Drying rate

Quality Control and Testing. Control of inks is done by examining their color strength, hue, tack, rheology, drying rate, stabiHty, and product resistance. Elaborate control equipment and laboratory testing procedures are employed to test the finished inks. Weather-Ometers,... 

Flexo and gravure inks are both known as Hquid inks because of their low viscosity. The inks for both systems have basic components in common with inks for other printing processes. Vehicles disperse and carry the pigment, and also contribute most to the end use properties. Colorants provide color. Solvents dissolve resins in the vehicle and determine drying rate. Additives modify ink properties to overcome deficiencies. 

Another aspect to consider in the design of closed-drying systems is the drydown time. The drydown time is the period requited for the system to dry down from its initial water concentration (or partial pressure) to a concentration that approaches equihbrium with the desiccant. During this time, the system is not fljlly protected from the negative effects of the moisture that the desiccant is designed to remove. In such a system, the instantaneous drying rate is proportional to the water content at any time (18). 

The drying rate is represented by differential equation (eq. 6) where h is mass transfer coefficient 1/(hcm ) , specific surface area of desiccant beads, cm /g mass of desiccant, g C, concentration by weight of water in the fluid being dried (7, concentration of water at the surface of the desiccant, ie, concentration of water in the fluid that would be in equihbrium with the instantaneous loading on the desiccant, wt-ppm and t — time, h. 

For materials that foUow equation 30 the drying rate is inversely proportional to material thickness falling rate drying time is estimated,... 

Fig. 8. Drying time and rate profiles for leather pasted on glass plates and dried in two temperature stages. Gas velocity = 5 m/s in parallel flow, 71°C in the first stage, 57°C in the second. The falling rate, drying rate is proportional to residual moisture content.

The products of these reactions with maleic anhydride, termed maleated oils, react with polyols to give moderate mol wt derivatives that dry faster than the unmodified oils. For example, maleated, esterified soybean oil is a drying oil with a drying rate comparable to that of a bodied linseed oil with a similar viscosity. Maleated linseed oil can be converted to a water-dilutable form by hydrolysis with aqueous ammonium hydroxide to convert the anhydride groups to ammonium salts of the diacid. Such products have not found significant commercial use, but similar reactions with alkyds and epoxy esters are used on a large scale to make water-dilutable derivatives. 

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