KR100783726B1 - Polyester film for optical use - Google Patents

Abstract

The present invention consists of a base layer made of biaxially stretched polyester and an easy-adhesive layer easily adhered to at least one surface of the base layer with an adhesive resin, and the base layer includes fine particles having an average particle diameter of 0.03 to 0.50 μm, In addition, the substrate layer relates to an optical polyester film, characterized in that it further comprises particles having an average particle diameter of 1.0 ~ 10.0㎛, while having high transparency and may have excellent running and scratch resistance, and furthermore, By improving the ductility it can have a very good planarity, and particularly relates to an optical polyester film suitable in the field of display.

Optical, polyester film, fine particles, transparency, scratch resistance

Description

Polyester film for optics {POLYESTER FILM FOR OPTICAL USE}

1 is a cross-sectional view of an optical polyester film according to an embodiment of the present invention.

2 is a device for measuring the flatness (flatness) of the optical polyester film of the present invention.

<Description of the symbols for the main parts of the drawings>

1: film 2: glass plate

3: acrylic plate

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an optical polyester film, and more particularly, to an optical polyester film having excellent good adhesiveness, transparency, light transmittance characteristics, scratch resistance, and running property, and excellent planarity of the film, particularly in the field of display. It relates to a suitable polyester film for optics.

In general, most plastic films including polyester film have the necessary functions through the post-processing process, it is essential to go through the post-processing process. In this post-processing process, since the film passes through many rolls, scratches and the like occur on the surface of the film due to friction and peeling with the rolls. It may cause problems such as scratching. In addition, since many rolls pass through the biaxially stretched polyester film in the manufacturing process of the biaxially stretched polyester film in addition to the defects of the film surface generated in the post-processing process, many surface defects are generated when the film surface is poor in running during this process. In particular, these surface defects cause fatal defects in products when applied to optical films in the display field.

Biaxially stretched polyester films are widely used as optical films because of their excellent dimensional stability, chemical resistance and transparency compared to other plastic films. In particular, in the field of display, off-line coating is used for inorganic EL and liquid crystal display device which deposit indium tin oxide (ITO), apply light emitting material and then process silver paste. Coating) base film for touch panel which undergoes hard coating processing, base film used for diffusion sheet, prism lens sheet, protective film, etc. of backlight unit among films used for LCD monitor, and display application In order to prevent glare caused by external light, it is mainly used as a base film for anti-reflection (AR), a near infrared ray blocking film used for plasma display panel (PDP), etc.

In particular, in such display applications, biaxially stretched polyester films used as base films require process running stability and transparency, light transmittance, and excellent scratch resistance and planarity. Particularly in the scratch problem, problems such as electrical defects (black spots) due to uneven coating on the transparent conductive film and uneven coating in a post-processing process such as hard coating may be caused to the defective portion.

Therefore, in application to an optical film, it is preferable not to allow a small scratch to a film surface with the outstanding transparency, adhesiveness, etc. In addition, in the planarity problem of the film, if the planarity of the film is poor, partial slippage phenomenon due to tension unevenness occurs in the production process of the base film, which causes scratch defects and other defects on the surface of the film. In addition, if the flatness of the film is poor, the coating amount becomes uneven in the post-processing coating process to produce a product in which partial coating failure occurs, thereby degrading the value as a product. Therefore, it is especially necessary to make the film flatness excellent in an optical film.

In order to solve this surface scratch in manufacturing a biaxially stretched polyester film, the method of including an inorganic particle in an easily bonding layer was used conventionally in the process of forming an easily bonding layer in a biaxially stretched polyester film base material. However, the biaxially stretched polyester film is an inline coating process for forming an adhesive layer in a manufacturing process (inline coating is a process of melting a raw material, extruding and cooling the raw material into a sheet, and then applying a coating liquid). Mostly, uniaxial longitudinal stretching is carried out before or after uniaxial stretching, but generally after uniaxial longitudinal stretching. In most cases, a large amount of water is used as a solvent, and then the stretching process in the width direction is performed. The thickness of the coating layer was bound to be limited to several micrometers or more by this stretching process. For this reason, the inorganic particles used in the coating process had to be limited in size. If a large particle size is used, the thickness of the coating layer holding the particle is relatively small, which causes a problem that the coating layer is peeled off even by fine friction during roll running. This can not only achieve the original purpose to give the film runability, but also causes the problem that the rolls are contaminated by the dropped particles. And the bigger problem is that in the biaxially stretched polyester film manufacturing process, most of the inline coating process is performed after the longitudinal (longitudinal) uniaxial stretching. In this case, the uniaxial stretching process (mostly the longitudinal stretching process by the longitudinal roll circumferential process) Most of the defects generated during the stretching process by the main speed difference of the before and after rolls could not be overcome. In addition, when the amount of the inorganic particles used during the coating process increases, the adhesiveness with the post-processing material may be deteriorated, which may adversely affect the physical properties of the product due to poor adhesion after the post-processing process.

In addition, when no particles are used in the film, the melted and extruded sheet has a problem of lowering the planarity of the film due to the stretching stress unevenness in the longitudinal stretching process by the roll circumferential speed. Poor planarity of the film may cause coating non-uniformity in the post-processing process, and may cause fatal defects in handling and running properties.

Conventional films do not use particles inside the film to improve the transparency of the product. This caused problems such as poor planarity of the film and scratches. In addition, in order to improve the scratch resistance of the film, in order to improve scratch resistance by using particles in the adhesive layer in the in-line coating process, there was a critical limitation on scratch generation in the longitudinal drawing process, which is the main source of scratch. Since the longitudinal stretching process is a step before the inline coating process, before the easy-adhesive coating layer is formed on the film, the function of the easy-adhesive layer could not overcome the scratch problem generated in the longitudinal stretching process. In addition, the defects generated during the longitudinal stretching process is a greater cause for product defects due to the lens effect that the defects appear rather large due to the application of the easily-adhesive coating layer.

Japanese Patent Laid-Open No. 9-183201 introduces a polyester film which suppresses the defects of the film by applying a surfactant to the film surface. However, as described above, it is possible to suppress the defects generated before the application process. There is a problem that can not meet the satisfactory function required in the display field due to the generation of fine defects.

The present invention has been made to solve the above problems, the object of the present invention, in particular, while maintaining the high transparency, which is essential for application to the optical film of the display field, while having excellent running properties, scratch resistance and stretchability of the film It is to provide an optical polyester film which can improve the planarity of a film by improving.

Optical polyester film according to the present invention for achieving the above object is composed of a base layer made of biaxially stretched polyester and an easy-adhesive layer easily adhesively bonded to an adhesive resin on at least one side of the base layer, the base layer is It characterized in that it comprises fine particles having an average particle diameter of 0.03 ~ 0.50㎛.

In addition, the optical polyester film according to the present invention is characterized in that the base layer further comprises particles having an average particle size of 1.0 ~ 10.0㎛.

In addition, the optical polyester film according to the present invention is characterized in that the haze of the film is 1.5% or less, and the film has a thickness of 25 μm or more.

It is preferable that the aromatic polyester which comprises the biaxially-oriented polyester film which is a base material layer of the optical polyester film which concerns on this invention is a copolymer which uses a polyethylene terephthalate homopolymer or ethylene terephthalate as a main repeating unit. In particular, the biaxially stretched film formed from polyethylene terephthalate is the most preferable. As the production method of these polymers, polyesters having reduced oligomer content by solid phase polymerization or solvent extraction of polymers may be used, but are not particularly limited thereto.

In addition, thermal stabilizers such as phosphoric acid or phosphorus compounds are used for the polyester film used in the present invention, which is a non-stretched sheet having a uniform thickness by solidifying the melted and extruded polyester resin by electrostatic application on a rotary cooling roll. It is essential to get                     

Moreover, if necessary, various additives, such as antioxidant, an organic lubricant, an antistatic agent, a ultraviolet absorber, a light resistant agent, and surfactant, can be contained in a polyester film.

Generally, particles are not included in the base film in order to maintain the transparency of the polyester film, but the optical polyester film according to the present invention maintains excellent transparency even when fine particles are used within the range applicable to the display field. It was confirmed that the uniformity of the stretching could be improved by dispersing the stretching stress generated during the stretching process of the film, thereby improving the planarity of the film.

The resin used for the easy-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 resin, an aqueous acrylic resin, and the like. Can be used.

The polyurethane resin used for the easily bonding layer of this invention can use a solvent type, a non-solvent type, or aqueous various coating agents. For example, as resin containing a block type isocyanate group, the heat-reactive type water-soluble urethane resin which blocked the terminal isocyanate group by the hydrophilic group is mentioned. Examples of the blocking agent for the isocyanate group include phenols, lactams, oximes, alcohols and active methylene compounds containing sulfonic acid groups and bisulfites.

The acrylic resin is one or more or two or more copolymers having an acid value of 200 eq / t or more, which is a value obtained by drying the resin solution at 80 ° C./2 hours under a reduced pressure of 100 Pa and titrating with a known concentration of ethanol potassium hydroxide solution. Is preferred.

On the other hand, the coating liquid used for forming the easily bonding layer of the optical polyester film which concerns on this invention is an aqueous coating liquid. When apply | coating an aqueous coating liquid to a film surface, in order to improve the wettability of a base film and to apply | coat a coating liquid uniformly, it is preferable to add a suitable amount of well-known nonionic surfactant and anionic surfactant.

Further, the adhesive layer may contain additives such as heat resistance and inorganic polymer particles, ultraviolet absorbers, antistatic agents, antibacterial agents, organic lubricants, and the like to impart other functionalities such as antistatic properties and handling properties.

Although the sequential biaxial stretching method mentioned later used the manufacturing method of the biaxially stretched polyester film of this invention, it is not limited to this.

After sufficiently vacuuming and drying the polyester raw material resin, it is melted and extruded through an extruder, and the molten hot polyester resin is formed into a sheet in a rotary cooling roll through a die. In this case, the polymer is brought into close contact with the cooling roll by the electrostatic application method, thereby obtaining an unstretched polyester sheet. At this time, the unstretched polyester sheet may have a single layer structure or a multilayer structure by coextrusion.

Here, when using the microparticles having an average particle diameter of 0.03 ~ 0.50㎛ and particles having an average particle diameter of 1.0 ~ 10.0㎛ constituting the technical features of the present invention, microparticles having an average particle diameter of 0.03 ~ 0.50㎛ are used alone or two kinds The microparticles are used together to obtain an undrawn sheet. The particles used at this time include inorganic particles such as calcium carbonate, calcium phosphate, kaolin, silica, talc, titanium dioxide, alumina, calcium fluoride, barium sulfate, zeolite, molybdenum sulfide, calcium hydroxide, and organic particles such as crosslinked polymer particles. have. If the refractive index of the particles differs from the refractive index of the resin constituting the easily adhesive layer by 0.1 or more, it may cause transparency.Since, among many kinds of particles, silica particles have a close refractive index with the resin of the easily adhesive layer, and excellent transparency can be obtained. It is most desirable to use it as it can.

At this time, if the average particle size of the microparticles is less than 0.03㎛, the microparticles not only help the running and scratch resistance in the sheet or film, but also do not affect the effect of the fine particles, and the average particle diameter of the microparticles is 0.50㎛. Exceeding the above problem may affect the visibility. This problem affecting the visual permeability is a problem that occurs when used in combination with particles having an average particle size of 1.0 to 10.0 μm. When the particles having an average particle size of 1.0 to 10.0 μm are used, a certain degree of visual permeability decreases. In addition, since the visual transmittance is further reduced when the fine particles having an average particle diameter of more than 0.50 μm are further used, it is preferable to use fine particles having an average particle diameter of 0.50 μm or less.

The obtained unoriented polyester sheet is stretched 2.0 to 4.5 times in the longitudinal direction while passing through a roll heated at 70 to 120 ° C. to obtain a uniaxially stretched polyester film. When driving the sheet on the roll for such uniaxial stretching, defects are mainly caused by the friction of the polyester sheet surface with the roll. The drawback in this process was a problem that could not be overcome by incorporating inert particles into the existing easily-adhesive layer to impart wear resistance. The optical polyester film according to the present invention is characterized by maintaining transparency while solving these process defects.

Both edge portions of the uniaxially stretched polyester sheet thus obtained are gripped with a clip, placed in a region heated at 80 to 150 ° C, and hot air is supplied to the upper and lower portions of the film and stretched 2.5 to 5.0 times in the width direction. Subsequently, it is led to a higher temperature range (150 ~ 250 ° C) to have a crystal orientation.

On the other hand, the step of coating the easily adhesive on at least one side of the polyester film is performed at any stage of the manufacturing process of the film. As a method of applying the easily-adhesive coating layer to such a polyester film, one or more of known coating methods such as a gravure coating method, a kiss coating method, a wire bar coating method, a spray coating method, an air knife coating method, and an impregnation coating method Can be used.

It is preferable that solid content concentration of an aqueous easily-adhesive coating liquid is 1 to 20 weight%, More preferably, it is 2 to 10 weight%.

The coating process of such an easily bonding layer may be performed to a biaxially stretched polyester film, and may be biaxially stretched after apply | coating to an unstretched or uniaxially stretched polyester film. The latter case is usually called an inline coating method, and the latter case is preferable in the present invention (inline coating method). At this time, the applied liquid is thermally crosslinked in a tenter region in which upper and lower hot air are supplied to form a complete coating layer. The coating amount of the easily adhesive layer thus formed is generally formed in 0.01 ~ 1.00g / ㎡.                     

The biaxially stretched polyester film is wound on bobbins through take-up and winder, and is wound while driving certain rolls in winding this wide film.

The easy-adhesive layer of the biaxially stretched polyester film according to the present invention has excellent adhesion with other materials, but in order to improve printability and adhesion, the surface of the film may be corona-treated, electron beam irradiation, flame treatment, etc. as necessary. May be subjected to surface treatment.

Hereinafter, the present invention will be described in detail with reference to embodiments and drawings of the present invention. These examples are only for illustrating the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples in accordance with the gist of the present invention. .

EXAMPLE

Preparation of Particles

Microparticle A is SiO ₂ microparticles produced by Toray Saehan's polymerization process, and the slurry prepared at 30% particle concentration is mixed with dimethyl terephthalate (DMT), ethylene glycol (EG) and other additives. It was prepared by adding the slurry (Slurry) in the process, the average particle diameter is 50nm. Particle B is produced in the same polymerization process as our particle A, and is characterized by an average particle diameter of 2 m manufactured by a manufacturing process similar to particle A. Particle C, like particle A, is a product produced in the polymerization process of our company, and is characterized by an average particle diameter of 4 µm manufactured by a manufacturing process similar to particle A.

Preparation of Optical Polyester Film

After the polyethylene terephthalate chip (CHIP) containing no particles as a raw material polymer of the embodiment was dried at a high temperature and reduced pressure (0.5 Torr) in a drier to remove moisture contained in the chip (CHIP) at a level of 0.4%, The polymer melted through an extruder was quenched and solidified on a metal roll (casting drum) maintained at a surface temperature of 25 ° C. to obtain an unstretched sheet having a thickness of 1300 μm. At this time, the microparticles are passed through an extruder together with the chips from which moisture is removed to introduce the microparticles and particles into the substrate layer. The unstretched sheet was heated with heated rolls and an infrared heater, and then stretched three times in the longitudinal direction of the film by a roll circumferential difference to obtain a uniaxially stretched PET (PET) film. Subsequently, the prepared coating solution was applied to both surfaces of the uniaxially stretched PET film by a MAYER BAR method. At this time, the corona treatment was performed on both sides (coating surface) of the film through a separate corona treatment device before application. The coated film was gripped at both ends with a clip to guide the hot air zone (STENTER), and the coating solution was dried four times in the width direction of the film to obtain a biaxially stretched PET film having a thickness of 100 μm. The substrate used in this embodiment is a biaxially stretched polyester film coated on at least one side with a copolyester polyester resin and a polyurethane-based resin, characterized in that the thickness is 100um, but in this embodiment, it is applied to both sides of the substrate by an inline coating method. The prepared film was used.

Example 1                     

The raw material is melt-extruded with 2.0% by weight of the fine particles A (based on 100% by weight of the base layer and the particles in total), and the content ratio (A / B) of the fine particles A and B is 3 After producing a biaxially stretched PET (PET) film of 100㎛ by the method, after applying the adhesive on both sides of the substrate layer to form an adhesive layer to prepare an optical polyester film.

Example 2

In the raw material particle content composition, an optical polyester film was manufactured in the same manner as in Example 1 except that Particle C was used instead of Particle B.

Example 3

In adjusting the raw material particle content, using 2.0% by weight of the fine particles A, the content ratio (A / B) of the fine particles A and B is 3, and the content ratio (A / C) of the particles A and C is 3 Except one, an optical polyester film was prepared in the same manner as in Example 1.

Example 4

In adjusting the raw material particle content, an optical polyester film was prepared in the same manner as in Example 1 except that 2.0 wt% of fine particles A were used, and particles B and C were not used.

Comparative Example 1

In adjusting the raw material particle content, an optical polyester film was prepared in the same manner as in Example 1 except that only the particle B was used instead of the fine particle A.

Comparative Example 2

In adjusting the raw material particle content, an optical polyester film was prepared in the same manner as in Example 1 except that only the particle C was used without using the fine particle A.

Comparative Example 3

In adjusting the raw material particle content, an optical polyester film was manufactured in the same manner as in Example 1 except that Particle B and Particle C were used instead of Fine Particle A.

[Comparative Example 4]

In adjusting the raw material particle content, an optical polyester film was prepared in the same manner as in Example 1 except that the fine particles A, B, and C were not used.

The composition of the examples and comparative examples according to the invention and the particles used are shown in the table in Table 1.

TABLE 1

division Substrate layer Adhesive layer Average Particle Size of Fine Particles A Average particle diameter of particle B Average particle diameter of particle C Adhesive coating surface 0.05 μm 2.0 μm 4.0 μm No particle use Example 1 U U radish both sides Example 2 U radish U both sides Example 3 U U U both sides Example 4 U radish radish both sides Comparative Example 1 radish U radish both sides Comparative Example 2 radish radish U both sides Comparative Example 3 radish U U both sides Comparative Example 4 radish radish radish both sides

Experimental Example

Haze assessment

Turbidity was measured using the method of ASTM D1003. The measurement equipment used NDH-300A by N / DENSHOKU.

Runability Evaluation

Runability indicates the running characteristics of the film, and the samples are attached so that the same surfaces face each other on the sample table so that the surface and the surface of the film can be rubbed. At this time, the size of the sample is 120mm x 63mm in the upper part, 150mm x 100mm in the lower part, and friction is measured by SPEED 150mm / min to 200g load during friction to measure the measured force. In this case, when this value is 0.50 or less, it is classified as "good", and when it is more than it, it was classified as "bad."

FLATNESS Assessment

Planarity used the apparatus of FIG. 2. First, the film 1 to be promptly adhered to the lower glass plate 2, and then the lamp is turned on at the rear of the acrylic plate 3 having the grid pattern engraved thereon, and the shape of the lattice is observed through the film placed on the lower side. At this time, if the planarity of the film is bad, the line of the reflected lattice is bent. In this case, when the number of bent lattice is 10 or more / m 2 or more, "bad", when less than 10 / m 2 was classified as "good".

Scratch Resistance

Samples of biaxially stretched polyester films for optics prepared in the same manner as in Examples and Comparative Examples were sampled at 1m × 1m, respectively, to illuminate the light of a 20W fluorescent lamp specially fabricated in a separate dark room from the back of the film, and the surface of the film through the light. Check for scratches. At this time, the light source may be placed on the back of the film, and also placed on the front of the film to inspect the film surface. In this case, those having a depth of 1 µm or more and a number of scratches having a length of 2 mm or more were 100 pieces / m 2 or less were classified as "good" and those having more than "bad".

Table 2 shows the film properties of the films of Examples and Comparative Examples according to the present invention.

TABLE 2

division Film properties Turbidity (%) Run Flatness Scratch resistance Example 1 0.55 Good Good Good Example 2 0.79 Good Good Good Example 3 1.02 Good Good Good Example 4 0.34 Good Good Good Comparative Example 1 0.54 Good Bad Bad Comparative Example 2 0.78 Good Bad Bad Comparative Example 3 1.00 Good Bad Good Comparative Example 4 0.32 Bad Bad Bad

As can be seen in Table 2, the optical polyester film according to the present invention has turbidity compared with the comparative example even when using only the microparticles A and the microparticles A and the particles B and / or particles C together. While maintaining almost the same, it can be seen that the driving, planarity and scratch resistance are also excellent.

The above embodiments are intended to specifically illustrate the present invention, and do not limit the scope of the present invention. In addition, it can be seen that all simple modifications and variations of the present invention are included in the scope of the present invention.

As described above, according to the optical polyester film according to the present invention, it can have excellent running and scratch resistance while maintaining the high transparency of the film, it can also have very excellent planarity by improving the stretchability of the film It can have such an effect.

Therefore, by applying the optical polyester film according to the present invention to the optical film of the display field that can cause a fatal defect in the product due to surface defects can have an effect such as to produce a very excellent product.

Claims (4)

delete In the polyester film for optics which consists of a polyester base material layer and the easily bonding layer which was easily adhere | attached on at least one surface of the said base material layer with adhesive resin, The base material layer is a biaxially stretched melt-extruded raw material containing particles in polyester, The particles in the raw material comprises 2.0% by weight of the fine particles (A) having an average particle diameter of 0.50㎛ based on 100% by weight of the raw material, and The particles in the raw material may contain another particle (B) having an average particle diameter of 2.0 μm or another particle (C) having an average particle diameter of 4.0 μm, and the content ratio (A) of the fine particles (A) and the other particles (B or C). / B or A / C) containing as much as 3 Optical polyester film, characterized in that. The method of claim 2, The haze of the film is optical polyester film, characterized in that less than 1.5%. The method of claim 2, The thickness of the said film is 25 micrometers or more, The optical polyester film characterized by the above-mentioned.

Images