SOLID BLOCKED CROSS-LINKING AGENTS BASED ON |,4-CYCLOHEXANE BIS(METHYLISOCYANATE)

Abstract: Novel adducts are prepared from 1,4-cyclohexane bis(methylisocyanate), which may be substituted in the cyclohexane ring, and active hydrogen-containing compounds, such as phenols, lactams, oximes, and alkyl acylacetates and alkoxycarbonylacetates. These adducts can be incorporated into resins containing isocyanate-reactive groups, such as hydroxyl groups, to give compositions which are cured by heating.

Description: SOLID BLOCKED CROSSLINKING AGENTS BASED ON 1, -CYCLQHEXANE BIS(METHYLISOCTANATE) This invention relates to new derivatives of 1,4-cyclohexane bis(methylisocyanate) (CHBMI) which are non-reactive under ambient conditions to resins containing active hydrogens, such as those in hydroxyl or a ino groups, but which become reactive when subjected to relatively low temperatures for short periods of time. These new compounds readily gel hydroxylated resins and thus are useful as crosslinkers for such resins in industrial coatings and related uses. Coating compositions comprising the reaction product of a polyfunctional isocyanate and a resin containing isocyanate-reactive functions such as hydroxyl groups are well known and widely used in industry. The isocyanate generally reacts very quickly with the resin at about room temperature, and therefore these components must be packaged, shipped and stored separately and mixed together only when the cross-linking reaction is desired. The disadvantages of such a system are obvious. Proposed alternatives generally embody the "one-pack" formulation concept, wherein blending and packaging of the isocyanate and resin without premature interaction is the goal. In one such approach, relatively unreactive phenol blocked isocyanate compositions which regenerate free iso- cyanates upon heating have been used. " With such formulations, however, free phenol is produced upon heating, with attendant undesirable odour, corrosive- ness and toxicity. Moreover, many such blocked isocyanates require high temperatures for commencement of the curing. Thus, it is highly desirable to OMPI provide blocked isocyanate formulations which become reactive at low temperatures and without the liberation of undesirable by-products. It has now been found that solid isocyanate adducts of formulae I and II below are highly useful in one-pack formulations, because they become reactive at relatively low temperatures to cross-link hydroxy¬ lated resins without attendant odour, corrosiveness and toxicity. These adducts are formed by reacting one mole of unsubstituted or substituted 1,4-cyclo- hexane bis(methylisocyanate) with two moles of a blocking compound having an active hydrogen, i.e. a precursor of A below, and preferably but not critically in the presence of an amine catalyst and a solvent. The adducts of the present invention have the formulae and II wherein A is R is 0 to three of the same or different substituents selected from alkyl, -NR-^R p , -NO p , halogen, alkoxy, aryl, alkaryl and cycloalkyl; R-, and R p are the same or different alkyl; R, is alkylene of from 2 to 8 carbons; X is selected from alkyl, aryl, and cycloalkyl, such as trimethylol propane, and wherein each of the aforesaid alkyl moieties of R, R-, , R and X contains from 1 to 10 carbons and is straight or branched; and n is 2, 3 or 4. These adducts in general have additional advantages in that they are solids at room temperature and so are easily handled, they are aliphatic and thus less susceptible to thermal yellowing, and they are capable of being used with a wide choice of cure temperature/time schedules based on the • blocking agent selected. FurthermOre, because of the relatively high -NC0 content of the CHBMI per mole in comparison with many commercial isocyanate crosslinkers, less of the blocked CHBMI is required to satisfy the stoichiometry of the hydroxylated resin. The present adducts are conveniently prepared by mixing the active hydrogen compound with a suitable amine catalyst in a solvent such as toluene or acetone, and slowly adding the CHBMI thereto, preferably but not critically in stoichiometric amounts, and preferably but not critically with heating, usually for several hours, until precipitation of the solid product is essentially completed. A temperature of from about 50 to 120°C. is typical, and 80 to 100°C. is preferred. The crude product may then be recrystallized from a suitable solvent such as toluene or acetone to yield the pure adduct. The compounds of formula II above are prepared by first reacting the CHBMI in excess with a polyfunctional hydroxy-containing compound and subsequently blocking the polyisocyanate thus formed with a suitable blocking agent in the manner described hereinabove. If desired, the crosslinking of the hydroxy- lated resins using the present adducts can be catalyzed using known catalysts for isocyanate- hydroxyl reactions such as tertiary amines or organo tin or organo zinc compounds. The concentration of the adduct is usually about the stoichiometric equivalent for reaction with all of the hydroxyl groups on the polymer, but may be varied widely depending on the cure rate and cured coating properties desired. Typical hydroxylated polymers with which the adducts of the present invention may be used are disclosed in, for example, United States Patent Specifications Nos. 3,659,003; 3,857,818; 3,912,691; and particularly No. 4,132,843 at columns 4 and 5. Particularly important are the polyesters which contain, in a co-condensed form, aliphatic and aromatic dicarboxylic acids having 4 to 12 carbon atoms and polyols having 2 to 10 carbon atoms and 2 to 4 primary or secondary hydroxyl groups. Saturated and unsaturated polyester resins of this type are described in Houben-Weyl "Makromolekulare Stoffe II" ("Macromolecular Materials II"), volume 14/2, pages 4 to 42. Crosslinking can occur over a broad temperature/time range varying, for example, from about 30 minutes or more at 150°C. to about 10 minutes or less at 180°C. depending on the resin, blocking agent and/or catalyst used. It is obvious that the flexibility in cure schedules allowed by the present adducts rendersthem useful in areas such as industrial coating applications. The present compounds, their preparation and use are illustrated in greater detail in the following examples which are illustrative only and CMPI -5- are not intended to limit the invention in any way. Example 1 - Synthesis of the Acetone Oxime Adduct of CHBMI ; A mixture of acetone oxime (14.6 g.), triethylamine (0.8 g.) and toluene (25 ml.) was stirred at about 18°C. To this solution was added 1,4-cyclohexane bis(methylisocyanate) (18.8 g.) over a period of about 30 seconds. The reaction was exothermic and a white precipitate appeared. The mixture was heated and stirred for four hours at 80°C. to ensure a complete reaction, and was then filtered and recrystallized from toluene (50 ml.), leaving a white microcrystalline solid having the structure Example 2 - Synthesis of the Acetoacetic Ester Adduct of CHBMI A mixture of ethyl acetoacetate (52 g), triethylamine (1.0 g.), and toluene (25 ml.) was stirred at room temperature.. To this solution was added 1,4-cyclohexane bis(methylisocyanate) (18.8 g.), with continued stirring over a period of about 30 seconds. The mixture was then heated to between 80-100°C. for three hours, cooled, filtered and washed with ethyl acetate (27 ml). The fine crystalline solid product was dried under reduced pressure and then recrystallized from acetone (50 ml.). The product was a white microcrystalline solid having the structure Exa ple 3 - Evaluation of CHBMI Adducts as Crσss- linkers for Hydroxylated Resins A hydroxylated polyester based on trimethyl- pentanediol, trimethylol propane, isophthalic acid and adipic acid, having a Number Average Molecular Weight (Mh) of 1,700 and a HydroxylNumber of 127 was used as the resin to be crosslinked. Mixes were made using this resin and a stoichiometric equivalent of each adduct, both with and without 2% by weight of a 1:1 molar mixture of dibutyl tin diacetate and hexadecyl trimethylammonium stearate as catalyst. The gel times for mixes at 140°C were determined using a Ferranti-Shirley melt viscometer and are shown in Table 1. TABLE 1 GEL TIMES AT 140°C. Gel Time (Minutes) Isocyanate Blocking No Precursor Agent Catalyst Catalyzed CHBMI Acetoxime 18.5 7.5 CHBMI Ethyl acetoacetate 14.5 13 CHBMI Caprolactam >20 > 20* *The CHBMI-caprolactam adduct gelled the polyester in approximately 10 minutes at 180°C. Example 4 - Relative Amounts, by Weight of Cross¬ linkers Required to Satisfy Sto chio- metries of Hydroxylated Resins When used in a powder coating based on commercially available hydroxylated polyester resin having a Hydroxyl Number of 56, only 20.5 g. of the CHMBI caprolactam adduct was required per 100 g. of resin for a stoichiometric reaction. The adduct had about 23% of its weight as available -NC0. By comparison, 36.5 g. of a commercial caprolactam- blocked isophorone diisocyanate (C3D) curing agent having an available -NC0 content of 11.5% by weight, and 27.5 g. of a commercial caprolactam-blocked cycloaliphatic isocyanate, having an available -NC0 content of 15.3% " by weight, were required for stoichiometric reactions. Table 2 lists the components of two coating compositions which were based on the same hydroxylated polyester resin. Composition A contained the commercial CID curing agent, and Composition B contained the CHBMI-caprolactam adduct. - TABLE 2 Parts by Weight Components A B Hydroxylated polyester resin, Hydroxyl Number 56 73.3 83.0 CID 26.7 — Caprolactam blocked CHBMI - 17.0 Di-Butyl Tin Dilaurate 1.0 1.0 Titanium Dioxide 50.0 50.0 Benzoin 1.0 1.0 Modaflow Powder (A flow aid made by Monsanto) 1.0 1.0 The performances of compositions A and B coated on a steel substrate 0.635 mm. thick and subjected to a curing step for 15 minutes at 180°C. metal temperature are given in the following Table 3, the measurements for each sample being obtained on the same test equipment by the same procedure. TABLE 3 Properties A B Thickness (microns) 57 60 20°/60° Gloss 61/93 71/93 Pencil Hardness F F Front/Reverse Impact Strength* 68/4 140/36 Orange Peel Rating (1 = Poor, 8 = Excellent) 4-5 4-5 Flexibility No cracking No cracking *[The front/reverse impact strength measurements were made in accordance with ASTM D 2794-69. The testing machine had a weight measured in pounds falling through a distance measured in inches, and the results are given in inch-pounds. (One pound = 454 grams, one inch = 25.4 mm.). However, these results are used to compare the impact strength of the CHBMI-cured material with that of other materials : the units in which they are expressed are immaterial for this purpose.] From Table 3, it can be seen that the CHBMI-cured material had superior impact strength, with the other properties being as good or better than those of the coating containing the commercial crosslinker at a much higher concentration. Example 5 - Curing Properties of DIBK (Di-Isobutyl Ketoxime) Blocked CHBMI at Different Temperatures As shown below in Tables 4 and 5, when used in a powder coating with hydroxylated polyester resin having a Hydroxyl Number of 59, DIBK blocked CHBMI (Column C) produced a finished coating having lower orange peel and higher gloss than that obtained using a commercial reduced temperature crosslinker (Column D). OMPI TABLE 4 Parts by Weight Components C D Hydroxylated polyester resin (Hydroxyl Number 59) 70 70.3 Caprolactam blocked poly- functional isocyanate adduct having 15.3% available -NC0 20.7 CHBMI-DIBK Adduct (Theoretical % -NCO - 16-5) 21 ^ Di-Butyl Tin Dilaurate 10 10 Titanium Dioxide 50 50 Benzoin 1.0 1.0 Modaflow Powder 1.0 1.0 TABLE 5 (A) After Curing for 15 Minutes at 160 °C. (Metal Temperature) Properties c D Thickness (microns) 57 60 20° Gloss 77 67 Pencil Hardness HB HB Front/Reverse Impact Strength >160/>160 >l6θ/140 Orange Peel Rating 6 4-5 Flexibility No No cracking cracking at 180°C (Metal Temperature) Properties C D Thickness (microns) 42 34 20° Gloss 76 42 Pencil Hardness HB IF Front/Reverse Impact Strength>160 >l6O >16θ/>16θ Orange Peel Rating 6-7 2-3 Flexibility No No cracking cracking From the above examples and tables it can be seen that the blocked CHBMI crosslinkers impart superior properties to the cured coatings in many important areas such as gloss, impact strength and surface appearance. As will be appreciated, these properties are of major importance for commercial coating formulations. ; R5„

Claims: CLAIMS 1. Compounds having the formulae II wherein A is selected from R is 0 to three of the same or different substituents selected from alkyl, -NR-,R p , -NO p , halogen, alkoxy, aryl, alkaryl and cycloalkyl; R-^ and R 2 are alkyl, wherein each of the aforesaid alkyl moieties of R,. R-, and R p contains from 1 to 10 carbons and is straight or branched; R-, is alkylene of from 2 to 8 carbons; X is selected from alkyl, aryl and cyclo- alkyl; and n is 2, 3 or 4. 2. Compounds according to Claim 1 wherein A is 3- -Compounds according to Claim 1 wherein A is OMPI _ " 4. Compounds according to Claim 1 wherein A is 5. Compounds according to Claim 1 wherein A is 6. A method of curing hydroxylated polymeric material comprising mixing therewith a compound as claimed in Claim 1 in a concentration sufficient to react with a substantial number of hydroxyl groups of the polymer, and thereafter heating the mixture to cause such reaction to take place. 7. A method as claimed in Claim 6, wherein the polymeric material is a polyester. 8. Polymeric material which has been cured by a method as claimed in Claim 6.

Inventors: MCBRIDE PAUL, RUSSELL GEORGE CHARLES, MCBRIDE, PAUL, RUSSELL, GEORGE, CHARLES
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1982
Main classification: C07C125
IPC codes: C07C67, C07C231, C07C233, C07C235, C07C239, C07C271, C07D223, C08G18