KR102378972B1 - Retardation film and use of retardation film - Google Patents

Abstract

The present application relates to a retardation film and the use of the retardation film. The present application may provide a retardation film having excellent reverse wavelength dispersion and high retardation expression. The retardation film may be used in a polarizing plate or a display device to improve display quality.

Description

Use of retardation film and retardation film {Retardation film and use of retardation film}

The present application relates to a retardation film and the use of the retardation film.

Based on the recent development of optical technology, plasma display panel (PDP), liquid crystal display (LCD), organic light emitting diodes (OLED), etc. Display devices using the method have been proposed and marketed. Recently, the characteristics required for such display devices are becoming more advanced, and accordingly, the characteristics required for peripheral components such as optical films applied to the display devices are also being advanced. In particular, in recent display devices, as thin film reduction, weight reduction, and screen area enlargement are promoted, wide viewing angle, high contrast, suppression of image tone change according to viewing angle, and uniformity of screen display are particularly important issues.

The retardation film is an optical film used in a display device for the purpose of improving a viewing angle and display quality, and can be divided into those having forward wavelength dispersion, flat wavelength dispersion, and reverse wavelength dispersion according to wavelength dispersion characteristics. The retardation film having constant wavelength dispersion means a retardation film having a characteristic that the retardation value generated as the wavelength of incident light increases, and the retardation film having flat wavelength dispersion has a similar degree regardless of the wavelength of incident light. It refers to a retardation film having a characteristic in which a retardation value occurs, and the retardation film having reverse wavelength dispersion means a retardation film having a characteristic in which a retardation value generated as the wavelength of incident light increases.

Most of the retardation films developed so far have positive wavelength dispersion or flat wavelength dispersion. There is a problem in that it is difficult to obtain a uniform color or visual sensation. In particular, among retardation films used in display devices such as LCD and OLED, an acrylic retardation film having a constant wavelength dispersion has a problem of making the visual sensation of the panel redish. On the other hand, in the case of reverse wavelength dispersion, the larger the optical wavelength, the larger the phase delay value. Therefore, it is attracting attention in that a relatively uniform phase delay can be implemented in a relatively wide optical wavelength band.

In order for the retardation film to exhibit good reverse wavelength dispersion, dispersion values such as R(450)/R(550) and R(650)/R(550) also need to be controlled. For example, in order to exhibit good reverse wavelength dispersion, it is necessary to decrease the R(450)/R(550) value and increase the R(650)/R(550) value. In Patent Document 1, there is a method of improving wavelength dispersion from normal dispersion to reverse dispersion by adding an ultraviolet absorber, but this is effective in lowering the R(450)/R(550) value, but R(650)/R(550) ), there is a limit to increasing the value.

Korean Patent Registration No. 10-1645776

The present application provides a retardation film having excellent reverse wavelength dispersion and high retardation expression and uses of the retardation film.

This application relates to retardation film. In the present specification, the retardation film may refer to an element capable of converting incident polarized light by controlling birefringence as an optically anisotropic layer. In the present specification, while describing the x-axis, y-axis, and z-axis of the retardation film, the x-axis means a direction parallel to the in-plane slow axis of the retardation film, and the y-axis is a direction parallel to the in-plane fast axis of the retardation film, unless otherwise specified. , and the z-axis refers to the thickness direction of the retardation film. The x-axis and the y-axis may be orthogonal to each other in a plane. In the present specification, while describing the optical axis of the retardation film, it means a slow axis unless otherwise specified. Unless otherwise specified, while describing the refractive index of the retardation film in the present specification, it means the refractive index for light having a wavelength of about 550 nm.

When defining an angle in the present specification, when a term such as vertical, horizontal, perpendicular or parallel is used, it means substantially vertical, horizontal, perpendicular or parallel in a range that does not impair the desired effect, for example, , including errors in consideration of manufacturing errors or variations. For example, each of the above cases may include an error within about ±15 degrees, an error within about ±10 degrees, or an error within about ±5 degrees.

The retardation film of the present application may include a resin component including a styrene monomer, a UV absorber, and a near-infrared absorption dye. The present application may provide a retardation film having excellent reverse wavelength dispersion and high retardation expression through a combination of an ultraviolet absorber and a near-infrared absorbing dye.

In the present specification, the ultraviolet absorber may refer to a compound exhibiting maximum absorbance (maximum absorption peak) in the wavelength region of ultraviolet rays, for example, 10 nm to 400 nm, specifically, 200 nm to 400 nm in the absorbance spectrum with respect to wavelength.

In the present specification, the near-infrared absorbing dye may refer to a dye exhibiting the maximum absorbance (maximum absorption peak) in the near-infrared, for example, a wavelength band of 800 nm or more in the absorbance spectrum with respect to wavelength.

The resin component including the styrene monomer, the ultraviolet absorber, and the near-infrared absorbing dye may be included in a single layer. Accordingly, the retardation film of the present application may be distinguished from a structure in which a layer of an ultraviolet absorber and a layer of a near-infrared absorbing dye are formed as separate layers.

In the resin component, the styrenic monomer may function as a retardation control agent. Examples of the styrene-based monomer include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxy styrene, p-phenylstyrene, 2,5-dichlorostyrene, pt-butylstyrene, etc. can be illustrated.

The styrene monomer may be included in an amount of 15 to 30 parts by weight based on 100 parts by weight of the resin component. If the content of the styrene monomer is too low, the phase difference expression becomes small, making it difficult to realize the target phase difference value. The problem of having to add too much absorbent dye may arise.

The styrene monomer may be included in the form of a styrenic copolymer. The styrenic copolymer is styrene-maleic anhydride copolymer (SMA), styrene-acrylonitrile copolymer (SAN), methyl methacrylate-styrene (MS) copolymer, styrene-maleic anhydride-methyl methacrylate copolymer synthesis, and the like. In terms of securing the heat resistance of the retardation film, it may be preferable to use SMA having a high glass transition temperature. However, as will be described later, when an acrylic resin having high heat resistance is used as the acrylic resin included in the resin component, heat resistance of the retardation film can be secured even when SAN is used.

The styrenic copolymer may be included in an amount of 20 to 50 parts by weight based on 100 parts by weight of the resin component. The content may specifically be 15 parts by weight or more or 20 parts by weight or more, and may be 50 parts by weight or less, 45 parts by weight or less, or 40 parts by weight or less. The technical meaning of the content of the styrene copolymer may be similar to the technical meaning of the content of the styrene monomer. That is, when the styrene copolymer is too low, the retardation expression becomes small and it is difficult to express the target retardation value. The problem of having to add an excessive amount of near-infrared absorbing dye may occur.

The resin component may further include an acrylic resin. In the present specification, when the content of the additive is described based on 100 parts by weight of the resin component, it may be based on the resin component in which the acrylic resin and the styrene-based copolymer are combined.

In the present specification, the acrylic resin may refer to a resin containing an acrylic monomer as a main component, for example, more than 50 wt%, more than 70 wt%, or more than 90 wt%. The acrylic monomer may mean acrylic acid, methacrylic acid, and derivatives thereof.

The acrylic resin can be obtained, for example, by polymerizing an acrylic monomer. Examples of the acrylic monomer include methacrylic acid esters such as cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, and methyl methacrylate; methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate, 2-ethyl acrylate Monomers, such as acrylic acid ester, such as hexyl, can be illustrated. The acrylic resin may be a polymer obtained by polymerizing one or more of the above monomers or a copolymer with other monomers. As acrylic resin, polymethyl methacrylate, polybutyl methacrylate, polycyclohexyl methacrylate, etc. can be illustrated, for example.

As the acrylic resin, an acrylic resin having at least one ring structure selected from the group consisting of a structure obtained by copolymerizing an N-substituted maleimide in a molecular chain, a lactone ring structure, and a glutarimide structure may be used.

The acrylic resin may exhibit negative birefringence. In the present specification, "negative birefringence" may refer to a characteristic in which, when the resin is oriented by stretching, the refractive index in the stretching direction is relatively small, and the refractive index in a direction orthogonal to the stretching direction is relatively large. Therefore, in the case of stretching the resin exhibiting negative birefringence, the direction of the slow axis may be indicated in a direction orthogonal to the stretching direction.

The acrylic resin may have high heat resistance. In one example, the glass transition temperature of the acrylic resin may be 120 ℃ or more. Through this, it is possible to provide a retardation film having excellent heat resistance.

The ultraviolet absorber may have a maximum value of 0.01 or more of dichroism expressed by Equation 1 below.

[Formula 1]

dichroism = |α _e - α _o |

In Equation 1, α _e is the extinction coefficient of extraordinary ray, and α _o is the extinction coefficient of ordinary ray.

The extinction coefficient α _e of the extraordinary ray and the extinction coefficient α _o of the ordinary ray may be calculated by measuring the polarization transmittance of the film including the ultraviolet absorber. For example, a polarizing plate is attached to a light source of a transmittance measuring device (eg, U-3310 of Hitachi) to generate polarized light, and then the polarized light is transmitted through a sample film to measure the transmittance To of normal light, In a state in which the sample film is rotated 90°, polarized light is transmitted to measure the transmittance Te of the abnormal light. Then, by substituting the measured normal light transmittance and abnormal light transmittance into the following equations, the extinction coefficients of the normal light and the abnormal light are calculated.

-Log T = αbc

(T: transmittance, α: extinction coefficient, b: sample thickness, c: UV absorber concentration)

The ultraviolet absorber may have a maximum value of dichroism defined by Equation 1 in a wavelength range of 200 nm to 400 nm of 0.01 or more, preferably 0.01 to 0.1, or 0.01 to 0.05.

In the case of stretching a film containing an ultraviolet absorber having a maximum dichroism of 0.01 or more in the 200nm to 400nm wavelength region, that is, in the ultraviolet wavelength band, positive birefringence characteristics are expressed in the visible wavelength region by the ultraviolet absorber after the film is stretched. The retardation is induced, and reverse wavelength dispersion may be expressed while the phase retardation of the UV absorber induced in this way and the phase difference of the resin having negative birefringence are offset. However, this characteristic occurs only when an ultraviolet absorber having a maximum dichroism of 0.01 or more in the ultraviolet wavelength band is used, and reverse wavelength dispersion is not expressed when an ultraviolet absorber with isotropic or a maximum dichroism of less than 0.01 is used. does not

The maximum value of the dichroism defined by Equation 1 in the 200 nm to 400 nm wavelength region of the ultraviolet absorber is 0.01 or more, and the type is not particularly limited, but considering compatibility and thermal stability with the resin component, tria It may be desirable to be an intrinsic ultraviolet absorber. For example, BASF's Tinuvin 460, Tinuvin477, Tinuvin479, Tinuvin1577, and/or ADEKA's LA46, etc. may be mentioned as a triazine-type ultraviolet absorber usable in this invention, but it is not limited to this.

The ultraviolet absorber may include a compound represented by the following formula (1).

[Formula 1]

In Formula 1, R ₁ to R ₆ are each independently a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, a dialkylamino group having 2 to 18 carbon atoms, an alkylcar having 2 to 18 carbon atoms. A bornyloxy group, an aryl group having 6 to 24 carbon atoms, a phenyl group substituted with an alkyl group having 1 to 18 carbon atoms, an arylalkyl group having 7 to 24 carbon atoms, an aryloxy group having 6 to 24 carbon atoms, an arylalkyloxy group having 7 to 24 carbon atoms, It may be an organic group selected from the group consisting of an arylcarbonyloxy group having 7 to 24 carbon atoms and a cycloalkyl group having 3 to 14 carbon atoms, and preferably, at least one of R ₁ to R ₆ is an alkoxy group having 1 to 18 carbon atoms. group, a phenyl group, a phenyloxy group, a benzyl group or a benzyloxy group.

More preferably, the ultraviolet absorber may include a compound represented by the following formula (2).

[Formula 2]

In Formula 2, R ₇ to R ₁₀ may each independently be an alkyl group having 3 to 7 carbon atoms, and R ₇ to R ₁₀ may be the same as or different from each other.

The ultraviolet absorber may be included in an amount of 1 to 10 parts by weight, specifically 3 to 7 parts by weight, based on 100 parts by weight of the resin component. When the content of the ultraviolet absorber satisfies the above range, it may be advantageous in terms of providing a retardation film having excellent reverse wavelength dispersion and optical properties.

The near-infrared absorbing dye may refer to a dye exhibiting maximum absorbance (maximum absorption peak) in a wavelength band of 800 nm or more, 900 nm or more, or 1000 nm or more. The upper limit of the wavelength band showing the maximum absorbance of the near-infrared absorbing dye may be, for example, 1300 nm.

When only the UV absorber is added to the retardation film, the R(450)/R(550) value can be lowered to a certain level or more, but the R(650)/R(550) value cannot be increased by adjusting the content of the resin component and the UV absorber. Although there is a limit or the wavelength dispersion is improved, the retardation expression may be low.

In the present application, not only R(450)/R(550) values but also R(650)/R(550) values, while sufficiently securing phase difference expression by adding a near-infrared absorbing dye having a maximum absorption peak in a region of a longer wavelength than visible light can also be increased. Regarding the reverse dispersion expression due to the near-infrared absorbing dye, when the film is stretched, styrene is a negative retardation material, so it is oriented perpendicular to the stretching direction, but since the near-infrared absorbing dye is a positive retardation material, the orientation occurs in the stretching direction. That is, since styrene and the near-infrared absorbing dye exhibit birefringence in different directions, in this case, wavelength dispersion is expressed as much as the difference in birefringence, thereby enabling expression of reverse wavelength dispersion.

As the near-infrared absorbing dye, if it exhibits a maximum absorption peak in a wavelength band of 800 nm or more, the type is not particularly limited, and, for example, a diimonium-based dye, a phthalocyanine-based dye or a naphthalocyanine-based dye can be used. According to an embodiment of the present application, dimonium-based dyes may be used, and as dimonium-based dyes, for example, commercially available products such as CIR1085, CIR1081, PDC-220C, ADS1065 may be used, but limited thereto it's not going to be

In one example, a compound represented by the following formula (3) may be used as the near-infrared absorbing dye.

[Formula 3]

In Formula 3, R ₁ to R ₈ are each independently a hydrogen atom, an alkyl group having 1 to 16 carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkoxy group having 1 to 16 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, a hydroxyl group , an alkylamino group having 1 to 16 carbon atoms, an arylamino group having 6 to 20 carbon atoms, a trifluoromethyl group, an alkylthio group having 1 to 16 carbon atoms, an arylthio group having 6 to 29 carbon atoms, a nitro group, a cyano group, or a halogen atom; , R ₉ to R ₁₂ are each independently a hydrogen atom, a halogen atom, a cyano group, a nitro group, a carboxyl group, an alkyl group, an alkoxy group, and X is an organic acid monovalent anion, an organic acid divalent anion, or an inorganic acid monovalent anion.

The near-infrared absorbing dye may be included in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the resin component. Specifically, the content of the near-infrared absorbing dye may be 0.5 parts by weight or more, 1.5 parts by weight or more, 2 parts by weight or more, or 2.5 parts by weight or more, and may be 5 parts by weight or less, 4 parts by weight or less, or 3 parts by weight or less. When the content of the near-infrared absorbing dye satisfies the above range, it is possible to provide a retardation film having good reverse wavelength dispersion and high retardation expression.

In one example, when the styrene monomer is included in the form of a styrenic copolymer, the near-infrared absorbing dye may be included in an amount of 1 to 20 parts by weight based on 100 parts by weight of the styrenic copolymer. Specifically, the content of the near-infrared absorbing dye may be 1 part by weight or more, 2 parts by weight or more, or 3 parts by weight or more, and 20 parts by weight or less, 17 parts by weight or less, 15 parts by weight or less, 13 parts by weight or less, or 10 parts by weight or less. may be below. The content of the near-infrared absorbing dye may be specifically 1 part by weight or more or 3 parts by weight or more, and may be 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less. When the content of the near-infrared absorbing dye is too small compared to the styrenic copolymer, R(650)/R(550) may not sufficiently increase, so it may be difficult to sufficiently express reverse dispersibility. On the other hand, when the content of the near-infrared absorbing dye is excessively high compared to the styrenic copolymer, R(650)/R(550) is sufficiently high to sufficiently express reverse dispersibility, but the expression of retardation per unit thickness may be lowered. In this case, since it is necessary to make the thickness of the retardation film very thick in order to obtain a desired retardation value, it becomes brittle, or it is necessary to draw at a very low stretching temperature or very high draw ratio, so heat resistance may deteriorate. .

In one example, the near-infrared absorbing dye may be included in an amount of 20 to 80 parts by weight based on 100 parts by weight of the ultraviolet absorber. Specifically, the content of the near-infrared absorbing dye may be 20 parts by weight or more, 22 parts by weight or more, or 24 parts by weight or more, and may be 80 parts by weight or less, 75 parts by weight or less, 70 parts by weight or less, or 65 parts by weight or less. When a UV absorber and a near-infrared absorbing dye are used in a single layer for reverse dispersion expression, the UV absorber does not invade the visible ray region even if the amount added is increased, but some NIR absorbing dyes partially invade the visible ray region in proportion to the content cases may occur. Therefore, it may be desirable to add less of the near-infrared absorbing dye than the ultraviolet absorber.

The retardation film may have excellent heat resistance. In one example, the retardation film may have a glass transition temperature of 118° C. or higher. The excellent heat resistance of the retardation film can be secured by using a resin component having a high glass transition temperature. As described above, excellent heat resistance of the retardation film can be obtained by using an acrylic resin having a glass transition temperature of 120° C. or higher as an acrylic resin or using an SMA copolymer as a styrenic copolymer.

The retardation film of the present application may exhibit reverse wavelength dispersion. In the present specification, the reverse wavelength dispersion property may refer to a characteristic satisfying the following Equation 2. The reverse wavelength dispersion is a normal wavelength dispersion property that satisfies R (450) / R (550) > R (650) / R (550), R (450) / R (550) = R ( It can be distinguished from a flat wavelength dispersion property that satisfies 650)/R (550).

[Equation 2]

R(450)/R(550) < R(650)/R(550)

In Equation 2, R(λ) is the in-plane retardation of the retardation film with respect to λnm light.

The retardation film may have excellent reverse wavelength dispersion. In one example, the retardation film may satisfy Equation 3 and/or Equation 4 below. As shown in Equations 3 and 4, the retardation film of the present application not only satisfies the reverse wavelength dispersion of Rin (450) / Rin (550) < Rin (650) / Rin (550), Rin (650) The /Rin(550) value may also represent a high value as 1.05 or more. Accordingly, the retardation film of the present application may be applied to a polarizing plate or a display device to realize excellent visibility and color.

[Equation 3]

0.7 ≤ Rin(450)/Rin(550) ≤ 1.0

[Equation 4]

1.05 ≤ Rin(650)/Rin(550) ≤ 1.2

In Equations 3 and 4, Rin(λ) is an in-plane retardation value of the retardation film with respect to a λnm wavelength.

The retardation value of the retardation film may be appropriately adjusted according to the use of the retardation film. In one example, when it is necessary for the retardation film to function as a quarter-wave plate, the Rin value for light of a wavelength of 550 nm of the retardation film may be 130 nm to 200 nm or 130 nm to 180 nm, or 130 nm to 150 nm.

The retardation film may exhibit high retardation expression. In one example, the retardation film may satisfy Equation 5 and/or Equation 6 below. Rin(550)/μm of Equation 5 below may be, for example, 0.1 or more, 0.2 or more, 0.3 or more, or 0.4 or more, and the upper limit is, for example, 10 or less, 8 or less, 6 or less, 4 or less, 2 or less, or 1 may be below. Rth(550)/μm of Equation 6 below may be, for example, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more, and the upper limit is, for example, 10 or less, 8 or less, 6 or less, 4 or less, 2 It may be less than or equal to 1 or less.

[Equation 5]

0 ≤ Rin(550)/μm ≤ 10

[Equation 6]

0.5 ≤ Rth(550)/μm ≤ 10

In Equation 5, Rin(550)/μm means a Rin(550) value (nm) per unit thickness (μm) of the retardation film, and Rin(550) is an in-plane retardation value of the retardation film with respect to a wavelength of 550nm. In Equation 6, Rin(550)/μm means a Rin(550) value (nm) per unit thickness (μm) of the retardation film, and Rth(550) is a thickness direction retardation value of the retardation film for a wavelength of 550nm.

In the present specification, the thickness direction retardation (Rth) value and the in-plane retardation (Rin) value of the retardation film may be defined by the following Equations 7 and 8, respectively.

[Equation 7]

Rth (unit: nm) = {nz-(nx+ny)/2} × d

[Equation 8]

Rin (unit: nm) = (nx - ny) × d

In Equations 7 to 8, d is the thickness (nm) of the retardation film, and nx, ny, and nz are refractive indices in the x-axis, y-axis, and z-axis directions, respectively, as defined above. In the present specification, while describing the in-plane retardation and the thickness direction retardation of the retardation film, it refers to the retardation with respect to light having a wavelength of about 550 nm unless otherwise specified.

The retardation film may have a thickness of 40 μm to 200 μm. When the thickness of the retardation film is too thin, the retardation may not be sufficiently expressed, and when the thickness of the retardation film is too thick, it may be difficult to reduce the thickness of the device.

The retardation film of the present application may be manufactured by a method of film-forming a resin composition and stretching it. Specifically, the retardation film of the present application may be manufactured by melt-extruding a resin composition in which a resin component, an ultraviolet absorber, and a near-infrared absorbing dye are mixed, molded in a film form, and then stretched.

The resin composition may be prepared by, for example, pre-blending the film raw material with any suitable mixer, such as an omni mixer, and then extrusion-kneading the obtained mixture. In this case, the mixer used for extrusion kneading is not specifically limited, For example, arbitrary suitable mixers, such as extruders, such as a single screw extruder and a twin screw extruder, and a pressure kneader, can be used.

As a method of molding the resin composition into a film form, injection molding, sheet molding, blow molding, injection blow molding, inflation molding, extrusion molding, foam molding, cast molding, etc. can be used, and secondary methods such as air pressure molding and vacuum molding can be used. A process molding method can also be used. Among them, extrusion molding and cast molding can be preferably used.

The solvent used for the said solution casting method (solution casting method), For example, aromatic hydrocarbons, such as benzene, toluene, and xylene; aliphatic hydrocarbons such as cyclohexane and decalin; esters such as ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; alcohols such as methanol, ethanol, isopropanol, butanol, isobutanol, methyl cellosolve, ethyl cellosolve, and butyl cellosolve; ethers such as tetrahydrofuran and dioxane; halogenated hydrocarbons such as dichloromethane, chloroform and carbon tetrachloride; dimethylformamide; Dimethyl sulfoxide etc. are mentioned. These solvents may be used independently and may use 2 or more types together.

As an apparatus for implementing the said solution casting method (solution casting method), a drum type casting machine, a band type casting machine, a spin coater etc. are mentioned, for example. On the other hand, examples of the melt extrusion method include a T-die method and an inflation method. The molding temperature may be 150°C to 350°C, or 200°C to 300°C.

When the film is molded by the T-die method, a T-die is attached to the tip of a known single-screw extruder or twin-screw extruder, and the extruded film is wound to obtain a roll-shaped film.

After a film is formed through the process as described above, a resin composition in which a resin component and a near-infrared absorbing dye are mixed is coated, and then the coated film is stretched. In the stretching process, longitudinal (MD) stretching and transverse direction (TD) stretching may be performed, respectively, or both may be performed. In addition, in the case of performing both longitudinal stretching and transverse stretching, stretching in either direction may be performed first and then stretching in the other direction, or stretching in both directions may be performed simultaneously. In addition, the stretching may be performed in one step or may be made over multiple steps. In the case of longitudinal stretching, stretching may be performed by a speed difference between rolls, and in the case of transverse stretching, a tenter may be used. The starting angle of the rail of the tenter is usually within 10 degrees, suppressing the bowing phenomenon occurring during transverse stretching and controlling the angle of the optical axis regularly. Even when transverse stretching is performed in multiple steps, a bowing suppression effect can be obtained.

The stretching temperature is preferably in a range near the glass transition temperature of the resin composition as a raw material for the film, and when the glass transition temperature of the resin composition is Tg, preferably (Tg-30°C) to (Tg+100°C) , more preferably (Tg-20°C) to (Tg+80°C). If the stretching temperature is less than (Tg-30°C), there is a possibility that a sufficient stretching ratio may not be obtained. Conversely, when the stretching temperature exceeds (Tg+100°C), flow (flow) of the resin composition occurs, and there is a fear that stable stretching cannot be performed.

Alternatively, the stretching may be performed in a temperature range of (Tg-20°C) to (Tg+30°C). The temperature range refers to a region from a temperature at which the storage modulus of the resin composition starts to decrease, at which the loss modulus becomes larger than the storage modulus, to a temperature at which the orientation of the polymer chain is relaxed and disappears. Alternatively, the temperature during the stretching process may be the glass transition temperature of the resin composition. The glass transition temperature of the resin composition may be measured by differential scanning calorimetry (DSC).

The draw ratio defined by the area ratio is preferably 1.1 to 25 times, more preferably 1.3 to 10 times. When the draw ratio is less than 1.1 times, there is a fear that the increase in toughness accompanying drawing does not lead to improvement. When a draw ratio exceeds 25 times, there exists a possibility that the effect to the extent of raising a draw ratio may not appear.

In addition, the stretching speed is within the range of 1 m/min to 100 m/min in the case of a universal testing machine (Zwick/Roell Z010), and 0.1 m/min to 2 m/min in the case of the pilot stretching equipment. It is preferable to perform an extending|stretching operation within this range, and it is preferable that a draw ratio is about 5 % - 300%.

The stretching direction, stretching speed, or stretching ratio may be appropriately adjusted according to the desired retardation characteristics, but in consideration of the wavelength dispersion characteristics, retardation value and ease of stretching of the film, preferably, (Tg-20 ℃) to It is preferably carried out at a magnification of 100% to 300% in the MD direction in a temperature range of (Tg+30°C).

In order to stabilize the optical isotropy or mechanical properties of the retardation film, heat treatment (annealing) may be performed after stretching treatment. The heat treatment conditions are not particularly limited and any suitable conditions known to those skilled in the art may be employed.

The present application also relates to the use of the retardation film. The retardation film may be usefully applied to a polarizing plate and/or a display device.

In one example, the present application relates to a polarizing plate including a polarizer and at least one retardation film.

As used herein, the term polarizer refers to a film, sheet, or device having a polarization function. A polarizer is a functional element capable of extracting light vibrating in one direction from incident light vibrating in multiple directions.

The optical axis of the retardation film and the absorption axis of the polarizer may be appropriately designed depending on the application. In the case of implementing a circular polarizing plate with the retardation film, the optical axis of the retardation film and the absorption axis of the polarizer may form an angle within the range of about 30 degrees to 60 degrees. The angle may be, for example, 35 degrees or more or 40 degrees or more, and may also be 55 degrees or less or 50 degrees or less.

The retardation film may be directly attached to one or both surfaces of the polarizer. In addition, it is attached on the protective film of a conventional polarizing plate having a protective film attached to both sides of the polarizer, and can be usefully used as a retardation film.

When the retardation film is directly attached to one or both sides of the polarizer, for example, the structure may be an upper protective film/polarizer/retardation film or retardation film/polarizer/lower protective film. The attachment method is, after coating a primer on the surface of the retardation film or the polarizer using a roll coater, a gravure coater, a bar coater, a knife coater, a capillary coater, or a micro chamber doctor blade coater, etc. , spraying an adhesive in a dropwise manner, heating and laminating a laminate including a retardation film and a polarizer with a laminating roll, laminating by pressing at room temperature, or UV curing.

For example, when the retardation film is directly attached to one or both sides of the polarizer using a water-based adhesive, a polyurethane diamine-based primer is coated on the surface of the retardation film by a bar coater method, and then the retardation film and It may be carried out by a method of spraying an adhesive between the polarizers in a dropwise manner, and heating and laminating the laminate of the retardation film and the polarizer with a lamination roll, or pressing and laminating at room temperature.

In addition, when the retardation film is directly attached to one or both sides of the polarizer using a UV-curable adhesive, the primer is coated on the surface of the retardation film by a microchamber doctor blade coater, and then the adhesive is applied between the retardation film and the polarizer in a drip method. After spraying and laminating, it can be carried out by a UV curing method.

When attaching the retardation film of the present invention on the protective film of the conventional polarizing plate, for example, the structure is upper protective film / polarizer / lower protective film / retardation film or retardation film / upper protective film / polarizer / lower protection It may be a film. In this case, the protective film and the retardation film may be attached through an adhesive layer and/or an adhesive layer. The attachment method is, for example, using a roll coater, a gravure coater, a bar coater, a knife coater, or a capillary coater, etc. to coat the adhesive on the surface of the retardation film or the protective film, and then include the retardation film and the protective film It can be carried out by a method of laminating the laminate by heating with a lamination roll, or by pressing and laminating at room temperature.

As the adhesive, adhesives used in the art, for example, polyvinyl alcohol-based adhesive, polyurethane-based adhesive, acrylic adhesive, and the like may be used without limitation. In addition, the pressure-sensitive adhesive layer is also not limited as long as it is used in the art.

The present application also relates to a display device including the polarizing plate or a display device including at least one retardation film. In this case, the display device may be a liquid crystal display device, a plasma display device, an organic light emitting device, etc., and is particularly suitable for a VA mode liquid crystal display device or an organic light emitting device.

The present application provides a retardation film having excellent reverse wavelength dispersion and high retardation expression and uses of the retardation film. Such retardation film may be used in a polarizing plate or a display device to improve display quality.

Hereinafter, the present application will be specifically described through Examples according to the present application and Comparative Examples not according to the present application, but the scope of the present application is not limited by the Examples presented below.

Example One

60 parts by weight of polymethyl methacrylate resin as an acrylic resin (hereinafter referred to as PMMA, product name: 830HR, manufactured by LGMMA) and a copolymer of styrene and maleic anhydride as a phase difference control agent (hereinafter referred to as SMA, product name: R00, Based on 100 parts by weight of the resin component mixed with 40 parts by weight of Denka (product name: Tinuvin 460, manufactured by BASF), 5 parts by weight of a UV absorber (product name: Tinuvin 460, manufactured by BASF) and 1.2 parts by weight of a near-infrared absorbing dye (product name: CIR1085, manufactured by Japan Carlit) were mixed. A resin composition was prepared. The styrene content in the SMA copolymer is about 65 wt %, and the content of maleic anhydride is about 5 wt %. The maximum value of the dichroism in the 200 nm to 400 nm region of the ultraviolet absorber is 0.03. The maximum absorption peak of the near-infrared absorbing dye appears at 1050 nm to 1150 nm. The glass transition temperature of the resin composition was 121°C.

The resin composition was put in an extruder and melt-extruded to form a film. The film was heated to 131° C. in UTM (Universal Testing Machine Z010, manufactured by Zwick/Roell) and then stretched twice in the MD direction to prepare a retardation film.

Example 2 to 4 and comparative example 1 to 4.

The retardation of Examples 2 to 4 and Comparative Examples 1 to 4 in the same manner as in Example 1, except that the type and content of the acrylic resin and the retardation control agent, and the content of the ultraviolet absorber and the near-infrared absorbing dye were adjusted as shown in Table 1 below. The film was prepared. In Table 2 below, Lactone-MMA is a lactone-methyl methacrylate copolymer (product name: RN240, manufactured by Japan Catalyst Company). SAN is a styrene-acrylonitrile copolymer (product name: 82TR, manufactured by LG Chem). The content ratio of styrene:acrylonitrile in the SAN copolymer is about 8:2.

In Table 1 below, the phr unit of the ultraviolet absorber and the near-infrared absorbing dye is based on 100 parts by weight of the total weight of the acrylic resin and the retardation control agent. In Table 1, Comparative Examples 3 and 4 without a description of the ultraviolet absorber did not use the ultraviolet absorber, and Comparative Examples 1 to 4 without the description of the near-infrared absorbing dye did not use the near-infrared absorbing dye.

Table 2 shows the glass transition temperature and stretching conditions of the resin compositions of Examples 1 to 4 and Comparative Examples 1 to 4. The glass transition temperature of the resin composition is measured by METTLER's DSC (Differential Scanning Calorymeter) equipment. Specifically, 3 mg to 20 mg of the resin composition for which the glass transition temperature is to be measured is placed in an aluminum crucible, and the resin composition is melted at a temperature increase rate of 10° C. per minute from 30° C. to 250° C., cooled to 30° C., and then again cooled to 200° C. per minute The resin composition is melted at a temperature increase rate of 10°C. At this time, through the DSC equipment of METTLER, the middle point of the temperature range at which the specific heat behavior of the resin composition is changed during the second melting process is measured, and this value is measured as the glass transition temperature value.

Acrylic resin phase difference regulator ultraviolet ray
absorbent near infrared
absorbent dye type content type content content content Example 1 PMMA 60wt% SMA 40wt% 5phr 1.2phr Example 2 PMMA 60wt% SMA 40wt% 5phr 1.2phr Example 3 Lactone-MMA 70wt% SAN 30wt% 4phr 1.5phr Example 4 Lactone-MMA 70wt% SAN 30wt% 4phr 2.5phr Comparative Example 1 PMMA 60wt% SMA 40wt% 5phr - Comparative Example 2 Lactone-MMA 70wt% SAN 30wt% 4phr - Comparative Example 3 PMMA 60wt% SMA 40wt% - - Comparative Example 4 Lactone-MMA 70wt% SAN 30wt% - -

resin composition
glass transition temperature Stretch conditions Stretching temperature (℃) draw ratio Example 1 121 131 2.0 Example 2 121 131 2.5 Example 3 122 132 2.5 Example 4 121 131 2.5 Comparative Example 1 122 132 2.5 Comparative Example 2 122 132 2.5 Comparative Example 3 123 133 2.5 Comparative Example 4 122 132 2.5

evaluation example One. phase difference Evaluation of film properties

Rin / μm and Rth / μm values and RD (450) and RD (650) values for the retardation films of Examples and Comparative Examples with respect to the retardation films of Examples and Comparative Examples using Axometrics' Axoscan equipment was measured and the results are shown in Table 3 below. Rin/μm and Rth/μm mean Rin and Rth values (nm) per unit thickness (μm) of the retardation film, respectively. RD(450) denotes a value of Rin(450)/Rin(550), and RD650 denotes a value of Rin(650)/Rin(550).

Thickness (㎛) Phase difference value variance value Rin/㎛ Rth/μm RD(450) RD(650) Example 1 42 0.44 0.53 0.822 1.106 Example 2 41 0.69 0.85 0.853 1.083 Example 3 45 0.53 0.79 0.842 1.092 Example 4 49 0.41 0.64 0.821 1.118 Comparative Example 1 41 0.71 0.93 0.911 1.009 Comparative Example 2 43 0.62 0.89 0.891 1.091 Comparative Example 3 48 0.92 1.31 1.061 0.961 Comparative Example 4 46 0.87 1.19 1.059 0.967

As a result of the evaluation of the physical properties of the retardation film, Comparative Examples 3 and 4 to which the ultraviolet absorber and the near-infrared absorbing dye were not applied had RD(450) and RD(650) more positively dispersed. In Comparative Examples 1 and 2 to which the UV absorber was applied, RD(450) expressed a smaller reverse dispersibility than RD(650), but the increase in RD(650) was not sufficient compared to the decrease in RD(450). On the other hand, in Examples 1 to 4 to which both the ultraviolet absorber and the near-infrared absorbing dye were applied, both the decrease in RD (450) and the increase in RD (650) were improved, thereby exhibiting excellent reverse dispersibility.

Claims (20)

A resin component comprising a styrene monomer, an ultraviolet absorber having a maximum dichroism of 0.01 or more defined by the following formula (1), and a near-infrared absorbing dye having a maximum absorption peak in a wavelength band within the range of 900 nm to 1300 nm, the near-infrared absorbing dye comprising: The retardation film, which is included in a ratio of 20 to 80 parts by weight based on 100 parts by weight of the ultraviolet absorber, and satisfies the following Equation 2:
[Formula 1]
dichroism = |α _e - α _o |
In Equation 1, α _e is the extinction coefficient of extraordinary ray, and α _o is the extinction coefficient of ordinary ray.
[Equation 2]
Rin(450)/Rin(550) < Rin(650)/Rin(550)
In Equation 2, Rin(λ) is the in-plane retardation value of the retardation film with respect to the λnm wavelength. The retardation film according to claim 1, comprising a resin component, an ultraviolet absorber, and a near-infrared absorption dye in a single layer. The retardation film according to claim 1, wherein the styrene monomer is included in an amount of 15 to 30 parts by weight based on 100 parts by weight of the resin component. The retardation film according to claim 1, wherein the styrene monomer is included in the form of a styrenic copolymer. The retardation film according to claim 4, wherein the styrenic copolymer is included in an amount of 20 to 50 parts by weight based on 100 parts by weight of the resin component. The retardation film according to claim 4, wherein the styrenic copolymer comprises a styrene-maleic anhydride copolymer or a styrene-acrylonitrile copolymer. The retardation film according to claim 1, wherein the resin component further comprises an acrylic resin. The retardation film according to claim 7, wherein the glass transition temperature of the acrylic resin is 120°C or higher. The retardation film according to claim 7, wherein the acrylic resin has at least one ring structure selected from the group consisting of a structure obtained by copolymerizing an N-substituted maleimide in a molecular chain, a lactone ring structure, and a glutarimide structure. The retardation film according to claim 1, wherein the ultraviolet absorber is a triazine-based ultraviolet absorber. The retardation film according to claim 1, wherein the ultraviolet absorber is included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the resin component. The retardation film according to claim 1, wherein the near-infrared absorbing dye comprises a dimonium-based dye, a phthalocyanine-based dye, or a naphthalocyanine-based dye. The retardation film according to claim 1, wherein the near-infrared absorbing dye is included in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the resin component. The retardation film according to claim 1, wherein the styrene monomer is included in the form of a styrenic copolymer, and the near-infrared absorbing dye is included in an amount of 1 to 20 parts by weight based on 100 parts by weight of the styrenic copolymer. delete The retardation film according to claim 1, wherein the glass transition temperature is 118°C or higher. The retardation film according to claim 1, wherein the retardation film satisfies the following Equations 3 and 4:
[Equation 3]
0.7 ≤ Rin(450)/Rin(550) ≤ 1.0
[Equation 4]
1.05 ≤ Rin(650)/Rin(550) ≤ 1.2
In Equations 3 and 4, Rin(λ) is an in-plane retardation value of the retardation film with respect to a λnm wavelength. The retardation film according to claim 1, which satisfies the following Equations 5 and 6:
[Equation 5]
0 ≤ Rin(550)/μm ≤ 10
[Equation 6]
0.5 ≤ Rth(550)/μm ≤ 10
In Equation 5, Rin(550)/μm means Rin(550) value (nm) per unit thickness (μm), Rin(550) is the in-plane retardation value of the retardation film for a wavelength of 550nm, Rth( 550)/μm means the Rth (550) value (nm) per unit thickness (μm), Rth (550) is the thickness direction retardation value of the retardation film for a wavelength of 550 nm, and the thickness direction retardation value is the following Equation 7 , and the in-plane retardation value is calculated by Equation 8 below.
[Equation 7]
Rth = {nz-(nx+ny)/2} × d
[Equation 8]
Rin = (nx-ny) × d
In Equations 7 to 8, nx, ny, and nz are refractive indices in the fast axis, slow axis, and thickness directions of the retardation film, respectively, and d is the thickness (nm) of the retardation film. A polarizing plate comprising at least one of a polarizer and the retardation film of claim 1. A display device comprising the polarizing plate of claim 19 .