WO2014200852A1

WO2014200852A1 - Apparatus for image controlled, localized polymerization, method of use thereof and article therefrom

Info

Publication number: WO2014200852A1
Application number: PCT/US2014/041294
Authority: WO
Inventors: Yi Qiao; Jack W. Lai; Christopher J. Campbell; Albert I. Everaerts; Robert L. D. Zenner
Original assignee: 3M Innovative Properties Company
Priority date: 2013-06-11
Filing date: 2014-06-06
Publication date: 2014-12-18
Also published as: TW201513931A

Abstract

A system for minimizing stress during curing includes a monitoring device for measuring non-conformities on a surface of a material to be cured and a UV array for selectively curing the surface. A method of selectively curing a surface is also provided and includes monitoring a region of the surface, measuring non-conformities on the surface and compensating for the non-conformities using a UV array.

Description

APPARATUS FOR IMAGE CONTROLLED, LOCALIZED POLYMERIZATION, METHOD OF

USE THEREOF AND ARTICLE THEREFROM Field of the Invention

The present invention is generally related to selective curing. In particular, the present invention is a system for monitoring non-conformities while curing and addressing the non-conformities in realtime. Background

Ultraviolet (UV) radiation is widely used for curing adhesives in a variety of applications. Traditionally, a UV source such as a UV lamp or light emitting diode (LED) is used to irradiate the adhesive and trigger the photochemical process of curing. The energy flux (i.e. number of photons delivered per unit area and time multiplied by the energy of each photon) or dosage from the UV source is generally delivered onto the adhesives without any spatial control. In situations when this power flux is non-uniform across the adhesive, stress from the curing process can develop due to the different dosages. This accumulated stress during the curing process can introduce mechanical and visual no-conformity, or distortion, to the adhesive. Additionally, due to non-uniform irradiation or uneven adhesive thickness, the reaction heat from the polymerization may be non-uniform and in some cases excessive, leading to non- conformity or damage of heat-sensitive substrates. For optically clear adhesives used in displays and graphics applications, it is not acceptable for the adhesive to cause distortion because it can result into optical defects known as Mura.

A lot of effort has been taken to maximize uniform UV dosage over the adhesive surface. However, it is still possible for curing stress to develop even with a uniform dosage. For example, curing sample geometry may cause stress to develop during the curing process even with uniform dosage.

When used in display and graphics applications, the absence of non-conformities and distortions is critical because if present, it can significantly impact an observer's visual perception of the product. For example, the mobile device and display industries have strict specifications about the visual quality of the display. The described invention is a useful tool for a wide range of products where minimizing curing stress and the resulting optical or mechanical distortion is critical for product performance.

Summary

In one embodiment, the present invention is a system for minimizing stress during curing. The system includes a monitoring device for measuring non-conformities on a surface of a material to be cured and a UV array for selectively curing the surface. In another embodiment, the present invention is a method of selectively curing a surface. The method includes monitoring a region of the surface, measuring non-conformities on the surface and compensating for the non-conformities using a UV array.

Brief Summary of the Figures

FIG. 1 is a schematic illustration of an embodiment of a curing system of the present invention. FIG. 2 is a schematic illustration of an embodiment of a sensor for measuring a non-uniformity of a sample region of a surface.

FIG. 3 is a picture of an UV array of the present invention with a collimating lenslet array.

FIG. 4 is a schematic illustration of a curing system of the present invention.

FIG. 5 is a schematic illustration of a 2D-WDS system.

FIG. 6 is a picture of a UV array and printed circuit board.

FIG. 7 is a screen shot of software output for controlling the UV array shown in FIG. 6.

FIG. 8 is a diagram of a mold used to fabricate a collimating lenslet array, including a top view, FIG. 8A and a cross-sectional side view, FIG. 8B.

FIG. 9 is a picture of a non-uniformity map of an adhesive initially cured with a donut-hole UG light pattern.

FIG. 10 is a picture of the adhesive initially cured with a donut-hole UG light pattern in FIG. 9 and then later cured with a different UV light pattern.

These figures are not drawn to scale and are intended merely for illustrative purposes.

Detailed Description

The curing system and method of the present invention can reduce or eliminate stress that develops during the curing process by monitoring non-conformities in real time and compensating for the non-conformities by tuning the light exposure of the adhesive being cured. The curing system of the present invention includes a real-time curing stress/non-uniformity monitoring device and an individually addressable UV array. The curing system uses the real-time stress/non-uniformity data as feedback to control the UV array to generate a light exposure pattern that compensates for the curing stress and resulting optical non-uniformity present during the curing process. Using the light exposure pattern, the UV array can generate a UV light profile at the appropriate energy flux over the surface of adhesive being cured to compensate for the non-uniformity in the stress or heat of reaction. As a result, a material being cured, such as an adhesive, using the curing system will have reduced stress and non-uniformity, resulting in higher visual quality and a more durable display. While the specification refers to the material to be cured as an adhesive, various other materials can be used in the system without departing from the intended scope of the present invention. FIG. 1 is a schematic drawing of the curing system 10 of the present invention. The system 10 includes a curing stress/non-uniformity monitoring device 12 and an individually addressable UV array 14. In FIG. 1, the dashed lines are the light rays from the monitoring device 12 for measuring non- uniformity and the solid lines are rays from the UV array 14 for curing. The monitoring device 12 and the UV array 14 are integrated together with a beam splitter 16. In one embodiment, the beam splitter 16 is a dichroic beam splitter or a partially transmitting mirror.

The monitoring device 12 measures any non-uniformity and generates a non-uniformity map 18 of the material being cured. In one embodiment, the real-time curing stress/non-uniformity monitoring device 12 is a Two Dimensional Web Distortion Sensor (2D-WDS) such as that described in PCT/US12/68935, hereby incorporated by reference. The 2D-WDS uses an array of beams to measure and monitor non-uniformities in the material to be cured. Generally, the monitoring device 12 includes a light source such as, for example, a laser, that projects an interrogating light beam onto a surface of the material to be cured. The light source forms a two-dimensional interrogating beam on a selected region of the surface of the material to be cured. Light is transmitted through or reflected from the region with an array of lenses 20 to form an array of focus spots. The array of focus spots is imaged on a sensor through an imaging lens, which can be a single element lens or multiple element lens combination. An image of the array of focus spots is compared to a reference array of focus spots taken with respect to a reference surface that is substantially flat and free of non-uniformity defects to determine any non- uniformity of the material under cure, such as, for example, distortion, banding, streaks and the like. The monitoring device 12 further includes a processor that determines, relative to the array of focus spots, any variations representative of non-uniformity in the region. For example, the processor may determine if any of the following variations are present: (1) the displacement in an X-Y plane of a focus spot in the array, (2) a size of a focus spot in the array, or (3) an energy flux of a focus spot in the array.

FIG. 2 shows an exemplary system and apparatus 100 for measuring surface non-uniformity and includes at least one light source 102 that emits an interrogating light beam 104. Suitable light sources 102 may vary widely depending on the type of surface to be analyzed, but light sources with well defined wavefronts, such as lasers, are particularly suitable, and suitable lasers include He-Ne lasers, diode lasers and the like.

The interrogating light beam 104 passes through an optional lens system 106 that further expands the beam to overlie a selected region 108 on a surface 110 of a material 112. If multiple interrogating light beams 104 are used as the light source 102, the lens system 106 may not be necessary to sufficiently expand the beams to overlie the region 108.

For example, the analysis method and apparatus described herein are particularly well suited, but are not limited to, to inspecting the surface of web-like rolls of materials 1 12. In general, the web rolls may contain a manufactured web material that may be any sheet- like material having a fixed dimension in one direction (cross-web direction) and either a predetermined or indeterminate length in the orthogonal direction (down-web direction). Examples of web materials that can be effectively analyzed using the system 100 include, but are not limited to, transmissive or reflective sample materials 112 in which the surface 1 10 is not highly scattering to the light emitted by the light source 102. Examples include, but are not limited to: metals, paper, wovens, non-wovens, glass, polymeric films, flexible circuits or combinations thereof. Metals may include such materials as steel or aluminum. Woven materials generally include various fabrics. Non-wovens include materials, such as paper, filter media, or insulating material. Films include, for example, clear and opaque polymeric films including laminates and coated films.

The surface 110 includes non-uniformities such as, for example, mottle, chatter, banding, streaks and distortion (not shown in FIG. 2), which may extend over broad areas of the material 1 12. The light source 102 and the lens system 106 may be selected to provide a suitably sized sample region 108 for a particular surface analysis application.

A two-dimensional light beam 114 is transmitted through and/or reflected off the surface 110 of the material 112 and is thereafter made incident on an array of lenses 120. The lens array 120, which may be linear or two-dimensional, includes a suitable number and arrangement of lens elements 122, which may be referred to herein as lenslets, to capture at least a portion of the transmitted or reflected light beam 114. While the lens array 120 can be of any suitable size and shape, the size and shape of the lens array 120 is particularly selected such that all the lenslets 122 in the lens array 120 are filled by the transmitted light beam 114. If multiple transmitted light beams 114 are utilized as the light source 102, the lenslets in the lens array 120 are arranged such that the combination of angular divergence from the lens system 106 (if present) and the amount of angular deviation caused by the material 112 do not cause multiple transmitted light beams to be incident on a single lenslet or to be incident in a region between lenslets. Multiple lens arrays 120 may optionally be placed adjacent to one another to match the size of the transmitted light beam 114.

Each of the lenslets 122 includes a curved surface selected to produce a focus spot 150, and the two-dimensional array of focus spots 152 produced by the lens array 120 is characteristic of the features in the sample region 108 of the surface 110. In the embodiment shown in FIG. 2, the array of focus spots 152 is imaged by an imaging lens system 130 onto a suitable sensor system 132 including for example, a CCD or CMOS camera 134.

The sensor system 132 includes a processor 136, which may be internal, external or remote from the camera 134. The processor 136 includes a reference array of focus spots 154 stored in memory. The reference array of focus spots 154 results from prior analysis using the apparatus 100 of a reference material 1 12 that is substantially free of non-uniformity defects, or may be calculated based on a theoretical model of the behavior of an ideal sample material. A non-uniformity defect in any portion of the region 108 causes a change in the light transmitted through that portion of the material 1 12, which is collected by the underlying lenslets 122 in the lenslet array 120. For example, non-uniformity defects in the sample region 108 can cause angular deflection, angular divergence, or altered transmittance of the interrogating light beam. These alterations can result in, relative to a reference array of focus spots, a change in at least one of: (1) the location of the focus spots in an X-Y plane, (2) the size of the focus spots, or (3) the energy flux of the focus spots.

In the embodiment shown in FIG. 2, an angular deflection of the interrogating beam 1 14 is detected by at least some of the lenslets 122 underlying the sample region 108, which causes a corresponding displacement in at least one of the X and Y directions between the focus spots 150 in the array 152, when compared to the reference array of focus spots 154 stored in the memory of the processor 136. The processor 136 utilizes any suitable algorithm to compare the location in the X-Y plane of each focus spot 150 in the two-dimensional array 152 to the location of its corresponding reference focus spot 154 in the reference focus spot array. This linear displacement between the centroid regions of the focus spots 150, 154 produced by each lenslet 122 in the lens array 120 is proportional to the severity of the non-uniformity defect in the corresponding overlying area of the sample region 108.

The apparatus of FIG. 2 simultaneously measures multiple points to enable rapid two- dimensional mapping of non-uniformity over a large region 108. The two-dimensional map of the array of the focus spots 150 is a true representation of sample uniformity in two directions (for example, in a web material, in the cross and down-web directions). In addition, the displacement of the two- dimensional array of the focus spots 150 from the reference array of focus spots 154 is relatively simple to process and interpret using algorithms in the processor 136.

After processing, the results may be displayed on an appropriate user interface as a non- uniformity map and/or may store the results in a database.

To spatially modulate the UV dosage across the adhesive being cured, an individually addressable UV array is used. In one embodiment, the array is a UV-LED array with collimating lenslet array to collimate each LED element is used. FIG. 3 shows an UV-LED array 200 with collimating lenslet array 202. The light from each LED element of the UV-LED array is collimated to cover a specific area. Each of the LED elements can be turned on and off and also energy flux modulated. In one embodiment, the light from the UV-LED array 200 can be pulsed to further minimize stress build-up in the adhesives as it is cured.

When the material to be cured is an adhesive, the UV-LED array 200 is designed such that the LED emission matches the wavelength required to initiate the photoinitiator of the adhesive to be polymerized. The UV-LED array 200 includes a plurality of LEDs in a matrix. In one embodiment, each of the LEDs is driven by a programmable constant current source, such as an LED Driver. The LED driver can be configured to run in either a continuous or pulsed mode. Each LED driver is connected to a single LED and is addressable under computer control. A customizable graphical programming platform can be used as the user interface software and is integrated with hardware and software. The software provides real time control of the individual LEDs using a custom user interface. The software is capable of controlling and programming the energy flux or power levels of the individual LEDs in a range of from 0 to about 100%. The software can also control the duration each LED is powered on, hence also controlling the general shape and area being cured.

The lenses of the lenslet array 202 function to provide beam colimation in order to prevent too much light overlap from adjacent LEDs. In one embodiment, the lenslet array includes about 180 lenses. In one embodiment, the lenslet array is formed by first making the inverse shape of the lenslet array in a mold. The lenslet array is then replicated and separated from the mold after curing. The resulting UV- LED array is configured in the apparatus such that it is centered on the lenslet array.

In another embodiment, a UV-Xenon array is used. The UV-Xenon array functions similarily to the UV-LED array and is a pulsed curing system including a plurality of Xenon elements using ultra high- peak power UV pulses. The high peak power UV pulses provides the needed energy to cure an adhesive over a short period of time. As with the UV-LED array, the duration and frequency of the pulses can be controlled as needed.

The non-uniformity created by curing stress can be continually measured and used as feedback to spatially modulate the curing light power flux from the UV array in order to allow the stress to be relieved and minimize the non-uniformity of the stress and resulting distortions. In one embodiment, the non- uniformity map generated by the monitoring device is manually analyzed and the proper specifications are manually inputted to guide the UV array to generate to correct for any non-uniformities. In another embodiment, a computer algorithm is used to analyze the non-uniformity map measured from the monitoring device and to calculate a desirable pattern for the UV array to generate. The computer algorithm may depend on the type of material being cured.

Any curable adhesive can be monitored and cured using the system of the present invention. For example, liquid optically clear adhesives (LOCAs), heat activated optically clear adhesives (HOCAs), silicon LOCAs, UV curable pressure sensitive adhesives and hot melt adhesives can be used in the system of the present invention. Exemplary liquid optically clear adhesives can be of the type disclosed in International Pub. No. WO2010/084405A1 and WO201 1/1 19828A1. A particularly suitable LOCA that can be cured using the present invention is 3M Liquid Optically Clear Adhesive 2321 available from the 3M Company, StPaul, Minnesota. Examples of suitable HOCAs include, but are not limited to: poly(meth)acrylates and derived adhesives, thermoplastic polymers like silicone (e.g., silicone polyureas), polyesters, polyurethanes and combinations thereof. The term (meth)acrylate includes acrylate and methacrylate. Particularly suitable are (meth)acrylates because they tend to be easy to formulate and moderate in cost, and their rheology can be tuned to meet the requirements of this disclosure. In one embodiment, the HOCA is a (meth)acrylic copolymer of a monomer containing a (meth)acrylic acid ester having an ultraviolet-cross-linkable site. The term (meth)acrylic includes acrylic and methacrylic. Silicon based adhesives may use addition curing chemistry between a silicon hydride functional silicone and a vinyl or allyl functional silicone. Addition curing silicones are well known in the art and they often incorporate platinum based catalysts that can be activated by heat or UV irradiation. Likewise, two- component silicone liquid adhesives or gel forming materials may be used as the basis for this thixotropic, printable material. These types of silicones may rely on condensation chemistry and require heat to accelerate the curing mechanism.

In practice, a thin film (i.e. a few microns to several hundred microns) of the uncured adhesive is positioned between a first substrate and a second substrate. A thin film of the adhesive is applied to the first substrate and then partially or fully cured using the UV array and cure monitored to minimize stress and/or deflection on the substrate. The partially or fully cured adhesive then can be optionally laminated to the second substrate and fully cured. In one embodiment, the first substrate and second substrates are optically clear. Representative examples of optically clear substrates include glass and polymeric substrates including those that contain polycarbonates, polyesters (e.g., polyethylene terephthalates and polyethylene naphthalates), polyurethanes, poly(meth)acrylates (e.g., polymethyl methacrylates), polyvinyl alcohols, polyolefins such as polyethylenes, polypropylenes, cyclic olefin copolymers, and cellulose triacetates. Exemplary optically clear substrates include, but are not limited to a display panel, such as liquid crystal display (LCD), an OLED display, a touch panel, electrowetting display or a cathode ray tube, a window or glazing, an optical component such as a reflector, polarizer, diffraction grating, mirror, or cover lens, another film such as a decorative film or another optical film. When curing an adhesive on a LCD where the backlight unit is attached to the LCD, the display module is non- transparent. In this and similar cases, a different technique from 2D-WDS can be used to monitor non- uniformity or distortion. For example, the LCD can be used to display a 2D array of spots and a camera can be used to image the displayed 2D array of spots. The non-conformity map can then be obtained and used as curing feedback.

In one embodiment, one of the substrates can include spacers to control the adhesive thickness. The substrates with adhesive are then mounted in the curing system such that the UV radiation from the LED or Xenon lamps (used to cure the adhesive) and the red light from the red LED (used to monitor the non-conformity) is incident to the major surface of one of the plates. Power is supplied to each of the UV LED or Xenon lamps. At the same time, the red LED is turned on and a non-uniformity map of the curing adhesive film is recorded by the two dimensional wave non-uniformity camera and viewed on the user interface. The resulting non-uniformity map shows any non-uniformities of the curing adhesive. The non-uniformities can be measured from the adhesive only, or the total non-uniformities can be measured from the substrate and the adhesive. Examples

The present invention is more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present invention will be apparent to those skilled in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following example are on a weight basis.

An apparatus designed to identify non-conformity or distortion of a film of polymerizing, i.e. curing, adhesive and provide real time feedback to the UV (Ultra Violet) LED (Light Emitting Diode) lights curing the adhesive was fabricated. FIG. 4 shows a schematic representation of the apparatus 400 which included a two dimensional web distortion sensor (2D-WDS) 410 (see FIG. 5), a UV LED array 420 and collimating lenslet array 430, a partial transmissive mirror beam splitter 440, a red LED (imaging light) 450, a lenslet array 460 for the imaging light (located between the adhesive 470 sample and the 2D- WDS camera 415), a computer 480a and corresponding monitor 480b, for displaying the non-conformity map of the curing adhesive laminate, and a controller 490 to control the individual UV LEDs (not shown) of the UV LED array 420. The camera 415 was in electrical communication with the computer 480a and integrated with the software to display a non-conformity map of the curing adhesive. The computer 480a was also in electrical communication and integrated with the controller 490 to facilitate control of the individual UV LEDs, the individual UV LEDs were also in electrical communication with the controller. Red light 455 from the red LED 450 was used for monitoring the non-conformity of the adhesive sample during curing, producing a non-conformity map. Radiation 425 from the UV LED array 420 contacted the beam splitter 440 and approximately 90% of the radiation 425 was reflected into and through the curing adhesive 470.

FIG. 5 shows a schematic diagram of the 2D-WDS 410 in more detail. THE 2D-WDS included a red LED 450, a beam expander 455, lenslet array 460 for the non-conformity measurement, an imaging lens 417a and 417b and camera 415. The red LED was part number LEDP1 available from Doric Lenses Inc., Quebec, Canada. An 8 inch (20.3 cm) x 10 inch (25.4 cm) lenslet array for the non-conformity measurement was purchased from Holographix LLC, Hudson. Massachusetts. Each lenslet is approximately 3 mm in diameter and packed in a square array across the 8 inch by 10 inch area of the lenslet.

The UV LED array was fabricated from UV LEDs, part number NCSU275TE with emission wavelength of 385nm available from Nichia Corporation, Anan-Shi, Tokushima, Japan. The LED emission of 385nm is selected to match the wavelength to initiate the photoinitiator of the adhesive to be polymerized. The UV LED Array comprised 180 LEDs in a matrix of 15 columns and 12 rows to cover an area of 10 inch (25.4 cm) x 8 inch (20.3 cm). FIG. 6 shows the LED array 420 and corresponding printed circuit board. Each of the LEDs 422 was driven by a programmable constant current source, i.e. an LED Driver, part number LDD-700L from Mean Well USA Inc., Fremont, California. The current supplied by the LDD-700L was programmable from 0-700 mA. This LED driver was operated in a continuous mode, for a fixed time, although a pulsed mode can also be used. Each LED driver was connected to a single LED 422 and was addressable under computer control. The 180 LED drivers were divided into 3 printed circuit boards (PCB); each PCB contains 60 LED drivers. The three LED drivers PCB were powered from a single power supply of 12-24 volts with an output of 30 amps. The 180 LED Drivers were controlled from a customized electronics controller. Internal to this controller was a single board computer CompactRlO, part number SbRIO-9606 available from National Instruments, Austin, Texas. The user interface software was National Instruments LAB VIEW version 2012 available from National Instruments, Austin, Texas. LAB VIEW is a graphical programming platform that can be customized and integrated with hardware and software. The software was customized to provide real time control of the 180 individual LEDs using a custom user interface and was used to control the individual LEDs. LED energy flux was programmable from 0-100%, based on an output current of 700 mA representing 100% energy flux. An image 700 of the software output, for control of the UV LED array, is shown in FIG. 7. The user interface screen shows a grid-map 710 of the individual UV LEDs 422 (see FIG. 6) and enables the control of individual power levels and duration of the UV LEDs 422. Different UV exposure and exposure patterns can be provided to the sample, depending on which UV LEDs 422 are powered, their corresponding power levels and the time of use.

The UV collimating lenslet array 430 array consisted of 180 lenses. The function of the lenses was to provide beam collimation, which prevents too much light overlap from adjacent LEDs . The inverse shape of the lenslet array is first made in a mold and then replicated on a quartz plate using a polydimethylsiloxane, available under the trade designation SYLGARD 184 from Dow Corning, Midland, Michigan. The quartz plate containing the lens is then separated from the mold after a 24 hour room temperature cure. The UV LED array was configured in the apparatus such that it was centered on the collimating lenslet array. A drawing of the mold 800, used to fabricate the UV collimating lenslet array 430 array, is shown in FIG. 8, including a top view, FIG. 8A and a cross-sectional side view, FIG. 8B. The dimensions shown in FIG. 8 are all in inches. Referring back to FIG. 3, a picture of the UV collimating lenslet array 202 positoned in front of the UV LED array is shown.

The adhesive used for curing was 3M LIQUID OPTICALLY CLEAR ADHEIVE 2321 available from the 3M Company, St.Paul, Minnesota. A thin film of Adhesive 2321 was formed by squeezing the adhesive between two glass plates, one of the plates having spacers, to control the adheive thickness. The glass plates were 5 inch (12.7 cm) x 5 inch (12.7 cm) x 0.7 mm plates of Corning Eagle alkaline boro- aluminosilicate glass, with cut edges, from Delta Technologies, Ltd., Loveland, Colorado. The spacer material was four strips, each 1 inch (2.54 cm) x 0.25 inch (0.64 cm) of SCOTCH FILAMENT TAPE 893, available from 3M Company. The filament tape strips were mounted in the center of each side, adjacent the edge, of one of the glass plates. A 2 inch (5.1 cm) diameter circle of LOCA was placed in the center of the glass having the tape spacers. A second piece of glass was hand laminated to the first plate, squeezing the adhesive over the entire plate surface. Excess adhesive was wiped from the edges of the glass plate. The glass plates, with adhesive, were mounted in the UV LED curing apparatus, such that the UV radiation from the LEDs and the red light from the red LED would be incident to the major surface of one of the plates. A small metal washer having an outside diameter of 4.5 cm and an inside cut out diameter of 1.7 cm was mounted on the surface in the glass plate adjacent the UV LED array, via double stick tape. The washer was mounted approximately in the center of the glass plate's surface. Power was supplied to each UV LED at a level of 350 mA for 5 seconds, the UV LEDs were operated in the continuous mode. At the same time, the red LED was turned on and a non-conformity map of the curing adhesive film laminate was recorded by the two dimensional wave distortion camera and viewed on the monitor. An image of the non-conformity map is shown in FIG. 9. The image clearly shows the non-conformity of the curing adhesive laminate caused by areas of the adhesive film that were masked by the washer, preventing UV radiation from uniformly curing the adhesive film.

After the initial cure, the washer was removed from the surface of the glass plate. Based on the non-conformity map of FIG. 9, UV LEDS from the LED array were selected, such that, they would provide radiation to the area of the adhesive previously masked by the washer. UV LEDs, forming an area of radiation in the shape of a ring, approximately that of the size of the washer, and centered on the uncured region of the adhesive film were turned on at a power level of 700 mA for 10 seconds. At the same time, the red LED was activated to obtain a non-conformity map of the film. FIG. 10 shows the non-conformity map after the second step of the curing process. Compared to FIG. 9, the ring shaped distortion is significantly decreased, after the second curing step.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. A system for minimizing stress during curing comprising:

a monitoring device for measuring non-conformities on a surface of a material to be cured; and a UV array for selectively curing the surface.

2. The system of claim 1, wherein the monitoring device measures non-conformities on the surface in real time.

3. The system of claim 1, wherein the monitoring device comprises:

a light source forming a two-dimensional interrogating beam on a region of the surface;

a lenslet array that captures light transmitted through or reflected from the region of the surface to form an array of focus spots;

an imaging lens that images the array of focus spots; and

a process that determines, relative to a reference array of focus spots, a variation in a

characteristic of the array of focus spots.

4. The system of claim 1, wherein the UV array is one of a UV-LED array and a UV-Xenon array.

5. The system of claim 1, wherein the UV array comprises a plurality of individually controllable elements.

6. The system of claim 1, wherein the UV array comprises a collimating lenslet array.

7. The system of claim 1, wherein the material to be cured is an adhesive.

8. A method of selectively curing a surface comprising:

monitoring a region of the surface;

measuring non-conformities on the surface; and

compensating for the non-conformities using a UV array.

9. The method of claim 8, wherein monitoring the region of the surface occurs in real time.

10. The method of claim 8, wherein measuring non-conformities on the surface comprises:

forming a two-dimensional interrogating beam on a selected region of the surface; collecting light transmitted through or reflected from the region with an array of lenses to form an array of focus spots;

imaging the array of focus spots through an imaging lens; and

comparing an image of the array of focus spots to a reference array of focus spots to determine a level of non-uniformity in the region.

1 1. The method of claim 8, wherein compensating for the non-conformities using a UV array

comprises modifying an energy flux of individual elements of the UV array based on the nonconformities.

12. The method of claim 8, wherein compensating for the non-conformities using a UV array

comprises pulsing individual UV-Xenon lamps.

13. The method of claim 8, wherein compensating for the non-conformities using a UV array

comprises collimating individual elements to cover a specific area of the surface.

14. The method of claim 8, wherein the surface comprises a surface of an adhesive.

15. The method of claim 8, wherein the UV array comprises one of a UV-LED array and a UV- Xenon array.

16. The method of claim 8, wherein measuring non-conformities on the surface comprises comparing the region of the surface with a reference surface.