Quality control in industry

Functional coatings and surfaces are utilised for property development or enhancement of raw materials. They are utilised for lifetime enhancement of products and enable the usage of new material types for improvement of material resource efficiency in industrial applications.

Online monitoring and characterisation of functional coatings by process analysis technology is crucial for a cost-efficient and more resource efficient production. The imaging spectrometer uniSPECx.xHSI and uniSPECx.xFOM enable an automated inline analysis for material testing, process monitoring and quality control in the UV-, VIS- and NIR spectral range.

The following examples regarding film thickness analysis provide an insight into specific applications. In case your application is not listed in the examples given below, please contact us for a custom-specific solution based on your specific requirements. Our application development team will provide a solution to your analytical problem utilising LLA’s process technology and analysis software.

2D spectroscopy for quality control of optical coatings

Analysis of functional coatings
Analysis of functional coatings

In optical applications, thin layers/coatings are utilised to customise the reflexion or transmittance of layers and optical components for UV-, VIS- and IR radiation. Typical fields of applications are production of reflective elements (e.g. mirrors) or usage as antireflective coating for optical surfaces (e.g. lenses, objectives, prisms, displays, panels and OLED´s). For these purposes, metals with high absorption- or reflexion capacity as well as dielectric materials with high transparency are utilised.

The imaging NIR hyperspectral cameras uniSPECx.xHSI are ideally suited for the evaluation of optical components. The transmittance or reflectance of components can be determined spatially resolved in the spectral range from 350 nm to 2200 nm. Automatic full-surface material control of spectacle or filter lenses in UV-, VIS or NIR spectral range directly after the dielectric coating process is a common application.

Monitoring of functional coatings for surface finishing

Monitoring of varnish thickness e.g. wind power plant
Monitoring of varnish thickness e.g. wind power plant

For surface protection purpose, various technical components and consumer products are furnished with a final coating.

Modern quality assurance often requires more than inspection of the final product by simply using the visible spectral range. Imaging NIR spectrometer are particularly suitable for monitoring systems supervising the chemical homogeneity of coatings.

In particular, important information about the following characteristics is received:

■ spatial distribution of fillings (e.g. polymer globules, metal particles, special pigments)
■ coating thickness,
■ coating damages.


The figure on the left shows the design of a 50 µm varnish film thickness, coated on a glass fibre reinforced synthetic resin plate (GFK material). The resin plate was planned utilising filling compound prior coating. Such a coating structure is often used in boat building industry to protect the GFK laminate boat hull against moisture. The chemical distribution of the PUR varnish film thickness and the filling compound can be detected by the imaging NIR hyperspectral camera uniSPEC1.9HSI.

The figure on the right shows the resulting total coating thickness on GFK substrate in false colour representation. Inhomogeneous coated parts or overlays of different layer types can be visualised. Analysis functional coatings

Adhesive application in production of material compounds

Adhesive application
Adhesive application

Adhesive technology plays an important role in modern industrial production. Applications range from self-adhesive products (e.g. self-adhesive film, packaging, envelopes, post-it notes) up to complexly formed components made of composite material for the automotive- and aircraft industry.

Insufficient glue application or wrong adhesions can be caused by a large number of possible error sources in the production process. Since the amount of composite material creates the major expense in production, preservation and improvement of the competitiveness must be improved by efficiency of material usage.


The imaging NIR spectrometer uniSPEC1.9HSI and uniSPEC2.2HSI are cost-effective and ideally suited for inline detection in real time. Presence and absence as well as thickness of applied adhesive layer on component surfaces can be determined for quality control purposes.
Determination of adhesive application quantity of raw paper
Figure: Mass determination of applied glue on a paper post-it note for three adhesive traces

Layer thickness and curing degree of UV-hardening layers

Installation of a NIR probe & sheet detection sensor in a slot in the window of a sheet-fed offset printing machine
Installation of a NIR probe & sheet detection sensor in a slot in the window of a sheet-fed offset printing machine

During drying and curing processes of UV-interlacing colorants and coatings, the reactivity of single components, the intensity of UV radiation, track speed and other process parameters affect the curing degree of a final product. Unnoticed changes of these process conditions can lead to severe quality defects and production of reject.

Insufficient UV curing of printing ink on food packaging can lead to a severe health risk. Non-cured printing ink components can be transferred to the backside of the substrate by either set-off in the delivery pile or by a roll in the printing machine. In addition, components exhibiting a low molecular weight are able to migrate from the printed food packaging into the food itself in case the UV curing is not sufficient.

A turnover inline-control can register changes in an early stage and regulate relevant process parameters accordingly.

Advantages of NIR spectroscopic method:
■ quantitative analysis of conversion rate or curing process respectively
■ applicable for coating systems drying by radical curing
■ applicable for different coating substrates such as foils, paper, cardboard, plastics
■ applicable for coating thickness of a few micrometers
■ high speed measurement enables inline analysis directly in industrial print- and coating process
■ rapid transfer of analysis result to process control


Monitoring of the conversion rate in relation to printing speed for printing color Uvalux yellow. Data obtained by NIR inline analysis is highlighted in black, data obtained by reference method is highlighted in grey for comparison purpose.
Turnover inline-control of coatings

Functional evaluation of industrial textiles

Quality control of textiles
Quality control of textiles

The surfaces of textiles can be selectively changed by several physical and chemical processes to optimise their material characteristics and practical value for the desired purpose. In addition to finishing and coating, these process steps include lamination as well. A practicable process monitoring was not available for these applications until now.

The imaging NIR spectrometers uniSPEC1.9HSI and uniSPEC2.2HSI including the customised textile application offer a powerful and cost-efficient solution for the online cloth inspection.

The following material characteristics can be monitored:
■ Distinction of chemically different materials (e.g. textile with synthetic or natural fibres; textiles consisting of synthetic fibre / adhesive / natural fibre),
■ Quality evaluation of surface pretreatment process as preparation for successive production steps,
■ Humidity of textiles prior finishing processes,
■ Uniformity and thickness of adhesive layer between laminated materials,
■ Identification of adhesive residues on texile originated from dripping adhesive during and
■ Detection of lamination defects

In cooperation with the IOM Leipzig, LLA's NIR technologies were compared to analyse different coatings. More information can be found here.


Common RGB color linescan cameras detect only the surface of textile foal laminates. Contaminants below the surface are not detected.

The imaging NIR hyperspectral camera uniSPEC1.9HSI exhibits a higher depth of penetration into the laminate. In combination with chemometrical methods, an extensive analysis of the underlying laminate layers is achieved.

Foreign body detection of textile laminates

The figure on the left side shows the RGB color image of a black textile - foam laminate. The screened surface appears impeccable.

Due to the larger depth of penetration of the NIR radiation, the NIR hyperspectral imaging camera uniSPEC1.9HSI can analyse the chemical composition of distinct layers. The figure on the right side shows the NIR identification result as false colour image. The accidentally inserted adhesive tape (red) is clearly distinguishable from overlying the black textile (green).

Color image of textile-foam-laminate including accidentally inserted adhesive strip NIR false color image of the inserted adhesive strip (red) over layered by the black textile (green)

Coating thickness determination of adhesives

The colour image on the left side shows the foam side of a laminated tubular fabric. The thin layer of the transparent adhesive is not recognisable.

The NIR hyperspectral imaging camera uniSPEC1.9HSI is able to detect thickness variations in adhesive layers. In the figure on the left side, the result of such an analysis is shown as NIR false colour image. Inhomogeneous adhesive application is shown as diagonal stripe pattern (red) on the foam substrate (green).

Schichtdickenmessung Rundstrickware mit Schaum und Klebstoffauftrag Schichtdickenmessung Rundstrickware mit Schaum und Klebstoffauftrag

Functional determination of prepregs

Online-process monitoring system
Online-process monitoring system

Prepregs (i.e. semi-finished parts impregnated with reactive resins) are used for the production of fibre-reinforced composite materials. They are cured at slightly elevated pressure and temperature and therefore ideal for mechanical processing in automated production processes. Prepregs are primarily used in aircraft industry. Especially glass fibre reinforced plastic (GRP) parts or carbon-fibre reinforced plastic (CFRP) parts are utilised.

In prepreg production, planar reinforcing fabric is impregnated with highly viscuous and reactive resin mixture. At slightly elevated temperature, the interlinking reaction is initiated. After a short period, the reaction is interrupted by cooling down.

The imaging NIR spectrometers uniSPEC1.9HSI and uniSPEC2.2HSI including the customised prepreg application offer a powerful and cost-efficient solution for the online quality control of prepregs. Both spectrometer can determine resin and fabric composition, solvent concentration as well as viscosity and hardness of prepregs.


Analysis results regarding resin and volatile binder agent for selected sample
Analysis results regarding resin and volatile binder agent for selected sample