amount of a weak acid means that there is 0.1 to 10% of weak acid by weight (w/w) of the aerosol dispersion, pref› erably from 0.1 to 5%, more preferably from 0.25 to 2% of weak acid by weight (w/w) of the aerosol dispersion. 

[0086] In a preferable embodiment of the present inven› tion the weak acid is added into paint forming dispersion an amount that will contribute to a higher adhesion to the paint surface by etching. 

[0087] The use of catalytic amount of weak acid in the present method and the aerosol dispersion used in this method enables making high quality paints regardless if all it is used at once or reused after an extended time period 

[0088] The dry paint film (undercoat, finishing coat or lacquer) prepared from said mixture should have gloss in the range of 10-100 preferable over 90, under an angle of 60°. 

[0089] The dry paint film prepared from said mixture should have the Konig-hardness over 40 after 10 hand over 100 after 120 h of drying-time, measured with pendel hardness meter. 

[0090] The dry paint film prepared from said mixture should have the adhesion >450 psi, in PosiTest. 

[0091] The aerosol formulation may even be prepared under ambient conditions without any particular need for pre-drying the components of aerosol formulation before packing them into aerosol can or operating under inert gas, such as nitrogen, atmosphere while preparing the formula› tion from its components or filling the can. Even technical grade or industrial quality components comprising hardener precursors may be used although they provide water into the formulation inside the can. 

[0092] The stable mixture of the polyurethane resin and the polyurethane precursor and the weak acid, together with at least one propellant, is packed as an aerosol dispersion into a conventional one-chamber aerosol can. As the aerosol formulation comprising polyurethane resins and hardener precursor is sprayed from the can, a cloud of fine particles suspended in gas or air is formed picking up water (mois› ture) from the air. The absorbance of water will have an effect on the hardener precursor, such as oxazole, preferable oxazolidine or bisoxazolidine, imine, enamine, aldimine and/or Mannich base or Schiff’s base compound. With the relatively overload of water present in the atmospheric air, the hardener precursor will hydrolyze and form a compound having amine and/or hydroxyl functionality(ties) which will react with the polyurethane resin an a possible epoxy resin and create a cross linking film. Together with the other paint/adhesive related ingredient this will form the eventual end product (paint) which can be an adhesive, a colored top coat, a varnish, lacquer, a primer or a clear coat. 

[0093] As the reaction between the amine compound and/or hydroxyl compound and the polyurethane resin and the possible epoxy group occurs outside of the aerosol can, the formulation inside the can stays stable. No additional moisture from the air gets inside the can, because pressure inside the can is greater than the pressure outside of the can. Compared to prior art wherein a kind of stable environment is achieved after removing water, this kind of moisture control method have a definitive advantage of being able to withstand moisture variations. 

[0094] There is also another significant advantage since the curing reaction begins only when the dispersion is sprayed outside of the sealed can; the surface quality of the paint will be better compared to prior art 2 compartment 2K-products wherein curing begins already in the can after 

puncturing said compartments so that their content is mixed (at least the hardener and the hardener precursor). 

[0095] As the formulation stays stable inside the can, only a desired portion of the two-component aerosol formulation may be used at a time. That is, the whole formulation does not have to be used at once, since the formulation remains stable inside the can due to reaction 2a in which hydrolyzed products of hardener precursors will not proceed into for› mation of hardener amines but back to forming original hardener precursors. 

[0096] Shelf life of the can containing the formulation is at least a year, possibly up to 3 years or even more. Moreover, an aerosol can containing the formulation is easier and faster to use, because there is no need to first separately mix the hardener and the binder as is the case with known solutions. 

[0097] The preparation of the formulation and can con› taining the formulation is essentially simplified as no pro› tection gas or pre-drying steps are necessary. The manufac› turing can take place in ambient conditions using regular mixing and can filling techniques. 

[0098] By ambient is meant the typical environmental conditions, temperature, pressure and humidity, prevailing at the point of preparation of the formulation at regular indus› trial surroundings. 

[0099] In one aspect, the present invention provides a two-component aerosol formulation suitable for use in an aerosol can, such as in a single chamber aerosol can. Naturally, also multiple chamber cans can be used, in a case paint forming chemicals, comprising epoxy resin and a hardener precursor, 

[0100] a weak acid and a possible solvent for obtaining a mixture; 

[0101] the components are brought into contact with each other once taking the can into use. 

[0102] More particularly, the present invention provides a two-component aerosol dispersion containing paint forming chemicals comprising at least one polyurethane resin and at least one hardener precursor, and at least one propellant. The formulation further contains at least a portion of a weak acid having the pKa value in the range from 1.2 to 5.2. 

[0103] In one embodiment the weak acid is selected from those having pKa value within the range from 3 to 5, for efficiently maintaining the equilibrium of the formulation at the hardener precursor’s side. 

[0104] In another embodiment the weak acid is selected from those having the pKa value within the range from 4.2 to 4.9 for optimized stability in storage and performance in use. 

[0105] Naturally, the type of weak acid has a further influence on the formulation properties, as well as the amount of weak acid used. 

[0106] In the dispersion of the present invention, the polyurethane resin does not substantially react with the hardener precursor or with the weak acid of the aerosol dispersion. 

[0107] The aerosol dispersion of the present invention comprises at least one latent hardener precursor which is selected from the group consisting of an imine, an enamine, an oxazolidine, a Mannich base, a Schiff’s base, aldimine and mixtures thereof. 

