Discussion on Printing Fastness of Waterproof Nylon Cloth

In the clothing printing industry, some manufacturers often encounter paint printing on waterproof nylon cloth, and the fastness is always difficult to meet the required technical problems. The author would like to make a brief analysis of this issue and propose several technical options for improving fastness, and discuss it with readers.

First, the reason analysis

1. The relationship between fiber properties and print fastness Unlike natural fibers, nylon or polyester fibers are synthetic fibers. Their basic characteristics are very close molecular structure, little or no water absorption, and the fiber surface is very smooth. Therefore, the paint printing paste cannot penetrate into the fiber but only adheres to the fiber surface. The fastness depends entirely on the adhesion of the binder (resin) to the fiber surface and the mechanical properties of the resin film itself. Therefore, the print fastness of nylon or polyester fabrics is far behind the natural fibers.
2. The relationship between waterproofness, water repellency, and print fastness of fabrics. In daily life, the water resistance and water repellency of fabrics are often confused. In fact, in the dyeing and finishing technology, the two are two different concepts that are both related and different. The so-called water-repellent is not the meaning of water, such as water on the lotus leaf, can form rolling beads, indicating that the lotus leaf has a strong water repellency. If the nylon cloth is water repellent, it will have water repellency like lotus leaf. The so-called waterproof is impermeable to water, such as a single-sided nylon poncho, pouring rain can not be permeable. If the nylon cloth is made of waterproof processing and water repellent finishing, a multifunctional product with water repellent, waterproof, windproof and warmth can be obtained.
In general, the printing of waterproof nylon cloth is not printed on the side of the glue, but on the uncoated side. Therefore, water resistance has little or no effect on print fastness, and water repellency affects the adhesion of the print paste to the fiber surface. The greater the water repellency, the greater the impact. In the dyeing and finishing process, the frequently used fabric water-repellent finishing agent organosilicon compound is precisely a kind of stripping agent used for processing the release film transfer printing paper. It can be imagined that the water repellency of printed nylon or polyester fabrics makes it difficult to print fastness.

Second, on the improvement of fastness of several process technology options

In the clothing printing, the nylon or polyester fabrics encountered are of different types. In the dyeing and finishing process, some of them are only waterproof, some are only water repellent, some are waterproof and water repellent, and some are There is neither waterproof nor water. Therefore, in the printing before the actual identification needs to be treated in order to distinguish between, according to the strength of fabric water repellency, to determine the choice of printing paste and process conditions.
1. Selection of printing paste Currently, there are two major types of printing pastes for nylon or polyester fabrics: water-based printing paste and solvent-based printing ink. As for their resin components, mainly polyacrylates and polyurethanes. These two types of resins can be made into aqueous slushes and solvent inks. In process applications, they are divided into single-component and two-component. For print fastness, solvent inks are better than aqueous ones, polyurethanes are better than polyacrylates, and the two components are better than single components. This shows that the two-component solvent-based polyurethane ink has the best fastness.
Of course, in the actual production, we must also consider the issue of labor insurance and the environment. Therefore, the choice of printing paste should be as practical and feasible as possible.
2. Application of cross-linkers Cross-linking agents, also known as bridging agents, are generally classified into two categories, water-based and oil-based. They can be used in combination with aqueous slush or solvent-based inks, respectively. However, it is not very strict in practical applications. For example, it is also feasible and effective to use oily cross-linkers and water-based creams. In the printing process, the cross-linking agent may cross-link with itself or with the printing resin to form a massive network structure, thereby strengthening the adhesion to the textile fibers, and improving the mechanical properties of the resin film, so that the printing fastness is greatly improved. improve. Single-component printing pastes can be used directly for printing and can also be used together with cross-linking agents, while two-component printing pastes must be used together with cross-linking agents.
It should be pointed out that the amount of cross-linking agent should not be too large, otherwise it will affect the hand feeling, and it is also not good for the fastness. When using an oil-based cross-linking agent, the prepared printing ink should be used up immediately. If the time passes, it will deteriorate the properties or even cause condensation failure.
3. The printing platen, screen plate, scraper shape, hardness and pressure used in the printing operation not only affect the surface effect of the pattern, but also have a certain impact on the fastness, the key is to control the appropriate amount of ink, so as to avoid The resin film formed on the fabric surface is too thick and affects the washing fastness.
4. Selection of technological conditions Currently, in the production of clothing printing industry, the drying process after printing is different. Some of them are dried naturally, some are dried by low-temperature hot air, and some are dried or dried after high temperature baking or pressing. The third process has the best fastness, because the high-temperature treatment can make the water or solvent volatilize cleanly; at the same time, the components in the printing ink can fully react, and the resin film and the fabric fiber can also be more closely bonded. This has an extremely important role in improving the fastness, especially the wash-fastness.
It should be pointed out that in the high temperature treatment, the temperature and time must be strictly controlled. If the temperature is too high, it will cause yellowing of the white fabric or thermal migration of the dye on the colored fabric to cause panning; it will cause damage to the resin film and decrease the fastness; it may even cause the fabric to melt or scorch. Therefore, before the formal production, all aspects of practical tests must be carried out to optimize the printing ink and determine the reasonable technological conditions.

Third, on the test method of fastness

The garment printing industry's production characteristics are small batches, many varieties, and many colors, especially some special printing, and the products are more complicated. There is still a lack of unified industry standards. For the print fastness of nylon fabrics, hand-washing and sticky tape methods are generally used for testing. Hand-washing includes drying and moistening (timely immersing the cloth in water or soap followed by destructive rinsing) and observing whether the tree finger is broken and how many times it can withstand. The self-adhesive tape method is to attach a self-adhesive tape to the printed part of the fabric, and then quickly pulls the adhesive tape apart to observe whether the resin film is peeled off from the fabric.
The above test methods are still not standardized nor standard, but they are also convenient and practical. With the continuous development of the garment printing industry, how to implement a standard that suits the characteristics of the product is also a question worth exploring.

Source: Screen Printing