Flame-retardant 3D print molding material and molded article

Abstract

The objective of the present invention is to provide a flame-retardant 3D print molding material which is capable of achieving both high flame retardancy and low cost, and with an increased content of a naturally derived component than ever before, the flame-retardant 3D print molding material containing a bio-based flame retardant aid.

Description

Flame-retardant Material for 3D Printing Molding and Molded Body

[0005]

[0001] The present invention relates to a flame-retardant material for 3D printing molding having flame retardancy and a molded body formed using this flame-retardant material for 3D printing molding.

[0002] In order to apply 3D printing technology to, for example, the construction field, parts of electric and electronic devices, automobile parts, interior materials, etc., high flame retardancy is required for the molded body formed by 3D printing.

[0003] As a method for imparting flame retardancy to a molded body formed by 3D printing, for example, it is conceivable to add a general flame retardant such as ammonium polyphosphate as shown in Patent Document 1 to the flame-retardant material for 3D printing molding.

[0004] Japanese Patent Application Laid-Open No. 2000-344960

[0005] However, the conventionally used flame retardants have a problem that the cost is high, and the cost of the flame-retardant material for 3D printing molding becomes high in order to obtain sufficient flame retardancy. Also, in recent years, regarding the flame-retardant material for 3D printing molding, it has been required to increase the content of natural-derived components with less environmental load from the perspective of SDGs compared to the conventional level. However, a flame-retardant material for 3D printing molding having flame retardancy while increasing the content of natural-derived components has not yet been developed.

[0006] The present invention has been made in view of the above-described problems, and the main object is to provide a flame-retardant material for 3D printing molding that can achieve both high flame retardancy and low cost, and further has a higher content of natural-derived components than the conventional level.

[0007] This invention is a groundbreaking invention that was completed based on the unexpected idea that by incorporating wood-based materials such as cellulose powder, cellulose fibers, or wood powder, which are inherently highly flammable, as flame retardant additives into 3D printing molding materials, the flame retardancy of molded bodies formed by 3D printing molding materials can be improved. One reason why this invention can produce such an unexpected effect is thought to be that when the surface of a molded body formed by 3D printing molding materials comes into contact with fire, the flame retardant additives such as cellulose powder, cellulose fibers, or wood powder present on the surface of the molded body carbonize, blocking the supply of oxygen to the inside of the molded body, thereby preventing further combustion of the molded body. In other words, the present invention is as follows: [1] A flame-retardant 3D printing molding material containing a bio-based flame retardant additive such as cellulose powder, cellulose fibers, or wood powder and a resin. [2] The flame-retardant 3D printing molding material according to [1], wherein the bio-based flame retardant additive is in powder form and the average particle size of the bio-based flame retardant additive is 0.01 μm or more and 200 μm or less. [3] The flame-retardant 3D printing molding material according to [1] or [2], wherein the content of the bio-based flame retardant aid is 20% by mass or more and 60% by mass or less. [4] The flame-retardant 3D printing molding material according to any one of [1] to [3], wherein the content of the resin is 20% by mass or more and 80% by mass or less. [5] The flame-retardant 3D printing molding material according to any one of [1] to [4], further comprising a non-combustible agent other than the bio-based flame retardant aid, wherein the content of the non-combustible agent is 20% by mass or less. [6] The flame-retardant 3D printing molding material according to any one of [1] to [5], wherein the resin is of natural origin. [7] A molded article made from the flame-retardant 3D printing molding material according to any one of [1] to [6]. [8] A method for producing a flame-retardant 3D printing molding material, comprising the step of mixing a resin with a bio-based flame retardant aid such as cellulose powder, cellulose fiber, or wood powder.

[0008] According to the present invention, by using bio-based flame retardant additives such as cellulose powder, cellulose fibers, or wood powder, which can enhance flame retardancy by carbonizing during combustion, it is possible to achieve both high flame retardancy and low cost, as well as reduce environmental impact by minimizing the use of conventionally used non-combustible agents for resins (halogen-based, ammonium phosphate, etc.). This provides flame-retardant 3D printing materials and molded articles.

[0009] The embodiments of the present invention will be described in detail below. However, the present invention is not limited thereto.

[0010] The flame-retardant 3D printing material according to this embodiment is used to form 3D printed molded bodies that are required to be flame-retardant, and can be widely applied not only to building materials such as interiors of buildings and structures in theme parks, but also to housings for electrical and electronic components and automotive parts.

[0011] The flame-retardant 3D printing material according to this embodiment is used, for example, in laser sintering powder bed 3D printing. Laser sintering powder bed 3D printing forms a molded body of a desired shape by repeatedly performing the steps of stacking particulate flame-retardant 3D printing material as thin layers and irradiating a laser beam at desired positions in these thin layers to melt and bond the particles together.

[0012] The flame-retardant 3D printing material according to this embodiment contains, for example, a resin and a bio-based flame retardant, and contains resin particles in which the bio-based flame retardant is dispersed within particles formed from the resin.

[0013] <<Resin Particles>> <Resin> The resin contained in the flame-retardant 3D printing molding material according to this embodiment is not particularly limited, and a wide range of resins used in conventional 3D printing molding materials can be used. For example, thermoplastic resins or photocurable resins can be used as such resins. Specific examples of the resin include, for example, one or more selected from the group consisting of acrylonitrile butadiene styrene copolymer (ABS), acrylonitrile styrene acrylic acid ester copolymer (ASA), polylactic acid (PLA), polyamides such as PA6 and PA12 (PA), polycarbonate (PC), polypropylene (PP), polyisoprene (PI), polyphenylene sulfide (PPS), polyethylene (PE), polybutylene terephthalate (PBT), and wax. One of these may be used as the resin, or two or more may be used in combination. Among these resins, crystalline thermoplastic resins may be used, and from the viewpoint of considering the burden on the environment and maximizing the content of natural components, naturally derived resins such as polylactic acid (PLA) or PA11 may be used as the resin.

[0014] The resin content is preferably 20% to 80% by mass, more preferably 30% to 75% by mass, and even more preferably 40% to 70% by mass, based on 100% by mass of the flame-retardant 3D printing molding material. If two or more types of resins are included, the content refers to the total content of the resin components.

[0015] <Bio-based flame retardant additive> The bio-based flame retardant additive contains, for example, wood-based natural components such as cellulose powder, cellulose fibers, or wood powder. Wood powder is made by crushing tree trunks and mainly consists of cellulose, hemicellulose, and lignin. Cellulose fibers are obtained from pulp from which lignin has been removed. When using fine particles (powder) such as cellulose powder or wood powder as the bio-based flame retardant additive, it is preferable that the average primary particle size is as small as possible, for example, preferably 0.01 μm or more and 200 μm or less, more preferably 0.1 μm or more and 100 μm or less, and even more preferably 1 μm or more and 50 μm or less. When cellulose fibers are used as the bio-based flame retardant, the diameter and length of the fibers are preferably 0.1 μm to 100 μm and 10 μm to 200 μm, respectively; more preferably 0.1 μm to 50 μm and 10 μm to 100 μm, respectively; and even more preferably 0.1 μm to 25 μm and 10 μm to 50 μm, respectively. The average primary particle size of cellulose powder, cellulose fibers, or wood powder, and the diameter and length of cellulose fibers are preferably about half or less of the average primary particle size of the resin particles described later. The average primary particle size of each of these particles and the diameter and length of the fibers can be measured, for example, by the following method. They can be obtained by arbitrarily selecting about 50 particles or fibers whose external shape can be determined from observation images using a scanning electron microscope (SEM), for example, and calculating the average value of their particle size, diameter, or length. As a method other than those described above, the average primary particle size can also be calculated by measuring the distribution of spherical equivalent diameters in water using a laser diffraction / scattering particle size distribution analyzer and calculating it as a volume-based average diameter. Furthermore, if the cellulose powder or wood powder has both a short diameter and a long diameter, it is preferable to determine the average primary particle size based on the long diameter, which is the maximum diameter of each particle. The average primary particle size of resin particles, as described later, can be measured in the same manner.

[0016] From the viewpoint of achieving both the properties required for flame-retardant 3D printing molding materials and flame retardancy, the content of the bio-based flame retardant additive is preferably 20% to 60% by mass, more preferably 25% to 55% by mass, and even more preferably 30% to 50% by mass, based on 100% by mass of the flame-retardant 3D printing molding material.

[0017] The resin particles may further contain additives other than the aforementioned resin and bio-based flame retardant, such as compatibilizers to facilitate their compatibility. As a compatibilizer, for example, an acid-modified resin obtained by acid-modifying the aforementioned resin can be used. For example, when polypropylene is used as the resin, maleic acid-modified polypropylene, which can improve the compatibility between polypropylene and the bio-based flame retardant, can be used as a compatibilizer. When a compatibilizer is included in the resin particles, the compatibilizer content in the resin particles is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less. If the resin contained in the resin particles is polylactic acid or bioplastic, which has high compatibility with the bio-based flame retardant, the compatibilizer content may be lower or omitted altogether.

[0018] <<Components other than resin particles>> The flame-retardant 3D printing material according to this embodiment preferably has the aforementioned resin particles as its main component (for example, containing 50% by mass or more), but it may also contain non-combustible agents, fillers, and other additives in addition to the aforementioned resin particles, as long as the properties are not lost.

[0019] From the viewpoint of providing higher flame retardancy to the flame-retardant 3D printing material and the molded article formed from this flame-retardant 3D printing material according to this embodiment, the flame-retardant 3D printing material may contain a non-combustible agent in addition to the bio-based flame retardant additive described above. As the non-combustible agent, those that have been conventionally used as non-combustible agents in resin compositions and molded articles made from resin compositions can be widely used. Specific examples of such non-combustible agents include nitrogen-based non-combustible agents such as melamine cyanurate, metal hydroxide non-combustible agents such as magnesium hydroxide and aluminum hydroxide, phosphorus-based non-combustible agents such as ammonium polyphosphate, melamine polyphosphate, metal phosphinate salts and red phosphorus, and halogen-based non-combustible agents such as brominated polystyrene, brominated polyphenylene oxide, brominated polycarbonate and brominated epoxy resin.

[0020] However, from the viewpoint of maximizing the content of natural ingredients and minimizing the manufacturing cost of flame-retardant 3D printing materials, it is preferable that the content of these anti-flammability agents be as low as possible. The content of the anti-flammability agents is preferably, for example, 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on 100% by mass of the flame-retardant 3D printing material.

[0021] The filler is not particularly limited as long as it can adjust the strength, rigidity, modulus of elasticity, etc., of the molded product to a desired range. Examples include glass beads, carbon fibers (e.g., carbon nanofibers), and other common organic and inorganic fillers. The shape of the filler is also not particularly limited and may be any shape, such as amorphous, spherical, fibrous, or flaky. These fillers may be used individually or in combination of two or more types.

[0022] If a filler is included, the filler content is preferably 1% to 30% by mass, more preferably 1% to 20% by mass, and even more preferably 5% to 10% by mass, based on 100% by mass of the flame-retardant 3D printing material.

[0023] <Method for Manufacturing Flame-Retardant 3D Printing Molding Material> The flame-retardant 3D printing molding material according to this embodiment includes, for example, a heating and mixing step (also called a kneading step), a solid formation step, and a pulverization step, as shown below. First, in the heating and mixing step, a material containing the aforementioned resin and a bio-based flame retardant is heated and mixed to obtain a molten product in which the bio-based flame retardant is dispersed in the molten resin. In this heating and mixing step, components other than those mentioned above may be added. For example, a compatibilizer or the like may be added as appropriate to facilitate the dispersion of the bio-based flame retardant in the resin. The kneading temperature in this heating and mixing step can be appropriately changed depending on the commonly used resin, as long as it is a temperature that can melt the resin used (i.e., a temperature above the melting point of the resin), but from the viewpoint of improving flame retardant performance, it is preferable to use the highest possible temperature. The kneading temperature is preferably 170°C or higher, more preferably 180°C or higher, and even more preferably 190°C or higher. This is thought to be because raising the mixing temperature sufficiently high promotes the carbonization of the bio-flame retardant during the mixing process. Furthermore, from the viewpoint of maintaining the strength of the resin particles within a sufficiently high range, it is preferable that the mixing temperature be 200°C or lower. This is because a high mixing temperature is sufficient to suppress the carbonization of the bio-flame retardant and the decrease in strength due to the decrease in viscosity of the resin. Subsequently, in the solid formation process, the molten material is molded into an appropriate shape (for example, pelletized) by extrusion molding or the like and solidified to obtain a solid material in which the bio-flame retardant is dispersed in the resin. Next, in the pulverization process, the solid material obtained as described above is physically crushed using a pulverizer or the like to obtain particulate resin particles.

[0024] Preferably, the resin particles produced in this manner have particles of the bio-based flame retardant agent dispersed within each individual particle. Furthermore, the average primary particle size of the resin particles is preferably 1 μm or more and 200 μm or less, more preferably 10 μm or more and 150 μm or less, and even more preferably 50 μm or more and 100 μm or less. It is more preferable that the average primary particle size of these resin particles be about half or less the thickness of one thin layer in the molding method described later.

[0025] The flame-retardant 3D printing molding material according to this embodiment may consist only of resin particles manufactured in this manner, or it may further contain the additional non-combustible agents, fillers, and other additives mentioned above. If additives other than resin particles are included, the flame-retardant 3D printing molding material may be manufactured by further providing an additive mixing step in which the resin particles and these additives are further mixed. Furthermore, it is also possible to omit the pulverization step described above and use the pellet-like material obtained by the solid formation step as is for the manufacture of molded bodies as a flame-retardant 3D printing molding material.

[0026] <Method for Manufacturing Molded Articles> The method for manufacturing molded articles using the flame-retardant 3D printing material according to this embodiment is not particularly limited, but as an example, a method for manufacturing molded articles by laser sintering powder lamination will be described below. When manufacturing molded articles by laser sintering powder lamination, the molded article is manufactured by repeatedly performing a thin-layer formation step of forming a thin layer with particulate flame-retardant 3D printing material and a laser irradiation step of forming a sintered layer by irradiating a laser at a desired position in the thin layer to melt and bond the resin. In addition, other steps such as a preheating step of preheating the flame-retardant 3D printing material may be included as needed.

[0027] The thin-layer formation process is a process of forming a thin layer containing a particulate resin composition. The method of forming the thin layer is not particularly limited, but for example, the resin composition may be spread evenly using a scraper or a lamination roller. The thin layer may be formed directly on the molding stage, or it may be formed on top of powder material that has already been spread or on another thin layer that has already been formed. The thickness of the thin layer formed in a single thin-layer formation process can be set arbitrarily, but it is preferably 10 μm or more and 300 μm or less, and more preferably 50 μm or more and 200 μm or less.

[0028] The laser irradiation process involves selectively irradiating a thin layer containing a resin composition with laser light at the location necessary to form the desired molded body, thereby melting and bonding the resin composition at the irradiated location. The molten resin composition melts and bonds with adjacent resin compositions within the same thin layer. At this time, if the thin layer is laminated on top of other thin layers that have already been formed, it will also melt and bond with the melted portions in the other thin layers, thus creating melt bonds between adjacent thin layers as well. The wavelength of the laser light used at this time should be set within the range of wavelengths absorbed by the resin composition. The beam diameter of the laser light can also be appropriately set according to the shape and molding accuracy of the molded body to be manufactured.

[0029] By repeating the aforementioned thin-layer formation process and laser irradiation process the required number of times, a molded body of the desired shape can be obtained.

[0030] <Effects of this Embodiment> According to the flame-retardant 3D printing molding material of this embodiment, the resin particles constituting the flame-retardant 3D printing molding material contain bio-based flame retardant aids such as cellulose powder, cellulose fibers, or wood powder inside. Therefore, the cellulose and wood powder carbonize during combustion, suppressing combustion and thus achieving both high flame retardancy and low cost. Furthermore, since the average primary particle size of the cellulose powder or wood powder contained in the resin particles is smaller than the average primary particle size of the resin particles, it is preferable that the cellulose powder or wood powder can be dispersed as uniformly as possible inside the resin particles. Moreover, since the average primary particle size of the resin particles is smaller than the thickness of the thin layer when manufacturing the molded body, the thickness can be made as uniform as possible when forming the thin layer, which is preferable because it improves the molding accuracy of the molded body.

[0031] <Other Embodiments of the Invention> The present invention is not limited to the embodiments described above. For example, the resin particles constituting the flame-retardant 3D printing material are not limited to those consisting of resin and a bio-based flame retardant additive, and may further contain other components as needed. Furthermore, the flame-retardant 3D printing material according to the present invention can be used not only in the laser sintering powder deposition method described above, but also in other 3D printing technologies. In addition, various modifications and combinations of embodiments are permitted as long as they do not contradict the spirit of the present invention.

[0032] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. First, 3D printing molding materials for Examples 1 to 4 and Comparative Examples with the formulations shown in Table 1 were prepared. The resin, bio-based flame retardant, and non-combustible agent in Table 1 were heated and mixed at 180°C using a twin-screw kneading extruder, and then extruded to form pellets. For Examples 5 and 6, pellets were prepared under the same conditions as Examples 1 to 4, except that the kneading temperature during heating and mixing and the type of bio-based flame retardant were changed. Furthermore, for Examples 7 and 8, pellets were prepared under the same conditions as Examples 1 to 4, except that the type of resin was changed. These solids were crushed to obtain resin particles, which were used as the 3D printing molding material in each example. The average primary particle size of these resin particles was kept within the range of 60 μm to 100 μm.

[0033] Next, using the 3D printing materials for Examples 1 to 4 and Comparative Example shown in Table 1, molded bodies for Examples 1 to 4 and Comparative Example were fabricated by laser sintering powder deposition. The shape of the molded bodies conformed to the horizontal and vertical test specifications of the UL94 standard. The size of each molded body used as a test specimen was 125 mm × 10 mm × 4 mm. The flame retardancy of the flame-retardant 3D printing materials manufactured as described above was evaluated. The results are shown in Table 1.

[0034] <Evaluation according to UL94 standard> Flame retardancy was evaluated according to the UL94 standard horizontal combustion test and UL94 50W (20 mm) vertical combustion test; protocols V-0, V-1, and V-2. Since all test pieces in Examples 1 to 4 and the comparative example met the acceptance criteria for the horizontal combustion test, the vertical combustion test was performed on all test pieces. The results are shown in Table 1. For each example and comparative example, the test was performed for N=4 or more cycles. <Oxygen index evaluation> The oxygen index (OI) was measured for each molded body. The results are shown in Table 1. This evaluation test investigates the combustion continuity based on oxygen concentration. A higher oxygen index indicates higher flame retardancy, and an OI of 23 or higher is preferable.

[0035]

[0036] The components in Table 1 are as follows: Resin 1: Polypropylene (Prime Polymer Co., Ltd., J108M) Resin 2: Polylactic acid (Hebei Luoxing Tech. Co., Ltd., powder sintered 3D printer powder) Resin 3: PA11 (Arkema Corporation, RILSAN INVENT NATURAL) Bio-based flame retardant 1: Cellulose (Nippon Paper Industries Ltd., W-100GK, average particle size 37 μm) Bio-based flame retardant 2: Cellulose (Nippon Paper Industries Ltd., W-200GK, average particle size 15 μm or less) Flame retardant: Ammonium polyphosphate (Taihen Chemical Industries Co., Ltd., Taihen K) Note that ammonium polyphosphate, used as a flame retardant here, is one of the most commonly used flame retardants.

[0037] <Discussion> From the results in Table 1, the comparative example, which used only a conventional non-combustible agent, achieved a V-2 (fireball fall) result in the UL94 vertical test. However, in Examples 1 to 4, which contained cellulose as a bio-based flame retardant, all test pieces achieved V-1 or higher (no fireball fall). In particular, in Examples 1 and 2, all test pieces achieved V-0, the highest rating in the UL94 50W (20mm) vertical combustion test. In Example 4, one sample out of N=4 also obtained a V-0 result. When the specific gravity of the molded bodies produced in Examples 1 to 4 and the comparative example was measured, the specific gravity of the molded bodies in Examples 1 to 4 was 0.44 to 0.59, while the specific gravity of the molded body in the comparative example was 0.99. This indicates that using a flame-retardant 3D printing molding material with cellulose as a bio-based flame retardant has the advantage of making the molded body lighter than conventional materials. These results show that when cellulose, a naturally derived component, is included as a bio-based flame retardant additive, flame retardancy can be significantly improved compared to when only conventional non-combustible agents are used. Furthermore, it was confirmed that sufficiently high flame retardancy can be achieved while reducing the amount of conventional non-combustible agents used. A similar trend was also observed in the oxygen index evaluation. In Examples 5 and 6, it was confirmed that by increasing the mixing temperature during the manufacturing process and using a particle size smaller than 30 μm for the bio-based flame retardant additive, the carbonization of the bio-based flame retardant additive can be promoted, further enhancing the flame retardancy of the flame-retardant 3D printing molding material. In these examples, cellulose was used as the bio-based flame retardant additive, but it can be inferred that similar results can be obtained even when using wood flour, since the main component of wood flour is cellulose and hemicellulose, which has a chemical composition similar to cellulose. From the results of Examples 7 and 8, it was confirmed that not only polypropylene but also polylactic acid and the bioplastic PA11 can be used as resins, confirming that similar results can be obtained regardless of the type of resin, as long as a bio-based flame retardant additive is added.

[0038] According to the present invention, it is possible to provide a flame-retardant 3D printing material that achieves both high flame retardancy and low cost, and furthermore, has a higher content of naturally derived components than conventional materials.

Claims

1. A flame-retardant 3D printing material containing resin and a bio-based flame retardant additive.

2. The flame-retardant 3D printing material according to claim 1, wherein the bio-based flame retardant is one or more selected from the group consisting of cellulose powder, cellulose fibers, and wood powder.

3. The flame-retardant 3D printing material according to claim 1, wherein the bio-based flame retardant is in powder form and the average particle size of the bio-based flame retardant is 0.01 μm or more and 100 μm or less.

4. The flame-retardant 3D printing material according to claim 1, wherein the content of the bio-based flame retardant additive is 20% by mass or more and 60% by mass or less.

5. The flame-retardant 3D printing material according to claim 1, wherein the resin content is 20% by mass or more and 80% by mass or less.

6. The flame-retardant 3D printing material according to claim 1, further containing a fire retardant, wherein the content of the fire retardant is 20% by mass or less.

7. The flame-retardant 3D printing material according to claim 1, wherein the resin is of natural origin.

8. A molded article made of the flame-retardant 3D printing material described in any one of claims 1 to 7.

9. A method for manufacturing a flame-retardant 3D printing material, comprising the step of mixing a resin with a bio-based flame retardant.

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