Product category:
Adhesives, threadlockers and other consumables
News Release from: Inseto (UK) | Subject: Delo-Katiobond
Edited by the Engineeringtalk Editorial
Team on 08 September 2006
Makers switch to radiation-curing
adhesives
The production of microswitches for the automotive sector often has the need to bond the housing to the base and seal the connectors or pins at the same time.
When manufacturing microswitches for the automotive sector for example, two main requirements are critical: fast processing for large volumes and extremely high reliability One important production step is the sealing of the switch housing and the connectors
This article was originally published on Engineeringtalk on 26 Jan 2004 at 8.00am (UK)
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Light cured adhesives are being used very successfully in this area.
They cure within seconds, are easy to process and are very efficient.
Inseto's Adhesives Division provides bonding solutions to the UK and Ireland's manufacturing industry that demand technically advanced bonding.
These include automotive, aerospace, military, telecommunications, audio, electronic and renewable energy industries.
Today electrical switches are available in many designs and for varied application areas.
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They are not only used in domestic appliances and consumer electronics but also in critical areas such as automotive applications.
The tasks the adhesives and casting resins have to perform are ever demanding.
Connection pins have to be sealed, components bonded or housings cast in more and more demanding environments.
New types of plastic and material combinations require the use of new adhesive systems.
High volume applications in the automotive sector demand fast inline bonding processes combining short cycle times and secure process control.
Two-component or heat-curing adhesives and casting resins don't easily meet these requirements.
Two-component products are not always suitable, especially for low adhesive amounts.
Heat-curing adhesives require extensive investment in curing ovens and cause high operating costs.
Due to their easy dispensability and fast curing, radiation-curing adhesives often meet the required parameters far more easily and so offer a better overall alternative.
The production of microswitches for the automotive sector often has the need to bond the housing to the base and seal the connectors or pins at the same time.
Process reliability is extremely important as these micro switches are often used in safety-relevant components such as airbag deactivation switches or for monitoring seatbelt locks.
At the same time however, the process has to be suitable for large volumes with short cycle times.
In one application the problem is solved, by using a low-viscosity and fluorescent Delo-Katiobond adhesive.
It is filled into the cavity of the component from two sides in one cycle.
The adhesives constant viscosity and unchanging flow properties are critical in order to ensure complete wetting and sealing without the material flowing into the housing gap.
In the next cycle the adhesive is cured in one second by means of a microwave area lamp.
Due to the fluorescent trace the application of the adhesive can be checked by an automated camera system.
Missing adhesive or possible contamination on the connector can be detected reliably.
For example, irregularities caused by dispensing problems can be recognised immediately after curing and the system can be stopped if necessary.
When using heat-curing adhesives, such failures are only picked up after oven curing and cooling and many reject parts may have been produced during this time.
Casting pins of tactile switches, which are used for keypads and control panels, is another example.
The connection pins of these switches must be bonded into a PBT housing and sealed against media influence at the same time.
The adhesives hardness has a major influence on the units switching behaviour so the adhesive must be tailored to the customer's requirements with regards to its mechanical properties too.
In one application, prior to the changeover to a red Delo-Katiobond, a one-component heat curing epoxy resin had been used.
The viscosity had to be adjusted by adding harmful solvents.
A long oven line using valuable space and energy was required to cure the adhesive.
With the oven removed, light curing adhesive technology could be integrated into the existing production line and cycle times were reduced considerably by using radiation curing epoxy.
The irradiation time until initial strength is 5s.
Narrow viscosity limits enable an unchanging flow behaviour and the adhesive's red colour allows easy and fast process control.
Recent tests show that the adhesive is also suitable for a subsequent lead-free soldering process with higher temperature requirements implemented further down the line.
In the examples given, the advantages of light-curing epoxies in these applications are fairly apparent.
The products are easy to process, achieve very fast initial strength and offer good temperature resistance.
The chemical structure of epoxies enables short-term stresses of up to +300C (reflow soldering process).
The typical long-term temperature range of use extends to +150C.
The epoxies developed for microelectronics have a very low ion content, especially corrosive acting ions such as CI-, Na+ and K+.
Light-curing epoxy resins, Delo-Katiobond, are available in graded flexibilities from hard to tension equalising and have a dry surface after curing.
In their uncured, liquid state, light-curing epoxies have many properties allowing easy and secure handling.
The solvent free products meet the highest requirements with regards to health and safety and environmental protection.
All photo initiated curing adhesives consist of only one component.
Two component mixing and dispensing systems, which involve high cost and maintenance, are not required.
Delo supplies numerous standard products from the Delo-Katiobond range with various viscosities, enabling the selection of a product with a suitable flow behaviour.
Options are available for dispensing: screen-printing or stencil printing for two-dimensional application, and spraying for two or three-dimensional application.
Dispensing is preferred in many industrial applications due to component geometry.
The most common dispensing types are time-pressure and volume dispensing.
Initial strengths are achieved after a few seconds by exposing the light-curing adhesive to high-level radiation.
The harmonisation of UV lamp and adhesive is an important parameter for the use of light and UV curing adhesives.
The market provides many different lamp systems.
In most cases the adhesive type used and the processing parameters heavily influence the selection of a device.
Curing speed and degree of light-curing adhesive are directly associated with the lamps emission spectrum and intensity.
Depending on the application, lamps are available, which allow either large area radiation or exposure of small areas with point radiation.
Regular monitoring of the intensity is important for all types of lamps in order to ensure a constant curing quality.
The automatic visual inspection of adhesive application is frequently required.
This can be easily achieved with Delo-Katiobond.
The adhesives can be pigmented with various dyes and fluorescent substances making application control easier.
However very intense dark colouring is not possible for photo initiating adhesive as these dyes absorb the light on the surface of the adhesive and stop deep curing.
The inspection of fluorescent adhesive, even on a very dark base material is possible with the correct camera system.
Radiation-curing epoxies cure through cationic polymerisation.
The curing reaction is triggered by irradiation with UV light and/or visible light.
Radiation sources used for adhesive curing have to meet the following requirements: high penetration depth into the adhesive to cure larger adhesive layer thickness; high intensity for fast curing; optimal occupational safety; no impairment of materials by the radiation; and low investment cost.
Curing of adhesives with UV or visible light is a photochemical process.
Therefore, adhesives cured by light of these wavelengths are called photo-initiated adhesives.
The penetration depth of this optical radiation into an adhesive depends on the radiations wavelength.
The UVA and visible wavelength ranges supplying enough energy for the start of polymerisation are predominantly used for curing layer thicknesses of approximately 0.2 to 5mm.
It is important that the complete adhesive volume is exposed as curing in shadowed areas will nor occur.
If complete irradiation is not ensured due to component geometry, dual-curing products with a second curing mechanism, such as Delo-Dualbond should be used.
Radiation-curing epoxies are not only an attractive alternative to heat-curing or two component adhesives, but also other joining methods.
Due to their easy processing, fast curing and high efficiency they are suited to fast processes and small components.
The examples given show that light-curing epoxy adhesives work reliably in safety-relevant component groups and meet demanding requirements.
The micro and tactile switches discussed have been produced in quantities of many millions for several years.
The experience gained and the continuously increasing product requirements, has resulted in further establishment of radiation-curing epoxy resins in many diverse, fast and automated processes around the world.
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