Main Factors Affecting Thermal Transfer Printing Ribbon Transfer Performance (I)

1 Introduction

Thermal transfer ribbon is a non-impact printing or thermal transfer printing method, which is a necessary consumption material, and its application field and development prospect are more and more extensive. In China, it has been widely used in commercial automation POS (Barcode Scanning Settlement System) terminal printing, label printing in fields such as post and telecommunications, bill printing in the financial sector, tax receipt printing, and ticket printing in the entertainment and transportation sectors. In particular, thermal transfer bar code printing methods using thermal transfer ribbons in the field printing of barcodes exhibit certain advantages and competitiveness [1, 2]. At present, domestic applications are thermal transfer ribbon products produced by foreign companies, which to a certain extent limits the application of thermal transfer technology in China. Therefore, it is imperative to develop our own thermal transfer ribbon products.

The thermal transfer ribbon is mainly composed of a tape base and a hot melt transfer ink layer, and the hot melt transfer ink layer is basically composed of a colorant, a resin or a rubber, a wax, a filler and other additives. Thermal transfer performance is one of the most important properties of thermal transfer ribbons. There are many influencing factors, such as thermal transfer printers, environmental factors, ribbon composition, and printing materials. This article focuses on the effects of ribbon composition and substrate materials on heat transfer performance.

2 experimental part

2.1 Sample preparation

The ball-coating method was used to uniformly disperse the coating solution of the ink layer so that the particle diameter of each component was ≤ 1 μm. The coating solution was applied to a pretreated base and dried to obtain a thermal transfer ribbon sample.

2.2 Measurement of Heat Transfer Rate

Install the thermal transfer ribbon on a PRODIGY MAX label printer and print 10 x 10 dots in a 1cm2 area. Count the number of points the print sample can recognize. The heat transfer rate is calculated using the following equation. The results are taken as the average of three measurements.

2.3 Thickness Measurement

Measured with Optical Thickness Gauge (Guilin Optical Instrument Factory).

2.4 Measurement of Heat Capacity of Ink Layer

Differential scanning calorimeter measurements. Heating rate 10°C/min, temperature range 45-120°C, N2 atmosphere.

2.5 Determination of the number of roll resistance

The upper end of the ribbon sample is bonded and wrapped around a smooth glass rod with a diameter of 5 mm, and the lower end is bonded to another glass rod, so that the weight of the lower glass rod flattens the ribbon sample. Rotate the upper glass rod clockwise and counterclockwise so that the ribbon is repeatedly wound on the glass rod and released. Observe the ribbon out condition every ten times. Record the number of curls appearing out of ink and take the average of the three data as experimental results.

3 Results and calculations

3.1 EVA Resins Five EVA resins, namely EVA5/2, EVA5/0.3, EVA14/0.7, EVA14/0.2, and EVA28/150, were selected and tested. The results are shown in Table 1.

Table 1 Effect of Different Brand EVA Resins

From the results in Table 1, it can be seen that the melt flow rate MFI is large and the heat transfer rate is also large. This is because the MFI is large and the resin flows easily, so it is easy to transfer. When the VA content is large, the heat transfer rate is also large. This is due to the fact that the VA content is large, the crystallinity of the molecular chain is decreased, and the flexibility is increased, which increases the resin's ability to accommodate fillers (such as wax and carbon black). At the same time, we found through experimentation that EVA28/150 with a higher VA content has better compatibility in molten wax. Obviously, when the ink layer is melted, the resin with a higher content of wax and VA tends to form a uniform melt, and thus is easy to be Transfer, heat transfer rate is greater. Therefore, we use EVA resin with relatively large melt flow rate and VA content as one of the main components of the ink layer.

3.2 Resin dosage

Change the amount of resin (set the amount of A%), the other components unchanged, the experimental results are shown in Table 2.
Table 2 Effect of resin dosage on heat transfer rate and roll resistance

From Table 2, it can be seen that as the amount of resin increases, the resistance of the ink layer is gradually increased, ie, the resin enhances the adhesion of the ink layer to the polyester tape base. However, as the amount of resin increases, the thermal transfer rate of the ink layer decreases accordingly. For the thermal transfer ribbon, it must be guaranteed to have more heat transfer rate, so that it can withstand more curling times. According to the experiment, we chose about 2% of resin.