Method for preparing cold-resistant chloroprene rubber by changing chloroprene rubber molecular chain structure regularity through monomer copolymerization

Abstract

The invention belongs to the technical field of chloroprene rubber preparation, and provides a method for preparing cold-resistant chloroprene rubber by changing the regularity of a chloroprene rubber molecular chain structure through monomer copolymerization. The preparation method comprises the following steps: adding a redox initiator at the emulsion polymerization temperature of 40 + / -0.2 DEG C to initiate a free radical emulsion copolymerization reaction, controlling the conversion rate of chloroprene monomers, adding a terminating agent to terminate the reaction when the polymerization degree is reached, removing unparticipated reaction monomers in the emulsion, acidizing and demulsifying latex, freezing and drum forming a film, and drying to obtain the high-cold-resistance chloroprene rubber emulsion. The technical innovation point of the chloroprene rubber is that the cold resistance of the chloroprene rubber is improved through copolymerization of chloroprene and unsaturated double-bond esters, and the defect that the performance of the chloroprene rubber is influenced by the difference of the use conditions of the chloroprene rubber is overcome. The poor cold resistance of common chloroprene rubber is improved, and the combination of excellent mechanical property and vulcanization property of the chloroprene rubber is maintained.

Description

Technical Field

[0001] The invention belongs to the technical field of chloroprene rubber preparation, and particularly relates to a method for preparing cold-resistant chloroprene rubber by utilizing monomer copolymerization to change the structural regularity of chloroprene rubber molecular chains. Background Art

[0002] Chloroprene rubber has excellent comprehensive properties such as weather resistance, ozone resistance, flame resistance, flex resistance, and chemical resistance. It is widely used in the manufacture of various capsules, air cushions, conveyor belts, transmission belts, lifeboats, shock-absorbing products, etc. However, chloroprene rubber has poor cold resistance, especially under low temperature conditions, it is easy to harden and embrittle and lose its unique characteristics. With the continuous improvement of industry technology, the performance requirements for chloroprene rubber products are more stringent. The disadvantage of poor cold resistance of chloroprene rubber limits its use value under low temperature conditions.

[0003] The poor low-temperature resistance of chloroprene rubber is mainly reflected in the fact that the proportion of trans 1,4-link structure in chloroprene monomer is about 85%. The main feature of trans 1,4-link structure is its good structural regularity, which indicates that they are very easy to form three-dimensional ordered crystalline polymers with high crystallinity. At the same time, the presence of chlorine atoms on the side groups of the molecular chain makes it higher than similar non-polar stereoregular rubbers. Its cold resistance and low-temperature resistance are poor, and it is more prone to hardening and brittleness, thus losing its unique comprehensive properties.

[0004] With the continuous development of polymer material technology, the innovation of new products and new technologies, the development of chloroprene rubber products is facing great pressure. Over the years, domestic and foreign manufacturers have conducted a lot of research on chloroprene rubber modification, especially Nippon Denka, which has made great breakthroughs in heat resistance, low temperature resistance, mechanical strength and oil resistance through copolymerization modification.

[0005] Foreign manufacturers of chloroprene rubber mainly include Denka, Tosoh, Showa, Alan Shinco, etc. The cold-resistant chloroprene rubber products with large usage in the market mainly include DCR66, DCR126, S-40V, PS-40, Neoprene WRT, Skyprene B-10 and other copolymer chloroprene rubber products. Domestic manufacturers include Huojia Changhua, and the main products on the market include DCR213, DCR114, SN21, etc. Whether at home or abroad, in the field of cold-resistant chloroprene rubber, the realization of cold-resistant performance is mainly based on the copolymerization of chloroprene monomer and 2-dichloro-1,3-butadiene. The addition of the two monomers reduces the regularity of the molecular structure of the homopolymer chloroprene polymer, thereby reducing its crystallization rate, improving the processing performance of the rubber, and improving its performance under low temperature conditions, so as to achieve the cold-resistant characteristics of the product.

[0006] The document "Development of Cold-Resistant Chloroprene Rubber" (Feng Chushuang, Synthetic Rubber Industry, 1992, Vol. 15, No. 3, 139-141) mainly achieves its cold resistance through copolymerization of chloroprene and 2,3-dichloroprene. Bayer's DCR216 and DCR66, Huo Changhua's DCR213 and DCR114 all use this method to improve the cold resistance of chloroprene rubber.

[0007] In "Chloroprene Rubber" (Jiao Shuke, China Petrochemical Press, 2016, Chapter 8 of the first edition), the copolymerization of chloroprene and styrene, and the copolymerization method of acrylonitrile are mentioned, and detailed explanations are given using examples. The copolymerization changes the stereoregularity of the chloroprene polymer macromolecules, that is, the degree of randomness of the copolymer molecules is greatly improved, and the obtained copolymer is microcrystalline. With the increase of styrene content, its crystallization rate is greatly reduced. When the styrene content is 10%, its crystallization rate is reduced by half, resulting in significant improvements in its processing performance, low temperature performance, and compression deformation resistance.

[0008] Some scholars have also used rubber to improve the cold resistance of chloroprene rubber, such as: application number 202310164356.8, patent name "A cold-resistant flame-retardant rubber outsole compound", the patent uses natural rubber and chloroprene rubber together, through the use of natural rubber under low temperature conditions, and make up for the lack of natural rubber in flame retardant performance, at the same time, improve the cold resistance of chloroprene rubber. It did not fundamentally change the cold resistance of chloroprene rubber itself.

[0009] The application number is CN202211393977.5, and the patent name is "A rubber airbag for an air spring". It uses chloroprene rubber and butadiene rubber together. In addition to improving the wear resistance and elasticity of the rubber airbag, reducing permanent compression deformation and compression heat generation, it can also significantly improve cold resistance.

[0010] However, few scholars have explored new comonomers. In order to expand the application of chloroprene monomer in new fields and improve its cold resistance, exploring new comonomers is a new direction for exploring the cold resistance of chloroprene. Summary of the invention

[0011] In order to solve the problem that chloroprene rubber becomes brittle and loses its original performance when used in a low-temperature environment, the present invention provides a method for preparing cold-resistant chloroprene rubber by using monomer copolymerization to change the regularity of the molecular chain structure of chloroprene rubber, which greatly broadens the application scope of chloroprene monomer.

[0012] The present invention is realized by the following technical scheme: a method for preparing cold-resistant chloroprene rubber by using monomer copolymerization to change the regularity of the molecular chain structure of chloroprene rubber, comprising unsaturated double-bond esters as the second monomer, adding a redox initiator to initiate a free radical emulsion copolymerization reaction of chloroprene and the unsaturated double-bond esters under the joint action of an anionic emulsifier at an emulsion polymerization temperature of 40±0.2°C, controlling the conversion rate of the chloroprene monomer, adding a terminator to terminate the reaction when the degree of polymerization is reached, removing unparticipated reaction monomers in the emulsion, acidifying and demulsifying the latex, freezing and drumming to form a film, and drying to obtain a chloroprene rubber latex with high cold resistance; Wherein: 90-97 parts of chloroprene, 3-10 parts of the second monomer, 0.1-0.5 parts of a regulator, 2.5-3 parts of an emulsifier, 80-90 parts of soft water, 0.4-0.6 parts of an alkaline substance, 0.4-0.6 parts of a dispersant, and 0.2-0.6 parts of a metal salt.

[0013] Furthermore, the second monomer is an olefin acid ester.

[0014] Furthermore, the second monomer is any one of versatate, ethylene glycol dimethacrylate, methoxy polyethylene glycol acrylate, and dibutyl itaconate, or a mixture of any two of them in any proportion.

[0015] The regulator is any one of n-dodecyl mercaptan, sulfur, regulator butyl, iodoform, tetrabutylthiuram disulfide, and tetraethylthiuram disulfide; the emulsifier is any one of rosin, hydrogenated rosin, rosin acid salt, sodium dodecyl sulfonate, sodium dodecyl diphenyl ether disulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium petroleum sulfonate; the alkaline substance is any one of sodium hydroxide, potassium hydroxide, or a strong base and weak acid salt; the dispersant is sodium methylene dinaphthalene sulfonate, sodium β-naphthalene sulfonate Any one of formaldehyde condensation product and petroleum sulfonate sodium salt; the metal salt is any one of sodium sulfite, sodium phosphate, sodium carbonate, ammonium carbonate and sodium bicarbonate; the initiator is any one of potassium persulfate, ammonium persulfate, methyl sulfinic acid and anthraquinone-2-sulfonate sodium; the terminator is toluene, p-tert-butyl o-phenol, antioxidant 168, antioxidant 1010 and sodium dodecyl sulfate; the terminator is an emulsion mixture prepared by 0-0.01 part of toluene, 0-0.01 part of p-tert-butyl o-phenol, 0-0.01 part of antioxidant 168, 0-0.01 part of antioxidant 1010, 0-0.005 part of sodium dodecyl sulfate and 0-0.01 part of rosin soap; the demulsifier for acidification and demulsification of latex is: 30% acetic acid aqueous solution.

[0016] The specific method is: (1) uniformly dissolving a regulator, an emulsifier, and a second monomer in chloroprene to prepare an oil phase; (2) Alkaline substances, dispersants, and metal salts are uniformly dissolved in soft water to prepare an aqueous phase; (3) At an emulsion polymerization temperature of 40±0.2°C, add an initiator to initiate emulsion polymerization. When the emulsion specific gravity reaches the designed specific gravity of 1.060-1.065, add a terminator to terminate the reaction; (4) After termination, the unreacted chloroprene monomer is removed from the emulsion, and after acidification and demulsification, the emulsion is frozen, washed with water, dried, and film-formed to prepare chloroprene rubber.

[0017] Furthermore, the specific gravity of the emulsion is 1.060-1.065; the freezing temperature is -21°C to -19°C, the drying temperature is 120°C, and the drying time is 30 minutes. The cold-resistant chloroprene rubber prepared by the present invention belongs to slow-crystallization chloroprene rubber, and the hardness of the product changes little during storage, and the degree of crystallization is low. Since ester substances are usually used as rubber plasticizers, due to their small molecular weight, they are very easy to homopolymerize in the emulsion polymerization process and appear as small molecular polymers to form gels, and cannot copolymerize with macromolecules. Such monomers have vinyl groups, which are more likely to copolymerize with chloroprene, and the substituents on the α-carbon atoms form large steric hindrance, and the glass transition temperature of the copolymer is reduced. Furthermore, the molecules are connected to the chloroprene macromolecular chain, reducing the regularity of the chloroprene macromolecular chain, and greatly improving the low-temperature resistance of the chloroprene rubber.

[0018] The cold resistance of the chloroprene rubber of the present invention is mainly evaluated based on the change in rubber hardness after vulcanization, the DSC crystallization degree and Tg after being placed for 30 days to evaluate the low temperature resistance of the chloroprene rubber. The smaller the hardness change and the lower the crystallization degree, that is, the less heat absorption per unit mass of crystallization, the lower the glass transition temperature Tg of the copolymer product. The above three indicators all evaluate the good cold resistance of the copolymer. And according to the infrared spectrum of the product after the copolymerization of chloroprene and unsaturated double bond esters at 1730-1740cm -1 The presence of carbonyl peaks fully demonstrates that the copolymerization reaction can be implemented, and the second monomer is copolymerized into the chloroprene macromolecular chain, which changes the molecular regularity of the chloroprene polymer, realizes the copolymerization of chloroprene and unsaturated double bond esters, improves the poor cold resistance of non-copolymerized chloroprene rubber, overcomes the effect of low temperature conditions on the rubber properties of chloroprene rubber, and maintains the excellent comprehensive mechanical properties and vulcanization properties of chloroprene rubber. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The infrared spectrum of the copolymerization of chloroprene and different types of unsaturated acid esters; experiments were carried out according to different contents and different types, and it was found that chloroprene can be copolymerized with unsaturated esters, and the copolymerization product was analyzed by infrared spectrum at 1730-1740cm -1The presence of carbonyl peaks indicates that this type of unsaturated acid esters can be copolymerized with chloroprene, and characteristic peaks appear in the chloroprene product. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the disclosure and materials cited therein are hereby incorporated by reference.

[0022] Technical equivalents to the specific embodiments described that are apparent to those skilled in the art using no more than routine experimentation are intended to be encompassed by this application.

[0023] The experimental methods in the following examples are all conventional methods unless otherwise specified. The instruments and equipment used in the following examples are all conventional laboratory instruments and equipment unless otherwise specified; the experimental materials used in the following examples are all purchased from conventional biochemical reagent stores unless otherwise specified.

[0024] The rubber prepared by the present invention is tested according to the test standards to examine the change of hardness of the prepared product over time, and to test its mechanical properties, glass transition temperature, and devitrification heat absorption to evaluate the cold resistance of the prepared product.

[0025] The steps and methods for testing the performance of chloroprene rubber are as follows: Rubber hardness: Test the Shore A hardness of raw rubber according to GB / T 531-1999.

[0026] Rubber plasticization: According to GB / T 21462-2008, prepare uniform plasticized rubber and let it stand at room temperature for mixing and use.

[0027] Rubber mixing: According to GB / T 21462-2008, add chloroprene rubber basic mixing formula to obtain a uniformly mixed rubber, and leave it for 6-24 hours before use.

[0028] Vulcanization of rubber: Cut the mixed rubber sample into 145mm×122mm×2mm samples evenly, and vulcanize them for 10-20min at a vulcanization pressure of 1-20Mpa and a vulcanization temperature of 120-180℃. After vulcanization, take out the samples and place them in room temperature water for 10-20min, drain the water, and prepare the samples after 2-4h for standby use.

[0029] The above vulcanized rubber samples were tested for their mechanical properties and hardness according to the test standards.

[0030] After the rubber sample was placed for 30 days, the glass transition temperature Tg and the decrystallization endotherm of the chloroprene rubber polymer were determined by differential scanning calorimetry (DSC).

[0031] Embodiment 1: The preparation method of the cold-resistant chloroprene rubber specifically comprises the following steps: In 1000 g of water, add 5 g of sodium β-naphthalenesulfonate formaldehyde condensate, 5.5 g of sodium hydroxide, and 3 g of sodium sulfite, and stir well to prepare an aqueous phase.

[0032] Under nitrogen protection, 970g of chloroprene monomer, 30g of disproportionated rosin, 30g of tert-butyl vinyl carbonate and 3g of a regulator are added to a reactor to fully dissolve the monomers. Then, the prepared aqueous phase is added to emulsify the monomers at 35°C-38°C, copolymerization is carried out at 40°C±2°C, and the temperature difference is controlled to be 10°C-12°C. When the specific gravity is measured to be 1.060-1.065, a pre-prepared terminator is added and stirred for 20min-30min to terminate the polymerization reaction. Unreacted monomers are removed by vacuum. After the emulsion is acidified, the emulsion is subjected to -21°C-19°C freezing demulsification and coagulation. After instant demulsification, the latex is frozen on a rotary drum to obtain a film. The film tape is washed with water for 1-2min, and then dried in a 120°C drying oven for 30min to prepare a dry glue for standby use.

[0033] Example 2: Under nitrogen protection, the water phase preparation remains unchanged, 950g of chloroprene monomer, 30g of disproportionated rosin, and 50g of versatate are added during the oil phase preparation process, the polymerization temperature and control conditions remain unchanged, the dry glue preparation method remains unchanged, and the detection method is the same as in Example 1.

[0034] Example 3: Under nitrogen protection, the water phase preparation remains unchanged, 900g of chloroprene monomer, 30g of disproportionated rosin, and 100g of versatate are added during the oil phase preparation process, the polymerization temperature and control conditions remain unchanged, the dry glue preparation method remains unchanged, and the detection method is the same as in Example 1.

[0035] Example 4: Under nitrogen protection, the water phase preparation remains unchanged, 970g of chloroprene monomer, 30g of disproportionated rosin, and 30g of dibutyl itaconate are added during the oil phase preparation process, the polymerization temperature and control conditions remain unchanged, the dry glue preparation method remains unchanged, and the detection method is the same as in Example 1.

[0036] Example 5: Under nitrogen protection, the water phase preparation remains unchanged, 970g of chloroprene monomer, 30g of disproportionated rosin, and 50g of dibutyl itaconate are added during the oil phase preparation process, the polymerization temperature and control conditions remain unchanged, the dry glue preparation method remains unchanged, and the detection method is the same as in Example 1.

[0037] Example 6: Under nitrogen protection, the water phase preparation remains unchanged, 970g of chloroprene monomer, 30g of disproportionated rosin, and 30g of ethylene glycol dimethacrylate are added during the oil phase preparation process, the polymerization temperature and control conditions remain unchanged, the dry glue preparation method remains unchanged, and the detection method is the same as in Example 1.

[0038] Comparative Example 1: In 1000 g of water, 5 g of sodium β-naphthalenesulfonate formaldehyde condensate, 5.5 g of sodium hydroxide and 3 g of sodium sulfite were added and stirred to prepare an aqueous phase.

[0039] Under nitrogen protection, 1000g of chloroprene monomer, 30g of disproportionated rosin and 3g of a regulator were added to a reactor to fully dissolve them, and then the prepared aqueous phase was added to emulsify them at 35°C-38°C. The emulsion polymerization temperature was 40°C±0.2°C for polymerization reaction, and the temperature difference was controlled to be 10°C-12°C. When the specific gravity was measured at 1.060-1.065, a terminator was added and stirred for 20min-30min, and then the polymerization reaction was terminated. Unreacted monomers were removed by vacuum, and the mixture was demulsified and condensed at -19°C. After instant demulsification, the latex was frozen on a rotary drum to obtain a film. The film tape was washed with water for 1-2min, and then dried in a 120°C drying oven for 30min to prepare a dry glue for standby use. The detection method was as in Example 1.

[0040] Comparative Example 2: Chloroprene cold-resistant dry glue prepared by adding 10% of environmentally friendly plasticizer emulsion to Comparative Example 1. The detection method is the same as that in Example 1.

[0041] The performance indicators of the cold-resistant chloroprene rubber prepared according to Examples 1-6, Comparative Example 1, and the chloroprene rubber prepared according to Comparative Example 2 are as follows, and the test data are shown in Tables 1 and 2 below.

[0042] Table 1 Mechanical properties Table 2 Changes of vulcanized rubber hardness over time The cold resistance of the chloroprene rubber of the present invention is evaluated from three aspects: its crystallization performance, hardness change after vulcanization, and glass transition temperature. By comparing the above embodiment with the comparative example, it can be seen that under the same polymerization conditions, the conventional medium-crystallized chloroprene rubber is crystallized at room temperature for 30 days, and the unit mass absorption heat of crystallization is about 7.73J. The unit mass absorption heat of crystallization of the rubber sample after 30 days of copolymerization with two monomers of unsaturated double bond esters is greatly reduced, which fully illustrates that chloroprene and unsaturated esters can be copolymerized, and the regularity of the chloroprene rubber is changed by copolymerization, and its crystallization is reduced. To improve the crystallinity of chloroprene rubber, the copolymerization products of tert-butyl carbonate and chloroprene were analyzed and found that with the increase of the content of the copolymer dimonomer, its cold resistance decreased. The main reason is that the large entanglement of the molecular chain structure increased the crosslinking density, increased its hardness, and limited the downstream processing. Therefore, the copolymerization dosage is 3% and the best. The performance of the copolymerization product of dibutyl itaconate and chloroprene is better than that of tert-butyl carbonate in terms of hardness change of vulcanized rubber, glass transition temperature, and crystallinity. It can be seen that among the copolymer dimonomers, dibutyl itaconate is more conducive to improving the cold resistance of chloroprene rubber. In addition, after infrared spectrum analysis of various copolymer samples, in the copolymer spectrum at 1730-1740cm -1 The presence of carbonyl peaks fully demonstrates that the copolymerization reaction can be implemented, and the second monomer is copolymerized into the chloroprene macromolecular chain, and exhibits excellent low-temperature resistance.

[0043] The cold-resistant chloroprene rubber prepared by the invention overcomes the shortcomings of common chloroprene rubber and chloroprene rubber prepared by adding plasticizer in low-temperature application, greatly expands the application scope of chloroprene rubber, and has the technical advantage of improving the cold-resistant performance of chloroprene rubber by copolymerizing chloroprene and unsaturated double-bond esters, overcoming the difference in the use conditions of chloroprene rubber that affects the rubber performance, breaking through the limitation of esters in copolymerization reaction, improving the poor cold-resistant performance of common chloroprene rubber, and maintaining the comprehensiveness of excellent mechanical properties and vulcanization properties of chloroprene rubber.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing cold-resistant chloroprene rubber by copolymerizing monomers to change the regularity of the molecular chain structure of chloroprene rubber, characterized in that: Containing unsaturated double-bond esters as the second monomer, chloroprene and the unsaturated double-bond esters are used together with an anionic emulsifier, and a redox initiator is added at an emulsion polymerization temperature of 40±0.2°C to initiate a free radical emulsion copolymerization reaction, and the conversion rate of the chloroprene monomer is controlled. When the degree of polymerization is reached, a terminator is added to terminate the reaction, and unparticipated reaction monomers in the emulsion are removed, the latex is acidified and demulsified, and a freeze-drum film is formed and dried to obtain a highly cold-resistant chloroprene rubber latex; Wherein: 90-97 parts of chloroprene, 3-10 parts of the second monomer, 0.1-0.5 parts of a regulator, 2.5-3 parts of an emulsifier, 80-90 parts of soft water, 0.4-0.6 parts of an alkaline substance, 0.4-0.6 parts of a dispersant, and 0.2-0.6 parts of a metal salt.

2. The method according to claim 1, characterized in that: The second monomer is olefin acid ester.

3. The method according to claim 2, characterized in that: The second monomer is any one of versatate vinyl carbonate, ethylene glycol dimethacrylate, methoxy polyethylene glycol acrylate, and dibutyl itaconate, or any two of them mixed in any proportion.

4. The method according to claim 1, characterized in that: The regulator is any one of n-dodecyl mercaptan, sulfur, regulator butyl, iodoform, tetrabutylthiuram disulfide, and tetraethylthiuram disulfide; the anionic emulsifier is any one of rosin, hydrogenated rosin, rosin acid salt, sodium dodecyl sulfonate, sodium dodecyl diphenyl ether disulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium petroleum sulfonate; the alkaline substance is any one of sodium hydroxide, potassium hydroxide, or a strong base and weak acid salt; the dispersant is any one of sodium methylene dinaphthalene sulfonate, sodium β-naphthalene sulfonate formaldehyde condensate, and sodium petroleum sulfonate; the metal salt is any one of sodium sulfite, sodium phosphate, sodium carbonate, ammonium carbonate, and sodium bicarbonate; the initiator is any one of potassium persulfate, ammonium persulfate, methyl sulfinic acid, and sodium anthraquinone-2-sulfonate; the terminator is 0-0.01 part of toluene, 0-0.01 part of p-tert-butyl o-benzene phenol, and antioxidant 168 An emulsion-like mixture prepared by 0-0.01 part of 1,0- ...

5. The method according to claim 1, characterized in that: The specific method is: (1) uniformly dissolving a regulator, an emulsifier, and a second monomer in chloroprene to prepare an oil phase; (2) Alkaline substances, dispersants, and metal salts are uniformly dissolved in soft water to prepare an aqueous phase; (3) At an emulsion polymerization temperature of 40±0.2°C, an initiator is added to initiate emulsion polymerization. When the specific gravity of the emulsion reaches the specific gravity of the formula, a terminator is added to terminate the reaction; (4) After termination, the unreacted chloroprene monomer is removed from the emulsion, and after acidification and demulsification, the emulsion is frozen, washed with water, dried, and film-formed to prepare chloroprene rubber.

6. The method according to claim 5, characterized in that: The specific gravity of the emulsion is 1.060-1.065; the freezing temperature is -21°C to -19°C, the drying temperature is 120°C, and the drying time is 30 minutes.

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