METHOD FOR PRODUCING A 3D PRINTED, FOAM-FILED OBJECT

Abstract

The invention relates to a method for producing an object comprising the the following steps: producing a shell, which surrounds a volume for holding a fluid, by means of an additive manufacturing method from a construction material; providing a reaction mixture comprising a polyisocyanate component and a polyol component in the volume and allowing the reaction mixture to react in the volume such that a polymer present at least partly in the volume is obtained. The reaction mixture has a setting time of 2 minutes. An object that can be obtained by means of a method according to the invention comprises a shell, which defines a volume located within the shell, and a foam, which completely or partly fills the volume. The shell comprises a thermoplastic polyurethane polymer, the foam comprises a polyurethane foam having a compressive strength at 10% compression (DIN EN 826) of 50 kPa or a compression hardness at 40% compression (ISO 3386) of 15 kPa and the foam and the shell are at least partly integrally bonded to each other. The object can be a football, for example.

Claims

1. A method of producing an article (10), comprising the steps of: producing a shell (4) encompassing a volume (3, 3, 3) for accommodating a fluid by means of an additive manufacturing method from a construction material; providing a reaction mixture comprising a polyisocyanate component and a polyol component in the volume (3, 3, 3); allowing the reaction mixture to react in the volume (3, 3, 3) to obtain a polymer present at least in part in the volume (3, 3, 3), characterized in that the reaction mixture has a setting time of 2 minutes.

2. The method as claimed in claim 1, characterized in that the construction material is free-radically crosslinkable and comprises groups having Zerewitinoff-active hydrogen atoms, in that the shell (4) is obtained from a precursor, and in that the process comprises the steps of: I) depositing free-radically crosslinked construction material on a carrier to obtain a ply of a construction material bonded to the carrier which corresponds to a first selected cross section of the precursor; II) depositing free-radically crosslinked construction material onto a previously applied ply of the construction material to obtain a further ply of the construction material which corresponds to a further selected cross section of the precursor and which is bonded to the previously applied ply; III) repeating step II) until the precursor is formed; wherein the depositing of free-radically crosslinked construction material at least in step II) is effected by exposure and/or irradiation of a selected region of a free-radically crosslinkable construction material corresponding to the respectively selected cross section of the precursor, and wherein the free-radically crosslinkable construction material has a viscosity (23 C., DIN EN ISO 2884-1) of 5 mPas to 100 000 mPas, wherein the free-radically crosslinkable construction material comprises a curable component in which there are NCO groups and olefinic CC double bonds, and in that step III) is followed by a further step IV): IV) heating the precursor obtained by step III) to a temperature of 50 C. to obtain the shell (4).

3. The method as claimed in claim 2, characterized in that the carrier is disposed within a vessel and is lowerable vertically in the direction of gravity, the vessel contains the free-radically crosslinkable construction material in an amount sufficient to cover at least the carrier and an uppermost surface of crosslinked construction material deposited on the carrier as viewed in vertical direction, before each step II) the carrier is lowered by a predetermined distance so that a layer of the free-radically crosslinkable construction material is formed above the uppermost ply of the crosslinked construction material as viewed in vertical direction and in step II) an energy beam exposes and/or irradiates the selected region of the layer of the free-radically crosslinkable construction material corresponding to the respectively selected cross section of the precursor.

4. The method as claimed in claim 2, characterized in that the carrier is disposed within a vessel and is liftable vertically counter to the direction of gravity, the vessel provides the free-radically crosslinkable construction material, before each step II) the carrier is lifted by a predetermined distance so that a layer of the free-radically crosslinkable construction material is formed below the lowermost ply of the crosslinked construction material as viewed in vertical direction and in step II) a multitude of energy beams simultaneously expose and/or irradiate the selected region of the layer of the free-radically crosslinkable construction material corresponding to the respectively selected cross section of the precursor.

5. The method as claimed in claim 2, characterized in that in step II) the free-radically crosslinkable construction material is applied from one or more print heads corresponding to the respectively selected cross section of the precursor and is subsequently exposed and/or irradiated.

6. The method as claimed in claim 1, characterized in that the production of the shell (4) by means of the additive manufacturing method comprises the steps of: applying a layer of particles including the construction material to a target surface; introducing energy into a selected portion of the layer corresponding to a cross section of the shell (4) to bond the particles in the selected portion; repeating the steps of applying and introducing energy for a multitude of layers to bond the bonded portions of the adjacent layers to form the shell (4).

7. The method as claimed in claim 1, characterized in that the production of the shell (4) by means of the additive manufacturing method comprises the steps of: applying a layer of particles including the construction material to a target surface; applying a liquid to a selected portion of the layer corresponding to a cross section of the shell (4), where the liquid is selected in such a way that it bonds the particles to one another in the regions of the layer with which it comes into contact by bonding, fusion and/or partial dissolution; repeating the steps of applying the layer and the liquid to bond the bonded portions of the adjacent layers to form the shell (4).

8. The method as claimed in claim 1, characterized in that the production of the shell (4) by means of the additive manufacturing method comprises the steps of: applying a filament of an at least partly molten construction material to a carrier to obtain a ply of the construction material corresponding to a first selected cross section of the shell (4); applying a filament of the at least partly molten construction material to a previously applied ply of the construction material to obtain a further ply of the construction material which corresponds to a further selected cross section of the shell (4) and which is bonded to the ply applied beforehand; repeating the step of applying a filament of the at least partly molten construction material to a previously applied ply of the construction material until the shell (4) has been formed.

9. The method as claimed in claim 1, characterized in that the reaction mixture reacts to form a foam having a compressive strength at 10% compression (DIN EN 826) of 50 kPa or to form a foam having a compression hardness at 40% compression (ISO 3386-1) of 15 kPa.

10. The method as claimed in claim 1, characterized in that the polyol component comprises a bifunctional polyether polyol and/or a bifunctional polyester polyol and/or a bifunctional polyether carbonate polyol.

11. The method as claimed in claim 1, characterized in that the polyol component comprises a blowing agent which is a mixture of water and at least one physical blowing agent.

12. The method as claimed in claim 1, characterized in that the reaction mixture is provided in the volume (3, 3, 3) in an uninterrupted manner.

13. An article (10) obtainable by a method as claimed in claim 1, comprising a shell (4) that defines a volume (3, 3, 3) within the shell (4) and a foam that wholly or partly fills the volume (3, 3, 3), characterized in that the shell (4) comprises a thermoplastic polyurethane polymer, the foam comprises a polyurethane foam having a compressive strength at 10% compression (DIN EN 826) of 50 kPa or a compression hardness at 40% compression (ISO 3386-1) of 15 kPa, and the foam and the shell (4) are at least partly cohesively bonded to one another.

14. The article (10) as claimed in claim 13, characterized in that the shell (4) comprises elements that project into the volume (3, 3, 3).

15. The article (10) as claimed in claim 13, characterized in that the article (10) is a ball.

Description

DESCRIPTION OF THE FIGURES

[0180] FIG. 1 shows a view from below of the 3D-printed shell (4) of an inventive article (10) according to example 1, composed of three intermeshing elements (2, 2, 2) with walls (1) and the polymer-filled volume (3, 3, 3) enclosed thereby.

[0181] FIG. 2 shows a side view of the mold from example 1, composed of three intermeshing elements (2, 2, 2).

[0182] FIG. 3 shows a top view of the mold from example 1, composed of three intermeshing elements (2, 2, 2).

EXAMPLES

Inventive Example 1

[0183] An inventive article 10 was produced by first additively manufacturing a shell 4 and then filling it with a reaction mixture. The shell 4 was produced by the SLA method. The UV-reactive resin used was the Greay FLGPGR03 photopolymer resin from Formlabs and was processed in the Form 2 SLA printer from the manufacturer Formlabs. The shell forms a mold composed of three intermeshing, hollow elements (2, 2, 2) having a wall thickness of 2 mm. The elements (2, 2, 2) were open at the bottom in order to enable the filling with polymer, as shown in FIG. 1. After printing and removing adhering liquid photopolymer, a reaction mixture was introduced into this shell in order to obtain an article 10 as shown in FIG. 2. FIG. 3 shows a top view of the inventive article 10. However, the articles 10 shown in FIGS. 1 to 3 are merely illustrative and may have any shape achieved by 3D printing.

[0184] As reaction mixture for the polymer for filling of the hollow elements (2, 2, 2) was firstly a prepolymer of 51% by weight of methylene diphenyl isocyanate, 29% by weight of trifunctional polypropylene polyether polyol having a hydroxyl number of 35, 18% by weight of a linear polypropylene polyether polyol having a hydroxyl number of 28, 1% by weight of para-toluenesulfonyl isocyanate, 0.6% by weight of a polyether-modified polysiloxane as foam stabilizer (Tegostab B 1903, sourced from Evonik industries AG) and 0.4% by weight of dibutyltin dilaurate as catalyst. 25 g of this prepolymer were mixed with 2.5 g of water as chemical blowing agent to give a prepolymer mixture and stirred rapidly with a wooden spatula within 2 to 3 minutes. Immediately thereafter, the prepolymer mixture was poured into the additively manufactured shell 4 in order to obtain the article 10 as shown in FIGS. 2 and 3. The prepolymer mixture has a drying time of 3 h, ascertained in a moisture curing system at 23 C. and 50% relative humidity.

[0185] After 24 h, the excess foam at the openings 5, 5, 5 was removed with a sharp knife. Thus, an inventive article 10 is obtained from an additively manufactured shell 4 filled completely with a polymer foam. The shell 4 and the cured polymer are bonded to one another in such a way which has little stress between the shell 4 and the volume 3, 3, 3 that encloses the shell 4 formed from the walls 1. Owing to this exact form-fitting, the article 10 has high stability. The shell 4 and the polymer are firmly bonded to one another, such that they preferably cannot be separated from one another again without destruction of the article 10. In this way, it is possible to very rapidly produce geometrically complex and simultaneously voluminous structures that would not be producible without 3D printing. At the same time, production of the complete article by a 3D printing method would be extremely time-consuming. There is additionally high flexibility in the selection and combination of the properties of the materials of the shell and of the polymer, which enables inexpensive production of a wide variety of different geometries in combination with a wide variety of different material properties.