Process and apparatus for finishing cotton knits

Abstract

 A finished knitted fabric of cotton or other natural or regenerated cellulosic material which is lustrous, flat and dense and lacks spirality and edge curling, is crease resistant and has in addition good dimensional stability uncharacteristic of mercerized fabrics. An apparatus for finishing knitted cotton or other natural or regenerated cellulosic fabric is described, and also a process for finishing such knitted fabric.

Description

[0001] This invention relates to knitted fabrics of cotton or other natural or regenerated cellulosic fibres, or blends thereof with other fibres.

[0002] Our Canadian Patent No. 765735 is concerned with an ammonia treatment of such fabrics, and also - and more particularly - of woven fabrics of the same materials, to impart thereto varying degrees of elasticity (stretchiness) and/or crease resistance. The process involves swelling the fibres of the fabric by impregnating it with liquid ammonia and, after a time interval, evaporating the ammonia from the still swelled fibres.

[0003] As a matter of fact, however, the processes of the aforementioned patent have only ever been used significantly in connection with the treatment of woven fabrics. We have now, however, after revising certain established ideas about the end uses to which fabrics of different constructions can be put, devised novel, finished fabric of cotton or other cellulosic fibre which, it turns out, can be made by modified techniques according to the said patent.

[0004] According to the invention, the novel, finished knitted fabric of cotton or other natural or regenerated cellulosic material is characterised by being lustrous, flat and dense and in that it lacks spirality and edge curling, and is crease resistant, all being characteristics of mercerized fabrics, and in that it has in addition good dimensional stability uncharacteristic of mercerized fabric.

[0005] Particularly useful are fabrics in which the linear shrinkage in the coursewise direction is less than 5%, and fabrics in which the linear shrinkage in either direction is less thanlC%.

[0006] A single jersey fabric according to the present invention preferably has a _Kr value in excess of 1.0, and more preferably in the range from about 1.1 to about 1.3. (The Kr value is the number of courses per unit length divided by the number of wales per unit length.)

[0007] A machine for carrying out the process of the aforementioned patent has a support for a supply of fabric to be treated, an impregnation bath in which the fabric is impregnated with liquid ammonia, an evaporating unit comprising a rotary heated drum against which the swollen fabric is held by a blanket, and further processing zones in which the fabric may be subjected to heat or steam, prior to being wound up or otherwise collected after the processing.

[0008] Such a machine is suitable for making the fabric according to the present invention, but it must be arranged that the knitted fabric is supported as it passes through the machine so that it is not under any tension. The knitted fabric may thus be passed through the machine while supported by a woven fabric.

[0009] A suitable woven fabric support is not affected by the ammonia and may comprise a polyester or polypropylene fabric - which should itself be dimensionally stable, of course, and may comprise a plain woven fabric which may be of relatively open or even mesh-like structure.

[0010] A roll of knitted fabric can be sent through together with a roll of woven support fabric, or a continuous "belt" of support fabric may be arranged to carry the knitted fabric through the apparatus. A really enterprising finisher might elect to finish a knitted fabric and a suitable woven fabric together, using the woven fabric as a support for the knitted fabric.

[0011] It is helpful if the support fabric is smooth so that the knitted fabric can pull in with respect thereto without catching or snagging or undue frictional resistance.

[0012] A particularly effective arrangement seems to be if a tubular knit fabric is placed as a sleeve on a woven carrier, but this, of course, would present difficulties in practice.

[0013] If, incidentally, a tubular fabric is processed, no problems seem to be encountered in marking at the creases.

[0014] The other properties of the finished fabrics processed according to the invention are produced or altered as described in our earlier patent aforementioned.

[0015] Embodiments of novel cotton and other natural and regenerated cellulosic material knitted fabrics and finishing processes and apparatus for producing the same are hereinafter described with reference to the accompanying drawings in which:-

Figure 1 is a diagrammatic illustration of one embodiment of finishing apparatus,

Figure 2 is a diagrammatic illustration of another embodiment of finishing apparatus.

[0016] Figures 1 and 2 illustrate machinery for carrying out an ammonia treatment of knitted cotton or other natural or regenerated cellulose fabric, comprising a support 11 for a supply of fabric 12 to be treated, an impregnation bath 13 in which the fabric is impregnated with liquid ammonia 14, a hot calender 15 on which the fabric 12 swollen by the ammonia is pressed by a blanket 16, a further processing zone 17 in which the fabric is subjected to heat or steam, and fabric collection means 18 which, as shown, comprise a trolley 19 into which the fabric drops from a folding apparatus 21, but which could equally be a take-up roll arrangement.

[0017] In the embodiment illustrated in Figure 1, there is an additional supply arrangement 22 for a support fabric 23 of woven polyester or polypropylene which is fed through the entire apparatus together with the fabric 12 under treatment so as to support the latter and guide it through the apparatus without any significant lengthwise tension being applied to it. The support fabric is rolled up on a take up arrangement 24 for subsequent re-use.

[0018] In the embodiment illustrated in Figure 2, a support fabric 23, again of woven polypropylene or polyester, is run as an endless belt through the machine from an input roller 25 to a return roller 26 with a return run 27 under the machine.

[0019] The machinery illustrated will, of course, also have the usual ancillary equipment for recovering evaporated ammonia, and heating and/or cooling means and so on.

[0020] By means of the machinery, processes can be applied to cotton and other cellulosic fabrics as more particularly described in the following Examples:

EXAMPLE

[0021] Treatment in a padding machine.

[0022] Four single jersey fabrics, from an ordinary mill production were treated in tubular form in the grey state(fabric weights 105, 110, 170 and 185 g/m²). Each experimental fabric sample was approx. 100 m long. The samples were before treatment sewn together and onto a machine runner (woven cotton fabric). To ensure tensionless treatment, a woven polyester fabric (fabric weight 65 g/m²) was also sewn onto the machine runner and fed into the machine parallel with the single jersey fabric samples:

The speed of the padding machine was 12 m/min. (The padding machine running speed ranges form 7 - 16 m/min.)

Treatment procedure.

[0023] In the treatment, the fabric passes through three zones:

1) The impregnation zone. (Foulard technique, temperature of ammonia - 33.4° C.)

2) The reaction zone.

3) The ammonia removal zone.

[0024] Assessment of dimensional stability of the treated fabric.

[0025] Fabric shrinkage or dimensional stability may be defined as:

(i) Relaxation shrinkage, which is measured shrinkage when the fabric is statically immersed in water for the first time and it is considered to be due to the release of strains built up and imposed on the fibres, yarn and fabric systems during manufacture.

(ii) Consolidation shrint lye. This is observed particularly on fabrics other than wool and shows itself as a continued shrinkage in washing treatments after the first immersion. Scientifically this shrinkage can be considered as a delayed relaxation of some processing strains that require agitation to assist in their full release.

[0026] Commersially, the dimensional stability of a knitted fabric is commonly expressed as a shrinkage measurement based on either the original dimensions of a fabric or on the dimensions after a soaking treatment. However, it has been shown that it is more informative, in terms of assessing the loop configuration to express the fabric diinensions in terms of the k_c, k_w and k values, where these constants are given by

[0027] The stitchlenght ℓ was found by measuring unravelled yarn lenghts from a known number of courses from the knitted dry-relaxed fabrics, using a Shirley Crimp Tester.

[0028] Relaxation and washing treatments. The fabric sample size was (60 x 60) cm². In the middle of the sample, a square of (10 x 10) cm² was measured by means of a smaller template and marked by three points in length and width direction respectively. The average of the three measurements was used in the subsequent calculations.

[0029] The. samples were machine washed according to Swedish Standard SIS 25 12 39 (V4), i.e. washed at 60°C and rinsed. They were hydroextracted for 6 mins. and samples were dried lying flat. The samples were given 13 washing treatments.

[0030] The climensional changes were measured after conditioning for at least 4 hours in an atmosphere of 20°C, 65 % R.H. The dimensional changes are expressed in k_c, k_w and k_s values and changes in stitch configuration in k_r values.

The results are given in Tables 1 + 2.

Claims

1. A finished knitted fabric of cotton or other natural or regenerated cellulosic material, characterised by being lustrous, flat and dense and in that it lacks spirality and edge curling, and is crease resistant, all being characteristics of mercerized fabrics, and in that it has in addition good dimensional stability uncharacteristic of mercerized fabrics.

2. A fabric according to claim 1, characterised in that it has a linear shrinkage in the coursewise direction of less than 5 %.

3. A fabric according to claim 1 or claim 2, characterised in that it has a linear shrinkage in either direction of less thanlO%.

4. A fabric according to any one of claims 1 to 3, characterised in that it is a single jersey fabric having a Kr value greater than 1.0.

5. A fabric according to claim 4, characterised in that it has a _Kr value between about 1.1 and about 1.3.

6. A process for finishing knitted fabric of cotton or other natural or regenerated cellulosic material comprising swelling the fibres thereof by impregnation with liquid ammonia and evaporating the ammonia from the still-swelled fibres, characterised in that the fabric is processed in substantially tension-free condition while held substantially flat.

7. A process according to claim 6, characterised in that the process is continuous and the fabric passes through the process on a carrier fabric.

8. Apparatus for finishing knitted cotton or other natural or regenerated cellulosic fabric comprising means for passing said fabric continuously through an impregnation zone for impregnating the fabric with liquid ammonia to swell the fibres thereof and means for evaporating the ammonia from the still-swelled fibres, characterised in that carrier means are provided for carrying the said fabric substantially free from tension through the apparatus.

9. Apparatus according to claim 8, characterised in that said carrier means comprise a woven fabric of a material that is not deleteriously affected by the ammonia.

10. Apparatus according to claim 9, characterised in that said woven fabric is of polyester or polypropylene.

11. Apparatus according to claim 8 or claim 9, characterised in that said carrier means comprise a fabric which is forwarded, together with the knitted fabric to be treated, from a supply to a take-up.

12. Apparatus according to claim 8 or claim 9, characterised in that said carrier means comprise a continuous belt of fabric.

13. Apparatus according to claim 11, characterised in that said fabric is itself a fabric intended to be processed together with the knitted fabric.

Drawing