Glossary of common terms used in the dipping and coating industries:
Accelerator: Compounding material used in small amounts with vulcanizing agent to increase the speed of vulcanization and enhance physical properties of the vulcanizate.
Activator: Compounding material used in small proportion to increase the effectiveness of an accelerator.
After Cure: Continuation of the process of vulcanization after the energy source has been removed.
Air-curing: Vulcanization at ordinary room temperature or without the aid of heat.
Anchor Coat: The layer of latex compound applied to the back of tufted carpet to secure the tufts to the backing fabric. Generally this coating is based on CSBR latex with large amount of added filler.
Anode process: Term for the coagulant dipping process where the former is first dipped into the coagulant, then into the latex compound.
Anticoagulant: Substance that prevents the coagulation of a colloid suspension or emulsion.
Antifoaming Agent: Chemical added to a liquid mix to prevent formation of foam, or added to the foam itself to break the foam already formed. Long chain saturated alcohols containing 6 to 18 carbon atoms and emulsions of certain silicone polymers are principal antifoams used.
Anti-gelling Agent: Material that prevents latex gelling. Ammonium hydroxide and other basic substances are anti-gelling agents of latex.
Anti-tack Agent: Material used to reduce the surface tack of latex products; usually, but not necessarily powders.
Anti-webbing Agent: Additive used to reduce web formation in latex dipping.
Antioxidant: Compounding material used to retard deterioration caused by oxidation.
Artificial Latex: Term to denote latex prepared by dispersing a preformed polymer in an aqueous medium to distinguish from synthetic latex made by emulsion polymerization.
Attritor: Type of grinding machine used for the preparation of aqueous dispersions. The grinding action is provided by an impeller stirring the gravel grinding medium. Attritors are faster in their grinding action than standard ball mills.
Autoclave: Pressure vessel used for vulcanizing rubber products by means of steam under pressure.
Ball Mill: Grinding machine most widely used by the latex industry for preparation of dispersions, consisting of a rotating container, part filled with pebbles or stones. Friction between the pebbles produce the grinding action.
Beading: Rolled ring at the open end to reinforce the dipped goods.
Bentonite: Colloidal clay, naturally occurring hydrated aluminum silicate. Bentonite is used to thicken latex, and as compounding material for natural rubber.
Biocide: Generic name for chemicals that eliminate or reduce microbial activity; those that kill fungi are called fungicides, those that kill bacteria are bactericides. Materials that merely prevent microbial multiplication are known as fungistats or bacteristats.
Blanc Fixe: Precipitated barium sulphate used in NR latex to obtain filled compounds, from which smooth strong film deposits are obtained.
Bloom: Thin layer of a compounding ingredient formed on the surface of rubber article (or a compound) when the ingredient is present at a concentration in excess of its solubility in rubber at the prevailing temperature.
Brownian Motion: Agitated movement of suspended colloidal particles, when a colloidal dispersion is examined using a light microscope at high magnification. This motion is caused by collision with the molecules of the continuous phase; the rate and extent of Brownian movement increases at higher temperatures.
Butyl latex: Latex produced by dissolving butyl rubber in a solvent and by emulsification of the solvent to get the latex.
Centipoise: One hundredth of a poise, which is a value for viscosity. The viscosity of water at 20°C (68°F) is approximately one centipoise.
Centrifuge: Machine for separating by centrifugal force the heavier components from the lighter components of a liquid solution, dispersion, or emulsion.
Centrifuge Latex: Latex, the rubber concentration of which has been increased by centrifuging.
China Clay: Kaolinite, a mineral hydrated aluminum silicate (Al2O32SiO22H2O), a white, mildly reinforcing rubber compounding ingredient.
Chloroform Number: Name given to the method of determining the cure of prevulcanized latex, mixing a portion of chloroform and accessing manually the physical nature of the coagulum produced.
Coacervant: Coating of a coagulant on the surface of former for producing dipped rubber products.
Coagulant: Substance used for causing coagulation. Salts, polyvalent cations such as calcium, acids (including volatile acids like acetic and formic), dehydrating solvents and combinations of these are commonly used as coagulants of latex, for preparing latex dipped goods.
Coagulation: An irreversible agglomeration of the dispersed particles of a colloid solution. In rubber latex, clotting together of the dispersed rubber globules to form coherent jelly-like mass.
Coagulant Dipping: Process of dipping former into a coagulant. Mainly two processes are used, “Anode” and “Teague”. In the “Anode” process, the former is first dipped into the coagulant, then into the latex compound. In the “Teague” process, the former is dipped first into the latex compound, then into the coagulant. The process may be repeated in either case to build up the desired film thickness. The film is cured on the former after dipping.
Coagulum: Piece of rubber formed by coagulation of latex.
Coagulum Content: Term to describe the weight of dry solid material retained when NRL is sieved under standard conditions.
Colloid: State of matter in which size of the particles is greater than normal molecular dimensions but too small to be seen without the aid of a microscope.
Compound: Term used in both latex and dry rubber technologies to denote the mixture (of rubber and additives) from which a rubber product is made.
Compounding: Process used to produce a compound.
Concentrated latex: Latex, the rubber content of which has been greatly increased by evaporation, creaming, filtration, or centrifuging. It usually contains a small percentage of added preservative or stabilizer such as ammonia, or a protective colloid, to prevent coagulation.
Copolymer: Polymer produced by polymerization of a mixture of two monomers.
Cord Dipping: Process of impregnation of tire cords passing them through rubber latex, and then drying side by side to make a sheet, or by passing them through a solvent solution of rubber and then removing the solvent.
Count: Method of defining the diameter of rubber threads the number of thread-diameters per inch.
Counter Ions: Ions of opposite electrical charge to the absorbed ions in the aqueous phase of latex or dispersion, associated with the latex particle.
Creaming: Reversible process consisting of gathering by gravitational force, rubber particles surround by serum, near the bottom or near the top of latex.
Creamed Latex - Cream latex: Latex concentrate produced by creaming process. Creamed latex is normally supplied at a higher TSC value than centrifuged latex e.g. at 66%
Creep: Continuing extension or flow exhibited by all rubbers held under tensile or compressive force.
Crosslinking: Process of bridging individual rubber molecules through the formation of covalent chemical bonds between the rubber molecules.
Cup Lump: Lump of rubber (coagulated field latex) remaining in the tapping cup after emptying out the latex.
Degradation: Loss of physical strength or other properties suffered by polymers under various influences, e.g. by oxidation, heat, ozone etc.
Diplomat™: DipTech Systems line of automatic dipping machines. Used in both laboratory and small part production, these units are known for providing exact, repeatable dipping motion profiles.
Dipped Goods: Articles of manufactured rubber, usually thin walled, by dipping suitable former into compounded latex and allowing the rubber coating to dry, vulcanizing the coating, and removing the articles from the former.
Dipping Process: Deposition of rubber on the article or former dipped directly into latex, pure gum or compounded, drying and vulcanzing the deposition after the former is withdrawn.
Dispersion: Any system consisting of one material subdivided into a continuum of another in which it is not soluble. Emulsions and Latices are specific types of dispersions.
Suspension: Often, but not exclusively, applied to relatively coarse dispersions.
Slurry: Exclusively used to describe coarse, or very coarse, suspensions of powders.
SOL: Usually applied to very fine particle size dispersions of solid material.
Double Centrifuged Latex: Natural latex centrifuged twice to yield a concentrate with approximately half the amount of NRS found in ordinary centrifuged concentrate.
Drum Lining: Material used to line the inside of mild steel latex drums to prevent contamination of the latex.
Dry Picking: The loss of (latex) coating from the paper surface during printing.
1. Rubber obtained from field latex by acid coagulation, washing, sheeting or crumbling, and drying.
2. Rubber made from field latex coagulum such cup lump, tree lace, etc.
Dry Rubber Content (DRC): Mass of rubber coagulated by acid from one hundred parts mass of latex.
Dry Stripping: Removal of dipped products from formers, usually after application of powder lubricant, by mechanical means (e.g. rotating brushes) without the aid of water.
Dwell Time: 1. Time of immersion of a dipping former in latex
2. Time that a dipping former is stationary in latex.
Emulsifier: Surfactant used to prepare an emulsion.
Emulsion: System in which a liquid is colloidally dispersed in another liquid. Emulsions for latex use are of the oil in water type in which water is the continuous phase and suspended droplets carry negative charge.
Emulsion Polymerization: The process of making synthetic polymers by free radical polymerization of an emulsion of a monomer or mixture of monomers.
Emulsifying Agent: Substance added to an emulsion to increase its stability and reduce the risk of separation of the two components. Soaps are widely used as emulsifying agents in the preparation of latex compounds for production of dipped goods.
Enzyme: Catalytic organic substance of animal or vegetable origin, not composed of living cells but capable of causing fermentation or other chemical changes in organic matter. Rubber latex is stated to contain a coagulating enzyme. When the latex is allowed to stand, this enzyme or bacteria, or both, causes the formation of acid substances that bring about coagulation.
Evaporated Latex: Concentrated natural rubber latex produced by evaporating some of the water from the field latex. This latex is normally supplied at high TSC (up to 72%).
Flocculation: Formation of loosely coherent partially agglomerated rubber distributed in the liquid phase of latex.
Field Latex: Latex obtained on tapping the Hevea tree.
Fish Eyes: Term commonly used to describe the small lens-like blemishes sometimes found in dipped goods. Such blemishes often arise from silicone based emulsions used as anti-foam or anti-webbing agents.
Flocculum: Aggregate of latex particles in latex or latex compound.
Flock Adhesive: Latex mix in which household glove gel is dipped prior to the application of flock.
Flock: Short cotton or other fibers used to line the inner surface of household gloves.
Form: Article having shape of the finished product immersed in latex in the dipping process.
Former: Same as form.
Gel: Chemically, colloidal solution set to a jelly
Gel Content: That fraction of a polymer insoluble in solvent. The gel content of rubber from mature NRL is usually of the order of 40-50% by weight, the actual amount being solvent dependent.
Gelation: Any process which converts latex into a gel of the same external shape as the vessel or mold in which it is placed.
Higher Fatty Acids: Fatty acids with 10 or more carbon atoms present in natural latex. The higher fatty acids (HFA) number is defined, similarly to the VFA number, as the equivalent quantity of potassium hydroxide.
Homogenizer: Machine for preparing emulsions, or for improving the homogeneity (and reducing the viscosity) of latex.
Hydrogel: Polymer capable of absorbing high proportions of water without passing into solution.
Hydrogel Coating: Low-friction coating employed on powder-free gloves and other products.
KOH Number: Number of grams of KOH (potassium hydroxide) equivalent to the acid radicals combined with the ammonia in natural rubber latex containing 100g of solids.
Latex concentrate: Preserved, stabilized latex obtained by adding preservatives to, and concentrating, field latex.
Latex, Creamed: Latex, the rubber concentration of which has been increased by creaming and removal of the separated serum.
Latex Rubber, Prevulcanized: Rubber latex in which the particles have been sufficiently vulcanized to produce films and useful articles by drying.
Latex Compound: Intimate mixture of latex with all the ingredients for the finished latex rubber product.
Latex Compounding Ingredients: Material added to rubber latex to form latex compound.
LATZ: Low ammonia preserved latex in which the preservatives comprise of 0.2% ammonia and 0.0125% each of TMTD and zinc oxide as dispersions and 0.05% lauric acid. VFA formation is effectively checked in this preservative system.
Leaching: Process normally carried out on all dipped goods for removal of all the water soluble substances on the latex film.
Leatherboard: Product made by binding group-up leather with latex. The latex may be natural or synthetic, or a mixture. Leatherboard is used mainly in the shoe industry.
Mechanical Stability Time: Time in seconds for the initiation of latex coagulation when subjected to high speed stirring.
Modulus: Force per unit cross sectional area required to distort rubber to a given extent. In extension it is an extensional or tensile modulus, and in compression a compression modulus. Conventionally, the moduli are calculated using the initial cross sectional area, i.e. the area before distortion.
Mold Release (agent): Substance applied to the inner surfaces of a mold to facilitate removal of the finished product. Particularly used in molded latex foam technology.
Mud-cracking: Phenomenon in which latex deposit on the formers for producing the dipped goods cracks on drying, like cracked dried mud.
Non-rubber Constituents: Material found in
the serum of latex apart from, but associated with, the actual rubber
hydrocarbon particles such as resins, sugars, proteins, minerals, salts, acid
Oxidation Catalyst: Any substance which accelerates the rate of oxidation of a polymer. Copper is such an oxidation catalyst and, in lesser degrees, Manganese, Chromium and Iron and other transition metals.
Ozone Cracks: Cracks that appear in the surface of natural rubber (and some synthetic rubber) articles when exposed to the atmosphere under and tensile strain. The direction of ozone cracks is always at right angles to the direction of strain.
pH Scale: Scale marked from 1 to 14 measuring the hydrogen ion concentration, that is acidity or alkalinity of material. As per this scale, materials having pH less than 7 are acidic substances and above 7 are alkaline substances.
Planetary Ball Mill: Ball mill that both spins on its own axis and, simultaneously, rotates about another axis, giving faster grinding action than a conventional mill.
Polyglycol Process: The method of heat sensitizing natural latex, using certain polypropylene glycols, developed in the 1950s by E.G. Cockbain at MRPRA.
Polymer: Macromolecular material formed by the chemical combination of monomers having either the same or different chemical composition.
Polymerization: Chemical reaction in which the molecules of a monomer are linked together to form large molecules, whose molecular mass is a multiple of the original substances.
Polyurethane: Synthetic rubber or resin prepared by the condensation of an organic isocyanate and a polyester or polyether. It has high abrasion resistance, high tear resistance and low hysteresis.
Positex: Form of NRL in which the particles possess a positive electrical charge. (In normal NRL the particles have a negative charge.)
Pre-coagulation: Coagulation or destabilization of field latex through bacterial action. Some of the bacteria feed on carbohydrates of the latex and convert them into volatile fatty acids such as formic acid and acetic acid, while some others feed on the proteins of latex and decompose them. The resultant thickening of latex is known as pre-coagulation, premature coagulation, auto coagulation and spontaneous coagulation.
Precure: Measure of the degree to which a latex compound pre-vulcanizes (cross links) during storage.
Preservatives: Chemical or bactericidal activity which destroys or deactivates micro-organisms and enhances the colloidal stability of latex. Ammonia is the most popular preservative. Certain other chemicals used along with lower concentration of ammonia are called secondary preservatives.
Prevulcanization: Process of vulcanizing latex prior to making a product. The prevulcanization may be either partial or complete, with respect to the ultimate level of cure required for the product.
Prevulcanized Latex: Latex produced by prevulcanization process.
PRM Test; Prem Test: Method of assessing the state of cure of a prevulcanized latex by measuring the relaxed modulus of a ring prepared from a dipped tube of the latex.
PRM Value: Value obtained from the PRM test, normally in units of Kg/cm2.
Redispersed Latex (latices): Latices made by dispersion of a performed polymer. Such latices include those of butyl rubber, EPDM, Hypalon, reclaimed rubber etc.
Rubber Latex, Evaporated: Latex, the rubber concentration of which has been increased by evaporation of some part of the water.
Rubber Latex, Preserved: Rubber latex treated to inhibit putrefaction and accompany coagulation.
Rubber Latex, Prevulcanized: Rubber latex in which the rubber particles have been sufficiently vulcanized to produce films and useful articles by drying.
Skim Rubber: Rubber obtained by coagulation of skim latex, this rubber has a very high protein content.
Skin: Partially dry film formed on the surface of latex left exposed to the air and unstirred.
Sludge: Substances that get settled at the bottom of the latex tank comprising the magnesium ammonium phosphate, sand, dirt and other heavier matter in the latex. A sludge trap is provided at the outlet of the latex tank to rid the latex outflow of the sludge.
Sol: A term, often used in academic publications, to denote a colloidal dispersion, usually of very fine particle size.
Solvent Roughening, Solvent Wrinkling: Terms used to describe the process of producing a rough, irregular pattern of wrinkles on the outside of a latex dipped product by immersing the wet gel in a solvent.
Solvent Stripping: A (rarely used) method of stripping in which the dipped product is swollen in a solvent to facilitate removal from the former.
Spontaneous Coagulation: Coagulation of field latex stored without the addition of preservatives. This coagulation is presumed to be due to the development of acidity from the activity of bacteria.
1. Resistance of colloidal dispersion to destabilization.
2. Resistance of polymer to degradation.
1. Term used to describe the increase in viscosity shown by natural (dry) rubber during storage.
2. Sometimes used to mean the similar increase in viscosity of rubber in natural latex (not the viscosity of the latex) that occurs in the first 2-3 months after concentration.
Straight Dipping: Dipping process which uses no coagulant or gelling agent.
Strainability: Ease with which latex concentrate can be sieved or filtered. Usually measured as the number of liters of latex that passes through a filter before it becomes clogged. This measure is used more in extruded thread technology than in other branches of latex processing.
Stripping: Removal of dipped latex products from the formers after drying/vulcanizing.
Stripping Aid: Substance, usually added to the coagulant in a coagulant dipping process, to facilitate subsequent removal of the latex product from the former. Various powders are usually used as stripping aids.
Styrene Butadiene Rubber (SBR): Most widely used synthetic rubber produced by the co-polymerization of styrene and butadiene. It rubber possesses good abrasion resistance and ageing characteristics.
Sub-stage Latex: Concentrated NRL produced (in effect) by one half concentrations, e.g. by partial creaming (or centrifugation) followed by full centrifugation. The resulting concentrate has approximately two thirds the amount of NRS found in normal concentrate. This latex can be an intermediate between normal latex concentrate and double centrifuged latex.
Sulphur: Main vulcanizing agent of rubber products including dipped latex goods.
Sulphur Donor: Chemical which acts as source of sulphur in the vulcanization reaction. Tetra methyl thiuraudisulphide is such a chemical.
Surfactant: Surface active agent substance preferentially adsorbed at an interface between two phases. In latex technology the interface is usually the rubber particle-serum interface but in foam technology, it may equally be the air-serum interface.
Synergies: Spontaneous contraction of latex gel, resulting in expression of serum to the surface.
Synergism, Synergy: Term used to describe the positive interaction of two additives in a formulation. For example, the increased rates of vulcanization given by combinations of dithiocarbamates and thiazole accelerators.
Synergist: Additive to enhance the action of another.
Synthetic Latex: Aqueous colloidal dispersion of any synthetic polymer (plastic or rubber) whether made directly by emulsion or polymerization or by emulsification of solution of a preformed polymer, or by any other means.
Tackifier: Compounding ingredient which enhances the surface tack of uncured rubber compounds. Tackifiers are exemplified by pine tar, and are classed under ‘softeners and processing aids.’
Tensile Strength: Breaking stress in tension of an elastomer expressed in Mpa, kg/cm2 or lb/in2. It is calculated on the original (unstressed) area of cross section of the test specimen.
Terpolymer: Polymer produced by polymerization of a mixture of three monomers.
Total Solids: Residue obtained from drying a sample of latex.
Total Solids Content: Weight percentage of solid material (both suspended and dissolved) in latex, measured by evaporating known weight of latex to dryness at a temperature of 100°C - 105°C. Usually referred to by its abbreviation, TSC.
Tree lace: Strips of dried rubber formed on the tapping panel of the rubber tree after latex collection.
Type I allergy: Allergy caused by certain residual proteins in a latex product, characterized by the rapidity of its occurrence and manifested as contact urticaria and anaphylaxis.
Type IV allergy: Allergy caused by some of the latex additives such as accelerators and occasionally antioxidants. This allergy normally manifests itself in the form of allergic contact dermatitis.
Volatile Fatty Acid: The steam-volatile fatty acids present in natural latex consisting, essentially, of formic, acetic and propionic acids. These are measured by the volatile fatty acid (VFA) test.
Vulcanization: Irreversible process during which a rubber compound becomes less plastic, more resistant to swelling by organic liquids and elastic properties are conferred, improved, or extended over a greater range of temperature through change in its chemical structure.
Vulcanizing Agent: Any material that can produce in rubber the change in physical properties known as vulcanization, such as sulphur, polysulfides, organic polynitro derivatives and peroxides.
Webbing: Formation of liquid film of webs between adjacent formers or between parts of the same former.
Zeta Potential: The electrical potential difference between the surface (strictly the slip plane) of a latex particle and the bulk of the aqueous phase. Theoretically this is a measure of the colloidal stability of a latex, i.e. the higher the zeta potential the higher the stability of the latex. However, this theory does not appear to apply to natural latex concentrate.
ZAAV Test: A test measuring the increase in viscosity of a latex after addition of a zinc tetra-amine acetate solution.
Zinc (oxide) Sensitivity: Response of a latex or latex compound to the addition of zinc oxide or other zinc containing chemicals. The more sensitive a latex is, the more unstable it becomes when zinc compound is added.
ZOA Process: Any process using zinc oxide and an ammonium salt to produce heat-sensitizing effect.
ZOV Test: Test measuring the increase in viscosity of latex after addition of zinc oxide.
ZST Test: Test measuring the mechanical stability of latex after addition of zinc oxide.
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