Primer
Selection Guide and Engineering Application Notes *
1)
These primers and adhesion promoters are very low viscosity,
low to medium concentration silane formulations with
a wide range
of functionality.
The A-3 was developed as a high moisture resistant, one part, one
coat, ambient or thermal cure primer for metal with our B-4811
semi-rigid epoxy as an over coat for cathodic protection.
Other materials, such as castable PU, Neoprene,
EPDM, or Nitrile are overmolded to the B-4811 using either the
A-3 primer which
provides very high chemical resistant bonds to metals and glass.
LDPE has also been injection molded to the A-3/B-4811 system using
primer C-21 and a RELTEK proprietary LDPE blend developed for a
new submarine program, which passed a twenty-year accelerated life
qualification testing (ALT).
The A-3 / B-4811 primer/adhesive system provides for
excellent transition from a rigid substrate to a high thermal
expansion polymer.
2) Experiments have shown the combination of metal/primer/epoxy
coating is synergistic and that produced exceptional cathodic
resistance. It has also been shown to have exceptional acid resistance,
and
both boiling water and high 95% / 95 degree C resistance on metal
and glass. That system was the only polymer coating system to
pass
U. S. Navy
cathodic disbondment testing for submarine applications in 1991.
ALT included 7 months exposure in 66 degree C artificial seawater
with daily thermal shock to 6 degree C and monthly pressure cycling
to 2500
PSI. It has resisted breakdown when placed directly in a high
power plasma beam in the formation of a laser beam used for welding
metal
on cars. The system has qualified as an adhesive and coating
and been successfully employed in a number of Navy programs with
testing
to -50 degree C.
3) The A-3 is used with B-482 it to seal large magnesium sonar
elements from corrosion from seawater in a cathodically active
submarine environment demonstrating long life.
4) The A-3 / B-4811 system is used to directly seal semiconductor
chips exposed in a high pH, biologically active, water solution
as part of a microbiological sensor system product. The adhesive
and sealing performance results have "exceeded wildest expectations."
5) From all the experience in using A-3 with adhesives such as
B-4811 semi rigid epoxy, HM-502 thermoplastic adhesive (PE /
Acrylic emulsion), and HM-505 thermoplastic adhesive (PE / Acrylic
solvent
based and solid hotmelt) we can generally say the A-3 has exceptional
moisture resistance as a primer for metals, glass, ceramics,
many polyolefins and engineering plastics.
6) Twenty year ALT in elevated temperature seawater showed no
loss of shear adhesion in bonding HDPE to HDPE and 50% increase
in peel
strength in bonding HDPE to Polyolefin shrink tubing using A-3
primer and HM-502 thermoplastic adhesive.
7) As a general rule, from the chemical design, A-3 is the most
moisture resistant primer followed by A-43 and then by C-6. That
is most apparent on hydrophilic substrates, particularly metals.
It
is much less noticeable on polymer to polymer interfaces because
they tend to form bonds other than oxane which is easily hydrolized.
A-43, C-6 and C-21 are higher concentration and higher reactivity,
especially amine functionality, then A-3. Hence, A-43 bond strengths
are expected to be typically higher with polymer interfaces compared
with A-3, require only one, or maybe two, coats compared to A-3
which requires three to four on some polymers, will be less hydrophobic
than A-3, and will take a little longer to cure than A-3.
8) The primers are IPA based for solvent and low in VOC. A new
VOC exempt solvent is available, TBA, that may be substituted
for the IPA. All ingredients of RELTEK formulations are TSCA
listed.
None of RELTEK formulations are listed.
9) For plastics, bond strengths tend to be very good when using
the A-3 primer and A-43. Glass filled Nylon 66 produced failure
of the nylon substrate using A-3 primer and HM-502 thermoplastic
adhesive.
10) All the polyethylenes, including UHMW, exhibit shear strengths
ranging from 300 PSI -- using the B-4X and B-536 series epoxies
-- to 500 - 900 PSI -- using the HM-502 and HM-505 thermoplastic
adhesives. The same result is obtained with POM (Acetal, Delrin).
Adhesion to some TPE's has been demonstrated.
11) Adhesion to Silicon, Fluoropolymers such as ETFE (Tefzel) and
PVDF, PPO (Noryl), Polyesters such as PBT (Vaylox) and PET (Ertlayte,
Hytrel), PPS (Ryton, Konduit), PolyEtherImide (Ultem), PEEK, PolyAmide-Imide
(Torlon), PolyImide (Vespel), and some styrene blends has been
demonstrated with A-3 and A-43 as a primer.
12) Virgin PP to A-3 to HM-505 to steel produced sheer strength
in testing of 543 PSI. PVDF to A-3 to HM-505 to PVDF yielded
at 641 PSI.
13) Bond joints of rigid PVC to PVC white and gray, ABS to ABS
white and black, and PVC gray to ABS white produced substrate
failure
in lap shear tests at below freezing and ambient, and mixed substrate & cohesive
failure at 140°F using A-43 primer with B-45TH flexible epoxy.
B-45TH epoxy bonds ABS to PVC, without primer, to produce substrate
failure.
14) The A-3 / B-4811 system is used to bond Delrin, Ultem, PPS
and PPO to iron stator coils in electric motors, and forms a
high
chemical and moisture resistant bond. These motors have been
successfully
operated inside natural gas lines coming direct from wells containing
corrosive Sulfur.
15) The A-3 / B-482 system is used to fill and repair cracks
in large PP tanks that hold caustic and acid baths operating
at
ambient
to 40 degree C.
16) The A-43 / HM-505 and B-45TH are used to bond PBT, PEEK,
and fiberglass to Mylar gloss surface and PU foam with substrate
failure of the PU, and mixed cohesive and Mylar (polyester) substrate
failure.
17) The A-3 is used to prime metal for molding with fluoro silicon
PPS and produces high bond strengths. The project is deployed in
space.
18) The A-3 / HM-502 system is used for bonding UHMW to stainless
steel for continuous submersion in hydroelectric dams.
19) The A-3 / HM-505 is used to bond leather to UHMW for an auto-racing
product with bulk failure of the leather in peel tests.
20) Nylon fabric and Gortex fabric peel strength reached 11 PLI
using A-3 / HM-505 as part of a project for the garment industries.
21) An offshore oil equipment supplier uses the A-3 / HM-505
system to bond molded PU parts to flexible PVC substrates for
use in
high shear/high peel wear surface applications on cable deployment
shivs.
22) A Canadian defense contractor identified the A-3 and C-6 as
the only primers to work successfully on highly plasticized PVC
wire and retain the bond over a period of time.
23) Peel strength for HPDE / castable PU (PRC 1592 with high modulus)
ranged from 7.6 to 11.3 PLI using only one coat of A-43 primer
on the HDPE, compared with A-3 in two coats which produced 1.4
PLI in the same test.
24) Customers use the A-3 as a primer on various metals including
aluminum, brass, gold and titanium for molding B. F. Goodrich Estane
TPU. They report bulk failure of the TPU in testing immediately
after molding and no loss of adhesion after months of deployment
at sea. The contractor for a U.S. Navy funded program selected
A-3 as the best primer for Estane molding to stainless steel and
Monel. A major cable assembly producer uses A-3 to prime silicon
rubber, followed with C-31 primer and overmolding with neoprene
rubber. That produces bulk failure of the silicon rubber in peel
tests. They also use A-43 as a primer for molding neoprene and
cast PU molding to LDPE and metal substrates.
25) The A-3 and A-43 primers are used for cable termination applications
to prime neoprene for castable PU overmolding, that yields bulk
rubber failure.
26) Major U.S. and European cable companies are using the A-3 in
priming HDPE and metals with PU and PE molding for their molded
cable systems. These companies, some of the largest in the industry,
use the A-3 with HM-502, HM-505, and B-4811 for sealing high voltage
fiber optic terminations deployed to full ocean depth (17,000 PSI)
with a twenty-year life rating. Bonds are to the fiber, fiber buffer,
MDPE, ceramic and stainless steel. The adhesive systems have provided
both sealing and blocking high voltage corona. The A-3, B-4811
and HM-505 systems are also used for fiber optic cable / sensor
encapsulation.
27) A-3 and A-43 have been used as a primer on Aflas (peroxide
cure), EPDM (peroxide cure), HSN (peroxide cure), Nitrile (sulfur
and peroxide cure) and bonded with B-45TH and B-4682TH flexible
epoxy adhesive.
28) Thermoset plastics demonstrate generally favorable results
from chemical bonding with A-3 and A-43. These typically produce
substrate failure, or bulk failure of adhesive in lap shear tests.
Cohesive bonds are produced with polyolefin shrink tubing, epoxy
and urethane.
29) Thermoplastics demonstrate favorable results from chemical
bonding with A-3 and A-43. Testing shows typical lap shear (ASTM
D3163) strengths of 300 PSI to 900 PSI when used with our HM 505
hot melt adhesive or B-4X series adhesives, sealants, potting and
coating formulations (with and without primers). Tests have included
ABS, PVC, Nylon, PVDF, PPO, PPS, PET, HDPE, UHMWPE, PEEK, PET,
ETFE, PEI, PI, POM (Acetal), PAI, PP.
30) Thermoplastic polyurethane (TPU) shows favorable field results
with A-3; sensitive to injection molding parameters. Customers
report cohesive failure in testing, with A-3 used as primer on
metals for molding TPU (Estane by B.F. Goodrich) and cohesive bond
failure of the TPU after months of exposure in the ocean. Similar
results can be expected from TPR applications, depending most on
the block polymer. Specific material testing is recommended for
each application to ensure compatibility.
31) Plasticized PVC shows favorable results with A-3 and C-6,
mostly A-3 with castable PU and epoxy potting and overmolds.
A-43 is also
excellent and affords a one-coat application. Plasticized PVC
is difficult to bond to due to the plasticizers used in the plastic,
whose job it is to break bonds. That’s how naturally rigid
PVC is made flexible. The plasticizers break up the crystalline
structure, which also break the bonds formed by adhesives. This
is overcome by the use of the A and C products.
32) BONDiT C-52 primer / adhesion promoter provides cohesive
bonds for molding polyethylene to metals and ceramics, including
brass
and aluminum. The bonds are stronger than the polyethylene.
33) Rubber. A-3 has worked well on most rubbers, particularly peroxide
cure types. A-43 is particularly formulated for peroxide, sulfur
and metal cure systems. HM 505 hotmelt adhesive works well in combination
with A-3 and A-43 to form cohesive bonds with most rubbers. The
B-4X epoxy cure series bonds well with and without primer to EPDM,
neoprene and butyl rubbers.
34) RELTEK normal test procedure is to grit blast all surfaces
with #100 AlOx clean grit, wash with isopropyl alcohol, prime
with one to four coats of primer, ambient cure 30 - 40 minutes
or 100 degree C
cure 10 - 15 minutes, followed by application of adhesive and
assembly of bond joint pressed together with finger pressure,
or clamped
with spring clamps, and using 0.007" copper wire for adhesive
gap control.
35) The cure system of an adhesive or overmold material will
have a great deal to do with the environmental resistance of
the bond.
For instance, the A-3 / HM-505 system will provide excellent
moisture resistance including boiling water but is poor with
acoustic
oils, compared with the use of the A-3 / B-4811 system which
has very high
moisture and oil resistance, and with the A-3 / B-4X system which
has moderate moisture and oil resistance. The B-4X adhesive,
sealant, potting epoxy and coatings are specifically formulated
for high
moisture, oil, and acid and alkyl resistance, with excellent
adhesion to a wide range of substrates — with and without
primer.
* These are historical examples,
some of which utilized the now discontinued B-1 or B-9X series
products. Those examples have been
modified for illustration purposes by replacing references to
the discontinued products by references to the equivalent new
and replacement
products in such applications. The BONDiT B-4811 replaced the
obsolete B-1. The B-4X flexible epoxy series replaced the obsolete
B-9X
flexible epoxy series. The new products are based on proprietary
modern resin technology and curing methods that have resulted
in performance improvement over the discontinued products. The
B-1
and B-9X series are no longer manufactured and no stock is available.
(back to top)
