Is the water-color fastness problem difficult to solve? Exhibition experts have a different view

Introduction
Some time ago, children's shoes in the PCI water-based industrial coatings WeChat group put forward such a question:
Water-based paint color fastness problem, usually how to improve?" There are replies that "usually waxing, increasing the amount of resin and adding crosslinkers", and children's shoes suggest that "the compatibleness of color materials in the system is very important" ... To see that everyone is so concerned about this issue, the editor then contacted Mr. Liu Zhigang, general manager of the Exhibition Technology Management Center, to invite him to this article. This paper analyzes the factors that are prone to water-resistant, friction-resistant and light-resistant color fastness problems in the application process of water-based coatings, and concludes that the color fastness of water-based coatings can be improved by adding resins, crosslinkers, ultraviolet absorbers, and hand-felt aids, but the most direct and effective method is to choose the right color fastness pigment slurry.
1. Foreword
Coatings in our country, traditionally known as paint, are coated on the surface of protected or decorated objects, and can form a solid attachment to the coating of a continuous film, usually resin, or oil, or emulsion-based, add or do not add pigments, fillers, corresponding additives, with organic solvents or water preparation of a viscous liquid, add pigment pigment coating, called paintThe color fastness of
paint refers to the degree of discoloration caused by external factors (squeezing, friction, washing, rain, exposure, light, sea water impregnation, saliva impregnation, water stains, sweat stains, etc.) during use or processing.
water-resistant coatings in the color fastness mainly refers to: water-resistant, solvent-resistant, chemical-resistant, light-resistant, sun-resistant, weather-resistant, friction-resistant, heat-resistant, migration-resistant, pull-resistant dyeing, sweat-resistant stains and so on. Among them: solvent resistance, chemical resistance, heat resistance, migration resistance, pull-resistant dyeing and other color fastness factors are pigment slurry and resin, do not discuss, the main analysis of water resistance, friction resistance, and light-related color fastness factors.
2. Water-resistant color fastness
Water-resistant paint water-resistant fastness refers to the ability of color paint to fade or seepage due to dissolution due to shocks such as rain.
2.1 pigments
pigments are oily, generally insoluble in water, water-resistant color fastness is generally at level 5. However, some pigments, dyes by the introduction of metal salts, pigment process and made of pigments, water resistance performance is only about 4 levels, such as: PR 49:1, PR 57:1 and so on. There are also pigments like chromophenol AS, such as PR 2, PR 112, these pigments heavy nitrogen ingredients are aniline and so on, water resistance is only about 4 levels.
2.2 additive effect
at room temperature, the surface temperature coefficient of water is 72mN/m, so water-based coatings in order to achieve the equal construction effect of perforation, penetration, flow, will generally add some substrate moisturizer, dispersant, leveling agent and so on. And the negative effect of these surfactants that reduce surface strain is to make pigment slurry more hydro-friendly, i.e. water-resistant coatings have poor water resistance.
2.3 resin impact
water-based paint formula resin accounted for the vast majority, resin water resistance, determines the water resistance of the paint, so, in order to meet other fastness, try to choose high hydroxy, high molecular weight, high glass temperature, acid value as low as possible water-based resin.
effects of 2.4 crosslinkers
these crosslinkers are mainly used in polymeric materials (rubber and thermo-solid resins). Because the molecular structure of polymeric materials is like a long line, there is no crosslinking when the strength is low, easy to pull off, and there is no elasticity, the role of crosslinkers is to create chemical bonds between online molecules, so that the line molecules are connected to each other, forming a mesh structure. After cross-link curing, the absorption rate of the resin is reduced and the water-resistant color fastness performance of the water-resistant coating is improved.
2.5 Effects of hydrophobic compounds and hydrophobic additives
In order to improve feel performance, water repulsive compounds such as wax emulsions are added to coating formulations that reduce or reduce water wetting of the paint film. Hydrophobic agent is a compound, mainly composed of substances with low surface tensor, added to the coating can react with film-forming additives, in the paint film surface to form a special water-resistant structure, so that the surface has a very strong hydrophobic, water-repugnant, waterproof effect, thereby improving the water-resistant properties of water-based coatings.
3. Wear-resistant friction fastness
wear-resistant friction fastness refers to the color paint anti-friction color ability, divided into dry friction and wet friction color fastness. The calculation formula for friction is f, i.e., the coefficient of friction is multiplied by the positive pressure. Water-based coatings affect frictional fastness due to: water-based coating friction coefficient, water resistance and substrate adhesion.
effects of 3.1 hand-felt additives
in water-based coating formulations, certain waxes and other types of hand-felt additives are often added to the formulation to enhance the feel of water-based coatings, etc. And these hand aid also improves the smoothness of the coating, that is, the coefficient of friction is reduced, improve the wear-resistant fastness of color paint.
3.2 pigments, wetting agent impact
pigments, wetting agents will affect the water resistance of water-based coatings, and in wet friction, water-resistant paint water resistance, directly affect its wear-resistant performance, water resistance is worse, wet friction fastener is worse

3.3 resin, crosslinker influence
resin determines the water resistance and adhesion of water-based coatings, and the addition of crosslinking agents will make the resin form a mesh structure, improve the adhesion of water-based coatings to the substrate, therefore, increasing the amount of resin and adding crosslinkers can improve the frictional fastness of water-based coatings.4. Light-resistant color fastness
water-based coating applications, and light-related color fastness is many, such as: sun-resistant, light-resistant, weather-resistant, UV-resistant, etc. , light-resistant color fastness refers to the color in the light exposure, anti-fading or discoloration ability.
the fading process of water-based paint after light exposure: a pigment molecule absorbs the energy of a photon, which causes the molecule's outer price electrons to jump from the base state to the exclamation state. Color paint in the light, pigment molecules absorb light energy, energy level rise, molecules in the state of intense, pigment molecules of the hair color system changes or is destroyed, resulting in pigment decomposition and discoloration or fading phenomenon, the stronger the light energy, the longer the light time, the more serious the color paint fade.
according to the fading factors, the factors affecting light fastness: light intensity, lighting time, molecular structure of pigments, resins for coatings, crosslinkers, UV absorbers.
The following light-resistant experimental conditions: pigment color paste added at 0.5% content in water-based white paint, stirred evenly, 200 micron wet film preparation film, after drying over UV light-resistant test machine, energy 350mJ/cm2, ten times.
4.1 pigments
pigments are an important factor in the color fastness of water-based coatings, and the light-resistant color fastness of different pigments varies greatly. Commonly used high-performance organic pigment structures such as DPP (PR.254, etc.), pyridine (PR.122, etc.), these pigments are light resistant at levels 7-8, while general pigment structures such as acetone pigments (P. Y.74 et al.), chromophenol AS (PR.112, etc.), these pigments have light resistance of 3-4 levels, and some (PR.2, PR.31, etc.) light resistance of only 1-2 levels. Add different pigment color paste light-resistant picture as follows:
4.2 color slurry addition effect
the larger the amount of water-based paint with the same color paste, the greater the concentration of the color paste used per unit area, the greater the concentration of pigment, the same amount of pigment and light contact with the surface area is smaller, the lower the pigment molecules are excited, that is, the higher the speed of light resistance, the smaller.
0.5% PR.112 light-resistant color fastness rating is only 3-4 in water-resistant coatings, while the 5% PR.112 light-resistant color fastness level is 6-7.
4.3 Effects of resins and crosslinkers for coatings
The effect of resins for coatings on light fastness is shown in two aspects: first, the resistance level of resins used in coatings;
different manufacturers of resins, due to different manufacturing processes, even if there are the same specifications, but molecular weight distribution, size and chain differences, its light resistance also varies.
color paint, is attached to the surface of the application medium through the resin, the same resin, the greater the resin content in its formula, the closer the resin and pigment binding, the unit area of the same pigment and light contact with the surface and the smaller, the lower the pigment molecules are excited, that is, the stronger the color resistance.
addition of resins and crosslinkers to improve the speed of light resistance is not much, only 0.5-1 levels.
4.4 Effects of UV absorbers
At present, the more ideal UV absorbers, light stabilizers are mostly compounding, especially with hydrochloric acid, phenyl ketones, benzene and triamcinolone, replacing acrylic compounds, can achieve more ideal results than any individual UV absorbers. Ultraviolet absorbers can absorb large amounts of ultraviolet light, reducing the intensity of light to the light, thereby improving the light-resistant color fastness of the material being lighted.
UV absorbent, the light-resistant fastness was increased from 3-4 to 4-5.
4.5 Water-color paint coating cover a varnish
since the light-resistant fastness and light energy and exposure time are also related, consider covering the surface of the water-color paint with a varnish to reduce the intensity of light exposure.
the same color, after covering a layer of varnish, the light fastness from 3-4 to about 7 levels.
5. Artificial color adjustment
Since it is the color fastness of water-based coatings, then the biggest factor affecting the color fastness of water-based coatings is naturally pigment slurry, water-based paint pigment selection directly affects the color fastness of water-based coatings, therefore, in considering how to increase the color fastness of water-based coatings, it is better to consider how to choose pigment slurry. The previous discussion of color fastness and pigment molecular structure, now the paint commonly used pigment color fastness rating included in the table below:
Note: the above pigment color fastness is based on my experience in pigment color paste application process, but different manufacturers of pigments, color additions, different application areas will have some differences.
many paint companies now color palette personnel, without professional, systematic training, color adjustment to the color of the standard board is similar to the standard. And some companies do some color rules, which colors can be added, or can not be added, high and low cost, so color palettes only consider two aspects: color and cost, and the real color needs to consider a lot of places: color, fastness, security, cost and so on. Therefore, we often see color formulations are:
1.PY.42 plus PR.112 plus PBK.7
2.PY.74 plus PR.101 plus PBK.7
These color formulations are not wrong in indoor applications, taking into account the color, but also consider the cost, but once applied outdoors, there will be color fastness problems. Although PR.101, PBK.7, PY.42 are high-fast pigments, but in the water-based paint added PR.112, PY.74 color paste, the actual color fastness in water-based coatings is PR.112, PY.74 color fastness, that is, light-resistant fastness 3-4 levels.
color fastness is related to the amount of pigment color paste added, the smaller the amount of addition, the lower the color fastness (except water resistance, wear-resistant color fastness), so, the smaller the amount of color added in the room, the more attention should be paid to the choice of pigment color paste, in order to avoid color fastness problems, it is best to use high-performance pigment color paste color.
6. Conclusion
In water-based coatings, color fastness can be improved by repugnants such as resins, crosslinkers, waxes, and ultraviolet absorbents, but to a lesser extent. The most important factor affecting the color fastness of water-based coatings is the pigment color paste, in trying to improve the color fastness, it is better to work the choice of pigment color paste. Some very bright colors, such as dyes, color essences, fluorescence, these can not choose pigments to replace, only through resins, crosslinkers, additives, ultraviolet absorbents, etc. to improve color fastness.
a