We learn from the past -- this week's editorial looks
at a short history of adhesives and sealants. It describes where we have
been and where we might be going. The list of past accomplishments and
innovations are, indeed, quite exceptional. It is no wonder that with
a past such as this, it is difficult to keep up with the many advancements
in the industry.
With new technology sweeping into business from every avenue, simply keeping
up sometimes feels overwhelming. In the article "Innovations in Adhesives
- Resins" , I try to mention just a few of the new resin technologies
that will hopefully make us more profitable. In 1965, Intel cofounder
Gordon Moore stated that computer speed would double every 18 months.
Now known as Moore's Law, it is applied to almost every growth area. It
also seems to apply to adhesives and sealants. I don't know if my file
cabinet (electronic and otherwise) can hold all of the information.
This seems like a good opportunity to look back as well
as forward. How did we get here? The history of adhesives and sealants
is interesting and probably deserving of a book on its own. It is certainly
a winding road, but one that is filled with innovation and excitement.
Adhesives and sealants were first used many thousands
of years ago. Early hunters may have seen improvement in their aim by
joining feathers to arrows with beeswax, a primitive form of adhesive.
The Tower of Babel was probably built with the aid of mortar and tar or
pitch. Carvings in Thebes (circa 1300 BC) show a glue pot and brush to
bond veneer to a plank of sycamore. Until relatively recently, most adhesives
evolved from vegetable, animal, or mineral substances.
In the early 1900s, synthetic polymeric adhesives began displacing many
of these naturally occurring products owing to their stronger adhesion,
greater formulation possibilities, and superior resistance to operating
environments. However, non-polymeric materials are still widely used and
represent the bulk of the total volume of adhesives and sealants employed
today. Common applications for these non-polymeric materials include bonding
porous substrates such as wood or paper. Casein adhesive (a diary by-product)
and soluble sodium silicate adhesive (an inorganic, ceramic material)
are commonly used in the cardboard packaging industries. Naturally occurring,
bitumen or asphalt materials have been accepted as sealants for many centuries.
The development of modern polymeric adhesives and sealants began about
the same time as the polymer industry itself, early in the 1900s. In fact,
the polymeric and elastomeric resins industry is bound very closely to
the adhesives and sealants industries. The following table summarizes
highlights of the historical development of adhesive and sealant products.
The modern adhesives age began about 1910 with the development of phenol
formaldehyde adhesives for the plywood industry. Adhesives and sealants
found important markets in the construction industry, which was providing
much of the growing infrastructure in the U.S. at the time. Significant
growth then again occurred in the 1940s and 1950s with the development
of structural adhesives and sealants for the military aircraft industry.
Because of their exceptional strength-to-weight ratio, the development
of modern adhesives and sealants is closely related to the history of
the aircraft and aerospace industries. With successful experiences in
these entry industries, it was soon realized that adhesives could be used
to economically replace mechanical fastening methods such as welding,
brazing, or riveting. It was also realized that sealants could be used
to provide additional function and value to products in industries ranging
from transportation to construction.
Decade of Commercial Availability
Pressure sensitve tapes
Phenolic resin adhesive films
Polyvinyl acetate wood glues
Acrylic pressure sensitive
||Tougheners for thermoset resins
Waterborne contact adhesives
Formable and foamed hot melts
||Polyurethane modified epoxy
Moisture cured polyurethanes
Curable hot melts
The science of adhesion is now well accepted, and the basic rules and
methods for achieving high performance joints have been well established.
The industry has a strong foundation of formulations and processes. Today,
many of the new adhesive and sealant developments are focusing on production
cycle time and cost; environmental enhancement; or application to new
substrates, such as engineering plastics, advanced composites, and ceramics
that are rapidly gaining acceptance.
Development efforts supporting adhesives and sealants are directed to
optimizing the manufacturing and assembly processes. For example, automated
meter, mixing, and dispensing equipment and weld-bonding adhesives have
been perfected to reduce production time in high manufacturing operations.
New adhesives and sealants are often applied with robotic equipment to
further enhance productivity. UV curable adhesives have been developed
to take advantage of their ease of application, elimination of mixing
and heat curing, and elimination of liquid solvent. Ultrasonic and other
fast thermal welding techniques have found a receptive home in the high-volume
transportation industry. Microwave assisted drying of water-based adhesives
and new hot melt systems have been developed to make bonding more agreeable
to the manufacturing world.