Screen Printing Blog » UV

How Long Do I Expose My Screen For?

steve — Wed, 18 Nov 2009 00:36:03 +0000

This is a question I get a lot. Any my answer is, That depends. Many things factor into the equation of how long to expose the screen for like, screen mesh, type and age of emulsion, type of lamps in the exposure unit, how old that lamps are, and the list goes on. So what to do? You need to do a step wedge test. A step wedge test is basicaly exposing the screen for a few different times and seeing which time produced the best image on wash out. There are a few ways to do this test. The expensive way is to buy a test strip for $30 bucks which is a piece of transparency that has a gradient of darker shades. The benefit of this test is you only have to expose once and the strip lets different levels of light hit the screen.

The cheap way to do a test wedge. Take construction paper and do 4-5 different exposures. Move the paper to expose more of the image each time. At the end you will have 4-5 different exposure times. Just pick the one that washes out the best and there ya go.

10 Tips For Applying Emulsion On A Screen

steve — Mon, 19 Jan 2009 22:53:10 +0000

When you grab your scoop coater your mission is to create a gasket in which ink will pass through the screen and create a clean crisp image on your t-shirt. many people over look the basics and the output shows it. The reason we coat the screen is two fold. Number one is we want to create a coating that will block the ink so it doesn’t go through where we don’t want it to. Second, we want to have crisp lines around the art work.

A lot of screen printers don’t follow the basics and create allot of grief for themselves including pin holes and emulsion breaking down during the print run. Sure, they are coating screens and getting by but, they could be producing better screens in a much more efficient way. I have put together 10 points to remember when coating your screens for screen printing.

Make sure you are using the right screen for the type of ink you are using and the item you are printing on.
The screen tension is tight. Tight screens will give you better prints and constancy.
Degrease the screens with “Simple Green” or a similar degreaser.
make sure the screen is completely dry prior to coating.
Mix your emulsion 2 hours prior to coating you screen. This will let air bubbles bleed out so you don’t get pin holes.
Use the sharp edge of your scoop coater.
Coat the t-shirt side of the screen first and then the squeegee side.
Do one coat on each side. Some people have other methods which involve more coats but this is what I do.
Dry your screen t-shirt side down.
make sure your screen is completely dry before you start printing.

I hope these tips help. I didn’t go into much detail here but I may break them out in more detail in future posts.

as always, if you don’t have the book “How to Print T-Shirts for Fun and Profit! By: Scott Fresener” you should pick it up.

Have Fun..

Steve

Exposure Unit F20T12-BL UV Lamps

steve — Thu, 15 Jan 2009 01:48:24 +0000

Exposure Unit Lamps Lit

I have gotten many emails about the lamps used in my home built exposure unit. I should probably write up a FAQ some day. Anyways, the lamps are a special unfiltered black light. The designation is F20T12-BL. These lamps don’t block UV rays like the ones you buy in the store. The emulsion you coat your screens with is sensitive to UV. When the emulsion is exposed to UV it will cure or harden. The art work blocks the UV and that area will wash out. That is the reason you need a good black art image in order to block the UV entirely.

The black lights you buy at the Walmart, filter the UV out. The UV is what we need to expose our screens so you you would end up with your image washing out.

I have heard of people using plant grow lights sold in the garden department. They will have a lower uv level and I don’t know how they will work.

So, to get the good lamps, you need to goto the local lighting supply or check out: http://www.1000bulbs.com/F20T12/1246/