Bonding polypropylene or polyethylene
Avoiding thermal expansion mismatch
problems?
Q. We are looking for
an adhesive that will cure clear and bond PE, PP to make small containers.
A. There are a number of clear hot melt adhesives designed to bond polypropylene and polyethylene. These products are economical and a variety of application equipment is available. If small quantities of parts are to be assembled, cyanoacrylate adhesive, used with a polyolefin primer, may be appropriate. This option can be implemented without purchase of equipment.
Q. We need to bond
pieces of ferrite (100 x 240mm total area) to a sheet of aluminum. The thermal coefficient of expansion of the
ferrite is around 7e-6 / K and aluminum is 25e-6 / K. The minimum shipping temperature is -20c max working is about
120c.
A. This is a difficult design issue that can't
be solved by the adhesive selection alone. Some suggestions are:
1. Complete a careful analysis of the stresses resulting from the different
expansion rates.
2. Determination of the physical thickness of adhesive layer needed to absorb
the mismatch. Generally this will be thicker than an ordinary joint.
3. Consideration of a surface treatment for the aluminum. This will improve the durability to the
aluminum side of the joint.
4. If possible, select a ferrite that has at least some small amount of
porosity to allow penetration of adhesive during the bonding process. The
resulting interlock between cured adhesive and the ferrite may be helpful in
getting the desired durability.
5. A rigorous thermal cycling program should be part of the qualification test.
Q. We manufacture galvanized and aluminum roof vents made up of 4 pieces, leaving 4 overlapping seams to seal weather We have been using a latex glue in a trigger type oil can to dispense glue on the product. The glue takes too long to dry (8 - 12 hours.)
A. I would suggest testing a 2-component
urethane adhesive for this application. These materials cure quickly have good
adhesion, flexibility and weathering resistance. Cost will be higher than latex
- especially for small packages. Larger sizes could bring the economics into
line.
Q. I am looking for a
fast curing adhesive that will bond wood to wood, to make a solid part. The
part must also be waterproof, easy to use, it can be a catalyzed product, but
it must have rapid set up time.
A. Marine grade polyurethane adhesives are
often a good choice for waterproof bonds.
Both single component and fast curing two component versions are
available.
Q. I am looking for
an FDA approved adhesive for neoprene. I will also need the adhesive to stay
flexible after adhesion. I will be connecting neoprene to itself. Any
suggestions would be greatly appreciated.
A. The US Food and Drug Administration covers
a wide regulatory area including food, drugs, medical devices, cosmetics,
biologics, veterinary products, and radiation emitting devices. The FDA has differing requirements for
adhesives depending on the regulatory area and the specific bonding
application. As an example, an adhesive
used for attaching a label to a food product would have entirely different
requirements from one used in a medical device. While there are many good adhesives available that have received
FDA approval, it is important to note that approval only covers a specific
application.
Q. I need to bond an aluminum name plate
(2.5"X4") to a powder coated metal computer server enclosure. The
powder coat paint is a textured finish. Please advise.
A. Transfer tapes should do the job. Transfer tapes are a pressure sensitive film
supplied on a release paper roll. They
can be die cut to the right size and easily applied to the back of the
nameplate. The release film is then
removed allowing mess free installation of the nameplate.
Last revised: 05/24/05