Method for making organically-modified, radiation-curable siloxane resins

Abstract: There is disclosed herein a radiation-curable, organically-modified siloxane resin composition which is prepared from (A) at least one multifunctional acrylate and (B) the reaction product formed from (a) an alkoxy-functional organometallic compound, (b) an alkoxysilane and (c) water. The alkoxysilane (b) includes at least one functional group that renders the alkoxysilane copolymerizable with the multifunctional acrylate (A). In the preferred embodiment, the alkoxy-functional organometallic compound (a) and the alkoxysilane (b) undergo cohydrolysis and cocondensation in the presence of a siloxane polymerization catalyst (d).

Description: The present invention relates generally to the field of organically-modified, radiation-curable siloxane resins and more particularly to such a resin that includes a multifunctional acrylate and the reaction product of a tetraalkoxy organometallic compound and an alkoxysilane. The alkoxysilane has at least one additional functional group which renders said alkoxysilane copolymerizable with said acrylate. A number of organically-modified, radiation-curable silicone resins are known in the art. Such resins are frequently used to provide abrasion- resistant coatings over easily-scratched substrates, such as polycarbonate or polyethylene terephthalate ("PET"). The product substrates are often used as a substitute for glass, such as lenses for automobile head lamps. Other uses include application over plastic containers that are adapted for receiving beverages. For non-refillable containers, the utility of the coating is directed solely at providing a barrier film that decreases the gas permeability of the container. For refillable containers, the coating utility is directed at providing a barrier film that exhibits abrasion-resistant properties, either alone or in combination with barrier properties. Other applications for organically-modified, radiation-curable siloxane resins include casting articles of manufacture and use as bonding agents. Many silicone resins of this type can also be impregnated with slip aids to increase the lubricity of their cured surface. The siloxane resin compositions of the prior art are generally formulated in a polar solvent, such as isopropyl alcohol and they utilize colloidal silica to impart abrasion resistance. The colloidal silica is usually added in the form of an aqueous dispersion. Silicone resin compositions of the above type are disclosed in US-A 4,455,205. The coatings comprise an ultraviolet (UV) light-curable composition prepared from a multifunctional acrylate monomer, an acryloxy-functional silane and aqueous colloidal silica in a polar solvent. After mixing the components, the solvent and remaining water are removed in vacuo, with gentle heating, a step which is termed "stripping." A photoinitiator is then added so that the composition may be UV-cured. Similarly, US-A 4,486,504 teaches a UV-curable composition prepared from the addition of a multifunctional acrylate monomer to a mixture of acryloxy-functional silanes and/or glycidoxy-functional silanes and aqueous colloidal silica. After stripping, a photoinitiator is added so that the composition may be UV-cured. EP-A1 0 544 465 describes a radiation-curable composition formed from: the hydrolysis product of an alkoxysilyl acrylate; aqueous colloidal silica; acrylate monomers; and a photoinitiator. Again, the examplary compositions are formulated in an alcohol solution. US-A 5,260,350 claims a radiation-curable composition which includes an aminoalkoxysilane and a multifunctional acrylate monomer (which form a Michael adduct) and colloidal silica in an aqueous dispersion. The composition is then formulated in a polar solvent, such as isopropyl alcohol. In the above prior art compositions, the water from the aqueous dispersion of colloidal silica causes the alkoxy groups on the silanes (and/or silyl acrylates) to hydrolyze. The term "hydrolysis," in its strictest sense and as applied to alkoxysilanes, describes the reaction of the silanes, at the alkoxy sites, with water, thus forming silanols and alcohol. The silanols, however, are also capable of undergoing a condensation reaction, to form Si-O-Si bonds and water. Accordingly, the term "hydrolysis", in whatever form used herein, is not meant to include the subsequent condensation reaction. Hydrolysis, followed by condensation, will be described as such. In the prior art compositions, it has been theorized that the colloidal silica includes residual silanol groups at the surface of the colloid particles. Further, according to the theory, at least some of these residual silanol groups then undergo a condensation reaction with at least some of the silanol sites derived from the hydrolysis of the alkoxysilanes. Likewise, at least some of the hydrolyzed silanes condense with each other, thereby forming a plurality of loosely crosslinked resin nuclei, at least some of which are chemically bonded to particles of colloidal silica. Further, upon curing, additional crosslinking provides a continuous resin network having colloidal silica particulate dispersed therethrough and chemically bonded therein. It is thus believed under this theory that the colloidal silica particles are largely responsible for imparting the compositions with abrasion-resistant properties. In the prior art compositions, free radical polymerization of the remaining acrylate groups provides further crosslinking to the resin network, thereby "curing" the composition. The initiation of free radical polymerization can be carried out by the addition of known photoinitiators and exposure to (UV) radiation or simple exposure to sufficiently high energy radiation such as an electron beam. The use of aqueous colloidal silica in the prior art formulations has numerous drawbacks. Colloidal silica has a tendency to gel, which tendency is particularly sensitive to changes in pH and solvent loss. For instance, as disclosed in US-A 5,260,350, unless an acid is first added to reduce the residual alkalinity imparted by the aminosilane, the addition of colloidal silica to the Michael adduct/acrylate solution results in gelling or the precipitation of silica from the colloidal suspension. Furthermore, the amount of water added to prior art compositions is dictated by the amount of water in the aqueous colloidal silica. Thus, to get an adequate amount of colloidal silica, the compositions are generally formulated with an excess of water. An excess of water creates several additional problems. The degree of hydrolysis and condensation is dictated by the amount of water. Accordingly, the degree of cross-linking in the uncured composition cannot be readily controlled. If excess water is left in the resin composition, it can have a deleterious effect on the finish of the cured coating, unless a lengthy drying time is employed before initiating cure. Thus, the prior art compositions are generally stripped of water. Stripping, however, also removes the polar solvent from the compositions greatly increasing the viscosity of the material. Thus, polar solvent must generally be reintroduced to achieve a coating composition having a viscosity in a usable range. The tendency of the prior art compositions to gel is also greatly increased during the stripping step. Therefore the likelihood of manufacturing scrap materials is increased. In addition to the foregoing, aqueous colloidal silica represents a substantial portion of the costs associated with the production of prior art resins. Thus, an organically-modified, radiation-curable silicone resin that does not require aqueous colloidal silica as a part of its formulation is considered highly advantageous and desirable. The organically-modified, radiation-curable siloxane resin of the present invention overcomes the manufacturing difficulties and high costs associated with the compositions of the prior art. In accordance with our invention, there is provided an organically-modified, radiation-curable siloxane resin comprising: (A) at least one multifunctional acrylate which is a monomer or oligomer which contains two or more acryloxy or methacryloxy groups; and (B) a reaction product formed from: (a) at least one alkoxy-functional organometallic compound of the general formuia M(OR) 4 , wherein M is selected from Si or Ti and each OR is the same or a different alkoxy group; (b) at least one alkoxy-functional silane of the aeneral formula wherein each OR is as defined above, each X is a monovalent radical that renders the alkoxysilane capable of copolymerization with the multifunctional acrylate (A) and which is independently selected from the group consisting of: alkylamines of the general formula [QNH] d QNZH wherein Q is a divalent hydrocarbon group, in which Q groups may be the same or different; Z is hydrogen atom or a monovalent hydrocarbon radical; and d is 0 or 1; and monovalent unsaturated hydrocarbon radicals, each R' is independently a monovalent hydrocarbon radical, and a is 1, 2 or 3, b is 1, 2 or 3, c is 0, 1 or 2 and a + b + c = 4; (c) a predetermined quantity of water; and (d) optionally, a catalytic amount of a siloxane polymerization catalyst. In our organically-modified, radiation-curable composition, the degree of crosslinking in the uncured resin network is readily controlled by the addition of a predetermined quantity of water. Furthermore, the compositions of this invention do not require the use of colloidal silica to render a cured product that exhibits highly abrasion-resistant properties. Another important feature of the invention is that certain embodiments thereof exhibit such low viscosities that no organic solvent need be added to render a usable coating material. These results are surprising and unexpected in view of the prior art. Thus, an object of the present invention is to provide an organically-modified, radiation-curable siloxane resin that can, when cured, exhibit highly abrasion-resistant properties without including colloidal silica in its formulation. It is another object of this invention to introduce an organically-modified, radiation-curable siloxane resin that does not require stripping. Another object of the invention is to produce an organically-modified, radiation-curable siloxane resin composition, wherein the degree of crosslinking of the siloxane resin in its uncured state, can be controlled. In our claimed composition, component (A) comprises at least one multifunctional acrylate. As used herein, the term "multifunctional acrylate" means a monomer or oligomer which contains two or more functional groups selected from acryloxy or methacryloxy groups. These multifunctional acrylates may be used singly or in combination. Those skilled in the art will recognize that the terms "oligomer" and "polymer" are frequently used interchangeably. Although "oligomer" is generally used to describe a relatively short polymer, the term has no generally accepted definition with respect to the number of repeating monomer units. As used herein, the term "oligomer" is meant to include molecules that may also be properly referred to as polymers. The only other restriction with respect to our multifunctional acrylates is that the acrylates are compatible with the remaining components of the invention. This means that they do not have a deleterious effect that defeats the desired application for the composition. It should be noted, however, that the tendency of a given acrylate to produce a deleterious effect can, in certain circumstances, be overcome. For instance, the use of certain multifunctional acrylates may raise the viscosity of the composition of this invention to a point where it is unusable to provide a satisfactory, thin abrasion-resistant coating on a substrate. If, however, the composition can be rendered usable by the addition of an appropriate solvent, then the use of that multifunctional acrylate is not considered to be excluded from the present invention. Likewise, if such a high viscosity composition has utility as a castable material, it is considered to be a part of the present invention. Several multifunctional acrylate monomers useable as component (A) are the following diacrylates 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, neopentyl glycol diacrylate, 1,4-butanediol dimethacrylate, poly(butanediol) diacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol diacrylate, triethylene glycol diacrylate, triisopropylene glycol diacrylate, polyethylene glycol diacrylate, and bisphenol A dimethacrylate; the following triacrylates trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol monohydroxy triacrylate, and trimethylolpropane triethoxy triacrylate; the following tetraacrylates pentaerythritol tetraacrylate, and di-trimethylolpropane tetraacrylate; and a pentaacrylate known as dipentaerythritol (monohydroxy) pentaacrylate. These multifunctional acrylate monomers are commercially available from Aldrich Chemical Company, Inc., Milwaukee, Wisconsin. Examples of some specific multifunctional acrylate oligomers usable as component (A) are epoxy acrylates: Bisphenol A epoxy diacrylate, available from Sartomer Company, Inc. of Exton PA. and sold under the designation CN104. CN104 has a viscosity of 3500 cps (mPa·s) at 65°C. and a specific gravity of 1.15. urethane acrylates: Hexafunctional aromatic urethane acrylate with an acrylated polyol diluent which is sold under the designation Ebecryl™ 220 by UBC Radcure, Inc. of Louisville, KY. Ebecryl™ 220 has a molecular weight of 1,000 and a viscosity of 28,000 cps (mPa·s) at 25°C. Aliphatic urethane diacrylate which is available under the designation Ebecryl™ 230 from UBC Radcure, Inc. of Louisville, KY. Ebecryl™ 230 has a molecular weight of 5,000 and a viscosity of 40,000 cps (mPa·s) at 25°C. polyester acrylate: Tetrafunctional polyester acrylate which is sold under the designation Ebecryl™ 80 by UBC Radcure, Inc. of Louisville, KY. Ebecryl™ 80 has a molecular weight of 1,000 and a viscosity of 3,500 cps (mPa·s) at 25°C. polybutadiene diacrylate: This material is available from Sartomer Company, Inc. of Exton, PA., CN300, under the designation CN300, has a molecular weight of 3,000, viscosity of 4,500 - 5,000 cps (mPa·s) at 25°C. As a general rule of thumb, the use of monomeric multifunctional acrylates in our compositions generally results in a cured coating having hard, abrasion-resistant characteristics. Contrastingly, the use of oligomeric multifunctional acrylates generally produces a slightly softer, but more flexible cured coating. We have also found that there is at least some correlation between the use of oligomeric multifunctional acrylates and decreased gas permeability of the cured coating. Thus, the use of monomeric/oligomeric multifunctional acrylate blends can be exploited to balance the desired properties of the cured coating composition of the invention. The second component (B) of the composition of the invention is the reaction product formed from: (a) at least one alkoxy-functional organometallic compound; (b) at least one alkoxy-functional silane; (c) a predetermined quantity of water; and (d) optionally, a catalytic amount of a siloxane polymerization catalyst. The alkoxy-functional organometallic compound (a) has the general formula M(OR) 4 , wherein M is selected from Si or Ti and each OR is the same or a different alkoxy group. Accordingly, examples of this component include tetraethoxysilane (also called tetraethyl orthosilicate) and tetrabutyl titanate. As used herein, the term "organometallic compound" is specifically meant to include compounds based upon silicon, even though silicon arguably does not possess all the characteristics of a true metal. The alkoxy-functional silane has the general formula wherein each OR is as defined above, each X is a monovalent radical that renders the alkoxysilane capable of copolymerization with the multifunctional acrylate (A) and which is independently selected from the group consisting of: alkylamines of the general formula [QNH] d QNZH wherein Q is a divalent hydrocarbon group, in which Q groups may be the same or different, Z is hydrogen atom or a monovalent hydrocarbon radical; and d is 0 or 1; or monovalent unsaturated hydrocarbon radicals; each R' is independently a monovalent hydrocarbon radical; and a is 1, 2 or 3, b is 1, 2 or 3, c is 0, 1 or 2 and a + b + c = 4. It should be noted that the alkoxysilane includes at least one monovalent radical, X, which renders the alkoxysilane capable of copolymerization with the multifunctional acrylate (A). Amino and diamino radicals are capable of forming a Michael adduct with an acrylate group and are, therefore, ideally-suited and preferred selections. Examples of such amino-functional alkoxysilanes include: 3-aminopropyltriethoxysilane; 3-aminopropyltrimethoxysilane; 3-aminopropylmethyldimethoxysilane; and n-(2-aminoethyl)-3-aminopropyltrimethoxysilane. These aminofunctional alkoxysilanes are commercially available from Huels America, Inc., Bristol, PA. Another supplier of aminofunctional alkoxysilanes is Dow Corning Corporation, Midland, Michigan. When the composition of the invention utilizes an aminofunctional alkoxysilane as component (b) (i.e. X is an amino radical), bonding between component (b) and the multifunctional acrylate (A) occurs during formulation of the composition and not upon curing. Other monovalent radicals that are reactive with the acrylate groups of component (A) so as to render component (b) copolymerizable therewith are monovalent unsaturated hydrocarbon radicals which include vinyl, hexenyl, methacryloxy, acryloxy, styryl and vinylether radicals. Thus, further examples of component (b) include vinyltrimethoxysilane, vinyltriethoxysilane, vinyldimethoxymethylsilane, (all available from PCR, Inc, Gainesville, FL), 3-(methacryloxy)propyltrimethoxysilane (sold as Dow Corning® Z6030, Dow Corning Corporation, Midland, MI) and 3-(acryloxy)propyltrimethoxysilane. When X is a monovalent unsaturated hydrocarbon radical copolymerization of component (b) with component (A) takes place under conditions of free radical polymerization when our composition is cured. Component (c) is a predetermined quantity of water. The importance and selection of the predetermined quantity is discussed below. Component (d) is a siloxane polymerization catalyst. Such catalysts are well-known in the art for promoting the formation of resin networks in the hydrolysis and condensation reaction of alkoxysilanes and other alkoxy-functional organometallic compounds. Examples of siloxane polymerization catalysts include strong protonic acids such as H 2 SO 4 and HClO 4 , trifluoromethane sulfonic acid and a variety of Lewis Acids. Also included are supported catalysts such as H 2 SO 4 -treated montmorillonite clay. Basic siloxane polymerization catalysts include KOH, NaOH and various amines. Because it is so compatible with component (A) the multifunctional acrylate, acrylic acid is the preferred siloxane polymerization catalyst for use in this invention. The use of the siloxane polymerization catalyst (d) is highly preferred, but is considered optional. When, for example, an aminoalkoxysilane is used for component (b), the residual alkalinity of the amino groups is sufficient to promote the hydrolysis and condensation of components (a) and (b) (as further explained below), albeit at a much slower rate and not to the same extent as when the catalyst (d) is employed. It is important to note that the second component (B) of the composition of our invention is described as a reaction product. It is well-known that alkoxy groups associated with the alkoxy-functional organometallic compounds (a) and alkoxysilanes (b) of the invention, will undergo hydrolysis reaction in the presence of water. In the hydrolysis reaction, water reacts at the alkoxy (OR) site, leaving a hydroxyl radical (OH) and forming a HOR alcohol. Thus, one mole of water reacts with one mole of alkoxy radicals, leaving one mole of hydroxyl radicals. It is known in the art that certain of the alkoxy sites are more amenable to hydrolysis than others. Thus, the hydrolysis reaction generally reaches equilibrium well before all alkoxy sites have been hydrolyzed. In the absence of a siloxane polymerization catalyst (d), the hydrolyzed organometallic compounds (a) and silanes (b) are fairly stable and any condensation that takes place is minimal [except as noted above, when utilizing aminoalkoxysilanes as component (b)]. However, in the presence of catalyst, both the hydrolysis and condensation reactions are driven forward. Because hydrolysis and condensation take place simultaneously, the equilibrium reached is dependent on both reactions. In the condensation reaction, two hydroxyl radicals react to yield a single molecule of water and establish a crosslinking oxygen bond. The water liberated though condensation is then available to carry out further hydrolysis. In a manner analogous to the hydrolysis of alkoxy groups, certain of the hydroxyl sites are more amenable to condensation than others. Thus, the condensation reaction generally reaches equilibrium well before all hydrolyzed sites have been condensed. It should be noted, however, that the hydrolysis reaction requires two molecules of water to hydrolyze two alkoxy radicals and that the condensation reaction between two hydroxyl radicals yields but a single water molecule. Theoretically, the water will eventually be consumed, unless present in an amount which exceeds that required to hydrolyze all the hydrolyzable alkoxy sites. Thus, when not present in excess, the amount of water added to the reaction determines the degree of crosslinking which occurs between components (a) and (b). In practice, we have found that adding too much water to the composition of the invention can result in two undesirable outcomes: the formation of a precipitate; or gelling of the composition. Separation of the composition into two phases has also been observed but it is believed to be a manifestation of precipitation. It is theorized that as the hydrolysis and condensation reactions proceed, the crosslinking of components (a) and (b) results in the formation of a sol having a multitude of resin network nuclei dispersed throughout. It is further theorized that if too much water is present, the resin network nuclei either grow large enough to precipitate from solution or numerous and large enough to allow condensation therebetween, resulting in gel formation. The undesirability of making a gelled composition is self-evident, especially if the composition is to be used for making an abrasion-resistant coating. When precipitation occurs, the composition looses its abrasion-resistant properties. In the preferred embodiment of the invention, components (a) and (b), the alkoxy-functional organometallic compound and the alkoxysilane, are blended with the multifunctional acrylate (A). Thereafter, the siloxane polymerization catalyst (d) and the predetermined amount of water (c) are added to the mixture. Thus, the reaction product (B) forms in the presence of the multifunctional acrylate (A). Indeed, if a low viscosity multifunctional acrylate (A) is used, components (a) and (b) are frequently found to be soluble therein and there is no need to use additional organic solvents, as was required in the prior art. When formulating the compositions of our invention in the preferred manner described above, the alkoxy-functional organometallic compound (a) and alkoxysilane (b) undergo cohydrolysis and cocondensation. In practice, we have found that combining the water (c) and catalyst (d) with the alkoxy-functional organometallic compound (a) or the alkoxysilane (b), independently, may yield a product that, when cured, exhibits substantially reduced abrasion-resistant properties. It is theorized that the cocondensation of the hydrolyzed alkoxy-functional organometallic compound (a) and alkoxysilane (b) produces a resin network that has a more homogeneous chemical structure, both before and after curing. Those skilled in the art will understand that while the composition of the present invention does not require the presence of colloidal silica, neither is it prohibited. Likewise, while many embodiments of the present invention can be successfully formulated without the use of a polar solvent, its use, for adjusting properties such as viscosity and the like, is not prohibited. Those skilled in the art will further appreciate that the selection of specific species of (A), the multifunctional acrylate, (a) the alkoxy-functional organometallic compound and (b) the alkoxysilane, will depend primarily upon the properties desired for the end-use of the composition (e.g. abrasion resistance or gas permeability) and cost. Other components can be added to the compositions of this invention to enhance their usefulness as coatings. For example, diluents, leveling agents, ultraviolet light absorbers, dyes and the like, can be included. Butylated hydroxytoluene (BHT) and phenothiazine (PTZ) are known in the art as inhibitors of autopolymerization of acrylates and may also be added. If the composition of our invention is used as a coating material, it may be applied to substrates by known methods such as flow coating, dip coating, spin coating, spray coating or curtain coating. A coating thickness between 3-25 micrometers, preferably 5 µm, is generally recommended for applications calling for abrasion resistance. Various examples of the coating composition of the invention were prepared, coated over substrates (to a thickness of 5 µm) and UV-cured. As used herein to describe the preparation of examples of the invention, the term "UV-cured" means that the coated substrate was subjected to at least 2000 millijoules of UV radiation/cm 2 . The abrasion resistance of the cured compositions of this invention was determined by ASTM Method D-1044. The instrument used was a Teledyne™ Model 503 Taber Abrader with two 250 gram auxiliary weights (500 gram load) for each of the CS10F abrasive wheels. In the ASTM method, coated polycarbonate Taber panels were subjected to 100 and 500 cycles on the abrader turntable (T-100 and T-500, respectively). The percent change in haze, which is the criterion for determining the abrasion resistance of the coating, was determined by measuring the difference in haze of the unabraded and abraded coatings. Haze is defined as the percentage of transmitted light which, in passing through the sample, deviates from the incident beam by forward scattering. In this method, only light flux that deviates more than 2.5 degrees on average is considered to be haze. The percent haze on the coatings was determined by ASTM Method D-1003. A Gardner Haze Meter was used and the haze was calculated by measuring the amount of diffused light, dividing by the amount of transmitted light and multiplying by one hundred. The above-described Taber abrasion testing is not limited to the use of polycarbonate test panels. In the event that a given composition does not adhere to a polycarbonate substrate, any other substantially transparent, preferably plastic, substrate may be used, so long as the composition adheres thereon. The measure of turbidity of the composition of the invention is made relative to a standard and expressed simply as an index. As reported herein, turbidity was measured on a Series 965 Digital Direct-Reading Turbidmeter (available from Orbeco Analytical Systems, Inc. Farmingdale, NY) and in accordance with the instructions provided therewith. Example 1 - Tetraacrylate Monomer/Aminoalkoxy Silane/Tetraethoxy Silane Composition. 11.8 g of a solventless pentaerythritol tetraacrylate (available from Sartomer, Inc., Exton, PA under the name Sartomer™ 295) 2.18 g of tetraethoxysilane and 1.24 g of aminopropyltriethoxysilane were stirred in 500 ml flask over night. (Typically, adequate mixing and the Michael adduct reaction between the aminosilane and acrylate can be achieved with one hour of stirring). Thereafter, 0.85 g of a siloxane polymerization catalyst in the form of acrylic acid was added dropwise and the resulting solution stirred for an additional hour. Then, 0.35 gram of water was added dropwise with continued stirring for an additional hour. The resulting solution had a turbidity index of 6.2 and a viscosity of 364 cps (mPa·s). Next, 0.68 g of a photoinitiator (Darocure™ 1173, from Ciba Geigy, hydroxymethylphenylpropanone) was added to the composition, applied to a polycarbonate test panel and cured with ultraviolet radiation. The resulting composition exhibited Taber abrasion resistance of T-100 = 2.3 and T-500 = 6.7. Example 2 - Triacrylate Monomer/Aminoalkoxy Silane/Tetraethoxy Silane Composition A composition identical to that described above Example (1) was prepared except that an identical weight of pentaerythritol triacrylate (Sartomer™ 444) was substituted for the pentaerythritol tetraacrylate (Sartomer™ 295.) The resulting solution had a turbidity index of 1.5 and viscosity of 322 cps (mPa·s). The cured composition exhibited Taber abrasion resistance of T-100 = 2.1 and T-500 = 6.5. Example 3 - Tetraacrylate Monomer/Methacryloxypropyltrimethoxy Silane/Tetraethoxy Silane Composition 11.8 g of a solventless pentaerythritol tetraacrylate (available from Sarotmer, Inc., as Sartomer™ 295), 2.18 g of tetraethoxysilane and 1.24 g of methacryloxypropyltrimethoxysilane were stirred in 500 ml flask over night. (Typically, adequate mixing can be achieved with one hour of stirring). Thereafter, 0.85 g of a siloxane polymerization catalyst in the form of acrylic acid was added dropwise and the resulting solution stirred for an additional hour. Then, 0.35 gram of water was added dropwise with continued stirring for an additional hour. The resulting solution had a turbidity index of 2.7 and a viscosity of 38.1 cps (mPa·s). Next, 0.68 g of a photoinitiator (Darocure™ 1173, Ciba Geigy) was then added to the composition, applied to a polycarbonate test panel and cured with ultraviolet radiation. The cured composition exhibited Taber abrasion resistance of T-100 = 1.6 and T-500 = 7.1. Example 4 - Triacrylate Monomer/Methacryloxypropyltrimethoxy Silane/Tetraethoxy Silane Composition A composition identical to that described above (Example 3) was prepared except that an identical weight of pentaerythritol triacrylate (Sartomer™ 444) was substituted for the pentaerythritol tetraacrylate (Sartomer™ 295). The resulting solution had a turbidity index of 7.3 and viscosity of 36.1 cps (mPa·s). The cured composition exhibited Taber abrasion resistance of T-100 = 2.4 and T-500 = 9.0. Example 5 - Triacrylate Monomer/Methacryloxypropyltrimethoxy Silane/Tetrabutyl Titanate Composition. 11.8 g of pentaerythritol triacrylate (Sartomer" 444) and 1.64 g of tetrabutyl titanate were stirred in 500 ml flask for one hour. 1.24 g of methacryloxypropyltrimethoxysilane was added, with continued stirring for an additional hour. Thereafter, 0.63 g of acrylic acid was added with continued stirring for an additional hour. Next, 0.7 g of water was added in a drop-wise manner and mixed for one hour. The resulting solution had a turbidity index of 2.1 and a viscosity of 54.1 cps (mPa·s). Then, 0.64 g of Darocure™ 1173, Ciba Geigy's photoinitiator, was stirred in and the composition applied to polycarbonate panels and UV-cured for Taber testing. Abrasion testing yielded T-100 of 2.2 and T-500 of 9.4, indicating excellent abrasion-resistant properties. Example 6 - Triacrylate Monomer/Methacryloxypropyltrimethoxy Silane/Tetrabutyl Titanate/Tetraethoxy Silane Composition. To test the compatibility of two different types of alkoxy-functional organometallic compounds [component (a)], a composition identical to that disclosed in Example 5, was prepared, except that tetraethoxysilane was substituted for one-half (0.82 g) of the tetrabutyl titinate, for a total of 1.64 g of mixed alkoxy-functional organometallic compounds. The resulting composition had a viscosity of 74.1 cps (mPa·s) and a turbidity index of 1.6. The UV-cured composition exhibited Taber abrasion of T-100 = 3.4. Example 7 - Tetracrylate Monomer/Methacryloxypropyltrimethoxy Silane/Aminopropyltriethoxy Silane/Tetraethoxy Silane Composition. To test the compatibility of two different types of alkoxy-functional silanes [component (b)], a composition identical to that disclosed in Example 3 was prepared, except that aminopropyltriethoxysilane was substituted for one-half (0.62 g) of the methacryloxypropyltrimethoxysilane, for a total of 1.24 g of mixed alkoxy-functional silanes. The resulting composition had a viscosity of 163 cps (mPa·s) and a turbidity index of 1.0. The UV-cured composition exhibited Taber abrasion of T-100 = 2.2 and T-500 = 8.2, indicating excellent abrasion resistance. Example 8 - Hexafunctional Aromatic Urethane Acrylate Oligomer/Aminopropyltriethoxy Silane/Tetraethoxy Silane Composition. 11.8 g of an hexafunctional aromatic urethane acrylate (with an acrylated polyol diluent) sold under the designation Ebecryl™ 220, 2.18 g of tetraethoxysilane and 1.24 g of aminopropyltriethoxysilane were added to a flask and stirred for one hour. Thereafter, 2.7 g of acrylic acid were added and the solution stirred for an additional hour. Then, 2.7 g of water were added in a dropwise manner and the solution stirred for an additional hour. The resulting solution had a viscosity of 600 cps (mPa·s) and a turbidity index of 10.7. Next, 0.64 g of Darocure™ 1173, Ciba Geigy's photoinitiator, was stirred in, the composition applied to polycarbonate panels and UV-cured for Taber testing. Abrasion testing yielded T-100 of 3.0 and T-500 of 7.6, indicating excellent abrasion-resistant properties. As previously mentioned, the compositions of the invention have diverse utility. Accordingly, the range of the most useful formulations depends upon the specific coating property that is of importance for a particular application. For instance, the range of formulations that provides a coating having barrier properties may be considerably different than the range that provides substantial abrasion-resistance. The technique described below was used to establish the range of the most useful formulations for providing abrasion-resistant properties, when the composition of the invention includes a specific tetraacrylate monomer and aminosilane. Referring again to Example 1, it can be seen that the formulation provided excellent abrasion resistance as measured by the Taber Abrasion test. Numerous samples of this composition were prepared in a manner identical to that described above, except that the quantities of tetraethoxysilane, aminopropyltriethoxysilane, acrylic acid and water were independently varied (all other constituents and quantities remaining constant). The Taber abrasion resistance of each of the varied formulations was measured and any difficulties associated with preparation were noted. The results are reported in Tables 1 through 4. The * specifically denotes the composition of Example 1. Variations in Tetraethoxysilane (TEOS) TEOS (g) T-100 T-500 Viscosity (mPa·s) 0.0 4.1 14.4 822 0.27 3.2 6.3 1130 1.09 3.4 6.8 750 2.18* 3.2 7.8 428 4.36 7.2 19.8 124 8.72 4.5 15.8 38.1 Variations in Aminopropyltriethoxysilane (AMPTES) AMPTES (g) T-100 T-500 Viscosity (mPa·s) 0.0 4.7 15.2 14.0 0.32 3.6 15.4 22.0 0.62 4.4 11.1 30.1 1.24* 3.4 6.8 750 2.48 5.3 20.9 1130 4.96 - - GEL Variations in Acrylic Acid (AA) AA (g) T-100 T-500 Viscosity (mPa·s) 0.0 4.2 15.2 90.2 0.42 3.6 9.7 750 0.85* 3.4 6.8 710 1.7 5.4 11.1 742 3.4 3.2 10.7 471 Variations in Water Water (g) T-100 T-500 Viscosity (mPa·s) 0.0 2.7 12.9 782 0.17 3.5 8.2 731 0.35* 3.4 6.8 750 0.70 2.9 7.5 481 1.4 3.8 6.8 230 2.8 3.8 7.0 291 5.6 45.4 - two phases Tables 1 through 4 illustrate how to determine the usable range of components for embodiments of the invention that utilize a pentaerythritol tetraacrylate [multifunctional acrylate (A)], tetraethoxysilane [alkoxy-functional organometallic compound (a)], aminopropyltriethoxysilane [alkoxy-functional silane (b)], (c) water and acrylic acid [siloxane polymerization catalyst (d)]. In this instance, the range of useful compositions was directed at those compositions that would yield the most abrasion-resistant properties, based upon a constant amount of pentaerythritol tetraacrylate (11.8 parts by weight). Referring to the Tables, it is seen that the most abrasion-resistant properties were exhibited when the level of tetraethoxysilane was at least 0.27 parts and something less than 4.36 parts (Table 1); aminopropyltriethoxysilane was greater than 0.32 parts and less than 2.48 parts; at least some acrylic acid was present in an amount up to 3.4 parts; and the predetermined quantity of water was maintained between 0.17 and 2.8 parts, inclusive. Optimizing the abrasion-resistant properties of our formulation can be achieved with further experimentation on a trial and error basis. With the above information, we prepared a composition having 11.8 parts of pentaerythritol tetraacrylate [multifunctional acrylate (A)], 1.64 parts tetraethoxysilane [alkoxy-functional organometallic compound (a)], 1.24 parts aminopropyltriethoxysilane [alkoxy-functional silane (b)], 0.70 parts water (c) and 0.63 parts acrylic acid [siloxane polymerization catalyst (d)]. The cured composition so-prepared exhibited Taber abrasion properties of T-100 at 3.1 and T-500 at 7.1.

Claims: A radiation-curable composition comprising: (A) at least one multifunctional acrylate which is a monomer or oligomer which contains two or more acryloxy or methacryloxy groups; and (B) a reaction product formed from the cohydrolysis and cocondensation of (a) at least one alkoxy-functional organometallic compound of the general formula M(OR) 4 wherein M is selected from Si or Ti and each OR is the same or a different alkoxy group; (b) at least one alkoxy-functional silane of the general formula wherein each OR is as defined above, each X is a monovalent radical that renders the alkoxysilane capable of copolymerization with the multifunctional acrylate (A) and which is independently selected from the group consisting of: alkylamines of the general formula [QNH] d QNZH wherein Q is a divalent hydrocarbon group, in which Q groups may be the same or different, Z is hydrogen atom or a monovalent hydrocarbon radical and d is 0 or 1; and monovalent unsaturated hydrocarbon radicals, each R' is independently a monovalent hydrocarbon radical; and a is 1, 2 or 3, b is 1, 2 or 3, c is 0, 1 or 2 and a + b + c = 4; with (c) a predetermined quantity of water sufficient to cause said cohydrolysis and cocondensation without gelling said reaction product (B) or causing a precipitate to form therefrom; and (d) optionally, a catalytic amount of a siloxane polymerization catalyst. The composition of claim 1 wherein said monovalent unsaturated hydrocarbon radicals are selected from the group consisting of vinyl, hexenyl, methacryloxy, acryloxy, styryl and vinylether radicals. Use of the composition of claim 1 or 2, to prepare an article of manufacture by coating at least one surface of a substrate with said composition and by then curing the coating on the coated substrate. Use according to claim 3 wherein said substrate is polyethylene terphthalate or polycarbonate. Use according to claim 4 wherein said substrate is in the form of a beverage container. A method of making an organically-modified, radiation-curable siloxane resin comprising the steps (1) and (2) which are performed sequentially or simultaneously: (1) cohydrolyzing and cocondensing: (a) at least one alkoxy-functional organometallic compound of the general formula M(OR) 4 wherein M is selected from Si or Ti, and (b) at least one alkoxy-functional silane of the general formula wherein each OR is as defined above, each X is a monovalent radical that renders the alkoxysilane capable of copolymerization with the multifunctional acrylate (A) and which is independently selected from the group consisting of: alkylamines of the general formula [QNH] d QNZH wherein Q is a divalent hydrocarbon group, in which Q groups may be the same or different, Z is hydrogen atom or a monovalent hydrocarbon radical and d is 0 or 1; and monovalent unsaturated hydrocarbon radicals, each R' is independently a monovalent hydrocarbon radical; and a is 1, 2 or 3, b is 1, 2 or 3, c is 0, 1 or 2 and a + b + c = 4; (c) a predetermined quantity of water sufficient to cause said cohydrolysis and cocondensation of said alkoxy-functional organometallic compound (a) and alkoxysilane (b), without gelling or causing a precipitate to form therefrom; and (2) blending at least one multifunctional acrylate which is a monomer or oligomer which contains two or more acryloxy or methacryloxy groups with components (a), (b) and (c) or the reaction product thereof as obtained in step (1). The method of claim 6 wherein said reaction product (B) further includes (d) a siloxane polymerization catalyst selected from the group consisting of H 2 SO 4 , HClO 4 , trifluoromethane sulfonic acid, acrylic acid, KOH, NaOH and amine-containing compounds. The method of claims 6 or 7 wherein (a), said at least one alkoxy-functional organometallic compound and (b), said at least one alkoxysilane, are simultaneously blended with (c), said predetermined quantity of water during said reacting step (1), such that components (a) and (b) undergo cohydrolysis and cocondensation. The method of claim 8 wherein said cohydrolysis and cocondensation take place in the presence of said multifunctional acrylate. The method of claim 9 further comprising the step of (3) blending at least one photoinitiator with the products obtained from steps (1) and (2).

Inventors: BLIZZARD JOHN D, TONGE JAMES S, BLIZZARD, JOHN D., TONGE, JAMES S.
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1996
Main classification: C09D183
IPC codes: C08F2, C09D183, C08L83, C09D4, C08F283