How to improve the performance and quality of wettable powders

Pesticide WP (wettable powder, the code WP) refers to dispersible in water to form a stable suspension formulations of powdered products, but also a long history, and processing technology is relatively mature, easy to use the basic formulation. It is a powdery product obtained by mixing and pulverizing components such as solid pesticide active ingredients, surfactants (wetting agents, dispersants), adjuvants (stabilizers), carriers or fillers. When the product is diluted with water to a field use concentration, a stable suspension for spray application can be formed which achieves a greater uniform coverage on the surface of the control target. In general, the same pesticide active ingredient is used to control the same target. The wettable powder is superior to the powder, and is less efficient than most liquid dosage forms (emulsifier, suspending agent, water emulsion, etc.), but their toxic effects on crops. It is relatively smaller than emulsifiable concentrate.

At present, the development trend of pesticide formulations is developing towards water-based, granular, sustained-release, multi-functional, labor-saving and convenient, and efficient, safe and environmentally friendly. Wettable powder is one of the four traditional pesticide formulations, and still has a large share (more than 20% at home and abroad). For example, there were 359 wettable powder products registered in China in 2015, ranking second after 767 suspension agents; much higher than 270 water-dispersible granules, 245 water-based agents, and 180 emulsifiable concentrates. 159 water emulsions, 126 other types of oil suspensions can be dispersed. It can be seen that wettable powders (with suspending agents and water-dispersible granules) are still the main body of research and development in China at present. Although many domestic pesticide manufacturers are researching and producing wettable powder products, their formulation research is mostly based on macroscopic empirical screening. Therefore, powder flowability is not good in production and use, and the package bag and wettability are poor. The problem of low suspension rate, and finally the performance is not good for the prevention and treatment of targets. Therefore, how to improve the performance and quality of today's wettable powder products is an important issue for dosage form processors.

1 characteristics and problems of wettable powder

Wettable powder is a typical solid-solid dispersion system. Generally, the characteristics of the dosage form are: 1 Does not contain any organic solvent, and does not cause environmental pollution and phytotoxicity of the solvent; 2 Processing and production process is mature, and the operation difficulty Smaller, relatively simple and easy to process; 3 The production cost of the processed product is relatively low; 4 The active ingredient of the pesticide has a long-lasting durability on the porous carrier or filler; 5 The range of active ingredients of the processed pesticide can be wide, and the minimum content can be 10%. Below, the maximum content can reach 90%; 6 the amount of fillers and additives used in processing high-content wettable powder products is limited, even than processed water emulsions (solvents and additives) and water-dispersible granules (fillers and additives) ) is also low; 7 products are less toxic to crops and relatively less toxic to crops.

The problems with this dosage form are: 1 Dust generated during processing increases the operator's inhalation and causes irritation to the eyes and skin. In addition, there is a risk of dust inhalation during application; 2 Failure to strictly take safety measures, crushing Powder may cause dust and sensitive substances (in the explosion range) to explode; 3 when diluted with water, sometimes difficult to wet, easy to form agglomerates, resulting in long dispersion and mixing; 4 mixed with other dosage forms Poor compatibility, wetting agent may be required for tank mixing; 5 low efficacy compared to other liquid dosage forms; 6 cleaned and hygienic conditions in the processing product workshop. Therefore, certain products of wettable powders are being gradually replaced by suspending agents, water-dispersible granules and other dosage forms.

2 Processing requirements for active ingredients of pesticides

(1) The active ingredient of solid pesticide (melting point above 80 °C) can be preferentially processed into wettable powder; the low melting point (melting point below 80 °C) pesticide active ingredient can also be processed into wettable powder, but it is not preferred to process it into Wettable powder; if the active ingredient of the pesticide is insoluble or poorly soluble in the conventional organic solvent, it can be preferentially processed into a wettable powder.

(2) The active ingredients of pesticides with certain water solubility are not suitable for processing into wettable powders, which are dissolved after inhalation of dust, increasing the risk of poisoning. However, certain techniques and measures are required to process the soluble powder. The biggest advantage of the dosage form is that it does not contain organic solvents, and at the same time avoids the problem that the wettable powder is not easily wetted during use. However, there are not many varieties of soluble powders that can be processed, as most of these pesticide active ingredients are processed into more effective and safe environmentally friendly suspension or water-dispersible granule products.

(3) The active ingredient of pesticide has certain volatility under normal temperature conditions (ie, high saturated vapor pressure data) and flammability, it is not suitable for processing into wettable powder, because of the loss of the processing agent and the safety hazard, storage There is a risk of inflation and breakage of the bag, which affects the use of the product.

(4) The liquid pesticide active ingredient can also be processed into a wettable powder, and one (or more) ones with strong adsorption capacity, such as white carbon black, diatomaceous earth, attapulgite, etc., must be selected, and more than 20% are adsorbed. The liquid active ingredient becomes a solid and is processed into a wettable powder; however, the processed wettable powder product has a relatively high cost, and is generally not required to be processed into such a wettable powder product unless it is necessary.

(5) When processing biological (body) pesticides into wettable powders, in addition to considering their effects on product properties (wetability, dispersibility, suspension rate, etc.), the use of carriers (or fillers) is also considered. It is necessary to consider their compatibility with biological (body) pesticides. Otherwise, the carrier (or filler) used does not match the biological (body) pesticide, which may cause biological (pore) pesticide poisoning and affect the use effect.

3 Measures to improve the quality of wettable powder

3.1 Process products with high levels of raw materials

To improve the quality of wettable powders, it is first necessary to use high-quality raw materials to process products, which will lay a good foundation for the production of high-quality products. In pesticides, the content of impurities is very low relative to the active ingredient, but in most cases, an impurity tends to exhibit one or more more significant toxicities than the active ingredient and affect the original or parent drug. Overall toxicity characteristics. The lower the impurity content, the less likely the potential impact will be in practice. The increase in the active ingredient content of the original drug is not brought into the formulation because the content of the formulation is usually determined by the active ingredient content, not the original drug content. However, if the active ingredient content of the original drug is reduced from 990 g/kg to 900 g/kg, the total amount of impurities increases from 10 g/kg to 90 g/kg (the toxicity of impurities increases by an average of 8 times), and these increase Impurities are brought into the formulation.

The problems caused by impurities are as follows: 1 If the impurities exceed the specified limit, it will cause unacceptable harm to humans and the environment; 2 impurities will affect the quality of the processed dosage form, if any cause decomposition of the active ingredients, or damage the packaging. Or corrosive application equipment; 3 the risk of phytotoxicity or contamination of food crops on the applied crops.

In the past five years, the domestically produced pesticide companies have produced 95% of the original drug content, and some products can reach more than 98%. At present, many domestic pesticide varieties have reached 98% or more. Therefore, qualified pesticide companies should use 98% of the original drug to process wettable powder products to ensure that the adverse effects of impurities on the wettable powder products are minimized.

3.2 Small particle size is conducive to improving the efficacy of WP

The processing particle size is small, which is more conducive to reducing the use of WP agents in controlling diseases, insects and grasses and prolonging the duration of action on target organisms, thereby improving the efficacy of the medicament. For a long time, the suspension rate of wettable powder processing is required to be >70%, so the particle size (fineness) of the processed WP product is required to be large. After several decades of improvement in the processing of powdered pesticide equipment, the particle size of the finely pulverized product reached 45-600 μm, the particle size of the finely pulverized product was <45 μm, and the particle size of the ultrafine pulverizer (air jet mill) was < 10 μm.

The current jet mill uses high-speed rotating airflow energy to accelerate the pulverized particles. Due to the high-speed impact, collision, friction between the particles and the shearing action of the gas molecules on the material particles, the particles can be pulverized to less than 10 μm. Since the jet mill is powered by compressed air, the temperature of the gas is low when it is expanded at the nozzle, so that the entire pulverization process does not generate a large amount of heat, so it can be used to pulverize low melting point and heat sensitive materials.

Although the jet mill equipment can reach the micron level, it is difficult to achieve a pass rate of 97% if the powder particles are required to be pulverized to 10 μm or less. A new type of jet mill can meet this requirement. For example, the environmentally-friendly intelligent airflow pulverizing device developed by Miyou Group-Kunshan Miyou Crushing Equipment Co., Ltd., the pulverized product can reach the micron size (1.0~5.0 μm), even Micron (100 nm ~ 1.0 μm), and the product particle size distribution is narrow and very uniform.

At present, the size of wettable powder products processed by domestic enterprises is mostly above 10 μm, which is generally much larger than that of liquid dosage forms (such as emulsifiable concentrates, suspending agents, water emulsions, etc.), resulting in poorer efficacy compared to liquid dosage forms. However, foreign countries have higher requirements on the processing of wettable powders, such as 3 to 5 μm in the United States and 5 to 7 μm in Japan, which is one reason why the use of foreign WP products is higher than that of domestic products.

When the wettable powder is used, it is diluted with water to form a suspension, wherein the particle sedimentation is mainly affected by the particle diameter. Therefore, the wettable powder product having a small particle size and a narrow particle size distribution can also improve the stability of the solid-liquid dispersion system, and is also advantageous for field use.

3.3 Use high quality surfactants

The surfactants used in the processing of wettable powders are mainly wetting agents and dispersing agents.

3.3.1 Wetting agent

Wetting agents commonly used in wettable powders are: sodium lauryl sulfate (K12), sodium alkylnaphthalene sulfonate (opened powder), alkyl succinic acid sulfonate (such as penetrant T), etc. Generally meet the wetting requirements of wettable powder products. The effect of using K12 is good, the color is also very white, and the price is a low-end wetting agent. However, there is a problem in sulphate that it is easy to cause decomposition when exposed to acid, and foaming is severe, and it is difficult to defoam the general defoaming agent. Pull-open powder BX is an old brand wetting agent often used in WP. It belongs to butyl naphthalene sulfonate, which has good water solubility and less bubbles. However, basically, the original product is not opened with powder BX. In fact, the BX content of the powder opened is different, so the price difference is very large, and the effect is also very different. For example, the Nekal BX Dry sold by BASF is also a BX series, which is very good and the price is several times more expensive than domestic ones.

The commonly used wetting agents on the market today are: Akso's Morwet EFW is a mixture of alkylnaphthalene sulfonate and anionic wetting agent, characterized by excellent water solubility and low bubbles. Morwet IP is mainly composed of sodium isopropylnaphthalene sulfonate. It is a low foaming product and is suitable for systems with strict foam control. Petro AA is mainly composed of alkylnaphthalene sulfonate and is white in color to meet the color requirements. T-1004 is a high performance wetting agent from Huntsman and is available at a higher price.

3.3.2 Dispersant

The main dispersing agents used in wettable powders are:

(1) Lignosulfonate dispersant: At present, domestic lignosulfonates and their modified products such as wood sodium MS and wood calcium M9 have molecular weights below 4,000, and the price is relatively cheap, and is used in wettable powders. Mainly occupied. However, for some hydrophobic pesticides, it is necessary to use a dispersing agent with a relatively high molecular weight and a low degree of sulfonation. For example, the 40% nitrile WP can be used with domestic lignosulfonates, and the 40% nitrile currently processed is poor. Pyrazole WP, mainly relies on foreign lignin sulfonate dispersant products for a long time.

To this end, Shang Jibing et al. studied the effects of different molecular weight sodium lignin sulfonate (wood sodium) on the performance of 40% myclobutanil wettable powder. The test results showed that the sulfonate content decreased from 2.66 mmol/L to 0.986 mmol/L as the molecular weight of wood sodium increased from less than 2,500 to 5,000 (in five grades). With the molecular weight of wood sodium increasing from less than 2,500 to 50,000, the suspension rate (74.21% at room temperature and 69.51% at heat storage) increased sequentially. The molecular weight of wood sodium was 30,000-50,000, and the suspension rate was the highest (normal temperature was 85.36% and heat storage). 81.38%), the average particle size of the dispersed phase in the suspension was 6.30 μm (normal temperature) and 9.19 μm (heat storage). The reason is that the dispersing agent of the large molecular weight dispersing agent on the surface of the pesticide particle has a large repellency, and the particle collecting ability is strong, and the dispersing effect is good.

Foreign lignosulfonate dispersant products such as Borreisse's Borresperse NA, Ufoxane 3A, etc., MeadWestvaco's REAX series, Japan's Zhuben Oil Company's YUS-WG4 and so on. These products have good dispersibility, heat stability and resistance to hard water, and are more expensive. The disadvantage of using a lignosulfonate dispersant is that the dispersant is colored (brown to brown) and affects the appearance of the product.

(2) Naphthalene and alkylnaphthalene formaldehyde condensate sulfonate dispersant: domestic sodium dibutyl naphthalene sulfonate formaldehyde condensate (NO), sodium naphthalene sulfonate formaldehyde condensate (NNO), sodium methyl naphthalene sulfonate Formaldehyde condensate (diffusion agent MF) and the like are commonly used products of such dispersants, and the price is relatively cheap, but the processed wettable powder has poor performance (such as suspension rate) than foreign products.

For example, Zhao Haijun developed 19% bensulfuron-chloroflupirate WP with the dispersing agent Morwet D-425 of Aksu. The final formulation obtained was: difensulfuron 2.5% (folded one hundred), flupiroxine 16.5% (folded one hundred), wetting agent ABS-Na 2%, dispersing agent Morwet D-425 3% and NO 2%, White carbon black 2%, light calcium to 100%. The technical indicators are levitation rate ≥85%, wetting time ≤30 s, good dispersibility, long-lasting foaming (1 min)≤25 mL, moisture ≤0.5%, suspension rate after heat storage decreased by 5% or less, heat storage The decomposition rate of active ingredients is ≤5%.

Foreign products of this type of dispersing agent include Morwet D-425 and Morwet D-500 from Aksu, Tamol NN and Tamol DN from BASF, and YUS-TXC from Nippon Oil & Fat Co., Ltd., which are better than domestic products. High suspension rate). These products have low foaming properties, are stable in hard water and acid-base media, and have good color (light yellow to yellow color). The processed wettable powder products have a good appearance.

(3) Alkylphenol polyoxyethylene ether formaldehyde condensate sulfate dispersant. Such as SOPA (Suber), it is a domestically developed dispersant, which has a certain wetting effect. It is a variety used in the early development of wettable powder products in China, but the ability to adsorb particles is poor, and the processed wettable powder products have poor performance and are rarely used now.

(4) The newly developed polycarboxylate dispersant. It is first used in pesticide water-dispersible granules and is very effective. It has been used in the development of high-content and high-quality wettable powders. Novel polycarboxylate dispersants generally have a relative molecular mass of from 4,000 to 30,000 copolymers. These novel polycarboxylate dispersants have surface points that provide a plurality of anchored pesticide particles and are strongly adsorbed on the surface of pesticide particles. It is not easy to desorb and transfer; it can provide strong electrostatic repulsion and/or steric barrier to prevent the re-aggregation and/or coalescence of pesticide particles. They are not only used in suspensions, water-dispersible granules, dispersible oil suspensions, etc., but also in the development of high-content and high-quality wettable powders, which can be used to improve the dispersion of these dosage forms. Properties, suspension and storage stability, and the resulting product is white in color.

These polycarboxylate dispersant products are: Solvay's Geropon T/36 and Geropon T/72 (polycarboxylates, all white powder), Huntsman's Tersperse 2700 (polyacrylic acid) Graft copolymer, white powder), Tersperse 2100 (solid powder, combined with wetting and dispersion), Sokalan HP 25 (modified polycarboxylate) from BASF (BASF) and Sokalan PA 80 S (polyacrylic acid), AkzoNobel (Akzo Nobel) company Agrilan 700 (modified polyacrylate copolymer, white powder), Beijing Guangyuan company's GY-D (D03-D08) series products (polycarboxylate of styrene sulfonate polymer) And D1001, D1002, D1003 (polycarboxylate) of Beijing Hammock Chemical Technology Co., Ltd. can be used to process wettable powders.

If the particle size is relatively small in the processed wettable powder product, the amount of wetting agent and dispersing agent should be appropriately increased. This is because the specific surface area of ​​the particle is small after the particle size is small, so the amount must be increased to reach the product. The required wetting and dispersing properties.

3.4 Selection of carrier and filler

The carrier or filler is an inert substance in the processing of wettable powder. Its main function is to ensure the content of the active ingredient of the pesticide in the product, and to disperse the active ingredient of the original drug and other components such as the added surfactant. A homogeneous mixture is formed to maintain the dispersion and fluidity of the product. At the same time, the performance of the product is improved and it can be safely and conveniently diluted in water.

Generally, substances having strong adsorption ability, such as diatomaceous earth, bentonite, attapulgite, and silica, are called carriers, and are commonly used as a substrate for producing a wettable powder, and can also be used as a filler for a wettable powder product. Substances with low or moderate adsorption capacity, such as talc, pyrophyllite, clay (such as kaolin, clay, etc.), are generally used as fillers or diluents for processing wettable powder products. Both the "carrier" or "filler" are designed to load or dilute the inert components of the pesticide, giving the pesticide formulation a fluid, dispersible and convenient use.

The most important characteristic of the carrier or filler is the adsorption capacity. Its main function is to distribute the active ingredient of the pesticide to most of the fine particles and evenly distribute it over the entire particle range. In addition to the narrow distribution of fine particles is an important factor, the bulk density will also determine the coverage of the active ingredients of the pesticide, wind drift, leaf surface penetration, sedimentation in water, and the ease of handling of the dosage form. When selecting a carrier or filler, their compatibility with the active ingredients of the pesticide is another important factor to consider (see examples).

In practice, it has been found that many of the pesticide solid products processed have been found to have poor chemical stability when stored in long-term high temperature. The most important reason for this is often related to the presence of acid, base and catalytic sites on the carrier or filler particles used. At this time, when a deactivating agent such as ethylene glycol, glycol ether, cyclohexanol or long-chain alcohol is added, the formulation can be stabilized. How to choose the right carrier and filler is critical to the performance of high quality wettable powder products. Table 1 shows the particle size and capacity of several carrier or filler products.

Table 1 Particle size and capacity of several carrier or filler products

Example 1: For example, when Song Xiaolei developed 50% aluminum-aluminum-manganese-zinc wettable powder, attapulgite with large specific surface area and strong adsorption capacity was used as the filler, and white carbon black adsorbed liquid surfactant was used as carrier to obtain performance. Superior wettable powder products. The determined formula is: aluminum triethylphosphinate (98.2%) 10% (100%), mancozeb (97.3%) 40% (100%), modified EO-PO block copolymer 4.5%, tea soap 1.5%, white carbon 2.5%, polycarboxylate surfactant 1.5%, attapulgite to 100%. The product was determined to be rapidly dispersed, with a wetting time of 8 s and a suspension rate of 94.6%. The remaining technical performance indicators were in accordance with the quality requirements of the wettable powder.

Example 2: Trichoderma microfungi, which has wide adaptability, broad spectrum of antibacterial activity and various mechanisms, is an antagonistic fungus with important utilization value and is increasingly used for plant disease control. Cheng Lijun et al. studied the compatibility of carrier and strain (TR1) with several carriers in the processing of Trichoderma wettable powder.

The results showed that kaolin, talc and activated clay had good compatibility with TR1 strain and had no obvious effect on mycelial growth. White carbon black has a great influence on the spore germination, and the number of colony formation is much less than that of the control colonies, while diatomaceous earth has the slowest growth rate of hyphae. Therefore, kaolin, talc, and activated clay can be finally considered as a carrier for the wettable powder of Trichoderma TR1 conidia.

Example 3: Wang Jian et al. isolated a broad-spectrum strain from the soil of the field, and identified it as Bacillus subtilis B99-2 by biochemical characteristics and 16S rDNA analysis. The results of field experiments showed that the strain could effectively control diseases such as tomato leaf mold, tomato gray mold and watermelon wilt. Then, the Bacillus subtilis B99-2 fermentation broth is mixed with a filler to prepare a mother liquid, which is dried to prepare a mother powder, and then added with an auxiliary agent, etc., and pulverized into a wettable powder by a jet mill. The results of the influence of the screening of the filler on the physical and chemical properties of the formulation processing are shown in Table 2.

Table 2 Effect of different fillers on the physical and chemical properties of preparations

It can be seen from Table 2 that the use of silica as the filler has the highest suspension rate, short wetting time and maximum adsorption capacity; but the lowest spore content indicates that the biocompatibility of silica and Bacillus is the worst; plus the price of white carbon black High, not suitable as a filler. The highest content of spores in diatomaceous soil indicates that it has the best biocompatibility with Bacillus. Although the adsorption capacity is much lower than that of silica, it is higher than other fillers, and the suspension rate and wetting time are in a moderate position. . Therefore, diatomaceous earth is most suitable as a filler after comprehensive consideration.

Thus, the highest content of the Bacillus subtilis B99-2 wettable powder can be prepared by screening the wetting agent, the dispersing agent and other additives up to 2.0×10 10 cfu/g. The optimum formulation of the wettable powder is: diatomaceous earth 10%, Morwet D-425 4.8%, PVA (polyvinyl alcohol) 7.2%, stabilizer CMC-Na 2%, FWA (ultraviolet protective agent) 0.1%.

The prepared samples were analyzed and determined: suspension rate 79%, wetting time 48 s, pH value 6.6, moisture content 3.5%, fineness pass rate 98.3%, heat storage decomposition rate 23.6%, and all test results were in line with national standards. . In addition, the storage stability of 2.0×1010 cfu/g wettable powder was investigated. The survival rate of Bacillus was 57.1% after storage for 360 days at room temperature, and the spore was preserved at (4±2) °C for 360 days. The survival rate of bacilli is as high as 79.9%, mainly because Bacillus is almost completely dormant at a lower temperature, and metabolism is slow. Therefore, the preparation should be stored at a low temperature as much as possible, which is advantageous for prolonging its storage period.

Example 4: Cai Xunchao et al. for the endophytic Bacillus amyloliquefaciens CC09 (a broad-spectrum, antifungal endophytic Bacillus amyloliquefaciens CC09 strain isolated from healthy eucalyptus leaves) as a raw material, through the screening and preparation process of additives, fillers, etc. Optimize and develop an endogenous Bacillus amyloliquefaciens WP that meets the national standard.

The difference of the mother liquor of CC09 strain adsorbed by five kinds of adsorption carriers was compared. The adsorption capacity was preferably bentonite (8.3 mL), followed by diatomite (8.0 mL), talc powder, kaolin and light calcium were 7.2 mL and 5.9 mL, respectively. 5.3 mL. In the carrier biocompatibility test, it was found that talc powder had the best compatibility (98.13%), diatomite followed (86.16%), and the worst bentonite compatibility was 0%, indicating that it was against CC09 strain. It has a toxic effect.

In addition to bentonite, the wettable powder prepared by using the other four kinds of carriers has the fineness (95% particle size ≤44 μm) and the wetting time (≤3 min) in line with the national standard. The levitation rate was determined to be 91.04% and 88.24%, respectively, with the highest talcum powder (98.19%), kaolin and light calcium. In the moisture content and thermal stability test of the wettable powder prepared by different carriers, the water content is ≤ 3%, and the thermal stability test using diatomaceous earth and bentonite does not reach the national standard (decomposition rate ≤ 30%), talcum powder, The thermal stability of kaolin and light calcium is higher than the national standard.

For comprehensive performance considerations, talc powder was selected as the carrier of the wettable powder of CC09 strain. The final results showed that the talc powder was used as the carrier, sodium dodecyl benzene sulfonate and Tween 60 were wetting and dispersing agents, sodium carboxymethyl cellulose was used as a stabilizer, and Vc was a protective agent for CC09 strain wettable powder. 10 billion live spores/g) meet the national standard requirements. The control effect against wheat powdery mildew with its 30-fold dilution was comparable to that of 15% triazolone wettable powder.

4 Optimization of wettable powder process

This mainly solves the problem of the particle size, distribution and mixing uniformity of the viscous powder composition after dispersion. Since the wettable powder product is diluted with water to form a suspension which is a coarse dispersion system, the smaller the average particle diameter and the narrower the particle size distribution, the higher the suspension rate in water. Therefore, in the processing, a large block or granular raw material (original drug, filler, auxiliary agent, etc.) is subjected to multi-stage pulverization and mixing to achieve the above requirements. The starting particle size of the raw materials is different, and different pulverizing equipment is required in the pulverizing stage. After multi-stage pulverization and mixing, the particle size of the desired granules of the product can be achieved. Table 3 lists the equipment used from coarse pulverization to ultrafine pulverization, the required raw material particle size, and the particle size of the final product.

Table 3 Requirements for equipment from coarse pulverization to ultrafine pulverization, particle size of raw materials, and product particle size

For the problem of mixing uniformity, it should be noted that it can not be improved by extending the mixing time. When the mixing and dispersion between the particles reach the dynamic equilibrium during the mixing process, the mixing uniformity will not increase any more, and sometimes the deterioration will occur. phenomenon. In addition, the mixing of raw materials (original drugs, fillers and additives) by a single mixer is long and the efficiency is low; in order to improve the mixing efficiency, the mixing and pulverizing process is often used to shorten the mixing time and save energy. This can first pre-mix the raw materials, fillers and auxiliaries with a spiral mixer, and then pulverize them in a free pulverizer to improve the uniformity of the product. After the pulverization and mixing process of the jet mill, the product can achieve the required fineness and distribution of the particle size and satisfactory mixing uniformity. At the same time, a suitable feed rate should be chosen to facilitate the particle size and distribution and mixing uniformity of the components.

For example, processing 50% Ligulong WP, the formula is: Ligulong 50% (100%), wetting agent K12 2%, dispersing agent Morwet D-400 3%, Borresperse CA-SA 5%, Petro AA 2 %, white carbon black 2%, light calcium to 100%. The jet mill was pulverized twice, and the product suspension rate was 94%. Another example is 50% thiaphinamide wettable powder, the formula is: phenothanil (95.5%) 50% (100%), wetting agent K12 2%, dispersant Borresperse NA 6%, white carbon black 2 %, kaolin is made up to 100%. The product has a suspension rate of 95% and a wetting time of 30 s.

5 wettable powder clean production

In the impression that the production workshop of wettable powder is relatively dirty, especially the production of dust in the production, and the solid particles floating in the production environment for a long time, the harm is obvious; if not controlled It will damage the working environment, endanger the health of the operator and damage the machinery and equipment, and pollute the atmosphere. Therefore, with the continuous development of the pesticide preparation processing industry, it is necessary to change the dust flying condition in the processing of wettable powder, and achieving clean production is the current goal. As early as 2001, during the work of Jiangsu Longlight Chemical Co., the company realized the operation of closed negative pressure workshop in the production of wettable powder, and could not see the dust flying and realized clean production. It shows that in the workshop of processing wettable powder enterprises, it is possible to achieve clean production.

In this regard, Jiangsu Kunshan Miyou Crushing Equipment Co., Ltd. has developed a new technology for environmentally-friendly intelligent airflow pulverizing mixing system to overcome the problem of dust flying in WP. It provides a gap-type production airflow pulverizing mixing system and a closed-loop inert gas protection airflow pulverizing mixing system. (Already used in DuPont Agrochemicals, USA), it is a reality to achieve clean production.

In particular, Jiangsu Limin Chemical Co., Ltd. has fundamentally innovated the production process of sensen Mn-Zn wettable powder in recent years, and has produced a new generation of “full complex manganese Mn-Zn” 80% mancozeb. Wet powder products, trade name "Limin Lingxiu®", all of which are similar to foreign products (Dasheng-M45® of Dow AgroSciences, New Wansheng® by US Express and Jinsuke® of Matsui Industry Co., Ltd.) Excellent performance. The production process of “Limin Lingxiu®” is completely different from the usual processing method of wettable powder. The additive is added at the same time as the original drug is synthesized, and the complexation is realized in the emulsification pulping process without physical grinding and grinding. After drying, the finished product is obtained, and clean production is achieved. In actual use, “Limin Lingxiu®” products can almost meet the performance requirements of mancozeb SC and DF, with an average particle size of 2 μm and high suspension rate. Dilution with water can dissolve quickly and evenly, and it does not block the nozzle; it has good adhesion to crops, strong rain-resistant ability, high efficacy and good safety, and can almost meet all the requirements of users for mancozeb products.

6 Application test cases

The following are some examples of application tests for high quality wettable powder products.

(1) Li Yunguo et al. used 80% mancozeb WP (Hebei Shuangji Chemical Co., Ltd.) to carry out a field efficacy test for controlling apple spotted leaf disease. The results showed that 80% mancozeb WP 600 times solution and 80% mancozeb WP (American Dow AgroSciences) 800 times liquid control effect, the average control effect was 79.41%, 80.5 %, the best control effect is 87.14% and 88.8%. The best control effect of 80% mancozeb WP 800 times solution is 85.14%, which is still lower than 88.80% of Dow AgroSciences' 800 times liquid control effect, as shown in Table 4. It indicates that there is a gap between the domestic 80% mancozeb wettable powder product and the American Dow AgroScience 80% mancozeb wettable powder product. This difference is likely caused by the difference in surfactants and fillers or processing particle size. .

Table 4 Field efficacy of apple spotted deciduous disease

(2) Spinach downy mildew is one of the most common diseases on spinach, but there is currently no registered drug in China. Since 2012, the Shanghai Agricultural Technology Extension Service Center has taken the lead in the field of 722 g/L propamocarb hydrochloride AS, 75% chlorothalonil WP and 50% dimethomorph WP to control spinach downy mildew. The efficacy test provides the basis for the pesticide registration test.

The results showed that the WP dosage of 75% chlorothalonil was 1,125, 1,687.5 and 2,250 g ai/hm2 to control the downy mildew of spinach, and the control effects on the 14th day after the third drug were 69.37%, 71.45% and 70.83%, respectively. The amount of 722 g/L propamocarb hydrochloride AS was 649.8, 974.7, 1,299.6 g ai/hm2 to control the downy mildew of spinach. The control effect on the 14th day after the third drug was 69.71%, 70.92% and 71.08%, respectively. 50% dimethomorph WP dosage 225, 300, 375 g ai / hm2 control spinach downy mildew, the control effect on the 14th day after the third drug was 95.59%, 96.64%, 96.30%. The conclusion is that 722 g/L of downy mildew Weiwei hydrochloride AS, 75% chlorothalonil WP and 50% dimethomorph WP have good control effect on spinach downy mildew, and the effect period is longer. Crop safety, but the difference in the effectiveness of the three is significant. 50% dimethomorph WP was significantly better than 722 g/L downy mildew Weiwei hydrochloride AS and 75% chlorothalonil WP, achieving excellent levels of control. The difference in control effect between 722 g/L downy mildew Weiwei hydrochloride AS and 75% chlorothalonil WP was not significant, and the control effect was moderate.

(3) Yan Kecheng et al. used 15% acetylene WP (Shenyang Research Institute of Chemical Industry) to control the efficacy of winter wheat field. The results showed that the control effect of the strains of A. serrata and Valeriana was 90.6% and 89.3%, respectively, at the dose of 45 g / hm2; the control agent 15% clodinafop- WP (Syngenta) at the same dose. The control efficacy of the strains of Niang and Valerian reached 89.9% and 90.5%, respectively. At the dose of 45 g/hm2, the fresh weight control effect of A. maiden and A. chinensis reached 91.7% and 92.1%, respectively; the control agent 15% clodinafop- WP (Syngenta) at the same dose was observed at the same dose. The control effects of the sorghum strains reached 91.2% and 91.5%, respectively. It shows that the domestic 15% acetylene ester WP is equivalent to the foreign 15% clodinafop WP product.

(4) Guangxi Research Institute of Chemical Industry has developed a new type of ternary mixed herbicide product for 60% glyphosate·2 methyl 4-chlorosodium·chloroflupironate isooctyl ester WP. Wei Maochun et al. tested the control effect of 60% glyphosate·2 methyl 4-chlorosodium·chloroflupirtine isooctyl ester WP on weeds in eucalyptus forest. The results showed that the control effect of 60% glyphosate·2 methyl 4-chlorosodium·chloroflupirtine isooctyl WP increased with the increase of dosage (1,687.5, 2,250, 3,375 g/hm2) for 15 days. The total grass plant control efficacy was 93.5%, 96.6%, 98.8%, respectively, and significantly higher than the control agent 1,690 g/hm2 dose of 50% glyphosate SP (92.9%), 1,125.6 g/hm2 dose of 56% 2 A 4 Sodium Chloride SP (46.5%) and 180 g/L chlorofluoxyacetic acid EC (57.9%) at a dose of 180 g/hm2.

The control effects of total grass plants at 30 d were 95.9%, 98.8%, and 99.7%, respectively, and were significantly higher than the dose of 1,690 g/hm2 for 50% glyphosate SP (91.6%) and 1,125.6 g/hm2. % 2 sodium tetrachlorosodium SP (49.9%) and 180 g/hm2 dose of 200 g/L flupiroxine EC (58.3%). The fresh grass weight control effect was 93.8%, 98.2%, and 99.1%, respectively, and the dose of 50% glyphosate SP (86.7%) and 1,125.6 g/hm2 was significantly higher than the dose of 1,690 g/hm2. 56% 2 sodium tetrachlorosodium SP (59.3%) and 180 g/hm2 dose of 200 g/L flufenoxyacetic acid EC (74.4%).

The formula is not only efficient, broad-spectrum, easy to use, low in cost, safe to eucalyptus; and can well control broad-leaved weeds such as S. serrata, C. serrata, Purslane, and Quercus.有效防除南方林地中的蟛蜞菊(华南各地林业、农业和环境危害严重杂草)、小飞蓬、桃金娘等恶性杂草和杂灌。

(5)李梦瑶等用新型、高效、低毒杀螨剂 45%哒螨灵·啶虫脒可湿性粉剂(陕西恒田化工公司)对苹果黄蚜进行了田间防效试验。试验结果表明，药后3 d有效剂量37.5、45、56.25 mg ai/kg的防效分别为93.5%、95.4%、97.6%;优于对照药剂的剂量33.3 mg ai/kg 10%吡虫啉WP、66.7 mg ai/kg 20%哒螨灵WP、20 mg ai/kg 5%啶虫脒WP的防效分别为91.4%、92.6%、92.2%。药后7 d有效剂量37.5、45、56.25 mg ai/kg的防效分别为99.09%、99.37%、99.76%;优于对照药剂的剂量33.3 mg ai/kg 10%吡虫啉WP、66.7 mg ai/kg 20%哒螨灵WP、20 mg ai/kg 5%啶虫脒WP的防效分别为98.15%、97.54%、97.78%。说明使用45%哒螨灵·啶虫脒可湿性粉剂产品防治苹果黄蚜效果较好，速效性强，持效期长达7 d以上。在田间药效试验期间，药剂除了对苹果树生长安全，无药害产生外，也未发现有刺激生长作用，对有益天敌种类和数量未出现任何不良影响。

7 Conclusion

可湿性粉剂是一种历史悠久、不含任何有机溶剂、加工农药有效成分含量范围较宽、加工技术比较成熟、生产成本相对较低、产品对作物毒性低、使用方便的基本剂型。虽然国内市场上销售的可湿性粉剂产品常会出现粉体流动性不好、包装袋鼓气(账袋)、润湿性差、悬浮率低等问题，但可湿性粉剂(与悬浮剂和水分散粒剂)仍是国内目前研发和登记的主体，如何提高可湿性粉剂产品的性能和品质是当今需要解决的重要问题。

提高可湿性粉剂性能和品质的方法是：① 采用高含量(98%或97%)的原药加工可湿性粉剂产品，以确保杂质给可湿性粉剂产品带来的不利影响降到最低;② 加工粒径小的产品，有利于提高产品的药效，同时降低WP药剂在防治病、虫、草害时的使用量和延长对靶标生物的持效期;③ 选用高质量的表面活性剂加工WP，赋予产品更好的润湿性、分散性、流动性、稳定性和高的悬浮率，在应用时提供高的药效;④ 选用合适的载体或填料，赋予农药固体剂型产品具有流动性、分散性和方便使用性。在加工生物体农药可湿性粉剂中，还需要考虑生物体与它们之间的相容性，以免使用后会对生物体菌株发生毒害作用，降低使用效果。

除此之外，对现有可湿性粉剂工艺进行优化，实行多级粉碎和混合工艺，提高可湿性粉剂品质;同时在可湿性粉剂加工中必须改变粉尘飞扬状况，实现清洁化生产也是当前的目标。

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