KR101218146B1 - Biaxially-stretched polyester film for optical use - Google Patents

Abstract

The present invention relates to an optical biaxially stretched polyester film, which has excellent adhesiveness, transparency, and transmittance characteristics, and particularly, on one side or both sides of a polyester film substrate in order to improve the adhesive force between the polyester film substrate and the post-working working layer. In forming an easily bonding layer, it is related with the biaxially stretched polyester film for optics in which the said easily bonding layer was formed using two types of resin different from each other.

Optical, biaxial stretching, lamination, polyester film, acrylic resin, polyester resin, post-processing resin, adhesive

Description

Biaxially oriented polyester film for optics {BIAXIALLY-STRETCHED POLYESTER FILM FOR OPTICAL USE}

1 is a cross-sectional view of a biaxially stretched polyester film for optics treated with double-sided easily adhesive according to an embodiment of the present invention.

The present invention relates to a biaxially stretched polyester film for optics, which has excellent adhesiveness, transparency and light transmittance properties, and in particular, one or both sides of a polyester film substrate in order to improve adhesion between the polyester film substrate and the post-working layer. In forming an easily bonding layer, it relates to the biaxially stretched polyester film for optics which formed the said easily bonding layer using two types of resin different from each other.

In general, biaxially stretched polyester films are widely used as optical films because of their excellent transparency, dimensional stability, chemical resistance, and the like compared to other plastic films. In particular, in order to use in liquid crystal display devices in the display field, a touch panel base film, transparent conductive material (ITO: IndiumTinoxide), which undergoes a hard coating process through off-line coating, is deposited, and a light emitting material Is used for inorganic EL for silver paste processing and after application of silver paste and base film for diffuser sheet, prism lens sheet, protective film, etc. In order to prevent glare caused by external light, it is mainly used for AR (Anti-Reflection) base film that suppresses light reflection, and a film used in plasma-display-panel (PDP), which has recently been in high demand.

In application to such optical applications, biaxially stretched polyester films used as base films are difficult and detailed in their required properties. The demands for process running stability and transparency, light transmittance, excellent scratch resistance and planarity, as well as post-working characteristics, in particular, adhesiveness with resins used in post-processing are increasing. In particular, most of the optical films listed above have post-processing operations on one or both sides of the biaxially stretched polyester film base material, so that the optical and industrial films have excellent transparency, scratch resistance and post-processing resins. It is desirable to improve the adhesive properties. Most of the optical films listed above are post-processed on one or both sides of the biaxially stretched polyester film substrate.

Conventionally, in the manufacture of biaxially stretched polyester films, it is preferred to use water-dispersible or water-soluble polyester resins or acrylic resins for films with relatively high polarity as anchor coating resins. Japanese Patent Publication No. 49-10243, Japanese Patent Patent Documents No. 52-19786, Japanese Patent Publication No. 54-43017, Japanese Patent Publication No. 54-43017, etc. are proposed. However, in order to improve the adhesiveness of a polyester film because it is not enough for the improvement effect of adhesiveness, the use of modified polyester resin centered on graft modification as a coating resin is Unexamined-Japanese-Patent No. 2-171243, Japan Patent Publication No. 2-310048, Japanese Patent Application Laid-Open No. 3-67626, and the like have been proposed. However, although the adhesiveness was improved by using such a modified polyester resin, there was a problem that the adhesiveness was insufficient under wet, so that the use of a crosslinking agent in combination is JP-A-5-744633, JP-A-5 6-39154 and Japanese Patent Laid-Open Publication No. Hei 6-39548. However, although adhesiveness was improved by wet use by using a crosslinking agent, such polyester resin has a problem that adhesiveness with resin used for a post-processing operation falls remarkably compared with an acrylic resin.

Therefore, there is an urgent need for an easy-adhesive layer that is excellent in adhesiveness with the resin used in the post-processing operation as well as with the polyester as the substrate while maintaining excellent transparency with the biaxially stretched polyester film.

The present invention has been made to solve the above problems, an object of the present invention by applying an adhesive layer comprising two different types of resin on one side or both sides of the optical polyester film substrate, It is an object of the present invention to provide a biaxially stretched polyester film for optics that can provide excellent adhesion between the adhesive layer and the resin of the processing layer used for post-processing, as well as improving the adhesion between the adhesive layers.

In particular, the present invention provides an optical composition comprising a polyester resin for excellent adhesion between a polyester substrate and an adhesive layer, and an acrylic resin for forming an excellent adhesive strength between a post-processing work layer and an adhesive layer. It is to provide a biaxially stretched polyester film.

The above and other objects and advantages of the present invention will become more apparent from the following description of the preferred embodiments with reference to the accompanying drawings.

The biaxially stretched polyester film for optics according to the present invention for achieving the above object is characterized in that an easily adhesive layer comprising two kinds of different resins is coated on one side or both sides of a polyester base material.

In a preferred embodiment, the two different kinds of resins are water-soluble or water-dispersible polyester resins and water-soluble or water-dispersible acrylic resins, and more preferably, the easy-adhesive layer is formed from the polyester base side. It is characterized in that the water-soluble or water-dispersible polyester resin and the water-soluble or water-dispersible acrylic resin is formed in turn.

The biaxially stretched polyester film for optics according to the present invention is characterized in that the concentration of the two different resins is 1% by weight to 8% by weight.

Moreover, the biaxially stretched polyester film for optics which concerns on this invention is characterized by the haze of the polyester film to which the said easily bonding layer was apply | coated 2% or less.

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. .

In the biaxially stretched polyester film for optics according to the present invention, the adhesive force between the polyester base film and the easily adhesive layer of the polyester base film is improved not only with the adhesive force between the base film and the easily adhesive layer but also with the resin of the processed layer used for post-processing. It is based on the premise of maintaining excellent adhesiveness. For this purpose, a polyester resin is used for post-processing of polyester resin for excellent adhesion between the polyester base layer and the easily adhesive layer by using a heterogeneous resin in the adhesive layer of the polyester base film. For excellent adhesion between the layer and the polyester substrate layer is characterized by forming an easily adhesive layer on the polyester substrate using an acrylic resin.

The aromatic polyester which comprises the biaxially stretched polyester film which is a base material of the biaxially stretched polyester film for optics which concerns on this invention is preferably a polyethylene terephthalate homopolymer or the copolymer which makes ethylene terephthalate the main repeating unit. In particular, biaxially oriented films formed of polyethylene terephthalate are most suitable. As a method for producing these polymers, polyesters having reduced oligomer content by solid phase polymerization or solvent extraction of polymers may be used, but are not particularly limited.

In addition, the polyester film used in the present invention uses a thermal stabilizer such as phosphoric acid or phosphorus compound, which solidifies the melted and extruded polyester resin by electrostatic application method on a rotary cooling roll to produce an unstretched sheet having a uniform thickness. It is essential to gain.

And if necessary, various additives such as antioxidants, organic lubricants, antistatic agents, ultraviolet absorbers, light resistant agents or surfactants may be contained in the polyester film.

On the other hand, in order to maintain transparency of a polyester film, it is common in an optical use application not to contain particle | grains in a base film. Although this invention relates to the biaxially stretched polyester film mainly used for optical use, the use is not restrict | limited and can be applied also to general industrial use.

The manufacturing method of the biaxially stretched polyester film of this invention is demonstrated below, but the sequential biaxial stretching method is not limited to this.

First, the raw material resin of polyester is fully vacuumed and dried, and then melted and extruded through an extruder, and the molten high-temperature polyester resin is formed into a sheet in a rotary cooling roll through a die. At this time, the unstretched polyester sheet is obtained by bringing the polymer into close contact with the cooling roll by the electrostatic application method. At this time, the unstretched polyester sheet may have a single layer structure or a multilayer structure by coextrusion. In this case, unstretched sheets are obtained by using single particles or two or more kinds of particles together. 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, organic particles such as crosslinked polymer particles, and the like. have. When the refractive index of the particles differs from the refractive index with 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. It is most preferable because it can be obtained.

The unstretched polyester sheet thus obtained is stretched 2.0 to 4.5 times in the longitudinal direction while passing through a roll heated to 70 to 120 ° C to obtain a uniaxially stretched polyester film.

Thereafter, both edge portions of the uniaxially stretched polyester sheet are gripped with a clip and enter the heated region at 80 to 150 ° C, and the heat is supplied by hot air of the upper and lower portions to be 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.

In addition, at any stage of the manufacturing process of the film is subjected to an easily adhesive coating process on one side or both sides of the polyester film, it forms the most important part in the present invention.

As a method of applying the easily-adhesive coating layer to such a polyester film in the known coating method such as gravure coating method, key coating method, wire bar coating method, spray coating method, air knife coating method, impregnation coating method It may be carried out in one or a combination of these methods. It is preferable that solid content concentration of an aqueous easily-adhesive coating liquid is 1-20 weight%, More preferably, it is 2-10 weight%. The application process of such an easily bonding layer may be performed to a biaxially stretched polyester film, may be applied to an unstretched or uniaxially stretched polyester film, and may be uniaxially stretched after drying. 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 water-soluble or water-dispersible resin used in the easily adhesive layer of the base film in the present invention is not particularly limited, but an aqueous polyurethane resin, an aqueous polyester resin, an aqueous acrylic resin, and the like can be used. Ester resin and acrylic resin were used.

In the acrylic resin used in the easy-adhesive layer of the present invention, an acid value of 200 eq / t or more, which is a value obtained by titrating a resin solution under a reduced pressure of 100 Pa at 80 ° C./2 hours and titrating with an ethanol potassium hydroxide solution having a known concentration, is solid. Preference is given to at least two or at least two copolymers.

In the present invention, the coating liquid used for forming the easily adhesive layer is preferably an aqueous coating liquid. In order to improve the wettability to a base film and to apply | coat a coating liquid uniformly when apply | coating an aqueous coating liquid to a film surface, it is preferable to add a suitable amount of well-known nonionic surfactant and anionic surfactant.

Conventionally, in constructing such an easily adhesive layer, one type of resin (binder) used for the easily adhesive layer is generally used. In the present invention, in forming such an adhesive layer, by using two different types of resins, the characteristics of the adhesive strength between the polyester substrate, the adhesive layer, and the adhesive layer and the post-working layer are remarkably improved. have.

In the present invention, the biaxially stretched laminated polyester film has a thickness of 50 to 300 µm, but the thickness is not particularly limited. In addition, it is preferable that the haze value of a film shall be 2.0% or less, In particular, when applying to an optical film, it is preferable to manage a haze value to 2.0% or less. If the haze value of the film exceeds 2.0%, it is not preferable because the film tends to decrease the sharpness of the screen when the film is used for a PDP mesh filter, an LCD lens film, or a CRT AR film.

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

[Example]

Preparation of Coating Liquid

The coating liquid to be applied to the base layer of the biaxially stretched polyester film was prepared as follows. As the water dispersible polyester resin, a coating liquid was prepared using Takamatsu's resin, and an acrylic resin was prepared using Rohm & Haas' EXP3208 resin. An HMMA melamine curing agent was used as a curing agent for the resin, and an acid catalyst (toluenesulfonic acid) for assisting curing was not used. Pure water was used to dilute the resin, and a small amount of surfactant was added to improve leveling properties.

Preparation of Polyester Film Substrate

The polyether terephthalate chip (CHIP), which does not contain particles as a raw material polymer, was dried at a high temperature and reduced pressure (0.5 Torr) in a dryer to remove water contained in the chip (CHIP) at a level of 0.4%. The molten polymer 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. 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 coated on both sides of a 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. In this embodiment, the film coated by the in-line coating method on both sides of the substrate was prepared and used.

Preparation of Finished Coating Solution for Evaluation of Adhesion

100 parts by weight of a polyester resin having a glass transition temperature of 80 ° C., 50 parts by weight of methyl methacrylate, and 50 parts by weight of butyl acrylate copolymerized 50 parts by weight of a mixture of methyl ethyl ketone and toluene (1: 1) It dissolved in to prepare a binder resin solution having a solid content of 30%. Here, 30 parts by weight of particles polymerized with butyl acrylate alone, 5 parts by weight of magnesium fluoride, and 2 parts by weight of modified silicone resin (WET KL 245) as a dispersant were dispersed and dispersed for 1 hour using a 2000 rpm disperser for post-processing coating. Prepare a composition for.

Example 1

2.0 wt% of the polyester resin (Takamatsu A215GE type) and 2.0 wt% of the acrylic resin (product name EXP3208 manufactured by Rohm & Haas) from the raw material (" coating solution " After diluting and preparing in pure water, longitudinal stretching, the sheet was coated on both sides of the sheet using a Mayer bar, and then stretched in the transverse direction to obtain a biaxially stretched polyester film having a thickness of 100 µm.

[Example 2]

4.0% by weight of the same polyester resin as in Example 1 and 4.0% by weight of the same acrylic resin were prepared by diluting in pure water, followed by longitudinal stretching. The obtained biaxially stretched polyester film of 100 micrometers was obtained.

Comparative Example 1

The same polyester resin as in Example 1 was prepared by diluting 2.0% by weight in pure water, followed by longitudinal stretching, coated on both sides of the sheet using a Mayer bar, followed by drying in a transverse direction, followed by transverse stretching to obtain a 100 μm biaxially stretched polyester film. Got.

Comparative Example 2

In the same manner as in Example 1, 2.0 wt% of an acrylic resin was prepared by diluting it in pure water, followed by longitudinal stretching, and then coated on both sides of the sheet using a Mayer bar, followed by drying in a transverse direction to obtain a biaxially stretched polyester film having a thickness of 100 μm. Got it.

[Comparative Example 3]

After longitudinal stretching, the film was stretched transversely without the step of applying to both sides of the sheet to obtain a biaxially stretched polyester film having a thickness of 100 µm which was not easily bonded.

[Evaluation method]

Haze assessment

It measured according to the method of ASTM D1003. The measurement equipment used NDH-300A by N / DENSHOKU.

Coefficient of friction evaluation

It measured according to the method of ASTM D1894. The measuring equipment used HEIDON-14D HEIDON.

Surface tension evaluation

It measured according to the method of ASTM D2578. The measuring equipment used WETTING TENSION STANDARD reagent of Enercone.

Evaluation of Adhesiveness with Base Film

Adhesiveness is adhesiveness calculated | required from following formula (1) based on the test method based on 8.5.1 description of JIS-K5400.

(1)

In the adhesive evaluation method, wounds are formed in 100 matrix structures with a gap interval of 2 mm using a cutter prepared on the surface of a biaxially stretched polyester film base material coated with an easily adhesive layer, and then, a cellophane adhesive tape (Nichi Reflection No. 405) (24 mm width) was attached to the wound surface of the matrix structure, rubbed by hand and completely attached, then peeled vertically, and adhesion was obtained from the above formula by visual observation.

Evaluation of adhesiveness with post-processing coating liquid

Adhesiveness is adhesiveness calculated | required from said Formula (1) based on the test method based on 8.5.1 description of JIS-K5400.

In order to satisfy the said adhesive force, selection of resin used for an easily bonding layer is important.

Table 1 shows the film properties of the film of the Example and Comparative Example through the above experiment.

[Table 1]

division In adhesive layer
Resin (Binder) Base Film
Adhesiveness Post Coating Liquid Adhesive Surface tension
(dyne / cm) Coefficient of friction
(μK) Haze
(%) Resin 1 Resin 2 Example 1 Polyester
(2% by weight) acryl
(2% by weight) 100 100 34 0.39 0.61 Example 2 Polyester
(4% by weight) acryl
(4% by weight) 100 100 34 0.37 0.62 Comparative Example 1 Polyester (2% by weight) 100 75 46 0.41 0.61 Comparative Example 2 Acrylic (2% by weight) 80 100 34 0.38 0.60 Comparative Example 3 radish 0 0 37 0.72 0.59

As can be seen in Table 1, the embodiments according to the optical biaxially stretched laminated polyester film according to the present invention, while maintaining excellent transparency, compared with the comparative examples, the adhesiveness with the base film and the adhesion with the post-coating solution It can be seen that the performance is excellent in both castles.

The above embodiments are intended to specifically illustrate the present invention, and do not limit the scope of the present invention. In addition, all the various modifications and changes of the present invention are included in the scope of the present invention.

As described above, the optical biaxially stretched polyester film according to the present invention has excellent adhesiveness, good transparency and transmittance, and in particular, the demand for adhesiveness with the resin used for post-processing in the optical polyester film is gradually increased. In the present situation, the adhesiveness between the base film and the adhesive layer, as well as the adhesiveness between the adhesive layer and the post-working layer can be improved.

Claims (5)

In the optical polyester film, As two kinds of different resins on one side or both sides of a polyester substrate, a water-soluble or water-dispersible polyester resin and a water-soluble or water-dispersible acrylic resin are used, and the acrylic resin is dried at 80 ° C./2 hours under a reduced pressure of 100 Pa. The biaxially stretched polyester film for optics characterized by apply | coating the easily bonding layer which consists of acrylic resin which is 1 type (s) or 2 or more types of copolymers whose acid value is 200eq / t or more which is the value calculated | required by the ethanol potassium hydroxide solution. delete The method of claim 1, The said easily bonding layer is the biaxially stretched polyester film for optics characterized by forming the said water-soluble or water-dispersible polyester resin and the said water-soluble or water-dispersible acrylic resin in order from the said polyester base material side. The method according to claim 1 or 3, The biaxially stretched polyester film for optics, characterized in that the concentration of the two different types of resin is 1% by weight to 8% by weight. The method according to claim 1 or 3, The haze of the polyester film to which the said easily adhesive layer was apply | coated is 2% or less, The biaxially-oriented polyester film for optics characterized by the above-mentioned.

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