Patent Publication Number: US-2023134305-A1

Title: Process For Manufacturing A Conveyor Belt

Description:
RELATED APPLICATION INFORMATION 
     This Patent Application is a Divisional Application of, and claims priority to, U.S. Nonprovisional Pat. Application No. 15/771,119 filed Apr. 27, 2018 as a National Stage Entry of PCT/US2016/059082, filed Oct. 27, 2016, which is incorporated herein in its entirety, by reference. This Patent Application also claims priority to U.S. Provisional Pat. Application No. 62/247,427 filed Oct. 28, 2015, which is incorporated herein in its entirety, by reference. 
    
    
     FIELD 
     The field to which the disclosure generally relates is conveyor belts, and more particularly to highly efficient and cost effective methods for manufacturing high performance conveyor belts having high temperature resistance which reduces the amount of calendaring and Banbury mixing required in manufacturing the conveyor belts. 
     BACKGROUND 
     This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. 
     Conventional conveyor belts used in a wide variety of applications are typically comprised of a cured rubber as a top layer, a cured rubber as a bottom layer, and a fabric reinforcement layer (a carcass) which is sandwiched between the top layer and the bottom layer. Rubber conveyor belts of this type can offer excellent performance characteristics and a relatively long service life. However, rubber conveyor belts are labor intensive to manufacture by virtue of requiring rubber mixing steps, such as Banbury mixing and calendaring, and also require a curing step wherein the rubber components of the belt are cured (vulcanized) into their final form to produce the belt as a finish product. 
     U.S. Pat. 8,910,780 discloses a method for manufacturing conveyor belts which are free of rubbery polymers that need to be cured and thereby eliminates that need for curing the belts in a cure step. This technique is carried out in a continuous process that reduces labor requirements. It offers a greatly simplified alternative to extrusion coating techniques and more importantly provides belts that offer improved carcass ply adhesion which can be used in heavy duty applications. By eliminating cured rubbers from the process, recycling is a viable option by allowing for trim waste and other scrap materials to be recycled. Accordingly, by practicing the process of U.S. Pat. 8,910,780 conveyor belts can be made by a simpler process that requires less labor in a shorter processing time. In many cases, manufacturing cost is also reduced by reduced energy requirements and by lower cost raw materials. 
     U.S. Pat. 8,910,780 more specifically reveals a method of manufacturing a belt which comprises: (1) impregnating a fabric material with a bonding agent in a plastisol to form coated fabric material, (2) applying a plastisol layer between two or more layers of coated fabric thereby creating a belt carcass, (3) continuously feeding the belt carcass into a double belt press which presses the-impregnated fabric materials together with the plastisol layer(s) at a pressure of at least 5 psi to produce a structured fabric carcass while (4) heating the structured fabric carcass to a temperature which is within the range of about 360° F. to about 450° F. for a period of at least 6 minutes, (5) continuously withdrawing the fabric carcass from the double belt press, (6) scattering a thermoplastic elastomer resin composition onto the upper and lower surfaces of the fabric carcass, (7) pressing the thermoplastic elastomer resin composition onto the upper and lower surfaces of the fabric carcass by continuously feeding the fabric reinforcement into a second double belt press which is maintained at a temperature of at least 340° F. and at a pressure of at least 5 psi, and (8) continuously withdrawing the finished belt from the second double belt press. However, the conveyor belts made in accordance with U.S. Pat. 8,910,780 have a carry layer and a pulley cover layer which is comprised of polyvinyl chloride (PVC) rather than a cured rubbery polymer. 
     There remains to be a long felt need for a technique of manufacturing conveyor belts having the beneficial attributes of being comprised of a cured rubber, such as high temperature resistance, by a simpler and less labor intensive process. For instance, it would be highly desirable to reduce the requirements for Banbury mixing and calendaring of the rubber utilized in making the carry cover layer and the pulley cover layer of such conveyor belts. However, a commercially viable method for manufacturing such a conveyor belt has proven to be elusive. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
     Aspects of this disclosure are methods of manufacturing conveyor belts having a top layer, a bottom layer, and a fabric reinforcement layer which is sandwiched between the top layer and the bottom layer. In the manufacture of the conveyor belts, an uncured belt structure, an uncured belt and a cured conveyor belt are successively produced in a single continuous operation, which is different from calendering in one step, and pressing a belt section in a second separate step. 
     In some aspects, methods include (1) applying a rubber composition to the bottom side of a fabric reinforcement and scattering a productive thermoplastic elastomer composition onto the top side of the fabric reinforcement to produce an uncured belt structure, and then (2) continuously feeding the uncured belt structure into a double belt press to press the productive thermoplastic elastomer composition together with the fabric reinforcement at a suitable pressure, such as at least 12 psi, to produce an uncured belt. (3) The uncured belt is heated the double belt press to a suitable temperature, which may be at least 300° F., and (4) then maintained in the double belt press under the suitable pressure and temperature for a suitable residence time, such as at least 20 minutes, to produce a cured conveyor belt. Then (5) the cured conveyor belt is continuously withdrawn from the double belt press, essentially in a synchronous manner with the step (2) of continuously feeding the uncured belt structure into a double belt press. In such continuous and successive stages, the uncured belt structure, the uncured belt and the cured conveyor belt are produced in a single continuous operation. 
     In some aspects, the productive thermoplastic elastomer composition, which may be in the form of pellets, is a blend of non-productive thermoplastic elastomer pellets and a peroxide crosslinking agent which is supported on a powdered carrier. In some cases, the nonproductive thermoplastic elastomer pellets are made by extrusion with a co-rotating, intermeshing twin screw extruder. The thermoplastic elastomer, at least one filler, and at least one processing oil may be blended in the co-rotating, intermeshing twin screw extruder in making nonproductive thermoplastic elastomer pellets, in an aspect. 
     In some embodiments, the productive thermoplastic elastomer composition is made by dry blending the nonproductive thermoplastic elastomer pellets with the peroxide crosslinking agent which is supported on the powdered carrier. Furthermore, a curative co-agent may be blended in the co-rotating, intermeshing twin screw extruder in making the nonproductive thermoplastic elastomer pellets. In some aspects, at least one processing aid is further blended in the co-rotating, intermeshing twin screw extruder in making the nonproductive thermoplastic elastomer pellets. Yet in other aspects, at least one antioxidant is further blended in the co-rotating, intermeshing twin screw extruder in making the nonproductive thermoplastic elastomer pellets. 
     In some cases, the non-productive thermoplastic elastomer pellets have an average particle size which is within the range of about 0.1 mm to about 2 mm, within the range of about 0.2 mm to about 1 mm, or even within the range of about 0.3 mm to about 0.7 mm. 
     In some aspects, the double belt press belt has belt surfaces which are contain polytetrafluoroethylene impregnated fiberglass or stainless steel. Further, the double belt press may heats the uncured conveyor belt by conduction heating. In some cases, the uncured belt is maintained in the double belt press in step (4) under a pressure which is within the range of 14 psi to 30 psi, and at a temperature which may be within the range of 320° F. to 400° F. In some cases, the uncured belt is maintained in the double belt press in step (4) under a pressure which is within the range of 15 psi to 25 psi and at a temperature which is within the range of 325° F. to 350° F. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the disclosure will hereafter be described with reference to the accompanying drawing, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying figure illustrates the various implementations described herein and is not meant to limit the scope of various technologies described herein, and wherein  FIG.  1    is a schematic drawing of one method aspect according to the disclosure, for manufacturing a conveyor belt which utilizes a double belt press. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the variations is merely illustrative in nature and is in no way intended to limit the scope of the disclosure, its application, or uses. The description and examples are presented herein solely for the purpose of illustrating the various embodiments of the disclosure and should not be construed as a limitation to the scope and applicability of the disclosure. In the summary of the disclosure and this detailed description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary of the disclosure and this detailed description, it should be understood that a value range listed or described as being useful, suitable, or the like, is intended that any and every value within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors had possession of the entire range and all points within the range. 
     Unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). 
     In addition, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of concepts according to the disclosure. This description should be read to include one or at least one and the singular also includes the plural unless otherwise stated. 
     The terminology and phraseology used herein is for descriptive purposes and should not be construed as limiting in scope. Language such as “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited. 
     Also, as used herein any references to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily referring to the same embodiment. 
     Some aspects of the disclosure provide methods for continuous production of a cured rubber conveyor belt having high temperature resistance by a simple process which is less labor intensive than prior art methods. These methods reduce or eliminate the requirements for Banbury mixing and calendaring, and accordingly reduce overall production cost. Additionally, these methods result in improved rubber formulation consistency and in some cases reduced energy requirements. 
     In some embodiments, methods of manufacturing a conveyor belt having a top layer, a bottom layer, and a fabric reinforcement layer which is sandwiched between the top layer and the bottom layer, include (1) applying a rubber composition to the bottom side of a fabric reinforcement and scattering a productive thermoplastic elastomer composition onto the top side of the fabric reinforcement to produce an uncured belt structure, (2) continuously feeding the uncured belt structure into a double belt press to press the productive thermoplastic elastomer composition together with the fabric reinforcement at a pressure of at least 12 psi to produce an uncured belt, (3) heating the uncured belt in the double belt press to a temperature of at least 300° F., (4) maintaining the uncured belt in the double belt press under a pressure of at least 12 psi and a temperature of at least 300° C. for a residence time of at least 20 minutes to produce a cured conveyor belt, and (5) continuously withdrawing the cured conveyor belt from the double belt press. 
     In the practice of some aspects of the disclosure, an uncured rubber composition is applied to the bottom side of a fabric reinforcement and a productive thermoplastic elastomer composition is scattered onto the top side of the fabric reinforcement to produce an uncured belt structure. The rubber utilized in the uncured rubber composition can be chosen from a wide variety of natural and synthetic rubbers. For instance, the rubber can be natural rubber, styrene-butadiene rubber, polybutadiene rubber, synthetic polyisoprene rubber, nitrile rubber, ethylenepropylene-diene monomer rubber (EPDM), polychloroprene, and the like or blends thereof. The uncured rubber composition will also typically include a curative as well as one or more of accelerators, antioxidants, fillers, processing oils, extending oils, and other desired rubber compounding chemicals. The curative will typically be sulfur, a sulfur containing compound, or a peroxide curative. The filler will typically be one or more of carbon black, silica, clay, and lignin. 
     The fabric reinforcement may be a material based upon cotton, a polyester, a nylon, polyaramid, fiberglass, or various blends thereof. For instance, the polyester may be polyethylene terephthalate or polyethylene naphthalate. In some cases the polyester may be a copolyester which contains repeat units that are derived from both terephthalic acid and isophthalic acid or dimethyl esters thereof. In such cases the copolyester will typically contain at least about 95 weight percent terephthalic acid and up to about 5 weight percent isophthalic acid. The copolyester may, in some cases, contain at least about 97 weight percent terephthalic acid and up to about 3 weight percent isophthalic acid. The polyester fabric may, in some aspects, be made from polyester staple yarn to improve adhesion characteristics. The nylon fabrics that may be used in conjunction with the disclosure, may be based upon virtually any type of nylon, such as nylon-6.6, nylon-6.12, nylon-6.10, nylon-6.9, nylon-6, nylon-11, or nylon-12. For commercial reasons, the nylon will typically be nylon-6.6 or nylon-6. In any case, the fabric material will normally be a woven fabric. The fabric reinforcement will normally be treated with a resorcinol-formaldehyde latex dip to improve the adhesion between the fabric and the rubber components of the conveyor belt (the top carry cover layer and the bottom pulley cover layer). 
     The productive thermoplastic elastomer composition may be a blend of non-productive thermoplastic elastomer pellets and a peroxide crosslinking agent which is supported on a powdered carrier. The nonproductive thermoplastic elastomer pellets may be made by extrusion with a co-rotating, intermeshing twin screw extruder. In an example extrusion process, a thermoplastic elastomer, at least one filler, and at least one processing oil are blended in co-rotating, intermeshing twin screw extruder to make the nonproductive thermoplastic elastomer pellets. A curative co-agent may be included in the nonproductive thermoplastic elastomer pellets. In some cases, such a curative co-agent may be an acrylate, a methacrylate, or a maleimide to attain a very fast cure rate or in the alternative may be a polybutadiene, a triallyl cyanurate (TAC), triallyl isocyanurate (TAIC) or triallyl phthalate (DAP) to attain a more moderate rate of cure. With reference to  FIG.  1   , these materials  100  may be premixed in a powder mixer  102  as before being fed into the co-rotating, intermeshing twin screw extruder  104 . In some aspects, the non-productive thermoplastic elastomer pellets have an average particle size which is within the range of 0.1 mm to 2 mm and more typically have an average particle size which is within the range of 0.2 mm to 1 mm. The non-productive thermoplastic elastomer pellets may even have an average particle size which is within the range of 0.3 mm to 0.7 mm. 
     Productive thermoplastic elastomer pellets  106  are then made by dry blending the nonproductive thermoplastic elastomer pellets with peroxide curing agent  108 , which is supported on the powdered carrier. For instance, this dry blending can be done in any suitable powder mixer such as a drum mixer  110  as illustrated in  FIG.  1   . The peroxide curing agents  108  which may be used in the practice of some aspects of the disclosure are those which are generally suitable for curing EPDM. Some representative examples of organic peroxides which can be used include, but not limited to, dicumyl peroxide, bis-(t-butyl peroxy-diisopropyl benzene, t-butyl perbenzoate, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, alpha-alpha-bis(t-butylperoxy) diisopropylbenzene, methylethyl ketone peroxide, cyclohexanone peroxide, cumene hydroperoxide, pinane hydroperoxide, p-menthane hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, and the like. Dicumyl peroxide and di-t-butyl peroxide are highly preferred peroxide compounds. In any case, the peroxide crosslinking agent will be supported on an inert powdered carrier, such as silica, clay or calcium carbonate. The peroxide may be present on the powdered carrier at a level which is within the range of about 40 weight percent to about 70 weight percent, or even within the range of about 50 weight percent to 60 weight percent, based upon the total weight of the peroxide and the carrier. In an embodiment, the curative co-agent can be included with the peroxide curing agent  108 . 
     Referring again to  FIG.  1   , a fabric reinforcement (carcass)  112 , having the uncured rubber composition  114  upon or applied to the bottom side thereof, may continuously advanced toward a double belt press  116  with productive thermoplastic elastomer pellets  106  being scattered from pellet distributor  118  over the top surface of the fabric reinforcement  112  to make an uncured belt structure  120 . The productive thermoplastic elastomer pellets  106  may be distributed in a relatively uniform manner over the top surface of the fabric reinforcement  112  with pellet distributor  118 . 
     The uncured belt structure  120  is then continuously fed into the double belt press  116  which heats the uncured belt structure  120  to a temperature at least about 300° F. in a heating zone  122 . In some aspects, the double belt press  116  heats the structured fabric reinforcement by conduction heating. The uncured belt structure  120 , in some cases, will be heated to a temperature which is within the range of about 320° F. to about 400° F., or even heated to a temperature which is within the range of about 325° F. to about 450° F. The uncured belt structure  120  may be held under a pressure of at least about 12 psi in the double belt press  116  to push the bottom layer formed of uncured rubber composition  114  and the top layer formed of productive thermoplastic elastomer pellets  106  into the fabric reinforcement  112 . The pressure applied in the double belt press  116 , in some aspects, may be within the range of about 14 psi to about 30 psi, or even within the range of about 15 psi to about 25 psi. Belts used as one or both belt component(s) of double belt press  116  may have surfaces which contain polytetrafluoroethylene (PTFE) impregnated fiber glass or even a thin layer of stainless steel. 
     The uncured belt structure  120  is maintained in the double belt press  116  at the desired temperature and under the desired pressure for a period of at least 20 minutes, in some cases. In some aspects, the uncured belt structure may have a residence time in double belt press  116  which is within the range of about 25 minutes to about 45 minutes and, may even have a residence time in double belt press  116  which is within the range of about 30 minutes to about 35 minutes. After being cured, the cured conveyor belt  130  will be cooled in a cooling zone  124  and continuously withdrawn from the double belt press  116 , as finished belt  126 . In some embodiments, excess material is continuously trimmed off of the edges of the cured conveyor belt  130  after it is continuously withdrawing from the double belt press  116 . 
     Conveyor belts  126  manufactured in accordance with the disclosure include an elastomeric body having a load carrying surface (top surface)  140  and a parallel pulley engaging surface (bottom surface)  142 , where a fabric reinforcement  112  is disposed within the elastomeric body of the belt  126 . In other words the fabric reinforcement  112  is situated between the pulley cover layer  142  and the load carrying layer  140  of the belt. 
     Some embodiments of the disclosure are illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the disclosure or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight. 
     Example 1 
     In this experiment a series of productive thermoplastic elastomer compositions for use in manufacturing conveyor belts in accordance with the disclosure were prepared. Previous testing on a twin screw extruder using only Tafmer D610 thermoplastic elastomer as the feed showed that a constant linear temperature profile of 390° F. at a screw speed of 75 rpm and a feed rate of 5 pounds per hour gave the most consistent, smooth pellets. The lab pelletizer could not pull at a constant rate at this low speed so a puller was employed to improve strand diameter, and was utilized in the following examples. 
     Experimental blends were made by first feeding the ingredients identified in Table 1 below into a Plastic Lab 25 mm Twin Screw Extruder using one loss-in-weight feeder located prior to Zone 1 of the extruder. In Table 1, all ingredient levels are shown in parts by weight. The strands were later fed at the end of the run to a pelletizer to achieve pellets in the 2 mm to 3 mm diameter range. The pressure at the die increased from 300 psi with the pure Tafmer D610 thermoplastic elastomer to 700 psi with polymer blend of Example 1. Pressures in the 400-430 psi range were observed with the polymer blends of Example 2 and Example 3. The screw motor ran at the 18 amp current level in the case of all of the materials tested. The temperature of the extrudate was measured by with an IR thermometer to be within the range of 360° F. to 370° F. and the extruder die thermometer measured the melt temperature to be 380° F. 
     All three of the non-productive thermoplastic polymer compositions made were dry mill mixed with a peroxide curative to make productive thermoplastic elastomer compositions which were suitable for use in making conveyor belts in accordance with the disclosure. 
     
       
         
           
               
               
               
               
             
               
                   
                 Example 1 
                 Example 2 
                 Example 3 
               
             
            
               
                 Non-Productive 
                   
                   
                   
               
               
                 Thermoplastic elastomer 
                 100 
                 100 
                 100 
               
               
                 N-330 carbon black 
                 35 
                 40 
                 40 
               
               
                 Silica 
                 10 
                 - 
                 - 
               
               
                 Antioxidants 
                 8 
                 9 
                 9 
               
               
                 Processing Aid 
                 1 
                 1 
                 1 
               
               
                 Zinc Oxide 
                 10 
                 5 
                 5 
               
               
                 Paraffinic Processing Oil 
                 5 
                 5 
                 5 
               
               
                 Curative Co-Agent 
                 0 
                 0 
                 2.75 
               
               
                 Productive 
                   
                   
                   
               
               
                 Bis(t-butylperoxy) isopropylbenzene 
                 4.5 
                 4.5 
                 4.5 
               
               
                 Curative Co-Agent 
                 2.75 
                 2.75 
                 - 
               
            
           
         
       
     
     This series of experiments illustrates that mixing of the non-productive materials can be done in a co-rotating, intermeshing twin screw extruder with a peroxide curative being added later by dry blending to make productive formulations. These productive formulations can then be used in manufacturing conveyor belts in accordance with the disclosure. 
     List of Reference signs (part of the description): 
     
       
         
           
               
               
            
               
                 
                   100 
                 
                 Raw Materials 
               
               
                 
                   102 
                 
                 Powder Mixer 
               
               
                 
                   104 
                 
                 Intermeshing Twin Screw Extruder 
               
               
                 
                   106 
                 
                 Productive Thermoplastic Elastomer Pellets 
               
               
                 
                   108 
                 
                 Peroxide Curing Agent 
               
               
                 
                   110 
                 
                 Drum Mixer 
               
               
                 
                   112 
                 
                 Fabric Reinforcement 
               
               
                 
                   114 
                 
                 Uncured Rubber Composition 
               
               
                 
                   116 
                 
                 Double Belt Press 
               
               
                 
                   118 
                 
                 Pellet Distributor 
               
               
                 
                   120 
                 
                 Uncured Belt Structure 
               
               
                 
                   122 
                 
                 Heating Zone 
               
               
                 
                   124 
                 
                 Cooling Zone 
               
               
                 
                   126 
                 
                 Finished Belt 
               
               
                 
                   128 
                 
                 Uncured Conveyor Belt 
               
               
                 
                   130 
                 
                 Cured Conveyor Belt 
               
               
                 
                   140 
                 
                 Top Layer 
               
               
                 
                   142 
                 
                 Bottom Layer 
               
            
           
         
       
     
     The foregoing description of the embodiments has been provided for purposes of illustration and description. Example embodiments are provided so that this disclosure will be sufficiently thorough, and will convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the disclosure, but are not intended to be exhaustive or to limit the disclosure. It will be appreciated that it is within the scope of the disclosure that individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 
     Although a few embodiments of the disclosure have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.