Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-05-14
2002-05-14
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S233000, C156S238000, C156S239000, C156S540000, C156S543000, C101S023000, C101S025000, C101SDIG029
Reexamination Certificate
active
06387201
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improved rotary hot foil stamping machine and an improved method for hot stamping foil images onto a substrate.
Hot foil stamping is a well-known printing process by which decorative images or text may be transferred or “stamped” onto a substrate such as paper. The medium transferred to the substrate may be pigment-based, metal-based, plastic-based or made of other known materials depending on the desired appearance of the final image to be stamped onto the product. Most common foils include five layers. First a polyester film or other carrier provides a flexible protective base on which the remaining layers are supported. Next, a release coat is applied to the carrier layer. The release coat allows the foil pigments and other layers to be separated from the film carrier when the decorative image or text is transferred to the substrate. Below the release coat, a color coat is provided which carries the various pigments which define the color of the transferred image. In metal-based foils, a metal layer, usually aluminum, is then provided to add reflective qualities to the foil image. Finally, an outer adhesive layer is provided to bond the transferred image to the substrate.
A press is provided for transferring the desired foil image onto the substrate. The press acts to stamp or compress, the foil and the substrate together between a heated die and a rigid counter-surface. The heated die includes a raised surface having the form of the image to be applied to the substrate. When the die compresses the foil against the substrate, only the foil area beneath the raised portion of the die is affected. The heat and pressure from the die releases the image-forming layers of the foil from the carrier, and bonds the image to the substrate. Thus, an image corresponding to the raised surface of the die is transferred to the substrate.
Rotary hot foil stamping is a variation of hot foil stamping that is carried out on a rotary press. In a rotary press, the die is cylindrical, with the image portion of the die protruding slightly from the outer circumference of the die. The cylindrical die is mounted adjacent a cylindrical counter roll such that the raised surface of the die engages the outer surface of the counter roll as the die is rotated past it. Both the foil and the product substrate are provided in the form of continuous webs that may be fed between the rotary die and the counter roll. As with other hot foil stamping processes, the die is heated, and when the raised surface of the die compresses the foil web against the product web, the pigments other layers between the raised portion of the die and the counter roll are released from the foil web and bonded to the product substrate. Thus, the foil image is rotationally stamped onto the substrate, as opposed to being vertically stamped as in a platen press.
Rotary hot foil stamping is well-suited for large volume applications in which an image is to be repeatedly stamped along the length of the product web at regular intervals. The product web may then be divided or cut into individual products. Mass mailing pre-printed envelopes, for example, are particularly well-suited for rotary hot foil stamping. Decorative text such as the sender's name and address or other important information may be consistently and accurately stamped along the length of a large paper roll. The pre-printed roll may then be cut up into envelope blanks which are later folded into envelopes. By properly spacing each foil image along the paper roll, the image will appear in exactly the same location on each envelope after it is cut from the web and folded. Of course the aesthetic advantages of rotary hot foil stamping need not be limited to pre-printed envelopes. The appearance of other products such as brochures and fliers and many others products bearing text or decorating images may also be enhanced through the use of rotary hot foil stamping.
A critical production parameter for the rotary hot foil stamping application is the overall product length on the product web. For example, if envelopes are being stamped, the overall product length must correspond to the length of the unfolded envelope blanks. The product length determines the distance separating each image along the length of the product web so that the images will appear in the same position on each product. This requires the product web to be accurately positioned each time a die surface is rotated past the counter roll such that when the next die surface causes the foil to be compressed against the product web, the product web has traveled exactly one product length since the beginning of the previous stamped image.
Another critical production requirement is that during the actual stamping of an image onto the product, the foil web and the product web must be traveling at the same linear speed as the working surface of the die. If the foil or product webs are traveling at speeds different from the die speed, the stamped image will be distorted, or one or the other of the foil and product webs may be torn. In the past, as a practical matter this has meant that the rotational speed of the die has determined the production rate of the entire rotary hot foil stamping process.
Prior art rotary stamping machines rely on the physical size of the rotary die to accurately position images along the product web. The product and foil webs are fed at the same speed as the surface of the die throughout the process. The die may have a single image or multiple images formed around circumference of the die. In order for images to be stamped the proper distance apart, the circumferential distance between adjacent die surfaces must equal the desired distance between images stamped onto the product web. The circumferential distance between image surfaces around the outer circumference of the die is a function of the die's diameter. Therefore, products requiring larger distances between images (corresponding to longer product lengths) require larger diameter dies, whereas short product lengths require smaller diameter dies. In other words, in prior art rotary hot foil stamping machines, the product length is dependent on, and established by, the diameter of the rotary die. Each die must be custom fit for a particular application, with the die circumference being dictated by the product length. Custom made rotary dies are expensive, and the expense has generally had a limiting effect on the use of rotary hot foil stamping, restricting its use to those applications having sufficiently large volumes to justify the production cost of a custom die.
It should be noted, however, that in most applications the foil image is to occupy only a short segment of the overall product length. Therefore, the actual stamping surface of the die is compressed against the foil and product webs for only a brief portion of the entire rotation of the die. At all other times a gap exists between the surface of the rotary die and the counter roll such that both the foil web and the product web can move freely therebetween. Observing this, the present inventors have discovered an improved rotary hot foil stamping machine wherein the foil web and the product web are fed independently of the rotary die and the counter roll. In such a machine, both the foil web and the product web must be accurately and synchronously positioned with respect to the rotating die such that a foil image is repetitively stamped in the proper location on each ensuing product. Further, the foil and product webs must be controlled such that both travel at the same speed as the surface of the die during the actual stamping of the image onto the product web. By removing the correlation between the diameter of the rotating die and the position of the foil and product webs, it becomes possible to provide a standard sized rotating die or a die holder on which dies may be removably attached to form different stamped images, and different product lengths may be selected independently of the diameter of the
Cortese Steven P.
Stuart John M.
Best Cutting Die Company
Mayes Curtis
Michael Best & Friedrich LLC
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