|Chapter 5 - Inks|
By Andy MacDougall. Copyright 1999 MacDougall Screen Printing Ltd. All rights reserved. __________________________________________________________________
Ink for Each Occasion
Without getting all technical, inks are made up of a carrier or base, which is a thick clear resin-type liquid, plus finely ground pigments or minerals for colour, and different thinners used to make the ink flow. Job number one for any ink is to stick to the substrate, and it follows that due to the many different materials screen printers have to print, and their different molecular make-ups, there is a large assortment of different ink types.
Many different manufacturers make inks specifically designed to bond to various plastics, papers, glass, metal, or whatever you are trying to print. Some are better than others. Many manufacturers produce a multi-purpose ink that will work well on a range of different materials. Manufacturers produce inks in lines that are based on the thinning and drying characteristics of the ingredients used in the clear resin or binder which makes up the bulk of the ink. Solvent-based, water-based, plastisols, and UV inks are the most common lines, and within these, different types of inks are available for different substrates. A colour system unique to each manufacturer is also common, with the colours having different names and code numbers, available in each of the manufacturers' lines and types of ink. In other words, brand x 'bright red' is not the same as brand y, and definitely not the same as some watercolour paint set or a magic marker.
Special Formulation Inks, which can include conductive metals, acid resists, adhesives, or ground glass, are used when screen printing is being used as part of an industrial process. These inks are usually supplied by specialized ink manufacturers, or formulated by the user.
Types of Ink
Semi-gloss or gloss finish: Usually solvent-based poster or satin poster. Used on paper or card, very popular with artists. Flatter finish, cheaper, doesn't stick well on plastics. Not suitable for long term outdoor use. Usually solvent based, one of the 'original' screen printing inks from the 40's.
Vinyl, Coroplast, Acrylic, etc.: Specific inks for specific material, usually contain thinners that bond or bite into the substrate. · Usually solvent based enamel. Slow drying, but high gloss, and very durable on wood or display signage.
Solvent-Based Lacquer:. Fast drying, glossy, and used on paper, over lacquer finishes, or for the production of waterslide decals. Holds excellent detail.
Solvent-Based Epoxy, or 2-component:. Used on glass or metal, sometimes fired or heated to set.· Maximun hardness and durability
Flock Adhesive:· Used on fabrics · An air dry solvent based ink · Used for 'flocking' on shirts and decorated penants.
Fabric Inks or Dyes: Used on textiles. Each type of ink listed above will probably require specific thinners and retarders. Most are solvent based. Some need special clean-up liquids as well. Most suppliers will provide a manufacturer's line card with all their different types, applications, and colour ranges available.
A WORD OF WARNING… Some different manufacturers' inks will intermix with others, but be very careful when trying to use two manufacturer's inks, and !!!TEST!!! a small amount first. So how do you know the new ink sticks like it should and won't crack or peel a day later???? Here you go, used by squeegee pros everywhere….. WORLD"S LEAST SCIENTIFIC (but most effective) INK ADHESION TEST A good ink adhesion test should be printed through the same mesh as the production run, thinned and mixed to a normal printing consistency, and thoroughly dried (24hrs) before checking the adhesion. (NOTE: Some inks may appear dry, but do not develop a permanent bond for a number of hours) (1) Scrape the ink vigorously with your fingernail or a sharp object. (2) Roll or stretch flexible materials. (3) Put a few light slices through the ink surface with a knife and then stick some masking tape on the ink. Rip the tape off. If ink comes away with the tape, or with scraping, it would be a good idea to continue the ink hunt. (4) A print job with peeling ink is embarrassing and can be very costly. I can tell you a few 'job from hell' stories about ink that didn't stick… (5) Save your test samples, and make notes on them so you know what you tried a week or a month later.
Ink Lines: In some cases, an ink line is also a type, such as Plastisol, which is used almost exclusively to print fabric and heat transfers. In most cases, the ink lines of a particular manufacturer are classified by how they cure or dry.
Solvent Based: All solvent based inks, which up until a few years ago included almost all the ink types, dry by solvent evaporation. The pigments and resins harden as the solvents evaporate into the air.· Most of these liquids are volatile, flammable organic solvents, and are rapidly being replaced because of environmental and workplace safety concerns. · In many cases they are the only inks that will stick to certain materials, and continue to be used when durability and function are required. · Adequate ventilation systems or respirators should be worn when using solvent based inks and cleaners.
Water Based: Water based inks thin with water, clean up with water, and evaporate off mostly water when they dry. · They produce very little odor and make for a pleasant printing environment. · They have been gaining in popularity over the last few years, but require better stencils and more attention to humidity, temperature, and other shop parameters to work properly. · They also have a more narrow type range and don't bond well to many materials. · Waterbase fabric inks require heatsetting for a full cure.
Plastisols: Used in T-shirt printing, these inks cure by heat setting at a certain temperature for a specific time. · This is carried out by a flash-cure unit or by passing through a tunnel dryer. · Plastisol inks are used to create heat transfers for shirts and hats. · Plastisols do not dry in screens.
UV Inks (Ultra Violet): These inks are similar to plastisols in that they must be cured to dry, but instead of heat, they pass under intense UV light, which cross-links and bonds the ink molucules to themselves and the substrate. · Although UV inks reduce the amount of organic solvents released into the air, they still smell, the inks themselves are even more toxic than regular inks, and they require solvent based wash-up. · Their big advantage is their quick curing/drying time, and their ability to hold fine detail without drying in the screen. · They will stick to most paper and plastics, and can produce an ultra-high gloss finish. · Well suited to high speed printing requirements in production environments.
Process and Halftones: Process colour inks for CYMK are produced in addition to the regular colours, and are specially formulated for half-tone printing. · They are usually semi-transparent and maintain a pasty (thixotropic) consistency.
Pantone (PMS):· Many manufacturers produce ink colours to match the Pantone Matching System (PMS), which is used by designers and offset printers worldwide as a universal reference system to accurately specify colours and provide mixing formulas to acheive those colours from a basic colour range. · All pantone specifiers and chips are created using offset inks, which are quite transparent. Sometimes exact PMS matches to screen inks are impossible. · Other manufacturers have come up with their own colour system and provide base colours, formulas, and colour chips.
Tips on mixing colours: When trying to mix a specific colour, start with a small amount on a card and determine if the component colours selected will give you the desired colour before mixing large amounts. · Also, always start light and mix darker, not the other way around. · Always mix more than you need of custom colors. Odds are you will never be able to exactly match an ink, especially if you are in a panic with 50 more pieces to print to finish the run.
Tints or Concentrates: Many manufacturers provide concentrated colour that will mix with various inks or clear base to provide extended colour matching. · These are not true inks, mostly comprised of pigments, and if they are not mixed properly with an ink base, they may not dry.
Custom Coulours: Custom mixed colours with specific formulas are available from many manufacturers for a fee. This is useful in ongoing corporate work where colours must match from job to job. · Many colours dry darker once printed, and can also change shade depending on the substrate, the mesh count, and the amount of thinners or base added to the ink. Always pretest when colour matching is critical.
Special Formulation Inks: Screen printing lends itself to manufacturing because a wide variety of materials, with different properties, can be ground up and suspended in a liquid carrier long enough to be applied to the surface of any flat object. New processes and products are constantly being invented using this technique.
Ceramic Inks: Frit (ground glass) and specific chemicals and minerals that produce colours are suspended in pine oil and then printed on tiles, glass, or metal. · The pine oil burns off when the material is fired, the frit melts and bonds to the surface, and the pigments produce different colours. · This is known as enamelling when used on metal.
Acid Etches: · Acids are mixed with a paste and then printed on metals or glass. The acid eats the surface, and when the etching process is complete, the acid is washed off. · Shower doors, decorative glass, jewellry, mirrored glass in pinball machines and some circuit boards are produced this way.
Conductive Inks:· Conductive metals such as silver, nickel, and gold are mixed with a carrier that will stick to lexan or other thin plastic films. · An actual circuit is printed on the material, and then the material is layered with other plastics to encase the circuit. · Membrane switches, back window heaters, radiant heating panels, and those new Duracell battery testers are typical uses of this process.
Sublimation Dyes: These inks are printed backwards on paper, and when positioned on a synthetic material and heat and pressure are applied, the pigments in the ink turn to a gas, jump from the paper to the substrate, and dye the surface of the substrate. · Keyboards on computers and phones use this method, as well as lycra sports clothing manufacturers. · Because the dye actually enters the material (sublimates) instead of just sitting on top, this produces a very durable image.
Resists and Photoresists: Printable resists allow a reverse image to be printed on metal or other material, and when the metal is acid etched, the uncovered areas are eaten away. Once the resist is removed, the design is now the only metal left. · Used to produce circuit boards, decorative effects, and jewellry.
Printable Adhesives: Liquid adhesives are printed in place on various materials, allowing precision assembly of parts.
Temperature Sensitive: These inks contain elements that change colour once they are subjected to heat or cold. · Novelty cups, clothing, and scientific testing instruments are produced this way.
Retarders: Similar to thinners, but designed to slow the drying of the ink to allow for fine detail printing, or when temperature, humidity, or print speed cause ink to dry in the open areas of the stencil. · Too much retarder will slow the drying time on the racks or dryer to unacceptable lengths.
Halftone Base or Extender:· These additives thin the ink without making the ink runnier. · They can be used to reduce opacity and colour density, stretch coverage, (way cheaper than an equivalent container of coloured ink) or lessen the tack (stickiness) of the ink while maintaining the viscosity.
Binder or Bronzebinder: This is essentially a clear ink, and is used to print metallic or other specialized pigments, which are supplied in powder form and mixed into the binder. · NOTE: When using binders and powders, mix the powder with a small amount of thinner first, and then mix with the binder. This avoids clumping.
Metallic and other Powders: A wide range of powdered additives ranging from aluminum and bronze, pearlescent colours, glow-in-the-dark, etc., can be mixed with binders or coloured inks.
Flow Agents: Similar to thinners, these liquids assist the ink to pass through the stencil and finish up smoothly on the substrate.
Hardeners: These are added to certain inks to allow them to stick better to slick materials, or in the case of two component inks, they are the catalyst that sets off the hardening process. · Once hardeners are added to inks, they have a limited working time, and unused ink must be discarded.
Tidbits in General
Compile safety data sheets on all inks and thinners, and keep handy in a binder. Suppliers and manufacturers will provide these on request. · Avoid mixing thinned ink left over from a run in with pure stock. It's always better to use another container to store the mix, and then try to use it up on other jobs. A good list of reputable ink manufacturers can be found on the various screenprinting websites in the links section of www.papapress.com Start with SGIA, Screenprinters.net , Screenweb, or Screen Graphics magazine.
What you want to find is a supplier in your local area you can trust and work with, who keeps a stock of a particular manufacturer's ink on hand. One point to remember…. If you assign a cost to all the components of screenprinting or a finished print, the thin little layer of ink is insignificant. So don't cheap out on your ink out of some misguided frugality program. Speaking of misguided programs, your printing efforts and all your careful work creating beautiful positives, making perfect screens and stencils, and mixing up the perfect color can be ruined in a few careless minutes if you start printing without thinking.
PRE-PRESS, the subject of Chapter 6 of Screenprinting Today…The Basics, takes you through a final screen and art check, stock prep, ink mix, printing tools, and essential make-ready. When the squeegee hits the mesh you want to be able to relax and enjoy the print run. It's called 'screen' printing, not "scream" printing, and a little preparation goes a long way…. In the meantime, remember, don't wipe your inky fingers on your clothes! Two words: printer's apron.
Keeping a Tidy Art Space
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