Abstract:
A system and method for fabricating multi-layer optical compensators which includes a rigid or flexible planar guide member having reference lines thereon for aiding in alignment of successive layers and further having a vacuum producing capability which stabilizes the compensator when it is processed, along with the guide member, through a roller machine.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to optical films, and more particularly relates to bonding of several optical films, and even more particularly relates to methods and apparatuses for maintaining critical parameters of angular alignment between several bonded optical films. 
     BACKGROUND OF THE INVENTION 
     In the past, optical films have been bonded together during fabrication of liquid crystal displays and other optical devices. Avionics engineers have routinely endeavored to utilize predetermined portions of previously manufactured optical film sheets because of the preferred nature of the portion in comparison to other portions of the optical film. When multiple optical films are used, in which each film has a predetermined preferred portion, it is often desirable to attempt to align these preferred portions during the process of bonding the optical films together. One approach has been to use a pen or other marker to encircle the preferred portion of each film and then attempt to manually align the encircled portions by a simple visual alignment of one encircling line on a first optical film with another encircling line on a second optical film. 
     While this approach has benefits of simplicity and ease of use, it also has significant drawbacks. A significant problem of this type of approach is that it often fails to provide sufficient angular alignment of the critical axes of the various films as is often required by the most rigorous performance specifications. 
     Consequently, there exists a need for improved methods and apparatuses for aligning preferred portions of optical films in a multi-film bonding process. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide high performance multi-film optical components. 
     It is a feature of the present invention to utilize a grid plate reference to aid in angular alignment of films. 
     It is an advantage of the present invention to achieve more precise angular alignment of the various optical axes of numerous films with respect to their predetermined preferred portions. 
     It is another advantage of the present invention to reduce any gradual accumulation of angular alignment errors caused by basing each successive film alignment upon placement with respect to a potentially already misaligned film. 
     It is another feature to use a vacuum chuck to maintain angular alignment of such films. 
     It is another advantage of the present invention to provide stability of the films during the rollering process often used in bonding multiple films. 
     The present invention is an apparatus and method for bonding multiple optical films which are designed to satisfy the aforementioned needs, provide the previously stated objects, include the above-listed features and achieve the already articulated advantages. The present invention is carried out in an “angular misalignment-less” manner in a sense that angular misalignment of the films has been greatly reduced. 
     Accordingly, the present invention is a method and apparatus which includes an indexed grid plate and in an alternate embodiment, a vacuum chuck, both for cooperation with optical films during a rollering segment of the film bonding process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be more fully understood by reading the following description of the preferred embodiments of the invention, in conjunction with the appended drawings wherein: 
     FIG. 1 is a simplified perspective drawing of the vacuum guide of the present invention, disposed in a roller machine with an optical film disposed thereon. 
     FIG. 2 is a more detailed view of the vacuum guide of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Now referring to the drawings, wherein like numerals refer to like matter throughout, there is shown in FIG. 1, a vacuum grid plate  102 , of the present invention. Vacuum grid plate  102  may be made of any suitable material which provides sufficient rigidity and stability, but it is believed that hard-coated aluminum, stainless steel, or equivalent may be preferred when a clean room is required. Vacuum grid plate  102  has a grid plate top  104  with milled or chemically etched reference grooves therein to aid in alignment of films. Horizontal grid lines  116  and vertical grid lines  118  are representative of such reference grooves. The depth of such etched or milled reference grooves may typically be 0.010 inch or as desired and may be etched or milled, using well-known techniques. The terms horizontal and vertical are used herein to aid in understanding; however, it should be readily understood that any pattern of reference lines may be used. It is believed that orthogonal horizontal and vertical lines with some identification scheme, such as numbering or lettering is a preferred embodiment. Vacuum hose connection edge  108  between grid plate top  104  and grid plate bottom  106  is shown having first vacuum port  110 , center vacuum port  112 , and second vacuum port  114  therein. The thickness of vacuum grid plate  102  across vacuum hose connection edge  108  is a matter of design choice but may be {fraction (1/2-3/4)} inch to facilitate necessary boring of passages through vacuum grid plate  102 . These ports are for connecting vacuum hoses  126  with vacuum source  124 . Vacuum grid plate  102  is shown having an optical film  101  thereon and being disposed between top roller  120  and bottom roller  122 . Optical film  101  may be any type of optical film; however, it is believed that the beneficial aspects of precision alignment offered by the present invention may be most advantageous when optical film  101  is an optical retardation film (optical compensator) or polarizing film. FIG. 1 shows an orientation of vacuum grid plate  102  and top roller  120  representing a middle point during a rollering process where optical film  101  is applied to another film disposed immediately below it. The process of rollering of optical films together and onto substrates, as well as the rollering machines deployed therein, are well known in the art. However, the use of a ruled grid plate is believed to be novel, as well as the use of vacuum stabilization in optical film bonding is also believed to be novel. 
     A more thorough understanding of the present invention may be achieved by now referring to FIG. 2, which gives a more detailed view of the vacuum grid plate  102  of FIG.  1 . Vacuum grid plate  102  is shown having on grid plate top  104  a vacuum channel system  202 , which may be voids in vacuum grid plate  102 . These voids or vacuum grooves are separate and distinct from the reference grooves and horizontal grid lines  116  and vertical grid lines  118 , and may have various dimensions, depending upon the details of the lamination process. However, it is believed that vacuum grooves with a depth of 0.032 and a width of 0.062 may be preferred. The length of vacuum grooves is also a matter of design choice which may vary, depending upon various factors, including size of any glass substrate being fed through top roller  120  and bottom roller  122 , as well as the amount of vacuum applied and others. The process used to create the vacuum grooves is dependent upon the dimensions desired, but either milling or chemical etching are contemplated. The vacuum grooves and reference grooves may be separated by a dead zone (an area without any grooves therein) to minimize any vacuum leakage. First vacuum groove pattern  206  is shown coupled to first vacuum port  110  by a first vacuum air passage  220 , which may be an air passage bored through vacuum grid plate  102  and coupled to first vacuum groove pattern  206 . Similarly, center vacuum groove pattern  208  and second vacuum groove pattern  204  are coupled to center vacuum port  112  and second vacuum port  114 , respectively through center vacuum air passage  222  and second vacuum air passage  224 , respectively. The dimensions of first vacuum air passage  220  are a matter of design choice; however, a diameter of 0.125 inches may be preferred. 
     In operation, and now referring to FIGS. 1 and 2, the present invention may provide its benefits as follows: A first optical film is disposed on grid plate top  104  and is aligned with one of said horizontal grid lines  116  and/or one of said vertical grid lines  118 . The film and vacuum grid plate  102  is inserted between top roller  120  and bottom roller  122 , which clamp down thereon. A second film, on a rigid substrate, is then disposed on vacuum grid plate  102  and is aligned with reference being made to horizontal grid lines  116  and vertical grid lines  118 . The alignment of the second film to the first film is, therefore, done indirectly through the horizontal grid lines  116  and the vertical grid lines  118 . The axes being aligned will depend upon the type of films being bonded. However, when polarizers are being bonded, then absorption axes are important, and when optical compensators are used, then the optical axes and rub directions are important to be maintained in angular alignment. Once the alignment is completed, then a vacuum is applied to one or more of first vacuum groove pattern  206 , center vacuum groove pattern  208  and second vacuum groove pattern  204 , by applying a vacuum to their respective ports. The amount of vacuum pressure is a matter of designer&#39;s choice based upon the particular details of the entire lamination and optical film system involved; however, a pressure of &lt;14 PSIA may be preferred. A vacuum is then sustained in all portions of vacuum channel system  202  when the substrate is placed thereon. This vacuum creates an increased pressure characteristic between the substrate and the grid plate top  104 . This increased pressure results in a higher friction characteristic between the substrate and grid plate top  104 , thereby stabilizing the substrate from motion with respect to vacuum grid plate  102  during the rollering process. In a preferred embodiment, first vacuum groove pattern  206 , center vacuum groove pattern  208 , and second vacuum groove pattern  204  are independent groove systems allowing for independent and selectable application of vacuum pressure across various portions of vacuum channel system  202 . Other methods of limiting unwanted motion between the grid plate and an object placed thereon are also contemplated, such as adhesives, clamps etc. The combination of the first film, the second film and its associated temporary glass substrate and the vacuum grid plate  102  are passed (without stopping at intermediate points) through top roller  120  and bottom roller  122 . After the first film and the second film are so bonded to each other, then the temporary glass substrate of the second film may be removed, using well-known techniques, such as the use of a release machine. This process is repeated for each successive film to be laminated to the stack of optical films. 
     Additionally, the optical films as discussed herein may include one or more o-plate compensators, a-plate compensators, c-plate compensators, or other birefringent materials. 
     It is thought that the method and apparatus of the present invention will be understood from the foregoing description, and that it will be apparent that various changes may be made in the form, construct steps and arrangement of the parts and steps thereof, without departing from the spirit and scope of the invention or sacrificing all of their material advantages. The form herein described is merely a preferred exemplary embodiment thereof.