A HIGH PERFORMANCE EPOXY BASED COVERLAY AND BOND PLY ADHESIVE WITH HEAT ACTIVATED CURE MECHANISM

REVETEMENT EPOXYDIQUE, A HAUT RENDEMENT, ET COLLE DE LAMELLATION THERMODURCISSABLE

English Abstract

A high performance laminating coverlay, and bond
ply adhesive material includes 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 reaction sequence includes a reaction between
an aziridine cure component and a polyester component. The
second stage of the sequence involves a reaction between the
aziridine/polyester component and the epoxy component(s).
The resulting adhesive material provides a flexible, fully
cross linked adhesive material with good Z-axis stability
and without the evolution of volatile by-products. This
resulting adhesive material can be used in bonding polyimide
films to etched circuit patterns to provide a high
temperature resistant, solvent resistant, moisture
resistant, insulating material with good flow properties
under normal elecronic circuit processing and environmental
conditions. The adhesive material can be used as a bond ply
adhesive material for flexible base, hardboard, and
multilayer electronic circuit material applications, as well
as surface to surface bonding of other materials. In
addition, the adhesive material, prior to the second
reaction, is stable and has a long shelf life.

Claims

11

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composite structure comprising:
a first construction material;
a second construction material; and
an adhesive material between a first surface of said
first construction material and a first surface of said
second construction material, said adhesive material
including:
(a) the reaction product of an aziridine with at
least one polyester compound having a melting
point of at least about 150°C and being the
reaction product of at least one aromatic diacid,
at least one aliphatic diacid, at least one diol
and at least one triol or higher polyhydric
alcohol; and
(b) an epoxy component selected from the family
of electronic grade resin epoxy components.
2. The composite structure of claim 1 wherein said first
and said second construction materials are chosen from the
group comprising polyimide films, metal foils and
hardboards.
3. The composite structure of claim 1 wherein said
electronic grade resin component is a tris methane novolac
epoxy component.
4. The composite structure of claim 1 wherein said epoxy
component includes at least one additional epoxy component


12

selected from the groups of bis-epi epoxy components and
novolac epoxy components.
5. The composite structure of claim 1 wherein said
aziridine component and said polyester component are
combined by a first reaction, said aziridine/polyester
component is combined with said epoxy component in a second
reaction wherein the group
Image
in said aziridine/polyester component reacts with
Image
groups in said epoxy component.
6. The composite structure of claim 1 wherein said first
and said second construction material are release
substrates; wherein a combination of said aziridine
component, said polyester component and said epoxy component
have not been heated.
7. A process for preparing a composite structure or a
storage media comprising:
reaction of an aziridine with at least one polyester
compound having a melting point of at least about 150°C and
being the reaction product of at least one aromatic diacid,
at least one aliphatic diacid, at least one diol and at
least one triol or higher polyhydric alcohol to form an
aziridine/polyester product;



13

mixing said aziridine/polyester product with at least a
tris (hydroxyphenyl) methane novolac epoxy; and
applying a resulting mixture to a location requiring
said adhesive material prior to reaction between said
aziridine/polyester product and said epoxy.
8. The process of claim 7 wherein the aziridine/polyester
product is reacted with a tris (hydroxyphenyl) methane
novolac epoxy in combination with a bisphenolepichlorohydrin
epoxy or a novolac epoxy or both.
9. The process of claim 7 further comprising using 50%-90%
by weight of said polyester and 90%-50% by weight of said
epoxy.
10. The process of claim 7 wherein reacting of said epoxy
with said aziridine/polyester product includes a step of
heating a mixture of said epoxy and said aziridine/polyester
product to a temperature between 250°F and 400°F.
11. The process of claim 7 wherein said aziridine, said
polyester and said epoxy are mixed together prior to
reacting.
12. An article having two surfaces bonded together by
applying to said surfaces the said resulting mixture of
claim 7 and causing a reaction between said aziridine/
polyester product and said epoxy.
13. A composite article with film to film bonding, foil to
foil bonding, or foil to film bonding having surfaces bonded




14

together by applying to said surfaces the said resulting
mixture of claim 7 and causing a reaction between said
aziridine/polyester product and said epoxy.

14. A mixture for application to surfaces to be bonded
together prepared in accordance with claim 7.

15. The process of claim 7 wherein said location requiring
said adhesive material is a substrate selected from the
group including film substrates, foil substrates and
hardboard substrates.

16. An adhesive coating storage media for application to a
surface to be bonded to a second surface, said media
including at least one release substrate with an adhesive
coating applied thereto, said coated substrate being
prepared as described in claim 15.

17. A process for providing an adhesive material which
comprises:
reacting an aziridine with at least one polyester
compound having a melting point of at least about 150°C and
being the reaction product of at least one aromatic diacid,
at least one aliphatic diacid, at least one diol and at
least one triol or higher polyhydric alcohol to form an
aziridine/polyester product; and
reacting said aziridine/polyester product with at least
a tris (hydroxyphenyl) methane novolac epoxy.




15

18. The process for providing an adhesive material of
claim 17, wherein the aziridine/polyester product is reacted
with a tris (hydroxyphenyl) methane novolac epoxy in
combination with a bisphenolepichlorohydrin epoxy or a
novolac epoxy or both.

19. The process for providing an adhesive material of
claim 17 further comprising using 50%-90% by weight of said
polyester and 90%-50% by weight of said epoxy.

20. The process for providing an adhesive material of
claim 17 wherein said polyester is selected from the group
of polyesters consisting of high molecular weight hydroxyl
terminated polyesters with a carboxylic acid functionality
as determined by an acid number ranging from 0.2 to 4Ø

21. The process for providing an adhesive material of
claim 17 wherein reacting of said epoxy with said aziridine/
polyester product includes a step of heating a mixture of
said epoxy and said aziridine/polyester product to a
temperature between 250°F and 400°F.

22. The process for providing an adhesive material of
claim 17 wherein said aziridine, said polyester and said
epoxy are mixed together prior to reacting.

Description

20~4131.
PATENT
A HIGH PERFORMANCE EPOXY BASED COVERLAY AND BOND
PLY ADHESIVE WITH HEAT ACTIVATED CURE MECHANISM
by
Thomas F. Gardeski
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, the development of higher perfor-
mance materials of construction has not resulted in the
development 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 currently
available meet some of the requirements for such properties
as peel strength, chemical resistance, moisture resistance,
high temperature stability, dimensional stability especially
in the Z-axis direction adequate flow, room temperature
storage stability prior to processing and ease of proces-
sing, but typically fail to meet one or more of the require-
ments for one or more of the properties.



2004131
PATENT
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.
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 for use in bonding electronic
circuit construction materials.
It is another feature of the present invention to
provide an adhesive material using a two stage reaction
sequence.
It is yet another feature of the present invention
to provide an adhesive material using a two stage reaction
sequence wherein the intermediate adhesive material result-
ing from the first reaction stage can be stored for long
periods of time without deterioration of the properties of
the adhesive material.
It is a still further feature of the present in-
vention to provide an improved adhesive material by provid-
ing a first reaction between an aziridine component and a
polyester component and by providing a second reaction




2004131.
PATENT
between the aziridine/polyester component and at least one
epoxy component, the at least one epoxy component being an
electronic grade resin.
The foregoing and other features are accomplished,
according to the present invention, by reacting a hydroxyl
terminated polyester component with an aziridine cure
component, the reaction proceeding at room temperature. The
resulting polyester/aziridine component reacts with at least
one and preferably two epoxy components, one of the epoxy
components being an electronic grade resin such as tris
methane novolac epoxy. The second reaction requires a
temperature of 250°F to 400°F. The high reaction
temperature permits the unreacted intermediate mixture of
the polyester/azirdine component and the epoxy components)
to have a long shelf life during which the implementation of
the second reaction phase will result in high performance
bonding. The intermediate mixture can be stored on a
substrate protected by a release substrate or can be stored
between two release substrates until needed.
These and other features of the present invention
will be understood from the following description.
DESCRIPTION
The composition of materials of the present
invention comprises at least one and preferably two epoxy
components, one epoxy component of which must be selected



. 2004131
4 PATENT
from a family of electronic grade resins such as tris
methane epoxy novolac sold by Dow under the designation
Quatrex 5010. The optional components are epoxies such as
the flexible "bis-epi" and hard "novolac" types such as
Celanese Epi-Rez*5132 and Dow D.E.N* 438, respectively. The
composition of materials includes a high molecular weight
hydroxyl terminated polyester component with minimal
carboxylic acid functionality, such as DuPont's 49002 and
an aziridine curative component such as Xama 2 or 7 supplied
by Cordova Chemical Co.
The two stage cure (reaction) sequence consists of
first reacting the aziridine with the carboxcylic acid
groups on the polyester as follows:
O H2C CH2
II ~-X-
2RCOH + H2C CHZ
R.T.
O O
2 5 II II
RCO-CHZCHZ-N-X-N-CHZCHZ-OCR
H H
where R designates the high molecular weight polyester
components and X designates the repeating unit of the
aziridine component. This reaction takes place at room
temperature.
* Trademarks



204131
PATENT
The second reaction, which is unique to the
present invention, is comprised of reacting the -~- groups
5 -~~ groups of the epoxy components as follows:
O O


- - CHz-OCR+ CHz-CH- X -CH-CHz
RCO-CH2CHz-N-X
N CH2


H H


Q (300-400F)



2 0 RCO-CH
CH


2 N X N CHZCHz-OCR
z


H -C-H H- C-H



H -C--- OH H-C--OH


X


I I


H -C-OH H- C-OH


H i H H i H


O


RCO-CH
CH


2 N X N CH2CHz-OCR
z


where Y designates the tris methane epoxy either alone or in
conjunction with a bis-epi and/or novolac epoxy having
structures shown below:
~Hs OH H3 O
z z~
4 5 CH -CH-CH L O-~- j -~-.-OCHz-CH-CHz ~O-s~--~-~-...OCH2--CH-CHZ
CH3 ~ CH3



200411
PATENT
"BIS-EPI" EPOXY
CH2 CHCHz -O /O
OCHZCH - CH2 O--CH2 C~HZ
Sb .--..~ CH2 ~ CH2
"NOVOLAC" EPOXY
E_xamole of the Process
A mixture is prepared with the following
components: a polyester resin component having a solids
content of 17-20%, composed of DuPont 49002 base resin in a
solvent mixture of 90% methylene chloride and 10% cyclohexa-
none by weight; an epoxy novolac is dissolved in methylethyl
ketone, with an 85% solids content by weight, known commer-
cially as Dow DEN 438 an electronic grade epoxy resin at 75%
solids in methylethyl ketone known commercially as Dow
Quatrex 5010; and a polyfunctional aziridine known commer-
cially as Xama 7. The components mixture is prepared by
combining 80% by solids content (by weight) of the polyester
component to 10% by solids content (by weight) of the epoxy
novolac to 10% by solids content (by weight) of the elec-
tronic grade epoxy and 0.25 parts (by weight) of the aziri-
dine to 100 parts by weight of the above mixture including
solvents. The component mixture can be prepared in two
ways:




7 ~ ~ PATENT
Procedure 1) The polyester and aziridine 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 aziridine/ carboxylic acid reaction; or
Procedure 2) The polyester, epoxies, and aziridine are
added separately without any mixing until all the components
are in the vessel then thoroughly blended and allowed to
stand for a minimum of 30 minutes prior to use to allow for
onset of the aziridine/ carboxylic acid reaction.
The homogeneous solution is then applied by
reverse roll coating technique to a 2 mil polyimide (e. g.,
Kapton) film to yield a 1 mil dry coating on the polyimide
film. The polyimide film is dried in a 75 foot oven at 25
fpm (feet per minute) and 212°F, combined to a 1 mil release
substrate at the coater/laminator combining station, rolled
up and stored at room temperature for future use. (Accord-
ing to another application, the homogeneous solution is
stored between two release substrates, the adhesive material
thereby being available for use with any surfaces to be
bonded:)
Sections are cut from the roll, the release
substrate is removed, then the coated film was placed over a
sheet of 1 oz. copper. The composite structure is then
placed between two caul plates with a high temperature
release material on both sides and pressed in a hydraulic
press for 1 hour at 375°F and 250 psi pressure. The
resulting composite laminate structure exhibits the
properties exhibited in Table I when tested in accordance
with the ANSIIPC-FC-232B and 241B procedures.
* Trademark
C



PATENT
Initial Peel 20 PLI


Peel After Solder 21 PLI


Chemical Resistance


MEK 21 PLI


TOL 20 PLI


IPA 21 PLI


T111/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


T111 = Trichloroethylene


MC - Methylene Chloride


TABLE I
____________________________________________________
OTHER EXAMPLES
1. The adhesive mixture is coated on polyimide
(and laminate) film to foil in line at 300°F and 90-100 psi
pressure. The resulting structure is post cured for 2 hours
at 150°F, 2 hours @ 275°F and 2 jpirs at 35-°F.
2. Coat release substrate and combine to another
release substrate to yield an unsupported film.


2004131.
PATENT
The adhesive composition of the present invention
provides a coverlay and bond ply adhesive coating material
consisting of 50-90% by weight polyester and 90-50~ by
weight epoxy with unique latent heat reactive cure mechanism
comprised of one and preferably two epoxy components, one of
which must be selected from a family of electronic grade
resins such as tris methane epoxy novolac and the other
epoxy or epoxies from the novolac or bis-epi epoxy families
and a high molecular weight hydroxyl terminated polyester
with a carboxcylic acid functionality as determined by an
acid number ranging from 0.2 to 4Ø The adhesive material
is cured in a two stage reaction sequence to provide a fully
crosslinked network without the evolution of volatile by-
products to provide an advanced laminating, coverlay, and
bond ply adhesive for film to film, foil to film, foil to
foil and hardboard to hardboard applications. The adhesive
material has with excellent flexibility, superior bond
strength, solder resistance, moisture and chemical resis-
tance and superior Z-axis stability along with continuous
and/or deferred processing capability. The high temperature
of the second stage curing process provides that the coating
material can be stored for long periods of time prior to the
implementation of the curing process. The epoxy based
adhesive materials can be coated on an insulating film or
release substrate by a continuous process and stored at room
temperature indefinitely prior to further processing, or
laminated in-line to various foils or films, and which can
be cured without the evolution of volatile by-products to
provide a flexible bond-ply with superior overall properties
to any currently available system with the added advantage
of excellent Z-axis stability.




200413..
PATENT
The foregoing description is included to illus-
trate 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.
5 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.