Printwear

2014 Resource Directory

For the Business of Apparel Decorating

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20 1 4 M i d - M a rc h Printwear | 25 24 | Printwear M i d - M a rc h 20 1 4 and repeat, sliding back the poster board one inch at a time, and expose each section for an additional minute. The end result with the step wedge test is a screen exposure representing five different exposure times. The filter type exposure calculator is a film positive comprising multiple columns, each with a resolution target, a set of half-tone tints, and lines of text. Each column is marked with a factor number and four columns are backed with gray neutral filters of different densities to allow light to pass through at different UV strengths. To use this device, the screen maker exposes and washes out the screen and examines each column on the test positive, then identifies the column that yields the best exposure. The next step is to multiply the total exposure time by the factor listed on the selected column to come up with the optimal exposure time. No matter which tools you select to use, or whether you buy pre-stretched frames or stretch your own frames in-house, it's important to have an understanding of the science behind screen-prep to help you gain control over your entire printing process. Frame tyPes: a Quick reFerence Wood Frames are still widely used in the screen-printing industry and are typically found in smaller to mid-sized shops that prefer less expensive frames for the type of work they are doing. When shopping for wood frames, make sure to pick a manufacturer that uses high-quality wood, mortise and tenon joints, and lacquer- coated wood to resist water. Static Aluminum Frames are popular in textile screen print shops and are considered an upgrade from wood frames, since aluminum frames are ridged, lightweight and impervious to reclaiming chemicals. The frames also don't warp due to over-exposure to moisture. Aluminum frames stretched with low elongation (LE) mesh can be purchased pre-stretched at 20 N/ cm and above. Square Retentionable Frames feature a groove in the sidebars where the mesh is locked in with plastic locking strips. The whole frame expands outward in all directions to provide the tensioning of the fabric. Fabric panels are also available for square retensionable frames. Roller Retensionable Frames are good for achieving high-tension screens for simulated process printing on dark garments and for everyday print runs. Roller frames have recently become easier to stretch with the introduction of pre-made mesh panels that snap into the side roller bars to allow the screen to be stretched in just minutes. Draw Bar Frames have been used for decades in the large format and electronics printing fields. The draw bar frame features a series of side bar mesh attachment strips that allow the screen to be tensioned uniformly in each quadrant of the print area. How To... PrePare a screen pw Every screen print shop needs to have an exposure calculator to determine the optimum expo- sure time for the emulsion, mesh and stencil materials that are being used in the shop. it is neces- sary to closely inspect the exposure calculator on screen, just as it is to check each screen once the proper exposure has been calculated. PW_MidMarch14.indd 24 3/3/14 12:51 PM

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