Abstract:
A plastic container having curved surfaces and digital printing is disclosed. An embodiment of the container provides a hollow plastic container including a multiple color, single-cured digital image on a first curved surface having a non-constant radius of curvature, and a second curved surface having a non-constant radius of curvature that is spaced from the first curved surface, such that the first and second curved surfaces are on opposed surfaces.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 11/446,792, filed Jun. 5, 2006, which is a division of application Ser. No. 11/219,411, filed Sep. 2, 2005, issued as U.S. Pat. No. 7,210,408 on May 1, 2007, which claims priority from Provisional Application No. 60/640,605, filed Dec. 30, 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to plastic containers having digital images printed thereon, particularly curved plastic containers. 
     Conventional techniques for printing onto curved plastic containers are subject to significant drawbacks. For example, it is difficult to obtain proper registration between colors, and changing images, designs or wording is expensive and time consuming. 
     Inkjet printing with multiple nozzles is useful for flat surfaces. However, it is difficult to satisfactorily use multiple nozzles on curved surfaces. 
     It would be highly desirable to print a digitally generated image directly onto a plastic container, particularly a curved plastic container, wherein the printing can be done at a reasonable speed and at a reasonable cost. 
     SUMMARY OF THE INVENTION 
     The present invention provides for printing digital images or indicia directly onto a plastic container, particularly a curved, plastic container, and accomplishing this in a continuous operation at a reasonable speed and at a reasonable cost. Full color digital graphic images or indicia may be directly printed onto containers at multiple areas thereon. 
     In accordance with the present invention a series of plastic containers are firmly held and moved to and from a first digital printing location and a first digital image is printed thereon at the first printing location on a first printing area on the containers, with the containers held at the top thereof and at a second position spaced from the top thereof, preferably at the base. Desirably, the containers are moved from the first digital printing location to a second digital printing location and a second digital image printed thereon on a second printing area on the containers spaced from the first printing area, with the containers held at the top thereof and at a second area spaced from the top, preferably at the base. The containers are preferably maintained under internal pressure while the digital image or images are printed thereon. 
     The steps of digitally printing the digital image directly onto the plastic container prints the digital images directly onto a preformed container, for example onto an injection molded or blow molded container, such as polyethylene terephthalate (PET) or high density polyethylene (HDPE). The digital printing operation may print the digital image directly onto the plastic container as by jetting ink through an inkjet print head and onto the container surface. The ink may be a UV-reactive ink, in which case after printing the ink may be cured by exposure to UV light. One may also, for example, treat the container surface to be printed prior to the printing operation, as by flame treatment, corona treatment or plasma jet treatment. 
     Further features of the present invention will be discussed hereinbelow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more readily understandable from a consideration of the following illustrative drawings, wherein: 
         FIG. 1  is a top view of the container conveyer with containers; 
         FIG. 2  is a side view of one embodiment of the container flow and treatment; 
         FIG. 3  is a side view of an alternate embodiment of the container flow and treatment; 
         FIG. 4  is a side view of the container clamp assembly; and 
         FIG. 5  is an enlarged side view of an alternate embodiment of the container flow and treatment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As can be seen from  FIGS. 1-3 , a conveyer assembly  10  is provided to move the containers  11  through the treatment procedure in the direction of flow  12 . The containers  11  enter the conveyer assembly from infeed conveyer  14  at container entry  16  and are secured in container clamp assembly  18 . The clamp assembly secures the containers  11  at two spaced areas, as shown in  FIGS. 1 and 4 , by container base holder  20  and container top holder  22 . It is preferred to hold the container at the top and bottom, although one could employ a top holder plus a second holder spaced therefrom, as on the sidewall. This prevents the containers from moving in any direction except for the direction of container flow  12 . The base holder  20  and top holder  22  are synchronized to maintain the same velocity and relationship to each other at all times. Naturally, a commercial operation may have more than one conveyer assembly line. 
     As can be seen, particularly in  FIGS. 2 and 3 , the containers  11  are curved, as for example, round or oval, and have a container radius or curved portion  24 . The container track  26  also contains a radius of the curved portion  28  at the first printing site  30  which should substantially equal the container radius  24  to be printed in order to facilitate the digital printing operation. 
     Upon clamping container  11  at the container entry  16  internal pressure is applied to the inside of the container via air pressure means  32  and pressure line  34  ( FIG. 4 ) through the clamp assembly  18 , as for example, through top holder  22 . Preferably, a pressure regulator  36  is provided to regulate the air pressure, as for example, from 0.125-10.0 psi. This internal pressure will be maintained throughout the treatment procedure and provides a consistent distance of the container surface from the inkjet head and/or a consistent contact pressure for the container surface to the ink roller if the indirect inkjet method is used. 
     As the containers enter the track curved portion or radius  28  they first pass through a first pre-treatment location A- 1 , see  FIGS. 2 and 3 . The pre-treatment location will serve to raise the surface energy of the container on the first container surface  38  to insure ink adhesion thereon, as for example, a heat treatment or corona treatment. 
     The containers will then pass the first printing site  30 , area B- 1  in  FIGS. 2 and 3 . The containers will then have the first printing applied on the first container surface  38  at printing site  30 , which may be a direct drop on demand inkjet head as shown in  FIG. 3 , or an indirect drop on demand inkjet pad  40  as shown in  FIG. 2 . U.V. ink will be applied directly to the first surface  38  of the containers in one pass. The inkjet may apply multicolor graphics of high quality as desired. 
     The printed containers will then pass through a first curing station C- 1 , which will cure the ink or inks applied at the first printing site  30 . This may be an ultra violet light source or other radiant curing method. 
     The containers  11  then enter a straight section  42  of container track  26  where they are rotated, as for example, 180°, to expose second surface  44  of the containers to the second printing site  46 , as by the clamp assembly  18  or other rotating means. The second container surface  44  is spaced from the first container surface  38 , desirably an area opposed to the first container surface, as 180° therefrom. 
     After rotation the containers  11  with container first surface  38  having printing thereon are moved through a second pre-treatment area A- 2  where the surface energy of the container on the container second surface  44  is raised as at the first pre-treatment area A- 1 . The containers will then pass the second printing site  46 , area B 2 , wherein the second printing will be performed on the second surface  44  of the containers. 
     Similar to first printing site  30 , printing at the second printing site may be a direct drop on demand inkjet head as shown in  FIG. 3  or an indirect drop on demand inkjet pad  40  as shown in  FIG. 2 . Also, at the second printing site  46  U.V. ink will be applied directly to the second surface  44  of the containers in one pass, as multicolor graphics of high quality, as desired. 
     The printed containers will then pass through a second curing station C- 2  which will cure the ink or inks applied at the second printing site. Here again, this may be an ultra violet light source other radiant curing method. 
     The container clamp assembly  18  will then release the containers, printed on two sides or two locations and pass them on to an out-feed conveyer or storage and return to repeat the cycle. 
     In the printing procedure it is desirable to maintain a plurality of print heads at a constant distance and perpendicularity from the non-planar container surface during the printing process. A plurality of print heads may be desirably articulated during the printing process to maintain a constant distance and perpendicularity from the non-planar container surface. A plurality of sensors may be used to measure the curvature of the non-planar surface and to control the articulation of the plurality of print heads to maintain the constant distance and perpendicularity from the non-planar surface. The print heads and/or container are desirably moved at a constant velocity relative to the non-planar surface during the printing process. Also real time control is preferably provided to the printing control system to determine the relative position of the non-planar surface to the printing process. The foregoing features provide improved digital printing on the curved container surface. 
     Thus, for example, as shown in  FIG. 5  which shows an enlarged view of the first printing site  30 , area B- 1 , the conveyer system or container track  26  can be straight. The containers  11  with their container radius or curved portions  24  pass under print heads  50  which are each separately movable up and down perpendicular to the direction of the container flow  52  in the direction of print head movement  54  by suitable motive means as articulation device  56 . A constant distance or spacing between the container surface to be printed and the print heads is therefore maintained by the use of measuring device or sensor  58 , such as a laser sensor, which determines the location of the surface to be printed and provides electronic feedback to the articulation device  56  for appropriately moving the print heads. Thus, as the containers pass under the print heads each head may move up and down as desired independent of each other and coordinated to the desired printing location. Subsequent processing will proceed in a manner after that shown in  FIGS. 2 and 3  with a straight container track, desirably rotating the container, and printing at the second printing side. 
     Thus, the present invention provides an improved procedure for printing digital images or indicia directly onto a curved plastic container. The procedure is continuous and efficient and enables two sides or two areas to be efficiently printed. 
     It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.