The silk printing ink should meet the requirements of reserves, printing, durability, economic and security, but in terms of technical performance, it is mainly printed and applied.

First, printing

Printing is also called the operation characteristics, in general, the ink should be able to smoothly print from the printing plate in printing, not blocking the net on the screen, drying fast on the printing property, and the blot reproducibility is good.

The influencing factors of printing admissions are complicated, with about 60 variables, talk about several major performance.

Viscosity? Is a characteristic that hinders its relative flow inside the ink. The viscosity unit is Pascose (Pa · s). The viscosity of the silk printing ink, in various inks, high levels (see Table 4-4). The viscosity has a great impact on the printing effect. Excessive viscosity, it will cause difficulty in the metastasis of ink, blotting integrity, and the faster and gloss will be deteriorated, and even cause the brushed, network section to lack in ink and blocking network; the viscosity is too small, which will make the blot, clearness Poor, easy-to-dirt printing and printing.

Ink viscosity comparison table

Ink type viscosity (Pa · S)

Running printing ink 10-100

Aniline ink 0.1-0.2

Gravure ink 0.05-0.20

Silk printing ink 1-100

Offset ink 100

Usually, the preparation of the ink is greater than 4pa · s, and the viscosity, the number of viscosity, the graphic size, the printing speed, the printing surface performance and the printing temperature are properly adjusted, allowed to change within the range of 1-100 Pa · S.

Some silk screen inks, in the printing process, their viscosity may change, such as the volatilization of the solvent, so that the ink is thickened, and the viscosity is also large. Some ink viscosity is different from the shear speed, which is three cases, as shown in Figure 4-2, where the curve A represents a Newtonian fluid, such as a low viscosity (less than 10 Pa · s), and liquid ink, viscosity is one Constant, not affected by shear speed; curve B pseudo-plastic fluid, the viscosity decreases with the shear speed, also known as shear-reducing fluid, such as cellulose solution, emulsion and most wire ink. Such ink is good, that is, the viscosity increases with the increase in shear speed, also known as the shear and thickening fluid, some high solids (pigment and filler) inks, easy to produce shear expansion. Some ink viscosity, decrease with the increase in shear speed or shear time or both, and after shearing is stopped, the viscosity can be recovered (Fig. 4-3), called this phenomenon is thixotropic.

The relationship between viscosity changes and printing is that the ink is in the plate, the viscosity is more embossed, but the viscosity is getting better and better after transferring to the print. Threeway is unfavorable to the former, which is advantageous for the latter, so appropriate thixotropism is desirable, while shearing is harmful to printing.

The viscosity of the viscosity, the solvent, the diluent or plasticizer can reduce viscosity, filled fillers, pigments, silicides, and viscous transparent groups, which can improve viscosity.

Yield value? The minimum shear stress required to start the ink is called yield value. The yield value is too large, the ink is hard, it is not easy to open, inconvenient in ink, and the difference in grainability; the yield value is too small, the printing thin line or the dot reproductionability is poor. The silk printing layer is thicker, and the yneasted value cannot be too small, usually between 10-2-10-3n / cm2. When the printing fine line is printed, the yield value is preferably high.

Liquidity? In flat, convex brush, the concept of common flow rates will describe the degree of flow showing the ink, which is in the case of parallel plate pressurization, and measures a certain amount of ink in the predetermined time, as a flow Numerical value. For silk screen, it is more convenient to use liquidity. The fluidity is the result of the viscosity, yield value, and the integrated reaction of the ink, indicating the flow properties of the ink itself under absence of external force. The wire printing ink is too fluidity, and the metastasis of the ink is difficult to control, and it will appear as a self-leak (refer to the ink on the green version, not pressing the pressure, it will be able to drain itself), paste (refers to the printing of the ink on the web version Face - back), and the tanker (Figure 4-4B) along the blaming direction. The liquidity is too small, the thin line print is difficult, the blot is poor, and even the network is lacking (Fig. 4-4A). Appropriate fluidity should be that the ink does not drip on the screen, and the blot surface should not be revealed.

The mobility experience judgment method is to use the ink knife to pick the ink, and then it will be down from itself, pull into a ink, and if the ink is long, the fluidity is good, and then it is poor.

Surface tension? The surface tension of the ink is related to the metastasis properties of the ink and the stability of the blot on the receiving surface. This relationship is more prominent when printing on the surface material, in particular plastic surfaces. For example, when the surface tension of the ink is greater than the surface tension of the receiving surface, the blot will shrink, even a small hole of the fish eye, and when the printing and the surface tension of the ink, the printing occurs. These conditions can be adjusted by adding a surfactant, a microcrystalline stone, silicide, or the like, so that the surface tension of the ink is equal to or smaller than the surface tension of the receiving surface to obtain a good printing effect. ?

Fineness? The ink fineness refers to the degree of dispersion of solid powder such as pigment and filler in the lifting. The fineness of the ink is different from the fineness of the solid powder, and the latter refers to the basic particle size of the powder, which is small, see Table 4-5. The basic particle size of the general pigment is less than 1 μm, in fact, the pigment is added to the aggregate state (size of 50 μm) together with a number of substantially particles, and is added to the ink, and the aggregate is dispersed. , The smaller ink particles (fineness). Generally, the fineness of the ink is about 5 μm, which is 1-2 μm in detail. The fineness will affect the gloss and the rheology of ink.

Several type of pigment particle size table

Pigment Name Particle Size (μm)

General pigment \\u003c1.0

Titanium dioxide 0.25

Carbon black 0.01-0.1

Fluorescent pigment thickness: 0.1-2.0

Gold, silver powder diameter: 1-200

Color Foil Pigment\\u003e 200

From the yield of silk screen, the fineness should be compatible with the aperture of the plate wire, that is, the ink particle size ≤

From the yield of silk screen, the fineness should be compatible with the aperture of the plate wire, that is, the ink particle diameter ≤ 1/3 wire diameter.

Dryness refers to the drying speed of the ink. It has two requirements: the ink drying in the printing plate is slower, and the more soaked and better in the printing surface. The dry version is dry and fast, which will affect the uniformity of ink viscosity, rheology and blot, even cause blockage, also known as junction, and the ink begins not less than 5 minutes. The print is slow, then the impact Production speed or increase dry cost.

It should be said that slowly and imprinting inks on the Internet are ideal for drying properties, light solid, thermosetting and thermal printing, etc., is therefore produced.

Natural adhesiveness refers to a mechanical properties of the substance and the adhesive (plasticity) of the substance and the viscous (plasticity) of the liquid under external force. Almost all of the high polymers have viscoelasticity, and most of them have this performance. The viscoelasticity of the ink, the smoothness of the drawing and the smooth surface of the imprinted surface is dense.

Differences in material viscoelasticity can be described as a loophore. Briefly, when the external force is less than a certain time, the material exhibits elasticity. When the external force is greater than this time, the material will flow, this time is called the relaxation time τ. The relationship between τ and material properties is:

When τ → ∞, the object is a complete solid, only flexible;

When τ → 0, the object is liquid, only viscous;

When \\u003cτ \\u003c∞, the object is touched.

The size of the τ value reflects the size of the combination of the object of the object. Therefore, the τ value of the linear structure is small; and the mean value of the mesh structure or the cross-linking point is large.

Surprise time has a function of adjusting the printing speed, especially the separation speed between the printing plate and the printing surface, such as the separation speed should not be less than τ, otherwise the ink transfer is elastic, the transfer rate is low. There is no viscous ink, it is difficult to transfer during printing; there is no flexible ink, or the brushed wire is severe, or the rheological failure is not possible.

The viscoelasticity provides appropriate elasticity, making the splitting ink, rebound quickly, ensuring a good blot effect.