Ceramic And Glass Ceramic Slips For Stereolithography

Abstract

Slip for the stereolithographic preparation of ceramic or glass ceramic shaped parts which comprises (a) at least one radically polymerizable monomer, (b) at least one photoinitiator, (c) ceramic and/or glass ceramic particles and (d) at least one non-ionic surfactant.

Claims

1. Slip for the stereolithographic preparation of ceramic or glass ceramic shaped parts, wherein said slip comprises (a) at least one radically polymerizable monomer, (b) at least one photoinitiator and (c) ceramic and/or glass ceramic particles, characterized in that said slip comprises (d) at least one non-ionic surfactant.

2. Slip according to claim 1, wherein said slip comprises as non-ionic surfactant (d), a surfactant with a melting point of from 30 C. to 120 C.

3. Slip according to claim 1, wherein said slip comprises as non-ionic surfactant a surfactant with an HLB value of from 3 to 16.

4. Slip according to claim 1, wherein said slip comprises as non-ionic surfactant (d) an ethoxylate of fatty alcohols, oxo alcohols or fatty acids, a fatty acid ester of sugars or hydrogenated sugars, an alkylglycoside, a block polymer of ethylene and propylene oxide, a short-chained block co-oligomer or a mixture thereof.

5. Slip according to claim 4, wherein said slip comprises as non-ionic surfactant (d) a fatty acid ester of hydrogenated sugars with the formula RCOO-sugar in which R is a branched or straight-chain alkyl radical with 10 to 25 carbon atoms and sugar means a hydrogenated sugar radical which is ethoxylated 1 to 5 times or not ethoxylated.

6. Slip according to claim 4, wherein said slip comprises as non-ionic surfactant (d) a fatty acid ethoxylate of the general formula R(CO)(OCH.sub.2CH.sub.2).sub.mOH in which R is a branched or straight-chain alkyl radical with 10 to 25 carbon atoms and m is an integer from 2 to 20.

7. Slip according to claim 4, wherein said slip comprises as non-ionic surfactant (d) a polyalkylene glycol ether with the general formula R(OCH.sub.2CH.sub.2).sub.nOH in which R is an alkyl radical with 10 to 20 carbon atoms and n is an integer from 2 to 25.

8. Slip according to claim 1, wherein said slip comprises as monomer (a) at least one (meth)acrylate and/or (meth)acrylamide.

9. Slip according to claim 1, wherein said slip comprises as component (c) ceramic particles based on ZrO.sub.2, Al.sub.2O.sub.3 or ZrO.sub.2Al.sub.2O.sub.3, or based on ZrO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2Al.sub.2O.sub.3 which is stabilized in each case with HfO.sub.2, CaO, Y.sub.2O.sub.3, CeO.sub.2 and/or MgO.

10. Slip according to claim 1, wherein said slip comprises as component (c) glass ceramic particles based on leucite, apatite and/or lithium disilicate glass ceramic.

11. Slip according to claim 1, wherein the particles of component (c) have a particle size in the range of from 10 nm to 100 m.

12. Slip according to claim 1, wherein said slip additionally comprises at least one surface modification agent and/or at least one additive which is selected from dyes, solvents, inhibitors, debinding accelerators, defoaming agents and/or antiskinning agents.

13. Slip according to claim 12, wherein the surface modification agent is selected from linear or branched carboxylic acids, formic acid, acetic acid, propionic acid, octanoic acid, isobutyric acid, isovaleric acid, pivalic acid, phosphonic acids, methyl-, ethyl-, propyl-, butyl-, hexyl-, octyl- or phenylphosphonic acid, propyltrimethoxysilane, phenyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, trimethylchlorosilane, trimethylbromosilane, trimethylmethoxysilane or hexamethyldisilazane, acidic phosphoric acid esters, dimethyl, diethyl, dipropyl, dibutyl, dipentyl, dihexyl, dioctyl or di(2-ethylhexyl) phosphate; and/or the dye is selected from organic dyes comprising azo dyes, carbonyl dyes, cyanine dyes, azomethine, methine, phthalocyanine, dioxazine, (4-(4-nitrophenylazo)aniline or a mixture thereof; and/or the solvent is selected from polyethylene glycols, polypropylene glycols, PEG-PPG co-polymers, glycerol and glycerol derivatives, phthalates, PEG 200-600 g/mol, PPG 200-800 g/mol, co-PEG-PPG 200-800 g/mol and polypropylene glycol 400 g/mol and mixtures thereof.

14. Slip according to claim 1 comprising 5 to 65 wt.-% monomer (a); 0.001 to 1.0 wt.-% photoinitiator (b); 33 to 90 wt.-% ceramic and/or glass ceramic particles (c); 1 to 30 wt.-% non-ionic surfactant (d).

15. Process of using the slip according to claim 1 for the preparation of ceramic or glass ceramic dental restorative shaped parts comprising an inlay, onlay, veneer, crown, bridge or framework.

16. Process for the preparation of a ceramic or glass ceramic shaped part, wherein (A) a green compact is prepared by curing a slip according to claim 1 by local introduction of radiation energy accompanied by the formation of the geometric shape of the green compact, (B) the green compact 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.

17. Slip according to claim 2, wherein the melting point of the non-ionic surfactant (d), is in the range of 40 C. to 100 C. or 40 C. to 60 C.

18. Slip according to claim 3, wherein the HLB value of the non-ionic surfactant is in the range of 4 to 13 or 4 to 10.

19. Slip according to claim 14 comprising 9 to 57 wt.-% monomer (a); 0.01 to 1.0 wt.-%, wt.-% photoinitiator (b); 40 to 88 wt.-% ceramic and/or glass ceramic particles (c); 2 to 15 wt.-% non-ionic surfactant (d).

20. Slip according to claim 14 comprising 10 to 40 wt.-% monomer (a); 0.1 to 1.0 wt.-% photoinitiator (b); 56 to 86 wt.-% ceramic and/or glass ceramic particles (c); 3 to 10 wt.-% non-ionic surfactant (d).

Description

[0093] FIG. 1 shows a schematic representation of a device for carrying out the process according to the present invention. As FIG. 1 shows, the device comprises a container 4 for the slip according to the present invention. The container 4 is also called polymerization tank or tank. In the embodiment shown, the tank 4 has a transparent window through which the slip is selectively illuminated and cured from below. A computer-controlled DMD chip (Digital Mirror Device) 2, which is irradiated with a light source 1, is arranged below the tank 4. The image of the mirror 2 is projected onto the transparent window in the base of the container 4 by an optical device 3. Arranged above the tank 4 is a substrate carrier 6 movable in Z direction which carries the body 7 constructed in layers. The substrate carrier 6 has a carrier plate 5. The carrier plate 5 is immersed in the slip until the distance between the carrier plate 5, or the body 7 attached thereto, and the inner surface of the tank 4 corresponds to the layer thickness of the layer to be produced. The slip layer between carrier plate and inner tank surface is then selectively illuminated and cured through the transparent window with the help of the DMD chip 2. Cured areas form which adhere to the carrier plate 5. 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 renewed illumination and the desired shaped body, preferably a dental restoration, is constructed in layers by repeating the process.

EXAMPLES

Example 1

Lithium Disilicate Slips

[0094] Except for the glass ceramic particles, the components listed in Table 1 were weighed out and stirred at 50 C. until all of the components had dissolved. The powder component (c) was then added in 2-3 batches. After each addition of powder, the slip was homogenized in a Hauschild Speedmixer DAC 400fvz at 2750 rpm for 2 min. The total weight of the slip was in each case approx. 50-100 g.

TABLE-US-00001 Component Substance Slip 1 Slip 2 Slip 3*) Monomer (a) 3 mole propoxylated 8.65% 8% 8.65% trimethylolpropane triacrylate.sup.1) Monomer (a) UDMA (RM3) 6.8% 6% 6.8% Initiator (b) Ivocerin.sup.2) 0.05% 0.05% 0.05% Non-ionic surfactant (d) Steareth-2.sup.3) 9.15% 3.9% Dye 4-(4-Nitrophenylazo)aniline 3.sup.4) 0.005% 0.005% 0.005% Dispersant Phosphoric acid ester.sup.5) 1% 1% 1% Solvent Polypropylene glycol (400 g/mol) 6.7% 9.15% Glass ceramic particles (c) Lithium disilicate.sup.6) 74.345% 74.345% 74.345% *)Comparison example .sup.1)SR492 (Sartomer) .sup.2)Bis(4-methoxybenzoyl)diethylgermanium .sup.3)Brij S2 (Croda Europe Ltd, England) .sup.4)Disperse Orange 3 (Sigma-Aldrich; CAS No. 730-40-5) .sup.5)Solplus D540 (CAS No. 1000871-74-8; Lubrizol) .sup.6)Lithium disilicate glass ceramic (e.max Transpa; Ivoclar Vivadent, Liechtenstein), ground; D50 = 6 m

[0095] Slips 1 to 3 are lithium disilicate slips. Slip 1 does not contain any solvent. Solvent (PPG400) is additionally present in slip 2 and the content of non-ionic surfactant (d) is reduced. The slip is thus less sensitive to temperature fluctuations during processing but in return is less solid and is softer at room temperature. Slip 3 (comparison example) does not contain any non-ionic surfactant.

[0096] The non-ionic surfactant effects a solidification of the slip at room temperature, whereby the storage stability is increased significantly. After 3 weeks, no sedimentation and no phase separation could be seen in the case of slips 1 and 2. Slip 3 clearly sedimented within 3 weeks and a clearly visible transparent liquid film formed on the surface. The sedimented slip could not be re-homogenized by manual shaking or stirring and could also only be re-homogenized to a limited extent by intensive machine stirring (Speedmixer). These possibilities are, however, not possible on the SL device.

Example 2

Wax-Containing Slips (Comparison Example)

[0097]

TABLE-US-00002 Component Quantity Proportion ZrO.sub.2 particles 150 g (35.7 vol.-%; 78.2 wt.-%) Paraffin wax 20.310 g (32.7 vol.-%; 10.6 wt.-%) PPG700DA 11.858 g (16.8 vol.-%; 6.2 wt.-%) 5-DAMS 5.442 g (7.7 vol.-%; 2.8 wt.-%) Octadecene 2.020 g (3.7 vol.-%; 1.1 wt.-%) Hypermer LP-1 2.000 g (3.2 vol.-%; 1.0 wt.-%) TEMPO 0.001 g (0.03 vol.-%; 5 wt.-ppm) Photoinitiator 0.300 g (0.017 vol.-%; 0.15 wt.-%) Key: ZrO.sub.2 TZ-3YS-E (commercial grade) from Tosoh Corporation, Tokyo, JP (ZrO.sub.2 stabilized with Y.sub.2O.sub.3, primary particle size 300-350 nm) Paraffin wax Melting point 54-56 C., viscosity (at 80 C. and at a shear rate of 1000 s.sup.1) 3-4 mPa .Math. s (Siliplast; Zschimmer & Schwarz, Lahnstein, DE; contains in total approx. 0.5% emulsifier) Hypermer LP-1 Surface modification agent based on a medium-chain polyester (Uniqema, GB.) PPG700DA Polypropylene glycol 700 diacrylate 5-DAMS Pentaerythritol diacrylate monostearate TEMPO 2,2,6,6-Tetramethylpiperidinyloxyl Photoinitiator Bis-(4-methoxybenzoyl)diethylgermanium

Preparation of the Slip:

[0098] The wax, the monomers PPG700DA and 5-DAMS, and the surface modification agent were introduced at 70 C. into a dissolver (Dispermat, VMA-Getzmann GmbH, Reichshof, DE). The ZrO.sub.2 powder was added portionwise at low rotation speeds. Once all of the powder had been incorporated, the rotation speed was increased to 20,000 min.sup.1 and mixing was carried out for at least 30 min. The heating occurring because of the high shear forces in the system made any external heating unnecessary, and under certain circumstances cooling may actually be necessary. After the 30 min. of intensive stirring, the slip was cooled while being gently stirred. As long as the slip was still liquid, octadecene and TEMPO were added, as well as the photoinitiator at the end.

Example 3

Preparation of Shaped Bodies

[0099] The prepared slip was converted into cylindrical test pieces with a diameter of 6 mm and a height of 6 mm in a self-built Digital Light Processing (DLP) stereolithography unit (Blueprinter, TU Vienna). The slip temperature was set to approx. 60 C. It is important that the slip and all of the components (in particular the components which come into contact with the layer to be formed) are heated to a temperature above the melting point of component (d). The wavelength of the light was 460 nm and the slips were illuminated with 150 mJ/cm.sup.2 per layer. The distance between the layers was set to 25 m.

[0100] After the construction, the parts were removed manually from the construction platform, cleaned in an ultrasonic bath in an aqueous washing-up liquid solution at 50 C. for 5-10 minutes and then blown dry. The temperature of the cleaning solution was above the melting point of component (d).

[0101] After the drying, the cleaned components were debound in a laboratory furnace (Nabertherm GmbH, Germany). The debinding program used for cylinders with a diameter of 6 mm and a height of 6 mm was: (i) heating from room temperature to 100 C. in 2 h 40 min.; (ii) further heating to 200 C. in 6 h 40 min.; (iii) then further heating to 420 C. in 7 h 20 min.; (iv) maintaining at 420 C. for 1 h. In the case of larger and thicker components, corresponding adaptations are necessary. A good circulation of air must be maintained in the furnace chamber throughout the entire debinding process so that the formed gases can be effectively removed.

[0102] At the start of the debinding, pores formed as a result of the evaporation of the solvent and the outflow of the non-ionic surfactant. In the case of slip 1, primarily the non-ionic surfactant (d) was responsible for the formation of the porosity. These pores make it easier for the formed gases to escape and defect-free white bodies were obtained which could be sintered without problems.

[0103] Thereafter, the green bodies were completely debound and could be dense-sintered in a sintering furnace (Programat P510, Ivoclar Vivadent) in a standard manner. The sintering program was: 10 K/min. to 700 C., 30 min. holding time at 700 C., 10 K/min. to 850 C., vacuum from 500 C., 1 min. holding at 850 C., cooling at (10 K/min.) to 700 C., approx. 90 min.

[0104] The photopolymerization of the slip from Example 2 proceeded slowly in the stereolithography process because of the low reactivity of the long-chained monomers and yielded a green body with low mechanical stability which required extremely careful handling. The printed objects were very fragile and sensitive also after the debinding.