An extrusion-die in-situ rapid high-crosslinking low compression permanent deformation conductive silicone rubber and preparation method thereof

Abstract

The present invention discloses an extruder-head in-situ fast high cross-linking low compression permanent deformation conductive silicone rubber and a preparation method thereof. The raw material composition of the conductive silicone rubber is: 100 parts by mass of high vinyl silicone rubber, 2-10 parts by mass of high vinyl silicone oil, 10-30 parts by mass of white carbon black, 150-250 parts by mass of coupling agent modified conductive powder, 2-5 parts by mass of vulcanizing agent, and 1-3 parts by mass of co-vulcanizing agent. The present invention adopts a plunger extruder to extrude the raw materials and then rapidly vulcanize and mold them in situ. The conductive silicone rubber after molding has a high cross-linking density and has a low compression permanent deformation, which solves the problem that the rubber strips of special-shaped and complex structures are easy to collapse and deform, and the extruded conductive rubber strips do not need to be sent to a vulcanization channel for secondary vulcanization. The conductive rubber strip prepared by the present invention has excellent electrical properties and electromagnetic shielding effectiveness, and has high mechanical properties, good resilience and good processing performance.

Description

Technical Field

[0001] The invention belongs to the technical field of conductive silicone rubber, and particularly relates to an extrusion-die head in-situ rapid high-crosslinking low-compression permanent deformation conductive silicone rubber and a preparation method thereof. Background Art

[0002] With the rapid development of electronic information technology, electronic products have been used more and more widely, bringing great convenience to people's work and life. At the same time, the problem of electromagnetic interference has also attracted people's great attention. It will not only affect the normal operation of electronic equipment, but also cause electromagnetic information leakage and electromagnetic environmental pollution. Conductive silicone rubber materials have excellent electrical conductivity and electromagnetic shielding properties, and are widely used in the sealing system of electronic equipment, playing a dual role of environmental sealing and electromagnetic sealing. In the prior art, the conductive mixed rubber material is usually extruded according to the extruder mouth shape to prepare a conductive rubber strip, and then vulcanized in a continuous pipeline hot air vulcanization device. However, the conductive rubber strips obtained by the existing extrusion process are not dimensional stable enough, especially the strips with complex structures, so they are very easy to collapse and deform, and the subsequent vulcanization channel is very long, the equipment occupies a large area, the extrusion speed is slow, and the production efficiency is low. Summary of the invention

[0003] In order to solve the problems in the prior art, the present invention provides an extrusion-die in-situ rapid high cross-linking low compression permanent deformation conductive silicone rubber and a preparation method thereof. The method can be used for in-situ rapid vulcanization molding after the conductive silicone rubber is extruded. The conductive silicone rubber after molding has a high cross-linking density, low compression permanent deformation, and high dimensional stability, which solves the problem that the rubber strips with special-shaped and complex structures are prone to collapse and deformation. And the extruded conductive rubber strip does not need to be sent to a vulcanization channel for secondary vulcanization. The conductive rubber strip prepared by the present invention has excellent electrical properties and electromagnetic shielding effectiveness, and has high mechanical properties, low compression permanent deformation, good resilience, and good processing performance.

[0004] The raw material composition of the extrusion-die in-situ rapid high cross-linking low compression permanent deformation conductive silicone rubber is: 100 parts by mass of high vinyl silicone rubber, 2-10 parts by mass of high vinyl silicone oil, 10-30 parts by mass of white carbon black, 150-250 parts by mass of coupling agent modified conductive powder, 2-5 parts by mass of vulcanizing agent, and 1-3 parts by mass of co-vulcanizing agent.

[0005] The high vinyl silicone rubber has a molecular weight of 200,000-1,000,000 and a vinyl molar content of 1.8-5%, and is specifically selected from one or more of methyl vinyl silicone rubber, methyl vinyl phenyl silicone rubber, and fluorosilicone rubber.

[0006] The high vinyl silicone oil has a viscosity of 500-3000 mPa·S and a vinyl molar content of 5-15%.

[0007] The conductive powder is one or more of aluminum-plated silver, glass-plated silver, copper-plated silver, nickel-plated silver, aluminum-plated nickel, graphene, nickel-plated carbon fiber, nickel-plated carbon nanotubes and graphite-plated nickel.

[0008] The aluminum silver-plated is ellipsoidal with a particle size of 20-80 microns; the glass silver-plated is round with a particle size of 10-60 microns; the copper silver-plated is dendritic with a particle size of 20-80 microns; the graphite nickel-plated is flake with a particle size of 50-200 microns; the nickel-plated carbon fiber is rod-shaped with a diameter of 5-30 microns and a length of 100-300 microns.

[0009] The coupling agent is one or more of 3-aminopropylmethylsilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane and γ-mercaptopropyltrimethoxysilane.

[0010] The preparation method of the coupling agent modified conductive powder is: adding the conductive powder into a coupling agent solution, soaking it for 1-2 hours and then drying it.

[0011] The coupling agent solution is an alcohol solution of the coupling agent, and the mass ratio of the coupling agent to the alcohol is 1:20-40.

[0012] The drying temperature is 80-100° C. and the drying time is 3-5 hours.

[0013] The vulcanizing agent is one or more of 1,1-di(tert-butylperoxy)3,3,5-trimethylcyclohexane (TMCH), 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (bis-25), diisopropylbenzene peroxide (DCP), benzoyl peroxide and platinum catalyst.

[0014] The platinum content in the platinum catalyst is 1000-20000 ppm.

[0015] The co-vulcanizing agent is one or more of tetramethylthiuram disulfide (TMTD), triallyl methyl triisocyanurate (TAIC), triallyl cyanurate (TAC), trimethylolpropane trimethacrylate (TMPTMA), and hydrogen-containing silicone oil.

[0016] Preferably, the raw material composition of the extrusion-die in-situ rapid high cross-linking low compression permanent deformation conductive silicone rubber is: 100 parts by mass of high vinyl silicone rubber, 2-8 parts by mass of high vinyl silicone oil, 20-30 parts by mass of white carbon black, 200-250 parts by mass of conductive powder, 2-8 parts by mass of coupling agent, 2-5 parts by mass of vulcanizing agent, and 1-3 parts by mass of co-vulcanizing agent.

[0017] The preparation method of the extrusion-die in-situ rapid high cross-linking low compression permanent deformation conductive silicone rubber is:

[0018] (1) according to the above ratio, high vinyl silicone rubber, high vinyl silicone oil, white carbon black and coupling agent modified conductive powder are put into an internal mixer for mixing and kneading at a speed of 20-60r for 8-10min; then the mixed rubber is added to an open mixer, and then a vulcanizing agent and a vulcanizing agent are added, and mixed and kneaded for 3-5 times to obtain a conductive mixed rubber;

[0019] (2) feeding the conductive rubber compound obtained in step (1) into the barrel of a plunger extruder for extrusion molding, setting the working temperature to 350-450°C, the pressure to 4.5-6.5 MPa, and the die head in-situ extrusion speed to 0.3-6 m / min;

[0020] (3) The rubber strip formed by extrusion-die in-situ vulcanization in step (2) is post-treated at 140-200° C. for 3-4 hours to obtain a finished conductive silicone rubber.

[0021] Step (1) extrudes one, two, three or special-shaped rubber strips at the same time.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The extrusion-die in-situ vulcanization conductive silicone rubber of the present invention uses silicone rubber with a high vinyl content and silicone oil with a high vinyl content and low viscosity to adjust the amount of vinyl double bonds, so that there are more double bonds, more cross-linking points after vulcanization, and a higher cross-linking density, which can reach 85-95%.

[0024] (2) The present invention uses conductive powders of different shapes and particle sizes for doping, thereby reducing the total amount of conductive powder and solving the problem of poor electrical properties and electromagnetic shielding properties at low dosage. The conductive rubber obtained has very good electrical properties and electromagnetic shielding properties, high mechanical properties and good processing fluidity.

[0025] (3) The present invention increases the interfacial bonding force between silicone rubber and the conductive powder after surface modification of the conductive powder, and transforms the rigid contact between the conductive powder in the silicone matrix into a flexible contact, so that the material has better rubber elasticity, high tensile strength and low compression permanent deformation.

[0026] (4) The present invention uses a vulcanizing agent with a shorter half-life and higher catalytic activity. In this way, at a higher temperature, the vulcanizing agent can be completely decomposed in a shorter time, thereby promoting the vulcanization reaction, making the vulcanization speed faster, and thus achieving rapid and high crosslinking.

[0027] (5) The present invention innovatively adopts an in-situ vulcanization method at the head of the rubber plunger extruder to extrude a conductive rubber strip with high dimensional stability at high temperature, quickly and highly cross-linked. The formed conductive rubber strip also has a low compression permanent deformation, which solves the problem that the rubber strip with a complex structure is prone to collapse and deformation. The extruded conductive rubber strip does not need to be sent to the vulcanization channel for secondary vulcanization, which greatly saves site resources, improves production efficiency, and reduces energy consumption and production costs. DETAILED DESCRIPTION Example 1

[0028] The ellipsoidal aluminum silver-plated conductive powder with a particle size of 20-80 microns was added to a vinyl tri(β-methoxyethoxy)silane alcohol solution (the mass ratio of coupling agent to alcohol was 1:30) at a mass ratio of 1:4, immersed for 2 hours, and dried at 100°C for 3 hours to obtain the coupling agent-modified aluminum silver-plated conductive powder.

[0029] Rod-shaped nickel-plated carbon fiber conductive powder with a diameter of 5-30 microns and a length of 100-300 microns is added to a vinyl tri(β-methoxyethoxy)silane alcohol solution (the mass ratio of coupling agent to alcohol is 1:30) at a mass ratio of 1:4, immersed for 2 hours, and dried at 100°C for 3 hours to obtain coupling agent-modified nickel-plated carbon fiber conductive powder.

[0030] The raw material composition of the extrusion-die in-situ rapid high cross-linking low compression permanent deformation conductive silicone rubber is calculated as follows by mass: 100 parts of methyl vinyl silicone rubber (molecular weight 550,000-600,000, vinyl molar content 2%), 5 parts of high vinyl silicone oil (viscosity 500mPa·S, vinyl molar content 5%), 20 parts of fumed silica, 240 parts of coupling agent modified aluminum silver-plated conductive powder, 10 parts of coupling agent modified nickel-plated carbon fiber conductive powder, 3 parts of platinum catalyst (platinum content 10000ppm), and 1 part of hydrogen-containing silicone oil.

[0031] Preparation process:

[0032] (1) According to the above ratio, methyl vinyl silicone rubber, high vinyl silicone oil, fumed silica, coupling agent-modified aluminum silver-plated conductive powder and coupling agent-modified nickel-plated carbon fiber conductive powder are put into an internal mixer for mixing and kneading at a speed of 40r for 10min; then the mixed rubber material is added to an open mixer, and then a platinum catalyst and hydrogen-containing silicone oil are added, and mixed and kneaded for 4 times to obtain a conductive mixed rubber;

[0033] (2) Extrusion process: the conductive rubber compound obtained in step (1) is fed into the barrel of a plunger extruder for extrusion molding at an operating temperature of 350°C, a pressure of 5 MPa, and an extrusion speed of 3 meters per minute;

[0034] (3) Post-treatment process: The rubber strip formed by extrusion-die in-situ vulcanization in step (1) is placed on a tray and placed in layers in an oven for post-treatment at a temperature of 200°C for 4 hours. After post-treatment, a finished conductive rubber strip is obtained. Example 2

[0035] The methyl vinyl silicone rubber in Example 1 was replaced by methyl vinyl silicone rubber with a molecular weight of 550,000-600,000 and a vinyl molar content of 5%, and the other reaction conditions were the same. Example 3

[0036] The high vinyl silicone oil in Example 2 was replaced with a high vinyl silicone oil with a viscosity of 500 mPa·s and a vinyl molar content of 15%, and the other reaction conditions were the same. Example 4

[0037] The flaky graphite nickel-plated conductive powder with a particle size of 50-200 microns was added to a γ-methacryloxypropyltrimethoxysilane alcohol solution (the mass ratio of coupling agent to alcohol is 1:30) at a mass ratio of 1:4, immersed for 2 hours, and dried at 100°C for 3 hours to obtain coupling agent-modified graphite nickel-plated conductive powder.

[0038] The flaky graphene conductive powder with a particle size of 10-40 microns was added to a γ-methacryloxypropyltrimethoxysilane alcohol solution (the mass ratio of the coupling agent to the alcohol was 1:30) at a mass ratio of 1:4, immersed for 2 hours, and dried at 100°C for 3 hours to obtain the coupling agent-modified graphene conductive powder.

[0039] The raw material composition of the extrusion-die in-situ rapid high cross-linking low compression permanent deformation conductive silicone rubber is calculated as follows by mass: 100 parts of methyl vinyl silicone rubber (molecular weight 550,000-600,000, vinyl molar content 5%), 5 parts of high vinyl silicone oil (viscosity 500mPa·S, vinyl molar content 15%), 20 parts of fumed silica, 200 parts of coupling agent modified graphite nickel-plated conductive powder, 10 parts of coupling agent modified graphene conductive powder, 2 parts of 1,1-di(tert-butylperoxy)3,3,5-trimethylcyclohexane (TMCH), 2 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (bis-25), and 1 part of tetramethylthiuram disulfide (TMTD).

[0040] Preparation process:

[0041] (1) According to the above ratio, methyl vinyl silicone rubber, high vinyl silicone oil, fumed silica, coupling agent-modified graphite nickel-plated conductive powder and coupling agent-modified graphene conductive powder are put into an internal mixer for mixing and kneading at a speed of 40r for 10 minutes; then the mixed rubber material is added to an open mixer, and 1,1-di(tert-butylperoxy)3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and tetramethylthiuram disulfide are added, and the mixture is mixed and kneaded for 4 times to obtain a conductive rubber compound;

[0042] (1) Extrusion process: the conductive rubber compound obtained in step (1) is fed into the barrel of a plunger extruder for extrusion molding at an operating temperature of 350°C, a pressure of 5 MPa, and an extrusion speed of 3 meters per minute;

[0043] (2) Post-treatment process: The rubber strip formed by extrusion-die in-situ vulcanization in step (1) is placed on a tray and placed in layers in an oven for post-treatment at a temperature of 150°C for 4 hours. After post-treatment, a finished conductive rubber strip is obtained. Example 5

[0044] The extrusion working temperature of step (1) of Example 4 was adjusted to 400° C., and the other reaction conditions were the same. Example 6

[0045] The extrusion working temperature of step (1) of Example 4 was adjusted to 450°C, and the other reaction conditions were the same. Comparative Example 1

[0046] The extrusion working temperature of step (1) of Example 4 was adjusted to 500° C., and the other reaction conditions were the same.

[0047] The extrusion-die in-situ vulcanized conductive silicone rubber prepared by the above-mentioned examples 1-6 and comparative example 1 was tested, and the test results are shown in Table 1. Reference standards for performance testing:

[0048] Rubber testing: GB / T 6038-2006 Rubber testing rubber compound mixing and vulcanization equipment and operating procedures;

[0049] Hardness: GB / T 531.1-2008 Test method for indentation hardness of vulcanized rubber or thermoplastic rubber, Part 1: Shore hardness tester method (Shore hardness);

[0050] Mechanical properties: GB / T 528-2009 Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber;

[0051] Compression set: GBT 7759.1-2015 Determination of compression set of vulcanized rubber or thermoplastic rubber, Part 1: At room temperature and high temperature conditions;

[0052] Electrical properties (volume resistivity): GB / T 36763-2018 General technical requirements for vulcanized rubber for electromagnetic shielding;

[0053] Cross-link density: GB / T 18474-2001 Test method for cross-link density of cross-linked polyethylene pipes and fittings.

[0054] Table 1 Test results of conductive rubber properties of Examples 1 to 6 and Comparative Example 1

[0055]

[0056] As can be seen from Table 1, the effects of the vinyl content of silicone rubber and silicone oil on the performance of the aluminum-silver conductive adhesive in Examples 1 to 3 were studied, and it was found that when the vinyl content of silicone rubber was 5% and the vinyl content of silicone oil was 15%, the tensile strength of the conductive adhesive was greater than 2MPa, the compression permanent deformation was low, the volume resistivity was low, the hardness and cross-linking density were high, and the comprehensive performance was significantly better than that of the low vinyl content. This shows that the conductive adhesive prepared with a high vinyl content has a high cross-linking density and excellent comprehensive performance.

[0057] In Examples 4 to 6 and Comparative Example 1, the effects of different temperatures (350°C, 400°C, 450°C and 500°C) on the performance of the conductive adhesive during in-situ extrusion molding are compared. It can be seen that: with the increase of temperature, the hardness of the graphite nickel-plated conductive adhesive increases, the tensile strength increases, the elongation at break decreases, the compression permanent deformation decreases, the volume resistivity decreases, and the cross-linking density increases. The performance of the graphite nickel-plated conductive adhesive is optimal at 400°C. In the comparative example, when the extrusion molding temperature is 500°C, the mechanical properties, electrical properties and compression permanent deformation all deteriorate.

Claims

1. An extrusion-die in-situ rapid high cross-linking low compression permanent deformation conductive silicone rubber, characterized in that: The raw material composition of the conductive silicone rubber is: 100 parts by mass of high-vinyl silicone rubber, 2-10 parts by mass of high-vinyl silicone oil, 10-30 parts by mass of white carbon black, 150-250 parts by mass of coupling agent-modified conductive powder, 2-5 parts by mass of vulcanizing agent, and 1-3 parts by mass of vulcanizing agent; the molecular weight of the high-vinyl silicone rubber is 200,000-1,000,000, the molar content of vinyl is 1.8-5%, and it is specifically selected from one or more of methyl vinyl silicone rubber, methyl vinyl phenyl silicone rubber, and fluorosilicone rubber; the viscosity of the high-vinyl silicone oil is 500-3000 mPa·S, and the molar content of vinyl is 5-15%; The preparation method of the conductive silicone rubber is: (1) according to the above ratio, high vinyl silicone rubber, high vinyl silicone oil, white carbon black and coupling agent modified conductive powder are put into an internal mixer for mixing and kneading at a speed of 20-60r for 8-10min; then the mixed rubber is added to an open mixer, and then a vulcanizing agent and a vulcanizing agent are added, and mixed and kneaded for 3-5 times to obtain a conductive mixed rubber; (2) feeding the conductive rubber compound obtained in step (1) into the barrel of a plunger extruder for extrusion molding, setting the working temperature to 350-450°C, the pressure to 4.5-6.5 MPa, and the die head in-situ extrusion speed to 0.3-6 m / min; (3) The rubber strip formed by extrusion-die in-situ vulcanization in step (2) is post-treated at 140-200° C. for 3-4 hours to obtain a finished conductive silicone rubber.

2. The conductive silicone rubber according to claim 1, characterized in that: The conductive powder is one or more of aluminum-plated silver, glass-plated silver, copper-plated silver, nickel-plated silver, aluminum-plated nickel, graphene, nickel-plated carbon fiber, nickel-plated carbon nanotubes and graphite-plated nickel.

3. The conductive silicone rubber according to claim 2, characterized in that: The aluminum silver-plated is ellipsoidal with a particle size of 20-80 microns; the glass silver-plated is round with a particle size of 10-60 microns; the copper silver-plated is dendritic with a particle size of 20-80 microns; the graphite nickel-plated is flake with a particle size of 50-200 microns; the nickel-plated carbon fiber is rod-shaped with a diameter of 5-30 microns and a length of 100-300 microns.

4. The conductive silicone rubber according to claim 1, characterized in that: The coupling agent is one or more of 3-aminopropylmethylsilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane and γ-mercaptopropyltrimethoxysilane.

5. The conductive silicone rubber according to claim 1, characterized in that: The preparation method of the coupling agent modified conductive powder is: adding the conductive powder into a coupling agent solution, soaking it for 1-2 hours and then drying it.

6. The conductive silicone rubber according to claim 1, characterized in that: The vulcanizing agent is one or more of 1,1-di(tert-butylperoxy)3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, diisopropylbenzene peroxide, benzoyl peroxide and platinum catalyst.

7. The conductive silicone rubber according to claim 1, characterized in that: The co-vulcanizing agent is one or more of tetramethylthiuram disulfide, triallylmethyl triisocyanurate, triallyl cyanurate, trimethylolpropane trimethacrylate, and hydrogen-containing silicone oil.

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