Low dielectric low warpage polypropylene wire for 3D printing and preparation method thereof

Abstract

The application discloses a kind of low dielectric low warping 3D printing polypropylene wire and its preparation method, the polypropylene wire is prepared by co-extrusion die, and the wire has core-shell structure.The application controls the proportion of shell layer resin of wire, so that it does not affect interlayer adhesion when high-temperature fused deposition printing, and can prepare higher mechanical properties of the workpiece, the inner layer material of wire has very low shrinkage, very low dielectric constant and dielectric loss, so that the workpiece prepared has very good dimensional stability, low warping, excellent dielectric properties, and can prepare medium lens antenna, 5G signal emitter and other electronic components.

Description

Technical Field

[0001] This invention relates to the field of materials, and more specifically to polypropylene alloy filaments for 3D printing. Background Technology

[0002] 3D printing is a rapid prototyping technology. Fused deposition modeling (FDM) is one type of 3D printing technology. It uses a printing nozzle to heat the material to its melting temperature, and the melt flows out and solidifies layer by layer to form the desired part. Compared to traditional injection molding, 3D printing technology can quickly manufacture complex three-dimensional solid parts without molds, which can greatly shorten product development cycles and reduce product development costs.

[0003] Polypropylene resin, one of the five major general-purpose resins, is one of the world's largest-produced, largest-consumed, and most widely used polymer materials. Polypropylene possesses advantages such as low density, high strength, heat resistance, good insulation, low dielectric constant, low dielectric loss, low price, and excellent chemical stability, making it highly favored in home appliances, automobiles, electronics, and medical fields.

[0004] Polypropylene resin is a crystalline polymer that undergoes significant shrinkage and deformation during cooling and crystallization, leading to severe warping in printed parts. To reduce the shrinkage and deformation of PP material and improve printing accuracy, inorganic fillers and elastomers can be added to reduce shrinkage and improve warping. However, adding inorganic fillers increases the dielectric constant and dielectric loss of the polypropylene resin, failing to meet the performance requirements of low-dielectric components. Adding elastomers reduces the mechanical properties of PP material, thereby decreasing the interlayer bonding strength of the printed parts.

[0005] Patent CN106554594A uses homopolymer polypropylene, SEBS, GPPS, white oil, and brominated flame retardants to prepare a SEBS composite material suitable for 3D printing. However, its formulation uses a high content of white oil, resulting in low tensile strength of the printed material. At the same time, the added brominated flame retardants will increase the dielectric constant of the material, making it unsuitable for manufacturing components with low dielectric requirements.

[0006] Patent CN105802210A uses nylon material as the main resin for printing. The mechanical properties of the prepared material are high, but the dielectric constant of nylon material is high, making it unsuitable for preparing components with low dielectric requirements.

[0007] Therefore, there is a need to develop a polypropylene filament with excellent printing performance, and to develop 3D printed parts with low dielectric constant, low dielectric loss, excellent dimensional stability and mechanical properties, in order to overcome the technical shortcomings of existing materials. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a low-dielectric, low-warpage polypropylene filament for 3D printing and its preparation method. This invention controls the ratio of the outer shell resin to the inner layer resin of the filament, ensuring that the interlayer bonding force is not affected during high-temperature fused deposition modeling. This allows for the fabrication of parts with high mechanical properties. The inner layer material of the filament exhibits extremely low shrinkage, extremely low dielectric constant, and dielectric loss, resulting in parts with excellent dimensional stability, low warpage, and superior dielectric properties.

[0009] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0010] A polypropylene filament has a core-shell structure, comprising an outer structural resin and an inner structural resin, wherein,

[0011] The outer structural resin comprises the following raw materials in parts by weight:

[0012] Metallocene random copolymer polypropylene: 90-96 parts

[0013] Antioxidant: 0.2-1 part,

[0014] Lubricant: 0.2-0.5 parts;

[0015] The inner layer structure resin comprises the following raw materials in parts by weight:

[0016] Metallocene random copolymer polypropylene: 35-60 parts

[0017] Polystyrene: 25-40 parts

[0018] Compatibilizer: 10-20 parts

[0019] AC type foaming agent: 1.5-5 parts,

[0020] Antioxidant: 0.2-1 part,

[0021] Lubricant: 0.2-0.5 parts

[0022] Based on the total mass of the outer and inner structural resins as 100%, the outer structural resin accounts for 10-25% of the total mass of the wire, and the inner structural resin accounts for 75-90% of the total mass of the wire.

[0023] In this invention, the metallocene random copolymer polypropylene of the outer layer structure resin has a melting point of 130-155℃ and a melt index of 5-15 g / 10min (230℃, 2.16 kg). Suitable examples include, but are not limited to, TPC FL7540L, TPCFL7632L, and Rakuten SFC-750.

[0024] In this invention, the antioxidant in the outer layer resin is one or more of hindered phenolic antioxidants, phosphite antioxidants, and thioester antioxidants.

[0025] In this invention, the lubricant in the outer layer resin is one or more of zinc stearate and ethylene bis-stearamide.

[0026] In this invention, the metallocene random copolymer polypropylene of the inner layer structure resin has a melting point of 130-155℃ and a melt index of 5-15 g / 10min (230℃, 2.16 kg). Suitable examples include, but are not limited to, TPC FL7540L, TPCFL7632L, and Rakuten SFC-750.

[0027] In this invention, the polystyrene of the inner layer structure resin is general-purpose polystyrene, which does not contain styrene-butadiene rubber phase, and its melt index is 5-15 g / 10 min (200℃, 5 kg). Suitable examples include, but are not limited to, INEOS GPPS2601, Formosa Plastics GP5000, INEOS GPPS2601, etc.

[0028] In this invention, the compatibilizer is a polystyrene-ethylene-propylene-styrene or a polystyrene-ethylene-butene-styrene block copolymer, wherein the mass fraction of polystyrene in the block copolymer is 20-40%, and the melt index of the block copolymer is 3-20 g / 10 min (230°C, 2.16 kg). Suitable examples include, but are not limited to, TSRC SEBS 6014 and TSRC SEBS 6152.

[0029] In this invention, the decomposition temperature range of the AC-type foaming agent is 200–230°C. Suitable examples include, but are not limited to, Hempel AC7000, Hempel AC1000, and DKU DGH-2.

[0030] In this invention, the antioxidant in the inner layer resin is one or more of hindered phenolic antioxidants, phosphite antioxidants, and thioester antioxidants.

[0031] In this invention, the lubricant in the inner layer resin is one or more of zinc stearate and ethylene bis-stearamide.

[0032] This invention also provides a method for preparing the core-shell structured flame-retardant polypropylene material, comprising the following steps:

[0033] (1) The outer layer raw material is placed in a twin-screw extruder for high-temperature melt dispersion extrusion granulation to obtain the outer layer resin;

[0034] (2) The inner layer raw material is placed in a twin-screw extruder for high-temperature melt dispersion extrusion granulation to obtain the inner layer resin;

[0035] (3) The outer layer resin and the inner layer resin are respectively placed in two single-screw extruders for plasticization, and the core-shell structure polypropylene alloy wire is obtained by extruding the die head through co-extrusion.

[0036] In this invention, the twin-screw extruder in steps (1) and (2) has a screw length-to-diameter ratio of (40-52):1, a screw speed of 100-300 r / min, and an extrusion temperature of 180-190℃.

[0037] In this invention, the screw length-to-diameter ratio of the single screw extruder in step (3) is (25-35):1, the screw speed is 100-300 r / min, and the extrusion temperature is 180-190℃.

[0038] The core-shell structured polypropylene alloy wire of the present invention can be used to prepare electronic components with excellent dimensional stability, low warpage, and excellent dielectric properties.

[0039] The technical solution of this invention has the following advantages over existing technical solutions:

[0040] (1) The polypropylene alloy wire in this invention adopts a core-shell structure. The shell resin uses metallocene random copolymer polypropylene, which has a slower crystallization rate and a lower shrinkage rate than polypropylene synthesized by ordinary Zn catalysis. It can maintain good interlayer bonding force during the printing process and reduce the risk of interlayer cracking and warping.

[0041] (2) The polypropylene alloy wire in this invention adopts a core-shell structure. The core layer resin uses metallocene random copolymer polypropylene and polystyrene as the resin body. Both have very low dielectric constant and dielectric loss properties. Polystyrene-ethylene-propylene-styrene or polystyrene-ethylene-butene-styrene block copolymers are used as compatibilizers for the two resins. These do not contain unsaturated double bonds and have very low dielectric constant and dielectric loss properties. At the same time, polypropylene and polystyrene have good compatibility, resulting in good mechanical properties of the final material. The introduction of polystyrene and compatibilizers reduces the crystallinity of polypropylene, resulting in a lower material shrinkage rate of the polypropylene alloy material. At the same time, through the chemical foaming of AC foaming agent during the 3D printing process, a cell structure is formed inside the material, which can further reduce the shrinkage rate of the material. This results in the printed parts having very good dimensional stability and low warpage performance. It can also further reduce the dielectric constant and dielectric loss of the material, and can be used to prepare electronic components such as dielectric lens antennas and 5G signal amplifiers that require high dielectric performance. Attached Figure Description

[0042] Figure 1 To observe the cross-section of the wire using a 3D microscope. Detailed Implementation

[0043] To better understand the technical solution of the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments. Unless otherwise specified, the raw materials used in the embodiments or comparative examples are commercially available raw materials.

[0044] The apparatus and main raw material sources used in the embodiments and comparative examples of this invention are as follows:

[0045] Twin-screw extruder: Model SK-26, screw length-to-diameter ratio 50:1; Nanjing Keya Chemical Complete Equipment Co., Ltd.

[0046] Single-screw co-extrusion equipment: Model HRJSJ-35, screw length-to-diameter ratio 28:1, Foshan Hairuijia Precision Extrusion Machinery Co., Ltd.;

[0047] 3D printer: Finder, Zhejiang Flashforge 3D Technology Co., Ltd.;

[0048] Metallocene random copolymer polypropylene: FL7540L, melt index 7 g / 10 min (230℃, 2.16 kg), melt temperature 138℃, Singapore Polyolefins Ltd.

[0049] Ordinary homopolymer polypropylene: 1100N, melt index 12g / 10min (230℃, 2.16kg), melt temperature 165℃, Shenhua Ningxia Coal Industry Co., Ltd.

[0050] Polystyrene: GPPS 525, melt index 8 g / 10 min (200℃, 5 kg), Guangzhou Petrochemical Co., Ltd.

[0051] High-impact polystyrene: HIPS2710, melt index 5 g / 10 min (200℃, 5 kg), Yangzi Petrochemical-BASF Co., Ltd.

[0052] Compatibilizer: SEBS 6152, melt index 4 (230℃, 5kg), TSRC Corporation;

[0053] AC-type foaming agent: AC7000 (decomposition temperature 204℃), Hangzhou Haihong Fine Chemical Co., Ltd.;

[0054] Lubricant: Zinc stearate, FARKS GmbH, Italy;

[0055] Main antioxidant: 1010, from a rising star in chemistry;

[0056] Co-antioxidant: 168, a rising star in chemistry;

[0057] All other raw materials were commercially available and of analytical grade.

[0058] The performance characterization method of the polypropylene material of the present invention is as follows:

[0059] Tensile strength: ISO 527;

[0060] Polypropylene printing interlayer bonding test method: The polypropylene filament prepared above is used to print a 200mm*150mm*4mm 3D printed template perpendicular to the base plate using a Finder 3D printer. A tensile strip of ISO527 standard is cut out along the Z-axis using a sample cutting machine, and the tensile properties are tested.

[0061] Polypropylene shrinkage test method: The polypropylene filament prepared above is used to print a 150*150*3mm flat plate using a Finder 3D printer. After the printed plate is left to stand at room temperature for 48 hours, the side length of the plate is measured. The absolute value of the difference between the printed plate and the design value (150mm) divided by the design value is the shrinkage rate.

[0062] Polypropylene warpage test method: Place the printed flat plate (150*150*3mm) on a horizontal table, place a 500g weight on one corner, and then measure the vertical distance from the endpoint of the diagonal direction of that corner to the horizontal table. The larger the vertical distance, the more severe the material warpage.

[0063] Polypropylene dielectric properties: ASTM D150, using a dielectric constant tester, using the 150*150*3mm plate printed above, the dielectric constant and dielectric loss of this material at a frequency of 1GHz were tested.

[0064] The printing method for polypropylene filament is as follows: The printing conditions for polypropylene filament are: a forming layer thickness of 0.17 mm and a scanning speed of 40 cm / s. 3 The nozzle temperature is 200-230℃, the molding chamber temperature is 60-80℃, and other parameters are set to the system default parameters for molding.

[0065] Examples 1-4 (i.e., S1-4) and Comparative Examples 1-7 (i.e., D1-7) were prepared according to the raw materials and amounts in Table 1 for 3D printing polypropylene filaments.

[0066] The preparation method of the shell resin is as follows: weigh each raw material according to the weight ratio, then put them into a high-speed mixer and mix for 3 minutes. Then feed them from the main feed port of a twin-screw extruder. The screw speed is 300 r / min and the extrusion temperature is 185℃. After high-temperature melting and dispersion, the shell resin is obtained by extrusion granulation.

[0067] The preparation method of the core layer resin is as follows: weigh each raw material according to the weight ratio, then put them into a high-speed mixer and mix for 3 minutes. Then feed them from the main feed port of a twin-screw extruder. The screw speed is 300 r / min and the extrusion temperature is 185℃. After high-temperature melting and dispersion, the core layer resin is obtained by extrusion granulation.

[0068] The preparation method of core-shell structured polypropylene wire is as follows: the shell resin and the core resin are respectively placed in two single-screw extruders for plasticization, the extrusion temperature is 185℃, and the core-shell composite polypropylene wire is obtained by extrusion through a co-extrusion die. The wire diameter is 1.75±0.05mm, and the wire is collected by winding the wire into filaments through a disc device.

[0069] Table 1. Raw material consumption and performance of printed parts in the examples and comparative examples.

[0070]

[0071]

[0072] Table 1 shows that Example 1 uses a core-shell structure. Compared with Comparative Example 5, the tensile strip prepared by 3D printing has excellent tensile strength properties, indicating that the printed part has excellent interlayer bonding force.

[0073] The polypropylene filaments printed in Examples 1-4 exhibit low shrinkage, low warpage, low dielectric constant, and low dielectric loss.

[0074] In Comparative Example 1, no GPPS was added to the core layer, which had a significant impact on the crystallization properties and shrinkage of polypropylene, resulting in the prepared parts having a high shrinkage and warpage properties.

[0075] Comparative Example 2 did not add compatibilizer SEBS6152 to the core layer, which led to severe phase separation between polypropylene and GPPS in the prepared core layer resin. This resulted in the printed parts having high shrinkage and warpage. Moreover, when the tensile properties were tested, the inner resin layer failed and destroyed preferentially, resulting in low interlayer tensile strength.

[0076] No chemical foaming agent was added to the core layer resin of Comparative Example 3, resulting in the printed parts having a higher shrinkage rate and warpage performance. This is because the hollow structure generated by foaming can significantly reduce the dielectric constant and dielectric loss performance, resulting in the printed parts having a higher dielectric constant and dielectric loss performance.

[0077] Comparative Example 4 lacks a core layer structure, resulting in printed parts exhibiting high shrinkage and warpage.

[0078] Comparative Example 5 lacks a shell structure. The core-layer resin foams during the printing process, which affects the interlayer bonding force of the printed part, resulting in poor tensile strength.

[0079] Compared to Example 1, Comparative Example 6 used high-impact polystyrene, which contains unsaturated double bonds, resulting in an alloy material with a higher dielectric constant and dielectric loss.

[0080] Compared to Example 1, Comparative Example 7 used ordinary homopolymer polypropylene, which has higher crystallinity, faster crystallization rate and larger shrinkage rate, resulting in a larger shrinkage rate and warping deformation of the alloy material, which leads to poor interlayer bonding of the material.

[0081] The above description of the embodiments is intended to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the embodiments and apply the general principles described herein to other embodiments without inventive effort. Therefore, the present invention is not limited to the embodiments described herein, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A low-dielectric, low-warpage polypropylene filament for 3D printing, comprising an outer structural resin and an inner structural resin, wherein, The outer structural resin comprises the following raw materials in parts by weight: Metallocene random copolymer polypropylene: 90-96 parts Antioxidant: 0.2-1 part, Lubricant: 0.2-0.5 parts; The inner layer structure resin comprises the following raw materials in parts by weight: Metallocene random copolymer polypropylene: 35-60 parts Polystyrene: 25-40 parts Compatibilizer: 10-20 parts AC type foaming agent: 1.5-5 parts, Antioxidant: 0.2-1 part, Lubricant: 0.2-0.5 parts Based on the total mass of the outer structural resin and the inner structural resin as 100%, the outer structural resin accounts for 10-25% of the total mass of the wire, and the inner structural resin accounts for 75-90% of the total mass of the wire; The polystyrene in the inner layer structure resin is general-purpose polystyrene, which does not contain styrene-butadiene rubber phase, and its melt index is 5~15g / 10min. The test conditions are 200℃ and 5kg. The compatibilizer is a polystyrene-ethylene-propylene-styrene or a polystyrene-ethylene-butene-styrene block copolymer, wherein the mass fraction of polystyrene in the block copolymer is 20-40%, the melt index of the block copolymer is 3-20 g / 10 min, and the test conditions are 230℃ and 2.16 kg.

2. The polypropylene wire according to claim 1, characterized in that, The outer layer resin, metallocene random copolymer polypropylene, has a melting point of 130-155℃ and a melt index of 5-15 g / 10 min. The test conditions are 230℃ and 2.16 kg.

3. The polypropylene wire according to claim 1, characterized in that, The antioxidant in the outer layer resin is one or more of hindered phenolic antioxidants, phosphite antioxidants, and thioester antioxidants.

4. The polypropylene wire according to claim 1, characterized in that, The lubricant in the outer layer resin is one or more of zinc stearate and ethylene bis-stearamide.

5. The polypropylene wire according to claim 1, characterized in that, The metallocene random copolymer polypropylene of the inner layer structure resin has a melting point of 130-155℃ and a melt index of 5~15g / 10min. The test conditions are 230℃ and 2.16kg.

6. The polypropylene wire according to claim 1, characterized in that, The decomposition temperature range of the AC-type foaming agent is 200~230℃.

7. The polypropylene wire according to claim 1, characterized in that, The antioxidant in the inner layer resin is one or more of hindered phenolic antioxidants, phosphite antioxidants, and thioester antioxidants; the lubricant in the inner layer resin is one or more of zinc stearate and ethylene bis-stearamide.

8. A method for preparing polypropylene wire according to any one of claims 1-7, comprising the following steps: (1) The outer layer raw material is placed in a twin-screw extruder for high-temperature melt dispersion extrusion granulation to obtain the outer layer resin; (2) The inner layer raw material is placed in a twin-screw extruder for high-temperature melt dispersion extrusion granulation to obtain the inner layer resin; (3) The outer layer resin and the inner layer resin are respectively placed in two single screw extruders for plasticization, and the core-shell structure polypropylene wire is obtained by extruding the die head through co-extrusion.

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