WO1994025629A1

WO1994025629A1 - White wooled sheepskin

Info

Publication number: WO1994025629A1
Application number: PCT/AU1994/000205
Authority: WO
Inventors: Andrew John Cameron Callender; Geoffrey Brian Eskriett
Original assignee: Crompton Group Holdings Pty. Limited
Priority date: 1993-04-23
Filing date: 1994-04-20
Publication date: 1994-11-10

Abstract

The present invention relates to a method of treating an animal skin comprising a hide and wool wherein said method comprises the step of treating the wool with a peroxide bleaching agent prior to tanning the hide.

Description

Title : WHITE WOOLED SHEEPSKIN

This invention relates to white wooled skins and, more particularly, to a method of manufacture of wooled tanned sheepskins of improved quality and appearance.

In the tanning of wooled sheepskins, it has been usual practice to soak the hides which are then fleshed, pickled and chrome tanned. After tanning, the wool is scoured to remove dirt and some grease. The wool is then bleached and/or dyed.

White wooled sheepskins are particularly difficult to manufacture because the wool fibres of the natural sheepskin are discoloured at the fibre tip as a result of weathering and solar ultra-violet irradiation. Typically, the tanned wooled skin is treated with from 2 to 4 grams per litre of sodium hydrosulfite at a pH of 3.2 - 3.5 to bleach the wool. However, the yellow weathered tips detract from the whiteness obtainable by bleaching. Increasing the severity of the bleach, for example by increasing the hydrosulfite concentration or treatment time, in order to overcome the yellowness, results in damage to the wool fibre and a harsh feel. Even when treated with optical brighteners and the like, it has not proved possible to obtain a desired degree of whiteness while retaining a soft handle. To date, the whitest sheepskins which have been manufactured have a CG-W index of 106.0 points when measured by means of the Ciba-Geigy "whiteness test" and more usually have a CG-W index of from 70 to 80 points.

It is especially desirable to obtain a high degree of whiteness and brightness in sheepskins while avoiding the use of formaldehyde or gluteraldehyde based tanning materials which leave aldehyde residues in the wool, thus making the fleece unsuitable for applications involving contact with human skin.

It is an object of the present invention to avoid or at least ameliorate some of the above discussed disadvantages of prior art.

According to one aspect, the invention consists in a method of treating an animal skin comprising a hide and wool wherein said method comprises the step of treating the wool with a peroxide bleaching agent prior to tanning the hide. According to a second aspect, the invention consists in a method according to the first aspect, comprising the steps of

(1) treating the wool with a peroxide bleaching agent, (2) tanning the hide, and (3) subsequently treating the wool with a sodium hydrosulfite bleaching agent at a concentration in excess of 6 grams per litre, or with an equivalent concentration of another hydrosulfite.

According to a further aspect, the invention consists in a tanned wooled animal skin whereof the wool has a Ciba-Geigy Whiteness index in excess of 110 points and more preferably in excess of 150 points.

In a highly preferred embodiment, the animal skin is sheepskin. However other animals skin such as those derived from goats may also be used.

In preferred embodiments of the invention, the rate of the bleaching step which is conducted prior to tanning is controlled by means of stabilizer so as to proceed gently over an extended period and the wool is treated with optical brighteners and the like during or after the hydrosulfite treatment.

It will be understood that peroxides have been used in the past to bleach yellow tips after tanning but because peroxide detrimentally effects the tanned leather, care must be taken that only the wool tips and not the skin are exposed to contact with peroxide. It was thought that the treatment of the fibres prior to tanning was undesirable as treatment was likely to make the fibres excessively absorbent during subsequent tanning with consequent staining during tanning and/or reduced ability to withstand subsequent bleaching. It is contrary to expectation that the use of a bleaching agent before the tanning stage enables a higher concentration of bleaching agent to be used after tanning without producing a harsh feel in the wool or detrimental effect to the tanned leather.

Preferred embodiments of sheepskins treated according to the invention have a combination of whiteness and handle considerably better than the best hitherto achievable.

The invention will now be more particularly described by way of example only.

Wooled sheepskins (50/58 quality wool 1st cross Merino (Sample A and Sample C) were treated according to the following method:- Soak - using 1.5 g/litre wetting agent. Flesh

38°C Scour 3 g/litre Dyamul SFA (a degreasing agent) 0.7 g/litre Soda Ash pH 8.5 - 9.0 Run 45 mins - drain 38° Rinse 10 mins - drain 30°C 3 g/litre Soda Ash pH 9.0

2 g/litre Hydroquest 888 (sequestering agent)

2 g/litre stabiliser CB (Peroxide stabilizer and rate control agent ex-ICI Valchem)

1 g/litre Tetrapol SAF (Wetting agent) Run 10 minutes BLEACH

4 g/litre Hydrogen Peroxide 50% Run 3 hours

4 g/litre Matexyl BA-PK (Peroxide neutralizing agent ex-ICI Valchem) Run 10 minutes Drain 25°C 60 g/litre salt

Acid to pH 2.8 - 3.0

1 g/litre Tetrapol SAF )

8 g/litre Coripol SLP ) Emulsify at 4:1

60°C

4 g/litre Fatliquor Run 45 minutes

1 g/litre Calgon T

15 g/litre )

45 g/litre ) Syntan. Run 6 hours or until penetrated Empty. Clean backs

Acidify to pH 2.8

PAD chrome 5 1 water 2kg Syntan 4Kg Cr 0

Check for penetration

S temp at 85°C

Acid rinse x 2 pH 2.8

55°C 8 g/litre Sodium hydrosulfite

Add Formic Acid pH 3.5

Run 2 hrs. - drain

55°C 0.6 g/litre Uvitex JRS (optical brightener) + 1 g/litre Sanitize T90-04 (Sanitizing agent)

0.3 g/litre Deodorised Run 10 minutes

Samples from sheepskins which had been treated according to the method were tested with the Ciba-Geigy Whiteness test method developed by Rolph Graisen of Ciba Geigy, Switzerland, which is internationally recognized as one of the most reliable methods for determining the whiteness and brightness of fluorescent samples and utilizes a spectrophotometer, as follows: Ciba-Geigy Whiteness Ilium: D65 -10' x y Y CG-W TV TD CIE-W TINT SAMPLE A

2341 0.3038 0.3174 79.2 152.2 2-1 G2 110.3 0.2

SAMPLE C

2342 0.3044 0.3161 80.8 157.6 0-5 113.6 -1.3 The samples according to the invention resulted in a whiteness index of 152.20 and 157.6 respectively compared with prior art controls of 70 to 80. The results in whiteness and brightness are significantly superior to samples made by traditional methods of bleaching while maintaining a soft, natural wool feeling and avoiding the harshness characteristic of heavily bleached fibres of the past. The method of the invention may be varied to an extent which will be apparent to those skilled in the art from the teaching hereof without departing from the scope of the inventive concept herein disclosed. Thus, although the sheepskins in the above example were treated with 4 g/1 of a 50 wt% hydrogen peroxide in water for 3 hours, the sheepskin may be treated with corresponding amounts of other hydrogen peroxide concentrations over shorter or longer periods. However, in the present invention the sheepskin is preferably treated with 3 g/1 of a 50% solution of hydrogen peroxide for 1 hour or more prior to tanning and more preferably 4 g/1 of a 50% solution of hydrogen peroxide for at least 3 hours. Peroxides other than hydrogen peroxide may be used as the pre-tanning bleaching agent and bleaching agents other than sodium hydrosulfite may be used after tanning. Chemical compositions known to have a function similar to the function of the reagents described may be substituted therefor and processing conditions may be varied to a degree which can readily be determined by simple routine testing.

Claims

CLAIMS : -

1. A method of treating an animal skin comprising a hide and wool wherein said method comprises the step of treating the wool with a peroxide bleaching agent prior to tanning the hide.

2. A method according to claim 1 wherein the peroxide bleaching agent is hydrogen peroxide.

3. A method according to any one of the preceding claims comprising the step of further treating the wool with a bleaching agent after tanning the hide.

4. A method according to claim 3 wherein the bleaching agent is sodium hydrosulfite.

5. A method according to claim 4 wherein the sodium hydrosulfite is present in a concentration of greater than 6 grams per litre.

6. A method according to any one of the preceding claims wherein the wool after treatment has a Ciba-Geigy whiteness index in excess of 110 points.

7. A method according to claim 6 wherein the wool after treatment has a Ciba-Geigy whiteness index in excess of 150 points.

8. A method according to any one of the preceding claims wherein the animal skin is soaked in a solution comprising a wetting agent prior to treatment with the peroxide bleaching agent.

9. A method according to any one of the preceding claims wherein the animal skin is further soaked in a solution comprising a peroxide stabilizer prior to treatment with the peroxide bleaching agent.

10. A method according to claim 9 wherein the solution further comprises a rate control agent.

11. A method according to any one of the preceding claims wherein the peroxide bleaching agent further comprised a peroxide neutralizing agent.

12. A method according to any one of the preceding claims wherein the animal skin is treated with a concentration of hydrogen peroxide in excess of 3 g/1 of a 50% solution of hydrogen peroxide (or equivalent) in water for in excess of 1 hour prior to tanning.

13. A method according to any one of claims 3 to 12 wherein the hide is chrome tanned.

14. A method according to any one of claims 3 to 13 wherein the bleaching agent applied after tanning the hide further comprises optical brighteners and/or sanitizing agents.

15. A wooled tanned sheepskin manufactured by a method according to any one of claims 3 to 14.

16. A tanned wooled sheepskin having a Ciba-Geigy whiteness index in excess of 110 points.

17. A tanned wooled sheepskin according to claim 16 having a Ciba-Geigy whiteness index in excess of 150 points.

18. A tanned wooled sheepskin substantially as herein described with reference to the example.