Need for Surface Modifying Agents
Need for Surface Modifying Agents
Decorative and industrial paints are used to protect coated substrates as well as for aesthetic purposes. While reaching the best balance between aesthetics, chemical and mechanical properties, there is a continuous struggle to avoid surface paint defects like:
- Pinholes
- Fish Eyes
- Orange Peel
- And more…
Because surface is the first accessible way to judge a paint quality, avoiding surface defects is a key to enhance customer confidence in the coating performance. Hence, surface modifying agent can help you improve:
- Surface properties and aesthetics of your coatings, as well as
- Paint protective performance as many surface defects lead to more serious issues than just a bad appearance
Let’s discuss about various surface defects in detail:
| Surface Defect |
Appearance |
Cause |
Solution |
 |
Pinholes:
This defect is characterized by pore-like holes of about the size of a pinpoint. |
Pinholes are the result of trapped solvents, air or moisture |
Pinholes are one of the most common surface issues especially in
sprayed application. Surfactants, will reduce the surface tension,
and help entrapped bubbles to move to the surface |
 |
Blocking:
Blocking is used to describe the fact that freshly painted surfaces stick when pressed together
|
It depends on the surface energy, the coefficient of friction and the topography of the paint surface |
The use of wax will produce a slight roughening of the surface and help to decrease the coefficient of friction which are critical parameters to control blocking |
 |
Fish Eyes:
Characterized by circular voids or separation in the coating
|
Can be caused by oily spots or silicone particles and/or by
air-borne droplets that are deposited on the painted surface. This
is a typical defect when paint is sprayed |
Reduction of the surface tension is required to avoid fish-eyes.
This can be achieved thanks to surface modifying agents such as
surfactants |
 |
Orange Peel:
Rather than being flat and smooth, the surface takes on the appearance of an orange peel, with numerous small bumps and indentations
|
It is often caused by poor leveling and is a common defect in both
spray and roll applied coatings |
Surface tension is a key parameter to control orange peel characteristic. Surfactants modify the surface properties & can help you to achieve very flat surfaces |
 |
Low Gloss:
Gloss is the shiny characteristic of a coating. The smoother the
surface is, the better the gloss
|
The presence of irregularities on the surface may prevent you from having good gloss property |
Surfactants can maximize surface smoothness by preventing pigment flocculation or increasing flow at the coating surface |
 |
Brush / Roller Marks:
Brush or roller marks are frequent defects encountered in coating applications that result in a poor quality image for end-users
|
This unintentional textured pattern left in the dried paint occurs when paint:
- Poorly wets the substrate during the application
- Fails to form a smooth film during the drying time
Such marks are typical of coatings with a too high surface tension
|
To facilitate spreading or impregnation of a surface, surface modifying additives like surfactants or suitable rheology modifiers should be added in the formulation |
How to Improve Surface Properties
How to Improve Surface Properties
In most cases, superior surface properties can be achieved with the addition of selected additives that alter the surface properties of the coating. Learn how to improve both aesthetic and protective performance of your coating by changing the film surface properties:
Let’s discuss them in detail:
Abrasion
Abrasion is degradation due to mechanical wear by hard and rough objects.
A low abrasion resistant coating will lead to many surface defects after a short period of time. It generally occurs when paint is exposed to mechanical erosion, rubbing or friction in applications such as:
- Floor finishes
- Enamels
- Varnishes
Abrasion resistance is related to paint's toughness and depends on its ability to dissipate the mechanical energy applied by the hard substrate to which it is in contact. The abrasion resistance of paint can be increased with the use of surface modifying agent such as wax.
Adhesion
Coatings perform their expected protective and decorative role only when the film well adheres to the substrate. Paint should have strong adhesion and cohesion properties so that it becomes an integrated part of the coated object.
Adhesion property is evaluated by the measure of the degree of attachment between:
- A coating film, and
- The underlying material to which it is in contact
Reaching adhesion that fit well with your application is essential to get high quality paint. Adhesion promoters, for example: Silanes will help you to improve this property… Get an in-depth knowledge on adhesion promoters selection with our exclusive guide.
Anti-blocking
Anti-blocking property is a non-stick situation between two surfaces. It is one of the key requirements for any type of coated items which are dried and immediately stacked or rolled up for storage or shipment. It tremendously reduces the occurring of surface defects induced by stickiness of freshly painted surface.
Coatings with enhanced anti-blocking ability have a good resistance to adhesion under the influence of temperature, relative humidity or even pressure fusing the surfaces together.
Gloss Enhancement
The glossy aspect of paint is due to a high reflectivity of the surface of the film.
Improving the gloss property makes paints easier to clean. The demand of a gloss or mat aspect is strongly related to the application it is intended to be used (kitchen, trim, bath, outdoor...).
Gloss paints are ideal for areas exposed to heavy traffic or heavy use - especially where fingerprints grease or grime are common.
Surface modifying additives help to enhance gloss by helping the paint to level out after application and by increasing pigment dispersion:
- Formulator will find specialties surfactants and additives especially designed to act as leveling agent and thus gloss enhancer.
- The use of dispersants will increase the homogeneity of pigment dispersion and reduce the incidence of large pigment particles on the surface. It will thus enhance the glossy aspect of the film.
Leveling
An insufficient leveling during the drying process, lead to numerous possible film defects, such as orange peel, brush marks...
This phenomenon induces a non-uniform surface tension in the coating majorly caused by gradients in:
- Temperature
- Concentration
- Viscosity, and
- Density
Leveling is the ability to form a smooth film when paint is drying. This property depends on surface tension which drives flow of an uneven liquid surface to a smoother one to lower the surface energy.
The use of surface modifying additives, especially surfactants or rheology modifiers, is a possible way to enhance the leveling property, and thereby improve both appearance and performance of your paint.
Mar / Scratch Resistance
High-quality paint is expected to keep great appearance and to provide substrate protection for a long period of time. To achieve this requirement, coatings need to be scratch and mar resistant as the film surface will have to face light abrasion, impact or pressure during its service life.
In practical terms, a scratch is the first visible sign of damage
The primary function of mar / scratch-resistant additives is to help maintain the original appearance of the coating by reducing physical damage.
Unlike abrasion, this property is independent of hardness. Therefore surface modifying additives such as waxes, silicone etc. help to improve this resistance by acting as lubricate agents.
Matting Effect
Matting effect is a subjective impression identified by our senses. This property depends on the intensity of light reflection.
To obtain a flat paint, the smooth surface of the paint film needs to be destroyed in order to scatter the incoming light and thereby reduce its reflection.
Incorporation of surface modifying additives such as silicas, waxes… will help you to introduce a kind of "micro-roughness". The matting effect relies on the particle size, shape of the matting agent. There is a difference between Silica and Wax. Changing the angle from e.g. 60 degree to 30 degree, a system matted with:
- Silica will show less matting - or more gloss
- A wax is much less sensitive to sheen
Depending on the desired effect and paint application, you can use several types of
matting agent. These additives are very effective in lowering the gloss of all kinds of coating systems - both solvent - as well as waterborne.
Slip Control
A way to avoid surface defects to appear is to ease the ability of two surfaces to glide over each other without causing any mechanical damages. In most case, addition of a slip additive is required to get good slip properties. » Find Out More Slip Control Agents for Your Formulation
Adequate surface modifying additives such as:
- Wax will act by lubricating the surface
- Some specific silicone additives also bring an improvement of the slip properties
To adjust correctly the slip properties, the wax stiffness should be taken into account because the harder the wax, the better the slip properties.
This can be explained by the fact that a softer wax would tend to be more easily liquified, and as a consequence, there remains less of it in a solid state to impart slip. In other words, the harder wax would have a relatively higher proportion of crystals in the solid state to impart slip.
Texturing / Soft-Feel
Some applications require the surface to have tactile properties to convey a feeling of comfort, smoothness and luxury.
Surface modifying additives can modify the paint film texture and promote a "touch-like" feeling.
Waxes as Texturizing Agents: They impact this tactile property by playing on the surface roughness and unevenness. This action is very similar to the one observed with matting agents. It is important that the wax particles protrude through the coating layer to be highly effective. Hence it requires a particle size larger than the film thickness.
Water Repellency
Surface modifying agents help to improve the water resistance by lowering the surface tension so that the wetting of the paint film becomes harder. The hydrophobic characteristic of the coating film is enhanced.
Two main additives categories can help to increase this property:
- Silicones bring a very high water repellency resulting in low water absorption. This resistance to water is particularly useful since it is relatively unaffected by temperature and climatic variations.
- Waxes perform also very well, particularly on porous surfaces. The oil penetrates easily within the pores and fissures, rapidly imparting a very hydrophobic character to the treated surface.
Wetting
Without a good wetting, the coating will "crawl" away from the surface, exposing large surface areas, or move away from low surface energy contaminants inducing surface defects such as fish eyes or brush marks.
Improving the wetting ability of coatings is thus important to maintain contact over the substrate surface
Good wetting requires a coating with a low surface tension. In fact the surface tension needs to be lower than the surface tension of the substrate. As plastic materials have particularly low surface tension, it is crucial for those applications to consider the wetting property of the coating.
Surfactants as wetting agents are the more adapted surface modifying additives used to enhance this property for their action on the surface tension.
Types of Surface Modifying Additives Used
Types of Surface Modifying Additives Used
Wax Emulsions
Waxes are typical additives that significantly influence the surface properties of any coatings by modifying the surface free energy. This has an impact on properties such as:
- Anti-blocking
- Slip & Mobility
- Abrasion Resistance
- Water repellency
- Tough & Feel
- Matting Agents
- Black Heel Marks
» Explore Benefits Offered by Wax Emulsions in Detail
Silicones as Surface Modifiers
Silicones materials are known to exhibit a very low surface energy value. Thanks to this, silicone additives have remarkable effects on coatings formulations, such as:
The main advantage of these additives is that - being a liquid product - they can just be stirred-in with a low energy mixer and they will not lower the gloss of a coating at all. If low surface energy is required without any influence on high gloss, there is no other alternative than Silicones.
Specific silicones additives have the ability to alter the optical appearance and "touch" of the surface, leading to the development of "Soft-Feel" coatings.
A negative effect on recoat-ability or inter-coat adhesion may be encountered. But in specific application, this apparent drawback can turn into advantage for anti-graffiti coatings when easy removal of a second coating is desired.
Silica as Surface Modifiers
Silica additives are very effective in lowering the gloss of all kinds of systems - both solvent - as well as waterborne. The matting effect relies on the porous and uneven shape of the silica particles.
When added in a sufficient quantity to a coating or ink, they will extend beyond the paint surface when the film shrinks during the drying process, thus altering the film from a smooth and even - glossy - surface to a mat one.
The silica matting ability suits particularly in both solvent borne and aqueous systems. However silica efficiency is limited in high-solid or solvent-free coatings because of the lack of film shrinkage when paint is drying.
» Check Out Silica Grades to Achieve Matt Finish in Your Formulation!
Surfactants as Surface Modifiers
Surfactants are mainly known as additives for improving dispersion properties of pigments and extenders -they are commonly called dispersants. However they also can be effective additives for resolving surface problems like leveling and substrate wetting.
Hydrocarbon surfactants impact the leveling and wetting properties in coatings formulations which are key point to avoid paint surface defects. The surface tension reducing part of these additives consists primarily of hydrogen and carbon.
Hydrocarbon surfactants are generally less expensive than fluorocarbon surfactants, and hydrocarbon surfactants are available with a variety of functional groups. It makes sense economically to try them first in the coating formulation.
Methods to Test Surface Properties
Methods to Test Surface Properties
Coefficient of Friction
Once they have migrated to the surface of the coating, wax particles have the ability to modify the Coefficient of Friction (CoF) of the substrate, imparting the desired characteristics. This explains why waxes are often classified as "Surface Conditioner Additives".
The Reduction of Coefficient of Friction (CoF) is illustrated by the equation below:
Two main types of coefficient of friction exist:
- Static CoF = Fr necessary to have an object starting to move
- Dynamic CoF = Fr necessary to stop the sliding object (Measure of the time or of the angle)
The coefficient of friction in coatings can be measured using testers.
Classic CoF Tester in Floor Coatings
Swellometer
Swellometer Test Procedure (ASTM D4446) measures how effective water repellents are to slow down dimensional changes in wood.
The principle is to compare the dimensional changes of a treated and an untreated piece of wood.
Here is the procedure to follow:
- Wood piece (1.5x6x.25 inches) is fully-immersed in coating for 3 minutes(waterborne) or 30 seconds (solventborne)
- Wood piece is removed from coating unblotted and rack-dried and normalized for four days at STP
- After 4-day normalization period, wood piece is placed in Swellometer and submerged in 70°C distilled water for 30 minutes
- An untreated control is submerged with each set of treated wood pieces
- Swell is measured by micrometer
Sutherland Rub
Sutherland RubTest is used to determine the dry rub resistance of coatings & inks.
Sutherland RubTest
A coated sample is placed in the Sutherland Rub Tester and a weight is mounted onto the moving arm of the rub tester. Then a certain number of cycles are runned, and the piece is rubbed by the weight. The results depend on the amount of ink or coating ruboff from the test sample. The rub evaluation is qualitative:
- EXCELLENT - No ink or coating ruboff noted; graphics unblemished
- VERY GOOD - Slight ink or coating ruboff noted; slight graphic damage
- GOOD - Moderate ink or coating ruboff noted; slight graphic damage
- POOR - Severe ink or coating ruboff noted; graphics blemished
Find Suitable Surface Modifying Agents for Coatings
View a wide range of surface modifying agents available in the market today, analyze technical data of each product, get technical assistance or request samples.