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The use of Sappi Warren Release Papers in the production of coated fabrics, often referred to as synthetic leather, dates back to the 1940’s. A casting line does not rely on pressure or compressive forces to mechanically emboss a texture. The process of casting can be most easily described as a molding process, where the release paper is the mold from which the synthetic leather acquires its aesthetic qualities of texture and gloss. The release paper also acts as the carrier onto which liquid plastic resin coatings are applied and transported through the long hot curing ovens of the typical casting line.
Sappi Warren release papers are provided in roll format, approximately 500 kg (1800 meters). The release paper is unwound from large spools and the first coating is applied, Section A in Figure 1. This first coating is most often referred to as the “skin” and is typically between 25 – 200 microns thick. Often, a 2nd skin coating, (not shown in diagram) is applied to impart other properties to the synthetic leather such as strength, bulk, and / or to add a 2nd color for a two-toned color effect. After application of the skin(s), the web enters a series of thermal ovens in order cure the resin. Once cured, the skins are now considered “cast”.
In most cases, a textile, non-woven substrate or split leather is laminated to the back of the cured plastic skins. This too involves a coating step – this time with an adhesive material, to bond the supporting substrate to the cast material forming the coated fabric, Section B in Figure 1.
Lastly, the coated fabric is released from the release paper web in a zone referred to as the stripping station, Section C in Figure 1. The coated fabric and release paper are rewound as separate rolls. The release paper roll can then be returned to the beginning of the casting line for repeat usage.
And that is, in simple terms, how release paper is used to make synthetic leather!