There are two main types of ink that are used for textile printing. Water-based Printing Ink & Plastisol Inks. The detail of each Ink is discussed as follows: Water-based ink utilizes either dyes or pigments in a suspension with water as the solvent. The evaporation of the water is necessary to set or cure the ink. This curing can take place either at room temperature or using a forced-air dryer depending upon the specific water-based ink used and the speed or volume of production. Plastisol ink is PVC (Some inks are Phthalate-free) based system that essentially contains no solvent at all. It is a 100% solid ink system. Plastisol is a thermoplastic ink in that it is necessary to dry by heating the printed ink film to a temperature high enough to cause the molecules of PVC resin called Gelling and plasticiser which cross-link and thereby solidify or cure. Temperature at which most "Plastisol" Inks for textile printing cures at is in range of 160°C to 200°C.


Plastisol is the ink of choice for printing of finished goods such as T-shirts, sweatshirts, jackets and tote bags. Water-based ink is the choice for the printing of yard goods; either in piece form or on the roll. Both inks have technical advantages and disadvantages for use in specific applications. They also have their own environmental impacts and these should be considered for the particular application and shop set-up. October 2008 > SCREEN PRINT INDIA


Technology Advantages of Plastisol waste Plastisol is a very simple process.


Type of Fabric/ Usage


Usage Recommendations Plastisol Water-base T-Shirts/Light Colours Excellent T-Shirts/Dark Coloured Good Poor Nylon Jackets Good Poor Woven/ Towels Poor Excellent Sporting Goods Excellent Poor smear the ink.


Plastisol ink also creates an ink film on the Surface of Fabric that can be felt with the hand. The, higher the opacity of the ink, the thicker the film


Plastisol Inks can be left in the screen for extended periods of time without clogging of mesh. It is ready to use right out of the container more than 90% of the time. In most applications, it can be printed wet-on wet, which allows for increased production speeds. It comes in formulations that can be printed on light and dark fabrics. The disposal of:


Ink Type Water Base Medium Plastisol Inks Properties


Dries Fast Low & Medium Low Medium / Medium Easy

Print Ease Easy

Opacity Low- High

Hand/Feel Medium- Heavy

Curing Easy Ink Recovery. This thicker the film layer is Easy layer considered a disadvantage at consumer level.


One of the most important practices when using Plastisol ink is to keep the ink clean. What this means, is that it is very beneficial and cost effective, to keep Plastisol colours from being contaminated by dirt or even other colours of ink. By maintaining clean shop practices, there will be a great reduction in ink wastage. Clean ink can be returned to the original ink container for reuse. There is no Degradation in the quality of Plastisol as long as it is not mixed with other colours or contaminated with foreign materials. Plastisol that has been contaminated with other colours can still be retained in a separate container for blending with other waste inks. Many times this waste ink can be used to create new colours or it can be over pigmented with fresh pigment to create a dark colour, such as black, for use on less critical jobs.


If the Plastisol needs to be disposed of in an uncured state, then hazardous chemical regulations apply for either cured or uncured disposal. The biggest environmental hazard in the use of Plastisol comes in the screen and equipment cleaning steps. In order to emulsify the ink for easy removal from screens, squeegees and other work surfaces, it is necessary to use some type of Solvent. Waste ink and the solvent must be disposed of properly in order to minimise environmental impact.


The screen printing industry has been very active in the creation of products that can minimise the impact of these cleaning processes. Solvents are available that are 'more' environmentally sensitive than the traditional petroleum based solvents.


Water-based Ink Systems 'MAGIC 5000 Series'


Water-based inks are defined as those that utilise water as the main solvent. That does not mean, Plastisol does not dry. In order for a compound to dry, there must be evaporation of some kind of solvent. Since Plastisol has little or no solvent, it cannot dry. Because of this characteristic, Plastisol can be left in screens; the lids can be left off of the ink containers (although keeping them covered is a good practice to keep lint and dirt out of the ink). And ink left at the end of the job can be returned to the container for reuse without any adverse affects.This last practice is a great benefit in reducing waste product. Plastisol is extremely versatile in that most printers never have to amend the ink. They are able to use it direct from the container without ever adjusting the viscosity or the strength.

"Plastisol Inks" comes in strengths from transparent to very opaque and most printers will have the various types available to use, depending upon the type and colour of fabric they are printing on.


Plastisol Ink- Disadvantages


Plastisol are Thermoplastic in nature, will Re melt if it comes in contact with anything hot enough. For that reason, Plastisol prints cannot be ironed. If an iron touches a print, Plastisol Inks comes in strengths from transparent to very opaque and most printers will have the various types available to use, depending upon the type and colour of fabric they are printing on.


However that water is the only solvent. It is significant to note that many water base inks contain 'Co-solvents' which may even be Petroleum based solvents. The reason these co-solvents are used varies, but one of the key reasons is to decrease the time and heat necessary to cure the ink film on the fabric. Advantages of Water-based Printing Ink 'Magic 5000 Series': Water-based inks are a good choice when a 'soft hand' is desirable. A soft feel is the condition where the Ink film cannot easily be felt with the hand when passed across the surface of the fabric. This affect is often used as an argument for why water-based is preferable to Plastisol.


Water-based ink also is a good choice where ink penetration is desirable, such as in towel printing. Towels have a high nap fabric that must be printed in a manner where the ink penetrates or wicks through to the base fabric for adequate coverage.


Water-based ink is having no 'Tact' when printed and cured fully; it can be ironed from the top. Because of some reason even during fusing and curing, Teflon sheet is not required. Water-based inks that are designed to wick into the fabric are excellent for this application. Ink wicking is not a desirable affect in most other fabric printing as it will destroy the design and registration of disadvantages of Water-based Printing Ink, 'Magic 5000 Series' Water-based ink is much more difficult to cure than Plastisol. The dryers used for water-based printing tend to be larger/ more than those needed for "Plastisol Inks" In Plastisol printing, the ink film must only reach the cure temperature for a recommended time. With water-based ink, the temperature must be reached and then held until all of the solvent (water) is removed. There are water-based inks that will air dry, as the room required for curing greatly reduces productivity.


Many water-based inks can also be more quickly cured with the addition of a catalyst 'Tex-Bond' that will assist the heat in the curing of the ink by continuing the cure even if all of the water is not removed. The disadvantage of a catalyst is that once it is added to a Water-based ink, it creates a time limit or 'Pot-Life' where the ink must be used in certain time or be discarded. Most catalysed water-based inks Pot-Life are between four and twelve hours. Since water-based inks contain water as an evaporative solvent, care must be taken to prevent the ink from drying in the screen. If water-based ink is left in open screen for even a short period of time, it can clog the mesh and ruin the screen. Experienced water-based ink printers must always be conscious of how long a screen can hold between prints to prevent the ink from 'drying in'. While modern water-based inks are less prone to this phenomenon, it is still a concern.


Water-based ink is also much more sensitive than Plastisol towards the Photo Emulsion that is used to make the screen/ stencil. Hence water resistance photo emulsion should be used. All leading manufacturers produce water-resistant emulsions. If water resistant emulsion is not used, then water-based ink will destroy the stencil by dissolving the coating chemicals in short time. Screen made by ' water resistant' emulsion cannot be used again for other printing job.


Summary


Whether printing with "Plastisol Inks" or a Water-Based ink system, you are still printing a chemical compound.


Therefore, it is essential that proper handling and disposal methods be used. As stated above, there are advantages and disadvantages of each ink system. The key is to use the proper ink for proper application, minimising waste product and always dispose of waste properly.


About the Author


He holds a B.Sc. (Tech). He started his work with Textile Processing & Printing Division of Shreeniwas Cotton Mills later he joined Pidilite Industries Ltd. as Technical Executive and worked for 15 years in various capacities related to Marketing (local as well as overseas). From last 18 years he is Director (Marketing) in Electron Group which is a leading manufacturer of Textile Inks & Textile related auxiliaries for the Textile Industries.