Patent Application
20230108593
The present invention is directed to one component (1 K) compositions based on epoxy resins. More particularly, the present invention is directed to curable, liquid one component (1 K) compositions comprising an epoxy resin, an organic borate compound, a (meth)acrylamide monomer and a free-radical photoinitiator.
Epoxy resins have found a broad range of application, predominantly on the basis that a particular selection of resin, modifier and cross-linking agent (or curative) can allow the properties of the cured epoxy resin to be tailored to achieve specific performance characteristics.
That versatility being acknowledged, properly cured epoxy resins also possess a plurality of other attributes including inter alia: excellent chemical resistance, particularly to alkaline environments; high tensile and compressive strengths; high fatigue strength; low shrinkage upon cure; and, electrical insulation properties and retention thereof upon aging or environmental exposure.
A known utility of epoxy resins resides in so-called “dual cure” or hybrid resin systems which are curable both photochemically and thermally. Such systems —conventionally based on a combination of epoxy resins with (meth)acrylate resins, (meth)acrylated bis-maleimide (BMI) resins or (meth)acrylated urethane resins — arose because the photochemical curing of compositions may not be appropriate in itself for the coating of certain substrates or the adhesion or sealing of certain components: regions may exist within substrates or between components which experience limited to no exposure to light. In a hybrid resin system, a fraction of the curable compositions that is exposed to light may be cured photochemically — for instance with ultraviolet light — to fix components to be adhered, sealed or coated within a desired tolerance limit: the remaining fraction of the curable composition that is disposed in the shaded region(s) is then thermally treated to complete the curing process.
The present invention is concerned with the development of a dual cure system based on an one-component (1 K) composition containing an epoxy resin. On account of the fact that the epoxy resin and hardener or curative are packaged together, the one-component (1 K) composition must exhibit a latent cure: curing cannot commence under ordinary conditions of storage and transportation but instead must be delayed until the composition is exposed to specific curing conditions, such as an elevated temperature or irradiation.
According to one conventional approach, one component (1 K) epoxy compositions may comprise suspensions of solid curative(s) in the epoxy resin, which curatives are latent by virtue of their low solubility in the epoxy matrix. Examples of such an approach are documented in inter alia: U.S. Pat. No. 3,519,576; U.S. Pat. No. 3,520,905; and, U.S. Pat. No. 4,866,133. A plurality of one-component compositions based on epoxy-dicyandiamide have been commercialized: for example, WO2014/165423 (Air Products and Chemicals Inc.) describes a one-component composition comprising: at least one tertiary amine salt, said salt being the product of at least one carboxylic acid and at least one tertiary amine selected from the group consisting of N-hydroxyethylpiperidine, N-hydroxyethylmorpholine, 1,4-bis(2-hydroxyethyl)piperazine, 1-ethylpiperidine, N,N-dimethylcyclophexane and dimethylethanolamine; at least one epoxy resin; and, at least one dicyandiamide.
Problematically, systems based on the use of such solid, particulate hardeners tend to have limitations of high viscosity and relatively long curing times. Moreover, any heterogeneous distribution of the particulate hardeners within the compositions can lead to uncured regions in the formed products: this would, of course, be extremely deleterious to hybrid systems which the user has elected to use specifically to obviate uncured regions in the coating, adhesive or sealant.
These identified problems of solid, particulate hardeners for epoxy resins, have led to a number of authors seeking to homogenize the distribution of the curatives in one component compositions. For instance, Japanese Patent Laid-Open Publication No. 2004-27159 describes an one component epoxy resin composition in which a liquid phenol resin is predominantly used as a curing agent in combination with a solid latent curing agent: whilst this composition is purported to provide excellent storage stability, using a liquid phenol resin as the majority curing agent diminishes the physical strength of the cured resin.
Further authors have sought to solubilize dicyandiamide in which regard may be noted: U.S. Pat. No. 4,859,761; U.S. Pat. No. 4,621,128; U.S. Pat. No. 3,420,794; and EP2180012A1.
In lieu of employing particulate hardeners, chemical blocking has been considered as an alternative approach to moderating the latency of curatives for epoxy resins. An example thereof may be found in US2007149727 (Okuhira et al.) wherein modified amines show low curing efficiency because the cross-linking depends on the hydrolysis of imine groups to generate amines. Further, EP 2999730 A (Inst. für Textil und Faserforschung Dekendorf Deustche) describes protected N-heterocyclic carbenes which are stable at room temperature for the order of days when stored under inert conditions. The development of protected functionalities such as those exemplified can however be complicated and uneconomical. Moreover, these citations do not disclose the use of such latent hardeners within hybrid resin systems.
The present inventors consider that there remains a need in the art to develop stable, one-component (1 K) liquid compositions based on epoxy resins which provide the combination of good processability and economic fabrication and further provide for effective utility in a dual cure system.
In accordance with a first aspect of the present invention there is provided a liquid one component (1 K) composition comprising, based on the weight of the composition:
In important embodiments, the liquid one component (1 K) composition comprises, based on the weight of the composition:
The liquid composition as defined above exhibits propitious storage stability at room temperature. Moreover, the liquid composition as defined above can advantageously possess a low viscosity at room temperature but can be fully cured under irradiation at an elevated temperature within a practicable duration. On account of the hybrid — irradiation and thermal — curing of the present composition, the composition does not suffer from the problems of poor shadow curing experienced when using light curable, (meth)acrylate-based compositions.
In certain exemplary embodiments of the liquid composition, part a) comprises at least one epoxy resin selected from: glycidyl ethers of polyhydric alcohols and polyhydric phenols; glycidyl esters of polycarboxylic acids; and, epoxidized polyethylenically unsaturated hydrocarbons, esters, ethers and amides. Independently of or additional to such preferred epoxy resins, part a) of the liquid composition may desirably comprise an epoxy functional group containing polymer having both epoxy and (meth) acrylate functional groups. Mention may be made of the combination, in part a) of the liquid composition, of: a glycidyl ether of a polyhydric alcohol or polyhydric phenol; and, an epoxy functional group containing polymer having both epoxy and (meth) acrylate functional groups.
The anion of the salt b) is desirably a tetra(C1-C6 alkyl)borate, tetraphenyl borate or substituted tetraphenylborate anion: a preference for tetraphenylborate may be mentioned. Whilst the monovalent cation of the salt b) may be a tetraalkylammonium ion, it is preferred that the cation is a heterocyclic moiety — which may be monocyclic, bicyclic or polycyclic — in which the charged nitrogen atom is part of the heteroaliphatic or heteroaromatic ring system. Thus, in a particular embodiment, part b) of the composition comprises a cycloamidinium tetrasubstituted borate salt and / or an imidazolium tetrasubstituted borate salt. For example, good results have been obtained where part c) comprises at least one salt selected from the group consisting of: imidazolium tetraphenylborate; methylimidazolium tetraphenylborate; 2-ethyl-4-methylimidazolium tetraphenylborate; 2-ethyl-1,4-dimethylimidazolium tetraphenylborate; 8-benzyl-1,8-diazabicyclo[5.4.0]undec-7-enium tetraphenylborate; 1,8-diazabicyclo[5.4.0]undec-7-ene tetraphenylborate; and, 1,5-diazabicyclo[4.3.0]-non-5-ene tetraphenylborate.
In accordance with a second aspect of the present invention, there is provided a cured product obtained from the liquid one component (1 K) composition as defined hereinabove and in the appended claims. The cured products of the present invention do not exhibit deleterious cure shrinkage.
The present invention also provides for the use of the cured reaction product as defined hereinabove and in the appended claims as a coating, sealant or adhesive.
As used herein, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.
The terms “comprising”, “comprises” and “comprised of” as used herein are synonymous with “including”, “includes”, “containing” or “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps.
As used herein, the term “consisting of” excludes any element, ingredient, member or method step not specified.
When amounts, concentrations, dimensions and other parameters are expressed in the form of a range, a preferable range, an upper limit value, a lower limit value or preferable upper and limit values, it should be understood that any ranges obtainable by combining any upper limit or preferable value with any lower limit or preferable value are also specifically disclosed, irrespective of whether the obtained ranges are clearly mentioned in the context.
Further, in accordance with standard understanding, a weight range represented as being “from 0” specifically includes 0 wt.%: the ingredient defined by said range may or may not be present in the composition.
The words “preferred”, “preferably”, “desirably” and “particularly” are used frequently herein to refer to embodiments of the disclosure that may afford particular benefits, under certain circumstances. However, the recitation of one or more preferable, preferred, desirable or particular embodiments does not imply that other embodiments are not useful and is not intended to exclude those other embodiments from the scope of the disclosure.
As used throughout this application, the word “may” is used in a permissive sense — that is meaning to have the potential to — rather than in the mandatory sense.
As used herein, room temperature is 23° C. plus or minus 2° C.
The term “monofunctional”, as used herein, refers to having one polymerizable moiety. The term “polyfunctional”, as used herein, refers to having more than one polymerizable moiety.
As used herein, the term “equivalent (eq.”) relates, as is usual in chemical notation, to the relative number of reactive groups present in the reaction.
The term “equivalent weight” as used herein refers to the molecular weight divided by the number of a function concerned. As such, “epoxy equivalent weight” (EEW) means the weight of resin, in grams, that contains one equivalent of epoxy.
As used herein, the term “epoxide” denotes a compound characterized by the presence of at least one cyclic ether group, namely one wherein an ether oxygen atom is attached to two adjacent carbon atoms thereby forming a cyclic structure. The term is intended to encompass monoepoxide compounds, polyepoxide compounds (having two or more epoxide groups) and epoxide terminated prepolymers. The term “monoepoxide compound” is meant to denote epoxide compounds having one epoxy group. The term “polyepoxide compound” is meant to denote epoxide compounds having at least two epoxy groups. The term “diepoxide compound” is meant to denote epoxide compounds having two epoxy groups.
The epoxide may be unsubstituted but may also be inertly substituted. Exemplary inert substituents include chlorine, bromine, fluorine and phenyl.
As used herein, “(meth)acryl” is a shorthand term referring to “acryl” and / or “methacryl”. Thus the term “(meth)acrylamide” refers collectively to acrylamide and methacrylamide.
As used herein, “C1—Cn alkyl” group refers to a monovalent group that contains 1 to n carbons atoms, that is a radical of an alkane and includes straight-chain and branched organic groups. As such, a “C1-C30 alkyl” group refers to a monovalent group that contains from 1 to 30 carbons atoms, that is a radical of an alkane and includes straight-chain and branched organic groups. Examples of alkyl groups include, but are not limited to: methyl; ethyl; propyl; isopropyl; n-butyl; isobutyl; sec-butyl; tert-butyl; n-pentyl; n-hexyl; n-heptyl; and, 2-ethylhexyl. In the present invention, such alkyl groups may be unsubstituted or may be substituted with one or more substituents such as halo, nitro, cyano, amido, amino, sulfonyl, sulfinyl, sulfanyl, sulfoxy, urea, thiourea, sulfamoyl, sulfamide and hydroxy. Where applicable, a preference for a given substituent will be noted in the specification. In general, however, a preference for unsubstituted alkyl groups containing from 1-18 carbon atoms (C1-C18 alkyl) - for example unsubstituted alkyl groups containing from 1 to 12 carbon atoms (C1-C12 alkyl) or from 1 to 6 carbon atoms (C1-C6 alkyl) - should be noted.
The term “C1-C18 hydroxyalkyl” as used herein refers to a HO-(alkyl) group having from 1 to 18 carbon atoms, where the point of attachment of the substituent is through the oxygen-atom and the alkyl group is as defined above.
An “alkoxy group” refers to a monovalent group represented by -OA where A is an alkyl group: non-limiting examples thereof are a methoxy group, an ethoxy group and an iso-propyloxy group. The term “C1-C18 alkalkoxy” as used herein refers to an alkyl group having an alkoxy substituent as defined above and wherein the moiety (alkyl-O-alkyl) comprises in total from 1 to 18 carbon atoms: such groups include methoxymethyl (—CH2OCH3), 2-methoxyethyl (—CH2CH2OCH3) and 2-ethoxyethyl.
The term “C2-C4 alkylene” as used herein, is defined as saturated, divalent hydrocarbon radical having from 2 to 4 carbon atoms.
The term “C3 -C30 cycloalkyl” is understood to mean an optionally substituted, saturated, mono-, bi- or tricyclic hydrocarbon group having from 3 to 30 carbon atoms. In general, a preference for cycloalkyl groups containing from 3-18 carbon atoms (C3-C18 cycloalkyl groups) should be noted. Examples of cycloalkyl groups include: cyclopropyl; cyclobutyl; cyclopentyl; cyclohexyl; cycloheptyl; cyclooctyl; adamantane; and, norbornane.
As used herein, an “C6-C18 aryl” group used alone or as part of a larger moiety — as in “aralkyl group” — refers to optionally substituted, monocyclic, bicyclic and tricyclic ring systems in which the monocyclic ring system is aromatic or at least one of the rings in a bicyclic or tricyclic ring system is aromatic. The bicyclic and tricyclic ring systems include benzofused 2-3 membered carbocyclic rings. Exemplary aryl groups include: phenyl; (C1-C4)alkylphenyl, such as tolyl and ethylphenyl; indenyl; naphthalenyl, tetrahydronaphthyl, tetrahydroindenyl; tetrahydroanthracenyl; and, anthracenyl. And a preference for phenyl groups may be noted.
As used herein, “C2-C20 alkenyl” refers to hydrocarbyl groups having from 2 to 20 carbon atoms and at least one unit of ethylenic unsaturation. The alkenyl group can be straight chained, branched or cyclic and may optionally be substituted. The term “alkenyl” also encompasses radicals having “cis” and “trans” configurations, or alternatively, “E” and “Z” configurations, as appreciated by those of ordinary skill in the art. In general, however, a preference for unsubstituted alkenyl groups containing from 2 to 10 (C2-10) or 2 to 8 (C2-8) carbon atoms should be noted. Examples of said C2-C12 alkenyl groups include, but are not limited to: —CH═CH2; —CH═CHCH3; —CH2CH═CH2; —C(═CH2)(CH3); —CH═CHCH2CH3; —CH2CH═CHCH3; —CH2CH2CH═CH2; —CH═C(CH3)2; —CH2C(═CH2)(CH3); —C(═CH2)CH2CH3; —C(CH3)═CHCH3; —C(CH3)CH═CH2; —CH═CHCH2CH2CH3; —CH2CH═CHCH2CH3; —CH2CH2CH═CHCH3; —CH2CH2CH2CH═CH2; —C(═CH2)CH2CH2CH3; —C(CH3)═CHCH2CH3; —CH(CH3)CH═CHCH; —CH(CH3)CH2CH═CH2; —CH2CH═C(CH3)2; 1-cyclopent-1-enyl; 1-cyclopent-2-enyl; 1-cyclopent-3-enyl; 1-cyclohex-1-enyl; 1-cyclohex-2-enyl; and, 1-cyclohexyl-3-enyl.
As used herein, “alkylaryl” refers to alkyl-substituted aryl groups and “substituted alkylaryl” refers to alkylaryl groups further bearing one or more substituents as set forth above. Further, as used herein “aralkyl” means an alkyl group substituted with an aryl radical as defined above.
The term “hetero” as used herein refers to groups or moieties containing one or more heteroatoms, such as N, O, Si and S. Thus, for example “heterocyclic” refers to cyclic groups having, for example, N, O, Si or S as part of the ring structure. “Heteroalkyl” and “heterocycloalkyl” moieties are alkyl and cycloalkyl groups as defined hereinabove, respectively, containing N, O, Si or S as part of their structure.
As used herein, the term “catalytic amount” means a sub-stoichiometric amount of catalyst relative to a reactant, except where expressly stated otherwise.
As employed herein a “primary amino group” refers to an NH2 group that is attached to an organic radical, and a “secondary amino group” refers to an NH group that is attached to two organic radicals, which may also together be part of a ring. The term “tertiary amine” thus references a nitrogen bearing moiety of which a nitrogen atom is not bound to a hydrogen atom. Where used, the term “amine hydrogen” refers to the hydrogen atoms of primary and secondary amino groups.
The term “photoinitiator” as used herein denotes a compound which can be activated by an energy-carrying activation beam — such as electromagnetic radiation — for instance upon irradiation therewith. The term is intended to encompass both photoacid generators and photobase generators. Specifically, the term “photoacid generator” refers to a compound or polymer which generates an acid for the catalysis of the acid hardening resin system upon exposure to actinic radiation. The term “photobase generator” means any material which when exposed to suitable radiation generates one or more bases.
The term “Lewis acid” used herein denotes any molecule or ion — often referred to as an electrophile — capable of combining with another molecule or ion by forming a covalent bond with two electrons from the second molecule or ion: a Lewis acid is thus an electron acceptor.
The molecular weights referred to in this specification can be measured with gel permeation chromatography (GPC) using polystyrene calibration standards, such as is done according to ASTM 3536.
As used herein, “anhydrous” means the relevant composition or reaction mixture includes less than 0.25% by weight of water. For example the composition may contain less than 0.1% by weight of water or be completely free of water.
Viscosities of the coating compositions described herein are, unless otherwise stipulated, measured using the Brookfield Viscometer, Model RVT at standard conditions of 23° C. and 50% Relative Humidity (RH). The viscometer is calibrated using silicone oils of known viscosities, which vary from 5,000 cps to 50,000 cps. A set of RV spindles that attach to the viscometer are used for the calibration. Measurements of the coating compositions are done using the No. 6 spindle at a speed of 20 revolutions per minute for 1 minute until the viscometer equilibrates. The viscosity corresponding to the equilibrium reading is then calculated using the calibration.
The composition of the present invention comprises epoxy resins a) in an amount of from 10 to 90 wt.%, preferably from 20 to 80 wt.% based on the weight of the composition. For example, the composition of the present invention may contain from 25 to 75 wt.% or from 30 to 70 wt.% of said epoxy resin(s) a), based on the weight of the composition.
Epoxy resins as used herein may include mono-functional epoxy resins, multi- or poly-functional epoxy resins, and combinations thereof. The epoxy resins may be pure compounds but equally may be mixtures of epoxy functional compounds, including mixtures of compounds having different numbers of epoxy groups per molecule. An epoxy resin may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and may be substituted. Further, the epoxy resin may also be monomeric or polymeric.
Without intention to limit the present invention, illustrative monoepoxide compounds include: alkylene oxides; epoxy-substituted cycloaliphatic hydrocarbons, such as cyclohexene oxide, vinylcyclohexene monoxide, (+)-cis-limonene oxide, (+)-cis,trans-limonene oxide, (-)-cis,trans-limonene oxide, cyclooctene oxide, cyclododecene oxide and α-pinene oxide; epoxy-substituted aromatic hydrocarbons; monoepoxy substituted alkyl ethers of monohydric alcohols or phenols, such as the glycidyl ethers of aliphatic, cycloaliphatic and aromatic alcohols; monoepoxy-substituted alkyl esters of monocarboxylic acids, such as glycidyl esters of aliphatic, cycloaliphatic and aromatic monocarboxylic acids; monoepoxy-substituted alkyl esters of polycarboxylic acids wherein the other carboxy group(s) are esterified with alkanols; alkyl and alkenyl esters of epoxy-substituted monocarboxylic acids; epoxyalkyl ethers of polyhydric alcohols wherein the other OH group(s) are esterified or etherified with carboxylic acids or alcohols; and, monoesters of polyhydric alcohols and epoxy monocarboxylic acids, wherein the other OH group(s) are esterified or etherified with carboxylic acids or alcohols.
By way of example, the following glycidyl ethers might be mentioned as being particularly suitable monoepoxide compounds for use herein: methyl glycidyl ether; ethyl glycidyl ether; propyl glycidyl ether; butyl glycidyl ether; pentyl glycidyl ether; hexyl glycidyl ether; cyclohexyl glycidyl ether; octyl glycidyl ether; 2-ethylhexyl glycidyl ether; allyl glycidyl ether; benzyl glycidyl ether; phenyl glycidyl ether; 4-tert-butylphenyl glycidyl ether; 1-naphthyl glycidyl ether; 2-naphthyl glycidyl ether; 2-chlorophenyl glycidyl ether; 4-chlorophenyl glycidyl ether; 4-bromophenyl glycidyl ether; 2,4,6-trichlorophenyl glycidyl ether; 2,4,6-tribromophenyl glycidyl ether; pentafluorophenyl glycidyl ether; o-cresyl glycidyl ether; m-cresyl glycidyl ether; and, p-cresyl glycidyl ether.
In an important embodiment, the monoepoxide compound conforms to Formula (I) herein below:
wherein: Rw, Rx, Ry and Rz may be the same or different and are independently selected from hydrogen, a halogen atom, a C1-C8 alkyl group, a C3 to C10 cycloalkyl group, a C2-C12 alkenyl, a C6-C18 aryl group or a C7-C18 aralkyl group, with the proviso that at least one of Ry and Rz is not hydrogen.
It is preferred that Rw, Rx and Ry are hydrogen and Rz is either a phenyl group or a C1-C8 alkyl group and, more preferably, a C1-C4 alkyl group.
Having regard to this embodiment, exemplary monoepoxides include: ethylene oxide; 1,2-propylene oxide (propylene oxide); 1,2-butylene oxide; cis-2,3-epoxybutane; trans-2,3-epoxybutane; 1,2-epoxypentane; 1,2-epoxyhexane; 1,2-heptylene oxide; decene oxide; butadiene oxide; isoprene oxide; and, styrene oxide.
In the present invention, reference is made to using at least one monoepoxide compound selected from the group consisting of: ethylene oxide; propylene oxide; cyclohexene oxide; (+)-cis-limonene oxide; (+)-cis,trans-limonene oxide; (-)-cis,trans-limonene oxide; cyclooctene oxide; and, cyclododecene oxide.
Again, without intention to limit the present invention, suitable polyepoxide compounds may be liquid or in solution in solvent. Further, such polyepoxide compounds should have an epoxide equivalent weight of from 100 to 700 g/eq, for example from 120 to 320 g/eq. And generally, diepoxide compounds having epoxide equivalent weights of less than 500 g/eq. or even less than 400 g/eq. are preferred: this is predominantly from a costs standpoint, as in their production, lower molecular weight epoxy resins require more limited processing in purification.
As examples of types or groups of polyepoxide compounds which may be polymerized in present invention, mention may be made of: glycidyl ethers of polyhydric alcohols and polyhydric phenols; glycidyl esters of polycarboxylic acids; and, epoxidized polyethylenically unsaturated hydrocarbons, esters, ethers and amides.
Suitable diglycidyl ether compounds may be aromatic, aliphatic or cycloaliphatic in nature and, as such, can be derivable from dihydric phenols and dihydric alcohols. And useful classes of such diglycidyl ethers are: diglycidyl ethers of aliphatic and cycloaliphatic diols, such as 1,2-ethanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,12-dodecanediol, cyclopentane diol and cyclohexane diol; bisphenol A based diglycidylethers; bisphenol F diglycidyl ethers; polyalkyleneglycol based diglycidyl ethers, in particular polypropyleneglycol diglycidyl ethers; and, polycarbonatediol based glycidyl ethers.
Further illustrative polyepoxide compounds include but are not limited to: glycerol polyglycidyl ether; trimethylolpropane polyglycidyl ether; pentaerythritol polyglycidyl ether; diglycerol polyglycidyl ether; polyglycerol polyglycidyl ether; and, sorbitol polyglycidyl ether.
Glycidyl esters of polycarboxylic acids having utility in the present invention are derived from polycarboxylic acids which contain at least two carboxylic acid groups and no other groups reactive with epoxide groups. The polycarboxylic acids can be aliphatic, cycloaliphatic, aromatic and heterocyclic. The preferred polycarboxylic acids are those which contain not more than 18 carbon atoms per carboxylic acid group of which suitable examples include but are not limited to: oxalic acid; sebacic acid; adipic acid; succinic acid; pimelic acid; suberic acid; glutaric acid; dimer and trimer acids of unsaturated fatty acids, such as dimer and trimer acids of linseed fatty acids; phthalic acid; isophthalic acid; terephthalic acid; trimellitic acid; trimesic acid; phenylene-diacetic acid; chlorendic acid; hexahydrophthalic acid, in particular hexahydroorthophthalic acid (1,2-cyclohexanedicarboxylic acid); diphenic acid; naphthalic acid; polyacid terminated esters of di-basic acids and aliphatic polyols; polymers and co-polymers of (meth)acrylic acid; and, crotonic acid.
Other suitable diepoxides which might also be mentioned include: diepoxides of double unsaturated fatty acid C1-C18 alkyl esters; butadiene diepoxide; polybutadiene diglycidyl ether; vinylcyclohexene diepoxide; and, limonene diepoxide.
And examples of highly preferred polyepoxide compounds include: bisphenol-A epoxy resins, such as DER™ 331, DER™ 332, DER™ 383, JER™ 828 and Epotec YD 128; bisphenol-F epoxy resins, such as DER™ 354; bisphenol-A/F epoxy resin blends, such as DER™ 353; aliphatic glycidyl ethers, such as DER™ 736; polypropylene glycol diglycidyl ethers, such as DER™ 732; solid bisphenol-A epoxy resins, such as DER™ 661 and DER™ 664 UE; solutions of bisphenol-A solid epoxy resins, such as DER™ 671-X75; epoxy novolac resins, such as DEN™ 438; brominated epoxy resins such as DER™ 542; castor oil triglycidyl ether, such as ERISYS™ GE-35H; polyglycerol-3-polyglycidyl ether, such as ERISYS™ GE-38; sorbitol glycidyl ether, such as ERISYS™ GE-60; and, bis(2,3-epoxypropyl)cyclohexane-1,2-dicarboxylate, available as Lapox Arch-11.
For completeness, the present invention is intended to encompass the use of an epoxy functional group containing polymer, wherein said polymer has both epoxy and (meth) acrylate functional groups. Such multifunctional epoxy (meth)acrylate compounds are conventionally obtained by the addition of (meth)acrylic acid to the epoxide groups present in multifunctional epoxide compounds. For example, one such resin having two types of functional groups is described in U.S. Pat. No. 4,751,138 (Tumey et al.). A commercial example is the polymer HCT-1, a partially acrylated bisphenol-A epoxy resin (CAS No. 55127-80-5).
Whilst it does not represent a preferred embodiment, the present invention does not preclude the curable compositions further comprising one or more cyclic monomers selected from the group consisting of: oxetanes; cyclic carbonates; cyclic anhydrides; and, lactones. The disclosures of the following citations may be instructive in disclosing suitable cyclic carbonate functional compounds: U.S. Pat. No. 3,535,342; U.S. Pat. No. 4,835,289; U.S. Pat. No. 4,892,954; UK Patent No. GB-A-1,485,925; and, EP-A-0 119 840. However, such cyclic co-monomers should constitute less than 20 wt.%, preferably less than 10 wt.% or less than 5 wt.%, based on the total weight of the epoxide compounds.
The composition of the present invention comprises b) at least one organoboron compound as defined herein below. More particularly, the composition of the present invention comprises, based on the weight of the composition, from 0.5 to 30 wt.%, preferably from 1 to 25 wt.%, of b) at least one organoboron compound as defined herein below. For example, the composition of the present invention may contain from 5 to 20 wt.% or from 5 to 15 wt.% of b) said at least one organoboron compound, based on the weight of the composition.
The at least one organoboron compound is selected from tetrasubstituted borate salts of monovalent cations of tertiary amines. The tetrasubstituted borate anion thereof may be represented by the general Formula (II):
R6, R7, R8 and R9 are independently selected from C1-C6 alkyl, C6-C18 aryl and C7-C24 alkylaryl. Whilst the monovalent cation may be a tetraalkylammonium ion, it is preferred that the cation is a heterocyclic moiety — which may be monocyclic, bicyclic or polycyclic — in which the charged nitrogen atom is part of the heteroaliphatic or heteroaromatic ring system.
Examples of the heterocyclic tertiary amines from which the monovalent cations may be derived include: pyridines, such as picoline (methylpryidine), isoquinoline, quinoline (1-benzopyridine), N,N-dimethyl-4-aminopyridine, bipyridine and 2,6-lutidine; imidazoles; pyrazoles, such as pyrazole and 1,4-dimethylpyrazole; morpholines, such as 4-(2-hydroxyethyl)morpholine, N-ethylmorpholine, N-methylmorpholine and 2,2'-dimorpholinediethyl ether; piperazines, such as 1-(2-hydroxyethyl)piperazine and N,N-dimethylpiperazine; piperidines, such as N-(2-hydroxyethyl)piperidine, N-ethylpiperidine, N-propylpiperidine, N-butylpiperidine N-hexylpiperidine, N-cyclohexylpiperidine and N-octylpiperidine; pyrrolidines such as N-butylpyrrolidine and N-octylpyrrolidine; and, cycloamidines. Further exemplary heterocyclic amines include hexamethylenetetramine, hexaethylenetetramine and hexapropyltetramine. However, a preference for cycloamidinium and imidazolium cations may be mentioned.
In a first embodiment, the organoboron compounds of this part of the composition are represented by general Formula (III) below:
wherein: R1, R2, R3, R4 and R5 are independently selected from hydrogen, C1-C18 alkyl, C6-C18 aryl, C3-C18 cycloalkyl, C2-C20 alkenyl, —C(O)Rq, —C(O)OH, —CN and —NO2;
Preferably R1, R2, R3, R4 and R5 are independently selected from hydrogen, C1-C12 alkyl, C6-C18 aryl, C3-C12 cycloalkyl, C2-C6 alkenyl, —CO2H, —CN and —NO2. Alternatively or additionally to that statement of preference for the imidazole moiety, at least three of R6, R7, R8 and R9 in the borate moiety are the same. More preferably R6, R7, R8 and R9 are all the same and are selected from C1-C6 alkyl and phenyl. A particular preference is noted for the tetraphenylborate anion.
Exemplary compounds according to Formula (III), which may be used alone or in admixture, include but are not limited to: imidazolium tetraphenylborate; methylimidazolium tetraphenylborate; 2-ethyl-4-methylimidazolium tetraphenylborate; 2-ethyl-1,4-dimethylimidazolium tetraphenylborate; 1-cyanoethyl-2-ethyl-4-methylimidazolium tetraphenylborate; 1-cyanoethyl-2-undecylimidazolium tetraphenylborate; 1-cyanoethyl-2-phenylimidazolium tetraphenylborate; 1-vinyl-2-methylimidazolium tetraphenylborate; 1-vinyl-2,4-dimethylimidazolium tetraphenylborate; 1-β-hydroxy-ethyl-2-methyl-imidazolium tetraphenylborate; 1-allyl-2-methylimidazolium tetraphenylborate; 1-allyl-2-phenylimidazolium tetraphenylborate; and, 1-allyl-2-undecylimidazolium tetraphenylborate. A particular preference for imidazolium tetraphenylborate, methylimidazolium tetraphenylborate, 2-ethyl-4-methylimidazolium tetraphenylborate and 2-ethyl-1,4-dimethylimidazolium tetraphenylborate may be noted.
Whilst there is no intention to limit the method of synthesis of compounds of Formula (III), an illustrative preparative procedure comprises the reaction of:
Preferably Xn- is a chloride, bromide, iodide, sulfate, nitrate or acetate anion. Independently or additionally, M+ is preferably Li+, Na+ or K+.
The aforementioned reaction may conventionally be performed in a polar protic solvent such as: water; acetic acid; methanol; ethanol; n-propanol; and, n-butanol. Further, the reaction temperature may conventionally be from 10° C. to 100° C., for example from 20° C. to 80° C.
For completeness, the imidazole salts of Formula (IV) may be prepared by the reaction of an imidazole as provided below
with: at least one acid selected from the group consisting of: inorganic acids, such as hydrochloric acid, sulfuric acid, and nitric acid; organic acids, such as acetic acid, oxalic acid and succinic acid; and, acidic aromatic nitro compounds, such as picric acid and picrolonic acid; and,
a quaternizing agent, such as an alkylhalide, arylhalide or arylalkylhalide.
The synthesis of the imidazole salt (IV) according to this reaction may conventionally be performed in a polar protic solvent such as: water; acetic acid; methanol; ethanol; n-propanol; and, n-butanol. Further, the reaction temperature may conventionally be from 10° C. to 100° C., for example from 20° C. to 80° C.
In a second embodiment of this part of the composition, the organoboron compounds are represented by the general Formula (VI) below:
wherein: R10 is selected from H, C1-C6 alkyl, C6-C18 aryl, C7-C24 aralkyl, C3-C18 cycloalkyl and C2-C20 alkenyl;
Preferably R10 is selected from H, C1-C6 alkyl, C3-C12 cycloalkyl, phenyl, naphthyl or C7-C12 aralkyl. More preferably R10 is selected from H, C1-C6 alkyl, C3-C12 cycloalkyl, phenyl, naphthyl, benzyl or tolyl. Alternatively or additionally to that statement of preference for the bicyclic moiety, at least three of R6, R7, R8 and R9 in the borate moiety are the same. More preferably R6, R7, R8 and R9 are all the same and are selected from C1-C6 alkyl and phenyl. A particular preference is noted for the tetraphenylborate anion.
Examples of compounds in accordance with Formula (VI) above include: 8-benzyl-1,8-diazabicyclo[5.4.0]undec-7-enium tetraphenylborate; 1,8-diazabicyclo[5.4.0]undec-7-ene tetraphenylborate; and, 1,5-diazabicyclo[4.3.0]-non-5-ene tetraphenylborate.
The composition of the present invention comprises c) at least one (meth)acrylamide monomer. More particularly, the composition of the present invention comprises, based on the weight of the composition, from 10 to 50 wt.%, preferably from 15 to 45 wt.%, of c) said at least one (meth)acrylamide monomer. For example, the composition of the present invention may contain from 15 to 40 wt.% or from 25 to 40 wt.% of c) said at least one (meth)acrylamide monomer, based on the weight of the composition.
The (meth)acrylamide monomers are monofunctional and meet the following general Formula (VII):
wherein: Ra is H or Me;
In embodiments of the (meth)acrylamide monomers according to Formula (VII):
Examples of suitable (meth)acrylamide monomers in accordance with Formula (VII) include but are not limited to: (meth)acrylamide; N-methyl (meth)acrylamide; N,N-dimethyl (meth)acrylamide; N-ethyl (meth)acrylamide; N,N-diethyl (meth)acrylamide; N-isopropyl (meth)acrylamide; N-n-butyl (meth)acrylamide; N-t-butyl (meth)acrylamide; N,N-di-n-butyl (meth)acrylamide; N-octyl (meth)acrylamide; N-dodecyl (meth)acrylamide; N-octadecyl (meth)acrylamide; N-phenyl (meth)acrylamide; N,N-dimethylaminoethyl (meth)acrylamide; N-(2-methoxyethyl) (meth)acrylamide; N-(2-ethoxyethyl) (meth)acrylamide N-(2-hydroxyethyl) (meth)acrylamide; and, N-(2-hydroxylpropyl) (meth)acrylamide.
Whilst it is does not represent a preferred embodiment, the present invention does not preclude the curable compositions further comprising one or more polyfunctional (meth)acrylamide compounds. However, within the curable composition, such polyfunctional (meth)acrylamide monomers should constitute less than 20 wt.%, preferably less than 10 wt.% or less than 5 wt.%, based on the total weight of c) said monofunctional (meth)acrylamide monomers.
Exemplary polyfunctional (meth)acrylamide compounds may be represented by Formula (VIII) below:
wherein: R is H or Me;
L is —O—, C2-C4 alkylene group or a divalent linking group formed by combining these.
Examples of the latter mentioned divalent linking group include but are not limited to: —OCH2CH2—, —OCH2CH2CH2—, —OCH2CH2CH2CH2—, —CH2OCH2—, —CH2OCH2CH2—, and —CH2OCH2CH2CH2—.
The compositions of the present invention include d) at least one free radical photoinitiator compound which initiates the polymerization or hardening of the compositions upon irradiation with actinic radiation. It is established that the compositions of the present invention could be cationically polymerizable or free-radically polymerizable: whilst epoxy groups are cationically active, the inventors have elected a free-radical polymerization mechanism based on the presence in the composition of free-radically active, unsaturated groups.
Typically, free radical photoinitiators are divided into those that form radicals by cleavage, known as “Norrish Type I”, and those that form radicals by hydrogen abstraction, known as “Norrish Type II”. The Norrish Type II photoinitiators require a hydrogen donor, which serves as the free radical source: as the initiation is based on a bimolecular reaction, the Norrrish Type II photoinitiators are generally slower than Norrish Type I photoinitiators which are based on the unimolecular formation of radicals. On the other hand, Norrish Type II photoinitiators possess better optical absorption properties in the near-UV spectroscopic region. Whilst active hydrogen species are indeed present in the compositions according to the present invention, the skilled artisan should be able to select an appropriate free radical photoinitiator based on the actinic radiation being employed in curing and the sensitivity of the photoinitiator(s) at that wavelength.
In accordance with an embodiment of the invention, the composition comprises d) at least one free radical photoinitiator selected from the group consisting of: benzoylphosphine oxides; aryl ketones; benzophenones; hydroxylated ketones; 1-hydroxyphenyl ketones; ketals; and, metallocenes. For completeness, the combination of two or more of these photoinitiators is not precluded in the present invention.
In accordance with a preferred embodiment of the invention, the composition comprises d) at least one free radical photoinitiator selected from the group consisting of: benzoin dimethyl ether; 1-hydroxycyclohexyl phenyl ketone; benzophenone; 4-chlorobenzophenone; 4-methylbenzophenone; 4-phenylbenzophenone; 4,4'-bis(diethylamino) benzophenone; 4,4'- bis(N,N'-dimethylamino) benzophenone (Michler’s ketone); isopropylthioxanthone; 2-hydroxy-2-methylpropiophenone (Daracur 1173); 2-methyl-4-(methylthio)-2-morpholinopropiophenone; methyl phenylglyoxylate; methyl 2-benzoylbenzoate; 2-ethylhexyl 4-(dimethylamino)benzoate; ethyl 4-(N,N-dimethylamino)benzoate; phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; and, ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate. Again, for surety, the combination of two or more of these photoinitiators is not precluded in the present invention.
The photoinitiator d) should be present in the composition in an amount of from 0.05 to 10.0 wt.%, for example from 0.1 to 5.0 wt.% or from 0.1 to 2.5 wt.%, based on the weight of the composition.
The purpose of irradiation of the curable compositions is to generate the active species from the photoinitiator d) which initiates the cure reactions. Once that species is generated, the cure chemistry is subject to the same rules of thermodynamics as any chemical reaction: the reaction rate may be accelerated by heat. The practice of using thermal treatments to enhance the actinic-radiation cure of monomers is generally known in the art.
The use of the photoinitiator d) — and also the photobase generator and photoacid generators mentioned herein below — may produce residue compounds from the photochemical reaction in the final cured product. The residues may be detected by conventional analytical techniques such as: infrared, ultraviolet and NMR spectroscopy; gas or liquid chromatography; and, mass spectroscopy. Thus, the present invention may comprise cured matrix (co-)polymers and detectable amounts of residues from a free radical photo-initiator and a photo-base/acid generator. Such residues are present in small amounts and do not normally interfere with the desired physiochemical properties of the final cured product.
As would be recognized by the skilled artisan, photosensitizers can be incorporated into the compositions to improve the efficiency with which the photoinitiator d) uses the energy delivered. The term “photosensitizer” is used in accordance with its standard meaning to represent any substance that either increases the rate of photoinitiated polymerization or shifts the wavelength at which polymerization occurs. Photosensitizers should be used in an amount of from 0 to 25 wt.%, based on the weight of d) said at least one free radical photoinitiator.
In certain embodiments, the composition may further comprise in an amount up to 15 wt.%, based on the weight of the composition, e1) at least one (meth)acrylate monomer represented by Formula M:
wherein: Q is hydrogen, halogen or a C1-C4 alkyl group; and,
R1 is selected from C1-C30 alkyl, C3-C30 cycloalkyl, C2-C20 alkenyl, C2-C12 alkynyl, C6-C18 aryl, C7-C18 alkaryl and C7-C18 aralkyl.
The composition may comprise, for example, from 0 to 10 wt.% or from 0 to 5 wt.% of e1) said at least one (meth)acrylate monomer represented by Formula M. Desirably, said monomer(s) (M) are characterized in that R1 is selected from C1-C18 alkyl and C3-C18 cycloalkyl. This statement of preference is expressly intended to include that embodiment wherein R1 is C1-C6 hydroxylalkyl.
Exemplary (meth)acrylate monomers in accordance with Formula (M), which may be used alone or in combination, include but are not limited to: methyl (meth)acrylate; ethyl (meth)acrylate; butyl (meth)acrylate; hexyl (meth)acrylate; 2-ethylhexyl (meth)acrylate; dodecyl (meth)acrylate; lauryl (meth)acrylate; cyclohexyl (meth)acrylate; isobornyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate (HEMA); 2-hydroxypropyl (meth)acrylate; ethylene glycol monomethyl ether (meth)acrylate; ethylene glycol monoethyl ether (meth)acrylate; ethylene glycol monododecyl ether (meth)acrylate; diethylene glycol monomethyl ether (meth)crylate; trifluoroethyl (meth)acrylate; perfluorooctyl (meth)acrylate; benzyl (meth)acrylate; phenoxyethyl (meth)acrylate; phenoxydiethylene glycol (meth)acrylate; phenoxypropyl (meth)acrylate; and, phenoxydipropylene glycol (meth)acrylate.
Independently of or additional to the presence of said (meth)acrylate monomers (M) described hereinabove, the compositions of the present invention may further comprise in an amount up to 10 wt.%, based on the weight of the composition, e2) at least one (meth)acrylate-functionalized oligomer, which oligomers do not possess epoxide groups. The composition may comprise, for example, from 0 to 10 wt.% or from 0 to 5 wt.% of e2) said at least one (meth)acrylate-functionalized oligomer. Said oligomers may have one or more acrylate and/or methacrylate groups attached to the oligomeric backbone, which (meth)acrylate functional groups may be in a terminal position on the oligomer and / or may be distributed along the oligomeric backbone.
It is preferred that e2) said at least one (meth)acrylate functionalized oligomers: i) have two or more (meth)acrylate functional groups per molecule; and / or, ii) have a weight average molecular weight (Mw) of from 300 to 1000 daltons.
Examples of such oligomers, which may be used alone or in combination, include but are not limited to: (meth)acrylate-functionalized urethane oligomers such as (meth)acrylate-functionalized polyester urethanes and (meth)acrylate-functionalized polyether urethanes; (meth)acrylate-functionalized polybutadienes; (meth)acrylic polyol (meth)acrylates; polyester (meth)acrylate oligomers; polyamide (meth)acrylate oligomers; and, polyether (meth)acrylate oligomers. Such (meth)acrylate-functionalized oligomers and their methods of preparation are disclosed in inter alia: U.S. Pat. No. 4,574,138; U.S. Pat. No. 4,439,600; U.S. Pat. No. 4,380,613; U.S. Pat. No. 4,309,526; U.S. Pat. No. 4,295,909; U.S. Pat. No. 4,018,851; U.S. Pat. No. 3,676,398; U.S. Pat. No. 3,770,602; U.S. Pat. No. 4,072,529; U.S. Pat. No. 4,511,732; U.S. Pat. No. 3,700,643; U.S. Pat. No. 4,133,723; U.S. Pat. No. 4,188,455; U.S. Pat. No. 4,206,025; U.S. Pat. No. 5,002,976.
In certain embodiments, part e2) may comprise or consist of at least one (meth)acrylate ester corresponding to Formula (O):
wherein: R4 may be selected from hydrogen, C1-C4 alkyl and
Of such polyether (meth)acrylates of Formula O mention may in particular be made of poly(ethylene glycol) di(meth)acrylates possessing the structure below:
wherein: n is ≥3, preferably from 3 to 30, more preferably from 3 to 20.
As such, specific examples include but are not limited to: PEG 200 DMA (n≈4); PEG 400 DMA (n≈9); PEG 600 DMA (n≈14); and, PEG 800 DMA (n≈19), in which the assigned number (e.g., 400) represents the weight average molecular weight of the glycol portion of the molecule.
Said compositions obtained in the present invention will typically further comprise adjuvants and additives that can impart improved properties to these compositions. For instance, the adjuvants and additives may impart one or more of: improved elastic properties; improved elastic recovery; longer enabled processing time; faster curing time; and, lower residual tack. Included among such adjuvants and additives are catalysts, plasticizers, coupling agents, adhesion promoters, stabilizers including UV stabilizers, antioxidants, secondary tougheners, fillers, reactive diluents, drying agents, fungicides, flame retardants, rheological adjuvants, color pigments or color pastes, and/or optionally also, to a small extent, non-reactive diluents.
Suitable catalysts are substances that promote the (homo-) polymerization of epoxide compounds. Without intention to the limit the catalysts used in the present invention, mention may be made of the following suitable catalysts: i) acids or compounds hydrolyzable to acids, in particular a) organic carboxylic acids, such as acetic acid, benzoic acid, salicylic acid, 2-nitrobenzoic acid and lactic acid; b) organic sulfonic acids, such as methanesulfonic acid, p-toluenesulfonic acid and 4-dodecylbenzenesulfonic acid; c) sulfonic acid esters; d) inorganic acids, such as phosphoric acid; e) Lewis acid compounds, such as BF3 amine complexes, SbF6 sulfonium compounds, bis-arene iron complexes; f) Bronsted acid compounds, such as pentafluoroantimonic acid complexes; and, e) mixtures of the aforementioned acids and acid esters; ii) phenols, in particular bisphenols; iii) phenol resins; iv) Mannich bases; and, v) phosphites, such as di- and triphenylphosphites.
In an embodiment, an amine catalyst for the curing a composition based on the epoxy resin may be photobase generator: upon exposure to UV radiation —typically in the wavelength from 320 to 420 nm — said photobase generator releases an amine. The photobase generator is not specifically limited so long as it generates an amine directly or indirectly with light irradiation. However, suitable photobase generators which may be mentioned include: benzyl carbamates; benzoin carbamates; o-carbamoylhydroxyamines; O-carbamoyloximes; aromatic sulfonamides; alpha-lactams; N-(2-allylethenyl)amides; arylazide compounds, N-arylformamides, and 4-(ortho-nitrophenyl)dihydropyridines.
For completeness, the preparation of photobase generator compounds is known in the art and an instructive reference includes U.S. Pat. No. 5,650,261 (Winkel).
In an alternative embodiment, an acid catalyst may be selected from photoacid generators (PAGs): upon irradiation with light energy, ionic photoacid generators undergo a fragmentation reaction and release one or more molecules of Lewis or Bronsted acid that catalyze the ring opening and addition of the pendent epoxide groups to form a crosslink. Useful photoacid generators are thermally stable, do not undergo thermally induced reactions with the forming copolymer and are readily dissolved or dispersed in the curable compositions.
Exemplary cations which may be used as the cationic portion of the ionic PAG of the invention include organic onium cations such as those described in U.S. Pat. No. 4,250,311, U.S. Pat. No. 3,113,708, U.S. Pat. No. 4,069,055, U.S. Pat. No. 4,216,288, U.S. Pat. No. 5,084,586, U.S. Pat. No. 5,124,417, and, U.S. Pat. No. 5,554,664. The references specifically encompass aliphatic or aromatic Group IVA and VIIA (CAS version) centered onium salts, with a preference being noted for I—, S—, P—, Se— N— and C-centered onium salts, such as those selected from sulfoxonium, iodonium, sulfonium, selenonium, pyridinium, carbonium and phosphonium.
As is known in the art, the nature of the counter-anion in the ionic photoacid generator (PAG) can influence the rate and extent of cationic addition polymerization of the epoxide groups with, for illustration, the order of reactivity among commonly used nucleophilic anions being SbF6 > AsF6 > PF6 > BF4. The influence of the anion on reactivity has been ascribed to three principle factors which the skilled artisan should compensate for in the present invention: (1) the acidity of the protonic or Lewis acid generated; (2) the degree of ion-pair separation in the propagating cationic chain; and, (3) the susceptibility of the anions to fluoride abstraction and consequent chain termination.
It is evident to the skilled artisan that the presence of photobase generators and photoacid generators in combination with d) said at least one free radical photoinitator is not precluded in the present invention. However, in toto photoinitiators should be present in the composition in amount less than 12 wt.%, preferably less than 10 wt.% based on the weight of the composition.
A “plasticizer” for the purposes of this invention is a substance that decreases the viscosity of the composition and thus facilitates its processability. Herein the plasticizer may constitute up to 10 wt.% or up to 5 wt.%, based on the total weight of the composition, and is preferably selected from the group consisting of: polydimethylsiloxanes (PDMS); diurethanes; ethers of monofunctional, linear or branched C4-C16 alcohols, such as Cetiol OE (obtainable from Cognis Deutschland GmbH, Dusseldorf); esters of abietic acid, butyric acid, thiobutyric acid, acetic acid, propionic acid esters and citric acid; esters based on nitrocellulose and polyvinyl acetate; fatty acid esters; dicarboxylic acid esters; esters of OH-group-carrying or epoxidized fatty acids; glycolic acid esters; benzoic acid esters; phosphoric acid esters; sulfonic acid esters; trimellitic acid esters; polyether plasticizers, such as end-capped polyethylene or polypropylene glycols; polystyrene; hydrocarbon plasticizers; chlorinated paraffin; and, mixtures thereof. It is noted that, in principle, phthalic acid esters can be used as the plasticizer but these are not preferred due to their toxicological potential.
In certain embodiments, the composition includes up to 5 wt.%, based on the weight of the composition, of at least one epoxy silane coupling agent which can serve to enhance the adhesion of the curing composition to a given surface. The hydrolyzable groups of the coupling agent can react with the surface to remove unwanted hydroxyl groups; the epoxy groups thereof react with the film-forming polymer to chemically link said polymer with the surface. Preferably, the coupling agents possess from 1 to 3 hydrolyzable functional groups and at least one epoxy group.
Examples of suitable epoxy silane coupling agents include but are not limited to: glycidoxy polymethylenetrialkoxysilanes, such as 3-glycidoxy-1-propyltrimethoxysilane; (meth)acryloxypolymethylenetrialkoysilanes, such as 3-methacrylyloxy-1-propyltrimethoxysilane; γ-methacryloxypropyltrimethoxysilane (A-174 available from GE Silicones); γ-glycidoxypropyltrimethoxysilane (A-187 available from Momentive Performance Materials, Inc.); α-glycidoxypropylmethyldiethoxysilane (A-2287 available from Momentive Performance Materials, Inc.); vinyl-tris-(2-methoxyethoxy)silane (A-172 from available Momentive Performance Materials, Inc.); and, α-chloropropyltrimethoxysilane (KBM-703 available from Shin-Etsu Chemical Co., Ltd.).
“Stabilizers” for purposes of this invention are to be understood as antioxidants, UV stabilizers or hydrolysis stabilizers. Herein stabilizers may constitute in toto up to 10 wt.% or up to 5 wt.%, based on the total weight of the composition. Standard commercial examples of stabilizers suitable for use herein include: sterically hindered phenols; thioethers; benzotriazoles; benzophenones; benzoates; cyanoacrylates; acrylates; amines of the hindered amine light stabilizer (HALS) type; phosphorus; sulfur; and, mixtures thereof.
As noted, the compositions according to the present invention can additionally contain fillers. Suitable here are, for example, chalk, lime powder, precipitated and/or pyrogenic silicic acid, zeolites, bentonites, magnesium carbonate, diatomite, alumina, clay, talc, titanium oxide, iron oxide, zinc oxide, sand, quartz, flint, mica, glass powder, and other ground mineral substances. Organic fillers can also be used, in particular carbon black, graphite, wood fibers, wood flour, sawdust, cellulose, cotton, pulp, cotton, wood chips, chopped straw, chaff, ground walnut shells, and other chopped fibers. Short fibers such as glass fibers, glass filament, polyacrylonitrile, carbon fibers, Kevlar fibers, or polyethylene fibers can also be added. Aluminum powder is likewise suitable as a filler.
The pyrogenic and/or precipitated silicic acids advantageously have a BET surface area from 10 to 90 m2/g. When they are used, they do not cause any additional increase in the viscosity of the composition according to the present invention, but do contribute to strengthening the cured composition.
It is likewise conceivable to use pyrogenic and/or precipitated silicic acids having a higher BET surface area, advantageously from 100 to 250 m2/g, in particular from 110 to 170 m2/g, as a filler: because of the greater BET surface area, the effect of strengthening the cured composition is achieved with a smaller proportion by weight of silicic acid.
Also suitable as fillers are hollow spheres having a mineral shell or a plastic shell. These can be, for example, hollow glass spheres that are obtainable commercially under the trade names Glass Bubbles®. Plastic-based hollow spheres, such as Expancel® or Dualite®, may be used and are described in EP 0 520 426 B1: they are made up of inorganic or organic substances and each have a diameter of 1 mm or less, preferably 500 µm or less.
Fillers which impart thixotropy to the composition may be preferred for many applications: such fillers are also described as rheological adjuvants, e.g. hydrogenated castor oil, fatty acid amides, or swellable plastics such as PVC.
The total amount of fillers present in the compositions of the present invention will preferably be from 0 to 40 wt.%, and more preferably from 0 to 20 wt.%, based on the total weight of the composition. The desired viscosity of the liquid, curable composition will typically be determinative of the total amount of filler added: in the present invention, it is desired that the liquid, curable compositions possess a viscosity of from 200 to 150,000, preferably from 200 to 50,000 mPas, or even from 200 to 10000 mPas.
Examples of suitable pigments are titanium dioxide, iron oxides, or carbon black.
In order to enhance shelf life even further, it is often advisable to further stabilize the compositions of the present invention with respect to moisture penetration through using drying agents. A need also occasionally exists to lower the viscosity of a coating, adhesive or sealant composition according to the present invention for specific applications, by using reactive diluent(s). The total amount of reactive diluents present will typically be up to 15 wt.%, and preferably from 1 to 5 wt.%, based on the total weight of the composition.
The presence of non-reactive diluents in the compositions of the present invention is also not precluded where this can usefully moderate the viscosities thereof. For instance, but for illustration only, the compositions may contain one or more of: xylene; 2-methoxyethanol; dimethoxyethanol; 2-ethoxyethanol; 2-propoxyethanol; 2-isopropoxyethanol; 2-butoxyethanol; 2-phenoxyethanol; 2-benzyloxyethanol; benzyl alcohol; ethylene glycol; ethylene glycol dimethyl ether; ethylene glycol diethyl ether; ethylene glycol dibutyl ether; ethylene glycol diphenyl ether; diethylene glycol; diethylene glycol-monomethyl ether; diethylene glycol-monoethyl ether; diethylene glycol-mono-n-butyl ether; diethylene glycol dimethyl ether; diethylene glycol diethyl ether; diethylene glycoldi-n-butylyl ether; propylene glycol butyl ether; propylene glycol phenyl ether; dipropylene glycol; dipropylene glycol monomethyl ether; dipropylene glycol dimethyl ether; dipropylene glycoldi-n-butyl ether; N-methylpyrrolidone; diphenylmethane; diisopropylnaphthalene; petroleum fractions such as Solvesso® products (available from Exxon); alkylphenols, such as tert-butylphenol, nonylphenol, dodecylphenol and 8,11,14-pentadecatrienylphenol; styrenated phenol; bisphenols; aromatic hydrocarbon resins especially those containing phenol groups, such as ethoxylated or propoxylated phenols; adipates; sebacates; phthalates; benzoates; organic phosphoric or sulfonic acid esters; and sulfonamides.
The above aside, it is preferred that said non-reactive diluents constitute less than 10 wt.%, in particular less than than 5 wt.% or less than 2 wt.%, based on the total weight of the composition.
In an exemplary embodiment of the present invention, the liquid one component (1 K) composition comprises, based on the weight of the composition:
To form a composition, the above described parts are brought together and mixed. As is known in the art, to form one component (1 K) curable compositions, the elements of the composition are brought together and homogeneously mixed under conditions which inhibit or prevent the reactive components from reacting: as would be readily comprehended by the skilled artisan, this might include mixing conditions which limit or prevent exposure to moisture, heat or irradiation or which limit or prevent the activation of constituent latent catalyst(s). As such, it will often be preferred that the curative elements are not mixed by hand but are instead mixed by machine — a static or dynamic mixer, for example — in pre-determined amounts under anhydrous conditions without intentional heating or photo-irradiation.
In accordance with the broadest process aspects of the present invention, the above described compositions are applied to a substrate and then cured in situ. Prior to applying the compositions, it is often advisable to pre-treat the relevant surfaces to remove foreign matter there from: this step can, if applicable, facilitate the subsequent adhesion of the compositions thereto. Such treatments are known in the art and can be performed in a single or multi-stage manner constituted by, for instance, the use of one or more of: an etching treatment with an acid suitable for the substrate and optionally an oxidizing agent; sonication; plasma treatment, including chemical plasma treatment, corona treatment, atmospheric plasma treatment and flame plasma treatment; immersion in a waterborne alkaline degreasing bath; treatment with a waterborne cleaning emulsion; treatment with a cleaning solvent, such as carbon tetrachloride or trichloroethylene; and, water rinsing, preferably with deionized or demineralized water. In those instances where a waterborne alkaline degreasing bath is used, any of the degreasing agent remaining on the surface should desirably be removed by rinsing the substrate surface with deionized or demineralized water.
In some embodiments, the adhesion of the coating compositions of the present invention to the preferably pre-treated substrate may be facilitated by the application of a primer thereto. Whilst the skilled artisan will be able to select an appropriate primer, instructive references for the choice of primer include but are not limited to: U.S. Pat. No. 3,671,483; U.S. Pat. No. 4,681,636; U.S. Pat. No. 4,749,741; U.S. Pat. No. 4,147,685; and, U.S. Pat. No. 6,231,990.
The compositions are then applied to the preferably pre-treated, optionally primed surfaces of the substrate by conventional application methods such as: brushing; roll coating using, for example, a 4-application roll equipment where the composition is solvent-free or a 2-application roll equipment for solvent-containing compositions; doctor-blade application; printing methods; and, spraying methods, including but not limited to air-atomized spray, air-assisted spray, airless spray and high-volume low-pressure spray. For coating and adhesive applications, it is recommended that the compositions be applied to a wet film thickness of from 10 to 500 µm . The application of thinner layers within this range is more economical and provides for a reduced likelihood of thick cured regions that may — for coating applications —require sanding. However, great control must be exercised in applying thinner coatings or layers so as to avoid the formation of discontinuous cured films.
Conventionally, the energy source used to initiate the curing of the applied compositions will emit at least one of ultraviolet (UV) radiation, infrared (IR) radiation, visible light, X-rays, gamma rays, or electron beams (e-beam). Subsequent to their application, the radiation curable coating compositions may typically be activated in less than 5 minutes, and commonly between 1 and 60 seconds — for instance between 3 and 12 seconds — when irradiated using commercial curing equipment.
Irradiating ultraviolet light should typically have a wavelength of from 150 to 600 nm and preferably a wavelength of from 200 to 450 nm. Useful sources of UV light include, for instance, extra high pressure mercury lamps, high pressure mercury lamps, medium pressure mercury lamps, low intensity fluorescent lamps, metal halide lamps, microwave powered lamps, xenon lamps, UV-LED lamps and laser beam sources such as excimer lasers and argon-ion lasers.
Where an e-beam is utilized to cure the applied coating(s), standard parameters for the operating device may be: an accelerating voltage of from 0.1 to 100 keV; a vacuum of from 10 to 10-3 Pa; an electron current of from 0.0001 to 1 ampere; and, power of from 0.1 watt to 1 kilowatt.
The amount of radiation necessary to satisfactorily cure an individual coating composition — such that said coating becomes fixed, for example — will depend on a variety of factors including the angle of exposure to the radiation and the thickness of a coating layer. Broadly, however, a curing dosage of from 5 to 5000 mJ/cm2 may be cited as being typical: curing dosages of from 50 to 500 mJ/cm2, such as from 50 to 400 mJ/cm2 may be considered highly effective.
The purpose of irradiation is to generate the active species from the photoinitiator which initiates the cure reactions. Once that species is generated, the cure chemistry is subject to the same rules of thermodynamics as any chemical reaction: the reaction rate may be accelerated by heat or retarded by lower temperatures.
The complete curing of the applied curable compositions should typically occur at temperatures in the range of from 100° C. to 200° C., preferably from 100° C. to 170° C., and in particular from 120° C. to 160° C. The temperature that is suitable depends on the specific compounds present and the desired curing rate and can be determined in the individual case by the skilled artisan, using simple preliminary tests if necessary. Where applicable, the temperature of the curable compositions may be raised above the mixing temperature and / or the application temperature using conventional means, including microwave induction.
The curable compositions according to the invention may find utility inter alia in: varnishes; inks; binding agents for fibers and / or particles; the coating of glass; the coating and bonding of mineral building materials, such as lime- and / or cement-bonded plasters, gypsum-containing surfaces, fiber cement building materials and concrete; the coating, sealing or bonding of wood and wooden materials, such as chipboard, fiber board and paper; the coating or bonding of metallic surfaces; the coating of asphalt- and bitumen-containing pavements; the coating, sealing or bonding of various plastic surfaces; and, the coating of leather and textiles.
In a particularly preferred embodiment, the composition of the present invention is applied to structural substrates to produce an adherent, highly abrasion resistant coating or bond. The bonding operation can often be effected at less than 200° C. and effective abrasion resistance can be attained after curing. Moreover, when bonding to the surface of mechanical structures or to a floor or pavement, the coating compositions can provide a strong, reliable bond, provide thermal stability and corrosion protection for the surface and can prevent the surface from being contacted with compounds which would deleterious to the operation or efficiency of the specific structure.
The following examples are illustrative of the present invention and are not intended to limit the scope of the invention in any way.
The following compounds and materials are employed in the Example:
The formulations described in Table 1 herein below were formed under mixing.
Each formulation was a clear, colorless liquid which showed no marked increase in viscosity when stored at room temperature for 28 days. Upon formation, Formulation 1 had an initial viscosity at 25° C. of 330 mPas. Upon formation, Formulation 2 had an initial viscosity at 25° C. of 2400 mPas. Both formulations were found to be independently curable under both UV irradiation and thermal curing conditions.
In a specific test, each formulation was cured by exposure to UV irradiation for 1 second at 100 mW/cm2 intensity from a high pressure mercury lamp under post-heating at a temperature of 150° C. for 60 minutes. The obtained cured products were both clear, amber solids.
In view of the foregoing description and example, it will be apparent to those skilled in the art that equivalent modifications thereof can be made without departing from the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20176983.3 | May 2020 | EP | regional |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2021/063805 | May 2021 | WO |
| Child | 18070161 | US |
