Knit Fabric Paint Printing Practice (1)

1 Introduction

Because of its good dimensional stability, elasticity, water absorption, softness, and breathability, knitted fabrics are beautiful and comfortable to wear, so they are loved by consumers. People in the market today are pursuing casual clothing, emphasizing comfort and personalization. Many knitted fabrics have been developed into outer wear of underwear, which has increased the number of knitwear printing products year by year.

In general, the equipment that can be used for knitwear printing is: flat screen printing, garden screen printing, roller printing, manual table printing. The printing process used is mainly paint printing and reactive dye printing, and a small amount of transfer printing. This article mainly describes eight years of paint printing process practice.

The key issue for coatings used in knitwear printing is the need to rationally select the components of the printing paste (including adhesives, paint pastes, and pastes) to maximize the balance between hand and feel. Since 1997, we have cooperated with Zhejiang Silk Science Institute and have used super soft type TYS-1 printing paste with imported raw materials and some domestic paints. We have applied directly on the rotary screen printing machine for coating direct printing, active printing, and special coating printing. (Including three-dimensional foam printing, gold and silver powder printing, pearl printing, flashing film printing) and the newly emerging paint discharge printing. So far it has produced more than 2,000 tons of knitted calico, accumulated some of the actual experience of rotary screen printing, and now will experience the written experience written, and printing and dyeing industry colleagues to discuss.

2 Knitted fabrics

2.1 Before knit fabric printing, the knit fabric must be subjected to pretreatment such as decontamination, bleaching, etc. in order to improve the performance and appearance quality of the knitted fabric, and prepare for the posterior printing process. The good pretreatment process is knitwear. The basis of rotary screen printing.

Due to the structure of the grey fabric, the processing quality requirements and the different processing equipment used, different pretreatment processes are possible. The process flow is generally:

Blank cloth → (alkaline shrink (mercerized)) → scouring → bleaching (chlorine bleaching or oxygen bleaching) → brightening → softening → dehydration → drying → calendering (double-sided fabric non-alkaline shrinkage)

The pre-treatment of knitted fabrics mainly consists of three parts: alkali shrink (mercerized), scouring and bleaching (whitening). Alkaline shrinkage is a process in which a cotton knitted fabric is piled in a flat (cylindrical) and no-tension state after padding caustic soda solution and then washed with alkali. By alkali shrinkage, the fabric shrinks, increases density, elasticity and gloss, enhances the smooth feel, reduces the shrinkage rate, and improves the dimensional stability of the finished product. In recent years, the mercerization process has gradually increased for knitted fabrics, and the mercerized product quality is much higher than that of alkali shrinkage products.

The role and principle of scouring and bleaching of knitted fabrics are the same as those of woven fabrics. However, due to the looser organization, the processing conditions (mainly the working fluid concentration) are lower than those of the woven fabrics. The processing methods for scouring and bleaching are batch type and continuous type. The batch type is generally performed by using a cooking pot or in an overflow dyeing machine; continuous type generally uses “D” type boxes or crawler boxes with flat steaming. The bleaching of semi-finished products for knitted printing often uses chlorine bleaching, oxygen bleaching, chlorine oxygen bleaching, and double oxygen bleaching.

Knitted printing semi-finished products require uniform scouring, consistent whiteness, good hair styling, small weft angle, and consistent weight. Improper pre-processing, quality problems caused by the same as the woven fabric processing, such as uneven scouring, uneven bleaching, lack of whiteness, etc., in the printing process will often lead to poor color and color, background color difference or shade Darkness, etc., but also some of its unique quality problems, should pay attention to when processing.

2.2 square meters weight problem

The finished product grammage weight is one of the important indicators of the customer's quality requirements and must be guaranteed; if it exceeds too much, it will increase the production cost, so under the premise of guaranteeing the weight of the finished product, the weight of the rough fabric will be controlled. It is very important. In the pre-processing and printing processes, there are factors that reduce the grammage, such as impurities in the pre-treatment, the fabric is stretched after being subjected to a certain tension during the printing process, and there are also factors that increase the grammage, such as the fabric of the pretreatment. Retraction, the amount of paint and additives added to the fabric during printing, etc. However, due to the different tensions of processing equipment and the different types of pattern printing, the grammage varies, and the grammage of the finished product fluctuates up and down based on the weight of the rough fabric. In order to avoid the problem of non-conformity of finished products after printing, unless there are many production experiences, they are generally required to be pioneer samples. After passing through the same process route as when producing large goods, the weight of knitted fabrics after processing equipment will change. To formulate and revise rough billet weight indicators for bulk production.

2.3 Mao effect problem

Inappropriate hairiness results in uneven coloration of the printing surface. In severe cases, there will be a "bottom out" phenomenon, or the depth cannot be increased. Attention should be paid especially when making dark-colored large surface patterns. The reason for this is that, in addition to the usual “undersampling”, the “soft handling” process that is unique to the pre-treatment of knitted fabrics is also an important cause of the bad hairiness of the knitted fabrics. Due to improper selection of softener, or excessive use amount, it will cause water repellency after finishing. Therefore, the pre-treatment for printing with knit should also pay attention to the “soft handling”. It should not simply apply the finishing technology of bleaching and dyeing of knitted fabrics. Choosing softeners and rationally setting their dosages will affect the fastness after printing. At the same time improving the fabric's hand feel, it will also take into consideration the gross effect of knitted semi-finished products to ensure the smooth printing process.

2.4 Weft problem

The pretreatment of knitted fabrics is mostly rope-like processing, and the organization is looser. The problem of latitudinal weaving is more serious than that of woven fabrics. If the floral pattern, the problem of weft can also be appropriately relaxed, if the lattice pattern is a higher demand for weft. Measures to control and improve the weft: Check the direction of the weft in front of the slits to make them consistent, and correct them when cutting the head together. The pre-press setting machine should be equipped with an automatic weft-setting device; the pre-press setting should be Set the width of the door to reduce the extent of post-press stretching, in order to reduce the arc-shaped flower skew caused by post-press stereotypes.

Quality requirements for knitted fabrics such as web width, shrinkage, weight per square meter (m2), physical strength, coil length, density, and other physical standards should meet national standards or standards required by customers. The intrinsic quality of the grey cloth has a large relationship with the width of the door, the weight of the square meter, and the shrinkage rate, and must be taken seriously.