KR102397408B1 - Polyester multi-layer film and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a polyester multilayer film having high transparency, excellent surface properties, and low shrinkage, and a method for manufacturing the same.

Description

Polyester multilayer film and manufacturing method thereof

The present invention relates to a polyester multilayer film having high transparency, excellent surface properties, and low shrinkage, which can be used for an optical film, and a method for manufacturing the same.

Optical film is a film used as an optical member for display and is used as an optical material for LCD BLU or as an optical member for surface protection of various displays such as LCD, PDP, and touch panel.

In order to be suitable for such an optical film, especially a touch panel or a mobile phone, it is an important factor to improve the quality of the film to show appropriate transparency, low shrinkage, and excellent surface properties.

In order to solve this problem, the polyester film was aged at a high temperature, or a high heat-resistant polymer such as polyethylene naphthalate (PEN) or polyimide (PI) was used. However, when the polyester film is aged and used at high temperature, the production yield of the film is not sufficient, there is a problem that deformation occurs due to moisture, etc. It was quite expensive, and there was a problem that post-processing was difficult.

The present invention is a polyester multilayer film that has high transparency, so it is easy to inspect the quality of foreign substances during the coating process in the post-process, and has excellent surface properties, so the coating processability is good, and the shrinkage rate is low so that no shrinkage occurs in the post-processing process. It aims to provide

Specifically, in order to prevent heat shrinkage from occurring in the post-processing process, an object of the present invention is to provide a polyester multilayer film in which heat shrinkage rates in a 45 degree direction and a 135 degree direction with respect to the film machine direction satisfy specific ranges.

The present invention is a polyester multilayer film composed of three or more layers by co-extrusion of a polyester resin,

Transparency is 2.5% or less based on 75㎛, the thermal contraction rate in the 45 degree direction and 135 degree direction with respect to the film machine direction satisfies Equation 1 below, and the inflection point in the machine direction when measured using a thermomechanical analyzer (TMA) It is 100 ~ 160 ℃, and after maintaining at 40 ℃ for 3 minutes, the length change when the temperature is raised to 180 ℃ at 5 ℃ / min relates to a polyester multilayer film that satisfies the following formula 2.

[Equation 1]

|S ₄₅ - S ₁₃₅ | ≤ 0.35

In Equation 1, S ₄₅ is the shrinkage ratio in the direction of 45 degrees with respect to the film machine direction, and S ₁₃₅ is the shrinkage ratio in the direction of 135 degrees with respect to the film machine direction.

[Equation 2]

0.4 ≤ Length change in machine direction / Length change in width direction ≤ 2.0

In Equation 2, the change in length means the changed initial length at a point of 120°C.

In addition, the present invention provides a) a first polyester resin composition for a core layer comprising a polyester resin having an intrinsic viscosity of 0.6 to 0.7 dl/g, and a polyester resin having an intrinsic viscosity of 0.65 to 0.8 dl/g and inorganic particles. Co-extruding a second polyester resin composition for a skin layer comprising: melt-extruding to laminate three or more layers;

b) preparing a film by biaxially stretching the co-extruded sheet to a range satisfying Equation 3 below;

[Equation 3]

E _MD × 1.1 ≤ E _TD ≤ E _MD × 1.5

In Equation 3, E _MD is the stretching ratio in the machine direction, and E _TD is the stretching ratio in the width direction.

c) heat-treating the stretched film while simultaneously relaxing 1.1 to 2.0% in the machine direction and 2 to 12% in the width direction;

It relates to a method for producing a polyester multilayer film comprising a.

The polyester multilayer film according to the present invention has high transparency, so it is easy to inspect the quality of foreign substances during the coating process in the post-process, and has excellent surface properties, so the coating processability is good. It is not possible to provide a polyester multilayer film with less deformation.

In addition, the polyester multilayer film according to the present invention is suitable for use as an optical film such as a tablet or a mobile phone, and since there is little thermal deformation during the post process, it can be suitably used in fields requiring post processes and thin displays.

Hereinafter, the present invention will be described in more detail through embodiments or examples including the accompanying drawings. However, the following specific examples or examples are only a reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

Also, unless defined otherwise, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description herein is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention.

Also, the singular forms used in the specification and appended claims may also be intended to include the plural forms unless the context specifically dictates otherwise.

One aspect of the present invention is a polyester multilayer film consisting of three or more layers by co-extrusion of a polyester resin,

Transparency is 2.5% or less based on 75㎛, the thermal contraction rate in the 45 degree direction and 135 degree direction with respect to the film machine direction satisfies Equation 1 below, and the inflection point in the machine direction when measured using a thermomechanical analyzer (TMA) It is 100 ~ 160 ℃, after 3 minutes at 40 ℃, the length change when the temperature is raised to 180 ℃ at 5 ℃ / min satisfies the following formula 2 is a polyester multilayer film.

[Equation 1]

|S ₄₅ - S ₁₃₅ | ≤ 0.35

In Equation 1, S ₄₅ is the shrinkage ratio in the direction of 45 degrees with respect to the film machine direction, and S ₁₃₅ is the shrinkage ratio in the direction of 135 degrees with respect to the film machine direction.

[Equation 2]

0.4 ≤ Length change in machine direction / Length change in width direction ≤ 2.0

In Equation 2, the length change means the length at the point of 120° C. - the initial length.

In one aspect of the present invention, the polyester multilayer film may be three or more layers, including a core layer and a skin layer in which at least one layer is laminated on one or both sides thereof.

In one aspect of the present invention, the skin layer may include a polyester resin having an intrinsic viscosity of 0.65 to 0.8 dl/g and inorganic particles.

In one aspect of the present invention, the inorganic particles may have an average particle diameter of 0.5 to 5 μm and a content of particles in the skin layer of 10 to 100 ppm.

In one aspect of the present invention, the polyester multilayer film may have a center line average roughness Ra of 6 to 25 nm, and a 10-point average roughness Rz of 80 to 400 nm.

In one aspect of the present invention, the polyester multilayer film may have a total thickness of 25 to 125 μm, a core layer of 70 to 90% by weight of the entire film, and a skin layer of 10 to 30% by weight.

Another aspect of the present invention relates to a method for manufacturing the polyester multilayer film, specifically

a) A first polyester resin composition for a core layer comprising a polyester resin having an intrinsic viscosity of 0.6 to 0.7 dl/g, and a skin layer agent comprising a polyester resin having an intrinsic viscosity of 0.65 to 0.8 dl/g and inorganic particles 2 by melt-extruding the polyester resin composition to co-extrusion so that three or more layers are laminated;

b) preparing a film by biaxially stretching the co-extruded sheet to a range satisfying Equation 3 below;

[Equation 3]

E _MD × 1.1 ≤ E _TD ≤ E _MD × 1.5

In Equation 3, E _MD is the stretching ratio in the machine direction, and E _TD is the stretching ratio in the width direction.

c) heat-treating the stretched film while simultaneously relaxing 1.1 to 2.0% in the machine direction and 2 to 12% in the width direction;

It is a method of manufacturing a polyester multilayer film comprising a.

In one aspect of the present invention, the stretching ratio in the machine direction may be 2 to 4 times, and the stretching ratio in the width direction may be 2.2 to 6 times.

In one aspect of the present invention, the polyester multilayer film has a transparency of 2.5% or less based on 75 μm, and the thermal contraction rate in the 45 degree direction and 135 degree direction with respect to the film machine direction satisfies the following formula 1, and a thermomechanical analyzer When measuring using (TMA), the inflection point in the machine direction is 100 ~ 160 ℃, and after holding at 40 ℃ for 3 minutes, when the temperature is raised to 180 ℃ at 5 ℃ / min, the length change may satisfy Equation 2 below.

[Equation 1]

|S ₄₅ - S ₁₃₅ | ≤ 0.35

In Equation 1, S ₄₅ is the shrinkage ratio in the direction of 45 degrees with respect to the film machine direction, and S ₁₃₅ is the shrinkage ratio in the direction of 135 degrees with respect to the film machine direction.

[Equation 2]

0.4 ≤ Length change in machine direction / Length change in width direction ≤ 2.0

In Equation 2, the length change means the length at the point of 120° C. - the initial length.

In one aspect of the present invention, the polyester multilayer film may have a center line average roughness Ra of 6 to 25 nm, and a 10-point average roughness Rz of 80 to 400 nm.

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

Specifically, the present invention is a polyester multilayer film composed of three or more layers including a core layer and a skin layer in which at least one layer is laminated on one or both surfaces of the core layer. More specifically, in one aspect of the present invention, one or more skin layers may be laminated on both sides of the core layer and the core layer.

The total thickness of the polyester multilayer film may be 25 to 125 μm, more preferably 50 to 100 μm, and may be suitably used for a display, which is produced as a thin film in the above range.

In addition, it is preferable that the core layer is 70 to 90% by weight of the entire film and the skin layer is 10 to 30% by weight because it is excellent in interfacial stabilization during co-extrusion, so that it is easy to form a film and a film with low surface roughness and shrinkage can be manufactured. Do.

The core layer is preferably made of a polyester resin, more specifically, a polyethylene terephthalate resin alone. In this case, it is preferable to use a polyethylene terephthalate resin having an intrinsic viscosity of 0.6 to 0.7 dl/g as the used polyethylene terephthalate resin because it has excellent heat resistance and does not cause interfacial instability during co-extrusion.

The skin layer laminated on one or both surfaces of the core layer may be laminated in one or two or more layers, and may be laminated by co-extrusion.

The skin layer contains a polyester resin having an intrinsic viscosity of 0.65 to 0.8 ㎗/g and inorganic particles, and interfacial instability does not occur in the range where the intrinsic viscosity satisfies the above range, and is stably laminated with the core layer to form a multilayer film It can be manufactured and is easy to process.

The skin layer may be used without limitation as long as it is an inorganic particle commonly used in the relevant field, and specifically, for example, silica, zeolite, kaolin, etc. may be used, but is not limited thereto. These particles come out to the surface of the film through the stretching process to improve the slip properties and winding properties of the film. The size and content of the inorganic particles are preferably used in a range that satisfies a center line average roughness Ra of 6 to 25 nm and a 10-point average roughness Rz of 80 to 400 nm. As an example to satisfy the above range, the inorganic particles may have an average particle diameter of 0.5 to 5 μm and a content of particles in the skin layer of 10 to 100 ppm. In the range where the centerline average roughness Ra and the 10-point average roughness Rz satisfy the above ranges, the coating property during the post-processing is excellent to satisfy the coating stability required by the user, and the transparency of the entire film is excellent for optical and touch panels, etc. It is suitable for use in the display of

If the average particle diameter is more than 5 μm, even if the particle content is less than 10 ppm, the transparency of the film is greatly reduced, and scratches may occur during the coating process. If the average centerline roughness Ra exceeds 25 nm and the 10-point average roughness Rz exceeds 400 nm, it may affect the optical properties of the final product, such as transfer of surface projections. Even when used in excess of 100 ppm, the transparency is low, so quality inspection is not easy during the coating process. As it deteriorates, scratches or blocking may occur during the coating process, resulting in uneven coating.

The polyester multilayer film of the present invention has a transparency of 2.5% or less based on 75 μm, and the thermal contraction rate in the 45 degree direction and 135 degree direction with respect to the film machine direction satisfies the following formula 1, and a thermomechanical analyzer (TMA) is used. Therefore, when measuring, the inflection point in the machine direction is 100 ~ 160 ℃, and after holding at 40 ℃ for 3 minutes, when the temperature is raised to 180 ℃ at 5 ℃ / min, the length change must satisfy all the physical properties that satisfy the following equation 2.

[Equation 1]

|S ₄₅ - S ₁₃₅ | ≤ 0.35

In Equation 1, S ₄₅ is the shrinkage ratio in the direction of 45 degrees with respect to the film machine direction, and S ₁₃₅ is the shrinkage ratio in the direction of 135 degrees with respect to the film machine direction.

[Equation 2]

0.4 ≤ Length change in machine direction / Length change in width direction ≤ 2.0

In Equation 2, the length change means the length at the point of 120° C. - the initial length.

More specifically, the transparency means haze measured according to JIS K 715, and is 2.5% or less, more specifically 0.5 to 2.5%, based on a laminated film having a total thickness of 75 μm. If the transparency is more than 2.5%, the transparency is low, so that it is not easy to check the quality of foreign substances during post-processing to use it as an optical film, so it cannot be used as an optical film.

In addition, it is preferable that the difference in the thermal contraction rate in the 45 degree direction and the 135 degree direction with respect to the film machine direction is 0.35 or less, and when it exceeds 0.35, the shrinkage is reduced in the process of going through a high temperature process in the post process for use as an optical film It is not preferable because twist curl occurs in the 45 degree and 135 degree directions.

In addition, when measuring using a thermomechanical analyzer (TMA), it is preferable that the inflection point in the machine direction is 100 ~ 160 °C, and it can be done within the above range. In the normal post-processing process, no shrinkage occurs, so the thermal deformation of the film is small. Here, the inflection point is when the base film is sampled in the machine direction and then measured by TMA, when the temperature is raised, it expands and contracts. The point at which it changes is called the inflection point. The inflection point in the machine direction is the same position in the width direction of the film, prepare three samples at different positions in the machine direction, measure each sample with a thermomechanical analyzer (TMA) to obtain the inflection point, and then It means that it is calculated from the average value.

In addition, when measuring using a thermomechanical analyzer (TMA), after maintaining at 40 ° C for 3 minutes, and then raising the temperature to 180 ° C at 5 ° C/min, the change in length in the machine direction at 120 ° C is less than 0.01 to 0.13%. Preferably, the change in length in the machine direction at 120 ° C. is difficult to achieve processally if it is less than 0.01%, and if it is 0.13% or more, it is difficult to achieve the physical properties of the product because the deformation of the film in the post-processing process is large.

The present invention is suitable for use as an optical film such as a thin display and a mobile phone within a range that satisfies all of the above physical properties.

The production of the polyester multilayer film including the core layer and the skin layer of the present invention is not limited, but can be obtained by extrusion and melting in at least two melt extruders, followed by casting, and biaxial stretching. More specifically, polyester is extruded in one extruder, and the polyester and additives such as silica, kaolin, and inorganic particles such as zeolite are simultaneously melt-extruded in another extruder, and then each melt meets in a feed block and co-extrudes After being cast, cooled, and then biaxially stretched sequentially, heat treatment and relaxation are performed. By controlling the stretching, heat treatment, and relaxation of these films, the physical properties of the film can be controlled.

More specifically, the method for producing the polyester multilayer film of the present invention is

a) A first polyester resin composition for a core layer comprising a polyester resin having an intrinsic viscosity of 0.6 to 0.7 dl/g, and a skin layer agent comprising a polyester resin having an intrinsic viscosity of 0.65 to 0.8 dl/g and inorganic particles 2 by melt-extruding the polyester resin composition to co-extrusion so that three or more layers are laminated;

b) preparing a film by biaxially stretching the co-extruded sheet to a range satisfying Equation 3 below;

[Equation 3]

E _MD × 1.1 ≤ E _TD ≤ E _MD × 1.5

In Equation 3, E _MD is the stretching ratio in the machine direction, and E _TD is the stretching ratio in the width direction.

c) heat-treating the stretched film while relaxing 1.1 to 2.0% in the machine direction and 2 to 12% in the width direction;

includes

In the present invention, after carrying out the stretching ratio in the range that satisfies Equation 3 as described above, heat treatment is performed while simultaneously relaxing 1.1 to 2.0% in the machine direction and 2 to 12% in the width direction. Since shrinkage does not occur, a film advantageous for post-processing can be produced.

Specifically, step a) is a step of manufacturing a polyester sheet by co-extruding the polyester resin constituting the base layer and the skin layer, then cooling and solidifying the polyester sheet with a casting drum, wherein the skin layer contains inorganic particles, Inorganic particles commonly used in the relevant field may be used without limitation, and specifically, for example, silica, zeolite, kaolin, etc. may be used, but the present invention is not limited thereto.

It is preferable that the intrinsic viscosity of the polyester resin used for the core layer is 0.6 to 0.7 dl/g, and the intrinsic viscosity of the polyester resin used for the skin layer is 0.65 to 0.8 dl/g.

The size and content of the inorganic particles are preferably used in a range that satisfies a center line average roughness Ra of 6 to 25 nm and a 10-point average roughness Rz of 80 to 400 nm. As an example to satisfy the above range, the inorganic particles may have an average particle diameter of 0.5 to 5 μm and a content of particles in the skin layer of 10 to 100 ppm. In the range where the centerline average roughness Ra and the 10-point average roughness Rz satisfy the above ranges, the coating property during the post-processing is excellent to satisfy the coating stability required by the user, and the transparency of the entire film is excellent for optical and touch panels, etc. It is suitable for use in the display of

Next, step b) is a step of preparing a film by stretching the co-extruded sheet, and may be uniaxially or biaxially stretched, preferably biaxially stretching.

More specifically, three or more layers are formed by co-extrusion, cooled on a casting roll and stretched in the machine direction by 2 to 4 times, more preferably 2 to 3.7 times. More preferably, it may be stretched 2.8 to 3.7 times, and when stretched in the width direction, 2.2 to 6 times, more preferably 3 to 5.5 times, and even more preferably 3.4 to 4.3 times. In the range where the stretching ratio in the machine direction is 2 to 4 times, the mechanical strength of the film is not reduced, and stretching in the width direction can be stably performed. In addition, in the width direction, the mechanical strength of the film is not reduced in the range of 2.2 to 6 times, and it is possible to prevent breakage of the film.

Step c) is a process of performing heat setting and relaxation, and the heat setting temperature may be performed at 200 to 245 ° C. During relaxation, 1.1 to 2.0% in the machine direction and 2 to 12% in the width direction are simultaneously relaxed. It is possible to provide a film having a low rate of thermal contraction at a high temperature by performing heat treatment while doing so.

The relaxation ratio can be calculated as follows.

Relaxation ratio (%) = (Maximum width length of film before relaxation treatment section - Minimum width length of film in relaxation treatment section) / Maximum width length of film before relaxation treatment section × 100

At this time, it is good to relax the machine direction and the width direction at the same time. If the machine direction is first relaxed and then relaxed in the width direction, even if the relaxation rate is high, it is difficult to lower the contraction rate in the width direction to 0.3% or less. It is difficult to lower below. In addition, if the relaxation rate in the machine direction is less than 1.1%, it is difficult to lower the shrinkage rate in the machine direction to less than 0.4%. can give In addition, when the relaxation rate in the width direction is less than 2%, it is difficult to make the contraction rate in the width direction less than 0.4%. It may cause scratches due to friction with the equipment, and operation may be quite difficult.

Specifically, the film produced by the above manufacturing method has a transparency of 2.5% or less based on 75 μm, and the thermal contraction rate in the 45 degree direction and 135 degree direction with respect to the film machine direction satisfies Equation 1 below, and a thermomechanical analyzer (TMA) The inflection point in the machine direction is 100 ~ 160 °C when measured using

[Equation 1]

|S ₄₅ - S ₁₃₅ | ≤ 0.35

In Equation 1, S ₄₅ is the shrinkage ratio in the direction of 45 degrees with respect to the film machine direction, and S ₁₃₅ is the shrinkage ratio in the direction of 135 degrees with respect to the film machine direction.

[Equation 2]

0.4 ≤ Length change in machine direction / Length change in width direction ≤ 2.0

In Equation 2, the length change means the length at the point of 120° C. - the initial length.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples. However, the following examples and comparative examples are merely examples for explaining the present invention in more detail, and the present invention is not limited by the following examples and comparative examples.

1) Intrinsic Viscosity

Add 0.4 g of PET pellets (sample) to 100 ml of reagent mixed with phenol and 1,1,2,2-tetrachloroethanol in a weight ratio of 6:4 and dissolve for 90 minutes, then transfer to an Uberode viscometer and place in a thermostat at 30°C was maintained for 10 minutes, and the number of seconds of falling of the solution was calculated using a viscometer and an aspirator. The number of seconds of falling of the solvent was obtained in the same way, and then R.V and I.V values were calculated by Equations 1 and 2 below.

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

[Equation 1]

[Equation 2]

2) Transparency

A specimen of the film formed was measured according to JIS K 715 using a HAZE METER (model name: Nipon denshoku, Model NDH 5000).

3) Surface roughness

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

4) heat shrinkage

After cutting the film to a size of 200 × 200mm, measuring the length and width, heat treatment in a hot air oven at 140°C for 60 min. At this time, length changes in the machine direction and the machine direction in the 45 degree direction, 135 degree direction, and the width direction were measured together.

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

5) Thermomechanical analyzer (TMA) measurement

After cutting the specimen of the film to 16 mm in the machine direction and 4.5 mm in the width direction, the thermal deformation length (Dimension change) was measured using TMA (TA, TMA Q400).

The measurement method was maintained for 3 minutes at 40 ℃ isothermal, then heated to 180 ℃ at 5 ℃/min, the inflection point, the point at which expansion and contraction change, and the length change at 120 ℃ point were measured.

[Example 1]

Polyethylene terephthalate (PET) having an intrinsic viscosity of 0.65 dL/g is used for the core layer, PET having an intrinsic viscosity of 0.64 dL/g and 70 ppm of silica particles having an average particle diameter of 2.5 μm are used for co-extrusion, respectively. The skin layer/core layer/skin layer was co-extruded into a laminated three-layer film, and cast on a cooling roll to prepare an unstretched sheet. In this case, the core layer was 80% by weight of the total film weight, and the skin layer was 20% by weight of the total film weight. It was sequentially stretched 3.8 times in the machine direction and 3.4 times in the width direction, and heat-treated while simultaneously relaxing at 230° C. at 1.2% in the machine direction and 3.0% in the width direction to prepare a film with a total thickness of 75 μm.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Examples 2 and 3]

A film was prepared in the same manner as in Example 1, except that the intrinsic viscosity of the skin layer raw material was changed as shown in Table 1 below.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Examples 4 and 5]

A film was prepared in the same manner as in Example 1, except that the weight of the skin layer was changed as shown in Table 1 below.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Examples 6 and 7]

A film was prepared in the same manner as in Example 1, except that the particle content of the skin layer was changed as shown in Table 1 below.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Examples 8 and 9]

A film was prepared in the same manner as in Example 1, except that the particle size and content of the skin layer were changed as shown in Table 1 below.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Examples 10 to 13]

A film was prepared in the same manner as in Example 1, except for changing the relaxation rates in the machine direction and the width direction as shown in Table 1 below.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Example 14]

It was carried out in the same manner as in Example 1, except that the draw ratio in the machine direction was 2.8 times and the draw ratio in the width direction was 4.3 times, and the rest were carried out in the same way.

[Comparative Examples 1 and 2]

A film was prepared in the same manner as in Example 1, except that the relaxation rates in the machine direction and the width direction were changed as shown in Table 1 below.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Comparative Examples 3 and 4]

It was carried out as shown in Table 1 below, except that relaxation in the machine direction and relaxation in the width direction were sequentially and reversely performed, and the rest of the film was prepared in the same manner as in Example 1.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Comparative Examples 5 and 6]

A film was prepared in the same manner as in Example 1, except that the intrinsic viscosity of the skin layer was changed as shown in Table 1 below.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Comparative Examples 7 and 8]

A film was prepared in the same manner as in Example 1, except that the content of the skin layer was changed as shown in Table 1 below.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Comparative Examples 9 to 12]

A film was prepared in the same manner as in Example 1, except that the particle size and content of the skin layer were changed as shown in Table 1 below.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Comparative Examples 13 to 16]

A film was prepared in the same manner as in Example 1, except for changing the relaxation rates in the machine direction and the width direction as shown in Table 1 below.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Comparative Example 17]

A film was prepared in the same manner as in Example 1 except that the draw ratio in the machine direction was 2.7 times and the draw ratio in the width direction was 4.4 times.

The physical properties of the prepared film were measured and shown in Table 2 below.

[Comparative Example 18]

A film was prepared in the same manner as in Example 1 except that the draw ratio in the machine direction was 3.9 times and the draw ratio in the width direction was 3.4 times.

The physical properties of the prepared film were measured and shown in Table 2 below.

division layer composition Raw material composition film production conditions Skin layer composition relaxation rate relaxation order Core layer weight Skin layer weight inherence
Viscosity particle
size
(μm) particle amount
(ppm) machine
direction width
direction Example 1 80%
20%
0.64 2.5 70 1.2 3.0 The same time Example 2 0.75 Example 3 0.6 Example 4 60% 40% 0.64
Example 5 90% 10% Example 6 80% 20% 100 Example 7 30 Example 8 5 10 Example 9 0.5 100 Example 10 2.5 70 1.5 3.0 Example 11 1.8 Example 12 1.2 2.0 Example 13 12.0 Example 14 3.0 Comparative Example 1 80% 20% 0.64 2.5 70 0 3.0 The same time Comparative Example 2 1.2 0 Comparative Example 3 1.2 3.0 Machine->Width Comparative Example 4 1.2 3.0 width->machine Comparative Example 5 0.55 1.2 3.0 The same time Comparative Example 6 0.85 Comparative Example 7 56% 44% 0.64
Comparative Example 8 95% 5% Comparative Example 9 80% 20% 0.5 110 Comparative Example 10 5 20 Comparative Example 11 0.4 110 Comparative Example 12 6 10 Comparative Example 13 2.5 70 0.8 3.0 Comparative Example 14 0.5 3.0 Comparative Example 15 1.2 1.0 Comparative Example 16 13.0 Comparative Example 17 0.64 1.2 3.0 Comparative Example 18 0.64

*Co-extrusion with A/B/A. (The weight of the skin layer is the total amount of both layers A)

division surface roughness transparency 140℃ heat shrinkage
(%) Equation (1) value
TMA ceremony
(2)
value Length
direction
inflection point
(℃) Ra
(nm) Rz
(nm) 45 degrees 135 degrees machine direction
Dimension change(㎛) Dimension change in the width direction (㎛) Example 1 13 350 1.0 0.35 0.2 0.15 30 29 1.03 140 Example 2 12 335 1.1 0.37 0.17 0.20 31 28 1.1 138 Example 3 14 345 1.1 0.34 0.2 0.14 30 29 1.03 137 Example 4 16 390 1.5 0.35 0.18 0.17 30 28 1.07 140 Example 5 14 320 0.8 0.36 0.15 0.21 31 27 1.15 142 Example 6 20 395 1.8 0.35 0.2 0.15 30 29 1.03 140 Example 7 10 108 0.6 0.35 0.18 0.17 31 28 1.1 140 Example 8 15 340 0.9 0.34 0.19 0.15 30 28 1.07 139 Example 9 16 350 1.2 0.34 0.19 0.15 30 29 1.03 139 Example 10 13 345 1.0 0.32 0.17 0.15 29 28 1.03 125 Example 11 13 340 1.0 0.28 0.15 0.13 28 27 1.03 115 Example 12 13 350 1.1 0.35 0.30 0.05 30 33 0.91 135 Example 13 12 350 1.0 0.32 0.01 0.31 30 24 1.25 135 Example 14 8 110 0.9 0.32 0.2 0.12 32 26 1.23 110 Comparative Example 1 13 345 1.0 0.75 0.20 0.55 -1.5 29 -0.05 91 Comparative Example 2 13 320 1.0 0.34 4.0 3.66 22 58 0.38 112 Comparative Example 3 13 350 1.0 0.70 0.05 0.65 25 60 0.41 89 Comparative Example 4 13 350 1.0 0.60 0.10 0.50 26 50 0.52 91 Comparative Example 5 Impossible to manufacture products due to interfacial instability and fracture Comparative Example 6 Operation impossible due to interfacial instability and continuous fracture Comparative Example 7 Operation impossible due to interfacial instability and continuous fracture Comparative Example 8 Operation impossible due to interfacial instability and continuous fracture Comparative Example 9 28 440 3.8 0.35 0.18 0.17 30 29 1.03 115 Comparative Example 10 30 370 3.5 0.32 0.12 0.20 29 29 1.0 135 Comparative Example 11 25 350 3.4 0.35 0.10 0.25 30 31 0.98 135 Comparative Example 12 28 390 3.7 0.35 0.11 0.24 31 30 1.03 138 Comparative Example 13 13 350 1.1 0.55 0.12 0.43 -1.0 38 -0.03 102 Comparative Example 14 13 345 1.1 0.65 0.15 0.50 -0.8 41 -0.02 95 Comparative Example 15 13 350 1.0 0.35 0.90 0.55 30 41 0.73 137 Comparative Example 16 Due to severe film sagging inside the tenter, front scratching and winding are impossible. Comparative Example 17 Unable to operate due to continuous breakage in the tenter Comparative Example 18 Operation impossible because the edge thickness control is not available

Claims (9)

A polyester multilayer film composed of three or more layers by co-extrusion of a polyester resin,
Transparency is 2.5% or less based on 75㎛, and the thermal contraction rate in the 45 degree direction and 135 degree direction with respect to the film machine direction satisfies Equation 1 below, and the inflection point in the machine direction when measured using a thermomechanical analyzer (TMA) It is 100 ~ 160 ℃, after holding at 40 ℃ for 3 minutes, the length change when the temperature is raised to 180 ℃ at 5 ℃ / min satisfies Equation 2 below.
[Equation 1]
|S ₄₅ - S ₁₃₅ | ≤ 0.35
In Equation 1, S ₄₅ is the shrinkage ratio in the direction of 45 degrees with respect to the film machine direction, and S ₁₃₅ is the shrinkage ratio in the direction of 135 degrees with respect to the film machine direction.
[Equation 2]
0.4 ≤ Length change in machine direction / Length change in width direction ≤ 2.0
In Equation 2, the length change means the length at the point of 120 ° C - the initial length,
The transparency means haze measured according to JIS K 715.
The method of claim 1,
The polyester multilayer film is a polyester multilayer film of three or more layers, including a core layer and a skin layer in which at least one layer is laminated on one or both sides thereof.
3. The method of claim 2,
The skin layer is a polyester multilayer film comprising a polyester resin having an intrinsic viscosity of 0.65 to 0.8 dl/g and inorganic particles.
4. The method of claim 3,
The inorganic particles have an average particle diameter of 0.5 to 5 μm, and the content of particles in the skin layer is 10 to 100 ppm of a polyester multilayer film.
5. The method of claim 4,
The polyester multilayer film is a polyester multilayer film having a center line average roughness Ra of 6 to 25 nm, and a 10-point average roughness Rz of 80 to 400 nm.
3. The method of claim 2,
The polyester multilayer film has a total thickness of 25 to 125 μm, the core layer is 70 to 90% by weight of the entire film, and the skin layer is 10 to 30% by weight of the polyester multilayer film.
a) A first polyester resin composition for a core layer comprising a polyester resin having an intrinsic viscosity of 0.6 to 0.7 dl/g, and a skin layer agent comprising a polyester resin having an intrinsic viscosity of 0.65 to 0.8 dl/g and inorganic particles 2 by melt-extruding the polyester resin composition to co-extrusion so that three or more layers are laminated;
b) preparing a film by biaxially stretching the co-extruded sheet to a range satisfying Equation 3 below;
[Equation 3]
E _MD × 1.1 ≤ E _TD ≤ E _MD × 1.5
In Equation 3, E _MD is the stretching ratio in the machine direction, and E _TD is the stretching ratio in the width direction.
c) heat-treating the stretched film while simultaneously relaxing 1.1 to 2.0% in the machine direction and 2 to 12% in the width direction;
A method for producing a polyester multilayer film comprising:
The polyester multilayer film has a transparency of 2.5% or less based on 75 μm, and the thermal contraction rate in the 45 degree direction and 135 degree direction with respect to the film machine direction satisfies Equation 1 below, and was measured using a thermomechanical analyzer (TMA). The inflection point in the machine direction is 100 ~ 160 ℃, and after holding at 40 ℃ for 3 minutes, the length change when the temperature is raised to 180 ℃ at 5 ℃ / min satisfies the following Equation 2 A method for producing a polyester multilayer film.
[Equation 1]
|S ₄₅ - S ₁₃₅ | ≤ 0.35
In Equation 1, S ₄₅ is the shrinkage ratio in the direction of 45 degrees with respect to the film machine direction, and S ₁₃₅ is the shrinkage ratio in the direction of 135 degrees with respect to the film machine direction.
[Equation 2]
0.4 ≤ Length change in machine direction / Length change in width direction ≤ 2.0
In Equation 2, the length change means the length at the point of 120 ° C - the initial length,
The transparency means haze measured according to JIS K 715.
8. The method of claim 7,
The stretching ratio in the machine direction is 2 to 4 times, and the stretching ratio in the width direction is 2.2 to 6 times.
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