A cross-linked PBT composite material suitable for lead-free soldering and a preparation method thereof

Abstract

The application discloses a cross-linked PBT composite material suitable for lead-free welding, which comprises the following raw materials in parts by mass: PBT resin: 30-80 parts, inorganic fiber: 0-60 parts, cross-linking auxiliary master batch: 5-40 parts, halogen-free flame retardant: 5-25 parts, antioxidant: 0.1-1 part, and lubricant: 0.2-1 part. After high-energy ray radiation, three-dimensional network cross-linking structure is generated between internal macromolecular chains of the composite material, the temperature resistance of PBT is significantly improved, and PBT does not melt even at a temperature of more than 400 DEG C, so that the temperature resistance limit of traditional thermoplastic PBT can be broken, and the lead-free welding process at a higher temperature can be applied. In addition, the cross-linking is carried out after the material is injection molded into a product, and the easy processing and molding advantages of PBT are not changed, so that the cross-linked PBT composite material is convenient to apply to the production of electrical elements such as connectors and relays which need lead-free welding. Compared with special engineering plastics which are high in price and difficult to process, the cross-linked PBT composite material has the remarkable advantages of low cost and easy processing.

Description

Technical Field

[0001] This invention relates to the field of polymer composite material processing, specifically to a lead-free weldable crosslinked PBT composite material and its preparation method. Background Technology

[0002] Polybutylene terephthalate (PBT) is one of the five major general-purpose engineering plastics. Most PBT is modified before use. Modified PBT engineering plastics possess excellent mechanical and electrical properties, dimensional stability, ease of processing, and fatigue resistance, making them widely used in the automotive, electronics, and machinery industries. The conventional modification method for PBT is physical melt blending, which can be specifically divided into fiber reinforcement modification, flame retardant modification, and alloy modification. Modification can improve and enhance the mechanical, flame retardant, and electrical properties of PBT materials. However, with technological advancements, the requirements for materials are becoming increasingly stringent. For certain applications or needs, more stringent requirements are being placed on the performance of PBT materials, such as high-temperature resistance, hydrolysis resistance, and stress cracking resistance.

[0003] Currently, due to the restrictions of the EU RoHS regulations, component manufacturers in the electronics and electrical industry are increasingly using lead-free solder to replace traditional lead-containing solder. However, because lead-free solder has a higher melting point—for example, the temperature of lead-free wave soldering is typically around 260℃, and the operating temperature of lead-free reflow soldering can even reach over 360℃—conventional PBT materials have a melting point in the range of 220~230℃, which cannot withstand the high temperatures of lead-free soldering processes. Therefore, manufacturers have to use special engineering plastics such as LCP or PPA with higher temperature resistance to meet the requirements of lead-free soldering. This not only results in high material prices but also makes the materials difficult to process and consumes a lot of energy. Even so, in some lead-free soldering applications, defects such as blistering and deformation of the product surface still occur when using LCP or PPA materials. Summary of the Invention

[0004] To address the shortcomings in this field, the present invention provides a cross-linked PBT composite material suitable for lead-free soldering. After high-energy radiation, a three-dimensional network cross-linked structure forms between the macromolecular chains within the composite material, significantly improving the temperature resistance of PBT. It will not melt even at temperatures exceeding its melting point, up to 400°C, thus overcoming the temperature limits of traditional thermoplastic PBT and enabling its application in higher-temperature lead-free soldering processes. Furthermore, the cross-linking is performed after the material has been injection molded, preserving the easy-to-process advantages of PBT and facilitating its use in the production of electrical components such as connectors and relays requiring lead-free soldering. Compared to expensive and difficult-to-process specialty engineering plastics, cross-linked PBT composite materials offer significant advantages in terms of low cost and ease of processing.

[0005] A lead-free solder crosslinked PBT composite material, comprising the following raw materials by weight: PBT resin: 30-80 parts Inorganic fibers: 0-60 parts Crosslinking masterbatch: 5-40 parts Halogen-free flame retardant: 5-25 parts Antioxidant: 0.1-1 part Lubricant: 0.2-1 part.

[0006] The intrinsic viscosity of the PBT resin is 0.8-1.1 dL / g.

[0007] The inorganic fiber is an alkali-free glass fiber with a diameter of 5-15 μm.

[0008] The crosslinking aid masterbatch is obtained by twin-screw extrusion granulation using high-viscosity PBT with an intrinsic viscosity of 1.2-1.4 dL / g as the matrix and adding allyl compounds and / or stabilizers.

[0009] The addition ratio of PBT matrix, allyl compound and stabilizer in crosslinking masterbatch is (58~88):(10~40):(0.2~2).

[0010] The allyl compound is selected from at least one of triallyl isocyanurate, trimethylallyl isocyanurate, triallyl cyanurate, triallyl phenyltriglyceride, and pentaerythritol tetraacrylate.

[0011] The stabilizer is selected from at least one of p-hydroxyanisole and di-tert-butyl-p-cresol, preferably di-tert-butyl-p-cresol.

[0012] The halogen-free flame retardant is selected from at least one of aluminum phosphonate, melamine polyphosphate, and melamine cyanurate.

[0013] The antioxidant is a combination of hindered phenolic antioxidants and phosphite antioxidants. The hindered phenolic antioxidant is selected from at least one of 1098, 1010, and GA-80. The phosphite antioxidant is selected from at least one of 168, 626, and 9228.

[0014] The lubricant is selected from at least one of hyperbranched polyester, silicone powder, and calcium stearate.

[0015] This invention also provides a method for preparing lead-free weld crosslinked PBT composite materials, the preparation steps of which include preparation of crosslinking aid masterbatch, preparation of crosslinkable PBT composite materials, and radiation crosslinking.

[0016] The crosslinking aid masterbatch is prepared by high-viscosity PBT resin and stabilizer being mixed uniformly at high speed and added through the main feed port of a twin-screw extruder. The allyl compound is added through the side feed port of the twin-screw extruder, followed by melt extrusion granulation. The twin-screw extruder has a length-to-diameter ratio of 36:1, with zone 1 being the main feed port, zone 4 having a vent, and zone 7 being the side feed port. The extrusion temperature is 200-230℃, and the screw speed is 250-350 rpm.

[0017] The crosslinkable PBT composite material is prepared by high-speed stirring and uniform mixing of PBT resin, flame retardant, antioxidant, and lubricant, and then feeding it into the main feed port of a high aspect ratio twin-screw extruder. Inorganic fibers and crosslinking aid masterbatch are added from the first and second side feed ports, respectively, followed by melt extrusion granulation. The high aspect ratio twin-screw extruder has an aspect ratio of 52:1, with zone 1 being the main feed port, zone 4 having an exhaust port, zone 5 being the first side feed port, zone 10 having a vacuum port, and zone 11 being the second side feed port. The extrusion temperature is 210~240℃, and the screw speed is 300-400 rpm.

[0018] The radiation crosslinking involves molding the above-mentioned crosslinkable PBT composite material into the desired product through injection molding, and then irradiating the product with an electron beam generated by a high-energy accelerator or gamma rays generated by cobalt-60, with a radiation dose of 100~500kG, preferably 150~300kGy.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) By designing the formula and preparing crosslinkable PBT composite materials using twin-screw melt extrusion, the molded products are then subjected to radiation crosslinking using high-energy rays to generate a three-dimensional network structure within the PBT macromolecules. This crosslinking process is green, environmentally friendly, convenient, and rapid, making it easy to achieve industrial-scale mass production.

[0020] 2) Crosslinking greatly improves the temperature resistance of PBT materials, enabling them to withstand high temperatures of 400℃ for short periods, making them particularly suitable for lead-free soldering applications in industries such as electronics and electrical engineering.

[0021] 3) The cross-linking process is carried out after the material is injection molded into a finished product. It does not change the advantages of PBT material itself, which is easy to process and mold. Compared with special engineering plastics that are expensive and difficult to process, cross-linked PBT composite materials have significant advantages of low cost and easy processing. Detailed Implementation

[0022] The following specific embodiments further illustrate the substantive content of the present invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0023] The raw material composition of the examples, in parts by mass, is detailed in Table 1, and the preparation method is as follows: First, prepare the crosslinking aid masterbatch (the composition of the masterbatch raw materials is shown in Table 2, by mass fraction). Mix the high-viscosity PBT resin and stabilizer at high speed until uniform, and add them from the main feed port of a twin-screw extruder with a length-to-diameter ratio of 36:1. Add the allyl compound from the side feed port of the twin-screw extruder and adjust the feeding speed according to the ratio. Set the extrusion temperature to 210~230℃ and the screw speed to 300rpm. After melt extrusion, cool and pelletize.

[0024] Then, crosslinkable PBT composite materials were prepared by mixing PBT resin, flame retardant, antioxidant, and lubricant at high speed until uniform, and adding them from the main feed port of a twin-screw extruder with a length-to-diameter ratio of 52:1. Inorganic fibers and crosslinking aid masterbatch were added from the first and second side feed ports of the extruder, respectively. The extrusion temperature was set to 220~240℃ and the screw speed was 350rpm. After melt extrusion, the material was cooled and pelletized.

[0025] Finally, the crosslinkable PBT composite material was used to prepare the required test strips through injection molding. The products were then subjected to radiation processing using an electron beam generated by a high-energy accelerator. The radiation dose is shown in Table 1.

[0026] Components name Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 resin PBT (0.8 dL / g) 51 36 36 36 36 36 36 36 36 Inorganic fibers Fiberglass 30 30 30 30 30 30 30 30 30 Crosslinking masterbatch MB-A — — — — 15 15 5 — — Crosslinking masterbatch MB-B — 15 — 15 — — 10 15 — Crosslinking masterbatch MB-C — — 15 — — — — — — Crosslinking masterbatch MB-D — — — — — — — — 15 Flame retardant Aluminum phosphonate 13 13 13 13 13 13 13 13 13 Flame retardant melamine cyanurate 5 5 5 5 5 5 5 5 5 antioxidants 1010 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 antioxidants 168 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 lubricant Hyperbranched polyester 0.5 0.5 0.5 0.5 0.5 — 0.5 0.5 0.5 lubricant silicone powder — — — — — 0.5 — — — Radiation dose (kGy) 300 0 300 300 300 300 300 450 300

[0027] Table 2 Components name MB-A MB-B MB-C MB-D resin PBT (1.2 dL / g) 69.5 69.5 70 69.5 Allyl compounds Triallyl cyanurate 30 — — — Allyl compounds Trimethylallyl isocyanurate — 30 30 30 stabilizer Di-tert-butyl-p-cresol 0.5 0.5 — — stabilizer p-hydroxyanisole — — — 0.5 The raw material composition of Comparative Example 1 is the same as that of Example 1, except that no crosslinking masterbatch was added and the corresponding ratio was replaced with PBT resin; the preparation method of Comparative Example 1 is exactly the same as that of Example 1.

[0028] The raw material composition of Comparative Example 2 is exactly the same as that of Example 1; the preparation method of Comparative Example 2 is the same as that of Example 1, except that no radiation processing is performed, that is, the radiation dose is 0 kGy.

[0029] The raw material composition of Comparative Example 3 is the same as that of Example 1, except that the added crosslinking aid masterbatch does not contain a stabilizer; the preparation method of Comparative Example 3 is exactly the same as that of the Example.

[0030] The samples prepared in the above embodiments and comparative examples were tested, and the test data are listed in Table 3.

[0031] Tensile strength was tested according to GB / T 1040.2; flexural strength and flexural modulus were tested according to GB / T 9341.

[0032] The degree of crosslinking of crosslinked PBT composite materials is characterized by testing gel content: 1g of sample is weighed and ground into small particles with a particle size of about 1mm, then 50mL of xylene is added, and Soxhlet extraction is performed for 6h. The insoluble matter is vacuum dried to constant weight and weighed. The percentage of organic matter in the insoluble matter relative to the organic matter in the initial sample is the gel content of the material.

[0033] The high-temperature resistance of cross-linked PBT composites was characterized by a hot needle test. The hot needle diameter was 2.0 mm, the temperature was 400 °C, and the load was 9.8 N. During the test, a 4.0 mm thick sample was placed at the bottom of the hot needle, and the depth of the hot needle indentation was read after 60 seconds.

[0034] project Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Tensile strength (MPa) 124 108 119 136 130 127 137 129 125 Bending strength (MPa) 191 173 193 204 199 196 202 195 195 Flexural modulus (MPa) 9456 8375 9534 10789 10218 9938 10256 10047 10019 Gel content (%) 20.5 3.2 61.2 77.6 73.5 71.8 74.7 73.3 70.0 Hot needle test (mm) >4.0 >4.0 1.2 0 0 0 0 0 0.2 A higher gel content indicates a higher degree of cross-linking within the PBT material. The test results of Examples 1-6 in Table 3 show that the cross-linked PBT composite material prepared by this invention can achieve a gel content of over 70%, exhibiting excellent cross-linking effects. Comparing Examples 5 and 1, a radiation dose of 300 kGy already allows the PBT material to reach its relatively highest gel content; further increasing the irradiation dose to 450 kGy does not further increase the gel content. A lower hot needle test value indicates better high-temperature resistance. Examples 1-5 all withstood a high temperature of 400°C for 60 seconds during the hot needle test without sinking, demonstrating excellent high-temperature resistance. Therefore, the cross-linked PBT composite material prepared by this invention is particularly suitable for lead-free soldering.

[0035] Compared with the comparative examples and the specific examples, PBT molecules have a certain degree of radiation resistance due to the benzene ring structure in the main chain. Comparative Example 1, which did not include a crosslinking masterbatch, showed poor crosslinking after radiation, with a gel content of only 20.5%. This low degree of crosslinking was insufficient to significantly improve the material's high-temperature resistance, and it easily penetrated a 4mm sample during hot needle testing. Comparative Example 2, which did not undergo radiation processing, also showed some crosslinking after high-temperature processing due to the presence of the crosslinking masterbatch, but the gel content was only 3.2%, also lacking high-temperature resistance. In Comparative Example 3, the crosslinking masterbatch formulation did not include a stabilizer, resulting in a final crosslinked PBT material with a gel content of 61.2% and a hot needle penetration of 1.2mm, indicating that the material has some high-temperature resistance but is insufficient to withstand 400℃ for 60 seconds. Since the active ingredient in the crosslinking masterbatch is an allyl compound, its unsaturated double bonds are heat-sensitive. If a stabilizer is not added during material production and processing for protection, the allyl compound is prone to volatilization or self-polymerization at high temperatures, affecting the final material's crosslinking and high-temperature resistance.

[0036] This invention provides a crosslinkable PBT composite material suitable for lead-free soldering and its preparation method. First, a crosslinking aid masterbatch is prepared. Then, a formulation is designed, and the crosslinkable PBT composite material is prepared by twin-screw melt extrusion. After the material is molded into a finished product, it undergoes radiation crosslinking. The crosslinked PBT composite material achieves a gel content of over 70%. This high degree of crosslinking significantly improves the temperature resistance of the PBT material, allowing it to withstand short-term high temperatures up to 400℃, making it particularly suitable for lead-free soldering applications in the electronics and electrical industries. Furthermore, the crosslinking of the PBT material is performed after the finished product is formed, preserving the inherent advantages of PBT material's ease of processing and molding. The preparation process is environmentally friendly, convenient, and easily achievable for industrial-scale mass production.

Claims

1. A lead-free solder crosslinked PBT composite material, comprising, by weight, the following raw materials: PBT resin: 30-80 parts Inorganic fibers: 0-60 parts Crosslinking masterbatch: 5-40 parts Halogen-free flame retardant: 5-25 parts Antioxidant: 0.1-1 part Lubricant: 0.2-1 part.

2. The PBT composite material suitable for lead-free welding crosslinking according to claim 1, characterized in that, The intrinsic viscosity of the PBT resin is 0.8-1.1 dL / g; the inorganic fiber is an alkali-free glass fiber with a diameter of 5-15 μm.

3. The PBT composite material suitable for lead-free soldering crosslinking according to claim 1, characterized in that, The crosslinking aid masterbatch is obtained by twin-screw extrusion granulation with high-viscosity PBT (1.2-1.4 dL / g intrinsic viscosity) as the matrix, adding allyl compounds and / or stabilizers. The addition ratio of PBT matrix, allyl compound and stabilizer in the crosslinking masterbatch is (58~88):(10~40):(0.2~2); The allyl compound is selected from at least one of triallyl isocyanurate, trimethylallyl isocyanurate, triallyl cyanurate, triallyl phenyltriglyceride, and pentaerythritol tetraacrylate. The stabilizer is selected from at least one of p-hydroxyanisole and di-tert-butyl-p-cresol.

4. The PBT composite material suitable for lead-free solder crosslinking according to claim 1, characterized in that, The halogen-free flame retardant is selected from at least one of aluminum phosphonate, melamine polyphosphate, and melamine cyanurate.

5. The PBT composite material suitable for lead-free soldering crosslinking according to claim 1, characterized in that, The antioxidant is a combination of hindered phenolic antioxidants and phosphite antioxidants. The hindered phenolic antioxidant is selected from at least one of 1098, 1010, and GA-80. The phosphite antioxidant is selected from at least one of 168, 626, and 9228.

6. The PBT composite material suitable for lead-free solder crosslinking according to claim 1, characterized in that, The lubricant is selected from at least one of hyperbranched polyester, silicone powder, and calcium stearate.

7. A method for preparing a lead-free solder crosslinked PBT composite material according to any one of claims 1 to 7, comprising the following steps: Preparation of crosslinking aid masterbatch, preparation of crosslinkable PBT composite materials, and radiation crosslinking.

8. A lead-free solder crosslinked PBT composite material according to claim 8, characterized in that, The crosslinking aid masterbatch is prepared by high-viscosity PBT resin and stabilizer being mixed uniformly at high speed and added through the main feed port of a twin-screw extruder. The allyl compound is added through the side feed port of the twin-screw extruder, followed by melt extrusion granulation. The twin-screw extruder has a length-to-diameter ratio of 36:1, with zone 1 being the main feed port, zone 4 having a vent, and zone 7 being the side feed port. The extrusion temperature is 200-230℃, and the screw speed is 250-350 rpm.

9. A lead-free solder crosslinked PBT composite material according to claim 8, characterized in that, The crosslinkable PBT composite material is prepared by high-speed stirring and uniform mixing of PBT resin, flame retardant, antioxidant, and lubricant, and then feeding it into the main feed port of a high aspect ratio twin-screw extruder. Inorganic fibers and crosslinking aid masterbatch are added from the first and second side feed ports, respectively, followed by melt extrusion granulation. The high aspect ratio twin-screw extruder has an aspect ratio of 52:1, with zone 1 being the main feed port, zone 4 having an exhaust port, zone 5 being the first side feed port, zone 10 having a vacuum port, and zone 11 being the second side feed port. The extrusion temperature is 210~240℃, and the screw speed is 300-400 rpm.

10. A lead-free solder crosslinked PBT composite material according to claim 8, characterized in that, The radiation crosslinking involves molding the above-mentioned crosslinkable PBT composite material into the desired product through injection molding, and then irradiating the product with an electron beam generated by a high-energy accelerator or gamma rays generated by cobalt-60, with a radiation dose of 100~500kG, preferably 150~300kGy.