KR20110001482A - Polyester film and manufacturing method of the same - Google Patents

Abstract

PURPOSE: A polyester film and a manufacturing method thereof are provided to display uniform brightness by indicating a haze value uniform over the entire surface of a film when adopting an optical film. CONSTITUTION: A polyester film includes: on one surface thereof a film which enables optical diffusion; and on the other surface thereof a polyester polymer base material film which has slip property and/or antistatic property. The polyester polymer base material film except the film which enables optical diffusion has a matrix shaped polyester resin having a melting point of Tm1. The film which enables optical diffusion includes optical diffusing particle having particles of 5 ~ 25μm, and a transparent resin matrix comprises a homopolyester resin of 30-50weight% and a copolymer resin of 50-60weight%.

Description

Polyester film and manufacturing method thereof {POLYESTER FILM AND MANUFACTURING METHOD OF THE SAME}

 The present invention relates to polyester films, and more particularly to polyester films that can be used for various displays.

Biaxially stretched polyester films have been widely used as base films for optical films because of their excellent transparency, dimensional stability, and chemical resistance, compared to other plastic films.

The light diffusing film is used by coating the light diffusing layer as a functional layer on a transparent base film in order to effectively use the light of the light source, in this case, not only has to go through a separate coating process, but also to maintain expensive optical properties The manufacturing cost is very high because a large amount of organic particles must be used.

In addition, in the drying process during coating, there is a problem that deformation is easily generated, curls are easily generated by the coating layer, and film smoothness is poor, and a series of post-processing processes such as sheet forming are used for product use. In this case, the coating layer is weak and easily damaged.

In view of this, attempts have been made to provide light diffusivity to the biaxially stretched polyester film itself. Attempts to provide light diffusivity to the biaxially stretched polyester film itself, which have been proposed so far, have lost one of the inherent characteristics of the biaxially stretched polyester film, or a light diffusing film such as light transmittance and light diffusivity. The loss of the characteristic to be provided has not been brought to practical use.

For example, Japanese Laid-Open Patent Publication No. 2001-272508 discloses a multilayer biaxially stretched polyester film using a low melting point polyester resin having a melting point of 200 ° C. or less as a base film of polyethylene terephthalate and constituting a light diffusion layer. Is disclosed. In the method disclosed here, the suppression of the void which expresses around a light-diffusion agent and inhibits transparency is considered. Accordingly, the balance between light transmittance and light diffusivity is comparable to that of the conventional light diffusing film obtained by coating a light diffusing layer of transparent resin containing fine particles on the surface of a biaxially stretched polyester film. However, the light-diffusion film obtained by the method described here has a large melting point difference between the polyester resin which comprises a base material layer, and the polyester resin which comprises a light-diffusion layer. The resulting biaxially stretched film has a different coefficient of linear expansion between the light diffusing layer and the base film, so that curling tends to occur when the biaxially stretched film itself is heat treated. For this reason, curl may generate | occur | produce by heat processing in a post-processing process, or curl may generate | occur | produce according to the use environment (temperature) of a liquid crystal display, and there exists a possibility that the brightness of a light emission surface may become uneven in a backlight unit.

In one embodiment of the present invention to provide a biaxially stretched polyester film having a uniform haze value over the entire surface of the film, and has a light diffusing property and slip to antistatic properties in the film itself.

In one embodiment of the present invention includes a polyester polymer base layer having a light diffusing layer on one surface and a layer having slip and / or antistatic properties on the other surface,

(A) A layer having slip and / or antistatic property and a polyester polymer base layer, except for a light diffusable layer, has a polyester resin having a melting point of Tm ₁ as a matrix;

(B) The light diffusable layer comprises (a) light diffusing particles having an average particle diameter of 5 to 25 μm dispersed in a transparent resin matrix, and (b) the transparent resin matrix is a homopolyester resin having a melting point of Tm ₁ 30 to 50% by weight and a melting point (Tm ₂₎ the _{Tm 1 - 60 ℃ <Tm 2} <Tm 1 - is a copolymer of 50 to 70% by weight satisfying the 10 ℃, (c) when observing the longitudinal section by the SEM Both the upper and lower surfaces have a protruding shape formed by particles;

(C) the layer having slip and / or antistatic property comprises particles having an average particle diameter of 0.5 to 5 탆,

(D) a polyester film having no interface extending substantially linearly on the surface of the substrate layer in contact with the light diffusable layer and the layer having slip and / or antistatic properties when the longitudinal section was observed by SEM; to provide.

According to one embodiment of the invention, the transparent resin matrix is polyethylene terephthalate; It may be composed of one or more copolymers selected from polyester copolymers, polycarbonate copolymers and polysulfone copolymers.

According to one embodiment of the present invention, in the light diffusing layer, the light diffusing particles are included in the total film weight of 20,000 to 70,000 ppm, and in the layer having slip property and / or antistatic property, the particles are all It may be included in the film weight of 200 to 700ppm, wherein the light diffusing particles or particles may be preferably selected from silicon beads or polymethyl methacrylate.

According to one embodiment of the invention, the slip and / or antistatic layer has a thickness of 1 to 5% of the total film thickness, and the layer having light diffusivity has a thickness of the entire film thickness. It may be 1 to 30%.

According to another embodiment of the present invention, at least one surface of the polyester film may include a coating layer containing particles having an average particle diameter of 10 to 500nm dispersed in an acrylic resin or a urethane resin binder. In this case, the coating layer may have a thickness of 10 to 1000 nm.

Considering the optical use, preferably, the polyester film according to one embodiment of the present invention may have a haze of 70% or more and a total light transmittance of 80% or more.

In one embodiment of the present invention

a) preparing a polyester resin having a melting point of Tm ₁ ; b) compounding a polyester resin having a melting point of Tm ₁ and particles having an average particle diameter of 0.5 to 5 μm to prepare a first masterbatch; c) 30 to 50% by weight of the homopolyester resin having a melting point of Tm ₁ and 50 to 70% by weight of the copolymer resin satisfying a melting point (Tm ₂ ) of Tm ₁ -60 ° C <Tm ₂ <Tm ₁ -10 ° C. Transparent resin; Compounding light diffusing particles having an average particle diameter of 5 to 25 μm to prepare a second masterbatch; d) coextruding the master batch 1, the polyester resin and the masterbatch 2 so that the layers formed from the masterbatch 1 and the masterbatch 2 are respectively placed on both sides of the polyester resin to prepare an unstretched sheet; e) stretching the unstretched sheet in the machine direction; f) stretching the film stretched in the machine direction in the width direction; And g) provides a method for producing a polyester film comprising the step of heat setting.

In the production method according to an embodiment of the present invention, a blend of polyethylene terephthalate and at least one copolymer selected from a polyester copolymer, a polycarbonate copolymer and a polysulfone copolymer as a transparent resin in step c) Can be used.

In the production method according to a preferred embodiment of the present invention, the copolymer resin in step c) may include a dicarboxylic acid containing terephthalic acid and a copolyester obtained from a glycol containing neopentyl glycol and ethylene glycol. have.

In the manufacturing method according to an embodiment of the present invention, the stretching in the machine direction may be carried out by the stretching method to 3.0 to 3.5 times the draw ratio under the temperature of 90 to 110 ℃. In addition, the stretching in the width direction may be carried out by a method of stretching to a draw ratio of 3.5 to 4.0 times at a temperature of 120 to 130 ℃.

In the manufacturing method according to an embodiment of the present invention, heat setting may be performed by heat treatment at a temperature higher than Tm ₂ and lower than Tm ₁ .

In the manufacturing method according to another embodiment of the present invention, before the stretching of the film stretched in the machine direction in the width direction, particles having an average particle diameter of 10 to 500nm on at least one surface of the co-extruded sheet stretched in the machine direction It may further comprise the step of in-line coating the acrylic resin or urethane resin coating solution comprising. In this case, the in-line coating may be performed so that the coating layer thickness is 10 to 1000 nm after drying.

The polyester film according to one embodiment of the present invention includes a polyester polymer base layer having a light diffusable layer on one surface and a layer having slip and / or antistatic property on the other surface. The term “polyester polymer substrate layer having a light diffusable layer on the surface” herein means a polyester polymer substrate layer and a light diffusable layer in the form of a separate adhesive layer, lamination layer or coating layer formed on the polyester polymer substrate layer. It will be understood that the light-diffusing layer is formed on the surface such that the polyester polymer base layer itself has light diffusivity. Likewise, the meaning of “polyester polymer substrate layer having a slip and / or antistatic property on the surface” also means that the polyester polymer substrate layer is in the form of a separate adhesive layer, lamination layer or coating layer formed on the substrate layer. It will be understood that a light diffusable layer is formed on the surface so that the polyester polymer base layer itself is slippery, rather than including a layer having slipability and / or antistatic property.

According to one embodiment of the present invention, except for the light diffusable layer, a polyester polymer base layer (hereinafter, abbreviated as a 'substrate layer') and a layer having slip property and / or antistatic property (hereinafter, 'slip layer') is abbreviated as') is a polyester resin having a melting point Tm ₁ of the matrix. More specifically, these layers are made of polyethylene terephthalate (PET) resin as a matrix. It is preferable that the polyester resin matrix has a melting point (Tm ₁ ) of 230 to 280 ° C in view of mechanical properties and thermal form stability.

Polyester film according to an embodiment of the present invention includes a slip layer on one surface of the base layer, the slip layer has an average particle diameter of 0.5 to 5㎛ dispersed in a polyester resin matrix having the same melting point range as the base layer The particles can be provided to impart slip or antistatic properties.

At this time, the type of particles is not limited, and organic or inorganic particles may be used. In addition, although the shape of the particles is not limited, it may be preferable to use spherical particles in view of optical properties. In addition, particle | grains can also be used individually or in mixture of 1 or more types. Non-limiting examples of particles include antiblocking such as hard calcium carbonate (CaO), silica sol, barium sulfate (BaSO ₄ ), sodium oxide (NaO ₂ ), sodium sulfate (Na ₂ SO ₄ ), kaolin, kaolin, talc, etc. Crosslinked acrylic resins such as inorganic particles, silicone resins, crosslinked divinylbenzene polymethacrylates and crosslinked polymethacrylates, and crosslinked polystyrene resins, benzoguanamine-formaldehyde resins, benzoguanamine-melamine-formaldehyde resins and melamine- Organic particles, such as formaldehyde resin, are mentioned.

Preferably, the particles may include silicon beads or polymethyl methacrylate beads.

The content of particles included in the slip layer is advantageous in terms of improving slipability and antistatic property in the range of about 200 to 700 ppm of the total film weight.

The thickness of the slip layer may be preferably about 1 to 5% of the total film thickness in expressing optical properties.

On the other hand, the light diffusable layer forming the other surface of the substrate layer includes (a) light diffusing particles having an average particle diameter of 5 to 25 μm dispersed in a transparent resin matrix, and (b) the transparent resin matrix has a melting point. Tm ₁ of homo-polyester resin 30 to 50% by weight and a melting point (Tm ₂₎ the _{Tm 1 - 60 ℃ <Tm 2} <Tm 1 - is a copolymer of 50 to 70% by weight satisfying the 10 ℃, (c) When the longitudinal section is observed by SEM, both the upper and lower surfaces have a protruding shape formed by particles.

Light diffusing melting point contained in the transparent resin matrix constituting a possible layer (Tm ₂₎ the _{Tm 1 - 60 ℃ <Tm 2} <Tm 1 - copolymer resin that satisfies the 10 ℃ is a light diffusion possible layer on the base layer surface that, for deriving the projection of the light-diffusing particles in forming, if the melting point (Tm ₂₎ the Tm ₁ - less than 60 ℃ the width direction (TD) stretching and up the deformation by the heat during the heat treatment portion side of the particles are loaded with If the melting point (Tm ₂ ) is higher than Tm _1-10 ℃, the heat treatment should be performed at high temperature for particle extrusion in the heat treatment section. It is difficult to use it as a low mechanical strength due to the low mechanical properties and low mechanical properties due to low particle protruding into the film.

However, in the case of forming a matrix of the light diffusing layer only with the copolymer resin having a melting point of Tm ₂ , the matrix of the light diffusing layer during heat treatment due to the difference in melting point with the base layer which is a polyester resin matrix having a melting point of Tm ₁ It is difficult to form a homogeneous layer due to melting, which may result in nonuniformity of haze value over the entire surface of the resulting polyester film. This non-uniformity of haze value for the entire surface of the film may ultimately lead to non-uniformity of brightness when applied for optical use.

In this regard, the polyester film according to the embodiment of the present invention is preferably a transparent resin matrix of the light diffusable layer is a copolymer resin having a melting point of Tm ₂ and a homo polyester resin having a melting point of Tm ₁ .

Specifically, a melting point Tm ₁ of homo-polyester resin 30 to 50% by weight and a melting point (Tm ₂₎ the _{Tm 1 - 60 ℃ <Tm 2} <Tm 1 - copolymer resin that satisfies the 10 ℃ comes to 50 to 70% by weight It is preferable that it is a transparent resin matrix.

If the homo-polyester resin having a melting point of Tm ₁ is less than 30% by weight in the resin matrix constituting the light diffusable layer, it is insufficient to reduce haze variation across the entire film, and if it is more than 50% by weight, protrusion of the light-diffusing particles May decrease so that the brightness may drop.

Meanwhile, examples of the copolymer resin having a melting point of Tm ₂ include a copolymer selected from a polyester copolymer, a polycarbonate copolymer, and a polysulfone copolymer. Among these, a polyester copolymer having a melting point of 180 to 225 ° C The use of is preferable since, after stretching, the copolymer polymer can be melted during heat treatment to form the same particle protruding effect as the coating process on the surface layer. More specifically, the polyester copolymer may use a polyester copolymer selected from polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate and polytrimethylene terephthalate, and may further include an additive.

The polyester copolymer is obtained by condensation polymerization of an acid component containing dicarboxylic acid as a main component and a glycol component containing 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 some of them are, for example, isophthalic acid, oxyethoxy benzoic acid, adipic acid, sebacic acid, and 5-sodium sulfoisophthalic acid. It may be used in place of a bifunctional carboxylic acid or an ester forming derivative thereof.

As the glycol component, ethylene glycol is the main object, but a part thereof is propylene glycol, trimethylene glycol, neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4- It is used in place of bisoxyethoxybenzene, bisphenol and polyoxyethylene glycol.

Meanwhile, the light diffusing layer includes light diffusing particles, which may be the same as or different from the particles included in the slip layer described above. However, the light diffusing particles may be preferably in the range of 5 to 25㎛, the average particle diameter is larger than the particles included in the slip layer, the content is 20,000 to 70,000 relative to the total film weight haze and brightness enhancement and light It may be advantageous in terms of diffusion function.

The thickness of the light diffusable layer may be preferably 1 to 30% of the total film thickness in terms of light transmission side due to the protrusion of particles and thermal morphological stability of the film.

The total thickness of the polyester film is not limited, but may be 188 to 220 μm in view of workability and luminance expression depending on the use.

The light-diffusing layer obtained by one embodiment of the present invention is formed on the surface of the base layer so that both the upper and lower surfaces have a protruding shape formed by particles when the longitudinal section is observed by SEM. In manufacturing the film from the resin matrix constituting the substrate layer, the transparent resin matrix constituting the light diffusable layer and the resin composition including the light diffusing particles are coextruded and stretched together to form a light diffusable layer. It can be achieved by including a copolymer resin having a melting point of Tm ₂ in the transparent resin matrix and undergoing a heat treatment process. The specific process is mentioned later.

In addition, the polyester film of the present invention may further include a coating layer on at least one surface as necessary, it may be advantageous to further include a separate coating layer in terms of expressing the anti-blocking effect without inhibiting the optical properties. Specifically, the coating layer may be an acrylic or urethane coating layer containing particles having an average particle diameter of 10 ~ 500nm. In addition, the coating layer may be preferably a thickness of 10 ~ 1000nm.

The average particle diameter of the particles included in the coating layer may be advantageous in terms of light transmittance and antiblocking effect, and the coating layer thickness may be advantageous in light transmittance and antiblocking effect.

The method of forming the coating layer is not particularly limited, but when the coating layer is formed on the surface of the film through inline coating (ILC), the light transmittance may be further improved. For example, in-line coating may increase the light transmittance by about 5% compared to the case without in-line coating. The coating liquid used for the inline coating can be used without limitation as long as it is a coating liquid for forming a polyurethane resin layer having a refractive index of 1.50 to 1.55 or a coating liquid for forming an acrylic resin layer having a refractive index of 1.40 to 1.48.

As a composition for forming such a polyurethane resin layer, an ester or a carbonate type is usually used as a polyol, an aliphatic isocyanate is used as an isocyanate, and a composition containing a diol or a diamine system as a chain extender can be used as a coating liquid. In addition, a coating liquid containing a mixture of methyl tetraacrylate, methacrylate, butyl acrylate, acrylic acid, etc. may be used as a composition for forming the acrylic resin layer. The binder component used in the coating solution preferably has a T _g of 20 ° C. to 100 ° C., and the coating liquid has a solid content of 2 to 10 wt% with respect to the weight of the coating liquid, and a viscosity of the coating solution of 20 cps (25 ° C.) or less. If the concentration of the solid content is less than 2% by weight, the amount of wet coating should be increased to obtain the desired thickness of the coating layer. In order to dry it, a large amount of energy is required, resulting in an increase in the manufacturing cost of the base film. If it exceeds the viscosity is higher than 20cps may cause a decrease in coating properties.

The polyester film according to the present invention has a haze of 70% or more, more specifically 70 to 99%, total light transmittance of 80% or more, more specifically 80 to 99% in consideration of optical use. It may be

If the haze is less than 70%, the pattern of the light guide plate light source is intact, and the efficiency of converting the linear light into surface light is inferior. If the total light transmittance is less than 80%, the brightness may be reduced.

In addition, the prism film using the optical polyester film which concerns on this invention is also included in the scope of the present invention. In this case, a method for forming a prism film is known, and a prism may be coated on one or both surfaces of the optical polyester film of the present invention by using a coating method that is commonly used in the art.

An example of the method of manufacturing the polyester film mentioned above,

a) preparing a polyester resin having a melting point of Tm ₁ ; b) compounding a polyester resin having a melting point of Tm ₁ and particles having an average particle diameter of 0.5 to 5 μm to prepare a first masterbatch; c) 30 to 50% by weight of the homopolyester resin having a melting point of Tm ₁ and 50 to 70% by weight of the copolymer resin satisfying a melting point (Tm ₂ ) of Tm ₁ -60 ° C <Tm ₂ <Tm ₁ -10 ° C. Compounding a transparent resin and light diffusing particles having an average particle diameter of 5 to 25 μm to prepare a second masterbatch; d) coextruding from the first masterbatch, the polyester resin and the second masterbatch so that the layers of the first masterbatch and the second masterbatch are respectively provided on both sides of the polyester resin layer; e) stretching the unstretched sheet in the machine direction; f) stretching the film stretched in the machine direction in the width direction; And g) heat setting.

After the heat setting step, it may be further added to relax in the machine direction (MD) and the width direction (TD). Although not limited, relaxation can be performed to be 1-5% of the length of the film.

The polyester film of the present invention obtained through this process does not have an interface extending substantially linearly on the surface of the substrate layer in contact with the light diffusable layer and the slip layer when the longitudinal section is observed by SEM.

In addition, after the step e), an additional step of in-line coating (in-line coating, ILC) of the acrylic or urethane coating liquid containing particles having an average particle diameter of 10 ~ 500nm may be further added. Regarding forming the coating layer on the film surface through inline coating, it is as described above.

In step e), the machine direction (MD) stretching is performed at a temperature of 90 to 110 ° C. to a draw ratio of 3.0 to 3.5 times, and in step f) the width direction (TD) stretching is at a temperature of 120 to 130 ° C. It is preferable to extend as possible.

Stretching at the stretching temperature and the stretching ban rate may be advantageous to project the particles to the light diffusable layered surface.

In addition, heat setting may be advantageous in that heat treatment at a temperature higher than Tm ₂ and lower than Tm ₁ may form irregularities on one surface of the polyester film, that is, the light diffusable layer surface. The unevenness thus formed can improve light diffusivity and brightness.

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.

1) Heat Shrinkage

After cutting the film in the forward direction of 20 cm × 20 cm, the lengths of the machine direction (MD) and the width direction (TD) of the film were measured, and then thermally contracted for 30 minutes in an unloaded state at 150 ° C. in an oven. The length of the machine direction (MD) and the width direction (TD) of the obtained film was measured, and the thermal contraction rate of the machine direction (MD) and the width direction (TD) was calculated | required according to following formula (1).

<Equation 1>

                 (Length before contraction-length after contraction)

Heat Shrinkage (%) = -------------------------------- × 100

                        Length before shrink

2) strength

The film is 15mm wide, the Gauge Length is 50mm, the cross head-up speed is 500mm / min, and the machine direction of the film is obtained by using a universal tensile test machine (Instron Tensile Test Machine). MD) and tensile properties in the width direction (TD) were measured.

3) Optical property evaluation (measuring haze, haze deviation and light transmittance)

The measurement 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 × 5cm sized haze measuring instruments (Nihonden Shoku NDH 300A). Haze (%) and Total Transmittance (%) were measured by transmitting light at a wavelength of 555 nm, and the average value of five values except the maximum and minimum values was obtained to calculate haze and total light transmittance. .

3) Optical property evaluation (measuring haze, haze deviation and light transmittance)

The measuring method was measured based on ASTM D-1003. Specifically, 7 parts of the A4 size film were randomly cut into 5cm × 5cm size at 2 sides and 1 center, and the haze meter (Nihonden Shoku NDH 300A). Haze (%) and total transmittance (%) were measured by transmitting light having a wavelength of 555 nm, and the average value of five values except the maximum and minimum values was obtained to calculate haze and total light transmittance.

On the other hand, the haze deviation is obtained by taking the A4 size specimens continuously in the width direction (TD) at each 100 m while unwinding the film roll in the machine direction (MD), and obtaining the haze value by the method described above for each specimen. Calculated as Contrast Deviation (%).

4) Measurement and Definition of Melting Point (Tm)

The polymer is placed in liquid nitrogen for 30 seconds and then taken out, and then is marked on the pulverizer (Hico-10-6-388) capillary tube. The polymer is powdered at a height above the marking line (usually 2/3 or more of the total tube length). After filling it into the Melting Point measuring instrument (Thomas Hoover Capillary Melting Point Apparatus), while checking the temperature of the melting point of the polymer in the capillary tube from the thermometer while raising the temperature at a rate of 30 ℃ / min, it was converted into Melting Point (Tm) define.

5) Cross section evaluation by SEM

The cross-section was observed by SEM for the Pilot-Scale film obtained according to the example, the light diffusion layer thickness ratio was calculated by the following equation 2 by analyzing the cross-sectional photograph.

<Equation 2>

                         (Total Film Thickness-Base Layer and Slip Layer Thickness)

Diffusion layer thickness ratio (%) = ------------------------------------------- --- × 100

                             Full film thickness

Reference Example 1

1004% terephthalic acid, 124 mol% ethylene glycol as the glycol component, 0.05 mol of antimony trioxide as the catalyst (for acid components), polycondensation by direct esterification, 0.64 dl / g, 256 melting point A homopolyester was prepared.

In addition, 1004% of terephthalic acid, 124 mol% of ethylene glycol as the glycol component, and 0.05 mol of antimony trioxide as the catalyst (relative to the acid component) were inherently viscosity 0.64 dl / g by direct esterification and melting point. The first masterbatch was prepared by adding 500 ppm of silicon beads having an average particle diameter of 2 µm to the homopolyester at 256 ° C. with respect to the entire film, and then compounding the same.

In addition, 100 mol% of terephthalic acid, 100 mol% of ethylene glycol and 24 mol% of neopentyl glycol were used as glycol components, and 0.05 mol of antimony trioxide (relative to acid components) was used as a catalyst. A second masterbatch was prepared by compounding a copolyester having a viscosity of 0.67 / g, a glass transition temperature of 76 ° C., and a melting point of 203 ° C. by adding 50,000 ppm of silicon beads having an average particle diameter of 25 μm to the entire film. .

The homopolyester used for the substrate layer was extruded at 275 ° C., the first masterbatch and the second masterbatch containing particles were extruded at 270 ° C., and the masterbatch 2 / homopolyester was used using a feed block. A sheet having a thickness ratio of 15/80/5 / master batch 1 was prepared. At this time, the thickness ratio between the layers was controlled by the discharge amount. The discharged sheet was cooled while passing through a casting roller at 30 ° C., thereby producing an unstretched film. The unstretched film was stretched 3.5 times at a temperature of 115 ° C. in a roller group (MDO: Machine Direction Organization) continuously conveyed in a mechanical direction. After stretching in the machine direction, it was continuously stretched 3.5 times with respect to the width at 135 ° C through a preheating section at 95 ° C, heat-treated at 210 ° C, and 3.5% relaxation at 180 ° C. A polyester film having a thickness of 188 μm having a slip layer on one surface and a light diffusion layer on the other surface was prepared.

[Reference Examples 2 to 10]

As shown in Table 1, a film having a thickness of 188 μm was manufactured in the same manner as in Reference Example 1, except that the resin melting point and the average particle diameter of the particles were changed.

Example 1

In preparing the unstretched film in the same manner as in Reference Example 1, the polymer of the second master batch forming the light diffusion layer was used by blending compounded copolyester and homopolyester in a weight ratio of 7: 3. In addition, except that the heat treatment temperature in Reference Example 1 was changed to 230 ° C., the stretching temperature and the draw ratio were the same to prepare a film having a thickness of 188 μm.

SEM photographs measured by the method described above with respect to the polyester film in which the light diffusion layer was formed on the surface thus obtained are shown in Figs.

From FIG. 1, the film has a light diffusing layer on one surface, a slip layer on the other surface, and the light diffusing layer has a protruding shape formed by particles on both the upper and lower surfaces when the longitudinal section is observed by SEM. ; In the case of the entire film, when the longitudinal cross section is observed, it can be seen that the surface extending substantially linearly does not exist on the surface of the substrate layer in contact with the light diffusing layer.

1 and 2 are observed from the same film specimen, but two pictures are separately shown in consideration of the characteristics of each layer.

In addition, the lower surface looks bright in the photograph because it is reflected by the illumination at the time of SEM photograph measurement, and does not mean the interface.

[Example 2]

In preparing the unstretched film in the same manner as in Reference Example 1, the polymer of the second master batch forming the light diffusing layer was used by blending the compounded copolyester and homopolyester in a weight ratio of 6: 4. In addition, except that the heat treatment temperature in Reference Example 1 was changed to 230 ° C., the stretching temperature and the draw ratio were the same to prepare a film having a thickness of 188 μm.

Example 3

In preparing the unstretched film in the same manner as in Reference Example 1, the polymer of the second master batch forming the light diffusion layer was used by blending compounded copolyester and homopolyester in a weight ratio of 5: 5. In addition, except that the heat treatment temperature in Reference Example 1 was changed to 230 ° C., the stretching temperature and the draw ratio were the same to prepare a film having a thickness of 188 μm.

Example 4-6

In Examples 1 to 3, the size of the particles contained in the second masterbatch forming the light diffusion layer was changed to 5㎛, all other processes are the same.

Example 7-9

In Examples 1 to 3, the size of the particles included in the second masterbatch forming the light diffusion layer was changed to 20㎛, all other processes are the same.

Example 10-12

In Examples 1 to 3, the size of the particles contained in the first masterbatch forming the slip layer was changed to 0.5㎛, all other processes are the same.

Example 13-15

In Examples 1 to 3, after the unstretched film was prepared, the stretched film was stretched 3.5 times at a temperature of 115 ° C. in a roller group (MDO: Machine Direction Organization) continuously fed in a mechanical direction. . After stretching in the machine direction, the mixture was cooled to room temperature, and the following coating solution was coated on both sides of the film stretched in the machine direction by the bar coating method. mayer-bar) was coated by adjusting the wire thickness. Continuously stretched 3.5 times the width at 135 ° C. through a preheating section at 95 ° C., followed by heat treatment at 210 ° C., and 3.5% relaxation at 180 ° C. to prepare a film having a thickness of 188 μm; The acrylic coating solution contains 4 g of an acrylic binder having a refractive index of 1.44, 0.1 g of a silicone wetting agent (polyester siloxane copolymer from TEGO), 0.1 g of 200 nm colloidal silica particles, and 0.15 g of a melamine curing agent (DIC) as a solvent. After adding to water, the mixture was stirred for 3 hours to prepare a coating solution having a solid content of 4.35% and a viscosity of 12 cps.

Reference Example 11

In Reference Example 1, after the unstretched film was prepared, the stretched stretched film was stretched 3.5 times at a temperature of 115 ° C. in a roller group (MDO: Machine Direction Organization) continuously transported in the mechanical direction. After stretching in the machine direction, the mixture was cooled to room temperature, and the following coating solution was coated on both sides of the film stretched in the machine direction by the bar coating method. mayer-bar) was coated by adjusting the wire thickness. Continuously stretched 3.5 times the width at 135 ° C. through a preheating section at 95 ° C., followed by heat treatment at 210 ° C., and 3.5% relaxation at 180 ° C. to prepare a film having a thickness of 188 μm; The acrylic coating solution contains 4 g of an acrylic binder having a refractive index of 1.44, 0.1 g of a silicone wetting agent (polyester siloxane copolymer from TEGO), 0.1 g of 200 nm colloidal silica particles, and 0.15 g of a melamine curing agent (DIC) as a solvent. After adding to water, the mixture was stirred for 3 hours to prepare a coating solution having a solid content of 4.35% and a viscosity of 12 cps.

Reference Example 12

In preparing the unstretched film in the same manner as in Example 1, when manufacturing the master batch 2 used for the second skin layer, except that 50,000 ppm of silicon beads having an average particle diameter of 30 μm were added to the entire film. Then, the layer structure, the discharge temperature, the stretching temperature and the draw ratio of Example 1 and the multilayer film were the same to prepare a film having a thickness of 188 μm.

[Reference Examples 13 to 17]

As shown in Table 1, a film having a thickness of 188 μm was manufactured in the same manner as in Reference Example 12, except that the melting point of the resin and the average particle diameter of the particles were changed.

Reference Example 18

In preparing the unstretched film in the same manner as in Reference Example 1, the polymer of the second master batch forming the light diffusion layer was used by blending the compounded polyester and homopolyester in a weight ratio of 4: 6. In addition, except that the heat treatment temperature in Reference Example 1 was changed to 230 ° C., the stretching temperature and the draw ratio were the same to prepare a film having a thickness of 188 μm.

Tables 1-2 below summarize the above examples and reference examples.

Slip layer Base layer (resin type, melting point ℃) Light diffusion layer In-line coating layer
The presence or absence Suzy
(Melting point, ℃) particle
(Average particle diameter, μm) Suzy
(Melting point, ℃) particle
(Average particle diameter, μm)





room
city
Yes
One







HOMO-PET
(256) Silicon Beads (2)







HOMO-
PET (256) CO-PET (203): HOMO-PET (256) = 7: 3 weight ratio Silicon Beads (25) radish 2 Silicon Beads (2) CO-PET (220): HOMO-PET (256) = 5: 5 weight ratio Silicon Beads (25) radish 3 Silicon Beads (2) CO-PET (197): HOMO-PET (256) = 6: 4 weight ratio Silicon Beads (25) radish 4 Silicon Beads (2) CO-PET (203): HOMO-PET (256) = 7: 3 weight ratio Silicon Beads (5) radish 5 Silicon Beads (2) CO-PET (220): HOMO-PET (256) = 5: 5 weight ratio Silicon Beads (5) radish 6 Silicon Beads (2) CO-PET (197): HOMO-PET (256) = 6: 4 weight ratio Silicon Beads (5) radish 7 Silicon Beads (2) CO-PET (203): HOMO-PET (256) = 7: 3 weight ratio Silicon Beads (20) radish 8 Silicon Beads (2) CO-PET (220): HOMO-PET (256) = 5: 5 weight ratio Silicon Beads (20) radish 9 Silicon Beads (2) CO-PET (197): HOMO-PET (256) = 6: 4 weight ratio Silicon Beads (20) radish 10 Silicon Beads (0.5) CO-PET (203): HOMO-PET (256) = 7: 3 weight ratio Silicon Beads (25) radish 11 Silicon Beads (0.5) CO-PET (220): HOMO-PET (256) = 5: 5 weight ratio Silicon Beads (25) radish 12 Silicon Beads (0.5) CO-PET (197): HOMO-PET (256) = 6: 4 weight ratio Silicon Beads (25) radish 13 Silicon Beads (2) CO-PET (203): HOMO-PET (256) = 7: 3 weight ratio Silicon Beads (25) U 14 Silicon Beads (2) CO-PET (220): HOMO-PET (256) = 5: 5 weight ratio Silicon Beads (25) U 15 Silicon Beads (2) CO-PET (197): HOMO-PET (256) = 6: 4 weight ratio Silicon Beads (25) U

Slip layer Substrate layer
(Resin type, melting point ℃) Light diffusion layer In-line coating layer
The presence or absence Suzy
(Melting point, ℃) particle
(Average particle diameter, μm) Suzy
(Melting point, ℃) particle
(Average particle diameter, μm)





Reference
Yes
One








HOMO-PET
(256) Silicon Beads (2)








HOMO-
PET (256) CO-PET (203) Silicon Beads (25) radish 2 Silicon Beads (2) CO-PET (197) Silicon Beads (25) radish 3 Silicon Beads (2) CO-PET (226) Silicon Beads (25) radish 4 Silicon Beads (2) CO-PET (247) Silicon Beads (25) radish 5 Silicon Beads (2) CO-PET (203) Silicon Beads (5) radish 6 Silicon Beads (2) CO-PET (203) Silicon Beads (10) radish 7 Silicon Beads (2) CO-PET (203) Silicon Beads (15) radish 8 Silicon Beads (2) CO-PET (203) Silicon Beads (20) radish 9 Silicon Beads (0.5) CO-PET (203) Silicon Beads (25) radish 10 Silicon Beads (5) CO-PET (203) Silicon Beads (25) radish 11 Silicon Beads (2) CO-PET (203) Silicon Beads (25) U 12 Silicon Beads (2) CO-PET (203) Silicon Beads (30) radish 13 Silicon Beads (2) CO-PET (203) Silicon Beads (2) radish 14 Silicon Beads (2) CO-PET (150) Silicon Beads (25) radish 15 Silicon Beads (2) HOMO-PET
(256) Silicon Beads (25) radish 16 Silicon Beads (2) CO-PET (203): HOMO-PET (256) = 7: 3 weight ratio Silicon Beads (30) radish 17 Silicon Beads (2) CO-PET (203): HOMO-PET (256) = 7: 3 weight ratio Silicon Beads (2) radish 18 Silicon Beads (2) CO-PET (203): HOMO-PET (256) = 4: 6 weight ratio Silicon Beads (25) radish

* Homo-PET: Homopolyester, Co-PET: Polyester copolymer

The physical properties of the films prepared by the above Examples, Reference Examples and Comparative Examples were measured and shown in Tables 3 to 4.

Strength (kg / ㎡) Shinto (%) Heat Shrinkage (%) Haze (%) Haze deviation (%) Total light transmittance (%) MD TD MD TD MD TD



room
city
Yes One 17.3 15.4 199.8 137.2 1.4 0.9 88 ± 2 89 2 17.2 16.1 195.7 140.7 1.3 0.8 86 ± 1 87 3 17.3 15.8 197.2 138.5 1.3 0.8 86 ± 2 86 4 16.9 16.2 199.2 138.1 1.3 0.9 87 ± 2 87 5 17.2 15.5 199.0 138.7 1.2 0.8 87 ± 1 85 6 18.0 15.2 197.8 138.5 1.3 0.7 88 ± 3 87 7 17.5 16.3 198.2 138.2 1.3 0.8 86 ± 2 88 8 17.7 15.8 195.3 137.3 1.2 0.7 85 ± 3 85 9 17.3 15.3 197.6 138.3 1.3 0.8 87 ± 1 88 10 17.5 16.2 199.5 139.3 1.3 0.8 86 ± 2 86 11 17.3 15.4 199.2 137.3 1.2 0.7 88 ± 2 86 12 17.3 15.3 198.2 137.5 1.4 0.9 87 ± 1 88 13 17.2 16.0 197.3 136.5 1.3 0.8 87 ± 3 86 14 17.2 15.3 198.8 136.2 1.4 0.8 88 ± 2 89 15 17.1 15.5 198.9 137.0 1.4 0.8 87 ± 2 87

Strength (kg / ㎡) Shinto (%) Heat Shrinkage (%) Haze (%) Haze deviation (%) Total light transmittance (%) MD TD MD TD MD TD




Reference Example One 16.0 16.9 200.3 142.5 1.1 0.8 82 ± 2 89 2 14.3 14.8 172.1 112.3 0.5 0.2 87 ± 5 91 3 15.7 16.1 198.7 139.6 2.0 1.3 85 ± 4 86 4 16.6 17.5 200.1 137.3 1.0 0.7 81 ± 5 82 5 15.4 15.9 190.2 133.1 1.5 0.9 89 ± 7 83 6 15.9 16.7 199.8 140.3 1.0 0.7 86 ± 7 87 7 17.5 18.4 201.5 143.7 0.8 0.4 80 ± 5 88 8 16.2 17.1 200.7 143.6 1.1 0.7 78 ± 3 88 9 15.3 16.2 200.4 145.2 1.0 0.8 83 ± 8 89 10 15.2 16.8 195.5 138.1 1.2 0.8 82 ± 5 88 11 14.8 15.7 194.2 141.8 1.1 1.0 87 ± 5 92 12 15.5 18.0 197.6 143.3 1.0 1.0 64 ± 4 91 13 17.9 17.7 200.4 135.7 1.3 0.6 86 ± 7 76 14 - - - - - - - - - 15 16.2 14.9 191.3 140.8 1.2 0.9 62 ± 6 96 16 15.8 17.3 192.8 142.7 1.4 0.6 55 ± 3 92 17 17.3 16.3 197.7 148.2 1.6 0.8 89 ± 8 67 18 16.2 18.2 198.8 147.2 1.3 1.1 88 ± 7 76

From the results of Tables 3 to 4 above,

Film according to the embodiments of the present invention is excellent in the haze and transmittance at the same time is suitable for use as an optical film, it can be seen that the haze deviation is small. In addition, it can be seen that the haze and the total light transmittance are further improved when the inline coating layer is further added.

In the case of the reference examples, it was found that the haze is low when the particle size constituting the slip layer or the light diffusion layer exceeds the range of the present invention, whereas the particle size constituting the slip layer or the light diffusion layer is the scope of the present invention. If less than, it was found that the total light transmittance was too low.

In addition, when the melting point of the low melting point resin included in the light diffusion layer is less than the range of the present invention, since the film is pushed out by the shrinkage of the particles, the center part becomes transparent, and thus it is impossible to use as a diffusion film, haze and total light transmittance. There was no meaning of the measurement. When the resin having the same melting point as the base layer was used for forming the light diffusion layer, the particles of the skin layer did not come out even by the heat treatment in the heat treatment step, and thus, the haze was low.

In particular, the use of low melting point Co-PET and Homo-PET as a resin matrix of the light diffusing layer is advantageous in view of mechanical properties such as strength, elongation and heat shrinkage, in particular in view of the results of the reference examples. It can be seen that the case is within a certain range.

1 to 2 are SEM images of the polyester film obtained in Example 1. FIG.

Claims (16)

A polyester polymer base layer having a light diffusable layer on one surface and a layer having slip and / or antistatic properties on the other surface, (A) A layer having slip and / or antistatic property and a polyester polymer base layer, except for a light diffusable layer, has a polyester resin having a melting point of Tm ₁ as a matrix; (B) The light diffusable layer comprises (a) light diffusing particles having an average particle diameter of 5 to 25 μm dispersed in a transparent resin matrix, and (b) the transparent resin matrix is a homopolyester resin having a melting point of Tm ₁ 30 to 50% by weight and a melting point (Tm ₂₎ the _{Tm 1 - 60 ℃ <Tm 2} <Tm 1 - is a copolymer of 50 to 70% by weight satisfying the 10 ℃, (c) when observing the longitudinal section by the SEM Both the upper and lower surfaces have a protruding shape formed by the particles; (C) the layer having slip and / or antistatic property comprises particles having an average particle diameter of 0.5 to 5 탆, (D) A polyester film having no interface extending substantially linearly on the surface of the substrate layer in contact with the light diffusable layer and the layer having slip and / or antistatic properties when the longitudinal section is observed by SEM. The method of claim 1, wherein the transparent resin matrix is polyethylene terephthalate; A polyester film comprising at least one copolymer selected from polyester copolymers, polycarbonate copolymers and polysulfone copolymers. The method of claim 1, wherein the light diffusing particles in the light diffusing layer comprises 20,000 to 70,000 ppm of the total film weight, the particles in the slip and / or antistatic properties the particles in the total film weight Polyester film is included in 200 to 700ppm. 4. The polyester film of claim 3, wherein the light diffusing particles or particles are selected from silicon beads or polymethylmethacrylate. The layer of claim 1 wherein the slip and / or antistatic layer has a thickness of 1 to 5% of the total film thickness, and the layer having light diffusivity has a thickness of 1 to 30 relative to the total film thickness. It is% polyester film. The polyester film of claim 1, further comprising a coating layer including particles having at least one particle having an average particle diameter of 10 to 500 nm dispersed in an acrylic resin or a urethane resin binder. The polyester film of claim 6, wherein the coating layer has a thickness of 10 to 1000 nm. The polyester film according to claim 1, wherein the polyester film has a haze of 70% or more and a total light transmittance of 80% or more. a) preparing a polyester resin having a melting point of Tm ₁ ; b) compounding a polyester resin having a melting point of Tm ₁ and particles having an average particle diameter of 0.5 to 5 μm to prepare a first masterbatch; c) 30 to 50% by weight of the homopolyester resin having a melting point of Tm ₁ and 50 to 70% by weight of the copolymer resin satisfying a melting point (Tm ₂ ) of Tm ₁ -60 ° C <Tm ₂ <Tm ₁ -10 ° C. Transparent resin; Compounding light diffusing particles having an average particle diameter of 5 to 25 μm to prepare a second masterbatch; d) coextruding the master batch 1, the polyester resin and the masterbatch 2 so that the layers formed from the masterbatch 1 and the masterbatch 2 are respectively placed on both sides of the polyester resin to produce an unstretched sheet; e) stretching the unstretched sheet in the machine direction; f) stretching the film stretched in the machine direction in the width direction; And g) a method of producing a polyester film comprising the step of heat setting. 10. The polyester of claim 9, wherein a blend of polyethylene terephthalate and at least one copolymer selected from polyester copolymers, polycarbonate copolymers and polysulfone copolymers is used as the transparent resin in step c). Method for producing a film. 10. The method of claim 9, wherein the copolymer resin in step c) comprises a dicarboxylic acid comprising terephthalic acid and a copolyester obtained from a glycol comprising neopentyl glycol and ethylene glycol. The method of claim 9, wherein the stretching in the machine direction is carried out by a method of stretching to a draw ratio of 3.0 to 3.5 times at a temperature of 90 to 110 ℃. 10. The method of claim 9, wherein the stretching in the width direction is carried out by a stretching method such that the stretching ratio is 3.5 to 4.0 times at a temperature of 120 to 130 ° C. 10. The method according to claim 9, wherein the heat setting is carried out by heat treatment at a temperature higher than Tm ₂ and lower than Tm ₁ . 10. The acrylic resin or urethane resin according to claim 9, further comprising particles having an average particle diameter of 10 to 500 nm on at least one surface of the co-extruded sheet stretched in the machine direction before the stretching of the film stretched in the machine direction in the width direction. Method for producing a polyester film comprising the step of coating the coating solution in-line. The method of claim 15, wherein the in-line coating is carried out so that the coating layer thickness is 10 to 1000 nm after drying.

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