As the outstanding representatives of Chinese offset ink manufacturers, Kingswood has the most advanced offset ink factory, which uses Buhler (Buhler) automatic production control system, in which the materials and semi-finished products through a closed pipe transportation. and it is the largest automatic offset printing ink manufacturer in Asia.
Now we will tell you how we produce inks here.
1. Ink manufacturing
Although the formulation of inks, based on the fundamental notions of the physics and chemistry of mixtures, remains an activity that is perpetually evolving and a source of constant innovation, the basic principles of ink manufacturing are now well established.
The same manufacturing principles apply to the different types of inks (conventional offset inks, UV inks, flexo / gravure inks), involving five essential steps that determine the final properties and performance of the inks. It is therefore useful to be familiar with the main manufacturing parameters and to understand the key steps.
A schematic diagram of the ink manufacturing process is given below :
2. Varnish manufacturing
The manufacturing of the varnish is the first step in the ink manufacturing cycle, involving the incorporation of the raw materials selected to provide the intrinsic characteristics of the ink. In fact, the varnish constitutes the body of the ink : the “structural” properties of the ink depend on the quality and the properties of the resins, diluents and oils (in the case of offset inks) or solvents (in the case of liquid inks) used in the composition of the varnish.
In the case of conventional offset inks, the manufacturing of the varnish consists in dissolving then cooking one or several hard resins in petroleum diluents and/or vegetable oils. This step, frequently automated, is generally carried out in an inerted reactor equipped with stirring and heating systems. The solubilisation and chemical recombinations, vital to obtain the final properties of the varnish, require cycles to be carried out at perfectly controlled rates and temperatures.
In the case of UV inks, the varnish is manufactured by physically mixing the basic constituents of the ink, without any heating. The chemical synthesis of the UV reagents themselves is outsourced.
The varnishes used in liquid inks are formed by cold dissolution of film forming resins in solvents, using appropriate dispersers.
3. Premix
The premix stage involves pre-dispersion of the pigment (organic or mineral) in a mixture of varnishes. In fact, several varnishes with different properties are used in a single ink and it is through their judicious combination that series of inks with completely different properties are obtained. Certain varnishes have very specific properties, while others may be used in the composition of several references.
The pigment, supplied in the form of powder, is in fact composed of a multitude of aggregates of elementary particles. The premix stage aims to divide these aggregates as finely as possible by coating the fine particles with the varnish (the binder of the ink). This “wetting" step allows the air surrounding the particles to be progressively replaced by binder and therefore to disperse the pigment in an optimal manner. Certain properties of the ink such as the color strength and the gloss depend on the quality of this coating / wetting step.
As a function of the type of ink to be manufactured, the dispersion is carried out either with a “disc” type mixer, of variable shape, or with a “butterfly” type mixer. The geometry of the agitator depends on the ink formula, but the principle remains the same : it involves creating sufficient shear at the heart of the dispersion to assure the break up of the aggregates and the coating of the pigment. The speed of agitation (obtaining a vortex), the temperature (rise in temperature due to the shear) and the rate and order of incorporation of the pigments and fillers are parameters that affect the pre-dispersion.
4. Grinding
Grinding is the step that makes it possible to refine the dispersion of pigment initiated at the premix stage, when the size of the aggregates is reduced. In fact, the pigment elements coated with binder obtained at the premix step can be dispersed even more finely using various types of mills. This step is essential to develop the colour strength of the pigment, because the more finely dispersed the pigment, the more intense the colour and the higher the gloss.
Different types of Grinding processes and equipments can be used. The most widely used arethree roll mills and bead mills.
Three roll mill :
This type of milling is used to manufacture what are known as “paste” inks (conventional
offset and UV inks). As its name suggests, the mill comprises three cylinders through which the ink circulates. Normally, the ink is passed through the mill three different times. Certain more difficult to mill pigments may need to be passed through the mill an additional time. The three passes follow on from each other with increasing pressure between the cylinders that perform the milling : the first milling stage, which fines down the premixed ink, the second milling stage, which breaks up any remaining agglomerates and the final milling stage, which completes the dispersion.
Bead mill :
All types of inks (conventional offset, UV and liquid) can be milled by this procedure, with only the configurations of the mills differing. In this case, the milling is assured by the balls (of variable diameter and made out of various materials) within the mill being brought into movement within a cylinder (stator) via the rotation of an axle (rotor). The stator and rotor are fitted with “fingers”, which are cooled to avoid too much overheating. The ink circulates inside the milling chamber and the agglomerates are broken up under the impact of the balls. The quality of the milling is optimised by adjusting the temperature and flow rate of the ink.
In the case of “paste” inks, one passage is generally sufficient. It may, if necessary, be followed by a passage through a three roll mill (this cools down the heated ink and removes any air bubbles). Liquid inks sometimes need to be recirculated several times.
The finesse of the milling is a key factor that has to be controlled on each batch. This control is carried out using a North gauge, which determines the particle size of the milled ink.
5. Dilution
The structural and colorimetric properties of the ink are obtained after milling. Dilution enables different additives indispensable to obtaining a high quality finished product to be incorporated. This is the step where the viscosity of the product is adjusted through the addition of thinner or solvent (depending on the type of ink manufactured). The different additions are made under slow agitation in order to correctly homogenise the ingredients and to avoid destroying the pigment / binder cohesion.
The principal manufacturing controls can be carried out on the product at this stage to ensure it meets the final specifications :
• Viscosity : This involves a physical measurement of the fluidity of the ink (which is always defined at a given temperature).
The viscometer enables the rheological characteristics of the ink, such as the flow threshold or the structure, to be determined.
• Tack : The measurement enables the ability of the film to split into two to be quantified. The tack is measured using a temperature controlled tack-o-scope device : this measures the force required to split the ink film.
• Flow : The ink is deposited on a ther- mostatically controlled plate set at a fixed angle. The distance covered by the ink after a given time enables the fluidity of the ink to be
characterised.
• Colorimetry : Colorimetric controls are carried out on each manufactured batch of ink to ensure it complies with the standards. The control may be carried out either visually, under controlled lighting, or by spectrocolorimetric measurement.
Other tests may be necessary, depending on the types of inks or the customers’ specifications.
6. Packaging
Once the controls have been completed to ensure the ink complies with the specifications, it may be released for packaging.
