Aerobic Adhesives VII – A New High Performance Bonding Option ...

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Figure 11. Stress/Strain Relationships Figure 12. Doublet Assembly 3000 Rigid Epoxies Stress (psi) 2000 1000 UV Aerobic Acrylic Urethanes Silicone 0 10 20 30 40 50 Strain % Lens Mounting As lenses get smaller and bonds more delicate, the strategies to overcome the stresses inherent in the materials and between adjacent bonded surfaces have become more exacting in order to survive the environmental rigors that the device will be exposed to. Choosing a material such as the OP-29 or OP-30 that is resilient and strong with low shrinkage characteristics may be ideal for an application of this type. Optimization of the adhesive in the bond line can be done with some calculations such as this simple model for calculating adhesive thickness for a lens mount. A preferred bond line might range from 0.002” to 0.005”, but can vary from 0.005” to 0.25” or more, with special applications requiring greater than a 0.25” bond line. Figure 13. Simple Lens Potting Model 4 . dg Lens Low Modulus Adhesive hr dm Cell / Mount For minimized stress on the lens: hr = dg(α m - α g ) 2(α r - α m ) Where: hr - Required Elastomer Thickness dg - Lens Outer Diameter α m - Cell thermal coefficient of expansion α g - Lens thermal coefficient of expansion
VII Curing Lamp Considerations α r - Adhesive thermal coefficient of expansion Choosing the right curing lamp for the application can be critical. The light source should be selected based on whether or not the light frequency and intensity matches the curing chemistry of the adhesive being used. One need to also consider is the throughput needed, matching the shape of the lamp to the area of curing, whether the manufacturing process is going to be a batch process or continuous, and the speed of cure needed to achieve a full cure. The parameters that define a successful cure are entirely dependent on the end-product requirements. In other words, the cure is only successful if the desired properties of the end product are achieved with ease, consistency and cost effectiveness. When setting up the process, it is important to determine the minimum light intensity and time of exposure needed to create a fully cured sample. Measuring the light energy required to achieve full cures easily does this. Simply increasing or decreasing either the intensity or the time of exposure, an acceptable cure range can be determined. This information is necessary in order to establish the most cost effective curing process. If the sample does not receive sufficient light intensity, then the bonds might not form fully, resulting in poor adhesion, or uncured adhesive. Thick layer industrial applications have given rise to a UV equipment industry all it’s own. This has been most noticeable in the last ten years with the development of high intensity spot, or wand style curing lamps designed to cure small, relatively thick spots of adhesive. Advancements in equipment technology have been directly attributed to the rapid growth in end use applications and the need for custom manufacturing solutions (rather than just new adhesives or sealants) to meet customer needs in the assembly of their products. Such responsiveness to individual end user manufacturing needs through the engineering of equipment systems that take full advantage of UV technology will continue to support application growth in the future. Many applications require only lower intensity curing lamps. Bonding between surfaces, one of which allows light to pass, is one of the applications where resin may be effectively cured with lower intensity, lower cost lamps. Most UV formulations are capable of curing within 1 to 30 seconds through clear glass or plastic parts under lower intensity lamps. Because the inhibiting effect of oxygen is not present, cures are relatively fast. Bond lines are usually fairly thin - 0.001 to 0.125 inches. The optimum shape or pattern of light emitted by a lamp for any specific application is called its “footprint”, and depends upon the size and geometry of the bond area and other process recommendations. 6 • Spot - Spot source lamps with light guides are typically used for curing small areas, or areas where light needs to reach partially obstructed areas that can not be reached by a flood type system. • Flood – Flood sources offer a large cure area but generally lower light intensity. The emit less heat as well, and are usually the product of choice for bonding heat sensitive plastic parts. The large area of flooded light also is useful for curing many parts at once. Flood lights may be fitted over a conveyor or turntable for continuous product assembly. • Focused beam – Focus beam lights may also be used over a conveyor, and focus the energy of light into a higher intensity 1”x6” beam. The lamps shown below represent a range of equipment available for Optical Adhesive applications.
Page 1 and 2: Aerobic Adhesives VII - A New High
Page 3 and 4: Adhesive Cure Mechanism Typical Pro
Page 5 and 6: During UV Cure, adhesion promoters
Page 7 and 8: AAA’s are designed to be sensitiv
Page 9: In many applications, rigid epoxies
Page 13: References: 1. A. Bachmann, “Ultr

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