Note: Descriptions are shown in the official language in which they were submitted.
39(~
T-4087 (US)
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CURABLE THERMOSETTING EPOXY-POLYESTER RESIN COMPOSITION
_ .. . . . _ _
Back~_ound of the Invention
Epoxy compositions and their curing techniques are well known
and the patents issued on curable epoxy compositions number in the
hundreds. Known curing agents include, among others, polycarboxylic
acids and anhydrides, am;nes, polyamides, imidizoles, and the like.
Representative curing agents are described in U.S. Patent No. 3,336,241.
These curing agents may be employed with one or more catalysts or
accelerators such as the stannous salts of monocarboxylic acids.
It will be appreciated that each and every one of the known
epoxy-curing systems exhibits advantages over other systems, and, as
importantly, disadvantages over the same systems. There is, of course, a
continuing need to develop better epoxy curing composit;ons.
The fahrication of thermoset polyester resin articles from
curable compositions comprising an ethylenically unsaturated polyester
dissolved in a liquid ethylenically unsaturated monomeric crosslinking
agent which is capable of polymerizing with the polyester is well known.
Articles having relatively high strength and low density can be produced
from such compositions by incorporating therein fibrous reinforcements
s~ch as glass fibers. F;llers, such as calcium carbonate and clays, are
usually added to such compositions as extenders. See for example, U.S.
Patent No. 3,959,209.
For convenience, the term "polyester resin" when used herein
refers to a composition which contains as an essential ingredient an
ethylenically unsaturated polyester and an ethylenically unsaturated
reactive diluent and which may contain other ingredients such as fillers,
fibers9 reinforcements~ curing catalysts, etc.
Polyester resins are widely used in molding applications in
liquid Form. Such liquid resins comprise a liquid solution of a liquid
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or solid polyester dissolved in a liquid crosslinking agent,
~or example r styrene monomer, the most widely used reactive
diluent.
For many types o~ molding applications, it may be
desirable for the polyester resin to be in solid form, for
example in the form of sheets, granules or powders. Solid
forms of polyester resins can be made from the liquid polyester
resin solutions ~entioned above. For example, a normally
liquid polyester resin solution can be converted into solid
form by ~he addition thereto of a chemical thickening agent
such as an oxide or hydroxlde of magnesium or calcium. Or the
liquld polyester resin solution can be converted into solid
form by adding thereto a solld filler, such as calcium
carbonate, whlch absorbs ~he liquld resin. Liquid or soli.d
amorphous polyes~ers which are soluble in the liquid
crosslinking a~ent are conventlonally used in this type o~
application.
There is a need for a curable thermosetting resin
composition which has improved tensile strength, tensile
modulus, and glass transitlon temperatures while adequate
tensile strain to break is maintained, over that of "pure"
epoxy resin or '~pure" polyester resin.
SummarY of the_Invention
The present invention provides a composition
comprising a blend of:
(~) from ahout 20 to about 80 parts by weight, based on
,~ I o~ ~Da~s j
the weight of (A) and (Bj~of a curable bisphenol-based epoxy
resin and a curing amount of an imidazole compound; and
~) a mixture of an ethylenically unsaturated polyester
resin, an ethylenically unsaturated diluent and an effective
amount of a free radical initiator.
B
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~ B
Preferably the ratio of (~) to (~) is in the range of
50:50 to about 75:25% by weight, the ~ost preferably 65:35 to
about 75:25% by weight.
: ~
3~
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Fig. 1 is a graph of tensile strength of the epoxy-polyester
blend in relation to the polyester content in weight percent.
Fig. 2 is a graph of the elongation or strain of the epoxy-
polyester blend at break in relation to the polyester content in weightpercent.
Fig. 3 is a graph of the modulus of the epoxy-polyester blend
in relation to polyester resin. The modulus continues to increase as the
weight percent of the Stypol is increased.
Fig. 4 is a graph of the glass transition temperatures (Tg) of
the epoxy-polyester blend in relation to the polyester content in weight
percent.
Description of the Preferred Embodiment
Ingredients
Epoxy Resin
Suitable polyepoxides useful in the present compositions
comprise those compounds containing at least one vicinal epoxy group,
i.e., at least one
/o\
C C
group. These polyepoxides may be saturated or unsaturated, aliphatic,
cycloaliphatic aromatic or heterocyclic and may be substituted, if
desired, with non-interfering substituents such as halogen atoms,
hydroxyl groups, ether radicals, and the like. They may also be
monomeric or polymeric.
For clarity, many of the polyepoxides and particularly those of
the polymeric type are described in terms of epoxy equivalent values.
The meaning of this expression is described in U.S. Patent No. 2,633,45~.
The polyepoxides used in the present process are preferably those having
an epoxy equivalency greater than 1Ø
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Various examples of liquid polyepoxides that may be
used in the process of the invention are given in U.S. Patent
No. 2,633,45~.
Other sultable polyepoxides are disclosed in U.S.
Patent No. 3,373,221 and U.S. Patent No. 3,377,406.
Polyepoxides, which may be used are the glycidyl
polyethers of polyhydric phenols and polyhydric alcohols,
especially the glycidyl polyethers of 2,2-bis(4~hydroxy-
phenyl)propane having an average molecular weight between about
300 and 3,000 and an epoxide equivalent weight between about
140 and 2,000. The epoxy resin is eommonly bisphenol based. A
commonly used epoxy resin is the reaction products o~
epichlorohydrin and bisphenol-A (Bisphenol of acetone). The
bisphenol based epoxy resin compound can contain from about 1%
to about 25~ by weiyht, preferably from about 10% to about 25
by weight styrene monomer and peroxide.
Other suitable epoxy compounds include those
compounds derived from polyhydric phenols and having at least
one vicinal epoxy yroup wherein the carbon-to-carbon bonds
wlthin the six-membered riny are saturated. Such epoxy resins
may be obtained by at least two well-known techniques, i.e. by
the hydrogenation of glycidyl polyethers of polyhydric phenols
or (2) by the reaction of hydrogenated polyhydric phenols with
epichlorohydrin in the presence of a suitable catalyst such as
Lewis acids, i.e. boron trihalides and complexes thereof, and
subsequent dehydrochlorination in an alkaline medium.
't ~
An idealized structural formula representing the preferred
unsaturated epoxy compound is as follows:
CH2 H-CH2---- ~ CH3 -0-CH2- H~ ~ 2----- C- ~ -
--0-CH2-CH-CH2
O CH n CH
wherein n has a value3 so that the average mole3cular weight of the
saturated polyepoxide is from about 350 to about 3000.
Unsaturated Polyester
The polyester of this invention should be unsaturated.
Unsaturated polyesters are the product of a condensation reaction between
difunctional acids and alcohols one of which (generally the acid)
contributes olefinic unsaturation. This polymer is dissolved in styrene
or other monomeric material containing vinyl unsaturation. With heat
and/or free radical initiation, the polyester and reactive diluent
crosslink into a solid, non-melting network.
Curing Agents
The curing agent used should contain a primary or secondary
amine. An amount is used which is sufficient to cure the blend. For
example, an imidizole curing agent may be used. Generally~ the amount
of imidizole will vary from about 1.5% to about 10%. Other primary or
secondary amine percentages required may be individually determined in
order to effectuate the curing.
Free Radical Initiator
An effective amount of a free radical initiator is employed.
The initiator may be a peroxide, but need not necessarily be a peroxide,
such as, but not limited to benzoyl peroxide, tertiary butylhydro-
peroxide, or ditertiary butylperoxide. The preferred initiator is
2,5-dimethyl-2,5-bis(2-ethyl-hexoyl peroxy)hexane.
In general, the amount of initiator employed will range widely,
but will be an amount which is sufficient to effect the desired cure or
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crosslinking. Preferably, the amount of initiator will vary
from about 0.25~ to about 5% based on the polyester resin.
The present compositions may be prepared by various
t~echniques. If, for example, the instant compositions are to
be utilized within a short time, they can be prepared by simply
mixing all the components, adding the customary additives, such
as fillers, impact modifiers, reinforcement flake or fibers,
mat or webs, pigments, flame retardant agents, plas~icizers,
stabilizers, extenders, antioxidants and promoters,
accelerators, thixotrophic agents, etc. and then molding and
curing the composition.
Under certain conditions it may be desirable to
utilize a 2--packacJe system utilizing a combination o~ two or
more of the four basic constituents.
The present compositions may be utilized in many
applications such as for making various ~astings and parts and
may be in the form of a dry mix, non-tacky free flowing
powders, granules or pellets.
By the addition of suitable promoters and the like,
the present compositlons are especially suitable in resin
transfer molding (RTM), pressure gelation molding and the like.
The following examples are given to illustrate the
preparation of the ins~ant heat-curable thermoset~ing
compositions. It is understood that the examples are
embodiments only and are given for the purpose of illustration
and the invention is not to be regarded as limited to any
specific components and/or specific conditions recited therein.
Unless other~ise indicated, parts and percentages in the
examples are parts and percentages by weight.
Experiment 1
A series of unreinforced resin castings were
fabricated to determine the effects of adding pol~ester resins
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to epoxy resins. A commercial polyester resin initiator
mixture was combinecl with a commercial epoxy resin curing agent
mixture at 20 wt%, 25 wt%, 30 wt%, 40 wt%, 50 wt% and 75 wt%.
Sample~ of 100 wt~ epoxy resin and 100 wt% polyester
.
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resin were also analyzed as controls by which to compare the blends.
Table 1 describes the casting mix ratio. Table 2 describes the (A/B)
weight ratio at which parts were evaluated.
Table 1
MIX RATIOS
A epoxy resin100 parts by weight (pbw)
curing agent 6
B polyester resin 100
initiator 0.5
Table 2
PARTS EVALUATED AT A/B WT RATIO
lno/o
80/20
75/25
70/30
60/40
50/SO
25/75
0/100
Figure 4 shows a synergistic improvement in glass transition
temperatures (as measured by Rheometrics D~lA) of the epoxy-polyester
blends over the 0/100 and 100/0 epoxy or polyester resins by more than
20C. Figures 1 through 3 show a synergistic improvement in tensile
strength and modulus without sacrifice to tensile elongation to break.
Figure 1 is a graph of tensile strength of the epoxy-polyester
blend in relation to polyester content in weight percent. As may be seen
in Figure 1, the tensile strength at all blend ratios is improved over
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tensile strength properties normally expected from an ideal mixture
(i.e., indicated by the dashed lines) of epoxy resin and polyester.
Figure 2 is a graph of the elongation or strain of the
Epoxy-polyester blend at break in relation to the strain normally
expected from a mixture of epoxy resin and polyester. The elongation or
strain at break is not sacrificed by the use of the polyester epoxy
blend.
Figure 3 is a graph of Young's modulus of the Epoxy-polyester
blend in relation to the modulus normally expected from a mixture of
epoxy resin and polyester. The modulus is improved by the use of the
polyester epoxy blend.
Figure 4 is a graph of the glass transition temperatures (T9)
of the epoxy-polyester blend in relation to the Tg normally expected from
an ideal mixture of epoxy resin and polyester. A polyester content up to
about 80% by wei~ht yielded an 1mprovement over the expected Tg of the
epoxy-polyester blend.
The ratio of blends of from about 60:40 to about 75:25 showed
the best results, however the other blends also had improved properties,
tensile strength and modulus and glass transition temperatures.
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