The present invention relates to a process for the production of leather intended for making uppers of footwears as well as to the prod¬ ucts thereof. More particularly, the present invention relates to a proc¬ ess for treating wool-bearing sheep skins in order to obtain punctured or pierced leather having the compactness and strength features which are needed to employ the same for making footwear uppers having wool on their inner surface, said uppers being intended for footwears to be worn during the spring-summer period- Such process distinguishes with respect to the traditional opera¬ tions performed on wool-bearing sheep skins by the operations of treat¬ ing said skins with acrylic resins of various compositions, respective¬ ly after the retanning and the puncturing steps.

Footwears are known at the present time which are suitable for hot months, more particularly for summertime, and employ pierced or punctured uppers obtained from calfskin and unlined on their inside, which uppers have the compactness and strength features required for that specific em¬ ployment.

However, such leather products show the drawback of being poorly hygienic because of the presence of the holes as well as of being quite uncomfortable as regards friction that inevitably arises between the inner surface of the upper and the skin of the foot and the unsatisfying heat exchange between the outside and the inside,said heat exchange being nec¬ essary for keeping in a reliable way the optimal temperature inside the footwear.

Otherwise, the solutions suggested in the prior art for leather in¬ tended for making foowears to be worn in summer involved generally the use

of materials, such as cloth,which are capable of assuring perspiration, but such materials certainly cannot be suggested for a long lasting footwear which does not undergo a rapid deterioration because of the action of weather, of impacts or of other external stresses, and so on.

Thus, the need is clearly evident for leather intended to make footwear uppers for the hot season, which uppers though provided with punctures or holes do not show the drawbacks mentioned above and allow in addition a footwear to be realized having the desired features of strength, durability and comfort.

In order to meet such requirement, the present invention suggests the employment, as the raw material for making uppers of summer foot¬ wears of punctured or pierced hides obtained from wool-bearing sheep skins, which are capable because of the presence of a wool layer on their inside surface to form a coating that is suitable because of its very nature to keep a constant inner temperature as well as to assure the circulation of air so avoiding overheating of feet and hence the sweating of the same, and, because of its intrinsic antistatic charac¬ ter, to reduce the introduction of dust. Moreover, the leather sugge¬ sted according to the present invention has the characteristic property of giving rise to no compression areas localized at any part of the foot so that a uniform comfort is assured and the leather in question final¬ ly shows advantageously suitable as a stimulator of the peripheral cir¬ culation of blood and useful as an agent capable of absorbing the elec¬ trostatic energy built up in the body.

However, in order to exploit a raw material consisting of wool- bearing sheep skins, it is impossible to leave some of its original fea¬ tures out of consideration, such as for instance the characteristic of having a quite open fibrous texture because of the large amount of hair and also the presence of very short fibers that make such material un¬ suitable per se for use as uppers for footwears.

As a consequence, in order to allow a pierced or punctured leath¬ er product suitable for spring-summer foowears to be realized starting from wool-bearing sheep skins, the present invention suggests to per¬ form acrylic resin treatment operations at the end of the retanning step and after the puncturing or piercing step.

Indeed by means of such operations, the double object is obtained of: a) giving the skins a higher compactness and strength so that,the skin can be next punctured or pierced with no risks of tearing the same and the upper can be made by adapting the same to the desired model; b) increasing the strength of the skin at the points corresponding to the inner surfaces of the holes so as to avoid the dilation of the same and the tearing of the skin as much as possible at the points cor¬ responding to said surfaces during wear.

As already mentioned above, the basis operations of the process according to the present invention consist in the application and the successive polymerization, in two successive steps, of acrylic resins inside the fibrous texture of the skin and at points corresponding to the inner surfaces of the holes or punctures during a tanning treatment with retanning and finishing according to the procedure of the traditional type.

Substantially such operations are carried out in the final part of the retanning operation and after the puncturing or piercing operation. The traditional flowsheet of treatment of the skins normally provides different steps of working in a bath as well as different steps of dry working.

More precisely, the traditional work performed in a bath proceeds according to the following successive operational steps:

a) the soaking step wherein hides are deprived of the organic re¬ sidual matter and blood and are softened, in order to avoid the need for

successive working of the fibers of the grain, by means of a bath that is made up of cool water and a surface active agent such as FORYLL BB (a mixture of imbibition agents, both anionic and non ionic, commer¬ cially available from the Henkel Company), the hides being then taken again to their natural concentration of water during the action of an enzyme product (an enzyme based product obtained from pancreatic bac¬ teria) such as REVERDASE 120 (Rohne Poulenc); b) the fleshing step wherein the shreds of flesh and the lumps of fat remaining after the skinning operation are removed, the subcutaneous layer being also removed so that the tanning products are allowed to penetrate the hide in a more uniform and rapid way; c) the washing step wherein the remaining dirt and a part of the natural fats which are present are removed from the hides, the natural fats remaining after this step becoming distributed in a more uniform way; this step being performed employing preferably emulsified perchlo- roethylene which speeds the treatment up; d) the pickling step which represents the step of transition from the biological to the anabiological state, in which operation hides are prepared to be chrome tanned by making them more suitable to be passed through by chromium salts; e) the tanning step wherein the traditional treatment with a chromium salt is performed (basic chromium sulfate, pH 2.8) so as to obtain hides which are both soft and sufficiently compact and poorly e- lastic, and capable of allowing perspiration to occur; f) the acid removal step, wherein after the tanning maturation period with about 48 hours rest on the beam, the hydrolyzable acid bound to the protein substance is neutralized (as such acid causes non-uniform dyeing) by means of a compound consisting of a mixture of buffer salts exerting a neutralizing action (for instance, the CORATIL ND available from the Henkel); g) the retanning step wherein the hides are given more strength

and body, as well as a better adaptability to fluffing, and so on.

The dry working of the traditional type is based on the contra¬ ry on the operational steps of finishing, puncturing or piercing and the successive finishing.

According to the present invention, such working steps become integrated with the two steps already mentioned above in which the treatment with acrylic resins is performed.

More particularly, during the retanning step and, more precisely, in the final part of the retanning operation, in order to obtain the strengthening of the fibrous structure recourse is made to the employ¬ ment of an acrylic type resin, more precisely to an acrylic ester which, when is incorporated in the fibers and becomes polymerized causes the fiber lattice to become thicker so as to give the hides, in addition to a higher compactness and strength, also the strength required for the successive piercing or puncturing operation.

The second operation which is characteristic of the process ac¬ cording to the present invention is performed during the dry working, after the piercing or puncturing step and it consists in treating the exposed surface of the hide, inside the holes, with an acrylic type resin which is made up of a mixture of an acrylic acid and an acrylic ester in order to increase the surface strength of the hide at the points corresponding to the inner walls of the holes, so as to avoid as much as possible the risk of dilating and tearing the hide during employment.

Accordingly, it is a specific object of the present invention a process for the production of leather intended for making uppers of footwears to be worn during the spring-summer period, said process being characterized in that after the bath working of the sheep skins, said working comprising the steps of soaking, fleshing, washing, pick-

ling, tanning, acid removal and retanning, skins are treated with an acrylic ester based resin in water solution, which resin is caused to polymerize so that the original fiber lattice becomes thicker and, during the dry working which consists in a first finishing step, a step in which skins are pierced or punctured, and a second finishing step, a further treatment is carried out with a resin base on acrylic acid and an acrylic ester in a water solution, which resin is poly¬ merized at the points corresponding to the inner surfaces of the holes.

The choice of the type of acrylic polymer suggested in the pres¬ ent invention for the final phase of the retanning operation shows in¬ teresting and innovative if a comparison is made with resin of the melamine type, or of the ureic, dicyandiamide, polyurethane and oleo- maleic types which are traditionally employed for that operation.

Indeed, it is well known that some of said resins and more par¬ ticularly the polyurethane and oleomaleic resins, which are the most commonly employed, do not succeed in giving the hides a sufficient degree of compactness and strength.

The melamine and the ureic resins also have to be excluded because of the same reason, though such resins show the advantage of giving the hides quite good properties of feel and softness.

The resins of the dicyandiamide type, that on the contrary could give the desired properties of strength, are unsuitable to satisfy the objects of the present invention as they spoil at a remarkable extent the characteristics of the chrome tanning step and, above all the adapta¬ bility of the hides to the dyeing step.

The suggestion of the present invention consisting in the employ¬ ment of acrylic resins in the form of water solutions and not in the form of water dispersions aims at obtaining a better and fuller penetra¬ tion into the hide instead of obtaining just a surface deposition which

might cause the product to become excessively hard, and, in addition, such suggestion allows the yield of the anionic dyes for leather em¬ ployed to be increased reliably.

In the process according to the present invention, the acrylic ester polymeric compound is added to a neutralization bath consisting of water at 50°C and of an acid removal agent (for instance the CORA- TIL ND mentioned above), in which bath the hides have been dipped and adjusted to a pH of about 6.

It is interesting to observe that the employment of the neutral¬ izing bath suggested according to the present invention, in addition to the effect of allowing the chromium to be fixed, also allows the acrylic ester polymeric compound employed in water solution to pene¬ trate effectively, for instance ICATAN 38 of the leap Company.

The acrylic ester resin is added preferably to the neutralization bath after about 1 hour, after the neutralization has occurred com¬ pletely, at the concentration of 7 g/1, in order to give the possibil- ility of penetration into the hide fibers at a larger extent at the points where the hide itself is less strong and, more precisely, in the side parts where the structure is less relaxed and the fibers are longer.

Again according to the present invention the acrylic ester resin after a period ranging from 30 minutes to 2 hours, when the resin it¬ self has completely gone into the hide, is caused to polymerze first with a slight addition of formic acid, so that the resin becomes bound to the fibers of the hide, and next it is caused to polymerize a second time in the dry state direct on the hides which now are completely dry,

2 under a pressure of 20 kg/cm and at a temperature of about 100-120°C for a period of 4-8 seconds.

After the piercing step of the wool-bearing hide, the piercing op¬ eration being performed by means of a press having a plate bearing small

punches, the treatment with a resin of acrylic acid and an acrylic ester is carried out according to the procedure disclosed above. Preferably said treatment is performed by dipping the pierced hide into a water bath at 50-60°C in which a prepolymerized resin of acrylic acid and acrylic ester has been introduced (for example, DRASIL-ANG available from the Henkel Company) at the concentration of about 4-6 g/1 and making the resin to polymerize definitively with the aid of the addition of formic acid for a period of about 30-45 minutes at a temperature of about 60°C.

Thus, the resin becomes deposited on the surface of the pierced hide at the points corresponding to the inner walls of the holes, where the resin itself becomes absorbed by the fibers uncovered as an effect of the piercing step, so that the advantageous effect, al¬ ready mentioned above, of the increase in the surface strength of the hide is obtained.

The object of the present invention concerns also the hides ob¬ tained by means of the process mentioned above.

The present invention will be disclosed in the following just for exemplification and not for limitative purposes with reference to the enclosed drawings wherein:

Figure 1 is a block diagram of the process according to the pres¬ ent invention, and

Figure 2 is a schematic perspective view of a shoe realized em¬ ploying leather obtained according to the present invention.

With particular reference to Figure 1, it is possible to observe the various operational steps for the treatment of a wool-bearing sheep skin, such steps being devided into the group A wherein the steps are collected which are characteristic of the bath working, and the group B wherein the steps are collected which are characteristic of the dry

working. The distinctive steps of the inventive teaching consist in two operations in which the treatment with acrylic resin is preformed, such .operations being inserted downstream the group A and after the piercing step of the group B.

In the group A, it is possible to distinguish a biological phase of the treatment, comprising the soaking step, the fleshing and the washing step, a transition step consisting in the pickling operation and an anabiological step comprising the tanning, acid removal and re¬ tanning operations.

The dry working (B) comprises the finishing, piercing, treatment with an acrylic polymeric compound which is a feature of the invention, and the successive finishing step.

More particularly, the technology illustrated above and charac¬ teristic of the present invention can be summarized as follows: a) a stock of sheep raw hides bearing wool is dipped into a cold water bath (one hide for each volume of 20 1 of water), said bath con¬ taining FORYLL BB, a surface active agent commercially available from the Henkel Company, at the concentration of 1 g/1, and the whole bath is left standing overnight, and in the morning it is next washed with tap running water till water comes out clean, then FORYLL BB (1 g/1) and REVERDASE 120 (0.2 g/1) are added, and the hides are left in the bath for 48 hours (the soaking step); b) after the fleshing step, a bath is prepared consisting of water at 35-38°C and of 1.5 g/1 of perchloroethylene (as the solvent) and 3 g/1 of FORYLL BB (the surface active agent), and the hides are left dipped in such bath at the proportion of one hide for each 20 1; then, the hides are washed with running water; c) a cold water bath is prepared with addition of 40 g/1 of salt (about 4°Be) and the hides are left in such bath in the proportion of

one hide for each 20 1 of the bath for 30 minutes; then, 2.5 g/1 of an organic acid is added (for instance BASCAF F of the BASF Company) and the bath is left standing for 2 hours, adding next 3 g/1 of formic acid and keeping the hides in the bath for 2-3 hours at pH 2.8 (the pickling step). Such pickling operation aims at preparing ^' the hides to the chrome tanning step, making them more suitable to be passed through rapidly by the chromium salts which as a result of the acid character of the bath become less reactive so that consequently their penetration is more uniform. The addition of salt is necessary to avoid the swelling of the hides as an effect of the acid present; d) said hides are then treated as follows (the tanning step) : 2 hours in a bath of cold water (one hide for each 20 1) contain¬ ing liquid chromium salt, the GRASSAN DHS commercially available form the Henkel Company is added in the proportion of 1.6 g/1, the bath is kept standing for 1 hour, then IMPLENAL AP commercially available from the BASF Company is added and the hides are kept in the bath for an additional hour, and finally 10 g/1 of liquid chromium salt is added keeping the hides in said bath for 2 or 3 hours; finally, 1 g/1 of sodium carbonate and 1 g/1 of sodium bicarbonate are added, keeping the hides dipped in the bath for 3-4 hours; next the hides are spread ^" out on a beam.

The procedure carried out in that way allows leather to be pre¬ pared suitable for making uppers of footwears as hides are obtained that are well tanned having a temperature Tg of about 90°C, and that are soft, with a rubber-like feel and sufficiently compact and poorly elastic in addition to be able to allow perspiration to occur freely.

Indeed, it can be observed that, in addition to the basic chromium sulfate added at a pH of about 2.8 which makes a uniform penetration easier, also a synthetic sulfite fat which is stable to electrolytes (GRASSAN DHS) as well as a masking agent (IMPLENAL AP) which shows a

filling and stabilizing action of the chrome tanning are added. The last addition of an alkaline compound in the final step serves the purpose of making the chromium compound molecule larger and of fixing the same to the hide between its fibers so as to obtain a well tanned hide that shows strong and firm; e) in the acid removal step that is carried out after the matu¬ ration of the tanned hides by a rest period of about 48 hours on a beam, a bath of water at 45°C is employed, in which bath said hides are dipped (at the proportion of one hide for each 20 1 of water); then, 2 g/1 of ' CORATIL ND is added, the treatment being performed for 1 hour, then 3 g/1 of GRASSAN DHS is added, the treatment being carried out for an ad¬ ditional hour; f) the retanning step is finished, after carrying out the re¬ tanning step according to the traditional procedure, by inserting a treatment with an acrylic resin, such treatment being a characteristic feature of the present invention; as a matter of practice, hides are treated in a bath of water at 45-50°C (in the proportion of one hide for each 8 1 of water) containing 7.8 g/1 of CORATIL ND and 7 g/1 of ICATAN 38.

After the fluffing operations of the flesh side of the hides and after the dyeing of the hides by previously drying the same, the dry working step is performed; g) after the traditional finishing operation by previously ap¬ plying to the hide a water dispersion of an aliphatic polyurethane (Astacin Finish PUD) in the proportion of 80-100 g/hide at 110°C and 150 at . with the consequent formation of a polymeric coating, the puncturing or piercing operation is carried out. The second step which forms a characteristic feature of the present invention occurs by dip¬ ping the hide in a bath of water kept at 50-60°C containing DRASIL-ANG available from the Henkel Company, which is a prepolymerized methacrylic

resin in water solution, at the concentration of 4-6 g/1. Then, formic acid is added at 60°C over a period of 45 minutes and the polymeriza¬ tion is completed with the formation of a deposit on the surface of the pierced or punctured hide at points corresponding to the inner parts of the holes (h) and a further finishing (i) is performed.

Figure 2 shows an application of the leather obtained according to the present Invention for the production of the upper of a footwear; the woll layer 1 can be seen on the inner side of the footwear, while the velvet leather or the napped leather 2 provided with holes 3 can be seen on the outer part of the same.

The results are reported in the following of some standard tests carried out for the determination of the properties that are asked of leather intended for the production of uppers of footwears.

The tests performed on a specimen of ram skin after treating the same according to the present Invention (specimen A) and on a specimen (B) of an untreated ram skin, are as follows: ^• determination of the tensile and elongation strength; determination of the tear resistance; determination of the stretching and of the tensile strength of the grain of leather by the method of the ball; determination of wear resistance by repeated continuous folding of light leather and of their surface sizing.

Specimen A (treated according to the invention)

Standard procedure: UNI ISO 3376 - determination of the tensile and stretching strength.

The specimens opportunely conditioned undergo a tensile stress to failure on a tensile test device.

The tensile strength is obtained dividing the breaking or failure

2 load by the cross section area of the specimen and is given as N/mm .

The ultimate elongation is calculated by the difference between the initial length of the specimen and its ultimate length. Such difference is expressed as the percentage with respect to the initial length of the specimen.

Conditioning and testing: Normal atmosphere, Al type (20+_ 2°C 65+ R.H.).

- UNI ISO 2589 ^■ - leather - mechanical t thickness

Specimen Tensile strength ultimate (N/mm ) elongation, %

1 11.4 39.4 %

2 12.35 42.2 %

3 12.52 44.0 %

2

Average tensile strength = 12.1 N/mm .

Average ultimate elongation, % = 41.87 %

Standard procedure UNI ISO 3377 IUP 8 - determination of tearing strength.

A rectangular specimen in which a slit has been out of the pre¬ scribed shape is hooked on the protruding ends of a pair of specimen holders fastened between the clamps of a tensile test device. The max¬ imum elongation stress required for causing said specimen holders to separate is considered as the value of the tearing strength.

Conditioning and testing: Normal atmosphere, A2 type (23+2°C 50+ 5 % R.H.).

Pulling speed: 100 + 10 mm/minute Specimen Tearing strength (N/mm)

1 51.6

2 _ 44.5

3 42.3 Average tearing strength = 46.12 N/mm

Standard procedure UNI ISO 3379 - determination of stretching and of tensile strength of leather grain - the ball method.

A steel ball is pressed onto the central part of the flesh side of a leather specimen cut in the shape of a disk which is firmly fas¬ tened along its peripheral part.

The ball pressure and the consequent stretching of the specimen are recorded at the very moment when the leather grain becomes cracked and bursting of leather (possibly) occurs.

Conditioning and testing: normal atmosphere, A1 type (20+2°C 65+5 % U.R.)

Specimen 1 2 3 crack formation load (N) ^' 137.2 303.8 250.8 cracking strength (mm) 5.4 6.1 6.0 bursting strength (N) 470.4 678.1 527.2 stretching at bursting (mm) 7.2 9.3 8.6

Average crack formation load: 230.6 N

Average stretching at crack formation: 5.8 mm

Average bursting load: 558.6 N

Average stretching at bursting: 8.3 mm

Standard procedure: UNI 8433/TUP 20 - determination of repeated employment resistance (the employment consisting in continuous folding) of light leather and leather surface sizing.

Such determination is performed by clamping each specimen to the two terminals of the testing apparatus.

One of the two clamping terminals is kept stationary while the other one is caused to oscillate with 22.5° amplitude at the frequency of 100+5 cycles/minute, so carrying with itself the folded specimen.

- Conditioning and testing: normal atmosphere of A1 type (20°+2°C 65+5 % R.H.).

- 6 rectangular specimens, size 70 x 45 mm, obtained by shearing. Number of test cycles: 50,000 cycles.

The specimens at the end off the test do not show any cracks or any other deterioration marks.

Specimen B (the untreated specimen)

Standard procedure: UNI ISO 3376 - determination of the tensile and elongation strength.

The specimens undergo after conditioning a tensile stress till failure on a tensile strength test machine.

The tensile strength is calculated by dividing the ultimate ten¬ sile load by the cross section area of the specimen and is expressed

2 as N/mm .

The ultimate elongation is obtained by calculating the difference between the initial length of the specimen and its ultimate length. Such difference is expressed as the percentage with respect to the ini¬ tial length of the specimen.

Conditioning and testing: normal atmosphere of the A1 type (20 +_ 2°C 65 + 5 % R.H.).

- UNI ISO 2589 - leather - mechanical tests - determination of thickness

Specimens Tensile strength Ultimate elongation, %

(N/mm ² )

1 21.28 60.6 %

2 19.7 46.8 %

3 15.96 45.6 %

2 Average tensile strength = 18.97 N/mm

Average ultimate elongation, % - 51.0 %

Standard procedure UNI ISO 3377 IUP 8 - determination of bearing strength.

A rectangular specimen in which a slit has been cut of the pre-

scribed shape is hoocked on the protruding ends of a pair of specimen holders fastened between the clamps of a tensile test machine. The maximum elongation load required for causing the specimen holders to separate is considered as the tearing strength.

Conditioning and testing: normal atmosphere of the A2 type (23 + 2°C 50 + 5 % R.H.).

Pulling speed: 100 _+ mm/minute

Specimen Tearing strength (N/mm)

1 73.1

2 68.6

3 64.1 Average tearing strength = 68.6 N/mm

Standard procedure UNI ISO 3379 - determination of the stretching and of the tensile strength of leather grain - the ball procedure.

A steel ball is pressed against the central part of the flesh side of a leather specimen cut in the shape of a disk and firmly fastened along its peripheral part.

The pressure of the steel ball and the stretching of the specimen are recorded at the very moment when the leather grain becomes cracked and the bursting (possibly) occurs.

Conditioning and testing: normal atmosphere of the A1 type (20 +_ 2°C 65 + 5 % R.H.).

Specimen 1 2 3 crack formation load (N) - cracking strength (mm) - bursting load (N) 510.0 589.0 478.0 bursting stretch (mm) 10.5 9.2 9.0

Average bursting load: 528.6 N

Average bursting stretch: 9.5 mm

Standard procedure UNI 8433/IUP 20 - determination of the resist-

ance to repeated employment (consisting in repeated continuous folding) of light leather and leather surface sizing.

Such determination is carried out by fastening each specimen to the two clamps of the testing apparatus.

One of the two clamps is kept stationary whereas the other one is made to oscillate with amplitude of 22.5° at the frequency of 100 +_ 5 cycles/minute so carrying with itself the folded leather specimen.

- Conditioning and testing: normal atmosphere of the A1 type (20° + 2°C 65 + 5 % R.H.).

- 6 rectangular specimen of sizes 70 x 45 mm obtained by shearing

- Number of testing cycles 50,000 cycles.

The specimens at the end of the test do not show any cracks or other evidence of deterioration.

The following Table 1 summarizes the results of the technological tests mentioned above.

TABLE 1

Property Specimen A Specimen B Parameters Parameters

(treated) (untreated) of the ram of the sheep skiin sk:in

Average tensile 12.1 N/mm ² 18.97 N/mm ² 10 8 strength

Elongation 41.87 % 51 % 40 % 40

Tearing strength 46.13 68.6 40 40

Average bursting load 558.6 528.6 120 120

Burst stretching 8.3 9.5 7.5 8

Average cracking load 230.6 120 120

Average cracking stretching 5.8 __. 7.5 8

Bally test (50,000 flexions) good good

It can be observed from such table that the values obtained for the specimen A not only are better than those obtained with sheep skins intended for the production of uppers for footwears, but also are better than the results concerning ram skins.

The present invention has been disclosed with particular ref¬ erence to some specific embodiments of the same, but it is to be un¬ derstood that modifications and changes can be introduced in the in¬ vention without departing from the ^" spirit and scope of the same for which an exclusive right is claimed.