Coating processes – With post-treatment of coating or coating material – Solid treating member or material contacts coating
Patent
1998-11-05
2000-12-05
Beck, Shrive
Coating processes
With post-treatment of coating or coating material
Solid treating member or material contacts coating
427359, 427363, 427365, 162199, 162179, 162 206, 1621647, B05D 312
Patent
active
061563870
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the improvement in thermomechanical surface treatment of flat webs of material, particularly paper and carton webs, by using agents which reduce or even prevent adhesion between the flat web of material and the surface of the tool, e.g., a roll, used in said thermomechanical surface treatment (so-called abhesive agents).
In the production process of special grades of paper and carton, the processes for thermomechanical surface treatment represent the final processing stage wherein the properties of the material web can be modified substantially and adjusted to the requirements of use. The catalog of requirements to be met by the types of paper and carton is diverse, including properties such as permeability, ink absorption, printability and/or special barrier properties, e.g., against solvent-containing or aqueous coatings, which in turn are influenced by paper properties such as micro- and macro-roughness, porosity, absorbency, picking and abrasion resistance, and absence of dust. Many of these characteristic properties affecting the surface are in close relationship to the local distribution of moisture and raw density.
All of the processes for thermomechanical surface forming of flat webs of material, particularly paper and carton, are based on the functional principle of simultaneous or directly successive action of heat and pressure on the flat material to be formed as the web passes between two or more rolls different in surface characteristics, hardness and flexibility. Frequently, such thermomechanical surface treatment is preceded by a wet pretreatment of the web to be formed, where the pre-moistening may be effected using water or steam. To this end, smoothers, glazing calenders, hot calenders, smoothing rolls, soft calenders and similar devices are used depending on the type of paper or carton grade, the required surface finish and production rate.
However, the well-known processes for thermomechanical surface treatment involve substantial drawbacks arising due to the fact that components of the material to be treated reach their melting and/or softening temperatures when the material is heated to elevated temperature. This results in partial or complete sticking of the material webs to the surface of the above-mentioned equipment, e.g., rolls, by adhesion so that it is not possible to utilize the attainable equipment conditions, e.g., with respect to heat supply and production rate, for an efficient flow of production.
In particular, these drawbacks arise in the production of coated papers having a high percentage of latex in the pigment coating, with surface-sized or coated papers containing water- and/or heat-sensitive binders, and with latex-reinforced, latex-impregnated or latex-coated special papers containing synthetic fibers, where disturbances in the course of production of the type indicated above occur at a specific temperature and/or flow rate.
The use of agents for reducing the adhesive forces between adjacent surfaces (so-called abhesive agents) is well-known. For this purpose, silicones, oil-in-water emulsions, metal soaps, waxes and particularly paraffins and talc are employed. In addition to these materials, film-forming tetrafluoroethylene polymers are employed as antiblocking agents in the processing of thermoplastics. The use of release emulsions based on oil-in-water emulsions made of self-emulsifying fatty acid mono- and triglycerides is familiar in the food industry.
According to EP 0 478 177 A1, and in accordance with this situation, anionic co-emulsions of carnauba wax and paraffin wax are used as antiblocking agents in carton production.
The abhesive agents mentioned so far are not suited for the thermomechanical surface treatment because they either have insufficient effectiveness or cannot be used in accordance with the process, e.g., without affecting the desired surface quality of the products.
The patent specification DE 43 01 677 C2 suggests the use of specific ethylene/acrylic ester copolymerizates in order to improve the printability of
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Reinhardt Bernd
Werres Joachim
Beck Shrive
Kaemmerer GmbH
Kolb Jennifer
Stockhausen GmbH & Co. KG
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