Patent Application
20140374009
The present invention is directed a method for adhering metal to rubber, and specifically, a method for adhering a cord to a rubber matrix, such as a pneumatic tire.
It is frequently desirable to reinforce rubber articles (such as pneumatic and non-pneumatic tires, conveyor belts, power transmission belts, timing belts, hoses, etc.) by incorporating reinforcing elements. Pneumatic tires are often reinforced with reinforcing elements. Such reinforcing elements may comprise high carbon steel, high carbon steel coated with a thin layer of brass, nylon, polyester, carbon, glass, polyamide, etc. Such a reinforcing element may be a monofilament, but may also be prepared from several filaments that are stranded together to produce a cord. The strands of filaments may also be cabled to form the cord. It is beneficial for the reinforcing elements in pneumatic tires to exhibit high strength and ductility, as well as high fatigue resistance.
Transformation of a metal alloy into a filament suitable for reinforcing a tire may involve multiple processing stages, including rough drawing, patenting, brass plating, and fine drawing of a metal rod. Such a transformation may include many variations of processing stages, such as repetition of different stages.
Drawing of the metal rod may reduce the original diameter to a smaller diameter by passing the wire through a conical die. Drawing of the metal rod may increase the strength characteristics of the reduced diameter rod. Cold drawing may be conducted with either wet or dry lubricants. Formation of a filament with desirable properties may include multiple drawing steps both prior to, and after, patenting of the filament.
Patenting may obtain a structure which combines high tensile strength with high ductility, and thus impart to the filament the ability to withstand a large reduction in area to produce the desired finished sizes possessing a combination of high tensile strength and increased toughness. Patenting may be a continuous process and consist of first heating the metal alloy to a temperature within the range of about 900° C. to about 1150° C. to form austenite. Then, the austenite may cool at a rapid rate to a lower temperature at which transformation occurs thereby changing the crystal structure of ferrite from face centered cubic into pearlite, a eutectoid mixture of ferrite and cementite, which may yield the desired mechanical properties of the filament. While it may be desired to form a fully pearlitic structure, additional phases may be present, such as undissolved carbides, pro-eutectoid cementite, bainite, etc.
For metal reinforcing elements, the goal may be an increase in strength of the filament without a loss in ductility and fatigue resistance. The resulting filament may be characterized as high tensile, super tensile, ultra tensile, and mega tensile wherein each strength is defined by a minimum tensile strength.
In adhering such metal reinforcing elements to a rubber matrix, such as a pneumatic tire, two dissimilar materials are joined. In many cases, one or both of the materials must have their surface properties adjusted. Adjustment of surface properties of materials in manufacturing often involves surface treatment technology. Non-limiting examples of these surface properties include surface energy, chemical inertness, conductivity, dye reception, and/or adhesion. Non-limiting examples of applications using surface treatment and preparation include anti-corrosion coatings on corrodible metals such as iron and steel; bio-compatible coatings on internal implants; waterproof layers on electronics; and inorganic and organic materials for tires.
Application of coatings, adhesives, sealants, and elastomers (CASE) to substrates often requires particular care in treating or pre-treating the surface to avoid adhesive failure between the substrate and the applied CASE compounds. Many CASE application processes involve steps of (a) cleaning or roughening the surface, (b) applying a primer that either bonds to the surface or etches it, and/or (c) applying an enhancement agent that adds additional bonding functionality. CASE compounds are used in industries including construction, automotive, medical, dental, labeling, electronics, and packaging.
In the automotive industry, CASE compounds are used in conjunction with rubber reinforcement processes. Disadvantageously, rubber reinforcement is susceptible to cracking due to poor adhesion of the reinforcement to the rubber. Other goals of joining dissimilar materials include improving accuracy of manufacturing, productivity, levels of automation, reliability, and/or manufacturability, while decreasing harmful side effects, quantity of materials used, and/or waste of energy and materials. For example, some CASE compounds have substantial amounts of waste. Often coupling agent primers are less than 1% active agent and 99% carrier solvent. In another example, cleaning materials have harmful side effects such as flammability and/or noxious solvents, such as isopropyl alcohol or toluene. In other cases, paint-like layers often have to air dry within 30 seconds and so use volatile solvents. Energy and money are wasted to remediate these emissions and to protect workers' health.
Plasma polymerization has been developed as a tool to modify material surfaces while improving manufacturability, levels of automation, and accuracy of manufacturing, while decreasing harmful side effects as well as waste of energy and materials. There are different types of plasmas that are defined by their output temperature, their pressure conditions, as well as the equilibration state regarding the chemistry and thermal state. For example, there are plasmas created under subambient pressure conditions. Examples include a high plasma density mode plasma and a low plasma density mode plasma generated with a magnetron, which is typically used in physical vapor deposition. Other ambient pressure examples include glow discharge, inductively-coupled, and recombining plasmas. The glow discharge is characterized by low velocity movement of gas of a few meters/second. It features both thermal and chemical non-equilibrium. An inductively-coupled plasma has low to moderate gas movement. It features local thermal equilibria. The recombining nitrogen or air plasmas have high gas velocities of approximately 1 km/sec and feature chemical equilibria. Additional examples of classes of plasmas are determined by their ionization methods, such as microwave resonance and electrical discharge.
When plasmas are applied to high volume production processes outside a laboratory, additional manufacturability and automation considerations arise, such as speed of operation, compatibility with substrates, and contamination. In many applications, the plasma treatments occur quickly, typically on the order of nanoseconds to a few minutes, which effectively preclude batch vacuum techniques such as physical vapor deposition.
The high temperature plasmas may thermally combust or thermally shock substrates, especially ones with low thermal conductivity as well as low melting or combustion points. In addition, some surfaces are imperfect, such as those having dust, organic body oils, and debris from shipment and handling. In light of the foregoing, a method that improves accuracy of manufacturing, productivity, levels of automation, reliability, and/or manufacturability while decreasing harmful side effects, quantity of materials used, and/or waste of energy and materials for a high volume production process for preparing a surface for joining two dissimilar materials or to receive CASE compounds.
One conventional method deposits a coating on to a clean surface during a first time period, and depositing a high-velocity impact polymer reaction coating on the surface at ambient air pressure during a second time period using an atmospheric pressure air plasma (APAP). Another conventional method may apply a coating of mixed prepolymer vapor and carrier gas or mist of small droplets. That mixture may be introduced into an atmospheric pressure air plasma to form a polymer reaction compound. The polymer reaction compound may then be applied with high-velocity impact driven by the exiting gases of the APAP.
A method in accordance with the present invention forms an adhesion joint between a cord and a rubber matrix. The method includes the steps of: providing a cord having an initial relatively smooth surface; texturing the smooth surface such that the resulting surface is rougher than the initial surface of the cord; depositing a uniform polymer coating on to the textured surface of the cord by plasma polymerization of an organic precursor and an air plasma; and inserting the cord into a rubber matrix such that the resulting surface provides enhanced adhesion to the rubber matrix compared to the adhesion of the initial surface to the rubber matrix or adhesion of the textured surface to rubber matrix.
According to another aspect of the method, the texturing step is performed by a laser.
According to still another aspect of the method, the cord is placed in a carcass ply of a pneumatic tire.
According to yet another aspect of the method, the cord is placed in a belt ply of a pneumatic tire.
According to still another aspect of the method, the cord is placed in a flipper of a pneumatic tire.
According to yet another aspect of the method, the cord is placed in a runflat insert of a pneumatic tire.
According to still another aspect of the method, the cord is placed in a chipper of a pneumatic tire.
According to yet another aspect of the method, the cord is placed in an overlay of a pneumatic tire.
According to still another aspect of the method, the cord is placed in an apex of a pneumatic tire.
According to another aspect of the method, the cord is placed in a gum strip of a pneumatic tire.
A pneumatic tire includes a carcass comprising a reinforcing ply structure extending between a pair of bead portions, a pair of sidewalls, each sidewall located radially outward of one of the pair of bead portions, a tread, a belt reinforcing structure located radially outward of the carcass and radially inward of the tread, and an apex located in each sidewall. The pneumatic tire has a reinforcing structure reinforced with a cord having a surface modified both by micro-texturing and plasma polymerization.
According to another aspect of the pneumatic tire, the surface is micro-textured by a laser.
According to still another aspect of the pneumatic tire, the reinforcing structure is the carcass.
According to yet another aspect of the pneumatic tire, the reinforcing structure is the carcass reinforcing ply structure.
According to still another aspect of the pneumatic tire, the reinforcing structure is the belt reinforcing structure.
According to yet another aspect of the pneumatic tire, the reinforcing structure is the apex.
According to still another aspect of the pneumatic tire, the cord is constructed of steel.
According to yet another aspect of the pneumatic tire, the cord is comprised of steel filaments micro-textured by a laser prior to being placed in the cord.
According to still another aspect of the pneumatic tire, the cord is comprised of steel filaments placed in the cord prior to the cord being micro-textured by a laser and prior to plasma polymerization coating of the cord.
According to yet another aspect of the pneumatic tire, the reinforcing structure is located adjacent one of the bead portions.
The following definitions are applicable for the present invention.
“Apex” means an elastomeric filler located radially above the bead core and between the plies and the turnup ply.
“Annular” means formed like a ring.
“Aspect ratio” means the ratio of its section height to its section width.
“Axial” and “axially” are used herein to refer to lines or directions that are parallel to the axis of rotation of the tire.
“Bead” means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim.
“Belt structure” means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having cords inclined respect to the equatorial plane of the tire. The belt structure may also include plies of parallel cords inclined at relatively low angles, acting as restricting layers.
“Bias tire” (cross ply) means a tire in which the reinforcing cords in the carcass ply extend diagonally across the tire from bead to bead at about a 25°-65° angle with respect to equatorial plane of the tire. If multiple plies are present, the ply cords run at opposite angles in alternating layers.
“Breakers” means at least two annular layers or plies of parallel reinforcement cords having the same angle with reference to the equatorial plane of the tire as the parallel reinforcing cords in carcass plies. Breakers are usually associated with bias tires.
“Cable” means a cord formed by twisting together two or more plied yarns.
“Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
“Casing” means the carcass, belt structure, beads, sidewalls and all other components of the tire excepting the tread and undertread, i.e., the whole tire.
“Chipper” refers to a narrow band of fabric or steel cords located in the bead area whose function is to reinforce the bead area and stabilize the radially inwardmost part of the sidewall.
“Circumferential” means lines or directions extending along the perimeter of the surface of the annular tire parallel to the Equatorial Plane (EP) and perpendicular to the axial direction; it can also refer to the direction of the sets of adjacent circular curves whose radii define the axial curvature of the tread, as viewed in cross section.
“Cord” means one of the reinforcement strands of which the reinforcement structures of the tire are comprised.
“Cord angle” means the acute angle, left or right in a plan view of the tire, formed by a cord with respect to the equatorial plane. The “cord angle” is measured in a cured but uninflated tire.
“Crown” means that portion of the tire within the width limits of the tire tread.
“Denier” means the weight in grams per 9000 meters (unit for expressing linear density). “Dtex” means the weight in grams per 10,000 meters.
“Density” means weight per unit length.
“Elastomer” means a resilient material capable of recovering size and shape after deformation.
“Equatorial plane (EP)” means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread; or the plane containing the circumferential centerline of the tread.
“Fabric” means a network of essentially unidirectionally extending cords, which may be twisted, and which in turn are composed of a plurality of a multiplicity of filaments (which may also be twisted) of a high modulus material.
“Fiber” is a unit of matter, either natural or man-made that forms the basic element of filaments. Characterized by having a length at least 100 times its diameter or width.
“Filament count” means the number of filaments that make up a yarn. Example: 1000 denier polyester has approximately 190 filaments.
“Flipper” refers to a reinforcing fabric around the bead wire for strength and to tie the bead wire in the tire body.
“Gauge” refers generally to a measurement, and specifically to a thickness measurement.
“High Tensile Steel (HT)” means a carbon steel with a tensile strength of at least 3400 MPa at 0.20 mm filament diameter.
“Inner” means toward the inside of the tire and “outer” means toward its exterior.
“Innerliner” means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire.
“LASE” is load at specified elongation.
“Laser” means Light Amplification by Stimulated Emission of Radiation; a device that creates and amplifies electromagnetic radiation of a specific frequency through the process of stimulated emission; the radiation emitted by a laser may consist of a coherent beam of photons, all in phase and having the same polarization.
“Lateral” means an axial direction.
“Lay length” means the distance at which a twisted filament or strand travels to make a 360 degree rotation about another filament or strand.
“Load Range” means load and inflation limits for a given tire used in a specific type of service as defined by tables in The Tire and Rim Association, Inc.
“Mega Tensile Steel (MT)” means a carbon steel with a tensile strength of at least 4500 MPa at 0.20 mm filament diameter.
“Normal Load” means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
“Normal Tensile Steel (NT)” means a carbon steel with a tensile strength of at least 2800 MPa at 0.20 mm filament diameter.
“Ply” means a cord-reinforced layer of rubber-coated radially deployed or otherwise parallel cords.
“Radial” and “radially” are used to mean directions radially toward or away from the axis of rotation of the tire.
“Radial Ply Structure” means the one or more carcass plies or which at least one ply has reinforcing cords oriented at an angle of between 65° and 90° with respect to the equatorial plane of the tire.
“Radial Ply Tire” means a belted or circumferentially-restricted pneumatic tire in which at least one ply has cords which extend from bead to bead are laid at cord angles between 65° and 90° with respect to the equatorial plane of the tire.
“Relief” means variation in height of a surface.
“Rivet” means an open space between cords in a layer.
“Roughness” means the coarseness or unevenness of a surface, such as from projections, irregularities, breaks, etc. (e.g., amount of nonsmoothness).
“Section Height” means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.
“Section Width” means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.
“Self-supporting run-flat” means a type of tire that has a structure wherein the tire structure alone is sufficiently strong to support the vehicle load when the tire is operated in the uninflated condition for limited periods of time and limited speed. The sidewall and internal surfaces of the tire may not collapse or buckle onto themselves due to the tire structure alone (e.g., no internal structures).
“Sidewall insert” means elastomer or cord reinforcements located in the sidewall region of a tire. The insert may be an addition to the carcass reinforcing ply and outer sidewall rubber that forms the outer surface of the tire.
“Sidewall” means that portion of a tire between the tread and the bead.
“Smoothness” means a surface of uniform consistency; a surface free from projections or unevenness or generally flat Of unruffled.
“Spring Rate” means the stiffness of tire expressed as the slope of the load deflection curve at a given pressure.
“Stiffness ratio” means the value of a control belt structure stiffness divided by the value of another belt structure stiffness when the values are determined by a fixed three point bending test having both ends of the cord supported and flexed by a load centered between the fixed ends.
“Super Tensile Steel (ST)” means a carbon steel with a tensile strength of at least 3650 MPa at 0.20 mm filament diameter.
“Tenacity” is stress expressed as force per unit linear density of the unstrained specimen (gm/tex or gm/denier). Used in textiles.
“Tensile” is stress expressed in forces/cross-sectional area. Strength in psi=12,800 times specific gravity times tenacity in grams per denier.
“Texture” means the general physical appearance of a surface, such as with respect to the size, shape, size variability, and geometric arrangement of its discontinuities (e.g., not smooth).
“Toe guard” refers to the circumferentially deployed elastomeric rim-contacting portion of the tire axially inward of each bead.
“Tread” means a molded rubber component which, when bonded to a tire casing, includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load.
“Tread width” means the arc length of the tread surface in a plane including the axis of rotation of the tire.
“Turnup end” means the portion of a carcass ply that turns upward (i.e., radially outward) from the beads about which the ply is wrapped.
“Ultra Tensile Steel (UT)” means a carbon steel with a tensile strength of at least 4000 MPa at 0.20 mm filament diameter.
“Vertical Deflection” means the amount that a tire deflects under load. “Yarn” is a generic term for a continuous strand of textile fibers or filaments. Yarn occurs in the following forms: 1) a number of fibers twisted together; 2) a number of filaments laid together without twist; 3) a number of filaments laid together with a degree of twist; 4) a single filament with or without twist (monofilament); 5) a narrow strip of material with or without twist.
The present invention will be described by way of example and with reference to the accompanying drawings, in which:
Reference will now be made in example detail to compositions, embodiments, and methods of the present invention known to the inventors. However, it should be understood that disclosed embodiments are merely exemplary of the present invention which may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, rather merely as representative bases for teaching one skilled in the art to variously employ the present invention.
In accordance with part of the present invention, a laser may form a micro-texture at the surface of tire reinforcing cords, such as cords of steel, inorganic material, organic material, aramid, etc. The micro-texture may roughen the smooth surface thereby improving adhesion between the cords and the rubber matrix of the tire, thereby improving the durability and fatigue performance of the tire. The micro-texture may be varied by adjusting the wavelength, focus (or accuracy), continuity of power, and/or angle of incidence of the laser. The power may have a power/accuracy comparable to conventional medical lasers.
An example method for achieving a micro-textured surface on a metal wire is shown in
However, the characteristics of the steel may be controlled by a defined chemical composition and processing to provide a high strength wire with ductility sufficient for wire drawing without premature cracks. A steel wire may be processed to have ductile properties similar to a 0.96% C steel with improved strength. Chromium, Cr, may be present in amounts of 0.2 to 1.8%. Cr reduces a carbon diffusion rate resulting in both refining of the pearlite and reducing the thickness of the pro-eutectoid cementite network during patenting. The Cr may partition into cementite, affecting the cementite crystal structure and thereby reducing the cementite brittleness. If the amount of Cr is less than 0.2%, the addition may induce a poor effect. Conversely, if the amount of Cr is greater than 1.8%, hardenability becomes high and martensite or bainite may be formed during patenting, resulting in deterioration of cold workability.
Manganese, Mn, may be present in amounts of 0.2 to 0.8%. Mn is a strong solid solution strengthener of ferrite. When the Mn content is less than 0.2%, the strengthening effect may not be achieved, and when the Mn content is in excess of 0.8%, there may be a deterioration of cold workability, particularly due to a higher number of Mn—S inclusions.
Silicon, Si, may be present in amounts of 0.2 to 1.2%. Si imparts a strong solid solution strengthening on ferrite. When the Si content is less than 0.2%, the effect may be lost, and when the Si content is greater than 1.2%, the silicate inclusions may form thereby increasing the probability of wire breakage during drawing.
Cobalt, Co, if present, may be not more than 2.2%. Co suppresses the formation of cementite networks in the steel when the carbon content is greater than 1.0%. If the amount of Co is greater than 2.2%, cobalt inclusions may form, negatively affecting wire drawability. Co also produces additional cost.
Niobium, Nb, if present, may be not more than 0.1% when carbon content is greater than 1.0%. The small amount of Nb may control the size of pearlite colonies by limiting growth of austenite grains at the austenitization stage of patenting and may prevent formation of large particles that may result in wire breaks during drawing. Small Nb may precipitate at austenite grain boundaries preventing excessive austenite grain growth, thereby improving wire ductility.
Boron, B, may be present in amounts of 0.006-0.0025 parts per million (ppm). The small amount of B may affect the structure of crystalline interfaces. During wire drawing, the volume fraction of ferrite/cementite interlamellar interfaces may increase up to ten percent. Boron atoms may aggregate at grain boundaries, thereby eliminating de-cohesion. Additionally, boron may tie free nitrogen, thereby reducing strain aging during drawing and improving ductility.
Exemplary Compositions for the Steel in Table 1.
After the desired steel composition is determined, the steel may be hot rolled into wires with an initial diameter of about 4.0 mm to about 5.5 mm. The wire may be directly drawn for an initial diameter reduction, patented to the tensile strength desired, brass plated, and finely drawn to reduce the wire to a final diameter of about 0.1 to 0.35 mm.
The hot rolled steel may be free of centerline carbon segregation with non-deformable inclusions having a size not more than 10 microns. The network of pro-eutectoid cementite, if present, may have a thickness of not more than 20 nm.
Each of the steps in
Following the rough/direct draw, the wire may be subject to intermediate patenting, which may include heat treating the wire to remove the effects of the rough/direct draw. Following the intermediate patenting, the wire may be subject to an intermediate draw/pass wherein the diameter of the wire is reduced to between about 0.15 mm to about 0.2 mm. Following the intermediate draw/pass, the wire may be subject to a fine patenting, which may include heat treating the wire to remove the effects of the intermediate draw. Following the fine patenting, the wire may be plated with brass to improve adhesion to the rubber matrix. Following the brass plating, the wire may be subject to a fine draw/pass wherein the diameter of the wire may be reduced by approximately 4.0% to about 0.15 mm. Following the fine draw/pass, in accordance with the present invention, a laser may form a micro-texture at the surface of the wire for improving adhesion between the wire and the rubber matrix of a tire, thereby improving the durability and fatigue performance of the tire (left arrow in
During an example patenting process, the ductility of the wire may be improved and the wire may have a microstructure capable of yielding the target strength required of the wire. The example patenting process may have three distinct steps: austenitization, cooling, and transformation. During austenitization, the wire may be quickly heated to an initial high temperature within the range of 930° to about 1100° C. The furnace temperature in the first furnace section may be about 50° C. to 100° C. higher than the targeted austenitization temperature such that the wire may be heated faster to the desirable temperature. After the wire is heated to the initial high temperature, the wire may pass into at least one lower temperature furnace section to maintain a desired wire temperature. Temperature in the remaining furnace zones may gradually taper down to the target austenitization temperature in the last zone.
The wire may be given sufficient time for the alloy to be fully austenitized as it passes through the different heating sections; however, the wire may not be subjected to an excessive heating period. The goal in this example step may be a small austenite grain size (e.g., 50 microns or less). The temperature gradient experienced by the wire may result in a formation of a fine grained austenite microstructure yielding improved ductility characteristics of the patented wire. Heating of the wire may be accomplished by electric resistance, fluidized bed, or an electric or gas fired furnace. The duration in each furnace may depend on furnace length and wire speed.
After passing through the heated zones, as described above, the wire may be rapidly cooled to a temperature below the ideal transformation temperature. Typical transformation temperatures may range from 525° C. to 620° C., depending on the amount of the alloying elements. The wire may be cooled to a temperature of about 20° C. to about 80° C. below the ideal temperature. This lower temperature may become the transformation temperature of the wire being worked.
The wire may be cooled at a rate higher than 30° C. per second, or even 50° C. per second. The wire may be cooled to the desired temperature within a period of 4 seconds or less. By quickly quenching the wire to a lower temperature, formation of a thick network of pro-eutectoid cementite may be suppressed thereby improving ductility of the wire.
After the wire is rapidly cooled to a transformation temperature, similar to the austenitization phase, the wire may pass through multiple, different temperature heat zones. The temperature in the first zone may be set to maintain the wire temperature at the transformation temperature. The second temperature zone may be 10° C. to 20° C. less than the prior zone to compensate for heat generated by the wire as transformation from the austenite phase to the pearlite phase progresses and to thereby prevent the wire from overheating. The time in the second zone may be approximately half of the total duration for the wire to transform; total time may be dependent upon the length of time for the wire to achieve full transformation and the exact wire composition.
By employing a temperature gradient at this transformation step, the release of latent heat may result in fine pearlitic microstructure with an interlamellar spacing of less than 60 nm, thereby improving strength characteristics of the wire. After the transformation is fully completed, the wire may be cooled to ambient temperature.
During an example fine drawing process, a tapered draft or a mixed tapered-even area reduction draft may be employed. The wire may be drawn through a die with an 8° approach angle. Again, similar to the direct draw, the wire may be subject to a skin pass wherein the diameter of the wire is reduced by 4% for the purpose of reducing delamination.
By using the above die design and process and applying true strains of greater than 3.8, and preferably 3.9 to 4.5 as defined by εd=2 ln(do/d) where do is the starting wire diameter and d is the final diameter filament of tensile strength greater than 3800 MPa at wire diameters 0.35 mm are achieved and wires with a tensile strengths greater than 4500 MPa at 0.20 mm are possible. For example, the true strain in the drawing of 1.65 mm wire to 0.20 mm diameter filament is 4.2.
As stated above, prior to a fine draw, the wire may be treated for corrosion resistance and to improve wire drawability. Joining of metals by adhesion is a conventional alternative to welding and mechanical fastening because adhesion joints may eliminate local stress concentrations and thermal distortion, and reduce weight by eliminating rivets, screws, and/or other fasteners. However, the durability of an adhesion joint may largely depend on the joint design, type of adhesive, and the surface structure of the adherent. Metallic medical implants may be used for internal fixation of body parts, such as bones. Some of these implants may be removed after a fractured bone is healed. Other implants, such as dental implants and joint replacements, may remain in the body indefinitely. As a result, strong and rapid fixation between a metallic implant and bone tissue has been of prime importance to surgeons. Different surface texturing techniques have thus been conventionally utilized. Some conventional fixation methods may be: (1) to use bone cement or ceramic coating for direct chemical bonding; (2) to use a screw thread for mechanical locking; and (3) to make use of the surface texture on the implant to facilitate the attachment of bone cells, and subsequently bone tissue growth on the implant.
The advantages for laser micro-drilling of medical implants, compared with other technologies, may produce highly precise machining and complex geometries. The more holes drilled on the adherent surface, the more mechanical locking sites may result. Similarly, the more holes on the medical implant surface, the easier bone cells may attach, resulting in higher adhesion strength. Thus, the adhesion strength of metal surfaces subject to different surface texturing treatment may be increased by micro-texturing, such as by laser, sand-blasting, electro-erosion, acid treatment, etc. In accordance with part of the present invention, this principle also applies to metal surfaces adhering to a rubber matrix, as stated above.
Referring to
The gases from the exit nozzle 50 may be a spray pattern with the outer penumbra 56 having mostly ionized gas for cleaning and/or activating. Closer to the center of the spray pattern may be an area of the higher concentration 54 of high-velocity impact polymer reaction coating material. The substrate 58 receiving the high-velocity impact polymer reaction coating 64 may be a rubber reinforcement material.
The substrate 58 may be activatable by ionization and heat and may be in pristine condition, having a covering of debris, or be corroded. The substrate 58 may be cleaned, and partially activated, by an atmospheric pressure air plasma. When the atmospheric pressure air plasma is also a device depositing high-velocity impact polymer coatings, the penumbra 56 of the atmospheric pressure air plasma exiting from the nozzle 50 may have a cleaning function associated with the ionization and heat. Accordingly, the time period between the cleaning and/or activation step and the deposition step may be greater than 1 ms, 5 ms, 10 ms, 25 ms, or 100 ms.
One or more separate atmospheric pressure air plasmas may be provided to clean and/or activate the surface, followed by one or more separate atmospheric pressure air plasmas depositing high velocity impact polymer coatings. The APAPs may be operated in a sequential manner, in a parallel manner, or a combination thereof. When operated as a parallel set of multi-APAPs, typical spacing may be about 2 mm.
The cleaning and/or activating operation may be capable of operating at higher travel speeds than the deposition operation or a combined cleaning and/or activating operation, as well as a deposition operation. A cleaning operation using broader width passes and a deposition operation using raster-type passes may also be included. The cleaning and/or activating operation may be accomplished using other ionization technologies, such as corona discharge or combustion sources. The time periods between the cleaning/activation step and deposition may be greater than 0.1 s, 1 s, 5 s, 10 s, 25 s, or 100 s, and less than 150 s, 300 s, 600 s, 1800 s, 3600 s, 12 hr, 1 day, 2 days, or 5 days.
Gradients of prepolymers may be developed where an additional feedstock vessel 24 holding other prepolymers feeds through a supply line 26 to the prepolymer feedstock vessel 22 in order to incrementally adjust the ratio or ratios of the prepolymers in the feedstock. Other prepolymers may be fed through a supply line 28 to a metering device 32 that may be adjusted incrementally or step-wise based on the ratio or ratios of prepolymers.
The APAP may deliver a plasma air treatment to the substrate 58 to reactivate the substrate. For example, the substrate 58 may be cleaned and coated in one location, and then shipped to a second location for reactivation at a later time.
Plasma polymerization yields polymers in arrangements not typically found under normal chemical conditions. The polymers may be have highly branched chains, randomly terminated chains, or functional crosslinking sites. Absent are regularly repeating units, in general. This is a result of the fragmentation of the prepolymer molecules when they are exposed to the high-energy electrons inherent in the plasma. The reactions appear to proceed by several reaction pathways including free radical formation, homolytic cleavage, cationic oligomerization, and combinations thereof.
The deposit resulting from reaction in an atmospheric pressure air plasma differs from some conventional polymers, oligomers, and monomers. In some conventional monomers, oligomers, and polymers, there is a standard series of one or more building block units, also called mers. As the polymeric chains grow the building block units are repeated and occasionally cross-linked. In a plasma polymer, the building block units may be fragmented and have new functional groups developed. When they recombine, there may be generally higher crosslink density, an increased presence of branched chains, randomly terminated chains, or a combination thereof. The crosslink density calculation becomes more difficult as the number of cross links divided by the number of backbone atoms approaches unity. Such may be the case in plasma polymers. A relative measure of the crosslink density may be the shift in glass transition temperature relative to the conventional polymer. One may expect that at low degrees of crosslinking the shift upwards of the glass transition temperature will be to the number of crosslinks. In plasma polymers, the slope of the proportion may increase relatively by about 10%, 15%, or 20% compared to conventional polymers.
Prepolymers that may be suitable for deposition by atmospheric pressure air plasma include compounds that can be vaporized. The vapors may be metered and blended with a carrier gas. This mixture of gases may be introduced into a plasma generated by an atmospheric pressure air plasma. The ionization gas of the atmospheric pressure air plasma may be chosen from gases typical of welding processes which may include, but are not limited to, noble gases, oxygen, nitrogen, hydrogen, carbon dioxide, and combinations thereof.
Prepolymers used to create a high velocity impact polymer coating may include, but are not limited to, reactive substituted compounds of group 14. Candidate prepolymers do not need to be liquids, and may include compounds that are solid but easily vaporized. They may also include gases that compressed in gas cylinders, or are liquefied cryogenically and vaporized in a controlled manner by increasing their temperature.
It would be desirable to coat the external surface of tire beads or cords to promote adhesion to the surrounding bead area rubber compound matrix. As described above, plasma deposition of polymerizable material and in-situ polymerization/crosslinking via ions of the plasma may produce films which promote adhesion to a substrate, such as rubber. The effectiveness of this method partially depends on the uniform deposition of a very thin film of the adhesion promoter.
A conventional plasma nozzle may be modified in accordance with the present invention to allow the continuous and concentric feed-through of a bead, cord, or any other elongated cylindrical object. A central bore of the modified nozzle may enable the elongated cylindrical object to pass through a center of a plasma stream, resulting in a uniform exposure of the elongated cylindrical object's surface to the plasma, and the uniform deposition of adhesion promoter.
The nozzle thus provides uniform plasma deposition of adhesion coatings on tire beads and cords that may significantly reduce cost and enhance tire properties relative to conventional nozzles. Conventionally, plasma nozzles were merely passed along one side of the bead leading to a non-uniform surface coating. Multiple passes along different sides of the bead improved the coating uniformity, though not significantly enough. Further, these multiple passes increased the process time and the amount of reagent used. Use of the plasma nozzle of the present invention, with a concentric fee-through of the bead, allows for the single-pass treatment of the bead while minimizing the consumption of coating reagent.
A plasma polymerization nozzle 200, as in
As shown in
A pneumatic tire and method in accordance with the present invention may combine the two above described methods for improving cord adherence to a rubber matrix at the cord surface rubber interface. The use of steel or textile cord micro-texturing combined with the deposition of a thin plasma coating improves rubber-cord adhesion and durability.
The laser texturing part of the present invention may be conducted on twisted cables and/or filaments. The textures on the cord may intrinsically improve the mechanical aspect of the adhesion to rubber while the ultra-thin plasma coating applied to the textured cord may provide a chemical aspect to the adhesion. The depth of the texturing may not exceed the thickness of the plating (approximately 2 to 5 micrometers) because bare/untextured metal or textile cords may be exposed which may quickly lead to a detrimental rust/bubble/separation formation.
A cord 1100 having a laser micro-textured surface beneath a plasma polymerized surface may exhibit improved adhesion to a rubber matrix, such as cords used in pneumatic tires (e.g., a carcass ply, belt ply, overlay, apex, flipper, chipper, runflat insert, gum strip, etc.) in accordance with the present invention. Such improved adhesion may thereby improve any or all functional properties of a pneumatic tire. This adhesion thus enhances the performance of the pneumatic tire, even though the complexities of the structure and behavior of the pneumatic tire are such that no complete and satisfactory theory has been propounded. Temple, Mechanics of Pneumatic Tires (2005). While the fundamentals of classical composite theory are easily seen in pneumatic tire mechanics, the additional complexity introduced by the many structural components of pneumatic tires readily complicates the problem of predicting tire performance. Mayni, Composite Effects on Tire Mechanics (2005). Additionally, because of the non-linear time, frequency, and temperature behaviors of polymers and rubber, analytical design of pneumatic tires is one of the most challenging and underappreciated engineering challenges in today's industry. Mayni.
A pneumatic tire has certain essential structural elements. United States Department of Transportation, Mechanics of Pneumatic Tires, pages 207-208 (1981). Important structural elements are the carcass ply, belt ply, overlay, possibly a runflat insert, and a tread, typically made up a low modulus polymeric material, usually natural or synthetic rubber. Id. at 207 through 208.
These complexities are demonstrated by the below table of the interrelationships between tire performance and tire components.
As seen in the table, the characteristics of a carcass ply, a belt ply, an overlay, a runflat insert, and a tread may affect the other components of a pneumatic tire, leading to a number of components interrelating and interacting in such a way as to affect a group of functional properties (noise, handling, durability, comfort, high speed, and mass (possibly in two modes of operation, inflated and deflated), resulting in a completely unpredictable and complex composite. Thus, changing even one component can lead to directly improving or degrading as many as the above ten functional characteristics, in either mode, as well as altering the interaction between that one component and as many as six other structural components. Each of those six interactions may thereby indirectly improve or degrade those ten functional characteristics. Whether each of these functional characteristics is improved, degraded, or unaffected, in which mode, and by what amount, certainly would have been unpredictable without the experimentation and testing conducted by the inventors.
Thus, for example, when the structure of the carcass ply of a pneumatic tire is modified with the intent to improve one functional property of the pneumatic tire, any number of other functional properties may be unacceptably degraded. Furthermore, the interaction between the carcass ply and the belt ply, overlay, and tread may also unacceptably affect the functional properties of the pneumatic tire. A modification of the carcass ply by improving cord adhesion to the rubber matrix may not even improve that one functional property (e.g., durability) because of these complex interrelationships.
Thus, as stated above, the complexity of the interrelationships of the multiple components makes the actual result of improved adhesion of cord reinforced structures in a pneumatic tire in accordance with the present invention, impossible to predict or foresee from the infinite possible results. Only through extensive experimentation has the improved adhesion of the present invention been revealed as an excellent, albeit unexpected and unpredictable, option for a pneumatic tire.
Except where expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the present invention. While the best mode for carrying out the present invention has been described in detail, those familiar with the art to which the present invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.
The description of a group or class of materials as suitable for a given purpose in connection with the present invention implies that mixtures of any two or more of the members of the group or class are suitable. Description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among constituents of the mixture once mixed. The first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation. Unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.
The previous descriptive language is of the best presently contemplated mode or modes of carrying out the present invention. This description is made for the purpose of illustrating an example of general principles of the present invention and should not be interpreted as limiting the present invention. The scope of the invention is best determined by reference to the appended claims. The reference numerals as depicted in the schematic drawings are the same as those referred to in the specification. For purposes of this application, the various examples illustrated in the figures each use a same reference numeral for similar components. The example structures may employ similar components with variations in location or quantity thereby giving rise to alternative constructions in accordance with the present invention.
Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.
