Processing technology and process of pesticide SC

1、Pesticide suspension concentrate is a formulation developed in the 1970s and has become one of the basic processing formulations.SC,also known as water suspension agent,colloidal suspension agent and concentrated suspension agent,is a kind of coarse suspension system which disperses insoluble or insoluble technical drug into water under the action of surfactant and other additives.Because the dispersing medium is water,the suspension agent has the characteristics of low cost,safe production,storage and transportation,and easy to mix with water and easy to use.Compared with the pesticide formulation using organic solvent as the medium,it has the advantages of less environmental impact and less pesticide damage.

The preparation technology of SC involves many subjects,such as pesticide chemistry,pesticide preparation,physical chemistry,chemical machinery and so on.Although SC has appeared as early as the 1970s,due to the impact of the development of grinding machinery and surfactant technology,its promotion scale is still difficult to compare with emulsifiable concentrate,wettable powder and other bulk formulations.At present,the physical stability of most of the suspension concentrate products produced in China is poor,stratification and precipitation are easy to occur during storage,and the effective ingredients of pesticide are difficult to be evenly dispersed,and even caking can not be poured out from the packaging materials,which seriously affects the promotion and use of the new pesticide formulation SC in agricultural production.

2、SC is mainly composed of pesticide,wetting agent,dispersant,thickener,antifreeze,pH regulator,defoamer and water.However,the formulation of different varieties and specifications are different.It is an important work to select a reasonable formulation.

The basic formula composition of water suspension concentrate is as follows:active ingredient:40%-50%(there are lower ones)

Antifreeze:about 5%(it can not be added in areas with minimum temperature higher than 0℃)

Wetting and dispersing agent:3%-7%thickening agent:0.1%-0.5%water added to 100%pH regulator and defoamer,generally not added.

The final determination of the formula is mainly based on experience.The more experience accumulated,the more abundant,we can sum up the rules and form a certain pattern.Therefore,there will be less mistakes,less detours and twice the result with half the effort.In this paper,it is difficult for the author to give the formula for the selection of suspension agent formula,and can only describe the principle of selecting each component.

1.To determine the effective components of solid,the following three conditions should be met:(1)the solubility in water should not be greater than 70mg/L,and it is better to be insoluble,otherwise crystallization may occur during the storage of the preparation.However,there are also some examples in which the solubility in the liquid phase exceeds 100mg/L to prepare the stable suspension,such as glutathione,imidacloprid and methomyl.By adjusting the wetting dispersant and thickener,the quality assurance period of the preparation can even reach 3 years.(2)It has good chemical stability in water,and buffer and antioxidant are usually used to improve the chemical stability of some active ingredients which are not very stable.(3)The melting point is generally above 60℃,so as to avoid melting during grinding,causing particles to agglomerate and affecting the stability of the preparation.(4)For the compound preparation,the best ratio and concentration of the two technical drugs should be determined on the principle of synergism,non toxicity and good compatibility and stability.

2.The wetting and dispersing agent of pesticide suspension concentrate has double functions of wetting and dispersing.The amount of wetting and dispersing agent is generally less than 10%,but it should be soluble in the selected dispersion medium or combine with the dispersing medium stably.

3.Select antifreeze,pesticide suspension concentrate can be stably stored in low temperature environment,it needs to add a certain amount of antifreeze.If ethylene glycol is used as antifreeze agent,it is generally added about 5%,and no more than 10%at most.The antifreeze selected generally requires good antifreeze performance,low volatility and insoluble to the effective components.

If the processed pesticide suspension concentrate is stored and used in the area where the temperature is higher than 0℃,antifreeze can not be added in the formula;otherwise,antifreeze must be added to maintain the stability of the preparation.

4.Selection of thickener thickener is one of the indispensable main components of pesticide suspension concentrate.The thickener is usually selected with low dosage,strong thickening effect and does not affect the dilution stability of the preparation.The general dosage is 0.1%-0.5%,and the maximum dosage is not more than 3%.

5.Choosing defoamer pesticide suspension concentrate is easy to produce a large number of bubbles in the process of processing,affecting the preparation of processing,measurement,packaging and use.If other additives in the formula do not control the amount of bubbles,it is necessary to consider adding defoamer.Generally choose ester material,the amount is also very small.In the process of production,ultrasonic and vacuum defoaming methods can also be used.(it doesn't seem realistic!)

6.The selection of pH regulator is an important means to ensure the chemical stability of the active components in the preparation.The vast majority of technical materials are stable in neutral medium conditions,while a few technical specifications require acidic or alkaline medium conditions.Therefore,it is necessary to adjust the medium by adding a pH regulator to meet the requirements of technical specifications for medium pH value.Generally,sulfuric acid or organic acid is used to adjust the acidity,while organic amine is used to adjust the alkalinity of the medium.The dosage is very small.

3、The equipment and technology of pesticide suspension concentrate processing are very important,which often affect the quality of products.

The main contents of suspension concentrate processing technology research are:1.Determine a processing method according to the properties of selected pesticide active ingredients,that is,determine the process route;2.Select the appropriate processing equipment;3.Determine the feeding sequence of each component.

There are two main processing methods of pesticide suspension concentrate.One is superfine grinding method(also known as wet grinding method),the other is coagulation method(also known as hot melt dispersion method).However,the superfine grinding method is used in the processing of agricultural suspension concentrate.

1.Suspension agent processing equipment there are three main processing equipment of ultra-fine grinding method:first,pre grinding equipment:ball mill or colloid mill;second,ultra-fine grinding equipment:sand mill,in which vertical open sand mill is the most commonly used;third,high-speed mixer(1000~15000r/min)and homogenizer(>8000r/min),which mainly play the role of homogenization.

(1)sand mill is the key equipment of pesticide suspension agent processing.In the multi-stage series continuous production process,the particle size of each grinding medium is different.Usually,four sand mills are used in series,and two kinds of glass sand,fine sand and coarse sand,are used.The first sanding mill is equipped with coarse sand,the second sanding mill with 2/3 coarse sand and 1/3 with fine sand.The third sanding mill is opposite to the second sanding mill,and the fourth sanding mill is all filled with fine sand.Because of the high grinding efficiency and poor uniformity in the primary stage(the first sanding mill).In the intermediate stage of sanding(the third and second sanding mills),the fineness meets the requirements,but the uniformity is not enough.In the final stage(the fourth sanding mill),the particles in the suspension agent are more uniform.This will greatly improve the suspension rate and storage stability of SC.At present,there are two types of sand mills in China,i.e.vertical open type,vertical closed type and horizontal type;the materials are carbon steel and stainless steel respectively.

(2)there are many colloidal mills in our country,and their specifications and models are different,so there is a great room for selection.The colloid mill has the advantages of small volume,large production capacity and fine particle size.Colloid mill is mainly used for pre comminution to prepare fine powder slurry for sand mill.

(3)ball mill there are many ball mill manufacturers in China,which are generally carbon steel or stainless steel,and the lining is granite.Ball mill is used as the first process of pesticide suspension concentrate processing,i.e.batching,mixing and pre grinding.

(4)homogenizer homogenizer is a kind of equipment which can crush and homogenize the medium through high-speed impact,shear and friction.In the processing of pesticide suspensions,the use of this equipment may gradually increase.

2.Brief introduction of continuous production process in China,after more than 20 years of research on the production process of pesticide suspension concentrate,a set of basic mode has been formed,that is:ingredients-pre powder-sand grinding-mixing and mixing-packaging.The main characteristics of this process are:(1)adopting the continuous production process of four machines(sanding mill)in series and air compression pipeline feeding;(2)shortening the operation time by one third compared with the intermittent operation;(3)adopting the wet process with little or no pollution;(4)reducing the operation process,reducing the labor intensity of workers and greatly improving the operating conditions.

The basic mode of pesticide suspension concentrate production process has many advantages,such as continuous superfine grinding,high production efficiency,good particle uniformity and good product quality.However,this process is not applicable to all technical drugs.Therefore,the processing process of the preparation should be selected according to the nature and characteristics of the technical drug.

4、Quality evaluation system 1.The performance of SC requires that a good SC should have the following properties:(1)particle size range.At present,it is generally considered that the optimum particle size range is 0.3-5μM.

(2)good dumping ability.

(3)it is stable when stored at room temperature for more than two years.It is allowed to have a small amount of(lt;5%volume)dialysis layer(water layer or clear liquid layer)after standing,and most of the rest are easy to form a good suspension by shaking.

(4)the stability of repeated freezing thawing and thermal storage is qualified.

(5)good automatic dispersion and high suspension rate.

(6)good barrel mixing compatibility.

(7)no drug damage.

(8)low foam.

2.Industrial control index in order to ensure the performance of pesticide suspension concentrate products,China's chemical industry standard"Specification for preparation of pesticide suspension concentrate product standards"(Hg/t2467.5-2003)stipulates that the content of active ingredients,the limit of relevant impurities,the range of pH or pH value,suspension rate,dumping ability,wet screening test,persistent foaming property and low temperature should be controlled for general pesticide suspension concentrate products And thermal storage stability.These indexes can ensure the content of active ingredients and some properties of pesticide suspension concentrate.However,in order to ensure its performance,some necessary items should be controlled.These include tests on Centrifugal stability,viscosity and adaptability to water quality.The test methods are summarized as follows:(1)determination of centrifugal stability:take 5ml suspension concentrate sample at 3000r/min and take it out after centrifugation for 30min,observe and record the water evolution and precipitation.The water separation rate is calculated according to the ratio of water volume to total volume.If the water separation rate is more than 5%,it is unqualified.

(2)determination of viscosity viscosity is one of the important factors affecting the stability of pesticide suspension concentrate,so it is an important technical index of pesticide suspension concentrate.On the premise that the stability of the preparation can be controlled,the rotary viscometer can be used,and the control index depends on the type of preparation.

(3)in the 250 ml measuring cylinder,249 ml distilled water and 342 mg/L and 500 mg/L standard hard water were respectively filled.1 ml suspension agent sample was taken by syringe and dropped into water from 5 cm away from the water surface of the measuring cylinder.Observe its dispersion.It is qualified if it can disperse automatically in water.The dispersion was also measured in this experiment.

Excellent grade:in the water,it is in the form of cloud and mist,and can disperse automatically without visible particles sinking.

Good grade:it can disperse automatically in water,and some particles sink.The sinking particles can disperse slowly or disperse after slight shaking.

Inferior grade:it can't disperse automatically in water.It sinks in granular or flocculent form,and can be dispersed after strong shaking.

5、Pesticide suspension concentrate is one of the environmental protection pesticide formulations,but its share in the pesticide market in China is still very limited.Pesticide additives are still one of the factors affecting the development of the pesticide formulation.With the foreign additives entering the Chinese market and the development of pesticide additives in China,the development of pesticide suspensions will be rapidly developed.