Aqueous injection molding binder composition and molding process

This invention provides a composition and a process for forming sintered, molded articles having improved dimensional stability. More particularly, this invention pertains to a composition having a sugar additive that increases the solids loading potential of the composition and a process for forming injection molded articles therefrom. Increasing the solids loading potential of the composition, enables the formation of metal or ceramic articles attaining about 98-99% of their theoretical maximum density, without cracking or shrinking significantly during sintering.

BACKGROUND OF THE INVENTION
 1. Field of Invention
 This invention relates to a composition and a process for forming sintered,
 molded articles having improved dimensional stability.
 2. Description of the Related Art
 Injection molding is a well known process for forming thermoplastic molded
 articles, such as plastic bottles or containers. Other types of useful
 injection molded articles are formed from metal powder (metal injection
 molding, or "MIM") or ceramic powder (ceramic injection molding, or
 "CIM"), rather than a thermoplastic material. Powder injection molding
 generally involves injecting a moldable fluid composition, comprising a
 combination of a ceramic or metal powder, a gel forming binder and a
 solvent into a mold of a predetermined shape under conditions sufficient
 to form a shaped article, referred to as a "green body." After forming a
 ceramic or metal green body, it is often desirable to sinter the article
 to remove any residual solvent and density the article. However, sintering
 frequently causes undesirable cracks or distortions in the article.
 In order to remedy this problem, it has been suggested to improve the
 mechanical strength of the fluid composition. This is accomplished through
 increasing its solid content. In particular, when using a powder
 containing composition, increasing the powder content will increase the
 mechanical strength of the composition and decrease the probability that a
 shaped article will crack during sintering. To the contrary, a composition
 having a lower powder content will cause cracking and shrinkage in molded
 articles formed therefrom during sintering.
 To increase the amount of powder a composition can retain, it may be
 necessary to augment the applicable binder with at least one viscosity
 reducing additive. The binder generally comprises a water soluble
 component or a polysaccharide that combines with the powder to form a
 flowable gel. Optimally, the additive will serve to increase the powder
 holding capacity of the binder, decrease the porosity of a molded article,
 and result in sintered articles having superior mechanical and physical
 properties.
 Compositions of the prior art have generally been unable to form green
 bodies having sufficiently high density and dimensional stability. Various
 attempts have been made using different additives to increase the solid
 holding capacity, and thus the mechanical strength, of a ceramic or metal
 composition. For example, U.S. Pat. No. 5,746,957 teaches a process for
 forming ceramic and/or metal articles comprising a ceramic and/or metal
 powder, a polysaccharide binder, a solvent and a gel strength enhancing
 agent comprising a borate compound. The borate compound is incorporated to
 increase the quantity of solid powder material that the composition can
 retain, thus increasing the density of the product. U.S. Pat. No.
 5,950,063 teaches a powder injection molding process using a composition
 comprising a powder and a binder incorporating additives such as coupling
 agents, antioxidants and surfactants. Also, U.S. Pat. No. 4,734,237
 provides a process for injection molding metallic or ceramic articles from
 a mixture comprising a metal or ceramic powder, a gel-forming material
 having specific desirable properties and a gel-forming material solvent.
 The specific gel-forming material allows for increased solid retention in
 the moldable composition.
 SUMMARY OF THE INVENTION
 The invention provides a composition for forming molded articles
 comprising:
 a) at least one metal powder, at least one ceramic powder, or a combination
 thereof;
 b) a gel forming polysaccharide binder; and
 c) a sugar.
 The invention further provides a process for forming molded articles
 comprising:
 A) forming a fluid composition comprising:
 a) at least one metal powder, at least one ceramic powder, or a combination
 thereof;
 b) a gel forming polysaccharide binder;
 c) a sugar; and
 d) a solvent; and
 B) molding the composition under conditions sufficient to form a solid
 molded article.
 The invention also provides a process for forming molded articles
 comprising:
 A) forming a fluid composition comprising:
 a) at least one metal powder, at least one ceramic powder, or a combination
 thereof;
 b) a gel forming polysaccharide binder;
 c) a sugar; and
 d) a solvent;
 B) molding the composition under conditions sufficient to form a solid
 molded article; and
 C) sintering the molded article.
 The invention still further provides articles produced by the processes of
 the invention.
 It would be desirable to provide a composition which enables a greater
 quantity of solid to be retained with in the composition. It has now been
 unexpectedly found that adding a sugar to a combination of at least one
 metal or ceramic powder, or combination thereof, and a polysaccharide
 binder reduces the viscosity of the composition and increases the solids
 loading. By increasing the solids loading, the sugar additive allows the
 formation a stable green body having increased shape retention, and a
 particle density sufficient to prevent cracking and deformation of the
 body during sintering. This also reduces the production cost of the
 injection molded components since less agar binder is used or replaced by
 less expensive glucose binder. Also, expensive supporting equipment is not
 needed and the components are not as sensitive to handling. When the green
 body is ultimately sintered, the sugar and solvent are burned away,
 leaving behind a high density, high strength ceramic or metal article.
 Sugar is generally inexpensive, commercially available as glucose that
 reduces the viscosity of the polysaccharide binder, and thus increases the
 amount of powder it can retain while in a fluid state. When the desired
 binder to sugar ratio is attained, the composition can be molded and
 sintered to produce an article having increased density compared to
 articles formed through prior art processes. The present invention also
 allows for the reduction of the amount of binder used in the composition,
 reducing the cost of forming the composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 The present invention provides a process and composition for forming metal
 or ceramic molded articles from metal or ceramic powders. This composition
 comprising at least one metal powder or at least one ceramic powder, or a
 combination thereof, a gel forming polysaccharide binder and a sugar is
 combined with a solvent and molded into a self-supporting shaped article.
 The article is then preferably heated at a high temperature to sinter the
 particles together to form a highly dense and stable metal or ceramic
 article. Adding sugar to the combination of the metal or ceramic powder
 and a polysaccharide binder reduces the viscosity of the composition and
 enables a greater quantity of solid to be retained in the composition. By
 increasing the solids loading, the sugar additive allows the formation of
 a stable body of densely packed particles having increased shape retention
 prior to sintering. When the green body is ultimately sintered, the sugar
 and solvent are burned away, leaving behind a high density, high strength
 metal or ceramic article.
 To form the moldable composition, the metal or ceramic powder is mixed with
 the gel forming binder, a solvent and a sugar such that a homogeneous
 composition is formed. Metallic powders generally comprise elemental
 powders, semi-elemental powders, prealloyed powders or mixtures thereof.
 An elemental powder is generally composed of one metal element only. For
 example, an iron or nickel powder or a mixture thereof. A semi-elemental
 powder is generally a powder composed of more than one metal element, such
 as a semi-elemental ferrochrome powder comprised of 50% iron and 50%
 chrome. A mixture of elemental and semi-elemental powders is referred to
 as an elemental/semi-elemental powder, such as mixing a ferrochrome powder
 with an iron powder to form stainless steel. A prealloyed powder is a
 powder composition that has been formed from an existing metal alloy. For
 example, solid high or low carbon steel or super alloys having the desired
 composition can be melted and pulverized to form a powder. Combining
 different types of metallic powders reduces the necessary sintering
 temperature for an article. This is desirable because higher sintering
 temperatures can give rise to problems such as the evaporation of lower
 temperature elements in an alloy.
 The preferred metal powders include elemental metal powder compositions
 such as copper, aluminum, gold, silver, nickel, titanium, tungsten,
 tantalum, iron and metal alloy powders such as steels (especially
 stainless steels), intermetallic components, and mixtures thereof.
 Preferred ceramic powders non-exclusively include powders of electronics,
 engineering and structural ceramics such as oxides, borides, nitrides, and
 silicides, carbides of metals or nonmetals, and mixtures thereof. Examples
 of such compositions are Ca-modified lead titanate, Samarium-modified lead
 titanate, lead metaniobate (PN), modified lead titanates such as (Pb,
 Ca)TiO.sub.3 or (Pb, Sm)TiO.sub.3, PZT (lead zirconate titanate,
 PbZr.sub.1-x Ti.sub.x O.sub.3).
 Other compositions that are preferred for the practice of this invention
 are K.sub.x Na.sub.1-x NbO.sub.3, where x is between 0 and 0.5, Na.sub.1-x
 Li.sub.x NbO.sub.3, where x is 0.02 to 0.13, Na.sub.0.75 Pb.sub.0.125
 NbO.sub.3, Pb.sub.0.95 Bi.sub.0.05 (Ti.sub.0.975 Zn.sub.0.025)O.sub.3,
 Pb.sub.0.95 Bi.sub.0.033 (Ti.sub.0.95 Zn.sub.0.017 Nb.sub.0.033)O.sub.3,
 Pb.sub.0.9625 La.sub.0.025 (Ti.sub.0.99 Mn.sub.0.01)O.sub.3,
 Pb(Ti.sub.0.95 Zn.sub.0.017 Nb.sub.0.033)O.sub.3, Pb(Ti.sub.0.606
 Zr.sub.0.394)O.sub.3, Pb(Ti.sub.0.526 Zr.sub.0.48)O.sub.3, Pb.sub.0.985
 Bi.sub.0.01 (Ti.sub.0.085 Zr.sub.0.915)O.sub.3, Pb.sub.0.95 Mg.sub.0.05
 (Ti.sub.0.54 Zr.sub.0.43 Cr.sub.0.03)O.sub.2.085, Pb.sub.0.985 La.sub.0.01
 (Ti.sub.0.085 Zr.sub.0.915)O.sub.3, Pb.sub.0.988 (Ti.sub.0.42
 Zr.sub.0.58)Nb.sub.0.024 O.sub.3, Pb.sub.0.995 (Ti.sub.0.074 Zr.sub.0.916
 Sb.sub.0.010)O.sub.3, and Na.sub.0.5 Bi.sub.0.5 TiO.sub.3. Certain of the
 above compositions can be more compactly described by the formula M.sub.x
 M'.sub.1-x NbO.sub.3, wherein M and M' are chosen from Na, Li, and K and x
 is less than one. Other ceramic compositions from this preferred list can
 be more compactly described by the formula Pb.sub.x M".sub.v (Ti.sub.y
 M.sub.z M'.sub.u)O.sub.3, wherein M and M' are selected from Zn, Nb, Zr,
 Sb, and Mn, M" is selected from Bi, La, and Nb, both x+v and y+z+u are
 about 1, and v is no more than about 0.05.
 Relaxor ferroelectric ceramics have the lead titanate type of structure
 (PbTiO.sub.3) and disorder on either the Pb-type of sites (called A sites)
 or the Ti-type of sites (called B sites). Examples of such relaxor
 ferroelectrics having B site compositional disorder are Pb(Mg.sub.1/3
 Nb.sub.2/3)O.sub.3 (called PMN), Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 (called
 PZN), Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 (called PNN), Pb(Sc.sub.1/2
 Ta.sub.1/2)O.sub.3, Pb(Sc.sub.1/2 Nb.sub.1/2)O.sub.3 (called PSN),
 Pb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3 (called PFN), and Pb(Fe.sub.1/2
 Ta.sub.1/2)O.sub.3. These are of the form A(BF.sub.1/3 BG.sub.2/3)O.sub.3
 and A(BF.sub.1/2 BG.sub.1/2)O.sub.3, where BF and BG represent the atom
 types on the B sites. Further examples of relaxor ferroelectrics with
 B-site disorder are solid solutions of the above compositions, such as
 (1-x)Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 -xPbTiO.sub.3 and (1-x)Pb(Zn.sub.1/3
 Nb.sub.2/3)O.sub.3 -xPbTiO.sub.3. Another more complicated relaxor
 ferroelectric that is preferred for the present invention is
 Pb.sub.1-x.sup.2+ La.sub.x.sup.3+ (Zr.sub.y Ti.sub.z).sub.1-x/4 O.sub.3,
 which is called PLZT.
 The preferred metal or ceramic powders of the composition are selected
 based on a variety of desired properties and characteristics, such as
 their size and shape distribution or surface chemistry. If a selected
 powder having a particular particle size, shape or surface chemistry is
 not be compatible with the chosen binder, it may be coated with one or
 more other additives.
 The characteristics of the powder chosen is important because the selection
 can influence and control the flowability, evaporation-condensation,
 lattice, grain boundary surface diffusion, moldability, shrinkage and
 sintering mechanisms of the moldable composition. The size distribution of
 the particles in a powder can also influence the solids loading and
 moldability of the composition. The shape of the particles is important
 for flow behavior and shape retention during thermal processing.
 Preferably the particles are substantially spherical. The powder
 preferably has an average particle size of from about 1 to about 200 .mu.m
 and more preferably from about 4.5 to about 150 .mu.m. Further, should a
 combination of ceramic and metal powders, or a selection of different
 varieties of ceramic or metal powders be used, then they are preferably
 blended to ensure that each powder is uniformly dispersed within the
 composition. This allows the additive and binder to perform their
 functions most effectively and ensures that a maximum solid loading is
 obtained.
 The metal or ceramic powder is preferably present in the unsintered
 composition in an amount of from about 50 to about 92 by weight of the
 composition. More preferably, the powder is present in an amount of from
 about 75 to about 91 by weight of the composition.
 The composition also includes a gel forming binder. The gel forming binder
 is used primarily to achieve good flowability, good green strength of the
 molded component, and a high solids loading potential. Suitable binders
 include water soluble polysaccharide binders. Particularly, the
 polysaccharide binder preferably comprises an agaroid. For the purposes of
 this invention, an agaroid refers to agar and any gums resembling agar,
 and derivatives thereof such as agarose.
 An agaroid is employed because it exhibits rapid gelation within a narrow
 temperature range, a factor which can increase the rate of production of
 articles. Additionally, the use of such gel-forming binders reduces the
 amount of binder needed to form a self-supporting article. Therefore,
 articles produced using gel forming binders comprising agaroids can
 significantly enhance the quality of and stability of green bodies and
 sintered articles.
 The preferred agaroids are those which are water soluble and comprise agar,
 agarose, carrageenan, and the like and combinations thereof, and most
 preferably comprise agar, agarose, and mixtures thereof. The gel forming
 binder preferably is present in an amount ranging from about 1.5% to about
 10% by weight of the composition. More preferably, the binder is present
 in an amount ranging from about 1.8% to about 5% by weight of the
 composition.
 The unsintered composition then contains a sugar. Suitable sugars for this
 invention non-exclusively include glucose, sucrose, dextrose and fructose.
 In the most preferred embodiment, the sugar additive is glucose, in
 particular, a glucose or Dextrose of the general formula
 (D-Glucose-CH.sub.2 OH(CHOH).sub.4 CHO). The sugar is generally
 commercially available. The sugar is preferably present in an amount of
 from about 0.5% to about 6% by weight of the composition. More preferably,
 the sugar is present in an amount of from about 1% to about 3.5% by weight
 of the composition. The preferred weight ratio of the binder to the sugar
 ranges from about 0.2 to about 3.5. More preferably, the weight ratio of
 the binder to the sugar ranges from about 0.1 to about 3.
 Suitable solvents for the purposes of this invention include deionized
 water, and mixtures of water and alcohol. The solvent is added in an
 amount sufficient to dissolve the gel forming binder at the melting
 temperature of binder. The preferred solvent is water.
 The compositions may include a gel strengthening agent, such as a borate,
 e.g., calcium borate, potassium borate, magnesium borate, zinc borate and
 mixtures thereof.
 Each of the metal and ceramic powders described above may have different
 surface chemistries that may influence the manner in which a composition
 is prepared. Accordingly, certain powders may need to be coated with a
 suitable additive prior to combination with other powders having different
 surface chemistries. Suitable optional additives include coupling agents,
 antioxidants, lubricants, dispersants, elasticizing agents, plasticizers
 and compatibilizers.
 The composition may also optionally contain a wetting agent or surfactant
 such as polyethylene glycol alkylether, or a lubricant such as zinc
 stearate, aluminum stearate or magnesium stearate.
 The additives are used, in part, to ensure that the binder effectively
 coats or attaches to the powder particles. Some powder may react or be
 incompatible with the binder and, therefore, need to be coated with an
 additive prior to introduction of the binder. Powders may be pretreated
 with different additives to allow the appropriate additives to perform its
 function most effectively. These additives are applied by known methods
 including solvent slurry techniques, wet/dry milling, fluidization
 techniques, spray drying, dry dispersion or other techniques. The
 additives designed to interact directly with the powder surface, such as
 the antioxidants, surfactants, dispersants or coupling agents, are used
 for the initial coating of the powder. Application sequence of
 surface-active agents is dependent on powder chemistry and varies
 according to known chemical properties.
 The composition components may be blended in a heated mixer by generally
 well known techniques. Suitable mixing equipment includes a tumbler with
 an agglomerate breaker, a ribbon mixer, a vertical screw mixer, a single
 or twin rotor mixer, and a turbine mixer. Also appropriate for this
 invention is a screw extruder. Screw extruders are frequently used for
 fluid processing and comprise a continuous rotating screw or screws in a
 closely fitting barrel. In practice, materials are fed into the extruder
 as a dry solids, then are heated and mixed within the barrel to form the
 fluid composition, and discharged at open end.
 Once the composition is mixed, it is preferably shaped into a solid molded
 article. Various molding processes are well known in the art, including
 injection molding, hot-rolling, hot-pressing, flat pressing, blow molding,
 extruding and slip casting. For the fabrication of complex shapes such as
 cylinders, injection molding and extrusion are especially preferred. In
 order to help avoid the formation of a porous structure, vacuum may be
 applied during the forming step for shaped articles. If a hot-pressing
 method is used, the stress used for compacting is preferably as high as
 can be conveniently applied without fracturing the particles. For the
 purposes of this invention, molding is preferably conducted in an
 injection molding device. The composition is injected into a mold of a
 predetermined shape and size while in a fluid state with heat and under
 conditions sufficient to conform to the shape of the mold. The appropriate
 mold temperature can be achieved before, during or after the mixture is
 supplied to the mold. The preferred temperature for melt processing is at
 least about 5.degree. C. above the melting point of the binder. More
 preferably, the temperature for melt processing is at least about
 35.degree. C. above the melting point of the binder. Molding is preferably
 conducted at a temperature ranging from about 75.degree. C. to about
 95.degree. C. More preferably, the composition is molded at a temperature
 ranging from about 82.degree. C. to about 95.degree. C.
 A wide range of molding pressures may be employed. Generally, the molding
 pressure is at least about 100 psi, preferably from about 100 psi (689.5
 KN/m.sup.2 )to about 50,000 psi (3.4.times.10.sup.5 KN/m.sup.2 ) psi,
 although higher or lower pressures may be employed depending upon the
 molding technique used. More preferably molding pressures range from about
 100 psi to about 2000 psi, and most preferably, are from about 150 psi to
 about 800 psi. Alternately, the composition may be extruded into pellet or
 particle form and stored for future molding.
 After the article is molded, it is cooled to a temperature below the gel
 point of the gel-forming material. For the purposes of this invention,
 this temperature ranges from about 15.degree. C. to about 40.degree. C.
 More preferably, this temperature ranges from about 30.degree. C. to about
 40.degree. C. Following this step, the green body is removed from the
 mold. The green body may be subsequently dried and placed into a furnace
 for sintering at high temperatures.
 The sintering times and temperatures are regulated according to the
 powdered material employed to form the fluid composition. In general, the
 sintering temperatures are selected depending on the individual powders
 used. Sintering conditions for various materials are easily determinable
 by those skilled in the art. Ordinarily for wax-based systems, an
 absorbent, supporting powder is employed to assist in removing the wax
 from the part and to aid in supporting the part so that the intended shape
 of the product is maintained during sintering. The present invention
 eliminates that need for such materials.
 For the purposes of this invention, the molded article is preferably
 sintered at a temperature ranging from about 1200.degree. C. to about
 1450.degree. C. More preferably, the article is sintered at a temperature
 ranging from about 1300.degree. C. to about 1400.degree. C. The resulting
 product is a shaped article attaining about 98 to 99% of its theoretical
 maximum density.
 The following non-limiting examples serve to illustrate the invention.
 Injection molding pressures quoted refer to machine hydraulic pressure.
 Solid wt % includes all residual material after removal of volatiles at
 150.degree. C. The result shown in each example is based on the average of
 ten samples unless otherwise stated.
 EXAMPLE 1
 A molding batch was prepared with stainless steel 17-4PH powder having a
 mean particle size of 22 .mu.m. The batch was made with 7842 g of 17-4PH
 metal powder, 110 g of agar, 50 g of glucose, and 680 g deionized water
 [DI/H.sub.2 O]. Also, a mixture of methyl-p-hydroxybenzoate and
 propyl-p-hydroxybenzoate 1.6g and 1.2 g respectively added as biocides. A
 sigma mixer was used for compounding this batch. The agar, biocides,
 glucose and water were pre-mixed and transferred to the sigma mixer.
 During agitation the temperature was raised to 90-95.degree. C.
 (194-203.degree. F.) and mixed for 30 min. to melt the mixture. The metal
 powder was added incrementally. The total mixing time was 1.5 h at
 90-95.degree. C. (194-203.degree. F.). After the material allowed to cool
 to 33.degree. C. (91.4.degree. F.), it was shredded into particulates
 using a food processor (Hobart shredder). Before molding and evaluating
 the flow characteristic for the shredded feedstock the moisture level was
 adjusted to 94.16 wt % by exposing the material to the atmosphere. Samples
 were taken periodically and analyzed by using Arizona moisture balance.
 Spiral testing was conducted by flowing the feedstock material through a
 hollow spiral mold to evaluate its flow properties, using a Boy 22M
 injection molding machine. The barrel temperature of the injection molding
 machine was set on 83.degree. C. (180.degree. F.) and mold temperature
 kept at 22-23 C. (71.6-73.4.degree. F.) during the molding. At 94.16 wt.
 solid the average flow for ten samples at 500, 1000 and 1500 psi
 (3.5.times.10.sup.3, 6.9.times.10.sup.3, 10.3.times.10.sup.3 KN/m .sup.2)
 injection pressures was 5.56.+-.0.63 (14.1.+-.1.6 cm), 9.89.+-.0.47
 (25.1.+-.1.2 cm), 12.47.+-.1.34 (inch) (31.7.+-.3.4 cm) respectively. This
 shows that by modifying the binder formulation (feedstock formulation),
 the viscosity of the feedstock material reduces and allow us to
 incorporated more metal powder in the feedstock formulation. By adding
 more metal (increasing the solid loading) the final shrinkage % will be
 reduced and better dimensional control can be achieved. Also, lesser water
 in the formulation provides lesser tendency for the moisture to separate
 from the feedstock and form water condensation.
 EXAMPLE 2
 The moisture content of the same feedstock material from Example 1 was
 adjusted to achieve 94.80 wt % solids. Spiral testing conducted on this
 material shows that the flow characteristic significantly decreased as the
 solid loading increased to 94.80 wt %. The material showed zero flow at
 500 and 1000 psi(3.5.times.10.sup.3, 6.9.times.10.sup.3 KN/m.sup.2)
 injection pressures. The average flow for ten samples at 1500
 psi(10.3.times.10.sup.3 KN/m.sup.2 injection pressure was only 2.66"
 .+-.0.3(6.76.+-.0.8). With this binder formulation (agar/glucose ratio)
 the feedstock solid loading has to be less than 94.80 wt. % to be used for
 molding.
 EXAMPLE 3
 A batch was prepared based on a 1:1 agar to glucose ratio, together with
 7842 g of 17-4PH metal powder, 110 g agar, 110g glucose, 680 g DI/H.sub.2
 O, 1.6 g methyl-p-hydroxybenzoate and 1.4 g propyl-p-hydroxybenzoate. The
 same mixing procedure was followed as described in Example 1. The solid wt
 % of the feedstock was adjusted to 95.04 wt % by evaporating the excess
 water from the material. Spiral testing was conducted on this material at
 500, 1000, 1500, 2000 and 2300 psi (3.5.times.10.sup.3,
 6.9.times.10.sup.3, 10.3.times.10.sup.3, 13.8.times.10.sup.3,
 15.9.times.10.sup.3 KN/m.sup.2) injection pressures to evaluate and
 compare the effect of this batch formulation on flow characteristics. The
 average flow for ten samples at 95.04 wt % solid is shown in following
 table.

Injection pressures
 500 (psi) 1000 (psi) 1500 (psi) 2000 (psi) 2300 (psi)
 0" 2.7" .+-. 3.51" .+-. 3.64" .+-. 5.23" .+-.
 0.33 0.31 0.30 0.35 (inch)
 6.9 .+-. 8.9 .+-. 9.2 .+-. 13.3 .+-.
 0.8 cm 0.8 cm 0.8 cm 0.9 cm
 With this binder formulation (agar/glucose ratio) the feedstock does not
 flow at 500 psi with 95.04 wt % solid. The solid loading has to be less
 than 95.04 wt. % to be used for molding. The objective is to optimize the
 formulation at 95 wt % solid to achieve 3" to 4" flow at 500 psi pressure.
 EXAMPLE 4
 The moisture content of the feedstock from Example 3 was adjusted to
 provide material with 94.82 wt % solid by evaporating the excess water
 from the material. The following spiral testing data shows slight flow
 improvement at this solids level.

Injection pressures
 500 (psi) 1000 (psi) 1500 (psi) 2000 (psi)
 1.68" .+-. 0.08 2.56" .+-. 0.10 5.68" .+-. 0.24 5.44" .+-. 0.4
 4.3 .+-. 0.2 cm 6.5 .+-. 0.3 cm 14.4 .+-. 0.6 cm 13.8 .+-. 1.0 cm
 By changing the agar to glucose ratio from 1 (in Example 3) to 0.82 in this
 example the material at 95.02 wt % solids started to flow at 500 psi
 injection pressure. However, in Example 3, the flow at 95.04 wt % solids
 at 500 psi was zero. With this formulation material start flowing at 500
 psi with high solid loading of 95.02 wt. % (also, see explanation in
 Example 1)
 EXAMPLE 6
 The flow characteristics of the feedstock from Example 5 were evaluated at
 94.49 wt % solids. The spiral testing was conducted at 500, 1000 and 1500
 psi injection pressures. The following results show, at slightly lower
 solid loading (94.49 wt %) the material flow was significantly improved.
 The comparative feedstock material (Example 13, below) does not flow at
 this solids loading.

Injection pressures
 500 (psi) 1000 (psi) 1500 (psi)
 5.05" .+-. 0.45 8.5" .+-. 1.45 9.22" .+-. 1.08
 12.8 .+-. 1.1 cm 21.6 .+-. 3.7 cm 23.4 .+-. 2.7 cm
 EXAMPLE 7
 This example illustrates a feedstock composition having 1:1 agar to glucose
 ratio, as in Example 3. However, the total amount of agar plus glucose in
 this example is 180 g vs. 220 g in Examples 3 and 4. This batch was
 compounded using 7842 g 17-4PH stainless steel powder, 90 g agar, 90 g
 glucose, 680 g DI/H.sub.2 O, 1.6 g methyl-p-hydroxybenzoate and 1.4 g
 propyl-p-hydroxybenzoate, using the same mixing steps and conditions as in
 Example 1. The excess moisture content of the feedstock was removed by
 evaporating the excess water from the material to reach a desired solids
 level of 94.50 wt %., and flow behavior was examined at this solids level.
 The following data shows the spiral results for this feedstock
 composition.

Injection pressures
 500
 (psi) 1000 (psi) 1500 (psi) 2000 (psi)
 0" 3.5" .+-. 0.13 5.73" .+-. 0.51 7.63" .+-. 1.05
 0 cm 8.9 .+-. 0.3 cm 14.6 .+-. 1.3 cm 19.4 .+-. 2.7 cm
 The agar to glucose ratio for this batch was selected to be the same as the
 batch in example 4 but, the material flow at 500 psi became zero, even
 with lower solid loading of 94.50 vs. 94.80 wt % (for the composition of
 Example 4). However, this batch contains total of 2.3 wt % binder
 (agar+glucose) vs. 2.8 wt % binder in Example 4. This is indicates the
 agar to glucose ratio as well as total wt % of binder significantly
 effects the flowablity of the feedstock material.
 EXAMPLE 8
 A feedstock composition comprising 7842 g 17-4PH stainless steel powder, 90
 g agar, 125 g glucose, 680 g DI/H.sub.2 O, 1.6 g methyl-p-hydroxybenzoate
 and 1.4 g propyl-p-hydroxybenzoate was used, with an agar to glucose ratio
 of 0.72,following the procedure of Example 1. The following table shows
 the flow behavior of the material at 94.99 wt % solids.

Injection pressures
 500 (psi) 1000 (psi) 1500 (psi)
 1.85" .+-. 0.14 3.32" .+-. 0.28 6.01" .+-. 0.28
 4.7 .+-. 0.4 cm 8.4 .+-. 0.7 cm 15.3 .+-. 0.7 cm
 Comparing this result with that of Example 3 shows that increasing the
 amount of glucose and lowering the agar content has a significant effect
 on flow characteristics of the feedstock material. The agar to glucose
 ratio in Example 3 is 1 with total of 2.8 wt % binder (agar+glucose)
 content. In this example the ratio is 0.72 and total amount of binder
 content is 2.74 wt %.
 EXAMPLE 9
 A feedstock composition comprising 7842 g of stainless steel 17-4PH powder,
 90 g agar, 180 g glucose, 680 g DI/H.sub.2 O, 1.6 g
 methyl-p-hydroxybenzoate and 1.4 g propyl-p-hydroxybenzoate was used, with
 an 1:2 agar to glucose ratio, following the procedure of Example 1. The
 spiral testing was conducted at 94.91 wt % solid at 500, 1000, and 1500
 psi injection pressures.

Injection pressures
 500 (psi) 1000 (psi) 1500 (psi)
 4.55" .+-. 0.93 7.28" .+-. 0.92 8.62".+-. 0.23
 11.6 .+-. 2.4 18.5 .+-. 2.3 21.9 .+-. 0.6 cm
 The results of this example shows that a higher amount (3.44 wt %) of
 binder content with lower agar to binder ratio of 0.5 further improves the
 flow behavior of the feedstock material (compared with Example 8)
 EXAMPLE 10
 The flow characteristics of the feedstock material from Example 9 were
 evaluated at 94.56 wt % solids. The spiral testing conducted at three
 different injection molding pressure. The following table shows the
 results of the experiment.

Injection pressures
 500 (psi) 1000 (psi)
 9.68" .+-. 0.55 16.60" .+-. 1.26
 24.6 .+-. 1.4 cm 42.2 .+-. 3.2 cm
 The feedstock exhibited excellent flow characteristics at 94.56 wt %
 solids. It should be mentioned that the comparative feedstock material
 (Example 13 below) could not be tested, molded or even fed into the
 injection molding machine at a 94.56 wt % solid.
 EXAMPLE 11
 A feedstock composition was designed based on the composition used in
 Example 9 with slightly higher agar/glucose ratio of 0.56. Similarly, the
 preparation of this batch was the same as Example 1. This batch was
 compounded using 7842 g 17-4PH stainless steel powder, 100 g agar, 180 g
 glucose, 680 g DI/H.sub.2 O (containing 0.27 wt % calcium tetra borate),
 1.6 g methyl-p-hydroxybenzoate and 1.4 g propyl-p-hydroxybenzoate. The
 moisture content of the feedstock adjusted to 5.46% (94.54 wt % solid).
 Eleven flat test bar (1/8" thickness, 1/4"-3/4" variation in width, 6.5"
 length) samples were molded using a 55 ton Cincinnati injection molding
 machine. The average weight of ten as molded samples was 42.66.+-.0.07 g.
 The results are shown in the table following Example 13.
 EXAMPLE 12
 The moisture content of feedstock material of Example 11 was adjusted to 5%
 (95 wt % solid). Ten flat test bar samples as in Example 11 were molded at
 95.0 wt % solid, with the average weight of ten as molded samples being
 43.8.+-.0.09 g. The following data shows a comparison of as molded weight
 variation of the feedstock material of Comparative Example 13 (contains no
 glucose) molded at 92.60 wt % solid and material from Examples 11 and 12
 molded at 94.54 and 95.0 wt % respectively. The results are shown in the
 following table.
 EXAMPLE 13 (COMATIVE)
 A molding composition was prepared without glucose as a comparison. The
 batch comprised 7842 g stainless steel 17-4PH powder, 165 g agar, 680 g
 DI/H.sub.2 O (containing 0.27 wt % calcium tetra borate), 1.6 g
 methyl-p-hydroxybenzoate and 1.4 g propyl-p-hydroxybenzoate. All the
 processing steps for preparation of this batch were the same as Example 1.
 The moisture level of the feedstock was adjusted to 7.40% (92.60 wt %
 solid). The average flow of ten samples at 500, 1000, and 1500 psi, was
 3.57".+-.0.16, 8.14".+-.0.08 and 11.76".+-.0.14 respectively. The average
 as molded weight for six samples with this batch was 37.45.+-.0.02 g.

As Molded weights (g)
 Comparative
 feedstock from Samples from Samples from
 Example 13 Example 11 Example 12
 Sample (92.60 wt % (94.54 wt % (95 wt %
 # solid) solid) solid)
 1 37.45 40.33 41.06
 2 37.42 40.39 41.10
 3 37.45 40.46 41.00
 4 37.43 40.28 41.15
 5 37.46 40.40 41.12
 6 37.46 40.35 41.10
 As the solid loading increases the as molded weight of the samples
 increases. This provides higher green density which significantly reduces
 the final skrinkage. (Also see the plot of as molded weight vs. solid
 loading).
 EXAMPLE 14
 Four samples from Example 11, six samples from Example 12 along with eight
 samples from Example 13 were sintered under hydrogen atmosphere for 2
 hours. The shrinkage for these samples evaluated and compared. The
 following table shows the results and the comparison.

Average
 % shrinkage Average Average
 Samples molded % shrinkage % shrinkage
 with comparative Samples molded Samples molded
 feedstock with feedstock with feedstock
 Example 13 from Example 11 from Example 12
 Width 15.83 14.31 14.11
 Thickness 17.93 14.87 14.67
 Length 15.80 13.66 13.62
 These data shows that the binder formulation of this invention improved the
 solid loading of the feedstock material from 92.5 wt % to 95.0 wt %. This
 provided greater dimensional control and improved the final (sintered)
 shrinkage by 10.9%, 18.2% and 13.8% for width, thickness and length of the
 parts respectively.
 While the present invention has been particularly shown and described with
 reference to preferred embodiments, it will be readily appreciated by
 those of ordinary skill in the art that various changes and modifications
 may be made without departing from the spirit and scope of the invention.
 It is intended that the claims be to interpreted to cover the disclosed
 embodiment, those alternatives which have been discussed above and all
 equivalents thereto.