U.S. patent number 5,280,053 [Application Number 08/026,913] was granted by the patent office on 1994-01-18 for machinable, high strength epoxy tooling compositions.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to Richard P. Atkins, Thomas J. Dearlove, Chen-Shih Wang.
United States Patent |
5,280,053 |
Dearlove , et al. |
January 18, 1994 |
Machinable, high strength epoxy tooling compositions
Abstract
A machinable, high strength epoxy tool which is the polymeric
reaction product of a mixture containing 5 to 12 weight percent of
a bisphenol A epoxy, 3 to 8 weight percent of at least one
polyoxypropylene amine catalyst, 60 to 85 weight percent of a
mixture of no less than three different sized particulate fillers,
the major portion of which is iron powder, 5 to 15 weight percent
of short (<250 .mu.m) glass fibers, and 0.02 to 1 weight percent
of a surface active agent.
Inventors: |
Dearlove; Thomas J. (Shelby
Township, Macomb County, MI), Atkins; Richard P. (Utica,
MI), Wang; Chen-Shih (Troy, MI) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
26701806 |
Appl.
No.: |
08/026,913 |
Filed: |
March 5, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
880382 |
May 8, 1992 |
|
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Current U.S.
Class: |
523/435; 428/413;
428/417; 523/444; 523/458 |
Current CPC
Class: |
C08K
3/08 (20130101); C08K 7/14 (20130101); C08L
63/00 (20130101); C08K 3/08 (20130101); C08L
63/00 (20130101); C08K 7/14 (20130101); C08L
63/00 (20130101); C08L 63/00 (20130101); Y10T
428/31511 (20150401); Y10T 428/31525 (20150401); C08L
2666/22 (20130101) |
Current International
Class: |
C08K
3/00 (20060101); C08K 3/08 (20060101); C08L
63/00 (20060101); C08K 7/00 (20060101); C08K
7/14 (20060101); C08K 003/34 (); C08K 003/40 ();
C08L 063/02 () |
Field of
Search: |
;523/435,444,458
;428/413,417 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Marquis; Melvyn I.
Assistant Examiner: Aylward; D.
Attorney, Agent or Firm: Grove; George A.
Parent Case Text
FIELD OF THE INVENTION
This is a continuation-in-part application of our co-pending
application Ser. No. 07/880,382, filed May 8, 1992 now abandoned.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A cast, high strength, machinable epoxy tool which is the
polymeric reaction product of a filled epoxy resin-curing agent
mixture consisting essentially of, on a weight percentage basis of
the total said mixture,
8 to 20 percent of epoxy resin-curing agent system consisting
essentially of a liquid diglycidyl ether of bisphenol A and at
least one liquid di-or tri-amine functional polyoxyalkylene amine
reactive with said bisphenol A as a curing agent,
60 to 85 percent particulate filler, a major portion of which is
iron powder, said filler being characterized by the presence of at
least three distinct size groupings of which each successively
smaller group is about one-quarter or less the mean size of the
next larger group,
5 to 15 percent glass fibers up to 250 micrometers in length,
and
0.02 to 1.0 percent of an agent consisting essentially of a
polymeric material selected from the group consisting of butadiene
polymer, poly(vinyl isobutyl ether) and alkyl siloxane
polymers.
2. A cast, high strength, machinable epoxy tool which is the
polymeric reaction product of a filled epoxy resin-curing agent
mixture consisting essentially of, on a weight percentage basis of
the total said mixture,
8 to 20 percent of epoxy resin precursors consisting essentially of
a liquid diglycidyl ether of bisphenol A and at least one liquid
di- or tri-amine functional polyoxyalkylene amine reactive with
said bisphenol A as a curing agent,
60 to 85 percent particulate filler sized for interstitial mixing,
at least 80 percent of which is iron powder, said filler being
characterized by the presence of at least three distinct size
groupings of which each successively smaller group is about
one-quarter or less the mean size of the next larger group,
5 to 15 percent glass fibers up to 250 micrometers in length,
and
0.02 to 1.0 percent of an agent consisting essentially of a
polymeric material selected from the group consisting of butadiene
polymer, poly(vinyl isobutyl ether) and alkyl siloxane
polymers.
3. A cast epoxy tool as recited in claim 2 where said polymeric
material is butadiene polymer.
4. A cast epoxy tool as recited in claim 2 where said polymeric
material is poly(vinyl isobutyl ether).
5. A cast epoxy tool as recited in claim 2 where said polymeric
material is an alkyl siloxane polymer.
Description
The present invention generally relates to a machinable, high
strength epoxy tooling composition for mass-cast and cast-to-size
forming tools used in metal sheet stamping and, more particularly,
it is concerned with a machinable, high strength epoxy tooling
composition for making mass-cast and cast-to-size forming tools for
metal sheet stamping which contains fillers, short glass fibers and
a surface active agent.
BACKGROUND OF THE INVENTION
Forming dies for the repetitive stamping of large numbers of
identical sheet metal parts are made of high strength tool steel
because of its rigidity and durability. In the automotive industry,
forming dies made of tool steel are used to stamp automobile body
parts from steel sheets. However, such dies are expensive and
require appreciable manufacturing time because large castings must
be made and complex forming surfaces accurately machined.
It is a common practice in the automotive industry that before a
new vehicle having a new body style is put in production, prototype
vehicles are first built for testing. Designing forming tools with
tool steel for stamping sheet metal parts used in these prototype
vehicles would not be practical for several reasons. First, a
prototype vehicle has to be built in a relatively short time which
prohibits the use of tool steel for stamping dies due to the
extensive machining required. Secondly, the design of a prototype
vehicle is frequently changed many times from its original design
before it reaches a final production model. This means that many
stamping dies would have to be built before the design of a sheet
metal part is finalized, thus making the building of stamping dies
with tool steel prohibitive for cost reasons.
Prototype stamping tools have been made using a zinc alloy material
called Kirksite. Even though a Kirksite tool is more economical to
make than a steel die, a Kirksite tool still requires the use of a
foundry as well as extensive machining to obtain the desired
contour and close match between the tool halves. Furthermore,
Kirksite tools are heavy and difficult to handle.
In recent years, there has been a renewed effort to develop
mass-castable polymeric materials to make large and durable sheet
metal forming tools. One family of these commonly used materials is
epoxy resins.
It is well known in the art that it is extremely difficult to
formulate a mass-castable, room temperature, fast curing epoxy that
can be cast-to-size into high strength tools. By mass-castable, we
mean the pouring of a liquid epoxy composition in one casting step
to produce a completed portion of a tool. By cast-to-size, we mean
a process in which the exact contour is obtained on the surface of
a tool such that no machining, barbering or spotting on the tool
surface is required.
For instance, U.S. Pat. No. 4,423,094 to Dearlove et al disclosed a
tough, durable bisphenol A epoxy composition for use in making
sheet metal stamping dies. While this material exhibits good
mechanical strength, it does not form a durable punch for stamping
tools. Moreover, it requires an extensive curing procedure, i.e.,
it must be hardened at room temperature overnight and then
post-cured at 150.degree. C. for two hours. Since most stamping
tools for automobile body panels are large in size and weight, it
is preferable to make dies that need no elevated temperature
curing.
Others have used room temperature-curable epoxy resin systems such
as those based on bisphenol A and an aromatic amine catalyst to
make plastic tools. An extensive curing period of from four days to
one week is required for this type of room temperature-curable
epoxy composition. To achieve rapid cure, i.e., to cure in less
than 24 hours, an aliphatic amine catalyst instead of an aromatic
amine catalyst must be used in an epoxy molding composition. This
type of rapid curing epoxy system has been used in adhesives and
coatings where the maximum thickness of the epoxy layer is no more
than 6.4 mm thick.
Attempts to use unfilled aliphatic amine catalyzed epoxy
compositions in bulk casting epoxy tools met with little success.
The major problems encountered in casting a bulk section epoxy tool
with a rapid curing epoxy composition were severe shrinkage and
dimensional distortion which led to unacceptable warpage of the
tool. These problems were caused by the extreme heat generated by
the exothermic curing process. Since the curing process proceeds
very rapidly, the exothermic heat accumulated in a bulk section
epoxy tooling could not be rapidly dissipated by heat transfer due
to the low thermal conductivity of epoxy. This caused the formation
of localized heat pockets and thermal shocks which led to
shrinkage, cracking, and dimensional distortions.
When a material is selected for building stamping tools, both its
compressive strength and its tensile strength are important
considerations. To sustain a high compressive load in the vertical
direction, a tooling material must have high compressive strength.
Similarly, to sustain a high tensile load in the horizontal
direction, a tooling material must also have high tensile strength.
This type of tensile load, for example, is frequently seen in the
cavity of a stamping tool having a V-shaped concave configuration
in the tool surface. No commercially available mass-cast epoxy
tooling materials have the necessary combination of compressive
strength and tensile strength for making stamping tools.
U.S. Pat. No. 4,920,161 to Wang et al disclosed that within a
specific range of formulations, 24-hour room temperature cured
cast-to-size epoxy tooling materials with high tensile strength can
be obtained. These formulations contained high loadings of specific
particle sizes of inert fillers, in particular, silicon carbide and
silica. The patent specifically taught rapidly-curable,
distortion-free compositions that achieved high tensile strength as
compared to commercial tooling materials.
It is desirable to use inert fillers other than silicon carbide or
silica in epoxy tooling compositions. Tools cast with silicon
carbide and/or silica fillers were found to be very difficult to
subject to post processing such as minor machining, drilling,
tapping, etc., for incorporating engineering changes. In addition,
silicon carbide is moderately expensive and adds to the cost of the
tooling material. However, substitution of other known suitable
particulate fillers for the silicon carbide resulted in significant
reductions in tensile strength.
It is, therefore, an object of the present invention to provide a
mass-castable, highly filled epoxy tooling composition that has
high tensile and compressive strength sufficient for making durable
stamping tools that can be machined to make post-processing
changes.
It is another object of the present invention to provide an epoxy
tooling composition that can be rapidly cured at room temperature
in less than 24 hours without significant dimensional
distortion.
It is yet another object of the present invention to provide an
epoxy tooling composition that can be rapidly cured at room
temperature in less than 24 hours to make a cast-to-size metal
sheet forming die by utilizing inert fillers other than silicon
carbide.
It is a further object of the present invention to provide an epoxy
tooling composition that can be rapidly cured into a dimensionally
stable machinable sheet metal forming tool by utilizing a suitable
combination of appropriately-sized iron fillers, short glass fiber
reinforcements, and a surface active agent.
SUMMARY OF THE INVENTION
We provide a machinable, high strength, cast-to-size epoxy tooling
composition that can be rapidly cured at room temperature in 12
hours and be used in casting a durable epoxy tool.
In accordance with a preferred embodiment of our invention, we
utilize a highly-filled aliphatic amine/bisphenol A epoxy system. A
diglycidyl ether of suitable viscosity is used preferably with at
least one polyoxypropylene amine reactant. This epoxy resin-curing
agent system constitutes about 8 to 20 percent by weight of the
moldable mixture.
We use a particulate filler mixture comprising interstitially
mixable particles of at least three different average sizes or size
ranges. Iron powder of at least two different average sizes (e.g.,
300 .mu.m and 30 .mu.m) constitutes 80 percent or more of the total
particulate filler by weight. Any suitable other filler material
(of complementary third particle size, e.g. about 3 .mu.m) such as
calcium carbonate is employed to accomplish the desired filler
loading. Our particulate filler mixture constitutes about 60 to 85
percent by weight of the total moldable mixture. The total mixture
serves, in part, as a heat sink to absorb and conduct away the heat
of reaction of the resin-forming constituents. The fillers are not
reactive with each other or the epoxy resin-curing agent system.
The iron powder assures that the cured tool is machinable.
In addition to the particulate filler, we use short glass fibers
(average length less than 250 micrometers). Surprisingly, such
fibers are found to not unduly increase the viscosity of the
castable mixture. The fibers do not increase the strength of the
tool. The fibers make up 5 to 15 percent by weight of the moldable
composition.
We have discovered unexpectedly that it is beneficial to use a
combination of short glass fibers and certain additives that we
call surface active agents in conjunction with iron fillers to
produce machinable epoxy tooling formulations that exhibit
excellent tensile strength. By surface active agents, we mean those
materials that, together with the glass fibers, iron powders and/or
other constituents, are found to markedly increase the tensile
strength of the cured stamping tool. We set a target tensile
strength at 58 to 60 MPa as a requirement for our stamping tools.
At the same time, in order to retain other desirable properties
such as low shrinkage and pourability, the formulations require the
use of high filler loadings of interstitially-mixed particle sizes.
We have discovered a group of surface active materials that are
required when added in small quantities to increase tool strength
without affecting its machinability.
Suitable additives are solid polymeric materials dissolved in a
liquid vehicle. Such additives include polybutadiene/di-n-butyl
adipate, poly(vinyl isobutyl ether) or poly(methyl n-octyl
siloxane)/poly(propylene glycol). These additives as solutions are
used in small amounts usually less than one percent by weight of
the total tool composition.
Other objects, features and advantages of the present invention
will become apparent upon consideration of the specification that
follows.
DESCRIPTION OF PREFERRED EMBODIMENTS
The concept of using an interstitially-matched filler system in
which the smaller particulate fillers fit in the interstitial
spacings left by the larger and median size particle fillers was
first proven and disclosed in our previous patent U.S. Pat. No.
4,920,161 assigned to the same assignee. While the compositions
disclosed lacked machinability, our experience indicated that at a
viscosity level of less than 150.times.10.sup.3 centipoise, the
filled epoxy composition was freely pourable and could be used in a
cast-to-size tool making operation.
The epoxy resin used in our invention is a diglycidyl ether of
bisphenol A supplied by Rhone-Poulenc, Inc., under the trade name
of Epi-Rez 509. This epoxy resin has an approximate epoxy
equivalent weight of about 180 to 196 and a viscosity at 25.degree.
C. in the range of 7500 to 9500 centipoise. Other commercial
products that are substantially equal to this epoxy compound are
Dow Chemical DER 330 resin, Ciba-Geigy Araldite 6005, and Shell
Epon 826.
To achieve the fast curing reaction of our epoxy casting
formulation, a blend of two aliphatic amines, polyoxypropylene
triamine and polyoxyalkyleneamine, is used as the curing agent. The
aliphatic amines are supplied by the Texaco Chemical Company under
the trade name of Jeffamine T-403 and Jeffamine D-400. Jeffamine
T-403 is a trifunctional primary amine having an average molecular
weight of approximately 440. Its amine groups are located on the
secondary carbon atoms at the ends of aliphatic polyether chains.
Jeffamine D-400 is a difunctional primary amine having an average
molecular weight of approximately 400.
Table I shows the effect of various particulate fillers on the
tensile strength, tensile modulus and percent elongation of
aliphatic amine/bisphenol A resin tooling formulations.
TABLE I ______________________________________ Effect of Various
Particulate Fillers (WT %) I II III IV V VI VII
______________________________________ Epoxy Resin 509 18.6 68.3
16.7 17.3 10.2 20.2 10.2 Jeffamine T-403 6.1 22.2 6.1 5.7 3.3 6.6
3.3 Jeffamine D-400 2.6 9.5 2.7 2.4 1.4 2.8 1.4 Silica-21 13.0 13.3
13.3 9.7 14.0 9.7 Silicon Carbide-100 43.2 Silicon Carbide-400 16.5
Silica-85 44.4 Silica-23 16.8 Al.sub.2 O.sub.3 -80 44.4 Al.sub.2
O.sub.3 -400 16.9 Iron ATW-432 55.7 Iron ATW-230 19.7 Aluminum 120
47.0 Aluminum 1401 9.4 Zinc 1206 55.7 Zinc 1222 19.7 Tensile
Strength 59.5 64.0 49.1 54.1 48.8 49.5 46.6 (MPa) Tensile Modulus
12.4 3.2 12.8 15.3 12.3 10.8 10.7 (GPa) Elongation (%) 0.5 4.5 0.9
0.4 0.3 0.7 0.6 ______________________________________
In Table I, compound I is a formulation that was disclosed in U.S.
Pat. No. 4,920,161. In this compound, silica-21 has a particle size
distribution of 51% smaller than 5 microns, 90% smaller than 15
microns and an average particle size of 2 microns. It is supplied
by Whittaker, Clark & Daniels, Inc. Silicon carbide-100 has
particle sizes in the range between 63 and 203 microns with an
average particle size of 122 microns. Silicon carbide-400 has
particle sizes in the range between 11 and 45 microns with an
average particle size of 22 microns. Both are commercially
available from Electro Abrasives Corporation.
Compound I has good strength, but the high silicon carbide content
causes difficulty in machining.
Compound II is a pure epoxy material which has a high tensile
strength and a very low tensile modulus value.
Compound III, instead of silicon carbide particles, has a total of
three different silica particulate fillers in which silica-85 is an
85 mesh washed silica sand supplied by the Weldron Silica Company.
Silica-23 is another silica commercially available from Whittaker,
Clark & Daniels, Inc. It has a particle size distribution of
80% smaller than 200 mesh, 70% smaller than 325 mesh. It is seen
that compound III, which eliminates silicon carbide, has a reduced
tensile strength value of only 49.1 MPa. This illustrates the need
for the selection of suitable filler combinations to complement the
rapid curing epoxy precursors.
Compound IV has one silica filler and two aluminum oxide fillers
supplied by Electro Mineral Corporation. Al.sub.2 O.sub.3 -80 is 80
mesh aluminum oxide powder and Al.sub.2 O.sub.3 -400 is 400 mesh
aluminum oxide powder. Aluminum oxide fillers contribute to the
strength of the filled epoxy composition, but the abrasiveness of
this filler will also cause difficulty in machining.
In compound V, two iron filler powders, ATW-432 and ATW-230
supplied by Hoeganaes, are used in place of the aluminum oxide.
These iron fillers contain 98 to 99 percent iron. The sieve
analysis of ATW-432 indicated 2% greater than 425 microns, 61%
between 180 and 425 microns, 32% between 75 and 180 microns and 5%
between 44 and 75 microns. For purposes of characterizing the mean
size of ATW-432 in formulating our compositions, we note that the
bulk of the iron powder lies between 180 microns and 425 microns.
We treat it as having a mean size of about 300 .mu.m. The sieve
analysis of ATW-230 indicated 4.7% between 62 and 88 microns, 17.6%
between 44 and 62 microns, 28.8% between 31 and 44 microns, 26.9%
between 22 and 31 microns, 15.1% between 16 and 22 microns, 5.5%
between 11 and 16 microns, and 2.4% at less than 11 microns. For
purposes of characterizing the mean size of ATW-230 in formulating
our compositions, we note that the preponderance of the powder lies
between 22 and 44 microns. We treat it as having a mean size of
about 33 .mu.m. It is seen in compound V that epoxy composition
with iron fillers alone does not meet our tensile strength value
target of 58 to 60 MPa.
Compound VI contains aluminum powder of aluminum 120 and aluminum
1401 supplied by Alcoa. Aluminum 120 has an average particle size
between 25 to 30 microns with 25% to 50% smaller than 44 microns
and containing 99.7% aluminum 1401 has an average particle size
between 6 to 9 microns with 98% smaller than 44 microns and
containing 99.7% aluminum. Aluminum powder-filled epoxy
compositions do not meet our target for tensile strength values.
Compound VII is an epoxy formulation containing zinc fillers of
zinc 1206 and zinc 1222 supplied by Zinc Corporation of America.
Zinc 1206 is 99% zinc with 45% smaller than 150 microns. Zinc 1222
is 99% zinc with 30% to 70% smaller than 44 microns. It is also
seen that zinc fillers do not provide a tensile strength value of
58 to 60 MPa to the epoxy composition.
Table II shows the unexpected result of using an additive
commercially known as an epoxy resin fortifier and a short glass
fiber to improve tensile strength of certain of our epoxy
compositions. We have now settled on the use of a high proportion
of iron filler because of its contribution of strength and
machinability.
TABLE II ______________________________________ Use of Fortifiers
and Glass Fibers to Improve Tensile Strength (WT %) II VIII V IX X
XI ______________________________________ Epoxy Resin 509 68.3 59.7
10.2 8.9 10.0 8.8 Jeffamine T-403 22.2 21.9 3.3 3.3 3.3 3.2
Jeffamine D-400 9.5 9.6 1.4 1.4 1.4 1.4 Silica 21 9.7 CaCO.sub.3
9.7 9.5 9.6 EF-20 8.9 1.3 1.3 Iron ATW-432 55.7 55.7 54.8 54.8 Iron
ATW-230 19.7 19.7 9.3 9.3 Glass Fibers 737BC 11.7 11.6 Tensile
Strength (MPa) 64.0 68.1 48.8 53.5 49.5 60.2 Tensile Modulus (GPa)
3.2 2.9 12.3 13.5 11.9 11.8 Elongation (%) 4.5 3.6 0.3 0.5 0.3 0.4
______________________________________
Compounds II and VIII are both compositions which do not contain
any fillers. The addition of the fortifier EF-20 to compound II led
to compound VIII and shows that an improvement in tensile strength
from 64 to 68.1 MPa was obtained. EF-20 is a non-elastomeric
modifier for cured epoxy resins supplied by the Polysar
Corporation. It is a liquid mixture of approximately molecularly
equivalent portions of 3,4-epoxy cyclohexylmethyl-3',4'-epoxy
cyclohexane carboxylate and a p-aminotoluene adduct of such
epoxylated cycloaliphatic material. It has a viscosity at
60.degree. C. between 200 to 1500 centipoise and a specific gravity
of 1.20 and an epoxy equivalent weight of 131 to 143. Compound IX
containing iron fillers and fortifier EF-20 and compound X
containing iron fillers and glass fibers both gave low tensile
strengths of 53.5 and 49.5 MPa, respectively. In compound X, short
glass fibers were used to avoid drastic increases in viscosity that
we experienced with longer fibers. Thus, we maintained the
pourability of the material. The combined effect of a fortifier
EF-20 and glass fibers when used in conjunction with iron fillers
is shown in compound XI. A synergistic effect between the
fortifier, the glass fibers and the iron fillers resulted in a
significantly higher tensile strength of 60.2 MPa.
The calcium carbonate used in Table II was supplied by Whittaker,
Clark & Daniels, Inc. under the trade name of Clarcal 9125. It
contains 97% to 99% CaCO.sub.3 and trace amount of MgCO.sub.3,
Al.sub.2 O.sub.3 and SiO.sub.2. It has a specific gravity of 2.71
and a mean particle size of 3.2 microns. The glass fibers 737BC is
commercially available from Owens Corning. It is a silane-treated
milled glass with an average length of 53 microns and an average
diameter of 16 microns. We believe glass fibers having a length up
to 250 microns may suitably be used.
The respective constituents of each compound were incorporated and
mixed so as to uniformly distribute all ingredients. The mixing was
done in vacuum so as to remove air from the liquid-solids mixture
and avoid bubble formation in the cast part. In these examples, the
formulation was cast into tensile test specimens which were cured
at room temperature for 12 hours.
Since EF-20 is not reactive in our epoxy system, we suspected that
it might be functioning as a surface active agent. Therefore, we
investigated another fortifier and several other known wetting and
dispersing (surface active) agents. The results are shown in Table
III.
TABLE III ______________________________________ Effect of Surface
Active Agents (WT %) X XI XII XIII XIV XV XVI XVII
______________________________________ Epoxy 10.0 8.8 8.8 10.0 10.0
10.0 10.0 10.0 Resin 509 Jeffamine 3.3 3.2 3.2 3.3 3.3 3.3 3.3 3.3
T-403 Jeffamine 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4 D-400 CaCO.sub.3
9.5 9.6 9.6 9.6 9.6 9.6 9.6 9.6 Iron 54.8 54.8 54.8 54.7 54.7 54.7
54.7 54.7 ATW-432 Iron 9.3 9.3 9.3 9.3 9.3 9.3 9.3 9.3 ATW-230
Glass 11.7 11.6 11.6 11.6 11.6 11.6 11.6 11.6 Fibers 737BC EF-20
1.3 EF-15 1.3 BYK-052 0.1 BYK-W980 0.1 BYK-W935 0.1 BYK-A525 0.1
BYK-A500 0.1 Tensile 49.5 60.2 63.2 58.1 53.4 51.2 56.1 59.6
Strength (MPa) Tensile 11.9 11.8 12.8 10.0 15.7 15.9 15.9 16.3
Modulus (GPa) Elongation 0.3 0.4 0.6 0.6 0.4 0.4 0.4 0.4 (%)
______________________________________
In Table III, EF-15 is another fortifier supplied by the Polysar
Corporation. It is a non-elastomeric modifier for improving the
physical properties and performance of amine-cured epoxy composites
and consists of 50 weight percent of an aromatic ether ester amide
(approximately 430 MW), 25 weight percent mono amide of glutaric
acid and 25 weight percent of diphenyl ether of glycerine. It has a
viscosity at 60.degree. C. approximately 1000 centipoise and a
specific gravity of 1.16.
The BYK additives were a series of wetting and dispersing agents
made by the BYK Chemie Company. It appears that these additives
enable better bonding between resin, glass and fillers. We found
that certain of them produced higher physical properties in our
epoxy tool compositions.
BYK-052 is a solution of poly(vinyl isobutyl ether) in Stoddard
solvent and 2-butoxy ethanol (about 28 percent solids by weight).
Stoddard solvent is a petroleum distillate per ASTM D-484-52.
BYK-W980 is a solution of a salt of unsaturated polyamine amides
and higher molecular weight acidic esters in xylene and 2-butoxy
ethanol (about 75% solids by weight). BYK-W935 is a solution of a
higher molecular weight unsaturated polycarboxylic acid in xylene
and 2,6 dimethyl-4 heptanone (about 50% solids by weight). BYK-A525
is a solution of poly(methyl-n-octyl siloxane) (72 weight percent)
and poly(propylene glycol) (28 weight percent) in Stoddard solvent
and 1-methoxy-2-propanol acetate. BYK-A500 is a solution of
polybutadiene (64 weight percent) and di-n-butyl adipate (36 weight
percent) in an aromatic/aliphatic petroleum naphtha.
Although these BYK surface active materials were added as solutions
to their respective formulations, the mixing was done in vacuum,
and it is believed that the solvent portions were evaporated. The
principal contribution of the additives was from their solid
residue.
In close examination of data contained in Table III, compound X,
which contains iron fillers and glass fibers but no surface active
agent, has a tensile strength of only 49.5 MPa and a low tensile
modulus of 11.9 GPa. Compound XI and compound XII containing
surface active agents of EF-20 and EF-15, respectively, produce a
much higher tensile strength of 60.2 MPa and 63.2 MPa,
respectively. However, the tensile modulii of these two compounds
are approximately the same as that of compound X. Compound XIII
through compound XVII all contain surface active agents produced by
BYK Chemie Company. It is seen that they all have improved tensile
strength when compared to compound X. Specifically, compound XVII
which contains BYK-A500 surface active agent has the best
combination of properties, i.e., a tensile strength of 59.6 MPa and
a tensile modulus of 16.3 GPa. Therefore, BYK-A500 surface active
agent appears to be the most effective additive for our epoxy
composition containing iron fillers and glass fibers. We also view
BYK-052 and BYK-A525 as suitable additives for use in our
compositions.
To further investigate the effect of using BKY-A500 surface active
agent, we have conducted another series of experiments by adding
different quantities of BYK-A500 as the surface active agent. These
data are contained in Table IV. A full range of concentration of
BYK-A500 was investigated in the range between 0.03 and 0.17 weight
percent of the total epoxy composition. It appears that compounds
XVIII, XIX, XX and XVII containing between 0.03 and 0.14 weight
percent of the surface active agent BYK-A500 all have greatly
improved tensile strength and tensile modulus values.
TABLE IV ______________________________________ Effect of
Concentration of BYK-A500 (WT %) X XVIII XIX XX XVII XXI
______________________________________ Compound X 100 99.97 99.93
99.90 99.86 99.83 BYK-A500 0 0.03 0.07 0.10 0.14 0.17 Tensile
Strength 49.5 60.3 63.4 60.6 59.6 53.2 (MPa) Tensile Modulus 11.9
15.9 14.2 12.8 16.3 11.3 (GPa) Elongation % 0.3 0.4 0.5 0.5 0.4 0.5
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In general, we found that the epoxy fortifiers EF-15 and -20 are
not preferred for use in our formulations because of their expense
and their high viscosity, which made it difficult to suitably
incorporate them into large volume formulations for the making of
epoxy tools.
Thus, our epoxy tool compositions contain, by weight, about 8 to 20
percent epoxy resin-curing agent system that consists essentially
of 5 to 12 percent of a diglycidyl ether of bisphenol A and 3 to 8
percent of an aliphatic di- or tri-amine curing agent. Preferably,
the bisphenol A has an epoxy equivalent weight in the range of 180
to 196 and/or a viscosity at 25.degree. C. in the range of 7500 to
9500 centipoise. For suitably rapid curing of our resin and for
as-cured properties, we prefer the use of polyoxyalkyline di-
and/or tri-amines. A mixture of polyoxypropylene di- and tri-amines
each having molecular weights of 400 to 440 is especially
preferred.
Our epoxy compositions are highly filled--using 60 to 85 percent of
three distinct size groupings of particulate fillers, mostly iron
powder, 5 to 15 percent short glass fibers up to about 250 .mu.m in
length, and a small amount, suitable up to one percent and
preferably 0.02 to 0.2 percent, of a suitable "surface active"
agent that enhances the contributions of all the ingredients to
form a surprisingly strong stamping tool.
An air bubble-free uniform mixture of epoxy resin precursors,
particulate filler, glass fibers and surface active agent is
completed just prior to casting of the tool. Of course, an accurate
pattern of the tool has been prepared and located in a suitable
container for the fluid mixtures. The castable mixture is carefully
poured into such mold so as to avoid entrainment of air or other
contamination. The cast mixture is then allowed to stand at room
temperature.
Typically within about 12 hours, the epoxy resin-curing agent
system has reacted to form a strong resinous matrix entraining iron
powder, other powder interstitially mixed with the iron, and short
glass fibers. The combination of iron, short glass fibers and
surface active material contributes to the castability of the
mixture and the strength, durability and machinability of the
substantially cast-to-size tool.
While our invention has been described in terms of certain specific
examples, it is apparent that suitable variations could be made in
view of our specification. Accordingly, we intend to be limited
only by the scope of the following claims.
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