Study on wetting dispersants for pigments in UV coatings.

1 Foreword
. UV coatings belong to one of the most environmentally friendly coatings in the world today, but UV coatings are still in the process of continuous development and improvement. We want to design a high-quality coating formula, relying only on the selection of some good paint resins, auxiliary additives, pigments, solvents, etc. is far from enough, we must also choose some appropriate pigments and their wet dispersant help. However, at present, there is less research on the selection of paint fillers and their wetting dispersants in China, and this paper is to carry out a simple study and exploration from this aspect.
UV coatings belong to a type of coating, a variety of coating systems are generally composed of resins, solvents, pigments and various additives. One of the key nodes in the wetting and dispersion of pigments to produce a high-quality coating is very critical. The so-called pigment dispersion, is that we use three-roll grinder and other equipment in the production of large particles of pigment grinding into very small pigment particles, so that it can be evenly dispersed in the paint, forming a stable coating system. In this process, in addition to choosing the right coating resin, auxiliary additives, pigments, solvents and so on, we also have to choose some appropriate coating wetting dispersants and other auxiliary additives to improve the various properties of the coating such as paint film iris, water resistance, weather resistance, acidity and alkali resistance, mechanical resistance, paint film gloss, storage time, leveling and other properties to meet the requirements of different customers.2 Pigment and wetting dispersion and its stability theory
(1) The current theory of wetting dispersion and stability of pigments mainly includes: (1) electrostation stability theory;
(2) pigment fillers (also known as pigments) are of different types according to different classification methods. The stability of the dispersion system has a lot to do with pigments.
(3) coating is a surfactant, which can be divided into different types according to the classification index. The main function of paint wetting dispersants is to reduce the interface pressure of various pigments during the pigment wetting process, which can improve their dispersion efficiency. Moreover, the coating wetting dispersant can be adsorbed on the surface of pigment particles and make the dispersion in a stable state by producing effects such as charge refractive force and spatial resistance.3 Types of pigments in coatings and surface treatment
In coatings, the performance of pigments depends primarily on their chemical composition, particle shape, particle size and surface treatment status.
3.1 Classification of pigments
(1) according to the charge to divide pigments generally divided into:
(1) positive charge;
(2) by particles to divide pigment powder particles are generally divided into:
(1) original particles: it is the most basic pigment particle unit. It is made up of a single pigment crystal or a set of crystals with a fairly small particle size.
(2) aggregation: it is a particle of the original particle that binds the face to the face. Its total surface area is smaller than the sum of the area of a single particle.
(3) a cluster: it is a group of particles formed by the original particles bonding to each other by their edges, angles, etc. Its total surface area is larger than the aggregate, but smaller than the sum of the surface area of a single particle.
(4) flocculation: it is a group formed by the re-gathering of primitive particles after dispersion in the fluid medium.
flocculants, aggregates and appendosomes are aggregates formed in the process of pigment dispersion, collectively called secondary clumps.
(3) the particle shape of the pigment
(1) needle state particles: it has enhanced, toughening effect, but the dispersion is difficult.
(2) flaky particles: it can be applied to coatings can significantly improve the tightness of the coating.
(3) porous structure of the particles: it is generally more solid structure pigments have rapid enhancements, but the de-light performance is obvious.
(4) pigments are acidic and alkaline
the vast majority of resins used in general coatings are acidic. So if the pigments we choose are not acidic or alkaline, then they produce an acid-base reaction, which directly results in the storage of coating products. and affect the physical and chemical properties of the paint film.
3.2 The type of surface treatment of pigments and their effects
(1) the surface treatment of pigments is divided into: inorganic surface treatment such as aluminum, silicon, titanium, zinc and organic surface treatment such as surfactant organic matter treatment methods.
(2) The role of pigment surface treatment:
(1) In order to prevent pigment adsorption of water, promote pigment adsorption of polymers, improve the strength of the coating film.
(2) to improve the dispersion of paint film, covering force, coloring force, durability, weather resistance, light resistance.
(3) to improve the paint film acid-base resistance, temperature-resistant performance.
(4) polymer treated pigments with partially reactive groups have significant storage stability compared to small molecule treatment agents, and have greatly improved performance (e.g. water resistance, mechanical properties, etc.). 4 Effect of pigment dispersion on coating performance
In coating formulations, the performance of a coating product is largely determined by the pigment dispersion system. Dispersing good pigment dispersion can improve the coloring force, leveling, transparency, reduce system viscosity, improve the color display of the system, improve the cover force, enhance surface gloss and fluidity. A poor dispersion system of paint products, often resulting in the quality of this coating products are not up to standard and failure. Therefore, pigment dispersion system is often used as an important quality parameter of paint products. 5 Wetting dispersant function and its type
5.1 Paint wetting dispersant function
In coating production, when liquid paint wetting dispersants come into contact with solid pigment particle surfaces, the original solid/gas interface is replaced by the newly formed solid/liquid interface, a phenomenon commonly known as the wetting of paint pigments. The main contribution of various coating wetting agents in the pigment wetting process is to reduce the surface pressure of liquid/solid, improve the chemical physical properties of paint pigments, and improve the dispersion efficiency of pigment particles. The main functions of coating wetting dispersants are summarized as follows: (1) reduce surface tensor and improve the effect of pigments. (2) Shorten the dispersion time of pigments. (3) Improve the coloring force and its covering force. (4) Improve color display and its color ability. (5) To prevent the paint from flocculation. (6) Prevent the precipitation of pigment fillers in coatings. (7) Improve the luster and wear resistance, weather resistance and other physicochemical properties of the paint film.
5.2 The wetting mechanism of the coating wetting dispersant
(1) When any liquid comes into contact with a solid, a contact surface is formed on the surface of the return body and a tentacle is pressed, and the size of a liquid against a solid wetting capacity is usually measured according to the size of the contact angle. The smaller the contact angle, the better its wetting effect. The dispersion principle of the paint by the wetting dispersant of the coating is the same as that of this wetting agent.
(2) Wetting dispersants on wetting effect
In the design of coating formulations, when pigments and resins are selected, people want to obtain more excellent paint performance, then they have to choose the most suitable paint wetting dispersants to reduce the surface pressure of pigments to improve the surface properties of paint pigments and their chemical theory performance, in order to obtain a high performance and stable paint products.
5.3 Types of coating wetting dispersants
(1) by use: water-based dispersants and solvent-based dispersants can be divided.
(2) by application type: anti-flocculation dispersant, coflocculation dispersant.
(3) according to the adsorption group classification: anion type, cation type, neutral type, non-ion class, etc.
(4) is classified by molecular weight: dispersants with small molecular weights (generally those with a molecular weight below the hundreds) and dispersants with large molecular weights (generally those with a molecular weight in the thousands or more).
5.4 The interaction between coating wetting dispersants and pigments and processes
(1) the moisturizing dispersants and pigments have the following factors:
(1) acid-base reaction. (2) The mechanism of forming a hydrogen bond. (3) The occurrence of water-repulsive effect is organic pigment in the horizontal system. (4) Metal mating, such as the metal mating process produced by indisium pigments.
(2) The process of wetting and dispersing pigments in
paint fillers in coatings after grinding and crushing by grinders, etc., the surface area of pigment particles will be significantly increased, the energy increased significantly, in a very unstable state. When the external mechanical forces are cast, particles collide with each other due to the Brown Games, which will cause the accumulation of color particles, resulting in flocs, that is, the coarse phenomenon as the saying goes. Therefore, in order to prevent this from happening, we must add some compatible and suitable coating wetting dispersants, the use of wetting dispersant charge rejection or spatial resistance and other effects, so that the grinding pigment particles independent of each other, maintain an appropriate distance from each other, without contact, thereby preventing the production of flocs, to maintain the stability and quality of the coating. 6 Wetting dispersant selection
Generally speaking, when the resin of the coating is selected, people will choose the corresponding pigment according to the performance of their resin, when the pigment is selected, we can choose according to the surface performance of the pigment to match the wetting dispersant selection. The selection of wetting dispersion is usually carried out according to the following rules:
(1) acidic pigment is best selected as a wetting dispersant for cations.
(2) neutral pigment filling is best chosen for electro-neutral wetting dispersants.
(3) alkaline pigment fillers are best selected as an anion moisturizing dispersant. 7 Conclusion
In summary, a good paint product must choose the corresponding pigment filler and the wetting dispersant that dissolves with it, a good paint wetting dispersant can be well adsorbed on the surface of the pigment particles, can improve the surface properties of pigment particles, so that the whole system remains stable, and ultimately determine the quality of a paint film. Therefore, in the work we must continue to study and explore in this regard. .