Whitening on the corners of 3D Laminate thermofoil doors
There are many different tips and tricks to pressing. Often I am asked for formulas however I often find that each company may require different settings based upon the material they are pressing, the profiles, glue type, stage height and so on. One common issue that all companies have or will eventually face are whitening on the corners.
There are many misconceptions about what causes whitening on the corners and typically the laminate is blamed for the issue. Although the laminate can be a reason it is not necessarily the culprit. Read more to delve into the issues and the solutions on whitened corners on the doors.
First I'd like to separate lightening from whitening. I define lightened corners as separations between the print layer and the base film layer and whitened corners as separations between the top cap and the print layer. When you see a corner that is lightened it is typically revealing the base layer of the foil. One over generalization is that a lighter backer of the foil is the issue. When thermofoils are produced typically the lighter backer is used as the base tone of the design. Quality manufacturers have dozens of backers whereas a low end manufacturer may have only a few bases to choose or may use a white backer on a dark woodgrain for example. But most common you will find mustard , almond or chocolate backers on most woodgrains and if any foil is over formed it will reveal the base layer and therefore have whitened or lightened corners.
Another common mistake is that you can bend a sample and when it whitens that is evidence that the material will whiten when pressing. When you bend a thermofoil sample and it whitens it typically is forcing the top layer away from the base layer and this is very common among quality manufacturers and will not necessarily cause whitening on the edges when pressing. It in fact shows how they produce their film in respect to the printing layers whether direct printed, reverse printed or at what temperature the material was laminated at. In fact, many high end manufacturers darker colors will whiten when you bend them. So if a sales person grins and bends his sample to show that it doesn't whiten they are trying to show their product is of a higher quality but it is really just a bi-product of how they produce their product or may even show that their company doesn't even have the capability to produce by direct print with a finished top cap. They may actually be showing a weakness of their product and not even knowing it. By bending a sample it will not necessarily stop whitening on the corners when membrane pressing. In the application of miter folding PVC bending the sample does in fact have a direct correlation to whitening issues because the part will be bent at a lower temp whereas in membrane pressing the part is formed at full temp.
Want to know how to tell the difference between a top cap separation and a print layer separation?.... The key way to tell is if your parts lighten to a clear or bluish edge or if they whitened to the color of the base of the film. If they whiten to the base of the film then its not caused by the top layer separating. If the corner of the door is in fact bluish or clear in tone you can test it by rubbing it with a block of wood or flaring it with a heat gun. In a miter folding application of a thermofoil a wooden block or heat gun can be used to reseal the top cap to the whitened area. In a membrane pressing application the key will typically be to use a higher heat so that it soaks through the foil and does not cause a separation between a top cap and a print layer.
The most common problem with lightened corners are caused by either too much or too little heat. With too much heat you will over stretch the material and will typically find the outer doors that do not have jigs or are not on the edge of the table. The material is heated up too high and then there is no jig or tray filler to capture material and then the laminate may get over stretched on the corners. A simple solution is to put a jig / tray filler close to the edge.
Another common problem with lightened corners are caused by too little heat. When the material is too soft or has cold spots on the table the material can separate on the print in the areas where it is being stretched the most which is typically the edge or corners of the doors. You can put a heat strip in various places on the press to find any cold or hot spots in your table.
For darker colors such as a Wenge which has ticking you may also find that these darker colors are more likely to have too much heat applied to fast. What I mean is that the dark woodgrains are likely to absorb heat faster than a lighter woodgrain and especially when using bulb heating elements. In addition if the foil has aggressive ticking you may find that these deep ticks become separation starters. So the material pulls apart faster between the ticks. The solution for this is to move a jig / table filler closer to that edge and it should solve the problem right away.
In general most press operators think in terms of board feed rate in their saws or imput data into the press machine but we often have to think of membrane pressing as more of an art. To recap,
1. Whitened corners can be due to the material being too hot. Solution: Put fillers closer to the edge of the part
2. Whitened corners can be due to the material being too cold. Solution: Increase the preheat by 10%. Be sure to use heat strips to ascertain this
3. Dark woodgrains or items with deep texture can whiten easier. Solution: Put fillers closer to the edge of the part
I hope that you find this post helpful and if you would like to add any tips or points please feel free to send me an email.
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