Screen printing ink 1000 ask (123- 136)

123. Why does the gelation occur?

A: The gelation, thickening, and agglomeration of the ink system are generally caused by the following factors. Because the basic pigments react with the binders with higher acid values ​​or containing free fatty acids, the soaps are formed; The ink system absorbs water; the pigment content in the ink system is too high; the used binder is not proper; the resin and oil in the binder are poorly miscible; in the macromolecular polymer system, the pigment absorbs the acidic substance to promote the gelation of the ink and the like.

124. What are the commonly used anti-gelatinizers?

A: Due to the thickened ink or the gelation formed due to the high degree of polymerization of the binder, appropriate dilute and soluble substances such as aliphatic hydrocarbons, esters and ketones can be added; Pine acid (rosin or rosin acid dissolved in linseed oil), linseed fatty acid, maleic acid or high acid maleic anhydride resin (in linseed oil) and other high acid value materials to dissolve .

125. What is anti-dirty agent? What are the commonly used anti-dirty agents?

A: Anti-dirty agents are also called anti-dirty auxiliaries. This is to prevent the ink on the previous print from sticking to the back of the other print when printing, and it can also prevent the print from sticking when stacking. Commonly used anti-dirty agents are solid type (powder, granules) and liquid type. When used, most of them are spray method, spray method is divided into powder spray and spray.

126. What is Newtonian fluid? Is ink a Newtonian fluid?

A: Newtonian fluid is a fluid that can flow under any small external force, and the velocity gradient (D) of the flow is proportional to the magnitude of the applied shear stress (τ). This fluid is called Newtonian fluid. The rheological equation of Newtonian fluid is: τ = ηD

Where: Ï„ - the added shear stress;

D--flow velocity gradient;

Η--a constant that does not depend on the shear rate, called the viscosity coefficient, is simply called the viscosity.

Most printing inks belong to Newtonian fluids.

127. What is viscosity?

A: Viscosity is the degree to which a fluid resists flow and is a measure of the ability of fluid molecules to absorb each other and hinder relative motion between molecules, ie, the internal resistance to fluid flow. Under the action of external forces, the material is displaced and friction occurs between molecules. The resistance to friction is called absolute viscosity. For short, the international system of viscosities and viscosities is Pascal seconds (Pa·s); The unit is Park (P).

128. ink viscosity unit how to convert?

Answer: In centigrams of seconds

1P (poise) = 100cp (centipoise) = 1000mp (millipoor)

International System of Units

1 Pa·s (Pascal seconds) = 1000 mPa·s (milli Pascals)

The conversion relationship between centimeters and international system of units is:

1Pa·s=10p; 1mPa·s=1cp

129. What is plastic fluid? What is the yield value?

A: When a fluid does not flow immediately when it is subjected to an external force, it must wait until the applied external force is large enough to start flowing. This fluid is called a plastic fluid and its flow pattern is called plastic flow. The minimum shear stress required before the fluid flow occurs is called the yield value and the unit is N/cm2.

130. What are the yield values ​​of commonly used printing inks?

A: The yield value of the sheetfed offset ink is 0.02 to 0.2N/cm2; the yield value of the flexographic ink is 0 to 0.0002N/cm2; the yield value of the plastic intaglio ink is 0 to 0.0002N/cm2; the screen printing ink The yield value is 0.001 to 0.005 N/cm2.

131. What is the thixotropy of ink?

A: The fluid will become thinner when it is agitated, but it will return to its original thick state after a certain period of time. This phenomenon is called fluid thixotropy. The inks belonging to plastic fluids all have thixotropy. It is generally believed that the thixotropy of ink is mainly caused by the flocculation of the pigment in the ink, while the flocculation of the pigment in the binder is often reversible.

132. What are the measurable indicators related to printing ink and ink?

A: The measurable indexes related to inkiness include viscosity, yield value, viscosity, fluidity, slope, intercept, and thixotropic index. The ink index of the offset ink commonly used for paper screen printing is shown in Table 1 and Table 2.

133. How to test the flow of ink by experience?

A: Take a small amount of ink on a glass plate, and use a small ink knife to move about 10 times. Put the ink together to observe the leveling of the ink, that is, determine the level of the contact angle after the leveling speed and leveling. . Faster ink flow with lower contact angle is better, and vice versa. However, there are differences in the type of ink and fluidity, and they cannot be generalized.

134. How to test the ink's body bone empirically?

Answer: After checking the ink flowability, use a small ink knife to scrape the ink from the bottom and reposition it on the glass plate. When it is put down, use the small ink knife's head to gently pull it up on the ink surface and pull up about 1cm or so. Repeat the motion of one press and pull to check the body of the ink. During the inspection, the thin ink is distinguished by observing whether the ink is easy to flow when the ink is returned to the glass plate by using a small ink knife; whether or not it is difficult to distinguish the softness and hardness of the ink with a small ink knife; whether it is laborious to pull up with a small ink knife. The ink is loosened when the ink is pulled up; the elasticity of the ink is distinguished by the size of the force applied by the small ink knife and the sense that the ink is not automatically retracted when the ink is pulled up. Repeatedly using the above method for many times, and careful observation and feeling, some of the general indicators of the ink can be roughly tested.

135. How to test the length of the ink using empirical methods?

A: Take a small amount of ink on the glass, use the head of the small ink knife to lightly press the ink and pull up. Observe the situation when the ink is flowing down. If the ink thread flows to the end, it will continue to be a continuous thread, indicating that the ink The filament length is longer; if the ink flows down, the disconnection is faster and the final filament is intermittent, indicating that the ink tip is shorter. The retraction of filaments often occurs when the ink head is disconnected, and the shrinkage of the filaments of the short ink head is smaller than the length of the ink.

136. How to test the viscosity and spreadability of ink by empirical methods?

A: Use a finger (usually ring finger) to take a small amount of ink and repeatedly print on the coated paper at a faster rate to make the print thin and uniform. Use the size of the finger when printing to identify the viscosity of the ink; use printing. When the ink layer is very thin, the print is completely clear to determine the printability of the ink.