Abstract:
A paper stock with at least one side dyed or tinted such that each side has a different color or shade to provide an indication of any erasures on the dyed or tinted side of the paper. Machinery and systems are disclosed for practicing the method of making the inventive paper.

Description:
RELATED APPLICATIONS  
       [0001]    This application, pursuant to 37 C.F.R. §1.78(c) claims priority based on provisional application serial No. 60/384,694, filed May 30, 2002. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    Tinted papers have been around for quite some time, especially papers converted to the small format of 8.5×11, 8.5×14 legal, and others up to about 11×17. The advantage of colored or tinted papers are reduced eye strain, varying levels of contrast with different kinds and colors of printing ink or toners, identification of printed matter, i.e. blue for one purpose and pink for another and individual consumer preference.  
           [0003]    Typically, tinted papers are produced at the paper mill, with the colorant or dye added at the wet end of the paper machine directly to the pulp before the formation of the sheet. This process is known as vat dyeing, and these papers are tinted on both sides and throughout the sheet because the fibers themselves are dyed.  
           [0004]    Some of the disadvantages of the mill produced tinted sheets are that the whole sheet itself is tinted. The mill will only make a few specific colors or tints of paper on a few specific types or grades of paper, and only run these specific sheets at certain times or when minimum tonnage is required. Therefore, if a paper converter requires a limited amount of a tinted paper, often it will not be available or the minimum amount the mill will produce is much greater than the converter&#39;s requirements necessitating an excessive inventory burden to the converter. These and other disadvantages of the common practice have contributed to the limited use of color-tinted papers into the large format markets, especially in the “A&amp;E” (Architect and Engineering) markets. By large format we mean paper larger than 11″×17″. For instance large format sheets are generally sold in sizes such as 18″×24″, 24″×36″, 30″×42″ and 36″×48″, but other sizes are available and the term “large format sheets” is meant to include all such sizes large format rolls are generally sold in sizes 24″-52″ wide and up to  500  feet in length. The term “large format rolls” is meant to include any width sheet larger than 17″ and any length roll.  
           [0005]    Historically, the A&amp;E field and building trades use a diazo-type copy of an A&amp;E drawing known as a blueprint for use in the field or the job site. Up to the 1960&#39;s, blueprints were a diazo coated sheet that when developed produced white line drawings and text on a blue field or background. These are known as traditional blueprint. Then the diazo process evolved into what is known as “whiteprinting”. These are diazo type prints that when exposed and developed, would produce blue line drawing and test into a white field or background. (Black lines, brown lines, and red lines were also achieved with the same process.) And although this process is properly known as “whiteprints”, the term blueprint is generally applied to this process as well. Some of the advantages of “whiteprints” are increased manufacturing speeds, lower costs, and the ability to process and develop the individual prints at a faster speed, thereby achieving maximum line and text densities, while allowing the background to be developed with a blue cast or shade. This practice, known as “pulling a background” was found to be very beneficial especially to those on the construction site, because no text or lines would be lost and the shaded background was easier to read outside, in direct sunlight, reducing eye strain and glare.  
           [0006]    In the 1980&#39;s and especially into the late 1990&#39;s xerographic type copiers became much more prolific in the wide format market and these copiers became known as large format copiers or plotters. Their popularity continues to increase, as diazo-type usage declines. These LDC (large document copiers) produce black toner developed images and texts on a white sheet of paper known as engineering, laser or xerographic or offset grades of bond papers. These sheets are often referred to as plain paper. These LDC produced plain paper copies are gradually replacing the traditional blueprint copies at every level in the A&amp;E market due to their lower cost commodity paper stock and lower labor costs to print.  
           [0007]    Some uses for vat dyed bonds have been used in the LDC market as stated before for identification or action of the document (blue=plumbing, pink=iron work−green=landscaping.) But the hidden cost of vat dyed sheet, limited uses, and inventory requirements have never made them cost effective to the A&amp;E printer or client.  
           [0008]    Our invention allows multiple uses of existing low cost sheets of bond, economically coated and tinted with the capability of producing limited or extended runs. The ability to produce multiple shades and colors each allowing its own unique features.  
         SUMMARY OF INVENTION  
         [0009]    An object of this invention is to provide a paper stock having a different color or shade on each side and method for producing same.  
           [0010]    Another object of the present invention is to provide a white base paper stock color or tinted on one side only.  
           [0011]    Yet another object of the invention is to convert the paper stock into a large format of roll or sheet stock, primarily for use in Large Document Copiers (and/or Plotters), particularly for the Architectural and Engineering markets. Still another object of the invention is to produce a large format paper which reduces glare in sunlight, shows changes or erasures and is economically produced.  
       
    
    
     BRIEF DESCRIPTION OF DRAWING  
       [0012]    [0012]FIG. 1 is a schematic drawing of a machine for producing the inventive paper and method of making same. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENT  
       [0013]    The invention preferably uses a paper stock of a neutral or alkaline bond (engineering, xerographic, laser, or offset grades are most desirable although other grades and/or an acid based paper is acceptable). An aqueous dye solution consisting of Water; Dye (acid, direct, or otherwise), in a concentration that produces acceptable color or tint; and may or may not include a polyester or olefinic resin up to 5%, for increased dye binding capabilities so as not to contaminate the fuser roll in the LDC during printing.  
         [0014]    Referring to FIG. 1, paper stock in a roll  2 A is loaded onto coating machine  10  and threaded throughout the machine in the typical manner. Paper in wet form  2  traverses a plurality of tensioning/idler rollers  3 , through the precoat station  4  which preferably does not contain any solutions, but assists in web guiding and tensioning. The precoat station  4  is optimal but may include a supply pan  5  and tension or pressure rollers  7 . A drip pan  8  is provided which is useful if an optional liquid coating is applied in precoat station  4 . Also included are the usual air knife doctor  9  and air knife backing roller  10  to remove excess liquid if present. The web  2  then enters the drying oven  30  via the lower-pass  11   a  and passes through the lower drying plenum  11 , exits and returns to the oven  30  over three more tensioning/idler rollers  3 , into the lower-middle-pass  11   b  traversing across the upper half of the lower drying plenum  11  and exiting to the sensitizing station  12 . The dye solution is pumped from a holding vessel (not shown) in to sensitizing supply pan  13  where the dye solution is picked up by the driven sensitizer applicator roller  14  and deposited onto the moving web  2 . The web  2  is held down onto driven sensitizer applicator roller  14  by two applicator pressure rollers  15 . These rollers  15  are adjustable and maintain an even pick-up of the dye solution. At this point, the web  2  is covered with an excess of dye solution and passes under another tensioning/idler roller  3  to an air knife doctor  17  and air knife backing roller  18  where the excess dye solution is doctored off via a blast of air from the air knife  17 . The excess solution is removed from the web  2  and deposited onto the sensitizer drip-pan  16  gravity fed back into the sensitizer supply pan to recirculated. The web then exits the sensitizer section  12 , traverses two more tensioning/idler rollers  3  and enters the drying oven  30  via the upper-middle-pass  19   a  and travels under the middle drying plenum  19  where the web  2  and dye solution are dried. The web  2  then exits the drying oven at  19   b , traverses two more tensioning/idler rollers  3  and enters the back-coat station  20  where a back-coating solution containing water and preferably up to 1% triethlyene glycol preferably but optionally may be applied, depending on the type or weight of the paper stock that is used, to control curl of the web  2 . The back-coat solution is applied in much the same manner as the dye solution in the sensitizer section  12  utilizing a supply pan  21 , an applicator roller  22 , and an air knife doctor  24  and air knife backing roller  25 . The web then exits the back-coat station  20 , passes two more tensioning/idler rollers  3 , enters the drying oven  30  one last time via the upper-pass  26   a , travels under the upper drying plenum  26  to re-dry the dye solution and dry the back-coat (if used) and exits the drying oven  30 . The finished web  2  then traverses seven tensioning/idler rollers  3 , passes over a chilled roller  27  to cool the web  2 , passes two more idler rollers  3 , and is guided to a driven, surface winder roller  29  or  30 , where the finished coated material is wound into a master roll  31 , ready to be taken from the coating machine&#39;s wind-up section  28 , and be converted into large format sized finished goods (i.e. large cut sheets or rolls).  
         [0015]    Although described schematically above, it is clear that the system  10  can be used to coat one or both sides of paper stock with tints or dyes in any combination of stations of  4 ,  12  and  20  or additional stations if required. Preferably, a white paper stock is coated on one side only with a blue dye; however, both sides of the paper may be individually coated with dyes of the same or different colors provided that the shade of the dyes are different if both sides are the same color. For instance, one side of the paper may be dyed a dark blue and the other side of the paper could be dyed a much lighter blue. In this circumstance, an erasure on the dark blue side would show as a light blue patch, thereby fulfilling an important and primary object of the present invention. Alternatively, one side of the paper could be coated pink and the other side some other color such as green. Again, a principal object of the invention is to individually coat one or both sides in either different shades or different colors so that an erasure on the side carrying the architectural or engineering indicia will be clearly seen. In this manner, drawings which are authorized by a governmental agency cannot be changed subsequent to the authorization without the agency being aware that changes have been made and without having painstakingly to compare an original drawing with a current drawing. This is a major advantage of the prior invention.  
         [0016]    As may be understood from the foregoing, a wide variety of colors may be used: pink, blue, green, yellow or the like. Further, the bond paper normally used in the A&amp;E fields has a felt side and a wire side with the felt side being smoother and on which the indicia normally is placed. In the preferred embodiment of the present invention, the wire side of the bond large format paper is left white (for purposes of this invention white is a color as that word is used herein) and the felt side of the paper is a light blue. In preparing the preferred embodiment of the present invention, a stock solution of direct dye obtained from the Andrews Paper and Chemical Company is made with 320 grams of direct dye per five gallons of very hot water. The water can be boiling or somewhat cooler than that such as about 165° F., but the exact temperature is not critical. A second dye used in the preferred embodiment of the present invention is methyl violet and a solution thereof is made from 113 grams of methyl violet dye and five gallons of hot water. Both of these dyes are preferably water soluble. The two stock dye solutions are then poured into ninety gallons of water and optionally one liter of isopropyl alcohol as a wetting agent may be added. This combination of direct dye and methyl violet is used in the station  12  in order to apply the dye to the felt side of the paper stock. If a deeper shade of blue is required, more dye may be used and if a lighter shade of paper is required, then obviously less dye will be used.  
         [0017]    The back wet solution applied in station  20  is preferably a triethylene glycol in which five gallons of triethylene glycol are added to about 200 gallons of water and this diluted mixture is applied to the wire side of the paper in station  20 . Glycols other than triethylene glycol are useful, as is diethylene glycol, and in general back wetting solutions are well known in the art and any suitable solution may be used although triethylene glycol is preferred. The back wet solution is applied to the reverse side of the dye coated paper to control the curl of the paper and also to control the moisture content to prevent the paper from becoming brittle.  
         [0018]    In the preferred embodiment of the present invention, the paper web  2  is run at about 84 yards per minute and the temperature in the oven  30  is maintained, preferably at about 250° F. in the first pass and about 340° F. in the second pass. The moisture of the paper is also controlled. Preferably the moisture range of the paper should be between about 4% and about 5% by weight and preferably between about 4% and 4.5% by weight. Normally, 40″ diameter rolls  2  A are used and the length of the roll determines the weight.  
         [0019]    Other materials can be added to the various solutions such as binders and other materials, all as is well known in the art, and it is intended to cover in the claims appended hereto all such art recognized additions to the various solutions in the paper making art.  
         [0020]    The inventive paper herein provides much less glare than standard white bond and is particularly advantageous working outside construction jobs in bright sunlight. Moreover, the paper of the subject invention offers security as any erasures will appear as white marks (provided that the wire side of the paper is white) or otherwise identifiable marks notifying the viewer that the original has been changed. In addition, whiteout changes can be detected instantly against the preferred blue background. With the preferred blue coating, the paper may be folded numerous times without toner or paper cracking or feathering as it is known in the field. The blue color of the paper also provides a higher level of contrast and definition to the indicia thereon, preferably on the felt side.  
         [0021]    Finally, the inventive paper shows an engineering seal significantly better than plain white paper allowing the felt side color and the wire side color (preferably white) to mingle together when sealed giving a clean, legible image that is readily apparent.  
         [0022]    While particular embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.