This invention relates broadly to compositions containing two or more reactive components which must not co-react until raised to above 100.degree. C., and which then must co-react rapidly. These compositions have utility in various fields, including the field of sealant compositions, the field of high solids coatings, and the field of reaction injection molding.
In the field of sealant compositions the invention relates, inter alia, to one package heat-curable compositions useful for sealing insulating glass.
The term "insulated glass" broadly refers to a structure comprising panes of glass, the faces of which are in spaced relationship, thereby providing between the glass panes a space which imparts insulating properties to the structure. In its most widely use form, 2 parallel panes of glass are positioned in spaced relationship by metallic spacers positioned around the perimeters of the panes, and indented a short distance from the edges of the panes, thereby forming a U-shaped channel in which the legs of the U comprise the interior surface edges of the panes and the base of the U comprises a side of the spacer. Typically, the spacer is a hollow member filled with a water-absorbent material, for example, a molecular sieve, to keep the enclosed air space between the glass panes dry. In such a structure, the aforementioned U-shaped channel is filled with a sealant, generally a polymeric composition, which must have a combination of properties for satisfactory use.
The sealant must have a very low water vapor transmission (WVT) rate so that moisture is prevented from entering the dry space between the panes of glass. The presence of moisture in the space tends to reduce the insulating value thereof. Moisture in the space can also condense on the panes of glass and create visibility or aesthetic problems. If the sealant does not have a satisfactory low WVT rate, the capacity of the water-absorbent material in the hollow spacer will be exceeded, and moisture will find its way into the space.
The sealant should form an excellent bond with glass which is not degraded over long periods of time under normal conditions of use, which generally include exposure to sunlight, moisture, and large changes in temperature.
Furthermore, the sealant itself should not be a source of material which enters the space between the panes of glass. Should one or more constituents comprising the sealant volatize into the space, fogging, often referred to as "chemical fogging" of the glass panes, may result.
Temperature variation will tend to cause contraction and expansion of the insulated glass structure. Therefore, the sealant should have an elongation of at least 100%, and preferably an elongation of at least 200%.
The sealant should also resist degradation due to contact with conventional caulks and putties.
Sealant compositions may be classified either as "two package" or "one package" formulations. The two package sealants store their reactants in separate packages which are mixed together immediately prior to application, thereby avoiding premature cure problems. However, in some applications, the premixing requirement is a decided commercial disadvantage which "one package" sealant formulations have attempted to overcome.
One package sealant formulations store all their reactants in a single package. Such a formulation must be indefinitely stable at room temperature or in the absence of moisture of air. These sealants should not cure during "hot storage" at 38.degree. C. (100.degree. F.). These reactants will be "activated," or begin to cure, upon exposure to more elevated temperature (100.degree.-200.degree. C.) or ambient moisture or air. The ideal sealant formulation will continue to cure upon removal of the activation.
"Blocking" of reactive functional groups with an inert derivative during organic synthesis is a well known synthetic tool. Once the desired synthetic transformation has been achieved the blocking agent is liberated, thereby regenerating the original reactive functional group. Removal of the blocking agent may be achieved by chemical reaction, and often by thermal dissociation at elevated temperature.
A "blocked isocyanate" is a compound which contains no free isocyanate groups, but which, though relatively inert at room temperature, will react at elevated temperatures in a manner which is similar to that of a free isocyanate. The formation of such compounds from isocyanates may be illustrated by the equation EQU RNCO+HZ.revreaction.RNHCOZ
The blocking agents (HZ) should have threshold dissociation temperatures of 80.degree.-130.degree. C., thereby ensuring total blockage of the isocyanate groups at ambient temperature and total dissociation at typical extrusion temperatures. Typical blocking agents include such compounds as phenols and thiols, tertiary alcohols, secondary aromatic amines, sodium bisulfite, imides, and 1,3-dicarbonyl compounds.
One example of a conventional one package sealant formulation system employs an isocyanate-terminated polymer and a curing agent, typically an alcohol or amine. Premature reaction between the isocyanate-terminated polymer and the curing agent is prevented by blocking the isocyanate groups with a thermal dissociation blocking agent.
Once unblocked, the free isocyanate will react with the curing agent. However, the rate of reaction is often unacceptable slow for commercial application. Addition of a Lewis acid catalyst, such as a tin salt, may greatly increase the reaction rate. However, coordination of the Lewis acid with the carbonyl group of the blocked isocyanate often allows direct attack of the curing agent on the blocked terminal, resulting in room temperature cure. Certain curing agents, such as aliphatic or aromatic di- or polyamines do react rapidly with the isocyanate. However, these compounds are sufficiently basic to attack the blocked isocyanate terminal, thereby resulting in room temperature cure over several hours.
N. Seeger, "Synthetic Elastomeric Isocyanate Modified Polymers And Method For Their Preparation," U.S. Pat. No. 2,801,990 Aug. 6, 1957), discloses the substituted urea reaction products of a polyisocyanate and an elastomeric diisocyanate-modified polyester or polyesteramide. The poly-isocyanate reactivity is controlled by blocking at least one but not all the isocyanate groups with a thermal dissociation blocking agent. The number of isocyanate groups which are blocked may be controlled by adjusting the molecular proportions of polyisocyanate and blocking agent employed to block the polyisocyanate.
G. Bowser, "Multiple Glazed Unit," U.S. Pat. No. 3,791,910 (Feb. 12, 1974), discloses a two package insulating glass sealant formulation composed of butyl rubber, polyisobutylene, polybutene, silica pigment with hydroxy groups, lead dioxide, and paraquinone dioxime. A two package formulation is required because the composition will cure slowly at room temperature. The sealant will attain a substantially full cure in about two weeks.
V. McGinniss et al, "Compositions Containing Carbamothioate Curing Agents And Their Uses," U.S. Pat. No. 4,246,369 Jan. 20, 1981), discloses temperature-sensitive carbamothiolic acid esters. At temperatures from 100.degree. to 250.degree. C. these compounds dissociate into free isocyanates and free thiols. The carbamothioate curing agents are employed in conjunction with a compound "A" which is reactive with isocyanate and a compound "B" which is reactive with thiol.
E. de Cleur et al, "Pulverulent Coating Compositions," U.S. Pat. No. 4,248,978 (Feb. 3, 1981), discloses a stable pulveruluent coating composition which consists of a monomer which has reactive hydroxyl, carboxyl, mercapto, amino, amide, urethane, urea, or thiourea groups and a blocked polyisocyanate compound having at least one uretone imine group per molecule.