Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2001-03-16
2004-06-01
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S183000, C162S184000, C252S380000, C252S384000, C422S040000, C427S439000
Reexamination Certificate
active
06743336
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the preservation of objects that contain cellulose-type materials, in particular, to a product, in the form of a solution, for de-acidification of cellulose-type materials composed of carbonated magnesium di-n-propylate, n-propanol and a hydrofluorocarbon diluent.
BACKGROUND OF THE INVENTION
There is a lot of concern for the deterioration undergone by cellulose-type materials (books, documents, maps, press, magazines and tissues) held in libraries, newspaper archives, museums and archives. This deterioration endangers the physical integrity of many documents, books and tissues and thus forces a restriction in access and handling thereof. The most significant cause of deterioration in cellulose-type materials is hydrolysis catalyzed by acids in the cellulose, giving rise to a shortening of the polymeric chains of the cellulose, which, in turn, leads to a weakening of the cellulose fibers and they become more fragile. Many factors contribute to the acidification of cellulose-type materials. For example, acidic gases present in contaminated air, the use of alum and colophony (abietic acid) in paper production, products for oxidative degradation of cellulose, inks and other substances that oxidize cellulose which are present in paper and books.
A great deal of effort has been put in to the development of processes to achieve de-acidification of cellulose-type materials and thus to prolong their useful life by stopping acidic hydrolysis degradation processes. Specific compositions and products have been studied for de-acidification, capable of neutralizing the acid present in cellulose-type materials and introducing an alkaline reserve, which inhibits re-acidification. Technology has moved on from expensive craft methods using aqueous medium to the development of methods for applying alkaline reagents, dissolved in non-aqueous vehicles, either in liquid or solid state, to prevent books from falling apart.
The North American patent U.S. Pat. No. 3,676,182 (R. D. Smith, 11th Jul. 1972) relates to a procedure for non-aqueous de-acidification of paper using magnesium methoxide, dissolved in methanol to a concentration lying between 5% and 11%, as the de-acidifying agent. The resulting solution can be diluted with a chlorofluorocarbon (CFC) diluent, such as trichlorofluoromethane or dichlorodifluoromethane, until a liquid is formed, under pressure, that contains between 1% and 2% of the de-acidifying agent. The CFC compound quickly evaporates from paper impregnated with the de-acidifying solution containing methanol, thus minimizing the solvent effect of methanol on certain inks. The books and papers can be treated by immersion in the de-acidifying solution, or the solution can be applied with a brush or using a spray. Nevertheless, this method is not free from drawbacks as the magnesium methoxide is extremely sensitive to water. So much so that even traces of moisture lead to immediate hydrolysis forming a gelatinous precipitate of magnesium hydroxide. This is insoluble in water and many organic solvents. Unless the paper has been sufficiently desiccated before treatment premature hydrolysis of the magnesium methoxide may occur, leading to the formation of unwanted white marks of powdered magnesium hydroxide on the surface of the paper, giving the paper a rough feel. On the other hand, the spray nozzles frequently become blocked and the brush bristles become caked, making it necessary to clean them and then dry them thoroughly before using them again.
The North American Patent U.S. Pat. No. 3,939,091 (Kelly, G. B., 7th Feb. 1976) discloses and claims a product for the de-acidification of paper that overcomes the problems of previous de-acidification solutions based on magnesium methoxide dissolved in CFC. The magnesium methoxide dissolved in methanol or in a methanol and trichlorotrifluoroethane (Freon® F7) mixture is reacted with gaseous carbon dioxide to obtained a colourless 20% solution of methoxymagnesium methylcarbonate. The resulting solution is more tolerant of water than the magnesium methoxide solutions, and obstructions are not produced in the spray nozzles as often as before.
The Canadian patent CA 1.147.510 (Smith, R. D., 7th of Jun. 1983) discloses a method for the production of methoxymagnesium methylcarbonate. Metallic magnesium is allowed to completely react with methanol to form magnesium methoxide. This is then re-dissolved in methanol saturated with carbon dioxide forming a methoxymagnesium methycarbonate solution. This solution is diluted with trichlorotrifluoro-ethane or with dichlorodifluoromethane. The diluted solution is sprayed onto the paper to be de-acidified. As an alternative, the paper can be submerged in the same solution, with the liquid state being maintained under pressure.
The North American patent U.S. Pat. No. 4,860,685 (Smith, R. D., 29th of Aug. 1989) and the corresponding Canadian patent CA 1.272.018 (31st of Jul. 1990) describe a flexible spraying system for the de-acidification of cellulose-type materials. A de-acidifying agent, preferable an alkoxide of magnesium carbonate, is combined with a CFC diluent, preferably trichlorotrifluoroethane, and with a propellant gas, preferably dichlorodifluoromethane. Additional pressurization and propulsion can be achieved using an inert gas such as nitrogen. The carbonated magnesium alkoxide, such as methoxymagnesium methylcarbonate or ethoxymagnesium ethylcarbonate, is produced by dissolving the corresponding magnesium alkoxide in alcohol in the presence of carbon dioxide.
The procedures described above use CFCs as these are essentially non-reactive and so do not imply a direct toxic risk for living beings. However, these same properties of chemical inertness that the CFCs possess make them problematic in the stratosphere. It has been demonstrated that the CFCs are the main factor responsible for the destruction of the stratospheric ozone layer and that they contribute to the greenhouse effect in the troposphere. The problem revolves around the chlorine that is liberated when the CFCs are exposed to ultraviolet radiation and other more penetrating radiations in the stratosphere. The chlorine destroys ozone by catalysing its transformation into molecular oxygen. The production of CFCs has been banned since the 1
st
of Jan. 1996 (Copenhagen Agreement which amends the Montreal Protocol of the 23-25
th
of Nov. 1992), and use thereof should be totally eliminated before the year 2030.
The Canadian patent CA 2.142.195 (Worsford, D. James, 8th of Feb. 1995) discloses and claims a product for de-acidification of cellulose-type materials which consists of a de-acidifying reagent, such as methoxymagnesium methylcarbonate or ethoxymagnesium ethylcarbonate, a solvent such as methanol or ethanol, and a hydrochlorofluorocarbon diluent (HCFC) or hydrofluorocarbon (HFC). The product patented can be applied to the cellulose-type material by spray or with a brush, or by immersing the cellulose-type material in the product. As a novelty with respect to the patents cited earlier this patent describes the use of diluents that are not prohibited by the Montreal Protocol [HCFCs and HFCs].
The use of HCFCs and HFCs as a substitute for CFCs substantially reduces the number of chlorine radicals that can be liberated in the stratosphere on exposure to cosmic radiation, thus reducing the potential for ozone destruction. On the other hand, the presence of hydrogen means that the compound is more reactive, such that it tends to decompose more easily before reaching the stratosphere. The rate of decomposition of HCFCs and HFCs is higher than that of the CFCs, whose lifetime is quoted at being between 60 and 100 years.
The object of the present invention is to find a new product for the non-aqueous de-acidification of cellulose-type materials, thus providing an addition to the arsenal of means available for combating acidification of cellulose-type materials.
Therefore, an object of this invention consists of a product, in the form of a solution, for the non-aqueous de-acidif
Alvo Steve
Notaro & Michalos P.C.
Universitat Politecnica de Catalunya
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