KR100558841B1 - Polyester films for diffusing light and manufacturing method of the same - Google Patents

Abstract

The present invention discloses a polyester film for light diffusion that is excellent in smoothness, durability, processability, and the like, and which is low in manufacturing cost. In the polyester film according to the present invention, at least 60% by weight of the repeating unit is made of ethylene terephthalate and has a first film layer made of a first polyester resin having an intrinsic viscosity of 0.4 to 0.9 dl / g, and an average particle diameter of 0.3 to 8. A second film layer made of a first polyester resin containing an organic particle having a diameter of 60 μm and at least 60 wt% of the repeating unit is made of ethylene terephthalate and has an intrinsic viscosity of 0.4 to 0.9 dl / g is laminated by co-extrusion. And, the total draw ratio is characterized in that more than nine times.

Description

 Light-diffusion polyester film and its manufacturing method {Polyester films for diffusing light and manufacturing method of the same}

The present invention relates to a light-diffusion film used for various displays, and more particularly, it is not only excellent in smoothness and durability, but also can be produced with industrially low manufacturing cost and can be used for various displays such as advertisement. An ester film and its manufacturing method are related.

Generally, a light diffusion film is used by coating a light diffusion layer on a transparent film. In this case, not only a separate coating process is required but also a large amount of expensive organic particles are used to maintain a predetermined light diffusion property. Very high.

In addition, in the drying process during coating, deformation is easy to occur, and curling occurs due to the coating layer, so that the smoothness of the film is not deteriorated, and a series of post-processing processes such as coating, printing, sheet forming, etc. In this case, the coating layer is weak and easily damaged.

Therefore, there is a demand for a light diffusion polyester film that is excellent in quality such as smoothness, durability, workability, and the like, and requires very low manufacturing cost.

Therefore, the technical problem to be achieved by the present invention is to provide a light diffusion polyester film excellent in durability, smoothness, processability and low manufacturing cost in order to solve the above problems.

In addition, another technical problem to be achieved by the present invention is to provide a method for producing the polyester film.

In order to achieve the above technical problem, the present invention is 60% by weight or more of the repeating unit is made of ethylene terephthalate and the first film layer and the average particle diameter of the first polyester resin having an ultimate viscosity of 0.4 ~ 0.9dl / g A second film layer made of a first polyester resin containing 0.3 to 8 μm of organic particles and at least 60% by weight of the repeating unit is made of ethylene terephthalate and has an intrinsic viscosity of 0.4 to 0.9 dl / g. It is laminated | stacked and provides the biaxially-oriented polyester film characterized by the total draw ratio being 9 times or more.

In order to achieve the above another technical problem, the present invention

(a) 60% by weight or more of the repeating unit is composed of ethylene terephthalate and extrudates a melt of the first polyester resin having an intrinsic viscosity of 0.4 to 0.9 dl / g to form a first film layer, and at the same time an average particle diameter of 0.3 An organic particle of ˜8 μm is contained, and 60 wt% or more of the repeating unit is made of ethylene terephthalate, and the melt of the second polyester resin having an intrinsic viscosity of 0.4 to 0.9 dl / g is obtained from any one of the first film layers. Forming an unstretched film having two layers by coextrusion to one side to form a second film layer; And

(b) providing a method for producing a polyester film, comprising stretching the unstretched film in a longitudinal direction and a transverse direction such that a total draw ratio is 9 times or more.

In the polyester film according to the present invention and a method for producing the same, the content of the organic particles is preferably 2 to 15% by weight based on the total film, the polyester film in this case has a light transmittance of 90% or more, haze May be 65-85%.

 In the polyester film and the method for producing the same according to the present invention, the thermal decomposition initiation temperature of the organic particles is preferably 270 ° C. or more, and the organic particles are crosslinked polymethylmethacrylate, crosslinked polystyrene and crosslinked polymethylmethacrylate. It is preferably at least one selected from the group consisting of copolymers of polystyrene and polystyrene.

The polyester film according to the present invention has excellent smoothness, durability, workability, etc. by laminating, biaxially stretching and heat setting a second film layer, which is a light diffusion layer, on either side of the first film layer by co-extrusion during manufacture. It has the advantage of low cost.

Hereinafter, the polyester film according to the present invention and its manufacturing method will be described in detail.

In the polyester resin constituting the first film layer and the second film layer of the polyester film according to the present invention, at least 60% by weight of the repeating unit is made of ethylene terephthalate.

Such ethylene terephthalate units may be formed by direct esterification of terephthalic acid with ethylene glycol or transesterification of dimethyl terephthalate with ethylene glycol.

The remaining 40% by weight may be copolymerized, and both acid and alcohol components may be used as the copolymerization component. As the acid component, dimethyl terephthalic acid, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, cyclohexane, dicarboxylic acid, diphenoxyethane dicarboxylic acid, anthracene dicarboxylic acid, αβ-bis (2-chlorophenoxy) And ethane-4,4-dicarboxylic acid. Examples of the alcohol component include ethylene glycol, trimethylene glycol tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, and hexylene glycol.

In addition, the polyester resin used in the present invention preferably has an intrinsic viscosity measured at a concentration of 0.3 g per 25 ml of orthochlorophenol at 35 ° C. in the range of 0.4 to 0.9 dl / g, and preferably 0.5 to 0.8 dl / g. Range is particularly preferred. If the film is made of polyester having an intrinsic viscosity of less than 0.4 dl / g, breakage occurs frequently during stretching, which greatly lowers the productivity, and lowers physical properties such as mechanical strength in the final film. In addition, when the intrinsic viscosity exceeds 0.9 dl / g, the melt viscosity is very high, it is not preferable because the increase in shear stress caused difficulties in the manufacturing process, such as extrusion instability, which greatly reduces the productivity in the post-process .

In addition, the second polyester resin used in the production of the second film layer to be the light diffusion layer includes organic particles having an average particle diameter of 0.3 to 8㎛. More preferable average particle diameter of the said organic particle | grain is 0.5-3 micrometers. This is because the light diffusion effect is changed by the difference in the scattering effect according to the average size of the organic particles.

If the particles are too large or the spacing is too small, the diffraction hardly occurs, and if the particles are too small, the light will not recognize the inorganic particles and will just pass, as opposed to the problem of excessive void formation resulting in deterioration of fairness and film properties. In addition, the voids are also less formed, so in order to maintain a predetermined brightness and hiding power, a problem arises in that the content of expensive organic additives must be increased. In the present invention, it is to use the organic particles having an average particle diameter as described above in consideration of this.

In addition, since the temperature of the melt extrusion process is 260 ° C. or more during film production, the heat resistance of the organic additive should be maintained above that. In order to have heat resistance in this temperature condition range, it is preferable to use a crosslinked organic additive. Preferred crosslinking organic additives for use in the present invention are any one or more selected from the group consisting of crosslinked polymethylmethacrylate, crosslinked polystyrene and copolymers of crosslinked polymethylmethacrylate and polystyrene.

And, the content of the organic particles as described above is preferably included in the 2 to 15% by weight based on the entire polyester film according to the present invention, the reason is that when included in less than 2% by weight lack of light diffusion and hiding power In addition, when included in excess of 15% by weight, due to excessive hiding force, rather than lowering the light diffusion effect, as well as poor stretchability during the manufacture of the film is due to the problem that the breakage increases.

As such an organic additive input method, both of the following methods are possible.

Firstly, the organic additives are slurried with ethylene glycol to the required concentration in the final film and directly added during esterification or transesterification or polycondensation, which is advantageous for mass production.

The second method is to manufacture a high-density master chip into which an organic additive is added by compounding, and then add it in an extrusion process. In this case, there is little risk of damage to the organic additive, and the additive depends on the degree of dilution of the master batch chip. It is preferable to the above-mentioned method because the concentration of the is easily controlled.

Hereinafter, the manufacturing method of the polyester film according to the present invention will be described in detail.

First, the first and second polyester resins produced by conventional methods are respectively dried under a nitrogen atmosphere. Subsequently, the first polyester resin melt is extruded to form a first film layer, and at the same time, a melt of the second polyester resin is formed on either side of the first film layer to form a second film layer. Coextrusion is carried out using a T-die equipped with a large extruder and a feeder block to prepare an unstretched film composed of two layers. Subsequently, the biaxially stretched and heat-set the unstretched film so that the total draw ratio is 9 times or more to prepare a polyester film according to the present invention.

The total draw ratio of the polyester film according to the present invention should be 9 times or more because the voids are formed by the organic particles to maintain the proper hiding power and to enhance the light diffusion effect.

The manufacturing method described above has been described mainly by extrusion by the Ti-die method, but can be used without particular limitation as long as it is well known in the art to which the present invention belongs, such as the inflation method. In addition, the polyester film according to the present invention may be designed to an appropriate thickness according to the intended use, and may be used by surface treatment by coating with another resin on the surface as necessary.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples.

In the Example and the comparative example of this invention, various performance evaluation of the produced film was performed with the following measuring method.

(1) luminance

Measurement was made using Topcon BM7 (Field 2 ^o , distance 50 cm).

(2) haze

It measured by the method of ASTM D1003.

(3) light transmittance

It measured by the method of ASTM D1003.

(4) Evaluation of Wear Resistance of Light Diffusion Layer

The light diffusion layer was evaluated by measuring the weight loss amount after polishing 100 times with a Tabor Abrasion Tester.

(5) smoothness measurement

According to the curl and wave generation amount of the film was evaluated in three grades, O is good, △ is normal, X is poor.

<Example 1>

Dimethyl terephthalate and ethylene glycol were mixed in a 1: 2 equivalent ratio, 0.03% by weight of manganese acetate was used as a transesterification catalyst to produce bis-hydroxyethylene terephthalate, a polyethylene terephthalate monomer, and 0.05% of antimony oxide as a polymerization catalyst. % Of the polycondensation reaction was completed to prepare a polyester resin having an intrinsic viscosity of 0.640 dl / g.

As the first polyester resin, 100% of the polyester resin without any additives was used, and as the second polyester water quality, the weight of the crosslinked polystyrene particles having an average particle diameter of 3 μm and 70 wt% of the polyester resin was 30 weight. The prepared master chip was prepared under a compound skew rpm of 300 and a temperature of 270 ° C., and then diluted with a mixing ratio of 1: 1 with a polyester resin without an additive.

Subsequently, the first polyester resin was used as a first film layer, the second polyester resin was used as a second film layer, and then co-extruded using a T-die equipped with two extruders and a feeder block. It contact | adhered to the cooling roll cooled with and obtained the unstretched film.

The unstretched film thus obtained was stretched three times in the longitudinal direction and four times in the transverse direction using a conventional biaxial stretching apparatus, and then heat-set at 200 ° C. to obtain a biaxially stretched two-layer polyester film.

The thickness of the said 1st film layer was 100 micrometers, and the thickness of the 2nd film layer was 20 micrometers when the said polyester film was measured with the scanning microscope photograph.

The haze, light transmittance, brightness, wear resistance and smoothness of the thus obtained film were measured and shown in Table 1.

<Example 2>

The organic particles added to the second polyester as in Example 1 were used as the crosslinked polymethyl methacrylate.

<Example 3>

A polystyrene having an average particle size of 0.3 μm was added to the second polyester in the same manner as in Example 1.

<Example 4>

It carried out by the same method as Example 3, the organic particles content of the second polyester was 20% by weight and the total draw ratio of the film was 9 times.

Comparative Example 1

A 100 micrometer polyester film made from the first polyester of Example 1 was prepared, and a light diffusion layer containing 15% by weight of crosslinked polystyrene in an acrylic resin was coated to complete the film.

Comparative Example 2

It carried out by the same method as the comparative example 1 but the content of the crosslinked polystyrene in the coating layer was 30% by weight.

Comparative Example 3

A polystyrene having an average particle size of 0.1 μm was added to the second polyester in the same manner as in Example 1.

Comparative Example 4

The draw ratio of the film was set to 7.5 in the same manner as in Example 1.

Condition Light Diffusion Layer Properties Haze Light transmittance Luminance Wear resistance Smoothness Recipe Additive type Additive particle diameter Additive content Elongation ratio (%) (%) (%) Weight loss (g) Rating Example 1 Coextrusion polystyrene 3 μm 15 wt% 12 78 90 99.0 0.08 O Example 2 Coextrusion Polymethyl methacrylate 3 μm 15 wt% 12 77 90 98.5 0.09 O Example 3 Pneumatic polystyrene 0.3 μm 15 wt% 12 76 91 99.0 0.08 O Example 4 Coextrusion polystyrene 3 μm 10% by weight 9 78 90 98.5 0.10 O Comparative Example 1 coating polystyrene 3 μm 15 wt% 62 97 98.5 0.19 △ Comparative Example 2 coating polystyrene 3 μm 30 wt% 78 90 98.5 0.22 X Comparative Example 3 Coextrusion polystyrene 0.1 μm 15 wt% 12 75 93 98.5 0.08 O Comparative Example 4 Coextrusion polystyrene 3 μm 15 wt% 7.5 75 93 99.0 0.10 △

Referring to Table 1, the films of Examples 1 to 4, which are polyester films according to the present invention, show the films of Comparative Examples 1 and 2 according to the coating method in haze, light transmittance, brightness, wear resistance and smoothness, and the scope of the present invention. It turns out that it is very excellent compared with the film of the comparative examples 3 and 4 which deviate.

As described above, the present invention can provide a polyester film for light diffusion that is excellent in smoothness, durability, processability, and the like, and also has low manufacturing cost.

Claims (9)

At least 60% by weight of the repeating unit is made of ethylene terephthalate and the first film layer made of a first polyester resin having an ultimate viscosity of 0.4 ~ 0.9dl / g and 10-15 wt% of organic particles composed of crosslinked polymethylmethacrylate, crosslinked polystyrene, or a copolymer of crosslinked polymethylmethacrylate and polystyrene having an average particle diameter of 0.3 to 8 µm are contained, wt.% or more, and composed of ethylene terephthalate and the second film layer made of a first polyester resin having an intrinsic viscosity of 0.4 ~ 0.9dl / g is laminated by coextrusion light, characterized in that a total draw ratio greater than 9 times Biaxially oriented polyester film for diffusion . delete The biaxially oriented polyester film according to claim 2, wherein the biaxially oriented polyester film has a light transmittance of 90% or more and a haze of 65-85%. The biaxially oriented polyester film according to claim 1, wherein the thermal decomposition initiation temperature of the organic particles is 270 ° C or higher. delete (a) 60% by weight or more of the repeating unit is composed of ethylene terephthalate and extrudates a melt of the first polyester resin having an intrinsic viscosity of 0.4 to 0.9 dl / g to form a first film layer, and at the same time an average particle diameter of 0.3 10 to 15% by weight of organic particles composed of crosslinked polymethylmethacrylate, crosslinked polystyrene, or a copolymer of crosslinked polymethylmethacrylate and polystyrene, which is ˜8 μm, are contained in the total film, and at least 60% by weight of the repeating unit The melt of the first polyester resin, which is composed of ethylene terephthalate and has an intrinsic viscosity of 0.4 to 0.9 dl / g, is formed on one surface of the first film layer and co-extruded to form a second film layer. Preparing an unstretched film; And (b) method for producing a light-diffusing polyester film characterized in that it comprises the step of stretching the unstretched film in the longitudinal direction and the transverse direction so that the total draw ratio is at least 9 times. delete The method for producing a biaxially oriented polyester film according to claim 7, wherein the organic particles have a thermal decomposition start temperature of 270 ° C or higher. delete