Product Fact Sheet
EPI-REZ鈩? Waterborne Resins for High Performance Nonwovens 1
SC: 2268 Re-issued: August 2005
Abstract Epoxy resins are well known in the coatings, aerospace and electrical industries for their high
performance properties. They exhibit superior chemical resistance, high mechanical strength,
adhesion to a wide range of substrates and good thermal properties. In the past, epoxy
systems have relied on organic solvents as carriers. Recent technology has made available a
number of waterborne epoxy dispersions which are attractive alternatives to the solvent
based resins. This waterborne technology now makes epoxies suitable for several
nontraditional application areas, including nonwoven binders, fiber finishes, chemical
resistant textiles and adhesion promoters for industrial fabrics. This technical bulletin will
provide general information on formulating with waterborne epoxies and a performance
comparison with formaldehyde based resins.
Introduction Some of the new technologies emerging for nonwoven products require modifications of the
traditional high performance binders. In addition, novel fiber types and processes place new
demands on resin binders. In the past, phenolics, urea formaldehyde resins, melamines and
some acrylics have been used for high performance nonwovens. The waterborne epoxy resins
now available are suitable for various types of industrial nonwoven products, including
filtration media, electrical insulating materials and building products.
The term epoxy or oxirane refers to a chemical group consisting of an oxygen atom bonded
with two carbon atoms which are also bonded in some way. The bulk of epoxy resins used
today are based on bisphenol A and have the basic structure shown in Figure 1.
When n=0, there are no OH groups present and the resin is a viscous liquid suitable for 100%
NV applications, such as filament winding, potting compounds and adhesives. Above n=1,
the resins are brittle solids until they are crosslinked with a suitable curing agent. The OH
groups can be used as reactive sites in the higher molecular bisphenol A based epoxies.
1
Based upon paper by Kathy L. Briggs, 鈥淲aterborne Epoxies for High Performance Nonwovens鈥?, February 1989.
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Figure 1 / Bisphenol A Epoxy Structure 鈥? EPI-REZ鈩? Resin 3522-W-60
Figure 2 / Cure of Epoxy Resins
Epoxy Resins 鈥? One of the most valuable characteristics of epoxy resins is their versatility in formulating.
General (cont.) Conversion to the thermoset stage can be accomplished via catalytic or stoichiometric
mechanisms to form linear chains or highly crosslinked networks. Cure can be obtained
at ambient or elevated temperatures, depending on the curing agent used with the epoxy.
Some of the most widely used curatives are polyamines, anhydrides, polyamides, mercaptans,
2
phenolic resins, tertiary amines and Lewis acids . Most of the epoxy curing mechanisms
proceed without the evolution of by-products as shown in Figure 2.
Epoxy resins can be used with other polymer types to form a variety of heteropolymers or
alloys. A number of resinous modifiers have been evaluated in connection with epoxies.
Vinyl resins are used to improve the impact resistance and peel strength in adhesive for-
2
mulations . Urethane and rubber modifications are sometimes used to toughen epoxies and
provide more elastomeric character to the polymer. Incorporating a small amount of epoxy
in acrylic resins provides a route to thermosetting acrylics without the evaluation of formal-
dehyde or other condensation products. Epoxies can also be used to enhance adhesion
characteristics and thermal resistance of other polymer types.
2
Lee, Henry and Kris Neville, Handbook of Epoxy Resins, McGraw-Hill, 1967, pg. 1.
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Waterborne The current waterborne epoxy technology is the result of several years of surfactant and
Epoxy Resins process development. Previous attempts involved the use of cosolvents, water sensitive
surfactants or chemical modifications which destroyed the epoxy functionality. Most of these
approaches produced dispersions which were inferior to the solvent based counterparts.
Today鈥檚 technology provides a means of dispersing solid and liquid epoxy resins with extremely
low levels of nonionic, reactive surfactants.
Advantages of these systems are as follows:
鈥? Excellent volatile release
鈥? Adhesion to a wide range of substrates
鈥? Can be formulated to be formaldehyde free
鈥? Good electrical properties
鈥? Compatible with other resin types
鈥? Two phase for longer pot life
鈥? Shear stable
鈥? Can be used with conventional epoxy curatives
鈥? Uniform particle size
鈥? Low water sensitivity
The types of dispersions commercially available are a bisphenol A based epoxy, a urethane
modified epoxy, a rubber-modified epoxy and a novolac epoxy. They all require a curing
agent or catalyst to be converted to a thermoset stage. For the sake of simplicity, only one
basic bisphenol A epoxy dispersion, EPI-REZ Waterborne Resin 3522-W-60, will be covered
in detail.
Physical The physical properties of EPI-REZ 3522-W-60 are shown in Table 1. The typical viscosity is
Properties excluded from this table because values are highly dependent on shear rate. Figure 3
illustrates the effect of spindle speed and temperature on Brookfield viscosity readings. This
rheology is typical of emulsions having a particle size in the one micron range.
Table 1 / Physical characteristics of EPI-REZ鈩? Resin 3522-W-60
Property Value
Weight per epoxide 635
Solids, percent 60
pH 7
Particle size, average (microns) 1.3
Weight/gallons, lbs. 9.2
Volatile content Water
Surface tension (dynes/cm) 50
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Figure 3 / Viscosity of EPI-REZ鈩? Resin 3522-W-60
Physical The resin particles in the bisphenol A epoxy dispersion are solid at room temperature, so air
Properties (cont.) drying of the resin results in a nontacky opaque film. The particles will fuse at approximately
170 掳F. When a water soluble curing agent is used with this resin, surprisingly long pot life
characteristics are obtainable due to the phase separation of the two components.
Surface Tension Surface tension data is useful in formulating for adhesion to specific substrates and also in
obtaining continuous coatings on fibers which are hard to wet. In general, a formulation should
have a surface tension less than or equal to the surface energy of the substrate. Table 2
shows the surface tension of the EPI-REZ 3522-W-60 and the effect of various curing agents.
Some of the amine and polyamide resins are highly effective wetting agents for the
waterborne resins. The surface tension can also be lowered by incorporating wetting agents
such as Aerosol OT (Rohm & Haas) or fluorosurfactants.
Table 2 / Surface Tension of EPI-REZ鈩? Resin 3522-W-60
Curing Agent Surface Tension (dynes/cm)
None 50
Amine adduct 30
Amidoamine 22
Polyamide 26
2-methylimidazol 50
Triethylene tetramine 52
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Curing Agents Most of the traditional epoxy curing agents can be used with the waterborne products.
Exceptions, of course, are those curatives which are not hydrolytically stable, such as
anhydrides.
When cured with catalysts which promote homopolymerization, the epoxy dispersions form
rigid, chemical resistant structures. Substituted imidazoles or zinc fluoborate are typically
used for catalytic cures of the waterborne epoxies. Polyamides are recommended for
flexibility, acid resistance and adhesion to thermoplastics. Some of the aliphatic amine
adducts provide an optimal balance of pot life and low temperature cure and offer high
solvent resistance.
For maximum thermal properties and B-stage capability, a formulation containing
dicyandiamide as the curing agent is generally used. B-stage stability is important when a
product
must be formed or laminated in a subsequent curing step. Examples are filter media which is
pleated and electrical insulating materials which are molded and cured under heat and
pressure. The saturated product supplied by the nonwoven manufacturer must be stable at
this intermediate stage of cure to ensure reflow and formability characteristics in the final
processing step.
To make a formulating recommendation for a specific application, the pot life requirements,
bake schedule, performance characteristics and mode of application must all be considered.
Table 3 shows typical combining ratios, pot life and cure temperatures for several of the
crosslinkers used with EPI-REZ Resin 3522-W-60.
Table 3 / Curing Agents for EPI-REZ鈩? Resin 3522-W-60
Recommended Recommended cure
level - phr temperature (掳F)
Curing Agent Pot life, days
Amine adduct 4.0 225-400
2
Polyamide 12.0 250-400
9
Amidoamine 8.0 250-400
9
Dicyandiamide 2.5 300-400
>10
2-methylimidazole 2.0 250-400
2
Filter Media Study Study I 鈥? Cellulosic substrate
Water based epoxy formulations were evaluated as saturants for cellulosic filter media using
tensile strength as a screening tool. The formulations which looked best in that evaluation
were also tested for burst strength.
Since phenolic resins are the most widely used class of resins in filtration products, a standard
solvent based phenolic was used for comparison. Three waterborne epoxies were chosen
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Filter Media Study for the study, EPI-REZ 3522-W-60, EPI-REZ 5520-W-60, and EPI-REZ 3519-W-50. They were
(cont.) formulated with polyamides and catalytic type curing agents. Only those systems which
provided more than 48 hours stability were included in the study.
Raw stock with a base weight of 60 pounds per 3000 square feet was saturated to obtain a
final resin content of 25%卤1%. The sheets were cured 10 minutes at 350 掳F. One inch strips
of saturated paper were exposed to the conditions listed in Table 4, then tested for tensile
properties on an Instron. The data in Table 5 reflects those formulations which exhibited
greater than 50% wet strength retention and good resistance to acid or hydraulic fluid.
The epoxy resins were comparable to the phenolic for resistance to hydraulic fluid. The
urethane modified and rubber modified epoxies were significantly better than the phenolic
for acid resistance.
Table 6 shows the burst strengths of the saturated papers used in the tensile strength
retention study. The results indicated the epoxy systems offered a much tougher and less
brittle matrix.
Table 4 / Filter Media Study I: Tensile Strength Test Conditions
Dry No conditioning
1
Wet 1 minute in 1% Triton X-100
Acid 3 hours in 5% hydrochloric acid, R.T.
HF 24 hours in hydraulic fluid, 200 掳F
1
Supplied by Rohn & Haas
Table 5 / Filter Media Study I: Tensile Strength
Initial
% % %
tensile
Retention
Curing strength Retention Retention
(HF)
Resin Agent (lbs/In2) (Wet) (Acid)
EPI-REZ Resin 3522-W-60 45 56
Polyamide 47 55
Bisphenol A epoxy
EPI-REZ Resin 5520-W-60 71 53
Polyamide 51 59
Urethane modified
EPI-REZ Resin 3519-W-50 76 53
Catalytic 51 57
Rubber modified
Phenolic Resin 56 39 51
鈥? 53
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Table 6 / Filter Media Study I: Bursting Strength
Mullen burst strength
Resin Curing Agent (lbs/In2)
EPI-REZ Resin 3522-W-60 Polyamide 57
EPI-REZ Resin 5520-W-60 Polyamide 50
EPI-REZ Resin 3519-W-50 Catalytic 46
Phenolic Resin -鈥? 27
Study II 鈥? A similar study was conducted on needle punched polyester, evaluating the effect of hot acid
Polyester and alkali solutions. Since polyester is more chemical resistant than cellulose, more
Substrate
severe conditioning was possible. Samples were saturated to achieve a 15% add on and
cured ten minutes at 350 掳F. They were exposed to 5% solutions of hydrochloric acid and
sodium hydroxide for two hours at 210 掳F. A self-condensing melamine and a resole type
phenolic resin were included in the tests. Tensile strength retention and weight loss were
the criteria for conclusions in this study.
Amine and polyamide cured epoxies were marginally better than the phenolic for acid
resistance and notably superior for alkali exposure. The melamine resin exhibited very poor
chemical resistance, with greater than 10% weight loss in both hydrochloric acid
and sodium hydroxide.
Summary Current waterborne epoxy technology provides high performance polymer systems free of
organic solvents and formaldehyde. The chemical resistance, thermal properties and adhesion
characteristics of these epoxy resins make them attractive for filtration media, electrical
grade papers and nonwovens utilizing exotic fiber types. These resins also provide an
alternative for industries faced with new EPA guidelines or increased emphasis on
workplace safety. Their utility has been proven in wet end processes, as well as saturating
and spray applications. Hopefully, epoxy resins will provide a route to development of new
applications for nonwoven products.
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