1. A method for tanning leather based on nano-clay non-chromium combination is characterized in that the used raw material is liming leather and is subjected to conventional procedures of deliming, softening and washing to obtain softened naked leather, and tanning agents used in combination with tanning are nano-clay, aldehyde and derivative tanning agents, and the specific operation method is as follows:

(1) pickling: adding 60% water and 7% salt into a rotary drum at normal temperature, dissolving completely, adding softened pelts, and rotating for 10 min; sequentially diluting, adding formic acid and sulfuric acid to adjust the pH value to 2.8-3.0, and rotating for 30 min;

(2) tanning: adding 2.0-8.0% of aldehyde and derivative tanning agent into the pickle liquor, and rotating for 2-3 h; then weighing 1.5-4.5% of nano clay, adding the nano clay for three times at intervals of 30 min each time until the pH value reaches 5.0-5.5, and continuing rotating for 60 min; standing overnight, rotating for 30 min the next day, draining liquid and washing;

the dosage of the chemical materials in the above procedures is based on the weight of the ash dipping skin.

2. The method for non-chromium combined tanning of leather based on nano-clay according to claim 1, characterized in that the aldehyde and derivative tanning agent is any one or more of glutaraldehyde tanning agent, modified glutaraldehyde tanning agent, oxazolidine tanning agent and sulfone synthetic tanning agent.

3. The method for tanning leather based on nanoclay non-chromium combination as recited in claim 1, wherein said nanoclay is any one or a mixture of laponite, rectorite, zeolite powder, sepiolite powder.

4. The magnesium-aluminum silicate mineral is rich in magnesium-aluminum silicate minerals, is derived from natural substances, and is environment-friendly and non-toxic.

5. The method for tanning leather based on non-chromium combination of nano-clay according to claim 1, characterized in that the nano-clay is added in three times, and the pH value of the tanning liquid is gradually increased by utilizing the self-alkalization capability of the nano-clay, so that the aldehyde and derivative tanning agents can be promoted to fully generate the synergistic crosslinking effect with the nano-clay in collagen, the moisture-heat resistance stability of the leather is remarkably improved, the tanning process can be simplified, alkali is not required to be extracted, and the content of neutral salt in the leather-making waste liquid is reduced.

Background

Tanning refers to the process of converting hides into leather that is not subject to microbial degradation through the interaction between tanning agents and collagen of the skin. The chromium salt can endow leather with the characteristics of higher humidity and heat resistance stability, light weight, softness and the like, and has the advantages of low cost, strong universality and the like, so the chromium salt is the most widely used tanning agent in the world. However, the current chrome tanning process still faces a serious challenge, and the low utilization of chrome tanning agent in the traditional chrome tanning process results in a large amount of difficult treatment of chrome-containing wastewater and accumulation of solid waste, and has environmental and health risks of forming carcinogenic Cr (vi) from Cr (iii). In recent years, the limit requirement of Cr (VI) in leather in developed countries or regions such as Europe and America is continuously upgraded (3 mg/kg), and 1 month in 2021, the international standard and European Union standard research council of the joint organization of the International leather technologist and the association of chemists (IULTCS-IUC) and the chemical working group of the leather technical Committee of the European Commission of standardization council propose to reduce the limit of hexavalent chromium from 3 mg/kg to 1 mg/kg; in 2008, the national ministry of environmental protection puts chromium-containing waste into the national records of hazardous waste, and policies at home and abroad urgently force the tanning industry to develop environment-friendly non-chrome tanning materials and process technology, so as to be dedicated to the clean production of leather industry.

The nano clay is nano-scale powder rich in elements such as magnesium, aluminum, silicon and the like, has the particle size of 1-100 nm, has good dispersibility in an aqueous solution, has negative charges on the surface of the particles, and can generate interaction such as coordination bonds, ionic bonds, hydrogen bonds and the like with the collagen, so that the heat and humidity resistance stability of the collagen is improved. The nano-clay also has a three-dimensional network multi-layer structure, and the special structure of the nano-clay not only can endow leather with excellent selective filling effect, but also can endow the leather with ultraviolet resistance and formaldehyde adsorption capacity, so that the light resistance of the finished leather is obviously improved, and the environmental and health risks caused by free formaldehyde are avoided. Meanwhile, the nano-clay exists in the crust in a large amount, has wide sources, is safe and non-toxic, and has biodegradability in leather products and tanning wastewater, so that the application of the nano-clay in the tanning process becomes an important way for sustainable development of tanning. However, the tanning with nanoclay alone is still insufficient to meet the tanning requirements and the leather shrinkage temperature rise is insignificant.

The invention provides a method for tanning leather based on non-chromium combination of nano-clay, which is mainly based on the synergistic tanning effect of nano-clay, aldehydes and derivative tanning agents, remarkably improves the wet heat resistance stability of the leather, and Ts can reach more than 85 ℃; meanwhile, the self-alkalization capability of the nano-clay simplifies the tanning process, alkali extraction is not needed, the content of neutral salt in the wastewater is further reduced, and the nano-clay is biodegradable and is an environment-friendly material, so that the method completely meets the requirement of clean leather making.

Disclosure of Invention

The invention aims to realize chromium-free and clean production of leather, overcome the defects that aldehyde and derivative tanning agents are easy to yellow and generate free formaldehyde when being used for tanning independently, and provide a method for tanning leather based on nanoclay and non-chromium combination.

In order to achieve the purpose, the invention adopts the following technical scheme, and the specific operation method comprises the following steps:

(1) pickling: adding 60% water and 7% salt into a rotary drum at normal temperature, dissolving completely, adding softened pelts, and rotating for 10 min; sequentially diluting, adding formic acid and sulfuric acid to adjust the pH value to 2.8-3.0, and rotating for 30 min;

(2) tanning: adding 2.0-8.0% of aldehyde and derivative tanning agent into the pickle liquor, and rotating for 2-3 h; then weighing 1.5-4.5% of nano clay, adding the nano clay for three times at intervals of 30 min each time until the pH value reaches 5.0-5.5, and continuing rotating for 60 min; standing overnight, and rotating for 30 min the next day to discharge liquid and wash.

The method for tanning leather based on nanoclay non-chromium combination is characterized in that the aldehyde and derivative tanning agent is any one or more of glutaraldehyde tanning agent, modified glutaraldehyde tanning agent, oxazolidine tanning agent and sulfone synthetic tanning agent.

The method for tanning leather based on nanoclay non-chromium combination is characterized in that the nanoclay is any one or a mixture of more of laponite, rectorite, zeolite powder and sepiolite powder. The magnesium-aluminum silicate mineral is rich in magnesium-aluminum silicate minerals, is derived from natural substances, and is environment-friendly and non-toxic.

The method for tanning leather based on non-chromium combination of nano-clay is characterized in that the nano-clay is added for three times, the pH value of the tanning liquid is gradually increased by utilizing the self-alkalization capacity of the nano-clay, the aldehyde and derivative tanning agents can be promoted to fully generate the synergistic crosslinking effect with the nano-clay among collagen, the humidity and heat resistance stability of the leather is remarkably improved, the tanning process can be simplified, alkali does not need to be extracted, and the content of neutral salt in the leather-making waste liquid is reduced.

The method for tanning leather based on the non-chromium combination of the nano-clay has the following advantages:

1) the nano clay used in combination with tanned leather belongs to natural products, has wide sources, is safe, environment-friendly and nontoxic, and is beneficial to clean production of leather;

2) the nano clay has self-alkalization capacity, can simplify the tanning process, and does not need to extract alkali; the synergistic tanning effect of aldehyde and derivative tanning agents and nano clay can be promoted, and the moisture-heat resistance stability and fullness of leather are obviously improved;

3) the nano-clay also has the ultraviolet resistance and formaldehyde adsorption capacity, can improve the light resistance of aldehyde tanned leather, and avoids the risk of free formaldehyde generation.

Detailed Description

Example 1

(1) Pickling: putting water and softened pelts in a weight ratio of 0.6: 1 into a rotary drum at normal temperature, adding 7% NaCl, and rotating for 10 min; sequentially diluting, adding formic acid and sulfuric acid to adjust pH to 2.8, and rotating for 30 min;

(2) tanning: adding 2.0% of aldehyde and derivative tanning agent, and rotating for 3 h; then adding 3.0% of nano clay for three times until the pH value reaches 5.0, and continuing rotating for 60 min; standing overnight, and rotating for 30 min the next day to discharge liquid and wash.

Example 2

(1) Pickling: putting water and softened pelts in a weight ratio of 0.7: 1 into a rotary drum at normal temperature, adding 8% NaCl, and rotating for 10 min; sequentially diluting, adding formic acid and sulfuric acid to adjust pH to 3.0, and rotating for 30 min;

(2) tanning: adding 8.0% of aldehyde and derivative tanning agent, and rotating for 3 h; adding 1.5% nanometer clay three times until pH reaches 5.0, and rotating for 60 min; standing overnight, and rotating for 30 min the next day to discharge liquid and wash.

Example 3

(1) Pickling: putting water and softened pelts in a weight ratio of 0.8: 1 into a rotary drum at normal temperature, adding 8% NaCl, and rotating for 10 min; sequentially diluting, adding formic acid and sulfuric acid to adjust pH to 2.9, and rotating for 30 min;

(2) tanning: adding 6.0% of aldehyde and derivative tanning agent, and rotating for 2 h; adding 4.5% nanometer clay for three times until pH reaches 5.5, and rotating for 60 min; standing overnight, and rotating for 30 min the next day to discharge liquid and wash.

Example 4

(1) Pickling: putting water and softened pelts in a weight ratio of 0.9: 1 into a rotary drum at normal temperature, adding 7% NaCl, and rotating for 10 min; sequentially diluting, adding formic acid and sulfuric acid to adjust pH to 2.8, and rotating for 30 min;

(2) tanning: adding 4.0% of aldehyde and derivative tanning agent, and rotating for 2 h; then adding 3.0% of nano clay for three times until the pH value reaches 5.0, and continuing rotating for 60 min; standing overnight, and rotating for 30 min the next day to discharge liquid and wash.