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Adhesives
used in printfinishing are classified
according to the source from which they are derived
Starch
Derived
Pastes
White or light
coloured, viscosity ranges from fluid to very heavy and
stiff.Low solids,
slow setting, good humidity resistance. Most are acid pH,
borated pastes or alkaline.
Uses: Bag
bottoms, lap paste, paper laminating, litho labelling,
convolute tube winding.
Dextrins Tan-brown,
very tacky, fluid, usually acid pH and high in solids.
Uses:
Remoistening adhesives, bottle labelling, cold pick-up for
labels.
Borated
dextrins White
to dark brown, most are fluid, filmy, moderately fast
setting and very
tacky. Alkaline pH. Fairly good humidity resistance.
Uses: Case and
carton sealing, tube winding, bag seams, wrapping,
laminating, lap paste.
Jelly
gums Rubbery,
cohesive, gummy, very tacky. Good humidity resistance.
Excellent glass
adhesion and non-crystallising characteristics. Most on
alkaline side for better stability and adhesion to coated
glass. Colour varies from white to amber or red-brown
depending on composition and pH.
Uses:
Automatic bottle labelling.
Protein
derived
Animal
glue Tan-brown
in colour, and supplied as granules or as pre-plasticized
cakesor liquids. Considered very tacky and rangy. Usually
run hot at about 140 F.
Uses:
Set up box light wrapping and stripping, tube winding,
gummed Remoistening tape.
Casein
Fairly light colour,
moderate to high water resistance, and good tack.May require
ammonia or alcohol as diluent. Dried films are usually
soluble in alcohol
alkaline solution. Usually supplied at alkaline pH level.
Uses:
Ice-proof label adhesive for cold drink bottles, foil
lamination (compounded with latex).
Synthetic
resin adhesives
Emulsion
Based on polyvinyl acetate and copolymers thereof. White
coloured, range very thin and fluid to heavy. Acid pH.
Strong tough films, usually water resistant but can be made
water sensitive for easy clean up. Fast setting, low odour,
taste, toxicity. Good machining, stable, good aging. Grease
resistant.
Uses:
Case and carton sealing and forming, tube winding, trays,
cups, bag seam and seal, carton windows.
Latex
Based on natural or synthetic rubber. Usually white to tan,
alkaline pH, some have ammonia odor. Some have self-sealing
property. Broad adhesion, relatively poor stability and
machining. Should avoid copper (brass, bronze, etc.)
contact, as this accelerates degradation.
Uses:
Self seal bags, envelopes and wrappers. Film bag duplexing,
waxed bag seam bottom, foil-paper lamination.
Hot
melt Solid
blends of polymer, resins, plasticizers and waxes,
considered 100%
solids. Must be heated to liquefy and run. Fastest setting
adhesive. Most common forms: slats, pellets, billets or
bulk. Broad adhesion. Colour ranges from white to brown.
Uses: Case and
carton sealing, trays, bag seam and seal, labelling cans and
bottles coatings for pressure sensitives labels, paper type
and wrapping paper lamination.
Solvent
borne Also
called solution or lacquer adhesives. A broad description of
a wide range of polymers and modifiers dissolved in organic
solvents. Usually mobile liquids, colour ranges from
water-white to brown. Usually fast drying depending on
solvent blend. Most are flammable. Films range from soft,
weak and tacky, to tough, hard and chemically cross linked.
Most are simple reactive systems, but some can have
properties enhanced by curing with coreactants (2 part
systems) or moisture cure one-part systems ( certain
urethanes).
Uses:
Graphic arts lamination of film to film, paper or foil.
Flexible, packaging,laminating film/film for pouches or
bags. Heat seal coatings such as blister pack. Pressure
sensitive coatings for labels and tapes.
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