KR20170002109A - Polyester Film For Optical Film - Google Patents

Abstract

The present invention relates to an optical film and, more specifically, to an optical polyester film comprising a core layer and a skin layer on both surfaces of the core layer. According to the present invention, the film realizes excellent slip, appearance, and coating process properties, and has high transparency and low shrinkage.

Description

TECHNICAL FIELD [0001] The present invention relates to an optical polyester film,

The present invention relates to an optical film. More specifically, the present invention relates to a polyester film comprising a core layer and a skin layer on both sides thereof, which is excellent in slipperiness, appearance and coating processability, and has high transparency and low shrinkage.

Optical films are films used as optical materials for displays. This is used as an optical material for surface protection of various displays such as an LCD BLU (Back Light Unit) or a touch panel.

Such optical films have recently been required to have high transparency to suit touch applications such as tablets and smart phones, and have properties such as excellent surface properties and low shrinkage. If the transparency is low, the brightness is decreased, the surface characteristics are poor, or the shrinkage percentage of the film is high, curl may occur after the coating, or the shape of the final product may be deformed.

In consideration of such physical properties, the optical film is produced by aging the polyester film at a high temperature or using a high heat-resistant polymer such as polyethylene naphthalate (PEN) or polyimide (PI). However, there is a problem that the process of aging the polyester film at a high temperature lowers the productivity or may be deformed by moisture or the like. In addition, the use of PEN or PI is advantageous in terms of heat resistance and dimensional stability, but causes an increase in manufacturing cost and difficulty in post-processing compared to polyester. On the other hand, Japanese Laid-Open Patent Application No. 2009-279923 (Patent Document 1) discloses a multilayer polyester film excellent in dimensional stability and heat resistance against humidity change and capable of suppressing curling. This is to achieve the object by using the copolymerization component, but there is a problem that the shrinkage rate of the post-processing step is very large and curling occurs, and the manufacturing cost is considerably high.

Japanese Patent Application Laid-Open No. 2009-279923 (2009.12.03)

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an optical film having high transparency, low shrinkage percentage and excellent surface characteristics.

It is another object of the present invention to provide an optical film excellent in coating processability and excellent in processability due to less thermal deformation.

It is an object of the present invention to provide an optical film which can realize excellent physical properties and manufacturing processability when applied to a display, particularly a touch panel or a BLU.

In order to achieve the above object, the present invention provides a polyester multilayer film comprising a core layer and a skin layer formed on both sides thereof. The polyester multilayer film may be a three-layer film comprising a core layer and a skin layer on both sides thereof, but not limited thereto, and may be a multilayer film comprising two or more skin layers on both sides of the core layer.

The polyester multilayer film according to the present invention can be produced by extrusion melting in two or more melt extruders, followed by heat treatment after casting and biaxial stretching, and shrinkage can be controlled by relaxing in the longitudinal direction and width direction during heat treatment.

In a specific embodiment, the polyester multilayer film is produced by extruding polyester in one extruder and melt extruding the polyester and the particles simultaneously in another extruder, and then co-extruding each melt in the feed block. Thereafter, it is cooled in casting and then biaxially stretched sequentially and then wound. At this time, the biaxial stretching can be performed first in the longitudinal direction and then in the width direction, but is not limited thereto.

At this time, the polyester multilayer film is characterized by having surface roughness satisfying the following formulas 1 to 2.

(Equation 1) 6? Ra? 20

(Equation 2) 80? Rz? 400

In the above equations 1 and 2, Ra is the center line average roughness, and Rz is the 10-point average roughness. This is the average roughness measured by a two-dimensional contact surface roughness tester (Kosaka SE3300).

If the polyester multilayer film according to the present invention has a centerline average roughness (Ra) of more than 20 nm and a 10-point average roughness (Rz) of more than 400 nm, the surface of the base film may be transferred to the adhesive layer, . In addition, when Ra is less than 6 nm and Rz is less than 80 nm, smoothness is excellent, but coating processability and product handling property are deteriorated, scratches or blocking may occur during the coating process, and coating unevenness may occur. Accordingly, the polyester multilayer film according to the present invention is characterized in that the centerline average roughness (Ra) is 6 to 20 nm and the 10-point average roughness is 80 to 400 nm. When any one of Ra and Rz does not satisfy the above range It is preferable to satisfy all of the above ranges because it causes deterioration of quality of the final product due to coating uniformity and coating unevenness.

The polyester multilayer film of the present invention is characterized by satisfying the conditions of the above-described average roughness and also exhibiting a shrinkage rate upon drying by hot air satisfying the following formula (3).

Specifically, as can be seen from FIG. 1, the ratio of the film shrinkage ratio (S ₁₃₅ ) at an angle of 135 degrees to the film shrinkage ratio (S ₄₅ ) at an angle of 45 degrees with respect to the longitudinal direction is preferably 2 May be less than or equal to 1.8. The shrinkage rate was measured while maintaining at 95 캜 for 60 minutes.

(Equation 3)

(In the formula 3, S ₄₅ denotes a shrinkage rate at an angle of 45 degrees with respect to the longitudinal direction, and S ₁₃₅ denotes a shrinkage rate at an angle of 135 degrees with respect to the longitudinal direction.)

At the same time, the polyester film according to the present invention is characterized in that the ratio of the change in length according to the temperature profile of FIG. 2 when measured using a thermomechanical analyzer (TMA) satisfies the following formula (4).

(Equation 4)

The length of the polyester multilayer film was changed from 40 ° C. to -20 ° C. (-10 ° C./min) for 10 minutes and then to 40 ° C. (10 ° C./min) (TMA). In Equation 4,? _L And [Delta] _w mean a length change (DELTA _l ) in the longitudinal direction and a length change (DELTA _w ) in the width direction.

And the ratio of the change in length in the width direction to the change in length in the longitudinal direction is 1.5 or less, preferably 1.3 or less. If it is out of the above range, thermal deformation will occur severely during post-processing at high temperature, which may cause deformation of the product. This can lead to curling or heat wrinkling in the hard coating or ITO sputtering process. In order to prevent such a problem, a separate off-line aging process is required, which may result in additional cost and time, and may further damage the process due to scratches or foreign matter. In particular, the ratio of the change in length can be improved by coating properties and coating workability in combination with the conditions of the surface roughness and shrinkage ratio, thereby realizing excellent physical properties and optical properties of the present invention.

The polyester multilayer film of the present invention comprises a core layer and a skin layer on both sides of the core layer, and the core layer may be made of a polyester resin. The polyester is not particularly limited, but may preferably be polyethylene terephthalate (PET) alone. The polyester preferably has an intrinsic viscosity of 0.6 to 1.0, preferably 0.6 to 0.8, and more preferably 0.62 to 0.75. If the intrinsic viscosity of the polyester resin of the core layer is less than 0.6, the heat resistance may be reduced and instability of the pneumatic release interface may occur. If the intrinsic viscosity is more than 1.0, extrusion processing may not be easy and workability may be decreased.

It is more preferable that the skin layer formed by co-extruding two or more layers on both surfaces of the core layer has an intrinsic viscosity of 0.6 to 0.8, preferably 0.64 to 0.8. When the above range is satisfied, it is effective in terms of heat resistance and workability. The polyester resin constituting the skin layer may be prepared by a conventional synthetic method so as to have the intrinsic viscosity range. If the intrinsic viscosity of the polyester resin constituting the skin layer is less than 0.6, the unstable interface may occur during co-extrusion, and the extrusion process is not easy because the viscosity is too low. When the intrinsic viscosity is more than 0.8, extrusion processing is not easy in a conventional extruder, and expensive facilities are required, and film properties may be deteriorated at the time of extrusion at a high temperature.

In addition, the skin layer of the present invention may contain inorganic particles. The inorganic particles are not particularly limited, but particles having an average particle diameter of 0.5 to 5 占 퐉 are preferably used. Preferably 0.5 to 3 占 퐉, more preferably 0.5 to 1.6 占 퐉. If the average particle diameter of the inorganic particles is more than 5 mu m, the transparency is remarkably decreased or the light transmittance is too much, and it is difficult to judge the defect by visual inspection in BLU evaluation. Is small.

The content of the inorganic particles in the skin layer is 5 to 100 ppm, which is more effective in improving the optical performance. Preferably, it is preferable to control by combining with the range of the average particle diameter of the inorganic particles. More preferably, the inorganic particles having an average particle diameter of 0.5 to 5 占 퐉 are used while satisfying the above content range. If the content of the inorganic particles is out of the above range, the transparency of the film may be lowered or the smoothness may be lowered, so that it may be difficult to use the composition for a touch panel.

The kind of the inorganic particles is not particularly limited, but preferably one or a mixture of two or more selected from the group consisting of silica, zeolite and kaolin can be used. Such an inorganic particle can improve the slipperiness and warpability of the film through a stretching process.

The polyester multilayer film according to the present invention is not particularly limited, but it is effective that the total film thickness is 25 to 250 mu m, preferably 50 to 200 mu m, more preferably 75 to 125 mu m.

The polyester multi-layer film according to the present invention is stretched in the machine direction in the machine direction after the stretching in the longitudinal direction. At this time, in order to control the shrinkage ratio, the heat treatment temperature is increased or relaxed in the longitudinal direction and the width direction, and it is more preferable to relax in the longitudinal direction and the width direction than the heat treatment temperature.

The content of the core layer in the polyester multilayer film is preferably 70 to 90% by weight, the content of the skin layer is preferably 10 to 30% by weight, more preferably 70 to 80% by weight, When the content of the layer is 20 to 30% by weight, the interface stability is more excellent in co-extrusion.

The polyester multilayer film according to the present invention may have a film haze (according to JIS K 715) of 0.5 to 3%, preferably 0.5 to 2%. The haze of the film before heat treatment can be controlled by the size and content of the particles, and when the above range is satisfied, excellent optical performance can be realized.

The present invention provides an optical film comprising the above-mentioned polyester multilayer film.

Hereinafter, a method for producing a polyester multilayer film according to the present invention will be described.

The present invention relates to a core layer made of a polyester resin having an intrinsic viscosity of 0.6 to 1.0 and a skin layer comprising a polyester resin and an inorganic particle having an intrinsic viscosity of 0.6 to 0.8 on both sides of the core layer, A step of producing a new sheet, a step of biaxially stretching the unstretched sheet in the longitudinal direction and a width direction, and a heat treatment step of loosening the biaxially stretched sheet in the longitudinal direction and the width direction do.

In the step of producing the unstretched sheet, co-extrusion may be carried out using a conventional extrusion method known in the art. In one embodiment, it can be cast by extrusion melting in at least two uniaxial melt extruders or biaxial melt extruders. In one embodiment, the polyester resin constituting the core layer component is extruded in the first extruder, and the components including the polyester resin and the inorganic particles are melt-extruded simultaneously in the second extruder, and then the respective melts meet in the feed block, , Cast and cooled to produce a polyester multilayered film undrawn sheet.

The unstretched sheet may include a core layer and a skin layer on both sides of the core layer, but is not limited thereto and may be a multilayer film in which two or more skin layers are laminated. At this time, the multi-layer film is preferably 70 to 90% by weight of the core layer and 10 to 30% by weight of the skin layer because the core layer is excellent in interfacial stability in the coextrusion process. Also, the skin layer may contain 5 to 100 ppm of inorganic particles to further improve optical performance. At the same time, it is preferable to combine with the constitution of controlling the average particle diameter of the inorganic particles. At this time, it is more effective that the average particle diameter of the inorganic particles is preferably 0.5 to 5 占 퐉.

The step of biaxially stretching is not particularly limited, but is preferably stretched in the longitudinal direction, then stretched in the width direction, and then wound. The stretching ratio is preferably 2 to 4 times in both the longitudinal direction and the width direction, and more preferably 3 to 3.5 times in both the longitudinal direction and the width direction.

The heat treatment step is a step of relaxing in the longitudinal direction and the width direction at a temperature of 200 to 250 ° C, respectively. This is performed in order to reduce heat shrinkage at a high temperature during post-processing such as hard coating or ITO sputtering to improve the durability of the polyester multilayer film and to maintain the appearance and optical properties of the film surface at an initial stage. If the heat treatment temperature is less than 200 ° C, the effect of reducing heat shrinkage at high temperature is insufficient because of insufficient relaxation. If the heat treatment temperature is more than 250 ° C, the film itself may be thermally decomposed and damaged. At this time, although the heat treatment method is not particularly limited, it is preferable to use a hot air oven because the damage to the film surface can be minimized.

The relaxation rate in the heat treatment step is preferably 1.0 to 2.0% in the longitudinal direction and more preferably 1.5 to 7.0% in the width direction. If the relaxation rate is out of the above range, the heat shrinkage ratio may increase in a post-process at a high temperature. If the heat shrinkage ratio is increased, curls or heat wrinkles are generated, the appearance of the multilayered film is deteriorated, and the optical characteristics are remarkably reduced, which may cause a problem that the optical film is not suitable. Further, when curling or heat wrinkling occurs in the polyester multilayer film, it is necessary to add a step of recovering the surface of the film through a separate off-line aging treatment, so that the process cost and time may be excessively consumed, Scratches or foreign matter can be increased.

The present invention provides a polyester multilayer film produced by the above-described method.

The polyester multi-layer film for an optical film according to the present invention has an advantage that high transparency, low shrinkage percentage and excellent surface characteristics can be realized.

Further, the present invention can provide an optical film excellent in coating processability and excellent in processability due to less thermal deformation.

In addition, the polyester multi-layer film for an optical film according to the present invention has an advantage that excellent physical properties and manufacturing processability can be realized when applied to a display, particularly a touch panel or a BLU.

FIG. 1 shows directions of 45 degrees and 135 degrees with respect to the longitudinal direction when measuring film shrinkage percentage.
Fig. 2 shows a temperature file when measuring the ratio of the longitudinal length change in the longitudinal direction to the longitudinal length change in the thermomechanical analyzer.

Hereinafter, the present invention will be described in detail with reference to the following examples. However, the present invention is not limited to the following examples.

The physical properties in the present invention are measured by the following method.

(1) intrinsic viscosity

0.4 g of the PET pellet (sample) was added to 100 ml of the reagent in which phenol and 1,1,2,2-tetrachloroethanol were mixed at a weight ratio of 6: 4, and after dissolving for 90 minutes, the solution was transferred to a Uberoide viscometer ° C in a thermostatic chamber for 10 minutes, and the falling seconds of the solution were determined using a viscometer and an aspirator. The number of drops of the solvent was also determined by the same method, and RV and IV values were calculated by the following equations (1) and (2).

In the following equation, C represents the concentration of the sample.

[Equation 1]

&Quot; (2) "

(2) Transparency (Haze)

The film thus formed was measured using a haze meter (Nipon denshoku, Model NDH 5000) according to JIS K 715 measuring method.

(3) Surface roughness (Ra)

Ra (centerline average roughness) and Rz (10-point average roughness) were measured using a two-dimensional contact surface roughness meter (Kosaka, SE3300).

(4) Shrinkage

The film was cut into 200 × 200 mm and the length and width were measured. The length and width of the film after heat treatment in a hot air oven at 95 ° C. for 60 minutes were measured and calculated as follows.

Shrinkage (%) = (length before heat treatment - length after heat treatment) / length before heat treatment × 100

(5) Thermomechanical analyzer (TMA) measurement

The film was cut to 16 mm in the longitudinal direction and 4.5 mm in the width direction, and then the dimension change was measured using TMA (TA company, TMA Q400). The measurement method was as follows: after cooling from room temperature 40 ℃ to 20 ℃ at 10 ℃ / min, keeping it at 20 ℃ for 10 minutes and then heating to 40 ℃ at 10 ℃ / min.

[Example 1]

A polyester chip (PET chip) having an inherent viscosity of 0.65 was used for the core layer, a polyester chip (PET chip) having an intrinsic viscosity of 0.64 and silica particles having an average particle size of 1.6 占 퐉 were used for the skin layer and 80 ppm, Extrusion cast (coextruded with skin layer / core layer / skin layer). Thereafter, the multilayer film was stretched three times in the machine direction and 3.4 times in the width direction and relaxed by 3% in the width direction and 0.8% in the length direction while being heat-treated at 230 캜 to produce a multilayer film of 75 탆. The multilayered film had a core layer of 80 wt% and a skin layer of 20 wt% based on the total film weight. The particle constitution and content of the skin layer are shown in Table 1, and the properties of the film after the production were measured and shown in Table 2.

[Example 2]

The same procedure as in Example 1 was carried out, except that the polyester chip of the skin layer had an intrinsic viscosity of 0.8.

[Example 3]

A polyester chip having a skin layer having an intrinsic viscosity of 0.6 was used in the same manner as in Example 1.

[Example 4]

The procedure of Example 1 was repeated except that 80 wt% of the core layer and 20 wt% of the skin layer were used for the total film weight.

[Example 5]

Except that 90 wt% of the core layer and 10 wt% of the skin layer were used for the total film weight.

[Example 6]

The procedure of Example 1 was repeated except that the silica particles were changed to contain 100 ppm of silica particles.

[Example 7]

The procedure of Example 1 was repeated except that the silica particles were changed to contain 5 ppm of silica particles.

[Example 8]

The procedure of Example 1 was repeated except that silica particles having an average particle diameter of 5 탆 were contained in an amount of 10 ppm.

[Example 9]

The procedure of Example 1 was repeated, except that silica particles having an average particle diameter of 0.5 탆 were contained in an amount of 100 ppm.

[Comparative Example 1]

A PET chip having an intrinsic viscosity of 0.65 was used and the same procedure as in Example 1 was carried out except that the polyethylene terephthalate resin was relaxed only in the transverse direction without loosening in the longitudinal direction during the heat treatment.

[Comparative Example 2]

The same procedure as in Example 1 was carried out, except that a polyester chip having a skin layer having an intrinsic viscosity of 0.55 was used.

[Comparative Example 3]

The same procedure as in Example 1 was carried out except that a polyester chip having a skin layer having an intrinsic viscosity of 0.85 was used.

[Comparative Example 4]

The procedure of Comparative Example 1 was repeated except that 60 wt% of the core layer and 40 wt% of the skin layer were used for the total film weight.

[Comparative Example 5]

The procedure of Comparative Example 1 was repeated except that the core layer was used in an amount of 95% by weight and the skin layer was used in an amount of 5% by weight based on the total weight of the film.

[Comparative Example 6]

The procedure of Comparative Example 1 was repeated except that silica particles having an average particle diameter of 0.5 탆 were contained in an amount of 110 ppm.

[Comparative Example 7]

The procedure of Comparative Example 1 was repeated except that silica particles having an average particle size of 6 탆 were contained in an amount of 10 ppm.

[Comparative Example 8]

The procedure of Comparative Example 1 was repeated except that silica particles having an average particle diameter of 0.4 탆 were contained in an amount of 110 ppm.

[Table 1] Raw material composition and thickness of each layer according to Examples and Comparative Examples

[Table 2] Evaluation results according to Examples and Comparative Examples

As shown in Table 1, the examples according to the present invention satisfied the physical properties of the surface roughness, shrinkage and dimensional change, and it was confirmed that high transparency, low shrinkage and excellent surface characteristics can be realized. It has been confirmed that it is easy to apply to optical films that can realize excellent physical properties and manufacturing processability when applied to displays, especially touch panels or BLU applications.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Various modifications and variations are possible in light of the above teachings.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (15)

A polyester multilayer film comprising a core layer and a skin layer on both sides of the core layer,
Wherein the skin layer is made of a polyester having an intrinsic viscosity of 0.65 to 0.8,
A polyester multi-layer film satisfying the following formulas (1) to (4).
(Formula 1) 6? Ra? 20
(Formula 2) 80? Rz? 400
(In the equations 1 and 2, the unit is nm, Ra is centerline average roughness, and Rz is 10-point average roughness.)
(Equation 3)

(In the formula (3), S ₄₅ and S ₁₃₅ are shrinkage ratios measured at 95 ° C for 60 minutes with respect to the longitudinal direction, where S ₄₅ is the shrinkage rate at an angle of 45 degrees with respect to the longitudinal direction, S ₁₃₅ is the length Means the shrinkage rate at an angle of 135 degrees with respect to the direction.)
(Equation 4)

(In the formula 4,? ₁ and? _W are obtained by cooling the polyester multilayer film at 40 ° C to -20 ° C (-10 ° C / min) for 10 minutes and then increasing the temperature to 40 ° C (10 ° C / min) after a measurement of a thermal mechanical analyzer (TMA). in this case, Δ _l is the length change in the longitudinal direction, Δ _w means the change in length in the transverse direction.)

The method according to claim 1,
Wherein the multilayered film has a haze of 0.5 to 3% in accordance with JIS K 715.
The method according to claim 1,
Wherein the multi-layer film has a core layer of 70 to 90% by weight of the total film and a skin layer of 10 to 30% by weight.
The method according to claim 1,
Wherein the multilayer film has a total thickness of 25 to 250 占 퐉.
The method according to claim 1,
Wherein the skin layer comprises 5 to 100 ppm of inorganic particles.
The method according to claim 1,
Wherein the inorganic particles have an average particle diameter of 0.5 to 5 占 퐉.
6. The method of claim 5,
Wherein the inorganic particles are any one or a mixture of two or more selected from the group consisting of silica, zeolite, and kaolin.
The method according to claim 1,
Wherein the multilayer film is coextruded, and at least one skin layer is laminated on both sides of the core layer.
9. An optical film comprising a polyester multilayer film of any one of claims 1 to 8.
An unoriented sheet production step of forming a core layer made of a polyester resin having an intrinsic viscosity of 0.6 to 1.0 and a skin layer comprising a polyester resin and an inorganic particle having an intrinsic viscosity of 0.6 to 0.8 on both sides thereof by coextrusion and casting ,
A biaxial stretching step of stretching the non-stretched sheet in the longitudinal direction and the width direction;
And a heat treatment step of loosening the biaxially stretched sheet in a longitudinal direction and a width direction.
11. The method of claim 10,
Wherein the heat treatment step is performed in a relaxation ratio in the range of 1.0 to 2.0% in the longitudinal direction and 1.5 to 7.0% in the transverse direction.
11. The method of claim 10,
Wherein the heat treatment step is performed at 200 to 250 ° C.
11. The method of claim 10,
Wherein the core layer is 70 to 90% by weight of the total film and the skin layer is 10 to 30% by weight.
11. The method of claim 10,
Wherein the skin layer contains 5 to 100 ppm of inorganic particles.
11. The method of claim 10,
Wherein the inorganic particles have an average particle diameter of 0.5 to 5 占 퐉.

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