Inkjet Ink Manufacturing

From the desk of Rick Bullock

Mister Inkjet Pty. Ltd. Australia

mrinkjet@mrinkjet.com

Technical Report
Water-Based Ink Jet Inks: A Quick Study

Everyone who works with inks for the office/desk top printer cartridge market realises that they are water-based, meaning the primary solvent is water. Everyone knows that there are many other ingredients that add significantly to the performance. What may not be known is how these ingredients are used and how they can affect the overall functionality of the product.
The more you know about inks, their raw materials and the processes used to qualify them, the better you are able to understand how they work. This knowledge provides the foundation on which to question your supplier's ink formulation and quality control processes. Knowing the basics of the technology can assure that you receive the highest quality inks available.
Any good ink manufacturer will have implemented a raw materials quality control program, which should be continually monitored and administered. This article covers most of these major ink components, discusses the characteristics each one brings to the formula and the methods used to test them. While all of them are not used in every ink formula every time, they are the building blocks of the majority of inks in use today. Similarly, there can be more than one ingredient of each type in some of these categories (multiple dyes, multiple humectants ... )

"Major" Components

Water
Water is the major component of ink. Water is the foundation on which everything else depends. So, to build a stable system and limit any outside contaminants, you must first ensure that the water used is as pure as possible. The use of a water softener or deionising columns alone to treat water is common with some ink manufacturers. However, such a simplified system can lead to concerns in several areas including longer-term ink storage. A multi-step purification process is preferred. These steps may include charcoal filtering, reverse osmosis and UV light purification to produce water with very minimal contaminants. Checking the water for conductivity is a good way to test purity. A reading of "O" for conductivity is a good standard to base acceptance. Testing for the contaminants in parts per million is another well-accepted method of determining water purity. Testing for purity must be done on an ongoing basis, preferably before each time the water is used to make ink.

Colourant
Ink colourants are either dye or pigment. They come in various styles and qualities from a wide range of suppliers. Much of the research for inks centres on the colourant itself and the functional characteristics it brings to the ink. Specific dyes and dye combinations require changes in other components of the ink to control performance.
As with anything, selection of a colourant must be based on more than price. Inexpensive dyes can sometimes lead to more work and greater cost in the long run than a pricier purified version. Purified dyes can be pH balanced, filtered, treated by reverse osmosis and/or contain various types of biocides or fungicides that prolong shelf life. Incoming tests on dyes should evaluate, at a minimum, viscosity, pH, surface tension, colour matching and quantitative and qualitative analysis by UV Vis Spectrophotometry. UV Vis analysis should include a minimum absorbance at a given dilution and a test for l Max (or the wavelength of light that has the maximum absorbance). A good additional step includes making specified ink with the new dye and print testing it against a standard. These steps allow the manufacturer to make a determination on the overall useability of the material.

Co-Solvent/Humectant
Co-solvents and humectants usually, including alcohols and glycols, are added to the ink as an additional vehicle or carrier for the colourant. They may also be used to control or limit evaporation of the ink. Most glycols are hygroscopic, which means they can remove moisture from the air. When added to ink, glycols reduce evaporative tendencies. Since the cartridges and print heads used in the office/desk top printers are designed to be drop-on-demand, the inks are exposed at the open orifices to the atmosphere.
Even when the cartridge is in the "parked" position while the printer is not in use, some evaporation of water from the ink can occur through these orifices. Because of this evaporation, the ink's characteristics can change slightly, including its viscosity or the level of concentration of materials (less water, more dye, more surfactants ... ).
The shift in ink characteristics can cause some of the orifices to become partially or completely plugged and result in a line print defect until the cartridge is cleaned. Humectants reduce the evaporation at the orifices and thereby reduce clogged print heads resulting from evaporation.
Humectants are usually tested for viscosity, surface tension and specific gravity. If there are questions concerning the test data received on a humectant, an ink can be formulated and print tested to confirm the acceptance of the material.

"Other" Components

Fixative/Penetrant
The fixative/penetrant component can be a number of materials all designed to facilitate the ink travelling to the paper. Once the ink is in the substrate, these materials can also fix or hold the ink and can reduce feathering or wicking tendencies to a certain degree. Fixative/penetrant materials must be added in a controlled amount to be sure the ink does not permeate the substrate too quickly, causing the colour to be seen on the back of the page.

Surfactants
Surfactants are added to adjust the surface tension of the resultant ink. If the surface tension of an ink is too high, the ink may not wet (or travel) through the cartridge correctly. Sporadic printing may occur under some high use conditions. A high surface tension also may cause the ink to not wet ' out (or penetrate) the substrate effectively, resulting in uneven prints and longer dry times. If the surface tension of an ink is too low, it could drip out of the cartridge and cause flooding of the print head at the orifices during use. Low surface tension can also cause the print to wick or feather excessively on certain substrates and as a result the character will be fuzzy. So, the surfactant must work in combination with the penetrant or fixative. The ink must travel out of the cartridge effectively and print evenly. Once on the substrate, it must be absorbed into the material quickly to adhere and reduce dry time but not so fast that it goes through the paper or feathers excessively.

Resin
Resins are added to give a specific durability to the printed character. Once the ink dries on the substrate, a resin can give it additional abrasion resistance. This effect is not always needed but is available. Care must be taken when resins are used because they can cause additional plugging of the orifices. If there is some evaporation at the orifices, the resin could cause a "film" to form and result in line defects in the print.

Biocides/Fungicides
Since inks are water-based and can be stored for long periods of time, biocides and fungicides are added to eliminate growth of bacteria and fungus in the materials. When these are added, care must be taken that other attributes of the ink, like pH and surface tension, are not adversely affected and the overall performance remains the same.

Buffering Agents/Other
These materials are used to add or control specific characteristics to the ink. For example, some dyes require pH control for longer-term storage so a buffering agent is needed to maintain the range required. Other characteristics include corrosion resistance and ink flow rate.
As you can see, your ink manufacturer needs to understand the "balance" required to make and maintain a high quality product. Having a working familiarity yourself can only enhance the dependability of the product you sell to your customers.

Water-Based Ink Jet Ink
Ingredients Amount Function
Water 50%-90% Ink Solvent
Colourant 1%-15% Colour Source
Co-Solvent/Humectant 2%-20% Ink vehicle, prevents evaporation
Fixative/Penetrant 0%-10% Assist fixing the ink to the substrate
Surfactant 0.1%-6% Surface tension and wetting
Resin 0.2%-10% Durability and adhesion
Biocide 0.02%-0.4% Prevents bacterial growth
Fungicide 0.01%-0.4% Prevents fungal growth
Buffering Agent 0.05%-1% Control ink pH level
Other 0.01%-1% Controls ink specific characteristics


Australian Universal Inkjet Specifications

Equipment used in conducting the following test:

Surface tension Tensiometer with 6 cm ring
Viscosity Brookfield Model LVT with UL
Adapter 72 degree temperature.
pH PHEP #3 ATC Meter
Colour Draw Downs Leneta #806 draw down meter


CYAN
pH 7.0 - 8.0
Surface Tension 34/40 Dynes
Viscosity 1.7 - 2.0
MAGENTA
pH 7.0 - 8.0
Surface Tension 34/40 Dynes
Viscosity 1.7 - 2.0
YELLOW
pH 7.0 - 8.0
Surface Tension 34/40 Dynes
Viscosity 1.7 - 2.0
BLACK
pH 7.0 - 8.0
Surface Tension 34/40 Dynes
Viscosity 1.7 - 2.0
LIGHT CYAN
pH 7.0 - 8.0
Surface Tension 34/40 Dynes
Viscosity 1.7 - 2.0
LIGHT MAGENTA
pH 7.0 - 8.0
Surface Tension 34/40 Dynes
Viscosity 1.7 - 2.0

The reality is that most inkjet cartridge manufacturers make ink that falls in these ranges. Some, about 10%, fall out side of these specifications however, when mixed with our ink the result is to normalize the pH.
Viscosity and surface tension are the same for everyone.