Not Applicable.
Common finishing practices for applying prime, base and top or finish paint coats to leather and non-leather substrates implement one or more of air spray and roll coat transfer systems. Curing processes that are used to dry the paint coats utilize industry-standard steam, hot oil, gas-fired or electric element convection ovens. Although these conventional ovens and curing processes meet their functional objectives, they possess several aspects of inefficiency. For example, these ovens have limited capabilities to adjust thermal conditions of a substrate being cured and include long response times (for example, up to 20 minutes) to obtain thermal energy changes without adversely affecting the substrate or coating. Also, current convection oven technology typically requires higher levels of energy to reach and maintain target temperatures to adequately dry coatings applied to a substrate surface. These downfalls result in potential over or under curing of the substrate resulting in mud cracking or tackiness, as well as excessive energy use for heat up conditions and extensive down time for cleaning of the oven heat sources to maintain radiant efficiencies. Furthermore, curing processes that use conventional ovens require additional equipment and floor space for inclusion of a final “air off” oven section to assure proper cure.
Therefore, a need exists for a system and method for finish curing leather-based substrates that overcome the above-identified inefficiencies of current industry standards.
According to one aspect, the present invention provides a method of finish curing a leather-based substrate. A base coat is applied onto a surface of a substrate to form a coated substrate and the coated substrate is passed through a first heating zone to heat the base coat. The coated substrate is passed through a second heating zone that emits infrared electromagnetic waves at a frequency corresponding to strong absorption by water to remove a desired amount of moisture from the base coat. The coated substrate is then passed through a third heating zone to completely cure the base coat on the coated substrate.
In some forms of this method, the frequency corresponding to strong absorption by water may be in a range of 2900-3100 nanometers.
In some forms of this method, a temperature of the coated substrate passing through the second heating zone may be sensed and a power level of the second heating zone may be adjusted to maintain a desired temperature of the coated substrate.
In some forms of this method, air may be directed over the coated substrate that is passing through the second heating zone to remove moisture building up on the coated substrate.
In some forms of this method, the coated substrate may be passed through a cooling unit to cool the base coat after the base coat has been completely cured.
In some forms of this method, a color coat may be applied onto the surface of the coated substrate after the coated substrate has been cooled by the cooling unit.
According to another aspect, the present invention also provides a system for finish curing a coated substrate. The system includes a conveyor that passes the coated substrate through a first heating zone, a second heating zone, and a third heating zone. The first heating zone includes a first infrared emitter module that heats the coated substrate. The second heating zone includes a second infrared emitter module that emits infrared electromagnetic waves at a frequency corresponding to strong absorption by water to remove a desired amount of moisture from the coated substrate. The third heating zone includes a third infrared emitter module to completely cure the coated substrate.
In some forms of this system, the frequency corresponding to strong absorption by water may be in a range of 2900-3100 nanometers.
In some forms of this system, the system may further include a controller providing power to the second infrared emitter module to heat the second emitter module to about 1300 degrees Fahrenheit. The controller may sense a temperature of the coated substrate passing through the second heating zone and further may adjust a power level of the second infrared emitter module to maintain a desired temperature of the coated substrate.
In some forms of the system, the system may further include an air manifold. The air manifold may direct air over the coated substrate as the substrate passes through the second heating zone to remove moisture building up on the coated substrate. The directed air may be warmed by the second infrared emitter module.
In some forms of the system, one or more of the second infrared emitter module and the third infrared emitter module may include ceramic fiber mounted panels with perforated ventilation holes.
In some forms of the system, the system may further include a cooling unit. After the coated substrate has been passed through the third heating zone, the conveyor may pass the coated substrate through the cooling unit.
According to another aspect, a method according to the present invention can include applying a base coat onto a surface of a substrate to form a coated substrate and passing the coated substrate through a first curing stage to heat, dry, and completely cure the base coat on the coated substrate. The first curing stage includes at least one heating zone emitting infrared electromagnetic waves at a frequency corresponding to strong absorption by water to remove a desired amount of moisture from the base coat. The method also includes applying a color coat onto a surface of the coated substrate to form a colored substrate and passing the colored substrate through a second curing stage to heat, dry, and completely cure the color coat on the colored substrate. The second curing stage includes at least one heating zone emitting infrared electromagnetic waves at the frequency corresponding to strong absorption by water to remove a desired amount of moisture from the color coat.
The foregoing and other objects and advantages of the invention will appear from the following detailed description. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention.
The present invention provides a high efficiency finish curing system and method for coatings applied to leather and non-leather alternative substrates. The finish curing process attains optimal finished product improvements through the utilization of multiple infrared (IR) emitter oven components in place of one or more conventional gas and electric-resistance element thermal units. These equipment changes, as well as other process enhancements further described below, result in a much more responsive curing process in comparison to current industry standards, which minimizes the amount of residence time within ovens and air off or cooling of the substrates.
Following step 24, the colored substrate proceeds to a second curing stage 26, including a first heating zone (step 28), a second heating zone (step 30), a third heating zone (step 32), and a cooling unit (step 34). The first curing stage 14 and the second curing stage 26 include substantially identical equipment (i.e., all heating zones include IR emitter modules). Following the second curing stage 26, the substrate proceeds to an accumulation/storage stage (step 36) for subsequent steps such as embossing and/or additional finishing.
The IR absorption and evaporation of water molecules described above also eliminates solidification of the coating on the substrate surface, thus promoting consistent curing which results in an even coating thickness. The consistent and even coating thickness allows evaporated water molecules to escape the coating surface, preventing the creation of surface defects such as pin holes and blistering, among other issues, due to entrapment of gases (that is., water vapor) under the substrate surface. The IR energy transmitted to the surface also elevates the solids temperature within the coating after the moisture is removed to achieve a complete, thermoset, cross-linked cure of the remaining solids in the coating system (for example, while in the third heating zone 48 described above).
In addition to IR emission, forced ambient air is applied in one or more of the heating zones 44, 46, and 48 to help accomplish consistent and even curing of the substrate coating. For example,
The IR emitter modules 52 described above each include a primary IR emitter source with stamped elements 56, as shown in
In addition, the use of Kanthal® heating elements 56 coupled to the ceramic fiber mounted panels 55 enables self cleaning capabilities of the IR emitter modules 52 and removes the need for reflectors. These are both unique benefits over standard industry convection ovens, and the self-cleaning capabilities also provide for reduced downtime in comparison to industry standard convection ovens.
The elements 56 of the IR emitter modules 52 each consist of a very low mass, allowing a higher responsiveness to applied current and, as a result, an approximate three to four-second heat up from standby temperatures of about 500 degrees Fahrenheit (260 degrees Celsius) to about 1300 degrees Fahrenheit (705 degrees Celsius) [about 1280 degrees Fahrenheit (693 degrees Celsius) achieves 3000 nanometer IR transmissions, which are absorbed by water molecules at almost 100% efficiency], and an approximate five-second cool down to below about 500 degrees Fahrenheit (260 degrees Celsius). Furthermore, quick changes in heating zone temperatures can be accomplished by adjusting power applied to the emitter modules 52.
The fast heat up and cool down aspects of the IR emitter elements 56 permit a relatively close distance between the elements 56 and a substrate along a conveyor line 39 in the heating zones 44, 46, and 48 and eliminates the need to utilize mechanical retraction to remove the IR emitter elements 56 away from the moving material substrate on the conveyor line 39. The ability to keep the IR emitter elements 56 close to the substrate produces high system efficiencies as compared to conventional methods. For example, conventional heating elements may require being positioned up to about 3 to 4 times further from the substrates than the IR emitter elements 56 of the present invention, thus causing about 10 to 20 times less radiant efficiency (due to the inverse square law regarding IR proximity to bodies as stated in Plank's Law and Wien's Constant). The fast heat up and cool down aspects also cause reduced energy usage and, as a result, reduced operating costs in comparison to conventional ovens.
The IR emitter module 52 in the second heating zone 46 (and/or in the first and the third heating zones 44 and 48) includes an embedded quartz thermowell (not shown) positioned in direct contact with a primary IR element 56. The thermowell includes a 1/16 inch diameter Chromel/Alumel (type “K”) thermocouple to provide precise analog process signals used as input to a controller of the system 38 or a separate closed loop element temperature digital control device. The controller also monitors temperatures within the second heating zone 46 and, more specifically, determines and monitors temperatures of the substrate surface. The controller adjusts the power (specifically, the voltage) applied to the IR emitter elements 56 in order to maintain a desired temperature profile of the substrate surface within the second heating zone 46. In addition, the controller modulates the voltage applied to the IR emitter elements 56 in the first, second, or third heating zones 44, 46 and 48 to accomplish specific IR wavelength emissions, within a range of peak wavelengths, based on required coating variations in thickness, exposure time to IR emissions, and chemical characteristics. In some implementations, the controller further controls the conveyor line 39 and thus, the speed at which the substrate passes through the curing stages 40 and 42.
While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention defined by the appended claims.
This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/704,239 entitled “Finish Curing Method and System for Leather-Based Substrates” filed Sep. 21, 2012, which is hereby incorporated by reference for all purposes as if set forth in its entirety herein.
Filing Document | Filing Date | Country | Kind |
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PCT/US13/60639 | 9/19/2013 | WO | 00 |
Number | Date | Country | |
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61704239 | Sep 2012 | US |