device for printing microstructured centimeter-sized objects

Abstract

The invention relates to a printer comprising a tray comprising a volume of photosensitive composition and a projection system comprising: - a digital screen (2) with a surface area greater than 100 cm², screen comprising a pixel matrix comprising a plurality of pixels each having optical dimensions greater than 10 µm * 10 µm, screen configured to display a first image comprising a plurality of adjacent illuminated pixels representing an object to be printed or a part of an object to be printed, and - a wide-angle and high-resolution projection optical system (3), optical system adapted to project, into the composition tray, a second image of the object to be printed from the first image, each pixel of the second image having optical dimensions reduced compared to the dimensions of a pixel of the first image by a reduction factor R greater than 5. Figure 1

Description

Title of the invention: device for printing microstructured centimetric objects Technical field of the invention

[0001] The present application relates to a printer using a photochemical reaction induced by absorption of energy provided by the projection of a light screen to modify the volume of a photoreactive composition, and more particularly to a printer allowing the projection of centimetric images having micronic resolutions for the printing of microstructured objects of centimetric size, that is to say objects of which at least one dimension is greater than 1 cm and of which production details have at least one dimension less than 10 μm. State of the art

[0002] In the state of the art of 3D printing by image projection, the images to be projected are obtained using liquid crystal spatial light modulators (LC-SLM) or digital micro-mirror arrays (DMD). These modulators, whose size is of the order of a centimeter, are made up of arrays of millions of pixels of micrometric size. The lateral resolution (XY) of the polymerized patterns and the dimension of the writing fields (or illuminated areas in the resin) are proportional to the magnification factor of the projection optics. For example, the SmartPrint UV printer from the company Microlight3D used with a 10x microscope objective, with 0.1x magnification, makes it possible to obtain a lateral resolution (along X, Y, perpendicular to the projection axis) of 1.5 pm, but only on a surface of 1.06 mm x 0.59 mm or 0.62 mm2.This requires breaking down the polymerization of centimeter patterns into numerous complementary writing fields offset in X and Y, for example 10x10 exposures to obtain polymerization on 1.06 cm x 0.59 cm or 0.62 cm2.

[0003] Thus, printing a photopolymerized layer having dimensions of the order of a few centimeters requires successively projecting a thousand images side by side, in the X, Y directions. So that, even if the polymerization of a writing field (or illuminated area) is ultra-fast, the dimensions of the objects that can be printed in a reasonable time are quite limited.

[0004] Recently, a new type of 3D printer without projection optics has been proposed to photopolymerize surfaces much larger than those accessible with centimeter-sized spatial light modulators (LC-SLM and DMD). This involves using technological advances in the manufacture of digital light screens, typically LCD, whose sizes are two orders of magnitude larger, as a light surface for photopolymerization. Liquid resins are poured directly into a transparent tank placed on the screen. Polymerization takes place in the resin tank as close as possible to the screen, under a printing support which gradually rises layer by layer to obtain the 3D structuring. The typical pixel sizes of these screens, and therefore of the lateral X,Y polymerization resolution, are 20 to 100 pm. The axial resolution, typically 10-300 pm, is obtained by the thickness of the layers imposed by the movements of the printing support and by the concentration of absorbers limiting the propagation of light in the resin.

[0005] A first drawback is the great technological difficulty of manufacturing large luminous screens, that is to say screens having a diagonal greater than 10 cm or a surface greater than 100 cm2, having hundreds of millions of pixels of micronic dimensions (that is to say of the order of a few square micrometers).

[0006] The recent development of non-linear resins, such as those described in document DI = WO2019025717, optimized for highly localized photopolymerization such as STTA-UC (for Triplet-triplet annihilation-based sensitized photon up-conversion) makes it possible to envisage the development of new 3D printers using the direct projection of 2D or 3D images into a tank containing a volume of photopolymerizable resin. Each voxel of light (or 3-dimensional pixel) illuminated in the composition is transformed by reaction into a voxel of polymerized material.

[0007] The projection, and therefore the chemical reaction, can take place inside the composition tank itself and not on the surface, so that it becomes possible to use 2D or 3D image projectors and solid or fragile photoreactive compositions.

[0008] Document D2= WO2022171704A1 shows a solution to enable printing by projection of images in a volume of resin with a desired fine axial resolution. The proposed solution consists of first decomposing an image to be solidified into a succession of images having small flat areas and optimized spatial distributions to obtain the specified optical, and therefore photochemical, axial resolution.By optical axial resolution is meant the thickness (along Z, the projection axis) of the optical image projected into the resin and by photochemical axial resolution is meant the thickness of polymerized resin corresponding to the projected optical image, when said polymerization is not slowed down or blocked by a physical means (for example a printing support moved layer by layer in the resin) or by a chemical means (for example a chemical additive mixed with the resin having the function of limiting the propagation of the chemical polymerization reaction).

[0009] One disadvantage of the new type of 3D printer with a light screen without optics is that projection is that this approach does not allow the projection of 2D images into the photopolymerizable resin volume but only the display of 2D images on the bottom of the tank. This excludes the use of viscous or solid resins. This approach also does not allow the direct projection of 3D holographic images which would allow the ultimate manufacturing speeds to be achieved.

[0010] In the case of the projection of images into the volume of the resin, experience shows that an increase in the lateral dimensions (along the X and Y axes) of the voxels mechanically leads to a decrease in the lateral resolution (X, Y, perpendicular to the projection axis) but also in the axial resolution (Z, along the projection axis). This is confirmed by the document D3 = “Hernandez-Cubero, O. "Advanced Optical methods for fast and three-dimensional control of neural activity." Paris Descartes University, France (2016)”.

[0011] It therefore remains necessary to resolve the problem of the loss of axial resolution linked to the lateral dimension of the luminous zones to be polymerized.

[0012] Document D4 = "One-Step Volumetry Additive Manufacturing of Complex Polymer Structures" Shusteff, Maxim, Allison E.M. Browar, Brett E. Kelly, Johannes Henriksson, Todd H. Weisgraber, Robert M. Panas, Nicholas X. Fang, and Christopher M. Spadaccini. "One-step Volumetry Additive Manufacturing of Complex Polymer Structures." Science advances 3, no. 12 (2017): eaao5496, describes a technology consisting of projecting a 3D volumetric image into the nonlinear photoreactive composition tank. For this new technology, the manufacturing of millimeter-sized objects requires the orthogonal addition of three 2D images to obtain the desired axial resolution by nonlinear polymerization only at the locations of addition of the projected irradiations. This optical assembly is particularly complex and furthermore limits the 3D geometric shapes that can be printed. Summary of the invention

[0013] The invention proposes a technical solution to overcome all or part of the drawbacks set out above.

[0014] For this purpose, the invention proposes a printer comprising a tray (1) comprising a volume of photosensitive composition and a projection system comprising: - a digital screen (2) with a surface area greater than 100 cm2, screen comprising a pixel matrix comprising a plurality of pixels each having optical dimensions greater than 10 pm * 10 pm, each pixel being configured to produce, when illuminated, a light signal whose wavelength and light intensity are adapted to generate a polymerization of the photosensitive composition, screen configured to display a first image comprising a plurality of adjacent illuminated pixels representing an object to be printed or a part of an object to be printed, print, and - a wide-angle, high-resolution optical projection system (3), an optical system adapted to project, into the composition tray, a second image of the object to be printed from the first image, each pixel of the second image having optical dimensions reduced compared to the dimensions of a pixel of the first image by a reduction factor R greater than 5.

[0015] According to one embodiment, the optical system is adapted to project a second image of the object to be printed onto the surface of the composition volume (or surface projection). According to another embodiment, the optical system is adapted to project a second image into the composition tank (or volumetric projection).

[0016] The invention makes it possible to print microstructured 3D objects of centimeter dimensions with very good axial resolution, maintained even in volumetric projection, as will be explained later. The invention is counter-intuitive. Indeed, the invention of LCD 3D printers had made it possible to replace 3D printers with expensive projection systems with printers without expensive projection systems by positioning the resin tank directly on the screen. The invention proposes, on the contrary, to put an optical system between the screen and the resin tank, in order to improve the axial resolution.

[0017] The invention also relates to a method of using a printer as described above. Presentation of figures

[0018] The invention will be better understood, and other characteristics and advantages of the invention will appear in light of the following description of examples of implementation of the invention. These examples are given without limitation. The description should be read in relation to the appended drawings in which: • [Fig.l] schematically presents the essential elements of a printer according to the invention, • [Fig.2] and [Fig.3] schematically represent embodiments of the printer according to the invention, • [Fig.4], [Fig.5] and [Fig.6] show results of tests carried out to validate the invention.

[0019] In the various figures, identical or similar elements are referenced with the same references.

[0020] By convention, we will use the adjective "adjacent" to speak of two objects which are side by side and which touch, for example adjacent pixels touch on one side. By convention also, we define an axial direction Z as being a direction of projection of an image 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 [Fig. 1]). Detailed description

[0021] As stated previously, the invention relates to a printer comprising a tray (1) comprising a volume of photosensitive composition and a projection system.

[0022] The projection system according to the invention is shown schematically in [Fig.l]; it comprises a digital screen 2 and a projection system 3.

[0023] The digital screen 2 has a surface area greater than 100 cm2; the screen comprises a pixel matrix comprising a plurality of pixels each having optical dimensions greater than 10 pm * 10 pm; each pixel is configured to produce, when illuminated, a light signal whose wavelength and light intensity are adapted to generate polymerization of the photosensitive composition. Preferably, the light intensity is homogeneous over the entire surface of the screen, and the emitted light is collimated.

[0024] The screen is configured to display a first image representing an object or a part of an object to be printed. The first image comprises a plurality of adjacent illuminated pixels representing an object to be printed or a part of an object to be printed, in contrast to the unilluminated pixels of the pixel matrix. The digital screen is for example a screen of the LCD, LED, OLED, QLED type, or a plasma screen. In a first practical example, the digital screen 2 is a 10-inch LCD screen of 21.8 cm * 12.3 cm whose pixels have dimensions of 19 pm * 24 pm. In a second practical example, the digital screen 2 is a 15-inch LCD screen of 33 cm * 18.5 cm whose pixels have dimensions of 43 pm2. In a third example, digital screen 2 is a 32-inch LCD screen of 69.5 cm * 38.5 cm whose pixels have dimensions of 91 pm2.

[0025] According to the invention, the optical system 3 is adapted to project, into the composition tank, a second image of the object to be printed constructed from the first image. Each pixel of the second image has optical dimensions reduced compared to the dimensions of a pixel of the first image by a reduction factor greater than or equal to 5, preferably by a reduction factor greater than or equal to 10, even more preferably greater than or equal to 20 and exceptionally greater than 40. After an appropriate projection time, the composition volume 6 illuminated by the illuminated pixels of the second image is polymerized. For example, with an LCD screen having pixels of 10pm*10pm and an optical system with a reduction factor of 5, projected pixels of 5pm are obtained, i.e. a micron printing resolution. The choice of the reduction factor will be detailed in more detail below.

[0026] According to one embodiment, the optical system is adapted to project a second image of the object to be printed onto the surface of the composition volume (or surface projection). Where appropriate for 3D printing, the composition (or resin) may be a composition known in the state of the art of layer-by-layer 3D printing. Preferably, said composition may comprise a propagation absorber. 3D printing is thus carried out layer by layer, by projection of a succession of images offset in an axial direction or by projection of 3D holographic images. The propagation absorber limits the propagation of the reaction in the axial direction and thus limits the thickness of each layer. The thickness of each layer may also be limited by the presence of a printing support. Where appropriate for 2D or 2.5D printing, the layer is deposited on the printing support

[0027] According to another embodiment, the optical system is adapted to project a second image into the composition tank (or volumetric projection). In this case, the composition may be a viscous, or even solid, resin; preferably, the composition is a resin optimized for photopolymerization according to a non-linear mechanism, for example a resin such as that described in D2. Such a resin has the advantage of polymerizing rapidly from limited light energy. It also has the advantage of polymerizing in a very localized manner in X, Y and Z. Indeed, the non-linearity limits the propagation of the reaction in the volume of the optical voxel, and therefore also in the axial direction.

[0028] The optical projection system (3) is a wide-angle, high-resolution optical system. It thus allows wide framing of close-up objects from which one cannot move away. In the example of [Fig.l], and the distance between the optical system and the image that it projects is of the order of 5 cm. According to one embodiment, the optical system comprises a wide-angle system constructed according to the “inverted telephoto lens” or “retrofocus” model formulated in 1950 by Angénieux.

[0029] In a first concrete example of embodiment of a printer according to the invention, the 10-inch digital screen mentioned above is coupled to an optical system of a wide-angle optical camera of 85°, with a focal length of 6.3 mm, optimized for optical sensors of 9.8 mm * 7.4 mm capable of detecting 200 million illuminated pixels with a resolution of 0.6 pm. In this case, when the screen is placed at the minimum focusing distance of 15 cm, the reduction factor is 24 (or magnification 0.0042x). The reduced image of the LCD screen, with maximum dimensions of 9.08 mm * 5.12 mm (i.e. 46.5 mm2) with an XY resolution of the illuminated pixels of 0.8 pm * 1 pm, is obtained at 6.95 mm from the optical system.

[0030] In a second concrete example of embodiment of a printer according to the invention, the 15-inch digital screen mentioned above is coupled to a system optics of a 122° wide-angle optical camera, with a focal length of 12 mm, optimized for 24x36 mm2 optical sensors with a resolution of 3.76 pm. In this case, when the screen is placed at the minimum focusing distance of 25 cm, the reduction factor is 10 (O.lx). The reduced image of the LCD screen, with a maximum dimension of 33 mm x 18.5 mm (i.e. 610 mm2) with an XY resolution of the illuminated pixels of 4.3 pm x 4.3 pm, is obtained at 44 mm from the optical system.

[0031] In a third concrete example of embodiment of a printer according to the invention, the 30-inch digital screen mentioned above is coupled to an optical system of a wide-angle optical camera of 87.3°, with a focal length of 28 mm, optimized for optical sensors of 53.4 mm x 40 mm having a resolution of 3.76 pm. In this case, when the screen is placed at the minimum focusing distance of 35 cm, the reduction factor is 13 (0.08x). The reduced image of the LCD screen, with a maximum dimension of 53x29.6mm2 (1570 mm2) with an XY resolution of the illuminated pixels of 7x7pm2, is obtained at 63 mm from the optical system.

[0032] In the case of a surface projection, the optical system is configured to project the second image onto a surface of the composition volume or at an interface of the composition volume and the tray. In the example of [Fig.2], the optical system is configured to project the second image onto a surface of the composition volume (2B) or at an interface of the composition volume and the tray (2A). The projection system is movable in translation relative to the composition tray or relative to a printing support 5 positioned in the composition tray, movable in the Z direction, Z being the axial projection direction of the optical system. In example 2A, the optical system 3, stationary, projects the second image at the bottom of the tray and an object holder 5 positioned in the tray is movable in axial translation.In example 2B, the object holder 5 is integral with the optical system 3 and the optical system is movable in axial translation relative to the composition tank 1 which is fixed. Although this is not shown in the figures, the optical system can also be movable in translation relative to the composition tank or relative to an object holder 5 positioned in the composition tank, movable in the X, Y directions. In these examples, the object is printed by projecting successive 2D images at the same location and by moving the printing support in the composition tank (or by moving the tank relative to the printing support). The axial resolution obtained, i.e. the thickness of the polymerized zone following the projection of an image in the resin, is in this case limited by the position of the printing support, the object forming step by step in the space located between the printing support and the edge of the tank where the second image is projected.

[0033] In the case of a volumetric projection, example of [Fig.3], the optical system is configured to project the second image directly into the volume of com position and no longer at the edge of the tray. In one variant, the object is printed by projecting successive 2D images at the same location and moving the composition tray. In another variant, the object is printed by moving the projection plane of the second image (or focal plane of the optical system) in the composition tray to move the illuminated composition volume 6, the composition tray and the optical system being stationary. In this last variant, the optical system comprises adjustment means for moving the projection plane of the second image relative to the composition tray and the optical system.

[0034] [Fig.6] shows optical results obtained by varying the reduction factor R of an optical projection system for illuminated areas of square shapes. Second images (or projected images) comprising luminous areas of dimensions 5pm*5pm, 10pm*10pm, 15pm*15pm and 20pm*20pm respectively are obtained in the focal plane; these projected images are obtained with: - for curve 1, an optical system comprising a reduction factor R = 10x, - for curve 2, an optical system comprising a reduction factor R = 20x, - for curve 3, an optical system comprising a reduction factor R = 40x, - for curve 4, an optical system comprising a reduction factor R = 100x.

[0035] It can be seen that, for a second projected image of a luminous zone of given dimensions, the axial resolution of the optical image, and therefore of the polymerized zone of the resin, decreases when the reduction factor R increases. For example, for a second image comprising a luminous zone of 5pm*5pm, the axial resolution of the polymerized zone is equal to: 20pm for a factor R = lOx, 8pm for a factor R = 20x, 4pm for a factor R = 40x and 1.7pm for a factor R = 100. In other words, with the invention, the use of an optical system with a reduction factor coupled with a screen displaying large first images makes it possible to reduce the axial resolution of the polymerized zone.

[0036] In the case of a volumetric projection, [Fig.4] shows results of the projection of a second image comprising a luminous zone of dimensions 150pm * 150pm in X, Y in a drop of non-linear resin in intensity deposited on a glass slide. The intensity distribution of the luminous zone of 150pm * 150pm in the XY plane (4A) penetrates into the resin over a thickness greater than 100 pm at the center of the luminous zone in the axial direction Z (4B), so that a dome of polymerized resin is formed on the slide with a height at the center of the order of 80 pm (4C, after removal of the unpolymerized resin). The axial resolution obtained in this example is thus of the order of 80 pm at the upper interface of foca- lization and 160pm in the volume. Document D2 describes a method for reducing the axial resolution and the thickness of the polymerized zone; the method consists of decomposing an image of an object to be printed into a sequence of partial images otherwise called mosaics, mosaics each comprising a plurality of flat areas or groups of pixels of reduced size and distributed over the surface of the mosaic and projecting the mosaic sequence.

[0037] To further improve the axial resolution, the invention proposes adapting the method of D2 to use the printer as described above, to print an object in a volume of photoreactive composition from a first image of the object to be printed, first image defined by a matrix of pixels comprising a plurality of adjacent illuminated pixels defining the object to be printed.

[0038] The method according to the invention is characterized in that it comprises the following steps, consisting of: - decomposing (ET2) the first image into a sequence of first mosaics, each first mosaic being defined by a matrix of pixels comprising a plurality of groups of adjacent illuminated pixels otherwise called flat areas, a superposition of all the first mosaics of the sequence making it possible to reconstruct the image of the object to be printed, and - successively displaying (ET3) each of the first mosaics of the sequence of mosaics on the digital screen so that the optical system successively projects second mosaics into the volume of photoreactive composition, each second mosaic corresponding to a first mosaic.

[0039] Each pixel of a second mosaic has optical dimensions reduced compared to the dimensions of a pixel of the corresponding first mosaic, by a reduction factor R greater than 10.

[0040] [Fig.5] shows results of implementing the above method for printing a second image comprising a luminous zone of dimensions 150pm * 150pm in X, Y in a drop of non-linear resin in intensity deposited on a glass slide, projected by a succession of second mosaic images comprising flat areas of 10pm*10pm. The screen and the optical system used are the same as those used to obtain the results of [Fig.4]. The total luminous intensity distribution of the luminous flat areas projected in the focal plane (5A) penetrates into the resin with a thickness of 16pm in the axial direction Z (5B). A zone of polymerized resin with dimensions 150pm * 150pm and a homogeneous thickness of the order of 10 pm is formed in the resin (5C). The result obtained is thus more qualitative than that obtained by the projection of a single second image comprising a luminous zone of the same size 150pm * 150pm in the resin as is the case in [Fig.4].The thickness of the polymerized zone being substantially homogeneous (5C), we . understands that it becomes possible to polymerize a larger area with the same axial resolution.

[0041] In conclusion, the printer and the 3D printing method by image projection in a photosensitive resin described above can thus be used to print large objects, up to a few centimeters or a few tens of centimeters, with a fine resolution of the order of a few micrometers and an acceptable printing time.

[0042] This new technology allows for the rapid creation of precise prototypes. It allows for the production of objects with very diverse shapes and surfaces, as well as surface textures. This technology finds applications in various sectors of the microtechnology industry, such as micromechanical construction, microfluidics, microelectronics, medical devices, and even various fields of art, etc.

Claims

Claims

1. Printer comprising a tray (1) comprising a volume of photosensitive composition and a projection system comprising: - a digital screen (2) with a surface area greater than 100 cm2, screen comprising a pixel matrix comprising a plurality of pixels each having optical dimensions greater than 10 pm * 10 pm, each pixel being configured to produce, when illuminated, a light signal whose wavelength and light intensity are adapted to generate a polymerization of the photosensitive composition, screen configured to display a first image comprising a plurality of adjacent illuminated pixels representing an object to be printed or a part of an object to be printed, and - a wide-angle and high-resolution projection optical system (3), optical system adapted to project, into the composition tray, a second image of the object to be printed from the first image,each pixel of the second image having optical dimensions reduced compared to the dimensions of a pixel of the first image by a reduction factor R greater than 5.,

2. Printer according to claim 1 in which the optical system has a reduction factor greater than 10, preferably greater than 20 and even more preferably greater than 40.

3. Printer according to one of claims 1 to 2 in which the optical system is adapted to project the second image onto the surface of the composition volume or at an interface of the composition volume and the tray.

4. A printer according to claim 3 wherein the composition comprises propagation absorbers for 3D printing.

5. Printer according to claim 3 in which the composition is deposited on a printing medium for 2D or 2.5D printing.

6. Printer according to one of claims 1 to 2 in which the optical system is adapted to project a second image of the object to be printed into the composition tray.

7. Printer according to the preceding claim in which the composition comprises a resin which is linear in intensity.

8. Printer according to one of the preceding claims in which the digital screen is a screen of the LCD, LED, OLED, QLED type, or a plasma screen.

9. Printer according to one of the preceding claims, in which the projection system is movable in translation relative to the composition tray or relative to a printing medium positioned in the tray, movable in the directions X, Y and / or Z, Z being an axial direction of projection of the optical system, and X,Y being perpendicular to Z and perpendicular to each other.

10. Method of using a printer according to one of the preceding claims for printing an object in a volume of photoreactive composition from a first image of the object to be printed, first image defined by a matrix of pixels comprising a plurality of adjacent illuminated pixels defining the object to be printed, printing method characterized in that it comprises the following steps, consisting of: - decomposing (ET2) the first image into a sequence of first mosaics, each first mosaic being defined by a matrix of pixels comprising a plurality of groups of adjacent illuminated pixels otherwise called flat areas, a superposition of all the first mosaics of the sequence making it possible to reconstitute the first image of the object to be printed,and - successively displaying (ET3) each of the first mosaics of the sequence of mosaics on the digital screen so that the optical system successively projects second mosaics into the volume of photoreactive composition, each second mosaic corresponding to a first mosaic.,

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