Abstract:
The invention provides an apparatus and method which can be utilized to apply a thin layer of viscous coating material to an elongated continuously moving filament whereby the filament can be cabled, coated, and spooled in a continuous operation. The apparatus has a coating material applicator to deliver a flowable material, an air applicator to supply compressed air, a mixer to mix the flowable material and compressed air, a delivery means to spray the mixed flowable material and air onto a filament, and a coating chamber through which the filament passes. The chamber has a material collector and a coating die, and a sealing attachment with an exit hole is located beneath the coating chamber. The filament is sprayed before it travels into the material collector.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a continuous coating apparatus and method. More particularly, the invention is directed to a cord coating apparatus and a method for the continuous coating of thin layer of viscous materials on a moving cord or filament. 
     BACKGROUND OF THE INVENTION 
     Coatings of 1-2 μm and less are needed for the treatment of the tire cord and wires to improve tire durability, wire-rubber interfacial bonding, and corrosion aging resistance. It is known to use a continuous method to produce coated wires using apparatus consisting of a coating die which surrounds a wire and an extruder that extrudes coating material into the die around the wire. In industry, such an apparatus has been used in the coating of insulating material around electrical conducting wire where the needed coating thickness was 1 mil and thicker. However, the needed coating of 1-2 μm and less for the tire cord surface treatment is impossible to apply by conventional extrusion die coating process. 
     In another known continuous method to control the coating thickness of tire cord down to 1-2 μm or less, an air-wipe is used that wipes off excess coating materials right after a conventional dip-coat procedure. However this method is mainly employed to control the thickness of water base latex coat of a low viscosity coating material. For a high viscosity coating material such as an oil base mixture having a viscosity of 100 SUS and higher, the conventional dip-coat with air-wipe method is very difficult to operate and control. Additionally, the air-wipe which uses a strong air blast to wipe off the excess coating may limit the penetration of the coating material into the inner cord because of the volume expansion of the trapped air inside the cord according to the Bernoulli principle of physical matter. 
     SUMMARY OF THE INVENTION 
     The advantages of the present invention are numerous and are as follows. 
     The invention provides an apparatus and method which can be utilized to apply a thin layer of viscous coating material to an elongated continuously moving filament whereby the filament can be cabled, coated, and spooled in a continuous operation. 
     The invention provides an apparatus and method for applying a thin layer of latex base coating material to a continuously moving cord for an improved coating penetration. 
     The invention provides an apparatus and method for applying a thin layer of coating material with a high coating efficiency. 
     The invention provides an apparatus and method that can be utilized to improve cord coating at processing speeds that are limited only by the pay-off and the wire take-up services. 
     The invention provides an apparatus and method which optimized the coating mist typically associated with coating operations, thereby reducing the cost of the pollution control equipment and the recycling of excess coating materials. 
     The invention provides an apparatus and method that eliminates the need for highly complex machinery. 
     The present invention provides an improved wire manufactured by a technique having all the advantages of a conventional wire process but none of the disadvantages. 
     The disclosed apparatus has a coating material applicator to deliver a flowable material, an air applicator to supply compressed air, a mixer to mix the flowable material and compressed air, a delivery means to spray the mixed flowable material and air onto a filament, and a coating chamber through which the filament passes. The chamber has a material collector and a coating die, and a sealing attachment with an exit hole is located beneath the coating chamber. The filament is sprayed before it travels into the material collector. 
     In one aspect of the invention, the coating material applicator is selected from the group consisting of a constant volume material ejector, an intermeshing positive displacement multi-screw delivery pump, and a gear pump. 
     In one aspect of the invention, the delivery means is inclined at an angle relative to the coating chamber and the lowermost end of the delivery means is adjacent to the material collector. 
     In another aspect of the invention, the sealing attachment is shaped to form a spherical cone with the hole at the apex, forming an open area through which the filament passes. 
     In another aspect of the invention, the coating chamber dimensions can be varied. For example, the top entrance of the coating chamber may have a diameter larger than the main portion of the coating chamber and the exit of the coating chamber may have a diameter less than the coating die. 
     In another aspect of the invention, the coating chamber is mounted on a frame capable of linear movement relative to a take-up spool. This helps to ensure smooth and even spooling of the coated filament. 
     In another aspect of the invention, the material collector has an interior converging wall to permit collection of any stray flowable material. 
     In another aspect of the invention, the coating chamber has a vertical orientation. The vertical orientation of the chamber assist the flow pattern of the flowable material as it is sprayed onto the moving filament and in forming a small volume dip bath through which the filament may pass. 
     In another aspect of the invention, a cabling device is operatively associated with the coating apparatus. 
     Also disclosed is a method of coating a filament with a flowable material. The method includes the steps of providing a flowable material, providing compressed air, mixing the flowable material and the compressed air, spraying the mixing flowable material and compressed air onto a moving filament to coat the filament, and passing the filament through a material collection die, a coating die, and an exit hole having a diameter not more than the diameter of the filament. 
     In another aspect of the method, the filament passes through an open area prior to passing through the exit hole. 
     Also disclosed is a method of applying a coating of less than 2 μm on a moving filament. The method includes the steps of moving a filament along a defined travel path, providing a mix of a flowable material and a compressed air, spraying the flowable material and compressed air onto the moving filament, passing the filament through a small volume dip pool, and pulling the filament through a hole having a diameter not more than the diameter of the filament. 
     In one disclosed aspect of the method of applying a coating of less than 2 μm on a moving filament, the small volume dip pool has a volume of not more than 1.0 cc of liquid. 
     In another aspect of the method of applying a coating of less than 2 μm on a moving filament, there is the further step of passing the filament through an open area after passing the filament through the small volume dip pool and before pulling the filament through the hole. 
     In both methods disclosed, the filament may be formed of either steel or an organic material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described byway of example and with reference to the accompanying drawings in which: 
     FIG. 1 is an illustration of the entire coating system with the coating chamber in cross sectional view; and 
     FIG. 2 is another cross sectional view of the coating chamber and other elements. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The Apparatus 
     Referring to the drawings, and specifically to FIG. 1, the apparatus of the invention will be described. The apparatus has a filament pay-off device  10 , a coating material applicator, a low-pressure air applicator  14 , an air-material mixer  16 , a centering die  18 , a material collector  20 , a coating die  22 , and a filament take-up device  24 . 
     The term “filament” is used herein for all strand materials whether a single filament or a cord formed of many filaments. The filaments may be steel, organic, or any other strand material. While the embodiments herein described primarily relate to the manufacture of steel cord for reinforcing various articles, the apparatus of the invention has utility in coating all sorts of filaments other than the filament used in the production of the reinforcement materials. 
     The filament pay-off device  10  includes a spool  26  on which the filament to be coated is stored. The spool  26  is mounted on a spindle (not illustrated) to permit free rotation of the spool  26 . Operatively associated with the spool  26  is a brake  28  that restrains the rotation of the spool  26  as the filament  2  is being pulled from the spool  26  so as to prevent entanglements. The filament  2  travels about pulleys  30  as it travels to the coating apparatus. 
     At any point  32  along the filament path, depending upon the end use of the coated filament or the initial state of the filament  2  on the pay-off device  10 , conventional wire cabling apparatus, such as twisting, bunching, or stranding machines, may be employed. Thus, many filaments  2  of similar or different sizes may be cabled to the desired wire structure by conventional cabling equipment prior to the coating. 
     Alternatively, if the coating apparatus is located in an organic filament manufacturing plant, the pay-off device  10  may be eliminated and the filament may be formed immediately prior to the coating operation. In all instances, conventional forming, twisting, and cabling operations can be used in add to or in substitution of the pay-off device  10 . 
     The term “flowable material” is used herein for the general class of coating materials applied by the method and apparatus of the invention. While the specific embodiments herein described refer to viscous oil that carry active ingredients to improve the tire durability, other flowable coating materials are contemplated as being within the general class of materials which can be applied by the method and apparatus of the invention. These materials include those which are initially flowable but later hardened by curing or thermosetting the material and also coating materials which may include up to about 90% by weight of solvent or water to render them flowable and later reversible by driving the solvent or water from the material. In the manufacture of tire steel cords, several different materials can be applied using the method and apparatus of the invention. These include rubber process oil with viscosity up to 2000 SUS, corrosion inhibitor such as calcium salts and the wire-bonding agent such as cobalt salts. 
     The flowable material is provided by the material applicator  12 , which may be described as a positive displacement delivery system. The flowable material applicator  12  has a chute  34  by which the material is supplied to the applicator  12 , a material reservoir  36  in which the material is stored, and a positive displacement pump  38  which delivers the flowable material to the air material mixer  16 . An additional control device (not illustrated) may be associated with the positive displacement pump  38  to control the actual amount of flowable material delivered. An exact amount of flowable material is delivered through the tube  40  to the air material mixer  16 . 
     If it is desired that the flowable material be mixed with solvent or water, both the coating material and the solvent may be fed into the applicator  12  via the chute  34 . The reservoir  36  may also be provided with a mixing apparatus  42  having associated therewith a separate control. When using temperature sensitive flowable materials, the reservoir  36  may be provided with a temperature control means  44  by which the temperature of the material in the reservoir  34  can be controlled. The fluid material applicator  12  may be a constant volume material ejector, an intermeshing multi-screw pump, or a gear pump, all having some or all of the features described above. 
     Since the coating thickness is less than 2 μm, at a regular wire process speed the amount of flowable material needed from a material applicator is about 0.06 cc/second or less. Under this situation, a stable flow rate of viscous material is not obtainable from a conventional fluid material applicator, resulting in poor coating uniformity on the filament  2 . To overcome this difficulty, compressed air is combined with the flowable material. The air applicator  14  supplies compressed air to the mixer  16  through the air tube  46 . The needed air pressure is controlled by device  48 . 
     Compressed air provides two major functions. First, the air that is introduced in to the mixer  16  crushes the flowable material into numerous tiny droplets so that the flowable material is uniformly dispersed through the material dispenser tube  52  toward the filament  2  without generating a hazardous mist. Secondly, the higher air pressure at the end of the delivery tube forces the flowable material onto the filament  2 , and toward any interior strands of filament  2 , thereby improving the coating penetration. 
     As already noted, flowable material via tube  40  and compressed air via air tube  46  are delivered to the air material mixer  16 . The material is crushed by the compressed air and is delivered to the coating chamber  50  by means of the material dispenser tube  52 . 
     Coating of the filament  2  occurs within the coating chamber  50 . The coating chamber  50  has a top entrance bore  54  and a bottom exit hole  56 . The coating chamber  50  houses the centering die  18 , the material collector  20 , and the coating die  22 . A sealing attachment  58  is located beneath the coating chamber  50  and operates with the chamber components to execute the desired coating. The major function and specification of each component will be best understood by reference to the following description. 
     Referring to FIGS. 1 and 2, the coating chamber  50 , commences with the entrance bore  54  and terminates with the exit hole  56  at the bottom. Centering die  18  is located below the entrance bore  54  and the coating die  22  is located above the exit hole  56 . 
     The size of the entrance bore  54  is determined by the size of the centering die  18 . To permit removal of the centering die  18  for replacement or general maintenance, the entrance bore  54  is slightly larger than the centering die  18 . Additionally, as illustrated in FIG. 1, to hold the centering die in position within the chamber  50 , the size of the centering die is larger than the size of the main portion of the chamber  50 . However, in a different variation, the centering die  18  may be larger than the entrance bore  54 , so that the centering die  18  stays in place at the top of the chamber  50  without any additional external support. 
     The size of the main portion of the chamber  50  is determined by the size requirements of the coating die  22 . In the illustrated embodiment, the chamber  50  is slightly larger in size than that of the coating die  22  so that the coating die  22  can be easily slide in or out of the chamber  56  when die replacement or a general maintenance is needed. 
     The exit hole  56  has a diameter less than that of the coating die  22  so that the coating die  22  stays at the bottom of the chamber  50  without additional support. 
     Located above the coating die  22  is the funnel-shaped material collector  20 . The material collector  20  has a converging interior wall  60  that interconnects with the underneath coating die  22 . The interior wall  60  defines a cavity into which stray coating material can be collected. Preferably, the cavity will hold about 1.0 cc of material. The collected material then drips down to the coating die  22  to continue coating the filament  2 . In a different embodiment, both the material collector  20  and the coating die  22  may be replaced with just a single coating die with a flared opening in order to collect any stray coating material. 
     Along the wall of the coating chamber  50  there is one or more inclined through-holes  62 , allowing the material dispenser tube  52  to slide into the coating chamber  50 . The tube  52  defines an angle a with filament  2 . Angle α can be any value between 10° and 90°. In a specific embodiment, the angle α is about 45°. As seen in FIG. 1, the end of the material dispenser tube  52  is located close to the material collector  22  and the moving filament  2  so that the flowable material is directed onto the filament  2  and any stray material will collect in the material collector  22 . 
     The coating chamber  50  is set inside a support frame  64 . In order to prevent material from leaking from the bottom of the coating chamber  50 , the sealing attachment  58  is inserted between the coating chamber  50  and the support frame  64 . At the center of the sealing attachment  58 , there is an exit hole  66  with a diameter equal or smaller than the overall diameter of the coated filament  4 . The sealing attachment  58  is shaped to form a spherical cone with the hole  66  at the apex, thereby forming an open area  68 . In one embodiment, the area  68  is defined about 120-degree angle bisected by the longitudinal centerline of the attachment  58 . The spherical cone configuration, and the open area  68 , can be preformed before inserting the sealing attachment  58  into position. The configuration can also be formed on a flat piece of sealing attachment  58  by a skillful practice of tightening the screws  70 . 
     The sealing attachment  58  provides two functions. First, there is a chance that the coating material may accumulate at the exit hole  66  and then the accumulation will start to drip downwards. Due to the presence of the sealing attachment  58 , the leaking drops are retained in the area  68  around the coated filament  4 , so that a coating of 100% efficiency is obtained. Second, it is possible, but not desired, that some of the tiny flowable material droplets inside the mixer  16  may combine into big droplets on the wire surface, potentially degrading the coating uniformity. To improve the coating uniformity, the sealing attachment  58  smears or smoothes out those big droplets by rubbing the surface of moving coated filament  4 . The sealing attachment  58  is preferably formed of resilience elastomeric material such as rubber with a preferred thickness of about 1-2 mm. 
     In FIG. 2, the support frame  64  is shown in side view to indicate the needed alignment of the centering die  18 , and the coating die  22 . Additionally, a housing  72  may be positioned with the support frame  64  to house the coating chamber  50  and maintain the chamber in a vertical orientation. 
     Below the base of the support frame  64  is a take-up pulley  74 . As illustrated in FIG. 1, the pulley  74  preferably has a v-groove in which the coated filament  4  travels. Due to the interaction between the surface of the pulley  74  and the coated filament  4 , the coating is further pushed into the filament  4  and any remaining excess spots of coating are smoothed out. To prevent a build up of coating and any possible contamination on the pulley  74 , a shield  76  may be added to the side of the support frame  64  that will wipe off any excess coating. The shield  76  can be formed of any type of cleaning paper. 
     A set of guide rollers  78  are mounted on top of the support frame  64  to pre-align the filament  2  prior to the filament  2  entering the centering die  18 . 
     The support frame  64  is also connected to a linear drive  80  for the take-up spool  82 . Linear drive  80  travels back and forth along the axis  84  in association with the rotation of the take-up spool  82  during the take-up operation to evenly spool the coated filament  4  onto the take-up spool  82 . The spool  82  may be a conventional spool on which coated filaments are conventionally stored or shipped. The spool  82  is mounted on a spindle (not illustrated) for rotation. Operatively connected to the spool  82  is a spool driver  86  that drives the spool  82  and pulls the filament  2  from the spool  26  of the pay-off device  10 . 
     The Method 
     Filament  2  is unwound from the pay-off spool  26 , passing over any necessary pulleys  30  to prevent the filament  2  from becoming entangled. The illustrated filament  2  may be cabled or otherwise formed prior to passing over the last pulley  30  and passing between the guide rollers  78 . The filament  2  is guided into the coating apparatus by the guide rollers  78  and passes through the centering die  18 . 
     A flowable material containing an oil-based, water-based, or organic based coating material to be applied to the filament  2  is stored in the reservoir  36  at a flowable temperature. The flowable material passes through tube  40  and into the air material mixer  16 . Compressed air is also delivered to the mixer  16  via air tube  46  at a desired pressure; the pressure being selected by controls  48 . 
     The specific air pressure is closely controlled. The air pressure must be high enough to mix the flowable material in the mixer and force the flowable material down to any central core or strands of the filament  2 , but still low enough to prevent the formation of a mist. To avoid forming a mist, the air pressure must be controlled in accordance to the viscosity of the flowable material. For an oil-based material of 500 SUS viscosity, the air pressure is preferable controlled at 2-3 psi. 
     The mixed flowable material and compressed air is delivered by the dispenser tube  52  and is deposited onto the surface of the filament  2  just before the filament enters the material collector  20  and the coating die  22 . Coating material that misses the filament  2  is collected by material collector  20 , and then either drips down to the coating die  22  or accumulates inside the cavity of the collector  20 . Normally the stray material that is collected by the material collector  20  quickly drips down to the coating die  22  with the help of the moving filament  2 . 
     The specific amount of the coating material to be applied to the filament  2  is accurately metered. If there is an excess of flowable material, the material may drip from the hole  66 . Also, too great an excess of flowable material of the coated filament  4  may also result in the dripping of the flowable material from the take up spool  82  causing problems in handling the spools  82 . For these reasons, the material applicator  12  is provided with controls. 
     However, if the coating layer is thicker than desired, the control is thereafter adjusted to reduce the amount of material being delivered. Conversely, if the coating layer proves to be insufficient, the control is adjusted so as to accumulate a tiny pool of flowable material inside collector  20  for an extra short-term dip coating before the filament  2  passes through the coating die  22 . 
     Additionally, if it is believed that at the initial coating act, the actual coating thickness may be slightly less than what is expected and desired, the operator can pre-spray flowable material into material collector  20  for 10-20 seconds before the coating start to generate a short-term dip pool. 
     After passing through the coating die  22 , the coated filament  4  passes through the chamber exit hole  56  and into the open area  68  and then through the exit hole  66  in the sealing attachment  58 . The provision of the sealing attachment  58  with the open area  68  provides the filaments  4  with a surprisingly uniform coating thickness along the wire. Conversely, when the open area  68  is not present, coating thickness of lower uniformity is found. 
     After passing through the attachment exit hole  66 , the coated filament  4  travels over the take up pulley  74  and is wound onto the take-up spool  82 . To maintain even winding of the coated filament  4  on the take-up spool  82 , as needed, the coating apparatus, by means of the linear drive  80  travels along the axis  84 . 
     The operation and function of the take-up device  24  was described earlier. However, the speed at which the take-up device  24  was driven was not mentioned. The speed is not limited in any way by the method of the invention. The pay-off device  10  and the take-up device  24  themselves solely limit the speed of coating when applying any of the coating materials mentioned herein. When the pay-off device  10  is eliminated and conventional cabling operations are substituted therefore, the speed at which the driver  84  drives the take-up device  24  is solely limited by the take-up device  24  itself. 
     The method of the invention has been successfully used with filaments in a wide range of sizes. The method and apparatus of the invention can also coat cords of rectangular cross-sections and of other cross-sections so long as the coating die  22  can be provided in geometrically similar shapes. 
     Coating materials of various types have been successfully applied to filaments of various sizes in accordance with the method of this invention by the apparatus above, the coating materials having a viscosity from about 100-2000 SUS. 
     The Tire Steel Cord 
     For the manufacture of cords used in reinforcing tires, metallic cords are treated to improve the ability of the cored to adhere to rubber and increase the corrosion resistance of the cord. A surprising characteristic of all steel cords coated in accordance with the apparatus and method of the present invention is the coating uniformity and the continuity. The continuity and uniformity of thin coatings applied from solution permits a reliance upon a single coat of the viscous material, something atypical in this industry. 
     The flowable material contains a soluble bonding agent and/or corrosion inhibitor. The deposit of the flowable material results in improved wire adhesion, improve cable fatigue resistance and wire corrosion resistance. The treated filaments are then contacted with vulcanizable rubber compositions to form metal reinforced rubber plies. These plies may be used to manufacturer tires and also other rubber articles such as conveyor belts, hoses, and the like. 
     The metallic cord to be coated according to the present invention may be steel, zinc-plated steel or brass-plated steel. Preferably, the metallic cord is brass plated steel. 
     The steel substrate may be derived from those known to those skilled in the art. For example, the steel used for wire may be conventional tire cord rod including AISI grades 1070, 1080, 1090 and 1095. The steel may additionally contain varying levels of carbon and microalloying elements such as Cr, B, Ni and Co. 
     The term “cord” means one or more of a reinforcing element, formed by one or more filaments or wires which may or may not be twisted or otherwise formed. Therefore, cords using the present invention may comprise from one (monofilament) to multiple filaments. The number of total filaments or wires in the cord may range from 1 to 134. Preferably, the number of filaments or wires per cord ranges from 1 to 49. 
     The number of cord constructions which can be treated according to the present invention are numerous. Representative examples of such cord constructions include 2×, 3×, 4×, 5×, 6×, 7×, 8×, 11×, 12×, 27×, 1+2, 1+3, 1+4, 1+5, 1+6, 1+7, 1+8, 1+14, 1+15, 1+16, 1+17, 1+18, 1+19, 1+20, 1+26, 2+1, 2+2, 2+5, 2+6, 2+7, 2+8, 2+9, 2+10, 2/2, 2/3, 2/4, 2/5, 2/6, 3+1, 3+2, 3+3, 3+4, 3×4, 3+6, 3×7, 3+9, 3/9, 3+9+15, 4+3, 4×4, 5/8/14, 7×2, 7×3, 7×4, 7×7, 7×12, 7×19, 5+1, 6+1, 7+1, 8+1, 11+1, 12+1, 2+7+1, 1+4+1, 1+5+1, 1+6+1, 1+7+1, 1+8+1, 1+14+1, 1+15+1, 1+16+1, 1+17+1, 1+18+1, 1+19+1, 1+20+1, 2+2+8, 2+6+1, 2+7+1, 2+8+1, 2+9+1, 2+10+1, 2+2+8+1, 3+9+15+1, 27+1, 1+26+1, 7×2+1, 3+9+1, 3/9+1, 7×12+1 and 7×19+1. The filaments in the cord constructions may be preformed, waved or crimped. The preferred cord constructions include 2×, 3×, 1+5, 1+6, 1+18, 2+7, 3+2, 3+3 and 3/9+1. 
     The diameter of an individual wire or filament that is encapsulated or used in a cord that is encapsulated may range from about 0.08 to 0.5 mm. Preferably, the diameter ranges from 0.15 to 0.42 mm. 
     The tensile strength of the steel filaments in the cord should be at least 3040 MPa −(1200×D) when D is the diameter of the filament. Preferably, the tensile strength of each filament ranges from about 3040—(1200×D) to 4400 MPa—(2000×D). 
     The flowable material is applied to the filament  2  in an amount equal to what is needed to form a coat of 1-2 μm or less in thickness. 
     While there have been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.