Classifications

• • C—CHEMISTRY; METALLURGY
  • C14—SKINS; HIDES; PELTS; LEATHER
  • C14C—CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING, IMPREGNATING, FINISHING; APPARATUS THEREFOR; COMPOSITIONS FOR TANNING
  • C14C3/00—Tanning; Compositions for tanning
  • C14C3/02—Chemical tanning
  • C14C3/08—Chemical tanning by organic agents
  • C14C3/22—Chemical tanning by organic agents using polymerisation products

Definitions

• This invention relates to a method for improving the processes in leather treatment, and more particularly to the use of selected polymers to improve the wringing, splitting and shaving steps in leather treatment.
• Animal hides and skins are converted into useful leather by processing involving both wet and dry operations.
• the wet operations include trimming and sorting, soaking, fleshing, unhairing, bating, pickling, tanning, wringing, splitting and shaving, retanning, coloring, fatliquoring and setting out.
• leather is produced from hide which is first pickled and then tanned and neutralized.
• the tanned stock is subsequently wrung to remove excess moisture from tanned stock so that it can be properly handled on the splitting and shaving machines which follow to adjust the thickness of the tanned stock to that required for the end use.
• Chromium salts are often used to tan hides because a stable hide is produced.
• residual waste is produced which contains some of the chromium salts.
• Some tanneries now attempt to complete the mechanical splitting and shaving operations before the hide is subjected to the chrome tanning so that the residual waste will not contain any chromium salts.
• These tanneries however experience difficulties because hides which have not yet been chrome tanned are characteristically sticky causing the hides to stick to the processing machinery used to split and shave them.
• Our invention permits the tannery to overcome this sticking problem if it chooses to split and shave the hides before chrome tanning. Furthermore, our invention improves the splitting and shaving steps even if the chrome tanning step is completed before the splitting and shaving steps.
• a dispersion of a selected amphiphilic copolymer formed from a predominant amount of at least one hydrophobic monomer and a minor amount of at least one copolymerizable hydrophilic monomer in the pretanning and tanning step improves moisture release in the wringing step and improves thickness adjustment in the splitting and shaving steps of leather treatment.
• a method of the present invention involves the use of a dispersion of a selected amphiphilic copolymer formed from a predominant amount of at least one hydrophobic monomer and a minor amount of at least one copolymerizable hydrophilic monomer in the pretanning and tanning step in addition to the other pretanning and tanning agents used.
• the resulting tanned leather has improved moisture release in the wringing step and improved thickness adjustment in the splitting and shaving steps of the leather treatment.
• the selected amphiphilic copolymer must contain at least one hydrophobic and at least one hydrophilic group.
• the copolymer is formed from greater than 10% by weight to less than 50% by weight of at least one hydrophilic monomer and greater than 50% by weight to less than 90% percent of at least one hydrophobic comonomer.
• the copolymer is formed from greater than about 15% by weight to less than about 45% by weight of at least one hydrophilic monomer and greater than about 55% by weight to less than about 85% by weight of at least one hydrophobic comonomer, and even more preferred if the copolymer is formed from greater than about 20% by weight to less than about 40% by weight of at least one hydrophilic monomer and greater than about 60% by weight to less than about 80% by weight of at least one hydrophobic comonomer.
• the hydrophilic monomer used to prepare the amphiphilic copolymer is at least one monomer selected from water-soluble ethylenically unsaturated, preferably monoethylenically unsaturated, acidic or basic monomers or mixtures thereof.
• hydrophilic monomers examples include acrylic acid; methacrylic acid; itaconic acid; fumaric acid; maleic acid;and anhydrides of such acids; acid substituted (meth)acrylates, such as for example, phosphoethyl methacrylate and sulfoethyl methacrylate; acid substituted (meth)acrylamides such as, for example, 2-acrylamido-2-methylpropylsulfonic acid; and basic substituted (meth)acrylates and (meth)acrylamides, such as for example, amine-substituted methacrylates including dimethylaminoethyl methacrylate, tertiarybutylaminoethylmethacrylate and dimethylaminopropyl methacrylamide and the like.
• the preferred water soluble hydrophilic monomers used to prepare the amphiphilic copolymer are acrylic acid and methacrylic acid.
• the selection of the nature and concentration of the hydrophilic monomer was made to impart the amphiphilic copolymer with the ability to be well dispersed in the continuous phase, such as for example in water, and for the amphiphilic copolymer to be prepared at high polymer solids at a handleable or shearable viscosity without adversely affecting the ability of the copolymer to penetrate the leather.
• the hydrophobic comonomer used to prepare the amphiphilic copolymer is at least one monomer selected from alkyl (meth)acrylates; primary alkenes, and vinyl esters of alkyl carboxylic acids, and mixtures thereof.
• Suitable hydrophobic monomers include C4 to C12 alkyl acrylates; C4 to C12 alkyl methacrylates; C4 to C12 1-alkenes, and vinyl esters of C4 to C12 alkyl carboxylic acids.
• the preferred hydrophobic monomers which have been found to provide the amphiphilic copolymer with the best performance characteristics are the C4 to C12 alkyl (meth) acrylates and mixtures thereof, most preferably 2-ethylhexylacrylate.
• (meth) refers to both acrylates or acrylamides and methacrylates and methacrylamides, respectively.
• Minor amounts of other ethylenically unsaturated copolymerizable monomers at concentrations equal to or less than 50% by weight of the total hydrophobic comonomer concentration may be used in combination with a predominant amount (greater than about 50% by weight) of at least one of the above types of hydrophobic comonomers.
• additional hydrophobic comonomers have been found to be useful as diluents for the other hydrophobic comonomers without adversely affecting the water release properties obtained upon treatment with the amphiphilic copolymer.
• Examples of such useful copolymerizable hydrophobic diluent comonomers include styrene, methylstyrenes, vinylacetate, (meth)acrylonitrile n-alkyl (meth) acrylamides and olefins.
• the amphiphilic copolymer may be prepared by the polymerization of the hydrophilic and hydrophobic monomers by any conventional polymerization technique. We have found a preference for conducting the polymerization using standard emulsion polymerization procedures using a water soluble free radical initiator at a concentration of from about 0.1% by weight percent to about 3 % by weight based on total weight of the monomers.
• the polymerization is preferably conducted at a temperature of from about 40°C to about 100°C, preferably from about 50°C to 70°C, using a chain transfer agent, such as for example a mercaptan, to control the molecular.weight.
• the weight-average molecular weight of the amphiphilic copolymer useful in the method of the invention can be as low as about 2500 to as high as about 100,000, preferably less than about 50,000.
• the polymerization may be conducted by polymerizing all monomers together or by the gradual addition of monomers until polymerization is essentially complete. Residual unreacted monomers can be incorporated into the polymer by the addition of subsequent initiator by techniques well known in the art.
• the polymerization produces a concentration of amphiphilic polymer solids in a non-organic solvent of from as low as about 20% solids to as high as about 60% solids.
• the treatment process of the invention involves subjecting leather during the pretanning or tanning step to the selected amphiphilic copolymer dispersion.
• the amount of copolymer used to treat the leather is in the range of from about 0.09% solids by weight to about 20% solids by weight polymer on weight of leather, preferably in the range of from about 0.35% solids by weight to about 10% solids by weight and most preferably in the range of from about 1% solids by weight to about 5% solids by weight.
• We evaluated the amphiphilic copolymers by comparing the relative ease of wringing, shaving and splitting among leathers pretanned with and without the selected amphiphilic copolymer dispersions.
• the polymerization was conducted under nitrogen atmosphere in a one liter, four-necked, round bottom flask equipped with a Teflon® blade stirrer in the center neck, a thermometer and a reflux condenser.
• Into the flask was charged 185 grams deionized water, 4 grams sodium lauryl sulfate, 1 drop of sulfuric acid and 0.3 grams of a 1% by weight solution of ferrous sulfate. This mixture was then heated to 60°C.
• the monomers 140 grams of 2-ethylhexyl acrylate and 60 grams of methacrylic acid
• 10 grams of n-dodecane thiol chain transfer agent were emulsified with 95 grams of deionized water and 4 grams of sodium lauryl sulfate, and, simultaneously with the initiators, 0.6 grams ammonium persulfate diluted with 22 grams water and 0.6 grams sodium bisulfite diluted with 22 grams water, were fed to the reaction flask over a three hour period maintaining the temperature of the reaction mixture at 60°C. At the end of the additions, any remaining monomer was converted to polymer by the shotwise addition of 0.1 gram additional redox and free radical initiators.
• the polymer emulsion was then cooled and the pH was adjusted by the addition of 20.4 grams of 13% aqueous solution of sodium hydroxide.
• the final product contained 37.8% solids by weight and has a pH of 5.5.
• the weight-average molecular weight of the polymer as measured by gel permeation chromatography using polyacrylic acid copolymer as the standard, was 8200 and the number average molecular weight was 6600.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Treatment And Processing Of Natural Fur Or Leather (AREA)

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• 1994
  • 1994-09-19 EP EP94306833A patent/EP0646651A3/de not_active Withdrawn
  • 1994-09-20 AU AU73070/94A patent/AU684529B2/en not_active Ceased
  • 1994-09-22 BR BR9403821A patent/BR9403821A/pt not_active IP Right Cessation
  • 1994-09-23 CN CN94116442A patent/CN1046959C/zh not_active Expired - Fee Related

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