Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1996-11-08
2001-07-10
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S560000, C524S561000, C524S562000, C428S508000, C428S510000, C428S514000, C428S522000
Reexamination Certificate
active
06258890
ABSTRACT:
The present invention relates to the use of an aqueous polymer dispersion whose polymer, present in disperse distribution, is composed in free-radically polymerized form of
from 20 to 65% by weight of at least one vinyl-aromatic monomer (monomers A),
from 35 to 80% by weight of at least one monomer having two conjugated ethylenically unsaturated double bonds (monomers B), and
from 0 to 10% by weight of other monomers having at least one ethylenically unsaturated double bond (monomers C)
and whose content of alkali metal ions, based on the mass of the dispersed polymer, is ≦0.5% by weight for producing water-vapor barriers. The present invention additionally relates to the preparation of such an aqueous polymer dispersion and to the aqueous polymer dispersion itself.
Air normally contains a certain amount of water vapor which exerts a defined partial pressure. This water vapor uptake by the air is limited and depends on the temperature. As the temperature rises, there is a great increase in the water vapor uptake capacity. At the maximum amount of vapor, the partial pressure is equal to the saturation pressure of water at the same temperature. The percentage ratio of the amount of vapor present in the air to the maximum possible amount is termed relative atmospheric humidity. Given a constant absolute moisture content, the relative atmospheric humidity falls as the temperature rises and, conversely, rises on cooling. On going below the dew point temperature, however, the amount of vapor present in excess of the saturation level condenses to form dew.
Where a porous wall, for example, separates two areas having different partial pressures of air and water vapor, then molecules of water vapor or, respectively, air pass through this wall in order to compensate the concentration or pressure. If the wall at the same time has a temperature gradient along its thickness, the saturation pressure of water may be exceeded within the wall and there may as a result be formation of dew which damages the wall (eg. reduction in its thermal insulating effect, development of molds, etc.). Against this background it is desirable, for example, to make the internal walls of damp rooms (the term damp rooms as used herein refers to rooms whose atmosphere has an increased water-vapor content relative to the atmosphere of their surroundings; examples of damp rooms are kitchens, bathrooms, dairy rooms, industrial rooms, cellar rooms) as impermeable as possible to water vapor, ie. to provide them with a water-vapor barrier. Similar comments apply to the external walls of rooms whose surrounding atmosphere has a relatively increased water-vapor content (eg. the external walls of refrigeration rooms). A further area of application for water-vapor barriers is constituted by wood coatings. Owing to its hygroscopic nature, wood shrinks or swells in accordance with changing relative atmospheric humidity, as a consequence of the uptake or release of water to which this change in humidity gives rise; the wood warps, which is generally accompanied by damage to the coating on the wood. It is therefore desirable either to give the wood surface a water-vapor impermeable finish before applying the actual protective coating, or to make the wood coating itself impermeable to water vapor.
From Römpps Chemie-Lexikon, eighth edition, 1981, Cm-G, Franck Verlag, Stuttgart p. 974 it is known that the aqueous Diofan® polymer dispersions of BASF AG are able to form films having high impermeability to water vapor. Correspondingly, the technical information bulletins TI/ED 1037 d, September 1993 and TI/ED 1652 d, May 1993 from BASF AG recommend films of Diofan A 601 and of Diofan A 690 as water-vapor barriers both for typical wall surface materials, such as cement slurry coats, concrete, gypsum, plasterboard, wooden particle board or chipboard, plywood, hardboard and masonry, and for wood itself.
In this context the water-vapor barrier effect can be obtained in a simple manner by coating the respective surface either with the aqueous polymer dispersion itself or with an appropriate composition containing the aqueous polymer dispersion as binder. When the coating dries, the polymer film exerting the barrier effect is formed.
It is worth noting that the abovementioned Diofan grades are aqueous dispersions of copolymers formed from relatively polar monomers (vinylidene chloride and n-butyl acrylate), which shows that the question of the water-vapor permeability of a polymer film must be considered separately from the question of the polarity of the polymer on which the film is based.
A further notable property of these Diofans is that they are able to form films of enhanced elasticity at the most common application temperatures (from 5 to 35° C.). This is important insofar as the substrates which are to be given a water-vapor impermeable finish generally have cracks whose expansion is subject to fluctuations in the case of temperature change. Owing to their enhanced elasticity, the Diofan films are able to follow these fluctuations in an advantageous manner without themselves cracking (crack sites open up the passage of water vapor) and thus forming a long-term barrier to water vapor.
A notable feature is that the Diofans are able to transfer the abovementioned profile of properties even to coating compositions which in addition to the Diofan comprise to a proportion of up to 60% of their overall volume solids content of added, finely divided mineral materials, such as fillers and pigments (while fillers and pigments are normally distinguished from one another on the basis of their different degrees of fine division and of their different refractive index, the term pigment as used herein should be interpreted here as including both; correspondingly, the volume proportion mentioned above forms the pigment volume concentration (PVC)). This opens up the possibility of giving the water-vapor barriers visual appeal and of producing them, in a simple manner, with variable coat thicknesses.
The Diofan films also have an outstanding capacity for adhering to the materials mentioned as possibilities for wall surfaces.
A disadvantage of the Diofans, however, is that the vinylidene chloride which they contain in polymerized form is subject to progressive hydrolysis over time under the action of the aqueous dispersion medium, in the course of which hydrolysis hydrogen chloride is formed. The latter is an unwanted contaminant and has an adverse effect, inter alia, on the stability on storage and the thickening of formulation properties of corresponding coating formulations (for example, finely divided CaCo
3
pigment is attacked by the evolution of hydrogen chloride).
It is an object of the present invention, therefore, to provide aqueous polymer dispersions for use for producing water-vapor barriers which on the one hand encompass the described, advantageous profile of properties of the Diofans and on the other hand do not have the described disadvantages of the Diofans.
We have found that this object is achieved in that aqueous polymer dispersions whose polymer, present in disperse distribution, is composed in free-radically polymerized form of
from 20 to 65% by weight of at least one vinyl-aromatic monomer (monomers A),
from 35 to 80% by weight of at least one monomer which contains two conjugated ethylenically unsaturated double bonds (monomers B), and
from 0 to 10% by weight of other monomers containing at least one ethylenically unsaturated double bond (monomers C)
(based on the total quantity of monomers A-C incorporated by polymerization) and whose content of alkali metal ions, based on the mass of the dispersed polymer and referred to below simply as GA, is ≦0.5% by weight are suitable in the manner required for producing water-vapor barriers.
Monomers A suitable in accordance with the invention include styrene and the vinyltoluenes (methylstyrene). Styrene is preferably employed. Monomers B suitable in accordance with the invention include butadiene, 2-methylbutadiene (isoprene) and 2,3-dimethylbutadiene.
Suitable monomers C inc
Anselmann Thomas
Dragon Andree
Schmidt-Thuemmes Jürgen
Wistuba Eckehardt
BASF Aktiengesellshaft
Mulcahy Peter D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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