Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2000-04-27
2002-01-29
Beck, Shrive P. (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S389700, C427S289000, C427S421100, C528S230000, C528S240000, C528S242000
Reexamination Certificate
active
06342271
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a phenolic resin intended especially to be employed in a sizing composition for material based on mineral wool, especially insulating products in felt or sheet form.
The manufacture of mineral wool-based products includes a first stage of manufacture of the wool itself, especially by the known technique of centrifugal drawing in which the molten mineral material is converted into filaments, and a stage of forming in which the filaments are drawn and entrained towards a receiving member by a gas stream at a high speed and temperature, to form a mat thereon. To ensure the cohesion of the mat, a so-called sizing composition, which contains a heat-curable resin is sprayed onto the wool during its travel towards the receiving member. The mat thus treated is next subjected to an oven heat treatment to polycondense (cure) the resin and obtain a product exhibiting desired properties, such as dimensional stability, tensile strength, thickness regain after compression and homogeneous colour.
The sizing compositions are generally sprayed onto the mineral wool and are prepared in the form of an aqueous composition (solution, dispersion). This composition is in general prepared shortly before spraying, on the actual production site, by addition of the usual constituents: a curing catalyst such as ammonium sulphate, urea and possible adjuvants such as lubricating mineral oils as antidust agent, aqueous ammonia, silanes as adhesiveness promoter and silicone as water-repellent.
The sprayability of such compositions is determined by the dilutability of the resin in water, which is generally defined as follows: the water-dilutability of a resin in the form of aqueous composition (resole) is the volume of deionized water which, at a given temperature, can be added to the unit volume of this composition before causing the formation of a permanent turbidity. The water dilutability of a resin suitable for being employed in a sprayable sizing composition is advantageously of the order of at least 1000% at 20° C., that is to say that 10 ml of resin can be diluted with 10×10 ml of water or more, without the mixture becoming turbid.
It is furthermore desirable that the resin should be stable in storage to allow use at the last moment: the dilutability must therefore remain high for as long a period as possible. A resin will advantageously have a water dilutability at 20° C. equal to or higher than 1000% for at least 8 days.
The heat-curable resin employed is generally a phenolic resole obtained by condensation of phenol and of formaldehyde, or equivalents, in the presence of a basic catalyst. To satisfy the requirement of a high water dilutability the degree of condensation of the monomers is limited, to avoid the formation of long, not very hydrophilic, molecular chains, which reduce the dilutability.
In this respect it is customary to terminate the condensation reaction at a degree of progress when the molecular chains are not very long, by neutralizing the reaction mixture to a pH of the order of 7 to 8 with a strong acid such as sulphuric acid, which has the effect of deactivating the basic catalysis. The resole then contains a certain proportion of starting materials, phenol and formaldehyde, which have not reacted.
Furthermore, to limit the risks of atmospheric pollution during the processing of the sizing composition, it is desirable that the composition employed should be as free as possible from volatile organic compounds such as the unconverted starting materials, free phenol and formaldehyde, or from other materials capable of being formed during the condensation of the monomers, and that it should generate as few polluting by-products as possible during the spraying onto the filaments at elevated temperature and/or when passing in the oven. The content of monomers, in particular free phenol and, above all, volatile phenolic derivatives, could in theory be reduced by increasing the duration and the degree of condensation of the resins, but there would then be a loss in the dilutability of the resin.
The problem which underlies the invention consists in satisfying as well as possible these two contradictory requirements.
To reduce the free phenol content in the resin it is generally proposed to prepare the phenolic resole by reacting phenol with formaldehyde in a form aldehyde/phenol molar ratio higher than 1, which promotes the consumption of the phenol, and then to add urea, which reacts with excess formaldehyde. Resins formed of formaldehyde/phenol and urea/formaldehyde condensates are thus obtained. The resin may be neutralized before or after the addition of urea, which has the additional effect of shifting the equilibrium of the reversible reaction between urea and formaldehyde towards the formation of the condensation product. It is generally preferred to neutralize the resin at a pH close to 7 to avoid the release of polluting starting materials.
Document EP-A-0 148 050 describes the preparation by this technique of resins which have a water dilutability of at least 1000% and which have a free phenol content (by weight relative to the total weight of liquid resin) lower than or equal to 0.5%, and a free formaldehyde content (by weight relative to the total weight of liquid resin) lower than or equal to 3%.
In the ideal case all the urea ought to be added to the resole at the time of the manufacture of the resin to simplify the preparation of the sizing composition on site. However, the modification of the resole by the urea can result in a partial precuring of the sizing and in difficulties in handling downstream. This is why the resole, which still contains a certain proportion of formaldehyde is modified only partially, and urea is added again to the sizing composition. These sizing compositions must nevertheless be employed fairly quickly because their storage period is relatively limited.
EP-A-0 512 908 provides a means for reducing the precuring and increasing the storage period before use of a sizing prepared from a modified resole of this type. It consists in reacting the neutralized resole with two nitrogenous reactors, namely aqueous ammonia and urea.
Other modifications of the resins, aimed at improving other properties of the sizing, are also known from the prior art.
Thus, U.S. Pat. No. 4,176,105 concerns the preparation of a binder for mineral fibres, based on a phenolic resol of improved heat resistance, capable of with-standing a heat curing operation without undergoing flameless exothermic decomposition (also known as “punking”) which is usually responsible for colour defects in mineral wool-based products. It proposes to prepare a modified phenolic prepolymer of low molecular weight in three stages consisting in combining a phenol-formaldehyde condensate of low molecular weight, consisting essentially of polyhydroxymethylphenols, with a water-soluble boron compound such as boric acid as far as an acidic pH of the order of 2, and then adjusting the pH of the mixture to a value of the order of 7 to 9 with a base such as ammonium hydroxide and, finally, adding a difunctional nitrogen compound such as urea.
U.S. Pat. No. 5,032,431 discloses the use of a water-soluble borate for improving the moisture resistance of phenolic resin-based compositions cured in alkaline medium, employed in the manufacture of glass fibre-based dark-coloured insulating materials. The borate, such as lithium, sodium or potassium metaborate, can be simply added to the alkaline phenolic resol of pH higher than 8.5 or else can be manufactured in situ by reaction of boric acid with the appropriate alkali metal hydroxide in a sufficient quantity for the pH of the composition to remain higher than 8.5.
SUMMARY OF THE INVENTION
While the resins and sizing compositions prepared in the way set out above offer quite a satisfactory compromise between the free phenol and formaldehyde content and the dilutability, it is always desirable to improve this performance. The aim of the invention is to provide a resin for sizing composition which ha
Espiard Philippe
Labbe Claire
Lericque Bernard
Tetart Serge
Beck Shrive P.
Calcagni Jennifer
Isover Saint-Gobain
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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