GB1591403A - Process for increasing the hydrothermal stability of chrome-tanned leather - Google Patents

Description

(54) PROCESS FOR INCREASING THE HYDROTHERMAL STABILITY OF CHROME-TANNED LEATHER (71) We, YORKSHIRE CHEMICALS LIMITED, a British Company of Black Bull Street, Leeds LS10 1HP, 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: This invention relates to a process for increasing the hydrothermal stability of chrome tanned leather and to chrome-tanned leather so heat when it is in the wet treated.

Leather is a material which is rather sensitive to heat when it is in the wet state, the most noticeable effect being a marked shrinkage which takes place quite abruptly at a fairly well-defined temperature known as the shrinkage temperature. This effect takes place at different temperatures according to the type of tanning material used in preparing the leather. Thus a particular type of leather is characterised by a shrinkage temperature. If a suitable method of measuring the shrinkage temperature is followed, the values obtained are reproducible. (Shrinkage temperatures referred to in this specification were determined according to Test Method No. SLP 18 of the Society of Leather Technologists and Chemists).

The highest degree of hydrothermal stability according to the present art is customarily obtained with chrome tanning agents. Depending upon the amount of chrome tanning agents offered, the shrinkage temperature of the tanned leather generally varies between 100" and 125 C.

The hydrothermal shrinkage of leather is however a rate process. If the leather is heated for an extended period of time at a temperature below its shrinkage temperature, it will slowly shrink. Thus chrome-tanned leather with a shrinkage temperature of over 1000C, may commence to shrink after continuous boiling for 5 to 10 minutes and then, on continued boiling, considerable further shrinkage may take place. This means that in the dyeing of leather the upper limit to the temperature of the dye-bath is commonly in the range 50-60 C.

If the dimensional stability of the leather could be improved, higher temperatures than this could be used and so increase the rate of dyeing and thereby bring the dyeing of leather more in line with the dyeing of textiles.

The present invention relates to a process in which chrome-tanned leather is treated in such a way that it may be subsequently treated whilst wet, and, in particular, dyed or printed at 100 C or thereabouts, without appreciable shrinkage. The treatment comprises contacting the chrome-tanned leather with a polycarboxylic acid of benzene containing three of more carboxylic acid groups. Instead of the polycarboxylic acid itself, the anhydride (where this exists) may be used, and in particular'the water-soluble salts such as those of ammonia and sodium.

The polycarboxylic acids of benzene containing three or more carboxylic acid groups are not unique among the polycarboxylic acids of benzene in increasing the shrinkage temperature of chrome-tanned leather. Phthalic acid, used for convenience as its sodium salt can bring about a slight increase of shrinkage temperature. This amounts only to some 3 0C. A rather larger effect is shown when terephthalic acid is used, of perhaps some 13"C, and isophthalic acid brings about a still larger increase perhaps about 16 C. These increases illustrate the effect of the acids on identically prepared leathers, and are believed to show the true order of their effect, but the absolute values for the increases are very dependent on the process used in preparing the leather.The increase in shrinkage temperature brought about by these dicarboxylic acids, however, is not accompanied by any substantial improvement in the dimensional stability of the leather in boiling water. It is possible, certainly, to reduce the shrinkage which takes place at 100 C, to about a half of the original value, but as this may still amount to 8% or more of the original area of the leather, it can only be looked upon as an amelioration of the situation. We have found, however, that although a somewhate larger increase in the shrinkage temperature can be brought about with a polycarboxylic acid of benzene such as pyromellitic acid, a substantial reduction in area shrinkage also results.It was not expected that this further, relatively small, increase in shrinkage temperature would bring about such a marked reduction in the area shrinkage on boiling. Area shrinkages of much less than 1/lOth of the original values can readily be attained. This effect can be seen from the results given in Table 1. These results were obtained from chrome-tanned leather (1.1 mm in thickness) treated with the salts shown and then re-chromed with 8% chrome liquor (15% Cr203: 33%basic).

Tablet Polycarboxylic acid Shrinkage Area * (%on dry leather) Temperature Shrinkage (%) Control (no addition) 116"C 13.8 5 No phthalic (sodium salt) 119"C 9.1 5% terephthalic (ammonium salt) 129"C 10.6 5Soisophthallic( " " ) 132"C 8.3 5%pyromellitic( " " ) 135"C 0.78 * Area shrinkage was measured by first neutralising the leather by an aqueous treatment in 1.5 % sodium bicarbonate (based on weight of dry leather) and then measuring the area of the leather both before and after boiling in water for 20 minutes.

According to the present invention, a process is provided in which chrome-tanned leather is further treated by contacting it with an aqueous solution of up to 5%, preferably 2 to 4% (based on the shaved weight of leather) of polycarboxylic acid of benzene containing 3 or more carboxylic acid groups, a water-soluble salt thereof or an anhydride thereof (where such exists).

In a preferred process, the polycarboxylic acid, its water-soluble salt or anhydride are applied to the chrome-tanned leather in an aqueous system at temperatures from 0 C to 600C preferably 35 to 500C, for times up to 4 hours, preferably 30 to 90 minutes.

The ammonium salts of the polycarboxylic acids are generally very soluble in water and are very suitable for the process. If however a powdered product is desired, prepared for instance by evaporating an aqueous solution of the ammonium salt to dryness, we find it advisable to make an addition of borax to stabilise the pH.

Specific examples of polycarboxylic acids suitable for use in the process of the invention are trimesic acid, trimellitic acid, hemimellitic acid, pyromellitic acid, prehnitic acid, mellophanic acid and mellitic acid.

In a further embodiment of the invention there is provided a chrome-leather treated in accordance with the process of the present invention.

Chrome-tanned leather treated in accordance with the process of the invention may be dyed or printed at temperatures in the region of 100 C without appreciable shrinkage and/or deterioration in the quality of the leather.

It should be understood that chrome tanned leather treated according to the process of the invention, may also be dyed under the conditions and with the dyes normally used for chrome tanned leather (i.e. in the temperature range 40 - 65"C). These are not exemplified in this specification because they are conventional processes. The process of the invention gives a product which can subsequently be processed in aqueous liquors up to temperatures of about 100"C. This allows for the greater choice in the selection of dyes and conditions for their application, than is normal with chrome tanned leather. Dyeing temperatures in the range 40-105 "C may be chosen as may be convenient for the dyes employed.

After treatment of chrome leather by the process of this invention there is obtained leather which may be dyed or printed by conventional processes at temperatures up to at least 1050C.

The leather may be submitted to other aqueous processing up to the same temperature. The additional stability of the leather is probabaly gained by further cross-linking of the hide protein and the basic chromium sulphate or chloride through the additional carboxylic acid groups supplied by the polycarboxylic acid which in effect can bond molecules of chrometanned collagen in three dimensions.

The increased stability of the leather confers other properties upon it. Thus the leather of the invention after dyeing at 100"C or thereabouts may then possess superior dye-fastness properties. For instance the rub-fastness and the perspiration fastness of such a dyed leather may be significantly superior to those of conventional chrome-tanned leather dyed at 50 60"C. At the present time, it is not clear whether this improvement is specifically due to the treatment by the polycarboxylic acid of-benzene, or to the higher temperature of dyeing, which of course would be unattainable without the treatment, or to a combination of both factors.

The fact that the leather is stable to aqueous treatments at about 100"C means that printing techniques pertaining to the textile industry, and which may involve treatment of the substrate with live steam, may also be applied.

It is also possible that leather prepared according to the process of this invention may be dried at temperatures appreciably higher than those used hitherto, thus accelerating the process of drying.

The invention also provides chrome-tanned leather, treated in accordance with the process of this invention and subsequently dyed from an aqueous dye-bath e.g. at 1000C or-thereabouts.

The present invention is illustrated by, although not restricted to, the following examples in which the percentages given are percentages by weight based on the shaved weight of the chrome tanned leather.

EXAMPLE 1 A commercially available full-chrome sheepskin was cut into three pieces. The first piece (a) was treated with 10% commercial chrome liquor (11% Cry03, 50% basicity) for an hour.

The second piece (b) was treated first with 3% ammonium pyromellitate for 30 minutes and then with 10% commercial chrome tanning agent (11% Cry03, 50% basicity) as was done in the case of the first piece. The third piece (c) was treated with 3 % ammonium pyromellitate alone for an hour. The shrinkage temperature of all these pieces when determined at the end of the treatment was found to be as follows: Treatment Shrinkage Temperature (a) 122"C (b) 135"C (c) 128"C This showed that the ammonium pyromellitate had increased the heat stability of the leather presumably by the introduction of further cross-linkage into the leather to make it more stable to wet heat.Pieces from similar locations on the three treated leathers were cut and after neutralization with 2% sodium bi-carbonate were dyed with 1 % or 2% Airedale Brown F3G. (C. I. Acid Brown 188), at 1000C. for 1 hour and then fixed with 1 %formic acid at the same temperature for a further 30 minutes. The area of all these pieces was measured before and after dyeing at 1000C. It was found that while the re-chromed control pieces were completely shrunk, pieces treated with the salts of pyromellitic acid either alone or in combination with chrome-tanning agent remained unchanged in area and soft.The results of area losses, as measured by planimeter, were as given below: Treatments Area (sq. in.) Before After Area Average Dyeing Dyeing Loss (percent) (percent) Rechromedcontrol 34.10 22.25 34.75 32.15 23.85 25.82 30.3 Ammoniumpyromellitate alone 27.15 27.10 NIL 24.35 24.40 NIL NIL Ammonium pyromellitate + chrome 29.50 29.55 NIL NIL 29.95 30.10 NIL Further, when explained under a scanning electron microscope, there was no evidence of internal heat damage in those pieces treated with the ammonium pyromellitate.

EXAMPLE 2 150g. pyromellitic dianhydride was dissolved with stirring at room temperature in 500 ml.

water containing 200 ml. conc. (0.880) ammonia. 4.5g borax was added to the mixture to stabilise the product which was then spray dried to obtain Product (I), which was used in subsequent treatment of leather.

One commercially chrome-tanned sheepskin was cut into three pieces. One piece (a) was re-chromed with 8% commercial chrome liquor (15 % Cr203,50% basicity) for an hour. The second piece (b) was re-chromed in the same manner as the first piece and then treated with 3%Product I for another hour. The third piece (c) was first treated with Product I as was done in the case of piece (b) and then re-chromed with 8%commercial chrome liquor(15%Cr203, 33% basicity) for an hour. Four sets of three matched pieces were cut (i.e. from similar location-approx. 4" x 3"), one each from the three treatments.After neutralization with 1.5%sodium bi-carbonate for 30 minutes, each set was dyed at 100"C. for 1 hour with one of the following dyes and fixed with 1 %formic acid at the same temperature for 30 minutes: SET (1) 2%Airedale Red RM (C. I. Acid Red 114) (2) 2%Airedale Rubine 2BLLD (C. I. Direct Red 83) (3) 2 % Airedale Black FB (C. I. Direct Black 160) (4) 2 % Airedale Brown RGL(C. I. Acid Brown 383) The area of each piece was measured before and after the dyeing with a fixed arm planimeter.The results as obtained are as follows: Treatments Area (sq. in.) Before After Area Loss Dyeing Dyeing percent 1st Set a) 14.55 6.65 54.3 b) 14.70 14.70 NIL c) 14.70 14.65 0.34 2nd Set a) 16.40 11.70 20.7 b) 14.30 14.35 NIL c) 13.90 13.90 NIL 3rd Set a) 15.50 12.40 20.0 b) 14.60 14.50 0.68 c) 15.35 15.30 0.32 4th Set a) 15.50 12.85 17.1 b) 14.25 14.30 NIL c) 14.80 14.75 0.35 Average Area Losses Treatmenta) 30.02% b) 0.17% c) 0.25% On assessment of the quality of the'dyed leather, it was found that re-chromed control had become wrinkled and stiff while the pieces treated with the salts of pyromellitic acid alone or in combination with chrome had remained soft and supple.

To examine the fastness properties of such leather, treated with salts of pyromellitic acid alone or in combination with chrome, 4 sets of three matched pieces (i.e. from similar location-approx. 4" x 4"), one each from each treatment, namely a), b), and c) were cut.

After neutralization with 1.5% sodium bi-carbonate for 30 minutes, each set was dyed with either of the following dves: i 2%Airedale Black 2BG200 (C. I. Acid Black 1) ii 2%Airedale Orange Black FB (C. I. Direct Black 160) iii 2%Airedale Orange AGD125 (C. I. Direct Orange 34) iv) 2 % Airedale Brown 2DS (C. I. Acid Brown 167) The re-chromed control (a) was dyed at 60"C for 1 hour and fixed at 600C. for another 30 minutes with 1 %formic acid. The other pieces (b) and (c), were dyed at 1000C for 1 hour and fixed at the same temperature for another 30 minutes with 1% formic acid. The pieces were then all dried in the same way and their perspiration fastnesses (SLF: Technologists & Chemists. The results shown below will indicate that there are considerable improvements in the properties of the leathers, dyed at 1000C after treatments with pyromellitic acid.

Effect ofhigh temperature dyeing on the Fastness Properties ofDyed Leather Staining ofFlesh Side (SLF: O) Cotton Wool Treatments Treatments Dyeing temperature (a) (b) (c) (a) (b) (c) DYES @60 C @100 C @100 C @60 C @100 C @100 C i) 2%Airedale Black 2BG200 (C.I. Acid Black 1) 1 1 1 1 1 1 ii) 2%Airedale Black FB (C.I. Direct Black 160) 1-2 3 2-3 2 3 3 iii) 2%Airedale Orange AGD125 (C.I.Direct Orange 34) 1 2-3 2-3 2 2-3 2-3 iv) 2%AiredaleBrown 2DS (C.I. Acid Brown 167) 1-2 3 2-3 1 2-3 2 Rub Fastness (SLF:5) Dry at Wet at 512 rev. 16rev.

Treatments Treatments Dyeing temperature (a) (b) (c) (a) (b) (c) DYES @60 C @100 C @100 C @60 C @100 C @100 C i) 2%Airedale Black 2BG200 (C.I. Acid Black 1) 1-2 3 3-4 1 4-5 4-5 ii) 2%Airedale Black FB (C.I. DirectBlack 160) 1-2 2 2-3 1-2 2-3 2-3 iii) 2%Airedale Orange AGD125 (C.I. Direct Orange 34) 2 3 2-3 2-3 4-5 4-5 iv) 2%Airedale Brown 2DS (C.I. Acid Brown 167) 1 2-3 2-3 1-2 4-5 4 EXAMPLE 3 One full-chrome sheepskin was cut into 4 quarters.One quater was re-chromed with 10% commercial liquor (11% Cry03, 33 basicity) for an hour and then basified to a bath pH 3.8 with sodium bi-carbonate over half an hour. The second, third and fourth quarters were treated first with 0.5 % 1 % and 1.5 % of Product I (described in example 2) respectively for 30 minutes and then re-chromed with 10% commercial chrome liquor (11% Cr203, 33% basicity) following the same procedure as was employed for the first quarter. The 4 quarters were then neutralized, fatliquored and crusted out using conventional processes. After buffing, a number of small pieces were cut from the 4 quarters.They were' then wet back with ammonia and dyed at 100"C for 1 hour with the following dyes and fixed at the same temperature with 1 %formic acid for a further 30 minutes: 2 %Airedale Rubine 2BLLD (C. I. Direct Red 83) ii 2%Airedale Brown DS (C. I. Acid Brown 73) ill 2%Airedale Scarlet 5BM (C. I. Acid Red 89) iv 2%Airedale Orange POS (C. I. Acid Orange 28) vd 2%Airedale Yellow 3GM (C. I. Acid Yellow 42) vi) 2%Airedale Brown RGL (C. I. Acid Brown 383) The area of the pieces were measured before and after dyeing at 100 C and the quality was assessed.All the untreated control pieces became shrunken whereas the pieces treated with pyromellitic acid gave uniform shades of dyeing and the leather in all cases remained supple and soft. There was slight area loss for pieces treated with 0.5% Product 1, but for all other treatments with higher percentages of Product 1, no area losses could be detected.

EXAMPLE 4 One full-chrome sheepskin was cut into two sides along the backbone. One side was re-chromed with 10% commercial chrome liquor (11% Cr2O3, 33% basicity) for an hour and then basified to a bath pH 3.8 with sodium bi-carbonate over half an hour. The other side was treated with 2% Product I (described in example 2) for 30 minutes and then re-chromed following the same procedure as was employed for the first side. The two sides were then neutralized, fatliquored and crusted out using conventional processes. After buffing, three matched pairs of pieces (i.e. from similar location - 6" x 4") were cut from the two sides and wet back with ammonia for 2 hours. They were then dyed with the following dyes: a) 2 % Metachrome Brown BR (C.I. Mordant Brown 4) b) 2%Metachrome Brown B (C.I.Mordant Brown 48) c) 2 % Durochrome Red ER (C.I. Mordant Red 7) first at 60"C for 30 minutes, partly fixed with 1% formic acid for 15 minutes and then the bath temperature raised to 1000C. 1.5% sodium dichromate was added to the dye bath and allowed to react for 40 minutes and then fixed with further 1% formic acid for 20 minutes maintaining the temperature at 100 C. The pieces were then finished in the normal manner.

All the three control pieces suffered severe shrinkage but the treated pieces gave uniform dyeings. Metachrome Brown B on chrome mordanting gave orange-brown tone, Metachrome Brown BR gave a paler brown shade and Durochrome Red ER gave a deeper and brighter red shade, blues - nearer to Bordeaux). It was clear that many of the textile mordant dyes currently available could be applied to leather treated by the process of the invention at temperatures about 100"C.

EXAMPLE 5 Wet blue side leather (1.1 mm) and wet blue sheepskin were taken and pieces were cut and allotted at random for the following treatments: a) Re-chromed with 10%chrome liquor (11 %Cr2O3, 50%basicity) for an hour.

5%pyromellitic dianhydride for an hour.

c) 5 pyromellitic dianhydride for an hour and then re-chromed as in (a) d) 5% trimesic acid for an hour.

e) 5 %trimesic acid for an hour + re-chromed as in (a) All the pieces were then washed, set and their areas measured with a fixed arm planimeter.

They were then boiled in water for 30 minutes. At the end of this period they were taken out and their area measured again. The resulting area losses obtained are given below: Treatments Average Area Losses (percent) Sides Sheepskin (a) 16% 9.4 % (b) 0.78% 0.58% (c) NIL 0.56% (d) NIL NIL (e) 1.36% 0.55% The untreated control became stiff and horny whereas leather treated with the benzene polycarboxylic acid alone or in combination with chrome remained soft and flexible. Two pieces of sheepskin from each of the treatments were taken, neutralized with 2% sodium bi-carbonate and then dyed at 100"C with 1%Airedale Yellow FY (C. I. Acid Yellow 83) for 30 minutes and then fixed at the same temperature with 1% formic acid for another 20 minutes. The area of the pieces was measured before and after dyeing with a planimeter - the results of which are given below: Treatments Area (sq. hi.) Before After Area Average Dyeing Dyeing Loss Area Loss (percent) (percent) (a) 27.65 25.55 7.60 8.13 29.00 26.49 8.66 (b) 29.00 29.00 NIL NIL 29.60 29.60 NIL (c) 29.10 29.00 0.34 31.20 31.25 0.16 (d) 28.25 28.25 NIL NIL 29.00 29.05 0.17 (e) 27.40 27.40 NIL 0.51 28.35 28.65 1.05 These showed that there were practically no area losses for those pieces treated with the benzene polycarboxylic acids.

EXAMPLE 6 One pickled sheepskin was taken and chrome tanned with 20% commercial chrome liquor (11 Cr2O3, 33%basicity) for 4 hours. After horsing, the skin was treated with Product I (as described in Example 2) for 30 minutes and re-chromed with 10% chrome liquor (11% Cr203, 33% basicity) and basified to the bath pH of 3.9 - 4.0 following normal commercial practice. The skin after aging was neutralized and fatliquored with 4%sulphated sperm oil for 40 minutes, washed and set out in the setting machine. The skin was then printed using a migration transfer printing process in which the wet skin was placed in a plating press with a sheet of paper carrying a printed design covering the grain face of the skin. This paper carried the design printed with inks based on dyes having affinity for the leather (e.g. acid, direct or reactive dyes).During the normal heat treatment in the plating press, the design becomes transferred and fixed onto the leather. The design was clearly defined and the area yield and softness quality of the leather was unaffected by the treatment.

WHAT WE CLAIM IS:- 1. A process for the further treatment of chrome-tanned leather by contacting the chrome-tanned leather with an aqueous solution of up to 54b(based on the shaved weight of leather) of a polycarboxylic acid of benzene containing 3 or more carboxylic acid groups, a water-soluble salt thereof or an anhydride thereof.

2. A process as claimed in claim 1, in which the chrome-tanned leather is contacted with 2 to 4% (based on the shaved weight of the leather) of a polycarboxylic acid of benzene containing 3 or more carboxylic acid groups, a water soluble salt thereof or an anhydride thereof.

3. A process as claimed in claim 1 or 2, in which the polycarboxylic acid, its water-soluble salt or anhydride is applied to the chrome-tanned leather in an aqueous system at temperatures from 0 C to 60"C for up to 4 hours.

4. A process as claimed in claim 3, in which the treatment is at a temperatures of 35 to 50"C.

5. A process as claimed in claim 3 or 4, in which the treatment is for from 30 to 90 minutes.

6. A process for the further treatment of chrome-tanned leather substantially as hereinbefore described in any one of the foregoing examples.

7. Chrome-leather treated in accordance with a process as claimed in any one of the preceding claims.

8. A process for the dyeing or printing of leather as claimed in claim 7, which is carried out at a temperature of up to 105 C.

9. A process as claimed in claim 8 substantially as hereinbefore described in any one of the foregoing Examples.

10. Chrome-tanned leather, whenever treated in accordance with the process as claimed

Claims (1)

1. in claim 8 or 9.