How to use fluorescent whitening agents in detergents: (1.) Powdered detergent
(1) Dry mixing method:
The dry mixing method is the simplest method of manufacturing laundry detergent. The molding process is: mixing dry concentrated or unconcentrated synthetic detergent active materials with various solid additives that need to be added. Stir, or rely on the water absorption of the additives to spray the active substances evenly, stir and mix, and adhere to the additives in the particles. The key technology is to add materials in sequence according to the different degrees of water absorption of the additives, and spray the active substances while stirring to avoid uneven adsorption of active substances on various solid additives.
(2) Solid phase neutralization molding method:
The solid phase neutralization molding method uses unneutralized alkyl benzene sulfonic acid and soda ash for neutralization. The soda ash is mixed and dried with the solid components in the formula before neutralization. The production process of this method is: first put the dry solid powder material into the mixer, and slowly add sulfonic acid while the mixer is running. If 90% sulfonic acid is used, the sulfonic acid immediately reacts with soda ash to form sodium alkylbenzene sulfonate. The acid addition rate should be such that the acid is fully absorbed by the alkali. The amount of unabsorbed sulfonic acid should not be too much, otherwise the acid addition rate should be reduced. . When the sulfonic acid is evenly dispersed, the powder will be uniform brown-blue. At this time, adding 2% of the mass of the powder to water can promote the neutralization reaction to proceed quickly. At this time, the powder will be light yellow without any black sulfonic acid. Clumping.
If there are sodium silicate and fluorescent whitening agent in the formula, they can be added in sequence after neutralizing the sulfonic acid. If you need to prepare whiter washing powder, you can bleach it with 2% mass sodium hypochlorite after neutralization and before adding the fluorescent whitening agent. Since the fluorescent whitening agent reacts with active chlorine and will lose its due effect, a qualitative measurement of active chlorine should be carried out before adding the fluorescent whitening agent.
(3) Spray drying molding method:
The spray drying method is also called the tower method. It occupies an extremely important position in the synthetic detergent industry. It is the main production process of traditional washing powder, and the resulting product is hollow particles. The spray drying process is roughly divided into three processes: pretreatment, drying and post-treatment. The process flow is:
① Pretreatment process:
The pretreatment process is to first neutralize alkylbenzene sulfonic acid and soda ash (concentration: 30%) in a mixing tank, and then mix it with organic or inorganic washing aids and process water at a temperature of 50~80℃ When mixing ingredients, the moisture content of the ingredients is generally 30% ~ 50%, and the solid content is 60% ~ 65%, which can reach up to 75%. However, it is best to reduce the solid content in the slurry as much as possible to obtain a uniform , stable and pumpable slurry.
In order to make the slurry mix evenly, the feeding sequence is generally as follows: materials that are difficult to dissolve, have low apparent density, and have a small proportion in the formula are added first, and then materials that are easily soluble, have high apparent density, and have a high proportion in the formula are added later, and each type must be added. Only after the materials are stirred evenly or dissolved can the next material be added. For example, surfactant can be added first, and after heating to a certain temperature, CMC, fluorescent whitening agent, etc. can be added. After they are dissolved, sodium sulfate, sodium carbonate, sodium tripolyphosphate (STPP), etc. can be added.
If the formula contains non-ionic surfactants, they can be sprayed together with the spices before packaging; or they can be directly added to the slurry. However, it should be noted that since non-ionic surfactants are easily oxidized, the drying time should be reduced. The temperature of the air. Fluorescent whitening agents can be added in this process, but the fluorescent whitening agents must be resistant to high temperatures. For varieties that are resistant to high temperatures and have poor solubility, such as the fluorescent whitening agent CXT, you can add it using the following methods:
Method 1: Add 1 part of optical brightener to 5 parts of cold water, stir into a slurry, and then mix as needed
Add a certain amount of boiling water and stir until it becomes a suspension. Use alkali to adjust the pH to 8~10, and then add it to the washing powder slurry.
Method 2: Take 1 part of fluorescent whitening agent, add a small amount of surfactant or sodium tripolyphosphate, add 5 parts of water, adjust the pH value to 8~10, adjust it to a suspension, and add it to the washing powder slurry.
For varieties with high temperature resistance and good solubility, such as fluorescent whitening agent CBS, it can be directly added to the laundry detergent slurry in powder form or dissolved in a small amount of water.
② Drying process:
The drying process is to spray the pre-treated slurry that meets the requirements into mist particles through a high-pressure pump and a sprayer. The particles contact the hot air at 200~300°C and become dry particles in a short time.
③Post-processing process:
The temperature of the granular products coming out of the drying tower is 50 ~ 80°C. The particles leaving the tower need to be cooled and aged with lower temperature air. The temperature of the air is generally controlled at around 30°C. The purpose of cooling aging is to promote the crystallization of various additives in the product and keep the product moisture in a stable form. The post-processing process also includes screening the powdery particles after aging and cooling, and mixing them with components that are not suitable for spray drying, such as bleach, enzymes, flavors, optical brighteners, etc., and then packaging and selling.
For fluorescent whitening agents that are not resistant to high temperatures, they should be added at this stage. When adding, make a solution or suspension and spray it into the washing powder, or add the powdery product directly and mix evenly.
(4) Agglomeration molding method: Compared with spray drying, agglomeration molding is also called tower-less molding. Agglomeration is the viscous mixing of powdery solid and liquid raw materials to form solid granular agglomerates. This is a mixing process involving physical and chemical effects at the same time. It is a new technology for producing granular synthetic detergents. The agglomeration molding method can be divided into simple agglomeration method and instantaneous agglomeration method.
① Simple agglomeration method: The simple agglomeration method is to first measure the solid materials (such as sodium carbonate, sodium sulfate, fluorescent whitening agent, methylcellulose, etc.) according to the proportion of the formula, premix them, and then sieve them. Mixing drum. At the same time, pre-mix the surfactant and other liquid components in the formula (fluorescent whitening agent can also be added here) according to the formula proportions, and adjust them.
To a concentration of more than 30%, after homogenization, pump it to a nozzle with a diameter of 2mm, and spray the slurry evenly onto the solid powder in the mixing drum under a pressure of 90~200kPa for agglomeration. After the finished product is qualified , the material is discharged from the other end of the drum, and after screening and aging on the belt conveyor, it can be packaged and stored in the warehouse.
②Instant agglomeration method:
This method is developed on the basis of simple agglomeration method. Compared with the simple agglomeration method, the product particles obtained by the simple agglomeration method are more uniform, the surface is smoother, the moisture content is less, the fluidity is better, and the appearance is more beautiful. .
The basic principle of the instantaneous agglomeration method is the same as that of fluidized granulation. It uses the blowing of the air flow at the bottom of the fluidized bed to make the solid powder (such as sodium carbonate, sodium sulfate, fluorescent whitening agent) in the synthetic detergent formula , methyl cellulose, etc.) to maintain a suspended fluidized state, and then atomize the liquid raw materials in the formula (the fluorescent whitening agent can be made into a liquid) and spray it into the bed, and the powder will gradually coalesce and form after boiling and rolling. For larger particles, this method can complete the mixing, granulating, and drying processes in one piece of equipment.
The agglomerated agglomerates can also be mixed with highly heat-sensitive materials such as brittle or non-ionic surfactants, enzymes, flavors, fluorescent whitening agents, etc., and can be added at the end of the fluidized bed, in a continuous mixing Simple agglomeration in the vessel.
It can be seen from the different production processes of the above-mentioned washing powder that there are many opportunities to add fluorescent whitening agents, but this timing is not suitable for all varieties. Some varieties, such as the fluorescent whitening agent CBS, can be added in any process of washing powder; High temperature resistant varieties can only be added together with spices before packaging, which is determined by the heat resistance of the fluorescent whitening agent. If only from the perspective of improving the appearance of washing powder, fluorescent whitening agents are generally added to the detergent slurry in the form of solutions, soft water suspensions or directly in the form of particles, which can significantly improve the appearance of white and light-colored washing powder.
(5) Application examples:
There are many varieties of washing powder according to different classification methods. Their basic differences are reflected in the type, dosage and additives of surfactants.
Application example 1:
Heavy-duty household laundry detergent.formula:
Branched alkyl benzene sulfonic acid 18kg
Sodium tripolyphosphate (15%) 15kg
Soda ash 58kg
CMC(66%) 2kg
Sodium silicate (40%) 5kg
Sodium perborate 10kg
Water 2kg
Fluorescent whitening agent 0. 1kg
Preparation method: First add soda ash, sodium tripolyphosphate and CMC into a mixer and stir, then add branched alkyl benzene sulfonic acid while stirring, then add water and continue stirring and mixing, then add sodium silicate solution and neutralize. After stirring for another 15 minutes, the mixed slurry material can be unloaded onto a moisture-proof, flat ground, spread out, aged, and crushed with a pulverizer one day later. The crushed and ground materials are then put into the original mixer or other mixers, and sodium perborate and fluorescent whitening agent are added. After a few minutes of mixing, the materials can be discharged and then packaged. If linear alkyl benzene sulfonates are used, tosylate or colloidal silica needs to be added to avoid sticking.
Application example 2: Ordinary bleaching laundry detergent. Formula (mass fraction):
Sodium alkyl benzene sulfonate 10%
Fatty alcohol polyoxyethylene ether 3%
Sodium Lauryl Sulfate 2%
Soap 2%
Soda ash 6%
Sodium silicate (modulus 2.4) 6%
Sodium carboxymethyl cellulose 1%
Sodium tripolyphosphate 20%
Sodium percarbonate 12%
Fluorescent whitening agent 0. 1%
Sodium sulfate 30. 8%
Spices 0. 1%
Water 7%
Preparation method: Slurry other materials except peroxide and spices. The fluorescent whitening agent is first dissolved in water, then added to the slurry, and spray-dried to obtain hollow particle powder. Add peroxide and spices (added below 30°C). ) and mix evenly.
Application example 3: Laundry powder for washing machines. Formula (mass fraction):
Sodium alkyl benzene sulfonate (100%) 1. 6%
Butter fatty acid 6. 4%
Sodium tripolyphosphate 10%
Sodium pyrophosphate 5%
Sodium hypochlorite 2%
Sodium silicate (40%) 8%
Sodium perborate 9. 8%
Sodium sulfate 55%
Fluorescent whitening agent 0. 2%
CMC (based on 60%) 2%
Preparation method: Mix sodium alkyl benzene sulfonate, tallow fatty acid, sodium tripolyphosphate and sodium pyrophosphite, mix sodium sulfate and CMC evenly, and add it to the aforementioned mixture while stirring. After it is evenly dispersed, add sodium hypochlorite. Then add sodium silicate, mix and grind, then add sodium perborate and fluorescent whitening agent to obtain washing powder for washing machines.
