MXPA96000899A

MXPA96000899A - Polyurethane coatings with ultra-basket based on volati organic components

Info

Publication number: MXPA96000899A
Application number: MXPA/A/1996/000899A
Authority: MX
Inventors: Lynn Bassner Sherri
Original assignee: Air Products And Chemicals Inc
Priority date: 1995-03-08
Filing date: 1996-03-07
Publication date: 1997-08-01

Abstract

The present invention relates to low-VOC polyurethane coatings, in two parts, comprising a low viscosity polyisocyanate component having an isocyanate functionality greater than two and a polyol component having a functionality equal to or greater than two. The improvement lies in the use of an isocyanato-mono component in the two-part polyurethane coating formulation. The isocyanate component comprises the low viscosity polyisocyanate component and an end-capped or isocyanate-terminated prepolymer formed by the reaction of a diisocyanate and a multifunctional polyol, the prepolymer having at least about 85 and, preferably, 90 percent by weight. weight of a 2: 1 adduct of isocyanate to polyol (NCO / OH) and less than about 1 and preferably less than about 0.5% by weight of residual diisocyanate monomer in the same

Description

POLYURETHANE COATINGS WITH ULTRA-LOW CONTENT OF VOLGAL ORGANIC COMPONENTS TECHNICAL CAMPQ PE INVECIÓ This invention relates to polyurethane systems comprising a mixture of low viscosity polyurethane prepolymers with polyisocyanate crosslinkers and coatings prepared therefrom. BACKGROUND OF THE INVENTION Two-part solvent based polyurethane based coating systems using aliphatic and polyester isocyanates or acrylic polyols have become the industry standard for top coatings, combining outstanding resistance to chemicals and against physical damage to high levels of brightness and retention of brightness, color and mechanical properties for a long time. Traditionally, these coating systems have been formulated with highly functional, low viscosity liquid polyisocyanate crosslinkers, such as a component and a high molecular weight polyol, high functionality and associated pigments and additives, such as the second component. A major driving force in the reformulation of coatings around the world has been the need to reduce solvent emissions. One disadvantage of these traditional polyurethane formulations to the reformulation is the high solvent demand of the polyol component. This factor has limited the reduction of volatile organic content (VOC) available with traditional polyol systems. One route to reduce VOC has been the use of lower molecular weight polyols. Since formulators have incorporated more and more lower molecular weight (lower viscosity) polyols or reactive diluents, such as low molecular weight hydroxy acrylics or blocked systems such as oxazolidines, into their systems, there has been an unavoidable trade-off in physical properties of the resulting low VOC coatings and / or the handling of the reactive mixture. For example, many of the VOC polyurethane coatings have poor solvent resistance, poor flexibility and extreme sensitivity at the catalyst level and their effect on the setting profile. As formulators of polyurethane coatings have reduced the volatile organic content (VOC) of their formulations, they have found it increasingly difficult to maintain good handling characteristics and mixing ratios. Traditionally, low VOC coatings tend to exhibit very short pot life (l hour or less), a high sensitivity at the aggregate catalyst level and the formulations often require mixing ratios of pigmented polyol to isocyanate from 3.5 to 6: 1 . The formulators seek ways to more efficiently control the reactivity of their systems and achieve more attractive mixing ratios preferably 1: 1, while continuing to reduce VOC to zero.

Concurrent with the trend towards less and less VOC for conventionally applied coatings, formulators and applicators have also increased the use of a multi-component application equipment. This type of equipment has been used for many years to apply quick reaction polyurethane coatings, 100% reagents for thick film linings and for adhesives and sealants. With this equipment, the reactive components are heated to generate a lower viscosity component, dosed in a chamber designed to quickly mix the components and then pumped to a traditional airless gun or air-assisted air for application. Representative patents relating to polyurethane coating formulations and their use as coatings are as follows: U.S. Pat. No. 3,218,348, describes a process for preparing polyurethane polyisocyanates that have high molecular weight and do not crystallize from a solution upon standing. The polyisocyanates are reacted with a trihydric alcohol such as trimethylolpropane in an organic solvent, followed by the addition of a dihydric alcohol such as 1,3-butylene glycol. The patent of the U.S.A. No. 3,384,624, describes a process for preparing polyurethane prepolymers free of unreacted polyisocyanate. The prepolymers that can be used to prepare coatings, moldings, paints and lacquers are prepared by reacting toluene diisocyanate with an active hydrogen-containing compound, for example a long-chain diol and then contacting the prepolymer with a phenolic material in an amount sufficient to remove excess unreacted polyisocyanate. Molar ratios of polyisocyanate to diol are in the range of about 1.3 to 2.1. The resulting blocked polyurethane prepolymer can then be deblocked and chain extended with an organic diamine or polyol. The patent of the U.S.A. No. 3,726,825, discloses polyurethane coatings having moisture vapor barrier properties as well as high gloss, abrasion resistance, etc., required for these coatings. The linear thermoplastic polyurethane resins are prepared by reacting a non-halogenated organic diisocyanate with an organic dihydroxy compound and from about 0.1 to 0.9 mole of neopentyl glycol. The resulting polyurethane prepolymer is then cured under anhydrous conditions. The patent of the U.S.A. No. 5,208,334, discloses a process for the production of a low viscosity diisocyanate system containing isocyanurate and allophanate groups, by catalytically trimerizing a portion of the isocyanate groups, adding a monoalcohol to the organic diisocyanate prior to or during the trimming reaction and ending the trierization by adding a catalyst poison. Unique isocyanurates overcome two problems associated with isocyanates containing isocyanurate groups, one is related to viscosity, thus allowing reduced solvent in the coating formulation and the other relating to incompatibility with the polyol. The patent of the U.S.A. No. 5,115,071, discloses high performance coating compositions based on the reaction of a prepolymer having a low oligomer content and a polyol. More specifically, the prepolymer is an end-terminated prepolymer that is formed by the reaction of a diisocyanate and a multifunctional polyol, the prepolymer having at least about 85, preferably 90 percent by weight of a 2: 1 adduct of isocyanate to polyol ( NCO / OH) and less than about 1 and preferably less than about 0.5% weight percent residual monomer diisocyanate. COMPENDIUM OF THE INVENTION This invention relates to low VOC polyurethane coatings, in two improved parts, comprising a low viscosity polyisocyanate crosslinker component having an isocyanate functionality greater than two and a polyol component having a functionality equal to or greater that two. The improvement lies in the use of a single isocyanate component in the two-part polyurethane coating formulation. The isocyanate component comprises the low viscosity polyisocyanate interleaver and an end-terminated or isocyanate-terminated prepolymer, which are formed by the reaction of a diisocyanate and a multifunctional polyol, the prepolymer having at least about 85, preferably 90 percent by weight. weight of a 2: 1 adduct of isocyanate to polyol (NCO / OH) and less than about 1 and preferably less than about 0.5% by weight of residual diisocyanate monomer. There are several advantages associated with the use of the single isocyanate component of a low VOC coating composition and these include: a capability to employ spray application technology, which allows the use of elevated temperatures to reduce the viscosity of the formulation, without concern to the duration of the formulation and that nevertheless can achieve desirable drying times; a capacity to reduce or eliminate the need for solvent and thus produce final polyurethane coatings with low or near zero VOC for high performance applications and produce low VOC polyurethane primer coatings; a capacity to diminish the potential disposition of the worker due to lower volatility and to reduce systems of toxicity to isocyanate, through the use of an isocyanate component comprising in part a prepolymer having a very narrow molecular weight distribution with very low residual diisocyanate monomer; an ability to formulate and apply the coating formulation at or near a 1: 1 ratio by volume; and a capacity to produce polyurethane coatings having excellent physical properties such as tensile strength, scratch and solvent resistance. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 Refers to a Thermal Profile of Isocyanate component with 100% Solids, which is a viscosity profile (mPa-s) against temperature (° C). Figure 2 refers to a Thermal Profile for Grinding of Polyol / Pig entado with Low VOC, of viscosity against temperature. DESCRIPTION OF THE INVENTION The standard procedure for preparing two-part low VOC polyurethane coatings involves the use of a low viscosity polyisocyanate interleaver and a high functionality, high molecular weight polyol component. . Traditional low viscosity polyisocyanate crosslinking components having a functionality greater than two, include isocyanurates, biurets, uretdiones and allophanates. Isocyanurates are formed by the trimerization of aliphatic or aromatic diisocyanates. Trimerization is effected by reacting 3 moles of the diisocyanate with itself or another polyisocyanate to produce a single isocyanurate ring. Phosphines, Mannich bases and tertiary amines, such as 1,4-diazabicyclo [2.2.2] octane dialkyl piperazines, etc., can be used as trimerization catalysts. The biurets are also formed by the addition of a small amount of water to two moles of isocyanate and reacting at slightly elevated temperature in the presence of a catalyst. The uretdione is formed by the dimerization of the isocyanate. The allophanates are prepared by the reaction of the diisocyanate with a urethane linkage. Another class of isocyanates that can be used are isocyanate adducts of low molecular weight polyols. These adducts are formed by the reaction of a low molecular weight polyol, for example a triol such as trimethylolpropane and polyether triols such as ethylene and propylene oxide triols with the diisocyanate. Representative diisocyanates useful in the synthesis of isocyanurate, biurets, uretdiones and adducts of diisocyanates described above, which are then used as one of the substituents in the formation of a 2-part polyurethane coating, include conventional aromatic and aliphatic diisocyanates. These diisocyanates which can be used alone or as a mixture include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HD1), 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, -isocyanate-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or 1PD1), tetramethylxylyl diisocyanate (TMXDI), bis (4-isocyanatocyclohexyl) methane (H12MDI) and bis (4-isocyanate-3) methyl-cyclohexyl) -methane. Aromatic diisocyanates can also be used in formulating the isocyanate component. They can be mixed with the aliphatic diisocyanate or used by themselves to generate the isocyanate component. The aromatic diisocyanates suffer from sensitivity to ultraviolet light and are thus not preferred for the formulation of final coatings that are resistant to the environment or to the weather. On the other hand, the aromatic diisocyanates can be mixed with the aliphatic diisocyanate component or used alone to improve chemical resistance, reaction rate, etc. Examples of aromatic diisocyanates include toluene diisocyanate (TD1), bis (4-isocyanato-phenyl) methane (MD1) and the like. The second part of the single isocyanate component for preparing low VOC polyurethane coatings is a diisocyanate prepolymer having an equivalent weight between 250 and 2000 (preferably between 350 and 1000) grams per equivalent. The prepolymers are generally formed by reacting an aliphatic or aromatic diisocyanate with a polyol or mixture of polyols having an average functionality greater than 2 (generally in the range of 2.2 to 4) and an average equivalent weight generally in the range of 200 to 1000 g / eq. An excess of diisocyanate is reacted with the polyol component at an equivalent ratio greater than 4: 1 equivalents of NCO per equivalent OH in the polyol, to generate a reaction product having at least 85, preferably 90% in weight of a 2: 1 NCO / OH adduct of isocyanate to polyol. The unreacted diisocyanate monomer is removed from the prepolymer by distillation or other treatment at a concentration of less than 1% and preferably less than 0.5% unreacted diisocyanate. Representative diisocyanates that can be used to produce the prepolymers include the above aliphatic and aromatic diisocyanates. Conventional long chain polyols are used to produce the isocyanate-terminated prepolymers. These include alkylene ether di- or multi-functional polyols, such as poly (tetramethylene glycol, PTMG) polyols; poly (propylene oxide) polyols; and poly (ethylene oxide) polyols. Polyether polyols may also comprise adducts of ethylene oxide or propylene oxide of polyols such as the ethylene oxide and propylene oxide adducts of ethylene or butylene glycol. Although in itself it is not a polyol, polycaprolactone acts only on a polyether polyol and can be used. Polyester polyols such as those formed by the reaction of aliphatic or aromatic dicarboxylic acids with glycols can also be used as the polyol component for preparing the polyurethane prepolymers. Specific examples of acids for forming polyester polyols include isophthalic, terephthalic and adipic acids. Specific glycols include ethylene glycol, diethylene glycol, butanediol, propylene glycol, neopentyl glycol and hexan diol and so on. Acrylic polyols can also be used as a polyol component. In addition to the conventional polyols described above, polyols having a functionality greater than 2 can be mixed with a long chain diol to produce a polyol component for reaction with the polyisocyanate in an amount such that the average functionality is greater than 2 and preferably between 2.2 and 4 and the average equivalent weight is between 100 and 2000. Representative short chain multifunctional polyols having functionality greater than 2 include trimethylolpropane (TMP), glycerol, pentaerythritol, dipentaerythritol, trihydroxybutane, sucrose, and alkoxylated or esterified adducts of the previous The isocyanate-terminated prepolymers of low oligomer content which is used to form the isocyanate component can be prepared by reacting the polyunuclear-polyol composition with a large excess of the diisocyanate equivalent (greater than 4 to 1 and typically 6-10: 1) a polyol. The prepolymers essentially comprise two equivalents diisocyanate per equivalent of polyol due to the high proportion of diisocyanate to polyol in the original reaction mixture. Excess diisocyanate is removed at levels less than 1%, preferably less than 0.5% by weight in the prepolymer.

Temperatures to effect the reaction between the diisocyanate and polyol are conventional, for example 0-120 ° C. Care must be taken during the separation of the excess diisocyanate, so that oligomeric allophanates and other by-products do not form. Additional description and / or examples are illustrated in U.S. Pat. No. 5,115,071 and the subject matter of that patent is incorporated herein by reference. The isocyanate component of the low VOC coatings is prepared by mixing the isocyanate-terminated prepolymer with the low viscosity polyisocyanate interleaver (s) such as hexamethylene diisocyanate isocyanurate (HDI trimer) and / or HD1 uretdione, as well as other isocyanurates, uretdiones, biurets, allophanates or low molecular weight polyol adducts of HDI, IPDI, H12MDI, TMXDI, TDI and MDI in a proportion by weight that is in the range of 10:90 to 90:10 of prepolymer to low viscosity polyisocyanates . Preferably, the weight ratio of the mixture is from about 40:60 to 60:40 based on a total weight of 100 parts by weight, allowing easy formulation of the 1: 1 ratio of the mixture. In contrast, conventional systems based on a mixture of pigment and acrylic polyol and cured with a polyisocyanate interleaver, for example typically exhibit pigment / polyol mixing ratios to the isocyanate component of 2.5 to 6: 1. The higher level of partially reacted prepolymer helps to moderate the high reactivity of the high functionality, low viscosity polyisocyanate allowing greater control over the reactivity and is less sensitive to catalyst level variations, particularly at higher application temperatures (> 23QC). With better control over the curing speed of the film, better appearance to the film can be achieved. These systems can be formulated in such a way that the reactant components have similar viscosity, thus improving the ease of mixing, particularly for dosing-mixing-supplying applicators. A conventionally prepared prepolymer, if employed in this mixture, will require large amounts of solvent to achieve sufficient viscosity of application. High molecular weight oligomers in these conventional prepolymers not only increase the solvent demand of the formulation, but also lead to shorter useful usage times due to the rapid accumulation of molecular weight. A retrospective view of the compositional analysis helps illustrate the previous points. First, by using a "pre" -polymer of the type employed herein, the monomer content of diisocyanate is reduced and the reactivity of this partially reacted system is simpler to control. Second, the casual inspection of traditional prepolymer compositions having from 55 to 60% of a 2: 1 adduct, oligomer content of 35-45% with isocyanate to polyol ratios of 3: 2, 4: 3 and 5: 4 and a residual isocyanate monomer content of 2-4% by weight, now helps explain why conventional prepolymers have seen limited use in coating formulations with higher solids content. In contrast, an examination of the composition of the prepolymers employed herein, which has from 85 to about 95% of a 2: 1 adduct, a low oligomer content of from 5 to 15% and < 1% and preferably < 0.5% by weight of residual isocyanate monomer content, shows that the combination of this prepolymer with the low viscosity polyisocyanate offers some of the observed improvements. Solvents of the formulation can be added to achieve the desired viscosity. Obviously, it will be preferred to use as little solvent as possible to produce these low VOC coatings. Typical solvents that may be used include but are not limited to xylene, toluene, methyl ethyl ketone, methylamyl ketone, ethyl acetate, tetrahydrofuran and n-butylacetate. Conventional catalysts used to accelerate the reaction between the isocyanate component and the polyol component, they can be incorporated into the formulation. Examples of catalysts include metal based compositions, such as dibutyl tin dilaurate and zinc carboxylate. The following examples are intended to represent various modalities and are not intended to restrict the scope of the same. EXAMPLES 1 AND 1A Polyurethane-based Coating Formulation Hexamethylene Diisocyanate / Acrylic Polyol Isocyanurate of the Prior Art A conventional polyisocyanate / polyol acrylic coating composition is prepared in a conventional manner.

First, the pigmented polyol mixture was prepared and then mixed with the isocyanate component. The formulation is illustrated in Table 1 and 2. A second sample 1A was prepared using the same formulation as Example 1, except that the Dabco and Mooney catalysts were omitted from the formulation. TABLE I Ma ria Prima QfflPQlM e Weight Eq. % of Solids Chempol 17-3855 polyol acrylic 637.50 80 Zoldine RD-4 oxazolidine 89.30 100 Ti-Pure R-960 pigment of Ti02 0.00 100 Nousperse 657 dispersant pigmentot 00..0000 70 TEGO 980 agent for liberation Anin-i to air 0.00 100 TINUVIN 384 adsorbent UV 0.00 95 Tinuvin 292 hindered amine light stabilizer 0.00 100 DABCO 120 tin catalyst (IV) 0.00 100 MOONEY 18% ZN zinc carboxylate catalyst 0.00 84 TABLE I (Continued) Raw Material Supplied Solvent Kg / i (Ibr / gal) kg / 1 (Ib./gaX) DISLON NS-30 pigment anti-sediment agent 0.00 15 Methyl amyl ketone 0.00 0 Desmodur N-3300 HDI isocyanurate 195.00 100 Chempol 17-3855 1.044 (8.70) .87 (7.26) Zoldine RD-4 .908 (7.57) 0.00 Ti-Pure R-960 3.98 (33.20) 0.00 Nuosperse 657. 948 (7.90) .786 (6.55) TEGO 980.954 (7.95) 0.00 TINUVIN 384 1.057 (8.81) .87 (7.26) Tinuvin 292 1.00 (8.34) 0.00 DABCO 120 .999 (8.33) 0.00 MOONEY 18% Zn 1.05 (8.77) ) .87 (7.26) DISLON NS-30 .883 (7.36) .87 (7.26) Methyl amyl ketone .816 (6.80) .816 (6.80) Desmodur N-3300 1.16 (9.70) 0.00 TABLE 2 Component Polyol Weight Volume Weight Só - Pigmented solids g (Ib) 1 (gal.) Lids Volume Chempol 17-3855 154.03 147.6 123.23 112.23 (339.28) (39.00) (271.43) (29.65) TABLE 2 (continuous) Component Polyol Weight Volume Weight Solids Pigmented kg ( Ib) 1 (gal.) Lidos Volume I. lb) 1 fsal. ^ Zoldine RD-4 30.80 33.91 30.80 33.91 (67.86) (8.96) (67.86) (8.96) Ti-Pure R-960 181.91 45.68 181.91 45.68 (400.68) (12.07) (400.68) (12.07) Nuosperse 657 1,997 2.12 1,398 1.36 (4.40) (0.56) (3.08) (0.36) TEGO 980 1.96 2.044 1.96 2.044 (4.32) (0.54) (4.32) (0.54) TINUVIN 384 4,417 4.16 4.2 3.94 (9.73) (1.10) (9.25) (1.04) Tinuvin 292 4.199 4.20 4.199 4.20 (9.25) (1.11) (9.25) (1.11) DABCO 120 .14 .151 .14 .151 (0.31) (0.04) (0.31) (0.04) MOONEY 18% Zn 1.666 1.59 1.398 12.87 (3.67) (0.42) (3.08) (0.34) DISLON NS-30 .745 .833 .114 .114 (1.64) (0.22) (0.25) (0.03) Methyl amyl ketone 22.86 28.0 (50.35) (7.40) 0.00 0.00 Total 404.7 270.3 31.57 204.92 TABLE 2 (continued) Component Polyol Weight Volume Weight Solids Pigmented kg (Ib) 1 (gal.) Lids Volume (891.49) (71.42) (69.51) (54.14) Isocyanate component II: 125.83 108.14 125.83 108.67 (277.15) (28.57) (277.15) (28.71) Desmodur N-3300 Total 530.56 378.5 475.17 313.06 fll68.64UlOO.00, (1046.641 (82.711 Solids in Weight,% = 89.56 Solids in Volume,% = 82.71 Proportion P / B = 0.65 (pigment / binder) PVC,% = 115.23 of pigment / volume Weight / 1 (gallon) = 3.089 (11.69) Proportion NCO: OH = 1.10 Mixing Ratio = 2.50 VOC, kg / 1 (lbs) / gal = .146 (1.22) One of the problems with the formulation of the Example 1 is that the useful use time is so short that there was hardly any time to handle after formulating Example 1 repeats as Example 1A eliminating the catalyst to extend the time of usable use EXAMPLE 2 Weathering Coating Formulation Prepolymer / Polyol 2: 1 Base of the Previous Technique and Coating Performance A high solids formulation for outdoor applications based on acrylic polyols is illustrated The formulation is detailed in Table 3. The isocyanate prepolymer this formulation is a p commercial repellent sold under the brand Airthane ** ASN-540M, based on isophorone diisocyanate (1PDI) and a mixture of neopentyl glycol adipates. The prepolymer was prepared to have a reacted 2: 1 ratio of NCO / OH and a residual diisocyanate monomer content of less than 0.5% by weight. More specifically, the prepolymer had a nominal equivalent weight of 540 g / eq (in solids) and an average functionality of about 2.5. It is used in this formulation as a solution at 85% solids in methyl amyl ketone (MAK). The content of oligomers is less than 15% by weight of the prepolymer. This formulation is supplied in a 1: 1 volume mixing ratio of prepolymer to polyol in conventional multi-component application equipment.

TABLE 3 Typical Formulation for End Coatings of Weather Resistant Polyurethane for High Solids Content Weight (% Volume% Supplier Comments Mixture of Qffipopei and PQIJQJ Chempol 17-3855 21.02 27.84 Polyol-acrylic CCP Zoldina RD4 1.87 2.84 Angus di luyente r e a c t i v oxazolidina Ti-Pure R960 33.36 11.58 DuPont pigment of Ti02 Disperbyk 110 1.58 2.14 Byk-Che ie dispersant pigment Dislon NS-30 0.14 0.21 King agent anti- Industries pigment sedimentation Tinuvin 292 0.77 1.06 Ciba-Geigy stabilizer in the light of a m i n a prevented Tinuvin 400 0.91 1.26 Ciba-Geigy ultraviolet light absorber TABLE 3 (Cont.) P * is? P (*) Vplwmenf-ft) Supplier omen os Compound Compound Polyol Tego 980 0.36 0.52 Tego Chemie agent for air release DABCO 120 0.05 0.07 Air Products catalyst tin (IV) 18% Zn-Oct 0 .31 0 .40 OMG catalyst for zinc carboxylation MAK 1 . 21 2 .05 methyl amyl ketone Subtotal 61.58 49.97 Isocyanate Component Airthane 38.42 50.03 Air Products isocyanate ASN-540M prepolymer Totals 100 * 00 100.00 Solids by weight = 87.76%; solids in volume = 79.94%; PVC = 15.27%; VOC = 169 g / L (1.41 Ib./gal); Mixing Ratio: 1: 1 EXAMPLE 3 Weatherproof Coating Formulation with 2: 1 Prepolymer and Isocyanate Mixture and Coating Performance A high solids formulation is illustrated for weathering applications, based on acrylic polyols and similar to Example 2. The formulation is detailed in Table 4. The isocyanate component consists of an isocyanurate of hexamethylene diisocyanate mixed with prepolymer. The prepolymer is a commercial prepolymer sold under the trademark Airthane ™ ASN-540M based on isophorone diisocyanate (1PDI) and a mixture of neopentyl glycol adipates. The weight ratio of isocyanurate to prepolymer was 20/80. This formulation is supplied at a 1: 1 volumetric mixing ratio of pre-polymer / isocyanurate in admixture with polyol in conventional multi-component application equipment. TABLE 4 Component of Solids Solid Materials Prima 1: Weight VOl-Un-en in Weight in Volume Chempol 17-3855 234.36 26.94 187.49 20.48 Zoldina RD-4 46.87 6.19 46.87 6.19 Ti-Pure R-960 408.75 12.31 408.75 12.31 Nuosperse 657 6.29 0.80 4.40 0.51 TEGO 980 4.40 0.55 4.40 0.51 TINUVIN 384 9.93 1.13 9.43 1.06 Tinuvin 292 9.43 1.13 9.43 1.13 TABLE 4 (cont.) Component of Solids Solid Matters Prima 1; Weight lWlffn in Weight DABCO 120 0.31 0.04 0.31 0. 04 MOONEY 18% Zn 3.74 0.43 3.14 0. 34 DISL0N NS-30 1.68 0.23 0.25 0. 03 Total 735.76 49.75 674.47 43 - 64 Isocyanate Component 11: AIRTHANE AS -54QM Desmodur N-3300 78.90 8.31 78.90 8.31 1175.95 IQQ.QO lQ68f9g 84.72 Solids by weight,% = 90.90 Solids by volume,% = 84.72 Weight / 1 (gallon) = 3.1 (11.76) Proportion NCO: OH = 1.10 Proportion P / B = 0.65 Proportion in Mix = 0.99 PVC,% = 15.19 VOC, kg / 1 (lb / gal) = .128 (1.07 EXAMPLE 4 Physical and Mechanical Tests Physical and mechanical tests were performed on samples prepared from Examples 1, 1A, 2 and 3. The results are set forth in Table 5.

TABLE 5 Test Example 1 Example 1A Example 2 Example 3 Without Catalyst Drying Time (hr.) STT 0.5 1 3 0.5 TF 0.5 12 10 2 TC 0.5 13.5 16 3.5 DFT mm (mils) .064 .066 .066 .058 (2.51 (2.61 (2.61 (2.31 Brightness 20 87.9 86.7 84.7 85 60 95 93.9 92.6 93.2 85 97.2 96.6 97.6 96.4 Hardness Persoz (s) .110 112 56 98 Pencil (gouge) HB HB HB HB Adhesion grated x dry 4B 4B 4B 4B cut x dry 4A 4A 5A 4A cut x, 24 hrs-wet 4A 4A 3-4A Scraping (g) 1800 2000 1500 TABLE 5 (Cont'd) PROCESSING. PHYSICAL AND MECHANICAL PROPERTIES Test Example 1 Example 1A Example 2 Example 3 Without Catalyst D / RI pact- (in kg (Ib)) 160/140 160/120 160/160 160/160 Chem 24 Spot NaOH 10% 4 4 3 4 HC1 10% S2 4 0 4 HN03 5% S2 4 1 1 xylene 2 2 1.2 2 MEK 2 2 0 0 1PA 2 2 2 2 Rubbed with MEK 100+ 100+ 100+ 100+ Comments slightly slightly soft, soft, smooth soft brightness STT = forges to the touch, TF = free of stickiness and TC = complete set; Chem-0 point = detached, 1 = presented blisters, 2 = softened, 3 = discolored and 4 without detectable discoloration, if = slightly. Although no useful employment was reported for Examples 2 and 3, it was estimated to be approximately 1 to 1.5 hours. Surprisingly, although the times of useful eumpleo were essentially the same, the setting rate of the 80/20 prepolymer / isocyanurate ratio was much higher. The TF and TC values for the formulation of Example 3 are much lower than for the formulation of Example 2 and lower than for the formulation of Example 1A, uncatalyzed. The example of the addition of isocyanurate to the prepolymer mixture is also noted in the Persoz hardness. A small amount of isocyanurate increases the Persoz hardness from 56 to 98; the 100% isocyanurate level employed in Example 1 and 1A was only slightly higher. The chemical resistance was also improved by the use of the prepolymer / isocyanurate mixture in the total delamination in 10% HC1, which occurred for the formulation of Example 2, while excellent results were obtained with the mixture used in Example 3. The resistance to Alkaline and aromatic solvents were also better. EXAMPLE 5 Mixture of Prepolymer / Isocyanurate with Polyester Polyol A formulation similar to Example 3 was prepared except that the isocyanate component consisting of Airthane prepolymer, an isocyanurate of hexamethylene diisocyanate and the uretdione of hexamethylene diisocyanate, does not contain solvent, the weight ratio of The mixture of the prepolymer mixture and the mixture of isocyanurate and uretdione was 50/50 and the polyol content is based on a mixture of polyester / polycaprolactone polyol as opposed to the acrylic polyol. It was formulated with less than 24 g / L (0.20 Ib./gal). A typical formulation is detailed in Table 6.

Viscosity versus temperature profiles for the isocyanate and polyol components are illustrated in Figures 1 and 2, respectively. TABLE 6 Typical Top Coat Formulation VOC Weight (% Polyol / Pigment Component 1 Chempol 18-224 15.00 20.11 CCP polyester polyol Tone 0301 6.43 9.10 Union polyol based on Carbide caprolactone solvent-free Ti-Pure R960 37.77 14.57 DuPont pigment Disperbyk 110 1.68 2.52 Byk-Chemie dispersion Dislon NS-30 0.16 0.27 King Industries thixotropic Tinuvin 292 0.58 0.89 Ciba-Geigy HALS Tinuvin 400 0.68 1.06 Ciba-Geigy stabilizer UV Tego 980 0.29 0.47 Tego Chemie air release Byk 320 0.33 0.61 Byk-Chemie auxiliary flow DABCO 120 0.03 0.04 Air Products catalyst 18% Zn-Oct 0.35 0.51 OMG zinc catalyst 63.30 5, 15 TABLE 6 (Cont.) Pesof% vni ?? tnt- * nf% Tester Comments Component Airthane 18.36 25.38 Air Products prepolymer ASN-540 isocyanate Desmodur 9.17 12.12 Miles / Bayer isocyanurate N3300 HDI Luxate HD-100 9.17 12.35 Olin HDI uretdione Subtotal 36.70 49.85 Total 100.00 100.00 Solids by weight = 98.74%, Solids by volume = 97.94%; PVC = 15.57%; VOC = 19 g / L (0.16 lb / gal); Mixing Ratio: 1: 1 Note the low level of VOC in the formulation. It is approximately one tenth of Example 3 which is approximately 50% less than the standard isocyanurate based polyurethane coating system. The use of low oligomer content prepolymer is critical to the success of this mixture. A conventional prepolymer would have very high viscosity and more likely would impart poor sprayability of the formulation. Again it should be noted that the materials have very similar viscosities at an application temperature of 60 ° C. The fact that these components have similar viscosity profiles means in part that the isocyanate and polyol can easily be mixed in the 1: 1 ratio. What is also surprising about the viscosity profiles is that the formulations were essentially at zero VOC, however the two components had very similar viscosities. Usually, with conventional systems, as the solvent is reduced to very low levels, differences in viscosity increase dramatically, an undesirable result that is avoided through the isocyanate component described herein. EXAMPLE 6 Comparisons of Physical and Mechanical Properties of the F m? Acongs i and z Comparisons of physical and mechanical properties of the formulations in Examples 1A, 3 and 5 were performed. The results are shown in Table 7. TABLE 7 Comparison of Property of Representative Film Property Example 1A Example 3 Polyol Example 5 Polyisocyanurate / Acrylic Inter-ester Polyol Polyol Acrylic lacer Polyisocyanate-Nail interlayer Prepolymer Polyisocyanate, Prepolymer Setting Time (hrs) 1 0.5 2 TABLE 7 (Cont.) Comparison of Property of Representative Film Ownership Example 1A Example 3 Polyol Example 5 Polyisocyanurate / Acrylic Inter-ester Polyol Polyol Acrylic lanyard Polyisocyanate-born interlayer Polyisocyanate prepolymer Drying time (hrs) 13.5 3.5 3 Pencil Hardness HB HB HB Dry Adhesion 4A 4A 4A (ASTM D3359) Adhesion in Wet 4A 4A 4A (24 h, D3359) Impact (D / R in-cm-kg (in- lb)) 184/184 184/184 184/184 160/160 160/160 160/160 MEK 100+ 100+ rubs 100+ Brightness 60 ° 94.7 92.6 95.3 Detent retention 88% 92% 97% (1000 UV-S313 ) It is important to note that the handling of the conventional isocyanurate / polyol acrylic or control formulation was much more difficult than the isocyanurate / prepolymer interlayer based formulation of Examples 3 and 5. In addition, the conventional or control formulation had to to be at 2.5: 1 parts by volume of isocyanurate to polyol, ie a non-whole mixing ratio and the control showed extreme sensitivity to the catalyst level. EXAMPLE 7 Catalyst sensitivity studies were performed in Examples 1, 2 and 5. The results are shown in Table 8. TABLE 8 SENSITIVITY STUDY AT CATALYZER LEVEL (ACRYLIC FORMULATIONS, Example 1 Time Level of Catalyzed Filter Time hr. Stickiness Drying none 5 16 20 1/2 X 0.75 1.25 6 X 0.17 0.5 3 Working time level Useful Catalyst time hr. Sel none 0.75 5942 TABLE 8 (Cont.) SENSITIVITY STUDY AT CATALYST LEVEL (ACRYLIC FORMULATIONS.

Example 2 Catalyst Timeout Time Level none 6.5 24 48 l / 2x 3 13 24 1.5 3 9 Useful Time Level Catalyst use hr. Gel none 3 7763 l / 2x 1.17 4715 X 0.67 2304 0.33 871 Example 5 Time Level of Catalyst Time Setting Fragmented hr. _P_ega osidad Dried none 16 34 48 l / 2x 1 2 6 X 0.5 1 4 TABLE 8 (Cont.) SENSITIVITY STUDY AT CATALYST LEVEL (ACRYLIC FORMULATIONS1 Useful Time Level Catalyst Time _sel _ none 3 8347 l / 2x 0.5 1139 E 0.5 632 The above results show that the formulation of Example 5, even when a polyester polyol was used, without catalyst, time of use and time of use. dried were similar to the prepolymer formulations of the prior art (Example 2). On the other hand, with the added catalyst, the sample of Example 5 showed very fast drying times with reasonable times of useful use.

Claims

CLAIMS 1. In a polyurethane-based coating composition comprising the reaction product of an aliphatic or aromatic polyisocyanate of low viscosity, having an isocyanate functionality greater than two and a polyol component having a hydroxyl functionality greater than or equal to two, the improvement comprising: the use of a polyisocyanate component comprising the low viscosity polyisocyanate and an isocyanate-terminated prepolymer, the prepolymer being incorporated in an amount of from about 10 to 90 parts by weight per 100 parts by weight of the polyisocyanate component, the prepolymer has an equivalent weight of 250 to 2000 grams per equivalent that is formed by the reaction of an aliphatic or aromatic diisocyanate, with a long-chain polyol component having an average functionality greater than 2.0, at least 85% having an NCO / OH ratio of 2: 1 and an oligomer content of less than about 15% by weight and having The content of residual diisocyanate monomer is less than about 1% by weight.
2. A polyurethane-based coating composition according to claim 1, wherein the low viscosity polyisocyanate is selected from the group consisting of an adduct of the aliphatic or aromatic diisocyanate and an aliphatic polyol, an aliphatic or aromatic polyisocyanurate, a biuret aliphatic or aromatic, an aliphatic or aromatic uretdione, an allophanate or mixtures thereof.
3. A polyurethane-based coating composition according to claim 2, wherein the long-chain polyol component used to form the prepolymer is an acrylic polyol, polyether polyol, polyester polyol or polycaprolactone and the functionality of the polyol component is 2.2.
4. The polyurethane-based coating composition according to claim 3, wherein the diisocyanate used to form the prepolymer is an aliphatic diisocyanate selected from the group consisting of isophorone, diisocyanate, hexamethylene diisocyanate, tetramethylxylyl diisocyanate, bis (4). -iso-cyanatocyclohexyl) methane.
5. A polyurethane-based coating composition according to claim 4, wherein the polyisocyanate used to form the low viscosity isocyanate is an adduct of an aliphatic diisocyanate, the biuret is an aliphatic biuret, the uretdione is an aliphatic uretdione, the isocyanurate is an aliphatic isocyanurate and the allophanate is an aliphatic alofonate.
6. A polyurethane-based coating composition according to claim 5, wherein the aliphatic isocyanate used to form the adduct of an aliphatic diisocyanate, the aliphatic biuret, the aliphatic uretdione and the aliphatic isocyanurate are selected from the group consisting of isophorone , diisocyanate, hexamethylene diisocyanate, tetramethylxylyl diisocyanate and bis (4-isocyanatocyclohexyl) methane.
7. A polyurethane-based coating composition according to claim 6, wherein the long-chain polyol used to form the prepolymer is a mixture of long-chain acrylic, polyether or polyester polyol and a multifunctional short-chain polyol.
8. A polyurethane-based coating composition according to claim 7, wherein the long-chain polyol is a polyether polyol selected from the group consisting of poly (ethylene oxide) polyols, poly (propylene oxide) polyols and poly (butylene). oxide) polyols or a combination thereof.
9. A polyurethane-based coating composition according to claim 7, wherein the short chain multifunctional polyol is selected from the group consisting of trimethylolpropane, glycerol, sucrose, pentaerythritol, alkoxylated versions of these polyols and mixtures thereof.
10. A polyurethane-based coating composition according to claim 6, wherein the proportion of low viscosity polyisocyanate to prepolymer is from 40 to 60 parts by weight to 60 to 40 parts by weight, the parts by weight total 100 parts. in weigh.
11. A polyurethane base coating composition according to claim 10, wherein the aliphatic polyisocyanate used to form the isophorone diisocyanate prepolymer.
12. Suitable isocyanate component for producing blends of polyurethane coatings, comprising: (a) from about 10 to 90 parts by weight of a prepolymer comprising the reaction product of a diisocyanate component and a long chain polyol component having a average hydroxyl functionality greater than 2.0, the prepolymer has an equivalent weight of about 250 to 2000 grams per equivalent, an unreacted diisocyanate monomer content of less than about 1% by weight, and a molar concentration of oligomers of less than 15%; and (b) from about 10 to 90 parts by weight of a low viscosity polyisocyanate interleaver, the polyisocyanate interleaver is selected from the group consisting of an adduct of an aliphatic or aromatic diisocyanate, an aliphatic polyol, an isocyanurate of an aliphatic diisocyanate or aromatic, a biuret of an aliphatic or aromatic diisocyanate; an uretdione of an aliphatic or aromatic diisocyanate, an allophanate of an aliphatic or aromatic diisocyanate or mixture thereof, the isocyanate mixture totals 100 parts by weight. An isocyanate mixture according to claim 12, wherein the diisocyanate used to form the prepolymer and the low viscosity polyisocyanate interleaver is selected from the group consisting of isophorone, diisocyanate, hexamethylene diisocyanate, tetramethylxylyl diisocyanate, bis (4-isocyanatocyclohexyl) methane. 14. Isocyanate mixture according to claim 13, wherein the long-chain polyol used to form the prepolymer is a polyether or polyester polyol. 15. Isocyanate mixture according to claim 14, wherein the long chain polyol component is a mixture of polyether or polyester polyol and a short chain multifunctional polyol. 16. Isocyanate mixture according to claim 13, wherein the long-chain polyol is a polyether polyol selected from the group consisting of poly (ethylene oxide) polyols, poly (propylene oxide) polyols and poly (butylene oxide) polyols or a combination thereof. 17. Isocyanate mixture according to claim 15, wherein the aliphatic diisocyanate used to prepare the prepolymer is isophorone diisocyanate and the low viscosity polyisocyanate crosslinker is an isocyanurate or uretdione of hexamethylene diisocyanate. This invention relates to low VOC polyurethane coatings, in two parts, comprising a low viscosity polyisocyanate component having an isocyanate functionality greater than two and a polyol component having a functionality equal to or greater than two. The improvement lies in the use of a single isocyanate component in the two-part polyurethane coating formulation. The isocyanate component comprises the low viscosity polyisocyanate component and an end-terminated or isocyanate-terminated prepolymer formed by the reaction of a diisocyanate and a multifunctional polyol, the prepolymer having at least about 85 and preferably 90 weight percent of a 2: 1 adduct of isocyanate to polyol (NCO / OH) and less than about 1 and preferably less than about 0.5% by weight of residual diisocyanate monomer. RS t > or / (*) / AIR910 J "