KR20190124401A - Polarizing plate protective film and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a protective film for a polarizing plate and a manufacturing method thereof and, more specifically, to a protective film for a polarizing plate having excellent mechanical properties while a rainbow stain does not occur because the difference in the orientation angle between a center portion and an end portion is minimized, and to a manufacturing method thereof.

Description

Protective film for polarizing plate and manufacturing method thereof {POLARIZING PLATE PROTECTIVE FILM AND MANUFACTURING METHOD THEREOF}

The embodiment relates to a protective film for a polarizing plate and a method for manufacturing the same, and more particularly, to a polarizing plate protective film for excellent mechanical properties and a method of manufacturing the same because the difference in the orientation angle between the center and the end is minimized will be.

In general, the polarizing plate is a protective film for protecting the polarizer of polyvinyl alcohol material to attach a protective film for polarizing plate on one side or both sides of the polarizer. Polyethylene terephthalate (PET) film was used as a protective film for such a polarizing plate, but the polyethylene terephthalate film was difficult to apply as a protective film for a polarizing plate because the anisotropy occurs greatly depending on the draw ratio.

As an alternative to this, triacetylcellulose (TAC) films with high light transmittance, optical isotropy, and defect-free surface have been widely applied. Specifically, Korean Patent No. 10-1222363 discloses a polarizing plate curling correction film whose main component is a cellulose ester, an in-plane retardation of 30 to 300 nm and a thickness direction retardation of 80 to 400 nm.

However, triacetylcellulose films have the disadvantage of being expensive, not having a variety of sources, and vulnerable to moisture. Therefore, protective films of various materials are being developed to replace the triacetyl cellulose film, for example, a cycloolefin polymer (COP, cycloolefin polymer), acrylic and polyester-based film, such as a scheme to use alone or mixed This has been proposed.

Republic of Korea Patent No. 10-1222363

However, the acrylic film has low processability due to brittle nature, and there is a problem in that the manufacturing cost increases when a copolymer copolymerized with other monomers is used to overcome this problem.

Accordingly, an object of the embodiment is to provide a protective film for a polarizing plate and a manufacturing method thereof having excellent mechanical properties without the polarization mura produced by minimizing the difference in the orientation angle between the center and the end including PET.

One embodiment to achieve the above object,

(1) melt extruding the polyester resin composition to prepare an unstretched sheet;

(2) preheating the unstretched sheet and stretching less than twice in the longitudinal direction while applying heat from 750 ° C. to 850 ° C. using a far-infrared heater (R / H);

(3) stretching the sheet stretched in the longitudinal direction at least three times in the width direction to produce a stretched film; And

(4) heat-setting the stretched film to prepare a protective film;

The protective film provides a method of manufacturing a protective film for polarizing plates having an in-plane retardation (Re) of 6,000 nm or more.

Another embodiment,

The longitudinal and width modulus is 250kgf / mm ² or more and 500kgf / mm ² or more, respectively, and the longitudinal and width tensile strengths are 9kgf / mm ² or more and 30kgf / mm ² or more, respectively. Is 30% or more and 60% or more, and the in-plane retardation (Re) is 6,000 nm or more, and there is no polarization mura generation, and a protective film for a polarizing plate is provided.

The method of manufacturing a polarizing plate protective film according to the embodiment may prepare a polarizing plate protective film having excellent optical and mechanical properties by appropriately adjusting the stretching ratio in the longitudinal direction and the transverse direction, and process conditions during stretching.

In addition, the protective film for a polarizing plate according to the embodiment is excellent in optical properties because the difference in the orientation angle between the central portion and the end and the in-plane retardation does not occur, the optical properties are excellent, and the elongation at break and tensile strength in the width direction and the length direction is appropriately It is maintained and excellent in mechanical properties.

1 is a view showing a manufacturing method of a protective film for a polarizing plate according to an embodiment.
FIG. 2 is an enlarged view of part (A) of FIG. 1.
3 is a view showing a method of manufacturing a protective film for a polarizing plate according to one embodiment.
4 is a schematic diagram showing an orientation angle measuring system used in a test example.
Fig. 5 is a schematic diagram in which a film is mounted on a display as an apparatus used for confirming polarization mura of a test example.

Hereinafter, the present invention will be described in detail through embodiments. The embodiments are not limited to the contents disclosed below and may be modified in various forms as long as the gist of the invention is not changed.

In this specification, when each film or layer or the like is described as being formed "on" or "under" of each film or layer or the like, "on" and "under" are described. "Includes" everything that is formed "directly" or "indirectly". In addition, the criteria for up / down of each component will be described with reference to the drawings. The size of each component in the drawings may be exaggerated for description, and does not mean a size that is actually applied. Also, like reference numerals refer to like elements throughout.

"Including" in the present specification means that it may further include other components unless otherwise specified.

In addition, all numbers and expressions indicating amounts of components, reaction conditions, and the like described herein are to be understood as being modified in all instances by the term "about" unless otherwise specified.

Manufacturing method of protective film for polarizing plate

Method of manufacturing a protective film for a polarizing plate according to an embodiment

(1) melt extruding the polyester resin composition to prepare an unstretched sheet;

(2) preheating the unstretched sheet and stretching less than twice in the longitudinal direction while applying heat from 750 ° C. to 850 ° C. using a far-infrared heater (R / H);

(3) stretching the sheet stretched in the longitudinal direction at least three times in the width direction to produce a stretched film; And

(4) heat-setting the stretched film to prepare a protective film;

The protective film has an in-plane retardation Re of 6,000 nm or more.

Step (1)

In this step, the polyester resin composition is melt-extruded to prepare an unstretched sheet.

The polyester resin composition may be formed by polymerizing after transesterifying the diol component and the dicarboxylic acid component. Specifically, the polyester resin composition may include polyethylene terephthalate. More specifically, the polyester resin composition may include at least 75 mol%, at least 80 mol%, at least 90 mol%, or at least 95 mol% of ethylene terephthalate as the monomer unit. When the polyester resin composition includes 75 mol% or more of ethylene terephthalate in monomer units, the sheet made from the polyester resin composition may have crystallinity, and the crystal plane of the sheet may have orientation in one direction.

The melt extrusion may be performed at a temperature of Tm + 10 ° C. to Tm + 70 ° C. Specifically, the melt extrusion may be carried out at a temperature of Tm + 20 ℃ to Tm + 60 ℃, or Tm + 30 ℃ to Tm + 60 ℃. At this time, Tm is the melting temperature of the polyester resin composition. When melt extrusion is performed within the above temperature range, there is an effect that the melting of the resin is smooth and the viscosity of the extrudate is properly maintained.

Referring to FIG. 1, through the T-die 10, a polyester resin composition may be melted and discharged, and the resin discharged to the casting roll 20 may be coated to form an unstretched sheet 100. The unstretched sheet 100 may be cooled and formed by the casting roll 20.

Surface temperature of the casting roll 20 is Tg-100 ℃ to Tg + 20 ℃, Tg-80 ℃ to Tg + 20 ℃, Tg-70 ℃ to Tg + 20 ℃, Tg-70 ℃ to Tg + 10 ℃, Or Tg-70 ° C to Tg-5 ° C. At this time, the Tg is the glass transition temperature of the polyester resin composition.

Step 2

In this step, the unstretched sheet is pre-heated and stretched less than twice in the longitudinal direction while applying heat at 750 ° C. to 850 ° C. using a far-infrared heater (R / H).

The preheating may be performed at 50 ℃ to 110 ℃. Specifically, the preheating may be performed at 50 ° C to 100 ° C, 50 ° C to 90 ° C, 60 ° C to 90 ° C, or 70 ° C to 90 ° C.

The longitudinal stretching may be performed using two rollers spaced 200 to 500 mm apart. Specifically, the longitudinal stretching may be performed by the circumferential speed difference between two rollers spaced apart (a) from 200 mm to 500 mm, 300 mm to 500 mm, 200 mm to 400 mm, or 400 mm to 500 mm (see FIG. 2). The peripheral speed difference can be adjusted according to the stretching ratio in the longitudinal direction.

The two rollers may have a temperature difference of 50 ° C to 60 ° C. Specifically, the two rollers may be a temperature difference of 52 ℃ to 60 ℃, 52 ℃ to 58 ℃, or 53 ℃ to 57 ℃.

Referring to FIG. 1, the unoriented sheet 101 is longitudinally driven by the peripheral speed difference between the first stretching roll 31 and the second stretching roll 32 while applying heat using the far infrared heaters 41 and 42. Can be stretched. Specifically, the temperature of the first stretching roll is 70 ℃ to 95 ℃, 80 ℃ to 95 ℃, or 82 ℃ to 93 ℃, the temperature of the second stretching roll is 15 ℃ to 45 ℃, 20 ℃ to 45 ℃. , 20 ° C. to 40 ° C., or 23 ° C. to 35 ° C.

The far-infrared heater may be spaced apart from the non-stretched sheet by 40 mm to 150 mm (c), and may be located on both upper and lower sides of the unstretched sheet (see FIGS. 1 and 2). Specifically, the far-infrared heater is spaced apart from the non-stretched sheet 70mm to 150mm, 70mm to 100mm, or 100mm to 150mm, may be located on both the top and bottom of the unstretched sheet.

The heat treatment length b may be 70% or more based on the total distance a between the two rollers (see FIG. 2). Specifically, the heat treatment length may be 80% or more, or 80% to 95% based on the total distance between the two rollers.

The temperature of the far infrared heater 42 located above the unstretched sheet is 20 ° C. to 50 ° C., 30 ° C. to 50 ° C., or 30 ° C. to 40 ° C., than the temperature of the far infrared heater 41 located at the bottom of the unstretched sheet. Can be high.

The temperature of the far-infrared heater located at the top of the unstretched sheet is 650 ° C to 850 ° C, 700 ° C to 840 ° C, 750 ° C to 850 ° C, or 800 ° C to 840 ° C, of the far-infrared heater located at the bottom of the unstretched sheet. The temperature may be 650 ° C to 800 ° C, 700 ° C to 800 ° C, 700 ° C to 790 ° C, or 750 ° C to 790 ° C.

The far-infrared heater may have a total power of 20 kW to 50 kW. Specifically, each far-infrared heater located on the upper and lower portions of the unstretched sheet has a power of 5 kW to 20 kW, or 10 kW to 20 kW, so that the total power is 30 kW to 50 kW, 35 kW to 50 kW, or 20 kW to 45 kW. To 5 can be used.

In this step, it may be drawn 1.4 to 1.8 times in the longitudinal direction. Specifically, in this step, it may be stretched from 1.45 times to 1.8 times, 1.5 times to 1.6 times, or 1.55 times to 1.6 times in the longitudinal direction.

In this step, the unstretched sheet may be preheated while moving at a speed of 20 m / min to 100 m / min and stretched in the longitudinal direction while applying heat to a far infrared heater. Specifically, in this step, the unstretched sheet may be performed while moving at a speed of 20 m / min to 80 m / min, 20 m / min to 60 m / min, or 25 m / min to 50 m / min.

Step 3

In this step, the stretched film is stretched three times or more in the width direction to prepare the stretched film.

Referring to FIG. 3, the stretched film 102 may be manufactured by stretching the sheet 101 stretched in the longitudinal direction in the width W direction.

In this step, it can extend | stretch 4.0 times or more in the width direction. Specifically, in this step, it may be stretched in the width direction from 4.0 times to 5.0 times, from 4.0 times to 4.8 times, or from 4.0 times to 4.5 times.

The stretching in the width direction may be performed at 80 ° C. to 120 ° C. Specifically, the stretching in the width direction may be performed at 82 ° C to 110 ° C, or 85 ° C to 95 ° C.

The stretching in the width direction may be performed while moving the sheet stretched in the longitudinal direction at a speed of 30 m / min to 100 m / min. Specifically, the stretching in the width direction may be performed while moving the sheet stretched in the longitudinal direction at a speed of 30 m / min to 100 m / min, 40 m / min to 80 m / min, or 45 m / min to 75 m / min.

Step 4

In this step, the stretched film is heat-set to produce a protective film.

The heat setting may be carried out at 150 ℃ to 250 ℃ for 0.2 seconds to 2 minutes. Specifically, the heat setting may be performed at 150 ° C to 220 ° C, 180 ° C to 250 ° C, or 180 ° C to 220 ° C for 0.2 seconds to 1.2 minutes, or 0.5 seconds to 1 minute.

In the heat setting, the stretched film may be relaxed at a relaxation rate of 0% to 5%.

In-plane retardation Re of the protective film manufactured by the above-described manufacturing method is 6,000 nm or more.

In-plane retardation is a parameter defined by the product (ΔNxy = d) of the refractive index of the biaxial orthogonal biaxial on the film (ΔNxy = | Nx-Ny |) and the film thickness d (nm), indicating optical isotropy and anisotropy. It is a measure. The in-plane retardation Re is an in-plane retardation value at a wavelength of 550 nm, and is represented by Equation 3 below.

[Equation 3]

Re = (n _x -n _y ) × d

At this time, n _x is a refractive index in the uniaxial direction in the film plane, n _y is a refractive index in the uniaxial direction orthogonal to the x axis in the film plane, and d is the thickness (nm) of the film.

Protective Film for Polarizer

Protective film for a polarizing plate according to one embodiment has a longitudinal direction and a width direction modulus of 250kgf / mm ² or more and 500kgf / mm ² or more, respectively, and the longitudinal and width direction tensile strength of 9kgf / mm ² or more and 30kgf / mm ^{2, respectively} The elongation at break in the longitudinal direction and in the width direction is at least 30% and at least 60%, respectively, and the in-plane retardation Re is 6,000 nm or more, and no polarization mura occurs.

The protective film for the polarizing plate has a longitudinal modulus of 250kgf / mm ² To ^{350kgf / mm 2, 250kgf / mm} 2 to ^{300kgf / mm 2, 250kgf / mm} 2 to 270kgf / mm ^2, or 250kgf / mm ² to 268kgf / mm ^2, and the transverse direction modulus of 500kgf / mm ² to 600kgf / mm ² , 500kgf / mm ² to 580kgf / mm ² , 500kgf / mm ² to 550kgf / mm ² , or 520kgf / mm ² to 550kgf / mm ² .

The protective film for the polarizing plate has a longitudinal tensile strength of 9kgf / mm ² to 18kgf / mm ² , 9kgf / mm ² to 15kgf / mm ² , 9kgf / mm ² to 13kgf / mm ² , 9kgf / mm ² to 12kgf / mm ² Or 9kgf / mm ² to 11kgf / mm ^2, and the tensile strength in the width direction is 30kgf / mm ² to 40kgf / mm ² , 30kgf / mm ² to 34kgf / mm ² , 30kgf / mm ² to 33kgf / mm ² , or 30kgf / mm ² to 32kgf / mm ² may be.

The protective film for the polarizing plate has a longitudinal elongation at break of 30% to 150%, 30% to 130%, 30% to 120%, 40% to 120%, or 45% to 110%, and 60% of elongation at break. To 85%, 65% to 85%, 67% to 85%, or 67% to 83%.

The protective film for the polarizing plate may satisfy the following Equations 1 and 2 in tensile strength and elongation at break. Specifically, the protective film for the polarizing plate may satisfy the following Equations 4 and 5 in tensile strength and elongation at break.

[Equation 1]

3.0 ≤ tensile strength in longitudinal direction (kgf / mm ² ) / tensile strength in width direction (kgf / mm ² ) ≤ 3.5

[Equation 2]

0.6 ≤ elongation at break (%) / longitudinal elongation at break (%) ≤ 3.0

[Equation 4]

3.1 ≤ tensile strength in longitudinal direction (kgf / mm ² ) / tensile strength in width direction (kgf / mm ² ) ≤ 3.4

[Equation 5]

0.7 ≤ elongation at break (%) / longitudinal elongation at break (%) ≤ 2.0

The elongation at break is a value measured for a sample having a thickness of 80 mm to 125 mm.

The polarizing plate protective film may have an in-plane retardation (Re) of 6,000 nm to 20,000 nm, 6,000 nm to 15,000 nm, 7,000 nm to 15,000 nm, 7,000 nm to 12,000 nm, or 7,500 nm to 12,000 nm.

The protective film for polarizing plates has an orientation angle deviation (optical axis) of ± 5.0 deg. (°) or less with respect to the full width, and ± 2.5 deg. It may have the following orientation angle deviation. Specifically, the protective film for the polarizing plate ± 0.1deg with respect to the full width. To ± 5.0 deg., ± 0.1 deg. To ± 3.0 deg., ± 0.1 deg. To ± 2.5 deg., ± 1.0 deg. To ± 2.5 deg., Or ± 1.5 to ± 2.5 deg., Having an orientation angle deviation of ± 0.1 deg for a center portion of 2 m of the full width of the protective film. To ± 2.5 deg., ± 0.1 deg. To ± 1.5 deg., ± 0.5 deg. To ± 1.3 deg., Or ± 0.6 deg. To ± 1.3 deg. Orientation angle deviation.

As the alignment angle deviation is closer to 0deg., The luminance of the film is improved, and when it is within the range, the luminance may be improved by 5% or more, while preventing polarization mura to prevent color distortion.

The protective film for the polarizing plate is excellent in mechanical properties because no burr is generated on the cut surface even after cutting and stacking a plurality of polarizing plates, and the in-plane retardation is high without polarizing mura.

The protective film for the polarizing plate satisfies the above-described physical properties, and when viewed from the side, no polarization mura is observed and excellent mechanical properties. Therefore, the protective film for the polarizing plate may be usefully used in the production of a polarizing plate having improved optical properties and mechanical properties.

EXAMPLE

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example  One.

Polyethylene terephthalate resin (100 mol% of ethylene glycol + 100 mol% of terephthalic acid, 0.61 dl / g of intrinsic viscosity (IV), SKC) was melt extruded through an extruder at 280 ° C, cooled by a casting roll at 25 ° C, An unstretched sheet was produced. The pre-heated sheet is preheated to 82 ° C. while moving at a speed of 32 m / min, and a far-infrared heater 80 mm away from the preheated unstretched sheet while moving the preheated unstretched sheet at a speed of 32 m / min. H), the first stretching roll (85 ° C.) and the second stretching roll spaced 300 mm apart, heating at 810 ° C. (total power: 25 kW) and the bottom to 780 ° C. (total power: 20 kW). It extended | stretched 155% in the longitudinal direction (MD direction) using (30 degreeC).

The sheet stretched in the longitudinal direction was stretched 419% in the width direction (TD direction) at 85 ° C. while moving at a speed of 48 m / min. Thereafter, the stretched film was heat set at a temperature of 200 ° C. for about 1 second to relax at a relaxation rate of about 5% to prepare a protective film for a polarizing plate having a thickness of 125 μm.

Example  2 and 3, and Comparative example  1 to 3.

A protective film for a polarizing plate was manufactured in the same manner as in Example 1, except that the stretching ratios in the longitudinal and width directions, the temperatures of the upper and lower portions of the far infrared heater, and the output were changed as shown in Table 1.

Thickness (㎛) Extension ratio (times) R / H process condition MD TD Power (kW) (top / bottom) Temperature (℃) (upper / lower) Example 1 125 1.55 4.19 25/20 810/780 Example 2 100 1.50 4.44 25.5 / 22 840/790 Example 3 80 1.58 4.42 23.5 / 21 800/755 Comparative Example 1 80 1.30 4.20 17/12 700/670 Comparative Example 2 100 3.10 4.25 21/16 750/720 Comparative Example 3 80 3.20 4.15 23.5 / 18.5 780/740

Test Example . Property measurement

The protective films for polarizing plates manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated as follows, and the results are shown in Table 2.

(One) Modulus  evaluation

In accordance with ASTM D 882, longitudinal / lateral elastic modulus was measured using a universal testing machine 4206-001 (Instron).

(2) tensile strength evaluation

Tensile strength was measured by dividing the maximum load by the original cross-sectional area of the film by applying a load to the film according to KS B 5521.

(3) Breaking Shinto

After the protective film for polarizing plates was cut into 15 mm x 100 mm (width x length), the breaking elongation was measured under a measurement condition of 200 mm / min using a breaking elongation measuring instrument (manufacturer: SKC UTM, model name: INSTRON 5566).

(4) optical axis evaluation

The orientation angle of a film (sample film) was measured using the orientation angle measuring system as shown in FIG. 4, and the deviation (optical axis) of the angle between the measured orientation angle and the width direction was calculated | required.

(5) in-plane Phase difference (Re)

Irrespective of the orientation axis direction of the film, the film was cut out into a rectangle of 4 cm × 2 cm in the width direction of the film and used as a sample for measurement. For this sample, the refractive indices (Nx, Ny) and the refractive indices (Nz) in the thickness direction orthogonal to each other were obtained by an Abbe refractive index meter (manufactured by Atago Co., Ltd., NAR-4T, measurement wavelength 550 nm), and the refractive index difference The absolute value (| Nx-Ny |) was made into the anisotropy ((DELTA) Nxy) of refractive index. The thickness d (nm) of the film was measured using the electric micrometer (Millitron 1245D by Pineryuf Co., Ltd.), and the unit was converted into nm. In-plane phase difference Re was calculated | required from the product ((DELTA) Nxyxd) of the refractive index anisotropy ((DELTA) Nxy) and the film thickness d (nm).

(6) Polarized light  Occurrence

On one side of the polarizer (manufacturer: Samsung SDI) made of PVA and iodine, the film (sample film) obtained in the above example or comparative example is attached so that the absorption axis of the polarizer and the orientation major axis of the film are perpendicular to each other. On the opposite side, a TAC film (manufacturer: Fujifilm Co., Ltd., product name: n-tac, thickness: 80 µm) was attached to produce a polarizing plate. The polarizing plate is provided on the exiting light side of a liquid crystal display device using a white LED composed of a light emitting element combining a blue light emitting diode and a yttrium aluminum garnet-based yellow phosphor as a light source (NSPW500CS, Nichia Chemical). Located on the side. The liquid crystal display device had a polarizing plate having two TAC films as protective films for polarizers on the incident light side of the liquid crystal cell (see FIG. 5). It was visually observed from the front side and the oblique direction of the polarizing plate of the liquid crystal display device to observe the presence or absence of polarization mura.

(7) Evaluation of cutting direction in width direction and length direction

After laminating 10 sheets of polarizer protective films of Examples and Comparative Examples of 800 mm × 1,000 mm (width × length), the cut film was cut in the width direction (TD direction) or the longitudinal direction (MD direction) using a cutting machine. Thereafter, the cut surface was observed under a microscope, and if burrs were generated on the cut surface, the burrs were bad, and if they did not, they were evaluated as good.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Modulus (kgf / mm ² ) MD 252.9 264.3 266.8 271 382.7 378 TD 532.1 528.9 544.6 499.4 435.7 445 Tensile Strength (kgf / mm ² ) MD 9.3 9.8 10 8.7 19.6 20.1 TD 30.8 30.5 31.8 34.2 26 27.2 Elongation at Break (%) MD 55 106 48 10 98 89 TD 69 81 68 88 42 51 Tensile Strength Ratio (MD / TD) 3.31 3.11 3.18 3.93 1.33 1.35 Elongation at Break (TD / MD) 1.25 0.76 1.42 8.8 0.43 0.57 Optical axis (deg.) At full width (5m) 1.9 2.2 1.8 3.1 32 28 2m width optical axis (deg.) 0.8 1.2 0.7 1.4 22 20 In-plane retardation (Re) (nm) 11,052 10,523 7,929 8,100 4,691 3,426 Polarized light Nil Nil Nil Nil A lecturer A lecturer Cutting state MD direction Good Good Good Good Good Good TD direction Good Good Good Bad Good Good

As shown in Table 2, Examples 1 to 3 have an appropriate modulus, tensile strength, and elongation at break, and are excellent in mechanical properties due to clean cross-sections in the width direction and the length direction, and the orientation angle deviation of the protective film for the polarizing plate with respect to the full width. Small, high in-plane retardation, excellent optical properties.

On the other hand, Comparative Example 1, in which the longitudinal draw ratio was too small and the far-infrared heater treatment conditions were not appropriate, had a low tensile strength and elongation at break in the longitudinal direction, and had a bad state of the cross-sectional cut surface. In addition, the biaxially stretched Comparative Examples 2 and 3 had a large variation in the orientation angle with respect to the full width of the film, and there was a polarization mura.

10: T-die 20: casting roll
31: first drawing roll 32: second drawing roll
41, 42: far infrared heater
100: unstretched sheet 101: sheet stretched in the longitudinal direction
102: stretched film
210: sample film 220: polarizer
230: protective film (TAC film) 240: LCD panel
250: polarizer 260: backlight unit
(a): distance between first drawing roll and second drawing roll
(b): length of heat treatment using far infrared heater
(c): distance between undrawn sheet and far infrared heater
W: width of stretched film

Claims (12)

(1) melt extruding the polyester resin composition to prepare an unstretched sheet;
(2) preheating the unstretched sheet and stretching less than twice in the longitudinal direction while applying heat from 750 ° C. to 850 ° C. using a far-infrared heater (R / H);
(3) stretching the sheet stretched in the longitudinal direction at least three times in the width direction to produce a stretched film; And
(4) heat-setting the stretched film to prepare a protective film;
The protective film is a manufacturing method of a polarizing plate protective film, the in-plane retardation (Re) is 6,000nm or more.
The method of claim 1,
The longitudinal stretching of the step (2) is carried out using two rollers spaced from 200mm to 500mm, the method of manufacturing a protective film for a polarizing plate.
The method of claim 2,
The two rollers have a temperature difference of 50 ℃ to 60 ℃, the manufacturing method of the protective film for polarizing plates.
The method of claim 1,
The far-infrared heater in the step (2) is 40mm to 150mm spaced apart from the unstretched sheet, located on the upper and lower sides of the unstretched sheet, the manufacturing method of the protective film for polarizing plates.
The method of claim 4, wherein
The temperature of the far-infrared heater positioned on the upper portion of the unstretched sheet is 30 to 50 ℃ higher than the temperature of the far-infrared heater positioned on the lower portion of the unstretched sheet, the manufacturing method of the protective film for polarizing plates.
The method of claim 1,
The far-infrared heater is a total output is 20kW to 50kW, the manufacturing method of the protective film for polarizing plates.
The method of claim 1,
Drawing in the lengthwise direction in the step (2) from 1.4 times to 1.8 times;
Stretching at least 4.0 times in the width direction in the step (3), the manufacturing method of the protective film for polarizing plates.
The method of claim 1,
Stretching in the width direction in the step (3) is carried out at 80 ℃ to 120 ℃, the manufacturing method of a protective film for a polarizing plate.
The method of claim 1,
The heat setting in the step (4) is carried out for 0.2 seconds to 2 minutes at 150 ℃ to 250 ℃, the manufacturing method of a protective film for polarizing plates.
A longitudinal and transverse direction modulus of each of 250kgf / mm ² or more and 500kgf / mm ² or more,
The tensile strength in the longitudinal direction and the width direction is 9kgf / mm ² or more and 30kgf / mm ² or more, respectively.
The elongation at break in the longitudinal direction and in the width direction is at least 30% and at least 60%, respectively,
In-plane retardation (Re) is 6,000 nm or more,
Protective film for polarizing plates which does not generate polarized mura.
The method of claim 10,
The protective film, the tensile strength and elongation at break satisfies the following equations 1 and 2, protective film for polarizing plates:
[Equation 1]
3.0 ≤ tensile strength in longitudinal direction (kgf / mm ² ) / tensile strength in width direction (kgf / mm ² ) ≤ 3.5
[Equation 2]
0.6 ≤ elongation at break (%) / longitudinal elongation at break (%) ≤ 3.0.
The method of claim 10,
The protective film has an orientation angle deviation of ± 5.0 deg. Or less with respect to the full width, and ± 2.5 deg. With respect to a center portion of 2 m of the protective film. The protective film for polarizing plates which has the following orientation angle deviations.

Images