Why Scratch and Mar Resistance Agent?
Why Scratch and Mar Resistance Agent?
High-end finishes offers the perfect aesthetic and the required durability. Nevertheless, across the time, the paint will be subject to numerous aggressions that may deteriorate its surface.
Besides the negative effect on the film aesthetic, these scratches can also lead to more severe issues. They reduce the film durability itself by causing corrosion spots when the paint itself is damaged down to the substrate.
Nowadays, consumer expects a product to look new even after time of use. This challenge obliged the formulator to search for solutions in order to reach this imperative requirement. Among all the type of agents available in the market, an introduction to Scratch & Mar Resistance Agents can help you select the best material for your formulation.
What is a Scratch Mar Resistance Agent
What is a Scratch Mar Resistance Agent
Scratch & mar refers to damage from impact, rubbing or abrasion that produces visible scratches or marring and hence damages the paint film. It sometimes can be rubbed out when they are very light.
A Scratch & Mar Resistance Agent is used to reinforce the coating’s resistance to these damages
These agents are present in various coatings, such as solventborne, waterborne, UV, Powder, where a specific need in the scratch and mar resistance is required, for instance, in:
In many cases, an excellent level of scratch resistance is required in order to improve the paint ageing. Indeed, depending on the amount of material removed from the surface during the scratch event, the depth of penetration may not only deteriorate the visible film, which affects the aesthetic view by reducing the gloss or let a visible line, but can also reach the substrate, affecting the paint integrity. This occurs especially after some times when the paint surface recovers its flatness.
The figure below depicts the paint surface when no scratch and mar resistance agent is added:
Work Mechanism of Scratch and Mar Agents
Work Mechanism of Scratch and Mar Agents
A scratch and mar resistance agent allows the reduction of the film degradation after a mechanical impact on the film layer by:
- Creating a sacrificial layer
- Reducing the surface tension
- Introducing some material that protude above the film surface
In most of the cases, a combination of these complex mechanisms perform the required level of resistance.
Scratch & Mar Resistance Agent improves the film properties by acting mainly on three parameters:
- Creating a thin layer at the paint surface that will act as a protective and sacrificial layer
- Reducing the film surface tension, that will make the scratching objects to slip more easily on the paint surface and reduce or negate the scratch
- Introducing some scratch resistant or some sacrificial material at the film surface that will
protrude above the surface of the paint
Types of Scratch and Mar Resistance Agents
Types of Scratch and Mar Resistance Agents
Various Scratch and mar resistance agents exist. Each family has its own properties and can be further adapted to fit the formulator's requirements. Here, we will focus on major types of scratch & mar resistance agents, namely:
Waxes
Following the definition of the European Wax Federation, Wax is a generic term for a range of natural or synthetic products. For convenience the range can be subdivided in:
- Natural waxes
- Synthetic waxes
- Mineral Hydrocarbon waxes
- Petroleum waxes
Waxes are usually defined by their characteristic properties:
- Solid at 20°C, varying in consistency from soft and plastic to brittle and hard
- As solids as coarse to finely crystalline, transparent to opaque, but not glass-like
- Have relatively low viscosity slightly above the melting point
- Melt above ca. 40°C without decomposition
- Consistency and solubility are highly temperature dependent
- Buffable under slight pressure
- Burn with yellow flame can form pastes or gels when dispersed in solvents
- Exhibit low thermal and electrical conductivity
Common waxes type used in coatings are:
Table below shows the general properties of wax in coatings:
Depending on their nature and molecular weight, waxes improve the mar & scratch resistance by combining the sacrificial protective layer (blooming mechanism) and some solid material at the surface (ball bearing mechanism). For this last mechanism, the particle size of the wax is extremely important as, of course, the solid material must protrude above the surface.
Let's take a look on these two mechanisms in detail:
- Blooming Mechanism: The molten wax particles float (or bloom) to the surface. When the coating cools down, re-crystallization of wax particles takes place, forming out a thin but continuous wax surface layer. Incompatibility between wax and coatings can enhance the migration phenomenon. Microcrystalline wax and paraffin wax work through this mechanism.
- Ball Bearing Mechanism: Solid wax particles migrate individually to the surface and act as a physical spacer by protruding above the coating surface, preventing another surface from coming into close contact. High-density polyethylene (HDPE) or PTFE work through this mechanism in some conditions. Both the particle density and the extent of protrusion influence the degree of effects.
Selecting the formulation products may be complicated. That is why, while selecting a wax, it is really important to consider all side effects, such as, besides the wax properties, the coating chemistry, properties, and end-use, the application method and curing conditions. Indeed, as the wax will migrate to the surface, it may considerably affect the transparency or the gloss. Nevertheless, some side effects such as the reduction of the surface coefficient of friction will make waxes a perfect product when anti-blocking properties are required.
Silicone-based Agents
They are usually modified PDMS (Polydimethylsiloxane). In the paint, silicone-based agents strongly reduce the surface tension and increase the slip. Consequently, the scratching item will “slip” on the paint surface and will not or less deteriorates the film surface.
Some specific modified structures can also form a thin protective layer at the paint surface.
Silicone-based agent may have also a positive influence on the film aspect
by reducing the orange peel for instance!
Fluoro- & PTFE-based Agents
They are generally modified chemistry, as pure fluorocarbons are too strong and provoke many defects.
PTFE waxes are PTFE polymers based on the monomer (CF2-CF2)n with n ~ 104.
PTFE Polymers Based on Fluorocarbon Monomers
Regarding the scratch & mar resistance, they are acting like the silicone-based products, thanks to their stronger surface tension reduction. They can resist at higher temperature than standard silicone-based agents (over 150°C). Fluoro-based agents are also more expensive than the silicone based products.
As PDMS-based products and fluorocarbons are active at the paint surface, they may also influence the film aspect.
Silica & Colloidal Silica
Silica is another name for silicon oxides, the most prevalent type being SiO2. The industrially manufactured variety, amorphous silica, is used to produce the colloidal silica.
The colloid silica is a stable dispersion of silica particles sizes range from about 1 to 100nm. They are small enough not to settle, but large enough to be stopped by a membrane and allow other molecules and ions to pass freely. Particle size and pH are what differ most between the grades of colloidal silica.
Colloidal silica will improve the mar & scratch resistance in mainly two ways:
- Increase the cross-linking density of reactive groups in organic resins thanks to its high number of hydroxyl surface groups. Those will have an effect on the film build density and improve the resistance
- Colloidal silica particles are very hard (5.5 on the Mohs scale) and significantly improve coating hardness, especially at the film surface
Among the inorganic fillers, silica colloids have the advantage
to not affect the transparency of coatings and can be used in various clear coats
Metal Oxides & Nanoparticles
Aluminum is significantly harder than silica-based materials and very performant as a scratch & mar resistant filler even at lower loadings. Nevertheless, its refractive index limits its use in clear coats and transparent coatings.
Thanks to their inherent small size (sub-micron) and particle morphology, nanoparticles based products can overcome the negative effects of metal and metal oxide based products. And reinforces the scratch& mar resistance property of the film.
Silicon oxides and Aluminum oxide are widely used in order to improve the scratch resistance
Nano Aluminum Oxide dispersions impart a variety of scratch and mar resistant properties to the coatings that are inaccessible with conventional as waxes and silicones. They are also active at low loading levels and do not have negative effect on gloss or other mechanical properties of the film.
The combination of Nano Aluminum Oxide and PDMS-based additives gives furthermore better improvement in the scratch resistance. Very versatile, nanoparticles dispersions can improve the scratch resistance of various coatings types such as:
However, conclusions are not limited to these cases, and can be enlarged to most of coatings systems.
Selecting Right Scratch and Mar Resistance Agents
Selecting Right Scratch and Mar Resistance Agents
The selection of a scratch and mar resistance agent will be determined by:
- Chemical nature and functonality of the resin system
- End-use of the paint
- Application Conditions
Testing and evaluating a new scratch & mar resistance agent may be fastidious; it is possible to focus on critical points to reduce the time and material spent on the study keeping a high pertinence of results.
The following table indicates the characteristics of main mar & scratch resistance agent. Final choice must be done after considering all side effects of each product type.
Besides all these considerations, the right reaction process using the right sratch and mar resistance agent will also depend on important factors, like:
- Compatibility of the agent
- Side Effects of the Agent
- Dosage and the type of agent
- End-use of the paint
- Processing and curing conditions
- Price
Once, you have chosen your scratch and mar resistance agent, it is equally important to conduct its tests to ensure good performance of your product. Let's understand various test methods used for the same...
Test Your Additive Before You Start!
Test Your Additive Before You Start!
Scratch Test: Gloss Evaluation
Each sample drawdown is evaluated for scratch resistance with 20 double rubs using 9-micron polishing paper pads on a dry abrasion tester. Gloss at 20° and 60° is measured before and after scratching the panels.
Percent gloss retention is ratio of gloss value of scratched area on original gloss value at the retain angle.
Lower gloss retention value indicates a better mar & scratch resistance property.
Abrasion Test TABER
Testing for scratch covers both areas of mar and scratch, this test is normalized following methods ISO 9352 or ASTM D 1044.
Important Characteristics to Check
Important Characteristics to Check
- Viscosity: Due to their intrinsic properties, some Scratch & Mar Resistance agent, especially waxes, may influence the viscosity
- Gloss: As agents active at the film surface, gloss may be influenced
- Hardness: As agents active at the film surface and may participates in the reaction, the film hardness will also be influenced
- Impact test: As agents active at the film surface and may participates in the reaction, flexibility of the film may be influenced
- Chemical resistance: Including - solvent, acid, alkali, water, etc.
- Influence on the color, blushing: Some agents may decrease the transparency value
- And of course: The general aspect of the film
Scratch/Scrub/Mar Resistance Agents for Coatings
View a wide range of scratch/scrub/mar resistance agents available in the market today, analyze technical data of each product, get technical assistance or request samples.