KR102526933B1 - Polyester-based film and preparation method thereof - Google Patents

Abstract

The embodiment includes a polyester resin in which a diol including 1,4-cyclohexanedimethanol and an aromatic dicarboxylic acid are polymerized, and a filler, and has a 10-point average roughness (Rz) of 0.5 μm to 5 μm, and surface kinetic friction A polyester-based film having a coefficient (F _d ) of 0.5 or less and a manufacturing method thereof, wherein the polyester-based film includes a filler so that the surface roughness and surface friction coefficient of the polyester-based film can be controlled, thereby Optical properties and mechanical properties as well as processability such as winding and running performance of the film may be improved.

Description

Polyester-based film and its manufacturing method {POLYESTER-BASED FILM AND PREPARATION METHOD THEREOF}

Embodiments relate to a polyester-based film and a method for producing the same.

Electronic boards, such as circuit boards, which are essential components in electronic devices, have conductive patterns formed on insulating base films.

Flexible printed circuit boards are generally manufactured by laminating copper foil on one side or both sides of a base film to manufacture a flexible copper clad laminate (FCCL), and etching the copper foil to form a conductive pattern.

In conventional electronic boards, polyester films and polyimide (PI) films were mainly used as base films, and recently, polyethylene naphthalate (PEN) films and liquid crystal polymer (LCP) films are also actively used (Korean Registered Patent No. 1275159 see No.).

Among them, polyester has been applied in various ways because it has excellent physical and chemical properties, and the scale of its use is increasing.

However, a polyester film using such a polyester resin has excellent heat resistance and hydrolysis resistance, but has difficulties in winding the film due to a soft and high surface friction coefficient and poor driving performance.

In order to solve this problem, various attempts have been made, such as primer coating on the surface of the film and the use of various additives, but there is still a limit to manufacturing a polyester-based film with improved mechanical properties, running properties such as blocking, and fairness such as winding. .

Korean Registered Patent No. 1275159

The present invention was devised to solve the problems of the prior art, and the technical problem to be solved by the present invention is to control the surface roughness and surface friction coefficient in a specific range, thereby improving the optical properties and mechanical properties, as well as winding and It is to provide a polyester-based film capable of improving processability such as driving performance.

Another technical problem to be solved by the present invention is to provide a method for manufacturing the polyester-based film.

According to one embodiment, a polyester resin in which diol and aromatic dicarboxylic acid including 1,4-cyclohexanedimethanol are polymerized, and a filler are included, and the 10-point average roughness (Rz) is 0.5 μm to 5 μm, A polyester-based film having a surface dynamic coefficient of friction (F _d ) of 0.5 or less is provided.

According to another embodiment of the present invention, preparing a resin composition by mixing a polyester resin and a filler in which diol and aromatic dicarboxylic acid including 1,4-cyclohexanedimethanol are polymerized; Extruding and casting the resin composition to prepare an unstretched sheet; And stretching and heat-setting the unstretched sheet; including, a 10-point average roughness (Rz) of 0.5 μm to 5 μm, and a surface dynamic coefficient of friction (F _d ) of 0.5 or less, manufacturing a polyester-based film A method is provided.

The polyester-based film according to the embodiment includes a filler, thereby controlling the surface roughness and surface friction coefficient of the polyester-based film, thereby simultaneously improving optical properties and mechanical properties as well as fairness such as winding and running performance of the film. can make it

In particular, the polyester-based film has a 10-point average roughness (Rz) and a coefficient of surface dynamic friction (F _d ) in a specific range, thereby further improving driving performance and simultaneously improving mechanical properties.

Hereinafter, the present invention will be described in more detail through the accompanying drawings.
1 is a schematic process flow diagram of a method for manufacturing a polyester-based film according to an embodiment of the present invention.
Figure 2 is a graph comparing the static friction coefficient and the dynamic friction coefficient of the polyester-based films of Examples 1 to 3 and Comparative Examples 1 and 2 according to an embodiment of the present invention, respectively.
3 is a graph comparing the 10-point average roughness (Rz) of the polyester-based films of Examples 1 to 3 and Comparative Examples 1 and 2 according to an embodiment of the present invention.
4 is a scanning electron microscope (SEM) picture of the polyester-based film of Example 1 according to an embodiment of the present invention.
5 is a scanning electron microscope (SEM) photograph of the polyester-based film of Example 2 according to an embodiment of the present invention.
6 is a scanning electron microscope (SEM) photograph of the polyester-based film of Example 3 according to an embodiment of the present invention.

In the following description of embodiments, it is described that one component is formed on or under another component, which means that one component is directly above or under another component, or indirectly through another component. Including everything formed by

"Including" a component in this specification means that other components may be further included, not excluding other components, unless otherwise stated.

In addition, it should be understood that all numerical ranges representing physical property values, dimensions, etc. of components described in this specification are modified by the term "about" in all cases unless otherwise specified.

[Polyester-based film]

The polyester film according to one embodiment includes a polyester resin in which a diol containing 1,4-cyclohexanedimethanol and an aromatic dicarboxylic acid are polymerized, and a filler, and has a 10-point average roughness (Rz) of 0.5 μm to 5 μm, and the surface dynamic coefficient of friction (F _d ) is 0.5 or less.

By including a filler in the polyester film according to an embodiment of the present invention, the surface roughness and surface friction coefficient of the polyester film can be controlled, thereby improving winding and running performance of the film. In addition, the polyester-based film can simultaneously improve mechanical properties and optical properties such as tensile strength, elongation at break and modulus.

The surface roughness of the polyester-based film is one of the important factors affecting the winding and running performance of the film.

In general, PCT films using poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) resin have excellent heat resistance and hydrolysis resistance, but difficulties occur when winding the film due to their soft and high surface friction coefficient. There was a problem.

Therefore, the polyester film according to the embodiment of the present invention can control the surface roughness by using a filler, and in particular, the 10-point average roughness (Rz) affects the lowering of the friction coefficient, thereby improving winding and driving performance. It can provide an effect of improving fairness.

Specifically, the 10-point average roughness (Rz) of the polyester film according to the embodiment of the present invention is 0.5 μm to 5.0 μm, 0.5 μm to 4.0 μm, 0.5 μm to 3.0 μm, 0.5 μm to 2.0 μm, 0.5 μm to 0.5 μm. 1.5 μm, or 0.5 μm to 1.0 μm.

The 10-point average roughness (Rz) is the surface roughness according to KS B 0161, for example, by taking a reference length from the roughness cross-section curve, drawing an arbitrary straight line (reference line) parallel to the average line of the cross-section curve, and drawing the highest five peaks It can be expressed as the difference between the average value of the distance from the baseline of , and the average value of the distance from the baseline of the lowest 5 valleys.

When the 10-point average roughness (Rz) of the polyester film satisfies the above range, the surface friction coefficient may be lowered to improve winding and running performance.

The center line average roughness (Ra) of the polyester film according to an embodiment of the present invention is 0.01 μm to 0.1 μm, 0.01 μm to 0.09 μm, 0.01 μm to 0.08 μm, 0.01 μm to 0.07 μm, or 0.02 μm to 0.07 μm. can

The center line average roughness (Ra) of the polyester film is a surface roughness according to KS B 0161, and the sum of the arithmetic mean roughness and the total upper and lower sides of the center line of the reference length is obtained, and the value is divided by the length of the measurement section is indicated by

The maximum height roughness (Ry) of the polyester film according to an embodiment of the present invention is 1.0 μm to 3.0 μm, 1.0 μm to 2.5 μm, 1.0 μm to 2.2 μm, 1.0 μm to 2.0 μm, or 1.2 μm to 2.0 μm. can

The maximum height roughness (Ry) of the polyester film is a surface roughness according to KS B 0161, taken as much as the reference length from the roughness cross-sectional curve, parallel to the center line of the cross-sectional curve, and between the two parallel lines contacting the highest peak and the deepest valley means distance.

Meanwhile, according to an embodiment of the present invention, the coefficient of surface friction can be reduced even when the surface roughness (surface roughness) of the film, for example, the 10-point average roughness (Rz) is low.

In particular, the surface roughness and surface friction coefficient of the polyester film are not exactly proportional, but when they simultaneously satisfy the above specific range, optimal winding and running performance effects can be exhibited, and mechanical properties can be improved at the same time.

The surface friction coefficient of the polyester film may consider the surface dynamic friction coefficient (F _d ) and the surface static friction coefficient (F _s ), in particular, the surface dynamic friction coefficient (F _d ) of the polyester film is within a specific range If satisfied, the driving performance can be further improved.

The surface dynamic friction coefficient (F _d ) of the polyester film may be 0.5 or less, specifically 0.45 or less, 0.40 or less, 0.39 or less, or 0.38 or less. In addition, the surface dynamic friction coefficient (F _d ) of the polyester film may be greater than 0.15, greater than 0.20, greater than 0.25, or greater than 0.30. For example, the surface dynamic friction coefficient (F _d ) of the polyester film may be greater than 0.15 and less than 0.5, greater than 0.20 and less than 0.45, or greater than 0.25 and less than 0.40.

When the surface dynamic friction coefficient (F _d ) of the polyester film exceeds 0.5, winding and running performance may be significantly deteriorated, and mechanical properties may also be reduced.

The surface static friction coefficient (F _s ) of the polyester film may be 0.2 to 0.7, 0.2 to 0.6, 0.3 to 0.6, 0.4 to 0.6, or 0.45 to 0.55.

When the surface static friction coefficient (F _s ) of the polyester film satisfies the above range, winding and running performance may be further improved.

Meanwhile, the polyester-based film may have an RF of 0.3 to 0.8 in Formula 1 below.

[Equation 1]

Ⅹ F_d RF =

X F _d

In Equation 1 above,

R _y is the maximum height roughness of the polyester film,

F _d is the coefficient of kinetic friction of the surface of the polyester film.

Specifically, RF in Equation 1 may be 0.3 to 0.78, 0.4 to 0.78, 0.45 to 0.75, or 0.49 to 0.75. The polyester-based film has excellent slip properties when RF of Equation 1 satisfies the above range, and can simultaneously improve winding and running performance and mechanical properties.

In Equation 1, the R _y value representing the maximum height roughness of the polyester film is as defined above, and when R _y satisfies the above range, RF in the specific range can be implemented, thereby Due to this, the slip property of the film is excellent, and the winding and running performance can be further improved.

Meanwhile, the polyester-based film may have F of 0.50 to 0.77 in Formula 2 below.

[Equation 2]

F = F _d /F _s

In Equation 2 above,

F _d is as defined above,

F _s is the static friction coefficient of the surface of the polyester-based film.

Specifically, F in Equation 2 is the ratio of the dynamic friction coefficient to the static friction coefficient of the surface of the polyester film, 0.55 or more to less than 0.77, 0.60 or more to less than 0.77, 0.65 or more to less than 0.77, or 0.67 or more to 0.76 may be below.

When F in Equation 2 satisfies the above range, winding and running performance can be further improved, and mechanical properties can be improved at the same time.

Meanwhile, F _t of the polyester-based film in Formula 3 below may be less than 1.

[Equation 3]

F _t = F _{d +} F _s

In Equation 3 above,

F _d and F _s are as defined above.

F _t of Equation 3 is the sum of the static friction coefficient and the dynamic friction coefficient of the surface of the polyester film, and may be 0.98 or less, 0.96 or less, 0.95 or less, or 0.93 or less, 0.40 or more, 0.50 or more, 0.60 or more, 0.70 or more. , or 0.80 or more.

When F _t of Equation 3 satisfies the above range, winding and running performance can be further improved, and mechanical properties can be improved at the same time.

The polyester film according to an embodiment of the present invention may have a thickness of 1 μm to 500 μm, 5 to 250 μm, 10 to 150 μm, 10 μm to 100 μm, 10 μm to 80 μm, or 40 μm to 60 μm. there is. As an example, the polyester-based film may have a thickness of 10 to 150 μm.

The polyester-based film is preferably a stretched film because of its high crystallinity and excellent mechanical properties. Specifically, the polyester film may be a biaxially stretched polyester film, and may be a film stretched in a first direction and a stretch ratio of 2.0 to 5.0 in a second direction perpendicular to the first direction. . In this case, the first direction may be a length direction (MD), and the second direction may be a direction perpendicular to the first direction and may be a width direction (TD). For example, the polyester-based film may be a film stretched at a stretch ratio of 2.0 to 5.0 in the MD and TD directions, respectively.

The polyester-based film according to an embodiment of the present invention may have a tensile strength of 15 kgf/mm ² or more at room temperature. Specifically, the tensile strength of the polyester film is 15.2 kgf/mm ² or more, 15.4 kgf/mm ² or more, 15.8 kgf/mm ^{2 or} more, 16.0 kgf/mm ^{2 or} more, 16.5 kgf/mm ² or more, 17 kgf at room temperature. /mm ² or more, 18 kgf/mm ² or more. In addition, the tensile strength of the polyester film may be 25 kgf/mm ² or less, 24 kgf/mm ^{2 or} less, 23 kgf/mm ² or less, 22 kgf/mm ^{2 or} less, or 20 kgf/mm ^{2 or} less at room temperature. .

Specifically, the polyester film has a tensile strength in the first direction of 15 to 25 kgf/mm ² , 15 to 22 kgf/mm ² , 15 to 20 kgf/mm ² , 16 to 20 kgf/mm ² , or It may be 17 to 20 kgf/mm ² .

In addition, the polyester film has a tensile strength in the second direction of 15 to 22 kgf/mm ² , 15 to 20 kgf/mm ² , 15 to 18 kgf/mm ² , 15 to 17 kgf/mm ² , or 15 to 16.5 kgf/mm ² .

When the polyester-based film satisfies the tensile strength in the above range, it can be used in various ways for metal replacement, electronic boards or display devices due to its excellent mechanical properties, and can be more advantageous in implementing weight reduction.

The polyester-based film may have an elongation at break of 60% or more. Specifically, the polyester-based film may have an elongation at break of 62% or more, 63% or more, 65% or more, 66% or more, or 70% or more. In addition, the elongation at break may be 88% or less, 85% or less, 82% or less, 81% or less, or 80% or less.

Specifically, the polyester-based film may have an elongation at break in the first direction of 60% to 88%, 65% to 88%, 68% to 88%, 70% to 88%, or 75% to 85%.

The polyester-based film may have an elongation at break in the second direction of 60% to 88%, 60% to 85%, 60% to 83%, 63% to 83%, or 65% to 85%.

When the polyester-based film satisfies the elongation at break in the above range, it can be used in a variety of ways such as for metal replacement, electronic boards or display devices due to its excellent mechanical properties, and can be more advantageous in implementing weight reduction.

The polyester-based film may have repeated folding at an angle of 135° until breakage of 100 times, 1000 times, 10,000 times, 50,000 times, 100,000 times, 150,000 times, or 200,000 times or more. When within the above range, it is advantageous to apply to a flexible electronic device because breakage does not occur even during frequent folding.

On the other hand, the polyester-based film has a modulus of 200 kg / ㎟ to 300 kg / ㎟, 220 kg / ㎟ to 300 kg / ㎟, 220 kg / ㎟ to 280 kg / ㎟, 220 kg / ㎟ to 270 kg at 25 ° C. /mm2, or 220 kg/mm2 to 260 kg/mm2.

Specifically, the polyester-based film has a modulus in the first direction of 200 kg/mm2 to 300 kg/mm2, 220 kg/mm2 to 300 kg/mm2, 220 kg/mm2 to 280 kg/mm2, 230 kg/mm2 to 270 kg/mm 2 , or 230 kg/mm 2 to 260 kg/mm 2 .

The polyester-based film has a modulus in the second direction of 200 kg/mm2 to 300 kg/mm2, 200 kg/mm2 to 280 kg/mm2, 220 kg/mm2 to 280 kg/mm2, 220 kg/mm2 to 270 kg /mm 2 , or 210 kg/mm 2 to 260 kg/mm 2 .

The modulus, the tensile strength, and the elongation at break can be measured by the following methods.

A load is applied to the film, and it is stretched at a constant speed. At this time, the load applied to the film according to the deformation of the film is derived until the film is broken. By the load according to the deformation of the film, the modulus, the tensile strength and the elongation at break can be obtained.

The modulus, the tensile strength, and the elongation at break may be measured by a universal testing machine (UTM). After the film is cut into a predetermined size, the modulus, the tensile strength, and the elongation at break may be measured by the UTM equipment.

Specifically, the film may be cut into a size of 15 mm X 100 mm to prepare a sample. When the sample is tested at a test speed of 200 mm/min of UTM measuring equipment, the modulus, the tensile strength, and the elongation at break can be measured.

According to an embodiment of the present invention, the polyester-based film may have a TE of 900 or more of the following formula 4:

[Equation 4]

Ⅹ

TE =

X

In Equation 4 above,

The TS is the tensile strength of the polyester film,

E is the elongation at break of the polyester film.

That is, the polyester-based film is a parameter of the product of the tensile strength and the elongation at break of the polyester-based film, and when it is 900 or more, various applications are possible in metal replacement, electronic boards or display elements due to excellent mechanical properties, , it may be more advantageous to implement weight reduction.

Specifically, the polyester-based film may have TE of Formula 4 of 950 or more, 970 or more, 990 or more, 992 or more, 994 or more, or 1000 or more. In addition, the polyester-based film may have a TE of Equation 4 of 1450 or less, 1430 or less, 1420 or less, or 1410 or less. The polyester-based film may have a TE of 950 to 1450, 970 to 1430, 990 to 1420, or 992 to 1410 in Formula 4.

The polyester-based film may have TE ₁ of Formula 4-1 below of 950 or more, 970 or more, 1000 or more, 1100 or more, 1200 or more, or 1250 or more. In addition, the polyester film may have TE ₁ of Formula 4-1 below of 1450 or less, 1430 or less, 1420 or less, or 1410 or less. The polyester-based film may have TE ₁ of Formula 4-1 of 950 to 1450, 970 to 1430, 1000 to 1420, or 1100 to 1410.

[Equation 4-1]

Ⅹ

TE ₁ =

X

In Equation 4-1 above,

TS ₁ is the tensile strength of the polyester film in the first direction,

E ₁ is the elongation at break in the first direction of the polyester film.

The polyester-based film may have TE ₂ of Formula 4-2 below of 950 or more, 960 or more, 970 or more, 980 or more, 990 or more, or 992 or more. In addition, the polyester film may have TE ₂ of Formula 4-2 below of 1450 or less, 1430 or less, 1420 or less, or 1410 or less. The polyester-based film may have TE ₂ of 950 to 1450, 960 to 1430, 970 to 1420, or 980 to 1410 in Formula 4-2 below.

[Equation 4-2]

Ⅹ

TE ₂ =

X

In Equation 4-2 above,

TS ₂ is the tensile strength in the second direction perpendicular to the first direction of the polyester film,

E ₂ is the elongation at break in the second direction perpendicular to the first direction of the polyester film.

Meanwhile, the polyester-based film may have a TS of 0.6 to 3 kgf/mm ² of Equation 5 below:

[Equation 5]

TS = │TS ₁ - TS ₂ │

In Equation 5 above,

TS ₁ and TS ₂ are as defined above.

TS in Equation 5 is a parameter of the absolute value of the difference between the tensile strength in the first direction of the polyester film and the tensile strength in the second direction perpendicular to the first direction of the polyester film, When TS is 0.6 to 3 kgf/mm ² , due to its excellent mechanical properties, it can be used in a variety of ways, such as for metal replacement, electronic boards or display devices, and can be more advantageous in implementing weight reduction.

Specifically, the TS of Equation 5 is 0.7 to 3 kgf/mm ² , 0.9 to 2.8 kgf/mm ² , 0.9 to 2.6 kgf/mm ² , 1.0 to 2.5 kgf/mm ² , or 1.0 to 2.3 kgf/mm ² can

In addition, the polyester film may have E of 5 to 15% of Formula 6 below:

[Equation 6]

E = │E ₁ - E ₂ │

In Equation 6 above,

E ₁ and E ₂ are as defined above.

E in Equation 6 is a parameter of the absolute value of the difference between the elongation at break in the first direction of the polyester film and the elongation at break in the second direction perpendicular to the first direction of the polyester film, When E is 5 to 15%, due to its excellent mechanical properties, it can be used in a variety of ways, such as for metal replacement, electronic boards or display devices, and it can be more advantageous to realize weight reduction.

Specifically, the polyester-based film may have E in Formula 6 of 5 to 14%, 5 to 13%, or 5.5 to 13%.

In addition, the polyester-based film has a moisture permeability of 10 g/m2·day to 100 g/m2·day, 10 g/m2·day to 50 g/m2·day, or 10 g/m2·day to 30 g/m2 ㆍIt can be day.

In addition, the polyester-based film may have a transmittance of 10% or less, 5% or less, or 3% or less at a wavelength of 380 nm. As an example, the polyester-based film may have a water vapor transmission rate of 10 g/m2·day to 50 g/m2·day, and a transmittance of 5% or less at a wavelength of 380 nm.

The polyester-based film may have a crystallinity of 35% to 55%. When within the above range, excessive crystallization can be prevented while excellent in mechanical properties such as tensile strength. For example, the crystallinity of the polyester film may be 35% to 50%, 40% to 55%, 35% to 45%, 45% to 55%, or 40% to 50%.

On the other hand, the glass transition temperature (Tg) of the polyester film is 80 ℃ to 110 ℃, 80 ℃ to 105 ℃, 85 ℃ to 105 ℃, 88 ℃ to 105 ℃, 88 ℃ to 100 ℃, or 88 ℃ to 95 ℃ may be °C.

In addition, the melting temperature (Tm) of the polyester film may be 240 ° C to 290 ° C, 240 ° C to 285 ° C, 240 ° C to 284 ° C, or 242 ° C to 282 ° C.

The polyester film may have a haze value of 9% to 22%, 10% to 22%, 10.5% to 22%, 12% to 22%, or 15% to 22%.

Light transmittance of the polyester film may be 80% or more, 85% or more, 88% or more, 90% or more, or 92% or more.

Composition of polyester film

In the polyester film according to an embodiment of the present invention, the 10-point average roughness (Rz) and the surface dynamic friction coefficient (F _d ) satisfy the specific range, and furthermore, the physical properties can be controlled within a specific range. Existence can be implemented by including the filler in the polyester-based film.

Specifically, according to the embodiment of the present invention, the 10-point average roughness (Rz) and surface dynamic coefficient of friction (F _d ), tensile strength, elongation at break and modulus of the polyester film according to the type, physical properties and content of the filler properties may vary. In particular, according to an embodiment of the present invention, by including the filler, the friction coefficient can be reduced even when the surface roughness of the film is low.

In particular, even if the same amount of the filler is used, the surface roughness and friction coefficient of the film may be significantly different depending on the particle size, shape, and physical properties thereof.

The filler has a span value of Equation 7 below when the particle sizes at which the cumulative volume concentration (%) in the particle size distribution is 10%, 50%, and 90% are D10, D50, and D90, respectively. 0.3 to 1.0:

[Equation 7]

.Span =

.

That is, the surface properties of the polyester film may vary according to the span value of Equation 7 of the filler.

The span value of Equation 7 is an index representing the distribution (particle size distribution) ratio to the particle diameter of the filler. In other words, it relates to the proportion of particles with different particle diameters, and if the composition ratio of particles smaller than the average particle diameter and particles larger than the average particle diameter is high, it has a value higher than 1 and consists of only particles of the same size. In the case of a complex with a span, the span value is 1.

In addition, as the span value of Equation 7 is smaller, it means that the width of the particle size distribution is narrower.

Specifically, the span value of Equation 7 may be 0.3 or more to less than 1.0, 0.4 or more to less than 1.0, 0.4 or more to 0.9 or less, 0.5 or more to 0.9 or less, 0.6 or more to 0.9 or less, or 0.6 or more to 0.8 or less.

When the span value of Equation 7 of the filler is within the above range, the surface roughness and friction coefficient of the polyester film can be efficiently controlled.

The D50 of the filler may be 0.5 to 5.0 μm, 0.5 to 4.5 μm, 0.6 to 4.0 μm, 0.7 to 4.0 μm, or 0.8 to 4.0 μm.

When the D50 of the filler is less than 0.5 μm, the surface roughness of the polyester-based film may be too low, and when the D50 exceeds 5.0 μm, the surface roughness of the polyester-based film is too increased, resulting in the polyester-based film. It may adversely affect the physical properties of the film.

D10 and D90 of the pillar may be appropriately adjusted within a range satisfying the span value of Equation 7 above.

The bulk density of the filler may be 0.1 g/cc to 0.8 g/cc. Specifically, the apparent density of the filler may be 0.2 g/cc to 0.75 g/cc, 0.2 g/cc to 0.7 g/cc, or 0.3 g/cc to 0.7 g/cc. The apparent density may increase as the D50 of the filler decreases, and the apparent density may decrease as the D50 of the filler increases.

According to an embodiment of the present invention, various fillers satisfying the physical properties may be used as the filler, and for example, a filler containing silicon may be included. Specifically, the filler may include spherical silicon beads having an aspect ratio of 0.8 to 1.2. The spherical silicon beads can further reduce the surface friction coefficient of the film compared to the amorphous silicon particles.

The polyester film may include 500 ppm to 2,000 ppm of the filler based on the total weight of the polyester resin solid content. Specifically, the filler may be 600 ppm to 2,000 ppm, 700 ppm to 1,500 ppm, 800 ppm to 1,300 ppm, or 800 ppm to 1,200 ppm. When the content of the filler satisfies the above range, the surface roughness and friction coefficient of the polyester film can be easily controlled, thereby further improving winding and running performance and mechanical properties of the film. When the content of the filler is less than 500 ppm, the 10-point average roughness (Rz) and surface dynamic coefficient of friction (F _d ) of the polyester film cannot be satisfied within the above ranges. In addition, when the content of the filler exceeds 2,000 ppm, mechanical properties of the polyester-based film may deteriorate.

The polyester film includes a polyester resin in which a diol and a dicarboxylic acid are polymerized. Such a polyester resin may be obtained by subjecting the diol and the dicarboxylic acid to transesterification, followed by polymerization.

The diol includes 1,4-cyclohexanedimethanol (CHDM), for example, 50 mol% or more, 70 mol% or more, 80 mol% or more, 85 mol% of CHDM based on the total number of moles of the diol or more, 90 mol% or more, 95 mol% or more, or 98 mol% or more. CHDM included in the diol can lower the modulus of the polyester resin, and also improve heat resistance and hydrolysis resistance by improving Tg. As an example, the diol may include 100 mol% of 1,4-cyclohexanedimethanol (CHDM).

The diol may further include diols other than CHDM. That is, the polyester resin may be a co-polyester resin.

Specific examples of the additional diol include ethylene glycol, 1,3-propanediol, 1,2-octanediol, 1,3-octanediol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1 ,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,5- pentanediol, 2,4-diethyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,1-dimethyl-1,5-pentanediol, and mixtures thereof.

The dicarboxylic acid includes one or more aromatic dicarboxylic acids.

For example, the aromatic dicarboxylic acid may include terephthalic acid, dimethyl terephthalic acid, or a combination thereof.

Specifically, the aromatic dicarboxylic acid is 75 mol% to 97 mol%, specifically 80 mol% to 95 mol%, 82 mol% to 95 mol%, or 85 mol% of terephthalic acid based on the total number of moles of the aromatic dicarboxylic acid. to 95 mol%. Alternatively, the aromatic dicarboxylic acid contains 80 mol% or more, or 90 mol% or more, specifically 80 mol% or more and less than 100 mol%, 90 mol% or more and less than 100 mol%, based on the total number of moles of the aromatic dicarboxylic acid, 93 mol% or more and less than 100 mol%, or 95 mol% or more and less than 100 mol%.

Accordingly, the polyester resin may include 1,4-cyclohexanedimethylene terephthalate as a repeating unit. Specifically, the polyester resin may include poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) resin.

The PCT resin is a crystalline polyester resin prepared by ester or transesterification and polycondensation of terephthalic acid (TPA) or dimethyl terephthalic acid (DMT) and 1,4-cyclohexanedimethanol (CHDM), and has an excellent melting point (Tm). ) and crystallization properties. In addition, the PCT resin may have excellent heat resistance, chemical resistance, moisture absorption resistance, and flowability compared to polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), which are general-purpose polyesters. By including the PCT resin in the polyester-based film, crystallinity may be increased and mechanical properties such as tensile strength may be improved during a manufacturing process through heating and stretching.

On the other hand, if the crystallinity of the PCT resin is too high, undesirable crystallization may occur during extrusion for film production or when the film is stretched. Accordingly, the polyester resin may further include isophthalic acid as the aromatic dicarboxylic acid in order to lower the crystallization rate.

For example, the aromatic dicarboxylic acid may include 3 mol% to 25 mol% of isophthalic acid based on the total number of moles of the aromatic dicarboxylic acid. Specifically, the aromatic dicarboxylic acid may include 5 mol% to 20 mol%, 5 mol% to 18 mol%, or 5 mol% to 15 mol% of isophthalic acid based on the total number of moles of the aromatic dicarboxylic acid. Alternatively, the aromatic dicarboxylic acid may include isophthalic acid in an amount of 10 mol% or less, specifically, 0 mol% to 7 mol% or less, or 0 mol% to 5 mol% or less based on the total number of moles of the aromatic dicarboxylic acid. can When within the above range, it is more advantageous to increase the handleability of the polymer by lowering the melting temperature (Tm) of the polymer while lowering the crystallization rate, which becomes excessively high as CHDM is included.

Accordingly, the polyester resin may include both 1,4-cyclohexanedimethylene terephthalate and 1,4-cyclohexanedimethylene isophthalate as repeating units. Specifically, the polyester resin may include poly(1,4-cyclohexylenedimethylene terephthalate-co-isophthalate) (PCTA) resin. In addition, the dicarboxylic acids include aromatic dicarboxylic acids such as dimethyl terephthalic acid, naphthalene dicarboxylic acid, and orthophthalic acid; Aliphatic dicarboxylic acids, such as adipic acid, azelaic acid, sebacic acid, and decane dicarboxylic acid; cycloaliphatic dicarboxylic acids; And it may further include one or more selected from the group consisting of esters thereof.

The polyester-based film may include a total of 85% by weight or more of a polyester resin, specifically, at least one of PCT and PCTA resin, based on the weight of the polyester-based film, and more specifically, 90% by weight or more, 95% by weight or more. % by weight or more, or 99% by weight or more.

As another example, the polyester-based film may further include other polyester resins in addition to the PCT or PCTA resin. Specifically, the polyester-based film may further include about 15% by weight or less of a polyethylene terephthalate (PET) resin or a polyethylene naphthalate (PEN) resin based on the weight of the polyester-based film. More specifically, the polyester film may further include about 0.1 wt % to 10 wt %, or about 0.1 wt % to 5 wt % of a PET or PEN resin based on the weight of the polyester film.

The polyester resin may have a weight average molecular weight (Mw) of 30,000 g/mol to 50,000 g/mol or 30,000 g/mol to 40,000 g/mol.

The polyester resin has an intrinsic viscosity (IV) of 50% or more, 60% or more, 70% or more, 80% or more, 70% to 90%, or 75% after treatment at 121 ° C. and 100% RH for 72 hours. to 85%.

Manufacturing method of polyester film

According to another embodiment of the present invention, preparing a resin composition by mixing a filler and a polyester resin in which diol and aromatic dicarboxylic acid including 1,4-cyclohexanedimethanol are polymerized (first step (S110) ); extruding and casting the resin composition to prepare an unstretched sheet (second step (S120)); and stretching and heat-setting the unstretched sheet (third step (S130)), wherein the 10-point average roughness (Rz) is 0.5 μm to 5 μm, and the surface dynamic coefficient of friction (F _d ) is 0.5 Below, a method for producing a polyester-based film is provided.

Specifically, referring to FIG. 1, in the method for producing a polyester film (S100), the first step (S110) is a poly polymerized diol and aromatic dicarboxylic acid including 1,4-cyclohexanedimethanol. A step of preparing a resin composition by mixing an ester resin and a filler may be included.

The composition of the polyester resin and the components, content and physical properties of the filler are the same as exemplified above.

In addition, the composition and process conditions may be adjusted so that the polyester film prepared by the above method has a 10-point average roughness (Rz) of 0.5 μm to 5 μm and a surface dynamic coefficient of friction (F _d ) of 0.5 or less. Specifically, in order to satisfy the 10-point average roughness (Rz) and the surface dynamic friction coefficient (F _d ) of the polyester film within a specific range, it may be implemented by adjusting the type, content, and physical properties of the filler.

In the polyester-based film manufacturing method (S100), the second step (S120) may include extruding and casting the resin composition to prepare an unstretched sheet.

Exemplary process conditions are described below, but are not limited thereto.

The polyester resin may be dried prior to extrusion, and the drying temperature at this time is preferably 150° C. or less to prevent discoloration. The extrusion may be performed at a temperature condition of 230 °C to 300 °C, or 250 °C to 290 °C.

The polyester-based film is preheated at a certain temperature before stretching. The range of the preheating temperature may be a range satisfying Tg+5°C to Tg+50°C based on the glass transition temperature (Tg) of the polyester resin, for example, a range of 70°C to 90°C. When within the above range, it is possible to secure flexibility for easy stretching of the polyester film and to effectively prevent breakage during stretching.

The stretching is performed by biaxial stretching, and may be biaxially stretched in the longitudinal direction (machine direction, MD) and the width direction (tenter direction, TD) through, for example, a simultaneous biaxial stretching method or a sequential biaxial stretching method. Preferably, a sequential biaxial stretching method of first stretching in one direction and then stretching in a direction perpendicular to that direction may be performed.

The stretching ratio in the longitudinal direction may be in the range of 2.0 to 5.0, and more specifically in the range of 2.8 to 3.5. In addition, the stretch ratio in the width direction may be in the range of 2.0 to 5.0, and more specifically in the range of 2.9 to 3.7. Preferably, the stretching ratio in the longitudinal direction and the stretching ratio in the width direction are similar, and specifically, the ratio (d2/d1) of the stretching ratio (d2) in the longitudinal direction to the stretching ratio (d1) in the width direction is 0.5 to 1.0, 0.7 to 1.0, or It may be 0.9 to 1.0. The stretching ratios d1 and d2 are ratios representing the length after stretching when the length before stretching is 1.0. In addition, the stretching speed may be 6.5 m/min to 8.5 m/min, but is not particularly limited.

The stretched sheet may be heat-set at 150°C to 250°C, more specifically at 200°C to 250°C. The heat setting may be performed for 5 seconds to 1 minute, and more specifically, for 10 seconds to 45 minutes.

After starting the heat setting, the film may be relaxed in the longitudinal direction and/or the width direction, and the temperature range at this time may be 150° C. to 250° C., and the relaxation rate may be 1% to 10%, or 3% to 7%. can

Since the polyester-based film according to the embodiment has excellent dielectric properties in a high frequency band and has properties equivalent to or better than conventional films in terms of flexibility and general physicochemical properties, it is possible to obtain a laminate with a conductive film such as FCCL and FPCB. It can be applied to the manufacture of the same electronic board to improve fairness, durability, transmission capacity, etc.

[Laminate]

According to an embodiment of the present invention, a laminate including the polyester film may be provided.

The laminate may further include, for example, a conductive layer and an adhesive layer.

In addition, the laminate may include a laminate for an electronic board, and the laminate for an electronic board may include a copper clad laminate (CCL), specifically, a flexible copper clad laminate (FCCL).

A laminate according to one embodiment may include a substrate layer and a conductive layer disposed on at least one surface of the substrate layer.

The base layer may have the same properties and composition as those of the polyester-based film according to one embodiment described above. That is, the base layer includes a polyester resin in which a diol containing 1,4-cyclohexanedimethanol and an aromatic dicarboxylic acid are polymerized, and has a 10-point average roughness (Rz) of 0.5 μm to 5 μm, and surface kinetic friction The coefficient (F _d ) is 0.5 or less.

The conductive layer may include a conductive material. For example, the conductive layer may include a conductive metal. Specifically, the conductive layer may be a metal foil. For example, the conductive layer may include one or more metals selected from the group consisting of copper, nickel, gold, silver, zinc, and tin. More specifically, the conductive layer may be copper foil (copper foil).

The thickness of the conductive layer may be 6 μm to 200 μm, specifically 10 μm to 150 μm, 10 μm to 100 μm, or 20 μm to 50 μm.

The laminate may further include an adhesive layer to increase bonding strength between components. For example, an adhesive layer may be inserted between the base layer and the conductive layer.

The adhesive layer may include a thermosetting resin, such as an epoxy resin. The said epoxy-type resin, For example, bisphenol-type epoxy resin; Spiro cyclic epoxy resin; naphthalene type epoxy resin; Biphenyl type epoxy resin; Terpene type epoxy resin; glycidyl ether type epoxy resins; glycidyl amine type epoxy resins; A novolak-type epoxy resin etc. are mentioned.

The epoxy-based resin may have an epoxy equivalent weight of about 80 g/eq to 1,000 g/eq, or about 100 g/eq to 300 g/eq. In addition, the epoxy-based resin may have a number average molecular weight in the range of about 10,000 g / mol to 50,000 g / mol.

The adhesive layer may have a thickness of 1 μm to 50 μm. In more detail, the adhesive layer may have a thickness of 10 μm to 50 μm, or 20 μm to 40 μm.

The laminate may further include vias that electrically connect the conductive layers while penetrating the base layer in a thickness direction.

Specifically, the laminate may include a hole penetrating the base layer in a thickness direction, and vias may be formed inside the hole to electrically connect the conductive layers stacked on both sides of the base layer.

The hole may have a diameter in the range of 100 μm to 300 μm, or in the range of 120 μm to 170 μm, for example.

A plurality of the holes may be present in the laminated body as needed.

The via may include a conductive material. For example, the via may include at least one metal selected from the group consisting of copper, nickel, gold, silver, zinc, and tin.

The via may be formed by filling the hole with a conductive material, inserting solder or a conductive rod, or plating the hole.

[Electronic board]

According to an embodiment of the present invention, an electronic board including the polyester film may be provided.

An electronic board according to an embodiment may include a substrate layer and a conductive pattern layer disposed on at least one surface of the substrate layer.

The electronic board may include a printed circuit board (PCB), specifically a flexible printed circuit board (FPCB).

The base layer may have the same properties and composition as those of the polyester-based film according to one embodiment described above.

The conductive pattern layer includes one or more conductive patterns.

The conductive pattern may include a conductive material. For example, the conductive pattern may include a conductive metal. Specifically, the conductive pattern may include one or more metals selected from the group consisting of copper, nickel, gold, silver, zinc, and tin. More specifically, the conductive pattern may include a copper pattern.

The shape of the conductive pattern is not particularly limited, and may include, for example, a line pattern or a planar spiral pattern.

Also, the conductive pattern layer may include a circuit pattern. More specifically, the conductive pattern layer may include a printed circuit pattern.

Also, the conductive pattern layer may include a terminal pattern. The terminal pattern may be electrically connected to an external circuit.

In addition, the electronic board may further include an adhesive layer to increase bonding strength between components. For example, an adhesive layer may be inserted between the base layer and the conductive pattern layer.

Composition and characteristics of the adhesive layer may be the same as those of the adhesive layer in the above-described laminate.

In addition, the electronic substrate may further include vias that electrically connect the conductive patterns while penetrating the substrate layer in a thickness direction.

Composition and characteristics of the via may be the same as those of the previously described via in the stacked body.

[Example]

It will be described in more detail through the following examples, but is not limited to these ranges.

Preparation Example 1: Preparation of poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) resin

100 parts by mole of 1,4-cyclohexanedimethanol (CHDM) as a diol, and 5 parts by mole of isophthalic acid (IPA) and 95 parts by mole of terephthalic acid (TPA) as dicarboxylic acids were put into an autoclave equipped with a stirrer and a distillation tower, and a transesterification reaction After adding manganese acetate as a catalyst in an amount of 0.01% by weight of terephthalic acid, a transesterification reaction was performed at 290 °C. After completion of the transesterification reaction, 0.001% by weight of Ti was added as a polymerization catalyst, followed by stirring for 10 minutes. Subsequently, the reactant was transferred to a separate reactor equipped with a vacuum facility, and then polymerized at 300° C. for 180 minutes to obtain poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) resin.

Example 1: Preparation of PCT film

After mixing the PCT resin obtained in Preparation Example 1 and the spherical silicone beads having the physical properties of Table 1 as a filler, extruded at about 280 ° C. with an extruder and cast at about 20 ° C. with a casting roll to obtain an unstretched sheet was manufactured. After preheating the unstretched sheet, it was stretched in the machine direction (MD) and width direction (TD) at a temperature of 110°C. Thereafter, the stretched sheet was heat-set for about 30 seconds to obtain a PCT film.

Examples 2 and 3: Preparation of PCT films

In the preparation of the PCT film of Example 1, the PCT film was obtained by performing the same method as in Example 1, except that spherical silicon beads having physical properties shown in Table 1 were used.

Comparative Example 1: Preparation of PCT film

In the preparation of the PCT film of Example 1, except that spherical silicon beads were not used, the same method as in Example 1 was performed to obtain a PCT film.

Comparative Example 2: Preparation of PCT film

In the preparation of the PCT film of Example 1, a PCT film was obtained by performing the same method as in Example 1, except that amorphous silicon particles (Fuji Silysia Chemical, Silysia 340) having physical properties shown in Table 1 were used.

Comparative Example 3: Preparation of PEN Film

A PEN film was obtained in the same manner as in Example 1, except that polyethylene naphthalate (PEN) resin was used instead of the PCT resin of Example 1, and spherical silicon beads having physical properties shown in Table 1 were used.

Experimental Example

Experimental Example 1: Measurement of average particle diameter of filler

After dispersing the particles in MEK using Malvern master size MSS, the particle size was measured.

Experimental Example 2: Film thickness measurement

Using a digital micrometer 547-401 from Mitutoyo Co., Ltd. in Japan, 5 points were measured in the width direction, and the thickness was measured as an average value.

Experimental Example 3: Surface roughness measurement

Ten-point average roughness (Rz), center line average roughness (Ra), and maximum height roughness (Ry) were measured using a two-dimensional contact type surface roughness meter (SE3300 from Kosaka).

The 10-point average roughness (Rz) is the surface roughness according to KS B 0161, taken as much as the reference length from the roughness cross-section curve, drawing an arbitrary straight line (reference line) parallel to the average line of the cross-section curve, and from the reference line of the highest five mountains It is expressed as the difference between the mean value of the distance and the mean value of the distance from the baseline of the lowest 5 goals.

The center line average roughness (Ra) of the polyester film is a surface roughness according to KS B 0161, and the sum of the arithmetic mean roughness and the total upper and lower sides of the center line of the reference length is obtained, and the value is divided by the length of the measurement section is indicated by

The maximum height roughness (Ry) of the polyester film is a surface roughness according to KS B 0161, taken as much as the reference length from the roughness cross-sectional curve, parallel to the center line of the cross-sectional curve, and between the two parallel lines contacting the highest peak and the deepest valley means distance.

Experimental Example 4: Friction Coefficient Measurement

According to the ASTM D1894 test method, after placing the specimen horizontally on the test table of the friction coefficient measuring instrument, the test equipment was driven at a constant displacement speed to measure the static friction coefficient and the dynamic friction coefficient.

Experimental Example 5: Measurement of tensile strength

The film was cut into a size of 15 mm X 100 mm, and the tensile strength was measured at room temperature by measuring the same sample three times at a test speed of 200 mm/min of the UTM measuring equipment.

Experimental Example 6: Measurement of elongation at break

The film was cut into a size of 15 mm X 100 mm, and the elongation at break was measured at room temperature by measuring the same sample three times at a test speed of 200 mm/min of the UTM measuring equipment.

In addition, after storing the film in a low-temperature environment of -20 ° C. for 24 hours, the elongation at break was measured as described above within 1 minute after taking it out of the low-temperature environment.

Experimental Example 7: Modulus measurement

The film was cut into a size of 15 mm X 100 mm, and the same sample was measured three times at a test speed of 200 mm/min of the UTM measuring equipment to measure the modulus at room temperature.

In addition, after storing the film in a low-temperature environment of -20 ° C. for 24 hours, the film was taken out of the low-temperature environment and the modulus was measured as described above within 1 minute.

Experimental Example 8: Measurement of haze and light transmittance

Light transmittance at 550 nm was measured using a haze meter NDH-5000W manufactured by Denshoku Kogyo Co., Ltd., Japan.

Experimental Example 9: Film fairness evaluation

Fairness evaluation such as winding and running performance evaluation of the polyester film was performed as follows:

O (8 to 10 points): Very good winding and running performance

Δ (more than 5 points and less than 8 points): Normal winding and running performance

X (1 to 5 points): Poor winding and running performance

Experimental Example 10: Scanning electron microscope (SEM) measurement

The surfaces of the PCT films of Examples 1 to 3 were observed using a scanning electron microscope (SEM) image (200 times).

As can be seen in FIGS. 4 to 6, even if the same silicon beads are used, the surface of the PCT film is significantly different depending on the particle size and span value of the silicon beads, and it can be seen that the surface roughness and friction coefficient of the PCT film are different as a result. there is.

As can be seen in Tables 1 and 2, the PCT films of Examples 1 to 3 according to an embodiment of the present invention have a 10-point average roughness (Rz) of 0.5 μm to 5 μm, and a surface dynamic coefficient of friction (F _d ) It can be seen that it is within the range of 0.5 or less.

Specifically, the PCT films of Examples 1 to 3 including PCT resin and spherical silicon beads as fillers had Rz of 0.57, 0.74, and 1.48, and F _d of 0.38, 0.35, and 0.38, respectively.

In contrast, the PCT film of Comparative Example 1 without filler had Rz of 0.3 and F _d of 0.57, and compared to the PCT films of Examples 1 to 3, Rz was significantly reduced and F _d was significantly increased. .

In addition, even if the filler is included, the PCT film of Comparative Example 2 containing amorphous silicon particles has Rz of 1.04, which is about twice as high as that of the PCT films of Examples 1 and 3, and F _d is 0.53, which is a coefficient of friction. was high.

On the other hand, in the case of the PEN film of Comparative Example 3 using the PEN resin instead of the PCT resin, even if a filler containing spherical silicon beads was used, Rz was 0.12, which was significantly reduced compared to the PCT films of Examples 1 and 3.

As described above, Examples 1 to 3 in which the 10-point average roughness (Rz) is 0.5 μm to 5 μm and the surface dynamic friction coefficient (F _d ) satisfies the physical properties in the range of 0.5 or less, as can be seen in Table 2 Likewise, it can be seen that the processability was improved due to excellent winding and running performance, and mechanical properties were simultaneously improved while the haze and light transmittance were excellent.

Claims (10)

A polyester resin in which a diol including 1,4-cyclohexanedimethanol and an aromatic dicarboxylic acid are polymerized, and a filler,
The 10-point average roughness (Rz) is 0.5 μm to 5 μm,
The surface dynamic friction coefficient (F _d ) is 0.5 or less,
RF of Equation 1 below is 0.3 to 0.8,
F of the following formula 2 is from 0.50 to less than 0.77,
E of the following formula 6 is 5 to 14%, a polyester-based film:
[Equation 1]
RF =

× F _d
[Equation 2]
F = F _d /F _s
[Equation 6]
E = │E ₁ - E ₂ │
In the above formulas 1, 2 and 6,
R _y is the maximum height roughness of the polyester film,
F _d is the coefficient of kinetic friction of the surface of the polyester film,
F _s is the static friction coefficient of the surface of the polyester film,
E ₁ is the elongation at break in the first direction of the polyester film,
E ₂ is the elongation at break in the second direction perpendicular to the first direction of the polyester film.
delete delete According to claim 1,
A polyester-based film in which F _t of the polyester-based film is less than 1 in the following formula 3:
[Equation 3]
F _t = F _{d +} F _s
In Equation 3 above,
F _d and F _s are as defined above.
According to claim 1,
The filler has a span value of Equation 7 below when the particle sizes at which the cumulative volume concentration (%) in the particle size distribution is 10%, 50%, and 90% are D10, D50, and D90, respectively. 0.3 to 1.0, a polyester-based film.
[Equation 7]
Span =

.
According to claim 5,
The filler has a D50 of 0.5 μm to 5 μm,
A polyester-based film having a bulk density of 0.1 g/cc to 0.8 g/cc.
According to claim 1,
The polyester-based film comprises 500 ppm to 2,000 ppm of the filler based on the total weight of the polyester resin solid content, the polyester-based film.
According to claim 1,
The polyester film has a haze value of 9% to 22%,
A polyester-based film having a modulus of 25 ° C. of 200 kg / ㎟ to 300 kg / ㎟.
According to claim 1,
The 1,4-cyclohexanedimethanol is a polyester-based film containing 50 mol% or more based on the total number of moles of the diol.
preparing a resin composition by mixing a filler and a polyester resin obtained by polymerizing a diol containing 1,4-cyclohexanedimethanol and an aromatic dicarboxylic acid;
Extruding and casting the resin composition to prepare an unstretched sheet; and
Including; stretching and heat-setting the unstretched sheet;
The 10-point average roughness (Rz) is 0.5 μm to 5 μm,
The surface dynamic friction coefficient (F _d ) is 0.5 or less,
RF of Equation 1 below is 0.3 to 0.8,
F of the following formula 2 is from 0.50 to less than 0.77,
Method for producing a polyester-based film in which E of Formula 6 is 5 to 14%:
[Equation 1]
RF =

× F _d
[Equation 2]
F = F _d /F _s
[Equation 6]
E = │E ₁ - E ₂ │
In the above formulas 1, 2 and 6,
R _y is the maximum height roughness of the polyester film,
F _d is the coefficient of kinetic friction of the surface of the polyester film,
F _s is the static friction coefficient of the surface of the polyester film,
E ₁ is the elongation at break in the first direction of the polyester film,
E ₂ is the elongation at break in the second direction perpendicular to the first direction of the polyester film.

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