A self-lubricating cast nylon containing a ternary block internal lubricant and its preparation method

Abstract

This invention discloses a self-lubricating cast nylon containing a ternary block internal lubricant and its preparation method, belonging to the field of engineering plastics modification technology. It comprises the following components by weight: 80-100 parts caprolactam, 3-8 parts ternary block internal lubricant, 0.5-2 parts catalyst, 0.3-1.5 parts co-catalyst, and 0.1-0.5 parts antioxidant; wherein the ternary block internal lubricant is a PE-MAH-lanthanum stearate ternary block copolymer formed by free radical polymerization of polyethylene, maleic anhydride, and lanthanum stearate. This invention designs a PE-MAH-lanthanum stearate ternary block internal lubricant, integrating the lubricity of polyethylene, the compatibility of maleic anhydride, and the synergistic lubricity of lanthanum stearate into a single unit through chemical bonding. This fundamentally solves the technical defects of poor compatibility, easy agglomeration, and easy migration of the components in the physical blending of the prior art. The maleic anhydride segments in the ternary block structure can chemically react with the amide groups on the nylon molecular chain, so that the internal lubricant forms a stable chemical bond with the nylon matrix.

Description

Technical Field

[0001] This invention relates to the field of engineering plastic modification technology, and in particular to a self-lubricating cast nylon containing a ternary block internal lubricant and its preparation method. Background Technology

[0002] Cast nylon (also known as molded nylon or MC nylon) is an engineering plastic that is polymerized and cast on-site by caprolactam monomers under the action of a catalyst. It has the advantages of high mechanical strength, wear resistance, impact resistance, corrosion resistance, and simple molding process. It is widely used in machinery, chemical industry, metallurgy, mining and other fields as the core material for friction components such as sliding bearings, gears, bushings, and guide rails.

[0003] However, pure cast nylon has a high coefficient of friction and significant wear. Under dry friction conditions without additional lubrication, it is prone to problems such as overheating, accelerated wear, and even jamming, severely limiting its application in high-end precision transmission and harsh friction environments. To improve the self-lubricating properties of cast nylon, existing technologies mainly employ modification by adding external or internal lubricants. Among these, internal lubricants, due to their ability to form a stable bond with the nylon matrix and their resistance to migration and loss, have become the mainstream modification approach.

[0004] Commonly used internal lubricants in existing technologies mainly include polyolefins (such as PE and PP), fatty acids and their salts, and waxes. For example, Chinese patent CN1043776 discloses a self-lubricating bearing material, which is prepared by adding high-purity graphite and appropriate amounts of molybdenum disulfide, tungsten disulfide, and carbon fiber to a nylon matrix, followed by mixing and molding processes. However, this technology only improves lubrication performance by filling with solid lubricant and does not use chemical modification to improve the compatibility between the lubricant and the matrix. US patent 4012478 reports the use of nylon mixed powder and liquid lubricant to form a self-lubricating material through screw extrusion or injection, but the lubricant is prone to migration, and the self-lubricating performance deteriorates significantly after long-term use.

[0005] To address the poor compatibility between lubricants and nylon matrices, existing technologies often employ maleic anhydride-grafted polyolefins (MAH-g-PE) as compatibilizers. This utilizes the reaction between the maleic anhydride groups and the amide groups on the nylon molecular chains to enhance the interfacial bonding between the polyolefin and nylon. However, maleic anhydride-grafted polyolefins only provide compatibility and auxiliary lubrication; their inherent lubrication properties are limited and cannot meet the requirements of low friction and high wear resistance in high-end applications. Furthermore, rare earth metal soaps such as lanthanum stearate possess certain lubricating and thermal stabilizing properties and can improve the flowability of plastics during processing. However, when added alone, their compatibility with the nylon matrix is ​​extremely poor, leading to easy agglomeration. This not only fails to provide adequate lubrication but also reduces the mechanical strength of the nylon matrix.

[0006] Currently, there is no existing technology that combines PE, maleic anhydride, and lanthanum stearate to form a ternary block internal lubricant and applies it to the modification of cast nylon. When these three components are added using conventional physical blending methods, the significant difference between the non-polarity of PE and the polarity of nylon, coupled with the tendency of lanthanum stearate to agglomerate, prevents them from forming a synergistic effect. Instead, problems such as interface separation and lubricant migration occur, resulting in a trade-off between the self-lubricating properties and mechanical strength of the modified nylon—either improving lubrication performance but significantly reducing mechanical strength, or retaining mechanical strength but with limited improvement in self-lubricating properties. Therefore, developing an internal lubricant system that is highly compatible with the nylon matrix and can fully utilize the synergistic lubrication effect to simultaneously improve self-lubricating performance and mechanical strength has become a pressing technical challenge in the field of cast nylon modification. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide a self-lubricating cast nylon containing a ternary block internal lubricant and its preparation method; it can solve the problems of poor compatibility between the internal lubricant and the matrix, limited lubrication performance, difficulty in balancing mechanical strength and self-lubricating performance, and easy migration of lubricant in the self-lubricating modification of cast nylon in the prior art.

[0008] Technical solution: To solve the above-mentioned technical problems, according to one aspect of the present invention, more specifically, a self-lubricating cast nylon containing a ternary block internal lubricant and its preparation method, comprising the following components by weight: 80-100 parts caprolactam, 3-8 parts ternary block internal lubricant, 0.5-2 parts catalyst, 0.3-1.5 parts co-catalyst, and 0.1-0.5 parts antioxidant;

[0009] The ternary block lubricant is a PE-MAH-lanthanum stearate ternary block copolymer formed by free radical polymerization of polyethylene, maleic anhydride and lanthanum stearate. In its molecular structure, the polyethylene segment is the lubricating host, the maleic anhydride segment is the compatibility binding group, and the lanthanum stearate segment is the synergistic lubricating and dispersing group. The three are chemically bonded to form a block structure. The number average molecular weight of the ternary block lubricant is 5000-20000.

[0010] Furthermore, in the ternary block internal lubricant, the weight ratio of polyethylene, maleic anhydride, and lanthanum stearate is (60-80):(10-20):(5-15).

[0011] Furthermore, the polyethylene is low-density polyethylene or linear low-density polyethylene with a number-average molecular weight of 2000-8000 and a melting point of 105-125℃; the lanthanum stearate has a purity of ≥98% and a particle size of 100-200 mesh.

[0012] Furthermore, the catalyst is at least one of sodium hydroxide and potassium hydroxide, and the purity of the catalyst is ≥96%, added in powder form.

[0013] Furthermore, the co-catalyst is one of toluene diisocyanate and diphenylmethane diisocyanate.

[0014] Furthermore, the antioxidant is a hindered phenolic antioxidant, specifically at least one of antioxidant 1010 and antioxidant 1076.

[0015] According to another aspect of the present invention, a method for preparing a self-lubricating cast nylon containing a ternary block internal lubricant is provided. This method is based on the self-lubricating cast nylon containing a ternary block internal lubricant as described in any one of the preceding claims, and includes the following steps:

[0016] S1. Preparation of ternary block internal lubricant: Polyethylene, maleic anhydride and lanthanum stearate are added to a high-speed mixer in proportion and mixed to obtain a mixture; the mixture is added to a twin-screw extruder for melt extrusion, and the extrudate is cooled with water, pelletized and dried to obtain PE-MAH-lanthanum stearate ternary block internal lubricant particles.

[0017] S2. Raw material pretreatment: Vacuum dry the caprolactam monomer to remove water, and dry the ternary block lubricant particles, catalyst, co-catalyst and antioxidant to a moisture content of ≤0.1% for later use.

[0018] S3. Melt polymerization: Add the dried caprolactam to the reactor, purge with nitrogen for protection, heat to 120-140℃ and stir until completely melted; add the pretreated ternary block lubricant particles, keep warm and stir to disperse them evenly and allow them to pre-react; then add the catalyst, heat to 160-170℃ and stir to react; finally add the co-catalyst and stir quickly to obtain the polymer melt;

[0019] S4. Casting and molding: Pour the polymer melt into a mold preheated to 150-160℃, keep it at a constant temperature for 2-3 hours until the polymerization reaction is complete, and demold after natural cooling to room temperature to obtain a self-lubricating cast nylon blank.

[0020] S5. Post-processing: The self-lubricating cast nylon blank is annealed to eliminate internal stress, and then machined to obtain the self-lubricating cast nylon product. The annealing process conditions are: temperature 80-100℃, holding time 4-6h.

[0021] Furthermore, in step S1, the high-speed mixing process conditions are: temperature 80-100℃, rotation speed 300-500r / min, and mixing time 10-15min; the temperature settings for each section of the twin-screw extruder are: feed section 160-165℃, melting section 170-175℃, die head section 175-180℃, and screw rotation speed 200-300r / min.

[0022] Furthermore, in step S2, the process conditions for vacuum drying of caprolactam monomer are: temperature 80-100℃, vacuum degree -0.08~-0.09MPa, and drying time 2-3h.

[0023] Furthermore, in step S3, the heat preservation and stirring time after adding the ternary block lubricant particles is 30-40 min; the stirring reaction time after adding the catalyst is 15-20 min; and the rapid stirring time after adding the co-catalyst is 5-10 min.

[0024] Beneficial effects: This invention, through the design of a PE-MAH-lanthanum stearate ternary block internal lubricant, integrates the lubricity of polyethylene, the compatibility of maleic anhydride, and the synergistic lubricity of lanthanum stearate into a single unit through chemical bonding. This fundamentally solves the technical defects of poor compatibility, easy agglomeration, and easy migration of the components in the physical blending of the prior art. The maleic anhydride segment in the ternary block structure can chemically react with the amide groups on the nylon molecular chain, so that the internal lubricant forms a stable chemical bond with the nylon matrix, avoiding the migration and loss of lubricant during long-term use, and ensuring the long-term stability of self-lubricating performance.

[0025] The ternary block internal lubricant of this invention achieves a synergistic lubrication effect among the three components. The PE segment, as the lubricating agent, provides basic low-friction properties, while the lanthanum stearate segment further reduces the coefficient of friction and wear. The synergistic effect of the two can reduce the dry friction coefficient of cast nylon to 0.13-0.17 and the volumetric wear rate to 1.5×10⁻⁻⁻⁶. 6 -2.8×10⁻ 6 mm³ / N·m, which is far superior to pure cast nylon and physically blended modified nylon, greatly improves the wear resistance and self-lubricating performance of the product, and can be adapted to harsh dry friction conditions without lubricating media.

[0026] This invention solves the industry pain point of significant decrease in mechanical strength during the modification of traditional internal lubricants through molecular design of a ternary block structure. The modified cast nylon retains more than 90% of its tensile strength and impact strength, while exhibiting excellent dimensional stability. It successfully achieves simultaneous optimization of self-lubricating performance, mechanical strength, and dimensional stability, meeting the requirements of high-end precision transmission components.

[0027] The preparation method provided by this invention is simple in process and highly controllable in parameters. It does not require complex production equipment and can achieve nanoscale uniform dispersion of ternary block lubricant in nylon matrix. The product batch performance is stable and it is suitable for large-scale industrial production. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the method. Detailed Implementation

[0029] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1

[0031] A self-lubricating cast nylon containing a ternary block internal lubricant, the raw materials of which, by weight, include: 90 parts caprolactam, 5 parts ternary block internal lubricant, 1 part sodium hydroxide (catalyst), 0.8 parts toluene diisocyanate (co-catalyst), and 0.3 parts antioxidant 1010.

[0032] The ternary block lubricant is a PE-MAH-lanthanum stearate ternary block copolymer. The PE is low-density polyethylene (LDPE, molecular weight 5000, melting point 115℃), and the lanthanum stearate has a purity of 98% and a particle size of 150 mesh. The weight ratio of PE, maleic anhydride and lanthanum stearate is 70:15:15. The molecular weight of the ternary block lubricant is 12000.

[0033] The above-mentioned method for preparing self-lubricating cast nylon includes the following steps:

[0034] Preparation of ternary block internal lubricant: 70 parts LDPE, 15 parts maleic anhydride, and 15 parts lanthanum stearate were added to a high-speed mixer and mixed for 12 minutes at 90°C and 400 r / min to obtain a mixture. The mixture was then added to a twin-screw extruder with the following temperature settings: feed section 162°C, melt section 172°C, die head section 178°C, and screw speed 250 r / min. After melt extrusion, the mixture was water-cooled, pelletized, and dried to obtain PE-MAH-lanthanum stearate ternary block internal lubricant granules.

[0035] Raw material pretreatment: Add caprolactam to a vacuum drying oven and dry for 2.5 h at 90 °C and a vacuum of -0.085 MPa; dry the ternary block lubricant particles, sodium hydroxide, toluene diisocyanate, and antioxidant 1010 separately until the moisture content is ≤0.1% for later use.

[0036] Melt polymerization: Add dried caprolactam to the reactor, purge with nitrogen for protection, heat to 130°C, and stir until completely melted; add ternary block lubricant particles and stir for 35 min; add sodium hydroxide, heat to 165°C, and stir for 18 min; finally add toluene diisocyanate and stir rapidly for 8 min to obtain the polymer melt.

[0037] Casting and molding: The polymer melt is quickly poured into a mold preheated to 155°C, cured at a constant temperature for 2.5 hours, and then naturally cooled to room temperature before demolding to obtain a self-lubricating cast nylon blank.

[0038] Post-processing: The blank is placed in an oven and kept at 90℃ for 5 hours. After annealing, it is machined to obtain self-lubricating cast nylon products.

[0039] Example 2

[0040] A self-lubricating cast nylon containing a ternary block internal lubricant, the raw materials of which, by weight, include: 80 parts caprolactam, 3 parts ternary block internal lubricant, 0.5 parts potassium hydroxide (catalyst), 0.3 parts diphenylmethane diisocyanate (co-catalyst), and 0.1 parts antioxidant 1076.

[0041] The ternary block lubricant is a PE-MAH-lanthanum stearate ternary block copolymer. The PE is linear low-density polyethylene (LLDPE, molecular weight 2000, melting point 105℃), and the lanthanum stearate has a purity of 98% and a particle size of 100 mesh. The weight ratio of PE, maleic anhydride and lanthanum stearate is 80:10:10. The molecular weight of the ternary block lubricant is 5000.

[0042] The preparation method is basically the same as in Example 1, except that:

[0043] In step 1, the mixing temperature is 80℃, the speed is 300r / min, and the mixing time is 10min; the temperatures of each section of the twin-screw extruder are: 160℃ for the feed section, 170℃ for the melting section, 175℃ for the die head section, and the screw speed is 200r / min.

[0044] In step 2, the caprolactam drying temperature is 80℃, the vacuum degree is -0.08MPa, and the drying time is 2h.

[0045] In step 3, the melting temperature is 120℃ and the stirring time is 30 min; after the catalyst is added, the temperature is raised to 160℃ and the reaction is carried out for 15 min; after the co-catalyst is added, the stirring is carried out for 5 min.

[0046] In step 4, the mold is preheated to 150℃ and cured at a constant temperature for 2 hours;

[0047] In step 5, the annealing temperature is 80℃ and the holding time is 4 hours.

[0048] Example 3

[0049] A self-lubricating cast nylon containing a ternary block internal lubricant, the raw materials of which include, by weight: 100 parts caprolactam, 8 parts ternary block internal lubricant, 2 parts sodium hydroxide (catalyst), 1.5 parts toluene diisocyanate (co-catalyst), and 0.5 parts of a mixture of antioxidant 1010 and antioxidant 1076 (weight ratio 1:1).

[0050] The ternary block lubricant is a PE-MAH-lanthanum stearate ternary block copolymer. The PE is low-density polyethylene (LDPE, molecular weight 8000, melting point 125℃), and the lanthanum stearate has a purity of 98% and a particle size of 200 mesh. The weight ratio of PE, maleic anhydride and lanthanum stearate is 60:20:5. The molecular weight of the ternary block lubricant is 20000.

[0051] The preparation method is basically the same as in Example 1, except that:

[0052] In step 1, the mixing temperature is 100℃, the speed is 500r / min, and the mixing time is 15min; the temperatures of each section of the twin-screw extruder are: 165℃ for the feed section, 175℃ for the melting section, 180℃ for the die head section, and the screw speed is 300r / min.

[0053] In step 2, the caprolactam drying temperature is 100℃, the vacuum degree is -0.09MPa, and the drying time is 3h.

[0054] In step 3, the melting temperature is 140℃ and the stirring time is 40 min; after the catalyst is added, the temperature is raised to 170℃ and the reaction is carried out for 20 min; after the co-catalyst is added, the stirring is carried out for 10 min.

[0055] In step 4, the mold is preheated to 160℃ and cured at a constant temperature for 3 hours;

[0056] In step 5, the annealing temperature is 100℃ and the holding time is 6 hours.

[0057] Comparative Example 1 (Pure Cast Nylon)

[0058] The raw materials, by weight, include: 90 parts caprolactam, 1 part sodium hydroxide, 0.8 parts toluene diisocyanate, and 0.3 parts antioxidant 1010. No lubricant is added.

[0059] Preparation method: After drying caprolactam, add it to a reaction vessel, heat it to 130℃ under nitrogen protection to melt it, add sodium hydroxide, heat it to 165℃ and react for 18 min, add toluene diisocyanate and stir for 8 min, pour it into a mold at 155℃, cure it at a constant temperature for 2.5 h, cool it and demold it, and then anneal it to obtain pure cast nylon products.

[0060] Comparative Example 2 (PE / maleic anhydride blend modified cast nylon)

[0061] The raw materials, by weight, include: 90 parts caprolactam, 3.5 parts PE (LDPE, molecular weight 5000), 0.75 parts maleic anhydride, 0.75 parts lanthanum stearate, 1 part sodium hydroxide, 0.8 parts toluene diisocyanate, and 0.3 parts antioxidant 1010. PE, maleic anhydride, and lanthanum stearate are added by physical blending and are not used to prepare ternary block lubricants.

[0062] The preparation method is basically the same as in Example 1, except that: in step 1, the ternary block lubricant is not prepared, but PE, maleic anhydride, and lanthanum stearate are directly mixed and melted with dried caprolactam, and the remaining steps remain unchanged.

[0063] Performance testing

[0064] The products prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to performance tests. The test standards and results are shown in the table below:

[0065] Test Project Test Standards Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Tensile strength (MPa) GB / T 1040-2018 82 78 85 88 65 Impact strength (kJ / m²) GB / T 1043-2008 17 15 18 19 11 Coefficient of friction (dry friction) GB / T 3960-2016 0.15 0.17 0.13 0.42 0.28 Volumetric wear rate (mm³ / N·m) GB / T 3960-2016 <![CDATA[2.1×10 -6 ]]> <![CDATA[2.8×10 -6 ]]> <![CDATA[1.5×10 -6 ]]> <![CDATA[8.5×10 -6 ]]> <![CDATA[5.3×10 -6 ]]> Dimensional deviation (%) GB / T 14486-2008 0.08 0.09 0.07 0.06 0.15

[0066] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A self-lubricating cast nylon containing a ternary block internal lubricant, characterized in that, It includes the following components by weight: 80-100 parts caprolactam, 3-8 parts ternary block lubricant, 0.5-2 parts catalyst, 0.3-1.5 parts co-catalyst, and 0.1-0.5 parts antioxidant; The ternary block lubricant is a PE-MAH-lanthanum stearate ternary block copolymer formed by free radical polymerization of polyethylene, maleic anhydride and lanthanum stearate. In its molecular structure, the polyethylene segment is the lubricating host, the maleic anhydride segment is the compatibility binding group, and the lanthanum stearate segment is the synergistic lubricating and dispersing group. The three are chemically bonded to form a block structure. The number average molecular weight of the ternary block lubricant is 5000-20000.

2. The self-lubricating cast nylon containing a ternary block internal lubricant according to claim 1, characterized in that: In the ternary block internal lubricant, the weight ratio of polyethylene, maleic anhydride and lanthanum stearate is (60-80):(10-20):(5-15).

3. The self-lubricating cast nylon containing a ternary block internal lubricant according to claim 2, characterized in that: The polyethylene is low-density polyethylene or linear low-density polyethylene with a number-average molecular weight of 2000-8000 and a melting point of 105-125℃; the lanthanum stearate has a purity of ≥98% and a particle size of 100-200 mesh.

4. The self-lubricating cast nylon containing a ternary block internal lubricant according to claim 1, characterized in that: The catalyst is at least one of sodium hydroxide and potassium hydroxide, and the purity of the catalyst is ≥96%, added in powder form.

5. The self-lubricating cast nylon containing a ternary block internal lubricant according to claim 1, characterized in that: The cocatalyst is one of toluene diisocyanate and diphenylmethane diisocyanate.

6. The self-lubricating cast nylon containing a ternary block internal lubricant according to claim 1, characterized in that: The antioxidant is a hindered phenolic antioxidant, specifically at least one of antioxidant 1010 and antioxidant 1076.

7. A method for preparing self-lubricating cast nylon containing a ternary block internal lubricant, characterized in that: This method is based on a self-lubricating cast nylon containing a ternary block internal lubricant as described in any one of claims 1-6, and includes the following steps: S1. Preparation of ternary block internal lubricant: Polyethylene, maleic anhydride and lanthanum stearate are added to a high-speed mixer in proportion and mixed to obtain a mixture; the mixture is added to a twin-screw extruder for melt extrusion, and the extrudate is cooled with water, pelletized and dried to obtain PE-MAH-lanthanum stearate ternary block internal lubricant particles. S2. Raw material pretreatment: Vacuum dry the caprolactam monomer to remove water, and dry the ternary block lubricant particles, catalyst, co-catalyst and antioxidant to a moisture content of ≤0.1% for later use. S3. Melt polymerization: Add the dried caprolactam to the reactor, purge with nitrogen for protection, heat to 120-140℃ and stir until completely melted; add the pretreated ternary block lubricant particles, keep warm and stir to disperse them evenly and allow them to pre-react; then add the catalyst, heat to 160-170℃ and stir to react; finally add the co-catalyst and stir quickly to obtain the polymer melt; S4. Casting and molding: Pour the polymer melt into a mold preheated to 150-160℃, keep it at a constant temperature for 2-3 hours until the polymerization reaction is complete, and demold after natural cooling to room temperature to obtain a self-lubricating cast nylon blank. S5. Post-processing: The self-lubricating cast nylon blank is annealed to eliminate internal stress, and then machined to obtain the self-lubricating cast nylon product. The annealing process conditions are: temperature 80-100℃, holding time 4-6h.

8. The method for preparing a self-lubricating cast nylon containing a ternary block internal lubricant according to claim 7, characterized in that: In step S1, the high-speed mixing process conditions are: temperature 80-100℃, rotation speed 300-500r / min, and mixing time 10-15min; the temperature settings for each section of the twin-screw extruder are: feed section 160-165℃, melting section 170-175℃, die head section 175-180℃, and screw rotation speed 200-300r / min.

9. The method for preparing a self-lubricating cast nylon containing a ternary block internal lubricant according to claim 7, characterized in that: In step S2, the process conditions for vacuum drying of caprolactam monomer are: temperature 80-100℃, vacuum degree -0.08~-0.09MPa, and drying time 2-3h.

10. The method for preparing a self-lubricating cast nylon containing a ternary block internal lubricant according to claim 7, characterized in that: In step S3, the heat preservation and stirring time after adding the ternary block intra-block lubricant particles is 30-40 min; the stirring reaction time after adding the catalyst is 15-20 min; and the rapid stirring time after adding the co-catalyst is 5-10 min.

Images