GB1558992A - Method of heat-treating a staple fibre yarn - Google Patents

Description

(54) METHOD OF HEAT-TREATING A STAPLE FIBRE YARN (71) We, NEDERLANDSE ORGANI SATIE VOOR TOEGEPAST - NATUUR WETENSCHAPPELIJK ONDERZOEK TEN BEHOEVE VAN NIJVERHEID, HANDEL EN VERKEER (a corporate body duly organised and existing under the laws of the Netherlands), of 148 Juliana van Stolberglaan, The Hague, The Netherlands, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of heattreating a staple fibre yarn that comprises at least 30% polyethylene terephthalate, to produce a yarn that can be used as a warp yarn.

To permit singly spun yarns of such a com- position to be used as warp yarns in a weav- ing mill it is customary to size these yarns with a sizing agent in the nature of an adhesive generally based on starch, polyvinylacetate or carboxylmethyl cellulose. This sizing agent, however, must be removed from the woven doth by, for example, enzymatic decomposition and washing, and this forms an important part of the total water pollution produced by the textile industry. Furthermore, drying the yarn after sizing and washing requires a large amount of energy.

The dust and the fly released on processing both sized and unsized yarns also present a problem. The dust accumulations, which are produced in spite of the general use of air extraction systems particularly in the rinsing and shearing departrnents, result in interferences and defects in production, while in halation of the dust present in the air may cause pulmonary diseases (byssinosis).

In weaving-mills, too, much inconvenience is experienced from dust, which, apart from the fibre dust, often consists largely of starch particles. With the aid of extraction the inconvenience can be checked. However, to keep the dust concentration below the permitted value, having regard to the equality of the fabric and the health of the personnel working in the weaving mill, exhaust systems are required whose power requirements are greater than those of the production machines.

It is an object of the invention to provide a method for the manufacture of a staple fibre yarn capable of being- used as a warp yam, in which the drawbacks and problems described above are eliminated or at least reduced.

According to the invention there is provided a method of heat-treating a staple fibre yarn comprising at least 30% of fibres consisting wholly of polyethylene terephthalate to produce a yam for use as a warp yam, wherein the yarn is exposed to a temperature of from 2300 to 2600C for at least one second, the time and temperature being sufficient to cause the polyethylene terephthalate fibres to become adhesive.

It has been found that this heat-treatment of the yam, preferably a blended yarn, at a temperature at which polyethylene terephthalate begins to soften produces a mutual adhesion of the fibres which raises the wearresistance of the yarn and lowers the sheddingvalue, so that the yarn can be used as warp yarn. In case of yarns spn on ring flames sizing agent. Moreover, it has been found that the formation of dust by this yarn is only a few per cent of similar yarns which are sized in the usual way.

The polyethylene terephthalate fibres used in the yarn may be continuous filaments but are preferably staple fibres.

Provided the heat-treatment is not continued for too long, it has little effect on the tensile strength and the elongation of the yarn. In case of yarns spun on ring flames these properties show a slight decrease of approximately 10%, whereas yarns spun by open-ended spinning show a tendency to increase somewhat in strength.

Depending on how long the treatment lasts, the modulus of elasticity increases by 1S 50%. No adverse effect of the heat-treatment was found in fabrics manufactured from these yarns. Indeed with regard to the tendency to pilling, which is always present in fabrics of blended yarns an improvement was found compared to fabrics manufactured according to known methods.

It has also been found that the fabric can be finished, for example bleached, dyed and made crease-resistant in known ways, without special pre-treatments that might extend the process.

E an over-severe heat-treatment is carried out e.g. heat-treatment at the highest temperature mentioned of 2600C for considerably more than 30 seconds, the properties of the yam, such as its tensile strength, deteriorate so that the yarn becomes useless for most applications. Apparently after such a severe treatment the molecular orientation of the fibres of the polyethylene terephthalate disappears and the adhesion between the fibres becomes so great that the yarn becomes rigid and brittle. In view of this the yarn is preferably exposed to the heat-treatment for not longer than 30 seconds, at least at such a high temperature.

it is desirable during the heat-treatment for the tensile stress in the yarn to be less than 8% of its tensile strength, because a greater stress in the fibres may start slippage of the fibres past one another as a result of the softening of the thermoplastics fibres and thin patches or ruptures may be produced in the yarn. Preferably, the yarn is substantially tensionless during heat-treatment, there being just enough tension to prevent crinkling of the yarn.

The invention is further described below with reference to the accompanying drawing, which schematically shows an embodiment of a device for carrying out the method according to the invention.

Blended staple-fibre yarns including at least 30% of fibres consisting wholly of polyethylene terephthalate are fed from a yarn supply consisting of yarn bobbins or cones 1 via a yarn brake 2 and a coarse reed 3 to a heating furnace 4, in which the yarn is subjected to a heat-treatment for at least one second in a closed heat-circulation system, for which purpose the heating furnace is provided with an electric heating device 5 and a fan 6.

In the heating furnace a temperature of approximately 2500C is maintained so that the blended yarn is heated to a temperature around the starting point of the melting range of the polyethylene terephthalate fibres.

Behind -the furnace a transport roller or tension roller 8 is mounted over which the blended yarn upon leaving the furnace is transported via a coarse reed 7 and is supplied via a coarse reed 10 to an adjustable winding unit 11.

The roller 8 is driven by a driving roller 9 which is driven at a constant speed by a suitable motor, the speed furthermore depending on the period of time desired for the heat-treatment of the blended yarn.

The adjustment of yarn brake 2 is such that during heating the tensile stress of the blended yarn is less than 8% of the tensile strength of the yarn.

The device just described was used in the following Examples.

EXAMPLE I Normally spun yarns of 30 tex, consisting of 65% polyethylene terephthalate and 35% cotton, were passed through the device, each yarn being passed through at a different speed, so that the heat-treatment lasted for a different period of time in each case. The temperature each time was adjusted to 2500 C.

The yarns treated in this way, as well as an untreated yarn, were tested to determine their resistance to wear, their shedding value and their elasticity modulus.

As using herein, "wear-resistance" it is to be understood as meaning the number of revolutions until rupture occurs of a yarn that is cross-wise fixed over a wearing device, the yarn worn by upward and downward movements against steel pins and against itself.

This is a standard test for the wear actually occurring in the weaving process (see Ir. K.

van Harten and Ir. N. J. Faasen - Transactions of The General Textile Institute 57 (1966) T 273). Preferably the wear resistance is more than 350.

The shedding value is to be understood as the sum of peaks of tension that may occur by splitting pre-worn layers of yarn (10 threads each) that are fixed over an irnitated weaving shed.

For blended yarns (normally adequately treated) this value is preferably less than 2,000, and more preferably not be more than 800 to 1,600 grams; a very well sized yarn has a value of 400-500 grams or lower and a value of e.g. 4,000-5,000 grams is bad and unweavable (see Ing. J. G. Feikema and Ir. N. J. Faasen - de Tex 29 (1970), No.

4 page 293, picture 5).

The results obtained are shown in Table A.

TABLE A Treatment of a normally spun blended yarn at 2500 C, polyethylene terephthalate/ cotton 65/35 tex.

Elasticity modulus Heating time (g/denier at 100% Wear-resistance number in seconds elongation) of revolutions Shedding-value 35 25 x > 25,000 16002' 19 24 x ,, 15002' 10 20 x " 2730 5 19 x 9,800 17002) 2 19 1,0251' 4901' 1 18 3452) 6901' 0.5 17 202 18302' 0.25 17 165 not able to be determined, ruptured.

x extremely high 1) favourable value 2) a value still usable in practice untreated normally spun blended yarn 17 17 160 not able to be determined, unweavable without sizing EXAMPLE II Yarns of 30 tex, spun by open end spinning and consisting of 65% polyethylene terephthalate and 35% cotton, were passed through the device, each yarn being passed through at a different speed, so that the heat-treatment lasted for a different period of time in each case. The temperature each time was adjusted to 2500 C. These treated yams, as well as an untreated yarn were tested to determine the wear resistance, their sheddingvalue and their elasticity modulus.

The results obtained are as shown in Table B.

TABLE B Treatment of a blended yarn spun by open ended spinning at 2500 C, polyethylene terephthalate/cotton 65/35, 30 tex.

Elasticity modulus Heating time (g/denier at 100% Wear-resistance number in seconds elongation) of revolutions Shedding-value 35 23 x 25,000 not determined 19 23 x 10 23 x 13,000 610 5 21 x 10,000 1110 2 21 x 3,400 1130 1 21 1) 725 548 1) 0.5 18 2) 380 2148 x extremely high 1) favourable value 2) still usable value o extremely low Untreated blended yarn spun by open ended spinning 11.5 360 unweavable without sizing WHAT WE CLAIM IS: 1. A method of heat-treating a staple fibre yarn comprising at least 30% of fibres consisting wholly of polyethylene terephthalate to produce a yarn for use as a warp yam, wherein the yarn is exposed to a temperature of from 2300 to 2600C for at least one second, the time and temperature being suffi

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE A Treatment of a normally spun blended yarn at 2500 C, polyethylene terephthalate/ cotton 65/35 tex. Elasticity modulus Heating time (g/denier at 100% Wear-resistance number in seconds elongation) of revolutions Shedding-value 35 25 x > 25,000 16002' 19 24 x ,, 15002' 10 20 x " 2730 5 19 x 9,800 17002) 2 19 1,0251' 4901' 1 18 3452) 6901' 0.5 17 202 18302' 0.25 17 165 not able to be determined, ruptured. x extremely high 1) favourable value 2) a value still usable in practice untreated normally spun blended yarn 17 17 160 not able to be determined, unweavable without sizing EXAMPLE II Yarns of 30 tex, spun by open end spinning and consisting of 65% polyethylene terephthalate and 35% cotton, were passed through the device, each yarn being passed through at a different speed, so that the heat-treatment lasted for a different period of time in each case. The temperature each time was adjusted to 2500 C. These treated yams, as well as an untreated yarn were tested to determine the wear resistance, their sheddingvalue and their elasticity modulus. The results obtained are as shown in Table B. TABLE B Treatment of a blended yarn spun by open ended spinning at 2500 C, polyethylene terephthalate/cotton 65/35, 30 tex. Elasticity modulus Heating time (g/denier at 100% Wear-resistance number in seconds elongation) of revolutions Shedding-value 35 23 x 25,000 not determined 19 23 x 10 23 x 13,000 610 5 21 x 10,000 1110 2 21 x 3,400 1130

1 21 1) 725 548 1) 0.5 18 2) 380 2148 x extremely high 1) favourable value 2) still usable value o extremely low Untreated blended yarn spun by open ended spinning 11.5 360 unweavable without sizing WHAT WE CLAIM IS: 1. A method of heat-treating a staple fibre yarn comprising at least 30% of fibres consisting wholly of polyethylene terephthalate to produce a yarn for use as a warp yam, wherein the yarn is exposed to a temperature of from 2300 to 2600C for at least one second, the time and temperature being suffi

cient to cause the polyethylene terephthalate fibres to become adhesive.

2. A method according to claim 1, wherein the yarn is exposed to the said temperature for not longer than 30 seconds.

3. A method according to claim 1 or 2, wherein during the heat treatment the tensile stress in the yarn is less than 3% of the tensile strength of the yarn.

4. A method according to claim 3, wherein the yarn is substantially tensionless during the heat-treatment.

5. A method according to any preceding claim, wherein the yarn comprises polyethylene terephthalate fibres blended with cotton fibres.

6. A method of heat-treating a staple fibre yam, substantially as herein described with reference to the accompanying drawing.

7. A method according to claim 1 of heattreating a staple fibre yarn, substantially as herein described with reference to Example 1 or Example 2.

8. A yarn obtained by the method according to any preceding claim.

9. A yarn according to claim 8, characterised by a wear-resistance, as hereinbefore defined, or more than 350 and a shedding-value as hereinbefore defined, of less than 2,000