The heat transfer printing technology was developed by European printing companies in the late 1960s. This process utilizes the sublimation principle of disperse dyes or inks, using paper as a carrier to transfer the printed patterns onto fabric through temperature sublimation.

Heat transfer printing technology began production in some printing factories in the early 1970s, but for most of this period, it involved the intermittent ironing of transfer printing paper patterns onto synthetic fabrics such as clothing, ready-to-wear, bags, and tailoring. By the mid-1970s, heat transfer printing technology began to be used in continuous production like traditional printing. With improvements in transfer paper equipment, the quality of transfer paper has correspondingly increased, and the production speed of machine transfer paper generally ranges from 2000 to 3000 m/h.

Classification

Heat transfer printing is generally divided into hot melt transfer printing and heat sublimation transfer printing. Hot melt transfer printing is mostly used for 100% cotton, but its disadvantage is poor breathability. Heat sublimation transfer printing was often used for polyester printing in the past, with the drawback of high plate-making costs.

The commonly used method for heat transfer printing is the sublimation method. The principle is to utilize the sublimation characteristics of disperse dyes to transfer and fix the dyes onto synthetic fibers such as polyester at high temperatures.

The specific process involves transferring the pattern through a roller or flat screen after plate-making, or using a rotary screen printing machine to print disperse dyes or inks on paper. Additionally, the printed transfer paper with floral patterns is applied to the fabric under suitable temperature and pressure conditions, where the physical and chemical actions instantaneously sublimate the paper pattern onto the fabric surface, diffusing into the inner layer of the fibers for fixation. This is the current heat transfer printing process for polyester fabrics.

Heat transfer printing can be classified based on the printing method: offset printing, gravure printing, screen printing, and digital printing.

Advantages

Compared to traditional processes, heat transfer printing has the following advantages:

Small footprint and short process flow;

Because it utilizes the high color characteristics of disperse dyes, it can completely fix the colors.

This is an environmentally friendly dyeing method that eliminates wastewater issues by reducing fixation, washing, and other post-processing steps.

Since the dye absorption of the transfer printing original paper is much lower than that of direct printing on fabric, it relatively reduces costs.

Defects caused by complex color arrangements and large pattern boards can be detected when printing transfer paper, allowing for the cutting of defective paper before transferring to fabric, ensuring the efficiency of the finished fabric after transfer.

Due to the limited penetration of the original paper, the patterns on the transfer dyeing paper are clearer, with more distinct layers and more uniform colors. The three-dimensional effect is strong, especially noticeable in halftone effects.

Disadvantages:

Suitable for small batches, multiple varieties, and bridge machine products.

The range of applicable fibers is limited. Because high temperature and pressure are required during the transfer process, it is mainly used for synthetic fabrics, primarily polyester fibers. The drawback of heat transfer printing is that it is difficult to achieve satisfactory large-scale production on natural fiber fabrics. The requirements for the board paper are high, and the usage is large.

Factors Affecting Heat Transfer Printing Conditions

1. Transfer temperature depends on the sublimation dyeing temperature, fiber heat resistance, heat transfer time, etc.

The disperse dyes used in heat transfer printing should have sublimation temperatures that do not damage the fiber macromolecule melting point and fabric strength. The processing temperature suitable for polyester is between 180 and 210 degrees. Within this temperature range, the molecular weight of the sublimated dye varieties is between 230 and 270.

2. Transfer pressure: A transfer pressure of 10 kPa is standard (for example, insufficient pressure) can lead to poor alignment between the transfer paper and the printed fabric, resulting in uneven patterns and unclear colors. Conversely, if the pressure is too high, the hand feel and style of the printed fabric will also change.

Rotary screen printing: It is necessary to securely cover the blanket on the surface of the hot roller, ensuring that the board paper and printed fabric are closely aligned, with appropriate pressure generally controlled at 12 kPa.

Vacuum negative pressure heat transfer: Under negative pressure conditions (13.3 kPa), good coloring and penetration effects can be achieved, resulting in a good hand feel for the printed fabric.

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The transfer time during actual processing is 15 to 45 seconds. Transfer temperature, fiber type, woven or knitted structure, and variety all affect the transfer time.

The color fastness of heat transfer printed fabrics mainly depends on three factors of the processed fabric.

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