Coating processes – Vacuum utilized prior to or during coating – Organic base
Patent
1984-07-09
1986-08-19
Lusignan, Michael R.
Coating processes
Vacuum utilized prior to or during coating
Organic base
427350, 427369, B05D 312
Patent
active
046069445
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to a foam treatment process for sheet materials and has particular reference to a process for reducing the water content of such sheet material.
Ways to reduce the water content of sheet material such as textile sheet material, are well known. The most widely used and oldest known method involves squeezing the sheet material between a pair or several pairs of mangle rollers. While certain constructions of mangles enable the water content to be reduced to low levels (e.g. 40 to 60% depending on the material to be treated), mangle-type equipment has several disadvantages. The higher the nip pressure the better are the mangling effects, but, of course, the deformation of the substrate by the nip pressure becomes more pronounced.
Another drawback of the mangle principle is the lack of a simple, easily predictable correlation between nip pressure and the extraction effect. Using water content measuring instrument feedback to control and predetermine water retention levels is thus very difficult.
Another method frequently used is the vacuum extraction of water from textile sheet material. While it is possible to remove a certain amount of the water present in the interstices of the material, the friction between the vacuum slot and the moving sheet presents problems, particularly at high speeds, since adequate sealing become very difficult. Energy input thus may be too high in relation to the effects obtained (this is particularly true for all high speed operations).
Another method recommended for the removal of water from air permeable substrates is the blowing of air at very high air speeds against the surface of the moving sheet, usually at an angle of about 90.degree. to the plane of the sheet. Energy input again is very substantial, and results vary greatly with the construction of the substrate (tightly woven/open weaves
onwovens, etc.) while support of the sheet at a low level of friction may present serious problems, particularly in the case of webs having a low cohesive strength.
All these known treatments which precede the final drying step are aimed at reducing the level of residual water prior to drying to lower the energy input required to remove the water still present at a given dryer speed, and/or to increase the speed of the dryer and/or lower the drying temperature.
U.S. Pat. No. 4,062,721 describes and claims a method for removing water from a wet fibrous sheet comprising the steps of mixing an aqueous slurry comprising mineral and binder, depositing said aqueous slurry on a wire mesh to form a wet sheet, adding a surfactant foaming agent to the slurry, said step of adding said surfactant foaming agent being performed at substantially the time that said slurry is deposited on said wire mesh whereby essentially no internal foam is present in said wet sheet at the time of depositing, draining water from said wet sheet through said wire mesh, said drainage being aided by the force of gravity and draining additional water from said wet sheet through said wire mesh, said additional drainage being aided by air pressure differential created across the wet sheet whereby foam is generated within the wet sheet due to the passage of air therethrough.
This specification is concerned the production of fire retardant felted mineral fibre panels and it is a feature of the invention that the generation of a foam should be confined to within the felted material itself. U.S. Pat. No. 4,062,721 teaches with considerable emphasis, the importance of avoiding substantial foaming until the wet sheet is juxtaposed the air pressure differential created across the sheet.
We have found that if an air permeable sheet material is treated with a foam containing an agent capable of reducing the surface tension of the foamed liquid, then improved permeation by the air/liquifying of the air permeable sheet material, can be effected.
According to the present invention, therefore, there is provided
a process for treating an air permeable sheet material for which process comprises:
applying f
REFERENCES:
patent: 4062721 (1977-12-01), Guyer et al.
patent: 4118526 (1978-10-01), Gregorian et al.
patent: 4365968 (1982-12-01), Gregorian et al.
Adnovum AG
Lusignan Michael R.
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