Patent Publication Number: US-2006011304-A1

Title: Apparatus and method of attaching optical films

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the priority benefit of Taiwan application serial no. 93121098, filed Jul. 15, 2004.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an apparatus and method of attaching optical films. More particularly, the present invention relates to a polarizer attaching device and method that can prevent or reduce the formation of bubbles.  
      2. Description of the Related Art  
      The rapid proliferation of multimedia system comes about as a result of the progress in the manufacturing of semiconductor devices and monitors. In the past, the cathode ray tubes (CRT) are the principal display devices in the market because of its superb display quality and moderate pricing. However, due to the bulkiness of CRT and the environmental concerns such as the production of hazardous radiation and consumption of too much power, CRT has been gradually phased out and replaced by more environ-friendly display devices with a compact, slim and light body. One such display device is the liquid crystal display (LCD). Because of the high display quality, superior spatial utilization, low power consumption and radiation free operation, LCD has become one of the mainstream products in the market.  
      A conventional thin film transistor liquid crystal display (TFT-LCD) typically comprises a thin film transistor (TFT) array, a color filter, a liquid crystal layer between the TFT array and the color filer and at least a polarizer attached to the TFT array and/or the color filter. The method of attaching a polarizer to a substrate includes stationing the substrate on a fixed location and attaching a sheet of polarizer onto the transparent substrate manually. Consequently, the conventional polarizer attachment method is slow and prone to have human attachment errors. In other words, the attachment quality of the polarizer is poor and the production yield is low.  
      At present, the process of attaching polarizers to substrates is mechanized to produce effective and accurately attached polarizers. However, the process of lifting off the protective film covering the polarizer or any residual stress in the multi-layered polarizer due to cutting often leads to a slight warping of the polarizer close to the edges. With a warped polarizer, the edges of the polarizer are often attached to the substrate before other areas in the process of attachment so that bubbles are trapped inside the finished products.  
      One effective measure to avoid the problems caused by a warped polarizer is to set up an inspection criterion and sort out the ones that do not meet the standard. Alternatively, the machines carrying out the polarizer attachment can be adjusted to provide some compensation. However, even the maximum range of adjustment is effective only for those that falls within the standard specification. In fact, machine adjustments simply cannot cater for the warping inside the polarizer due to stress arising from other physical phenomena.  
     SUMMARY OF THE INVENTION  
      The present invention is directed to provide an optical film attaching apparatus capable of preventing the edges of an optical film from attaching to a substrate ahead of time, such that fewer bubbles are generated.  
      The present invention is directed to provide a method of attaching optical films capable of delaying the warped edges of an optical film attaching to a substrate so that fewer bubbles are trapped.  
      The present invention is directed to provide a method of attaching optical films to a substrate such that fewer bubbles are trapped between the optical film and the substrate. In addition, bubbles preferentially trapped in one area due to a front adsorption failure resulting from material thickness variation or difference in material properties occur less frequently.  
      As embodied and broadly described herein, the invention provides an optical film attaching apparatus. The optical film attaching apparatus comprises a substrate conveyer, an optical film adsorber, an attaching device and a stop element. The substrate conveyer has a carrying surface for carrying and conveying a substrate. The optical film adsorber carries an optical film and has an adsorbing surface facing the substrate conveyer. The attaching device is disposed on the conveying path of the substrate for attaching the optical film to the substrate. The stop element is disposed between the carrying surface of the substrate conveyer and the adsorbing surface of the optical film adsorber and between the optical film adsorber and the attaching device to stop the edges of the optical film from attaching to the substrate ahead of time.  
      The present invention further provides a method of attaching optical films. The method comprises transporting substrates using a substrate conveyer and carrying optical films on an optical film adsorber. Thereafter, using an attaching device disposed on the conveying path of the substrates, the optical film is attached to the substrate following the direction of conveyance of the substrate. A stop element is disposed between the optical film adsorber and the attaching device to stop the edges of the optical film from attaching to the substrate ahead of time.  
      In the present invention, a stop element (similar to an idler) is disposed on the adsorbing element on each side of the optical film adsorber. When the edges of the optical film warp up, the stop element is able to delay the warped section on each side of the optical film from attaching to the substrate ahead of time. Ultimately, the number of bubbles trapped between the optical film and the substrate is minimized.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
       FIGS. 1A through 1C  are schematic cross-sectional views showing consecutive snapshot of an operating optical film attaching apparatus in the process of attaching an optical film on a substrate according to one preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
       FIGS. 1A through 1C  are schematic cross-sectional views showing consecutive snapshot of an operating optical film attaching apparatus in the process of attaching an optical film on a substrate according to one preferred embodiment of the present invention. As shown in  FIG. 1A , the optical film attaching apparatus  100  comprises a substrate conveyer  102 , an optical film adsorber  110 , an attaching device  120   a  and  120   b  and a stop element  130 . The optical film attaching apparatus  100  is a polarizer attaching device or a device for attaching other types of optical films, for example. The substrate conveyer  102  has a carrying surface  104  for carrying and transporting substrates  10 . The optical film adsorber  110  carries an optical film  20  and is a polarizer or other types of optical films, for example. Furthermore, the optical film adsorber  110  has an adsorbing surface  112  facing the substrate conveyer  102 . The optical film adsorber  110  may further comprise a plurality of adsorption elements  116  disposed on the adsorbing surface  112 . The attaching device  120   a  and  120   b  is disposed along the conveying path of the substrates  10  so that the optical film  20  can be attached to the substrate  10 . The attaching device  120   a  and  120   b  is a group of driving rollers specially designed for attaching optical films. The stop element  130  is disposed between the carrying surface  104  and the adsorbing surface  112  and between the optical film adsorber  110  and the attaching device  120   a  and  120   b  to stop the edges of the optical film  20  from attaching to the substrate  10  ahead of time.  
      In the present embodiment, the stop element  130  can have a plurality of different configurations. For example, the stop element  130  may comprise a plurality of idlers. If the stop element  130  includes only a single idler, the edges of the optical film  20  can be balanced so that the edges of the optical film  20  is prevented from attaching to the substrate  10  ahead of time. When two or more idlers are used in the stop element  130 , the idlers can be disposed along the edges of the optical film to reduce contact with the optical film  20  and prevent the attachment of optical film edges to the substrate  10  ahead of time. The stop element  130  can be fabricated using, for example, steel or other suitable materials. Furthermore, the surface of the stop element  130  is preferably fabricated using a non-sticky material because a protective film (not shown) is normally formed over the optical film  20 . The protective film has to be removed to expose an underlying plastic layer before attaching to the substrate  10 . To prevent the plastic layer on the optical film  20  from adhering to the stop element  130 , a detaching film or some other material is disposed on the surface of the stop element  130 .  
      The substrate conveyer  102  in the present invention is a roller conveyer or other types of conveyers such as a chain conveyer, for example. In addition, a dust-proof cover  106  may also be disposed between the optical film adsorber  110  and the substrate conveyer  102  to prevent particles from depositing on the optical film  20  underneath the substrate conveyer  102  and affecting subsequent display quality of the optical film. Furthermore, the adsorbing element  116  can be an adsorption pad for adsorbing the optical film  20  but also permits the optical film  20  to move along with the attaching device  120   a  and  120   b . Because the optical film  20  adheres to the adsorbing elements  116  in the first part of the process for attaching the optical film  20  to the substrate  10  through the attaching device  120   a  and  120   b , warped sections of the optical film  20  are not attached to the substrate  10 .  
      As shown in  FIG. 1B , the edge of the optical film  20  detaches from the adsorbing elements  116  of the optical film adsorber  110 . Meanwhile, peeling the protective layer (not shown) from the optical film produces a warping edge  22  in the optical film  20 .  
      The warped edge  22  of the optical film  20  will attach to the substrate  10  ahead of time to trap bubbles between the substrate  10  and the optical film  20  if no stop element is set up to restrain the edge  22  already detached from the adsorbing elements  116 . As shown in  FIG. 1C , a stop element  130  is set up in the present invention to prevent an early attachment of the warped edge  22  of the optical film  20  to the substrate  10  thereby reducing the quantity of trapped bubbles.  
      In summary, one major aspect of the present invention is the disposition of a stop element between the optical film adsorber and the attaching device. When the edges of the optical film warp up, the stop element is able to prevent the warped section on each side of the optical film from attaching to the substrate ahead of time. Ultimately, the quantity of bubbles trapped between the optical film and the substrate is minimized. Furthermore, aside from attaching polarizers, the film attaching apparatus of the present invention can also be used to attach other kinds of optical films.  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.