Low-density polyethylene resin for pharmaceutical packaging material and method for preparing the same

Abstract

The application belongs to the technical field of high polymer materials, and discloses a low-density polyethylene resin for medicine packaging materials and a preparation method thereof. 3 ~0.930g / cm 3 , a melt flow rate is 0.1-1.5 g / 10 min, and a n-hexane extract is less than or equal to 1.1 wt%. The polyethylene resin of the application generates little low-molecular-weight polyethylene component in the preparation process, reduces residual solvent oil, greatly reduces the content of the n-hexane extract, meets the requirements of medicine packaging materials, and can be applied to the fields of medical and health products, personal care products, food packaging and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a low-density polyethylene resin for pharmaceutical packaging materials and its preparation method. Background Technology

[0002] Low-density polyethylene (LDPE) resin possesses excellent flexibility and transparency, stable chemical properties, good processability, high degree of automation in production, and ease of transportation, making it widely used in pharmaceutical packaging. Hexane extract content is an important hygiene indicator for LDPE used in pharmaceutical packaging materials. It indicates substances that can be extracted from pharmaceuticals or oils in food. GB4806.6-2016 stipulates that the hexane extract content of food-grade LDPE resin should be ≤2%. Excessive hexane extract can affect the safety of pharmaceuticals. LDPE hexane extract mainly consists of short-chain, low-molecular-weight polyethylene oligomers, and their content is the main factor affecting the hexane extract content.

[0003] LDPE resin is produced using a high-pressure tubular or batch process. Under the initiation of an initiator, ethylene undergoes free radical polymerization under high temperature and pressure. This production process results in LDPE having a low density, a wide molecular weight distribution, and a high proportion of low molecular weight components. In addition, the initiator is formulated into a solution using alkane solvent oil. The residual solvent oil has a low molecular weight and is easily dissolved by n-hexane, just like polyethylene oligomers. This makes LDPE unable to meet the requirements for pharmaceutical packaging materials.

[0004] Chinese patent application CN 117402274 A discloses a low-density polyethylene resin for food packaging bottle caps. The resin is prepared by adding a compound of two peroxides and compressed air as an initiator and propionaldehyde as a modifier to a first reactor, and then adding compressed air as an initiator and propionaldehyde as a modifier to a second reactor. The polymerization reaction is carried out at 310–330℃ and 240–270 MPa pressure, resulting in a density of 0.919–0.924 g / cm³. 3 The melt flow rate was 5–9 g / 10 min, and the hexane extract content was 1.4–1.8%. Although the hexane extract content was reduced to some extent, it was necessary to further reduce the hexane extract content and melt flow rate in order to further improve the safety and strength of pharmaceutical packaging materials. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a low-density polyethylene resin for pharmaceutical packaging materials and its preparation method. This polyethylene resin has low oligomer content and residual solvent oil, low hexane extract content, and low melt flow rate, thereby improving the safety and strength of pharmaceutical packaging materials and meeting the requirements of pharmaceutical packaging.

[0006] This invention provides a method for preparing low-density polyethylene resin for pharmaceutical packaging materials, which employs a tubular high-pressure polymerization process and includes the following steps:

[0007] (1) Ethylene gas is compressed by the front and rear compressors and divided into mainstream and side feed gas. The pressure of mainstream feed gas is 260-285 MPa and the temperature is 85-105℃, while the pressure of side feed gas is 230-255 MPa and the temperature is 75-95℃.

[0008] (2) The main feed gas, peroxide, catalyst air and modifier propionaldehyde enter the first tubular reactor for polymerization reaction. The polymerization temperature is controlled at 300-320℃, the pressure is controlled at 268-285MPa, and the reaction time is controlled at 7-8 seconds.

[0009] (3) The side-flow feed gas, peroxide, catalyst air and modifier propionaldehyde are fed into the second tubular reactor along with the material after the reaction in step (2) to carry out the polymerization reaction. The reaction temperature is 280-310℃, the reaction pressure is 236-255MPa, and the reaction time is 11-12 seconds.

[0010] (4) The material after the reaction in step (3) is sent to the third tubular reactor for another polymerization reaction. The reaction temperature is 270-300℃, the reaction pressure is 225-245MPa, and the reaction time is 11-13 seconds.

[0011] (5) After the reaction in step (4) is completed, the material is sent to the cooler and rapidly cooled by chilled water. After cooling, the temperature is 200-250℃ and the pressure is 28-30MPa. Then, it is sent to the high-pressure product separator and the low-pressure product separator in sequence to separate the ethylene gas from the molten polyethylene material. Finally, the molten polyethylene is sent to the extruder for extrusion granulation to obtain the polyethylene resin.

[0012] The peroxide mentioned is a low-temperature peroxide.

[0013] The materials remaining after the reaction in step (2) include polyethylene and unreacted ethylene.

[0014] The materials remaining after the reaction in step (3) include polyethylene, unreacted ethylene, unreacted first initiator, unreacted second initiator, and unreacted modifier.

[0015] The materials remaining after the reaction in step (4) include molten polyethylene and ethylene.

[0016] Preferably, the low-temperature peroxide is tert-butylperoxypentyl ester (TBPV).

[0017] Preferably, the peroxide and IP solvent (isoparaffin solvent oil) are prepared into a solution and then added to the tubular reactor. The tert-butylperoxypentanoate and IP solvent are prepared into a solution with a concentration of 13-16 wt%, more preferably 13.5-15.5 wt%.

[0018] Preferably, in the first tubular reactor, based on the mainstream feed gas, the amount of peroxide added is 40-80 ppm; the amount of catalyst air added is 250-500 ppm; and the amount of the modifier propionaldehyde added is 200-450 ppm.

[0019] Preferably, in the second tubular reactor, based on the side-flow feed gas, the amount of peroxide added is 0-80 ppm; the amount of catalyst air added is 250-500 ppm; and the amount of the modifier propionaldehyde added is 0-360 ppm.

[0020] Preferably, in step (1), the pressure of the main feed gas is 272-278 MPa and the temperature is 90-95°C, and the pressure of the side feed gas is 240-246 MPa and the temperature is 85-90°C.

[0021] Preferably, in step (2), the polymerization temperature is 305-320℃ and the pressure is 268-280MPa; in the first tubular reactor, the amount of peroxide added is 55-65ppm, the amount of catalyst air added is 350-400ppm, and the amount of the modifier propionaldehyde added is 350-400ppm.

[0022] Preferably, in step (3), the reaction temperature is 285-310°C and the pressure is 236-250 MPa; in the second tubular reactor, the amount of peroxide added is 0-45 ppm, the amount of catalyst air added is 320-360 ppm, and the amount of the modifier propionaldehyde added is 0 ppm.

[0023] Preferably, in step (4), the reaction temperature is 275–300°C and the reaction pressure is 225–242 MPa;

[0024] Preferably, in step (5), the temperature after cooling is 210-245°C.

[0025] The present invention also provides a low-density polyethylene resin for pharmaceutical packaging materials prepared by the preparation method described above, having a density of 0.920 g / cm³. 3 ~0.930g / cm 3 The melt flow rate is 0.1–1.5 g / 10 min, and the n-hexane extract content is ≤1.1 wt%.

[0026] This invention also provides the application of the low-density polyethylene resin for pharmaceutical packaging materials, wherein the polyethylene resin meets the requirements for pharmaceutical packaging materials and can be applied to fields such as medical and health products, personal care products, and food packaging.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] Compared with the prior art, the present invention adopts a three-stage reactor. Through the optimization and adjustment of temperature, pressure, modifier, initiator and their formulation, and the rapid cooling of the material by chilled water in the aftercooler after the reaction, the low-density polyethylene resin of the present invention forms very little low molecular weight polyethylene component and residual solvent oil during the preparation process, which significantly reduces the content of n-hexane extract and melt flow rate, and meets the requirements of pharmaceutical packaging materials. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions in this application, the present invention will be further described below with reference to embodiments. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0030] Examples 1-3

[0031] The preparation steps for Example 1 are as follows:

[0032] (1) The initiator peroxide is prepared into a solution by low-temperature peroxide tert-butylperoxypentyl ester (TBPV) and IP solvent, with a concentration of 13.5-14 wt%.

[0033] (2) Ethylene gas is compressed by the front and rear compressors and divided into mainstream and side feed gas. The pressure of mainstream feed gas is 272-278 MPa and the temperature is 90-95℃, while the pressure of side feed gas is 240-246 MPa and the temperature is 85-90℃.

[0034] (3) The mainstream feed gas, initiator and modifier enter the first tubular reactor for polymerization reaction. The polymerization temperature is controlled at 310-315℃, the pressure is 272-278MPa, and the reaction time is 7-8 seconds. Based on the mainstream feed gas ethylene, the initiator peroxide content is 55-65ppm, the initiator catalyst air content is 350-400ppm, and the modifier propionaldehyde content is 350-400ppm.

[0035] (4) The side-flow feed gas, initiator and modifier are fed into the second tubular reactor along with the polyethylene and ethylene in the first tubular reactor to carry out the polymerization reaction. The reaction temperature is 295-305℃, the reaction pressure is 240-246MPa, and the reaction time is 11-12 seconds. Based on the ethylene in the side-flow feed gas, the peroxide content of the fresh initiator is 35-45ppm, the catalyst air content of the fresh initiator is 320-360ppm, and the propionaldehyde content of the fresh modifier is 0ppm.

[0036] (5) The polyethylene and unreacted ethylene in the second tubular reactor are fed into the third tubular reactor along with the initiator and modifier for a second polymerization reaction. The reaction temperature is 285-295℃, the reaction pressure is 232-238MPa, and the reaction time is 11-13 seconds. Fresh initiator peroxide, fresh initiator catalyst air, and fresh modifier propionaldehyde are not added.

[0037] (6) The polyethylene and ethylene in the third tubular reactor are sent to the cooler and rapidly cooled by chilled water. After cooling, the temperature is 235-245℃ and the pressure is 29-30MPa. Then, the molten polyethylene and ethylene are sent to the high-pressure product separator and the low-pressure product separator in sequence to separate the gas and the material. Finally, the molten polyethylene is sent to the extruder for extrusion granulation to prepare low-density polyethylene resin for pharmaceutical packaging materials.

[0038] The preparation steps for Examples 2 and 3 are the same as those for Example 1, except that:

[0039] Example 2: In the first, second, and third tubular reactors, the reaction temperatures were 315–320°C, 305–310°C, and 295–300°C, respectively. Everything else was the same as in Example 1.

[0040] Example 3: In the first, second, and third tubular reactors, the reaction temperatures were 305–310°C, 285–295°C, and 275–285°C, respectively. Everything else was the same as in Example 1.

[0041] In Examples 1-3, the polymerization reaction temperature was adjusted, and the melt flow rate and density changed slightly. The n-hexane extract content in this example was low, as shown in Table 1.

[0042] Examples 4-5

[0043] The preparation steps for Examples 4 and 5 are the same as those for Example 1, except that:

[0044] Example 4: In the first, second, and third tubular reactors, the reaction pressures were 275–280 MPa, 244–250 MPa, and 235–242 MPa, respectively. Everything else was the same as in Example 1.

[0045] Example 5: In the first, second, and third tubular reactors, the reaction pressures were 268–272 MPa, 236–242 MPa, and 225–232 MPa, respectively. Everything else was the same as in Example 1.

[0046] In Examples 4 and 5, the polymerization reaction pressure was adjusted, and the melt flow rate and density changed slightly. The content of n-hexane extract in this example was low, as shown in Table 1.

[0047] Example 6

[0048] The preparation steps of Example 6 are the same as those of Example 1, except that the amount of initiator added in step (4) is as follows: based on ethylene, the peroxide content of the initiator is 0 ppm, so that the reaction temperature of the second reactor is reduced to 285-300°C, while the reaction pressure remains at 240-246 MPa; the air content of the initiator catalyst remains at 320-360 ppm. Everything else is the same as in Example 1.

[0049] In Example 6, the amount of peroxide added in the second tubular reactor was adjusted, resulting in slight changes in melt flow rate and density. The content of n-hexane extract in this example was low, as shown in Table 1.

[0050] Example 7

[0051] The preparation steps for Example 7 are the same as those for Example 1, except for step (1):

[0052] The initiator peroxide, namely tert-butylperoxypentanoate, and IP solvent were prepared into a solution with a concentration of 15.0-15.5%. Everything else was the same as in Example 1.

[0053] Example 7: The concentration of peroxide was adjusted. In this example, the content of n-hexane extract was low, as shown in Table 1.

[0054] Example 8

[0055] The preparation steps of Example 8 are the same as those of Example 1, except that the temperature of the aftercooler in step (6) is 230-240°C and the pressure is 28-29 MPa. The rest is the same as that of Example 1.

[0056] Example 8 adjusted the temperature and pressure of the cooler. This example has a low content of n-hexane extract, as shown in Table 1.

[0057] Comparative Example 1

[0058] The preparation steps for Comparative Example 1 are as follows:

[0059] (a) The low-temperature initiator peroxide is prepared into a solution by mixing tert-butyl peroxypentyl ester with IP solvent, with a concentration of 11.5 to 12.0 wt%; the high-temperature initiator peroxide is prepared into a solution by mixing di-tert-butyl peroxide (DTBP) with IP solvent, with a concentration of 0.4 to 0.6 wt%.

[0060] (b) Ethylene gas is compressed by the front and rear compressors and divided into mainstream and side feed gas. The pressure of mainstream feed gas is 264-268 MPa and the temperature is 90-95℃, while the pressure of side feed gas is 232-236 MPa and the temperature is 85-90℃.

[0061] (c) The main feed gas, initiator and modifier enter the first tubular reactor for polymerization reaction, and the polymerization temperature is controlled at 320-325℃ and the pressure is 264-268MPa; based on ethylene, the peroxide content of the low-temperature initiator is 55-65ppm, the air content of the initiator catalyst is 700-1000ppm, and the propylene content of the modifier is 1400-1800ppm;

[0062] (d) The side-flow feed gas, initiator, and modifier are fed into the second tubular reactor along with the polyethylene and ethylene in the first tubular reactor for polymerization. The reaction temperature is 310–320°C and the reaction pressure is 232–236 MPa. Based on ethylene, the peroxide content of the fresh low-temperature initiator is 35–45 ppm, the catalyst air content of the fresh initiator is 1200–1800 ppm, and the propylene content of the fresh modifier is 900–1300 ppm.

[0063] (e) After the material in the second tubular reactor has finished reacting, it is sent to the third tubular reactor. At the same time, the high-temperature initiator peroxide is also sent to the third tubular reactor for a second polymerization reaction. The reaction temperature is 300-310°C and the reaction pressure is 215-225 MPa. Based on ethylene, the content of high-temperature initiator peroxide is 1-5 ppm. Fresh low-temperature initiator peroxide, fresh initiator catalyst air, and fresh modifier propylene are not added.

[0064] (f) The polyethylene and ethylene in the third tubular reactor are sent to the aftercooler and cooled by circulating water. After cooling, the temperature is 255-265℃ and the pressure is 30-31MPa. Then, the molten polyethylene and ethylene are sent to the high-pressure product separator and the low-pressure product separator in sequence to separate the gas and the material. Finally, the molten polyethylene is sent to the extruder for extrusion granulation to prepare low-density polyethylene resin.

[0065] Comparative Example 1 used conventional process parameters and had a high content of n-hexane extract, as shown in Table 1.

[0066] Comparative Example 2

[0067] The preparation steps of Comparative Example 2 are the same as those of Comparative Example 1, except that the modifier used is propionaldehyde from Example 1. The amount of propionaldehyde injected into the first tubular reactor and the second tubular reactor is 300-350 ppm. The amount of initiator catalyst air added is adjusted accordingly, also using Example 1, that is, the content of initiator catalyst air in the first tubular reactor is 350-400 ppm, and the content of initiator catalyst air in the second tubular reactor is 320-360 ppm. Everything else is the same as Comparative Example 1.

[0068] Comparative Examples 3-4

[0069] The preparation steps of Comparative Example 3 are the same as those of Comparative Example 1, except that the reaction temperature is the same as that of Example 1.

[0070] The preparation steps of Comparative Example 4 are the same as those of Comparative Example 1, except that the reaction pressure is the same as that of Example 1.

[0071] Comparative Example 5

[0072] The preparation steps of Comparative Example 5 are the same as those of Comparative Example 1, except that the concentration of the initiator tert-butylperoxypentanoate is the same as in Example 1, while the rest are the same as those of Comparative Example 1.

[0073] Comparative Example 6

[0074] The preparation steps of Comparative Example 6 are the same as those of Comparative Example 1, except that in step (f), the aftercooler is changed from circulating water cooling to chilled water cooling, with a temperature of 285-300℃ and a pressure of 28.6-29.8MPa. The rest is the same as Comparative Example 1.

[0075] Table 1 shows a comparison of the performance of the polyethylene resins in each embodiment and comparative example.

[0076] In this invention, the testing standards and methods for polyethylene are as follows:

[0077] Density: Tested according to GB / T1033.2-2010;

[0078] Melt flow rate: tested according to GB / T3682.1-2018;

[0079] n-Hexane extract: tested according to GB4806.6-2016.

[0080] Table 1 Comparison of Polyvinylhexane Extract Content

[0081] sample Melt flow rate g / 10min <![CDATA[Density g / cm 3 > hexane extract wt% Example 1 0.30 0.9243 0.96 Example 2 0.32 0.9241 1.03 Example 3 0.29 0.9244 0.95 Example 4 0.28 0.9245 0.90 Example 5 0.31 0.9240 1.06 Example 6 0.27 0.9249 0.82 Example 7 0.30 0.9245 0.93 Example 8 0.30 0.9244 0.94 Comparative Example 1 0.30 0.9198 3.21 Comparative Example 2 0.30 0.9228 1.95 Comparative Example 3 0.28 0.9203 2.78 Comparative Example 4 0.29 0.9206 2.63 Comparative Example 5 0.30 0.9200 3.03 Comparative Example 6 0.29 0.9202 2.82

[0082] As shown in Table 1, the low-density polyethylene (LDPE) produced using conventional process parameters in Comparative Example 1 had a hexane extract content far exceeding the ≤2wt% specified in GB4806.6-2016. Based on Comparative Example 1, the inventors, through experimentation with process parameters and raw materials at each step (e.g., Comparative Examples 2-6), found that using only the process parameters or raw materials of this invention could reduce the hexane extract content to a lesser extent, achieving only minor results. It can also be seen that a significant reduction in the hexane extract content is the result of the combined effect of multiple process parameters and raw materials.

[0083] Therefore, the pharmaceutical packaging material of the present invention uses low-density polyethylene resin to generate very little low molecular weight polyethylene component, reduces residual solvent oil, and significantly reduces the content of n-hexane extract, which meets the requirements of pharmaceutical packaging materials and can be safely used in medical and health products, personal care products, food packaging and other fields.

Claims

1. A method for preparing low-density polyethylene resin for pharmaceutical packaging materials, comprising a tubular high-pressure polymerization process, characterized in that, Includes the following steps: (1) Ethylene gas is compressed by the front and rear compressors and divided into mainstream and side feed gas. The pressure of mainstream feed gas is 260-285 MPa and the temperature is 85-105℃, while the pressure of side feed gas is 230-255 MPa and the temperature is 75-95℃. (2) The main feed gas, peroxide, catalyst air and modifier propionaldehyde enter the first tubular reactor for polymerization reaction. The polymerization temperature is controlled at 300-320℃, the pressure is controlled at 268-285MPa, and the reaction time is controlled at 7-8 seconds. In the first tubular reactor, based on the mainstream feed gas, the amount of peroxide added is 40-80 ppm, the amount of catalyst air added is 250-500 ppm, and the amount of the modifier propionaldehyde added is 200-450 ppm. (3) The side-flow feed gas, peroxide, catalyst air and modifier propionaldehyde are fed into the second tubular reactor along with the material after the reaction in step (2) to carry out the polymerization reaction. The reaction temperature is 280-310℃, the reaction pressure is 236-255MPa, and the reaction time is 11-12 seconds. In the second tubular reactor, based on the side-flow feed gas, the amount of peroxide added is 0-80 ppm, the amount of catalyst air added is 250-500 ppm, and the amount of the modifier propionaldehyde added is 0-360 ppm. (4) The material after the reaction in step (3) is sent to the third tubular reactor for another polymerization reaction. The reaction temperature is 270-300℃, the reaction pressure is 225-245MPa, and the reaction time is 11-13 seconds. (5) After the reaction in step (4) is completed, the material is sent to the cooler and rapidly cooled by chilled water. After cooling, the temperature is 200-250℃ and the pressure is 28-30MPa. Then, it is sent to the high-pressure product separator and the low-pressure product separator in sequence to separate the ethylene gas from the molten polyethylene material. Finally, the molten polyethylene is sent to the extruder for extrusion granulation to obtain the polyethylene resin. The peroxide mentioned is a low-temperature peroxide.

2. The preparation method according to claim 1, characterized in that, The low-temperature peroxide is tert-butylperoxypentanoate.

3. The preparation method according to claim 2, characterized in that, The tert-butylperoxypentanoate was prepared into a solution with IP solvent, and the concentration was 13-16 wt%.

4. The preparation method according to claim 3, characterized in that, The concentration of the solution is 13.5-15.5 wt%.

5. The preparation method according to claim 1, characterized in that, In step (1), the pressure of the main feed gas is 272-278 MPa and the temperature is 90-95°C, and the pressure of the side feed gas is 240-246 MPa and the temperature is 85-90°C.

6. The preparation method according to claim 1, characterized in that, In step (2), the polymerization temperature is 305-320℃ and the pressure is 268-280MPa; in the first tubular reactor, the amount of peroxide added is 55-65ppm, the amount of catalyst air added is 350-400ppm, and the amount of the modifier propionaldehyde added is 350-400ppm.

7. The preparation method according to claim 1, characterized in that, In step (3), the reaction temperature is 285-310℃ and the pressure is 236-250MPa; in the second tubular reactor, the amount of peroxide added is 0-45ppm, the amount of catalyst air added is 320-360ppm, and the amount of the modifier propionaldehyde added is 0ppm.

8. The preparation method according to claim 1, characterized in that, In step (4), the reaction temperature is 275–300°C and the reaction pressure is 225–242 MPa; In step (5), the temperature after cooling is 210-245℃.

9. A low-density polyethylene resin for pharmaceutical packaging materials prepared by the preparation method according to any one of claims 1-8, characterized in that, The density of the polyethylene resin is 0.920 g / cm³. 3 ~0.930g / cm 3 The melt flow rate is 0.1–1.5 g / 10 min, and the n-hexane extract content is ≤1.1 wt%.

10. An application of the low-density polyethylene resin for pharmaceutical packaging materials as described in claim 9, characterized in that, The polyethylene resin described meets the requirements for pharmaceutical packaging materials and can be used in fields such as medical and health products, personal care products, and food packaging.