U.S. patent application number 13/630558 was filed with the patent office on 2013-09-05 for copolymer of styrene and maleic anhydride comprising an epoxy resin composition and co-cross-linking agent.
This patent application is currently assigned to ISOLA USA CORP.. The applicant listed for this patent is ISOLA USA CORP.. Invention is credited to Karl Walter Kopp, Karl-Heinz Leis, Franz Tikart.
Application Number | 20130230727 13/630558 |
Document ID | / |
Family ID | 38749895 |
Filed Date | 2013-09-05 |
United States Patent
Application |
20130230727 |
Kind Code |
A1 |
Tikart; Franz ; et
al. |
September 5, 2013 |
Copolymer of Styrene and Maleic Anhydride Comprising an Epoxy Resin
Composition and Co-Cross-Linking Agent
Abstract
A composition useful as an impregnant for the making of
laminates for printed wiring boards including an epoxy resin a
first cross-linking agent of a strene-maleic anhydride copolymer
and a second co-cross-linking agent.
Inventors: |
Tikart; Franz; (Erlenback,
DE) ; Leis; Karl-Heinz; (Weilbach, DE) ; Kopp;
Karl Walter; (Reinheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ISOLA USA CORP. |
Chandler |
AZ |
US |
|
|
Assignee: |
ISOLA USA CORP.
Chandler
AZ
|
Family ID: |
38749895 |
Appl. No.: |
13/630558 |
Filed: |
September 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13224604 |
Sep 2, 2011 |
8313836 |
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13630558 |
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11637222 |
Dec 11, 2006 |
8022140 |
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13224604 |
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11002045 |
Dec 3, 2004 |
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11637222 |
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10314602 |
Dec 9, 2002 |
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11002045 |
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09269014 |
Jun 14, 1999 |
6509414 |
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PCT/EP97/05308 |
Sep 24, 1997 |
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10314602 |
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Current U.S.
Class: |
428/418 ;
525/109; 525/117; 525/132 |
Current CPC
Class: |
Y10T 428/31511 20150401;
C08K 5/3445 20130101; H05K 1/0353 20130101; B32B 15/14 20130101;
H05K 1/0326 20130101; C08G 59/621 20130101; C08G 59/4246 20130101;
Y10T 428/31529 20150401; H05K 1/0366 20130101; Y10T 428/31522
20150401 |
Class at
Publication: |
428/418 ;
525/109; 525/117; 525/132 |
International
Class: |
C08G 59/62 20060101
C08G059/62; H05K 1/03 20060101 H05K001/03 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 1996 |
EP |
96203016.9 |
Claims
1. A resin composition comprising an admixture of a copolymer of
styrene and maleic anhydride (SMA) as cross-linking agent, a
curable composition of oxirane ring-containing compounds, and a
co-cross-linking agent that is an optionally brominated bisphenol A
(BPA) an optionally brominated bisphenol A diglycidyl ether
(BPADGE) or a mixture of both an optionally brominated bisphenol A
and an optionally brominated bisphenol A diglycidyl ether.
2. The resin composition of claim 1 wherein the co-cross-linking
agent is tetrabromobisphenol A (TBBPA), tetrabromobisphenol A
diglycidyl ether (TBBPADGE), or a mixture thereof.
3. The resin composition of claim 2 wherein the co-cross-linking
agent is a mixture of tetrabromobisphenol A (TBBPA) and
tetrabromobisphenol A diglycidyl ether (TBBPADGE).
4. The resin composition of claim 3 including at least 10% by
weight of TBBPA and at least 10% by weight of TBBPADGE are
employed.
5. The resin composition of claim 1 wherein the epoxy resin is a
derivative of bisphenol A.
6. The resin composition of claim 1 wherein the SMA has a molecular
weight of about 1400 to about 50,000, and an anhydride content of
more than 15% by weight.
7. The resin composition according to claim 1 wherein the SMA is
selected from one SMA or a mixture of SMAs having a styrene:maleic
anhydride ratio of 1:1, 2:1, 3:1, or 4:1, and a molecular weight
from about 1400 to about 2000.
8. The resin composition according to claim 1 wherein a copolymer
is used such as to give an equivalency ratio of anhydride and
aromatic hydroxy groups:epoxy groups in the range of 50 to 150% by
weight.
9. A laminate comprising a synthetic layer and a metal layer,
characterized in that the synthetic layer is composed of the resin
composition of claim 1.
10. A printed wiring board (PWB) comprising the laminate of claim
9.
11. The laminate of claim 9 wherein the synthetic layer is
reinforced with fibers.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/224,604, filed on Sep. 2, 2011, now U.S.
Pat. No. 8,313,836, which is a continuation of U.S. patent
application Ser. No. 11/637,222, filed on Dec. 11, 2006, now U.S.
Pat. No. 8,022,140, which is a continuation of U.S. patent
application Ser. No. 11/002,045, filed on Dec. 3, 2004, now
abandoned, which in turn is a continuation of U.S. patent
application Ser. No. 10/314,602, filed Dec. 9, 2002, now abandoned,
which is a divisional of application Ser. No. 09/269,014, filed
Jun. 14, 1999, now U.S. Pat. No. 6,509,414, which was filed as a
.sctn.371 of international application number PCT/EP97/05308, filed
Sep. 24, 1997, which claims priority from European patent
application number 96203016.9, filed Oct. 29, 1996
BACKGROUND OF THE INVENTION
[0002] The invention pertains to a resin composition comprising a
styrene maleic anhydride copolymer as a cross-linking agent (curing
agent), an epoxy resin, and a co-cross-linking agent.
[0003] The use of cross-linking agents for epoxy resin is described
in BE 627,887. This patent also discloses a proposal to use
copolymers of maleic anhydride and styrene (SMA) as cross-linking
agent for epoxy resin. A drawback to such epoxy resin compositions
is that they have low Tg and low thermal stability, rendering them
unsuitable for use in prepregs, which are applied in laminates for
printed wiring boards (PWBs).
[0004] The resin generally used in electrolaminates is an epoxy
resin. The present practical standard is the FR4-laminate, which is
based on a brominated epoxy resin prepared from a diglycidyl ether
of bisphenol-A and tetrabromo-bisphenol-A, dicyanodiamide as curing
agent, an organic solvent, and an accelerator. The drawback to such
an epoxy resin is its low Tg (110-130.degree. C.), while in
addition the dicyanodiamide has a tendency to crystallize in the
resin and the prepreg made therefrom.
[0005] An improvement has been sought in the preparation of an
interpenetrating polymeric network (IPN). Such resin compositions
are known from EP 413,386. This document relates to IPNs having
very favorable properties, in particular for use in the electronics
industry. This is the case when the cross-linking agent used for
the epoxy resin is a polybrominated phenol. In actual practice, the
embodiment using anhydride cross-linking agents proves
unsatisfactory. Notably, the Tg obtained is too low, and the
electrical properties and the prepreg stability also leave room for
improvement.
[0006] In addition, it is desired that the use of inexpensive
difunctional epoxy resins should give thermal properties which are
of the same standard as can be obtained using the multifunctional
epoxy resins preferably employed in EP 413,386. Resins based on
multifunctional epoxy compounds have been described in WO 85/03515
and WO 86/02085.
[0007] Other publications describing epoxy resin compositions
employing anhydrides as cross-linking agent for the epoxy resin are
U.S. Pat. No. 2,707,177; DE 3,521,506; GB 994,484; and EP 417,837.
This last patent specification teaches the use of ethylenically
unsaturated anhydrides, such as maleic anhydride, where the
anhydride not only cross-links the epoxy resin but also takes part
in the forming of the network.
[0008] A solution to the above-mentioned problems has been
suggested in WO 96/07683, which discloses a resin composition where
the carboxylic anhydride is a copolymer of an ethylenically
unsaturated anhydride and a vinyl compound. In such a copolymer the
ethylenically unsaturated portion of the anhydride is incorporated
into the backbone. The carboxylic anhydride groups remain intact,
and they are available as functional groups for cross-linking the
epoxy resin. More specifically, those resin compositions contain
triallyl cyanurate (TAC) as allyl polymerizing agent. In this type
of resin TAC is necessary to obtain compositions with high Tg and
acceptable thermal stability, which can be applied in prepregs.
[0009] Resin compositions which comprise dicyandiamide as
co-cross-linking agent have been disclosed in DE 38,39,105.
According to this document, dicyandiamide is an essential
constituent of the resin composition. Dicyandiamide, however, has
the disadvantage that it only dissolves in toxic and expensive
solvents, and it would be an advantage to find suitable
co-cross-linking agents, devoid of the disadvantages of
dicyandiamide.
[0010] Epoxy resin compositions containing low-molecular weight
copolymers of .alpha.-methylstyrene and maleic anhydride have been
disclosed in U.S. Pat. No. 4,042,550. Such compositions are
unsuitable for the manufacture of PWBs.
[0011] Prepregs are widely employed in the manufacture of laminates
for the electronics industry, in particular for printed wiring
boards. Such manufacture involves impregnating a supporting or
reinforcing fabric with a resin, followed by partial curing of said
resin. Such impregnated fabric is commonly referred to as prepreg.
Manufacturing a printed wiring board involves laminating one or
more layers of prepreg with, say, one or more layers of copper.
[0012] Processing prepregs into boards usually involves their being
cut down to size and laminated. Both these process steps make
stringent demands on the resin with which the fabric is
impregnated. For instance, the partially cured resin has to have
sufficient sturdiness and a high viscosity, yet it must be
sufficiently sticky and liquid to give good adhesion when
laminated, and hence good interlaminar strength. The resin may not
be too highly reactive, since this will render the required partial
curing impossible.
[0013] In this connection resin compositions where the epoxy resin
is cross-linked with an anhydride-containing copolymer have the
drawback of being too brittle to be processed as prepregs. For
instance, it proves impossible to cut up such prepregs without a
portion of the resin blowing about in the form of a large quantity
of dry dust. This is sometimes called a "mushroom effect," after
mushroom spores blowing about.
[0014] It has now been found that in contrast to the previous
solutions for obtaining suitable polymers for use in prepregs, IPNs
are not necessary, and that epoxy resins free from TAC can be
prepared having high Tg and/or improved thermal stability.
[0015] On the one hand, the invention has the object to enhance the
thermal and electrical properties of resin compositions based on
epoxy resin cross-linked with styrene maleic anhydride copolymer
(SMA). On the other hand, the invention envisages resin
compositions based on difunctional epoxy resin which have thermal
and electrical properties comparable to IPNs the resin composition
of which is based on multifunctional epoxy compounds. Furthermore,
the invention aims to provide resin compositions where the problem
of brittleness, which occurs when SMA is used as epoxy
cross-linking, agent, can be prevented.
SUMMARY OF THE INVENTION
[0016] To this end, the invention consists of a resin composition
comprising a copolymer of styrene and maleic anhydride (SMA) as
cross-linking agent, an epoxy resin, and a co-cross-linking agent,
characterized in that the co-cross-linking agent is an optionally
brominated bisphenol A (BPA), or an optionally brominated bisphenol
A diglycidyl ether (BPADGE), or a mixture thereof, and that the
composition is free from an allyl network forming compound.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] It is known from WO 96/07683 that epoxy resin compositions
which are free from allyl network forming compound, such as TAC,
have low Tg, usually not higher than 130.degree. C., and low
thermal stability. The present invention is based on the finding
that use of BPA as co-cross-linking agent significantly improves
the thermal stability of the co-polymer. To this same end it was
found that BPADGE as co-cross-linking agent considerably increases
the Tg, so that Tg values of 190.degree. C. are attainable.
[0018] Preferably, the co-cross-linking agent is a brominated BPA,
a brominated BPADGE, or a mixture thereof. More preferably, the
co-cross-linking agent is tetrabromobisphenol A (TBBPA) or
tetrabromobisphenol A diglycidyl ether (TBBPADGE). Most preferably,
the co-cross-linking agent is a mixture of tetrabromobisphenol A
(TBBPA) and tetrabromobisphenol A diglycidyl ether, leading to
resin compositions with high thermal stability and a high Tg.
Moreover, the stability of prepregs made of the resin composition
of the invention is considerably improved with respect to the prior
art prepregs. A further advantage is that post-curing, which is
necessary with IPNs, is not longer required.
[0019] Copolymers of styrene and maleic anhydride have been
described, inter alia, in Encyclopedia of Polymer Science and
Engineering Vol. 9 (1987), page 225 ff. Within the framework of the
invention the term "copolymer" likewise refers to SMA or mixtures
of SMA.
[0020] Copolymers of styrene and maleic anhydrides (SMA) are
commercially available in two types. Type 2 comprises mostly
high-molecular weight copolymers (MW generally higher than 100,000,
for instance, 1,000,000). These are in fact thermoplasts, which are
unsuitable for use in the manufacture of prepregs. Moreover,
because of their low anhydride content (5-15%) they are not
particularly suitable for use as a cross-linking agent for epoxy
resin either. The type 1 SMA copolymers, on the other hand, which
have a molecular weight in the range of about 1400 to about 50,000
and an anhydride content of more than 15% by weight, are
pre-eminently suited to be used. Preference is also given to SMA
copolymers having a molecular weight in the range of 1400 to
10,000. Examples of such copolymers, include the commercially
available SMA 1000, SMA 2000, SMA 3000, and SMA 4000. These
copolymers have a styrene:maleic anhydride ratio of 1:1, 2:1, 3:1,
and 4:1, respectively, and a molecular weight ranging from about
1400 to about 2000. Mixtures of these SMAs may also be used.
[0021] The amount of copolymer employed can be such as will give an
anhydride and aromatic hydroxy groups: epoxy groups equivalency
ratio in the range of 50 to 150% by weight. The preferred ratio is
between 75 and 125% by weight, and more preferably between 90 and
110% by weight. Optimum results are obtained when at least 10% by
weight of TBBPA and at least 10% by weight of TBBPADGE are employed
as co-cross-linking agents.
[0022] The term "epoxy resin" in this context refers to a curable
composition of oxirane ring-containing compounds as described in C.
A. May, Epoxy Resins, 2.sup.nd Edition, (New York & Basle:
Marcel Dekker Inc.), 1988.
[0023] Examples of epoxy resins include phenol types such as those
based on the diglycidyl ether of bisphenol A, on polyglycidyl
ethers of phenol-formaldehyde novolac or cresol-formaldehyde
novolac, on the triglycidyl ether of tris(p-hydroxyphenol)methane,
or on the tetraglycidyl ether of tetraphenylethane; amine types
such as those based on tetraglycidyl-methylenedianiline or on the
triglycidyl ether of p-aminoglycol; cycloaliphatic types such as
those based on 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane
carboxylate. The term "epoxy resin" also stands for reaction
products of compounds containing an excess of epoxy (for instance,
of the aforementioned types) and aromatic dihydroxy compounds.
These compounds may be halogen-substituted.
[0024] Preference is given to epoxy-resins which are derivative of
bisphenol A, particularly FR4, especially on account of their low
price. FR4 is made by an advancing reaction of an excess of
bisphenol A diglydicyl ether with tetrabromobisphenol A. Mixtures
of epoxy resins with bismaleimide resin, cyanate resin and/or
bismaleimide triazine resin can also be applied.
[0025] It should be noted that epoxy resins are generally
represented by a single, unequivocal structural formula. The
skilled person will know that this should be taken to include
deviating products resulting from side reactions occurring during
epoxy resin preparation. As these side products constitute a normal
component of cured epoxy resins, they likewise constitute a normal
component of the resins according to the invention.
[0026] The BPA and BPADGE may optionally be brominated, i.e.
substituted with one or more bromine atoms. Brominated
co-cross-linking agents are preferred because of their flame
retarding properties. Preferably, the aromatic moieties of both BPA
and BPADGE are substituted with two bromine atoms, to give
tetrabromo substituted TBBPA and TBBPADGE, respectively. Optionally
brominated novolacs can also be used as co-cross-linking agent.
[0027] Cross-linking of the epoxy resin generally proceeds with the
aid of an accelerator. As suitable accelerators may be mentioned
imidazoles, more particularly alkyl substituted imidazoles such as
2-methylimidazole and 2-ethyl-4-methylimidazole, and tertiary
amines, e.g. benzyldimethylamine.
[0028] The amount used of such an accelerator is dependent on the
type of epoxy resin, the type of cross-linking agent, and the type
of accelerator. Employing a too large amount of accelerator will
lead to a too highly reactive resin system. Such a system is not
serviceable for making prepregs. The skilled person can easily
determine within which range a resin system will be just
sufficiently little reactive to allow ready processing into
prepregs. In general, such a processing range will be between 0.01
and 5% by weight of accelerator, calculated on the overall weight
of epoxy resin and cross-linking agent. In many cases this will be
the 0.01-0.075% by weight range. The gel time for its part is
dependent on the type and amount of accelerator, the type and
amount of solvent, and the type of prepreg to be manufactured. In
the specific case of 2-methylimidazole (2MI) being used as
accelerator, it is preferred not to use more than about 0.05% by
weight of 2MI. By way of general guideline it can be said that it
is advisable not to have a varnish gel time of less than 120
seconds.
[0029] The desired resin properties determine the amount of BPA and
BPADGE to be incorporated into the resin. According to the
invention, for instance, it has surprisingly been found that the Tg
of epoxy resins cross-linked with SMA can be increased
substantially by the use of at least 5% by weight of BPA. Most
surprisingly of all, it is now possible, as indicated above, to
obtain resins having glass transition temperatures of 130.degree.
C. and higher even with simple difunctional epoxy compounds.
[0030] As a rule, an organic solvent is employed when preparing
resins according to the invention. If a solvent is used, it must be
one in which the epoxy resin, cross-linking agent, and
co-cross-linking agent are soluble, while the solvent itself should
be sufficiently volatile to evaporate before or during the
curing.
[0031] As suitable solvents may be mentioned dimethylformamide;
glycol ethers such as ethylene glycol mono-ethyl ether or propylene
glycol mono-ethyl ether and their esters such as ethylene glycol
mono-ethyl ether acetate; ketones such as methyl isobutyl ketone,
methylethyl ketone, acetone, and methyl isopropyl ketone; and
aromatic hydrocarbons such as toluene and xylene. Alternatively,
mixtures of solvents can be employed. The preferred solvents are
ketones, notably acetone and methylethyl ketone, or mixtures of
these with ethers, notably propylene glycol mono-ethyl ether.
[0032] The invention further pertains to laminates for use in the
electronics industry incorporating resins of the aforementioned
type.
[0033] Laminates for use in the electronics industry (particularly
for printed wiring boards) are generally produced by impregnating a
supporting or reinforcing material (usually based on glass fibres,
either as a woven fabric or in the form of a cross-ply laminate of
unidirectionally oriented parallel filaments) with a resin,
followed by the resin being cured wholly or in part. The latter
process is the most common one, and a fabric impregnated with a
partially cured resin is usually referred to as a "prepreg." To
make a printed wiring board from a prepreg fabric one or more
layers of the prepreg are laminated with, say, one or more layers
of copper.
[0034] The resins according to the invention are highly suitable
for impregnating, e.g., woven fabric and cloth of a variety of
materials such as glass, quartz, carbon, aramid, and boron fibres,
more particularly to make laminates for printed wiring boards. This
application preferably calls for the resin to be employed in
combination with a glass fabric.
[0035] It was found that even when it is based on simple
difunctional epoxy compounds, the combination of resin components
according to the invention will give excellent properties for
application in the electronics industry. The Tg effect has been
mentioned earlier: as compared with the corresponding standard
epoxy resins (cured with dicyanodiamide) the resins according to
the invention have a Tg of about 30-50.degree. C. higher.
Furthermore, it was found that resins according to the invention
exhibit a much better resistance to short, intense temperature,
increases than do standard FR4 epoxy resin and IPNs according to EP
413,386 and have better prepreg stability. The thermal stability is
demonstrated by the pressure cooker test and the solder shock test,
which are known to the skilled man. The pressure cooker test is a
procedure for evaluating glass epoxy laminate integrity. In this
test a specimen of the laminate to be tested is placed in a
pressure cooker for some time, after which the specimen is immersed
in a solder bath at 260.degree. C. The specimen is thereafter
graded on the occurrence of measles, blisters, delamination,
convolution, and surface erosion. The longer the cooker time
without said occurrence is, the more thermally stable the laminate
will be. In the solder shock test a material is transferred
abruptly from room temperature to solder having a temperature of
288.degree. C. The material (in this case a laminate made of a
resin according to the invention) floats in the solder, and so will
be subject to a temperature gradient (and hence a tension
gradient). The material should be capable of withstanding these
conditions for at least 30 seconds without bubble formation or
delamination occurring. The longer the material can stand the test,
the more serviceable it will be for use in printed wiring boards.
The resins according to the invention are capable of standing the
solder shock test for 10 minutes, which represents a substantial
improvement over both the aforementioned known IP Ns, which bear it
for about 3 minutes, and FR4 epoxy resin (about 4 minutes).
Furthermore, the resins according to the invention exhibit a
significant reduction of dielectric loss.
[0036] Also, the resins according to the invention can be employed
wherever use is made of conventional epoxy resins: as a glue,
coating, molding resin, embedding resin, encapsulating resin, sheet
molding compound, bulk molding compound.
[0037] In addition to being used as composites for printed wiring
boards, the resins according to the invention can be employed to
make composites for, inter alia, the construction, aviation, and
automobile industries. The manufacture of appropriate structural
composites may proceed in a known manner, e.g., by impregnating
reinforcing material with molten or dissolved resin, or via resin
transfer molding, filament winding, pultrusion, or RIM (reaction
injection molding).
[0038] The resins according to the invention may contain the usual
additives such as dyes or pigments, thixotropic agents, fluidity
control agents, and stabilizers.
[0039] The invention will be further illustrated with reference to
the following examples.
EXAMPLE 1
[0040] In a typical example 925 g of BPADGE (DER 535 EK 80) were
mixed under stirring with methylethyl ketone (MEK) to a 80%
solution. To this solution were added subsequently 1560 g of SMA
3000 as a 50% solution in MEK, 200 g of TBBPA, 280 g of TBBPADGE
(Quatrex 6410), 400 g of MEK, and 8 g of a 10% solution of
accelerator (2-methylimidazole) in methoxypropanol. The
concentration of the accelerator is 0.04% relative to the solid
contents of the complete resin. The equivalency ratio of
* * * * *