Whats Screen Printing Chemicals you must have?
A well-informed screen printer keeps an eye, not only the economy of the Screen Printing Chemicals being used in the industry, but pays a great attention to the quality (effectiveness and the way it works), safety, both in terms of health and environment. The value of a product must be looked in terms of its value. A subtle improvement or better performance of a product makes the whole difference. But the business community cannot simply ignore the cost producing the end product. We will look into the detail of chemical compositions and how they work, doing a specific function. We will start from the beginning of the screen preparation, applying the emulsion, Plastisol ink, cleaning the ink, reclaiming the screen (removing the emulsion), de-hazing or haze removing.
It All Starts With the Pre-Cleaning Chemicals.
A new screen may require degreasing and in some cases an abrader. A typical degreaser is basically an industrial soap, in most cases, Sodium Laurel Sulfate & some surfactants, so that the liquid can penetrate into the oily film on the screen. A simple test for a good degreaser is to wash dirty and oily hands. The price should be as low as possible as you are buying essentially soap & water. The second product in this regard is the abrader. Most abraders have either micro grits or pumice suspended in soap in paste form, strong enough to knock out any oily film within the filament of the mesh. These products are generally pretty safe in terms of health and environment.
It’s Not Screen Printing Without Emulsion
The fundamental building blocks of all emulsions are polyvinyl acetate and polyvinyl alcohol. Polyvinyl alcohol carries a hydroxyl group that gets cross-linked to the Diazo when it gets activated by the light. So the opening in the positive gets exposed to the UV light and thereby cured and would not wash out by water. When you wash the screen, the unexposed area where the positive has black ink would wash out- that creates the image.
The second category is the Dual Cure emulsions. What that means is that besides the Diazo reaction the emulsion also carries monomers with photoinitiators. When the dried emulsion film on the screen is exposed to the light, the initiators activate the monomers and they form a chain, becoming a polymer film. So there is dual action going on between the diazo part and the monomer portion of the emulsion.
Then we have one part emulsions which are based on SBQ monomers that do not necessitate the use of Diazo, but Diazo may be added for water resistance added to the emulsion film. The SBQ monomer, in this case, is being grafted to PVA. The hybrid class of emulsion is simply adding the monomers to the SBQ based emulsion to improve water & solvent resistance and also a better edge definition and resolution. The SBQ monomer itself is water sensitive. The PVA & PVAC are pretty safe. You still do not like to wash any emulsion into the sewer system.
The Dual Cure emulsions have acrylate monomers and pose some health issues. It is advisable to have a good recommended exhaust system. The SBQ emulsions have come down in prices quite a bit. There is no reason to spend so much money as the technology has become simpler and very economical. You should look at the speed of exposure, solids, resistance to the type of ink that are you are using. With the high solids hybrid emulsions (over 45%), the chances of getting an excellent edge definition and resolution are very high. You need to apply less emulsion on the screen. The other factor is the viscosity of the emulsion- One part emulsions should be over 10,000cps and Diazo, as we add water to the Diazo, the viscosity should be over 14,000cps. Most emulsions carry quality surfactants so that you may get a smooth emulsion film without pinholes. The properly applied good emulsion should not have hills and valleys.
What we see in the industry is a trend to use One Part emulsions that should cost you less than $40.00/gallon (large quantities should be a lot cheaper) for an excellent SBQ emulsion. The Diazo based emulsion provide a better latitude and therefore for very fine details, a good Dual Cure should be used. For most solid numbers and images a simple Diazo based emulsion would do a good job. These Diazo based and Dual cure emulsions are available at 33.00/gallon (larger quantities should be a lot cheaper). The newer SBQ emulsions have better resistance to water ink, but for water base ink a Diazo emulsion would be a better choice or adding a little Diazo to SBQ emulsion will also do the trick for a long run printing.
Plastisol Screen Printing Chemicals
Plastisol ink is basically a combination of PVC, Plasticizer (essentially a non-phthalate), and fillers, Titanium Oxide in white inks, pigments, dispersers, and thickeners. The PVC is suspended in a paste form. By applying heat the PVC fuses with the plasticizer- through this process a plastic film is developed on the fabric. If the cost of material is important to you, the prices are all over the place. A good white ink should not cost more than $62.00/gallon in the case of the highest grade and for cotton & 50/50, the price should be less than $35.00/gallon (larger amounts should be a lot cheaper).
Printers also use some additives that provide the latitude in terms of lowering viscosity, added adhesion, gloss, puffing affect and stretching properties. Xenon’s Xenbond provides adhesion, stretching, and gloss. Reducer is being used to thin down the ink- should be bought at less than $30.00/gallon. The Curable Reducer (Milky Reducer) is simply a reducer plus some PVC added into the product ($35.00/gallon). The numbers of factors relevant to the selection of a good Plastisol ink:
1. The opacity of the ink is extremely important.
In the case of white ink being applied on dark or black shirts, you may apply one coat with a high opacity ink through 110 mesh count. But if the fabric is not very smooth, you have to put two coats on 110 mesh count with high tension (over 26 Newton). The colored inks should also be high opacity and the colors should be bright. In the case of dark shirts, some printers have to apply an under-base, then apply the color. High opacity inks in most cases allow you to get away with one screen by applying two coats (Print/Flash/print/Drier).
2.The consistency of the ink plays an important role
The consistency of the ink plays an important role as it determines how much ink will be transferred to the fabric and how it would flow as you are pushing or pulling the squeegee to apply the ink. The ink should be creamy or thixotropic. If the ink is too gummy, it pulls the shirt upward as the screen is pulling away from the shirt- It may splatter ink onto the fabric and the surrounding areas.
3. High Heat Resistance
The ink should have high heat resistance so that the white ink should not easily burn and change color.
4. A Great Viscosity
The viscosity or call it consistency should be just right. In other words, Plastisol ink should not be too heavy or too thin. We feel that the viscosity should not be more than 500,000 cps and lower than 150,000 cps. You may use heavier or thinner ink for a specific purpose. The printers sometimes use Reducers or Curable Reducer (Milky Reducer) to reduce the viscosity of the ink. By adding a little bit too much of these reducers affect the opacity of the ink. You need heavier white for darker shirts so that you apply a thicker coat. For higher mesh counts, a lower viscosity Plastisol ink is preferable.
5. Look out for ink
Bleeding of the pigments is a very serious issue for the printers. As the cheap dying process on fabrics allow the ink to bleed through the fabric, especially dark colors, such as red, blue, purple and green. There is two probable causes for the bleeding: (a) migration (b) sublimation. For migration special formulations are formulated to avoid migration and for sublimation, one of the most important factors is the flashing that must be done at the lowest possible temperature around 180F. The low temperature curing ink should be used so that the curing should be complete between 230 to 250F (Xenon Xenwhite-poly & Mustang White cure at 250F- dryer time remains 1 minute and 20 seconds.
Recommended Post Screen Printing Chemicals
There are few different screen chemicals are being used for various reasons and purpose. We will go by each category:
- PRESS WASH: Almost all Press washes are based on solvents. They dissolve or liquefy the uncured Plastisol ink left off on the screen. They are supposed to dry faster as you may be able to use it on the press. Those which dry faster have lower flash points, lower than 146F (falls into the flammable category). Then you have press wash between 146F (combustible) and may be shipped without much restriction by DOT (Department of Transportation) laws. Most of these products are all VOCs (Volatile Organic Compound). Under the federal regulations, the allowable quantity for this specific usage is 28mg. /liter. There are water base cleaners but they are slower drying. printers should not allow these products to be drained into sewer systems, as there is no need to do it; and more importantly, it is against all local, counties, cities, state and federal laws.
- INKDEGARDENT OR INK WASH: Ink degradants are used to clean the ink in dip tanks, automatic cleaning machines some by spraying or by using rags. They are also based on solvents and some surfactants are added to them for removing the haze on the screen. The same applies to the VOC laws; 280mg/liter. We would strongly recommend using safe products for this operation; preferably a water base product would save you headaches and conforming to all the laws. A good ink-degradent is also recommended to remove the haze from the screen. Most of the ink degradent is slow drying- The question is: how slow? – It is a relative term used in the industry. Some of the so-called soy based cleaners are terribly slow. There is no doubt that every printer should be well conscious and sensitive regarding the safety of these products. There biodegradable products that should be preferred.
- RECLAIMER: There are two types of reclaimer, one based on Sodium Metaperiodate (the crystals) and periodic acid. They are both strong oxidizing agents. They attack the hydroxyl group in the emulsion and thereby liquefying the emulsion film on the screen. Little surfactants are added for de-greasing the screen at the same type. The reclaimer should be left on the screen for thirty seconds and then wash out thoroughly so that there is no trace of reclaimer left on the screen. The most economical method is to buy crystals and add water to it. The second option is to use highly concentrated liquid and add water to it. The cost of ready to use reclaimer should not exceed $3.00/gallon.
- HAZE REMOVER: The haze on the screen is mostly the pigment in the ink that stains the screen. Sometimes under exposed emulsion and Diazo appear on the screen. The most potent haze remover is based on Sodium Hydroxide (Caustic soda) with some surfactants and solvents. The problem with these haze removers is the issues with extreme health hazards such as a severe attack on the skin and eyes. They even damage the screen if the caustic haze remover is left off the screen for more than fifteen minutes. The safest haze removers are biodegradable- they work pretty good and in most haze problems. These products are expensive and should cost you around or less than $45.00/gallon.
- SPOT REMOVER: To remove the cured Plastisol ink spot, the spot removers are being used by using a gun that throws the liquid with a powerful mist. Mostly chlorinated solvents are being used which are the not very safe for breathing. We suggest as much precaution a printer may take by providing a recommended mask and a recommended ventilation system to avoid breathing any of these products mist. It is important to look at the weight of the spot remover gallon that should not be less than 10.5/lbs/gallon. If it is less than that, it means the formulation has something to make product less effective and cheaper. The price for a single gallon should not exceed to more than $26.00/ gallon.
It is also true that those printers producing high profits do not have to spend few hours in their busy schedule to locate and worry about comparing the cost of raw materials. The screen printers charge enough to offset the high cost that they are willing to let vendors press for higher prices based on the art of amiable persuasion, swaying and influencing the need to spend more money. We, at Xenon, were selling twenty drums of Diazo based emulsion to a Chinese supplier- after three years doing business with them raw material prices went up and we raised fifty cents a gallon. They fought like hell and we had to back off.
The Chinese phenomenon
The Chinese phenomenon of lower prices is not truly a marvel of the twentieth century, merely hidden in its cheap labor or the value of Yuan vs. dollar manipulation; though they contribute to cheaper prices to a great extent. What is of utmost magnitude is the mindset of Chinese business community, small or big, is to fight for every penny from their vendors. While we in America are more attuned to the personal relationships and complacency for the compromising cost negligence.
Once a company makes money, they lose focus on the bottom line, saving money from every possible avenue they can find. The existing sources must be pushed to bring down the cost of their products to the American printers. The American emulsion manufacturers sell their products lot cheaper in India and China. While the raw material, labor, and operating costs remain the same for both domestic and foreign customers, the Chinese and Indian are paying a lot less than for the same emulsion. The Indian and Chinese understand the emulsion as nothing more than PVA & PVAC; the American buyers are duped by the mystery and sweet words of the complexity and technology of the product.