Method for preparing acrylic emulsion with continuously variable ratio of soft and hard monomers

Abstract

The invention discloses a method for preparing an acrylic emulsion with a continuously variable ratio of soft and hard monomers, the method comprising the following steps: step 1: mixing an emulsifier with water, adding ammonia water, heating and stirring, and placing and cooling to room temperature after the emulsifier is completely dissolved; step 2: pouring the emulsifier solution into a three-necked flask, adding an initiator and a hard monomer, stirring and heating for reaction, and discharging; step 3: pouring the emulsifier solution into a three-necked flask, adding an initiator and a soft monomer, stirring and heating for reaction, and discharging; step 4: mixing an emulsion using only a hard monomer and an emulsion using only a soft monomer to prepare a mixed emulsion. The invention quickly obtains a series of emulsions with different ratios of soft and hard monomers by mixing an emulsion using only a soft monomer and an emulsion using only a hard monomer, without the need to prepare from monomers again, which is convenient and quick, and greatly saves time and material costs.

Description

Technical Field

[0001] The invention relates to a method for preparing an acrylic ester emulsion, in particular to a method for preparing an acrylic ester emulsion with a continuously variable ratio of soft and hard monomers. Background Art

[0002] Acrylic emulsion is a product obtained by emulsion polymerization with acrylic or methacrylate monomers as the main components. It uses water as the dispersion medium, so it is cheap, environmentally friendly, and easy to transport. It is used in many fields such as paints, coatings, and adhesives. As the problem of air pollution becomes increasingly serious, people's environmental awareness has gradually increased, and strict laws and regulations have been formulated on the emission of organic gases. Therefore, it is of great research significance to use water-based materials instead of traditional organic coatings or adhesives.

[0003] For emulsion products, the glass transition temperature (T g ) is a very important property, which is determined by the ratio of soft and hard monomers in the emulsion formula. The higher the content of hard monomer, the higher the T g The higher the soft monomer content, the higher the T g The lower. T g It directly affects the mechanical properties, thermal properties and minimum film-forming temperature of the product. g High, the material has good thermal stability, suitable for applications under high temperature conditions, and the minimum film-forming temperature of the coating is high, so the coating has high hardness and high gloss, but the material is brittle; the T of the emulsion g The material has good flexibility, the minimum temperature of the coating is low, and it is easier to form a film, but the coating exhibits viscoelasticity under high temperature conditions and is easier to soften.

[0004] In the traditional emulsion preparation process, the performance of the emulsion is achieved by continuously adjusting the soft and hard monomers to the appropriate ratio during the experimental stage. For example, in the application of pressure-sensitive adhesives, the polymer molecular segments need to have good flexibility, so the formula is mainly composed of soft monomers, and some hard monomers are added to provide mechanical strength; in the application of water-based paints, the emulsion needs to have rigidity, so the formula is mainly composed of hard monomers, and some soft monomers are added to provide a certain film-forming property. It can be seen that the ratio of soft and hard monomers plays a vital role in the performance of emulsion products. In order to explore the optimal ratio, the current research method is to directly change the formula and prepare emulsions with different ratios of soft and hard monomers to compare their performance. However, this method has cumbersome steps. Whenever the ratio of soft and hard monomers is changed, it is necessary to start preparation from the monomers, which consumes a lot of time and resources. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for preparing an acrylic emulsion with a continuously variable ratio of soft and hard monomers. Compared with the traditional method, the method of the present invention can quickly obtain a large number of emulsions with different ratios of soft and hard monomers, eliminating repeated emulsion preparation steps and saving a lot of time and resources.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A method for preparing an acrylic emulsion with a continuously variable ratio of soft and hard monomers, first preparing an emulsion using only a soft monomer and only a hard monomer, and then mixing the two emulsions in different ratios to obtain a mixed emulsion, specifically comprising the following steps:

[0008] Step 1: Mix the emulsifier with water in a certain proportion, add ammonia water to make the solution pH value between 7 and 9, then heat and stir, and place and cool to room temperature after the emulsifier is completely dissolved, wherein: the emulsifier is one of sodium dodecyl sulfate (K12) and a macromolecular surfactant, and the addition amount is 4.3-8.0% of the water mass; the lipophilic end of the macromolecular surfactant is styrene, and the hydrophilic end is maleic anhydride, which dissolves in water under alkaline conditions to generate carboxylic acid heel groups, and the molecular weight is 1000-3000; during the dissolution process of the emulsifier, if the pH value decreases, add ammonia water to make the pH value between 7 and 9;

[0009] Step 2: Pour the emulsifier solution prepared in step 1 into a three-necked flask, add initiator and hard monomer, stir and heat to 71-76°C, react for 3-5 hours, raise the temperature to 81-86°C and keep warm for 1-2 hours, and discharge the material, wherein: the initiator is potassium persulfate, and the addition amount is 0.5-2.0% of the mass of the hard monomer; the hard monomer is one or two of styrene and methyl methacrylate; the emulsifier can be used as an effective component together with the hard monomer, and the mass of the effective component accounts for 30-40% of the total mass of the emulsion;

[0010] Step 3: pour the emulsifier solution prepared in step 1 into a three-necked flask, add initiator and soft monomer, stir and heat to 71-76° C., react for 3-5 hours, raise the temperature to 81-86° C. and keep warm for 1-2 hours, and discharge the material, wherein: the initiator is potassium persulfate, and the addition amount is 0.5-2.0% of the mass of the soft monomer; the soft monomer is a mixture of isooctyl acrylate and butyl acrylate, and the mass of isooctyl acrylate is 0-40% of the total mass of the soft monomer; the emulsifier can be used as an effective component together with the soft monomer, and the mass of the effective component accounts for 30-40% of the total mass of the emulsion;

[0011] Step 4: Mix the emulsion using only hard monomers prepared in step 2 and the emulsion using only soft monomers prepared in step 3 according to the use requirements to prepare a mixed emulsion, wherein: the mixing condition is stirring at a temperature of 50-60°C for 1-4 hours; in the mixed emulsion, the state of the two molecules mixed is macroscopically compatible and microscopically separated.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] The present invention quickly obtains a series of emulsions with different soft and hard monomer ratios by mixing an emulsion using only a soft monomer and an emulsion using only a hard monomer, without the need to prepare from monomers again, which is convenient and fast and greatly saves time and material costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is the appearance photo of the emulsion and mixed emulsion prepared using only soft and hard monomers;

[0015] Figure 2 It is the microscopic morphology of the mixed emulsion after film formation (soft:hard = 2:1);

[0016] Figure 3 It is the microscopic morphology of the mixed emulsion after film formation (soft:hard = 1:1);

[0017] Figure 4 This is the microscopic morphology of the mixed emulsion after film formation (soft:hard=1:2). DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below in conjunction with the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0019] Embodiment 1:

[0020] This embodiment provides a method for preparing an acrylic emulsion with a continuously variable ratio of soft and hard monomers, the method comprising the following steps:

[0021] Step 1: Mix a macromolecular surfactant with a molecular weight of about 1000 and water (the mass of the macromolecular surfactant is 8.0% of the mass of water), add ammonia water and heat and stir, adjust the pH value to about 8, and place and cool to room temperature after the macromolecular surfactant is completely dissolved.

[0022] Step 2: Pour the emulsifier solution prepared in step 1 into a three-necked flask, add hard monomer methyl methacrylate to an effective content of 30%, and add 1% of the monomer weight of potassium persulfate, start stirring, and heat to 71°C after stirring evenly. After reacting for 4 hours, the temperature is raised to 86°C and kept warm for 2 hours to prepare an emulsion using only hard monomers.

[0023] Step 3: Pour the emulsifier solution prepared in step 1 into a three-necked flask, add a mixture of soft monomers butyl acrylate: isooctyl acrylate = 2:1 to an effective content of 30%, and add 1% of the monomer weight of potassium persulfate, start stirring, and heat to 71°C after stirring evenly. After reacting for 4 hours, the temperature is raised to 86°C and kept warm for 2 hours to prepare an emulsion using only soft monomers.

[0024] Step 4: The emulsion using only soft monomers and the emulsion using only hard monomers in step 2 are mixed in a mass ratio of 1:1, and stirred at 60° C. for 1 hour to prepare an emulsion with a soft:hard ratio of 1:1.

[0025] Embodiment 2:

[0026] The difference between this embodiment and embodiment 1 is that in step 4, an emulsion using only soft monomers and an emulsion using only hard monomers are mixed in a mass ratio of 1:2 to prepare an emulsion with a soft:hard ratio of 1:2.

[0027] Embodiment 3:

[0028] The difference between this embodiment and embodiment 1 is that in step 4, an emulsion using only soft monomers and an emulsion using only hard monomers are mixed in a mass ratio of 2:1 to prepare an emulsion with a soft:hard ratio of 2:1.

[0029] Experimental Example 4:

[0030] The difference between this embodiment and embodiment 1 is that in step 2 and step 3, the effective content is 40%.

[0031] Embodiment 5:

[0032] The present embodiment is different from the embodiment 1 in that in step 1, the macromolecular surfactant with a molecular weight of about 1000 is replaced with a K12 emulsifier, and the mass of the emulsifier accounts for 4.3% of the mass of water.

[0033] Comparative Example 1:

[0034] The difference between this comparative example and Example 1 is that in step 1, the mass of the emulsifier is 7.5% of the mass of water.

[0035] The difference between this comparative example and Example 1 is that in step 3, only the monomers in the soft monomer emulsion are all isooctyl acrylate.

[0036] Comparative Example 3:

[0037] The difference between this comparative example and Example 1 is that in step 4, the mixing condition is stirring at 70° C. for 4 hours.

[0038] The test results of the emulsions obtained in Experimental Examples 1-5 and Comparative Examples 1-3 are as follows:

[0039] In the present invention, the macromolecular surfactant is used as the emulsifier in Examples 1-4, which avoids the problem of precipitation of the small molecule emulsifier during use, is beneficial to the stability and service life of the product, and the emulsifier can be used as an effective component. Among them, the content of the effective component in Examples 1-3 is 30%, and the appearance of the mixed emulsion and the emulsion using only the soft and hard monomers is as follows: Figure 1 As shown in the figure, the mixed emulsion has the same appearance as the emulsions using only soft and hard monomers, with uniform color and no phase separation or flocculation, reflecting macroscopic compatibility. This is because both emulsions use water as the dispersion medium and have similar solubility in water, which is conducive to the mixing of the two molecular chains. The mixed emulsion was dried into a film and its microscopic morphology was observed by scanning electron microscopy. The results are shown in the figure. Figure 2 to Figure 4 As shown, fine cracks can be observed on the surface of the film prepared from the mixed emulsion. This is because the two emulsions do not reach mutual compatibility at the molecular level, and therefore present a phase separation state at the microscopic level. The effective component content of Example 4 is 40%, and Example 5 uses a small molecule emulsifier, both of which show similar effects to the above, indicating that the mixing method of the present invention has a relatively common application. The above experiments prove that the mixed emulsion has good stability, and the emulsion mixing state is macroscopically compatible and microscopically separated.

[0040] In the preparation process of Comparative Example 1 of the present invention, the amount of macromolecular emulsifier was reduced, and the stability of the prepared emulsion was poor, indicating that the emulsification ability of the macromolecular emulsifier was weaker than that of the small molecule emulsifier of the same quality. In Comparative Example 2, all isooctyl acrylate with a lower glass transition temperature was used as a soft monomer, and the emulsion could not be prepared, and the product had a monomer odor, indicating that the reaction activity of isooctyl acrylate was too low, and the emulsion could not be prepared alone in the process of the present invention. In Comparative Example 3, the stirring temperature and time were increased, the emulsion demulsified, and the state of the emulsion could not be maintained, indicating that excessive stirring would destroy the structure of the emulsion, and the emulsion mixing required a moderate temperature and stirring time.

Claims

1. A method for preparing an acrylic emulsion with a continuously variable ratio of soft and hard monomers, characterized in that The method comprises the following steps: Step 1: Mix the emulsifier with water in a certain proportion, add ammonia water to make the pH value of the solution between 7 and 9, then heat and stir, and place and cool to room temperature after the emulsifier is completely dissolved, wherein: the emulsifier is one of sodium dodecyl sulfate and a macromolecular surfactant, the amount of sodium dodecyl sulfate added is 4.3% of the water mass, and the amount of the macromolecular surfactant added is 8.0% of the water mass; Step 2: Pour the emulsifier solution prepared in step 1 into a three-necked flask, add initiator and hard monomer, stir and heat to 71-76°C, react for 3-5 hours, raise the temperature to 81-86°C, keep warm for 1-2 hours, and discharge, wherein: the amount of initiator added is 0.5-2.0% of the mass of the hard monomer; the hard monomer is one or two of styrene and methyl methacrylate; the emulsifier and the hard monomer are used as effective components together, and the mass of the effective components accounts for 30-40% of the total mass of the emulsion; Step 3: Pour the emulsifier solution prepared in step 1 into a three-necked flask, add initiator and soft monomer, stir and heat to 71-76°C, react for 3-5 hours, raise the temperature to 81-86°C, keep warm for 1-2 hours, and discharge, wherein: the amount of initiator added is 0.5-2.0% of the mass of the soft monomer; the soft monomer is a mixture of isooctyl acrylate and butyl acrylate, and the mass of isooctyl acrylate is 0-40% of the total mass of the soft monomer; the emulsifier and the soft monomer are used as effective components together, and the mass of the effective components accounts for 30-40% of the total mass of the emulsion; Step 4: Mix the emulsion using only the hard monomer prepared in step 2 and the emulsion using only the soft monomer prepared in step 3 according to the use requirements to prepare a mixed emulsion, wherein the mixing condition is stirring at a temperature of 50-60° C. for 1-4 hours.

2. The method for preparing an acrylic emulsion with a continuously variable ratio of soft and hard monomers according to claim 1, characterized in that The lipophilic end of the macromolecular surfactant is styrene, and the hydrophilic end is maleic anhydride, which dissolves in water under alkaline conditions to generate a carboxylate group.

3. The method for preparing an acrylic emulsion with a continuously variable ratio of soft and hard monomers according to claim 2, characterized in that The molecular weight of the macromolecular surfactant is 1000-3000.

4. The method for preparing an acrylic emulsion with a continuously variable ratio of soft and hard monomers according to claim 1, characterized in that The initiator is potassium persulfate.

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