The Science and Technology of Latex Dipping

  • ID: 4450963
  • Book
  • Region: Global
  • 274 Pages
  • Smithers Information Ltd
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This book describes, in practical terms, the raw materials used in modern latex dipping and how these materials are prepared for use.

Many rubber products that have a direct impact on our health and quality of life today – gloves, condoms, baby bottle teats, catheters and various other medical devices – are made by dipping elastomers in a latex form. Whilst there are many technical articles covering polymer latices, there are few that look in detail into the actual processes employed by the manufacturers to make these products, the constraints that they face and the problems that they must overcome to compete successfully in the market place.

This book looks to help fill that gap by describing, in practical terms, the raw materials used in modern latex dipping, how these materials are prepared for use and the actual processes employed to convert these materials into a finished product. Some of the scientific principles that will be encountered in the production procedures are described in simplified form to help those involved in the manufacturing understand the critical principles involved in latex dipping. In addition, advice is given on the reinforcement of dipped latex products, quality control, problem solving and the validation of the manufacturing processes in an industry that is becoming increasingly regulated.

The book will be of value to all those engaged in the manufacture of dipped latex products, the production plant supervisors, those working in quality control, testing laboratories and technical support functions. It is hoped that those involved in the research and development of latex dipping, together with interested workers outside of the direct manufacturing industry, for example in universities and colleges, will also find it a useful insight into modern manufacturing with latex products, and how science and technology are coming together to provide products to make our world a better place in which to live.

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1 Raw Materials
1.1 Polymer Latex or Polymer Solution?
1.1.1 Natural Rubber Latex
1.1.2 Styrene-Butadiene Rubber Latex
1.1.3 Acryonitrile-Butadiene Rubber Latex
1.1.4 Polychloroprene Latex 
1.1.5 Artificial Latices
1.1.5.1 Synthetic Cis-1,4-Polyisoprene Latex
1.1.5.2 Isoprene-Isobutylene Rubber (or Butyl Rubber) Latex
1.1.5.3 Chlorosulfonated Polyethylene Latex
1.1.5.4 Polyurethane Latex
1.1.5.5 Ethylene-Propylene Rubber Latex
1.1.6 Other Naturally Occurring Latices
1.2 Alkalis
1.3 Surfactants
1.4 Accelerators
1.4.1 Health and Safety of Accelerators
1.4.2 Types of Accelerators
1.4.2.1 Dithiocarbamates
1.4.2.2 Thiuram Disulfides and Polysulfides
1.4.2.3 Thiazoles
1.4.2.4 Xanthates
1.4.2.5 Thioureas
1.4.2.6 Guanidines
1.5 Other Vulcanisation Materials
1.5.1 Sulfur
1.5.2 Peroxides
1.5.3 Zinc Oxide
1.5.4 Zinc Carbonate
1.5.5 Other Materials that can Activate Vulcanisation
1.6 Rubber Antioxidants
1.6.1 Phenolic Antioxidants
1.6.1.1 Antioxidant 2246
1.6.1.2 Antioxidant 425
1.6.1.3 Wingstay L 
1.6.1.4 Butylated Hydroxytoluene
1.6.2 Liquid Antioxidants
1.6.3 Para-phenylene diamines
1.6.4 Network-Bound Antioxidants
1.6.5 Synergistic Enhancement of Antioxidant Activity
1.7 Antiozonants
1.8 Fillers and Pigments
1.8.1 Fillers
1.8.2 Pigments and Dyes
1.9 Testing of Raw Materials
1.9.1 Latex
1.9.1.1 Mechanical Stability Time
1.9.1.2 Measurement of pH
1.9.1.3 Measurement of Viscosity
1.9.2 Other Raw Materials
1.10 Storage of Raw Materials
1.10.1 Latex
1.10.2 Other Raw Materials
1.10.2.1 Sulfur
1.10.2.2 Accelerators
1.10.2.3 Ammonia
1.10.2.4 Acids
1.10.2.5 Other Raw Materials
1.10.2.6 Time-Expired Materials
References

2 Latex Compounding
2.1 Introduction
2.2 Compounding Equipment
2.3 Raw Material Preparation - Liquid Materials
2.4 Raw Material Preparation - Solid Materials
2.4.1 Ball Mill
2.4.2 Attrition Mill
2.4.3 Vibration Mill
2.4.4 Bead Mill/Sand Mill
2.4.5 High-Shear Mixers
2.5 Measurement of Particle Size 
2.6 Storage of Dispersions
2.7 Compounding Procedure
2.7.1 Representation of a Latex Formulation
2.7.2 Addition of Compounding Ingredients
2.7.3 Latex Prevulcanisation
2.7.4 Measurement of Prevulcanisation
2.8 Storage of Compounded Latex
References

3 Vulcanisation
3.1 Introduction
3.2 Brief Overview of the Mechanism of Sulfur Vulcanisation
3.3 Other Vulcanisation Procedures
3.4 Effect of Vulcanisation on Physical Properties
References

4 Degradation of Elastomers
4.1 Introduction
4.2 Mechanism of Oxidative Degradation
4.2.1 Initiation
4.2.2 Propagation
4.2.3 Termination
4.3 Mechanism of Ozone Degradation
References

5  Reinforcement of Latex Systems by the Use of Fillers
5.1 Introduction
5.2 Mechanism of Reinforcement
5.3 Comparisons with Dry Rubber
5.4 The Effect of Vulcanisation
5.5 Materials Used as Fillers
5.5.1 Silicone Dioxide (Silicas)
5.5.2 Clays
5.5.3 Other Inorganic Materials
5.5.4 Polymeric Particles
5.5.5 Graft Copolymers
5.5.6 Polyurethane Dispersions
5.5.7 Proteins
5.6 Conclusions
References

6 Latex Stability and Film-Forming
6.1 Latex Stability
6.1.1 Introduction
6.1.2 Electrostatic Repulsion
6.1.3 Steric Repulsion
6.1.4 Solvation Stabilisation
6.1.5 Depletion Stabilisation
6.1.6 Controlling Latex Stability
6.1.7 Measuring Latex Stability
6.1.8 Using Latex Stability
6.1.9 Zinc Oxide Thickening
6.1.10 Final Thoughts on Latex Stability
6.2 Latex Film-Forming
6.2.1 Introduction
6.2.2 Film-Forming
6.2.3 Effect of Shrinkage and Uneven Pick-up
6.2.4 ‘Orange Peel’
References

7 Latex Dipping
7.1 Introduction 
7.2 Straight Dipping 
7.2.1 Former Entry into the Latex
7.2.2 Former Exit from the Latex
7.2.3 Drying
7.2.4 Subsequent Dips
7.2.5 Beading
7.2.6 Vulcanisation
7.2.7 Leaching
7.2.8 Stripping
7.2.9 Former Clean
7.3 Coagulant Dipping
7.3.1 Former Preheat
7.3.2 Coagulant Dip
7.3.3 Coagulant Dry
7.3.4 Latex Dip
7.3.5 Latex Drying
7.3.6 Subsequent Dips
7.3.7 Flocking
7.3.8 Beading
7.3.9 Leach
7.3.10 Vulcanising
7.3.11 Prestrip Soak
7.3.12 Stripping
7.3.13 Former Clean
7.4 Heat-Sensitised Dipping 
7.5 Electrodeposition
7.6 Spray Coating
References

8 Wetting
8.1 Wetting of a Solid Surface by a Liquid
8.2 Measurement of Wetting
References

9 Latex Dipping Tanks
9.1 Chain Plants - General
9.1.1 Entry/Exit Mechanisms on a Chain Plant
9.2 Batch Dipping Plants
9.3 Latex Dipping Tank Construction
9.4 Latex Dipping Tank Design
9.4.1 Dipping Tanks for Straight Dipping
9.4.2 Dip Tanks for Coagulant Dipping
9.4.3 Dip Tanks for Heat-Sensitised Dipping
Reference

10 Formers for Latex Dipping
10.1 Former Materials
10.2 Former Design
10.3 Former Mounting

11 Finishing Operations for Dipped Latex Products
11.1 Introduction
11.2 Halogenation
11.3 Powdering
11.4 Silicone Oil 
11.5 Polymer Coating
11.6 Other Approaches to Finishing
References

12 Troubleshooting in Latex Dipping
12.1 Introduction
12.2 Sampling
12.3 Examination of any Defects
12.4 Collection of Data
12.5 Corrective Action 
12.6 Some Types of Defect and Suggested Corrective and Preventive Actions
12.6.1 Mechanical Damage
12.6.2 Other Causes of Holes
12.6.3 Coagulum and Cream
12.6.4 Bubbles
12.6.5 Foreign Bodies
12.6.6 Damaged Formers
12.6.7 Stuck Work (also known as ‘Flats’ or ‘Stickies’)
12.6.8 Unwetted Marks (also known as ‘Fish Eyes’)
12.6.9 Bead Defects
12.6.10 Discolouration
12.6.11 Double Imaging
12.7 Conclusion
References

13 Quality Control in Latex Dipping
13.1 Introduction
13.2 Analysis of Data
13.3 Data Considerations - Variables Data or Attributes Data?
13.4 Control Charts
13.4.1 Control Charts for Variables
13.4.2 Control Charts for Attributes
13.5 Process Capability
13.5.1 Relative Precision Index
13.5.2 Cp and Cpk Indices
13.6 Cumulative Sum Charts
References

14 Process Validation
14.1 Introduction
14.2 Design Qualification
14.3 Installation Qualification
14.4 Operational Qualification
14.5 Process Qualification
14.6 Reporting
14.7 Revalidation
14.8 Concurrent and Retrospective Validation
14.8.1 Concurrent Validation 
14.8.2 Retrospective Validation
14.9 Example of a Process Validation
14.9.1 Installation Qualification
14.9.2 Operational Qualification
14.9.3 Process Qualification
References

15  Some Analytical Methods used in Latex Dipping Operations
Reference

16 Allergies, Proteins and N-nitrosamines
16.1 Allergic Reactions
16.2 Extractable Latex Proteins
16.3 N-nitrosamines
References

17  Potential Future Trends in the Latex Dipping Industry
17.1 Introduction
17.2 Possible Manufacturing Processes
17.2.1 Spray Coating
17.2.2 Electrodeposition
17.2.3 Drying and Vulcanisation
17.3 Possible New Materials
17.3.1 New Latices
17.3.2 Fillers
17.3.3 Nanotechnology
17.4 Increasing Regulatory Requirements
17.5 Increasing Environmental Requirements
17.6 Drug Delivery
17.7 Specialised Coatings
17.8 New Materials
17.9 Reducing Costs
17.10 Improving Measurement Processes
17.10.1 Measuring the Extent of Prevulcanisation
17.10.2 Predicting the ‘Dippability’ of Latices
References

Abbreviations
Index

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