Frame system with heat spreader for a liquid crystal display device

Technical field [0002] The present invention relates to an optimized frame assembly used together with a heat spreader in a display device such as a liquid crystal display (LCD) etc., and to the construction and use of the frame assembly due to the unique thermal emissions caused by these devices.

Background of the Invention [0003] An LCD liquid crystal display is an image display device using an image display panel made of two transparent plates of polarizing material separated by a layer of liquid containing rod-shaped crystals, where the axes of polarization of the two plates are mutually perpendicular. The LCD is built to display an image by passing an electric current through the liquid, which causes the crystals to line up to block light. Each crystal can be controlled separately and basically works like a shutter. When current is applied to specific pixel-like areas, these crystals align to form a dark area or images. Dark areas combine with light areas to create text or images on the panel. LCD panels do not emit light, but are usually backlit from the back or side for better viewing of text and images on the display panel. Generally, LCD backlit LCD monitors are used for larger screens (usually larger than about 24 inches in diagonal), while side-lit LCDs are used for smaller screens, usually together with optical light distribution systems so that light does not appear on the side.

[0004] In liquid crystal displays, backlight or side lighting used to illuminate and improve image viewing generates heat and is therefore a heat source that causes the temperature of the entire liquid crystal display to increase. Traditionally, one or more heat-generating light sources, such as cold cathode fluorescent lamps (CCFL) or flat fluorescent lamps (FFL) have been used as illuminating light. Recently, LEDs have been used as the light source to eliminate environmental emissions caused by fluorescent lamps and to improve the range of displayable colors.

[0005] The heat generated by the light source is detrimental to the operation and image quality of liquid crystal displays. The heat emitted by the light source (s) is then transferred to the image display panel, other electronic components in the liquid crystal display and to the support structure of the liquid crystal display. In fact, some electronic components in the display panel themselves are a source of heat, which aggravates this problem. However, these other components of liquid crystal displays usually have poor heat dissipation properties and are usually not designed to remove heat from a light source, especially in directions parallel to the front of the image display panel.

[0006] In addition, the illuminating light of the liquid crystal display remains under voltage and power consumption, regardless of the image properties on the display panel. Changes in the image are controlled by arranging and aligning the crystals in the image display panel. As such, the elements of the liquid crystal display must be freed from the constant heat generated by the lighting light. Constant heat generation can accelerate deterioration of the liquid crystal material and shorten the useful life of the liquid crystal display device. Heat can also negatively affect the screen refresh rate.

[0007] The use of so-called "High-order graphite layers" as a thermal interface material for plasma display panels to fill the space between the back of the panel and the heat sink assembly, has been proposed by Morita, Ichiyanagi, Ikeda, Nishiki, Inoue, Komyoji and Kawashima in US Patent 5,831,374. However, this disclosure focuses on the use of pyrolysis graphite as graphite material and does not mention the use or explicit advantages of plates of compacted particles of detached graphite. In addition, the use of a heavy aluminum heat sink assembly is a critical element of the invention of Morita et al. In addition, US Patent 6,482,520 to Tzeng discloses the use of compacted particle boards of detached graphite as heat spreaders (referring to thermal interfaces in this patent) for a heat source such as an electronic component. In fact, such materials are commercially available from Advanced Energy Technology Inc. from Lakewood, Ohio, as an eGraf® SpreaderShield class. Tzeng graphite heat spreaders are placed between the heat generating electronic component and, preferably, a heat sink, to increase the effective surface area of ​​the heat generating element; Tzeng's patent does not deal with specific thermal emissions caused by display devices.

[0008] Graphites are made of planes of layers of hexagonal systems or networks of carbon atoms. These patches of layers of hexagonally arranged carbon atoms are substantially flat and oriented or ordered to be substantially parallel and equidistant from each other. Such substantially flat, parallel equidistant sheets or layers of carbon atoms usually refer to graphite layers or base planes, are connected or bonded together, and their groups form crystallites. Strongly oriented graphites consist of crystallites of considerable size: such crystallites are highly aligned and oriented in a similar way and have well ordered carbon layers. In other words, highly ordered graphites have a high level of orientation of privileged crystallites. It should also be noted that graphites have an anisotropic structure and thus exhibit or possess many highly directed properties, e.g. thermal and electrical conductivity and fluid diffusion.

[0009] Briefly, graphites can be characterized as carbon plate structures, i.e. structures consisting of overlapping layers or plates of carbon atoms joined together by van der Waals weak intermolecular forces. When referring to the graphite structure, two axes or directions "c" and "a" are usually distinguished. For simplicity, it is assumed that the axis or direction "c" is a direction perpendicular to the carbon layers. Axes or directions "a" are directions parallel to the carbon layers or perpendicular to the direction "c". Graphites suitable for producing flexible graphite sheets have a high degree of orientation.

[0010] As mentioned above, the binding forces holding the parallel layers of carbon atoms together are only weak van der Waals forces. Natural graphites can be treated so that the spaces between the overlapping layers or carbon plates can open significantly so as to ensure significant expansion in a direction perpendicular to the layers, i.e. in the "c" direction, and thus form expanded or foamed graphite structures in which the laminated form of the carbon layers is essentially preserved.

[0011] The graphite husk, which has been very expanded, and more specifically, expanded to obtain a final thickness, or dimension in the "c" direction about 80 times greater than the original dimension in the "c" direction, can be formed without the use of an adhesive , in coherent or integrated sheets of expanded graphite, e.g. fabrics, papers, belts, tapes, foils, mats, etc. (usually referred to as "flexible graphite"). Forming graphite particles that have been expanded to such an extent that their final thickness or dimension in the "c" direction is at least 80 times greater than the original value in the "c" dimension to consolidate the flexible sheets by compression without using any binding materials seems to be possible due to mechanical tacking or cohesion that has been achieved between the volume expanded graphite particles.

[0012] In addition to flexibility, it has been found that the sheet material, as mentioned above, has a high degree of anisotropy with respect to thermal and electrical conductivity and fluid diffusion, comparable to the natural graphite starting material, due to the orientation of the expanded graphite particles and graphite layers substantially parallel to opposing faces of the sheet, which is the result of very strong compression, e.g. roller compaction. The sheet material produced in this way is characterized by excellent elasticity, good strength and a very high degree of particle ordering.

Briefly, the production process of flexible, anisotropic, non-welded graphite sheet material, e.g., fabrics, papers, belts, tapes, foils, mats, etc., includes compression or compaction, under a predetermined load and in the absence of a binder, expanded graphite particles, which have a dimension in the "c" direction at least about 80 times larger than the original particles to produce a flat, flexible, coherent graphite sheet. Expanded graphite particles, which usually look similar to a worm or appendix, will retain permanent deformation and alignment with opposing major sheet surfaces after compression. The density and thickness of the sheet material can be changed by controlling the degree of compression. The density of the sheet material can range from about 0.04 g / cm³ up to about 2.0 g / cm³. The flexible graphite sheet material exhibits a significant degree of anisotropy due to the orientation of the graphite particles parallel to the main opposing parallel surfaces of the sheet, the degree of anisotropy increasing when press rolling the sheet material to increase orderliness. In roller-pressed anisotropic sheet materials, thickness i.e. the direction perpendicular to the opposite, parallel surfaces of the sheet, includes the direction "c" and directions lying along the length and width, i.e. along or parallel to opposite, major surfaces includes the directions "a", and the thermal, electrical and diffusion properties of the sheet fluids are very different , by orders of magnitude, for the directions "a" and "c".

[0014] Although the use of compressed sheets of detached graphite particles (i.e. flexible graphite) as thermal spreaders, thermal interfaces and heat sink components to dissipate heat generated by heat sources, has already been proposed (see, for example, patents US 6,245,400; US 6,482,520; US 6,503,626; and US 6,538,892), however, it is a use Graphite material was previously independent and not considered in connection with other elements such as the display panel frame assembly.

[0015] Conventional display devices typically use a thick, heavy metal bracket (often a thick aluminum sheet or a set of multiple sheets) to which is mounted both a display panel assembly, a light source (which, in the case of LEDs, can be mounted on circuit boards) printed circuits, such as the metal core of printed circuit boards (PCBs) with heat-conducting dielectric material) and other related electronic components. The heat transmitted by these heat sources contributes to the uneven temperature distribution generated on the panel assembly itself, which adversely affects the image presented on the display panel, as well as the reliability of the display panel.

[0016] The conventional cantilever element performs both a mechanical function (i.e. mounting the panel assembly and accompanying electronics) and a thermal function (i.e. assisting the outlet and dissipation of heat generated by the light source (s) and / or associated electronic components). Accordingly, the support elements are usually made of hard aluminum sheets about 2.0 mm thick. In other words, conventional display panels have cantilever members that have a support factor of about 440 mm-W / m ° K or higher. The support factor is determined by multiplying the thickness of the support element present in the display panel by its flat thermal conductivity (thus, a 2.0 mm aluminum sheet has a support factor of 440 mm-W / m ° K, because the flat thermal conductivity of commonly used high conductivity aluminum thermal energy is 220 W / m ° K). It should also be noted that since most metals are relatively thermally isotropic, the flat thermal conductivity does not differ significantly from the material's cross-conductivity.

[0017] A support element such as this can add a significant amount of weight and can be expensive and difficult to construct, due to physical requirements, the need for many threaded mounting components for electronics and the high cost of aluminum sheet with high thermal conductivity. In addition, a skeleton structure (often made of steel or aluminum) is used to add further mechanical support to the cantilever element, and to take into account the solid assembly means for attaching the display panel to the cantilever wall or rack unit. Together, the skeleton of the structure and the cantilever element form a frame assembly in conventional display panels.

[0018] Manufacturers of LCD devices are under extreme pressure to reduce the costs and weight of their existing display devices, while at the same time there are demands to increase the brightness and luminescent efficiency of the panel units. This means that more energy is supplied to the light sources, which increases the thermal load on the system and requires additional heat dissipation capability within the display assembly. Active cooling solutions, such as fans and / or heating pipes, are undesirable due to unreliability, noise and the fact that they negatively affect the cost and weight of the system. In addition to increasing the brightness and light output of the displays, display manufacturers are under constant pressure to produce ever larger panels, which increases the weight of the frame assembly (especially the cantilever component) in proportion to the size of the device.

[0019] US Patent 6,007,209 describes a light source for a display panel, the type used in notebooks, which light source consists of a housing whose internal bottom and side surfaces, forming a cavity, have diffusion reflecting properties. This housing limits the aperture that is located next to the back surface of the display panel. The first series of LEDs are mounted in a recess around the aperture circumference and is obstructed from the aperture by a peripheral partition that extends around the aperture circumference. A second series of LEDs is mounted inside the recess on the bottom of the housing. Between the second series of LEDs and the aperture there is a series of partitions. A number of coatings are placed between the recess and the display panel to improve light quality. The light source produces uniform light with relatively high brightness and intensity. The features given in the preamble of claim 1 are known from this document.

[0020] EP 1 519 217 discloses a display device that includes a display panel and a heat transfer sheet attached close to one of the surfaces of the display panel. The heat transfer sheet may have an open cell and / or closed cell structure. A number of pores are formed in the heat transfer sheet, with the pores in the open cell structure connected to each other and in the closed cell structure the pores are not connected to each other.

[0021] Therefore, what is desirable is the low weight and economic efficiency of the frame system for display devices, especially what provides increased heat transfer capacity, however it is a solid construction sufficient to provide both hooking for panel assemblies and accompanying electronics, as well as structural integrity for attaching and supporting the display device itself. The desired frame arrangement reduces or eliminates the need for a cantilever member, especially made of high conductivity aluminum.

Summary of the invention [0022] The invention is defined in the independent claim 1. Further advantageous developments are defined in the independent claims.

Accordingly, it is an object of the present invention to provide a frame system for a display device such as a liquid crystal display or the like that is lightweight and structurally sound.

[0024] Another object of the present invention is to provide a frame system for a display device that includes a skeleton structure with a low support factor.

[0025] Another object of the present invention is to provide a display device that includes a heat dissipating material, sometimes referred to as a heat diffuser, disposed near heat generating sources such as light emitting diodes, cold cathode fluorescent lamps or flat fluorescent lamps, display devices.

[0026] Another object of the present invention is to provide a frame system for a display device that includes a skeleton structure comprising a peripheral edge ensuring the structural integrity of the display device.

[0027] Another object of the present invention is to provide a frame for a display device equipped with an internal aperture to facilitate heat transfer and heat dissipation by means of heat dissipating material inside the display device.

[0028] Another object of the present invention is to provide a frame system for a display device that includes a skeleton structure comprising a support element rather than a sheet of heavy aluminum or a set of sheets.

[0029] These objectives, as well as others that will be apparent to those skilled in the art after reading the present description, can be achieved by providing a display device consisting of: an image display panel; a frame assembly comprising: (i) a structure skeleton operably coupled to an image display panel; a framework of the structure, optionally including a support element for mounting the panel assembly; and (ii) multiple heat sources operatively coupled to the frame; a heat dissipating material consisting of at least one sheet of compressed particles of detached graphite, operably coupled to the skeleton of the structure in operational thermal contact with heat sources; whereby the frame assembly has a support coefficient of less than 375 mm-W / m ° K, and the support coefficient is determined by multiplying the thickness of the bracket element present in the frame assembly by its plane thermal conductivity.

[0030] Preferably, the frame assembly has a support coefficient of less than about 150 mmW / m ° K, and in the most preferred embodiment, the frame assembly has a support coefficient of 0 mm-W / m ° K; this means that the frame assembly has no supporting element at all.

[0031] The LCD can be backlit from the back or from the side. In backlit LCDs, rows of light sources such as LEDs mounted on a printed circuit board are located directly behind the LCD back panel, providing light directly to the back of the LCD panel. In side-lit LCDs, the light sources are arranged along the sides of the LCD panel, and the optical system (usually a fiber optic system) is usually used to compensate for the light scattering at the back of the LCD panel so that the light does not appear to come from or be more pronounced edges or sides of the panel. In addition, both LCDs with backlight and side illumination often have reflective material so positioned to further facilitate the dispersion of aligned light from the light sources to the rear of the LCD panel.

[0032] The skeleton of the LCD structure consists of metals such as steel, aluminum or other construction materials, and they can be bolted, riveted, glued or otherwise securely attached to the bracket, if present.

[0033] The skeleton of the structure may include transverse brackets including the skeleton of the structure where electronic components may connect the transverse brackets. In addition, the skeleton of the structure may include a flange for supporting the heat dissipating material and electronic components, or alternatively may include at least one transverse member that connects the electronic components. Light sources and heat dissipating material may be located substantially inside the skeleton of the structure, and the height and width of the skeleton of the structure may be such that the heat dissipating material smoothly covers height and width.

[0034] In addition, a plurality of cross beams may include a skeleton of the structure, and at least one light source such as a light emitting diode may couple at least one of the cross brackets or any other structure skeleton. Although such a skeleton layout is preferred, other similar arrangements, such as multiple rows of cross beams, can be used in the skeleton of the structure.

[0035] The heat dissipating material is preferably arranged between the light sources and the support element, although this is not required. In any case, the heat dissipating material is in thermal contact with the heat-generating light sources, meaning that thermal transfer occurs between the light sources and the heat dissipating material. The support element may be placed between the heat dissipating material and light sources, provided that the material of the support element has sufficient thermal conductivity to effectively transfer heat from the light sources to the heat dissipating material. More preferably, however, the heat dissipating material is placed near light sources, such as light emitting diodes, and is substantially exposed to the light sources.

[0036] In a backlit LCD, there may be a gap between the heat dissipating material and the printed circuit boards or other light source supporting structure and / or between the cantilever element and the printed circuit boards or other light source supporting structure; in side-lit displays, printed circuit boards or other structure supporting the light source (s) are mounted at the edges of the optical scattering assembly, and the gap may be between the optical assembly and the heat dissipating material.

[0037] In another embodiment, the image display panel includes a side of the image display connected to the peripheral frame of the structure, and the heat dissipating material connects to the frame of the structure opposite the side of the image display. The peripheral skeleton of the structure comprises a top, bottom, first side and second side of the peripheral skeleton of the structure. Many electronic components are connected to the perimeter frame. The top, bottom, first side and second side of the peripheral structure limit the aperture, and the heat dissipating material may include the aperture and may engage the top, bottom, first side and second side of the peripheral skeleton of the structure. Heat dissipating material and many electronic components (especially light sources) can be placed substantially inside the aperture. The skeleton of the structure may contain an orifice supporting the heat dissipation material and many electronic components. The image display device may be a liquid crystal display assembly, electronic components may be light sources such as light emitting diodes, and heat dissipating material may be delaminated graphite.

[0038] In another embodiment, the image display device includes a frame assembly including a skeleton structure operatively connected to the image display device and an orifice disposed opposite the image display panel. Many electronic components are connected to the orifice while heat dissipating material is placed near many electronic components and opposite to the image display panel. The frame assembly has a support factor of less than about 375 mm-W / m ° K. A plurality of cross beams may substantially enclose the skeleton of the structure and be connected to the orifice, each electronic component being operatively connected to at least one cross bearer. A heat dissipation material may be placed between the orifice and a plurality of crossbars, while many connectors may attach the heat dissipation material and a plurality of crossbars to the orifice. The skeleton of the structure has height and width, and the aperture essentially includes this height and width. Many electronic components such as. light sources, connect the skeleton of the structure, can be positioned inside the structure's skeleton, and can be positioned to coincide with the aperture.

[0039] The support element is usually formed as a sheet, possibly with arms or other extensions, and is located on the skeleton of the structure. The bracket may include a metal having a lower thermal conductivity than previously thought to be sufficient to provide effective heat dissipation in the display panel, even when graphite or other type of heat dissipating material is used. For example, instead of using a thick aluminum sheet with high thermal conductivity, a steel sheet with planar thermal conductivity of less than 20 W / m ° K may be used. Because steel is much cheaper than aluminum with high thermal conductivity, this results in significant savings, even when using the same levels of material thickness as aluminum with high thermal conductivity, i.e. about 2 mm. Such a steel sheet should provide a support factor of 40 mmW / m ° K. Alternatively, the support element may be made of aluminum with high thermal conductivity, but made of a much thinner sheet than was previously thought to be achievable, even in an image display panel assembly also using graphite or other type of heat dissipating material. For example, an aluminum sheet with high thermal conductivity 0.5 mm thick could provide a support factor of about 110 mm-W / m ° K, resulting in a much lighter structure skeleton.

[0040] As already mentioned, the heat dissipating material used is formed from sheets of compressed particles of detached graphite, commonly referred to as flexible graphite. Graphite is a crystalline form of carbon consisting of atoms covalently bonded to flat layered planes with weak bonds between planes. By subjecting graphite particles, such as natural graphite flakes, to an intercalant, e.g. sulfuric and nitric acid solution, the graphite crystal structure reacts to form a graphite compound and intercalant. The treated graphite particles are hereinafter referred to as 'intercalation graphite particles'. When exposed to high temperature, the graphite intercalant decomposes and volatilizes, causing the particles of intercalation graphite to increase their dimensions, as much as about 80 times or more, their original volume, assuming a harmonica-like shape, in the "c" direction , i.e. in a direction perpendicular to the crystalline plane of the graphite. The detached graphite particles look like worms and are therefore usually called worms. The worms can be pressed together into flexible sheets and, unlike the flakes of the original graphite, they can be formed and cut into various shapes.

[0041] Graphite starting materials suitable for use in this invention include materials containing high-graphite carbon, capable of intercalating with organic and inorganic acids, as well as hydrocarbyl acids, and then swelling under the action of heat. It is most preferred that these high-graphite carbon-containing materials have a degree of graphitization of about 1.0. As used in this disclosure, the term "degree of graphitization" refers to the value of g according to the formula:

<a name="caption1"></a>4» 3-45 - ¢/(002)

0.095 where d (002) is the distance between the graphite layers of carbon in the crystal structure, expressed in angstroms. The distance d between the graphite layers is measured using standard X-ray diffraction techniques. Peak positions are measured that correspond to Miller (002), (004) and (006) and by means of the mean square approximation technique, spaces are derived, which minimizes the overall error for all maximum values. Examples of high-graphite carbon-containing materials are: natural graphites from various sources, as well as other carbon-containing materials such as graphite produced by chemical deposition of gas phase layers, high-temperature polymer pyrolysis or crystallization from molten metal solutions, etc. However, the preferred source is natural graphite.

[0042] The graphite starting materials used in this invention may contain non-graphite components as long as the crystal structure of the starting materials maintains the required degree of graphitization and they are capable of delaminating. Generally, any carbon-containing material whose crystal structure maintains the required degree of graphitization and which is capable of being detached is suitable for use in the present invention. Preferably, such graphites have a purity of at least about 80% by weight. More preferably, the graphite used in the present invention will have a purity of at least about 94%. In the most preferred embodiment, the graphite used will have a purity of at least about 98%.

[0043] The usual method for producing a graphite sheet is described by Shane et al. in US Patent 3,404,061. In typical practice of the Shane method and others, natural graphite flakes are intercalated by dissolving these flakes in a solution containing e.g. a mixture of nitric and sulfuric acid, preferably at a level of about 20 to about 300 parts by weight of the intercalation solution per 100 parts by weight of graphite flakes (pph ). The intercalation solution contains oxidizing agents and other intercalating agents known in the art. Examples include those containing oxidants and oxidizing mixtures, such as solutions containing nitric acid, potassium chlorate, chromic acid, potassium permanganate, potassium chromate, potassium dichromate, perchloric acid, etc., and mixtures such as e.g. concentrated nitric acid and chlorate, chromic acid and phosphoric acid, sulfuric acid and nitric acid or mixtures of strong organic acid, e.g. trifluoroacetic acid and a strong oxidizing agent soluble in organic acids. Alternatively, it is possible to use the electrical potential to induce graphite oxidation. The types of chemicals that can be introduced into a graphite crystal using electrolytic oxidation include sulfuric acid and other acids.

In a preferred embodiment, the intercalation agent is a solution of a mixture of sulfuric acid or sulfuric acid and phosphoric acid and an oxidizing agent, i.e. nitric acid, perchloric acid, chromic acid, potassium permanganate, hydrogen peroxide, iodine or periodic acid or similar compounds. Although less preferred, the intercalation solution may contain metal halides, such as ferric chloride and ferric chloride, mixed with sulfuric acid, or a halide, such as bromine, as a solution of bromine and sulfuric acid, or as bromine in an organic solvent.

[0045] The amount of intercalation solution may range from about 20 to about 350 pph, and more typically from about 40 to about 160 pph. After the process of intercalating the flakes, the excess solution is filtered off from the flakes, and the flakes are washed with water. Alternatively, the amount of intercalation solution may be limited from about 10 to about 40 pph, which allows elimination of the washing step as assumed and described in US Patent 4,895,713.

[0046] The graphite flake particles treated with the intercalation solution, optionally, can be contacted by, e.g. ° C to 125 ° C. Suitable specific organic agents include: hexadecanol, octadecanol, 1-octanol, 2-octanol, 1-decanol 1,10-decanediol, decanal, 1-propanol, 1,3-propanediol, ethylene glycol, polypropylene glycol, dextrose, fructose, lactose, sucrose, potato starch monostearate ethylene glycol, diethylene glycol dibenzoate, propylene glycol monostearate, glycerol monostearate, dimethyl oxalate, diethyl oxalate, methyl formate, ethyl formate, ascorbic acid and lignin derivatives, such as sodium lignosulfonate. The amount of organic reducing agents is suitable in the range of about 0.5% to 4% of the weight of the graphite flake particles.

[0047] The use of expansion aids provided before, during or immediately after intercalation may also provide improvement. According to this improvement, the detachment temperature can be lowered and the expanded volume increased (also referred to as "worm volume"). The expansion aid, in this context, is preferably an organic material with solubility in the intercalation solution sufficient to achieve enlargement improvement. More specifically, organic materials of this type can be used that contain carbon, hydrogen and oxygen. Carboxylic acids have been found to be particularly effective here. A suitable carboxylic acid, useful as expansion aid, may be selected from aromatic, aliphatic or cycloaliphatic, straight or branched chain, saturated and unsaturated monocarboxylic acids, dicarboxylic or polycarboxylic acids, which have at least one carbon atom, and preferably up to about 15 carbon atoms, and which are soluble in the intercalation solution in an amount effective to provide measurable growth of one or more aspects of delamination. It is also possible to use other suitable organic solvents to improve the solubility of the organic expansion aid in the intercalation solution.

[0048] Representative examples of saturated aliphatic carboxylic acids are acids such as those of the general formula H (CH₂)_nCOOH, where n is a number from 0 to about 5, including formic, acetic, propionic, butyric, pentanoic, hexanoic acids, etc. Instead of carboxylic acids, it is also possible to use anhydrides or reactive derivatives of carboxylic acids, such as alkyl esters. Representative examples of alkyl esters are methyl formate and ethyl formate. Sulfuric acid, nitric acid and other known aqueous intercalation compounds have the ability to break down formic acid, ultimately into water and carbon dioxide. For this reason, formic acid and other sensitive expansion aids are preferably contacted with graphite flakes prior to immersion of the flakes in the aqueous intercalation compound. Representative dicarboxylic acids are aliphatic dicarboxylic acids having 2-12 carbon atoms, in particular oxalic acid, fumaric acid, malonic acid, maleic acid, succinic acid, glutaric acid, adipic acid, 1,5-pentanedicarboxylic acid, 1,6-hexanedicarboxylic acid, 1,10-decanedicarboxylic acid, cyclohexane-1,4-dicarboxylic acid, and aromatic dicarboxylic acids such as phthalic acid or terephthalic acid. Representative alkyl esters are dimethyl oxalate and diethyl oxalate. Representative cycloaliphatic acids are cyclohexane carboxylic acid, while aromatic carboxylic acids are benzoic acid, naphthoic acid, anthranilic acid, p-aminobenzoic acid, salicylic acid, o-, m- and p-tolylic acids, methoxy and ethoxybenzoic acids, and aceto-benzoic acid acetamidobenzoic acid, phenylacetic acid and naphthalene carboxylic acids. Representative hydroxyaromatic acids are: hydroxybenzoic acid, 3-hydroxy-1-naphthalenecarboxylic acid, 3-hydroxy-2-naphthoic acid, 4-hydroxy-2-naphthoic acid, 5-hydroxy-1-naphthoic acid, 5-hydroxy-2 acid - naphthoic acid, 6-hydroxy-2-naphthoic acid and 7-hydroxy-2-naphthoic acid. Among the polycarboxylic acids, the most important is citric acid.

[0049] The intercalation solution should be an aqueous solution and should preferably contain a certain amount of expansion aid from about 1 and 10%, this amount is effective to increase detachment. In an embodiment in which the adjuvants come into contact with the graphite flakes before or after immersion in the aqueous intercalation solution, the expansion aid can be mixed with the graphite by suitable means, such as type V mixers, typically in an amount of from about 0, 2% to approx. 10% by weight of graphite flakes.

[0050] After intercalating the graphite flakes and then mixing the intercalating coated graphite flakes with the organic reducing agent, the mixture is subjected to a temperature in the range of 25 ° C to 125 ° C to enhance the reaction of the reducing agent and the intercalation coating. The heating period lasts up to about 20 hours, and with a shorter heating period, e.g. up to about 10 minutes, temperatures are higher than in the above range. Times around half an hour or less, e.g. 10-25 minutes can be used at higher temperatures.

[0051] The graphite particles treated in this way are sometimes called "intercalation graphite particles". When exposed to high temperatures, e.g. temperatures of at least about 160 ° C, especially temperatures of about 700 ° C to 1000 ° C and higher, the intercalation graphite particles expand about 80 to 1000 times their original volume, shaped close to the harmonica in the "c" direction, ie in a direction perpendicular to the crystal plane of the graphite component particles. Expanded, i.e., detached, graphite particles have the appearance of a worm and are therefore usually called worms. The detached particles of graphite look like worms and are therefore usually called worms. The worms can be pressed together into flexible sheets that, unlike the original graphite flakes, can be formed and cut into various shapes.

[0052] The flexible graphite sheet and foil are coherent, with good handling strength and are suitable for high compression, e.g. by roller compression, to a thickness of about 0.075 mm to 3.75 mm and a typical density of about 0.1 to 1.5 gram to cubic centimeter (g / cm³). From about 1.5-30% by weight of the ceramic additives can be mixed with the intercalated graphite flakes, as described in US Patent 5,902,762 (which is incorporated herein by reference), to provide better resin impregnation in the final flexible graphite product. Additives include ceramic fiber particles about 0.15 to 1.5 millimeters long. Particle widths from about 0.04 to 0.004 mm, respectively. Ceramic fiber particles are inactive and do not adhere to graphite, and are also stable at temperatures up to about 1100 ° C, preferably up to about 1400 ° C or higher. Suitable ceramic fiber particles are formed with macerated quartz glass fibers, carbon and graphite fibers, zirconium, boron nitrate, silicon carbide and magnesium fibers, naturally occurring mineral fibers such as calcium metasilicate fibers, calcium aluminum silicate fibers, aluminum oxide fibers etc.

[0053] The above described methods of intercalation and detachment of graphite flakes can be advantageously improved by pretreatment of graphite flakes at graphitization temperatures, i.e. temperatures in the range of about 3000 ° C and higher, and by inclusion of lubricating additives in the intercalation agent, as described in WO 03 051 772A .

[0054] Pre-treatment, or annealing, of graphite flakes causes a significant increase in expansion (i.e., an increase in expansion volume to about 300% or more) when the petal is subsequently intercalated and detached. In fact, it is desirable for the expansion increase to be at least 50%, compared to a similar process without annealing step. The temperatures used in the annealing step should not be significantly lower than 3000 ° C, because the temperature even by 100 ° C lower significantly reduces expansion.

[0055] The annealing according to the present invention is carried out for a period of time sufficient to result in flakes having a high degree of expansion after intercalation and subsequent detachment. Usually the required time is 1 hour or more, more preferably 1 to 3 hours, and most preferably it is carried out in an inert environment. For best results, the annealed graphite flake will also undergo other processes known in the art to increase the degree of expansion - namely, intercalation in the presence of an organic reducing agent, intercalation aid such as organic acid, and washing with a surfactant after completion intercalation. In addition, the intercalation step may be repeated to achieve the maximum advantageous results.

[0056] The annealing step may be carried out in an induction furnace or other such equipment as is known and recognized in the art of graphitization; for temperatures used here, which are in the range of 3000 ° C, this is the upper end of the range found in graphitization processes.

[0057] Since it has been observed that worms made using annealed graphite prior to intercalation tend to "clump" together, which can negatively affect the uniformity of weight distribution, it is highly desirable to add compounds that promote the formation of "free flowing" worms. The addition of a lubricant additive to the intercalation solution facilitates a more even distribution of the worms on the bed of the squeezing device (such as the bed of the calendering station usually used for squeezing (or "calendering") graphite worms into a flexible graphite sheet. The resulting sheet therefore has better uniformity of surface loading and higher strength for stretching. The lubricating additive is preferably a long chain hydrocarbon, more preferably a hydrocarbon having at least about 10 carbon atoms. Other organic compounds having long chain hydrocarbon groups even if other functional groups are present can also be used.

[0058] More preferably, the lubricating additive is oil, with mineral oil being most preferred, especially considering the fact that mineral oils are less prone to rancidity and odors, which can be an important aspect in long-term storage. It should be noted that some of the expansion aids mentioned above also fulfill the definition of a lubricating additive. When these materials are used as an expansion aid, it is not necessary to include a separate lubricant additive in the intercalating solution.

[0059] The lubricating additive is present in the intercalating solution in an amount of at least about 1.4 pph, and more preferably at least about 1.8 pph. Although the upper limit for inclusion of the lubricant additive is not as critical as the lower limit, it does not appear to be a significant additional advantage for the inclusion of the lubricant additive at a level greater than about 4 pph.

[0060] The flexible graphite sheet can sometimes, preferably, also be resin-treated and the absorbed resin, after curing, increases moisture resistance and tampering, i.e. the rigidity of the flexible graphite sheet and "fixing" the morphology of the sheet. A suitable resin content is preferably at least about 5% by weight, more preferably about 10% to 35% by weight and suitably up to about 60% by weight. Resins that are considered particularly useful in the practice of the present invention include acrylic, epoxy and phenolic resin-based systems, fluorine-based polymers and mixtures thereof. Suitable epoxy resin systems include those based on 2,2'-bis (p-hydroxyphenyl) propane di-glycidyl ether resin (DGEBA) and other multi-functional resin systems; phenolic resins that may be used including resole and novalac phenol. Optionally, flexible graphite can be impregnated with fibers and / or salts as a resin additive or in place of a resin. In addition, active or passive additives can be used in the resin system to modify their properties (such as stickiness, material flow, hydrophobicity, etc.).

[0061] Alternatively, flexible graphite sheets according to the invention may use particles of shredded flexible graphite sheets instead of freshly expanded worms, as discussed in WO 02 096 615A. The sheets can be made of newly-formed material, recycled material, waste material or other suitable material source.

[0062] Also, the processes of the present invention may use a blend of virgin and recovered materials.

[0063] The source material for recycled materials may be sheets or cuttings of sheets that have been formed by stamping as described above, or sheets that have been compressed, e.g. by means of pre-smoothed rollers, but have not yet been impregnated with resin. In addition, the source material may be sheets or cuttings of sheets that have already been impregnated with resin but have not yet been cured, or sheets or cuttings of sheets that have been impregnated with resin and cured. The source material can also be recovered proton exchange membranes (PEM) from flexible graphite, fuel cell elements such as flow plates or electrodes. Each of these graphite sources can be used as such or mixed with natural graphite flakes.

[0064] As soon as the source material of the flexible graphite sheets is delivered, it can be comminuted by well-known processes or devices such as a jet mill, air mill, bulk material mixer, etc., to produce particles. Preferably, most particles have a diameter such that it can pass through the US 20 mesh; more preferably, a larger proportion of the particles (more than about 20%, and most preferably more than about 50%) will not pass through the US 80 mesh. Most preferably, the particles have a size not larger than the US 20 mesh mesh. It may be desirable to cool the resin impregnated flexible graphite sheet before it is comminuted to avoid thermal damage to the resin system during the comminution process.

[0065] The size of the particulate particles can be selected so as to balance the machinability and deformability of the graphite article with the desired thermal properties. Thus, smaller particles result in a graphite product that is easier to process and / or shape, while larger particles result in a graphite product with higher anisotropy and thus, greater planar thermal and electrical conductivity. [0066] If the source material has been impregnated with a resin, it is preferable to remove the resin from the particles. Details of the resin removal process are described below.

[0067] After the source material has been crushed and the resin removed, the material is then expanded again. The re-extension process may be accomplished using the intercalation and delamination process described above and described in the US Patent

3,404,061 Shane et al. And in US Patent 4,895,713 to Greinke et al.

[0068] Typically, after intercalation, the particles are detached by heating the intercalated particles in an oven. During the detachment step, the intercalated natural graphite flakes can be added to the recovered intercalated particles. Preferably, during the re-expansion step, the particles expand until a suitable volume in the range of at least about 100cc / g to about 350 cc / g or more is reached. Finally, after the re-expansion step, the re-expanded particles can be compressed into flexible sheets as described below.

[0069] If the starting material has been impregnated with resin, it is preferable to at least partially remove the resin from the particles. The resin removal step should take place between the comminution step and the re-expansion step.

[0070] In one embodiment, the removal step comprises heating the resin containing the ground particles, e.g. over an open flame. More specifically, the impregnated resin can be heated to a temperature of at least about 250 ° C to remove the resin. During the heating step, care must be taken to avoid flashing resin decomposition products; this can be achieved by careful heating in air or by heating in an inert atmosphere. Preferably, the heating temperature should be in the range of from about 400 ° C to about 800 ° C for a time in the range of, at least about 10 to about 150 minutes or more.

[0071] In addition, the resin removal step may result in an increase in tensile strength in the product produced by the pressing process compared to a similar process in which the resin is not removed. The resin removal step may also be advantageous because during the expansion step (i.e. intercalation and detachment), when the resin is mixed with intercalation substances, toxic by-products can be formed in some cases.

[0072] Thus, by removing the resin before the expansion step, a first-class product with better strength properties, as discussed above, is obtained. Better strength properties are partly the result of increased expansion. With the resin present in the particles, expansion may be limited.

[0073] In addition to strength properties and environmental considerations, the resin can be removed prior to intercalation due to concerns about the possibility of the resin causing an uncontrolled exothermic reaction with the acid.

[0074] Considering the above, it is preferable to remove most of the resin. It is more preferred to remove more than about 75% of the resin. It is most preferred to remove more than 99% resin.

[0075] After the flexible graphite sheet is crushed, it is formed into the desired shape and then cured (when it is impregnated with resin) in a preferred embodiment. Alternatively, the sheet may be cured before comminution, however post-comminution curing is recommended.

[0076] Optionally, a flexible graphite sheet used to form the inventive heat dissipation material can be used as a laminate, with or without an adhesive between the laminate layers. The non-graphite layers may also be included in the laminate stack, although this may necessitate the use of binders that may be disadvantageous as described above. Such graphite-free layers may contain metals, plastics or other non-metals, such as glass fibers or ceramics.

[0077] As described above, the sheets of compressed particles of detached graphite thus formed are anisotropic in nature; i.e. the thermal conductivity of the sheets is greater in the plane or in the "a" direction than transverse to the plane or in the "c" direction. In this way, the anisotropic nature of the graphite sheet directs heat along the plane direction of the heat dissipating solution (i.e. towards the "a" of the graphite sheet). Such graphite sheet has thermal conductivity in the plane direction, at least about 140, more preferably, at least about 200, and preferably at least about 250 W / m ° K, and in a transverse direction to the plane not more than about 12, more preferably not more than about 10, and preferably not more than about 6 W / m ° K. Thus, the heat dissipating material has a thermal anisotropy coefficient (i.e. ratio of thermal conductivity in the plane to thermal conductivity transverse to the plane) not less than about 10.

[0078] The value of thermal conductivity along the plane and in the transverse direction of the laminate can be changed by changing the orientation direction of the graphite layers of flexible graphite sheets used to form the thermal solution, including when it will be used to form the laminate, or by changing the orientation direction of the graphite layers in laminate itself, after being formed. In this way, the thermal conductivity of the thermal solution increases, while the thermal cross-conductivity of the thermal solution decreases, which increases the thermal anisotropy factor.

[0079] One way to achieve the directional orientation of the graphite layers is to apply pressure to the components of the flexible graphite sheets, both by calendering the sheets (i.e. by applying shear force) and by compression or mutual compression (i.e. by applying compression); with calendering being more effective in producing a directional setting. For example, by calendering sheets to a density of 1.7 g / cc, as opposed to 1.1 g / cc, thermal conductivity along the plane increases from about 240 W / m ° K to about 450 W / m ° K or more, and the cross-conductivity is proportionally reduced, thereby increasing the thermal anisotropy rate of the individual sheets and the laminate formed from them.

[0080] Alternatively, if the laminate is formed, the directional orientation of the graphite layers that make up the laminate as a whole is increased such that by applying pressure, the density increases above the original density of the flexible graphite sheets making up the laminate. Indeed, the final density of the laminated product obtained by this method is at least about 1.4 g / cc, more preferably at least about 1.6 g / cc to about 2.0 g / cc. Pressure can be applied by conventional means such as stamping or calendering. To achieve a density of 2.0 g / cc, a pressure of at least about 60 MPa, preferably a pressure of at least about 550 MPa, and most preferably at least about 700 MPa is preferred.

Increasing the directional orientation of the graphite layers can increase the thermal conductivity of the graphite laminate along the plane to values ​​equal to or even greater than the thermal conductivity of pure copper, while the density remains only a fraction of the density of pure copper. In addition, oriented laminate also exhibits increased strength compared to non-oriented laminate.

[0082] Surprisingly, by using a graphite-based heat dissipating material, it is possible to reduce the support coefficient of the frame assembly, to actually completely eliminate the cantilever element, while providing the necessary mechanical support and effective heat dissipation.

[0083] Also included is a method of manufacturing a frame assembly for an image display device. The method includes providing the display panel assembly, heat dissipating material, structure skeleton, and at least one light source such as a light emitting diode. The method includes placing the heat dissipating material so that it is in thermal contact with the light source, more preferably so that it is near the light source and between the light source and the skeleton of the structure. The heat dissipating material is preferably substantially open or exposed opposite the light source. The light source is positioned to improve the image presentation on the display panel assembly.

[0084] It is understood that both the above general description and the following detailed description provide embodiments of the invention and are intended to provide a view or structure, an understanding of the nature and nature of the invention as claimed. The accompanying drawings have been included to further understand the invention and are incorporated and form part of the description. These drawings show various embodiments of the invention and together with the description serve to describe the principles and operation of the invention.

Brief Description of the Drawings [0085] Fig. 1 is a perspective view of components of a backlit LCD device according to the present invention, comprising LEDs, reflective material, heat dissipating material, and a support element.

[0086] Fig. 2 is an exploded view in cross section of the backlight LCD device of Fig. 1.

[0087] Fig. 3 is a cross-sectional view of the backlight LCD device of Fig.

1.

[0088] Fig. 4 is a side perspective view of the components of a side-illuminated LCD device according to the present invention, comprising LEDs mounted on the printed circuit board, reflective material, heat dissipating material, light diffusing optical elements and a support element.

[0089] Fig. 5 is an exploded view in cross section of the side-lit LCD device of Fig. 4.

[00890] Fig. 6 is a cross-sectional view of the LCD device with side illumination z

Fig. 4.

[0091] Fig. 7 is a cross-sectional view of an alternative embodiment of a side-lit LCD device according to the invention.

[0092] Fig. 8 is a cross-sectional view of another alternative embodiment of a side-lit LCD device according to the invention.

[0093] Fig. 9 is a front view of the image display device made according to the present invention.

[0094] Fig. 10 is an exploded side perspective view of an embodiment of an image display device made according to the present invention.

[0095] Fig. 11 is a rear view of a skeleton structure made in accordance with the present invention.

Detailed Description of Preferred Embodiments [0096] Referring generally to Figs. 1-3, the backlight LCD display device shown is indicated by the number 10. The device 10 includes a series of world sources, such as LED 20, mounted to face image display panel page (not shown). The device 10 further comprises a heat dissipating material 30 formed from sheets of compressed particles of detached graphite. The heat dissipating material 30 is operably contacted with the LEDs 20 so that the heat generated by the LEDs 20 is transferred to the heat dissipating material 30. In addition, the LCD device 10 may also include a bracket 40 such that the support factor of the device 10 is less than about 375 mm-W / m ° K. More preferably, the support element 40 provides a support factor of the device 10 with a value less than about 150 mm-W / m ° K. As described above, however, in the most preferred embodiment of the present invention, the support coefficient of the device 10 is 0 mm-W / m ° K, which means that the LCD device 10 has no support 40. Reflective material 50 can be placed between the diodes LED 20 to facilitate even distribution of light from the LEDs 20.

[0097] Referring to Figs. 4-6, the side-mounted LCD device shown is indicated by 100. The device 100 includes a series of light sources such as LEDs 120 mounted along at least part of the perimeter of the device 100; optical elements for light scattering, such as optical fiber 170 supporting in directing light from LED 120 to the image display panel (not shown). The apparatus 100 further includes heat dissipation material 130 formed from one or more sheets of compressed particles of detached graphite. The heat dissipation material 130 operably contacts the LEDs 20 so that the heat generated by the LEDs 20 is transferred to the heat dissipation material 30. However, due to the arrangement of the LEDs 120 around the periphery of the LCD device 100, the functional thermal contact between the heat dissipation material 130 and the LEDs 120 is provided via thermal switches 135.

[0098] The thermal connectors 135 can be made of any material capable of creating thermal contact between the LEDs 120 and the heat dissipation material 130. Preferably, the thermal connectors 135 are also made of compressed particles of detached graphite, like the heat dissipation material 130. In fact, in a particularly preferred embodiment, the heat dissipation material 130 is formed to have thermal connectors 135 integrally formed therein (as shown in Fig. 7). In other words, the heat dissipating material 130 may have sections inclined at an angle of approximately 90 ° thereto, thereby forming thermal connectors 135.

[0099] In an alternative embodiment, the printed circuit boards PCB 160 on which the LEDs 120 are mounted can be extended and bent at an angle of 90 ° to achieve a thermal connection between the LEDs 120 and the heat dissipation material 130. As noted above, the PCB 160 printed circuit boards on which LED 120 is normally mounted are the ordinary metal core of a PCB; therefore, the metal core of the printed circuit board 160 can be extended and bent at the right angle to provide a thermal connection between the LEDs 120 and the heat dissipation material 130, as shown in Fig. 8. Alternatively, PCB 160 circuits can be made as so-called PCB flexible printed circuit with LEDs mounted on them, with PCB 160 printed circuit attached or otherwise attached directly to the heat dissipation material 130. The flexible circuit material from which the PCB160 is formed may be polyamide, polyester, liquid crystal polymer (LCP) , etc. and it may have multiple thermal conduction paths running through the thin flexible PCB 160 to heat dissipation material 130 to keep the thermal resistance between them as low as possible. An adhesive may be used to attach the PCB 160 to the heat dissipation material 130.

[0100] The LCD device with lateral backlight 100 may also include a bracket 140 such that the support factor of the device 100 is less than about 375 mmW / m ° K. More preferably, the support element 140 provides a device support factor of 100 less than 150 mm-W / m ° K. In the most preferred embodiment of the present invention, the support factor of the device 100 is 0 mm-W / m ° K, which means that the LCD device 100 does not contain any support element 140. In addition, the reflective material 150 can be positioned around the LEDs 120 or downstream of the optical fiber 170 to facilitate even distribution of the light of the LEDs 120.

[0101] Referring to Figs. 9-11 (directed to LCD backlight devices 10, although the concepts may also be applicable to LCS backlight devices), the backlight image display device 10 includes an image display panel 12 for displaying the image 14, the frame assembly 18 and the heat dissipation material 30 operably coupled to the frame assembly 18 and disposed on the opposite side of the image display panel 12. The frame assembly 18 may include a structure skeleton 17, which may be called a peripheral structure skeleton 17, supporting the image display panel 12 and a plurality of LEDs 20 supported by the structure skeleton 17. The structure skeleton 17 has a height 22, width 24, and an opening 26 essentially connecting the height 22 and width 24. The heat dissipating material 30 may generally include a height 22 and a width 24 of the skeleton of structure 17. Alternatively, the heat dissipation material 30 may consist of a plurality of smaller pieces of heat dissipation material, which together may include a height 22 and a width 24 of the skeleton of structure 17.

[0102] The LEDs can be substantially aligned in the skeleton of the structure 17, and can partially overlap the opening 26. This alignment facilitates the heat dissipation material 30 to dissipate the heat generated by the LEDs 20. The LEDs 20 can be located inside the opening 26 of the skeleton of the structure 17.

[0103] In a preferred embodiment, the heat dissipation material 30 consists of compressed particles of detached graphite, while the skeleton of structure 17 is composed of steel.

[0104] The LCD image display panel 12 may include a side 13 of the image display in which the image 14 is displayed. The side 13 of the image display may be visible through the housing 11 of the image display device 10, as best shown in Fig. 9.

[0105] The heat dissipation material 30 may also include an adhesive and / or thermal joint material (not shown) disposed on the surface facing the LEDs 20. Such adhesive, e.g. pressure sensitive adhesive, may facilitate good thermal contact between the LEDs 20 and heat dissipation material 30 to improve heat dissipation in the device 10.

[0106] In addition, as shown in Fig. 10, transverse brackets 34 may be attached to the skeleton of structure 17. The transverse brackets 34 may be used to strengthen and stabilize the skeleton of structure 17 and the entire image display device 10. The cross brackets 34 preferably support the LEDs 20 and attach the LEDs 20 to the skeleton of structure 17, regardless of whether the LEDs 20 are mounted on printed circuit boards. A plurality of cross beams 34 can be used to further stiffen the frame of the structure 17 and the LCD device 10. The connection between the cross beams 34 and the skeleton of the structure 17 may include known mechanical fasteners such as screws, bolts, rivets, paper clips etc. (not shown).

[0107] The directional elements 36 can also be used to give the structural skeleton 17 further rigidity. The directional elements 36 preferably include the skeleton of structure 17 and may engage the orifice 28 with the skeleton of structure 17. The directional elements 36 may be assembled individually or in combination of steel, aluminum and plastic. The directional elements 36 can be used to secure the housing 11 and secure the housing 11 as a component of the display device 10. The directional elements 36 can support many other electronic components, such as printed circuit boards, to provide control for the LCD 10. The directional elements 36 can completely cut the skeleton of structure 17 as shown in Fig. 10, or alternatively extend partially across the opening 26.

[0108] The skeleton of the structure 17 can be made as a single element pressed and bent or folded into shape. Alternatively, the skeleton of the structure 17 can be made of many components and mechanically assembled by means of rivets, welds, Tox-lok® mechanical joints, etc. thereby eliminating the need to frame the structure of the structure 17 with a single sheet of material.

[0109] Thus, by means of the practice of the present invention, a display panel, such as a liquid crystal display, etc., can be built with a reduced need to use cantilever components, resulting in significant savings in both weight and cost of the display panel, while maintaining or increasing heat dissipation from components that produce them inside the image display device.