Whether thermoforming prelaminated vinyl/plastic sheeting into simple pan faces or raised letters each aspect of fabrication from material dehydration and lamination to releasing the formed piece is critical to the success of the finished sign.
For successful thermoforming, the following factors must be considered:
Remove protective masking from the surface to receive vinyl and predry all acrylic and polycarbonate sheets prior to lamination of film. Predrying prevents bubbling during the forming cycle. Predrying is more critical to forming success when working with vinyl laminated plastic sheet than with sheet alone – especially for polycarbonate signfaces.
Oven drying of suspended and separated sheets at approximately 200°F (93°C) for six hours. The simplest method is to load the drying ovens at the end of the workday for the following days fabrication. This allows the use of lower temperatures, down to 180°F (82°C) and more than enough time for adequate ventilation. For example, 6 hrs at 200°F is minimum drying time for .080 in. thickness, according to a major polycarbonate fabrication guideline.
Alternate method: (adequate for thin gauge acrylic sheeting)
1.2 Quick dry suspended and separated sheets at 230°F (109°C) for 30 minutes.
1.3 Slow dry sheets by removing masking and putting in a warm/dry area of the shop for 24 hours.
Note: Once the sheet has been dried it should be further processed within 12 hours of being removed from dryer.
Although lamination may be wet or dry, wet lamination, can lead to problems with bubbles and cracking of film if all the surface water is not squeegeed away and dried before heating and forming.
When applying full sheets of uncut film with a mechanical laminator use the highest practical laminating pressure at throughput speed of about 30’/min. (10m/min).
This method is used when lamination is done by hand, either as background color or at the point of multicolor registration of cut graphics.
Use only proven application fluids such as Rapid Tac, Splash, or the following mix of water, clear unscented liquid detergent and alcohol: 20 oz. and 1/2 tsp. respectively
If the vinyl has been dry laminated no dwell time or additional dehydration is needed prior to forming.
If wet laminated, all residual surface moisture must be removed prior to the thermoforming process. Temperature and time needed to dry the laminate vary according to facility and can range from 24 hours at room temperature to as little as 2 hours at 210°F (96°C). As with the initial dehydration step it is important to separate the sheets for best ventilation and fastest drying and least chance of “mark-off”.
Prior to forming it is important to store the sheets in such a way that they are uniformly warm and dry. Warm sheets going to the thermoformer will process faster and more consistently than if taken from cold or moist environments. The best possible practice is to store sheets in drying ovens or other options include racks along walls free from direct contact with the ground moisture.
For extremely thick polycarbonate materials that demand high forming temperature, a modification of standard technique is needed. Rather than bring a bare sheet immediately to its closest position relative to heating elements it is better to bring the laminated construction toward the heat source in two stages. For example; if the distance for successfully forming unlaminated sheet is 6.5 inches (17cm) from the heat elements and the dwell is 7 minutes but excessive staining or bubbling is observed in a finished sign made from a laminated construction a good solution is to lengthen the distance and time, i.e. 12 inches (30 cm) from elements for 3 minutes, 6.5 inches (17cm) inches for 5 minutes.
The tooling and design used for forming a laminated piece is only successful where the vinyl does not come in contact with the mold.
If one tries to mold vinyl against the mold face a variety of problems develop.
Mold depth and consequent distortion and stretching of translucent film should be kept in mind while designing draw distance, corner radius, wall relief and draft angle.
The film may be drawn over mold depths of 4 inches (10 cm) providing the sheeting stretches uniformly. Corners should be radiused generously to avoid “bright spots” at the outer corners and angles.
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