Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1999-11-01
2002-10-08
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031860
Reexamination Certificate
active
06461419
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to moisture curable ink compositions, particularly to those having reactive silyl functionality and their use.
BACKGROUND OF THE INVENTION
Moisture-curable compositions cure in the presence of moisture to form crosslinked materials. 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.
Most moisture-curable compositions are based on isocyanate containing compounds. However, these compositions have well known disadvantages. Other moisture-curable compositions comprise polymers having groups (for example, alkoxysilyl or acyloxysilyl moieties) that react in the presence of moisture to form cured (i.e., crosslinked) materials. Moisture-curable compositions comprising alkoxysilyl or acyloxysilyl functionality typically cure in two reactions. In the first reaction, the alkoxysilyl or acyloxysilyl 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, alkoxysilyl, or acyloxysilyl 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. A single material may catalyze both reactions.
The hydrolysis reaction is schematically illustrated below for a polymer having alkoxysilyl groups:
The resulting silanol (SiOH) groups are not stable in the presence of the acid catalyst and immediately condense with other silanol or alkoxysilyl group to form O—Si—O—Si— linkages as shown below schematically for the condensation reaction of a silanol-functional compound and an alkoxysilyl-functional compound:
Preferably, the hydrolysis and condensation reactions proceed quickly once the moisture-curable composition has been applied, for example, to a substrate.
Such compositions have been described as being useful as adhesives, sealants, and coatings.
Some known silane ink compositions contain an acid or a base added as catalysts in the ink binder. Such inks tend to have short pot-lives. The shelf life of such ink compositions is dependent upon the concentration of hydrolyzible silane compounds so the inks typically contain large amounts of solvents or water. Attempts to increase the shelf life of such inks include first hydrolyzing and condensing the alkoxysilyl compounds under controlled conditions and then use the reaction product as part of the ink binder.
Other curable siloxane ink compositions do not contain a catalyst, in some instances, to increase that storage stability of the ink. These inks require that they be heated to 150-200° C. for 5-10 minutes to accelerate the hydrolysis reaction or that they are reacted very slowly at controlled temperature and humidity. Inks that require heating are not suitable for use on substrates that have a relatively low melting point or are easily distorted with heat. And, such slow curing will affect the printing resolution, due to uncontrolled spread of the drops, and color bleeding.
Most curable inks are based on acrylate and epoxy chemistries. The acrylate based inks cure rapidly by free-radical reaction and have good weatherability. However, the acrylate-based inks also typically suffer from oxygen inhibition during cure and surface shrinkage that can contribute to low gloss.
Epoxy-based inks have less shrinkage than acrylate-based inks, provide good adhesion, and have no oxygen inhibition during cure. However, epoxy-based inks typically provide poor weatherability and may have relatively slow cationic reaction rates as compared to free radical reaction rates.
SUMMARY OF THE INVENTION
The invention provides curable ink compositions that are inkjet printable and that adhere to a variety of substrates, for example, glass and polymer. “Curable” means that either reactive silyl groups hydrolyze in the presence of moisture to form compounds having silanol groups that react in the presence of an activated catalyst to form —Si—O—Si— linkages or silanol groups react in the presence of an activated catalyst to form —Si—O—Si— linkages.
The ink compositions of the invention can be formulated so as to provide cured inks that are very flexible, that is, polydimethylsiloxane, or very rigid, that is, silicate, depending upon the desired application. The curable ink compositions are also shelf stable and are cured-on-demand in that they may be cured rapidly at a predetermined time. “Shelf stable” means that the compositions are stable in a light protected container for at least 3 weeks and preferably for at least 6 months. The ink compositions of the invention also provide inks having high gloss and transparency. The ink compositions of the invention also are not required to be diluted with water or solvent in order to be stable.
In one aspect, the invention provides a cure-on-demand curable ink composition comprising a homogeneous mixture of at least one of: (a) a compound having 2 reactive silyl groups, and (b) a compound having at least 3 reactive silyl groups; acid generating catalyst; and pigment or pigment chip. The acid generating catalyst may be activated (liberate a Brönsted or Lewis acid) by heat or irradiating the composition with, for example, ultraviolet, visible light, electron beam, or microwave radiation.
In another aspect, the invention provides inks that are ink-jet printable.
In another aspect, the invention provides imaged ceramic articles comprising a cured ink composition of the invention on a ceramic substrate.
In another aspect, the invention provides a method of making a cure-on-demand curable ink composition comprising the steps of:
sequentially combining a compound having at least 3 reactive silyl groups, pigment chip, and acid generating catalyst with constant mixing.
In another aspect, the invention provides a method of forming an imaged article comprising the step of inkjet printing a moisture curable ink composition of the invention onto a substrate.
In another aspect, the invention provides a cure-on-demand curable composition for overprinting images comprising a homogeneous mixture of at least one of: (a) a compound having 2 reactive silyl groups, and (b) a compound having at least 3 reactive silyl groups; and acid generating catalyst.
The curable ink compositions of the invention can be formulated to have excellent adhesion to a variety of substrates, for example, those of polymethylmethacrylate (PMMA), silicone rubber, ceramics, and glass. The ink compositions of the invention also cure rapidly at room temperature and are expected to have excellent outdoor weatherability due to their inorganic backbone.
DETAILED DESCRIPTION OF THE INVENTION
Reactive Silyl Functional Compounds
The curable ink compositions of the invention contain at least one of 1) a compound having at least two reactive silyl groups per molecule, typically a silicon atom bonded to either two hydroxysilyl groups or two alkoxysilyl groups and 2) a compound having at least 3 reactive silyl groups per molecule. The ink compositions of the invention also may contain a mixture of compounds from both of the above classes of compounds.
Reactive silyl functional compounds useful in the invention can incorporate a wide variety of backbones to support the reactive silyl groups and, as a result, such compounds may be generally represented by the following structures:
wherein,
A is a k-valent group which may be selected from, for example, a chemical bond (i.e., no atoms); —OR; alkyl groups (preferably having 1 to 30, more preferably, 12 to 20 carbon atoms); cycloalkyl groups (preferably having 3 to 30, more preferably, 6 to 10 carbon atoms), aryl groups (preferably having from 6 to about 30 carbon atoms); a chalcogen (group VIb elements), such as oxygen, sulfur, etc., and polymeric radicals which may be of linear, branched, block, or graft construction. Non-limiting examples of suitable polymeric groups include polysiloxanes,
Dennison Kathleen A.
Liu Junkang
Wu Dong
3M Innovative Properties Company
Bardell Scott A.
Klemanski Helene
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