Patent Application
20080176066
This application claims priorities to Taiwan Patent Application No. 096102110 filed on Jan. 19, 2007 and Taiwan Patent Application No. 096127149 filed on Jul. 25, 2007.
Not applicable.
1. Field of the Invention
The subject invention relates to a wavelength converting structure. More particularly, the invention relates to a structure comprising a wavelength converting coating that can convert ultraviolet rays with a wavelength of no more than 280 nm (i.e. UVC) into a visible light. The coating may be used in conjunction with a UVC light source to convert a UVC wavelength into a visible light wavelength in the presence of air. The steps for manufacturing the wavelength converting structure are simple. Likewise, a flat light source with a large emitting area can be made in simply as well. Additionally, the subject invention further relates to the application of the wavelength converting structure in a light emitting module and a backlight module.
2. Descriptions of the Related Art
The trend for light sources used in displays has become increasingly flat with large emitting areas. The flat light sources with large emitting areas are very important for backlight modules in large-sized flat panel liquid crystal displays. For various conventional light sources, the means currently used to provide visible light through energy/wavelength conversion includes cold cathode fluorescent lamps (CCFL), external electrode fluorescent lamps (EEFL), light emitting diodes (LED), carbon nanotubes (CNT), flat fluorescent lamps (FFL), and organic light emitting displays (OLED).
Among the approaches described above, the CCFL technique involves a phosphor layer coating on the interior wall of the glass tube. A small amount of inert gas and Hg vapor is also encapsulated into the fluorescent tube. Then, during the electrode discharge process, the Hg vapor emits ultraviolet rays due to the electron impact. The ultraviolet rays are then converted by the phosphor layer on the tube wall into visible light, thus providing a visible light wavelength. The CCFL technique offers many advantages, such as improved production technology, relatively lower costs, etc. However, the phosphor coating and the light emitting source have to be disposed in the same vacuum lamp tube, and thus, it is difficult to produce large-sized lamps and allow for wavelength conversions in large areas. Moreover, if a larger light emitting area is obtained by lengthening the lamp tube, there are some disadvantages such as low production yields and a substantial increase in costs.
The EEFL differs from the CCFL mainly in that the electrodes are disposed outside the lamp tube, so that multiple fluorescent lamp tubes may be driven by the same converter, resulting in decreased costs and a higher power efficiency. However; the limitations in application still exist with the EEFLs. For example, if the EEFL lamp gives out inadequate brightness and the current is increased under an increased lamp tube voltage to improve the output brightness, the size of the converter will be increased dramatically. As a result, there will be poor heat dissipation. Moreover, just like the CCFL, the EEFL also cannot provide a larger light emitting area.
The LED is a light emitting device made of a semiconductor material. The III-V group compound (e.g. GaP, GaAs and etc.) is used as the material. Through the application of a current into the semiconductor compound, the LED may emit light as a result of the combination of electrons and holes. The LED features a small volume, a prolonged service life, a low driving voltage, and a fast response speed. Unfortunately, the LED still has some shortcomings, such as color mixing inaccuracies, high manufacturing costs, inferior uniformity, poor heat dissipation, and low power efficiency.
In the CNT, the electrons are released from the tip using an intense electric field, and accelerated with a high voltage to impact a fluorescent plate, thus, generating a light wavelength energy. Although the CNT has advantages, such as low power consumption, low temperature operation, and lack of Hg, the CNT still presents some problems due to its complicated manufacturing process, high cost, poor brightness stability, and inferior uniformity. Furthermore, the manufacturing technology for the large-sized CNT is still under development.
The FFL uses the ultraviolet rays generated from the discharge of an inert gas to excite colored phosphor powders, and then a light wavelength visible to human eyes is generated. Similarly, although the FFL has advantages, such as a lack of Hg, prolonged service life and simplified optical design, the FFL still presents some problems due to their complicated manufacturing process, high manufacturing costs, low efficiency, and poor heat dissipation.
In the OLED, a biasing voltage is applied externally to drive the injection of the electrons/holes from the positive/negative electrodes, respectively, so that under the presence of an electric field, the holes and electrons will move towards each other for recombination. As a result, the energy of the light wavelength will be released. Although the OLED features a thinner structure, greater brightness, wider operational temperature range, lower power consumption and lower driving voltage, the OLED currently available still has problems due to difficulties with the production of large-sized models, high manufacturing costs, low efficiency and a short service life.
It can be seen from the above description that the existing sources of visible light either lack the maturity in terms of their production technology (e.g., LED, CNT, OLED and FFL), or are prevented from being produced at large-sizes due to their innate limitations in production, both failing to convert light in a large area using simple and inexpensive means.
In view of the above, the subject invention provides a method for wavelength conversion in a large area using a simple process in combination with the existing technology.
In this disclosure, the term “UVC” refers to the ultraviolet rays with a wavelength of no more than 280 nm. It is preferred for the wavelength to fall between 200 nm to 280 nm, and particularly from 250 nm to 260 nm. It is best to have a wavelength of 253.7 nm. The term “UVB” refers to the light rays with a wavelength ranging from 280 nm to 320 nm, while the term “UVA” refers to the light rays with a wavelength ranging from 320 nm to 400 nm. The phrase “macromolecular adhesive” refers to the molecule with a molecular weight greater than 1,000, including an oligomer and polymer. The phrase “phosphor that can be excited by ultraviolet ray (or by UVC, UVA or UVB)” refers to a material that can absorb ultraviolet rays (or UVC, UVA or UVB) and emit visible light when irradiated by ultraviolet rays (or by UVC, UVA or UVB).
One objective of the subject invention is to provide a wavelength converting structure, comprising:
a substrate; and
a wavelength converting coating which is disposed on the substrate and comprises:
(a) a phosphor powder which can be excited by UVC; and
(b) an anti-UVC adhesive,
wherein the thickness of the wavelength converting coating is about 2 to about 10 times the average particle size of the phosphor powder, and the amount of the phosphor powder in the wavelength converting coating conforms to at least one of the following requirements:
(i) the phosphor powder is about 30% to about 85% by volume of the wavelength converting coating based on the total volume of the phosphor powder and the adhesive; and
(ii) the weight ratio of the phosphor powder to the adhesive ranges from about 1:1 to about 20:1.
In combination with a UVC light source, the wavelength converting structure of the subject invention can provide a flat source of visible light with a large area. The visible light source can further be used in a backlight module to provide a display panel with a large area by simple means.
Another objective of the subject invention is to provide a method for producing a wavelength converting structure, comprising the following steps:
providing a substrate;
coating a slurry on a surface of the substrate, wherein said slurry is placed in a storage vessel and comprises:
(a) a phosphor powder which can be excited by UVC;
(b) an anti-UVC adhesive; and
(c) an organic solvent,
wherein the weight ratio of the phosphor powder to the adhesive ranges from about 1:1 to about 20:1, and
drying the coated substrate.
After reviewing the embodiments described below, persons having ordinary skill in the art can easily appreciate the basic spirit and other inventive objective of the subject invention and the technical means and preferred embodiments implemented for the subject invention.
To provide a flat light source with a large area, phosphor is used to convert the ultraviolet rays into a visible light. Particularly, a slurry containing phosphor powder is applied directly over a flat substrate to form the wavelength structure. As a result, the ultraviolet rays, particularly those with the UVC spectrum band, are converted into a visible light through the wavelength converting structure. That is, the phosphor powder is excited by the ultraviolet rays to generate visible light. Such a wavelength converting structure can enhance the uniformity of the light emission and optionally provide the desired light emitting area.
As described above, although the CCFL has advantages such as improved production technology and lower costs, it is difficult to produce a large-sized lamp tube and achieve the wavelength conversion in a large area since the phosphor coating and the light emitting source have to be disposed in the same vacuum lamp tube. In more detail, in the CCFL, a phosphor slurry solution (a composition composed of a phosphor powder, an organic component, an inorganic component, and a solvent) is coated on the interior wall of a glass tube, after which the organic component contained in the composition is removed by sintering to form a phosphor layer on the interior wail of the glass tube. Subsequently, the Hg vapor is injected into the glass tube and encapsulated therein. The Hg vapor is excited using electrodes to emit an UVC light, and then, the UVC is converted into a visible light through the phosphor layer on the glass tube.
In the above conventional CCFL manufacturing process, the coating of the phosphor layer is carried out vertically. For example, the phosphor slurry is first siphoned to the top of the standing lamp tube, and then is allowed to coat the interior wall thereof from the top to the bottom by gravity. Subsequently, the organic component in the coating is removed by sintering to eventually form the desired phosphor layer. However; such a coating approach will result in a non-uniform thickness between the top and the bottom, which is especially the case when the lamp tube has a large size requirement (i.e., a long lamp tube is required).
Furthermore, in the current CCFL structure, the phosphor layer is sintered onto the interior wall of the glass tube. It is also difficult to prevent the leakage of the ultraviolet rays through the interstice of the phosphor layer. For example, in current LCD technology, the leakage of ultraviolet rays may detrimentally affect the properties of the optical materials such as the diffusion plate and brightness enhancement film, causing the degradation of such optical materials. For this reason, most of the materials need to be treated with an anti-ultraviolet coating to prolong its service life.
In view of the above, the inventors have attempted to separate the lamp tube from the phosphor layer by coating the phosphor slurry directly onto the individual substrates rather than the interior wall of the glass tube. As a result, the non-uniformity of the CCFL phosphor layer will be eliminated, enhancing the light emission uniformity, and also providing a large light emitting area as desired. It has been found through research that, by use of a specific solvent and a specific adhesive and by controlling the amounts of the adhesive and the phosphor powder; the resulting slurry composition may form a wavelength converting coating on the substrate; said coating can effectively convert the ultraviolet rays into visible light, without using a sintering process. The slurry can be coated on the substrates in a relatively simple coating approach (e.g., a roll-to-roll coating approach) such that mass productivity would not be a problem. Alternatively, other coating approaches may be employed, for example (but not limited to) dip coating, comma coating, spraying coating, spin coating, slot coating, curtain coating, gravure coating, or meyer rod coating. The coating can be optionally dried in any appropriate manner, for example (but not limited to), through natural volatilization, or through forced volatilization such as under ventilation and/or heating (for example, through the injection of hot air). The processed coating in combination with the substrate can become a simple wavelength converting coating structure, which may be used in combination with existing backlight sources, lamps, or solid state lighting (e.g., LED and OLED) without modifying the preexisting structure design. As a result, the coating is highly applicable.
Additionally, the wavelength converting coating structure can effectively prevent the degradation of the phosphor powder as was present in the conventional CCFL. For the conventional CCFL, light with a wavelength of 185 nm generated during the discharge will cause the phosphor powder to generate a color center, resulting in a new absorptive spectrum band and degrading the brightness of the phosphor powder (see the description in U.S. Pat. No. 6,402,997, the disclosure of which is incorporated herein by reference). Secondly, the recombination of the Hg+ ions and the electrons at the tube wall will release an energy of 10.42 eV, which may disrupt the lattice structure of the phosphor powder, leading to a further degradation of the brightness. Moreover, Na+ ions normally exist normally inside the CCFL tube and tend to recombine with electrons generated during the discharge process to form Na atoms. These Na atoms may diffuse into the crystal grains of the phosphor powder to cause the performance degradation of the phosphor powder. Therefore, since the wavelength converting coating is separate from the UVC light source (i.e., the phosphor powder is separate from the UVC light source) in the wavelength converting structure of the subject invention, the above problems due to the collocation of the phosphor power and the UVC light source in the same lamp tube of the conventional CCFL can be effectively eliminated when the wavelength converting structure is applied in a backlight module.
Specifically, the subject invention provides a wavelength converting structure, an embodiment of which is illustrated in respectively denote the phosphor powders of different colors. The wavelength converting structure 102 comprises a substrate 1021 and a wavelength converting coating 1023. The coating 1023 is disposed on the substrate 1021, and comprises a phosphor powder excitable by UVC and an anti-UVC adhesive. The thickness of the wavelength converting coating 1023 is 2 to 10 times the average particle size of the phosphor powder, and the amount of the phosphor powder in the wavelength converting coating 1023 conforms to at least one of the following requirements:
(i) the phosphor powder is 30% to 85% by volume of the wavelength converting coating based on the total volume of the phosphor powder and the adhesive; and
(ii) the weight ratio of the phosphor powder to the adhesive ranges from 1:1 to 20:1.
Any appropriate phosphor powder excitable by UVC may be adopted in the wavelength converting coating. For example (but not limited thereto), the phosphor powder may be selected from a group consisting of europium doped yttrium oxide, terbium doped cerium lanthanum phosphate, europium doped barium magnesium aluminum oxide, and combinations thereof. Appropriate products available directly in the market can also be used as the phosphor powder of the wavelength converting coating.
In the wavelength converting coating, the adhesive used can bond the phosphor powder to form a wavelength converting layer; and is usually selected from macromolecular adhesives. However, when used in combination with UVC, anti-UVC adhesives are preferred in the wavelength converting coating to prevent the degradation of the adhesive itself caused by the exciting process.
A detailed description is provided using a 253.7 nm UVC as an example. Because the light energy of such UVC is about 113 kcal/mol, it is believed without the limitation by theory that a macromolecular adhesive with at least one chemical bond with a molecular bond energy of higher than 113 kcal/mol will be sufficient to resist the energy of the UVC spectrum band. As a result, the degradation of the adhesive itself is prevented due to the excitation. Since the carbon-fluorine bond has a molecular bond energy of 132 kcal/mol, if a 253.7 nm UVC is used, the following fluorine-containing polymeric adhesive will be appropriate: polytetrafluoroethylene (PTFE), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), ethylene-tetrafluoroethylene copolymer (ETFE), fluorinated ethylene propylene copolymer (FEP), perfluoroalkoxy (PFA), fluoro-rubber; fluoro-elastomer, amorphous fluoropolymers, and combinations thereof Alternatively, the following silicon-containing polymers may also be employed: silicon rubber, polysiloxane, and combinations thereof. Also, other high-efficiency polymers such as polyimide (PI) and polyethersulfone (PES) may be employed as an adhesive in the wavelength converting coating when the ultraviolet rays of 253.7 nm UVC is used. Preferably, the macromolecules containing a carbon-fluorine bond are employed as the adhesive. Alternatively, other inorganic or organic-inorganic compounds that have a bonding capability or can serve as a phosphor matrix, e.g., inorganic materials such as silicon dioxide, titanium dioxide and zirconium dioxide or sol-gel materials, can be used in the wavelength converting coating in combination with the 253.7 nm UVC wavelength.
As described above, the amount of the phosphor powder in the wavelength converting coating shall conform to the following requirements: (1) the phosphor powder should be about 30% to about 85% by volume based on the total volume of the phosphor powder and the adhesive; and/or (2) the weight ratio of the phosphor powder to the adhesive ranges firom about 1:1 to about 20:1. Obviously, the lower the amount of the adhesive, the weaker the adhesion between the individual phosphors in the resulting phosphor layer and also between the phosphors and the substrate will be. Conversely, the higher the amount of the adhesive, the better the adhesion effect will be. However, the chance for the adhesive to be exposed to the UVC is enhanced, which will not only cause performance degradation of the adhesive, but also reduce the light emitting efficiency of the resulting wavelength converting structure over a long period of time. Therefore, to obtain an appropriate wavelength converting coating, it is preferred for the wavelength converting coating to contain an amount of the phosphor powder conforming to the following requirements to form a sachima-like structure (i.e., the adhesive in the coating is coated in a film form on the phosphor powder rather than in a continuous phase): (1) the phosphor powder should be about 50% to about 70% by volume; and/or (2) the weight ratio of the phosphor powder to the adhesive ranges from about 2.5:1 to about 10:1. More preferably, the weight ratio of the phosphor powder to the adhesive ranges from about 3:1 to about 6:1.
In consideration of the light emitting efficiency, the particle size distribution of the phosphor powder preferably ranges from 1 μm to 30 μm, and more preferably from 1 μm to 10 μm. Alternatively, two or more particle size distributions may be used in combination to improve the stacking efficiency and enhance the ultraviolet absorption efficiency and visible light emitting efficiency of the resulting wavelength converting coating. In this case, there may be only one of them falling within the aforesaid range. For example, the first particle size distribution may range from 1 μm to 10 μm, while the second particle size distribution may range from 1 nm to 1000 nm.
In the wavelength converting structure, if the converting coating is excessively thick, the converted visible light may be blocked thereby. If the converting coating is excessively thin, UVC leakage may occur due to insufficient UVC absorption, resulting in the yellowing of the substrate of the wavelength converting structure or the polymeric materials such as the adhesive. Hence, to provide an adequate UVC converting efficiency and avoid yellowing, it is desirable to control the thickness of the wavelength converting coating. It has been found that, if the thickness of the converting coating is about 2 to about 10 times the average particle size of the phosphor powder, the coating can consist of a stack of multiple phosphor powder layers, so that multiple times of UVC reflection and/or refraction may occur in the coating to improve both the light emitting efficiency and the blockage of UVC. The thickness of the converting coating should be about 3 to about 5 times the average particle size of the phosphor powder. For example, if the average particle size of the phosphor powder ranges from about 3 μm to about 4 μm, the thickness of the converting coating preferably ranges from about 6 μm to about 40 μm, and more preferably from about 10 μm to about 20 μm.
The substrate of the wavelength converting structure can be a flexible film, especially a flexible film made of a polymer to facilitate the conventional roll-to-roll coating approach for mass production. The flexible film is preferably transparent, if not, highly transparent. For example (but not limited thereto), the substrate can be a film made of a material selected from a group consisting of polyethylene terephthalate (PET), triacetyl-cellulose (TAC), poly(ethylene-2,6-naphthalate) (PEN), polyether sulfone (PES), poly(vinylidene fluoride) (PVDF), poly(ethylene-co-octene) (PE-PO), poly(propylene-co-ethylene) (PP-PB), atactic polypropylene (aPP), isotactic polypropylene (iPP), functionalized polyolefin, and linear low density polyethylene-g-maleic anhydride (LLDPE-g-MA). The optical level PET and TAC are more preferred.
A transparent thin sheet may also be used as the substrate of the wavelength converting structure. For example (but not limited thereto), the substrate can be a thin sheet made of glass, quartz, poly(methyl methacrylate) (PMMA), polystyrene (PS), methyl methacrylate-co-styrene (MS), or polycarbonate (PC). Alternatively, a light transmissive fiber fabric (typically made of glass) may be used as the substrate. Still alternatively, a composite layer composed of two or more aforesaid films and/or thin sheets may be adopted as the substrate, in which case a pressure sensitive polymer adhesive may be utilized to bond the individual layers.
The wavelength converting structure may be produced by a method comprising the following steps:
providing a substrate;
coating a slurry on a surface of the substrate, wherein said slurry is placed in a storage vessel and comprises:
drying the coated substrate.
Any appropriate organic solvent may be used as a carrier for the phosphor powder and the adhesive. Generally, in consideration of the simplicity of a continuous coating process, the viscosity of the slurry is typically controlled within a range from 10 cps to 10000 cps. In this case, an organic solvent with a low boiling point is preferred to prevent phosphor sedimentation and color deviation during the drying process due to the low volatility of the solvent Suitable solvents with a low boiling point include (but is not limited to) those selected from a group consisting of C3-C4 ketones, C1-C4 linear alkanes substituted with one or more halo groups, C5-C7 linear alkanes, C5-C6 cycloalkanes, C1-C4 linear alkanols, C2-C4 ethers, ethyl acetate, benzene, toluene, acetonitrile, tetrahydrofuran, petroleum ether, a fluoro-solvent, and combinations thereof More preferably, the organic solvent is selected from a group consisting of C3-C4 ketones, C1-C4 linear alkanes substituted with one or more halo groups, C5-C7 linear alkanes, C5-C6 cycloalkanes, acetonitrile, and combinations thereof.
Specific examples of suitable organic solvents with a low boiling point include (but is not limited to): acetone, methyl ethyl ketone, 1,2-dichlorethane, dichloromethane, chloroform, pentane, n-hexane, heptane, cyclopentane, cyclohexane, methanol, ethanol, propanol, isopropanol, tertiary-butanol, ethyl ether, ethyl acetate, benzene, toluene, acetonitrile, tetrahydrofuran, petroleum ether, and combinations thereof. Preferred specific examples are toluene, methyl ethyl ketone, ethyl acetate, 1,2-dichlorethane, or combinations thereof.
The content of the organic solvent in the slurry is not critical to the subject invention, and may be adjusted depending on the desired viscosity of the slurry. Generally, the content of the organic solvent based on the total weight of the slurry ranges from about 20 wt % to about 80 wt %, and preferably ranges from about 35 wt % to about 55 wt %.
Optionally, other components can be added to the slurry to prolong the service life of the wavelength converting structure. The other component added optionally includes (but is not limited to) a stabilizer, an absorbent, a blocker, and combinations thereof. In respect of this, the metal oxides (preferably those with nanometer size) such as alumina zinc oxide, and titanium dioxide may provide a blockage effect. Organic compounds such as benzophenone and benzothiazole are typical absorbents that can absorb the ultraviolet rays to release heat. Photo stabilizers such as a hindered amine can absorb the excited groups to prevent them from any chemical reaction. Generally, to avoid any adverse effect on the performance of the wavelength converting structure, these components are typically added in a total amount of no more than 10 wt % based on the total weight of the slurry.
In the aforesaid method, the phosphor powder and the adhesive can be blended into the solvent prior to or during the coating process to form a desired slurry, which is then coated onto the surface of the substrate. Subsequently, the solvent is removed through a drying process to eventually form the desired wavelength converting coating. The slurry in the storage vessel should be properly stirred during the coating process to avoid solid sedimentation and phase separation due to the density difference therebetween. The stirring may be achieved via various suitable means. For example (but not limited thereto), the stirring action can be achieved by mechanically stirring, homomixing, blending, ultrasonic-mixing, three-roll-mills, ball-mills, planet mixing, or pulse pressurizing the slurry to form a turbulence in the vessel.
The coating process may be accomplished in any appropriate approach, for example (but not limited to), dip coating, comma coating, spraying coating, spin coating, slot coating, curtain coating, gravure coating, or roll-to-roll coating. Optionally, the coating may be applied to achieve a desired thickness through one or more coating operations. Additionally, the coating may be dried in any appropriate manner, for example (but not limited to), through natural volatilization, or through forced volatilization under such as ventilation and/or heating (for example, through the injection of hot air).
The wavelength converting structure may be applied in a light-emitting module. In this case, an optical enhancement structure such as a prismatic or a particulate structure can be formed on one side of the substrate opposite to the wavelength converting layer to further enhance the optical effect. Optionally, to enhance the brightness or the polarizing effect, the wavelength converting structure may further comprise any appropriate optical elements, for example, an optical film or sheet such as a diffusion plate, a diffusion film, a brightness enhancement film (BEF), a dual brightness enhancement film (DBEF), a prism plate, a lenticular film, a polarizer, and combinations thereof. Another embodiment of the wavelength converting structure is illustrated in respectively denote the phosphor powders of different colors. In
The light-emitting modules (including backlight modules) to be described hereinafter can all be optionally provided with light source holders. However, for purpose of simplicity, these modules will be described in a context without such light source holders unless otherwise stated.
In reference to
The desired color of the visible light can be obtained by the color mixing principle. For example, a substantially white visible light is obtained by mixing red, green and blue visible light.
In the light-emitting module 30 of
In addition to direct coating on the interior wall of the frame 301 (as shown in
As is well known, in addition to ultraviolet rays of the UVC spectrum band, light emitted from a typical UVC light source also comprises a small amount of light in the UVA spectrum band and/or the UVB spectrum band. To effectively utilize the UVC light, a UVC light absorptive phosphor powder, or a combination of phosphor powders absorbing other ultraviolet wavelengths can be selected for use as the phosphor powder in this invention. For example, a phosphor powder that may substantially absorb 365 nm UVB light or 400 nm UVA light may be used so that the ultraviolet rays are converted sufficiently.
To eliminate the adverse influence of the small amount of UVA light and/or UVB light, a UV-blocking coating may be further included in the wavelength converting structure of the light-emitting module of the light-emitting module, in addition to the phosphor powders that can absorb UVC, UVA and UVB, to mitigate any possible UV leakage. An illustration of the embodiment of a light-emitting module with such a UV-blocking coating is depicted in FIGS. 4A to 4C, wherein
As shown in
The UV-blocking coating 4055 can be made of any material that can block UV light, for example, a UV-blocking material, a UV-stabilizing material, a UV absorptive material, a UV reflective material, or combinations thereof The common UV-blocking material comprises metal oxides, the specific examples of which are alumina, titanium dioxide, zinc oxide, and combinations thereof. Preferably, a metal oxide with a particle size substantially smaller than 1 μm is used. A suitable UV-stabilizing material is hindered amine, while suitable examples of the UV absorptive material comprise benzophenone, benzotriazole, or a combination thereof.
To further block leakage of UV light, a protection layer may be further disposed on the interior wall of the frame in the light-emitting module. In reference to
These light-emitting modules described above can also be applied in various backlight modules of liquid crystal devices (LCDs), such as in the side-emission type backlight module or direct-emission type backlight module.
As described above in
However, it has been found that when the conventional mean of supporting the optical film 707 with a supporting post is employed in the direct-emission type backlight module 70 shown in
To avoid both the curvature due to the damage by the supporting post in the wavelength converting structure or the insufficient stiffness of the wavelength converting structure, a fixing device that can impart a tension to the wavelength converting structure is further provided in the backlight module to keep the surface of the wavelength converting structure flat without supporting posts. In particular, prior to the disposition of a wavelength converting structure on the backlight module, a tension is pre-applied to the wavelength converting structure to make the surface substantially flat. Subsequently, with the surface of the wavelength converting structure kept substantially flat, a fixing device is used to fix its shape in that state.
A variety of appropriate fixing devices may be used. For example, the fixing device comprises a first element and a second element corresponding to each other, which, when joined together, may keep the shape of the wavelength converting structure fixed. Alternatively, the fixing device comprises an element with a profile matching the frame, so that it can cooperate with the frame to keep the shape of the wavelength converting structure fixed.
For example, in reference to
As shown in
The two frames included in the fixing device do not necessarily have to be the same size, but rather may be of different sizes, as shown in
Alternatively, as shown in
The frames described in the above embodiments can be formed integrally or be assembled by a plurality of strip-like elements. Additionally, the frames are not limited to a rectangular shape, but rather can be formed into other shapes (e.g., an ellipsoid shape) as desired in specific application.
Alternatively, special features may be designed in the fixing device to fix the wavelength converting structure through the interaction of such features. In reference to
Of course, as shown in
The wavelength converting structure may also be fixed by the frame body and the fixing device in combination.
In the above embodiments, the first elements 1071, 1075, 1079, 1081 and the second elements 1073, 1077 are arranged along the sides of the wavelength converting structure 103. However; they are not just limited thereto, but can also be arranged along the entire sides or at other appropriate locations in the wavelength converting structure 103. Similarly, the concave structures and the convex structures are not just limited to the specific shapes illustrated therein. In addition, the fixing device can optionally comprise two or more first or second elements.
For example, for a frame body with a rectangular opening, the first element and the second element are strip-like elements encircled into a rectangular, or are rectangular elements assembled by L-shaped or I-shaped strip elements nested into each other. In this case, when the concave/convex portions respectively on the frame body and the fixing device are used in a nested engagement manner to fix the wavelength converting structure, two I-shaped strip-like elements with concave/convex portions corresponding to those of the frame body can be included in the fixing device. The opposite sides of the wavelength converting structure can then be fixed by nesting these 1-shaped strip-like elements into the top surface sides of the frame body to maintain a substantially flat surface of the wavelength converting structure. Alternatively, two L-shaped strip-like elements with concave/convex portions corresponding to those of the frame body can be included in the fixing device to fix the opposite corners of the wavelength converting structure by a nested engagement between these strip-like elements and the top surface corners of the frame body. As a result, substantially flat surface of the wavelength converting structure is maintained.
The fixing device may also exist in other forms, as shown in
Another embodiment of the backlight module is illustrated in
Yet another embodiment of the backlight module is shown in
The wavelength converting structure disclosed herein and its applications will now be further exemplified in specific embodiments.
The components, materials and instruments employed in the following examples are as follows:
(1) Components of the adhesive:
Adhesive solution A: Chipaste from CANDLE LABORATORY CO., Ltd, which was a solution containing 20 wt % of fluoric macromolecules. A wet film with a thickness of about 100 μm resulted from the adhesive solution A was dried completely within 30 sec under 50° C.
Adhesive solution B: Polyvinylidene difluoride (PVDF) from Dyneon was dissolved in acetone to get an acetone solution containing about 7 wt % of PVDF. A wet film with a thickness of about 100 μm resulted from the adhesive solution B was dried completely within 20 sec under 50° C.
Adhesive solution C: Polyvinylidene difluoride-co-hexafluoropropylene (PVDF-HEP) from Atofina (No. Kynar2801) was dissolved in acetone to get an acetone solution containing about 7 wt % of PVDF-HFP. A wet film with a thickness of about 100 μm resulted from the adhesive solution C was dried completely within 20 sec under 50° C.
(2) Phosphor Powder: Manufactured by Kasei Co., Ltd, Japan, No. LP-W1, Color No. EX-D.
(3) Brightness Testing Method I:
Measurement module: A module of a UVC light source (253.7 nm) was used. The module had a size of 60 cm in length and 36 cm in width, in which 16 UVC lamp tubes (590 cm in length, 3.5 cm in diameter, and 0.7 cm in wall thickness, with an intensity of 3100 μW/cm2) were provided with an interval of 2 cm; an aluminum reflective sheet was provided below the light source; and an area for placing a sample was reserved above the module.
Testing method: The sample to be tested was positioned above the light source with the phosphor coating facing the UVC light source. An optical measurement detector from Radiotek Corporation (No. RK828) was arranged 0.5 cm above the sample to measure the color coordinates and brightness.
(4) Brightness Testing Method II:
Measurement module: A module of a UVC light source (253.7 nm) was used. The module had a size of 72 cm in length and 42 cm in width, in which 16 UVC lamp tubes (710 cm in length, 3.5 cm in diameter, and 0.7 cm in wall thickness, with an intensity of 3450 μW/cm2) were provided with an interval of 3.5 cm; a reflective sheet coated with the same wavelength converting coating was provided below the light source; and an area for placing the sample was reserved above the module.
Testing method: The sample to be tested was positioned above the light source with the phosphor coating facing towards the UVC light source. The brightness/colorimeter from TotalSmart technology Co., Ltd. (No. Topcon BM7) was arranged 50 cm above the sample to measure the color coordinates and brightness.
900 g of the adhesive solution A was put into a 2000 ml beaker and stirred by a magnet for 10 mins. Then, 900 g of phosphor powder was added thereto, and the mixture was stirred by a mechanical impeller for 20 mins at room temperature to get a homogeneously mixed slurry. Once mixed homogeneously, the slurry was put into an air pressure type pulsing circulator for stirring for 30 mins before being coated onto a PET substrate (125 μm in thickness) by a slot coating method. During slot coating, the film was coated with a coating pressure of 0.12 MPa and a speed of 15 cm/min, with the coating slot being spaced 15 μm from the PET substrate. The resulting wet film was then dried with a hot air at 50° C., thus obtaining a sample that had a wavelength converting coating of 12 to 15 μm in thickness on the PET substrate.
The brightness testing method I was adopted, where the area for placing the sample was in a size of 30 cm in length and 20 cm in width and the sample was 1.5 cm away from the light source. The x coordinate, y coordinate and brightness value were measured on the sample according to the color coordinate measurement approach set forth in CIE 1931. The results were listed in Table 1 below:
The results of the wavelength conversion are shown in
The slurry preparation, coating and drying steps of Example 1 were repeated, except that the slurry was coated onto a PET substrate of 125 μm in thickness to obtain a sample that had a wavelength converting coating of 12 to 15 μm in thickness on the PET substrate.
Subsequently, using a scraper, an acrylic-based adhesive from PANTECH TAPE CO., Ltd. (No. S3277) was coated onto the other side of the sample to achieve a thickness of 25 μm. Then, the sample was laminated with an acrylic-based substrate (2 cm in thickness) and a PET protection substrate (25 μm in thickness) together by a roll laminator from CSUN MEG. Ltd. (No. CSL-M25R). Thus, the adhesive side of the sample was laminated onto one side of the acrylic-based substrate while the PET protection substrate was laminated onto the other side of the acrylic-based (polymethyl methacrylate) substrate. The laminating process was carried out at a speed of 1.5 m/min with a pressure of 3 kgf/cm2 at 40° C. Similarly, the above steps were repeated, but with a polycarbonate substrate (2 cm in thickness) replacing the acrylic-based substrate.
The brightness testing method I was adopted, where the area for placing the sample had a size of 30 cm in length and 20 cm in width and the sample was 2 cm away from the light source. The x coordinates, y coordinates and brightness values were measured on the samples according to the color coordinate measurement approach set forth in CIE 1931. The results were listed in Table 2 below:
A metered amount of phosphor powder and a metered amount of adhesive solution were formulated into mixtures with the weight ratios listed in Table 3, respectively. The mixtures were then put into six 50 ml sealed vials respectively to be stirred therein by a magnet for 10 mins, followed by an ultrasonic oscillation for another 10 mins to obtain six slurries.
A PET substrate (125 μm in thickness) sized 10 cm in width and 15 cm in length was adsorbed onto a vacuum adsorption table and was coated with one of these slurries by a meyer rod coating approach with a coating speed of 10 m/min. Such a coating process was repeated for the six slurries to obtain six PET substrates coated with individual slurries, which were then subjected to a natural drying process through air circulation for 3 mins to finally obtain coatings in a thickness of about 15 to 18 μm.
The brightness testing; method I was adopted, where the area for placing the sample had a size of 30 cm in length and 20 cm in width and the sample was 2 cm away from the light source. The x coordinates, y coordinates and brightness values were measured on the samples according to the color coordinate measurement approach set forth in CIE 1931. The results were listed in Table 3 below:
I. Adhesive Containing a Carbon-Fluorine Bond
The slurry preparation, coating and drying steps of Example 3 were repeated, except that an adhesive solution A, an adhesive solution B and an adhesive solution C were used in this example, with a weight ratio of the phosphor powders to individual adhesive contained in the respective adhesive solutions of 5:1 respectively. The resulting slurries were coated onto the respective PET substrates of 125 μm in thickness to obtain samples that had a coating thickness of 12 to 15 μm. Here, the samples prepared from the adhesive solutions A, B and C were called Samples A, B and C, respectively.
The brightness testing method I was adopted, where the area for placing the sample had a size of 10 cm in length and 10 cm in width and the sample was 2 cm away from the light source. The x coordinates, y coordinates and brightness values were measured on the samples according to the color coordinate measurement approach set forth in CIE 1931. The results were listed in Table 4-1 below:
Additionally, Sample A and Sample C underwent an accelerated test in the following manner Sample A and Sample C were placed above a single UV lamp and were 0.5 cm away from the light source. An area of 2 cm×2 cm on each sample was illuminated by the UV with an intensity of 10000 μW/cm2. Intensity and chromatic values were measured on the samples at the outset and 1000 hrs later respectively. The results were listed in the table below:
II. Hydrocarbon-Based Adhesive (A Comparison Example)
With a weight ratio of 5:1, the phosphor powder and the adhesive solution A were taken and put into a 50 ml sealed vial to be stirred therein by a magnet for 10 mins, followed by an ultrasonic oscillation for another 10 mins to finally obtain a fluoro slurry. Additionally, a polyvinyl alcohol (PVA) adhesive solution (with deionized water as a solvent and containing 20 wt % of PVA) was prepared and mixed homogeneously with an equal weight of phosphor powder by means of a mortar to obtain a hydrocarbon-based slurry with a hydrocarbon bond energy of 98 kcal/mol.
Two PET substrates (125 μm in thickness) with a size of 10 cm in width and 15 cm in length were adsorbed onto a vacuum adsorption table and were coated with the slurries respectively by a scraper clearance of 50 μm and at a coating speed of 10 m/min. Then, the PET substrate coated with the fluoro slurry was subjected to a natural drying process through air circulation for 3 mins, while the PET substrate coated with the hydrocarbon-based slurry was heated in an oven by hot air at 80° C. for 30 mins. The resulting coatings had a thickness of about 17 to 20 μm.
The brightness testing method I was adopted, where the area for placing the sample had a size of 30 cm in length and 20 cm in width and the sample was 1.5 cm away from the light source. The x coordinates, y coordinates and brightness values were measured on the samples according to the color coordinate measurement approach set forth in CIE 1931. The results were listed in Table 4-2 below:
The results in the table indicate that, as compared to an almost 50% brightness attenuation of the hydrocarbon-based slurry, the wavelength converting coating made from the adhesive solution containing a carbon-fluorine bond in this disclosure can still provide a brightness comparable to the value in the beginning even after being illuminated for 180 hours.
III. Other Adhesive Solutions
10 g of tetraethoxysilane (TEOS) was taken, to which 10 g of methyltriethoxysilane (MTEOS), 3 g of ethanol, 2 g of deionized water and 1 ml of 1% aqueous HCl solution were added. Subsequently, the resulting mixture was stirred for 30 mins at room temperature into a homogeneous phase. Then, the aqueous inorganic solution, to which 8 g of phosphor powder was further added, was stirred by a magnet for 60 mins, followed by an ultrasonic oscillation for 10 mins, and then was stirred again by a magnet for another 30 mins, thus obtaining a slurry.
In the same way as described in Part II, the slurry was coated onto a PET substrate of 100 μm in thickness. The coated PET substrate was then dried in an oven at 100° C. for 60 mins, and was allowed to cool before being taken out.
The brightness testing method I was then adopted, where the area for placing the sample was 5 cm in diameter (i.e., 19.6 cm2) and the sample was 2 cm away from the light source. The x coordinates, y coordinates and brightness values were measured on the sample according to the color coordinate measurement approach set forth in CIE 1931. The results were listed in Table 4-3 below:
The brightness testing method II was adopted to compare the performance of the sample made from the acrylic-based substrate in Example 2 with a conventional CCFL module at the same lamp voltage, current and with the same measuring method. The comparison results are listed in Table 5-1 and Table 5-2 below:
The results demonstrate that, the performance of the wavelength converting coating of the subject invention is superior to that of the conventional CCFL.
The brightness testing method II was then adopted, where the acrylic-based substrate sample (i.e., the one corresponding to the “a converting coating |a lower diffuser” column listed in Table 5-2) was illuminated in the UVC module for a long time. The variations of the color coordinates and brightness were shown in Table 6 and
20 g of adhesive solution A and 20 g of phosphor powder were put into a 50 ml sealed vial to be stirred therein by a magnet for 10 mins, followed by an ultrasonic oscillation for another 10 mins. The resulting slurry was coated onto a surface of a piece of quartz (10 cm×10 cm) with a scraper clearance of 50 μm and at a coating speed of 10 m/min. Then, the coated quartz was subjected to a natural drying process through air circulation for 3 mins, thus obtaining a coating with a thickness of about 17 to 20 μm. Thus, a wavelength converting coating sample without a UV-blocking coating was provided.
The other wavelength converting coating sample was prepared in substantially the same manner, except that a piece of quartz was pre-coated with a layer of UV-blocking nanosized zinc oxide (No. NanoZ, made by Advanced Nanotechnology, Australia) on the surface by a meyer rod coating approach (RDS No. 06) with a coating speed of 10 m/min. The coated quartz was then put into an oven to dry by hot air at 100° C. for 30 mins.
The brightness testing method I was then adopted, where the area for placing the sample had a size of 30 cm in length and 20 cm in width and the sample was 2 cm away from the light source. The x coordinates, y coordinates and brightness values were measured on the samples according to the color coordinate measurement approach set forth in CIF 1931. The results are listed in Table 6 below and in
It can be seen from comparing
This example was the same as Example 6, except that a PET (polyethylene terephthalate) substrate was used and the UV light transmissivity was measured, as shown in
Two sets of structures shown in
The first and the second wavelength converting coatings of the first set were prepared in the following way. A phosphor powder that could emit a red visible light when excited by UVC rays (“R phosphor powder”), a phosphor powder that could emit a green visible light when excited by UVC rays (“G phosphor powder”), and a phosphor powder that could emit a blue visible light when excited by UVC rays (“B phosphor powder”) were mixed in a ratio of 4.4:1.6:4.0 to obtain a phosphor powder mixture. The resulting mixture was poured into 10 g of adhesive solution A contained in a 50 ml sealed vial to be stirred therein by a magnet for 10 mins, followed by an ultrasonic oscillation for another 10 mins to obtain a slurry. A PET substrate (100 μm in thickness; 10 cm×15 cm) was adsorbed onto a vacuum adsorption table and was coated with the slurry using a scraper coating approach. The coating process occurred with a scraper clearance of 50 μm and at a coating speed of 10 m/min. Thereafter; the coated PET substrate was subjected to a natural drying process through air circulation for 3 mins to finally obtain a coating with a thickness of about 17 to 20 μm.
The first wavelength converting coating of the second set was prepared in the same way as that of the first set, except that 6.4 g of a phosphor powder mixture was produced by mixing the R phosphor powder and the G phosphor powder in a ratio of 4.9:1.5, and was then put into 6.4 g of adhesive solution A to obtain a slurry.
The second wavelength converting coating of the second set was prepared in the same way as that of the first set, except that 10 g of B phosphor powder was mixed with 10 g of adhesive solution A to obtain a slurry, which was then coated onto a PET substrate with a thickness of 225 μm.
The two sets of PET substrates with the first wavelength converting coatings were disposed above the openings of both sets of the frame bodies, while the PET substrates with the second wavelength converting coatings were disposed on the interior walls of the frame bodies. Then, optical characteristics of the two sets of structures were measured, with the results being listed in Table 8:
Table 8 demonstrates that the brightness provided by the second set has an increase of about 5% to 6% over the first set.
The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not filly disclosed in the above descriptions, they have substantially been covered in the following claims as appended.
| Number | Date | Country | Kind |
|---|---|---|---|
| 096102110 | Jan 2007 | TW | national |
| 096127149 | Jul 2007 | TW | national |
