KR20220052425A - Polyester film for display protection - Google Patents

Abstract

A polyester film for display protection according to the present invention comprises: a biaxially stretched base film; a first primer layer formed on one side of the base film; and a second primer layer formed on the other side of the base film, comprises a configuration in which a difference in refractive index between the first primer layer and the second primer layer is 0.1 or more, and has a high combat rate and a high fingerprint recognition rate.

Description

Polyester film for display protection

The present invention relates to a polyester film for display protection, and to a polyester film for display protection having excellent adhesion and excellent optical and mechanical properties.

Recently, as interest in liquid crystal display devices, organic light emitting displays, and electronic papers has rapidly increased, a movement to improve durability by forming a protective film on the outermost surface of these display devices is actively progressing.

In general, polyester films have excellent dimensional stability, thickness uniformity, and optical transparency, so that their use ranges are very wide as display devices as well as various industrial materials. In particular, studies of such a polyester film as a display protection film requiring high optical properties are being actively conducted in recent years.

In this way, when the polyester film is used as an optical protective film, high transmittance and low light loss are required to provide the optical fingerprint recognition function adopted in most portable display devices. The light loss rate for the polyester film is related to the physical properties represented by the orientation angle or the optical axis. Basically, the polyester film has an orientation angle by crystallization and bowing in the stretching process, and In this case, since there are two optical axes, the polarized light coming up from the polarizer is changed to elliptical or circular polarized light, and changes in color or iridescent stains are often seen by the human eye.

In order to solve this problem, the invention using a polyester film has been actively progressed. As one of such inventions, Japanese Patent Application Laid-Open No. 2011-532061 reduces optical anisotropy due to birefringence to secure visibility without rainbow spots. However, in the case of this invention, a decrease in the fingerprint recognition rate has emerged as a problem with respect to the display protective film that needs to be subjected to surface processing. has been a problem in using the polyester film for display protection.

In addition, research to improve the optical properties of the polyester film by increasing the transmittance by double-sided heterogeneous coating has also been conducted, but the general double-sided heterogeneous coating has a problem in that it cannot adjust the orientation angle or suppress the light loss rate and improve the oligomer precipitation.

Therefore, in addition to the optical properties of the polyester film itself, a polyester film for display protection that reflects the design of an appropriate structure that can minimize the stress at the interface of each layer, such as the primer layer and the AG or hard coating, and the design to suppress the occurrence of foreign substances. It is being demanded.

Japanese Patent Laid-Open No. 2011-532061

The present invention has been devised to solve the above problems, and an object of the present invention is to control the main chain crystal angle of the film and lower the main orientation angle as much as possible to minimize rainbow stains that may occur when obliquely observed. To provide a polyester film.

In addition, an object of the present invention has a high combat transmittance, and when used as a protective film for a display device having an optical fingerprint recognition function, suppresses light loss that may lower the fingerprint recognition rate, and minimizes the occurrence of foreign matter. To provide a polyester film.

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

The above object includes a biaxially stretched base film, a first primer layer formed on one surface of the base film, and a second primer layer formed on the other surface of the base film, and the difference in refractive index between the first primer layer and the second primer layer is It is achieved by a polyester film for display protection of 0.1 or more.

Here, the polyester film for display protection may have a haze change of 1% or less after heat treatment at 150° C. for 1 hour.

Preferably, the polyester film for display protection may have a light loss ratio of 11% or less according to Equation 1 below.

(Equation 1)

Light loss rate = (Maximum amount of light in parallel polarizer - maximum amount of light after film is inserted between two polarizers)/(Maximum amount of light in parallel to polarizer).

Preferably, the polyester film for display protection may have a difference between an orientation angle and an optical axis of 9 degrees or less.

Preferably, the polyester film for display protection may have a difference in orientation angle between the center portion and the edge portion of 20 degrees or less.

Preferably, the polyester film for display protection may have an orientation angle of the main chain of 20 degrees or less.

Preferably, the refractive index of the first primer layer may be 1.58 to 1.62, and the refractive index of the second primer layer may be 1.45 to 1.49.

Preferably, the polyester film for display protection may have a MD direction: TD direction draw ratio of 1:1.45 to 1:1.75.

Preferably, the polyester film for display protection may have a transmittance of 93% or more.

Preferably, the first primer layer may include a polyester copolymer resin, a polyurethane-based resin, an oxazoline-based curing agent, an epoxy-based curing agent, an anionic surfactant, and inorganic particles.

Preferably, the second primer layer may include a polyacrylic resin having a carboxyl group as a functional group, a melamine-based curing agent, an anionic surfactant, and inorganic particles.

Preferably, the second primer layer may have an oligomer block function.

Preferably, the base film may include at least one material selected from polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, and polycarbonate.

Preferably, the thickness of the base film may be 25 to 200㎛.

In addition, the above object is a first step of melt-extruding a polyester resin to form an unstretched sheet, a second step of applying and drying a coating solution for forming a first primer layer on one surface of the unstretched sheet, and an unstretched sheet A third step of applying and drying a coating solution for forming a second primer layer on the other surface of the , a fifth step of biaxially stretching the uniaxially-stretched sheet in the width direction (TD) and a sixth step of heat-setting the biaxially-stretched sheet to form a polyester film for display protection.

Preferably, the thickness of the first primer layer and the second primer layer may be 10 to 200 nm.

Preferably, the heat setting temperature of the sixth step may be 180 to 220 ℃.

The polyester film for display protection according to an embodiment of the present invention can suppress light loss through a high transmittance. In addition, since both LCD and OLED, which are display devices, use a polarizing plate, in order to have a high fingerprint recognition rate, the optical axis of the polyester film for display protection and the optical axis of the polarizing plate are matched to minimize the light loss rate, and through this, the present invention The polyester film for display protection according to an embodiment of the present invention may have a high fingerprint recognition rate due to a small change in the optical axis.

In addition, the polyester film for display protection according to an embodiment of the present invention can have a high fingerprint recognition rate by suppressing foreign substances in the film and minimizing the generation of oligomers.

In addition, the polyester film for display protection according to an embodiment of the present invention can increase the yield at the time of punching by minimizing the generation of foreign substances during the thermal process.

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

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

With reference to the accompanying drawings, the embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

In order to clearly express various layers and regions in the drawings, the thicknesses are enlarged. Throughout the specification, like reference numerals are assigned to similar parts. When a part, such as a layer, film, region, plate, etc., is “on” another part, it includes not only cases where it is “directly on” another part, but also cases where there is another part in between. Conversely, when we say that a part is "just above" another part, we mean that there is no other part in the middle.

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

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

Referring to Figure 1, the polyester film for display protection according to an embodiment of the present invention is a base film (2), a first primer layer (1) formed on one surface of the base film (2), and another of the base film (2). and a second primer layer 3 formed on one surface (the other surface). At this time, the positions of the first primer layer 1 and the second primer layer 3 may be changed.

In one embodiment, the base film 2 preferably includes at least one polyester selected from among polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate and polycarbonate, and may be a biaxially stretched film.

In one embodiment, the thickness of the base film (2) is preferably 25 to 250㎛. When the thickness of the base film (2) is less than 25㎛, wrinkles are likely to be mixed in the surface processing and polarizing plate lamination process, and the yield may be reduced. If the thickness of the base film (1) exceeds 250㎛, it is difficult to control the retardation and There is a problem that the thickness increases.

In addition, the base film 2 may further include an additive material such as an ultraviolet absorber capable of absorbing ultraviolet rays or an antioxidant for suppressing browning of the ultraviolet absorber according to the required purpose.

In one embodiment, the difference in refractive index between the first primer layer 1 formed on one surface of the base film 2 and the second primer layer 3 formed on the other surface of the base film 2 is preferably 0.1 or more. When the difference in refractive index between the first primer layer (1) and the second primer layer (3) is less than 0.1, the transmittance is lowered and the light loss of the film is increased.

In one embodiment, since the first primer layer (1) often constitutes a hard coating, its refractive index is preferably 1.58 to 1.62 in order to control rainbow stains due to interference when forming a hard coating on the surface, It is more preferably 1.59 to 1.60.

In one embodiment, the first primer layer 1 includes at least one main material selected from a polyester copolymer resin and a polyurethane-based resin as a binder resin. Preferably, two types of main material may be included.

In addition, the first primer layer 1 includes at least one material selected from among oxazoline-based, carbodiimide-based and melamine-based curing agent resins. In particular, the oxazoline-based curing agent suppresses moisture permeation into the film through moisture resistance, and the melamine-based curing agent also reacts with the main material, but improves the strength of the coating film through its own curing reaction between melamines, which may occur during double-sided coating. It plays a role in preventing the blocking phenomenon. Preferably, it may include a curing agent mixture consisting of an oxazoline-based curing agent and a melamine-based curing agent.

In addition, the first primer layer 1 preferably contains an anionic surfactant as an additive.

In addition, the first primer layer 1 may further include an additional additive in the coating solution to improve coating properties and functionality. As such, as an additive used in the first primer layer 1, organic particles, inorganic particles, an antifoaming agent, and the like may be used.

In the present invention, the first primer layer (1) can secure running properties through the inorganic particles, it is preferable that the average particle diameter of the inorganic particles is 10 to 300 nm. When the average particle diameter of the inorganic particles exceeds 300 nm, a problem of increasing haze occurs, and when it is less than 10 nm, it is not possible to secure runability.

In addition, the inorganic particles are preferably at least one selected from silica particles and a silica-organic composite, and the refractive index of the inorganic particles is preferably 1.5 or more in consideration of the refractive index of the first primer layer 1 .

In one embodiment, the first primer layer 1 is a binder resin consisting of a mixture of a polyester copolymer resin and a polyurethane resin, a curing agent consisting of a mixture of an oxazoline-based curing agent and a melamine-based curing agent, an anionic surfactant, and inorganic particles It is preferable to form by coating a coating liquid containing a base film (2).

The composition constituting the first primer layer (1) is prepared as a coating liquid in the form of an aqueous dispersion with water and is applied to one surface of the base film (2). In one embodiment, the coating thickness of the first primer layer (1) is preferably 10 to 200nm. If the coating thickness is less than 10 nm, a reflective rainbow may be observed after surface processing, and there is a problem in that adhesion is reduced, and if it exceeds 200 nm, reflective rainbow and blocking occur.

In one embodiment, the adhesion between the first primer layer (1) and the base film (2) and moisture-resistant adhesion is preferably 95 to 100%.

Next, since the processing of the pressure-sensitive adhesive or adhesive is made on the surface of the second primer layer 3, it is preferable to constitute a primer layer capable of processing the pressure-sensitive adhesive or adhesive, and an oligomer block to suppress the generation of foreign substances after heat treatment It is desirable to have a function. The second primer layer 3 increases the functional group capable of reacting with the curing agent on the main material, and by using a curing agent having excellent reactivity with the functional group, the network structure after curing of the primer layer is made smaller than the size of the oligomer. Precipitation on the layer can be prevented. As described above, the polyester film for display protection according to an embodiment of the present invention can increase the yield at the time of punching by minimizing the generation of foreign substances during the thermal process.

In one embodiment, the refractive index of the second primer layer is preferably 1.45 to 1.49 so that the difference in refractive index between the first primer layer and the second primer layer is 0.1 or more.

In one embodiment, the second primer layer 3 is a binder resin, it is preferable to apply a polyacrylic resin and / or polyalkylene oxide resin having a carboxyl group as a functional group, and to design a specific crosslinking system. Preferably, it may include a polyacrylic resin having a carboxyl group as a functional group.

In addition, the second primer layer 3 includes at least one material selected from oxazoline-based, carbodiimide-based and melamine-based curing agents. In particular, the oxazoline-based curing agent suppresses moisture permeation into the film, and the melamine-based curing agent also reacts with the main material, but improves the strength of the coating film through its own curing reaction between the melamines, thereby preventing the blocking phenomenon that may occur during double-sided coating perform the role Preferably, it may include a melamine-based curing agent.

In addition, the second primer layer 3 preferably contains an anionic surfactant as an additive.

In addition, the second primer layer 3 may further include an additional additive in the coating solution to improve coating properties and functionality. As an additive used in the second primer layer 3 as described above, organic particles, inorganic particles, antifoaming agents, and the like may be used.

In the present invention, the second primer layer 3 may secure running properties through the inorganic particles, and the average particle diameter of the inorganic particles is preferably 10 to 300 nm. When the average particle diameter of the inorganic particles exceeds 300 nm, a problem of increasing haze occurs, and when it is less than 10 nm, it is not possible to secure runability. And it is preferable that the inorganic particles are at least one selected from silica particles and silica-organic composites. In this case, as the inorganic particles, the same inorganic particles as those of the above-described first primer layer 1 may be used.

The composition constituting the second primer layer 3 is prepared as a coating liquid in the form of an aqueous dispersion with water, and is applied to the other surface of the base film 2 (the surface to which the first primer layer is not applied). In one embodiment, the coating thickness is preferably 10nm ~ 200nm. At this time, when the coating thickness is less than 10 nm, it is difficult to ensure runability and there is a high possibility that a problem occurs in adhesion with the adhesive, and when it exceeds 200 nm, it is not preferable because the color of the film itself is highly likely to appear yellow.

In one embodiment, it is preferable that the adhesion and moisture resistance adhesion between the second primer layer 3 and the base film 2 is 95 to 100%.

The polyester film for display protection according to an embodiment of the present invention is preferably a film biaxially stretched in the longitudinal direction (MD) and/or the width direction (TD). In particular, since polyethylene terephthalate constituting the base film 2 does not have crystallinity in an unstretched state, mechanical strength is weak, and it is more preferable to be a biaxially oriented film because it is difficult to control low thickness.

In the polyester film for display protection, the orientation angle in the main chain direction is set by the crystallinity of the polyester material in the stretching direction when heat setting is performed through the stretching process.

The orientation angle of the main chain refers to the angle formed by the crystals of the main chain compared to the width direction of the film. The orientation angle direction in the main chain direction is set by the crystallinity of the polyester-based material (polyester resin) with respect to the stretching direction in the process of heat-setting the film through a biaxial stretching process. First, stretching in the longitudinal direction (MD) is finished for an unstretched film formed of polyester, and stretching in the width direction (TD) is performed. And during the heat setting treatment, a bowing phenomenon occurs due to residual stress after stretching, and the bowing phenomenon has a bow-shaped gradient in the opposite direction to the film advancing direction.

Since the orientation of the main chain crystal causes a change in the optical axis, if the orientation angle is not adjusted low, light loss occurs after the protective film is constructed, thereby lowering the fingerprint recognition rate. In order to minimize this phenomenon, it is necessary to suppress the bowing phenomenon so that the edge portion (edge portion of the film) can be set as similar as possible to the physical properties of the width center. In order to suppress the bowing phenomenon, it is necessary to increase the stretching in the TD direction compared to the stretching in the MD direction. It is preferable to adjust to

In one embodiment, the orientation angle of the main chain of the polyester film for display protection is preferably 20 degrees or less, more preferably 17 degrees or less, and even more preferably 12 degrees or less. When the orientation angle of the main chain of the polyester film for display protection exceeds 20 degrees, the deviation between the optical axis and the orientation angle increases, so that the light loss rate increases.

In addition, the light loss rate can be expressed by Equation 1 as a numerical value representing the loss of light according to an angle when a film is inserted in the parallel polarizing plate nicol.

(Equation 1)

Light loss rate = (Maximum amount of light in parallel polarizer - maximum amount of light after film is inserted between 2 polarizers) / (Maximum amount of light in parallel to polarizer)

At this time, it is preferable that the light loss ratio according to Equation 1 of the polyester film for display protection according to an embodiment of the present invention is 11% or less. When the optical loss rate exceeds 11%, a problem occurs in that the fingerprint recognition rate is lowered due to the high optical loss.

In the polyester film for display protection according to an embodiment of the present invention, the light loss ratio according to Equation 1 usually has a minimum value in the center portion near an orientation angle of 0 degrees, and tends to increase as the orientation angle increases. Therefore, in the polyester film for display protection according to an embodiment of the present invention, the edge portion may have properties similar to the center portion as much as possible through the adjustment of the orientation angle in order to minimize the light loss rate. For this purpose, the polyester film for display protection preferably has a difference in orientation angle between the center portion and the edge portion of 20 degrees or less. When the orientation angle difference between the center portion and the edge portion is more than 20 degrees, the light loss rate increases.

In one embodiment, the polyester film for display protection preferably has a difference between an orientation angle and an optical axis of 9 degrees or less. If the difference between the orientation angle and the optical axis is more than 9 degrees, the difference between the optical axis and the polarizing plate in the display device becomes large, so that the punching cannot be performed according to the optical axis of the polarizing plate. This causes a problem in that it cannot function as a protective film.

In addition, the polyester film for display protection according to an embodiment of the present invention preferably has a total light transmittance of 93% or more, more preferably 95% or more. If the total light transmittance is less than 93%, the fingerprint recognition rate is lowered and the brightness of the display material is lowered.

In addition, the polyester film for display protection according to an embodiment of the present invention preferably has a haze change of 1% or less after heat treatment at 150° C. for 1 hour. When the haze exceeds 1%, transparency is lowered, and a problem occurs in that the contrast ratio is lowered.

The method of manufacturing a polyester film for display protection according to an embodiment of the present invention as described above includes a first step of melt-extruding a polyester resin to form an unstretched sheet, forming a first primer layer on one surface of the unstretched sheet A second step of applying and drying a coating solution, a third step of applying and drying a coating solution for forming a second primer layer on the other surface of the unstretched sheet, an unstretched sheet having a first primer layer and a second primer layer formed thereon A fourth step of uniaxially stretching in the longitudinal direction (MD), a fifth step of biaxially stretching the uniaxially stretched sheet in the width direction (TD), and heat setting the biaxially stretched sheet to form a polyester film for display protection a sixth step of

In one embodiment, the heat setting treatment temperature is preferably 180 to 220 ℃, more preferably 180 to 200 ℃. At this time, if the heat setting treatment temperature is less than 180 ℃, the heat setting of the base film 2 and the first primer layer 1 and the second primer layer 3 is not performed properly, and when it exceeds 220 ℃, a bowing phenomenon occurs. A difference between the orientation angle and the optical axis may be large. In this way, by performing heat treatment at a temperature lower than the normal heat setting temperature, it is possible to minimize the stress difference between the stretched part and the heat part.

In the method for manufacturing a polyester film for display protection according to an embodiment of the present invention, the description overlapping with the polyester film for display protection described above will be omitted.

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.

[Example]

[Production Example]

(coating solution 1)

As a binder resin, 70% by weight of water, 30% by weight of polyurethane resin (H-15, Jeil Industries), 70% by weight of water, and 30% by weight of polyester-based copolymer resin (TR620K, Takamatsu Oil Corporation) % of the main material 2 was mixed with each 12.5 wt%. 20.0% by weight of the aqueous dispersion of the main resin composition, 40% by weight of an oxazoline-based curing agent (WS500, Nippon Carbide) and 60% by weight of water, and a melamine-based curing agent (PM80, DIC) as a curing agent to improve moisture resistance ) The curing agent 2 composed of 70% by weight and 30% by weight of water was mixed at 1.87% by weight, respectively. Water composed of 1.0% by weight of aqueous dispersion of surfactant composed of 90% by weight of water and 10% by weight of anionic surfactant (RY-2, Goo Chemical), 70% by weight of silica particles, and 30% by weight of water in the thus prepared coating solution Coating solution 1 was prepared using 0.5 wt% of the dispersed particle coating solution and the remaining amount of water.

(coating liquid 2)

As a binder resin, 70% by weight of water and 30% by weight of a polyacrylic resin having a carboxyl group as a functional group (RX-7013ED, Nippon Carbide) 20% by weight of an aqueous dispersion of the main resin and a melamine-based curing agent (PM80, DIC) 30% by weight and In a mixture prepared by mixing 70% by weight of water and 10% by weight of an aqueous dispersion of a curing agent, 1.0% by weight of a surfactant aqueous dispersion consisting of 90% by weight of water and 10% by weight of an anionic surfactant (RY-2, Goo Chemical) and silica particles A coating solution 2 was prepared using 0.5% by weight of the aqueous dispersion particle coating solution composed of 70% by weight and 30% by weight of water and the remaining amount of water.

(coating solution 3)

Coating solution 3 was prepared in the same manner as in coating solution 1, except that a polyurethane resin (AP-40F, DIC) was used as a binder resin instead of a polyurethane resin (H-15, Jeil Industries).

[Examples 1-4]

After melt-extruding the polyethylene terephthalate raw material chip, an unstretched sheet is prepared on a casting roll, and then the coating solution is applied to one side and the other side of the unstretched sheet using a metal bar #4, respectively, and dried at 80° C. A first primer layer and a second primer layer having a thickness of 100 nm were formed. Next, after stretching in the longitudinal direction (MD) and the width direction (TD), respectively, heat-setting at 190° C. to prepare a biaxially stretched polyester film for display protection.

In this case, the composition of the coating solution, the stretching conditions and the thickness of the entire film are shown in Table 1, and the refractive indices of the first and second primer layers are shown in Table 3, respectively.

[Comparative Examples 1 to 5]

A polyester film for display protection was prepared in the same manner as in Example 1, except that the composition and stretching conditions of the coating solution were changed as shown in Table 1 below.

division MD
draw ratio TD
draw ratio MD: TD
draw ratio film thickness
(μm) first primer layer second primer layer Example 1 3.0 4.35 1:1.45 125 coating solution 1 coating liquid 2 Example 2 3.0 4.65 1:1.55 125 coating solution 1 coating liquid 2 Example 3 3.0 4.95 1:1.65 125 coating solution 1 coating liquid 2 Example 4 3.0 5.25 1:1.75 125 coating solution 1 coating liquid 2 Comparative Example 1 3.0 3.5 1:1.17 125 coating solution 1 coating liquid 2 Comparative Example 2 3.0 3.5 1:1.17 125 coating solution 1 coating solution 3 Comparative Example 3 3.0 4.95 1:1.65 125 coating solution 1 coating solution 1 Comparative Example 4 3.0 4.95 1:1.65 125 coating liquid 2 coating liquid 2 Comparative Example 5 3.0 3.0 1:1 125 coating solution 1 coating liquid 2

Physical properties were measured through the following experimental examples using the polyester films according to Examples 1 to 4 and Comparative Examples 1 to 5, and the results are shown in Tables 2 and 3 below.

[Experimental example]

(1) Measurement of combat success rate

The transmittance of the film was measured with a haze meter (NDH-4000, Nippon Denshoku).

(2) thickness measurement

The thickness of the film was measured using a micrometer (VL-50aS, Mitsutoyo Co.).

(3) Measurement of light loss rate

After cutting the film to 5 cm in width and 5 cm in length, make two polarizing films in a 100% transmission state (parallel nicol) to check the maximum amount of light, place the cut film between the two polarizing films, and then The change in the maximum amount of light was measured while changing the angle of , and the light loss rate was calculated through Equation 1.

(Equation 1)

Light loss rate = (Maximum amount of light in parallel polarizer - maximum amount of light after film is inserted between two polarizers)/(Maximum amount of light in parallel to polarizer)

(4) Measurement of orientation angle

After the film was biaxially stretched, the crystal direction of the main chain with respect to the width direction of the film was measured at the center portion and the edge portion, respectively, using an orientation angle measuring device (SST-4000, Nomura Shoji Co., Ltd.) for the film sample. At this time, since the orientation angle of the center part is 0 degrees, the orientation angle of Table 2 below represents the orientation angle of the edge part.

(5) Optical axis measurement

After the film was placed between two polarizing plates in a polarizing plate cross nicol state, the angle at which the black mode was realized was checked and measured with a protractor.

(6) Rainbow Stain Inspection

An insulating tape (Niito) was attached to the back of the prepared film, and visually inspected under the reflection of a fluorescent light, and then evaluated as follows.

○: Non-observation of rainbow spots

X; rainbow blotch observation

(7) Haze change measurement

For the prepared film, haze was measured before heat treatment using a haze meter (NDH-4000, Nippon Denshoku Co., Ltd.), and haze after heat treatment in an oven at 150° C. for 1 hour was measured, respectively.

(8) Measurement of adhesion force

A #20 wire bar is used to apply an acrylic UV curing resin to the surface of the first primer layer, and then cut lines are made on the film made with a cutter, and 1 mm × 1 mm squares are arranged in a 10 × 10 matrix. Then, a cellophane tape (No. 405, NICHIBAN company, width: 24 mm) is attached to the film on which the cut line is formed, and the tape is strongly attached to the film by rubbing the tape using velvet, and then the tape is removed vertically. At this time, the adhesion force was calculated by substituting the area of the primer layer remaining on the coating layer formed of the acrylic UV curing resin into Equation 2 below.

(Equation 2)

In addition, after leaving the film prepared in the same manner at a temperature of 60° C. and a humidity of 90% for 100 hours, the moisture resistance adhesion was measured in the same manner.

(9) Measurement of the refractive index of the primer layer

After applying each of the coating solutions of Coating Solutions 1 to 3 on the glass plate and thermosetting, a black insulating tape was attached to the back of the glass plate that was not coated with the coating solution, and then an ellipsometer (Elli-SE, Ellipso Technology Co., Ltd.) ) was used to measure the refractive index.

division battle rate
(%) orientation angle
(°) optical axis
(°) rainbow
stain haze change
(%) light loss rate Example 1 94.2 20 27 ○ 0.8 11 Example 2 93.8 17 22 ○ 0.9 10.3 Example 3 93.5 14 18 ○ 0.8 9.2 Example 4 93 11 13 ○ 1.0 6.8 Comparative Example 1 93 47 52 ○ 0.9 15 Comparative Example 2 91 47 52 ○ 3.2 18 Comparative Example 3 89 14 18 ○ 3.1 20 Comparative Example 4 92 14 18 X 0.6 16 Comparative Example 5 93 50 62 ○ 0.8 22

division first primer layer refractive index Second Primer Layer Refractive Index Primer interlayer
refractive index difference adhesion
(%) moisture resistance
(%) Example 1 1.59 1.47 0.12 100 100 Example 2 1.59 1.47 0.12 100 100 Example 3 1.59 1.47 0.12 100 100 Example 4 1.59 1.47 0.12 100 100 Comparative Example 1 1.59 1.47 0.12 100 100 Comparative Example 2 1.59 1.55 0.04 100 100 Comparative Example 3 1.59 1.59 0 100 100 Comparative Example 4 1.47 1.47 0 100 100 Comparative Example 5 1.59 1.47 0.12 100 100

As described in Tables 2 and 3, Examples 1 to 4 according to the present invention all have excellent adhesion and excellent optical and mechanical properties. , it can be seen that the amount of change in haze satisfies all the physical properties required for the protective film.

On the other hand, in Comparative Example 1, the difference in refractive index between the first primer layer and the second primer layer located on both sides of the base film is 0.1 or more, but the orientation angle of the main chain exceeds 20 due to the low draw ratio in the MD and TD directions, and excessive light It can be seen that there is a loss.

In addition, the difference in refractive index between the first primer layer and the second primer layer located on both sides of the base film is less than 0.1, and Comparative Example 2 having a low elongation ratio in the MD and TD directions has an orientation angle of the main chain exceeding 20 and a haze change is large, and it can be seen that excessive light loss occurs.

In addition, Comparative Examples 3 and 4, in which the first primer layer and the second primer layer located on both sides of the base film were formed of the same coating solution, had the same refractive index between the primer layers, and thus had a low transmittance, and rainbow stains or high haze change occurred. it can be seen that

Also, in Comparative Example 5, it can be seen that, as a result of the difference between the orientation angle and the optical axis exceeding 9 degrees, the optical loss rate exceeded 11%, resulting in excessive optical loss.

As such, the polyester film for display protection according to an embodiment of the present invention can improve productivity during post-processing by minimizing the interference mura phenomenon after hard coating on the surface, and suppress the generation of foreign substances through the oligomer block function, and By controlling the light loss rate according to the orientation angle, the fingerprint implantation rate can be increased. In addition, since it has excellent optical properties, it can be widely used as an optical film other than a protective film.

Although 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 by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

1: first primer layer 2: base film
3: second primer layer

Claims (17)

biaxially stretched base film;
a first primer layer formed on one surface of the base film; and
a second primer layer formed on the other surface of the base film;
including,
The difference in refractive index between the first primer layer and the second primer layer is 0.1 or more, a polyester film for display protection. According to claim 1,
The polyester film for display protection has a haze change of 1% or less after heat treatment at 150° C. for 1 hour, a polyester film for display protection. According to claim 1,
The polyester film for display protection has a light loss rate of 11% or less according to Formula 1 below, a polyester film for display protection.
(Equation 1)
Light loss rate = (Maximum amount of light in parallel polarizer - maximum amount of light after film is inserted between two polarizers)/(Maximum amount of light in parallel to polarizer). According to claim 1,
The polyester film for display protection has a difference between an orientation angle and an optical axis of 9 degrees or less, a polyester film for display protection. According to claim 1,
The polyester film for display protection has a difference in orientation angle between the center portion and the edge portion of 20 degrees or less, a polyester film for display protection. According to claim 1,
The polyester film for display protection has an orientation angle of the main chain of 20 degrees or less, a polyester film for display protection. According to claim 1,
The refractive index of the first primer layer is 1.58 to 1.62, and the refractive index of the second primer layer is 1.45 to 1.49, a polyester film for display protection. According to claim 1,
The polyester film for display protection is a MD direction: TD direction stretch ratio of 1:1.45 to 1:1.75, a polyester film for display protection. According to claim 1,
The polyester film for display protection has a combat transmittance of 93% or more, a polyester film for display protection. According to claim 1,
The first primer layer comprises a polyester copolymer resin, a polyurethane-based resin, an oxazoline-based curing agent, a melamine-based curing agent, an anionic surfactant, and inorganic particles, a polyester film for display protection. According to claim 1,
The second primer layer is a polyester film for display protection comprising a polyacrylic resin having a carboxyl group, a melamine-based curing agent, an anionic surfactant, and inorganic particles. According to claim 1,
The second primer layer has an oligomer block function, a polyester film for display protection. According to claim 1,
The base film is at least one selected from polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate and polycarbonate, a polyester film for display protection. According to claim 1,
The thickness of the base film is 25 to 250㎛, a polyester film for display protection. A first step of melt-extruding a polyester resin to form an unstretched sheet;
a second step of applying and drying a coating solution for forming a first primer layer on one surface of the unstretched sheet;
a third step of applying and drying a coating solution for forming a second primer layer on the other surface of the unstretched sheet;
a fourth step of uniaxially stretching the unstretched sheet on which the first primer layer and the second primer layer are formed in the longitudinal direction (MD);
a fifth step of biaxially stretching the uniaxially stretched sheet in a width direction (TD); and
a sixth step of heat-setting the biaxially stretched sheet to form a polyester film for display protection;
A method for producing a polyester film for display protection, comprising a. 16. The method of claim 15,
The thickness of the first primer layer and the second primer layer is 10 to 200 nm, a method for producing a polyester film for display protection. 16. The method of claim 15,
The heat setting temperature of the sixth step is 180 to 220 ℃, a method of manufacturing a polyester film for display protection.

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