Modified powder suitable for three-dimensional inkjet printing and method of printing thereof

Abstract

The application discloses a modified powder suitable for three-dimensional inkjet printing and a printing forming method thereof. Firstly, an amine or acid with a mercapto group is used as a modifier, a reaction between the modifier and polymer powder is realized in an aqueous solution, a mercapto-modified powder is obtained, then the modified powder is laid into a powder layer according to a pre-designed thickness, and solidified ink is applied on the powder layer according to designed printing parameters, and a three-dimensional inkjet printing forming is realized by applying a mercapto-ene click reaction means to the powder layer. The acid or amine with a mercapto group is used as the modifier, the reaction between the amino group or the carboxyl group and the powder is used, a polymer powder with a mercapto group is obtained as a mercapto donor in advance, the mercapto donor can participate in the mercapto-ene click reaction, and solidification between the mercapto donor and most ene inks can be realized, so that the selection range of the ink is expanded, and a new way is provided for forming printing of a brittle powder such as polylactic acid.

Description

Technical Field

[0001] This invention relates to 3D printing technology for powders, and in particular to a three-dimensional printing (3DP) method using modified powders as a substrate. Background Technology

[0002] The rise of additive manufacturing technology has greatly facilitated the customization of personalized products. Polylactic acid (PLA) has moderate viscosity, low shrinkage, and is not prone to warping, exhibiting excellent 3D printing processing performance and making it an important consumable for fused deposition modeling (FDM). However, FDM's precision is not high, and the control parameters involved are complex, making it difficult to meet the demands of precision and high-efficiency 3D printing. Therefore, seeking applications for PLA in precision and rapid additive manufacturing is an urgent problem to be solved.

[0003] Currently, most PLA powder molding is achieved through selective laser sintering (SLS), which relies on high-energy laser beams to sinter points one by one. This process is slow and difficult to mass-produce. 3D inkjet printing (3DP) is another important form of powder molding. It achieves rapid molding by bonding powder and ink, and its processing speed is 10 times that of SLS. It is suitable for mass production and represents an important direction for the development of polymer powder 3D printing. In this technology, improving the bonding force between powder and ink is key to improving material properties. Currently, HP's heat-absorbing ink is the most successful example of solving this problem (patent number WO2015108543A). This technology utilizes the infrared radiation absorption capacity of carbon black to convert absorbed infrared radiation into heat energy, thereby causing sintering and solidification, thus enhancing the bonding between powder and ink. However, it requires precise control of printing parameters such as temperature, and the addition of carbon black currently limits its application to the production of almost exclusively black products. In addition, a paper (Journal of PolymerScience Part A: Polymer Chemistry, 2004, 42(3): 624-638.) describes how lysine ethyl ester diisocyanate is infiltrated into the pores of a pre-printed starch scaffold, and a cross-linked network is formed through the chemical reaction between isohydrocyanic acid and starch hydroxyl groups. However, this process takes up to two days to fully solidify and form.

[0004] For brittle polymer materials like PLA, weak physical bonding makes it difficult to meet the performance requirements. When the adhesive force is improved through chemical reaction, the side methyl groups in its molecular chain are inactive, and the number of hydroxyl groups at the chain ends is small and the reactivity is poor. Therefore, it has been impossible to achieve its 3DP molding process.

[0005] To overcome the shortcomings of 3DP molding in processing brittle polymer materials like PLA, researchers have attempted to achieve rapid molding through a chemical bonding between powder and ink. In this technology for PLA 3DP printing, other polymers capable of in-situ polymerization are added to the PLA powder, while curing agents and initiators are added to the ink. The ink then initiates the bonding of the PLA with these in-situ polymerizable substances. The powder does not chemically react with the ink; the bonding between the powder particles remains physical. Summary of the Invention

[0006] To develop a 3DP printing method suitable for PLA powder and realize the stable and efficient industrial and commercial application of PLA powder, this invention provides a modified powder suitable for three-dimensional inkjet printing, and also provides a three-dimensional inkjet printing method for this powder.

[0007] A modified powder suitable for three-dimensional inkjet printing is characterized in that it uses a thiol-containing amine or acid as a modifier, and realizes the reaction between the modifier and the polymer powder in solution to obtain a thiol-modified powder.

[0008] The polymer powder is selected from various polyester or polycarbonate powders, or polyester or polycarbonate powders of various shapes with a size of less than 500 micrometers prepared by various physicochemical methods.

[0009] Furthermore, the powder is polylactic acid, various aliphatic polyesters, aromatic polyesters, aliphatic polycarbonate, or aromatic polycarbonate.

[0010] Furthermore, the modifiers include various thioglycolic acids and thioamines, such as mercaptoethylamine, thioglycolic acid, cysteine, etc.

[0011] Further: The modified powder preparation method is as follows: using a polymer as raw material, adding it to a modifier solution with a mass fraction of 0-50%, wherein the polymer accounts for 0-30 wt% of the modifier solution content; stirring rapidly at 10-90 ℃ for a reaction time of 0.5 h or more; filtering, washing and collecting the solid precipitate after the reaction to obtain the thiolized powder.

[0012] A method for three-dimensional powder inkjet printing, characterized by comprising the following steps: The first step is to spread the pre-prepared modified powder into a powder layer according to the pre-designed thickness; The second step is to pre-dissolve an initiator with a mass fraction of 0.1-5% in the olefin ink to pre-form a cured ink. The mass fraction refers to the proportion of the initiator in the olefin ink after it is dissolved. The olefin inks described herein are various monomers containing double bonds, and are required to undergo a mercapto-olefin click reaction with the modified powder; The initiator is any type of initiator suitable for click reactions of mercapto-olefins; Step 3: Apply the cured ink to the powder layer according to the designed printing parameters, and at the same time apply an auxiliary mercapto-olefin click reaction to the powder layer to form a 3D inkjet print.

[0013] Furthermore, the olefin ink is a variety of olefin monomers, including one or more of ethylene, styrene and acrylic monomers, such as glycidyl methacrylate, methyl acrylate, limonene, ethyl acrylate, styrene, etc.

[0014] Furthermore, the initiator is a free radical initiator such as a thermal initiator or a photoinitiator. Examples include diphenyl ethyl ketone, α-hydroxyalkyl phenyl ketone, azobisisobutyronitrile, 1-hydroxycyclohexylphenyl ketone, 4-phenylbenzophenone, and peroxide initiators.

[0015] Furthermore, the methods for assisting the click reaction of mercapto-olefins include various methods such as light irradiation, heating, and ultrasound.

[0016] Further: The viscosity of the olefin ink is 5-80 cps.

[0017] Of course, to improve printing performance, some active ingredients, such as plasticizers, antioxidants, and fluorescent agents, can be added to the ink of this invention. However, these additives are conventional technologies in the field and are not within the scope of protection of this invention, nor are they the focus of this invention.

[0018] The positive effects of this invention are: 1. This invention modifies PLA by reacting the amino or carboxyl groups of a modifier with the ester groups on the PLA backbone without altering its synthetic route. Therefore, commercially available PLA can be directly purchased as raw material, facilitating industrial-scale application. Furthermore, the powder modification process of this invention is an all-aqueous production process, without the use of organic solvents, achieving zero-waste production throughout.

[0019] This invention uses an acid or amine with a thiol group as a modifier. By means of the reaction between amino or carboxyl groups and powder, a polymer powder with a thiol group is obtained in advance as a thiol donor. The thiol donor can participate in the thiol-alkene click reaction and can be cured with most alkene inks, thus expanding the range of ink choices and providing a new approach for the molding and printing of brittle powders such as polylactic acid.

[0020] 3. This invention utilizes the reaction between amino or carboxyl groups and ester groups on the PLA backbone to simultaneously achieve thiolation modification of PLA and regulation of its molecular structure and properties.

[0021] 4. The thiolized PLA prepared by the reaction of this invention is a thiol donor that can participate in the thiol-alkene click reaction and can be cured with most alkene inks. By changing the alkene ink, it can be widely used to prepare products with different properties. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. The accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 Here is a SEM image of the thiolized PLA powder prepared in Example 1; Figure 2 The FTIR curve of the mercaptolated PLA powder prepared in Example 1 is shown. Figure 3 The image shows the FTIR curve of the curing scaffold prepared in Example 2. Figure 4 The stress-strain curve of the solidified scaffold prepared in Example 4 is shown in the tensile test. Detailed Implementation

[0024] To make the technical problem to be solved, the technical solution and the beneficial effects of the present invention clearer, the following description is provided in conjunction with the appendix. Figure 1 The present invention will be further described in detail with specific examples. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0025] Example 1: Preparation of PLA modified powder Prepare 500 mL of a 25% (w / w) cysteine ​​aqueous solution, add 50 g of PLA microspheres that have passed through an 80-mesh standard sieve, and stir rapidly at 60 °C for 1 h. Filter, wash, and collect the solid precipitate to obtain thiolated PLA.

[0026] The thiolized PLA powder prepared in Example 1 was observed using scanning electron microscopy and its chemical structure was detected using Fourier transform infrared spectroscopy (FTIR). SEM images are attached. Figure 1 As shown in the scanning electron microscope image, the PLA powder treated under these conditions exhibits a dense fibrous network structure on the surface of microspheres.

[0027] Figure 2 The image shows the FTIR curve of the thiolized PLA powder prepared in Example 1. The FTIR curve shows Cys at 1535 cm⁻¹. -1The nearby amino NH in-plane bending vibration peak shifts to 1508 cm⁻¹ in the PLA-Cys sample after reaction with PLA. -1 Near this point, the amide II band appears, indicating amide formation. PLA-Cys occurs at 2500-2600 cm⁻¹. -1 The presence of a unique thiol characteristic peak in the vicinity of Cys indicates that an amino-ester reaction occurred between the two, introducing thiol groups into the PLA molecular chain.

[0028] Examples 2 to 4 below are examples of three-dimensional inkjet printing using the modified powder prepared in Example 1. Example 2

[0029] Azobisisobutyronitrile (AIB) initiator with a mass fraction of 0.5% was pre-dissolved in methyl acrylate to prepare an ink with a viscosity of 15 cps. Thioylated PLA powder was then spread into a layer. The ink was slowly added dropwise to the layer, and the mixture was heated to 70 °C for 5 min to obtain a 3DP-cured scaffold.

[0030] The FTIR curve of the curing scaffold prepared in Example 2 is as follows: Figure 3 As shown. FTIR detection revealed that the 2550 cm⁻¹ region in the cured sample... -1 The -SH characteristic peak of the modified microsphere sample is at 1612 cm⁻¹. -1 The C=C characteristic peaks of methyl acrylate in the vicinity have all disappeared, indicating that a complete reaction occurred between -SH and C=C. (1758 cm⁻¹) -1 With 1631cm -1 The two retained strong C=O absorption peaks originated from PLA and methyl acrylate, respectively. Therefore, click curing of PLA powder was achieved. Example 3

[0031] A 1% (w / w) initiator α-hydroxyalkyl phenyl ketone was first dissolved in methyl acrylate to pre-prepare a curable ink with a viscosity of 30 cps. A layer of mercaptoethylamine-modified polycarbonate was then laid flat. The ink was slowly dripped onto the layer, and ultraviolet light at a wavelength of 365 nm was applied for 20 seconds to achieve 3DP molding. Example 4

[0032] A 1% (w / w) initiator, diphenyl ethyl ketone, was first dissolved in glycidyl methacrylate to pre-prepare a 40 cps cured ink. Mercaptopropionic acid-grafted PLA powder was then spread into a layer. The ink was slowly added dropwise to the layer, and ultraviolet light at a wavelength of 365 nm was applied for 20 s to obtain a scaffold.

[0033] The stress-strain curve of the bracket obtained in Example 4 under a tensile test on a universal testing machine is shown below. Figure 4 As shown in the figure, the tensile strength of the sample reaches 12 MPa, the elongation at break is 10%, and the Young's modulus is 885 MPa. This demonstrates that it is entirely feasible to prepare PLA molded products using the method of this invention.

[0034] The above are embodiments of the present invention and do not represent limitations on the technical solutions of the present invention, especially the selection of powder, modifier and ink. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principles described in the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for three-dimensional powder inkjet printing, characterized in that, It includes the following steps: The first step is to spread the modified powder into a powder layer of a pre-designed thickness; the method for preparing the modified powder is as follows: Prepare 500 mL of cysteine ​​aqueous solution with a mass fraction of 25%, add 50 g of PLA microspheres that have passed through an 80-mesh standard sieve, stir rapidly at 60 ℃ for 1 h, filter, wash and collect the solid precipitate to obtain thiolized PLA; The second step is to pre-dissolve the initiator in the olefin ink to pre-prepare a curable ink with an initiator content of 0.1-5 wt%. The olefin ink is methyl acrylate; the initiator is any initiator suitable for mercapto-olefin click reactions; Step 3: Apply the cured ink to the powder layer according to the designed printing parameters, and at the same time apply an auxiliary mercapto-olefin click reaction to the powder layer to form a 3D inkjet print.

2. The powder three-dimensional inkjet printing method as described in claim 1, characterized in that, The initiator is a thermal initiator or a photoinitiator.

3. The powder three-dimensional inkjet printing method as described in claim 1, characterized in that, The viscosity of the olefin ink is 5-80 cps.

4. The powder three-dimensional inkjet printing method as described in claim 1, characterized in that, The means of assisting the click reaction of mercapto-alkene include, but are not limited to, various light, heating or ultrasonic methods.

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