Polycaprolactam as well as preparation method and application thereof

Abstract

The invention relates to the field of polymers, and discloses polycaprolactam as well as a preparation method and application thereof, the number-average molecular weight of the polycaprolactam is 30000-40000 Da, and the molecular weight distribution index is 2.5-4; the melt index of the polycaprolactam under the conditions that the temperature is 230 DEG C and the weight is 2.16 kg is 30 to 60 g / 10 min; the crystallization temperature of the polycaprolactam is 180 to 190 DEG C; the relative viscosity of the polycaprolactam is 2 to 4; wherein the testing temperature of the relative viscosity of the polycaprolactam is 25 DEG C, the solvent is 96wt% sulfuric acid, and the concentration of the polycaprolactam is 0.005 g / mL. The polycaprolactam has the advantages of wide molecular weight distribution, high crystallization temperature, higher relative viscosity, high melt index, favorable flowability and high processability.

Description

Technical Field

[0001] The present invention relates to the field of polymers, and in particular to polycaprolactam and a preparation method and application thereof. Background Art

[0002] High-flow, fast-molding nylon has the advantages of short molding cycle and easy demolding. Compared with traditional nylon, it improves the demolding success rate of injection molded parts and reduces the time required for injection molding, which can greatly increase the production efficiency of injection molding plants. It will be widely used in electronic appliances, fasteners, clips, connectors, cams, housings, industrial parts, cable ties and cable ties, especially for large and thin-walled glass fiber reinforced products.

[0003] To further improve nylon's fluidity and other properties, most manufacturers currently melt-blend and extrude nylon chips with fluidity additives, as exemplified by the technical solutions disclosed in CN116675980A, CN109627752A, and CN114437383A. Because these additives require a large amount to achieve the desired fluidity improvement, the addition of these additional components can affect the material's inherent mechanical properties, making the modified nylon material unsuitable for complex, high-strength applications.

[0004] CN103980485A discloses a technical solution for preparing nylon powder by slurry polymerization. However, this technical solution is a high-temperature polycondensation slurry polymerization technical route, which has high viscosity, poor fluidity, and high manufacturing cost. Summary of the Invention

[0005] In order to overcome the problem that the polycaprolactam provided in the prior art cannot simultaneously have high processability and high mechanical strength, the present invention provides a polycaprolactam and a preparation method and application thereof. The polycaprolactam has a wide molecular weight distribution and a high crystallization temperature, and has a high relative viscosity and a high melt index, good fluidity and high processability.

[0006] In order to achieve the above object, the first aspect of the present invention provides a polycaprolactam, wherein the number average molecular weight of the polycaprolactam is 30000-40000 Da and the molecular weight distribution index is 2.5-4;

[0007] The melt index of the polycaprolactam at 230° C. and 2.16 kg is 30-60 g / 10 min;

[0008] The crystallization temperature of the polycaprolactam is 180-190°C;

[0009] The relative viscosity of the polycaprolactam is 2-4;

[0010] The test temperature for the relative viscosity of polycaprolactam is 25° C., the solvent is 96 wt % sulfuric acid, and the polycaprolactam concentration is 0.005 g / mL.

[0011] A second aspect of the present invention provides a method for preparing polycaprolactam, comprising the following steps:

[0012] (1) In the presence of an inert solvent, caprolactam, a catalyst, and an activator are mixed to form a mixture, and the mixture is reacted under heating conditions;

[0013] (2) reducing the temperature of the reaction system by 20-80°C at a rate of 0.2-4°C / min, separating, drying, and quenching the catalyst to obtain polycaprolactam.

[0014] The third aspect of the present invention provides a polycaprolactam prepared by the method provided by the second aspect of the present invention.

[0015] The fourth aspect of the present invention provides a use of the polycaprolactam provided by the first and third aspects of the present invention in injection molding or 3D printing.

[0016] The beneficial technical effects of the present invention are:

[0017] The polycaprolactam provided by the present invention has a wide molecular weight distribution and a high crystallization temperature, and has a high relative viscosity and a high melt index, good fluidity and high processability.

[0018] Anionic slurry polymerization processes generally produce polymers with narrow molecular weight distribution. The polycaprolactam preparation method provided by the present invention improves the existing anionic slurry polymerization process. By controlling the cooling rate, polycaprolactam with a wide molecular weight distribution and a high crystallization temperature is obtained. In addition, the polycaprolactam has a high relative viscosity and a high melt index, good fluidity, and high processability.

[0019] Furthermore, the present invention can further broaden the molecular weight distribution of polycaprolactam by optimizing the stirring characteristic torque at the start of temperature reduction, thereby further improving the mechanical strength and processability of polycaprolactam. DETAILED DESCRIPTION

[0020] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0021] In the present invention, unless otherwise specified, pressure refers to absolute pressure.

[0022] The first aspect of the present invention provides a polycaprolactam having a number average molecular weight of 30,000-40,000 Da and a molecular weight distribution index of 2.5-4;

[0023] The melt index of the polycaprolactam at 230° C. and 2.16 kg is 30-60 g / 10 min;

[0024] The crystallization temperature of the polycaprolactam is 180-190°C;

[0025] The relative viscosity of the polycaprolactam is 2-4;

[0026] The test temperature for the relative viscosity of polycaprolactam is 25° C., the solvent is 96 wt % sulfuric acid, and the polycaprolactam concentration is 0.005 g / mL.

[0027] The polycaprolactam provided by the present invention has a wide molecular weight distribution and a high crystallization temperature, and has a high relative viscosity and a high melt index, good fluidity and high processability.

[0028] According to a preferred embodiment of the present invention, the number average molecular weight of the polycaprolactam is 32,000-38,000 Da, and the molecular weight distribution index is 2.5-3.

[0029] In the present invention, when the number average molecular weight and the molecular weight distribution index of the polycaprolactam are within the above ranges, the polycaprolactam has better fluidity and higher mechanical strength.

[0030] According to the present invention, preferably, the polycaprolactam has a melt index of 35-50 g / 10 min at 230° C. and 2.16 kg.

[0031] In the present invention, when the melt index of the polycaprolactam is within the above range, the processability of the polycaprolactam is further improved.

[0032] According to the present invention, preferably, the crystallization temperature of the polycaprolactam is 180-185°C.

[0033] According to the present invention, preferably, the relative viscosity of the polycaprolactam is 2.5-3.5.

[0034] According to a preferred embodiment of the present invention, the tensile strength of the polycaprolactam is 70-80 MPa.

[0035] More preferably, the tensile strength of the polycaprolactam is 75-80 MPa.

[0036] According to the present invention, preferably, the elongation at break of the polycaprolactam is 35-60%.

[0037] More preferably, the elongation at break of the polycaprolactam is 50-60%.

[0038] A second aspect of the present invention provides a method for preparing polycaprolactam, comprising the following steps:

[0039] (1) In the presence of an inert solvent, caprolactam, a catalyst, and an activator are mixed to form a mixture, and the mixture is reacted under heating conditions;

[0040] (2) reducing the temperature of the reaction system by 20-80°C at a rate of 0.2-4°C / min, separating, drying, and quenching the catalyst to obtain polycaprolactam.

[0041] In the polycaprolactam preparation method provided by the present invention, polycaprolactam with a wide molecular weight distribution and a high crystallization temperature is obtained by controlling the cooling rate, and the polycaprolactam has a high relative viscosity and a high melt index, good fluidity and high processability.

[0042] According to a preferred embodiment of the present invention, the cooling rate in step (2) is 0.5-2°C / min.

[0043] In the present invention, when the cooling rate is within the above range, polycaprolactam with a more suitable molecular weight distribution can be obtained, and has more balanced mechanical strength and processability.

[0044] According to the present invention, preferably, the temperature of the reaction system is lowered by 30-50°C in step (2).

[0045] According to the present invention, preferably, the catalyst is selected from at least one of alkali metals, alkali metal hydrides, alkali metal alkyl compounds, alkali metal hydroxides and alkali metal alkoxides.

[0046] More preferably, the catalyst is an alkali metal hydride, such as NaH, KH.

[0047] According to the present invention, preferably, the mass ratio of the catalyst to caprolactam is 0.05-0.2:100.

[0048] In the present invention, when the mass ratio of the catalyst to caprolactam is within the above range, the number average molecular weight and relative viscosity of polycaprolactam can be better balanced, thereby better balancing its mechanical strength and processability.

[0049] More preferably, the mass ratio of the catalyst to caprolactam is 0.05-0.1:100.

[0050] According to the present invention, preferably, the activator is selected from at least one of nitrogen acetyl caprolactam, isocyanate, acid anhydride and acid chloride.

[0051] More preferably, the activator is an isocyanate, such as toluene diisocyanate (TDI).

[0052] According to the present invention, preferably, the mass ratio of the activator to caprolactam is 0.1-0.3:100.

[0053] In the present invention, when the mass ratio of the activator to caprolactam is within the above range, the reaction rate and the number average molecular weight of polycaprolactam can be better balanced.

[0054] According to a preferred embodiment of the present invention, in step (1), the reaction temperature is 120-160° C. and the pressure is 0.6-1 MPa.

[0055] According to the present invention, preferably, the caprolactam is dehydrated and has a water content of no more than 50 ppm.

[0056] More preferably, the water content of the caprolactam does not exceed 30 ppm.

[0057] The present invention does not particularly limit the specific method of dehydration, and those skilled in the art can routinely select. According to the present invention, specifically, the dehydration temperature is 100-120°C, the pressure is 5-10 kPa, and the time is 30-60 minutes.

[0058] The present invention does not particularly limit the specific type of the inactive solvent, and those skilled in the art can routinely select. According to the present invention, specifically, the inactive solvent is selected from C6-C 20 At least one of alkanes, paraffin, white oil and vaseline oil. 20 The alkane may be at least one of n-hexane, cyclohexane, n-heptane, n-nonane, toluene and p-xylene.

[0059] According to the present invention, preferably, the mass ratio of the caprolactam to the inactive solvent is 1:0.8-1.6.

[0060] In the present invention, when the mass ratio of the caprolactam to the inactive solvent is within the above range, the mixture has a more suitable viscosity, is easy to process, and can further improve the yield of polycaprolactam.

[0061] More preferably, the mass ratio of the caprolactam to the inactive solvent is 1:1-1.2.

[0062] According to a preferred embodiment of the present invention, the reaction is carried out under continuous stirring, and the temperature of the reaction system is reduced when 0.05≤T0≤0.07;

[0063] T0 is the characteristic torque of the stirring, and its expression is shown in formula (I):

[0064]

[0065] Wherein, T is the stirring torque, Nm;

[0066] ρ is the density of the mixture, kg / m 3 ;

[0067] d is the stirring diameter, m;

[0068] N is the stirring speed, rps.

[0069] In the present invention, the stirring torque T can be monitored in real time by a torque sensor.

[0070] The mixture density ρ can be measured online by a vibration densitometer, a differential pressure densitometer, an ultrasonic densitometer, etc.

[0071] The stirring diameter d has the conventional meaning in the art, that is, the diameter of the circle formed by the rotation of the stirring blade.

[0072] The stirring speed N can be monitored in real time by a magnetic induction sensor, a Hall effect sensor, etc., or output by a stirring motor frequency converter.

[0073] The present invention does not limit the specific stirring diameter and stirring speed, which can be adjusted according to the specific size of the reaction apparatus, as long as the characteristic stirring torque T0 meets the above range. In the present invention, when T0 is within the above range, the molecular weight distribution of the polycaprolactam can be further improved, resulting in a polycaprolactam with higher mechanical strength and processability.

[0074] More preferably, 0.055≤T0≤0.065.

[0075] According to the present invention, preferably, in step (2), the temperature of the reaction system is lowered to 80-100°C.

[0076] The present invention does not particularly limit the specific method of separation, and those skilled in the art can routinely select. According to the present invention, specifically, the separation is centrifugal separation at a rotation speed of 100-120 rpm for 3-5 min.

[0077] The present invention does not particularly limit the specific drying method, and those skilled in the art can routinely select. According to the present invention, specifically, the drying temperature is 100-120° C. and the drying time is 6-8 hours.

[0078] The present invention does not particularly limit the specific method of quenching the catalyst, and those skilled in the art can routinely select. According to the present invention, specifically, the method of quenching the catalyst is to mix polycaprolactam with 6-10 times its mass of water, shake and wash, repeat three times, and further dry at 100-110°C for 8-10 hours.

[0079] According to the present invention, specifically, the polycaprolactam prepared by the method is a powder, and the median particle size of the polycaprolactam powder is 100-200 μm.

[0080] According to a specific embodiment of the present invention, the method for preparing polycaprolactam comprises the following steps:

[0081] The temperatures of kettles A and B are adjusted to the first temperature, and the caprolactam is divided into two parts. One part of the caprolactam is dehydrated in kettle A and then the catalyst is added thereto, while the other part of the caprolactam is dehydrated in kettle B and then the activator is added thereto.

[0082] The inactive solvent is preheated in kettle C.

[0083] The materials in kettles A and B are added to kettle C. After the temperature is raised to the second temperature, the temperature is maintained for reaction. When the characteristic torque of the stirring reaches the target value, the temperature of the reaction system is reduced by 20-80°C at a rate of 0.2-4°C / min. The catalyst is separated, dried, and quenched to obtain polycaprolactam.

[0084] In the present invention, the specific implementation method can improve production efficiency.

[0085] More specifically, the inactive solvent is preheated to a temperature 20-30° C. below its boiling point.

[0086] More specifically, before the materials in kettles A and B are added to kettle C, vacuum is applied to remove small molecular by-products.

[0087] The third aspect of the present invention provides a polycaprolactam prepared by the method provided by the second aspect of the present invention.

[0088] The fourth aspect of the present invention provides a use of the polycaprolactam provided by the first and third aspects of the present invention in injection molding or 3D printing.

[0089] The present invention will be described in detail below through examples.

[0090] In the following examples, the water content of caprolactam was determined by Karl Fischer titration;

[0091] The relative viscosity of polycaprolactam was determined according to GB / T 12006.1-2009 using an Ubbelohde viscometer, 96 wt% sulfuric acid as the solvent, and a polycaprolactam concentration of 0.005 g / mL.

[0092] The tensile strength and elongation at break are determined according to GB / T 1040.2-2022, at a test temperature of 23°C.

[0093] The melt index was measured using a melt indexer at 230°C and 2.16 kg;

[0094] The crystallization temperature was determined by differential scanning calorimetry (DSC);

[0095] The molecular weight distribution was determined by gel permeation chromatography (GPC) to obtain the number average molecular weight (M n ) and weight average molecular weight (M w ), calculate the molecular weight distribution index (PDI);

[0096] In the present invention, PDI=M w / M n ;

[0097] The median particle size of the polycaprolactam powder was measured by a laser particle size analyzer.

[0098] Unless otherwise specified, all reagents and raw materials were purchased from commercial sources.

[0099] Examples 1-9

[0100] The preparation method of polycaprolactam is as follows:

[0101] (1-1) 500 g of caprolactam was added to kettle A, and 500 g of caprolactam was added to kettle B. Both kettles A and B were heated to 100° C., stirred continuously, and vacuumed to maintain a pressure of 5 kPa until the water content of the caprolactam did not exceed 50 ppm.

[0102] (1-2) Adjust the temperature of kettles A and B to the first temperature, add the catalyst NaOH to kettle A, and add the activator to kettle B. Continue stirring kettles A and B while evacuating the mixture and allow the reaction to proceed for 60 minutes.

[0103] Add the inert solvent into kettle C, stir and heat to a temperature 20°C below the boiling point.

[0104] (1-3) Nitrogen is introduced into kettles A and B, pressurizing them to 0.6 MPa. The materials in kettles A and B are then passed into kettle C. The materials in kettle C are continuously stirred, heated to the second temperature, and then maintained at this temperature for reaction.

[0105] (2) When the characteristic torque of stirring reaches the target value, the temperature is lowered to 100°C, the material is discharged, and centrifuged at 100 rpm for 5 minutes, and then dried in a vacuum oven at 100°C for 6 hours. The dried material is extracted three times with 8 times the mass of 100°C water and dried again in a forced air drying oven at 110°C for 8 hours to obtain polycaprolactam powder.

[0106] In the above preparation method, the specific types and amounts of the catalyst, activator and inactive solvent are shown in Table 1; the first temperature, the second temperature, the characteristic torque target value and the cooling rate are shown in Table 2.

[0107] Table 1

[0108]

[0109] Table 2

[0110] First temperature (℃) Second temperature (℃) Characteristic torque target value Cooling rate (℃ / min) Example 1 120 140 0.055 0.67 Example 2 120 140 0.06 0.67 Example 3 120 140 0.065 0.67 Example 4 120 140 0.06 0.67 Example 5 120 140 0.055 0.67 Example 6 120 140 0.06 1 Example 7 120 140 0.06 1 Example 8 120 140 0.065 2 Example 9 120 140 0.065 2

[0111] Comparative Example 1

[0112] Polycaprolactam chips are prepared using conventional hydrolysis ring-opening polymerization process:

[0113] Add 400g of caprolactam, 20g of deionized water, 6g of phosphoric acid, 4g of aminocaproic acid, and 0.8g of adipic acid to a reactor. Evacuate to 5kPa at 20°C, then fill with nitrogen to 0.1MPa. Repeat this process three times. Then, fill with nitrogen to 0.1MPa, heat to 100°C, and start stirring.

[0114] The temperature was then raised to 190°C and maintained for 2 hours; then to 210°C and maintained for 3 hours; and finally to 240°C and maintained for 3 hours. The pressure was then released to atmospheric pressure, nitrogen purging was initiated, and stirring was continued. After the characteristic torque reached 0.3, the mixture was vacuumed to 5 kPa and stirring was continued. After the characteristic torque reached 0.6, the mixture was pulled into strands and pelletized. Extraction was then performed with 8 times the mass of 100°C water for 8 hours. This process was repeated twice, and the mixture was dried at 110°C for 8 hours to obtain polycaprolactam chips.

[0115] Comparative Example 2

[0116] Polycaprolactam was prepared according to the method of Example 2, except that in step (2), the cooling rate was 10°C / min.

[0117] Test Case

[0118] The physicochemical parameters and performance parameters of the polycaprolactam powders obtained in the above examples and comparative examples were measured, and the results are shown in Table 3.

[0119] Table 3

[0120]

[0121] The results in Table 3 show that the polycaprolactam prepared by the method provided by the present invention has a wide molecular weight distribution and a high crystallization temperature, and has a high relative viscosity and a high melt index, good fluidity and high processability.

[0122] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A polycaprolactam, characterized in that The number average molecular weight of the polycaprolactam is 30,000-40,000 Da, and the molecular weight distribution index is 2.5-4; The melt index of the polycaprolactam at 230° C. and 2.16 kg is 30-60 g / 10 min; The crystallization temperature of the polycaprolactam is 180-190°C; The relative viscosity of the polycaprolactam is 2-4; The test temperature for the relative viscosity of polycaprolactam is 25° C., the solvent is 96 wt % sulfuric acid, and the polycaprolactam concentration is 0.005 g / mL.

2. The polycaprolactam according to claim 1, characterized in that The number average molecular weight of the polycaprolactam is 32000-38000 Da, and the molecular weight distribution index is 2.5-3; Preferably, the polycaprolactam has a melt index of 35-50 g / 10 min at 230° C. and 2.16 kg; Preferably, the crystallization temperature of the polycaprolactam is 180-185°C; Preferably, the relative viscosity of the polycaprolactam is 2.5-3.

5.

3. The polycaprolactam according to claim 1 or 2, characterized in that The tensile strength of the polycaprolactam is 70-80 MPa; Preferably, the elongation at break of the polycaprolactam is 35-60%.

4. A method for preparing polycaprolactam, characterized in that: The method comprises the following steps: (1) In the presence of an inert solvent, caprolactam, a catalyst, and an activator are mixed to form a mixture, and the mixture is reacted under heating conditions; (2) reducing the temperature of the reaction system by 20-80°C at a rate of 0.2-4°C / min, separating, drying, and quenching the catalyst to obtain polycaprolactam.

5. The method according to claim 4, characterized in that The cooling rate in step (2) is 0.5-4°C / min; Preferably, in step (1), the catalyst is selected from at least one of alkali metals, alkali metal hydrides, alkali metal alkyl compounds, alkali metal hydroxides and alkali metal alkoxides; Preferably, the mass ratio of the catalyst to caprolactam is 0.05-0.2:100; Preferably, the activator is selected from at least one of nitrogen acetyl caprolactam, isocyanate, acid anhydride and acid chloride; Preferably, the mass ratio of the activator to caprolactam is 0.1-0.3:

100.

6. The method according to claim 4 or 5, characterized in that In step (1), the reaction temperature is 120-160° C. and the pressure is 0.6-1 MPa; Preferably, the caprolactam is dehydrated and has a water content of no more than 50 ppm; Preferably, the dehydration temperature is 100-120° C., the pressure is 5-10 kPa, and the time is 30-60 min.

7. The method according to any one of claims 4 to 6, characterized in that The inactive solvent is selected from C6-C 20 at least one of alkanes, paraffins, white oils, and vaseline oil; Preferably, the mass ratio of the caprolactam to the inactive solvent is 100:80-160.

8. The method according to any one of claims 4 to 7, characterized in that The reaction is carried out under continuous stirring, and the temperature of the reaction system is lowered when 0.05≤T0≤0.07; T0 is the characteristic torque of the stirring, and its expression is shown in formula (I): Wherein, T is the stirring torque, Nm; ρ is the density of the mixture, kg / m 3 ; d is the stirring diameter, m; N is the stirring speed, rps; Preferably, in step (2), the temperature of the reaction system is lowered to 80-100°C.

9. A polycaprolactam prepared by the method according to any one of claims 4 to 8.

10. Use of the polycaprolactam according to any one of claims 1 to 3 and claim 9 in injection molding or 3D printing.

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