Latex rubber foam products
INTRODUCTION
Latex is originally defined as the stable dispersion of natural rubber particles in aqueous medium as produced in the rubber tree. They are complex colloid systems containing polymer molecules as major fraction. The polymer may be a homo polymer or co-polymer .Stereo regularity and the complexity of the polymer molecules (linear / branched / cross linked) is maintained in the latex form. Lattices are rubbery or resinous in nature and the rubber molecules can be cross linked. Lattices can be plasticized or oil extended. Lattices have their own mechanical properties and temperature limits of serviceability. Latex products are subject to degradation and adequate antioxidant protection is necessary. They can be classified broadly into four main types: natural, synthetic, artificial and modified latices. In Natural lattices large number of plant species secretes lattices containing polyisoprenes, but only Hevea braziliensis latex is industrially important. In á Synthetic lattices with the rapid growth of polymer chemistry since 1940, a large number of synthetic lattices are now available commercially. Artificial lattices are the dispersions of reclaimed rubber, butyl rubber or other polydiene rubbers. They also include latices made by solution polymerization and conversion of the polymer solution into latex. Modified lattices are produced by the chemical modification of the existing types. For e.g., controlled vulcanization of the rubber in latex would produce modified latex generally known as the prevulcanized latex. Natural Rubber Latex (NR Latex) is the most widely used latex for the manufacture of latex based rubber products. Natural rubber (NR) processing sector is an industry which produces raw materials used for the manufacture of rubber industrial products (conveyor belts, rubber rollers, etc.), automotive products (fan belts, radiator hoses, etc.), latex products (rubber gloves, toys hygienic products, etc.) and many kinds of adhesives. The major users of natural rubber are tire and footwear industries.
LATEX PROCESSING
Latex is a dispersion of rubber particles in an aqueous phase. Most types of rubber, both natural and synthetic, can be made into a latex form. Latex gets used in specialized applications such as those requiring oil, solvent or flame resistance. Different mixing techniques produce different grades of dispersions i.e. ball milling or ultrasonic's for fine particle dispersions and simple stirring or colloid milling for coarse dispersions. Latex dipping is used to make thin articles such as gloves, balloons, catheters, bladders; hot water bottles etc and very fine particle dispersions are needed. Coarser particle sized dispersion (slurry) is acceptable for latex foam, used mainly for carpet backing. The following range of additives can be mixed with the latex dispersion or emulsion:
Stabilisers: to maintain the rubber particles in a stable state of suspension. These include sulphonates, inorganic complex phosphates and soaps.
Curing agents, usually sulphur.
Accelerators- including dithiocarbamates, thiazoles, thiurams, and xanthates.
Thickeners- including casein, glue, cellulose derivatives.
Anti degradants- including waxes, substituted phenols, amine based antioxidants.
PH adjusters- including ammonia, sodium and potassium hydroxide, and formaldehyde.
Biocides, mostly halogen derivatives, for suppression of bacterial decay and fungal infection.
Coagulants and gelling agents, include calcium, magnesium and aluminum salts, acetic and formic acid, cyclohexylamine acetate and ammonium acetate.
LATEX DIPPING AND CASTING
This uses a porcelain or aluminum mould (or former) that is repeatedly dipped in the latex compound. Once set, the coated former is washed, air-dried and vulcanized in steam autoclaves before the product is removed. To increase the thickness of the deposit obtained per dip, the former is immersed in coagulant before and after each latex dip.
Latex casting is a similar technique to dipping but is used to make hollow seamless articles. The product forms on the inside of the mould (in contrast to dipping) giving a better surface definition. This process is uncommon.
MECHANICAL HAZARDS
Latex mixing plant and processing equipment such as carpet backing machines, may present a range of mechanical hazards that will require effective safe guarding by the latest available techniques..
LATEX CONCENTRATION
The process of Concentration involves removal of substantial quantity of serum from the latex and increases its rubber content to about 60%. In creaming process, a creaming agent (tamarind seed powder) is added and allowed to remain undisturbed till the desired level of creaming (concentrated rubber) is obtained. In Centrifuging, the latex is subjected to centrifuge force in a bowl rotating at speed around 6,000 surrounding the axis of rotation.
Uses and Applications
- The rubber latex pillows, mattresses, cushions, bedding etc. are used in luxury purposes. The latex foam mattresses are used for manufacturing of sheets in automobiles, cars, tempos, buses, jeeps, aero plane, etc. In hotel some time the floor mat are also used
• In Bed Pillows this item has been widely accepted. They are produced by a large number of the accepted shape used for feather or down pillows, they are generally very soft, but not flabby, retain their shape without "fluffing," and are particularly advantageous for allergy sufferers.
• Decorative Pillows are comparatively new application for foam, but is being received enthusiastically by the buying public.
• Reversible Furniture Cushions is very popular in the furniture field. A similar application is non-reversible furniture seats and backs, airplane, bus, and truck seating.
• Mattresses. Its application is the largest latex volume consumer. They are widely used in hospitals where they permit maximum comfort with minimum replacement where they permit maximum comfort with minimum replacement.
• Automotive Pads. The automobile producers are the largest users of foam rubber in view of number of pieces used. Foam rubber topper pads are now considered standard equipment in most automobiles.
• Composite Products. Latex foam slab is frequently combined during processing with various other materials. A layer of ungelled foam can be deposited directly to the back of a rug, sheeting, upholstery fabric, curled hair and similar types of materials for use as under carpet padding, ironing board padding, lining materials, etc. Applications in this field are limited only by one's imagination.
• Latex foam rubber recovered as manufacturing scrap or recovered from post consumer use can be chopped and utilized when mixed with polyurethane scrap, as bonded carpet cushion.
Properties
• Latex foam is suitable for disposal via municipal landfill or incineration in most states and municipalities.
• Latex foam rubber derives its physical performance properties from the vulcanization process that creates long molecular chains with strong cross linked bonds.
• Latex foam rubber generally has a relatively high density and is soft, thus latex foam rubber can only be used in limited amounts in the production of bonded carpet cushion.
• Latex Foam Producers has a high level of grip, some others are designed to offer maximum durability.
• Latex mattresses are naturally therapeutic and provide extraordinary orthopedic support.
• Superior Thermal Qualities Latex's thermal properties are truly outstanding. Its superior cell structure gives it maximum breath-ability.
Various Products of Latex
1. Foamed latex products: Mattresses, Pillows, Upholstery, Carpet Backings, Packaging materials etc.
2. Dipped latex products: Surgical gloves, House hold gloves, Industrial gloves, Contraceptives, Feeding Bottle teats, Toy balloons etc.
3. Latex extrusions: Latex thread.
4. Latex spreading: Carpet backing, Textile treatment, Paper Coatings.
5. Latex castings: Toys, Bulbs.
6. Miscellaneous: Rubberized coir /fiber products, Battery Separators, Adhesives and PV-latex.
The two modern routes to latex foam products concern the way in which the foam is made
(i) Chemical foaming
(ii) Mechanical foaming
The mechanical foaming processes used today on such a large scale for the production of latex foam goods, uses for most of the part, a concentrated natural rubber latex which is prepared by one of the processes involving partial removal of the non-rubber substances as well as concentration of the rubber (e.g. processes such as centrifugation or creaming). Successful operation of latex foam processes normally demands a concentrated latex one containing a minimum content of the latex, during compounding, to a Valve between 0.1% and 0.25%. This facilitates gelatin and to control the process which is usually done by stirring and blowing a current of air over the surface of the compounded latex as part of the "Maturing process".
Chemical Foaming agents are used in a wide range of applications in plastics and rubber processing. By choosing the right foaming agent system following properties could be achieved.
• Weight Reduction
• Raw Material and Cost Saving
• Dimensional Stability
• Heat Insulation
• Noise Absorption
• Special Surface Effects.
Chemical foaming agents decompose during processing in a chemical reaction which is induced by heat. The decomposition can be exothermic or endothermic.
As Latex foam products are cellular (open cell, closed cell or a combination of open cell and close cell structures) products directly produced from liquid latex compounds. The skin is a smooth surface formed by contact with the mould surface. Since Latex foam has an open cell structure because of this interconnect cell it is spongy in nature.
Natural rubber (NR) latex is a natural commodity that has tremendous economic and strategic importance. Among the applications of NR latex is the production of dipped goods, extruded threads, and adhesives, carpet-backing and moulded foams. This is primarily because of the unique characteristics of NR latex, such as high strength, flexibility and elasticity. Most NR latex products are derived via a sulphur vulcanization system, which achieves the desired physical properties for the product application.
Synthetic latex foam rubber is not flexible polyurethane foam. Synthetic latex foam rubber represents a group of materials manufactured using methods similar to natural latex foam rubber on the same processing equipment.
Synthetic latex foam rubber can be the product of natural rubber suspension and rubber substitute blends, or it can be produced using a totally synthetic process such as used to produce styrene-butadiene rubber (SBR) and polymerized chloroprene, known as neoprene.
Manufacturing Process of Latex (Rubber) Foam Products
Basic Raw Material
• NR Latex (deammoniated).
• Potassium olaste soap solution.
• Sulphur Dispersion
• Zinc diethyl dithiocarbamate Dispersion
• Zinc salt of mercapto benzothizole Dispersion
• Anti oxidant dispersion
• Filler Dispersion
• Zinc Oxide Dispersion
• Secondary Gelling Agent
• Sodium Silico Fluoride Dispersion
• Cure Open Steam
Basic Formula
Parts by wt
60% NR Latex (deammoniated) 167.0
20% Potassium olaste soap solution 5.0
50% Sulphur Dispersion 4.0
50% Zinc diethyl dithiocarbamate Dispersion 2.0
50% Zinc salt of mercapto benzothizole Dispersion 2.0
50% of anti oxidant dispersion 2.0-3.0
Filler Dispersion up to 40.00
50% Zinc Oxide Dispersion 8.0
Secondary Gelling Agent As required
20% Sodium Silico Fluoride Dispersion 5.0-7.5
Cure Open Steam 30-45 min
Process
a. Compounding of Latex
b. Expanding (Foaming) to a desired volume.
c. Setting (Gelling) the rubber particles and
d. Vulcanizing
There are mainly two methods of making Latex Foam, namely
1. Dunlop process, and
2. Talalay Process.
DUNLOP PROCESS
The typical Formulations for the Dunlop process for making Foam is listed below.
Parts by wt.
60% NR Latex (Deammoniated) 167.0
20% Potassium Olaste Soap Solution 5.0
50% Sulphur Dispersion 4.0
50% Zinc Diethyl Dithiocarbamate Dispersion 2.0
50% Zinc Salt of Mercapto Benzothizole Dispersion 2.0
50% of Anti Oxidant Dispersion 2.0-3.0
Filler Dispersion up to 40.00
50% Zinc Oxide Dispersion 8.0
Secondary Gelling Agent As required
20% Sodium Silico Fluoride Dispersion 5.0-7.5
Cure Open Steam 30-45 min
Compounding of Latex
Latex is deammonniated and then Sulphur, Accelerator, Antioxidants and fillers (in the form of dispersion) are added to it in a mixing tank, fitted with a slow speed stirrer. The compound is then allowed to mature by keeping it slowly stirred for several hours.
Foaming and Gelling
Mechanism of Gelling Sodium Silico Fluoride is sparingly soluble in water but hydrolyses in it into hydrofluoric acid and silicic acid.
Na2SiF6 ----------------à 2Na++SiF6-
SiF6- + 4H2O ----------------à Si(OH)4 + 4H+ + 6F-
Liberation of hydrofluoric acid alone is not the cause of gelling as gelling is found to occur at alkaline Ph. The silicic acid formed also plays a vital role in gelling.
In the batch process a planetary mixer is used for foaming. The mixer is provided with a wire cage which rotates in a planetary motion at about 200 rpm. The Latex compound is weighed out into the mixer bowl; soap is then added and whipped into foam by rotating cage beater. Beating time normally varies 15 to 20 min when volume of mix increases from four to six times. The Zinc oxide and the secondary gelling agent are added, followed by Sodium Silico Fluoride. The foamed compound is then poured into the mould.
In the Continuous Process, a frothing machine known as Oakes Frother is normally used. In the machine air is injected into a stream of latex forming coarse foam which is forced between a toothed rotor and stator plate to refine foam. The Gellant is injected late in the Frothing stage. Foam is conducted through a hold to the mould. The rotar speed is adjustable for optimum foaming.
For manufacture of large blocks of Foam Rubber moulds are fitted with metal pins for better heat transfer and easy removal of the products.
Some thickening agents are gelling agents (gellants), forming a gel, dissolving in the liquid phase as a colloid mixture that forms a weakly cohesive internal structure. Others act as mechanical thixotropic additives with discrete particles adhering or interlocking to resist strain.
Thickening agents can also be used when medical condition such as Dysphagia causes individuals difficulty when swallowing.
Vulcanization: Moulded foam products are normally cured by open steam (at 100°C (like carpet under lays) can be cured by hot air.
Working: Vulcanized foam is stripped off from the mould and worked in water by passing the product between the rollers under the surface of water bath. Excess water is then removed by passing through squeeze rollers.
Drying: The worked products are dried in the hot ovens at 60-80°C temperature. Heavier foam grades need longer drying but shorter curing, then the lighter slabs.
TALALAY PROCESS
The original Talalay Process utilized hydrogen peroxide to generate oxygen for expansion. A later development uses Oakes type Mixer. Partially Foamed Latex compound is taken into the mould where foaming is completed by vaccum. The foamed latex is then chilled and gelled by passing carbon dioxide gas. Curing is done by hot air impingement or suction dryers. But this type of plant requires very high capital investment.
Moulded foam rubber can carry loads depending on the density of the foam. It can absorb energy and damp vibrations, also acting as a sound insulator. In mattresses and pillows, it does not require dusting or mechanical rearrangement: natural rubber latex foam is also known to have bactericidal properties.
Compared with natural rubber latex, SBR latex yields foam of lower tensile, strength and elongation at break. The hot tear is also poor, making the removal of the cured foam from the mould difficult. Therefore, SBR latex is rarely used alone but is usually blended with NR Latex.
PLANT ECONOMICS
Rated Plant capacity = 1.00 MT/day
= 300.00 MT/annum
LATEX (RUBBER) FOAM PRODUCT
Basis
No. of working days = 25 days/month
= 300 days/annum
No. of shifts = 1 per day
One shift = 8 hours
LAND & BUILDING COST TOTAL Rs. 92,40,000.00
PLANT & MACHINERY
1. Planetary Mixing Machine Made by SS for slow mixing & compounding of Latex with complete accessories.
2. Mounds for Setting of Latex Foam
3. Vulcanization Chamber with automatic temp. Control and all accessories.
4. Conveyor Belt
5. Demonizing Tank SS with Complete accessories
6. Pot Mill (SS)
7. High Speed Mixture
8. Washing Tank (SS)
9. Squeezing Machine with Rubber Rolls
10. Boiler
11. Dryer Turnnel Type with automatic heating and air blowing system
12. Miscellaneous Machines like Valves, Motors, pipes & Fittings etc.
13. Erection & Installation TOTAL Rs. 79,70,000.00
FIXED CAPITAL
1. LAND & BUILDING Rs. 92,40,000.00
2. PLANT & MACHINERY Rs. 79,70,000.00
3. OTHER FIXED ASSETS Rs. 64,50,000.00
TOTAL Rs. 2,36,60,000.00
WORKING CAPITAL REQUIREMENT/MONTH
RAW MATERIALS
1. Latex (60%)
2. Castor Oil
3. Potassium Hydroxide
4. Darvan
5. Valcastab T.M.
6. 10% Casein Solution
7. Piperidine-Pentamethylene Dithio carbamate
8. Sulphur
9. Notax L.M.
10. Z M B T
11. 10% Silicate Solution
12. Zinc Oxide
13. Bentonite
14. Sodium Silicofluoride
15. Ammonium Oleate
16. Printed Packing Materials
17. Laboratory & ETP Chemicals
18. Consumable Stores TOTAL Rs. 28,28,407.00
TOTAL WORKING CAPITAL/MONTH
1. RAW MATERIAL Rs. 28,28,407.00
2. SALARY & WAGES Rs. 2,79,600.00
3. UTILITIES & OVERHEADS Rs. 4,51,000.00
TOTAL Rs. 35,59,007.00
COST OF PROJECT
TOTAL FIXED CAPITAL Rs. 2,36,60,000.00
MARGIN MONEY Rs. 26,69,255.25
TOTAL Rs. 2,63,29,255.25
TOTAL CAPITAL INVESTMENT
TOTAL FIXED CAPITAL Rs. 2,36,60,000.00
TOTAL WORKING CAPITAL FOR 3 MONTHS Rs. 1,06,77,021.00
TOTAL Rs. 3,43,37,021.00
TURN OVER/ANNUM
By Sale of Latex (Rubber)
Foam Product TOTAL Rs. 6,30,00,000.00
PROFIT SALES RATIO = 23.32%
RATE OF RETURN = 42.78%
BREAK EVEN POINT (B.E.P) = 38.27%
