Environment-friendly formaldehyde-free melamine resin retanning agent and preparation method thereof

Abstract

The invention belongs to the field of leather tanning, and particularly relates to an environment-friendly formaldehyde-free melamine resin retanning agent and a preparation method thereof. The preparation method comprises the following steps: slowly dropwise adding a polyepoxy compound into melamine, mixing and stirring, adjusting the pH value of a system, and then heating for reaction to obtain a prepolymer solution; and adding a monoamino compound into the prepolymer solution, and continuously heating to react. According to the preparation method disclosed by the invention, firstly, melamine reacts with a polyepoxy compound, the reaction process is an irreversible reaction, the ring-opening cross-linking reaction conditions of amino groups and epoxy groups are mild, cross-linking can be quickly formed, and subsequent release of free formaldehyde by using formaldehyde as a cross-linking agent is avoided; and secondly, a monoamino compound is used for end-capping condensation, so that the reaction activity is reduced, and the water solubility of the product can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the field of leather tanning, and particularly relates to an environmentally friendly formaldehyde-free melamine resin retanning agent and a preparation method thereof. Background Art

[0002] Traditional melamine resin retanning agents are a class of macromolecular compounds obtained by methylolation, etherification and polycondensation of melamine and formaldehyde under neutral or slightly alkaline conditions. Since methylolation is a reversible reaction process, the resin will undergo a slow decomposition reaction to release formaldehyde during use. Although the consumption of formaldehyde can be promoted by reducing the molar ratio of formaldehyde to melamine, it is still impossible to completely eliminate the release of formaldehyde in the resin. As an improvement, researchers have added formaldehyde scavengers and other measures to reduce the free formaldehyde content in the finished product. Although these solutions effectively inhibit the release of formaldehyde, the application performance of the finished product has been significantly reduced.

[0003] Invention patent CN117903392A discloses a melamine resin retanning agent and a preparation method thereof, the method comprising the following steps: reacting melamine with hydroxymethyldiethanolamine to obtain a prepolymer with good water solubility, reducing the activity of free amino groups in the system by adjusting pH, adding the prepolymer obtained above to epichlorohydrin, reacting the hydroxyl group of the prepolymer with the epoxy group to obtain a chlorine-terminated prepolymer, and finally adjusting pH again to combine the chlorine-terminated prepolymer with the free amino group to achieve the purpose of crosslinking. Although this method can effectively reduce the content of free formaldehyde, the subsequent hydroxyl group and epoxy group ring-opening reaction conditions are relatively harsh, making the epichlorohydrin combination efficiency low, resulting in a large amount of epichlorohydrin residues affecting human health. Invention patent CN103665290A discloses a method for preparing a low-formaldehyde amino resin retanning agent, which prepares a low-formaldehyde melamine resin retanning agent by selecting phenolic monomers with a functionality of 1-6, end-capping modification and end-capping condensation with hydroxymethyl melamine. The formaldehyde content in the melamine resin retanning agent prepared by the invention is 75ppm, which is still relatively high.

[0004] Therefore, it is urgent to develop an environmentally friendly melamine resin retanning agent that does not contain formaldehyde and has excellent application performance. In view of this, the technical solution of the present invention is proposed. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention provides an environmentally friendly formaldehyde-free melamine resin retanning agent and a preparation method thereof. The preparation method reduces the formation of nitrogen hydroxymethyl and methylene ether, not only greatly reduces the content of free formaldehyde in the retanning agent, but also improves the water solubility and storage stability of the product, and is a new formaldehyde-free melamine retanning agent with excellent performance.

[0006] The solution of the present invention is to provide a method for preparing an environmentally friendly formaldehyde-free melamine resin retanning agent, the preparation method comprising the following steps:

[0007] (1) slowly dropping a polyepoxide into melamine, mixing and stirring, adjusting the pH value of the system, and then heating the system to react to obtain a prepolymer solution;

[0008] (2) adding a monoamine compound to the prepolymer solution and continuing to heat the reaction to obtain the environmentally friendly formaldehyde-free melamine resin retanning agent.

[0009] Preferably, in step (1), the polyepoxide compound comprises one or a combination of two or more of ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, and glycerol triglycidyl ether.

[0010] Preferably, in step (1), the pH value of the system is adjusted to 8.4-8.6.

[0011] Preferably, in step (1), the reaction temperature is 40-70° C., and the reaction time is 120-240 min.

[0012] Preferably, in step (2), the monoamine compound includes one or a combination of two or more of sodium 3-aminopropanesulfonate, sodium p-aminobenzenesulfonate, and taurine.

[0013] Preferably, in step (2), the reaction temperature is 80-85° C., and the reaction time is 120-180 min.

[0014] Based on the same technical concept, another embodiment of the present invention is to provide an environmentally friendly formaldehyde-free melamine resin retanning agent obtained by the above preparation method.

[0015] The beneficial effects of the present invention are:

[0016] The preparation method of the present invention firstly reacts melamine with a polyepoxide, and the reaction process is an irreversible reaction. The ring-opening crosslinking reaction conditions of the amino group and the epoxy group are mild, and crosslinking can be formed quickly, thereby avoiding the release of free formaldehyde after using formaldehyde as a crosslinking agent. Secondly, a monoamine compound is used for end-capping condensation to reduce the reaction activity and effectively improve the water solubility of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is the structural formula of the formaldehyde-free melamine resin retanning agent obtained in Example 1 and Example 2.

[0019] Figure 2 It is the structural formula of the formaldehyde-free melamine resin retanning agent obtained in Example 3 and Example 4.

[0020] Figure 3 It is the structural formula of the formaldehyde-free melamine resin retanning agent obtained in Example 5 and Example 6. DETAILED DESCRIPTION

[0021] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0022] Example 1

[0023] This embodiment provides a method for preparing an environmentally friendly formaldehyde-free melamine resin retanning agent, the preparation method comprising the following steps:

[0024] (1) 10 g of melamine and 20 g of ethylene glycol diglycidyl ether were placed in a reactor, the pH was adjusted to 8.5 with liquid alkali, and then the temperature was raised to 40° C. and the reaction was carried out for 240 min to obtain a prepolymer product;

[0025] (2) Weigh 10 g of sodium p-aminobenzenesulfonate and dissolve it in 40 g of water, slowly drip it into the above reactor and react at 80° C. for 180 min to obtain a formaldehyde-free melamine resin retanning agent (structural formula: Figure 1 shown).

[0026] Example 2

[0027] This embodiment provides a method for preparing an environmentally friendly formaldehyde-free melamine resin retanning agent, the preparation method comprising the following steps:

[0028] (1) 30 g of melamine and 60 g of ethylene glycol diglycidyl ether were placed in a reactor, the pH was adjusted to 8.5 with liquid alkali, and then the temperature was raised to 70° C. and the reaction was carried out for 120 min to obtain a prepolymer product;

[0029] (2) Weigh 30 g of sodium p-aminobenzenesulfonate and dissolve it in 120 g of water, slowly drip it into the above reactor and react at 85° C. for 120 min to obtain a formaldehyde-free melamine resin retanning agent (structural formula: Figure 1 shown).

[0030] Example 3

[0031] This embodiment provides a method for preparing an environmentally friendly formaldehyde-free melamine resin retanning agent, the preparation method comprising the following steps:

[0032] (1) 10 g of melamine and 20 g of 1,4-butanediol diglycidyl ether were placed in a reactor, the pH was adjusted to 8.5 with liquid alkali, and then the temperature was raised to 50° C. and the reaction was carried out for 180 min to obtain a prepolymer product;

[0033] (2) Weigh 10 g of sodium 3-aminopropanesulfonate and dissolve it in 40 g of water, slowly drip it into the above reactor and react at 82° C. for 160 min to obtain a formaldehyde-free melamine resin retanning agent (structural formula: Figure 2 shown).

[0034] Example 4

[0035] This embodiment provides a method for preparing an environmentally friendly formaldehyde-free melamine resin retanning agent, the preparation method comprising the following steps:

[0036] (1) 30 g of melamine and 60 g of 1,4-butanediol diglycidyl ether were placed in a reactor, the pH was adjusted to 8.5 with liquid alkali, and then the temperature was raised to 60° C. and the reaction was carried out for 160 min to obtain a prepolymer product;

[0037] (2) Weigh 30 g of sodium 3-aminopropanesulfonate and dissolve it in 120 g of water, slowly drip it into the above reactor and react at 85° C. for 160 min to obtain a formaldehyde-free melamine resin retanning agent (structural formula: Figure 2 shown).

[0038] Example 5

[0039] This embodiment provides a method for preparing an environmentally friendly formaldehyde-free melamine resin retanning agent, the preparation method comprising the following steps:

[0040] (1) 10 g of melamine and 20 g of glycerol triglycidyl ether were placed in a reactor, the pH was adjusted to 8.5 with liquid alkali, and then the temperature was raised to 70° C. and the reaction was carried out for 180 min to obtain a prepolymer product;

[0041] (2) Weigh 10 g of sodium p-aminobenzenesulfonate and dissolve it in 40 g of water, slowly drip it into the above reactor and react at 80° C. for 160 min to obtain a formaldehyde-free melamine resin retanning agent (structural formula: Figure 3 shown).

[0042] Example 6

[0043] This embodiment provides a method for preparing an environmentally friendly formaldehyde-free melamine resin retanning agent, the preparation method comprising the following steps:

[0044] (1) 30 g of melamine and 60 g of glycerol triglycidyl ether were placed in a reactor, the pH was adjusted to 8.5 with liquid alkali, and then the temperature was raised to 50° C. and the reaction was carried out for 120 min to obtain a prepolymer product;

[0045] (2) Weigh 30 g of sodium p-aminobenzenesulfonate and dissolve it in 120 g of water, slowly drip it into the above reactor and react at 85° C. for 120 min to obtain a formaldehyde-free melamine resin retanning agent (structural formula: Figure 3 shown).

[0046] Comparative Example 1

[0047] This comparative example is to prepare a melamine resin retanning agent by referring to the method of Example 1, except that the pH of the system is not adjusted in step (1). Specifically, the following steps are included:

[0048] (1) 10 g of melamine and 20 g of ethylene glycol diglycidyl ether were placed in a reactor, and then the temperature was raised to 40° C. and reacted for 240 min to obtain a prepolymer product;

[0049] (2) Weigh 10 g of sodium p-aminobenzenesulfonate and dissolve it in 40 g of water. Slowly drip the mixture into the above reactor and react at 80° C. for 180 min to obtain a test sample.

[0050] Comparative Example 2

[0051] This comparative example is used to prepare a melamine resin retanning agent by referring to the method of Example 1, except that sodium p-aminobenzenesulfonate is not added for modification in this comparative example, and specifically comprises the following steps:

[0052] 10 g of melamine and 20 g of ethylene glycol diglycidyl ether were placed in a reactor, the pH was adjusted to 8.5 with liquid alkali, and then the temperature was raised to 40°C and reacted for 240 minutes to obtain a test sample of a stratified white retanning agent.

[0053] Comparative Example 3

[0054] This comparative example is used to prepare a melamine resin retanning agent by referring to the method of Example 1, except that an excess amount of melamine is added to carry out the reaction, and specifically comprises the following steps:

[0055] (1) 20 g of melamine and 20 g of ethylene glycol diglycidyl ether were placed in a reactor, the pH was adjusted to 8.5 with liquid alkali, and then the temperature was raised to 40° C. and the reaction was carried out for 240 min to obtain a prepolymer product;

[0056] (2) Weigh 10 g of sodium p-aminobenzenesulfonate and dissolve it in 40 g of water. Slowly drip the mixture into the above reactor and react at 80° C. for 180 min to obtain a test sample.

[0057] Test example

[0058] Test method:

[0059] (1) The formaldehyde-free melamine resin retanning agents prepared in Examples 1 to 6 and the test samples prepared in Comparative Examples 1 to 3 were placed at 50° C. / 5° C. for 48 hours to observe whether precipitation was generated, so as to test the stability of their aqueous solutions.

[0060] (2) The formaldehyde-free melamine resin retanning agent prepared in Examples 1 to 6 and the samples prepared in Comparative Examples 1 to 3 were used as retanning agents to retan cowhide shoe upper leather, and the formaldehyde content, softness and thickening rate of the leather after retanning were tested.

[0061] The raw material of cowhide upper leather is shaved and put into a drum, and then backwater, retanning, neutralization and washing are carried out in sequence according to conventional processes, and then 6% of the weight of the blue leather and 100% of water are added, and the drum is rotated for 2 hours at a temperature of 35°C and a pH of 5.0-5.5, and then the retanning process is completed according to conventional fatliquoring and fixing processes.

[0062] Leather formaldehyde content: tested in accordance with standard GB / T19941-2005 "Determination of formaldehyde content in leather and fur chemical experiments".

[0063] Test of leather softness: According to the standard GB / T39371-2020 "Leather-Physical and Mechanical Tests-Determination of Softness", the leather softness tester is used to test the retanned leather.

[0064] Thickening rate: Use a leather thickness tester to take 5 points on each sample, measure the thickness before and after retanning accordingly and take the average value, and calculate the thickening rate after retanning according to the following formula.

[0065] Thickening rate = (average thickness of leather after tanning - average thickness of leather before tanning) / average thickness of leather before tanning

[0066] The test results are shown in Table 1.

[0067] Table 1

[0068]

[0069]

[0070] As shown in Table 1, the comprehensive performance of the wet blue leather after retanning prepared by the formaldehyde-free melamine resin retanning agent of Examples 1 to 6 is excellent, and the performances such as thickening rate, softness and formaldehyde content are better than those of the samples prepared by Comparative Examples 1 to 3, which fully demonstrates that the formaldehyde-free melamine resin retanning agent prepared by the present invention has excellent application performance and environmental performance. Comparative Example 1 does not adjust the pH in step (1), resulting in incomplete reaction between the amino group and the epoxy group, resulting in a small amount of precipitation; Comparative Example 2 does not add water-soluble sulfonate modification, resulting in a significant decrease in solubility, and the molecular weight of the product is too small to form multi-point crosslinking with skin collagen, resulting in poor comprehensive performance; Comparative Example 3 has excessive cyanuric chloride, resulting in a decrease in the activity of the reaction product, and the binding effect with skin collagen is weak, resulting in poor retanning effect.

[0071] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing an environmentally friendly formaldehyde-free melamine resin retanning agent, characterized in that: The preparation method comprises the following steps: (1) slowly dropping a polyepoxide into melamine, mixing and stirring, adjusting the pH value of the system, and then heating the system to react to obtain a prepolymer solution; (2) adding a monoamine compound to the prepolymer solution and continuing to heat the reaction to obtain the environmentally friendly formaldehyde-free melamine resin retanning agent.

2. The method for preparing the environmentally friendly formaldehyde-free melamine resin retanning agent according to claim 1, characterized in that: In step (1), the polyepoxide compound includes one or a combination of two or more of ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, and propylene glycol triglycidyl ether.

3. The method for preparing the environmentally friendly formaldehyde-free melamine resin retanning agent according to claim 1, characterized in that: In step (1), the pH value of the system is adjusted to 8.4-8.

6.

4. The method for preparing the environmentally friendly formaldehyde-free melamine resin retanning agent according to claim 1, characterized in that: In step (1), the reaction temperature is 40-70° C., and the reaction time is 120-240 min.

5. The method for preparing the environmentally friendly formaldehyde-free melamine resin retanning agent according to claim 1, characterized in that: In step (2), the monoamine compound includes one or a combination of two or more of sodium 3-aminopropanesulfonate, sodium p-aminobenzenesulfonate, and taurine.

6. The method for preparing the environmentally friendly formaldehyde-free melamine resin retanning agent according to claim 1, characterized in that: In step (2), the reaction temperature is 80-85° C., and the reaction time is 120-180 min.

7. The environmentally friendly formaldehyde-free melamine resin retanning agent obtained by the preparation method according to any one of claims 1 to 6.

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