Chrome-free leather retanning

Abstract

A method for forming chrome-free retanned leather including: (a) contacting wet white with from 1% to 8%, by solids weight, based on the wet weight of wet white, retanning agent selected from the group consisting of: i) an aqueous emulsion polymer including, as copolymerized units, from 2% to 35%, by weight, based on the weight of the emulsion polymer, ethylenically-unsaturated monomer bearing at least one epoxy group, the emulsion polymer having a weight average molecular weight of from 2,000 to 100,000; ii) a compound selected from the group comprising piperazine, piperazine hydrates, salts of piperazine, and combinations thereof; and iii) combinations of i) and ii); (b) heating the contacted wet white; and (c) drying the contacted, heated wet white is provided. The present application also relates to chrome-free retanned leather formed by the method of the invention.

Claims

1. A method for forming chrome-free retanned leather comprising: (a) contacting wet white with from 1% to 8%, by solids weight, based on the wet weight of wet white, retanning agent selected from the group consisting of: i) an aqueous emulsion polymer comprising, as copolymerized units, from 2% to 35%, by weight, based on the weight of said emulsion polymer, ethylenically-unsaturated monomer bearing at least one epoxy group, said emulsion polymer having a weight average molecular weight of from 2,000 to 100,000; ii) a compound selected from the group comprising piperazine, piperazine hydrates, salts of piperazine, and combinations thereof; and iii) combinations of i) and ii); (b) heating said contacted wet white; and (c) drying said contacted, heated wet white.

2. The method of claim 1 wherein said ethylenically-unsaturated monomer bearing at least one epoxy group is selected from the group consisting of glycidyl (meth)acrylate, allyl glycidyl ether, and mixtures thereof.

3. The method of claim 1 wherein said compound is a mixture of piperazine phosphate and piperazine pyrophosphate.

4. A chrome-free retanned leather formed by the method of claim 1.

Description

EXAMPLES 1-7 and COMPARATIVE EXAMPLES A-B

Test Results

(1) TABLE-US-00002 TABLE 1.1 Emulsion polymer samples used in evaluation Weight Average Sample ID Composition Molecular Weight Sample 1 95BA/5GMA/3MMP 34000 Sample 2 47.5EHA/47.5BA/5GMA/3MMP 12500 Sample 3 95EHA/5GMA/3MMP 7300 Sample 4 95EHA/5GMA/5nddm 21500 Sample 5 90EHA/10GMA/5MMP 5900 Sample 6 80EHA/20GMA/5MMP 8000 Sample 7 65EHA/35GMA/5MMP 12400 Comparative 100EHA/3MMP 6700 Sample a Comparative 100EHA/5MMP 4300 Sample b

(2) Note: Sample 1 is the emulsion polymer used in Example 1; Sample 2 is the emulsion polymer used in Example 2, etc. Comparative Sample a is the emulsion polymer used in Comparative Example A and Comparative Sample b is the emulsion polymer used in Comparative Example B.

(3) TABLE-US-00003 TABLE 1.2 Dye Delivery Evaluation Sample ID Composition Usage Coloring Results Blank 3.sup.rd best brown hue, slightly bleached - fair color Example 1 95BA/5GMA/3MMP 3% 2.sup.nd best brown hue, less vivid - good color Example 2 47.5EHA/47.5BA/ 3% 2.sup.nd best brown hue, less 5GMA/3MMP vivid - good color Example 3 95EHA/5GMA/3MMP 3% The best brown hue, vivid - good color

(4) There is no significant difference on color expression when changing the composition of copolymerized (meth)acrylic ester from BA to EHA.

(5) TABLE-US-00004 TABLE 1.3 Dye Delivery Evaluation Sample ID Composition Usage Coloring Results Blank 5.sup.th best brown hue, bleached to pastel - fair color Example 4 95EHA/5GMA/ 3% 4.sup.th best brown hue, slightly 5nddm bleached - good color Example 5 90EHA/10GMA/ 3% 2.sup.nd best brown hue, less vivid - 5MMP good color Example 6 80EHA/20GMA/ 3% 3.sup.rd best brown hue, slightly 5MMP bleached - good color Example 80EHA/20GMA/ 6% The best brown hue, vivid - very 6 5MMP good color

(6) Increasing usage of inventive polymer benefits the color expression (Example 6 vs Example 6), while there is not much effect of the GMA level from 5 to 20 weight %.

(7) TABLE-US-00005 TABLE 1.4 Dye Delivery Evaluation Sample ID Composition Usage Coloring Results Blank 3.sup.rd best brown hue, bleached to pastel - fair color Example 3 95EHA/5GMA/ 3% The best brown hue, vivid - 3MMP good color Comparative 100EHA/3MMP 3% 2.sup.nd best brown hue, less Example A vivid - good color Example 5 90EHA/10GMA/ 3% The best brown hue, vivid - 5MMP good color Example 6 80EHA/20GMA/ 3% The best brown hue, vivid - 5MMP good color Example 7 65EHA/35GMA/ 3% 2.sup.nd best brown hue, slightly 5MMP bleached - fair color Comparative 100EHA/5MMP 3% 2.sup.nd best brown hue, slightly Example B bleached - fair color

(8) GMA in the emulsion polymer provides the leather better color expression than the emulsion polymer without GMA. When the GMA level is too high (>35%), the effect may be lessened.

(9) TABLE-US-00006 TABLE 1.5 Uptake of Emulsion Polymers Float Clarity & Sample ID Composition Usage Color Blank Semi-turbid, yellow Example 3 95EHA/5GMA/3MMP 3% Semi-turbid, yellow Comparative 100EHA/3MMP 3% Turbid, milky Example A white

(10) The GMA-containing polymer exhibits an improved uptake by chrome-free leathers, thus showing a less turbid float.

(11) TABLE-US-00007 TABLE 1.6 Touch Evaluation Sample ID Composition Usage Touch Blank Slightly dry, smooth Example 4 95EHA/5GMA/5nddm 3% Natural Example 5 90EHA/10GMA/5MMP 3% Slightly draggy Example 6 80EHA/20GMA/5MMP 3% Slightly draggy Example 6 80EHA/20GMA/5MMP 6% Draggy

(12) Increasing the GMA level or the level of GMA-containing emulsion polymer usage improves the grain surface touch by increasing the humid feeling.

EXAMPLE 8

Formation and Evaluation of Chrome-Free Retanned Leather

(13) A retanning agent compound, piperazine (AR) mixture, was added to wet white leather in a retanning process at 45 C. for 90 minutes. The materials were added as 3% (solids %) to wet white hides (taking the hide weight as 100%). The hides were drummed for 90 minutes, and then dried for 24 hr and the properties were assessed through hand feel or instrument testing. Table 8.1 shows the final properties of each hide.

(14) TABLE-US-00008 TABLE 8.1 Evaluation of chrome-free retanned leather Comparative Example B Properties (test method) (No retanning agent) Example 8 Softness (BLC) 4.0 4.3 Softness (handling) soft Very soft Dye intensity (inspection) 3.sup.rd best brown 3.sup.rd best hue; slightly brown hue; bleached-fair slightly color bleached- fair color

(15) For BLC softness, higher values indicate softer leather. Note: The dye intensity for Examples 8 and 9 were rated relative to each other.

(16) Piperazine (AR) mixture is a 1.0/0.8, on a molar basis, mixture of piperazine phosphate and piperazine pyrophosphate.

(17) Example 8 of the invention affords improved softness compared with the Comparative Example.

EXAMPLE 9

Formation and Evaluation of Chrome-Free Retanned Leather

(18) For Example 9, the aqueous emulsion polymer, Sample 3, was blended with piperazine (AR) mixture as 2:1 (solids). A 3% (solids %) blend mixture was added to the wet white hides (taking the hide weight as 100%) in the leather retanning process. The conditions were similar to those used in Example 8. Table 9.1 shows the final properties of each hide.

(19) TABLE-US-00009 TABLE 9.1 Evaluation of chrome-free retanned leather Properties (test Comparative Example C method) (No retanning agent) Example 9 Softness (BLC) 3.4 3.5 Softness Fair Very soft (handling) Dye intensity 2.sup.nd best brown hue; slightly Best brown hue, less (inspection) bleached-fair color vivid-good color

(20) For BLC softness, higher values indicate softer leather. Note: The dye intensity for Examples 8 and 9 were rated relative to each other.

(21) The use of piperazine mixture along with the aqueous emulsion copolymer (Example 9 of the invention) provided leathers with better softness (hand feel) and dye intensity (visual inspection) compared with the Comparative Example.