Special resin for low-odor high-density polyethylene food-grade bottle cap and preparation method thereof

Abstract

The invention discloses a low-odor high-density polyethylene food-grade resin special for bottle caps and a preparation method thereof, the low-odor high-density polyethylene food-grade resin special for bottle caps is prepared from the following materials in parts by mass: 100 parts of polyethylene powder, 0.1-0.3 part of a composite antioxidant, 0.03-0.05 part of a high-efficiency catalyst, ethylene and hydrogen, the low-odor high-density polyethylene food-grade resin is obtained by performing catalytic polymerization on a butene-1 comonomer in a solvent, and the high-efficiency catalyst is used. When the polyethylene resin with narrow molecular weight distribution is produced, low polymers are removed in the polymerization process; five-stage solvent separation is adopted, and the content of solvent volatile components in final powder is controlled to be 300 ppm or below; the molecular weight and distribution of the granular resin are accurately controlled, and meanwhile, low-molecular polymers generated by temperature rise and shear degradation in the extrusion granulation process are reduced, so that the low-odor high-density polyethylene bottle cap material resin is obtained.

Description

Technical Field

[0001] The invention relates to a resin and a preparation method thereof, and more specifically to a low-odor high-density polyethylene food-grade bottle cap special resin and a preparation method thereof, belonging to the technical field of petrochemical-polyethylene materials. Background Art

[0002] The market demand for polyethylene food-grade bottle cap materials is increasing day by day. In addition to the increasing requirements for mechanical properties and processing properties, the requirements for odor are also getting higher and higher. For example, food packaging, beverage packaging, pharmaceutical packaging, cosmetic packaging and other fields require strict low odor indicators. The main sources of polyethylene resin odor are solvent volatilization, degradation of oligomers during processing, and additives. The polyethylene food-grade bottle caps on the market currently have odors brought in by solvents, additives and oligomers, resulting in the disadvantages of polyethylene raw materials having strong odor and poor sensory properties. Therefore, the research on polyethylene bottle cap raw materials is of great significance to the preparation process, downstream product processing and other aspects. Summary of the invention

[0003] In order to solve the above-mentioned problems of the prior art, the present invention provides a low-odor high-density polyethylene food-grade bottle cap special resin and a preparation method thereof, which have the technical characteristics of being able to reduce the odor brought into the polyethylene resin by the antioxidant, and due to its extremely high antioxidant property, the prepared polyethylene can maintain better stability during processing and use, thereby greatly reducing the odor of the polyethylene resin and its products.

[0004] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0005] The present invention discloses a low-odor high-density polyethylene food-grade bottle cap special resin, which comprises the following materials in parts by mass:

[0006] Polyethylene powder 100 parts

[0007] Compound antioxidant 0.1~0.3 parts

[0008] 0.03-0.05 parts of high-efficiency catalyst.

[0009] Preferably, the high-efficiency catalyst is magnesium ethoxide-supported titanium trichloride, and its components, by mass fraction, include titanium trichloride <25.0%, magnesium ethoxide <20.0%, oils <10.0%, aluminum triglycolate <10.0%, and alkyl aluminum chloride <10.0%, and the catalyst activity is >20000.

[0010] Preferably, the composite antioxidant comprises a primary antioxidant and a secondary antioxidant with low volatility and a heat stabilizer, and the thermal weight loss volatiles of the primary antioxidant and the secondary antioxidant are ≤0.05% at 250°C.

[0011] Preferably, the main antioxidant is main antioxidant 1010, whose chemical name is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate); the auxiliary antioxidant is auxiliary antioxidant 168, whose chemical name is tris[2,4-di-tert-butylphenyl] phosphite; the thermal stabilizer is calcium salt of octadecanoic acid; the mass ratio of the main antioxidant, the auxiliary antioxidant and the thermal stabilizer is 1:2:5 to 1:3:5.

[0012] The present invention discloses a method for preparing a low-odor high-density polyethylene food-grade bottle cap special resin, which is characterized in that the preparation method comprises the following steps:

[0013] Step 1) Using ethylene and hydrogen as raw materials and butene-1 as a comonomer, ethylene, hydrogen and butene-1 are continuously fed into a reactor in a hexane solvent environment (hexane is a diluent), and a catalyst is used to convert them into a single-peak high-density polyethylene powder in the reactor, with a yield of 97%-99% (wt); wherein the polymerization reaction is carried out in parallel in reactors R-1201 and R-1202 equipped with stirrers, the reaction temperature is 81-85° C., and the polyethylene powder forms a polyethylene slurry with the hexane solvent under stirring;

[0014] Step 2) The polyethylene slurry enters a decanter centrifuge, and three decanter centrifuges are connected in parallel and run simultaneously. By centrifugal action, 70-75% (wt) of the hexane solvent in the polyethylene slurry is separated, and the moisture content of the polyethylene wet powder separated by centrifugation is up to 35% (wt, dry basis). The polyethylene wet powder is discharged from the decanter centrifuge and conveyed to the fluidized bed dryer by gravity;

[0015] Step 3) in a fluidized bed dryer, hot nitrogen is used for drying and evaporation to reduce the residual hexane content in the polyethylene wet powder to below 1.0% (wt), thereby purifying the polyethylene powder;

[0016] Step 4) The purified polyethylene powder is transported to the powder intermediate silo and the extruder feed silo by nitrogen in sequence, and nitrogen is used to purge and remove hydrocarbons in the two silos respectively;

[0017] Step 5) The separated polyethylene powder resin and the composite antioxidant are uniformly mixed in a mixer, the mixer speed is 50 rpm, the mixing time is 5 to 10 minutes, and then extruded and granulated by an extruder at a temperature of 170 to 250° C., the main motor speed of the extruder is controlled to be 800-900 rpm, corresponding to the screw speed of 273-325 rpm, to reduce the shear and thermal degradation of the powder polyethylene resin in the extruder, and obtain a low-odor high-density polyethylene food-grade bottle cap special resin.

[0018] Preferably, in step 3), in order to reduce the residual hexane content in the polyethylene HDPE powder product, the polyethylene HDPE powder will be further dried in the powder degassing bin, the polyethylene HDPE powder passes through the bin in the form of piston flow, and the residence time in the powder processing tank is 4-6 hours. In order to achieve a better separation effect, the temperature of the dried polyethylene HDPE powder is controlled at 95-100° C., and the nitrogen added to the bottom of the powder processing tank is also used to remove hexane, so that the residual hexane content reaches a level of <0.01% (wt).

[0019] Preferably, the polymerization production temperature is 81-85°C; the total reaction pressure is controlled at 500-700kPa, the ethylene partial pressure is controlled at 200-300kPa, the H2 / C2 concentration ratio is controlled at 0.60-0.76mol / mol, the C4 / C2 concentration ratio is controlled at 0.0035-0.0075mol / mol, and the powder degassing temperature is 95-100°C; the product density (23°C) is 0.956-0.960g / cm3, the melt flow rate (2.16kg, 190°C) is 3.0-4.0g / 10min, the tensile yield strength is ≥20mpa, and the nominal strain at break is ≥400%.

[0020] Beneficial effects: The invention adopts a high-efficiency catalyst, increases the reaction temperature, improves the catalyst activity, controls the composition content of low molecular weight and high molecular weight fractions in the polyethylene resin, reduces the low molecular weight fraction, is conducive to reducing the odor in the resin, reduces the high molecular weight fraction, can reduce the shearing in the extrusion granulation process, and prevents the low molecular weight polymer produced thereby; by increasing the residence time in the reactor and increasing the temperature of the centrifuge feed buffer tank, the low molecular weight polymer produced in the polymerization reaction can be dissolved into the solvent, and the content of the low molecular weight fraction in the powder resin can be reduced; increasing the residence time of the degassing bin, the intermediate buffer bin, and the extruder feed bin greatly reduces the content of hydrocarbon volatiles entrained in the powder, and reduces the odor of the polyethylene powder; using a high-efficiency, low-thermal volatility composite antioxidant, greatly reduces the odor brought into the polyethylene resin by the antioxidant, and due to its extremely high antioxidant property, the prepared polyethylene can maintain better stability during processing and use, thereby greatly reducing the odor of the polyethylene resin and its products; a low-odor, easy-to-unscrew polyethylene bottle cap material resin is prepared, and the research and development of this product breaks the technical barriers of production and preparation difficulties and plays a positive role in replacing imported products. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0022] The principle of the technical solution of the present invention is as follows: low-odor high-density polyethylene bottle cap material resin is obtained by catalytic polymerization of ethylene, hydrogen and butene-1 comonomer in a solvent. High-efficiency catalyst is used to produce polyethylene resin with narrow molecular weight distribution, and oligomers are removed during the polymerization process; five-stage solvent separation is used to control the content of solvent volatiles in the final powder to below 300ppm; and a high-efficiency composite antioxidant component is used for granulation preparation; the extruder uses a variable frequency extruder to accurately control the molecular weight and distribution of the pellet resin, while reducing the temperature rise and shear degradation during the extrusion granulation process to produce low molecular weight polymers.

[0023] The invention discloses a low-odor high-density polyethylene bottle cap material resin and a preparation method thereof, which can produce low-odor high-density polyethylene food-grade resin, create greater economic benefits for enterprises, meet the needs of market product processing users, and provide consumers with a more hygienic and safe bottle cap material.

[0024] Embodiment 1:

[0025] Polyethylene powder, polymerization load 35t / h, polymerization temperature 84℃, one-reaction ethylene partial pressure 239kpa, one-reaction total pressure 524kpa, H2 / C2 concentration ratio 0.696mol / mol, C4 / C2 concentration ratio 0.006mol / mol; two-reaction ethylene partial pressure 251kpa, two-reaction total pressure 533kpa, H2 / C2 concentration ratio 0.684mol / mol, C4 / C2 concentration ratio 0.0060mol / mol. The catalyst activity is 21tPE / kg, the temperature of the centrifuge feed tank is 44°C, the solvent content of the polyethylene slurry after centrifuge separation is 23.85%, the fluidized bed circulation air volume is 25000kg / h, the temperature of the first and second chambers of the fluidized bed are 80 and 100°C respectively, the temperature of the degassing bin is 98°C, the material level of the degassing bin is 40%, the residence time of the powder intermediate bin and the extruder feed bin is 6h, the composite antioxidant calcium stearate / 1010 / 168, the compounding ratio is 5 / 1 / 2, and the mass fraction is 0.3. The above polyethylene powder and compounding agent are measured according to a certain ratio and fully mixed, and then extruded and granulated by a twin-screw extruder. The temperatures of each zone of the extruder are 201°C, 197°C, 220°C, and 216°C, and the extruder speed is 880rpm.

[0026] The density of the obtained polyethylene resin product is 0.9583 g / cm 3 , melt mass flow rate 3.40g / 10min, tensile yield stress 24.4MPa, nominal strain at break 801%, simple supported beam notched impact strength 10kJ / m 2 , odor level 1.

[0027] Embodiment 2:

[0028] Polyethylene powder, polymerization load 36t / h, polymerization temperature 85℃, one-reaction ethylene partial pressure 243kpa, one-reaction total pressure 546kpa, H2 / C2 concentration ratio 0.772mol / mol, C4 / C2 concentration ratio 0.0050mol / mol; two-reaction ethylene partial pressure 231kpa, two-reaction total pressure 543kpa, H2 / C2 concentration ratio 0.796mol / mol, C4 / C2 concentration ratio 0.0049mol / mol. The catalyst activity is 23000tPE / kg, the temperature of the centrifuge feed tank is 45℃, the solvent content of the polyethylene slurry after centrifuge separation is 17.50%, the fluidized bed circulation air volume is 27000kg / h, the temperature of the first and second chambers of the fluidized bed are 80 and 100℃ respectively, the temperature of the degassing bin is 100℃, the material level of the degassing bin is 45%, the residence time of the powder intermediate bin and the extruder feed bin is 6h, the composite antioxidant calcium stearate / 1010 / 168, the compounding ratio is 5 / 1 / 2, and the mass fraction is 0.3. The above polyethylene powder and compounding agent are measured according to a certain ratio and fully mixed, and then extruded and granulated by a twin-screw extruder. The temperatures of each zone of the extruder are 208℃, 196℃, 212℃, and 232℃, and the extruder speed is 850rpm.

[0029] The density of the obtained polyethylene resin product is 0.9580 g / cm 3 , melt mass flow rate 3.72g / 10min, tensile yield stress 24.5MPa, nominal strain at break 612%, simple supported beam notched impact strength 9.8kJ / m 2 , odor level 1.

[0030] The product of the present invention is tested using national standards. The specific test method is as follows:

[0031] Density is in accordance with GB / T 1033.2-2010;

[0032] Melt flow rate (MFR) is carried out according to GB / T 3682.1-2018;

[0033] The tensile yield stress is carried out according to GB / T 1040-2018, type I spline, and the tensile speed is 50 mm / min;

[0034] The nominal strain at break was carried out according to GB / T 1040-2018, type I spline, and the tensile speed was 50 mm / min;

[0035] The specific method of odor test is dry method, placing at 50℃ for 1 day, 3 days and 5 days, and adopting artificial olfactory evaluation on the samples. The judging criteria of the odor level are: the odor is not easily felt at level 1, the odor is felt but not pungent at level 2, the odor is obviously felt but not pungent at level 3, the odor is pungent at level 4, the odor is very pungent at level 5, and the odor is unbearable at level 6.

[0036] 1. The physical and mechanical properties of the product are shown in Table 1.

[0037]

[0038] Product analysis data are all within the technical indicators.

[0039] 2. Molecular weight and its distribution are shown in Table 2

[0040]

[0041] The molecular weight distribution of the resin is relatively narrow, which effectively reduces the odor generated during the extrusion process, and the medium molecular weight part is beneficial to the torsion feel of the bottle cap products.

[0042] 3. The thermodynamic behavior of the product is shown in Table 3

[0043]

[0044] The resin has high crystallinity, which is conducive to good product appearance.

[0045] The present invention adopts a high-efficiency catalyst, increases the reaction temperature, improves the catalyst activity, can adopt two reactors for parallel production, controls the composition content of low molecular weight and high molecular weight fractions in the polyethylene resin, reduces the low molecular weight fraction, is beneficial to reduce the odor in the resin, and reduces the high molecular weight fraction to reduce shearing in the extrusion granulation process, thereby preventing the generation of low molecular weight polymers.

[0046] By increasing the residence time in the reactor and raising the temperature of the centrifuge feed buffer tank, the low molecular weight polymer produced in the polymerization reaction can be dissolved into the solvent, thereby reducing the content of low molecular weight fractions in the powder resin.

[0047] A five-stage series solvent-powder separation system can be used. At the same time, by modifying the centrifuge overflow weir, increasing the circulating air volume / feed ratio in the fluidized bed dryer, and increasing the residence time in the degassing bin, intermediate buffer bin, and extruder feed bin, the content of volatile hydrocarbons entrained in the powder is greatly reduced, and the odor of the polyethylene powder is reduced.

[0048] The use of high-efficiency, low-thermal volatility composite antioxidants greatly reduces the odor brought into the polyethylene resin by the antioxidants. Due to its extremely high antioxidant properties, the prepared polyethylene can maintain better stability during processing and use, thereby greatly reducing the odor of the polyethylene resin and its products.

[0049] The present invention can adopt an extruder with controllable processing degree, and by adjusting the rotation speed of the extruder, the molecular weight range of the powder can be controlled to be 115000<Mw<125000, 6.5<Mw / Mn<7.5, and the content of Mw<3000 fraction is less than 0.3%. Under the premise of ensuring the mixing, plasticization and extrusion of the powder, the shearing of the molecular chain and the influence of high temperature are effectively controlled, and the odor caused by the small molecule polymer generated thereby is reduced.

[0050] Through production process research, a low-odor, easy-to-unscrew polyethylene bottle cap resin was prepared. The research and development of this product broke the technical barriers to production and preparation difficulties and played a positive role in replacing imported products.

[0051] Finally, it should be noted that the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by ordinary technicians in this field should be considered as the protection scope of the present invention.

Claims

1. A low-odor high-density polyethylene food-grade bottle cap special resin, characterized by: The following materials are included in proportion by mass: Polyethylene powder 100 parts Compound antioxidant 0.1~0.3 parts 0.03-0.05 parts of high-efficiency catalyst.

2. The low-odor high-density polyethylene food-grade bottle cap resin according to claim 1, characterized in that: The high-efficiency catalyst is magnesium ethoxide-supported titanium trichloride, and its components include titanium trichloride <25.0%, magnesium ethoxide <20.0%, oil <10.0%, aluminum triglycolate <10.0%, alkyl aluminum chloride <10.0%, and the catalyst activity is >20000.

3. The low-odor high-density polyethylene food-grade bottle cap resin according to claim 1, characterized in that: The composite antioxidant comprises a primary antioxidant and an auxiliary antioxidant with low volatility and a heat stabilizer. The thermal weight loss volatility of the primary antioxidant and the auxiliary antioxidant is less than or equal to 0.05% at 250°C.

4. The low-odor high-density polyethylene food-grade bottle cap resin according to claim 2, characterized in that: The main antioxidant is main antioxidant 1010, whose chemical name is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate); the auxiliary antioxidant is auxiliary antioxidant 168, whose chemical name is tris[2,4-di-tert-butylphenyl] phosphite; the thermal stabilizer is calcium salt of octadecanoic acid; the mass ratio of the main antioxidant, the auxiliary antioxidant and the thermal stabilizer is 1:2:5 to 1:3:

5.

5. A method for preparing a low-odor high-density polyethylene food-grade bottle cap resin, characterized in that The preparation method comprises the following steps: Step 1) Using ethylene and hydrogen as raw materials and butene-1 as a comonomer, ethylene, hydrogen and butene-1 are continuously fed into a reactor in a hexane solvent environment (hexane is a diluent), and a catalyst is used to convert them into a single-peak high-density polyethylene powder in the reactor, with a yield of 97%-99% (wt); wherein the polymerization reaction is carried out in parallel in reactors R-1201 and R-1202 equipped with stirrers, the reaction temperature is 81-85° C., and the polyethylene powder forms a polyethylene slurry with the hexane solvent under stirring; Step 2) The polyethylene slurry enters a decanter centrifuge, and three decanter centrifuges are connected in parallel and run simultaneously. By centrifugal action, 70-75% (wt) of the hexane solvent in the polyethylene slurry is separated, and the moisture content of the polyethylene wet powder separated by centrifugation is up to 35% (wt, dry basis). The polyethylene wet powder is discharged from the decanter centrifuge and conveyed to the fluidized bed dryer by gravity; Step 3) in a fluidized bed dryer, hot nitrogen is used for drying and evaporation to reduce the residual hexane content in the polyethylene wet powder to below 1.0% (wt), thereby purifying the polyethylene powder; Step 4) The purified polyethylene powder is transported to the powder intermediate silo and the extruder feed silo by nitrogen in sequence, and nitrogen is used to purge and remove hydrocarbons in the two silos respectively; Step 5) The separated polyethylene powder resin and the composite antioxidant are uniformly mixed in a mixer, the mixer speed is 50 rpm, the mixing time is 5 to 10 minutes, and then extruded and granulated by an extruder at a temperature of 170 to 250° C., the main motor speed of the extruder is controlled to be 800-900 rpm, corresponding to the screw speed of 273-325 rpm, to reduce the shear and thermal degradation of the powder polyethylene resin in the extruder, and obtain a low-odor high-density polyethylene food-grade bottle cap special resin.

6. The method for preparing a low-odor high-density polyethylene food-grade bottle cap special resin according to claim 5, characterized in that: In step 3), in order to reduce the residual hexane content in the polyethylene HDPE powder product, the polyethylene HDPE powder will be further dried in the powder degassing bin. The polyethylene HDPE powder passes through the bin in the form of piston flow and stays in the powder processing tank for 4-6 hours. In order to achieve a better separation effect, the temperature of the dried polyethylene HDPE powder is controlled at 95-100° C. The nitrogen added to the bottom of the powder processing tank is also used to remove hexane, so that the residual hexane content reaches a level of <0.01% (wt).

7. The method for preparing a low-odor high-density polyethylene food-grade bottle cap special resin according to claim 5, characterized in that: The polymerization production temperature is 81-85°C; the total reaction pressure is controlled at 500-700kPa, the ethylene partial pressure is controlled at 200-300kPa, the H2 / C2 concentration ratio is controlled at 0.60-0.76mol / mol, the C4 / C2 concentration ratio is controlled at 0.0035-0.0075mol / mol, and the powder degassing temperature is 95-100°C; the product density at 23°C is 0.956-0.960g / cm3, the melt flow rate at 190°C is 3.0-4.0g / 10min, the tensile yield strength is ≥20mpa, and the nominal strain at break is ≥400%.

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