Hot Melt Adhesive Applications

HOT MELT ADHESIVE APPLICATIONS

Adhesives are widely used in many industry sectors, where their use is essential in
manufacturing thousands of everyday products.

There are many kinds of formulations and methodologies capable of performing bonding or the
joining of various substrates.

The adhesive material must be capable of wetting the surface to which it is applied, at least for an
instant, be used in a relatively thin layer, so that it forms a joint capable of transmitting stress and
be both strong and lightweight.
Adhesives often provide advantages over mechanical fastening techniques as a result of flexibility,
versatility, weight reduction, or labor savings.

Nearly 80 percent of the demand for all adhesives comes from the packaging and construction
industries.
Several industrial sectors and applications in which adhesives are commonly used.

Common Uses of Adhesives

Industry Applications

Construction
Manufacture and installation of laminated wood panels, prefabricated beams, wall panels, general
building construction; installation of flooring, tile, carpeting, ceiling panels and wall coverings.

Consumer goods
Manufacture of office supplies, hobby and model supplies, and stationery.

Nonrigid bonding
Bonding of woven and non-woven fabrics; manufacture of athletic shoes, rugs, filters, books, and
sporting goods.

Packaging
Manufacture of cartons, boxes and corrugated boards; bags, envelopes, disposable products
(diapers, paper products); cigarettes; and labels and stamps.

Rigid bonding
Manufacture of appliances, electronics, household products and furniture.

Tapes
Manufacture of all tapes, including those used for surgery, packaging, industrial applications,
consumer applications and masking applications.

Transportation
Aircraft and aerospace structural assemblies; automotive, truck, boat, and bus assembly; mobile
home manufacturing.

Adhesives Market Trends
The need for high-strength bonding materials is expected to grow substantially over the next
several years. U.S. demand for adhesives is expected to reach 14 billion pounds and a market
value of $9 billion next year. In the U.S., the
packaging and construction industries are responsible for 80% of adhesives demand, and the
packaging market continues to grow.

Within the packaging industry, corrugated boxes are the single largest adhesive-consuming
product within the sector, and pressure sensitive adhesives are also used extensively in this
industry.
U.S. consumption of pressure sensitive products is projected to grow at an average annual growth
rate of 7-8%. Of these pressure sensitive adhesives, labels and decals are the most likely to have
the highest growth rate, followed by tapes and miscellaneous products.

Environmental/Safety Issues for Solvent-based Adhesives
There are significant environmental issues associated with the use of solvent-based adhesives.
Solvents such as toluene, methyl ethyl ketone (MEK), and trichloroethane (TCA, also known as
methyl chloroform), typically act as carrier
fluids for the bond forming materials comprising a conventional solvent-based adhesive
formulation. These solvents are volatile organic compounds (VOCs), which makes them ideal as a
carrier fluid, but also causes environmental and
safety concerns. Solvents such as toluene, MEK and TCA are subject to regulation as Hazardous
Air Pollutants (HAPs) under the Clean Air Act Amendments (CAAA), because they are suspected of
causing cancer, birth defects, or nervous
system damage, and are emitted (at varying degrees) during application, product life and disposal.

Additionally, TCA is a halogenated compound that depletes the stratospheric ozone layer; U.S.
production and importation of TCA ended as part of the phase out required by amendments to the
Montreal Protocol. VOCs also contribute to
the formation of ground-level ozone smog that can cause respiratory damage, and are regulated
under Occupational Health and Safety Administration (OSHA) standards as well.

The solvent carrier fluid is designed to evaporate after application to the substrate and during the
curing process. Most solvent air emissions occur during application. Other solvent air emissions
occur during the storage, transfer,
formulation, coating, drying and curing, and equipment cleaning process stages. For example,
before the ban on production of ozone-depleting solvents, the Source Reduction Research
Partnership estimated that 26,000 metric tons (MT) of TCA were used in adhesive formulations and
5,000 MT of halogenated solvent, primarily TCA, were consumed annually in cleaning adhesive
spray application equipment.

Cleaning equipment actually generates the largest amount of liquid solvent wastes during the
adhesive application process.

Environmental statutes and international treaties affecting adhesives include: U.S. Clean Air Act;
Regulates ground-level ozone smog precursors such as VOCs. This Act also regulates 188
chemicals that emit HAPs. At least 50 solvents
used in adhesives are found among these 188 chemicals. The Ozone Depletion rules of this Act ban
the manufacture and use of certain substances, including TCA

United Nations Economic Commission for Europe Convention on Trans-boundary Air Pollution
Commits to reducing VOC emissions 30 percent.

The U.S. Environmental Protection Agency (EPA) also has an initiative that targets specific sectors,
mandating compliance with certain Maximum Achievable Technologies (MACT) Standards, and the
adhesives sector is one of the MACT
target categories. Generally, a MACT standard does not ban a HAP from use, but sets a level of
control designed to protect public health. EPA has not yet established the MACTs for the
adhesives sectors, but there is a congressionally
mandated deadline for setting these standards.

Drying and Curing
Drying and curing of solvent-based adhesives relies on large ovens to evaporate carrier fluids and
cure the adhesive. Eighty-five to 90 percent of the carrier fluid must be evaporated during drying
and curing. This requirement leads to longer process times. Additionally, ovens consume plant
floor space that could be used for other purposes.

In response to regulatory drivers described above, manufacturers have developed reformulated
products with either reduced HAP-emitting solvent content or HAP-free content.

The end-use market trend appears to lean toward zero-emission adhesives such as hot melt
adhesives.

The hot melt adhesives have been projected to grow at a rate of 8-12% per year.

Hot Melt Adhesives Technology Review

Pacific Northwest Pollution Prevention Resource www.pprc.org