Colour measurement in the paper industry

Variants of the color measurement paper machine

There are several ways to control the color production of paper. Here you get an overview and the advantages
the different methods:


Inline color measurement before reel up

The final product is measured before reeling. The measured values have a very good correlation to the laboratory values.
Deviations from the specifications can be automatically controlled by a Closed Loop Color Control (CLCC). This color measurement quickly pays for itself through short transition times, less waste and lower dyeing costs.

For contactless color measurement operation on the machine. The opacity of paper and board in color the stack and the opacity of paper and board are measured; for white grades also the optical brightener. The finished paper is measured directly before the reel. This ensures a very good correlation to the laboratory measurement results. The device works in a rough environment. Ambient light, web speed and web flutter have no influence on the measurement results.

The colorimeter is mounted directly in front of the reel. The ERX50 is used to measure coloured paper (i.e. without opticaloptical brightener) and white paper and cardboard. Here the is measured optical brightener separately. If there is no paper on the machine, the customized measuring frame (EFX) swivels the measuring device out of the web. As soon as the paper is listed again, the measuring device automatically swivels into measuring position and starts the measurement.

Quality Control

The quality control software (ES15Win and ES18Win) controls the measuring device and displays the measured values clearly on the screen. Colored bars indicate the deviation of the produced paper from the target value. The machine operator can see at a glance whether his paper is too light or too dark, too red or too green, too yellow or too blue.

Closed Loop Color Control

The color control software (ES19Win) controls up to 3 ink pumps plus one brightener pump. This ensures a very constant quality even with fluctuations in raw materials. Even colour transitions can be run in automatic mode. This 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 the color measurementcontrol, another day is needed for the control. A machine stop of only one hour is necessary. A connection to the control system is also possible.


color measurement between press and dryer section

Measurements after the press section give optimum results for decor paper. The wet paper looks very similar to the laminated samples from the laboratory. The machine operator can quickly detect changes in the process and take countermeasures if necessary.

The measurement between the press and dryer sections provides a very good correlation to the laboratory measurements. This is especially important for the production of decor paper, as very tight tolerances must be maintained here.

Measuring in the wet helps to significantly reduce the transition times between productions, as the machine operator has a measurement result immediately after a strip has been applied. He can therefore see immediately whether the correction is going in the right direction. This color can then be continuously monitored during production, even the smallest color deviations are immediately displayed.

The ERX50 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 measurement without damaging the paper.

The ES15Win and ES18Win software controls the measuring device and clearly displays the measurement results. Colored bars indicate the deviation of the produced paper from the nominal value. The machine operator can see at a glance whether his paper is too light or too dark, too red or too green, too yellow or too blue.

The installation of the system normally takes one day. A machine stop of only one hour is necessary. A connection to the control system is also possible.


Inline color measurement in the liquid pulp

By measuring in the pulp, you get the first information about the colorpulp even before it comes onto the machine. Any change in the raw material or in the dyeing process can be monitored continuously. Any deviation from the specification is detected immediately and can be stopped immediately by the machine operator.

In paper production, the paper pulp is the first place where information about which can be color collected. Although the measurement results do not correspond to the results for the finished paper, a colour shift in the pulp is already an indication that the one color in the wet paper will differ. In this measuring phase, the optical optical brightener control can also be controlled.

pulp

The one color measurement in the fabric is used for:

  • Early detection of disorders
  • Control of dye addition
  • Mixture of 2 types of raw materials (e.g. dark and light) at a constant level
  • Monitoring the addition of recovered paper without significantly changing that color of the entire pulp
  • Testing the homogeneity of the paper pulp after dye addition

The ERX40 system for whiteness measurement is mounted in a stainless steel housing:

  • It measures directly in the thick matter (concentration: 3 % to 5 %) through a bypass system.
  • EG 50 R: The thin substance (approx. 1 % concentration) flows through a bypass to the measuring instrument. The measuring instrument then measures that color of water and fibres, and calculates what it will be like color in wet paper. Small changes in concentration have no effect on the measurement.
  • The ER40WF is a "lite" system that can only measure white levels.

ESWin

The ES15Win and ES18Win software controls the measuring instrument and displays the data. These measurements can be connected to a control system. Colored bars indicate the deviation of the produced paper from the target value. The machine operator can see at a glance whether his paper is too light or too dark, too red or too green, too yellow or too blue, as well as the whiteness with and without UV excitation (ERX50P only).

Trend measurement

The installation of the system normally takes one day. A connection to the control system is also possible.

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

The first laboratory measuring instrument with 45°:0° geometry and adjustable UV radiation for reliable determination of optical brighteners. This ensures comparable measurement results, especially for the manufacturers of printing papers: inline on the machine, in the laboratory and at the customer's premises in the printing plant are measured with the same measuring geometry. The measurement results are thus comparable. So printers and paper manufacturers speak the same "color language".

Determination of the optical brightener with and without UV radiation

The ERX30 is the first spectrophotometer with 45°:0° geometry and adjustable UV component. This allows an exact measurement of the basic whiteness and the optical brightener in the paper. Even critical colors and demanding applications can be measured accurately due to the excellent spectral resolution of 1 nm.

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 inlinecolor measurement. Printers and paper manufacturers now speak the same "colour language".


Advantages of Inline Color Control

An automatic Closed Loop Color Control one ensures constant quality. Even colour transitions can be run automatically. For the machine operators this means:

  • 100% control during the production process
  • Shorter transition periods
  • Avoidance of rejects
  • Saving of dyes or optical optical brightener

Advantages of the Xrite Inline System:

  • Xrite supplies a complete turnkey system
  • Installation of a color control system takes 3 days
  • A machine downtime of typically one hour is necessary
  • Extremely low maintenance costs

How to install the system

This video shows the complete installation of an inline measuring system on a production machine