Colour measurement in the paper industry

How does the measurement and control of color paper in production work?

There are several places where a measurement is useful. The earliest possible point in time is that incolor measurement the still liquid substance. A measurement between the press and dryer sections gives a good correlation with the laboratory for the decor papers. However, in most cases the one color measurement at the end of the machine is installed shortly before the reel, where the finished paper is measured as in the laboratory. This measurement location is also used for automatic Closed Loop Color Controlmeasurement.

color measurement before rewinding
color measurement between press and dryer section
color measurement in liquid pulp

Inline color measurement before rewinding

The finished paper is measured before winding. The measured values have a very good correlation to the laboratory values. Deviations from the target values can be automatically corrected by a Closed Loop Color Control. Due to fast start-up times and short transition times, there is less waste and due to the lower dyeing costs, the colour measurement pays for itself quickly.

The measurement is contactless at the machine. A background arm can be applied to the web for stabilization or opacity measurement. The measuring device as well as the background automatically swivels off in case of a paper break to facilitate the threading of the new web. As soon as the paper is stable again, the measuring device automatically swings into measuring position and starts measuring.

By means of the opacity measurement, the stack values are displayed in the software. Thus, there is an optimal correlation to the laboratory, where the paper is also measured in the stack.

The device operates in a harsh environment. Ambient light, vibrations, web speed and web flutter have no influence on the measurement results.

The ERX50 is designed to measure colored paper, white paper (with optical brightener and without nuances) and cardboard. Here, it is measured optical brightener separately. Typical applications are testliner, colored tissue, fine papers (colored or white), cardboard, decor papersecurity papers, thin printing papers, etc.

Advantages at a glance

ROI only color measurement

< 9 months

ROI with Closed Loop Color Control

< 6 months

Color correlation to the laboratory

<0,5 dE*

Automation with Closed Loop Color Control

95%

Our recommendation

color measurement systematically

Advantages of Inline Color Control

Advantages of the X-Rite Inline System

For decor paper: color measurement between press and dryer sections

For the production of decor paper, the color of the pressed paper must match exactly. The refractive index of the resin or varnish changes the colour impression of the paper. To adjust this on the paper machine, measurements are taken between the press and dryer sections, since the water in the paper has a similar refractive index to that of the pressed paper. Thus, a good correlation between the color measurement on the machine and in the laboratory is achieved.

With the inline color measurement system, the machine operator can quickly detect changes in the process and take countermeasures if necessary. A measurement result is available immediately after the strip has been applied. The machine operator can immediately see whether the correction made also produces the expected result. If necessary, the strip can be redyed without having to make another lamination. Thus, the transition times are considerably shortened. This color is then continuously monitored during production and even the smallest colour deviations are immediately displayed. The narrow tolerances can thus be reliably maintained.

The ERX50C (with circumverential illumination) is installed on a customized measuring frame (EFX) directly after the press section. The measuring distance of 10 mm to the paper web guarantees a reliable measurementwithoutdamaging the paper.

Advantages at a glance

ROI

< 9 months

Correlation to laboratory grouting

85%

Automation

70%

Our recommendation

erx50

Inline color measurement in the liquid paper stock

The color measurement in the pulp provides information even before the pulp is on the machine. Although the measured color does not correspond to that of the finished paper, a colour change in the pulp will automatically lead to a colour change in the finished paper. It therefore serves as an "early warning system".

Use of the measurement in the pulp

  • for monitoring whether the one ofcolor the current vat also corresponds to the last one
  • for the defined mixing of two material flows (e.g. waste paper with "clean" material)
  • to determine the influence of the addition of scrap
  • for displaying the dyeing results during manual dyeing in the vat

(at this point the optical optical brightener one can also be reliably detected)

Advantages at a glance

ROI

< 9 months

Reduction of the changeover times to

80%

Detection of colour variations

95%

You want a consistent color result for your paper production? 

We will be happy to advise you!

Give us a call

Consistent quality through Closed Loop Color Control

The color control software (ES19Win) controls up to 3 ink pumps plus one brightener pump. Additional pumps can be added manually. This ensures a very constant quality even with raw material fluctuations. Even the machine start-up and colour transitions are run in automatic mode. This not only saves time but also relieves the machine operator during this critical phase. He can take care of all the other settings.

The installation of the system normally takes two days. For that color measurement one more day is needed for the regulation. This requires a machine stop of only one hour. A connection to the control system is also possible.

eswin clcc software

ERX30: color measurement in the laboratory with 45°:0° geometry (CIE standard)

The ERX30 is the first laboratory measuring instrument with 45°:0° geometry and adjustable UV radiation for reliable determination of optical brighteners and opacity

The wide spectrum from 330 nm to 730 nm provides information not only in the visible range but also in the UV range. Due to the 45°:0° geometry the measurements correlate excellently with the visual impression. This geometry is also a standard in the printing industry and in inline color measurementprinting. Printers and paper manufacturers now speak the same "colour language".

This ensures comparable measurement results, especially for manufacturers of printing papers: Both Inline on the machine, as well as in the laboratoryThe same measuring geometry is used for measurements at the customer's site and at the printing plant.

color measurement at the lab

Inline color measurement

➡ supports coloring when starting up a new color
➡ Color transitions run automatically: saves approx. 50% of the time
➡ helps to keep
the color transitions constant color on the paper machine ➡ gives machine operators security during production
➡ no longer needs to estimate which color and how much must
be changed ➡ creates color consistency even with different production lots
➡ 100% quality assurance of the entire production

How is the inline colour measuring system installed?

FAQ's

In principle, a measurement at the machine should be contactless, preferably with a standardized measuring geometry. Ball measurement geometries (d:0°) as used in the laboratory (e.g. Elrepho) cannot be used on the machine, as they have to touch the sample. The paper would not only get quirks, but the "integrating sphere" would gather dust and give unusable results.

Therefore only the 45°:0° geometry is suitable. Here the illumination of the sample is done at 45° and the measurement at 0° (i.e. vertically from above). The distance between the ERX50 and the paper web is 10 mm. A special optical system ensures that normal web flutter has no influence on the measurement results.

To guide the paper web, the measuring device and, if present, the background is swung away from the web. This ensures problem-free threading. As soon as the web is spread and stable, the measuring system swings in and delivers the first measured values.

In the paper industry d:0° devices are standard. Often you can find Elrepho devices in the laboratories which correspond to this standard. The inline measurement can be well adapted to these devices.

However, sometimes it would be advantageous to use 45°:0° instruments in the laboratory. All inline colorimeters have a 45°:0° geometry, even the printers use 45°:0° exclusively. If the paper manufacturer's laboratory now uses a ball geometry for measuring, conflicts are pre-programmed. Both geometries deliver different values.

The sphere geometry measures the pure body colour, independent of the surface, whereas the 45°:0° geometry measures similar to the human eye. The laboratory measurements with the 45°:0° geometry therefore not only fit better to the inline measurements and the measurements of our customers, they also correlate much better to the visual impression.

The system is called turnkey system supplied by X-Rite. For this purpose, it is necessary to define the installation situation in the paper machine and determine it together with the customer's machine operators and technicians. The entire scope of supply must also be discussed. Is it only a "simple" color measurement one on the machine or should the system be capable of more. The following options are available:

  • color measurement on the front and back
  • Closed Loop Color Control for automatic control of the dyes / pigments used
  • Measurement in the laboratory
  • Operation from the control station
  • Connection to a process control system

Getting to the installation Service technician from X-Rite and install the system into the machine within a few days. This requires a Machine downtime of only one hour required. Of course not only the Operating personnel trained in several shifts, but also the Maintenance staff and Administrators.