Method for improving water resistance of vinyl acetate-ethylene emulsion for redispersible latex powder

Abstract

The invention discloses a method for improving the water resistance of a vinyl acetate-ethylene emulsion for redispersible latex powder. The emulsion is prepared from raw materials including a vinyl acetate monomer, an ethylene monomer, an initiation system, an emulsification system and a post-treatment aid, and after defoaming is completed, a post-treatment monomer is added. By adopting the technical scheme that the reactive emulsifier is adopted and the post-treatment monomer is added after defoaming, the water resistance of the emulsion is good, the emulsion does not become white or fall off after being soaked in water, the emulsion can be used as a basic raw material of redispersible latex powder, and the construction strength is met.

Description

Technical Field

[0001] The invention relates to a vinyl acetate-ethylene emulsion, in particular to a method for improving the water resistance of the vinyl acetate-ethylene emulsion for redispersible latex powder. Background Art

[0002] Redispersible latex powder refers to the polymer emulsion modified by adding other substances and then spray-dried. It can be redispersed into emulsion with water as the dispersion medium. It aggregates from the initial 2μm to form spherical particles of 80-120μm. The surface of these particles is coated with an inorganic anti-hard structure powder to obtain dry polymer powder. They are very easy to pour and bag and store in warehouses. When the powder is mixed with mortar with water, cement or gypsum as the base material, it can be redispersed. The basic particles (2μm) will re-form into a state equivalent to the original latex, so it is called redispersible latex powder. Vinyl acetate-ethylene emulsion (VAE) type redispersible latex powder refers to redispersible latex powder produced with vinyl acetate-ethylene copolymer emulsion as the main raw material. It is usually used in combination with inorganic binders such as cement, which can significantly improve the bonding and cohesion of mortar, reduce elastic modulus, water absorption, and enhance flexural strength.

[0003] Chinese patent document CN111100235A discloses a high-ethylene content vinyl acetate-ethylene copolymer emulsion and a preparation method thereof, comprising: an ethylene content of 18.0%-18.6%, prepared from raw materials including monomers, an initiator 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 degree of polymerization of 400-3500 and a degree of alcoholysis of 80%-90%.

[0004] The prior art has the following disadvantages: the water resistance of the emulsion obtained by the prior method does not meet the requirements for redispersible latex powder. Summary of the invention

[0005] On the one hand, the present invention provides a method for improving the water resistance of a vinyl acetate-ethylene emulsion for redispersible latex powder, wherein the emulsion is prepared by using raw materials including vinyl acetate monomer and ethylene monomer, an initiator system, an emulsifying system, and a post-treatment auxiliary agent; and a post-treatment monomer is added after degassing is completed.

[0006] Furthermore, the post-treatment monomer is acrylate.

[0007] Furthermore, the post-treatment monomer is selected from one or more of methacrylic acid, methyl methacrylate, and ethyl acrylate.

[0008] Furthermore, the emulsification system includes a protective colloid and an emulsifier; the emulsifier is a reactive emulsifier.

[0009] Furthermore, the reactive emulsifier is selected from one or more of allyl ether sulfonate, acrylamide sulfonate and allyl carboxyl sulfonate.

[0010] Furthermore, the post-treatment aid is added after the post-treatment monomer is added to perform post-treatment.

[0011] Furthermore, the post-treatment aid and the initiation system both include a reducing agent and an oxidizing agent.

[0012] Furthermore, the amount of the post-treatment monomer used is 5-20 times the amount of the post-treatment auxiliary agent used, calculated by mass.

[0013] Further, the following steps are included:

[0014] Add protective colloid, reactive emulsifier, initial vinyl acetate accounting for 39%-48% of the total mass of vinyl acetate, and ethylene, continuously add initial oxidant and reductant, when the pressure rises to 7.8-8.0MPa, add the remaining vinyl acetate, degas to the degassing tank, add post-treatment monomer, and then add post-treatment additive for post-treatment.

[0015] In a second aspect, the present invention provides the use of the vinyl acetate-ethylene copolymer emulsion prepared by the method described in the present invention in redispersible latex powder.

[0016] The present invention has the following beneficial effects:

[0017] (1) The vinyl acetate-ethylene emulsion prepared by adding acrylate monomers and using a reactive emulsifier during post-treatment has good water resistance and does not turn white or fall off when immersed in water. The mechanical properties of the film are greatly improved and the film can be used as a basic raw material for redispersible latex powder and meets the construction strength requirements.

[0018] (2) The present invention adopts a reactive emulsifier to prepare a vinyl acetate-ethylene emulsion, and the obtained latex has high stability under high shear force and freeze-thaw stability; no emulsifier remains in the water phase, which can avoid the generation of foam, does not pollute the environment, and accelerates the film formation speed; the mechanical properties of the film are greatly improved.

[0019] (3) The raw materials of the present invention are widely available and inexpensive, and the existing production process is not significantly changed. While improving the quality of the existing vinyl acetate-ethylene copolymer emulsion products, the production batch time and pressure are slightly increased, and the increased cost is negligible. The preparation method is simple, the raw materials are easily available, and no special equipment is required. The industrial implementation is convenient and the application prospect is broad. DETAILED DESCRIPTION

[0020] 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.

[0021] The monomers used in the present invention are vinyl acetate and ethylene.

[0022] The protective colloid of the present invention is polyvinyl alcohol; further, it is polyvinyl alcohol with a polymerization degree of 400-1700 and an alcoholysis degree of 88 (mol)%.

[0023] The oxidant of the present invention is one or more of hydrogen peroxide, potassium persulfate, ammonium persulfate and tert-butyl hydroperoxide.

[0024] The reducing agent of the present invention is one or more of ascorbate, tartrate, bisulfite, thiosulfate and formaldehyde sulfoxylate.

[0025] The pH regulator of the present invention is one or more of formic acid, bicarbonate, acetate and phosphate.

[0026] The emulsion of the present invention is prepared from raw materials including 36-38 parts of vinyl acetate, 12-13 parts of ethylene, 3.3-3.5 parts of protective colloid, 0.3-0.5 parts of emulsifier, 0.1-0.3 parts of reducing agent, 0.2-0.4 parts of oxidant, 0.04-0.06 parts of pH regulator, 0.02-0.04 parts of post-treatment agent, 0.2-0.4 parts of post-treatment monomer and 36-38 parts of deionized water, calculated by weight.

[0027] The method for preparing the vinyl acetate-ethylene emulsion of the present invention comprises the following steps:

[0028] A. Preparation of raw materials

[0029] 1) Prepare the oxidant solution system: add 3 parts of deionized water and 0.2-0.4 parts of oxidant into the oxidant tank, and stir to dissolve;

[0030] 2) Prepare the reducing agent solution system: add 3 parts of deionized water and 0.1-0.3 parts of reducing agent to the reducing agent tank, and stir to dissolve;

[0031] 3) Post-treatment additives: 0.01-0.02 parts of oxidant, 0.8 parts of deionized water, 0.01-0.02 parts of reducing agent and 0.8 parts of deionized water;

[0032] 4) pH adjuster: 0.04-0.06 parts of pH adjuster and 0.4 parts of deionized water;

[0033] B. Feed production

[0034] Add 36-38 parts of deionized water, 0.5-0.7 parts of PVA1788, 2.6-3.0 parts of PVA0488 to the reactor, heat and stir to dissolve, then add 0.3-0.5 parts of emulsifier, 15-17 parts of vinyl acetate monomer, and add ethylene to the reactor. When the temperature reaches 54-62°C and the pressure reaches 5.1-5.5MPa, add the initial oxidant solution and the reducing agent solution at 0.024-0.026 parts / min, and reset to 68-70°C and cool completely; then the computer controls the reaction and the oxidant solution and the reducing agent solution. The solution is added at a rate, the reactor continues to increase the pressure to 7.8-8.0MPa, and 21-23 parts of vinyl acetate are continuously added dropwise, which is completed after about 90-100 minutes; when the temperature is 75-78°C and the pressure is 1.50-1.52MPa, it enters the finishing period, and the remaining oxidant solution and reducing agent solution are continued to be added dropwise; after degassing to the degassing tank, 0.2-0.4 parts of post-treatment monomer are first added, and then 0.02-0.04 parts of post-treatment auxiliary agent are added for post-treatment; after cooling, 0.04-0.06 parts of pH adjuster are added, and the material is discharged, filtered and packaged after keeping warm for 10 minutes.

[0035] Determination methods of various indicators

[0036] 1. Determination of solid content:

[0037] Instrument: HR83 infrared moisture meter, stainless steel weighing pan;

[0038] Operating conditions: standard temperature rise 165℃;

[0039] Method: Adjust the operating panel properly, open the sample chamber automatically, weigh the weighing pan, remove the skin, quickly add 1-2g of sample, push it flat, press the start button, and read the analysis result directly after the measurement is completed.

[0040] 2. Determination of viscosity:

[0041] Instrument: Constant temperature water bath 25+0.2℃, Brookfield viscometer;

[0042] Method: Place the sample in a 25+0.2℃ water bath, keep the temperature constant for 30 minutes, select the correct rotor, adjust the mark on the shaft to be consistent with the emulsion surface, start the viscometer motor, rotate for 45 seconds, and read the value directly.

[0043] 3. Determination of ethylene:

[0044] Instruments: infrared spectrometer, infrared drying lamp, water-resistant AgBr slide;

[0045] Method: Read the data directly according to the operating steps.

[0046] 4. Determination of glass transition temperature

[0047] Differential Scanning Calorimetry (DSC)

[0048] DSC characterizes the glass transition temperature of a material by measuring the change in the specific heat capacity of the material with temperature. The specific heat capacity will change greatly before and after Tg, and the glass transition temperature can be determined based on the curve. The glass transition temperature is usually a step in the direction of heat absorption. The glass transition is a region. This method usually takes the intersection of the line with equal distance from the two extrapolated baselines and the curve as the glass transition temperature.

[0049] 5. Water resistance test

[0050] Water resistance test method: room temperature immersion test method (GB / T1733-1993), water temperature is (23±2)℃; add distilled water or deionized water to the glass water tank, adjust the water temperature to the specified temperature, and maintain the temperature during the entire test process, immerse 2 / 3 of the test film in water for the specified time (30min), then take it out, dry it with filter paper, and check for loss of gloss, discoloration, bubbling, wrinkling, whitening, rubbing, etc. If not, the product is qualified.

[0051] 6. Membrane tensile breaking strength test

[0052] Refer to GB / T1040.1 2 2006 Molded and extruded plastic tensile properties test (testing instrument: MTS tensile testing machine, model 43).

[0053] Example 1

[0054] A. Raw material preparation

[0055] 1) Prepare the oxidant solution system: add 0.3 parts of hydrogen peroxide to 3 parts of deionized water and stir to dissolve;

[0056] 2) Prepare reducing agent solution system: add 0.2 parts of sodium formaldehyde sulfoxylate to 3 parts of deionized water and stir to dissolve;

[0057] 3) Preparation of post-treatment auxiliary agent solution: 0.01 parts of tert-butyl hydroperoxide and 0.8 parts of deionized water, 0.02 parts of sodium formaldehyde sulfoxylate and 0.8 parts of deionized water are mixed evenly and used for post-treatment;

[0058] 4) Preparation of pH adjuster solution: Mix 0.05 parts of sodium bicarbonate and 0.4 parts of deionized water;

[0059] B. Process

[0060] Add 38 parts of deionized water, 0.5 parts of PVA1788, and 2.8 parts of PVA0488 to the reactor, heat and stir to dissolve, then add 0.4 parts of sodium allyl ether sulfonate, 15 parts of vinyl acetate monomer, and add ethylene to the reactor. When the temperature reaches 55°C and the pressure reaches 5.2MPa, add the initial oxidant and reductant at 0.024 parts / min, and reset to 68°C and cool completely; then the computer controls the reaction and the rate of initiator addition, the reactor continues to increase the pressure to 7.8MPa, and continues to drip 22 parts of vinyl acetate continuously, which is completed in about 96 minutes; when the temperature is 76°C and the pressure is 1.50MPa, it enters the finishing period, and the remaining initiator is dripped at full speed; after degassing to the degassing tank, add 0.2 parts of post-treatment monomer methyl acrylate first, and then add post-treatment additives for post-treatment; after cooling, add 0.05 parts of sodium bicarbonate to adjust the pH, keep warm for 10 minutes, discharge, filter, and package. The results are shown in Table 1

[0061] Table 1

[0062] Appearance White emulsion Solid content 54.22％ Viscosity mPa.s 1300 Ethylene content% 23.5 <![CDATA[T g ,℃]]> -5 Water resistance No whitening, no pulp loss Membrane strength MPa 2.31

[0063] Example 2

[0064] A. Raw material preparation

[0065] 1) Prepare the oxidant solution system: add 3 parts of deionized water to 0.2 parts of hydrogen peroxide tank and stir to dissolve;

[0066] 2) Prepare reducing agent solution system: add 0.3 parts of potassium tartrate to 3 parts of deionized water and stir to dissolve;

[0067] 3) Preparation of post-treatment agent solvent: 0.02 parts of tert-butyl hydroperoxide and 0.8 parts of deionized water, 0.02 parts of potassium tartrate and 0.8 parts of deionized water are mixed evenly and used for post-treatment;

[0068] 4) Preparation of pH adjuster solution: Mix 0.05 parts of sodium acetate and 0.4 parts of deionized water;

[0069] B. Process

[0070] Add 37 parts of deionized water, 0.6 parts of PVA1788, and 2.9 parts of PVA0488 to the reactor, heat and stir to dissolve, then add 0.3 parts of sodium acrylamide sulfonate, 16 parts of vinyl acetate monomer, and add ethylene to the reactor. When the temperature reaches 56°C and the pressure reaches 5.3MPa, add the initial oxidant and reductant at 0.025 parts / min, and reset to 69°C and cool completely; then the computer controls the reaction and the rate of initiator addition, the reactor continues to increase the pressure to 7.9MPa, and continues to drip 21 parts of vinyl acetate continuously, which is completed in about 94 minutes; when the temperature is 77°C and the pressure is 1.50MPa, it enters the finishing period, and the remaining initiator is dripped at full speed; after degassing to the degassing tank, add 0.3 parts of post-treatment monomer methyl methacrylate first, and then add post-treatment agent for post-treatment; after cooling, add 0.04 parts of sodium acetate to adjust the pH, keep warm for 10 minutes, discharge, filter, and package. The results are shown in Table 2

[0071] Table 2

[0072]

[0073]

[0074] Example 3

[0075] A. Raw material preparation

[0076] 1) Prepare the oxidant solution system: add 3 parts of deionized water to 0.2 parts of hydrogen peroxide tank and stir to dissolve;

[0077] 2) Prepare reducing agent solution system: add 0.3 parts of sodium isoascorbate to 3 parts of deionized water and stir to dissolve;

[0078] 3) Preparation of post-treatment agent solution: 0.02 parts of tert-butyl hydroperoxide and 0.8 parts of deionized water, 0.01 parts of sodium isoascorbate and 0.8 parts of deionized water are mixed evenly and used for post-treatment;

[0079] 4) Preparation of pH adjuster solution: Mix 0.05 parts of sodium dihydrogen phosphate and 0.4 parts of deionized water;

[0080] B. Process

[0081] Add 36 parts of deionized water, 0.7 parts of PVA1788, and 2.7 parts of PVA0488 to the reactor, heat and stir to dissolve, then add 0.5 parts of sodium allyl carboxyl sulfonate, 17 parts of vinyl acetate monomer, and add ethylene to the reactor. When the temperature reaches 58°C and the pressure reaches 5.4MPa, add the initial oxidant and reductant at 0.026 parts / min, and reset and cool to 70°C; then the reaction and initiator addition rate are controlled by a computer, the reactor continues to increase the pressure to 8.0MPa, and 20 parts of vinyl acetate are continuously added, which is completed in about 92 minutes; when the temperature is 78°C and the pressure is 1.52MPa, it enters the finishing period, and the remaining initiator is added at full speed; after degassing to the degassing tank, add 0.4 parts of post-treatment monomer ethyl acrylate first, and then add post-treatment agent for post-treatment; after cooling, add 0.06 parts of sodium dihydrogen phosphate to adjust the pH, keep warm for 10 minutes, discharge, filter, and package. The results are shown in Table 3

[0082] Table 3

[0083] Appearance White emulsion Solid content 55.72％ Viscosity mPa.s 1370 Ethylene content% 24.8 <![CDATA[T g ,℃]]> -6 Water resistance No whitening, no pulp loss Membrane strength MPa 2.08

[0084] Comparative Example 1

[0085] A. Raw material preparation

[0086] 1) Prepare the oxidant solution system: add 3 parts of deionized water to 0.2 parts of hydrogen peroxide tank and stir to dissolve;

[0087] 2) Prepare reducing agent solution system: add 0.3 parts of sodium isoascorbate to 3 parts of deionized water and stir to dissolve;

[0088] 3) Preparation of post-treatment agent solution: 0.02 parts of tert-butyl hydroperoxide and 0.8 parts of deionized water, 0.01 parts of sodium isoascorbate and 0.8 parts of deionized water are mixed evenly and used for post-treatment;

[0089] 4) Preparation of pH adjuster solution: Mix 0.05 parts of sodium dihydrogen phosphate and 0.4 parts of deionized water;

[0090] B. Process

[0091] Add 36 parts of deionized water, 0.7 parts of PVA1788, and 2.7 parts of PVA0488 to the reactor, heat and stir to dissolve, then add 0.5 parts of nonylphenol polyoxyethylene ether, 17 parts of vinyl acetate monomer, and add ethylene to the reactor. When the temperature reaches 58°C and the pressure reaches 5.4MPa, add the initial oxidant and reductant at 0.026 parts / min, and reset and cool to 70°C; then the computer controls the reaction and the rate of initiator addition, the reactor continues to increase the pressure to 8.0MPa, and continues to drip 20 parts of vinyl acetate continuously, which is completed in about 92 minutes; when the temperature is 78°C and the pressure is 1.52MPa, it enters the finishing period, and the remaining initiator is dripped at full speed; after degassing to the degassing tank, the post-treatment agent is directly used for post-treatment; after cooling, add 0.06 parts of sodium dihydrogen phosphate to adjust the pH, keep warm for 10 minutes, discharge, filter, and package. The results are shown in Table 4

[0092] Table 4

[0093] Appearance White emulsion Solid content 55.42％ Viscosity mPa.s 1170 Ethylene content% 23.5 <![CDATA[T g ,℃]]> -5 Water resistance Whitening, pulping Membrane strength MPa 1.65

[0094] It can be seen from Examples 1-3 that the present invention adopts a reactive emulsifier and a specific means of adding a post-treatment monomer after degassing, while in Comparative Example 3, a reactive emulsifier is not used and the means of post-treatment monomers are cancelled. The results obtained in the examples show that the vinyl acetate-ethylene copolymer emulsion film prepared by the present invention has good water resistance, does not turn white or lose pulp when immersed in water, has a film strength of 2.08-2.31 MPa, can be used as a basic raw material for redispersible latex powder, and meets the construction strength; while the water resistance of the emulsion film prepared in Comparative Example 1 is whitening and pulping, and the film strength is 1.65 MPa, which is much lower than the construction strength; it can be seen that the technical scheme including the use of a reactive emulsifier and the specific means of adding a post-treatment monomer after degassing can make the emulsion have good water resistance, does not turn white or lose pulp when immersed in water, can be used as a basic raw material for redispersible latex powder, and meets the construction strength.

[0095] 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 water resistance of vinyl acetate-ethylene emulsion for redispersible latex powder, characterized in that: The emulsion is prepared by using raw materials including vinyl acetate monomer and ethylene monomer, an initiating system, an emulsifying system, and a post-processing auxiliary agent; and the post-processing monomer is added after degassing is completed.

2. The method for improving the water resistance of vinyl acetate-ethylene emulsion for redispersible latex powder according to claim 1, characterized in that: The post-treatment monomer is acrylate.

3. The method for improving the water resistance of vinyl acetate-ethylene emulsion for redispersible latex powder according to claim 1, characterized in that: The post-treatment monomer is selected from one or more of methacrylic acid, methyl methacrylate and ethyl acrylate.

4. The method for improving the water resistance of vinyl acetate-ethylene emulsion for redispersible latex powder according to claim 1, 2 or 3, characterized in that: The emulsification system comprises a protective colloid and an emulsifier; the emulsifier is a reactive emulsifier.

5. The method for improving the water resistance of vinyl acetate-ethylene emulsion for redispersible latex powder according to claim 4, characterized in that: The reactive emulsifier is selected from one or more of allyl ether sulfonate, acrylamide sulfonate and allyl carboxyl sulfonate.

6. The method for improving the water resistance of vinyl acetate-ethylene emulsion for redispersible latex powder according to any one of claims 1 to 5, characterized in that: The post-treatment auxiliary agent is added after the post-treatment monomer is added to perform post-treatment.

7. The method for improving the water resistance of vinyl acetate-ethylene emulsion for redispersible latex powder according to claim 6, characterized in that: The post-treatment auxiliary agent and the initiation system both include a reducing agent and an oxidizing agent.

8. The method for improving the water resistance of vinyl acetate-ethylene emulsion for redispersible latex powder according to claim 7, characterized in that: The amount of the post-treatment monomer used is 5-20 times the amount of the post-treatment auxiliary agent used, calculated by mass.

9. The method for improving the water resistance of vinyl acetate-ethylene emulsion for redispersible latex powder according to claim 1, characterized in that: The following steps are involved: Add protective colloid, reactive emulsifier, initial vinyl acetate accounting for 39%-48% of the total mass of vinyl acetate, and ethylene, continuously add initial oxidant and reductant, when the pressure rises to 7.8-8.0MPa, add the remaining vinyl acetate, degas to the degassing tank, add post-treatment monomer, and then add post-treatment additives for post-treatment.

10. Use of the vinyl acetate-ethylene copolymer emulsion prepared according to any one of claims 1 to 9 in redispersible latex powder.

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