Optimization of Dispersion

Processes for Liquid Inks
By
Gisbert Schall & Edward Casama

Printing inks are used to convey a message or to decorate. Because of the special requirements, such as visual appearance, printing process, drying systems and other conditions, different types of printing ink systems and formulations have been developed.

The intent of this paper is to deal with optimization of dispersion processes for liquid ink systems, namely Flexographic and Gravure inks.

The main components of liquid inks:

Pigments,
Resins,
Solvents & Additives

are manifold, due to the different substrates and end uses. Almost any kind of substrate from newsprint to coated papers, paper and containerboards, to flexible films and foils, can be printed.

Therefore, ink formulations and dispersion processes are of greatest importance.

Inks which are printed by the Flexographic and Gravure printing processes are characterized by their extremely fluid nature, hence the name, liquid inks. The fluidity of Gravure inks allows the recessed cells of the gravure cylinder to be filled rapidly. Similar fluidity is required for the Flexographic process as the inking systems depend upon an engraved cylinder metering the printing ink onto the raised rubber image.

Highly volatile solvents are used and most Flexographic and Gravure inks are fast drying and therefore, the ink is transferred to the substrate as quickly as possible.

Liquid inks are formulated to dry by the physical removal of the volatile solvents from the ink formulation. The pigment is bound to the substrate by the resin material. The rate of drying depends upon the evaporation rate of the solvents selected. Evaporation (Fig.1) of water or solvents in ink depends primarily on the vapor pressure of the vehicle utilized. The choice of vehicle systems is determined by the materials of the printing plate, speed requirements and nature of the substrate.

Figure 1. Surface action of liquid ink curing (Evaporation)
Schematic diagram of ink drying by evaporation The volatile solvents evaporate, leaving a dry ink film on the printed stock. Evaporation is usually speeded by application of heat and air.

Most evaporation inks consist of such solvents as hydrocarbons, alcohols, ketones and esters and synthetic resin or cellulosic material, which acts as a binder to hold the pigment to the substrate. Evaporation can be speeded up by using infrared lamps or by flushing the vapors by gas jets.

Each type of ink requires a very careful balance of properties to meet the requirements of the printing process and the end use of the printed article.

An ink will exhibit a good adhesion to the substrate if the pigments are properly dispersed.

In the Gravure process, printing is achieved by passing the substrate between the Gravure cylinder and an impression roller. The substrate is fed from reels into a nip between the edged cylinder and a rubber covered impression roller, which supplies the pressure needed to transfer ink from the cells to the substrate.

Figure 2. Grainting Process

The printed web runs upwards through a heated drying system where the solvents are evaporated and extracted. In Gravure printing, each color must be nominally dry before the succeeding color is printed over it, therefore, each printing station has its' own individual drying equipment. The Gravure ink, which usually stored underneath each unit, is pumped up to the ink trough and usually ink viscosity control is incorporated in such systems.

In the Flexographic printing process, the printing images stand up in relief, similarly to the letterpress process. Low printing pressure is essential to the process because of the combination of very fluid inks and solt and flexible printing plates. Rapidly, drying liquid inks are utilized; therefore, fast-printing speeds can be achieved on non-absorbent materials, such as films and foils.

For high quality Flexographic printing, the printing unit is built to very tight tolerances. Te ability to manufacture to these standards is one of the factors which is contributing to the current growth in Flexographic printing in its' use for higher quality product.

Figure 3. Flexographic Printing Process

Printed images are given color by pigments that are substantially insoluble in the vehicle and in water. In addition to color, pigments determine such ink properties as bulk, opacity, specific gravity, viscosity and yield value. Pigments are finely divided particles, when adequately dispersed in the medium, absorb and scatter light. If the absorption is selective, the pigmented will be colored. Pigments may be entirely inorganic or organic, they may also be metallic salts of complex acids, or consists of organic dyes laked on to inorganic substances. Pigment opacity depend normally upon its' ability to scatter incident light, but absorption also plays a part and the overall opacity is due to combination of both properties. In the case of titanium dioxide, little or no absorption occurs, and opacity is due almost entirely to scatter. On the other hand, as the refractive index of a pigment approaches that of the medium, in which it is dispersed, the amount of light scattered decreases and the pigment becomes more transparent. Transparency of a pigment therefore is partially dependent upon the medium used o disperse it.

The tinting strength of a pigment is a measure of its' ability to impart color to a system. The color strength of a pigment is primarily related to chemical composition, particle size and distribution. In the case of printing ink, the actual value will depend also upon the film thickness and concentration of pigment in the in the ink. Most printing inks are more or less transparent. The substrate will influence the final color of the printed matter.

The film forming materials of liquid inks are typically solvent/resin vehicles, which cure by evaporation. In Gravure inks, low boiling hydrocarbon solvents are generally used with gums and resins. Flexographic inks normally contain alcohols, water or other fast evaporating solvents mixed with suitable resins and/or gums.

Resins contribute to the properties of hardness, gloss, adhesion and flexibility in the ink. Resins are of two types, natural and synthetic. Synthetic resins are prepared by polymerization involving condensation or addition reactions between relatively small molecules.

Solvents used in liquid inks are capable of dissolving another substance, such as resins to form a solution. They are used to dissolve materials in the vehicle, assist in the dispersing of the pigments and additives and to adjust viscosity. Combinations of solvents are often selected for different types of ink on the bases of printability, drying speed, economy and odor. Flexographic and Gravure inks contain as much as 80% organic solvents. Gravure inks usually employ one solvent, either xylene or toluene. The printing of solvent-based inks is under regulation to control solvent emissions to the atmosphere.

INK MANUFACTURING PROCESSES

The manufacture of printing ink is a technologically advanced, highly specialized and complex process. The manufacturing systems utilized in the process depends upon the volume of the particular ink to be manufactured, the properties of the materials in the formulation and the end use requirements of the printing ink. Essentially, printing ink manufacturing is the combining of the basic ingredients such as pigments, vehicles and additives in such a manner so that the ink will meet its' product specifications required for its' intended use. A number of printing inks are completed in a one or two-step mixing/dispersing process because pigments are purchased in such pre-dispersed forms as chips, bulk or other wetted forms.

Gravure inks or Flexographic inks are typically prepared by a combination of batch and continuous processing in totally enclosed media mills, sometimes even stir ball mills. These types of inks are to be processed only in totally enclose dispersion systems because of the very volatile nature of the solvents used.

As the pigment in most printing inks is the most expensive part of the formulation, economics of pigment selection and proper dispersion equipment, is vital importance. In the case of Gravure inks, the process of dispersion of the pigment into the vehicle system can be achieved by a number of different manufacturing techniques. Here, the relationship of the dispersion process to the end properties of the ink is of great importance. The options available for dispersion of the pigment range from the use of chips and pre-dispersed pigments to conventional dispersion methods in equipment such as small media mills, ball mills or sometimes, high speed dispersers.

The uses of pigment chips and to a lesser extent, pre-dispersed pigments, tend to produce short thixotropic inks with very high gloss and transparency. Dissolving the pigment chips or pigment paste is usually carried out on a high shear mixer, suitable to produce ink with acceptable dispersion. There are advantages in using pigment chips, particularly with pigments that are difficult to grind.

The high cost of the pre-dispersion process, together with shortness of the flow, which places a limit on ink strength attainable, means that such techniques are normally used only when no other option is feasible. The most common process for the production Gravure inks is dispersion of the pigments utilizing a small media mill. Different media mills are available which enable different diameter bead sizes to be utilized. In general terms, the smaller the bead size, the better the dispersion. Alterations in milling conditions will give rise to variations in quality of dispersion, therefore, they have carefully monitored.

While dispersion process represents a major part in producing dispersion, there is considerable influence and inner dependence between the binder, pigment and solvent. All are equally important to the final result, particularly with respect to the dispersion stability. Finding the optimum conditions and formulation balance for maximizing dispersion can be time consuming with many experiments required.

Ink makers are required to provide consistent quality and quick delivery. Moreover, the ink maker must cater to a wide variety of requirements. Therefore, flexibility in formulation and dispersing methods has to be retained.

The basic need to grind out pigment agglomerates/aggregates represents a high share of the cost in making printing inks. Therefore, it is imperative to continuously improve and further develop the process of pigment dispersion. These efforts concentrate on improving:
a) Pigment dispersability
b) The efficiency of available wet grinding and dispersing equipment

The physical properties of pigments such as particle size and particle surface are of great influence in the dispersion process. Primary dispersions for ink production demand that the pigment particles are thoroughly wetted by the liquid phase and that the particles in the finished ink are in a size range of 1 micron to 5 microns maximum. If this dispersion level is not achieved, printing problems will arise.

Pigments such as those mostly used for printing inks typically are crystalline solids. They usually feature primary particle sizes of 0.5 micron or providing for specific surface areas of 30 to 100 square meters per gram.

Pigments are generally precipitated from aqueous solutions. At the time of chemical reaction causing the precipitate, these particles are molecular in size. The molecules of the pigment are strongly attracted to each other by physical forces and immediately from larger pigment particles, the size of which will depend on the nature of the material and the physical conditions existing at the time reaction. The primary particles cluster together during processing to form agglomerates / aggregates. The particles in agglomerate / aggregate form are strongly bound together and high energy is required in the dispersion process to break them down. A dried press cake will contain a mixture of primary particles, aggregates and agglomerates. The presscake is normally crushed to reduce the size of the largest agglomerates, providing what appears to be a fine powder. It is the most important part of the dispersion process to break down these large particles exposing a greater surface area of pigment to the wetting medium in order to produce a finished, evenly wetted product. There are several routes by which ink dispersions can be produced. While there are similarities in the way the individual types on inks are made, and since much of the machinery involved is also similar in concept, there are distinct differences between them. The primary purpose of the dispersion process is to break down pigment aggregates and agglomerates to their optimum pigmentary particulate size and distribute these pigment particles evenly throughout the similar medium i.e. the carrier. To achieve the optimum benefits of a pigment, it is necessary to obtain as full a reduction as possible to the primary particle size. The color strength of a pigment depends on its' exposed surface area, and the smaller the particle size, the higher the surface area and thus the stronger the color. Also, the pigment is generally the most expensive constituent of any printing ink; therefore, one would normally want to obtain optimum performance with the least amount of pigment. Ideal pigment dispersion consists mainly of primary particles with only a minimum of loose aggregates and agglomerates.

In practice, reduction to the primary particle size is largely determined by the nature of the pigment, the dispersion system and processing equipment and by the end use requirement of the printing ink. As pigment agglomerates are broken down, larger and larger pigment surfaces are created. At this point, relatively powerful short range surface energy to re-form pigment particle agglomerates or aggregates. To prevent this re-agglomeration, it is imperative to neutralize the surface energies through a suitable stabilization process. Dispersions of pigment in organic solvents are stabilized by a mechanism known as steric stabilization. This effect occurs when a suitable dispersion is absorbed onto the particle surface by the "anchor group" portion of the dispersed molecule, while the remainder of the dispersed molecule remains in solution in the solvent.

DISPERSION PROCEDURE

The dispersion procedure is the most important part in the field of wet grinding. Normally, this process is divided into four distinct stages, namely:

a) Separation
b) Wetting
c) Distribution
d) Stabilization Separation

Separation

Separation means not only commutation of large primary pigment particle agglomerates or aggregates under mechanical stress, but also the dispersion of agglomerates and aggregates into the single constituents of primary particles and aggregates. This process is also referred to as dispersion/grinding.

Wetting

Wetting means that portion of the process in which a liquid spreads over the surface of a solid particle or the penetration of agglomerates through a liquid. This involves the removal of absorbed molecules of gas (air) liquid or other materials from the surface of the pigment particle and their replacement with molecules of the vehicle system. Therefore, wetting efficiency depends upon the comparative surface tension properties of the pigment and the vehicle system.

Distribution

Distribution is the process of balancing the concentration of the separated pigment particles within the carrier liquid. Homogenous distribution of the pigment particles throughout the vehicle system is usually achieved by mechanical action, mostly in small media mills, such as Perl mills, so called because the grinding media are spherical beads made of glass, ceramic or metal.

Stabilization

Stabilization is the process responsible to retain the quality of separation and the grade of wetting achieved within the vehicle system. If the pigment dispersion has not been stabilized, flocculation can occur from powerful short-range forces. A properly designed dispersing process combined with an adequate formulation will prevent flocculation. Since an understanding of the mechanism of steric stabilization has developed, new dispersants have been designed providing for far superior performance, compared to previous systems.

Simultaneous Process

The four stages of the dispersion process occurs simultaneously rather in sequence. Again, the primary purpose of the dispersion process is to break down pigment agglomerates and aggregates to their primary particle size and distributes these pigment particles evenly throughout the vehicle system.

There are two main types of formulation for liquid inks, water based and solvent based. The volatile nature of the liquid phase of both solvent and water-based inks requires similar manufacturing techniques, but they are often produced in separate units to avoid contamination. The flammable nature of a large number of solvents used requires special precautions to prevent the risk of fire and explosion. Generally, the optimum manufacturing path for manufacturing of liquid inks consists of high speed mixing, followed by small media milling and filtration. Also, liquid inks can be made by utilizing conventional ball mill technology.

Wet grinding and/or dispersing of pigments in liquid ink vehicles can be achieved in a large variety of machines. However, a very economical solution is to employ an equipment combination consisting of a high-speed disperser and a small media mill. This typically is a three-stage process, consisting of:
a) Pre-mixing
b) Wet grinding/dispersing
c) Let down adjustment
While the ball mill may be considered as an original totally enclosed system for manufacturing liquid inks, the introduction of small media mills gave opportunities for introducing faster and continuous production methods. Bulk amounts of concentrates and inks can be manufactured from dry pigment and vehicle systems using a combination of mixers and media mills. The typical process entails:

a) Weigh out pigment and vehicle system and pre-mix on a high speed disperser,
b) Disperse the pre-mix on a small media mill,
c) Add additives and solvents in a high speed mixer,
d) Filter and pump to the storage tank after quality control procedures are completed.

Small Media Mills (PERL MILLS)

Agitated bead mills are mostly used in modern wet grinding and dispersing processes. This mill system is firmly established in the making industry. In most industries it has prevailed over other grinding and dispersing systems, such as ball mills, roller mills, rod mills and similar machines long employed in the past for the wet grinding and dispersion of solids in liquid vehicles. Modern agitated bead mill are widely used in different industries for demanding grinding and/or dispersing applications. The basic principles of small media mills have been known for almost 60 years.

Industrial breakthrough of high-speed media mills occurred in 1948 with the introduction of Dupont' s sand mill, which has been used within the paint and coatings industry primarily as a pigment grinder.

NEW DEVELOPMENTS

In recent years remarkable developments have taken place to favorably adapt small media mills for the fine grinding needs of many industries. As a result, there are many different types of small media mills available today. Specific design features allow for milling processes not conceivable some years ago. In recent years, the applicability of small mills has been extended to coarser feedstock and to finer product particle sizes. This development has been made possible by design and process innovations, such as the invention of new agitating and media separating systems and a device for continuous grinding processes that avoids separate premix preparation completely.

In the past, primary particles, which were considered indivisible by media milling, have successfully been ground to primary pigment particle size via special new mill designs. Spectacular results can be achieved with a specially designed bead mill when it is properly operated with 250 micron grinding media. The conversion of crude pigments to finished pigment dispersions is an example.

ENERGY CONVERSION

From general point of view, fine grinding, as well as dispersing, must be viewed as an energy converting procedure. Typical applications require that internal mill conditions be created in which the local energy density is above the minimum required for grinding process. Since the energy introduced into the system is mostly converted into heat, special consideration must be given to efficient heat removal/exchange. This is particularly important since practically all processes require product temperatures that can be confined to predetermined limits.

HIGH SPEED MILLS

The introduction of high-speed agitated media mills represented a great advance in standard manufacturing methods. The essential features of these mills are high agitator speed and the use of small attritive elements for particular purposes. One can increase grinding performance by reducing the diameter of the balls, thereby increasing the number of points contact. Modern high-speed units use this finding to the ultimate extent.

The Perl Mill is characterized by very small grinding particles, which are largely spherical in shape. These perls or beads are made of glass, ceramic or metal and are accelerated to approximately up to 200 times gravity.

REDUCED MEDIA SIZE

With a reduction in the size of grinding media in a media mill, the number of contact points is increased exponentially resulting in improved grinding and dispersing action. Furthermore, when grinding media in the 250-micron range is used, processing of crude pigments into directly highly loaded pigment dispersions can be accomplished in a single step process, which may eliminate intermediate pigment preparation stages.

IMPROVED COST EFFICIENCY

With an improved grinding procedure manufacturers of high quality printing inks can realize substantial cost savings by using less costly raw materials (pigments). Also, improved dispersion can be achieved resulting in higher pigment yields.

HORIZONTAL vs. VERTICAL

Small media mills can be operated either horizontally or vertically. The preferred orientation depends upon product and process related parameters such as viscosities, feed rates, size and density of grinding media. As a basic rule, the most advantageous grinding chamber orientation is the one that results in an equal media distribution within the grinding chamber. Opinions vary considerably as to whether the grinding chamber should be vertical or horizontal arrangement. There are no hard and fast rules, but the following comments apply generally. In spite off the differences in designs, both vertical and horizontal grinding chamber arrangements provide equal grinding efficiency in wide fields of applications.

Vertical Mill

When a structurally viscous product, flush base printing ink for example, is to be processed, experience has shown the vertical mill to be advantageous because the force of gravity counters the accumulation of grinding beads at discharge point. It thereby makes for more uniform distribution of the grinding media within the mill chamber.

Horizontal Mill

The benefit of the horizontal arrangement, on the other hand, is the ease with which the filled bead mill can be restarted after stoppage. For applications where the product has a medium to low viscosity, the horizontal mill definitely provides an advantage since gravity is basically eliminated and the grinding media is more uniformly distributed throughout the grinding chamber. Therefore, the grinding media is being totally activated without densification on either end of the mill chamber. Naturally, there are other considerations for giving preference to one or other design.

DIRECT DISPERSION SYSTEM

For standard machines, it is necessary to prepare premixed slurry in order to feed the agitated media mill. Since the development of the Direct Dispersion System, it is possible to operate agitated media mills continuously, without premixing or pre-dispersing solids and liquids.

The DDA system features a specially designed feeding screw, which is flanged on directly to the grinding chamber. This can produce superior product quality at reduced operating costs, because of the constantly maintained processing parameters. Such systems are successfully employed in the printing ink, magnetic media and chemical industries.

The grinding chamber can be positioned either in vertical or horizontal design. The system applied to the entire line of DRAIS Perl Mills. The output rate and fineness of finished product is controlled mainly by the residence time of the material in the grinding chamber.

Control functions of the Direct Dispersion System are performed steplessly. The solid and liquid constituents of a formulation meet for the first time at the right formulation ratio under intense mixing, grinding and shear forces. This prevents the forming of any so-called "secondary agglomerates". For example, the Direct Dispersion System can be applied to disperse, fully continuously pigments such as carbon black pellets in highly viscous polymers. Today Perl Mills of the Direst Dispersion Design are also in operation for the production of adhesives and sealants, successfully replacing batch type kneaders.

The system processes, with equal efficiency, materials that are not readily flowable, inadequately wetted or completely dry. The Direct Dispersion System also proved to be highly advantageous for large scale processing of materials not readily wettable or containing components that tend to settle out rapidly.

Because only small amounts of product are being introduced into the mill at any given time, large tanks for mixing, dispersing or material handling are not required. The system lends itself to total automation and computerization and therefore allows for precise process controls.

SPECIAL CONSIDERATIONS

The different stages of liquid manufacturing have to be addressed separately. For the first stage the formulation of the printing ink has to be such that the amount of vehicle system required wetting out the pigment properly has to be assured. Also, very important, is the proper pigment / vehicle ratio for optimum dispersion and the next state in the small media mill. Lately, the increased availability of easily dispersible pigments provides fro much less problems in the media mill dispersion step. The next step of adding the remainder of any vehicle portion and solvents to adjust viscosity together with other additives not suitable for the intense grinding process should also include final quality control check. The last step of filtering the ink should prevent any chance of contaminating the final product. Therefore, the ink is filtered through a fine mesh filter. This could be sometimes a multistage process, especially if the printing ink is held in stock for any length of time.

Finally, we would like to add the two latest developments in processing of liquid printing inks, namely the new DRAIS DCP Mill, and totally automated ink-manufacturing process by the DRAIS SOM Computer System. While the newly developed DCP mill system is usable for the entire range of printing inks, special considerations have been given for liquid inks, and also to liquid inks by replacing the conventional pigment chip process.

For the achievement of outstanding quality characteristics of liquid inks, particularly special Gravure and Flexographic inks, it is state of the art to use high quality pigment chips. For the following reasons, however, the chip technology is getting more and more problematic:

a) Stock keeping
b) Availability
c) Cost situation
d) Danger potential (in chip production)

This is why attempts have been made for a long time to achieve the gloss and transparency values, which are characteristics of chips, by direct wet dispersion of powdered pigments.

DRAISWERKE has achieved the decisive break through in solving this problem. The advantageous process technology is made possible by the use of the newly developed DRAIS agitated media mill series PM-DCP.

Typical Constructional Features

• Energy input by a large number of turbulence pegs (rotor-stator principle)
• Grinding media separation by centrifuging
• Defined product transport by internal series connection of two grinding chambers
• Small mill volume, easy to clean
• Large surface area for heat exchange

These features enable the effective use of extremely small grinding beads at highest volumetric energy density in the system of up to 6 kW per liter product to be dispersed. In spite of this, remaining below the dispersing temperatures, which are critical for NC inks, is no problem at all.

Even pigments considered very difficult to disperse can, in a highly economical process, be refined in liquid inks in such a way that the quality standards of chip-based inks are matched, if not even exceeded. The new DRAIS agitated media mill generation PM-DCP has additionally proved its' outstanding performance in raising the quality level of standard inks drastically. For water-based inks, the same excellent results are achieved as for inks on the basis of organic solvents. The better development of desired coloristic characteristic, especially the color strength, enable interesting savings of raw materials. In connection with unusually high throughput rates in relatively small mill units, which are easy to clean, the innovative dispersing technology of DRAIS introduces a system in the manufacture of liquid inks, which is unequalled in economical respects.

Increasing demands on quality printing inks regarding the development of coloristic characteristics such as gloss, transparency or color strength require the use of more effective dispersing techniques.

For securing the quality level as it has been achieved by newly developed dispersing machines and techniques, the use of an intelligent measuring, control and regulating technology is indispensable.

Moreover, there is an increasing desire to use production plants in night operation without supervision.

To solve this problem in an economical way, DRAISWERKE has developed a modular control and regulating system for Perl Mills. The compact process computer SOM 10. With keypad and LED display enables the functions:

• Operation
• Indication
• Supervision
• Control
• Regulation
• Communication with central computer

At the most sophisticated stage of expansion, the mill regulation is done according to a patented process. As essential measured values, the power consumption of the rotor, the product flow rate as well as the product discharge temperature are taken into account. Regulated values are the pump speed, the rotor speed and the cooling agent flow rate. The system works in a self optimizing way in so far as a maximum throughput rate is automatically set while at the same time an even distribution of the grinding media is secured and the product outlet temperature as well as the mass specific energy input are regulated to pre-selectable parameters. Thus, a constant, reproducible product quality is guaranteed at any time.

All operational data, limit and alarm values, which are relevant for the dispersion of a product, are filed in the data store of the computer. By selecting a particular product code, the corresponding data record is loaded in the working store. The fully automatic mode of operation comprises the starting cycle, the optimized production as well as the stopping and rinsing cycles.

All the parallel working dispersing lines are operated from a central control room. All information on the operating states of a production are indicated and filed by a superset visualization and recording system. The concept is most suitable for both the automation of the batch size manufacture of e.g. Flexo / Gravure inks and the fully continuous dispersing of e.g. web offset inks.

The elimination of undesired states, found in manual operation, guarantees an absolutely constant, reproducible product quality at maximum utilization of the plant capacity, which makes this system highly economical.

Modern Production Trends Also Include the Computerization of the Processing Systems

The computer is already an established tool in ink manufacture. The routine procedures of preparing manufacturing instructions, processing of orders, stock control, etc. are carried out at high speed and high efficiency. The latest advances in computer and microchip technology are automating ink manufacturing as a whole. Quality ink producers are adapting more automated and computer controlled manufacturing methods. While production costs are ultimately greatly reduced, one of the major reasons to employ new technologies is achievable consistent high quality of the printing inks. With DRAISWERKE's SOM System, greatly enhanced product qualities and consistencies can be achieved.

SUMMARY

An attempt has been made to describe the dispersion of pigments in vehicles and the process equipment mostly utilized especially in view of liquid ink manufacturing. All discussion of dispersion stabilization, in view of hyper dispersants, has been avoided since this is a field onto itself. There is no question as to the desirability and effectiveness of a fully dispersed and stabilized pigmented system. Such dispersion brings out the optimum color properties of the pigment in terms of color strength, gloss, transparency and rheology. When a pigment is completely dispersed it contains a large number of primary particles and therefore, a lesser amount is required to produce the necessary coverage and color strength than one which is not as well dispersed and contains a larger number of aggregates/agglomerates and flocculates. The trend today is toward production of more easily dispersed pigments. Pigment manufacturers always are improving pigment dispersability through the use of surface treatments. There has been increase in the use of plastic films and foils for packaging. Thin films of ink, if they are to provide greatest gloss and clarity of color for these applications, require very small particle sizes and complete wetting of the pigment by the vehicle. As the requirements of inks increase, efforts also will increase to use of the entire pigment surface. This becomes more and more important as the price per pound of pigment rises. More costly pigments, with greater stability, can be used when this newly developed dispersion processes, as discussed before, has released all of the color and prepared the pigment surface correctly for its' ultimate application. Surely, the future will bring more efficient dispersion equipment as well. From the process equipment side, the main target is the constant mass specific energy input into a dispersion system under optimized conditions. This will allow full utilization of dispersion equipment capacity. Such processing systems allow for attaining the highest product quality and minimum operating costs. Recent successes and ongoing development work in the field grinding/dispersing technology (equipment and process related) are essential pre-requisites in order to convert any possible progress in raw materials or formulations into technical/economical benefits.