Vinyl acetate-ethylene copolymer emulsion with high ethylene content and preparation method thereof

Abstract

The invention provides a preparation method of a vinyl acetate-ethylene copolymer emulsion with high ethylene content, small particle size and narrow particle size distribution and the emulsion prepared by the preparation method, and the emulsion is prepared by taking vinyl acetate, ethylene, an initiator and a protective colloid as raw materials through a semi-continuous emulsion polymerization method. Wherein the protective colloid comprises polyvinylpyrrolidone. The emulsion product with the performance indexes has excellent adhesive force while ensuring high ethylene content, can be used as an adhesive base material with better quality, and can be widely applied to manufacturing industries such as paper coating, packaging and laminating, textile printing and the like.

Description

Technical Field

[0001] The invention relates to a vinyl acetate-ethylene copolymer emulsion, and in particular to a method for preparing the vinyl acetate-ethylene copolymer emulsion with a high ethylene content. Background Art

[0002] Vinyl acetate-ethylene copolymer emulsion (VAE emulsion for short) is a polymer emulsion made by copolymerizing vinyl acetate monomer and ethylene monomer as basic raw materials with other auxiliary materials through emulsion polymerization. This emulsion is mainly used in adhesives, coatings, cement modifiers and paper processing, and has permanent flexibility, good acid and alkali resistance, UV aging resistance, good film-forming properties, good adhesion and other functions.

[0003] In the 1980s, my country introduced the production technology of vinyl acetate-ethylene copolymer emulsion from the United States, and it has been more than 40 years. During this period, a lot of research has been done on how to increase the ethylene content of VAE emulsion.

[0004] Sun Xianwu studied the effects of increasing ethylene pressure, extending reaction time and changing the order of addition on the ethylene content of vinyl acetate-ethylene emulsion. Finally, by improving the main process parameters and operating procedures, the ethylene content was increased to 16%-18%. The main method was to extend the reaction time and divide the continuous addition of vinyl acetate into three stages under the condition of unchanged formula ("Development of New High Ethylene Content VAE Emulsion", Sun Xianwu, Anhui Science and Technology, Issue 10, 2014, Pages 47-48).

[0005] Cao Yong developed a vinyl acetate-ethylene emulsion with an ethylene mass fraction of 16%-20% by extending the continuous addition time of vinyl acetate and increasing the concentration of the initiator ("Development and Application Research of New VAE for Cement Waterproofing", Cao Yong, Adhesion, Issue 07, 2010, Page 45).

[0006] Chinese patent document CN 111100235A discloses a method for preparing a high-ethylene-content vinyl acetate-ethylene copolymer emulsion, which is prepared from raw materials including monomers, an initiation system, an emulsification system and water; the emulsification system includes an emulsifier and a protective colloid, and the protective colloid is polyvinyl alcohol with a polymerization degree of 400-3500 and an alcoholysis degree of 80%-90%. The vinyl acetate-ethylene copolymer emulsion prepared by the method has a high solid content (55.3%-56.7%), a high ethylene content (18.0%-18.6%), better flexibility and water resistance, and can be used in the fields of construction, adhesives, light chemical industry, etc.

[0007] Chinese patent document CN 109651556A discloses a monodisperse vinyl acetate-ethylene copolymer emulsion and its preparation method: prepared from raw materials including monomers, initiation system and emulsification system; the monomers are vinyl acetate, ethylene and seed emulsion; the initiation system includes an oxidant and a reducing agent; the emulsification system includes an emulsifier and a protective colloid, and the protective colloid is polyvinyl alcohol. The obtained emulsion has a narrow particle size distribution, a high solid content (≥54.5%), a high ethylene content (14-16%), better flexibility and water resistance, can be used as a general adhesive, and is widely used in paper processing, coating decoration, wood processing, non-woven fabrics and carpets and other manufacturing industries.

[0008] Chinese patent document CN 112708004A discloses a vinyl acetate-ethylene copolymer emulsion and a preparation method thereof, which is prepared from raw materials including monomers, an emulsifying system, an initiator, a reducing agent, a pH regulator and water, wherein the monomers include alcohols with 2-8 carbon atoms and ≥2 alcoholic hydroxyl groups; the emulsifying system is a protective colloid or an emulsifier or a combination thereof, wherein the protective colloid is one or a combination of polyvinyl alcohols with a polymerization degree of 500-2400 and an alcoholysis degree of 88%-99%. The peel strength of the obtained vinyl acetate-ethylene copolymer emulsion is 0.338-0.387N / mm, and the bonding performance is significantly improved.

[0009] Chinese patent document CN 114426620A discloses a vinyl acetate-ethylene copolymer emulsion and a preparation method thereof, which is prepared from raw materials including monomers, surfactants, initiators, reducing agents and pH regulators. The surfactants include protective colloids and emulsifiers with a cloud point of ≤80°C. The protective colloids include one or more polyvinyl alcohols with a degree of polymerization of 400-2000 and a degree of alcoholysis of 88%-99%.

[0010] In summary, the current preparation method of vinyl acetate-ethylene copolymer emulsion includes not only optimizing and adjusting conventional raw materials and reaction parameters (such as raw material dosage, temperature, time, etc.), but also adding foreign additional monomers for copolymerization or introducing existing polymers as emulsification seeds to improve the performance of the emulsion. As for the protective colloid, although it is believed that any surface-active water-soluble polymer or emulsifier can be used as the protective colloid, from the actual production process, polyvinyl alcohol or polyvinyl alcohol is almost always used as the protective colloid.

[0011] The particle size and particle size distribution of emulsion are important technical indicators of polymer emulsion, which have a direct impact on the emulsion performance indicators such as emulsion color, gloss, adhesion, etc. In many fields, the demand for vinyl acetate-ethylene copolymer emulsion with high ethylene content, small particle size and narrow particle size distribution is urgent. Summary of the invention

[0012] In order to solve the above technical problems, the present invention provides a method for preparing a vinyl acetate-ethylene copolymer emulsion with high ethylene content, small particle size and narrow particle size distribution, which is prepared by a semi-continuous emulsion polymerization method using vinyl acetate, ethylene, an initiator and a protective colloid as raw materials; wherein the protective colloid comprises polyvinyl pyrrolidone.

[0013] Preferably, the polyvinyl pyrrolidone of the present invention is selected from one or more of K17, K25 and K30.

[0014] Furthermore, the protective colloid of the present invention further comprises polyvinyl alcohol, and the content of polyvinyl pyrrolidone in the protective colloid is not less than 80% by weight. The polyvinyl alcohol is preferably low-polymerization degree and medium-polymerization degree polyvinyl alcohol, and particularly preferably one or more of polyvinyl alcohol 0488, 0588 and 1788.

[0015] More preferably, the semi-continuous emulsion polymerization method of the present invention consists of three stages: an initial feeding stage, a pre-reaction stage and a polymerization reaction stage, wherein in the initial feeding stage, 10-40% of the total weight of the vinyl acetate raw material is first added as an initial monomer, and in the polymerization reaction stage, the remaining vinyl acetate raw material is continuously fed at a rate of 0.35-0.53 parts / min.

[0016] Furthermore, in the pre-reaction stage, the ethylene pressure is controlled to be 3.5-4.5 MPa and the temperature is controlled to be 52-60°C, and in the polymerization reaction stage, the ethylene pressure is controlled to be 5.8-6.1 MPa and the temperature is controlled to be 80±2°C.

[0017] Most preferably, the method of the present invention uses 42.0-44.0 parts of vinyl acetate, 11.7-12.9 parts of ethylene, 2.2-2.7 parts of protective colloid, 0.06-0.27 parts of initiator peroxide, 0.12-0.17 parts of reducing agent and an appropriate amount of water as raw materials, and after replacing the reactor, water, protective colloid and reducing agent solution are added to the reactor under stirring, and then vinyl acetate accounting for 10-40% of the total amount of vinyl acetate raw materials is added as the initial monomer; in the pre-reaction stage, the temperature and pressure are increased, and when the ethylene pressure reaches 4.0MPa and the temperature rises to 52-60°C, the initiator peroxide is continuously added to the reactor until the temperature reaches 80°C; when the temperature of the reaction materials rises To 80℃, raise the ethylene pressure to 5.8-6.1MPa, start the polymerization reaction stage, and at the same time, continuously add the remaining vinyl acetate raw material at a rate of 0.35-0.55 parts / min. During the continuous vinyl acetate addition in the polymerization reaction stage, the ethylene pressure is maintained at 5.8-6.1MPa, and the reaction temperature is maintained at 80±2℃. After the continuous vinyl acetate addition is completed, the ethylene addition is turned off, and the reaction temperature is continued to be controlled at 80±2℃ to continue the polymerization reaction; when the ethylene pressure is lower than 1.5MPa, stop adding the initiator oxide and the reaction is terminated; when the material temperature drops below 35℃, add an appropriate amount of sodium hydroxide solution to adjust the pH of the emulsion; finally filter and discharge the material.

[0018] The present invention also provides a vinyl acetate-ethylene copolymer emulsion prepared by the above preparation method, wherein the average particle size of the emulsion is less than 0.8 μm, preferably 0.7-0.8 μm.

[0019] The present invention has the following beneficial effects:

[0020] In the preparation process of vinyl acetate-ethylene copolymer emulsion, the emulsion particle size and its particle size distribution are one of the important indicators of the emulsion product and have a significant impact on the performance of the emulsion. Many factors in the polymerization reaction will affect the emulsion particle size, including monomer type, monomer water solubility, monomer dosage, emulsifier type, emulsifier dosage, initiator type, initiator dosage, reaction temperature, reaction pressure, reaction time, polymerization reaction type, etc. These factors have been extensively studied in the prior art.

[0021] The inventor team found that replacing all or most of the polyvinyl alcohol used as a protective colloid in the existing vinyl acetate-ethylene copolymer emulsion preparation process with polyvinyl pyrrolidone can help obtain a vinyl acetate-ethylene copolymer emulsion with high ethylene content, low average particle size and narrow particle size distribution. The emulsion product with these performance indicators has excellent adhesion while ensuring high ethylene content, can be used as a better quality adhesive base, and can be widely used in manufacturing industries such as paper coating, packaging lamination, and textile printing.

[0022] The inventor team believes that using polyvinyl pyrrolidone as the main protective colloid may increase the mass transfer area of ​​the polymerization system, and polyvinyl pyrrolidone has less effect on ethylene diffusion, which is conducive to more ethylene participating in the reaction, thereby increasing the ethylene content of the polymer and forming a smaller latex particle size. The inventor team found that in this case, the VAE emulsion prepared under normal ethylene pressure can have a higher ethylene content, thereby ensuring that without changing the major production process conditions, a VAE emulsion with a higher ethylene content, a smaller average emulsion particle size and a narrower distribution can be obtained, which can better meet the higher demand for this product in industrial production and specific fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate and explain the technical solution of the present invention, the following is a brief introduction to the drawings that need to be used in conjunction with the specific implementation methods. Those skilled in the art understand that the drawings attached to the specification of the present invention are only used to illustratively explain some specific implementation methods of the present invention. For those skilled in the art, without paying creative labor, due to changes in specific experimental parameters, the obtained drawings may be modified, adjusted, combined, etc., but it does not affect the implementation of the technical solution of the present invention.

[0024] Figure 1 The particle size data and particle size distribution diagram of the emulsion product of Example 1 of the present invention measured by Malvern laser particle size analyzer are shown.

[0025] Figure 2 The particle size data and particle size distribution diagram of the emulsion product of Example 2 of the present invention measured by Malvern laser particle size analyzer are shown.

[0026] Figure 3 The particle size data and particle size distribution diagram of the emulsion product of Example 3 of the present invention measured by Malvern laser particle size analyzer are shown.

[0027] Figure 4 The particle size data and particle size distribution diagram of the emulsion product of Example 4 of the present invention measured by Malvern laser particle size analyzer are shown.

[0028] Figure 5 The particle size data and particle size distribution diagram of the emulsion product of Example 5 of the present invention measured by Malvern laser particle size analyzer are shown.

[0029] Figure 6 The particle size data and particle size distribution diagram of the emulsion product of Example 6 of the present invention measured by Malvern laser particle size analyzer are shown.

[0030] Figure 7 The particle size data and particle size distribution diagram of the emulsion product of Comparative Example 1 of the present invention measured by Malvern laser particle size analyzer are shown.

[0031] Figure 8 The particle size data and particle size distribution diagram of the emulsion product of Comparative Example 2 of the present invention measured by Malvern laser particle size analyzer are shown. DETAILED DESCRIPTION

[0032] The following is further described in detail through specific implementation methods. However, it should be pointed out that the following embodiments of the present invention are only for better illustrating the content of the present invention, but do not mean that the content of the present invention is limited to the examples. Therefore, those skilled in the art can make non-essential improvements and adjustments to the implementation scheme according to the above invention content, which still belongs to the protection scope of the present invention and is subject to the protection scope of the attached claims.

[0033] Vinyl acetate-ethylene copolymers are generally classified into three forms, namely resin, rubber and emulsion, according to the different vinyl acetate contents: products with vinyl acetate contents less than 40wt% are resins, products with vinyl acetate contents of 40-70wt% are rubbers, and products with vinyl acetate contents in the range of 70-95wt% are emulsions. The vinyl acetate-ethylene copolymers described in the present invention specifically refer to the emulsion form, so the content of ethylene units therein is less than 30wt%, and is generally in the range of 15-20wt%. In the present invention, the terms such as vinyl acetate-ethylene copolymer, vinyl acetate-ethylene copolymer emulsion, VAE, and VAE emulsion have the same meaning and can be used interchangeably.

[0034] The existing preparation process of the vinyl acetate-ethylene copolymer described in the present invention generally includes the steps of displacement deoxygenation in a kettle, initial feeding, polymerization reaction, post-treatment and the like.

[0035] The step of replacing and deoxygenating in the kettle is usually carried out by introducing an inert gas (such as nitrogen) into the reaction kettle to remove the oxygen present in the kettle. The monomer gas ethylene gas of the present invention can also be used simultaneously or alone to remove the oxygen. Ethylene gas is originally one of the reaction raw materials, and its residue in the kettle will not affect the reaction.

[0036] Since the raw materials are in different forms such as solid, liquid and gas, the order of feeding is usually to add vinyl acetate monomer to water containing an emulsifier, then introduce gaseous monomer ethylene, and then add initiator (if it is an initiator of a redox system, the oxidant or reductant can be added to the initial charge first, and the other initiator can be added after the polymerization reaction starts). After the temperature is raised to the polymerization reaction temperature (for example, 60°C), the polymerization reaction can be started. The feeding order known in the prior art can be to add the above raw materials in appropriate proportions simultaneously or successively. There are also studies that try to add a certain reaction raw material in several stages to obtain products with different properties.

[0037] The product of the present invention is in the form of an emulsion, so it is preferably prepared by emulsion polymerization. The so-called emulsion polymerization refers to the process of dispersing the polymerization monomer raw materials in water to form an emulsion with the help of an emulsifier and mechanical stirring, and then initiating the polymerization of the monomers with an initiator to obtain an emulsion product.

[0038] Emulsion polymerization includes continuous emulsion polymerization and semi-continuous emulsion polymerization. Continuous emulsion polymerization refers to the continuous addition of monomer raw materials during the polymerization process, and the continuous extraction of reaction products through the emulsion polymerization reaction process. Semi-continuous emulsion polymerization refers to the slow and continuous addition of monomer raw materials to the aqueous emulsifier solution in the polymerization reactor, while dripping the aqueous solution of the initiator, and controlling the polymerization temperature by the dripping speed; there is also a method of first adding part of the monomers and other raw materials (initiator, emulsifier, etc.) to the polymerization reactor, and then adding the remaining monomers and other raw materials to complete the entire polymerization process after polymerization to a certain extent. The present invention adopts the latter semi-continuous emulsion polymerization method, first adding 10-40% of the total weight of vinyl acetate as the initial monomer and protective colloid, reducing agent and other raw materials, and then continuously adding the initiator and the remaining vinyl acetate monomer.

[0039] The initiator described in the present invention, also known as a free radical initiator, refers to a class of compounds that are easily decomposed into free radicals by heat, which can be used to initiate free radical polymerization and copolymerization reactions of olefinic and diene monomers, and is essential in ethylene-vinyl acetate copolymerization reactions. According to the molecular structure of the initiator, the initiator can be divided into azo, peroxide and redox initiators; it can also be divided into water-soluble initiators (soluble in aqueous solvents) and oil-soluble (soluble in organic solvents) according to its solubility; it can also be divided into high-temperature (above 100°C) initiators, medium-temperature (40-100°C) initiators and low-temperature (0-40°C) initiators according to the use temperature range of the initiator. The present invention preferably uses hydrogen peroxide or tert-butyl hydroperoxide (TBHP) as the initiator, and sodium isoascorbate or zinc formaldehyde sulfoxylate as the reducing agent. Of course, the polymerization reaction of the present invention can also select other peroxide initiators, such as persulfate, dibenzoyl peroxide, isopropylbenzene peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, etc.; the reducing agent can also use other reducing agents with free radical initiation. Those skilled in the art can select any suitable initiator according to the system and conditions of the polymerization reaction. The amount of the initiator can be 0.005-5% of the weight of the vinyl acetate monomer, preferably 0.01-1%, more preferably 0.05-0.1%, for example, 0.005%, 0.01%, 0.05%, 0.1%, 1%, 5% can be selected. Those skilled in the art can select a suitable initiator and its amount according to the specific circumstances of the reaction.

[0040] The specific conditions for the polymerization of the vinyl acetate-ethylene copolymer of the present invention are well known to those skilled in the art, and the polymerization temperature is 40-90° C., preferably 60-80° C., for example, 60° C., 70° C., 75° C., 80° C., etc. During the polymerization reaction, the ethylene gas pressure is maintained at 1-10 MPa, preferably 5-7 MPa, and most preferably 5.8-6.1 MPa.

[0041] The post-treatment process of the present invention includes pH adjustment, filtration, adding bactericides, etc., and these steps all adopt conventional operation methods known in the art.

[0042] The latex particle size of the present invention refers to the diameter of the latex particles in the latex after the high molecular weight polymer is dispersed in the aqueous solution to form the latex; since the size of the latex particles is not exactly the same, the average value is the emulsion evaluation particle size. The emulsion particle size is generally normally distributed, and the width of the particle size distribution is characterized by the polydispersity index (PDI) of the emulsion.

[0043] The solid content and ethylene content of the present invention are determined according to the test methods of the corresponding indicators in the national standard for vinyl acetate-ethylene copolymer emulsion "GB / T27573-2011 Vinyl acetate-ethylene copolymer emulsion".

[0044] The viscosity of the emulsion of the present invention is tested according to the viscosity test method in the national standard of vinyl acetate-ethylene copolymer emulsion "GB / T27573-2011 Vinyl acetate-ethylene copolymer emulsion", the test temperature is 25±0.1°C, the instrument model is; Brookfield LVDV-II+, the rotor model is No. 4 shaft, 60 rpm.

[0045] The particle size and distribution of the emulsion of the present invention are tested using a laser particle size analyzer from Malvern Company of the United Kingdom, the instrument model is Mastersize 2000, and the test method is the general method of this type of instrument.

[0046] Example 1

[0047] Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps:

[0048] A. Preparation of raw materials

[0049] A1. Preparation of initiator solution: Add 3.17 parts of deionized water and 0.225 parts of a 27.5% hydrogen peroxide solution (ie, 0.062 parts of initiator) to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 1.8%;

[0050] A2. Preparation of protective colloid solution: Add 19.8 parts of deionized water to the dissolution tank, start stirring, add 2.2 parts of polyvinyl pyrrolidone K30, raise the temperature to 80°C until the protective colloid is completely dissolved, and prepare a protective colloid solution with a mass fraction of 10%.

[0051] B. Feed production

[0052] After replacing the reactor with nitrogen three times, 21.03 parts of deionized water and 22 parts of the protective colloid solution obtained in step A2 were added to the reactor, the stirrer was started, and then 0.125 parts of sodium isoascorbate were added, and finally 4.67 parts of vinyl acetate were added as the initial monomer;

[0053] After completion, the temperature was raised with a jacket and the reactor was pressurized with ethylene. When the pressure reached 4.0 MPa and the temperature of the reaction mass rose to 60° C., the initiator solution prepared in step A1 was added to the reactor at a rate of 0.083 parts / min until the temperature reached 80° C.;

[0054] When the reaction temperature rises to 80°C, the reactor pressure is raised to 6.0 MPa with ethylene, and 37.88 parts of remaining vinyl acetate are added at a rate of 0.54 parts / min, while the jacket temperature is reduced to 5°C and the temperature is maintained at 80°C by controlling the initiator addition rate;

[0055] During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 6.0 MPa, and the reaction temperature was maintained at 80°C by computer-controlled initiator addition rate variation;

[0056] After the continuous addition of vinyl acetate is completed, the ethylene addition is turned off, and the reaction temperature continues to be maintained at 80°C by computer-controlled initiator addition rate changes;

[0057] When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends;

[0058] When the temperature of the reaction material drops to 35° C., 0.25 parts of 10% sodium hydroxide solution is added to adjust the pH; finally, the reaction material is filtered and discharged.

[0059] Example 2

[0060] Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps:

[0061] A. Preparation of raw materials

[0062] A1. Preparation of initiator solution: Add 3.17 parts of deionized water and 0.255 parts of a 27.5% hydrogen peroxide solution (ie, 0.070 parts of initiator) to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 1.8%;

[0063] A2. Preparation of protective colloid solution: Add 24.3 parts of deionized water to the dissolution tank, start stirring, add 2.16 parts of polyvinyl pyrrolidone K17 and 0.54 parts of polyvinyl alcohol 0588, raise the temperature to 80°C until the protective colloid is completely dissolved, and prepare a protective colloid solution with a mass fraction of 10%.

[0064] B. Feed production

[0065] After replacing the reactor with nitrogen three times, 16.53 parts of deionized water and 27.0 parts of the protective colloid solution obtained in step A2 were added to the reactor, the stirrer was started, and then 0.13 parts of zinc formaldehyde sulfoxylate were added, and finally 12.3 parts of vinyl acetate were added as the initial monomer;

[0066] After completion, the temperature was raised with a jacket and the reactor was pressurized with ethylene. When the pressure reached 4.0 MPa and the temperature of the reaction mass rose to 52° C., the initiator solution prepared in step A2 was added to the reactor at a rate of 0.05 parts / min until the temperature reached 80° C.;

[0067] When the reaction temperature rises to 80°C, the reactor pressure is raised to 6.1 MPa with ethylene, and the remaining 30.3 parts of vinyl acetate are added at a rate of 0.43 parts / min. At the same time, the jacket temperature is reduced to 5°C and the initiator addition rate is controlled by a computer to maintain the temperature at 80°C;

[0068] During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 6.1 MPa, and the reaction temperature was maintained at 80°C by computer-controlled initiator addition rate variation;

[0069] After the continuous addition of vinyl acetate is completed, the ethylene addition is turned off, and the reaction temperature continues to be maintained at 80°C by computer-controlled initiator addition rate changes;

[0070] When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends;

[0071] When the temperature of the reaction material drops to 35° C., 0.575 parts of 10% sodium hydroxide solution is added to adjust the pH; finally, the reaction material is filtered and discharged.

[0072] Example 3

[0073] Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps:

[0074] A. Preparation of raw materials

[0075] A1. Preparation of initiator solution: Add 3.42 parts of deionized water and 0.24 parts of a 27.5% hydrogen peroxide solution (ie, 0.066 parts of initiator) to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 1.8%;

[0076] A2. Preparation of protective colloid solution: Add 21.45 parts of deionized water to the dissolution tank, start stirring, add 2.03 parts of polyvinyl pyrrolidone K25 and 0.35 parts of polyvinyl alcohol 0488, raise the temperature to 80°C until the protective colloid is completely dissolved, and prepare a protective colloid solution with a mass fraction of 10%.

[0077] B. Feed production

[0078] After replacing the reactor with nitrogen three times, 29.13 parts of deionized water and 23.8 parts of the protective colloid solution obtained in step A2 were added to the reactor, the stirrer was started, and then 0.133 parts of sodium isoascorbate were added, and finally 16.9 parts of vinyl acetate were added as the initial monomer;

[0079] After completion, the temperature was raised with a jacket and the reactor was pressurized with ethylene. When the pressure reached 4.0 MPa and the temperature of the reaction mass rose to 58°C, the initiator solution prepared in step A1 was added to the reactor at a rate of 0.1 part / min until the temperature reached 80°C;

[0080] When the reaction temperature rises to 80°C, the reactor pressure is raised to 6.0 MPa with ethylene, and the remaining 25.39 parts of vinyl acetate are added at a rate of 0.36 parts / min. At the same time, the jacket temperature is reduced to 5°C and the initiator addition rate is controlled by a computer to maintain the temperature at 80°C.

[0081] During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 6.0 MPa, and the reaction temperature was maintained at 80°C by computer-controlled initiator addition rate variation;

[0082] After the continuous addition of vinyl acetate is completed, the ethylene addition is turned off, and the reaction temperature continues to be maintained at 80°C by computer-controlled initiator addition rate changes;

[0083] When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends;

[0084] When the temperature of the reaction material drops to 35° C., 0.25 parts of 10% sodium hydroxide solution is added to adjust the pH; finally, the reaction material is filtered and discharged.

[0085] Example 4

[0086] Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps:

[0087] A. Preparation of raw materials

[0088] A1. Preparation of initiator solution: Add 4.55 parts of deionized water and 0.38 parts of 70% TBHP solution (ie, 0.266 parts of initiator) to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 5.4%;

[0089] A2. Preparation of protective colloid solution: Add 21.9 parts of deionized water to the dissolution tank, start stirring, add 2.09 parts of polyvinyl pyrrolidone K25 and 0.34 parts of polyvinyl alcohol 1788, raise the temperature to 80°C until the protective colloid is completely dissolved, and prepare a protective colloid solution with a mass fraction of 10%.

[0090] B. Feed production

[0091] After replacing the reactor with nitrogen three times, 17.55 parts of deionized water and 24.3 parts of the protective colloid solution obtained in step A2 were added to the reactor, the stirrer was started, and then 0.16 parts of zinc formaldehyde sulfoxylate were added, and finally 6.79 parts of vinyl acetate were added as the initial monomer;

[0092] After completion, the temperature was raised with a jacket and the reactor was pressurized with ethylene. When the pressure reached 4.0 MPa and the temperature of the reaction mass rose to 55° C., the initiator solution prepared in step A1 was added to the reactor at a rate of 0.016 parts / min until the temperature reached 80° C.;

[0093] When the reaction temperature rises to 80°C, the reactor pressure is raised to 5.9 MPa with ethylene, and the remaining 37.2 g of vinyl acetate is added at a rate of 0.48 g / min. At the same time, the jacket temperature is reduced to 5°C and the initiator addition rate is controlled by a computer to maintain the temperature at 80°C.

[0094] During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.9 MPa, and the reaction temperature was maintained at 80°C by computer-controlled initiator addition rate variation;

[0095] After the continuous addition of vinyl acetate is completed, the ethylene addition is turned off, and the reaction temperature continues to be maintained at 80°C by computer-controlled initiator addition rate changes;

[0096] When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends;

[0097] When the temperature of the reaction material drops to 35° C., 0.6 parts of 10% sodium hydroxide solution is added to adjust the pH; finally, the reaction material is filtered and discharged.

[0098] Example 5

[0099] Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps:

[0100] A. Preparation of raw materials

[0101] A1. Preparation of initiator solution: Add 3.77 parts of deionized water and 0.27 parts of 70% TBHP solution (ie, 0.189 parts of initiator) to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 4.6%;

[0102] A2. Preparation of protective colloid solution: Add 21 parts of deionized water to the dissolution tank, start stirring, add 1.93 parts of polyvinyl pyrrolidone K30, 0.3 parts of polyvinyl alcohol 0488, and 0.1 parts of polyvinyl alcohol 1788, raise the temperature to 80°C until the protective colloid is completely dissolved, and prepare a protective colloid solution with a mass fraction of 10%.

[0103] B. Feed production

[0104] After replacing the reactor with nitrogen three times, 19.2 parts of deionized water and 23.3 parts of the protective colloid solution obtained in step A2 were added to the reactor, the stirrer was started, and then 0.13 parts of sodium isoascorbate was added, and finally 11.28 parts of vinyl acetate was added as the initial monomer;

[0105] After completion, the temperature was raised with a jacket and the reactor was pressurized with ethylene. When the pressure reached 4.0 MPa and the temperature of the reaction mass rose to 60°C, the initiator solution prepared in step A1 was added to the reactor at a rate of 0.033 parts / min until the temperature reached 80°C;

[0106] When the reaction temperature rises to 80°C, the reactor pressure is raised to 5.8 MPa with ethylene, and the remaining 31.06 parts of vinyl acetate are added at a rate of 0.44 parts / min. At the same time, the jacket temperature is reduced to 5°C and the initiator addition rate is controlled by a computer to maintain the temperature at 80°C.

[0107] During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.8 MPa, and the reaction temperature was maintained at 80°C by computer-controlled initiator addition rate variation;

[0108] After the continuous addition of vinyl acetate is completed, the ethylene addition is turned off, and the reaction temperature continues to be maintained at 80°C by computer-controlled initiator addition rate changes;

[0109] When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends;

[0110] When the temperature of the reaction material drops to 35° C., 0.25 parts of 10% sodium hydroxide solution is added to adjust the pH; finally, the reaction material is filtered and discharged.

[0111] Comparative Example 1

[0112] Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps:

[0113] A. Preparation of raw materials

[0114] A1. Preparation of initiator solution: Add 3.2 parts of deionized water and 0.225 parts of 27.5% hydrogen peroxide solution (ie, 0.062 parts of initiator) to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 1.8%;

[0115] A2. Preparation of protective colloid solution: Add 24.3 parts of deionized water to the dissolution tank, start stirring, add 0.3 parts of polyvinyl alcohol 1788, 0.35 parts of polyvinyl alcohol 0488 and 2.04 parts of polyvinyl pyrrolidone K25, raise the temperature to 80°C until the protective colloid is completely dissolved, and prepare an initiator solution with a mass fraction of 5.4%.

[0116] B. Feed production

[0117] After replacing the reactor with nitrogen three times, 16.5 parts of deionized water and 27.0 parts of the protective colloid solution obtained in step A were added to the reactor, the stirrer was started, and then 0.13 parts of zinc rubidium were added, and finally 12.3 parts of vinyl acetate were added as the initial monomer;

[0118] After completion, the jacket was used to increase the temperature and the reactor was pressurized with ethylene. When the pressure reached 4.0 MPa and the temperature of the reaction mass rose to 52°C, the initiator was added to the reactor at a rate of 0.05 parts / min until the temperature reached 80°C;

[0119] When the reaction temperature rises to 80°C, the reactor pressure is raised to 6.1 MPa with ethylene, and the remaining 30.3 parts of vinyl acetate are added at a rate of 0.43 parts / min. At the same time, the jacket temperature is reduced to 5°C and the initiator addition rate is controlled by a computer to maintain the temperature at 80°C.

[0120] During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 6.1 MPa, and the reaction temperature was maintained at 80°C by computer-controlled initiator addition rate variation;

[0121] After the continuous addition of vinyl acetate is completed, the ethylene addition is turned off, and the reaction temperature continues to be maintained at 80°C by computer-controlled initiator addition rate changes;

[0122] When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends;

[0123] The temperature of the reaction material was lowered to below 35° C., and 0.57 parts of 10% sodium hydroxide solution was added to adjust the pH; finally, the reaction mixture was filtered and discharged.

[0124] Comparative Example 2

[0125] Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps:

[0126] A. Preparation of raw materials

[0127] A1. Preparation of initiator solution: Add 4.55 parts of deionized water and 0.38 parts of 70% TBHP solution (ie, 0.266 parts of initiator) to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 5.4%;

[0128] A2. Preparation of protective colloid solution: Add 21.8 parts of deionized water to the dissolution tank, start stirring, add 1.68 parts of polyvinyl alcohol 0588 and 0.75 parts of polyvinyl pyrrolidone K30, raise the temperature to 80°C until the protective colloid is completely dissolved, and prepare a protective colloid solution with a mass fraction of 10%.

[0129] B. Feed production

[0130] After replacing the reactor with nitrogen three times, 17.55 parts of deionized water and 24.3 parts of the protective colloid solution obtained in step A2 were added to the reactor, the stirrer was started, and then 0.167 parts of zinc chlorite was added, and finally 6.8 parts of vinyl acetate was added as the initial monomer;

[0131] After completion, the jacket was used to increase the temperature and the reactor was pressurized with ethylene. When the pressure reached 4.0 MPa and the temperature of the reaction mass rose to 55°C, the initiator was added to the reactor at a rate of 0.016 parts / min until the temperature reached 80°C;

[0132] When the reaction temperature rises to 80°C, the reactor pressure is raised to 5.9 MPa with ethylene, and the remaining 37.2 parts of vinyl acetate are added at a rate of 0.48 parts / min. At the same time, the jacket temperature is reduced to 5°C and the initiator addition rate is controlled by a computer to maintain the temperature at 80°C;

[0133] During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.9 MPa, and the reaction temperature was maintained at 80°C by computer-controlled initiator addition rate variation;

[0134] After the continuous addition of vinyl acetate is completed, the ethylene addition is turned off, and the reaction temperature continues to be maintained at 80°C by computer-controlled initiator addition rate changes;

[0135] When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends;

[0136] When the temperature of the reaction material drops to 35° C., 0.6 parts of 10% sodium hydroxide solution is added to adjust the pH; finally, the reaction material is filtered and discharged.

[0137] The test results of the products obtained in Examples 1-5 and Comparative Examples 1-2 are shown in Table 1 below.

[0138] It can be seen from the above Examples 1-5 and Comparative Examples 1-2 that there are significant differences in ethylene content, with the lowest ethylene content of the embodiment being 21.1% and the highest being 22.9, while the highest of the comparative example is only 18.9; there are also significant differences in average particle size, with the lowest emulsion particle size of the embodiment being 0.732 and the highest being 0.781, while the lowest of the comparative example is only 0.917; there are also significant differences in emulsion particle size distribution PDI, with the lowest PDI of the embodiment being 1.486 and the highest being 1.753, while the lowest of the comparative example is more than 2.0.

[0139] Table 1 Performance indicators of vinyl acetate-ethylene copolymer emulsion products

[0140] Solid content, % Ethylene content, % Viscosity / mPa.s Average particle size, μm Particle size distribution PDI Example 1 54.8 22.9 4365 0.732 1.671 Example 2 56.2 21.6 3896 0.755 1.669 Example 3 55.4 22.6 2981 0.735 1.753 Example 4 56.3 22.3 3754 0.752 1.616 Example 5 55.7 21.8 4378 0.751 1.486 Comparative Example 1 55.7 18.9 3945 0.917 2.063 Comparative Example 2 55.7 18.1 3621 0.965 2.173

[0141] In summary, the technical solution using polyvinyl pyrrolidone as the main protective colloid has achieved the excellent technical effect of low emulsion particle size and narrow particle size distribution under high ethylene content compared with the solution in which the protective colloid does not contain or contains only a small amount of polyvinyl pyrrolidone. The emulsion products with these performance indicators have excellent adhesion while ensuring high ethylene content, can be used as adhesive base materials of better quality, and can be widely used in manufacturing industries such as paper coating, packaging lamination, and textile printing.

[0142] The above is only an embodiment of the present invention. The commonly known technical common sense in the scheme is not described in detail here. The ordinary technicians in the relevant field are aware of all the common technical knowledge in the technical field to which the invention belongs before the application date, can obtain all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical commonly known technologies should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, they can also make some adjustments and improvements, which should also be regarded as the scope of protection of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection claimed by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a high-ethylene content vinyl acetate-ethylene copolymer emulsion, which is prepared by a semi-continuous emulsion polymerization method using vinyl acetate, ethylene, an initiator, and a protective colloid as raw materials; wherein the protective colloid comprises polyvinyl pyrrolidone.

2. The preparation method according to claim 1, wherein the polyvinyl pyrrolidone is selected from one or more of K17, K25 and K30.

3. The preparation method according to claim 1 or 2, wherein the protective colloid further comprises polyvinyl alcohol, and the content of polyvinyl pyrrolidone in the protective colloid is not less than 80% by weight.

4. The preparation method according to claim 3, wherein the polyvinyl alcohol is a polyvinyl alcohol with a low degree of polymerization or a medium degree of polymerization.

5. The preparation method according to claim 3 or 4, wherein the polyvinyl alcohol is selected from one or more of polyvinyl alcohol 0488, 0588 and 1788.

6. According to the preparation method according to any one of claims 1 to 5, the semi-continuous emulsion polymerization method consists of three stages: The initial feeding stage, the pre-reaction stage and the polymerization reaction stage are as follows. In the initial feeding stage, 10-40% of the total weight of the vinyl acetate raw material is first added as the initial monomer, and in the polymerization reaction stage, the remaining vinyl acetate raw material is continuously added at a rate of 0.35-0.53 parts / min.

7. The preparation method according to claim 6, wherein the ethylene pressure in the pre-reaction stage is controlled to be 3.5-4.5 MPa and the temperature is 52-60°C, and the ethylene pressure in the polymerization reaction stage is controlled to be 5.8-6.1 MPa and the temperature is 80±2°C.

8. The preparation method according to any one of claims 1 to 7, wherein, in parts by weight, 42.0-44.0 parts of vinyl acetate, 11.7-12.9 parts of ethylene, 2.2-2.7 parts of protective colloid, 0.06-0.27 parts of initiator peroxide, 0.12-0.17 parts of reducing agent and an appropriate amount of water are used as raw materials, and after replacing the reactor, water, protective colloid and reducing agent solution are added to the reactor under stirring, and then vinyl acetate accounting for 10-40% of the total amount of vinyl acetate raw materials is added as an initial monomer; in the pre-reaction stage, the temperature and pressure are increased, and when the ethylene pressure reaches 4.0 MPa, when the temperature rises to 52-60°C, continuously add the initiator peroxide solution to the reactor until the temperature reaches 80°C; when the temperature of the reaction material rises to 80°C, the ethylene pressure is increased to 5.8-6.1MPa, the polymerization reaction stage begins, and the remaining vinyl acetate raw material is continuously added at a rate of 0.35-0.55 parts / min. During the continuous vinyl acetate addition in the polymerization reaction stage, the ethylene pressure is maintained at 5.8-6.1MPa, and the reaction temperature is maintained at 80±2°C. After the continuous vinyl acetate addition is completed, the ethylene addition is turned off, and the reaction temperature is continued to be controlled at 80±2°C to continue the polymerization reaction; when the ethylene pressure is lower than 1.5MPa, the initiator oxide addition is stopped and the reaction is terminated; when the material temperature drops below 35°C, an appropriate amount of sodium hydroxide solution is added to adjust the pH of the emulsion; finally, the material is filtered and discharged.

9. The vinyl acetate-ethylene copolymer emulsion prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The content of ethylene units in the emulsion is 21-23%, and the average particle size of the emulsion is less than 0.8 μm.

10. The vinyl acetate-ethylene copolymer emulsion according to claim 9, characterized in that: The content of ethylene units in the emulsion is 21-23%, and the average particle size of the emulsion is 0.7-0.8 μm.

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