Q & A and formulation design of the hottest latex

2022-07-28
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Q & A on latex coating knowledge and formulation design Q & A on latex coating knowledge and formulation design July 1, 2019 generally speaking, we first select the base resin and pigment according to the application requirements of the coating, that is, the performance indicators that the coating should have in the working environment, then determine the solvent according to the construction requirements and the selected base material, and then consider the additives or other additives of the coating on this basis, Form a preliminary formula. The absolute quantity and relative proportion of each component in the coating have a great influence on the performance of the coating. As long as one of the components is improperly selected, the performance of the coating will deteriorate

what is the color/base ratio (p/b) of latex paint

in latex coatings, the base material and pigment are important components. When the pigment and base material have been determined, the structure and physical properties of the film basically depend on the ratio of the two. The so-called color/base ratio refers to the mass ratio between the mass percentage of pigment (i.e. pigment and filler) and the mass percentage of solid resin (nonvolatile), which is usually expressed in p/b

pigment volume concentration (PVC)

in the formulation design of latex coating, it is often expressed by mass percentage. However, the density of resins, pigments, fillers and other solid additives that make up latex coatings varies greatly, so their volume fraction in the whole film is significantly different. The volume fraction is more important than the mass fraction in determining the dry film performance of coatings. In particular, the importance of volume fraction is more prominent when comparing the performance of different formulations of coatings. The volume concentration of pigment is the percentage of the volume of pigment in the film in the total volume of the film, expressed in PVC. Critical pigment volume concentration (CPVC)

critical pigment volume concentration refers to the pigment volume concentration when the base polymer just covers the surface of pigment particles and fills the accumulation space of pigment particles, which is usually expressed by CPVC

What is the role of

p/b in designing paint formulations

when studying the quality relationship between pigment and base material in paint, it only needs simple numerical calculation, which is very practical in the initial design stage of formula. In practical application, it is feasible to classify internal and external latex coatings according to the p/b of coatings. Generally, the p/b of external type is (2.0 ~ 4.0): 1.0, and the more appropriate is 3.0:1.0. The internal latex coating is (4.0 ~ 7.0): this process needs to reduce energy consumption by 75% within the range of 1.0. If it is a light emulsion coating, the p/b is often less than 1.0

some properties of the coating can be roughly inferred from p/b. The performance of the high p/b formula is not suitable for outdoor use, because the exterior wall coating requires good durability and weather resistance, and less base material can not form a continuous film around a large number of pigment and filler particles. Using the concept of p/b, the formulation of various types of latex coatings can be designed

what is the role of PVC and CPVC in designing paint formulations

it is difficult to explain the problem only by using p/b in the comparative test of coatings with different compositions. It is more scientific to interpret the test data through the understanding of PVC. Because many physical properties of coatings have a very clear corresponding relationship with their composition changes. C. P.v.c. value is an important parameter in paint formulation. When the p.v.c. value in the formula is lower than the c.p.v.c. value, the amount of the base material can not only wet the pigment, but also make the pigment particles firmly dispersed in the middle of the base, so that the film has high gloss, difficult to rust, low water permeability and air permeability, and bubbles are generated

in the preparation of low PVC coatings, pigment particles are dispersed in the continuous phase of the base polymer to form the so-called "Sea Island" structure

when the CPVC value is reached, there is just enough base material wetting particles in the film. However, with the increase of pigments, when PVC exceeds a certain limit value, the matrix polymer cannot completely fill the voids between pigment particles, and these unfilled voids are hidden in the film. Therefore, the physical properties of the film begin to decline sharply with the limit value of PVC. Therefore, PVC with high performance or external coating formula should not exceed CPVC, otherwise many physical properties of the coating film will be adversely affected. On the contrary, PVC with general performance or internal coating formula can exceed CPVC. The PVC of external coating is generally 30% ~ 55%, and the PVC of internal coating can be larger, generally 45% ~ 70%. In order to save resources and reduce costs, the research of high PVC latex coatings has become one of the important contents of the development of architectural coatings, so attention should be paid to the lotion products of high PVC coatings

take the design of an interior wall emulsion paint as an example

1 First, determine the performance requirements of the emulsion paint to be designed

the operating environment of the emulsion paint for the interior wall has no special requirements for the physical properties of the emulsion paint, but the stains can be easily cleaned with water and detergent. For the construction performance, the requirements of the interior wall emulsion paint are to have good leveling, and there shall be no brushing joints or too obvious brush marks during construction. In addition, most of the current construction habits of emulsion paint in China are the combination of roll coating and brush coating. For this construction method, the viscosity of the emulsion paint (coating - 4 cups) shall be controlled within the range of 45 ~ 55s

as for storage performance, it is generally required that there should be good suspension during storage, at least no caking sediment, so as to facilitate construction and ensure coating performance. Finally, attention should also be paid to the film formation of emulsion paint during low-temperature construction and mold resistance during storage

2. Select the type of base material and determine its dosage

there are two base materials for the formulation of the coating, one is polyvinyl acetate emulsion paint, the other is styrene acrylic lotion material, which is easy to buy. In addition, it is popular in the market, so styrene acrylic lotion is selected for preparation, that is, the formulation of styrene acrylic emulsion paint is designed

according to experience, emulsion paint with good performance can be prepared when the content of styrene acrylic lotion for internal use is 25%; It can also be seen from the pigment base material ratio introduced above that the pigment base material ratio of internal emulsion paint ranges from 3 to 7:1, and the amount of styrene acrylic lotion selected here is 25%

3. Determine the type and dosage of pigments (fillers)

taking white emulsion paint as an example, the pigments (fillers) commonly used in general-purpose internal emulsion paint include titanium dioxide (anatase type can be used for internal emulsion paint), lithopone, calcium carbonate, talc, wollastonite powder or heavy calcium carbonate. 3.3:1 is selected here according to the range that the pigment base material ratio of internal emulsion paint is 3 ~ 7:1. If the amount of styrene acrylic emulsion paint is 25%, and assuming that its solid content in the emulsion paint is 12%, the total amount of pigments (fillers) is 40%

obviously, with such a large amount of pigments, it is not necessary to use titanium dioxide and lithopone only, which makes the market price of latex paint unbearable. Therefore, the method of using pigments and fillers together is adopted

according to experience, the above five pigments (fillers) are used together as follows (%): titanium dioxide 10; Lithopone 40; Calcium carbonate 15; Talc powder 20; Wollastonite powder 15. According to 40% of the total amount, the amount (%) converted into emulsion paint is: titanium dioxide 4; Lithopone 16; Calcium carbonate 6; Talc powder 8; Wollastonite powder 6

4. Determine the type and dosage of additives

what is determined above is the basic component of emulsion paint, in order to meet the performance requirements

5. Trial preparation and inspection after the preliminary design formula is determined, trial preparation can be carried out according to this procedure, and the most intuitive brushing performance (leveling, sagging, etc.) and viscosity of the obtained emulsion paint can be preliminarily tested

6. Formula adjustment

during the preliminary test of performance, it may be found that the viscosity of emulsion paint is very low, there is obvious precipitation after a short period of storage, and the paint film may look very rough, and the cost may also be high

7. Carry out comprehensive test

this step mainly uses the adjusted formula (viscosity, brushing performance, etc. have been satisfied) to prepare the appropriate equivalent of emulsion paint, carry out comprehensive performance test, and adjust the formula appropriately according to the test results

production process of emulsion paint

generally, there are two methods for the production of emulsion paint. One is the color paste method, that is, the pigment and filler are first mixed into the formula water with wetting dispersant dissolved, and then the color paste is prepared by high-speed dispersion or grinding. After the pH value of lotion is adjusted to 7 ~ 8 with ammonia or other pH value regulator, it can be directly mixed with additives and color paste according to the process conditions, and then mixed with lotion to make emulsion paint; The other method is the direct method, that is, the pigment and filler are dispersed in the base material, and then evenly dispersed together with the additives before grinding

in the former method, the color paste is prepared first, which can be dispersed or ground repeatedly for many times. The fineness of the finished product is high, which brings a series of excellent properties to the paint. Both coloring pigments and physical pigments are composed of hundreds to thousands of secondary particles condensed by primary particles when they are purchased. When mixing with lotion, the secondary particles of pigment are either reduced to primary particles and then mixed, or the secondary particles are directly added to lotion. Therefore, the preparation methods are obviously different. The former mixing method is called grinding coloring method or color paste method. The latter method is called dry coloring

color paste water is to apply a large amount of mechanical energy to the secondary particles of pigment, so that they first depolymerize and disperse in water to form color paste, and then mix with the base material. In contrast, the dry coloring method is to add the pigment secondary particles directly to the base material for stirring. Therefore, the solid content and the depolymerization and dispersion state of the paint produced by the two preparation methods are obviously different

(1) paste method

the process of making emulsion paint by paste method: first, the pigment dispersant, wetting agent, thickener aqueous solution, water and other components are premixed with kneader or agitator, and then the secondary particles of pigment are depolymerized and dispersed by colloid mill or sand mill to prepare pigment paste. Transfer the pigment slurry to the mixer, and then add the lotion with plasticizer and film-forming agent in advance (as required) for mixing. Add water to adjust the viscosity, so as to prepare emulsion paint. Finally, the finished product is obtained by filtering and canning

(2) dry coloring method

dry coloring method is to mix lotion, pigments and additives in a mixer or kneader to produce coatings. The dry coloring method is simpler than the paste method, and can produce high concentration coatings. Its disadvantage is that the dispersion state of pigments can not meet the required standards. In addition, because the lotion used as the base material has to undergo relatively harsh conditions, the requirements for pigment mixing stability are very high. These problems of dry coloring method are entirely caused by the formation of secondary particles in pigment particles. It can be operated automatically, that is to say, when the secondary particles are added to the lotion, the porous secondary particles will quickly suck water into the pores, and the lotion particles will be locally concentrated due to the filtering effect on the surface of the secondary particles to form a wet membrane. If an external force is applied to the film, the secondary particles will depolymerize, but if the wet film is too tough, it is difficult to depolymerize

what effect does the hardness of lotion polymer have on the film performance

generally speaking, polymer lotion is a copolymer, which is obtained by combining the monomer (hard monomer) that can form a rigid polymer with the monomer (soft monomer) that can form a flexible polymer

typical hard

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