Knitwear dyes testing standards

Knitwear dye detection

At present, most of the fabrics in our country are divided into knitted and woven. Woven fabrics are fabrics formed by weaving warp yarns and weft yarns perpendicular to each other. Knitted fabrics are made by forming loops of yarn or filaments with knitting needles, and then stringing the loops into each other.

Knitting refers to the process of using knitting needles to form loops of various raw materials and yarns, and then connect them to form knitted fabrics. It can be done horizontally or vertically, horizontal knitting is called weft knitted fabric, and longitudinal knitting is called warp knitted fabric.

The loop is the smallest basic unit of the knitted fabric, and the loop is composed of the loop stem and the extension line in a space curve.

At present, knitted fabrics are widely used in clothing fabrics and linings, home textiles and other products, and are loved by consumers. In the process of printing and dyeing knitted fabrics, various problems will always appear. This article focuses on six of the most common problems.

1.Unqualified color fastness

Color fastness refers to the resistance of the color of textiles to various effects during processing and use. The fastness grade is evaluated according to the discoloration of the sample and the staining of the undyed lining fabric. Textile color fastness test is a routine test item in the internal quality test of textiles.

There are many types of color fastness, including light fastness, soaping fastness, perspiration fastness, rubbing fastness, sublimation fastness, ironing fastness, etc. The key to these fastnesses lies in the structural properties of the dye, and is also related to fiber , Dye concentration, dyeing and finishing process, external conditions, etc. are closely related, so whether the color fastness meets the standard, the key is to select dyes, followed by the application of dyeing process and auxiliaries.

When the dyeing process is formulated, it must be reasonably determined according to the dye, fiber and customer indicators, so that the dye can dye the fiber as firmly as possible under certain conditions with the help of the auxiliary agent to make it fully fixed. For the auxiliary agent, one is to choose A good leveling agent and dye accelerating agent can make the dyes dye fibers slowly, evenly and fully; the second is to add a chelating agent to overcome the complexation of the dye and the metal ion in the water to form a floating color, and reduce the hydrolysis of the reactive dye in the water; The third is to choose an excellent soaping agent to remove the floating color and prevent the floating color from re-staining the fabric; the fourth is to select an appropriate fixing agent. At present, there is no ideal fixing agent for sublimation fastness and light fastness. , For soaping fastness, perspiration fastness, rubbing fastness and other indicators, there are excellent fixing agents to choose from.

2.Brittle damage

Brittle damage is manifested by a decrease in strength. In addition to brittle damage or even holes caused by improper oxygen bleaching in the pretreatment process, there are generally two reasons for brittle damage caused by the dyeing stage. One is the photosensitive brittleness caused by dyes such as sulfur black. It is necessary to use anti-brittle agents to improve the damage, as well as the brittle damage to the fiber such as strong reducing agents and strong oxidants in the dyeing of vat dyes; the second is the improper use of acid in the dyeing or neutralization stage. The general acid used for neutralization is glacial acetic acid Some substitute acids are currently available on the market. Some of these substitute acids are organic buffer acids from BASF. They do not contain strong inorganic acids such as sulfuric acid, hydrochloric acid and phosphoric acid. The performance is even better than acetic acid. The organic acid of Ningbo Huake Textile Auxiliary The same is true. These buffer acids can also improve some of the disadvantages of glacial acetic acid (such as inconvenient use in winter, irritating taste, residual acidity, and metal ions in water (such as Ca2+, Mg2+) and leaving behind on the fabric to cause color fading. Wait secretly). Some substitute acids containing H2S04, HCl, H3P04, etc. not only cause changes in dyeing shade, but also corrosive to dyeing and finishing equipment and pumps, and acid residues after neutralization can also cause fabric brittleness under acidic conditions.

3.Wrinkles

The main reasons are equipment, as well as the amount of cloth, the bath ratio and the processing technology operation. The difference in equipment is the amount of cloth in a tube, the pressure and friction between the cloth and the cloth, the pump force and the strength All affect the flatness of the fabric surface, and the size of the bath ratio will also affect the flatness of the fabric surface. Too much auxiliary foam in the process operation causes the fabric to float up and the temperature rise and drop during the process operation will cause the phenomenon of rapid cooling and heating. Wrinkle phenomenon. The current bath lubricating and anti-wrinkle agents, bath treasures, and bath softeners can all improve the phenomenon of fine wrinkles, but if the equipment is not improved and the process control is not good, adding the lubricant in the bath alone cannot completely avoid the wrinkles produced.

4.Wind seal

Wind printing has little to do with additives. The key is the performance of the dye itself (acid and alkali resistance) and the acidity and alkalinity of the fabric, the humidity of the air and the acid gas, such as the light fast blue GC and freeze yellow in the direct dye. G, etc. are easy to produce windprints when exposed to acid gas, while active Turquoise KN-G, Brilliant Orange X-GN, etc. are sensitive to acid and alkali, but also easy to produce windprints. Disperse dyes such as yellow RGFL are sensitive to alkalis and also easy to produce windprints. For additives, neutralization must be done well to make the cloth surface as possible as PH=7. Therefore, we must also pay attention to the types of acids and bases during neutralization. Use glacial acetic acid or organic substitute acids as much as possible, and never use substitute acids containing strong mineral acids such as H2S04 and HCl. The choice of alkali should also be as gentle as possible .

5.Color flowers (including color difference, color not attached, etc.)

6.Color points (including white point)

There are many reasons for the color spots, such as white spots, which may be the reason that immature cotton is not dyed with dyes, or it may be caused by solids such as soda ash sticking to the cloth and causing partial non-staining. The main causes of color points are:

①Improper selection of dye: the dye particles are too large or they are easy to agglomerate to form color spots;

② Poor dye dissolution: undissolved dye enters the dye solution and stains on the fabric to form color spots;

③Poor water quality: Poor water quality causes dye condensation:

④Equipment is not exhausted: the tar substance of the dyeing vat falls down to cause color spots;

⑤Auxiliary reason: The auxiliary agent added during dyeing sometimes causes the dye to agglomerate and produce color points; the auxiliary agent foams too much, and the foam and the dye combine to form a colored foam, which is attached to the fabric to form a color point; the auxiliary agent precipitates and stains the dye. On the fabric and equipment, the agglomerates on the equipment will transfer to the fabric to cause color spots.