Analysis of Factors Affecting Thermal Transfer Quality

Thermal transfer is a process that is an important part of the entire printing process and is closely related to other processes. How to control the stability of this process is an important guarantee for the quality of printed matter. Let’s first look at the important factors affecting the thermal transfer process.

1. Thermal print head

The thermal print head is mainly composed of a surface film protective layer, a bottom film protective layer and a heating element. The heating element is a conductive mesh screen, and the heat generated by the voltage pulse is thermally diffused, so that the ink particles in the image portion are embossed and melted to complete the ink transfer.

The printing speed of thermal transfer depends on the time required for each line of text. Therefore, the thermal transfer head and the transfer paper should have good heat transfer properties, so that the heat generated by the heating element can be quickly transmitted to the surface of the substrate through the protective layer, the transfer paper substrate and the void to ensure that the ink has Enough transfer time.

2. Ink

The composition of the thermal transfer ink is generally three parts of a pigment (pigment or dye), a wax and an oil, wherein the wax is a main component of the thermal transfer ink.

3. Transfer medium

The substrate of the transfer paper is generally divided into a paper substrate, a polyester substrate and a celluloid substrate, and different substrates have different properties, so the following reference factors of the substrate should be noted when selecting the transfer paper.

1) Physical properties

● The thickness of the substrate should generally not exceed 20 μm;
● The substrate should have a high degree of smoothness to ensure the transfer rate of the ink;
● The substrate should have sufficient strength to ensure that it is not torn during transfer paper processing and printing.

2) Chemical properties

The uniform adhesion of the ink is two important manifestations of the chemical properties of the transfer paper substrate. The chemical properties of the transfer paper in production directly affect the quality of the print. If the transfer paper does not allow the ink to adhere well, or if the amount of ink is not well mastered in production, printing waste is caused. A good printing process and good prints must be based on a good grasp of the chemical properties of the transfer paper.

3) Good thermal performance

Since the transfer process is carried out by means of high temperature means, the material of the transfer paper must be able to withstand the influence of the transfer temperature and maintain the properties. In general, the thermal properties of the substrate of the thermal transfer paper are good and can be expressed by the following factors:
● The lower the heat resistance of the heat-resistant substrate, the thinner the thickness, the better the heat transfer, and the better the thermal properties;
● Smoothness The smoother the surface of the substrate, the lower the heat resistance, and the better the thermal performance;
●The heat-resistant thermal head temperature is generally around 300 °C.

4. Substrate

Experience has shown that the print quality of a substrate with a rough surface is better, which is a remarkable feature of thermal transfer. Because the rough surface of the substrate indicates that the substrate has a large surface energy, the ink on the transfer paper can be transferred to the substrate well, and the desired level and tone are obtained. However, too rough will affect the normal transfer of ink, which is not conducive to the realization of the printing process.

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What are the emerging types of processes derived from the traditional thermal transfer process?

Emerging types of processes derived from traditional thermal transfer processes.

1. In-mold decoration process (IMD)

The in-mold decoration process is a plastic decoration technology that uses a plastic molding (including injection molding, blow molding) temperature, pressure and a certain time to simultaneously attach a functional layer, a structural layer or a decorative layer in a mold. In-mold decoration is generally classified into in-mold labeling (IML), in-mold transfer film (IMR), and in-mold coating (IMC). The in-mold decoration process, especially the IML and IMR processes, has many advantages, which can effectively reduce the re-machining process and cycle of the product, solve the decorative problems of multi-faceted and profiled surfaces, improve the quality and grade of the product, and have a high degree of automation and efficiency. , environmentally friendly production and environmental performance use outstanding. The in-mold decoration process is mainly applied to the in-mold decoration of electronic products such as electronic products, room supplies, gifts, stationery, toys, handicrafts, etc.

2. Vacuum transfer process (TOM)

The vacuum transfer process is a technique in which a thermoplastic film is used as a carrier and a variable type of heat and external force is applied, and a profiled decoration is performed on a formed workpiece by heating, pressurizing, and a certain time. Vacuum transfer is also called stereo transfer process or high-pressure transfer process, and its biggest advantage is to solve the problem of positioning and decoration of large and small difference profile workpieces. The vacuum transfer process can realize the decoration of the transfer method or the decoration of the cover method. The process and application have just started in the country, which has been widely concerned, and the process of using the process characteristics to extend the process, the process market The potential is huge. The vacuum transfer process is mainly applied to shoes, boutiques, building materials, automotive interiors, electrical panels, and the like.

3. Sublimation (gas dyeing) process (Thermal Dye)

Sublimation is a decorative technique that uses a sublimation property of a disperse dye (ink) to transfer a disperse dye to a substrate under a condition of temperature, time and pressure through a substrate carrier. Early in the sublimation process, fabric transfer was very common. With the promotion of its application, the transfer decorative wood grain on various sprayed metal profiles began to rise in recent years and was favored by home decoration. The thermal sublimation (gas dyeing) process is mainly applied to metal surface transfer decoration after spraying, baking paint, electrophoresis and the like.

4. Water Transfer Printing Technique

There are two types of water transfer printing technology, one is watermark transfer technology, and the other is water drape transfer technology. The former mainly completes the transfer of the local text and the photo pattern of the workpiece, while the latter tends to be fully transferred on the entire product surface. Here we focus on the water-drawing transfer technology: using a polymer film that is easily dissolved in water to carry the image, due to the excellent tension of the water-coated film, the water pressure and the activator, the image on the film It is easy to wrap around the surface of the product to form a graphic layer, and can be combined with paint to form different texture effects such as matte and bright light. Draping transfer technology can cover color graphics (such as grain, wood grain, jadeite and marble) on any shape of the workpiece, while avoiding the common virtual position and avoiding damage in general workpiece printing. The surface of the product and its integrity solve the problem of three-dimensional product printing for customers. The water drape process is mainly used in automotive supplies, electronic products, room supplies, gifts, stationery, toys, handicrafts, indoor building materials, and the like.