EP4291384A1

EP4291384A1 - Method for printing a 3d object in a photoreactive composition, and printer suitable for implementing the method

Info

Publication number: EP4291384A1
Application number: EP22704913.7A
Authority: EP
Inventors: Patrice Baldeck; Azeddine TELLAL; Kevin Heggarty
Original assignee: Centre National de la Recherche Scientifique CNRS; Universite Claude Bernard Lyon 1 UCBL; Ecole Normale Superieure de Lyon; Institut Mines Telecom IMT
Current assignee: Centre National de la Recherche Scientifique CNRS; Universite Claude Bernard Lyon 1 UCBL; Ecole Normale Superieure de Lyon; Institut Mines Telecom IMT
Priority date: 2021-02-09
Filing date: 2022-02-09
Publication date: 2023-12-20
Also published as: WO2022171704A1; US20240051233A1; FR3119562A1

Abstract

A method for printing a 3D object in a photoreactive composition space, which object is defined by a 3D image comprising a plurality of illuminated points, the printing method comprising the following steps consisting of: • extracting (ET2) from the image a sequence of partial images otherwise referred to as mosaics, the sequence comprising at least one mosaic, each mosaic comprising a plurality of solid areas and each solid area comprising an illuminated point or a group of adjacent illuminated points, • in an axial direction (Z) and inside the composition space, projecting (ET3) the sequence of mosaics, the projection of each mosaic forming, in the composition space, a plurality of light areas, each light area corresponding to a solid area of the projected mosaic and each being suitable for causing a photoreaction in an associated composition block, • in a solid area of a mosaic, adjusting the number of illuminated points and the distribution of the illuminated points in the solid area such that, when the mosaic is projected into the composition space, the light area associated with the solid area causes the photoreaction in an associated composition block with a desired axial resolution, and • in the same mosaic, distributing the solid areas such that, when the mosaic is projected into the composition space, the composition does not react between the light areas associated with the plurality of solid areas of the mosaic. The invention also relates to a printer suitable for implementing a printing method as described above. The disclosure relates to the 3D printing of objects having microscopic and/or macroscopic dimensions by projecting images with high-axial resolution into non-linear irradiated photoreactive compositions.

Description

DESCRIPTION

Title of the invention: Process for printing a 3D object in a photoreactive composition, and printer suitable for implementing the process.

Technical area

The present application relates to an optical projection method suitable for printing in three dimensions (3D) in a volume of composition, as well as a 3D printer, using a nonlinear photochemical reaction induced by absorption of an energy supplied by a beam luminous to modify a photoreactive composition.

State of the art

The composition to be modified can be of various types. This composition may comprise a resin solidifying by polymerization or photo-crosslinking, a resin whose solubility properties are modified by photochemistry, proteins solidifying by photo-crosslinking, or metal salts solidifying by photo-reduction, or more generally any composition of which a physical (color, mechanical resistance, etc.) or chemical property is modified under the effect of a light signal. The excess of unmodified composition is dissolved by a suitable solvent after the modification. The modification of the composition is very localized because the yields of these photochemical reactions result from a nonlinear chemistry in irradiation or in fluence. For example, the yields of these photochemical reactions induced by two-photon absorption are proportional to the square of the intensity of the laser source used, so that the modification of the composition is very localized. In other examples, the nonlinearity is obtained by a mechanism of successive addition of photons, or by a threshold polymerization mechanism, or by a nonlinear chemical mechanism.

The patent DI = FR3023012 describes a 3D printer in which a laser beam of appropriate wavelength and power is focused successively at points of a reactive composition so that the volumes of the material located at the successive focusing points of the beam are modified by a photochemical reaction induced by two-photon absorption.

In Dl, the 3D printer comprises a laser source, a focusing lens and a composition tray to be modified resting on a table, said table being able to be moved according to directions orthogonal (X, Y directions) or parallel (Z axial direction) to the direction of propagation of a laser beam produced by the source.

In operation, the laser beam is focused by the lens at a focal point located in the composition to be modified, the power of the beam decreasing as it moves away from the focal point.

Around the focal point, where the power of the light beam is sufficient, the composition changes locally to form a voxel of this composition. Focal volume is a volume of composition centered on a focal point, volume in which the energy of the light beam is sufficient to trigger the modification of the composition.

In Dl, the XYZ table is controlled so that the focal volume associated with the focal point of the beam is moved through the material to form voxels one after another until the volume of the 3D object to be printed has been solidified. The object is thus printed voxel by voxel, first in a plane orthogonal to the beam and defined by the directions X, Y then plane by plane along the direction Z.

As expressed in the prior art of Dl, the use of such a 3D printer makes it possible to print voxels of dimensions less than a micrometer, or even a hundred nanometers with a very high resolution, of the order of a few tens of nanometers. Such a printer is thus suitable for producing objects of very small size, comprising a small number of voxels.

But for the production of objects having dimensions at least 1000 times greater than the dimensions of a voxel, i.e. of the order of a millimeter or more, the printing time becomes very long when a very high resolution is sought.

To shorten the printing time, Dl proposes a solution for adjusting the size of the voxels during printing, thus making it possible to print successively very small voxels and larger voxels. This technical solution effectively makes it possible to accelerate the printing time of an object, but to the detriment of the resolution, in particular the axial resolution (along the Z axis), in the zones where the voxels are of larger size. This is explained because an increase in the lateral dimensions (along the X and Y axes) of the voxels mechanically leads to a reduction in the lateral but also axial resolution as shown in the document D2 = "Hernandez-Cubero, O. "Advanced Optical methods for fast and three-dimensional control of neural activity." Paris-Descartes University, France (2016)”. Document D3 = "Microstereophotolithography using a liquid crystal display as dynamic mask-generator", A. Bertsch, S. Zissi, JY Jézéquel, S. Corbel, JC André, Microsystem Technologies (1997)42-47, Springer Verlag 1997, proposes a faster 3D printing process by light-curing 2D images on the surface of the resin. Axial resolution is obtained by stereolithography fabrication (layer by layer) and the addition of an absorber to limit the propagation of light outside the layer. The implementation of this method is moreover limited to the use of liquid resins in order to be able to move the object being manufactured in the resin when the layer is changed.

Document D4 = “Saha, Sourabh K., et al. "Scalable submicrometer additive manufacturing." Science 366.6461 (2019): 105-109. describes the use of a space-time compression technique to achieve axial resolution when projecting a 2D image within the volume of a light-cured composition. This process requires the use of laser sources with femtosecond pulses and cannot be generalized to other photopolymerization light sources.

The document D5= “Regehly, Martin, et al. "Xolography for linear volumetry 3D printing." Nature 588.7839 (2020): 620-624. describes the use of a 3D light-curing technique based on the intersection of two light beams of different colors. The first beam projects, without axial resolution, the images to be polymerized into the resin tank. Propagation takes place without photochemical reaction up to the point of intersection with the second beam, a perpendicular sheet of light, which makes the photoinitiator molecules sensitive to the color of the first beam, and therefore makes it possible to obtain the axial resolution. This process is limited to the use of very specific photoinitiator molecules and radical polymerization resins. It cannot be generalized to the photo-chemical systems used in the state of the art.

Document D6 = "One-Step volumetry additive manufacturing of complex polymer structures" Shusteff, Maxim, Allison EM Browar, Brett E. Kelly, Johannes Henriksson, Todd H. Weisgraber, Robert M. Panas, Nicholas X. Fang, and Christopher M Spadaccini. "One-step volumetric additive manufacturing of complex polymer structures." Science advances 3, no. 12 (2017): eaao5496, describes a new technology of projecting a solid 3D image into the nonlinear photoreactive composition tray, which can dramatically speed up print time. In addition, the projection, and therefore the chemical reaction, takes place inside the composition tank itself and not on the surface, so that it is no longer necessary to move the table supporting the composition tray or to use a mobile sample holder in the composition tray. Also, it becomes possible to use viscous photoreactive compositions insofar as the projection is carried out inside the volume of composition and where it is no longer necessary to move a sample holder in the composition tank. For this new technology, the fabrication of millimetric objects requires the orthogonal addition of three 2D images to obtain the axial resolution by nonlinear polymerization only at the places of addition of the projected irradiations. This makes the optical assembly complex and limits the 3D geometric shapes that can be printed.

The recent development of non-linear resins, such as those described in document D7 = WO2019025717, optimized for very localized photopolymerization such as STTA-UC, makes it possible to envisage the development of new ultra-fast 3D printers using the direct projection of 2D or 3D images. in the volume of the resin.

However, it is still necessary to solve the problem of the loss of axial resolution linked to the lateral dimension of the luminous zones to be polymerized.

Description of the invention

The present invention aims to overcome at least one of the drawbacks of the known printing methods and printers mentioned above, and in particular the problem of the loss of axial resolution in the luminous zones to be reacted by the image projection.

To this end, the invention proposes a process for printing a 3D object in a volume of photoreactive composition, an object defined by a 3D image comprising a plurality of illuminated points, a printing process characterized in that it comprises the following steps, consisting of:

- extracting (ET2) from the image a sequence of partial images otherwise called mosaics, the said sequence comprising at least one mosaic, each mosaic comprising a plurality of flat areas and each flat area comprising an illuminated point or a group of adjacent illuminated points , and

- in an axial direction (Z) and inside the composition volume, project (ET3) the sequence of mosaics, the projection of each mosaic forming, in the composition volume, a plurality of light zones, each light zone corresponding to a flat area of the projected mosaic and each light zone being adapted to generate a photoreaction of an associated composition block, and method characterized in that:

- in a solid of a mosaic, the number of illuminated points and the distribution of the illuminated points in the said solid are adjusted so that the projection of the said mosaic in the composition volume, the luminous zone associated with the said solid generates the photoreacting a composition block having a desired axial resolution, and

- in the same mosaic, the flat areas of illuminated dots are distributed so that, during the projection of the said mosaic in the volume of composition, the composition does not photoreact between the luminous zones associated with the plurality of flat areas of the said mosaic.

The desired axial resolution is a process parameter, chosen by the user, depending on the resolution he wishes to obtain for the printed physical object.

In mosaics, solids can have various shapes, for example a compact shape, an elongated shape, a hollow shape, etc.

The resolution of a printed object is directly related to the resolution of the optical image projected into the composition for printing. The projection of a digital image comprising solid areas (or groups of illuminated dots) comprising a large number of illuminated dots results in practice in an optical image with low axial resolution, and results in a printed object with low axial resolution. Also, rather than printing an object by projecting a single digital image resulting in the composition by an optical image with low axial resolution and resulting in a printed object having a low axial resolution, the invention proposes to print the same object by successive projections of partial images (or mosaics) comprising solid areas each comprising a smaller number of illuminated points to maintain optimum axial resolution. Indeed, the small flat areas have sufficient irradiations to polymerize only around their focal points, and their diffracted intensities are too low to trigger a parasitic polymerization reaction degrading the axial resolution, as will be better seen further on. The essential step ET2 of the invention thus aims to limit the size of the flat areas projected. According to one embodiment of the method, the image of the object to be printed is a 3-dimensional image, and the mosaics and the solid areas in said mosaics are also in 3D.

According to another mode of implementation, the method can comprise an initial step (ET1) consisting in cutting the 3D image of the 3D object into a series of 2D images representative of the object to be printed in parallel planes between them and perpendicular to the axial direction of image projection in the composition volume, and in that it also comprises the following steps ET2 to ET4, repeated for each 2D image and consisting of:

- extracting (ET2) the sequence of mosaics from said 2D image and projecting (ET3) the sequence of mosaics along the axial direction in a focal plane located in the volume of photoreactive composition and perpendicular to the axial direction, and:

- move (ET4) the focal plane in the composition volume.

This embodiment allows layer-by-layer printing of the 3D object directly in the composition volume, and not on the surface of the composition as is the case with conventional layer-by-layer stereolithography methods. In addition, moving the focal plane in the composition avoids moving the object being printed in the composition volume. It thus becomes possible to use viscous or even solid compositions. Also, it is no longer necessary to use reinforcements to maintain, during its movement in the composition, a fragile object being printed.

The invention also proposes a printer suitable for the implementation of a printing method described above, printer comprising in particular:

- a tank (2) containing a volume of photoreactive composition, for example a photopolymerizable resin solidifying by a nonlinear polymerization mechanism and

- an image projector (10) arranged to project a focused image, with a desired axial resolution, in the composition volume, the printer also comprising means arranged to implement the printing method according to one of preceding claims, said means comprising a generator (15) of mosaic sequences arranged to extract from the image of the object to be printed a sequence of mosaics and supplying the sequence of mosaics to the projector for performing step ET3 of projection.

The image projector is chosen with lateral and axial optical resolutions adapted to the lateral and axial resolutions desired for the object to be printed.

Brief description of figures

Other characteristics and advantages of the invention will appear on reading the detailed description of exemplary embodiments of the invention, given by way of example only, and with reference to the appended drawings in which:

- [Fig. 1] schematically presents a printer according to the invention,

- [Fig. 2] schematically presents an essential step of a printing process according to the invention

- [Fig. 3] presents test results facilitating the understanding of the essential step of the invention, and

- [Fig. 4] presents other test results facilitating the understanding of the essential step of the invention.

Definitions

A digital image of a physical object to be printed is defined by a plurality of illuminated dots distributed in a matrix comprising illuminated dots and unlit dots, the illuminated dots defining the object to be printed. A flat object can be represented by a two-dimensional (2D) dot matrix, the dots of which are commonly called pixels. A three-dimensional (3D) solid object can be represented by a three-dimensional point matrix, a matrix whose points are commonly called voxels.

By convention, we will use the adjective “adjacent” to talk about two elements that are side by side and that touch each other; for example, in an image or a matrix representing an image, adjacent points touch on one side.

Also by convention, an axial direction Z is defined as being a direction of projection of an image by a projector in a composition volume, and we define two lateral directions, X, Y, perpendicular to each other and perpendicular to the axial direction Z (see the reference figure 1).

By “volume of composition” is meant conventionally the contents of a container containing said composition, the volume of composition being delimited by the edges of the container.

By "projection in a composition volume", we mean a projection of an image inside the composition volume, and not a projection under the surface of the composition volume, as is commonly carried out according to conventional methods of layer-by-layer printing (stereolithography).

A "solid" comprises a lit point or a group of adjacent lit points in which each lit point is adjacent to at least one other lit point of the same group. For the purposes of the invention, it is considered that the dimension of a compact solid corresponds to its mean diameter, and that the dimension of an elongated solid corresponds to its mean width.

A spacing between two flat areas is a measured spacing (in millimeters, micrometers, nanometers, etc.) between an illuminated point located on one edge of one of the areas and an illuminated point located on an edge of the other of the areas. The distance between two solids is the minimum value of the spacing between two solids.

By "bright area" is meant an illuminated area in the composition during the projection of a solid area of illuminated dots, where the light intensity is sufficient to generate a reaction of the composition. A luminous zone is generally larger than a zone in which a solid color is projected, as will be seen later in the examples of FIGS. 3 and 4, due to the propagation of the light beam beyond the projection zone.

A mosaic is a partial digital image of the global digital image of a real object; a mosaic is extracted from a (complete) image of said object; a mosaic is of the same size, in terms of number of light points, as the digital image from which the mosaic is extracted; a mosaic includes only part of the illuminated points of the image from which the mosaic is extracted.

The optical "axial resolution", also called optical "axial length", of a light beam is the distance in the direction of propagation between two opposite points of a maximum intensity peak which correspond to half of the maximum intensity. The optical "lateral resolution" of a light beam is the distance, in a lateral direction perpendicular to the direction of propagation, between two opposite points of a peak of maximum intensity which correspond to half of the maximum intensity. Finally, for a photoreactive composition, the “resolution of the photoreaction” is determined by the optical resolution of the light beam generating the photoreaction; it can be smaller or larger than the optical resolution of the light beam, depending on the type of composition and the conditions of irradiation above the minimum irradiation necessary for the photoreaction.

Detailed description of embodiments of the invention

As said previously, the invention relates to the printing of 3D objects by projection of images in a volume of photoreactive composition, the modification of the composition of which is localized in the places of intense irradiation. The invention more specifically proposes a method for printing a 3D object in a volume of photoreactive composition, an object defined by a 3D image comprising a plurality of illuminated points.

The printing process according to the invention comprises the following steps, consisting of:

- in an axial direction (Z) and inside the composition volume, projecting (ET3) the sequence of mosaics into the photoreactive composition volume, the projection of each mosaic forming, in the composition volume, a plurality of zones luminous zones, each luminous zone corresponding to a flat area of the projected mosaic and each luminous zone being adapted to generate a photoreaction of an associated composition block.

A solid can be two-dimensional (X, Y) or three-dimensional (X, Y, Z), depending on whether the mosaic that contains the solid is two-dimensional or three-dimensional. FIG. 3 shows the influence of the dimensions of the solid tints on the optical resolution necessary to obtain the axial resolution of the transformed composition block after projection of a solid tint image. The projected image was generated by the holographic projection of the spatial phase modulation of the laser beam, using a Zeiss *100 Aplan NA=1.3 microscope objective. Figures 3a, 3b represent the XY projections, Figures 3ay, 3by represent the YZ projections and Figures 3az, 3bz represent the XZ projections of the images obtained with a CMOS camera at different axial positions around the XY focal plane in which the images are projected.

FIG. 3a shows an optical image comprising a single luminous zone resulting from the projection of a digital image comprising a single square solid area. The luminous zone corresponding to the solid area, of dimension 20 pm * 20 pm, is well delimited in the X,Y plane of projection (fig 3a), it spreads out on the other hand very widely in the YZ plane (fig. 3ay) as in the X,Z plane (fig. 3az) on either side of the focal plane in the Z axial direction and in very diffracted directions with respect to the Z axial direction. The optical axial resolution is 22 pm whereas the axial resolution of an optical solid with a single light point is 0.5 µm.

FIG. 3b shows an optical image comprising luminous zones resulting from the projection of a digital image comprising a plurality of smaller square flat areas, fairly distant from each other; the distance between two luminous zones is 10 μm in the X, Y plane of projection. Each luminous zone, with dimensions 2pm * 2pm in the X, Y, Z reference (fig. 3b), remains very bright in the Z direction (fig 3by and fig3bz) over a depth substantially equal to the dimensions X, Y (2pm) of the luminous zone, said depth defining the axial resolution of the printed object. Beyond that, the light intensity is lower and is not sufficient to cause a reaction of the composition.

FIGS. 4 show the influence of the distance between flat tints each comprising an illuminated point on the luminous zones resulting from the projection of said flat tints, and therefore the influence of said distance on the reaction of the illuminated composition. The tests are carried out here with the same optical projection system as that of the tests presented in fig 3.

Figures 4 are results of projection tests of a digital image comprising a plurality of equidistant areas, the projections of the areas having dimensions of 0.25 μm * 0.25 μm, in the X,Y projection plane, and dimensions of 0.5 μm in Z. the diffraction limit, that is to say with perfect focusing, imposed by the characteristics of the optical system used.

When the flat areas are separated by a distance of 2 μm from each other in the projection plane, the light areas they generate are very sharp and distinct from each other, both in the projection focal plane (fig. 4a) than along the axial plane X Z (fig 4az). Between the luminous zones, the luminous intensity is weak and insufficient to cause a modification of the composition.

When the flat areas are only separated by a distance of 0.8 μm from each other in the projection plane, the light areas they generate are not very sharp and not very distinct from each other in the XY projection plane (fig. 4b). In the axial direction Z, in the plane XZ (FIG. 4bz) and more generally in any plane parallel to the axial direction, the light zones spread out to the point of overlapping. At the places where the luminous zones resulting from two flat areas overlap, the resulting energy can become sufficient to trigger a reaction of the composition. This results in a strong degradation of the axial resolution, as well as an undesired reaction of the composition between the flat areas where the beams of light overlap.

In other words, if two solid areas in an image to be projected are too close to each other, during projection, the addition of their diffracted lights may become sufficient to trigger an undesired reaction of the composition.

From these tests and findings, the inventors deduced the method according to the invention, allowing rapid printing and having a desired axial resolution.

The printing time is reduced by carrying out the steps ET2 and ET3 described above, which make it possible, from a breakdown into mosaics, partial images of the object to be printed, to simultaneously print pluralities of illuminated dots , instead of printing them one by one, which greatly speeds up printing.

The axial resolution desired for the printed object is maintained by an appropriate distribution of the illuminated points in the mosaics and in the flat areas of the mosaics:

- in a flat area of a mosaic, the number of lit points and the distribution of illuminated points in the said flat area are adjusted so that, during the projection of the said mosaic in the composition volume, the luminous zone associated with the said flat area generates the photoreaction of a composition block having a desired axial resolution, and

The breakdown into mosaics of flat tints according to the invention thus results from compromises.

In a solid, the number of lit points and the distribution of the lit points in the solid (that is to say the shape of the solid) must be optimized. The number of illuminated points must be as large as possible to project as few mosaics as possible to print the complete object. At the same time, the number of illuminated points must be limited and the distribution of illuminated points in a solid area must be optimized to maintain the desired axial resolution. The distribution of the lit points is materialized by the shape of the solid.

Also, in the same mosaic, the flat areas must be distributed in an optimized way. The distance between two flat areas must be minimized so that the number of illuminated points in a mosaic is as large as possible. At the same time, the distance between two flat areas must be sufficient so that the composition does not react between two flat areas.

Tests carried out under the test conditions presented in FIG. 3 and 4 show that, in a mosaic, flat areas having a dimension less than the desired axial resolution and preferably twice as small, give good results in terms of axial resolution.

Other tests carried out under the conditions of the tests presented in fig. 3 and 4 show that, in a mosaic, flat areas distributed so that a distance between the edges of two flat areas is greater than the desired axial resolution and preferably three (3) times the desired axial resolution give good results.

Experience also shows that the decomposition of the mosaic image is facilitated by the choice of flat areas having general shapes such as:

- a compact shape, for example a disc, a solid ball, a square, a cube, .etc. ; , for the purposes of the invention, it is considered that the dimension of such a solid is its average diameter

- an elongated shape, for example an elliptical shape, an oblong shape, a cylinder, a bar, etc. ; , for the purposes of the invention, it is considered that the dimension of such a flat area is its average width

- or a hollow shape, for example a ring, a hollow sphere, a hollow cylinder, a hollow rectangle...

The method according to the invention can be used to produce an object to be printed having macroscopic properties and having a desired lateral (XY) and/or axial (Z) resolution of the details which can be greater than 10 μm.

The method can also be used to produce a printable object having microscopic properties with a desired lateral (XY) and/or axial (Z) resolution of detail which may be less than 10 µm.

FIG. 2 shows, by way of simple example, the decomposition of an initial 2D image into a sequence of four 2D mosaics, the 2D image and the mosaics comprising 24*24 pixels (2D luminous points). In this simple example, the solid areas of the initial 2D image include 2*10 pixels, and the decomposition is such that the solid areas in the mosaics include at most 2*2 lit points. The decomposition according to the invention of images into mosaic sequences applies in a similar way to the decomposition of a 3D image representing a 3D object and defined by a three-dimensional matrix.

Also, in the simplified example of FIG. 2, where the flat areas in the initial image comprise at most 20 adjacent lit points, a breakdown into four mosaics only makes it possible to obtain mosaics comprising flat areas comprising at most 4 lit points. Of course, for larger objects to be printed, for example of the order of 1 to 10 millimeters, represented by larger images, for example images of microscopic or macroscopic images defined by a matrix of 10000* 10000 pixels (in 2D) or by a matrix of 10000*10000*10000 voxels (in 3D) the number of mosaics in a sequence can quickly become large, even if flat areas comprising more than 1 lit point are acceptable. The number of mosaics will thus depend in practice on the density of the object to be printed or said, otherwise, the number of illuminated dots and the size of the initial solids in the initial image representing the object to be printed, and the desired resolution for the printed object.

The step ET2 of extracting the sequence of mosaics can be carried out by trial and error, by choosing flat areas of simple shapes in line with the general shape or the local shapes of the object to be printed.

For any objects, step ET2 can be performed iteratively. For the first mosaic, a first version (ET21) comprising alternately an illuminated point and an extinguished point can be tested with the composition to be modified and the associated optical means. Depending on the depth of composition having reacted, and of the possible presence of composition having reacted in undesired zones, turning points off or on (ET22). Repeat steps ET21 and ET22 until a first satisfactory mosaic is obtained. Then repeat steps ET21 and ET22 for the following mosaics.

The distance between solids and the distribution of solids in each mosaic, as well as the number and distribution of illuminated dots in each solid of a mosaic according to the desired axial resolution for the object to be printed must be characterized by tests with the projection means and the photoreactive composition chosen.

For example, tests carried out under the material conditions (projection means and choice of composition) of the experiment described in document D2 show that the axial resolution of a spot (modified composition element) obtained by holographic projection is equal at 1.6 times the diameter of the projected solid. In other words, to obtain, for the object to be printed, an axial resolution equal to 16 μm, 8 μm or 1.6 μm, the maximum dimension of an isotropic solid is chosen equal to 10 μm, 5 μm or 1 μm.

According to one mode of implementation of the method, each illuminated point of the image of the object is present in at least one solid area of a mosaic; the successive projection of each of the mosaics of the mosaic sequence thus makes it possible to constitute the entire object in the volume of composition. If each lit point is present in a single mosaic dataset, all points will be projected only once during the projection of the mosaic sequence; this makes it possible to obtain a printed object produced in a homogeneous material. A lit point present in several mosaics will be projected as many times, which amounts to increasing the projection time of said point, and therefore increasing the conversion rate of the composition; this makes it possible, for example, to locally reinforce a physical or chemical property of the printed object.

According to another mode of implementation, at least one mosaic is projected several times, successively shifted along the axial direction and/or in a focal plane (XY) in the composition volume. This embodiment makes it possible, for example, to print parallel bars.

According to another aspect of the invention, it is possible to associate a first desired axial resolution with a first part of a mosaic and at least one second desired axial resolution with at least a second part of said mosaic. This is particularly interesting for making an object for which:

- a very fine resolution is necessary locally, for example on the edges of the object,

- a slightly degraded resolution is acceptable locally, for example at the center of the object.

The choice of a greater depth of axial resolution makes it possible to produce mosaics comprising flat areas of larger size, which makes it possible to reduce the number of mosaics. This can be used to make a lens for example.

According to yet another aspect, when printing an object, the mosaics of the sequence of mosaics can each be projected for an identical time, necessary for the reaction of the composition. This makes it possible, for example, to produce an object in a substantially homogeneous material. Alternatively, the mosaics of the sequence of mosaics are projected for different exposure times; this makes it possible, for example, to locally refine the mechanical properties of an object.

According to yet another aspect, it is possible to project a mosaic with different intensities for certain flat areas or for each flat area (projection in level of gray). This can make it possible to compensate for the thermal increase of the photo-active effect which appears in the center of the flat areas transformed in certain materials.

As said previously, a method according to the invention comprises an essential step ET2 of extracting a sequence of mosaics in an image of an object to be printing, and a step ET3 of projecting said sequence of mosaics into the volume of photoreactive composition.

In an embodiment where the object to be printed is in 2D (object with a very small thickness), the image to be projected and the mosaics are also in 2D. The mosaics are projected successively in the same focal plane (perpendicular to the axial direction) in the composition volume inside the composition tray so that the object is formed in the composition volume as the projecting mosaics.

In another mode of implementation, the image of the object to be printed is a 3D image and the mosaics and the flat areas in the mosaics, obtained during step ET2, are also in 3D. 3D mosaics are projected, either as a real or holographic 3D image, into the composition volume within the composition so that the object forms in 3D within the composition volume as the projecting mosaics.

In yet another mode of implementation, the printing of a 3D object is carried out layer by layer by the successive printing of adjacent 2D layers. To implement this, the method according to the invention comprises an initial step (ET1) consisting in cutting the 3D image of the 3D object into a series of 2D images representative of the object to be printed in parallel planes between them and perpendicular to the axial direction of image projection in the composition volume, and it comprises the following steps ET2 to ET4, repeated for each 2D image and consisting in

- extracting (ET2) the sequence of mosaics from said 2D image and projecting (ET3) the sequence of mosaics extracted in a focal plane located in the volume of photoreactive composition and perpendicular to the axial direction, and:

- move (ET4) the focal plane in the composition volume.

By way of example, for objects with microscopic properties, our tests show that the polymerization of a mosaic 2D image can be obtained with an exposure time of one millisecond. It is necessary to use a hundred mosaic images to obtain an axial resolution of 1 µm, ie a projection sequence lasting 0.1 second. The manufacture of an array (100×100 μm ² ) of microlenses 5 μm high requires the spraying of 10 layers, ie a manufacturing time of 1 second. Thus, the manufacture of a microstructured surface of 1 mm ² would be possible in a few minutes, and of 1 cm ² in a few hours instead of a few days with the state of the art. According to a variant, the step ET4 of displacement of the focal plane is carried out:

- by moving a tray containing the volume of composition in relation to a projector used to carry out step ET3 of projection, or

- by moving the projector relative to the tray containing the composition volume.

According to another variant, step ET4 of displacement of the focal plane is carried out by spatial modulation of an initial light beam produced by a light source of the projector used to carry out step ET3 of projection, the modulated beam integrating information relative to the position of the focal plane. The concrete realization of these steps will be detailed later.

The invention also proposes a printer for implementing the method described above, the principle of which is shown in a deliberately simplified manner in FIG. 1. The printer comprises:

- a tank 2 containing a volume of a photoreactive composition, for example a photopolymerizable resin solidifying by a nonlinear polymerization mechanism,

- an image projector 10 arranged to project a focused image, with a desired axial resolution, in the composition volume.

The photoreactive composition is for example a photopolymerizable resin solidifying by a multiphoton absorption process, by a photon addition mechanism, by a threshold polymerization mechanism, or by a nonlinear chemistry mechanism.

The printer according to the invention also comprises means arranged to implement the printing method as described above, in particular a generator (15) of mosaic sequences arranged to extract from the image of the object to printing a sequence of mosaics and supplying the sequence of mosaics to the projector for carrying out step ET3 of projection.

During printing, the projector 10 projects an image into the composition and the illuminated areas react by forming all or part of the object to be printed.

According to the embodiment of Figure 1, the projector 10 comprises:

- a light source (4) producing, for each mosaic to be projected, an initial beam having appropriate parameters to trigger a photoreaction of the composition, the said parameters comprising for example a power, a wavelength and/or an exposure time,

- a spatial light modulator (12), arranged to, from the initial beam and the mosaic to be projected, produce a beam to be projected by the optical device, and

- an optical imaging device (11) arranged to focus the beam to be projected in a focal plane associated with the mosaic to be projected.

The means for implementing the printing process can also comprise cutting means, for cutting a 3D image into a series of 2D images representative of the object to be printed in planes parallel to each other and perpendicular to the axial direction. image projection in the composition volume. The slicing means supply the mosaic generator 15 one after the other with the 2D images of the series of 2D images resulting from the decomposition.

With a view to carrying out step ET4, the means for implementing the printing method according to the invention also comprise means for controlling the positioning of the focal plane.

According to one embodiment, the composition tray 2 is placed on a motorized table 3 movable in axial translation in the direction of projection of the projector 10, and means for controlling the motorized table are arranged to provide said motorized table with a movement command signal in the axial direction or in a lateral direction (X, Y). The focal plane in the tray is thus moved by moving the tray.

According to another embodiment, the composition tray 2 is placed on a fixed table, and projector control means are arranged to supply the projector with a control signal comprising an axial position of a focal plane. Thus, the distance between the tray and the projector remains fixed, but the focal plane is moved in the tray. In an implementation variant, the projector control means supply the imaging device 11 with the control signal comprising the axial position of the focal plane and the imaging device focuses the beam to be projected in the focal plane at the interior of the composition volume. In another implementation variant, the projector control means supply the modulator 12 with the control signal comprising the axial position of the focal plane and the modulator produces a phase-modulated beam to be projected incorporating information relating to the focal plane. In a practical embodiment, the printer according to the invention can be an electro-opto-mechanical machine such as that conventionally used in a photoplotter, in a DLP 3D printer, in an LCD 3D printer, in a printer implementing a microstereolithography process or in a microscope; the machine is diverted from its usual use, and adapted and supplemented by the means of implementing the invention in particular: a generator of mosaic images 15, a projector 10 and means for controlling the electro-opto-mechanical machine and, if the table is mobile, means for controlling the mobile table.

Also, the composition tray 2 and/or the optical imaging device 11 can be arranged with lateral displacement means (in the XY plane) to produce larger objects by the successive projection of several sequences of mosaics in the lateral plane .

Other embodiments can easily be imagined by those skilled in the art. For example, to extend the manufacturing area limited by the lateral optical field of an image projector, it is possible to use several spatial modulation components simultaneously or to perform lateral movements of the optical projector or the resin tank. Also, to extend the length of the liquid resin manufacturing zone, it is possible to axially move a suitable element of the optical projector in the resin tank. To diversify the method of depositing resins without using a composition tank, it is possible to make localized deposits of viscous or solid resins on components or functional surfaces. Or, to reach hard-to-reach areas to be polymerized, it is possible to use unconventional image projectors based on optical fibers or miniature optical components.

In summary, the invention proposes a 3D printing process and means for implementing said process, which in particular provide the following technical and economic benefits:

- the possibility of producing, by volume 3D printing, large-scale objects, of the order of 1,000 to 10,000 times the dimensions of a point, with a very high axial resolution and in relatively short times, of the order from a few tens of seconds to a few tens of minutes depending on the size of their axial dimension,

- the possibility of printing an object directly in a tray containing the composition to be modified, without moving the sample holder positioned in the tray and on which the object is printed, without using a sample holder and / or without moving the composition tray

- viscous compositions, or even solids, can be used; they just need to be transparent.

Claims

1. Process for printing a 3D object in a volume of photoreactive composition, object defined by a 3D image comprising a plurality of illuminated points, printing process characterized in that it comprises the following steps, consisting of:

- in an axial direction (Z) and inside the composition volume, projecting (ET3) the sequence of mosaics, the projection of each mosaic forming, in the composition volume, a plurality of light zones, each light zone corresponding to a solid of the projected mosaic and each luminous zone being adapted to generate a photoreaction of an associated block of composition, and method characterized in that:

- in a solid of a mosaic, the number of illuminated points and a distribution of the illuminated points in said solid are adjusted so that, during the projection of said mosaic in the composition volume, the luminous zone associated with said solid generates the photoreaction of an associated composition block having a desired axial resolution, and

- in the same mosaic, the flat areas are distributed so that, during the projection of the said mosaic in the composition volume, the composition does not react between the luminous zones associated with the plurality of flat areas of the said mosaic.

2. Method according to claim 1 used to produce an object to be printed having macroscopic properties and having a desired lateral (XY) and/or axial (Z) resolution of the details which may be greater than 10 μm.

3. Method according to claim 1 used to produce an object to be printed having microscopic properties having a desired lateral (XY) and/or axial (Z) resolution of the details which may be less than 10 μm.

4. Method according to one of the preceding claims, in which the dimension of the flat areas is less than the desired axial resolution and preferably twice as small.

5. Method according to one of the preceding claims, in which a distance between the edges of two flat areas is greater than the desired axial resolution and preferably greater than 3 times the desired axial resolution.

6. Method according to one of the preceding claims wherein a solid has an isotropic shape, an elongated shape or a hollow shape.

7. Method according to one of claims 1 to 6 wherein each illuminated point of the image of the object is present in at least one solid area of at least one mosaic, the successive projection of each of the mosaics of the sequence of mosaic allowing to constitute the object in the volume of composition.

8. Method according to one of claims 1 to 6 wherein at least one illuminated point of the image of the object is present in a solid area of at least two mosaics.

9. Method according to one of claims 1 to 8 wherein at least one mosaic is projected several times, successively offset in the axial direction and/or in a focal plane (XY) in the composition volume.

10. Method according to one of the preceding claims, in which a first desired axial resolution is associated with a first part of a mosaic and a second desired axial resolution is associated with a second part of said mosaic.

11. Method according to one of the preceding claims, in which the mosaics of the sequence of mosaics are projected for different exposure times.

12 Method according to one of the preceding claims, in which certain flat areas of a mosaic are projected with different intensities.

13. Method according to one of claims 1 to 12, characterized in that the image of the object to be printed is a three-dimensional (3D) image and in that the mosaics and the solid areas in the said mosaics are in three-dimensional (3D).

14. Method according to one of claims 1 to 12, characterized in that it comprises an initial step (ET1) consisting in cutting the 3D image of the object to be printed into a series of 2D images representative of the object to be printed in planes parallel to each other and perpendicular to the axial direction (Z) of image projection in the composition volume, and in that it comprises the following steps ET2 to ET4, repeated for each 2D image and consists in - extracting (ET2) the sequence of mosaics from said 2D image and projecting (ET3) the sequence of mosaics along the axial direction in a focal plane located in the volume of photoreactive composition and perpendicular to the axial direction, and:

- move (ET4) the focal plane in the composition volume.

15. Method according to claim 14, in which step ET4 of displacement of the focal plane is carried out:

- by moving the projector relative to the tray. .

16. Method according to claim 14, in which step ET4 of displacement of the focal plane is carried out by spatial phase modulation of an initial light beam produced by a light source of the projector used to carry out step ET3 of projection, the modulated beam integrating information relating to the position of the focal plane.

17. Printer adapted for the implementation of a printing method according to one of the preceding claims, printer comprising in particular:

- an image projector (10) arranged to project a focused image, with a desired axial resolution, in the composition volume, the printer also comprising means arranged to implement the printing method according to one of the preceding claims, said means comprising a generator (15) of mosaic sequences arranged to extract from the image of the object to be printed a sequence of mosaics and supply the sequence of mosaics to the projector for performing step ET3 of projection.

18. Printer according to claim 17 in which the projector comprises:

- a light source (4) producing, for each mosaic to be projected, an initial beam having appropriate parameters to trigger a photoreaction of the composition, said parameters comprising for example a power, a wavelength and/or a time exhibition,

- a spatial light modulator (12), arranged for, from the initial beam and of the mosaic to be projected, producing a beam to be projected by the optical device, and

19. Printer according to claim 17 or 18 in combination with claim 14, in which, in order to move (ET4) the projection focal plane, the means for implementing the printing method also comprise:

- means for controlling a motorized table supporting the composition tray, arranged to supply said motorized table with a movement control signal in the axial direction or in a lateral direction (X, Y) and/or

- Projector control means, arranged to provide the projector with a control signal comprising an axial position of the focal plane.