Injection molding grade nylon 6 slice as well as preparation method and application thereof

Abstract

The invention relates to an injection molding grade nylon 6 slice and a preparation method and application thereof, and relates to the technical field of new materials. According to the injection molding grade nylon 6 slice, monobasic acid is added as a molecular weight stabilizer in the caprolactam hydrolysis ring-opening polymerization process, the finally prepared slice has better viscosity stability, and the flowing property of a nylon melt is improved.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to injection-molded nylon 6 chips, their preparation methods, and applications. Background Technology

[0002] Nylon 6 is widely used in engineering plastics due to its excellent mechanical properties, self-lubricating properties, chemical stability, and good molding and processing performance. However, during injection molding, pure nylon 6 resin, due to its strong molecular polarity, easy formation of hydrogen bonds between molecular chains, and hygroscopic properties, faces difficulties in demolding from metal molds, making it difficult to meet the requirements of rapid prototyping, dimensional stability, and smooth surface finish. To overcome these shortcomings, in the development of new injection-grade nylon 6 chips, modifying agents are added to shorten the injection molding cycle, reduce energy consumption, and meet the injection molding requirements of complex-shaped parts. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for preparing injection-grade nylon 6 chips. In this method, a monobasic acid is added as a molecular weight stabilizer during the hydrolytic ring-opening polymerization of caprolactam. The resulting chips exhibit superior viscosity stability, thereby improving the flow properties of the nylon melt.

[0004] This invention provides a method for preparing injection-grade nylon 6 chips, comprising the following steps: melting caprolactam and mixing it with a monobasic acid having a carboxyl group to obtain a mixture; adding a ring-opening agent and carrying out a hydrolysis ring-opening polymerization reaction to obtain a polymer melt; cooling and pelletizing to obtain polymer particles; extracting and drying to obtain base material nylon 6 chips; adding additives and blending to obtain injection-grade nylon 6 chips.

[0005] After extraction and drying, the base material nylon 6 chips are added to a blending device and thoroughly mixed with a certain proportion of additives such as dispersants, antioxidants, lubricants, and nucleating agents. After thorough mixing, the additives and the base material nylon 6 chips achieve a stable, uniform, and tight bond, yielding injection-grade nylon 6 chips. During the injection molding process of injection-grade nylon 6 chips, the nylon mixed with additives reduces the coefficient of friction between the product and the mold surface. This not only means better surface finish but also reduces mold opening force and ejection force. Due to the higher crystallinity and crystallization rate of the product, the surface solidifies and hardens faster, allowing for demolding at higher temperatures, shortening the injection molding cycle, improving production efficiency, and reducing the scrap rate.

[0006] In one embodiment, the monocarboxylic acid having a carboxyl group includes at least one of acetic acid and benzoic acid, and the ring-opening agent includes deoxygenated desalinated water. In the raw materials for preparing the base material nylon 6 chips, the mass ratio of the monobasic acid is (0.5~5):1000, the mass ratio of the ring-opening agent is (1~3):100, and the balance is caprolactam.

[0007] In one embodiment, the additive includes at least one of a dispersant, an antioxidant, a lubricant, or a nucleating agent; In the raw materials for preparing injection-grade nylon 6 chips, the mass ratio of the additive is 1‰-3%, and the remainder is the base material nylon 6 chips.

[0008] In one embodiment, the hydrolysis ring-opening polymerization reaction is achieved using a VK tubular polymerization reactor.

[0009] In one embodiment, the hydrolytic ring-opening polymerization reaction includes: adding the mixture to a VK-shaped polymerization reactor, adding a ring-opening agent, heating the upper part of the VK-shaped polymerization reactor to 250-260°C to carry out a ring-opening reaction and an addition polymerization reaction, carrying out a polycondensation reaction in the middle and lower part of the VK-shaped polymerization reactor, and the hydrolytic ring-opening polymerization reaction reaching an equilibrium state in the lower part of the VK-shaped polymerization reactor to obtain a polymer melt.

[0010] During the aforementioned hydrolysis-ring-opening polymerization reaction, caprolactam in the VK tube undergoes ring-opening, addition polymerization, and condensation polymerization. Simultaneously, the monocarboxylic acid also participates in the polymerization reaction, its carboxyl groups condensing with the amino groups in the resulting macromolecular chains, thus sealing some of the active amino groups. The upper tube heater in the polymerization tube primarily provides sufficient heat for the ring-opening reaction of caprolactam, with the process temperature controlled at 250-260℃. In addition to the ring-opening reaction, the addition polymerization reaction also occurs simultaneously, and the acidic additive catalyzes and promotes the reaction rate. In the lower middle part of the VK tube, the polymerization reaction gradually reaches equilibrium. At this point, the heat released by the condensation polymerization reaction is carried out of the reaction system by the low-temperature heat transfer oil (235-245℃) circulating within the coil. Lowering the temperature facilitates the exothermic reaction, not only shifting the condensation polymerization reaction towards the formation of large-molecule polymers but also resulting in a more uniform molecular weight distribution. After the equilibrium reaction, a homogeneous polymer melt is obtained. This nylon polymer has a certain viscosity and better viscosity stability.

[0011] After the reaction is complete, the polymer melt is discharged through the casting strip holes, cooled in a water bath, and then cut into cylindrical particles by a pelletizer. Since the polymer still contains 8%-10% unreacted monomers when the polymerization reaction reaches equilibrium, the residual monomers need to be removed in an extraction tower using hot demineralized water. The extracted chips are then dried in a drying tower using countercurrent nitrogen gas to ensure that the final chip moisture content is less than 600 ppm.

[0012] The present invention also provides injection-grade nylon 6 chips obtained by the preparation method described above.

[0013] The present invention also provides the application of the aforementioned injection-grade nylon 6 chips in injection-molded products.

[0014] An injection molded part, the raw material for which the injection molded part is prepared includes: the injection-grade nylon 6 chips.

[0015] The present invention also provides a method for preparing the injection molded part, comprising the following steps: adding the injection-grade nylon 6 chips into an injection molding machine and performing injection molding to obtain the injection molded part.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention relates to injection-grade nylon 6 chips, their preparation method, and applications. The injection-grade nylon 6 chips are prepared by adding a monobasic acid as a molecular weight stabilizer during the caprolactam hydrolysis ring-opening polymerization process. The resulting chips exhibit superior viscosity stability, improving the flow properties of the nylon melt. The nylon melt, after being cast, cooled, pelletized, extracted, and dried, is fed into a mixing device and thoroughly mixed with added antioxidants, lubricants, nucleating agents, and other molding and processing aids. This eliminates the need for subsequent twin-screw extrusion modification.

[0017] The injection-grade nylon 6 chips obtained by this method can be directly used in injection molding machines, which improves the crystallization speed and demolding speed of the injection molding process, shortens the injection cycle, increases the strength and modulus of the product, and improves the color stability, while not affecting its chemical corrosion resistance and improving production efficiency. Attached Figure Description

[0018] Figure 1 This is a production flow diagram of the injection-molded nylon 6 chips of the present invention. Detailed Implementation

[0019] To facilitate understanding of the present invention, a more complete description will be given below with reference to relevant embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] Unless otherwise specified, all reagents, materials, and equipment used in this embodiment are commercially available; unless otherwise specified, all test methods are conventional test methods in this field.

[0022] Example 1 I. An injection-molding grade nylon 6 chip and its preparation method.

[0023] The specific preparation method is as follows: Caprolactam is melted and mixed with a monobasic acid containing carboxyl groups to obtain a mixture. This mixture is then added to a VK-type polymerization reactor, where hot deoxygenated and desalinated water is used as a ring-opening agent to carry out a hydrolytic ring-opening polymerization reaction. In the VK tube, caprolactam undergoes ring-opening, addition polymerization, and condensation polymerization reactions. Simultaneously, the monobasic acid also participates in the polymerization reaction; its own carboxyl groups undergo condensation reactions with the amino groups in the resulting macromolecular chains, sealing some of the active amino groups. The mass of the deoxygenated and desalinated water accounts for approximately 1%-3% of the raw material mass for preparing nylon 6 chips, and the mass of the monobasic acid additives (such as acetic acid, benzoic acid, etc.) accounts for approximately 0.5‰-5‰ of the raw material mass for preparing nylon 6 chips, depending on the process conditions and product performance indicators.

[0024] The upper tube heater of the VK tubular polymerization reactor mainly provides sufficient heat for the ring-opening reaction of caprolactam. The process temperature is controlled at 250-260℃. In addition to the ring-opening reaction, the addition polymerization reaction is also carried out simultaneously. The monocarboxylic acid additive has a catalytic promoting effect on the reaction rate.

[0025] In the lower middle part of the VK tube, the polymerization reaction gradually reaches an equilibrium state. At this time, the heat released by the polycondensation reaction is carried out of the reaction system by the low-temperature heat transfer oil (235-245℃) circulating in the coil. Lowering the temperature is conducive to the exothermic reaction, which not only promotes the polycondensation reaction to move towards the formation of large molecular polymers, but also makes the molecular weight distribution more uniform. After the equilibrium reaction, a uniform polymer melt is obtained. This nylon polymer has a certain viscosity and better viscosity stability.

[0026] After the reaction is complete, the polymer melt is discharged through the casting strip holes, cooled in a water bath, and then cut into cylindrical particles by a pelletizer. Since the polymer still contains 8%-10% unreacted monomers when the polymerization reaction reaches equilibrium, the residual monomers need to be removed in an extraction tower using hot demineralized water. The extracted chips are then dried in a drying tower using countercurrent nitrogen gas to ensure the final chip moisture content is less than 600 ppm, yielding nylon 6 chips made from the base material.

[0027] In this embodiment, the monocarboxylic acid with a carboxyl group is acetic acid, the mass of which is 1‰ of the mass of the raw material for preparing nylon 6 chips, the mass of the ring-opening agent is 1.5% of the mass of the raw material for preparing nylon 6 chips, and the remaining raw material is caprolactam.

[0028] The nylon 6 chips prepared above are added to a blending apparatus and thoroughly mixed with a certain proportion of dispersants, antioxidants, lubricants, nucleating agents, and other additives to obtain injection-grade nylon 6 chips. These chips can be directly used for injection molding to obtain injection-molded parts.

[0029] In the raw materials for preparing injection-grade nylon 6 chips, the proportion of each additive is about 1‰-1%, and the remainder is base material nylon 6 chips. After thorough mixing, the additives and base material nylon 6 chips achieve a stable, uniform and tight bond.

[0030] During the injection molding process of injection-grade nylon 6 chips, the addition of additives to the injection-grade nylon 6 chips can reduce the coefficient of friction between the injection molded product and the mold surface. This not only means better surface finish, but also reduces mold opening force and ejection force. Due to the higher crystallinity and crystallization rate of the product, the product surface solidifies and hardens faster, and demolding can be performed at higher temperatures, shortening the injection molding cycle, improving production efficiency, and reducing scrap rate.

[0031] In this embodiment, the additives include dispersants, antioxidants, lubricants, nucleating agents, etc. The mass of dispersants, antioxidants, lubricants, and nucleating agents accounts for 1‰ of the mass of the raw materials used to prepare the injection molded parts, and the remainder is nylon 6 chips as the base material.

[0032] Experimental Example The injection-grade nylon 6 slices prepared in Example 1 were tested.

[0033] I. Detection methods.

[0034] Test method for slice quality indicators: FZ / T 51004-2011; The test methods for each mechanical performance index are shown below.

[0035] II. Test Results.

[0036] 1. Section quality indicators: (1) Relative viscosity: 2.53; (2) Hot water extractable content: 0.3%; (3) Moisture content: 0.03%; (4) Terminal amino value: 37.8 mmol / Kg; (5) Terminal carboxyl group value: 58 mmol / Kg.

[0037] 2. DSC thermal analyzer test results: (1) Crystallization peak temperature: 171.89℃; (2) Melting point: 221.88℃; (3) Crystallinity: 31.24%.

[0038] 3. Mechanical property test results: (1) Melt index: 35 g / 10 min; Test method: GB / T 3682, (230℃, 2.16 kg) (2) Tensile strength: 72 MPa; Test method: GB / T 1040 (3) Elongation at break: 38%; Test method: GB / T 1040 (4) Tensile modulus: 1980 MPa; Test method: GB / T 1040 (5) Bending strength: 104 MPa; Test method: GB / T 9341 (6) Flexural modulus: 2322 MPa; Test method: GB / T 9341 (7) Notched impact strength: 5 KJ / m²; Test method: GB / T 1843 (8) Shore hardness: 75; Test method: GB / T 2411 (9) Molding shrinkage: parallel to the fluid direction: 1.29%, perpendicular to the fluid direction: 0.79%; test method: GB / T15585.

[0039] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0040] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. 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 all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing injection-molding grade nylon 6 chips, characterized in that, The process includes the following steps: melting caprolactam and mixing it with a monocarboxylic acid with a carboxyl group to obtain a mixture; adding a ring-opening agent and carrying out a hydrolysis ring-opening polymerization reaction to obtain a polymer melt; cooling and pelletizing to obtain polymer particles; extracting and drying to obtain base material nylon 6 chips; adding additives and blending to obtain injection-grade nylon 6 chips.

2. The preparation method according to claim 1, characterized in that, The monocarboxylic acid having a carboxyl group includes at least one of acetic acid and benzoic acid, and the ring-opening agent includes deoxygenated desalinated water. In the raw materials for preparing the base material nylon 6 chips, the mass ratio of the monobasic acid is (0.5~5):1000, the mass ratio of the ring-opening agent is (1~3):100, and the balance is caprolactam.

3. The preparation method according to claim 1, characterized in that, The additives include at least one of dispersants, antioxidants, lubricants, or nucleating agents; In the raw materials for preparing injection-grade nylon 6 chips, the mass ratio of the additive is 1‰-3%, and the remainder is the base material nylon 6 chips.

4. The preparation method according to claim 1, characterized in that, The hydrolysis ring-opening polymerization reaction is achieved through a VK tubular polymerization reactor.

5. The preparation method according to claim 4, characterized in that, The hydrolytic ring-opening polymerization reaction includes: adding the mixture to a VK-shaped polymerization reactor, adding a ring-opening agent, heating the upper part of the VK-shaped polymerization reactor to 250-260°C to carry out ring-opening and addition polymerization reactions, carrying out polycondensation reactions in the middle and lower parts of the VK-shaped polymerization reactor, and the hydrolytic ring-opening polymerization reaction reaching equilibrium in the lower part of the VK-shaped polymerization reactor to obtain a polymer melt.

6. Injection-molding grade nylon 6 chips obtained by the preparation method according to any one of claims 1-5.

7. The application of the injection-grade nylon 6 chips as described in claim 6 in injection-molded products.

8. An injection molded part, characterized in that, The raw materials for preparing the injection molded part include: the injection-grade nylon 6 chips as described in claim 6.

9. The method for preparing the injection molded part according to claim 8, characterized in that, The process includes the following steps: adding the injection-grade nylon 6 chips as described in claim 8 into an injection molding machine for injection molding to obtain an injection-molded part.

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