Method for improving dilution stability of vinyl acetate-ethylene copolymer emulsion

Abstract

The invention discloses a method for improving the dilution stability of vinyl acetate-ethylene copolymer emulsion. The vinyl acetate-ethylene copolymer emulsion is prepared from raw materials including a monomer, a protective colloid, an initiator, an emulsifier and a reducing agent, the dilution stability of the emulsion is 0.6%-0.9%; the protective colloid is composed of (1) polyvinylpyrrolidone or (2) polyvinylpyrrolidone and polyvinyl alcohol. The dilution stability of the vinyl acetate-ethylene copolymer emulsion prepared by the method can be reduced to 0.6-0.9%, and the emulsion particles are small in particle size and good in stability, can be used as an adhesive base material, and are suitable for manufacturing industries such as paper coatings, packaging and laminating, textile printing and the like.

Description

Technical Field

[0001] The invention relates to the field of vinyl acetate-ethylene copolymer emulsion, in particular to a method for improving the dilution stability of vinyl acetate-ethylene copolymer emulsion. Background Art

[0002] Vinyl acetate-ethylene copolymer emulsion is widely used in adhesives, coatings, cement modification, fabric and paper processing and other fields. The addition of ethylene to vinyl acetate-ethylene copolymer emulsion strengthens the discontinuity of acetyl distribution, making the polymer main chain soft, and its softness increases with the increase of vinyl content. This increase in its own softness can play the role of a plasticizer, and the plasticization effect is permanent, without the shortcomings of migration, volatilization, and exudation of external low molecular weight plasticizers. In addition, due to the non-polarity, low glass transition temperature, and hydrophobicity of ethylene, the emulsion has good initial viscosity, flexibility, weather resistance, saponification resistance, and water resistance.

[0003] Emulsion is a thermodynamically unstable dispersion. It may have stratification problems under storage, transportation and processing conditions, which may affect its use. The stability of conventional polyvinyl acetate-ethylene copolymer emulsions relies on the hydration layer formed by the protective colloid to prevent the latex particles from adhering to each other. Therefore, the ability of the protective colloid to adsorb on the surface of the latex particles is an important factor affecting the dilution stability. The protective colloid of polyvinyl acetate-ethylene copolymer emulsions usually uses polyvinyl alcohol. Polyvinyl alcohol exists on the surface of the latex particles in a grafted and adsorbed form, but a considerable part of it exists in a free form and does not act as a stabilizer. A lot of research has been done in China to improve the dilution stability of VAE emulsions.

[0004] Chinese patent document CN109651556A discloses a method for preparing a vinyl acetate-ethylene copolymer emulsion, specifically a monodisperse vinyl acetate-ethylene copolymer emulsion prepared from raw materials including monomers, an initiation system and an emulsification system. The prepared emulsion has a dilution stability of 1.10-1.50%.

[0005] Chinese patent document CN108219054A discloses that a protective colloid is added in the continuous polymerization stage while a reactive emulsifier (alkylphenol polyoxyethylene ether ammonium sulfate, alkylphenol polyoxyethylene ether ammonium sulfonate, ethoxy polyether sulfate or ethoxy polyether sulfonate) is added to obtain a vinyl acetate-ethylene copolymer emulsion with a dilution stability of 1.0%-1.5%.

[0006] The prior art has the following shortcomings: At present, the technical research on improving the dilution stability of vinyl acetate-ethylene copolymer emulsion in my country mainly focuses on optimizing the process, using reactive emulsifiers, etc. Although these methods can improve the dilution stability of the emulsion, they have some shortcomings, such as increased costs, complex processes, etc. Summary of the invention

[0007] In one aspect, the present invention provides a method for improving the dilution stability of a vinyl acetate-ethylene copolymer emulsion, wherein the emulsion is prepared from raw materials including a monomer, an initiator, an emulsifier, and a reducing agent; the method maintains the dilution stability of the emulsion at 0.6%-0.9% by using a protective colloid; the protective colloid is composed of (1) polyvinyl pyrrolidone or (2) polyvinyl pyrrolidone and polyvinyl alcohol.

[0008] Furthermore, the polyvinyl pyrrolidone is one or more of K17-K30.

[0009] Furthermore, the polyvinyl pyrrolidone accounts for 80%-100% of the protective colloid, by mass percentage.

[0010] Furthermore, the polyvinyl alcohol has a degree of alcoholysis of 86.5%-88.5% and a degree of polymerization of 400-1750, calculated in molar percentage.

[0011] Furthermore, the polyvinyl alcohol is one or more of 0488, 0588 and 1788.

[0012] Furthermore, the emulsifier consists of an anionic emulsifier and a nonionic emulsifier.

[0013] Furthermore, the anionic emulsifier accounts for 20%-40% of the total amount of the emulsifier.

[0014] Furthermore, the ratio is as follows, based on mass: 42.0-44.0 parts of vinyl acetate, 11.7-12.9 parts of ethylene, 1.6-2.2 parts of protective colloid, 0.6-1.2 parts of emulsifier, 0.06-0.27 parts of initiator and 0.12-0.17 parts of reducing agent.

[0015] Further, the following steps are included: A. Preparation of raw materials: A1 Initiator solution preparation: 3.0-5.1 parts of deionized water and 0.06-0.27 parts of initiator are stirred to prepare a 1.8%-5.4% initiator solution, calculated by mass percentage; Preparation of A2 protective colloid solution: 14.8-19.2 parts of deionized water and 1.6-2.2 parts of protective colloid are stirred and heated to 80-85°C until the protective colloid is completely dissolved to prepare a protective colloid solution; B. Feed production Add water and protective colloid solution, start stirring, then add emulsifier and reducing agent, and finally add 10%-40% of the total amount of vinyl acetate as the initial monomer; use a jacket to increase the temperature of the reaction materials, and use ethylene to increase the pressure at the same time. When the pressure reaches 3.8-4.0MPa and the temperature rises to 52-60°C, add the initiator at a rate of 0.016-0.1 parts / min; When the temperature of the reaction mass rises to 78-80°C, the ethylene pressure is raised to 5.8-6.1 MPa, and the remaining vinyl acetate is added at a rate of 0.35-0.54 parts / min, while the jacket temperature is lowered to 4-6°C and maintained; During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.8-6.1 MPa, and the reaction temperature was maintained at 80±2°C by computer-controlled initiator addition rate changes; After the continuous addition of vinyl acetate is completed, the ethylene feed is turned off, and the reaction temperature continues to be controlled at 80±2℃ by the change of the initiator feed rate; When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends; When the material temperature drops below 35°C, add sodium hydroxide solution to adjust the pH; finally filter and discharge the material.

[0016] The present invention has the following beneficial effects: (1) By using the method for preparing vinyl acetate-ethylene copolymer emulsion of the present invention, the latex particles have good stability and the emulsion dilution stability can be reduced to 0.6%-0.9%.

[0017] (2) The latex particles obtained by the preparation method of the present invention have small particle size and few coarse particles, which reduces the precipitation of latex particles in the emulsion and maintains a relatively stable state, thereby making the emulsion stable and can be used as an adhesive base material, and is suitable for manufacturing industries such as paper coating, packaging lamination, and textile printing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The particle size and distribution diagram of the vinyl acetate-ethylene copolymer emulsion prepared in Example 1; Figure 2 The particle size and distribution diagram of the vinyl acetate-ethylene copolymer emulsion prepared in Example 2; Figure 3 The particle size and distribution diagram of the vinyl acetate-ethylene copolymer emulsion prepared in Example 3; Figure 4 The particle size and distribution diagram of the vinyl acetate-ethylene copolymer emulsion prepared in Example 4; Figure 5 The particle size and distribution diagram of the vinyl acetate-ethylene copolymer emulsion prepared in Example 5; Figure 6The particle size and distribution diagram of the vinyl acetate-ethylene copolymer emulsion prepared in Example 6; Figure 7 The particle size and distribution diagram of the vinyl acetate-ethylene copolymer emulsion prepared in Comparative Example 1; Figure 8 This is the particle size and distribution diagram of the vinyl acetate-ethylene copolymer emulsion prepared in Comparative Example 2. DETAILED DESCRIPTION

[0019] The examples are provided to better illustrate the content of the present invention, but the content of the present invention is not 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 content of the invention, which still fall within the protection scope of the present invention.

[0020] The initiator used in the present invention is one of hydrogen peroxide and tert-butyl hydroperoxide (TBHP); the reducing agent is one of sodium isoascorbate and zinc formaldehyde sulfoxylate; the anionic emulsifier is one of sodium dodecyl sulfate, sodium hexadecyl sulfonate and dodecylbenzene sulfonate; and the nonionic emulsifier is one of octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether or fatty alcohol polyoxyethylene ether.

[0021] The following solid content and dilution stability are tested according to the test methods of corresponding indicators in the national standard of vinyl acetate-ethylene copolymer emulsion "GB / T27573-2011 Vinyl acetate-ethylene copolymer emulsion"; The following particle sizes were tested using a laser particle size analyzer from Malvern, UK. The instrument model is Mastersize 2000 and the test method is the general method for this type of instrument.

[0022] The following viscosity 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℃, the instrument model is; Brookfield LVDV-II+, the rotor model is No. 4 shaft, 60 rpm.

[0023] Example 1 Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps: A. Preparation of raw materials A1. Preparation of initiator solution: Add 3.16 parts of deionized water and 0.225 parts of 27.5% hydrogen peroxide solution by mass to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 1.8%; A2. Preparation of protective colloid solution: Add 14.85 parts of deionized water to the dissolution tank, start stirring, add 1.65 parts of polyvinyl pyrrolidone K30; raise the temperature to 80°C until the protective colloid is completely dissolved; B. Feed production After replacing the reactor with nitrogen three times, 25.98 parts of deionized water and 16.5 parts of the protective colloid solution obtained in step A were added to the reactor, the stirrer was started, and then 0.41 parts of nonionic emulsifier X-100, 0.20 parts of sodium lauryl sulfate, 0.125 parts of sodium isoascorbate were added in sequence, and finally 4.26 parts of vinyl acetate were added as the initial monomer; 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 58°C, the initiator was added to the reactor at a rate of 0.083 parts / min; When the reaction temperature rises to 80°C, the reactor pressure is raised to 6.1 MPa with ethylene, and 38.2 parts of remaining vinyl acetate are added at a rate of 0.53 parts / min, while the jacket temperature is reduced to 4°C and maintained; During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 6.0 MPa, and the reaction temperature was maintained at 80 ± 2 °C by computer-controlled initiator addition rate changes; 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±2℃ by computer-controlled initiator addition rate changes; When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends; The temperature of the reaction material was lowered to below 35°C, and 3.0 parts of 10% sodium hydroxide solution was added to adjust the pH; finally, the reaction material was filtered and discharged.

[0024] The solid content, ethylene content, viscosity and dilution stability of the emulsion prepared in this example were tested, and the results are shown in Table 1.

[0025] Example 2 Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps: A. Preparation of raw materials A1. Preparation of initiator solution: Add 3.16 parts of deionized water and 0.225 parts of 27.5% hydrogen peroxide solution by mass to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 1.8%; A2. Preparation of protective colloid solution: 17.1 parts of deionized water were added to the dissolution tank, stirring was started, 1.52 parts of polyvinyl pyrrolidone K17 and 0.38 parts of polyvinyl alcohol 0588 were added, and the temperature was raised to 80 ° C until the protective colloid was completely dissolved; B. Feed production After replacing the reactor with nitrogen three times, 23.73 parts of deionized water and 19 parts of the protective colloid solution obtained in step A were added to the reactor, the stirrer was started, and then 1.19 parts of nonionic emulsifier X-305 (concentration 70%), 0.35 parts of sodium hexadecyl sulfate, 0.13 parts of zinc chlorate were added in sequence, and finally 12.38 parts of vinyl acetate were added as the initial monomer; 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; When the reaction temperature rises to 78°C, the reactor pressure is raised to 5.8 MPa with ethylene, and 30.03 parts of remaining vinyl acetate begins to be added at a rate of 0.425 parts / min, while the jacket temperature is reduced to 6°C and maintained; During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.8 MPa, and the reaction temperature was maintained at 80 ± 2 °C by computer-controlled initiator addition rate changes; 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±2℃ by computer-controlled initiator addition rate changes; When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends; The temperature of the reaction material was lowered to below 35°C, and 0.575 parts of 10% sodium hydroxide solution was added to adjust the pH; finally, the reaction material was filtered and discharged.

[0026] The solid content, ethylene content, viscosity and dilution stability of the emulsion prepared in this example were tested, and the results are shown in Table 1.

[0027] Example 3 Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps: A. Preparation of raw materials A1. Preparation of initiator solution: Add 3.58 parts of deionized water and 0.25 parts of 27.5% hydrogen peroxide solution to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 1.8%; A2. Preparation of protective colloid solution: Add 19.2 parts of deionized water to the dissolution tank, start stirring, add 1.78 parts of polyvinyl pyrrolidone K19 and 0.35 parts of polyvinyl alcohol 0488, and heat to 80 ° C until the protective colloid is completely dissolved; B. Feed production After replacing the reactor with nitrogen three times, 21.22 parts of deionized water and 21.33 parts of the protective colloid solution obtained in step A were added to the reactor, the stirrer was started, and then 0.475 parts of nonionic X-100, 0.125 parts of sodium hexadecyl sulfate, 0.13 parts of sodium isoascorbate were added in sequence, and finally 17.45 parts of vinyl acetate were added as the initial monomer; 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 60°C, the initiator was added to the reactor at a rate of 0.1 part / min; When the reaction temperature rises to 80°C, the reactor pressure is raised to 6.0 MPa with ethylene, and 25.19 parts of remaining vinyl acetate are added at a rate of 0.35 parts / min, while the jacket temperature is reduced to 5°C and maintained; During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 6.0 MPa, and the reaction temperature was maintained at 80 ± 2 °C by computer-controlled initiator addition rate changes; 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±2℃ by computer-controlled initiator addition rate changes; When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends; The temperature of the reaction material was lowered to below 35°C, and 0.25 parts of 10% sodium hydroxide solution was added to adjust the pH; finally, the reaction material was filtered and discharged.

[0028] The solid content, ethylene content, viscosity and dilution stability of the emulsion prepared in this example were tested, and the results are shown in Table 1.

[0029] Example 4 Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps: A. Preparation of raw materials A1. Preparation of initiator solution: Add 4.55 parts of deionized water and 0.38 parts of 70% TBHP solution by mass into the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 5.4%; A2. Preparation of protective colloid solution: 16.65 parts of deionized water were added to the dissolution tank, stirring was started, 1.59 parts of polyvinyl pyrrolidone K25 and 0.258 parts of polyvinyl alcohol 1788 were added, and the temperature was raised to 80 ° C until the protective colloid was completely dissolved; B. Feed production After replacing the reactor with nitrogen three times, 20.95 parts of deionized water and 18.5 parts of the protective colloid solution obtained in step A were added to the reactor, the stirrer was started, and then 0.525 parts of non-ionic (EH-9), 0.2 parts of sodium dodecylbenzene sulfonate, 0.17 parts of zinc chlorite were added in sequence, and finally 7.13 parts of vinyl acetate were added as the initial monomer; 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 60°C, the initiator was added to the reactor at a rate of 0.0166 parts / min; When the reaction temperature rises to 80°C, the reactor pressure is raised to 5.9 MPa with ethylene, and 35.38 parts of remaining vinyl acetate are added at a rate of 0.39 parts / min, while the jacket temperature is reduced to 5°C and maintained; During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.9 MPa, and the reaction temperature was maintained at 80 ± 2 °C by computer-controlled initiator addition rate changes; 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±2℃ by computer-controlled initiator addition rate changes; When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends; The temperature of the reaction material was lowered to below 35°C, and 0.6 parts of 10% sodium hydroxide solution was added to adjust the pH; finally, the reaction material was filtered and discharged.

[0030] The solid content, ethylene content, viscosity and dilution stability of the emulsion prepared in this example were tested, and the results are shown in Table 1.

[0031] Example 5 Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps: A. Preparation of raw materials A1. Preparation of initiator solution: Add 3.09 parts of deionized water and 0.283 parts of a 27.5% hydrogen peroxide solution to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 2.3%; A2. Preparation of protective colloid solution: 17.03 parts of deionized water were added to the dissolution tank, stirring was started, 1.54 parts of polyvinyl pyrrolidone K30, 0.175 parts of polyvinyl alcohol 1788, 0.175 parts of polyvinyl alcohol 0488 were added, and the temperature was raised to 80 ° C until the protective colloid was completely dissolved; B. Feed production After replacing the reactor with nitrogen three times, 21.99 parts of deionized water and 18.92 parts of the protective colloid solution obtained in step A were added to the reactor, the stirrer was started, and then 0.57 parts of nonionic emulsifier X-100, 0.24 parts of emulsifier sodium dodecylbenzene sulfonate, 0.14 parts of zinc chlorite were added in sequence, and finally 10.6 parts of vinyl acetate were added as the initial monomer; 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 60°C, the initiator was added to the reactor at a rate of 0.075 parts / min; When the reaction temperature rises to 80°C, the reactor pressure is raised to 6.0 MPa with ethylene, and 31.4 parts of remaining vinyl acetate are added at a rate of 0.44 parts / min, while the jacket temperature is reduced to 5°C and maintained; During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.9 MPa, and the reaction temperature was maintained at 80 ± 2 °C by computer-controlled initiator addition rate changes; 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±2℃ by computer-controlled initiator addition rate changes; When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends; The temperature of the reaction material was lowered to below 35°C, and 0.5 parts of 10% sodium hydroxide solution was added to adjust the pH; finally, the reaction material was filtered and discharged.

[0032] The solid content, ethylene content, viscosity and dilution stability of the emulsion prepared in this example were tested, and the results are shown in Table 1.

[0033] Example 6 Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps: A. Preparation of raw materials A1. Preparation of initiator solution: Add 4.02 parts of deionized water and 0.3 parts of 70% TBHP solution by mass into the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 4.9%; A2. Preparation of protective colloid solution: Add 15.975 parts of deionized water to the dissolution tank, start stirring, add 1.775 parts of polyvinyl pyrrolidone K30, and raise the temperature to 80 ° C until the protective colloid is completely dissolved; B. Feed production After replacing the reactor with nitrogen three times, 24.01 parts of deionized water and 17.75 parts of the protective colloid solution obtained in step A were added to the reactor, the stirrer was started, and then 0.94 parts of nonionic emulsifier EH-9, 0.23 parts of sodium lauryl sulfate, 0.14 parts of sodium isoascorbate were added in sequence, and finally 10.77 parts of vinyl acetate were added as the initial monomer; 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 60°C, the initiator was added to the reactor at a rate of 0.033 parts / min; When the reaction temperature rises to 80°C, the reactor pressure is raised to 5.8 MPa with ethylene, and 33.23 parts of remaining vinyl acetate are added at a rate of 0.475 parts / min, while the jacket temperature is reduced to 5°C and maintained; During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.8 MPa, and the reaction temperature was maintained at 80 ± 2 °C by computer-controlled initiator addition rate changes; 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±2℃ by computer-controlled initiator addition rate changes; When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends; The temperature of the reaction material was lowered to below 35°C, and 0.25 parts of 10% sodium hydroxide solution was added to adjust the pH; finally, the reaction material was filtered and discharged.

[0034] The solid content, ethylene content, viscosity and dilution stability of the emulsion prepared in this example were tested, and the results are shown in Table 1.

[0035] Comparative Example 1 Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps: A. Preparation of raw materials A1. Preparation of initiator solution: Add 4.016 parts of deionized water and 0.3 parts of 70% TBHP solution by mass to the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 4.9%; A2. Preparation of protective colloid solution: Add 15.96 parts of deionized water to the dissolution tank, start stirring, add 1.775 parts of polyvinyl alcohol 1788, and raise the temperature to 80 ° C until the protective colloid is completely dissolved; B. Feed production After replacing the reactor with nitrogen three times, 24.01 parts of deionized water and 17.75 parts of the protective colloid solution obtained in step A were added to the reactor, the stirrer was started, and then 0.94 parts of nonionic emulsifier EH-9, 0.23 parts of sodium lauryl sulfate, 0.14 parts of sodium isoascorbate were added in sequence, and finally 10.77 parts of vinyl acetate were added as the initial monomer; 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 60°C, the initiator was added to the reactor at a rate of 0.0333 parts / min; When the reaction temperature rises to 80°C, the reactor pressure is raised to 5.8 MPa with ethylene, and 33.23 parts of remaining vinyl acetate are added at a rate of 0.475 parts / min, while the jacket temperature is reduced to 5°C and maintained; During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.8 MPa, and the reaction temperature was maintained at 80 ± 2 °C by computer-controlled initiator addition rate changes; 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±2℃ by computer-controlled initiator addition rate changes; When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends; The temperature of the reaction material was lowered to below 35°C, and 0.25 parts of 10% sodium hydroxide solution was added to adjust the pH; finally, the reaction material was filtered and discharged.

[0036] The solid content, ethylene content, viscosity and dilution stability of the emulsion prepared in this comparative example were tested, and the results are shown in Table 1.

[0037] Comparative Example 2 Vinyl acetate-ethylene copolymer emulsion is prepared specifically according to the following steps: A. Preparation of raw materials A1. Preparation of initiator solution: Add 4.55 parts of deionized water and 0.38 parts of 70% TBHP solution by mass into the initiator tank, stir and mix well to prepare an initiator solution with a mass fraction of 5.4%; A2. Preparation of protective colloid solution: Add 16.65 parts of deionized water to the dissolution tank, start stirring, add 1.59 parts of polyethylene 0588 and 0.258 parts of polyvinyl alcohol 1788, and heat to 80 ° C until the protective colloid is completely dissolved; B. Feeding production After replacing the reactor with nitrogen three times, 20.95 parts of deionized water and 18.5 parts of the protective colloid solution obtained in step A were added to the reactor, the stirrer was started, and then 0.525 parts of non-ionic (EH-9), 0.2 parts of sodium dodecylbenzene sulfonate, 0.17 parts of zinc chlorite were added in sequence, and finally 7.13 parts of vinyl acetate were added as the initial monomer; 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 60°C, the initiator was added to the reactor at a rate of 0.0166 parts / min; When the reaction temperature rises to 80°C, the reactor pressure is raised to 5.9 MPa with ethylene, and 35.38 parts of remaining vinyl acetate are added at a rate of 0.39 parts / min, while the jacket temperature is reduced to 5°C and maintained; During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.9 MPa, and the reaction temperature was maintained at 80 ± 2 °C by computer-controlled initiator addition rate changes; 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±2℃ by computer-controlled initiator addition rate changes; When the ethylene pressure is lower than 1.5 MPa, stop adding the initiator and the reaction ends; The temperature of the reaction material was lowered to below 35°C, and 0.6 parts of 10% sodium hydroxide solution was added to adjust the pH; finally, the reaction material was filtered and discharged.

[0038] The solid content, ethylene content, viscosity and dilution stability of the emulsion prepared in this comparative example were tested, and the results are shown in Table 1.

[0039] Table 1 Indices of emulsions prepared in Examples 1-6 and Comparative Examples 1-2 As can be seen from Table 1, the dilution stability of the vinyl acetate-ethylene copolymer emulsions prepared in Examples 1-6 of the present invention is 0.6%-0.9%, and the particle size is 0.616-0.712 μm; the dilution stability of the vinyl acetate-ethylene copolymer emulsions prepared in Comparative Examples 1-2 is 1.8%-2.1%, and the particle size is 0.869-0.890 μm. Compared with the comparative examples, the particle size of the emulsions prepared in Examples 1-6 is significantly smaller than that of the emulsions prepared in Examples 1-6, and the dilution stability of the emulsions prepared in the present invention is significantly reduced. This proves that the vinyl acetate-ethylene copolymer emulsions prepared in the present invention using the protective colloid composed of (1) polyvinyl pyrrolidone or (2) polyvinyl pyrrolidone and polyvinyl alcohol have good dilution stability.

[0040] The present invention Figure 1-6 The particle size of the emulsions prepared in Examples 1-6 is 0.616-0.712 μm. Figure 7-8 The particle size of the emulsion prepared in Comparative Example 1-2 is 0.869-0.890 μm, which proves that the latex particles of the emulsion prepared by the present invention are small in size and have fewer coarse particles, so that the latex particles in the emulsion will not precipitate and maintain a relatively stable state, thereby making the emulsion stable. The emulsion can be used as an adhesive base material and is suitable for manufacturing industries such as paper coating, packaging lamination, and textile printing.

[0041] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for improving the dilution stability of a vinyl acetate-ethylene copolymer emulsion, wherein the emulsion is prepared from raw materials including a monomer, an initiator, an emulsifier and a reducing agent; characterized in that: The method maintains the dilution stability of the emulsion at 0.6%-0.9% by using a protective colloid; the protective colloid is composed of (1) polyvinyl pyrrolidone or (2) polyvinyl pyrrolidone and polyvinyl alcohol.

2. The method for improving the dilution stability of vinyl acetate-ethylene copolymer emulsion according to claim 1, characterized in that: The polyvinyl pyrrolidone is one or more of K17-K30.

3. The method for improving the dilution stability of vinyl acetate-ethylene copolymer emulsion according to claim 1 or 2, characterized in that: The polyvinyl pyrrolidone accounts for 80%-100% of the protective colloid, calculated by mass percentage.

4. The method for improving the dilution stability of vinyl acetate-ethylene copolymer emulsion according to any one of claims 1 to 3, characterized in that: The polyvinyl alcohol has a degree of alcoholysis of 86.5-88.5% and a degree of polymerization of 400-1750, calculated in mole percentage.

5. The method for improving the dilution stability of vinyl acetate-ethylene copolymer emulsion according to claim 4, characterized in that: The polyvinyl alcohol is one or more of 0488, 0588 and 1788.

6. The method for improving the dilution stability of vinyl acetate-ethylene copolymer emulsion according to any one of claims 1 to 5, characterized in that: The emulsifier consists of anionic emulsifier and nonionic emulsifier.

7. The method for improving the dilution stability of vinyl acetate-ethylene copolymer emulsion according to claim 6, characterized in that: The anionic emulsifier accounts for 20%-40% of the total amount of the emulsifier.

8. The method for improving the dilution stability of vinyl acetate-ethylene copolymer emulsion according to any one of claims 1 to 7, characterized in that: The proportions are as follows, by mass: 42.0-44.0 parts of vinyl acetate, 11.7-12.9 parts of ethylene, 1.6-2.2 parts of protective colloid, 0.6-1.2 parts of emulsifier, 0.06-0.27 parts of initiator and 0.12-0.17 parts of reducing agent.

9. The method for improving the dilution stability of vinyl acetate-ethylene copolymer emulsion according to claim 8, characterized in that: The following steps are involved: A. Preparation of raw materials: A1 Initiator solution preparation: 3.0-5.1 parts of deionized water and 0.06-0.27 parts of initiator are stirred to prepare a 1.8%-5.4% initiator solution, calculated by mass percentage; Preparation of A2 protective colloid solution: 14.8-19.2 parts of deionized water and 1.6-2.2 parts of protective colloid are stirred and heated to 80-85°C until the protective colloid is completely dissolved to prepare a protective colloid solution; B. Feed production Add water and protective colloid solution, start stirring, then add emulsifier and reducing agent, and finally add 10%-40% of the total amount of vinyl acetate as the initial monomer; use a jacket to increase the temperature of the reaction materials, and use ethylene to increase the pressure at the same time. When the pressure reaches 3.8-4.0MPa and the temperature rises to 52-60°C, add the initiator at a rate of 0.016-0.1 parts / min; When the temperature of the reaction mass rises to 78-80°C, the ethylene pressure is raised to 5.8-6.1 MPa, and the remaining vinyl acetate is added at a rate of 0.35-0.54 parts / min, while the jacket temperature is reduced to 4-6°C and maintained; During the continuous addition of vinyl acetate, the ethylene pressure was maintained at 5.8-6.1 MPa, and the reaction temperature was maintained at 80±2°C by computer-controlled initiator addition rate changes; After the continuous addition of vinyl acetate is completed, the ethylene feed is turned off, and the reaction temperature continues to be controlled at 80±2°C by the change of the initiator feed rate; When the ethylene pressure is lower than 1.5MPa, stop adding the initiator and the reaction ends; When the material temperature drops below 35°C, add sodium hydroxide solution to adjust the pH; finally filter and discharge the material.

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