WO2023101191A1 - Polyester-based film and production method therefor - Google Patents

Abstract

One embodiment relates to: a polyester-based film which comprises a filler and a copolymerized polyester-based resin formed by copolymerizing a diol and a dicarboxylic acid, and which has a Rd, according to formula 1 for centerline average roughness (Ra) and maximum height roughness (Rmax), of at most 2.5; and a production method therefor. The polyester-based film comprises a specific filler, and thus the surface roughness of the polyester-based film may be controlled, and accordingly, processability, including winding and running performance, is improved, and also, mechanical and optical properties are improved, and thus the polyester-based film has excellent quality.

Description

Polyester-based film and manufacturing 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, and in particular, flexible printed circuit boards (FPCB) mounted on smart devices such as mobile phones and tablet PCs are representative. Recently, as the demand for thinning, lightening, flexibility, and high performance of electronic products increases with the growth of these smart devices, the performance of Flexible Copper Clad Laminate (FCCL), the main material of flexible circuit boards, can be improved. Research is ongoing.

Flexible copper clad laminates are generally manufactured by laminating copper foil on one side or both sides of a base film. was used as a base film. However, such liquid crystal crystalline polymers or polyimide-based resins have problems in that they have high unit price and high permittivity and low moisture resistance.

On the other hand, since polyester-based resins are excellent in mechanical properties such as durability, chemical resistance, heat resistance, and optical properties such as transparency, they are widely used as various industrial materials such as display devices as well as materials such as fibers, films, and molded products. However, polyester-based films manufactured using such polyester-based resins have excellent heat resistance and hydrolysis resistance, but have difficulties in processes such as winding due to soft and high surface friction coefficients, and poor driving performance. .

In order to solve this problem, attempts have been made such as primer coating on the surface of the film or injecting various additives into the polyester resin, but at the same time, fairness such as winding without degrading the mechanical properties or optical properties of the polyester film There is also a limit to improvement. Therefore, research on a polyester-based film having excellent processability such as winding and running performance as well as mechanical and optical properties is being continued.

For example, Korean Patent Publication No. 2006-0060082 discloses a flexible copper-clad laminate film in which the surface of a polyimide film is modified and applied to copper foil, but such a polyimide film has a high unit price and high permittivity and low moisture resistance. There is a limit to performance improvement, and since the film is immersed in a solution in the reforming step, moisture resistance may be further deteriorated.

[Prior art literature]

[Patent Literature]

(Patent Document 1) Korean Patent Publication No. 2006-0060082

Accordingly, embodiments are intended to provide a polyester-based film and a method for manufacturing the same, which are excellent in processability such as winding and running performance, as well as mechanical properties and optical properties.

A polyester-based film according to an embodiment includes a co-polyester-based resin in which a diol and two or more dicarboxylic acids are copolymerized; and a filler, and R _d according to Equation 1 below is 2.5 or less.

[Equation 1]

In the above formula 1,

R _max is the maximum height roughness (μm) of the polyester film,

R _a is the center line average roughness (μm) of the polyester-based film.

A method for manufacturing a polyester-based film according to another embodiment includes preparing a resin composition by mixing a co-polyester-based resin in which diols and dicarboxylic acids are copolymerized with a filler; Melting and extruding the resin composition to prepare an unstretched sheet; preparing a stretched sheet by first stretching the unstretched sheet in a first direction and secondarily stretching the unstretched sheet in a second direction perpendicular to the first direction; and preparing a polyester-based film by heat-setting the stretched sheet at 200° C. to 260° C., wherein the polyester-based film has an R _d of 2.5 or less according to Formula 1.

By including a specific filler, the polyester-based film according to the embodiment has excellent processability such as winding and running performance of the film by controlling the surface roughness, as well as excellent mechanical properties and optical properties.

In particular, the polyester-based film has excellent dispersibility while satisfying 10-point average roughness (R _z ), center line average roughness (R _a ), and maximum height roughness (R _max ) within preferred ranges, thereby providing mechanical properties and optical properties. It is possible to improve the surface properties at the same time without degrading.

1 shows a scanning electron microscope (SEM) image of the polyester film of Example 1.

Figure 2 shows a scanning electron microscope (SEM) image of the polyester film of Example 2.

Figure 3 shows a scanning electron microscope (SEM) image of the polyester-based film of Example 3.

Figure 4 shows a scanning electron microscope (SEM) image of the polyester-based film of Comparative Example 1.

5 shows a scanning electron microscope (SEM) image of the polyester film of Comparative Example 2.

6 shows a scanning electron microscope (SEM) image of the polyester film of Comparative Example 3.

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

In this specification, when a certain component is said to "include", this means that it may further include other components, not excluding other components, unless otherwise stated.

It should be understood that all numbers and expressions representing amounts of constituents, reaction conditions, etc. described herein are modified by the term "about" in all cases unless otherwise specified.

In this specification, terms such as first, second, primary, and secondary are used to describe various components, and the components are not limited by the terms. These terms are only used for the purpose of distinguishing one component from another.

polyester film

A polyester-based film according to an embodiment includes a co-polyester-based resin in which a diol and two or more dicarboxylic acids are copolymerized; and a filler, and R _d according to Equation 1 below is 2.5 or less.

[Equation 1]

In the above formula 1,

R _max is the maximum height roughness (μm) of the polyester film,

R _a is the center line average roughness (μm) of the polyester-based film.

Since a polyester film is generally manufactured using a roll, it is important to improve fairness such as winding property and driving performance in order to improve the quality of the polyester film produced.

Conventionally, organic and inorganic additives have been used to improve fairness such as film winding and running performance, but when these additives are used, there is a problem in that mechanical properties such as tensile strength and modulus, in particular, transparency are greatly deteriorated. Specifically, when a polyester film is prepared by adding additives to the polyester resin, processability may be improved, but mechanical properties such as tensile strength and modulus of the prepared polyester film are lowered, and in particular, haze is reduced. increased, resulting in very low transparency.

However, the polyester-based film according to the embodiment includes a co-polyester-based resin in which a diol and two or more kinds of dicarboxylic acids are copolymerized and a filler, thereby effectively controlling the surface roughness of the film to improve fairness such as winding and driving performance of the film. In addition to improving the mechanical properties and optical properties can be improved at the same time. In particular, the polyester film has excellent dispersibility while satisfying 10-point average roughness (R _z ), center line average roughness (R _a ) and maximum height roughness (R _max ) within preferred ranges, thereby improving mechanical properties and optical properties. Surface properties can also be improved at the same time without deterioration.

Specifically, the polyester-based film has an R _d of 2.5 or less according to Formula 1 below.

[Equation 1]

In the above formula 1,

R _max is the maximum height roughness (μm) of the polyester-based film, and R _a is the center line average roughness (μm) of the polyester-based film.

Specifically, the R _d represents the ratio between the surface roughness characteristics of the polyester film, and the R _d may be 2.3 or less, 2.0 or less, 1.8 or less, or 1.6 or less, 0.3 to 2.5, 0.5 to 2.3, 0.5 to 2.1 , 0.6 to 1.8, 0.8 to 1.6 or 0.9 to 1.6. When the R _d value satisfies the above range, it is possible to simultaneously improve mechanical properties and optical properties while controlling the surface roughness to a more preferable range to improve fairness such as winding and running performance of the film, and in particular, transparency by reducing haze. can maximize

In addition, the 10-point average roughness (R _z ) of the polyester film is 0.8 μm or less. For example, the 10-point average roughness (R _z ) of the polyester film may be 0.7 μm or less, 0.6 μm or less, 0.5 μm or less, or 0.3 μm or less, 0.01 μm to 0.8 μm, 0.05 μm to 0.6 μm, or 0.1 μm. μm to 0.5 μm or 0.15 μm to 0.3 μm.

The center line average roughness (R _a ) of the polyester-based film is 0.05 μm or less. For example, the center line average roughness (R _a ) of the polyester film may be 0.04 μm or less, 0.03 μm or less, or 0.02 μm or less, 0.001 μm to 0.05 μm, 0.005 μm to 0.04 μm, 0.01 μm to 0.03 μm, or It may be 0.01 μm to 0.03 μm.

In addition, the maximum height roughness (R _max ) of the polyester-based film is 1.5 μm or less. For example, the maximum height roughness (R _max ) of the polyester film may be 1.4 μm or less, 1.3 μm or less, 1.1 μm or less, or 1.0 μm or less, 0.1 μm to 1.5 μm, 0.2 μm to 1.4 μm, or 0.5 μm. to 1.3 μm, 0.6 μm to 1.1 μm, or 0.7 μm to 1.0 μm.

When the 10-point average roughness (R _z ), the center line average roughness (R _a ), and the maximum height roughness (R _max ) of the polyester-based film each satisfy the above ranges, the surface roughness is controlled to a desirable range to wind and run the film. Processability, such as performance, can be improved, and surface properties can be improved at the same time without deteriorating mechanical properties and optical properties.

Surface roughness such as the 10-point average roughness (R _z ), center line average roughness (R _a ), and maximum height roughness (R _max ) may be measured using a two-dimensional contact surface roughness meter (SE3300 manufactured by Kosaka).

Specifically, the 10-point average roughness (R _z ) is surface roughness according to KS B 0161. When the surface is cut with a plane perpendicular to the surface of the film, a portion of the section appearing on the cut surface is enlarged and taken as much as the reference length from the recorded cross-sectional curve, and an arbitrary straight line parallel to the average line of the cross-sectional curve is set as the reference line. At this time, it can be calculated as the difference between the average value of the distance from the reference line for the five highest peaks and the average value for the distance from the reference line for the five lowest valleys.

The center line average roughness (R _a ) is a surface roughness according to KS B 0161, and a straight line generated when a mountain is cut from a roughness curve to fill a valley is called a center line, and a measured length is taken in the direction of the center line, and from the center line It can be calculated by dividing the area of the upper part obtained by folding the lower part upwards by the measured length.

The maximum height roughness (R _max ) is a surface roughness according to KS B 0161, a reference length is taken from a cross-sectional curve, and it is parallel to the center line of the cross-sectional curve and the highest peak and the deepest valley. Can be calculated as the distance between two parallel lines. there is.

In addition, the polyester-based film may have an RF of 0.8 or less according to Equation 2.

[Equation 2]

In Equation 2,

R _max is the maximum height roughness (μm) of the polyester-based film, and F _d is the kinetic friction coefficient of the polyester-based film.

Specifically, the RF represents the ratio between the surface properties of the polyester-based film, the RF may be 0.75 or less, 0.7 or less, 0.65 or less, 0.6 or less, or 0.55 or less, 0.05 to 0.8, 0.05 to 0.8, 0.08 to 0.7 , 0.1 to 0.65, 0.15 to 0.6, 0.2 to 0.6 or 0.3 to 0.55. When the RF value satisfies the above range, surface roughness can be controlled to a more preferable range to simultaneously improve mechanical properties and optical properties, and in particular, transparency can be maximized by reducing haze.

The polyester-based film may have a dynamic coefficient of friction (F _d ) of 0.6 or less, and a static coefficient of friction (F _s ) of 0.75 or less. For example, the surface dynamic friction coefficient (F _d ) of the film may be 0.5 or less or 0.55 or less, and the surface static friction coefficient (F _s ) of the film may be 0.74 or less, 0.73 or less, 0.7 or less, or 0.68 or less.

When the kinetic coefficient of friction (F _d ) and the coefficient of static friction (F _s ) of the film satisfy the above ranges, both mechanical properties and optical properties can be improved. Specifically, the surface roughness and the surface friction coefficient are not exactly proportional, and when the surface roughness and the surface friction coefficient satisfy the above ranges, respectively, haze can be reduced without deterioration of mechanical properties, thereby maximizing transparency.

Haze of the polyester film may be 8% or less. For example, the haze of the polyester film may be 8% or less, 6% or less, 5% or less, or 4.5% or less. The polyester-based film according to the embodiment has excellent transparency while having excellent mechanical properties by having a haze that satisfies the above range while including a filler.

In addition, the transmittance of the polyester-based film may be 88% or more at a wavelength of 400 nm to 700 nm. For example, the transmittance of the polyester film at a wavelength of 400 nm to 700 nm may be 88.5% or more, 89% or more, or 89.5% or more.

Tensile strength of the polyester film may be 19 kgf/mm ² or less. Specifically, the tensile strength of the in-plane first direction of the polyester film may be 19 kgf/mm ² or less, 18 kgf/mm ² or less, 16 kgf/mm ² or less, or 15 kgf/mm 2 or less, and 10 kgf/mm ² or less. mm ² to 19 kgf/mm ² , 10 kgf/mm ² to 16 kgf/mm ² or 10 kgf/mm ² to 15 kgf/mm ² .

In addition, the tensile strength in the second direction perpendicular to the first direction in the plane of the polyester film may be 19 kgf/mm ² or less or 18.5 kgf/mm ² or less, 10 kgf/mm ² to 19 kgf/mm ² , 12 kgf/mm ² to 19 kgf/mm ² , 13 kgf/mm ² to 18.5 kgf/mm ² or 14.5 kgf/mm ² to 18.5 kgf/mm ² .

When the tensile strength of the polyester-based film satisfies the above range, 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 due to excellent mechanical properties.

In the present specification, the first direction may be a width direction (TD) or a length direction (MD). Specifically, the first direction may be a length direction (MD), and the second direction perpendicular to the first direction may be a width direction (TD).

In addition, the elongation at break of the polyester-based film may be 30% or more. Specifically, the elongation at break in the first in-plane direction of the polyester-based film may be 30% or more, 35% or more, 40% or more, or 42% or more, and the second in-plane direction perpendicular to the first direction of the polyester-based film The elongation at break in the direction may be 30% or more, 32% or more, or 34% or more.

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

Modulus of the polyester-based film may be 320 kgf/mm ² or less. Specifically, the modulus of the polyester-based film in the first direction in the plane is 320 kgf/mm ² or less, 310 kgf/mm ² or less, 300 kgf/mm ² or less, 290 kgf/mm ^{2 or} less, or 288 kgf/mm ^{2 or} less. May be, 230 kgf / mm ² to 300 kgf / mm ² , 250 kgf / mm ² to 290 kgf / mm ² , 255 kgf / mm ² to 290 kgf / mm ² , 260 kgf / mm ² to 300 kgf / mm ² , 260 kgf/mm ² to 290 kgf/mm ² or 260 kgf/mm ² to 288 kgf/mm ² .

In addition, the modulus of the polyester film in the second direction perpendicular to the first in-plane direction is 320 kgf/mm ² or less, 310 kgf/mm ² or less, 305 kgf/mm ² or less, 300 kgf/mm ² or less, or 299 kgf/mm ² or less, 230 kgf/mm ² to 320 kgf/mm ² , 260 kgf/mm ² to 310 kgf/mm ² , 275 kgf/mm ² to 320 kgf/mm ² , 275 kgf/mm ² to 300 kgf/mm ² or 280 kgf/mm ² to 299 kgf/mm ² .

The tensile strength, elongation at break and modulus may be measured at room temperature according to ASTM D 882 by using a universal testing machine (4206-001, manufactured by INSTRON).

In addition, the polyester-based film 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 30 μm to 60 μm.

In addition, the polyester-based film includes a co-polyester-based resin in which a diol and two or more kinds of dicarboxylic acids are copolymerized.

The diol includes cyclohexanedimethanol or a derivative thereof. For example, the diol may include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol or 1,4-cyclohexanedimethanol, preferably 1,4-cyclohexanedimethanol can include More specifically, the diol may include 1,4-cyclohexanedimethanol or a derivative thereof.

In addition, the diol may include 70 mol% or more of cyclohexanedimethanol or a derivative thereof. For example, the copolyester-based resin contains cyclohexanedimethanol or a derivative thereof in an amount of 72 mol% or more, 75 mol% or more, 85 mol% or more, 88 mol% or more, or 90 mol% based on the total number of moles of the diol. or more, 93 mol% or more, 95 mol% or more, 97 mol% or more, 99 mol% or more, or 100 mol%.

Flexibility, durability, and hydrolysis resistance can be improved by including cyclohexanedimethanol or a derivative thereof in the diol, and durability, heat resistance, and hydrolysis resistance can be maximized when the diol is composed of only cyclohexanedimethanol. .

In addition, the diol may include at least one selected from the group consisting of ethylene glycol, neopentyl glycol, and diethylene glycol, if necessary. For example, the copolymerized polyester-based resin contains 1 mol% to 30 mol%, 1 mol% to 1 mol% of at least one selected from the group consisting of ethylene glycol, neopentyl glycol and diethylene glycol based on the total number of moles of the diol. 20 mol%, 1 mol% to 15 mol%, 1 mol% to 10 mol%, or 1 mol% to 5 mol%.

The dicarboxylic acid may include two or more dicarboxylic acids. Specifically, the dicarboxylic acid may include a first dicarboxylic acid and a second dicarboxylic acid, the first dicarboxylic acid may be terephthalic acid, and the second dicarboxylic acid may be isophthalic acid. there is.

More specifically, the dicarboxylic acid may include 70 mol% to 99 mol% of terephthalic acid and 1 mol% to 30 mol% of isophthalic acid. For example, the copolyester-based resin contains 73 mol% to 99 mol%, 75 mol% to 99 mol%, 80 mol% to 98 mol%, 83 mol% of terephthalic acid based on the total number of moles of the dicarboxylic acid. % to 98 mol% or 85 mol% to 98 mol%, and 1 mol% to 28 mol%, 1 mol% to 25 mol%, 1 mol% to 20 mol%, 2 mol% to 2 mol% isophthalic acid 15 mol%, 3 mol% to 13 mol%, 3 mol% to 10 mol%, or 3 mol% to 8 mol%. When the contents of terephthalic acid and isophthalic acid satisfy the above ranges, flexibility, durability, heat resistance and hydrolysis resistance may be improved.

In addition, the co-polyester-based resin may include an additional dicarboxylic acid other than the first and second dicarboxylic acids. The additional dicarboxylic acid may include dimethyl terephthalic acid, and for example, the co-polyester-based resin is present in an amount of 1 mol% to 15 mol%, 1 mol% to 10 mol% based on the total number of moles of the dicarboxylic acid. Or 3 mol% to 7 mol% of dimethyl terephthalic acid may be further included.

The co-polyester-based resin according to the embodiment may include a polycyclohexylenedimethylene terephthalate (PCT) resin.

Specifically, since the copolymerized polyester-based resin includes polycyclohexylenedimethylene terephthalate (PCT) resin, it has excellent heat resistance and chemical resistance compared to polyethylene terephthalate (PET) resin and polybutylene terephthalate (PBT) resin. and hygroscopicity. Therefore, mechanical properties such as tensile strength and modulus may be improved while crystallinity increases due to excellent crystallization characteristics during the manufacturing process through melt extrusion, stretching, etc. at a high temperature.

At this time, undesirable crystallization may occur during the manufacturing process, but since the copolyester-based resin contains 1 mol% to 30 mol% of isophthalic acid as dicarboxylic acid, it may be excessively high as cyclohexylenedimethylene is included. It is more advantageous to increase the handleability of the polymer by lowering the melting point (Tm) while lowering the possible crystallization rate.

In addition, the polyester-based film may include 85% by weight or more of the co-polyester-based resin. For example, the content of the co-polyester-based resin is 88% by weight or more, 90% by weight or more, 93% by weight or more, 95% by weight or more, 98% by weight or more, 99% by weight or more based on the total weight of the polyester-based film. % or more than 100%, 85% to 100%, 90% to 100%, 95% to 100% or 98% to 100%.

In addition, the co-polyester-based resin may further include at least one additive selected from the group consisting of an ultraviolet stabilizer, a heat stabilizer, an antioxidant, and an inert particle.

Specifically, the UV stabilizer may be at least one selected from the group consisting of benzophenone-based, benzotriazole-based, cyanoacrylate-based, and salicylic acid ester-based compounds, the heat stabilizer may be an iodine-based compound, and the antioxidant may be a phosphorus-based antioxidant, a phenol-based antioxidant, or a sulfur-based antioxidant, and the inert particle may be silica or potassium carbonate, but is not limited thereto.

The content of the additive is 0.5% to 15% by weight, 1% to 13% by weight, 1.2% to 12% by weight, 1.5% to 10% by weight, 1.7% by weight based on the total weight of the co-polyester-based resin. % to 8% or 1.8% to 7.5%.

In addition, the polyester-based film may include a filler.

Specifically, the polyester film according to the embodiment has a 10-point average roughness (R _z ), center line average roughness (R _a ) and maximum height roughness (R _{max )} of the polyester film according to the type, physical properties and content of the filler. ), as well as mechanical properties such as friction coefficient, tensile strength, elongation at break and modulus, and optical properties such as haze and light transmittance may vary. In particular, the polyester-based film, by including the filler, controls the surface roughness to a desirable range and has excellent optical properties, particularly low haze, and excellent transparency without deteriorating mechanical properties.

In addition, even if the content of the filler is the same, the surface roughness characteristics and optical characteristics of the film may be significantly different depending on the particle size, shape, and physical properties of the filler.

The filler may include at least one selected from the group consisting of titanium dioxide, barium sulfate, calcium carbonate, magnesium carbonate, zinc carbonate, zinc oxide, magnesium oxide, alumina, and silica. Specifically, when the filler includes silica, it may be preferable in terms of optical properties, but is not limited thereto.

In addition, the filler may be spherical having a spherical shape. Specifically, by including a spherical filler having a spherical shape, the polyester film can further improve dispersibility and control the surface roughness more effectively, as compared to the case of including a bulky filler in the form of a lump. may have characteristics.

More specifically, the filler may include spherical silica beads, and when the filler includes spherical silica beads, surface roughness can be more effectively controlled and haze can be reduced to maximize transparency. can

The average particle diameter (D _sem ) of the filler may be 0.01 μm to 2.0 μm. For example, the average particle diameter (D _sem ) of the filler is 0.01 μm to 1.9 μm, 0.01 μm to 1.8 μm, 0.02 μm to 1.3 μm, 0.03 μm to 1.0 μm, 0.05 μm to 0.8 μm, 0.1 μm to 0.5 μm, or It may be 0.15 μm to 0.4 μm. When the average particle diameter (D _sem ) of the filler satisfies the above range, surface roughness can be more effectively controlled and haze can be reduced to maximize transparency.

In particular, polyester-based films have limitations in mechanical properties such as tensile strength, elongation at break, and modulus that can be improved by adjusting process conditions such as stretching temperature, elongation rate, and heat setting temperature. However, the polyester-based film according to the embodiment may further improve mechanical properties such as tensile strength, elongation at break and modulus without additional process cost by maintaining existing process conditions by including a filler having an average particle diameter satisfying the above range. there is.

D ₁₀ of the filler may be 0.05 μm to 0.5 μm. For example, the D ₁₀ of the filler may be 0.05 μm to 0.45 μm, 0.1 μm to 0.4 μm, 0.13 μm to 0.36 μm, 0.18 μm to 0.33 μm, 0.2 μm to 0.31 μm, or 0.21 μm to 0.28 μm.

In addition, D ₅₀ of the filler may be 0.12 μm to 0.65 μm. For example, the D ₅₀ of the filler may be 0.14 μm to 0.55 μm, 0.16 μm to 0.5 μm, 0.18 μm to 0.35 μm, 0.22 μm to 0.32 μm, or 0.25 μm to 0.3 μm.

D ₉₀ of the filler may be 0.25 μm to 0.75 μm. For example, the D ₉₀ of the filler may be 0.26 μm to 0.65 μm, 0.28 μm to 0.58 μm, 0.31 μm to 0.52 μm, 0.35 μm to 0.48 μm, or 0.36 μm to 0.46 μm.

D ₁₀ of the filler, When D ₅₀ and D ₉₀ respectively satisfy the above ranges, surface roughness can be more effectively controlled and haze can be reduced to maximize transparency.

The particle diameter of the filler may be measured by a laser diffraction particle size distribution measurement method, for example, a wet laser diffraction particle size distribution measurement method.

Specifically, 0.3 g of the filler is mixed with 30 ml of isopropyl alcohol and ultrasonicated for 5 minutes at a power of 45 W to prepare a dispersion, and the particle size distribution of the filler in the dispersion may be measured with a particle size distribution analyzer. In the particle size distribution thus obtained, the cumulative 50% particle size based on the volume was indicated as D ₅₀ .

In addition, the polyester film may include the filler in an amount of 500 ppm to 2,000 ppm. For example, the content of the filler may be 550 ppm to 2,000 ppm, 600 ppm to 2,000 ppm, 700 ppm to 1,500 ppm, or 800 ppm to 1,300 ppm based on the total weight of the polyester film.

When the content of the filler satisfies the above range, surface roughness and dispersibility of the polyester film can be easily controlled, and thus mechanical properties, optical properties, and fairness such as winding property of the film can be further improved. Specifically, when the content of the filler exceeds 2,000 ppm, fairness such as windability may be improved, but haze is greatly reduced, resulting in very low transparency and poor surface properties due to dispersibility problems. In addition, when the content of the filler is less than 500 ppm, the surface roughness of the polyester film is out of the preferred range, and the dispersibility and transparency are not lowered, but the degree of improvement in windability is not great, so effective processability cannot be obtained.

Manufacturing method of polyester film

A method for manufacturing a polyester-based film according to another embodiment includes preparing a resin composition by mixing a co-polyester-based resin in which diols and dicarboxylic acids are copolymerized with a filler; Melting and extruding the resin composition to prepare an unstretched sheet; preparing a stretched sheet by first stretching the unstretched sheet in a first direction and secondarily stretching the unstretched sheet in a second direction perpendicular to the first direction; and preparing a polyester-based film by heat-setting the stretched sheet at 200° C. to 260° C., wherein the polyester-based film has an R _d of 2.5 or less according to Formula 1.

First, a resin composition is prepared by mixing a co-polyester-based resin in which diols and dicarboxylic acids are copolymerized with a filler .

The co-polyester-based resin may be formed by polymerization after a diol and a dicarboxylic acid undergo transesterification. Descriptions of the diol, dicarboxylic acid, and co-polyester-based resin are as described above.

Specifically, a copolymerized polyester-based resin may be prepared by mixing a diol and a dicarboxylic acid, performing an ester exchange reaction by introducing a transesterification catalyst, and then proceeding with a polymerization reaction.

The catalyst for the transesterification reaction may be at least one selected from the group consisting of manganese acetate tetrahydrate, calcium acetate, and zinc acetate. The amount of the transesterification catalyst may be 0.02 part by weight to 0.2 part by weight, 0.02 part by weight to 0.1 part by weight, or 0.05 part by weight to 0.1 part by weight based on the total weight of the dicarboxylic acid.

In addition, at least one additive selected from the group consisting of potassium and magnesium in the polymerization reaction; stabilizers such as trimethylphosphate; And titanium, such as titanium isopropoxide, tetrapropyl titanate, tetrabutyl titanate or tetraisopropyl titanate, germanium oxide, germanium methoxide, germanium ethoxide, tetramethyl germanium, tetraethyl germanium or germanium sulfide and A polymerization catalyst such as germanium-based or antimony-based such as antimony trioxide, antimony trioxide, antimony acetate, or antimony triethylene glycol may optionally be added.

The content of the polymerization catalyst may be 0.00001 wt % to 0.001 wt % or 0.00005 wt % to 0.0005 wt % based on the total weight of the co-polyester resin.

A resin composition may be prepared by adding and mixing a filler to the co-polyester-based resin prepared above. Description of the filler is as described above.

According to another embodiment, the step of preparing the resin composition may include the step of first mixing the co-polyester-based resin and the filler, and the step of secondarily mixing the first mixture with a base resin. .

Specifically, the quality of the polyester film produced by first mixing the co-polyester-based resin and the filler and additionally using a raw resin having the same components and contents as the co-polyester-based resin can be further improved. .

The raw material resin may include a diol and a dicarboxylic acid. Specifically, the diol and dicarboxylic acid of the raw resin may have the same type and content as the diol and dicarboxylic acid of the co-polyester-based resin. When the components and contents of the raw material resin and the co-polyester-based resin are the same, the quality of the produced polyester-based film can be further improved.

In the first mixing step, 95% by weight or more of the co-polyester-based resin and 5% by weight or less of the filler may be mixed. For example, the content of the co-polyester-based resin added in the first mixing step may be 95% by weight or more or 97% by weight or more, 95% to 99.5% by weight, 95% to 99% by weight or 97% by weight. % to 99% by weight. In addition, the content of the filler added in the mixing step may be 5% by weight or less, 4% by weight or less, or 3% by weight or less, 0.5% to 5% by weight, 0.5% to 4% by weight, or 1% to 3% by weight. weight percent.

In the second mixing step, the first mixture may be mixed in an amount of 1 part by weight to 10 parts by weight. For example, in the second mixing step, 1 part by weight to 10 parts by weight, 1 part by weight to 8 parts by weight, 1.5 parts by weight to 6 parts by weight, or 2 parts by weight to 5 parts by weight may be introduced and mixed.

Thereafter, the resin composition is melt-extruded to prepare an unstretched sheet .

Specifically, after melting and extruding the mixture or secondary mixture with a T-die, cooling may be performed to prepare an unstretched sheet.

The melt-extruding step may be performed at a temperature of Tm+5°C to Tm+70°C, Tm+5°C to Tm+50°C or Tm+7°C to Tm+35°C, and the cooling step is Tg-120°C. to Tg+20℃, Tg-110℃ to Tg+10℃, Tg-105℃ to Tg-30℃, Tg-105℃ to Tg-50℃, Tg-105℃ to Tg-65℃, Tg-105℃ to Tg-80 °C.

For example, the melt extrusion temperature may be 260 ° C to 320 ° C, 270 ° C to 310 ° C or 270 ° C to 295 ° C, and the cooling temperature may be -20 ° C to 100 ° C, 0 ° C to 90 ° C, 5 ° C to 75°C, 10°C to 60°C, 10°C to 50°C or 15°C to 45°C. When the melt-extrusion temperature satisfies the above range, the viscosity of the extrudate may be appropriately maintained while melting is smooth.

Then, a stretched sheet is prepared by first stretching the unstretched sheet in a first direction and secondarily stretching it in a second direction perpendicular to the first direction.

The primary stretching may be performed at a stretching rate of 2 to 5 times at a temperature of 60° C. to 120° C. For example, the first stretching step is 2 to 5 times, 2.5 times at a temperature of 60 ° C to 120 ° C, 70 ° C to 110 ° C, 75 ° C to 105 ° C, 80 ° C to 100 ° C or 85 ° C to 100 ° C. to 4.5 times, 2.5 times to 4 times, or 2.9 times to 3.5 times. When the temperature and elongation rate of the primary stretching satisfy the above ranges, heat resistance, durability and hydrolysis resistance can be improved.

After the primary stretching, secondary stretching is performed in a second direction perpendicular to the first direction. The secondary stretching may be performed at a stretching rate of 2 to 5 times. For example, the secondary stretching is 2 to 5 times, 2.5 times to 2.5 times at a temperature of 70 ℃ to 140 ℃, 80 ℃ to 140 ℃, 90 ℃ to 135 ℃, 100 ℃ to 130 ℃ or 115 ℃ to 125 ℃. It may be performed at a stretch rate of 5x, 3x to 4.5x or 3.5x to 4.5x.

In addition, a preheating step or a coating step may be additionally performed before the second stretching.

The preheating step may be performed at 70 °C to 120 °C for 0.01 to 1 minute. For example, the preheating temperature may be 70°C to 120°C, 75°C to 115°C, or 80°C to 110°C, and the preheating time may be 0.01 to 1 minute, 0.05 minutes to 0.5 minutes, or 0.08 minutes to 0.2 minutes. there is.

The coating step is a step capable of imparting functionality such as antistatic to the polyester film, and may be performed by spin coating or in-line coating, but is not limited thereto.

A ratio (d1/d2) of the stretching ratio d1 in the first direction and the stretching ratio d2 in the second direction may be 0.5 to 1. For example, the ratio (d1/d2) of the stretching ratio d1 in the first direction and the stretching ratio d2 in the second direction may be 0.5 to 0.95, 0.65 to 0.95, or 0.7 to 0.9.

Finally, the stretched sheet is heat-set at 200° C. to 260° C. to prepare a polyester-based film .

The heat setting may be annealing, and may be performed at 200° C. to 260° C. for 0.01 minute to 1 minute. For example, the heat setting temperature may be 200 ° C to 260 ° C, 210 ° C to 250 ° C, 225 ° C to 250 ° C, or 235 ° C to 245 ° C, and the heat setting time is 0.05 to 0.5 minutes or 0.08 minutes to 0.08 minutes. It may be 0.2 minutes, but is not limited thereto.

After the heat-setting, a step of relaxing the heat-set sheet in a first direction or in a second direction perpendicular to the first direction may be further performed.

Alternatively, after the heat setting, the heat-set sheet is firstly relaxed in a first direction and then secondarily relaxed in a second direction, or the heat-set sheet is firstly relaxed in a second direction and then the first direction A second relaxation step may be additionally performed. For example, the heat-set sheet may be first relaxed in the TD direction and then secondarily relaxed in the MD direction.

When the heat-set sheet is relaxed in a first direction or in a second direction perpendicular to the first direction, the relaxation step is 0.5% to 5%, 0.8% at a temperature of 100 ° C to 180 ° C or 110 ° C to 175 ° C. % to 4% or 0.8% to 3.5% relaxation rate.

In the relaxation step, the first relaxation may be performed at an elongation rate of 1% to 10% in the second direction, and the second relaxation may be performed at an elongation rate of 0.5% or more to less than 2% in the first direction. Specifically, when the second relaxation is performed after the first relaxation of the heat-set sheet, the first relaxation step may be performed at a relaxation rate of 0.5% or more to less than 2% at a temperature of 150 ° C to 200 ° C, The second relaxation step may be performed at a relaxation rate of 0.5% to 5% at a temperature of 110°C to 190°C.

For example, the first relaxation step is 1% to 10%, 1% to 9%, 1.5% at a temperature of 150 ° C to 200 ° C, 155 ° C to 200 ° C, 160 ° C to 180 ° C or 165 ° C to 175 ° C. to 8%, 1.5% to 7%, 2% to 6%, or 2% to 5% relaxation rate, and the second relaxation step is 110°C to 190°C, 110°C to 180°C, 110°C 0.5% to less than 2%, 0.5% to 1.95%, 0.7% to 1.8% or 0.9% to 1.6% at a temperature of from 170 ° C, 115 ° C to 150 ° C, 115 ° C to 140 ° C or 115 ° C to 130 ° C. It can be done with a relaxation rate.

When the temperature and relaxation rate of the first relaxation step and the second relaxation step satisfy the above ranges, heat resistance and hydrolysis resistance may be improved.

In addition, the first relaxation rate: the second relaxation rate may be 1:0.1 to 1.0. For example, the first relaxation rate: the second relaxation rate may be 1:0.1 to 0.9, 1:0.1 to 0.8, 1:0.2 to 0.7, or 1:0.25 to 0.65. When the ratio of the first relaxation rate and the second relaxation rate satisfies the above range, heat resistance and hydrolysis resistance may be maximized.

Specifically, the second relaxation step may be performed in two or more sections, and the second relaxation rate may be the total sum of the relaxation rates of each section. For example, when the second relaxation step is divided into 4 sections and the relaxation rates of the 4 sections are sequentially performed at 0%, 0.5%, 0.5%, and 1%, the second relaxation rate is 2 %am. By dividing the second relaxation step into sections as described above, the relaxation rate can be more easily controlled, and thus heat resistance and hydrolysis resistance can be maximized.

The transport speed of the film in the second relaxation step may be 1% to 10% slower than the transport speed of the film in the first relaxation step. For example, the transport speed of the film in the secondary relaxation step may be 2% to 10% or 2% to 8% slower than the transport speed of the film in the first relaxation step.

The above will be described in more detail by the following examples. However, the following examples are only for illustrating the present invention, and the scope of the examples is not limited only to these.

[Example]

Preparation of co-polyester-based resin

Preparation Example 1-1

100 mol% of cyclohexanedimethanol (CHDM) as a diol, and 88 mol% of terephthalic acid (TPA) and 12 mol% of isophthalic acid (IPA) as dicarboxylic acids were put into an autoclave equipped with a stirrer and a distillation column, and transesterification After adding manganese acetate as a reaction catalyst in an amount of 0.07 parts by weight based on 100 parts by weight of the dicarboxylic acid, the transesterification reaction was performed while raising the temperature to 290 °C.

After the transesterification reaction was completed, 0.0001 parts by weight of tetrabutyl titanate based on 100 parts by weight of the dicarboxylic acid was added as a polymerization catalyst and stirred for 10 minutes. Thereafter, the reactants were transferred to a separate reactor equipped with a vacuum facility, and a polymerization reaction was performed at 300 ° C. for 180 minutes to prepare a copolymerized polyester-based resin (polycyclohexanedimethylene terephthalate (PCT) resin). .

Preparation of resin composition

Preparation Example 2-1

97.5% by weight of the co-polyester-based resin prepared in Preparation Example 1-1 and 2.5% by weight of spherical silica beads (D _sem : 0.3 μm) as a filler were first mixed.

Thereafter, a resin composition was prepared by secondarily mixing 4 parts by weight of the primary mixture with 96 parts by weight of a base resin. At this time, the raw material resin contained 100 mol% of cyclohexanedimethanol (CHDM) as a diol, and 96 mol% of terephthalic acid (TPA) and 4 mol% of isophthalic acid (IPA) as dicarboxylic acids. In addition, the content of the silica beads in the resin composition prepared by the secondary mixing was 1,000 ppm.

Preparation Example 2-2

A resin composition was prepared in the same manner as in Preparation Example 2-1, except that blocky silica beads (D _sem : 3.5 μm) were used.

Manufacture of polyester-based film

Example 1

After putting the resin composition prepared in Preparation Example 2-1 into an extruder, melt-extruding at 290 ° C. with a T-Die and then cooling with a casting roll at 25 ° C. to prepare an unstretched sheet. Thereafter, the unstretched sheet is first stretched at 90° C. in the MD direction at a stretch rate of 3.0 times, preheated at 90° C. for 0.1 minute, and secondarily stretched at 120° C. in the TD direction at a stretch rate of 4.0 times. has manufactured Thereafter, the stretched sheet was heat-set at 240° C. for 0.1 minute to prepare a polyester-based film having a thickness of 25 μm.

Examples 2 and 3, and Comparative Examples 1 to 3

A polyester-based film was prepared in the same manner as in Example 1, except that process conditions were applied as shown in Table 1 below.

division	resin composition	MD elongation (ship)	TD elongation (ship)	MD stretching Temperature (℃)	TD stretching Temperature (℃)	heat fixation Temperature (℃)
Example 1	Preparation Example 2-1	3.0	4.0	90	120	240
Example 2	Preparation Example 2-1	3.2	3.9	90	120	240
Example 3	Preparation Example 2-1	3.4	4.0	90	120	240
Comparative Example 1	Preparation Example 2-2	3.0	3.9	90	120	240
Comparative Example 2	Preparation Example 2-2	3.2	4.0	90	120	240
Comparative Example 3	Preparation Example 2-2	3.4	3.9	90	120	240

[Experimental example]

Experimental Example 1: Surface Roughness

With respect to the films prepared in Examples 1 to 3 and Comparative Examples 1 to 3, 10-point average roughness (R _z ) and center line average roughness (R _a ) using a two-dimensional contact type surface roughness meter (SE3300 from Kosaka) and maximum height roughness (R _max ) were measured. At this time, the 10-point average roughness (R _z ), the center line average roughness (R _a ) and the maximum height roughness ( R _max ) was measured.

The 10-point average roughness (R _z ) is a surface roughness according to KS B 0161, and when the surface is first cut with a plane perpendicular to the surface of the film, a section appearing on the cut surface is enlarged and recorded by a reference length in the cross-sectional curve was collected, and an arbitrary straight line parallel to the average line of the cross-sectional curve was set as the reference line. At this time, the difference between the average value of the distance from the baseline for the five highest peaks and the average value for the distance from the baseline for the five lowest valleys was calculated.

The center line average roughness (R _a ) is a surface roughness according to KS B 0161, and a straight line generated when a mountain is cut from a roughness curve to fill a valley is called a center line, and a measured length is taken in the direction of the center line, and from the center line It was calculated by dividing the area of the upper part obtained by folding the lower part upward by the measured length.

The maximum height roughness (R _max ) is a surface roughness according to KS B 0161, a reference length is taken from a cross-sectional curve, and the distance between two parallel lines that are parallel to the center line of the cross-sectional curve and touch the highest peak and the deepest valley was calculated. .

In addition, R _d was calculated according to Equation 1 below.

[Equation 1]

In the above formula 1,

R _max is the maximum height roughness (μm) of the polyester-based film, and R _a is the center line average roughness (μm) of the polyester-based film.

Experimental Example 2: Coefficient of Friction

With respect to the films prepared in Examples 1 to 3 and Comparative Examples 1 to 3, in accordance with ASTM D1894, after horizontally placing the specimen on the test table of the friction coefficient measuring instrument, the test equipment was driven at a constant displacement speed to measure the dynamic friction coefficient. (F _d ) and static friction coefficient (F _s ) were measured.

In addition, RF was calculated according to Equation 2 below.

[Equation 2]

In Equation 2,

R _max is the maximum height roughness (μm) of the polyester-based film, and F _d is the kinetic friction coefficient of the polyester-based film.

Experimental Example 3: Tensile strength

Samples were prepared by cutting the films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 into a size of 150 mm in width and 100 mm in length, and in accordance with ASTM D 882, an INSTRON universal testing machine (4206 -001, manufacturer: UTM) at a test speed of 200 mm/min, the tensile strength was measured three times for the same sample, and the average value was calculated.

Experimental Example 4: Elongation at break

Samples were prepared by cutting the films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 into a size of 150 mm in width and 100 mm in length, and in accordance with ASTM D 882, an INSTRON universal testing machine (4206 -001, manufacturer: UTM) at a test speed of 200 mm/min, the elongation at break was measured three times for the same sample, and the average value was calculated.

Experimental Example 5: Modulus

Modulus of the films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured according to KS B 5521.

Experimental Example 6: Haze

The haze of the films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured using a haze meter (SEP-H, manufactured by Nihon Semitsu Kogaku).

Experimental Example 7: Light Transmittance

For the films prepared in Examples 1 to 3 and Comparative Examples 1 to 3, the light transmittance at 380 nm was measured using UltraScan PRO (manufacturer: Hunterlab).

Experimental Example 8: Surface observation

The surfaces of the films prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were observed using a scanning electron microscope (SEM).

Specifically, FIGS. 1 to 3 show scanning electron microscope (SEM) images of the polyester films of Examples 1 to 3, and FIGS. 4 to 6 are scanning electron microscope images of the polyester films of Comparative Examples 1 to 3 ( SEM) images are shown.

As shown in FIGS. 1 to 6, it was confirmed that the polyester films of Examples 1 to 3 had better dispersibility than the films of Comparative Examples 1 to 3, so that the surface roughness was effectively controlled while having excellent surface properties.

division		Example 1	Example 2	Example 3	Comparative Example 1	Comparative Example 2	Comparative Example 3
surface roughness (CR, μm)	R z	0.170	0.200	1.000	0.830	1.420	0.280
	R a	0.008	0.012	0.057	0.057	0.058	0.015
	R max	0.803	0.903	1.835	2.063	1.970	0.961
	R d	0.996	1.329	3.106	2.763	2.944	1.561
surface roughness (Ratio CR, μm)	R z	0.240	0.240	1.120	0.880	1.360	0.270
	R a	0.013	0.011	0.053	0.064	0.063	0.012
	R max	0.889	0.573	1.644	1.876	1.916	0.600
friction coefficient	F d	0.48	0.53	0.44	0.43	0.42	0.54
	F s	0.62	0.63	0.57	0.54	0.54	0.67
	RF	0.39	0.48	0.81	0.89	0.83	0.52
tensile strength (kg/mm 2 )	MD	12.07	14.32	12.26	11.24	12.08	14.84
	TD	14.52	18.13	13.67	14.69	13.50	18.42
Elongation at break (%)	MD	49.02	55.77	57.12	42.02	32.85	42.97
	TD	34.66	57.44	34.49	46.17	32.71	49.19
modulus (kg/mm 2 )	MD	261.03	281.49	248.89	241.18	253.81	285.30
	TD	284.61	292.23	273.91	261.00	262.41	298.59
Haze (%)		3.50	3.07	4.36	9.03	8.25	9.74
Light transmittance (%)		89.96	89.96	90.06	90.61	90.36	90.40

As shown in Table 2, the polyester films of Examples 1 to 3 exhibited superior optical properties and mechanical properties compared to the films of Comparative Examples 1 to 3.

Specifically, in the polyester films of Examples 1 to 3, the 10-point average roughness (R _z ), the center line average roughness (R _a ), and the maximum height roughness (R _max ) are all controlled within a specific range, thereby increasing the friction coefficient and tensile strength. , optical properties such as haze and light transmittance were all excellent without degradation of mechanical properties such as elongation at break and modulus.

On the other hand, in the films of Comparative Examples 1 to 3, the 10-point average roughness (R _z ), the center line average roughness (R _a ), and the maximum height roughness (R _max ) do not satisfy desirable ranges, and thus have poor optical properties such as haze and light transmittance. has been lowered

Claims (12)

1. co-polyester-based resins obtained by copolymerization of diols and two or more types of dicarboxylic acids; and a filler;

   R _d according to the following formula 1 is 2.5 or less, a polyester-based film:

   [Equation 1]

   

   In the above formula 1,

   R _max is the maximum height roughness (μm) of the polyester film,

   R _a is the center line average roughness (μm) of the polyester-based film.
2. According to claim 1,

   The 10-point average roughness (Rz) is 0.8 μm or less,

   The center line average roughness (Ra) is 0.05 μm or less,

   A polyester-based film having a maximum height roughness (Rmax) of 1.5 μm or less.
3. According to claim 1,

   A polyester-based film having a 10-point average roughness (Rz) of 0.3 μm or less.
4. According to claim 1,

   The filler includes at least one selected from the group consisting of titanium dioxide, barium sulfate, calcium carbonate, magnesium carbonate, zinc carbonate, zinc oxide, magnesium oxide, alumina, and silica,

   The average particle diameter (D _sem ) of the filler is 0.01 μm to 2.0 μm, a polyester-based film.
5. According to claim 4,

   The filler is a spherical silica bead, a polyester-based film.
6. According to claim 1,

   A polyester-based film comprising 500 ppm to 2,000 ppm of the filler based on the total weight of the polyester-based film.
7. According to claim 1,

   A polyester-based film having an RF of 0.8 or less according to the following formula 2:

   [Equation 2]

   

   In Equation 2,

   R _max is the maximum height roughness (μm) of the polyester film,

   F _d is the coefficient of kinetic friction of the polyester film.
8. According to claim 7,

   The dynamic friction coefficient (F _d ) is 0.6 or less,

   A static friction coefficient (F _s ) of 0.75 or less, a polyester-based film.
9. According to claim 1,

   Haze is 8% or less,

   A polyester-based film having a transmittance of 88% or more at a wavelength of 380 nm.
10. According to claim 1,

    Tensile strength is 19 kgf / mm ² or less,

    The elongation at break is 30% or more,

    A polyester-based film having a modulus of 320 kgf/mm ² or less.
11. According to claim 1,

    The diol includes 1,4-cyclohexanedimethanol or a derivative thereof,

    A polyester-based film, wherein the two or more dicarboxylic acids include 70 mol% to 99 mol% of terephthalic acid and 1 mol% to 30 mol% of isophthalic acid.
12. preparing a resin composition by mixing a co-polyester-based resin in which diols and dicarboxylic acids are copolymerized with a filler;

    Melting and extruding the resin composition to prepare an unstretched sheet;

    preparing a stretched sheet by first stretching the unstretched sheet in a first direction and secondarily stretching the unstretched sheet in a second direction perpendicular to the first direction; and

    Heat-setting the stretched sheet at 200 ° C to 260 ° C to prepare a polyester-based film,

    Method for producing a polyester-based film wherein the polyester-based film has R _d of 2.5 or less according to the following formula 1:

    [Equation 1]

    

    In the above formula 1,

    R _max is the maximum height roughness (μm) of the polyester film,

    R _a is the center line average roughness (μm) of the polyester-based film.

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