Preparation of microcapsule dyes
1. Preparation method of disperse dye microcapsules
There are many preparation methods of microcapsule dyes, and they are all recorded in relevant data. Herein, only the production of the disperse dye microcapsules is described because it is insoluble in water, but it is easily dispersed in water and can be coated with a water-soluble outer film material such as methyl cellulose, and is most suitable for dye microcapsules. Therefore, water-insoluble dyes can be formed into microcapsules by phase separation of the single coagulation method, the complex coacervation method, or the physical method, and it is difficult to prepare microcapsules using water-soluble dyes.
1) Complex coacervation
In the preparation of disperse dye microcapsules by the complex coacervation method, traditional gelatin-Arabic gum may not be used because the gum arabic is more expensive, and the commercial disperse dye formulation contains a large amount of a diffusion agent NNO, which is a naphthalenesulfonic acid and formaldehyde The polycondensate, which has a negative charge in an aqueous solution, is a dye diffusion agent commonly used in the printing industry and can be used instead of gum arabic. The isoelectric point of pH = 8 ~ 9 pigskin gelatin was dissolved in water at 40 °C, and then disperse dyes containing the diffusion agent NNO dispersed in gelatin aqueous solution, stirring to form fine dye suspension particles, dilute hydrochloric acid solution was added to adjust When pH=4, the amphoteric polyelectrolyte gelatin transforms from being negatively charged to positively charged, and then it is attracted to the negatively charged diffusing agent NNO particles to cause coagulation. However, because the gelatin and the diffusing agent NNO are likely to attract and agglomerate directly into each other and lose the function of the coating dye, in order to obtain the state of the coated dye particles, some synthetic agglomerates may be added as a protective colloid to prevent agglomeration.
In order to meet the requirements of various printing methods, the strength of the dye microcapsule wall film is increased so that it can withstand the pressure of a printing rubber roller, a copper blade or a magnetic bar, and the dye microcapsules need to be hardened. Hardening can be done by adding a certain amount of 37% formaldehyde and using sodium hydroxide solution to adjust pH=8~9 when cooled to 10°C. The degree of hardening can be adjusted by controlling the temperature, the reaction time, and the amount of added formaldehyde, and it requires repeated trial and error to find a suitable condition. If it is hardened excessively, the wall film is too hard, which will affect the post-processing effect of the printing. For example, the microcapsules cannot be quickly broken when steaming, and no dye can be released to make printing failure. If you want to get smaller microcapsules, you can reduce the amount of synthetic agglutinate, and speed up the speed of dropping the hydrochloric acid solution and slow the stirring speed; if you want to get larger microcapsule particles, you can add some gelatin or diffusion agent NNO .
Since the conversion process between the gel and the sol prior to the curing process is reversible, after the coacervation phase separation occurs, if the size of the obtained microcapsule particles is not appropriate, the pH may be increased again by adding a base to re-dissolve the gel. The dye-encapsulated core was dispersed again by stirring, and hydrochloric acid was added to adjust the acidity of the solution to about pH=4, again producing coacervation phase separation until satisfactory particles were obtained. This method of repeatedly adjusting the pH to achieve particle size requirements is simple and relatively common. After forming the dye microcapsules, the dispersion can be layered after being placed, the supernatant liquid is filtered off, and the dye microcapsule particles are dried to be the product. The dye coverage of this method is generally around 50%.
2) Gelatin-Arabic gum complex coacervation
The preparation of dye microcapsules using gelatin-Arabic gum complex coacervation can be divided into three different methods of operation, namely pH adjustment, dilution and adjustment of temperature. Since the actual application of the temperature adjustment method is relatively small and the dilution method has poor reproducibility, the pH adjustment method is mainly introduced.
Water-insoluble microcapsules can be prepared by complex coacervation. A typical application of the complex coacervation microencapsulation technology is the preparation of gelatin-Arabic gum microcapsules. Gelatine is a water-soluble natural amphoteric polymer compound. It is non-toxic, inexpensive, and has good film-forming properties. Gelatin is a commonly used raw material for microencapsulation of coacervation. Gelatin A (acid treatment) is generally used, and gelatin B (alkaline treatment) is relatively rare. When the pH value is neutral, Gelatin A has a high proportion of positive charge and its isoelectric point is 8 to 9.5. Gelatin B has a high proportion of negative charge when the pH value is neutral, and its isoelectric point is 4.7- 5.3. Due to the different preparation methods of gelatin raw materials, the properties of the prepared microcapsules will also be different.
2. Formulation example
Disperse dye microcapsule printing paste formula:
Microcapsule disperse dyes 20% to 40%
Sodium alginate pulp 50% to 85%
Urea 5%
Anti-stain salt S 2%
Tartaric acid (adjusting pH)
Water amount
Total 100%
The application of microencapsulated dyes in the textile printing industry is currently limited to spot printing, which is a promising dye in the long run. For example, in a vat dye suspension dyeing, the reducing agent cannot coexist with the dye, and the immersed vat dye suspension must be firstly dried, and then the reducing liquid is dipped. If the reducing agent is microencapsulated, it can be used together with the dye. use. Another example is the use of the chromic phenolic base of the ice dye and the chromogenic base coloration. The polyester/polyacrylonitrile and polyester/wool blended fabrics need to be dyed or printed separately with two dyes because the two dyes meet each other. The sedimentation effect will affect the use of one-bath dyeing printing. If one of the two component dyes is microencapsulated, it can be used once, thereby simplifying the printing process. In addition, some additives with special properties can also be coated to achieve simultaneous dyeing of the fiber with additives and dyes.
It can be foreseen that the use of microcapsule dyes in the textile dyeing and printing industry will be more extensive, and will continue to open up new uses.
Author: China Materials Storage and Transportation Company in Shenyang Liu Yongqing Source: "Printing Technology"