005133058A - Polyester film for optical use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film for optical use that is desirable for displays. <P>SOLUTION: This polyester film for optical use comprises a substrate layer made of a biaxially-stretched polyester and an adhesive layer or layers that are easily adhered to at least one surface of the substrate layer. This substrate layer comprises particles having an average particle size of 1.0-10.0 μm as well as minute particles having an average particle size of 0.03-0.50 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical polyester film, and more specifically, excellent easy adhesion, transparency, light transmission, scratch resistance, and running properties, and excellent film flatness. The present invention relates to an optical polyester film, and more particularly to an optical polyester film suitable for the display field.

  In general, most plastic films including a polyester film have a necessary function through a post-processing step, and thus it is essential to perform the post-processing step. In such a post-processing step, since the film passes through many rolls, scratches and the like are generated on the surface of the film due to friction and peeling with the rolls. In particular, in the case of a highly transparent film, the running property is poor due to the characteristics of low surface roughness, which may cause problems such as poor coating and generation of scratches in the post-processing step. In addition to the film surface defects that occur in such post-processing steps, many rolls pass through the biaxially stretched polyester film manufacturing process. Many surface defects will occur. In particular, such surface defects can cause fatal defects to products when applied to optical films in the display field.

  Biaxially stretched polyester films are widely used as optical films because they have excellent dimensional stability, chemical resistance, transparency and other properties compared to other plastic films. In particular, in the display field, a transparent conductive material (ITO: Indium Tin oxide) is vapor deposited and a luminescent material is applied, and then silver paste (Silver Paster) processing is applied to inorganic EL and liquid crystal display devices. Base film for touch panel that undergoes processes such as hard coating processing through off-line coating, diffusion film that corresponds to the backlight unit among films used for LCD monitors, Base film used for prism lens sheets, protective films, etc., and base film for AR (Anti-Reflection) that suppresses light reflection to prevent glare caused by external light, plasma display panel Mainly used for near-infrared shielding film used in (PDP) Has been.

  In particular, when applied to such a display, a biaxially stretched polyester film used as a base film is required to have process running stability, transparency, light transmittance, and excellent scratch resistance and flatness. . In particular, in the problem of scratches, there are problems such as the occurrence of electrical defects (black spots) due to non-uniform application to the transparent conductive film and non-uniform application in post-processing steps such as hard coating in the above-mentioned defect occurrence part. May cause.

  Accordingly, when applied to an optical film, it is preferable that fine scratches are not allowed on the surface of the film, together with excellent transparency and easy adhesion. Also, in the film flatness problem, if the film flatness is poor, a partial sliding phenomenon due to non-uniform tension is induced during the production process of the base film. Scratches such as the occurrence of scratches and other drawbacks will occur. In addition, when the flatness of the film is poor, in the post-processing coating process, the amount of application becomes non-uniform, and a product having a partial application failure is produced and the value as a product is reduced. Therefore, it is particularly necessary for the optical film to improve the flatness of the film.

  In order to solve such surface scratches in the production of a biaxially stretched polyester film, conventionally, in the step of forming an adhesive layer on the base material of the biaxially stretched polyester film, a method of incorporating inorganic particles in the adhesive layer Was used. However, biaxially stretched polyester film is an in-line coating process that forms an adhesive layer in the manufacturing process. (Inline coating is a process for manufacturing a film by melting and extruding raw materials and then cooling to produce a sheet. After that, the coating liquid is applied, which is performed before uniaxial longitudinal stretching or after uniaxial stretching, but generally performed after uniaxial longitudinal stretching. As a large amount of water is used as the film, and then a stretching process in the width direction is performed, the thickness of the easy-adhesion coating layer is limited to several μm or more by such a stretching process. As a result, the inorganic particles used in the coating process are limited in size. If large particles are used, the thickness of the coating layer holding the particles will be relatively thin, and when the roll runs, the coating layer will peel off even by fine friction. Cause problems. As a result, the original purpose for imparting running properties to the film cannot be achieved, and furthermore, the problem that each roll is contaminated by the dropped particles is caused. And the bigger problem is that in the biaxially stretched polyester film manufacturing process, inline coating process is usually performed after uniaxial stretching in the longitudinal direction (longitudinal direction). Most of the disadvantages that occur during the uniaxial stretching step by peripheral speed (in most cases, the stretching step in the longitudinal direction is a step of stretching by the peripheral speed difference between the front and rear rolls) cannot be overcome. In addition, the inorganic particles used during the coating process may cause the adhesiveness with the post-processed material to drop when the amount of use increases, and therefore the physical properties of the product may be adversely affected due to poor adhesiveness after the post-processing process. There was a problem of affecting.

  Also, when particles (Filler) are not used inside the film, the melted / extruded sheet deteriorates the flatness of the film due to uneven stretching stress in the longitudinal stretching process due to the peripheral speed of the roll. There was a point. When the flatness of the film is poor, it causes a problem of non-uniform coating in a post-processing process, and causes a fatal defect in handling and running properties.

  Conventional films did not use particles inside the film to improve product transparency. As a result, problems such as the above-described poor planarity of the film and the occurrence of scratches have been caused. In addition, in order to improve the scratch resistance of the film, an attempt was made to improve scratch resistance by using particles in the adhesive layer in the in-line coating process. Had a fatal limit to the occurrence of This longitudinal stretching process is a stage before the in-line coating process and before the easy-adhesion coating layer is formed on the film, so the function of the adhesive layer has a problem of scratches generated in the longitudinal stretching process. Could not be overcome. In addition, defects that occur during the longitudinal stretching process are a greater cause of product defects due to the so-called lens effect, which appears to be larger by application of an easy-adhesion coating layer.

  The following Patent Document 1 discloses a polyester film that suppresses the defects of the film by applying a surfactant to the film surface, but this also has the disadvantages that occur before the coating process as described above. There is a problem that a satisfactory function required in the display field cannot be satisfied due to the occurrence of minute defects that cannot be suppressed.

JP-A-9-183201

  The present invention has been devised to solve the above problems. The object of the present invention is to have excellent running properties and scratch resistance while maintaining high transparency, which is essential when applied to optical films in the display field, and to improve the stretchability of the film. It is providing the optical polyester film which can improve the planarity of a film by making it.

  In order to achieve the above object, an optical polyester film according to the present invention comprises a base material layer made of biaxially stretched polyester and an adhesive layer that is easily bonded to at least one surface of the base material layer. Includes fine particles having an average particle diameter of 0.03 to 0.50 μm, and the coating liquid for forming the adhesive layer has a solid content of 2 to 10% by weight.

  In the optical polyester film according to the present invention, the base material layer further includes particles having an average particle diameter of 1.0 to 10.0 μm.

  The optical polyester film according to the present invention is characterized in that the turbidity (haze) of the film is 1.5% or less and the thickness of the film is 25 μm or more.

  The aromatic polyester constituting the biaxially oriented polyester film that is the base layer of the optical polyester film according to the present invention is preferably a copolymer having polyethylene terephthalate homopolymer or ethylene terephthalate as the main repeating unit. In particular, a biaxially stretched film made of polyethylene terephthalate is suitable. As a method for producing these polymers, polyesters in which the oligomer content is reduced by solid polymerization or solvent extraction of the polymer may be used, but the invention is not particularly limited thereto.

  In addition, the polyester film used in the present invention uses a heat stabilizer such as phosphoric acid or a phosphorus compound. This is because the melted and extruded polyester resin is adhered to the rotating cooling roll by an electrostatic application method. It is indispensable for solidifying and obtaining an unstretched sheet having a uniform thickness.

  Further, if necessary, the polyester film may contain various additives such as an antioxidant, an organic lubricant, an antistatic agent, an ultraviolet absorber, a light-resistant agent, and a surfactant.

  In general, in order to maintain the transparency of the polyester film, the base film does not contain particles, but the optical polyester film according to the present invention may use fine particles within the range applicable to the display field. , While maintaining excellent transparency, it is possible to disperse the stretching stress generated during the film stretching process and improve the uniformity of stretching, thereby eventually improving the flatness of the film It was confirmed.

  The resin used in the adhesive layer provided on at least one side of the base layer of the optical polyester film according to the present invention is not limited to a water-soluble or water-dispersible resin, but an aqueous polyurethane resin, an aqueous polyester Resins, aqueous acrylic resins, and the like can be used.

  As the polyurethane resin used in the adhesive layer of the present invention, various solvent-type, solventless-type or water-based coating agents can be used. Examples of the resin containing a blocked isocyanate group include a heat-reactive water-soluble urethane resin in which a terminal isocyanate group is blocked with a hydrophilic group. Examples of the isocyanate group blocking agent include phenols, lactams, oximes, alcohols and active methylene compounds containing sulfonic acid groups and bisulfites.

  The acrylic resin was obtained by drying a resin solution at 80 ° C. for 2 hours under a reduced pressure of 100 Pa, and then adjusting the solid content with an ethanolic potassium hydroxide solution having a known concentration. It is preferably a copolymer of 1 or more or 2 or more of / t or more.

  On the other hand, the coating solution used for forming the adhesive layer of the optical polyester film according to the present invention is preferably an aqueous coating solution. In order to improve the wettability of the substrate film and apply the coating solution uniformly when applying a water-based coating solution to the surface of the film, a known nonionic surfactant or an anionic interface is used. It is preferable to add an appropriate amount of activator.

  In addition, in the adhesive layer, additives such as heat-resistant polymers and inorganic polymer particles, ultraviolet absorbers, antistatic agents, antibacterial agents, and organic lubricants are provided to give different functions such as antistatic properties and handling properties. May be included.

  Although the sequential biaxial stretching method described later was used as the method for producing the biaxially stretched polyester film of the present invention, it is not limited to this.

  The polyester raw material resin is sufficiently dried in a vacuum, and then melted and extruded through an extruder, and the molten high-temperature polyester resin is formed into a sheet mold in a rotary cooling roll through a die. In this case, since the polymer is brought into close contact with the cooling roll by an electrostatic application method, an unstretched polyester sheet can be obtained. At this time, the unstretched polyester sheet may have a single layer structure or a multilayer structure by coextrusion.

  Here, when using fine particles having an average particle diameter of 0.03 to 0.50 μm and particles having an average particle diameter of 1.0 to 10.0 μm, which are technical features of the present invention, the average particle diameter is An unstretched sheet is obtained by using 0.03 to 0.50 μm fine particles alone or by using two kinds of fine particles together. Examples of particles used at this time include calcium carbonate, calcium phosphate, kaolin, silica, talc, titanium dioxide, alumina, calcium fluoride, barium sulfate, zeolite, molybdenum sulfide, and potassium hydroxide, and crosslinked polymers. Examples thereof include organic particles such as particles. When the difference between the refractive index of the particle and the refractive index of the resin constituting the adhesive layer is 0.1 or more, it may cause damage to transparency. Since the refractive index is close to the refractive index of the resin of the adhesive layer and excellent transparency is obtained, it is preferable to use this.

  If the average particle size of the fine particles used at this time is less than 0.03 μm, the fine particles do not contribute to the running property and scratch resistance of the sheet or film, and the effect of adding fine particles cannot be obtained. . Further, when the average particle size of the fine particles exceeds 0.50 μm, there arises a problem that the luminous transmittance is hindered. Such a problem occurs when the particles are mixed with particles having an average particle diameter of 1.0 to 10.0 μm, and if particles having an average particle diameter of 1.0 to 10.0 μm are used, the problem is to some extent. The luminous transmittance decreases. If fine particles having an average particle size exceeding 0.50 μm are further added to this, the luminous transmittance is further lowered. Therefore, it is preferable to use fine particles having an average particle size of 0.50 μm or less.

  While passing the obtained unstretched polyester sheet on a roll heated to 70 to 120 ° C., it is stretched 2.0 to 4.5 times in the longitudinal direction to obtain a uniaxially stretched polyester film. Due to such uniaxial stretching, when the sheet is run on a roll, defects caused mainly by friction occur between the surface of the polyester sheet and the roll. The disadvantage of such a process was a problem that could not be overcome by the existing method of adding inert particles to the adhesive layer to give abrasion resistance. The optical polyester film according to the present invention is characterized in that it retains transparency while solving the drawbacks of such processes.

  The edge portions on both sides of the uniaxially stretched polyester sheet thus obtained are gripped with clips, put in a region heated to 80 to 150 ° C., hot air is supplied from above and below the film, and 2. in the width direction. Stretch 5 to 5.0 times. Next, it is guided to a higher temperature region (150 to 250 ° C.) to be crystal-oriented.

  On the other hand, the process of coating at least one surface of the polyester film for easy adhesion is performed at any stage of the film production process. Known polyester coating methods such as gravure coating method, kiss coating method, wire bar coating method, spray coating method, air knife coating method, impregnation coating method, etc. One or more of these methods may be used.

  The concentration of the solid content of the water-based easy-adhesion coating solution is preferably 1 to 20% by weight, more preferably 2 to 10% by weight. The weight% is a weight ratio with respect to the coating solution (100% by weight) containing a solid content.

The application step of the adhesive layer may be performed on the biaxially stretched polyester film, or may be performed on the unstretched or uniaxially stretched polyester film and then biaxially stretched. The latter method is usually referred to as an inline coating method, but the latter inline coating method is preferred in the present invention. At this time, the applied liquid is subjected to a thermal crosslinking reaction in a tenter region where hot air is supplied from above and below to form a complete coating layer. The application amount of the adhesive layer thus formed is generally 0.01 to 1.00 g / m ² .

  The biaxially stretched polyester film is wound around a bobbin by a take-up and a winder, and the wide film is wound while running on a predetermined roll.

  The adhesive layer of the biaxially stretched polyester film according to the present invention exhibits excellent adhesiveness with other materials, but in order to improve the printability and adhesiveness, it can be applied to the film surface as necessary. Surface treatment such as corona treatment, electron beam irradiation, and flame treatment may be performed.

  As mentioned above, according to the polyester film for optics of the present invention, it has excellent runnability and scratch resistance while maintaining high transparency of the film. Moreover, there exists an effect of having the outstanding planarity by improving the stretchability of a film.

  Therefore, by applying the optical polyester film of the present invention to an optical film in the display field that may cause a fatal defect to the product due to surface defects, there is an effect that a very excellent product can be produced.

  Hereinafter, the present invention will be described in detail with reference to examples and drawings. It is obvious to those skilled in the art that these examples are only for explaining the present invention more specifically, and that the scope of the present invention is not limited by these examples. That would be true.

(Example)
Structure of Particles The fine particles A, particles B, and particles C used in the base material layer of the present invention are fine particles of SiO ₂ , and the average particle size thereof is as follows: fine particles A are 50 nm, and particles B are 2 μm and particle C is 4 μm.

As a raw material polymer for the production example of optical polyester film, a polyethylene terephthalate chip containing no particles is dried in a dryer at a high temperature under a reduced pressure (0.5 Torr) to obtain 0.4 in the chip. After removing the moisture contained at the level of%, the polymer melted through the extruder is rapidly cooled and solidified in a metal roll (casting drum) whose surface temperature is maintained at 25 ° C., and an unstretched sheet having a thickness of 1300 μm Got. At this time, the fine particles are passed through an extruder together with the chips from which moisture has been removed, and the fine particles and the particles are taken into the base material layer. The unstretched sheet was heated with each heated roll and an infrared heater, and then stretched 3 times in the longitudinal direction of the film due to the peripheral speed difference of the roll to obtain a uniaxially stretched PET (PET) film. Next, the prepared coating solution was applied to both sides of the uniaxially stretched pet film by the Mayer bar method. At this time, before coating, corona treatment was performed on both surfaces (coating surfaces) of the film through a separate corona treatment device. Biaxially stretched PET film having a thickness of 100 μm is obtained by holding both ends of the coated film with clips and guiding them to a hot air zone (tenter). After the coating solution is dried, it is stretched 4 times in the width direction of the film. Got. The substrate used in this example is a biaxially stretched polyester film in which a copolyester resin and a polyurethane-based resin are applied on at least one side, and has a thickness of 100 μm. In this example, a film having an adhesive layer applied on both sides of a substrate by an in-line coating method was prepared and used.

Example 1
The raw material contains 2.0% by weight of fine particles A (based on 100% by weight of the base material layer and the particles. The same applies hereinafter), and the content ratio of fine particles A and B (A / B) 3 was melt-extruded to produce a 100 μm biaxially stretched PET film by the above method, and then an undercoat solution was applied to both sides of the base material layer to form an adhesive layer, thereby producing an optical polyester film.

Example 2
An optical polyester film was produced using the same method as in Example 1 except that the particle C was used in place of the particle B in the composition of the content of the raw material particles.

Example 3
In adjusting the content of raw material particles, the use of 2.0% by weight of fine particles A, the content ratio (A / B) of fine particles A and particles B to 3, the content of fine particles A and particles C An optical polyester film was produced using the same method as in Example 1 except that the ratio (A / C) was 3.

Example 4
In the adjustment of the content of the raw material particles, an optical polyester film was produced using the same method as in Example except that 2.0% by weight of fine particles A was used and particles B and C were not used.

Comparative Example 1
In the adjustment of the content of the raw material particles, an optical polyester film was produced using the same method as in Example 1 except that only the particles B were used alone without using the fine particles A.

Comparative Example 2
In the adjustment of the content of the raw material particles, an optical polyester film was produced using the same method as in Example 1 except that only the particles C were used alone without using the fine particles A.

Comparative Example 3
In the adjustment of the content of the raw material particles, an optical polyester film was produced using the same method as in Example 1 except that the particles B and C were used without using the fine particles A.

Comparative Example 4
An optical polyester film was produced using the same method as in Example 1 except that all the fine particles A, fine particles B, and particles C were not used in adjusting the content of the raw material particles.

  The constitution of each Example and each Comparative Example according to the present invention and the particles used are shown in Table 1.

Experimental example
Evaluation of Turbidity Turbidity was measured using the method of ASTM D1003. As measuring equipment, NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd. was used.

Evaluation of runnability The runnability represents the running characteristics of the film, and the sample is mounted on the sample table so that the same surface faces each other so that the surface of the film is rubbed. At this time, the size of the sample is 120 mm wide x 63 mm long for the upper part, 150 mm wide x 100 mm long for the lower part, and friction is caused by friction at a load of 200 g and a speed of 150 mm / min. Measure the force measured when A case where the value was 0.50 or less was classified as “good”, and a case where the value was more than that was classified as “bad”.

Evaluation of flatness The apparatus shown in FIG. 2 was used to measure the flatness . First, after the film 1 to be measured was brought into close contact with the lower glass plate 2, an electric lamp was turned on from the rear surface of the acrylic plate 3 engraved with a lattice pattern on the front, and the lattice pattern was observed through the film placed on the lower portion. . At this time, if the flatness of the film is poor, the lines of the reflected grating are bent. At this time, the case where the number of bent lattices was 10 pieces / m ² or more was classified as “bad” and the case where it was less than 10 pieces / m ² was classified as “good”.

The biaxially stretched polyester film for optics produced by the methods as in the scratch-resistant examples and comparative examples was sampled by 1 m × 1 m each, and the light of a 20 W fluorescent lamp specially manufactured in a separate dark room was used as the back of the film. The surface of the film is inspected for scratches through the light. At this time, the light source is positioned on the back surface of the film or the entire surface of the film to inspect the surface of the film. At this time, those having a depth of 1 μm or more and a length of 2 mm or more having a number of scratches of 100 pieces / m ² or less were classified as “good”, and those having more than that were classified as “bad”.

  Table 2 shows the film properties obtained by evaluating the films of the examples and comparative examples according to the present invention.

  As can be seen from Table 2 above, the optical polyester film according to the present invention was compared not only when only fine particles A were used, but also when both fine particles A and particles B and / or particles C were used. Compared to the example, it can be confirmed that the turbidity is kept substantially the same, and the running property, flatness and scratch resistance are also excellent.

  The above-mentioned examples are for specifically illustrating the present invention, and do not limit the scope of rights of the present invention. In addition, all simple modifications or changes of the present invention can be considered to be included in the scope of the present invention.

It is sectional drawing of the polyester film for optics by one Example of this invention. It is an apparatus for measuring the flatness of the optical polyester film of the present invention.

Explanation of symbols

1 Film 2 Glass plate 3 Acrylic plate

Claims (4)

In optical polyester film,
A base material layer formed of biaxially stretched polyester;
An adhesive layer easily adhered to at least one surface of the base material layer;
With
The base material layer includes fine particles having an average particle size of 0.03 to 0.50 μm,
The coating liquid for forming the adhesive layer has a solid content of 2 to 10% by weight, and is an optical polyester film.   2. The optical polyester film according to claim 1, wherein the base material layer further includes particles having an average particle diameter of 1.0 to 10.0 μm.   The optical polyester film according to claim 1 or 2, wherein the turbidity (haze) of the film is 1.5% or less.   The optical polyester film according to claim 1, wherein the film has a thickness of 25 μm or more.

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