WO2000064653A2

WO2000064653A2 - Method and material for producing model bodies

Info

Publication number: WO2000064653A2
Application number: PCT/EP2000/003316
Authority: WO
Inventors: Wolfgang Podszun; David Bryan Harrison; Jean-Marie Dewanckele; Frank Louwet; Gabriele Alscher
Original assignee: Bayer Aktiengesellschaft
Priority date: 1999-04-27
Filing date: 2000-04-13
Publication date: 2000-11-02
Also published as: HK1046116A1; CZ20013851A3; EP1173314A2; CA2371181A1; CN1348408A; IL145779A0; JP2002542080A; AU4548200A; BR0010074A; WO2000064653A3; MXPA01010931A; DE19918981A1; KR20010114248A; TR200102922T2

Abstract

Model bodies of any form or shape can be produced from special plastic powders with the aid of selective sintering using infrared lasers. Also described are plastic powders containing an infrared absorber and suitable for laser-assisted model production.

Description

Process and material for the production of model bodies

The invention relates to a method for the production of model bodies, in which any three-dimensional structure can be built up with the aid of selective sintering using laser light in the IR range using plastics, in the form of selected plastic powders. The invention also relates to a special plastic powder which contains an IR absorber and is particularly well suited for sintering with IR laser light.

The invention relates in particular to a method for producing three-dimensional models from plastic in accordance with stored, geometric data with the aid of a computer-assisted system for direct production of prototypes and models (rapid prototyping system) which works with IR laser beams.

Rapid prototyping is the term used to summarize the computer-controlled additive, automatic model building methods known today. Laser sintering is a rapid prototyping process in which fillings made of certain powdery materials are heated and sintered in layers at certain plane positions under the influence of laser beams, preferably controlled by a program.

The use of plastic powders for laser sintering using CO ₂ lasers is known (A. Gebhardt, Rapid Prototyping, Carl Hanser Verlag, Munich, Vienna 1996, pages 115-116). A method for the production of model bodies is described in which, using plastics with the aid of light from a CO laser, any three-dimensional structure can be built up by selective sintering.

A disadvantage of the previously known methods is the limited accuracy of the moldings obtained. Because of this inaccuracy, they have to be this way today generated moldings can be manually reworked in a complex manner in many cases. The low accuracy is partly a result of the CO ₂ laser used, which has a wavelength of 10.6 μm and is difficult to focus. Up to now, better focusable lasers, such as the ND-Y AG laser with a wavelength of 1064 nm, have not been used for laser sintering since the usual plastics do not show any absorption at this wavelength.

The invention relates to a method for producing three-dimensional models from plastic in accordance with stored geometric data with the aid of laser beams of a wavelength 500 to controlled according to this data

1500 nm, preferably 800 to 1200 nm, laser beams being directed to certain spatial zones of a bed of fine-grained plastic powder and the material being melted or sintered, characterized in that the plastic powder has an average particle size of 2 to 200 μm and contains an IR absorber.

In a special embodiment of the present invention, the plastic powder is essentially spherical.

Another object of the present invention are plastic powders for use as a starting material for laser-assisted production of models, the powder particles having an average particle size (i.e. weight average diameter) of 2 to 200 μm and containing an IR absorber.

Different types of lasers are suitable for the method according to the invention. Solid-state lasers and semiconductor diode lasers are particularly suitable. Examples of solid lasers are Nd-YAG lasers with a wavelength of 1064 nm and Nd-YLF lasers with a wavelength of 1053 nm. Diode lasers which emit at 823 nm or 985 nm are mentioned. The irradiated energy on the surface of the powder bed is preferably from 0.01 to 100 mJ / mm ² , preferably 1 to 50 mJ / mm ² during the irradiation.

Depending on the application, the effective diameter of the laser beam is in particular from 0.001 to 0.05 mm, preferably from 0.01 to 0.05 mm.

Pulsed lasers are preferably used, a high pulse frequency, in particular from 1 to 100 kHz, having proven particularly suitable.

The preferred procedure can be described as follows:

The laser beam strikes the uppermost layer of the bed made of the material to be used according to the invention and melts or sinters the material in a certain layer thickness. This layer thickness can be from 0.005 mm to 1 mm, preferably from 0.01 mm to 0.5 mm.

The first layer of the desired component is produced in this way. The working space is then lowered by an amount which is less than the thickness of the sintered layer. The work space is filled up to the original height with additional polymer material. As a result of the renewed irradiation with the laser, the second layer of the component is sintered and connected to the previous layer. By repeating the process, the additional layers are created until the component is finished.

The laser beam is applied at a speed of 1 to 1,000 mm / s, preferably 10 to 100 mm / s.

Plastic powders suitable for the invention can belong to different polymer classes. Examples include: polyolefins such as polyethylene and polypropylene, polyamides such as polyamide 6 and polyamide 6,6, polyesters such as polyethylene terephthalate and polybutyl terephthalate, polycarbonates, meltable polyurethanes,

Polystyrene, styrene-acrylonitrile copolymers and polyacrylates. Plastic powder on The base of partially crystalline polymers are particularly suitable for the production of pore-free model bodies.

The particle size of the powder particles is of particular importance for the process according to the invention. Generally the average particle diameter is 2 to

200 μm, preferably 5 to 100 μm, particularly preferably 5 to 50 μm. The weight average is meant here as the mean particle diameter (particle size).

To produce the particle size essential for the process, the plastics which are usually present as coarse granules can be ground. However, this may result in an angular or angular shape of the plastic particles. These particles with an irregular or torn surface sometimes have poor flow properties, which have an unfavorable effect on processing in laser sintering systems. It is therefore usually necessary to add flow aids to the plastics in order to improve the flowability of the shredded plastics and to ensure the operation of automated systems.

Polymers with an essentially spherical shape (bead polymers) are particularly suitable for the process according to the invention.

It has been shown that such bead polymers are also accessible to laser sintering according to the invention. However, they have inherently much more favorable flow properties than ground other plastics and therefore do not require any flow aids to improve their flow properties.

Another important advantage of the bead polymer is that it does not leave any annoying residues when it is incinerated, for example as the core of a hollow ceramic mold. In the case of ground artificial particles mixed with flow aids, it has been observed that these do not incinerate without residues. This is of particular importance if the plastic models, which are primarily created using laser sintering, are further processed in subsequent processes for investment casting. For this purpose, for example after the model produced with the method according to the invention has been coated with wax to further improve the model surface, the model is immersed in a slurried ceramic mass and this with

Ceramic coated model fired in the oven. The model should burn completely when fired and leave the free hollow shape made of ceramic. Since conventional ground plastics do not burn completely due to the flow aid, the metallic models subsequently cast in the ceramic mold often have surface inaccuracies.

Another advantage of the use of bead polymers results in the surface accuracy and surface roughness of the models produced by the process according to the invention. Because of their round shape and their good flow properties, they are made with the preferred bead polymers

Models smoother and therefore more precise.

The bead polymers preferably consist of homopolymers or copolymers of monoethylenically unsaturated compounds (monomers). Copolymers in the sense of the invention include polymers which consist of two or more different

Monomers are built up, understood. Suitable monomers are e.g. Styrene, alpha-methylstyrene, chlorostyrene, acrylic acid esters, such as ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, dodecyl acrylate, methacrylic acid esters, such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, iso-butyl methacrylate, Decyl methacrylate, dodecyl methacrylate, stearyl methacrylate, furthermore acrylonitrile, methacrylonitrile, methacrylamide and vinyl acetate.

It has been shown that the molecular weight of the bead polymers is important for the suitability for the process according to the invention. The molecular weight

(Weight average, Mw) should in particular be from 10,000 to 500,000, preferably 20,000 to 250,000 daltons. To set the desired molecular weight, molecular weight regulators can be used in the preparation of the bead polymers. Suitable molecular weight regulators are in particular sulfur compounds, for example n-butyl mercaptan, dodecyl mercaptan, thioglycolic acid ethyl ester and diisopropyl xanthogen disulfide. The sulfur-free regulators mentioned in DE 3 010 373 are also very suitable for adjusting the molecular weight, for example the enol ethers of the formula I.

Particularly suitable bead polymers can be prepared by processes known per se. So bead polymers with a particle size of about 10 to 200 can be obtained by suspension polymerization or bead polymerization. The term suspension polymerization is understood to mean a process in which a monomer or a monomer-containing mixture which is soluble in the monomer (s)

Initiator contains, in a phase which is essentially immiscible with the monomer (s) and which contains a dispersant, is divided into droplets, optionally in a mixture with small, solid particles, and is cured by increasing the temperature with stirring. Further details of the suspension polymerization are described, for example, in Ulimann's Encyclopedia of Industrial Chemistry, Vol. A21

5th edition, VCH, Weinheim 1992 on pages 363 to 373.

Bead polymers with particle sizes of 2 to 10 μm can be produced by the so-called dispersion polymerization. Dispersion polymerization uses a solvent in which the monomers used are soluble but the polymer formed is insoluble. Dispersion polymerization generally provides bead polymers with a narrow particle size distribution. In principle, all compounds which absorb light at a wavelength of 500 to 1500 nm, preferably 800 to 1200 nm, are suitable as IR absorbers. Both IR pigments and IR dyes can be used independently of one another.

Carbon black, in particular synthetically produced carbon black, is particularly suitable as the IR pigment. The carbon black preferably has a specific surface area of 10 to 500 m ² / g, measured by the BET method. Suitable types of carbon black are gas blacks (channel blacks), furnace blacks (furnace blacks) and lamp blacks.

Furthermore, certain mixed metal oxide pigments of the rutile or spinel type are well suited. Examples of suitable metal oxide pigments are the commercially available products HEUCODUR ^® -Brown 859 and HEUCODUR ^® -Black 953.

IR dyes (infra-red absorbing dyes, IRD) are known per se. IR dyes from different substance classes are preferably suitable, e.g. Indoaniline dyes, oxonol dyes, porphine derivatives, antrachinone dyes, mesostyryl dyes, pyrilium compounds and squarylium derivatives.

IR dyes according to the published patent application DE 4 331 162 are also particularly suitable, since they have no or only a slight absorption in the visible range and thus enable the production of uncolored or only slightly colored 3D models by the process according to the invention.

The IR dye according to formula II may be mentioned as an example:

The amount of IR absorber according to the invention is from 0.01 to 10% by weight, preferably from 0.05 to 5% by weight, based on the plastic powder.

Plastic powder containing an IR absorber can be produced in different ways. It is thus possible to mix the plastic with the LR absorber in the melt using an extruder and to break the extrudate obtained into the desired particle size in a mill. It is also possible to add the IR absorber during the manufacture of the plastic so that the LR absorber is enclosed in the plastic that is being formed. In the preparation of bead polymers by suspension polymerization, the IR absorber can be added to the monomers.

It has been found that plastic particles with soluble IR

Dyes can be doped. In this process, the plastic particles are dispersed in a liquid phase which does not dissolve the plastic, preferably in water, it being possible for a wetting agent or a surfactant to be used. In this case, suitable surfactants are, for example, sodium alkyl sulfonate, isooctyl sodium sulfosuccinate or ethoxylated nonylphenol. A solution of the IR dye is added to the dispersion obtained, it being possible preferably to use a water-immiscible solvent, such as, for example, ethyl acetate, toluene, butanone, chloroform, dichloroethane or methyl isobutyl ether. During this treatment, the solvent, including the IR dye, swells in the plastic particles. The water can then be filtered or animals and the solvent by evaporation, e.g. B are removed at reduced pressure, the IR dye remaining in the plastic particle.

The plastic powders according to the invention, which contain an IR absorber, are particularly well suited for the laser sintering process with LR lasers, in particular ND-YAG lasers, and deliver models or components with particularly good attention to detail.

Figure 1 shows the schematic representation of a rapid prototyping system.

The following examples show the production of fine-particle plastic materials as well as attempts to sinter these materials with the help of an IR laser.

example 1

Preparation of a carbon black polymer according to the invention

a) Carbon black dispersion 6 g of carbon black (Printex G from Degussa, BET surface area 30 m ² / g), 24 g of polymethyl methacrylate and 216 g of methyl methacrylate were treated in a ball mill for 2 hours, a homogeneous, settable dispersion being obtained.

b) Bead polymer 200 g of the dispersion from a) and 2.0 g of 2,2'-azobis (isobutyronitrile) were mixed intensively. The mixture is transferred to a stirred reactor which has previously been treated with 1.0 liter of a 1% strength by weight aqueous alkaline solution of a copolymer of 50% by weight methacrylic acid and 50% by weight adjusted to pH 8 with sodium hydroxide solution .-% methyl methacrylate was filled. The stirring speed was set to 700 revolutions per minute and the temperature was kept at 60 ° C. for 3 hours, then at 78 ° C. for 10 hours and then at 85 ° C. for 2 hours. The mixture was then cooled to room temperature within 2 hours. The bead polymer formed was isolated by decanting, washed several times with water and dried at 50 ° C. in vacuo. 168 g of an intensely black-colored bead polymer with an average particle size of 18 μm and a molecular weight Mw of 230,000 were obtained.

Example 2

Preparation of a carbon black polymer according to the invention

a) Soot dispersion

12 g of carbon black (Printex G from Degussa), 28.8 g of polymethyl methacrylate, 216 g of methyl methacrylate and 43.2 g of n-butyl methacrylate were treated in a ball mill for 2 hours, a homogeneous, settable dispersion being obtained. b) bead polymer

250 g of the carbon black dispersion a) and 2.5 g of 2,2'-azobis (isobutyronitrile) were mixed intensively. The mixture was transferred to a stirred reactor which had previously been treated with 1.25 liters of a 1% by weight aqueous alkaline solution of a copolymer of 50% by weight methacrylic acid and pH adjusted to 8 with sodium hydroxide solution 50 wt .-% methyl methacrylate was filled. The stirring speed was set at 600 revolutions per minute and the temperature was kept at 78 ° C. for 10 hours and then at 85 ° C. for 2 hours. The mixture was then cooled to room temperature within 2 hours. The bead polymer formed was isolated by decanting, washed several times with water and dried at 50 ° C. in vacuo. 205 g of an intensely black-colored bead polymer with an average particle size of 25 μm and a molecular weight Mw of 220,000 were obtained.

EXAMPLE 3 Preparation of a Pearl Polymer Using IR Dye According to the Invention

a) Preparation of the bead polymer

In a 4 1 reactor equipped with a grid stirrer, 2,340 g of methanol,

180 g of polyvinylpyrrolidone, 210 g of methyl methacrylate and 90 g of ethyl methacrylate are mixed to form a homogeneous solution. This solution was brought to 55 ° C. in the course of one hour under nitrogen at a stirring speed of 100 rpm and a solution of 6 g of 2,2'-azobis (isobutyronitrile) in 165 g of methanol was added to the reactor. The polymerization mixture was stirred for a further 20 hours at 55 ° C. and 100 rpm. The finished polymer dispersion was then cooled to room temperature and the bead polymer was isolated by sedimentation. You got

193 g of bead polymer with a molecular weight Mw of 75,000, an average particle size of 12 μm and a 0 (9O) / 0 (Ιθ) value of 1.18. The ratio of the 90% value (0 (90)) and the 10% value (0 (10)) of the volume distribution, the 0 (9O) / 0 (10) value, is a good measure for the broad range Distribution. Narrow particle size distributions are found at 0 (9O) / 0 (Ιθ) values of less than 2.0. b) doping the bead polymer with IR dye

100 g of bead polymer from a) were dispersed in a solution of 900 g of water and 200 mg of isooctyl sodium sulfosuccinate. A solution of 284 mg of IR dye of the formula II and 100 g of ethyl acetate was added dropwise to this dispersion with stirring. The mixture was stirred for 4 hours at room temperature and then treated with ultrasound for 10 min. The bead polymer was filtered off, washed several times with water and dried to constant weight at 50 ° C. in vacuo to remove the ethyl acetate completely.

Example 4

Preparation of a bead polymer according to the invention with IR dye

a) Preparation of the Bead Polymer In a 4 l reactor equipped with a grid stirrer, 2,500 g of methanol,

64 g of polyvinylpyrrolidone, 240 g of styrene and 60 g of ethyl methacrylate are mixed to form a homogeneous solution. This solution was brought to 70 ° C. in the course of one hour under nitrogen at a stirring speed of 100 rpm and a solution of 3.75 g of 2,2'-azobis (isobutyronitrile) in 75 g of styrene was added to the reactor. The polymerization mixture was stirred for a further 15 hours at 70 ° C. and 100 rpm.

The polymer dispersion formed was then cooled to room temperature and the bead polymer was isolated by sedimentation. 247 g of bead polymer were obtained with an average particle size of 14 μm and a 0 (90) / 0 (Ιθ) value of 1.6 and a molecular weight Mw of 60,000.

b) doping the bead polymer with IR dye

10 g of bead polymer from a) were dispersed in a solution of 90 g of water and 20 mg of isooctyl sodium sulfosuccinate. A solution of 28.4 mg IR dye of the formula II and 10 g of ethyl acetate was added dropwise to this dispersion with stirring. The mixture was stirred at room temperature for 4 hours. The bead polymer was filtered off, washed several times with water and Dried to constant weight at 50 ° C. in vacuo to remove the ethyl acetate completely.

Example 5 Sintering Experiments with the Pearl Polymers from Examples 1 to 4

1, 20 g of bead polymer from Examples 1 to 4 were introduced into the storage vessel 4.

The beam of an ND-YAG laser 1 (effective cross section 5 mm ² , pulse frequency 10 Hz) is directed via the deflecting mirror 2 at a speed of 10 mm / s onto the surface of the bed 3 of the bead polymer and an area of 20 x 20 with the laser beam mm scanned. The radiated energy was 40 mJ / mm ² . Hard beads were obtained with the bead polymers from Examples 1b), 2b), 3b) and 4b). The test baskets were broken mechanically in liquid nitrogen and the fracture surfaces were examined in a scanning electron microscope. In the case of the bead polymer from Example 3a) (comparative experiment, without IR absorber), the product remained unchanged as a powder.

Claims

claims

1. Process for the production of three-dimensional models made of plastic in accordance with stored geometric data with the aid of laser beams of a wavelength of 500 to 1500 nm, preferably 800 to 1200 nm, which are controlled according to these data, laser beams corresponding to the geometric data onto specific spatial zones of a bed of fine-grained plastic powder and the material is melted or sintered, characterized in that the plastic powder has an average particle diameter of 2 to 200 microns and contains an IR absorber.

2. The method according to claim 1, characterized in that the plastic powder is a bead polymer.

3. The method according to claim 1 or 2, characterized in that the laser used is a solid-state laser, in particular an Nd-YAG laser with a wavelength of 1064 nm or an Nd-YLF laser with a wavelength of 1053 nm, or that a semiconductor -Diode laser, especially one that is used rather, which is emitted at 823 nm or 985 nm.

4. The method according to any one of claims 1 to 3, characterized in that the energy density on the surface of the powder bed during the irradiation is from 0.01 to 100 mJ / mm ² , preferably from 1 to 50 mJ / mm ² .

5. The method according to any one of claims 1 to 4, characterized in that the effective diameter of the laser beam is from 0.001 to 0.05 mm, preferably from 0.01 to 0.05 mm.

6. The method according to any one of claims 1 to 4, characterized in that a pulsed laser is used, the laser having a pulse frequency of 1 to 100 kHz.

7. Plastic powder for use as a raw material for laser-based

Production of models in which the powder particles have an average particle diameter of 2 to 200 μm and contain an IR absorber.

8. Plastic powder according to claim 7, characterized in that the plastic powder consists of bead polymer.

9. Plastic powder according to claim 7 or 8, characterized in that they contain, as IR absorbers, compounds which absorb light at a wavelength of 500 to 1500 nm, preferably 800 to 1200 nm, in particular LR pigments and / or TR dyes.

10. Plastic powder according to claim 9, characterized in that it contains a dye from the series indoaniline dyes, oxonol dyes, porphine derivatives, antrachinone dyes, mesostyryl dyes, pyrilium compounds and squarylium as IR pigment soot or as IR dye. Derivatives included.

11. Plastic powder according to one of claims 7 to 10, characterized in that it contains IR absorbers in an amount of 0.01 to 10% by weight, preferably 0.05 to 5% by weight, based on the plastic powder contain.

12. A process for producing an IR dye-containing plastic powder, characterized in that an aqueous dispersion of a plastic powder is brought into contact with the solution of an IR dye in a water-immiscible solvent and then the water and the

Solvent is removed.