MXPA98000834A - Transparent polyurethane coatings and pigments in color of hardening with hume - Google Patents

Abstract

A composition of hardening coatings with moisture comprising in an organic solvent a polyurethane prepolymer, optionally a pigment and a drier in which the polyphosphoric acid is dry

Description

TRANSPARENT POLYURETHANE COATINGS AND PIGMENTED IN COLOR OF HARDENING WITH HUMIDITY DESCRIPTION OF THE INVENTION The present invention relates to polyurethane coating compositions containing a polyurethane prepolymer, which are hardened by moisture. There are many commercial and industrial protective and / or decorative coatings to be applied to walls, machines and other similar entities that require protective coatings. Polyurethane coatings are known in the industry as one of the most resistant coatings that exist. However due to certain problems there is little willingness to use these coatings. The industry uses one of two systems, the simple, moisture hardening polyisocyanate component and the two-pack system consisting of a polyol component and a separate isocyanate component, the polyol being selected to be chemically combined with the suitable polyisocyanate. In addition, the polyol portion is pigmented to obtain the desired color and opacity, etc. One problem with single-component systems is that color pigments contain moisture absorbed on their surfaces which causes the polyurethane formula to gel over a few days, becoming hard and unsuitable for commercial use. Additionally the reaction of the isocyanate with water produces carbon dioxide gas which can cause the formation of dangerous pressure during storage of the coating in sealed containers. Two pack or component systems have the advantage that they overcome the problems of combining color pigments and isocyanate polymers when creating a single-component polyurethane. In the two component system, the pigmented polyol portion and the polyisocyanate are presented in separate containers to the end user or consumer. The consumer mixes the two portions according to the proportion specified by the manufacturer before use. However, this mixture has a limited life time and should be used in a relatively short period of time or it will harden and could not be used. This option is not only laborious but also expensive because it results in a quantity of hardened and wasted material, if the whole mixture is not used. There is also a danger that the pigmented polyol portion and the polyisocyanate portion will not mix in the correct ratio causing serious damage to the performance of the resulting polyurethane coating. In addition, atmospheric humidity is an important factor when using the two pack method because water also hardens the isocyanate. On a hot, humid day a large portion of the polyisocyanate is hardened by atmospheric moisture leaving a portion of the polyol with nothing to re-bind, resulting in a less desirable coating than if the polyol had been completely cross-linked. Likewise, on a dry and cold day more polyol will crosslink with the polyisocyanate. It is evident that the two-pack polyurethane coating method will produce coating quality dependent on atmospheric conditions that are almost always almost impossible to control. Moisture-hardening polyurethane coatings can be made with a simple packing method eliminating all the above-mentioned problems of the two-pack types. There are many polyisocyanates that react with atmospheric water at room temperature and form useful films that are used in limited form as polyurethane coatings that harden by moisture. This type of coating is one of the finest existing coatings that can be produced without the use of heat or the application of other external sources of energy. They are very useful for objects that can not be heated. However, making those systems from a single package is also laborious and expensive. Existing methods for preparing color-pigmented polyurethane coatings in a simple package require careful drying of all components such as color pigments, for reasons mentioned above; this often requires very slow procedures and the use of expensive equipment or require the sacrifice of some critical properties of the final coating film, such as loss of gloss, high risk of toxicity during application, lack of strength in the film, etc. The materials for example drying agents that are used to dry, and the passive pigments in a single package, the color pigmented polyurethane coatings of hardening with moisture:. molecular sieves that cause the coatings to lose their shine and sometimes gel due to the alkalinity of some monofunctional isocyanate molecular sieves, such as p-toluenesulfonyl isocyanate [PTSI], which are expensive and dangerous due to their highly volatile diisocyanates , such as isophorone diisocyanate [IPDI] and di (phenyl isocyanato) methylene derivatives [MDI], which require an excess and can generate a toxicity problem ortho-alkyl esters, such as ethylotroformate, which results in the formation of alcohols that degrade the final coating film. Most manufacturers of moisture hardening polyurethane, for the above reasons, manufacture moisture hardening polyurethanes in a transparent or pigmented form with hydrophobically treated metal pigments such as aluminum. These metallic pigments contain little or no moisture and therefore the moisture problems inherent in the color pigments do not exist; the color pigments have sufficient moisture absorbed to render them unsuitable for use in polyurethane coatings that harden with moisture. U.S. Patent 4,304,706 discloses a process for making wet hardening polyurethanes that are pigmented with color by preparing a slurry of specific color pigments, solvents and additives to which a specific amount of a selected monomeric diisocyanate is added. A polyol [or other suitable hydrogen donors] is added to the slurry and the monomeric diisocyanate. To the aforementioned mixture, called a color pigment dispersion, pigments were then added followed by isocyanate prepolymers. The complete mix results in a moisture hardening polyurethane [air-dried] with stable color for use as a protective and decorative coating.

The present invention relates to a polyurethane coating composition that hardens by moisture consisting of a polyurethane prepolymer [also called isocinanate or polyisocyanate prepolymer] optionally in an organic solvent to which polyphosphoric acid [PPA] has been added as a stabilizer /drying. The coating composition may be a clear coat or a color pigmented coat. Another embodiment of the invention is to stabilize a moisture-curing polyurethane coating composition containing an isocyanate-terminated prepolymer, optionally in an organic solvent, by adding a statically effective amount of PPA. As another embodiment of the invention, a substrate coated with a polyurethane coating deposited on a clear or color-hardening color coating composition described above is provided. The addition of PPA to the coating composition gives the following advantages: PPA is effective both as a stabilizer against thermal degradation for the isocyanate-containing composition and is a pigment drying agent. . PPA also provides improved corrosion resistance and better adhesion to metal substrates including oxidized steel.

A moisture hardening coating composition basically consists of a polyisocyanate component and an organic solvent. Suitable polyisocyanate materials can be any of the isocyanate-terminated prepolymers well known in the art for preparing moisture-curing polyurethane coatings. The prepolymers typically consist of a partially prereacted mixture of a polyisocyanate and a polyether of polyether or polyester. Many polyisocyanates can be used to prepare the prepolymers such as eg hexamethylene diisocyanate, phenylene diisocyanate, toluene diisocyanate [TDIJ and 4,4'-diphenylmethane diisocinanate ["MDI]." Isopropyl diisocyanate [IPDI] is especially suitable for making prepolymers for top coatings and trimethylhexamethylene diisocinanate [TMDI] is excellent for flexible coatings and for exterior use.TDI is cheap but has poor exterior characteristics.MDI has low exterior durability but forms a strong coating resistant to chemicals. of polyols suitable for use in the preparation of prepolymers such as polyalkylene polyether and polyester polyols Polyalkylene polyether polyols include poly (alkylene oxide) polymers such as poly (ethylene oxide) and poly (propylene oxide) and copolymers with terminal hydroxyl groups derived from a compound or polyhydric, including idoles and thiols; for example among others ethylene glycol, propylene glycol, 1,3-butane diol, 1,4-butane diol, 1,6-hexane diol, neopentyl glycol, diethylene glycol, dipropylene glycol, pentaerythritol, glycerol, diglycerol, trimethylol propane and similar low molecular weight polyols. Obviously a single polyether polyol of high molecular weight can be used. Mixtures of high molecular weight polyether polyols such as mixtures of difunctional and trifunctional materials and / or materials of different molecular weight or different chemical composition can also be used. Polyester polyols include those produced by reacting a dicarboxylic acid with an excess of a diol, for example adipic acid with ethylene glycol or butane diol,. or reacting a lactone with an excess of a diol such as caprolactone with propylene glycol. In addition to or in place of some of the polyols, polyamines such as ethylenediamine may be used. The prepolymers should have an NCO content of 1 to 30% by weight, preferably 6 to 16% by weight. Polyisocyanate prepolymers suitable for transparent and colored pigmented coatings are well known in the art and commercially available., such as AIRTHANE * ™ PCG-475 prepolymers and AIRTHANE ASN-540 [Air Products and Chemicals, Ine], prepolymer and Des-Odur E-23 [Bayer Corp.], To prepare the polyurethane coating composition that hardens with pigmented moisture With color any of the pigments well known in the art can be used obviously they can be used except possibly for those pigments, such as iron oxide, which have a high reduction power because the PPA can reduce them. Pigments suitable for color pigmented coatings are commercially available from different sources, such as Hüls, Inc. and Bayer, Inc. PPA used in the invention is a well-known chemical material and consists of the condensation products of orthophosphoric acid above. of 400 * C, to which it returns when diluted with water and includes pyrophosphoric acid. PPA is also called phospholeu and tetraphosphoric acid. PPA can also be prepared by heating orthophosphoric acid with sufficient phosphoric anhydride. To carry out the invention, commercial PPA or PPA prepared in situ can be used using phosphoric pentoxide [P2Os] which will react with the existing moisture. As with the other components, organic solvents suitable for use in the present invention are any of those well known in the art of transparent and color pigmented coatings that harden with moisture. Examples of suitable solvents are methyl amyl ketone, butyl acetate, toluene and mixtures thereof. Other additives that are frequently used in clear and color-pigmented coating compositions include, for example, plasticizers, surfactants, pigment dispersants, flow aids and levellers, defoamers, antioxidants and light stabilizers. A typical clear coating composition according to the invention will comprise 10 to 90% by weight of polyisocyanate prepolymer, 1 to 70% by weight of pigment and 0.1 to 10% by weight, preferably 2 to 6% by weight of PPA, in base to the prepolymer, optionally in a suitable solvent. In carrying out the invention, the PPA is simply added in the process of making the paint or can be added so easily to the prepolymer in or during its manufacture. When used in the process of making the paint for pigments that are not ground, for example zinc dust, the prepolymer is first heated or diluted in solvent to reduce the viscosity and the PPA is added with low tearing and mixing well. The pigment is then added slowly with moderate tearing and allowed to mix well. For pigments that are reduced to the particle size, for example titanium dioxide, the PPA can be added either as described above or under high tear after the pigment has been dispersed. For a clearcoat application, the PPA is simply mixed in the prepolymer, the viscosity of the prepolymer is reduced by heating or diluting with a solvent as needed. The transparent and pigmented coatings prepared according to the invention show good shelf stability and the panels coated with the compositions have shown corrosion resistance equal to or better than that of isocyanate-dried systems. No heat is required to accelerate the drying process as is the case with isocyanate drying agents. The PPA improves the corrosion resistance and improves the shelf stability of the prepolymer. Although PPA must be handled with care since it is essentially a very strong acid, its use does not present the problems of toxicity or exposure potential of isocyanate dryers. The coating compositions according to the invention can be applied on different substrates with or without a base coat including steel, aluminum, concrete and wood. In the following examples of top coatings of moisture hardening, the following components were used: Molecule sieve based on zeolite Davidson Syloid 120 Titanium dioxide DuPont TiPure R960 Pigment dispersant Hüls Nuosperse N657 Polyacrylate / polyethylene blend King Dislon NS-30 King Kkat metal salt catalyst XC-4205 Neopentyl adipate prepolymer Airthane "r ASN 540M IPDI Tego Chemie Airez 980 silicone-based foaming agent Para-toleunsulfonyl paraisocyanate PTSI Metacure Metallic Salt Catalyst" 120 EXAMPLE 1 This example demonstrates a composition of standard topcoat moisture-curing polyurethane. STANDARD TOP COVER WITH PTSI EXAMPLE 2 This example demonstrates a moisture hardening polyurethane coating composition for top layer containing PPA.

STANDARD TOP COVER WITH PPA EXAMPLE 3 Table 1 presents the comparative data for the coating compositions of examples 1 and 2. It can be seen from the data that the topcoat composition containing PPA of example 2 worked the same or better than the composition containing PTSI of the example 1. Example 2 was superior with respect to the loss of brightness and the retention of brightness under the exposure of UV stabilized fomulations.

TABLE 1 DECLARATION OF INDUSTRIAL APPLICATION The present invention provides transparent and color pigmented coating compositions that harden with moisture, which contains a polyurethane prepolymer and polyphosphoric acid as stabilizer and pigment drying agent.

Claims (9)

1. CLAIMS 1.- In a polyurethane coating composition that hardens with moisture consisting of a polyurethane prepolymer and a drying agent, optionally in an organic solvent, the improvement consists of the drying agent which is polyphosphoric acid.
2. 2. - The coating composition according to claim 1, wherein the polyphosphoric acid is present in 0.1 to 10% by weight based on the prepolymer.
3. 3. The coating composition of claim 1 in which the polyphosphoric acid is present in 2 to 6% by weight, based on the prepolymer.
4. 4. In a pigmented coating composition that hardens with moisture consisting of a polyurethane prepolymer, a pigment, a drying agent, and optionally an organic solvent, the improvement consists in that the drying agent is polyphosphoric acid.
5. 5. The coating composition according to claim 1, wherein the polyphosphoric acid is present in 0.1 to 10% by weight based on the prepolymer.
6. 6. The coating composition of claim 1 in which the polyphosphoric acid is present in 2 to 6% by weight, based on the prepolymer.
7. 7. In a method for stabilizing a polyurethane coating composition that hardens with moisture containing a polyurethane prepolymer, optionally in an organic solvent, the improvement consists in adding 0.1 to 10% by weight of polyphosphoric acid based on the prepolymer.
8. 8. The method according to claim 7, wherein the coating composition is a transparent coating.
9. 9. The method according to claim 7, wherein the coating composition is a color pigmented coating.