a˜2c are schematic sectional views showing the optical films having conducive and/or low-reflection layer on the back surface of the transparent substrate according to alternative embodiments of the present invention.
a˜3d are schematic sectional views showing the optical films having a second hard coat layer as an anti-Newton Ring layer on the back surface of the transparent substrate according to additional alternative embodiments of the present invention.
a˜4d are schematic sectional views showing the optical films having separate functional layers on the front surface of the first hard coat layer according to additional alternative embodiments of the present invention.
a˜5e are schematic sectional views showing the optical films having a low-reflection layer as the topmost layer according to additional alternative embodiments of the present invention.
The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims.
The present invention provides a multi-function, multi-layer optical film for attaching to the front surface of a display device so as to enhance the physical, mechanical, and optical performance of the display device. The optical film can also be attached to the front surface of the backlight module of the display device. In the following, the former application will be described first. For ease of reference, throughout the specification, the terms “front” and “back” are referred relative to the display device for locations farther away and closer from the light source of the display device, respectively. In the accompanied drawings, the display device is omitted for simplicity and the layers of the optical film from back to front are expressed as stacked rectangular blocks from bottom to top. Additionally, all percentages referred in the following are weight percentages (i.e., wt %).
The first hard coat layer 20 has its back surface interfacing with the front surface of the transparent substrate 10 so as to prevent the transparent substrate 10 from abrasive or scratch damage. The hardness performance is typically over 2 H pencil hardness in accordance with JIS K5400, K5600, or ASTM D3363 standard. The first hard coat layer 20 is formed by wet coating and is made of radiation curable or thermosetting acrylate resin containing at least 0.001˜10% polyoxetane polymers with pendant side chain having 1 to 18, preferably 1 to 4, carbon atoms and at least a fluorocarbon (C—F) bond. UV light curable ionizing radiation curing resin is the most typical resin for this application. The resin also contains 30-60% multi-acrylate monomer and preferably triacrylate monomer, 30-60% urethane acrylate oligomer, and 0.1-5% photo initiator. All the above chemicals are combined to achieve a surface energy (EHCl—F) of 10-50 dyne/cm on the front surface and a refractive index (IHCl) of 1.4˜1.7. The thickness (THCl) of the first hard coat layer 20 is between 0.05˜500 μm (preferably between 0.1˜10 μm) and should satisfy the equation: 0.0005 TSUB≦THCl≦0.1 TSUB.
The polyoxetane polymer has a general formula as follows:
where X and Y represent H, OH, or any hydrocarbon elements, and at least one of the X and Y has (meth)acrylate functionalized group which has one or two or multi-functional (meth)acrylate group. Rf represents a partially fluorinated or perfluorinated group including alkyl, ether bond, ester bond, amide group, or urea group having 1 to 18, preferably 1 to 4, carbon atoms. Also in the formula, n is between 2 to 1000 and 6 to 100 is preferred. Some examples of the polyoxetane polymers represented by the general formula are given below, but it should not be construed that the invention is limited thereto:
According to experiments, the refractive index of the polyoxetane polymer is reversely and linearly related to the amount of fluorine content. As such, the first hard coat layer 20 can be tuned to a desired refractive index by controlling the amount of the polyoxetane polymer. To enhance the hardness of the first hard coat layer 20 against scratch, the resin can further contain 1˜40% nano particles of silicon oxide, or metal oxide such as titanium oxide and alumina oxide, or both. The particle size is preferably between 0.01˜1 μm.
In addition to the foregoing anti-scratch function, the optical film of
One way to ensure the desired anti-glare function of the first hard coat layer 20 is by counting the number of the micro particles within the resin protruding from the front surface in a randomly selected 1-mm2 area (DHCl—F). According to the present inventor, DHCl—F should satisfy the equation: 0.1×HHCl×GHCl≦DHCl—F≦100×HHCl×GHCl, where HHCl is the haze in percentage and GHCl is the gloss at 60° in GU (Gloss Unit) of the front surface of the first hard coat layer 20. Gloss is the ability of a surface to reflect light without scattering, and is measured by directing a constant power light beam at an angle to the test surface and then by monitoring the amount of reflected light. Typically speaking, the higher the gloss at 60° is, the lower the average surface roughness (Ry) is. On the other hand, some surfaces appear to have considerable difference in gloss yet give comparable readings when measured with a glossmeter at one angle. These surfaces can be separated by their respective hazes by measuring at a second angle and comparing the difference of the two readings. ASTM D4039 defines haze as the difference between the gloss at 60° and the gloss at 20°.
Anti-smudge function can also be integrated into the first hard coat layer 20 to help preventing the optical film from exposure to skin oils, cosmetics, stains, inks, adventitious dirt, etc., and to help making the optical film easier to clean. As mentioned earlier, the resin of the first hard coat layer 20 contains at least 0.001˜10% polyoxetane polymers. To integrate the anti-smudge function, the amount of the polyoxetane polymers should be at least 0.1% and at least 0.01˜10% siloxane polymers such as polydimethylsiloxane (PDMS) is added to the resin so as to help leveling the resin during the coating and to reduce the surface energy (EHCl) of the first hard coat layer 20 for at least 5 dyne/cm.
It is well known that an object exposed to UV light (wavelength 280-400 nm) for an extended period of time would become yellowed or deformed or even cracked. To prevent UV deterioration, one of two mechanisms, namely the UV absorption and the UV scattering, is usually adopted. For the optically transparent applications such as the present invention, the UV absorption is more favorable, which transforms the absorbed UV light into heat and dispels the heat through cooling. To integrate the UV absorption function into the optical film, 0.01˜5% organic and/or inorganic UV absorbers can be added to the resin of the first hard coat layer 20. Oxalanilide derivatives, benzotriazole derivatives, benzophenone derivatives, and triazine derivatives are typical examples of organic UV absorbers. On the other hand, metal oxides such as ZnO, TiO2, and Al2O3 are typical inorganic UV absorbers. Metal oxide additives are generally more stable in the long run, but at the cost of inferior optical transparency.
To prevent dust from being attracted to the optical film and thereby affecting the visibility of the display device, the anti-static function can be integrated into the first hard coat layer 20 so as to reduce the surface resistivity to be at least less than 1012 Ω/□ (ohm per square), preferably 1010 Ω/□. Ohm per square is a unit of resistivity for surface films whose thicknesses are considered to be negligible. The resistivity of a very thin conductor is defined to be its resistance (in ohms) multiplied by its width and divided by its length. If the conductor is square in shape, then its length and width are the same and its resistivity is numerically equal to the resistance of the square, which is actually the same no matter what the size of the square is. Therefore the resistivity could be stated in ohms, but it is conventional to state it in “ohms per square.” One can consider the square to have sides equal to one unit, and the size of the unit being immaterial. To realize the anti-static function, 1˜30% of at least one of a conductive polymer and a conductive inorganic element can be added into the resin of the first hard coat layer 20. The conductive polymer can be polyacetylene, polythiophene, polyphenylene, polypyrrole, polyparaphenylene, polyparaphenylene vinylene, pyrolytic polymers, polypolyaniline, etc. Some examples of the inorganic element are indium tin oxide (ITO), indium zinc oxide (IZO), antimony tin oxide (ATO), Al2O3, TiO2, and Fe2O3.
As shown in
b is a schematic sectional view showing the optical film according to a third embodiment. As illustrated, a low-reflection layer 50 (hereinafter, the second low-reflection layer so as to distinguish it from a separate first low-reflection layer described later) is attached to the back surface of the transparent substrate 10. The second low-reflection layer 50 is incorporated to prevent reflection loss due to the light travels from one medium (e.g., the display device) to another (e.g., the transparent substrate 10) with different refractive indices. As such, the refractive index (ILR2) of the second low-reflection layer 50 should satisfy the equation: ILR1≦ISUB-0.05. The second low-reflection layer 50 is made of radiation curable or thermosetting acrylate resin containing at least 0.01˜10% polyoxetane polymers with pendant side chain having 1 to 18 carbon atoms and at least a fluorocarbon (C—F) bond. The resin also contains at least one of 10% of fluoroalkyl acrylate polymer with 20˜60% fluorine, siloxane polymer with 20˜60% silicon, and silica nano particles which can be hollow in structure or surface treated with fluorine or silica/polymer coupling agents, so that the back surface of the second low-reflection layer 50 has a surface energy (ELR2-B) satisfying the equation: ELR2-B≦ESUB-B-5 dyne/cm. The second low-reflection layer 50 is formed by wet coating up to a thickness (TLR2) of 0.01˜1 μm which is a multiple integral of ¼λ of the reflection light and satisfies the equation: 0.001 THCl≦TLR2≦THCl. As such and according to experiment, the anti reflection performance of the present embodiment can reach 0.2% with over 300 nm wavelength coverage.
Newton Ring is an optical phenomenon when two optical devices are close together to produce rainbow like interference fringe pattern. To prevent the Newton Rings from being developed between the multi-layer optical film of the present invention and the display device, another hard coat layer 70 (hereinafter, the second hard coat layer) with anti-Newton Ring function is formed on the back surface of transparent substrate 10, which has random roughness over the back surface of the second hard coat layer 70 to reduce the undesirable interference phenomena. The second hard coat layer 70 is made of radiation curable or thermosetting acrylate resin containing at least 1˜20% micro particles of 0.1˜10 μm in diameter so as to achieve an average surface roughness (RyHC2-B) of 0.1˜5 μm on the back surface. In an alternative embodiment, the radiation curable or thermosetting acrylate resin contains a number of micro particles of 0.1˜10 μm in diameter protruding from the back surface (DHC2-B) in a 1-mm2 area so as to satisfy the equation: 0.1×HHC2×GHC2≦DHC2-B≦100×HHC2×GHC2. The particles are preferred to be transparent polymers or glass-typed particles, such as PS, PMMA, silica, etc. The second hard coat layer 70 is formed by wet coating up to a thickness (THC2) of 0.1˜10 μm satisfying the equation: 0.0005 TSUB≦THC2≦0.1 TSUB. In addition, the second hard coat layer 70 should have a surface energy (EHC2-B) of 20˜50 dyne/cm on the back surface and an appropriate refractive index (IHC2).
b˜3d are additional embodiments of the present invention, which are similar to those shown in
ILR2≦IHC2-0.05,
0.001 THC2≦TLR2≦THC2, and
ELR2-B≦EHC2-B-5 dyne/cm.
a˜4d are schematic sectional views showing the optical films according to additional alternative embodiments of the present invention. The major characteristic of this set of embodiments is that multiple enhancement functions are integrated into separate layers on the front surface of the first hard coat layer 20, instead of directly into the first hard coat layer 20. As illustrated in
The anti-glare layer 40 is made of radiation curable or thermosetting acrylate resin containing at least 1˜40% micro particles of 0.1˜10 μm in diameter so as to achieve an average surface roughness (RyAG-F) of 0.1˜5 μm on the front surface. In an alternative embodiment, the radiation curable or thermosetting acrylate resin contains a number of micro particles of 0.1˜10 μm in diameter protruding from the front surface (DAG-F) in a 1-mm2 area so as to satisfy the equation: 0.1×HAG×GAG≦DAG-F≦100×HAG×GAG, where HAG is the haze in percentage and GAG is the gloss at 60° in GU of the anti-glare layer 40. The anti-glare layer 40 is formed by wet coating up to a thickness (TAG) of 0.05˜10 μm satisfying the equation: 0.05 THCl≦TAG≦5THCl. The anti-glare layer 40 has an appropriate surface energy (EAG-F) on the front surface.
Similar to the integration of multiple enhancement functions into the first hard coat layer 20, the anti-smudge function, the anti-UV, and the anti-static function can be integrated individually or together into the anti-glare layer 40 as well. For example, the resin for the anti-glare layer 40 can further contain at least 0.1˜10% siloxane polymer and polyoxetane polymers so as to reduce the surface energy (EAG-F) of the anti-glare layer 40 for at least 5 dyne/cm for anti-smudge function. Alternatively, the resin for the anti-glare layer 40 can further contain 0.01˜5% of one or more types of UV absorbers such as oxalanilide derivatives, benzotriazole derivatives, benzophenone derivatives, triazine derivatives, TiO2, Al2O3, and ZnO for anti-UV function. Again, for integrating anti-static function, the resin for the anti-glare layer 40 can further contain 1˜30% of at least one of a conductive polymer and a conductive inorganic element.
As illustrated in
a˜5e are schematic sectional views showing the optical films having a low-reflection layer as the topmost layer to enhance the anti-reflection performance of the optical films. As shown in
The embodiments shown in
ELR1-F≦EAG-F-5 dyne/cm,
0.001 THCl≦TLR1≦THCl, and
ILR1≦IAG-0.05.
Following the same principle, as shown in
ELR1≦EAS′-5 dyne/cm,
0.001 THCl≦TLR1≦THCl, and
ILR1≦IHCl-0.05 (for the embodiment of FIG. 5c ) or
ILR1≦IAG-0.05 (for the embodiment of FIG. 5e )
As mentioned earlier in the specification, the optical film of the present invention can also be used in front of the backlight module of a display device to achieve better brightness uniformity. For this application, the first hard coat layer 20 can further contain 1˜40% nano particles of silicon oxide and 1˜70% micro particles of 1˜30 μm in diameter so as to achieve the degree of haze from 1˜99% for integrating the light diffusing function into the first hard coat layer 20. An extension to the foregoing diffusing optical film is shown in
Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.