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Author Gerhard John, Europaring 24 and distributor: D-68623 Lampertheim Phone + fax: 49-6206-3242 Translation by: Dorothee Mayer and Susan Keller Gardistenstraße 13 D-64289 Darmstadt Phone: 49-6151-783070 Fax: -783071 Printed: Copyright 1996 CD-ROM ISBN 3-00-001555-8 3 Preface While studying the available literature on tanning I discovered that there are only occasional references to possible sources of defects in leather manufacturing in the respective specialist books. For this reason I have tried to present in this manual a comprehensive look at possible problems as well as their remedies. During 47 years of working in the leather industry, including 30 years in the leather department of BASF in Ludwigshafen, I was confronted with the smaller or more serious production problems of many leather factories both in Germany and abroad. In most cases it was possible to identify and pin-point the problems and also to remedy them. However, in some cases correction of defects was not possible as the skin and leather material had suffered irreversible damage. Every responsible leather specialist is familiar with the many influences to which the entire manufacturing process is subject. Therefore, he should always adhere strictly to the formula developed for each respective type of leather at all stages of the production process in order to produce leather of consistently high quality. When changing the production method, only one change should be introduced at a time and its effect thoroughly examined before adding another step which might prove necessary. I hope that this manual provides quick informative help for practicians, engineers, leather merchants and all those involved in the interesting matter "leather". However, due to further product developments and technical progress in the field of leather making, it will not be possible to prevent other new sources of defects in future. Lampertheim, April 1997 Gerhard John 4 Foreword This book by Mr Gerhard John fills a gap in an area which has not been thoroughly covered until now by providing a detailed description of possible defects in the complex and complicated subject of leather technology. A book of this kind can be written only by someone who, like Mr John, has many years of practical experience as a leather specialist. His survey is of special value in that it deals with all fields of leather technology in the same detail. This was possible because he formerly worked for BASF, a leading company in all fields of leather technology. For instance, he was able to include his experience with a very wide range of chemical products. However, the subject can only be adequately treated using the respective technical terms for the manifold processes. This book therefore provides at the same time an introduction to leather vocabulary and the concepts of leather technology. This book is addressed above all to experts and aspiring experts. Even specialists should find it useful to consult the "Big John" when researching into the causes of problems. They might find many a solution which they have never thought of or had not considered in a particular situation. The book is therefore a screening aid. Moreover, the second part of the book provides an excellent survey of methods for leather testing, a description of the many kinds of leather and fundamental information on leather production and leather characteristics. With their systematic arrangement, commendable brevity and accuracy the final chapters are highly recommended as a reference for people with less experience in leather manufacture, namely leather processors and merchants. Professor Dr. Seeheim-Jugenheim, E. Heidemann April 1997 (retired) Contents 5 Preface 3 Foreword 4 Indruction - The "natural product leather" 11 Rawstock 13 Mainly used raw hides and skins 13 Raw hide magazine 21 General structural conditions 21 Storage conditions for raw hides 21 Raw hide and skin defects 22 Defects in the living animals 22 Flaying damage 25 Damage caused by preservation 26 Water quality 31 Classification according to source: 31 Possible defects due to substances contained in the water 31 Soaking 33 Determine soaking completed by checking condition of the hide 33 Controls during the soaking process: 33 Soaking defects 34 Depilation and opening up the skin 36 Controls of the liming process 36 Test of the liming chemicals 36 Lime painting methods 37 Liming methods 37 Liming defects 41 Deliming 45 Control of the deliming process 45 Test of the deliming chemicals 45 Commonly used deliming products 46 Deliming methods 47 Deliming defects 48 Bating 49 6 Contents Determining the final stage of bating 49 Controls of the bating process 49 Test of the bating agents 50 Bating intensity 50 Bating defects 51 Degreasing 52 Defects due to inadequate degreasing 52 Mechanical processes in the beamhouse 54 Vessels 54 Fleshing machine 54 Splitting machine 55 Unhairing, slating and scudding machine 55 Rinsing or washing processes 56 Pickling 57 Control of the pickling process 57 Parameters of the pickle 58 Pickling defects 59 Tannage-general 60 Tanner´s golden rule 60 Chrome tannage 61 Controls of chrome tannage 61 Testing the chrome tanning agents 61 One-bath tanning process 62 Two-bath tanning process 62 Increase of basicity, basification 63 Masking, masking agents 63 Defects caused in chrome tannage 64 Wet blue production 67 Standard for wet blue 67 Aluminium tannage 68 Parameters of aluminium tanning agents 68 Wet white production 69 Procedure 69 Zirconium tannage 70 Parameters of zirconium tanning agents 70 Contents 7 Iron tannage 71 Parameters of iron tannage 71 Sulphur tannage 72 Procedure of sulphur tannage 72 Vegetable / synthetic tannage 73 Vegetable tanning materials 73 Manufacture of tannin extract 74 Lignin extracts 74 Tanning properties of the most important tanning agents 75 Production of syntans 76 Classification and properties 76 Tanning methods 78 Bleaching, filling, fixation of vegetably tanned leathers 80 Controls of vegetable tannage 81 Testing vegetable and synthetic tanning agents 81 Defects by vegetable tannage 82 Reactive tannage 85 Resin tanning agents 85 Aldehyde tannage 86 Formaldehyde 86 Glutaraldehyde 86 Tannage with polymers 87 Polymer tanning agents 87 Polyphosphates 88 Aluminium silicates 88 Tanning with fatty substances 89 Chamois tannage 89 Tannage with sulphochlorides 89 Tannage with fatty alcohol sulphates 89 Pretannage 90 Possible types of pretannage 90 Retanning 91 The most important retanning methods 91 Combination tannings 92 Possible types of combination tanning 92 Storage of tanned leathers 93 Damp storage 93 Possible defects 93 8 Contents Mechanical processes after tannage 94 Processing of area measured leathers 94 Processing of vegetably tanned, heavy leathers 95 Detannage 96 Measures and elimination of disturbing factors 96 Detannaging procedure 96 Deacidification (neutralization) 97 Controls of deacidification 97 The most important neutralizing agents 98 Parameters of deacidification 100 Possible defects 100 Fatliquoring 101 Fatliquoring methods for leather 101 Principal basic fatliquoring substances 103 Fatliquoring products used 104 Testing the fatliquoring agents 104 Parameters of fatliquoring 105 Controls of fatliquoring 106 Errors in application 107 Possible defects in the leather 108 Water-repellent treatment 114 Methods of water-repellent treatment 114 Disturbing factors and possible mistakes 116 Controls of the water-repellent treatment 118 Dyeing 119 Classification of the dyes (according to application) 119 Dyeing methods 122 Requirements to be met by leather dyes 125 Requirements to be met by leather dyeing 128 Factors which influence of leather dyeing 132 Leather defects due to incorrect dyeing 140 Stripping of incorrect dyeings 146 Drying of leather 147 Drying methods 147 Drying defects 150 Contents 9 Mechanical processes after drying 153 Finishing 158 Structure of finishes (schematic) 158 Classification of finishes 159 Basic products for finishing applications 165 1. Leather coating colours (pigment preparations) 165 2. Organic dyes for finish preparations 169 3. Thermoplastic and cross-linking binders 170 4. Non-thermoplastic binders 172 5. Grain impregnation agents 178 6. Base coating agents 179 7. Top coating agents 181 8. Plasticizers 183 9. Finishing auxiliaries 184 10. Organic solvents and diluents 188 General composition of finishing floats 189 Application of finishes 190 Drying of finishes 194 Requirements to be met by leather finishes and testing 195 Flesh side finishes 202 Lustre treatment of suéde and nubuk leathers 203 Grain-forming operations 206 Finishing defects 209 Defects of the finishing products 209 Defects of the finishing floats 211 Possible defects of application 212 Finishing defects on the leather 215 Requirements and tests for leather 227 Chemical requirements and tests 228 Physical requirements and tests 250 Ecological factors and requirements 275 In the production processes 275 Waste water 281 Waste 286 Production of leatherboard 290 Requirements for leatherboard materials 290 Processes of manufacture 291 Properties of the substances used 292 10 Contents Types of leather 294 1. Leather for shoe upper construction 296 2. Leather for shoe inside construction 307 3. Leather for shoe underside construction 309 4. Furniture and upholstery leathers 314 5. Garment, glove and hat leathers 318 6. Leather for sports equipment 327 7. Saddlery leathers and leathers for bags 328 8. Fancy and fine leathers 330 9. Orthopaedic leathers 335 10. Leather for safety and work protection 339 11. Technical leathers 342 12. Raw skin products 346 Sorting and storage of the leather 348 Leather compared to synthethic substitute materials 350 Care of leathers 351 Leather care products 351 Recommendations for the care of different leathers 352 Some stains and how to treat them 354 Cleaning of leather 356 Cleaning procedure 356 Index 360 Technical books, literature-bibliography 377 References 377 Information sources 377 Introduction 11 The "natural product leather" Leather and fur making is one of the oldest trades of mankind. In the early days, the skins of animals killed for food were made fast to putrefaction by kneading them with grease, which also made them supple and soft.