Abstract:
A method and apparatus for the bonding of one or more material layers to a display panel which yields a resulting bonded assembly which is transparent and substantially free of optical defects such as entrapped dirt and air bubbles. During the bonding process of the present disclosure, a moving dispensing probe, or needle, dispenses a liquid bonding material into an air gap between the surfaces to be bonded in a manner which continuously touches (wets) each surface simultaneously. By simultaneously wetting each surface, and by dispensing the liquid bonding material in a predetermined pattern between the surfaces, the introduction of entrapped dirt and the formation of air bubbles is prevented as the two mating surfaces are subsequently pressed together and the adhesive is cured.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is the United States National Stage under 35 U.S.C. 371 of International Application Serial No. PCT/US2009/048618, having an International Filing Date of Jun. 25, 2009. The present application is related to, and claims priority from, U.S. Provisional Patent Application Ser. No. 61/076,456 filed on Jun. 27, 2008, and U.S. Provisional Patent Application Ser. No. 61/114,682 filed on Nov. 14, 2008, both of which are herein incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention is generally related to methods and apparatus for the assembly of display panels such as liquid crystal display (LCD) devices, and in particular, to a method and apparatus for bonding one or more layers of glass, plastic, or other material of appropriate optical properties to a display module. 
     Display panels, such as liquid crystal display modules, are widely used in all parts of modern technology, including such areas as consumer electronics, computer equipment, industrial machinery controls, automobiles and aerospace applications. These display panels may include one or more layers of material disposed over the raw liquid crystal display module. For example, a protective overlay is most often desired for protection of the raw liquid crystal display module from mechanical and environmental forces. Raw display panes such as LCD modules, for example, usually have no protection for the top polarizer layer and the underlying glass layers. The protective overlay can provide additional features such as support for anti-reflective coatings which can enhance the display visibility under varying lighting conditions. Other layers of material which may be disposed over the raw liquid crystal display module include touch-sensitive panels, optical filers, heaters, and EMI shields. 
     Since this bonding process is for visible displays, the bonding layer which secures each layer of material must be transparent and completely free of optical defects such as entrapped dirt and air bubbles. Freedom from entrapped air bubbles are a particular advantage of the invention. Using traditional bonding techniques and apparatus, a bonding material such as an adhesive is utilized to secure a layer such as a protective overlay to a display module is applied in a bead first to only one surface, either the top surface of the display module or the underside of the protective overlay, followed by pressing another, un-wetted surface against the bead, and is likely to trap air bubbles when the second un-wetted surface first touches the bead of bonding material. 
     Accordingly, it would be advantageous to provide a method and apparatus for the bonding of one or more material layers to a display module surface which yields a resulting assembly which is transparent and completely free of optical defects such as entrapped dirt and air bubbles. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly stated, the present disclosure provides a method and apparatus for the bonding of one or more material layers to an exposed surface of a display module such as an LCD assembly, to produce a resulting assembly which is transparent and substantially free of optical defects such as entrapped dirt and air bubbles. During the bonding process of the present disclosure, a moving dispensing probe, or needle, dispenses a liquid bonding material between the exposed surface of the display module and the material to be bonded thereto over a pattern in a manner which continuously touches (wets) both the material layer and the display module surface simultaneously. 
     By simultaneously wetting both surfaces, and by dispensing the liquid bonding material in a predetermined pattern between the surfaces, the introduction of entrapped dirt and the formation of air bubbles is prevented as the two mating surfaces are subsequently pressed together. 
     The foregoing features, and advantages set forth in the present disclosure as well as presently preferred embodiments will become more apparent from the reading of the following description in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the accompanying drawings which form part of the specification: 
         FIG. 1  is cross-section of an assembled LCD and a material layer forming a protective overlay assembled by methods of the present disclosure; 
         FIG. 2  is a perspective view of a portion of the assembled LCD and the protective overlay of  FIG. 1 ; 
         FIG. 3  is an enlarged portion of the cross-section of  FIG. 1 ; 
         FIG. 4  is a perspective illustration of a liquid bonding material dispenser of the present disclosure; 
         FIGS. 5A and 5B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and a material layer forming a protective overlay prior to the application of a bonding material; 
         FIGS. 6A and 6B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an adhesive dispenser, the assembled LCD, and the material layer forming a protective overlay as the bonding material is initially dispensed; 
         FIGS. 7A and 7B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay as the bonding material is dispensed along a first segment; 
         FIGS. 8A and 8B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay as the bonding material is dispensed along a second segment; 
         FIGS. 9A and 9B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay as the bonding material dispenser is withdrawn from between the layers; 
         FIGS. 10A and 10B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay as the bonding material dispenser is repositioned between the layers; 
         FIGS. 11A and 11B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay as the bonding material is dispensed along a third segment; 
         FIGS. 12A and 12B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay as the bonding material is dispensed along a fourth segment 
         FIGS. 13A and 13B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay as the bonding material dispenser is again withdrawn from between the layers; 
         FIGS. 14A and 14B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay as the bonding material dispenser is repositioned for dispensing adhesive to the central region; 
         FIGS. 15A and 15B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay as the bonding material dispenser applies the bonding material to the central region between the first through fourth previously applied segments; 
         FIGS. 16A and 16B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay upon completion of the dispensation of the bonding material; 
         FIGS. 17A and 17B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay as pressure is applied to uniformly distribute the bonding material between the layers; 
         FIGS. 18A and 18B  illustrate a side view and a top view (looking through the transparent material layer) of the relative positions of an bonding material dispenser, the assembled LCD, and the material layer forming a protective overlay after application of pressure has fully dispensed the bonding material between the layers; and 
         FIG. 19  is a representation of an exemplary assembly line configuration for assembling and bonding LCDs with one or more material layers according to the present disclosure. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. It is to be understood that the drawings are for illustrating the concepts set forth in the present disclosure and are not to scale. 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. 
     DETAILED DESCRIPTION 
     The following detailed description illustrates the invention by way of example and not by way of limitation. The description enables one skilled in the art to make and use the present disclosure, and describes several embodiments, adaptations, variations, alternatives, and uses of the present disclosure, including what is presently believed to be the best mode of carrying out the present disclosure. Various aspects of the present disclosure are set forth and described in association with an LCD module, but those skilled in the art will recognize the wider range of application for the methods and apparatus set forth herein, and that such applications are not limited to LCD modules, but rather, may be utilized in many environments wherein one or more material layers are required to be bonded to a display panel or other surface in an optically transparent and uniform manner. For example, the method and apparatus of the present invention may be utilized to provide bonding of one or more material layers such as touch panels, optical filters, heaters, EMI shields, or protective overlays to the surfaces of display modules which utilize plasma technology, vacuum fluorescent technology (CRT&#39;s), and LED technology as well as LCD modules. 
     Turning to the figures, and to  FIGS. 1-3  in particular, a bonded assembly  100  manufactured according to the methods of the present disclosure is shown generally. The bonded assembly  100  consists of an assembled display panel  102 , such as an LCD module having an active display or LCD region  104  onto which has been bonded an one or more layers of material  106 , such as a touch panel, an optical filter, a heater, an EMI shield, or an optically transparent protective overlay. The bonded assembly  100  may optionally further include a framework  108  surrounding the perimeter of the LCD module  102 , as well as other device frames or supporting structures as required for the particular application in which the bonded assembly  100  is to be utilized. The material  106  may overlap a portion of the framework  108  to ensure a uniformly smooth upper surface to the bonded assembly  100 . Those of ordinary skill will recognize that the characteristics of the material layers may be selected according to the application requirements of the bonded assembly  100 , and may include desired optical properties, material strengths, glare or glint optical properties, and scratch resistant properties as required. One suitable material which may be utilized is an optical glass. As best seen in  FIGS. 1 and 3 , the material layers  106  may be bonded directly to the surface of the LCD module  102  over the active LCD region  104 , or optionally to the surface of another material layer (not shown) previously bonded to the LCD module  102 , by a layer of substantially uniform bonding material  110  which is free from entrapped air bubbles, unbonded regions, and contaminates. 
     To ensure the bonding material  110  is applied uniformly between the surfaces to be bonded, an bonding material dispenser  200 , such as shown in  FIG. 4  is utilized. The bonding material dispenser  200  as shown consists generally of an elongated and flattened neck  202  extending from a base coupling  204 . The base coupling is configured with a suitable adapter  206  to be operatively connected to a dispenser (not shown) for a supply of liquid bonding material  110  (adhesive) which is dispensed to the base coupling  204  at a controlled rate of flow. The bonding material  110  flows through an internal passage  208  within the flattened neck to a dispensing tip  210 . The dispensing tip  210  of the flattened neck includes dispensing openings  212 A and  212 B on both an upper and lower surface, which enable the flow of bonding material  110  to disperse from the internal passage  208  and out the dispensing tip  210  in two directions simultaneously. Those skilled in the art will recognize that the specific configuration of the bonding material dispenser  200  may be varied from that shown in  FIG. 4 , depending upon the particular application in which it is to be utilized. For example, the neck portion  202  may have different geometry, and the dispensing tip  210  may include a varied number of dispensing openings  212 , positioned as required to achieve the desired flow rate and flow uniformity of the bonding material  110  as it is dispensed there from. 
     During a bonding operation, the material layer  106  to be bonded to the LCD module  102  is positioned and held in close proximity to the surface  104  of the LCD module or to a previously bonded material layer (not shown), but is separated there from by a uniform air gap  300 , as shown in  FIGS. 5A and 5B . Next, the elongated and flattened neck portion  202  of the bonding material dispenser  200  is moved into the air gap  300  between the material layer  106  to be bonded and the surface  104  of the LCD module  102  (or previously bonded material layer) to an initial predetermined position at which the bonding material  110  will be initially introduced. The dispensing of the bonding material  110  is controlled in a way that allows beads of bonding material  110  emerging from the dispensing tip  210  to touch each of the opposing mating surfaces simultaneously and continuously as the dispensing tip  210  is subsequently moved in a predetermined pattern between the surfaces. Preferably, the predetermined pattern is selected to ensure that the proper amount of bonding material  110  is dispensed between the surfaces, and that the bonding material  110  uniformly disperses without trapping air bubbles or excessive overflow. Those of ordinary skill will recognize that while  FIGS. 5A through 18B  illustrate the positioning and placement of a material layer  106 , such as a protective overlay, over an LCD module  102  from above, the process of the present disclosure may be carried out in different orientations as may be required to facilitate assembly. For example, the process may be implemented by positioning the LCD module  102  above the material layer  106 , and lowering it downward thereon during the bonding procedure. 
     In one embodiment of the present disclosure, a predetermined pattern for dispensing the bonding material  110  between the surfaces, such as between a protective overlay material layer  106  and the LCD surface  104  is illustrated in  FIGS. 6A through 16B . The predetermined pattern consists generally of four linear segments S 1 , S 2 , S 3 , and S 4  of bonding material applied between the layers  106 ,  104  to form a pair of inwardly directed chevrons ( FIG. 13B ). A fifth segment S 5  of bonding material  110  is then applied as shown in  FIG. 15B  to connect the apexes of each chevron across the central region surfaces, after which the bonding material dispenser  200  is withdrawn from between the layers ( FIG. 16B ). 
     Once the bonding material  110  has been uniformly applied between the surfaces of the material layers  104 ,  106  in the predetermined pattern, and the bonding material dispenser  200  withdrawn, a uniform compressive force F is applied to the assembled layers, as shown in  FIGS. 16A and 17A  to urge the material layer  106  to be bonded towards the surface  104  of the LCD module  102 . As the compressive force F is applied ( FIGS. 17A and 17B ), the bonding material  110  flows from the dispenses segments S 1 -S 5  between the layers  104 ,  106  and uniformly disperses there between ( FIGS. 18A and 18B ). Wetting and capillary forces as well as the precisely calculated amount of bonding material  110  that is utilized in the predetermined pattern, and the pressed alignment, ensure an uniform bonding layer between the LCD display  102  and each material layer  106 . Subsequent hardening or curing of the bonding material  110  by any suitable means, such as a high intensity ultraviolet light source, finalizes the process of bonding the material layer  106  to the surface  104  of the LCD module  102  or to the surface of a previously bonded material layer (not shown). 
     It will be recognized that the predetermined pattern in which the bonding material  110  is delivered between the layers to be bonded may be varied depending upon the various flow characteristics of the bonding material  110 , the size of the region to be bonded, and the desired thickness of the bond. 
     Those of ordinary skill in the art will further recognize that the bonding process of the present disclosure may be incorporated into an assembly line for the manufacture of the bonded display panels  100  or LCD assemblies, such as shown in  FIG. 19 . For example, as seen in  FIG. 19 , the apparatus for performing the bonding process of the present disclosure may be disposed at the juncture of an assembly line  400  which delivers individual LCD modules  102  and an assembly line  500  which delivers the material layers  106  to be bonded thereto, i.e., protective overlays. In one exemplary system, the protective overlays may be manufactured by an injection molding process (Box  502 ), receive one or more layers of a desired optical coating, such as by sputtering techniques (Box  504 ), which is then hardened (such as by UV light) (Box  506 ) prior to delivery to the bonding apparatus (Box  508 ) wherein they are joined with individual LCD modules  102 . The finished bonded assemblies  100  are then distributed to a quality control check station (Box  510 ), packing station, or subsequent step in a manufacture of a finished product. 
     The present disclosure can be embodied in-part in the form of computer-implemented processes and apparatuses for practicing those processes. The present disclosure can also be embodied in-part in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or an other computer readable storage medium, wherein, when the computer program code is loaded into, and executed by, an electronic device such as a computer, micro-processor or logic circuit, the device becomes an apparatus for practicing the present disclosure. 
     The present disclosure can also be embodied in-part in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the present disclosure. When implemented in a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits. 
     As various changes could be made in the above constructions without departing from the scope of the disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.