KR20090073605A - Polyester film - Google Patents

Abstract

A method for manufacturing a biaxially oriented polyester film is provided to prepare a biaxially oriented polyester film with excellent transparency while maintaining process runnability. A method for manufacturing a biaxially oriented polyester film comprises the steps of: (i) mixing and melting polyester and particles with a particle size of 30~540 nm and refraction index differential (Deltan) with polyester of 0.3 or less, and extruding the molten material to a sheet; (ii) quickly cooling the sheet; (iii) drawing the sheet 2~5 times at 80~150 °C longitudinally and drawing the sheet 2~5 times transversely to prepare a film; and (iv) heat-setting the sheet at 220~250 °C.

Description

Polyester film {Polyester film}

The present invention relates to a polyester film used in various electronic material release film.

Polyester film has excellent stability of physical properties in a wide range of low temperature to high temperature, excellent chemical resistance compared to other polymer resins, and good mechanical strength, surface properties, and uniformity of thickness. Because of its excellent applicability in process conditions, 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.

These polyester films are used alone, but are also used as release films by coating other polymer resins on polyester films. In particular, silicone-coated polyester release film is used for applications requiring beautiful appearance, high transparency and chemical resistance.

The silicone resin used in the release film was initially used in the solvent-type silicone, but there is a problem that not only increases the manufacturing cost by using an organic solvent when coating, but also causes environmental pollution due to the air emissions of the organic solvent. In order to solve this problem, US Patent No. 4,851,166 discloses a method of using a solvent-free silicon, and Canadian Patent No. 1,120,176 and US Patent No. 5,672,482, etc., disclose a method of using an emulsion-type silicone. .

In order to produce a release film, running, adhesion, uniform surface shape, high transparency, etc. are required. In order to meet these demands, the modification of the base film itself has emerged as an important requirement as well as a method of improving the silicone coating bath solution.

In particular, as the base film is used in polarizing plates, ceramic sheets, and the like, transparency of the base film has become an important base film requirement.

As a method for improving the transparency of the film, a method of securing transparency by minimizing the amount of inorganic inert particles added during polyester production has been proposed, but it has lowered the production yield due to deterioration of process permeability.

In order to improve the release polyester film, Japanese Patent No. 2006-003687 discloses a release polyester film which is excellent in visibility and handling, and Japanese Patent No. 2006-249210 discloses a polyester film having excellent adhesion and light scattering properties. In Korea Patent No. 2000-0019274, a biaxially stretched polyester film having improved adhesion to a silicone resin is provided.

The present invention provides a biaxially stretched polyester film having excellent transparency while maintaining process runability as a polyester film used as a base film of a release film.

In order to achieve the above object, the present invention has a polyester film having an average particle diameter of 30 to 540 nm and containing 0.03 to 1.5 wt% of particles having the same refractive index as the polyester substrate or having a refractive index difference (Δn) of 0.3 or less. To provide.

Polyester used as a base material 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 dicarboxylic acid, but a part thereof is transferred, such as isophthalic acid, oxyethoxy benzoic acid, adipic acid, sebacic acid, and 5-sodium sulfoisophthalic acid. It can be used in place of a functional carboxylic acid or its esterifying derivative.

As the glycol component, ethylene glycol is mainly used, but a part thereof is propylene glycol, trimethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-bisoxyethoxy It can also be used by replacing with benzene, bisphenol, and polyoxyethylene glycol, and if it is a small content, you may use together a monofunctional compound or a trifunctional compound.

The polyester film usually adds particles such as inorganic particles. This is because polyester films have a high coefficient of friction, which leads to poor activity and severe blocking properties, and not only the handleability of the film, but also a fatal defect in the product during film forming and slitting, so that the coefficient of friction of the polyester film is reduced. This is because unevenness is formed on the film surface by the addition of the added particles, and the unevenness formed reduces the coefficient of friction of the polyester film.

The particles used for the polyester substrate are selected and mixed with particles having the same refractive index difference or 0.3 or less. If the difference in refractive index is close to 0, light scattering is almost suppressed, and transparency is increased. If the difference in refractive index is 0.3 or more, transparency is greatly increased at the interface between the substrate and the particle, which greatly reduces the transparency and increases the haze (Haze). Done.

The said particle size uses an average particle diameter whose average particle diameter is 30-540 nm. If the average particle size is 30nm or less, the transparency is excellent, but the surface effect such as the winding property and the releasability is inferior due to the surface area reduction effect due to the particle injection, and when the average particle size is 540nm or more, the haze rises and a film having excellent transparency cannot be obtained. .

The content of the particles is 0.03 ~ 1.5 wt% based on the polyester substrate. When the content of the particles is less than 0.03 wt%, the amount used is small, the winding and release property is reduced, and at 1.5 wt% or more, light scattering occurs a lot and the haze of the film increases.

The polyester film according to the present invention has a haze of 1 to 3.5%. Films having a haze of 1% or less have excellent transparency but are difficult to be manufactured in an actual process, and films having a haze of 3.5% or more have low transparency and are not suitable for use in polarizing plates and the like.

The particles include inorganic particles such as silica, kaolin and barium sulfate, crosslinked acrylic resins such as silicone resins, crosslinked divinylbenzene polymethacrylates and crosslinked polymethacrylates, crosslinked polystyrene resins, benzoguanamine-formaldehyde resins, benzo Organic particles, such as guanamine-melamine-formaldehyde resin and melamine-formaldehyde resin, can be used.

The polyester film according to the present invention may further contain large particles having an average particle diameter of 1 to 5 μm. It is because containing more large particles can increase the surface area to prevent blocking and bone wrinkles and improve the appearance. If the average particle size of the large particles is 1 µm or less, the effect of adding more large particles is inferior, and if the average particle diameter of the large particles is 5 µm or more, the haze increases.

Particles having an average particle diameter of 1 to 5 μm are used at 0.007 to 0.5 wt% or less with respect to polyester. If it is less than 0.007wt% of polyester, the effect of preventing blocking and wrinkles by particles having an average particle diameter of 1 ~ 5㎛ is insignificant, and if it is used more than 0.5wt%, the possibility of coarseness or agglomeration may occur. do.

Polyester film according to the present invention has a surface roughness of 0.01 ~ 0.21㎛. If the surface roughness is less than 0.01㎛ the haze of the film is reduced, but there is a side effect that the releasability is reduced by increasing the coefficient of friction due to the small surface projections, the surface roughness is more than 0.21㎛ haze caused by light scattering and irregularities of the surface projections The increase can cause other process defects such as surface chipping during winding and bubble marks in the transfer layer due to projections. Therefore, the polyester film according to the present invention may have a surface roughness of 0.01 to 0.21 μm and more preferably have a surface roughness of 0.015 to 0.21 μm for process convenience of the film.

The polyester film according to the invention also has a heat shrinkage of 4.0% or less in the longitudinal direction (MD) for 10 minutes at 200 ° C. If the heat shrinkage is 4.0% or more, the thermal stability of the film is poor, which limits the use of the product.

In the polyester film according to the present invention, the number of foreign matters of 15 to 50 μm is 1 to 20 per m 2. The larger and larger the size of the foreign material, the higher the haze and surface roughness of the film.

The present invention to obtain a polyester film as described above

a) mixing the melt with a polyester having a particle diameter of 30 to 540 nm and having a refractive index difference (Δn) equal to or less than 0.3 of the polyester to melt and extrude the sheet;

b) quenching the sheet;

c) preparing a film under the condition that the sheet is stretched by 2 to 5 times after longitudinal stretching at 80 to 150 ° C. by 2 to 5 times; And

d) heat setting the stretched film at 220 to 250 ° C .;

Provided is a method for producing a biaxially stretched polyester film having a haze (Haze) of 1 to 3.5%, including.

In the step c) of the manufacturing method, when the stretching temperature is 85 ° C. or less, stretching may occur in the sheet and the sheet may become cloudy. When the stretching temperature is 150 ° C. or higher, yellowing and deterioration of physical properties may occur. Therefore, transparency can be improved by extending | stretching a film at 80-150 degreeC in which the physical property fall of resin does not occur.

The polyester film according to the present invention has a low haze so that a high transparency film can be obtained, and thus has a good requirement for use as a base film such as a release film for MLCC, a polarizing plate protective film, and a polarizing plate release film.

Looking at the present invention in detail through the following examples, the following examples are not intended to limit the present invention.

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

Average particle size measurement: The average particle size was measured using a particle size distribution analyzer (Beckman-Coulter, LS13 320) .In this case, the average particle size was obtained by converting the particles into spherical shape, which resulted in 100% of the cumulative volume from the small particle size. Particle diameter;

Haze measurement: The measurement method was measured based on ASTM D-1003. The polyester film was randomly extracted from 7 parts at 2 sides and 1 center, and then sliced into 5cm x 5cm sizes to measure haze (Nihonden Shoku). NDH 300A) and the light having a wavelength of 555 nm was transmitted to calculate the average value except the maximum / minimum value.

Haze (%) = (total scattered light / total transmitted light) ㅧ 100;

Measurement of surface roughness: Using a two-dimensional surface roughness measuring instrument (Kousaka Lab. Surfcorder SE-3300), the conditions were measured under the conditions of 1 탆 radius, a load of 0.7 mN, and a cutoff value of 80 µm. The average value was calculated after measuring a total of five times by selecting the 1.5 mm length section, and when the roughness curve was expressed as y = f (x) with the center line as the x-axis and the vertical direction as the y-axis, the following equation was calculated. It was.

Surface roughness Ra = (1 / L) ∫f (x) dx;

Measurement of heat shrinkage conversion: The measurement method was measured based on ASTM D-2305. After extracting the transverse and longitudinal samples from two sides and one center of the polyester film, they were cut into 10cm X 10cm and left in a hot air oven. After 10 minutes, the shrinkage was calculated by the following equation.

Heat Shrink = ((Initial Length-Length After Measurement) / Initial Length) X 100

Foreign material level measurement: After extracting 100cm X 100cm samples from 2 sides and 1 center of polyester film, each sample is divided into 8 pieces and placed on a non-reflective black sheet and reflected light on the top. Visual inspection is performed at intervals. At this time, the intensity of illumination at the top of the seat is appropriately 300 ~ 700 Lux. After visual inspection, the suspected foreign body is sliced, and the size is compared using a 10-fold magnifier.

Example 1 Preparation of Polyester Film 1.

1000 g of dimethyl terephthalate, 576 g of ethylene glycol, and 300 ppm of magnesium acetate, 400 ppm of trimethyl phosphate were added to the reactor, and the reaction was transesterified for 230 hours at 230 ° C. for 5 hours while methanol was discharged. After the transesterification reaction, Particle A (Daegusa OX-50, Silica particles, Average particle diameter: 50nm, Refractive index = 1.47 Δn = 0.2) was added to the product in the form of ethylene glycol sludge in the form of ethylene glycol sludge with 1wt% content of 1mmHg. Under a 280 ° C., 4 hours of polycondensation, a polyester chip having an intrinsic viscosity of 0.61 was obtained.

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.

Haze, surface roughness, heat shrinkage, and foreign matter levels of the polyester film were measured and shown in Table 1 below.

EXAMPLES 2-6 The manufacture of the polyester films 2-6.

Experiment in the same manner as in Example 1, except that particle A and particle B (Satleben OF-40, barium sulfate particles, average particle diameter 400nm, refractive index = 1.61, Δn = 0.06) and particle C (Fuji Silysia SY310, silica Particles, an average particle diameter 3㎛, refractive index = 1.46, Δn = 0.21) were used as shown in Table 1 to obtain a polyester film 2-6. The content in Table 1 below is wt% relative to the polyester substrate. The physical properties of the obtained polyester films 2-6 are shown in Table 1.

Comparative Example 1 Preparation of Comparative Polyester Film 1.

Experiment in the same manner as in Example 1, but instead of Particle A Particle C (Fuji Silysia SY310, silica particles, average particle diameter 3㎛, refractive index = 1.46 Δn = 0.21) using a comparative polyester film as shown in Table 1 below 1 was obtained. The content in Table 1 below is wt% relative to the polyester substrate. The physical properties of the obtained comparative polyester film 1 are shown in Table 1.

Table 1. Physical Properties of Particles and Polyester Films Used

1 is an SEM photograph of a polyester film according to the present invention.

Claims (8)

A polyester film having an average particle diameter of 30 to 540 nm and containing 0.03 to 1.5 wt% of particles having the same refractive index as the polyester substrate or having a refractive index difference (Δn) of 0.3 or less. The method of claim 1, The polyester film is a polyester film having a haze of 1 to 3.5%. The method of claim 2, The particles include silica, kaolin, barium sulfate, silicone resin, crosslinked divinylbenzene polymethacrylate, crosslinked polymethacrylate, crosslinked polystyrene resin, benzoguanamine-formaldehyde resin, benzoguanamine-melamine-formaldehyde resin, And melamine-formaldehyde resin any one or more selected from the group consisting of resin. The method of claim 3, wherein The particles have an average particle diameter of 1 ~ 5㎛, polyester film further contained in 0.007 ~ 0.5 wt% with respect to the polyester resin. The method of claim 4, wherein The polyester film is a polyester film having a surface roughness Ra of 0.01 ~ 0.21㎛. The method of claim 5, The polyester film is a polyester film of 200%, 10 minutes or less heat shrinkage in the longitudinal direction of 4.0% or less. The method of claim 5, The polyester film is a polyester film having an average number of foreign matters of 15 to 50㎛ 1 ~ 20 (/ ㎡) level. a) mixing the melt with a polyester having a particle diameter of 30 to 540 nm and having a refractive index difference (Δn) equal to or less than 0.3 of the polyester to melt and extrude the sheet; b) quenching the sheet; c) preparing a film under the condition that the sheet is stretched by 2 to 5 times after longitudinal stretching at 80 to 150 ° C. by 2 to 5 times; And d) heat setting the stretched film at 220 to 250 ° C .; Method for producing a biaxially stretched polyester film having a haze (Haze) is 1 to 3.5%, including.

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