GB2106031A - Method of manufacturing conveyor belting - Google Patents

Abstract

A method of manufacturing conveyor belting comprises forming an assembly (10) consisting of a plurality of substantially parallel textile yarns (12), which may be woven having high tensile strength, low stretch, and uniform shrink characteristics, at least one bat (24, 28) of discrete staple textile fibres (22, 26), and a synthetic thermoplastic polymeric resin in solid form, e.g. sheets (18, 20). The assembly (10) is then needled together, and the needled assembly is consolidated under heat and pressure so that the resin (18, 20) softens and flows to encapsulate and bind the yarns (12) and fibres (22, 26). <IMAGE>

Description

SPECIFICATION Method of manufacturing conveyor belting The invention relates to the manufacture of textile based elastomeric conveyor belting.

A review of the prior art is contained in Man Made Textile Encyclopedia, pages 309-312. A common method of making textile based elastomeric conveyor belting is by the so-called "wet-woven PVC" method wherein polyester warp yarns are immersed in a polyvinyl chloride plastisol compound and then woven together while wet. Alternatively, such belting may be made by lamination of textile cloths with elastomeric sheets, but the resultant belting is not entirely satisfactory. For example, the laminated belts are subject to delamination and structural failure over periods of use.

Recently, as described in U.S. Patents 4,154,335 and 4,157,752, a method of making conveyor belting has been developed in which non-woven bats of staple fibres are needled to woven scrims, the needled structure is saturated with a liquid elastomer forming resin, and the resin is cured under sufficient heat and pressure to consolidate the saturated mass into a unitary, non-layered structure.

The mono-ply belting so manufactured is an improvement over multi-ply laminated belting, in having greater structural integrity and abrasion resistance.

However, this method of making unitary, nonlaminated belting has not been entirely satisfactory in all respects. The resin impregnation or saturation of porous sheet materials, including fabrics, is traditionally accomplished by a dip into a wet dispersion of the resin, a squeeze to remove excess liquid, and drying and curing under heat and pressure. This requires the use of costly equipment and specially prepared plastisol resin compositions.

Such compositions (ie. resin dispersions) are relatively expensive (compared with extrusion grade resins) and create a number of problems by their use. For example, the use of liquid plastisols is potentially hazardous and has waste disposal problems. The waste liquids very often have to be solidified by heating in orderto prepare them for disposal in land fills. Alternatively, the solids must be incinerated for disposal. In addition, with regard to the use of liquid plastisol dip compositions, the curing steps are energy demanding and slow up production speeds. Furthermore, solvents are employed which must be handled, stripped, and disposed of, creating additional process costs.

According to the present invention we propose a method of manufacturing conveyor belting which comprises forming an assembly of a plurality of substantially parallel, uncrimped textile yarns hav ing high tensile strength, low stretch, and uniform shrink characteristics, a bat of discrete staple textile fibres, and a synthetic thermoplastic polymeric resin in solid form, needling the assembly of yarns, fibres and resin together, and consolidating the needled assembly under heat and pressure so that the resin softens and flows around individual yarns and fibres to beind them together and form a non-layered structure in which the yarns and fibres are wholly or substantially wholly encapsulated in the resin.

This method can produce unitary, non-laminated, conveyor belting having all the advantages of the non-layered belting produced by the methods described in the aforementioned U.S. patents but without the disadvantages of those methods described above, since the method in accordance with the invention eliminates the need for plastisols, solvents and similar hazardous materials with their attendant disposal problems. The method in accordance with the invention requires less energy, eliminates the need for drying steps, and faciliatates a continuous production line at higher production speeds. The method also permits variation of the product properties to a considerable degree without changing or interrupting the process production line.

In addition to these advanages, the method in accordance with the invention also produces a product of superior quality to that produced by the previous process. In the drying and curing of plastisol saturated fibrous masses, the plasticiser component often vaporises. The vapour is driven through the elastomer matrix, leaving vent channels as it migrates to the surface of the belting. Blisters result on the product surface and inherent weaknesses are created in the belt due to the channelling and blistering. In the method of the present invention, high concentrations of volatiles are not employed, thus avoiding the formation of blisters, channels, and similar imperfections in the belting produced by the method.

Examples of the method in accordance with the method will now be described with reference to the accompanying drawings, in which: Figure 1 is a block diagram indicating the main steps in the method of the invention; Figure2 is a diagrammatic cross-sectional and side elevational view of a portion of the assembly of yarns, resin, and fibres used in one example of the method in accordance with the invention; Figure 3 is a view similar to that of Figure 2, but showing the assembly after it has been needled together; Figure 4 is a view similar to that of Figures 2 and 3, but showing the needled assembly after it has been consolidated under heat and pressure; Figure 5 is a view similar to that of Figure 4, but showing the conveyor belting produced by a second example of the method of the invention; and, Figure 6 is a view similar to that of Figure 4, but showing conveyor belting produced by a third example of the method of the invention.

In carrying out the method of the invention, the textile yarns used may be provided incorporated in a cloth. For example, the textile yarns used may be in the form of the lengthwise yarns in a woven cloth or its equivalent in a knitted cloth. This is not essential however, and the yarns may be provided in a substantially parallel warp array, wherein the yarns are independent of each other. The term "substantially parallel" as used herein means that the yarns, for the most part, do not cross over each other indiscriminately. The provided textile yarns require a relatively high tensile strength, i.e.; on the order of at least about 20 lbs./end.

Advantageously, the provided textile yarn will be uncrimped and have low stretch properties, for example on the order of at least about 4 to 5 percent (1/2 nominal breaking load) to about 15 to 20 percent.

It is important that the yarns exhibit uniformity in their shrink characteristics, i.e., yarns of a high degree of shrinkability should not be mixed with yarns of a low degree of shrinkability to minimize buckling or cockling of the belting product.

The provided yarns may be selected from a wide variety of synthetic yarns, such as polyester, polyamide and like yarns. Preferbly the yarns will be spun yarns orthe like having a tendency to anchor in and hold softened thermoplastic resins.

In one embodiment of the invention, the textile yarns are provided in an open weave scrim as lengthwise yarns. Any weave may be used, a plain weave being stable and advantageous. In this embodiment, the nature of the crosswise yarns is not critical and any conventional synthetic or natural fiber yarn can be used. Advantageously the denier of the yarns and the density of the weave is selected to provide a scrim weight of from about 4 to about 40 oz./square yard for optimum strength.

The synthetic, thermoplastic, poymeric resins are provided in solid forms such as films, granules, discrete particles, powders and the like. Preferred are thin films and discrete particles which may be quickly softened to a flowable state upon heating under pressure. Representative of such forms are sheets or films having a thickness of from about 15 mils to about 90 mils and particles having an average diameter of from about 20 to about 200 microns.

A wide variety of synthetic, thermoplastic, polymeric resins may be used in the method of the invention. Representative of such resins are polyethylene, polypropylene, polybutadiene, poly- vinyl chloride, polyurethane, neoprene, polyamides, styrene-butadiene copolymers and the like. Preferred are elastomeric resins although this is not essential so long as the resins are flexible enough to be employed in a conveyor belting.

In a step of the method of the invention, one provides a non-woven bat of discrete, staple, textile fibers. The bats may be of randomly oriented staple fibers such as synthetic polyamide, polyester, polyolefin, acrylic and like fibers including blends thereof and natural fibers such as jute and blends thereof. Optionally if desired the fibers may be directionally oriented within the bats by methods known to the art.

The bats of staple fibers selected for needling to the textile yarns advantageously have a weight of from about 2 to about 20 oz./square yard. The staple fibers may have a wide denier range. The bats may be preneedled using conventional techniques to obtain some integrity of the fibers prior to needling the bat to the yarns.

The provided yarns function as a core in the belting prepared by the method of the invention. As indicated in the block diagram of Figure 1, the core of yarns is assembled with the bat of staple fibers and the resin material in an initial step of the method of the invention. Figure 2 is a cross-sectional side elevation of a portion of an embodiment assembly 10. The assembly 10 comprises a core of warp 12 and weft 14 yarns woven together to form a scrim 16.Yarnsl2,l4maybe,forexample,yarnsofspun polyester. Assembled on upper and lower surfaces of scrim 16 are films 18,20 of a solid, synthetic, thermoplastic resin. Covering the exposed surfaces of films 18,20 are bats 24 and 28, of staple fibers 22 and 26, respectively.This is the preferred positions of the assembly components, but the positions of the resin films may be changed with the positions of the adjacent bats of staple fibers if desired.

In one embodiment of the invention, discrete particles of the thermoplastic resin are assembled with the yarn core and the staple fibers. This may be carried out in part by homogeneously dispersing the discrete resin particles within the body of the staple fiber bat.

The proportion of resin material assembled with the bats of staple fibers and the yarns is one, by weight, at least sufficient to encapsulate all of the fibers and yarns. In general, such a proportion will be such that the belting product will comprise resin matrix constituting from 50 to 500 percent, preferably 100 to 350 percent of the textile fabric component weight.

In the next step of the method of the invention, the discrete staple fibers such as presented in a nonwoven fibrous bat, are needled to the abovedescribed textile yarns and the associated solid resin. As shown in Figure 3, a view as in Figure 2 but after needling of the assembly, there is formed a layer of consolidated staple fibers 22,26 whih through entanglement with the yarns 12, 14 becomes integrated threwith. If fibrous bats are needled to only one side of the yarns, fibers are carried to the opposite side to produce a light "nap" on that side, incorporating the yarns 12, 14. The latter embodiment is also one within the scope of the present invention. It will also be seen in Figure 3 that the films 18,20 of resin are secured by the needling.

When discrete particles of resin are used instead of films, the needling usually aids in dispersion of the particles throughout the assembly 10.

The techniques of needling fibrous bats to yarns and cloths woven or knitted from textile yarns are well known and details need not be recited here. The coarseness of the felting needles used; the barb configurations, number, size and other variables are dependent somewhat on the degree of openness between the textile yarns, so as to avoid rupture of the textile yarns. In general, we have found a No. 28 guage needle, with the barbs oriented so as not to tear the lengthwise yarns, adequate for needling.

The needling frame may be fitted with either high or low density needle boards, a 34 density board being illustrative. Needling is preferably carried out to produce a needled fabric having a weight within the range of from about 6 to about 90 oz./square yard.

Following needling, it may be advantageous to calender those needled materials wherein further consolidation is desired, particularly in those embodiments where a bat was needled to one side of the yarns only. The calendering further compacts and consolidates the staple fibers to reduce fluid permeability of the needled fabric. This enhances the retention of the resin which will be heat softened to flow in a subsequent step. Generally, it is desirable to have a fabric for resin retention which will retain the softened resin until resolidification occurs. If the needled fabric lacks this characteristic, calendering may be advantageous. Calendering is not generally necessary if fibrous bats have been needled to both sides of the textile yarns 12,14.

In an optional step of the method of the invention, the needled and possibly calendered fabric may be heat set in an oven to selectively shrink the fabric.

During heat setting, the fabric may be tensioned in the lengthwise direction (along the axis of the textile yarns) under from 0.5 to 20 Ibs. per inch or more of fabric width. This eliminates a large degree of stretching in the final product, and obviates wrinkles across the width and along the length of the belt product of the invention. Heat setting is carried out under temperatures dependent on the nature of the fibres and yarns employed in the needled fabric.

Those skilled in the art will know which temperatures to select. For example, when all polyester components are employed, heat setting may be carried out at temperatures within the range of from 300 F to 420 F.

In the final step of the method of the invention, the needled assembly is consolidated under sufficient heat and pressure to soften the thermoplastic resin and cause the resin to flow throughout the textile mass encapsulating the fibres 22, 26 and the inte grated yarns 12, 14, as shown in Figure 4, a cross-sectional side elevation of the assembly 10 shown in Figure 3, but after consolidation. Consolidation is advantageously carried out by passing the assembly 10 (of Figure 3) through a heated platen press at a temperature sufficient to soften (but not melt) the resin. Advantageously the assembly 10 is simultaneously pressed to produce a belting 10 as shown in Figure 4. Pressures of from about 50 to about 200 Ibs./square inch are practical and illustrative of pressures which may be employed.Preferably the assembly 10 is pressed and cured under pressures of from about 90 to 30 Ibs./square inch.

The resulting belting, upon cooling to re-soldifythe resin matrix is free of voids, blisters, etc. and generally exhibits a high degree of bonding between the fibers 22,26, the yarns 12, 14 and the resin matrix 18,20.

Simultaneously with consolidation of the assembled and needled resin/textile material, one may mold the surface of the belting to produce an impression (discontinuous) surface. Impression suface belting is useful in conveying applications for the sorting and separation of articles, particularly sheet materials such as tobacco leaves and the like.

In addition to consolidating the belting by passage through a platen press as described above, consolidation may be carried out by passing the needled and assembled material through the nip of heated calender rollers, particularly if a continuous process is desired.

In a continuous operation, the resin containing fabric may be passed through a ROTO-CURE unit and hot pressed between a heated impression roller and a travelling steel belt. Under heat and pressure in the ROTO-CURE an impression surface may be molded and a continuous sheet of the resin containing fabric travels continuously through the apparatus to provide a continuous sheet of product belting.

Whether belting is produced by the method of the invention by batch or continuous technique, one advantage resides in the ability to produce a wide variety of different belt structures without interrupting the flow of a process line. For example, in the Figure 5, one may see a cross-sectional, side elevation of an alternate embodiment conveyor belting prepared by the method of the invention. The belting 10' of Figure 5 is prepared in the same manner described above for the preparation of the belting 10 shown in Figure 4 except that the platen or calender roller on the upper side was maintained at a temperature substantially lower than the temperature of the platen or roller pressed against the lower side. As a result, a proportion of the ends of the fibers 22 remain free of the resin 20.The results is a "textile faced" belting which is unique and of use in certain applications where a textile facing is desired such as for a low coefficient of friction surface.

In a number of experiments we have observed that when in the method of the invention, consolidation is effected between two surfaces of different temper- atures, one being heated and one being cold, difference of flow from side to side occurs with more flow toward the hot roll than the cold roll. This indicates that controlled flow of the thermoplastic material can be achieved by proper selection of calender roll temperatures. For example, with 2 heated rolls, flow to the outer surfaces is achieved.

When it is desirable, flow to one side and partial flow to the other side producing a low coefficient of friction surface occurs.

Other variations are permitted by the method of the invention, even in a continuous line. Figure 6 is a cross-sectional, side elevation of a portion of another embodiment conveyor belting prepared by the method of the invention. In the belting 10" of Figure 6, a facing 30 of a synthetic polymeric resin such as a polyethylene or polyvinyl chloride film has been secured to the base, a structure such as belting 10 shown in Figure 4. This facing 30 can be laminated to a base 10 simultaneously with the above-described consolidation, thereby conserving energy.

The following examples describe the manner and process of making and using the invention and set forth the best mode contemplated by the inventors of carrying out the invention, but are not to be construed as limiting.

Example 1 Afabric is woven with a plain weave using 5000 denier Multiplex Dacron polyester (DuPont Type 97; average elongation percent [1/2 nominal breaking load ] 8.4; break strength 59 Ibs; dry heat shrinkage at 160 C. is 9.0 percent) in the lengthwise direction and 1150 denier spun polyester yarn in the crosswise direction. The cloth is composed of 11 ends per inch and 10 picks per inch and weighs 9 oz./square yard.

The cloth is combined with a needled bat of 100 percent polyester fibers (non-woven) having fiber denier of 6 and staple length of 3 inches, weighing 4 ozs./square yard and a 15 mi sheet of polyvinyl chloride on each side in one pass through a needle loom. The needled fabric is calendered at 6 yards/ minute to an average thickness of 0.070 inches and then heat set under moderate lengthwise tension by running at 9 feet per minute through a 90 foot long oven with a temperature of 320 F. in the initial zone, 350 F. in a intermediate zone, and 390 F. in the final zone.The heat set fabric is then pressed at 300 F. for 3 3 minutes at 120 psi in a flat, smooth platen hydraulic press to obtain a flexible belting product 0.075" thick weighing 57 oz./squareyard and having an ultimate tensile strength of 1200 Ibs./inch of width and a 2% elongation at 1001bs./inch of width.

Example 2 A fabric is woven with a plain weave using 5000 denier multiplex Dacron polyester in the lengthwise direction and 1150 denier spun polyester in the crosswise direction. The cloth is composed of 17 ends per inch and 20 picks per inch and weighs 12.5 ounces/square yard.

Polyvinyl chloride (PVC) particles are uniformaly distributed on the cloth scrim surface which may be as woven or prepared by combining with a lightweight (1 -3 oz/sq yd) web of polyester fibers to act as a retaining layer for the PVC particles. The treated scrim is of 100 percent polyester fibers (nonwoven) having fiber denier of 6 and staple length of three inches, weighing 7 oz/sq yd. The needled scrim with PVC prticle distribution is then turned over and a second application of PVC particles distributed and a second 7 oz/sq yd batt combined by needling.

By weight, PVC particles have been added within the range of 18 to 30 ox/sq yd. A weight of 25 oz/sq yd gave the best result of flow and belt integrity in this construction.

After needling, the resin treated fabric is passed through an air circulating oven at time/temperature conditions to heat the mass to 375"F. Immediately after preheating, the belt is consolidated and calendered to desired thickness, in this example approximately 0.125". This represents a reduction in thickness of .040" from the 0.165" thickness of the needled composite. Various calender process conditions were evaluated, however, processing a 3 ft/minute with both roll temperatures at 375"-400"F. gave satisfactory results.

Those skilled in the art will appreciate that many modifications may be made to the above-described preferred emodiments without departing from the spirit and the scope of the invention. For example, the belting may be produced from assembled resin/ textile materials wherein the resin is in the form of thermoplastic fibers or wherein the staple fiber component is coated with the thermoplastic resin prior to needling.

Claims (10)

1. A method of manufacturing conveyor belting, comprising forming an assembly of a plurality of substantially parallel, uncrimped textile yarns having high tensile strength, low stretch, and uniform shrink characteristics, a bat of discrete staple textile fibres, and a synthetic thermoplastic polymeric resin in solid form, needling the assembly of yarns, fibres, and resin together, and consolidating the needled assembly under heat and pressure so that the resin softens and flows around individual yarns and fibres to bind them together and form a non-layered structure in which the yarns and fibres are wholly or substantially wholly encapsulated in the resin.

2. A method according to claim 1, in which the assembly is formed with a bat of discrete staple textile fibres on each side of the yarns.

3. A method according to claim 1 or claim 2, in which the yarns are contained in a woven cloth.

4. A method according to any one of the preceding claims, in which the assembly is needled from one side only, and the needled assembly is then calendered to compress it further.

5. A method according to any one of the preceding claims, in which the needled assembly is heat set, the yarns being held under tension during the heat setting.

6. A method according to any one of the preceding claims, in which consoldiation is effected by passing the needled assembly through a heated platen press.

7. A method according to any one of the preceding claims, in which consolidation is carried out between two surfaces, one of which is at a lower temperature than the other so that portions of some of the fibres are not encapsulated in the resin on the side of the consolidated structure formed adjacent the cooler surface.

8. A method according to claim 1, substantially as described with reference to Figures 2 to 4, of Figure 5, or Figure 6 of the accompanying drawings.

9. A method according to claim 1, substantially as described in Example 1 or Example 2.

10. Conveyor belting manufactured by a method according to any one of the preceding claims.