June_AMP_Digital

29 / 66

ADVANCED MATERIALS & PROCESSES • JUNE 2014 29
completely eliminated. Taking all measurements from the
exact same point on the web prevents measurement errors
caused by nonflat base substrates, sheet flutter, and ambi-
ent light change.
Because full spectrum IR web gauging sensors lack the
moving parts of a filter wheel, they have significantly fewer
possible failure points. This makes themmore reliable and
less likely to require maintenance. They can also be easily
recalibrated for new material measurements via software
and require no hardware or filter changes.
Chemometrics software like that offered by Thermo
Scientific, Waltham, Mass., called EZCal, offers easy recal-
ibration for maximum product measurement flexibility.
Using a broad set of mathematical manipulation tech-
niques, this software can analyze complex sets of overlap-
ping spectra to provide accurate measurements of mono-
and multi-component webs. It also eliminates the effects
of printing and additives, which can cause spinning filter
wheel sensors to provide inaccurate measurements.
In a full spectrum measurement, web component
thickness is determined by measuring total absorption
across the material’s unique fingerprint. Figure 2 shows an
example of the absorption pattern for a given material,
with thicknesses varying from 5-25 µm. Typically, graphs
like this are only seen in an FSIR instrument’s output in di-
agnostic mode. Most of the time, the chemometrics soft-
ware performs thickness analysis on its own and provides
an easy-to-read figure for each web component. Accurate
multi-component analysis offered by full spectrum IR web
gauging instruments makes them well suited for both sim-
ple and complex web process monitoring applications, in-
cluding cast film, biax film, extrusion coating and
laminating, blown films, and nonwovens.
A typical multilayer blown filmmay contain skin layers
of polyethylene (PE), a barrier layer of ethylene vinyl alco-
hol (EVOH) or Surlyn, and tie layers. For this application,
a full spectrum IR sensor analyzes the spectra of the mul-
tilayer structure and is able to separate the thicknesses of
each material across the entire web. Full spectrum IR sen-
sors also excel in multilayer extrusion coating and lamina-
tion applications, as they are capable of accurately
measuring thin layers of polyethylene terephthalate (PET),
PE, and polyacetylene (PA) simultaneously, for example.
Applications
Production of nonwovens, including spunbond, spun-
lace, spunlaid, and airlaid webs, is a good application for
full spectrum IR web gauging technology. Applicable ma-
terials measurements for analysis of nonwovens include
polyethylene (PE) or polypropylene (PP) fibers, latex
binders, superabsorbent polymers/materials, and total
basis weight. Full spectrum IR instruments can also contin-
uously monitor the moisture content of nonwoven materi-
als—important for nonwovens with personal hygiene,
medical, and geotextile purposes.
In addition to a transmission mode that measures web
absorption of the NIR spectrum, full spectrum IR sensors
such as Thermo Scientific’s PROSIS can be configured to
measure a web in reflection mode. This configuration ex-
cels at measuring coating thickness on metal sheets or
other opaque substrates. Typical measurements for coated
metal sheets include top and bottom paint thickness, oil
film thickness, and primer or lacquer layers. Reflection
measurements are also useful for tandem extrusion coating
and aseptic packaging production.
Another important application of full spectrum IR sen-
sor technology is lithium ion battery (LIB) production.
Complex multilayer separator films, which separate the
cathode and anode in all LIBs and facilitate the flow of
charged ions, are critical to battery efficiency and lifetime.
Full spectrum IR instruments can help improve thickness
consistency and ensure a more homogenous distribution
of pores in the separation film to maximize performance.
Essentially any web production industry could benefit from
the versatility, ease of use, increased precision, and reduced
maintenance costs of full spectrum IR web gauging instru-
ments. In certain cases, nuclear sensors can also be
switched to full spectrum IR sensors, to reduce regulatory
burdens. Through their full spectral response measure-
ment capabilities and advanced chemometrics analysis
technique, full spectrum IR thickness sensors enable pro-
duction of more on-spec products and reduce material
waste without compromising profitability.
For more information: Tam Nguyen is product marketing
manager – web gauging, Thermo Fisher Scientific Inc.,
81 Wyman St., Waltham, MA 02451, 978.663.2300,
, .
Fig. 2 — Absorbance levels for various material thicknesses.
Fig. 3 — PROSIS IR process
analysis thickness sensor.
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Absorbance
Infrared absorbance vs. Wavelength
Thickness = 25 µm
Thickness = 5 µm
Wavelength (µm)