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What makes a good metallizing substrate? Part 1
January 12, 2008
There are many parts to making a great metallizing substrate, some seem obvious such as a glossy surface to make it bright and reflective (if that is what you want) or the surface texture that will give it the look you want (brushed or patterned) such as a hologram.
However, in my opinion, the most important part of a great metallizing substrate is its ability to wind a great roll in the absence of air during the vacuum-deposition process. If you cannot make a usable roll without damaging the film by winding, then you have nothing to sell. Winding a great roll is accomplished by formulating the film for winding which involves the addition of particles to a film surface to control the film-to-film spacing in the roll. Now, if the particles are added to the surface onto which the metal is to be deposited, it will create pinholes in the metal surface or areas of thin metal deposition because of the shadowing which might occur due to the particle on the surface. If this happens, then the moisture and gas barrier will be damaged. Therefore, it is customary to keep the metallizing surface free of particles. The particles are therefore added to the side opposite of the metal layer.
The purpose of the particles is to space the film layers apart to replace the air which is missing in the metallizing chamber. The size and type of particle has a large impact on the effectiveness of the winding effect. The particles have to create bumps on the film surface and decrease the film surface contact to surfaces over which they move (decreasing COF). Some particles are covered by the polymer, and some are not covered and can come loose on the film surface. The type of particle or its surface chemistry will affect this behavior as will its shape. In general, the best particles are spherical with a narrow size distribution.
Indeed, if the particles are chosen to create bumps which are larger than the air layer which would be trapped by the winding tension, then the film will wind well in air as well. I term this "formulating for winding," and in my estimation it is more important than almost anything else. When we control the film-to-film spacing, we are in effect controlling the density of the roll. I will speak more of this in the future. To control cost and to improve the effectiveness of the particles, they are best place on the surface of the film in a coextruded layer. Here the thickness of the layer relative to the particle size will also impact the effectiveness of the particles. More to come on this as well.
Posted by Eldridge M. Mount on January 12, 2008 | Comments (0)