Binder system and method for particulate material

The present invention relates to a binder composition comprising a polycarbonate polymer; an ethylenebisamide wax; and a guanidine wetting agent. The present invention further relates to a method for forming a sintered part by powder injection molding, including the steps of forming a green composition comprising a binder and an inorganic powder, wherein binder is a composition comprising a polycarbonate polymer, an ethylenebisamide wax, and a guanidine wetting agent; melting the composition; injecting the composition into a mold for a part; heating the part to a temperature at which the binder decomposes; heating the part to a temperature at which the inorganic powder is sintered. The binder composition of the present invention is useful for press and sinter applications as well as for powder injection molding applications.

FIELD OF THE INVENTION 
The present invention relates to binder compositions for use in forming 
sintered parts by powder injection molding and to green compositions of 
the binder composition and inorganic powders. The binders of the present 
invention require fewer steps to produce a part, have higher thixotropic 
energy, melt at a lower temperature, provide a green body having high 
strength, and decompose thermally in a clean, substantially ash-free 
burnout to yield simple, environmentally safe products. 
BACKGROUND OF THE INVENTION 
Processes for forming shaped articles from particulate mixtures are known 
in the art. Classically, a desired particulate material is mixed with a 
binder and then formed into the desired shape, this being called a green 
body. The green body is then fired to provide a fusion of the particulate 
material and to drive off the binder, thereby producing the desired shaped 
product with proper surface texture, strength, etc. Modern methods include 
press and sinter (P&S) and powder injection molding (PIM). In P&S, a 
mixture of one or more of a metal, metal oxide, intermetallic or ceramic 
powder and a small amount of binder (about 5% of the powder volume) are 
placed in a relatively simple mold, pressed into a green body, and then 
sintered. The small amount of binder is decomposed during the sintering 
step, so a separate step of removing the binder is not necessary. However, 
P&S is limited to simple parts. 
In PIM, a mixture of one or more of a metal, metal oxide, intermetallic or 
ceramic powder and a quantity of binder from 30% to 60% of the volume of 
powder are heated to a liquid state and then injected under pressure into 
a mold to form a part. Once in the mold, the binder is removed in one or 
more separate steps and the part is fired to sinter the particles into a 
solid part. PIM is capable of producing quite complex parts. 
In the production of shaped objects by PIM in the manner above described, 
it has been found that the binder, while necessary to the process, creates 
problems. The binder must be used in order to form an object of practical 
use, but most of it must be removed before the part can be sintered, 
although in some cases a portion of the binder remains until sintering is 
completed. 
Direct removal of the PIM binder during sintering is problematic. Many 
binders leave behind ash upon decomposition. When such ash combines with 
certain ingredients in the powder component, eutectic mixtures may be 
formed. Such eutectic compounds as TiC may be formed from titanium and 
carbon ash, and these can result in serious problems in the formed part. 
Thermoplastic binders which decompose on heating have been used. However, 
these materials tend to soften or melt first and then decompose, creating 
problems on decomposition. Thermoplastic materials have been tried which 
decompose below their melting point and thereby remain in place until 
decomposition. Binders have been removed by exposure to a decomposing 
atmosphere, such as an acid atmosphere to decompose an acid-labile organic 
binder. The drawback of this approach is the use of an acid atmosphere, 
requiring a special chamber and hazardous material handling capabilities. 
Similar binders which are subject to catalytic decomposition have been 
used, such as a polyacetal. The drawback of this approach is that the 
decomposition product is formaldehyde, which also requires special 
equipment to collect and decompose the formaldehyde. 
The prior art has recognized this problem and has therefore attempted to 
remove the binder from the shaped green body prior to the step of firing. 
Such processes have used various solvents, including organic solvents, 
triple-point CO2, and water to dissolve and remove the binder. While 
systems using such procedures can provide advantages over procedures 
wherein the binder is removed during firing, articles formed by removing 
the binder prior to firing still have the tendency to crack during the 
binder removal as well as during the firing operation. One reason for this 
is that the binder is removed from the green body by means of a solvent 
when the binder is in the solid state, and upon dissolution the binder, 
the binder-solvent mixture has a tendency to expand. This problem has been 
approached by various means, including heating the green body prior to 
exposing it to the solvent, by using a solvent to remove a portion of the 
binder and removing the remainder by firing, and by using a two-part 
binder, each part of which is soluble in a different solvent, so each 
solvent removes a portion of the binder, and by using the different 
solvents in a stepwise manner. Each of these methods includes its own 
drawbacks. 
Thus, the need remains for binders which are useful, particularly in powder 
injection molding, which require a minimum number of steps to remove, 
which have high thixotropic energy, which melt at a low temperatures, 
which provide a green body having high strength, and which decompose 
thermally to yield simple, environmentally safe products, substantially 
free of ash, thereby yielding a binder which performs its function but 
which provides a process of powder injection molding which proceeds with a 
minimum number of process steps, can be carried out in an air atmosphere 
in many cases, and does not leave behind deleterious residues, either in 
the part or in the environment. The present invention requires only 
simple, standard equipment which is inexpensive and commonly available. 
The steps of debinding and sintering may be carried out in the same 
equipment, on a continuous basis, thereby avoiding downtime for cooling 
and transfer from debinding equipment to sintering equipment. 
SUMMARY OF THE INVENTION 
The present invention relates to a binder composition comprising a 
polycarbonate polymer; an ethylenebisamide wax; and a guanidine wetting 
agent. The present invention further relates to a method for forming a 
sintered part by powder injection molding, including the steps of forming 
a green composition comprising a binder and an inorganic powder, wherein 
binder is a composition comprising a polycarbonate polymer, an 
ethylenebisamide wax, and a guanidine wetting agent; transferring the 
green composition into a mold for a part; heating the part to a 
temperature at which the binder decomposes; and heating the part to a 
temperature at which the inorganic powder is sintered. 
Thus, the binder composition and method of making sintered parts using the 
binder composition of the present invention provide the features missing 
from the prior art. The binder composition may be removed in a minimum 
number of steps, has high thixotropic energy, melts and becomes flowable 
at a low temperature, provides a green body having high strength, and 
decomposes thermally to yield simple, environmentally safe products, 
substantially free of ash. The binder composition thereby performs its 
function while providing a process of powder injection molding which 
proceeds with a minimum number of steps, can be debound in air, hydrogen, 
oxygen, argon, nitrogen and similar gas atmospheres or in vacuum, and does 
not leave behind deleterious residues, either in the part or in the 
environment.

DETAILED DESCRIPTION 
The binder composition and the green composition comprising the binder 
composition and an inorganic powder, each in accordance with the present 
invention, are applicable both to powder injection molding (PIM) 
techniques and to press and sinter (P&S) applications. In PIM, a green 
composition or feedstock comprising an inorganic powder and a binder 
composition is used for powder injection molding, which includes steps of 
debinding and sintering. In P&S applications, a green composition 
comprising an inorganic powder and a binder composition are pressed into a 
mold and sintered to form a part, without a step of debinding. The 
inorganic powders which may be used in the green compositions and method 
of the present invention may be metal, metal oxide, intermetallic and/or 
ceramic, or mixtures of these, depending upon the desired characteristics 
of the final product. The green composition comprising an inorganic powder 
and binder composition of the present invention, may be injection molded 
with an increased loading of the powder compared to prior processes, 
resulting in less shrinkage and deformation during debinding and 
sintering. The components of the binder composition allow debinding of the 
nascent part with decomposition of the binder to yield environmentally 
safe products in a relatively rapid, controllable process, thereby 
efficiently overcoming the deficiencies of the prior art. 
The components of the binder composition are partially miscible with one 
another, such that when the green composition is ready for use, the 
components thereof are sufficiently miscible that the desired parts are 
formed when the composition is pumped into the mold, but the components 
are sufficiently immiscible that the phases can separate and the 
components will "come apart" in a step-wise, controllable manner in an 
oven or kiln during the debinding step. The binder composition of the 
present invention may be removed thermally, in the same oven or chamber in 
which the part is sintered, thereby avoiding a multiple oven, multiple 
step process of debinding and sintering the part 
The present inventor has discovered that the components of the binder 
composition controllably debind in an order which is the opposite of that 
normally sought in the PIM industry. In conventional binder compositions, 
which include, e.g., stearic acid as a surface agent, paraffin wax as the 
wax, and polypropylene as the major binder component, during the debinding 
step of a PIM process, the surface agent releases first, the wax component 
releases next, and the major binder component releases last. 
The components of the binder composition of the present invention, in 
contrast, release in the opposite order. In the binder composition of the 
present invention, the major binder component, a polycarbonate polymer, 
has a decomposition temperature of about 185.degree. C. The wax component, 
an ethylenebisamide wax, has a decomposition temperature of about 
285.degree. C. The guanidine wetting or surface agent is the last 
component to decompose, having a decomposition temperature in the range of 
about 350.degree. C. to about 450.degree. C. Thus, according to the 
present invention, during the debinding step of a PIM process, the 
components of the binder composition debind in an order opposite to that 
of conventional binder compositions. 
As a result of the debinding profile of the binder composition according to 
the present invention, the surface agent, is the last to decompose in the 
debinding step. As a result, the inorganic powder is retained in position 
for a longer time in the pre-sintering portion of the process. Retaining 
the inorganic powder particles in position for a longer time provides the 
benefit of allowing the transition from debinding to sintering to occur 
with a significantly reduced possibility that the inorganic powder 
particles will move or be distorted from their original position in the 
mold. As a result, superior sintered parts are obtained from the PIM 
process using the binder composition of the present invention. 
The partial miscibility of the components of the binder composition 
facilitates the reverse debinding of the present invention. Since the 
polycarbonate polymer is only partially miscible with the other components 
and has a lower glass transition (T.sub.g) and melting or decomposition 
temperature, it can melt and separate from the other components of the 
binder composition, then wick out of the green part first. When the 
polycarbonate component has been removed, the temperature may be raised to 
a temperature at which the next component may be debound. In the present 
invention, the ethylenebisamide is the next component to decompose or be 
debound. Again the partial miscibility of the components aids the 
separation, allowing the ethylenebisamide to decompose with affecting the 
guanidine wetting agent. When the ethylenebisamide has been removed, only 
the guanidine wetting agent remains. At this time, the temperature is 
again increased to the decomposition temperature of the guanidine wetting 
agent, which is in the range from about 350.degree. C. to about 
450.degree. C., depending on the exact nature of the guanidine wetting 
agent, i.e., which acid has been reacted with guanidine to form the 
guanidine wetting agent. Once the guanidine wetting agent has been 
debound, the remaining inorganic powder may be sintered to form the 
desired final part. 
The binder composition of the present invention comprises a polycarbonate 
polymer, a wax such as ethylenebisamide wax, and a guanidine wetting 
agent. Each of these three general component materials is more fully 
disclosed in the following. 
Guanidine Wetting Agent 
In one embodiment, the guanidine wetting agent is a reaction product of 
guanidine and an acid selected from a fatty acid, an organic acid, acid 
and a stronger acid such as an alkyl sulfonic acid. The guanidine wetting 
is a reaction product which may be an amide or actually may be more in the 
nature of a hydrated salt. For example, according to the CRC Handbook of 
Chemistry and Physics, 74th Ed., guanidine acetate has the formula 
(H.sub.2 N).sub.2 C.dbd.NH.CH.sub.3 COOH, rather than an amide-type 
formula such as H.sub.2 N--C.dbd.NH(NH)COCH.sub.3, as would be expected 
for an amide. This is due to the fact that guanidine is a very strong 
base, and is much more likely to simply abstract a proton from a 
relatively weak organic acid, rather than react with the organic acid in a 
"standard" amidization reaction forming an amide with concomitant loss of 
H.sub.2 O. However, in some cases, the reaction of guanidine and the acid 
may yield an amide in the "standard" manner. For this reason, the 
guanidine surface agent of the present invention will be referred to 
herein as the reaction product of guanidine and an acid. The term 
"reaction product of guanidine and an acid" includes both of the 
above-described forms of the product of a reaction between or mixture of 
guanidine and an acid, and mixtures of these forms or other possible 
forms. 
The particular acid used to make the reaction product of guanidine and an 
acid is selected based upon the surface charge of the inorganic powder 
with which the binder composition is to be used. In one embodiment, the 
guanidine wetting agent is guanidine stearate. Guanidine stearate and 
guanidine compounds of similar acids are selected for use with powders 
having a positive surface charge and an isoelectric point at a low pH. In 
one embodiment, the guanidine wetting agent is guanidine ethyl-hexanoate. 
Guanidine ethyl-hexanoate and guanidine compounds of similar acids are 
selected for use with powders having an amphoteric surface charge, and an 
isoelectric point at a near-neutral pH. In one embodiment, the guanidine 
wetting agent is guanidine lauryl sulfonate. Guanidine lauryl sulfonate 
and guanidine compounds of similar acids are selected for use with powders 
having a negative surface charge, and an isoelectric point at a high pH. 
In other embodiments, the guanidine wetting agent may be the reaction 
product of guanidine and other acids. The selection of the appropriate 
acid for preparation of the reaction product of guanidine and an acid 
depends upon the isoelectric point of the inorganic powder. The 
relationship is further described in the following detailed description. 
The many acids which may be reacted with the guanidine to form the 
reaction product of guanidine and an acid are described in detail 
hereafter. 
In general, the appropriate acid depends on the surface charge, or point of 
zero charge (PZC), which may be expressed as the isoelectric point (IEP) 
of the inorganic powder with which the binder composition is to be used in 
the green composition. Isoelectric points may be found in reference 
sources, or may be determined experimentally, by determining the pH at 
which no charge exists on the powder particle. The point of zero charge is 
the average of the pK's for the particular powder, and indicates the 
average acid-base character of the surface. Isoelectric points of a number 
of ceramic oxide materials are shown in the following table: 
TABLE 
______________________________________ 
Isoelectric Points of Oxides 
Material Nominal Composition 
IEP 
______________________________________ 
Muscovite KAl.sub.3 Si.sub.3 O.sub.11 H.sub.2 O.sub.11 
1 
Quartz SiO.sub.2 2 
Delta manganese oxide MnO.sub.2 2 
Soda lime silica glass 1.00Na.sub.2 O 0.58CaO 3.70SiO.sub.2 2-3 
Albite Na.sub.2 O Al.sub.2 O.sub.3 
6SiO.sub.2 2 
Orthoclase K.sub.2 O A1.sub.2 O.sub.3 6SiO.sub.2 3-5 
Silica (amorphous) SiO.sub.2 3-4 
Zirconia ZrO.sub.2 4-5 
Rutile TiO.sub.2 4-5 
Tin Oxide SnO.sub.2 4-7 
Apatite 10CaO 6PO.sub.2 2H.sub.2 O 4-6 
Zircon SiO.sub.2 ZrO.sub.2 5-6 
Anatase TiO.sub.2 6 
Magnetite Fe.sub.3 O.sub.4 6-7 
Hematite .alpha.F.sub.3 O.sub.3 6-9 
Goethite FeOOH 6-7 
Gamma iron oxide .gamma.Fe.sub.2 O.sub.3 6-7 
Kaolin (edges) Al.sub.2 O.sub.3 SiO.sub.2 2H.sub.2 O 6-7 
Chromium oxide .alpha.Cr.sub.2 O.sub.3 6-7 
Mullite 3Al.sub.2 O.sub.3 2SiO.sub.2 7-8 
Gamma alumina .gamma.Al.sub.2 O.sub.3 7-9 
Alpha alumina .alpha.A1.sub.2 O.sub.3 9-9.5 
Alumina (Bayer process) Al.sub.2 O.sub.3 7-9.5 
Zinc oxide ZnO.sub.2 9 
Copper oxide CuO 9 
Barium carbonate BaCO.sub.3 10-11 
Yttria Y.sub.2 O.sub.3 11 
Lathanum oxide La.sub.2 O.sub.3 10-12 
Silver oxide Ag.sub.2 O 11-12 
Magnesium Oxide MgO 12-13 
______________________________________ 
Source: Temple C. Patton, Paint Flow and Pigment Dispersion, 
WileyInterscience. New York, 1979; E. G. Kelly and D. J. Spottiswood, 
Introduction to Mineral Processing, WileyInterscience, New York, 1982; 1. 
M. Cases, Silic. Ind., 36, 145 (1971); R. H. Toon, T. Salman, and G. 
Donnay, J. Colloid Interface Sci., 70, 463 (1979). 
According to the present invention, the reaction product of guanidine and 
organic acids in the C.sub.12 to C.sub.22 range are used with materials 
having a low isolectric point, i.e., which have a low pH at the point of 
zero charge. Thus, for example the reaction product of guanidine and oleic 
acid (C.sub.17 H.sub.33 CO.sub.2 H) would be suitable for use with quartz 
powder (SiO.sub.2), which has an IEP of 2, according to Table 1 above. 
Other suitable acids for use with inorganic powders having a low 
isoelectric point include such saturated fatty acids as (common names in 
parentheses) dodecanoic (lauric) acid, tridecanoic (tridecylic) acid, 
tetradecanoic (myristic) acid, pentadecanoic (pentadecylic) acid, 
hexadecanoic (palmitic) acid, heptadecanoic (margaric) acid, octadecanoic 
(stearic) acid, eicosanoic (arachidic) acid, 
3,7,11,15-tetramethylhexadecanoic (phytanic) acid, monounsaturated, 
diunsaturated, triunsaturated and tetraunsaturated analogs of the 
foregoing saturated fatty acids. 
According to the present invention, the reaction product of guanidine and 
organic acids in the C.sub.6 to C.sub.12 range are used with materials 
having a mid-range isolectric point, i.e., which have a pH around 6 at the 
point of zero charge. These materials may also be referred to as 
amphoteric. For example, the reaction product of guanidine and an organic 
acid such as ethylhexanoic acid (C.sub.7 H.sub.15 CO.sub.2 H) would be 
suitable for use with an inorganic powder having an IEP of about 6.0, for 
example with zircon (SiO.sub.2.ZrO.sub.2), which has an IEP of 5-6, or 
anatase (TiO.sub.2), which has an IEP of 6, each according to Table 1 
above. Hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, 
decanoic acid, dodecanoic acid are other straight-chain carboxylic acids 
which may be reacted with guanidine for use with inorganic powders having 
a mid-range isoelectric point. Branched-chain carboxylic acids in the 
C.sub.6 to C.sub.12 range may also be used with materials having a 
mid-range isolectric point. 
According to the present invention, the reaction product of guanidine and 
stronger acids such as sulfonates, phthalates, benzoates, phosphates and 
phenols are used with materials having a high isolectric point, i.e., 
which have a pH around 10-12 at the point of zero charge. For example, the 
reaction product of guanidine and an acid such as benzenesulfonic acid may 
be used with an inorganic powder such as silver oxide, which has an IEP of 
11-12, as shown in Table 1 above. 
According to the present invention, for materials having intermediate IEPs, 
such as, for example, mullite (3Al.sub.2 O.sub.3.2SiO.sub.2), IEP=7-8, a 
mixture of guanidine wetting agents may be used. As an alternative, 
intermediate acids may be selected for reaction with guanidine. Thus, for 
example, if mullite is the inorganic powder, the guanidine wetting agent 
used in the binder composition therewith may be a mixture of the reaction 
product of guanidine and benzenesulfonic acid and the reaction product of 
guanidine and ethylhexanoic acid. Alternatively, for mullite, the 
guanidine wetting agent used in the binder composition therewith may be 
the reaction product of guanidine and a weaker acid such as benzoic acid 
may be used. 
Similarly, according to the present invention, for materials having 
intermediate IEPs, such as, for example, amorphous silica (SiO.sub.2), 
IEP=3-4, a mixture of guanidine wetting agents may be used. As an 
alternative, intermediate acids may be selected for reaction with 
guanidine. Thus, for example, if silica is the inorganic powder, the 
guanidine wetting agent used in the binder composition therewith may be a 
mixture of the reaction product of guanidine and octadecanoic (stearic) 
acid and the reaction product of guanidine and ethylhexanoic acid. 
Alternatively, for silica, the guanidine wetting agent used in the binder 
composition therewith may be the reaction product of guanidine and 
dodecanoic acid may be used. Dodecanoic acid, C.sub.11 H.sub.23 CO.sub.2 
H, appears in both groups of acids, those for use with the low IEP powers 
and those for use with intermediate IEP powders. The intermediate 
character of such an acid makes it suitable for use with an intermediate 
IEP powder. 
While a certain amount of trial and error may be required to optimize the 
reaction product of guanidine and an acid for a particular inorganic 
powder, and particulary for a combination of inorganic powders, the 
selection can be guided by the foregoing disclosure. Thus, the low IEP 
powders work best with a "very fatty", relatively weak acid, intermediate 
IEP powders work best with a mid-range organic acid, and the high EIP 
powders work best with a stronger acid having relatively less organic 
character, such as an alkyl sulfonic acid. The acid selected should be 
Theologically compatible with the compounding and injection molding 
equipment. Some testing may be required in order to optimize the acid for 
reaction with guanidine to form the guanidine wetting agent for a given 
inorganic powder. 
Polycarbonate Polymer 
In the binder composition of the present invention, the polycarbonate 
polymer is a low molecular weight polycarbonate polymer. In one 
embodiment, the polycarbonate polymer is poly(propylene carbonate). 
Poly(propylene carbonate) is prepared from the reaction of carbon dioxide, 
CO2, and propylene oxide, CH.sub.2 .dbd.C(O)CH.sub.2, as shown in the 
following: 
##STR1## 
The poly(propylene carbonate) shown above, on application of sufficient 
heat, decomposes cleanly into the following, which is a liquid having a 
boiling point near the decomposition temperature of the poly (propylene 
carbonate): 
##STR2## 
In one embodiment, the polycarbonate polymer has a number average molecular 
weight in the range from about 25,000 to about 75,000. In one embodiment, 
the polycarbonate polymer has a number average molecular weight in the 
range from about 35,000 to about 65,000. In one embodiment, the 
polycarbonate polymer has a number average molecular weight in the range 
from about 35,000 to about 40,000. In one embodiment, the polycarbonate 
polymer has a number average molecular weight of about 50,000. In one 
embodiment, the polycarbonate polymer has a number average molecular 
weight in the range from about 45,000 to about 55,000. 
In one embodiment, the polycarbonate polymer is Q-.TM. 40, available 
from Polymers, a division of Axcess Corporation, Newark, Del. 
Q-.TM. 40 is a low molecular weight polycarbonate, having a number 
average molecular weight in the range of about 50,000. Q-.TM. 40 has a 
glass transition temperature, T.sub.g =40.degree. C. Q-.TM. 40 is a low 
boiling liquid, having a boiling point of 242.degree. C. Thus, at 
relatively moderate temperatures, Q-.TM. 40 melts and may exit the 
green form as a liquid having only a slightly increased volume with 
respect to the solid, rather than decomposing into a gas having a greatly 
increased volume with respect to the solid. As above, the partial 
miscibility of the polycarbonate polymer allows it to melt and separate 
from the remaining components of the green composition during the 
debinding process. 
The decomposition product of poly(propylene carbonate) is shown above. This 
cyclic propylene carbonate has a melting point below the temperature at 
which the polymer decomposes. Thus, as the binder composition of the 
present invention, when mixed with the inorganic powder to form the green 
composition and injected into a mold, is heated, the poly(propylene 
carbonate) first melts and then begins to decompose into the liquid cyclic 
propylene carbonate shown above. On further heating in the debinding 
process, the cyclic propylene carbonate decomposes cleanly in air to form 
CO.sub.2 and water. Thus, according to the present invention, the 
polycarbonate polymer is the first component to be lost from the green 
composition in the debinding process. In contrast, in the prior art 
binders, the polymeric component has been designed to be the last 
component lost from the binder during the debinding process. 
Ethylenebisamide Wax 
The binder composition of the present invention includes an 
ethylenebisamide wax. The ethylenebisamide wax is a wax formed by the 
amidization reaction of ethylene diamine and a fatty acid. The fatty acid 
may be in the range from C.sub.12 to C.sub.22, but is usually made from 
stearic acid, the saturated C.sub.18 fatty acid. Thus, in one embodiment, 
the ethylenebisamide wax is ethylenebisstearamide wax. 
Ethylenebisstearamide has a discrete melting point of about 142.degree. C. 
In one embodiment, the ethylenebisamide wax has a discrete melting point 
in the range from about 120.degree. C. to about 160.degree. C. In one 
embodiment, the ethylenebisamide wax has a discrete melting point in the 
range from about 130.degree. C. to about 150.degree. C. In one embodiment, 
the ethylenebisamide wax has a discrete melting point of about 140.degree. 
C. 
In one embodiment, the ethylenebisstearamide is ACRAWAX.RTM. C, available 
from LONZA, Inc. ACRAWAX.RTM. C has a discrete melt temperature of 
142.degree. C. 
In other embodiments of the binder composition, other ethylenebisamides 
include the bisamides formed from the fatty acids ranging from C.sub.12 to 
C.sub.30. Illustrative of these acids are lauric acid, palmitic acid, 
oleic acid, linoleic acid, linolenic acid, oleostearic acid, stearic acid, 
myristic acid, and undecalinic acid. Unsaturated forms of these fatty 
acids may also be used. 
Quantities of Components in the Binder and Green Compositions 
It is a practice in the art of powder metal to refer to a binder 
composition in terms of parts by weight, or percent of each component on a 
weight basis, and to refer to a green composition in terms of parts by 
volume, or percent of each component on a volume bases. Thus, the amount 
of each component in the binder composition is expressed as weight 
percent, or wt %. The amounts of the inorganic powder and the binder 
composition combined to form the green composition are expressed as volume 
percent, or vol %. This practice is followed throughout the present 
specification and claims. 
In one embodiment, the binder composition comprises the guanidine wetting 
agent in the range from about 5 wt % to about 30 wt % based on the binder 
composition, the polycarbonate polymer in the range from about 30 wt % to 
about 85 wt % based on the binder composition, and the ethylenebisamide 
wax in the range from about 10 wt % to about 40 wt % based on the binder 
composition. In one embodiment of the binder composition, the guanidine 
wetting agent is present at about 15.5 wt %, the polycarbonate polymer is 
present at about 59.4 wt %, and ethylenebisstearamide is present at about 
25.1 wt %, each weight percent based on the binder composition. In one 
embodiment, the polycarbonate polymer is Q-.TM. 40 brand of 
poly(propylene carbonate), and is present at about 60 wt %. In one 
embodiment, the ethylenebisamide is ACRAWAX.RTM. C brand of 
ethylenebisstearamide, and is present at about 25 wt %. 
In one embodiment, the binder composition comprises the guanidine wetting 
agent in the range from about 10 wt % to about 25 wt % based on the binder 
composition, the polycarbonate polymer in the range from about 40 wt % to 
about 60 wt % based on the binder composition, and the ethylenebisamide 
wax in the range from about 15 wt % to about 35 wt % based on the binder 
composition. 
The binder composition of the present invention may also be used for P&S 
applications. In such applications, the binder composition comprises the 
guanidine wetting agent in the range from about 5 wt % to about 30 wt % 
based on the binder composition, the polycarbonate polymer in the range 
from about 10 wt % to about 50 wt % based on the binder composition, and 
the ethylenebisamide wax in the range from about 30 wt % to about 70 wt % 
based on the binder composition. 
The binder composition of the present invention is designed to be combined 
with an inorganic powder, to form a green composition for use in PIM. In 
one embodiment, the green composition includes the binder composition, as 
described above, and at least one inorganic powder selected from a metal 
powder, a metal oxide powder, a non-metallic powder and a ceramic powder. 
In one embodiment, the green composition includes the binder composition 
in an amount in the range from about 30 vol % to about 60 vol % and the 
inorganic powder or powders in an amount from about 70 vol % to about 40 
vol %. In one embodiment, the green composition includes the binder 
composition in an amount in the range from about 40 vol % to about 50 vol 
% and the inorganic powder is present in an amount from about 60 vol % to 
about 50 vol %. In one embodiment, the green composition includes the 
binder composition in an amount of about 35 vol % and the inorganic powder 
in an amount of about 65 vol %. 
The binder composition of the present invention is also suitable for use 
with an inorganic powder, to form a green composition for use in P&S. In 
one embodiment, the green composition includes the binder composition, as 
described above, and at least one inorganic powder selected from a metal 
powder, a metal oxide powder, a non-metallic powder and a ceramic powder. 
In one embodiment, the green composition includes the binder composition 
in an amount in the range from about 1 vol % to about 10 vol % and the 
inorganic powder or powders in an amount from about 99 vol % to about 90 
vol %. In one embodiment, the green composition includes the binder 
composition in an amount in the range from about 2 vol % to about 5 vol % 
and the inorganic powder is present in an amount from about 98 vol % to 
about 95 vol %. In one embodiment, the green composition includes the 
binder composition in an amount of about 2.5 vol % and the inorganic 
powder in an amount of about 97.5 vol %. 
Inorganic Powers 
Inorganic powders used in the present invention include metallic, metal 
oxide, intermetallic and/or ceramic powders. The powders may be oxides or 
chalcogenides of metallic or non-metallic elements. An example of metallic 
elements which may be present in the inorganic powders include calcium, 
magnesium, barium, scandium, titanium, vanadium, chromium, manganese, 
iron, cobalt, nickel, copper, zinc, yttrium, niobium, molybdenum, 
ruthenium, rhodium, silver, cadmium, lanthanum, actinium, gold or 
combinations of two or more thereof. In one embodiment, the inorganic 
powder may contain rare earth or ferromagnetic elements. The rare earth 
elements include the lanthanide elements having atomic numbers from 57 to 
71, inclusive and the element yttrium, atomic number 39. 
Ferromagnetic metals, for purposes of this invention, include iron, nickel, 
cobalt and numerous alloys containing one or more of these metals. In 
another embodiment, the metals are present as alloys of two or more of the 
aforementioned elements. In particular, prealloyed powders such as low 
alloy steel, bronze, brass and stainless steel as well as nickel-cobalt 
based super alloys may be used as inorganic powders. 
The inorganic powders may comprise inorganic compounds of one or more of 
the above-described metals. The inorganic compounds include ferrites, 
titanates, nitrides, carbides, borides, fluorides, sulfides, hydroxides 
and oxides of the above elements. Specific examples of the oxide powders 
include, in addition to the oxides of the above-identified metals, 
compounds such as beryllium oxide, magnesium oxide, calcium oxide, 
strontium oxide, barium oxide, lanthanum oxide, gallium oxide, indium 
oxide, selenium oxide, zinc oxide, aluminum oxide, silica, zirconia, 
mullite, mica, indium tin oxide, rare earth oxides, titania, yttria, etc. 
Specific examples of oxides containing more than one metal, generally 
called double oxides, include perovskite-type oxides such as NaNbO.sub.3, 
SrZrO.sub.3, PbZrO.sub.3, SrTiO.sub.3, BaZrO.sub.3, BaTiO.sub.3 ; 
spinel-type oxides such as MgAl.sub.2 O.sub.4, ZnAl.sub.2 O.sub.4, 
CoAl.sub.2 O.sub.4, NiAl.sub.2 O.sub.4, NiCr.sub.2 O.sub.4, FeCr.sub.2 
O.sub.4, MgFe.sub.2 O.sub.4, ZnFe.sub.2 O.sub.4, ect.; illmenite-types 
oxides such as MgTiO.sub.3 MnTiO.sub.3, FeTiO.sub.3, CoTiO.sub.3, 
ZnTiO.sub.3, LiTaO.sub.3, etc.; and garnet-type oxides such as Gd.sub.3 
Ga.sub.5 O.sub.12 and rare earth-iron garnet represented by Y.sub.3 
Fe.sub.5 O.sub.12. The inorganic powder may also be a clay. Examples of 
clays include kaolinite, nacrite, dickite, montmorillonite, montronite, 
spaponite, hectorite, etc. 
An example of non-oxide powders include carbides, nitrides, borides and 
sulfides of the metals described above. Specific examples of the carbides 
include SiC, TiC, WC, TaC, HfC, ZrC, AlC; examples of nitrides include 
Si.sub.3 N.sub.4, AlN, BN and Ti.sub.3 N.sub.4 ; and borides include 
TiB.sub.2, ZrB.sub.2, B.sub.4 C and LaB.sub.6. In one embodiment, the 
inorganic powder is silicon nitride, silicon carbide, zirconia, alumina, 
aluminum nitride, barium ferrite, barium-strontium ferrite or copper 
oxide. In another embodiment, the powder is a semiconductor, for example, 
GaAs, Si, Ge, Sn, ALAs, AlSb, GaP, GaSb, InP, InAs, InSb,CdTe, HgTe, PbSe, 
PbTe, and any of the many other known semiconductors. In another 
embodiment, the inorganic powder is alumina or clay. 
Acids for Reaction With Guanidine 
The acidic compounds useful in making the reaction product of guanidine and 
an acid of the present invention include carboxylic acids, sulfonic acids, 
phosphorus acids, phenols or mixtures of two or more thereof. Preferably, 
the acidic organic compounds are carboxylic acids or sulfonic acids. The 
carboxylic and sulfonic acids may have substituent groups derived from the 
above described polyalkenes. Selection criteria for the appropriate acid 
are provided above, based on the surface charge and isoelectric point of 
the inorganic powder used in preparing the green composition. 
The carboxylic acids may be aliphatic or aromatic, mono- or polycarboxylic 
acid or acid-producing compounds. The acid-producing compounds include 
anhydrides, lower alkyl esters, acyl halides, lactones and mixtures 
thereof unless otherwise specifically stated. 
Illustrative fatty carboxylic acids include palmitic acid, stearic acid, 
myristic acid, oleic acid, linoleic acid, behenic acid, hexatriacontanoic 
acid, tetrapropylenyl-substituted glutaric acid, polybutenyl 
(Mn=200-1,500, preferably 300-1,000)-substituted succinic acid, 
polypropylenyl, (Mn=200-1,000, preferably 300-900)-substituted succinic 
acid, octadecyl-substituted adipic acid, 9-methylstearic acid, 
stearyl-benzoic acid, eicosane-substituted naphthoic acid, 
dilauryl-decahydronaphthalene carboxylic acid, mixtures of these acids, 
and/or their anhydrides. Aliphatic fatty acids include the saturated and 
unsaturated higher fatty acids containing from about 12 to about 30 carbon 
atoms. Illustrative of these acids are lauric acid, palmitic acid, oleic 
acid, linoleic acid, linolenic acid, oleostearic acid, stearic acid, 
myristic acid, and undecalinic acid, alpha-chlorostearic acid, and 
alphanitrolauric acid. Branched fatty acids, both saturated and 
unsaturated, in the range from about 6 to about 25 carbon atoms are 
included. Such branched fatty acids include versatic acids, available from 
Shell Chemicals. For example, Shell Chemical produces a versatic acid 
known as Monomer Acid, which is the distilled product obtained during the 
manufacture of tall oil-based dimer acid. Monomer Acid is a mixture of 
both branched and straight-chain predominantly C.sub.18 mono fatty acids. 
One example is Versatic 10, a synthetic saturated monocarboxylic acid of 
highly branched structure containing ten carbon atoms. Its structure may 
be represented as: 
##STR3## 
where R1, R2 and R3 are alkyl groups at least one of which is always 
methyl. 
The sulfonic acids useful in making the guanidine wetting agents include 
the sulfonic and thiosulfonic acids. Generally they are salts of sulfonic 
acids. The sulfonic acids include the mono- or polynuclear aromatic or 
cycloaliphatic compounds. The oil-soluble sulfonates can be represented 
for the most part by one of the following formulae: R.sup.7 
--T--(SO.sub.3).sub.d and R.sup.8 --(SO.sub.3).sub.e, wherein T is a 
cyclic nucleus such as, for example, benzene, naphthalene, anthracene, 
diphenylene oxide, diphenylene sulfide, petroleum naphthenes, etc.; 
R.sup.7 is an aliphatic group such as alkyl, alkenyl, alkoxy, alkoxyalkyl, 
etc.; (R.sup.7)+T contains a total of at least about 15 carbon atoms; 
R.sup.8 is an aliphatic hydrocarbyl group containing at least about 15 
carbon atoms and d and e are each independently an integer from 1 to about 
3, preferably 1. Examples of R.sup.8 are alkyl, alkenyl, alkoxyalkyl, 
carboalkoxyalkyl, etc. Specific examples of R.sup.8 are groups derived 
from petrolatum, saturated and unsaturated paraffin wax, and the 
above-described polyalkenes. The groups T, R.sup.7, and R.sup.8 in the 
above formulae can also contain other inorganic or organic substituents in 
addition to those enumerated above such as, for example, hydroxy, 
mercapto, halogen, nitro, amino, nitroso, sulfide, disulfide, etc. In the 
above Formulae, d and e are at least 1. 
Illustrative examples of these sulfonic acids include 
monoeicosane-substituted naphthalene sulfonic acids, dodecylbenzene 
sulfonic acids, didodecylbenzene sulfonic acids, dinonylbenzene sulfonic 
acids, cetylchlorobenzene sulfonic acids, dilauryl beta-naphthalene 
sulfonic acids, the sulfonic acid derived by the treatment of polybutenyl, 
having a number average molecular weight (Mn) in the range of about 500, 
preferably about 800 to about 5000, preferably about 2000, more preferably 
about 1500, with chlorosulfonic acid, nitronaphthalene sulfonic acid, 
paraffin wax sulfonic acid, cetyl-cyclopentane, sulfonic acid, 
lauryl-cyclohexane sulfonic acids, polyethylenyl (Mn=300-1,000, preferably 
750) sulfonic acids, etc. Normally the aliphatic groups will be alkyl 
and/or alkenyl groups such that the total number of aliphatic carbons is 
at least about 8, preferably at least 12. 
A preferred group of sulfonic acids are mono-, di-, and tri-alkylated 
benzene and naphthalene (including hydrogenated forms thereof) sulfonic 
acids. Illustrative of synthetically produced alkylated benzene and 
naphthalene sulfonic acids are those containing alkyl substituents having 
from about 8 to about 30 carbon atoms, preferably about 12 to about 30 
carbon atoms, and advantageously about 24 carbon atoms. Such acids include 
di-isododecyl-benzene sulfonic acid, polybutenyl-substituted sulfonic 
acid, polypropylenyl-substituted sulfonic acids of Mn=300-1,000, 
preferably 500-700, cetylchlorobenzene sulfonic acid, di-cetylnaphthalene 
sulfonic acid, di-lauryldiphenylether sulfonic acid, diisononylbenzene 
sulfonic acid, di-isooctadecylbenzene sulfonic acid, stearylnaphthalene 
sulfonic acid, and the like. 
The production of sulfonates from detergent manufactured by-products by 
reaction with, e.g., SO.sub.3, is well known to those skilled in the art. 
See, for example, the article "Sulfonates" in Kirk-Othmer "Encyclopedia of 
Chemical Technology", Second Edition, Vol. 19, pp. 291 et seq. published 
by John Wiley & Sons, New York (1969). 
The phosphorus-containing acids useful in making the guanidine wetting 
agents include any phosphorus acids such as phosphoric acid or esters; and 
thiophosphorus acids or esters, including mono and dithiophosphorus acids 
or esters. Preferably, the phosphorus acids or esters contain at least 
one, preferably two, hydrocarbyl groups containing from 1 to about 50 
carbon atoms, typically 1, preferably 3, more preferably about 4 to about 
30, preferably to about 18, more preferably to about 8. 
In one embodiment, the phosphorus-containing acids are dithiophosphoric 
acids which are readily obtainable by the reaction of phosphorus 
pentasulfide (P.sub.2 S.sub.5) and an alcohol or a phenol. The reaction 
involves mixing at a temperature of about 20.degree. C. to about 
200.degree. C. four moles of alcohol or a phenol with one mole of 
phosphorus pentasulfide. Hydrogen sulfide is liberated in this reaction. 
The oxygen-containing analogs of these acids are conveniently prepared by 
treating the dithioic acid with water or steam which, in effect, replaces 
one or both of the sulfur atoms with oxygen. 
In one embodiment, the phosphorus-containing acid is the reaction product 
of the above polyalkenes and phosphorus sulfide. Useful phosphorus 
sulfide-containing sources include phosphorus pentasulfide, phosphorus 
sesquisulfide, phosphorus heptasulfide and the like. 
The reaction of the polyalkene and the phosphorus sulfide generally may 
occur by simply mixing the two at a temperature above 80.degree. C., 
preferably between 100.degree. C. and 300.degree. C. Generally, the 
products have a phosphorus content from about 0.05% to about 10%, 
preferably from about 0.1% to about 5%. The relative proportions of the 
phosphorus sulfide to the olefin polymer is generally from 0.1 part to 50 
parts of the phosphorus sulfide per 100 parts of the olefin polymer. 
The phenols useful in making the guanidine wetting agents may be 
represented by the formula (R)f--Ar--(OH)g, wherein R and Ar are defined 
above; f and g are independently numbers of at least one, the sum of f and 
g being in the range of two up to the number of displaceable hydrogens on 
the aromatic nucleus or nuclei of Ar. Preferably, f and g are 
independently numbers in the range of 1 to about 4, more preferably f to 
about 2. R and f are preferably such that there is an average of at least 
about 8 aliphatic carbon atoms provided by the R groups for each phenol 
compound. Examples of phenols include octylphenol, nonylphenol, propylene 
tetramer substituted phenol, tri(butene)-substituted phenol, 
polybutenyl-substituted phenol and polypropenyl-substituted phenol. 
Other Additives 
Other additives used in prior art binder compositions are not necessary 
with the binder composition of the present invention. In one embodiment, 
no additives beyond the inventive binder composition are used. In one 
embodiment, as deemed necessary, small amounts of other materials may be 
added to the composition of the present invention. For example, 
plasticizers may be added to the compositions to provide more workable 
compositions. Examples of plasticizers normally utilized in inorganic 
formulations include dioctyl phthalate, dibutyl phthalate, benzyl butyl 
phthalate and phosphate esters. 
Methods 
The present invention further relates to a method for forming a part by 
powder injection molding, comprising the steps of (a) forming a green 
composition comprising a binder composition and an inorganic powder, 
wherein the binder composition comprises a polycarbonate polymer, an 
ethylenebisamide wax, and a guanidine wetting agent, (b) transferring the 
green composition into a mold for a part, (c) heating the part to a 
temperature at which the binder composition decomposes, (d) heating the 
part to a temperature at which the powder is sintered to form the part, 
and (e) cooling and removing the part from the mold. In one embodiment, 
the transferring step (b) includes heating and injection of the green 
composition into a mold for powder injection molding. In one embodiment, 
the transferring step (b) includes gravity feeding the green composition 
into a mold for press & sinter molding. In one embodiment of the method, 
the heating step (d) is performed as a series of temperature increases to 
selected temperatures, in which the selected temperatures correspond to 
debinding temperatures of the components in the binder composition. In one 
embodiment, the selected temperatures are held for a period of time, to 
allow the component to be debound prior to increasing the temperature to a 
debinding temperature of another component. In one embodiment of the 
method, the order of debinding is polycarbonate polymer first, 
ethylenebisamide second, and guanidine wetting agent last. In one 
embodiment, a wicking agent may be used in the debinding step. In one 
embodiment, the wicking agent may be used in both the debinding step and 
the sintering step. The wicking agent may be, for example, a fine alumina 
or zirconia sand. 
In one embodiment of the method, the inorganic powder is selected from a 
metal powder, a metal oxide powder, a non-metallic powder and a ceramic 
powder. In one embodiment of the method, the guanidine wetting agent is a 
reaction product of guanidine and an acid selected from organic acid, a 
fatty acid and a stronger acid such as an alkyl sulfonic acid. In one 
embodiment of the method, the guanidine wetting agent is guanidine 
stearate. In one embodiment of the method, the guanidine wetting agent is 
guanidine ethylhexanoate. In one embodiment of the method, the guanidine 
wetting agent is guanidine lauryl sulfonate. 
In one embodiment of the method, the polycarbonate polymer has a number 
average molecular weight in the range from about 25,000 to about 50,000. 
In one embodiment of the method, the polycarbonate polymer has a number 
average molecular weight in the range from about 30,000 to about 45,000. 
In one embodiment of the method, the polycarbonate polymer has a number 
average molecular weight in the range from about 35,000 to about 40,000. 
In one embodiment of the method, the ethylenebisamide wax has a discrete 
melting point in the range from about 120.degree. C. to about 160.degree. 
C. In one embodiment of the method, the ethylenebisamide wax has a 
discrete melting point in the range from about 130.degree. C. to about 
150.degree. C. In one embodiment of the method, the ethylenebisamide wax 
has a discrete melting point of about 140.degree. C. In one embodiment of 
the method, the ethylenebisamide is ACRAWAX C.RTM. brand of 
ethylenbisstearamide and has a discrete melting point of about 142.degree. 
C. 
In one embodiment of the method, the binder composition comprises the 
guanidine wetting agent in the range from about 5 wt % to about 30 wt % 
based on the binder composition, the polycarbonate polymer in the range 
from about 30 wt % to about 85 wt % based on the binder composition, and 
the ethylenebisamide wax in the range from about 10 wt % to about 40 wt % 
based on the binder composition. In one embodiment of the method, the 
binder composition comprises the guanidine wetting agent at about 15.5 wt 
%, the polycarbonate polymer at about 59.4 wt %, and ethylenebisstearamide 
at about 25.1 wt %, each weight percent based on the binder composition. 
In one embodiment of the method, the polycarbonate polymer is Q-.TM. 40 
brand of poly(propylene carbonate), and is present at about 60 wt %. In 
one embodiment of the method, the ethylenebisamide is ACRAWAX.RTM. C brand 
of ethylenebisstearamide, and is present at about 25 wt %. 
In one embodiment of the method, the binder composition comprises the 
guanidine wetting agent in the range from about 10 wt % to about 25 wt % 
based on the binder composition, the polycarbonate polymer in the range 
from about 40 wt % to about 60 wt % based on the binder composition, and 
the ethylenebisamide wax in the range from about 15 wt % to about 35 wt % 
based on the binder composition. 
In one embodiment of the method, the binder composition is present in an 
amount in the range from about 30 vol % to about 60 vol % of the green 
composition and the inorganic powder is present in an amount from about 70 
vol % to about 40 vol % of the green composition. In one embodiment of the 
method, the binder composition is present in an amount in the range from 
about 40 vol % to about 50 vol % of the green composition and the 
inorganic powder is present in an amount from about 60 vol % to about 40 
vol % of the green composition. In one embodiment, the green composition 
includes the binder composition in an amount of about 35 vol % and the 
inorganic powder in an amount of about 65 vol %. 
Preparation 
FIG. 1 is a schematic diagram of the steps in a method of making a part by 
powder injection molding in accordance with the present invention. FIG. 1 
shows a generalized process for powder injection molding which may be 
performed in accordance with the present invention. In a first step 10 an 
inorganic powder and a binder composition according to the present 
invention are obtained and combined. In one embodiment, the step of 
preparing the binder composition includes steps of mixing, blending and 
dispersing the components of the binder composition as needed to prepare a 
homogenous, or nearly homogenous mixture of the components in the binder 
composition, in a powder form. In one embodiment, the binder composition 
and the inorganic powder are first dry blended to produce a homogenous mix 
of dry materials. In one embodiment, the binder composition is micronized 
to a size similar to that of the inorganic powder with which it will be 
combined to form the green composition. In one embodiment, the binder 
composition is ground to a particle size in the range from about 10 .mu.m 
to about 100 .mu.m. 
In an optional second step (not shown) the inorganic powder and the binder 
composition are combined in a premixing of the green composition. The 
optional premixing step may include mixing in, e.g., a ball mill. In this 
optional step, additional components, if used, may be added and blended 
into the mixture as desired. 
In a step 20 the components of the green composition are fed into a twin 
screw compounding extruder. In the step 20, while passing through the twin 
screw compounding extruder, the components of the green composition are 
subjected to a high shear for effectively combining the inorganic powder 
and binder composition. In one embodiment, the output from the twin screw 
compounding extruder is a string of the green composition, which is then 
fed to a pelletizer. In one embodiment, the output from the twin screw 
compounding extruder is pelletized by a pelletizing apparatus directly 
attached to the extruder apparatus. Forming the green composition into 
pellets facilitates handling, both for immediate and for subsequent use. 
The mixing in the twin screw compounding extruder in the step 20 
facilitates blending the various green compositions as may be required for 
particular applications. The mixing in the twin screw compounding extruder 
in the step 20 combines, compounds and pelletizes the green composition. 
The pellets formed by the step 20 are cooled, and may be stored for later 
use. 
In one embodiment of the step 20 the binder composition is dry blended with 
the inorganic powder prior to feeding to the twin screw compounding 
extruder, and the blended components of the green composition are fed into 
the extruder together. In one embodiment, the binder composition and 
inorganic powder components of the green composition are fed separately 
into the twin screw compounding extruder. In one embodiment, the binder 
composition is fed into the twin screw compounding extruder at a first 
point, and the inorganic powder component is fed in at a second point, 
downstream from the first point. In one embodiment, the twin screw 
compounding extruder is a Leistritz 18 mm co-rotating twin screw 
compounding extruder. In one embodiment, the Leistritz twin screw extruder 
has the design shown in FIG. 5. A further description of FIG. 5 is 
provided below. In one embodiment, the green composition exiting the twin 
screw compounding extruder emerges in the form of a string, passing onto a 
conveyor, which is subsequently cooled and then cut into pellets. 
Referring still to FIG. 1, in an injection molding step 30, the pellets of 
the green composition are heated, melted, mixed and injected into a mold 
having the desired shape of the part of interest. The part formed at this 
stage is known as a green part or a compact for a part. In one embodiment, 
the molten green composition is injected into the mold at a pressure in 
the range from about 100 psi (about 70,307 Kg m.sup.2) to about 2000 psi 
(about 1,406,139 Kg m.sup.2). In one embodiment, the molten green 
composition is injected into the mold at a pressure of about 800 psi 
(about 562,455 Kg/m.sup.2). In the injection step 30, pellets having 
different green compositions may be blended. Following the injection step 
30, the green part is cooled and released from the mold. 
In one embodiment, the pellets are fed into a hopper and thence into a 
horizontal injection molding machine. In one embodiment, the injection 
molding machine is a standard injection molding machine used for injection 
molding parts in known processes. 
In one embodiment, the green part has a green strength in the range of 
about 800 psi (about 562,456 Kg/m.sup.2) to about 12,000 psi (about 
8,436,835 Kg/m.sup.2). In one embodiment, the green part has a green 
strength in the range of about 2000 psi (about 1,406,139 Kg/m.sup.2) to 
about 8000 psi (about 5,624,556 Kg/m.sup.2. In one embodiment, the green 
part has a green strength in the range of about 4000 psi (about 2,812,278 
Kg/m.sup.2) to about 6000 psi (about 4,218,418 Kg/m.sup.2). 
The green part is then transferred to a debinding/sintering oven, in which 
one or more steps of debinding 40 are carried out. In one embodiment, the 
debinding step 40 includes a plurality of temperature increases to 
elevated temperatures. In one embodiment of the debinding step 40, each of 
the elevated temperatures are maintained constant for a period of time. In 
one embodiment of the debinding step 40, the elevated temperatures 
correspond to temperatures at which individual ingredients of the binder 
composition are debound. In one embodiment of the debinding step 40, a 
first elevated temperature corresponds to the debinding temperature of the 
polycarbonate polymer, a second elevated temperature corresponds to the 
debinding temperature of the ethylenebisamide wax, and a third elevated 
temperature corresponds to the debinding temperature of the guanidine 
wetting agent. In one embodiment of the debinding step 40, the third 
elevated temperature is higher than the second elevated temperature, and 
the second elevated temperature is higher than the first elevated 
temperature. 
Following the debinding step 40, the green part is subjected to a step 50 
of sintering. The sintering step 50 may be performed in the same oven in 
which the debinding step 40 was performed, or the green part may be moved 
to a separate sintering oven for the sintering step 50. 
The variables for the debinding process conditions include selection of the 
identity, pressure and flow rate of the atmosphere in the debinding oven 
chamber, selection of the temperatures for each debinding step, selection 
of the rate of increase in temperature during the transition from one 
debinding step to the next, and selection of the time each debinding 
temperature is held while a particular component is debound from the green 
composition. Additional variables arise from the exact nature of both the 
components of the binder composition and the inorganic powder used in the 
green composition. The time period at which a particular debinding 
temperature is held during a debinding process is known as "soaking" the 
green composition at that temperature. The time periods for soaking, and 
the rate of increase between those temperatures must be selected for a 
given binder composition and a given green composition. A certain amount 
of trial and error is required to optimize the debinding conditions for a 
given binder composition and green composition. The following general 
principles may be applied to make an initial selection of debinding 
conditions, but the number of variables make it likely that some testing 
will be required. 
In selecting the environment for the debinding and sintering, the 
temperatures selected for each step of the debinding are primarily 
influenced by the melting and decomposition temperature of each component 
of the binder composition and by the atmosphere in the debinding oven 
chamber. However, other factors may be involved as well. 
Generally, the temperature at which a part is soaked for removal of each 
component during the debinding corresponds to the onset temperature of its 
decomposition. In a debinding process, it is helpful if a component melts 
before decomposing, but the important step is the decomposition. If the 
component melts prior to decomposing, as has been described herein for the 
poly(propylene carbonate) polymer, it is helpful to the overall debinding 
process due to the relatively small expansion of volume in melting as 
compared to decomposing into gaseous products. Thus, for example, a 
component may have a certain melting point, such as ethylenebisstearamide 
has a melting point of 142.degree. C., but its debinding via decomposition 
is carried out at temperatures in the range from about 190.degree. C. to 
about 225.degree. C., depending on the atmosphere in the debinding oven 
chamber. 
The atmosphere in the debinding over chamber determines the speed of 
debinding at a given temperature. Generally, at a given temperature, an 
atmosphere of hydrogen results in faster debinding than a vacuum (e.g., 
4-12 hours for hydrogen vs. 6-18 hours for vacuum), and a vacuum results 
in faster debinding than an inert atmosphere, for example of argon or 
nitrogen (e.g., 6-18 hours for vacuum vs. 8-24 hours for an inert gas 
atmosphere). Alternatively, for a given time for a debinding step, using 
an atmosphere of hydrogen allows the debinding step to be carded out at a 
lower temperature than the same debinding step carried out in a vacuum, 
and a vacuum allows the same debinding step to be carried out at a lower 
temperature than it would in an inert gas atmosphere. Thus, for example, a 
polycarbonate debinding step which may be carried out by soaking for 60 
minutes at 160.degree. C. in a hydrogen atmosphere, would need to be 
carried out by soaking for 60 minutes at about 190.degree. C. in a 
nitrogen atmosphere. Alternatively, a polycarbonate debinding step which 
may require soaking for 60 minutes at 160.degree. C. in a hydrogen 
atmosphere, may require soaking for about 90 minutes at 160.degree. C. in 
a nitrogen atmosphere. The examples provided below provide an indication 
of the temperatures and times which may be required for debinding the 
binder compositions of the present invention. Suitable atmospheres 
include, e.g., air, nitrogen, hydrogen, oxygen, argon, and other inert 
gases. 
The pressure and flow rate of the gases used in the debinding oven chamber 
provide an other variable which must be considered in designing a 
debinding profile. In a hydrogen atmosphere, the pressure is typically 
from about 10% to about 20% above atmospheric , and the hydrogen is passed 
through a 2 ft.sup.3 chamber at the rate of about 10 ft.sup.3 /hr (CFH) to 
about 15 CFH, or in one embodiment in the same chamber at the rate of 
about 12 CFH. When at atmosphere other than air is used, it is normally 
provided at a super-atmospheric pressure in order to avoid leakage ingress 
of air into the debinding oven chamber. In one embodiment, the pressure in 
the debinding oven chamber is about 780 torr. Sub-atmospheric pressures 
may also be used. In one embodiment, a vacuum is placed upon the oven 
chamber, by reducing the pressure to about 76 torr. In other embodiments, 
similar reduced pressures may be used. Suitable pressures range from a 
vacuum, i.e. about 10.sup.-5 to about 10.sup.-7 torr, to at least about 2 
atmospheres, i.e., about 1540 torr. Suitable flow rates range from a flow 
rate sufficient to produce from about 1 atmospheric exchange per hour to a 
flow rate sufficient to produce at least about 20 atmospheric exchanges 
per hour, determined by the volume of the chamber and the flow rate of 
gas. 
Further variables of properties of the inorganic powder which affect time 
and temperature for the debinding steps for a particular green composition 
are: particle size, particle morphology, percent porosity and continuity 
of porosity. The effects of these variable are complex, and some testing 
may be required to obtain the optimum for each of these properties for a 
given inorganic powder and binder composition combination used in a green 
composition. For example, decreased particle size increases the surface 
area which in turn increases the sinterability to produce fully dense 
parts. When particles are more closely packed, less porosity is formed and 
the likelihood of pore continuity decreases. This means the binder 
composition will be retarded in finding a means of escape from the part as 
the debinding process proceeds. Thus, the result of smaller inorganic 
powder particle size is likely to be a longer debind time, since the 
temperature increases may be required to proceed at a reduced rate of 
increase. 
A further variable which affects time and temperature for the debinding 
steps for a particular green composition is the chemical nature of the 
inorganic powder. A powder may tend to act as an activator, or even like a 
catalyst, in the decomposition of one or more of the components of a 
binder composition, and so may result in faster debinding of those 
components. Alternatively, if the inorganic powder is a relatively inert 
material, such as alumina, Al.sub.2 O.sub.3, the primary factors affecting 
the debinding process are the temperature, time and atmosphere of the 
debinding. 
Alternatives to the preparation of green parts as described above by PIM 
include pressing the green composition into a mold for P&S, followed by a 
sintering step. Alternatively, the blended green composition can be 
extrusion- or ejection-molded to form a green body, or the green body can 
be prepared by casting the mixture on a tape. The green body may also be 
prepared by spray-drying rotary evaporation, etc. Following the formation 
of the blended green composition into the desired shape, the shaped mass 
is subjected to the above described elevated temperature treatments. These 
treatments first eliminate the binder composition, as described more fully 
above, and then sinter the inorganic powders resulting in the formation of 
a shape having the desired properties including suitable densities. 
For metal powders, the sintering generally occurs between about 400.degree. 
C. to about 2100.degree. C., typically to about 1000.degree. C. For 
ceramic processes, the sintering generally occurs from about 600.degree. 
C., preferably about 700.degree. C. up to about 1700.degree. C. Of course, 
the sintering temperature is characteristic of the particular inorganic 
powder used in the green composition, and may be affected by impurities or 
additives. For example, carbonyl iron is frequently doped with nickel, at 
the level of, for example, about 2 wt %, as a sintering aid. The presence 
of the nickel allows the sintering to take place at a lower temperature 
and/or in a shorter amount of time than would otherwise be required for 
carbonyl iron. When the inorganic powders are oxide powders, baking and 
sintering can be effected in the presence of oxygen. When the inorganic 
powders are non-oxide powders such as the nitrides and carbides, sintering 
is effected in a nonoxidizing atmosphere such as an atmosphere of 
hydrogen, argon or nitrogen gas. 
The debinding step takes place at moderately elevated temperatures, and is 
generally completed by ramping to a series of temperatures below about 
700.degree. C. It is the debinding steps which are the primary focus of 
the present invention. 
Removal of the organic materials of the binder composition is generally 
completed before the inorganic powders are subjected to sintering. In this 
process, substantially all of the binder composition is removed. Some of 
the binder composition materials may remain following the debinding, 
although the amount is relatively small. These remaining portions of the 
binder composition will be essentially completely removed in the sintering 
steps, depending of course, on factors such as the decomposition 
temperature of the remaining binder component, the sintering temperature 
and the sintering atmosphere. 
Each of the three ingredients of the binder composition, the polycarbonate 
polymer, the ethylenebisamide and the guanidine wetting agent, may be 
initially formed in a solid, pelletized form. To form the pellets, these 
ingredients are combined and heated to melting, at approximately 
100.degree. C., in the manner indicated above. The three ingredients are 
partially miscible with each other, so that when actively mixed in a twin 
screw compounding extruder at approximately 100.degree. C., the binder 
composition is almost homogenous, and the binder composition quickly and 
easily forms a uniform heterogeneous mixture with a minimum of shear. 
Thus, the binder composition forms a uniform heterogeneous mixture with 
only one extrusion cycle. In one specific case, the liquid binder 
composition was mixed at a temperature of approximately 100.degree. C. to 
form a uniform heterogeneous mixture within 10 minutes of extrusion. 
The heated heterogeneous liquid mixture of the binder composition may be 
mixed with the inorganic powder to form the green composition. The mixing 
of the binder composition and inorganic powder to form the green 
composition is best undertaken in the twin screw compounding extruder, 
which, among other benefits, results in thorough mixing with a minimum of 
exposure of the green composition components to atmospheric air. Such 
exposure may be deleterious to either or both the binder composition and 
the inorganic powder. 
The green composition, when mixed at a temperature of about 100.degree. C. 
form a liquid with a viscosity of between 5 and 300 Pascal-seconds 
depending on the shear rate. As the shear rate increases, the viscosity 
generally decreases to some degree, although as would be understood, there 
is a limit to the decrease. 
The heated green composition may be extruded at approximately 100.degree. 
C. to form feedstock pellets. The feedstock pellets, once made, may be 
injection molded at any subsequent time by heating to a temperature of 
approximately 100.degree. C. and pumping into a mold to make a green part, 
which is also known as a compact of a part. The resulting green part was 
then subjected to the series of temperature increases to debind the 
compact and thence to sinter the inorganic powder, as has been described 
above. 
In one embodiment, the method includes, in step (d), a plurality of 
temperature increases to elevated temperatures. In one embodiment, the 
method includes maintaining each of the elevated temperatures constant for 
a period of time. In one embodiment of the method, the elevated 
temperatures correspond to temperatures at which individual ingredients of 
the binder composition are debound. In one embodiment, the elevated 
temperatures include a first elevated temperature which corresponds to the 
debinding temperature of the polycarbonate polymer, a second elevated 
temperature which corresponds to the debinding temperature of the 
ethylenebisamide wax, and a third elevated temperature which corresponds 
to the debinding temperature of the guanidine wetting agent. In one 
embodiment, the third elevated temperature is higher than the second 
elevated temperature, and the second elevated temperature is higher than 
the first elevated temperature. 
Debinding of the compact may be completed when the temperature of the 
compact reaches about 600.degree. C. The temperature should be maintained 
at this level for a period of up to about 12 hours. This heating process 
removed the binder composition from the compact. The compact was then 
sintered by heating the compact to a temperature of approximately 
1,650.degree. C. for a period of up to 4 hours. The resulting product is a 
part made of the inorganic material of which the inorganic powder had been 
made. 
FIG. 5 is a schematic engineering drawing of one screw 60 of a twin screw 
compounding extruder 62 in accordance with one embodiment of the 
invention. The twin screw compounding extruder 62 shown in FIG. 5 is a 
schematic depiction of a Leistritz 18 mm twin screw compounding extruder, 
which is used in one embodiment of the method of the present invention. 
The Leistritz twin screw compounding extruder 62 provides a high level of 
combining and compounding the components of the green composition of the 
present invention. As shown in FIG. 5, the screw 60 is used in the twin 
screw extruder 62. The twin screw extruder 62 includes a main feed 64, a 
secondary feed 66 and a vent 68. In one embodiment, the binder composition 
is fed into the main feed 64 and the inorganic powder is fed into the 
secondary feed 66. The vent 68 is provided to vent entrapped gases and to 
maintain the internal pressure in the twin screw compounding extruder 62 
at a desired level. 
EXAMPLES 
The following exemplary formulations are intended to provide a better 
understanding of the invention, and are not intended as limiting. 
Example 1 
A green composition comprising a binder composition and carbonyl iron, 
according to the present invention, was prepared as follows. 
The binder composition was as follows: 
______________________________________ 
poly(propylene carbonate) Q- .TM. 40 
59.43 wt % 
ethylenebisstearamide ACRAWAX .RTM. C 25.15 wt % 
guanidine ethyl hexanoate 8.49 wt % 
guanidine stearate 6.94 wt % 
Total 100.0 
______________________________________ 
The binder composition was prepared by combining the ingredients in a twin 
screw compounding extruder, heating to about 100.degree. C. for about 10 
minutes, until the mixture is substantially homogenous, and then 
pelletizing the binder composition in, e.g., a strand cutter pelletizing 
apparatus. This binder composition is designated APEX.TM. 201. 
The ingredients for the green composition, comprising 59 vol % carbonyl 
iron doped with 2 wt % nickel powder as a sintering aid, and 41 vol % of 
pellets of the above binder composition were combined, compounded and 
pelletized in a twin screw compounding extruder as described above. 
Expressed on a weight basis, the green composition comprised 91 wt % 
carbonyl iron/Ni and 9 wt % of the above binder composition. After the 
green composition was thoroughly compounded, it was extruded and 
pelletized. The pellets were subsequently fed into an injection molding 
machine, and injected into a mold. 
Example 2 
A green composition comprising a binder composition and titanium CP powder, 
according to the present invention, was prepared as follows. 
The binder composition was the same as in Example 1. 
The ingredients for the green composition, comprising 59 vol % titanium CP 
grade powder, and 41 vol % of the binder composition prepared in Example 
1, were combined were combined, compounded and pelletized in a twin screw 
compounding extruder as described above. Expressed on a weight basis, the 
green composition comprised 83 wt % titanium CP grade powder and 17 wt % 
of the above binder composition. After the green composition was 
thoroughly compounded, it was extruded and pelletized. The pellets were 
subsequently fed into an injection molding machine, and injected into a 
mold. 
Example 3 
A green composition comprising a binder composition and sub-micron zirconia 
powder stabilized with yttria, according to the present invention, was 
prepared as follows. 
The binder composition was the same as in Example 1. 
The ingredients for the green composition, comprising 47 vol % zirconia 
powder stabilized with yttria powder, and 53 vol % of pellets of the 
binder composition prepared in Example 1, were combined, compounded and 
pelletized in a twin screw compounding extruder as described above. 
Expressed on a weight basis, the green composition comprised 80 wt % 
zirconia/Y.sub.2 O.sub.3 powder and 20 wt % of the above binder 
composition. After the green composition was thoroughly compounded, it was 
extruded and pelletized. The pellets were subsequently fed into an 
injection molding machine, and injected into a mold. 
FIG. 2 is a graph of a debinding profile of a first exemplary green 
composition according to the present invention. The debinding profile 
shown in FIG. 2 reflects the following steps of a debinding process: 
______________________________________ 
Step Time, Elapsed 
No. Action in Step min. Time, min. 
______________________________________ 
21 Heat from RT @ 75.degree. C./hr to 110.degree. C. 
68 68 
22 Soak (hold) @ 110.degree. C. 60 128 
23 Heat from 110.degree. C. @ 100.degree. C./hr to 140.degree. C. 18 
146 
24 Heat from 140.degree. C. @ 75.degree. C./hr to 190.degree. C. 40 186 
25 Soak (hold) @ 190.degree. C. 60 246 
26 Heat from 190.degree. C. @ 150.degree. C./hr to 425.degree. C. 94 
340 
27 Soak (hold) @ 425.degree. C. 60 400 
28 Heat from 425.degree. C. to sintering temperature 
______________________________________ 
The following binder composition was used in the green composition which 
was subjected to the debinding process shown in FIG. 2: 
______________________________________ 
poly(propylene carbonate) Q- .TM. 40 
59.43 wt % 
ethylenebisstearamide ACRAWAX .RTM. C 25.15 wt % 
guanidine ethyl hexanoate 8.49 wt % 
guanidine stearate 6.94 wt % 
Total 100.0 
______________________________________ 
In FIG. 2, the poly(propylene carbonate) was debound in steps 21 and 22. 
The ethylenebisstearamide was debound in steps 23, 24 and 25. The 
guanidine wetting agent was debound in steps 26 and 27. Following 
substantially complete debinding, and the end of step 27, at an elapsed 
debinding time of 400 minutes, the part was sintered by heating in step 28 
at the rate of 300.degree. C./hr to a sintering temperature of 
1425.degree. C. In the steps 21 to 26, the atmosphere was hydrogen at a 
pressure of 780 torr. In the steps 27 and 28, the chamber was held under a 
vacuum of about 10.sup.-6 torr. 
FIG. 3 is a graph of a debinding profile of a second exemplary green 
composition according to the present invention. The debinding profile 
shown in FIG. 3 reflects the following steps of a debinding process: 
______________________________________ 
Step Time, Elapsed 
No. Action in Step min. Time, min. 
______________________________________ 
31 Heat from RT @ 75.degree. C./hr to 160.degree. C. 
108 108 
32 Heat from 160.degree. C. @ 30.degree. C./hr to 210.degree. C. 100 
208 
33 Soak (hold) @ 210.degree. C. 60 268 
34 Heat from 210.degree. C. @ 60.degree. C./hr to 325.degree. C. 115 
383 
35 Heat from 325.degree. C. @ 30.degree. C./hr to 450.degree. C. 250 
633 
36 Soak (hold) @ 450.degree. C. 60 693 
37 Heat from 450.degree. C. to sintering temperature 
______________________________________ 
The following binder composition was used in the green composition which 
was subjected to the debinding process shown in FIG. 3: 
______________________________________ 
poly(propylene carbonate) Q- .TM. 40 
59.43 wt % 
ethylenebisstearamide ACRAWAX .RTM. C 25.15 wt % 
guanidine ethyl hexanoate 8.49 wt % 
guanidine stearate 6.94 wt % 
Total 100.0 
______________________________________ 
In FIG. 3, the poly(propylene carbonate) and ethylenebisstearamide were 
debound together in steps 31, 32 and 33. The guanidine wetting agent was 
debound in steps 34, 35 and 36. Following substantially complete 
debinding, and the end of step 36, at an elapsed debinding time of 693 
minutes, the part was sintered in step 37 by heating at the rate of 
300.degree. C./hr to a sintering temperature of 1425.degree. C. The 
atmosphere was the same as that set forth above with respect to FIG. 2. 
Example 4 
A green composition comprising a binder composition and carbonyl iron doped 
with 2 wt % nickel, according to the present invention, was prepared as 
follows. 
The binder composition was the same as in Example 1. 
The ingredients for the green composition, comprising 51 vol % carbonyl 
iron doped with 2 wt % nickel powder, and 49 vol % of the binder 
composition prepared in Example 1, were combined, compounded and 
pelletized in a twin screw compounding extruder as described above. 
Expressed on a weight basis, the green composition comprised 88 wt % 
carbonyl iron w/2 wt % Ni powder and 12 wt % of the above binder 
composition. After the green composition was thoroughly compounded, it was 
extruded and pelletized. The pellets were subsequently fed into an 
injection molding machine, and injected into a mold. 
FIG. 4 is a graph of a debinding profile of the green composition of 
Example 4, according to the present invention. Following a five hour soak 
at 90.degree. C. to remove surface moisture, which is not shown in FIG. 4, 
the debinding profile shown in FIG. 4 reflects the following steps of a 
debinding and sintering process (the sintering steps 52 to 57 are not 
shown in FIG. 4): 
______________________________________ 
Step Time, Elapse 
No. Action in Step min. Time, min. 
______________________________________ 
41 Heat from RT @ 90.degree. C.; hold 5 hours 
300 300 
42 Heat from 90.degree. C. @ 48.degree. C./hr to 180.degree. C. 112 
412 
43 Soak (hold) @ 180.degree. C. 30 442 
44 Heat from 180.degree. C. @ 6.degree. C./hr to 225.degree. C. 450 
892 
45 Soak (hold) @ 225.degree. C. 30 922 
46 Heat from 225.degree. C. @ 30.degree. C./hr to 325.degree. C. 200 
1122 
47 Soak (hold) @ 325.degree. C. 30 1152 
48 Heat from 325.degree. C. @ 15.degree. C./hr to 400.degree. C. 300 
1452 
49 Soak (hold) @ 400.degree. C. 30 1482 
50 Heat from 400.degree. C. @ 78.degree. C./hr to 780.degree. C. 295 
1778 
51 Soak (hold) @ 780.degree. C. 60 1838 
52 Heat from 780.degree. C. @ 600.degree. C./hr to 800.degree. C. 2 
1840 
53 Soak (hold) @ 800.degree. C. 10 1850 
54 Heat from 800.degree. C. @ 480.degree. C./hr to 1330.degree. C. 68 
1918 
55 Soak (hold) @ 1330.degree. C. 5 1923 
56 Heat from 1330.degree. C. @ 60.degree. C./hr to 1380.degree. C. 50 
1973 
57 Soak (hold) @ 1380.degree. C. 80 2053 
______________________________________ 
The binder composition shown in Example 1 was used in the green composition 
which was subjected to the debinding process shown in FIG. 4. In the 
debinding process shown in FIG. 4, the atmosphere was hydrogen, at a flow 
rate of 12 CFM and a debinding oven chamber pressure of 780 torr. In the 
debinding process shown in FIG. 4, the poly(propylene carbonate) was 
debound in steps 42 and 43, ethylenebisstearamide was debound in steps 44 
and 45. The guanidine wetting agent was debound in steps 46 and 47. Steps 
48 and 49 provide an extra backup or "insurance" step to make certain that 
the debinding process is complete. Such "insurance" steps are not always 
necessary, but may be desirable, particularly during the development of a 
debinding protocol. Following substantially complete debinding, and the 
end of step 49, at an elapsed debinding time of 1482 minutes, the part was 
sintered in steps 50-57, as shown in the foregoing table to a final 
sintering temperature of 1380.degree. C. Steps 52-57 are not shown in FIG. 
4 due to space limitations, however, the profile would continue in 
accordance with the data shown in the foregoing table in a manner similar 
to that shown for the debinding steps as shown in the table and FIG. 4. It 
is noted that the initial step of soaking at 90.degree. C. for five hours 
can be eliminated with proper materials handling. If the binder 
composition and the inorganic powder are maintained in a suitably dry 
condition, a step of drying would not be required. 
A wide variety of parts can be made by PIM in accordance with the present 
invention. Such parts include for example, for an inorganic powder which 
is a metal, gun parts, shear clipper blades and guides, watch band parts, 
watch casings, coin feeder slots, router bits, drill bits, disk drive 
magnets, VCR recording heads, jet engine parts, orthodontic braces and 
prostheses, dental brackets, orthopedic implants, surgical tools and 
equipment, camera parts, computer parts, and jewelry. Such parts include 
for example, for intermetallic inorganic powders, turbochargers, high 
temperature insulators, spray nozzles and thread guides. Such parts 
include for example, for ceramic inorganic powders, optical cable 
ferrules, ski pole tips, haircutting blades, airfoil cores, piezoelectric 
(e.g., lead zircon titanate, PZT) parts, oxygen sensors and spray nozzles. 
Binder Compositions for Press & Sinter Application 
The binder composition of the present invention may also be used for press 
& sinter applications. In press & sinter application, the inorganic powder 
loading is considerably higher than in PIM. The trade-off for the higher 
loading is the limitation that the parts made by a press & sinter process 
are quite limited in complexity. In fact, press & sinter can be considered 
to be limited to quite simple parts. The types of inorganic powders which 
can be used in press & sinter applications are more limited, due to the 
requirement that the powders be sufficiently malleable and compactable to 
be useable in press & sinter applications. Powders having a high hardness 
values, such as for example WC, are generally not useable in press & 
sinter applications. The hardness value becomes an issue in press & sinter 
applications due to the low binder loadings used in press & sinter as 
compared to PIM. 
In a press & sinter application, the loading of the binder composition in 
the green composition is typically in the range from about 1% by volume to 
about 10% by volume of the green composition from which the part will be 
formed. (As with PIM applications, the green composition is measured on a 
volume basis, with the loadings expressed in volume percentages.) In one 
embodiment, the loading of the binder composition is 1% by volume. In one 
embodiment, the loading of the binder composition is 2% by volume. In one 
embodiment, the loading of the binder composition is 3% by volume. In one 
embodiment, the loading of the binder composition is 4% by volume. In a 
press & sinter process, the green composition is pressed into the desired 
shape by means of, e.g., a hydraulic press. Once the part is pressed into 
its shape, it has a green strength in the range from about 1,000 psi 
(about 703,070 Kg m.sup.2) to about 4,000 psi (about 2,812,278 
Kg/m.sup.2). The part is then sintered. 
For a press & sinter application, the binder composition according to the 
present invention has the following ranges of components (as previously, 
the binder composition is prepared on a weight by weight percentage bases 
(wt %)). 
______________________________________ 
polycarbonate polymer 
10-50 wt % 
ethylenebisamide wax 30-70 wt % 
guanidine wetting agent 5-30 wt % 
______________________________________ 
For press & sinter applications, the foregoing descriptions with respect to 
the selection of polycarbonate polymer, ethylenebisamide wax and guanidine 
wetting agent continue to apply. Thus, the acid used to form the reaction 
product of guanidine and acid is selected on the basis of the isoelectric 
point of the inorganic powder. Similarly, the same range of inorganic 
powders can be used, as long as these are useable in a press & sinter 
application. 
In view of the foregoing description, it is apparent that the present 
invention provides a new and improved binder which is formed and/or used 
in accordance with a new and improved method.