Abstract:
A method for the production marking of liquid crystal displays whereby the closure bar of the liquid crystal cell is produced and encoded by a screen printing process. Several coding techniques which minimize production interruptions are also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for the production marking of liquid crystal displays (LCD) whereby the closure bar of the liquid crystal cell is produced by the screen printing process. 
     2. Description of the Prior Art 
     Liquid crystal displays have typically been formed by sandwiching a liquid crystal material between transparent plates. A closure bar, formed by screen printing, has typically been used to seal the peripheral edges of the sandwich. Such a liquid crystal display is illustrated in U.S. Pat. No. 3,995,941 in which the closure bar is a low melting point glass, the disclosure of which is hereby incorporated by reference. 
     Liquid crystal displays have hitherto generally been marked by means of a lettering machine so that the week number and year of manufacture were printed on them. This lettering is necessary in order to ensure watch identification for customer warranty purposes. With a fairly large production volume, a plurality of lettering machines with a plurality of operators must be employed, otherwise a production bottleneck can result. 
     Recently it has been proposed to superimpose a production code in the photoresist process for the segmentation of the electrode layer. But this involves two difficulties: 
     (a) The exposure occurs by multiple process, so that a corresponding multiple pattern must be typed and produced once per week; 
     (b) Several weeks may elapse between electrode segmentation and further processing. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of this invention is to provide a novel method for the production marking of liquid crystal displays which obviates the above-described difficulties. 
     Another object of this invention is to develop a method whereby the step of production marking coincides approximately with the decisive step of the manufacturing process. 
     These and other objects of the present invention are achieved by providing the screen used to print the closure bar of a liquid crystal display with an information code relating to period of manufacture, so that the closure bar is marked with the same code during printing. 
     Compared to previous methods, the coding system according to this invention has the advantage that only a few patterns are printed per screen printing operation, and that in any event normal wear of the screen necessitates relatively frequent screen renewal, at which time it is advantageous to update the screen coding. Furthermore, experience shows that details of graphics and cell technology are subject to modifications at fairly short intervals, so that unmistakable identification is possible with a minimum of coding. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a view of a screen geometry with code projections representative of a production marking; 
     FIG. 2 is a detailed view of code projection openings in a screen for glass solder paste printing; 
     FIG. 3 is a table relating to the programming of the code projection openings of FIG. 1; and 
     FIG. 4 is a table relating to another programming embodiment for code projection openings. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1 thereof, a screen geometry 1 is provided for a closure bar 2a and 2b in which all the code cams projections 3a-3h and 4a-4b are initially open. (Open corresponds to binary `0`). The programming of the code is done by selective masking of specific code openings using masking paint. 
     To enable the week code to be marked, six bits are required in the dual binary system. Two bits, corresponding to a four year cycle, are generally sufficient for the year code. In a practical embodiment, it is advantageous for technological reasons to employ a specific week code. Therefore the code provided is not a straight dual binary code (2 n  code), but a code according to the table shown in FIG. 3. In the code shown in FIG. 3, the four least significant bits 3a, 3b, 3c and 3d, are changed consecutively, that is, one opening is closed after the other. The corresponding cycle covers approximately one month. &#34;Wo&#34; in FIG. 3 denotes the week number. The four most significant bits 3e, 3f, 3g, 3h, of the table shown in FIG. 3 represent the month of the year, and are coded as a dual binary code. After the expiration of the four week cycle represented by the least significant bits 3a, 3b, 3c, 3d, the monthly binary code 3e, 3f, 3g, 3h, is increased by one unit. This embodiment has the advantage that with a minimum of bits, only a few already programmed screens become unserviceable at the weekly exchange. On the average, the opening of previously closed code projections would only be necessary at one fifth of the week changes. Because this is technologically difficult, the screens already programmed are replaced in these cases if necessary. 
     FIG. 1 illustrates an embodiment wherein the weekly code 3a . . . 3h is applied along the one edge 2a of the closure bar, while the yearly code (dual binary code) 4a, 4b is arranged along the opposite edge 2b of the closure bar 1. This facilitates the reading of the entire code. Furthermore, projections 5 and 6 are used to define the starting points of weekly code 3a . . . 3h and yearly code 4a, 4b respectively. Projections 5 and 6 are designed to be twice as long as the projections 3 and 4 in order that the code starting point can be easily distinguished. 
     Typical dimensions of the code cam openings in the screen for glass solder paste printing are, according to FIG. 2: 
     b=0.1 mm 
     l 1  =1.0 mm 
     l 2  =0.5 mm 
     d=0.5 mm 
     The width b is chosen minimum so as not to restrict appreciably the field used for the display. It is advantageous to apply a projection of e.g. double length l 1  as reference mark in order to define the starting point. 
     The table shown in FIG. 4 represents a code more easily legible than table 1, although it requires 10 bits for the week identification. Here the first 4 bits 3a to 3d together with the bit 3e embody the units of the week number and the remaining bits the tens of the week number. Once again, the heading &#34;Wo&#34; in Table 4 denotes the week number. 
     Obviously, numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.