Eight Ways to Build a Better Process
Davis presents eight ways to build a better textile-printing operation, including a standardized procedure that ensures consistent quality from production run to production run.
As another year comes to an end, I would like to summarize my thoughts on achieving consistent quality control through process standardization. The greatest challenge in developing standardized procedures is that once the standards are established, you must maintain those procedures so that the quality-control process is ongoing and does not fall by the wayside. It is easy to allow standardized procedures to slip, and if they do, you'll inevitability see a decrease or loss of quality.
A well-known Wonder Bread ad campaign once told us that the bread would "build better bodies, eight ways." This month, I present eight ways for building a better textile-printing operation. The following suggestions form a totally standardized procedure that ensures consistent quality from production run to production run.
1. Stencil reclaiming
Maintaining a standardized procedure in screen reclaiming--a work area that is inherently wet and messy--is no easy task. The point that some overlook is that while reclaiming is one of the most rudimentary and basic procedures, it has enormous impact on the overall productivity and quality delivered by your facility. To ensure consistent quality in screen reclaiming, do the following:
First, make sure to use at least a 2000- to 2500-psi pressure washer, which will extract residue from between the knuckles of the mesh (the residue can create "ghost" images). Using the correct washing technique in conjunction with the correct screen tension and exposure often eliminates the need for ghost or haze removers. Insufficient tension requires more squeegee pressure, which puts wear and tear on the screen, making it harder to reclaim. Also, underexposed stencils like to fuse with ink and then refuse to be reclaimed.
The second tip involves technique. Many screen breakdowns and pinholes occur due to poor washing and rinsing procedures. Screenroom personnel must reclaim screens in a slow and methodical manner to ensure that the most possible residue is removed.
In addition, make sure that the frame also has been thoroughly rinsed to prevent residual chemicals from contaminating the image area of the screen. Slacking off on that procedure can lead to horrific loss of production time and have a negative impact on quality. A screen is not properly reclaimed until all traces of the stencil and cleaning chemicals have been removed.
2. Stencil-coating consistency
With the drive for increased production efficiency and the popularity of specialty applications, such as high-density printing, the need for consistent and uniform stencil thickness has become more critical than ever. As printers attempt to print smaller and smaller degrees of detail and extreme levels of acutance, it's more important than ever to produce uniform and consistent stencils from screen to screen and job to job, regardless of the mesh count. For this reason, many larger shops have invested in automatic coating machines, which offer more control than manual emulsion coating.
3. Screen tension
Of all the procedures in the facility that impact quality, none is as crucial as the ability to deliver consistent and adequate screen tensions. Virtually every aspect of print quality is determined by the tension of the screen, including the following characteristics: hand (softness) of the print, total ink-film thickness, opacity, resolution, saturation of process-color prints, and registration accuracy.
Besides influencing what you see in the print, screen tension also affects how you set other processing parameters, such as squeegee speed, pressure, and angle, as well as off-contact distance. These settings influence both print quality and production speed.
The key is to establish the minimum requirements that meet your quality standards. Document your tensioning (and retensioning) procedures, then make sure these standards are always applied. Every screen that goes to press should be in "new screen condition" if your procedures have been followed correctly.
4. Flashing temperature
As I have mentioned on many occasions, printers have a "more is better" mentality. This is why many do not study and standardize their flashing procedures, but simply run their flash units as hot as possible in the name of productivity.
When printing with higher screen tensions and thinner ink-film thicknesses, the need for higher flashing temperatures diminishes. The problems that are caused by excessive temperatures include scorched fabric, ink blistering, dye sublimation on synthetics, poor intercoat adhesion between different ink colors, and remelting of ink films.
I have seen flash units with digital controls set as low as 450°F (230°C)--1/3 of the unit's output limit--that still gel printed ink properly. By standardizing flashing procedures to run cooler rather than hotter, you can minimize the occurrence of troublesome variables associated with higher temperatures.
5. White-ink usage
Although most printers like to find one all-purpose white product and apply it in all applications, this approach may not always be the best if you print on multiple fabric types. Few textile screen-printing shops print only one type of fabric.
The best option to avoid being limited by a single white ink is to standardize your whites to include only two products: one white with bleed-resistant qualities for synthetic fabrics, such as 50/50 cotton-poly blends, and another standard white for 100%-cotton garments.
The need for bleed-resistant white on synthetics is a subject that's been covered extensively in this and other industry journals. But you should avoid using bleed-resistant whites on 100% cotton because the dye-blocking agents in the ink may lead to the formation of residual images on the unprinted side of the garment--some cotton dyes are sensitive to those dye-blocking agents.
6. Squeegee profiles
When it comes to squeegee edges, there is more than one school of thought. Some believe that the squeegee should be razor sharp, and others believe that you should have one edge for fine mesh counts and one for coarser mesh counts. I happen to subscribe to the latter school. Inks requiring coarser mesh counts such as puffs and high-density inks need a slightly rounded squeegee edge to help minimize any potential over shearing that may occur with a squeegee that is too sharp.
7. Wash-test procedures
In the past, I have discussed different means for determining the level of cure on your prints. My enduring viewpoint is that the best way to judge cure is the same way the consumer judges it--by washing the garment. On each job you produce, set aside at least one garment and wash it 3-5 times. If the print survives, then you know you've achieved a successful cure. The results of each wash test should be documented and filed along with the printing parameters and dryer settings to ensure that the process can be repeated (or avoided).
8. Process documentation
As any experienced printer knows, you can't over-document the procedures you use to deliver a quality product. In order to properly reproduce prints from one production run to the next, you must be able to achieve identical results time and time again. And very few printers can get those repeatable results by reconstructing a successful job from memory. That is why proper documentation is critical. The main job parameters you should document include number of colors, screen (color) order, mesh parameters (thread counts/diameter, weave, color), mesh-tension levels, ink-mixing formulas, squeegee durometer and edge profile, settings for flash curing, and dryer settings
Variations in any one of these variables can throw a wrench into the works and adversely affect the quality of the finished product. Documenting procedures is a repetitive and mundane task that is easily overlooked during hectic times on the production floor. So make sure your employees understand that proper documentation at each step of the production process is as important as meeting the customer's deadline.
Standardizing each of your production procedures is a necessity if you want to achieve proper and repeatable control of the variables inherent in textile screen printing. Set your standards in stone, and establish a record-keeping procedure that forces employees to use and maintain the standards. Once standardized procedures become second nature to your staff, the ability to deliver high-quality products will, too.