Method and apparatus for forming a rotary embossing die with a support plate

A rotary embossing die includes a curved metallic plate having an inner and an outer surface. An embossing design is etched on the outer surface of the metallic plate and an epoxy-based support plate is formed on the inner surface of the metallic plate. The metallic plate and the support plate preferably cooperate to define a shoulder. Die clips positioned around the shoulder are used to fasten the embossing die to the die cylinder of a rotary embossing machine. The metallic plate can be formed from brass or magnesium, and is preferably curved to any suitable radius.

BACKGROUND OF THE INVENTION 
The present invention relates generally to the field of rotary die 
embossing, and more particularly to rotary embossing dies and a method for 
making and using such dies. 
Although they are relative newcomers to the centuries-old printing and 
embossing trade, rotary embossing machines and their attendant dies have 
been manufactured and used for numerous years. Conventionally, rotary 
embossing dies are formed of resinous or metallic material and cover, or 
are integrally formed with, the surface of an embossing machine 
die-cylinder. Additionally, conventional metallic dies are generally thick 
(approximately 1/4" to 1/2") and, therefore, heavy and difficult to 
manipulate. 
Conventional embossing dies have been successfully used in the embossing 
field. However, because they cover, or are integrally formed with, the 
entire surface of a die cylinder, they are often cumbersome and costly to 
use. Thus, if an embossing design is required to be changed or an 
embossing die needs to be replaced, the die cylinder must be removed from 
the embossing machine and replaced with a new cylinder (if the embossing 
die is integrally formed with the die cylinder), or the embossing die must 
be removed from substantially the entire surface of the die cylinder. 
Because separate die cylinders are often required for each embossing 
design, and the replacement of embossing dies is a time consuming process, 
the use of conventional rotary embossing dies results in increased die 
costs and lengthy embossing machine down-time when changing dies. 
A typical three-step process for forming rotary embossing dies includes 
first etching or otherwise forming a desired embossing shape or design on 
a metallic plate. Second, a negative image of the embossing design is 
formed on a rubber mat (or other flexible material) by a flexoplating or 
etching technique, as is commonly known in the art. Lastly, the rubber mat 
is placed face-up (i.e., with the design exposed) in a die mold and an 
epoxy material is injected into the mold to form an epoxy die plate having 
a positive image of the design. The resultant epoxy rotary die plate is 
then used on a rotary embossing machine to form embossed images of the 
design originally present on the metallic plate on paper, or other 
suitable material. 
While the above-described method of forming rotary embossing dies has 
produced satisfactory rotary embossing dies, there are a number of 
associated problems and/or disadvantages. For example, the sharpness of 
the original design is reduced through transfers of the design to a 
flexible, soft material such as the rubber mat and, subsequently, to the 
epoxy die plate. This reduction in sharpness directly translates to the 
final embossed product and results in embossments that are not as clear, 
sharp and distinct as the desired original design. Also, because epoxy 
rotary die plates do not wear as well as regular metallic die plates, 
there is a frequent need to replace the epoxy die plates, which further 
increases down-time and costs. 
SUMMARY OF THE INVENTION 
According to a first aspect of the invention, a method of forming a rotary 
embossing die is provided, which includes the steps of: providing a flat 
metallic plate having an inner surface and an outer surface; forming a 
design on the outer surface of the metallic plate; curving the metallic 
plate to a predetermined radius; and forming a support plate on the inner 
surface of the metallic plate. 
According to a second aspect of the invention, a method of embossing is 
provided, which includes the steps of: providing a rotary die comprising a 
flat metallic plate having an inner surface and an outer surface; forming 
an embossing design on the outer surface of the metallic plate; curving 
the metallic plate to a predetermined radius; forming a support plate on 
the inner surface of the metallic plate; mounting the rotary die to a die 
cylinder of a rotary embossing machine; and feeding an embossment material 
between the die cylinder and an opposing cylinder such that the rotary 
embossing die imparts an embossed design on the embossment material. 
According to a third aspect of the invention, a rotary embossing die 
includes: a metallic plate having an inner surface and an outer surface, 
the metallic plate being curved to a predetermined radius; an embossing 
design formed on the outer surface of the curved metallic plate; and a 
support plate formed on the inner surface of the curved metallic plate, 
the support plate and the metallic plate defining a shoulder between the 
support plate and the metallic plate for securing the embossing die to a 
rotary embossing machine. 
According to a fourth aspect of the invention, a rotary embossing machine 
includes: a die cylinder; a rotary embossing die mounted on a discrete 
section of the die cylinder, the rotary embossing die including a metallic 
plate having an inner surface and an outer surface, the metallic plate 
being curved to fit the radius of the die cylinder, an embossing design 
formed on the outer surface of the metallic plate, and a support plate 
formed on the inner surface of the curved metallic plate, the support 
plate and the metallic plate defining a shoulder between the support plate 
and the metallic plate for securing the embossing die to the rotary 
embossing machine; and an opposing cylinder positioned in opposite rotary 
relationship to the die cylinder, the opposing cylinder and the rotary 
embossing die cooperating to impart the embossing design on an embossment 
material. 
The present invention provides a rotary embossing die for use on a discrete 
section of a die cylinder. The rotary embossing die includes a thin 
metallic plate that is relatively light-weight and, thereby, allows the 
embossing die to be easily removed from the die cylinder. By providing a 
two-step method for forming rotary embossing dies, the present invention 
eliminates the extra forming step, and the attendant increased costs, that 
is present in the conventional die-formation method. Also, the present 
invention provides a method for forming a rotary embossing die having 
increased wear capabilities over conventional epoxy embossing dies. 
Importantly, the present invention improves the sharpness reduction that 
occurs when the design image is transferred between different die plate 
media. 
These and other features and advantages of the present invention will 
become apparent to those skilled in the art upon review of the following 
detailed description of the presently preferred embodiments of the 
invention taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
Referring now to the drawings, FIG. 1 shows a flat metallic plate 10 having 
an inner surface 30 and an outer surface 62. An embossing design 14 is 
chemically etched or otherwise formed on the outer surface 62 of the 
metallic plate 10. 
Preferably, the metallic plate 10 is formed of brass or magnesium and is 
1/32" to 1/16" thick. However, the plate 10 may be formed of any suitable 
metallic material and may be of any suitable thickness. Additionally, the 
design 14 is preferably a "single level" embossing design, although a 
"multiple level" design may also be formed on the metallic plate 10. 
As best shown in FIG. 2, a rotary embossing die 18 comprises the metallic 
plate 10 and an epoxy-based support plate 26 formed on the inner surface 
30 of the plate 10. The rotary embossing die 18 is formed by curving the 
metallic plate 10 to a desired or predetermined radius of curvature, and 
then forming the support plate 26 on the inner surface 30 of the metallic 
plate 10. 
(FIGS. 4-5 show a second rotary embossing die 22 formed according to the 
present invention. The rotary embossing dies 18, 22 are identical except 
for, as best shown in FIGS. 3 and 5, their different radii of curvature.) 
Because the surface area of the outer surface 62 of the metallic plate 10 
is increased when the plate 10 is curved, the size of the embossing design 
14 may be required to be increased before the design 14 is formed on the 
plate 10. As is known in the art, the required size increase may be 
determined by means of mathematical formulas which account for, among 
other things, the radius of curvature of the embossing die 18. 
Specifically regarding the formation of the embossing die 18, the metallic 
plate 10 is curved to the predetermined radius of curvature in a 
three-roll curver (not shown). As shown in FIG. 7, the curved metallic 
plate 10 is then placed "face-down" (i.e., with its inner surface 30 
exposed) in the base 42 of a rotary die mold 34. After the mold cylinder 
38 is lowered onto the inner surface 30 of the metallic plate 10 and the 
mold 34 is sealed, epoxy-based support plate material (preferably having a 
low shrink factor) is injected into the mold 34 at ambient temperature. 
The epoxy-based material is cured at 180.degree. F. for approximately one 
hour, until the epoxy hardens and forms the support plate 26 on the 
metallic plate 10. After the epoxy is sufficiently cured, the mold 
cylinder 38 is raised and the resultant rotary embossing die 18 is removed 
from the die mold 34. 
Before the metallic plate 10 is placed in the die mold 34, the inner 
surface 30 thereof may be abraded or "roughed" to increase the adhesion of 
the support plate material to the metallic plate 10. Also, to firmly 
secure the metallic plate 10 to the support plate 26, at least one section 
of the metallic plate 10 may be cut and notched (i.e., dovetailed) such 
that it will extend into the support plate when the embossing die 18 is 
formed. 
As shown in FIG. 6, the rotary embossing die 18 is preferably sized to be 
mounted on a discrete section of the die cylinder 50 of the rotary 
embossing machine 54. (If desired, however, the rotary embossing die of 
the present invention may be constructed to cover substantially the entire 
die cylinder 50.) To properly fit on the die cylinder 50, the radius of 
curvature of the embossing die 18 must match that of the die cylinder 50. 
As best shown in FIGS. 2-5, the die mold 34 is constructed such that a 
shoulder 46 is formed between the metallic plate 10 and the support plate 
26 of the rotary embossing die 18. The embossing die 18 is mounted on the 
die cylinder 50 by means of a plurality of die clips 58 secured between 
the shoulder 46 of the embossing die 18 and the die cylinder 50. The 
shoulder 46 provides sufficient clearance between the support plate 26 and 
the outer surface 62 of the metallic plate 10 for the clips 58 to secure 
the embossing die 18 to the die cylinder 50 without interfering with the 
embossing operation performed by the embossing machine 54. 
The rotary embossing machine 54 shown in FIG. 6 also includes an opposing 
cylinder 66 positioned opposite the die cylinder 50. During the operation 
of the embossing machine 54, embossment material (e.g., paper) (not shown) 
is fed between the die cylinder 50 and the opposing cylinder 66, and the 
rotary embossing die 18 imparts the embossing design 14 on the embossment 
material. 
The opposing cylinder 66 preferably has an opposing material 70 positioned 
thereon in opposite relationship to the embossing die 18. The opposing 
material 70, preferably an epoxy-based material, is spread on the opposing 
cylinder 66 before the embossing operation is commenced. After the 
opposing material 70 is sufficiently cured, i.e., not tacky to the touch, 
the embossing machine 54, and thus the die cylinder 50 and the opposing 
cylinder 66, is turned through one rotation so that the embossing die 18 
and the opposing material 70 contact one another. This rotational 
engagement results in a negative image of the embossing design 14 being 
formed on the opposing material 70. 
During the embossing operation, the positive image of the design 14 on the 
embossing die 18 and the negative image of the design 14 on the opposing 
material 70 cooperate to increase the embossed effect on the embossed 
material (e.g., paper) processed through the embossing machine 54. 
Preferably, so as not to distort the negative image of the design 14 
formed on the opposing material 70, the opposing material 70 is preferably 
formed of an epoxy material having a low shrink factor. 
The following materials are suitable for use in the present invention: the 
metallic plate 10 may be formed of brass or magnesium; the epoxy support 
plate material is Epoxical 301 supplied by U.S. Gypsum, which has a low 
shrink factor; and the opposing material 70 is BondAide P-1500. 
Alternately, the metallic plate 10, the support plate material and the 
opposing material 70 may be formed of any material suitable for the 
application. 
As can be readily seen, it is contemplated that numerous individual 
embossing dies may be mounted on a single die cylinder. Therefore, a 
variety of embossing designs may be formed from the combination of 
individual embossing dies. Also, because of the relative light-weight and 
small size of the embossing dies 18 of the present invention, the 
embossing dies 18 may be easily removed from or added to a die cylinder to 
form a completely new design. Furthermore, because the embossing die 18 
includes a metallic plate 10, the die 18 will wear well. 
It should be appreciated that the present invention may be performed or 
configured as appropriate for the application. The embodiments described 
above are to be considered in all respects only as illustrative and not 
restrictive. The scope of the invention is indicated by the following 
claims rather than by the foregoing description. All changes which come 
within the meaning and range of equivalency of the claims are to be 
embraced within their scope.