U.S. patent application number 11/185307 was filed with the patent office on 2006-02-23 for fireproofing polyamide powders and their use in a sintering process.
Invention is credited to Patrick Douais, Gregory Filou.
Application Number | 20060041041 11/185307 |
Document ID | / |
Family ID | 35910491 |
Filed Date | 2006-02-23 |
United States Patent
Application |
20060041041 |
Kind Code |
A1 |
Douais; Patrick ; et
al. |
February 23, 2006 |
Fireproofing polyamide powders and their use in a sintering
process
Abstract
A subject-matter of the invention is the use of a polyamide
powder possessing a fireproofing property in a process for the
manufacture of an object made of polyamide by sintering this powder
using radiation, the said powder comprising, by weight, 2 to 40% of
at least one flame retardant for respectively 98 to 60% of at least
one polyamide, the flame retardant being a blend of at least one
organic phosphinate of a metal and of at least ammonium
polyphosphate.
Inventors: |
Douais; Patrick; (Le Noyer
en Duche, FR) ; Filou; Gregory; (Pont Audemer,
FR) |
Correspondence
Address: |
Thomas F. Roland, Esq.;Arkema Inc.
2000 Market Street
Philadelphia
PA
19103
US
|
Family ID: |
35910491 |
Appl. No.: |
11/185307 |
Filed: |
July 20, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60616363 |
Oct 6, 2004 |
|
|
|
Current U.S.
Class: |
524/115 |
Current CPC
Class: |
C08K 5/0066 20130101;
C08K 3/32 20130101; C08K 9/08 20130101; C08K 5/0066 20130101; C08L
77/00 20130101; C08K 5/13 20130101; B33Y 70/00 20141201 |
Class at
Publication: |
524/115 |
International
Class: |
C08K 5/49 20060101
C08K005/49 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 20, 2004 |
FR |
04.08016 |
Claims
1. A process for the manufacture of an object made of polyamide
comprising sintering a polyamide powder using radiation, said
polyamide powder comprising, by weight, 2 to 40% of at least one
flame retardant for respectively 98 to 60% by weight of at least
one polyamide, the flame retardant being a blend of at least one
organic phosphinate of a metal and of at least ammonium
polyphosphate.
2. The process according to claim 1, wherein the powder comprises,
by weight, of (the total forming 100%): 2 to 40% of at least one
flame retardant, the flame retardant being a blend of at least one
organic phosphinate of a metal and of at least ammonium
polyphosphate; 98 to 60% of at least one polyamide; and at least
one agent selected from the group consisting of UV stabilizers,
antioxidants, dyes, pigments, bactericides and rheological
agents.
3. The process according to claim 1, wherein the phosphinate is
selected from the group consisting of phosphinic salts of formula
(I) and diphosphinic salts of formula (II): ##STR2## in which
R.sub.1 and R.sub.2 are identical or different and are linear or
branched C.sub.1 to C.sub.6 alkyl groups and/or aryl groups;
R.sub.3 is a linear or branched C.sub.2 to C.sub.10 alkylene group,
a C.sub.6 to C.sub.10 arylene group, a C.sub.6 to C.sub.10
alkylarylene group or a C.sub.6 to C.sub.10 arylalkylene group; M
is a calcium, aluminium and/or zinc ion; m is 2 or 3; n is 1 or 3;
x is 1 or 2.
4. The process according to claim 1, in which the polyamide is
chosen from PA 11, PA 12, aliphatic polyamides resulting from the
condensation of an aliphatic diamine having from 6 to 12 carbon
atoms and of an aliphatic diacid having from 9 to 18 carbon atoms,
and copolyamides 11/12 having either more than 90% of 11 units or
more than 90% of 12 units.
5. An article comprising a polyamide powder possessing a
fireproofing property, said powder comprising, by weight, 2 to 40%
of at least one flame retardant for respectively 98 to 60% of at
least one polyamide, the flame retardant being a blend of at least
one organic phosphinate of a metal and of at least ammonium
polyphosphate, the said powder being sintered using radiation.
6. (canceled)
7. The process according to claim 1, in which the radiation
originates from a laser beam.
Description
[0001] This application claims benefit, under U.S.C. .sctn.119 or
.sctn.365 of French Application Number 04.08016, filed Jul. 20,
2004; and U.S. 60/616,363 filed Oct. 6, 2004.
FIELD OF THE INVENTION
[0002] The present invention relates to fireproofing polyamide
powders and to their use in a sintering process, for example a
process for sintering under the action of radiation, such as a
laser beam. The invention relates to compositions based on
fireproofing powders (for example formed of polyamide 11 or 12)
which are compatible with the technique for processing by
sintering, for example, under a laser beam. The object is to
develop materials which have a good performance with regard to fire
resistance without this being made at the expense of the other
performance characteristics of the material
(viscosity/rheology/flow which are suitable for the targeted
application, satisfactory level of mechanical properties) and which
can be converted by a sintering technique which uses radiation,
more particularly a laser sintering technique.
BACKGROUND OF THE INVENTION
[0003] The technology for sintering polyamide powders under a laser
beam is used to manufacture three-dimensional objects, such as
prototypes and models. A fine layer of polyamide powder is
deposited on a horizontal plate maintained in a chamber heated at a
temperature lying between the crystallization point CP and the
melting point MP of the polyamide powder. The laser sinters powder
particles at different points in the powder layer according to a
geometry corresponding to the object, for example using a computer
which has the shape of the object in memory and which reconstructs
it in the form of slices. The horizontal plate is subsequently
lowered by a value corresponding to the thickness of a powder layer
(for example, between 0.05 and 2 mm and generally of the order of
0.1 mm), then a fresh powder layer is deposited and the laser
sinters powder particles according to a geometry corresponding to
this new slice of the object. The procedure is repeated until the
complete object has been manufactured. A block of powder is
obtained in which the object is present internally. The parts which
were not sintered have thus remained in the powder form.
Subsequently, the combined product is gently cooled and the object
solidifies as soon as its temperature falls below the
crystallization point CP. When completely cool, the object is
separated from the powder, which can be reused in another
operation.
[0004] It is recommended for the powder to have a difference MP-CP
which is as great as possible in order to avoid phenomena of
deformation (or curling) during manufacture. This is because, at
the time to immediately after the action of the laser beam, the
temperature of the sample is greater than the crystallization point
(CP) of the powder but the introduction of a fresh, colder, powder
layer causes the temperature of the component to rapidly fall below
the CP and brings about deformations.
[0005] Furthermore, an enthalpy of fusion (.DELTA.Hf) which is as
high as possible is required in order to obtain good geometrical
definition of the components manufactured. This is because, if the
enthalpy of fusion is too low, the energy introduced by the laser
is sufficient to sinter by thermal conduction the powder particles
close to the growing walls but the geometrical precision of the
component is no longer satisfactory.
[0006] It is clear that everything which has just been explained
with regard to the sintering of polyamide powders under a laser
beam is valid whatever the radiation which brings about the
melting.
[0007] For specific uses, it is necessary for the objects obtained
to have flame-retardant properties, indeed even fireproofing
properties, but also to fulfil criteria for emission of fumes and
for toxicity. In the continuation of the text, for simplicity, the
term "fireproofing" is used for flame-retardant properties and for
fireproofing properties. It is shown that organic phosphorus
additives based on an organic phosphinate of a metal and on
ammonium polyphosphate are suitable for the laser sintering
process. It is sufficient to dry blend these products with the
polyamide powder. It has also been discovered that the usual
fireproofing agents for polyamides are not all suitable. For
example, melamine cyanurate is not suitable.
SUMMARY OF THE INVENTION
[0008] The present invention relates to the use of a polyamide
powder possessing a fireproofing property in a process for the
manufacture of an object made of polyamide by sintering this powder
using radiation, the said powder comprising, by weight, 2 to 40% of
at least one flame retardant for respectively 98 to 60% of at least
one polyamide, the flame retardant being a blend of at least one
organic phosphinate of a metal and of at least ammonium
polyphosphate.
[0009] According to one embodiment, the powder is composed, by
weight, of (the total forming 100%): [0010] 2 to 40% of at least
one flame retardant, the flame retardant being a blend of at least
one organic phosphinate of a metal and of at least ammonium
polyphosphate; [0011] 98 to 60% of at least one polyamide; and
[0012] at least one agent taken from UV stabilizers, antioxidants,
dyes, pigments, bactericides and rheological agents.
[0013] According to one embodiment, the phosphinate used is chosen
from phosphinic salts of formula (I) and diphosphinic salts of
formula (II): ##STR1## in which R.sub.1 and R.sub.2 are identical
or different and are linear or branched C.sub.1 to C.sub.6 alkyl
groups and/or aryl groups; [0014] R.sub.3 is a linear or branched
C.sub.2 to C.sub.10 alkylene group, a C.sub.6 to C.sub.10 arylene
group, a C.sub.6 to C.sub.10 alkylarylene group or a C.sub.6 to
C.sub.10 arylalkylene group; [0015] M is a calcium, aluminium
and/or zinc ion; [0016] m is 2 or 3; [0017] n is 1 or 3; [0018] x
is 1 or 2.
[0019] According to one embodiment, the polyamide is chosen from PA
11, PA 12, aliphatic polyamides resulting from the condensation of
an aliphatic diamine having from 6 to 12 carbon atoms and of an
aliphatic diacid having from 9 to 18 carbon atoms, and copolyamides
11/12 having either more than 90% of II units or more than 90% of
12 units.
[0020] The invention also relates to an article manufactured with a
polyamide powder possessing a fireproofing property, the said
powder comprising, by weight, 2 to 40% of at least one flame
retardant for respectively 98 to 60% of at least one polyamide, the
flame retardant being a blend of at least one organic phosphinate
of a metal and of at least ammonium polyphosphate, the said powder
being sintered using radiation.
[0021] It also relates to the process for the manufacture of an
object made of polyamide by sintering polyamide powder using
radiation, the said powder comprising, by weight, 2 to 40% of at
least one flame retardant for respectively 98 to 60% of at least
one polyamide, the flame retardant being a blend of at least one
organic phosphinate of a metal and of at least ammonium
polyphosphate.
[0022] According to one embodiment, the radiation originates from a
laser beam.
[0023] This powder can be prepared by simple dry blending of the
constituents, this being the preferred embodiment.
[0024] It is also possible to add the flame retardant to the molten
polyamide in a mixing device and to reduce the product obtained to
the powder form but with, in this case, the risk of a fall in the
enthalpy of fusion and the consequences mentioned above during the
conversion of the powder by sintering technology.
[0025] The polyamide can be a homopolyamide or a copolyamide. It
can be a blend of polyamide and of at least one other polymer, the
polyamide forming the matrix and the other polymer or polymers
forming the phase dispersed in the matrix.
[0026] Mention may be made, as an example of radiation, of that
supplied by a laser beam (the process is then referred to as "laser
sintering"). Mention may also be made of the process in which a
mask is positioned between the powder layer and the source of the
radiation; the powder particles protected from the radiation by the
mask are not sintered.
DETAILED DESCRIPTION OF THE INVENTION
[0027] As regards the polyamide, the term "polyamide" is understood
to mean the condensation products: [0028] of one or more amino
acids, such as aminocaproic, 7-aminoheptanoic, 11-aminoundecanoic
and 12-aminododecanoic acids, or of one or more lactams, such as
caprolactam, oenantholactam and lauryllactam; [0029] of one or more
salts or mixtures of diamines, such as hexamethylenediamine,
dodecamethylenediamine, meta-xylylenediamine,
bis-(p-aminocyclohexyl)methane and trimethylhexamethylenediamine,
with diacids, such as isophthalic, terephthalic, adipic, azelaic,
suberic, sebacic and dodecanedicarboxylic acids, as well as
C.sub.14 to C.sub.18 diacids.
[0030] Mention may be made, as examples of polyamide, of PA 6, PA
6-6, PA 11, PA 12, PA 6-10, PA 6-12 and PA 6-14.
[0031] Use may also be made of copolyamides. Mention may be made of
the copolyamides resulting from the condensation of at least two
.alpha.,.omega.-aminocarboxylic acids or of two lactams or of one
lactam and of one .alpha.,.omega.-aminocarboxylic acid. Mention may
also be made of the copolyamides resulting from the condensation of
at least one .alpha.,.omega.-aminocarboxylic acid (or one lactam),
at least one diamine and at least one dicarboxylic acid. Mention
may also be made of the copolyamides resulting from the
condensation of an aliphatic diamine with an aliphatic dicarboxylic
acid and at least one other monomer chosen from aliphatic diamines
other than the above and aliphatic diacids other than the
above.
[0032] Mention may be made, as examples of lactams, of those which
have from 3 to 12 carbon atoms on the main ring and which can be
substituted. Mention may be made, for example, of
.beta.,.beta.-dimethylpropiolactam,
.alpha.,.alpha.-dimethylpropiolactam, amylolactam, caprolactam,
capryllactam and lauryllactam.
[0033] Mention may be made, as examples of
.alpha.,.omega.-aminocarboxylic acid, of aminoundecanoic acid and
aminododecanoic acid. Mention may be made, as examples of
dicarboxylic acid, of adipic acid, sebacic acid, isophthalic acid,
butanedioic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic
acid, the sodium or lithium salt of sulphoisophthalic acid,
dimerized fatty acids (these dimerized fatty acids have a dimer
content of at least 98% and are preferably hydrogenated) and
dodecanedioic acid HOOC--(CH.sub.2).sub.10--COOH.
[0034] The diamine can be an aliphatic diamine having from 6 to 12
atoms; it can be saturated cyclic and/or arylic. Mention may be
made, by way of examples, of hexamethylenediamine, piperazine,
tetramethylenediamine, octamethylenediamine, decamethylenediamine,
dodecamethylenediamine, 1,5-diaminohexane,
2,2,4-trimethyl-1,6-diaminohexane, polyoldiamines,
isophoronediamine (IPD), methylpentamethylenediamine (MPDM),
bis(aminocyclohexyl)methane (BACM) or
bis(3-methyl-4-aminocyclohexyl)methane (BMACM).
[0035] Mention may be made, as examples of copolyamides, of
copolymers of caprolactam and of lauryllactam (PA 6/12), copolymers
of caprolactam, of adipic acid and of hexamethylenediamine (PA
6/6-6), copolymers of caprolactam, of lauryllactam, of adipic acid
and of hexamethylenediamine (PA 6/12/6-6), copolymers of
caprolactam, of lauryllactam, of 11-aminoundecanoic acid, of
azelaic acid and of hexamethylenediamine (PA 6/6-9/11/12),
copolymers of caprolactam, of lauryllactam, of 11-aminoundecanoic
acid, of adipic acid and of hexamethylenediamine (PA 0.6/6-6/11/12)
or copolymers of lauryllactam, of azelaic acid and of
hexamethylenediamine (PA 6-9/12).
[0036] Use may be made of blends of polyamide. These are, for
example, blends of aliphatic polyamides and of semiaromatic
polyamides and blends of aliphatic polyamides and of cycloaliphatic
polyamides.
[0037] Mention may be made, for example, of the compositions
disclosed in Patent Application EP 1 227 131 comprising, by weight,
the total being 100%: [0038] 5 to 40% of an amorphous polyamide (B)
which results essentially from the condensation: [0039] either of
at least one diamine chosen from cycloaliphatic diamines and
aliphatic diamines and of at least one diacid chosen from
cycloaliphatic diacids and aliphatic diacids, at least one of these
diamine or diacid units being cycloaliphatic, [0040] or of a
cycloaliphatic .alpha.,.omega.-aminocarboxylic acid, [0041] or of a
combination of these two possibilities, [0042] and optionally of at
least one monomer chosen from .alpha.,.omega.-aminocarboxylic acids
or the corresponding possible lactams, aliphatic diacids and
aliphatic diamines, [0043] 0 to 40% of a flexible polyamide (C)
chosen from copolymers comprising polyamide blocks and polyether
blocks and copolyamides, [0044] 0 to 20% of a compatibilizing agent
(D) for (A) and (B), [0045] 0 to 40% of a flexible modifier (M),
[0046] provided that (C)+(D)+(M) is between 0 and 50%, [0047] the
remainder to 100% of a semicrystalline polyamide (A).
[0048] Mention may also be made of the compositions disclosed in
Patent Application EP 1 227 132 comprising, by weight, the total
being 100%: [0049] 5 to 40% of an amorphous polyamide (B) which
results essentially from the condensation of at least one
optionally cycloaliphatic diamine, of at least one aromatic diacid
and optionally of at least one monomer chosen from: [0050]
.alpha.,.omega.-aminocarboxylic acids, [0051] aliphatic diacids,
[0052] aliphatic diamines, [0053] 0 to 40% of a flexible polyamide
(C) chosen from copolymers comprising polyamide blocks and
polyether blocks and copolyamides, [0054] 0 to 20% of a
compatibilizing agent (D) for (A) and (B), [0055] (C)+(D) is
between 2 and 50% [0056] with the condition that (B)+(C)+(D) is not
less than 30%, [0057] the remainder to 100% of a semicrystalline
polyamide (A).
[0058] It would not be departing from the scope of the invention to
replace a portion of the polyamide with a copolymer comprising
polyamide blocks and polyether blocks, that is to say to use a
blend comprising at least one of the above polyamides and at least
one copolymer comprising polyamide blocks and polyether blocks.
[0059] The copolymers comprising polyamide blocks and polyether
blocks result from the copolycondensation of polyamide sequences
comprising reactive ends with polyether sequences comprising
reactive ends, such as, inter alia: [0060] 1) Polyamide sequences
comprising diamine chain ends with polyoxyalkylene sequences
comprising dicarboxyl chain ends. [0061] 2) Polyamide sequences
comprising dicarboxyl chain ends with polyoxyalkylene sequences
comprising diamine chain ends obtained by cyanoethylation and
hydrogenation of aliphatic .alpha.,.omega.-dihydroxylated
polyoxyalkylene sequences, known as polyetherdiols. [0062] 3)
Polyamide sequences comprising dicarboxyl chain ends with
polyetherdiols, the products obtained being, in this specific case,
polyetheresteramides. Use is advantageously made of these
copolymers.
[0063] The polyamide sequences comprising dicarboxyl chain ends
originate, for example, from the condensation of
.alpha.,.omega.-aminocarboxylic acids, of lactams or of
dicarboxylic acids and diamines in the presence of a chain-limiting
dicarboxylic acid.
[0064] The polyether can be, for example, a polytetramethylene
glycol (PTMG). The latter is also known as polytetrahydrofuran
(PTHF).
[0065] The number-average molar mass {overscore (M)}.sub.n of the
polyamide sequences is between 300 and 15 000 and preferably
between 600 and 5000. The mass {overscore (M)}.sub.n of the
polyether sequences is between 100 and 6000 and preferably between
200 and 3000.
[0066] The polymers comprising polyamide blocks and polyether
blocks can also comprise randomly distributed units. These polymers
can be prepared by the simultaneous reaction of the polyether and
of the precursors of the polyamide blocks.
[0067] For example, polyetherdiol, a lactam (or an
.alpha.,.omega.-amino acid) and a chain-limiting diacid can be
reacted in the presence of a small amount of water. A polymer is
obtained which has essentially polyether blocks and polyamide
blocks, the latter being of highly variable length, but also the
various reactants which have reacted randomly, which are
distributed statistically along the polymer chain.
[0068] These polymers comprising polyamide blocks and polyether
blocks, whether they originate from the copolycondensation of
polyamide and polyether sequences prepared beforehand or from a
one-stage reaction, exhibit, for example, Shore D hardnesses which
can be between 20 and 75 and advantageously between 30 and 70 and
an intrinsic viscosity between 0.8 and 2.5, measured in meta-cresol
at 25.degree. C. for an initial concentration of 0.8 g/100 ml. The
MFI values can be between 5 and 50 (235.degree. C. under a load of
1 kg).
[0069] The polyetherdiol blocks are either used as is and
copolycondensed with polyamide blocks comprising carboxyl ends or
are aminated, in order to be converted into polyetherdiamines, and
condensed with polyamide blocks comprising carboxyl ends. They can
also be blended with polyamide precursors and a chain-limiting
agent in order to prepare polymers comprising polyamide blocks and
polyether blocks having statistically distributed units.
[0070] Polymers comprising polyamide and polyether blocks are
disclosed in U.S. Pat. No. 4,331,786, U.S. Pat. No. 4,115,475. U.S.
Pat. No. 4,195,015, U.S. Pat. No. 4,839,441, U.S. Pat. No.
4,864,014, U.S. Pat. No. 4,230,838 and U.S. Pat. No. 4,332,920.
[0071] The ratio of the amount of copolymer comprising polyamide
blocks and polyether blocks to the amount of polyamide can be, by
weight, between 1/99 and 15/85.
[0072] As regards the blend of polyamide and of at least one other
polymer, it is provided in the form of a blend comprising a
polyamide matrix and the other polymer or polymers form the phase
dispersed in this matrix. Mention may be made, as examples of this
other polymer, of polyolefins, polyesters, polycarbonates, PPO
(abbreviation for polyphenylene oxide), PPS (abbreviation for
polyphenylene sulphide) or elastomers.
[0073] The invention is of particular use for polyamides chosen
from PA 11, PA 12, aliphatic polyamides resulting from the
condensation of an aliphatic diamine having from 6 to 12 carbon
atoms and of an aliphatic diacid having from 9 to 18 carbon atoms,
and copolyamides 11/12 having either more than 90% of 11 units or
more than 90% of 12 units.
[0074] Mention may be made, as examples of aliphatic polyamide
resulting from the condensation of an aliphatic diamine having from
6 to 12 carbon atoms and of an aliphatic diacid having from 9 to 12
carbon atoms, of: [0075] PA 6-12, resulting from the condensation
of hexamethylenediamine and of 1,12-dodecanedioic acid, [0076] PA
9-12, resulting from the condensation of C.sub.9 diamine and of
1,12-dodecanedioic acid, [0077] PA 10-10, resulting from the
condensation of C.sub.10 diamine and of 1,10-decanedioic acid,
[0078] PA 10-12, resulting from the condensation of C.sub.9 diamine
and of 1,12-dodecanedioic acid.
[0079] With regard to the copolyamides 11/12 having either more
than 90% of 11 units or more than 90% of 12 units, they result from
the condensation of 11-aminoundecanoic acid with lauryllactam (or
.alpha.,.omega.-amino(C.sub.12)acid).
[0080] It would not be departing from the scope of the invention to
use a blend of polyamides.
[0081] The polyamide can, before being blended with the
fireproofing agent, be treated with water or with steam according
to the process disclosed in Patent EP 1 413 595. In this patent,
the disclosure is made of a process for enhancing at least one of
the following two parameters of a polyamide: (i) its melting point
and (ii) its enthalpy of fusion .DELTA.Hf, in which process: [0082]
this polyamide is brought into contact in the solid state with
water or steam at a temperature close to its crystallization point
CP for a period of time sufficient to bring about this enhancement,
[0083] then the water (or the steam) is separated from the
polyamide and the polyamide is dried.
[0084] The polyamide can be a homopolyamide or a copolyamide. It
can be a blend of polyamide and of at least one other polymer, the
polyamide forming the matrix and the other polymer or polymers
forming the dispersed phase.
[0085] Advantageously, the polyamide is in the divided form, such
as powder or granules. The granules thus treated can subsequently
be ground to form powders.
[0086] The treatment with water or with steam can also be preceded
by a conventional treatment with methanol to extract the possible
oligomers present in the polyamide.
[0087] According to another form, the water or the steam can
comprise methanol. It is thus possible simultaneously to extract
oligomers or impurities present in the polyamide to be treated. In
this form of the invention, it is recommended to rinse the
polyamide before drying it in order to thoroughly remove any traces
of methanol.
[0088] As regards the fireproofing agents or flame retardants,
their proportion is between 2 and 40% by weight, advantageously
between 5 and 35%, for respectively 98 to 60% and 95 to 65% by
weight of polyamide. Preferably, it is between 5 and 30% by weight
for respectively 95 to 70% of polyamide. It is also possible, in
addition to the organic phosphinates of a metal and the ammonium
polyphosphate, to add zinc borate as synergist. The proportion of
zinc borate can be between 0 and 10% by weight for respectively 100
to 90% by weight of the fireproofing agent or flame retardant, the
total (synergist+fireproofing agent) forming 100% by weight.
[0089] As regards the powders, they can be of different sizes. For
example, the powders of use in the laser sintering process can have
a size of up to 350 .mu.m and advantageously have a size of between
10 and 100 .mu.m. Preferably, the D50 is 60 .mu.m (that is to say,
50% of the particles have a size of less than 60 .mu.m).
[0090] As regards their preparation, it can be carried out by
simple dry blending of the constituents. The usual mixers for
powdered products, for example Henschel.RTM. mixers, can be used.
Blending is carried out at standard temperature and pressure. The
blending time must be sufficient for the blend to be homogeneous;
this time can be between 2 and 15 minutes.
[0091] It is also possible to add the fireproofing agent to the
molten polyamide in a mixing device and to reduce the product
obtained to the powder form. The blending time must be sufficient
for the blend to be homogeneous. An extruder, for example, is used.
The product recovered in the form of granules at the extruder
outlet is then subsequently ground to the same particle size cited
for the polyamide powder used in the dry blend process.
[0092] The powder of the invention can also comprise additives UV
stabilizers, antioxidants, dyes, pigments or bactericides, inter
alia. These products are preferably incorporated in the polyamide
before the addition of the fireproofing agent.
[0093] The invention will now be described in more detail. The
percentages are expressed by weight.
1) Manufacture of PA Powders Possessing Fireproofing Properties
[0094] A polyamide powder blend is formulated using a Henschel.RTM.
rapid mixer and by incorporating therein PA 11 suitable for
sintering under a laser beam with a D50 of 48 .mu.m and treated
according to Patent FR 2 846 333 A1 with a melting point of
201.degree. C. and an enthalpy of fusion of 105 J/g, a blend of
flame retardants being added according to the proportions defined
below along with 0.6% of a phenolic antioxidant and 0.1% of a fumed
silica as rheological agent. The blending time is 150 s. The blend
thus prepared is sieved through a cloth having an opening of 160
.mu.m.
[0095] The nature of the flame retardants, their proportions and
the proportion of PA are set out in the description of the examples
and comparative examples below.
2) Conversion of the PA Powder Possessing Fireproofing
Properties
[0096] The powder blend prepared according to the above
manufacturing process 1) is charged to a laser sintering device
used to manufacture objects in three dimensions by depositing a
fine layer of polyamide powder on a horizontal surface maintained
in a chamber heated to a temperature lying between the
crystallization point and the melting point. The laser sinters
powder particles according to a geometry corresponding to the
object, for example using a 3D System Vanguard.RTM. device which
has the shape of the object in memory and which reconstructs it in
the form of slices.
[0097] Plaques with a size of 12.times.3 inches and with a
thickness of 0.05 of an inch are manufactured for fire tests. The
combustion time in seconds (s) and the combustion length in inches
are measured on these plaques. The fire properties are satisfactory
when the combustion length is <6 inches and the combustion time
is as short as possible.
[0098] Three comparative examples (Cp1 to Cp3) of a PA blend with
various flame retardants which are unsuitable for the invention
will now be described:
[0099] With Melamine Cyanurate (Cp1)
[0100] A powder blend comprising 89.3% of PA 1, 10% of melamine
cyanurate (for example, Melapur C25) as flame retardant, 0.6% of a
phenolic antioxidant and 0.1% of a fumed silica as rheological
agent is manufactured according to the process described in 1)
above. However, during the phase of conversion of the powder, the
process for which is disclosed in 2), the components in the course
of manufacture by laser sintering are observed to deform.
[0101] With Ammonium Phosphate (Cp2)
[0102] A powder blend comprising 89.3% of PA 11, 10% of ammonium
phosphate (for example, Exolit AP 752) as flame retardant, 0.6% of
a phenolic antioxidant and 0.1% of a fumed silica as rheological
agent is manufactured according to the process described in 1).
However, during the phase of conversion of the powder described in
2), it is found that this composition is not very suitable for the
construction of components due to the sublimation of a compound in
the manufacturing chamber which tends to weaken the power of the
laser beam and to foul the construction chamber. Furthermore, the
components obtained do not show satisfactory fire resistance
properties since the combustion time is 129 s.
[0103] With Ammonium Polyphosphate (Cp3)
[0104] A powder blend comprising 89.3% of PA 11, 10% of ammonium
polyphosphate (for example, Exolit AP 423) as flame retardant, 0.6%
of a phenolic antioxidant and 0.1% of a fumed silica as rheological
agent is manufactured according to the process described in 1).
However, during the phase of conversion in 2), it is found that
this composition is not very suitable for the construction of
components due to the formation of fumes in the manufacturing
chamber which tend to weaken the power of the laser beam.
Furthermore, the components obtained do not show satisfactory fire
properties since the combustion length is 8.9 inches, whereas the
objective to be achieved must be <6 inches, and the combustion
time is 116 s.
[0105] It is thus found that melamine cyanurate, ammonium phosphate
and ammonium polyphosphate, alone, do not make it possible to
obtain a composition suitable for the use which it is desired to
make thereof.
[0106] Two examples (Ex. 1 and Ex. 2) of a PA blend with flame
retardants appropriate to the invention will now be described:
[0107] With 10% of a Phosphinate/Ammonium Polyphosphate Blend (Ex.
1)
[0108] A powder blend comprising 89.3% of PA 11, 10% of a blend of
phosphorous compounds (Exolit OP1311 from Clariant) as flame
retardant, 0.6% of a phenolic antioxidant and 0.1% of a fumed
silica as rheological agent is formulated as described in 1). After
conversion of the powder thus obtained according to the conversion
process described in 2), the components manufactured show
satisfactory fire properties since the combustion length is 3
inches and the combustion time is 36 s. The elongation at break is
49% and the tensile strength is 40 MPa (ASTM 638).
[0109] With 15% of a Phosphinate/Ammonium Polyphosphate Blend (Ex.
2)
[0110] A powder blend comprising 84.3% of PA 11, 15% of a blend of
phosphorus compounds (Exolit OP1311 from Clariant) as flame
retardant, 0.6% of a phenolic antioxidant and 0.1% of a fumed
silica as rheological agent is formulated as described in 1). The
components obtained on conclusion of the conversion described in 2)
show satisfactory fire properties with a combustion length of 3.6
inches and a combustion time of 23 s. The elongation at break is
32% and the tensile strength is 36 MPa (ASTM 638).
[0111] When a powder comprising 99.3% of PA 11, 0.6% of a phenolic
antioxidant and 0.1% of a fumed silica as rheological agent is
prepared according to 1) with 0% of flame retardant, the combustion
is greater than 10 inches, the elongation at break is 52% and the
tensile strength is 39 MPa (ASTM 638).
[0112] A marked reduction in the combustion time is found, without
this having a damaging effect on the mechanical properties of the
objects manufactured with the composition according to the
invention by the sintering process.
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