U.S. patent application number 13/024629 was filed with the patent office on 2011-06-02 for polymer powder comprising a copolymer, use in a shaping method which uses a non-focused application of energy and moulded body that is produced from said polymer powder.
This patent application is currently assigned to DEGUSSA AG. Invention is credited to Franz-Erich Baumann, Maik Grebe, Sylvia MONSHEIMER, Eva Von Der Bey.
Application Number | 20110130515 13/024629 |
Document ID | / |
Family ID | 34853906 |
Filed Date | 2011-06-02 |
United States Patent
Application |
20110130515 |
Kind Code |
A1 |
MONSHEIMER; Sylvia ; et
al. |
June 2, 2011 |
POLYMER POWDER COMPRISING A COPOLYMER, USE IN A SHAPING METHOD
WHICH USES A NON-FOCUSED APPLICATION OF ENERGY AND MOULDED BODY
THAT IS PRODUCED FROM SAID POLYMER POWDER
Abstract
A molding produced by a layer-by layer process of selectively
melting regions of a respective pulverulent layer via unfocused
introduction of electromagnetic energy, using a polymer powder,
where the powder has at least one thermoplastic random copolymer
with an ISO 1133 MFR value of from 12 to 1 g/10 min.
Inventors: |
MONSHEIMER; Sylvia; (Haltern
am See, DE) ; Baumann; Franz-Erich; (Duelmen, DE)
; Grebe; Maik; (Bochum, DE) ; Von Der Bey;
Eva; (Haltern am See, DE) |
Assignee: |
DEGUSSA AG
Duesseldorf
DE
|
Family ID: |
34853906 |
Appl. No.: |
13/024629 |
Filed: |
February 10, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10590935 |
Dec 20, 2006 |
7906063 |
|
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PCT/EP04/53505 |
Dec 15, 2004 |
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13024629 |
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Current U.S.
Class: |
524/605 ;
524/607; 528/301; 528/305; 528/324 |
Current CPC
Class: |
C08L 95/005 20130101;
C08L 77/06 20130101; C08L 77/02 20130101; B29C 64/153 20170801;
C08L 67/02 20130101; B33Y 70/00 20141201; B29C 64/165 20170801 |
Class at
Publication: |
524/605 ;
528/324; 528/301; 528/305; 524/607 |
International
Class: |
C08G 69/14 20060101
C08G069/14; C08G 63/672 20060101 C08G063/672; C08G 63/183 20060101
C08G063/183; C08L 67/02 20060101 C08L067/02; C08L 77/12 20060101
C08L077/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2004 |
DE |
10 2004 010 162.0 |
Claims
1: A molding produced by a layer-by layer process, comprising
selectively melting regions of a respective pulverulent layer via
unfocused introduction of electromagnetic energy, using a polymer
powder, wherein the powder comprises at least one thermoplastic
random copolymer with an ISO 1133 MFR value of from 12 to 1 g/10
min.
2: The molding as claimed in claim 1, wherein the powder comprises
at least one thermoplastic random copolymer with an ISO 1133 MFR
value of from 10 to 1 g/10 min.
3: The molding as claimed in claim 1, wherein the powder comprises
at least one thermoplastic random copolymer with an ISO 1133 MFR
value of from 12 to 1 g/10 min, the selectivity being achieved via
application of susceptors or of absorbers, or via masks.
4: The molding as claimed in claim 1, wherein the powder comprises
at least one thermoplastic random copolymer with an ISO 1133 MFR
value of from 10 to 1 g/10 min, the selectivity being achieved via
application of susceptors or of absorbers, or via masks.
5: The molding as claimed in claim 1, wherein the powder comprises
at least one thermoplastic random copolymer with an ISO 1133 MFR
value of from 12 to 1 g/10 min, the selectivity being achieved via
application of inhibitors.
6: The molding as claimed in claim 1, wherein the powder comprises
at least one copolyester.
7: The molding as claimed in claim 6, wherein the powder comprises
at least one copolyester containing at least one of the monomer
units from the group of adipic acid, isophthalic acid, dimethyl
phthalate, 1,4-butanediol, 1,6-hexanediol, and polyethylene
glycol.
8: The molding as claimed in claim 1, wherein the powder comprises
at least one copolyamide.
9: The molding as claimed in claim 8, wherein the powder comprises
at least one copolyamide containing at least one of the units
selected from the group of the lactams, the diamine/dicarboxylic
acid salts, and/or the aminocarboxylic acids.
10: The molding as claimed in claim 8, wherein the powder comprises
at least one copolyamide containing at least one of the units
selected from the group of laurolactam, caprolactam,
aminoundecanoic acid, and also containing approximately equimolar
amounts of the dicarboxylic acids adipic acid, sorbic acid, azelaic
acid, sebacic acid, dodecanedioic acid, brassylic acid,
tetradecanedioic acid, pentadecanedioic acid, octadecanedioic acid;
terephthalic acid, isophthalic acid, and of the diamines
hexamethylenediamine, 2-methylpentamethylenediamine,
2,2,4-trimethylhexamethylenediamine,
2,4,4-trimethylhexamethylenediamine, isophoronediamine, piperazine,
bis(4-aminocyclohexyl)methane, or of the nylon salts formed
therefrom.
11: The molding as claimed in claim 8, wherein the powder comprises
at least one copolyamide containing caprolactam, laurolactam, and
AH salt.
12: The molding as claimed in claim 8, wherein the powder comprises
at least one copolyamide containing caprolactam, laurolactam, and
DH salt.
13: The molding as claimed in claim 8, wherein the powder comprises
at least one copolyamide containing caprolactam and
laurolactam.
14: The molding as claimed in claim 8, wherein the powder comprises
at least one copolyamide, the DIN 53727 relative solution viscosity
in m-cresol being from 1.55 to 1.9.
15: The molding as claimed in claim 8, wherein the powder comprises
at least one copolyamide, the DIN 53727 relative solution viscosity
in m-cresol being from 1.6 to 1.7.
16: The molding as claimed in claim 1, further comprising
auxiliaries and/or filler and/or pigments.
17: The molding as claimed in claim 16, comprising flow aids as
auxiliary.
18: The molding as claimed in claim 16, comprising glass particles
as filler.
19: The molding as claimed in claim 16, comprising metal soaps as
auxiliary.
20: The molding as claimed in claim 1, comprising at least one
copolyester.
21: The molding as claimed in claim 1, comprising at least one
copolyester containing at least one of the monomer units selected
from the group of adipic acid, isophthalic acid, dimethyl
phthalate, 1,4-butanediol, 1,5-hexanediol, polyethylene glycol.
22: The molding as claimed in claim 1, comprising at least one
copolyamide.
23: The molding as claimed in claim 1, comprising at least one
copolyamide containing at least one of the units selected from the
group of the lactams, the diamine/dicarboxylic acid salts, and/or
the aminocarboxylic acids.
24: The molding as claimed in claim 1, comprising at least one
copolyamide containing at least one of the units from the group of
laurolactam, caprolactam, aminoundecanoic acid, and also containing
approximately equimolar amounts of the dicarboxylic acids adipic
acid, sorbic acid, azelaic acid, sebacic acid, dodecanedioic acid,
brassylic acid, tetradeoanedioic acid, pentadecanedioic acid,
octadecanedioic acid, terephthalic acid, isophthalic acid, and of
the diamines hexamethylenediamine, 2-methylpentamethylenediamine,
2,2,4-trimethylhexamethylenediamine,
2,4,4-trimethylhexamethylenediamine, isophoronediamine, piperazine,
bis(4-aminocyclohexyl)methane, or of the nylon salts formed
therefrom.
25: The molding as claimed in claim 1, comprising at least one
copolyamide containing caprolactam, laurolactam, and AH salt.
26: The molding as claimed in claim 1, comprising at least one
copolyamide containing caprolactam, laurolactam, and DH salt.
27: The molding as claimed in claim 1, comprising at least one
copolyamide containing caprolactam and laurolactam.
28: The molding as claimed in claim 1, comprising at least one
copolyamide, the DIN 53727 relative solution viscosity in m-cresol
being from 1.55 to 1.9.
29: The molding as claimed in claim 1, comprising at least one
copolyamide, the DIN 53727 relative solution viscosity in m-cresol
being from 1.6 to 1.7.
30: The molding as claimed in claim 1, further comprising
auxiliaries and/or filler and/or pigments.
31: The molding as claimed in claim 30, comprising flow aids as
auxiliary.
32: The molding as claimed in claim 30, comprising glass particles
as filler.
33: The molding as claimed in claim 30, comprising metal soaps as
auxiliary.
Description
[0001] The rapid production of prototypes is a task often required
in very recent times. Particularly suitable processes are those
whose operation is based on pulverulent materials and which produce
the desired structures layer-by-layer via selective melting and
hardening. Support structures for overhangs and undercuts can be
omitted here, because the powder bed surrounding the molten regions
provides adequate support. Nor is there any need for subsequent
operations to remove supports. These processes are also suitable
for short-run production.
[0002] The invention relates to a polymer powder based on
thermoplastic random copolymers with an ISO 1133 MFR value of from
12 g/10 min to 1 g/10 min, preferably from 10 g/10 min to 1 g/10
min, preferably on copolyamides with a DIN 53727 relative solution
viscosity in m-cresol of from 1.55 to 1.9, preferably from 1.6 to
1.7, or else on copolyesters, to the use of this powder in shaping
processes, and also to moldings produced via a layer-by-layer
process by which regions of a powder layer are selectively melted
via introduction of electromagnetic energy, using this powder. Once
the previously molten regions have been cooled and hardened, the
molding can be removed from the powder bed.
[0003] The selectivity of these layer-by-layer processes can be
achieved, by way of example and with no intention of restricting
the invention thereto, by applying susceptors, absorbers, or
inhibitors, or via masks. The selectivity does not arise by way of
the introduction of the electromagnetic energy.
[0004] A number of processes are described below by which inventive
moldings can be produced from the inventive powder, but there is no
intention to restrict the invention thereto.
[0005] Processes with good suitability are the SIB process as
described in WO 01/38061, or a process described in EP 1 015 214.
Both processes operate with full-surface infrared heating to melt
the powder. The selectivity of melting is achieved in the first by
applying an inhibitor and in the second via a mask. DE 103 11 438
describes another process. In this, the energy needed to melt the
powder particles is introduced via a microwave generator, and the
selectivity is achieved via application of a susceptor.
[0006] For the rapid protyping or rapid manufacturing process (RP
process or RM process) mentioned use may be made of pulverulent
substrates, in particular polymers, preferably selected from
polyester, polyvinyl chloride, polyacetal, polypropylene,
polyethylene, polystyrene, polycarbonate,
poly(N-methylmethacrylimides) (PMMI), polymethyl methacrylate
(PMMA), ionomer, polyamide.
[0007] DE 44 33 118 considers polymer blends exposed to
electromagnetic energy. However, a blend is a mixture prepared in
the melt from two or more polymers under defined temperature
conditions and shear conditions, and is usually processed to give
pellets. Here, the individual polymer chains are mixed with one
another ("intermolecularly"), but no recombination of the starting
components takes place within a chain. (For an example of a
definition see Sachtling Kunststofftaschenbuch [Plastics Handbook],
24th edition, pp 7 at seq.).
[0008] A processing disadvantage is that in order to avoid what is
known as curl the temperature in the construction space or
construction chamber has to be kept with maximum uniformity at a
level just below the melting point of the polymeric material. In
the case of amorphous polymers, this means a temperature just below
the glass transition temperature, and in the case of
semicrystalline polymers this means a temperature just below the
crystallite melting point. Curl means distortion of the region
after melting, the result being at least some protrusion out of the
construction plane. There is a resultant risk that when the next
powder layer is applied, for example via a doctor or a roller, the
protruding regions may be shifted or even entirely broken away. The
consequence of this for the process is that the overall
construction space temperature has to be kept at a relatively high
level, and that the volume change brought about via cooling and via
crystallization of the moldings produced by these processes is
considerable. Another important factor is that the period required
for cooling is significant specifically for "rapid" processes.
[0009] Another disadvantage of the semicrystalline thermoplastics
in many instances is their crystallinity, and the volume change
caused thereby during cooling from the melt. Although it is
possible to use very complicated and precise temperature control to
achieve a substantial equalization of the volume change due to the
crystallinity of an individual layer, the volume change due to
crystallization in three-dimensional moldings of any desired
structure is not uniform throughout the molding. By way of example,
the formation of crystalline structures is dependent on the cooling
rate of the molding, and at locations of different thickness or at
angled locations this rate differs from that at other locations
within the molding.
[0010] A disadvantage of amorphous thermoplastics is high
viscosity, permitting coalescence only markedly above the melting
point or the glass transition temperature.
[0011] Moldings produced by the above processes using amorphous
thermoplastics are therefore often relatively porous; the process
merely forms sinter necks, and the individual powder particles
remain discernible within the molding. However, if the amount of
energy introduced is increased in order to reduce viscosity there
is the additional problem of precision of shape; by way of example,
the contours of the molding lose sharpness as a result of heat
conducted from the melting regions into the surrounding
regions.
[0012] Another disadvantage is that a single material cannot always
meet other diverse requirements, for example viscosity, thermal
stability, shrinkage, strength, impact resistance, and
processability. The use of powder mixtures for this purpose is well
known, but has other associated disadvantages. By way of example,
the constancy of the mixtures has to be ensured through
preparation, processing, and, where appropriate, recycling. If the
components have different melting points, the scope for adjusting
the mixture simply as required by the desired properties of the
molding is very restricted. In practice it has been found that the
lower melting point then dominates during processing, the result
being that the higher-melting component does not melt and merely
acts as a filler, so that sometimes its desired properties are
ineffective or only partially effective.
[0013] It was therefore an object of the present invention to
provide a polymer powder which can be more versatile in achieving
tailored properties in relation to processing, but also in relation
to the desired properties of the molding. The process here is a
powder-based layer-by-layer process in which regions of the
respective layer are selectively melted via the unfocused
introduction of electromagnetic energy, and after cooling bond to
give the desired molding, the selectivity being achieved here, by
way of example, by way of the application of susceptors or of
absorbers or of inhibitors, or via masks.
[0014] Surprisingly, it has now been found, as described in the
claims, that the use of thermoplastic random copolymers with an MFR
value of from 12 to 1 g/10 min, preferably from 10 to 1 g/10 min,
can produce polymer powders from which it is possible, via a
layer-by-layer process in which regions of the respective layer are
selectively melted via introduction of electromagnetic energy, to
produce moldings which have advantages in relation to
processability, or which combine different properties of moldings
in one component.
[0015] The invention therefore provides a polymer powder for
processing in a layer-by-layer process in which regions of the
respective layer are selectively melted via introduction of
electromagnetic energy, which comprises at least one thermoplastic
random copolymer with an ISO 1133 MFR value of from 12 g/10 min to
1 g/10 min, preferably from 10 g/10 min to 1 g/10 min, preferably a
copolyamide with a DIN 53727 relative solution viscosity in
m-cresol of from 1.55 to 1.9, preferably from 1.6 to 1.7;
particular preference is given to a copolyamide containing at least
one of the units from the group of the lactams, the
diamines/dicarboxylic salts, and/or the aminocarboxylic acids. The
inventive powders very particularly preferably contain monomer
units from the group composed of laurolactam, caprolactam,
aminoundecanoic acid, and also containing approximately equimolar
amounts of the dicarboxylic acids adipic acid, sorbic acid, azelaic
acid, sebacic acid, dodecanedioic acid, brassylic acid,
tetradecanedioic acid, pentadecanedioic acid, octadecanedioic acid,
terephthalic acid, isophthalic acid, and of the diamines
hexamethylenediamine, 2-methylpentamethylenediamine,
2,2,4-trimethylhexamethylenediamine,
2,4,4-trimethylhexamethylenediamine, isophoronediamine, piperazine,
bis(4-aminocyclohexyl)methane, or of the nylon salts formed
therefrom.
[0016] The present invention also provides moldings produced via a
layer-by-layer process in which regions of the respective powder
layer are selectively melted via unfocused introduction of
electromagnetic energy, the selectivity being achieved, by way of
example, by way of masks, or via the application of susceptors, of
inhibitors, or of absorbers, where the moldings comprise at least
one thermoplastic random copolymer with an MFR value of from 12
g/10 min to 1 g/10 min, preferably from 10 g/10 min to 1 g/10 min,
preferably a copolyamide with a solution viscosity of from 1.55 to
1.9, preferably from 1.6 to 1.7. The inventive moldings
particularly preferably comprise a copolyamide containing at least
one of the units from the group of the lactams, the
diamine/dicarboxylic acid salts, and/or the aminocarboxylic acids.
The inventive moldings very particularly preferably comprise
copolyamides having monomer units from the group composed of
laurolactam, caprolactam, aminoundecanoic acid, and also containing
approximately equimolar amounts of the dicarboxylic acids adipic
acid, sorbic acid, azelaic acid, sebacic acid, dodecanedioic acid,
brassylic acid, tetradecanedioic acid, pentadecanedioic acid,
octadecanedioic acid, terephthalic acid, isophthalic acid, and of
the diamines hexamethylenediamine, 2-methylpentamethylenediamine,
2,2,4-trimethylhexamethylenediamine,
2,4,4-trimethylhexamethylenediamine, isophoronediamine, piperazine,
bis(4-aminocyclohexyl)methane, or of the nylon salts formed
therefrom.
[0017] The inventive polymer powder has the advantage that, via a
layer-by-layer process in which regions of the respective layer are
selectively melted, it can produce moldings at temperatures
markedly lower than for moldings composed of conventional polymer
powders. The result is faster production of moldings by one of the
processes described, and improved process reliability.
[0018] The moldings produced here from the inventive powder have
good mechanical properties similar to those of moldings produced
from conventional powder. Although they are mostly softer than
moldings composed of the non-inventive PA12 polymer powder usually
used during laser sintering, they often compensate for this with
much higher tensile strain at break, permitting, for example, very
efficient production of snap-action hooks. In order to achieve the
mechanical properties, it is useful for the MFR value of the
inventive powder to be from 12 g/10 min to 1 g/10 min, preferably
from 10 g/10 min to 1 g/10 min. In the case of the preferred
copolyamide, a solution viscosity of from 1.55 to 1.9, preferably
from 1.6 to 1.7, gives the desired mechanical properties. If the
MFR value of the inventive powder is higher than stated, or,
respectively, the solution viscosity values are lower than stated,
the mechanical properties of the moldings constructed by one of the
inventive processes using the powder become markedly poorer.
[0019] Another advantage of the inventive powder is that it can be
processed effectively using the inventive processes. If the
solution viscosity values for the inventive powder are lower than
stated or, respectively, the MFR value is higher than stated, the
reproducibility of the construction process becomes markedly
poorer. In particular, it is likely that powder particles will
stick to the application device, such as a roller or a doctor,
after melting of the intended regions of a sequence of a few
layers. If the values for the solution viscosity of the inventive
powder are higher than stated in the specific case of the
copolyamide, the mechanical properties again become markedly
poorer, because it is no longer certain that the individual polymer
particles will coalesce on melting to form the molding.
[0020] Surprisingly, it was also found that the processing
latitude, i.e. a temperature difference between the
"non-occurrence" of curl and full-surface melting of the powder not
intended for melting, is mostly greater than when using
conventional powders. Another advantage is the low shrinkage of the
moldings produced using inventive powders, in comparison with
moldings composed of semicrystalline homopolyamides, both produced
by a layer-by-layer shaping process where regions of the respective
powder layer are selectively melted via introduction of
electromagnetic energy. The inventive powder is particularly
preferably used in processes which are not based on focusing of the
energy introduced via a laser. The speed advantage of simultaneous
energy introduction over all of the selected regions has the
associated disadvantage that thermal conductivity becomes more
important. At locations with poor heat dissipation, for example
cutouts, it is quite likely that further particles will cake onto
the material, thus causing deviation from the desired profile. The
lower processing temperature of the inventive powders is found here
to be an advantage because the amount of energy which has to be
introduced is smaller. The temperature difference between the
regions to be melted and their surroundings can therefore be kept
smaller.
[0021] The inventive copolymer powder is described below, but there
is no intention that the invention be restricted thereto.
[0022] A feature of the inventive copolymer powder for processing
in a layer-by-layer process in which regions of the respective
powder layer are selectively melted via unfocused introduction of
electromagnetic energy is that the powder comprises at least one
thermoplastic random copolymer with an MFR value of from 12 g/10
min to 1 g/10 min, preferably from 10 g/10 min to 1 g/10 min,
prepared from at least two monomer units. The preparation process
may in the simplest case be a free-radical, or an anionic, or a
cationic copolymerization process, or may be a Ziegler-Natta
copolymerization process. There is a large number of suitable
monomer units, such as ethene and vinyl acetate, acrylonitrile and
styrene, tetrafluorethene and propene, ethene and 1-butene,
trioxane and ethylene oxide, styrene and butadiene, or else a
combination of three monomer units composed of acrylonitrile,
styrene, and butadiene, known as ABS. The monomer units may be
aliphatic or aromatic, and the resultant copolymer may be linear or
branched. The invention uses at least one unit which at least is
present in different isomeric forms, or two units, or three
(ternary systems) or more units. The copolymers are mostly
amorphous.
[0023] Particular preference is given to copolyamides the
crystallinity of which can be controlled by way of the composition
of the monomer units. The preparation process uses
diamine/dicarboxylic acid salts and/or aminocarboxylic acids or
lactams. Examples of the monomer units used are aminoundecanic
acid, or else approximately equimolar amounts of the dicarboxylic
acids adipic acid, sorbic acid, azelaic acid, sebacic acid,
dodecanedioic acid, brassylic acid, tetradecanedioic acid,
pentadecanedioic acid, octadecanedioic acid, terephthalic acid,
isophthalic acid, and of the diamines hexamethylenediamine,
2-methylpentamethylenediamine, 2,2,4-trimethylhexamethylenediamine,
2,4,4-trimethylhexamethylenediamine, isophoronediamine, piperazine,
bis(4-aminocyclohexyl)methane, or of the nylon salts formed
therefrom.
[0024] In particular, combinations composed of caprolactam,
laurolactam and AH salt are known, as are also combinations
composed of caprolactam, laurolactam and DH salts, or caprolactam
and laurolactam. These copolyamides in particular feature a low
melting point.
[0025] Besides aliphatic dicarboxylic acids, use is made of
aromatic dicarboxylic acids, which generally contribute to higher
glass transition temperatures. Furthermore, low-symmetry
comonomers, in particular trimethylhexamethylendiamine (TMD, isomer
mixture), isophoronediamine (IPD), bis-(4-aminocyclohexyl)methane
(PACM, isomer mixture) reduce the crystallinity--the result in the
extreme case being a completely amorphous copolyamide--giving
higher dimensional accuracy and sometimes increased translucency of
the molding. Suitable other comonomers and rules for their
selection are known to the person skilled in the art and are
described by way of example in J. G. Dolden, Polymer (1976, 17),
pp. 875-892.
[0026] Particular preference is given to random thermoplastic
copolyamides with a solution viscosity of from 1.55 to 1.9,
preferably from 1.6 to 1.7, attained via thermal polycondensation
of monomer mixtures composed of diamine/dicarboxylic acid salts
and/or of aminocarboxylic acids or of lactams. The method is
similar to that for the homopolyamides, but of course the
respective physico-chemical properties have to be taken into
account, for example water-solubility of the monomers, melting
point and thermal stability of the polymers. It is sufficient here
for one monomer to be present in the form an isomer mixture.
[0027] Alternating copolyamides are preferably produced via
solution polycondensation under mild conditions. However, in the
melt transamidation reactions convert them into random
copolyamides.
[0028] Block copolymers composed of various polyamides are
generally obtained in two stages, first producing a prepolymer and
then mixing with the second component. The resultant structures of
the block copolymers are not stable, however, and at higher
temperatures revert to random distribution with regard to the
arrangement of the monomer units.
[0029] Graft copolymers can be obtained via reaction of previously
formed polymers with other monomers. The graft reaction is
initiated ionically or by a free-radical route on the NH groups
along the polymer chain. An example is the reaction of PA6 with
ethylene oxide to give hydrophilic to water-soluble products.
[0030] The DIN 53727 solution viscosity of the inventive
copolyamides in 0.5% strength m-cresol solution is from 1.55 to
1.9, preferably from 1.6 to 1.7. The preparation of copolyamides is
described by way of example in DE 32 48 776, and is known to the
person skilled in the art.
[0031] The MFR value is determined to ISO 1133. The conditions,
namely load and temperature, are specified as appropriate as a
function of the material in the standards for molding compositions,
e.g. in ISO 2580-1 for ABS. The normal method is to test a
semicrystalline copolyamide at a relatively low temperature, for
example 160.degree. C., and a completely amorphous copolyamide at a
higher temperature, for example 230.degree. C. A typical weight
here is 2.16 kg, but this value, too, is to be specified in
accordance with the appropriate standards for molding compositions,
as a function of the material.
[0032] Other preferred copolymers are copolyesters. Examples of the
monomer units are adipic acid, isophthalic acid, dimethyl
terephthalate, 1,4-butandiol, 1,6-hexandiol, polyethylene
glycol.
[0033] The pellets prepared and comprising thermoplastic random
copolymer are then ground at low temperatures, for example at
-30.degree. C. under nitrogen in an impact mill or pinned-disk
mill, to give pulverulent particles. The material should be
subjected to at least one precautionary sieving to remove the very
coarse particles. A subsequent fractionation is usually useful.
Inventive powders have the grain size range from 1 to 150 microns,
preferably from 1 to 120 microns. The distribution of the grains
here remains relatively broad. Typical values for the D90/D10 range
are from 1:2 to 1:15, preferably from 1:3 to 1:5. Mechanical
post-treatment can also be useful, for example in a high-speed
mixer, in order to round the sharp-edged particles produced during
the grinding process, and thus improve capability for applying
relatively thin layers.
[0034] The inventive polymer powder preferably comprises at least
one thermoplastic random copolymer with an ISO 1133 MFR value of
from 12 g/10 min to 1 g/10 min, preferably from 10 g/10 min to 1
g/10 min, and with an average particle size of from 10 to 250
.mu.m, preferably from 45 to 150 .mu.m and particularly preferably
from 50 to 125 .mu.m.
[0035] Inventive copolyamide powders or copolyester powders are
marketed, for example with the tradename Vestamelt by Degussa.
[0036] Inventive copolymer powder may also comprise auxiliaries
and/or filler and/or other organic or inorganic pigments. These
auxiliaries may, by way of example, be flow aids, e.g. precipitated
and/or flumed silicas. By way of example, precipitated silicas are
supplied with the product name Aerosil by Degussa AG, with various
specifications. Inventive copolymer powder preferably comprises
less than 3% by weight, preferably from 0.001 to 2% by weight and
very particularly preferably from 0.05 to 1% by weight, of these
auxiliaries, based on the entirety of the polymers present. By way
of example, the fillers may be glass particles, metal particles or
ceramic particles, e.g. glass beads, steel shot or granulated metal
or foreign pigments, e.g. transition metal oxides. By way of
example, the pigments may be titanium dioxide particles based on
rutile or anatase, or carbon black particles.
[0037] The median size of these filler particles is preferably
smaller than or approximately equal to the size of the particles of
the copolymers. The extent to which the median particle size
d.sub.50 of the fillers is less than the median particle size
d.sub.50 of the copolymers is preferably not more than 20%,
preferably not more than 15%, and very particularly preferably no
more than 5%. A particular limitation on the particle size is given
by the permissible overall height or, respectively, layer thickness
in the rapid prototyping/rapid manufacturing system.
[0038] Inventive copolymer preferably comprises less than 75% by
weight, with preference from 0.001 to 70% by weight, with
particular preference from 0.05 to 50% by weight, and with very
particular preference from 0.5 to 25% by weight, of these fillers,
based on the entirety of the copolymers present.
[0039] If the stated maximum limits for auxiliaries and/or fillers
are exceeded the result, depending on the filler or auxiliary used,
can be marked impairment of the mechanical properties of moldings
produced by means of these copolymer powders.
[0040] It is also possible to mix conventional polymer powders with
inventive copolymer powders. This method can produce polymer
powders with another combination of mechanical properties and
processing latitude. The process for preparing these mixtures may
be found in DE 34 41 708, for example.
[0041] To improve melt flow during the production of the moldings,
use may be made of a flow promoter, such as metal soaps, preferably
the alkali metal or alkaline earth metal salts of the underlying
alkanemonocarboxylic acids or dimer acids, may be added to the
precipitated or low-temperature-ground powder. The metal soap
particles may be incorporated into the copolymer particles, or else
mixtures of fine-particle metal soap particles and copolymer
particles may be used.
[0042] The amounts used of the metal soaps are from 0.01 to 30% by
weight, preferably from 0.5 to 15% by weight, based on the entirety
of the copolymers, preferably copolyamides, present in the powder.
The metal soaps used preferably comprise the sodium or calcium
salts of the underlying alkanemonocarboxylic acids or dimer acids.
Examples of commercially available products are Licomont NaV 101 or
Licomont CaV 102 from Clariant.
[0043] To improve the processability of the polymer powder or for
its further modification, inorganic foreign pigments may be added
to the powder, examples being transition metal oxides, stabilizers,
e.g. phenols, in particular sterically hindered phenols, flow
promoters and flow agents, e.g. fumed silicas, or else filler
particles. The amount of these substances added to the polymer,
based on the total weight of polymers in the copolymer powder,
preferably complies with the concentration stated for fillers
and/or auxiliaries for the inventive copolymer powders.
[0044] The present invention also provides processes for producing
moldings via layer-by-layer processes in which regions are
selectively melted via unfocused introduction of electromagnetic
energy, using inventive polymer powders which comprise at least one
thermoplastic random copolymer with an MFR value of from 12 g/10
min to 1 g/10 min, preferably from 10 g/10 min to 1 g/10 min,
preferably a copolyamide with a solution viscosity of from 1.55 to
1.9, preferably from 1.6 to 1.7. The inventive powder particularly
preferably comprises copolyamides containing at least one of the
units from the group of the lactams, of the diamine/dicarboxylic
acid salts and/or of the aminocarboxylic acids. The powders very
particularly preferably used in these processes are those which
comprise copolyamides which contain monomer units from the group
composed of laurolactam, caprolactam, aminoundecanoic acid, and
also containing approximately equimolar amounts of the dicarboxylic
acids adipic acid, sorbic acid, azelaic acid, sebacic acid,
dodecanedioic acid, brassylic acid, tetradecanedioic acid,
pentadecanedioic acid, octadecanedioic acid, terephthalic acid,
isophthalic acid, and of the diamines hexamethylenediamine,
2-methylpentamethylenediamine, 2,2,4-trimethylhexamethylenediamine,
2,4,4-trimethylhexamethylenediamine, isophoronediamine, piperazine,
bis(4-aminocyclohexyl)methane, or of the nylon salts formed
therefrom.
[0045] The energy is introduced in unfocused form via
electromagnetic radiation, for example simultaneously over the
entire layer, or via unfocused traverse over parts or all of the
powder layer, and the selectivity is achieved, by way of example,
via masks, or via application of inhibitors, of absorbers, or of
susceptors. Once all of the layers have been cooled, the inventive
molding can be removed. The unmelted powder can be reused in the
next construction process, where appropriate in a blend with virgin
powder. The polymer powder is processed at a construction chamber
temperature of from 80 to 160.degree. C., preferably from 85 to
120.degree. C.
[0046] The following examples of these processes serve for
illustration, but with no intention that the invention be
restricted thereto.
[0047] Processes with good suitability are the SIB process as
described in WO 01/38061, or the process described in EP 1 015 214.
Both processes operate with full-surface infrared heating to melt
the powder. In the first, the selectivity of the melting process is
achieved via the application of an inhibitor, and in the second
process it is achieved via a mask. DE 103 11 438 describes another
process. In this, the energy needed for the fusion process is
introduced via a microwave generator, and the selectivity is
achieved via application of a susceptor.
[0048] A feature of the inventive moldings produced via a
layer-by-layer process in which regions are selectively melted via
unfocused introduction of electromagnetic energy is that they
comprise at least one random thermoplastic copolymer with an ISO
1133 MFR value of from 12 g/10 min to 1 g/10 min, preferably from
10 g/10 min, to 1 g/10 min. The inventive moldings preferably
comprise at least one copolyamide with a DIN 53727 solution
viscosity in m-cresol of from 1.55 to 1.9, preferably from 1.6 to
1.7. Inventive moldings very particularly preferably comprise at
least one copolyamide containing at least one of the units from the
group of the lactams, of the diamine/dicarboxylic acid salts and/or
of the aminocarboxylic acid. The inventive moldings very
particularly preferably comprise at least one copolyamide composed
of monomer units from the group composed of laurolactam,
caprolactam, aminoundecanoic acid, and also containing
approximately equimolar amounts of the dicarboxylic acids adipic
acid, sorbic acid, azelaic acid, sebacic acid, dodecanedioic acid,
brassylic acid, tetradecanedioic acid, pentadecanedioic acid,
octadecanedioic acid, terephthalic acid, isophthalic acid, and of
the diamines hexamethylenediamine, 2-methylpentamethylenediamine,
2,2,4-trimethylhexamethylenediamine,
2,4,4-trimethylhexamethylenediamine, isophoronediamine, piperazine,
bis(4-aminocyclohexyl)methane, or of the nylon salts formed
therefrom.
[0049] The moldings may also comprise fillers and/or auxiliaries,
e.g. heat stabilizers, e.g. sterically hindered phenol derivatives.
Examples of fillers are glass particles, ceramic particles and also
metal particles, e.g. iron spheres, or corresponding hollow
spheres. The inventive moldings preferably comprise glass
particles, very particularly preferably glass beads. Inventive
moldings preferably comprise less than 3% by weight, preferably
from 0.001 to 2% by weight, and very particularly preferably from
0.05 to 1% by weight, of these auxiliaries, based on the entirety
of the polymers present. Inventive moldings also preferably
comprise less than 75% by weight, preferably from 0.001 to 70% by
weight, particularly preferably from 0.05 to 50% by weight, and
very particularly preferably from 0.5 to 25% by weight, of these
fillers, based on the entirety of the polymers present.
[0050] The examples below are intended to describe the inventive
polymer powder which comprises at least one thermoplastic random
copolymer with an ISO 1133 MFR value of from 12 g/10 min to 1
g/min, preferably from 10 g/10 min to 1 g/10 min, preferably
copolyamide powder with a DIN 53727 solution viscosity of from 1.55
to 1.9, preferably from 1.6 to 1.7, and to describe their use,
without restricting the invention to the examples.
[0051] The laser scattering values measured were obtained using the
Malvern Mastersizer S, version 2.18.
EXAMPLE 1
Reprecipitation of Nylon-12 (PA 12), Non-Inventive
[0052] 400 kg of unregulated PA 12 prepared by hydrolytic
polymerization and having a relative solution viscosity of 1.62 and
an end group content of 75 mmol/kg of COOH and 69 mmol/kg of
NH.sub.2 are heated to 145.degree. C. with 2500 l of ethanol
denatured with 2-butanone and 1% water content within a period of 5
hours in a 3 m.sup.3 stirred tank (d=160 cm), and kept at this
temperature for 1 hour with stirring (blade stirrer, d=80 cm,
rotation rate=49 rpm). The jacket temperature is then reduced to
124.degree. C., and the internal temperature is brought to
125.degree. C. using a cooling rate of 25 K/h with the same stirrer
rotation rate, while ethanol is continuously removed by
distillation. From now on, using the same cooling rate, the jacket
temperature is kept below the internal temperature by from 2 K to 3
K. The internal temperature is brought to 117.degree. C., at the
same cooling rate, and then kept constant for 60 minutes. The
internal temperature is then brought to 111.degree. C., at a
cooling rate of 40 K/h with further removal of material by
distillation. At this temperature precipitation begins, detectable
via heat generation. The distillation rate is increased to an
extent that keeps the internal temperature at not above
111.3.degree. C. After 25 minutes, the internal temperature falls,
indicating the end of the precipitation process. The temperature of
the suspension is brought to 45.degree. C. via further removal of
material by distillation and cooling by way of the jacket, and then
the suspension is transferred to a paddle dryer. The ethanol is
distilled off from the mixture at 70.degree. C./400 mbar, and the
residue is then further dried for 3 hours at 20 mbar/86.degree. C.
This gives a precipitated PA 12 with a median grain diameter of 55
.mu.m. The bulk density was 435 g/l.
EXAMPLE 2
[0053] A powder composed of a random copolyamide composed of 40
parts of laurolactam, 30 parts of caprolactam, and 30 parts of
equimolar mixture composed of dodecandioc acid and
hexamethylenediamine, obtained via hydrolytic polycondensation, was
produced via low-temperature grinding followed by fractionation.
The powder thus obtained was treated with 0.1 part of Aerosil 200
in a Henschel mixer. The solution viscosity is 1.7. The MFR value
was determined as 4 g/10 min at 160.degree. C./2.16 kg. The bulk
density is 491 g/l. The distribution of grains was determined as
follows: d.sub.10=17 .mu.m, d.sub.50=62 .mu.m, d.sub.90=112
.mu.m.
EXAMPLE 3
[0054] A powder composed of a random copolyamide composed of 33
parts of laurolactam, 33 parts of caprolactam, and 33 parts of
equimolar mixture composed of adipic acid and hexamethylenediamine,
obtained via hydrolytic polycondensation, was produced via
low-temperature grinding followed by fractionation. The powder thus
obtained was treated with 0.1 part of Aerosil 200 in a Henschel
mixer. The solution viscosity is 1.7. The MFR value was determined
as 6 g/10 min at 160.degree. C./2.16 kg. The bulk density is 475
g/l. The distribution of grains was determined as follows:
d.sub.10=11 .mu.m, d.sub.50=65 .mu.m, d.sub.90=105 .mu.m.
EXAMPLE 4
[0055] A powder composed of a random copolyamide composed of 50
parts of laurolactam, 20 parts of caprolactam, and 30 parts of
equimolar mixture composed of dodecandioc acid and
hexamethylenediamine, obtained via hydrolytic polycondensation, was
produced via low-temperature grinding followed by fractionation.
The powder thus obtained was treated with 0.1 part of Aerosil R812
in a Henschel mixer. The solution viscosity is 1.55. The MFR value
was determined as 12 g/10 min at 160.degree. C./2.16 kg. The bulk
density is 458 g/l. The distribution of grains was determined as
follows: d.sub.10=13 .mu.m, d.sub.50=66 .mu.m, d.sub.90=111
.mu.m.
EXAMPLE 5
[0056] A powder composed of a random copolyamide composed of 60
parts of laurolactam, 25 parts of caprolactam, and 15 parts of
equimolar mixture composed of adipic acid and hexamethylenediamine,
obtained via hydrolytic polycondensation, was produced via
low-temperature grinding followed by fractionation. The powder thus
obtained was treated with 0.1 part of Aerosil 200 in a Henschel
mixer. The solution viscosity is 1.6. The MFR value was determined
as 9 g/10 min at 160.degree. C./2.16 kg. The bulk density is 462
g/l. The distribution of grains was determined as follows:
d.sub.10=18 .mu.m, d.sub.50=75 .mu.m, d.sub.90=112 .mu.m.
EXAMPLE 6
[0057] A powder composed of a random copolyamide composed of 15
parts of laurolactam and 85 parts of an equimolar mixture composed
of dodecanedioic acid and isophoronediamine, obtained via
hydrolytic polycondensation, was produced via low-temperature
grinding followed by fractionation. The powder thus obtained was
treated with 0.05 part of Aerosil 200 in a Henschel mixer. The
solution viscosity is 1.7. The MFR value was determined as 5 g/10
min at 230.degree. C./2.16 kg.
[0058] The bulk density is 458 g/l. The distribution of grains was
determined as follows: d.sub.10=12 .mu.m, d.sub.50=56 .mu.m,
d.sub.90=105 .mu.m.
EXAMPLE 7
[0059] A powder composed of a random copolyester composed of 100
parts of butanediol, 45 parts of terephthalic acid and 55 parts of
isophthalic acid, obtained via hydrolytic polycondensation, was
produced via low-temperature grinding followed by fractionation.
The powder thus obtained was treated with 0.2 part of Aerosil 200
in a Henschel mixer. The MFR value was determined as 12 g/10 min at
160.degree. C./2.16 kg. The bulk density is 459 g/l. The
distribution of grains was determined as follows: d.sub.10=10
.mu.m, d.sub.50=61 .mu.m, d.sub.90=119 .mu.m.
EXAMPLE 8
[0060] A powder composed of a random copolyester composed of 100
parts of butanediol, 11 parts of polyethylene glycol, 42 parts of
terephthalic acid and 58 parts of isophthalic acid, obtained via
hydrolytic polycondensation, was produced via low-temperature
grinding followed by fractionation. The powder thus obtained was
treated with 0.1 part of Aerosil 200 in a Henschel mixer. The bulk
density is 471 g/l. The MFR value was determined as 10 g/10 min at
160.degree. C./2.16 kg. The distribution of grains was determined
as follows: d.sub.10=17 .mu.m, d.sub.50=63 .mu.m, d.sub.90=122
.mu.m.
[0061] A concrete mixer is used to prepare the mixture of powder
from examples 1 and 5, and also the mixture of powder from example
6 with glass beads. The glass beads used comprised Spheriglass A
glass with a coating from Potters with a diameter of 35 .mu.m.
Further Processing and Test
[0062] An open-topped box measuring 10.times.10 cm was provided
with a base which can be moved by way of a spindle. A heating tape
was wound around the box and was set to 90.degree. C. during the
experiments. The base was moved to a position half a centimeter
from the upper edge; the remaining space was filled with powder,
which was smoothed using a metal plate. A metal frame of thickness
1 mm was then placed on the edge of the box, and above this was
placed a metal plate with a relatively small round aperture, its
distance from the powder layer being 1 mm. The powder layer within
the circular aperture was melted using a radiant heater with power
rating 1000 W from AKO, which was moved downward toward the
experimental arrangement until the separation was 2 cm, for two
seconds. The next steps, turning of the spindle to lower the base
by 0.2 mm, and application of the next powder layer, and then again
lowering the radiant heater to melt the powder, were repeated a
number of times. The intention was to attain a disk after cooling
of the experimental arrangement.
TABLE-US-00001 TABLE 1 Results of the experiments of the examples
Melting point (DSC) Example .degree. C. Comment Example 1 (non- 187
Markedly more energy inventive) introduction required than in the
other examples Example 2 112 Good edge sharpness, almost no curl
Example 3 115 Good edge sharpness, almost no curl Example 4 113
Good edge sharpness, almost no curl, slight adhesion tendency after
a plurality of layers Example 5 123 Good edge sharpness, almost no
curl 75% of powder n.d. Good edge sharpness, no from example 5 curl
and 25% of powder from example 1 Example 6 120 Good edge sharpness,
almost no curl Example 7 114 Good edge sharpness, almost no curl
Example 8 110 Good edge sharpness, almost no curl, slight adhesion
tendency after a plurality of layers 80% of powder n.d. Good edge
sharpness, from example 6 no curl and 20% of glass beads
[0063] The examples very clearly show that inventive polymer
powders can be processed very effectively in an inventive
process.
[0064] Disks, with some relatively sharp edges, could be obtained
in all of the examples using inventive powder. In contrast, the
non-inventive powder of example 1 exhibited curl which was too
marked to permit sintering of more than one layer. The
non-inventive powder of example 1 also had to be exposed to the
radiant heater for at least 5 seconds in order for any melting at
all to occur. The single layer exhibited marked cakeing beyond the
desired profile. Shortening the exposure time while at the same
time reducing the distance from the radiant heater improved the
profile sharpness, and a plaque could likewise be produced but the
quality of the component remained below that of the inventive
examples.
[0065] The powders of examples 4 and 8 exhibited slight adhesion
tendency on smoothing of the newly applied powder, as the duration
of the experiment increased. However, they are also at the lower
limit for solution viscosity and, respectively, the upper limit for
MFR value. The mixtures of 75% of powder of example 5 with 25% of
powder of example 1, and also 80% of powder of example 6 with 20%
of glass beads had very advantageous behavior with respect to
tendency to curl.
* * * * *