WO1987007364A1

WO1987007364A1 - Method for measuring of the thickness profile of plastic films

Info

Publication number: WO1987007364A1
Application number: PCT/FI1986/000056
Authority: WO
Inventors: Pertti Puumalainen
Original assignee: Puumalaisen Tutkimuslaitos Oy
Priority date: 1984-12-04
Filing date: 1986-05-27
Publication date: 1987-12-03
Also published as: SE8602424L; FI73319B; DE3618518A1; FI73319C; FI844785A0; SE453691B; FI844785L; SE8602424D0

Abstract

The measuring of the thickness profiles of plastic films is by applying the presently known methods difficult and the measuring results are not dependable. According to the invention the thickness measuring of the plastic films (1) is performed by using infrared transmission in such a manner, that on the one side of the plastic film is placed a resistance wire (2) reaching over the plastic film, the intensity of the infrared radiation emitted by which is directed by means of the turnable reflecting device (3) to the analyzer (4) placed on the other side of the plastic track. The method is suitable for the on-line thickness profile determination of plastic film manufactured both by the planar as by the fan-tail die extrusion method.

Description

METHOD FOR MEASURING OF THE THICKNESS PROFILE OF PLASTIC FILMS

*" The object for the invention is a method for measuring of

^_f. the thickness profiles of plastic films.

Plastic films are most commonly produced by extrusion mould- 5 ing method either by extruding fluid plastic mass through a straight nozzle into a planar film or through a circular nozzle, whereat the film becomes tubelike, and by adding the pressure within the tube through blowing the product is stretched in the width direction. Multilayer plastics 10 are produced by melting on the one or on the both surfaces a new plastic layer, which can be of different plastic qual¬ ity. But also other materials, such as for instance paper can be surface coated by the extrusion method.

15 It is endeavoured to measure and to follow the thicknesses and the thickness profiles with care during the manufactur¬ ing process. Most commonly the damping of the infrared or beta emission when _*the radiation is passing through the plastic film is used in measurings. To a certain extent

20 the infrared reflection is taken use of, whereat the part of the infrared light reflected back from the back surface of the plastic film is measured.

The thickness profile is measured in planar machines by 25 moving as well the transmitter as the receiver parts trans¬ versely in regard of the plastic film at the same phase one above the plastic film and the other one below. Such contrivances are complicated and expensive and it is not Φ possible to get with the help of them accurate information

-_Ϊ 30 about the thickness profile of the plastic film quickly.

"?

In the extrusion moulding method the measuring of the pro¬ file is difficult and often the measuring is performed based on the sense of sight by observing the blurring of the plas- tic film when cooling down. The peripherical profile of the plastic film can also be measured by rolling the mea¬ suring device around the congealed plastic film tube. These measurings are very inaccurate and difficult to perform in a dependable way.

The aim of the invention is to bring forth a method for measuring of the thickness profile of plastic films, which eliminates the disadvantages of the early known methods. In particular is the aim of the invention to bring about a method, with which the thickness profile can be measured accurately and in a dependable way during the manufacturing process. In addition the aim of the invention is to bring forward a method, which is suited for quick measu- ring of the transverse profile of plastic films as well in the planar as in the fan-tail die extrusion moulding methods.

The aim of the invention is reached with a method, which is characterized in, what is .presented in the claims.

The method in accordance with the invention is explaned in detail by referring to the attached drawing, in which figure 1 presents ane set-up for application of the method in accordance with the invention in connection with the planar extrusion moulding method, partly in cross-profile seen from the side, and figure 2 presents an another set-up for application of the method in accordance with the invention in connection with the fan-tail die extrusion moulding method, partly in crossprofile seen from the side.

In the set-ups presented in the figures 1 and 2 as the infrared source is used an on the one side of the plastic film 1 placed resistance wire, such as a glowing filament 2, the by which emitted infrared light of a suitable wave¬ length is directed by means of a turnable or rotatable re¬ flecting device, for instance a mirror 3, to the analyzer 4. The wavelengths to be analyzed can be one or more. For instance with two wavelengths a relative method of measuring is reached, when the differences in the intensity of the glowing filament do not influence the measuring re¬ sults .

In the in figure 1 presented application the glowing fila¬ ment 2 is placed on the one side of the plastic film 1 trans¬ verse in regard to the film. The glowing filament is fasten- ed and kept straight with a tensioning device, for instance with the help of a spring. On the other side of the plas¬ tic film the mirror 3 is placed and close to the mirror the analyzer 4. The mirror is arranged turnable around its axis in accordance with the arrow and to direct the infrared radiation coming through from the different spots of the plastic film to the analyzer. The measuring is started from the one edge of the plastic film and by turning the mirror the whole transverse profile of the plastic film is measur¬ ed. In the analyzer the infrared light is divided by means of a semi-permeable mirror 8 to two detectors 9, 10, in front of which are interference filters. The one of the de¬ tectors measures the measuring value from the region of the specific peak of the plastic and the other one next to the peak a reference value. When the mirror has been slight¬ ly turned, new values are measured from the plastic film beside the previous spot and in such a manner is proceeded over the whole plastic film. The thickness profile is com¬ posed by comparing the absorption with values given by known calibration samples and by taking into account the trigono¬ metrical correction in measurings taking place from differ- ent angles.

In the application presented in figure 2 the glowing fila¬ ment/is placed to go round the already cooled-off plastic film 6 by supporting the glowing filament into a circular orbit formed ring 11 with the help of the springs 12. In the middle of the extrusion moulding nozzle 13 is in this application placed the analyzer 4 and on top of the analyzer axially the mirror 3. The mirror is arranged to be rotated with the help of the motor 14 and arranged to direct the infrared radiation coming through the plastic film on dif¬ ferent spots into the analyzer. The analyzing takes place in the same manner as presented above in the application in accordance with- figure 1. The measuring of the profile can be started for instance from the dark joint spot of the glowing filament returning again after the circle measuring to the same spot.

In the applications presented in the figures 1 and 2 a single glowing filament has been used, but in order to in¬ crease the intensity in some applications a strip formed glowing filament or several glowing filaments placed beside each other can be used.

In one application of the invention the resistance wire and the analyzer are placed on the same side of the plastic film. Hereat the from the plastic film or from the behind it located mirror reflected infrared radiation is directed with the help of the reflecting device 3 into the analyzer.

Other applications of the method is the use of the method for multilayer materials, in which for instance from a planar extrusion press on the material web, which can be plastic, paper or similar material, a plastic film is laid. Hereat the resistance wire is put behind the oncoming plas¬ tic film near to the place, where the webs come together and the plastic surface coating profiles can be measured directly.

One remarkable application is the separation of plastic from in a planar direction transported sequence of bodies quickly and accurately. Herewith can for instance from wood chips or paper the plastic pieces be separated. For instance wood chip pieces on their way to the pulping pro¬ cess are let drop in front of the resistance wire or the falling chips form instead of the plastic film 1 in figure 1 a planar formed flow of bodies, when with a sufficiently quick analysis can be read, whether there is plastic along in the material or not, by setting in for analyzing wave- lenths at the above mentioned specific peak (e.g.λ 5* 3.5 am) of the plastics and beside it (e.g.λ 3.0 μ ) . The in this way wood chips observed containing plastic can be taken separately and used in a wished way.

The invention is not limited to the presented applications, but it can vary within the limits of the patent claims.

Claims

PATENT CLAIMS

1. Method for measuring of thickness profiles of plastic films, c h a r a c t e r i z e d in, that on the one side of the material to be examined (1), favourably a plastic film, is placed an over the plastic film reaching resistance

5 wire (2) to be heated, the infrared radiation emitted of which is measured by directing the infrared radiation, which in regard of the plastic track transversely has in several spots passed through it, with a turnable reflecting device (3) to the analyzer (4) placed on the other side of the plas- 10. tic track, whereby the thickness profile of the plastic web is calculated by comparing the values received with results achieved with the help of known samples.

2. Method in accordance with the patent claim 1, c h a r - 15 a c t e r i z e d in, that when manufacturing the plastic tubelike by extrusion moulding the resistance wire (5) is wound around the plastic film (6), the rotatable reflecting device (3) is placed axially within the tube formed by the plastic film, the analyzer (4) is placed close to the reflect

20 ing device and by rotating the reflecting device within the plastic tube the infrared radiation emitted from the resist¬ ance wire, wtϊich has passed through the plastic film on dif¬ ferent spots, is directed into the analyzer, whereat the rotative profile of the plastic film is calculated.

25

3. Method in accordance with the patent claim 2, c h a r ¬ a c t e r i z e d in, that the analyzer (4) is placed insid the plastic tube axially in regard of the plastic tube.

30 4. Method in accordance with some of the patent claims 1-3, c h a r a c t e r i z e d in, that in the analyzer the in¬ frared radiation directed from the resistance wire is divide by means of a semi-permeable mirror into two parts, which ar measured with two detectors equipped with wavelength filters

35 in such a way, that the one wavelength is corresponding to the specific absorption wavelength of the plastic ^anc- ^tne other a reference wavelength from beside the previous one and the final measuring result is calculated with the help of the relation between these wavelengths.

5. Method in accordance with some of the patent claims 1-4, c h a r a c t e r i z e d in, that the materials of the bodies to be transported in the space between the resistance wire and the reflecting device are observed by moving the reflecting device very rapidly and by determining with the help of the in the analyzer into two parts divided infrared radiation the visibility of the specific absorption peak of the plastic the contents of plastic in the bodies is follow¬ ed.

6. Method in accordance with some of the patent claims 1-5, c h a r a c t e r i z e d in, that the resistance wire is strip-formed or several resistance wires are placed beside each other are used in order to increase the intensity in the analyzer.

7. Method in accordance with some of the patent claims 1-6, c h a r a c t e r i z e d in, that the resistance wire and the analyzer are placed on the same side of the plastic track and the reflected infrared radiation is directed with the help of the reflecting device into the analyzer.