Abstract:
A print pad for printing on a concave surface is molded to the forward surface of a cylindrical base. The base has a cavity therein and at least one hole extending from the forward surface thereof to the cavity. The print pad is made by filling a female mold with liquid polymer and positioning the forward surface of the base against the rear of the mold. Excess liquid polymer from the mold flows through the hole and into the cavity. As the polymer cures it contracts and draws liquefied polymer out of the cavity so that the cured print pad is not deformed.

Description:
The applicant claims priority from his provisional application filed Jul. 18, 2006 and assigned Ser. No. 60/831,716. The present invention relates to print pads of the type used to print on a concave surface of a mold used to form a contact lens. 

   BACKGROUND OF THE INVENTION 
   It has become common to print the design of an iris of an eye on the surface of a contact lens so as to change the color of the eyes of one wearing the contact lenses. The colorings that make up the human eye are concentrated in numerous radially extending strands with various shades of color in the strands. In order to have the appearance of a natural eye, the pigments must be applied in narrow radially outwardly extending strands similar to the strands of pigment in the eye. 
   The inks that apply the pigment to the contact lens may be applied to the outer surface of the lens after the lens is manufactured, or may be printed on the concave inner surface of a mold used to manufacture the lens such that when the lens is withdrawn from the mold, the pigment is already imbedded into the convex outer surface of the lens. To apply a colored ink to the concave surface of a mold used to form a lens, the ink is applied by a compressible print pad having a precisely contoured outer surface that deforms as the pad is compressed against the concave surface so as to apply printing across the entire concave surface of the mold. 
   The outer surface of a print pad used to apply printing to the concave surface of such a mold must also be highly polished in order that the fine lines of color printing be released from the surface of the pad after the surface of the print pad is withdrawn. A print pad useable for printing the design of an eye to the concave surface of a mold, therefore, must be precisely shaped and have a highly polished outer surface. 
   The manufacturers of print pads have had difficulty obtaining the degree of polish needed and the precise body contour required for such a print pad. Once manufactured, the print pads are therefore carefully checked to insure that the print pad as manufactured has the desired contour and degree of polish. A very high percentage of the print pads manufactured are discarded as failing to meet the required standards. It is desirable, therefore, to provide a method of uniformly manufacturing print pads that meet very high standards with respect to contour and polish. 
   SUMMARY OF THE INVENTION 
   Briefly, the present invention is embodied in a method of manufacturing a print pad where the print pad includes a print pad body made of a compressible material such as a polymer and a rigid base for retaining the print pad to a machine. In accordance with the method, a male mold is provided in the shape of the desired print pad. The contour of the male mold must be carefully checked to confirm that it conforms to the exact contour required to maximize the application qualities of the print pad. The outer surface of the male mold is also polished to a shine such that even under a high magnification, the surface of the male mold is smooth. The male mold is then used to form a female mold using an injection molding process. 
   The injection molded female mold has a generally bulbous forward portion, the inner portions of which are complementary to the bulbous end of the print pad body, and rearward of the bulbous end is a generally frustoconical midportion ending in an annular rearward end. The female mold also has an annular flange extending radially outward around the circumference of the rearward end, and extending rearwardly of the rearwardly surface of the annular flange is a rearwardly extending annular ridge. 
   To form the female mold, including the annular flange and the rearwardly facing annular ridge, a parent female mold of the type required for injection molding is formed having a cavity corresponding to the outer surfaces of the female mold needed to form the print pad body. This parent female injection mold therefore has an annular radially extending groove corresponding to the radially extending flange of the female mold formed therein, and a rearwardly extending annular cavity complementary to the rearwardly extending ridge of the female mold needed to form the print pad. The parent female mold is then used as an injection mold to form the female mold. 
   To manufacture the print pad, the female mold is positioned with the open end of the female mold extending upwardly and the bulbous cavity portion extending downwardly. Thereafter, the mold is filled with a liquid polymer of the type that will harden to form the body of a print pad. The mold is filled until the liquid overflows the rearwardly extending annular ridge. After excess liquid poured into the mold has flowed away from the annular ridge, surface tension will retain a bubble of liquefied polymer above the annular ridge surrounding the rearward opening of the female mold. Thereafter a base is provided having a planar forward surface and having a cavity extending into the rearward end of the base. At least one hole extending through the forward surface to the cavity within. The base is then positioned with the forward surface applied against the rearwardly extending flange of the female mold. When the base is positioned against the rearwardly extending tubular flange, excess liquid in the female mold will pass through the hole and enter the cavity within the base. 
   The liquefied polymer is then allowed to harden into a mass. As the liquefied material hardens, it contracts, and as the liquid contracts, some liquid is withdrawn from the cavity in the base through the hole and into the body of the female mold. As a result, the hardened polymer retains the exterior contour of the inner shape of the female mold. Also, since the female mold has been manufactured from a male mold having a polished outer surface, the inner surface of the female mold is also highly polished and print pads formed in the female mold have a highly polished surface. 
   Once the liquefied polymer has hardened into a mass, the print pad body will be formed to the surface of the base. The base with the print pad body attached thereto can thereafter be removed from the mold and the manufactured print pad will have the desired contour and polish required to apply inks to the concave surfaces of a mold for making a contact lens. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention will be had after a reading of the following detailed description taken in conjunction with the drawings wherein: 
       FIG. 1  is a side view of a print pad in accordance with the invention; 
       FIG. 2  is a cross-sectional view of a pair of injection molds used to form a female mold needed to make the print pad shown in  FIG. 1 ; 
       FIG. 3  is a cross-sectional view of a female mold manufactured from the injection mold shown in  FIG. 2 ; 
       FIG. 4  is an isometric view of a base for the print pad shown in  FIG. 1 ; 
       FIG. 5  is a second isometric view of the base shown in  FIG. 4 ; 
       FIG. 6  is a cross-sectional view of the base shown in  FIG. 4 ; 
       FIG. 7  is a cross-sectional view of the female mold shown in  FIG. 3  filled with a liquid polymer until the liquid overflows the mold; and 
       FIG. 8  is a cross-sectional view of the mold and polymer shown in  FIG. 8  after the base shown in  FIG. 4  has been positioned across the open end thereof. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a print pad  10  made in accordance with the present invention has a body  12  made of a suitable polymer and includes a bulbous forward end  14  and behind the bulbous forward end a bell shaped midsection  16  and a frustoconical rearward end  18 . The body  12  is molded to a cylindrical plastic base  20  and the body  12  and base  20  are symmetric about a longitudinal axis  22 . The base  20  has a radially outwardly extending annular flange  21  around the forward end thereof that extends radially outward of the largest diameter of the body  12 . The base is shaped to be received in a retainer of a printing machine, not shown, that applies the bulbous forward end  14  of the body  12  against a concave surface of a mold, also not shown, for manufacturing a contact lens having printing to the surface thereof. 
   When the print pad  10  is inserted into a machine, the print pad  10  is retained with the base  20  extending upward where it is received in a retainer, not shown, with the bulbous forward end  14  extending downwardly. The bulbous forward end  14  also extends downwardly when the body  12  of the print pad  10  is being manufactured as described herein. Even though the print pad  10  is oriented with the bulbous end  14  directed downwardly both while it is manufactured and while it is in use, for the purpose of this discussion the various parts of the print pad  10  will be described as being directed forwardly, when directed towards the bulbous end  14 , and directed rearwardly when directed towards the base  20 . In similar fashion, the parts of the various molds used to make the body  12  of the print pad  10  will also be described as having forward parts that are positioned adjacent the forward end  14  of the print pad body  12  and as having rearward parts that are adjacent the frustoconical rearward end  18  of the body  12 . 
   Referring to  FIG. 3 , the body  12  is formed in a unitary plastic female mold  24 , the forward end  26  of which has a cavity therein shaped complementary to the bulbous forward end  14  of the body  12 . Rearward of the forward end of the cavity  26 , is a tapered midsection  28 , the interior of which is shaped complementary to the midsection  16  of the body  12 , and a more rearward frustoconical portion  30  having inner walls complementary to the outer surfaces of frustoconical rearward end  18  of the body  12 . At the rearward end of the mold  24  is a radial flange  32  that extends radially outward of the frustoconical portion  30 . The radial flange  32  has a planar rearward surface  34 , and extending rearwardly of the planar rearward surface  34  is a rearwardly extending annular ridge  36 . The rearwardly extending tubular ridge  36  has a circular rearward edge  35  that defines a plane perpendicular to the rotational axis  38  of the mold  24 . The tubular ridge  36  has a cylindrical inner surface  37  having an inner diameter a little larger than the diameter of the annular flange  21  at the forward end of the base  20 . Also, a short distance forward of the rearward edge  37  and along the inner surface of the mold  24  is an annular shoulder  39  that extends between the inner opening of the tubular portion  36  and the rearward end of the frustoconical portion  30 . 
   Referring to  FIG. 7 , when the mold  24  is used to form the body  12  of the print pad  10 , the mold  24  is positioned on a retainer  41  with the planar surface  34  oriented horizontally and directed upwardly and the longitudinal axis  38  extending vertically. Liquefied polymer  40  is then poured into the cavity of the mold  24  until the polymer  40  overflows over the annular rearwardly extending ridge  36 . Excess liquid  40  that overflows over the edge  35  of the ridge  36 , then falls away from the ridge  36  to the planar surface  34  and flows away from the mold  24 . The surface of the liquefied polymer  40  left in the mold mounds above the rearward ridge  36  because of the surface tension of the liquid. 
   Referring to  FIGS. 4 ,  5 , and  6 , the base  20  for assembly to the body  12  has a tubular outer body  42  and across one end of the tubular outer body  42  is a planar forward surface  44 . A tubular retainer  46  extends axially through the center of the tubular outer body  42  and the central opening  47  of the tubular retainer  46  is closed at the forward end. The open rearward end of the tubular retainer  46  receives a retaining screw for retaining the base to a printing machine, not shown. Between the inner wall of the tubular outer body  42  and the outer wall of the tubular retainer  46  is an annular cavity  50 , the rearward end of which is open to the ambient. A pair of diametrically spaced transverse holes  52 ,  54  extend through the planar forward surface  44  and into the annular cavity  50 . 
   Referring to  FIGS. 7 and 8 , once the female mold  24  has been filled with liquefied polymer as depicted in  FIG. 7 , the base  20  is positioned across the open end of the mold  24  with the annular flange  21  fitted into the cylindrical surface  37  within the tubular ridge  36  and the planar forward surface  44  against the annular shoulder  39 . As the planar forward surface  44  is positioned against the annular shoulder  39 , excess liquid mounded up over the open end of the mold  24  enters through the transverse holes  52 ,  54  and flows into the cavity  50 . With the forward surface  44  of the base  20  positioned tightly against the annular shoulder  39  of the mold  24 , the liquid polymer  40  is allowed to harden and cure. As the polymer  40  hardens, it contracts. As the polymer contracts, it applies a contractive force throughout the polymer. Simultaneously, atmospheric pressure applies force to the polymer in the open end of the cavity  50  and urges excessive liquid in the cavity  50  through the transverse holes  52 ,  54  and into the cavity of the mold  24 . As the polymer shrinks the outer surfaces of the print pad body  12  formed within the mold  24  do not become deformed because polymer from the cavity  50  compensates for the shrinkage that occurs as the polymer cures. The holes  52 ,  54  between the forward surface  44  and the cavity  50  enable the polymer  40  of the print pad  10  to shrink without causing the outer surface of the polymer to pull away from the surface of the female mold  24  and thereby avoid deformities in the formed print pad  10 . After the polymer  40  is hardened, the body  12  of the print pad  10  can be withdrawn from the female mold  24 . 
   As can be seen, a critical element to the manufacture of the print pad  10  is the forming of the female mold  24 . Female molds used to manufacture print pads in accordance with the prior art are manufactured using a thermal molding process. The inner surfaces of molds used in a thermal forming process must be manually polished, however, manual polishing of the inner surfaces of a mold frequently results in the mold being deformed such that it no longer retains the precise configuration required of a print pad used to print on the concave surface of a contact lens mold. The result is that many molds made using a thermal molding process must be discarded. This problem is avoided where the female mold  24  is injection molded. 
   Referring to  FIG. 2 , the mold  24  employed in the present invention is manufactured using a injection molding process in which a male mold  60  is formed with the forward end  61  having an outer surface exactly as described with respect to the outer surface  14 ,  16 ,  18  of the print pad body  12 . Rearward of the forward end  61  is a cylindrical rearward end  62  having an outer diameter equal to the inner diameter of the tubular ridge  36  of the finished mold  24 , leaving an annular shoulder  63  between the forward end  61  and the rearward end  62 . The outer surface of the forward end  61  of the mold  60  is also highly polished. It should be appreciated that the outer surface of male mold  60  can be highly polished without disturbing the contour of its outer surface. In the injection molding process, the male mold  60  is spaced from and generally surrounded by a parent female mold  64  having an inner cavity with a forward end  65  that is complementary to the outer surface of the forward end  26  of the mold  24 . The mold  64  also has a midsection  66  that is generally complementary to the outer surface of the midsection  28  of mold  24 , and a rearward portion  68  complementary to the outer surface of the rearward portion  30  of mold  24 . The mold  64  also has an annular shoulder  70  complementary to forward surface  34  of the radial flange  32  of the mold  24 . An annular plate  72  extends around the rearward end of the mold  64  and has a surface  73  complementary to the planar annular surface  34  of the mold  24 , and a central opening  74  the inner contour of which is complementary to the annular ridge  36  of the mold  24 . The mold  62  also has a suitable access port  76  through which liquefied plastic, not shown, is injected to fill the inner cavity of the parent mold assembled from the various parts  60 ,  64 ,  72 . The liquefied plastic is then allowed to harden after which the completed female mold  24  is removed. 
   While the present invention has been described with respect to a single embodiment, it will be appreciated that many modifications and variations may be made without departing from the true spirit and scope of the invention. It is therefore the intent of the appended claims to cover all such modifications and variations that fall within the true spirit and scope of the invention.