Abstract:
A module for a modular conveyor belt, is described. The module is of a sandwich layer construction having a core polymeric material completely surrounded by a skin polymeric material. The skin material includes an antimicrobial material for inhibiting bacterial growth on the module, and the conveyor belt is particularly useful for conveying and transporting foods including food processing and food handling applications.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to beltings and more particularly to a modular conveyor belt comprising interconnected modules of a similar integral construction. The modules comprising the conveyor belt preferably include an antimicrobial material associated therewith to inhibit bacterial growth and which is safe for human contact. More particularly, the modules are formed of an injection molding process as a sandwich layer construction.  
           [0003]    2. Prior Art  
           [0004]    Modular conveyor belts are well known. For quality control purposes in the food industry it is desirable that the conveyor be readily inspected to assure cleanliness. Government and industry regulations also specify standards of inspection and cleanliness for equipment used in processing products for human consumption. There is, therefore, a need for a conveyor belt having associated therewith an antimicrobial material that inhibits bacterial growth and promotes improved hygiene conditions on the belting through extended wear, and that is safe for human contact. The antimicrobial material must also conform to the regulatory requirements of the country in which it is used. As will be explained in detail presently, the conveyor belt of the present invention built from modules comprising a central core of a first polymeric material completely encased by a polymeric skin of a second material and having an antimicrobial material associated with at least the skin material meets these criteria. This module configuration is referred to as a sandwich layer construction.  
         SUMMARY OF THE INVENTION  
         [0005]    The sandwich layer construction provides a module whose cross-section has a three-layer configuration. The outer or “skin” surface is of a polymeric material containing the antimicrobial material or compound, and the inner or “core” structure consists of another material, preferably a polymeric material. Antimicrobial materials are relatively expensive. In order to inhibit bacterial growth on a module, they only need to be present in the outer regions of the polymeric module. Also, in today&#39;s environmentally conscious society, there is an increased emphasis on recycling, which has prompted many molders to look for ways to use reground material.  
           [0006]    The sandwich layer module configuration effectively uses reground material as the core since it still has adequate physical properties. This construction takes advantage of the fact that the outer (skin) material is relatively thin, thereby helping reduce the cost of the molded article by minimizing the amount of virgin material and the amount of polymeric material containing an antimicrobial material. According to the present invention, the core of the sandwich module can also be a relatively inexpensive polymeric material, such as polyethylene, in comparison to the skin material which is of a higher grade.  
           [0007]    In one preferred molding technique referred to herein as the sandwich molding method, the sandwich configuration is achieved when two polymeric materials are conveyed one after the other into the mold cavity. When the polymeric materials are injected under laminar flow conditions, the injection melt begins to solidify immediately as it contacts the mold wall so that the melt at the center of the flow advances faster than the melt in the vicinity of the mold wall. Accordingly, polymeric material injected later displaces material injected earlier, particularly in the middle of the cross-section of the flow stream, while the melt that contacts the cold mold walls solidifies to form and maintain the outer or skin layer of the module. In this manner, the second polymeric material devoid of the antimicrobial material serves as the core structure and provides the module of the present invention having a sandwich or three-layer configuration.  
           [0008]    To ensure that the polymeric material intended to be the core of the module does not mix with the skin polymeric material in the sandwich molding method, the skin material having the antimicrobial material provided therein is always injected first. The core material then follows at a short timed overlap. The overlap in injection of the two materials is necessary to prevent the melt flow front from momentarily stopping which would result in surface blemishes called “knit lines”. With this type of timed sequence, the second (core) material must be a subsequent melt stream that flows through the flow cross-section of the first injected antimicrobial-containing polymeric material in order to form the sandwich configuration.  
           [0009]    Another preferred method for manufacturing a module having a sandwich layer configuration is termed an over molding method and comprises providing the core of the module in a first mold. The core is then centered in a second mold of a somewhat larger shaped cavity to provide an annulus about the entire surface of the core. A second polymeric material containing the antimicrobial material is then injected into the second mold to fill the annulus and bond to the core as the skin polymeric material.  
           [0010]    In that respect, the present invention relates to a modular conveyor belt having antimicrobial characteristics that inhibit bacterial growth and which is safe for human contact, the belting comprising: a plurality of like modules of a polymeric material, each module comprised of a polymeric material and including a first plurality of link ends, a second plurality of link ends and an intermediate section integrally formed with and joining the first and second plurality of link ends, wherein the link ends of each of the modules are releasably engaged between link ends of an adjacent module except for individual link ends disposed at the extreme sides of the module; a pivot rod for pivotally connecting the modules at engaged link ends; and an antimicrobial material incorporated into the polymeric material thereof, wherein the antimicrobial material is selected from the group consisting of antimicrobial compounds based on Mg +2 , Ca +2 , Zn +2 , Ag +2 , Cu +2 , Al +3 , their oxides and hydroxides, zinc pyrithione, imidazole, mixtures thereof, and wherein when the antimicrobial agent is incorporated into the polymeric material comprising the modules, the antimicrobial agent continuously inhibits bacterial growth on the belting and is safe for human contact. Further, the polymeric material comprising the module is in a sandwich layer construction having a first skin polymeric material supported on a second core polymeric material, and wherein the antimicrobial material is incorporated into the skin polymeric material at a greater concentration than that in the core.  
           [0011]    It is also contemplated by the present invention that the pivot rod can be of a sandwich molded configuration having the antimicrobial compound concentrated in the skin material.  
           [0012]    These and other aspects of the present invention will become more apparent to those of ordinary skill in the art by reference to the following description and to the appended drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0013]    [0013]FIGS. 1A to  1 C show a diagrammatic section through an injection molding apparatus suitable for manufacturing a module for a modular conveyor belt according to the present invention.  
         [0014]    [0014]FIG. 2 is a plan view, partly broken away, of one embodiment of a mold for the sandwich molding method for constructing a flat top module according to the present invention.  
         [0015]    [0015]FIG. 3 is a cross-sectional view along line  3 - 3  of FIG. 2.  
         [0016]    [0016]FIG. 4 is a plan view of a flat top module according to the present invention.  
         [0017]    [0017]FIG. 5 is a plan view, partly broken away, of one embodiment of a mold for the sandwich molding method for constructing a radius module according to the present invention.  
         [0018]    [0018]FIG. 6 is a cross-sectional view along line  6 - 6  of FIG. 5.  
         [0019]    [0019]FIG. 7 is a cross-sectional view along line  7 - 7  of FIG. 5.  
         [0020]    [0020]FIG. 8 is a perspective view of a radius module according to the present invention.  
         [0021]    [0021]FIG. 9 is a plan view, partially broken away, of another embodiment of a mold for an over mold method for constructing a flat top module according to the present invention.  
         [0022]    [0022]FIG. 10 is a cross-sectional view along line  10 - 10  of FIG. 9.  
         [0023]    [0023]FIG. 11 is a side elevational view of the core for a flat top module made by the over molding process.  
         [0024]    [0024]FIG. 12 is a cross-sectional view of the module shown in FIG. 11 positioned in a second mold for finishing the flat top module.  
         [0025]    [0025]FIG. 13 is a cross-sectional view of the second mold housing the module shown in FIG. 12 having a skin polymeric material molded to the core of the module.  
         [0026]    [0026]FIG. 14 is a cross-sectional view along line  14 - 14  of FIG. 13.  
         [0027]    [0027]FIG. 15 is a plan view of a flat top module made by an over molding process according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    Turning now to the drawings, FIGS. 1A to  1 C show a sandwich molding apparatus  10  including a mold  11  for making a sandwich module for a modular conveyor belt according to the present invention. An exemplary sandwich layer constructed flat top module  12  is shown in FIGS.  2  to  4  and  9  to  15  and an exemplary sandwich layer constructed radius module  14  is shown in FIGS.  5  to  8 . The structure of these modules will be described in detail below.  
         [0029]    The mold  11  for producing the modules  12 ,  14  having a sandwich layer construction includes first and second mating mold halves  11 A,  11 B forming a mold cavity  16  for receiving a plastic melt from an injection unit  18 . The mating mold halves  11 A,  11 B are mounted on a stationary platen  20  and a moving platen  22 , respectively. The stationary platen  20 , moving platen  22  and injection unit  18  are supported by a common base  24 . The mold  11  includes a sprue channel  26  through the first mold half  11 A which is in fluid flow communication with a nozzle  28  on the injection unit  18  when material is injected into the mold cavity  16 . The nozzle  28  is equipped with a shut-off valve (not shown) of the type that is well-known in the art.  
         [0030]    The main injection unit  18  has a barrel  30  which includes a feed screw  32  of a configuration that is typical for injection molding. The feed screw is controlled to reciprocate in the barrel  30  to plasticize and inject plastic into the mold  11 . The injection unit  18  is equipped with means, such as a hydraulic cylinder (not shown), to move the unit  18  linearly toward and away from the mold  11 . More specifically, the injection unit  18  is moved against the mold  11  for injection, then is retracted away from the mold  11  and stationary platen  20 , so that a second polymeric skin material can be fed into the injection unit barrel  30 . The significance of a polymeric skin material will be described in detail below.  
         [0031]    An auxiliary plasticizing unit  34  is mounted adjacent the injection unit  18  on the stationary platen  20  and is capable of movement along a line perpendicular to the injection unit  18 . Connected to the end of the auxiliary plasticizing unit  34  is a hot runner manifold  36 . This orientation of the auxiliary unit  34  facilitates its positioning so that the hot runner manifold  36  is properly aligned in front of the injection unit  18 , enabling direct connection with the nozzle  28 . The auxiliary unit  34  is a non-reciprocating extruder; however, it could also be a second reciprocating screw injection unit, if desired.  
         [0032]    A cycle of operation for the production of a sandwich layer module made by a sandwich molding method according to the present invention will now be described with respect to FIGS. 1A to  1 C. The injection unit  18  is retracted to a rearward position (FIG. 1A), that provides clearance between the stationary platen  20  and the nozzle  28 . The auxiliary unit  34  is then moved downward so that the hot runner manifold  36  is disposed in front of the injection unit  18 . The nozzle  28  of injection unit  18  then moves against the hot runner manifold  36  to establish a fluid tight connection between the injection unit  18  and the auxiliary unit  34 . The auxiliary unit  34  is then activated to transfer plasticized skin material  38  via the hot runner manifold  36 , through the nozzle  28  and into the end of the barrel  30  of the injection unit  18 , causing the screw  32  to move backward within the barrel. As shown in FIG. 1B, transfer of the skin material  38  from the auxiliary unit  34  continues until a sufficient volume of polymeric material as defined by the module  12 ,  14  geometry has been transferred.  
         [0033]    When the transfer of the polymeric skin material  38  is complete, the injection unit  18  plasticizes a sufficient quantity of the core material  40  by rotating and retracting the feed screw  32  in a conventional manner so that a full shot of melt is prepared. Simultaneously with the plasticizing function, the injection unit  18  disconnects from the auxiliary unit  34  by retracting slightly. The auxiliary unit  34  moves upward so that the injection unit  18  can now move forward unobstructed to a position where the nozzle  28  communicates with the sprue channel  26  of the mold  11 . As shown in FIG. 1C, the injection unit  18  then injects the accumulated shot of skin polymeric material  38  followed by the core polymeric material  40  into the mold  11  by advancing the feed screw  32  in a manner typical of the injection molding process.  
         [0034]    Now that the molding apparatus  10  has been described in detail, an exemplary flat top module  12  and an exemplary radius module  14 , both having a sandwich layer construction provided by a sandwich molding process or method according to the present invention, will be described. The modules  12  and  14  preferably include a broad spectrum antimicrobial agent associated therewith to inhibit bacterial growth on the module  12  while being safe for human contact. More particularly, the modules  12  and  14  are manufactured by the injection molding apparatus  10  shown in FIGS. 1A to  1 C with the antimicrobial material predominantly incorporated into the polymeric material of the skin layer.  
         [0035]    [0035]FIGS. 2 and 3 show the flat top module  12  being formed inside mold  11  while FIG. 4 shows the module  12  in its final form. The sandwich construction flat top module  12  comprises a core portion  42  surrounded by a skin portion  44 . The polymeric material comprising the skin portion  44  contains the antimicrobial materials of the present invention. These include inorganic antimicrobial materials based on Mg +2 , Ca +2 , Zn +2 , Ag +2 , Cu +2 , Al +3 , their oxides and hydroxides, zinc pyrithione, imidazole, and mixtures thereof. The concentration of the antimicrobial material in the polymeric material of the skin portion  44  preferably varies from about 0.5% to about 10.5%, by weight. The polymeric material of the core portion  42  preferably contains little if any of the antimicrobial materials. If the core portion  42  does contain antimicrobial materials, their concentration is preferably less than that of the skin portion  44 . Otherwise, the polymeric materials for the core and skin portions can be the same or different. Suitable polymeric materials include polyethylene, polypropylene homopolymer or copolymer, POM and ABS.  
         [0036]    The sandwich construction flat top module  10  includes a generally rectangular plate-like body  46  having a first plurality of link ends  48  and a second plurality of link ends  50  extending in opposite directions therefrom. A transverse rib  52  extends across the width of the underside of the body  46  to form opposed channels  54  and  56  terminating at respective edges  58  and  60  from which the respective link ends  48  and  50  project. The rib  52  and the inside of the link ends  48 ,  50  are adapted to mate with corresponding sprocket teeth of a sprocket wheel (not shown) to impart a driving force to the conveyor belt formed by the interconnected modules  12 . The under structure of the module  12  formed by the transverse rib  52  serves to strengthen the module and to prevent any significant binding of the module  10  about its longitudinal or transverse axes.  
         [0037]    The link ends  48  and  50  circumscribe corresponding aligned cylindrically shaped openings  62 . The openings  62  are provided by the provision of similarly shaped rods  64  in the mold  11  (FIGS. 2 and 3) and receive pivot pins or rods (not shown) adapted to pivotally connect a plurality of the modules in an end to end configuration while laterally aligning adjacent modules to form a modular conveyor belt (not shown). Preferably, the modules  12  are of link end configuration to be end-to-end reversible. In other words, either end of a module can mate with either end of any other link module.  
         [0038]    FIGS.  5  to  7  show another embodiment of a sandwich construction module, in this case a radius module  14 , being formed inside the mold  11 , while FIG. 8 shows the module  14  in its final form. The module  14  is referred to as a radius module because, as will be described in detail below, it is adapted for construction of conveyor belts that are capable of traveling around a radius turn. In a similar manner as the flat top module  12 , the radius module  14  is of a sandwich construction comprising a core portion  70  surrounded by a skin portion  72 . The module  14  further has an intermediate section  74  supporting a plurality of first link ends  76  and a plurality of second link ends  78 . The first link ends  76  are disposed in the direction of belt travel and the plurality of second link ends  78  extend opposite the first link ends  76 . The intermediate section  74  is comprised of an upper, transverse stiffening web  80  forming into a lower corrugated portion  82 . The corrugated portion  82  forms a series of ridges  84  and valleys  86  in a sinusoidal manner. Along with the transverse web  80  of the intermediate section  74 , the ridges  84  extending toward the right of FIG. 5 support the first link ends  76  while the ridges  84  extending toward the left in the drawing support the second link ends  78 .  
         [0039]    Module  14  further includes generally cylindrically-shaped pivot rod openings  88  in link ends  76  provided by the provision of a cylindrical rod  90  in the mold  11 . Similarly, oblong slots  92  are disposed through the link ends  78  transverse to the direction of belt travel. The oblong slots  92  are provided by the provision of a similarly shaped rod  94  in the mold  11 . With a plurality of modules  14  forming a conveyor belt, a pivot rod (not shown) passes through the openings  88  in the first link ends  76  and through the slots  92  in the second link ends  78 . The pivot rod preferably cannot move in the direction of belt travel inside the openings  88 . However, due to the oblong shape of slots  92 , the pivot rod pivots inside the slots  92 . This enables a conveyor belt constructed of a plurality of the modules  14  to travel around a radius turn by collapsing on one side while the other side fans out due to the pivoting of the pivot rod in the oblong slots  92 . For a more detailed description of a radius module, reference is made to U.S. application Ser. No. 09/579,090, filed May 25, 2000, which is assigned to the assignee of the present invention, and incorporated herein by reference.  
         [0040]    It is further contemplated by the scope of the present invention that the polymeric material comprising the skin portion  44  of the exemplary flat top module  12  and the skin portion  72  of the exemplary radius module  14  may include additives other than those which impart antimicrobial characteristics. These include additives such as those that enhance electrical conductivity (carbon black and graphite particle fillers), flame retardants and pigments. As with the antimicrobial material, these additives are preferably provided in the polymeric material in a concentration of about 0.15% to about 10.5%, by weight.  
         [0041]    FIGS.  9  to  15  show a second embodiment for manufacturing a flat top module  100  of a sandwich layer construction having antimicrobial characteristics by an over molding process according to the present invention. FIGS.  9  to  14  show the module  100  being formed while FIG. 15 shows the module  100  in its final shape. It should be pointed out that module  100  is similar in structure to the module  12  of FIGS.  2  to  3 , and for that reason its structural details will not be described again.  
         [0042]    The over molding process begins with a first mold  102  of mating mold halves  102 A and  102 B providing a first cavity for a core  104  of the flat top module  100 . The mold halves  102 A,  102 B support rods  106  having the shape, but not the exact size of the pivot rod openings  108  (FIG. 14) provided in the link ends of the completed module. For the same reason that the first mold cavity for the core  104  of the module is somewhat under sized, the openings  110  (FIG. 11) provided in the link ends by rods  106  are enlarged with respect to the final size of the pivot rod openings  108 .  
         [0043]    The first mold half  102 A includes first and second extension portions  112  and  114  which depend into the mold cavity to contact the rods  106 . That way, when the injection unit barrel  30  is moved against the mold half  102 A to inject the core polymeric material into the first cavity, there is provided a break or channel  116  (FIG. 12) communicating through the thickness of each link end.  
         [0044]    The core  104  shown in FIG. 11 is then positioned in a second mold  118  (FIGS.  11  to  14 ) comprising mating mold halves  118 A and  118 B providing a second cavity that is somewhat greater in size about the entire periphery of the core  104 . FIGS. 9 and 14 further shows that the core  104  is provided with two pairs of spaced apart tabs  120 A and  120 B at its opposed ends. These mate with similarly sized indentations in mold half  118 B for suspending the core  104  inside the second cavity. In that manner, mold  118  provides an annulus space  122  about the entire outer surface of the core  104 . This annulus space is generally consistent, however, it need not be. In fact, those skilled in the art will readily understand that the core  104  can have a myriad of different sizes and shapes, which are not limited to that of the final module  100  shape.  
         [0045]    As shown in FIG. 12, the location of the extension portions  116  now provides for communication between the annulus space  122  and a pivot rod space  124  between rods  126  and the inside of the link ends  128 . Rods  126  are sized smaller than the rods  106  used with the mold  102  to manufacture the core  104  by the intended thickness of the skin  128  to be molded about the core  104 .  
         [0046]    As shown in FIGS. 13 and 14, the injection unit barrel  30  is moved against the mold half  118 A to inject the skin polymeric material into the second cavity and completely about the perimeter of the core  104 . The skin polymeric material is similar to that described for this purpose with respect to the injection molding process shown in FIGS. 1A to  1 C and includes the antimicrobial materials. That way, the skin  128  material bonds to the core material to completely encase the core  104 , including inside the link ends  128 , except for where the tabs  120 A,  120 B reside at either end of the core  104 .  
         [0047]    [0047]FIG. 15 shows the finished flat top module  100  of this embodiment of the present invention. This module is similar to the flat top module  12  shown in FIG. 4 except for the presence of extending tabs  120 A,  120 B. The tabs are then removed in a conventional manner such as by being ground off, and the module  100  is ready for use.  
         [0048]    While the present invention has been described with respect to the exemplary flat top modules  12 ,  100  and the radius module  14 , that is by way of example only. Those skilled in the modular belt arts will readily recognize that the present molding process can be used to manufacture a variety of modules including flush grid modules, raised rib modules and flight modules as well as various accessories for modular conveyor belts such as sprockets, pivot rod, side guards, finger boards, and the like. In short, the sandwich construction of the present invention can be used to manufacture any component for a modular conveyor belt where it is desired to have an antimicrobial material incorporated into the polymeric material of the component.  
         [0049]    It is intended that the foregoing description be only illustrative of the present invention and that the present invention be only limited by the hereinafter appended claims.