Underestimated risk in the surface treatment of plastics or painted components
Why this topic is crucial for the industry:
The optical digitization of components using 3D scanning has become established in industrial quality assurance, reverse engineering, and prototype creation. Especially for components with reflective, transparent, or dark surfaces, the use of scanning sprays is indispensable for obtaining digitizable surfaces.
What many users underestimate: These sprays usually contain solvents that can cause serious damage to certain materials. Plastics such as PMMA (polymethyl methacrylate), PS (polystyrene), or 1K coatings are particularly affected when alcohol-based sprays are used. Incorrect use can result in milky clouding, cracking, or coating detachment—faults that can destroy a component or render it worthless.
This issue is by no means limited to individual product lines. Rather, it is a technical challenge that affects all solvent-based scanning sprays, regardless of the manufacturer.
Challenges posed by solvent-based scanning sprays
Most commercially available scanning sprays are based on a combination of propellants, carrier fluids, and matting agents. The carrier fluids usually contain organic solvents such as isopropanol, acetone, cyclopentane, or hydrocarbon compounds. Depending on their concentration and exposure time, these can react with certain plastics.
One example is PMMA: this material is severely attacked by acetone, which can lead to visible surface changes after just a few minutes. PS is also sensitive to alcohol or ketone compounds.
Scientific principles: Why materials react
The reaction of plastics with organic solvents can be attributed to molecular interactions and the principle of solubility: “like dissolves like.” Organic solvents such as acetone or isopropanol are polar substances. Many plastics, especially PMMA or PS, also have polar molecular structures. The polar molecular structures can interact with the polar solvents. These ensure that the individual polymer chains, which are tightly “entangled” with each other, are pushed apart, which can lead to swelling, stress cracks, or structural changes.
The surface tension of the solvents also plays a role: substances with low surface tension penetrate fine pores or microstructures more easily. This promotes penetration into paints or coatings and can lead to detachment or softening.
In the case of paintwork, solvents act as plasticizers that can weaken the bond between the paint and the substrate. Single-component paints are particularly sensitive, as they do not have the same chemical resistance to organic compounds as chemically cross-linked paints.
2K paints, ferrous materials, and non-ferrous metals can generally be wetted without any problems using all scanning sprays.
Common errors and misunderstandings
A common misconception is the assumption that a spray that sublimates without leaving any residue is automatically compatible with the material. In fact, the chemical reaction with the substrate can already take place during spraying. The statement “the thinner the application, the less critical” does not apply without restriction either: even small amounts of solvent can have a major effect on sensitive surfaces.
Another misconception concerns the exposure time. Some users assume that damage only occurs after prolonged contact. However, practical experience shows that reactions with critical materials usually occur within a few minutes.
Making the right choice using material compatibility tables
We at MR Chemie GmbH know our products best and have collaborated with the 3D Scan Academy in Göppingen to create a material compatibility table that helps users quickly select the right spray.
As a user, you should nevertheless carry out a small compatibility test on an inconspicuous area, as it is often not possible to make a general statement. The respective generic terms for the types of plastic allow for countless variations, which means that the interaction with organic substances changes depending on the length of the polymer chains, the degree of branching, or additives (such as plasticizers or fillers).
Conclusion: Safety through knowledge and choosing the right product
The choice of the right scanning spray should not only depend on scanning performance, but should always take material compatibility into account. Careless use can be risky, especially with sensitive plastics and coated surfaces.
By understanding the chemical mechanisms of action, knowing the ingredients, and using material compatibility tables, damage can be avoided and the quality of optical digitization ensured. With the REFLECON® series, MR Chemie not only offers high-performance products, but also the necessary guidance for safe use in industrial environments.
Your contact
Mario Montalti
Sales Development Engineer Reflecon
0160 94750556
m.montalti@mr-chemie.de
