Wax Emulsions for Coatings: Uses, Benefits & Formulation

What are Wax Emulsions?

Wax emulsions and dispersions are formulated additives made of fine and stabilized wax particles, homogeneously distributed in water. Being in the liquid form, they are easily incorporated into coatings and inks formulations by simple mixing.

Wax emulsions normally have particle size < 1µm, and therefore, a minimized effect on the coating gloss
Wax dispersions (either water or solvent-based), have a particle size typically > 1-2µm

Their very fine particle size ensures thorough, homogeneous incorporation with other ingredients of the formulation, maximizing the required effects.

Wax emulsions can be stabilized by either non-ionic emulsifiers (steric mechanism) or by ionic emulsifiers, most often anionic (electrostatic mechanism). Combining anionic and non-ionic emulsifiers provides the emulsion the optimum stability because wax particles are protected through both stabilization mechanisms.

In addition, each stabilization mechanism not only has its own advantages and limitations but also significantly impacts the overall formulation giving added flexibility in formulating.

Factors to be Considered While Formulating Wax Emulsions

Wax emulsions are now well established and extensively used in various aqueous formulations. These ready-to-use wax emulsions can be easily incorporated into a formula by simple mixing.

The wax properties that have the greatest impact on formulation performances include:

The Melting Point: When curing is required, it is important that the wax has a lower melting point than the curing temperature. Thus, the wax can:

The Coating Thickness Layer: In order to maximize the wax effects, it is important to have the highest dried wax density to be at dried film surface.

Hence, the wax emulsion should have a particle size as closest as possible to the thickness of the coating layer

Sometimes a wax emulsion with a smaller particle size performs equally well, provided that the concentration is correctly adapted.

pH of the Wax Emulsion should be within approximately one unit of the system to which it is added. If necessary, the pH of the emulsion can usually be adjusted using aqueous ammonia or acetic acid.

The Type of surfactant can also influence compatibility with the other components, as well as the overall formulation stability. Matching the emulsion charge with the coating charge enhances stability.

The Order of Component Addition: In water-based formulations, the order of component addition can be a critical factor in maintaining stability. Agglomeration can be prevented and overall stability maximized by adding the wax emulsion last. A further dilution of the emulsion with soft or demineralized water before incorporation can also reduce the shock.

The Regulatory Aspects of Waxes: If the emulsion is intended for food contact use (in a coating or in a package), both the wax and other incorporated additives (emulsifiers, antifoams, biocides etc.) must be in compliance with applicable statutes and regulations (FDA, BfR, European Directives, Kosher Certification etc.).

Determination of Wax content in a Formulation

Drying Optimization Strategies for Waterbased Systems

Mechanism of Action of Wax Emulsions

The Blooming Mechanism

Molten wax particles float (or bloom) to the surface. The coating cools and re-crystallization of wax particles takes place, forming a thin but continuous wax-enriched surface layer.

The softer the wax or lower the melting point, the more predominant the blooming mechanism becomes
The compatibility between the wax emulsion and other formulation components determines the wax migration rate

Blooming Mechanism for Formulating Wax Emulsions

The Ball Bearing Mechanism

In this case, solid wax particles migrate individually or protrude through to the surface.

By protruding slightly above the coating surface like ping-pong balls floating on a pool of water, they:

Act as a physical spacer, and
Prevent another surface from coming into close contact

Hard and high melting point waxes (HDPE, PTFE) operate using this mechanism under certain conditions. Both the particle density and the extent of protrusion influence the magnitude of the effect.

Once at the surface, the layer of wax particles has 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".

Ball Bearing Mechanism for Formulating Wax Emulsions

Benefits of 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 described below. All of them are critical properties in the paint, coating and ink applications. Hence, waxes are often classified as Surface Conditioner or Modifier Additives.

Wax Emulsions as Anti-block Agents

Anti-blocking is a term defining a non-stick condition between two surfaces or the resistance to adhesion between two surfaces under the influence of:

Temperature
Relative humidity, or
Pressure

A very well-known example of a blocking condition is when a freshly painted window frame is closed too soon. Sometimes, it can be very difficult to open the window again. Factors affecting blocking include:

Coating surface-free energy
Topography of the coatings
Hardness, and
Tg of the polymer

Wax emulsions as anti-blocking agents are also used extensively for items that are coated, dried and immediately stacked, rolled up for storage or shipment.

Effect of Wax on Slip & Mobility

Slip properties (or lubricity) represent the ability of two surfaces to glide over each other without causing any mechanical damage. Good slip properties require that the slip additive concentrate to the surface during and immediately after application and curing.

Generally speaking, the harder the wax, the better the slip properties

This is explained by the fact that wax crystals in the solid state are the main factor responsible for the characteristic of slip.

Thanks to this property, wax is widely used in applications:

Inks, OPV's & Primers,
Paper, Film, & Foil Coatings
Metal coatings

Slip resistance is the ability to manipulate the surface energy by increasing the coefficient of friction of a cured coating. This can be realized by addition of wax surface modifiers.

In particular, polypropylene waxes or wax emulsions:

Control slip without adversely affecting scratch and mar resistance
Have good migration performance which results in an increased wax density on the coating surface

When formulating with polypropylene wax emulsions, it is crucial to adapt the particle size of the emulsion to the coating layer, in order to maximize the wax effects on the coating surface.

Wax emulsions are used for their slip resistance property in Floor Polish.

» Check Out Various Wax Grades used as Slip Control Agents!

Effect of Wax on Abrasion Resistance

Abrasion resistance is produced by a combination of basic characteristics such as elasticity, hardness, strength, toughness, and in some cases, thickness.

Abrasion Resistance in Coatings using Wax Emulsions

It has also been established that a trend similar to that of slip additives exists between the wax hardness and the capability of the wax to resist rubbing damage.

Hard wax resists abrasion better than soft wax

Thanks to its mar, scratch and rub resistance properties, wax emulsions are used in a wide range of applications such as:

Architectural Coatings & Floor Polishes
Paper Film, & Foil Coatings
Inks, OPV's & Primers
Metal Coatings

» View Commercially Available Waxes for Scrub & Mar Resistance

Wax Emulsions for Water Resistance

Water repellency or water resistance is another important property obtained or improved with waxes. As the name implies, this characteristic is the protection of a surface against water penetration (in liquid form).

Depending on formulation, the protection may be temporary or very durable and long-lasting.

Water Resistance in Coatings Using Wax Emulsions

Thanks to this property, wax emulsion is a key ingredient in a wide range of formulation for:

Wood Coatings
Architectural Coatings & Floor Polishes

Effect of Wax on Touch & Feel

Although coatings are usually applied to provide optical effects (color, gloss or matting etc.) or to protect a substrate, some applications also require the surface to have tactile properties.

In modern car interiors, coatings with a soft-feeling are applied on plastic substrates (mainly PVC) such as instrument panels and door handles to convey a "leather-like touch", i.e. a feeling of smoothness and luxury.

With electronic devices (PCs, mobile phones, etc.) a "soft-feeling" effect created by specialized coatings is becoming increasingly more in demand.

By employing a coating that incorporates coarse wax particles, a rough and uneven surface is created at the microscopic level that is very similar to that observed with matting agents. Because tactile properties are largely dependent on the coating formulation, it is important that the wax particles protrude through the coating layer and this requires a particle size larger than the film thickness.

Thanks to this texturizing effect, wax emulsions are commonly used in Wood and Plastic Coatings.

Matt Effect Using Wax Emulsions

Providing wax dispersions have a particle size much higher than 1 µm, they will significantly reduce the gloss, by introducing micro-roughness on the coating surface. The so-created uneven surface will cause the light to be scattered.

The degree of the micro-roughness is determined by the number of particles present at the surface, which directly depends on wax properties such as:

Particle size and particle size distribution
Particle density
Amount of matting agent incorporated

Thanks to this matting property, wax emulsions are widely used in wide range of applications such as: Architectural, Wood coatings and Inks, OPV's & Primers.

» Select Waxes to Obtain Desired Matting Effect in your Application

Effect of Wax on Black Heel Marks

Black heel marks occur in a floor coating when the heel or sole of a shoe leaves residue on the floor after a shoe scuffs or scrapes the coating surface. Grocery carts, platform trucks, hand trucks and fork lifts can all produce black marks.

By reducing the coefficient of friction of the coating, carefully selected waxes such as HDPE will have better mobility across a coating surface improving the heel mark resistance.

Thanks to its heel mark resistance property, wax emulsions are used in Floor Polish.

Wax Types and Properties

Wax is a generic term that encompasses materials that have some specific properties such as:

Solid at 20°C, varying from soft / plastic to brittle / hard
A mp > 40°C without decomposing
A relatively low viscosity slightly above the melting point
Transparency to opaque, but not glass-like
Buffable under slight pressure

This includes:

Natural products based on C16 - C 36 Fatty Acids or
Some synthetic polymers with Mw from 700 to 10.000

Waxes are often classified according to their origin as illustrated in the table below:

Naturally Occurring Waxes			Synthetic Waxes
Animal	Vegetable	Mineral	Synthetic Waxes
Beeswax	Carnauba	Montan	PP, PE & PTFE
Lanolin	Candellila	Paraffin	Fischer-Tropsch
Lanocerin	Jojoba	Microcrytalline	Fatty Acid Amine
Shellac	Ouricourl	Intermediate	PTFE
Ozokerite			Polyamide

Where:

PP = polypropylene
PE = polyethylene
HDPE = High Density Polyethylene
PTFE = Polytetrafluoroethylene

Table below summarizes the main wax properties and corresponding effects imparted or improved in paint, coating and ink formulations.

Type	Properties	Main Performances
Carnauba	High melting naturally occuring wax Different grades (T1, T2, T3) Hard & brittles Excellent clarity Generally Recognised As Save	Slip & Lubricity Anti-Blocking Mar Resistance
Paraffin	Various grades, hence properties depending on refinement degree Hard to oily feeling Mainly composed of straight alkane chains, hence some parafffin's have good crystalline structure, giving excellent barrier effects against water repellency Very low polarity	Anti-Blocking Water Repellency Slip & Lubricity
PE	Obtained by polymerization of Ethylene monomers Various grades, hence properties depending on Mw and polymerisation process Two main families: LDPE and HDPE (Low and High Density PE) whose difference is the extend and type of branching LDPE's display more thoughness, better scuff / mar resistance and are more flexible HDPE's contribute to better slip properties and abrasion resistance	Slip Abrasion Resistance Anti-Blocking
PP	Obtained by polymerization of propylene monomers Good film toughness but poor slip & lubricity properties Not really a wax but often classify as such because of impact to surface properties	Anti-Slip Anti-Blocking Abrasion Resistance
PTFE	Obtained by polymerization of C2F4 monomers High melting point and outstanding heat resistance properties (up to 600°F) Give the lowest known CoF, hence excellent slip & lubricity, anti-blocking and abrasion resistance Chemically inert Not really a wax but often classify as such because of impact to surface properties	Slip & Lubricity Anti-Blocking Abrasion Resistance

Find Suitable Forms of Wax Grades

View a wide range of wax grades available in the market today, analyze technical data of each product, get technical assistance or request samples.

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Wax Emulsions for Coatings