TW202214415A - Polyester film and method for preparing the same - Google Patents

Abstract

The present disclosure relates to a polyester film and a method for preparing the same. According to the present disclosure, there is provided a polyester film having excellent drivability and winding properties with low surface roughness, and a method for preparing the same. The polyester film may be suitably used as a base film for release in the manufacture of a multi-layer ceramic capacitor (MLCC), a polarizing plate, and an optically transparent adhesive.

Description

Polyester film and preparation method thereof

The present disclosure is related to a polyester film and a method for preparing the same.

Polyester films have excellent physical stability over a wide temperature range from low to high temperatures, and have excellent chemical resistance compared to other polymer resins. In addition, mechanical strength, surface properties, and thickness uniformity are good, so it can be applied to various purposes. Therefore, polyester films are being applied to capacitors, photographic films, labels, pressure-sensitive tapes, decorative laminates, transfer tapes, polarizing plates, ceramic green sheets for release, and the like, And the demand is gradually increasing.

Among these, in the case of films for electronic materials, the optical market has recently stagnated and competition has intensified, thus requiring higher levels of physical properties and cost reduction.

According to the trend of miniaturization of electronic devices, electronic components such as capacitors and inductors are also being miniaturized, and the ceramic green sheets themselves are also being thinned. Recently, stacking more ceramic layers in the same volume by thinning ceramic green sheets has become a major problem.

The ceramic green sheet is a thin ceramic sheet prepared by coating a ceramic slurry on a silicone release layer formed on the surface of a polyester film. During the process of manufacturing ceramic capacitors or the like, the polyester film is removed.

In general, particles for controlling surface roughness are added to polyester films. However, when the surface roughness of the polyester film is high, the film itself can satisfy drivability and winding properties, but there is a problem that the protruding shapes of particles protruding from the surface of the polyester film are transferred to the silicone release layer. Transfer problems result in reduced workability, such as unbalanced coating and pinholes in the ceramic layer laminated on the polyester film.

On the contrary, in the case of reducing the surface roughness of the polyester film, when the ceramic slurry is applied on the polyester film, the coating stability and drivability of the film are deteriorated, and the forming roll may be damaged during winding on the roll fall off. In addition, during the process of applying the silicone release layer to the surface of the polyester film, defects such as scratches may appear on the surface of the film.

Therefore, there is an increasing demand for polyester films having excellent physical properties while solving the above problems.

[technical problem]

In the present disclosure, there is provided a polyester film having excellent driveability and winding properties with low surface roughness, which is a base film for a polyester release film.

In addition, a method for producing the polyester film is also provided. [Technical Solutions]

According to an embodiment of the present disclosure, there is provided a method for preparing a polyester film, the method comprising the following steps A melt of a resin composition containing a polyester resin was supplied on an embossing roll having a concavo-convex pattern formed on its outer circumferential surface to obtain an unstretched film having a concavo-convex surface corresponding to the concavo-convex pattern.

In one embodiment, the melt supplied on the embossing roll may have a temperature of 200°C to 300°C.

In one embodiment, the embossing roll may have an outer surface temperature of 25°C to 130°C.

In one embodiment, the melt supplied on the embossing roll may be embossed while being cast by the embossing roll.

In one embodiment, the melt supplied on the embossing roll may pass through a gap between the embossing roll and a nip roll adjacent to the embossing roll.

In one embodiment, the nip roll may have an outer surface temperature of 25°C to 130°C.

In one embodiment, the concavo-convex pattern formed on the outer circumferential surface of the embossing roller may have a depth of the concave portion may be 5 to 100 μm and a period of the concave portion may be 10 to 100 μm microns.

In one embodiment, the concavo-convex pattern formed on the outer circumferential surface of the embossing roller may have a cross-sectional shape having an arc or a cross-sectional shape having one or more inner corners.

In one embodiment, the method may further include the step of uniaxially or biaxially stretching the unstretched film having the uneven surface.

In one embodiment, the stretching may be performed 2 to 6 times in the machine direction (MD) of the unstretched film, or in the machine direction (MD) of the unstretched film, respectively. MD) and on the transverse direction (TD) of the unstretched film from 2 to 6 times.

According to another embodiment of the present disclosure, there is provided a polyester film having a concavo-convex surface on one surface and having a centerline average of 7.0 nm or more according to JIS B-0601:1994 standard Roughness (Ra).

In one embodiment, the concavo-convex surface has a height of the convex portion that may be 0.1 to 50 μm and a period of the convex portion that may be 50 to 400 μm.

In one embodiment, the relief surface may have a cross-sectional shape having an arc.

In one embodiment, the polyester film may have a coefficient of static friction (μS) of 0.40 or less and a coefficient of dynamic friction (μD) of 0.40 or less according to the standard test method of ASTM-D-1894.

Hereinafter, the polyester film and the method for preparing the polyester film according to embodiments of the present invention will be explained in more detail.

Unless otherwise defined in this disclosure, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the relevant art to which this invention belongs. Therefore, the phraseology used in the detailed description is for the purpose of illustrating particular embodiments only and is not intended to limit the invention.

The singular expressions of the present disclosure may also include the plural expressions unless they are expressed differently in the context.

The terms "include," "comprise," and similar terms in this disclosure are used to designate certain features, regions, integers, steps, operations, elements, and/or components, and these do not exclude certain other features , region, integer, step, operation, element, component and/or group presence or addition.

Since the invention is capable of various modifications and forms, specific embodiments of the invention are shown by way of example and will be described in detail. However, it is not intended to limit the present invention to the specific forms disclosed, and it should be understood that the present invention includes all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention.

In this disclosure, when terms such as "on", "above", "below" and "next" are used to describe the positional relationship between two components, unless The terms are used in conjunction with the terms "immediately" or "directly", otherwise one or more other components may also be located between the two components.

In the context of describing a temporal relationship, for example, when terms such as "after", "subsequent to", "next to", and "before" are used to describe the temporal order relationship, unless the term is used in conjunction with the term "immediately" or "directly," the situation may also include situations where the chronological relationship is discontinuous.

In this disclosure, the term "at least one" includes all possible combinations of one or more related items. I. Method for making polyester film

According to an embodiment of the present disclosure, there is provided a method for preparing a polyester film, the method comprising the following steps A melt of a resin composition containing a polyester resin was supplied on an embossing roll having a concavo-convex pattern formed on the outer circumferential surface to obtain an unstretched film having a concavo-convex surface corresponding to the concavo-convex pattern.

In general, particles for controlling surface roughness are added to polyester films. Particles protrude on the surface of the polyester to increase surface roughness. The polyester film whose surface roughness is increased by adding particles can exhibit excellent driveability and winding properties. However, the protruding shapes of the particles protruding from the surface of the polyester film are transferred to the release layer, and transfer problems lead to reduced workability, such as causing uneven coating and pinning of other layers laminated on the polyester film hole.

However, as a result of studies by the present inventors, it was confirmed that an unstretched film was obtained by supplying a melt of a resin composition containing a polyester resin on an embossing roll having a concavo-convex pattern formed on the outer circumferential surface, followed by stretching stretch to provide a polyester film with excellent driveability and winding properties with low surface roughness.

The polyester film provided according to the production method of the embodiment has a concavo-convex surface formed by an embossing roller. That is, in the method for producing a polyester film according to the embodiment, unlike the conventional method of controlling the surface roughness by adding particles, the uneven surface is formed on one surface of the film by using the embossing roller, Appropriate surface roughness can be provided without the inclusion of particles. Therefore, the above-mentioned problems caused by the conventional protruding particles can be solved by the preparation method of the embodiment. In addition, the polyester film provided according to the production method of the embodiment can exhibit excellent drivability and winding properties by the concavo-convex surface formed on one surface.

The polyester film having these properties can be suitably used as a base film for release in the manufacture of multilayer ceramic capacitors (MLCCs) for high smoothing, polarizing plates, and optically transparent adhesives.

In one embodiment of the present disclosure, the resin composition contains polyester resin.

The resin composition may contain two or more types of polyester resins having different compositions.

Optionally, a pinning agent, an antistatic agent, an ultraviolet stabilizer, a water repellant, a slip agent, a heat stabilizer, and the like may be added to the resin composition to which the present invention belongs. Additives commonly used in technology.

In addition, the resin composition may further contain: inorganic particles, such as calcium carbonate, titanium oxide, silica, kaolin and barium sulfate; organic particles, such as silicone resin, cross-linked divinyl benzene polymethacrylate, cross-linked Linked polymethacrylates, cross-linked polystyrene resins, benzoguanamine-formaldehyde resins, benzoguanamine-melamine-formaldehyde resins, and melamine-formaldehyde resins; or mixtures thereof.

The additives and particles may be added during the polymerization of the polyester resin, during the preparation of a master batch chip containing the polyester resin, or during the preparation of the resin composition.

In an embodiment of the present disclosure, the type of polyester resin is not particularly limited.

The polyester resin can be obtained by polycondensation of an acid component containing a dicarboxylic acid as a main component and a diol component containing an alkylene glycol as a main component.

As the dicarboxylic acid, terephthalic acid or its alkyl or phenyl ester can be used. In addition, bifunctional carboxylic acids such as isophthalic acid, ethylparaben, adipic acid, sebacic acid, and sodium 5-sulfoisophthalic acid or ester-forming derivatives thereof can be used as the acid component.

Ethylene glycol can be mainly used as the glycol component, and propylene glycol, neopentyl glycol, trimethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4 - Dioxyethoxybenzene, bisphenol, polyoxyethylene glycol and the like can be used together.

As a non-limiting example, 50 mol % of the diol component containing diethylene glycol and ethylene glycol in a molar ratio of 5:5 can be obtained with 50 mol % of a diol component containing in a molar ratio of 8.5:1.5 Polycondensation of acid components of terephthalic acid and sulfoterephthalic acid to obtain polyester resins.

Preferably, polyethylene terephthalate (PET), polyethylene naphthalate or the like can be used as the polyester resin.

It may be advantageous for the polyester resin to have a weight average molecular weight of 40,000 g/mol to 70,000 g/mol so that the polyester film has suitable solvent resistance and mechanical properties. Preferably, the weight average molecular weight of the polyester resin may be 40,000 g/mol to 70,000 g/mol, 45,000 g/mol to 65,000 g/mol or 50,000 g/mol to 60,000 g/mol .

In the present disclosure, the weight average molecular weight means the weight average molecular weight converted by polystyrene measured by gel permeation chromatography (GPC). In the measurement of the weight-average molecular weight using polystyrene conversion by GPC measurement, well-known analysis devices, detectors such as refractive index detectors, and columns for analysis can be used, and commonly used temperature conditions, solvents and flow rates.

50毫米）與兩根安捷倫PL凝膠5微米混合D管柱（Agilent PLgel 5 μm Mixed D）（7.5

300毫米）串聯連接的管柱，且使用安捷倫1260無限II系統（Agilent 1260 Infinity Ⅱ System）RI檢測器在40℃下進行了量測。透過0.45微米孔徑注射器過濾器對藉由將具有各種分子量的聚苯乙烯以為0.1（重量/重量）%的濃度溶解於四氫呋喃中而獲得的聚苯乙烯標準樣品（STD A、B、C、D）進行了過濾，且然後注射至GPC中，以使用自此形成的校準曲線獲得聚合物的重量平均分子量（Mw）。 STD A（Mp）：791,000/27,810/945 STD B（Mp）：282,000/10,700/580 STD C（Mp）：126,000/4430/370 STD D（Mp）：51,200/1920/162 As a specific example of measurement conditions, a polymer resin was dissolved in tetrahydrofuran (THF) at a concentration of 1.0 (w/w) % (solid content of about 0.5 (w/w) %), and then 0.45 micron was used A pore size syringe filter was filtered and 20 microliters were injected into the GPC. The mobile phase of the GPC was tetrahydrofuran (THF) and flowed at a flow rate of 1.0 ml/min. Use one of the Agilent PLgel 5 μm Guard columns (Agilent PLgel 5 μm Guard) (7.5

50 mm) with two Agilent PLgel 5 μm Mixed D columns (Agilent PLgel 5 μm Mixed D) (7.5

300 mm) columns connected in series and measured at 40°C using an Agilent 1260 Infinity II System RI detector. Polystyrene standards (STD A, B, C, D) obtained by dissolving polystyrene with various molecular weights in tetrahydrofuran at a concentration of 0.1 (w/w) % through a 0.45 micron pore size syringe filter Filtration was performed and then injected into GPC to obtain the weight average molecular weight (Mw) of the polymer using a calibration curve formed therefrom. STD A (Mp): 791,000/27,810/945 STD B (Mp): 282,000/10,700/580 STD C (Mp): 126,000/4430/370 STD D (Mp): 51,200/1920/162

The resin composition containing the polyester resin is heated in a melt extruder to form a melt having a temperature of 200°C to 300°C.

1 , a melt of a resin composition containing a polyester resin is continuously extruded by a T-die 10 provided at one end of the melt extruder.

The melt extruded from the T-die 10 is supplied on the embossing roll 20 having a concavo-convex pattern formed on its outer circumferential surface.

The melt supplied on the embossing roll 20 is cooled and processed into a film. That is, the melt supplied on the embossing roll 20 is embossed while being cast by the embossing roll 20 .

The embossing roller 20 has a concave-convex pattern formed on the outer circumferential surface of the embossing roller 20 , the concave-convex pattern including repeated and continuous concave and convex portions. Therefore, the unstretched film 100 having the uneven surface corresponding to the uneven pattern is obtained by the film processing. Film processing of the melt and formation of the uneven surface are performed simultaneously and continuously.

The concavo-convex pattern formed on the outer circumferential surface of the embossing roller 20 may have a cross-sectional shape having an arc. That is, the concavo-convex pattern may have a circular shape such as an arc or circular arc whose cross section does not have an inner angle.

In addition, the concavo-convex pattern formed on the outer circumferential surface of the embossing roller 20 may have a cross-sectional shape having one or more inner corners. Herein, an inner angle refers to an angle formed in a cross section of a concavo-convex pattern by connecting two or more straight lines. For example, when there is one interior angle, it means a triangular cross-section, and when there are two interior angles, it means a rectangular cross-section. Preferably, the concavo-convex pattern may have a cross-sectional shape having 1 to 5 inner corners.

As a non-limiting example, the concavo-convex pattern formed on the outer circumferential surface of the embossing roller may have conical, triangular pyramid or quadrangular pyramid-type concave portions, wherein the concave portion of the concavo-convex pattern has a triangular cross-section.

In one embodiment of the present disclosure, the concave-convex pattern formed on the outer circumferential surface of the embossing roller 20 has a depth of the concave portion that may be 5 to 100 μm and a period of the concave portion that may be 10 to 100 μm.

The depth of the concave portion means the vertical distance from the outer circumferential surface of the embossing roller 20 to the deepest point of the concave portion. The period of a concave portion means the length of an arc connecting any point of any concave portion with a corresponding point of another concave portion adjacent to said arbitrary concave portion.

Preferably, the concave-convex pattern formed on the outer circumferential surface of the embossing roller 20 has a depth of the concave portion of 5 μm to 50 μm or 5 μm to 20 μm; and the period of the concave portion may be 10 μm to 70 μm or 30 μm. microns to 60 microns.

Preferably, the ratio (T:D) of the period (T) of the concave portion to the depth (D) of the concave portion is 1:0.1 to 1:2, 1:0.1 to 1:1.5, 1:0.15 to 1:1 or 1:0.15 to 1:0.5.

In the concave-convex pattern, when the depth (D) of the concave portion is increased compared to the period (T) of the concave portion, it is difficult for the melt of the resin composition to penetrate into the concave-convex pattern, so that a uniform concave-convex surface may not be obtained. Therefore, the ratio (T:D) is preferably 1:2 or less.

However, when the depth (D) of the concave portion is too small compared to the period (T), the height of the uneven surface formed on the unstretched film is low, and the height of the uneven surface is increased by stretching the unstretched film. It is further reduced, making it difficult to have an appropriate surface roughness. Therefore, the ratio (T:D) is preferably 1:0.1 or more.

Meanwhile, the melt supplied on the embossing roller 20 preferably has a temperature of 200°C to 300°C.

That is, in order to maintain sufficient processability of the resin composition in the molten state, the melt preferably has a temperature of 200°C or higher. However, when the resin composition is heated to a high temperature, the components may be denatured due to deterioration, and the cooling efficiency of the melt in the embossing roller 20 may decrease. Therefore, it is preferable that the melt has a temperature of 300°C or lower.

Specifically, the embossing roller 20 preferably has an outer surface temperature of 25°C to 130°C. Specifically, the embossing roller 20 may have an outer surface temperature of 25°C to 130°C, 25°C to 100°C, 30°C to 100°C, or 30°C to 80°C.

The degree of crystallinity increases as polyester resins (especially polyethylene terephthalate) are heated. However, when the degree of crystallinity is excessively increased, the fracture rate may increase during stretching. Therefore, the temperature of the outer surface of the embossing roller 20 is preferably 130°C or less, 100°C or less, or 80°C or less.

However, when the melt is processed at a low temperature, the uneven pattern may not be properly formed on the melt. Therefore, the temperature of the outer surface of the embossing roller 20 is preferably 25°C or higher or 30°C or higher.

Referring to FIG. 2 , the melt supplied on the embossing roll 20 may pass through a gap (also referred to as a nip) between the embossing roll 20 and a nip roll 30 adjacent to the embossing roll 20 . Thereby, an unstretched film having a uniform thickness and a uniform uneven pattern can be obtained.

The size of the gap can be determined in consideration of the thickness of the polyester film. For example, the size of the gap may be 200 microns to 2000 microns.

In order to perform film processing using the embossing roll 20 and the nip roll 30 more efficiently, the material of the nip roll 30 is preferably metal or polymer.

Here, the pressure applied by the nip roll 30 to the embossing roll 20 is important. When a constant pressure is applied by the nip roll 30, the melt penetrates into the concavo-convex pattern formed on the embossing roll 20, and is cooled, thereby forming an unstretched film having a concavo-convex surface corresponding to the concavo-convex pattern.

Preferably, the pressure applied by the nip roller 30 to the embossing roller 20 may be 1 kgf/cm2 to 100 kgf/cm2 or 1 kgf/cm2 to 50 kgf/cm2. In order to make the melt penetrate well into the concave-convex pattern of the embossing roller 20, the pressure applied by the nip roller 30 to the embossing roller 20 is preferably 1 kgf/cm2 or more. However, when the pressure is too high, it can be difficult to control the thickness of the melt passing through the gap. Therefore, the pressure applied by the nip roll 30 to the embossing roll 20 is preferably 100 kgf/cm2 or less or 50 kgf/cm2 or less.

To achieve improved workability, it may be preferable that the nip roll 30 has an outer surface temperature equivalent to that of the embossing roll 20 . For example, the nip roll 30 may have an outer surface temperature of 25°C to 130°C, 25°C to 100°C, 30°C to 100°C, or 30°C to 80°C.

Meanwhile, according to another embodiment of the present disclosure, as shown in FIG. 3 , an imprint nip roll 35 having a concavo-convex pattern on an outer circumferential surface may be performed to obtain an untouched surface having a concavo-convex surface corresponding to the concavo-convex pattern. Steps to stretch the film.

Specifically, the step of supplying the melt of the resin composition containing the polyester resin on the casting roll 25 and by passing the melt through the casting roll 25 and adjacent to and adjacent to the casting roll 25 may be performed. A step of forming a gap between the embossing nip rolls 35 having a concavo-convex pattern on the outer circumferential surface to obtain an unstretched film having a concavo-convex surface corresponding to the concavo-convex pattern.

Here, the description of the concavo-convex pattern formed on the outer circumferential surface of the embossing nip roll 35 may refer to the description of the concavo-convex pattern formed on the outer circumferential surface of the above-mentioned embossing roll 20 .

Meanwhile, an unstretched film (or referred to as a "casting sheet") having a concavo-convex surface corresponding to the concavo-convex pattern is obtained by the above-described method.

In one embodiment of the present disclosure, the unstretched film obtained by the above method may have a concave-convex surface corresponding to the concave-convex pattern on one surface thereof.

In general, depending on the viscosity of the melt of the resin composition, the density of the concavo-convex pattern, the processing speed, and the like, the degree to which the melt of the resin composition fills the concavo-convex pattern formed on the outer circumferential surface of the platen roller can vary. Therefore, the height of the convex portion of the concavo-convex surface of the unstretched film may be equal to or smaller than the depth of the concave portion of the concavo-convex pattern.

Meanwhile, the method for producing a polyester film may further include a step of uniaxially or biaxially stretching the unstretched film having the uneven surface.

Uniaxial stretching can be performed in the machine direction (called MD or longitudinal direction) or the transverse direction (called TD or width direction) of the unstretched film.

It can be by sequential stretching in the machine direction (MD) of the unstretched film, followed by stretching in the transverse direction (TD) of the unstretched film, or by simultaneous stretching in the machine direction (MD) and transverse direction (TD) Simultaneously stretch to perform biaxial stretching.

The stretching may be performed 2 to 6 times in the machine direction (MD) of the unstretched film, or 2 to 6 times in the machine direction (MD) of the unstretched film and in the transverse direction (TD) of the unstretched film Second-rate. For example, uniaxial stretching can be performed 2 to 6 times in the machine direction (MD) or in the transverse direction (TD). Biaxial stretching can be performed 2 to 6 times in the machine direction (MD) and in the transverse direction (TD), respectively.

The stretched film obtained by the stretching step has a reduced thickness compared to the unstretched film, and the shape of the uneven surface formed on one surface thereof is changed.

Referring to FIG. 4 , changes in the uneven surface and its cross-sectional shape can be confirmed from sequential biaxial stretching of the unstretched film. (a) of FIG. 4 shows an unstretched film having a concavo-convex surface corresponding to the concavo-convex pattern. As shown in (b) of FIG. 4 , when the unstretched film is stretched in the longitudinal direction, the height of the convex portion of the uneven surface decreases, the period of the convex portion increases, and the thickness of the film decreases. As shown in (c) of FIG. 4 , when the film stretched in the longitudinal direction is stretched in the transverse direction, the height of the convex portion of the uneven surface is further reduced, the period of the convex portion is further increased, and the thickness of the film is further reduced. further reduced.

5 is a cross-sectional view of a polyester film according to the present disclosure, wherein (a) shows the unstretched film 100 and (b) shows the stretched film 105 .

In one embodiment of the present disclosure, in the case of an unstretched film having a concavo-convex surface on one surface, the period (T) of the convex portion of the concavo-convex surface is increased by stretching, and the height (H) of the convex portion lowered by stretching.

Preferably, the stretched film obtained by stretching may have an uneven surface on one surface thereof, wherein the depth of the convex portion is 0.1 to 50 μm, 0.2 to 20 μm, or 0.4 to 10 μm, and the convex portion has a depth of 0.1 to 50 μm, 0.2 to 20 μm, or 0.4 to 10 μm The period is 50 microns to 400 microns, 50 microns to 300 microns, 100 microns to 300 microns, or 150 microns to 250 microns.

Preferably, in the uneven surface formed on one surface of the stretched film, the ratio (T:H) of the period (T) to the height (H) of the convex portion may be 1:0.001 to 1:1, 1:1 0.002 to 1:0.5, 1:0.002 to 1:0.1 or 1:0.002 to 1:0.05.

In order to prevent the film from breaking during the stretching process while ensuring the efficiency of the stretching process, stretching is preferably performed at 80°C to 120°C, 90°C to 110°C, or 90°C to 100°C.

In addition, it is preferable to provide the unstretched film at a temperature equal to or higher than the glass transition temperature (Tg) of the polyester resin during stretching to ensure a proper level of crystallinity. Preferably, the temperature of the unstretched film provided in the stretching process may be 80°C to 120°C, 90°C to 110°C, or 90°C to 100°C.

Meanwhile, after the stretching process, if necessary, a heat treatment step of heat-treating and relaxing the stretched film may be further performed.

The heat treatment step may be performed at a temperature of 180°C to 260°C, 190°C to 250°C, or 200°C to 240°C. The relaxation rate during relaxation can be adjusted to 0.1% to 10% with respect to the machine direction and the transverse direction.

When the temperature of the heat treatment step is too low, the degree of crystallinity of the polyester may be reduced, and thus mechanical properties may be reduced or residual stress may not be sufficiently reduced, thereby increasing heat shrinkage. When the temperature of the heat treatment step is too high, mechanical properties may be deteriorated due to thermal decomposition of polyester, or quality may be deteriorated due to thermal deformation of the film at high temperatures. II. Polyester film

According to another embodiment of the present disclosure, there is provided a polyester film having a concavo-convex surface on one surface and having a centerline average of 7.0 nm or more according to JIS B-0601:1994 standard Roughness (Ra).

The polyester film can be obtained by the above-mentioned [I. Method for producing polyester film].

Preferably, the polyester film may be a biaxially stretched film according to the above-mentioned preparation method.

The concavo-convex surface formed on one surface of the polyester film may have a cross-sectional shape having an arc. That is, the concavo-convex surface may have a circular shape such as an arc or circular arc whose cross section does not have an internal angle.

In one embodiment of the present disclosure, the concavo-convex surface formed on one surface of the polyester film has a height of the convex portion that may be 0.1 to 50 μm and a period of the convex portion that may be 50 to 400 μm.

Preferably, the concavo-convex surface formed on one surface of the polyester film has a height of the convex portion that may be 0.1 to 50 μm, 0.2 to 20 μm, or 0.4 to 10 μm; and the period of the convex portion may be 50 μm to 400 microns, 50 microns to 300 microns, 100 microns to 300 microns, or 150 microns to 250 microns.

Preferably, in the uneven surface formed on one surface of the polyester film, the ratio (T:H) of the period (T) to the height (H) of the convex portion may be 1:0.001 to 1:1, 1:0.002 to 1:0.5, 1:0.002 to 1:0.1, or 1:0.002 to 1:0.05.

When the height (H) of the convex portion in the concavo-convex surface is too small compared to the period (T), it may be difficult to have an appropriate surface roughness due to the concavo-convex surface. Therefore, the ratio (T:H) is preferably 1:0.001 or more.

However, when the height (H) of the convex portion in the concavo-convex surface is too large compared to the period (T), the surface roughness due to the concavo-convex surface becomes excessively large, resulting in a decrease in workability, for example, causing lamination in Unbalanced coating of any layer on the polyester film. Therefore, the ratio (T:D) is preferably 1:1 or less.

The polyester film having an uneven surface on one surface can exhibit excellent driveability and winding properties with low surface roughness.

In one embodiment of the present disclosure, the polyester film may have a centerline average roughness (Ra) of 7.0 nm or more according to the JIS B-0601:1994 standard. Preferably, according to JIS B-0601:1994 standard, the polyester film may have 7.0 nm to 35.0 nm, 7.5 nm to 35.0 nm, 7.5 nm to 33.0 nm, or 7.6 nm to 33.0 nm Centerline mean roughness (Ra) in meters.

In one embodiment of the present disclosure, the polyester film may have a coefficient of static friction (μS) of 0.40 or less or 0.35 to 0.40 and 0.40 or less or 0.33 to 0.40 according to the standard test method of ASTM-D-1894 The coefficient of kinetic friction (μD).

The polyester film may have a thickness of 10 microns to 250 microns, 10 microns to 200 microns, 20 microns to 150 microns, or 30 microns to 100 microns. Herein, the thickness means the thickness measured including the convex portion in the concavo-convex surface formed on one surface of the polyester film.

Additionally, the polyester film may have a haze of 1.0% or less, 0.1% to 1.0%, or 0.3% to 0.6%; and a total of 90.0% or more, 90.0% to 92.0%, or 90.0% to 91.0% Transmittance. [Beneficial effect]

In the present disclosure, a polyester film having excellent driveability and winding properties with low surface roughness and a method for producing the same are provided. The polyester film can be suitably used as a base film for release in the manufacture of multilayer ceramic capacitors (MLCCs), polarizing plates, and optically clear adhesives.

In the following, preferred examples are presented to aid understanding of the present invention. However, the following examples are provided only for easier understanding of the present invention, and the present invention is not limited thereto. Preparation Example 1

By 50 mol % of the diol component containing diethylene glycol and ethylene glycol in a molar ratio of 5:5 with 50 mol % containing terephthalic acid and a sulfo group in a molar ratio of 8.5:1.5 Polycondensation of the acid component of terephthalic acid yields polyester resins. Example 1

The polyester resin obtained in Preparation Example 1 was put into a melt extruder to form a melt (intrinsic viscosity: 0.63) at 300°C. The melt is continuously extruded through a T-die 10 .

The melt is supplied on the embossing roll 20 . As the embossing roller 20 , an embossing roller having a concave-convex pattern on its outer circumferential surface was used, in which the period (T) of the concave portion was 50 μm and the depth (D) of the concave portion was 19.2 μm. The concave portion has a conical shape with an apex toward the center of the platen roller.

The temperature of the outer surface of the embossing roller 20 was maintained at 80°C.

The melt passes through the gap between the embossing roll 20 and a nip roll 30 adjacent to the embossing roll 20 . The temperature of the outer surface of the nip roll 30 was maintained at 80°C. The pressure applied by the nip roll 30 to the platen roll 20 was maintained at 50 kgf/cm².

When the melt passes through the nip, an unstretched film having a concave-convex surface corresponding to the concave-convex pattern of the embossing roller 20 on one surface thereof is formed.

The unstretched film was transferred to the stretching process while having a temperature of 90° C., which was higher than the glass transition temperature (Tg) of the polyester resin. The unstretched film was stretched twice in the machine direction (MD) and three times in the transverse direction (TD) at a temperature of 95°C.

After the stretching process, the stretched film was heat-treated at 230° C. for 10 seconds to obtain a polyester film. Examples 2 to 6 and Comparative Examples 1 to 4

The polyester films of Examples 2 to 6 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1 except that the uneven pattern, outer surface temperature, and stretching conditions of the embossing roller 20 were changed as shown in Table 1. [Table 1] Embossing roller stretch Crystallinity of unstretched film (%) Depth of concave part (microns) Period (microns) Temperature (℃) MD (times) TD (times) Total (MD*TD) Example 1 19.2 50 80 2 3 6 4.1 Example 2 9.8 50 30 3.5 4.0 14 4.2 Example 3 14.9 50 55 3.5 4.0 14 4.1 Example 4 19.2 50 80 3 3 9 4.0 Example 5 19.2 50 80 3.5 3.5 12.25 4.1 Example 6 19.2 50 80 3.5 4 14 4.1 Comparative Example 1 0 0 80 3 3 9 4.1 Comparative Example 2 0 0 80 3.5 3.5 12.25 4.0 Comparative Example 3 0 0 80 3.5 4 14 4.0 Comparative Example 4 2.7 50 20 3.5 4.0 14 4.0 Experimental example

100 （100%非晶PET的密度：1.335克/立方公分，理論上100%結晶PET的密度：1.455克/立方公分） (1) Crystallinity of unstretched film: The degree of crystallinity was calculated by the following equation using the measured density of the sample (measured at 25° C. using a gradient tube). The values are shown in Table 1 above. *Crystalline degree = {[(density of sample) - (density of 100% amorphous PET)] / [(density of theoretical 100% crystalline PET) - (density of 100% amorphous PET)]}

100 (density of 100% amorphous PET: 1.335 g/cm3, theoretical density of 100% crystalline PET: 1.455 g/cm3)

(2) Thickness of film: Using an electric micrometer measuring device (manufactured by Mahr, Millimar-1240) at five points at intervals of 1 cm in the width direction of the film, Germany ) measured the thickness (based on the convex portion of the concave-convex surface), and calculated its average value.

(3) Roughness (Ra) of the film: A sample was prepared by selecting an arbitrary center point from the entire width of the prepared polyester film and cutting the film to a size of 5 cm wide and 5 cm long based on the point. The Ra (center line average roughness) of the sample was measured using a two-dimensional contact surface roughness meter (manufactured by KOSAKA, SE-3300, Japan) in accordance with the JIS B-0601:1994 standard. The cut-off (λc) value of the surface roughness meter was set to 0.08 mm, and the measurement length was 1.50 mm.

(4) Shape of the concave-convex surface: After cutting the film using a Microtome device (manufactured by LEICA, EM-UC7, Germany), its cross section was placed on an optical microscope (manufactured by Olympus). (Olympus), BX51, Japan) on a sample holder. The line width of the uneven surface and the depth of the concave portion on the cut surface of the film were measured.

(5) Haze and total light transmittance: The haze (%) and total light transmittance (T.t, %) of the film were measured according to the standard test method of ASTM D-1003. A haze meter (manufactured by NIPPON DENSHOKU, NDH-5000, Japan) was prepared, and the instrument was calibrated. The sample (5 cm wide, 5 cm long) was placed on the sample holder of the instrument, the sample was fixed with the holder, and then the measurement was performed by pressing the start button. Five measurements were made and the average value was derived.

(6) Coefficient of friction: The static friction coefficient (μS) and the dynamic friction coefficient (μD) of the film were measured according to the standard test method of ASTM-D-1894. A friction coefficient tester (manufactured by Toyoseiki, TR-2, Japan) was prepared. The sample (20 cm wide, 11 cm long) was placed on the measuring table of the tester without wrinkles, and the sample was then attached to the back side of a sled (10.5 cm wide, 9.5 cm long). The pulley was connected to a load cell, and the static friction coefficient (μS) and the dynamic friction coefficient (μD) were measured five times, respectively, and their average values were derived.

(7) Driveability: Driveability was evaluated using the coefficient of kinetic friction according to the following criteria. *Very good (◎) – coefficient of kinetic friction: less than 0.35 *Good (○) – coefficient of kinetic friction: 0.35~0.40 *Difference (X) – Coefficient of Kinetic Friction: Greater than 0.40

(8) Stretch workability: The stretch workability was evaluated based on whether or not breakage occurred during the stretching of the film. *X: not broken *O: broken [Table 2] Thickness (microns) Ra (nano) Concave and convex surface Haze (%) Tt (%) friction coefficient drivability Tensile Processability (Break) Height of convex part (microns) Period (microns) μS μD Example 1 75.3 33.0 2.7 163.9 0.6 90.9 0.37 0.37 ○ X Example 2 30.6 7.6 0.4 165.7 0.4 90.2 0.39 0.39 ○ X Example 3 31.2 10.6 0.9 164.1 0.4 90.2 0.35 0.34 ◎ X Example 4 49.2 27.5 2.0 166.8 0.5 90.3 0.36 0.36 ○ X Example 5 35.4 20.1 1.5 227.8 0.4 90.9 0.36 0.34 ◎ X Example 6 30.5 17.2 1.0 229.6 0.3 90.1 0.37 0.33 ◎ X Comparative Example 1 50.4 0.5 0 0 0.5 90.1 0.44 0.42 X X Comparative Example 2 35.2 0.5 0 0 0.4 90.5 0.41 0.40 X X Comparative Example 3 29.7 0.5 0 0 0.4 90.2 0.42 0.42 X X Comparative Example 4 30.2 2.6 0.1 160.7 0.4 90.3 0.41 0.41 X X

Referring to Table 2, compared to the films of Comparative Examples 1 to 3 having no uneven surface, the films of Examples had higher surface roughness and exhibited excellent drivability without breakage during stretching.

It was confirmed that the films of Comparative Examples 1 to 3 having no uneven surface had lower surface roughness and thus poor drivability compared to the films of Examples. It was confirmed that the film of Comparative Example 4 did not exhibit appropriate surface roughness due to the uneven surface including the concave portions whose depth was too low, and had poor drivability.

10: T-die head 20: Embossing roller 25: Casting Roller 30: Pinch roller 35: Impression nip roller 100: Unstretched film 105: stretch film

FIG. 1 illustrates an embodiment of a method for producing a polyester film according to the present disclosure. FIG. 2 illustrates another embodiment of a method for producing a polyester film according to the present disclosure. FIG. 3 illustrates another embodiment of a method for producing a polyester film according to the present disclosure. FIG. 4 illustrates changes in the uneven surface and its cross-sectional shape due to sequential biaxial stretching of the unstretched film in the preparation of the polyester film according to the present disclosure. 5 is a cross-sectional view of a polyester film according to the present disclosure, wherein (a) shows the polyester film before stretching and (b) shows the polyester film after stretching.

10: T-die head

20: Embossing roller

100: Unstretched film

Claims (14)

A method for preparing polyester film, comprising the following steps A melt of a resin composition containing a polyester resin was supplied on an embossing roll having a concavo-convex pattern formed on its outer circumferential surface to obtain an unstretched film having a concavo-convex surface corresponding to the concavo-convex pattern. The method for producing a polyester film as claimed in claim 1, wherein the melt supplied on the embossing roll has a temperature of 200°C to 300°C. The method for producing a polyester film as claimed in claim 1, wherein the embossing roll has an outer surface temperature of 25°C to 130°C. The method for producing a polyester film as claimed in claim 1, wherein the melt supplied on the embossing roll is embossed while being cast by the embossing roll. The method for producing a polyester film as claimed in claim 1, wherein the melt supplied on the embossing roll passes through a gap between the embossing roll and a nip roll adjacent to the embossing roll. The method for producing a polyester film as claimed in claim 5, wherein the nip roll has an outer surface temperature of 25°C to 130°C. The method for producing a polyester film as claimed in claim 1, The concave-convex pattern formed on the outer circumferential surface of the embossing roller has a depth of the concave portions of 5 to 100 μm and a period of the concave portions of 10 to 100 μm. The method for producing a polyester film as claimed in claim 7, wherein the concavo-convex pattern formed on the outer circumferential surface of the embossing roller has a cross-sectional shape having an arc or a cross-sectional shape having one or more inner corners. The method for producing a polyester film as claimed in claim 1, It further includes the step of uniaxially or biaxially stretching the unstretched film having the uneven surface. The method for producing a polyester film as claimed in claim 9, wherein the stretching is performed 2 to 6 times in the machine direction (MD) of the unstretched film, or in the machine direction (MD) of the unstretched film and in the unstretched film, respectively Perform 2 to 6 times on the transverse direction (TD) of the stretch film. A polyester film having an uneven surface on one surface and having a centerline average roughness (Ra) of 7.0 nm or more according to JIS B-0601:1994 standard. The polyester film of claim 11, The concave-convex surface has a height of the convex portion of 0.1 to 50 μm and a period of the convex portion of 50 to 400 μm. The polyester film of claim 12, wherein the concavo-convex surface has a cross-sectional shape having an arc. The polyester film of claim 11, Wherein, according to the standard test method of ASTM-D-1894, the polyester film has a static friction coefficient (μS) of 0.40 or less and a dynamic friction coefficient (μD) of 0.40 or less.

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