GB2190190A - Measurement of the lustre of a yarn - Google Patents

Abstract

A method of measuring the lustre of a moving monofilament or multifilament yarn 1 comprises illuminating the yarn with a beam of laser light 4, such beam being at an angle of 45 DEG to a plane containing the yarn, and measuring the light which is reflected and scattered from the yarn in that plane over a suitable arc or subtended angle by means of one or more stationary sensitive devices 6. The light may be measured by a self-scanning photodiode array, a computer controlled photodiode array, a series of separate photodiodes or a vidicon-type tube. The lustre is calculated from the maximum intensity and the angular half peak width of the resulting photogoniometric curve. <IMAGE>

Description

SPECIFICATION Measurement of the lustre of a yarn This invention relates to the measurement of the lustre of a moving monofilament or multifilament synthetic yarn and more particularly while it is a running threadline during the manufacture of the yarn.

Various attempts have been made to measure and compare the lustre of synthetic yarns.

Lustre is an important aesthetic property of textile fibres. It is a feature of the total visual appearance determined in a complex way by reflections at fibre surfaces and internal scattering (see pages 580 to 583 of Physical Properties of Textile Fibres-Second Edition 1975-by W E Morton and JWS Hearle and published by The Textile Institute).

In rapidly crystallising polymers such as ny lon 6.6, lustre can be considerably affected by, for example spherulitic, crystallisation occurring in the spinning chimney which, in addition to affecting appearance, can give rise to faults during subsequent processing. Consequently it is of utility both to be able to determine the lustres of yarns during manufacture and to check them before subsequent processing/sale.

For many years it was common to segregate at spinning, yarns having good and bad lustre by a subjective method. One method consists of illuminating the threadline with a light source with a fixed intensity and distance and judging the lustre to be good or bad according to whether or not a reflection of the light is seen in the yarn. The lamp intensity may also be used to control the cut-off at any predetermined level and this can be equated to a laboratory measurement of lustre.

It has, however, been more reliable to measure the lustre of a sample of the yarn which has been wound onto a shaped former with one or more flat faces. For example, a solid rectangular pad or card or an open frame structure where the yarn is not supported in the area illuminated. The filament is wound onto the open frame former as a single layer, with adjacent filaments abutting one another, or as a number of superimposed layers for the solid pad. Using a parallel beam light source the wound former is illuminated at an angle of 45" in the plane of the fibre axis and the angular spread of reflected light in the same plane is measured by moving a carriage, supporting a lens and photocell system, around a circular arc about the former as centre and observing the photocell output (see Fig. 1).

The carriage is moved by hand or by means of a motorised drive and a photogoniometric curve is derived from the photocell output over an angular range (see Fig. 2).

A clear, smooth, highly lustrous yarn will have a high Imax and a low half peak width (W). On the other hand a dull, rough, low lustrous yarn will have a low Imax and a high half peak width (W).

In the Textile Research Journal, November 1985, at page 686 there is described a goniometric light scattering technique applied to a slow moving yarn which was passed through an instrument at 8 yards per minute. The sample of yarn used was 300 yards in length.

The light scattering measurements were made with white light with the yarn axis in the scattering plane at an angle of 45" to the incident beam. Relative scattered intensity data were obtained by conventional photogoniometric techniques on the moving yarn at 2" steps in the range 6" to 134 .

From the data a photogoniometric curve was produced which gave an indication of the lustre of the yarn.

According to the present invention we now provide a method of measuring the lustre of a moving monofilament or multifilament yarn comprising illuminating the yarn with a beam of laser light, such beam being at an angle of 45" to a plane containing the yarn, and measuring the light which is reflected and scattered from the yarn in that plane over a suitable arc or subtended angle by means of one or more stationary sensitive devices.

The light sensitive device may be a self scanning photodiode array, a computer controlled photodiode array, a series of separate photodiodes, a vidicon type tube or any light sensitive device capable of measuring the angular distribution of light intensity. The mid point of the device is set normally at 90 to the incident laser beam and at a convenient distance from the illuminated part of the filament.

The output from the light sensitive device is processed to obtain the equivalent of a photogoniometric curve. This is, of course, obtained without any mechanical movement of the light sensitive device.

A significant advantage of the method of the invention is that it may be used at high wind up speeds actually during spinning and typically in the range 1,000 to 6,000 metres/ minute.

The method of the invention offers a very quick technique of measuring yarn lustre and, because it utilises a compact apparatus, it can easily be used with a spinning threadline.

It will be realised that the performance of the method would be impaired by any lateral movement of the moving yarn. Accordingly we have found it currently desirable, in order that the yarn might be held at the correct position relative to the laser beam, and light detecting device to constrain the yarn with guides.

According to another aspect of the invention, therefore, we provide an apparatus for measuring the lustre of a moving monofilament or multifilament yarn including means for producing a laser beam and directing such beam so that it illuminates the yarn, and a plurality of stationary light sensitive means for measuring the light which is reflected and scattered from the yarn over an arc or subtended angle.

In a preferred apparatus according to the invention, we provide yarn guide means which are located above and below the point of illumination of the yarn by the laser beam and which serve to constrain the yarn so that the yarn is held in the correct position relative to the laser beam and the light detecting device.

Using the method of the invention we have successfully carried out measurements on monofilaments from 2.5 to 40 decitex and multifilaments from 30 to 500 decitex at speeds in the range 2 metres/minute up to 6,000 metres/minute but there is no reason to believe that the invention could not be carried out with monofilaments and multifilaments having a decitex outside this range and moving at a speed outside this range.

The laser beam can totally illuminate (ie immerse) the overall width of the threadline at the point of illumination or alternatively completely the opposite ie the laser beam being completely located within the confines of the threadline at the point of illumination.

The invention will now be described with reference to the following Examples.

EXAMPLE 1 Nylon 6,6 polymer was spun as a 20 dpf monofil at wind up speeds of 1K, 1.16K, 1.5K and 4K metres/minute and the lustre thereof measured with an apparatus according to the invention.

Referring to Fig. 3, the spinning threadline (1) is passed in a vertical direction between ceramic guides (2), each of which is provided with a slot of approximately 12 mmxO.35 mm.

Prior to passing through a guide, the threadline runs in contact with a fixed 4 mm diameter ceramic rod (3) which, together with the guide, serves to restrain movement of the threadline. The angle at which the threadline contacts the rod is kept to a minimum in order to reduce the risk of any damage to the threadline. After leaving the lower guide, the threadline passes to a conventional wind up unit.

While following its path between the two guides, the threadline is illuminated by a laser beam (4) generated by a laser unit (5) (details below). Light which is reflected and scattered from the threadline is measured by a light sensitive device (6) in conjunction with a driver board (7)-details of both are provided below. As a safety measure a laser beam stop (8) is provided to stop the beam after it has illuminated the threadline.

The signal received by the photodiode array is fed to a Datalab 901 Transient Recorder. A 5 ms time period (1 frame) is recorded by the Datalab 901 and this is played back at a slower rate to a Commodore PET computer fitted with an internal Analogue/Digital interface. The computer is used to reset the Datalab 901 and then collect and average a number of frames. Also the computer applies a running mean smoothing technique and allows a print out of the data points to be obtained.

The equivalent of a photogoniometric curve is then obtained by plotting the data points and the characteristics Imax and half peak width (W) calculated (see Fig. 4).

The laser unit (5) was a Spectra Physics Model 120 Stabilite Gas Laser with a Model 256 Exciter. The power generated was 5 mw at 632.8 nm wavelength. A vertically polarised beam of 0.65 mm diameter at 1/e2 points with a 1.7 milliradian beam divergence was produced.

The light sensitive device (6) was a IPL 4064 self scanning 64 element photodiode array and this was used in conjunction with a Type K 4064 driver board.

EXAMPLE 2 (A laboratory test) Yarns from bobbins of 78 f20 nylon yarn at a tension of 0.1 gms decitex with a range of 'lustre' values as previously measured by a conventional pad (former) test technique, were transported at 343 mpm through the apparatus used in Example 1.

Twenty frames from the self scanning photodiode array were taken and averaged to give a mean curve as described in Example 1. The value of the maximum intensity (Imax) in arbitrary units and the angular half peak width (W) in degrees were calculated.

A good correlation between the results obtained by the method of the invention and the laboratory pad test is evident from Figs. 5 and 6.

Claims (2)

1. A method of measuring the lustre of a moving monofilament or multifilament yarn comprising illuminating the yarn with a beam of laser light, such beam being at an angle of 45" to a plane containing the yarn, and measuring the light which is reflected and scattered from the yarn in that plane over a suitable arc or subtended angle by means of one or more stationary sensitive devices.

2. An apparatus for measuring the lustre of a moving monofilament or multifilament yarn including means for producing a laser beam and directing such beam so that it illuminates the yarn, and a plurality of stationary light sensitive means for measuring the light which is reflected and scattered from the yarn over an arc or subtended angle.