Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a method of measuring the
~oating rate or amount of material applied as one or several
surface coatings on a base material.
It is known in the prior art, from Finnish Patent No.
53757 in ~he name of Pertti Puumalainen, published March 13,
1978, to measure the base weights of a CaCO3 layer applied as
a pre-coating on cardboard or paper and of a caolin-containing
surface coating by employing X-ray radiation which excites the
characteristic secon~ary X-ray radiation of the Ca in the pre-
coat. The intensit~ of this radiation is measured from above
and below the cardboard by means of detectors. The absorption
of the primary radiation coming from the source of radiation in
the various coatings is measured. From the mutually independent
results of measurement, the base weights of coatings can be cal-
culated by solving three equations with three unknown variables.
It is also known in the art to measure the coating rate
in one coating on paper by utilizing the characteristic secon-
dary X-ray radiation excited by primary X-ray radiation in a
marker substance added to the coating material.
The method described in the above-mentioned Finnish
Patent No. 53757 suffers from the drawback that the work involved
in tlle calibration of a coating rate meter capable of measuring
in on-line conditions two different coating layers is cumber-
some. In order to be operative, the method re~uires several
difficult to determine constants to be measured before the e~ua~
tions forming the basis of the method can be solved and the dif-
ferent base weights determined. The method is moreover sensi-
tive to variations in the geometry of measurement, since no pri- ;
mary radiation must be allowed to strike the fluorescence detec-
tor on the side opposite from the source.
The method above has the drawback that tlle coating
rate of only one coating layer can be measured, and only when
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coating layer gives rise to a measura~le amount of secondary
X-ray radiation.
An object of the present invention is to avoid the
drawbacks mentioned above and to provide a method, having simple
operating characteristics and particularly suitable for on-line
measurements, for the measuring of the coating rate and amount
of material applied as one or several coatinss on a base layer.
The invention is particularly suitable for use in connection
with the manufacture of paper, cardboard or like material.
Accordingly, the present invention provides an improve-
ment in a method of determining the quantities of material in a
first coating layer applied to cardboard or equivalent base ma-
terial as well as in a second coating layer applied to said first
coating layer, said method comprising the steps of subjecting
said first coating layer to a primary X-ray radiation derived
from an outside source and travelled via said second coating la-
yer, so as to excite a characteristic fluorescence radiation in
said first coating layer, and measuring the intensity of said
fluorescence radiation by means of a detector placed above said
second coating layer, whereby the determination is based on the
absorption of the primary X-ray radiation and the fluorescence
radiation while travelling through said second coating layer,
the improvement comprising that, in addition to exciting the
fluorescence radiation of the first coating layer, the primary
X-ray radiation is used to excite a characteristic fluorescence
radiation in the second coating layer, which is measured by means
of a detector and used as the basis for determination of the
quantity of material in the second coating layer, while the mea-
surement of the fluorescence radiation of the first coating layer
is performed for the determination of the quantity of material
in the first coating layer, with the aid of the quantity of ma-
terial in the second coating layer as determined.
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The invention will now be described in more detail,
by way of example only, with reference to the accompanying
drawings, in which:-
Fig. l shows diagrammatically an arrangement for put-
ting into practice the method according to the invention, with
a supporting web and coatings therein being shown in section;
Fig. 2 is a view similar to Fig. 1 showing an alter-
native arrangement; and
Fig. 3 is a view similar to Fig. l showing a further
arrangement.
In Fig. l the cardboard web constitutes a base mater-
ial l and has formed therèon a precoating layer 2, which may,
for instance~ consist of CaCO3, and on the precoating layer 2 a
surface coating 3, for instance, of caolin. When subsequent to
precoating the combination 1,2 is irradiated ~ith a radiation
source 4, which may for instance be a 55-Fe radio isotope -~
source, the Ca atoms in the precoating 2 emit their own charac-
teristic secondary X-ray radiation, or fluorescence radiation,
the intensity of which is proportional to the amount of material
present, or of Ca in this case. When the intensity of Ca fluore-
scence radiation arriving at the detector is known as a function
of the amount of CaC03 present, the amount of CaCO3 is
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calculable from the intensity of the pulses delivered by the
detector 5.
The web 1 moves forward to another coating unit, where
- the surface coating 3 is applied to the web 1. Hereafter, the
combination is irradiated once again with radiation ~rom the
radiation source 6. This causes the Ca atoms to emit fluore-
scence radiation which passes through the surface coating layer
3 and is measured by the aetector 7 located above the surface
coating layer 3. Part of the primary and fluorescence radia-
tions is abs~rbed, according to a certain experimentally deter-
minable function, in the surface coating, and the number of
pulses delivered by the detector 7 decreases. In evaluating
the decrease in the number of pulses, one takes into account
the ratio of efficiencies of measurement of the two pick-ups,
which can be determined by running a web having only a base
coating through the apparatus. From the pulse reduction found,
the surface coating rate can be calculated.
If the base material contains, in significant amounts,
fillers which are able to emit a significant amount of measur-
able secondary X-ray ~adiation, or if the base material 1 is
coated on the other side as well with a coatiny capable of emit- -
ting measurable secondary radiation, these effects may be ac-
counted for by irradiating the web with a radiation source 8
prior to the coating step and measuring the secondarv X-ray
radiation by means of the detector 9. I~hen this is done, vari-
ations of the base material 1 cause no possible sources of er-
ror in the measurment of coating rates. The efficiency of
measurement of the pick-up monitoring the raw cardboard must,
however, be taken into account.
In the arrangement shown in Fig. 2, a CaCO3 coating is
applied to the base material 1 and thereupon a coating 3 which
contains Tio2 is applied. It is possible, by irradiating with
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the source 5 the combination of courses 2 and 3, to measure the
coating rates as follows: The quantitY of coatina layer 3 is a -
function of the ~uantity of TiO2 contained in the coatin~ layer
3. If the amount of X-ray radiation with energy 4.5 keV emitted
by TiO2 is measured, this enables the quantity of the surface
coating 3 to be calculated. The primary radiation from the
source 5 also excites the Ca in the base coating 2, which emits
secondary radiation with energy 3.7 keV. Knowing the absorptions
of the primary and secondary radiations in the surface coating
3, of which the quantity is already known, one can calculate
which is the quantity of CaCO3 able to give rise from under this
surface coating 3 to the measured secondary radiation. If
required, the effect of the raw cardboard may be eliminated by
the same procedure as was applied in the case of Fig. 1.
In Fig. 3, the base material 1 contains a substance
capable of emitting secondary radiation, either as filler, as
background coating, or as a material with which the base ma-
terial has been impregnated. When the base material is irradia- ~
ted by the source 3 and the secondary radiation is measured with ;
the detector 4, information is gained concerning the secondar~
radiation emitted by the base material.
As the web moves forward to the coating unit, in which
the surface coating 2 is applied on the web, the combination is
irradiated from the source 5. This causes the atoms in the
web to emit fluorescence radiation under the influence of the
primary radiation that has penetrated through the surface coat-
ing 2. The number of pulses received by the detector 6 then de-
creases as part of the primary and fluorescence radiations is
absorbed in the surface coating in accordance with a given ex-
perimentally determinable function. Qne then calculates thecoating rate on the basis of the pulse reduction, taking into
account the ratio of the efficiencies of measurement of the two
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pick-ups.
One advantage of the descri~ed methods is that the
sources of error arisiny from the variations of the uncoated
base material are eliminated therein, thus achieving an e~ceed-
ingly high accuracy of measurement. In addition, the need to
repeat the most cumbersome steps in the calibration procedure
is minimized because the ratios of the efficiencies of measure-
ment of the pick-ups and the isotope activities may be left to
the computer to resolve, the former in fact point by point
across the web. The accuracy requirements of the traversing
beams may be quite appreciably reduced. The two or three con-
stants most cumbersome to determine are mainly dependent on the
chemical composition of the coating materials and therefore
the need to be redetermined then is quite minimal.
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