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Expériences client "Plastique"

Expériences client "Plastique"

La fabrication et les exigences d’assemblage des pièces en matières en plastiques nécessitent une grande précision. Les films plastiques constitués de plusieurs couches complexes nécessitent une surveillance étroite de la production. Les technologies utilisées dans les capteurs Precitec permettent à la fois de mesurer l’épaisseur de matériaux transparents, translucides ou opaques. Les formes complexes telles que des lentilles en plastiques (ex. Fresnel) peuvent être contrôlées avec précision. Les revêtements fonctionnels de type vernis (ex. anti-rayure) peuvent aussi être mesurés sans difficulté et cela même avant séchage complet. L’avantage des capteurs Precitec est de pouvoir s’intégrer facilement en ligne de production et de permettre une vitesse d’acquisition ultra-rapide qui est compatible avec le volume et le flux de production élevés dans ce domaine d’application.


The triumphant history of plastics began many years ago and there is yet no end in sight. Due to the fact that its technical characteristics, as the molding ability, toughness, elasticity, its breaking and temperature stability as well as its chemical consistency are continuously evolving by being able to choose from a vastly growing collection of production processes and raw materials. This is why plastics are more and more used in new fields of application. For example PET (Polyethylene terephthalate): It is increasingly utilized as a raw material in producing bottles for drinks, food packaging or cosmetics in behalf of their lightness and transparency compared to conventional glass. But also in others sectors there is an accretive demand for plastics. Newly inferred applications are lenses or eyeglass-lenses, medical products, electrical engineering and the car industry. The packaging sector could not sustain without synthetic foils. By increasing the complexity of the foils layer structure it can be used for completely new applications. This leads the in-process measurement and quality assurance to entirely new challenges - Especially for plastics with extremely precise thicknesses and layer structures.

Breakthrough: Interferometric measurements

Whereas the confocal chromatic measuring technology prevailed in the segment of container glass, there are additional interferometric measuring methods for plastic products, offering multiple advantages: They can be used for almost every type of plastic, whether it is transparent or opaque. Both measurement techniques are based on reflecting light in the boundary layers of the material with which the layer thickness can be appointed. These thicknesses can be interferometrically measured in many fields of applications by using SLD (super luminescent)-diodes as a light source. SLD-diodes not only emit light near the infrared range: An additional advantage is their high light density, which also allows roentgenizing colored plastics. Both confocal chromatic and interferometric sensors work contact-free favoring (inline-) measuring during the production process with high-speed operations and material transportation.

Precitec Optronik in Neu-Isenburg offers for both measuring technologies an extensive portfolio of optical CHRocodile-sensors, allowing distance and thickness measurements within a wide measuring range designed for many different materials.

Picture to the right:
Interferometric measuring system for plastics
(CHRocodile K). In Front: The probe.
© Precitec Optronik


Measuring plastic foils

Plastics are often produced as foils. Many of their technical characteristics can be modified, making it possible to use these foils for example as card films for check cards or membrane keyboards. The packaging industry uses foils which can be heat sealed or printed on. Then again other base materials grant special heat and aging resistances. These foils can protect solar cells from external influences. Thanks to specific materials it is now possible to produce biodegradable foils (polyactic acid). Its raw materials are renewable resources. A simple multilayer structure, e.g. an adhesive film, consisting of two layers (adhesive layer, basic foil). The trend is heading towards foils with increasing layer counts for which there are various reasons: The more layers a foil consist of, the better it can be configurated. Furthermore by increasing the amount of layers the complete thickness of the foil is decreased and with that less material is consumed. This means it is very important to have enough knowledge about layer thicknesses and the measurement techniques for creating a good quality product.

These multilayer foils are ongoingly spreading, caused by the ability to fulfill barrier properties against oxygen, water vapor and flavors. Having the same qualities as usual packaging materials the main benefits are tremendous weight savings. Abiding the exact layer thicknesses and structures, monitored by interferometric measurement techniques, is substantial for the foils desired functionality and properties. Modern multilayer structures consist of up to ten layers.

Interferometric measurement systems are capable of measuring multilayer foils in between a few micrometers up to the millimeter range. All layers are measured simultaneously.

Picture to the right:

Fourier-transformed spectrum of a two-layer system (transparent adhesive foil). The Peaks show the backing layer thickness, the adhesive layer thickness and thickness of the whole foil.
Bild © Precitec Optronik


Even though it is possible to measure from just one side, inline measurements during the production process are relatively easy to implement. The needed probes are very compact, which facilitates the implementation of traversing production systems. The probes are orientated crosswise to the advance direction of the foil, allowing to measure its whole width. One of the greatest perks of the interferometric measuring method is the high tolerance of varying measuring distances. That is why the foil can waver around without compromising the outcome of the measurements.

Measuring PET-bottles

Contact-free measurement techniques – the confocal chromatic measurement systems, which also rely on x-raying the object being measured - are standard for container glass (e.g. glass bottles), being produced in high-speed production lines and therefore have to be measured in production time. The contact-free optical CHRocodile-sensors measuring wall thicknesses can be integrated in the production line.

The industry works especially on reducing the wall thicknesses of PET-bottles leading to lower input and decreasing the transportation costs, thereby the wall thickness determination gains further importance. When measuring PET-bottles the best choice is the interferometric measuring method, being in a position to also measure colored bottles with impressive measuring rates of multiple kilohertz. The diameter of the measurement spot merely covers a few hundredth millimeters and therefore even the smallest faults are discovered. An additional advantage is not only the freedom of choosing bigger measuring distances but also having precise data whilst changing distances. This helps determining derivations during the production process before the product quality is compromised.

Additional application potentials in the plastics sector

There are more than the foregoing fields of application for this promising measuring technology. Applications from medical technology report of successful measurements of wall thicknesses on balloons, which are used for angioplasty applications e.g. expanding or reopening contracted or closed blood vessels. Wall thicknesses of disposable plastic syringes can also be measured that way.

Picture to the right:

Wall thickness measurement of a balloon used for angioplasty. On top, in the middle: probe.
© MPT Europe


Moreover, measuring the scratch-resist coatings of plastic eye-lenses is another featured application as well as thickness control for head-up-display foils. Even layer thickness measurements of fluids are possible: e.g. varnishes or water. Several tasks in the automobile industry, including plastic coatings or oil films on steel can be measured. And yet again medical applications as filling levels of fluids are measureable.


Apparently, there are almost no boundaries for interferometric measurements in the plastics sector. The contact-free measuring principle paired with infrared light sources with a high light density can roentgenize nearly every plastic and therefore being capable of measuring complex unilateral layer thicknesses up to the micrometer range. The optical probes needed for interferometric determinations are not only very compact but they can also be arranged at various customer-specific measuring distances. This allows low expense installations of inline measurement systems. Even in mass productions with varying measuring distances and high speed productions can be easily fitted with our systems. It has to be said that the practical measuring experiences of non-contact glass measurements have taught us valuable lessons which can be applied to the plastics sector. Blow molding and extruding have also been adapted by the glass sector. All appearances suggest an exciting future for the interferometric measuring techniques within the plastic industry.

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