KR101751573B1 - Optical film and preparing method for the same - Google Patents

Abstract

The present invention relates to a thermoplastic resin composition comprising a first polymer resin having a glass transition temperature of 70 ° C to 100 ° C and forming a continuous phase and a second polymer resin having a glass transition temperature difference from 0 ° C to 40 ° C, An optical film containing a polymer resin and satisfying the following formulas (1) to (2), and a method of producing the same.
(1): 0? | Nx ₁ - nx ₂ | 0.10
(2): 0.15? | Ny ₁ - ny ₂ | ≤ 0.35
In the above formulas (1) to (2), nx ₁ means the refractive index in the polarization transmission axis direction after stretching of the first polymer resin forming the continuous phase, and nx ₂ means the refractive index of the second polymer resin forming the discontinuous phase Ny ₁ means a refractive index in a direction perpendicular to the polarization transmission axis direction of the first polymer resin forming the continuous phase, and ny ₂ means a refractive index in a direction perpendicular to the polarization transmission axis direction, 2 Refractive index in the direction perpendicular to the polarization transmission axis direction after stretching of the polymer resin.

Description

[0001] OPTICAL FILM AND PREPARING METHOD FOR THE SAME [0002]

The present invention relates to an optical film and a manufacturing method thereof, and more specifically, to an optical film having scattering polarization characteristics capable of improving light utilization efficiency and a manufacturing method thereof.

The polarizing plate is generally composed of a polarizer having a structure in which a polyvinyl alcohol (hereinafter, referred to as PVA) molecular chain is oriented in a certain direction and has a structure containing an iodine compound or a dichroic polarizing material, triacetyl And a cellulose (TAC) film. At this time, the polarizer and the protective film are generally adhered by an aqueous adhesive composed of a polyvinyl alcohol-based solution.

On the other hand, in the case of the polarizing plate as described above, the polarizer transmits only the polarized light component parallel to the polarized light transmission axis and absorbs the polarized light component perpendicular to the polarized light transmission axis. In order to solve such a problem, a technique of attaching a separate brightness enhancement film to one side of a polarizing plate has been proposed. A representative brightness enhancement film is DBEF film of 3M Company. However, the DBEF film is very expensive, and a new light scattering type polarizing film or the like has been actively developed to replace such an expensive commercial film product.

In general, such a light scattering type polarizing film includes a dispersed phase inside a continuous matrix, and the polarization transmitted axis component of the incident light component passes through the continuous matrix and the different refractive index difference of the dispersed phase, Reflection or scattering of the light reflected by the lower sheet, so that the process of re-entering again is repeated, thereby improving the light utilization efficiency according to the principle of polarizing recycling.

Meanwhile, the light scattering type polarizing film proposed so far uses a liquid crystal, a nanofiber, and a core cell as a dispersion material. However, when liquid crystals, nanofibers, or core cells are used as the dispersed phase, there is a limitation in high-magnification stretching, there is a limit in the difference in refractive index between the matrix phase and the dispersed phase, and it is difficult to realize uniform physical properties. There is a limit in improving the efficiency of the characteristics. In addition, the manufacturing process is also complicated, and these materials are generally expensive, so that the production cost is also high.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and it is an object of the present invention to provide an optical film having a scattering polarization characteristic capable of maximizing the efficiency of scattering polarization characteristics and capable of being manufactured by a simple method, .

In one aspect, the present invention provides a thermoplastic resin composition comprising a first polymer resin having a glass transition temperature of 70 to 100 캜 and forming a continuous phase, and a second polymer resin having a glass transition temperature difference of 0 캜 to 40 캜, (1) to (2), which comprises a second polymer resin which forms a second polymer resin.

(1): 0? | Nx ₁ - nx ₂ | 0.10

(2): 0.15? | Ny ₁ - ny ₂ | ≤ 0.35

In the above formulas (1) to (2), nx ₁ means the refractive index in the polarization transmission axis direction after stretching of the first polymer resin forming the continuous phase, and nx ₂ means the refractive index of the second polymer resin forming the discontinuous phase Ny ₁ means a refractive index in a direction perpendicular to the polarization transmission axis direction of the first polymer resin forming the continuous phase, and ny ₂ means a refractive index in a direction perpendicular to the polarization transmission axis direction, 2 Refractive index in the direction perpendicular to the polarization transmission axis direction after stretching of the polymer resin.

At this time, it is preferable that the optical film satisfies the following formulas (3) to (4).

(3): 0.15? Ny ₁ - nx ₁ ? 0.30

(4): 0? Nx ₂ - ny ₂ ? 0.10

In the above formulas (3) to (4), nx ₁ means the refractive index in the polarization transmission axis direction after stretching of the first polymer resin forming the continuous phase, and nx ₂ means the refractive index of the second polymer resin forming the discontinuous phase Ny ₁ means a refractive index in a direction perpendicular to the polarization transmission axis direction of the first polymer resin forming the continuous phase, and ny ₂ means a refractive index in a direction perpendicular to the polarization transmission axis direction, 2 Refractive index in the direction perpendicular to the polarization transmission axis direction after stretching of the polymer resin.

It is preferable that the second polymer resin comprises 1 to 20 parts by weight of the second polymer resin relative to 80 to 99 parts by weight of the first polymer resin.

On the other hand, it is preferable that the polarizing axis of the optical film is formed in a direction perpendicular to the stretching direction.

The optical film preferably has a maximum draw ratio of 4.5 times or more.

Further, it is preferable that the thickness of the optical film is 20 탆 to 100 탆.

The present invention also provides a polarizing plate and a display device comprising the optical film.

In another aspect, the present invention provides a thermoplastic resin composition comprising a first polymer resin having a glass transition temperature of 70 캜 to 100 캜 and forming a continuous phase, and a second polymer resin having a glass transition temperature difference of 0 캜 to 40 캜, Preparing an unoriented film comprising a second polymeric resin to form a second polymeric resin; And stretching the non-stretched film so as to satisfy the following expressions (1) to (2).

(1): 0? | Nx ₁ - nx ₂ | 0.10

(2): 0.15? | Ny ₁ - ny ₂ | ≤ 0.35

In the above formulas (1) to (2), nx ₁ means the refractive index in the polarization transmission axis direction after stretching of the first polymer resin forming the continuous phase, and nx ₂ means the refractive index of the second polymer resin forming the discontinuous phase Ny ₁ means a refractive index in a direction perpendicular to the polarization transmission axis direction of the first polymer resin forming the continuous phase, and ny ₂ means a refractive index in a direction perpendicular to the polarization transmission axis direction, 2 Refractive index in the direction perpendicular to the polarization transmission axis direction after stretching of the polymer resin.

At this time, in the step of preparing the unstretched film, it is preferable to blend the first polymer resin and the second polymer resin, and melt-extrude the blend to produce an unstretched film.

The step of drawing the non-stretched film preferably has a thickness of 50 to 300 占 퐉 and a thickness of 20 to 100 占 퐉 after stretching.

In the step of drawing the non-stretched film, it is preferable that the stretching magnification is 5 to 7 times.

The stretching step of the non-stretched film preferably has a stretching temperature of 70 to 110 캜.

The optical film of the present invention uses a polymer resin having a glass transition temperature of 70 to 100 DEG C as a continuous phase and a polymer resin having a continuous phase and a glass transition temperature different from 0 DEG C to 40 DEG C as a discontinuous phase, Stretching at a low drawing temperature is possible, and as a result, excellent birefringence can be obtained.

In addition, the optical film of the present invention is manufactured by a general film forming method by blending two kinds of polymer resins forming a continuous phase and a discontinuous phase, so that the production method is simple, the productivity is excellent, and the price competitiveness is excellent.

In the optical film of the present invention, birefringence occurs in both of the two polymer resins due to stretching, and high-magnification stretching can be performed, so that the optical film can have improved scattering polarization characteristics as compared with the conventional art.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

1. Optical film

As a result of extensive research, the present inventors have found that, in the case of producing an optical film by blending two kinds of polymer resins having specific birefringence characteristics and having a specified glass transition temperature by stretching and stretching them, Has excellent scattering polarization characteristics and can improve light utilization efficiency, thus completing the present invention.

More specifically, the optical film of the present invention has a glass transition temperature of 70 to 100 占 폚, a first polymeric resin forming a continuous phase, and a glass transition temperature difference of 0 占 폚 to 40 占 폚 with the first polymeric resin, And a second polymer resin forming a discontinuous phase, and is characterized by satisfying the following expressions (1) to (2).

(1): 0? | Nx ₁ - nx ₂ | 0.10

(2): 0.15? | Ny ₁ - ny ₂ | ≤ 0.35

In the above formulas (1) to (2), nx ₁ means the refractive index in the polarization transmission axis direction after stretching of the first polymer resin forming the continuous phase, and nx ₂ means the refractive index of the second polymer resin forming the discontinuous phase Ny ₁ means a refractive index in a direction perpendicular to the polarization transmission axis direction of the first polymer resin forming the continuous phase, and ny ₂ means a refractive index in a direction perpendicular to the polarization transmission axis direction, 2 Refractive index in the direction perpendicular to the polarization transmission axis direction after stretching of the polymer resin.

Here, in the present invention, "continuous phase" means a matrix phase of an optical film, and "discontinuous phase" means a dispersed phase dispersed on the matrix.

If the refractive indexes of the continuous phase and the discontinuous two materials constituting the optical film are the same in the polarization transmission axis direction as in the formula (1), the light parallel to this direction will transmit due to no difference in refractive index, (1) is not satisfied, scattering occurs also in the light parallel to the polarization transmission axis direction, resulting in a problem that the light utilization efficiency is lowered. In addition, as the refractive index in the direction perpendicular to the polarization transmission axis direction of the continuous phase and the discontinuous phase of the optical material constituting the optical film must be different as in the formula (2), the light parallel to this direction can not transmit due to the difference in refractive index, If the above formula (2) is not satisfied, a light leakage phenomenon occurs, so that the scattering efficiency is lowered, and as a result, the light utilization efficiency is lowered.

On the other hand, the optical film of the present invention preferably satisfies the following formulas (3) to (4). In the optical film of the present invention, a polarized light transmission axis is formed in a direction perpendicular to the stretching direction (to be described later), and the following formula (3) is obtained when the continuous phase constituting the optical film has a refractive index in a direction parallel to the stretching direction (4) indicates that a discontinuous phase constituting the optical film is a material having a negative birefringence in which a refractive index in a direction perpendicular to the stretching direction is developed after the stretching, and a material having positive birefringence ≪ / RTI > The optical film of the present invention can have particularly excellent light utilization efficiency particularly when the numerical ranges of the following formulas (3) to (4) are satisfied.

(3): 0.15? Ny ₁ - nx ₁ ? 0.30

(4): 0? Nx ₂ - ny ₂ ? 0.10

In the above formulas (3) to (4), nx ₁ means the refractive index in the polarization transmission axis direction after stretching of the first polymer resin forming the continuous phase, and nx ₂ means the refractive index of the second polymer resin forming the discontinuous phase Ny ₁ means a refractive index in a direction perpendicular to the polarization transmission axis direction of the first polymer resin forming the continuous phase, and ny ₂ means a refractive index in a direction perpendicular to the polarization transmission axis direction, 2 Refractive index in the direction perpendicular to the polarization transmission axis direction after stretching of the polymer resin.

When the optical film of the present invention satisfies the above-mentioned expressions (1) to (2), and preferably satisfies the expressions (3) to (4), the optical film has excellent scattering polarization characteristics, As a result, the light utilization efficiency can be improved by selectively transmitting the polarized light parallel to the polarized light transmission axis and selectively reflecting or scattering the polarized light perpendicular to the polarized light transmission axis.

For example, the polarization component in the direction perpendicular to the polarization transmission axis of the optical film is scattered forward or backward, and the scattered light can be rotated in the polarization direction to be depolarized, It becomes possible to have a polarization component parallel to the transmission axis. Therefore, the component polarized in the polarization direction is increased, and the light utilization efficiency can be improved.

On the other hand, the optical film of the present invention has a glass transition temperature of 70 to 100 占 폚, a first polymer resin forming a continuous phase, and a glass transition temperature difference of 0 占 폚 to 40 占 폚 with the first polymer resin, And a blending resin of a second polymer resin forming an image. When two kinds of polymer resins are blended and used, the birefringence is generated by stretching in both of the two types of polymer resins, and as a result, the scattering polarization characteristics become better, and thus the light utilization efficiency can be further increased There are advantages.

In the case of blending two polymer resins as described above, it is possible to produce a film-like optical film, which enables high-magnification stretching. Since high-magnification stretching is possible in this way, Birefringence, and when the optical film is used as a base film for producing a thin polarizer, the optical characteristics of the thin polarizer manufactured using the optical film are excellent.

On the other hand, the optical film of the present invention preferably comprises 1 to 20 parts by weight of the second polymeric resin with respect to 80 to 99 parts by weight of the first polymeric resin, more preferably 85 to 97 parts by weight of the first polymeric resin, 2 polymer resin is more preferably contained in an amount of 3 to 15 parts by weight, and it is particularly preferable that the second polymer resin is contained in an amount of 5 to 10 parts by weight based on 90 to 95 parts by weight of the first polymer resin. Generally, since the first polymer resin forming the continuous phase and the second polymer resin forming the discontinuous phase are low in compatibility, when the composition ratio of the second polymer resin forming the discontinuous phase is higher than the above range, phase separation occurs Therefore, there is a problem that a continuous phase and a discontinuous phase can not be realized in the optical film, and further, only the scattering polarization characteristic is maximized. On the other hand, if the composition ratio of the second polymer resin forming the discontinuous phase is lower than the above-mentioned range, the scattering polarization characteristic is poor and the light utilization efficiency is lowered.

On the other hand, the first polymer resin forming the continuous phase of the present invention may be used in a continuous phase in the optical film of the present invention blended with a second polymer resin forming a discontinuous phase to be described later, Is 70 to 100 DEG C, and more preferably the glass transition temperature is 70 to 90 DEG C or so. When the glass transition temperature of the first polymer resin is higher than the above range, the refractive index developability of the first polymer resin becomes too large and the light scattered without being transmitted increases, resulting in a decrease in brightness. The refractive index of the first polymer resin is low and the scattering property may be deteriorated. At this time, the glass transition temperature can be measured by a differential scanning calorimeter (DSC). For example, in the case of using a differential scanning calorimeter (DSC), when a sample of about 10 mg is sealed in a dedicated pan and heated at a constant temperature, the amount of endothermic heat The transition temperature can be measured.

On the other hand, the first polymer resin can be used without particular limitation as long as it has the above-mentioned glass transition temperature and can satisfy the above formulas (1) to (2) by stretching. For example, polyethylene terephthalate resin, Co-polyethylene terephthalate resin, polyethylene terephthalate glycol resin, polycarbonate resin, polyarylate resin, cyclic polyolefin resin and polyether sulfone resin.

The second polymer resin forming the discontinuous phase of the present invention may be used as a discontinuous phase in the optical film of the present invention blended with the first polymer resin forming the continuous phase described above, The glass transition temperature difference with the polymer resin is about 0 캜 to 40 캜, more preferably about 0 캜 to 30 캜. When the glass transition temperature difference exceeds the above range, the stretching temperature of the film formed after the blending is biased to the glass transition temperature of one material. In this case, the optical anisotropy development rate of the continuous phase or the discontinuous phase is biased to one side, There is a problem that the effect becomes poor.

On the other hand, the second polymer resin can be used without particular limitation as long as it has the glass transition temperature as described above and can satisfy the formulas (1) to (2) by stretching. For example, it may be an acrylic resin, a styrene resin, an acryl-co-styrene resin, a polycarbonate resin, or the like.

At this time, the acrylic resin contains a (meth) acrylate-based unit as a main component, and is not limited to a homopolymer resin composed of a (meth) acrylate-based unit but also a copolymer resin . For example, the acrylic resin may be, but is not limited to, polymethyl methacrylate resin.

The styrene-based resin includes a styrene-based unit as a main component, and is a concept including not only a homopolymer resin composed of styrene-based units but also a copolymer resin in which monomer units other than styrene-based units are copolymerized. For example, the styrenic resin may be, but is not limited to, polystyrene resin, styrene-acrylonitrile copolymer resin,? -Methylstyrene-acrylonitrile copolymer resin, and the like.

The acrylic-co-styrene-based resin contains, as a main component, a (meth) acrylate-based unit and a styrene-based unit, and is not limited to a copolymer resin in which (meth) acrylate monomer and styrene- Methacrylate monomer and a monomer unit other than a styrene monomer. For example, the acrylic-co-styrene resin may be, but is not limited to, a methyl methacrylate-co-styrene copolymer resin, a methyl methacrylate-co-butyl methacrylate- And so on.

On the other hand, in the optical film of the present invention, it is preferable that the polarization transmission axis is formed in a direction perpendicular to the stretching direction. When the polarized light transmission axis is formed in the perpendicular direction to the stretching direction by the stretching, alignment of the polarized light transmission axis with the polarizer or the polarizing plate including the polarizer can be easily performed. In contrast to the conventional DBEF film, And the like are unnecessary.

On the other hand, the optical film having the above-described scattering polarization characteristics preferably has a maximum draw magnification of 4.5 times or more, more preferably from 5 times to 7 times. More specifically, the maximum draw ratio may be about 5 to 7 times at a temperature of 80 to 130 캜. Herein, the maximum stretching magnification means a stretching magnification immediately before the film breaks in the stretching process, and when the maximum stretching magnification of the optical film is in the above range, high magnification stretching is possible.

On the other hand, the thickness of the optical film having the above-described scattering polarization characteristics is preferably 20 탆 to 100 탆, more preferably 20 탆 to 80 탆 or 20 탆 to 60 탆. If it is thicker than the above range, the thickness of the pre-stretched film must be very thick, so that the processability of film-forming may not be obtained, and further, it is difficult to make the film thin and light. On the other hand, if it is thinner than the above range, the scattering polarization characteristic may be deteriorated and the light utilization efficiency may be lowered.

2. Manufacturing method of optical film

Hereinafter, a method for producing the optical film of the present invention will be described.

The production method of the optical film of the present invention is characterized in that the first polymer resin having a glass transition temperature of 70 캜 to 100 캜 and forming a continuous phase has a glass transition temperature difference from 0 캜 to 40 캜, Preparing an unoriented film comprising a second polymeric resin forming a discontinuous phase; And stretching the non-stretched film so as to satisfy the following formulas (1) to (2).

(1): 0? | Nx ₁ - nx ₂ | 0.10

(2): 0.15? | Ny ₁ - ny ₂ | ≤ 0.35

In the above formulas (1) to (2), nx ₁ means the refractive index in the polarization transmission axis direction after stretching of the first polymer resin forming the continuous phase, and nx ₂ means the refractive index of the second polymer resin forming the discontinuous phase Ny ₁ means a refractive index in a direction perpendicular to the polarization transmission axis direction of the first polymer resin forming the continuous phase, and ny ₂ means a refractive index in a direction perpendicular to the polarization transmission axis direction, 2 Refractive index in the direction perpendicular to the polarization transmission axis direction after stretching of the polymer resin.

As the method of producing the unstretched film, a film forming method generally used in the related art may be used. For example, the first polymer resin and the second polymer resin may be mixed To prepare a resin composition, and then molding it into a film. More specifically, for example, the resin composition may be prepared by blending the film raw material with an arbitrary suitable mixer such as an omni mixer, and then extruding and kneading the obtained mixture. As the mixer used for the extrusion kneading, , An extruder such as a twin screw extruder, or a pressurized kneader.

As the film forming method, any suitable film forming method such as a solution casting method (solution casting method), a melt extrusion method, a calendering method, a compression molding method and the like can be used. In the case of the present invention, . Examples of the melt extrusion method include a T-die method and an inflation method. In particular, when a film is formed by the T-die method, a T-die is attached to the tip of a known single-screw extruder or a twin-screw extruder And a roll-shaped film can be obtained by winding a film extruded in the form of a film, since the film can be continuously produced, which is advantageous in productivity. On the other hand, the molding temperature is preferably 150 to 350 占 폚, more preferably 200 to 300 占 폚.

Next, when the unstretched film is produced, it satisfies the above-mentioned expressions (1) to (2), and preferably stretches it to satisfy the expressions (3) to (4). At this time, in the case of the present invention, the optical film has a scattering polarization characteristic by stretching, and a polarization transmission axis is formed in a direction perpendicular to the stretching direction.

In this case, the stretching method is not particularly limited. For example, uniaxial stretching can be performed in the longitudinal direction (MD) of the unstretched film, or uniaxial stretching can be performed in the transverse direction (TD) . Also, longitudinal MD shrinkage may be caused by simultaneous biaxial stretching in the transverse direction (TD) of the unstretched film. On the other hand, the transverse (TD) stretching method of the laminate is, for example, a fixed one uniaxial stretching method in which one end is fixed through a tenter, and the longitudinal (MD) stretching Examples of the method include an inter-roll stretching method, a compression stretching method, and a free-end uniaxial stretching method. On the other hand, the stretching treatment may be carried out in multiple stages, or by biaxial stretching, warp stretching, or the like.

On the other hand, in the optical film of the present invention, a transmission axis is formed in a direction perpendicular to the stretching direction. Generally, the polarizer has an absorption axis in the longitudinal direction (MD). In the case where the polarizing film is produced by stretching in the longitudinal direction (MD) It is more advantageous to align the light source with the light source.

The stretching is preferably performed at a temperature of 70 ° C to 110 ° C, and more preferably 70 ° C to 100 ° C or 80 ° C to 100 ° C. If the stretching temperature is higher than the above range, crystallization of the first polymer resin may occur or the orientation may become less so that the refractive index may not rise. If the stretching temperature is lower than the above range, the first polymer resin is not stretched well, May occur and manufacture may not be possible.

In addition, the stretching is preferably performed at a stretching magnification of 5 to 7 times, more preferably at a stretching magnification of 5 to 6 times. If the stretching magnification is higher than the above range, stretching may be difficult. If the stretching temperature is lower than the above range, the difference between nx ₁ and ny ₁ of the first polymer resin may be small and it may be difficult to exhibit the scattering effect.

The stretching is preferably performed so that the thickness of the film before stretching is 50 to 300 占 퐉 and the thickness is 20 占 퐉 to 100 占 퐉 by stretching. The thickness of the film before stretching is 50 占 퐉 to 200 占 퐉, More preferably 20 占 퐉 to 80 占 퐉, more preferably 50 占 퐉 to 150 占 퐉 in thickness before stretching and 20 占 퐉 to 60 占 퐉 in thickness by stretching. If the thickness of the film before stretching is larger than the above range, film forming processability may not be obtained. Further, there is a problem that it is difficult to reduce the thickness and thickness of the thick bar film after stretching. When the thickness of the film before stretching is thinner than the above range, the thickness of the film after stretching is too thin, so that the scattering polarization effect may be deteriorated, and as a result, the light utilization efficiency may deteriorate.

3. Polarizer, display device

The present invention also provides a polarizing plate comprising the optical film. At this time, the structure of the polarizing plate is not particularly limited as long as it includes the optical film of the present invention. For example, the polarizer / the optical film, the protective film / polarizer / the optical film, or the protective film / polarizer / protective film / Optical film or the like.

At this time, the polarizer may be a film made of polyvinyl alcohol (PVA) including a polarizer well-known in the art, for example, iodine or a dichroic dye. The polarizer may be prepared by dyeing a polyvinyl alcohol film with iodine or a dichroic dye, but the production method thereof is not particularly limited.

On the other hand, when the polarizer is a polyvinyl alcohol-based film, the polyvinyl alcohol-based film can be used without any particular limitation as long as it contains a polyvinyl alcohol resin or a derivative thereof. At this time, derivatives of the polyvinyl alcohol resin include, but are not limited to, polyvinyl formal resins and polyvinyl acetal resins. Alternatively, the polyvinyl alcohol-based film may be a commercially available polyvinyl alcohol-based film commonly used in the art for producing polarizers, such as P30, PE30, PE60 manufactured by Kuraray Co., Ltd. or M3000 M6000 manufactured by Nippon Synthetic Chemical Industry Co., .

The protective film is used for supporting and protecting the polarizer. Various protective films of various materials such as a cellulose film, a polyethylene terephthalate (PET) film, a cycloolefin film, An olefin polymer (COP, cycloolefin polymer) film, an acrylic film, and the like can be used without limitation. Of these, it is particularly preferable to use an acrylic film in consideration of optical characteristics, durability, economical efficiency and the like.

On the other hand, the acrylic film usable in the present invention can be obtained by molding a molding material containing a (meth) acrylate resin as a main component by extrusion molding. In this case, the (meth) acrylate-based resin contains a resin containing a (meth) acrylate-based unit as a main component, and includes not only a homopolymer resin composed of a (meth) acrylate- But also a copolymer resin in which other monomer units are copolymerized and a blend resin in which another resin is blended with the above-mentioned (meth) acrylate resin.

On the other hand, the (meth) acrylate-based unit may be, for example, an alkyl (meth) acrylate-based unit. Here, the alkyl (meth) acrylate-based unit means both an alkyl acrylate-based unit and an alkyl methacrylate-based unit, and the alkyl (meth) acrylate-based alkyl group preferably has 1 to 10 carbon atoms , More preferably from 1 to 4 carbon atoms.

Examples of the monomer unit copolymerizable with the (meth) acrylate-based monomer unit include a styrene-based monomer unit, a maleic anhydride-based monomer unit, and a maleimide-based monomer unit. Examples of the styrene-based monomer include, but are not limited to, styrene and? -Methylstyrene. The maleic anhydride monomer includes, but is not limited to, maleic anhydride, cyclohexylmaleic acid Examples of the maleimide-based monomer include, but are not limited to, maleimide, N-methylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide and the like For example. These may be used alone or in combination.

The polarizing plate may include a retardation film for compensating the optical retardation. Here, the retardation film usable in the present invention is not particularly limited, and a retardation film commonly used in the art may be used depending on various liquid crystal modes.

Meanwhile, the optical film according to the present invention can be included in various display devices. For example, the optical film may be applied to various display devices such as a liquid crystal display (LCD) and an organic light emitting diode (OLED).

Hereinafter, the present invention will be described in more detail with reference to specific examples.

Example  One

95 parts by weight of polyethylene terephthalate (TK chemical, TEX-PET) and 5 parts by weight of polystyrene-co-methyl methacrylate (LG Chem, PS-co-PMMA) Followed by melting to produce a raw material pellet. The raw material pellets thus produced were vacuum-dried, melted in an extruder at 250 ° C, passed through a T-die of a manifold type, and passed through a chrome casting roll and a drying roll to obtain a film- To prepare an optical film.

Next, the optical film was uniaxially stretched using a tenter at a stretching magnification of 5 times by a dry stretching method at a temperature of 80 캜. The thickness of the finally obtained optical film after stretching was 50 占 퐉.

Example  2

A resin composition obtained by physically mixing 95 parts by weight of polyethylene terephthalate (TK Chemical, TEX-PET) and 5 parts by weight of polymethyl methacrylate (LG MMA, PMMA) was supplied to an extruder and melted at 250 ° C to form a raw pellet. . The raw material pellets thus produced were vacuum-dried, melted in an extruder at 250 ° C, passed through a T-die of a manifold type, and passed through a chrome casting roll and a drying roll to obtain a film- To prepare an optical film.

Next, the optical film was uniaxially stretched using a tenter at a stretching magnification of 5 times by a dry stretching method at a temperature of 80 캜. The thickness of the finally produced optical film after the stretching was 50 탆.

Comparative Example  One

A resin composition containing 100 parts by weight of polyethylene terephthalate (TK Chemical, TEX-PET) was supplied to an extruder and melted at 250 캜 to prepare a raw material pellet. The raw material pellets thus produced were vacuum-dried, melted in an extruder at 250 ° C, passed through a T-die of a manifold type, and passed through a chrome casting roll and a drying roll to obtain a film- To prepare an optical film.

Comparative Example  2

A resin composition obtained by physically mixing 95 parts by weight of polyethylene naphthalate (Teijin, TEONEX) and 5 parts by weight of polystyrene-co-methyl methacrylate (LG Chem, PS-co-PMMA) was supplied to an extruder and melted at 260 ° C, A pellet was prepared. The obtained raw material pellets were vacuum dried, melted in an extruder at 260 占 폚, passed through a T-die of a manifold type, passed through a chrome casting roll and a drying roll, To prepare an optical film.

Next, the optical film was uniaxially stretched using a tenter at a stretching magnification of 5 times by a dry stretching method at a temperature of 120 캜. The thickness of the finally obtained optical film after stretching was 50 占 퐉.

Comparative Example  3

A resin composition obtained by physically mixing 95 parts by weight of polyethylene naphthalate (Teijin, TEONEX) and 5 parts by weight of polymethyl methacrylate (LG MMA, PMMA) was supplied to an extruder and melted at 260 ° C to prepare a raw material pellet . The obtained raw material pellets were vacuum dried, melted in an extruder at 260 占 폚, passed through a T-die of a manifold type, passed through a chrome casting roll and a drying roll, To prepare an optical film.

Next, the optical film was uniaxially stretched using a tenter at a stretching magnification of 5 times by a dry stretching method at a temperature of 120 캜. The thickness of the finally obtained optical film after stretching was 50 占 퐉.

Comparative Example  4

A resin composition obtained by physically mixing 95 parts by weight of polypropylene (LG Chem, SEETEC) and 5 parts by weight of polymethylmethacrylate (LG Chem, PMMA) was supplied to an extruder and melted at 250 ° C to produce a raw material pellet . The raw material pellets thus produced were vacuum-dried, melted in an extruder at 250 ° C, passed through a T-die of a manifold type, and passed through a chrome casting roll and a drying roll to obtain a film- To prepare an optical film.

Next, the optical film was uniaxially stretched using a tenter at a stretching magnification of 5 times by a dry stretching method at a temperature of 70 캜. The thickness of the finally obtained optical film after stretching was 50 占 퐉.

Comparative Example  5

95 parts by weight of polypropylene (LG Chem, SEETEC) and 5 parts by weight of polystyrene-co-methyl methacrylate (LG Chem, PS-co-PMMA) were physically mixed and fed to an extruder, A pellet was prepared. The obtained raw material pellets were vacuum dried, melted in an extruder at 260 占 폚, passed through a T-die of a manifold type, passed through a chrome casting roll and a drying roll, To prepare an optical film.

Next, the optical film was uniaxially stretched using a tenter at a stretching magnification of 5 times by a dry stretching method at a temperature of 80 캜. The thickness of the finally obtained optical film after stretching was 50 占 퐉.

Experimental Example  1 - Glass transition temperature measurement

Each of the polymer resins used in Examples 1 and 2 and Comparative Examples 1 to 5 was heated to -30 to 200 ° C using a differential scanning calorimeter (DSC Mettler) to measure a glass transition temperature in a second run The results are shown in Table 1 below.

Experimental Example  2 - Measurement of refractive index

In order to measure the refractive indexes of the polymer resins used in Examples 1 and 2 and Comparative Examples 1 to 5, each of these polymer resins was melt-extruded in the same manner as described in Example 1 to prepare a film. The refractive index of the produced film was measured using a prism coupler (SPA) and is shown in Table 1 below.

division Polymer resin Glass transition temperature (캜) nx ny Example 1 First Resin: PET 78 1.54 1.69 Second Resin: PS-co-MMA 108 1.51 1.51 Example 2 First Resin: PET 78 1.54 1.69 Second Resin: PMMA 59 1.48 1.48 Comparative Example 1 First Resin: PET 78 1.58 1.58 Second Resin: - - - - Comparative Example 2 First Resin: PEN 120 1.57 1.88 Second Resin: PS-co-MMA 108 1.51 1.51 Comparative Example 3 First Resin: PEN 120 1.57 1.88 Second Resin: PMMA 59 1.48 1.48 Comparative Example 4 First Resin: PP -10 1.52 1.52 Second Resin: PMMA 59 1.48 1.48 Comparative Example 5 First Resin: PP -10 1.52 1.52 Second Resin: PS-co-MMA 108 1.51 1.51

In Table 1, PET means polyethylene terephthalate, PS-co-MMA means polystyrene-co-methyl methacrylate, PMMA means polymethyl methacrylate, and PEN means polyethylene naphthalate And PP means polypropylene.

As shown in Table 1, in Examples 1 and 2, unlike Comparative Examples 1 to 5, the first resin was a polymer resin having a glass transition temperature of 70 to 100 ° C, and the second resin had a glass transition temperature of Is 40 占 폚 or lower. It is also understood that the refractive indices of the first resin and the second resin satisfy the above-mentioned expressions (1) to (2), and preferably the expressions (3) to (4) are also satisfied.

Experimental Example  3 - Optical properties measurement

The optical films prepared in Examples 1 to 2 and Comparative Examples 1 to 5 were measured for birefringence and polarization degree using a JASCO V-7100 Spectrophotometer, and are shown in Table 2 below.

Experimental Example  4 - Luminance measurement

A polarizing plate was produced by laminating a PVA polarizing element in which iodine was adsorbed and aligned on the optical film prepared in Examples 1 to 2 and Comparative Examples 1 to 5, and the polarizing plate was cut into 3 cm x 3 cm to obtain a backlight unit (BLU) The relative luminance values of the comparative examples of Examples 1 to 3 were measured using a luminance meter BM-7, and the results are shown in Table 2 below.

division Ts (%) PE (%) Brightness improvement (%) Example 1 43.6 90.2 109 Example 2 41.3 75.6 107 Comparative Example 1 90.4 0 100 Comparative Example 2 35.7 52.0 98 Comparative Example 3 30.5 45.0 93 Comparative Example 4 24.3 24.5 91 Comparative Example 5 17.2 19.5 90

As can be seen from the above Table 2, when the optical films of Examples 1 and 2 are used, the brightness of about 7 to 9% can be improved as compared with Comparative Example 1 which is an ordinary optical film.

On the other hand, in the case of Comparative Example 2 in which PEN having a glass transition temperature of 120 캜 was used as the first resin, the difference between the refractive index of the first resin and the refractive index perpendicular thereto and the difference between the refractive index of the first resin and the refractive index of the second resin It is not transmitted, but scattered light is scattered, so that it plays a role of diffusing light, and it can be seen that luminance is rather reduced. The luminance is affected only by the light transmitted straight.

Further, in the case of using PEN having a glass transition temperature of 120 ° C as the first resin, and in Comparative Example 3 using PMMA having a glass transition temperature difference of 61 ° C as the second resin, the draw temperature increased and the birefringence development rate And as a result, the difference in refractive index becomes greater, and the above-described problems are more severely caused.

In the case of Comparative Example 4 using a PP having a glass transition temperature of -10 占 폚 as the first resin, the birefringence of the first resin was insufficient during stretching due to the low glass transition temperature of PP, resulting in no scattering polarization effect .

Further, in the case of Comparative Example 5 in which PP having a glass transition temperature of -10 DEG C was used as the first resin and further PS-co-MMA having a glass transition temperature difference of 118 DEG C as the second resin was used, the birefringence It can be understood that it is not possible to have a scattering polarization effect due to a lowered development rate.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be obvious to those of ordinary skill in the art.

Claims (13)

A first polymer resin having a glass transition temperature of 70 ° C to 100 ° C and forming a continuous phase and a second polymer resin having a glass transition temperature difference of 0 ° C to 40 ° C and forming a discontinuous phase with the first polymer resin ,
An optical film satisfying the following formulas (1) to (2)
Wherein the first polymer resin is a polyethylene terephthalate resin,
Wherein the second polymer resin is an acrylic resin containing a (meth) acrylate-based unit.
(1): 0? | Nx ₁ - nx ₂ | 0.10
(2): 0.15? | Ny ₁ - ny ₂ | ≤ 0.35
In the above formulas (1) to (2), nx ₁ means the refractive index in the polarization transmission axis direction after stretching of the first polymer resin forming the continuous phase, and nx ₂ means the refractive index of the second polymer resin forming the discontinuous phase Ny ₁ means a refractive index in a direction perpendicular to the polarization transmission axis direction of the first polymer resin forming the continuous phase, and ny ₂ means a refractive index in a direction perpendicular to the polarization transmission axis direction, 2 Refractive index in the direction perpendicular to the polarization transmission axis direction after stretching of the polymer resin.
The method according to claim 1,
Wherein the optical film satisfies the following formulas (3) to (4).
(3): 0.15? Ny ₁ - nx ₁ ? 0.30
(4): 0? Nx ₂ - ny ₂ ? 0.10
In the above formulas (3) to (4), nx ₁ means the refractive index in the polarization transmission axis direction after stretching of the first polymer resin forming the continuous phase, and nx ₂ means the refractive index of the second polymer resin forming the discontinuous phase Ny ₁ means a refractive index in a direction perpendicular to the polarization transmission axis direction of the first polymer resin forming the continuous phase, and ny ₂ means a refractive index in a direction perpendicular to the polarization transmission axis direction, 2 Refractive index in the direction perpendicular to the polarization transmission axis direction after stretching of the polymer resin.
The method according to claim 1,
And 1 to 20 parts by weight of the second polymer resin relative to 80 to 99 parts by weight of the first polymer resin.
The method according to claim 1,
Wherein the optical film has a polarization transmission axis formed in a direction perpendicular to the stretching direction.
The method according to claim 1,
Wherein the optical film has a maximum draw ratio of 4.5 times or more and 7 times or less.
The method according to claim 1,
Wherein the optical film has a thickness of 20 to 100 占 퐉.
A polarizing plate comprising the optical film of any one of claims 1 to 6.
A display device comprising the optical film of any one of claims 1 to 6.
A first polymer resin having a glass transition temperature of 70 ° C to 100 ° C and forming a continuous phase and a second polymer resin having a glass transition temperature difference of 0 ° C to 40 ° C and forming a discontinuous phase with the first polymer resin Preparing an unstretched film; And
A process for producing an optical film comprising the step of stretching the non-stretched film so as to satisfy the following formulas (1) to (2)
Wherein the first polymer resin is a polyethylene terephthalate resin,
Wherein the second polymer resin is an acrylic resin containing a (meth) acrylate-based unit.
(1): 0? | Nx ₁ - nx ₂ | 0.10
(2): 0.15? | Ny ₁ - ny ₂ | ≤ 0.35
In the above formulas (1) to (2), nx ₁ means the refractive index in the polarization transmission axis direction after stretching of the first polymer resin forming the continuous phase, and nx ₂ means the refractive index of the second polymer resin forming the discontinuous phase Ny ₁ means a refractive index in a direction perpendicular to the polarization transmission axis direction of the first polymer resin forming the continuous phase, and ny ₂ means a refractive index in a direction perpendicular to the polarization transmission axis direction, 2 Refractive index in the direction perpendicular to the polarization transmission axis direction after stretching of the polymer resin.
10. The method of claim 9,
Wherein the step of preparing the unstretched film comprises blending the first polymer resin and the second polymer resin and then melt-extruding the unstretched film to produce an unstretched film.
10. The method of claim 9,
Wherein the step of stretching the non-stretched film has a thickness of 50 mu m to 300 mu m before stretching and a thickness of 20 mu m to 100 mu m after stretching.
10. The method of claim 9,
And the step of stretching the non-stretched film is a stretching magnification of 5 to 7 times.
10. The method of claim 9,
And the step of stretching the non-stretched film has a stretching temperature of 70 ° C to 110 ° C.