KR20210038242A - Polyester multilayer-film and methof for preparing thereof - Google Patents

Abstract

The present invention relates to a biaxially stretched polyester multilayer film in which the stretching speed and magnification of MD and TD are appropriately adjusted during biaxial stretching, to minimize the deviation of the low orientation angle and phase difference, thereby dramatically suppressing polarization unevenness; and at the same time, which has excellent optical properties, optical functionality and appearance quality, minimizes thickness deviation, has improved productivity, and has running properties suitable for high-speed machining. The present invention also relates to a method for preparing the polyester multilayer film.

Description

Polyester multilayer film and its manufacturing method {POLYESTER MULTILAYER-FILM AND METHOF FOR PREPARING THEREOF}

The present invention relates to a polyester multilayer film and a method of manufacturing the same.

An optical film is a film used as an optical material for a display. It is used as an optical material for surface protection and process carriers of various optical displays such as LCD BLU (Back Light Unit) or touch panel. As such an optical film, a polyester film is mainly used.

At this time, when the polyester film used for the optical display is used in the polarizing plate manufacturing process, when inspecting the defect of the polarizing plate, conduct the inspection while the orientation main axis of the polarizing plate with the release film attached and the crystal axis of the inspector are arranged vertically. Therefore, when the orientation angle of the polyester film, which is the base material of the release film, is low, color distortion during inspection can be prevented and inspection sensitivity can be improved.

The prior art has proposed a method of lowering the orientation angle through uniaxial stretching or biaxial stretching close to uniaxial stretching in order to suppress polarization irregularities or rainbow irregularities.

However, the above method has a limitation in productivity, and there is a problem in that it is not possible to completely control the distortion of color that may decrease the inspection sensitivity when inspecting defects in the polarizing plate. In addition, in the case of a conventional polyester film, the orientation angle of the film could not be lowered to a desired level, and both optical properties and photofunctionality did not exhibit excellent effects.

It is an object of the present invention to reduce the orientation angle in order to manufacture a polyester film suitable for optical displays, and at the same time reduce the retardation deviation in the width direction to suppress polarized spots (mura) or rainbow spots, and to achieve a low thickness deviation rate and high light transmittance. It is to provide a polyester multilayer film shown.

Another object of the present invention is to provide a method for producing a polyester film for a polarizing plate excellent in productivity.

According to an embodiment of the present invention, a core layer comprising a first polyester resin; And

Including; at least one or more skin layers including a second polyester resin and an anti-blocking agent formed on both sides of the core layer,

Within the range that satisfies the conditions represented by the following equations 1 and 2, which are relational equations for the stretching speed and stretching ratio of MD and TD, based on the width direction, the orientation angle measured by the microwave molecular aligning machine is Equation 3 And the in-plane retardation standard deviation (Re standard deviation) measured at 590 nm with a retardation meter satisfies Equation 4,

Polyester multilayer films are provided:

[Equation 1]

45,000%/min. ≤ MDs ≤ 55,000%/min.

[Equation 2]

4,500%/min. ≤ TDs ≤ 5,500%/min.

[Equation 3]

0 degree <|Orientation angle| <12 degrees

[Equation 4]

0 ≤ Re standard deviation ≤ 100

(In Equation 1, MDs is the stretching speed in the machine direction calculated by Equation 5 below,

[Equation 5]

Average MD drawing speed = (S _1st + S _2nd )/2

In Equation 5, S _1st and S _2nd are the drawing speeds (%/min) for each section represented by Equations 6 and 7 in the two-stage drawing process with the first to third drawing rolls,

[Equation 6]

S _1st = E ₁ /[L ₁ /{(R ₂ -R ₁ )/2}]

[Equation 7]

S _2nd = E ₂ /[L ₂ /{(R ₃ -R ₂ )/2}],

In Equations 6 and 7 above,

E ₁ and E ₂ are the draw ratios (%) in each section of the two-stage stretching process, respectively,

R _1, R ₂ , and R ₃ are each independently a rotation speed (m/min) of an individual drawing roll (R/L),

L ₁ is the distance between the first draw roll and the second draw roll (m), L ₂ is the distance between the second draw roll and the third draw roll (m),

In Equation 2, TDs is the softening speed in the width direction calculated by Equation 8 below.

[Equation 8]

TD drawing speed = E/(L/LSP)

(In Equation 8, E is the draw ratio (%) in the plurality of draw zones in the tenter-type drawing process after the two-stage drawing process with the first to third drawing rolls,

L is the total length (m) of the plurality of stretching zones,

LSP is the line speed (m/min) in the tenter-type drawing process)

In addition, according to another embodiment of the present invention, using a composition comprising a) i) a first polyester resin chip, ii) a second polyester resin chip and an anti-blocking agent, the core layer and both sides of the core layer Coextrusion and quenching at 30° C. or less to produce an unstretched sheet so that at least one or more skin layers are included in the multilayer; And

b) preparing a film by sequentially biaxially stretching the unstretched sheet; And

c) heat setting the biaxially stretched film; includes,

The step of producing a film by sequentially biaxially stretching,

First longitudinally stretching the unstretched sheet 2 to 5 times at a rate of 45,000 to 55,000%/min. in the machine direction at 85 to 110° C.; And

Comprising the step of 2 to 5 times the secondary transverse stretching at a rate of 4,500 ~ 5,500% / min. in the width direction at 95 ~ 140 ℃ the first stretched sheet; Containing

It provides a method of manufacturing the polyester multilayer film.

Hereinafter, a polyester film and a method of manufacturing the same according to embodiments of the present invention will be described in detail.

Prior to that, unless expressly stated in the specification, terminology is only intended to refer to specific embodiments and is not intended to limit the invention.

The singular forms used in the present specification also include plural forms unless the phrases clearly indicate the opposite meaning.

The meaning of'comprising' as used herein specifies a specific characteristic, region, integer, step, action, element and/or component, and other specific characteristic, region, integer, step, action, element, component and/or group It does not exclude the existence or addition of

Further, in the present specification, terms including ordinal numbers such as'first' and'second' are used for the purpose of distinguishing one component from other components, and are not limited by the ordinal number. For example, within the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

Hereinafter, the present invention will be described in detail.

According to one embodiment of the invention, a core layer comprising a first polyester resin; And at least one skin layer including a second polyester resin and an anti-blocking agent formed on both sides of the core layer, including, and the following Equations 1 and 2, which are relational expressions for the elongation rate and elongation ratio of MD and TD. Within the range that satisfies the displayed conditions, the orientation angle measured by the microwave molecular aligning machine satisfies Equation 3 based on the width direction, and the in-plane retardation standard deviation (Re standard deviation) measured at 590 nm with a retardation meter. ) Satisfies Equation 4, a polyester multilayer film may be provided.

[Equation 1]

45,000%/min. ≤ MDs ≤ 55,000%/min.

[Equation 2]

4,500%/min. ≤ TDs ≤ 5,500%/min.

[Equation 3]

0 degree <|Orientation angle| <12 degrees

[Equation 4]

0 ≤ Re standard deviation ≤ 100

(In Equation 1, MDs is the stretching speed in the machine direction calculated by Equation 5 below,

[Equation 5]

Average MD drawing speed = (S _1st + S _2nd )/2

In Equation 5, S _1st and S _2nd are the drawing speeds (%/min) for each section represented by Equations 6 and 7 in the two-stage drawing process with the first to third drawing rolls,

[Equation 6]

S _1st = E ₁ /[L ₁ /{(R ₂ -R ₁ )/2}]

[Equation 7]

S _2nd = E ₂ /[L ₂ /{(R ₃ -R ₂ )/2}],

In Equations 6 and 7 above,

E ₁ and E ₂ are the draw ratios (%) in each section of the two-stage stretching process, respectively,

R _1, R ₂ , and R ₃ are each independently a rotation speed (m/min) of an individual drawing roll (R/L),

L ₁ is the distance between the first draw roll and the second draw roll (m), L ₂ is the distance between the second draw roll and the third draw roll (m),

In Equation 2, TDs is the softening speed in the width direction calculated by Equation 8 below.

[Equation 8]

TD drawing speed = E/(L/LSP)

(In Equation 8, E is the draw ratio (%) in the plurality of draw zones in the tenter-type drawing process after the two-stage drawing process with the first to third drawing rolls,

L is the total length (m) of the plurality of stretching zones,

LSP is the line speed (m/min) in the tenter-type drawing process)

When the polyester film used for the optical display is used in the polarizing plate manufacturing process, when inspecting the defect of the polarizing plate, the release film is inspected with the orientation principal axis of the polarizing plate attached with the release film and the crystal axis of the inspection machine arranged vertically. When the orientation angle of the polyester film, which is the base material of, is low, color distortion can be prevented and the inspection sensitivity can be improved.

In addition, the present invention suppresses polarization unevenness, which is a major requirement for use as a protective film for a polarizing plate and a base film for a release film, among subsidiary materials used for a polarizing plate in the field of optical displays, and an orientation angle for securing excellent appearance quality and post-processing process stability. And the retardation deviation is controlled to provide a polyester film excellent in photofunctionality.

Accordingly, as a result of research in order to achieve the above object, the TD reference and orientation angle were lowered by appropriately adjusting the stretching speed and stretching ratio of the machine direction and the transverse direction, and the phase difference deviation was lowered to reduce the orientation of the TD. , Optical properties and photofunctionality were imparted.

Therefore, in order to manufacture a polyester film suitable for an optical display, the present invention reduces the orientation angle and lowers the phase difference deviation in the width direction to suppress polarization or rainbow stains, and a polyester multilayer exhibiting a low thickness deviation ratio and high light transmittance. Characterized in that to prepare a film.

In addition, in general, in order to lower the orientation angle of the film, it is common to select a stretching method close to uniaxial stretching or uniaxial stretching, but productivity is poor. Therefore, in the present invention, in order to maximize productivity, a multi-layered polyester film with improved optical properties is prepared by applying a biaxial stretching method in which the stretching speed is controlled.

More specifically, an aspect of the present invention relates to a biaxially stretched polyester film, wherein the polyester film includes a core layer including a first polyester resin; And at least one or more skin layers including a second polyester resin and an anti-blocking agent formed on both surfaces of the core layer.

In addition, the polyester multilayer film satisfies the following equations 1 to 2, which are relational equations for the stretching speed and stretching ratio of MD and TD, and the orientation angle with a molecular orientation angle analyzer (MOA) for the entire width direction. At the time of measurement, the orientation angle of the center is 0 degrees based on the TD, and the orientation angle of the outermost part satisfies Equation 3 below, with an absolute value of less than 12 degrees, and the main orientation measured at 590 nm with a phase difference meter. The in-plane phase difference (Re) value, which is the standard deviation of the value obtained by multiplying the thickness (d) by the birefringence index (Δn), which is a value of the difference in refractive index in the direction of the main orientation axis and the vertical direction with respect to the axis, can satisfy Equation 4 below.

[Equation 1]

45,000%/min. ≤ MDs ≤ 55,000%/min.

[Equation 2]

4,500%/min. ≤ TDs ≤ 5,500%/min.

[Equation 3]

0 degree <|Orientation angle| <12 degrees

[Equation 4]

0 ≤ Re standard deviation ≤ 100

(In Equation 1, MDs is the stretching speed in the machine direction, and TDs is the stretching speed in the width direction)

In Equation 1, if the value of MDs is less than 45,000%/min., it is difficult to secure thickness uniformity due to insufficient orientation crystal, and if it is greater than 55,000%/min., MD orientation crystal becomes high and it is difficult to lower the orientation angle.

If the value of TDs in Equation 2 is less than 4,500%/min., it is difficult to secure the thickness uniformity due to insufficient stress transfer uniformity to the TD, and if it is greater than 5,500%/min. As a result, the film may be torn or fractured, which may reduce moldability or productivity.

If the TD reference orientation angle in Equation 3 is more than 12 degrees, when applied as a protective film or release film for a polarizing plate, the detection sensitivity of foreign matters or defects is significantly lowered due to color distortion, so it is necessary to manage it to less than 12 degrees. .

In Equation 4 measured based on the width direction, if the standard deviation of Re, which is the in-plane phase difference value, is greater than 100 based on the TD, the uniformity of light transmittance is insufficient, making it difficult to increase the optical functionality.

At this time, in Equations 1 to 2, MDs is the drawing speed in the machine direction (MD drawing speed), TDs is the drawing speed in the width direction (TD drawing speed), and each drawing speed is calculated by the following Equations 5 to 8. I can.

Specifically, the stretching speed in the machine direction can be calculated by Equation 5 below.

[Equation 5]

Average MD drawing speed = (S _1st + S _2nd )/2

(In Equation 5, S _1st and S _2nd are the drawing speeds (%/min) for each section represented by Equations 6 and 7 in the two-stage drawing process with the first to third drawing rolls,

[Equation 6]

S _1st = E ₁ /[L ₁ /{(R ₂ -R ₁ )/2}]

[Equation 7]

S _2nd = E ₂ /[L ₂ /{(R ₃ -R ₂ )/2}],

In equations 6 and 7,

E ₁ and E ₂ are the draw ratios (%) in each section of the two-stage stretching process, respectively,

R _1, R ₂ , and R ₃ are each independently a rotation speed (m/min) of an individual drawing roll (R/L),

L ₁ is the distance between the first draw roll and the second draw roll (m), L ₂ is the distance between the second draw roll and the third draw roll (m))

An example of a two-stage drawing roll provided with the first to third drawing rolls is as shown in FIG. 1.

As shown in Fig. 1, the stretching speed in the machine direction represents the MD stretching speed in the Roll to Roll MD stretching process using the circumferential speed difference. In addition, this stretching process may be calculated according to the parameters of Equations 5 to 7 described above based on the stretching process diagram during two-stage stretching of the MD Flat. In addition, the stretching step is divided, the stretching speed of each section is calculated, and the finally obtained average value is defined as the MD stretching speed.

In addition, the stretching speed in the width direction can be calculated by Equation 8 below.

[Equation 8]

TD drawing speed = E/(L/LSP)

(In Equation 8, E is the draw ratio (%) in the plurality of draw zones in the tenter-type drawing process after the two-stage drawing process with the first to third drawing rolls,

L is the total length (m) of the plurality of stretching zones,

LSP is the line speed (m/min) in the tenter-type drawing process)

2 is a schematic diagram of a tenter-type stretching process including a plurality of stretching zones.

The draw ratio of longitudinal drawing refers to the ratio of the length after drawing to the length before drawing, that is, (length after drawing/length before drawing), but when calculated in an actual continuous process, roll-to-roll longitudinal drawing (machine direction In the case of stretching), the ratio of the roll speed after stretching to the roll speed before stretching can be used as the stretching ratio. In the case of lateral stretching (stretching in the width direction) using the tenter, the ratio of the width of the outlet to the width of the entrance of the tenter may be defined as the stretching ratio.

In addition, the polyester multilayer film exhibits a lower thickness deviation ratio than the conventional one, and thus optical properties can be improved.

In addition, according to the present invention, it is possible to provide a biaxially oriented polyester film having excellent high-speed processing and running performance by suppressing polarization unevenness and having an Ra value, which is the surface roughness of the center line of the irregularities generated by organic/inorganic particles, satisfies the following Equation 9 . The polyester film having the above characteristics may have a thickness of 19 to 75 μm.

[Equation 9]

15nm ≤ Ra ≤ 25nm

In Equation 9, if the value of the surface roughness (surface roughness) is less than 15 nm, the probability of causing scratches in the process of passing the roll in the stretching process increases, and if it is greater than 25 nm, the air layer between the film and the film in the winding process Due to the excessive formation, there is a high probability that the foaming phenomenon will occur, resulting in a high probability of winding defects.

In this case, the orientation angle defined in Equation 3 means an orientation angle based on TD, and Re described in Equation 4 means an in-plane phase difference, and can be calculated by Equation 10. In addition, the standard deviation (Re standard deviation) of the in-plane phase difference in Equation 4 can be calculated by Equation 11.

[Equation 10]

Re=(nx-ny)×d

(In Equation 10, nx is the refractive index in the direction of the main orientation axis, ny is the refractive index corresponding to the vertical direction in the main orientation axis direction, and d is the thickness of the film.)

[Equation 11]

는 위상차 측정치의 개별값이고,

는 위상차 측정치 전체의 평균이고, n 은 위상차 측정횟수이다)(In Equation 11 above,

Is the individual value of the phase difference measurement,

Is the average of all phase difference measurements, and n is the number of phase difference measurements)

When the MD and TD stretching speeds satisfy both the orientation angle deviation and the in-plane phase difference deviation that satisfies Equation 4 within the range that satisfies Equation 1 to 2, the phenomenon of occurrence of polarization irregularities can be suppressed. In addition, when the orientation angle is used as a protective film and a release film for a polarizing plate within the range satisfying the above equation 3, it is possible to increase the detection sensitivity of foreign matters or defects by preventing color distortion, and more preferably, the orientation angle is 0 degrees or more. 10 degrees or less may exhibit a more excellent effect.

In addition, the film has excellent runability and winding property within the range of the surface roughness that satisfies Equation 9, so that scratches can be prevented when the film passes through the roll, and the foam can be prevented from falling out due to an excessive air layer when winding. It is preferable because it has excellent coating properties during post-processing, so that the coating stability required by the user can be satisfied, and the release agent can be applied uniformly and at high speed. More preferably, Ra may be 16 to 23 nm.

In the polyester multilayer film of the present invention, the core layer may be 70 to 90% by weight of the total film, and the skin layer may be 10 to 30% by weight of the total film.

The anti-blocking agent may include organic particles, inorganic particles, or mixtures thereof.

More specifically, the polyester resin used for the core layer and the skin layer and constituting the polyester film of the present invention is not particularly limited, and a conventional polyester resin may be used. The polyester resin is obtained by condensation polymerization of an acidic component containing a dicarboxylic acid as a main component and a glycol component containing an alkylene glycol as a main component. The dicarboxylic acid is not limited, but terephthalic acid or its alkyl ester or phenyl ester may be used, and some are difunctional carboxylates such as isophthalic acid, oxyethoxy benzoic acid, adipic acid, sebacic acid and 5-sodium sulfoisophthalic acid. It can be used by substitution with the main acid or its ester-forming derivative. In addition, although not limited to the glycol component, ethylene glycol is mainly used, and propylene glycol, neopentyl glycol, trimethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-bisoxy Ethoxybenzene, bisphenol, and polyoxyethylene glycol may be mixed and used, and a monofunctional compound or a trifunctional compound may be partially used in combination.

In addition, it is possible to include one or two or more components selected from additives commonly used in the film field, that is, pinning, antistatic agents, ultraviolet stabilizers, waterproofing agents, slip agents, and thermal stabilizers when polymerizing polyester resins. However, it is not limited thereto.

The polyester resin may be prepared by terephthalic acid (TPA) polymerization or dimethyl terephthalate (DMT) polymerization, which are conventional polymerization methods in the art, but is not limited thereto.

In one aspect of the present invention, the polyester resin may be polyethylene terephthalate. That is, the polyester resin may be polyethylene terephthalate prepared using terephthalic acid as a dicarboxylic acid and ethylene glycol as a glycol. In addition, it is preferable that the polyester film of the present invention contains particles as an anti-blocking agent in order to form a uniform surface roughness. The anti-blocking agent is added to form scratch resistance and uniform surface roughness, and may be any one or a mixture of two or more selected from organic particles and inorganic particles. As the inorganic particles, any particles that are obviously used in the art may be used without limitation. For example, any one or two or more selected from calcium carbonate, silica, titanium dioxide, kaolin, barium sulfate, alumina silicate, calcium carbonate, etc. may be mixed and used, but is not limited thereto. The organic particles are silicone resin, crosslinked divinylbenzene polymethacrylate, crosslinked polymethacrylate, crosslinked polystyrene resin, benzoguanamine-formaldehyde resin, benzoguanamine-melamine-formaldehyde resin, and melamine-formaldehyde resin. It may be any one or a mixture of two or more selected from the group consisting of, but is not limited thereto.

The content of the anti-blocking agent is not limited, but may be included as 200 to 2,000 ppm in the entire film, and more specifically, may be included in 400 to 1,000 ppm. In addition, the size of the anti-blocking agent is not limited, but may have an average particle diameter of 0.01 to 5 μm, more specifically 0.1 to 3 μm. And, the addition of the anti-blocking agent in the form of a slurry dispersed in glycols when synthesizing a polyester resin is effective because it has excellent dispersibility and can prevent re-aggregation between particles, but is not limited thereto. It may be added when manufacturing a chip.

Therefore, in one aspect of the present invention, the biaxially stretched polyester film may be a multilayer film in which at least two or more layers are stacked, and the multilayer film includes a core layer and at least one layer on both sides of the core layer, respectively. It may include a laminated skin layer. At this time, since the core layer is 70 to 90% by weight of the total film, the skin layer is 10 to 30% by weight, and the skin layer contains an anti-blocking agent, the interfacial stability is excellent during coextrusion, so that the film formation is easy and the haze is reduced. It is low, satisfies Equations 1 to 3 described above, and can produce a film with little shrinkage.

The core layer may be made of a polyester resin, more specifically a polyethylene terephthalate resin alone. In the case of the coater layer, an anti-blocking agent may be included, but from the viewpoint of improving film forming stability and film running property, the anti-blocking agent is preferably included in the skin layer. The polyethylene terephthalate resin used for the core layer has an intrinsic viscosity of 0.6 to 0.7 ㎗/g, which is excellent in heat resistance, and interfacial instability does not occur during coextrusion, but is not limited thereto.

In addition, the skin layer contains a polyester resin having an intrinsic viscosity of 0.6 ~ 0.7 dl/g and an anti-blocking agent, and interfacial instability does not occur within the range of the intrinsic viscosity satisfying the above range, and is stably laminated with the core layer Although it is easy to manufacture a multilayer film and has an advantage of easy processability, it is not limited thereto. In addition, the skin layer may improve film forming stability and film running property by using an anti-blocking agent.

In one aspect of the present invention, the biaxially stretched polyester film may have a total thickness of 19 to 75 μm, more preferably 38 to 50 μm, and a base for electronic materials, which is a thin film within the above range. It can be suitably used as a film.

Meanwhile, according to another embodiment of the present invention, a) i) a first polyester resin chip, ii) a second polyester resin chip, and a composition comprising an anti-blocking agent are used to provide a core layer and both sides of the core layer. Coextrusion and quenching at 30° C. or less to produce an unstretched sheet so that at least one or more skin layers are included in the multilayer; And b) sequentially biaxially stretching the unstretched sheet to prepare a film. And c) heat setting the biaxially stretched film; including, wherein the step of producing a film by sequentially biaxially stretching the unstretched sheet at 85 to 110° C. in the machine direction of 45,000 to 55,000%/min. 2 to 5 times the primary longitudinal stretching at a speed; And secondary transverse stretching of the firstly stretched sheet at a rate of 4,500 to 5,500%/min. in the width direction at 95 to 140° C.; Can be.

In one aspect of the present invention, the biaxially stretched polyester film includes any one or two or more anti-blocking agents selected from organic particles and inorganic particles, and may be a single layer or a multilayer film in which two or more layers are laminated. More specifically, it includes a core layer and a skin layer in which at least one or more layers are stacked on both sides of the core layer, respectively, the core layer is 70 to 90% by weight of the total film, and the skin layer is 10 to 30% by weight, The skin layer may include any one or two or more anti-blocking agents selected from organic particles and inorganic particles.

More specifically, one aspect of the method for producing a biaxially stretched polyester film of the present invention includes a first polyester resin chip comprising a polyester resin having an intrinsic viscosity of 0.6 to 0.7 dl/g, and an intrinsic viscosity of 0.6 to 0.7 dl/g. Using a composition containing a second polyester resin chip containing g of polyester resin and an anti-blocking agent, melt at 260 ~ 300°C and coextrusion, and then discharge into a single layer or multiple layers of two or more layers through a die, and less than 30°C. To prepare an unstretched sheet by rapid cooling.

In the heat setting of the film, the secondary stretched film is heat-set at 200 to 250°C in a total of five heat treatment zones including the first heat treatment zone to the fifth heat treatment zone, and from the fourth heat treatment zone to the fifth heat treatment zone. It may include the step of relaxing so that the total relaxation rate of the MD relaxation rate and the TD relaxation rate of 1 to 5%.

In this way, a core layer comprising a first polyester resin; And at least one or more skin layers including a second polyester resin and an anti-blocking agent formed on both sides of the core layer, and satisfying all parameter properties according to the above-described formula may be provided. .

In the present invention, by applying the sequential biaxial stretching method to specifically control the stretching speed and magnification of MD and TD, polarization mura is significantly suppressed by minimizing the deviation of low orientation angle and phase difference, and excellent optical properties and optical functionality and excellent appearance It has quality, minimizes thickness variation, has excellent productivity, and can manufacture a polyester film having a running property suitable for high-speed processing.

FIG. 1 is a schematic diagram of a roll-to-roll process diagram of two-stage stretching of an MD Flat for calculating an MD stretching speed according to an embodiment of the present invention.
FIG. 2 is a simplified illustration of a stretching zone in a tenter-type stretching facility for calculating a TD stretching speed according to an embodiment of the present invention.
3 is a simplified illustration of a method for evaluating rainbow spots on a polarizing mirror.

Hereinafter, the action and effect of the invention will be described in more detail through specific embodiments of the invention. However, these embodiments are only presented as examples of the invention, and the scope of the invention is not determined thereby.

[Example 1]

The core layer uses a polyethylene terephthalate (PET) chip with an intrinsic viscosity of 0.65 dl/g that does not contain inorganic particles, and the skin layer has an intrinsic viscosity of 0.65 dl containing 400-1000 ppm of silica particles with an average particle diameter of 2.6 µm. A three-layer film in which a skin layer/core layer/skin layer was laminated was prepared using a polyethylene terephthalate chip of /g. Thereafter, the laminated film was coextruded and cast on a cooling roll controlled to 30° C. or less to prepare an unstretched sheet. At this time, the core layer was made to be 80% by weight of the total film weight, and the skin layer was made to be 20% by weight of the total film weight.

Thereafter, using the unstretched sheet, stretching was performed in the machine direction and in the width direction, but the stretching speed and the stretching ratio were adjusted by the method calculated according to Equations 1 and 2.

That is, it was stretched using the MD flat two-stage stretching process including the configuration of FIG. 1 and the tenter-type process of FIG. 2. Accordingly, after drawing 3.2 times at a drawing rate of 54631%/min. in the machine direction (MD), then drawing at 4.5 times at a rate of 4,875%/min. in the width direction (TD), and heat treatment at 215°C. From the 4th heat treatment zone to the 5th heat treatment zone of the heat treatment zone consisting of a total of 5 zones, MD relaxation and TD relaxation are combined to a total of 2.8% as shown in Table 1 below, and a 38㎛-thick multilayer The film was prepared. Film film formation conditions are shown in Table 1.

[Examples 2 to 3 and Comparative Examples 1 to 4]

As shown in Table 1 below, a multilayer film was prepared in the same manner as in Example 1, except that the MD draw ratio and the MD draw speed, the TD draw ratio and the TD draw speed, and the film thickness were changed.

division thickness
(㎛) Draw ratio (times) Drawing speed (%/min.) Stretching temperature (℃) Heat setting temperature (℃) MD and TD
Total relaxation rate
(%) MD TD MD TD MD TD Zone1 Zone4 Example 1 38 3.2 4.5 54631 4875 84 146 215 140 2.8 Example 2 38 3.0 4.5 49550 4875 83 145 215 140 2.8 Example 3 38 3.0 4.7 49550 5091 83 146 215 140 2.8 Comparative Example 1 38 2.7 4.5 42345 4875 83 145 215 140 2.8 Comparative Example 2 38 3.0 4.0 49550 4333 84 146 215 140 2.8 Comparative Example 3 38 2.7 4.0 42345 4333 83 147 215 140 2.8 Comparative Example 4 50 2.7 4.4 36708 3090 86 148 215 140 2.9

[Experimental Example]

The physical properties of the films of Examples 1 to 3 and Comparative Examples 1 to 4 were measured according to the measurement method for each evaluation item below, and the results are shown in Table 2.

<Method of measuring and evaluating physical properties>

1) Haze measurement

Each manufactured film was measured according to the ASTM D-1003 measurement method using a Haze Meter (NIPPON DENSHOKU, NDH-5000, Japan).

2) Polarizing mirror rainbow stain evaluation method

Using a polarization warp evaluation device (Shinto Scientific, Heidon-24W, Japan), adjust the lower polarization axis and the upper polarization axis to be orthogonal (90 degrees), and then place the sample cut into A4 size on the bottom of the evaluation device and from above. The presence or absence of a rainbow stain of the film was visually evaluated (see FIG. 3).

* Evaluation Criteria: When a rainbow stain is recognized as "Yes", when a rainbow stain is not recognized as "No".

3) Orientation angle evaluation method

Each film sample was mounted on a dedicated sample holder using a microwave molecular aligner (Oji Scientific Instruments, MOA-7015, Japan), and then inserted into the molecular aligner to measure the orientation angle. Since the orientation angle value is based on the MD, the absolute value of the value obtained by subtracting the actual measured value from 90 degrees to have the orientation angle based on the TD is shown in Table 2.

4) In-plane phase difference measurement

The retardation value was measured at a measurement wavelength of 590 nm using a parallel Nicole rotation type retardation meter (Oji Scientific Instruments, KOBRA-WPR, Japan).

5) Thickness evaluation method and thickness deviation R value calculation method

Films manufactured with an electric micrometer measuring device (Mahr, Millimar-1240, Germany) were measured at intervals of 5 cm in the width direction, and the measured thickness was calculated by Equation 12 below to calculate the thickness deviation R value.

[Equation 12]

는 두께 측정치의 개별값이고,

는 두께 측정치의 평균이고, n 은 두께 측정횟수이다) (In Equation 12,

Is the individual value of the thickness measurement,

Is the average of the thickness measurements, and n is the number of thickness measurements)

6) Surface roughness evaluation method

Using a two-dimensional contact surface roughness meter (SE-3300, KOSAKA, Japan), according to the measurement method JIS B-0601, Ra (center line average roughness), Rz (10 point average roughness), and Rmax (maximum height roughness) were measured. It was measured.

Specifically, the polyester film prepared based on JIS-B0601 was cut into an A4 size in the transverse reference center of the entire width, and then cut into a size of 30 mm×30 mm with scotch tape on the sample stand of the surface roughness meter. After attaching, the surface roughness was measured under the conditions of a measurement speed of 0.05 mm/sec and a reference length (Cut-Off) of 0.08 mm.

The average value was calculated by selecting a reference length of 1.5mm in the direction of the center line from the curve of the film cross section and measuring a total of 5 times, and the Arithmetical Average Roughness (Ra) is the average height from the center line to the cross section curve as the center line average roughness value.

7) Scratch evaluation method

After dropping a sheet of film on the wall, it was visually evaluated by turning it at an angle of 0 to 180 degrees with Search Light (Polarion, PS-NP1, Korea) to check visibility.

* Evaluation Criteria: Visually evaluate the case of becoming a poet as "Yes" and the case of not becoming a poet as "No".

8) How to evaluate the winding form

The length from which the film came out from the end face of the rolled roll was measured after setting the zero point with a length measuring machine (Mitutoyo, CA-30PSX, Japan).

* Evaluation Criteria: "Yes" is judged if the length of the film is protruding more than 2mm, and "None" is determined if the length of the film is less than 2mm.

division Haze
(%) Polarizer stain
The presence or absence Orientation angle
(Degree) In-plane phase difference
Average
(Nm) In-plane phase difference
Standard Deviation
(Nm) Thickness deviation
R value
(㎛) Surface roughness
(Ra, nm) Scratch
The presence or absence Winding
Out of form
The presence or absence Example 1 2.3 radish 10 1,513 60 0.6 16.9 radish radish Example 2 3.8 radish 10 1,656 85 0.8 22.3 radish radish Example 3 3.0 radish 10 1,743 75 0.8 19.8 radish radish Comparative Example 1 2.5 U 12 1,866 175 1.2 12.7 U radish Comparative Example 2 2.7 U 14 1,444 110 1.4 21.0 radish radish Comparative Example 3 2.8 U 11 1,660 338 1.8 28.0 radish U Comparative Example 4 2.7 U 13 1,817 270 1.3 26.5 radish U

From the results of Table 2, Examples 1 to 3 specifically control the stretching speed and magnification of MD and TD during film production, so that compared to Comparative Examples 1 to 4, the orientation angle was lower to reduce the deviation of the phase difference The polarization unevenness was remarkably suppressed because it could be remarkably reduced. Accordingly, the polyester film of the present invention has excellent optical properties and photofunctionality, has excellent appearance properties, and has a low thickness variation ratio, and thus can be used for a polarizing plate in an optical display field to contribute to performance improvement. In addition, the present invention provides a method for producing a polyester film having superior productivity and running properties suitable for high-speed processing, and economical effects can be achieved.

Claims (9)

A core layer comprising a first polyester resin; And
Including; at least one or more skin layers including a second polyester resin and an anti-blocking agent formed on both sides of the core layer,
Within the range that satisfies the conditions represented by the following Equation 1 and Equation 2, which are relational expressions for the stretching speed and the stretching ratio of MD and TD, the orientation angle measured by the microwave molecular aligning machine based on the width direction is Equation 3 And the in-plane retardation standard deviation (Re standard deviation) measured at 590 nm with a retardation meter satisfies Equation 4,
Polyester multilayer film:
[Equation 1]
45,000%/min. ≤ MDs ≤ 55,000%/min.
[Equation 2]
4,500%/min. ≤ TDs ≤ 5,500%/min.
[Equation 3]
0 degree <|Orientation angle| <12 degrees
[Equation 4]
0 ≤ Re standard deviation ≤ 100
(In Equation 1, MDs is the stretching speed in the machine direction calculated by Equation 5 below,
[Equation 5]
Average MD drawing speed = (S _1st + S _2nd )/2
In Equation 5, S _1st and S _2nd are the drawing speeds (%/min) for each section represented by Equations 6 and 7 in the two-stage drawing process with the first to third drawing rolls,
[Equation 6]
S _1st = E ₁ /[L ₁ /{(R ₂ -R ₁ )/2}]
[Equation 7]
S _2nd = E ₂ /[L ₂ /{(R ₃ -R ₂ )/2}],
In Equations 6 and 7 above,
E ₁ and E ₂ are the draw ratios (%) in each section of the two-stage stretching process, respectively,
R _1, R ₂ , and R ₃ are each independently a rotation speed (m/min) of an individual drawing roll (R/L),
L ₁ is the distance between the first draw roll and the second draw roll (m), L ₂ is the distance between the second draw roll and the third draw roll (m),
In Equation 2, TDs is the softening speed in the width direction calculated by Equation 8 below.
[Equation 8]
TD drawing speed = E/(L/LSP)
(In Equation 8, E is a stretching ratio (%) in a plurality of stretching zones in a tenter-type stretching step after a two-stage stretching step provided with the first to third stretching rolls,
L is the total length (m) of the plurality of stretching zones,
LSP is the line speed (m/min) in the tenter-type drawing process)
The polyester multilayer film according to claim 1, wherein the surface roughness (Ra) satisfies the following formula:
[Equation 9]
15nm ≤ Ra ≤ 25nm
The polyester multilayer film according to claim 1, wherein the core layer is 70 to 90% by weight of the total film, and the skin layer is 10 to 30% by weight of the total film.
The polyester multilayer film of claim 1, wherein the anti-blocking agent includes organic particles, inorganic particles, or mixtures thereof.
According to claim 1, The polyester multilayer film is a polyester multilayer film having a thickness of 19 to 75㎛
a) i) a first polyester resin chip, ii) a second polyester resin chip and a multilayer comprising at least one skin layer on both sides of the core layer using a composition containing an anti-blocking agent Coextrusion so as to be, and rapidly cooling to 30 ℃ or less to prepare an unstretched sheet; And
b) preparing a film by sequentially biaxially stretching the unstretched sheet; And
c) heat setting the biaxially stretched film; includes,
The step of producing a film by sequentially biaxially stretching,
First longitudinally stretching the unstretched sheet 2 to 5 times at a rate of 45,000 to 55,000%/min. in the machine direction at 85 to 110° C.; And
Comprising the step of 2 to 5 times the secondary transverse stretching at a rate of 4,500 to 5,500%/min. in the width direction at 95 to 140° C.
The method of manufacturing the polyester multilayer film of claim 1.
The method of claim 6,
The step of heat setting the film
MD relaxation rate and TD relaxation from the fourth heat treatment zone to the fifth heat treatment zone while heat setting the secondly stretched film at 200 to 250°C in a total of five heat treatment zones including the first heat treatment zone to the fifth heat treatment zone Comprising the step of relaxing so that the total relaxation rate of the rate is 1 to 5%,
Method for producing a polyester multilayer film.
The method of claim 6,
The i) first polyester resin chip and ii) the second polyester resin chip have an intrinsic viscosity of 0.6 to 0.7 dl/g.
The method according to claim 6, wherein the amount of the anti-blocking agent is added so that the content of the anti-blocking agent is 200 to 2,000 ppm in the entire film.

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