KR101157805B1 - Biaxial streched polyester film - Google Patents

Abstract

The present invention relates to a biaxially stretched polyester film having excellent transparency and improved running property and processability, comprising a particle having a bimodal particle size distribution satisfying Equation 1 below, wherein the difference in refractive index between the substrate and the particle is represented by Equation 2 below. It relates to a biaxially stretched polyester film that satisfies.

[Formula 1]

0.3 ≤ D ≤ 10, D = Vh / Vs

(D is the ratio of Vh to Vs, Vh is the volume percentage of the peak with the largest particle size in the Bimodal particle size distribution, and Vs is the volume percentage of the peak with the smallest particle size in the Bimodal particle size distribution.)

[Formula 2]

ΔN ≤ 0.3

(ΔN is the difference between the refractive index and the particle intrinsic refractive index of the biaxially stretched polyester)

Polyester film, biaxial stretching, haze, runability

Description

Biaxially oriented polyester film {BIAXIAL STRECHED POLYESTER FILM}

The present invention relates to a biaxially stretched polyester film used in the field of display, and relates to a polyester film having improved running property and processability such as scratching and blocking.

Polyester film has excellent stability of physical properties over a wide temperature range from low temperature to high temperature, excellent chemical resistance compared to other polymer resins, and good mechanical strength, surface properties and thickness uniformity. It has excellent applicability in process conditions, so it is applied to capacitors, photo films, labels, pressure-sensitive tapes, decorative laminates, transfer tapes, polarizers, and ceramic sheets, and the demand is increasing day by day to meet the trend of high speed and automation. The trend is.

Usually, in order to improve the running property and the scratch resistance of a film, particle | grains of several nano-several micro unit are used classically inside resin. However, when the film using the particles is applied to a display field such as FPD, which is currently in the spotlight in the film field, haze increases due to the light scattering effect of the particles and the difference in refractive index between the substrate and the particles. As the amount of particles prescribed for minimizing the contact area increases, the scattering effect is increased, and the haze greatly increases.

In order to solve this problem, much research has been conducted on the maximization of particle size and dispersion, but there is much controversy in its effect, and in the case of the film still requiring high transparency, there is a need for high technical barrier of film forming technology according to the particle-free prescription. As a result, the failure rate may increase due to careless handling in a later process.

Particularly, in the case of the polyester film proposed in the present invention, the intrinsic properties of the resin have some adhesiveness, and when the particles are not prescribed, the polyester film has a problem that is vulnerable to blocking, scratching, etc. There is a problem in that workability greatly decreases.

The present invention is to provide a film that not only reduces the adhesion phenomenon of the polyester film, but also has excellent transparency required in the display field, and improves the running and processing properties such as scratching and blocking caused during the film manufacturing process.

The present invention relates to a biaxially stretched polyester film comprising particles having a bimodal particle size distribution satisfying the following formula 1, wherein the difference in refractive index between the substrate and the particles satisfies the following formula (2).

[Formula 1]

0.3 ≤ D ≤ 10, D = Vh / Vs

(D is the ratio of Vh to Vs, Vh is the volume percentage of the peak with the largest particle size in the Bimodal particle size distribution, and Vs is the volume percentage of the peak with the smallest particle size in the Bimodal particle size distribution.)

[Formula 2]

ΔN ≤ 0.3

(ΔN is the difference between the refractive index and the particle intrinsic refractive index of the biaxially stretched polyester)

In the present invention, the particles are used by mixing the particles having an average particle diameter of 2 ~ 6㎛ and particles having an average particle diameter of 0.01 ~ 1㎛ or using a mixture thereof, the particles are 0.05 to 0.2% by weight in the film It is used, characterized in that the haze of the biaxially stretched polyester film thus prepared is 1 to 3.5%.

Hereinafter, the present invention will be described more specifically.

The polyester used as a base material in this invention is obtained by condensation polymerization of the acid component which has dicarboxylic acid as a main component, and the glycol component which has alkyl glycol as a main component. Terephthalic acid or its alkyl ester or phenyl ester is mainly used as the main component of the dicarboxylic acid, but a part thereof is, for example, isophthalic acid, oxyethoxy benzoic acid, adipic acid, sebacic acid, and 5-sodium sulfoisophthalic acid. It may be used by substituting with difunctional carboxylic acid or ester forming derivative thereof. As the glycol component, ethylene glycol is mainly used, but for example, propylene glycol, neopentyl glycol, trimethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and 1,4-bisoxy It may be used in combination with oxybenzene, bisphenol, polyoxyethylene glycol, or may be used in combination with a monofunctional compound or trifunctional compound if the content is small.

The polyester resin can be produced by a conventional polymerization method, that is, a method such as DMT polymerization method, but is not limited thereto. In addition, it may include any one or more components selected from additives commonly used in the film field, that is, a pinning agent, an antistatic agent, an ultraviolet stabilizer, a waterproofing agent, a slipping agent, and a thermal stabilizer.

In the present invention, the particles are important factors for determining not only the transparency of the film, but also the runability and processability, and the present invention is excellent in transparency while adding particles to satisfy the runability, in particular, by using bimodal particles. This excellent film can be produced.

Specifically, the particles used in the present invention may be adjusted to have a bimodal particle size distribution satisfying the following Equation 1 in order to satisfy the transparency.

[Formula 1]

0.3 ≤ D ≤ 10, D = Vh / Vs

(D is the ratio of Vh to Vs, Vh is the volume percentage of the peak with the largest particle size in the Bimodal particle size distribution, and Vs is the volume percentage of the peak with the smallest particle size in the Bimodal particle size distribution.)

When D is less than 0.3, the small particle content under the half wavelength of visible light increases, the transparency of light is improved as the light transmittance is increased, but the runability and processability are deteriorated. When D exceeds 10, the processability such as winding characteristics and runability Is excellent, but the transparency of the film is extremely poor because of the relatively increased particle size with a large particle size that induces light scattering. Therefore, the above range must be satisfied to be excellent in transparency while satisfying the running property and processability.

Particularly, the peak range showing a small particle size in the Bimodal particle size distribution is preferably a particle having a range of 0.01 to 1 μm, and the peak range showing a large particle size in the Bimodal particle size distribution is a particle having a size of 2 to 6 μm. That is, in the present invention, the particles may be used by mixing particles having an average particle diameter of 2 to 6 µm and particles having an average particle diameter of 0.01 to 1 µm, or using particles mixed with these particles.

In addition, the thing in which the difference in refractive index between a polyester base material and particle | grains satisfy | fills following formula 2 is used.

[Formula 2]

ΔN ≤ 0.3

(ΔN is the difference between the refractive index and the particle intrinsic refractive index of the biaxially stretched polyester)

More preferably, it is preferable to use a refractive index difference of 0.1 to 0.3, and when the refractive index difference exceeds 0.3, it causes large scattering at the interface between the substrate and the particle, greatly lowering the transparency and increasing the cloudiness. The biaxially stretched polyester film excellent in transparency cannot be produced.

As the particles satisfying the above characteristics, inorganic particles or organic particles may be used, and inorganic particles may include silica, kaolin, barium sulfate, and the like, but are not limited thereto. Examples of the organic particles include silicone resins, crosslinked divinylbenzene polymethacrylates, crosslinked polymethacrylates, crosslinked polystyrene resins, benzoguanamine-formaldehyde resins, benzoguanamine-melamine-formaldehyde resins, and melamine-formaldehyde resins. Organic particles such as but may be used, but are not limited thereto.

When producing particles having a particle size distribution satisfying the above conditions, a single particle having a bimodal structure can be used, or two or more particle types are mixed with each other, or a single component particle is crushed, centrifuged, or precipitated and purified. Can be separated and then recombined.

In the present invention, the particles are more preferably used in the film at 0.05 to 0.2% by weight, and when used in the above range, the inherent winding property and release property of the film are improved. Within this range, the haze should satisfy 3.5% or less, more preferably 1 to 3.5% to accomplish the purpose of the present invention.

If the above conditions are satisfied, it is possible to produce a film having an improved transparency of 30% or more compared to the general-purpose film currently used in the same particle content.

Next, the method of manufacturing the biaxially stretched polyester film of this invention is demonstrated. Film production method of the present invention

 a) preparing a polyester chip by adding 0.05 to 0.2% by weight of particles having a bimodal distribution having a particle size distribution of Formula 1;

[Formula 1]

0.3 ≤ D ≤ 10, D = Vh / Vs

(D is the ratio of Vh and Vs, Vh is the Vol% of the peak on the right of the Bimodal particle size distribution, and Vs is the Vol% of the peak on the left of the Bimodal particle size distribution.)

b) melting and extruding the polyester chip to prepare a polyester sheet;

c) stretching the sheet 2 to 5 times in the machine direction MD, and then stretching the sheet 2 to 5 times in the vertical width direction TD in the machine direction; And

d) heat setting the stretched film;

It includes.

In addition, the polyester film and the difference in refractive index between the particles satisfy the following formula 1, it is more preferable to use a mixture of particles having an average particle diameter of 2 ~ 6㎛ and particles having an average particle diameter of 0.01 ~ 1㎛.

[Formula 1]

ΔN ≤ 0.3

(ΔN is the difference between the refractive index and the particle intrinsic refractive index of the biaxially stretched polyester)

Preferably, the temperature range is 85 to 150 ° C. at the time of drawing in the machine direction MD in step c), and the temperature range is 220 to 250 ° C. at the time of heat setting in step d).

When explaining the manufacturing method in more detail,

In the present invention, it is preferable to prepare an inorganic particle during the polymerization of the polyester-based resin to prepare a chip, but the present invention is not limited thereto.

The manufactured chip is melt-extruded at a temperature of 260 to 300 ° C., the melt discharged through a die is quenched with a large roll, and stretched 2 to 5 times in the machine direction MD. Then, the film stretched 2 to 5 times in the vertical width direction (TD) in the machine direction is heat-treated at 220-250 ° C. and then wound to obtain a film.

In order to manufacture a film having excellent transparency during the above process, the crystallinity is low and the resin is lowered by giving a high stretching temperature between the main stretching sections in the stretching ratio condition near the stretching crystallization point in the machine direction (MD) and a temperature range of 85 to 150 ° C. -Longitudinal stretched sheet excellent in particle adhesion can be obtained. In order to prevent the occurrence of particle-substrate voids on the surface of the film, the reason for applying the temperature condition is to select particles having a high affinity with the substrate, as well as the problem that the interfacial-substrate breakdown may occur due to stretching stress. To block. In particular, the temperature of the main draw section is set to a high temperature, when the draw temperature is below 85 ℃ cold drawing occurs in the sheet may cause the sheet to become cloudy, when the draw temperature is 150 ℃ or more, yellowing and There may be a decrease in physical properties. Therefore, transparency can be improved by extending | stretching a film in high temperature conditions in which the physical property fall of resin does not occur.

In addition, it is important to select a draw ratio that can minimize stretching at the same time as the temperature range and at the same time to minimize the interface breakage and deformation of the resin surrounding the particles. When high magnification stretching is performed, the stretching stress may increase, which may cause deformation and destruction of particles in the film. When the compatibility between substrate and particles decreases, interfacial fracture occurs due to stretching, and voids are generated to maximize scattering. . In order to prevent this, it is preferable to stretch 2 to 5 times in the longitudinal stretching process, and most preferably, 2 to 4 times longitudinal stretching can effectively block interfacial breakage and void generation with the resin.

The biaxially stretched polyester film according to the present invention has a high resistance to scratches that may occur during processing by reducing the contact area of the film surface by adding a large amount of particles, and by dispersing the particle size of the particles in a bimodal distribution in the display It can satisfy | fill the required transparency and can provide the excellent film with a haze of 3.5% or less.

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

The measuring method used in the present Example is as follows.

1) Average particle size measurement of particles:

The average particle size was measured using a particle size distribution analyzer (Beckman-Coulter, LS13 320), and Vs was centered on the left peak of the bimodal point, and Vh was centered on the right peak in the same manner. The optimum result was calculated by calculating D in terms of its ratio.

 2) Haze measurement:

The measuring method was measured based on ASTM D-1003, and the polyester film was randomly extracted from 7 parts at 2 sides and 1 center, and then sliced into 5cm x 5cm sized haze measuring instruments (Nihonden Shoku NDH 300A). It was added to the light of 555nm wavelength and calculated by the following equation to calculate the average value except the maximum / minimum value.

Haze (%) = (total scattered light / total transmitted light) × 100

3) Scratch Measurement:

In order to measure the degree of scratch of the film according to the particle content and particle size distribution, the scratch and the surface resistance were measured using the Surface Property Tester of Haydon. 3 parts of polyester film were randomly extracted from 2 edges and 1 center, and then cut into 10cm × 20cm, placed on the measuring device, zeroed and randomly rubbed to produce scratches. Calculate the initial loading point value, deposit gold on the scratch-producing area, and evaluate the scratch form before and after deposition by 100 times microscope. ○ If there is no scratch before gold deposition, if there is no scratch after gold deposition △ If a scratch is found after the gold deposition, it is marked with an X. The measurement conditions are as follows.

Load: 5g

Travel Speed: 500 mpm

Measuring length: 50 mm

Repeat count: 50 times

Film Contact Material and Geometry: Ceramic Ball

[Example 1]

Preparation of Polyester Film

 1000g of dimethyl terephthalate, 576g of ethylene glycol, and 300ppm of magnesium acetate, 400ppm of trimethyl phosphate were added to the reactor, and transesterification was carried out while methanol was discharged. Particle A (silica, average particle diameter 3㎛, refractive index = 1.46, Δn 0.21) and particle B (silica, average particle diameter 50nm, refractive index = 1.47 Δn = 0.2) were added to the product after the transesterification reaction. The ethylene glycol sludge was added in the form of%, but Bimodal Point was applied to adjust the D value to 5.0 and subjected to condensation polymerization under vacuum to obtain a polyester chip having an intrinsic viscosity of 0.60.

The polyester chip was melt-extruded at 280 ° C. and then quenched with a large roll to obtain a polyester sheet. The obtained polyester sheet was stretched 3 times in the longitudinal direction at 110 ° C., stretched 4 times in the horizontal direction at 130 ° C., and then heat treated at 250 ° C. to obtain a polyester film 1 having a thickness of 25 μm. After measuring the haze, surface scratches, etc. of the obtained polyester film, it is shown in following Table 1.

[Examples 2 to 3]

Preparation of Polyester Film

The experiment was performed in the same manner as in Example 1, but the particle content was changed to 0.07% by weight relative to the resin, and then used as shown in Table 1 to obtain a polyester film.

[Examples 4 to 5]

Preparation of Polyester Film

The experiment was performed in the same manner as in Example 1, but changed to a content of 0.1% by weight relative to the resin, and then used as shown in Table 1 to obtain a polyester film.

[Example 6]

Preparation of Polyester Film

Experiment in the same manner as in Example 1, except that the particle C (silica, average particle diameter 3㎛, refractive index = 1. 47, Δn = 0.24) is added, the particle content is changed to 0.07% by weight relative to the resin and then applied It used like Table 1 and obtained the polyester film.

Example 7

Preparation of Polyester Film

Experiment in the same manner as in Example 1, except that the particle D (silica, average particle diameter 3㎛, refractive index = 1. 47, Δn = 0.26) is added, the particle content is changed to 0.06% by weight relative to the resin and then applied It used like Table 1 and obtained the polyester film.

Comparative Example 1

Preparation of Polyester Film

The experiment was performed in the same manner as in Example 1, except that Particle A (average particle diameter: 3 µm, refractive index = 1.46 Δn = 0.21) was used as in Table 1 below to obtain a polyester film.

Comparative Example 2

Preparation of Polyester Film

The experiment was carried out in the same manner as in Example 1, but the D value was adjusted to 0.2 to obtain a polyester film using Table 1 below.

Comparative Example 3

Preparation of Polyester Film

The experiment was carried out in the same manner as in Example 1, but the D value was adjusted to 12 to obtain a polyester film using the following Table 1.

Table 1. Physical Properties of Particles and Polyester Films Used

As shown in the table, as a result of using the bimodal particles in the present invention, it was found that in Examples 2 and 3 used in the same amount as in Comparative Example 1, a film having excellent optical properties with lower haze could be prepared.

In addition, in the case of Comparative Example 2 in which the particle size distribution was outside the scope of the present invention, the haze was low, but scratches occurred, and it was found that the initial load was higher when the ceramic ball was rubbed. Compared with Example 1, it was found that when a large amount of particles having a small particle size were prescribed even at the same content, scattering caused by the particles was greatly reduced, but it did not contribute significantly to the effect of reducing the film contact area.

In addition, in the case of Comparative Example 3, it was found that the haze was very high compared to Examples 2 and 3.

Claims (5)

A large particle having an average particle diameter of 2 to 6 µm and a small particle having an average particle diameter of 0.01 to 1 µm are mixed and used, wherein the large particles having an average particle diameter of 2 to 6 µm and small particles having an average particle diameter of 0.01 to 1 µm are used. It contains 0.05 to 0.2% by weight of particles having a bimodal particle size distribution satisfying the following [Formula 1] by having a high content of the same or larger particles, and the refractive index difference between the substrate and the particle ] And a biaxially stretched polyester film having a haze of 1 to 3.5%. [Formula 1] 0.3 ≤ D ≤ 10, D = Vh / Vs (D is the ratio of Vh to Vs, Vh is the volume percentage of the peak representing the larger particles in the Bimodal particle size distribution, and Vs is the volume percentage of the peak representing the smaller particles in the Bimodal particle size distribution.) [Formula 2] ΔN ≤ 0.3 (ΔN is the difference between the refractive index and the particle intrinsic refractive index of the biaxially stretched polyester) delete delete delete The method of claim 1, The film has a temperature range of 85 to 150 ° C. at the time of stretching in the machine direction (MD), and a biaxially stretched polyester film prepared by stretching 2 to 5 times.