EP1004225A1 - Method of radiation heating substrates and applying extruded material - Google Patents

Abstract

A method for applying extrudable material (26) from nozzle (28) to substrate (32), in which concentrated light beam (30) as from lamp (22) is directed onto the substrate before or after application of the extrudable material. The beam energy is concentrated by mirror (24) on the substrate surface. It is subsequently transferred to the deposited extrudable material, thereby increasing the temperature and lowering the viscosity of the closely situated material, facilitating material penetration into the substrate. This allows use of illumination of modest energy density and of wavelengths not absorbed by the extrudable material. When the extrudable material is an adhesive and is applied to a plurality of substrates, of which at least one is treated with a light beam according to this method, and the extrudable materials adhered to the substrates are brought into contact, joining of the extrudable materials creates a strong bond between the substrates. The invention includes articles made by the method.

Description

METHOD OF RADIATION HEATING SUBSTRATES AND APPLYING EXTRUDED MATERIAL

Cross-Reference To Related Patent Applications

This application is related to and claims priority from Provisional Patent Application No. 60/016,905, filed May 6, 1996, titled "Method for Extrudable Material Application with Light- Mediated Heating of the Substrate," the contents of which are incorporated herein by reference.

Technical Field

This invention relates to the application of extrudable materials to substrates, which may be used for the adhesive bonding of a plurality of substrates.

Background Art The application of extrudable materials to substrates to form thick protective films, penetrating films, thick films with beneficial optical, electrical, aesthetic or physical properties, or for adhesive bonding is widely used. Such practices include the use of varnishes to protect wood surfaces, paints to protect and embellish wood, plastic, ceramic or metallic surfaces, and the use of hot-melt and solvent-based adhesives to bond a wide variety of substrates. Examples of extrudable adhesive use include the bonding of metallic, fabric, foam, wood, leather, and plastic substrates in the assembly of such products as furniture, packaging, automotive sub-assemblies, wooden and metallic windows, trade show exhibits and point-of-purchase displays, electrical components, apparel, luggage, and more.

Many treatments are known to affect the joining of an applied extrudable material to a substrate. Many of these include the use either of chemical reagents to pre-treat the substrate, or the use of laser irradiation either as a pre-treatment (U.S. Patent No. 4,931,125 to Volkmann et al. and U.S. Patent No. 4,644,127 to LaRocca), a post-treatment (U.S. Patent No. 4,861,404 to Neff and U.S. Patent No. 4,636,609 to Nakamata), or simultaneous with the application of the material to the substrate (U.S. Patent No. 5,348,604 to Neff). U.S. Patent No. 4,931,125 to Volkmann et al. describes a method for pre-treatment of components using a laser beam to create projections and/or depressions in the substrate. This treatment is limited in the tjrpes of substrates to which it can be applied, and is generally useful only for non-porous substrates. Also, because of the multiple processes (pre-treatment, followed by bonding) required by this method, it may be expensive to implement in certain industrial environments.

U.S. Patent No. 4,636,609 to Nakamata teaches the joining of two different kinds of solid synthetic resins, wherein the laser irradiation is used to melt together the two dissimilar resins.

This method involves the direct fusion of dissimilar solid synthetic substrates only, and requires specific physical and optical properties for the combination of substrates that significantly limit the range of substrates that may be used.

U.S. Patent No. 4,644,127 to La Rocca uses a laser to assist in the bonding of metallic pieces. This method teaches the melting of the applied metal by the laser beam prior to its application to the substrate surface, and therefore the substrates are limited to metallic substrates and the applied materials are limited to gas streams containing powdered metals.

The method of U.S. Patent No. 4,861,404 to Neff involves the transfer of heat from a laser directly to the bulk extrudable material for purposes of heating the material. However, this requires extremely high energy densities, since the energy is not concentrated at the interface between the substrate and the material, where the deposited energy has its greatest effect, but is distributed throughout the material. Furthermore, because the extrudable material is heated in bulk, this greatly increases the time required for the material to regain structural integrity (the "closing" time), an important factor in many manufacturing applications. In addition, this method requires certain optical properties of the extrudable material that limit the range of its application.

The method of U.S. Patent No. 5,348,604 to Neff requires that light-energy pass through the extrudable material within the nozzle apparatus. Because of the high energy densities required in the technique, this is generally practical only with light energy from a laser which, as discussed below, is difficult and expensive in many manufacturing environments. Furthermore, this method precludes the use of the light energy which passes through the adhesive from initiating a catalysis of the extrudable materials, such as those used to strengthen certain hot- melt adhesives, since the curing of any adhesive that resides within the nozzle would render the nozzle inoperable. In addition, this method requires special optical properties of the extrudable material that limit its range of applications. Also, this method places limits on the extrusion apparatus for the material that increases the cost and complexity of the apparatus.

The prior art described above generally involves laser irradiation of the extrudable material or the substrate. While lasers excel at providing highly concentrated radiation, high-power lasers tend to be complicated and costly to operate, including YAG lasers, which are often used because of the superior quality of the wavelength of light produced. Furthermore, due to the requirement of precisely orienting and placing the laser mirrors, as well as the use of sophisticated water- cooling mechanisms for certain laser classes, including YAG lasers, which require water-purifiers, heat-exchangers, and refrigerator systems, lasers in industrial environments may require frequent maintenance. Also, many high-power lasers, including YAG lasers, output only a small fraction of the electrical-energy input, requiring large power supplies, waste heat elimination systems, and large power usage for relatively small power applications. In general, high-power lasers are expensive to purchase, operate and maintain. All of these disadvantages make high-power lasers, and the methods that employ them, unsuitable for many industrial applications.

It was our intention to create a method that could use simple and inexpensive devices to enhance the bonding of extrudable materials to a substrate. It was our intention to solve the problems of the prior art that gave rise to the current invention. SiiTnmarv Of The Invention

It is an object of the present invention to provide a method of applying an extrudable material to a substrate with a strong bond.

It is in addition an object of the present invention to provide a method of applying an extrudable material to a substrate that is applicable in a wide range of applications.

It is another object of the present invention to provide an inexpensive method of applying an extrudable material to a substrate that uses inexpensive devices.

It is still another object of the present invention to provide an inexpensive method of applying an extrudable material to a substrate that uses easy-to-maintain devices. It is further an object of the present invention to provide an energy-efficient method of applying an extrudable material to a substrate.

It is also an object of the present invention to provide a method of applying an extrudable material to a substrate that is suitable for large-area surfaces.

It is additionally an object of the present invention to provide a method of applying a wide range of extrudable materials to a substrate with a strong bond.

It is still further an object of the present invention to provide a method of applying an extrudable material to a wide range of substrates.

It is yet another object of the present mvention to provide a method of applying an extrudable material to a substrate, in such a way that the "closing time" of the substrate is short. It is still further an object of the present invention to provide a method of applying an extrudable material to a substrate, using low energy density irradiation sources.

It is yet another object of the present invention to provide a method of applying an extrudable material to a substrate, wherein the material can be applied to the substrate through small orifices. Additional objects, advantages and novel features of this invention shall be set forth in part in the description that follows, and will become apparent to those skilled in the art upon examination of the following specification or may be learned through the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities, combinations, and methods particularly pointed out in the appended claims. To achieve the foregoing and other objects and in accordance with the purposes of the present invention, as embodied and broadly described therein, the present invention is directed to a method for applying an extrudable material to a substrate which is heated using an electro¬ magnetic energy field. The method includes the steps of generating a concentrated electromagnetic energy field, irradiating the substrate with the concentrated energy field with sufficient energy to substantially heat the substrate, but not to pyrolyze its constituents, and applying the extrudable material to the substrate at a location upon which the energy field was directed.

The concentrated electromagnetic energy field may be generated by a laser, which may be a carbon-dioxide laser or a linear diode array. The concentrated electromagnetic energy field may also be generated by a substantially isotropic energy illumination source, which may be a high-pressure xenon arc lamp, or a coiled tungsten wire. The longitudmal axis of the coiled tungsten wire may be longer than 5 mm. The energy from the substantially isotropic energy illumination source may be collected using a reflecting surface. This reflecting surface may be constructed so that one of its cross-sections may contain a shape selected from the group consisting of ellipses, circles and parabolas.

The energy from the substantially isotropic energy illumination source may be collected using a converging optical lens.

The concentrated electromagnetic energy field may have at least one cross-sectional dimension greater than 3 mm when it irradiates the substrate.

The substrate may be treated to improve its absorption of electromagnetic energy, prior to the step of irradiating. This treatment may involve the application of a highly absorbing material to the substrate.

The substrate may be protected from oxidation while irradiating by means of a stream of non-reactive gas which excludes oxygen-bearing atmosphere from contacting the substrate.

The extrudable material may be a heat-activatable polyamide.

The present mvention is also related to an article made in accordance with the method. The article may a plurahty of substrates bonded together by the extrudable material. The present invention is also related to an article made in accordance with the method, wherein at least one substrate is bonded to an object not made according to the present invention, wherein the extrudable material bonds the substrate to the object.

The present invention is also related to a method which includes the steps of applying the extrudable material to the substrate, generating a concentrated electromagnetic energy field, and irradiating the substrate with the concentrated energy field at a location upon which the extrudable material has previously been applied, using sufficient energy to substantially heat the substrate, but not to pyrolyze its constituents.

The concentrated electromagnetic energy field may be generated by a laser, which may be a linear diode array.

The concentrated electromagnetic energy field may also be generated by a substantially isotropic energy illumination source, which may be a high-pressure xenon arc lamp, or a coiled tungsten wire. The longitudinal axis of the coiled tungsten wire may be longer than 5 mm. The energy from the substantially isotropic energy illumination source may be collected using a reflecting surface. This reflecting surface may be constructed so that one of its cross-sections may contain a shape selected from the group consisting of ellipses, circles and parabolas. The energy from the substantially isotropic energy illumination source may be collected using a converging optical lens.

The concentrated electromagnetic energy field may have at least one cross-sectional dimension greater than 3 mm when it irradiates the substrate. The substrate may be treated to improve its absorption of electromagnetic energy, prior to the step of irradiating. This treatment may involve the application of a highly absorbing material to the substrate.

The extrudable material may be a heat-activatable polyamide or a light-activatable cross- linkable material.

The present invention is also related to an article made in accordance with the method. The article may a plurality of substrates bonded together by the extrudable material. The present mvention is also related to an article made in accordance with the method, wherein at least one substrate is bonded to an object not made according to the present invention, wherein the extrudable material bonds the substrate to the object.

Brief Description Of The Drawings

Fig. 1 is a cross-sectional schematic view of a sinuous deposition device according to the present invention, carried out with an arc lamp whose energy is collected with an ellipsoidal reflector, in which the substrate is heated after extrudable material application. Fig. 2 is a cross-sectional view of a second embodiment of the present invention, including a linear deposition device, using a lamp containing a coiled tungsten wire whose energy is collected with a trough ellipsoidal reflector, in which the substrate is heated after extrudable material application, in which lamp and reflector are shown in an oblique view.

Fig. 3 is a cross-sectional view of a third embodiment of the present invention, including a linear deposition device that contains a linear diode array whose energy is collected with a trough converging lens, using a non-reactive gas to prevent oxidation of the substrate, in which the substrate is heated before extrudable material application, and in which the linear diode array and lens are shown in an oblique view.

Fig. 4 is a cut-away top view of a fourth embodiment of the present invention, including an areal deposition device, in which the substrate is heated prior to extrudable material application.

Fig. 5 is a cross-sectional schematic of the areal deposition device of Fig. 4, taken along line 5-5 of Fig. 4.

Fig. 6 is a cut-away top view of a fifth embodiment of the present invention, including an areal deposition device, in which the substrate is heated after extrudable material application. Fig. 7 is a cross-sectional schematic of a sixth embodiment of the present invention, depicting the initiation of cross-linking in a light-activatable cross-linkable extrudable material by means of a broad spectrum lighting source that simultaneously performs light-mediation heating of the substrate.

Fig. 8 is a schematic cross-section of an article made using the sinuous or linear deposition method of this invention, as might be made using the devices of Fig. 1, Fig. 2, Fig. 3, or Fig. 7, in which light-mediated substrate heating is used on surfaces which are closely opposed, where the cross-section is perpendicular to the direction of movement of the substrate. Fig. 9 is a schematic cross-section of an article made using the sinuous or linear deposition method of this invention, as might be made using the devices of Fig. 1, Fig. 2, Fig. 3, or Fig. 7, in which light-mediated substrate heating is used on surfaces which are separated by a more substantial gap than shown in Fig.8, where the cross-section is perpendicular to the direction of movement of the substrate.

Fig. 10 is a cross-sectional schematic of a seventh embodiment of the present invention, including a method for bonding two substrates in which the substrates are positioned so that the deposition on both substrate surfaces uses a single material applicator.

Fig. 11 is a cross-sectional schematic of an eighth embodiment of the present mvention, including a method for bonding two substrates in which the substrates are positioned so that the deposition on both substrate surfaces uses a different material applicator for each substrate.

Fig. 12 is a cross-sectional view of a ninth embodiment of the present invention, in which a light-absorbing substance is applied to the substrate in order to enhance substrate heating through light absorption. Fig. 13 is a cross-sectional view of a tenth embodiment of the present invention, in which a

"cold mirror" is used to remove unwanted radiation.

Best Mode for Carrving-Out the Invention

Functional Overview The penetration of an extrudable material into a substrate is highly dependent on the viscosity of the material. Thus, many materials are heated prior to deposition onto a substrate, in order to minimize material viscosity. At the same time, these high temperatures must be balanced with other considerations, including the pyrolysis of the material, the melting of the substrate, and the "closing" time for the material (i.e. when the material regains structural integrity and loses its tackiness). When an extrudable material, such as a hot-melt adhesive, is applied to a room- temperature substrate, cooling occurs very rapidly at the contact surface between the material and substrate. In the case of hot-melt adhesives, it should be noted that most adhesives are applied at temperatures very close to their melting points in order to minimize the damage that can occur to adhesives that are maintained at highly elevated temperatures. Furthermore, an important parameter in the industrial use of most hot-melt adhesives is their closing times - that is, the time until the adhesive hardens to the point that it can be manipulated with structural integrity and without surface tackiness. Many adhesives are engineered to minimize the closing time, thereby increasing the process throughput. With adhesives engineered for fast closing times, however, even relatively small decreases in temperature can result in rapid increases in viscosity in the adhesive.

This increase in viscosity slows or prevents the penetration of adhesive into the substrate, and prevents the adhesive from engulfing exposed prominences or strands of substrate, or penetrating into crevices in the substrate. Thus, the rapid cooling of the extrudable materials at the substrate interface results in only superficial bonding of the material to the substrate for many industrial applications.

This invention teaches the directed heating of the substrate using an electromagnetic energy field, which will hereinafter be refered to as a light or laser beam, eventhough the field may lack sharp boundaries. In most applications, wavelengths from the infrared to ultra-violet in the electromagnetic energy spectrum will be used, due to their ease of generation, transmission, reflection, and focusing. However, in other applications, electromagnetic radiation from other frequency bands, including microwaves, could be profitably employed.

If the light beam travels through the applied extrudable material on its path towards the substrate, some fraction of the light energy will be absorbed by the material, leading to heating of the bulk extrudable material rather than the substrate. In general, even if a large fraction of the incident illumination is absorbed by the extrudable material, because of the large local mass of the material relative to the substrate surface to which it is immediately applied, the material temperature will be relatively little affected by the absorbed light. Furthermore, these heating effects will not be concentrated at the interface between substrate and material, where the physical processes affecting bond strength are occurring. Therefore, either the light beam used for heating the substrate should be directed so that it does not pass through the extrudable material, or the material should be largely transparent to the majority of the heat energy in the light beam.

Once the substrate has absorbed the heat energy from the incident illumination, its temperature will rise dramatically. According to the method of this invention, it is desirable to transfer some of the heat captured by the substrate to that extrudable material that is in close contact with the substrate. In the case where the extrudable material is a hot-melt adhesive, this local heating at the substrate-material interface permits rapid cooling of the bulk adhesive distant from the interface after it has been deposited on the substrate. This promotes the closing of the adhesive within a reasonable period of time, while still altering the adhesion properties of that extrudable material closest to the substrate.

It should be noted that the materials used in the following description are generally materials which are heat-activatable, such as hot-melt adhesives. The method, however, works more generally on any material deposition in which the penetration of the material is dependent on its temperature, and the temperature of the substrate. This might include, for example, the penetration of resins and curable varnishes into wood.

The preferred embodiments of this invention depend on whether the apparatus deposits a sinuous line of extrudable material, a linear stream of material, or an areal deposition of material. Each of these cases is covered in the following sections. Sinuous Deposition Of Extrudable Material

In order to deposit a sinuous bead of material mediated with light engendered heating of the substrate, the position on the substrate which is heated must be very closely situated to the position where the extrudable material is deposited. The substrate will be simultaneously translated and rotated around the material application position for a sinuous bead to be deposited, and if the light is applied distantly from the material application position, it cannot be guaranteed that the substrate location on which the light is trained will be the same substrate location to which the adhesive is deposited. In general, for sinuous deposition, the position of light application and the position of material deposition will be closely situated, which requires that the light must be highly concentrated on the substrate. In the case of light-mediated heating of the substrate where the light is supplied by a laser, the focusing of the illumination source is not difficult, since light produced by a laser is either naturally collimated, or comes from a small point source, as in a laser diode. Lasers with sufficient energy to perform light-mediated heating of the substrate, however, are generally expensive to purchase, expensive to operate, and difficult to maintain. Alternative light supplies include traditional incandescent lamps, halogen lamps, and high- pressure arc lamps. Compared, for instance, with a YAG laser, these lamps are 20-30 times more efficient at converting electrical energy into light and heat energy. However, while laser light is naturally collimated, for the most part these alternative light supplies produce light that is substantially isotropic. Thus, the light must be optically collected or focused, and the degree to which this is possible will be the primary restriction on the use of these light sources in light- mediated substrate heating.

Fig. 1 is a cross-sectional schematic view of a sinuous deposition device that utilizes light- mediated heating of the substrate after extrudable material deposition, carried out with an arc lamp whose energy is collected with an ellipsoidal reflector. An illuminating high-pressure arc lamp 22 is placed at one focus of an ellipsoidal mirror 24, and the material deposition location is placed near the other focus of the mirror. The salient property of an ellipsoidal mirror is that raypaths emanating from one focus are intercepted by the ellipsoidal mirror, and subsequently reflect off the mirror surface and collect at the other focus. This property of ellipsoidal mirrors is often utilized in optical devices, and is frequently used, for example, in lamps which illuminate fiber optic bundles.

Because the lamp 22 is not a point source of light energy, not all of the energy source can be contained within the point focus of the ellipsoidal mirror, and those parts of the arc not located precisely at the focus of the ellipsoidal mirror will not precisely intercept the point at which it is desirable for light to impinge on the substrate. Thus, light sources with the smallest hght emission volume are highly desirable. Arc lamps have the advantage of a very high radiance, with large amounts of their energy being emitted from a very small surface volume. High-pressure xenon arc lamps often emit more than half of their energy at longer than visible wavelengths, which is of great benefit in light-mediated heating of the substrate because such wavelengths are very efficiently absorbed by a variety of substrates. Examples of suitable high-pressure arc lamps are the Cermax Xenon arc lamp series with integrated reflectors (e.g. EX990C-10F) from ILC

Technology of Sunnyvale, CA, or the water-cooled Photomax reflector from Oriel Corporation of

Stratford, CT, which may be fitted with a range of matched arc lamps. As an alternative, one may use tungsten-halogen lamps, which are generally very inexpensive, require unsophisticated and inexpensive power sources, are extremely efficient in their use of input electrical energy, and which emit the vast majority of their light output in infrared wavelengths. In general, low voltage tungsten-halogen bulbs have smaller filaments than those of high- voltage halogen bulbs, and many inexpensive versions of these bulbs are commercially available in the range of up to 250 watts or more. If additional power is required, multiple bulbs or reflectors can be used. Alternatively, these bulbs can be run at voltages higher than their nominal rating, which increases the light output at the expense of significantly lower bulb lifetimes. The MR16 EKE 150 Watt projector lamp, available from a number of suppliers including General Electric, is suitable for lower power applications, and includes an integrated ellipsoidal reflector to collect the output light.

In Fig. 1, an extrudable material 26 is deposited onto a substrate 32 by means of a nozzle 28, which is situated in such a manner as to interfere as little as possible with a plurality of incident hght rays 30 from the lamp. The extrudable material 26 is administered in the preferred case through means of a positive displacement pump attached to the nozzle, although simpler air pressure-mediated devices are possible, such as the Polygun II hot-melt adhesive applicator from 3M Adhesive Systems of St. Paul, MN.

The illuminating lamp is located in such a manner as to illuminate the substrate 32 after the extrudable material 26 has been deposited on its surface. It is also possible to locate the illuminating lamp so that it heats the substrate 32 before deposition of the material 26. In such cases that application throughputs require larger energy fluxes than that available from a single lamp, it may be necessary to place a plurality of lamp assemblies (including in each case a lamp 22 and a mirror 24) in positions adjacent to the position that the material is deposited.

It should be understood with regard to Fig. 1 that there exist alternative schemes for capturing the illumination from the lamp 22 other than the use of an ellipsoidal mirror. For instance, non-ellipsoidal mirrors can be used to converge the light energy to a pseudo-focus. Alternatively, the lamp 22 can be placed at the focus of a parabolic mirror, in which case the reflected light rays would become nearly collimated. Such collimated rays can then be focused using standard converging lens arrays. It is considered within the teachings of this invention that the mirror can be any shape that collects light energy from the light source onto the substrate, and need not be specifically derived from a conic section such as a parabola, circle or an ellipse. In certain applications, it may be useful for the mirror to be asymmetric, such that the collected light is distributed on the substrate in a linear, elliptical or other shape, rather than focused into the smallest possible area. Such illumination geometries would be of particular benefit in those cases where the extrudable material is not deposited in a narrow line, or where the extrudable material is illuminated for some duration. Linear Deposition Of Extrudable Material

In order to raise the substrate temperature to that at which light mediation of deposition occurs, a certain amount of heat must be projected onto the substrate. When the extrudable material is deposited as a sinuous stream, the topology of the deposition process requires that the light energy be concentrated to a small area near to the material deposition location, since the substrate which is to be heated can otherwise not be located predictably with respect to the application apparatus. However, when the extrudable material is deposited in a linear fashion on the substrate, then the light energy can be projected onto the substrate over a linear distance overlaying the extrusion path, requiring far less concentrated light energy. In algebraic terms, H = PT, where H is the heat deposited by the illumination system on a certain area of substrate (e.g. in units of watt-sec per cm²), P is the illumination power density (e.g. in units of watt-cm²) and T is the time during which the light is applied to a given area of substrate (e.g. in units of seconds). Thus, with a sinuous bead, the topology demands a high power illumination P, since the time T during which the light can be focused on a particular substrate is small. On the other hand, when a linear stream of extrudable material is used, a longer time may be used with a lower power density. This low power density allows for simple and inexpensive light illumination systems.

Fig. 2 is a cross-sectional view of a second embodiment of the present invention, including a linear deposition device that utilizes light-mediated heating of the substrate after extrudable material deposition, using a lamp containing a coiled tungsten wire whose energy is collected with a trough ellipsoidal reflector, in which lamp and reflector are shown in an oblique view. In the description of this second and subsequent embodiments, like components such as the extrudable material 26, nozzle 28, and substrate 32 will be referenced with the same reference numbers. An extended length lamp 34 is bounded above by a trough mirror 36, whose cross-section perpendicular to the long axis is roughly elliptical. The longitudinal ends of this mirror 36 may either be open, or alternatively and more efficiently, they may be turned down to collect hght from the ends and direct it towards the substrate 32. The extended length lamp 34 is placed at the one focus of the trough mirror 36, and a large fraction of the illuminating light collects near the other focus of the elliptical trough reflector, where the collection of such foci is coincident with the linear distribution of sites on the substrate 32 on which the extrudable material 26 is deposited via the nozzle 28.

There are many additional options for collecting the source illumination. For instance, if the lamp may be placed quite close to the substrate surface, the elliptical reflector 36 can be replaced with a cylindrical trough reflector. In this case, the lamp is placed at the center of the semi- cylinder, and light rays that are emitted away from the substrate are reflected off of the mirror, and back to the lamp, where they combine with rays generated by the lamp directed downwards to the substrate. In addition, one could use a parabolic trough reflector behind the lamp to collimate the hght rays, with a converging cylinder lens between the lamp and the substrate to collect lamp illumination. The extended length lamp 34 and the semi-elliptical trough mirror 36 as a unit may be called the heating element. This heating element may be placed in such a way to heat the substrate either after the application of the extrudable material, as shown in Fig. 2, or the heating element may come before the application of extrudable material. The decision regarding the placement of the heating element involves application specific considerations that will generally deal with the nature of the substrate and extruded materials and the topological requirements of the apparatus. In general, the amount of heat entering the substrate prior to material deposition must overcome heat losses by means of conduction, convection and radiation prior to encountering the deposited material. Heating the substrate before the application of the extrudable material has the advantage that the radiant heat will not be lost through reflection at the air/extrudable material interface, or be absorbed within the bulk of the extrudable material. On the other hand, heat transferred to the substrate may be lost through radiation, convection and conduction before the extrudable material has touched the substrate. In general, the effects of this heat loss will be minimal when the extrudable material is applied soon after illumination. The heat captured by the substrate may translate into temperature rises in the substrate that can either pyrolyze the substrate, or subject the substrate to oxidation in the presence of the atmosphere. Thus, the amount of heat transmitted to the substrate must be regulated to limit the temperature increase below that which causes substrate degradation. Fig. 3 is a cross-sectional view of a third embodiment of the present invention, including a linear deposition device that utilizes light-mediated heating of the substrate before extrudable material deposition, containing a linear diode array whose energy is collected with a trough converging lens, using a non-reactive gas to prevent oxidation of the substrate, and in which the linear diode array and lens are shown in an oblique view. A laser diode array 37, optionally in conjunction with a cylinder converging lens 39, is used to heat the substrate prior to deposition of the extrudable material. The converging lens 39 is used to compensate for the divergence of light energy typically found in laser diodes, and allows the laser diode array to stand back from the substrate surface. In order to prevent oxidation, a stream of a non-reactive gas 38 directed out of a gas-dispensing nozzle 40 may optionally be directed at the substrate 32 to exclude the majority of the oxygen present at the substrate surface. The non-reactive gas 38 will be chosen both on the basis of its non-reactivity to the substrate, its lack of toxicity, its cost, its transparency to the light-energy emanating from the laser diode array 37, and its thermal conductivity. In general, gases with low thermal conductivity are to be preferred, as they will remove less heat from the substrate prior to the application of the extrudable material 26. Gases which will frequently meet these criteria include nitrogen and argon. It is within the teachings of this patent for the placement of the nozzle 40 to be such that the stream of non-reactive gas is directed either towards the point of extrudable material deposition, or it may be placed near the nozzle with the stream of non-reactive gas directed away from the deposition point. Heating after the extrudable material has been applied suffers from fewer problems related to pyrolysis, since as the substrate temperature rises, it efficiently transmits heat to the overlying material through conduction. Also, the overlying material excludes atmospheric oxygen, so oxidation of the substrate material is a less significant problem. In practice, both methods of light-mediated heating of the substrate can provide significant increases in penetration of the extrudable material into the substrate. In certain circumstances, it may be beneficial to illuminate the substrate both before and after the deposition of the extrudable material. This case might be useful, for instance, when using a low power illumination source, or where the topological constraints of the deposition apparatus permits only a short illumination distance on either side of the deposition location.

Because the deposition process allows for heat illumination over an extended length, a variety of illumination sources are possible, including high wattage tungsten-halogen lamps, quartz and ceramic heating rods, and high-power linear diode arrays. It should be noted that laser diodes and laser diode arrays are efficient laser power sources whose emitting surface cross- section has one relatively small dimension (on the order of a micron) and one much larger linear dimension (on the order of centimeters). Because of the long linear dimension, laser diode arrays are difficult to implement in the prior art, which requires the illumination to pass through a topologically-constrained nozzle along with the extrudable material. In the current invention, such constraints are eliminated by illuminating the substrate before or after the point of deposition. An example of a suitable laser diode array is the B1-81-15C-19-30-A laser diode array from

Coherent, Inc., of Santa Clara, CA, which output 15 watts of continuous wave power.

It should be understood that other highly-concentrated light sources may still be used in this process. For example, in cases where the substrate is heated prior to deposition of the extrudable material, a carbon dioxide laser may be beneficial. Such lasers are generally inexpensive and efficient compared to many other laser light sources, and are available in very high power outputs.

Because their light output at 10.6 microns is efficiently absorbed by many extrudable materials, they cannot be used in many cases where the illumination light passes through the extrudable material. However, these carbon dioxide lasers may be used when light-mediated heating of the substrate is performed prior to deposition of the extrudable material, as depicted in Fig. 2, where the extended length lamp 34 and the mirror 36 could be replaced in certain applications with a carbon dioxide laser of the appropriate power.

Areal Deposition Of Extrudable Material

In certain applications, it will be desirable to deposit areal coverings of extrudable material.

The linear deposition scheme previously discussed could conceivably be used for such circumstances, in which a plurality of parallel linear depositions could be used to cover an area.

This requires, however, a significant amount of material handling, and may not result in the most efficient use of the light energy. Alternatively, trough deposition of extrudable material over the surface can be performed, using commercially available apparatus. Light-mediation of this process can be performed by areal heating before, after, or both before and after the deposition of extrudable material. The use of areal heating before the deposition of extrudable material is described in the fourth embodiment of the present invention shown in Figs. 4 and 5. When light-mediation is performed by before and after extrudable material deposition, light energy may impinge on the substrate simultaneously on either side of the deposition apparatus ~ that is, the processes may run either simultaneously or sequentially. Fig. 4 is a cut-away top view of an areal deposition device that utilizes light-mediated heating of the substrate prior to extrudable material deposition. The substrate 32 lies across the entire deposition surface, moving in the direction indicated by the arrow at the bottom of the figure. The extrudable material 26 is deposited along the width of the substrate by a trough material spreader 42. Such trough material spreaders are widely used in industry, and employ a variety of mechanical means to lay a wide bead of extrudable material perpendicular to the direction of movement of substrate. Before the extrudable material is deposited, a lamp array 44 illuminates the substrate 32. The lamp array 44 includes a plurality of extended length illumination devices oriented with their long axes perpendicular to the direction of movement of the substrate. Above the lamp array 44 is an areal reflector 46, which reflects light that is emitted by the lamp array away from the substrate, so that it is redirected toward the substrate. This reflector will generally be roughly planar, although its shape may be molded in order to increase light directed at the substrate. For example, the reflector may be turned down on the edges to capture stray light.

It should be understood that within the teachings of this invention the orientation of the lamp array 44 may be different from that shown in Fig. 4 and Fig. 5, with the long axis of the lamps oriented along the axis of substrate movement. Furthermore, this invention teaches that the lamp array 44 may be placed over the substrate 32 after the deposition of the extrudable material, according to the same principles enunciated above with reference to the linear stream of extrudable material. Such a configuration is depicted in Fig. 6, which is a schematic top view of a fifth embodiment of the present invention, including an areal deposition device that utilizes light- mediated heating of the substrate after deposition of the extrudable material. Alternatively, lamps could be placed both before and after the deposition point.

Characteristics Of The Extrudable Material

In such cases that the substrate illumination occurs subsequent to the extrudable material deposition, it is beneficial to reduce the amount of light absorbed by or reflected at the surface of the extrudable material. Thus, the material should be largely transparent to the incident illumination. This generally precludes the use of certain dyes or additives with high absorption in the infrared, or large particles which scatter the light.

In many applications of industrial importance, hot-melt adhesives will be used as the extrudable material. In many of these applications, the strength of the adhesive can be improved using catalyzed cross-linking. One frequently used method to initiate such cross-linking involves the use of light initiation, particularly with short wavelength ultra-violet light. Given the presence of intense light provided by the illumination source of this invention, it would be useful to utilize some fraction of this hght for initiation of the cross-linking catalysis, especially in those cases where broad spectrum sources such as a tungsten-halogen lamp or a halogen arc lamp are used.

Fig. 7 is a cross-sectional schematic of a sixth embodiment of the present invention, depicting the initiation of cross-linking in a light-activatable cross-linkable extrudable material by means of a broad spectrum lighting source that simultaneously performs light-mediation heating of the substrate. The light collecting apparatus is not shown. A broad spectrum lamp 50, which could, for example, be an arc lamp or an incandescent lamp such as a tungsten-halogen bulb, is positioned above a Ught-activatable, cross-linkable extrudable material 52 which has been deposited by the nozzle 28 onto the substrate 32. It should be noted that most light-activatable, UV-cured material is activated by shorter wavelength light, generally UV light, due to the higher energy of the UV photons. Two light rays are depicted emanating from the lamp 50. A short wavelength UV ray 54 is absorbed by the UV-cured material 52, initiating a cross-linking reaction within the material 52. Light curable extrudable material 52 should be chosen so that the UV Ught rays can penetrate significantly into the material, so as to initiate the cross-Unking throughout the thickness of the material. A long- wavelength visible or infrared Ught ray 56 passes through the UV-cured extrudable material 52, which is largely transparent to Ught rays of these wavelengths, and impinges on the substrate 32, where it is absorbed and its energy is converted into heat. It should be understood that the broad spectrum lamp may be substituted with Ught sources that emit a limited number of discrete wavelengths, given that some of these wavelengths are suitable to initiate cross-linking reactions, and others are longer wavelengths more suitable for heating the substrate. This mode of deposition using the light used in heating the substrate to additionally initiate cross-Unking or other catalyzed processes within the extrudable material can function whenever the light is positioned to illuminate the substrate at a point after deposition of the extrudable material. Thus, the devices of Fig. 2 and Fig. 6, used respectively in linear and areal deposition using Ught-mediated heating of the substrate, could also utiUze the Ught to initiate a reaction within the extrudable substrate.

Such catalyzed reactions can be used in conjunction with conventional UV-initiated cross- Unking of high-viscosity adhesives, such as the high-viscosity, UV-curable 60-7016 urethane acrylate adhesive from Epoxies, Etc. of Greenville, RI. These could also be used in conjunction with surface treatments on an areal basis, in which the cross-Unking can occur after the extrudable material has penetrated into the substrate surface.

Deposition Topologies And Sequences This mvention teaches a variety of possible deposition topologies. Fig. 4, Fig. 5 and Fig. 6 describe the areal deposition of the material on a near-planar surface, with the general intent of

U providing a film on the surface of a substrate. Fig. 1, Fig. 2 and Fig. 3 depict the deposition of a film on a substrate surface in a linear or sinuous bead, such as might be used in decorative purposes, or positioning electrical or optical lines on a substrate surface.

When the method of the present invention is applied to a plurality of surfaces, using an adhesive as the extrudable material, it can be used to bond like or dissimilar materials together.

The present invention teaches a variety of topologies relating the substrates and the bonding adhesive.

Fig. 8 is a schematic cross-section of an article made using sinuous or linear deposition methods, as might be made using the first, second, third or sixth embodiments of the present invention, where the cross-section is perpendicular to the direction of movement of the substrate, in which Ught-mediated substrate heating is used on surfaces in close opposition. In this figure, a plurality of the substrates 32 are placed in close opposition, and the surfaces most exposed are bonded using light-mediated substrate heating, with a resulting adhesive bead 58. The substrates are held together due to the structural integrity of the adhesive bead, which resists forces, largely shear in nature, when the substrates are pulled apart. The substrates bonded by this method may be of similar or dissimilar composition.

Fig. 9 is a schematic cross-section of an article made using sinuous or linear deposition methods, as might be made using the first, second, third or sixth embodiments of the present invention, where the cross-section is perpendicular to the direction of movement of the substrate, in which Ught-mediated substrate heating is used on surfaces which are separated by a more substantial gap than shown in Fig. 8. In this figure, a plurality of the substrates 32 are placed in wide opposition, containing a gap 60, into which the adhesive 58 is deposited using Ught- mediated substrate heating. The substrates are held together due to the structural integrity of the adhesive, which resists tensile or cleavage forces when the substrates are pulled apart. Articles can be made by a combination of the bonds described in Fig. 8 and Fig. 9, where the form of the bond is controlled by the separation of the substrates, the amount of adhesive appUed, and the specific topology of adhesive deposition. When both types of bonds are combined in a single article, increased strength against tensile, shear and cleavage forces is produced.

Bonds of the types depicted in Fig. 8 and Fig. 9 may be combined or configured in a variety of different manners, other than the "butt" bonds shown. For example, one substrate may be placed on top of another, and the edge of the upper substrate may then be bonded to the lower substrate using material deposition at the boundary region. Light-mediation of this bond can be accomplished using illumination that straddles the boundary, heating both upper and lower substrates. It should be noted that the substrates bonded through light-mediation may be of different compositions. For example, fabric can be bonded to wood, in which both substrates are treated with light-mediation of the material appUcation. Furthermore, the method wiU also have beneficial effects when only one of the substrates utilizes light-mediation. Thus, if one of the substrates bonds tightly to the adhesive in the absence of light-mediation, whereas the bond with the other substrate is greatly enhanced by light-mediation, then it is within the teaching of the current invention to heat only one of the substrates through the light-mediation methods described above in order to have a beneficial effect.

In addition, substrates may be treated over a broad surface area so that the adhesive will lie between the substrates as a wide area film. In order to allow this type of joint, two possible deposition sequence embodiments are illustrated. Fig. 10 is a cross-sectional schematic of a seventh embodiment of the present invention, showing a method for bonding two substrates where the two substrates are positioned so that the deposition on both substrate surfaces uses a single material applicator. A plurality of unbonded substrates 62 are brought into close approximation in the presence of an adhesive applicator 64, which may be a trough or nozzle adhesive applicator. The applicator deposits the adhesive 58 into the space between the substrates, and the unbonded substrate 62 is continuously fed into position adjacent to the applicator 64 under the influence of a plurality of rollers 68, which both feed in new unbonded substrate 68, as well as maintain the proper gap between bonded substrates. Alternatively, the rollers 68 could apply pressure against the substrates 32, in order to improve bond strength.

During the bonding process, a plurality of lamps 70, extending the width of the substrate to be bonded, and in conjunction with a plurality of elliptical or circular trough reflectors 72, illuminate and heat the substrate at light application points 74, prior to its contact with the adhesive 58. If the width of adhesive bead 58 is small, the lamps and reflectors may be similar to those used in applying linear or sinuous beads as depicted in Fig. 1, 2, and 3.

In bonding two substrates, the bonding of the adhesive to itself is not difficult to achieve. Rather it is the bonding of the adhesive to the substrate which is most important. Thus, Ught- mediated heating of the substrate may be used to independently allow penetration of the adhesive to a plurality of substrates, which may subsequently be brought together for the remaining surface adhesives to join.

Fig. 11 is a cross-sectional schematic of an eighth embodiment of the present mvention, showing a method for bonding two substrates in which the substrates are positioned so that the deposition on both substrate surfaces uses a different material applicator for each substrate. The substrates 32 may be of similar or dissimilar composition. Two trough applicators 64 are used to spread the adhesive 58 separately on each substrate. After adhesive application, both substrates are heated using illumination from the extended lamp 70, some of whose rays are reflected onto the substrate 32 using the trough reflector 72. The joined substrates are pressed together and transported via the rollers 68, bringing fresh unbonded substrate 62 under the trough adhesive applicators 64. It is understood that this same effect can be achieved using alternative methods. For example, a plurality of lamps can replace the single lamp 70 of Fig. 11, each lamp to be used to heat a separate substrate. Also, a plurality of lamps could be used to heat the substrate prior to the application of the adhesive. In addition, in case the substrate pieces are inflexible and the substrate cannot be bent around rollers 68, it would be within the teachings of this invention to treat each substrate separately, depositing the extrudable material with light-mediated heating of the substrate using any of the sinuous, linear or areal methods described above. Both substrates, each with a linear or areal distribution of adhesive on its surface, are then placed in close opposition, so that the adhesive depositions on each substrate interact physicaUy, and thereby form a tight bond.

In order to derive the largest efficiencies from the light sources used in Ught-mediated heating of the substrate, it is useful for the substrate to have a high absorption of the Ught energies emitted by the illumination device. Certain substrates, however, may be either transparent to the majority of the Ught energy impinging on the substrate surface, or may be highly reflective. In both circumstances, the efficacy of light-mediated substrate heating will be reduced.

In order to overcome these effects, the extrudable material application apparatus may contain a module for altering the light-absorbing properties of the substrate. Fig. 12 is a cross- sectional view of a ninth embodiment of the present invention, showing a linear deposition device in which light-mediated heating of the substrate is performed prior to the deposition of the extrudable material 26, and in which a light-absorbing substance is applied to the substrate in order to enhance substrate heating through light absorption. In Fig. 12, the extrudable material 26 is deposited through the nozzle 28 onto a transparent or reflective substrate 76. The substrate 76 differs from typical substrate 32 of the previous figures, in that this substrate 76 is either somewhat transparent to or relatively reflective of a substantial fraction of a plurality of collimated Ught rays 77 emanating from the Ught source, in this case a carbon dioxide laser 78. In this figure, a low reflection, high light-absorption composition 80 is deposited on the substrate 76 through a spray nozzle 82. The composition 80 may contain carbon black as the Ught absorptive agent. It is within the teachings of this invention that the nozzle 82 could be replaced with a roUer for spreading the composition 80, possibly with a reservoir in contact with the roUer for the purpose of maintaining a surface of the composition 80 on the surface of the roUer. It is also within the teachings of the invention that coating the transparent or reflective substrate 76 with the composition 80 may occur well before the deposition of the extrudable material 26, and possibly as two processes carried out on different apparatuses. It is also within the teachings of this invention that the coating of the transparent or reflective substrate 76 with the composition 80 may be of benefit when the light-mediated heating of the substrate occurs prior to or after the deposition of the extrudable material 26. Furthermore, the carbon dioxide laser 78 could be replaced with any light source of a suitable energy density. As an alternative to depositing a highly light-absorbent compound, other means of altering the surface properties can have similar effects. For example, roughening the surface with an abrasive surface can serve either to increase the absorbency of a highly reflective surface, or alternatively, may remove a surface treatment or layer on the substrate, revealing a more Ught- absorbent underlying substrate composition.

\ 7 Removal Of Unwanted Light Energy

In general, it is of benefit to aUow all collectable light from the light sources to fall onto the substrate surface. Any light that is absorbed by the substrate will generaUy be converted into heat energy, with beneficial effects for the application of an extrudable material. However, in certain cases, particularly where a human operator is involved in the control of the apparatus, intense visible light may interfere with the visual observation of the process. Such observation may be important in process control, such as in the case where this invention is used for an apparatus for bonding fabrics, as in the manner of a sewing machine. In such cases, it is beneficial for safety purposes either not to produce visible light or to shield the operator from some fraction of the unwanted visible light emanating from the illumination source.

In order to shift the wavelength of the illumination toward the invisible infrared, one can use a lamp which operates at a lower temperature. Since most lamps produce a large fraction of their light through black body radiation, a lower operating temperature, usually regulated through the amount of electrical energy input to an arc or filament source, will generate a larger fraction of the energy in longer wavelengths. This control over wavelength is usually compromised by the need to generate large radiances at the illumination source, so as to keep the illumination source small, allowing more efficient capture of the generated light energy.

It is also possible to remove some of the visible wavelengths via optics which are designed to transmit infra-red wavelength light, while absorbing or reflecting shorter visible wavelengths. These optical devices are frequently called "cold mirrors," and are commerciaUy available from a number of commercial sources with different cut-offs between transmitted and reflected Ught. An example is the #66239 cold mirror from Oriel Corporation of Stratford, CT. Fig. 13 is a cross- sectional view of a tenth embodiment of the present invention, including a depositional device in which a cold mirror is used to remove unwanted radiation. The arc lamp 22 produces wide spectrum Ught energy consisting of long wavelength light rays 56 and short wavelength visible and

UV rays 54, which are concentrated by the ellipsoidal mirror 24 and projected at the substrate 32, on which lies the extrudable material 26 which has been deposited with the nozzle 28. A cold mirror 84 lies between the illumination source and the substrate, and which reflects the short wavelength rays 54 away from the substrate, but which allows the longer wavelength rays 56 to pass through unimpeded. The rays 54 that are reflected by the cold mirror 84 are coUected on absorbing heat sink 86, where the heat is removed with a passive radiating fin structure, possibly in conjunction with forced air cooling or with a water-cooling apparatus. Other means of removing the reflected Ught rays are possible, including dispersing them into a part of the room, such as the railing, where they will not pose a safety hazard. All such configurations would allow a human operator to monitor and control the process, minimizing the possibility of damage to the operator's vision.

It is understood that such a method of removing unwanted light may be practiced with any of the broad spectrum wavelength sources hereabove mentioned, either as point, linear or areal light sources. It is also within the teachings of this mvention to use a "hot mirror" which selectively reflects longer wavelengths, and which may be placed in such a way to reflect only longer wavelengths at the substrate, and in which shorter wavelengths pass through towards a heat sink.

As mentioned above, it is most efficient to make use of both long and short wavelength illumination, which practice is interfered with by both hot and cold mirrors. As an alternative, light filters and or protective glasβes or goggles may be interposed between the substrate, where considerable reflection of the incident light frequently occurs, and the operator's eyes. Such filters may be neutral density filters, or may be also designed to absorb UV wavelengths, which are particularly damaging to eye health. Benefits and Advantages of Light-Mediated Material AppUcation

The principles and designs of this invention have been reduced to practice using a simple device in the manner of Fig. 1 and alternatively with light irrdiation of the substrate prior to material deposition. The substrates used were different woven and non-woven fabrics, leather, and wooden pieces, which were placed on an aluminum plate which was propelled by a variable speed motor along a linear track at a rate of 2 to 25 mm per second. Polyamide hot-melt adhesive 3379 from 3M Adhesive Systems of St. Paul, MN was used as the extrudable medium, and was deposited at 196°C at a fixed point using a #9946 nozzle attached to a 3M Adhesive Systems bench-mounted Polygun II hot-melt adhesive applicator, pressurized to 80 pounds per square inch, and whose applicator trigger was variably set using a threaded-screw device that could be adjusted to provide an adhesive bead of approximate dimensions 3-6 mm wide and 2-4 mm in height. The Ught source used in illuminating the substrate was a 21 Volt General Electric EKE MR16 projector bulb mounted on a moveable holder, powered by a Techni-Quip Corporation (El Segundo, CA) T-Q/FOI-1 power supply. The EKE projector lamp includes an integrated elUpsoidal mirror, and the lamp was placed so that the substrate was at the approximate second focus of the ellipsoidal mirror. The dichroic coating of the lamp reflector (designed to pass infrared light through the reflector) was over-coated with pure evaporated aluminum in the inside surface so as to include the infrared energy in the focused Ught. A 5 mm-by-5 mm aperture was made with a metal casing to limit the area of light output, and in general, the lamp was placed so that the amount of Ught projected onto the fabric was contained within an approximately square- shaped spot approximately 7 mm on a side.

This test device was used to bond together, in the manner of Fig. 8, pieces of fabric or wood which had been cut to provide complimentary linear edges, and the efficacy of the Ught-mediated application of the extrudable material was measured by the static strength of the resulting bond between the pieces of cut substrate. In certain cases, a small gap was maintained between the substrate pieces so that the adhesive and Ught energy were able to penetrate between the substrate pieces, in the manner of Fig. 9.

In the foUowing tables, the resulting strength of bonds made with and without Ught are compared for various materials. In Table 1, the illuminating lamp was placed so that the substrate was heated approximately 1 cm after the deposition of the adhesive. In Table 2, the iUuminating lamp was placed so that the substrate was heated 0.5-1.0 centimeter before the deposition of the adhesive.

Table 1 - Substrate Illumination After Adhesive Deposition

Substrate Average Strength Strength Approximate

IUumination without with Improvement

Energy Density Light Light

(watts-sec/mm²) (lb/inch) (lb/inch)

Darlexx (Pink) 0.95 18.7 59.4 320%

Leather (Black) 0.42 <4.4-30.8 63.8 >210%

Denim (Black, moderate 0.34 <4.4 39.6 >900% weight)

Neoprene Wetsuit with 0.21 17.6 37.4 210%

Nylon SheU

Acetate Felt 0.21 <4.4 24.2 > 550%

Basswood (1/16" thick) 0.95 12.7 57.2 450%

Birch Plywood (1/16" 0.95 9.5 81.4 860% thick)

Cherry Wood (1/16" thick) 0.95 27.5 61.6 230%

Table 2 - Substrate Illumination Before Adhesive Deposition

Substrate Average Strength Strength Approximate

IUumination without with Improvement

Energy Density Light Ught

(watts-sec/mm² ) (lb/inch) (lb/inch)

Darlexx (Pink) 0.58 18.7 37.4 200%

Leather (Black) 0.42 <4.4-30.8 72.6 >240%

Denim (Black, moderate 0.34 <4.4 26.4 >600% weight)

Acetate Felt 0.12 <4.4 24.2 > 550%

Basswood (1/16" thick) 0.95 12.7 52.8 420%

Birch Plywood (1/16" 0.95 9.5 72.6 760% thick)

Cherry Wood (1/16" thick) 0.95 27.5 44.0 160%

It should be noted that on many of the materials, the bond strength varied considerably between different samples generated without Ught, but was much less variable in cases where light-mediated heating of the substrate was employed. Tests were also performed which varied the length of time between the illumination of the substrate and the deposition of the hot-melt adhesive. It was noticed that when the illumination preceded adhesive deposition, there was a relatively rapid decrease in the strength of the bond with increasing time between the two steps. After approximately 17 seconds between the illumination and the deposition, approximately 60% of maximal bond strength remained.

However, when the deposition preceded the illumination by a similar time lag, the bond strength remaining was 80% of that which was observed when the illumination immediately succeeded the deposition.

It should be noted that the prior art applying extrudable materials to soUd substrates involved the projection of light energy into the extrudable material, not to the substrate (e.g. U.S.

Patent No. 4,861,404 to Neff and U.S. Patent No. 5,348,604 to Neff). Furthermore, U.S. Patent No. 5,348,604 to Neff requires that the laser energy must impinge on the material through the flow path of the material deposition, placing severe restraints on the energy density of the Ught source required. In light of these and other examples of prior art, the present invention provides a number of advantages relative to methods of material application practiced in the prior art, including:

• The method provides bond strengths significantly stronger than bonds made without Ught mediation.

• The method exhibits large benefits on a wide variety of substrates. • The method utilizes inexpensive components. For comparison purposes, the illumination experiments described above were carried out using a lamp with a retail price of $18, and with an inexpensive rheostat control, whereas a YAG laser, used in the prior art, may cost weU in excess of $20,000 including its power supplies, water circulators, water purifiers, and laser optics. • The method exhibits benefits over a wide range of operating conditions. The treatment may be carried out before or after the deposition of the extrudable material. Furthermore, the Ught energy may be provided with a short duration intense illumination, or with a less intense illumination of longer duration. This operating parameter flexibiUty indicates the ease with which the method can be applied to a variety of manufacturing environments. • The method utiUzes equipment that requires little and inexpensive maintenance. The system used in the experiments required minimal calibration and maintenance, and can be compared with the intense and expensive maintenance required, for example, for an industrial YAG laser, where water, optics and illumination system components require frequent replacement with expensive components, as well as lengthy calibration. • The method is energy efficient. The system used in the experiments was over 12% efficient at converting input electrical energy into light energy at the substrate, and the method described above for areal surfaces should be well over 50% efficient. On the other hand, for comparison purposes, YAG laser-based systems are generally less than 3% efficient, and often less. The energy-efficiency of the method increases the operational cost effectiveness of the method.

• The method can be applied when the material deposition apparatus utiUzes small apertures. Because of this, lower energy density illumination sources, which are generaUy inexpensive to purchase and operate, can be used.

• The method can be used with extrudable materials which are largely opaque to the incident illumination, by iUuminating the substrate prior to material deposition. This increases the number of materials in which light mediation of material application can be practiced.

• The method can be used in areal applications. With laser-based light mediation that uses small irradiation apertures, the material deposition apparatus must be passed many times over the substrate to assure even coverage, or a multitude of deposition points must be used. With the present method, wide array illumination of moderate power density can be used, allowing the use of appropriate wide-array material deposition apparatuses.

• Because the method effectively uses broad wavelength illumination sources, materials which absorb in a restricted number of wavelengths can be used. With laser-based Ught mediation, light-mediation may not be used if the material has discrete light absorption at the wavelength of laser emission.

• Because the electromagenetic energy used in heating the substrate never passes through the deposition apparatus, and because wide-epectrum energy sources may be used, the intense Ught sources used for light-mediation may serve a second purpose in initiating cross-Unking of Ught-activatable cross-linkable extrudable materials. This reduces the cost of using the method since a focused, high-power UV source may not need to be separately provided.

It should be apparent to one skilled in the art that the above-mentioned embodiments are merely iUustrations of a few of the many possible specific embodiments of the present invention. Numerous and varied other arrangements can be readily devised by those skiUed in the art without departing from the spirit and scope of the invention.

Claims

CJaim£What is claimed is:

1. A method for applying an extrudable material to a substrate, the method comprising the steps of:

(a) generating a concentrated electromagnetic energy field;

(b) irradiating the substrate with a concentrated electromagnetic energy field with an energy sufficient to heat the substrate without causing pyrolysis of the substrate; and

(c) applying the extrudable material to the substrate at a location upon which the concentrated energy field was previously directed.

2. The method of claim 1 wherein the concentrated electromagnetic energy field is generated by a laser.

3. The method of claim 2 wherein the laser is a carbon-dioxide laser.

4. The method of claim 2, wherein the laser is a linear diode array.

5. The method of claim 1, wherein the concentrated electromagnetic energy field is generated using a substantially isotropic energy illumination source.

6. The method of claim 5 wherein the isotropic energy illumination source is a high- pressure xenon arc lamp.

7. The method of claim 5 wherein the isotropic energy illumination source is a coiled tungsten wire.

8. The method of claim 7, wherein the longitudinal axis of the coiled tungsten wire is longer than 5 mm.

9. The method of claim 5 wherein the energy from the substantially isotropic energy illumination source is collected using a reflecting surface.

10. The method of claim 9 wherein the reflecting surface contains a shape selected from the group consisting of eUipses, circles and parabolas through one of its cross-sections.

11. The method of claim 5 wherein the energy from the substantially isotropic energy iUumination source is collected using a converging optical lens.

12. The method of claim 1 wherein irradiating the substrate includes the additional step of removing unwanted Ught frequencies.

13. The method of claim 12 wherein unwanted light frequencies are removed using a cold mirror.

14. The method of claim 1, wherein the concentrated electromagnetic energy field has at least one cross-sectional dimension greater than 3 mm when it irradiates the substrate.

15. The method of claim 1, wherein the method contains the additional step of treating the substrate to improve its absorption of electromagnetic energy, prior to the step of irradiating.

16. The method of claim 15, wherem treating the substrate involves the appUcation of a material to the substrate that strongly absorbs the electromagnetic energy..

17. The method of claim 1, wherein the method contains the additional step of protecting the substrate from oxidation while irradiating by means of a stream of non-reactive gas which excludes oxygen-bearing atmosphere from contacting the substrate.

18. The method of claim 1, wherein the extrudable material is a heat-activatable polyamide.

19. A method for applying a substantially transparent extrudable material to a substrate, the method comprising the steps of:

(a) applying the substantially transparent extrudable material to the substrate;

(b) generating a concentrated electromagnetic energy field;

(c) irradiating the substrate with the concentrated energy field at a location upon which the extrudable material has been previously applied with an energy sufficient to heat the substrate without causing pyrolysis of the substrate.

20. The method of claim 19 wherein the concentrated electromagnetic energy field is generated by a laser.

21. The method of claim 20, wherein the laser is a linear diode array.

22. The method of claim 19, wherein the concentrated electromagnetic energy field is generated using a substantially isotropic energy iUumination source.

23. The method of claim 22 wherein the isotropic energy illumination source is a high- pressure xenon arc lamp.

24. The method of claim 22 wherein the isotropic energy illumination source is a coiled tungsten wire.

25. The method of claim 24, wherein the longitudinal axis of the coiled tungsten wire is longer than 5 mm.

26. The method of claim 22 wherein the energy from the substantially isotropic energy illumination source is collected using a reflecting surface.

27. The method of claim 26 wherein the reflecting surface contains a shape selected from the group consisting of ellipses, circles and parabolas through one of its cross-sections.

28. The method of claim 22 wherein the energy from the substantially isotropic energy illumination source is collected using a converging optical lens.

29. The method of claim 19 wherein irradiating the substrate includes the additional step of removing unwanted Ught frequencies.

30. The method of claim 29 wherein unwanted Ught frequencies are removed using a cold mirror.

31. The method of claim 19, wherein the concentrated electromagnetic energy field has at least one cross-sectional dimension greater than 3 mm when it irradiates the substrate.

32. The method of claim 19, wherein the method contains the additional step of treating the substrate to improve its absorption of electromagnetic energy, prior to the step of applying the extrudable material.

33. The method of claim 32, wherein treating the substrate involves the appUcation of a material to the substrate that highly absorbs the electromagnetic energy.

34. The method of claimlθ, wherein the substantially-transparent extrudable material is a heat-activatable polyamide.

35. The method of claim 19, wherein the substantially-transparent extrudable material is a light-activatable cross-linkable material.

36. An article made in accordance with the method of claim 1.

37. An article according to claim 36 comprising a plurality of substrates bonded together by the extrudable material.

38. An article according to claim 36 comprising a plurality of substrates in which at least one substrate is bonded to an object not made according to the method of claim 1, wherein the extrudable material bonds the substrate to the object.

39. An article made in accordance with the method of claim 19.

40. An article according to claim 39 comprising a plurality of substrates bonded together by the substantially-transparent extrudable material.

41. An article according to claim 39 comprising a plurality of substrates in which at least one substrate is bonded to an object not made according to the method of claim 19, wherein the extrudable material bonds the substrate to the object.