Organosols, preparation of plastisols
In cases where in order to achieve certain properties of the plasticizer concentration must be less than 50 hours.100 h.PVC, volatile organic additives are added to form organosols.The most common hydrocarbons due to their relatively low cost and ease of regeneration.In the plastisol compositions containing 25-50 h.ester plasticizer, the addition of 5-10 h.hydrocarbon diluent leads to a low and stable viscosity.Selected brands should provide the ignition temperature, consistent with the terms of the safe operation.
Instead of the hydrocarbon diluent can use ketone or ester;such a substance commonly referred to not as a diluent, dispersant and to reflect its compatibility with the vinyl.Typical additives of this class are diizobutil ketone and hexyl acetate.They have a greater impact on viscosity than hydrocarbons, but they require more costs for solvent recovery.Savings can be achieved by mixing the hydrocarbons with ketones or esters, but they are not only difficult to efficiently regenerate, but also difficult to maintain a constant composition during the recycling.In the absence of adequate systems solvent recovery should consult with the manufacturer on the use of other options, such as, for example, vinyl latex compounding.
In addition to the influence of shear rate on viscosity for efficient mixing of the plastisol is required addressing the dispersion, heat, and possibly de-aeration.As for any confusion, it is necessary to destroy the solid agglomerates (good dispersion) and to achieve a homogeneous composition (good distribution).Need for dispersion shift.This must be done without excessive heat generation in order to prevent the onset of gelation, which can easily occur at temperatures of 40 ° C or above.It is desirable to maintain the temperature below 30 ° C using a cooling jacket, short cycles and the corresponding rate of mixing.
is important that all the contents of the mixer and stirred uniformly active.This is especially important for those plastisol having a viscosity decreases with shear (shear thinning).In these cases, the desirable number of blades on the shaft.Compositions whose viscosity decreases with increasing shear rate, is usually more efficient mixing at higher speeds, whereas dilatant (thicken with increasing shear rate), plastisol better mix on low speed.
For low-intensity mixers include ribbon blenders, conical screw mixers, planetary and double planetary testosmesiteli.Belt and conical screw mixers are used for the compositions with a viscosity of low to medium, where the need for dispersion is absent or low, such as application processes many coatings, spraying and dipping.If you need small amounts of trudnodispergiruemyh ingredients such as pigments, it is best to add them as a plasticizer in the form of a dispersion paste.
Planetary mixers are suitable for plastisol having a viscosity of medium to high;here requires a high homogeneity and the need for dispersion of small.Typical applications include:sealants, adhesives, molding hollow articles casting, coating fabric, applied knife device.Low Intensity Mixers are usually equipped with cooling jackets, heat them a little and there is a slight tendency to take air.On the other hand, the duration of mixing is high, often exceeding one hour, if there is no cooling.Planetary mixers, such as Ross, and are suitable for organosols, because they can be easily connected to the plant for solvent recovery.
High intensity mixers are two main types:high-speed mixers, such as a Cowles Dissolver, and mixers with a sigmoid blades, such as a Littleford.Despite the cooling jacket, heat and air capture can be high, so the cycles should be short (10-20 min.).On the other hand, mixing with the sigmoid blades are better suited for the average viscosity of plastisols.Heat and air capture lower due to the cycle time.Faucets with sigmoid blades have a good ability to disperse.High-speed and have sigmoid blade mixer can be equipped with equipment for removing fumes diluent to use for organosols.
In the low intensity mixers are usually loaded 60-80% of plasticizer and liquid stabilizer.After the start of the cooling water and turn the mixer is a quick introduction and distribution of resin.Then, if necessary, add powdered stabilizers.This is often accompanied by a short period of mixing to complete homogenization of the resin introduced.At this point you can take a sample for quality control.Then add filler at the introduction into the mixture, add an equal speed.Then enter the pigment dispersion or other pasta.At this point add the rest of the plasticizer include a vacuum to remove trapped air and continue mixing on the experience of the laboratory results.For plastisols with high viscosity and do not contain fillers is usually not necessary to hold parts of a plasticizer to improve the shear.
In a high intensity mixer entire softener and liquid ingredients all at once downloaded.Resin, and then the other solids are added to funnel high-speed impeller, cooling and stirring, or metered into the mixer with the sigmoid blades, and then include the vacuum.
The largest variety in the preparation of plastisols are combined in the mixers, which are low-and high-intensity and mixer, such as a combined dissolver Cowles (Morehouse Industries) or a combined mixer Ross Versamix.They are two or more of the shaft, which can operate independently.Load all liquid ingredients and include a low speed impeller mixer.Then successively charged resin, filler and other ingredients.At this point, include high-speed stirrer, cooling and vacuum and finally stirred.For low-viscosity compositions can be used from the very beginning both impeller mixers - low and high shear.If necessary to use closed organosols motors and controls for fumes.
For satisfactory deaeration is usually possible to combine resin mixing, which lowers the viscosity, dispersed pre trudnodispergiruemye ingredients, use surface-treated fillers, substances to reduce the viscosity of matter that make it easier to use and deaeration vacuum during the mixing.When it is impracticable to remove the air can be an extra stage;the most suitable equipment for this purpose is Cornell Machine Co.Versator.This vacuum-mixer-deaerator, which improves the homogeneity.There are other types of equipment, including laboratory options.It can be assumed that the trapped air can be useful for foamed plastisols, but it is not.Isolation of the said air foaming leads to the formation of through holes and loss of uniformity of cellular structure.
Plastisols moderate viscosity is usually filtered through a stainless steel sieve to remove incidental impurities, often resulting from the use of cheap fillers.For use in thin-film coatings and low-viscosity plastisols organosols filtered under pressure through the cartridge or bag filters.Organosols can be cleaned and triple roll kraskoterke to improve the dispersion and separation of impurities.
Plastisols should be stored at temperatures below 27-30 ° C, to prevent swelling and increase in viscosity of the resin.Under proper conditions, the viscosity increases for a few days after mixing and then levels off.Reaches a value of viscosity depends on the solvating power of plasticizer;plasticizers to facilitate the rapid melting, leading to obtaining the highest values \u200b\u200bof viscosity.If the temperature reaches the range of 45-60 ° C, the gelatinization starts, which makes the product unusable.Proper storage involves no contact with the surrounding air.The absorption of moisture from the air can destabilize the viscosity of plasticizer to reduce the thermal stability of the finished product at the expense of hydrolysis stabilizer, and affect cellular foam in foam products.It may be useful in dry air cover to store stock;for very sensitive products using dry nitrogen.