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A Functional Family: Personalities of Direct Emulsions

(December 1999) posted on Tue Dec 14, 1999

A comparison of three direct emulsions


By Tina Scarpelli

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Selecting a direct emulsion used to be so simple. Ten years ago, only two kinds were available: solvent resistant and water resistant. With the exception of the few remaining bichromate-sensitized emulsions, all of them were sensitized with diazo. We made our selections from a menu of about 50 products and accepted their limitations. When exceptional quality was demanded, we treated ourselves to capillary film.

Today, all of that has changed as the market for screen-printed products continues to expand. Printers have demanded direct emulsions that print better, expose faster, and resist a wider variety of solvents and adverse shop conditions. As a result, the number of direct emulsions available in North America has climbed over the 100 mark, and the profile of the list illustrates a drastic change from those available in 1984. Diazo-sensitized emulsions are no longer the only game in town. They have been elbowed aside by two technologies: dual-cure emulsions and one-part photopolymer emulsions.

What are the differences among these types of direct emulsions, and which one should you use? To determine that, you need to learn the benefits and drawbacks to each. Tables 1, 2, and 3 below list the basic properties of the three most commonly used direct-emulsion systems for garment printing. With this information, you'll be able to select an appropriate emulsion for your applications--and you may find that you need to use more than one type depending on what you want to achieve. But before we get into stencil selection, let's look at the components that give these emulsions their personalities.

Table 1 Properties of Conventional Diazo-Sensitized Emulsions
Feature1
Conventional solvent-resistant emulsion
Solvent-resistant fast emulsion
Conventional water-resistant emulsion
Solvent resistance
XX
XX
Limited
Water resistance
XX
Humidity resistance
X
Fast exposure
XX
Wide exposure latitude
X
X
Image resolution
XX
X
Print definition
X
X
Reclaimability
X
X
X
Drying time
Stencil build
XX
XX Outstanding feature
X Secondary feature
1Relative to all other diazo emulsions listed

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