Patent Application
20230234891
The present invention relates to a binder for an injection molding composition and to an injection molding composition comprising said binder.
Powder injection molding makes it possible to obtain a wide variety of shapes of parts in a wide variety of materials, in particular plastics, metals and ceramics. This method also makes it possible to manufacture large quantities of parts, while reducing production times.
A method for manufacturing a sintered part which implements powder injection molding conventionally comprises the following steps:
A) producing the molding composition,
B) injection molding said molding composition in order to obtain a preform,
C) at least partially debinding the preform,
D) sintering the at least partially debound preform in order to obtain a sintered part.
Step A) consists in mixing an organic binder and a powder, for example a metal or ceramic powder, optionally functionalized with the aim of improving contact with the binder.
The binder conventionally comprises a polymer base, a wax and a surfactant. The role of the binder is to facilitate the flow of the molding composition during the injection molding in step B), and to afford sufficient mechanical strength to the preform in order to enable handling thereof.
Ceramic powders and metal powders have different properties, particularly different grain surface properties and flow properties. The problems raised by the injection molding of molding compositions comprising metal powders and ceramic powders, and the technical solutions adopted to solve said problems, are generally different. In particular, a binder developed for a molding composition based on a metal powder cannot a priori be used as is for a molding composition based on a ceramic powder.
At the end of step A), a molding composition, conventionally referred to as “feedstock”, is obtained.
Step A) also conventionally comprises a granulation, so that the molding composition is in the form of granules.
In step B), after being heated, the molding composition is injection molded, conventionally using an injection molding machine, so as to obtain a preform.
Step C) consists in eliminating, at least partially, preferably entirely, the binder present in the preform, conventionally by subjecting said preform to an attack by a solvent (“solvent” debinding) then a thermal attack (thermal debinding).
The debinding may deform the preform, leading to the manufacture of an unacceptable sintered part.
Step D) consists in consolidating the preform by sintering so as to obtain the desired part, and also in eliminating any potential binder which was not eliminated during step C). In one embodiment, the thermal debinding of step C) and the sintering of step D) are performed within the same step, during a single heat cycle.
There is a persistent need fora method which limits the deformation of the preform in step C) while leading to a sintered part having a relatively high density.
One aim of the invention is to at least partially meet this need.
The invention relates to a binder for an injection molding composition, said binder consisting of, in percentage by weight:
Remarkably, the inventors have observed that the presence of such a polymer base at the indicated contents limits the deformation of the preform in step C) while leading to a sintered part having a relatively high density.
A binder according to the invention advantageously makes it possible to limit operations of reworking by machining, which are expensive or even impossible in the case of complex shapes.
A binder for an injection molding composition according to the invention may further have one or more of the following optional characteristics:
The invention also relates to an injection molding composition comprising a binder according to the invention at an amount of between 30% and 65% in percentages by volume based on the volume of the molding composition, the remainder being, for more than 90% by weight, a ceramic powder.
An injection molding composition according to the invention may further have one or more of the following optional characteristics:
The invention further relates to a method for manufacturing a sintered part, said method comprising steps A) to D) described above, the molding composition being in accordance with the invention.
All the percentages in the present description are percentages by weight, unless indicated otherwise.
All the characteristics of the binder and of the molding composition can be measured in accordance with the protocols described for the examples.
The verbs “contain”, “comprise” and “have” should be interpreted broadly and non-limitingly, unless indicated otherwise.
Other characteristics and advantages of the invention will become clearer upon reading the following detailed description and upon examining the appended drawing, wherein
A binder for an injection molding composition according to the invention can be manufactured by a conventional manufacturing method, by simply mixing the components (a), (b), optionally (c) and optionally (d), for example at ambient temperature.
This mixing may also be carried out while the molding composition is being produced.
Component (a) is the polymer base and represents 35% to 60% of the weight of the binder.
Preferably, the amount of polymer base is greater than or equal to 40%, preferably greater than or equal to 45% and/or less than or equal to 55%, preferably less than or equal to 50% of the weight of the binder.
The polymer base consists of an amphiphilic polymer or a mixture of non-amphiphilic polymers which, unlike the polymer or mixture of polymers of the wax, each have a weight-average molar mass of greater than or equal to 5,000 g/mol.
Each constituent of the polymer base preferably has a weight-average molar mass of greater than 8,000 g/mol, preferably greater than 10,000 g/mol, preferably greater than 20,000 g/mol, preferably greater than 30,000 g/mol.
In particular, the polymer base preferably comprises a polymer, which preferably constitutes the remainder to the SEBS in the polymer base, selected from polypropylenes, polyethylenes, ethylene-vinyl acetates, ethylene-ethyl acrylates, polystyrenes, polyethylene carbonates, diethyl phthalate, dioctyl phthalate, dibutyl phthalate, polyvinyl alcohol, polyvinyl acetate, ethylene-methacrylic acid copolymers, polyvinyl chloride, polyvinyl butyral, a polyacetal, a polymethyl methacrylate, a polybutyl methacrylate, a methacrylic acid ester copolymer, a methyl ethyl ketone, resins, preferably acrylic resins, ketone resins and mixtures thereof, and mixtures thereof.
Preferably, the polymers of the polymer base which constitute the remainder to the SEBS in the polymer base are selected from polypropylenes, polyethylenes, ethylene-vinyl acetates, ethylene-ethyl acrylates, polystyrenes, polyethylene carbonates, polyvinyl chloride, acrylic resins and mixtures thereof.
Preferably, as the remainder to the SEBS, the polymer base comprises, preferably consists of, a mixture of polypropylene and of polyethylene, preferably in a polypropylene/polyethylene weight ratio of greater than 25/75, preferably greater than 30/70, and less than 50/50. The polyethylene is preferably a high-density polyethylene.
According to the invention, the polymer base comprises 2% to 15% of a SEBS in percentage by weight based on the weight of the binder. Preferably, the content of SEBS is greater than or equal to 3%, preferably greater than or equal to 4% and/or less than or equal to 13%, preferably less than or equal to 11%, or even less than or equal to 9%, or even less than or equal to 7%.
According to the invention, the content by weight of styrene in the SEBS is greater than 15% in percentage by weight based on the weight of said SEBS. Preferably, the content of styrene in the SEBS is greater than 20%, preferably greater than 25%, and/or preferably less than 60%, preferably less than 58%, in percentage by weight based on the weight of said SEBS.
Also according to the invention, the weight-average molar mass of the SEBS is greater than 100,000 g/mol. Preferably, the weight-average molar mass of the SEBS is greater than 130,000 g/mol, preferably greater than 160,000 g/mol, preferably greater than 200,000 g/mol, and/or preferably less than 400,000 g/mol, preferably less than 350,000 g/mol.
Component (b) is the wax and represents 30% to 55% of the weight of the binder.
Preferably, the amount of wax is greater than or equal to 35%, preferably greater than or equal to 40%, preferably greater than or equal to 45% and/or less than or equal to 53%, preferably less than or equal to 50% of the weight of the binder.
A constituent of the wax, preferably each constituent of the wax, preferably has a weight-average molar mass of less than 4,000 g/mol, preferably less than 3,000 g/mol, preferably less than 2,000 g/mol, preferably less than 1,500 g/mol and/or greater than 400 g/mol, preferably greater than 500 g/mol.
In particular, the wax can comprise, or even consist of, a polymer selected from carnauba wax, a paraffin wax, a beeswax, a polyethylene wax, a microcrystalline wax, a vegetable oil, a groundnut oil, a mineral oil, glycerol and mixtures thereof, preferably a paraffin wax.
Preferably, the wax consists of a non-amphiphilic polyolefin or a mixture of non-amphiphilic polyolefins which each have a weight-average molar mass of less than 5,000 g/mol, preferably less than 4,000 g/mol, preferably less than 3,000 g/mol, preferably less than 2,000 g/mol, preferably less than 1,500 g/mol and/or greater than 400 g/mol, preferably greater than 500 g/mol.
The constituents of the wax, particularly the polyolefins, may or may not be functionalized.
The melting point of the wax is preferably greater than 40° C., preferably greater than 45° C. and/or preferably less than 110° C., preferably less than 100° C., preferably less than 90° C.
Component (c) is the surfactant and represents less than 10% of the weight of the binder.
Preferably, the amount of surfactant is greater than or equal to 0.5%, preferably greater than or equal to 1%, preferably greater than or equal to 2% and/or less than or equal to 9%, preferably less than or equal to 8%, preferably less than or equal to 6%, preferably less than or equal to 5%, preferably less than or equal to 4% of the weight of the binder.
The surfactant consists of an amphiphilic constituent or a mixture of amphiphilic constituents. Each amphiphilic constituent of the surfactant preferably has a weight-average molar mass of less than 1,000 g/mol, preferably less than 800 g/mol, preferably less than 500 g/mol.
In particular, the surfactant comprises, or even consists of, an amphiphilic constituent selected from an ethylene bis(stearamide), stearin, palmitic acid, butyl stearate, boric acid, oleic acid, lauric acid, stearic acid and mixtures thereof, preferably from an ethylene bis(stearamide), stearic acid and mixtures thereof.
In one embodiment, the surfactant comprises stearic acid and/or an ethylene bis(stearamide), preferably in a stearic acid/ethylene (bis)stearamide weight ratio of greater than 0.8, preferably greater than 0.9 and less than 1.2, preferably less than 1.1.
In a preferred embodiment, the surfactant consists of an amphiphilic constituent selected from an ethylene bis(stearamide), stearic acid and mixtures thereof; preferably, the surfactant is stearic acid.
The other components (d) are all the optional components which are not components (a), (b) or (c). They represent less than 10%.
Preferably, more than 80%, preferably more than 90%, preferably more than 92%, preferably more than 95%, preferably more than 97%, preferably more than 99%, preferably more than 99.5%, preferably more than 99.9% by weight of the other components (d) are organic components.
Preferably, the amount of the other components (d) is less than or equal to 8%, preferably less than or equal to 6%, preferably less than or equal to 5% preferably less than or equal to 4%, preferably less than or equal to 3% of the weight of the binder.
In one embodiment, the amount of the other components (d) is greater than or equal to 0.5%, preferably greater than or equal to 1% and less than or equal to 8%, preferably less than or equal to 6%, preferably less than or equal to 5%, preferably less than or equal to 4%, preferably less than or equal to 3% of the weight of the binder.
Preferably, in this embodiment, the other components are selected from compounds which make it possible to slow down, delay or even eliminate the degradation of the components (a) and/or (b) and/or (c) of the binder under the action of heat, light, moisture and/or oxygen. These components are conventionally referred to as stabilizers. A stabilizer making it possible to slow down, delay or even eliminate the degradation of the components (a) and/or (b) and/or (c) of the binder under the action of heat, under the action of light, under the action of oxygen, is conventionally referred to as a heat stabilizer, light stabilizer, or antioxidant, respectively. Said stabilizers are preferably selected from aluminum, zinc, lead, sodium, cadmium, magnesium, calcium, barium stearates and mixtures thereof, barium, cadmium, tin laurates and mixtures thereof, magnesium or sodium maleates and mixtures thereof, magnesium or sodium phthalates and mixtures thereof, magnesium or sodium naphthenates and mixtures thereof, epoxidized soybean or castor oil and mixtures thereof, aliphatic amines, hindered phenolic compounds, organic phosphites, mercaptans, butylated hydroxytoluenes, butylated hydroxyanisoles, pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate), and mixtures thereof. The stabilizer is preferably pentaerythritol tetrakis(3,5-di-tert-butyl hydroxyhydrocinnamate). The presence of processing stabilizers, in particular components acting as an antioxidant, advantageously makes it possible to increase the shelf life of the binder.
In a preferred embodiment, the binder according to the invention has, in percentage by weight based on the binder:
An injection molding composition according to the invention can be manufactured by a conventional manufacturing method, as long as the binder is a binder according to the invention.
The amount of binder is between 30% and 65%, in percentage by volume based on the volume of the molding composition.
Preferably, the amount of binder is greater than or equal to 35%, preferably greater than or equal to 40%, preferably greater than or equal to 45% and/or less than or equal to 60%, preferably less than or equal to 55%, in percentage by volume based on the volume of the molding composition. Advantageously, the homogeneity of the sintered part obtained at the end of step D) is improved thereby and the injection molding carried out in step B) is facilitated thereby.
The remainder to 100% preferably consists, for more than 90%, preferably for more than 95%, preferably for more than 98%, preferably for more than 99%, preferably for more than 99.9% by weight, of a ceramic powder.
The ceramic powder preferably comprises more than 90%, preferably more than 95%, preferably more than 98%, preferably more than 99% by weight of nitride(s) and/or of carbide(s) and/or of oxide(s).
Preferably, the nitride(s) are selected from AlN, Si3N4, Si2ON2, BN, TiN, GaN and mixtures thereof.
Preferably, the carbide(s) are selected from TiC, TaC, SiC, WC, ZrC, B4C and mixtures thereof.
Preferably, the oxide(s) are selected from ZrO2, Y2O3, CeO2, CaO, MgO, Sc2O3, TiO2, Al2O3, La2O3, Nd2O3, Yb2O3 and mixtures thereof.
Preferably, the ceramic powder is a powder comprising more than 90%, preferably more than 95%, preferably more than 98%, preferably more than 99% by weight of oxides, said oxides preferably being selected from ZrO2, Y2O3, CeO2, CaO, MgO, manganese oxides, ZnO, praseodymium oxides, copper oxides, BaO, iron oxides, Sc2O3, TiO2, Al2O3, La2O3, Nd2O3, Yb2O3 and mixtures thereof, preferably selected from ZrO2, Y2O3, CeO2, Al2O3 and mixtures thereof.
In a first embodiment, the ceramic powder has the following chemical analysis, in percentages by weight based on the oxides:
Y2O3: 0.5-2 mol %,
with the proviso that, if Al2O3<10%, the following formula (1) must be complied with:
CeO2>−0.57.Al2O3+8.2, (1)
CeO2 being expressed in molar percentage based on the sum of ZrO2, CeO2 and Y2O3, and Al2O3 being expressed in percentage by weight based on the weight of the product,
In a second embodiment, the ceramic powder has the following chemical analysis, in percentages by weight based on the oxides:
Y2O3: 0.5-2 mol %.
The ceramic powder preferably has a median size of less than 2 μm, preferably less than 1 μm, preferably less than 0.8 μm, preferably less than 0.6 μm, preferably less than 0.5 μm, preferably less than 0.4 μm.
More preferably still, the ceramic powder has a moisture content of less than 1.5%, preferably less than 1%, preferably less than 0.5%.
The following non-limiting examples are given with the aim of illustrating the invention.
The weight-average molar mass of the components is determined by size exclusion chromatography according to standard ISO16014-4, on a Viscotek HT-GPC apparatus sold by Malvern Panalytical, equipped with a PSS-Polefin combination medium column, sold by PSS-Polymer.
During the measurements, the column and the Viscotek HT-GPC detector are at a temperature equal to 150° C.
For each component for which the molar mass is to be determined, a solution is prepared in the following manner: said component is introduced into 1,2,4-trichlorobenzene (solvent) so as to obtain a concentration of said component equal to 5 mg/cm3. During this step, the solvent is kept at a temperature equal to 150° C., and the component is introduced into the solvent without stirring, with a dissolution time equal to 1 hour. 2,6-di-tert-butyl-4-methylphenol is subsequently added at an amount equal to 200 mg/l of solution, to prevent degradation of the component. The temperature of the solution is kept at 150° C. until the measurement.
Each solution is injected at a flow rate equal to 1 ml/min.
For all the components with the exception of the SEBS, the column is calibrated using PSS-pekit polyethylene standards, sold by PSS-Polymer. For the SEBS, the column is calibrated using High Temperature PSS-pskitr10ht polystyrene standards, sold by PSS-Polymer.
The Omnisec Software sold by Malvern Panalytical is used for processing the data and measuring the weight-average molar mass.
For each component, the weight-average molar mass is the arithmetic mean of three measurements.
The styrene content of the SEBS is determined by proton nuclear magnetic resonance (NMR) spectroscopy according to the following method. SEBS is introduced into chloroform at ambient temperature at an amount equal to 60 mg/ml chloroform. The mixture is subsequently stirred for 5 minutes using a vibrating stirrer plate. The mixture is subsequently analyzed by proton NMR at a rotational frequency equal to 500 Hz, over an average of 124 measurement points. The NMR spectrum obtained makes it possible to determine the content by weight of styrene, expressed as percentage by weight based on the weight of the SEBS.
The following measurement methods enable an excellent simulation of the actual behavior during the manufacture of the sintered part.
Deformation after debinding using a solvent is measured as follows:
A binder and a powder, CZ3Y, sold by Saint-Gobain Zirpro are introduced into a Haake Rheomix mixer sold byThermo Fisher Scientific. The amount of binder and the amount of CY3Z powder are equal to 50% by volume based on the sum of the volume of binder and CY3Z powder, respectively. The binder and the CY3Z powder are subsequently mixed for 45 minutes, at a rate equal to 30 rpm, the temperature in the mixer being brought to 180° C., the mixture being kept at this temperature for 10 minutes so as to obtain the injection molding composition. After cooling, the hardened injection molding composition is ground so as to pass through the square holes in a screen having 2 mm opening in order for it to be in the form of granules. The injection molding composition thus obtained is subsequently injected, using a babyplast injection molding machine, sold by Martiplast, at a pressure equal to 100 bar, at a temperature, measured in the injection screw, equal to 170° C., in a bar mold at a temperature equal to 40° C. and shaped so as to obtain a bar having dimensions equal to 75 mm×13 mm×2 mm after removal from the mold. 5 bars are produced for each molding composition to be characterized.
As shown in
The deformation of the bar is subsequently measured by the deflection F, as described in
Deformation after thermal debinding is measured as follows:
Bars are produced according to the same manufacturing protocol as described above for measuring deformation during debinding using a solvent. 5 bars are produced for each molding composition to be characterized.
The bars are then placed flat on an open metal grid, and the entire set-up is arranged in a glass container, said glass container being arranged in a heating bath temperature controlled to ambient temperature. Isopropanol is subsequently introduced into the glass container so as to fully cover the bars. The glass container is subsequently closed. The isopropanol is subsequently brought to a temperature equal to 60° C. by virtue of the action of the temperature-controlled heating bath. This temperature is maintained for 24 hours, with care being taken to ensure that the isopropanol entirely covers the bars over the whole of this period. The temperature-controlled heating bath is subsequently switched off and the isopropanol is removed from the glass container when its temperature reaches 55° C. The glass container is subsequently opened, the bars are recovered and subsequently dried for 24 hours at ambient temperature. This procedure makes it possible to obtain, after debinding using a solvent, bars which are not deformed.
As shown in
The deformation of the bars after thermal debinding is subsequently measured by the deflection F, as described in
Bars of molding composition to be tested were produced using the method described for the manufacture of the bars required for measuring the deformation during debinding using a solvent and during thermal debinding.
The following products were used for the different binder compositions:
The compositions of the binders used in the examples, and also the characterizations performed on the molding compositions, are described in the following table 1, with the absolute density of the products of examples 1 to 9 being fixed at 6.095 g/cm3 after sintering, said sintering being performed on bars which have been subjected to debinding using a solvent and thermal debinding as described previously, followed by sintering in an electric oven according to the following thermal cycle:
A comparison of comparative example 1 and example 2 according to the invention shows the critical impact, on deformation after debinding using a solvent and on the relative density after sintering, of the presence of a SEBS in the claimed amounts in the binder.
A comparison of example 2 according to the invention and comparative example 3 obtained with a binder comprising a SEBS having a weight-average molar mass lower than the subject matter of the invention shows the critical impact, on deformation after debinding using a solvent, on deformation after thermal debinding, and also on the relative density after sintering, of a SEBS having a weight-average molar mass of greater than 100,000 g/mol.
A comparison of example 2 according to the invention and comparative example 4 obtained with a binder comprising a SEBS having too low a styrene content in relation to the present invention shows the critical impact, on deformation after debinding using a solvent, of a SEBS having a content by weight of styrene of greater than 15%, in percentage by weight based on the weight of said SEBS.
A comparison of example 2 according to the invention and comparative example 5 obtained with a binder comprising too low an amount of SEBS in relation to the present invention shows the critical impact, on relative density after sintering, of a minimum content of 2% of SEBS in the binder: the relative density of example 5 was not determined because said example exhibited unacceptable cracking.
A comparison of example 2 according to the invention and comparative example 6 obtained with a binder comprising too great an amount of SEBS in relation to the present invention, shows the critical impact, on deformation after debinding using a solvent and on the relative density after sintering, of a maximum content of 15% SEBS in the binder.
Examples 7, 8 and 9 also illustrate the invention and the advantages thereof.
As is now clearly apparent, the invention makes it possible to limit the deformation of the preform in step C) while leading to a sintered part having a relatively high density.
Of course, the invention is not limited to the embodiments described, which are provided merely for illustrative purposes.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005887 | Jun 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2021/051003 | 6/2/2021 | WO |
