Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
1998-09-16
2001-03-20
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S039000, C427S515000, C427S516000, C427S195000
Reexamination Certificate
active
06204350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to moisture-curable compositions and, in particular, to those having reactive silane functionality. The compositions of the invention may be cured on demand using an acid generating material. The invention further relates to methods of using such compositions.
2. Description of the Related Art
Moisture-curable compositions cure in the presence of moisture to form crosslinked materials such as adhesives, sealants and coatings that are useful in many industries. The moisture is typically obtained from the atmosphere or from a substrate to which the composition has been applied, although it may be added to the composition.
Moisture-curable compositions usually comprise polymers having groups (for example, alkoxysilane or acyloxysilane moieties) that react in the presence of moisture to form cured (i.e., crosslinked) materials. A wide variety of polymers may be rendered moisture curable, including polyolefins, polyesters, polyethers, polyacrylates, polyvinyl chloride, polyphosphazenes, polysiloxanes, polysulfides, block copolymers and fluorinated derivatives thereof, the particular polymer being selected based on the intended use. For example, a polysiloxane or fluorinated polyether is often selected to provide release coatings suitable for use with pressure-sensitive adhesives.
Moisture-curable compositions comprising alkoxysilane or acyloxysilane functionality typically cure in two reactions. In the first reaction, the alkoxysilane or acyloxysilane groups hydrolyze in the presence of moisture and a catalyst to form compounds having silanol groups. In the second reaction, the silanol groups condense with other silanol, alkoxysilane, or acyloxysilane groups in the presence of a catalyst to form —Si—O—Si— linkages. The two reactions occur essentially simultaneously upon generation of the silanol-functional compound. Commonly used catalysts for the two reactions include Brönsted and Lewis acids and are described in the
Encyclopedia of Polymer Science and Engineering,
2nd Edition, Volume 15, page 252, (1989). A single material may catalyze both reactions.
The hydrolysis reaction is schematically illustrated below for a polymer having alkoxysilane groups:
The resulting silanol (SiOH) groups are not stable in the presence of the acid catalyst and immediately condense with other silanol or alkoxysilane group to form —Si—O—Si— linkages as shown below schematically for the condensation reaction of a silanol-functional compound and an alkoxysilane-functional compound:
Preferably, the hydrolysis and condensation reactions proceed quickly once the moisture-curable composition has been applied, for example, to a substrate. At the same time, however, the reactions must not occur prematurely, for example, during processing or storage.
A good balance between these properties is often difficult to obtain as rapid reactivity and storage stability are opposite properties to each other. For example, highly active catalysts such as tetraalkyl titanate esters rapidly accelerate the moisture-curing reaction but at the same time make it difficult to process the materials without risking premature gelation in feed tanks, coating equipment, and other manufacturing and handling apparatus. On the other hand, conventional catalysts such as dibutyl tin dilaurate yield stable moisture-curable compositions that may be processed and stored without premature gelation, but the cure rate is often too slow to be commercially practical for most manufacturing operations.
A variety of approaches have been used for providing moisture-curable compositions that have acceptable cure rates without processing and storage difficulties. For example, U.S. Pat. No. 2,843,555 describes a two-part system, one part comprising a functional polymer and the other part comprising a catalyst with the two parts being mixed just prior before use. While this approach is useful in small-scale applications, it is less efficient for large-scale manufacturing where delays caused by having to mix the two parts are undesirable. Furthermore, coating operations must be completed expeditiously before the composition cures in the pot, and this can be difficult when working with large surface area substrates or a large volume of composition.
U.S. Pat. No. 5,286,815 discloses an ammonium salt catalyst that is inactive until heated sufficiently to liberate an acid compound that initiates the moisture curing reaction. However, liberation of the acid also generates an amine that must be removed by evaporation. In addition, the heat used to activate the catalyst may damage heat-sensitive substrates onto which the composition has been applied.
An article entitled “Cationic Photopolymerization of Ambifunctional Monomers” (J. V. Crivello et al.,
Macromolekular Symposia,
95, 79-89, (1995)) describes the photopolymerization of “Ambifunctional” monomers (i.e., monomers bearing two chemically different reactive functional groups within the same molecule) using cationic catalysts. In one example, an ambifunctional monomer having both epoxycyclohexyl and trimethoxysilyl reactive functional groups is prepared and then subsequently UV irradiated in the presence of a cationic triarylsulfonium catalyst. According to the authors, the polymerization of these monomers, “ . . . is characterized by a rapid polymerization of the epoxy group followed by a slow consumption of the trialkoxysilyl groups.”
Thus, there remains a need for moisture curable compositions that afford acceptable cure rates without processing and storage difficulties (e.g., premature gelation). Ideally, these compositions will be able to be processed efficiently, for example, without the need for mixing prior to cure, and will employ catalysts that do not generate species that have to be removed. Preferably, the compositions will not require heat activation so as to avoid damage to a heat sensitive substrate.
SUMMARY OF THE INVENTION
Broadly, and in one aspect, the present invention provides a moisture-curable composition that can be “cured on demand.” That is, the composition can be cured at a preselected or predetermined time. To achieve such properties, the moisture-curable compositions of the invention include an acid generating material that remains inactive or inert (i.e., it does not initiate the moisture curing reaction) until it is activated at the preselected or predetermined time. Consequently, the acid generating material can be incorporated into the moisture-curable compositions without risking premature curing during processing or storage, and without special mixing just before use. In addition, once the acid generating material has been activated, curing proceeds rapidly and without producing undesirable species that must be removed.
More specifically, the present invention provides a moisture-curable composition comprising at least one compound having reactive silane functionality or groups, and an acid generating material. The reactive silane groups typically comprise a silicon atom bonded to one or more acyloxy or alkoxy groups. The average reactive silane functionality of the moisture curable composition is greater than 2 so as to form a crosslinked network upon curing, and the reactive silane groups are the only acid-curable groups in the composition.
It was found that the best results are obtained in the absence of acid curable groups other than reactive silane groups. In particular, it is believed that acid curable groups such as epoxides adversely effect the reaction of moisture with silanes, thereby resulting in a slow consumption of the trialkoxysilyl groups. Accordingly such other acid curable groups may inhibit the moisture curing of the silane reactive groups. Further water also is known to inhibit the polymerization of acid sensitive monomers.
A wide variety of acid generating materials can be used in the practice of the invention to catalyze the moisture curing reaction, including onium salts such as sulfonium and iodonium salts. These catalysts are known for use in the chain polym
Boulos Marie A.
Everaerts Albert I.
Leir Charles M.
Liu Junkang Jacob
Moore George G. I.
3M Innovative Properties Company
Dawson Robert
Peng Kuo-Liang
LandOfFree
Cure-on-demand, moisture-curable compositions having... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cure-on-demand, moisture-curable compositions having..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cure-on-demand, moisture-curable compositions having... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2519525