The deployment and use of reversible thermochromic printing inks

The reversible thermochromic pigment is a novel coloring agent that can rapidly change color with changes in the ambient temperature so that the object to be colored has a dynamically changing color effect. At present, in the printing industry, color-changing pigments have been applied more and more widely. The use of color-changing pigments can be used to modulate various inks such as screen printing, gravure printing, offset printing, and pad printing. In particular, the use of screen printing and gravure color changing inks is more common.

Due to the special surface treatment process, the reversible thermochromic pigment produced by our company has good affinity and dispersibility in the oily carrier. Manual operation or use of simple mixing equipment can be easily formulated into a variety of printing inks.

Reversible thermochromic pigments have some special properties that differ from ordinary pigments, and must be used in order to obtain good results.

1. Basic properties of reversible thermochromic pigments:

Reversible thermochromic pigments are spherical particles with an average diameter of 3 to 8 microns (one micron equals one-thousandths of a millimeter). The inside is discolored and the surface is a transparent shell about 0.15 to 0.3 microns thick. This shell protects the internal discoloration from moisture, oxygen and other chemicals.

The discoloration temperature of the reversible thermochromic pigment is not a temperature point but a temperature range. In other words, it is the temperature range from the start of discoloration to the end of discoloration. The width of this temperature range is generally 3 - 5 °C, and some are even wider. Normally, the color temperature we define is the temperature at which the color change is completed. This should be especially noted. The pigment is a 7°C color change powder, that is, its temperature range is 5-9°C.

Tests have shown that the color-changing pigments produced by the company can be used for more than 1000 times without obvious deterioration, and can be used for 2 to 4 years under direct sunlight conditions.

Coloring pigments have a lower color strength than ordinary pigments, which is determined by their reversible discoloration properties. Therefore, the amount of color-changing pigments in the ink is generally required to reach 20 to 40% in order to obtain a satisfactory printing effect. In addition, the use of a three-roll mill, a sand mill, and certain low-boiling organic solvents can destroy the protective layer on the surface of the thermochromic pigment and cause it to lose its discoloration properties. Therefore, the formulation and use of color-changing inks must follow the following principles:

1.1 Cannot be ground with three-roller or sand mill after adding color pigment

Grinding destroys the protective layer on the surface of the pigment, causing it to lose its discoloration. Therefore, when formulating inks, components such as resin, solvent, and filler should be ground in advance to form a resin solution (dipping oil). Finally, a color-changing pigment is added. Because the color pigments produced by our company have been specially treated to have a lipophilic surface, uniform dispersion of single particles can be achieved in oily carriers (inks, paints, adhesives, etc.) with proper agitation, without the use of grinding equipment. Finally add the appropriate amount of normal color ink for color matching.

1.2 Select the appropriate solvent when adjusting the ink

The color-changing pigments are well tolerated for gasoline, kerosene, mineral oil, toluene, xylene, butyl acetate, cyclohexanone, ethyl cellosolve, turpentine, and plasticizers, and soaked for one month at room temperature. Basically it will not affect its discoloration properties. However, low-boiling solvents such as methanol, ethanol, acetone, propanol, isopropanol and butanol can affect the discoloration performance of the pigment within a few days and reduce its color concentration. Therefore, the following measures should be taken when dispensing and printing:

(A) Use as little or as little alcohol solvent as possible instead of using other solvents. For example, butyl acetate can be used instead of isopropanol, with cyclohexanone instead of butanol.

(B) In the case where the solvent must be adjusted with ethanol, propanol, etc., the ink should be used with the device to avoid storage.

Since the color pigment produced by our company can be easily dispersed in the resin solution, all the ink groups other than the color changing pigment can be well distributed, and a predetermined amount of color pigments can be added before printing, and the ink can be added to the ink fountain to start printing. It is also possible to dispense inks other than ethanol, acetone, propanol, isopropanol, and butanol (including color-changing pigments), and then add a predetermined amount of the above-mentioned solvent immediately before use, and start the printing evenly after stirring. Note that the amount of ink dispensed should not be too large. Do not store it as you use it.

1.3 Do not arbitrarily increase or decrease the amount of thermochromic pigment:

The color of the thermochromic pigment is related to the temperature, so the change of the ambient temperature directly affects the hue of the ink. This is more pronounced when using a 'hand-touch color pigment' with a discoloration temperature of about 30°C. Therefore, after the ink formulation is determined, do not adjust the amount of color-changing pigment by feel, otherwise it will cause the product color difference.

1.4 Do not add other materials to the company's already equipped ink, otherwise the printing effect will be affected. If you need to add thinner, you can only add toluene, xylene.

2. Reference formula for gravure printing ink with plastic film:

Thermochromic pigments 30 to 35%

Polyamide resin 15 to 30%

Solvent 35 to 50%

Other additives 0.5 to 2.0%

Ordinary ink (for color matching) 0 ~ moderate

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Total 100%

2.1 Gravure printing plate:

Thermochromic gravure is mainly used for logos and other block patterns. Because its coloring ability is lower than that of ordinary inks, thicker printing ink layers can achieve good results. Therefore, the depth of gravure nets should be larger, generally 40 to 50 microns is preferable, 150-170 lines, and the inclination is 45 degrees.

2.2 Gravure Printing Process:

The intaglio rotary printing press used for general plastic film printing can be used for color printing. There are no special requirements for printing equipment. In the case that the composite film needs to be printed on the reverse side, the color layer should be printed first, and other ink layers should be printed afterwards to prevent the color layer from being covered by other ink layers with strong hiding power.

2.3 Composite film:

Because of the high pigment content in the heat-sensitive color-changing ink and the low resin content, the gloss of the printed product is weak. Therefore, the thermal color-change prints are preferably covered with light or composite plastic films, which not only can protect the color-changing print layer, but also can improve the appearance and grade of the product. The color-changing composite film can be produced by a dry laminator without special requirements for the composite process and adhesive.