Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Various solid epoxy resins have been developed which can be made to
satisfy a wide range of properties, such as softening point and melt
viscosity, in order to improve the selection and augment the capabili-
ties of epoxy resins available to molding formulations and end users.
Among the solid epoxy resins used in the manufacture of molding grade
compounds are included difunctional resins based on advancement
products of bisphenol A diglycidyl ethers, or various multifunctional
resins such as epoxy novolacs, epoxy cresol novolacs, tri-glycidyl
isocyanurate and tetra-[p-glycidyloxyphenyl]ethane.
Resin choice depends partly upon several processing considerations
amongst which are ease of handlingg amount and type of flow during
molding and cure rate. Cured properties such as glass transition
temperature, moisture absorption and resistance to thermal and
mechanical stress also affect resin choice. It has been determined
that the multifunctional resins are superior to -the difunctional
resins in molding applications both in terms of pre- and post-cured
properties. Functionalities greater than two are desirable since
they enhance the formation of a crosslink network during curing.
Such superiority is primarily evidenced in thermal properties and
electrical properties at elevated temperatures. Correspondingly,
physical blends of multiEunctional and difunctional resins exhibit
performance characteristics which are inferior to those of the pure
multifunctional resin, such differences being once again primarily
observed in thermal performance charac-teristics.
Although it may thus be reasoned that multifunctional resins are
the logical choice for such areas of application, there are a number
of instances where this reasoning does not follow. For example,
solid multifunctional resins in many cases provide performance
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characteristics well in excess of that which is required for a given
application. Since these resins are expensive in comparison to solid
bisphenol A based epoxies, their use in such instances is uneconomical.
Accordingly, the beneficial properties that could be provided by such
resins are sacrificed by practitioners who may opt not to use the
resins in view of the unfavorable cost factors.
It is also to be noted that the multifunctional resins exhibit
various disadvantages. Thus, they exhibit restricted flow and vis-
cosity characteristics. Subsequent to curing, these resin-based
formulations exhibit extensive brittleness as evidenced by reduced
tensile elongation and higher flexural and tensile moduli. Such
brittleness is a distinct detriment when, for example, the resins
are utilized as encapsulants. Finally, these resins exhibit moisture
absorption characteristics which still could be improved upon. The
water absorption of an encapsulant, for example, is a most important
characteristic since it is known that device failure by corrosion
can be caused by the reaction of various ionic species, hydrolyzable
chlorine, and other substances present in the molding compound with
small amounts of water.
Accordingly, it is the primary object of this invention to provide
modified solid epoxy resin systems having processing characte-ristics
and cured properties at least comparable to those of pure m~llti-
functional resins. It is a further object to reduce the level of
multifunctional resin in these systems without adversely effecting
the performance characteristics thereof. It is another ob;ect to
provide solid epoxy reaction products which improve upon the pro-
cessing characteristics and flexibility of multifunctional resins.
It has now been surprisingly discovered that by reacting a poly-
epoxide compound having a functionality greater than two with a
diglycidyl ether of a polyhydric phenol and a polyhydric phenol, it
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is possible to retain most and improve upon other properties of the
multifunctional resin while still being able to reduce the content
of said multifunctional resin in the system by about 10-40%. These
systems facilitate great flexibility in terms of achieving optimum
softening points and melt viscosities or the desired end use. Corre-
spondingly, the degree of grind ability of the resin system con be
readily adjusted to meee the practi~ioneris specific needs. These
properties thus enable the resin systems Jo be tailored for speciEic
applications.
Therefore the present invention relates to a solid advanced epoxy
resin comprising the reaction product resulting from a cataly7ed
advancement reaction of
(a) a polyepoxide resin having a functionality greater than two
said resin corresponding to the formula
J i9~
CH2~ !I c~l2~ 1!
wherein R i6 H or CH3 and n is about 0.2-6.09 or being the tetr~-
glycidyl ether of tetra-[p-hydroxyphenyl]ethane;
(b) a diglycidyl ether of a polyhydric phenol or the alkyl or
halogen derivatives thereof; and
(c) a polyhydric phenol or the alkyl or halogen derivatives ther~o;
components (a) and (b) being present in concentration ranges of rom
60-90% by weight, and 10-40%! by weight respectivelyg and component
a being present in a concentration range of from 2 to 23%, based
on the total weight o components (a) and (b).
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3~L
Similar performance benefits are obtained when the resin system is
formulated with a phenol novolac hardener and various other ingrP-
dients to prepare molding compounds. Although 10-40% of extensive
multifunctional resin is eliminated, the resulting system substan-
tially maintains tha thermal and mechanical properties of molding
systems based solely on multifunctional resinO The maintaince of
such thermal properties, including thennal stability, heat deflec-
tion, ehermal coefficient of expansion, retention of Plec~rical
properties, and the like, is evidenced by glass transition tempera-
tures comparable to those of the multifunctional resin systems.
Furthermore, performance improvements in the molding formulations are
noted in properties such as flexibility, tensile elongation and
moisture absorption. Thus, the instant systems provide great2r per-
centages of tensile elongation and lower flexural and tensile moduli.
They demonstraee superior water moisture resistance which can be
expected to minimize corrosion problems and the like which can be
encountered.
Accordingly, it is seen that the instant systems provide the benefits
of a pure multifunctional resin system without incurring the adverse
economic factors associated therewith. These modified syste~ns are
available for use in a broad range of molding applications such D for
exa~nple, in the encapsulation of semi-conductor devices. They also
find U9e in the manufacture of powder coatings, reinforcad articles,
and the like.
Applicable ~ultirunctional resin of Eunctionality greater than two
correspond to the formula
I, 2 1 2 ~0/ 2 1 / 2
CH2t~ I' CH2~ i1
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wherein R is hydrogen or methyl, and n is about 0.2~0.6. These com-
ponents are exemplified by the epoxidation products of cresol novolacs
and phenol novolacs of varying molecular weight with cresol novolacs
being preferred. The preparation of such materials is well known in
the art. Likewise, such materials are commercially available.
In addition, the tetra-glycidyl ether of tetra-[p-hydroxyphenyl]-
ethane is applicable as the multifunctional resin to prepare appro-
priate solid resins suitable for molding applications. This material
i9 commercially available.
It is also to be noted that multifunctional resins such as tetra-
-glycidylated methylene dianiline, tri-glycidylated p-aminophenol,
tri-glycidyl isocyanurate and tri-glycidyl ether of tris-(p-hydroxy-
phenyl)methane may have corresponding applicability.
Among the applicable diglycidyl ethers of polyhydric phenols are
included those corresponding to the formula
_
H2C\ C/HCH2- o_-\ ox -OCH2CHCH2~ 0--~ ~--X- ~--OCH2C~H-,CH2
- OH J m
CH3 O
wherein m is 0-50 and X is -CH -, -C- or -S- .
2 1 11
CH3 0
These represent, respectively, bisphenols F, A and S. Other appli-
cable ethers include the diglycidyl ethers of resorcinol, catechol,
hydroquinone, and the like. The various ethers may be substituted
on the respectively phenyl rings by such non-reactive substituents
as alkyl, halogen, and the like. The diglycidyl ether of bisphenol
A and the tetra-brominated derivative thereoE are preferred for
purposes of this invention.
.
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The polyhydric phenol functions primarily to adjust the softening
point, melt viscosity and degree of grindability of the resin system.
Applicable phenols include the phenols noted in the above description
of the diglycidylated ethers absent, of course, the glycidyl ether
groups. ~isphenol A and the tetra-brominated derivative thereof are
preferred for purposes of this invention.
The epoxy-containing components of the instant systems will generally
be present in concentrations ranging from 60-90% of multifunctional
resin and 10~40% of diglycidyl ether, and preferably 65-75% of multi-
functional resin and 25-35% of diglycidyl ether. The polyhydric phenol
will be present in concentrations ranging from 2 to 23%, based on the
total weight of epoxy-containing components, and preferably 5 to 12%.
As previously noted, the amount of polyhydric phenol will help deter-
mine the basic properties of the resin systems. It is essential that
the selection of the specific amount of polyhydric phenol within the
noted range for any particular system be based on the components of
the system and on the need to avoid premature gelling of the resin
components.
The reaction procedure, i.e. advancement reaction, is well known to
those skilled in the art and generally involves the reaction of the
multifunctional resin, diglycidyl ether and polyhydric phenol in the
presence of an advancing catalyst or accelerator. Typical accelerators
include alkali metal hydroxides, imidazoles, phosphonium compounds,
and the like. The specific choice of catalyst will depend on the in-
tended end use application. In order to facilitate the initial
blending operation, it is preferred to warm the multifunctional resin
and diglycidyl ether to about 80-100C and then to add the dihydric
phenol. Stirring at this point provides a clear melt blend. The
catalyst is then added and the temperature is raised to 140-180C to
effect the advancement reaction. The progress of the reaction can be
monitored by titration of the epoxide groups using samples taken
during the reaction. Completion of the reaction will generally take
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1 to 6 hours to provide resin systems having epoxy values in the
range of 0.2-0.5 epoxy equivalents per 100 grams of resin.
The resulting advanced resins are solid and will generally having a
softening point range of 60-95C, a melt viscosity range ox 700-15,000
centipoises a 130C and, as previously noted, an epoxy value range
of 0.2-0.5 epoxy equivalent pPr 100 gram of resin.
Depending upon the desired end use application, the r2sin Jill he
fonmulated with the appropriate ingredient and combined with the
appropriate hardener and accelera or components. For ehe pr;mary area
of utility of the instant resin sys~em~ as molding compounds, no~olac
hardeners art utilized. Suck hardener can include phenol or cresol
novolacs as dçfined under the mNltifunc~ion~l re3ins absent the
epoxy groups. Such n~v~lae~ are know ant are widely used in ehe
manufacture of encapsulant 8y hems. The hardener is utilized in con-
centration~ ranging from about 25 to 40%, by weight of the total
advanced resin.
The resin-hardener system can furthermore be mixed, prior to cure,
with usual modifiers such a extenders, fillers and reinforcing agents,
pigments, dyeseuffs, plasticizers, diluents, accelerators, and thy
like. As extender, reinforcing agent, fillers and pigment which
can be employed in the curable system accorting to the invention
where may be mentioned, for example: cowl jar, bitumen, glas3 fibers,
carbon fiber, cellulose, polyethyle4e powder, polypropylene powder,
mica, asbestos, Yarious quartz powder, fused silicas, silicate3)
silanes, magnesium and calcium carbonates, gypsum, Bentone I, silica
aerogen (Aerosil ) , lithopone, barite, titanium dioxide, carbon
black, graphite, iron oxide, or metal powders such as aluminium
powder or iron powder. Ie i5 also possible to add other usual addi-
tives, for example, flameproofing agents such as antimony triox;de,
agents for conferring thixo~ropy, flow control agents such as sili-
cones, cellulose acetate butyrate, polyvinyl butyral, waxes, stearates,
.,',~, .
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ant the like (which are in part also used as mold release agents)
to the curable systems. The accelerators that are added may be iden-
tical to the advancement catalysts or may additionally include boron
trifluoride monoethylamine complexes, tertiary amines, and the like.
The end products can be manufactured in the usual manner with the
aid of known mixing equipment (kneaders, extruders, rollers, and the
like). For purposes of preparing molding compositions, one satis-
factory approach involves utilizing heated two roll mills, wherein
the resin system and the hardener system are separately combined
with filler and milled and the resulting phases are ground to the
desired size and then blended.
Curing will generally be conducted at temperatures ranging from
140 to 185C. The expression "cure", as used herein, denotes the con-
version of the above systems into insoluble and infusible crosslinked
products, with simultaneous shaping to give shaped articles such as
moldings, pressings or laminates, or to give two-dimensional struc-
tures such as coatings, enamels or adhesive bonds.
Although major emphasis has been placed on the use of the instant
resin system for moLding compounds, it is to be noted that they Like-
wise may be utilized for the preparation of powder coatings, rein-
forced articles (substrates), and the like. In these other areas of
use, it is possible to utilize additional hardeners such as dicyan-
diamide, polyesters, enhydrides, aromatic amines, and the like. The
benefits derived in powder coating Eormulations include chemical and
thermal resistanceO Typical powder coating formulations include the
resin, hardener, accelerator, pigment and flow agent. Preparation
and application of such powder coatings are known to those skilled
in the art.
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The following examples will further illustrate the embodiments of
the instant invention. In these examples, all parts given are by
weight unless otherwise noted.
Example I: This example illustrates the preparation of a typical
resin system of this invention.
The following components were utilized:
.
Formulation A Parts
_
Epoxy cresol novolac l 70
Diglycidyl ether of bisphenol A (2) 30
Bisphenol A 11
l epoxy value = 0.44 equivalents/100 g,
softening point = 82C and
viscosity at 130C = 5,7 Paos
(2) epoxy value = 0,52 equivalents/100 gg
viscosity at 25C = 17 Paus
The epoxy cresol novolac and the diglycidyl ether were blended and
warmed to 80C to provide a uniform mixture. The bisphenol A was
then admixed to form a clear melt blend. Thereafter, 40 ppm oE 2-
phenyl imidazole catalyst were added, the temperature was raised to
160C and the advancement allowed to continue for a period oE 3 hours.
The resulting solid epoxy resin system was determined to have an
epoxy value of 0.34 per 100 grams with a softening point of 80C and
a melt viscosity of 10,7 Paos at 130C.
: The following resin systems were prepared according
to the procedure of Example I.
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parts
B C D E F G
Epoxy cresol novolac (1) -- 60 80
Epoxy cresol novolac (3) 70 -- -- -- -- --
Epoxy cresol novolac (4) -- -- -- 75 -I ~~
Epoxy phenol novolac (5) -- -- -- -- 75 --
Tetraglycidyl ether of tetra-
[p-hydroxyphenyl]ethane (6) -- -- -- -- -- 70
Diglycidyl ether of bisphenolA (2) -- 40 20 25 25 30
Diglycidyl ether of bisphenol A (7~ 30 --
Bisphenol A 9 15 8 22.3 22.3 8
(3) epoxy value = 0.46 equivalents/100 g,
softening point = 73C,
viscosity at 130C = 1,9 Paas
(4) epoxy value = 0.47 equivalents/100 g,
viscous liquid at room temperature.
(5) epoxy value = 0.56 equivalents/100 g,
viscous liquid at room temperature.
(6) epoxy value = 0.55 equivalents/100 g,
softening point = 60C.
(7) DER 331 from Dow Chemical Corporation.
These resin systems exhibited the following characteristics:
Formulation Epoxy Value/100 g Softening point (C)
B 0.37 75
C 0.30 91
D 0.35 90-91
E 0.24 83
F 0.30 85
G 0.41 72.5
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Example III: This example illustrates the preparation of molding
compounds utilizing the resin systems of this invention.
The following formulations were prepared:
parts
1 2 3 4 5 6 7 8
. . . _
Resin A 100 --- --- --- --- --- 100 ---
Resin B --- 100 --- --- --- --I --I ~~~
Resin C --- --- 100 --- --- --- --- ---
Resin D --- --- --- 100 --- --- -I
Resin E --- --- --- --- 100 --- --- ---
Resln F --- --- --- --- --- 100 --- ---
Resin G --- --- --- --- --- --- --- 100
Novolac hardener(8) 30 33 27.6 32.221.8 27.3 30.7 37.3
Wax (release agent)
Imidazole
(accelerator)
Silica filler (9) 244249 241 2~9 230 240 2~6 260
(8) BRWE 5833 (solid phenol-novolac having 1 OH group/100 g) Erom
Union Carbide Corporation,
(9) NOVACITE 325 from Malvern Minerals Corporation.
In each instance, the molding compounds were prepared by a two com-
ponent hot two roll mill method. The first phase involved blending
the resin components with 65 weight % of the Eiller and hot two
rolling the blend at 85-100C. The second phase involved blending
the remaining filler with accelerator, hardener and release agent and
hot two rolling the blend at 95-100C. The phases were then separately
subjected to size reduction by hammer milling and uniformly combined
by ball milling in proper proportions at room temperature to form
the complete molding compound formulation.
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Correspondingly, control systems reflecting pure multifunctional
resin and physical blends of multifunctional resin and glycidylated
dihydric phenol were prepared by grinding all the components and then
combining them in the desired proportions using a ball mill. These
control systems are as Eollows:
parts
9 10 11 12 13 14
Epoxy cresol novolac (1) 100 75 50 25 --- ___
Tetraglycidyl ether(6) --- --- --- --- --- lOO
Diglycidylated ether of
bisphenol A --- 25 50 75 100 ---
Novolac hardener (40) 40 34.629.1 23.618.2 50.0
Imidazole
Wax
Filler (9) 264 254 243 233 223282.3
The instant systems and the control systems were then subjected to
the varlous test procedures.
Glass Transition Temperature
. . . _ .
Specimens for this test were prepared by transfer molding of the
sample and then post-curing Eor 4 hours at 175C. The glass transi-
tion determinations were made by thermo-mechanical analysis in the
expansion mode and gave the following results:
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Glass Transition Temp. (C)
_,
1 151
2 149
3 137
4 144
115
6 130
7 147
8 152
9 147
140
11 132
12 123
13 110
14 147
It is seen that in most instances, the glass transition temperatures
of the instant systems are comparable to those of the multifunctional
resins (~8 and ~14) indicating a retention of the beneficial thermal
characteristics of the multiftmctional resin despite a reduction in
the concentration thereof. It is also important to note that sub
stantially equal percentage of multifunctional resin gives a higher
glass transltion temperature when used in the resin advancemen-t
formulation l than when used in the resin blend (~10).
Physical/Mechanical Properties
Flexural, tensile as well as tensile elongation data for the various
systems were obtained at room temperature according to ASTM test
methods D--790 and D-638, respectively. Heat deflection temperatures
(HDT) were determined by ASTM - D-648.
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The results are noted hereinbelow:
l ~2 ~9
_,. .
Flexural Strength (psi)12,000 13,800 12,860
Flexural Modulus (psi)1.4xlO 1.6xlO 1.7xlO
Tensile Strength (psi)10,160 9,268 8,300
Tensile Modulus (psi?1.5xlO 1.5xlO 1.6xlO
Tensile Elongation (%)0.70 0.70 0.59
HDT (C) 201 201 203
The similarity in most values provides f~lrther indication that the
resin systems bf the instant invention provide comparable mechanical
properties to systems based on pure multifunctional resin. It is
important to note, however, that the respective values for room
temperature flexural modulus and room temperature % tensile elonga-
tion provide a clear indication that the instant systems show im-
proved flexibility and elongation characteristics.
Moisture Absorption
Molded samples were weighed, subjected to the conditions noted in
the following table and then reweighed in order to determine moisture
absorption.
Percent l~eight Increase
Test Condition l ~2 ~9 ~13
24 hr. complete immersion at R.T. 0.05 0.04 0.04 0.06
48 hr. complete immersion at50C0.27 0.29 0.32 0.33
24 hr. in steam at 121C and 1.42 1.31 1.52 1.51
15 pSig
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Once again, it is to be noted that the instant systems show improved
performance characteristics in an important variable. Thus, the con-
trols ~9 and ~13 exhibit increased moisture absorption, particularly
at the more severe test conditions.
Summarizing, it is seen that this invention provides novel solid
epoxy resin systems which exhibit excellent performance characteris-
tics. Variations may be made in proportions, procedures and materials
without departing from the scope of the invention as deEined by the
following claims.
