CH628571A5 - Process for manufacturing artificial leather having a protein content - Google Patents

Description

The object of the present invention is a process for manufacturing artificial leather from animal waste. These tanned artificial leathers have characteristics very similar to those of natural tanned leathers.

Various methods for the manufacture of artificial leather have also been known for a long time. These procedures can be divided into two main categories:

- on the one hand, processes which use only synthetic materials,

- on the other the processes which also use natural products, such as waste of natural tanned hides, or leather, and to which the process according to the invention is closer.

The processes of this second type have been the subject of various studies and improvements, all tending to bring the characteristics of the product obtained closer to the characteristics of the natural leathers.

In the past, we have mainly carried out a fine shredding of scraps of leather or tanned tannery waste, and then the mixing of this shredded material with natural or synthetic binders, to form a semi-dense mixture; a layer of this mixture was then formed which, when pressed and dried, formed the artificial leather sought.

In order to improve the mechanical characteristics of the products obtained with these processes - that is, on the one hand, the tear resistance, and on the other hand, the softness and other characteristics related to comfort - procedures have been more recently proposed (see example French patents No. 1 348 716 and USA No. 3 223 551, 3 285 775, 3 345 201) according to which a mass of finely ground leather fibers, kept in a non-colloidal aqueous suspension, is applied on fiber supports synthetic, by penetrating, with mechanical and chemical means, the single leather fibers, in a separate state, inside the support and providing to fix the fibers themselves on the synthetic fibers of the support, preferably through the use of binders, for example to base of dissolved «NYLON».

The procedure is very complex (both from a mechanical and a chemical-physical point of view) and is complicated - as well as severely limited in its application - by the need to use, as a starting material, leather fibers that have undergone a tanning process well defined in its parameters, and then proceed to grinding in equally well defined pH conditions: in fact, small variations both in pre-tanning and in grinding conditions can make the leather fibers unable to penetrate into the felt of synthetic fibers. The latter in turn must be prepared under conditions that are also limiting (non-hydrophilic fibers, density of defined structure, and others).

The problem of making the fibers of ground leather penetrate into the synthetic felt is evident, in all its difficulty, from German patent no. 1 930 523 or French patent no. 2 040 211 in which an attempt is made to remedy the aforementioned limiting conditions by spreading the ground leather paste on fabric or non-woven supports, and mechanically penetrating and binding the ground leather fibers within the synthetic fibers, by needling on the wet material. This system, however, generates significant plant engineering problems, having to operate wet on needle punching machines born and built to operate dry, and having to use special serrated stainless steel needles for this purpose, which are, among other things, relatively fragile.

A method has also been proposed, such as that described in French patent no. 2 105 639, according to which leather or possibly natural collagen is dissolved in more or less concentrated sulfuric acid5

I

15

20

25

30

35

40

45

50

55

60

65

3

628571

and the solution is mixed with solutions, always highly acidic, of NYLON or other altopolymer dissolved in concentrated hydrochloric acid. This polyamide-collagen solution is then applied on a cotton support. However, this type of process has the drawback that the extremely acid solution degrades the material which constitutes the support and the leather fibers themselves, so as to originate a material having modest physical characteristics. In fact, the action of these acids is so violent that the protein fibers give rise to a precipitate which, after drying, takes on a dry and fragile physical structure, or cornea, with no real possibility of practical use.

The object of the present invention is an artificial leather manufacturing process which allows to overcome the drawbacks of the above mentioned processes, allowing to obtain an artificial leather having excellent structural and mechanical characteristics, excellent softness, breathability and comfort in the use of the articles, and this through a considerable simplification of the single phases of the process itself and consequently with a clear reduction both of the plant costs and of the production costs themselves.

The object of the present invention is a process for manufacturing artificial leather from animal waste. This process is characterized in that it comprises the following steps:

(a) preparation of a colloidal solution of protein substance of collagenic origin by simply dissolving in untreated calcined tannery flesh in hot water, slaughtering waste or mixtures thereof;

(b) thoroughly imbibing a synthetic support having good porosity with said collagen solution and condensation and cross-linking of said collagen substance on the synthetic fibers of the support, by means of a simple action of cross-linking reagents and

(c) tanning of the so soaked support.

In this process, the soaked substrate can be tanned with tanning processes according to the tanning technique of natural leathers, for example using a solution of basic chromium sulphate in water.

Other characteristics and advantages of the process according to the present invention, as well as its fundamental differences with respect to the processes of the prior art, are however evident from the detailed description that follows.

As mentioned, for the preparation of the collagen solution [step a) of the procedure] - not already leather scraps or in general material that has already been tanned, as in the prior art - but waste of raw leather, flesh or even waste of slaughter. With this, on the one hand, there is the advantage of not being tied to any specific limiting condition with regard to pre-tanning or grinding, nor to dissolution processes in such drastic conditions and in an acidic environment that particular systems and supports must be used considerably. resistant; on the other hand, there is the advantage of being able to use a vastly greater quantity of the waste material coming from a slaughtered animal, compared to the waste coming exclusively from the tannery.

When choosing the support which must be soaked in the collagen solution, it will be sufficient to consider any fabric, or non-woven fabric, or felt, or other support that can be easily found on the market, and which has a sufficient porosity. In fact, according to the invention, the penetration of a material reduced in defined dimensions and in distinct fibers which, however small, are normally "filtered" by the support and retained on its surface, must not be guaranteed , which implies the need to resort to supports of particular structure or to complicated penetration techniques; on the other hand, the imbibition takes place very quickly and easily thanks to the "solution" state of the collagen substance, for example also by simple direct immersion of the support in the solution.

Therefore, when choosing the substrate, it should only be borne in mind that the fundamental characteristics that it must have are sufficient porosity and resistance to the chemicals used in the final tanning operations: for example, the substrate should not contain cellulosic fibers if it is tanned next will take place in an acidic environment for mineral acid.

In addition to the aforementioned ease of penertation in the support, the protein solution according to the present invention also has a great ease of crosslinking.

According to the present invention, the condensation and cross-linking of the protein substance on the synthetic support are in fact easily obtained thanks to the action of cross-linking reagents. As reagents, it is possible to use for example a solution containing from 20 to 30% of sulphate or chloride of an ME (II) and from 10 to 20% of sulfate or chloride of an ME (I), wherein ME (II) can be Mg and ME (I) can be Na. Alternatively, it is possible to use other reagents which can also simultaneously perform a pre-tanning action such as the synthetic tanning agents known on the market with the generic name of "syntans".

It is however very important to note how this condensation or coagulation and the cross-linking of the protein substance are in themselves completely sufficient to ensure the adhesion or the binding of the protein particles to the synthetic fibers of the support. Therefore, contrary to what occurs in the prior art, it is no longer absolutely necessary to use other synthetic binders, or adhesives, for this purpose.

Some considerations below highlight these circumstances even more, which constitute a truly important and original feature of the process according to the invention.

The dermal substance, i.e. the part of animal skin that is used for the manufacture of leather, essentially consists of a protein called collagen.

Collagen originates from the combination of simpler molecules, amino acids, of general formula

H2N — CHR — COOH which condense by eliminating water

I i

H2N — CHR — CCjOH HHN — CHR — COOH - »

- »H2N — CHR — CO — NH — CHR —- COOH

The groups -NH2 and -COOH (dissociated at the isoelectric point in the ions -NH3 © and -C009) and the ketoimidic group

-CO — NH, are the protein groups interested in tanning, that is, in the fixing of tanning reagents.

The ketoimidic group, however, has a particular and very important function; being able to assume an enolic structure by resonance

OR OH R

II I I!

—N — C — C—; = ± —N— = C C—

I I I

H H H

the ketoimidic group generates binding forces between adjacent molecules through the establishment of hydrogen bridges, generating a structure of the type

5

I

15

20

25

30

35

40

45

50

55

60

65

628571

4

0 HR H 0

H 0 HR H

• • •

0 H HR 0

.C. _, C

N N- ^

H HR 0 H

These bonding forces are responsible for the solidity of the structure in animal skin. In fact, it has been shown that the elimination of these hydrogen bridges - by means of neutral salts, such as, for example, CaCl2 - decreases the shrinkage temperature of the skin in water (shrinkage temperature) from 60 ° C to 20 ° C, since it is known that this contraction temperature is the measure of the structural stability of collagen expressed in terms of temperature (GD McLaughlin).

This said, it is understandable how self-cross-linking can take place without the intervention of foreign binders, through the action of the cross-linking rods indicated above.

In fact, the elevation of the temperature in the dissolution of collagen in hot water - as required by the process according to the invention - allows the elimination of hydrogen bridges and the release of protein molecules: these recondense and crosslink, then, when the bridges of hydrogen are reconstituted either directly through reagents that decrease solubility or through the use of reagents (syntans) which being made up of molecules with a high chain of conjugated double bonds

—C = C — C = C—

I I I I

H H H H

will have the property of building bridges or strong coordinated bonds with the ketoimidic groups of adjacent protein molecules, through the polarization generated by the cloud of electrons ti (unsaturation), made mobile on the chain due to the simultaneous presence in their molecule of dissociated phenolic groups = C © -O.

THE

This phenomenon cannot occur if collagen fibers - which are - as in all the known art - already tanned or pre-tanned. For this reason they will need - to be able to connect with each other and with the synthetic fibers of the substrate - external synthetic binders. The latter, however, have a negative effect, due to the fact that they also block the reactive groups of the protein, which instead must remain free because they are very important for the mechanism of water fixation. The fixation capacity of the water, the intensity of which is a peculiar characteristic of the protein molecule which alone possesses such groups in such a high measure, is on the other hand responsible for the comfort characteristics presented by the products manufactured with protein products.

In the publication "Protein fibers and the warmth of textiles" published by "Butterworths scientific publications -London", the author Wormell affirms, with regard to the particular comfort presented by the products manufactured with yarns of animal origin and therefore of a protein nature:

"It is known that protein fibers have a warmer and softer hand than that presented by cellulosic or synthetic fibers ... In light of the corpuscular theory, the heat and the high moisture absorption of protein fibers can be considered due to the rapid balance that occurs between the humidity in the corpuscles and that of the air between the corpuscles themselves; the total area of all corpuscles is very large and this leads to rapid permeation. We have seen that the surface of the corpuscles is polar and this helps the rapid dispersion of each water droplet that invades the interstices. The acidic and basic centers chemically combine with water and become hydrated, so that a protein fiber can retain up to 30% humidity without appearing wet. The absorption of water vapor is accompanied by the development of heat: the polar groups not only effectively disperse humidity, but generate heat in the process ".

The characteristic comfort properties of animal origin textile fibers are also observed with real leather products, which are also of a protein nature, and cannot be offered by synthetic materials given the lack of so many reactive groups in their structure.

It is important to note immediately that the chemical reaction with water is a phenomenon that obviously affects only the surface of the protein micelle since if it affects the whole structure it would cause, by hydrolysis, the degradation of the structure itself.

On the basis of the considerations made above, one immediately realizes the two fundamental reasons why artificial leather obtained with known processes still has characteristics far removed from those of natural leather, namely:

- first of all because, despite all the improvements, the prior art has not yet proposed, to date, a truly valid method for ensuring a sufficiently abundant and widespread penetration of collagen fibers into the synthetic support (fabric or felt);

- moreover, since the fixing of these collagen fibers on the synthetic fibers of the substrate is obtained by the known technique, at least to date, with the contribution of synthetic binders and, as known, these binders create a film covering the micellar surface of almost all of the protein fibers that have penetrated the support, blocking their ability to carry out the reactions described above.

On the basis of the same considerations reported above, it is also realized how the process according to the present invention - thanks to the easy penetration of the protein substance in solution into the synthetic support, and to the effective condensation and cross-linking of this protein substance on the synthetic fibers of the support itself - instead allows the manufacture of an artificial leather very similar to the natural one: in fact its internal surface, capable of reacting with humidity, is almost totally of a protein nature thanks to the fact that the protein particles have covered almost all of the the surface of the synthetic fibers of the substrate.

Therefore, the artificial leather manufactured according to the present invention has excellent comfort characteristics, which until now they have never been able to obtain (and which, in certain aspects and from tests carried out, have even been superior to those of natural leather), combined with excellent mechanical characteristics, resistance to stress and wear.

The diffusion of the protein solution and its neutrality also allow the processing of semi-finished substrates, which represents a further important advantage. In fact, it is possible to apply the procedure according to the

5

I

15

20

25

30

35

40

45

50

55

60

65

5

628571

invention also for a synthetic non-woven fabric, a face of which has already been coated with a porous synthetic film, such as coagulated polyurethane in a microporous form, per se known in the trade, or even on a fabric coated on both sides with microporous and frosted polyurethane; in both cases the imbibition of this semi-finished support with the protein solution according to the invention takes place without problems, so as to generate, also in this case, that internal protein surface, free, which is the substantial aim pursued by the present invention.

The following table clearly shows how the characteristics of a commercial support, and specifically of a semi-finished support - for example of the type generically called "poromeric" - which is already sold as a "fake leather", are substantially modified:

before treatment after treatment weight - gr / m2

472

628

liquid permeability 45 "

8 '

(Salade method)

absorption of H20 after 1 '

5.5%

35.6%

absorption of H20 after 30 '

21.8%

50.0%

The table therefore shows that:

- the support undergoes, after treatment, an increase in weight of more than 30%, and this increase is attributable exclusively to the protein substance adhered to the synthetic fibers of the support

- the permeability to liquids has clearly decreased, from the side corresponding to the grain of the skin, that is, from the side which in the manufactured article - for example a shoe - faces outwards. Therefore, a shoe obtained with the product according to the invention is much more resistant to the penetration of water from the outside

- the absorption of H20, both after 1 'and after 30' is, on the other hand, higher: this indicates the ability of the product according to the invention to easily absorb the humidity of human skin or sweat, this effect, as already mentioned,

of fundamental importance for the comfort of a product, such as a shoe, which remains in contact with the human body all day long.

A complete example of practical application of the process according to the invention is provided below, which is however susceptible of considerable modifications, especially as regards the final tanning phase, which can be adapted - moreover like tanning on hides natural - from time to time in relation to the needs of the finished product:

- kg. 100 of tannery flesh, split, calcined, are washed in a tanning barrel for 30 'with running water, then descaled with 1% of diluted HCl for 30', subsequently neutralized with IHS Na03 for 30 'and finally washed again in running water for 30 ';

- the material is then transferred to a double bottom boiler, containing 100 liters of water, where it is heated until it is almost completely dissolved;

- the solution is concentrated under vacuum to a 30% dry concentration;

- in a tanning barrel, synthetic support sheets are introduced, in a quantity, by weight, on which the water absorption capacity has been previously determined (for example this absorption can be 200% 5 on the weight of the material), and while the rotating barrel is fed, through its hollow axis, the protein solution obtained as above, at a temperature of about 70 ° C, in an amount equal to the absorbable quantity. After a rotation sufficient to allow the total imbibition of the solution in the io support (for example after 15 to 30 minutes), always through the hollow axis of the barrel an equal quantity of a crosslinking reagent is introduced - for example an aqueous solution containing 20% of magnesium sulphate and 10% of sodium sulphate - and the rotation is continued for 15 ';

15 - again with a rotating barrel, and using the normal tanning barrel devices, wash with running water until the excess of reagent disappears (possibly checking with the normal reagents of the chemical analysis, such as AgN03, BaCl2 and others);

2o - a 10% solution in water of basic chromium sulphate [Cr2 (0H) 2 (H20) 6S04] ++ is introduced into the barrel, at the basicity of 33 ° Schörlemmer, in an amount sufficient to pass 7%, on the weight of dry material, of Cr203 and the rotation is continued for 60 ';

25 - at the end of the rotation it is washed in running water to eliminate the excess of chromium and is de-acidified up to pH 5.5 with NaHC03 for 30 ', after which it is washed again in running water for 30'.

At this point the material can be extracted and dried in normal leather dryers.

Before proceeding with the drying, however, it is possible, where required, to proceed with dyeing, retanning and / or fattening operations - if known by the technique of processing natural leathers - which can be carried out in the usual way and without special precautions.

As it is easily understood, upon reading the example of application described above, one of the remarkable advantages of the process described above is that of being able to be put into practice, if desired, with usual equipment, such as the normal barrels of the tannery processes; the result is a great eclecticism in processing, without the need for rigid production schemes.

In the example above, it has been indicated to carry out the procedure according to the steps of:

45

- • dissolution of the collagen substance,

- imbibition of the support,

- condensation and cross-linking by addition of cross-linking reagents,

50 - tanning,

however, it has been found possible, and in some cases advantageous, to carry out the addition of the cross-linking reactants directly into the collagen solution and therefore to imbib the support with this mixture. In this case, however, attention will be paid to momentarily blocking the action of the cross-linking reagent - for example by keeping the pH value sufficiently high - so that condensation cannot occur before the imbibition of the support is completed.

60 Once the imbibition is ensured and while the support is still in the soaking bath, the pH value is lowered - for example with the addition of Al2 (S04) 3

- to allow rapid condensation and cross-linking. According to the process of the invention it can be obtained

65 a product whose physical characteristics are extremely close to those of natural leathers, so that practically all techniques can be applied to this product and to the same process of the invention by simple transposition

628571

6

already known in the processing of natural leathers. Thus, for example, the product can be obtained with more or less accentuated softness, according to the needs, also by simple difference of the drying methods (pasting, vacuum, oven and others), therefore differentiated types can be easily obtained; likewise, it possesses an accentuated sensitivity to the treatment with the retanning reactants used in the tanning of natural hides and, like the latter, easily assumes the characteristics expected and which are required by the user of the finished product.

v

Claims (13)

628571 1. Procedure for manufacturing artificial leather from animal waste, characterized in that it comprises the following steps: (a) preparation of a colloidal solution of protein substance of collagenic origin by simply dissolving in untreated calcined tannery flesh in hot water, slaughtering waste or mixtures thereof; (b) thoroughly imbibing a synthetic support having good porosity with said collagen solution and condensation and cross-linking of said collagen substance on the synthetic fibers of the support, by means of a simple action of cross-linking reagents and (c) tanning of the so soaked support. 2. Process as in claim 1, characterized in that, in the case of using calcined tannery flesh as the starting material, the dissolution phase in hot water is preceded by a descaling and neutralization phase. 2 CLAIM 3. Process as in claim 1, characterized in that, in the case of using slaughterhouse waste as the starting material, the dissolution phase in hot water is preceded by a phase of chemical depilation and neutralization. 4. Process as in claim 1, characterized in that the soaking step of the synthetic support it is preceded by a phase of concentration of the collagen solution, preferably up to a concentration of the dry comprised between 10 and 30% by weight. 5. Process as in claim 1, characterized in that the quantity of solution used for the imbibition of the synthetic support does not exceed the absorption capacity of the support itself. 6. Process as in claim 1, characterized in that the synthetic support is first soaked with the collagen solution, and subsequently with the cross-linking reagent. 7. Process as in claim 1, characterized in that the collagen solution is first mixed with a deactivated cross-linking reagent, then this mixture is used for the imbition of the synthetic support, the condensation and cross-linking of the glue substance on the synthetic fibers of the support being obtained by subsequent activation of the cross-linking reagent. 8. Process as in claim 7, characterized in that the deactivation and the activation of the crosslinking reagent are respectively obtained by variation of the pH. 9. Process as in claim 1, characterized in that said synthetic support is constituted by a non-woven fabric. 10. Process as in claim 1, characterized in that said synthetic support is constituted by a non-woven fabric previously impregnated with synthetic rubber latex and having good porosity. 11. Process as in claim 1, characterized in that said synthetic support is constituted by a non-woven fabric previously impregnated with microporous polyurethane. 12. Process as in claim 1, characterized in that said synthetic support is constituted by a fabric previously impregnated with microporous polyurethane. Method as in one of claims 10 to 12, characterized in that said synthetic support is also previously coated with microporous polyurethane on at least one of its faces.