A method for preparing low-warpage nylon 12 powder suitable for rotational molding

Abstract

The present invention discloses a method for preparing nylon 12 powder for rotational molding. The method comprises the following steps: copolymerizing maleic anhydride with olefin monomers in an anhydrous and oxygen-free environment to obtain copolymer A; prepolymerizing laurolactam and an amine end-capping agent in a prepolymerization reactor to obtain prepolymer B; reacting copolymer A, prepolymer B, a catalyst, an antioxidant, and an end-capping agent to produce copolymer C; granulating copolymer C to obtain copolymerized nylon 12 slices, and then cryogenically crushing, separating, drying, and sieving the nylon 12 slices to obtain nylon 12 powder suitable for rotational molding. Copolymerized nylon 12 prepared from maleic anhydride-olefin copolymer and nylon 12 polyamide effectively solves the problem of warping and deformation in rotational molded products.

Description

Technical Field

[0001] The invention belongs to the field of materials, and in particular relates to a method for preparing low-warpage nylon 12 powder that can be used for rotational molding. Background Art

[0002] Rotomolding is a thermoplastic molding process. Rotomolded products are characterized by their light weight, low cost, ease of processing, and simple installation. They are widely used in everyday life, for example in water tanks, storage tanks, and manholes. The basic principle of rotomolding is to add resin powder to a mold. The mold is then heated to above the melting point of the resin powder and rotated continuously. Under the influence of gravity, the resin powder in the mold continuously contacts the entire interior of the mold, gradually melting and evenly coating and adhering to the inner surface of the mold, forming it into the same shape as the mold. Finally, a series of steps, including cooling, demolding, and finalizing the shape, produce the final rotomolded product.

[0003] During the heating process, the temperature gradually decreases from the mold surface toward the interior. During the cooling process, the cooling rate of the plastic part inside the mold is much lower than that outside the mold. For amorphous materials, the cooling rate has little impact. However, for crystalline resins such as nylon 12, the difference in cooling rate can lead to differences in crystallinity between the inner and outer layers, causing internal stress in the cylinder and making it prone to cracking and breakage. Furthermore, for large parts, the difference in crystallinity leads to different shrinkage rates, which can cause warping.

[0004] CN1036392A discloses a method for granulating a rotomoulding base material by adding 1% to 50% filler to improve the rigidity (tensile strength) of the material and reduce shrinkage. Theoretically, this method of directly adding filler will significantly reduce the toughness of the material, resulting in a brittle product.

[0005] Chinese Patent 200810023368.4 improves the material by adding a cross-linking material through a blending modification method. Although the cross-linking material can reduce the crystallization rate, it is difficult to disperse it in the powder and cannot achieve a uniform effect. It does not fundamentally solve the problem of the material's own characteristics. Summary of the Invention

[0006] This invention aims to address the warping problem of nylon rotationally molded products. A new material has been developed. By modifying the molecular structure of nylon 12, and thereby changing the motion of its molecular chains, this new material reduces its crystallization rate while improving its toughness and impact resistance. This allows for a constant cooling time and minimizes the difference in crystallinity between the inner and outer layers of the product. The resulting product exhibits high impact strength, good toughness, and a smooth, warp-free appearance.

[0007] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0008] A method for preparing low-warpage nylon 12 powder that can be used for rotational molding comprises the following steps:

[0009] 1) Maleic anhydride and olefin monomers are added to a reaction kettle, dissolved in a solvent in an anhydrous and oxygen-free environment, heated to a certain temperature, and polymerized under the action of an initiator to obtain a maleic anhydride olefin copolymer.

[0010] 2) In a prepolymerization reactor, laurolactam, an amine end-capping agent, and water are subjected to a melt prepolymerization reaction to obtain a nylon 12 prepolymer.

[0011] 3) The maleic anhydride olefin copolymer, nylon 12 prepolymer, antioxidant, catalyst and end-capping agent are subjected to polycondensation reaction to form a copolymer, which is then cooled and granulated to obtain copolymerized nylon 12 particles.

[0012] 4) Slicing, crushing, drying, and sieving the copolymerized nylon 12 particles to obtain nylon 12 powder that can be used for rotational molding.

[0013] Furthermore, in step 1), the molar content of maleic anhydride is 0%-50% and is not 0;

[0014] The olefin monomer is selected from at least one of ethylene, propylene, 1-butene, 1-octene, and styrene;

[0015] The solvent is preferably cyclohexanone;

[0016] The initiator is one or both of azobisisobutyronitrile and dibenzoyl peroxide, and the amount of the initiator is 0.1-3% of the total mass of maleic anhydride and olefin monomer, preferably 0.6-1.0%;

[0017] The polymerization temperature is 50-100°C, preferably 70-80°C, and the polymerization time is 1-8 hours, preferably 2-3 hours.

[0018] Furthermore, in step 2), the amine end-capping agent is at least one of butanediamine, pentamethylenediamine, hexamethylenediamine, decanediamine, dodecanediamine, p-phenylenediamine, and m-phenylenediamine;

[0019] Melt prepolymerization temperature is 240-290°C, preferably 260-280°C, and the time is 0.5-10h, preferably 3-6h;

[0020] The amount of water added is about 5-25% of the mass of laurolactam, preferably 10-15%;

[0021] The molecular weight of the obtained nylon 12 prepolymer is between 1,000 and 60,000, preferably between 10,000 and 50,000.

[0022] Furthermore, in step 3), the reaction of the maleic anhydride olefin copolymer and the nylon 12 prepolymer (molar ratio 1:1) is carried out in a reactive screw extruder at a processing temperature of 200-300° C., preferably 250-290° C., for 1-10 min, preferably 5-8 min;

[0023] The catalyst is one or more of phosphoric acid, phosphorous acid, hypophosphorous acid, sodium phosphate, and sodium hypophosphite, and the amount of the catalyst is 0.1-1.0% of the total mass of the maleic anhydride olefin copolymer and the nylon 12 prepolymer, preferably 0.1-0.4%;

[0024] The antioxidant is one or more of 1010, 1098, 245, 168, and T10, and the amount of the antioxidant is 0.1-1.0% of the total mass of the maleic anhydride olefin copolymer and the nylon 12 prepolymer, preferably 0.2-0.5%;

[0025] The end-capping agent is one or more of acetic acid, benzoic acid, and lauric acid, and the amount of the end-capping agent is 0.01-1.0% of the total mass of the maleic anhydride olefin copolymer and the nylon 12 prepolymer, preferably 0.1-0.6%;

[0026] Furthermore, in step 4), the powder making process is a cryogenic pulverization method, and requires drying and screening treatment. The powder particle size D10 is 30-110 microns, D98 is 300-800 microns, preferably D10 is 30-50 microns, and D98 is 500-600 microns.

[0027] The nylon powder prepared by the present invention can be used as a rotational molding material.

[0028] The beneficial effects of the present invention are:

[0029] 1. The present invention forms a new molecular structure by inserting maleic anhydride olefin copolymer into the molecular structure of nylon 12, so that nylon 12 has anti-warping function. The obtained nylon 12 powder can be used for rotational molding. The powder can improve the impact resistance of the parts, improve the appearance regularity of the parts, and improve the yield rate.

[0030] 2. The post-polymerization process adopts reactive extrusion technology, which greatly shortens the production process and improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a comparative example of a conventional PA12 rotationally molded product;

[0032] Figure 2 This is a diagram of a low-warpage nylon 12 rotationally molded product according to an embodiment;

[0033] Figure 3 This is the comparative example nylon 12 powder image;

[0034] Figure 4 This is an image of low-warpage nylon 12 powder from the example. DETAILED DESCRIPTION

[0035] The present invention will be further described below through specific examples. The examples of the present invention are only for illustration of the present invention and do not limit the scope of the present invention.

[0036] In the embodiment of the present invention, maleic anhydride styrene copolymer and nylon 12 prepolymer are used as examples for experiments.

[0037] [Example 1]

[0038] 1) adding 0.8% by mass of dibenzoyl peroxide to 1041.50 g, 833.5 g, 624.9 g, 416.6 g, and 104.15 g of styrene, respectively, and preparing the above five mixtures into 20% concentration cyclohexanone solutions, and adding them into a reaction kettle;

[0039] Prepare a 20% cyclohexanone solution with 98.06g of maleic anhydride and add it to the dropping tank;

[0040] The entire reaction apparatus and its pipelines were purged with high-purity nitrogen for 20 minutes. The temperature of the entire apparatus was maintained at 80°C. After the temperature stabilized, the material in the dropping tank was slowly added dropwise to the reactor. The reaction was terminated after 5 hours. The obtained reactants were precipitated and separated, and the precipitate was washed three times with ether and granulated to obtain five different maleic anhydride styrene copolymers. Each of the five different maleic anhydride styrene copolymers was prepared in duplicate.

[0041] 2) To a prepolymerization reactor, 50,000 g, 40,000 g, 30,000 g, 20,000 g, and 10,000 g of laurolactam were added, respectively, followed by 172.3 g of decanediamine and 10% pure water by mass of the laurolactam. The reaction was heated to 260° C. and allowed to react for 5 hours. The pressure was then released under vacuum for 2 hours before discharging the reaction mixture to obtain five different nylon 12 prepolymers. Five portions of each of the five prepolymers were prepared repeatedly.

[0042] 3) The above maleic anhydride styrene copolymer and nylon 12 prepolymer were mixed in equal parts (as shown in Table 1) to form 25 combinations. To each of the 25 combinations, 0.3% of the total mass of an antioxidant (1098:168 = 1:1 mixture), 0.1% of the total mass of a catalyst sodium hypophosphite, and 0.3% of the total mass of a capping agent benzoic acid were added. The reaction temperature was set to 260° C., the screw residence time was 8 min, and nylon 12 copolymer particles were obtained after cooling and granulation.

[0043] 4) The obtained nylon 12 slices are cryogenically crushed, dried, and sieved to obtain a powder with a particle size range of D98 of 500-600 μm and D10 of 30-60 μm.

[0044] [Comparative Example 1]

[0045] The commonly used homopolymer nylon 12 resins on the market (Evonik L1670, L1940, L2140) were added with an antioxidant accounting for 0.3% of the total mass (1098:168=1:1 mixture), mixed evenly and then added to a reactive screw extruder at a uniform speed. The reaction temperature was set to 260°C and the screw residence time was 8 minutes. After cooling and granulation, nylon 12 homopolymer resin particles were obtained.

[0046] The obtained nylon 12 homopolymer resin particles are cryogenically crushed, dried, and sieved to obtain a powder having a particle size range of D98 of 500-600 microns and D10 of 30-60 microns.

[0047] Performance testing:

[0048] The nylon powder prepared in the embodiment (styrene dosage 833.5 g / prepolymer theoretical value Mn30000) and the comparative example (L1940) is as follows Figure 4 / Figure 3 As shown in the figure, it can be seen that the powder edge of the present invention has a tough and broken morphology, the powder has high light transmittance and low crystallinity, indicating that it has strong anti-warping and impact resistance. Figure 2 / Figure 1 As shown, it can be seen that Figure 2 The appearance is smooth.

[0049] The nylon powder obtained above was subjected to a warpage angle test. The test method was as follows: equal weight of powder was added to the same square mold and flattened. The mold was coated with a release coating. The sample was placed in a nitrogen-protected oven and heated to 240°C for 30 minutes. After slowly cooling to room temperature, the sample was removed and the angle between the sample and the horizontal plane was measured. The following experimental results were obtained:

[0050] Table 1 Warping angle of the product in the embodiment (°)

[0051]

[0052]

[0053] Table 2 Warping angle of comparative products (°)

[0054] Comparative grade L1670 L1940 L2140 Warping angle 8 7 7

[0055] After the above tests, the samples were cut and made into standard specimens according to the requirements of ISO 527, and then mechanical properties were tested. The following experimental results were obtained:

[0056] Table 3 Example product modulus (MPa)

[0057] Styrene dosage g / prepolymer theoretical value Mn 1041.5 833.5 624.9g 416.6 104.15 50000 1180 1220 1260 1320 1376 40000 1099 1120 1180 1299 1359 30000 1002 1050 1129 1280 1341 20000 946 990 1099 1222 1320 10000 880 935 1002 1180 1302

[0058] Table 4 Comparative Example Product Modulus (MPa)

[0059] Comparative grade L1670 L1940 L2140 Modulus 1400 1400 1450

[0060] The nylon 12 copolymer particles obtained in the example (styrene dosage 833.5 g / prepolymer theoretical value Mn 30000) were cryogenically crushed and dried. The powder was then sieved using sieves with pore sizes of 300, 400, 500, 600, and 700 μm to obtain powders with increasing particle sizes D98 and D10 of 30-60 μm. Samples were then prepared for warpage angle testing using the same sample preparation method as above. The following experimental results were obtained:

[0061] Table 5 Effect of crushed particle size on warpage of rotomolded products

[0062] Screen aperture (micrometer) 300 400 500 600 700 Powder D98 (micron) About 300-400 About 400-500 About 500-600 About 600-700 About 700-800 Warping angle 1° 1° 1° 1° 2°

[0063] Increasing the sieve aperture can improve powder yield. Experimental results show that when the sieve aperture is larger than 600 microns, the warpage angle increases. Therefore, to improve powder yield without affecting warpage, it is necessary to select an appropriate sieve aperture.

[0064] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing low-warpage nylon 12 powder that can be used for rotational molding, comprising the following steps: 1) polymerizing maleic anhydride and olefin monomers under the action of an initiator to obtain a maleic anhydride-olefin copolymer; 2) performing melt prepolymerization reaction of laurolactam, an amine end-capping agent, and water to obtain a nylon 12 prepolymer; 3) reacting maleic anhydride olefin copolymer, nylon 12 prepolymer, antioxidant, catalyst, and end-capping agent to form a copolymer, cooling and granulating to obtain copolymerized nylon 12 particles; wherein, The molar ratio of maleic anhydride olefin copolymer to nylon 12 prepolymer is 1:

1.

2. The preparation method according to claim 1, wherein The following steps are also included: 4) Slicing, crushing, drying, and sieving the copolymerized nylon 12 particles to obtain nylon 12 powder that can be used for rotational molding.

3. The preparation method according to claim 1, wherein In step 1), the molar content of maleic anhydride is 0%-50% and is not 0.

4. The preparation method according to claim 1, wherein In step 1), the olefin monomer is at least one of ethylene, propylene, 1-butene, 1-octene, and styrene.

5. The preparation method according to claim 1, wherein In step 1), the polymerization temperature is 50-100° C. and the polymerization time is 1-8 hours.

6. The preparation method according to claim 1, wherein In step 2), the amine end-capping agent is at least one of butanediamine, pentamethylenediamine, hexamethylenediamine, decanediamine, dodecanediamine, p-phenylenediamine, and m-phenylenediamine.

7. The preparation method according to claim 1, wherein In step 2), the amount of water added is 5-25% of the mass of laurolactam.

8. The preparation method according to claim 1, wherein In step 1), the melt prepolymerization temperature is 240-290° C. and the time is 0.5-10 h.

9. The preparation method according to any one of claims 1 to 8, wherein In step 2), the molecular weight of the obtained nylon 12 prepolymer is between 1000 and 60000.

10. The preparation method according to claim 1, wherein Step 3) is carried out in a reactive screw extruder at a processing temperature of 200-300° C. for 1-10 minutes.

11. The preparation method according to claim 1, wherein In step 3), the catalyst is one or more of phosphoric acid, phosphorous acid, hypophosphorous acid, sodium phosphate, and sodium hypophosphite. The antioxidant is one or more of 1010, 1098, 245, 168, and T10.

12. The preparation method according to claim 11, wherein In step 3), the amount of the catalyst is 0.1-1.0% of the total mass of the maleic anhydride olefin copolymer and the nylon 12 prepolymer; the amount of the antioxidant is 0.1-1.0% of the total mass of the maleic anhydride olefin copolymer and the nylon 12 prepolymer.

13. The preparation method according to any one of claims 1, 10-12, wherein In step 3), the end-capping agent is one or more of acetic acid, benzoic acid, and lauric acid. The amount of the end-capping agent used is 0.01-1.0% of the total mass of the maleic anhydride olefin copolymer and the nylon 12 prepolymer.

14. The preparation method according to claim 13, wherein In step 3), the amount of the end-capping agent is 0.1-0.6% of the total mass of the maleic anhydride olefin copolymer and the nylon 12 prepolymer.

15. The preparation method according to any one of claims 1 to 2, wherein: In step 4), the powder particle size D10 is 30-110 microns, and D98 is 300-800 microns.

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