Patent Publication Number: US-2005136153-A1

Title: Mold apparatus and method

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to molding systems, including devices, apparatus and methods for producing molded optical elements such as lenses More particularly, the present invention relates to an injection molding apparatus for forming optically transmissive products with micro-refractive and/or diffractive surfaces.  
      2. Discussion of the Related Art  
      It is has been suggested to form a mold apparatus by etching diffractive patterns in a flat substrate, cutting the patterns from the substrate, and applying them to mold pins. The pins are used in mold cavities to form molded products with the desired patterns. According to this technique, a separate optical pattern is provided for each mold pin. The technique is disadvantageous because it requires the step of cutting the mold pins from the patterned substrate.  
      It has also been suggested to form a mold apparatus with a flat portion and a “stamper” opposed to the flat portion. Audio or video data may be digitally patterned in the stamper by lithography. The stamper is used to define disc-shaped molded products. This approach is disadvantageous because it produces only one product per injection mold cycle. Additional processing steps are required to form multiple products per mold cycle.  
     SUMMARY OF INVENTION  
      The present invention overcomes to a great extent the deficiencies of the prior art. The present invention relates to a mold apparatus for producing molded optical elements. The apparatus includes a first mold unit for defining mold cavities and flow passageways, and a second mold unit having a patterned surface for sealing against the first unit. The patterned mold surface may be formed with a plurality of optical patterns.  
      According to another aspect of the invention, mold pins are used to define die mold cavities. The mold pins are located in the first unit so as to be opposed to the optical patterns in the mold surface. According to a preferred embodiment of the invention, the first mold unit has a front face opposed to the mold surface of the second mold unit, and the mold passageways are formed in the front face.  
      According to another aspect of the invention, the first mold unit is a removable cutter unit, and the apparatus is arranged to receive other cutter units to produce molded products of different sizes and shapes.  
      According to another aspect of the invention, the mold surface is in the form of a metal disc-shaped puck. The metal puck may be removed and replaced by like-shaped metal pucks having different optical mold patterns. The various metal pucks may be readily interchangeable so that the apparatus can be used to produce molded elements having different optical characteristics.  
      According to another aspect of the invention, the mold apparatus may be used to form transparent or optically transmissive lenses and other optical elements or devices. The optical elements may have micro-refractive and/or diffractive patterns molded into first surfaces and planar opposite surfaces. The patterned surfaces may be formed by the metal puck. The planar opposite surfaces may be formed by the mold pins. The molded products may be formed of optical-grade polycarbonate or other suitable materials.  
      The present invention also relates to a method of making molded optical elements and devices. In a preferred embodiment of the invention, the method involves an injection molding process. The method may also involve changing or replacing components of the mold apparatus to produce elements of different sizes, shapes and/or optical characterstics.  
      The present invention also relates to the production of analog topographic patterns and other patterns on a metal puck for use in a mold apparatus. The patterns may be spaced apart from each other on the otherwise flat surface of the metal puck. According to one aspect of the invention, the metal puck is formed by using an analog gray scale mask to pattern photoresist material. In alternative embodiments of the invention, the patterns are formed by ion milling or electron beam lithography.  
      According to the present invention, many molded products may be formed by a single mold apparatus during a single injection cycle. The optical surfaces of the multiple products may be defined by a single patterned puck. There is no need to separate the products from each other after molding. The products may be formed individually and simultaneously within a single apparatus. The same apparatus may be used to produce molded elements of different sizes, shapes and/or optical characteristics by changing out the respective mold surfaces.  
      These and other objects and advantages of the invention may be best understood with reference to the following detailed description of preferred embodiments of the invention, the appended claims and the several drawings attached hereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a partially broken-away side view of a mold apparatus constructed in accordance with a preferred embodiment of the present invention.  
       FIG. 2  is a front view of a cutter unit for the apparatus of  FIG. 1 .  
       FIG. 3  is a rear view of the cutter unit of  FIG. 2 .  
       FIG. 4  is a cross-sectional view of the cutter unit of  FIG. 2 , taken along line  4 - 4 .  
       FIG. 5  is a side view of a cutter pin for the apparatus of  FIG. 1 .  
       FIG. 6  is a front view of a puck for the mold apparatus of  FIG. 1 .  
       FIG. 7  is a cross-sectional view of the puck of  FIG. 6 , taken along line  7 - 7 .  
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Referring now to the drawings, where like reference numerals designate like elements, there is shown in  FIG. 1 a  mold apparatus  10  constructed in accordance with a preferred embodiment of the present invention. The mold apparatus  10  has a cutter unit  12  and a disc-shaped metal puck  14 . The cutter unit  12  may be formed of machined metal or another suitable material. The cutter unit  12  and the puck  14  cooperate to define mold cavities  86  and flow passageways  84  for use in an injection molding process, as described in more detail below. The cutter unit  12  and the puck  14  are removably attached to respective mold units  16 ,  18 .  
      In the illustrated embodiment, the first mold unit  16  is operated by a suitable operating mechanism  20 . The mechanism  20  may be used to move the mold unit  16  and the cutter unit  12  toward and away from the puck  14  in the directions of arrows  22 ,  24 . If desired, the mechanism  20  also may be used to control the positions of cutter pins  90  within the cutter unit  12 , as described in more detail below. The second mold unit  18  may be fixed in place or movable toward and away from the cutter unit  12 . The present invention should not be limited to the specific instrumentalities shown and described in detail herein.  
      In operation, the cutter unit  12  is attached to the first mold unit  16  and the puck  14  is attached to the second mold unit  18 . Then the operating mechanism  20  moves the cutter unit  12  into face-to-face sealing contact with the puck  14  to define the mold cavities  86 . Then, molten plastic (not shown) is injected into the apparatus  10  through an inlet conduit  26  in the direction of arrow  28 . The plastic material may be polycarbonate, for example. The plastic fills the mold cavities  86  and solidifies to form diffractive optical elements.  
      Then the cutter unit  12  is separated from the puck  14  by the operating mechanism  20 , and the molded products (not shown) are removed from the mold cavities  86 . In a preferred method of operation, the apparatus  10  remains closed until the products are sufficiently solid to be removed from the cutter unit  12  and handled without damage. If desired, a replacement cutter unit and/or a replacement puck (not shown) may be substituted for the original components  12 ,  14  to reconfigure the apparatus  10  to form molded optical elements of different sizes and/or different optical characteristics.  
      Referring now to  FIGS. 2 and 3 , the cutter unit  12  has a front face  30  and a back face  32 . The front face  30  is sealed against the puck  14  when the apparatus  10  is in the closed position shown in  FIG. 1 . The back face  32  of the cutter unit  12  is attached to the first mold unit  16 . Suitable structures, such as threaded openings  34 , are provided for removably connecting the cutter unit  12  to the first mold unit  16 . A notch  36  may be provided for aligning the cutter unit  12  with respect to the apparatus  10  during assembly. If desired, the cutter unit  12  may be removed from the mold unit  16  and replaced with another cutter unit that defines mold cavities  86  of different shapes and/or sizes.  
      Mold openings  46 ,  48 ,  50 ,  52 ,  54 ,  56 ,  58 ,  60  extend axially through the cutter unit  12 . Each mold opening  46 - 60  may extend from the front face  30  of the cutter unit  12  to the back face  32 . In the illustrated embodiment, each mold opening  46 - 60  has the same cylindrical construction. The present invention should not be limited, however, to the specific embodiments shown and described herein. Thus, for example, some of the mold openings may have different diameters than others, and/or some of the openings may be square or rectangular. If desired, each mold opening  46 - 60  may be provided with a counter bore  62  ( FIG. 3 ) for accommodating suitable pin-handling equipment as described in more detail below.  
      A resin flow passageway  64  ( FIG. 6 ) extends axially through the center of the puck  14 . In addition, radial passageways  66 ,  68 ,  70 ,  72 ,  74 ,  76 ,  78 ,  80  ( FIG. 2 ) are formed in the front face  30  of the cutter unit  12 . The radial passageways  66 - 80  are in fluid communication with the axial passageway  64  when the mold apparatus  10  is in the closed position shown in  FIG. 1 . In the closed position ( FIG. 1 ), the radial passageways  66 - 80  are enclosed and sealed by the front face  82  of the puck  14 . In the illustrated embodiment, the enclosed passageways  66 - 80  have semi-circular cross-sectional configurations.  
      During the injection molding process, molten resin flows through the inlet conduit  26 , then through the axial passageway  64 , then through the radial passageways  66 - 80  (formed between the cutter unit  12  and the puck  14 ), and from there into the mold openings  46 - 60 . Necked-down gate regions  84  may be formed between the radial passageways  66 - 80  and the respective mold openings  46 - 60 . The necked-down gate regions  84  have reduced cross-sectional flow areas to facilitate removal of finished products from the associated runner system (scrap). A scrap removal pin (not shown) may be located in an axial opening  65 . The scrap removal pin may be used at the conclusion of the injection molding process to assist in the removal of the runner system from the cutter unit  12 .  
      It should be understood that the use of the word “cutter” in the term “cutter unit” does not necessarily mean that the unit  12  performs a cutting function. In the illustrated embodiment, the cutter unit  12  is intended to form the illustrated mold cavities. The cutter unit  12  is not used to cut molded plastic into finished products.  
      The mold cavities  86  are formed in the mold openings  46 - 60 . When the apparatus  10  is in the closed position, the bottom surfaces of the mold cavities  86  are defined by the puck  12 . The puck  12  forms optical patterns in the bottom surfaces of the molded products as described in more detail below. The side walls of the mold cavities  86  ( FIG. 4 ) are defined by the sides of the mold openings  46 - 60 . In the illustrated embodiment, the mold openings  46 - 60  have cylindrical side walls. The top surfaces of the mold cavities  86  are defined by the front end faces  88  of suitable mold pins  90  ( FIG. 5 ). A separate mold pin  90  may be provided for each mold opening  46 - 60 .  
      The diameters  92  of the pins  90  may be the same as the internal diameters  94  ( FIG. 4 ) of the mold openings  46 - 60 . The pins  90  are axially slidable within the mold openings  46 - 60 . In the illustrated apparatus  10 , there are eight mold cavities  86  and eight pins  90  so that eight optical elements (not shown) can be formed in each injection molding cycle. More or fewer mold cavities may be employed, however. The present invention should not be limited to the specific arrangements shown in the drawings or described herein.  
      The front end faces  88  of the mold pins  90  may be smooth or mirrored. In a preferred embodiment of the invention, the end faces  88  are formed of polished metal. The polished faces  88  form corresponding planar surfaces in the finished products. In an alternative embodiment of the invention, the end faces  88  may be provided with an optical pattern to produce products with patterns on both sides. In other embodiments of the invention, the faces  88  may have curvatures to form molded products with convex or concave surfaces. The thicknesses of the optical elements formed by the apparatus  10  may be defined by the lengths of the pins  90 . If relatively long pins  90  are used, the ends  88  of the pins  90  are located close to the puck  14  to form relatively thin optical products. Shorter pins  90  may be used to form thicker products.  
      After the optical elements are formed within the mold cavities  86 , and the cutter unit  12  is moved away from the puck  14 , the pins  90  may be used to push the molded elements out of the cutter unit  12 . The positions and movements of the pins  90  may be controlled by the operating mechanism  20 . The pins  90  are attached to the operating mechanism  20  by suitable means (not shown) which may be received within the counterbores  62 . Suitable slots  96  ( FIG. 5 ) may be provided to prevent rotation of the pins  90  with respect to the actuating mechanism  20  and/or the cutter unit  12 .  
      The front face  82  of the puck  14  is shown in  FIG. 6 . Suitable bolt holes  100 ,  102 ,  104 ,  106  may be used to connect the puck  14  to the second mold unit  18 . In addition, openings  108 ,  110  may be arranged to receive alignment pins (not shown) extending from the second mold unit  18  to precisely align the puck  14  within the apparatus  10 . If desired, countersunk portions  112  ( FIG. 7 ) may be machined into the holes  100 - 106  to receive bolt heads (not shown). This way, the front face  82  of the puck  14  fits flat against the front face  30  of the cutter unit  12  when the puck  14  is mounted in the apparatus  10 .  
      According to a preferred embodiment of the invention, micro-refractive or diffractive optical patterns  114 ,  116 ,  118 ,  120 ,  122 ,  124 ,  126 ,  128  are formed in the front face  82  of the puck  14 . Each pattern  114 - 128  is aligned with respect to the mold openings  46 - 60 . The patterns  114 - 128  are spaced apart from each other. The patterns  114 - 128  are formed on only one side of the puck  18 . Except for the patterns  114 - 128 , the face  82  of the puck  14  may be perfectly flat. Such flatness makes it easier to use lithographic and other techniques to form the desired patterns  114 - 128 .  
      In a preferred embodiment of the invention, the patterns  114 - 128  are identical to each other, within each puck  12 . Replacement pucks for the apparatus  10  may be provided with different etched patterns to form products with different optical characteristics. The replacement pucks may have the same connection and alignment structure  100 - 110  so as to be readily installed into the apparatus  10 . In addition, the replacement pucks may have the same arrangement of patterns as the illustrated puck  14  such that the optical patterns in the replacement pucks are aligned with the mold openings  46 - 60 .  
      In operation, the cutter unit  12  is pressed tightly against the face  82  of the puck  14 , causing the individual mold cavities  86  to be defined by the mold openings  46 - 60 , the front polished ends  88  of the pins  90 , and the puck patterns  114 - 128 . After the desired number of molded products are formed, the puck  14  may be removed from the second mold unit  18  and replaced with a different puck insert having the same overall configuration but different optical patterns opposed to the mold openings  46 - 60 .  
      Molded products formed by the illustrated apparatus may have planar surfaces on one side formed by the polished end faces  88  of the pins  90  and patterned surfaces on the other side formed by the patterns  114 - 128  in the puck  14 . The products may be formed of a suitable transparent or optically transmissive material. Thus, the finished products may be used as micro-refractive and/or diffractive lenses. As described in more detail below, the patterns  114 - 128  may be formed by photolithographic mastering with analog relief patterns.  
      The patterns  114 - 128  may be formed in the puck surface  82  by a variety of lithographic and other techniques, including the techniques disclosed in U.S. patent application Ser. No. 08/788,289, filed Jan. 24, 1997. The entire disclosure of U.S. patent application Ser. No. 08/788,289 is expressly incorporated herein by reference.  
      In addition, the patterns  114 - 128  may be formed by an analog gray scale mask technique, with the puck surface  82  being patterned by ultraviolet (UV) lithography. According to this technique, a metal surface is covered with photoresist. Then an analog gray scale mask is used to pattern the photoresist either by contact printing or by reduction lithography. After the photoresist is patterned, it is developed according to known procedures. The relief pattern on the photoresist is the negative of the desired mold pattern. Then at least three different techniques may be employed to complete the puck  14 .  
      In a first completion technique, the patterned photoresist is metalized. The metalized substrate is then inserted into an electroplating bath. A metal surface is grown on the substrate. The process is stopped when the substrate attains the desired thickness. The original substrate is removed and the photoresist is removed. The back side of the patterned and electroformed disc is then polished flat to form the puck  14 .  
      In a second completion technique, the patterned photoresist-on-metal structure is placed in an ion milling machine. The ion milling machine transfers the analog pattern in the photoresist directly into the metal material to form the patterned puck  14 .  
      In a third completion technique, a non-metallic substrate is etched in a reactive ion etching (RIE) chamber. The etched substrate is then metalized, and then the electroformed product is removed from the non-metallic substrate. The back side of the patterned disc is then polished fiat to form the finished puck  14  for the apparatus  10 .  
      As an alternative to the analog gray scale mask technique described above, the puck  14  may be formed with an analog profile by a focused ion beam (FIB) apparatus. According to this aspect of the invention, a metal substrate is used without photoresist. The desired refractive or diffractive analog pattern is milled or written directly into the metal material of the puck  14 . The desired patterns  114 - 128  may be formed either by removal or deposition of metallic material.  
      According to yet another method of making the puck  14 , analog profiles may be formed by a direct write technique with electron beam lithography. According to this aspect of the invention, the patterns  114 - 128  are generated by electron beam lithography with the exposure of the electron beam being controlled at each position to form a relief pattern in the electron resist. The photoresist is then developed and the resulting patterned substrate is then used to create the puck  14  according to any one of the three completion techniques described above.  
      The above description and drawings are only illustrative of preferred embodiments which can achieve and provide the objects, features and advantages of the present invention. It is not intended that the invention be limited to the embodiments shown and described in detail herein. Modifications coming within the spirit and scope of the following claims are to be considered part of the invention.