Dry Flowable (DF)
Dry Flowable (referred to as DF) is a solid particulate product obtained directly from pesticide by wet grinding and then spray dried and granulated to remove moisture. China's pesticide registration department uses the name of WG (water dispersible granule) instead of DF to register WG and DF. According to the different production processes, WG is divided into dry process and wet process. DF is water dispersible granule produced by wet process. Due to the process, some DW is registered as water dispersing granule, while some DW is registered as dry suspending agent, which puzzles the users. In fact, there are obvious differences between dry WG and wet WG (i.e. DF) in appearance, and their water entry performance is also different, so it is not difficult to distinguish them.
Pilarquim has been listed on Xinming and Xinming Li, which are produced by wet process, and have obvious advantages compared with those produced by dry process.
The popularity of water dispersing agent (Dry Flowable agent) products is due to its best safety (no dust and solvent), good appearance (free flowing particles), easy measurement, good fluidity (no adhesion, agglomeration and wall sticking), small and simple packaging containers (paper bag packaging and minimum packaging handling problems), good automatic dispersion (pouring into different water temperature, and hard water) It can disintegrate quickly with water temperature and hard water, and has excellent suspending property (usually without stirring or just stirring a little), that is to form uniform spray suspension, the suspension rate can be as high as 90% or even above, and the content of pesticide active ingredient is high (the content is generally above 60%, the highest can reach 90%), and the stability is super good. It can be maintained for 1~2 years without deterioration) and easy to use. It is more attractive in the market than using wettable powder (WP), suspending agent (SC) and emulsifiable products.
1. Characteristics of Dry Flowable
Dry suspending agent is a kind of particulate pesticide formulations. It is an international upgrading product in the following aspects: content, packaging, process, cost, quality stability and application technology. Its excellent properties make it the top product of water dispersible granules.
Since Dry Flowables are suspended in dry state before drying and granulation, spray drying is made into solid particles after granulation, while water is diluted and reverted to suspension state when used, and the solid pesticide particles with a particle size of 1~10 μm are dispersed phase and water is the dispersed phase of continuous phase. After drying, the solid particle state is returned to the suspension state when the water is used. The inherent quality of the product has all the benefits of the suspending agent.
The benefits of Dry Flowable are:
1) It can rapidly disintegrate, disperse and suspend in water. If water is disintegrated and dispersed immediately, and stable suspensions are formed quickly, there will be no precipitation, no agglomeration, and no nozzle will be blocked when using.
2) The suspension with a small amount of water diluent can be used directly for aircraft or ground micro spray. A small amount of spray can improve the working efficiency by 10 times.
3) The product liquid particles are fine enough. After spraying, they can be uniformly attached to the surface of the crop and form a dense protective film. With good adhesion agent, it can enhance the adhesion performance and rain scour, and can prolong the retention period.
4) The particle size distribution of the product liquid is reasonable, which can not only ensure the quick effect and persistence of the medicament, but also ensure the full contact between the agent and the crop surface energy and improve the efficacy.
5) It has good safety and is not easy to cause phytotoxicity.
6) Safe and environment-friendly dosage forms: no organic solvent is used, no pollution caused by solvents, no dust, safe use of drugs, and pesticide damage caused by pesticide drift can be avoided.
7) No dust collection, no adhesive bags, more adequate use, and more safe for the operator and the surrounding environment.
8) After diluted with water, the size of pesticide particles is very fine, which is easy to play a role on the target and has high efficacy.
9) There are two ways to use Dry Flowables: one is the most commonly used product, the product is diluted with water (into suspension), then the stem leaves are sprayed, and the other is mixed with Dry Flowables, and then spayed (such as paddy field herbicides).
2. Production principle of dry suspending agent
There are two essential conditions for Dry Flowables processing. One is to use wet sand milling (SC process) technology to produce suspension, with an average particle size of 1~10 μm. Secondly, spray drying granulation technology is needed to remove moisture and directly produce DF products after sieving.
The specific process is as follows: first, the pesticide suspension slurry containing 20% to 50% pesticide effective ingredients, wetting agent, dispersant, filler and so on is prepared according to the formula, then the material is injected into the spray drying granulation equipment, and the droplets are sprayed out through the nozzle holes (pressure or centrifugal type). After the droplets are heated, the water evaporates rapidly, and the internal moisture moves outwards through the gaps to replenish the surface moisture. The surface quickly forms half dry body, and the internal moisture moves outward and slows down. As the particle temperature rises, the internal moisture starts to vaporize, and the gas pressure increases continuously. When a certain pressure limit is reached, the gas escapes from the weak part of the particle shell and is dried directly (in the same equipment), and then gets the loose DF pellet product directly.
The inner part of DF product is hollow, small and even spherical product, the diameter of which is 50-200 μ m, smaller than that of other granulation methods. The DF product is short in water disintegration time and generally dispersed in cloud and fog. It can disperse spontaneously in 10 s to form original particle size suspensions with high suspension rate. Spray drying granulation method is suitable for large scale continuous production, with large output, professional equipment design and high investment cost. High air consumption, high energy consumption and high production cost are required to be sensitive to heat sensitive materials and suitable for materials with less than 80-degree melting point of active components of pesticides.
Compared with other dry granulating methods such as disc, high-speed agglomeration, extrusion and fluidized bed granulation, DF products are obviously difficult to process, require continuous production, produce large quantities, have high investment costs, high operating costs, and trouble with cleaning equipment. They also need skilled personnel who understand the technology of WG. However, the DF products, excluding the economy, are all superior to other dry granulating methods in WG and other physical and chemical properties (such as suspension, dispersion, disintegration, fluidity and homogeneity).
3. Dry suspending agent processing technology
The technology of Dry Flowables is the formulation of effective ingredients of pesticides. After wet grinding, DF products are produced by spray drying granulation technology. The key technology is closely related to the composition, heat resistance and nebulizer type.
1) Formula composition requirements
The main components of Dry Flowables are composed of effective components of pesticides, surfactants (wetting agents, dispersants), disintegrating agents, defoamer, fillers and auxiliaries. The obtained DF products not only have fast wettability, disintegration, redispersibility and excellent suspension rate, but also have excellent storage stability and dust-proof properties. These are the results of interaction and coordination among components. When some DF products are used, they can also increase the retention of pesticides on the plant surface, prolong the detention time and improve the penetration ability to the plant epidermis by adding auxiliaries, so as to improve the pesticide efficacy, reduce the dosage of medicament, reduce the cost and reduce the environmental pollution.
In addition to the physical and chemical properties and characteristics of pesticides, the surfactant selected in DF products should also consider the impact of surfactant itself on the biological control of the target; in addition, the surfactant selected should have good compatibility to ensure that the pelletized products have excellent comprehensive performance.
(1) Particles should have enough fineness
The formulation of Dry Flowables should meet the ideal fineness attained after wet grinding. Particle fineness is one of the important factors that show the efficacy of the product. In general, the finer particles of the product are, the higher the efficacy is; the fine particles mean that there are more contact points when spraying, that is, the larger area of the pesticide on the target surface, the higher the efficacy. In the formula, the performance of dispersant, wetting agent and other additives, as well as the amount of additives, will affect the grinding efficiency when wet grinding, and also affect the fineness of the product after grinding; therefore, the fineness when processing dry suspending agent should generally be controlled between 1-10 μ m, better between 2-5 μ m, and the excessively fine particle size will increase the grinding time and power consumption, and the grinding equipment may not be able to meet the requirements It is easy to get the bigger diameter, but the efficacy will be reduced when the product is applied.
(2) Heat resistance of components
When the Dry Flowables are prepared, the granulation and drying process should be considered. The composition of the effective ingredients of the pesticides should undergo 1 heating processes. During the spray granulation process, the inlet temperature of the general hot air operation of the spray dryer is above 150 degrees, and the outlet temperature is about 80 degrees Celsius. As we all know, there are many pesticides which are heat sensitive varieties. In order to prevent the agglomeration of the effective components of pesticides from melting after heating, they must be screened for a formula with excellent heat resistance so as to ensure that the products are not affected by heat and cause the performance degradation, so that the final product can keep the fineness of the particles before drying. Therefore, the amount of dispersant used in the preparation of Dry Flowables is always larger than that in suspending agent.
(3) Selection of dispersant
The dispersants used in Dry Flowables formulations are at different stages (sand milling and spray drying granulation). The choice and dosage of dispersants not only affect the agglomeration and dispersion of suspension particles, but also affect the heat resistance of the components.
2) Granulator sprayer type
Spray drying granulation technology is related to the type of spray dryer applied. There are basically 3 kinds of sprayers in industry:
(1)Pressure sprayer: it is necessary to use high-pressure pump to feed, and materials need to be filtered before entering. Otherwise, the clogging problem of sprayer will easily occur. By adjusting the pressure and aperture of the sprayer, the spray flow rate is adjusted. The aperture of the nozzle of the sprayer will be worn after a period, and the aperture will be enlarged. The sprayer has low cost and no need of maintenance, so it can be used only after replacement. However, the sprayer nozzle needs to be specially designed, which has a great influence on the size of granulation and the rate of granulation. The product is a loose (hollow) spherical particle with the size of 50-200 μ m.
(2)Centrifugal sprayer: the material enters the centrifugal force generated by the high-speed rotating disc and atomized the material. The advantage is that it can be applied to materials with large viscosity. The control operation is simple and convenient, and the production elasticity is large. The shortcomings of the sprayer need to be cooled, the dust will fly up, the equipment cost is high, and the maintenance is very difficult. The product is solid powder and granular, and the particle size of the powder product is slightly larger.
(3)The airflow sprayer has a smaller diameter, and is especially suitable for materials with large viscosity. The gas-liquid two phase contacts are flexible, and can be operated in parallel flow, mixed flow and countercurrent, and it is not easy to generate gambling. Usually the power consumption is higher than the other two forms, generally 6~8 times the other two. The product is also powdery and granular, but the particle size of powder product is smaller than that of pressure sprayer. Sometimes the particle is too thin, and it is easy to generate static electricity. Dust flying is also the most serious and generally used less.
4. Similarities and differences betweenDF and SC dosage forms
It is generally believed that the production of Dry Flowables by spray granulation is based on the further processing of granulation and drying based on suspending agents. In fact, these two formulations have similarities and differences. Dry Flowables and suspending agents are in the same way in the earlier stage processing. They are treated by wet grinding to form suspensions. However, the difference between Dry Flowables and suspending agents is not only in the form of final products, but also in different formulations. In the suspension agent, the effective components of pesticides are stored in the water phase for a long time. Therefore, a certain amount of antifreeze (glycol or propylene glycol, etc.) needs to be added to the formula to prevent the use from being affected by freezing, thickener (xanthan gum and aluminum magnesium silicate, etc.) needs to be added to prevent the product from agglomeration and sedimentation, mildew inhibitor (to prevent the xanthan gum from mildew and causing the product to stink), and suspending aid and other auxiliaries, while Dry Flowable is needed Agents often do not need to add such substances. In DF, filler or small amount of binder must be added, and suspending agent usually does not need to add filler or binder.
In addition, as the Dry Flowables are dried and granulated, the active ingredients of the pesticide need to undergo 1 heating processes. In the process of spray granulation, the operating temperature is generally the inlet temperature of the hot air of the spray dryer. The temperature is generally above 150 degrees, and the outlet temperature is about 80 degrees Celsius. As we all know, pesticide products are chemically synthesized organic chemicals, some of which are heat sensitive products. In order to prevent the effective component of the pesticide from melting after heating, it is necessary to select a formula with excellent heat resistance to ensure that the product will not be lowered because of heat, so that the final product will retain the fineness of the particles before drying. In addition, the amount of dispersant used in the preparation of Dry Flowables is also more than that of suspending agents. This is due to the high content of effective components of pesticides and the heat resistance when spray drying is needed. In addition, in order to ensure a high granulation rate in the granulation process, the suspension should have a certain viscosity and surface tension. The viscosity of the suspension affects the particle size of the product, while the surface tension affects the sphericity of the particles. When the surface tension is reduced below 50 × 10-3 n / M and the viscosity is reduced below 50 × 10-3 PA · s, the granulation rate will be significantly reduced.