GAMECHANGER

Encapsulated lubricants and active ingredients in applications that are dry to the touch are becoming increasingly important, since they indicate solutions for many problems. Through their use in the area of injection molding, they’re becoming a technological gamechanger. The innovative microcapsules are the result of the continual refinement of anti-friction coatings.

Special lubricants are becoming more important in the industry, especially the automotive industry. Depending on the requirement profile, it contributes to low-noise functionality of various assemblies. The targeted vibration damping and friction value optimization enable reproducible processes in the various components over the long term.

Lubrication solutions that are dry to the touch and have great problem-solving potential

Besides lubricants, pastes, and lubricant dispersions, coatings have long been included in the most effective lubricant systems. “These anti-friction coatings have great problem-solving potential as lubrication solutions that are dry to the touch,” says Dr. Thomas Löhl, product manager for anti-friction coatings in BECHEM’s Special Lubricants unit. On the one hand, BECHEM anti-friction systems are already indispensable in large-scale series production (the production of premium engine pistons, for example), and, on the other, BECHEM experts believe that many developers and suppliers are not yet fully aware of the wide range of possible applications for anti-friction coatings. This type of coating involves dispersions of selected solid lubricants in organic or inorganic binders in solvents or water. After the application and hardening, the varnish forms a solid composite of binding agents and solid lubricants.

In a tribological loading, the integrated solid lubricant is transmitted to the counterbody. As part of that process, a transfer film is formed that leads to a reduction of the shear forces (and therefore, to reduced friction values). A number of binding agents and solid lubricants with various qualities, including those based on nanotechnology, are available for various development requirements.

Embedding microcapsules filled with active ingredients into the anti-friction coating can greatly support the lubricating ability of the solid lubricants contained. In the microcapsules with a size of 1–1000 μm, both solid, liquid, and gaseous materials (the actual core material) in the smallest portions, surrounded by a wall/matrix material, can be immobilized. The operating principle of the microcapsule technology in anti-friction coatings is illustrated by the SEM images in Fig. 1. Only identifiable under the scanning electron microscope, spherical containers are embedded in anti-friction coatings with lubricants or other effective ingredients. If the cured lacquer layer is under stress, it transfers its load (here, lubricant) to the point of friction or lubrication.

In this way, it forms a powerful, dosed lubrication film between the friction partners involved, which significantly reduces friction values and wear and tear. The encapsulation serves as a protection here, to avoid incompatibilities between the resin binding system and encapsulated lubricants. Minimal wear can be detected on the surface after every movement. This uses the microcapsule technology to its advantage: The mechanical effect on the anti-friction coating opens the capsule shell, freeing a dose of the additional lubricant. Through the continuous friction movement in the tribological gap, it is further distributed and ensures a surface that is dry to the touch. With additional wear and tear, deeper lying capsules are reached that guarantee a constant supply of lubricant.

Fig. 1: Operating principle of the microcapsule technology in anti-frictions coating (Source: De Martin GmbH, Surface Technology)

A new dimension: Micro-capsules in the injection molding

Using microcapsule technology in plastic injection molding is completely new. The compound, which is equipped with microcapsules loaded with active substances, is processed to molded parts in the injection molding tool that literally “have what it takes.” In this case, the entire plastic contains microcapsules, not only the top coats.
The phrase “active substance” entails more than lubricants
here. Varying the process parameters makes microcapsules possible in various sizes and wall thicknesses. The free choice of the ingredient enables the formation of a wide range of application possibilities.

During injection molding, this means that the technology used can help improve the functionality and service life of plastic components, parts, and assemblies, and create real added value for the products. Alternative approaches are also indicated with a view to construction practice regarding the type of construction and material specification that can be chosen. It is entirely possible that certain qualities demanded by the construction can also be fulfilled with less demanding plastic materials. This is possible if the microcapsules added to the raw polymers compensate for the quality deficit according to requirements.

Possible examples of applications are stiff plastic mechanisms such as drawer systems, sliding guides, and large screw threads, that should preferably be lubricated to be dry to the touch. The integrated microcapsule lubrication effects a lighter handling, higher operational safety, and higher service life of the component. An example of these are hinged windows with sliding guides or crank mechanisms as found in boats and mobile furniture. Lubricants that can no longer meet these requirements through UV light influence, oxidation, or wash-out effects can be replaced by the integrated lubrication with micro-capsules. After the mechanical abrasion of the injection-molded web at the plastic component, the actual lubrication begins or the microcapsules lying on the surface open.

Fig. 2: Friction gradient over testing distance (plastic injection molding)

The BECHEM developers determined in laboratory trials that the static and dynamic friction value (CoF) can be reduced by an average factor of 2.5 by adding 10% of microcapsules in POM (polyoxymethylene). The amount of capsules that should be added to the plastic depends on the load on the friction point. When contact pressure is high, no appreciable difference results between 10% and 20% of the capsule addition. “The plastic component then receives lubrication during frictional contact through the compounded microcapsules if lubrication is necessary. The plastic component lubricates itself through compressive loading. This is a real alternative to lubricant modification with solid lubricants (graphite) or oils that sweat out,” says Dr. Löhl. Clear added value can be provided not only by the core material lubricant or the topic of lubrication, but also by capsules with other additives. For example, microcapsules might take on an important function as a carrier medium for PFAS replacements.

In the subject area of interior acoustics, sound management, and noise reduction in the automobile industry, applications exist in which plastic compounds added through microcapsules can have a great influence on the developmental work and the construction principles. Depending on the type, size, and number, an acoustic emission can be suppressed for certain frequencies with microcapsules. “A ‘two-in-one effect’ can often be seen,” says Stephan Henzler, head of tribology in the BECHEM company, meaning the coinciding of product qualities such as lubrication and damping, damping and acoustic control, or damping and thermal effects.

By “thermal effect,” Henszler means that, with the microcapsule technology in the plastic component, integrated latent heat accumulators, which work with a phase switch from solid to liquid, are possible, which store and reemit a large part of the thermal energy added to them. Such heat accumulators are conceivable for applications in the vehicle interiors for comfort control or in construction facade technology. “Strong temperature fluctuations in the outer area affect the inner area. Therefore, surfaces that remain cool when it’s hot – not warm when it turns cold – are preferable,” Dr. Löhl adds.