DE1912351A1 - Process for finishing leather - Google Patents

Description

Dr. Ing. E. BERKENFELD · D i ρ I, -1 η g. H. B E R K E N F E LD, patent attorneys, Cologne Attachment file number

to the input from 11 March 1969 ζ Sch name d. Note Lankro Chemicals Ltd.

Process for dressing leather.

The invention relates to a method for finishing leather, i.e. the application of coloring and / or film-forming materials on the outer surfaces of leather. Compared to numerous other substrates to which surface coatings are applied leather has, among other properties, greater elasticity and flexibility and is more irregular in shape and shape more porous. In addition, leather shows differences in the extent to which these and other properties are present. Those differences occur from skin to skin and even between different parts of the same skin. These individual characteristics and differences create considerable difficulties in dressing leather and those used for leather dressing Materials must therefore be particularly suitable for this purpose.

Methods hitherto used for dressing leather have generally emerged from conventional methods for covering surfaces developed, such as brushing, and are carried out using known methods such as brush coloring, impregnation, spraying or pouring on (curtain coating).

Additional surface effects, such as smooth or decorative scarring at ·, are often desired and are generally carried out by Pressing process received, so the pattern can be used for example on leather surfaces, which have been finished using the known processes mentioned, are attached or embossed,

Ec5 an attempt was also made to use pre-formed foils (b & for example from

L 5Vy - ¹ -

909841/0997

BAD ORlQfNAL

* 1312351

plastic materials such as polyvinyl chloride) to be applied to leather surfaces by gluing or laminating processes. .

All of the above and the other proposed methods however, have known disadvantages. For example, common methods of surface covering leather require -in- careful application of several layers of coating from different film-forming masses, whereby waiting times must be observed between the individual applications. Particularly undesirable Quantities can occur when these procedures are applied will. For example, the coating liquid can often penetrate unevenly into the porous leather surface and not only lead to unsuitable surface effects but also hardening of the leather due to an adhesive effect on the leather

f <XStrr \

· Cause near the surface.

In addition, the porous surfaces of heavy smooth leathers or split leathers can only be dressed in this way with great difficulty become so that they resemble fullness. In addition, the

before choosing finishing materials that are suitable for pressing or Embossing can be applied, limited to those substances that are capable of deformation under the action of pressure and / or heat are. Valuable materials such as Certain polyurethanes and other substances that give leather surfaces valuable properties, such as enhanced properties, are excluded Wear resistance and better kinkability.

Another disadvantage of the known method for covering leather surfaces, specifically beta lamination with plastic films occurs, is the impairment of the valuable property of porosity towards water vapor, which is not finished leather due to its unique three-dimensional fiber fabric structure having. Surface coating treatments such as those described above affect this porosity or very much reduced, whereby undesired poles occur, such as reducing the spread of perspiration vapors through leather items, shoes, gloves or items of clothing.

L 5V9 -2-

909841/0997

._ *,, ■ ν "» «SU

Another disadvantage of the known method is made in the Production of high-gloss coating layers, for example the so-called "patent leather" equipment noticeable. Some well-known Processes for making such coatings require-either repeated, intermittent. Applications of drying oils, such as linseed oil or the application of a high-gloss, polymer film-forming material, such as of polyurethanes. In both cases, strict precautions must be taken to avoid dust particles and to keep the high gloss coating film away from other contaminants during drying, if not appearance should suffer.

According to the invention, a method for dressing leather is provided, which avoids the disadvantages mentioned above.

The invention relates to a method for dressing leather by applying a film-forming coating composition to the leather surface, which is characterized in that it is a laminate forms, which contains the leather, a film of the coating composition and a separating layer as successive layers and the The separating layer is then removed from the leather surface provided with the covering layer.

Pressure can be applied to the laminate or laminate, to promote the adhesion between the leather surface and the film of the coating mass.

Preferably, the method of the present invention comprises the following Process stages:

1) applying a film-forming coating composition to the release layer;

2) The leather surface will be in contact with that on the release liner placed film of the coating mass;

3) Applying pressure to the composite to force adhesion to convey the leather surface and the film of the coating mass and

4) Remove the release liner, the one with the leather surface bonded film of the coating composition remains.

90 98A1 / 0997.

ORIGINAL INSPECTED

Levels 1-4 can be with or without a break between each Stages are carried out. . .

According to a further preferred embodiment of the invention, a coating mass is applied to a leather surface in the following stages: ...

1) Separate application of at least two film-forming coating layers on the release layer. You wait until you are educated a film of each of the coatings before applying the next one Applying coating compound;

2) Bringing the leather surface into contact with that on the release liner existing films of the coating composition; J5) Applying pressure to the entire assembly to ensure adhesion to promote between the leather surface and the cover layers

4) Removal of the separating layer, leaving behind the films of the coating composition, which are bonded to the leather surface.

The successive process steps 1-4 can be carried out with or without waiting times between the individual stages. The coating compositions applied to the release layer can have the same or different compositions.

Optionally, the coating material can first be applied to the leather surface and then or later the separating layer can be brought into contact with the coating material. Then or to one later, the separating layer is removed, with the the surface of the leather bonded film of the coating composition remains. This process prevents dust from spoiling the coating and is preferably in! connection with a not in the leather penetrating coating mass (e.g. a mass with high viscosity) or a well sealed leather surface (as described in Examples 7 and 9).

Suitable coating compositions are liquids that are either only can form films through the escape of volatile constituents and / or through chemical reactions such as polymerisation.

L 54/9 ■ "■ - - - ^: ■ '-4-

909841/0997

The coating compositions which can be used according to the invention can, for example natural or synthetic film-forming polymers such as proteins (e.g. casein), or synthetic resins, e.g. Contain vinyl or acrylic compounds, nitrocellulose or polyurethanes. The preferred film-forming ingredients of the Coating compounds are nitrocellulose or polyurethanes.

Particularly preferred constituents of coating compositions according to the invention are reactive polymers such as polyester or polyether type urethane polymers. Suitable polyester urethane polymers include Compounds obtained from polyesters with hydroxyl end groups by reaction with compounds containing isocyanate groups, such as diphenylmethane diisocyanate or with adducts which contain excess isocyanate groups and which are made from a polyhydroxy compound and a polyisocyanate such as tolylene diisocyanate received. Suitable polyether urethane polymers include polymers derived from polyethers having terminal hydroxyl groups by reaction with compounds containing isocyanate groups, such as tolylene diisocyanate. These polymers contain an excess of isocyanate residues and there are therefore to implementation capable of compounds containing active hydrogen atoms, such as water. These polyether urethane polymers are called "moisture curable" Polymers "known.

To accelerate the ongoing reactions and in particular to accelerate the hardening reaction in the presence of moisture Catalysts are usually required. Suitable catalysts include tertiary alkyl, cycloalkyl and aralkyl amines such as Triethylamine, dimethylcyclohexylamine, dimethylbenzylamine and dimethylethanolamine.

In addition, metal-containing organic compounds can be used as catalysts are used, such as certain salts of transition metals with organic acids, for example cobalt or manganese naphthenate, and organic compounds of zinc and tin such as stannous octoate, zinc octoate and dibutyltin dilaurate.

The term "release layer" is intended to mean a material with a surface which in comparison with the leather surface L 5V9 -5-

909841/0997

exhibits poor adhesion to the selected coating composition. Preferred materials are polyethylene, polypropylene and halogen-containing analogs of these compounds, such as polytetrafluoroethylene. These products can either be used in film form without a carrier or together with a carrier layer such as paper. Particularly preferred materials are the general group of so-called release papers, i.e. Papers that either by impregnation or superficial coating with agents such as silicone oils, treated as opposed to their adhesion To reduce materials that would normally stick to the untreated surface of the paper.

The surface properties of the separating layer determine the appearance the coating layer that is transferred to the leather from this separating layer. So can "the shine, the surface pattern and other features of the release layer can be reproduced in the cover layer when transferred to the leather. Furthermore can the surface layer can be embossed or printed in situ in any pattern. This is done by pressing a suitable patterned object, such as an embossing roller or plate, on the uncoated side of the release liner while printing is applied to the laminate. Optional catfish can be embossed or printed on the separating layer before it is used according to the invention will.

Suitable for the treatment according to the invention? Leather surfaces are the surfaces of leather that come from all types of skin through all Types of tanning processes are made. Preferred leathers are leathers obtained from the hides of mammals, such as from Cattle, sheep and goats or other animals such as reptiles. Particularly preferred leathers are from the hides of cattle and sheep and goats leather obtained by tanning methods customary at the time.

The method of the invention is especially for applying a coating layer to surfaces such as so-called surfaces with corrected scar made by grinding the surface of the scar of the leather can be obtained with an abrasive and on other porous surfaces, such as those of the so-called split leather.

^L 5V9 _6-

909841/0 9 97

suitable .which the inner surfaces of the. Represent leather and hats, : d.that are exposed by splitting longitudinally in layers, known in the trade as "columns".

The application of the method according to the invention comprises various factors which can be varied within a wide range.

Thus, according to a preferred embodiment, the coating composition of the method according to the invention can be applied to the release layer by any known method. The viscosity of the Liquid and other factors determine the application method chosen. Suitable processes are impregnation, brush coloring, Spraying on, rolling on and pouring on (curtain coating) or combinations this procedure. Between the application of the coating composition to the release layer and the contacting of the coated Surface required with the leather surface :: Time depends on factors such as the drying speed and / or Speed of hardening of the coating mass. These speeds are in turn determined by the volatility of the solvents present.

ie.
tel and de * ¹ reactivity of all reactive compounds present, such as the preferred reactive urethane polymers. By suitably coordinating the effective factors, any desired time interval can be set in order to meet special requirements, such as, for example, a production cycle in which a certain throughput rate is desired. It is preferred to work under such conditions that the time is between about one minute and about 1 hour. A procedure in which this time is between about 2 minutes and about 30 minutes is particularly preferred.

In order to bring the leather surface and the coated surface of the separating layer into contact with one another, various Procedural measures are applied. So can the two surfaces either simply placed on top of one another or pressure can preferably be applied to keep them in contact with one another to press standing surfaces together.

L 5V9. . · .. ■ -. -7-

909841 / Q 9 9 7

The time after the end of the contact level just described until the separation layer is removed can vary within wide limits. It depends on the time it takes to freeze or curing of the transferred film of the coating composition is required is in order to be able to remove the separating layer, which in turn is caused by factors such as the type of leather surface Structure and chemical reactivity, if any, of the coating compound is influenced.

This stage of the process according to the invention is preferably taken under such conditions that the curing time is between 5 minutes and about 3 hours. Particularly preferred a work with a hardening time between about 15 minutes and about jJO minutes.

If desired, the separating layer can be used as a protective cover for the covered <leather surface during the subsequent process steps, such as storage and transport, can be left in their position without incurring disadvantages.

When using a separating layer that is provided with several layers of coating, there can be much greater leeway for the Bringing the coated separating layer and the leather surface into contact exist. In certain circumstances, previously coated rolls or webs of the release liner can be made and subsequently can be used at any time to apply a coating film to the leather surface. In general, a good adhesion between the coating and the substrate is ensured if the coating compounds applied to the separating layer are the same or are of the same type (e.g. polyurethane type).

Applying it as a coating on the separating layer is also advantageous if the separating layer by a single application of, for example, a colored polyurethane mass, difficult to coat evenly. In such a case, the application ensures, for example, a transparent one Lower layer of a different film-forming mass (e.g. a solution of nitrocellulose) a more even surface

L 5V9 -8-

909841/0997

pull through the subsequently applied polyurethane mass.

The following examples illustrate the invention. All parts and percentages are parts by weight or percent by weight, unless otherwise stated.

example 1

A sheet of paper with a matte finish, the one made with silicone materials had been treated to obtain good release properties, was using a spray gun with a polyurethane coating composition coated, which contained the following components:

a) 100 parts by weight of a 40 # solution of a polyurethane prepolymer terminal isocyanate groups in methyl isobutyl ketone as a solvent, prepared by reacting the following compounds under known reaction conditions

Parts

1) Glycerine-based polyoxypropylenetriol, with the 44.4

Molecular weight 1000

2) Glycerine-based polyoxypropylenetriol, molecular weight 600 11.1

J5) Polyoxypropylene ^ llr, molecular weight 1000 11.1

4) Toluene diisocyanate (80/20 mixture of the 2,4 and 2,6 isomers) 33 * 3

The hydroxy components were first premixed and this Mixture then reacted with the toluene diisocyanate.

b) 10 parts by weight of a black pigment paste, obtained by grinding together a carbon black pigment (50 parts) in a medium made from castor oil (first press, 95 parts) and blown castor oil (5 parts).

c) 0.8 part by weight of dimethylaminoethanol.

After standing for 10 minutes, a piece of air-dry,

-Chrome-tanned KunlederJ whose grain layer previously on L 54/9 'CVolkdtr] ^ _9m

909841/0997

a / ft * splitting machine had been removed, leaving a rough surface has remained, brought into contact with the coating composition on the paper as a separating layer. The laminated body thus obtained was used at room temperature in a conventional plating press smooth surfaces exposed to a pressure of about 200 kg / cm. After one hour the release paper sheet was removed and it A film of the polyurethane surface coating was left behind, which adhered firmly to the leather surface.

The treated surface was matt and would have an attractive, grain leather-like appearance and a pleasant grip. It also showed good abrasion resistance and other desirable properties, which are characteristic of polyurethane coatings.

Example 2

A polyethylene film 0.06 mm (250 gauge) thick was used as the release liner in place of the paper described in Example 1 used with a matt surface. Using the same apparatus, materials, and procedures as in Example 1, a piece of split leather was obtained which had a firmly adhering surface covering made of a polyurethane film exhibited. The treated surface had an attractive, semi-glossy grain leather-like appearance, a good handle and exhibited excellent wet and dry rub resistance. It also showed good abrasion resistance and other desirable properties that are characteristic of polyurethane surface coatings «

Example 3

In this example, the same apparatus and procedures were used as in Example 1, except that the fully chrome-tanned split leather with a piece of fully chrome ™ tanned, air-dried leather with corrected grain has been replaced. The grain side of this leather was beyond sanding has not been subjected to any other surface treatment. The trimmed Ls = obtained with the aid of the method according to the invention

L 5V9 -10-

909841/0997

The piece had an adherent surface coating made of polyurethane. The coating layer was matte, and gave the leather surface a pleasant appearance and touch, and was excellent Abrasion resistance in hate and dry condition.

Example 4

In this example, the same device and the same Procedure as in Example 1 except that the final pressure treatment was carried out in a plating press whose smooth metal plate was replaced by a plate with a surface pattern was replaced, as is typical for the usual leather embossing process.

The surface of the die was so in contact with that not coated side of the release paper that the surface pattern of the plate in situ into the underlying, only partially cured surface coating layer made of polyurethane was pressed.

After this embossing treatment, the laminated body was made of paper, The coating layer and leather were left untouched for one hour and then the release paper was peeled off. It was left behind firmly adhering polyurethane film on the leather surface. The film

, en

had an impression of the pattern of the die and also showed the properties of polyurethane coating layers described above.

Example 5

the

In this example, the same apparatus and procedures were used as in Example 4, with the exception that the piece of split leather was previously prepared by spraying on a typical base coat for leather finishing, which consists of an aqueous dispersion of a synthetic rubber latex and an aqueous casein wax. Dispersion existed, was first provided with a coating layer. After the base coat had been produced and dried, the coated surface was ^{embossed at 65 °} C. with a pressure of 200 kg / cm before the polyurethane film was

L 5V9 -11-

909841/0997

driving example 1 was transferred to them.

After peeling off the release paper, the finished piece of leather possessed an adherent polyurethane coating which had properties similar to the coating layers previously described.

Example 6

This example shows the implementation of the method according to the invention using a release paper, with a beforehand embossed pattern in its surface. A sheet of the release paper used in Example 1 was pressed under the embossing plate used in example 4 in a conventional embossing press (Turner's Gloria type) embossed with a grain pattern. This embossed paper sheet was then used in place of that in Example 1 fkpiers are used, the same type of leather, the same device and the same materials as in this one Example were used.

After removing the embossed release paper, it was left on the leather surface a tightly adherent polyurethane film left behind. The film had an imprint of what was embossed on the release paper Sample and also showed the desired properties of the polyurethane films applied in the other examples.

Example 7

A piece of fully chrome-tanned cow flank leather with corrected Scar, the sanded surface of which by applying a base coat with the help of an impregnation application and two Spray coatings had been sealed with a conventional acrylic resin emulsion and then hot-pressed as follows treated:

The sealed leather surface provided with a base coat was sprayed with a coating mixture of polyurethane, whose Composition of the mixture described in Example 1 corresponded. After standing for 10 minutes, the sprayed leather surface became with a sheet of the release paper used in Example 1 L 5V9 -12-

909841/0997

covered with matte surface. The release paper was pressed onto the coating mass by hand with the aid of a felt-covered wooden roller. After the laminated body produced in this way had hardened overnight, the release paper was peeled off. It was left behind Film of the polyurethane coating layer firmly adhered to the leather surface.

Example 8

This example shows the use of nitrocellulose film forming lacquers for the method according to the invention.

A sheet of silicone-treated release paper with semi-matte finish and a ^e <§ingeprägten fine grain pattern was coated by spraying with a layer of conventional, black pigmented nitrocellulose lacquer. This nitrocellulose lacquer was obtained from the following components according to known processes:

Weight percent

low viscosity nitrocellulose

(I.C.I., Grade DHL 25/45, modified

with 30% butanol) 11.0

Carbon black pigment (Dixigloss NI, Anchor Chemicals Ltd.) 1.5

Castor oil (1st press) 6.0

Castor oil (blown) 1.0

Dibutyl phthalate 2.5

Nonylacetate 4.0

Ethylene glycol monoethyl ether acetate (cellosolve

Acetate) 24.0

Ethylene glycol monoethyl ether 18.0

Butanol 8.0

Shellsol A (aromatic hydrocarbon solvent, Shell Chemicals Ltd.) 24.0

This mass was partially air dried for 15 minutes. Then a piece of the primer-sealed, fully chrome-tanned cowhide with corrected grain, as shown in

L 54/9 -15-

909841/0997

Example J used was brought into contact with the partially dried nitrocellulose lacquer film on the embossed release paper. The two surfaces in contact were pressed together with a hand roller and allowed to dry for two hours.

After removing the release paper at the end of the drying time became a pigmented and plasticized nitrocellulose film obtained, which adhered firmly to the leather surface. The treated leather surface had an attractive, semi-matt finish » see and had a faithful reproduction of the embossed paper surface. It also had good rub resistance in the wet and dry condition.

Example 9

The procedure according to Example 7 was repeated in all measures ,, except that the polyurethane coating layer used in this example is replaced by that used in Example 8 Nitrocellulose lacquer was replaced.

After peeling off the release paper from the leather, a nitrocellulose film adhering firmly to the leather surface was obtained. showed good rub resistance when wet and dry.

Example 10

This example illustrates the embodiment of the invention, according to which a release paper provided with several layers of coating is used,

A sheet of silicone-treated release paper with a semi-matt surface, which has an embossed fine grain pattern, was slightly coated by spraying with a clear nitrocellulose lacquer corresponding to the Laot used in Example 8 and not provided with the carbon black pigment. After drying this coating, a further, strong coating was sprayed * which consisted of a ⁵ polyurethane coating composition according to Example 1, "the LAOH Trock-L 5V9 ... -14-

909841/0937

A light, sprayed-on coating of the same polyurethane mixture was applied to this coating and the coated one Release paper cut into four parts with the same dimensions.

Pieces of chrome-tanned split leather were then brought into contact with each of these four pieces of coated paper. The contact was, at different time intervals after spraying, im Range from j5 - 10 minutes recorded.

The four laminated bodies thus formed were then subjected to a pressure of 200 kg / cm at 65.degree. After 12 minutes the release paper became dense removed, in each case grease-adhering coating films remained from the coating materials. The treated Surfaces had an attractive, grain leather-like appearance and a pleasant feel.

The nitrocellulose film applied to this orphan had improved Solvent resistance compared to its solvent resistance when simply sprayed on. It is believed, that this improved solvent resistance on it This is because the nitrocellulose coating layer is more or less an integral part of the polyurethane coating layer which is applied afterwards.

It has already been said that coated release films have been used previously that have a suitable storage life. It has been found that all of the invention Coated release liners used have good shelf life for a suitable period of time.

The invention therefore also relates to a release film which at least comprises one and preferably more than one film of a coating composition. The film or the Fllmetier are coating compounds transferable to a leather surface when this leather surface is brought into contact with the film or films on the release layer will. The film or films cannot be transferred when fully cured; in this case it is

L 5V9 ■ -15-

909841/0997

It is necessary to apply another film of the coating mass re-activate them to make them transferrable.

Examples of such release films is a release paper which is coated with a composition containing nitrocellulose and a Release paper which was coated first with a composition containing nitrocellulose and then with a composition containing polyurethane.

Patent claims

L 54/9 -16-

909841/0997

Claims (1)

Dr. Ing. E. BERKENFELD · Di ρ I.-1 ng. H. BERKENFEI.D, patent attorneys, Cologne Attachment file number on the submission of March 11, 1909 Sch Na _me d. AnmLankro Chemicals Ltd. Claims 1. Method of dressing leather by applying a film-forming coating composition on the leather surface, characterized in that a laminate is formed as successive Layers containing the leather, a film of the coating composition and a separating layer and then the separating blade from the one with the Covering layer provided leather surface removed. 2. The method according to claim 1, characterized in that a film-forming coating composition is used for the production of the laminate is applied to a separating layer and the leather surface is brought into contact with the coating film located on the separating layer. 5. The method according to claim 1 or 2, characterized in that that to produce the laminate, a coating material is applied to the leather surface and then the release layer with the coating film brings in touch. 4. The method according to any one of claims 1-3, characterized in, that pressure is applied to the successive layers to form the laminate. 5. The method according to any one of claims 1-4, characterized in that, that the coating composition in the form of at least two different coating films and after each application the obtained coating film is solidified. 6. The method according to any one of claims 1-5, characterized in that that a coating compound is used that contains nitrocellulose L 54/9 -17- 909841/0997 loose or contains a polyurethane. 1912351 7 · The method according to claim 6, characterized in that one a coating composition used, which is a curable polyurethane based on polyester or KLyäther and a curing catalyst for which contains polyurethane. 8. The method according to any one of claims 1-7 *, characterized in that that one verwei det a separating layer, whose with the coating composition The surface layer in contact is made of polyethylene, polypropylene or polytetrafluorethylene. 9. The method according to any one of claims 1 -?, Characterized in that eifil separating layer a paper film is used whose surface in contact with the coating compound has been treated with a silicone oil. 10. The method according to any one of claims 1-9> characterized in that that the leather surface to be treated is a surface with corrected grain, which is created by grinding the grain surface of the leather was obtained with an abrasive. 11. The method according to any one of claims 1 -9, characterized characterized in that the leather surface to be treated is the surface of a split leather. 12. The method according to any one of claims 1-11, characterized in-r draws that one uses an embossed or printed release layer. 13. Method according to one of claims 1-12, characterized in that that in the manufacture of the laminate by the action of a patterned roller or plate on the uncoated side impresses a pattern on the separating layer. L 5V9 -18- 909841/0997