Abstract:
A decorated strip of coated, heat-shrinkable, plastic sheet material is placed in a spiral slot formed in a silicone rubber mold. The spiral slot is defined by a spiral wall having a uniform wall thickness. Upon heating in an oven, the material shrinks, forming a resiliently expansible arc-shaped band that can be worn as a bracelet or wristband.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to hobby crafts, and particularly to a bracelet mold and to the use of the mold to produce a bracelet from a decorated strip of coated, heat-shrinkable, polystyrene film. 
       BACKGROUND OF THE INVENTION 
       [0002]    For about forty years, a popular hobby craft activity for both children and adults has been the production of three-dimensional objects from a heat-shrinkable sheet material known by the trademark SHRINKY DINKS, a registered trademark of K &amp; B Innovations, Inc. The material consists of a sheet of thin plastic material that can be colored and/or cut out, and then heated to cause it to shrink and form thickened and hardened art forms. Typically the plastic sheet material is composed of a heat-shrinkable polystyrene base material coated with a water-insoluble, ink-receptive coating. The sheet material and some of its uses are described in U.S. Pat. No. 4,102,456, granted Jul. 25, 1978, and U.S. Pat. No. 6,157,865, granted Dec. 5, 2000. Coatings for the base material are described in U.S. Pat. No. 3,889,270 granted Jun. 10, 1975, U.S. Pat. No. 4,503,111 granted Mar. 5, 1985, U.S. Pat. No. 4,555,437 granted Nov. 26, 1985, U.S. Pat. No. 5,190,805 granted Mar. 2, 1993 and U.S. Pat. No. 5,206,071, granted Apr. 27, 1993. The disclosures of all of the aforementioned United States patents are incorporated by reference. 
         [0003]    As supplied, the plastic sheet material is usually flat, and accordingly to form a wristband, bracelet, or the like, from a decorated strip of such material, it would be necessary to provide for a connection of one end of the strip to the other end. Heating the strip will cause it to curl, but, because shrinkage takes place unevenly, the result is usually not aesthetically acceptable. 
         [0004]    There has been a need for a simple, convenient, and reliable way to utilize SHRINKY DINK sheet material to produce wearable jewelry in the nature wrist bands, bracelets and the like. 
       SUMMARY OF THE INVENTION 
       [0005]    The mold in accordance with the invention comprises a block of silicone rubber having a bottom side and a top side parallel to the bottom side. A spiral slot is formed in said block, and open at the top side of the block and closed at the bottom side of the block. The spiral slot extends by at least two full turns, i.e., through an angle of at least 720°, and preferably 810°, around an axis that is in perpendicular relation to the top and bottom sides of the block A cover, preferably also made of silicone rubber, fits removably over the top side of said block, for enclosing the spiral slot. 
         [0006]    Preferably, each of the bottom and top sides of the silicone rubber block has a central opening, and the central opening in the bottom side is connected to the central opening in the top side by a through passage. The spiral slot is preferably bounded by walls having a uniform thickness and extending from the bottom side of the block to the top side of the block. 
         [0007]    The process for making a bracelet in accordance with the invention comprises inserting a strip of heat-shrinkable sheet material into a spiral slot in a silicone rubber mold, heating the strip while the strip is in the mold, thereby causing said strip to shrink, to become resilient, and to assume an arc-shaped configuration when relaxed, and removing the strip from the mold. 
         [0008]    Preferably the spiral slot has a minimum radius not greater than 15 mm. and a maximum radius not greater than 25 mm. Ideally, the minimum radius of the spiral slot should be 15 mm, and its maximum radius should be 25 mm. The strip, in its arc-shaped configuration, can be expanded to receive an individual&#39;s wrist, and contracts by reason of its resilience to fit snugly but comfortably onto the individual&#39;s wrist. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an exploded perspective view of a mold in accordance with the invention, consisting of a mold body and a cover; 
           [0010]      FIG. 2  is a bottom plan view of the mold body; 
           [0011]      FIG. 3  is a perspective view illustrating the step of decorating a shrinkable strip in the process of making a bracelet using the mold; 
           [0012]      FIG. 4  is a perspective view illustrating the insertion of the decorated strip into the mold; 
           [0013]      FIG. 5  is a perspective view of the bracelet removed from the mold after heat treatment; and 
           [0014]      FIG. 6  is a perspective view showing the completed bracelet worn on an individual&#39;s wrist. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    A shown in  FIG. 1 , the mold comprises a mold body  10  and a removable cover  12 , both composed of a silicone rubber. Most silicone rubbers will withstand typical household oven temperatures which can exceed 230° C. (446° F.), and high heat resistant silicone rubbers are available that will withstand considerably higher temperatures. 
         [0016]    The mold body  10  is in the form of a block of silicone rubber having a flat bottom side  14  and a top side  16  in a plane parallel to the bottom side. The top side  16  has a central opening  18 , and the bottom side  14  has a central opening  20 , shown in  FIG. 2 . These openings  18  and  20  are connected to each other by a through passage  22  extending from the bottom side  14  to the top side  16 . 
         [0017]    As seen in  FIG. 1 , a spiral slot  24  is formed in the silicone rubber block  10 . This slot is open at the top side of the block but closed at the bottom side. The slot has a uniform width, and extends at least two full turns) (720° around a vertical axis, preferably extending through an angle of 810°, i.e., two and one quarter turns. 
         [0018]    The term “spiral” as used herein refers to a curve defined by a point on a radial line that rotates about a center, where the distance along the radial line from the center to the point increases at a rate proportional to the angle between the radial line and a fixed reference radial line extending through the center. That is, a spiral is defined in polar coordinates as a continuous portion of a curve r=kθ, where r is the distance from the center to the point, θ is the angle, and k is a constant. 
         [0019]    As seen in  FIG. 1 , the spiral slot is bounded by a spiral wall  26  that extends from an inner face of the bottom side  14  of the block to the top side  16  of the block. The spiral wall  26  has a uniform thickness, preferably 2 mm. The inner and outer ends of the spiral slot are closed respectively by wall portions  28  and  30 , each of which crosses the spiral slot and extends from an end of the spiral wall to an adjacent part of a next turn of the spiral wall. 
         [0020]    The uniform thickness of the spiral wall  24 , promotes uniform heating of a heat-shrinkable strip placed in the spiral slot. The central passage  22  makes it possible for the inner part of the spiral wall to have the same thickness as its other parts. 
         [0021]    The cover  12  is shaped to fit over the top of the mold body  10 , and has a flange  32 , which extends downward and is shaped to fit the upper portion of the outer wall of the mold body closely. 
         [0022]    The height of the mold body, i.e., the distance from the bottom side  14  to the top side  16 , is preferably about 32 mm, and the vertical height of the spiral slot  24  is slightly less, e.g., 30 mm. 
         [0023]    To make a bracelet, a user can first decorate a coated strip  34  of heat-shrinkable material as shown in  FIG. 3 , using an ink pen  36 , brush or similar utensil. Alternatively various printing techniques can be used, such as printing using an ink-jet printer controlled by a computer program to generate a decorative pattern, or image. 
         [0024]    The decorated strip, the length of which should be slightly less than the length of the spiral slot  24 , e.g. about 250 mm, is placed into the spiral slot as shown in  FIG. 4 . The strip is typically transparent, and therefore the decorated side of the strip can face either toward the inside or toward the outside of the spiral. The cover  12  ( FIG. 1 ) is then placed over the mold body  10 , and the covered mold body, with the heat-shrinkable strip inside it, is placed in an oven (which can be a conventional oven or a toaster oven), preheated to a temperature of 177° C. (350° F.), and allowed to bake for 6-7 minutes. Upon removal, the strip will have shrunk to about one-half its original length, and will have assumed an arc-shaped as shown in  FIG. 5 . To produce a wrist bracelet suitable for wearing both by children and adults, the spiral slot should have a minimum radius not greater than 15 mm. and a maximum radius not greater than 25 mm. Ideally, the minimum radius of the spiral slot should be 15 mm its maximum radius should be 25 mm. 
         [0025]    If the spiral slot in the mold has these minimum and maximum radii, the radius of the relaxed, arc-shaped strip shown in  FIG. 5  will be in the range of about 17 to 25 mm, smaller than the average radius of a child&#39;s wrist, and the size of the gap  38  between the ends of the strip will be in the range of about 10 to 25 mm. The strip can be expanded to receive an individual&#39;s wrist, and, because of its resilience, it will contract to fit the individual&#39;s wrist snugly but comfortably, as shown in  FIG. 6 .