Stereolithography method

Abstract

The invention relates to a stereolithography method comprising the steps of: containing a photo-hardening suspension (100) with filler particles (103) in a vat (105); setting the photo-hardening suspension to a layer thickness smaller than the diameter of the filler particles (103) with respect to the bottom (109) of the vat (105) by means of a structure platform (107); and selectively hardening the set layer thickness of the suspension by means of light.

Description

TECHNICAL FIELD

[0001] The present invention relates to a stereolithography method for selectively hardening a suspension comprising filler particles and a stereolithography apparatus for the method. BACKGROUND

[0002] Stereolithography-based techniques are limited in physical properties by the layer-wise build-up of the material. By the defined maximum layer thickness in the process, the handling of larger fillers is generally not possible. However, it is precisely these fillers that can fundamentally change the properties of the material system used, for example in the field of composite materials. In the field of dental materials, the wear resistance can be increased using fillers, for example. Fillers particles also have a positive influence on the polishability or the tendency to discolor of the material.

[0003] In theory, the use of larger fillers can be achieved at the expense of accuracy by correspondingly increasing the layer thickness. However, many resins used for stereolithography are completely unfilled or contain microparticles with a size of less than 1 pm as thickening agents, rheological additives or pigments. Current formulations for stereolithography dental materials do not have fillers with a diameter of more than 1 pm. Therefore, the subject is mainly to try to circumvent the deposition of particles in the resin.

[0004] The usual stereolithography resins based on di(meth)acrylates for the manufacture of prostheses usually do not contain fillers. Occasionally, a low share of pigments is used, which can also function as fillers in principle. With exposure (DLP, SLA), the material is shaped and fixed by polymerization, but here the polymerization is not completely carried out. This state is also called "green state".

[0005] The maximum degree of completion of the process is then carried out in the so-called tempering process. This process continues the polymerization as much as possible by irradiation and / or heating. Here, the material reaches its final physical properties, such as the modulus of elasticity, the bending strength, the hardness and the final geometry. Here, due to the reaction, changes in shape occur, such as shrinkage or stresses in the material.

[0006] The use of fillers for reducing these effects is in principle possible. However, fillers with small particles often lead to a strong thickening of the system, for example nanofillers, such as fumed silica. However, fillers with larger particles, which do not trigger this thickening to the same extent, cannot be used in the build-up process due to the maximum layer thickness fixed. Most stereolithography machines currently work with a minimum structure thickness of 20 pm, preferably 50 pm. SUMMARY

[0007] It is the technical task of the present invention to improve the physical properties of components manufactured by suspensions with filler particles.

[0008] According to a first aspect, this technical task is solved by a stereolithography method comprising the following steps: accommodating a photohardening suspension with filler particles in a bath; setting the photohardening suspension to a layer thickness of less than the diameter of the filler particles with respect to the bottom of the bath by means of a structure platform; and selectively hardening the set layer thickness of the suspension by means of light. Fillers with a maximum diameter exceeding the planned maximum structure height can be used in the stereolithography method.

[0009] The following technical advantage is achieved by the stereolithography method, namely that the structure change of the internal construction of the workpiece proceeds away from the layer-like arrangement pattern of the fillers towards an arbitrary distribution on the base layer (consisting of a polymeric resin) in the system. Thus, the anisotropic properties associated with the method are reduced and the manufactured component behaves isotropically. This has great advantages, in particular in tooth materials (analogously machined teeth), but also in composite materials.

[0010] In a technically advantageous embodiment of the stereolithography method, the layer thickness is less than at least 5% of the diameter of the filler particles. The following technical advantage is achieved thereby, for example, that the properties of the manufactured component are further improved.

[0011] In another technically advantageous embodiment of the stereolithography method, the structured layer is separated from the bottom for the subsequent layer. The following technical advantage is achieved thereby, for example, that further layers can be structured on this layer.

[0012] In another technically advantageous embodiment of the stereolithography method, the filler particles penetrate into the flexible bottom of the bath during setting of the first and / or further layer thickness. The following technical advantage is achieved thereby, for example, that a compact construction of the manufactured component is achieved.

[0013] In another technically advantageous embodiment of the stereolithography method, the mechanical stress of a membrane covering the bottom of the bath is determined by means of a force measuring device. The following technical advantage is achieved thereby, for example, that a rupture of the membrane can be prevented.

[0014] In another technically advantageous embodiment of the stereolithography method, the filler particles are accommodated in recesses of a pressure surface of the structure platform during the first setting of the layer thickness. The recesses can be formed in a removable replacement part of the structure platform. The recesses can be arranged in a hexagonal pattern or other symmetrical geometric structure. The following technical advantage is achieved thereby, for example, that the arrangement of the filler particles can be predetermined.

[0015] In a further technically advantageous embodiment of the stereolithography method, the filler particles are accommodated in recesses in the bottom of the vat or in a reference plane during the setting of the layer thickness. The recesses can be constituted in a removable replacement of the vat or the reference plane. The recesses can be arranged in a hexagonal pattern or other symmetrical geometry. Thereby, for example, the following technical advantage is also achieved, that the arrangement of the filler particles can be predetermined.

[0016] In a further technically advantageous embodiment of the stereolithography method, the vat and / or the structure platform is moved along the layer after hardening in order to arrange the filler particles staggered in the next layer. By alternatingly staggering along the lateral direction of the structure platform or the vat, for example, the following technical advantage is achieved, that the filler particles can be arranged staggered layer by layer and a uniform construction is achieved.

[0017] According to a second aspect, the technical task is solved by a stereolithography apparatus for carrying out the method according to the first aspect. The same technical advantages are achieved by the stereolithography apparatus as by the stereolithography method.

[0018] In a technically advantageous embodiment of the stereolithography apparatus, the stereolithography apparatus comprises a vat with a bottom, which can be constituted by a material, into which the filler particles can penetrate. Thereby, for example, the following technical advantage is also achieved, that a compact construction of the manufactured component is achieved.

[0019] In a further technically advantageous embodiment of the stereolithography apparatus, the material comprises a transparent, elastic film or a silicone layer. Thereby, for example, the following technical advantage is achieved, that a particularly suitable material is used, which allows the penetration of the filler particles.

[0020] In a further technically advantageous embodiment of the stereolithography apparatus, the structure platform, the bottom of the vat or the reference plane comprises recesses for accommodating the filler particles. Thereby, for example, the following technical advantage is achieved, that the filler particles can be arranged at predetermined positions.

[0021] In a further technically advantageous embodiment of the stereolithography apparatus, the bottom of the vat is replaceable. Thereby, for example, the following technical advantage is achieved, that the bottom can be adapted to the filler particles. BRIEF DESCRIPTION OF DRAWINGS

[0022] Embodiments of the application are shown in the drawings and are described in detail next.

[0023] In the drawings:

[0024] Figures 1A-1D a schematic construction of a stereolithography apparatus is shown;

[0025] Figure 2 a cross-sectional view of a workpiece of different manufacture is shown;

[0026] Figure 3A a schematic configuration of another stereolithography apparatus is shown;

[0027] Figure 3B a top view of a structured build platform is shown; and

[0028] Figure 4 a block diagram of a stereolithography method is shown. DETAILED DESCRIPTION

[0029] Figures 1A-1D A schematic configuration of a stereolithography apparatus 200 is shown. The stereolithography apparatus 200 is used for layerwise manufacturing of a workpiece or component 113. For this purpose, a photopolymer or monomer mixture of a suspension 100 is layerwise hardened by means of light. In addition to the photopolymer, the suspension 100 comprises filler particles 103. The filler particles 103 are embedded in the polymer matrix after hardening. The strength and wear resistance are improved by the filler particles 103. Furthermore, the filler particles 103 can improve the polishability of the workpiece 113 or reduce the tendency to discoloration.

[0030] The filler particles 103 are present, for example, with an average diameter of 30 μm to 80 μm. These fillers can be composed, for example, of metal oxide particles such as aluminum oxide particles, silicic acid particles, ceramic particles, particles composed of cross-linked polymers, composite particles, glass particles, thermosetting plastic particles or polymer particles.

[0031] In Figure 1A , the photohardened suspension 100 (resin) with the filler particles 103 is in a vat 105 of the stereolithography apparatus 200. The build platform 107 is in a return state. The filler particles 103 are randomly distributed in the suspension 100.

[0032] The vat 105 has a transparent bottom 109, so that the suspension 100 can be irradiated with light through the bottom 109 of the vat 105 to harden the polymer. For this purpose, an exposure control device 115 is present below the bottom 109, which can generate different light patterns. By means of the exposure control device 115, the polymer can be selectively layerwise hardened in desired contours and surfaces. Thereby, each individual layer can be structured in an arbitrarily predetermined surface.

[0033] In Figure 1BThe construction process is started. Here, the desired layer thickness for the first layer is initiated by the construction platform 107. The layer is constructed between the bottom 109 of the basin 105 and the flat underside of the construction platform 107. The minimum layer thickness is smaller than the diameter of the filler particles 103. The filler particles 103 penetrate completely or partially into the bottom 109 of the basin 105.

[0034] For this purpose, the basin 105 can have an elastic membrane 117, which is deformed by the filler particles 103. Then, the selective exposure of the set layer thickness takes place by the exposure control device 115, for example by a light pattern, so that this layer thickness is hardened on the illuminated sites. The pressure exerted by the construction platform 107 on the filler particles 103, which penetrate into the bottom 109 of the basin 105. This state is fixed by the exposure control device 115.

[0035] The bottom 109 of the basin 105 can be replaceable. The bottom 109 can also have an elastic membrane 117, which covers the bottom 109 of the basin 105 and presses the filler particles 103 into the membrane. The mechanical stress of the membrane 117 can be determined by means of a force measuring device. In this case, the construction platform 107 can only be moved up to the point at which the mechanical stress of the membrane 117 does not exceed a predetermined value. In addition, a rupture of the membrane 117 can be prevented.

[0036] The bottom 109 of the basin 105 can be placed on a glass plate, which constitutes a separate reference plane. Here, the glass bottom supports the bottom 109 of the basin 105 from below. If a membrane 117 or a basin 105 with a layer of silicone is used, the glass plate can prevent the overflow of the suspension 100 in the event of a rupture of the membrane 117 or the layer of silicone.

[0037] In the Figure 1C The construction platform 107 is returned again for the following layer. The constructed layer is separated from the bottom 109 for the following layer. The filler particles 103 protrude from the plane of the polymerized resin matrix, which lies on the construction platform 107 and constitutes a rough surface structure. The level of the suspension 100 is balanced in the basin 105. Thereafter, the stereolithography apparatus 200 is ready for the next layer construction. During the stereolithography process, the construction platform 107 does not completely protrude from the basin 105. The content of the basin 105 usually has a height of several mm, so that the suspension 100 flows in again after the construction platform 107 is lifted a little.

[0038] In the Figure 1DThe construction process is continued in such a way that the desired layer thickness is reinitiated by the construction platform 107. The layer thickness is in this case set between the already hardened layer and the bottom 109 of the pool 105. The filler particles 103 of the new layer thus also penetrate into the bottom 109 of the pool 105. A layer-like staggered arrangement of the filler particles 103 results because the filler particles 103 of the new layer deviate from the protrusions of the filler particles 103 of the already hardened layer.

[0039] A further exposure is then carried out, so that this layer also hardens. The filler particles 103 of the new layer fill the gaps between the filler particles 103 of the previous layer. The process of layer construction is repeated until the desired construction height of the workpiece 113 is reached.

[0040] The workpiece 113 producible using the stereolithography method has an internal filler distribution which is similar to the filler distribution of a bulk prozess, for example in injection molding or in a ground body from a blank. The wear resistance and other physical properties are close to ideal, since there are no longer parallel, filler-free matrix layers. The orientation at the time of construction plays only a minor role. The individual layers are parallel and can also only comprise a small number of filler particles 103 which extend into the next layer.

[0041] The additively manufactured workpiece 113 can be set to completely new physical properties using the filler of the interlayer bonding. In the case of dental materials, for example tooth materials or composite materials, it is possible to achieve materials whose properties are significantly close to conventionally manufactured tooth materials, prosthetic materials or composite materials. By using the filler, the gloss stability, the wear resistance or physical properties such as the bending strength or the impact toughness can be optimized. Furthermore, a (hard) rubber type which can be deformed poorly or less can be used for a prosthetic base material in order to adjust the impact resistance.

[0042] Figure 2 Cross-sectional views of workpieces 113-L and 113-R with different manufacture of layers 1 to 4 are shown. The workpiece 113-L on the left is manufactured using a conventional stereolithography method. In this workpiece 113-L, the filler particles 103 are arranged in parallel layers which are separated by filler-free intermediate layers. By concentrating the filler particles 103 on the layers, a non-uniform construction of the workpiece 113-L results.

[0043] Conversely, the workpiece 113-R on the right is manufactured in a new stereolithography method. In this workpiece 113-R, the filler particles 103 are distributed uniformly and structured over the entire volume, without the filler particles being separated by filler-free intermediate layers. Thereby it is achieved that the filler particles are partially extruded from their original layer during hardening. When the next layer is constructed, the filler particles then partially protrude into the layer. Although the filler particles 103 are shown uniformly large, the filler particles can have a size distribution.

[0044] Figure 3A A schematic construction of another stereolithography apparatus 200 is shown. In this stereolithography apparatus 200, the structure platform 107 comprises on its pressure face 119 recesses 111, into which the filler particles 103 can be partially accommodated during the first setting of the layer thickness. The structure platform 107 can also comprise protrusions, which the filler particles 103 have to deviate from when setting the layer thickness.

[0045] The structured structure platform 107 is moved to the correct distance for shaping the first layer. The filler particles 103 deviate from the structuring on the structure platform 107 and shape the arrangement scheme for the first layer. The filler particles 103 can then or can not sink into the bottom 109 of the pool 105.

[0046] Figure 3B A top view of the structured structure platform 107 is shown. The recesses or protrusions 111 are formed in the pressure face 119 of the structure platform 107. The recesses or protrusions 111 can be arranged in a hexagonal pattern or other symmetrical geometry in the structure platform 107. Thereby, the filler particles 103 can be arranged at desired locations.

[0047] The functionality of the stereolithography method is related to the filler distribution in the constructed first layer, since the position of the filler particles 103 determines the corresponding position in the next layer. The filler distribution in the constructed first layer is arbitrary by difficult-to-predict physical processes, for example based on rheology.

[0048] By the structured structure platform 107, a prescription for the spatial distribution of the excess filler particles is made for the first layer. It is thereby prevented that the particles are arbitrarily arranged in the first layer and this pattern is continued in the following layers by corresponding deviations into gaps.

[0049] The structured structure platform 107 prescribes a clear structure, so that the desired material properties of the workpiece can be set. For this, adapters or kits for the structured structure platform 107 with differently arranged recesses or protrusions 111 can be envisaged, which prescribe the structure for different filler sizes.

[0050] Of course, the protrusions or recesses 111 for positioning the filler particles 103 can also be formed in the bottom 109 of the basin 105 or in the reference plane.

[0051] Figure 4 A block diagram of a stereolithography method is shown. In a first step S101, a photohardening suspension 100 with filler particles 103 is accommodated in a basin 105. Next, in step S102, the photohardening suspension is set to a layer thickness of less than the diameter of the filler particles 103 with the aid of a structure platform 107 relative to the bottom 109 of the basin 105. In step S103, the set layer thickness of the suspension is hardened with the aid of light. Next, the structure platform 107 is raised, whereby the hardened layer is separated from the bottom of the basin 105 and steps S102 and 103 are repeated.

[0052] After repeating the steps, the basin 105 and / or the structure platform 107 can be moved laterally, i.e. to the left or to the right, relative to the basin 105 after hardening along the layers in order to set the filler particles 103 staggered in the next layer. Thereby, the uniformity of the construction of the workpiece 113 can be improved. Instead of the structure platform 107, the basin 107 can also be moved alternately relative to the structure platform 107 in the lateral direction. Thereby, a uniform construction of the workpiece 113 can also be achieved.

[0053] All features explained and shown in connection with the individual embodiments of the present application can be arranged in different combinations in the technical solution according to the present application in order to achieve its advantageous effects at the same time.

[0054] All method steps can be carried out by devices which are suitable for carrying out the respective method steps. All functions carried out by specific features can be method steps of the method.

[0055] The scope of protection of the present application is given by the claims and is not restricted to the features explained in the description or shown in the drawings.

[0056] List of reference signs

[0057] 100 suspension

[0058] 103 filler particles

[0059] 105 basin

[0060] 107 structure platform

[0061] 109 bottom

[0062] 111 recesses

[0063] 113 workpiece

[0064] 115 exposure control device

[0065] 117 film

[0066] 119 pressure surface

[0067] 200 stereolithography apparatus

Claims

1. A stereolithography method, wherein the stereolithography method comprises the following steps: - Contain (S101) a light-cured suspension (100) with filler particles (103) in a pool (105); - Using a structural platform (107), the light-cured suspension is adjusted (S102) relative to the bottom (109) of the pool (105) to a layer thickness smaller than the diameter of the filler particles (103); and -The adjusted layer thickness of the suspension is selectively hardened by light (S103). - For the next layer, the constructed layer is separated from the bottom (109).

2. The stereolithography method according to claim 1, wherein, The layer thickness is less than 5% of the diameter of the filler particles (103).

3. The stereolithography method according to claim 1 or 2, wherein, The filler particles (103) are infiltrated into the flexible bottom (109) of the pool (105) during the adjustment of the first and / or another layer thickness.

4. The stereolithography method according to claim 1 or 2, wherein, The mechanical stress of the membrane (117) covering the bottom (109) of the pool (105) is determined by means of a force measuring device.

5. The stereolithography method according to claim 1 or 2, wherein, The filler particles (103) are contained in the voids (111) of the pressure surface (119) of the structural platform (107) during the first adjustment of the layer thickness.

6. The stereolithography method according to claim 1 or 2, wherein, The filler particles (103) are contained in the voids (111) in the bottom (109) of the pool (105) or in the reference plane (110) during the adjustment of the layer thickness.

7. The stereolithography method according to claim 1 or 2, wherein, The pool (105) and / or the structural platform (107) are moved along the layers after hardening so that the filler particles are staggered in the next layer.

8. A stereolithography apparatus (200) for carrying out the method according to any one of claims 1 to 7.

9. The stereolithography apparatus (200) according to claim 8, wherein, The stereolithography apparatus (200) includes a pool (105) having a bottom (109) made of a material into which the filler particles (103) can permeate.

10. The stereolithography apparatus (200) according to claim 9, wherein, The material includes a transparent, elastic film (117) or a silicone layer.

11. The stereolithography apparatus (200) according to any one of claims 8 to 10, wherein, The bottom (109) or reference plane (110) of the structural platform (107) and the pool (105) includes a void (111) for accommodating the filler particles (103).

12. The stereolithography apparatus (200) according to claim 11, wherein, The bottom (109) of the pool (105) is replaceable.

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