Shelf-stable silane-modified aqueous dispersion polymers

Abstract

Disclosed herein is a process for preparing a shelf-stable, one-pack, silane modified (meth)acrylic latex interpolymer composition, wherein the process comprises continuously adding at least a portion of a mixture comprising at least 0.5 mole percent of a vinyl silane comprising hydrolyzable groups and up to 99.5 mole percent of a (meth)acrylic monomer to water and a surfactant in a reaction vessel, wherein said addition is carried out in the presence of a polymerization initiator and buffer sufficient to maintain the pH of the reaction at a level of at least 6 throughout the reaction, while simultaneously hydrolyzing from about 10 to about 60% of the hydrolyzable groups of the vinyl silane.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to (meth)acrylic latex copolymers. As employed herein, the terminology “(meth)acrylic” is intended to mean “acrylic or methacrylic”. More particularly, the present invention relates to an aqueous (meth)acrylic latex copolymer, modified by incorporation of a vinyl silane bearing hydrolyzable groups, such as alkoxy groups, which cures at room temperature without added catalyst after application to a substrate to provide a crosslinked, solvent resistant film or object, wherein said copolymer is stable for at least one year at room temperature.

[0003] 2. Description of Related Art

[0004] There is extensive prior art on free radical copolymerization of unsaturated silanes with organic comonomers, in solvent-borne systems as well as in waterborne systems. Although not completely absent, shelf life problems and problems due to high levels of silane incorporation are not of overriding importance in non-aqueous systems. In waterborne systems, most of the art ignores shelf life issues, or does not attempt to provide long shelf lives, particularly when higher concentrations of silanes are involved. For specialized applications, these systems can be used shortly after synthesis.

[0005] Aqueous dispersion polymers (commonly, latex, latexes, latices) are well known. Some general references include:

[0006] Waterborne and Solvent Based Acrylics and their End user Applications, ed. P. Oldring and P. Lam, Volume I of Surface Coatings Technology, John Wiley and Sons, New York, 1997, especially chapter II, and;

[0007] Resins for Surface Coatings, Volume 1, Acrylics and Epoxies, H. Coyard, P. Deligny and N. Tuck, John Wiley and Sons, New York, 2001.

[0008] In these references typical synthesis conditions, initiator techniques, comonomers, end use properties and application conditions are described.

[0009] Latexes can be provided with superior properties for use in coatings, sealants, and adhesives by incorporation of organofunctional alkoxy silanes in the polymer. The superior properties include resistance to common household chemicals and to solvents, as well as resistance of latex paints to scrubbing with household cleaning agents. In sealants, a sealant that can be obtained that produces joints that are resistant to the environment, are flexible, and do not flow after curing in place. The properties arise from the crosslinking of the polymer chains in the latex after application and flow out or coalescence of the latex. Inclusion of silanes provides an effective mechanism for creating “self-crosslinkable” latex polymers, which do not need the addition of a separate crosslinking agent—that is, they are “one pack” systems, not “two pack” systems. There are also chemistries that do not involve silicon-containing comonomers that achieve some of the benefits of one pack, self-crosslinkable latex systems. Silicon (silane) based technologies offer superior resistance to degradation by UV light and the environment, compared to most other technologies.

[0010] This technology—based on alkoxysilane comonomers—has been practiced to some degree for years in a limited number of latex applications. However, there are deficiencies in what has been achieved to date, particularly with regard to combining good stability and good low temperature cure.

[0011] First—alkoxy silanes are reactive with water. Hydrolysis of the alkoxy groups attached to silicon, such as methoxy or ethoxy groups, occurs readily and produces free alcohol, such as methanol or ethanol. Remaining on the silicon atom after hydrolysis is an —OH group, viz., a silanol. The condensation of two silanols to form an Si—O—Si bond, with the release of water, is thermodynamically favored. Unfortunately, premature hydrolysis and condensation can destroy a silane and make a siloxane polymer of it before it has a chance to be incorporated into a latex in a uniform and well controlled fashion during polymerization. Hydrolysis and condensation after incorporation of the silane can prematurely crosslink the latex polymers during storage, resulting in solidification and gelation of the latex or latex-containing product in the container. If the crosslinking occurs within the latex microparticles, gelation may not be apparent, but the particles will not flow together and will not coalesce after application. This can result in reduced gloss (for coatings) or brittle films that have no integrity when exposed to solvents, or sealants with poor integrity. On the other hand, if this process can be controlled, a latex can be produced which uses this chemistry to crosslink the polymer system after application, to give superior properties.

[0012] In some applications, it is possible to heat the substrate after application of a silane-containing latex coating. The “stoving” or baking of articles coated with paint is well known. This heat can be used to “activate” the silane chemistry described, provided the chemistry can be kept “latent” while the silane-modified polymer system is stored on the shelf awaiting use. However, heating uses energy and some substrates may not be able to withstand heating. Catalysts, such as acids, bases, and metallic compounds (tins, titanium derivatives, etc.) may be used to catalyze the reaction. This is normally accomplished by using a two-pack system, which is less desirable than a one-pack system. Two-pack systems require control of the amount of additive, and may have very limited “open life” or “pot life” after addition of the catalytic agent.

[0013] Thus, it is particularly desirable to have a one-pack system, which cures under ambient conditions after application, and which, at the same time, does not prematurely react during storage. For practical use, a product such as a coating must be stable during storage for many months or years. This is an extremely difficult goal to achieve, owing to the conflicting needs of reactivity and stability. Any approach that relies on the use of an extremely unreactive silane that can survive storage because of its low reactivity faces the problem of to how make the unreactive silane become reactive on command. To achieve this without heat or a catalyst is very difficult.

[0014] In some cases, the goal of shelf stability and room temperature cure in a one-pack system can be achieved by using extremely low concentrations of silanes. The rate of condensation of two silanols to form a siloxane crosslink is proportional to the square of the concentration of silanol groups. (The rate equation is second order in silanol concentration.) Thus, the condensation reaction can be slowed by reducing the silane concentration, and the effect is very strong because of the dependence on the square of the concentration. However, if one wishes to obtain a higher level of properties and faster cure of the system after application, it is desirable to increase the silane concentration above levels that are typically stable through the use of very low silane concentrations, i.e., above small fractions of one weight percent in the polymer.

[0015] As can be seen from these comments, trying to control the chemistry occurring in a latex polymer system is not simple or straightforward. Factors which can influence the results are:

[0016] 1. Temperature. Polymerizations are typically carried out at elevated temperatures, such as 60 to 65 degrees Celsius. Storage may be at room temperature. Application is usually at or near room temperature, but the applied coating may be heated.

[0017] 2. Water concentration. While water concentration is high in the aqueous phase—nearly 55 moles per liter—it will be much less in the oil phase. Hydrolysis and condensation rates are influenced by water concentration.

[0018] 3. Solubility. A hydrolyzed silane, carrying silanols, is much more water soluble than the unhydrolyzed silane. A vinyl silane has a different ratio of polar and non-polar groups than a silane with a methacryloxypropyl substituent on silicon.

[0019] 4. Chemical structure. Monomeric vinyl silanes tend to be more reactive to hydrolysis than silanes with the same alkoxy groups in which the silicon is not directly attached to a vinyl (unsaturated) group. Once polymerized into an organic copolymer, the alkoxy groups on silicon that is derived from a vinyl silane, and that is, in turn, directly on the polymer backbone, will have reduced reactivity due to steric shielding by the bulky polymer chain. The same factor reduces reactivity for condensation as well as for hydrolysis. In comparison, the silicon derived from a methacryloxypropyl silane is several atoms away from the backbone, and its chemistry is less influenced by steric factors.

[0020] 5. Environmental variables. Factors, such as pH and the concentration of acidic or basic groups or metal ions and nucleophiles in the reactants, will influence the silane chemistry in different ways, depending on the type of silane, whether hydrolysis and/or condensation are being considered, and the like.

[0021] The complexity of these interactions makes it extremely difficult to predict the results of a synthesis before actually running the reaction and testing the results.

[0022] Commercially available silanes that can copolymerize by free radical induced addition polymerization with acrylic and vinyl organic comonomers, and that are available in sufficiently large production quantities to be practical for large scale industrial use, are either vinyl functional silanes or methacrylate functional silanes. An example of a vinyl functional silane is vinyltrimethoxysilane. An example of a methacrylate functional silane is methacryloxypropyltrimethoxysilane. As a class, vinyl functional silanes are substantially less expensive per pound than methacrylate silanes. For large scale industrial applications, therefore, the use of vinyl functional silanes is preferred on a cost per alkoxy silane (or per silanol) group. In fact, both the lower cost per pound of vinyl silanes (relative to methacrylate silanes) as well as their lower equivalent weight per alkoxy silane group, may be necessary to achieve a commercially viable and economically feasible technology. Owing to the selective nature of the reactivity of the double bond during copolymerization with vinyl and methacrylic or acrylic monomers, vinyl silanes can copolymerize readily with vinyl monomers, such as vinyl acetate. Vinyl monomers do not readily copolymerize with (meth)acrylate double bonds and special care is required to achieve uniform incorporation of any vinyl monomer (whether it is a silane or not) into polymers consisting primarily of methacrylate or styrenic monomers. However, for many end uses, more expensive methacrylate or acrylate organic comonomers are preferred, because the resulting polymers have superior durabilty, weatherabilty, higher glass transition temperatures, and other superior properties, even in the absence of silane comonomers.

[0023] When considering the rate of reaction to incorporate the silane into the polymer, one must also consider the rate of hydrolysis of the silane before and after incorporation in the latex polymer, as noted above. In general, trialkoxyvinylsilanes hydrolyze more quickly than (meth)acryloxyalkyltrialkoxysilanes as free monomers. Once the silanes have been incorporated into the polymer, the trialkoxy silane residue will tend to be less reactive in hydrolysis and condensation because of the steric shielding arising from the location of the silicon directly on the polymer backbone.

[0024] Thus, overall, the problem to be solved is how to achieve a shelf stable, one-pack, silane modified aqueous dispersion polymer (latex) system using vinyl silanes with (meth)acrylic organic comonomers, while achieving silane concentrations well above 1% by weight, up to 5% or even more, that will cure at room temperature to a solvent and chemical resistant product, and that can be stored for at least six months and, preferably, over one year, without premature crosslinking to a degree sufficient to render them substantially useless for coatings applications.

[0025] U.K. Patent No. 1,407,827 discloses a process for the manufacture of stable coagulate-free aqueous vinyl dispersions having improved adhesion. In this process, (i) (a) one or more monomers selected from vinyl esters of carboxylic acids, acrylic acid esters, and methacrylic acid esters, and optionally up to 25% by weight (relative to the total weight of component (i)) of one or more other singly-olefinically-unsaturated water-insoluble monomers, or (b) a mixture of styrene and up to 40% by weight (relative to the mixtue) of butadiene, is copolymerized with (ii) from 0.3 to 5% by weight (relative to the total weight of component (i)) of a silicon compound of a given general formula. Polymerization is carried out at a temperature within the range of from −15 to +100° C. in an aqueous phase, and in the presence of a water-soluble free-radical initiator and an emulsifier and/or protective colloid.

[0026] U.S. Pat. No. 3,575,910 discloses silicone-acrylate copolymers, aqueous emulsions of these copolymers, latex paints containing the copolymers and articles of manufacture having a coating containing the copolymers.

[0027] U.S. Pat. No. 3,706,697 discloses that the aqueous emulsion polymerization of acryloxyalkyl alkoxysilane, alkyl acrylic esters, and optionally other vinyl monomers produces copolymers that are curable at low temperatures. The silane may be introduced to the polymerization after a portion of the other monomers are polymerized. It is said that heat curing improves the solvent resistance of cured as-cast films of the latex and that silanol curing catalysts enhance the cure rate.

[0028] U.S. Pat. Nos. 3,729,438 and 3,814,716 disclose latex polymers comprising a dispersion of an interpolymer selected from the class consisting of (A) a copolymer of vinyl acetate and vinyl hydrolyzable silane and (B) a terpolymer of vinyl acetate, an ester, e.g., acrylic ester, maleic ester or fumarate ester, and vinyl hydrolyzable silane, as well as the crosslinked polymers derived therefrom. The latex polymers are said to have utility as protective surface coatings and as vehicles for paint formulations.

[0029] U.S. Pat. No. 4,716,194 discloses that the removability of acrylate based pressure sensitive adhesives is substantially improved by the addition thereto of a small amount of an organofunctional silane monomer.

[0030] U.S. Pat. No. 5,214,095 discloses stable, aqueous emulsion copolymers with controllable siloxane crosslinking functionality. These copolymers are prepared by a concurrent free radical and cationic initiated emulsion polymerization of at least one free radical initiatable monomer, at least one linear siloxane precursor monomer, and at least one bifunctional silane monomer having both free radical polymerizable and silicon functional groups. The copolymers are said to be useful in curable coatings, paints, caulks, adhesives, non-woven and ceramic compositions and as modifiers, processing aids and additives in thermoplastics, cements and asphalts.

[0031] U.S. Pat. No. 5,482,994 discloses polymer latices that are compositions formed by adding an unsaturated alkoxy silane and an initiator to a preformed emulsion polymer. The polymer latices are said to have utility as protective surface coatings, adhesives, sealants and as vehicles for paint formulations.

[0032] U.S. Pat. No. 5,599,597 discloses unreinforced or reinforced concrete moldings, for example concrete pipes, with improved corrosion resistance to acids and acidic sewage, improved permeation resistance to inorganic and organic liquids and gases and improved mechanical stability, produced by molding with machines, for example in press molding machines or extrusion machines or concrete pipe pressing machines, and allowing to harden plastic-viscous concrete mixtures of hydraulic inorganic binders, preferably cement, aggregates and water, where, in the preparation of the plastic-viscous concrete mixtures, to the latter has been added in a positive mixer an effective amount of an aqueous plastics dispersion based on anionic and hydrolysis-resistant copolymers of ethylenically unsaturated monomers, the minimum film forming temperature (MFT) of which is above the setting temperature of the concrete mixture, preferably above 23° C.

[0033] U.S. Pat. No. 5,932,651 discloses emulsion copolymerizing a particular crosslinker, i.e., either a siloxane or silazane, with an organic monomer. An emulsion can be formed having particles consisting of polymer chains formed from organic monomer. Depending on the crosslinker and reaction conditions, these emulsion polymer chains can be either crosslinked or uncrosslinked. The uncrosslinked polymer chains can be crosslinked at a later point by the addition of a suitable catalyst.

[0034] U.S. Pat. No. 5,994,428 discloses storage-stable, silane-modified core-shell copolymers comprising a shell-forming copolymer 1 of a) from 70 to 95% by weight, based on the overall weight of the shell, of acrylic and/or methacrylic C1- to C10-alkyl esters of which from 20 to 80% by weight have a water solubility of not more than 2 g/l and from 80 to 20% by weight, based in each case on the comonomers a), have a water solubility of at least 10 g/l, and b) from 5 to 30% by weight, based on the overall weight of the shell, of one or more ethylenically unsaturated, functional and water-soluble monomers including a proportion of from 25 to 100% by weight, based on the comonomers b), of unsaturated carboxylic acids, and a core-forming copolymer II of one or more monomers c) from the group of the vinyl esters, monoolefinically unsaturated mono- or dicarboxylic esters, vinylaromatic compounds, olefins, 1,3-dienes and vinyl halides, wherein the shell contains no silane compounds and the core comprises one or more silane compounds d) from the group of the mercaptosilanes alone or in combination with olefinically unsaturated, hydrolyzable silicon compounds.

[0035] U.S. Pat. No. 6,130,287 discloses an emulsion polymer comprising a protective colloid and a functionalized silane component which is of a given structural formula.

[0036] WO 98/35994 discloses emulsion polymers that are said to have an excellent combination of blocking resistance, water spotting resistance and ethanol spotting resistance. These polymers are made from a monomer mixture including a monomer with a highly polar group that includes either a carboxylated or sulfonated monomer, or both, a monomer having a hydrolyzable silicone group, and a nonfunctional monomer that can be selected to provide a desired minimum film formation temperature. These polymers are said to be useful in paint and coatings applications.

[0037] European Patent Publication No. 0 327 376 discloses copolymers of vinyl esters and silicon monomers, with very low levels of the silicon monomer, that are said to be especially suitable as binders for emulsion paints, giving good scrub resistance. Vinyltrimethoxysilane is copolymerized with organic comonomers comprising at least 40% vinyl acetate. Substantial or full hydrolysis of the silanes to silanols is expected. pH is not mentioned as a critical variable, and no pH ranges are indicated.

[0038] Bourne et al., J Coatings Technology, 54:69-82, #684, (January, 1982) describe attempts to obtain stable silane-modified latex copolymers from a variety of acrylate and methacrylate organic monomers by copolymerization with various methacrylate functional alkoxy silanes. These attempts met with failure. A range of pH conditions was attempted with ethyl acrylate as the comonomer. Conditions including starting at pH 9 or pH 7 and allowing the pH to drift, as well as pH 9 or no pH adjustment resulted in gelation (coagulation) during the reaction. Runs made at pH 7 did not coagulate during synthesis. However, even those preparations gave unacceptable levels of coagulum and inadequate shelf stability.

[0039] Marcu et al., Macromolecules, 36:328-332 (2003) carried out extensive studies using extraordinary techniques in attempts to obtain stable silane modified emulsion polymers. These authors attempted to copolymerize vinyltriethoxysilane with butyl acrylate. In order to obtain stable emulsion polymers, they had to resort to the use of a “mini-emulsion” technique. This technique involved addition of hexadecane to the reaction mixture to form an oil phase that might “protect” the silane from hydrolysis, plus the use of ultrasound to achieve extremely high shear and agitation. pH control is mentioned as being prominent in the literature and is used in their work. The experiments were run using sodium bicarbonate buffer at one mole % on monomers, at pH 6.5 (page 330, experimental section.) Even with these techniques, using the reaction scheme of batch reaction, they were unable to get the silane to copolymerize by free radical addition polymerization with the butyl acrylate. Instead, hydrolysis and condensation reactions of the reactions of vinyltriethoxysilane produced some form of oligomer, which eventually reacted with the organic latex polymer, possibly by transesterification or some other heterolytic mechanism. Control reactions run without the oil phase were also run, and gave poor results.

[0040] Cooke et al., Emulsion Polymerization with Hindered Silane Monomers, presented at Silicones in Coatings III, Barcelona, Spain, Mar. 28-30, 2000, addresses the use of highly hindered silanes with reduced hydrolytic reactivity, such as vinyl-tri-isopropoxysilane and methacryloxypropyl-tri-isopropoxysilane, with acrylate or methacrylate comonomers. Further studies with this type of silane were reported in Silicones in Coatings IV, at Guildford, UK, May 30-31, 2002. In this work, the use of sodium bicarbonate buffer to control pH is described and it is stated not to be necessary with the vinyl silanes, only with the methacrylate silanes. This work does not involve vinyltriethoxysilane.

[0041] Many other publications and patents exist, related to the objective of this work to a lesser degree than those cited above. A review is presented in Silanes in Coatings Technology, published in The Journal of the Oil and Colour Chemists' Association, 79:539-550 (December, 1996). The large number of publications and patents since the 1970's attests to the difficulty of this problem. Many give conflicting advice about conditions, such as pH and reaction conditions, and many involve other reagents, other comonomers, and the like, all of which have the potential to change the complex balance among hydrolysis, condensation, and free radical polymerization in a system with a water phase and an oil phase.

[0042] The disclosures of the foregoing are incorporated herein by reference in their entirety.

SUMMARY OF THE INVENTION

[0043] In accordance with the present invention, there is provided an (meth)acrylic latex, modified with a vinyl silane, e.g., vinyltriethoxysilane, under specified conditions by a novel process and synthesized to a specific range of composition, that is stable to storage up to three years at room temperature and provides self curing latex systems that cure to solvent resistant films with no added catalyst or heat.

[0044] In one embodiment, the present invention is directed to a composition that is an aqueous (meth)acrylic latex copolymer, modified by incorporation of a vinyl silane bearing hydrolyzable groups, such as alkoxy groups, that cures at room temperature without added catalyst after application to a substrate to provide a crosslinked, solvent resistant film or object, and that is stable for at least one year at room temperature. Preferably, the latex comprises at least about 10% and up to about 60% of the alkoxy groups derived from the vinylalkoxysilane hydrolyzed to release alcohol during the polymerization. More preferably, the vinyl silane is a vinyltrialkoxysilane, where the alkoxy moiety is ethoxy or n-propoxy.

[0045] In another embodiment, the present invention is directed to a process for making this latex that is broadly similar to known latex polymerizations, but is unique in that a specific range of pH is maintained during the polymerization, the preferred vinyl silane is vinyltriethoxysilane, and the silane concentration is up to 3 mole %, possibly as much as 5 mole %, and greater than 0.5 mole % relative to other monomers. This process deliberately hydrolyzes some of the alkoxy silane groups to release alcohol and form silanols, but does not produce such a high level of silanols that the system becomes unstable and will not survive shelf aging.

[0046] In contrast to known art, which describes pH control during synthesis of silane-containing latexes in many conflicting references with many different polymer systems and silanes, and discusses avoiding silane hydrolysis and/or condensation, in this invention silane reactions of hydrolysis and further silane reactions are controlled to specific, desirable levels.

[0047] More particularly, the present invention is directed to a process for preparing a shelf-stable, one-pack, silane modified (meth)acrylic latex interpolymer composition comprising continuously adding at least a portion of a mixture comprising at least 0.5 mole percent of a vinyl silane comprising hydrolyzable groups and up to 99.5 mole percent of a (meth)acrylic monomer to water and a surfactant in a reaction vessel, wherein said addition is carried out in the presence of a polymerization initiator and buffer sufficient to maintain the pH of the reaction at a level of at least 6 throughout the reaction, while simultaneously hydrolyzing from about 10 to about 60% of the hydrolyzable groups of the vinyl silane.

[0048] In another embodiment, the present invention is directed to a shelf-stable, one-pack, silane modified (meth)acrylic latex interpolymer composition prepared by a process comprising continuously adding at least a portion of a mixture comprising at least 0.5 mole percent of a vinyl silane comprising hydrolyzable groups and up to 99.5 mole percent of a (meth)acrylic monomer to water and a surfactant in a reaction vessel, wherein said addition is carried out in the presence of a polymerization initiator and buffer sufficient to maintain the pH of the reaction at a level of at least 6 throughout the reaction, while simultaneously hydrolyzing from about 10 to about 60% of the hydrolyzable groups of the vinyl silane.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] The process of the present invention comprises the aqueous copolymerization of acrylate monomers and a vinyl alkoxy silane under conditions that are similar to, but distinct from, the conventional. Continuous addition of silane along with the other comonomers, preferably from the very beginning of the reaction, is necessary to incorporate some of the vinyl silane in the polymer by free radical addition polymerization. If the vinyl silane is not added continuously, it will not copolymerize, and may form a separate siloxane copolymer, which may or may not be grafted or otherwise reacted with the organic polymer during the course of the reaction. As another possibility, the vinyl double bonds may not react until all of the acrylate monomers have hydrolyzed. Meanwhile, the vinyl silanes may be hydrolyzing, to form condensable silanols with unreacted vinyl groups, and, in turn, a siloxane condensate polymer or oligomer. This causes an undesirable and non-uniform incorporation of silane, or, in some cases, may result in a physical mixture of two materials—an organic polymer and a siloxane polymer, which is undesirable.

[0050] Vinyl silanes that can be employed in the practice of the present invention include, but are not limited to, vinylalkoxysilanes, especially vinylalkoxysilanes where the alkyl moiety of the alkoxy group is primary, e.g., vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyl-tri-n-propoxysilane, vinyl-tri-(methoxyethoxy)silane, and the like. Other vinyltri- and dialkoxy silanes may be used under some circumstances, but control of the reaction to obtain the desired degree of partial hydrolysis becomes more difficult. Silanes solely substituted with methoxy groups hydrolyze too readily and release toxic methanol. Most higher alkoxy silanes, i.e., above propoxy, hydrolyze too slowly for convenient use. Secondary alkoxysilanes, such as vinyl-tri-isoproxysilane, are definitely too unreactive, as are tertiary alkoxysilanes. Butoxy silanes generally hydrolyze too slowly and cause undesirable odors from the butanols released. Vinyltriethoxysilane and vinylmethyldiethoxysilane are preferred. The most preferred silane is vinyltriethoxysilane.

[0051] A wide range of acrylic and methacrylic comonomers common in the art can be employed in the practice of the present invention. (For reference, see Waterborne and Solvent Based Acrylics and their End user Applications and Resins for Surface Coatings, Volume I, Acrylics and Epoxies, supra, which also describe process details, optional comonomers, test methods, and conventional process methods that can be employed.) Styrenic monomers may be included readily, as they copolymerize easily with acrylic monomers, but not at levels sufficient to cause property deterioration. Styrenic materials, however, are strong absorbers of UV light and may reduce durability to exterior exposure. Optionally, up to 20 weight percent of one or more vinyl organic comonomers, such as vinyl acetate, vinyl propionate, or vinyl neodecanoate (VEOVA™), may be added, but preferably at a level low enough to produce no significant deterioration of the durability properties of the final product. Still other comonomers can be included to a small degree, if desired, as long as the system retains its substantially (meth)acrylic characteristics.

[0052] In the process of the present invention, a buffer, such as sodium bicarbonate at a level of from about 0.4% up to about 0.7% of the aqueous phase, is used to keep the pH in the range above 6. Higher and lower levels of buffer may be used if higher or lower amounts of acidic or basic materials are present in the reaction. The reaction typically starts at a pH above 8, and after 15-20 minutes lowers to a range of 6 to 7, where it is maintained as monomer is fed. Additional buffer may be added during the reaction. If shelf stability is not necessary for a given application, acceptable latexes can be produced in preparations that have a pH lower than these preferred levels.

[0053] During the reaction process, some of the vinyltrialkoxysilane, e.g., vinyltriethoxysilane, hydrolyzes, and the amount of alcohol released can be determined. The desired alcohol release is above 10%, but less than 60%, preferably 19% to 48%, and may vary somewhat with the silane concentration and structure chosen.

[0054] The composition produced is an aqueous (meth)acrylic copolymer, in which at least 1 mole %, preferably 1 to 5 mole %, more preferably 3 to 5 mole % (approx. 7 to 9 wt %, depending on the other comonomers) of vinyltrialkoxysilane has been incorporated primarily by copolymerization. In the examples described herein, with the particular comonomers used, 3 mole % of vinyltriethoxysilane corresponds to 5.2 weight %.

[0055] The composition may be further characterized by its ability to form a crosslinked solvent resistant film when applied to a metal panel and allowed to stand at room temperature for 7 days. The ability to withstand at least 75 MEK (methyl ethyl ketone) double rubs is one measure of satisfactory crosslinking. (This technique is described in ASTM D 4752-87 and is well known to those of ordinary skill in the coatings art.)

[0056] Initiation of polymerization in the working examples was by a standard method known as redox initiation. Thermal initiation or other initiation methods may be used. In the reactions of the examples, a temperature between 60 and 65 degrees Celsius, which is optimum for the redox initiator system used, was desired. Temperature is not narrowly critical, and any temperature can be used at which initiation methods can be used effectively.

EXAMPLES

[0057] I. Reagents and Materials

[0058] Methyl methacrylate (MMA)

[0059] Butyl acrylate (BA)

[0060] Methacrylic acid (MAA)

[0061] Vinyltriethoxysilane-Silquest® A-151 silane (Crompton Corporation, OSi Specialties Group.)

[0062] Sodium bicarbonate (NaHCO3)

[0063] Ferrous sulfate (FeSO4)

[0064] Sodium formaldehyde sulfoxylate (SFS)

[0065] Potassium persulfate (K2S2O8)

[0066] t-Butyl hydroperoxide, 70 wt. % in water (t-BHPO-70)

[0067] IGEPAL® CA-897 (Rhodia)

[0068] Deionized water

[0069] Ammonium hydroxide

[0070] II. Apparatus

[0071] 800 mL jacketed reaction flask (for 300 grain preparations.)

[0072] Heating fluid circulator

[0073] Thermometer

[0074] Overhead Stirrer

[0075] Metering pump for monomer solution (FMI piston pump RP-G400)

[0076] Syringe pump for initiator solutions (Syringe infusion pump 22, from Harvard Apparatus)

[0077] III. Formulation (Based on 300 Gram Total)

[0078] A. Water, Optional Buffer (Sodium Bicarbonate), Surfactant(s):

[0079] Deionized Water: 150 g

[0080] Sodium Bicarbonate buffer varied amounts

[0081] IGEPAL CA-987 13.5 g

[0082] B. Monomers

[0083] Monomers were chosen in these particular examples to keep a constant percentage of MAA, and a constant ratio of MMA to BA, as silane content was varied. There is no limitation implied on the process. For each 100 grams of monomers, the following ratios were used, presented to allow percent amounts to be seen easily. As the syntheses all used 125 grams of monomer, the weight amounts are to be multiplied by 1.25 to calculate the amount of monomer charged in the working examples. For example, for a 3 mole % silane incorporation, the amounts of monomers used would be 6.50 grams of vinyltriethoxysilane, 38.50 grams of BA, 78.125 grams of MA, and 1.875 grams of MAA. 1 Mole (Weight) Percent Silane Desired in Copolymer 0% (0.0%) 1% (1.73%) 2% (3.5%) 3% (5.2%) Vinyltriethoxysilane   0 g 1.75 g  3.5 g  5.2 g BA 32.5 g 31.9 g 31.5 g 30.8 g MMA 66.0 g 64.8 g 63.6 g 62.5 g MAA  1.5 g  1.5 g  1.5 g  1.5 g Total  100 g  100 g  100 g  100 g

[0084] C. Initiators:

[0085] FeSO4 (0.15%, in water) 1.20 g

[0086] K2S2O8 (solid) 0.9 g

[0087] SFS (2%, in water) 9.0 g

[0088] t-BHPO-70 0.1 g

[0089] Note: All initiator solutions should be freshly prepared prior to use.

[0090] IV. Synthesis

[0091] 1. 150 mL of deionized water were added to an 800 mL jacketed reaction flask, and 13.5 grains of surfactant and the indicated amount of sodium bicarbonate were added with gentle stirring. The contents were heated to 63° C. with constant temperature fluid in the jacket while purging the flask with N2. The N2 blanket was maintained throughout the run.

[0092] 2. The silane and acrylic monomers (125.2 grams total) were mixed and transferred to a separate addition funnel.

[0093] 3. Initiator was added, FeSO4 (1.2 grams, 0.15% aq) followed by K2S2O8 (0.9 g), with agitation to the surfactant solution prepared in Step 1. Stirring was continued for 5 minutes.

[0094] 4. The first portion of monomer was added to the flask. Ten percent of the monomer mixture prepared in Step 2 (12.5 grams) and 10% of the SFS solution (0.9 gram) were added to the reaction flask via two separate pumps over a period of about one minute. An exotherm was usually noted. The reaction was allowed to run at a temperature of 65° C. for 15 minutes maintaining good agitation. The reaction temperature was maintained within 2-3 degrees of 65° C. for steps 5-7.

[0095] 5. The remainder of monomer mixture (112.7 grains) and an additional 70% of the SFS solution (10.5 grams) were fed continuously through separate pumps over a period of three hours. Sometimes a slight viscosity increase was noted.

[0096] 6. The reaction mixture was allowed to stir for another 30 minutes after the monomers and this portion of initiator were completely added.

[0097] 7. At that point, the t-BHPO-70 (0.01 grain), followed by the remaining SFS solution (1.8 grains) were added over a period of 30 minutes.

[0098] 8. The latex was allowed to cool to room temperature. The pH was adjusted to 7.5 using ammonium hydroxide solution (<10% aq). The latex was filtered using a 200 mesh nylon screen.

[0099] V. Application

[0100] A suitable coalescent system for the silylated latexes has been found to be 2% dipropylene glycol butyl ether plus 4% 2-(2-butoxyethoxy)ethyl acetate based on the total weight of the latex including water. The formulation can be drawn down on zinc phosphate-treated steel or thermoplastics (for making a free film) to a dry thickness of about 1 mil (25 &mgr;m) and cured at ambient conditions or at elevated temperature, for various times.

[0101] Freshly synthesized latexes were allowed to remain at room temperature for at least 24 hours, usually 2 to 3 days, and never more than 7 days before the samples were taken for “unaged” testing.

[0102] A small sample of latex was mixed with 2% dipropylene glycol butyl ether containing 4% 2-(2-butoxyethoxy)ethyl acetate based on the total weight of the latex including water. It was allowed to stand for 30 minutes. It was drawn down on a phosphated steel panel to give a dry film thickness of approximately 1 mil film by using wire-wound rod, number 24 (from The Gardner Company.) This coating rod gives a wet film thickness of approximately 2.5 mil.

[0103] Coating films were tested after they were cured at ambient condition for a certain time—usually 7 days and 30 or 40 days. In some cases they were baked at 120° C. for 20 minutes before testing or before further ambient cure then testing. Baking can represent some end use conditions where heat is acceptable, and it also causes faster curing (formation of a crosslinked polymer network) than ambient curing. This is useful for an understanding of theoretical limits of whether and how much a system can cure with the ambient temperature limitation removed.

[0104] VI. Characterization of Silylated Acrylic Latexes and Properties of Coatings

[0105] Gel content: An accurately weighed (±0.1 mg) sample of coating films was placed in a fine wire cage in a Soxhlet extractor, and extracted with refluxing acetone for 8 hours. The loss of weight from the coating sample was measured accurately, with the gel content calculated according to:

Gel Content (%)=(1−&Dgr;W/W0)×100

[0106] where:

[0107] W0 is the initial weight of coating sample, and

[0108] &Dgr;W is the weight lost during solvent extraction.

[0109] If the film was brittle and fragmented into small pieces, as with over-crosslinked films, gel content could not be measured because the film was incompletely retained by the mesh. This procedure is based on ASTM D2765-95.

[0110] MEK resistance: Double rubs according to ASTM D 4752-87, modified to continue rubbing until the substrate was exposed, even if the number of double rubs was greater than the value of 50 as specified in the ASTM method.

[0111] Spot tests: This test was performed according to ISO 2812-1974. A one inch square piece of filter paper was placed on the film. Eight drops of solvent was added and the film was covered with a watch glass. In the case of acetone tests, the watch glass was removed after two minutes and the film wiped with a soft tissue paper. The result was rated from 1 to 5, with 1 being complete removal, 2 having substantial spots removed, and 5 being no effect. In the case of MEK, the watch glass was removed after 30 minutes and the specimen observed without wiping.

[0112] Measurement of alcohol of hydrolysis released during the latex synthesis or after completion of synthesis: A trap-to-trap (T-T) distillation apparatus was employed to separate the latex solids from the volatile components. The apparatus consisted of a 250 mL flask, a receiving tube, and connecting U-tube with a stopcock outlet at the bend of the U-tube. Sample size used was 7 to 10 grains, typically 8 grams. The distillation procedure included 4 major steps:

[0113] 1. Pre-freeze: The sample was frozen by rotating the sealed sample flask in dry ice. A frozen thin coating (shell) of sample on the flask wall was formed that ensured efficient vapor flow from sample to condenser during the subsequent distillation. This markedly speeds up the distillation owing to the higher surface area of the frozen latex.

[0114] 2. Deep freeze: The sample flask was attached to the distillation apparatus, and the sample flask was partly immersed in liquid nitrogen to cool it further in preparation for the trap-to-trap distillation. The system was sealed to outside air during this procedure.

[0115] 3. Vacuum: The distillation system was evacuated with a mechanical pump to a pressure of approximately 0.05 mm Hg while the sample was maintained at liquid nitrogen temperature.

[0116] 4. Distillation: The system was closed (under full vacuum) and the liquid nitrogen bath was removed from the sample flask and moved to the receiving tube. As the sample slowly warned, volatiles evaporated and condensed in the cold receiving tube. The distillation was considered complete when the sample was a dry, white powdery solid.

[0117] A gas chromatograph (Hewlett Packard 5890 series II) equipped with a capillary column packed with crosslinked phenyl/methyl siloxane (DB5, Agilent) and FID detector was used to analyze the distillate samples. GC-MS spectrometric techniques were used to identify the separated species. To determine quantitatively the content of alcohol in liquid distillate samples, a weighed amount of 2,4-dioxane was added as internal standard after the distillation was complete.

Examples 1, 2, 3, and 4

[0118] Data from examples 1 through 11 and comparative example 1 are provided in Table 1.

[0119] Latexes were prepared according to the general procedure, using 2 mole % vinyltriethoxysilane, and the indicated amount of buffer.

Example 1a and 1b

[0120] This preparation was carried out in duplicate. It involved no buffer, and the pH during the reaction was allowed to drift downward from an initial pH of 4-5, rapidly decreasing within 15 minutes to less than pH 3 for the 3.5 additional hours of reaction time.

Example 2

[0121] This preparation used 0.2 gram of sodium bicarbonate buffer (0.13% in the water phase.) The pH during reaction was allowed to drift downward from an initial pH of 8.5, rapidly decreasing within 15 minutes to pH 6.5 to 7, and further decreasing steadily to pH 2-3 at the end of the reaction.

Examples 3a and 3b

[0122] These duplicate preparations used 0.25 gram of sodium bicarbonate buffer (0.17% in the water phase.) The pH during the reaction was allowed to drift downward from an initial pH of 8.5, rapidly decreasing within 15 minutes to pH 6.5 to 7, and further decreasing steadily to pH 3.5 (3a) and 4 to 5 (3b) at the end of the reaction.

Example 4

[0123] This preparation used 1.0 gram of sodium bicarbonate buffer (0.67% in the water phase.) The pH during reaction was allowed to drift downward from an initial pH of 8.5, slightly decreasing within 15 minutes to pH 8 to 8.5, and further decreasing steadily to pH 6.5 at the end of the reaction.

[0124] Examples 1a and b showed acceptable performance in the initial tests within a week of preparation. However, after one year of shelf storage, performance deteriorated substantially.

[0125] Example 2 gave acceptable performance in the as-made tests, but showed notable deterioration after one year.

[0126] Examples 3 (a and b) and 4 gave excellent performance as made and after one year. After one year, the slightly better initial performance of Example 3 had decreased and the performance of Example 4 was equal or higher. At 2 mole % (3.5 wt. %) vinyltriethoxysilane, avoidance of the extreme lows of pH during reaction is sufficient to obtain acceptable storage for one year at room temperature.

Examples 5, 6, 7, and 8

[0127] Latexes were prepared according to the general procedure, using 3 mole % vinyltriethoxysilane, and the indicated amount of buffer.

Example 5

[0128] This preparation was carried out with no buffer, and the pH during reaction was allowed to drift downward from an initial pH of 4, rapidly decreasing within 15 minutes to less than pH 3 for the 3.5 additional hours of reaction time.

Example 6

[0129] This preparation used 0.15 gram of sodium bicarbonate buffer (0.10% in the water phase.) The pH during the reaction was allowed to drift downward from an initial pH of 8.5, rapidly decreasing within 15 minutes to pH 6.5, and further decreasing steadily to pH 2-3 at the end of the reaction.

Example 7

[0130] This preparation used 0.2 gram of sodium bicarbonate buffer (0.13% in the water phase.) The pH during the reaction was allowed to drift downward from an initial pH of 8.5, rapidly decreasing within 15 minutes to pH 5.5 to 6, and further decreasing steadily to pH 2-3 at the end of the reaction.

Example 8

[0131] This preparation used 0.5 gram of sodium bicarbonate buffer (0.33% in the water phase.) at the beginning. The pH during the reaction was allowed to drift downward from an initial pH of 9, decreasing within 15 minutes to pH 8, and further decreasing steadily to pH 5.5-5 at the end of three hours of monomer addition. An additional 0.3 gram of buffer was added at that point and the pH was 7-7.5 until the end of the reaction. Total buffer was 0.8 gram, 0.53% in the aqueous phase.

[0132] Under the more stringent conditions of higher silane concentration (3 mole % vs. 2 mole %), the ability of systems that finished their reaction at substantially acidic pH's to provide good shelf life and good performance in room temperature cure testing was diminished when compared to the samples made with 2 mole % silane. Since the rate of silanol condensation is proportional to the square of the concentration of silanol groups, the rate of premature crosslinking under storage (all other things being equal) would increase by the ratio of 9 (i.e., 3 squared) to 4 (i.e., 2 squared), i.e., 225%. While Example 5 was clearly inferior at both as-made and one year tests, examples 6, 7, and 8 were all acceptable in “as made” testing. It is interesting to note that allowing panels to cure for 30, 40, or 50 days at ambient conditions gave much better solvent resistance for Example 8 than for Examples 6 and 7. After one year, Example 8 was clearly superior to examples 5, 6, and 7.

Examples 9 and 10

[0133] Latexes were prepared according to the general procedure, using 3 mole % vinyltriethoxysilane, and the indicated amount of buffer. Example 10 was prepared in duplicate, as 10a and 10b.

Example 9

[0134] This preparation was carried out with no buffer, and the pH during the reaction was allowed to drift downward from an initial pH of 1.64. After 15 minutes the pH was 1.54 to 1.69. After one hour of monomer addition, the pH was 1.26, and it remained strongly acidic over the remainder of the reaction.

Examples 10a and 10b

[0135] These duplicate preparations used 0.65 gram of sodium bicarbonate buffer (0.43% in the water phase.) The pH during reaction was allowed to drift downward from an initial pH of 9, rapidly decreasing within 15 minutes to pH 6.5, and holding at 6 to 6.5 for the remainder of the reaction.

[0136] Room temperature tests were not carried out on these samples as made or at one year of storage. After 21 months of storage, 10 and 10b showed substantial superiority on MEK rub tests. At 33 months of storage, the superiority was still clear, even though the films of Examples 10a and b were brittle and fragmented in the gel test. At least 21 months shelf life was obtained.

Example 11

[0137] A latex was prepared according to the general procedure, using only 0.5% vinyltriethoxysilane, and no buffer. The pH profile was not measured, but was similar to that of examples 1, 4, and 9, since the same procedure was followed. The reaction mixture was substantially acidic.

[0138] Data were taken on Example 11 as made and after 30 months. The latex was not overly crosslinked at 30 months, as evidenced by a coherent sample after extraction, but showed only 49% gel and only 50 MEK rubs after 7 days at ambient.

[0139] The as-made sample also showed poor solvent resistance at 7 days: only 15 MEK rubs and 2 to 3 on the MEK spot test. These results show that stable systems can be produced, albeit with lower properties, by reducing the amount of silane. This property set may be sufficient for some applications, but the cured film is not substantially resistant to solvents. Not enough silane was incorporated.

Comparative Example 1

[0140] A latex was prepared with no buffer and no silane. “As made” testing showed only 10 MEK rubs after 7 days at ambient, and spot test results were only 1 for acetone and MEK tests at 7 days. Aged samples were not tested, but no change in values is expected, because no “self-crosslinking” chemistry mechanism is built into the latex. 2 TABLE 1 Data on Preparation and Testing of Examples 1 Through 11 and Comparative Example 1 Table 1A-A Buffer Buffer Working Composition NaHC03 NaHC03 pH profile - pH measured at time tin minutes Example mole % of wt. % in grams in t = 200 to % ROH Coagulum Number silane water phase water phase t = 5 t = 20 t = 80 t = 140 t = 200 260+ released wt % Comp 1 No Silane 0 0  1a   2% A-151 0 0 4-5 3-2 2-3 — — — 2%  1b   2% A-151 0 0 3.0 2-3 — — — 41% 2% 2   2% A-151 0.13 0.2 8.5 6.5-7     5-4.5 4.0 2-3 2-3 3%  3a   2% A-151 0.17 0.25 8.5 6.5-7   5.0 5.0 5-4   4-3.5 3%  3b   2% A-151 0.17 0.25 8.5 7.0 5.5 5.5-5.0 5.0 5-4 1% 4   2% A-151 0.67 1.0 8.5   8-8.5   7-7.5 6.5-7   6.5 6.5 29% 3% 5   3% A-151 0 0 4 3   <3 — — — 62% 4% 7   3% A-151 0.13 0.2 8.5 5.5-6   5 4   3   2-3 2% 6   3% A-151 0.10 0.15   8-8.5 6.5 5 4.0 2-3 2-3 48% 1% 8   3% A-151 0.53 0.5 then +0.3 9 8   6.5-6   6   5.5-5     7-7.5 29% 2% 9   3% A-151 0 0 1.64  154-1.69 1.26 — — — 3% 10a   3% A-151 0.43 0.65 9 6.5 6-6.5 6   6     6-6.5 2% 10b   3% A-151 0.43 0.65 8.6-9.0 7.0-8.2 8.1-5.4 5.4 5.6 6.3 1% 11 0.5% A-151 0 0 1% Table 1A-B Room Temperature Cure Data on Fresh Latex Preparations Working spot test Example age of SAL MEK Rubs MEK Rubs MEK Rubs acetone, MEK, get content Number months baking 7 day 30 day 40 day 7 day 7 day % Comp 1 0 none 10 1 1  1a 0 none 80 500 4 4 80.4  1b 0 none 80  200* 4 4 83 2 0 none 70 4-5 4-5 79.8  3a 0 none 50 4-5 4 71.2  3b 0 none 40 5 5 69.2 4 0 none 90 4 4 71.9 5 0 none 60 60  60 4 1,3-4   83.9 7 0 none 70 140 200 4-5 4 82 6 0 none 85 220 230 4-5 4-5 81.9 8 0 none 100 400 650 4-5 4-5 76 9 0 none No Data 10a 0 none 10b 0 none 11  0 none 15 2-3 56.6 *Fifty days, not forty days. Table 1A-C Room Temperature Cure Data on 12 Months Old Latex Preparations Working spot test Example age of SAL MEK rubs acetone, Number months baking 7 day 7 day MEK, 7 day get content % Comp 1 10 none 11 1 1  1a 12 none 10 3-4 3 (brittle)  1b 12 none 18 4 3-4 92.4 (brittle) 2 12 none 40 4 4 94.6  3a 12 none 90 4 4-5 94.7  3b 12 none 130 4 4-5 97.5 4 12 none 110 4 4-5 94.5 5 11 none 16 3 1 (brittle) 7 11 none 40 4 4 (brittle) 6 11 none 40 4 4-5 (brittle) 8 11 none 130 4 4-5 95   9 10a 10b 11  Table 1A-D Room Temperature Cure Data on 21 Months Old Latex Preparations MEK rubs Working Example Number age of SAL months baking 2 day 7 day 30 day 40 day Comp 1  1a  1b 2  3a  3b 4 5 7 6 8 9 21 none 10 150 10a 21 none 210 350 10b 21 none 120 350 11  Table 1A-E Room Temperature Cure Data on 33 Months Old Latex Preparations Working gel Example age of MEK rubs spot test content Number SAL months baking 2 day 7 day acetone, 1 day acetone, 7 day MEK, 7 day % Note Comp 1  1a  1b 2  3a  3b 4 5 7 6 8 9 33 none  7 11 1 3 1 (brittle) viscous  10a 33 none 30 130  4 4-5 4 (brittle) viscous  10b 33 very viscous 11  30 none 50 4-5 5 49 Table 1B-A gel content of age of coating, % MEK rub spot test latex baked at 120° C., 120° C. MEK, acetone, Composition buffer months 20 min. baked RT baked baked MEK, RT acetone, RT Acrylic latex 0 0 — 10 6 1 1 1 1 (no silane) Acrylic latex 0 0 — 20 (no silane) Table 1B-B gel content of coating, % MEK rub Composition buffer age of latex months baked at 120° C., 20 min. 120° C. baked Acrylic latex 0 (no silane) Acrylic latex 0 2 0 7 (no silane) Table 1B-C age of latex gel content of MEK rub spot test Composition buffer months coating, % 120° C. baked RT MEK, baked acetone, baked MEK, RT acetone, RT Acrylic latex 0 10 — 12 11 1 1 1 1 (no silane) Acrylic latex 0 13 —  7 1 1 (no silane)

Examples 12 and 13

[0141] The above Examples 1 through 10 indicate that excessive hydrolysis of the alkoxy silane to release alcohol during the latex preparation produces a latex that may be acceptable as made, but that deteriorates in storage, probably by excessive premature crosslinking. However, if the silane does not hydrolyze at all during the latex preparation, properties will develop much too slowly, if at all, upon application. These examples were synthesized using a different vinyl silane, vinyl tri-isopropoxysilane, which allows much less hydrolysis because of its structure. While not perfectly comparable in all ways to Examples 1 through 10, the data do provide a strong indication that there is a lower limit to the amount of hydrolysis that must occur during synthesis. In particular, a film cast at room temperature that has cured to only 4% gel gives poor properties, and corresponds to hydrolysis of only 19% of the available alcohol. Even after baking to force the cure, the 65% gel was soft, indicating poor crosslinking.

Example 12

[0142] A latex was prepared according to the general procedure, using 3 mole % vinyl tri-iso-propoxysilane, instead of vinyltriethoxysilane, and no buffer. The pH profile was not measured, but was similar to that of examples 1, 4, and 9, since the same procedure was followed. The reaction mixture was substantially acidic.

Example 13

[0143] This preparation also employed vinyl tri-iso-propoxysilane and used 0.22 gram of sodium bicarbonate buffer (0.15%) in the water phase. The pH during the reaction was allowed to drift downward from an initial pH of 8.5, rapidly decreasing within 15 minutes to pH 6.5, and further decreasing steadily to pH 2-3 at the end of the reaction. Poor performance at room temperature was improved by baking, but MEK rub tests were only acceptable even after baking. Example 12, more filly hydrolyzed, cures at room temperature and gives good properties when baked. 3 TABLE 2 Correlation of Degree of Hydrolysis with Properties of Cured Acrylic Latex Modified with Vinyl Silanes Gel content of Buffer Hydrolyzed coating film, % MEK rubs Example Grams and % in silane in latex, Baked at 120° C., 120° C., Number water phase % 20 min. R.T cure baked 5 none 62 (too brittle to 84 900 have film) 6 0.15 g, 0.1%  48 88 82 1000 8  0.8 g; 0.53% 29 87 80 600 12 none 63 88 84 350 13 0.22 g, 0.15% 19  65*  4* 60 *Gel in Example 13 after 120° bake was a soft gel, indicating an incompletely formed network.

[0144] These data suggest that an acceptable range of hydrolysis for latexes of this general composition and with a vinyl silane as the silane component require more than 19% hydrolysis to provide acceptable properties in room temperature cure. The upper limit is less clear from the data, but for vinyltriethoxysilane-containing materials, it is less than approximately 62% (Example 5).

[0145] In view of the many changes and modifications that can be made without departing from principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection to be afforded the invention.

Claims

1. A process for preparing a shelf-stable, one-pack, silane modified (meth)acrylic latex interpolymer composition comprising continuously adding at least a portion of a mixture comprising at least 0.5 mole percent of a vinyl silane comprising hydrolyzable groups and up to 99.5 mole percent of a (meth)acrylic monomer to water and a surfactant in a reaction vessel, wherein said addition is carried out in the presence of a polymerization initiator and buffer sufficient to maintain the pH of the reaction at a level of at least 6 throughout the reaction, while simultaneously hydrolyzing from about 10 to about 60% of the hydrolyzable groups of the vinyl silane.

2. The process of claim 1 wherein the vinyl silane comprising hydrolyzable groups is a vinylalkoxysilane.

3. The process of claim 2 wherein the vinylalkoxysilane is selected from the group consisting of vinyltriethoxysilane and vinylmethyldiethoxysilane.

4. The process of claim 3 wherein the vinylalkoxysilane is vinyltriethoxysilane.

5. The process of claim 1 wherein the (meth)acrylic monomer is selected from the group consisting of methyl methacrylate, butyl acrylate, methacrylic acid, and mixtures thereof.

6. The process of claim 1 wherein the buffer is sodium bicarbonate.

7. The process of claim 6 wherein the buffer is employed at a level of from about 0.4% to about 0.7% of the aqueous phase.

8. The process of claim 1 wherein the mixture further comprises up to about 20 weight percent of at least one vinyl organic polymer.

9. The process of claim 8 wherein at least one vinyl organic polymer is vinyl acetate.

10. A shelf-stable, one-pack, silane modified (meth)acrylic latex interpolymer composition prepared by a process comprising continuously adding at least a portion of a mixture comprising at least 0.5 mole percent of a vinyl silane comprising hydrolyzable groups and up to 99.5 mole percent of a (meth)acrylic monomer to water and a surfactant in a reaction vessel, wherein said addition is carried out in the presence of a polymerization initiator and buffer sufficient to maintain the pH of the reaction at a level of at least 6 throughout the reaction, while simultaneously hydrolyzing from about 10 to about 60% of the hydrolyzable groups of the vinyl silane.

11. The composition of claim 10 wherein the vinyl silane comprising hydrolyzable groups is a vinylalkoxysilane.

12. The composition of claim 11 wherein the vinylalkoxysilane is selected from the group consisting of vinyltriethoxysilane and vinylmethyldiethoxysilane.

13. The composition of claim 10 wherein the (meth)acrylic monomer is selected from the group consisting of methyl methacrylate, butyl acrylate, methacrylic acid, and mixtures thereof.

14. The composition of claim 10 wherein the buffer is sodium bicarbonate.

15. The composition of claim 14 wherein the buffer is employed at a level of from about 0.4% to about 0.7% of the aqueous phase.

16. The composition of claim 10 wherein the mixture further comprises up to about 20 weight percent of at least one vinyl organic polymer.

17. The composition of claim 16 wherein at least one vinyl organic polymer is vinyl acetate.

18. An interpolymer composition comprising:

A) at least about 0.5 mole percent of a vinylalkoxysilane moiety in which from about 10 to about 60% of the alkoxy groups have been hydrolyzed; and, correspondingly,

B) up to about 99.5 mole percent of at least one (meth)acrylic moiety.

19. The interpolymer of claim 18 wherein the vinylalkoxysilane is vinyltriethoxysilane.

20. The interpolymer of claim 18 wherein the (meth)acrylic moiety is selected from the group consisting of methyl methacrylate, butyl acrylate, methacrylic acid, and mixtures thereof.