Flexo printing 1000 questions (383-402)

383. What are the water-soluble dyes for fabrics?
A: According to the different conditions of water dissolution, fabrics can be divided into three groups with water-soluble dyes:
(1) Dyes dissolved in water, such as direct dyes, acid dyes, cationic dyes, reactive dyes, diazo dyes, etc. The solubility of these dyes in water is generally 40 to 100 g/L, which is characterized by having soluble ionizable groups. Group (-SO3Na, -COOH, -OSO3Na, -NH2HCl).
(2) Solubility dyes, such as vat dyes, sulfur dyes. The temporary solubility when applied is 1 to 50 g/L, characterized by the presence of ionized groups (-ONa and -SNa) in the dye.
(3) Limited solubility dyes refer to dyes that dissolve in water at 60-90°C. Dyes with limited solubility are due to polar groups that can hydrate (-OH, -NH2, -SO2NH2, -NO2) .

384. How do insoluble pigments in water adhere to fibers?
A: Pigments that are completely insoluble in water, because they cannot penetrate into the unit structure of the fiber, its connection with the fiber is adhered to the surface of the fiber by the binder resin in the binder.

385. What is the role of the paste in a dye-based printing ink?
A: Slurry is an organic substance with general colloidal properties. It dissolves or swells in water and becomes a viscous and plastic paste. It can be used as a transfer agent for attaching dyes and other chemicals to fabrics. It is cleared after completion. The paste itself does not participate in the chemical reaction in the printing, but only serves as a medium.

386. Why does the slurry have the appropriate melting temperature?
A: It is mainly to improve the suitability of printing. In the process of mechanical stirring or ink transfer, the printing paste becomes thinner and fluidity is better, which improves the permeability of the printing paste. When the stirring is stopped, the original thick state is restored to make the print pattern clear and the dots do not overflow.

387. How to make the slurry have good wetting properties?
Answer: In order to make the slurry have good wetting properties, surfactants such as oleic soap are often added to reduce its surface tension and improve its wettability.

388. How to avoid foaming?
A: First of all, in the choice of materials, we should try to use less protein gel material slurry; Second, in the printing, we must pay attention to mechanical agitation, to avoid changes in the slurry.

389. According to the nature of printing paste can be divided into several categories?
A: The printing pastes can be classified into 6 categories according to their properties and properties:
(1) Starch and its derivatives, such as wheat starch, maize starch, flour, dextrin, etc.
(2) Plant-type gums such as dragon gum, gum, seaweed gum, and white gum.
(3) Animal-type pastes, such as chitin glue.
(4) Mineral-type slurries, such as white clay (bentonite).
(5) Chemical slurries: such as hydroxymethyl cellulose; methyl cellulose; hydroxymethyl starch, emulsified pulp, etc.
(6) Other slurries, such as wood syrup, acorn powder, and field flour.

390. What are the main properties of printing pastes with wheat starch paste?
A: The printing paste using wheat starch as a paste has high coloring power, clear printed lines, simple cooking and paste procedure, good stability, resistance to general chemicals, but is not resistant to strong acids and alkalis, so it cannot be applied to vat dye printing. Pulp and strong acid anti-white pulp; In addition, because the finished product feels harsh when washing, so when printing starch with wheat starch, often oil lubrication, in order to facilitate printing. It can be used alone, but it is generally better to use it with synthetic rubber paste.

391. What are the main properties of yellow dextrin?
A: The yellow paste paste is easy to operate, has good permeability and hygroscopicity, uniform coloration, strong alkali resistance, and is easy to wash out. The finished product is soft to the touch. But at the same time, because of its good permeability, the coloring power of the surface is low, and the quality of the printed contour line is poor; due to the excessive adhesion, it also causes unclear scratching. The dextrin has a low paste ratio, which is 1 to 4 times more than that of general pastes. When the solid content reaches 50% or so, its anti-dyeing properties are good. Therefore, it is commonly used in vat dye printing pastes as well as in anti-pollution pastes. And because of its strong reducibility, it is not appropriate to use azo dyes or chrome mordant dyes. It is usually mixed with starch.

392. Give an example of a common formula for starch pastes?
Answer: The commonly used formulas for starch pastes are 12-15kg starch, 1-2kg vegetable oil, and 100kg water.

393. How to make flour paste?
A: Preparation of flour flour paste flour 20kg, acetic acid (98%) 2kg, vegetable oil 1 ~ 2kg, add water to 100kg.

394. What are the main ingredients of natural rubber?
A: Natural agglutinin, also known as astragalin gum, belongs to the leguminous family and is obtained by coagulating the juice secreted from the shrub skin of the same name. It consists of a mixture of C6H10O5 and C5H8O4, containing astragalin, viscose, and starch. And some acidic components exist as calcium, magnesium and potassium salts.

395. What are the main properties of natural rubber?
A: Natural Long Jiao is hardly soluble in water, and it is generally first allowed to naturally swell in cold water or boiled with hot water. It has a certain viscosity and emulsifying ability. Its viscosity is highest at pH 8, and it is acid-soluble. Alkaline, metal, salt or long-term heating viscosity will decrease. Relatively speaking, Longjiao's acid resistance is better. Long glue has good permeability, clear printing lines, uniform printing on large areas, and good detergency of finished products. It has a wide range of uses and is often mixed with starch equivalent. Generally, the consistency of puree is 6% to 8%.

396. What are the raw materials for synthetic dragon rubber?
A: Synthetic dragon collagen material is mainly formed by the etherification of legume seed gum. The basic composition is a polysaccharide polymer.

397. What are the characteristics of synthetic dragon rubber?
A: The main features of Synthetic Long Jiao are:
(1) It has the basic characteristics of natural agglomerates, good permeability, fine and uniform printed patterns, and excellent detergency.
(2) It has good rheological properties and is not easily adhered to the blade.
(3) High rate of paste formation, large swelling, can be obtained directly with cold or warm water, and does not require long infiltration process.
(4) Low solid content, suitable for screen printing, better mixing with emulsified paste.
(5) The scope of application of acid and alkali is wide, preferably from acidic to weak alkaline.
(6) Better printability of hydrophobic synthetic fibers or blended fabrics.
(7) Thixotropic. For screen printing, the squeegee force should be heavier.
(8) After etherification, especially after modification by carboxymethylation, it is sensitive to certain metal salts, such as copper, chromium, aluminum and other metal salts, it will produce gel, so it is not appropriate Metal complex dyes are used. If necessary, a certain amount of complexing agent may be added to the paste first.

398. How to formulate agar paste?
A: Long rubber pastes are prepared at a ratio of 6%:94%. When preparing, solid agglomerates are first impregnated with about 6 times water for 24 to 48 hours to fully puff and then heated in the pot for 4 to 5 hours. After cooking thoroughly, use water for cooling. Synthetic longan powder is easily dissolved in warm water, just stir it. It's better to do it in a quick stirrer.

399. How is alginate (seaweed gum) made?
A: The common alginate - sodium alginate is extracted from the algae of the brown algae in the seaweed. After adding alkali into sodium salt, made into powder, it is the main paste to prepare reactive dyes.

400. What are the characteristics of sodium alginate?
A: There are two kinds of wet and dry products on the market. The wet product is fibrous, insoluble in water, and must be neutralized with alkali prior to use; dry products are generally sold in powder form and can be stored for prolonged periods of time. When heated, water can be dissolved.

How does the 401.p H value affect the stability of sodium alginate?
Answer: The stability of sodium alginate is better with a pH of 6-11. When the pH is less than 6, alginic acid that is insoluble in water precipitates and gels; when the pH is higher than 11, coagulation occurs.

402. Why do we need to add sodium hexametaphosphate in the alginate paste?
A: When sodium alginate encounters hard water or calcium ions, calcium alginate precipitates easily, negative carboxyl groups and negative reactive dyes cause repulsion, and reactive dyes with strong reactivity may have secondary alcohol groups in the alginate molecule. Compounding under high-temperature alkali conditions produces color dots or lighter shades. Therefore, sodium hexametaphosphate, a complexing agent, is added to the sodium alginate paste to remove calcium ions and increase the fluidity of the color paste.

--"Printing Technology"