Abstract:
A laminator assembly and lamination method which comprise: a first roller located on a first side of a media passage; 
     a second roller located on a second side of said media passage so as to oppose said first roller, wherein a nip portion is defined between said first and second rollers so as to apply pressure to media in said media passage which passes through said nip portion; and 
     wherein at least one of said first and second rollers is a roller comprising a substantially solid layer ( 42 ), a deformable layer ( 48 ) surrounding said substantially solid layer, and a perforated layer ( 46 ) surrounding said deformable layer forming an outer surface of said at least one of said first and second rollers.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the art of color proofing, and in particular, to an improved lamination assembly and roller for preparing prepress color proofs, such as by the use of pressure and heat to laminate media together. It should be known that this invention could be used in any field that uses rollers or belts to convey or fuse media. 
     BACKGROUND OF THE INVENTION 
     Pre-press color proofing is a procedure used by the printing industry to create representative images of printed material. The proof is used to check for color balance and other important image quality control parameters, without the high cost and time that would be required to actually produce printing plates set up a printing press to produce an example of an intended image. The pre-press color proof of the intended image may require several corrections and may be reproduced several times to satisfy or meet the requirements of the customers, resulting in a large loss of profits and ultimately higher costs to the customer. 
     Color proofs sometimes called “off press” proofs or prepress proofs, are one of three types. The first is a color overlay that employs an image on a separate base for each color. The second a single integral sheet process in which the separate color images are transferred by lamination onto a single base. The third is a digital method in which the images are produced directly onto or transferred by lamination onto a single base from digital data. 
     In one typical process for a prepress color proofing system used in the printing industry, a multicolor original is separated into individual transparencies, called color separations, the three subtractive primaries and black. Typically a color scanner is used to create the color separations and in some instances more than the four standard color separations are used. The color separations are then used to create a color proof that is sometimes called an “off press” proof or prepress proof as described above. 
     In one type of laminator, noted in a copending patent application cited above, a lamination sandwich sits on an entrance table. A leading edge of the lamination sandwich is fed into the laminator. An upper pressure roller and a lower pressure roller receive this lamination sandwich. The lamination sandwich passes completely between the upper heated pressure roller and a lower heated pressure roller coming to rest on an exit table. With the configuration of an upper heated pressure roller and a lower heated pressure roller as described above, the laminator is termed a straight-through laminator. As an additional reference U.S. Pat. No. 5,203,942 describes a lamination/de-lamination system as applied to a drum laminator. 
     While the above-described laminator works well for some materials and in limited conditions, there are many conditions and materials that cannot be laminated successfully using the above-described laminator. One problem is the intended image shifting from one color to another such that the dots/image from one color to the next are not overlaid correctly causing a misregistration of the intended image. The intended image may suffer from overall image growth and damage to some intended images may occur in the form of creases commonly know as rivers or valleys. 
     The aforementioned problems are for the most part due to the heated pressure rollers and the application thereof. The upper heated pressure roller and the lower heated pressure roller have hollow heater elements that are typically made of metal. The hollow portion of the heater element is for accepting a heating rod or lamp while a rubber layer or shell typically of silicone rubber is formed around the outside of the heater element. When the upper heated pressure roller and the lower heated pressure roller are pressed together, they form a nip or indentation. Within the nip formed by the upper heated pressure roller and the lower heated pressure roller, lateral shear stresses and overdrive conditions are formed. These lateral sheer stresses and overdrive conditions act upon the media being laminated together to cause the intended image to shift from one color to another color. These lateral sheer stresses and overdrive conditions can also cause a defect in the final lamination in the form of creases commonly known as rivers or a valley, as described above. These lateral sheer stresses and overdrive conditions can also cause image growth which can be different with each color, causing the intended image to be misregistered from one color to the next color or to be larger than the original image or printed image. Although adding a deformable layer as described in U.S. patent application Ser. No. 09/676,877 helps to eliminate the above mentioned problems there is still room for improvement. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide for an apparatus and method that overcome the drawbacks noted above. 
     The invention relates to a laminator assembly comprising: a first roller located on a first side of a media passage; a second roller located on a second side of said media passage so as to oppose said first roller, wherein a nip portion is defined between said first and second rollers so as to apply pressure to media in said media passage which passes through said nip portion; and wherein at least one of said first and second rollers is a roller comprising a substantially solid layer which may be solid. Surrounding this substantially solid layer is a deformable layer. Surrounding the substantially solid layer is a perforated layer which in alternative embodiments can be a solid layer upon which have disposed a coating, leaving a portion of the solid layer uncoated. These uncoated portions can be in the shape of arcs, curves, or circles or any one of a number of shapes. Alternatively, the perforations on this layer may be in the form of a shapes as well. One or more of the rollers can be heated or adapted to accept a heating element. 
     The present invention provides for a roller arrangement that overcomes lateral shear stresses and overdrive conditions, and allows the use of low durometer rubber or of a compressible rubber, and can be used in laminators or any number of devices, including copiers and fax machines. 
     The present invention further provides for a heated pressure roller embodiment that allows a wider range of conditions for lamination. 
     The present invention further provides for a pressure roller that allows a wider range of conditions for conveying media. 
     The present invention also provides for a roller arrangement that helps overcome image shift from one color to another and overall image growth. Additionally, the present invention provides for a heated pressure roller that improves defects such as creases/rivers or valleys. 
     According to a feature of the present invention, a laminating system for bonding, to a paper receiver stock, a thermal print media of the type including a carrier and a material to be applied to the paper receiver stock, includes an improved pair of pressure rollers, which can be heated. Through these rollers, media or a lamination sandwich of thermal print media and paper receiving stock can be fed. The pair of rollers having been improved by adding, to at least one of the pressure rollers, a metal or plastic perforated belt or tube over a rubber or otherwise deformable material layer of the heated roller. This coating serves to prevent lateral stresses, overdrive conditions from acting on the thermal print media or paper receiving stock or allow the media to slip. 
     The present invention relates to a drive roller assembly for conveying media, which is comprised of opposing rollers. The rollers of this assembly, which optionally can comprise a heater element, consist of a first deformable layer, a second perforated layer which surrounds the first de-formable layer and forms an outer surface of one of the first and second opposing rollers or both. 
     The present invention relates to a belt for conveying media, which is comprised of a de-formable layer and a perforated layer or covering. 
     The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiments presented below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
     FIG. 1 is a perspective view showing a laminator known in the related art; 
     FIG. 2 is a perspective view showing the loading operation of a laminator according to a preferred embodiment of the present invention; 
     FIGS. 3-5 are schematic side elevation views showing progressive stages of operation of the laminator of FIG. 2; 
     FIGS. 6-8 are schematic side elevation views showing alternative details of the pressure rollers according to the present invention of FIG. 2; 
     FIG. 9 is a perspective view showing a laminator roller of the present invention; 
     FIG. 10 is a perspective view showing a belt of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed, in particular, to elements forming part of, or cooperating more directly with, an apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. For the sake of discussion, but not limitation, the preferred embodiment of the present invention will be illustrated in relation to a laminating apparatus for making image proofs on a paper receiver stock, since the usual proofing practice is to make a hard copy of the image proof on paper. The present invention, however, is not limited to making hard copies of proof images on paper, since it can produce hard copies of images on a wide variety and thicknesses of media that may be used in the printing process. 
     Referring to the drawings, wherein like reference numerals represent identical or corresponding parts throughout the several views, FIG. 1 shows an embodiment of a laminator  12  incorporating the present invention. Laminator  12  receives lamination sandwich  10 , which is initially placed on entrance table  20 . The laminator sandwich  10  is passed through the rollers shown in more detail in FIG. 2, and exits the rollers onto exit table 14. 
     FIG. 2 shows a portion of laminator  12 , particularly the pair of rollers, in the form of an upper pressure roller  16  and a lower pressure roller  18 , one or more of these rollers can be heated. Upper pressure roller  16  is provided with a roller cover  22  or a heat shield. 
     As shown in FIG. 2, media in the form of an assembled lamination sandwich  10  is made up of thermal print media  24  and paper receiving stock  26 . Thermal print media  24  can include a transfer layer, not shown, on an image bearing side of thermal print media  24  which faces paper receiving stock  26 , and which is to be applied to paper receiving stock  26  when pressure and optionally heat, are applied to lamination sandwich  10 . 
     Referring now to FIGS. 3-5, lamination sandwich  10  is made up of thermal print media  24  positioned on paper receiving stock  26 . This lamination sandwich  10  travels along a media passage  200  to a nip portion  32  between pressure rollers  16  and  18 . Upper pressure roller  16  and lower pressure roller  18  can may optionally, each contain a heating element, noted as heating element  30  and heating element  31 , respectively, which are shown in more detail in FIG.  6 . 
     Heating elements  30  and  31 , respectively apply, heat which migrates to the surfaces of upper pressure roller  16  and lower pressure roller  18 . The heating of rollers  16  and  18  can be done wherein only one roller is heated, or both rollers are heated simultaneous depending on the embodiment of the invention. Both embodiments are considered within the scope of this invention. 
     In the most preferred embodiment, pressure is applied to upper pressure roller  16  and lower pressure roller  18  in a known manner by, for example, eccentric rollers, pressure levers, or other means that are not shown. Lower pressure roller  18  can be driven such that when upper pressure roller  16  and lower pressure roller  18  are pressed together, they both rotate. 
     Returning again to FIG. 2, the lead edge  34  of lamination sandwich  10  is fed into nip portion  32  formed by moving upper pressure roller  16  and lower pressure roller  18 . 
     FIG. 3 shows lamination sandwich  10  enters media passage  200  wherein the thermal print media  24  is pressed onto paper receiving stock  26  as they pass through nip portion  32  which is formed by upper pressure roller  16  and lower pressure roller  18 . 
     FIG. 4 shows lamination sandwich  10  once it has emerged from the nip portion  32  formed by upper pressure roller  16  and lower pressure roller  18  being pressed together. 
     FIG. 5 shows that after lamination sandwich  10  cools sufficiently, a support layer of thermal print media  75  is peeled from the laminated sandwich  10  leaving behind a prepress proof  76 . 
     FIGS. 6-8 are schematic side elevation views showing details as well as alternate details of pressure rollers  16  and  18  according to the present invention. 
     In FIG. 6, upper pressure roller  16  and lower pressure roller  18  are shown with the lamination sandwich  10  disposed between the rollers. In this embodiment, both upper pressure roller  16  and lower pressure roller  18  have identical construction. Alternative embodiments of this invention are contemplated wherein upper pressure roller  16  has a different construction from lower pressure roller  18 . 
     FIG. 6 shows upper pressure roller  16  and lower pressure roller  18 , each having a substantially solid layer  42 , and substantially solid layer  43  respectively, which can be made from a thermally conductive material. These layers  42  and  43  may be either (i) substantially solid or (ii) hollow. The substantially solid layers  42  and  43  can be adapted to receive heater elements  30  and  31 , respectively. Surrounding layers  42  and  43 , are deformable sleeves or layers,  48  for roller  16 , and  49  for roller  18 . The deformable layers  48  and  49  can contact the substantially solid material layers in one embodiment, in the form of a bond. The bonding can be performed with an adhesive layer. 
     Deformable layers  48  and  49  can made from one or a combination of materials, including but not limited to a low durometer rubber, a compressible rubber, a solid rubber silicone, a foam silicone rubber or others materials having similar deformable characteristics, such as urethane. A low durometer rubber usable in the invention is available from the Dow Corning Corporation. 
     A perforated roller sleeve or layer  46  for roller  16 , and  47  for roller  18  is disposed over the deformable layer. This perforated layer can comprise, at least in part, a second deformable material. 
     In an alternative embodiment, perforated roller sleeves or layers  46  and  47  may, encapsulate the entire surface area of layers  48  and  49 . Perforated roller sleeves or layers  46  and  47  can be a material selected from the group: a metal layer, a plastic belt, a plastic tube or a plastic coating. Any number of usable thermoplastics could be used as the plastic coating or for the plastic belt or tube. A fluropolymer could be used as the perforated layer. Other usable materials include polyamindes, polyisocyanates, polyphenylene sulfides, polycarbonates, copolymers thereof, and combinations thereof. A preferred polyamide is nylon 6,6. Nylon 6,10 is also contemplated as usable for perforated layers  46  and  47 . 
     As lamination sandwich  10  passes nip portion  32 , deformable layers  48  and  49  and perforated roller sleeves or layers  46  and  47  deform to increase the width of nip portion  32  to form an enlarged nip width for nip portion  32 . The arrangement of the present invention permits the width of nip portion  32  to be decreased or increased as needed by between about 5 millimeters to 30 millimeters. 
     Nip portion  32  is substantially uniform as it extends along the rotational axis of pressure rollers  16  and  18 . This configuration eliminates or minimizes lateral shear stresses and overdrive as lamination sandwich  10  passes nip portion  32 . 
     In the embodiment of FIG. 6, given that both rollers are of the same construction, the increased width nip portion  32  is formed on both sides of media passage  200 . 
     In the embodiment of FIG. 7, the upper roller  16  has the same construction as the pressure roller  16  shown in FIG.  6 . However, in this embodiment, pressure roller  18  is made of a different construction, wherein a heater element  31  is surrounded only by a layer of solid or substantially solid material layers  43  such that only pressure roller  16  deforms to form nip portion  32 . In an alternative version of the embodiment of FIG. 7, roller  18  can additionally have a deformable layer over a second solid layer  43 . 
     FIG. 8 shows another embodiment in which pressure roller  16  has the same construction as pressure roller  16  of FIG. 7, however, in this embodiment, instead of a second roller  18 , a movable platen  500  is shown disposed on the other side of roller  16 , retaining lamination sandwich  10  on the platen as the platen  500  moves under pressure roller  16 . Platen  500  additionally causes rotation of pressure roller  16 . In this embodiment, pressure roller  16  deforms as shown in FIG.  7 . 
     FIG. 9 shows still another embodiment of the invention wherein pressure roller  16  has the same construction as pressure roller  16  of FIGS. 6,  7  and  8 . Pressure roller  18  now has a construction consisting of heater element  30 , a substantially solid or solid material layer  42  disposed around the heater element  30  which layers are preferably the same materials used in the embodiment of FIG.  6 . Disposed on the outer circumference of layer  42  is deformable layer  48 . Surrounding deformable layer  48  is perforated layer  46  which can be a solid layer with a coating disposed on at least a portion of the layer  46 , such that the non-coated portion forms geometric shapes, including but not limited to rectangular shapes, curves, arcs, circles and squiggles. 
     FIG. 9 shows several variations or the shapes of the non-coated areas on a solid layer  46 , and the shapes of perforations for a perforated layer  46  on roller  16  which are within the scope of the invention. 
     The perforations or holes may take one or more of a variety of shapes including but not limited to radially disposed rectangular perforations  502 , with or without opposing rectangular perforations  504 , circular shaped perforations  506 , radially diaposed rectangular perforations  508 , or any of the numerous geometric shapes that are available. 
     To be clear, it is intended to be within the scope of the invention that the perforations could be omitted altogether and instead the perforated layer can be defined as a solid layer having an at least partially coated surface. The surface of layer  46  could be coated or masked with a material such as ones with a low coefficient of friction which particularly resist heat and deformation. A usable coating could be Teflon. These coatings could be disposed on the surface of the roller to form any number of uncoated shapes, including all the patterns shown in FIG. 9, such as the small arcs  510  or squiggles  512 . This type of coating could be used on the roller which rotates over the lamination sandwich, such as pressure roller  16  which deforms to form nip portion  32 . It also within the scope of the invention to use the coatings and create shapes on the moveable platen 
     FIG. 10 shows a belt from a belted laminator from an end view. In this embodiment, the belt has a coating disposed on the outer surface and non-coated areas in the form of circles are presented. The belt can be coated in the same manner as the roller shown in FIG.  9 . 
     Although the illustrated embodiments show both pressure rollers as heated pressure rollers, it is recognized that only one pressure roller may be the heated pressure roller. It is further recognized that both pressure rollers do not have to be heated for cold lamination applications. It is also further recognized that the pressure rollers do not have to be used for lamination applications but as conveying or drive rollers. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
     PARTS LIST 
       10 . Lamination sandwich 
       12 . Laminator 
       14 . Exit table 
       16 . Upper pressure roller 
       18 . Lower pressure roller 
       20 . Entrance table 
       22 . Roller cover 
       24 . Thermal print media 
       26 . Paper receiving stock 
       30 . Heating element for roller  16   
       31 . Heating element for roller  18   
       32 . Nip portion 
       34 . Lead edge 
       42 . Substantially solid layer for roller  16   
       43 . Substantially solid layer for roller  18   
       48 . Deformable layer for roller  16   
       49 . Deformable layer for roller  18   
       50 . Perforation layer or in an alternative embodiment, layer with coatings 
       75 . Support layer of thermal print media 
       76 . Pre-press proof 
       200 . Media passage 
       500 . Movable platen 
       502 . First set of axial rectangular perforations or coatings 
       504 . Second set of axial rectangular perforations 
       506 . Circular perforations 
       508 . Transverse rectangular perforations 
       510 . Non-coated roller surface having the shape of small arcs 
       512 . Non-coated roller surface having the shape of squiggles