Stock material or miscellaneous articles – Composite – Of carbohydrate
Reexamination Certificate
2001-10-02
2004-08-17
Jones, Deborah (Department: 1773)
Stock material or miscellaneous articles
Composite
Of carbohydrate
C428S537100, C428S537500, C428S689000, C428S907000, C428S401000, C428S372000, C428S364000, C428S332000, C428S326000, C162S010000, C162S013000, C162S024000, C162S072000, C162S074000, C162S076000, C162S079000, C162S080000, C162S082000, C162S087000, C162S090000, C162S141000, C162S146000, C162S145000, C162S154000, C162S155000, C162S157100, C162S157200, C162S157600, C162S160000, C162S161000, C162S163000, C162S164100, C162S175000, C162S180000, C162S181100, C162S181200, C162S182000, C162S183000, C162S218000, C162S
Reexamination Certificate
active
06777103
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to cellulose fiber reinforced cement composite materials using biocide treated cellulose fibers, including fiber treatment methods, formulations, methods of manufacture and final products with improved material properties relating to the same.
2. Description of the Related Art
Ordinary Portland cement is the basis for many products used in building and construction, primarily concrete and steel reinforced concrete. Cement has the enormous advantage that it is a hydraulically settable binder, and after setting it is little affected by water, compared to gypsum, wood, wood particle boards, fiberboard, and other common materials used in building products. The high pH of cement usually provides cement products good resistances to the damages by biological attacks.
Asbestos Fiber Cement Technology
About 120 years ago, Ludwig Hatschek made the first asbestos reinforced cement products, using a paper-making sieve cylinder machine on which a very dilute slurry of asbestos fibers (up to about 10% by weight of solids) and ordinary Portland cement (about 90% or more) was dewatered, in films of about 0.3 mm, which were then wound up to a desired thickness (typically 6 mm) on a roll, and the resultant cylindrical sheet was cut and flattened to form a flat laminated sheet, which was cut into rectangular pieces of the desired size. These products were then air-cured in the normal cement curing method for about 28 days. The original use was as an artificial roofing slate.
For over 100 years, this form of fiber cement found extensive use, for roofing products, pipe products, and walling products, both external siding (planks and panels), and wet-area lining boards. Asbestos cement composite was also used in many applications requiring high fire resistance due to the great thermal stability of asbestos. The great advantage of all these products was that: they were relatively lightweight; water affected them relatively little, and they had a good resistance to biological damages, since the high-density asbestos/cement composite is of low porosity and permeability. Asbestos fiber cement composites also have pretty good biological resistance. The disadvantage of these products was that the high-density matrix did not allow nailing, and methods of fixing involved pre-drilled holes.
Although the original Hatschek process (a modified sieve cylinder paper making machine) dominated the bulk of asbestos cement products made, other processes were also used to make specialty products, such as thick sheets (for example, greater than 10 mm which required about 30 films). These used the same mixture of asbestos fibers and cement. Sometimes some process aid additives are applied in the processes such as extrusion, injection molding, and filter press or flow-on machines.
Two developments occurred around the middle of the last century that are of high significance to modern replacements of asbestos based cement composites. The first was that some manufacturers realized that the curing cycle could be considerably reduced, and cost could be lowered, by autoclaving the products. This allowed the replacement of much of the cement with fine ground silica, which reacted at autoclave temperatures with the excess lime in the cement to produce calcium silica hydrates similar to the normal cement matrix. Since silica, even when ground, is much cheaper than cement, and since the autoclave curing time is much less than the air cured curing time, this became a common, but by no means universal manufacturing method. A typical formulation would be 5-10% asbestos fibers, 30-50% cement, and 40-60% silica.
The second development was to replace some of the asbestos reinforcing fibers by cellulose fibers from wood or other raw materials. This was not widely adopted except for siding products and wet-area lining sheets. The great advantage of this development was that cellulose fibers are hollow and soft, and the resultant products could be nailed rather than by fixing through pre-drilled holes. The siding and lining products are used on vertical walls, which is a far less demanding environment than roofing. However, cellulose reinforced cement products are more susceptible to water induced damages and biological attacks, compared to asbestos cement composite materials. A typical formulation would be 3-4% cellulose, 4-6% asbestos, and either about 90% cement for air-cured products, or 30-50% cement, and 40-60% silica for autoclaved products.
Asbestos fibers had several advantages. The sieve cylinder machines require fibers that form a network to catch the solid cement (or silica) particles, which are much too small to catch on the sieve itself. Asbestos, although it is an inorganic fiber, can be “refined” into many small tendrils running off a main fiber. Asbestos fibers are strong, stiff, and bond very strongly with the cement matrix. They are stable at high temperatures. They are stable against alkali attack under autoclave conditions. Asbestos fibers are also biologically durable. Hence, asbestos reinforced fiber cement products are themselves strong, stiff (also brittle), and could be used in many hostile environments, except highly acidic environments where the cement itself is rapidly attacked chemically.
Alternative Fiber Cement Technologies
In the early 1980′s, the health hazards associated with mining, or being exposed to and inhaling, asbestos fibers started to become a major health concern. Manufacturers of asbestos cement products in the USA, some of Western Europe, and Australia/New Zealand in particular, sought to find a substitute for asbestos fibers for the reinforcement of building and construction products, made on their installed manufacturing base, primarily Hatschek machines. Over a period of twenty years, two viable alternative technologies have emerged, although neither of these has been successful in the fall range of asbestos applications.
In Western Europe, the most successful replacement for asbestos has been a combination of PVA fibers (about 2%) and cellulose fibers (about 5%) with primarily cement, about 80%. Sometimes the formulation contains 10-30% inert fillers such as silica or limestone. This product is air-cured, since PVA fibers are, in general, not autoclave stable. It is generally made on a Hatschek machine, followed by a pressing step using a hydraulic press. This compresses the cellulose fibers, and reduces the porosity of the matrix. Since PVA fibers can't be refined while cellulose can be, in this Western European technology the cellulose fiber functions as a process aid to form the network on the sieve that catches the solid particles in the dewatering step. This product has reasonably good biological durability due to its high density and non-biological degradable PVA fiber. The major application is for roofing (slates and corrugates). It is usually (but not always) covered with thick organic coatings. The great disadvantage of these products is a very large increase in material and manufacturing process costs. While cellulose is currently a little more than asbestos of $500 a ton, PVA is about $4000 a ton. Thick organic coatings are also expensive, and the hydraulic pressing is a high cost manufacture step.
In Australia/New Zealand and the USA, the most successful replacement for asbestos has been unbleached cellulose fibers, with about 35% cement, and about 55% fine ground silica, such as described in Australian Patent No. 515151 and U.S. Pat. No. 6,030,447, the entirety of which is hereby incorporated by reference. This product is autoclave cured, as cellulose is fairly stable in autoclaving. It is generally made on a Hatschek machine, and it is not usually pressed. The products are generally for siding (panels and planks), and vertical or horizontal tile backer wet area linings, and as eaves and soffits in-fill panels. The great advantage of these products is that they are very workable, even compared to the asbestos based products, and they are low cost.
However, cellulose fiber cement materials
Luo Caidian
Merkley Donald J.
Boss Wendy
James Hardie Research Pty Limited
Jones Deborah
Knobbe Martens Olson & Bear LLP
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