Method for recovering depolymerized products containing monomers, method for producing resin powder, method for producing resin molded products, resin powder and resin molded products

Abstract

This process enables the complete recycling of resin molded objects or resin powder within the additive manufacturing process, providing high-quality resin molded products using an environmentally friendly method. [Solution] A method for adding a resin molded product formed by an additive manufacturing process, or resin powder used in an additive manufacturing process, to water, heating at 100°C to 400°C to depolymerize, and recovering a depolymer containing monomers. A method for recovering a depolymer containing monomers and then polymerizing it to produce a resin powder with an average particle size of 1 to 100 μm, and a method for producing a resin molded product used in an additive manufacturing process with resin powder.

Description

Technical Field

[0001] The present invention relates to a method for recovering a monomer-containing decomposed polymer after treating a three-dimensional resin shaped article formed by an additive manufacturing process typified by a powder bed fusion bonding method, or a resin powder used in the additive manufacturing process into a monomer-containing decomposed polymer, a method for producing a resin powder having an average particle diameter of 1 to 100 μm by polymerizing the monomer-containing decomposed polymer, and further a method for recycling the resin powder to the additive manufacturing process, and relates to a process for circulating highly reliable resin powder and shaped articles.

Background Art

[0002] As a technique for producing a three-dimensional shaped article (hereinafter sometimes simply referred to as a shaped article), an additive manufacturing process typified by a powder bed fusion bonding method is known. In the powder bed fusion bonding method, after forming a thin layer of resin powder, a laser or an energy beam is selectively irradiated only to a portion to be shaped, and the resin powder is repeatedly fused and bonded to produce the shaped article. Such an additive manufacturing process is expected to expand rapidly because it can achieve high dimensional accuracy and mechanical strength of shaped articles.

[0003] On the other hand, only a few percent of the total resin powder in the additive manufacturing process becomes a shaped article, and most of the resin powder is recovered as used resin powder, which is desired to be recycled and reused. However, the resin powder is exposed to a temperature near the melting point for a long time in order to suppress warpage during the additive manufacturing process, so it is difficult to recover and reuse all of it. In addition, there are many uncertain factors that promote deterioration such as residual oxygen during the additive manufacturing process, which makes recovery more difficult. A method of materially recycling the resin powder itself into an injection molding material (Patent Document 1), a method of reusing it as resin powder for the additive manufacturing process (Patent Documents 2 and 3), and a method of decomposing the used powder resin into oligomers and then polymerizing it (Patent Document 4) have been studied.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] US2022 / 0064405A1 [Patent Document 2] US2023 / 0192981A1 [Patent Document 3] Special Publication No. 2023-513252 [Patent Document 4] Special Publication No. 2022-503962 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the technology described in Patent Document 1 makes it difficult to implement recycling that is completed within the additive manufacturing process, and in particular, the 3D-formed objects created in the additive manufacturing process have no option but to be discarded.

[0006] The method described in Patent Document 2 is only applicable to resin powder. The method described in Patent Document 3 is a method for reducing the intrinsic viscosity of resin powder after use by processing the resin powder whose intrinsic viscosity has increased, but there is still room for improvement in providing high-quality, morphologically controlled resin powder for use in additive manufacturing processes. Patent Document 4 is also a method for decomposing used powdered resin from polymers to oligomers with multiple repeating structures and then polymerizing it, and like Patent Document 3, there is room for improvement.

[0007] Therefore, the object of the present invention is to recover resin molded products formed by an additive manufacturing process, or resin powder used in an additive manufacturing process, after decomposing them into depolymers containing monomers, using the monomers to produce new resin powder, and recycling the resin powder back into the additive manufacturing process. The aim is to provide highly reliable resin powder that can maintain the high quality of resin molded products in an environmentally friendly manner. [Means for solving the problem]

[0008] To solve the above problems, the present invention has the following configuration. That is, (1) A method of adding a resin molded product formed by an additive manufacturing process, or resin powder used in an additive manufacturing process, to water, heating at 100°C to 400°C to depolymerize, and recovering a depolymer containing monomers. (2) A method for recovering a depolymer product containing the monomer described in (1), characterized by crushing a resin molded product formed by an additive manufacturing process and then adding it to water. (3) A method for recovering a depolymer containing the monomer described in (1) or (2), characterized in that the water is selected from an acidic aqueous solution, a basic aqueous solution, supercritical water, and subcritical water. (4) A method for recovering a depolymer containing a monomer according to any one of (1) to (3), characterized in that the monomer concentration contained in the recovered depolymer is 60% by mass or more. (5) A method for recovering a depolymer containing the monomer described in (3), characterized in that the acidic aqueous solution is an aqueous phosphoric acid solution. (6) A method for recovering a monomer-containing depolymer according to (5), characterized by adding a basic substance to the monomer-containing depolymer. (7) A method for recovering a depolymer containing a monomer according to any one of (1) to (6), characterized in that the resin molded product formed by the additive manufacturing process, or the resin powder used in the additive manufacturing process, contains a polyamide. (8) A method for recovering a depolymer containing the monomer described in (7), wherein the polyamide is at least one selected from polyamide 12, polyamide 11, polyamide 6, polyamide 66, and copolymers thereof. (9) A method for producing a resin powder with an average particle size of 1 to 100 μm by recovering a depolymer containing monomers using any of the methods described in (1) to (8), and then polymerizing it. A method for manufacturing a resin molded object, characterized by manufacturing a resin powder by the method of (10)(9), and then using the resin powder in an additive manufacturing process. (11) A resin powder characterized by containing 1% or less of phosphate and having an average particle size of 1 to 100 μm. (12) The resin powder according to (11), characterized in that the polyamide constituting the resin powder is at least one selected from polyamide 12, polyamide 11, polyamide 6, polyamide 66, and copolymers thereof. A resin molded product manufactured by an additive manufacturing process using the resin powder of (13)(11) or (12), characterized in that it contains 1% or less of phosphate. [Effects of the Invention]

[0009] According to the present invention, resin molded products formed by an additive manufacturing process, or resin powder used in an additive manufacturing process, can be decomposed into a depolymer containing monomers and recovered. This allows for the production of new resin powder using the monomers, and then the recycling of the resin powder back into the additive manufacturing process. This completes the recycling process within the additive manufacturing process, enabling the circulation of high-quality resin molded products in an environmentally friendly manner. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing an example of a manufacturing apparatus for three-dimensional objects according to the present invention. [Modes for carrying out the invention]

[0011] The present invention will be described in more detail below.

[0012] In this invention, a resin molded product formed by an additive manufacturing process, or resin powder used in an additive manufacturing process, is added to water, heated at 100°C to 400°C to depolymerize, and a depolymer product containing monomers is recovered.

[0013] The resin molded object formed by the additive manufacturing process of the present invention, or the resin powder used in the additive manufacturing process, refers to a three-dimensional resin molded object formed by an additive manufacturing process such as powder bed fusion, or resin powder that was supplied to an additive manufacturing apparatus to produce a three-dimensional molded object by powder bed fusion, but remained without forming a three-dimensional molded object. The resin constituting the resin molded product has the same composition as the resin powder used in the additive manufacturing process and exhibits a structure consisting of repeating monomer units of one or more types. Specifically, polyamide, polyester, polyolefin, polyurethane, polycarbonate, polyetheretherketone, polyaryleneetherketone, polyphenylene sulfide, and polyetherimide are preferred, with polyamide and polyester being preferred from the viewpoint of monomer recovery, and polyamide being the most preferred from the viewpoint of improving the quality of the resin molded product.

[0014] Polyamides are composed of repeating units containing amide groups. Specific examples of such polyamides include polycaproamide (polyamide 6), polyhexamethylene adipamide (polyamide 66), polyhexamethylene terephthalamide (polyamide 6T), polyhexamethylene sevacamide (polyamide 610), polyhexamethylene dodecamide (polyamide 612), polydecamethylene adipamide (polyamide 106), polydodecamethylene adipamide (polyamide 126), polyamide 4, polytetramethylene adipamide (polyamide 46), polytetramethylene sevacamide (polyamide 410), polypentamethylene adipamide (polyamide 56), and poly Examples include ripentamethylene sebamid (polyamide 510), polynonanamide (polyamide 9), polydecamethylene terephthalamide (polyamide 10T), polydecamethylene sebamid (polyamide 1010), polydecamethylene dodecamide (polyamide 1012), polyundecanamide (polyamide 11), polylauroamide (polyamide 12), polydodecamethylene dodecamide (polyamide 1212), polydodecamethylene terephthalamide (polyamide 12T), polycaproamide / polyhexamethylene adipamide copolymer (polyamide 6 / 66), or copolymers thereof. Among these, polycaproamide (polyamide 6), polylauroamide (polyamide 12), polyundecaneamide (polyamide 11), and their copolymers are preferred from the viewpoint of ease of monomer recovery, and polylauroamide (polyamide 12) and its copolymers are particularly preferred from the viewpoint of availability of resin molded products and resin powders.

[0015] These resin shaped articles and the used resin powder are added to water, and heated at a temperature of 100°C or higher and 400°C or lower to perform depolymerization, so as to obtain a depolymerized product containing a monomer.

[0016] Here, the term "monomer" refers to the repeating unit that constitutes the resin. For example, in the case of polyamide, the monomers include lactams, diamines and dicarboxylic acids, amino acids, etc.; in the case of polyester, the monomers include lactones, dicarboxylic acids and dialcohols. Specifically, in the case of polyamide 6, the monomers are ε-caprolactam and aminocaproic acid; in the case of polyamide 66, the monomers are hexamethylenediamine and adipic acid; in the case of polyamide 610, the monomers are hexamethylenediamine and sebacic acid; in the case of polyamide 11, the monomers are undecanolactam and aminoundecanoic acid; and in the case of polyamide 12, the monomers are laurolactam and aminododecanoic acid, etc.

[0017] Depending on the type of monomer, there are monomers that dissolve in water and monomers that are insoluble in water. When the monomer dissolves in water, the depolymerized product dissolves in water. When the monomer is insoluble in water, the depolymerized product becomes a water-insoluble precipitate. When the depolymerized product is insoluble in water, it can be isolated using a known method such as centrifugation, centrifugal dehydration, or filtration.

[0018] The concentration of the monomer contained in the depolymerized product recovered in this manner is 60% by mass or more. The higher the monomer concentration, the easier the recycling of the resin powder and resin shaped articles described later, so the concentration is preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more.

[0019] The monomer concentration is measured by liquid phase chromatography using a solvent that dissolves the depolymerized product.

[0020] Here, since the resin molded object is usually too large to fit in the reaction vessel, it can be micronized by known methods such as grinding. Preferably, the size is 5 mm square or smaller, and the grinding method can be appropriately selected from room temperature grinding to freeze grinding, hammer milling, jet milling, cutter milling, etc. The finer the grinding, the more the reaction proceeds and the higher the concentration of monomer, which is preferable. When the amount of pulverized resin molded material or resin powder used is 100 parts by mass, the amount of water to be added is 50 to 300 parts by mass. From the viewpoint of increasing monomer concentration and using high-pressure equipment, the lower limit of water is preferably 60 parts by mass or more, and particularly preferably 70 parts by mass or more. The upper limit is preferably 250 parts by mass or less, and particularly preferably 200 parts by mass or less.

[0021] The water used in this invention may be in the form of an acidic aqueous solution, a basic aqueous solution, supercritical water, or subcritical water, and the optimal form may be appropriately selected depending on the type of resin used.

[0022] When depolymerization is carried out using only water, it is particularly preferable to use water in a state that is neither liquid nor gaseous, such as supercritical or subcritical water. The lower limit of the temperature is preferably 250°C or higher, and particularly preferably 280°C or higher, as this dramatically improves penetration into the resin and increases the concentration of monomers. Since side reactions increase around 400°C where the supercritical state is reached, the upper limit is preferably 370°C or lower, where the subcritical state is reached, and particularly preferably 320°C or lower.

[0023] In the depolymerization process of this invention, water may be in a liquid or gaseous state, but it is preferable for the water to be in a liquid state from the viewpoint of stable reaction and the formation of a critical state to promote high concentration of monomers. There is no particular upper limit on the water pressure, but it is 20 MPa or less.

[0024] Furthermore, selecting an acidic or basic aqueous solution is preferable because it suppresses polymerization reactions and increases the monomer concentration of the depolymer after depolymerization. As the acid, sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, formic acid, acetic acid, etc., can be appropriately selected. As the base, sodium hydroxide, potassium hydroxide, magnesium hydroxide, ammonia, etc., can be selected. In particular, phosphoric acid, formic acid, and acetic acid are preferred from the viewpoint of suppressing side reactions, and phosphoric acid is especially preferred from the viewpoint of improving yield.

[0025] When using acidic or basic aqueous solutions, the temperature range can be selected as appropriate, but it is preferable to use them even at low temperatures because the monomer concentration increases even at low temperatures. In this case, the upper limit of the temperature is preferably 300°C or lower, and particularly preferably 250°C or lower.

[0026] When carrying out depolymerization, catalysts or additives may be added to the water, such as acidic aqueous solutions, basic aqueous solutions, supercritical water, or subcritical water, to promote depolymerization.

[0027] The reaction time can be selected as appropriate, and is typically between 0.1 and 3 hours.

[0028] While depolymerization is carried out in this manner, if an acidic or basic aqueous solution is selected, for example, dicarboxylic acids, diamines, and amino acids are ionic, so it is also acceptable to neutralize them by adding a base or acid to obtain the desired monomer.

[0029] The resin molded products and resin powders used in this invention may be copolymerized or contain end-modifying agents. Furthermore, they may contain fluidizers, inorganic reinforcing agents, and other additives used in additive manufacturing processes, as long as they do not impair the present invention.

[0030] Fluids include silica (silicon dioxide) such as fused silica, crystalline silica, and amorphous silica, as well as alumina (aluminum oxide), alumina colloid (alumina sol), and alumina white. Inorganic reinforcing materials include glass-based fillers such as glass fibers, glass beads, glass flakes, and foamed glass beads, carbon-based fillers such as carbon fibers, carbon nanotubes, and carbon particles, and organic fibers such as cellulose nanofibers. Other additives include antioxidants, heat stabilizers, weathering agents, lubricants, pigments, dyes, plasticizers, antistatic agents, flame retardants, carbon black, and titanium dioxide to improve the stability and moldability of the resin powder.

[0031] The amount of fluidizers and other additives is preferably 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of resin molded product or resin powder, and the amount of inorganic reinforcing material is preferably 10 parts by mass or more and 200 parts by mass or less. Two or more of these may be used simultaneously, and they may be dry blended with the resin powder or encapsulated within it.

[0032] In this invention, a monomer-containing depolymer is recovered from an aqueous solution or slurry containing a monomer-containing depolymer obtained by depolymerization using known methods such as distillation, solid-liquid separation, and crystallization. It is preferable that the monomer-containing depolymer recovered by this recovery method be purified, as this facilitates the recycling of the resin powder in subsequent processes. Examples of purification methods include known methods such as distillation and crystallization.

[0033] The recovered monomers can then be polymerized and used in various methods such as resins, films, fibers, and additive manufacturing processes. In particular, their use in additive manufacturing processes is preferred because they can be recycled only within the additive manufacturing process. Furthermore, while resin powder is used in additive manufacturing processes, chemically treated resin powder is preferred over pulverized resin powder to improve the quality of the molded product. In these cases, the quality of the monomer is important, and the monomers recovered using this method are particularly preferred because they have a low impurity content and allow for stable production of resin powder through chemical treatment.

[0034] When the monomer of the present invention is 100 parts by mass, the impurity content is 2 parts by mass or less, preferably 1 part by mass or less, particularly preferably 0.5 parts by mass or less, and most preferably 0.1 parts by mass or less.

[0035] Methods for producing resin powder include grinding and chemical processing, but chemical processing is preferred because it makes it easier to form the resin powder into a spherical shape and improves the quality of the additive manufacturing process. Examples include the dissolution precipitation method, in which polyamide is polymerized, dissolved in a solvent, and then cooled to precipitate; the anionic polymerization precipitation method, in which monomers are polymerized anionically by adding a metal catalyst in liquid paraffin and precipitated; and the phase separation polymerization method, previously described by the present inventors in International Publication WO2022 / 181634, in which monomers are polymerized and precipitated in a polymer component that is charged with the monomer. The dissolution precipitation method and the phase separation polymerization method are preferred due to the ease of recovering the monomers, and the phase separation polymerization method is particularly preferred because it makes it easy to control the shape of the resin powder into a spherical shape.

[0036] The average particle size of the resin powder of the present invention is in the range of 1 μm to 100 μm. The smaller the average particle size, the better the surface smoothness of the resin molded product. The upper limit of the average particle size of the resin powder is preferably 90 μm or less, more preferably 80 μm or less, and even more preferably 75 μm or less. If the average particle size is too small, the productivity of the resin particles deteriorates. The lower limit is more preferably 5 μm or more, even more preferably 10 μm or more, and particularly preferably 20 μm or more.

[0037] The average particle size of the resin powder in this invention refers to the D50 particle size. The D50 particle size of the resin powder is measured using a laser diffraction particle size distribution analyzer. The D50 particle size of the resin powder is the particle size at which the cumulative frequency from the smallest particle size side of the particle size distribution measured by the laser diffraction particle size distribution analyzer reaches 50%.

[0038] The sphericity of the resin particles of the present invention is preferably 70 or higher. A higher sphericity is preferable because it reduces the surface area, improving moldability and the surface smoothness of the resin molded object. The sphericity is preferably 75 or higher, more preferably 80 or higher, and even more preferably 90 or higher. Theoretically, the upper limit is 100.

[0039] The sphericity of the resin powder of the present invention is calculated by observing 30 randomly selected particles from scanning electron microscope images and using the average value of the ratio of their short axis to long axis.

[0040] The rate of change in average particle size and sphericity when monomers are recovered and resin powder is recycled can be calculated by dividing the average particle size and sphericity of the resin powder before monomer recovery by the average particle size and sphericity of the resin powder produced using the recovered monomers.

[0041] The rate of change of the resin powder in this process is preferably between 0.8 and 1.2. The closer the rate of change is to 1, the better the resin powder can be recycled by recovering the monomers, and good resin molded products can be produced in the additive manufacturing process. The upper limit is more preferably 1.15 or less, and even more preferably 1.1 or less. The lower limit is more preferably 0.85 or more, and even more preferably 0.9 or more. This method, which recovers the depolymerized product containing monomers, is suitable because it allows the resin powder to be recycled repeatedly.

[0042] The resin powder polymerized using the recovered monomers in this manner may be copolymerized or end-modifying agents used, as long as it does not impair the present invention. Furthermore, as long as it does not impair the present invention, the resin powder composition may include fluidizers, inorganic reinforcing agents, and other additives used in the addition process.

[0043] Fluids include silica (silicon dioxide) such as fused silica, crystalline silica, and amorphous silica, as well as alumina (aluminum oxide), alumina colloid (alumina sol), and alumina white. Inorganic reinforcing materials include glass-based fillers such as glass fibers, glass beads, glass flakes, and foamed glass beads, carbon-based fillers such as carbon fibers, carbon nanotubes, and carbon particles, and organic fibers such as cellulose nanofibers. Other additives include antioxidants, heat stabilizers, weathering agents, lubricants, pigments, dyes, plasticizers, antistatic agents, flame retardants, carbon black, and titanium dioxide to improve the stability and moldability of the resin powder.

[0044] The amount of fluidizers and other additives is preferably 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of resin powder, and the amount of inorganic reinforcing materials is preferably 10 parts by mass or more and 200 parts by mass or less. Two or more of these may be used simultaneously, and they may be dry-blended with the resin powder or encapsulated within it.

[0045] The resin powder or resin powder composition prepared in this manner can be used in additive manufacturing processes. Below, an example of a method for manufacturing a three-dimensional object using the resin powder or resin powder composition of the present invention will be illustrated with reference to Figure 1.

[0046] (a) In step (a), the stage 2 of the tank 1 in which the molded object is formed is lowered.

[0047] (b) In step (b), the stage 4 of the tank 3 (hereinafter sometimes referred to as the supply tank), which is pre-filled with resin powder or resin powder composition P to be supplied to the tank 1 for forming the molded object, is raised to a height that allows for the supply of a sufficient amount of resin powder or resin powder composition P to fill the tank 1 to a predetermined layer height. Then, the recoater 5 is moved from the left end of the supply tank 3 in the diagram to the right end of the tank 1, and the resin powder or resin powder composition P is layered into the tank 1. The direction parallel to the movement of the recoater 5 is the X direction, and the direction perpendicular to the direction of movement of the recoater 5 on the powder surface of the resin powder or resin powder composition P is the Y direction. Reference numeral 7 indicates a coordinate system representing the X, Y, and Z directions. Reference numeral 8 indicates the surface direction in which the resin powder or resin powder composition is layered, and reference numeral 9 indicates the height direction in which the resin powder or resin powder composition is layered.

[0048] (c) In step (b), the resin powder or resin powder composition P that was filled into the tank 1 to a predetermined stacking height in step (b) is given meltable thermal energy 6 and selectively melted and sintered according to the molding data.

[0049] In the powder bed fusion method, a three-dimensional object 10 can be obtained by repeatedly performing steps (a) to (c) described above.

[0050] (d) In step (d), the three-dimensional molded object 10 in the tank 1 and the resin powder or resin powder composition 11 that remained without becoming part of the molded object 10 are separated and recovered.

[0051] (c) As a method for selectively melting and sintering in step (c), examples include a selective laser sintering method in which a laser is irradiated to a shape corresponding to the cross-sectional shape of the object to be fabricated to bond the resin powder or resin powder composition. Other examples include a printing step in which an energy absorption accelerator or energy absorption inhibitor is printed to a shape corresponding to the cross-sectional shape of the object to be fabricated, and a selective absorption (or suppression) sintering method in which the resin powder is bonded using electromagnetic radiation.

[0052] The laser light used in selective laser sintering is not particularly limited as long as it does not impair the quality of the resin powder or resin powder composition or the resin molded object. Examples include carbon dioxide lasers, YAG lasers, excimer lasers, He-Cd lasers, and semiconductor-pumped solid-state lasers. Among these, carbon dioxide lasers are preferred because they are easy to operate and control.

[0053] Furthermore, the electromagnetic radiation used in selective absorption (suppression) sintering can be any type as long as it does not impair the quality of the resin powder or resin powder composition or the fabricated object, but infrared radiation is preferred because it is relatively inexpensive and provides energy suitable for fabrication. Also, the electromagnetic radiation may or may not be coherent.

[0054] Energy absorption enhancers are substances that absorb electromagnetic radiation. Examples of such substances include carbon black, carbon fibers, copper hydroxyphosphate, near-infrared absorbing dyes, near-infrared absorbing pigments, metal nanoparticles, polythiophene, poly(p-phenylene sulfide), polyaniline, poly(pyrrole), polyacetylene, poly(p-phenylene vinylene), polyparaphenylene, poly(styrene sulfonate), poly(3,4-ethylenedioxythiophene)-poly(styrenephosphonate)p-diethylaminobenzaldehyde diphenylhydrazone, or conjugated polymers consisting of combinations thereof. These may be used individually or in combination.

[0055] Energy absorption inhibitors are substances that do not readily absorb electromagnetic radiation. Examples of such substances include materials that reflect electromagnetic radiation, such as titanium, heat-insulating powders such as mica powder and ceramic powder, and water. These can be used individually or in combination.

[0056] These selective absorbers or selective inhibitors may be used individually or in combination.

[0057] In the process of printing a selective absorbent or selective inhibitor in a shape corresponding to the cross-sectional shape of the object to be fabricated, known methods such as inkjet printing can be used. In this case, the selective absorbent or selective inhibitor may be used as is, or it may be dispersed or dissolved in a solvent before use.

[0058] The resin molded object of the present invention, thus reshaped, exhibits good surface smoothness because the resin powder is spherical. Surface smoothness can be expressed as surface roughness, which is calculated by observing the surface of the molded object with an optical microscope, creating a 3D image of the surface irregularities in automatic synthesis mode, obtaining a cross-sectional height profile over a length of 1 mm or more, and calculating the surface roughness Ra (centerline mean roughness) using the arithmetic mean.

[0059] The surface roughness of the three-dimensional resin molded product of the present invention is 20 μm or less. The more spherical the shape, the smaller the surface roughness and the better the smoothness, so 15 μm or less is preferred, and 12 μm or less is more preferred. The lower limit is not particularly limited, and a smaller value is preferred, but the lower limit is usually 1 μm.

[0060] The rate of change in the surface roughness of resin molded objects obtained through recycled molding can be calculated by dividing the surface roughness of molded objects made using resin powder and resin powder compositions before monomer recovery by the surface roughness of resin molded objects made using resin powder and resin powder compositions produced using recovered monomers.

[0061] The rate of change in the surface roughness of the resin molded product is preferably 0.8 or more and 1.2 or less. The closer the rate of change is to 1, the better the mechanical strength can be maintained even in recycled resin molding. The upper limit is more preferably 1.15 or less, and even more preferably 1.1 or less. The lower limit is more preferably 0.85 or more, and even more preferably 0.9 or more. This method, which recovers a depolymer containing monomers, is suitable because it allows the resin molded product to be recycled repeatedly.

[0062] Furthermore, the rate of change in the mechanical strength of a 3D resin molded object when recycled can be calculated by dividing the bending strength of a molded object made using resin powder and resin powder composition before monomer recovery by the bending strength of a resin molded object made using resin powder and resin powder composition produced using recovered monomers.

[0063] The rate of change in the mechanical strength of the 3D molded object after recycling is preferably 0.8 to 1.2. The closer the rate of change is to 1, the better the mechanical strength can be maintained even after recycling. The upper limit is more preferably 1.15 or less, and even more preferably 1.1 or less. The lower limit is more preferably 0.85 or more, and even more preferably 0.9 or more. This method, which recovers a depolymer containing monomers, is suitable because it allows the resin molded object to be recycled repeatedly.

[0064] The bending strength of the molded object is the value of the maximum bending stress measured in accordance with the Japanese Industrial Standard (JIS) JIS K7171 (2016) "Plastics - Method for determining bending properties". [Examples]

[0065] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0066] (1) Monomer concentration of the depolymerized product (HPLC) 0.1 g of the depolymer containing monomers was dissolved in 10 g of ethanol, and the monomer yield was calculated by high-performance liquid chromatography. The measurement conditions are as follows. Equipment: Shimadzu Corporation LC-10Avp series Column: Mightysil RP-18GP150-4.6 Detector: Photodiode array detector (UV=205nm) Flow rate: 1mL / min Column temperature: 40℃ Mobile phase: 0.1% aqueous acetate solution / acetonitrile Monomer quantification: Monomers in polyamides are quantified using the absolute calibration curve method.

[0067] (2) Average particle size of resin powder A dispersion of approximately 100 mg of resin powder and a resin powder composition dispersed in approximately 5 mL of deionized water was added to a laser diffraction particle size distribution analyzer (Microtrac MT3300EX II) manufactured by Nikkiso Co., Ltd. until it reached a measurable concentration. After ultrasonic dispersion at 30 W for 60 seconds in the analyzer, the average particle size was measured from the particle size distribution measured after 10 seconds. The particle size refers to the D50 particle size, which is the particle size at which the cumulative frequency from the smallest particle size side becomes 50%. The refractive index used during measurement was 1.52, and the refractive index of the medium (deionized water) was 1.333.

[0068] (3) Weight-average molecular weight of the polyamide constituting the resin powder The weight-average molecular weight of resin powders or resin powder compositions was calculated using gel permeation chromatography and compared with a calibration curve using polymethyl methacrylate. A sample was prepared by dissolving approximately 3 mg of polymer particles in approximately 3 g of hexafluoroisopropanol. Equipment: Waters e-Alliance GPC system Columns: Showa Denko Corporation HFIP-806M x 2 Mobile phase: 5 mmol / L sodium trifluoroacetate / hexafluoroisopropanol Flow rate: 1.0ml / min Temperature: 30℃ Detection: Differential refractometer

[0069] (4) Method for measuring the melting point of polyamide constituting resin powder Using a differential scanning calorimeter (DSCQ20) manufactured by TA Instruments, the peak top of the endothermic peak observed when heating under a nitrogen atmosphere from 30°C to a temperature 30°C higher than the end of the melting peak at a rate of 20°C / min was defined as the melting point.

[0070] (5) Sphericity of resin powder The sphericity of the resin powder was calculated by observing 30 randomly selected particles from scanning electron microscope (JEOL Ltd. JSM-6301NF) images and using the average ratio of their short axis to long axis.

[0071] (6) Measurement of the bending strength of the molded object The bending strength of the 3D-printed object was measured using a RaFaElII150 powder bed fusion 3D printer manufactured by Aspect Co., Ltd. A test specimen measuring 10 mm in width, 80 mm in length, and 4 mm in thickness was fabricated with the 80 mm length direction as the X-direction. The bending strength in the X-direction of this specimen was then measured using a Tensilon TRG-1250 universal testing machine manufactured by A&D Company, Limited. In accordance with JIS K7171 (2016), a three-point bending test was performed with a support distance of 64 mm and a test speed of 2 mm / min. The maximum bending stress measured was defined as the bending strength. The measurement temperature was room temperature (23°C), and the number of measurements was n=5. The average value was calculated.

[0072] (7) Surface roughness of 3D printed objects The surface roughness of 3D printed objects was determined using an Aspect Co., Ltd. powder bed fusion 3D printer (RaFaElII300). The surface of the printed object was observed using a Keyence Corporation optical microscope (VHX-5000) with a VH-ZST (ZS-20) objective lens at a magnification of 200x. During this process, the surface irregularities of the printed object were first created as a 3D image using the software included with the device (system version 1.04) in automatic synthesis mode. Then, the height profile of the cross-section was obtained over a length of 1 mm or more, and the surface roughness Ra was calculated using the arithmetic mean.

[0073] [Example 1] Monomer recovery: Using polyamide 12 resin powder (Evonik PA2200) as the raw material, a 3D object was created using a powder bed fusion 3D printer (RaFaElII300) manufactured by Aspect Co., Ltd., followed by freeze-grinding and passing through a 5mm sieve. 600g of the pulverized polyamide 12 object after sieving and 1590g of 75% phosphoric acid aqueous solution were added to a 3L autoclave. After purging with nitrogen, the autoclave was maintained at 230°C for 6 hours with stirring, and then cooled to 25°C to obtain a precipitated depolymer. A portion of the obtained depolymer was filtered and dried, and the monomer concentration was measured, revealing an aminododecanoic acid concentration of 70%. Next, the depolymer was filtered, and 1800g of water and 383g of sodium bicarbonate were added to the filtered product. After stirring for 1 hour, the precipitate was filtered, dissolved in 500g of ethanol, and 100g of water was added to obtain a white solid. By treating it with vacuum drying at 80°C for 12 hours, 410 g of aminododecanoic acid was obtained. This procedure was repeated three times to obtain a total of 1230 g of depolymerized product.

[0074] Manufacturing of resin powder: 400g of the aminododecanoic acid obtained above, 600g of polyethylene glycol (grade 1 polyethylene glycol 20,000 manufactured by Wako Pure Chemical Industries, Ltd.), 1.4g of IRGANOX 1098 (manufactured by BASF Japan Ltd.) as an antioxidant, and 400g of deionized water were added to a 3L autoclave. After sealing, the pressure was adjusted to 0.1MPa with nitrogen and the container was sealed. Then, the stirring speed was set to 30rpm and the temperature was raised to 220°C while controlling the pressure to 1.0MPa. Subsequently, the pressure was released at a rate of 0.02MPa / min to reduce the internal pressure to 0MPa, and polymerization was carried out for 3 hours at a temperature of 220°C with nitrogen flowing at a rate of 5mL / min. After discharging the polymerization solution into a 700g water bath, a slurry was prepared and filtered. 700g of water was added to the filtered product and washed at 80°C. The filtered product was then filtered and isolated, and dried at 80°C for 12 hours to obtain 320g of polyamide 12 resin powder (yield 80%). This procedure was repeated four times to obtain a total of 1280 g of polyamide 12 resin powder. The D50 particle size of the particles was 50 μm, the weight-average molecular weight was 20,000, the melting point was 179°C, and the sphericity was 95.

[0075] Additive manufacturing process: 1200 g of the polyamide 12 resin powder prepared as described above was mixed with 1.2 g of trimethylsilylated amorphous silica (X-24-9500, manufactured by Shin-Etsu Chemical Co., Ltd.) as a flow aid to create a polyamide 12 powder composition. A 3D object was fabricated using a powder bed fusion fusion apparatus (RaFaElII150) manufactured by Aspect Co., Ltd. The flexural strength of the polyamide 12 object was 60 MPa and the surface roughness was 10 μm.

[0076] [Example 2] The polyamide 12 molded object prepared in Example 1 was subjected to monomer recovery using the same method as in Example 1. As a result, aminododecanoic acid was obtained with a monomer concentration of 99% in the depolymerized product. Using this aminododecanoic acid, powder particles were prepared using the same method as in Example 1. As a result, polyamide 12 resin powder was obtained with a yield of 80%, and the D50 particle size of the resin powder was 49 μm, the weight-average molecular weight was 20,000, the melting point was 180°C, and the sphericity was 94, which were equivalent to Example 1. A polyamide 12 molded object was prepared in the same manner as in Example 1, and its flexural strength was 62 MPa and surface roughness was 9 μm, which were equivalent.

[0077] [Example 3] The polyamide 12 resin powder prepared in Example 1 was subjected to monomer recovery using the same method as in Example 1. As a result, aminododecanoic acid was obtained with a monomer concentration of 99% in the depolymerized product. Using this aminododecanoic acid, powder particles were prepared using the same method as in Example 1. As a result, polyamide 12 powder was obtained with a yield of 80%, and the D50 particle size of the resin powder was 52 μm, the weight-average molecular weight was 20,000, the melting point was 178°C, and the sphericity was 94, which were equivalent to Example 1. A polyamide 12 molded object was prepared in the same manner as in Example 1, and its flexural strength was 59 MPa and surface roughness was 10 μm, which were equivalent.

[0078] [Comparative Example 1] Except for changing the monomer recovery time from 230°C for 6 hours to 50°C for 12 hours, the depolymer was obtained using the same method as in Example 1. However, measurement of the monomer concentration showed that aminododecanoic acid was not produced, and the yield was 0%.

[0079] Comparing the rate of change between the resin powder and resin molded object in Example 1 and Example 2 of the present invention, the D50 particle size was 1.02, sphericity was 1.01, surface roughness was 1.11, and bending strength was 0.97. Furthermore, comparing the rate of change between the resin powder and resin molded object in Example 1 and Example 3, the D50 particle size was 0.96, sphericity was 1.01, surface roughness was 0.91, and bending strength was 1.03, indicating that the recycling was reproducible. [Industrial applicability]

[0080] According to the present invention, it is possible to reduce the waste of resin molded products and resin powder in additive manufacturing processes, thereby contributing to the creation of a circular economy. Furthermore, because it is an additive manufacturing process that is easy to manufacture using monomaterials, it becomes easier to recover high-quality monomers, and the obtained monomers can be repurposed for injection molding and other applications besides resin powder. [Explanation of Symbols]

[0081] 1. Tank for forming the molded object 2. Stage of the tank for forming the molded object. 3. A supply tank pre-filled with polymer particles or polymer particle compositions to be supplied. 4. Stage of a tank pre-filled with polymer particles or polymer particle composition to be supplied. 5 Recorder 6. Thermal energy 7 X, Y, Z coordinate system 8 Planar direction for stacking polymer particles or polymer particle composition 9. Height direction for stacking polymer particles or polymer particle compositions 10 3D objects 11. Polymer particles or polymer particle compositions that remain without forming a molded object. P polymer particles or polymer particle composition

Claims

1. A method for recovering a depolymerized product containing monomers by adding a resin molded product formed by an additive manufacturing process, or a resin powder used in an additive manufacturing process, to water, heating at a temperature of 100°C to 400°C, and performing depolymerization.

2. A method for recovering a depolymer product containing a monomer according to claim 1, characterized by crushing a resin molded product formed by an additive manufacturing process and then adding it to water.

3. A method for recovering a depolymer containing a monomer according to claim 1, characterized in that the water is selected from an acidic aqueous solution, a basic aqueous solution, supercritical water, and subcritical water.

4. A method for recovering a monomer-containing depolymer according to claim 1, characterized in that the monomer concentration in the recovered depolymer is 60% by mass or more.

5. A method for recovering a depolymer product containing a monomer according to claim 3, characterized in that the acidic aqueous solution is an aqueous phosphoric acid solution.

6. A method for recovering a monomer-containing depolymer according to claim 5, characterized by adding a basic substance to the monomer-containing depolymer.

7. A method for recovering a monomer-containing depolymer according to claim 1, characterized in that the resin molded product formed by an additive manufacturing process, or the resin powder used in the additive manufacturing process, contains polyamide.

8. A method for recovering a depolymer containing a monomer according to claim 7, wherein the polyamide is at least one selected from polyamide 12, polyamide 11, polyamide 6, polyamide 66, and copolymers thereof.

9. A method for producing a resin powder having an average particle size of 1 to 100 μm by recovering a depolymer containing a monomer by any of claims 1 to 8, and then polymerizing it.

10. A method for producing a resin molded product, characterized by producing resin powder by the method of claim 9, and then using the resin powder in an additive manufacturing process.

11. A resin powder characterized by containing 1% or less of phosphate and having an average particle size of 1 to 100 μm.

12. The resin powder according to claim 11, characterized in that the polyamide constituting the resin powder is at least one selected from polyamide 12, polyamide 11, polyamide 6, polyamide 66, and copolymers thereof.

13. A resin molded product manufactured by an additive manufacturing process using the resin powder of claim 11 or 12, characterized in that it contains 1% or less of a phosphate.

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