KR20220051047A - combined optical film and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to a combined optical film for diffusing light and increasing brightness. The combined optical film comprises: a prism sheet having a prism pattern formed on the surface thereof; an adhesive layer formed on the back surface of the prism sheet; and a prism sheet of which the tip is compressed against the adhesive layer. The prism sheet is a fluorene-containing polyester resin. The adhesive layer includes a photocurable composition including fluorine (meth)acrylate, a (meth)acrylate monomer, a urethane oligomer, and a photoinitiator. Therefore, the combined optical film having the layers stacked therein can increase brightness, increase an adhesive force between the prism sheets, and has the adhesive layer with a low refractive index to suppress the surface reflection of light, thereby improving transmittance in a multilayer prism sheet.

Description

Composite optical film and manufacturing method thereof

The present invention relates to a composite optical film formed by laminating and bonding a lower diffusion film, a prism sheet, and an upper diffusion film constituting a backlight unit of a liquid crystal display device.

In general, optical films include a film in which a function is imparted to the film itself to exhibit a specific function, or a functional laminated film is laminated and coated on a film or a film support to impart functionality.

Among the optical films, there are a diffusion film and a prism sheet used in a backlight unit (BLU) of a liquid crystal display (LCD), and the like.

Since the liquid crystal display is a non-luminous element that does not emit light by itself, a liquid crystal display panel for displaying an image requires a backlight unit that supplies a separate light.

Light emitted from a cold cathode fluorescent lamp (CCFL) reaches the display screen through a backlight unit, and the backlight unit has a diffusion film and diffusion for uniformly transmitting the light to the entire surface of the liquid crystal display device A prism sheet for condensing the light emitted from the film and transmitting it to the liquid crystal display device is included.

The diffusion film is required to diffuse the light generated from the light source so as not to show the image of the light source, and to maintain the brightness of the entire screen without impairing the brightness of the light source.

The diffusion film scatters the light emitted from the light guide plate and incident on the display screen to make the luminance distribution of the light uniform. There is a milky white diffusely reflective film that diffusely reflects white like film and paper.

Conventionally, as a diffusion film, the surface of a transparent base film such as glass, acrylic resin, polycarbonate, or polyester is processed into a prism shape, or a transparent film to which inorganic fine particles or transparent resin particles are added has been used. In addition, some are manufactured by coating the surface of the transparent film with a resin to which the particles are added.

On the other hand, the prism sheet is used for the purpose of improving the luminance of the backlight unit disposed on the rear side of the liquid crystal display device. In order to increase the front luminance of the backlight unit, the prism sheet is usually disposed on the light diffusion plate or the diffusion film to be uniformly diffused. It is a film that improves the luminance by allowing light sources in various directions to be emitted to the front using the function of total reflection and refraction of the prism structure.

In general, a prism sheet is repeatedly formed with a prism having a triangular cross-sectional shape on its surface, and serves to condense the light diffused by the diffusion film in a vertical direction on the display screen to emit light.

Conventionally, each optical film composed of the diffusion film and the prism sheet is laminated in a predetermined order to constitute a backlight unit, and the light emitted from the cold cathode fluorescent lamp is transmitted to the display screen through the backlight unit. There have been problems of cost and time consumption and a decrease in production yield due to stacking the backlight unit.

That is, in order to compose a backlight unit by combining individual optical films, the double-sided protective liner that protects the optical film is first removed. It takes time required to remove the protective liner and there is a possibility of film damage when the protective liner is removed. .

Moreover, as the thickness of the entire liquid crystal display device becomes thinner and thinner, the thickness of each optical film is also reduced, and accordingly, the strength of each optical film is lowered. And, since these optical films require precise optical functionality, the occurrence of surface defects such as scratches or foreign substances can have a fatal effect on the performance of the entire liquid crystal display device.

In addition, in the above fastening process, there is a high possibility of adhesion of lint or other foreign substances to the film surface due to the generation of static electricity, which increases cost and time consumption, decreases production yield, and increases manufacturing cost. do.

Korean Patent Registration No. 1170013 discloses a method for manufacturing a composite film in which an optical film is laminated. The above patent describes a composite optical film produced by applying a resin composition containing acrylate as a main component to the tip of a prism pattern of a prism sheet, pressing it on the back surface of another diffusion film or prism sheet, and curing it with ultraviolet light and heat. According to this, it is possible to provide an integrated composite optical film while reducing costs by easily laminating the prism sheet and the diffusion film or the prism sheet.

However, improvement of physical properties such as brightness required for composite optical film and improvement of interlayer adhesion according to lamination are still required.

In order to respond to the above needs, the present invention has an object to develop a novel material constituting a composite optical film.

In order to solve the above problems, the present invention provides a composite optical film comprising a prism sheet having a prism pattern on its surface, an adhesive layer formed on the back surface of the prism sheet, and a prism sheet in which the prism pattern is compressed on the adhesive layer, the prism sheet is It is a fluorene-containing polyester resin, and the adhesive layer contains 60 to 80% by weight of fluorine (meth)acrylate, 2 to 15% by weight of (meth)acrylate monomer, 10 to 20% by weight of urethane oligomer, and 0.5 to 5% by weight of photoinitiator. It provides a composite optical film comprising a photocurable composition comprising.

In addition, the present invention, manufacturing a prism sheet in which a prism pattern is formed on the surface of the sheet made of a fluorene-containing polyester resin as a transparent resin; forming an adhesive layer by applying a photocurable composition to the back surface of the prism sheet, and laminating the adhesive layer so that the prism pattern of the prism sheet is compressed; and curing the adhesive layer with ultraviolet rays or heat, wherein the photocurable composition comprises 60 to 80% by weight of fluorine (meth)acrylate, 2 to 15% by weight of (meth)acrylate monomer, 10 to 20% by weight of urethane oligomer % and provides a method for producing a composite optical film, characterized in that it contains 0.5 to 5% by weight of the photoinitiator.

According to the present invention, the prism sheet is formed of fluorene-containing polyester to improve transparency and transmittance, so that the luminance is improved in the composite optical film in which the prism sheet is laminated.

In addition, by using a photocurable composition containing fluorine (meth)acrylate as a main component in the adhesive layer between the prism sheets, the adhesive layer exhibits a low refractive index while improving the adhesion between the prism sheets, thereby suppressing the surface reflection of light and thus transmittance in the multilayer prism sheet. This is improved.

1 is a schematic view showing a prism sheet according to the present invention.
2 is a schematic view showing a composite optical film in which a prism sheet according to the present invention is laminated.

The present invention relates to a composite optical film laminated by an adhesive layer interposed between prism sheets composed of a transparent resin, wherein the transparent resin is a fluorene-containing polyester resin having a refractive index of 1.6 or higher, and the adhesive layer is fluorine (meth)acrylic 60 to 80% by weight of the rate, 2 to 15% by weight of a (meth)acrylate monomer, 10 to 20% by weight of a urethane oligomer, and 0.5 to 5% by weight of a photoinitiator.

The transparent resin constituting the prism sheet is a thermoplastic resin having a refractive index of 1.6 to 1.7, and a fluorene-containing polyester resin is used because scratch resistance and heat resistance can be improved.

It is preferable that the said fluorene containing polyester resin is polyester which superposed|polymerized the fluorene containing diol and diol, and dicarboxylic acid from a viewpoint of adhesiveness and an optical characteristic.

The fluorene-containing diol includes 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis(hydroxyethoxynaph) in order to balance reactivity and optical properties. tyl)fluorene, 9,9-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]fluorene, 9,9-bis[4-(2-hydroxyethoxy)-3-tri Phenyl] fluorene and the like are preferable.

Another diol component that can be used together with the fluorene-containing diol is a C ₂ to C ₄ alkanediol, more preferably ethylene glycol or 1,4-butanediol.

The said dicarboxylic acid is C5- _C10 cycloalkanedicarboxylic _acid , such as ₁ , 4- cyclohexanedicarboxylic acid, and C6-C14 _{areenedicarboxylic} acid, such as terephthalic acid and isophthalic acid, from a viewpoint of an optical characteristic. desirable.

The fluorene-containing polyester resin preferably has a weight average molecular weight of 15,000 to 60,000 (GPC, measured at 40° C. using THF as a solvent).

The fluorene-containing polyester resin preferably has a glass transition temperature of 100 to 200°C.

When the prism sheet is formed with the fluorene-containing polyester resin of the present invention, luminance and stability at high temperature can be improved even in a prism sheet (composite optical film) formed in a multilayer structure due to high refractive index and transparency.

In addition, since scratch resistance is improved, damage to the prism sheet is suppressed during the lamination process, thereby improving lamination workability.

The prism sheet of the present invention may consist of a base part on which a prism pattern is not formed and a prism part on which a prism pattern is formed. It can be manufactured so that a prism pattern is formed in it.

As mentioned above, it is preferable that the temperature at the time of melt-extrusion is 220-300 degreeC.

As for the method of forming the prism shape using the mold, a method capable of forming the prism shape by pressing the mold against the surface of the softened transparent resin can be used without limitation, but from the viewpoint of continuous production, the concavo-convex portion corresponding to the prism unit A method of transferring the prism shape by pressing while rolling on a metal roll having (a plurality of adjacent V-shaped grooves, etc.) may be preferably used.

It is preferable that the temperature at the time of crimping|bonding with casting_mold|templates, such as a metal roll, is 100-170 degreeC.

After the prismatic shape is imparted, it is preferably solidified in an annealing roll at 10 to 60°C.

Next, the photocurable composition for forming the adhesive layer will be described.

In the photocurable composition, the fluorine (meth)acrylate has 4 or more fluorine atoms per molecule and has a refractive index of 1.38 or less, and tetrafluoroethyl acrylate or octafluoropentyl acrylate is preferable.

This can be used to control compatibility and refractive index in the photocurable composition.

If the content of the fluorine (meth)acrylate in the photocurable composition of the present invention is less than 60% by weight, the refractive index of the adhesive layer does not become 1.42 or less and the transmittance deteriorates, and when it exceeds 80% by weight, the adhesive strength decreases.

The (meth) acrylate monomer is hydroxypropyl (meth) acrylate, dimethylaminoethyl methacrylate, dimethyl acrylamide and hydroxyethyl (meth) acrylate, and hydrophilic groups such as a hydroxyl group, an amino group and an amide group Eggplant is a (meth)acrylate monomer.

By using this, the adhesive layer formed after the photocurable composition is cured maintains transparency to improve luminance, and adhesion to polycarbonates can be improved.

When the content of the (meth)acrylate monomer in the photocurable composition of the present invention is less than 2% by weight, the transparency and adhesiveness of the adhesive layer decreases, and when it exceeds 15% by weight, the refractive index of the adhesive layer does not become 1.42 or less.

The urethane oligomer may be used without limitation in which at least one terminal is urethane (meth) acrylated, and it is preferable that the number average molecular weight is 2,500 to 500,000. Commercial examples of these include urethane oligomers having a number average molecular weight of 2,500 (PPG-UMA, 東亞合成 (株), Japan) and urethane oligomers having a number average molecular weight of 10,000 (PPG-UMA-L, 東亞合成 (株), Japan). can be heard

It can be used to control the viscosity of the composition, the mechanical properties, and the stress relief that contributes to the durability of the bond.

In the photocurable composition of the present invention, when the content of the urethane oligomer is less than 10% by weight, the adhesiveness decreases, and when it exceeds 20% by weight, the refractive index of the adhesive layer does not become 1.42 or less.

The photoinitiator is a general photoradical initiator, 2-hydroxy-2-methyl-1-phenyl propan-1-one, 1-hydroxy-cyclohexyl-phenyl ketone, 2,4,6-trimethylbenzoyl diphenyl phosphine Oxide and the like can be used without limitation.

In the photocurable composition of the present invention, when the content of the photoinitiator is less than 0.5% by weight, the adhesion is reduced, and when it exceeds 5% by weight, the transmittance is reduced by the unreacted initiator.

The photocurable composition of the present invention is applied to the prism sheet, and visible or ultraviolet light is irradiated using a high-pressure mercury lamp, a halogen lamp, a metal halide lamp, etc. as a light source to cure the composition to improve adhesion.

In this case, when irradiated as described above, the composition can be cured in a short time of 1 to 60 seconds at an illumination intensity of 100 to 1,000 mJ/cm 2 .

The thickness of the cured adhesive layer may be 1 to 10 μm.

The adhesive layer formed by curing the prism sheet made of a specific fluorene-containing polyester resin is laminated and bonded while improving the adhesion between the multi-layer sheets, and the adhesive layer has a refractive index of 1.42 or less. It is possible to manufacture a composite optical film having improved transmittance in the multilayer prism sheet.

Hereinafter, the present invention will be specifically described by way of Examples and Comparative Examples. However, the following examples are only for illustrating the present invention, and the present invention is not limited by the following examples, and can be changed to other examples that are substituted and equivalent within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in the art to which the present invention pertains.

<Production Example 1>

Using 1 mol of terephthalic acid, 0.3 mol of ethylene glycol, 0.7 mol of 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene as raw materials, fluorene as a transparent resin using a conventional polyester polymerization method Polyester containing (glass transition temperature 145°C, refractive index 1.63) was prepared.

<Preparation Example 2>

Using 1 mol of cyclohexanedicarboxylic acid, 0.2 mol of ethylene glycol, and 0.8 mol of 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene as raw materials, it is transparent using a conventional polyester polymerization method. As a resin, fluorene-containing polyester (glass transition temperature of 120° C., refractive index of 1.61) was prepared.

<Example 1>

Polyester containing fluorene as a transparent resin is melted in an extruder at 230°C and extruded through a T-die to form a sheet. Thereafter, the prism has an embossed shape in which an isosceles triangular pattern with an apex angle of 90° and a pitch between prisms of 50 μm is arranged in parallel, and the surface of the sheet is pressed on a metal roll heated to 135° C. A prism sheet on which a pattern was formed was manufactured.

Thereafter, the photocurable composition shown in Table 1 is applied to the back surface of the prism sheet to form an adhesive layer, and the adhesive layer is laminated so that the tip of the prism pattern of another prism sheet is compressed on the adhesive layer, and the adhesive layer is applied with an ultraviolet light of 800 mJ/cm 2 A composite optical film in which a prism sheet was laminated was prepared by irradiating with illuminance for 10 seconds.

<Examples 2 to 4>

A composite optical film was prepared in the same manner as in Example 1, except that the transparent resin and the photocurable composition were used in Example 1 as shown in Table 1 below.

<Comparative Examples 1 to 4>

A composite optical film was prepared in the same manner as in Example 1, except that the transparent resin and the photocurable composition were used in Example 1 as shown in Table 1 below.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Prism sheet Polyester of Preparation Example 1 Polyester of Preparation Example 2 ← ← polycarbonate Polyester of Preparation Example 1 ← ← photocurable composition Tetrafluoroethyl acrylate 70 65 66 70 70 50 85 77 dimethyl acrylamide 8 0 12 8 8 25 3 14 hydroxy propyl methacrylate 0 13 0 0 0 0 0 0 PPG-UMA-L 20 20 20 20 20 23 10 7 Darocur 1173 *2) 2 2 2 2 2 2 2 2 Adhesive layer thickness (㎛) 2 2 2 8 2 2 2 2 *1) Urethane oligomer with a number average molecular weight of 10,000 (東亞合成(株), Japan)
*2) 2-hydroxy-2-methyl-1-phenylpropan-1-one is a trade name of Ciba Specialty Chemicals.
* The unit of the above numerical value is % by weight

The following evaluation was performed on the composite optical films prepared in Examples and Comparative Examples, and the results are shown in Table 2.

<Evaluation method>

1. refractive index

Measure at 25°C with a light source wavelength of 589 nm using an Abbe type refractometer.

2. Luminance

Use CA-S1500W ver.2.1 (KONICA MINOLTA, Japan) to indicate relative values based on 3M BEF Ⅲ film.

3. curl

Measure using a steel ruler.

4. Peeling Value

It is measured using a COAD.203 push-pull type adhesion tester (Ocean Science, Korea).

refractive index luminance
(%) warp
(mm) peel value
(gf/25mm) Gyeonghwajeon after curing Example 1 1.39 1.42 126 0 23 Example 2 1.39 1.42 124 0 21 Example 3 1.39 1.42 125 0 22 Example 4 1.39 1.42 118 0 39 Comparative Example 1 1.39 1.42 96 0 6 Comparative Example 2 1.43 1.46 94 0 8 Comparative Example 3 1.39 1.42 106 0 3 Comparative Example 4 1.40 1.43 102 0 4

From Table 2 above, the luminance of the composite optical film using polycarbonate for the prism sheet is lowered (Comparative Example 1), and when the fluorine-containing acrylate is used in the photocurable composition in an amount less than the content of the present invention, the luminance is also lowered (Comparative Example 2), when the acrylate monomer and the urethane oligomer were used in less than the content of the present invention, it was confirmed that the peeling force was lowered and the adhesiveness was deteriorated.

In comparison, the composite optical film according to the present invention has excellent transparency and transmittance, so that the luminance is improved. In particular, the luminance is improved even when the thickness of the adhesive layer increases. It becomes possible to form a sheet.

Claims (6)

In the composite optical film comprising a prism sheet having a prism pattern formed on the surface, an adhesive layer formed on the back surface of the prism sheet, and a prism sheet in which the prism pattern is compressed on the adhesive layer,
The prism sheet is a fluorene-containing polyester resin,
The adhesive layer is a photocurable composition comprising 60 to 80% by weight of fluorine (meth)acrylate, 2 to 15% by weight of a (meth)acrylate monomer, 10 to 20% by weight of a urethane oligomer, and 0.5 to 5% by weight of a photoinitiator composite optical film. The method of claim 1,
The fluorene-containing polyester resin has a refractive index of 1.6 or more, and the adhesive layer has a refractive index of 1.42 or less. Preparing a prism sheet in which a prism pattern is formed on the surface of the sheet made of a fluorene-containing polyester resin as a transparent resin;
forming an adhesive layer by applying a photocurable composition to the back surface of the prism sheet and laminating the adhesive layer so that the prism pattern of the prism sheet is compressed; and
Including; curing the adhesive layer with ultraviolet rays or heat;
The photocurable composition comprises 60 to 80% by weight of fluorine (meth)acrylate, 2 to 15% by weight of (meth)acrylate monomer, 10 to 20% by weight of urethane oligomer, and 0.5 to 5% by weight of photoinitiator. A method of manufacturing an optical film. 4. The method of claim 3,
The fluorene-containing polyester resin is a polyester obtained by polymerizing fluorene-containing diol and diol and dicarboxylic acid,
The fluorene-containing diol is 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis(hydroxyethoxynaphthyl)fluorene, 9,9-bis[4 -(2-hydroxyethoxy)-3-phenylphenyl]fluorene and 9,9-bis[4-(2-hydroxyethoxy)-3-triphenyl]fluorene,
The diol is a method of manufacturing a composite optical film, characterized in that C ₂ ~ C ₄ alkanediol. 4. The method of claim 3,
The prism sheet is formed of a base part and a prism part on the surface,
A method of manufacturing a composite optical film, characterized in that the transparent resin is melt-extruded to form a sheet, and a mold having an uneven portion corresponding to a prism unit is pressed against the surface of the formed sheet to form a prism shape. 4. The method of claim 3,
The fluorine (meth) acrylate is a method of manufacturing a composite optical film, characterized in that tetrafluoroethyl acrylate or octafluoropentyl acrylate.

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