Assembly and method for bath-based 3D printing

Abstract

The invention relates to an assembly for bath-based 3D printing comprising a receiving container for a liquid starting material, having a base which is formed by a flexible membrane (200) permeable to optical radiation (400), a vertically adjustable construction platform (302) and a print head (100) arranged on the membrane (200) below the base of the receiving container for emitting optical radiation. The print head (100) has an end face (105) directed towards the base of the receiving container, and can be moved by means of a movement device in parallel with the construction platform (302) in the printing region for 3D printing. A flow of a medium can be generated between the end face (105) and the membrane (200). Using the proposed assembly, the relevant layer thickness of the layer to be solidified can be set with high accuracy and improved control.

Description

[0001] Arrangement and method for bath-based 3D printing

[0002] Technical application area

[0003] The present invention relates to an arrangement for bath-based 3D printing, which has a receptacle for a liquid starting material that can be solidified by irradiation with optical radiation, said receptacle having a base or base region or an upper cover formed by a flexible membrane that is permeable to optical radiation, a build platform that can be moved vertically relative to the receptacle, and a print head arranged on the membrane below the base or base region or above the upper cover of the receptacle, via which print head the starting material for 3D printing can be irradiated through the membrane. The invention also relates to a method for bath-based 3D printing using such an arrangement.

[0004] In bath- or VAT-based 3D printing, thin liquid layers of a starting material, in particular photo resin, are solidified or cross-linked by optical radiation, usually UV radiation, with the radiation source carrying out the lateral xy structuring. The resolution in the vertical direction (z-direction) is determined by the thickness of a cured layer. To ensure good adhesion between successive layers, the curing depth is usually significantly greater than the layer thickness. The layer thickness is defined here by specifying the thickness of a new layer of the liquid, unsolidified or cured starting material. The layer thickness can be defined either by squeegeeing the free bath surface or by the distance to a transparent window or a transparent membrane.With a free bath surface equipped with a squeegee, the light is irradiated from above; with a transparent window / membrane at the bottom of the bath, the light is irradiated from below. In both cases, a z-axis moves the position of the build platform downwards (squeegee) or upwards (window). Furthermore, an arrangement is also possible in which a transparent membrane or window is placed on top of the bath surface, and the irradiation occurs from above.

[0005] The defined creation of thin layers of liquid photo resin is a prerequisite for the layer-by-layer construction of components through photocrosslinking in 3D printing to achieve high geometric fidelity. Depending on the application and size, as well as the desired resolution of a component, either squeegee coating or exposure through a transparent window is used. Typically, layer thicknesses are in the range of 25–200 μm, depending on the required resolution. For the exact reproduction of the data model, the layers in the printing process must have a homogeneous thickness and form a plane-parallel surface to the image plane.

[0006] In practice, doctor blade coating of the free surface results in deviations from a uniform layer for layer thicknesses < 100 pm. The structure of the component "models" the bath surface, for example by not completely filling pockets in the component or by creating a bulge at the edges that leads to an excessive build-up. For this reason, in high-resolution printing processes, an arrangement with irradiation from below through a transparent window or a transparent membrane with a geometric limitation of the layer thickness is preferred. This allows layer thicknesses in the range of approximately 25 - 200 pm to be produced in a defined manner.

[0007] However, it is necessary to control the forces arising from hydrodynamic effects between the last component layer and the confining window. When a thin gap is formed between two plates in a viscous medium, the hydrodynamic forces exert a normal force on the plates. The acting force can be estimated using the Stefan adhesion formula:

[0008] F = 3 / 2*nü*v* r 4 / h 3

[0009] Where r| is the viscosity of the medium, v is the detachment velocity, r is the radius of the plates and h is the gap height.

[0010] The viscosity of photo resins is typically around 1 Pas or even higher. For a free-standing structural element with a radius of 1 mm, a detachment rate of 1 mm / s and a gap of 25 pm results in a force of 0.3 N. If the radius is increased to 5 mm and the gap reduced to 10 pm, the force becomes 2945 N, which can destroy the structures. The forces that occur increase significantly with the lateral expansion of a component, so a solution must be found here.

[0011] In practice, the detachment force is limited by reducing the detachment speed, which significantly increases the process time. The forces generated can be limited by a slow, force-controlled movement of the build platform away from the window, forming a large gap many times the layer thickness, followed by a slow, force-controlled approach to the next target position. However, this process places a strain on the mechanical integrity of the components and represents a significant time factor in the overall process time.

[0012] State of the art

[0013] The doctor blade coating of the free bath surface is described in US 5258146 A. The doctor blade can have a rectangular, rounded or bevelled cross-section and can also be provided with slots. The fill level in the resin bath is measured and adjusted if necessary. A main difficulty here is achieving a flat surface. The flatness of the surface depends, for example, on the geometry of the component; in particular, the fill level over pockets is often different than over closed surfaces. The repeatability and flatness of individual thin layers of liquid resin over a component therefore depend not only on the exact fill level of the resin bath, but also on the locally different geometry of the 3D component and the already cross-linked structures.In numerous doctor blade studies, the influence of component geometry, doctor blade geometry, and doctor blade parameters on the hydrodynamic flow conditions and the uniformity of the resulting layers was investigated in detail. From this, rules of thumb were derived for a favorable design of the doctor blade shape and suitable doctor blade parameters, such as the size of the gap between the doctor blade and the bath surface, the doctor blade speed, and the number of passes. However, the experimental results show that a defined production of uniform layers with a thickness of less than 100 μm is not reliably possible in this way.

[0014] US 11312074 B2 and US 2021078251 A1 describe a structure consisting of a container that is open at the top and whose bottom is transparent to the radiation used to crosslink the photo resin. A liquid is layered on this transparent bottom. This liquid does not mix with the photo resin above it and has a higher specific density than the photo resin. In the resting state, this should create a flat interface between the two liquids. In addition, a movable element similar to a beam is provided which can be moved through both liquids at the height of the interface. The layer thickness of each layer is determined by the distance between the build platform or the previously crosslinked layer and the interface between the two liquids. The heavy layer of liquid at the bottom is intended to prevent the recently crosslinked layer from adhering to the bottom. The movable beam or beamThe squeegee serves to level the interface between the two liquid layers, which can be disturbed by the up-and-down movement of the component. Alternatively, an open, trough-like element can be moved along the interface instead of a solid beam.

[0015] US 2021 / 0178745 A1 describes a bending process of the resin bath floor to peel off the final built layer from the bottom of the bath. The bottom of the bath is formed by a freely clamped membrane that can sag under the weight of the resin and the component. A wiper or scraper can be positioned beneath the membrane to wipe the membrane from below, thereby positioning it correctly. The wiper can be designed, for example, as a cylindrical roller.

[0016] US 9895843 B2 describes a device which enables rotation of the component on the build platform relative to the membrane. The axis of rotation lies in the plane of the membrane, typically at the edge of the resin bath. However, with a special design, the axis of rotation can also lie within the build area. Due to the angular movement around the axis, with increasing distance from the axis there is an increasing path increment and an increasing speed with which the component and membrane are separated from one another. Due to minimal deformation of the component and membrane, a gap forms starting from the point with the greatest incremental movement. With increasing relative movement, this gap runs further into the interface between the component and membrane and separates it. The speed of the relative movement can be variable in order to limit the maximum shear and tensile forces that occur.From US 2022 / 0193987 A1 an arrangement for bath-based 3D printing according to the preamble of patent claim 1 is known, in which the print head has rollers via which it rests against the membrane. After completion of a layer of the component, the component is lifted with the build platform, whereby the membrane is deformed so that a linear peel-off edge is created on one edge, from which a gap arises between the cured layer and the membrane. When the component is lowered again to produce the new layer, the membrane is deflected in the opposite direction. By moving the print head with the rollers resting against the membrane, the membrane is then brought back into the correct position at a defined distance parallel to the build platform so that the next exposure process can take place.

[0017] WO 2022 / 224079 A1 describes an arrangement for bath-based 3D printing, comprising a receptacle for a liquid starting material that can be solidified by irradiation, an upper membrane, a build platform, and an irradiation device. A subunit has a first opening and a second opening, with air being directed from the first to the second opening, generating a flow between the membrane and the end face of the subunit. A fixed distance can be set between the membrane and the underside of the subunit.

[0018] The object of the present invention is to provide an arrangement and a method for bath-based 3D printing which, without contact of the print head with the membrane, enable an adjustment of the layer thickness of the respective layer to be newly solidified with an accuracy of a few pm or better and in which a simple detachment of the respective hardened layer from the membrane is achieved even with larger printing areas.

[0019] Description of the invention

[0020] This object is achieved by the arrangement and the method according to patent claims 1 and 9. Advantageous embodiments of the arrangement and the method are the subject of the dependent patent claims or can be derived from the following description and the exemplary embodiment.

[0021] The proposed arrangement comprises, in a known manner, a receptacle for a liquid starting material which can be solidified by irradiation with optical radiation, in particular UV radiation, and a building platform which can be moved vertically relative to the receptacle. Alternatively, the receptacle can also be correspondingly movable relative to the building platform. In a first alternative of the arrangement, the base or a base region of the receptacle is formed by a flexible membrane which is permeable to the optical radiation used for irradiating or exposing the starting material. Optical radiation is therefore to be understood as optical radiation of a wavelength range which is suitable for solidifying the starting material, preferably a photo resin. In a second alternative of the arrangement, an upper cover for the liquid starting material is formed by such a membrane.In this second alternative, the bath surface is covered by the membrane during 3D printing. The vertical mobility of the build platform or the receiving container relative to the build platform is achieved by an adjustment device of the arrangement to which the build platform or the receiving container is fastened. The arrangement further comprises a print head which is arranged on the membrane below the base or base region of the receiving container in the first alternative and above the upper cover in the second alternative, via which print head the area of ​​the starting material to be solidified is irradiated or exposed through the membrane. For this purpose, the print head has an end face directed towards the base of the receiving container with an opening or window for the passage of the optical radiation and with a surface area which is smaller than the surface area of ​​the flexible membrane.Preferably, the extent or area of ​​the front surface is less than 1 / 4, particularly preferably less than 1 / 10 of the membrane surface. The print head is attached to a traversing device with which it can be moved with its front surface parallel to the build platform at least within a printing area intended for 3D printing, in order to be able to irradiate the starting material through the membrane at any point in the printing area if necessary.

[0022] In the proposed arrangement, the print head has a plurality of openings and / or porous sections in the end face, hereinafter referred to as first and second opening(s) or first(r) and second porous section(s) for the purpose of differentiation, of which the first is(are) connected to at least one supply channel and the second is(are) connected to at least one suction channel for a liquid or gaseous medium. The openings and / or porous regions are arranged and designed in the end face in such a way that a flow of the medium can be generated between the end face and the membrane, via which flow a parallel gap of a defined gap thickness can be formed and maintained between the end face and the membrane.

[0023] In the proposed method for bath-based 3D printing with such an arrangement, each location of the layer to be solidified within the printing area that is to be exposed for printing is exposed one after the other by moving the print head. The flow between the membrane and the end face of the print head is adjusted in such a way that a gap of constant thickness is maintained between the end face of the print head and the membrane during irradiation of the layer. The thickness of the individual layers during 3D printing can be precisely adjusted by the defined thickness of the gap, the thickness of the membrane and the distance between the build platform and the membrane, which can be adjusted using the adjustment device. The layer thicknesses are preferably between 2 pm and 200 pm, particularly preferably between 5 pm and 50 pm.

[0024] In the proposed method and the associated arrangement, a print head, the front surface of which is generally much smaller than the entire build area or the entire 3D printing area, is moved over this printing area so that each location in the printing area to be exposed for printing can be exposed or irradiated one after the other. During irradiation, the membrane is outside the section of the front surface of the print head at a distance from the last solidified layer of the component that is greater than the desired layer thickness of the layer currently being processed and can be in a range from twice to 20 times this layer thickness. The membrane is only exposed by the print head or the 3D printing area directly at the print head in the current exposure area.the flow generated at the front face of the print head is positioned in such a way that exactly the desired layer thickness is achieved between the membrane and the last solidified layer of the component. The deflection or positioning of the membrane is achieved by pressurising it with a flowing medium and the hydrodynamic forces acting in this process. The exact position of the membrane can also be measured and adjusted using one or more sensors, preferably one or more optical sensors, on the print head. The or each sensor supplies the current distance to a control device for the supply and extraction of the medium, in which a control loop then ensures that the specified distance or the specified gap thickness is maintained. The thickness of the individual layers in 3D printing can therefore be precisely determined by the position of the component orThe build platform, the thickness of the membrane used, the position of the print head's face, and the thickness of the resulting gap between the print head's face and the membrane are determined. A gas, e.g., air, is preferably used as the flowing medium.

[0025] With the proposed method and the associated arrangement, the special design of the print head allows the layer thickness of the still liquid starting material to be controlled locally with an accuracy of a few microns or better in the area where the starting material, preferably a photopolymer or photoresin, is solidified or crosslinked by the optical radiation. In principle, the total printable area is not limited, so that even large components can be exposed.

[0026] When building up components layer by layer with a thin layer, the detachment of a cured layer from the membrane in the bath is associated with high forces, since the viscous starting material has to fill the resulting gap. This detachment becomes more difficult with increasing surface area, as the occurring forces can damage the stability and integrity of a component. However, with the proposed arrangement and the associated process, the thickness of the liquid layer of the starting material is only restricted locally in the area of ​​the front surface of the print head. The print head only exposes a portion of the entire surface to be exposed, moving over this area until all areas are exposed. The exposure of the entire surface is possible both by "stitching" (several individual exposures next to one another) and by "scrolling" (the image content is moved synchronously during a movement).The layer thickness only needs to be reduced to the target thickness of a layer to be solidified in the area of ​​the print head or the front face of the print head. Outside of this area, the layer thickness—and thus the gap between the component and the membrane—can be many times greater than the target thickness, thereby reducing the hydrodynamic forces between the membrane and the component. The membrane remains movable up and down in these areas, allowing the gap to adapt flexibly to the forces occurring in the viscous flow of the starting material.

[0027] The front face of the print head is a flat surface that is plane-parallel to the component surface or the surface of the build platform and preferably has an angled or conical edge to make it easier to move the membrane to the desired position. In the first arrangement alternative, the front face of the print head is arranged directly beneath the membrane that seals off the receiving container and thus also the build space of the 3D printer at the bottom. In the second arrangement alternative, the front face of the print head is arranged directly above the membrane that covers the bath surface. The front face of the print head is selected to be smaller than the surface area of ​​the membrane and also smaller than the printing area of ​​the 3D printer, i.e. the area within which 3D printing is possible.A section of the end face, preferably the center of the end face, is transparent to the optical radiation required to harden the starting material, particularly UV radiation. This can be achieved by an open channel or a corresponding window in the end face. The optically transparent channel or the corresponding window typically has a cross-sectional area of ​​1 to 4 cm. 2 so that the radiation from a digital light processor (DLP) or a laser scanner (SLA) can pass through unhindered. The light source and the DLP or SLA can be part of the print head or arranged independently of the print head, with the radiation then being guided to the print head via a suitable beam guide, for example, via one or more light guides.

[0028] The openings or porous sections for supplying and extracting the liquid or gaseous medium on the front face of the print head are preferably arranged coaxially around the optically transparent channel or the optically transparent window in an annular or otherwise shaped zone. The medium used, preferably air or other gases, can flow through these openings or bores or porous sections. One or more of these openings or porous sections are used to supply the medium, for example by blowing in air (pressure line), and one or more others are used to extract the medium, for example the air (vacuum line). The individual supply and discharge areas can be arranged differently. For example,an inner coaxial arrangement for pressurizing around the central optically transparent channel and an external coaxial arrangement of extraction openings (or porous extraction sections) are effective. Alternatively, both functions can be carried out by a grid of openings or holes that overlap on the same surface. The openings or holes are pressurized or negatively pressurized in such a way that, due to the flow dynamics, a stable gap, e.g. an air gap, is formed between the membrane and the front face of the print head. This gap ensures precise positioning of the membrane at a predetermined distance from the front face of the print head. The thickness of the gap, in particular of an air gap created by an air cushion, is determined by the number, diameter and density of the openings or holes or pores in the front face and by the pressure ratio between the pressure line orsupply line and vacuum line or extraction line. The vacuum preload increases the stiffness of the arrangement and the position of the diaphragm is precisely defined. The stiffness of an air bearing can be increased by "preloading". For this to happen, an external force must act normal to the gap to reduce it. The hydrodynamic pressure of the medium flowing into the gap acts in contrast. The external force can be generated by applied masses (weight), magnetic forces, or vacuum. For this purpose, pockets can be introduced into the bearing surface around the extraction openings, for example. The maximum pressure difference and the surface area of ​​the pockets determine the preload. Alternatively, the print head could be preloaded normal to the air gap using electromagnetic forces.The cushion formed between the front surface of the print head and the membrane from the flowing medium, in particular air cushion, reduces friction and prevents abrasion of the membrane when the print head is moved over the membrane in order to expose areas to be printed across the entire printing area.

[0029] In an advantageous embodiment, the front surface of the print head is heated to a temperature of 30 to 90°C by a heating device formed in the print head in order to reduce the viscosity of the starting material located directly above it. In another embodiment, the flowing medium is heated to a temperature of 30 to 90°C in order to heat the front surface and the membrane and thus also reduce the viscosity of the starting material located directly above it.

[0030] In a further embodiment, in addition to the radiation source for solidifying the starting material, infrared radiation can also be passed through the optically transparent channel or the optically transparent window to locally increase the temperature of the starting material, in order to thereby reduce the viscosity of the starting material in this area.

[0031] The optically transparent channel or the optically transparent window in the front face of the print head can have different cross-sectional shapes, for example, a round or rectangular cross-section. In an advantageous embodiment, in a special design of the print head, a microscope objective with a high numerical aperture (0.4 < NA < 1.4) for the use of MPP (multiphoton polymerization) can be mounted in the optically transparent channel at a short distance from the membrane. This enables the use of MPP in air or with liquid (immersion objective) to solidify the build material.

[0032] A liquid medium such as water, isopropanol, or other organic liquids can be used as the medium for forming the defined gap between the front face of the print head and the membrane. The flowing medium is preferably gaseous, e.g., air, nitrogen, or other gases. When using porous sections in the front face, the pore size is preferably in the range of 1 to 50 pm; the diameters of bores or openings are typically in the range of 0.1 to 0.5 mm.

[0033] The proposed arrangement and the associated process enable 3D printing with photopolymers at high lateral and axial resolutions of < 30 pm. They can be used, for example, in the jewelry industry, earmolds, dental technology, or for the production of microfluidic chips and micromechanical components. This is, of course, not an exhaustive list.

[0034] Short description of the drawings

[0035] The proposed arrangement and the associated method are explained in more detail below using an exemplary embodiment in conjunction with the drawings.

[0036] Fig . 1 is a schematic representation of a

[0037] Section of an exemplary arrangement according to the present invention in

[0038] cross-sectional view; and

[0039] Fig. 2 is a plan view of the front face of the print head from Figure 1.

[0040] Ways to implement the invention

[0041] An essential component of the proposed arrangement is the design of the print head for exposing the starting material through a membrane which is transparent to the optical radiation used and which, in the first alternative of the arrangement, forms the base or a base region of the holding container for the liquid starting material and, in a second alternative of the arrangement, covers the bath surface of the liquid starting material. Figure 1 shows a section of an exemplary arrangement according to the first alternative, in which only the membrane 200 forming the base region or base of the holding container can be seen. The side walls of this holding container are not shown. In the present example, liquid photo resin is filled into this holding container, which is not visible in the illustration.A build platform 302 is immersed in this liquid photo resin and can be moved in a defined vertical direction via an adjustment device 303 in order to set a defined distance from the bottom of the receiving container and thereby a defined layer thickness of the still liquid material between the bottom and the build platform or the last hardened layer 301 for the production of the component. In the proposed arrangement, the print head 100 used has an end face 105 which, in this example, has a central opening or a corresponding optically transparent window 104 for the passage of the radiation 400 used to expose the photo resin. Supply openings 102 (or corresponding porous sections) and suction openings 103 (or corresponding porous sections) are arranged around this central opening or this central window 104, as is shown schematically in Figure 1.The supply openings 102 are used to apply pressure through a flowing medium, and the suction openings 103 are used to suction out the flowing medium, air in the present example. By suitable control of the supply and suction, an air cushion can be created between the end face 105 of the print head 100 and the membrane 200. By creating this air cushion, the membrane 200 is raised accordingly in this area, as is shown very schematically in Figure 1. In this way, a gap of defined thickness can be maintained between the end face 105 and the membrane 200 during exposure and thus a defined distance between the membrane 200 and the build platform 302 or the last cured layer 301 can be ensured. The correct thickness of the air cushion is preferably monitored via distance sensors 101 in the print head 100.In the remaining areas, the membrane 200 has a correspondingly greater distance from the build platform 302, as is also schematically indicated in Figure 1. This enables exposure of a defined layer thickness of the starting material without complicating the detachment of the solidified layer from the membrane 200 when printing larger areas.

[0042] Figure 2 shows a plan view of the front face 105 of the print head shown in Figure 1, in which the coaxial arrangement of the supply and suction openings 102, 103 around the central channel or the central window 104 in the front face 105 can be seen in this example.

[0043] Reference symbol list

[0044] 100 printhead

[0045] 101 Distance sensor to the membrane

[0046] 102 Opening for pressurization by a flowing medium

[0047] 103 Extraction opening for the extraction of the flowing

[0048] Medium

[0049] 104 optional window

[0050] 105 Front surface of the print head

[0051] 200 membrane

[0052] 301 last layer of a component in construction

[0053] 302 construction platform

[0054] 303 Adjustment device for adjusting the construction platform in the vertical direction

[0055] 400 radiation to crosslink the photo resin

Claims

Patent claims 1. Arrangement for bath-based 3D printing, the - a receptacle for a liquid starting material which can be solidified by irradiation with optical radiation (400), having a bottom or bottom region formed by a flexible membrane (200) permeable to optical radiation, or having an upper cover for the liquid starting material formed by a flexible membrane (200) permeable to optical radiation, - a construction platform (302) and an adjustment device (303) by means of which the construction platform (302) and the receiving container can be moved vertically relative to one another, and - a print head (100) arranged below the bottom or bottom area of the receptacle or above the upper cover on the membrane (200), -- which has an end face (105) directed towards the bottom of the receiving container with an opening or a window (104) for the passage of the optical radiation (400) and with a surface which has a smaller extent than a surface of the flexible membrane (200), -- and which is fastened to a displacement device with which it can be moved with its end face (105) parallel to the construction platform (302) at least in one printing area for 3D printing in order to supply the starting material to to be able to irradiate any point of the printing area through the membrane (200), characterized in that the print head (100) has first and second openings (102, 103) and / or porous sections in the end face (105), of which the first (102) are connected to at least one supply channel and the second (103) are connected to at least one suction channel for a liquid or gaseous medium and which are arranged and designed such that a flow of the medium can be generated between the end face (105) and the membrane (200), via which flow a parallel gap of defined thickness can be maintained between the end face (105) and the membrane (200).

2. Arrangement according to claim 1, characterized in that the print head (100) has one or more sensors (101) by means of which the thickness of the gap between the end face (105) and the membrane (200) can be measured, and which is connected to a control device for the supply and suction of the liquid or gaseous medium in order to keep the thickness of the gap constant at a certain value.

3. Arrangement according to claim 1 or 2, characterized in that the opening or window (104) for the passage of the optical radiation (400) has a cross-sectional area of between 1 cm 2 and 4 cm 2 has .

4. Arrangement according to one of claims 1 to 3, characterized in that the first and second openings (102, 103) and / or porous sections in the end face (105) are each arranged on coaxial paths around the opening or window (104) for the passage of the optical radiation (400).

5. Arrangement according to one of claims 1 to 4, characterized in that the porous sections in the end face (105) have a pore size in the range of 1 to 50 pm.

6. Arrangement according to one of claims 1 to 5, characterized in that the print head (100) has a heating device with which the end face (105) can be tempered to a temperature between 30°C and 90°C.

7. Arrangement according to one of claims 1 to 6, characterized in that a microscope objective with a high numerical aperture NA of 0.4 < NA < 1.4 for the use of multiphoton polymerization is arranged in the opening for the passage of the optical radiation (400).

8. Arrangement according to one of claims 1 to 7, characterized in that that the end face (105) has an area which is less than 1 / 4 of an area of the membrane (200).

9. Method for bath-based 3D printing with an arrangement according to one or more of the preceding claims, in which for irradiation of several areas of a layer of the starting material to be solidified within the receiving container of the arrangement - the print head (100) is positioned by moving parallel to the construction platform (302) below the respective area in the case of a membrane (200) forming the bottom or bottom area of the receiving container, or above the respective area in the case of a membrane (200) forming the upper cover for the liquid starting material, - by supplying and sucking off a liquid or gaseous medium via the first and second openings and / or porous regions in the end face (105) of the print head (100), a flow is generated between the membrane (200) and the end face (105) of the print head (100) and is adjusted such that a parallel gap of a gap thickness is formed between the end face (105) and the membrane (200), wherein the gap thickness is selected such that, with a corresponding position of the build platform (302), a desired layer thickness of the layer of the starting material to be solidified is established in the receiving container, - and the irradiation of the layer then at this gap thickness through the membrane (200) occurs .

10. Method according to claim 9, characterized in that the gap thickness is monitored with one or more sensors (101) in the print head (100) and regulated to the selected value.

11. Method according to claim 9 or 10, characterized in that the position of the building platform (302) and the gap thickness are adjusted so that a target layer thickness between 2 pm and 200 pm is obtained.

12. Method according to one of claims 9 to 11, characterized in that the irradiation with a digital light processor or a laser scanner takes place through the opening or the window (104) of the end face (105) of the print head (100).

13. Method according to one of claims 9 to 12, characterized in that the end face (105) of the print head (100) is tempered to a temperature between 30°C and 90°C.

14. Method according to one of claims 9 to 12, characterized in that the liquid or gaseous medium is tempered to a temperature of between 30°C and 90°C becomes .

15. Process according to one of claims 9 to 14, characterized in that water or isopropanol is used as the liquid medium.

16. A method according to any one of claims 9 to 14, characterized in that air or nitrogen is used as the gaseous medium.

17. Method according to one of claims 9 to 16, characterized in that for solidifying the layer of The technique of multiphoton polymerization is used to produce the starting material.

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