How to control the sensitivity of color sensitive synthetic paper color developer?

Controlling the sensitivity of color sensitive synthetic paper colorants is a complex process involving multiple factors. Here are some key control methods:

1、 Choose the appropriate color developer

Dye type:

Early thermal paper often used CVL (crystal violet lactone) as a colorant, but the color reaction of CVL is reversible and prone to fading.

With the development of technology, fluoranthene dyes have gradually replaced CVL. Fluorine black dye can form black when combined with other colorless dyes, but its color stability is poor.

At present, some special near-infrared dyes are also used in thermal sensitive products for special labels, which are usually used together with ordinary firefly black to improve sensitivity.

Substituting groups:

The substituent groups of firefly black dye have a significant impact on its color sensitivity and stability. Generally speaking, the substituent group is small, and the color sensitivity is high but the stability is poor; The substituent group is relatively large, with poor reaction sensitivity but good stability.

Therefore, the sensitivity of the color developer can be changed by adjusting the substituent groups.

2、 Optimize coating formula

Dispersion ratio:

Coatings are typically composed of two types of dispersions: one containing colorless dyes, adhesives, and additives (referred to as dispersion A), and the other containing colorants, adhesives, fillers, and other additives (referred to as dispersion B).

The optimal combination of coating formula should be determined based on the interaction between colorless dyes and color developing agents to achieve the desired sensitivity.

PH control:

The pH value of the coating has a significant impact on the color reaction. Generally speaking, coatings should be controlled within a slightly alkaline range (such as pH 8.0~8.5) to avoid premature color development under acidic conditions.

Solid content and fluidity:

The solid content and flowability of coatings can also affect color sensitivity. If equipment and process requirements permit, increasing the solid content as much as possible can increase the reaction rate of reactants. At the same time, the coating should have a certain degree of fluidity for easy application and uniform dispersion.

3、 Improve production process

Grinding process:

Grinding is one of the key steps in the coating preparation process. Grinding can reduce particle diameter and increase specific surface area, thereby improving reaction rate and color sensitivity.

During the grinding process, it is necessary to choose the appropriate diameter and quantity of abrasive particles, as well as the appropriate grinding time and speed.

Coating technology:

The use of advanced coating technology can ensure that the coating is evenly distributed on the surface of the paper, thereby improving the color rendering effect. Common coating methods include roller coating, air knife coating, and scraper coating.

Drying conditions:

During the drying process, it is necessary to control the temperature curve and humidity conditions to ensure that the coating does not undergo color reactions or fading during the drying process.

4、 Quality control and testing

Raw material testing:

Strictly inspect the quality of raw materials to ensure they meet production requirements. Especially, the purity, stability, and reactivity of colorants and colorless dyes need to be carefully tested.

Production process monitoring:

Real time monitoring and recording of each process in the production process to ensure the stability and controllability of the production process.

Finished product testing:

Conduct testing on finished products in terms of color sensitivity, color stability, weather resistance, etc., to ensure that the products meet relevant standards and customer requirements.

In summary, controlling the sensitivity of color sensitive synthetic paper colorants requires starting from multiple aspects such as selecting appropriate colorants, optimizing coating formulations, improving production processes, and quality control and testing. By comprehensively considering these factors and taking corresponding measures, the color sensitivity and product quality of colored thermosensitive synthetic paper can be effectively improved.