A processing aid additives
A processing aid additives that with the aim of solving process problems, to the mixture is added. The range of the process additive function is very wide and all levels cover the rubber process. A variety of additives, including: Lubricants, Peptizers, Homogenizing Agents, Tackifiers, Dispersing Agents, Plasticizers.
Lubricants:
The largest group of modern process additives includes lubricants. The major positive effects which can be achieved in various processing stage by using lubricants are listed below:
Mixing
- Faster filler incorporation
- Better dispersion
- Lower dump temperature
- Reduced viscosity
- Improved release
Processing
- Faster & easier calendaring and extrusion
- Improved release
- Less energy consumption
Molding
- Faster cavity fill at lower operating pressure
- Reduced stress in molded parts through easy cavity fill
- Shorter cycle time
- Improved relese
- Reduced mold fouling
In some cases, lubricants are used at the beginning of the mixed cycle, along with fillers, to influence the dispersion. They improve flow characteristics due to the effect of special lubrication. Therefore, the processing behavior of the Compound during the extrusion, calendering, molding, etc. will be especially improved. These additives reduce the viscosity, promote dispersion, shorten mixing time and lower mixing temperature and energy requirements. Often the mold removal is made easier due to the reduce tackiness of cured compound.
Peptizers:
Mastication and peptization are processing stage, mastication denotes the thermomechanical break down of rubber at relatively low temperatures. Physical peptization and mastication relate to the same process.
Chemical peptization describes the thermo-oxidative, catalysed break down of rubber at elevated temperatures.
Peptization facilitates the incorporation of fillers and other compounding ingredients and can improve their dispersion. Improved compound flow leads to leads to easier production of semi products such as profile or molding blanks. Shorter processing times and lower power consumption are obtained.
It is often difficult to homogeneously blend rubbers with very different viscosities. In this cases the high viscosity rubber can be broken down through peptization to enable improved blending with the other, lower viscosity, elastomer.
Since most of todays synthetic rubbers are supplied with easy to process viscosity levels the peptization is mainly restricted to natural rubber.
Struktol, well-known as a leading producer of peptizing agents, has lunched several highly effective peptizer products. They permit the break down of natural rubber during production and processing and ensure optimum dispersion of the peptizer in the rubber, so that a fast viscosity reduction is achieved.
During recent times physical peptizers have gained major importance. They act as internal lubricants and reduce the viscosity whitout breaking the polymer chain. One can distinguish between chemical peptization and break down or viscosity reduction through lubrication.
Benefits of peptizing agent:
- Reduced mixing time
- Reduce power consumption
- Promote batch to batch uniformity
- Facilitate blending of elastomers
- Reduce mixing costs
- Improve dispersion
Time and energy saving when using peptizing agents can add up to 50% in the mixing process. Because of the high effectiveness of peptizing agents the dosages are very low and their own costs are nearly of no consequence compared with production costs saving that may be obtained.
Homogenizing Agents:
Homogenizing agents are products which improve the homogeneity of difficult to blend elastomers, they also assist the incorporation of other compounding materials.
Benefits of homogenizing agent:
- Improve compound homogeneity
- Improve batch compactness
- Reduce energy/ time to complete mix
- Improve smoothing of stock
- Normalise processing characteristics (extrusion, calendaring etc.)
- Enhance tack
- Improve filler dispersion
In homopolymer compounds :
- Reduce nerve
- Improve processing uniformity
- Enhance tack
- Improve filler dispersion
- Smooth out rough stocks
They are resin based mixtures which exhibit a good compatibility with various elastomers and facilitate blending through early softening and wetting the polymer interfaces. Since the softening resins exhibit a certain tackiness polymer which tend to crumble and polymer blends will coalesce more easily, energy input is maintained at a high level, i.e., mixing is more effective and mixing time can often be reduced. Due to the excellent wetting properties of the homogenizing agents fillers are incorporated at a faster rate and are more evenly distributed. Filler agglomerates can frequently be avoided.
Homogenisers lead to enhanced green strength when used as a partial replacement for processing oil and compound flow is facilitated through improved homogeneity and a certain softening effect. They increase green tack of many compound and boost the efficiency of tackifying agents.
Tackifiers:
As most synthetic rubber are less tacky than natural rubber it is often necessary to add tackifiying substances. These should lead to improved uncured ply adhesion (building tack) on assembling and improved knitting of contact areas. They are also used in highly filled “dry” natural rubber compounds. They should give rubber compounds a high degree of tack witch is maintained on storage and facilitate processing through viscosity reduction. Tackiness should not be reduced by compounding materials like waxes.
Tackifires are products which may occasionally act as homogenizing agents. They comprise rosin, coumarone-indene resins, alkylphenol acetylene and alkyphenol- aldehyde resins.
Dispersing Agents:
Dispersing agents can be considered a subgroup of lubricants. the central property, however, is dispersion. In particular they improve dispersion of solid compounding materials. They reduce mixing time and have a positive influence on subsequent processing stages. Dispersing agents have distinct wetting properties. They are often less polar fatty acid esters. Because often a combination of dispersing properties and good lubrication is desirable the dispersing agents available on the market are occasionally mixtures of higher molecular weight fatty acids and metal soaps.
Dispersing agents are usually added together with the filler. Their products form and the low melting point facilitate incorporation. When fillers are added in two steps the dispersing agents should be added at the beginning.
Plasticizers:
Plasticizers improve the flexibility and the elastic behaviour of the vulcanizate. They have a favourable effect on the procesibility of the compounds. Certain types provide good hot-air resistance or increase the electrical conductivity. Often plasticizers make the incorporation of high loadings of filler easier and improve the dispersion.
Influence of Plasticizers:
On physical properties
- Lower hardness
- Higher elongation
- Improved flex life
- Better low temperature performance
- Swelling tendency
- Flame resistance
- Antistatic performance
On processing
- Lower viscosity
- Faster filler incorporation
- Easier dispersion
- Lower power demand and less heat generation during processing
- Better flow
- Improved release
- Enhanced building tack
Vulcan sanat sepahan Co., in order to improve the quality of products and enjoy economical, Based on knowledge and using these processing aid additives, it has been able to optimize the process conditions and improve the properties of rubber compounds.
Ref:
Handbook struktol Rubber