Application of sodium hexametaphosphate in coatings and common problems

In the process of pigment dispersion, especially in the process of organic pigment dispersion, sodium hexametaphosphate manufacturers often encounter problems such as insufficient color rendering or transparency, poor rheology or stability. How to eliminate these problems by selecting appropriate raw materials and dispersed mechanical equipment, and what role does sodium hexametaphosphate play in coatings? Let's introduce it to you.

The dispersion quality of pigments from sodium hexametaphosphate manufacturers will affect many important coating properties:

（1） As a soft water agent, so that dyes and soap do not precipitate and agglomerate

There are many ways to soften hard water, which can generally be selected according to the hardness of water quality and specific conditions. The principle of softening hard water with sodium hexametaphosphate is that the calcium ion Ca + + or magnesium ion Mg + + that causes the hardness in water enters the sodium hexametaphosphate molecule and becomes a very stable soluble complex: Na2 [Ca2 (PO3) 6] and Na2 [Mg2 (PO3) 6]. The Ca + + or Mg + + in this complex is not easy to run out again, so Ca + + or Mg + + will not precipitate or agglomerate when encountering dyes or soaps, so dyes and soaps can be saved, Achieve the effect of water purification.

Note:

1. In the water softened by sodium hexametaphosphate, the presence of calcium ion Ca + + can not be seen even with a sensitive reagent such as ammonium oxalate.

2. Sodium hexametaphosphate is used as soft water agent in dyeing or post-treatment. It can capture calcium and magnesium ions from the generated insoluble calcium soap, magnesium soap or calcium dye and magnesium dye precipitation, and make the precipitation dissolve again. In other words, sodium hexametaphosphate can regenerate sodium soap by introducing sodium hexametaphosphate into the solution. Even when the formed calcium soap or magnesium soap is formed, the clot of calcium soap or magnesium soap will disappear. Similarly, sodium hexametaphosphate can regenerate dyes.

3. The reaction between sodium hexametaphosphate and calcium soap or magnesium soap is carried out according to the following equation:

2(RCOO)2Ca＋Na2〔Na4(PO3)6〕→Na2〔Ca2(PO3)6〕＋4RCOONa

2(RCOO)2Mg＋Na2〔Na4(PO3)6〕→Na2〔Mg2(PO3)6〕＋4RCOONa

4. When dyeing rayon with direct dyes, soft water is an important condition to ensure the quality, especially for some direct copper salt dyes. Soda ash soft water is often used in cotton fabric dyeing; However, when dyeing viscose fabric, the following problems should be considered:

(1) The pH value of soda ash is high. Due to the low degree of polymerization of viscose fiber, if the winding dyeing temperature is set at the boiling point, it is very easy to cause the fracture and hydrolysis of fiber molecular chain, affect the strength and cause the rough feel of fabric. In addition, it can lead to the reduction of aldehyde group and glucose products in alkaline dye bath, so that some direct dyes that are not resistant to reduction are reduced and damaged, resulting in color stripping.

(2) Soda ash is an electrolyte, which will increase the sodium ion in the dyeing bath and promote the dyeing. For rayon, it matters more. Some dyes with high dyeing affinity and very sensitive to electrolyte, especially direct copper salt dyes, such as soda ash soft water, often have serious surface dyeing phenomenon and affect the product quality.

(3) The ideal water softener should be sodium hexametaphosphate. The pH value of sodium hexametaphosphate is close to neutral, so it has no above disadvantages of soda ash. Sodium hexametaphosphate can form complex with calcium ions in hard water to "block" calcium ions, so as to achieve the purpose of soft water.

(4) The general dosage of sodium hexametaphosphate is about 10 grams of sodium hexametaphosphate per 100 liters of hard water of 10 ppm.

(5) In order to prevent the hydrolysis of fiber caused by strong alkali in the dyeing bath, resulting in the reduction damage of dye, anti dyeing salt s can be added in the dyeing bath, 2 ~ 5g per liter. It can oxidize and avoid the above disadvantages.

（2） Prevent the precipitation of sodium alginate in the presence of calcium

Sodium alginate slurry is the most practical slurry for reactive dyes, but attention should be paid to prevent sodium alginate from penetrating into calcium in hard water to form calcium alginate.

Note:

The negative charge of the alginate coo group in the alginate dye has no effect on the anionic carboxyl of the alginate group, which makes the alginate group in the alginate printing paste as resistant as possible. This not only damages the performance of the color paste, but also affects the color fastness.

2. Therefore, sodium hexametaphosphate must be added to prevent the formation of calcium alginate. Under normal conditions, the dosage of 5 ~ 10 g / L is enough, and can be increased to 15 ~ 20 g / L under special circumstances. It can be added when preparing printing paste or raw paste.

（3） As scouring assistant:

When nylon strand (polyamide fiber) is boiled with soap and soda ash before dyeing, the addition of sodium hexametaphosphate (about 0.3% of the weight of textured silk) can prevent the soap from being consumed by hard water and improve the scouring effect.

（4） Treatment of circulating water:

In the circulating water, due to the addition of sodium hexametaphosphate to reduce the hardness, it is not easy to produce calcium carbonate sediment and avoid blocking the water pipe. The dosage is about 2 parts per million.

（5） Boiler water treatment:

Sodium hexametaphosphate can also be used to treat hard water in the furnace, which can not only avoid pot scale, but also re dissolve the generated pot scale, but the price is higher than that of trisodium phosphate.

（6） Synthetic detergent as ingredient:

Sodium hexametaphosphate is an important ingredient in synthetic detergents (such as sodium alkyl sulfonate and Sodium Alkylbenzene Sulfonate), because it has good water softening ability and washing aid ability.