Patent Publication Number: US-2021178643-A1

Title: Overmolded two-component friction element in a plastic pallet

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention claims priority to and the benefit of U.S. Provisional Patent Application No. 62/947,332 filed Dec. 12, 2019, the contents of which are incorporated herein by reference and made a part hereof. 
    
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     FIELD OF THE INVENTION 
     The present invention is directed to a method for forming a pallet having a two-component friction element overmolded into the pallet, and to the resultant pallet. 
     DESCRIPTION OF THE PRIOR ART 
     One downside of certain plastic transportation systems, such as plastic pallets, is that they have a coefficient of friction that is inherently lower than their wood counterparts. This results in possible slippage of products on the system. Increasing the friction improves the handling property of loaded and unloaded systems. 
     There are a number of methods currently utilized to increase the friction on the upper surfaces of plastic transportation systems. As described below with respect to plastic pallets, each such known method has one or more drawbacks. 
     Some plastic pallets are roughed up after molding (e.g., with a disk grinder) to create a more textured upper surface. This has been found to have a relatively low increase of friction, and tends to wear off over time. Additionally, the process creates a large amount of dust and noise which must be dealt with. 
     In some instances a pallet can be molded to have various textures on the upper surface. Again, this only leads to a relatively low increase in friction and requires more complex molds. Similarly, the pallets can be formed with molded in spikes on the pallet deck (i.e., upper surface). However, the spikes tend to wear or break off over time, and can damage product placed on the pallet. 
     Adhesive-backed friction tape has been applied to a pallet deck to increase friction. However, good adhesion (of the tape) is difficult to achieve with typical pallet materials (e.g., HDPE, PP) and sometimes requires pre-treatment of the pallet (e.g., flaming). Additionally, tape can contaminate the recycling stream. 
     Snapped-in elastic grommets have also been used to increase friction. However, the grommets can fall out in use. This can be problematic for certain applications, such as transportation of food products. 
     Spin disks—quarter-sized molded thermoplastic-elastomer disks that are spin-welded to the upper surface of the pallet—have also been used. Spin disks, however, can only be placed onto well supported areas of the pallet due to high downward forces required during welding them on. Moreover, because the spin disk must be weldable, the material choices are limited. 
     One other method is to utilize integrated multi-shot friction elements where one or more elastic TPE materials are injected into the same mold that makes the pallet. Very expensive tooling having a multi-shot injection press is required. Additionally, the material selection for friction material is very limited. In this method, the technology requires the friction elements to be present in every pallet formed from the tooling—it is not optional. 
     Another method to increase friction is spray urethane on the pallet deck (i.e., this is similar to a truck bed liner). However, this method is extremely expensive and requires pretreatment of the pallet. The urethane becomes a contaminant when the pallet is placed in a regrind stream. 
     The present invention avoids many of the downsides of known methods, and provides a unique method and structure for providing increased friction on a transportation system. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a two-component friction element that is overmolded into a transportation system, such as a plastic pallet, and to a method for forming the pallet. In particular, the present method provides for integrating friction elements into a pallet without the risk of such elements falling out or dislodging. This makes the pallet suitable for all applications (e.g., including food transportation). Moreover, the same friction elements can be designed to provide simultaneous friction points on the top of the pallet deck, as well as on the bottom of the pallet deck. However, the elements can also be configured to provide only friction points on one surface (top or bottom), and can be placed in other areas of the pallet (e.g., the bottom deck). 
     The two-component friction element includes an outer carrier member formed from a rigid material, and an interior elastomeric material. The elastomeric material is contained in one or more cavities in the carrier member and has one or more exposed surfaces. A large variety of injection-moldable elastomeric materials can be used. The elastomeric materials do not have to chemically bond to the rigid materials of the carrier component. 
     The friction elements are preferably formed in an injection mold having two cavities (or multiples of two cavities). The mold is run in an injection molding machine having two barrels. The first barrel injects a relatively rigid material (preferably the same material type that is used for forming the pallet) into the first mold cavity to produce the outer carrier member. This outer carrier member is then transferred into the second mold cavity, preferably by an end-of-arm tool (EOAT) that is manipulated by an on-press robot. The second cavity of the mold is connected to the second barrel which, on the next shot, injects an elastomeric material, such as a thermoplastic elastomer, into the outer carrier member. While this elastomeric material is injected, a new outer carrier member is simultaneously produced in the first mold cavity. After the resins in both cavities solidify, the EOAT simultaneously removes the outer carrier member from the first mold cavity and the two-material finished friction element from the second cavity. The EOAT then transfers the freshly molded outer carrier member to the second cavity and unloads the friction element. 
     The friction elements are then loaded into a mold that forms the pallet (or a portion of the pallet that includes the friction element), preferably with an EAOT of the pallet mold. In some instances, the friction element can include an internal cylindrical or conically shaped (or possibly other shapes) channel, and can be loaded onto a standing pin in the mold. A pallet resin is then injected into the mold and the friction element is overmolded into the pallet (or portion thereof). The overmolded friction element is positioned so that the exposed elastomeric material forms a part of the surface (top and/or bottom) of the pallet deck. The outer rigid carrier member of the friction element can be chemically bonded to the pallet resin material (this is particularly true when the outer carrier member is formed from the same or similar material as that of the pallet), and/or have a structure (e.g., one or more recesses or extensions on the outer surface of the carrier member) that allow the pallet resin to mechanically hold the friction element in place. 
     In accordance with one aspect, the present invention provides a method for forming a transportation system with an over-molded friction element. The method comprises the steps of forming a rigid outer carrier member of a first friction element wherein the rigid outer carrier member has a cavity, placing an elastomeric material into the cavity of the outer carrier member to complete formation of the first friction element, and placing the completed first friction element into a mold for a transportation system. The method further comprises molding over an outer surface of the carrier member of the first friction element in the mold for the transportation system so that a first portion of the elastomeric material of the first friction member is exposed on a surface of the transportation system. 
     The steps of forming a rigid outer carrier member and placing an elastomeric material into the cavity of the rigid outer carrier member can comprise injecting the rigid material into a first cavity of a multi-cavity injection mold to form the outer carrier member, moving the rigid outer carrier member to a second cavity of the multi-cavity injection mold, and injecting the elastomeric material into the cavity of the rigid outer carrier member. The step of moving the outer carrier member to a second cavity of the multi-cavity injection mold can include using an end-of-arm tool to transfer the rigid outer carrier member from the first cavity of the multi-cavity injection mold to the second cavity of the multi-cavity injection mold. After forming the first friction element, the method can then include moving the first friction element from the multi-cavity injection mold onto a transportation system mold. 
     The step of forming a rigid outer carrier member can include forming the outer surface of the rigid outer carrier member into a conical shape. Moreover, the method can include forming a first recess on a top portion of the rigid outer carrier member and forming a second recess on a bottom portion of the rigid outer carrier member. In fact, the carrier member could also be formed into a variety of other shapes, such as cylindrical or oval, or having a plurality of planar surfaces with a rectangular cross-sectional shape (e.g., a pyramid shape having a rectangular base). 
     The step of molding over an outer surface of the carrier member of the first friction element in the mold for the transportation system so that a first portion of the elastomeric material of the first friction member is exposed on a first surface of the transportation system can comprise loading the first friction element onto a pin in the mold for the transportation system, and injecting a resin that forms the transportation system into the mold over portions of the first friction element. This step can also include exposing a second portion of the elastomeric material on a second surface of the transportation system opposed to the first surface. Additionally, this step can include mechanically trapping the first friction element in the transportation system. 
     A preferred transportation system that would benefit from the present method is a plastic pallet. Such pallets are typically used to transport a variety of goods from one location to another. The plastic pallets are typically formed using a plastic resin. 
     The rigid outer member of the friction elements is preferably formed from the same plastic resin as that used to form the pallet. The elastomeric material injected into the rigid carrier member of the friction element is preferably a thermoplastic elastomer. 
     In accordance with another aspect of the present invention, a method of forming a pallet with friction elements is provided. The method comprises forming a plurality of friction elements having an outer rigid carrier member and an elastomeric material positioned in a cavity of the outer rigid carrier member, positioning the plurality of friction elements into a pallet mold and injecting a resin into the pallet mold. 
     The step of forming a plurality of friction elements having an outer rigid carrier member and an elastomeric material positioned in a cavity of the outer rigid carrier member can include injecting a rigid material into a first cavity of an injection molding machine to form the outer rigid carrier member for each of the plurality of friction elements. This step can also include injecting an elastomeric material into the cavity of the outer rigid carrier member. Moreover, this step can also include moving the outer rigid carrier member from the first cavity of the injection molding machine to a second cavity of the injection molding machine prior to the step of injecting an elastomeric material into the cavity of the outer rigid carrier member. Additionally, the method can include forming one or more recesses or other structures into an outer surface of the rigid outer carrier member. 
     In accordance with yet another aspect of the invention, a pallet with molded in (i.e., overmolded) friction elements is provided. The pallet comprises a first friction element having a rigid outer carrier member having a first interior chamber, and an elastomeric material in the first interior chamber having an exposed upper surface. A pallet structure is molded over the first friction element so that the exposed upper surface of the elastomeric material of the first friction element forms part of the upper surface of the pallet structure. Additionally, the pallet can include a plurality of molded over friction elements. 
     The friction elements can also be formed to have a second interior chamber in the rigid outer carrier member and an elastomeric material in the second interior chamber having an exposed lower surface. Additionally, the rigid outer carrier member can include one or more recesses or other structure about an outer surface. This allows the resin of the plastic to lock the friction elements in place. 
     The friction elements can be formed in a variety of shapes. For example, the friction element can have a generally conical shape, or a cylindrical or oval shape. Additionally, the friction elements could be formed to have planar faces with a polygonal cross-sectional shape (e.g., rectangular), or to have other shapes including irregular shapes. 
     The pallet structure is formed from the resin material. Preferably, the rigid carrier member is also formed with the same or similar resin as the pallet. This facilitates thermal and/or chemical bonding of the pallet material to the outer surface of the rigid carrier member of the friction element. The elastomeric material in the cavities of the rigid carrier member is preferably a thermoplastic elastomer. 
     The rigid carrier member of the friction element can include an interior channel extending all or partway through the element. The channel can be cylindrical, or can have other shapes. The channel allows for easily placing the friction element on a post in the pallet mold. 
     Other features and advantages of the invention will be apparent from the following description, claims and drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To understand the present invention, it will now be described by way of example, with reference to the accompanying drawings in which: 
         FIG. 1  is a top perspective view of a friction element in accordance with an aspect of the present invention; 
         FIG. 2  is a bottom perspective view of a friction element of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the friction element of  FIG. 1 ; 
         FIG. 4  is a cut-away view of the friction element of  FIG. 1 ; 
         FIG. 5  is a perspective view of a friction element of  FIG. 1  being placed on a portion of a cavity side of a mold for a pallet; 
         FIG. 6  is a bottom perspective view of a portion of a core side mold for the pallet for placement of a friction element; 
         FIG. 7  is a top perspective view of a portion of a pallet formed in the mold portions of  FIGS. 5 and 6  with a molded over friction element; 
         FIG. 8  is a bottom perspective view of the portion of a pallet of  FIG. 7  formed in the mold portions of  FIGS. 5 and 6  with the molded over friction element; 
         FIG. 9  is a perspective view of a pallet with a plurality of friction elements molded into the pallet; 
         FIG. 10  is a perspective view of a portion of a core side mold for a pallet for instances where a friction element is not desired; 
         FIG. 11  is a perspective view of a portion of a pallet without a friction element; 
         FIG. 12  is a top perspective view of an outer carrier member of a friction element having a first and second recessed portion in accordance with another aspect of the invention; 
         FIG. 13  is a bottom perspective view of the outer carrier member of  FIG. 12 ; 
         FIG. 14  is a side plan view of the outer carrier member of  FIG. 12 ; 
         FIG. 15  is a top plan view of the outer carrier member of  FIG. 12 ; 
         FIG. 16  is a bottom plan view of the outer carrier member of  FIG. 12 ; 
         FIG. 17  is a vertical cross-sectional view of the outer carrier member of  FIG. 12 ; 
         FIG. 18  is a horizontal cross-sectional view of the outer carrier member of  FIG. 12 ; 
         FIG. 19  is a to perspective view of a friction element formed from the outer carrier member of  FIG. 12  with an elastomeric material in an interior cavity of the outer carrier member; 
         FIG. 20  is a bottom perspective view of the friction element of  FIG. 19 ; 
         FIG. 21  is a side plan view of the friction element of  FIG. 19 ; 
         FIG. 22  is a vertical cross-sectional view of the friction element of  FIG. 19 ; 
         FIG. 23  is a perspective view of a friction element in accordance with another aspect of the present invention; 
         FIG. 24  is a perspective top view of a friction element in accordance with another aspect of the present invention; 
         FIG. 25  is a bottom perspective view of the friction element of  FIG. 24 ; 
         FIG. 26  is perspective view of a portion of a pallet mold and the friction element of  FIG. 24 : 
         FIG. 27  is a cross-sectional view of the portion of the pallet mold and the friction element of  FIG. 26 ; 
         FIG. 28  is a perspective top view of a friction element in accordance with another aspect of the present invention; 
         FIG. 29  is a bottom perspective view of the friction element of  FIG. 28 ; 
         FIG. 30  is perspective view of a portion of a pallet mold and the friction element of  FIG. 28 : 
         FIG. 31  is a cross-sectional view of the portion of the pallet mold and the friction element of  FIG. 30 ; 
         FIG. 32  is a perspective top view of a friction element in accordance with another aspect of the present invention; 
         FIG. 33  is a bottom perspective view of the friction element of  FIG. 32 ; 
         FIG. 34  is perspective view of a portion of a pallet mold and the friction element of  FIG. 32 ; 
         FIG. 35  is a cross-sectional view of the portion of the pallet mold and the friction element of  FIG. 34 ; 
         FIG. 36  is a perspective top view of a friction element in accordance with another aspect of the present invention; 
         FIG. 37  is a bottom perspective view of the friction element of  FIG. 36 ; 
         FIG. 38  is perspective view of a portion of a pallet mold and the friction element of  FIG. 36 ; 
         FIG. 39  is a cross-sectional view of the portion of the pallet mold and the friction element of  FIG. 38 ; 
         FIG. 40  is a perspective top view of a friction element in accordance with another aspect of the present invention; 
         FIG. 41  is a bottom perspective view of the friction element of  FIG. 40 ; 
         FIG. 42  is perspective view of a portion of a pallet mold and the friction element of  FIG. 40 ; 
         FIG. 43  is a cross-sectional view of the portion of the pallet mold and the friction element of  FIG. 42 ; 
         FIG. 44  is a perspective top view of a friction element in accordance with another aspect of the present invention; 
         FIG. 45  is a bottom perspective view of the friction element of  FIG. 44 ; 
         FIG. 46  is perspective view of a portion of a pallet mold and the friction element of  FIG. 44 ; and, 
         FIG. 47  is a cross-sectional view of the portion of the pallet mold and the friction element of  FIG. 46 . 
     
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated. 
     The present invention is directed to a pallet (or other similar transportation system for moving products) with overmolded friction elements. The friction elements are formed in a first mold, and then placed in a mold for forming the pallet. The friction elements are then molded over in the pallet mold to form a pallet having exposed friction material on one or more surfaces. 
       FIGS. 1-4  show a two-component friction element  10  in accordance with an aspect of the present invention. The friction element  10  includes a rigid outer carrier member or portion  12  having a conically shaped outer surface  14 . The friction element also includes an elastomeric material  16  that is shown exposed on and extending slight past the top and bottom ends of the outer carrier member. As illustrated in  FIGS. 3 and 4  (and  FIG. 17 ), the elastomeric material  16  is contained within cavities  18 ,  20  formed in the interior of the outer carrier member  12 . The cavities  18 ,  20  extend between an outer wall  22  of the outer carrier member  12 , and an inner wall  24  of the carrier member  12 . The inner wall  24  defines a channel that extends through the friction element  10 . 
     The friction elements  10  are preferably formed in a two shot injection molding process. The process is performed in an injection mold having two cavities (or in some instances multiples of two cavities can be used to form a plurality of friction elements at the same time) and two barrels of injectable material. In a first shot, the outer rigid carrier member  12  is formed in the first cavity with an injection of material from the first barrel. In most cases, the material used in the first barrel is the same or similar to the material used to form the pallet. The outer carrier member  12  is then moved to the second cavity of the mold (typically by an EAOT). The second shot is injection of an elastomeric material, such as a thermoplastic elastomer (TPE) that has the desired friction properties, from the second barrel into the cavities  18 ,  20  of the outer carrier member  12  (this occurs while a new carrier member is formed in the first cavity of the friction element mold). 
     The completed friction element  10  is then loaded into a pallet forming mold. As shown in  FIG. 5 , the pallet mold includes one or more mold portions  26  having pins or posts  28 . The friction element  10  is positioned so that the pin  28  fits in the channel defined by the inner wall  24  of the friction element  10 . In addition to being used during the pallet molding process, the channel defined by the inner wall  24  of the carrier member  12  of the friction element  10  allows for drainage on the finished pallet. 
     Preferably, the friction elements  10  are loaded on the mold portion  26  in the cavity side (i.e., stationary side) of the pallet mold. A core portion or side (i.e., moving side)  30  of the pallet mold, illustrated in  FIG. 6 , includes a cavity  32  that conforms to the outer shape of the friction elements  10 . The pallet mold is closed and the resin that forms the pallet is injected into the mold, surrounding the outer surfaces  14  of the friction elements  10 .  FIGS. 7 and 8  show the top and bottom of a friction element  10 , respectively, in a portion of a pallet  34 . The pallet portion  34  includes a portion  36  surrounding the friction element  10  (i.e., overmolded), and a plurality of interconnecting ribs  38 . The entire pallet  40  having a plurality of overmolded friction elements  10  is shown in  FIG. 9 . Typically, the pallet can include 20 or more friction elements  10 . 
     In instances where a friction element is not desired at a particular location on the pallet, a modified mold portion  42 , shown in  FIG. 10 , can be used. The mold portion  42  has an enlarged post  44  to replace the friction element. The top or core portion of the mold can be the same as that shown in  FIG. 6 . A portion  46  of the pallet formed from the mold portion  42  is shown in  FIG. 11 . 
     Another friction element  48  and its outer carrier member  50  are shown in  FIGS. 12-20 . The outer carrier member  50  includes a central outer surface portion  52  having a conical shape similar to the friction element  10  of  FIGS. 1-11 . However, the carrier member  50  also includes a first recessed groove  54  at the top of the carrier member  50  and a second recessed groove  56  at the bottom of the carrier member  50 . The area defined by the recessed grooves  54 ,  56  is filled with resin when in the pallet mold (during the overmold process). This geometry creates a locking mechanism to mechanically trap the friction element  48  to the pallet portion  34  or pallet  40 . Clearly, a large variety of structures (e.g. internal grooves, or ribs that extend outward) can be designed into the carrier member to lock the friction element to the pallet. This mechanical locking effectively holds the friction element  48  in place regardless of whether the pallet material thermally or chemically bonds to the material forming the outer surface of the carrier member. 
     As evident in  FIGS. 19-22 , the recessed grooves  54 ,  56  do not prevent the elastomeric material  58  from being exposed at the top or bottom of the friction element  48 . As more clearly shown in  FIGS. 21 and 22 , the elastomeric material extends slightly above and below, respectively, the material of the carrier member  50 . 
     Another version of a friction element  60  is shown in  FIG. 23 . The friction element  60  has an outer carrier member with a central portion having an outer surface  62  with a more cylindrical shape than the friction elements  10 ,  48  previously discussed. Recessed grooves  64 ,  66  are formed at the top and bottom of the carrier member. An elastomeric material  68  is shown on the top of the friction element  60 . 
       FIGS. 24-27  show a friction element  70  having an internal channel that is closed at one end. The friction element  70  can be loaded on a pallet mold portion  34  through the opening at the top of the channel  72  evident in the top view of  FIG. 24 . The bottom view of  FIG. 25  shows the bottom end including a central bottom wall  74 . The friction element  70  can be formed with recessed grooves or other similar structure. 
       FIGS. 28-31  show a friction element  76  having a rectangular shaped top end and bottom end. The carrier member  78  of the friction element  76  has a plurality of planar outer surfaces  80 . Again, recessed grooves can be formed in the friction element  76 . Fewer or more planar faces can be formed for other polygonal shaped ends. 
       FIGS. 32-35  show a friction element  82  having oval shaped ends and corresponding oval shaped outer surface  84 . In each of the above alternatively shaped elements, a post that corresponds to the channel in each element is provided in the mold portion  34 . 
       FIGS. 36-39  show a friction element  86  having an oval shape similar to that of  FIGS. 32-35 . In this example, the element includes two channels  88 ,  90 . A mold portion having two posts  92 ,  94  is provided for positioning the friction element  86 . The friction element can also be formed with more than two channels. 
       FIGS. 40-43  show a friction element  96  that only has an elastomeric material  98  exposed on one side. The channel also has a closed end similar to the friction element  70 . 
       FIGS. 44-47  show a friction element  100  that does not include any internal channels for positioning on a mold portion. Instead, posts  102  on the mold fit into grooves  104  on the sides of the element  100 . This friction element  100  only has the elastomeric material  106  exposed at one end. 
     While the friction elements are seen being held by posts in the mold portions, other means for securing the elements can be used. For example, a vacuum in the receptacle area for the friction element in the pallet mold can be used. Alternatively, the friction element can have a protruding structure which mates with a channel or opening in the mold portion. Moreover, an adhesive can utilized. 
     Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood within the scope of the appended claims the invention may be protected otherwise than as specifically described.