The benefits of waxes in coatings and inks

Waxes are a useful formulation tool that can enable the developer to alter many performance-improving functions of an ink or coating’s surface to meet the requirements of their everyday use. Wax additives are used extensively due to their flexibility of use and significant positive impact on many formulation types. Properties which may be altered include:

• Slip or lower coefficient of friction
• Scratch resistance
• Rub and abrasion resistance
• Matting effect
• Hydrophobicity
• Blocking or anti-blocking

These important functions can be achieved with relatively low addition of the wax additive based on its solids and 2-4% may be considered normal to achieve any or some of the above.

Lawrence Industries is pleased to be able to offer our customers CERETAN® micronized waxes and LUBA-print® wax dispersions or emulsions produced by MÜNZING CHEMIE GmbH.

What is a wax?

Waxes can include many different synthetic or natural chemical compositions. However, it is not just this chemical composition that defines a compound as a wax, it is more so its physical properties. These are as follows:

Table 1: Basic properties of waxes. To be classified as a wax, a material must meet at least 5 of these criteria. 

In order to be defined as a wax, five of the above criteria should be met.

As an aside, PTFE does not fit these definitions. However, PTFE is often included in the same class of surface modifiers due to the properties it can exhibit. MÜNZING have PTFE products in their product range as promoted by Lawrence Industries and for the purposes of this blog they will be included as such.

From here, waxes can be broadly split into Natural Waxes and Synthetic Waxes:

Figure 1: The different types of natural and synthetic waxes

What properties can you expect from different wax types?

Since waxes display a myriad of different physical characteristics, we can also expect different wax types to offer different benefits in our coating systems. Below is a simple break down of what you may expect from different wax selections and all are available as CERETAN® or LUBA-print® variants:

Polyethylene – a hard synthetic wax used for slip, scratch and abrasion resistance. Oxidised grades may be easily incorporated.

Polypropylene – a hard wax useful for abrasion resistance and matting. The only wax which will not increase slip property and may impart a textured or rubbery feel.

Fischer-Tropsch – a hard wax used for scratch resistance, slip and anti-blocking.

Amide – used for slip, anti-blocking and very sandable. A wide range of melting points to suit processing or drying conditions.

Paraffin – the wax of choice when hydrophobicity is required. May also be recommended for slip and release properties.

Carnauba – the hardest natural wax. Used for slip, anti-blocking and scratch resistance. Food contact status E903.

PTFE – chemically resistant and recommended for high degrees of slip.

Formulation and mechanisms of waxes in coatings

A micronized wax’s efficiency is partly governed by its particle size which must be in the formulator's thoughts when factoring the coating’s dry film thickness (Figure 3). Too small a particle in relation to the film weight will result in too little protection; and too large a particle will result in the wax being more easily removed from the binder when abraded and therefore in the long run offering little protection. A “just right” scenario where 25% to 33% of the wax protrudes from the dry film surface should offer adequate protection to the coating as well as to impart other properties which may be desired. This emergence of the particles from the coating layer is called the “Ball-Bearing Effect”. As well as offering physical improvements to the coating, this effect may also give rise to matting of the coating due to protruding particles scattering light reflected from the surface.

When thinking about particle size it is also important to note that this may have an effect on the surface properties within the working limits of the particle size. For example, a smaller particle will have less of an effect on gloss and as particle size increases, an improvement in slip and anti-blocking may be seen.

Figure 2: Wax particle size is important; too small and the coating is not protected, too large and the protection is easily removed.

With respect to wax emulsions, floatation is required to obtain adequate levels of wax to the surface and this is controlled by the speed of curing of the ink or coating. Wax emulsions are very easy to incorporate and as such are used extensively in inks, coatings and graphics arts or OPV. This consideration to floatation is important for stoving paints where the curing temperature is above the melting point of the wax. In this case the formulator will be looking to achieve a layer of wax on the surface of the coating whether using a solid wax or an emulsion, this is known as the “Bloom” or “Floatation Theory”. The drying diagram below illustrates both points:

Figure 3: Method of surface protection using waxes.  If the drying temperature is higher than the wax melting point, the wax will melt and form a homogenous layer at the surface.  For coatings where the drying temperature is below the wax melting point, micronized waxes will sit at the surface resulting in a ball-bearing effect.  Film-forming emulsions will form a homogenous layer irrespective of drying temperatures.

MÜNZING Chemie Wax Range

MÜNZING’s vast range of CERETAN® spray-micronized waxes and LUBA-print® wax emulsions and dispersions are available through Lawrence Industries.

The wax types mentioned already in this blog are available for sampling. Chemistry type coupled with a range of particle sizes in most cases for CERETAN® grades means there is a micronized wax for all systems. LUBA-print® grades are available in water, solvent and UV curable monomers, again offering many options for most situations.

MÜNZING are a specialist in spray-micronizing of waxes with tightly controlled production which can offer the following features benefits when using CERETAN® products:

• Easier to disperse spheres
• Smoother surface when compared to granular waxes
• Less agglomerated particles
• Tightly controlled particle size with guaranteed D99
• Blended waxes available for multiple property types
• Coated waxes available for example silica for extra matting

Features and benefits for LUBA-print® dispersions and emulsions can also be considered:

• Easy to handle liquids
• No possibility to dust
• Easy incorporation with simple mixing in most cases
• Excellent stability achieved using MÜNZING’s additive knowhow
• High gloss achievable due to the action of the wax on the surface of the coating
• Can produce closed films (useful for paraffinic hydrophobic layers for example)

Please get in touch with your Lawrence Industries account manager for further information and assistance in formulating using MÜNZING waxes.