PT86161B - PROCESS OF PRODUCTION OF CABEDAL AIMED FOR THE MANUFACTURE OF THE UPPER PART OF CALCADO AND DERIVED PRODUCTS - Google Patents

Abstract

A process for the production of leather intended for making uppers of footwears to be worn in the spring-summer period, in which process, after the traditional bath working step and during the dry working, after the operation of puncturing or piercing the hides, two separate treatments are carried out with acrylic resins which, once polymerized, give the hides respectively on one hand a better compactness and strength and, on the other hand, as a result of coating the skin inner surface at the points corresponding to the punctured or holes, an increase in the surface strength of the skin so that the risks of dilation or stretching and tearing phenomena during wear are avoided. Leather obtained by such a process is intended specifically for making uppers of footwears to be worn during the spring-summer period.

Description

DESCRIPTIVE MBMORIA present invention describes a process for producing leather intended for the execution of the upper parts of the shoe as well as derived products. More particularly, the present invention describes a process for treating woolen sheep skins in order to obtain perforated or open skin having the necessary compactness and strength to be used in the manufacture of shoe upper parts with wool on the inner face, the aforementioned being upper parts (bodies) intended for footwear to be used during spring-summer.

The process in question differs from the traditional operations practiced on sheep skins with wool, in that these skins are treated with acrylic resins of various compositions, respectively after the retanning and drilling steps.

Presently, shoes that employ perforated or open bodies obtained from calf skin and without inner lining are considered suitable for the hot months, more particularly for the summer, bodies that have the required compactness and strength for this purpose.

However, these latter products have the disadvantage of being very unhygienic because of the presence of openings as well as being very uncomfortable with respect to the friction that inevitably takes place between the inner surface of the shoe body and the skin of the foot and the changes of foot. unsatisfactory heat between the outside and the inside, the heat exchanges being necessary to ensure the optimal temperature inside the shoe.

on the other hand, the solutions previously suggested for leather intended for the execution of footwear to be used in the summer generally involved the use of materials, such as fabrics, that are capable of ensuring perspiration, but that type of materials cannot certainly be suggested for long-lasting footwear that does not rapidly deteriorate due to the weather, impacts from other external aggressions, etc.

Thus, the need to have

944

Tg. 20,053 (MAF)

-3 leather for making shoe bodies for the hot season, bodies that one sees perforated or with openings do not show the above mentioned inconveniences and let in addition manufacture a shoe that has the desired quality of resistance, durability and comfort.

to achieve this fineness, the present invention suggests the use, as raw material to make bodies of summer shoes from perforated leathers or with openings obtained from sheepskins with wool that are capable, thanks to the presence of a layer of wool in the its internal face, to form a coating that is appropriate, by its very nature, to maintain a constant internal temperature as well as to ensure air circulation thus avoiding overheating of the feet and consequently the perspiration of them, and, because of their intrinsic static feature, to reduce the introduction of dust. In addition, the leather suggested in accordance with the present invention has the characteristic of not compressing any area of the foot, thus ensuring uniform comfort and, finally, the leather in question proves to be advantageous as a stimulator of peripheral circulation and as an agent capable of absorb the electrostatic energy accumulated in the body.

However, when it comes to using a raw material consisting of sheepskin with fur, it is impossible to fail to take into account some of its original limitations, such as for example the characteristic of having a very fibrous and open texture motivated by the large amount of hair and also the presence of very short fibers that make this material unsuitable for use as shoe bodies.

Consequently, in order to make lambskins with wool a good starting point to arrive at a leather suitable for spring-summer shoes, perforated and open, the present invention suggests treatment operations with acrylic resin at the end of the retanning and after the drilling or opening cut phase.

Undoubtedly, through these operations the double objective of achieving:

a) give skins greater compactness and resistance to

94-4

Tg. 20,053 (MAF)

-4that the skin can be punctured or struck without risk of tearing and the body made adapting it to the desired model;

b) increase the resistance to the skin at the points corresponding to the internal surfaces of the holes (contours) in order to avoid their dilation and the tearing of the skin, as much as possible, at the points corresponding to the mentioned surfaces during use.

As already mentioned, the basic operations of the process, according to the present invention, consist of the application and successive polymerization, in two successive steps, of acrylic resins within the fibrous texture of the skin and at points corresponding to the internal surfaces of the holes or holes during tanning treatment with retanning and finishing according to the traditional process.

Most of the time, such operations are carried out at the end of the grooving and after the openings and drilling have been carried out. The traditional sequence of skin care usually comprises different stages of work in a bath as well as different stages of dry dressing.

More precisely, the traditional work carried out in a bath takes place with the following sequence:

a) the soaking step in which the skins are cleared of residual organic matter and blood and are softened, in order to avoid additional work with the grain fibers, by means of a cold water bath with an active surfactant such as FORYLL BB (a mixture of imbibition agents, both anionic and non-ionic, marketed by HENKEL Company), returning the skins to their natural water concentration during the action of an enzymatic product (an enzyme obtained from a pancreatic bacterium ) such as REVERDASE 120 (Rohne Poulenc);

b) scraping, in which the remains of meat and fat that remained after skinning are then removed and the subcutaneous layer is also removed so that the tanning products can penetrate the skin more quickly and evenly;

c) washing phase, in which remaining dirt and

944

Tg. 20,053 (MAF)

-5a part of the natural fats that are present are removed from the skins, redistributing the remaining natural fats more evenly after this stage; in this phase, emulsified perchlorethylene is preferably used, which speeds up the treatment;

(pickling)

d) the piclagem phase / which represents the transition phase from the biological to the anabiological state, in which the skins are prepared for tanning the chromium making them more suitable to be crossed by the chromium salts;

e) tanning phase in which the traditional treatment with a chromium salt is carried out (basic sulfate and chromium, pH 2.8) in order to obtain skins that are both soft and sufficiently compact and weakly elastic and capable of leaving stop sweating;

f) phase of acid removal, in which after the tanning maturation period of about 48 hours in the tank, the hydrolyzable bond of the acid to the protein substance is neutralized (as this acid causes non-uniform coloring) by means of a compound consisting of a mixture of buffer salts that exert a neutralizing action (for example, CORATIL ND marketed by Henkel);

g) retanning phase in which the skins are made stronger and fuller as well as better adapted to softening, etc.

Dry work of the traditional type is based, on the contrary, on the finishing steps, cutting openings or drilling and subsequent finishing.

According to the present invention, these work phases are integrated into the phases already mentioned above in which the treatment with acrylic resins is carried out.

More particularly, during the retanning phase and, more precisely, in the final part of the retanning operation, in order to obtain the reinforcement of the fibrous structure, an acrylic type resin is used, more precisely an acrylic ester that when it is incorporated into the fibers and polymerizes it causes the thickening of the fiber web in order to give it to the skins, in addition to

944 “

Tg. 20,053 (MAF)

-6 greater compactness and strength, also the strength required for the subsequent drilling and cutting of openings.

The second operation that is characteristic of the process according to the present invention is carried out during dry work, after drilling and cutting openings and consists of treating the exposed surface of the skin inside the openings, with an acrylic type resin. which is prepared with a mixture of an acrylic acid and an acrylic ester in order to increase the resistance of the skin surface at the points corresponding to the inner walls of the holes, thus avoiding as much as possible the risk of dilation and tearing the skin during its use.

Therefore, it is a specific objective of the present invention to establish a leather production process suitable for making shoe bodies to be used during the spring-summer period, the aforementioned process being characterized by, after the bathing of the sheepskins, the aforementioned work comprising the phases of demolition, fleshing, washing, recycling, tanning, acid removal and retanning, the skins being treated with a resin based on an acrylic ester in aqueous solution, a resin that is polymerized so that the original fiber web is thicker and, during dry work consisting of a first finishing step in which the skins are drilled and cut openings, and a second finishing step, in which a further treatment is carried out with a resin based on an acrylic acid and in a acrylic ester in aqueous solution, resin that is polymerized at the points corresponding to the internal surfaces of the holes.

The choice of the type of acrylic polymer suggested in the present invention for the final stage of the retanning operation is of interest and innovation if we compare it with resins of the melamine type, or of the ureic, dicyandiamide, polyurethane and oleomaleic types that are traditionally employed for this operation.

Undoubtedly, it is well known that some of the aforementioned resins, and more particularly the polyurethane and oleomaleic resins, which are the most commonly used, fail to give the skins a sufficient degree of compactness and strength.

944

Tg. 20,053 (MàF)

Melamine and urea resins must also be excluded for the same reason, although such resins show the advantage of giving the skins very good qualities of touch and lightness.

Resins of the dicyandiamide type, which on the contrary can confer the desired resistance properties, are unsuitable to meet the objectives of this invention because they spoil the characteristics of the tanning phase to chromium to a considerable extent and, above all, the adaptation of skins to the dye stage.

The suggestion of the present invention is to use acrylic resins in the form of aqueous solutions and not in the form of aqueous dispersions with the aim of obtaining a better and more complete penetration into the skin instead of obtaining only a deposition on the surface which can lead to it is excessively hard and, in addition, the same suggestion allows to increase the yield of anionic dyes used for leather.

In the process according to the present invention, the acrylic ester polymer compound is added to a neutralizing bath consisting of water at 50 ° C and an acid-removing agent (for example, CORATIL ND mentioned above), bath in which the skins are dipped and the pH adjusted to about 6.

It is interesting to note that the use of the neutralizing bath suggested according to the present invention, in addition to the effect of allowing the fixation of chromium, also allows the acrylic ester polymer compound used in aqueous solution to penetrate effectively, for example ICATAN 38 from Icap Company .

The acrylic ester resin is preferably added to neutralize the bath after about 1 h after complete neutralization has occurred, at a concentration of 7g / l in order to make it possible to penetrate the skin fibers to a great extent in the points where the skin itself is less strong and, more precisely, on the sides where the structure is less relaxed and the fibers are longer.

Again according to the present invention, the acrylic ester resin, after a period of between 3θ minutes and 2 hours, when the resin has completely penetrated the skin, is polymerized prior to 944 .. ί

Tg. 20,053 (MAF)

-8th with a slight addition of formic acid, thus keeping the resin bound to the fibers of the skin, and then curing for the second time in a dry state directly on skins that are now completely dry, under a pressure of 20 kg / / cm and at a temperature of about 100 - 120 C for 4-8 seconds.

After the piercing of the skin with wool, and the piercing is carried out by means of a press with a plate provided with small punches, the treatment is carried out with an acrylic acid resin and an acrylic ester according to the process described above. Preferably, said treatment is carried out by immersing the perforated skin in a water bath at 50-6 ° C in which a prepolymerized resin of acrylic acid and acrylic ester (for example, DRASIL-ANG marketed by Henkel Company) was introduced into the concentration at about 4-6 g / 1 and causing the resin to polymerize definitively with the help of the addition of formic acid for about 3θ “45 minutes at a temperature of about 60 ° C.

Thus, the resin is deposited on the surface of the perforated skin at points corresponding to the interior of the hole walls, where the resin itself is absorbed by the exposed fibers as a result of the drilling phase, thus showing the advantageous effect, already above mentioned, of the increase of the superficial resistance of the skin.

the present invention will be developed below precisely for example and not for limiting purposes with reference to the drawings included here:

Figure 1 is a condensed diagram of the process according to the present invention, and

Figure 2 is a schematic perspective view of a shoe made using leather obtained in accordance with the present invention.

With particular reference to figure 1, it is possible to observe several operational steps for the treatment of a sheepskin provided with fur, the said steps being grouped so as to constitute group A with the characteristic of bathing and group B with the dry work characteristic.

944

Tg. 20,053 (MA.F)

The distinct steps of the process of the invention consist of two operations in which the treatment with acrylic resin is carried out, these operations being inserted into the downstream of group A and after the drilling phase of group B.

In group A, it is possible to distinguish a biological phase of the treatment, comprising the soak phase, the stripping and washing phases, a transition phase consisting of the picling operation and an anabolic phase comprising the tanning, acid removal and retanning .

Dry-work (B) comprises finishing, drilling, treatment with an acrylic polymeric compound which is a characteristic of the invention, and the subsequent final finishing phase.

More meticulously, the technology set out above and characteristic of the present invention can be summarized as follows:

a) a batch of sheepskins preserving the wool and raw is dipped in a cold water bath (one skin for each volume of 20 l of water), containing FORYLL BB, a commercially available surfactant from the Henkel Company, at concentration of 1 g / 1, and the set left to stand overnight; the next morning, wash with tap water until the water is clean, add FORYLL BB (lg / 1) and REVERDASE 120 (0.2 g / 1) and the skins stay in the new bath for 48 h (demolition phase);

b) after the stripping phase, a bath consisting of water at 35 “38 ° C and 1.5 g / 1 of perchlorethylene (as solvent) and 3 g / 1 d® FORYLL BB (surfactant) is prepared, and the skins are immersed in this last bath in the proportion of one skin for every 20 1; then, the skins are washed under running water;

c) a cold water bath follows, prepared with the addition of 40 g / 1 of salt (about 4 ^o Bé), where the skins are introduced in the proportion of one skin for every 20 l of bath for 30 minutes; then 2.5 g / 1 of an organic acid (eg BASCAF from BASF Company) is added and the bath is allowed to stand for 2 h, after which 3 g / 1 of formic acid are added and the skins are kept in the bath for 2 - 3 h at pH 2.8 (picling step). This picling operation aims to prepare the skins for the chromium tanning phase, making them more ra66 944

Tg. 20,053 (MAF)

-leptically permeable to 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 prevent the skin from swelling as a result of the presence of acid;

d) the skins are then treated as follows (tanning phase):

h in a cold water bath (one skin per 20 l) containing liquid chromium salt, the GRASSAN DHS marketed by Henkel Company is added in the proportion of 1.6 g / 1, the bath rests for 1 h, then added if IMPLENAL AP marketed by BASE Company and the skins stay in the bath for another 1 h; finally 10 g / 1 of liquid chromium salt are added, leaving the skins in the aforementioned bath for 2 or 3 h: finally, 1 g / 1 of sodium carbonate and 1 g / 1 of sodium bicarbonate are added, leaving if the skins soaked in the bath for 3-4 hours; then the skins are spread over an easel.

The process carried out in the manner described leads to an appropriate leather for making shoe bodies because the hides were well tanned having a Tg temperature of around 90 ° C, and are soft, with a touch like rubber and compact enough and inelastic in addition to being capable of allowing sweating to occur freely.

It can undoubtedly be observed that in addition to the basic chromium sulphate added at a pH of about 2.8 which makes uniform penetration easier, a synthetic sulphited fat that is electrolyte-stable (GRASSAN DHS) and a coating agent (IMPLENAL AP) which has a filling and stabilizing action by the chromium. The last addition of an alkaline compound in the final stage serves the purpose of increasing the molecules of the chromium compound and fixing them to the skin between its fibers in order to obtain a well-tanned skin that presents resistance and firmness;

e) in the phase of acid removal that is carried out after the maturation of the tanned skins for a rest period of about 48 h on an easel, a water bath at 45 ° C is used, a bath in which the aforementioned skins are dipped (in proportion to a skin

944

Tg. 20,053 (MAF)

for every 20 l of water); then, 2 g / 1 of GORATIL ND is added, the treatment being carried out for 1 h, then 3 g / 1 of GRASSAN DHS are added, continuing the treatment for an additional hour;

f) the retanning phase is finished, after the retanning step according to the traditional process, introducing a treatment with an acrylic resin, with this treatment having a characteristic of the present invention; in practical terms, the skins are treated in a water bath at 4 ^ - ^ 0 ° C (in the proportion of one skin for every 8 1 of water) containing 7.8 g / 1 of CORATIL ND and 7 g / 1 of ICATAN 38.

After the softening operations on the flesh side of the hides and after dyeing the hides with prior drying, the dry work phase is carried out;

g) after the traditional finishing operations, previously applying to the skin a water dispersion of an aliphatic polyurethane (Astacin Finish PUD) in the proportion of 80-160 g / skin at 110 ° C and 15o atm., with the consequent formation of a coating polymer, the cut-out and drilling operation is then carried out. The second phase that constitutes a characteristic of the present invention is accomplished by immersing the skin in a water bath maintained at 5θ - 60 C containing DRASIL-ANG sold by Henkel Company, which is a methacrylic resin prepolymerized in aqueous solution, in the concentration of 4 -6 g / 1. Then, formic acid is added to ÓG ^C G for 45 minutes and the polymerization is completed with the formation of a deposit on the surface of the skin with openings and perforations at the points corresponding to the internal parts of the holes (h) and proceed to a further finish (i).

Figure 2 illustrates an application of the leather obtained according to the present invention for the production of shoe bodies; the wool layer 1 can be seen inside the shoe, while softened leather or carded leather 2 with holes 3 can be seen on the outside of the shoe.

The results are described below in the standard tests carried out to determine the properties that are required for leather intended for the production of shoe bodies.

944

Tg. 20,053 (HAF)

The tests carried out on a sample of sheepskin after treatment of the same according to the present invention (sample A) and on a sample (B) of an untreated sheepskin, are as follows:

determination of resistance to tension and elongation determination of resistance to tearing;

determination of the stretch and the resistance to tension of the leather grain by the ball method;

determination of resistance to use by repeated and continuous use of light leather and its surface (surface sizing).

Sample A (treated according to the invention)

Standard process: UI7I ISO 3376 - determination of resistance to tension and stretching.

Timely conditioned samples are subjected to a strain and tension until they break, in a tension test apparatus.

The stress intensity is obtained by dividing the break or failure load by the area of the straight section of the sample and is expressed as N / mm.

final elongation is calculated by the difference between the initial length of the sample and its final length. This difference is expressed as a percentage of the initial sample length.

Conditioning and testing: normal atmosphere, type Al (20 + 2 ° C, 65 + 5 / HR)

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

Sample Voltage intensity Final stretch (N / mm ^) % 1 11.4 39.4% 2 12.35 42.2 / 3 12.52 44.0 /

P

Average stress intensity = 12.1 N / mm

Final average elongation, / = 41.87 /

Process for UNI ISO 3377 IUP 8 - determination of tear resistance.

944

Tg. 20,053 (MF)

A rectangular sample in which a slit of the stipulated size has been opened is attached to the protruding ends of a pair of sample holders connected between the hooks of a tension tester. The maximum elongation stress required to cause the sample fixers to move apart is considered to be the tear resistance value.

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

Traction speed 100 + 10 mm / min

Sample Tear resistance (N / mm ^)

151.6

244.5

342.3

Average tear strength = 46.12N / mm

UNI ISO 3379 standard process - determination of the stretch and intensity of the stretch tension of the leather grain ball method

A steel ball is pressed over the central part of the flesh side of a leather sample cut in the form of a disc that is firmly attached along its peripheral part.

The pressure of the ball and the consequent stretching of the sample are recorded at the exact moment when the grain of the leather becomes brittle and (possibly) the leather breaks.

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

Sample 1 2 3 load to break formation (Ν ') 137.2 303.8 250.8 breaking intensity (mm) 5.4 6.1 6.0 breaking load (N) 470.4 678.1 527.2 breakage stretch (mm) 7.2 9.3 8.6

Average load for breaking formation: 230.6 N Average stretch for breaking formation: 5.8 mm

Average breaking load: 55θ, 6 N

Average breakout stretch: 8.3 mm f

944

Tg. 20,053 (MF)

-14Standard process: UNI 8433 / TUP 20 - determination of resistance to repeated use (use consists of continuous folds) of light leather and of the surface to the leather.

This determination is carried out by attaching each sample to two test device terminals.

One of these two terminals is kept stationary while the other is oscillated with an amplitude of 22.5 ° at a frequency of 100 + 5 cycles / minute, carrying the doubled sample.

- Conuition and test: normal atmosphere of type Al (20 ° + 2 ° C, 65 + 5% H.R.).

- 6 rectangular samples, size 70 ^x 45 mm, obtained by cutting.

Number of test cycles: 50,000 cycles

The samples at the end of the test must not show any breaks or any other marks of deterioration.

Sample B (the untreated sample)

Process for; UNI IS0 3376 - determination of the intensity of tension and stretching.

The samples are subjected, after conditioning, to a tension effort until rupture in a machine and a tensile strength test.

The tensile strength is calculated by dividing the final tensile load by the area of the straight section of the sample and expressed in N / mm final elongation is obtained by calculating the difference between the initial length of the sample and its final length. This difference is expressed by the percentage in relation to the initial length of the sample.

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

- UNI IS0 25θ9 - leather - mechanical tests - determination

the thickness Samples Voltage intensity (N / mm ² ) Final elongation% 1 21.28 6th, 6% 2 19.7 46.8 3 15.96 45.6

i $ r

944

Tg. 20,053 (MÀF)

Γ

-15 Average stress intensity = 18.97 N / mm ^

Average final elongation,% = 51.0%

Standard process UNI ISO 3377 IUP 8 - determination of tear resistance.

A rectangular sample in which a crack of the prescribed shape has been cut is hooked on the protruding ends of a pair of sample holders fixed between the clamps of a tensile testing machine. The maximum stretching load required to cause the sample holders to move apart is considered to be the tear strength.

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

Traction speed: 100,000mm / minute

Sample Tear resistance (N / mm)

173.1

268.6

364.1

Average tear strength = 68.6 N / mm

UNI ISO 3379 standard process - determination of the stretch and tensile strength of the grain of the leather-ball process

A steel ball is pressed against the central part of the flesh side of a leather sample cut in the shape of a disc and firmly fixed along its peripheral part.

The pressure of the steel ball and the stretching of the sample are recorded at the precise moment when the grain of the leather becomes brittle and (possibly) rupture occurs.

Conditioning and testing: normal atmosphere of type A1 (20 + 2 ° C _? 65 + 5% RH)

Sample 1 2 3 break forming load (N) - - - breaking intensity (mm) - - - breaking load (N) 5io, o 589.0 478.0 breaking length (mm) io, 5 9.2 9.0

Average breaking load: 528.6 N Average breaking length: 9.5 mm

944

Tg. 20.053 (W)

-16 Standard process UNI 8433 / IUP 20-determination of resistance to repeated use (consisting of continuous and repeated folding) of light leather and the leather surface.

Such determination is carried out by fixing each sample with two clamps to the test apparatus.

One of the two clamps is stationary while the other is oscillated with the amplitude at 22.5 ° and the frequency at e 100 + 5 cycles / minute, thus carrying the folded leather sample with it.

- Conditioning and testing: normal Al-type atmosphere (20 ° + 2 ^C C, 65 + 5% RH).

- rectangular samples of size 70 x 45 mm obtained by cutting.

- Number of test cycles 50,000 cycles.

The samples at the end of the test do not show any evident breaks or other deterioration.

Table 1, below, summarizes the results of the technological tests mentioned above.

Table 1

properties Sample A (treated) Sample B (untreated) Sheepskin parameters Sheep skin parameters intensity average of tension 12.1 N / mm ² 18.97 N / mm ² 10 8 Stretching $ 41.87 51% 40% 40 Resistance to tear 46.13 68.6 40 40 Average load in disruption 558.6 523.6 120 120 Stretch in disruption o, 3 9.5 7.5 8 Average load in smash 230.6 120 120 Stretch medium break 5.8 - 7.5 8 Bally essay (50,000 push-ups) good good

944

Tg. 20,053 (MàF)

-17It can be seen from this table that the values obtained for sample A are not only better than those obtained with sheep skins for the production of shoe bodies, but they are also better than the results regarding sheep skins .

The present invention has been developed with particular reference to some specific arrangements of the same, but it should be understood that modifications and variations that can be introduced into the invention without departing from the spirit and purpose of the same are covered by the exclusive right of the claims.

Claims (5)

1 ^δ . - Leather preparation process for the manufacture of the upper part of the footwear to be used during the Spring and Summer period, characterized by the fact that, after the work of brook and sheepskin tanning with wool, this work comprises the operations of soaking, fleshing, washing, recycling, tanning, acid removal and retanning, the skins being treated with a resin based on an acrylic ester in aqueous solution, a resin that is polymerized in order to thicken the original fibrous structure and, during the drying consisting of a first finishing step, a perforation or perforation phase of the skin and a second finishing step, with an additional treatment, after the drilling operation, with a resin based on an acrylic acid and an acrylic ester in aqueous solution, said resin being polymerized at the points corresponding to the interior surfaces of the holes. 2®. - Process according to claim 1, characterized in that the polymeric acrylic ester is added to a neutralization bath consisting of water at 5θ ° 0 and an acid removal agent, bath in which the skins are dipped until reaching a pH of about 6. 3®. Process according to claim 2, characterized in that the acrylic ester resin is added to the neutralization bath, approximately one hour after the neutralization is completed, until a concentration of 7 g / 1 is obtained. 4®. Process according to claim 3, characterized in that, after a period of 30 minutes to 2 hours, when the resin itself has completely penetrated the skin, the acrylic ester resin is first polymerized by means of a small addition of acid formic so that the resin binds to the fibers of the skin, and then polymerizes a second time in the dry state, directly on dry skin, under a pressure of 20 kg / cm ^ and at a temperature of about 100- 120 ° C for 4 to 8 seconds. 5®. Process according to any of claims 1 to 4, characterized in that the treatment with an acid resin 66 944 Tg. 20,053 (MAF) -19 of acrylic and an acrylic ester is made by immersing the perforated skin in a water bath maintained at 50-60 ° C in which an acrylic acid and acrylic ester resin has been introduced after previous polymerization, its proportion being in the bath of about 4-6 g / 1 and then the definitive polymerization of said resin is carried out with the help of the addition of formic acid, for about 30 to 45 minutes at a temperature of about 60 ° G.