Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2002-05-17
2004-08-03
Crispino, Richard (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S067000, C156S272200, C156S275500, C156S378000
Reexamination Certificate
active
06770158
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a pre-processed workpiece having a surface deposition of absorber dye for the express purpose of being consumed in future welding process. More particularly, it relates to a quality management system for certifying the mechanical and chemical characteristics of the workpiece.
2. Description of the Prior Art
Joining plastic parts by through transmission laser welding in known, for example, from U.S. Pat. No. 5,893,959. U.S. Pat. No. 5,893,959 utilizes pigments to increase the absorption properties along the welding zone. However, since the disclosed pigments survive the welding process, they unfavorably affect the appearance of the joint. The patent compensates for reduced aesthetics by incorporating the pigment into the entirety of both upper and lower substrates to render them opaque, both before and after joining. The upper substrate is described as having a concentration of pigment throughout of less than 1% that provides a transmission of greater than 60% at the welding laser wavelength. The lower substrate receives a pigment concentration of between 1-2% resulting in a negligible transmission.
Accordingly, it would be desirable to define the range of design criteria and engineering characteristics of a weldable workpiece that can: provide minimal occlusion at the joint, and may further include visual, even optical, clarity at the joint; selectively deposit absorber dye only onto the welding zone to eliminate absorber-induced occlusion throughout the remainder of the ensemble; incorporate dyes in such a way that they will undergo decomposition into inert, soluble, invisible by-products; utilize absorber dyes which primarily effect transmission at the 5 welding wavelength; utilize absorber dyes that minimally effect transmission at wavelengths numerically spaced from the welding wavelength; utilize absorber dyes that minimally effect transmission within the visible spectrum; and in certain embodiments, have no effect or even beneficial transmission effects within the visible spectrum.
The relationship between applications utilizing carbon black pigmentation and absorber dyes is discussed as a function of line energy in the Russek article entitled “Laser Beam Welding of Polymers with High Power Diode Lasers: Joining Innovation for Micro and Macro Technologies”. The article proposes three dimensional, volumetric thermodynamic process modeling to address concerns in gap bridging during welding. A significant drawback of such approach is that the weld must be completed and cross-sectioned to obtain the energy density distribution, as shown in FIG.
6
. Russek does not suggest the dye density on a single workpiece, nor does it suggest the range of energy per surface area that will correspond to the inherent capacity of the surface dye deposition. The published PCT application bearing International Application Number PCT/GB99/03241, discloses a process for welding parts having an infrared absorber dye sandwiched therebetween.
SUMMARY OF THE INVENTION
Accordingly, it would be desirable to manage the quality of a pre-processed polymer workpiece so that is can be flexibly welded to another freely selectable mating part.
It is therefore an object of the present invention to provide a system for monitoring the minimum mechanical and chemical requirements for such a polymer workpiece.
It is another object of the present invention to provide a system for monitoring the optical transmission properties of such workpiece under ideal conditions.
These and other related objects are achieved according to the invention by a method and system for monitoring the quality of the mechanical and chemical properties of the pre-processing stages of a workpiece.
A weldable workpiece having at least its surface made from a first polymer which softens on heating adapted for fusing to a material which softens on heating and is freely-selectable from a second polymer which is the same or similar to the first polymer or a different polymer which is at least locally mutually miscible with the surface of the first polymer, wherein the first polymer and the freely-selectable second polymer have overlapping melting temperature ranges. The workpiece has a surface extending across a bulk portion. An absorber dye possessing both strong absorption and a high extinction coefficient at a welding wavelength of a radiant energy source is deposited on or above the surface thereby defining a welding zone via a vehicle having necessary viscosity and which avoids undue interference with or occlusion of the welding zone. The deposition comprising a generally uniform density of about 5 to about 3000 nanograms of dye per mm
2
to provide predictable and consistent heating thereby rendering the workpiece weld-enabled. The welding zone has the capacity to convert inbound radiant energy at the welding wavelength over about 0.1 j/mm
2
into thermal energy via vibronic relaxation immediately followed by exothermic decomposition of at least a portion of the dye into inert, invisible by-products, the combination of which being capable of delivering (i) a first quantity of thermal energy directed in the direction of the bulk portion to elevate the surface into the melting temperature range of the surface and (ii) an approximately equal quantity of thermal energy directed in the opposite direction away from the bulk portion. The dye, the vehicle, the by-products, and the surface of the first polymer are mutually miscible. The workpiece, and any film, may be made from a thermoplastic polymer. The dye may be a visible light absorbing dye, a near infrared absorbing dye, an infrared absorbing dye, or combinations thereof. If the vehicle is a liquid solvent it must be capable of dissolving the absorber dye to provide uniform surface density. If the liquid vehicle delivers absorber dye below the surface, it should be to a depth sufficiently small to avoid foaming during welding. In liquid solvents, the absorber dye is present in a concentration of about 1×10
−2
to about 1×10
−4
grams per milliliter to deliver dye within the stated surface deposition density range following solvent evaporation.
These properties are monitored by a method wherein electromagnetic radiation is transmitted through the workpiece toward a sensor. The system controller determines if dye was properly placed, at the correct density, in the proper locations, and certifies the workpiece as being weld-enabled based on the test wavelength or wavelengths, or stored data, containing information similar to that shown in the graphs. The transmitted radiation may be at or near the anticipated welding wavelengths, in the blue or red visible spectrums, or may comprise a scan to determine the color coordinates or color profile of the workpiece. The test transmissions occur at wavelengths in which the various curves are sufficiently spaced apart from each other to allow the method to assess if the workpiece has successfully passed from one state, represented by one curve, to another state, represented by another curve.
These and other related objects are achieved according to the invention by a second embodiment thereof, relating to a method and system for monitoring the quality of the mechanical and chemical properties of the post-processing stages of a workpiece.
A transmission-enhancing formulation disposed between a first reflective surface of a first radiant energy-transmissive workpiece having a first bulk portion and a second reflective surface of a second workpiece having a second bulk portion. Both reflective surfaces are made of a polymer material which softens on heating, wherein the transmission at a welding wavelength of a radiant energy source along an optical path through the formulation and the bulk portions and the reflective surfaces is lower than the optical transmission through just the bulk portions and the reflective surfaces only. The first and second reflective surfaces are made of polymers having overlapping melting temperature ranges. The transmission
Hartley Scott M
Sallavanti Robert A.
Crispino Richard
Gentex Corporation
Keusey, Tutunjian & & Bitetto, P.C.
Koch, III George R.
LandOfFree
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