HIGH PERFORMANCE EPOXY BASED LAMINATING ADHESIVE

COLLE EPOXYDIQUE A HAUT RENDEMENT, POUR LAMELLATION

English Abstract

PATENT
ABSTRACT
A high performance laminating adhesive material is
prepared using one or more epoxy components which inter-
react with a high molecular weight polyester component
through a two-stage reaction sequence. The first stage of
the sequence is the reaction of a isocyanate component with
a polyester component. The stage of the sequence is the
reaction of the isocyanate/polyester component with the
epoxy component(s). The result of the reaction process is
an adhesive material providing a flexible, high temperature
resistant, fully crosslinked adhesive with good Z-axis sta-
bility without the evolution of by-products. The adhesive
material has application to the bonding of polyimide films,
copper or other metal foils and hardboards for use in the
manufacture of flexible, hardboard or multilayer substrates
as well as surface to surface bonding of other materials.

Claims

9 PATENT
CLAIMS:
1. The process for providing an adhesive material
which comprises:
reacting an isocyanate component with at least 1
polyester compound;
and reacting a isocyanate/polyester component resulting
from said isocyanate/polyester reacting step with at least
one epoxy component from the groups of bis epi and novolac
epoxy components.
2. The process for providing an adhesive
material of Claim 1 further comprising:
mixing said isocyanate/polyester component with said
epoxy compound and applying a resulting mixture to a
location requiring said adhesive material prior to reaction
between said isocyanate/polyester component and said at
least one epoxy component.
3. The process for providing an adhesive
material of Claim 2 further comprising:
applying said resulting mixture between substrates to
bond said substrates, wherein said substrate are selected
from the group including film substrates, foil substrates
and hardboard substrates.
4. The process for providing an adhesive
material of Claim 1 further comprising;
using 50% - 90% by weight of the said polyester
compound and 90% - 50% by weight of said at least one epoxy
compound.

PATENT
5. The process for providing an adhesive
material of Claim 1 further comprising:
selecting said polyester compound from the group of
high molecular weight hydroxyl terminated polymer.
6. The process for providing an adhesive
material of Claim 1 wherein said reacting said epoxy
component with said isocyanate/polyester component involves
heating a mixture of said epoxy and said isocyanate/poly-
ester components to a temperature between 250°F and 400°F.
7. An article having two surfaces bonded
together in accordance with the process for providing an
adhesive material of Claim 1.
8. A composite article with film to film
bonding, foil to foil bonding or foil to film bonding having
surfaces bonded together in accordance with the process of
Claim 2.
9. The process of providing an adhesive material
of Claim 1 wherein said isocyanate component, said polyester
component and said epoxy component are mixed together prior
to reacting of components.
10. An adhesive composite for application to
surfaces to be bonded together prepared in accordance with
Claim 2.
11. The process for providing an adhesive mater-
ial of Claim 1 wherein said reacting said isocyanate/poly
ester component with said at least one epoxy component

11 PATENT
includes reacting -?- group in the formed urethane linkage
with the epoxide ?-c groups of the epoxy components.
12. A composite structure comprising:
at least a first and a second structure; and an
adhesive material bonding a first surface of said first
structure to a first surface of said second structure, said
adhesive material including;
an isocyanate component,
a polyester component, and
at least one epoxy component chosen from the group of
bis-epi epoxy family and the novolac epoxy family.
13. The composite structure of Claim 12 wherein
said first and said second structures are chosen from the
group consisting of polyimide films, metal foils and
hardboards.
14. The composite structure of Claim 13 wherein
said polyester component is a high molecular weight hydroxyl
terminated polymer, said polyester component and said
isocyanate component having a reaction take place prior to a
reaction involving said at least one epoxy component.
15. The composite structure of Claim 14 wherein a
isocyanate/polyester component resulting from said reaction
between said polyester component and said isocyanate and
said at least one epoxy component are applied between said
first structure first surface and said second structure
second surface before a reaction between said isocya-

12 PATENT
nate/polyester component and said at least one epoxy
component has taken place.
16. The composite structure of Claim 15 wherein
said composite structure is heated to a temperature between
250°F and 400°F to permit a reaction between said isocya-
nate/polyester component and said at least one epoxy com-
ponent to take place.
17. The composite structure of Claim 16 wherein
said reaction between said isocyanate/polyester component
and said at least one epoxy component includes a reaction
between isocyanate/polyester <IMG> groups and epoxy <IMG>
groups.

Description

2~
PATENT
A HIGH PERFORMANCE EPOXY BASED LAMINATING ADHESIVE
by
Thomas F. Gardeski
and
Diane G. Novak
BACKGROUND
During the past quarter century, the growth of the
electronic circuits industry at an unrivaled pace has resul-
ted in the development of higher performance materials of
construction. However, with the development of higher per-
formance materials of construction has not resulted in thedevelopment of corresponding high performance adhesive
materials and systems to bond the materials of construction
together, especially in severe environmental conditions
found in under-the-hood automotive and military applica-
tions. Adhesive materials and systems that are currentlyavailable meet somP of the requirements for such properties
as peel strength, chemical resistance, moisture resistance,
high temperature stability, dimensional stability especially
in the Z-axis direction and ease of processing, but typic-
ally fail to meet one or more of the requirements for one ormore of the properties.
A need has therefore been felt for an adhesive
material that meets all the requisite property requirements
for severe environmental conditions while retaining the ease
of application.

Z~ 3
2 PATENT
SUMMARY
It is an object of the present invention to pro-
vide an improved adhesive material.
It is a feature of the present invention to pro-
vide an improved material suitable for US2 with electronicconstruction materials.
It is yet another feature of the present invention
to provide an adhesive material that requires a two stage
reaction process for bonding.
It is yet a further feature of the present inven-
tion to combine an isocyanate component, a polyester compo-
nent and one or more epoxy components using a two stage
reaction to provid~ a high performance adhesive material.
The foregoing and other features are accomplished,
according to the present invention, by combining at least
one epoxy component chosen from the flexible bis-epi and the
hard novolac epoxy families and at least one high moleculax
weight polyester component along with an isocyanate cure
mechanism. The isocyanate curing agent and the polyester
component interact in a first reaction stage. The isocya-
nate/polyester compound resulting from the first reaction
stage and the epoxy components are combined. The resulting
combination can be applied to a surface of a laminate layer
or another first surface. A second surface can be placed in
contact with the first sur~ace and a second reaction stage
permitted to take p]ace, forming the high performance bond.

3~
3 PATENT
These and other features will be understood by the
reading of the following description.
DESCRIPTION
The composition of materials of the present
invention comprises at least one and preferably two epoxy
components selected from the flexible bis-epi and hard
novolac families, such as Celanese Epi-Rez-5132 and Dow
D.E.N. 438 respectively; at least one high molecular weight
polyester component such as DuPont's 49002 or DeSoto's 301
resin systems; and an isocyanate cure mechanism such as
Upjohn's PAPI-135 or Mobay's Mondur MRS.
The cure sequence of the present invention
consists of first reacting the isocyanate component with the
hydroxyl groups which terminate the polyester component as
shown in the following reaction sequence known in the
related art.
HO~R)XOH + OCN-~C6H4 (CH2)]n N-C-O
1 R.T. to ~
P~
- o-~CH2) X- O-C-N--~C6~ -(CH2)~n
H
where (R)x represents a high molecular weight polyester
repeating unit with alcohol type hydroxyl end group func-
tionality. This reaction takes place at room temperature

2~ 3~
4 PATENT
slowly and more rapidly with heating of the composition to
approximately 250P. The secondary reaction, which is
unique to the present invention, is comprised of reacting
the - - group in the formed urethane linkage with the
epoxide Cf~C groups of the epoxy components as follows:
- O-tR)X O-C-N-~C6H4 -(CE~2)~n + CH2 - CH - Rx - CH -~CH2
H ¦ ~(250-400~F) ~ O \ 0
o
- 0-~CH2)x O-C ~ C~H4-(CH2)~n
H - C - H
H - C - 0 H
~Rx
H - IC - O H
H - C - H
-0-~CH2)X O-C-N ---[CeH4 (CH2)]n
where Rx in this formula represents the bis epi and/or
novolac epoxy structures as shown below:
CH2-CH ~ CH2-~-0-0-C-0-OCH2-CH-CH23-n- -O-0-C-0-OC~ ~ CH-CH2
CH3 CH3
"BIS-EPI" EPOXY
CH2- CHCH2-O r ~~ ~O~
l OCH2--~H--CH2 O ~CH2-CH-~ CH2
~ -CH2- - ~ CH2
, 0

2(:~0a~30
PATENT
"NOVOLAC"_EPOXY
Example of the Process
The components of the adhesiv~ material of the
present invention, according to one embodiment, are: a
polyester resin having a solids content of 17-20~ composed
of DuPont 49002 base in a solvent mixture of 90~ methylene
chloride to 10% cyclohexanone by weight; an epoxy novolac at
85~ solids composed of Dow DEN 438-EK85 in methylethylke-
tone; and a bis-epi epoxy composed of Celanese Epi-Rez 5132
at 100% solids; and a curative component of a polyfunctional
isocyanate sold by Mobay under the trade name Mondur MRS.
The components can be combined according to the following
two procedures:
Procedure l) The adhesive coating composition is made by
adding 80% by solids of the polyester component to 10% by
solids of the epoxy novolac to 10% by solids of the bis-epi
epoxy to 1.2 parts by weight of the isocyanate in an open
container without agitation. The composition is then agi-
tated well for 1-5 minutes. The container is then capped
with an air-tight lid for 30 minutes to allow for the onset
of isocyanate/polyester reaction; or

3~)
6 PATENT
Procedure 2) The polyester and isocyanate are combined,
thoroughly mixed, then allowed to stand at room temperature
for a minimum of 30 minutes prior to the epoxy additions to
allow onset of the isocyanate/hydroxyl reaction.
The adhesive coating composition resulting from
either of the foregoing procedures is then applied by means
of the reverse roll coating technique to a 1 mil polyimide
film to yield a 1 mil thick dry coat weight. Drying (i.e.,
removal of the solvents) is accomplished through a 75 foot-3
zone oven at 212F and 25 feet per minute. The coated
substrate is then positioned next to the treated side of
1 oz. copper foil, wherein the copper foil surface is
treated with Oak CMC-lll compound (to enhance bondability).
The polyimide film and copper foil are heated to 300F to
325F with an applied pressure of 80 psi (pounds/square
inch) to 120 psi through a coater/laminator combining
station as part of a continuous operation. The resulting
composite is rolled onto a 6" core, left at room temperature
for one to seven days then post cured as follows:
2 hours @ 150F
2 hours @ 275F
2 hours @ 350F
The resulting composite structure exhibited the properties
shown in Table I when tested per ANSI/IPC-FC-232B and 241 B
procedures:

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7 PATENT
Initial Peel 20 PLI
Peel After Solder 21 PLI
Chemical Resistance
M~K 21 PLI
TOL 20 PLI
IPA 21 PLI
Tlll/MC 21 PLI
Solder Float Pass
Aging (96 hrs @ 275F No Bond Strength
in air circulating oven) Change
where;
PLI = Pounds per lineal inch
MEK = Methylethyl ketone
TOL = Toluene
IPA = Isopropylalcohol
Tlll = Trichloroethylene
MC = Methylene Chloride
TABLE I
-~
The polyester compound of the preferred embodiment
is a high molecular weight hydroxyl terminated polymer,
while the curative compound is a polymeric isocyanate. In
the preferred embodiment, a combination of a flexible bis-
epi epoxy compound and a hard novolac epoxy compound are
both included to achieve the properties of both compounds.
The second reaction provides a fully cross-linked network
between the - - groups formed in the first reaction and
the ~-~ in the epoxy components without evolution of by-
products.

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8 PATENT
The present invention provides what is believed to
be the first adhesive system with extremely balanced proper-
ties and the added benefit of superior Z-axis stability
through a unique and here-to-now undescribed cure mecha-
nism. More specifically, the present invention provides thefirst epoxy based laminating adhesive which can be continu-
ously processed and cured without the evolution of by-pro-
ducts to provide a flexible bond-ply with overall properties
superior to any currently available system with the added
property of excellent Z-axis stability. The adhesive mater-
ial is applicable to film substrates (e.g., polyimide), foil
substrates (e.g., copper) and hardboard substrates (e.g.,
FR4 (fiberglass impregnated) hardboard).
The foregoing description is included to
illustrate the operation of the preferred embodiment and is
not meant to limit the scope of the invention. The scope of
the invention is to be limited only by the following claims.
From the foregoing description, many variations will be
apparent to those skilled in the art that would yet be
encompassed by the spirit and scope of the invention.