Crust leather improvement

Abstract

An aqueous composition comprising swellable and expandable microspheres, a polymeric binder, and optionally further additives, as well as a method of repairing and finishing a defective crust leather comprising: A) repairing a defective crust leather by: i) applying a layer of the aqueous composition on the crust leather, the aqueous composition comprises swellable and expandable microspheres, a polymeric binder, and optionally further additives; ii) drying the layer and expanding the expandable microspheres; and B) finishing the leather obtained in the step ii) without mechanically polishing the surface of the leather.

Description

Technical Field

[0001] The present invention relates to a composition and method for improving the quality of defective semi-finished leather (i.e., semi-tanned leather, hereinafter also referred to as "crust leather") by repairing its defects. The composition comprises a polymeric binder and microspheres; the method can make the surface of the crust leather smooth, uniform and flat, ready for the subsequent finishing step. Background Art

[0002] It is well known that natural leather may develop defects such as holes and scars after tanning, retanning and drying (crust, semi-tanned or semi-finished leather).

[0003] Therefore, crust leather, especially full-grain crust leather, is rarely used in its original state for the finishing process.

[0004] Today, the consolidated technique for covering defects in full-grain leather (hereinafter referred to as "repairing") includes: 1. applying stucco to the leather to fill the defects; 2. drying it; 3. polishing the leather to remove excess stucco and make its surface uniform.

[0005] After that, the treated, repaired and polished leather can enter the finishing step, which usually includes:

[0006] 4. Application of a basecoat, which in most cases is a dyed formulation of acrylic resins, is used to protect the crust leather and give it the color that is visible in the finished product;

[0007] 5. Drying;

[0008] 6. Embossing (optional), if embossing is done, usually a nitro emulsion layer is applied before embossing, followed by another drying step, and after embossing, treatment is carried out in a grinding drum;

[0009] 7. Applying the overcoat or color coat, which is the second layer of the dyeing formula, usually based on acrylic resins, is used to adjust the color, create the desired visual effect, cover the substrate to a satisfactory degree (usually the base coat cannot achieve perfect coverage) or provide superior performance that cannot be achieved by the top coat alone. In the case of embossed leather, the overcoat must be applied because the leather will become dirty during the sanding process and its color must be corrected before the final clear top coat is applied. The overcoat also serves as a coupling layer for the outer layer (top coat);

[0010] 8. Drying;

[0011] 9. Applying a top coat, which is a polyurethane-based clear protective coating;

[0012] 10. Dry.

[0013] The drying step in the finishing process is usually carried out in a heated tunnel at a temperature of about 60-70°C.

[0014] For a proper finishing of leather it is of the utmost importance that the crust leather has no depressions and ridges (uniformity) during the finishing process.

[0015] The existing technical patents have conducted in-depth discussions on the main problems encountered in repairing raw leather.

[0016] Prior art repair techniques typically use synthetic adhesives including hollow expanded microspheres or hollow expandable microspheres.

[0017] In one well-known repair technique, a composition comprising a water-based binder (usually acrylic and / or polyurethane), fillers (such as inorganic silica and kaolin), and optionally expanded microspheres is applied with a spatula or machine and dried; however, the removal of water causes the volume of the applied material to shrink and leave a depression.

[0018] US 6,746,774 discloses a similar repair treatment, in which a layer containing "bubbles" is applied to the back of the crust leather. This layer can be constructed with or without microspheres by adding a foaming agent; a thermal curing process cures the layer, and water is said to be at least partially absorbed by the leather. The reduction in volume is not a problem here, because the surface of the back of the crust leather has much lower quality requirements than the upper surface.

[0019] In the process disclosed in AT6040 (which also repairs the back of crust leather), the presence of expandable microspheres is essential, the process is characterized by a heating mode (short exposure to hot air), and the creation of a mushroom-like structure.

[0020] US2007 / 0074352 repairs crust leather using an aqueous dispersion of an adhesive containing expandable microspheres that can produce expanded microspheres when heated and pressurized. According to the specification, the microspheres expand under the action of temperature and pressure and can completely fill the valleys (defects); however, the (same) inventor later questioned this goal in EP2004864, arguing that it is the permanent deformation caused by pressure that causes the depression to persist and must be removed mechanically.

[0021] US4016326 and EP2004864 both apply a layer made of an aqueous adhesive containing expandable microspheres on a leather support, but simultaneously dry and expand them by infrared radiation. The specific wavelength used by EP2004864 is said to solve all the problems caused by the heat and pressure treatment of US2007 / 0074352: the leather does not deform, does not harden, all microspheres expand, and defects are repaired.

[0022] However, since the volume of expandable microspheres increases significantly (up to sixty times), their use may be limited, and the resulting filled leather usually requires mechanical grinding (polishing).

[0023] As far as the applicant knows, in the prior art, there is no known process for repairing crust leather using a composition that does not require high temperature and high pressure and does not require mechanical grinding to make the surface uniform and free of dents.

[0024] It has now been discovered that a method for repairing defective crust leather can be performed by applying an aqueous repair composition comprising a polymer binder and both hollow expanded microspheres (hereinafter referred to as "expanded microspheres") and hollow expandable microspheres (hereinafter referred to as "expandable microspheres").

[0025] The combined use of expanded and expandable microspheres allows perfect filling of gaps (scratches, natural blemishes and holes) while creating a uniform, smooth coating on the leather crust that does not require mechanical sanding.

[0026] Without being bound by any theory, it can be assumed that the lighter expanded microspheres partially migrate uniformly to the still wet coating surface while the water evaporates, making the coating ultimately uniform, while a controlled amount of expanded microspheres sink into the depressions where they eventually swell up, compensating in volume for the loss of water and filling the gaps.

[0027] The method of the present disclosure is particularly valuable as it allows an un-buffed full-grain leather article to be obtained from a defective full-grain crust leather, since it avoids the buffing step or any other polishing step required in the prior art methods.

[0028] It has also been found that the repair composition according to the present disclosure also functions as a primer composition. In other words, the repair composition and method of the present disclosure can allow the omission of one finishing step (application of the primer) and one drying step (also the omission of the polishing step that usually follows the plastering process). This is, of course, very advantageous in terms of saving time, energy and cost. Summary of the invention

[0029] Thus, the aqueous composition for repairing crust leather comprises expanded microspheres and expandable microspheres, a polymer binder and optionally other additives such as rheology modifiers, oils and fillers.

[0030] The method for repairing defective crust leather disclosed in the present invention comprises: i) applying a layer of the above-mentioned aqueous composition on the defective crust leather, wherein the aqueous composition comprises expanded and expandable microspheres, a polymer binder and optionally other additives such as rheology modifiers, oils, fillers; ii) drying the layer and expanding the expandable microspheres.

[0031] The present disclosure also relates to a method for repairing and finishing defective crust leather, comprising: A) repairing the defective crust leather by the following steps: i) applying a layer of an aqueous composition comprising expanded and expandable microspheres, a polymer binder and optionally other additives such as rheology modifiers, oils, fillers on the crust leather; ii) drying the layer and expanding the expandable microspheres; B) finishing the surface of the crust leather obtained in step ii) without mechanically grinding the surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figures 1-5 are original and painted pictures of the defective crust leather of Examples 1-5, respectively.

[0033] Example 1, Example 3 and Example 4 represent prior art methods.

[0034] Examples 2 and 5 are representative of the methods of the present disclosure. DETAILED DESCRIPTION

[0035] The aqueous composition for repairing crust leather mainly comprises:

[0036] (a) 0.05 to 8 wt % (percent by weight), preferably 0.2 to 3 wt %, more preferably 0.5 to 2.5 wt % of expandable microspheres and expanded microspheres, in a weight ratio of 0.1 to 5, preferably 0.2 to 1, the weight percentage being the sum of the expanded microspheres and expandable microspheres in the composition,

[0037] (b) 10 to 40% by weight, preferably 15 to 40% by weight, of a polymer binder,

[0038] (c) 50-80%, preferably 60-80% water.

[0039] Advantageously, the above aqueous composition further comprises at least one additive selected from rheology modifiers, oils and fillers in the following amounts:

[0040] (d) 0 to 3 wt. %, preferably 0.5 to 2 wt. %, of a rheology modifier,

[0041] (e) 0 to 3% by weight, preferably 0.5 to 2% by weight, of oil,

[0042] (f) 0 to 10% by weight, preferably 1 to 6% by weight, of fillers.

[0043] Most advantageously, the remedial aqueous composition further comprises:

[0044] (d) 0.5 to 2% by weight of a rheology modifier,

[0045] (e) 0.5 to 2% by weight of oil,

[0046] (f) 1 to 6% by weight of filler.

[0047] The weight percentages of (b)-(f) are also based on the weight of the remediation aqueous composition.

[0048] The diameter of the expandable microspheres may be about 2 to 60 microns, preferably 5 to 35 microns, more preferably 10 to 20 microns, even more preferably 10 to 16 microns (before expansion).

[0049] Preferred expandable microspheres are those that expand at atmospheric pressure at a temperature of about 80°C (starting temperature) to about 190°C (ending temperature). Particularly preferred are expandable microspheres having a starting temperature of about 80-95°C and an ending temperature of about 120-140°C.

[0050] The diameter of the expanded microspheres may be about 10 to 150 microns, preferably 15 to 100 microns, more preferably 15 to 50 microns, even more preferably 20 to 30 microns, and is characterized by a very low true density, typically about 20 to 50 Kg / m 3 , as measured by a picnometer.

[0051] As a blowing agent, expandable microspheres and expanded microspheres usually contain hydrocarbons with a boiling point lower than the softening point of the microsphere shell, such as n-butane or isobutane, n-pentane, neopentane, isopentane, isobutane being preferred; other blowing agents may also be used.

[0052] The shell of the expandable microsphere and the expanded microsphere preferably comprises an organic polymer or copolymer. Suitable monomers for synthesizing the shell of the hollow microsphere include acrylonitrile, (meth) acrylates (such as ethyl acrylate, methyl acrylate, methyl methacrylate, isobornyl methacrylate and hydroxyethyl methacrylate), vinyl halides (such as vinyl chloride and vinylidene chloride), vinyl esters (such as vinyl acetate and vinyl formate), styrene, substituted styrene compounds. The polymer or copolymer can be cross-linked, for example with a small amount of polyunsaturated compounds, such as allyl methacrylate, diallyl maleate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate.

[0053] Vinylidene chloride, (meth)acrylate monomers and acrylonitrile are preferred monomers.

[0054] Polyurethane can also be used as the shell material of expandable microspheres and expanded microspheres.

[0055] For example, expandable microspheres and expanded microspheres are available from Nouryon under the trade names or WU (expandable or unexpanded) and DE or WE (expanded).

[0056] The polymer binder is preferably selected from emulsion polymers (eg, emulsion (meth)acrylic polymers and copolymers, styrene-butadiene copolymers, styrene (meth)acrylic copolymers, vinyl acrylic copolymers, and combinations thereof) and water-based dispersion polymers.

[0057] The polymer binder may be uncrosslinked or crosslinked.

[0058] Mixtures of polymer binders may be used.

[0059] The polymer binder preferably has a Tg below 30°C, more preferably a Tg below 10°C, especially a Tg below 0°C, and in any case a Tg above -50°C, as measured according to ASTM D6604-00 (2017) standard.

[0060] The "soft polymer" described herein refers to a polymer (or copolymer) having a Tg lower than 30°C (and higher than -50°C).

[0061] Particularly preferred polymer binders are soft (meth)acrylic emulsion copolymers, which are usually obtained by polymerizing at least 90% by weight of one or more (meth)acrylic acid esters (such as ethyl acrylate, n-butyl acrylate, ethylhexyl acrylate) and less than 10% by weight of one or more unsaturated carboxylic acids (such as methacrylic acid, acrylic acid, itaconic acid).

[0062] Water-based polyurethane dispersions can also be used as adhesives.

[0063] Another particularly useful polymer binder is a mixture of a soft (meth)acrylic emulsion copolymer and a soft polyurethane.

[0064] The rheology modifier may be selected from associative polyurethane thickeners, polyacrylic acid thickeners or polysaccharide derivative thickeners.

[0065] Advantageously, the rheology modifier is a mixture of an associative polyurethane thickener and a polyacrylic acid thickener.

[0066] The preferred polyacrylic acid thickener is an emulsion polyacrylic acid thickener.

[0067] Suitable emulsion polyacrylic thickeners are emulsion alkali swellable acrylic thickeners (ASE) which may include crosslinked or non-crosslinked associative hydrophobic monomers (HASE).

[0068] ASE and HASE are typically based on methacrylic acid (typically 30 to 40% by weight of the thickener) and ethyl acrylate (typically 60 to 70% by weight of the thickener).

[0069] The dosage of the rheology modifier is such that the viscosity of the repair aqueous composition is between 500 and 30000 mPa*s. The aqueous composition is pourable.

[0070] In a preferred embodiment, the aqueous composition also contains at least one oil which helps to delay the drying of the composition itself during application, and one or more fillers which reduce the gloss and stickiness of the final leather.

[0071] The preferred oil is mineral oil, but vegetable oils can also be used.

[0072] The filler may be organic or inorganic, preferably an inorganic filler, more preferably silica, kaolin or a mixture thereof.

[0073] The method for repairing defective crust leather comprises: i) applying a layer of the above-mentioned aqueous composition comprising expanded and expandable microspheres and a polymer binder on the defective crust leather, usually by spraying or roller coating, preferably by roller coating; ii) drying the aqueous layer and expanding the expandable microspheres by heat treatment.

[0074] The repair composition applied in step i) of the method is generally used at 0.2 to 5 grams, preferably 0.5 to 2.0 grams (dry matter) per square foot, i.e. generally 2.2 to 21.5 grams per square meter, preferably 5.4 to 21.7 grams per square meter (1 square foot = 0.092903 square meters).

[0075] In an advantageous embodiment, step ii) is performed in two consecutive distinct sub-steps: ii-1 and ii-2.

[0076] In ii-1, the aqueous layer is dried at a temperature of 50 to 80°C; in ii-2, the expandable microspheres are expanded at their characteristic expansion temperature (usually 80 to 190°C, preferably 80 to 140°C) according to the properties of the expandable microspheres and the expansion method.

[0077] Step ii-1 is preferably carried out in a heating tunnel, or by infrared irradiation, more preferably by infrared irradiation; step ii-2 is preferably carried out by rotopressing or infrared irradiation, more preferably by infrared irradiation.

[0078] In a particularly preferred embodiment, both sub-steps ii-1 and ii-2 are carried out by infrared irradiation at temperatures of about 60° C. and 120° C., respectively, since such thermal irradiation allows only surface heating and thus does not deteriorate the leather.

[0079] The repaired crust leather obtained by the above method can directly enter the finishing step without any mechanical grinding, such as polishing; the appearance and quality of the leather surface are thus preserved. Therefore, the method disclosed in the present invention is particularly suitable for repairing full-grain crust leather.

[0080] Most advantageously, in a subsequent finishing process, such repaired full-grain crust leather can be directly embossed (possibly with an auxiliary secondary treatment) or, if embossing is not required, directly applied with a topcoat and then subjected to the other conventional steps of the finishing process. In other words, generally, there is no need to apply and dry a separate basecoat prior to embossing or prior to applying a topcoat.

[0081] The coated and repaired crust leather disclosed herein can be used for various high-quality leather goods: leather clothing, automotive and furniture interiors, leather accessories, etc.

[0082] Advantages of the repair compositions and methods of the present disclosure are demonstrated in the following examples.

[0083] Example

[0084] In the following examples, the following products were used:

[0085] Binder PA-1: A soft, uncrosslinked acrylic copolymer (made from about 95% by weight of acrylic acid ester and about 5% of unsaturated carboxylic acid), emulsified in water at a ratio of about 35% by weight to provide a

[0086] Binder PA-2: A soft, cross-linked acrylic polymer (made from about 96% by weight of acrylic acid ester and about 4% by weight of unsaturated carboxylic acid), emulsified in water at a ratio of 35% by weight to provide a

[0087] Binder PU-1: polyurethane based on anionic polyester, dispersed in water at a ratio of 35 wt % to provide in the composition

[0088] Adhesive PU-2: polyurethane acrylate dispersion, dispersed in water at a ratio of 40 wt % to provide in the composition

[0089] Binder PU-3: polyurethane based on anionic cycloaliphatic polyether, dispersed in water at a ratio of 30 wt. % to provide in the composition

[0090] Binder PU-4: a polyurethane based on anionic cycloaliphatic polycarbonate-polyester, provided in the composition in a proportion of 35% by weight dispersed in water.

[0091] WE-MS: Wet-expanded microspheres from Nouryon (d50 20-30 μm; density 32-40 Kg / m 3 ), about 15 wt %.

[0092] WU-MS: wet expandable microspheres from Nouryon (d50 10-16 μm; density <12 Kg / m 3 ), about 80 wt%.

[0093] Filler-1: Kaolin-based filler, about 60 wt.%

[0094] Filler-2: Kaolin and silica based filler, about 25 wt%

[0095] Filler-3: Silica-based filler, about 100 wt.%

[0096] Oil: Morbidol GS from Lamberti SpA, about 100% by weight

[0097] RM-1: polyacrylic acid thickener (ASE), emulsified in water at a ratio of 30 wt % to provide in the composition

[0098] RM-2: polyurethane thickener, dispersed in water at a ratio of about 20 wt % to provide in the composition

[0099] Crosslinker-1: Polyurea crosslinker, about 30 wt%

[0100] Crosslinker-2: Isocyanate crosslinker, unreacted NCO accounts for about 10%, about 70% by weight

[0101] Crosslinker-3: Isocyanate crosslinker, unreacted NCO accounts for about 15%, about 70% by weight

[0102] Pigment: covering pigment paste in water dispersion

[0103] Silicone: Polyurethane silicone

[0104] Matting agent: Polyurethane based matting agent

[0105] Example 1 - Traditional plaster repair process (comparative example).

[0106] The following repair composition (dm = dry matter) was prepared and applied with a spatula to a defective full-grain crust leather ( Figure 1a ):

[0107]

[0108] The leather was dried, polished and then 32 g / m2 dm of the following basecoat composition 1 was applied by spraying:

[0109]

[0110]

[0111] The leather was dried, 1.2 g / m2 dm of nitro emulsion was applied by spraying and dried; the leather was then embossed and buffed, and 10.7 g / m2 dm of the following topcoat composition was applied by spraying:

[0112]

[0113] The leather was dried and then 4.8 g / m2 dm of the following topcoat composition was applied by spraying and dried:

[0114]

[0115] The resulting product is a polished finished leather with a uniform appearance and no defects ( Figure 1b ).

[0116] Example 2 - Repair and Finishing of Defective Full Grain Crust Leather

[0117] The following repair composition was prepared by mixing the ingredients and then 13.4 g / m2 dm of the composition was applied by roller coating to the defective full-grain crust leather ( Figure 2a ):

[0118] product dm weight% Adhesive PA-2 12 Adhesive PU-2 8 WU-MS 0.5 WE-MS 1.0 Filler-2 2.5 Oil 1.0 RM-1 1.0 Diaminoethylethanol 1.0 water 74

[0119] The leather is dried at a temperature of about 60°C and then the microspheres are expanded by infrared radiation at a temperature of about 120°C.

[0120] 1.21 g / m2 dm of nitro emulsion was applied by spraying and dried; the leather was subsequently embossed and sanded.

[0121] Then 10.7 g / m2 dm of the following topcoat composition was applied by spraying:

[0122]

[0123] The leather was dried and then 4.8 g / m2 dm of the following topcoat composition was applied by spraying and dried:

[0124]

[0125]

[0126] The resulting product is a full-grain finished leather characterized by a uniform and flawless appearance ( Figure 2b ), which can be used for furniture interior. Without polishing, the quality of the obtained product is higher than that of the product obtained from Comparative Example 1.

[0127] Example 3 - Repair and finishing of defective full-grain leather (comparative example)

[0128] Example 2 was repeated, but only expandable microspheres were used according to EP2004864. The following repair composition was prepared by mixing the ingredients and then 13.4 g / m2 dm of the composition was applied by roller coating to the defective full-grain crust leather ( Figure 3a ):

[0129] product dm weight% Adhesive PA-2 12 Adhesive PU-2 8 WU-MS 1.5 Filler-2 2.5 Oil 1.0 RM-1 1.0 Diaminoethylethanol 1.0 water 74

[0130] The leather is dried at a temperature of about 60°C and then the microspheres are expanded by infrared radiation at a temperature of about 120°C.

[0131] 1.21 g / m2 dm of nitro emulsion was applied by spraying and dried; the leather was subsequently embossed and drummed.

[0132] Then 10.7 g / m2 dm of the overcoat composition used in Example 1 was applied by spraying:

[0133] The leather was dried and then 4.8 g / m2 dm of the topcoat composition used in Example 1 was applied by spraying and dried.

[0134] The resulting full-grain finished leather still shows signs of blemishes ( Figure 3b ).

[0135] Example 4 - Repair and finishing of defective full-grain leather (comparative example)

[0136] Example 2 was repeated, but using only expanded microspheres.

[0137] The following repair composition was prepared by mixing the ingredients and then 13.4 g / m2 dm of the composition was applied by roller coating to the defective full-grain crust leather ( Figure 4a ):

[0138] product dm weight% Adhesive PA-2 12 Adhesive PU-2 8 WE-MS 1.5 Filler-2 2.5 Oil 1.0 RM-1 1.0 Diaminoethylethanol 1.0 water 74

[0139] The leather is dried at a temperature of about 60°C.

[0140] 1.21 g / m2 dm of nitro emulsion was applied by spraying and dried; the crust leather was subsequently embossed and tumbled.

[0141] Then 10.7 g / m2 dm of the overcoat composition used in Example 1 was applied by spraying:

[0142] The leather was dried and then 4.8 g / m 2 dm of the topcoat composition used in Example 1 was applied by spraying and dried.

[0143] The resulting full-grain finished leather still shows signs of blemishes ( Figure 4b ).

[0144] Example 5 - Repair and Finishing of Defective Full Grain Crust Leather for Automotive Interiors

[0145] The following repair composition was prepared by mixing the ingredients and then 13.4 g / m2 dm of the composition was applied by roller coating to the defective full-grain crust leather ( Figure 5a ):

[0146] product dm weight% Adhesive PA-2 10 Adhesive PU-3 15 WU-MS 0.3 WE-MS 0.7 Filler-2 2.5 Oil 1.0 RM-1 1.0 Diaminoethylethanol 1.0 water 68

[0147] The leather is dried at a temperature of about 60°C and then the microspheres are expanded by infrared radiation at a temperature of about 120°C.

[0148] 1.21 g / m2 dm of nitro emulsion was applied by spraying and dried; the leather was subsequently embossed and sanded.

[0149] Then 10.7 g / m2 dm of the following topcoat composition was applied by spraying:

[0150]

[0151] The leather was dried and then 4.8 g / m2 dm of the following topcoat composition was applied by spraying and dried:

[0152] product dm weight% Adhesive PU-4 5 Matting agent 12 Silicone 3 RM-2 1 Crosslinker-3 3 water 76

[0153] The resulting product is a full-grain, unfinished finished leather characterized by a uniform and blemish-free appearance ( Figure 5b ).

Claims

1. An aqueous composition for repairing defective crust leather, comprising: (a) 0.05 to 8 wt % of expandable microspheres and expanded microspheres in a weight ratio of 0.1 to 5; (b) 10 to 40 wt % of one or more polymeric binders; (c) 50 to 80% by weight of water.

2. The aqueous composition of claim 1, comprising: (a) 0.2 to 3 wt% of expandable microspheres and expanded microspheres in a weight ratio of 0.2 to 2.

3. The aqueous composition of claim 1 or 2, further comprising at least one of a rheology modifier, a mineral oil and a filler in the following amounts: (d) 0 to 3% by weight of a rheology modifier, (e) 0 to 3% by weight of mineral oil (f) 0 to 10% by weight of filler.

4. The aqueous composition of claim 3, comprising: (d) 0.5 to 2% by weight of a rheology modifier, (e) 0.5 to 2% by weight of mineral oil (f) 1 to 6% by weight of filler.

5. The aqueous composition according to claim 1, wherein The polymer binder has a Tg lower than 30°C and higher than -50°C, and the Tg is measured according to ASTM D6604-00 (2017) standard.

6. Methods for repairing defective crust leather, including: i) applying a layer of the repair aqueous composition according to any one of claims 1 to 5 on the defective crust leather; ii) drying the aqueous layer and expanding the expandable microspheres by heat treatment.

7. A method for repairing defective crust leather according to claim 6, wherein step ii) is carried out in two consecutive sub-steps: ii-1, in which the aqueous layer is dried at a temperature of 50 to 80°C; iii-2, in which the expandable microspheres are expanded.

8. The method for repairing defective crust leather according to claim 6 or 7, further characterized in that the leather obtained in step ii) is not mechanically polished.

9. Method for repairing and finishing defective crust leather, including A) performing steps i) and ii) of the method of claim 6, 7 or 8, and B) Finishing the leather obtained in step ii).

10. The method for repairing and finishing defective crust leather according to claim 9, wherein step B comprises the following steps: iii) applying a topcoat directly on the repaired crust leather from step A without applying a basecoat and drying; iv) optionally applying a nitro emulsion on the painted leather, embossing and drum drying; and v) applying a top coat on the leather of step iii) or iv) and drying.

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