ADHIGENT AGING PROTECTION IN STEEL CORD-BOUND RUBBER PRODUCTS MADE OF ZINC OXIDE

Description

FIELD

[0001] The field to which the disclosure relates is conveyor belts having zinc coated steel reinforcement cords therein.BACKGROUND

[0002] Many rubber articles, such as conveyor belts, automobile tires, hoses, power train belts, e.g., transmission belts, and the like, are usually reinforced with fibrous or metal cords. In all such instances, the fiber or metal cord must be firmly bonded to the rubber. This is so whether the fiber or cord is a natural or synthetic polymer, or metallic, and whether the rubbers are natural or synthetic.

[0003] Conventional conveyor belts which are used in heavy duty applications are typically comprised of a cured rubber or polyvinyl chloride (PVC) based material as a top layer, a cured rubber or PVC based material as a bottom layer, and one or more reinforcement layers (a carcass) disposed between the top layer and the bottom layer. The cured rubber or polyvinyl chloride based material may also serve to adhere various components of the reinforcing carcass. For example, individual layers and reinforcing elements included in the carcass may be encapsulated in a matrix of polymeric elastomeric resin, such as a polyvinylchloride based material. The individual layers are commonly saturated with the liquid elastomer-forming polymeric resin prior to being joined together, and the reinforcing elements may be inserted, for example, by tufting, sewing, or stitch-bonding. In cases where the liquid saturate is a polyvinylchloride plastisol, the resin is gelled, or otherwise cured, by application of heat.

[0004] Some conveyor belts contain reinforcement elements which include zinc coated steel cords. Conveyor belts of these types can offer excellent performance characteristics and a relatively long service life. However, under some conditions where the conveyor belts are exposed to repeated high temperatures and / or humidity over long periods of time, the zinc coated steel cord reinforcements can delaminate, or otherwise lose adhesion, from the rubber matrix of the conveyor belt.

[0005] For bonding the rubber to the zinc coated steel cord surface, special rubber formulations have been known to be used in the form of adhesion compounds. One solution to provide protection against aging / corrosion and loss of adhesion has been addition of lead oxide (PbO). However, PbO is considered a hazardous substance and is rated as SVHC substance in the REACH regulation, which could ultimately be banned for use. Also, currently available alternative compounds without PbO can achieve good adhesion to the cord surface, but the generated bonding is more susceptible to aging / corrosion than with compounds containing PbO.

[0006] The document US 3 221 869 A discloses conveyor belts with embedded rubber layers comprising metal cables and 5 phr zinc oxide.

[0007] Thus, there is an ongoing need for conveyor belts including zinc coated steel cordage with improved bonding between the zinc coated steel cord surface and rubber matrix, while be exposed to thermal and / or humidity aging conditions, such need met, at least in part, with embodiments according to the following disclosure.SUMMARY

[0008] In a first aspect of the disclosure, a conveyor belt includes a carry cover layer, a reinforcement layer which is situated below the carry cover layer, and a pulley cover layer which is situated below the reinforcement layer, where the reinforcement layer has steel cordage and rubber matrix, wherein the steel cordage comprised in the reinforcement layer are zinc coated steel cords, and wherein the rubber matrix includes zinc oxide in an amount of 11 phr to 16 phr. In some cases the rubber matrix includes zinc oxide in an amount of 16 phr.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Certain embodiments of the disclosure will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. FIG. 1 is a cross-sectional view of a conveyor belt having a carry cover layer, a reinforcement layer which is situated below the carry cover layer, where the reinforcement layer includes steel reinforcing elements, and a pulley cover layer which is situated below the reinforcement layer, according to an embodiment of the disclosure; FIG. 2 is a cross-sectional view of a conveyor belt having a carry cover layer, a reinforcement layer which is situated below the carry cover layer, where the reinforcement layer includes three layers of reinforcements, and a pulley cover layer which is situated below the reinforcement layer, according to another embodiment of the disclosure. FIG. 3 is a cross-sectional view of a conveyor belt having a carry cover layer, a second layer in the cover, which is situated immediately below the carry cover layer, a reinforcement layer which is situated below the cover, and a pulley cover layer which is situated below the reinforcement layer, according to another embodiment of the disclosure; and, FIG. 4 is a cross-sectional view of a conveyor belt having a carry cover layer, a second layer in the cover, which is situated immediately below the carry cover layer, a reinforcement layer which is situated below the cover, a pulley cover layer which is situated below the reinforcement layer, and another layer situated immediately adjacent the pulley cover layer, before the reinforcement layer, according to another embodiment of the disclosure. DETAILED DESCRIPTION

[0010] Conveyor belts according to the disclosure typically include an elastomeric body having a load carrying surface atop a carry cover layer, a parallel pulley engaging pulley cover layer, and a reinforcement containing carcass disposed within the elastomeric body of the belt. The reinforcement carcass typically includes one or more reinforcement layers, with optional intermediate layers disposed thereon. In some embodiments, the conveyor belts are formed as a continuous belt, and the ends cut and shaped in such way to enable splicing among the plurality of layers. In some aspects, stepped splice are used which insure that all layers in the splice seam do not approach a drive pulley simultaneously. These features, although not required, can improve the splice joint in some applications.

[0011] Now referencing FIG. 1 which illustrates an embodiment according to the disclosure. A conveyor belt 1 embodiment includes a carry cover layer 2 which is comprised of a synthetic and / or natural rubber based composition, a reinforcement layer 4 which situated below the carry cover layer 2, and a pulley cover layer 7 which is situated below the reinforcement layer 4. The pulley cover layer 7 is comprised of a synthetic and / or natural rubber based composition. In this embodiment, the reinforcement layer 4 includes a plurality of steel reinforcing elements 6 which are embedded within the rubber matrix 8 of the reinforcement layer 4, and disposed in an orientation essentially parallel with the longitudinal direction of the conveyor belt 1. The plurality of steel reinforcing elements 6 may, in some cases, be zinc-coated steel cords.

[0012] In some other embodiments, as depicted for conveyor belt 10 in FIG. 2, the reinforcement layer 4 may include a first layer of reinforcement 5A, a second layer of reinforcement 5B reinforcement layer including a plurality of steel reinforcing elements in a rubber matrix, and a third layer of reinforcement 5C. However, in alternative embodiments the reinforcement layer 4 can contain two layers of reinforcement, or four or more layers of reinforcement.

[0013] In embodiments of the disclosure, one or more of the carry cover layer 2, the pulley cover layer 7, or rubber matrix 8 of the reinforcement layer(s) contain zinc oxide (ZnO) in amounts greater than conventional levels. By significant increasing the amount of zinc oxide, either alone or in combination with other additional ingredients, the resistance of the bonding to the zinc coated steel cord against aging processes (i.e. thermal and / or humidity exposure) is improved. Such discovery is counter to previous teachings where negative effects on rubber adhesion to brass-plated steel cord surface at higher ZnO concentrations were found (see "Effect of ZnO contents at the surface of brass-plated steel cord on the adhesion property to rubber compound" by Gyung Soo Jeon, Min Hyeon Han and Gon Seo, Korean J, Chem. Eng., 16(2), 248-252 (1999)).

[0014] While FIGS. 1 and 2 depict a carry cover layer and pulley cover layer which are each formed of one layer of material, it is within the scope of this disclosure that any of the carry cover layer and pulley cover layer could be formed of multiple layers of materials. As illustrated in FIG. 3, in one embodiment of this disclosure, the conveyor belt 20 is reinforced with steel cords, and has a carry cover layer 2, a second layer 3 in the cover, which is situated immediately below the carry cover layer 2, a reinforcement layer 4 which includes steel cords 6 which are embedded in a rubber matrix, and a pulley cover layer 7 which is situated below the reinforcement layer 4. Similarly, as shown in FIG. 4, the pulley cover layer 7 may have another layer 9 situated immediately adjacent the pulley cover layer 7, before the reinforcement layer 4.

[0015] Any of a variety of natural or synthetic elastomeric materials suitable for conveyor belt applications may be used to form the carry cover layer 2, rubber matrix 8, and pulley cover layer 7, including, but not limited to elastomeric materials with resilient properties. In some aspects, the elastomeric material is a rubber selected from the group consisting of natural rubber (NR) and / or butadiene rubber (BR) and / or chloroprene rubber (CR) and / or styrene-butadiene rubber (SBR) and / or nitrile rubber (NBR, HNBR) and / or synthetic polyisoprene rubber and / or butyl rubber (IIR) and / or ethylene-propylene rubber (EPM) and / or ethylene-propylene-diene rubber (EPDM) and / or polyacrylate rubber (ACM) and / or isoprene-butadiene rubber and / or polybutadiene rubber and / or styrene-isoprene-butadiene rubber and / or ethylene-propylene-diene rubber and / or epichlorohydrin rubber (ECO) and / or chlorosulfonated polyethylene rubber (CSM) and / or silicone rubber (MVQ) and / or fluoro rubber (FPM).

[0016] The elastomeric materials used in forming conveyor belts in accordance with the disclosure may also include additives for enhancing flame retardancy, wear and chunk resistance, rolling resistance, aging resistance (e.g., ozone and UV resistance), and the like. Vulcanization aids, cross-linking agents, oils, accelerators, or other formation aids may also be used. Other polymers may also be included to obtain certain properties, such as polyacrylates, polyurethanes, melamine formaldehydes, polyesters, polyethers, and the like.

[0017] The reinforcing layers may also include any of a variety of other materials, in additional to steel cordage, either woven or non-woven, in any desirable weight and orientation, and is comprised of multiple individual plies separated by appropriate elastomeric or adhesive layers. Such materials may include a wide variety of wires, or even synthetic and manmade fibers, including polyester, nylon, aramid (e.g., Kevlar), glass, polypropylene, cellulose, wool, or others. The fibers may be multifilament, monofilament, or staple fibers. In one embodiment, the reinforcing layer further includes one or more plies of polyester and / or nylon.

[0018] In some cases, the reinforcement layer(s) may include textile layers with filaments which are disposed in a direction transverse to the longitudinal direction of the conveyor belt. Referring again to FIG. 2, such textile layers may be incorporated in reinforcement layers 5A, 5C, or both 5A and 5C.Examples

[0019] The following examples, shown in Table 1, were prepared to illustrate that embodiments of the disclosure provided improved bonding between a zinc coated steel cord surface and rubber matrix, while be exposed to thermal and humidity aging conditions. Examples 1 and 4 are reference examples. As a model system, zinc coated steel cords were embedded in rubber matrix adhesion compounds, containing different amounts of zinc oxide, and subjected to different aging conditions. In order to test the behavior of different compounds, the zinc coated steel cords embedded in the rubber matrix adhesion where formed into 10x10 mm T-Test-Block (with hot-dip galvanized steelcord 3x3x0.15mm) and subjected to the following aging conditions: a) Exsiccator for 14 days / 70°C / 95% humidity b) Salt water (10%NaCl) submergence for 14 days c) Autoclave water steam for 5 days / 105°C Table 1: Compound no.Ex. 1Ex. 2Ex. 3Ex. 4Ex. 5Ex. 6SBR 1500818181818181BR high cis191919191919Silica353535373737TESPT 50% on carbon black444444Styrene resin (a)111111111111Nytex 4700 (plasticizer)161616161616carbon black N339131313131313carbon black N330111111111111zinc oxide5111651116stearic acid1.11.11.11.11.11.1Manobond 680 C3.23.23.23.23.23.2resorcinol 80% in SBR4.34.34.34.34.34.3sulfur1.91.91.91.91.91.9Sulfur, unsoluble1.91.91.91.91.91.9retarder CTP0.40.40.40.40.40.4accelerator CBS1.41.41.41.41.41.4HMMM 50% on carrier (b)7.17.17.10.00.00.0HMMM 65% on carrier (b)0.00.00.05.55.55.56PPD (antioxidant)1.11.11.11.11.11.1phr in total:218.2223.6229.0217.7223.1228.5 a) Hot polymerized emulsion high styrene resin with a typical styrene / butadiene ratio of 82.5 / 17.5%. ca. 3.4% resin / fatty acid mixture b) Methylated melamine formaldehyde resin. on an inert silica base (50% or 65% active ingredient)

[0020] The above example compounds were mixed with a standard mixing procedure (3-step process) in a laboratory mixer (Shaw K1 mark 4 Intermix). Resorcinol was added in the second pass at moderate dump temperature.

[0021] T-Test-Block test samples were prepared from two batches at each zinc oxide level, and each exposure / test was conducted 10 times for each batch at each zinc oxide level. Zinc coated steel cord pullout testing was performed by a 10 kN universal tensile test machine (Zwick) with a pre-tension of 5 N / mm and a test speed of 125 mm / min. The force at pullout was recorded in newtons (N). Samples exposed to the aging conditions were measured in comparison to control samples which were not exposed to any aging conditions. Pullout force results are shown in Table 2, as an average of the 20 pullout tests conducted for each, and the values are expressed in N units. Table 2:Rubber Matrix ZnO phrControlSalt Water Bath (14d @ 10% NaCl)Warm Humidity (14d @ 70°C / 95%)Autoclave (5d @ 105°C)5phr3641471486911 phr35617520323116phr362191293263

[0022] As illustrated in Table 2, increasing the zinc oxide in the rubber layer, to levels ranging from 11 phr to 16 phr provides significant increase, and thus improvement in requisite pullout force of zinc coated steel cord from a rubber matrix, after exposure to the aging conditions.List of Reference Numerals

[0023] 1Conveyor belt 2Carry cover layer 3Second Layer 4Reinforcement layer 5AFirst layer of reinforcement 5BSecond layer of reinforcement 5CThird layer of reinforcement 6Steel reinforcing elements / steel cords 7Pulley cover layer 8Rubber matrix 9Another layer 10Conveyor belt 20Conveyor belt 30Conveyor belt

Claims

1. A conveyor belt (1) which is comprised of a carry cover layer (2), a reinforcement layer (4) which is situated below the carry cover layer (2), and a pulley cover layer (7) which is situated below the reinforcement layer (4), wherein the reinforcement layer (4) is comprised of steel cordage (6) and rubber matrix (8), wherein the steel cordage (6) comprised in reinforcement layer (4) are zinc coated steel cords; and, characterized in that the rubber matrix (8) comprises zinc oxide in an amount of 11 phr to 16 phr.

2. The conveyor belt (1) according to any of the preceding claims, wherein the rubber matrix (8) comprises zinc oxide in an amount of 16 phr.

3. The conveyor belt (1) according to any of the preceding claims, wherein the carry cover layer (2) comprises at least one rubbery polymer selected from the group consisting of styrene-butadiene rubber, synthetic polyisoprene rubber, nitrile rubber, isoprene-butadiene rubber, polybutadiene rubber, styrene-isoprene-butadiene rubber, chloroprene rubber and ethylene-propylene-diene rubber.

4. The conveyor belt (1) according to any of the preceding claims, wherein the pulley cover layer (7) comprises at least one rubbery polymer selected from the group consisting of styrene-butadiene rubber, synthetic polyisoprene rubber, nitrile rubber, isoprene-butadiene rubber, polybutadiene rubber, styrene-isoprene-butadiene rubber, chloroprene rubber and ethylene-propylene-diene rubber.

5. The conveyor belt (1) according to any of the preceding claims, wherein the rubber matrix (8) comprises at least one rubbery polymer selected from the group consisting of styrene-butadiene rubber, synthetic polyisoprene rubber, nitrile rubber, isoprene-butadiene rubber, polybutadiene rubber, styrene-isoprene-butadiene rubber, chloroprene rubber and ethylene-propylene-diene rubber.

6. The conveyor belt (1) according to any of the preceding claims, wherein the carry cover layer (2) includes zinc oxide at a level of greater than 5 phr.

7. The conveyor belt (1) according to any of the preceding claims, wherein the pulley cover layer (7) includes zinc oxide at a level of greater than 5 phr.

8. The conveyor belt (1) according to any of the preceding claims, wherein the carry cover layer (2) is devoid of lead oxide.

9. The conveyor belt (1) according to any of the preceding claims, wherein the pulley cover layer (7) is devoid of lead oxide.

10. The conveyor belt (1) according to any of the preceding claims, wherein the rubber matrix (8) is devoid of lead oxide.