Glass filament for 3D printing, and use thereof

Abstract

The invention relates to a glass filament (1) for 3D printing, comprising a filament core (2) and a filament sheath (3) which surrounds the outer circumferential surface of the filament core (2), wherein the filament core (2) consists of a core glass having the refractive index nK and a coefficient of thermal expansion CTEK, and wherein the filament sheath (3) consists of a sheath glass having the refractive index nM and a coefficient of thermal expansion CTEK, wherein CTEK > CTEM, and the absolute value of nK – nM is less than 0.2. The invention also relates to a roll and / or spool (10) on which the glass filament (1) is wound. The glass filament (1) may be used in particular as a consumable material for 3D printers.

Description

[0001] Glass filament for 3D printing and its use

[0002] The invention relates to a glass filament for the 3D printing of glass and its use.

[0003] There are a number of 3D printing technologies for glass, which use different starting materials for the actual printing process.

[0004] These include a number of powder-based 3D printing technologies, such as SLA printing, binder jetting, SLM printing, and SLS printing. All of these technologies share the common feature that the starting material is in powder form and is then either directly shaped into the final glass component via a thermal process, or indirectly, by mixing it with a polymer to form a green body, which then requires debinding and sintering to obtain the final 3D-printed glass object. However, none of these technologies is capable of producing a transparent glass object from a multi-component glass. The only known method to date for producing a transparent glass object using powder-based 3D printing is the use of fused silica, i.e., pure SiO2, via SLA printing.

[0005] On the other hand, attempts are also being made to produce directly transparent 3D-printed glass objects using transparent, glassy, ​​non-powdered starting materials. Technologies such as FDM (Fused Deposition Modeling) or DED (Direct Energy Deposition) 3D printing are used for this purpose. Quartz glass is typically used as the starting material. The necessary process temperatures of up to 2000°C when using quartz glass pose a significant technical challenge for 3D printing.

[0006] In FDM printing, pre-fabricated glass rods are typically extruded through a hot, heated metal or ceramic nozzle. The molten glass is then deposited onto a build plate, and the 3D object is built up layer by layer. The starting material consists of glass rods with diameters of several millimeters, while the nozzle has a smaller diameter, for example, one millimeter. However, the resolution of the resulting 3D object is limited by the nozzle, and the 3D-printed glass objects cannot be as detailed. Furthermore, the glass becomes contaminated through contact with the nozzle and can change color, crystallize, or exhibit other undesirable effects.

[0007] In contrast, DED printing involves heating the glass rod at its end directly by a radiation source, such as a laser, without physical contact. This creates a small volume of liquid glass, which is then applied to a build plate, layer by layer, similar to FDM 3D printing, to create the 3D-printed object. A CO2 laser is typically used for this process. Because the material does not need to be forced through a nozzle, it remains contamination-free.

[0008] DED printing also uses quartz glass fibers with a diameter of approximately 200 micrometers. These are typically so-called PCS fibers (polymer-clad silica), which are commercially available. A disadvantage here is that these quartz glass fibers have a plastic coating that must be removed before the actual 3D printing process, as the polymer would carbonize due to the intense heat generated during the 3D printing process, thus preventing the 3D printed object from being built up.

[0009] Existing multi-component glass fibers are unsuitable for 3D printing because they are designed for optical applications, primarily for transmitting visible radiation. These fibers always consist of at least two different glasses, a cladding glass and a core glass, with different refractive indices to allow radiation to be conducted through total internal reflection. When such fibers are reheated and melted during DED printing, the two different glasses mix, leading to various negative effects such as striae, scattering, or crystallization.

[0010] The invention is based on the objective of providing a starting material and thus a consumable material made of multi-component glass for 3D printing, which in particular enables the 3D printing of glass objects with high resolution, can be produced efficiently, transported and stored efficiently and can also be processed efficiently in 3D printing processes.

[0011] The problem is solved by the independent claims. Preferred embodiments are described in the dependent claims.

[0012] A glass filament according to the invention comprises a filament core and a filament sheath surrounding the outer circumferential surface of the filament core, wherein the filament core consists of a core glass with refractive index nK and a coefficient of thermal expansion CTEK, and wherein the filament sheath consists of a sheath glass with refractive index nM and a coefficient of thermal expansion CTEM, wherein CTEK > CTEM and the magnitude of nK - nM is less than 0.2.

[0013] Furthermore, the small difference in refractive indices between the core and cladding offers the advantage that the radiation source used to heat the filament during 3D printing, such as a laser, can penetrate the filament effectively. This allows for at least a largely uniform heating, which in turn enables efficient printing of the filament.

[0014] For the purposes of this description, a filament is defined as a flexible fiber. Flexible means that the element can be repeatedly bent with reasonable force without breaking. For glass elements, this property is present for diameters of less than 1 mm, particularly less than 0.5 mm. In this context, the term filament can also be understood as glass fiber.

[0015] The glass filament consists of at least two elements: a core and a cladding. The core is surrounded by the cladding, specifically along its outer surface. The core consists of a core glass, and the cladding of a cladding glass. The core glass has a refractive index of nK, and the cladding glass has a refractive index of nM. Furthermore, the core glass has a coefficient of thermal expansion CTEK, and the cladding glass has a coefficient of thermal expansion CTEM. In this context, CTEM refers to the linear coefficient of thermal expansion in the temperature range of 20°C to 200°C.

[0016] According to the invention, the glass filament, also referred to here as filament, is designed such that the coefficient of thermal expansion of the core glass CTEK is greater than that of the cladding glass CTEK, thus the relation CTEK > CTEM applies.

[0017] Furthermore, in a glass filament according to the invention, the refractive indices of the core and cladding glass differ only slightly, which is expressed by the magnitude of the difference between nK and HM, where this magnitude is less than 0.2, thus lying in the range of 0.0 to 0.2. Mathematically expressed, the relationship 0 < |nK - nM| < 0.2 applies.

[0018] The glass filament according to the invention thus possesses two important properties simultaneously: its mechanical fracture strength must be high, and optical distortions caused by the melting of the core and cladding glass, forming a glass mixture of both glasses, should be minimized. This means, in particular, that the molten glass mixture should remain optically transparent, without streaks, optical distortions, or similar defects.

[0019] The high mechanical strength is achieved by adjusting the coefficients of thermal expansion, specifically by ensuring CTEK is greater than CTEM. Because the glass filament is manufactured from preforms using a thermal drawing process similar to that used for optical fibers, the core glass contracts more than the cladding glass when the filament cools after drawing. As a result, the filament surface, i.e., the filament sheath, exhibits compressive stress at room temperature. This prevents crack propagation if the filament is damaged or bent, allowing the glass filament to be wound onto a spool or reel without breakage. The reduction and / or prevention of optical distortions, etc., is achieved by selecting the appropriate refractive indices (nK) and (nM) for the core and cladding glass.This is achieved by ensuring that the glass filament according to the invention for 3D printing has the smallest possible difference in refractive index between core and sheath and / or is at least within the aforementioned range.

[0020] It is generally assumed that the glass filament has a round cross-section, in particular a round core. However, in accordance with the invention, it is equally possible to provide different diameter shapes.

[0021] A particularly advantageous glass filament is one in which both the core and cladding glass are multicomponent. Multicomponent glasses are defined as glasses consisting of more than one component, more precisely, a plurality of oxide components forming an amorphous glass matrix. Such multicomponent glasses can be produced, in particular, by a melting process. They thus differ from quartz glass, which consists only of SiH₂.

[0022] A particularly advantageous glass filament is one in which the core glass and the cladding glass have the same glass components, with different contents of at least one glass component.

[0023] This means that the glass compositions of core and cladding glass differ, particularly advantageously, only in their proportions, but not in the components themselves. For example, both core and cladding glass can be borosilicate glass containing Si, Al, and B, with the proportion of Si in the cladding glass differing from the proportion of Si in the core glass.

[0024] This advantageously ensures that the core and cladding glass are compatible with each other, in particular that they are miscible upon remelting without segregation, crystallization, discoloration, or other effects occurring. An advantageous embodiment of the aforementioned glass filament provides that at least one of the following conditions applies:

[0025] CTEK's readings are in the range of 3.7 to 4.5 ppm / K,

[0026] CTEM is in the range of 3.2 to 3.6 ppm / K, nK is in the range of 1.45 to 1.55 nM is in the range of 1.45 to 1.55 .

[0027] As is generally known, the simplified value ppm / K for CTE stands for the unit 10⁻⁶. 6 / K.

[0028] These conditions can be combined with one another and are applicable to the designs described herein. They describe a particularly advantageous range of the parameters mentioned, which provide both favorable mechanical stability and good optical properties.

[0029] Another advantageous embodiment of the glass filament provides that the core glass has a softening temperature EWK of 815 °C to 835 °C and the cladding glass has a softening temperature EWivi of 820 °C to 840 °C. Particularly advantageously, the core glass has a VAK of 1240 °C to 1265 °C and the cladding glass a VAM of 1250 °C to 1270 °C.

[0030] VA stands for the processing point at which the heated glass has a viscosity of 10 4 dPas is present. VAK indicates the value for the core glass, VAM the value for the cladding glass.

[0031] An advantage here is that the viscosity values ​​of the core glass are lower than those of the cladding glass at the same temperature, preventing the cladding glass from being drawn over or running off the still-solid core during the drawing process. Identical viscosity values ​​at the same temperature also do not pose a problem in fiber production. Furthermore, a glass filament is advantageous in that the filament has a diameter dF of 40 to 600 microns, the core dK advantageously has a diameter of 38 to 598 microns, and the cladding advantageously has a thickness SM of 1 to 200 microns.

[0032] The filament diameter dF refers to the total diameter of the filament, measured perpendicular to the filament axis, or in other words, its thickness. The diameter dK of the filament core is measured in the same way as the diameter dF because the filament sheath, with a thickness SM, has a smaller diameter than dF. The thickness SM of the filament sheath corresponds, so to speak, to a layer thickness. Therefore, the following relationship results for the filament diameter dF: dF = dK + 2 ■ SM.

[0033] The thickness of the sheath relative to the core determines the magnitude of the compressive stress present on the finished fiber and is advantageously chosen such that a 200 pm thick fiber can be wound onto a ring with a diameter of 200 mm without the fiber breaking. A filament is particularly advantageous if the following relationship holds: dK / (2 ■ SM) < 15.

[0034] The high breaking strength of the glass filament can be described by its minimal bending radius.

[0035] A particularly advantageous glass filament has a minimum bending radius of 200 mm or less, determined by a loop test. In this test, an attempt is made to form a large loop and slowly tighten it until the fiber breaks.

[0036] A glass filament is particularly advantageous in which the core and / or the cladding glass comprises or consists of a borosilicate glass. This is especially advantageous for both the core and the cladding glass. For the purposes of the invention, a borosilicate glass comprises a glass containing SiO2 and B2O3 as glass formers and optionally Al2O3 as an additional component. The term includes the subgroups alkaline earth-free borosilicate glasses and alkaline earth-containing borosilicate glasses.

[0037] In this description, all numerical values ​​relating to glass composition components are given in wt.% based on oxides. Advantageous glass compositions for core and / or cladding glass contain the following wt.% based on oxides:

[0038] SiO270 - 82

[0039] B2O3 7 - 13

[0040] AI2O3 2 - 7

[0041] Na2O + K2O 0 - 8

[0042] Alkaline earth metals 0 - 5

[0043] Other components are possible. The alkaline earth metals may include, in particular, MgO and / or CaO.

[0044] Na2O + K2O represents the sum of these two alkaline earth metals, which can be present individually or in combination.

[0045] The Fe2O3 content is particularly advantageous at less than 0.02%.

[0046] The coefficient of thermal expansion of these glass compositions lies within the aforementioned ranges.

[0047] The Kem and Mantel glasses with the described compositions can be combined in particular.

[0048] A filament is particularly advantageous if the glass composition of the core and cladding glass differs in at least one of the following components by no more than the stated amount in wt.% on an oxide basis:

[0049] SiÜ2 ± 2, advantageous ± 1

[0050] B2O3 ± 4, advantageous ± 3

[0051] AI2O3 ± 2, advantageous ± 1

[0052] Na2Ü ± 2, advantageous ± 1

[0053] K2O ± 2, advantageous ± 1

[0054] Alkaline earth metals ± 2, advantageous ± 1

[0055] In particular, this differentiation is based on the core glass composition. This means, for example, that if the core glass contains 70% SiO2, the cladding glass should advantageously contain at least 68% and / or at most 72% SiO2. The same applies to the other components mentioned. In these areas, chemical and optical compatibility between the core and cladding glass is ensured.

[0056] It is also possible for the glass compositions to contain coloring substances, especially oxides. These can serve to adjust the color of the filament and thus the color of the glass object and / or areas thereof. In this sense, it is possible for the 3D printing system to have, for example, a plurality of spool holders with the uncolored or colored glass filament according to the invention, and then, depending on the desired color of the corresponding area of ​​the glass object to be printed, the appropriate glass filament is used.

[0057] A particularly advantageous glass filament is one as described above, wherein a layer, in particular a separating layer, is located on the outer circumferential surface of the filament sheath, which is advantageously selected from stearate-based sizing, inorganic separating agent, in particular a SiÜ2-based sol-gel layer or a nanoparticle-filled sizing.

[0058] This layer can, in particular, prevent or at least reduce the adhesion of the glass filament to itself, for example, when wound onto a spool or reel, and / or to other objects. This applies especially to all components in contact with the 3D printer, and, with a suitable coating, also to the guide nozzle near the melting point. Likewise, the filament can be coated with the release agent during the drawing process, which is typically used for its production, to prevent the filaments from sticking together on a spool. Advantageously, a release agent is selected that can be removed without residue before the 3D printing process (e.g.,...)an organic, stearate-based sizing (which is solvent-soluble) or an (inorganic) release agent that remains on the filament even during the 3D printing process and is melted along with it, such as a SiO2-based sol-gel or a nanoparticle-filled sizing.

[0059] Equally advantageous is a previously described glass filament without a sizing, wherein the glass surfaces, in particular those of the sheath, have no tendency to stick, either due to the glass composition itself or due to passivation of the filament surface, so that the sizing can be dispensed with.

[0060] The invention also includes a spool or reel comprising the glass filament described herein.

[0061] The glass filament is typically wound onto a spool or reel. The spool or reel thus represents, so to speak, the byproduct of the glass filament. In this form, the glass filament can be efficiently transported and / or fed into 3D printing equipment. The invention also encompasses the use of a glass filament according to at least one of the preceding claims for 3D printing a glass object.

[0062] Also included is the use of a spool or roll of the described glass filament as a consumable for a 3D printer.

[0063] The glass filament can be used in all areas where there is a potential application for 3D-printed glass components. For example, as ferrules, holders, and fiber bundle end caps in fiber optics; as syringes, cartridges, and bypass cartridges in the pharmaceutical sector; as brackets, handles, haptic structures, and decorative elements in the home technology sector; as lightweight structures in the optics sector; and as control elements, brackets, and haptic structures in the flat glass sector, among others.

[0064] The figures are intended to further illustrate the invention. The figures are schematic; real objects may differ from the illustrations, particularly in size and / or proportions. They show:

[0065] Fig. 1 shows the cross-section through a glass filament according to the invention, Fig. 2 shows the basic 3D printing process with a glass filament.

[0066] The cross-section shown in Fig. 1 is perpendicular to the longitudinal axis of the glass filament (1). The entire glass filament (1) has a diameter dF. The round core (2) is surrounded by the sheath (3), i.e., as is generally known, along its outer circumferential surface. The core (2) has a diameter dK, and the sheath has a thickness SM. As can be readily seen, the relationship dF = dK + 2 ■ SM applies to the overall diameter.

[0067] Fig. 2 schematically shows a laser-based 3D printing process using the glass filament (1) according to the invention. The laser beam (7), in particular that of a CO2 laser, is absorbed by the glass filament (1) and melts it. The glass filament (1) is wound on a spool or reel (10) and can thus be used as a consumable for the 3D printing process. The molten glass material of the filament (1) is applied to the base plate (6), particularly in the form of small droplets or as a continuous flow of glass, and the 3D object made of glass, called the glass object (5), is built up layer by layer. The base plate can be moved in a controlled manner, particularly in the xyz direction.

[0068] The following describes the production of the glass filament and provides examples of its application. The table below shows an example of the core and cladding glass composition of a filament (1) produced as an example:

[0069] The casing material used, for example, was a glass tube with an outer diameter of 35 mm and an inner diameter of 32 mm, such as a tube made of Duranglas. The coefficient of thermal expansion (CTEM) for this is 3.3 x 10⁻⁶. 6 / K. A glass rod with a diameter of 30 mm served as the core material. Its coefficient of thermal expansion (CTEK) is 4.0 x 10⁻⁶. 6 / K. Since both glasses represent the same glass family and have a very similar composition, miscibility as well as a slight difference in refractive index are present.

[0070] The outer tube and the core rod were then assembled to form a preform, a vacuum was applied between the core and the outer tube, the preform was heated to a temperature of approximately EW of the core glass using a fiber drawing machine, and drawn into a filament (1) with a filament diameter dF of 200 pm. The filament (1) was wound directly onto a suitable spool immediately after drawing. This filament can be used directly for the 3D printing process. In one embodiment, the filament was coated with a suitable release agent during the drawing process. This at least reduced the possibility of the filament sticking to the spool. In another embodiment, it was produced without any release agent and wound onto a spool. This spool can be the same spool and / or reel (10) on which the glass filament (1) is supplied as a consumable to 3D printing systems and / or 3D printing processes.

[0071] The invention thus enables the provision of an efficiently produced and transportable glass filament (1) as a starting material for the 3D printing of glass objects. The glass object (5) can have very small structures and / or a high resolution and thus good contour fidelity. It can also exhibit good optical properties. The glass filament (1) is easy to transport and can be used efficiently as a consumable in the 3D printing process and / or in 3D printing systems.

Claims

Patent claims 1. Glass filament (1 ) for 3D printing, comprising a filament core (2) and a filament sheath (3) surrounding the outer circumferential surface of the filament core (2), wherein the filament core (2) consists of a core glass with refractive index nK and a coefficient of thermal expansion CTEK, and wherein the filament sheath (3) consists of a sheath glass with refractive index nM and a coefficient of thermal expansion CTEK, where CTEK > CTEM and the magnitude of nK - nM is less than 0.

2.

2. Glass filament according to the preceding claim, wherein both the core glass and the cladding glass are a multi-component glass.

3. Glass filament (1) according to at least one of the preceding claims, wherein the core glass and the cladding glass have the same glass components, with different contents of at least one glass component.

4. Glass filament (1) according to at least one of the preceding claims, wherein at least one of the following conditions applies: CTEK ranges from 0.5 to 10.0 ppm / K, CTEM ranges from 0.4 to 9.9 ppm / K, nK ranges from 1.4 to 2.0, nM ranges from 1.4 to 2.

0.

5. Glass filament (1) according to at least one of the preceding claims, wherein the core glass has a softening temperature EWK of 815 °C to 835 °C and the cladding glass has a softening temperature EWM of 820 °C to 840 °C and preferably the core glass has a VAK of 1240 °C to 1265 °C and particularly preferably the cladding glass has a VAM of 1250 °C to 1270 °C.

6. Glass filament (1) according to at least one of the preceding claims, wherein the filament has a filament diameter dF of 40 pm to 600 pm, wherein preferably the filament core ÖK has a diameter of 38 pm to 598 pm and the filament sheath preferably has a thickness SM of 1 pm to 200 pm.

7. Glass filament (1 ) according to at least one of the preceding claims, having a minimum bending radius of 200 mm, determined by a loop test.

8. Glass filament (1) according to at least one of the preceding claims, wherein the core glass and / or the cladding glass comprise a borosilicate glass; preferably the core glass and / or cladding glass comprises the following components (in wt.% on an oxide basis). SiO270 - 82 B2O3 7 - 13 AI2O3 2 - 7 Na2O + K2O 0 - 8 Alkaline earth metals 0 - 5 9. Glass filament (1) according to at least one of the preceding claims, wherein the glass composition of the core and the cladding glass differs in at least one of the following components by at most the stated amount in wt.% on an oxide basis: SiO2± 2 B2O3 ± 4 AI2O3 ± 2 Na2O ± 2 K20 ± 2 Alkaline earth metals ± 2 10. Glass filament (1) according to at least one of the preceding claims, wherein a layer is located on the outer circumferential surface of the filament sheath, in particular a separating layer, which is preferably selected from stearate-based sizing, inorganic separating agent, in particular a SiÜ2-based sol-gel layer or a nanoparticle-filled sizing.

11. Spool or reel (10) comprising the glass filament (1) according to at least one of the preceding claims.

12. Use of a glass filament (1) according to at least one of the preceding claims 1 to 10 for 3D printing a glass object (5).

13. Use of a glass filament (1) of at least one of claims 1 to 10 and / or a spool or roll (10) according to claim 11 as a consumable of a 3D printer.

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