A low voc high flowability block copolymerized polypropylene material and a method for preparing the same

Abstract

The application discloses a kind of low VOC high flowability block copolymerization polypropylene material and preparation method thereof, belong to polypropylene material field.The preparation method disclosed in the application uses complex external electron donor system to keep polypropylene molecule high activity and high stereoregularity, simultaneously regulates and control polypropylene molecular weight distribution and melt index, without introducing high concentration hydrogen or special auxiliary agent such as degrading agent, effectively reduce the production difficulty and cost of high flowability block copolymerization polypropylene, simple operation step and no additional reactant residue, production efficiency is improved;The application also discloses the low VOC high flowability block copolymerization polypropylene material prepared by the preparation method, the material has good mechanical properties and low organic volatile content, no residual special smell, green and environmental protection, can be used in automobile, household appliance, commodity and food and multiple application fields.

Description

Technical Field

[0001] This invention relates to the field of polypropylene materials, specifically to a low-VOC, high-flowability block copolymer polypropylene material and its preparation method. Background Technology

[0002] Polypropylene resin, due to its advantages such as low relative density, ease of processing, excellent mechanical and chemical resistance, and low price, has become one of the most widely used synthetic resins globally. Based on different polymerization methods, polypropylene resin can be classified into homopolymer polypropylene, random copolymer polypropylene, and block copolymer polypropylene. Among them, block copolymer polypropylene, due to its excellent impact resistance, is widely used in automobiles, home appliances, and daily necessities. In recent years, various industries have placed increasingly higher demands on environmental protection, especially in the automotive industry, where volatile organic compound (VOC) content has become the most concerning indicator.

[0003] Currently, there are two main methods for producing high-flowability block copolymer polypropylene in China's industrial sector:

[0004] The first method is to produce the product by increasing the amount of polymerization inhibitor added (such as increasing the hydrogen concentration). The polypropylene resin obtained by this method has a wider molecular weight distribution and higher isotacticity, but it has higher requirements for the polymerization process. At the same time, the increase in hydrogen concentration will generate a large number of small polypropylene molecules, which will have an adverse effect on the impact resistance of the product and will also increase the VOC content of the product.

[0005] The second method is to produce the product using degradation methods (such as adding peroxides for degradation). The polypropylene obtained by this method has a narrow molecular weight distribution, but the melt index is not easy to control, the VOC content is high, and the residual odor will be caused when the peroxide is not completely reacted, making it unsuitable for food-grade use. At the same time, compared with polypropylene resin produced by non-degradation methods, this production method requires the addition of additional peroxides and high doses of antioxidants, so the cost is higher.

[0006] In summary, there is an urgent need for a low-cost method to prepare low-VOC content, high-flowability block copolymer polypropylene materials. Summary of the Invention

[0007] Based on the shortcomings of existing technologies, the present invention aims to provide a method for preparing low-VOC, high-flowability block copolymer polypropylene materials. This method uses a compounded external electron donor system to maintain the high activity and high isotacticity of polypropylene molecules, while controlling the molecular weight distribution and melt index of polypropylene. This effectively reduces the production difficulty of high-flowability block copolymer polypropylene, and the operation steps are simple and do not require the introduction of additional reagents or equipment, thus improving production efficiency. The resulting product has good mechanical properties and low volatile organic compound content.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a low-VOC, high-flowability block copolymer polypropylene material includes the following steps:

[0010] (1) Ethylene and propylene are added to a loop-gas phase polypropylene polymerization apparatus, and hydrogen is introduced at the same time. A catalyst and a compound external electron donor are added to the loop reactor or prepolymer reactor of the apparatus, and a second external electron donor is added to the gas phase reactor to react and obtain a propylene multiphase copolymer. The compound external electron donor includes tetraethoxysilane and cyclohexylmethyldimethoxysilane. The second external electron donor includes dicyclopentyldimethoxysilane.

[0011] (2) Add nucleating agent, antioxidant and acid scavenger to the propylene multiphase copolymer obtained in step (1) and mix evenly. Place the mixture into a twin-screw extruder and melt blend and extrude granulation to obtain the low VOC high flowability block copolymer polypropylene material.

[0012] The inventors of this application have discovered that different external electron donors have different effects on the isotacticity, molecular weight and molecular weight distribution of polypropylene, and also have different effects on hydrogen regulation sensitivity. Therefore, when different preferred external electron donors are used to form a compound external electron donor, the advantages of both can be brought into play, and a product with better overall performance can be prepared.

[0013] In the preparation method of the low-VOC, high-flowability block copolymer polypropylene material of the present invention, a compounded external electron donor is used to maintain the high activity and high isotacticity of polypropylene molecules, while simultaneously controlling the molecular weight distribution and melt index of polypropylene. The resulting product maintains good mechanical properties, effectively reduces the production difficulty of high-flowability block copolymer polypropylene, and also reduces the content of low molecular weight compounds in polypropylene resin, resulting in a lower content of volatile organic compounds. Compared with the preparation method using a single external electron donor system, the preparation method can achieve lower cost and energy consumption, and the operation steps are simpler and the production rate is higher.

[0014] Preferably, the concentration of hydrogen introduced into the loop-gas phase polypropylene polymerization apparatus is 2000-3000 ppm.

[0015] The method for preparing low-VOC, high-flowability block copolymer polypropylene material described in this invention uses a compounded external electron donor to prepare propylene multiphase copolymers, which can effectively control their molecular weight and flowability. This allows the final product to have a high melt flow rate even when the hydrogen concentration is kept low. At the same time, the inventors found that if the hydrogen concentration is too high, it may weaken the product performance and cause fluctuations in the production equipment, thus increasing the difficulty of production.

[0016] Preferably, the mass ratio of tetraethoxysilane to cyclohexylmethyldimethoxysilane in step (1) is 8 to 10:1;

[0017] More preferably, the mass ratio of tetraethoxysilane to cyclohexylmethyldimethoxysilane in step (1) is 9:1.

[0018] After optimization, the compound external electron donor obtained under the specified ratio has the best effect on controlling the molecular weight and melt index of the produced product.

[0019] Preferably, the pressure of the loop reactor or prepolymer reactor is set at 3.4–3.8 MPa and the temperature is set at 69–71 °C.

[0020] Preferably, the gas phase reactor is set at a pressure of 1.2–1.4 MPa, a temperature of 70–85°C, and a material level of 70–80%.

[0021] The preparation method of the low-VOC high-flowability block copolymer polypropylene material of the present invention does not require high temperature or high pressure environment for product property control, and has low requirements for production equipment and environment, and low energy consumption.

[0022] Preferably, the catalyst comprises a main catalyst and a co-catalyst;

[0023] More preferably, the main catalyst is a titanium-based catalyst and the co-catalyst is an aluminum-based catalyst;

[0024] More preferably, the main catalyst is catalyst DQC602, and the co-catalyst is triethylaluminum.

[0025] Preferably, the mass ratio of the propylene multiphase copolymer, nucleating agent, antioxidant, and acid scavenger in step (2) is: m(propylene multiphase copolymer): m(nucleating agent): m(antioxidant): m(acid scavenger) = 100: (0.08~0.2): (0.1~0.2): (0.03~0.08).

[0026] In the reaction system, a suitable nucleating agent can accelerate the crystallization rate and refine the grains during product processing, thereby improving the rigidity and impact resistance of the product; the introduction of antioxidants can enhance the heat aging resistance of the product during processing and use.

[0027] Preferably, the nucleating agent comprises at least one of a metal carboxylate salt, a metal phosphate salt, dibenzyl sorbitol, and a dibenzyl sorbitol derivative;

[0028] More preferably, the nucleating agent is aluminum hydroxyl p-tert-butylbenzoate.

[0029] Preferably, the antioxidant includes at least one of hindered phenolic antioxidants and phosphite antioxidants;

[0030] More preferably, the antioxidant is a mixture of hindered phenolic antioxidants and phosphite antioxidants, wherein the mass ratio of hindered phenolic antioxidants to phosphite antioxidants in the mixture is 1 to 2:1.

[0031] Preferably, the acid absorbent includes at least one of calcium stearate and hydrotalcite.

[0032] Another object of the present invention is to provide a method for preparing the low-VOC, high-flowability block copolymer polypropylene material, wherein the block copolymer polypropylene material has a melt flow rate of 30-40 g / 10 min at 230°C and 2.16 kg load, and a VOC content of ≤70 μg / g.

[0033] The block copolymer polypropylene prepared by the method described in this invention has the characteristics of low VOC content and good flowability compared with existing products. At the same time, the product has excellent mechanical properties, with a notched impact strength of simply supported beam ≥8kJ / m. 2 With a flexural modulus ≥1250MPa, it fully meets the application requirements of high-performance polypropylene materials in the automotive, home appliance and other fields. No additives such as degradation agents are introduced in the preparation process of the product, so it does not have any special residual odor, is green and environmentally friendly, and can also be used for food-grade applications.

[0034] The beneficial effects of this invention are as follows: This invention provides a method for preparing a low-VOC, high-flowability block copolymer polypropylene material. This method uses a compounded external electron donor system to maintain the high activity and high isotacticity of polypropylene molecules, while simultaneously controlling the molecular weight distribution and melt index of polypropylene. It eliminates the need for the introduction of high-concentration hydrogen or special additives such as degradation agents, effectively reducing the production difficulty and cost of high-flowability block copolymer polypropylene. The operation steps are simple and there are no additional reactant residues, thus improving production efficiency. This invention also provides a low-VOC, high-flowability block copolymer polypropylene material prepared by the aforementioned method. This material has good mechanical properties, low volatile organic compound content, no residual special odor, and is environmentally friendly. It can be used in multiple application fields such as automobiles, home appliances, daily necessities, and food. Detailed Implementation

[0035] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and comparative examples. The purpose of this description is to provide a detailed understanding of the invention, not to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention. Unless otherwise specified, the experimental reagents and instruments designed for implementation of this invention are commonly used reagents and instruments.

[0036] Example 1

[0037] An embodiment of the low-VOC, high-flowability block copolymer polypropylene material and its preparation method according to the present invention includes the following steps:

[0038] (1) Ethylene and propylene are added to a loop-gas phase polypropylene polymerization apparatus, and hydrogen is introduced simultaneously. The main catalyst DQC602 (a titanium-based catalyst produced by Sinopec), the co-catalyst triethylaluminum, and a compound external electron donor are added to the loop reactor or prepolymer reactor of the apparatus. A second external electron donor is added to the gas phase reactor, and a reaction occurs to obtain a propylene multiphase copolymer. The compound external electron donor comprises tetraethoxysilane and cyclohexylmethyldimethoxysilane in a mass ratio of 9:1. The second external electron donor comprises dicyclopentyldimethoxysilane. The pressure of the loop-gas phase polypropylene polymerization apparatus is set to 3.6 MPa, the reaction temperature to 70°C, and the hydrogen concentration to 2500 ppm. The pressure of the gas phase reactor is set to 1.3 MPa, the reaction temperature to 81%, and the material level to 75%.

[0039] (2) Add 1200ppm nucleating agent NAA-325P (produced by Chenghe Technology Co., Ltd.), 1200ppm antioxidant B225 (produced by BASF, USA), and 300ppm acid scavenger calcium stearate to the propylene multiphase copolymer obtained in step (1) and mix them evenly. The ratio of m (propylene multiphase copolymer):m (nucleating agent):m (antioxidant):m (acid scavenger) = 100:0.12:0.12:0.03. The resulting mixture is placed in a twin-screw extruder and melt-blended and extruded to granulate, thereby obtaining the low-VOC high-flowability block copolymer polypropylene material.

[0040] Example 2

[0041] The only difference between this embodiment and Embodiment 1 is that the hydrogen concentration of the loop-gas phase polypropylene polymerization apparatus is set to 2800 ppm.

[0042] Comparative Example 1

[0043] The preparation method of the block copolymer polypropylene material described in this comparative example includes the following steps:

[0044] (1) Ethylene and propylene are added to a loop-gas phase polypropylene polymerization apparatus, and hydrogen is introduced simultaneously. The main catalyst DQC602 (a titanium-based catalyst produced by Sinopec), the co-catalyst triethylaluminum, and a compound external electron donor are added to the loop reactor or prepolymer reactor of the apparatus. A second external electron donor is added to the gas phase reactor, and a reaction occurs to obtain a propylene multiphase copolymer. The compound external electron donor comprises tetraethoxysilane and cyclohexylmethyldimethoxysilane in a mass ratio of 9:1. The second external electron donor comprises dicyclopentyldimethoxysilane. The pressure of the loop-gas phase polypropylene polymerization apparatus is set to 3.6 MPa, the reaction temperature to 70°C, and the hydrogen concentration to 2000 ppm. The pressure of the gas phase reactor is set to 1.3 MPa, the reaction temperature to 81%, and the material level to 75%.

[0045] (2) Add 1200ppm nucleating agent NAA-325P, 1200ppm antioxidant B225 (BASF B225 type antioxidant), 300ppm acid scavenger calcium stearate and 800ppm degradation agent (Shanghai Arkema LOW TBOH type degradation agent) to the propylene multiphase copolymer obtained in step (1) and mix them evenly. m(propylene multiphase copolymer):m(nucleating agent):m(antioxidant):m(acid scavenger) = 100:0.12:0.12:0.03. The resulting mixture is placed in a twin-screw extruder and melt-blended and extruded to granulate to obtain the block copolymer polypropylene material.

[0046] Comparative Example 2

[0047] The preparation method of the block copolymer polypropylene material described in this comparative example includes the following steps:

[0048] (1) Ethylene and propylene are added to a loop-gas phase polypropylene polymerization apparatus, and hydrogen is introduced simultaneously. The main catalyst DQC602 (a titanium-based catalyst produced by Sinopec), the co-catalyst triethylaluminum, and a compound external electron donor are added to the loop reactor or prepolymer reactor of the apparatus. A second external electron donor is added to the gas phase reactor, and a reaction occurs to obtain a propylene multiphase copolymer. The compound external electron donor comprises tetraethoxysilane and cyclohexylmethyldimethoxysilane in a mass ratio of 9:1. The second external electron donor comprises dicyclopentyldimethoxysilane. The pressure of the loop-gas phase polypropylene polymerization apparatus is set to 3.6 MPa, the reaction temperature to 70°C, and the hydrogen concentration to 6500 ppm. The pressure of the gas phase reactor is set to 1.3 MPa, the reaction temperature to 81%, and the material level to 75%.

[0049] (2) Add 1200ppm nucleating agent NAA-325P, 1200ppm antioxidant B225 (BASF B225 type antioxidant) and 300ppm acid scavenger calcium stearate to the propylene multiphase copolymer obtained in step (1) and mix them evenly. The ratio of m (propylene multiphase copolymer): m (nucleating agent): m (antioxidant): m (acid scavenger) = 100: 0.12: 0.12: 0.03. The resulting mixture is placed in a twin-screw extruder and melt-blended and extruded to granulate, thereby obtaining the block copolymer polypropylene material.

[0050] Example 1

[0051] The products obtained from each embodiment and comparative example, as well as the existing commercially available product K7726, were tested for flowability, mechanical properties, and volatile organic compound (VOC) content. The results are shown in Table 1. The melt flow rate of each product was measured at 230°C and 2.16 kg. The flexural modulus was tested according to the ISO 178-2010 standard method. The notched impact strength of the simply supported beam was tested at 23°C according to the GB / T 1043-2008 standard method.

[0052] Table 1

[0053]

[0054] As shown in Table 1, the block copolymer polypropylene material prepared in this embodiment has high fluidity, with an MFR of approximately 35 g / 10 min or higher, which is higher than existing products. Its mechanical properties are not significantly different from existing K7726 products. The VOC content of the obtained product is less than 70 μg / g, far lower than the 236 μg / g of K7726 products. Therefore, the product obtained in this embodiment possesses excellent fluidity and mechanical properties, and is also environmentally friendly, effectively replacing existing products of the same type. The product obtained in Comparative Example 1 is a block copolymer polypropylene product prepared using a degradation agent. The fluidity of this product is inferior to that of the product in the embodiment. Although the impact strength is significantly improved, the flexural modulus (i.e., rigidity) is insufficient, and the VOC content is also higher. The preparation method in Comparative Example 2 uses a higher hydrogen concentration, resulting in lower fluidity compared to Example 1, insufficient impact strength, and a higher VOC content. Furthermore, it increases production difficulty and can easily cause fluctuations in production equipment.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a low-VOC, high-flowability block copolymer polypropylene material, characterized in that, Includes the following steps: (1) Ethylene and propylene are added to a loop-gas phase polypropylene polymerization apparatus, and hydrogen is introduced simultaneously. A catalyst and a compound external electron donor are added to the loop reactor or prepolymer reactor of the apparatus, and a second external electron donor is added to the gas phase reactor to react and obtain a propylene multiphase copolymer. The compound external electron donor includes tetraethoxysilane and cyclohexylmethyldimethoxysilane, and the mass ratio of tetraethoxysilane to cyclohexylmethyldimethoxysilane is 8~10:

1. The second external electron donor includes dicyclopentyldimethoxysilane. The concentration of hydrogen introduced into the loop-gas phase polypropylene polymerization apparatus is 2000~3000ppm. The set pressure of the gas phase reactor is 1.2~1.4MPa. (2) Add nucleating agent, antioxidant and acid scavenger to the propylene multiphase copolymer obtained in step (1) and mix evenly. Place the mixture into a twin-screw extruder and melt blend and extrude granulation to obtain the low VOC high flowability block copolymer polypropylene material. The melt flow rate of the low VOC high flowability block copolymer polypropylene material at 230℃ and 2.16kg load is 30~40g / 10min, and the VOC content is ≤70μg / g.

2. The method for preparing the low-VOC, high-flowability block copolymer polypropylene material as described in claim 1, characterized in that, The set pressure of the loop reactor or prepolymer reactor is 3.4~3.8MPa, and the temperature is 69~71℃.

3. The method for preparing the low-VOC, high-flowability block copolymer polypropylene material as described in claim 1, characterized in that, The gas phase reactor is set at a temperature of 70-85℃ and a material level of 70-80%.

4. The method for preparing the low-VOC, high-flowability block copolymer polypropylene material as described in claim 1, characterized in that, The catalyst includes a main catalyst and a co-catalyst.

5. The method for preparing the low-VOC, high-flowability block copolymer polypropylene material as described in claim 4, characterized in that, The main catalyst is a titanium-based catalyst, and the co-catalyst is an aluminum-based catalyst.

6. The method for preparing the low-VOC, high-flowability block copolymer polypropylene material as described in claim 1, characterized in that, The mass ratio of the propylene multiphase copolymer, nucleating agent, antioxidant, and acid scavenger in step (2) is: m(propylene multiphase copolymer): m(nucleating agent): m(antioxidant): m(acid scavenger) = 100: (0.08~0.2): (0.1~0.2): (0.03~0.08).

7. The method for preparing the low-VOC, high-flowability block copolymer polypropylene material as described in claim 1, characterized in that, Includes any one of the following (a) to (c): (a) The nucleating agent includes at least one of a metal salt of carboxylic acid, a metal salt of phosphate, dibenzyl sorbitol, and a dibenzyl sorbitol derivative; (b) The antioxidant includes at least one of hindered phenolic antioxidants and phosphite antioxidants; (c) The acid absorbent includes at least one of calcium stearate and hydrotalcite.

8. The block copolymer polypropylene material prepared by the preparation method of the low VOC high flowability block copolymer polypropylene material according to any one of claims 1 to 7.

Images