Abstract:
An abrasion-resistant coating composition for use on transparent plastic substrates and the like is formed from a first component derived by partial hydrolysis from a hydrolyzable epoxysilane and a second component comprising the reaction product of a non-silane-based aliphatic polyamine and a ketone or aldehyde. The two components are mixed to allow regenerated amino groups of the first component to react with the epoxy groups of the second component to form a partially polymerized mixture which is diluted with a solvent and applied to the substrate and heated to complete the curing process.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a siloxane-based tintable coating composition for forming abrasion-resistant coatings on lenses or other optical articles, especially those formed from synthetic plastics. 
     In recent years, synthetic plastics such as polycarbonate have replaced glass in many optical applications, particularly opthalmic lenses, because of the lighter weight and superior impact resistance of the plastics. However, plastics such as polycarbonate are relatively soft, and must receive an abrasion-resistant coating to provide an acceptable level of abrasion or scratch resistance. Many abrasion-resistant coating compositions of the prior art are of the polysiloxane type, in which crosslinking is provided by condensation of silane groups formed by hydrolysis of alkoxysilanes. Representative compositions of this type are disclosed in Treadway et al U.S. Pat. No. 4,378,250 and the references cited therein. Although the compositions disclosed in these references are useful in the formation of abrasion-resistant coatings, considerable room for improvement remains in terms of abrasion resistance and tintability. 
     SUMMARY OF THE INVENTION 
     One object of our invention is to provide a coating that is more abrasion-resistant than those of the prior art. 
     Another object of our invention is to provide an abrasion-resistant coating that is more readily tintable than those of the prior art. 
     Still another object of our invention is to provide an abrasion-resistant coating that is readily applied to the substrate. 
     A further object of our invention is to provide an abrasion-resistant coating that satisfactorily adheres to the substrate to which it is applied, both before and after tinting. 
     A still further object of our invention is to provide an abrasion-resistant coating that is cosmetically acceptable. 
     Other and further objects will be apparent from the description that follows. 
     In general, our invention contemplates an abrasion-resistant coating composition, for use on transparent plastic substrates and the like, which is formed from a first component derived by partial hydrolysis from a hydrolyzable epoxysilane and a second component comprising the reaction product of a non-silane-based aliphatic polyamine and a carbonyl-containing compound selected from the group consisting of ketones and aldehydes. The two components are mixed to allow regenerated amino groups of the second component to react with the epoxy groups of the first component to form a partially polymerized mixture, which is diluted with a solvent and applied to the substrate and heated to complete the curing process. 
     The second component of the composition should be present in an amount sufficient for the polyamine regenerated therefrom to react with the majority of the epoxy groups otherwise available for forming the reaction product. Preferably there should be enough of the polyamine present to react with all or substantially all of such groups. This implies that if there are other amines present, the non-silane-based aliphatic polyamine supplies a major portion of the amino groups that react with the epoxy groups to form the final cured coating. 
     Suitable hydrolyzable epoxysilanes include compounds of the formula ##STR1## where Q is a group containing the epoxy structure ##STR2## R 1  is a bivalent hydrocarbon radical; R 2  and R 3  are independently selected hydrocarbon radicals, and m is an integer betwe 0 and 2. 
     Preferably the epoxy-containing group Q is glycidoxy or epoxycyclohexyl, preferably 3,4-epoxycyclohexyl if the latter. R 1  is preferably C 1  -C 4  alkylene, especially trimethylene (--CH 2  CH 2  CH 2  --) if Q is glycidoxy and ethylene (--CH 2  CH 2  --) if Q is 3,4-epoxycyclohexyl. Thus the preferred choices for Q--R 1  -- are γ-glycidoxypropyl and β-(3,4-epoxycyclohexyl)ethyl. 
     Preferably R 2  is C 1  -C 4  alkyl, especially methyl, while R 3  is preferably C 1  -C 4  alkyl, especially methyl or ethyl, or alkenyl, especially isopropenyl. Although it is possible to use compounds of Formula I in which m is 2, m is preferably 0 or 1 and more preferably 0. The preferred compound of Formula I, which was used in the bulk of our work, is γ-glycidoxypropyl-trimethoxysilane. 
     Compounds of Formula I are hydrolyzed to a stoichiometrically determined degree by the addition of appropriate amounts of water followed by modest heating, in accordance with the following reaction scheme: ##STR3## where R 3  is defined as above. 
     Hydrolysis (reaction A) occurs when the --OR 3  groups of the epoxysilane (I) react with water to generate a silanol (III), bearing hydroxy groups, together with the alcohol R 3  OH. Hydrolysis is also accompanied by some degree of condensation (reaction B), in which the hydroxy groups of the silanol (III) condense to form the siloxy moiety (IV). Sufficient water should be used to produce at least about 40% hydrolysis, and preferably between about 70% and about 95% hydrolysis, of the epoxysilane. The alcohol R 3  OH formed by the condensation remains in the system. Residual hydroxy groups are converted to siloxy groups by condensation when the final coating composition is cured. In general, any non-silane-based aliphatic polyamine will satisfy the requirements for the polyfunctional amine. By &#34;polyamine&#34; as used herein is meant a compound having at least two reactive (i.e., primary or secondary) amino groups. By &#34;aliphatic&#34; as used herein is meant a compound in which the reactive-amino nitrogens are attached to carbon atoms that do not form part of an aromatic nucleus. 
     Suitable amines include compounds of the formula ##STR4## in which each R is independently hydrogen, a univalent aliphatic hydrocarbon radical or ##STR5## with each R of the latter group being similarly defined and with at least two R&#39;s on different nitrogens being hydrogen; and each A is an independently selected bivalent aliphatic hydrocarbon radical. Preferably A is alkylene, especially a straight-chain alkylene of the formula --(CH 2 ) n  --, while each R is ##STR6## or hydrogen. 
     A particular subgroup of said amines include compounds of the formula ##STR7## in which m is a positive inreger and each A is a bivalent aliphatic hydrocarbon radical. Particular amines of Formula Va in which A is ethylene (--CH 2  CH 2  --) include ethylenediamine (m=1), diethylenetriamine (m=2) and triethylenetetramine (m=3). Most of our work involved the use of ethylenediamine, which is the preferred polyamine. 
     The polyamine ultimately reacts with the epoxy groups of the epoxysilane to form a crosslinked polymeric network. The polyamine is, however, first stabilized by the addition of a carbonyl-containing compound (i.e., a ketone or aldehyde) to form a reaction product. The reaction product regenerates the amine when heated during the curing cycle, allowing it to crosslink the network at that time. 
     The reaction product of the polyamine and the carbonyl compound depends on the starting materials. Primary amino groups of the polyamine react with the carbonyl compound (VI) to form ketimine groups (VII) according to the scheme ##STR8## 
     Secondary amino groups react with carbonyl compounds containing α-hydrogens (VIII) to form enamines (IX) according to the reaction scheme ##STR9## and with carbonyl compounds containing no α-hydrogens (X) to form aminals (XI) according to the overall reaction scheme ##STR10## The particular reactions are described in further detail in March, Advanced Organic Chemistry, pp. 817-818 (1977) and the references cited therein. 
     Suitable carbonyl-containing compounds include aliphatic ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and diacetone alcohol; aromatic ketones such as acetophenone and benzophenone; aliphatic aldehydes such as acetaldehyde and propionaldehyde; and aromatic aldehydes such as benzaldehyde. Diacetone alcohol, however, is preferred. Ultimately the carbonyl-containing compound is driven off as a vapor when the amine is regenerated during cure. Preferably an excess of carbonyl compound over the stoichiometric amount is used to ensure that reaction C, D or E is driven to completion. 
     Suitable solvents include alcohols such as methanol, ethanol, n-propanol, isopropanol and n-butanol; ketones such as acetone, methyl ethyl kerone, methyl isobutyl ketone and diacetone alcohol; and mixtures thereof. Also contemplated are glycol ethers such a propyleneglycol methyl ether (available under the trademark Dowanol PM), higher acetate esters and the like. The preferred solvent is a mixture of isopropanol, n-butanol and diacetone alcohol, preferably in a volumetric ratio of 4:3:3. The particular step at which the solvent is added is not critical. The first and second components may be prepared in solution, or all or part of the solvent added later. We have found it convenient, however, to add part of the solvent chilled to the reaction mixture of the first and second components to quench the polymerization reaction and later add the rest of the solvent to achieve the desired viscosity. 
     The composition preferably includes a surfactant, used as a flow-control agent for regulating film thickness and enhancing the cosmetic appearance of the coated article. Of the numerous surfactants that are known, a commonly available one used in the preferred composition is the fluorinated surfactant available from Minnesota Mining and Manufacturing Co. under the trademark Fluorad FC-430. 
     The composition may also include a partially hydrolyzed alkyltrialkoxysilane such as methyltriethoxysilane to increase the siloxy content of the network. However, no improvement in abrasion resistance was noted using this additive, and it is therefore not included in the preferred formulation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     EXAMPLE 1 
     807 ml of γ-glycidoxypropyltrimethoxysilane is hydrolyzed with 188 ml of distilled water by adding them together and warming to 80° C. for one hour or until the mixture clarifies. The mixture is allowed to cool to room temperature in a covered container. This effects 95% hydrolysis. 
     In a separate container, 121 ml of ethylenediamine is mixed with 1302 ml of diacetone alcohol, or 1 mole of the diamine per 6 moles of diacetone alcohol. This latter mixture is allowed to stand at room temperature for one hour to allow the amino groups of the diamine to react with the carbonyl groups of the alcohol to form ketimine functional groups. 
     The two prepared components are then mixed together with stirring at room temperature. This effects a ratio of 2 moles of epoxysilane to 1 mole of ethylenediamine. The molecular weight builds as the system undergoes an exothermic reaction. About one hour later the reaction is quenched by the addition of 414 ml of cold (10° F.) diacetone alcohol, and the entire mixture is placed in a refrigerator at 10° F. for a minimum of 3 to 4 hours. 
     To the mixture are then added 414 ml of n-butanol, 550 ml of isopropanol, and 2 ml of Fluorad FC-430, all at 10° F. The solution thus formed is mixed until homogenized and stored at 10° F. The above-described formulation provides one gallon of coating. 
     Typically the solution is maintained at a working temperature of 30° F. The viscosity of the solution prepared in this manner at 30° F. is 27 centipoise. Solids content is 18%. The coating is applied to polycarbonate lenses by dipping them into the solution and withdrawing them at a rate of 0.2 inch per second. The lenses are pre-cured at 167° F. for 15 minutes and finally cured for 3 hours at 265° F. 
     The resultant lenses were tested as follows 
     
         ______________________________________Test        Method        Result______________________________________Adhesion    Crosshatch,   100% adhesion       16 squaresAbrasion    84 psi,       No scratches       0000 steel woolTintability 25 minutes,   15% transmission       Gentone Tru-       Grey Dye at       205° F.Adhesion    Crosshatch,   100% adhesionafter       16 squarestintingCoating     Interferometer                     4.5 ± 0.5 micronsthickness______________________________________ 
    
     EXAMPLE 2 
     The general procedure of Example 1 is followed except that the ethylenediamine is mixed with 953 ml of methyl ethyl ketone instead of diacetone alcohol. The resultant lenses exhibited properties similar to those noted above but with a modest decrease in the coating adhesion after tinting. 
     EXAMPLE 3 
     The general procedure of Example 1 is followed except that instead of the butanol-isopropanol-diacetone alcohol system described, a system comprising 691 ml methanol, 481 ml isopropanol and 206 ml diacetone alcohol is used. The resultant lenses, although useful, exhibited surface cosmetic defects commonly known as orange peel. 
     EXAMPLE 4 
     The general procedure of Example 1 is followed except that 390 ml of methyltriethoxysilane is independently hydrolyzed with 84 ml of distilled water at 80° C. for one hour. The mixture is cooled to room temperature and added to the hydrolyzed epoxy-silane just as it is added to the stabilized diamine. The resultant coated lenses exhibited good adhesion and only moderate abrasion, and tinted to a transmittance of 0.25 (25% transmission) at 205° F. in the dye bath. 
     EXAMPLES 5 TO 10 
     Diethylenetriamine (DTA), triethylenetetramine (TTA) and p-phenylenediamine (PDA) were evaluated as alternatives to ethylenediamine. In each example, the first component was formed from 94 ml γ-glycidoxypropyltrimethoxysilane and 21.6 ml water, while the second component was formed from the indicated amount of the amine listed in the table below and (except for Example 10) 150 ml diacetone alcohol, in a 6:1 molar ratio of alcohol to amine. The solvent used in each example was a mixture of 46 ml n-butanol, 46 ml diacetone alcohol and 61 ml isopropanol, to which 0.2 ml of the surfactant Fluorad FC-430 was also added. In Examples 7 and 9, equimolar amounts of amine were used with respect to the amine of Example 5; in Examples 6 and 8, amounts of amine were used that were equivalent in nitrogen content to the amine of Example 5. Reaction conditions were otherwise similar to those of Example 1. Percent transmission (T) was measured after a tinting time of 30 minutes. The results are summarized in the following table: 
     
         ______________________________________Exam-                     Adhe-ple       Amine           sion    % T______________________________________5         EDA     14 ml       Pass  15%6         DTA     15 ml       Pass   1%7         DTA     23 ml       Pass   4%8         TTA     16 ml       Pass  54%9         TTA     32 ml       Pass  10%10        PDA     22.5 ml     --    --______________________________________ 
    
     The p-phenylenediamine exhibited only very slight solubility in diacetone alcohol, acetone or methyl ethyl ketone. We were unable to make a coating sample using this aromatic amine, owing to its poor solubility in the solvents tested. The other, aliphatic amines readily formed coatings. The triethylenetetramine of Example 8 was less tintable than the control of Example 5, but appeared more abrasion-resistant. 
     EXAMPLES 11 to 15 
     Various carbonyl-containing compounds were evaluated as alternatives to diacetone alcohol. In each case 150 ml of the carbonyl compound was used. Ingredients and reaction conditions were otherwise similar to those of Example 5. The results are summarized in the following table: 
     
         ______________________________________      Carbonyl       Adhe-Example    Compound       sion    % T______________________________________11         Propionaldehyde                     Fail     312         Ethyl propionate                     --      --13         Acetophenone   Pass    1014         Benzaldehyde   Pass    1015         Diacetone alcohol                     Pass     6______________________________________ 
    
     In Example 12, a liquid coating was formed which precipitated on the lens. The adhesion test of Example 11 and the other examples is a relatively severe test normally performed on commercial articles; the coating of Example 11 yielded a useful article. Improved adhesion results would be expected given suitable reaction conditions such as a longer curing time. The aldehydes of Examples 11 and 14 reacted exothermically with the amine, which had to be added dropwise to prevent the solution from boiling over. 
     EXAMPLE 16 
     97 ml of Union Carbide A186 β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane was used instead of the glycidoxysilane of Example 15. Reaction conditions were otherwise similar. The coated lens tinted to a transmittance of 0.10 (10% transmission) and passed the adhesion test. 
     EXAMPLE 17 
     108 ml of Petrarch G6710 γ-glycidoxypropylmethyldiethoxysilane was used instead of the trialkoxysilane of Example 15. Reaction conditions were otherwise similar. The coated lens tinted to a transmittance of 0.03 and passed the adhesion test. Both this composition and that of Example 16 formed good coatings. 
     It will be seen that we have achieved the objects of our invention. Our coating composition, which is readily applied to the substrate, provides a highly abrasion-resistant, readily tintable coating that satisfactorily adheres to the substrate to which it is applied, both before and after tinting. 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of our claims. It is further obvious that various changes may be made in details within the scope of our invention. It is, therefore, to be understood that our invention is not to be limited to the specific details shown and described.