Selection of steel screen printing ink in different environments (1)

Selection of steel screen printing ink in different environments (1)

Xin Qiaojuan

At present, domestic barrel-making enterprises have adopted more and more screen printing processes. However, in terms of printing, barrel-making enterprises should be said to be laymen, so quality problems, process problems, efficiency problems, etc. often occur in actual production. Especially in the winter, the ambient temperature is low. Many steel drum manufacturers in the north will have some quality problems when they screen-print the surface of the steel drum, such as slow drying speed and poor adhesion. Brushing, cracking and scenting. These phenomena directly affect the sales of steel drums and the economic benefits of enterprises. At the same time, it has caused many adverse effects to enterprises. So what are the causes and influencing factors of these phenomena? How should we prevent it in production? To answer these questions, you first need to understand the structure and properties of the steel screen printing ink to understand how to choose. Therefore, we first discuss the performance of the screen printing ink from steel drums.

First, the performance of steel drum screen printing ink

In order to make the ink of screen printing of steel drums have good performance and quality, regardless of the type of ink used by steel drum manufacturers in screen printing, the inks must satisfy the conditions that the color is not easy to wipe off or peel off. Requirements. The main properties of the ink during screen printing of steel drums are represented by the following parameters. Such as viscosity, thixotropy, fluidity, plasticity, viscoelasticity, dryness, hardness, light resistance, chemical resistance, adhesion strength.

1, the viscosity of the ink

Viscosity is the resistance produced by a layer of fluid moving relative to another fluid, ie the internal resistance of the fluid as it flows. The viscosity of the ink is generally expressed in terms of poise and centipoise. The viscosity of the screen printing ink is between 4 and 12 Pa·s. The viscosity of the ink is closely related to printing. The faster the printing speed, the lower the viscosity of the printing ink is required; according to the actual production experience, in the winter, when the steel drum is screen printed outdoors, the viscosity of the printing ink should be correspondingly lower; the viscosity index of the ink can be used for viscosity. Take measurements. Excessive viscosity The ink has poor wettability to the steel drum, and the ink is not easily transferred to the steel drum through the screen. Difficult to print, the printed graphics are lack of ink; when the viscosity is too small, the printing will cause the imprint to expand, causing the printed graphic lines to coincide, resulting in waste.

There are several factors that affect the viscosity of the screen printing ink in the drum:

1 At present, most of the screen printing inks of steel drums are monochromatic. For such inks using the same pigment, the viscosity of the binder is larger, and the viscosity of the ink produced is also large.

2 For the same binder, if the amount of pigment and filler is more, the viscosity of the ink is greater;

3 For the same binder, if the pigment and the filler are used in the same amount in the two inks, the larger the particles of the pigment and the filler, the smaller the viscosity of the ink produced, and the smaller the particle, the greater the viscosity;

4 The better the pigment and filler are dispersed in the same ink binder, the smaller the viscosity of the ink, and conversely, the viscosity of the ink is large.

2. Thixotropy of the ink

Thixotropy refers to the ability of a liquid to return to its original viscosity due to a decrease in stress viscosity. In the screen printing process, it is a reversible phenomenon in which the ink becomes thick after a certain period of inactivity, the viscosity becomes large, becomes thinner after stirring, and the viscosity also becomes small. Because the shape of the pigment particles in the ink is irregular, although it adsorbs a layer of binder, it is an irregular sphere. Therefore, after a certain period of rest, the pigment particles will contact or be close to each other, causing mutual attraction, hindering the free movement of the particles, and the ink becomes thick and sticky. However, this temporarily stable structure is quickly destroyed by the external force, and the mutual attraction between the particles is released, the free movement of the particles is restored, the fluidity is improved, the ink is thinned, and the viscosity is lowered.

The thixotropy of the drum screen printing ink should be as small as possible. In order to eliminate this unfavorable factor, the ink is sufficiently stirred to return to the normal state before printing, and then printed. The more irregular the pigment particles in the ink, the greater the thixotropy, and conversely, the thixotropy is small. For example, black ink, thixotropy is large; while white ink and yellow ink have small thixotropy. In addition, there are many binders in the ink, less pigment, and small thixotropy. On the contrary, the thixotropy is large.

3, the fluidity of the ink

The fluidity of the drum screen printing ink is the reciprocal of the viscosity. That is, the viscosity is large, the fluidity is small, the viscosity is small, and the fluidity is large.

The fluidity of the screen printing ink of the steel drum can be regarded as the degree of natural flow of a certain amount of ink in a certain period of time and a certain flat surface without external force. The fluidity of the ink can be measured as the thickness of the ink. In steel drum screen printing inks, the fluidity is generally controlled at 30 to 50 mm. The measurement method is to take one milliliter of ink, and the diameter of 50 grams can be measured after 15 minutes.

Practice has proved that when the steel drum is screen-printed, the greater the fluidity of the ink, the greater the degree of diffusion of the ink after printing, and the thin line stripes with small gaps are unclear and merged; the ink has a small fluidity and is printed. There are broken lines and lack of ink in the ink of the graphic, and printing is also difficult.

4, the plasticity of the ink

Plasticity refers to the property of being able to completely or partially retain its deformation after being deformed by an external force. Screen printing inks are both fluid and malleable. High in pigment and other solids, the ink is thick and plastic, and the pigment and other solids are low, the ink is thin, and the plasticity is small. Screen printing inks require a certain degree of plasticity to maintain the accuracy of printing.

5, the viscoelasticity of the ink

The viscoelasticity of the screen printing ink of the steel drum refers to the performance that the ink is sheared and broken after being pressed by the squeegee pressure, and the screen plate bounces and the ink rebounds rapidly. The ink is bonded to the steel drum and detached from the wire mesh, which is rapidly retracted, which is a typical ink viscoelastic phenomenon.

The viscoelasticity of the ink, which has a great influence on the screen printing, is the phenomenon of drawing. The drawing phenomenon is that when the squeegee is scraped, the screen plate springs up, and a lot of ink filaments appear between the screen and the steel drum. This is the most taboo phenomenon in the screen printing of steel drums. It not only makes the steel drums and screens dirty, but even makes the screen printing of steel drums impossible.

The length of the draw is related to the viscosity of the ink. The viscosity is large and the ink is long; otherwise, it is short. For this reason, a viscosity reducing agent or a molecular weight of the resin is often added to reduce the viscosity of the ink, improve the viscoelasticity of the ink, and reduce the drawing phenomenon.

The drawing phenomenon is also related to the time of the force. The same ink, if the separation speed is elastically split, the ink is short; the separation speed is very slow, and the ink completely flows down like a pure liquid, and does not form a filament.

6, the drying of the ink

Screen printing of steel drums requires that the ink can not dry the conjunctiva on the screen plate for a long time, and it is required to dry on the steel drum as soon as possible after printing. This keeps the printed image clear and clean, not only the quality of the steel drum can be guaranteed, but also meets the requirements of timely delivery.

7, the hardness of the ink

The hardness of the steel screen printing ink coating refers to the degree of deformation of the ink film, which can be divided into penetration hardness and scratch resistance. From the practical application of the steel drum, using the scratch resistance measure, such as using the same force, the ink film with sufficient hardness is used to score the fully dried ink film, and the H value of the pencil capable of breaking the ink film is the hardness of the measured ink. . The hardness of the ink in the barrel printing is an important parameter for the screen printing of the steel drum.

8, the light resistance of the ink

The light resistance of the screen printing ink of the drum is the intensity of the ink against light. Ink fading is caused by the absorption of light energy by the pigment molecules. The light resistance of the ink mainly depends on the light resistance of the pigment or dye. The light resistance of the printed image on the surface of the steel drum depends on the light resistance of the pigment, the material of the steel drum, the thickness of the ink layer, the thickness of the binder and the ink.

9, the chemical resistance of the ink

The ability of steel drum screen printing inks to resist water, acids, alkalis and solvents is collectively referred to as chemical resistance. The measurement standards and methods are currently commonly used in the soaking method and the wet rubbing method. The immersion method is to immerse the dried steel drum in the selected water, acid, alkali and solvent, and take it out after a certain period of time to compare the degree of change before and after the printing of the steel drum; the wet rubbing method is cloth. After soaking with the selected solution, the wet rub was rubbed back and forth on the dried steel drum several times, and then the difference before and after the wet printing of the steel drum was compared.