LU83709A1 - CURABLE POLYURETHANE, ONE-PART - Google Patents

Description

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The present invention relates to prepolymer compositions with blocked isocyanate groups having a certain degree of stability at room temperature. One aspect of the present invention relates to prepreg compositions having ld1 blocked isocyanate groups usable as an adhesive '', which compositions can be cured (chain lengthening and / or crosslinking) by the application of small amounts of heat . Yet another aspect of the present invention relates to one part polyurethane adhesives having a long pot life, which adhesives can be cured by heating a film of adhesive (either directly or by heating the substrate on which it is coated) at a moderately high temperature. Yet another aspect of the invention relates to a process for the manufacture of a prepolymer composition with thermally piped, partially isocyanated groupings of isocyanate groups and methods of using such composition including methods for forming a cured polymer film and for bonding substrates together. Yet another aspect of the invention relates to a cured polymer film or the cured substrates obtained by these methods.

The field of polyurethane chemistry has been a generally growing field since the basic principles of the formation of prepolyiaers and polymers, modifications and / or hardening have been discovered a few decades ago. One of the first uses of polyurethane chemistry was in the manufacture of cellular structure polymers where expanded foam / but the early 1950s saw the start of a new era of non-cellular elastomers of polyurethanes. Part of the momentum for spillage in this area of chemistry came from discoveries of more efficient catalysts such as organometallic compounds which typically have a very accelerating accelerating effect on the reaction between hydroxyl groups and isocyanate groups. Like other elastomers / * those of the polyurethane type can be used in adhesives / coatings / and in sealant technology. In these branches of polyurethane technology, as in elastomeric polyurethane technology in general, it is practical to use a prepolymer system which can be hardened to a higher molecular weight material. Typical prepolymers include a repeating unit chain terminated at all ends with a molecule fragment containing unreacted isocyanate groups. Such prepolymers / when reacted with a crosslinker or chain extender / can at least be doubled in terms of their molecular weight, and often the increase in molecular weight greatly exceeds twice. The crosslinker or chain extender may itself contain repeat units. Alternatively, it can be a polyfunctional monomer. (Monofunctional reagents are * - 3 - considered as chain terminating reagents rather than lengthening or crosslinking the chain with regard to their contribution to the polymer structure ultimately obtained.)

A monomer very commonly used for chain extension and / or crosslinking is water or water vapor. (A certain crosslinking can result from water / NCO reactions by the formation of 7 ′ biuret bonds). Many polyurethanes curable, to a part so named are really curable in the presence of moisture. They are, in a sense, two part systems in that the second "part" of the polyurethane of the polyurea forming system is not present in the prepolymer composition but is supplied by the surrounding medium when the first "part "is coated on a substrate or exposed to moisture which is present under normal ambient atmospheric conditions. One-part / curable polyurethane systems comprising the second "part" incorporated in latent form are rather less common. Theoretically, any curable / two part polymer formation system can be formed into a one part system if some technique can be found to get the second part to be latent under normal ambient conditions. When this latent hardening approach is used, perhaps one of the most typical means of activating the latent co-reactant is the application of heat. This technique is particularly advantageous in the field of epoxide chemistry, since there may be a temperature range where the epoxy or oxyran ring will be relatively inactive.

The thermosetting technique is somewhat more difficult to apply in the field of polyurethane or polyisocyanate chemistry because of the reactivity of the -NCO radical at the lowest temperatures. This reactivity is very often observed in the case of aromatic isocyanates (that is to say those isocyanates where the radical-NCO is substituted directly on an aromatic ring), but less in the case of aliphatic and cycloaliphatic polyisocyanates. Isocyanates of the xylylene type tend to have an intermediate behavior with regard to the reactivity between the aromatics and the aliphatics or cycloaliphatics.

Even in these cases where there is very little tendency for NCO radicals to react with co-reactants containing active hydrogen at room temperature, the presence of catalysts such as tertiary amines, organometallic compounds, and the like can add to the complexity of formulating thermosetting prepolymer systems, one part comprising the polyfunctional chain extender and / or crosslinking agent "incorporated" into the composition.

The organometallic catalysts used in polyurethane chemistry typically have the capacity to accelerate a polyol / polyisocyanate reaction at room temperature "and it is normally expected that, if a monomeric polyfunctional alcohol is in intimate contact with a polyisocyanate at room temperature, presence of an organometallic catalyst, the resulting system will not have latent hardening properties. On the contrary, it is normally expected that the viscosity of the system will increase fairly quickly over time and even reach the gel point within a few hours.

A technique usually used during storage consists in "blocking" the NCO-terminal radicals of the prepolymer by means of a monofunctional, removable blocking agent such as phenol.

Phenol reacts fairly easily with isocyanate groups, forming a urethane bond (-NH-C0-0-), but the reaction is reversible, especially at moderately elevated temperatures. An interesting and potentially annoying phenomenon, however, occurs as a consequence of the unlocking step. It has been observed that the heat release (exotherm) pattern of the polyurethane system during the curing step is complex, often with at least two exothermic peaks.

(Once the release of the polymer has occurred, the reaction between the free -NCO and the free hydroxyl group is exothermic).

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In the absence of blocking of -NCO with phenol or other heat-removing blocking agents, it is to be hoped a polyether or polyether polyol by modified / ester, isocyanate-containing prepolymer, organometallic catalyst , a crosslinking polyhydroxyl compound of chain extension such as glycerin or pentaerythritol to obtain a rapidly hardening elastomer, see US Patent No. 3,725,355. However, it is known that solid monomer polyols, under suitable conditions , can be introduced into one-part prepolymer systems to obtain slowly or even stable curing blends. See US Patent No.

3,488,302. The relatively stable mixtures of isocyanate prepolymers and polyolefins described in patent 3,488,302 are believed to be useful as a sealing and sealing material and may be applied in the form of tapes or coatings. By the implementation of hot curing, the mixtures are firmly bonded to the surfaces to which they have been applied. During the hot cure step, the cure temperature is described as being below the melting point of the solid polyol present in the blend. It is difficult to produce even a representative sample of publications relating to the field of polyurethane prepolymer chemistry, this field being so vast and so highly developed. The following publications, all of US patents, are accepted as being rep- »..... .. ................ - ·; iw. al - 7 - sentatives:

Patent Owner No. Date of patent agreement 3,351,573 Skreckoski November 7, 1967 3,488,302 Pyron January 6, 1970 3,549,569 Farah et al. December 22, 1970 3,691,135 Schulze et al. September 12, 1972 3,725,355 Parrish et al. April 3, 1973

It has now been discovered that it is possible to prepare a composition of blocked isocyanate group prepolymers, having unusual stability and highly desirable adhesive properties and exothermic properties, from an aliphatic or cycloalip-natic prepolymer group containing blocked isocyanate groups and a monomer, dimer or trimer polyol of the pentaerythritol type. The prepolymer composition is stable for at least about 48 hours at normal ambient temperature and pressure, typically for several weeks or even months.

The prepolymer composition is curable at temperatures above 60 ° C (preferably above 85 ° C). It is desirable that the curing temperature or range of curing temperatures is below the melting point of the pentaerythritol polyol. The “hardening” is, in the present context, a chain extension and / or crosslinking reaction between hydroxyl groups of the pentaerythritol type polyol and the free radical -NCO of the prepolymer with blocked isocyanate group, resulting in at least a doubling of the molecular weight of the prepolymer, more typically a very large increase in molecular weight which results in the formation of a solid polymer or resin which by nature is typically non-cellular.

A one-part composition according to the present invention comprises: * (a) in a generally continuous phase, a generally aliphatic or cycloaliphatic prepolymer, with blocked isocyanate groups which is fluid at temperatures above 60 ° C., has a molecular weight exceeding 250, and contains a chain of repeated units chosen from the group comprising oxyalkylenes, esters, or mixtures thereof, and uniformly distributed through this generally continuous phase,

(b) a phase comprising a finely divided solid polyol having the formula: (ROCH2) 3C — fCH2OCH2C (CH2OR) 2 Jjj — CH2OR

5 where R represents hydrogen or an aliphatic, cycloaliphatic or aromatic radical, provided that more than one of the groups R is hydrogen, and n is a number between 0 and 2, this polyol being at less partially incompatible with the prepolymer at temperatures below about 60 ° C, and 4 - 9 - (c) distributed through the generally continuous phase, an organometallic catalyst or metal salt for the reaction between the isocyanate radicals and the free groups hydroxyls of component (b) mentioned above.

Polyisocyanate blocking agents have substituents of uneven reactivity. A good example of such a diisocyanate is isophorone diisocyanate (DIIP). The preferred polyol polymer blocked by the diisocyanate is a polyether diol, triol, or tetrol, triols being particularly preferred.

The prepolymer compositions according to the invention are made by blocking the polymer polyol with the aliphatic or cycloaliphatic polyisocyanate in an NCO / OH ratio in the range of about 0.8 to about 3: 1, even better greater than about 2: 1, thereby obtaining a prepolymer with a generally blocked isocyanate group which is fluid or can be extruded at normal ambient temperatures.

The monomer, dimer or trimer polyol is distributed uniformly through the generally continuous phase containing the prepolymer. Since the dispersed or suspended phase is a solid, it is introduced in finely divided form and is preferably mixed with a plasticizer which is inert towards hydroxyl groups, and isocyanates. A water fixing agent can be added to this plasticizer.

The prepolymer compositions according to the present invention can be coated on a substrate and cured by heating as previously described. Since prepolymer compositions (which preferably include very little solvent and can be essentially "100% solid" compositions) have excellent adhesive properties when cured, they can be used to bond substrates together . The prepolymer compositions can contain viscosity adjusting agents such as thickeners and thixotropic agents. Some thickening is particularly desirable for adding body to the compositions, so that they can be delivered from an adhesive dispenser or shutter gun which forces the composition through a small orifice, resulting in the formation of 'a ribbon or "pearl" of material.

In the description and claims of the present invention, the expressions indicated below have the meanings mentioned.

- "Active hydrogen" is considered to be defined by the Zerewitinoff test described in J. Amer. Chem. Soc. 49: 3181 (1927). A typical example of an "active hydrogen atom." d 'is hydrogen in hydroxyl radicals / mono or polyfunctional alcohols. Such "active hydrogen" * is preferred in the context of the present invention, although mercaptans, amines, acids and the like are recognized as containing "active hydrogen".

/ - 11 - The expression "aliphatic polyisocyanates" embraces any polyisocyanate which has at least one -NCO radical attached to an alicyclic aliphatic group. The "preferred aliphatic polyisocyanates" / according to the invention are non-aromatic and therefore do not contain NCO radicals attached to aromatic groups} however it is both permitted and preferable that -NCO of the "aliphatic polyisocyanate" be attached to a cycloaliphatic radical.

The expression "cycloaliphatic polyisocyanates" includes any polyisocyanate which comprises at least one - NCO radical attached directly to a cycloaliphatic group. The preferred "cycloaliphatic polyisocyanates" are not aromatic in the sense indicated above.

"DIIP" designates isophorone diisocyanate also known under the name of 3-isocyanatomethyl -3,5 / 5-trimethÿl-cyclohexyl isocyanate.

"Percent solids" is an expression used in the chemistry of paints and the technology of polyester resin coatings. This term designates the quantity of matter ^ whether solid or liquid]! remaining after volatiles or materials not participating in the curing of the composition had been removed. So, for example, a polyurethane prepolymer composition that had 85% prepolymer, 5% pigment, and 10% organic solvent would typically be characterized as a "90% solids" composition. / plasticizers, as opposed to solvents, would be incorporated into "solids" due to their substantially non-volatile nature, in addition / the plasticizer can normally be considered as part of the solid elastomeric or resinous system formed after curing the prepolymer with the dispersed or suspended phase of solid polyol.

The expression "uniformly distributed" refers to discontinuous phases which are dispersed or suspended through a generally continuous phase, the degree of suspension or dispersion and the degree of uniformity being sufficient to prevent substantial deposition of the phase discontinuous under normal ambient conditions.

As is apparent from the preceding summary of the invention, a key point of the invention relates to the combination of a generally continuous phase comprising a prepolymer terminated by an isocyanate group with a second phase comprising a curing agent finely divided / solid polyol. This second phase is not easily soluble in the generally continuous phase, but is nevertheless uniformly distributed through the continuous phase so as to be in intimate contact with the prepolymer. After heating to a temperature above 60 ° C, preferably at least 85 ° C, the curing reaction begins and continues exothermically until it is completed, at which time a polymer or resin is obtained polyurethane solid. By varying the NCO / OH ratios, the functionalities of the starting materials, etc., the properties of the finally obtained polyurethane prepolymer can vary in accordance with the principles known in the art. For example, relatively high NCO / OH ratios tend to create resins with adhesive properties. When the NCO / OH ratio is less than 1: 1, polymers can be obtained with a significant degree of hydroxyl- and low molecular weights. When the NCO / OH ratio approaches 1: 1, a significant amount of linear chain elongation can occur, thereby creating some degree of thermoplastic behavior (as opposed to thermosetting) and, with starting materials of selected polymeric polyoDs suitably for the prepolymer, a certain degree of elastomeric behavior. The present invention relates to one-part curable polyurethane compositions which are paved, to be cured either in highly crosslinked adhesive or in relatively elastomeric compositions having low to moderate crosslinking densities.

Like other types of resins, the highly cross-linked hardened polyurethanes produced according to the present invention can be plasticized. Uncured, one-part polyurethane prepolymer systems can therefore be mixed with plasticizers and other modifiers which do not necessarily react with isocyanate or hydroxyl groups. Indeed, it is preferred that the plasticizer is substantially inert towards these groups. Similarly, if viscosity modifiers are added, it is usually preferred that these ingredients are relatively inert during the NCO OH reaction. Plasticizers can also have a viscosity-modifying effect and are preferably, for all practical purposes, insoluble in water.

High boiling point hydrocarbons such as hydrogenated polynuclear aromatics are particularly useful as plasticizers in the present invention. To obtain the thickening or thixotropic effects in order to make the polyurethane in one part more suitable for use as a filling, sealing, resistant coating, adhesive or the like, usual organic and inorganic thickening and / or thixotropic agents can be added, thereby increasing viscosity or shear dependent viscosity. The agents: organic thickeners and thixotropics which are inert towards isocyanate and hydroxyl groups are not always easy to find. Even thickening and inorganic agents can contain groups reactive with isocyanates, for example silanol (SiOH). Techniques for masking silanol groups on finely divided silica, silicates such as hydrated aluminum and magnesium silicates, and the like are well known. For example, the particles of silica or of silicates can be treated with silicones, with reactive monomers containing silicone, or with other compounds compatible with silanols or reactants towards hydroxide to eliminate or significantly reduce the availability of groups. silanols on the surface of silica or silicate particles. Despite such treatments, silica or silicate particles retain certain thickening or thixotropic effects. The ultimate particle size of these inorganic agents is generally in the colloidal domain - typically greater than one nanometer but smaller than one micrometer. These colloidal particles have a strong tendency to agglomerate together to form agglomerates or other enlarged porous particles having a large surface area per unit of weight. Modified hydrophobic silicas / silicone are generally preferred agents for giving body (or a false body) to one-part polyurethane compositions according to the present invention. (The expression "silicone" is synonymous with organopolysiloxane polymers).

The polyurethane prepolymers ending in (1¾ preferred isocyanate group of the invention are derived from starting materials of polymer polyos and aliphatic or cycloaliphatic polyisocyana which starting materials will now be described in more detail. The polyol polymer

Suitable polymer polyols are preferably fluid at normal ambient temperatures and have a molecular weight in excess of 250, more typically in excess of 500. A chain of repeating units of oxyalkylenes and / or esters is a major contribution to molecular weight. A typical polymer polyol consists essentially of either a straight or branched chain of repeat units ending in hydroxyl groups, and, for reasons of simplicity, these hydroxyl groups will normally be the only substituents containing active hydrogen in the structure of the polyol. Polyesteis and polyétheis polyols having molecular weights in the hundreds of miners and even millions are commercially available, but the viscosity of the resulting prepolymer system is more likely to be adjustable when synthesized from polymer polyols having a weight molecular less than 20,000, more typically less than 5,000 or 10,000, the optimum range being about 500 to 3,000. The functionality of the polymer polyol can be varied within a wide range by choosing a monomer polyol core or other core containing a active hydrogen having the desired number of active hydrogen atoms or substituents containing active hydrogen.

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For example, a polymer polyol having a functionality of three can be "developed" from an initiator or nucleus such as glycerin, trimethylolpropane, triethanolamine, and similar monomer triols. (If the functionality desired is only two, the initiator or nucleus can be water, glycol, or the like.) For a polyol polymer functionality of four, ethylene diamine and other di-primary amines have been used successfully, since both Hydrogens active on each amine substituent have substantially equal reactivity. Carbohydrates or carbohydrate derivatives having very little (or only a saccharide or similar units or saGcharides can be used to form an initiator with a very high functionality, for example up to eight. Oils containing hydroxides (vegetable oils, etc.) have also been used to form polyols with high functionality. If the polyol has reacted with the polyisocyanate, the resulting prepolymer may have an isocyanate functionality greater than one and up to three or four or even six, but typically not more than nine. Polyols. containing polyoxyalkylenes or polyesters according to the invention will therefore normally be diols, triols or tetrols. The; equivalent weight of these preferred polymer polyols will typically be between about 125 to about 2500, the range of 200-1000 being generally considered to have optimum properties for an adhesive system.

Polyester polyols having a functionality greater than two are particularly useful in adhesive systems Poly (epsilon-caprolactone) polyols of various functionalities and equivalent weights are readily available and are well suited for the present invention. Among the commercially available compounds of these dark polyols may be mentioned the "NIAX Polyol PCP" series which melt at temperatures below 60 ° C # more typically at temperatures below 40 ° C. The average hydroxyl numbers of these polyol series can range from values as low as 37 to values as high as 560, indicating equivalent weights as high as about 1,520 and as low as 100. The weights The average molecular sizes of these polyol series are reported to range from as low as 300 to as high as 3000. Not all of these polyols work for the present invention with equal efficiency, and those having a weight average molecular greater than 500 and an average hydroxyl number less than about 450 are most advantageous.

Polyisocyanate blocking agent

The polymer polyols described above are blocked with a polyisocyanate to form a polyurethane prepolymer ending in an isocyanate group. To obtain a one part curable polyurethane prepolymer system having the desired degree of stability at room temperature, the blocking agent should be an aliphatic or cycloaliphatic polyisocyanate typically having a functionality greater than one but less than four. Aliphatic and cycloaliphatic di- and tri-isocyanates are commercially available, the most common of these compounds being diisocyanates such as alkylene diisocyanates, DIIP, and hydrogenated aromatic and xylylene diisocyanates. previously, the "aliphatic polyisocyanates" and "the cycloaliphatic polyisocyanates" according to the present invention are non-aromatic, therefore, all / aromatic rings initially present in the starting material have been partially or fully hydrogenated. However, as is well known in the art, polynuclear polyisocyanates can be selectively hydrogenated so that one ring becomes cycloaliphatic while the other remains aromatic. As aromatic / cycloaliphatic diisocyanates such compounds react much more easily with the hydroxyl groups at the aromatic end of the molecule, generally resulting in a prepolymer ending in an isocyanate group in which the free-NCQ groups are virtually all attached to the cycloaliphatic end of the blocking agent. Accordingly, "it is to be hoped that the prepolymer will behave as a cycloaliphatic isocyanate blocking material which is virtually free of any aromatic isocyanate character. The kinetic conditions of the reaction governing the formation of the prepolymer will generally favor such a result, but, because of the statistical possibility of free aromatic isocyanate, fully non-aromatic polyisocyanates are the generally preferred blocking agents.

Non-aromatic polyisocyanates do not have to have symmetrical structures or -NCO groups of equal reactivity to be useful in the present invention. Indeed, DIIP is the preferred polyisocyanate, and the -NCO groups of this compound do not have an equal reactivity. One of the -NCOs is attached directly to the cycloaliphatic ring while the other is "isolated" from the ring by a methylene group. Although the present invention is not bound by any theory, it is assumed that a polyurethane prepolymer according to the invention will generally end in the less reactive of the two radicals -NCO of the molecule dIIP -a result which will probably be favored by the kinetic conditions prevailing during the formation of the prepolymer. These relatively poorly reactive isocyanate end groups can contribute to the surprising room temperature stability of the one-part curable polyurethane systems according to the present invention. Again, the invention is not bound by any theory, but another possible contributing factor is the relative incompatibility of the solid penta- erythritol curing agent distributed uniformly across one-part system uncured prepolymer. Apparently, at temperatures above 60 ° C, more typically above 85 ° C, this incompatibility is significantly reduced, resulting in a long step towards a more homogeneous and, perhaps, more reactive system in which the free -NCO Slowly reacting from the DllP residue quickly becomes more capable of reacting with the curing agent. The result observed is a curing reaction with a single exothermic peak.

For the blocking step which forms the curable prepolymer, the NCO / OH ratio can vary over a wide range, depending on the properties desired in the polymer finally obtained. For a high level of chain elongation and the possibility of elastomeric properties in the cured polymer, an NCO / OH ratio in the range of about 0.8 to about 1.2 is generally the most effective. For a coating composition having a certain degree of elasticity, impact resistance and relaxation properties, the NCO / OH ratio can be considerably higher, for example up to about 2: 1. Adhesive systems can even have higher NCO / OH ratios and are typically greater than 2: 1. In the context of the present invention, there does not appear to be any advantage in a ratio greater than 3: 1. Adequate rigidity, adhesion strength and relaxation properties can be obtained with an NCO / OH ratio of less than 2.8: 1.

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The curing agent (which will be described in greater detail later) is a polyhydric alcohol and therefore lowers the general NCO / OH ratio when added to the system. For example, the curing agent can be added in an amount sufficient to lower the NCO / OH ratio of the total composition from 10 to 75%. When the NCO / OH ratio for the formation of the uncured prepolymer is greater than 1.5 (for example 2: 1-3: 1), the presence of the curing agent can reduce the NCO / OH ratio up to less than 1.5, but the ratio will preferably remain greater than about 0.8. In adhesive systems according to the invention, it is preferred that the general NCO / OH ratio remains greater than 1: 1, even after the addition of the curing agent.

Curing agent

The monomeric or substantially monomeric polyhydric alcohols used as curing agents in the dispersed or suspended phase of one-part curable polyurethane systems according to the present invention are solids having melting points above the preferred curing temperatures.

These cure temperatures are ordinarily well below 250 ° C / and are typically in the range of 85-200 ° C. For example, a so-called "point welding" hardening is typically carried out for a few minutes (for example 0.5-10 minutes) at r 150-190 ° C., the duration and the temperature being, of course, related - 23 - to each other. Typical oven cures are carried out for a longer period of time at even lower temperatures. As noted previously / no significant curing is observed at temperatures below 60 ° C or even at temperatures as high as 85 ° C.

Pentaerythritol is a polyhydric alcohol curing agent ideal in the context of the present invention. Its melting point has been variably given at 260 ° C and 262 ° C. It appears to have substantial incompatibility with preferred hardened polyurethane prepolymers for use in the present invention. The hydroxyl groups of pentaerythritol do not seem to react with the free-NCO radicals of the DUP residue at normal ambient temperatures and pressures, even in the presence of an organometallic catalyst.

Esterification of pentaerythritol, particularly with lower aliphatic acyl groups can significantly reduce the melting point of the resulting ester, hence, such esterification is not usually not desired. In addition, at least two hydroxyl groups of pentaerythritol (or its dimer or trimer) must remain available for interaction with the NCO groups during the curing reaction. The non-esterified dimer: and trimer of pentaerythritol are however both usable for the present invention being f ........

Since technical grade pentaerythritol may contain measurable amounts of these higher analogs. Of the two higher analogs, we admit that the dimer behaves in a similar way to that of pentaerythritol itself (the dimer, also called dipentaerythritol is present in penta-erythritol in much greater quantity than the trimer, also called tripentaerythritol). For these and other reasons, the curing agent need not be pentaerythritol of higher purity than that of technical grade pentaerythritol. Conversely, the present invention is not limited to the use of technical grade pentaerythritol or its dimer or its trimer. High purity pentaerythritol is commercially available and is used in large quantities to make the explosive pentaerythritol tetranitrate. If the pentaerythri-tol esters or the esters of its dimer or trimer are used as the curing agent in the present invention, up to two of the methylol / pentaerythritol groups can be converted to -CH2OR, where R represents an aliphatic acyl radical , cycloaliphatic or aromatic, preferably a radical which does not lower the melting point of the resulting ester up to a temperature below 50 ° C. In the dimer, up to four methylol groups can be transformed into ester groups without reducing the hydroxyl functionality to a value less than two - and this number increases to six in the case of the trimer.

However, there does not appear to be any benefit to this high degree of esterification. Again, it should be borne in mind that the trimer is not as readily available as the dimer and is even less available when compared to pentaerythritol itself. Penta-erythritol is commercially produced by a large number of relatively simple methods, including condensation of aldol / cross-reaction / Cannizarro between an acetaldehyde and four moles of formaldehyde. Dipentaerythritol is normally considered a side product of such reactions, and it is difficult to obtain more than trimer by this means.

Curing catalyst

To obtain a complete advantage of a one-part curable polyurethane composition according to the invention, it is preferred to include a catalyst for the reaction between the isocyanate radicals and the free hydroxyl groups of the curing agent. As is known in the art, a variety of organometallic compounds and metal salts have the ability to accelerate the NCO / OH reaction. In fact, it has been found that organomercuric catalysts selectively accelerate the NCO / polyol reaction even in the presence of other compounds containing tek active hydrogen than water. Organometallic catalysts and metal salts used in polyurethane chemistry typically contain metals or metal ions from groups VIII, 'IB, II-B, and IV-A of the periodic table, for example tin, lead , iron, and mercury. Organo-metallic compounds of bismuth, titanium, antimony, uranium, cadmium, cobalt, thorium, aluminum, zinc, nickel, molybdenum, vanadium, copper, manganese and zirconium have also been described as a usable catalytic material "see, for example, US Patent No. 3,961,135 (Schulze et al.), granted September 12, 1972, column 3, line 35 and seq. The use of organotin compounds is particularly usual, for example compounds having the structure R2SnX2 * where R is a hydrocarbon radical, X is chlorine or an acyloxy, alkoxy, aryloxy, alkylthio or arylthio radical, or in which X2 represents an oxygen atom or sulfur.

It has also been described that the compounds having the structure R ^ SnX have the desired catalytic activity. See, for example, U.S. Patent No. 3,351,573 (Skreckoski), granted November 7, 1967, column 4, line 12 and seq. Mercury salts such as mercury acetate are known to have catalytic activity towards the NCO / OH reaction. These salts tend to be less effective in catalytic amounts, however, and molar amounts may be required. Compounds having the formula RHgX, where R is an aliphatic, aromatic or cycloaliphatic group and X is OCOR '(R' being defined in the same way, but not necessarily the same radical as R) are highly effective in catalytic amounts - 27 - and are among the preferred organometallic catalysts used in the present invention. Typical catalytically effective amounts of organomercury compounds are in the range of 0.1-1% by weight of the total system of the one-part curable polyurethane. Organotin compounds are typically effective in about the same amounts. There does not appear to be any advantage in using larger amounts of the more effective organometallic compounds, although, as noted above, metal salts not containing direct carbon-metal bonds can be used with much advantage in quantity / larger compared to organometallic.

Other ingredients

As is well known in the art, fillers, extenders, pigments and the like can be incorporated into the prepolymer-polyurethane compositions. Neutral fillers are usually preferred, since highly alkaline materials can have an undesirable catalytic effect, and highly acidic materials; can attack uretha-ne (carbamate) bonds in the prepolymer. As noted previously, it is preferred to include viscosity modifiers in the prepolymer compositions of the present invention. For practical reasons of description, the plasticizer (for example hydrogenated terpheny) and the thickener or thixotropic (for example hydrophobic silica modified by silicone) can be considered as being part of a viscosity-modifying system, although each of these components may have other desired effects on the prepolymer composition and the resulting cured product. Preferably, the viscosity modifying system is not a major component of the polyurethane prepolymer composition and can be omitted entirely, although · at least about 1% by weight of plasticizers is a most useful aid for introducing and dispersing the solid curing phase of the one-part hardened polyurethane composition. If the one-part polyurethane composition is to be used as an adhesive, sealant, sealant, or tough coating agent, at least about 1% by weight of the system will normally include the thickener or thixotropic. Normally, the amount of either the plasticizer or the thickener would not exceed about 25% by weight of the solids in the one-part curable systems. Indeed the combined total of these two components will normally not exceed 25 or 35% by weight. weight of solids.

The Eäastifiant is typically introduced in two portions.

A modest amount (for example 5-15% by weight of the total solids) can be mixed with the prepolymer with isocyanate groups blocked in the generally continuous phase.

A smaller amount (eg 1-5% or more, depending on the amount of curing agent used) is incorporated into a premix which becomes the continuous phase containing the curing agent. Measured in terms of the amount of curing agent, this second part of plasticizer will typically range from about 25 to about one hundred and 150 parts by weight (tpc). When organic water binding agents are used (e.g. alkyl orthoformates) it is generally practical to incorporate this agent in the premix. Very small amounts of alkyl orthoformates provide good protection against unwanted side reactions with any trace of water that may be present. Therefore, less than 1 or 2% by weight of the total composition will typically comprise the water fixing agent. Certain inorganic fillers and the like can also fix water and thus protect against the formation of carbon dioxide and other undesirable side reactions. However, some of these inorganic agents (such as calcium oxide) are · alkaline and / are ordinarily not preferred.

Manufacturing processes and use

The formation of a polyurethane prepolymer from a polymer polyol and a suitable isocyanate blocking agent is carried out according to the principles well known in the art of polyurethane chemistry. Heat and / or catalysis can be used to accelerate the NCO / OH reaction. The introduction of the solid curing agent into the generally continuous phase constituted by the prepolymer can be carried out using a premixing step, as described above. The mixing of the two phases can be carried out with a usual mixing installation.

The same installation or a similar installation can be used to introduce the organometallic or metallic salt catalyst and the thickener or thixotropic if there is any.

The amount of volatile solvent in the composition is preferably minimal, if solvent must be present. When used, the solvent is preferably introduced into the continuous phase to a level of, for example 25% by weight of the total composition. However, any solvent which would tend to significantly reduce the incompatibility ratio between the continuous phase and the phase of solid curing agent in suspension could have a severe detrimental effect on the stability of one-part systems according to the invention. For this and other reasons the solvent can be excluded entirely from the composition, thus achieving a system with substantially 100% solids. The plasticizers such as hydrogenated aromatic compounds typically used in the preferred compositions according to the invention do not seem to have any detrimental effect on the stability or on the ratio / phases "described above. Consequently, if it is desired to reduce the viscosity, it is generally preferable to increase the amount of plasticizer rather than introducing the usual solvents. ...... j- -. - .... -JW. .1.1 III ’λ - * jr ~. trjj ****:. · s. . , eA * '* - 31 - polyurethane te] s as acetone, alcohol or the like. Hydrocarbon solvents such as mineral spirits are less likely to have such a deleterious effect.

One-part polyurethane systems according to the present invention can be used in the same manner as other adhesives, coatings, sealants, sealants, repair compounds, and one-part curable moldable resin systems. Curing, as noted above, is started very simply by heating the system to a part or its environment or the substrate on which it is coated.

As an adhesive, the one-part polyurethane systems according to the invention are particularly useful for bonding sheet molded compounds to themselves and to aluminum or other metals. Good adhesion strength has also been obtained with aluminum to aluminum connections. One-part curable systems according to the invention can also be used to coat these substrates, for example; as a decorative protective coating. The cured polymer or adhesions obtained with the cured polymer withstand the severe tests of immersion in water and meets the specifications of the adhesion forces required in industry when cured according to the teachings of the present invention. .

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Examples

In these examples, the following brands or trade names are used to identify the materials described below.

"NIAX Polyol PCP-0310" is a polycaprolactone polyol which is essentially trifunctional and has an average molecular weight of the formula of 900 / an apparent specific weight (55/20 ° C) of 1.073, an average hydroxide number of 187 mg KOH / acid g, an index / which does not exceed 0.25 m KOH per gram of sample, a melting point range of 27-32 ° C, a water content at the time of delivery does not not exceeding 0.03% by weight, and a viscosity at 54.4 ° C of 270 centistokes.

In the molten state, the maximum color of this polyol is 100 (Pt-Co). "NIAX" is a trademark of Union Carbide Corporation.

"HB-40" (trademark of Monsanto) is a high boiling hydrogenated aromatic compound which dissolves a wide variety of polymers and rubbers as well as asphalfes and tars. It is a clear oily liquid with a maximum coloration (APHA) of 180, a maximum moisture content (KF in methanol) of 125 parts per million (ppm), a refractive index at 25 ° C lying in the interval from 1.560 to 1.575, a specific gravity (25 ° / 15.5 ° C) of 1.001 -1.007, a pour point of -26 ° C, a boiling point of 180 ° C at 10 mm of mercury, a surface tension at 25 ° C of 40.1 dynes / cm, a flash point (COG) of 345 ° C and a point,. 'V. ‘' Λ ,. . '7 * läVBHMKX.1 *! * <Λ <ί. ”Ί · '4ίί' * Α .. · ..: /.-. ί ·. '·. · ** '' £ - 33 - ignition-196 ° C. Chemically, "ΗΒ-40" is a hydrogenated terphenyy and is practically insoluble in water. Its vapor pressure is, expressed in mm of mercury at 150 ° C, 2.6, at 200 ° 22, and at 250 ° C 95. Its viscosity in centisto kes is 70 at 0 ° C, 29.0 at 37.8 ° C and 3.8 at 98.9 ° C. "HB-40" was used as a partial replacement for plasticizers for usual vinyl resins of the diester type.

"Additive OF" (trade designation of Mobay Chemical Company) is an alkyl orthofornate having a boiling point of about 145 ° C, a specific gravity at 90 ° C of about 0.90 and a flash point (DIN 51755 closed tank) at 36 ° C.

It is an aqueous white liquid which has been used as such or in combination with other additives to stabilize one component polyurethane coatings. According to the manufacturer's recommendations, 2-3% of this additive should be added for clear coatings. For pigmented coatings, 4.5% must be incorporated. For two-component systems, 1% of Additive OF is recommended, calculated on the total weight of the formulation. This additive is known to reduce the moisture sensitivity of polyurethane systems.

"COCURE 32" (registered trademark of Cosan Chemical Corporation of Cliffton, New Jersey, USA) is a liquid organomercuric urethane catalyst for the isocyanate / hydroxyl reaction containing 60% of active ingredients, 20% of mercury, ·· '· Λ> * Λ ι. ·. If V- 'Ç WWCUMTC Λ * "**". ". *. *.".; Γί. Î - 34 - calculated as metal. This liquid composition contains a non-reactive solvent system which is free of any hydroxyl. "COCURE 32" has been formulated to be compatible with the polyols of polyëtfreis and polyesters and with polymeric isocyanates.

"CAB-Ö-SIL TS-200" (registered trademark of Cabot Corporation) is a smoked inorganic silica powder which has been modified by treatment with an organic silicone. The treated powder is generally hydrophobic. It has a surface area of 2 70 plus or minus 15 m / g. It contains at least 99.8% silica and has a pH of around 4.7.

The DIIP (disophorone diisocyanate) used in these examples was supplied by Veba-Chemie AG. This compound is a low viscosity liquid with no tendency to crystallize at low storage temperatures. Thanks to its relatively high molecular weight, the vapor pressure is low: 0.0004 mbar at 20 ° C and 0.009 mbar at 50 ° C. As the terminal residue of the blocked isocyanate prepolymer, the vapor pressure is of course further reduced as is the odor. „The molecular weight of the compound is 222.3 and the NCO equivalent weight is 111.1. The flash point (closed) is 155 ° C, and the sealing temperature is 430 ° C. The minimum NCO content specified is 37.5% by weight, the minimum purity specified is 99.0% by weight? and the density specified at 20 ° C is between 1.058 to 1.064 g / ml. The total chlorine content must not exceed 0.05% by weight, and the maximum hydroishable chlorine must not exceed 0/02% by weight. The melting point is around -60 ° C and the boiling point at 13/33 mbar is 158 ° C. The viscosity should not exceed approximately 150 centipoise (cps) even at -20 ° C.

The pentaerythritol used in the present example is designated "PE-200" (trade designation of Hercules Incorporated) and it is a high quality technical grade of this compound which has been ground to a particle size sufficiently fine to pass through a 0/074 mm mesh screen. Only about 1% or less of the particles are retained on a 0/044 mm mesh screen. Monopentaerythritol (C [CH2 OHj ^) is specified as constituting 88% plus or minus 2%, a percentage fairly typical of technical quality. A major amount of the remaining 10-14% is accepted as dipentaerythritol. The specified hydroxy content is 48 plus or minus 1%, and the ash content is less than 0.01%. Less than 0/5% of the "PE-200" includes secondary products or liquid contaminants. The average equivalent weight for this technical grade of pentaerythritol is 35.4. (Other polypentaerythritols in addition to dipentaerythritol may be present.)

Example 1

One-part curable polyurethane adhesive

It has been found that the thixotropic adhesive is suitable for bonding a molded polyester sheet compound for application in the automotive industry. The continuous phase of the one-part curable composition essentially consists of polycaprolactone triol blocked by DIIP mixed with a little plasticizer. The discontinuous phase is introduced in the form of a premix containing a technical quality of pentaerythri-tol, plasticizer and alkyl esterimide. The composition also contains the organomercuric catalyst and a hydrophobic silica to communicate thixotropy. The ingredients of these one-part systems containing a dispersed or suspended curing agent are listed in the order in which they were added.

Ingredient Quantity (% by weight)

Polyurethane prepolymer ^ 14

obtained from 53.0% of "NIAX Polyol PCP-0310" and 47.0% of DIIP

"HB-40" (plasticizer 7.31

Premix 7.8 "COCURE 32" (catalyst) 0.25 "CAB-O-SIL TS-200" 11.5 (thixotropic)

The premix contained technical grade pentaerythritol "PE-200", plasticizer "HB-40", and "Additive OF" in ·; ? ·: I * u: w ^ saβL · & ila »MmMmÊÈιnM * MmM * '*%. y.y ·. ,,, ·. · ·; - 37 - (weight) ratio of 59.75: 39.4: 0.85 (respectively). Example 2

Welding by jEOinbset oven curing

The part-curable composition of Example 1 was used to bond acid-etched aluminum to itself and aluminum to a sheet molded compound (CMF). Rockwell CMF was used for these tests and the thickness of the adhesive coating was between 250-380 micrometers. Spot welding was simulated with a heated plate press.

1. Spot welding (plate press - Hardening condition Adhesion strength (Temperature / Duration) _ at break of the substrate * (MPa) 177 ° C / 2 minutes 5,178 177 ° C / 3 minutes 6,308 177 ° C / 4 minutes 5.922 177 ° C / 5 minutes 6.288 * In no case did the bond break before the substrate ruptured.These adhesion forces transmitted exceed industry specifications by a factor of at least 10.

2. Oven hardening

Two stages Adhesion strength (Temperature / Duration) at break of the substrate ** (MPa]

Step 1: 127 ° C / 30 minutes 5,295

Step 2: 166 ° C / 30 minutes 6.501. ..: / - - Λ *, ·; ·. n ^ .OL ^ r:,; . \ <·. <- 38 -

Industry specification 0.689 MPa after step 1 and 4.137 MPa or CMF failure after step 2. CMF failure was observed after the two curing steps.

3. Water immersion test

Immersion in water or Adhesion force treatment with humidity at the rupture of the substrate (MPa

Duration / Temperature_ 14 days of immersion / 4,654

23.9 ° C

14 days / 93 ° C 4,530 14 days / 37.8 ° C / 4.743 100% relative humidity Other tests were carried out for the bonding between various substrates.

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Claims (17)

1. Composition of prepolymer with a group of iso cyanates generally blocked / with a part which is stable for at least about 48 hours at normal ambient temperature and pressure and hardenable at temperatures above 60 ° C. in a solid polymer having at least twice the molecular weight of this prepolymer, characterized in that this prepolymer composition comprises: (a) in a generally continuous phase, an aliphatic or cycloaliphatic prepolymer, with isocyanate group generally blocked which is fluid at temperatures above 60 ° C., has a molecular weight exceeding 250, and contains a chain of repeat units selected from the group consisting of oxyalkylenes, esters or mixtures thereof; and uniformly distributed throughout this generally continuous phase, (b) a phase comprising a finely divided solid polyol having the formula: (ROCH2) 3C- £ CH2OCH2C (CH2OR 2 ”] CHgOR where R represents hydrogen or an aliphatic acyl radical , that cycloaliphatic, or aromatic, provided / more than one of the groups R is hydrogen, and n is a number between 0 and 2, this polyol being at least partially incompatible with this prepolymer at temperatures below 60 ° C? And (c) distributed through this generally continuous phase, an organoraetallic or metal salt catalyst for the reaction between the isocyanate radicals and the free hydroxyl groups of this component (b). 2. Composition according to claim 1, characterized in that this generally uniformly distributed phase consists essentially of a finely divided solid polyol mixed with a plasticizer which is essentially inert towards the active hydrogen and the isocyanate. 3. Composition according to claim 3, character-risœen that this generally continuous phase is substantially solvent-free. 4. Composition according to claim 1 / characterized in that (a) this prepolymer is the product of the reaction of components comprising an aliphatic or cycloaliphatic diisocyanate having radicals -NCO with unequal reactivity and μη polyester polyol or polyoxyalkylene, having reacted together in an NCO / OH ratio in the unesterified range of about 0.8 to 3: 1. and (b) this polyol / is an unreacted unreacted pentaerythritol or dipentaerythritol present in an amount sufficient to lower the NCO / OH ratios of the total composition by about 10 to 75%. 5. Composition according to claim 4, characterized in that these constituents of this prepolymer react together in an NCO / OH ratio greater than about 1.5 and the presence of this constituent (b) reduces the NCO / OH ratio to less than 1 , 5 but greater than about 0.8. - 42 - 6. Polyurethane adhesive with a heat-curable portion and having a pot life exceeding 48 hours at normal ambient conditions / characterized in that this adhesive comprises; (a) in a generally continuous, fluid phase containing less than 25% by weight of solvent, a prepolymer with generally blocked isocyanate groups comprising a polyester polyol generally blocked by an aliphatic or cycloaliphatic polyisocyanate, this prepolymer being fluid at 60 ° C. , having an average molecular weight exceeding 500, and having an isocyanate functionality greater than i but less than 9. r (b) in a solid, plasticized phase, distributed through this generally continuous, fluid phase, of solid particles of unreacted monomer or dimer pentaerythritol or esters of pentaerythritol or its dimer having at least two free hydroxyl groups. f (c) distributed through this generally continuous phase of fluid, an organometallic catalyst or metal salt for the reaction between the isocyanate radicals and the free hydroxyl groups of this component (b). 7. Adhesive according to claim 6, characterized in that this polyester polyol is glycol, triol, or tetrol of polycaptrolactone and this pentaerythritol or its dimer are not esterified. This adhesive containing an organometallic catalyst for the NCO / OH reaction . 8. Adhesive according to claim 7, characterized in that the molecular weight of this glycol, triol, or tetrol of polycaptrolactone is in the range of 500 - 5000. 9. Adhesive according to claim 7, characterized in that the aliphatic or cycloaliphatic polyisocyanate is a diisocyanate having an aliphatic -NCO group and a cycloaliphatic -NCO group. 10. A method of manufacturing a prepolymer with isocyanate groups generally blocked, in one part, thermosetting characterized in that it comprises the steps of: (a) blocking a polyol containing a polyoxyalkylene or polyester by means of a polyisocyanate aliphatic or cycloaliphatic with an NCO / OH ratio in the range of about 0.8 to 3: 1, thereby obtaining a generally blocked isocyanate prepolymer which is a fluid at normal ambient temperatures, (b) uniformly distributing a finely divided solid polyol through this prepolymer, this solid polyol being generally incompatible and non-reactive with this prepolymer at temperatures below 60 ° C, but relatively more reactive with this prepolymer at a range of temperatures above 60 ° C and below decomposition temperature of the prepolymer, this sidid polyol having the formula: (ROCH2) 3C - £ CH2OCH2C (CH2OR) 2-J ^ CH2OR where R represents hydrogen or an aliphatic acyl radical e, cycloaliphatic or aromatic, provided that more than one of the groups R is hydrogen, and n is a number between 0 and 2. έ 11. Method according to claim 10, characterized in that the blocking step is carried out with (1) a polyester or polyoxyalkylene polyol having a functionality greater than 1 but less than 9, and (2) an aliphatic diisocyanate or cycloaliphatic, during which this solid polyol is a non-esterified pentaerythritol, and this non-esterified pentaerythritol is mixed in this prepolymer using a liquid plasticizer which is essentially inert towards hydroxyl and isocyanate groups at the curing temperature the lowest of this prepolymer. 12. A method of manufacturing a cured polymer film characterized in that it comprises the steps of: (a) coating the prepolymer composition of claim 1 on a substrate, and / (b) heating the resulting coating on it substrate up to a temperature above about 60 ° C. - 45 - "'♦ 13. Method for bonding substrates together, characterized in that it comprises the steps of: (a) coating the prepolymer composition according to claim 1 on a substrate and adjusting / this substrate a second substrate, and (b) heating the resulting coating on this substrate at a temperature above 60 ° C. 14. Bound substrates obtained by the implementation of the method according to claim 13. 15. Cured polymer characterized in that it comprises the composition according to claim 1 which has been heated to a temperature above 60 ° C. 16. Polyurethane composition with a part which is hardenable with heat and having a pot life exceeding 5 days at normal ambient temperatures, characterized in that this. adhesive includes: 7 (a) in a generally continuous fluid phase, at substantially 100% solids, a trifunctional polyester polyurethane prepolymer a blocked isophorone diisocyanate having a molecular weight of 500-5000, (b) in a phase solid plastic coated uniformly distributed through this fluid phase, solid particles of non-esterified pentaerythritol which have not reacted. and (c) a catalytic amount of an organometallic catalyst or metal salt for the reaction between the free hydroxytes Λ 'r' * “·· * * '·“ * ”·· •' β · * · ~ ΛΊ ΙΜ · IIIWI Mil,. . χ _. {*. -I.i v t, **:. · * _. ·, **> - 46 - of this pentaerythritol and the terminal radicals -NCO of this prepolymer. 17. A polyurethane composition according to claim 16, curable at temperatures above 60 ° C into a solid polymer with a non-cellular structure which has a molecular weight at least double that of the prepolymer of -, polyurethane, characterized in that this composition - includes: (a) in this generally continuous fluid phase, substantially 100% solids, a poly-epsilon-caprolactone) triol fluid blocked by isophorone diisocyanate having a molecular weight of 500-3000, the diisocyanate isophorone and the triol having reacted together in an NCO / OH ratio of 2: 1 to 3: 1. r (b) in this plasticized solid phase, a moisture-fixing agent, pentaerythritol of purity at least of technical quality, and a plasticizer which is inert towards * the hydroxyl groups, and the isocyanate groups; the amount of this pentaerythritol was sufficient to reduce the general NCO / OH ratio of this composition in the range of 1: 1 to about 1.5: 1; and (c) a catalytic amount of organometallic catalyst.