U.S. patent application number 13/172955 was filed with the patent office on 2012-01-12 for light-curing ceramic slips for the stereolithographic preparation of high-strength ceramics.
This patent application is currently assigned to IVOCLAR VIVADENT AG. Invention is credited to Urs Karl Fischer, Johannes Homa, Werner Langle, Norbert Moszner, Volker Rheinberger, Wolfgang Wachter.
Application Number | 20120010066 13/172955 |
Document ID | / |
Family ID | 43216299 |
Filed Date | 2012-01-12 |
United States Patent
Application |
20120010066 |
Kind Code |
A1 |
Fischer; Urs Karl ; et
al. |
January 12, 2012 |
LIGHT-CURING CERAMIC SLIPS FOR THE STEREOLITHOGRAPHIC PREPARATION
OF HIGH-STRENGTH CERAMICS
Abstract
Slip based on radically polymerizable binder, polymerization
initiator and filler, which comprises (A) at least one acidic
monomer of general formula I (HG-Y--).sub.aX Z--PG).sub.b Formula I
(B) photoinitiator, and (C) ceramic and/or glass ceramic
particles.
Inventors: |
Fischer; Urs Karl; (Arbon,
CH) ; Moszner; Norbert; (Mauren, LI) ;
Rheinberger; Volker; (Vaduz, LI) ; Wachter;
Wolfgang; (Schaan, LI) ; Homa; Johannes;
(Feldkirch, AT) ; Langle; Werner; (Frastanz,
AT) |
Assignee: |
IVOCLAR VIVADENT AG
Schaan
LI
|
Family ID: |
43216299 |
Appl. No.: |
13/172955 |
Filed: |
June 30, 2011 |
Current U.S.
Class: |
501/32 ; 264/17;
501/1; 501/134; 501/135; 501/152; 501/153; 501/154 |
Current CPC
Class: |
A61K 6/887 20200101;
C04B 35/6264 20130101; A61K 6/822 20200101; A61K 6/833 20200101;
A61K 6/807 20200101; C04B 35/63424 20130101; C04B 35/111 20130101;
C04B 2235/3229 20130101; C04B 35/6263 20130101; C04B 35/64
20130101; C04B 35/63488 20130101; C04B 2235/3208 20130101; C04B
2235/96 20130101; C04B 2235/9661 20130101; C08L 33/00 20130101;
C04B 2235/6026 20130101; A61K 6/887 20200101; C08L 33/00 20130101;
C04B 2235/3206 20130101; A61K 6/818 20200101; C04B 2235/449
20130101; C04B 35/6325 20130101; A61K 6/887 20200101; C04B 35/6346
20130101; C04B 2235/44 20130101; C04B 35/486 20130101; C04B 35/4885
20130101; C04B 2235/3225 20130101 |
Class at
Publication: |
501/32 ; 501/1;
264/17; 501/134; 501/153; 501/135; 501/154; 501/152 |
International
Class: |
A61C 13/20 20060101
A61C013/20; C04B 35/622 20060101 C04B035/622; C04B 35/48 20060101
C04B035/48; C04B 35/10 20060101 C04B035/10; C04B 35/00 20060101
C04B035/00; C03C 14/00 20060101 C03C014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 2010 |
EP |
10007066.3 |
Claims
1. Slip based on radically polymerizable binder, polymerization
initiator and filler, which comprises the following components: A)
1 to 30 wt.-% of at least one acidic monomer of general formula I
(HG-Y--).sub.aX Z--PG) Formula I in which X is not present or is an
(a+b)-valent, substituted or unsubstituted, straight-chained
aliphatic residue with at least 2 carbon atoms, a branched
aliphatic residue with at least 3 carbon atoms, a cycloaliphatic,
bi- or tricylic or aromatic residue with 6 to 20 carbon atoms or a
combination of these residues, wherein these residues can contain
one or more ether groups, PG is a radically polymerizable group; HG
is --COOH--, --PO(OH).sub.2, --O--PO(OH).sub.2 or --SO.sub.3H; Y is
not present or is a divalent, straight-chained aliphatic group with
2 to 40 carbon atoms, a branched aliphatic group with 3 to 40
carbon atoms or a cycloaliphatic or aromatic group with 5 to 40
carbon atoms, wherein these groups can contain one or more ether,
thioether, amide and/or ester groups; Z is not present or is a
divalent, straight-chained aliphatic group with 2 to 40 carbon
atoms or a branched aliphatic group with 3 to 40 carbon atoms,
wherein these groups can contain one or more ether, thioether,
amide and/or ester groups; a is an integer from 1 to 5; and b is 1
or 2; A2) 0 to 50 wt.-% of at least one non-acidic radically
polymerizable monomer; B) 0.001 to 2.0 wt.-% photoinitiator; and C)
30 to 90 wt.-% ceramic and/or glass ceramic particles; in each case
relative to the total mass of the slip.
2. Slip according to claim 1, wherein the variables of formula (I)
have the following meaning: X is not present or is an (a+b)-valent,
substituted or unsubstituted, straight-chained aliphatic residue
with 3 to 15 carbon atoms, a branched aliphatic residue with 3 to
15 carbon atoms, a cycloaliphatic, bi- or tricylic or aromatic
residue with 6 to 15 carbon atoms or a combination of these
residues, preferably an aromatic or cycloaliphatic C.sub.6 residue
and in particular is a straight-chained or branched aliphatic
C.sub.3-C.sub.15 residue, particularly preferably C.sub.3-C.sub.8
residue, wherein these residues can contain one or more ether
groups; PG is a vinyl (CH.sub.2.dbd.CH--), allyl
(CH.sub.2.dbd.CH--CH.sub.2--), allyl ether
(CH.sub.2.dbd.CH--CH.sub.2--O--), styryl (CH.sub.2.dbd.CH-phenyl),
(meth)acrylate (CH.sub.2.dbd.C(--H/--CH.sub.3)--CO--O--) or
(meth)acrylamide group (CH.sub.2.dbd.C(--H/--CH.sub.3)--CO--NH-- or
CH.sub.2.dbd.C(--H/--CH.sub.3)--CO--NR-- with R.dbd.C.sub.1-C.sub.4
alkyl), particularly preferably a (meth)acrylate or
(meth)acrylamide group and quite particularly preferably an
acrylate (CH.sub.2.dbd.CH--CO--O--) or acrylamide group
(CH.sub.2.dbd.CH--CO--NH--); HG is --COOH; Y is not present or is a
straight-chained aliphatic residue with 2 to 10 carbon atoms, a
branched aliphatic residue with 3 to 12 carbon atoms, a
cycloaliphatic, bi- or tricylic or aromatic residue with 6 to 15
carbon atoms or a combination of these residues; Z is not present
or is a straight-chained aliphatic residue with 2 to 10 carbon
atoms, a branched aliphatic residue with 3 to 12 carbon atoms, a
cycloaliphatic, bi- or tricylic or aromatic residue with 6 to 15
carbon atoms, a combination of these residues or an oligoethylene
glycol (--(CH.sub.2--CH.sub.2--O).sub.n--, n=1-5) or an
oligopropylene glycol residue
(--(CH(CH.sub.3)--CH.sub.2--O).sub.n--, n=1-5); a is 1, 2 or 3; and
b is 1.
3. Slip according to claim 2, wherein the variables of formula (I)
have the following meaning: X is not present or is an (a+b)-valent,
unsubstituted, branched or straight-chained aliphatic residue with
3 to 15, preferably 3 to 8 carbon atoms, which residue can contain
1 or 2 ether groups; PG is an acrylate or acrylamide group; HG is
--COOH; Y is a divalent, straight-chained aliphatic group with 2 to
8 carbon atoms or a branched aliphatic group with 3 to 8 carbon
atoms, wherein these groups can contain 1 ester group; Z is a
divalent, straight-chained aliphatic group with 2 to 10 carbon
atoms or a branched aliphatic group with 3 to 10 carbon atoms,
wherein these groups can contain 1 or more, preferably 0 to 3,
ether groups; a is 1, 2 or 3; and b is 1.
4. Slip according to claim 1, which further comprises D) 0.001 to
1.0 wt.-% inhibitor, relative to the total mass of the slip.
5. Slip according to claim 1, which further comprises 0 to 20 wt.-%
debinding accelerator (E), 0 to 20 wt.-% plasticizer and 0 to 70
wt.-% solvent, in each case relative to the total mass of radically
polymerizable components.
6. Slip according to claim 1, which further comprises F) 0.00001 to
2.0 wt.-% coloring components, relative to the mass of component
(C).
7. Slip according to claim 1, which comprises as component (C)
glass ceramic particles or ceramic particles based on pure
ZrO.sub.2, pure Al.sub.2O.sub.3, pure ZrO.sub.2--Al.sub.2O.sub.3,
ZrO.sub.2 which is stabilized with HfO.sub.2, CaO, Y.sub.2O.sub.3,
CeO.sub.2 and/or MgO, ZrO.sub.2--Al.sub.2O.sub.3 which is
stabilized with HfO.sub.2, CaO, Y.sub.2O.sub.3, CeO.sub.2 and/or
MgO or non-oxide ceramics.
8. Slip according to claim 1, wherein the particles of component
(C) are surface-modified with a linear or branched carboxylic acid,
in particular formic acid, acetic acid, propionic acid, octanoic
acid, isobutyric acid, isovaleric acid or pivalic acid; an acidic
phosphoric acid ester, in particular dimethyl, diethyl, dipropyl,
dibutyl, dipentyl, dihexyl, dioctyl or di(2-ethylhexyl)phosphate; a
phosphonic acid, in particular methyl, ethyl, propyl, butyl, hexyl,
octyl or phenyl phosphonic acid; or a silane, in particular
propyltrimethoxysilane, phenyltrimethoxysilane,
hexyltrimethoxysilane, octyltrimethoxysilane,
trimethylchlorosilane, trimethylbromosilane, trimethylmethoxysilane
or hexamethyldisilazane, wherein the surface-modification agent
does not contain radically polymerizable groups.
9. Slip according to claim 1, wherein the particles of component
(C) have a particle size in the range from 20 nm to 50 .mu.m.
10. Slip according to claim 5, which comprises as debinding
accelerator (E) a chain transfer agent, in particular a mercaptan,
a disulphide or a photoiniferter, preferably lauryl mercaptan, a
dithiourethane disulphide, tetramethylthiuram disulphide or
isopropylxanthogenic acid disulphide; and/or a comonomer which has
one or more thermally labile groups, in particular one or more
peroxide, azo or urethane groups; and/or a comonomer with a ceiling
temperature of -10 to 150.degree. C., in particular
.alpha.-methylstyrene, polytetrahydrofuran (PTHF), or a telechel
with radically polymerizable groups, in particular a PTHF
di(meth)acrylate telechel.
11. Slip according to claim 6, which comprises as coloring
component (F) a transition metal compound, in particular an acetyl
acetonate and/or a carboxylic acid salt of the elements iron,
cerium, praseodymium, terbium, lanthanum, tungsten, osmium, terbium
and manganese, in particular iron (III) acetate or iron (III)
acetyl acetonate, manganese (III) acetate or manganese (III) acetyl
acetonate, praseodymium (III) acetate or praseodymium (III) acetyl
acetonate or terbium (III) acetate or terbium (III) acetyl
acetonate.
12. Slip according to claim 1, which further comprises at least one
further component from the group of dispersants, defoaming agents,
and antiskinning agents.
13. Slip according to claim 1, which comprises at most 40 wt.-% of
multifunctional monomers relative to the total mass of radically
polymerizable components.
14. Process of using the slip according to claim 1 for the
preparation of ceramic or glass ceramic shaped articles.
15. Process according to claim 14, wherein the ceramic shaped
article is a dental restoration, such as an inlay, onlay, veneer,
crown, bridge or framework.
16. Process for the preparation of a ceramic or glass ceramic
shaped article, wherein (a) a green body is prepared by curing a
slip according to claim 1 by local introduction of radiation energy
with formation of the geometric shape of the green body, (b) the
green body is then subjected to a heat treatment to remove the
binder (debinding), in order to obtain a white body, and (c) the
white body is sintered.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of European Patent
Application No. 10007066.3 filed Jul. 8, 2010, which are hereby
incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to light-curing ceramic slips
for the stereolithographic preparation of high-strength ceramics,
such as ceramic shaped parts or articles, dental inlays, onlays,
veneers, crowns, bridges and frameworks.
BACKGROUND
[0003] The term "rapid prototyping" (RP) covers generative
manufacturing processes in which 3-dimensional models or components
are prepared from computer-aided design data (CAD data) (A.
Gebhardt, Vision of Rapid Prototyping, Ber. DGK 83 (2006) 7-12).
These are processes, such as stereolithography (SL), selective
laser sintering (SLS), 3D printing, fused deposition modelling
(FDM), ink-jet printing (IJP), 3D plotting, multi-jet modelling
(MJM), solid freeform fabrication (SFF), laminated object
manufacturing (LOM), laser powder forming (LPF) and direct ceramic
jet printing (DCJP), with which models, components or shaped parts
can be prepared cheaply even on a small scale (A. Gebhardt,
Generative Fertigungsverfahren, 3rd edition, Carl Hanser Verlag,
Munich 2007, 77 et seq.). Stereolithography involves RP processes
(A. Beil, Fertigung von Mikro-Bauteilen mittels Stereolithographie,
Dusseldorf 2002, VDI-Verlag 3 et seq.) in which a shaped part is
constructed in layers from a liquid and curable monomer resin on
the basis of CAD data.
[0004] Stereolithographic processes for the preparation of dental
shaped articles, such as inlays, crowns or bridges, are highly
advantageous particularly with ceramic materials, because the
impression-taking and casting processes and the grinding and
milling operations, respectively, which involve considerable manual
outlay in the dental laboratory, can thus be greatly simplified and
at the same time the large material loss which occurs with
non-generative processes can be avoided. As a complete digital
process chain is in place today, the standard process steps for the
preparation of e.g. multi-unit bridge frameworks (alignment in the
articulator, wax modulation, embedding and casting) can be replaced
by the digitalization of the model, the virtual design of the
dental shaped article and its generative stereolithographic
manufacture.
[0005] In the stereolithographic preparation of ceramic shaped
parts a ceramic green compact is firstly prepared by radiation
curing layer-by-layer of a free-flowing ceramic slip which is then
sintered after debinding to form a dense ceramic shaped article.
The green compact is also referred to as a green body. The term
debinding is used to describe the elimination of the binder. In
this step, the binder employed is usually removed by heating the
green compact to a temperature of about 90.degree. C. to
600.degree. C. It is essential that the formation of cracks and
deformations are very largely avoided. The green body becomes the
so-called white body as a result of the debinding.
[0006] In debinding, purely thermal as well as thermochemical
processes take place. Mixtures of water, solvents, polymers, waxes
or oils are usually employed as binders in the pressing of ceramic
powders. Polypropylene, polyethylene, polyvinyl acetate, polyvinyl
alcohol, methylcellulose, polyvinylpyrrolidone, polystyrene or
polyethyl methacrylate are most often used as polymers (cf. R.
Moreno, Amer. Cer. Soc. Bull. 71 (1992) 1647-1657). These are
linear polymers which are broken down more or less easily at
increased temperature into volatile components through
depolymerization or chain-splitting.
[0007] The sintering of the white body takes place in the sintering
furnace during high-temperature firing. This results in a
compacting and solidifying of the finely-dispersed ceramic powder
by exposure to a temperature below the melting temperature of the
main components, whereby the porous body becomes smaller and its
strength increases.
[0008] EP 1 021 997 A2 and US 2005056350 (A1), which is hereby
incorporated by reference, describe the use of the laser-sintering
process for the preparation of dental restorations. Here, metal
powders are sintered in layers using a laser. US
[0009] DE 101 14 290 A1 and U.S. Pat. No. 6,939,489, which is
hereby incorporated by reference, relate to the preparation of
dental shaped parts by 3D plotting using materials that are
meltable, condensable, curable thermally or with UV or visible
light, filled or unfilled. For the preparation of green bodies
inorganic pastes are proposed which are composed of glass, glass
ceramic or ceramic powder, which is converted into a shapable paste
with solvent, binder and plasticizer. The powders used are not
surface-modified.
[0010] WO 97/29901, which is hereby incorporated by reference,
describes a process and an apparatus for the preparation of
3-dimensional components from a liquid, curable medium. The
component is constructed in layers by scanning each individual
layer with a laser and curing it. The next layer of the curable
material is then deposited by means of a coating device and then
likewise cured.
[0011] A stereolithographic process for the preparation of dental
implants is known from WO 95/28688and U.S. Pat. No. 5,768,134,
which is hereby incorporated by reference.
[0012] U.S. Pat. No. 5,496,682, which is hereby incorporated by
reference, discloses light-curable compositions for the preparation
of three-dimensional bodies by stereolithography, which contain 40
to 70 vol.-% ceramic or metal particles, 10 to 35 wt.-% monomer, 1
to 10 wt.-% photoinitiator, 1 to 10 wt.-% dispersant and preferably
also solvent, plasticizer and coupling agent.
[0013] U.S. Pat. No. 6,117,612, which is hereby incorporated by
reference, describes resins for the stereolithographic preparation
of sintered ceramic or metal parts. The resins have a viscosity of
less than 3000 mPas. For their preparation, monomers with a low
viscosity are used, preferably in aqueous solution. A high solids
content and low viscosity are said to be achieved through the use
of dispersants.
[0014] DE 10 2005 058 116 A1, which is hereby incorporated by
reference, discloses suspensions for the stereolithographic
preparation of ceramic implants in the manner described in U.S.
Pat. No. 6,117,612, which is hereby incorporated by reference,
which do not contain diluents such as water or organic solvents, as
the latter are said to increase the viscosity through local
evaporation when energy is introduced. The viscosity of the
suspension is adjusted to less than 20 Pas by varying the
concentration of a dispersant. Alkyl ammonium salts of copolymers
with acidic groups are used as dispersants, which can also be
coated onto the particles of the ceramic powder.
[0015] Methods and compositions for the stereolithographic
preparation of ceramic components are described in US 2005/0090575
A1, which is hereby incorporated by reference. It is stated that
shaped parts prepared with the liquid materials known from U.S.
Pat. No. 5,496,682, which is hereby incorporated by reference, are
soft and therefore require an additional curing step in order to
avoid deformations during firing, while shaped articles obtained
from paste-like materials develop internal stresses during
debinding which lead to cracks during sintering. To avoid these
problems, plasticizers are used and the quantity of ceramic powder
is chosen such that the viscosity of the compositions is at least
10,000 Pas.
[0016] Compositions curable with visible light and their use for
the preparation of dental restorations from plastic materials by RP
processes are described in DE 199 38 463 A1 and DE 199 50 284 A1,
which are hereby incorporated by reference.
[0017] For the preparation of high-strength ceramics, the process
chain must be carried out in such a way that cracks, separated
layers, pores and other defects or deformations do not occur during
the preparation of the green body, brown body and white body. In
this regard, the composition and the properties of the
radiation-curable slip are of decisive importance. Thus as high as
possible a proportion by volume of the ceramic particles in the
slip is required in particular for a high density and final
strength as well as good accuracy of fit of the ceramic shaped
part. Furthermore, a properly adjusted rheology of the slip is a
basic requirement for a rapid and problem-free stereolithographic
construction of a green body with few defects, wherein however the
viscosity and the flow behaviour depend among other things on the
size and the content of the ceramic particles in the slip as well
as on the type and quantity of added rheology additives.
[0018] The stability of the stereolithographically produced green
bodies can be improved by using cross-linking monomers. The curing
time which is required to obtain a stable solid can thereby be
significantly shortened. However, at the same time, the polymer
network that forms also displays a much higher thermal stability
compared with linear polymers, which adversely affects the
debinding process. Moreover, the polymerization shrinkage increases
with the functionality of the monomers which can lead to
considerable shrinkage stresses. As a result, green bodies, brown
bodies and sintered white bodies which have porosities and defects
are often obtained even during optimized processing methods. A
particular problem with the stereolithographic preparation of
shaped articles is that the individual layers do not adhere to each
other sufficiently, which can lead to delamination.
[0019] The known slips fail to satisfy the above-named
requirements. The object of the invention is therefore to provide
light-curing ceramic slips for the stereolithographic preparation
of ceramic shaped parts, which display a good stereolithographic
processability, result in sufficiently strong and dimensionally
stable green bodies and, after debinding and sintering, lead to
defect-free, high-strength ceramics. In particular, delamination is
to be prevented.
SUMMARY
[0020] This object is achieved according to the invention by slips
based on radically polymerizable binder, polymerization initiator
and filler which comprise the following components: [0021] A) 1 to
30 wt.-% of at least one acidic monomer of general formula I
[0021] (HG-Y--).sub.aX Z--PG).sub.b Formula I [0022] in which
[0023] X is not present or is an (a+b)-valent, substituted or
unsubstituted, straight-chained aliphatic residue with at least 2,
preferably 3 to 15 carbon atoms, a branched aliphatic residue with
at least 3, preferably 3 to 15 carbon atoms, a cycloaliphatic, bi-
or tricylic or aromatic residue with 6 to 20, preferably 6 to 15
carbon atoms or a combination of these residues, preferably is an
aromatic or cycloaliphatic C.sub.6 residue and in particular is a
straight-chained or branched aliphatic C.sub.3-C.sub.15 residue,
particularly preferably a C.sub.3-C.sub.8 residue, wherein these
groups can contain 1 or more ether groups; [0024] PG is a radically
polymerizable group, preferably a vinyl (CH.sub.2.dbd.CH--), allyl
(CH.sub.2.dbd.CH--CH.sub.2--), allyl ether
(CH.sub.2.dbd.CH--CH.sub.2--O--), styryl (CH.sub.2.dbd.CH-phenyl),
(meth)acrylate (CH.sub.2.dbd.C(--H/--CH.sub.3)--CO--O--) or
(meth)acrylamide group (CH.sub.2.dbd.C(--H/--CH.sub.3)--CO--NH-- or
CH.sub.2.dbd.C(--H/--CH.sub.3)--CO--NR-- with R.dbd.C.sub.1-C.sub.4
alkyl), particularly preferably a (meth)acrylate or
(meth)acrylamide group and quite particularly preferably an
acrylate (CH.sub.2.dbd.CH--CO--O--) or acrylamide group
(CH.sub.2.dbd.CH--CO--NH--); [0025] HG is --COOH--, --PO(OH).sub.2,
--O--PO(OH).sub.2 or --SO.sub.3H, preferably --COOH; [0026] Y is
not present or is a divalent, straight-chained aliphatic group with
2 to 40 carbon atoms, a branched aliphatic group with 3 to 40
carbon atoms or a cycloaliphatic or aromatic group with 5 to 40
carbon atoms, wherein Y can contain one or more ether, thioether,
amide and/or ester groups, preferably a straight-chained aliphatic
residue with 2 to 10 carbon atoms, a branched aliphatic residue
with 3 to 12 carbon atoms, a cycloaliphatic, bi- or tricylic or
aromatic residue with 6 to 15 carbon atoms or a combination of
these residues; [0027] Z is not present or is a divalent,
straight-chained aliphatic group with 2 to 40 carbon atoms or a
branched aliphatic group with 3 to 40 carbon atoms, wherein Z can
contain one or more ether, thioether, amide and/or ester groups,
preferably a straight-chained aliphatic residue with 2 to 10 carbon
atoms, a branched aliphatic residue with 3 to 12 carbon atoms, a
cycloaliphatic, bi- or tricylic or aromatic residue with 6 to 15
carbon atoms, a combination of these residues or an oligoethylene
glycol (--(CH.sub.2--CH.sub.2--O).sub.n--, n=1-5) or an
oligopropylene glycol residue
(--(CH(CH.sub.3)--CH.sub.2--O).sub.n--, n=1-5); [0028] a is an
integer from 1 to 5, preferably 1, 2 or 3; and [0029] b is 1 or 2,
preferably 1; [0030] A2) 0 to 50 wt.-% of at least one non-acidic
radically polymerizable monomer; [0031] B) 0.001 to 2.0 wt.-%
photoinitiator; and [0032] C) 30 to 90 wt.-% ceramic and/or glass
ceramic particles; in each case relative to the total mass of the
slip.
[0033] The ester groups optionally present in Y and/or Z preferably
have 1 to 4 carbon atoms. The amide nitrogen of the
(meth)acrylamide groups can be substituted by alkyl, preferably
C.sub.1-C.sub.3 alkyl.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Embodiments of the present invention will be more fully
understood and appreciated by the following Detailed Description in
conjunction with the accompanying drawings, in which: FIG. 1 shows
a schematic representation of a device for carrying out the process
according to the invention.
DETAILED DESCRIPTION
[0035] The slips according to the invention comprise, as radically
polymerizable binder, at least one acidic monomer according to
general formula (I) (component A), preferably a mixture of at least
one acidic monomer and at least one non-acidic monomer (component
A2). In the following, the acidic monomer is also referred to as
adhesive monomer and the non-acidic monomer as comonomer.
[0036] It was surprisingly found that the slips according to the
invention have only a low polymerization shrinkage and thus allow
the preparation of dimensionally stable, flexible green bodies with
good dimensional stability and low deformation stress. The slips
result in defect-free green bodies which are characterized by an
excellent adhesion between the individual stereolithographically
produced layers. After debinding and sintering of the green bodies,
high-strength ceramic or glass ceramic shaped parts are obtained
which are suitable in particular for dental purposes. Furthermore,
it was very surprisingly shown that monofunctional adhesive
monomers of formula (I) also have an exceptionally high radical
photopolymerization activity. By monofunctional monomers are meant
monomers with one radically polymerizable group and by
multifunctional monomers are meant monomers with two or more
radically polymerizable groups. Monomers with two or more radically
polymerizable groups effect a cross-linking and are therefore also
called cross-linking monomers.
[0037] Monomers that contain COOH groups can be obtained e.g. by
stoichiometric addition of hydroxyalkyl(meth)acrylates or
N-(hydroxyalkyl)(meth)acrylamides to aliphatic, cycloaliphatic, bi-
or tricyclic or aromatic di-, tri- or tetracarboxylic acid
anhydrides. Anhydrides of dicarboxylic acids are preferred.
Hydroxyalkyl(meth)acrylates or N-(hydroxyalkyl)(meth)acrylamides
suitable for this are for example 2-hydroxyethyl(meth)acrylate,
2-hydroxypropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate,
10-hydroxydecyl(meth)acrylate, OH-terminated poly(ethylene glycol)
or poly(propylene glycol)mono(meth)acrylate,
.alpha.-hydroxymethylacrylic acid ethyl ester,
N-(2-hydroxyethyl)(meth)acrylamide,
N-methyl-N-(2-hydroxyethyl)acrylamide,
N-(5-hydroxypentyl)(meth)acrylamide or
N-(10-hydroxy-decyl)(meth)acrylamide. Preferred dicarboxylic acid
anhydrides are succinic, maleic, fumaric acid or glutaric
anhydride, cyclohexane-1,2-dicarboxylic acid anhydride,
1,2-cyclopropanedicarboxylic acid anhydride,
norbornene-2,3-dicarboxylic acid anhydride, the Diels-Alder adduct
of maleic anhydride and 1,3-cyclopentadiene or phthalic anhydride.
Furthermore, COOH-containing monomers can be synthesized by
ring-opening addition of di- or higher functionalized carboxylic
acids, such as oxalic, malonic, succinic, glutaric, adipic,
sebacic, pimelic, suberic, maleic, terephthalic, isophthalic,
phthalic, cyclohexane dicarboxylic, gallic, tartaric, or citric
acid to e.g. glycidyl (meth)acrylate or 4-vinyl-1-cyclohexene
1,2-epoxide or are obtainable as half-esters by esterification of
the above-mentioned hydroxyalkyl(meth)acrylates or
N-(hydroxyalkyl)(meth)acrylamides with the listed dicarboxylic
acids.
[0038] Examples of suitable acidic polymerizable phosphoric acid
esters (HG=--O--PO(OH).sub.2) are 2-methacryloyloxypropyldihydrogen
phosphate, 2-methacryloyloxyethyldihydrogen phosphate,
10-methacryloyloxydecyldihydrogen phosphate,
6-(methacrylamido)hexyldihydrogen phosphate and
1,3-bis-(N-acryloyl-N-propyl-amino)-propan-2-yl-dihydrogen
phosphate.
[0039] Examples of suitable phosphonic acid monomers
(HG=--PO(OH).sub.2) are vinylphosphonic acid,
4-vinylphenylphosphonic acid, 4-vinylbenzylphosphonic acid,
2-methacryloyloxyethylphosphonic acid,
2-methacrylamidoethylphosphonic acid,
4-methacrylamido-4-methyl-pentyl-phosphonic acid or
2-[4-(dihydroxyphosphoryl)-2-oxa-butyl]-acrylic acid.
[0040] Examples of suitable polymerizable sulphonic acids
(HG=--SO.sub.3H) are vinyl sulphonic acid, 4-vinylphenyl sulphonic
acid or 3-(methacrylamido)propyl sulphonic acid.
[0041] Preferred are monomers that contain COOH groups (HG=COOH),
and above all reaction products of hydroxyalkyl acrylates, such as
hydroxyethyl or hydroxypropyl acrylate, with aliphatic,
cycloaliphatic or aromatic carboxylic acid anhydrides, in
particular with succinic, glutaric, cyclohexane-1,2-dicarboxylic
acid or phthalic anhydride.
[0042] Particularly preferred are monomers with COOH groups
(HG=COOH) which have vinyl, allyl, allyl ether, styryl,
(meth)acrylate or (meth)acrylamide groups as polymerizable group(s)
PG, in particular (meth)acrylate or (meth)acrylamide residues,
wherein acrylate or acrylamide residues are quite particularly
preferred.
[0043] Particularly preferred are monomers according to formula (I)
in which the variables independently of each other have the
following meanings: [0044] X is not presently or is an
(a+b)-valent, unsubstituted, branched or straight-chained aliphatic
residue with 3 to 15, preferably 3 to 8 carbon atoms, which can
contain 1 or 2 ether groups; [0045] PG is an acrylate or acrylamide
group, [0046] HG is --COOH, [0047] Y is a divalent,
straight-chained aliphatic group with 2 to 8 carbon atoms or a
branched aliphatic group with 3 to 8 carbon atoms, wherein these
groups can contain 1 ester group, and [0048] Z is a divalent,
straight-chained aliphatic group with 2 to 10 carbon atoms or a
branched aliphatic group with 3 to 10 carbon atoms, wherein these
groups can contain 1 or more, preferably 0 to 3, ether groups,
[0049] a is 1, 2 or 3, and [0050] b is 1.
[0051] According to the invention, monomers of formula (I) in which
all the variables have one of the preferred or particularly
preferred meanings are particularly preferred.
[0052] The radically polymerizable binder preferably comprises at
least one non-acidic monomer A2. In the radically polymerizable
resins, mono- or multifunctional(meth)acrylates, (meth)acrylamides,
vinyl monomers or mixtures thereof can in particular be used as
non-acidic comonomers. Examples of (meth)acrylates are ethyl,
hydroxyethyl, hydroxypropyl, butyl, benzyl, tetrahydrofurfuryl or
isobornyl(meth)acrylate, bisphenol-A-di(meth)acrylate, bis-GMA (an
addition product of methacrylic acid and bisphenol-A-diglycidyl
ether), addition products of 2-hydroxyalkyl(meth)acrylate and
diisocyanates, such as hexamethylene diisocyanate or
2,2,4-trimethylhexamethylene diisocyanate, di-, tri- or
tetraethylene glycol di(meth)acrylate, (meth)acrylate-terminated
poly(ethylene glycols) or poly(propylene glycols),
trimethylolpropane tri(meth)acrylate, pentaerythritol
tetra(meth)acrylate, as well as glycerol di- and tri(meth)acrylate,
1,4-butanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate
or 1,12-dodecanediol di(meth)acrylate.
[0053] Preferred examples of (meth)acrylamides are N-ethyl
acrylamide, N,N-dimethacrylamide, N-(2-hydroxyethyl)acrylamide,
N-methyl-N-(2-hydroxyethyl)acrylamide, N-ethyl methacrylamide or
N-(2-hydroxyethyl)methacrylamide,
N,N'-diethyl-1,3-bis(acrylamido)propane,
1,3-bis(methacrylamido)propane, 1,4-bis(acrylamido)-butane or
1,4-bis(acryloyl)piperazine. Suitable vinyl monomers are
N-vinylpyrrolidone or vinyl acetate.
[0054] The slips according to the invention preferably comprise
less than 40 wt.-% and particularly preferably less than 20 wt.-%
cross-linking monomers relative to the total mass of radically
polymerizable components.
[0055] The ceramic slips or glass ceramic slips according to the
invention can comprise, as components B, the known radical
photoinitiators (cf. J. P. Fouassier, J. F. Rabek (ed.), Radiation
Curing in Polymer Science and Technology, vol. II, Elsevier Applied
Science, London and New York 1993, which is hereby incorporated by
reference,) for the visible range, such as acyl or bisacyl
phosphine oxides, titanocene photoinitiators, such as
bis(.eta..sup.5-cyclopentadienyl)bis[2,6-difluoro-3-(1H-pyrr-1-yl)phenylt-
itanium or
bis(.eta..sup.5-methylcyclopentadienyl)bis[2,3,4,5,6-pentafluor-
ophenyl)-titanium, but above all .alpha.-diketones, such as
9,10-phenanthrenequinone or diacetyl, furil, or 4,4'-dialkoxybenzil
and camphorquinone. Furthermore, suitable photoinitiators for the
visible range are combinations of photoreducible dyes, such as
acridine, xanthene, azine or polymethine dyes with accelerators,
such as phosphines, sulphinates, enolates or suitable borates (cf.
J. V. Crivello, K. Dietliker, Photoinitiators for Free Radical,
Cationic & Anionic Photopolymerization, 2nd Ed., In: Surface
Coating Technology, Editor: G. Bradley, Vol. III, Wiley & Sons,
Chichester etc. 1998, 239 et seq., which is hereby incorporated by
reference). Particularly suitable are amine-free Norrish type I
photoinitiators which absorb above 400 nm, above all
monoacyltrialkyl or diacyldialkyl germanium compounds, such as
benzoyltrimethylgermanium, dibenzoyldiethylgermanium or
bis(4-methoxybenzoyl)diethylgermanium as well as bisacyl phosphine
oxides which all lead to a high polymerization rate even without
amine accelerator. Mixtures of the different photoinitiators can
also be used, such as mixtures of dibenzoyl diethyl germanium
combined with a bisacyl phosphine oxide.
[0056] Reducing agents, such as 4-(dimethylamino)-benzoic acid
ester, N,N-dimethylaminoethyl methacrylate,
N,N-dimethyl-sym.-xylidine or triethanolamine can be used as
accelerators for .alpha.-diketones. Further accelerators are
ascorbic acid, barbiturates or sulphinic acids, which are
advantageous above all in combination with suitable peroxides.
Moreover, known cationic photoinitiators, such as diaryliodonium or
triarylsulphonium salts, can also be used as accelerators.
[0057] Photoinitiators are preferably used in an amount of
0.001-2.0 wt.-%, particularly preferably 0.01-1 wt.-%, and
accelerators in an amount of 0 to 2.0 wt.-%, particularly
preferably 0.01 to 1 wt.-%.
[0058] The slips according to the invention comprise as component C
ceramic and/or glass ceramic particles.
[0059] By ceramics are meant inorganic materials which have a
crystalline structure and are usually prepared from corresponding
powders. The preparation of the ceramic preferably takes place by
sintering (sintered ceramic). Oxide ceramics are preferably
obtained by sintering metal oxide powders such as ZrO.sub.2 or
Al.sub.2O.sub.3. In addition, oxide ceramics can also contain one
or more glass phases. Glass ceramics are materials which are
usually prepared from amorphous glasses, in particular silicate
glasses, by controlled crystallization and in which a glass phase
and one or more crystal phases are present simultaneously in the
solid. In the case of sinterable glass ceramics, both glass powders
and glass ceramic powders can be used as a starting material.
[0060] Preferred are sinterable glass ceramic particles based on
leucite- or lithium disilicate-reinforced glasses and/or ceramic
particles based on ZrO.sub.2 or Al.sub.2O.sub.3, preferably pure
ZrO.sub.2 or pure Al.sub.2O.sub.3, particles based on ZrO.sub.2
stabilized with HfO.sub.2, CaO, Y.sub.2O.sub.3, CeO.sub.2 and/or
MgO, particles based on other metal oxides and also ceramic
composite materials which are prepared from several oxides and are
thus constructed from various crystalline oxide phases, preferably
ZrO.sub.2--Al.sub.2O.sub.3, in particular pure
ZrO.sub.2--Al.sub.2O.sub.3 or ZrO.sub.2--Al.sub.2O.sub.3 stabilized
with HfO.sub.2, CaO, Y.sub.2O.sub.3, CeO.sub.2 and/or MgO.
[0061] The term "pure" is to be understood to mean "chemically
pure", i.e. a ZrO.sub.2 or Al.sub.2O.sub.3 ceramic is constructed
only from ZrO.sub.2 or Al.sub.2O.sub.3 respectively. In addition to
the base oxide such as ZrO.sub.2 or Al.sub.2O.sub.3, stabilized
ceramics contain a stabilizer which is preferably selected from
HfO.sub.2, CaO, Y.sub.2O.sub.3, CeO.sub.2, MgO and mixtures
thereof. The stabilizer is preferably used in a quantity of 3 to 5
wt.-%, relative to the mass of the stabilized ceramic.
High-strength ZrO.sub.2 ceramics preferably contain 3 to 5 wt.-%
Y.sub.2O.sub.3 (yttrium oxide) to stabilize the tetragonal crystal
structure. This ZrO.sub.2 ceramic is referred to as Y-TZP
(yttrium-stabilized tetragonal zirconium dioxide polycrystals).
Ceramic particles which comprise only base oxide and stabilizer are
particularly preferred.
[0062] The above-mentioned ceramic and glass ceramic particles are
suitable in particular for dental applications. In addition,
particles of non-oxide ceramics can also be used in particular for
non-dental purposes. Preferred non-oxide ceramics are carbides,
above all silicon carbide or boron carbide, nitrides, in particular
silicon, aluminium or boron nitride, borides and/or silicides.
[0063] The particle size of component C is preferably in the range
from 20 nm to 50 .mu.m. It depends on the ceramic used. In the case
of Al.sub.2O.sub.3, the size of the particles used as component C
is preferably in the range from 20 to 5000 nm, particularly
preferably between 75 and 200 nm; in the case of glass ceramic in
the range from 100 nm to 50 .mu.m, quite preferably between 0.1 and
10 .mu.m; in the case of Y-TZP zirconium dioxide in the range from
20 to 5000 nm, quite preferably between 50 and 3500 nm. The
particle size is preferably chosen such that sedimentation-stable
slips are obtained. The particle sizes are the absolute upper and
lower limits.
[0064] Furthermore, ceramic or glass ceramic particles with a
particle size in the range from 10-200 nm can also be used as nano-
or organosols, i.e. as a dispersion of the nanoparticles in a
solvent, a suitable monomer of component A or a mixture
thereof.
[0065] In a preferred embodiment of the invention, the particles
are surface-modified with suitable substances. Compounds which are
chemically bound, i.e. by ionic or covalent bonds, to the surface
of the ceramic or glass ceramic particles are preferably used for
the surface modification. Compounds which contain either acid
groups, preferably carboxylic acid, phosphonic acid, hydrogen
phosphate groups or acidic phosphoric acid ester groups, or silyl
groups, preferably alkoxysilyl groups, are preferred. The particle
surface can be partially or preferably completely covered with the
modification agent. The modification agents used according to the
invention are monomeric compounds.
[0066] Compounds which, unlike the so-called adhesion promoters or
coupling reagents, contain groups only reacting with the particle
surface but not polyreactive groups such as radically polymerizable
groups, e.g. (meth)acryl, (meth)acrylamide, vinyl, vinyl ether or
epoxide groups which form a covalent bond with the resin matrix
(A), are particularly suitable according to the invention. Such
compounds are referred to as non-polymerizable surface modifiers
herein. These compounds have the advantage that a stable bond does
not form between the ceramic particle surface and the polymer
matrix in the cured green body, which simplifies the complete
removal of the polymer portions in the debinding process.
[0067] Linear or branched carboxylic acids, such as formic acid,
acetic acid, propionic acid, octanoic acid, isobutyric acid,
isovaleric acid, pivalic acid, acidic phosphoric acid esters, such
as dimethyl, diethyl, dipropyl, dibutyl, dipentyl, dihexyl, dioctyl
or di(2-ethylhexyl)phosphate, or phosphonic acids, such as methyl,
ethyl, propyl, butyl, hexyl, octyl or phenyl phosphonic acid, are
particularly suitable as non-polymerizable surface modifiers.
Silanes suitable as non-polymerizable surface modifiers are for
example propyltrimethoxysilane, phenyltrimethoxysilane,
hexyltrimethoxysilane, octyltrimethoxysilane,
trimethylchlorosilane, tri-methylbromosilane,
trimethylmethoxysilane or hexamethyldisilazane.
[0068] According to a preferred embodiment, the slips according to
the invention comprise as component D an inhibitor as stabilizer to
prevent a spontaneous polyreaction. The inhibitors or stabilizers
improve the storage stability of the slips and also prevent an
uncontrolled polyreaction in the stereolithographic tank. The
inhibitors are preferably added in such an amount that the slips
are storage-stable over a period of about 2-3 years. The inhibitors
are preferably used in an amount of 0.001 to 1.0 wt.-%,
particularly preferably 0.001 to 0.50 wt.-%, in each case relative
to the total mass of the slip.
[0069] Phenols such as hydroquinone monomethyl ether (MEHQ) or
2,6-di-tert-butyl-4-methyl-phenol (BHT), which are really effective
only in the presence of oxygen and are usually employed in a
concentration range from 200-2000 ppm are used as so-called aerobic
inhibitors for radical reaction resins. Anaerobic inhibitors, such
as phenothiazine, 2,2,6,6-tetramethyl-piperidine-1-oxyl radical
(TEMPO), iodine, copper(I) iodide, on the other hand, are effective
in smallest concentrations (10-50 ppm) even in the absence of
oxygen. A polymerisation normally takes place only when these
additives are consumed. It is often also advantageous to use a
mixture of aerobic and anaerobic inhibitors.
[0070] Aerobic inhibitors are preferably used in an amount of 0.01
to 0.50 wt.-% and anaerobic inhibitors in an amount of 0.001 to
0.02 wt.-%, each relative to the total mass of the slip. Preferred
mixtures comprise 0.02 to 0.2 wt.-%, in particular 0.01 to 0.10
wt.-% aerobic inhibitors and/or 0.001 to 0.01 wt.-% anaerobic
inhibitors, again relative to the total mass of the slip.
[0071] Furthermore, to avoid scattering effects or to adjust the
through-curing depth, suitable dyes can be added which absorb above
all in the wavelength range of the photoinitiators or sensitizers
used, above all azo and acridine dyes. Specific examples of these
are 2,4-dihydroxy-4-nitroazobenzene, Sudan Yellow 146, Sudan Orange
220, Sudan M Red 380, Sudan Yellow 177 liquid. Finally, organic
white pigments or matting agents, such as e.g. based on PE waxes,
polyamide 12 or polymethyl urea resins, can also be used to avoid
scattering effects or to adjust the through-curing depth. The
absorption of the slip can be influenced in a controlled manner
(reduced) by the mentioned dyes and the over-radiation caused by
scattering effects or too small an absorption of the slip can
thereby be minimized. Scattering and over-radiation can have a
disadvantageous effect on the shape fidelity of the
stereolithographically prepared component.
[0072] According to a further preferred embodiment of the
invention, the slips comprise a so-called debinding accelerator as
component E. This is preferably used in an amount of 0 to 20 wt.-%,
particularly preferably 0.01 to 10 wt.-%, in each case relative to
the total mass of the slip. By debinding accelerators are meant
substances which facilitate the removal of the binder during the
debinding process.
[0073] The debinding of the green compact can be promoted or
influenced in targeted manner by suitable, i.e. polyreactively
effective, substances in the polyreaction resin. On the one hand,
these are additives which influence the network formation, such as
in particular chain-transfer-active substances, so-called chain
transfer agents, which result in a reduction in the polymer network
density and thus in a better thermal decomposability. Known chain
transfer agents e.g. for radical polymerization are in particular
mercaptans, such as e.g. lauryl mercaptan, and disulphides.
Disulphides, in particular dithiourethane disulphides, such as
tetramethyl-thiuram disulphide or isopropylxanthogenic acid
disulphide, act as so-called photoiniferters in radical
photopolymerization. These are compounds which both act as
photoinitiator (photoini-) and participate in transfer reactions
(-fer-) and termination reactions (-ter) (cf. T. Otsu, M. Yoshida,
Makromol. Chem., Rapid. Commun. 3 (1982) 127-132: Role of
Initiator-Transfer Agent-Terminator (Iniferter) in Radical
Polymerizations: Polymer Design by Organic Disulfides as
Iniferters, which is hereby incorporated by reference). The
addition of chain-transfer-active substances, i.e. chain transfer
agents or photoiniferters, effects a reduction of the network
density of the polyreaction network with a virtually unchanged
reactivity of the polyreaction resin mixture. Chain transfer agents
and photoiniferters are preferably used in an amount of 0.005 to 2
wt.-% each and particularly preferably 0.01 to 1.0 wt.-%, relative
to component (A).
[0074] According to the invention, comonomers which result in a
reduction in the thermal stability of polymer networks can
advantageously also be used as debinding accelerators. Comonomers
which contain thermally labile groups, such as peroxide, azo or
urethane groups, which are incorporated into the polymer network
during the stereolithographic process and then accelerate the
degradation of the polymer network in the thermal debinding process
are suitable for this. A preferred example of a polymerizable
peroxide is 4,4'-divinyl benzoyl peroxide which can be obtained by
reaction of 4-vinyl benzoyl chloride with sodium peroxide. A
preferred example of a polymerizable azo compound is the ester from
2-hydroxyethyl methacrylate and 4,4'-azobis-(4-cyanovaleric acid).
Preferred thermally labile urethanes can be obtained from
diisocyanates, for example by reaction of
2,2,4-trimethylhexamethylene diisocyanate (TMDI) or toluylene
diisocyanate (TDI) with hydroxypropyl acrylate (HPA) or
2-hydroxyethyl acrylate (HEA). A further example of a thermally
labile monomer building block is
.alpha.,.alpha.,.alpha.',.alpha.'-tetramethyl-1,4-benzene-dimethyl
acrylate, the incorporation of which into a Michael addition
network for example of diacrylates and diacetoacetates in the
presence of catalytic acid quantities leads to an accelerated
decomposition of the polymer network.
[0075] Moreover, comonomers the polyreaction products of which are
readily thermally degradable are suitable as debinding
accelerators. Comonomers which, like .alpha.-methylstyrene, have a
low ceiling temperature T.sub.c are preferred for radical
polymerization resins. The ceiling temperature is the limit
temperature at which the polymerization is in equilibrium with the
depolymerization, and can be calculated from the quotient of the
polymerization enthalpy and the polymerization entropy (cf. H.-G.
Elias, Makromolekule, vol. 1, 6.sup.th Edition, Wiley-VCH, Weinheim
etc. 1999, 193 et seq., which is hereby incorporated by reference).
For example, T.sub.c is 61.degree. C. for a-methylstyrene. The
ceiling temperature T.sub.c of polytetrahydrofuran (PTHF) is
80.degree. C. Accordingly, the decomposability of
poly(meth)acrylate networks can be accelerated e.g. by using
telechels with radically polymerizable groups as comonomer, in
particular PTHF di(meth)acrylate telechels. According to the
invention, comonomers with a ceiling temperature of -10 to
150.degree. C., preferably 10 to 150.degree. C. and particularly
preferably 20 to 130.degree. C. are particularly suitable. The
comonomers are preferably used in an amount of 0.1 to 30 wt.-% and
particularly preferably 0.5 to 20 wt.-%, relative to component
(A).
[0076] The slips according to the invention preferably comprise a
coloring component as component F. The coloring component is
preferably used in an amount of 0.00001 to 2.0 wt.-%, particularly
preferably 0.001 to 1.0 wt.-% and quite particularly preferably
0.01 to 0.5 wt.-%, relative to the mass of component C.
[0077] The customary dyes or pigments are not suitable as coloring
component according to the invention, since they are not stable
enough to survive the debinding or sintering process. According to
the invention, reactive transition metal compounds are used as
component F which on the one hand are soluble in binder A and do
not adversely affect the course of the photocuring and which on the
other hand form coloring transition metal ions during the debinding
of the stereolithographically prepared ceramic green compact or the
sintering of the ceramic white body obtained therefrom. Transition
metal compounds preferred as coloring component are in particular
acetylacetonates or carboxylic acid salts of the elements iron,
cerium, praseodymium, terbium, lanthanum, tungsten, osmium, terbium
and manganese. The salts of the carboxylic acids acetic, propionic,
butyric, 2-ethylhexylcarboxylic, stearic and palmitic acid are
preferred. Above all the corresponding Fe, Pr, Mn and Tb compounds,
such as iron (III) acetate or acetyl acetonate, manganese (III)
acetate or acetyl acetonate, praseodymium (III) acetate or acetyl
acetonate or terbium (III) acetate or acetyl acetonate as well as
the corresponding carboxylic acid salts are particularly
preferred.
[0078] The coloring components are preferably chosen such that
tooth-coloured ceramic shaped parts are obtained after the
debinding and sintering.
[0079] The transition metal compounds used as component F are
incorporated (usually as ions) into the structure as coloring
component and influence the colour of the sintered bodies after the
sintering process. In contrast to this, the previously mentioned
organic dyes serve to adjust the through-curing depth of the slips.
These are decomposed completely during the debinding and
sintering.
[0080] According to the invention, those slips are preferred which,
in addition to the components A, B and C, comprise an inhibitor D,
a debinding accelerator E and/or a coloring component F.
Particularly preferred are slips which comprise the components A,
B, C and D; A, B, C and E; A, B, C and F, quite particularly
preferred are slips which comprise the components A, B, C, D and E;
A, B, C, D and F; A, B, C, E and F, and in particular slips which
comprise the components A, B, C, D, E and F. It is preferred in
each case to use the above-defined components and preferred
components preferably in the above-mentioned amounts.
[0081] In addition to the components A to F, the slips according to
the invention can comprise further components as additives.
[0082] For example, the slips according to the invention can
comprise one or more dispersants which prevent the formation of
agglomerates and the depositing of the ceramic particles. Suitable
dispersants for ceramic slips are above all polymers such as
polycarboxlic acids, polycarboxylic acid salts or non-ionic
polymers, such as polyethylene glycol or carboxy-methylcellulose.
In particular suitable as dispersants are polymers which are
soluble in the polyreaction resin. For example poly(meth)acrylates
which are soluble in light-curable (meth)acrylate resins, wherein
the achievable solids content normally decreases as the molar mass
and content of these polymers in the slip increase. Furthermore,
the particles of component C can even be pre-treated with the
dispersants before the preparation of the slips. Dispersants are
preferably used in an amount of 0 to 5 wt.-% and particularly
preferably 0.5 to 3.0 wt.-%, relative to the total mass of the
slip.
[0083] The ceramic slips according to the invention can comprise,
as further components, one or more plasticizers which prevent the
ceramic green compact from becoming brittle after the photochemical
hardening and a possible drying. In addition, plasticizers ensure a
sufficient flexibility. Typical plasticizers are phthalates, such
as dibutyl or dihexyl phthalate, non-acidic phosphates, such as
tributyl or tricresyl phosphate, n-octanol, glycerol or
polyethylene or polypropylene glycols or corresponding ester or
ether derivatives. Plasticizers are preferably used in an amount of
0 to 20 wt.-% and particularly preferably 0 to 10 wt.-%, relative
to the total mass of radically polymerizable components.
[0084] Furthermore, the slips according to the invention can
advantageously also comprise a solvent. For example the compounds
mentioned above as plasticizers are suitable as solvents.
[0085] Components which have a boiling point of at least about
120.degree. C. and a relatively high evaporation enthalpy are
preferably used as solvents, with the result that there is no
premature evaporation during the stereolithographic processing of
the slip. Particularly preferred are solvents with a boiling point
of 150 to 250.degree. C., quite particularly preferably of 180 to
230.degree. C. Particularly suitable are 1-octanol, 1- or
2-nonanol, diethylene glycol diethyl ether,
2,5-dimethoxytetrahydrofuran, oxalic acid dibutyl ester,
cyclohexanol, polypropylene glycol diacetate, cyclohexanone,
acetoacetic acid ethyl ester and mixtures thereof. The solvent or
solvents are preferably used in an amount of 0 to 70 wt.-%,
particularly preferably 10 to 50 wt.-%, relative to the total mass
of radically polymerizable components.
[0086] Mixtures of compounds which can be progressively evaporated
in a temperature range between 150 and 250.degree. C. are
particularly suitable as plasticizers and/or solvents.
Progressively evaporated means here that mixtures of one or more
plasticizers and/or one or more solvents which have different
boiling points are used, with the result that these components can
be evaporated in succession, preferably in a temperature range from
150.degree. C. to 250.degree. C., and can thus be removed in a way
that treats the shaped parts much more carefully.
[0087] The evaporation of the solvents can favour the debinding of
the polymer portions taking place at increased temperature. It was
found that the evaporation of the above solvents leads to the
formation of micropores in the green compact which close again upon
sintering but which make possible the escape of the gases in the
debinding step and thus prevent the formation of stresses and
cracks. Moreover, the danger of a separation of the
stereolithographically produced layers is reduced and a complete
removal of the organic components is made easier.
[0088] Alternatively, a porosity of the green body can also be
achieved by removing by extraction elutable portions before heat
treatment. Suitable extractable components are water-soluble
polymers, such as polyvinyl alcohol, polyvinyl pyrrolidone and
polyethylene glycols. Furthermore, petrol-soluble substances such
as paraffins or waxes and long-chained fatty acid esters can be
used. The preferred amount of extractable components in the resin
matrix is between 0 and 40 wt.-%, particularly preferably between
0.1 and 30 wt.-%, relative to component (A).
[0089] In addition, the slips according to the invention can
comprise defoaming and/or antiskinning agents which prevent foaming
during the preparation of the slips or the formation of a skin
during the processing of the slips. Defoaming and/or antiskinning
agents are preferably used in each case in an amount of 0 to 5
wt.-% and particularly preferably 0.1 to 2 wt.-% in the organic
matrix, relative to the mass of component (A).
[0090] Slips which comprise the above-mentioned components in the
following quantities are particularly preferred according to the
invention: [0091] Component A: 1 to 30, preferably 5 to 20 wt.-%
[0092] Component A2: 0 to 20, preferably 0 to 10 wt.-% [0093]
Component B: 0.001 to 2, preferably 0.01 to 1.0 wt.-% [0094]
Component C: 30 to 90, particularly preferably 35 to 85 and quite
particularly preferably 40 to 85 wt.-% [0095] Solvent and/or [0096]
plasticizer 0 to 30, preferably 0 to 15 wt.-%
[0097] The rheological properties of the slips according to the
invention are preferably adjusted such that their viscosity is in
the range from 0.02-20000 Pas, particularly preferably 0.05-5000
Pas. It is advantageous if there are no yield points if at all
possible. The viscosity and the yield points are determined at
23.degree. C. with a plate-plate viscometer.
[0098] The slips according to the invention are particularly
suitable for the preparation of ceramic or glass ceramic shaped
articles in particular for the preparation of dental restorations,
such as inlays, onlays, veneers, crowns, bridges or frameworks.
[0099] A subject of the invention is also a process for the
preparation of ceramic or glass ceramic shaped articles, wherein
[0100] (a) a green body is prepared by curing a slip according to
the invention by local introduction of radiation energy with
formation of the geometric shape of the green body, [0101] (b) the
green body is then subjected to a heat treatment to remove the
binding agent (debinding), in order to obtain a white body, and
[0102] (c) the white body is then sintered.
[0103] The preparation of the green body in step (a) takes place by
rapid prototyping, preferably by stereolithography. A ceramic green
body, which is debound in step (b), is prepared through
layer-by-layer radiation curing of a free-flowing ceramic slip. The
binder used is removed by heating the green body to a temperature
of preferably 90.degree. C. to 600.degree. C., and the so-called
white body is obtained. The white body is sintered in step (c) to
form a dense ceramic shaped article. The sintering of the white
body takes place in the sintering furnace, preferably at a
temperature of 650 to 1100.degree. C., preferably 700 to
900.degree. C., for glass ceramic, 1100 to 1600.degree. C.,
preferably 1400 to 1500.degree. C., for zirconium dioxide, and 1400
to 1800.degree. C., preferably 1600 to 1700.degree. C., for
aluminium oxide. The ceramic shaped articles prepared according to
the process according to the invention are characterized by a high
strength and great accuracy of detail. The bending strength
according to ISO 6872 is preferably more than 100 MPa, in
particular in the range from 150 to 500 MPa, for shaped articles
made of glass ceramic. Shaped articles made of Al.sub.2O.sub.3 have
a bending strength of preferably more than 300 MPa, in particular
from 500 to 700 MPa and shaped articles made of ZrO.sub.2 of over
500 MPa, in particular from 800 to 1100 MPa.
[0104] The invention is explained in more detail below by means of
drawings and examples.
[0105] As FIG. 1 shows, the device comprises a container 1 for the
slip 7 according to the invention. The container 1 is also referred
to as a polymerization tank or tank. In the embodiment shown, the
tank 1 has a transparent window 2 through which the slip is
selectively irradiated and cured from below. Arranged underneath
the tank 1 is a computer-controlled, movable mirror 3, a so-called
micro-minor array, which is irradiated with a radiation source 4.
The image of the mirror 3 is projected onto the transparent window
2 by an optical device 5. Arranged above the tank 1 is a substrate
carrier 6 movable in Z direction which carries the body 8
constructed in layers. The substrate carrier 6 can have a carrier
plate, not shown here. The substrate carrier 6 is immersed in the
slip until the distance between the carrier 6 or the body 8
attached thereto and the inner surface of the tank 1 corresponds to
the layer thickness of the layer to be produced. The slip layer
between carrier 6 and inner tank surface is then selectively
irradiated and cured through the transparent window 2 with the help
of the mirror 3. Cured areas form which adhere to the carrier 6.
The carrier 6 is then raised in Z direction, with the result that a
slip layer with the desired thickness forms again between the
adhering layer and the inner tank surface. This layer is also
selectively cured by irradiation and the desired shaped articles,
preferably a dental restoration, is constructed in layers by
repeating the process.
EXAMPLES
Example 1
Light-Curing Ceramic Slips and Stereolithographically Produced
Shaped Articles
[0106] To prepare the ceramic slips, the monomers listed in the
following table (PS-m-HEA=reaction product of 1 mol phthalic acid
anhydride with 1 mol 2-hydroxyethyl acrylate; NK-ester
CBX-1N=pentaerythritol triacrylate monophthalate 70%), the solvents
PEG-400 and PPG-400 respectively and a dispersant were introduced
and homogeneously mixed. The photoinitiator K-69
(bis(4-methoxybenzoyl)diethylgermanium, Ivoclar Vivadent AG) or
Irgacure 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide,
Ciba SC) was then added and dissolved in the mixture by simple
stirring. Finally, the zirconium oxide powder TZ-3YS-E (Tosoh) was
added portionwise and dispersed. Free-flowing, homogeneous, stable
slips with a filler level of about 37% by volume formed.
[0107] Biaxial testpieces were manufactured generatively with the
slips A and B using a SL device. The testpieces were cleaned and
then sintered.
[0108] The sintered biaxial plates were prepared and measured
according to ISO 6872:2008. For the slips A and B ceramic shaped
articles with a biaxial strength of 1043 and 1055 MPa respectively
resulted.
TABLE-US-00001 A B Component [wt.-%) [wt.-%] Dispersant 1.00 1.00
PS-m-HEA 12.00 11.00 NK-ester CBX-1N -- 1.00 PEG 400 9.95 -- PPG
400 -- 9.75 K-69 0.05 -- Irgacure 819 -- 0.25 TZ-3YS-E Tosoh 77.00
77.00 Total 100.00 100.00
[0109] Although preferred embodiments have been depicted and
described in detail herein, it will be apparent to those skilled in
the relevant art that various modifications, additions,
substitutions, and the like can be made without departing from the
spirit of the invention and these are therefore considered to be
within the scope of the invention as defined in the claims which
follow.
* * * * *