Patent Description:
Adhesive formulations based on methyl methacrylate (MMA) have been extensively investigated over the past decades resulting in a number of improvements as disclosed, for example, in <CIT>, <CIT> and <CIT>.

One remaining problem of adhesive formulations containing MMA is the pungent odor and flammability of MMA.

<CIT> discloses compositions using low odor methacrylate monomers instead of MMA to solve this problem.

To replace MMA while maintaining desired adhesion and mechanical properties, mixtures of methacrylate esters need to be used. Catalyst packages to properly cure such monomer mixtures are known from the prior art. <CIT>, for example, discloses adhesive compositions with a catalyst system based on an aromatic perester free-radical precursor (preferably together with an amine/aldehyde adduct activator), an organic acid capable of cyclic tautomerism and a transition metal cure accelerator.

However, due to the high reactivity of certain methacrylate monomers, there is a need to slow down reactivity in order to achieve a long open time (as defined below) without impacting mechanical and adhesion properties.

<CIT> discloses retarding additives for methacrylate adhesives on the basis of non-protonic Lewis acids and zinc salts. However, such retarding agents are usually hygroscopic which has a negative impact on the handling of the retarding agents. Such retarding agents usually also have a negative impact on storage stability of the adhesive such as elongation at break.

<CIT> discloses the use of secondary amines, inter alia <NUM>,<NUM>,<NUM>-trimethyl-<NUM>,<NUM>-dihydroquinoline, in an acrylate-based adhesive composition including a catalyst, but the secondary amines are used therein as a radical chain inhibitor, i.e. providing for discoloration resistance (heat/weather resistance), rather than as a retarding additive.

<CIT> relates to adhesive acrylic compositions comprising retarding additives of the open time, which are based on different compounds (e.g. inorganic salts).

Therefore, there is a continuous need for retarding agents for adhesive compositions based on methacrylate monomers to slow down the reactivity without any negative impact on the mechanical and adhesion properties.

Unless otherwise defined herein, technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those having ordinary skill in the art.

All patents, published patent applications, and non-patent publications mentioned in the specification are indicative of the level of skill of those skilled in the art to which the present disclosure pertains.

All of the compositions and/or methods disclosed herein can be made and executed without undue experimentation in light of the present disclosure.

As utilized in accordance with the present disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings.

The use of the word "a" or "an", when used in conjunction with the term "comprising", "including", "having", or "containing" (or variations of such terms) may mean "one", but it is also consistent with the meaning of "one or more", "at least one", and "one or more than one".

The use of the term "or" is used to mean "and/or" unless clearly indicated to refer solely to alternatives and only if the alternatives are mutually exclusive.

Throughout this disclosure, the term "about" is used to indicate that a value includes the inherent variation of error for the quantifying device, mechanism, or method, or the inherent variation that exists among the subject(s) to be measured. For example, but not by way of limitation, when the term "about" is used, the designated value to which it refers may vary by plus or minus ten percent, or nine percent, or eight percent, or seven percent, or six percent, or five percent, or four percent, or three percent, or two percent, or one percent, or one or more fractions therebetween.

The use of "at least one" will be understood to include one as well as any quantity more than one, including but not limited to, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc. The term "at least one" may extend up to <NUM> or <NUM> or more depending on the term to which it refers. In addition, the quantities of <NUM>/<NUM> are not to be considered as limiting since lower or higher limits may also produce satisfactory results.

As used herein, the words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or openended and do not exclude additional, unrecited elements or method steps.

The phrases "or combinations thereof" and "and combinations thereof" as used herein refers to all permutations and combinations of the listed items preceding the term. For example, "A, B, C, or combinations thereof" is intended to include at least one of: A, B, C, AB, AC, BC, or ABC and, if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more items or terms such as BB, AAA, CC, AABB, AACC, ABCCCC, CBBAAA, CABBB, and so forth. In the same light, the terms "or combinations thereof" and "and combinations thereof" when used with the phrases "selected from" or "selected from the group consisting of" refers to all permutations and combinations of the listed items preceding the phrase.

The phrases "in one embodiment", "in an embodiment", "according to one embodiment", and the like generally mean the particular feature, structure, or characteristic following the phrase is included in at least one embodiment of the present disclosure, and may be included in more than one embodiment of the present disclosure. Importantly, such phrases are non-limiting and do not necessarily refer to the same embodiment but, of course, can refer to one or more preceding and/or succeeding embodiments. For example, in the appended claims, any of the claimed embodiments can be used in any combination.

"Open time", as used herein, is meant to be the amount of time after the adhesive is applied onto a first substrate, that the adhesive maintains sufficient tack to bond effectively to a second substrate.

The objective of the present disclosure is solved by the use of secondary amine or a mixture of secondary amines as retarding additive for an adhesive composition comprising one or more (meth)acrylate ester monomers, wherein the secondary amine is a secondary aryl amine selected from compounds having formula (<NUM>)
<CHM>
wherein R1 and R2 are independently selected from C<NUM>-C<NUM> alkyl groups,
<CHM>
wherein R1 is selected from C<NUM>-C<NUM> alkyl groups and R2 is selected from hydrogen or C<NUM>-C<NUM> alkyl groups, or
<CHM>
wherein R1 and R2 are independently selected from hydrogen or C<NUM>-C<NUM> alkyl groups.

In an alternative embodiment of the present disclosure, the secondary amine is a cyclic secondary amines. In a preferred embodiment, the cyclic secondary amine is a <NUM>,<NUM>,<NUM>-trimethyl-<NUM>,<NUM>-dihydroquinoline polymer.

In one embodiment of the present disclosure, the retarding additive is comprised an amount of <NUM> % to <NUM> % by weight, based on the total weight of the adhesive composition.

In another preferred embodiment of the present disclosure, the one or more methacrylate ester monomers are comprised in an amount of <NUM> % to <NUM> % by weight, based on the total weight of the adhesive composition.

The present disclosure is also related to an adhesive composition comprising one or more (meth)acrylate ester monomers, a catalyst system and a secondary amine or a mixture of secondary amines as a retarding additives, wherein the secondary amine is a secondary aryl amine ass defined as above.

In one embodiment of the present disclosure, the adhesive composition comprises an amount of <NUM> % to <NUM> % by weight of the retarding additive, based on the total weight of the adhesive composition.

In another preferred embodiment of the present disclosure, the adhesive composition comprises an amount of <NUM> % to <NUM> % by weight of the one or more methacrylate ester monomers, based on the total weight of the adhesive composition.

The compounds used as retarding additives in the compositions of the present disclosure are known per se in the art, for example, as antioxidants in the rubber industry. Surprisingly, it has now been found that they are very effective in extending the open time of methacrylate-based adhesive compositions without affecting the mechanical and adhesive properties or the storage stability.

The following Table <NUM> shows preferred compositions for an adhesive composition in accordance with the present disclosure (with both part A (resin part) and part B (hardener part)). Any preferred, more preferred or most preferred weight percentages or weight percentage ranges of any component can be combined with any preferred, more preferred or most preferred weight percentage or weight percentage range of any of the other components.

The (meth)acrylate ester monomer is usually a mixture of (meth)acrylate ester monomers. These may be methacrylates selected from, for example, hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), <NUM>-ethylhexyl methacrylate (EHMA), tetrahydrofuryl methacrylate (THFMA), cyclohexyl methacrylate (CHMA), benzyl methacrylate (BMA), isobornyl methacrylate (IBOMA), isodecyl methacrylate (IDMA), phenoxyethyl methacrylate (PEMA) and butyl methacrylate (BMA), or acrylates selected from, for example, methyl acrylate (MA), butyl acrylate (BA), cylohexyl acrylate (CHA), hexyl acrylate (HA), <NUM>-ethylhexyl acrylate (EHA), lauryl acrylate (LA) and ethyl acrylate (EA), or mixtures of the above methacrylates, acrylates or both.

Less preferably, (meth)acrylate ester monomers may be used wherein the alcohol portion of the ester groups contains <NUM> to <NUM> carbon atoms. Even less preferably, other (meth)acrylate ester monomers known in the art may be used.

The acid monomer, which is a preferred optional component of the adhesive composition of the present disclosure, is preferably methacrylic acid (MAA), less preferably acrylic acid, maleic acid, crotonic acid, and fumeric acid, less preferably other free-radical polymerizable acid monomers known in the art.

The polymeric modifier, which is another preferred optional component of the adhesive composition of the present disclosure, is preferably a core-shell impact modifier, less preferably nitro-rubber particles or powder or polymeric resin which acts as a thixotropic agent and/or toughener. The core-shell impact modifier is preferably a graft copolymer of the "core-shell" type. Preferred core-shell graft copolymers are acrylonitrile-butadiene-styrene (ABS), methacrylate-butadiene-styrene (MBS), and methacrylate-acrylonitrile-butadiene-styrene (MABS). Another preferred core-shell impact modifier is the so-called Acrylic Impact Modifier (AIM), a core-shell product with a butylacrylate rubber core and a polymethylmethacrylate (PMMA) shell.

The antioxidant, another preferred optional component of the adhesive composition of the present disclosure, is preferably an antioxidant from the IRGANOX® series available from BASF, such as IRGANOX® <NUM> (N,N'-<NUM>,<NUM>-hexanediylbis[<NUM>,<NUM>-bis(<NUM>,<NUM>-dimethylethyl)-<NUM>-hydroxy]-benzenepropanamide] or IRGANOX® <NUM> (a <NUM>,<NUM>',<NUM>',<NUM>,<NUM>',<NUM>'-hexa-tert-butyl-a,a',a'-(mesitylene-<NUM>,<NUM>,<NUM>-triyl)tri-p-cresol), less preferably other antioxidants known in the art.

The inhibitor, which is another preferred optional component of the adhesive composition of the present disclosure, is a free-radical polymerization inhibitor, which increases shell life and prevents or inhibits premature polymerization and is preferably hydroquinone (HQ) or methylhydroquinone, less preferably butylated hydroxytoluene (BHT) or other known free-radical polymerization inhibitors.

The toughening agent, another preferred optional component of the adhesive composition of the present disclosure, is selected from polymers from the group consisting of polychloroprene, copolymers of butadiene and other monomers, such as acrylonitrile, copolymers of isoprene with styrene, acrylonitrile, acrylate esters, methacrylate esters, copolymers of ethylene and acrylate esters, homopolymers of epichlorohydrine and copolymers of epichlorohydrine and ethylene, polychloroprene with blockcopolymers of styrene and butadiene or isoprene and blockcopolymers of styrene, diene monomers and mixtures thereof.

Any catalyst system useful for initiation and activation of the polymerization reaction in the adhesive composition of the present disclosure which is known for (meth)acrylate adhesive systems can be used. Preferred catalyst systems to be used with the adhesive composition of the present disclosure may be the ones as described in <CIT>. The use of known accelerators and promoters can be advantageous.

Further details can be seen from the following examples.

The following materials were used in preparation of the example formulations:.

The amounts shown in Table <NUM> are in weight %.

First, maleic acid was dissolved into THFMA at room temperature (about <NUM>). All components for the resin in Table <NUM> were added together and mixed using a speed mixer (centrifugal mixer) until a homogenous product resulted.

A solution of <NUM> ppm of soligen copper in EHMA was prepared. All components for the hardener in Table <NUM> were added together and mixed using a speed mixer (centrifugal mixer) until a homogenous product resulted. VULKANOX® HS LG was ground prior to addition, and then dissolved in post addition into the matrix.

Mix <NUM> resin + <NUM> hardener into a cup, then transfer into a silicon mold and follow exotherm reaction over time with a thermocouple.

Record time to reach <NUM>, maximum temperature, and time to reach maximum temperature.

The CFRP (Carbon Fibre Reinforced Polymer) and ABS (Acrylonitrile Butadiene Styrene) substrates were degreased by wiping with isopropanol and abraded. The aluminum substrates were sandblasted and rinsed with acetone. The adhesive composition was dispensed onto one surface of the substrate pair. The two surfaces were mated and held to each other with a compressor-type tubing clamp. The overlap area was <NUM> x <NUM>. The bonded joints were left to cure for <NUM> at <NUM>. The clamps were then removed and the bonded joints were tested for tensile shear strength (TSS) according to ISO <NUM> at crosshead speed of <NUM>/min. The TSS values were recorded in megapascals (MPa). The average value of <NUM> tested joints is reported.

A plate of <NUM> thickness was prepared under press and cured for <NUM> week at room temperature (about <NUM>) before to be tested according to ISO <NUM>.

Samples from the same plate were tested in torsion according to ISO <NUM> from -<NUM> to +<NUM> to determine glass transition temperature.

Claim 1:
Use of a secondary amine or a mixture of secondary amines as a retarding additive for an adhesive composition comprising one or more (meth)acrylate ester monomers
, wherein the secondary amine is a secondary aryl amine selected from compounds having formula (<NUM>)
<CHM>
wherein R1 and R2 are independently selected from C<NUM>-C<NUM> alkyl groups,
<CHM>
wherein R1 is selected from C<NUM>-C<NUM> alkyl groups and R2 is selected from hydrogen or C<NUM>-C<NUM> alkyl groups, or
<CHM>
wherein R1 and R2 are independently selected from hydrogen or C<NUM>-C<NUM> alkyl groups, or wherein the secondary amine is a cyclic secondary amine, and wherein the retarding additive extends the open time of methacrylate-based adhesive compositions without affecting the mechanical and adhesive properties or the storage stability thereof.