Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-12-15
2003-03-04
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S247000, C524S249000, C524S556000, C106S505000, C106S823000
Reexamination Certificate
active
06528563
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to gelled adhesives, tile adhesives and dry-set mortars and methods for their formulation, and more particularly to low solids, high strength multi-use gelled mastic adhesives and adhesive mastics which can be used “as is” for the installation of various types of tile, flexible sheet goods, carpet and other uses, and can be mixed with a Portland cement and silica sand to form a powerful latex-modified mortar having the added utility of a crack suppressive adhesive and functioning as a waterproofing membrane.
2. Brief Description of the Prior Art
Latex-based adhesives have long been known and enjoy wide use. They owe their superior adhesion to their strong molecular attraction to the surface molecules of many types of substrates as well as strong cohesion between the latex molecules themselves. There is little value if an adhesive has superior “wetting” or “spreading” attraction and bonding to a substrate surface if the internal strength of the adhesive is so weak that the joint fails leaving adhesive on both surfaces or on either surface alone. Therefore the strength of an adhesive is dependent on the relative magnitude of the forces of cohesion between the adhesive molecules themselves (such as latex to latex) and the forces of surface energy adhesion (bonding) to the surfaces to be bonded (such as latex to the surfaces to be bonded together). If a material preferentially interacts with and bonds to a surface of a substance it will be a good adhesive provided it has sufficient internal strength to maintain the bond. For instance, water has excellent surface bonding strength or initial tack (it readily “wets” or “spreads” on a surface) but it has virtually no internal strength because the molecular attraction between water molecules themselves is very weak. This is the reason water molecules readily move so that the water conforms to the vessel in which it is held at ordinary temperatures.
Aqueous suspensions of latex can be formulated to make excellent adhesives by providing for the easy application and distribution of the latex. Suspending colloidal latex in water is therefore an efficient method to provide for the application of latex to surfaces. The terminal molecular groups of the latex have a strong affinity for substrates especially those high in oxygen and hydroxyl groups such as silicates and cellulose as present in ceramics, stone, wood and drywall. When the water is removed by evaporation, absorption or other means, the dispersed latex is forced together where they coalesce to produce the strong internal strength necessary for a good adhesive. Furthermore latex polymers retain some elasticity inherent to their linked component conjugated diene sub-units.
Adhesive applied with a trowel or by roller must be thickened sufficiently to allow efficient application and to prevent slippage of tile, stone or other layments especially with installations on walls.
Thickening of mastics may also be necessary to provide for the application of a heavy or thick layer especially used to assure sufficient adhesive to “wet” and bond to the material being installed in the presence of uneven surfaces, embossed tile backs, etc. Thickening has previously been achieved with the use of supposedly inert fillers such as calcium carbonate, clays, polysaccharides, gums, etc.
These fillers serve to thicken the aqueous latex polymer suspension but they are not totally inert and therefore may cause a multitude of problems. In the context of this patent they will continue to be referred to as inert fillers. As evaporation begins to remove the water, surface drying of these inert fillers causes the adhesive to “skin” or form a film on the surface of the adhesive. This skin blocks wetting of underside of the applied layment and prevents adequate bonding. The adhesives of the present invention retain their wet surface because there are no drying fillers and the gel strength will hold water minimizing evaporation while yet allowing the water to be released to the absorption of the layment and the substrate.
Conventional adhesives with a high loading of fillers will form skin that will have little tackiness and disallow the wetting of the layment undersurface resulting in bond failure. Therefore the open time necessary for the installer to spread the adhesive and then fit and make the installation becomes very limited. The installer is limited to the installation of sufficiently small areas that will not skin before the exposed mastic is covered. If this is not done, the skin causes weak joints to form due to the incomplete wetting of the undersurface of the layment which prevents the establishment of the surface energy necessary to produce the strong bond. Additionally the dry skin barrier dramatically slows further evaporation so that even if enough tackiness remained sufficiently long enough for wall tile to stick, the underlying moisture will allow the tile to slip after the tile is positioned. Furthermore, ceramic and vinyl tile, most sheet goods and other impervious materials act as additional efficient vapor barriers to prevent water evaporation or absorption thereby forming long-standing weak joints because, with inefficient water loss, the polymerization of the latex proceeds very slowly. It is much as though the mastic were left in an almost sealed shipping container.
The inert filler thickening agents greatly compromise the effective polymerization and coagulation of the latex. They mechanically interfere with the intermolecular attachments of the conjugated dienes that must polymerize for the adhesive to become functional. If the polymers are uninterrupted and continuous without having to bridge around and between molecules and particles of calcium carbonate, for instance, the resulting strength of the surface attachments and internal cohesion will be greatly enhanced. The inert fillers also produce undesired mechanical characteristics. Trowel applications require a strong hand and excellent technique for the inert fillers add significant weight and drag.
The present invention eliminates the large percentages (commonly 25% to 80%) of compromising inert fillers found in conventional mastic adhesives and provides a low solids, yet high strength latex adhesive. By using chemicals that stiffen the aqueous carrier after the desired additives such as latex are thoroughly mixed into the formulation, the present mastic adhesives require less than about 10% of inert fillers.
There are several patents which disclose the use of various types of latex to formulate adhesives and mastics but all require inert fillers and other materials in one form or another.
Takahashi et al, Japan patent JP 58017157A discloses a transparent gel that is prepared by using a highly water-absorbing synthetic resin (e.g. modified polysodium acrylate) as a gelling agent and adding to the gel at least one additive selected from among ethylenediamine-tetraacetic acid (or its disodium salt), triisopropanolamine, ethanolamine, n-propyl gellate, nickel dibutyldithiocarbamate, phenyl-alpha-naphthylamine and benzophenone derivative in an amount of 5 wt% or less, to prevent lowering of viscosity caused by sunlight, etc.
Bowden, U.S. Pat. No. 4,204,876 discloses a method of using thixotrophic compositions to carry additives in the liquid portion of cementitious products as a method of attempting to gain homogeneity of the end product.
Kwok et al, U.S. Pat. No. 4,471,082 discloses the use of a polyacrylic acid mixture as a thickening agent with a water based polymer in latex form to manufacture adhesives. The adhesives disclosed therein are re-wetable and designed to separate in the presence of water. There is no suggestion that the adhesives thus produced will function as a construction adhesive where a given degree of water resistance is mandatory and/or form a vapor barrier impervious to water.
Johansen et al, U.S. Pat. No. 5,558,708 discloses a “two-component” system and method for dispensing pigment in cement based composition using a predete
Collins James R.
Collins Jock R.
Kaiser Conard E.
Egwim Kelechi C.
Roddy Kenneth A.
Wu David W.
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