KR20230111342A - Polyester film for optical use - Google Patents

Abstract

The present invention relates to an optical polyester film having excellent transmittance, low haze and scratch resistance and excellent particle coating stability, comprising a polyester base film and a primer layer positioned on at least one side of the polyester base film, wherein the primer layer is coated with a primer coating solution containing an acrylic resin, a crosslinking agent and organic particles.

Description

Optical polyester film {POLYESTER FILM FOR OPTICAL USE}

The present invention relates to an optical polyester film, and more particularly, to an optical polyester film having excellent transmittance, low haze and scratch resistance and excellent particle coating stability.

Conventionally, various types of displays used in TVs, computers, mobile phones, etc., from liquid crystal displays (LCDs) to light-emitting type display devices such as OLED displays have been developed and commercialized. Optical films used in such displays started later than general polymer films used in packaging materials, household goods, or automobiles, but as LCD-related technologies develop and research on high-functionality of films progresses, the possibility of use and demand for them are increasing day by day.

Optical films include a viewing angle expansion film, an anti-reflection film, a compensation film, a luminance increasing film, and the like, and a polyester film is most often used for such an optical film.

This polyester film has excellent stability of physical properties in a wide temperature range from low to high temperatures, excellent chemical resistance compared to other polymer resins, good mechanical strength, surface characteristics, and good thickness uniformity, so it has excellent applicability in various uses and process conditions. Therefore, it is applied to capacitors, photo films, labels, pressure-sensitive tapes, decorative laminates, polarizers, and ceramic sheets, and the demand for it is steadily increasing in response to the recent trend of high-speed and automation.

Optical polyester films used in the display field go through post-processing processes such as offline coating and adhesive processing to be used in liquid crystal display devices. In order to suppress the defect rate occurring in the post-processing process and achieve excellent optical properties, various properties such as driving stability, transparency, scratch resistance, flatness, and permeability are required in the process of forming an optical polyester film.

The reason why so many requirements are required is that the optical specificity, which is the purpose of using the base film in the display field, must be satisfied. For example, in relation to flatness, which is one of the characteristics required for a base film, if the flatness of the film is poor, a slipping phenomenon is induced due to uneven tension during the production process of the base film, which causes defects in appearance such as scratches on the surface of the film. In the post-processing coating process, the coating amount is non-uniform, resulting in a decrease in production yield due to poor coating.

Korean Registered Patent Publication No. 10-2016-0076025

The present invention has been made to solve the above problems and to meet the conventional requirements, and an object of the present invention is to provide an optical polyester film having excellent transmittance, low haze and scratch resistance and excellent particle coating stability.

The above and other objects and advantages of the present invention will become apparent from the following description of preferred embodiments.

The above object is achieved by an optical polyester film comprising a polyester base film and a primer layer positioned on at least one surface of the polyester base film, wherein the primer layer is coated with a primer coating solution containing an acrylic resin, a crosslinking agent and organic particles.

Preferably, the ratio of the refractive index of the primer layer and the refractive index of the polyester base film satisfies the following formulas 1 and 2,

(Equation 1)

0.90 ≤ a1/a2 ≤ 0.97

(Equation 2)

0.05 ≤ a2-a1 ≤ 0.16

Here, a1 is the refractive index of the primer layer, and a2 is the refractive index of the polyester base film.

Preferably, the optical polyester film satisfies the following formula 3,

(Equation 3)

0.05 ≤ (b1/b2)*b3 ≤ 0.25

Here, b1 is the number of effective protrusions, b2 is the area of the film surface of 120 μm ² , and b3 is the haze.

Preferably, the crosslinking agent may be at least one compound selected from the group consisting of carbodiimide, isocyanate and melamine.

Preferably, the organic particles may be at least one of polyethylene, polystyrene, or polypropylene particles whose surfaces are surface-treated with carboxyl groups or hydroxyl groups.

Preferably, the organic particles may include first particles having an average particle diameter (D50) of 100 nm or more and 250 nm or less, and second particles having an average particle diameter (D50) of more than 250 nm and 400 nm or less.

Preferably, the weight ratio of the second particles to the first particles may be 1:0.4 to 1.1.

Preferably, the polyester film for optical use may have 15 to 40 effective protrusions per 120 μm ² of surface area of the film.

Preferably, the refractive index of the primer layer may be 1.45 to 1.60.

Preferably, the polyester base film may not contain particles.

Preferably, the thickness of the polyester base film is 20 to 300 μm, and the thickness of the primer layer may be 0.01 μm to 0.2 μm.

Preferably, the haze of the optical polyester film may be 0.6 to 0.8%.

Preferably, the transmittance of the optical polyester film may be 90% or more.

Preferably, the optical polyester film may have a surface roughness of 40 to 70 nm.

According to the polyester film for optics according to the present invention, the quality of the optical film can be improved by having excellent transmittance, low haze and scratch resistance.

Furthermore, the present invention has effects such as achieving high quality through securing product productivity and reducing defect rates.

However, the effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

1 is a cross-sectional view of an optical polyester film coated with a primer layer on one side according to an embodiment of the present invention.
2 is a cross-sectional view of an optical polyester film coated with a primer layer on both sides according to another embodiment of the present invention.

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

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

In addition, although methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention, suitable methods and materials are described herein.

Unless otherwise stated, all percentages, parts, ratios, etc. are by weight. Further, when an amount, concentration, or other value or parameter is given as either a range, preferred range, or list of upper preferred and lower preferred values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether the ranges are separately disclosed.

When a range of numerical values is recited herein, the range is intended to include its endpoints and all integers and fractions within the range, unless stated otherwise. It is intended that the scope of the present invention not be limited to the specific values recited when defining the range.

As used herein, the terms "comprise", "comprising", "include", "including", "containing", "characterized by", "has", "having" or any other variation thereof are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that includes a list of elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Also, unless expressly stated to the contrary, “or” refers to an inclusive or and not an exclusive or.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of an optical polyester film coated with a primer layer on one side according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of an optical polyester film coated with a primer layer on both sides according to another embodiment of the present invention.

Referring to FIGS. 1 and 2 , an optical polyester film according to an embodiment of the present invention includes a primer layer 10 on at least one surface of a polyester base film 20 . 1 shows that the primer layer 10 is formed on one side of the polyester base film 20, but as shown in FIG. 2, a film in which the primer layer 10 is formed on both sides of the polyester base film 20 is also included in the scope of the present invention.

In the optical polyester film according to an embodiment of the present invention, organic particles are applied in the primer layer to prevent process instability and scratches that may occur while applying a particle-free polyester base film design for high transmittance and low haze properties.

The primer layer according to an embodiment may be coated with a primer coating solution containing an ionic acrylic resin, a crosslinking agent, and organic particles.

In the optical polyester film according to an embodiment of the present invention, the ratio of the refractive index of the primer layer and the refractive index of the polyester base film preferably satisfies Equations 1 and 2 below.

(Equation 1)

0.90 ≤ a1/a2 ≤ 0.97

(Equation 2)

0.05 ≤ a2-a1 ≤ 0.16

Here, a1 is the refractive index of the primer layer, and a2 is the refractive index of the polyester base film.

At this time, when the value of Equation 1 is less than 0.90 or the value of Equation 2 is less than 0.05, there is a problem that the haze exceeds 0.8%, and when the value of Equation 1 exceeds 0.97 or the value of Equation 2 exceeds 0.16, the haze is the same. Since there is a problem of exceeding 0.8%, it is preferable to satisfy the range of Equation 1 and Equation 2 above.

In one embodiment, the polyester base film is preferably a film obtained by drying polyester obtained by polymerizing dicarboxylic acid and glycol, then melting and supplying it with a known extruder, extruding it from a slit die into a single-layer or multi-layer sheet state, adhering to a casting drum by a method such as applying static electricity, cooling and solidifying, manufacturing an unstretched sheet, and then biaxially stretching and then heat-treating.

Dicarboxylic acids used in polyester resins include aromatic dicarboxylic acids such as terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenyl carboxylic acid, diphenyl sulfone dicarboxylic acid, zephenoxyethane dicarboxylic acid, 5-sodium sulfone dicarboxylic acid and phthalic acid, aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, maleic acid and fumaric acid, and cyclohexyl acid. There are alicyclic dicarboxylic acids such as acid dicarboxylic acids, oxycarboxylic acids such as paraoxybenzoic acid, and the like, and glycols include aliphatic glycols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, and neopentine glycol, polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, and polypropylene glycol, alicyclic glycols such as cyclohexane dimethanol, bisphenol A, Aromatic glycols, such as bisphenol S, etc. can be used.

In addition, considering mechanical strength, weather resistance, chemical resistance and transparency, it is preferable to use terephthalic acid or naphthalene dicarboxylic acid as dicarboxylic acid and ethylene glycol as glycol. In addition, it is preferable to use alkaline earth metals, metal compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, germanium compounds and the like as catalysts during polymerization. The kind of dicarboxylic acid, the kind of glycol, or a catalyst may each use 2 or more types together.

In addition, particles may be added to the film raw material so that the film has functions such as runability, weather resistance, and heat resistance, but in the present invention, it is preferable not to add particles to the film raw material in order to realize high transmittance and low haze properties of the film. That is, it is preferable that the polyester base film does not contain particles.

In one embodiment, the thickness of the polyester base film is preferably 20 to 300 μm.

In addition, in the primer coating liquid forming the primer layer of the optical polyester film according to an embodiment of the present invention, the acrylic resin preferably contains 10 to 20% by weight of the total solid content of the primer coating liquid, and the glass transition temperature (Tg) of the acrylic resin is preferably 40 to 80 ° C. At this time, if the content of the acrylic resin is less than 10% by weight or the glass transition temperature is less than 40 ℃, the oligomer precipitation inhibitory effect of the polyester base film may be reduced, and if the content of the acrylic resin exceeds 20% by weight or the glass transition temperature exceeds 80 ℃, it is preferable to set the above range because there is a possibility of reducing the adhesive force and cracking the resin layer during the film forming process of the biaxially stretched film.

In addition, the primer coating liquid preferably contains 1.0 to 6.5 parts by weight of organic particles based on 100 parts by weight of the acrylic resin, and the resin constituting the organic particles preferably has a weight average molecular weight of 100 to 10,000. At this time, if the organic particle content is less than 1.0 parts by weight or the weight average molecular weight of the resin constituting the organic particles is less than 100, the degree of crosslinking with the acrylic resin is insufficient, resulting in uncured appearance and poor adhesion of the coating layer. Appearance defects may occur.

The polyester film for optical use according to an embodiment of the present invention is characterized by designing a structure in which at least one compound selected from the group consisting of carbodiimide, isocyanate and melamine is crosslinked as a crosslinking agent in the primer layer in order to maintain the transparency of the polyester film in the heating process and high temperature process of the polyester base film and the secondary post-processing process.

The melamine compound that can be used in the present invention is not particularly limited, but from the viewpoint of hydrophilization, a methylol melamine derivative obtained by condensing melamine and formaldehyde is preferably etherified by dehydration condensation reaction of methyl alcohol, ethyl alcohol, isopropyl alcohol, etc. as a lower alcohol. However, it can be preferably used because the moisture-heat adhesiveness, flexibility, toughness, and solvent resistance are improved. As a methylolation melamine derivative, monomethylol melamine, dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, and hexamethoxymethylol melamine are mentioned, for example.

Further, in order to disperse in water, it is necessary to react a structure that does not react with a hydroxyl group with an isocyanate terminal group. As a so-called blocking agent, a blocked isocyanate protecting the isocyanate group reactive group is used, and this blocking agent is characterized in that it dissociates at 100° C. or higher. As the blocking agent, phenolic, alcohol, active methylene, acidamide, lactam, acidimide, imidazole, urea, oxime, and amine compounds may be used. More specifically, phenolic compounds such as phenol, cresol, and ethylphenol, propylene glycol monomethyl ether, and ethylene glycol alcohol compounds such as col, benzyl alcohol, methanol, and ethanol; active methylene compounds such as dimethyl malonate and acetylacetone; mercaptan compounds such as butyl mercapdan and dodecyl mercaptan; acid amide compounds such as acetoanilide and acetic acid amide; lactam compounds such as caprolactam and valerolactam; oxime-based compounds such as acetone oxime and methyl ethyl ketoxime, amine-based compounds such as diphenylaniline, aniline, and ethylenimine, and sodium sulfite. Any of the above blocking agents may be used, but it is preferable to use an oxime-based compound.

The crosslinking agent included in the primer coating solution of the present invention is preferably maintained in an amount of 10 to 25 parts by weight based on 100 parts by weight of the acrylic resin. At this time, if the crosslinking agent is less than 10 parts by weight, the polymer crosslinking degree is insufficient and the effect of suppressing oligomer precipitation of the polyester film may be reduced, and if it is more than 25 parts by weight, a large number of unreacted crosslinking reactants are generated, resulting in a decrease in adhesive strength and a biaxially stretched film. Cracks in the resin layer and product appearance damage may occur during the film forming process.

In addition, although particles may be added to the film raw material in order to impart functions such as runability, weather resistance and heat resistance of the film, sufficient attention is required to the amount and material of the addition so that the transparency of the film is not impaired. Regarding the addition amount, it is preferably a very small amount, more preferably not added, and it is preferable to assist with the addition of particles in the primer layer regarding the runability of the film.

An optical polyester film according to an embodiment of the present invention may include organic or inorganic nanoparticles in the primer layer to prevent scratches during the process. The amount of nanoparticles is preferably 1.0 to 6.5 parts by weight based on 100 parts by weight of the acrylic resin. The average particle diameter of the nanoparticles is usually 1.0 μm or less, preferably 0.5 μm or less, and more preferably 100 to 400 nm, from the viewpoint of transparency of the film. In addition, when it is necessary to further enhance the slipperiness or the effect of improving blocking, it is preferable to use particles having an average particle diameter larger than the film thickness of the primer layer in combination. Examples of the particles to be used include inorganic particles such as silica, alumina and metal oxide, and organic particles such as crosslinked polymer particles.

In one embodiment, organic particles are preferred from the viewpoint of the dispersibility of the primer layer and the transparency of the obtained coating film. More specifically, the organic particles are preferably olefin-based particles such as polyethylene, polystyrene, and polypropylene whose surface is surface-treated with a carboxy group or a hydroxyl group.

In addition, the organic particles preferably include first particles having an average particle diameter (D50) of 100 nm or more and 250 nm or less, and second particles having an average particle diameter (D50) of more than 250 nm and 400 nm or less.

In one embodiment, the weight ratio of the second particles to the first particles is preferably 1:0.4 to 1.1. At this time, when the weight ratio is less than 1:0.4, the surface roughness is 40 nm or less, and scratch resistance of the film is not secured.

In addition, within the scope of not impairing the gist of the present invention, antifoaming agents, coating improvers, thickeners, organic lubricants, antistatic agents, ultraviolet absorbers, antioxidants, foaming agents, dyes, pigments, etc. may be used in combination to form the primer layer as necessary.

In one embodiment, the refractive index of the primer layer is usually 1.45 to 1.60, preferably 1.50 to 1.59. When the refractive index of the primer layer is out of the above range, the uniformity of light transmittance as an optical film may be weakened or the appearance defect may occur due to light interference with the processed layer in post-processing. In the present invention, it has excellent characteristics as an optical product by proposing an appropriate refractive index for optical applications.

In one embodiment, the film thickness of the primer layer is usually 0.002 μm to 1.0 μm, preferably 0.005 μm to 0.5 μm, more preferably 0.01 μm to 0.2 μm. When the film thickness is out of the above range, the adhesion, coating appearance, and blocking characteristics may deteriorate. In addition, the primer layer in the present invention is characterized by excellent adhesion even when the film thickness is thin.

In one embodiment, the optical polyester film satisfies the following formula 3,

(Equation 3)

0.05 ≤ (b1/b2)*b3 ≤ 0.25

Here, b1 is the effective number of protrusions of organic particles that can be seen in the SEM image, b2 is the area of the film surface that can be seen in the SEM image and is 120 μm ² , and b3 is the haze.

At this time, when the value of Equation 3 is less than 0.05, it is difficult to secure scratch resistance due to insufficient number of protrusions, and when it exceeds 0.25, there is a problem in that the haze exceeds 0.8%, so it is preferable to satisfy the range of Equation 3 above.

In one embodiment, the polyester film for optics preferably has an effective number of protrusions of 15 to 40 per 120 μm ² area of the surface of the film. At this time, when the number of effective protrusions is less than 15, there is a problem in that scratch resistance of the film is not secured, and when the number of effective protrusions is more than 40, there is a disadvantage in that a sense of particle is recognized on the surface of the film.

In one embodiment, the haze of the optical polyester film may be 0.6 to 0.8%.

In one embodiment, the transmittance of the optical polyester film may be 90% or more.

In one embodiment, the optical polyester film may have a surface roughness of 40 to 70 nm.

Next, a method for manufacturing an optical polyester film according to an embodiment of the present invention will be described in detail, but is not limited to the following manufacturing method.

In addition, as a method for stretching the film, known techniques such as a method of biaxial stretching in the order of stretching in the transverse direction after stretching in the machine direction or a method of simultaneous biaxial stretching in which the film is stretched in the machine direction and the transverse direction almost simultaneously can be used. The preheating temperature and the stretching temperature before stretching are 60 to 130° C., and the stretching ratio is 2.0 to 5.0 times. If necessary, heat treatment at 140°C to 240°C is performed after stretching. In the present invention, a sequential biaxial stretching method in which longitudinal stretching is followed by transverse stretching is preferred.

In addition, the method of forming the primer layer is preferably carried out in a step before stretching in the transverse direction after stretching in the machine direction in the above-described biaxial stretching film forming process of the polyester base film. In addition, as the coating method, any of various known coating methods such as a bar coating method using a Mayer bar, a gravure coating method, a slit die coating method, and a comma coating method may be used, but since a water-dispersed coating liquid is used, the bar coating method is preferable in order to obtain an excellent appearance in a low viscosity state.

In addition, in the coating process, it is preferable to prepare an optical polyester film including a primer layer by applying a primer coating solution having a solid concentration of 0.1% to 15% by weight on the polyester base film. Further, within a range that does not impair the gist of the present invention, the coating liquid may contain an organic solvent for the purpose of improving dispersibility into water, improving film formation, and the like. One kind of organic solvent may be used, and two or more kinds may be used suitably.

Hereinafter, the configuration of the present invention and its effects will be described in more detail through Examples and Comparative Examples. However, these examples are for explaining the present invention in more detail, and the scope of the present invention is not limited to these examples.

[ manufacturing example ]

[Production Example 1] Production of polyester base film

The manufacturing method of the polyester film used as the polyester base film in this embodiment is as follows.

First, polyethylene terephthalate resin pellets were dried under reduced pressure (1.3 hPa) at 135 ° C. for 6 hours, then fed into an extruder, melt-extruded into a sheet at about 280 ° C., and quenched on a metal roll maintained at a surface temperature of 20 ° C. A casting film having a thickness of 1,024 μm was obtained.

Next, the cast film was heated with a heated roll (roll group) and an infrared heater at 100° C., and then stretched in the machine direction at a draw ratio of 3.2 times with a roll having a difference in circumferential speed to obtain a uniaxially oriented PET film. Subsequently, the film was held at the end with a clip, introduced into a hot air area, and dried. After that, it was stretched at 130 ° C. in the transverse direction at a draw ratio of 3.5 times, heat-set at 240 ° C., and then transversely relaxed at 200 ° C. by 3%. In this way, a polyester base film having a thickness of 75 μm was obtained.

[Production Example 2] Production of optical polyester film

During the manufacturing process of the polyester base film prepared in Preparation Example 1, a coating solution for forming a primer layer was applied to one side of a uniaxially oriented PET film prepared by stretching at a stretch ratio of 3.2 times in the machine direction by a reverse roll method to have a solid weight of 0.08 g / m 2, and then an optical polyester film was prepared.

In all Examples and Comparative Examples described later, the total molecular weight was adjusted to be 10,000 g/mol or less, and the thickness of the final primer layer was 0.08 μm.

At this time, the abbreviated names for the components of the coating liquid forming the primer layer are as follows.

A1: ionic acrylic resin and melamine crosslinking agent

(40:7.5 weight ratio, refractive index 1.46 ~ 1.55)

A2: ionic acrylic resin and melamine crosslinking agent

(55:7.5 weight ratio, refractive index 1.36 ~ 1.45)

A3: ionic acrylic resin and melamine crosslinking agent

(25:7.5 weight ratio, refractive index 1.56 ~ 1.65)

B1: Polystyrene particles having an average particle diameter of 100 nm or more and 250 nm or less, surface treatment ○

B2: Polystyrene particles with an average particle diameter greater than 250 nm and less than or equal to 400 nm, surface treatment ○

B3: polystyrene particles having an average particle diameter of 100 nm or more and 250 nm or less, surface treatment X

B4: Polystyrene particles with an average particle diameter of more than 250 nm and less than or equal to 400 nm, surface treatment X

B5: Silica particles having an average particle diameter of 100 nm or more and 250 nm or less, surface treatment X

B6: Silica particles with an average particle diameter of more than 250 nm and less than or equal to 400 nm, surface treatment X

The aforementioned B1 and B2 are polystyrene particles surface-treated with a hydroxyl group.

[Examples 1 to 9]

As shown in Table 1 below, an optical polyester film was prepared as in the above-described Preparation Example with solid components and parts by weight of the coating liquid (water dispersion) forming the primer layer, and the components were indicated by abbreviated names.

division Ingredients of primer layer coating solution parts by weight Example 1 A1/B1/B2 100/1.4/0.9 Example 2 A1/B1/B2 100/1.4/1.2 Example 3 A1/B1/B2 100/1.4/1.5 Example 4 A1/B1/B2 100/1.7/0.9 Example 5 A1/B1/B2 100/1.7/1.2 Example 6 A1/B1/B2 100/1.7/1.5 Example 7 A1/B1/B2 100/2.0/0.9 Example 8 A1/B1/B2 100/2.0/1.2 Example 9 A1/B1/B2 100/2.0/1.5

[ comparative example 1 to 24]

An optical polyester film was prepared in the same manner as in Example 1, except for adjusting the components and contents of the coating solution forming the primer layer as shown in Table 2 below.

division Ingredients of primer layer coating solution parts by weight Comparative Example 1 A1/B3/B4 100/1.4/0.9 Comparative Example 2 A1/B3/B4 100/1.4/1.2 Comparative Example 3 A1/B3/B4 100/1.4/1.5 Comparative Example 4 A1/B3/B4 100/1.7/0.9 Comparative Example 5 A1/B3/B4 100/1.7/1.2 Comparative Example 6 A1/B3/B4 100/1.7/1.5 Comparative Example 7 A1/B3/B4 100/2.0/0.9 Comparative Example 8 A1/B3/B4 100/2.0/1.2 Comparative Example 9 A1/B3/B4 100/2.0/1.5 Comparative Example 10 A1/B5/B6 100/1.4/0.9 Comparative Example 11 A1/B5/B6 100/1.4/1.2 Comparative Example 12 A1/B5/B6 100/1.4/1.5 Comparative Example 13 A1/B5/B6 100/1.7/0.9 Comparative Example 14 A1/B5/B6 100/1.7/1.2 Comparative Example 15 A1/B5/B6 100/1.7/1.5 Comparative Example 16 A1/B5/B6 100/2.0/0.9 Comparative Example 17 A1/B5/B6 100/2.0/1.2 Comparative Example 18 A1/B5/B6 100/2.0/1.5 Comparative Example 19 A2/B1/B2 100/1.7/0.9 Comparative Example 20 A2/B1/B2 100/1.7/1.2 Comparative Example 21 A2/B1/B2 100/1.7/1.5 Comparative Example 22 A3/B1/B2 100/1.7/0.9 Comparative Example 23 A3/B1/B2 100/1.7/1.2 Comparative Example 24 A3/B1/B2 100/1.7/1.5

Using the optical polyester films according to Examples 1 to 9 and Comparative Examples 1 to 24, physical properties were measured through the following experimental examples, and the results are shown in Table 3 below.

[Experimental example]

1. Transmittance and haze measurement

The coating solution according to Examples and Comparative Examples was applied to a polyester film and cured by heat, and transmittance (T.T) and haze were measured using a HAZE meter manufactured by NIPPON DENSHOKU. It was calculated as the average of the measured values of a total of 10 identical samples.

2. Appearance evaluation

After film formation of the optical polyester film according to Examples and Comparative Examples, appearance evaluation was performed for scratches according to each particle type and content. At this time, the evaluation criteria for scratch resistance are as follows.

◎: No scratches

○: Occurrence of non-periodic scratches

X: Occurrence of periodic/aperiodic scratches

3. Surface roughness measurement

The coating solution according to Examples and Comparative Examples was applied to a polyester film and cured by heat, and then the surface roughness was measured using a three-dimensional surface shaper manufactured by VEECO.

4. Evaluation of particle coating stability and measurement of effective protrusions

The coating solution according to Examples and Comparative Examples was applied to a polyester film and cured by heat, and then, using an SEM manufactured by HITACHI, the presence or absence of particles on the surface was confirmed and the number of effective protrusions was confirmed. At this time, the effective number of protrusions represents the number of particles per 120 μm ² area of the film surface. In addition, the evaluation criteria for particle coating stability are as follows.

○: Traces of crater-shaped particle drop-out could not be confirmed (SEM image confirmed)

X: Confirmation of traces of particle dropout in the form of a crater (confirmation of SEM image)

5. Refractive index measurement

For Examples and Comparative Examples, the refractive index of the primer layer and the polyester film was measured using an ellipsometer from Ellipso Technology.

division TT
(%) Haze
(%) nask
latching particle
coating
stability surface
illuminance
(Rz) available
number of projections
(ea) formula 1 formula 2 formula 3 Example 1 91.8 0.60 ○ ○ 48 15 0.91 0.14 0.060 Example 2 91.7 0.61 ○ ○ 49 16 0.91 0.14 0.068 Example 3 91.9 0.71 ◎ ○ 51 18 0.91 0.14 0.107 Example 4 91.3 0.61 ○ ○ 50 15 0.91 0.14 0.066 Example 5 91.6 0.69 ◎ ○ 52 17 0.91 0.14 0.098 Example 6 91.5 0.77 ◎ ○ 54 20 0.91 0.14 0.128 Example 7 91.6 0.71 ◎ ○ 53 17 0.91 0.14 0.101 Example 8 91.4 0.77 ◎ ○ 55 22 0.91 0.14 0.141 Example 9 91.4 0.79 ◎ ○ 57 35 0.91 0.14 0.248 Comparative Example 1 91.5 0.46 X X 47 6 0.91 0.14 0.023 Comparative Example 2 91.3 0.50 X X 50 8 0.91 0.14 0.033 Comparative Example 3 91.2 0.63 X X 51 12 0.91 0.14 0.063 Comparative Example 4 91.3 0.52 X X 51 8 0.91 0.14 0.035 Comparative Example 5 91.5 0.65 X X 51 12 0.91 0.14 0.065 Comparative Example 6 91.4 0.73 X X 52 14 0.91 0.14 0.085 Comparative Example 7 91.2 0.67 X X 52 13 0.91 0.14 0.073 Comparative Example 8 91.8 0.74 ◎ X 54 20 0.91 0.14 0.123 Comparative Example 9 91.3 0.89 ◎ X 55 34 0.91 0.14 0.252 Comparative Example 10 91.5 0.61 X X 37 3 0.91 0.14 0.015 Comparative Example 11 91.5 0.65 X X 39 5 0.91 0.14 0.027 Comparative Example 12 91.3 0.78 X X 42 10 0.91 0.14 0.065 Comparative Example 13 91.4 0.67 X X 41 8 0.91 0.14 0.045 Comparative Example 14 91.7 0.80 X X 42 10 0.91 0.14 0.067 Comparative Example 15 91.6 0.88 X X 42 13 0.91 0.14 0.095 Comparative Example 16 91.2 0.82 X X 45 11 0.91 0.14 0.075 Comparative Example 17 91.6 0.89 X X 44 14 0.91 0.14 0.104 Comparative Example 18 91.9 0.97 ◎ X 46 17 0.91 0.14 0.137 Comparative Example 19 89.7 0.87 ○ ○ 52 15 0.86 0.23 0.109 Comparative Example 20 89.2 0.91 ◎ ○ 52 17 0.86 0.23 0.129 Comparative Example 21 89.3 1.00 ◎ ○ 53 20 0.86 0.23 0.167 Comparative Example 22 89.2 0.88 ○ ○ 52 16 0.98 0.04 0.116 Comparative Example 23 89.4 0.93 ◎ ○ 52 17 0.98 0.04 0.129 Comparative Example 24 89.9 1.20 ◎ ○ 53 22 0.98 0.04 0.183

As can be seen in Table 3 above, it can be seen that the optical polyester films according to Examples 1 to 9 of the present invention can secure excellent transmittance, low haze, scratch resistance and particle coating stability. Through this, it is possible to improve the quality of the optical film, thereby achieving high quality through securing the productivity of products using the same and reducing the defect rate.

On the other hand, when the optical polyester films according to Comparative Examples 1 to 9 used organic particles whose surfaces were not treated with functional groups, it could be confirmed that the coating stability of the particles was poor.

In addition, when the optical polyester films according to Comparative Examples 10 to 18 use silica particles whose surfaces are not treated with functional groups, it can be confirmed that the coating stability of the particles is poor.

In addition, since the polyester films for optical use according to Comparative Examples 1 to 7 have an effective number of protrusions per 120 μm ² of the film surface area of less than 15 and/or the value of Equation 3 is less than 0.05, it can be confirmed that the scratch resistance of the film is not secured.

In addition, the optical polyester films according to Examples 4 to 6 of the present invention and the optical polyester films according to Comparative Examples 19 to 21 used the same content of particles, but the optical polyester films according to Comparative Examples 19 to 21 are Equations 1 and 2. It can be seen that the haze is high when the values are out of the configuration of the present invention.

In addition, the optical polyester films according to Examples 4 to 6 of the present invention and the optical polyester films according to Comparative Examples 22 to 24 used the same content of particles, but the optical polyester films according to Comparative Examples 22 to 24 are the case in which the values of Equations 1 and 2 are out of the configuration of the present invention, and it can be confirmed that the haze is high.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also within the scope of the present invention.

10: primer layer
20: polyester base film

Claims (14)

polyester base film; and
Including a primer layer located on at least one side of the polyester base film,
The primer layer is coated with a primer coating solution containing an acrylic resin, a crosslinking agent and organic particles, an optical polyester film. According to claim 1,
The ratio of the refractive index of the primer layer and the refractive index of the polyester base film satisfies Equations 1 and 2 below,
(Equation 1)
0.90 ≤ a1/a2 ≤ 0.97
(Equation 2)
0.05 ≤ a2-a1 ≤ 0.16
Here, a1 is the refractive index of the primer layer, and a2 is the refractive index of the polyester base film, a polyester film for optics. According to claim 1,
The optical polyester film satisfies the following formula 3,
(Equation 3)
0.05 ≤ (b1/b2)*b3 ≤ 0.25
Here, b1 is the number of effective protrusions, b2 is the area of 120 micrometer ² of the film surface, and b3 is a polyester film for optics which is a haze. According to claim 1,
The crosslinking agent is a compound selected from at least one compound selected from the group consisting of carbodiimide, isocyanate and melamine, an optical polyester film. According to claim 1,
The organic particle is at least one of polyethylene, polystyrene or polypropylene particles whose surface is surface-treated with a carboxy group or a hydroxyl group, an optical polyester film. According to claim 1,
The organic particles include first particles having an average particle diameter (D50) of 100 nm or more and 250 nm or less and second particles having an average particle diameter (D50) of more than 250 nm and 400 nm or less, an optical polyester film. According to claim 6,
The weight ratio of the second particles to the first particles is 1: 0.4 to 1.1, an optical polyester film. The method of claim 1,
The optical polyester film has an effective number of protrusions per 120 μm ² of the film surface area of 15 to 40, an optical polyester film. According to claim 1,
The refractive index of the primer layer is 1.45 to 1.60, an optical polyester film. According to claim 1,
The polyester base film is an optical polyester film that does not contain particles. According to claim 1,
The polyester base film has a thickness of 20 to 300 μm, and the thickness of the primer layer is 0.01 μm to 0.2 μm, an optical polyester film. According to claim 1,
Haze of the optical polyester film is 0.6 to 0.8%, an optical polyester film. According to claim 1,
Transmittance of the optical polyester film is 90% or more, an optical polyester film. According to claim 1,
The surface roughness of the optical polyester film is 40 to 70 nm, an optical polyester film.