KR20210118512A - Polyester film and manufacturing method thereof - Google Patents

Abstract

A polyester film according to one embodiment of the present invention comprises a film made of a copolymerized polyester resin, wherein the film includes a primer layer on at least one surface thereof, the light loss factor at a wavelength of 550 nm both in the machine direction (longitudinal direction, MD) and the transverse direction (TD) of the film is 10% or less, and the deviation of the optical axis angle is ±5˚ or less. Therefore, using the polyester film according to one embodiment of the present invention as a protective film for a curved display can prevent lifting of a curved edge portion of the display, thereby increasing the fingerprint recognition rate of optical fingerprint recognition using a display.

Description

Polyester film and its manufacturing method

The present invention relates to a polyester film that can be used to protect a smartphone display, and more specifically, in a curved display equipped with an optical fingerprint recognition function, excellent fingerprint recognition rate and full curve through optimization of film components and optical axis It relates to a polyester film capable of being covered and a method for manufacturing the same.

Recently, the smartphone market is growing very rapidly because it provides users with various functions and uses. In this rapidly growing smartphone, the adoption of curved display is increasing to satisfy both design and functionality, and at the same time, the number of smartphones equipped with fingerprint recognition function for information security is increasing. Aside from the type that has a fingerprint recognition part mounted on a smartphone, a smartphone with a fingerprint recognition function on the display itself is being released.

As such, a smartphone having a fingerprint recognition function in which the display itself is not exposed to the outside of the smartphone has a great advantage in terms of design and can provide convenience to the user.

In particular, in the case of fingerprint recognition using a display, it is classified into a capacitive method, an ultrasonic method, and an optical method, and those that can be mounted on the dual display itself are ultrasonic and optical methods. In the case of the ultrasonic method, there is an advantage in that errors due to foreign substances are small, but the ultrasonic sensor has a disadvantage in that it is expensive. For this reason, the optical method is adopted in most smartphones of the fingerprint recognition method using the display. In a smartphone that recognizes fingerprints on the display through the optical method, a polarizer is placed in the outermost part of the display. there is no problem

For example, Korean Patent Application Laid-Open No. 10-2018-0080747 relates to a mobile phone liquid crystal protective film, and provides a film for protecting a liquid crystal screen using a PET film fabric. However, in the above patent, the general PET film is used and the flexibility is not good, so a phenomenon occurs in the curved part of the screen edge having a curve, and the fingerprint recognition rate in the optical type in-display fingerprint recognition is lowered due to the problem of the occurrence of optical axis deviation. have

As such, the PET film used as a conventional protective film has poor flexibility, which causes it to float when attached to the curved surface of the edge of the screen. There are disadvantages. Glass or TPU (urethane) material is used to replace PET film having such a problem, but in the case of glass, it is expensive and has the disadvantage of being easily broken by impact. It has the problem of tearing easily.

Korean Patent Publication 10-2018-0080747

An object of the present invention is to provide a polyester film capable of suppressing a lifting phenomenon in a region having a curvature such as an edge portion when used in a curved display.

In addition, an object of the present invention is to provide a polyester film having an excellent fingerprint recognition function by controlling the optical axis of the film by optimizing the manufacturing method.

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 film made of a copolymer polyester resin and a primer layer on at least one surface of the film, and the optical loss rate in the wavelength 550 nm region in the longitudinal direction (MD) and in the transverse direction (TD) is 10% or less, and the optical axis angle is achieved by a polyester film having a deviation of ±5° or less.

Preferably, the copolymerized polyester resin may be a copolymer of dicarboxylic acid or an ester-forming derivative thereof and a diol component including ethylene glycol.

Preferably, the dicarboxylic acid may be at least one selected from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid.

Preferably, the diol component containing ethylene glycol is 70 to 99 mol% of ethylene glycol and 1 to 30 mol of at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, propanediol and butanediol. % may be included.

Preferably, the polyester film may satisfy the following Equations 1 and 2 in a draw ratio in the longitudinal direction (MD) and the transverse direction (TD).

(Equation 1)

0.3≤Longitudinal Stretch Ratio/Transverse Stretch Ratio≤0.6

(Equation 2)

2 times ≤ longitudinal stretch ratio ≤ 4 times

Preferably, the polyester film may have a fingerprint recognition rate of 98% or more in an optical fingerprint recognition type.

Preferably, the polyester film may have a flexibility of 15gr or less in the longitudinal direction (MD) and the transverse direction (TD).

Preferably, the thickness of the polyester film may be 25 ~ 100㎛.

Preferably, the polyester film may be a biaxially oriented film.

Preferably, the primer layer may have a polyurethane-based binder or an acrylic binder as a main component, and the thickness of the primer layer may be 5 to 200 nm.

Preferably, the haze of the polyester film is 1.5% or less, and the transmittance may be 90% or more.

Preferably, the copolymerized polyester resin may further include 2 to 20% by weight of particles based on 100% by weight of the copolymerized polyester resin. Also, preferably, the particles may be silica particles having an average diameter of 1 to 10 μm.

In addition, the above object is to form bishydroxyethylene terephthalate or an oligomer thereof by heating and reacting dicarboxylic acid or an ester-forming derivative thereof with a diol component containing ethylene glycol, the resulting bishydroxyethylene terephthalate Alternatively, a polycondensation catalyst and a phosphoric acid-based thermal stabilizer are added to the oligomer to form a copolyester resin by polycondensation reaction, extruding the copolyester resin and then stretching in the longitudinal direction to prepare a uniaxially stretched film step, coating a primer layer on the uniaxially stretched film, stretching the uniaxially stretched film coated with the primer layer in the transverse direction to prepare a biaxially stretched film and heat treatment of the biaxially stretched film It is achieved by a method for producing a polyester film comprising the step of.

Preferably, the diol component containing ethylene glycol is selected from 70 to 99 mol% of ethylene glycol and at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, propanediol and butanediol 1 to 30 % by mole.

Preferably, the step of heat treatment may be heat treatment at 190 to 220 ℃.

Preferably, the step of uniaxial stretching and the step of biaxial stretching may satisfy the above-described Equations 1 and 2 in the stretching ratios in the longitudinal direction (MD) and the transverse direction (TD).

In addition, the above object is achieved by the polyester film described above is a polyester film used as a protective film of a curved display capable of optical fingerprint recognition.

The polyester film of the present invention uses a copolymerized polyester resin prepared in the present invention instead of a conventional PET resin, thereby improving flexibility to protect the entire surface of a curved display type optical fingerprint recognition smart phone, and in a curved display It is possible to prevent the floating phenomenon of the curved edge part.

In addition, the polyester film of the present invention can increase the fingerprint recognition rate in the optical fingerprint recognition type using a curved display by controlling the optical axis by optimizing the manufacturing 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 flowchart showing a method of manufacturing a polyester film 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 many 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 of a layer, film, region, plate, etc. is said to be “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.

Hereinafter, the present invention will be described in more detail.

The polyester film according to an embodiment of the present invention includes a film made of a co-polyester resin and a primer layer on at least one surface of the film, and a light loss rate in a wavelength band of 550 nm in the longitudinal direction (MD) and the transverse direction (TD). This is 10% or less, and the deviation of the optical axis angle is ±5° or less.

The polyester film according to an embodiment of the present invention uses a co-polyester resin as a main material of the film. More specifically, the copolymerized polyester resin constituting the polyester film according to an embodiment of the present invention is a resin copolymerized with dicarboxylic acid or its ester-forming derivative and a diol component containing ethylene glycol, in which case ethylene glycol is The included diol component includes at least one diol (second glycol) selected from ethylene glycol (first glycol), neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, propanediol, and butanediol. At this time, it is preferable that the substance other than ethylene glycol among the diol components is neopentyl glycol.

Further, in the present invention, the dicarboxylic acid is preferably a material selected from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. In this case, the dicarboxylic acid is preferably terephthalic acid.

By adopting the above-described configuration and changing the conditions of the manufacturing process, the edge lifting phenomenon of the curved display can be suppressed, and a polyester film suitable for optical fingerprint recognition can be provided.

More specifically, the copolymer polyester resin is formed by polycondensation reaction of terephthalic acid or an ester-forming derivative and a diol component including ethylene glycol in the presence of a polycondensation catalyst and a heat stabilizer.

At this time, among the diol components containing ethylene glycol, at least one diol selected from neopentyl glycol other than ethylene glycol (first glycol), 1,4-cyclohexanedimethanol, diethylene glycol, propanediol, and butanediol (second glycol) is preferably contained in an amount of 1 to 30 mol%. That is, the diol component preferably contains 70 to 99 mol% of ethylene glycol (first glycol) and 1 to 30 mol% of other diol components (second glycol).

Hereinafter, the present invention will be described in more detail with reference to FIG. 1 , which is a flowchart of a method for manufacturing a polyester film according to an embodiment of the present invention.

Referring to FIG. 1 , the method for producing a polyester film according to an embodiment of the present invention comprises a step of forming bishydroxyethylene terephthalate or an oligomer thereof through a heating reaction (S101), and a polycondensation reaction through a polycondensation reaction. Forming an ester resin (S102), uniaxially stretching in the longitudinal direction (S103), forming a primer layer on one surface of the uniaxially stretched film (S104), biaxially stretching in the transverse direction (S105) ) and heat-treating (S106).

First, in the step (S101) of forming bishydroxyethylene terephthalate or an oligomer thereof through a heating reaction, dicarboxylic acid or an ester-forming derivative thereof and a diol component including ethylene glycol are heated to react at 260 to 300°C. This is a step of forming bishydroxyethylene terephthalate or an oligomer thereof.

At this time, the diol component includes 70 to 99 mol% of ethylene glycol (the first glycol), and at least one diol (the first glycol) selected from neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, propanediol and butanediol. 2 glycol) in an amount of 1 to 30 mol%. When the second glycol component is less than 1 mol%, the flexibility of the film increases and when it is attached to a curved display smartphone, there is a risk of edge lifting. because sex is declining.

Next, in the step (S102) of forming a copolymer polyester resin through a polycondensation reaction, the bishydroxyethylene terephthalate or its oligomer produced in step S101 is mixed with various additives such as a polycondensation catalyst and a phosphoric acid-based thermal stabilizer and ethylene In the presence of particles dispersed in glycol, a polycondensation reaction is usually performed at 280 to 310° C. to form a copolymer polyester resin.

In addition, the polycondensation catalyst used in step S102 is preferably at least one selected from an antimony compound, a titanium compound, and a germanium compound, and among these, a glycol-soluble antimony compound such as antimony oxide and antimony acetate is more preferable.

In this case, the content of the polycondensation catalyst is preferably 150 to 350 ppm with respect to the copolymerized polyester resin. If the addition amount of the polycondensation catalyst is less than 150 ppm, the polymerization time is prolonged and the intrinsic viscosity (IV) increase rate is significantly reduced, making it difficult to obtain a polymer having a desired molecular weight. To overcome this, the polycondensation temperature is maintained at a high temperature. Therefore, the coloring phenomenon by the side reaction product occurs, and the haze is improved during film production, but the friction coefficient with the roll during film production is lowered, which has the disadvantage of worsening the runability of the film. In addition, when the addition amount of the polycondensation catalyst exceeds 350 ppm, the polycondensation reaction time is shortened, but there is a disadvantage of obtaining a colored polymer with non-uniform molecular weight, and the haze deteriorates during film production and coarse particles are formed. do.

In addition, the heat stabilizer used in step S102 is preferably a phosphoric acid-based compound, for example, trimethyl phosphate, triethyl phosphonoacetate or phosphoric acid.

At this time, the content of the heat stabilizer is preferably 100 to 300 ppm with respect to the copolymer polyester resin. If the content of the heat stabilizer is less than 100 ppm, the product due to side reactions increases to color the polymer and deteriorates heat resistance, which is undesirable. It is undesirable because it causes the life cycle of the filter and shortens the LIP cleaning cycle in the film manufacturing process.

In addition, in step S102, particles may be added to ensure film running properties. In this case, the particles are preferably silica particles. The content of the particles is preferably 2 to 20% by weight based on 100% by weight of the co-polyester resin. When the content of particles is less than 2% by weight, it is difficult to ensure sufficient runability of the film. Conversely, when the content of particles exceeds 20% by weight, the surface of the film is very rough and it is difficult to secure the appearance of the molded article, and when the film is stretched, There is a possibility that the film breakage due to the particles may occur.

Moreover, it is preferable that the average diameter of particle|grains is 1-10 micrometers. When the average diameter of the particles is less than 1㎛, it is easy to cause agglomeration between the particles, it is difficult to obtain uniform particles, and it is difficult to secure the runability of the film. On the other hand, when the average diameter of the particles exceeds 10㎛, the film surface roughness is large, making it difficult to secure the appearance of the molded product.

In addition, the prepared copolymer polyester resin may include a step of sufficiently drying at 150 to 170 ℃ for 6 to 9 hours using a vacuum dryer. At this time, if necessary, pre-crystallization may be performed.

Next, in the step of uniaxial stretching in the longitudinal direction (S103), the co-polyester resin formed in step S102 is melted with an extruder after vacuum drying and extruded into a sheet through a T-die (T-DIE) through a feed block, An unstretched sheet is obtained by adhering to the casting drum by electrostatic pinning and cooling and solidifying with a cooling roll. It is a step of producing a uniaxially stretched film by stretching in the direction (MD direction).

Next, in the step of forming a primer layer on one surface of the uniaxially stretched film (S104), the primer layer may be formed by a coating method of various methods such as bar type, gravure, slot die, and the like.

In this case, the primer layer may include a polyurethane-based binder or an acrylic binder as a main component and at least one crosslinking agent selected from the group consisting of an oxazoline-based, carbodiimide-based, and melamine-based crosslinking agent.

In addition, it is preferable that the thickness of the primer layer is 5 to 200 nm. When the thickness of the primer layer is less than 5 nm, the adhesion with the coating layer applied on the primer layer is lowered, and when it exceeds 200 nm, the rainbow is visible due to the difference in refractive index, so it is preferable to set it within the above range.

Next, the step of biaxially stretching in the transverse direction (S105) is a step of preparing a biaxially-stretched film by re-stretching the uniaxially-stretched film on which the primer layer obtained in step S104 is formed. At this time, the stretching is performed in a direction perpendicular to the uniaxial stretching direction (TD), and at this time, the stretching temperature is 100 ~ 130 ℃ at the beginning of the stretching zone and 130 ~ 160 ℃ at the end of the stretching zone based on the tenter.

According to an embodiment of the present invention, in steps S103 and S105, the draw ratios in the longitudinal direction (MD) and TD (transverse direction) satisfy Equations 1 and 2 below.

(Equation 1)

0.3≤Longitudinal direction draw ratio (MD) / Transverse direction draw ratio (TD)≤0.6

(Equation 2)

2 times ≤ longitudinal stretch ratio (MD) ≤ 4 times

With respect to Equation 1, when the value of Equation 1 exceeds 0.6 because the draw ratio in the transverse direction (TD) is lowered, the bowing phenomenon increases, so optical axis deviation occurs, and the draw ratio above a certain level increases so that the value of Equation 1 is 0.3 If it is less than, the risk of breakage increases, and due to the increase in stretching crystallization due to excessive stretching, the flexibility of the film is poor, resulting in springback, and there is a limitation in equipment.

In addition, when the draw ratio in the longitudinal direction (MD) is less than 2 times, there is a problem of stretching mura due to the stretching non-uniformity. When the stretching ratio in the longitudinal direction exceeds 4 times, the deviation of the optical axis due to the bowing phenomenon increases do.

Next, in the step of heat-treating the biaxially stretched film (S106), the biaxially stretched film is heat-treated at 190 to 220° C. to prepare a biaxially stretched polyester film. In particular, in the case of heat treatment, when the temperature is lower than 190℃, there is a risk of curling in the customer processing process due to increased heat shrinkage. Recognition is difficult to apply.

In the polyester film according to an embodiment of the present invention, the deviation of the optical axis is preferably ±5° or less. As described above, the polyester film of the present invention does not use a separate fingerprint recognition module, but can be used as a protective film used for a display having an optical fingerprint recognition function on the display itself, so that the deviation of the optical axis is ±5 If it exceeds ˚, the fingerprint is not recognized or the time required for fingerprint recognition increases.

In addition, the polyester film according to an embodiment of the present invention preferably has a light loss ratio of 10% or less in a wavelength band of 550 nm in the longitudinal direction (MD) and the transverse direction (TD). If the light loss rate exceeds 10%, the fingerprint in contact with the display is not recognized properly or the time required for fingerprint recognition increases.

In addition, the polyester film according to an embodiment of the present invention preferably has a flexibility of 15gr or less in the longitudinal direction (MD) and the transverse direction (TD). When the flexibility exceeds 15gr, a springback phenomenon occurs.

In addition, the polyester film according to an embodiment of the present invention preferably has a thickness of 25 ~ 100㎛. If the thickness of the polyester film is less than 25㎛ has a problem of poor protection, if it exceeds 100㎛ has a problem of poor moldability.

In addition, the polyester film according to an embodiment of the present invention preferably has a haze of 1.5% or less. If the haze exceeds 1.5%, the fingerprint may not be recognized properly due to high haze in the fingerprint recognition process using an optical fingerprint recognition type display.

In addition, the polyester film according to an embodiment of the present invention preferably has a transmittance of 90% or less. If the transmittance is less than 90%, similarly, a contacted fingerprint may not be recognized properly.

In addition, the polyester film according to an embodiment of the present invention preferably has a fingerprint recognition rate of 98% or more in the optical fingerprint recognition type. If the fingerprint recognition rate is less than 98%, the user's fingerprint may not be recognized or an incorrect fingerprint may be recognized, and the time required for fingerprint recognition may increase.

Hereinafter, the present invention will be described in more detail through examples. The present embodiment is intended to explain the present description in more detail, and the scope of the present invention is not limited to the embodiment.

[Example]

[Example 1]

The co-polyester resin is a one-step reaction of forming bishydroxyethylene terephthalate or an oligomer thereof by heating a diol component containing terephthalic acid and ethylene glycol at 270° C. The polymer is prepared by a two-step reaction to produce a liquid PET by a smooth polycondensation reaction at 290°C in the presence of silica particles dispersed in ethylene glycol and various additives such as an antimony compound catalyst and phosphoric acid-based thermal stabilizer. At this time, the diol component containing ethylene glycol is prepared by adding 99 mol% of ethylene glycol and 1 mol% of neopentyl glycol.

The copolymer polyester resin prepared above is dried at 160° C. for 7 hours using a vacuum dryer. After that, the dried co-polyester resin is melted with an extruder and adhered to the casting drum (cooling drum) through the feed block and T-die by the electrostatic application method to make a non-linear unstretched sheet, and heated again at 95°C in the longitudinal direction (film After stretching 2.5 times in the moving direction), a primer layer coating solution having a refractive index of 1.5 was coated on one surface of the polyester resin layer of the sheet to a thickness of 100 nm using gravure. At this time, the coating solution used for coating the primer layer is prepared with 30% by weight of a urethane-based binder, 15% by weight of an oxazoline-based curing agent, 1% by weight of silica particles, 5% by weight of a fluorine-based surfactant, and 49% by weight of water. After stretching 5 times at a temperature of 130° C. in the transverse direction (vertical direction) of the film advancing direction, heat treatment at 200° C. was performed to prepare a film. At this time, the thickness of the film was set to 50㎛.

[Example 2]

A film was prepared in the same manner as in Example 1, except that 70 mol% of ethylene glycol and 30 mol% of neopentyl glycol were added in the diol component containing ethylene glycol.

[Example 3]

A film was prepared in the same manner as in Example 1, except that the film was stretched twice in the longitudinal direction and 6.5 times in the transverse direction.

[Example 4]

A film was prepared in the same manner as in Example 1, except that the film was stretched 2 times in the longitudinal direction and 3.4 times in the transverse direction.

[Example 5]

A film was prepared in the same manner as in Example 1, except that the film was stretched 4 times in the longitudinal direction and 13 times in the transverse direction.

[Example 6]

A film was prepared in the same manner as in Example 1, except for stretching 4 times in the longitudinal direction and 6.8 times in the transverse direction.

[Example 7]

After stretching in the transverse direction, a film was prepared in the same manner as in Example 1, except that heat treatment was performed at 190°C.

[Example 8]

After stretching in the transverse direction, a film was prepared in the same manner as in Example 1, except that heat treatment was performed at 220°C.

[Comparative Example 1]

A film was prepared in the same manner as in Example 1, except that neopentyl glycol was not added during the preparation of the polyester resin.

[Comparative Example 2]

A film was prepared in the same manner as in Example 1, except that 99.5 mol% of ethylene glycol and 0.5 mol% of neopentyl glycol were added in the diol component containing ethylene glycol when preparing the polyester resin.

[Comparative Example 3]

A film was prepared in the same manner as in Example 1, except that 68 mol% of ethylene glycol and 32 mol% of neopentyl glycol were added in the diol component containing ethylene glycol when preparing the polyester resin.

[Comparative Example 4]

A film was prepared in the same manner as in Example 1, except that the film was stretched 1.5 times in the longitudinal direction and 3 times in the transverse direction.

[Comparative Example 5]

A film was prepared in the same manner as in Example 1, except that it was stretched 4.5 times in the longitudinal direction and 7.5 times in the transverse direction.

[Comparative Example 6]

A film was prepared in the same manner as in Example 1, except that the film was stretched 2.5 times in the longitudinal direction and 3.9 times in the transverse direction.

[Comparative Example 7]

A film was prepared in the same manner as in Example 1, except that the film was stretched 2.5 times in the longitudinal direction and 9 times in the transverse direction.

[Comparative Example 8]

After stretching in the transverse direction, a film was prepared in the same manner as in Example 1, except that heat treatment was performed at 180°C.

[Comparative Example 9]

After stretching in the transverse direction, a film was prepared in the same manner as in Example 1, except that heat treatment was performed at 230°C.

For the films prepared in Examples 1 to 8 and Comparative Examples 1 to 9, physical properties were evaluated through the following experimental examples, and the results are shown in Table 1.

[Experimental example]

(1) Springback

After coating a silicone adhesive having a thickness of about 20 μm on one side of the urethane coating layer in an A4 size film, attach it to a glass having a curved surface of 10R, and observe peeling or bubble generation.

Good: No peeling or foaming

Bad: peeling or blistering

(2) Light loss rate

After cutting the film to 5cm in width and 5cm in length, two polarizing films are made in a 100% transmission state (non-cross nicol), and then the film is rotated in the lateral direction (TD) at 45˚ and positioned. After that, light having a wavelength of 550 nm is transmitted from the bottom and the amount of light passed through the photometer from the other side is measured. Then, the light loss rate is calculated through Equation 3 from the measured light quantity.

(Equation 3)

Light loss rate = (Amount of light before film installation - Amount of light after film installation)/Amount of light before film installation X 100%

In measuring the optical loss rate, the loss rates in the lateral and longitudinal directions and the loss rates at 45˚, 90˚, 180˚, 270˚, and 360˚ are all the same due to the characteristics of the loss rate.

(3) Optical axis measurement

In the measurement of the light loss rate of Experimental Example 2, when the film is rotated between the polarizing films, the angle with the lowest light loss rate is read as the optical axis. At this time, the longitudinal direction (TD) is referred to as 0˚.

(4) Yeonshin Village

After cutting the film to A4 size, sandwiching the film between two polarizing films, when viewed with the naked eye under a white LED light source, judged according to the following criteria.

Steel: Deformation of the film is seen.

Medium: There is no deformation of the film, but a color difference is seen.

About: No color difference is visible.

(5) pencil hardness

Pencil hardness was measured at room temperature using an evaluation device manufactured by Pencil Hardness Tester (Yuyu Keiki Trading Co., Ltd.) in accordance with JIS K 5400, 5600 standards. The 6H hardness range was used. In the measurement process, the acrylic hard coating was coated on the film to a thickness of 2 μm, and then measured 5 times to confirm whether pressing or scratches occurred with the naked eye. In the case of being pressed or scratched more than 3 times out of 5 times, a failure process was performed, and the occurrence of up to 2 times was judged as success (OK). If it is difficult to identify the fracture with the naked eye, it was confirmed using a microscope.

(6) Fingerprint recognition rate

The film is laminated on OCA with a thickness of 50㎛, cut to the size of a smartphone (smartphone equipped with optical fingerprint recognition, appo R17 model) at an angle of 45˚ in the TD direction, and then attached to the smartphone. Thereafter, the fingerprint recognition rate at the time of performing fingerprint recognition 100 times is calculated by Equation 4 below.

(Equation 4)

Fingerprint recognition rate = Number of successful fingerprint recognition/100 times X 100%

(7) Curl occurrence

After coating an acrylic hard coating to a thickness of 2 μm on one side of the film, drying and UV curing at 120° C. for 1 minute are performed to check whether curl occurs when the film is made.

(8) Flexibility

After the film was cut into lengths of 100 mm and width of 3.81 mm, the flexibility of the film was measured using a softness measuring device (T5000, Toyoseiki).

division spring
the people Yeonshin Village optical axis
Deviation light loss rate Fingerprint
recognition rate curl pencil hardness flexibility
(gr) Example 1 Good Good ±3˚ 7% 100% non-occurring 2H 5.2 Example 2 Good Good ±3˚ 7% 100% non-occurring 2H 3.7 Example 3 Good Good ±1˚ 8% 100% non-occurring 2H 5.0 Example 4 Good Good ±4˚ 8% 100% non-occurring 2H 4.7 Example 5 Good Good ±1˚ 8% 100% non-occurring 2H 6.7 Example 6 Good Good ±3˚ 8% 100% non-occurring 2H 5.8 Example 7 Good Good ±2˚ 8% 100% non-occurring 2H 5.1 Example 8 Good Good ±5˚ 9% 100% non-occurring 2H 5.3 Comparative Example 1 error Good ±3˚ 7% 100% non-occurring 2H 18.2 Comparative Example 2 error Good ±3˚ 7% 100% non-occurring 2H 16.7 Comparative Example 3 Good Good ±3˚ 7% 100% non-occurring B 5.3 Comparative Example 4 Good error ±3˚ 7% 100% non-occurring 2H 5.6 Comparative Example 5 error Good ±9˚ 15% 80% non-occurring 2H 17.1 Comparative Example 6 Good Good ±10˚ 25% 65% non-occurring 2H 5.9 Comparative Example 7 error Good ±1˚ 8% 100% non-occurring 2H 16.9 Comparative Example 8 Good Good ±2˚ 7% 100% generation 2H 5.7 Comparative Example 9 Good Good ±15˚ 32% 30% non-occurring 2H 5.2

As can be seen from Table 1, in the case of Examples 1 to 8, the copolymerization was carried out by including 1 to 30 mol% of neopentyl glycol, and the draw ratio in the longitudinal and transverse directions satisfies Equations 1 and 2, thereby providing springback properties. It can be seen that an excellent film can be provided in all of the optical axis deviation, light loss rate, and fingerprint recognition rate.

On the other hand, in the case of Comparative Example 1, it can be seen that the flexibility is increased and the springback property is poor, and also in the case of Comparative Example 2, the flexibility is increased and it can be seen that the springback property is poor as in Comparative Example 1. .

In addition, in Comparative Example 3, it can be seen that by adding neopentyl glycol excessively, the pencil hardness deteriorates and the scratch resistance decreases.

In addition, in Comparative Example 4, it can be seen that the draw ratio in the longitudinal direction (MD) was low, and thus, stretch mura occurred.

In addition, in Comparative Example 5, due to excessive stretching in the longitudinal direction (MD) and transverse direction (TD), the flexibility due to stretching and crystallization was increased, resulting in poor springback properties, and at the same time as the optical axis deviation was large, the fingerprint recognition rate was lowered. Able to know.

In addition, Comparative Example 6 has a low draw ratio in the transverse direction (TD) compared to the longitudinal direction, so that the value of Equation 1 exceeds 0.6. it can be seen that

In addition, in Comparative Example 7, the elongation ratio in the transverse direction (TD) to the longitudinal direction is too large, and the value of Equation 1 is less than 0.3, indicating that the springback property is poor. This result is because the flexibility of the film is deteriorated due to an increase in stretching crystallization due to excessive stretching in the transverse direction (TD).

In addition, in Comparative Example 8, the heat treatment temperature was low and curl occurred due to the high heat shrinkage rate, whereas in Comparative Example 9 with a high heat treatment temperature, bowing was severe, the optical axis deviation increased, the light loss rate increased, and the fingerprint recognition rate was lowered. Able to know.

As described above, the polyester film according to an embodiment of the present invention may be used as a protective film used in a smartphone employing a display for recognizing fingerprints, and peeling phenomenon of edge bends in a curved display By suppressing (springback) and satisfying Equations 1 and 2 for optical axis control while using a copolymer polyester resin at the same time, it is possible to increase the fingerprint recognition rate of optical fingerprint recognition.

Although the preferred embodiment of the present invention has 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

Claims (19)

A film made of a copolymer polyester resin,
A primer layer is included on at least one side of the film,
The optical loss rate in the wavelength 550nm region in the longitudinal direction (MD) and in the transverse direction (TD) is 10% or less,
A polyester film with a deviation of the optical axis angle of ±5˚ or less. According to claim 1,
The copolymer polyester resin,
A polyester film that is copolymerized with dicarboxylic acid or an ester-forming derivative thereof and a diol component containing ethylene glycol. 3. The method of claim 2,
The dicarboxylic acid is at least one selected from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid, the polyester film. 3. The method of claim 2,
The diol component containing the ethylene glycol,
A polyester film comprising 70 to 99 mol% of ethylene glycol and 1 to 30 mol% of at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, propanediol and butanediol. According to claim 1,
The polyester film is a polyester film that satisfies the following Equations 1 and 2 in the draw ratio in the longitudinal direction (MD) and the transverse direction (TD).
(Equation 1)
0.3≤Longitudinal Stretch Ratio/Transverse Stretch Ratio≤0.6
(Equation 2)
2 times ≤ longitudinal stretch ratio ≤ 4 times According to claim 1,
The polyester film has a fingerprint recognition rate of 98% or more in an optical fingerprint recognition type, a polyester film. According to claim 1,
The polyester film has a flexibility of 15gr or less in the longitudinal direction (MD) and the transverse direction (TD). According to claim 1,
The thickness of the polyester film is 25 ~ 100㎛, the polyester film. According to claim 1,
The polyester film is a biaxially stretched film, polyester film. According to claim 1,
The primer layer has a polyurethane-based binder or an acrylic-based binder as a main component, a polyester film. According to claim 1,
The thickness of the primer layer is 5 to 200nm, the polyester film. According to claim 1,
The haze of the polyester film is 1.5% or less, and the transmittance is 90% or more, the polyester film. According to claim 1,
The co-polyester resin further comprises 2 to 20 wt% of particles based on 100 wt% of the copolyester resin, the polyester film. 14. The method of claim 13,
The particles are silica particles having an average diameter of 1 to 10 μm, a polyester film. forming bishydroxyethylene terephthalate or an oligomer thereof by heating and reacting dicarboxylic acid or an ester-forming derivative thereof with a diol component containing ethylene glycol;
forming a copolymerized polyester resin by adding a polycondensation catalyst and a phosphoric acid-based thermal stabilizer to the generated bishydroxyethylene terephthalate or an oligomer thereof and performing a polycondensation reaction;
Extruding the copolymer polyester resin and then stretching in the longitudinal direction to prepare a uniaxially stretched film;
coating a primer layer on the uniaxially stretched film;
preparing a biaxially-stretched film by transversely stretching the uniaxially-stretched film coated with the primer layer; and
heat-treating the biaxially stretched film;
A method for producing a polyester film comprising a. 16. The method of claim 15,
The diol component containing ethylene glycol contains 70 to 99 mol% of ethylene glycol and 1 to 30 mol% of at least one selected from neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, propanediol and butanediol A method for producing a polyester film. 16. The method of claim 15,
The heat treatment step is to heat treatment at 190 to 220 ℃, a method for producing a polyester film. 16. The method of claim 15,
The step of uniaxial stretching and the step of biaxial stretching,
A method for producing a polyester film, wherein the draw ratio in the longitudinal direction (MD) and the transverse direction (TD) satisfies the following Equations 1 and 2.
(Equation 1)
0.3≤Longitudinal Stretch Ratio/Transverse Stretch Ratio≤0.6
(Equation 2)
2 times ≤ longitudinal stretch ratio ≤ 4 times The polyester film according to any one of claims 1 to 14, wherein the polyester film is used as a protective film for a curved display capable of optical fingerprint recognition.

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