Preparation Method and Application of High and Low Temperature Resistant PVDF Backplane Film Polymer

Abstract

The invention discloses a preparation method of a high and low temperature resistant PVDF backplane film polymer, belonging to the technical field of polymer polymerization. The technical scheme is as follows: The method comprises the following steps: 1) adding pure water and an emulsifier into a closed container; 2) heating the closed container, adding vinylidene fluoride monomer until the pressure rises to 4.5-5.0 MPa, and adding an initiator and a chain transfer agent; 3) when the reaction pressure of the closed container drops to 2.9-3.1 MPa, adding vinylidene fluoride monomer until the pressure rises to 3.5-3.8 MPa, adding the initiator and the chain transfer agent for the second time, and after reacting for 35-45 min, adding an initiator; 4) stopping the reaction, replacing and recovering the remaining monomer, and obtaining polyvinylidene fluoride resin after post-treatment of washing and drying. By adding different initiators in segments, the invention can well avoid the generation of explosive polymers caused by excessive highly active initiators, does not affect the polymerization time, and prevents the gas-phase PVDF resin from sticking to the reaction kettle.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer polymerization, and particularly relates to a preparation method and application of a polymer for a PVDF backplane film resistant to high and low temperatures. Background Art

[0002] Polyvinylidene fluoride resin combines the characteristics of fluororesin and general resin. In addition to having good chemical corrosion resistance, high temperature resistance, oxidation resistance, weather resistance, and radiation resistance, it also has special properties such as piezoelectricity, dielectricity, and pyroelectricity. It has good mechanical properties and is easy to be processed into various products and film materials. It is widely used in the chemical industry, electronic and electrical industries, and mechanical industry. It is the second largest product in terms of output among fluoroplastics, with a global annual production capacity of more than 80,000 tons.

[0003] In the photovoltaic field, the PVDF film can greatly protect the PET film layer in the middle of the solar cell backplane, ensuring that it can play a role in supporting components, blocking water and oxygen safely, reliably, and for a long time. Currently, PVDF photovoltaic backplane films have the following major advantages: First, a higher fluorine content, which gives it better ultraviolet irradiation resistance and chemical resistance; second, more excellent flame retardant properties, which are crucial for safety performance. Also because of this feature, PVDF has become the best choice in transportation fields such as aviation and high-speed rail; third, better denseness, and thus more excellent sand and wind resistance; fourth, recyclability, with the greatest environmental protection advantage, laying a solid foundation for future component recycling technology.

[0004] The solar photovoltaic backplane film is an important encapsulation material for solar photovoltaic cell modules. Generally, commercial crystalline silicon solar photovoltaic cell modules require a service life of 25 years. Therefore, the solar group has high requirements for performance indicators such as the thickness, tensile strength, elongation at break, shrinkage, interlayer adhesion, and bonding strength with EVA of the backplane. And the PVDF film, as the protective film of the backplane, needs to have excellent weather resistance.

[0005] The solar photovoltaic backplane film is an important encapsulation material for solar photovoltaic cell modules. Generally, commercial crystalline silicon solar photovoltaic cell modules require a service life of 25 years. Therefore, the solar group has high requirements for performance indicators such as the thickness, tensile strength, elongation at break, shrinkage, interlayer adhesion, and bonding strength with EVA of the backplane. And the PVDF film, as the protective film of the backplane, needs to have excellent weather resistance.

[0006] Under the existing technology, the performance of PVDF backplane films significantly deteriorates in some extremely cold and hot regions. During the experiment, it was found that better weather resistance is exhibited by PVDF with higher molecular weight, smaller molecular weight distribution, and lower melting point. Therefore, based on these findings, it can be concluded that the larger the molecular weight, the smaller the molecular weight distribution, and the lower the melting point of PVDF, the better its performance under extremely high and low temperature conditions. To develop a PVDF backplane film with even better performance, it is urgent to prepare a PVDF backplane film with larger molecular weight, smaller molecular weight distribution, lower melting point, and better thermal stability. Summary of the Invention

[0007] The present invention provides a method for preparing and applying a polymer of PVDF backplane film resistant to high and low temperatures. By adding different initiators in segments, it can effectively avoid the formation of explosive polymers caused by excessive highly active initiators, without affecting the polymerization time, and prevent the adhesion of gaseous PVDF resin to the reaction kettle. The PVDF resin powder prepared by the present invention has small particle size, large molecular weight, a molecular weight distribution coefficient between 1.2 and 1.7, low melting point, and better thermal stability.

[0008] The technical solution of the present invention is as follows:

[0009] In the first aspect, a method for preparing a polymer of PVDF backplane film resistant to high and low temperatures is disclosed, which includes the following steps:

[0010] 1) In a closed container, pure water and an emulsifier are added. The amount of pure water is 60 - 80% of the volume of the closed reaction container, and the oxygen content in the closed container is replaced until it is less than or equal to 15 ppm.

[0011] 2) The closed container is heated to 60 - 95 °C, and vinylidene fluoride monomer is first added until the pressure rises to 4.5 - 5.0 MPa. Then, the initiator and the chain transfer agent are added for the first time.

[0012] 3) Keeping the reaction temperature in step 2) unchanged, a polymerization reaction occurs. When the reaction pressure in the closed container drops to 2.9 - 3.1 MPa, vinylidene fluoride monomer is added for the second time until the pressure rises to 3.5 - 3.8 MPa. It is stabilized for 0.5 - 2 min and vinylidene fluoride is continuously introduced to maintain the pressure at 3.5 - 3.8 MPa. Then, the initiator and the chain transfer agent are added for the second time. After reacting for 35 - 45 min, the initiator is added for the third time.

[0013] 4) When the amount of vinylidene fluoride monomer is 30 - 50% of the amount of deionized water used, the reaction is stopped, and the remaining monomer is recovered by replacement. After post-treatment, washing, and drying, polyvinylidene fluoride resin is obtained.

[0014] Preferably, in step 1), the emulsifier is polyoxyethylene ether of nonylphenol, polyoxyethylene ether of octylphenol, polyoxyethylene ether of lauryl alcohol, polyoxyethylene ether of primary alcohol, or polyoxyethylene ether of isooctyl alcohol.

[0015] Preferably, in step 2), an organic initiator is used as the initiator, and the organic initiator is cumene hydroperoxide or tert-butyl hydroperoxide or p-menthane hydroperoxide; in step 3), an inorganic initiator is used as the initiator, and the inorganic initiator is a persulfate, preferably potassium persulfate or sodium persulfate or ammonium persulfate.

[0016] Preferably, in steps 2) and 3), a thiocarbonyl sulfide is used as the chain transfer agent, preferably a thiocarbamate or a dithiol ester or a xanthate.

[0017] Preferably, the dosage of the emulsifier in step 1) is 0.5-1.1% of the total mass of vinylidene fluoride.

[0018] Preferably, in step 2), the dosage of the organic initiator is 0.05-0.8% of the total mass of vinylidene fluoride; in step 3), the dosage of the inorganic initiator is 0.1-1.1% of the total mass of vinylidene fluoride.

[0019] Preferably, in steps 2) and 3), the dosage of the chain transfer agent is 0.4-2.2% of the total mass of vinylidene fluoride.

[0020] Preferably, in step 4), the closed container is a high-pressure resistant horizontal kettle, the stirring form is ribbon stirring, and the rotational speed range of the stirrer is 30-120 rpm / min.

[0021] In the second aspect, the application of the PVDF backplane film polymer prepared by the preparation method of the high and low temperature resistant PVDF backplane film polymer as a backplane film is disclosed.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) In the present invention, different initiators are added in segments, which can well avoid the generation of explosive polymers by excessive high-activity initiators, and does not affect the polymerization time, prevent the gas-phase PVDF resin from adhering to the reaction kettle, and is easy to clean the high-pressure resistant horizontal kettle subsequently; (2) In the present invention, the emulsifier uses a non-ionic surfactant, which has lower toxicity compared with perfluorooctanoic acid surfactant, is not easily affected by electrolytes and pH values, is non-toxic, non-irritating, and has good biodegradability; (3) The emulsion produced by the present invention is suitable for production washing, with less water consumption and shorter washing time, greatly improving the production capacity; (4) The mixed use of organic and inorganic initiators can avoid the increase of explosive polymers and self-polymers generated by using organic initiators alone, and can also avoid the problem that the reaction time is too long when using inorganic initiators alone, affecting the production efficiency; (5) The PVDF resin powder prepared by the present invention has a small particle size, a large molecular weight, a molecular weight distribution coefficient between 1.2 and 1.7, a low melting point, and better thermal stability. Detailed Embodiments

[0024] Example 1

[0025] 1) In a 100 L high-pressure resistant horizontal reactor, the stirring form is ribbon stirring, the rotational speed range of the stirrer is 80 rpm / min, add 65 L of pure water and 1% of the mass of polyoxyethylene lauryl ether and vinylidene fluoride, evacuate and displace with nitrogen 8 times, and take a sample to detect that the oxygen content is less than 15 ppm;

[0026] 2) Heat the high-pressure resistant horizontal reactor to 80 °C, add vinylidene fluoride monomer until the pressure reaches 4.6 MPa, add an organic initiator cumene hydroperoxide with a content of 0.6% of the total mass of vinylidene fluoride and a chain transfer agent thiocarbamate with a content of 0.5% of the total mass of vinylidene fluoride.

[0027] 3) Keep the temperature constant and carry out the polymerization reaction. When the pressure drops to 3.0 MPa, add vinylidene fluoride monomer for the second time until the pressure rises to 3.65 MPa, and stabilize for one minute. Thereafter, continuously add vinylidene fluoride monomer to maintain the pressure at 3.65 MPa. Add potassium persulfate with a content of 0.3% of the total mass of vinylidene fluoride and a chain transfer agent thiocarbamate with a content of 0.5% of the total mass of vinylidene fluoride. After reacting for 20 minutes, add potassium persulfate with a content of 0.2% of the total mass of vinylidene fluoride. Stop the reaction when the vinylidene fluoride monomer is 48.5% of the amount of deionized water used, displace and recover the monomer, and obtain polyvinylidene fluoride resin after plate-frame demulsification washing and oven drying.

[0028] Example 2

[0029] 1) In a 100 L high-pressure resistant horizontal reactor, the stirring form is ribbon stirring, the rotational speed range of the stirrer is 80 rpm / min, add 65 L of pure water and 1% of the mass of polyoxyethylene lauryl ether and vinylidene fluoride, evacuate and displace with nitrogen 8 times, and take a sample to detect that the oxygen content is less than 15 ppm;

[0030] 2) Heat the high-pressure resistant horizontal reactor to 80 °C, add vinylidene fluoride monomer until the pressure reaches 4.6 MPa, add an organic initiator cumene hydroperoxide with a content of 0.8% of the total mass of vinylidene fluoride and a chain transfer agent thiocarbamate with a content of 0.5% of the total mass of vinylidene fluoride.

[0031] 3) Keep the temperature constant and carry out the polymerization reaction. When the pressure drops to 3.0 MPa, add vinylidene fluoride monomer for the second time until the pressure rises to 3.65 MPa, and stabilize for one minute. Thereafter, continuously add vinylidene fluoride monomer to maintain the pressure at 3.65 MPa. Add potassium persulfate with a content of 0.4% of the total mass of vinylidene fluoride and a chain transfer agent thiocarbamate with a content of 0.5% of the total mass of vinylidene fluoride. After reacting for 20 minutes, add potassium persulfate with a content of 0.2% of the total mass of vinylidene fluoride. Stop the reaction when the vinylidene fluoride monomer is 48.5% of the amount of deionized water used, displace and recover the monomer, and obtain polyvinylidene fluoride resin after plate-frame demulsification washing and oven drying.

[0032] Example 3

[0033] 1) In a 100 L high-pressure resistant horizontal reactor, the stirring form is a ribbon agitator, the agitator speed ranges from 80 rpm / min. Add 65 L of pure water and 1% of the mass of lauryl alcohol polyoxyethylene ether with a purity greater than 99% of the mass of vinylidene fluoride. Evacuate and replace with nitrogen 8 times, and take a sample to detect that the oxygen content is less than 15 ppm;

[0034] 2) Heat the high-pressure resistant horizontal reactor to 80 °C, add vinylidene fluoride monomer until the pressure reaches 4.6 MPa, add 1.0% of the total mass of vinylidene fluoride of cumene hydroperoxide as an organic initiator and 0.5% of the total mass of vinylidene fluoride of thiocarbamate as a chain transfer agent.

[0035] 3) Keep the temperature constant and carry out the polymerization reaction. When the pressure drops to 3.0 MPa, add vinylidene fluoride monomer for the second time until the pressure rises to 3.65 MPa, and stabilize for one minute. Thereafter, continuously add vinylidene fluoride monomer to maintain the pressure at 3.65 MPa. Add 0.6% of the total mass of vinylidene fluoride of potassium persulfate and 0.5% of the total mass of vinylidene fluoride of thiocarbamate as a chain transfer agent. After reacting for 20 minutes, add 0.2% of the total mass of vinylidene fluoride of potassium persulfate. Stop the reaction when the vinylidene fluoride monomer is 48.5% of the amount of deionized water used. Replace and recover the monomer, wash through plate-frame demulsification, and dry in an oven to obtain polyvinylidene fluoride resin.

[0036] Comparative Example 1

[0037] Different from Example 1, in step 2), the addition amount of thiocarbamate as a chain transfer agent is 0.3% of the total mass of vinylidene fluoride; in step 3), the addition amount of thiocarbamate as a chain transfer agent is 0.3% of the total mass of vinylidene fluoride, and the rest of the reaction conditions and parameters are the same as those in Example 1.

[0038] Comparative Example 2

[0039] Different from Example 1, in step 2), the addition amount of thiocarbamate as a chain transfer agent is 0.3% of the total mass of vinylidene fluoride; in step 3), the addition amount of thiocarbamate as a chain transfer agent is 0.2% of the total mass of vinylidene fluoride, and the rest of the reaction conditions and parameters are the same as those in Example 1.

[0040] Comparative Example 3

[0041] Different from Example 1, in step 2), the addition amount of thiocarbamate as a chain transfer agent is 0.3% of the total mass of vinylidene fluoride; in step 3), the addition amount of thiocarbamate as a chain transfer agent is 0.1% of the total mass of vinylidene fluoride, and the rest of the reaction conditions and parameters are the same as those in Example 1.

[0042] Comparative Example 4

[0043] Different from Example 1, in step 3), it is stabilized for one minute, and the initiator is changed to an organic initiator, cumene hydroperoxide, with a content of 0.3% of the total mass of vinylidene fluoride. After reacting for twenty minutes, an organic initiator, cumene hydroperoxide, with a content of 0.2% of the total mass of vinylidene fluoride is added, and the remaining reaction conditions and parameters are the same as those in Example 1.

[0044] Comparative Example 5

[0045] Different from Example 1, in step 2), the initiator is changed to an inorganic initiator, potassium persulfate, with a content of 0.6% of the total mass of vinylidene fluoride, and the remaining reaction conditions and parameters are the same as those in Example 1.

[0046] The polyvinylidene fluoride resins prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to corresponding tests on molecular weight, molecular weight distribution coefficient, thermal decomposition temperature, and weather resistance. The particle size was tested by laser light scattering method, and the test standard was HG / T2901. The molecular weight and molecular weight distribution coefficient were tested by gel permeation chromatography, and the test standard was ISO 16014. The thermal decomposition temperature was tested by thermogravimetric analysis, and the weather resistance test standard was IEC61215, as shown in Table 1 specifically.

[0047]

[0048] As can be seen from Table 1 above, in Examples 1-3 of the present invention, pressure is applied in stages and different initiators are supplemented, and organic initiators and inorganic initiators are used in combination, resulting in polyvinylidene fluoride resin with high molecular weight, narrow molecular weight distribution, and excellent weather resistance. At the same time, it was found that in Examples 1-3, as the initiator dosage increased gradually, the polymerization time became shorter, the molecular weight decreased, the molecular weight distribution became wider, and the weather resistance also decreased gradually. In Comparative Examples 1-3, the dosage of the chain transfer agent was reduced. Compared with Example 1, the particle size in Comparative Examples 1-3 increased significantly, the thermal decomposition temperature decreased, the molecular weight decreased, the molecular weight distribution became wider, and the weather resistance was also significantly inferior to that of Example 1, indicating that the reduction of the chain transfer agent has a more obvious impact on this reaction system.

[0049] Comparing Comparative Example 4 with Example 1, cumene hydroperoxide, an organic initiator, was used for all three initiators. It was found that there would be explosive polymers and self-polymers in the high-pressure horizontal autoclave, and the resulting emulsion was 20% less than that in Example 1, and the material properties also declined significantly. Comparing Comparative Example 5 with Example 1, the reaction time was longer, the melting point of the resulting material was relatively high, and the material properties were also poor.

[0050] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all fall within the scope covered by the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. Preparation method of high and low temperature resistant PVDF backplane film polymer, characterized in that, It includes the following steps: 1) In a closed container, add pure water and an emulsifier. The amount of pure water is 60 - 80% of the volume of the closed reaction container, and displace until the oxygen content in the closed container is less than or equal to 15 ppm; 2) Heat the closed container to 60 - 95 °C, first add vinylidene fluoride monomer until the pressure rises to 4.5 - 5.0 MPa, and first add an initiator and a chain transfer agent; 3) Keep the reaction temperature in step 2) unchanged and carry out a polymerization reaction. When the reaction pressure in the closed container drops to 2.9 - 3.1 MPa, second add vinylidene fluoride monomer until the pressure rises to 3.5 - 3.8 MPa, stabilize for 0.5 - 2 min and continuously introduce vinylidene fluoride to maintain the pressure at 3.5 - 3.8 MPa. Second add an initiator and a chain transfer agent. After reacting for 35 - 45 min, third add an initiator; 4) When the amount of vinylidene fluoride monomer is 30 - 50% of the amount of deionized water used, stop the reaction, displace and recover the remaining monomer, and after post-treatment of washing and drying, obtain polyvinylidene fluoride resin; In step 1), the emulsifier is nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, lauryl alcohol polyoxyethylene ether, primary alcohol polyoxyethylene ether, isooctyl alcohol polyoxyethylene ether; In step 2), the initiator uses an organic initiator, and the organic initiator is cumene hydroperoxide or tert-butyl hydroperoxide or p-menthane hydroperoxide; in step 3), the initiator uses an inorganic initiator, and the inorganic initiator is a persulfate; In step 2) and step 3), the chain transfer agent uses a thiocarbamate or a dithioester or a xanthate; In step 1), the amount of the emulsifier used is 0.5 - 1.1% of the total mass of vinylidene fluoride; In step 2), the amount of the organic initiator used is 0.05 - 0.8% of the total mass of vinylidene fluoride; in step 3), the amount of the inorganic initiator used is 0.1 - 1.1% of the total mass of vinylidene fluoride; In step 2) and step 3), the amount of the chain transfer agent used is 0.4 - 2.2% of the total mass of vinylidene fluoride.

2. The preparation method of the high and low temperature resistant PVDF backplane film polymer according to claim 1, characterized in that, In step 3), the initiator is potassium persulfate or sodium persulfate or ammonium persulfate.

3. The preparation method of the high and low temperature resistant PVDF backplane film polymer according to claim 1, characterized in that, In step 4), the closed container selects a high-pressure resistant horizontal kettle, the stirring form uses a ribbon stirrer, and the rotational speed range of the stirrer is 30 - 120 rpm / min.

4. Application of the PVDF backplane film polymer prepared by the preparation method of the high and low temperature resistant PVDF backplane film polymer according to any one of claims 1 - 3 as a backplane film.

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