Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Substance for Bonding, Coating and Sealing, Consisting of
Cyanoacrylates and Aldehyde or Ketone Condensation Products
This invention relates to a bonding, coating and sealing composition
based on a mixture of A) cyanoacrylates and B) condensation products of
aldehydes and ketones.
Cyanoacrylates adhesive such as these are known. Thus, DE 43 17
886 describes a cyanoacrylate adhesive which, to reduce adhesion to the
skin, contains 1 to 40% by weight of fatty derivatives in the form of certain
aliphatic alcohols or certain aliphatic carboxylic acid esters. 10 to 100,000
ppm of an anionic polymerization accelerator are added to this mixture. A
large number of substances are mentioned, including inter alia
formaldehyde and acetaldehyde condensation products and ethers of
polyalkylene oxides, for example with sorbitol as hydroxyl-containing
compound. Polyoxyethylene sorbitan esters and polyoxyeth~tlene/sorbitol
addition products are specifically mention.~d. In order td make the
cyanoacrylate - a low-viscosity liquid - more viscoirs_ ox-'thixotropic, a
thickener, for example polymethyl methacrylate, acrylate rubber, cellulose
derivative or silicate, is dissolved or dispersed. According to the Examples,
the thickener is added in a quantity of 0 to 10% by weight. The
disadvantage of this composition is that, even with a high concentration of
thickener, the cyanoacrylate adhesive is liquid and, accordingly, cannot be
used as a sealing compound, for example, or is unsuitable for bonding
porous substrates and, quite generally, is difficult to apply.
Against the background of this prior art, the problem addressed by
the present invention was to provide a cyanoacrylate composition with
improved handling behavior which of course would exhibit at least usable, if
not outstanding performance properties for bonding, coating and sealing
and, above all, adequate stability in storage at room temperature. In
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addition, production would be simple.
The solution provided by the invention is defined in the claims and
consists essentially in the use of a gel former based on a condensation
product of aldehydes and ketones with polyols for cyanoacrylates in order
to produce compositions dimensionally stable at 20°C.
Dimensionally stable means that the composition does not change
shape over a period of 10 days at 20°C solely under the effect of its
own
weight when the cylindrical composition is stored horizontally at 20°C
in an
open tube 1.5 cm in diameter and 5 cm in length; at least the stick then
projects less than 10 mm and preferably less than 0.1 mm beyond the tube.
On the other hand, however, dimensional stability should also be only so
great that, when a light external pressure is applied, the composition rubs
off onto paper in the same way as commercially available adhesive sticks.
Suitable gel formers are certain condensation products of aldehydes
or ketones with polyols.
Compounds containing at least one acetal or ketal group are used
as gel formers. Such compounds can be obtained by condensation
reactions and are also typically prepared, for example, by partial or
complete dehydration of polyols with aldehydes or ketones in a ratio (OH: _
C = O) of 1:0.5 to 1:0.01 and preferably 1:0.5 to 1:0.1, for example in the
presence of an acid as catalyst. The acetals and ketals according to the
invention may also be prepared by reaction of the polyols with derivatives
of the aldehydes or ketones, for example by reaction of geminal dichlorides
with evolution of hydrogen chloride or acetals or ketals with elimination of
alcohol. Suitable compounds have a melting point of at least 50°C, more
particularly of at least 100°C and preferably of at least 150°C.
Mixtures of
the acetals and ketals may also be used.
Suitable polyols contain at least one 1,2-diol, 1,3-diol or 1,4-diol
group. Other functional groups, for example ether, acid, ester, amide,
cyano, hemiacetal and halide groups, may also be present. Examples of
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such polyols are ethane-1,2-diol, propane-1,3-diol, propane-1,2-diol,
butane-2,3-diol, butane-1,4-dioi, 2,2-dimethylpropane-1,3-diol, 2,2-bis-
(hydroxymethyl)-propane-1,3-diol, 2-(bromomethyl)-2-(hydroxymethyl)-
propane-1,3-diol, butane-1,3,4-triol, 1-phenylpropane-1,2,3-triol, hexane-
1,2-diol, neopentyl glycol, 1,4-bishydroxymethyl cyclohexane, 2-
methylpropane-1,3-diol, hexane-1,2,6-triol, 2-(2-hydroxyethoxy)-butane-
1,3,4-triol, glycerol, di- and polyglycerol, diglycerol diacetate, trimethylol
propane, di-(trimethylolpropane), trimethylol ethane, pentaerythritol,
bicyclo[2.2.1]heptane-2,3,5,6-tetrol, 2,2,3,3-tetrahydroxybutanedioic acid,
dipentaerythritol, sorbitol, formitol, xylitol, inositol, glucitol, glucose,
sucrose, starch, cellulose, ascorbic acid, partly or completely hydrolyzed
polyvinyl acetate, 9,10-dihydroxystearic acid methyl ester, diacetyl sorbitol
and methyl glycoside.
Preferred polyols are sorbitol, xylitol and mannitol, more particularly
sorbitol.
Suitable aldehydes or ketones contain at least one substituted or
unsubstituted aromatic, heteroaromatic or alicyclic ring. Other functional
groups, for example ether, ester, amide, cyano and halide groups, may
also be present.
Examples of suitable ketones are cyclopentanone, cyclohexanone,
cycloheptanone, 1-(3,3-dimethylcyclohexyl)-ethanone, 1-
cyclopropylethanone, 3-methyl-5-propylcyclohex-2-en-1-one, dicyclopropyl
methanone, 4-tert.butyl cyclohexanone, dicyclohexyl methanone, 4-methyl
cyclohexanone, 1-(1-methylcyclopropyl)-ethanone, (4-chlorophenyl)-
cyclopropyl methanone, 1-(1 H-pyrrol-2-yl)-ethanone, 1-(2,4,6-
trimethylphenyl)-ethanone, 1-{2-furanyl)-2-propanone, 1-(2-naphthalenyl)-
ethanone, 1-(2-thienyl)-1-propanone, 1-(4-bromophenyl)-ethanone, 1-(4-
methoxyphenyl)-ethanone, 1-(naphthalenyl)-ethanone, 1,1-Biphenyl-2-
propanone, 1,2-Biphenyl ethanone, 1,3-Biphenyl-2-propanone, 1-phenyl-1-
butanone, 1-phenyl-1-decanone, 1-phenyl-1-dodecanone, 1-phenyl-1-
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hexanone, 1-phenyl-1-octanone, 1-phenyl-1-pentanone, 1-phenyl-1-
penten-3-one, 1-phenyl-1-tetradecanone, 1-phenyl-2-butanone, 1-phenyl-2-
propanone, 1-pyrazinyl ethanone, 2,2,2-trifluoro-1-phenyl ethanone, 1-(2-
furanyl)-ethanone, ~ 1-(2-pyridinyl)-ethanone, 1-(2-thienyl)-ethanone, 4-
chloro-1-(~--fluorophenyl)-1-butanone, 4-phenyl-2-butanone, 1-phenyl
ethanone, bis-(2-hydroxyphenyl)-methanone, bis-(4-chlorophenyl)-
methanone, cyclopentyl phenyl methanone, cyclopropyl-(4-methoxy-
phenyl)-methanone, cyclopropyl-(4-methylphenyl)-methanone, cyclopropyl-
2-thienyl methanone, cyclopropyl phenyl methanone, 1,5-diphenyl-1,4-
pentadien-3-one, phenyl-2-pyridinyl methanone, 2-bromo-1-(4-nitrophenyl)-
ethanone, 2-napthalenyl phenyl methanone, 3-chloro-1-phenyl-1-
propanone, 4-(4-hydroxyphenyl)-2-butanone, 4-(4-methoxyphenyl)-3-buten-
2-one, 1-(4-pyridinyl)-ethanone, 1-(4-hydroxyphenyl)-ethanone, 1-phenyl-1-
propanone, 4-phenyl-3-buten-2-one, diphenyl methanone, 1-phenyl-2-
butanone, 1-phenyl-2-buten-1-one, bis-(4-methylphenyl)-methanone, 2-
methyl-1-phenyl-1-propanone, 2-chloro-1-phenyl ethanone, cyclopropyl-(4-
fluorophenyl)-methanone, 1-(p-methoxyphenyl)-2-propanone, cyclohexyl
phenyl methanone and phenyl-(2-thienyl)-methanone.
Examples of suitable aldehydes are benzaldehyde, 3
chlorobenzaldehyde, 4-chlorobenzaldehyde, 2,6-dichlorobenzaldehyde,
2,4-dinitrobenzaldehyde, 3,4-dichlorobenzaldehyde, 3-fluorobenzaldehyde,
4-bromobenzaldehyde, 2-methyl tetrahydrobenzaldehyde,
tetrahydrobenzaldehyde, 2-methyl-5-isopropylcyclopentene-1-aldehyde,
2,2,4-trimethylcyclohexa-4,6-diene-1-aldehyde, 3(4)-methyl-1
propylcyclohexene-3-aldehyde, 1,3(4)-dimethylcyclohexene-3-aldehyde, 2-
methyl-1-propylcyclohexene-3-aldehyde, 3-cyclohexene-1-aldehyde,
2,3,4,5,6-pentafluorobenzaldehyde, 2,4,6-trihydroxybenzaldehyde, 4-tolyl
acetaldehyde, 2-methylbenzaldehyde, 4-hydroxybenzaldehyde, 3-methyl
benzaldehyde, 2-hydroxy-1-naphthaldehyde, 4-methylbenzaldehyde, 3,5-
dimethoxy-4-hydroxybenzaldehyde, cinnamaldehyde, 3-nitrobenzaldehyde,
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2-pentylcinnamaldehyde, 4-diethylaminobenzaldehyde, 4-methoxy-
benzaldehyde, 2-phenylpropionaldehyde, 2-methoxycinnamaldehyde, 4-
methylbenzaldehyde, phenoxyacetaldehyde, methylpyrrole-2-aldehyde,
2,5-dimethorytetrahydrofuran-3-aldehyde, 2,5-dipropyl-3,4-dihydropyran-2-
aldehyde, 2,5-diethyl-3,4-dihydropyran-2-aldehyde, 2,5-diisopropyl-3,4-
dihydropyran-2-aldehyde, 2,5-dimethyl-3,4-dihydropyran-2-aldehyde, 2,5-
dibutyl-3,4-dihydroypyran-2-aldehyde, thiophene-3-aldehyde, indole-3-
aldehyde, thiophene-3-aldehyde, pyridine-3-aldehyde, pyridine-4-aldehyde
and N-methylpyrrole-2-aldehyde.
Preferred aldehydes are benzaldehyde, 3-chlorobenzaldehyde and
3-fluorobenzaldehyde, more particularly benzaldehyde.
Examples of acetals and ketals according to the invention are di-O-
benzylidene mannitol, di-O-(2-chlorobenzylidene)-mannitol, di-O-(4-
nitrobenzylidene)-mannitol, di-O-(3-fluorobenzylidene}-mannitol, O-
benzylidene sorbitol, di-O-benzylidene sorbitol diacetate, di-O-(2-
chlorobenzylidene)-sorbitan diacetate, tri-O-(4-chlorobenzylidene)-sorbitol,
O-benzylidene threitol, O-benzylidene tartaric acid dimethyl ester, O-
cyclohexylidene glycerol, O-cyclohexylidene ascorbic acid and O-
benzylidene-9,10-dihydroxystearic acid methyl ester.
Preferred acetals and ketals are di-O-benzylidene mannitol, di-O-(3-
fluorobenzylidene)-mannitol and di-O-benzylidene sorbitol, more
particularly di-O-benzylidene sorbitol.
The percentage content of the aldehyde or ketone condensation
products is 0.1 to 10% by weight, preferably 0.4 to 6% by weight and more
particularly 1 to 3% by weight, based on the cyanoacrylate composition.
The cyanoacrylate composition is essentially based on typical
cyanoacrylates, i.e. on monoacrylates and/or biscyanoacrylates. Their
percentage content is at least 29.5% by weight and preferably at least 50%
by weight, based on the cyanoacrylate compositions as a whole.
"Typical monocyanoacrylic acid esters" in the context of the
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invention are understood to be compounds corresponding to general
formula (I):
H2C = C(CN)-CO-O-R (I)
where R is an alkyl, alkenyl, cycloalkyl, aryl, alkoxyalkyl, aralkyl or
haloalkyl
group with up to two conjugated C-C double bonds, with a cycloaliphatic b-
ring, with an aromatic nucleus derived from benzene and preferably with Br
or CI as halogen and containing 1 to 18 and preferably 2, 3 or 4 carbon
atoms, more especially a methyl, ethyl, n-propyl, isopropyl, n-butyl,
isobutyl, pentyl, hexyl, cyclohexyl, heptyl, 2-ethylhexyl, n-octyl, n-nonyl,
oxononyl, n-decyl, d-dodecyl, 2,2,2-trifluoroethyl, hexafluoroisopropyl,
allyl,
methallyl, crotyl, propargyl, benzyl, phenyl, cresyl, 2-chloroethyl, 3-
chloropropyl, 2-chforobutyl, tetrahydrofurfuryl, 2-methoxyethyl,
butoxyethoxyethyl, 3-methoxybutyl and 2-ethoxyethyl group. The
cyanoacrylates mentioned above are known to the expert on adhesives, cf.
Ullmann's Encyclopedia of Industrial Chemistry, Vol. A1, page 240,
Verlag Chemie Weinheim (1985), US-PS 3,254,111. Preferred
monomers are the allyl, methoxyethyl, ethoxyethyl, methyl, ethyl, propyl,
isopropyl or butyl esters of 2-cyanoacrylic acid.
"Biscyanoacrylates" are compounds corresponding to general
formula (II):
[H2C = C(CN)-CO-OJ2R~ (II)
where R' is a branched or unbranched difunctional alkane group containing
2 to 18 and, more particularly, 6 to 12 carbon atoms which may also
contain hetero atoms, such as halogens and oxygen, or aliphatic or
aromatic rings. However, R' is preferably a pure hydrocarbon. It is
important that the biscyanoacrylates be particularly pure. This requirement
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is satisfied, for example, by the following production and purification
methods: essentially, monocyanoacrylates are transesterified with diols and
the reaction mixtures are subsequently worked up by fractional
crystallizatioh.
Accordingly, a suitable process for the production of
biscyanoacrylates comprises transesterifying 2-cyanoacrylic acid or an
alkyl ester thereof corresponding to general formula (III):
H2C = C(CN)-CO-O-R2 (III)
where R2 is a branched or unbranched alkyl group containing 1 to 6 carbon
atoms,
with diols corresponding to general formula (IV):
[HO]2R1 (IV)
where R' is a branched or unbranched difunctional alkane group containing
2 to 18 carbon atoms, which may also contain hetero atoms, such as
halogens and oxygen, or aliphatic or aromatic rings,
to form biscyanoacrylates corresponding to general formula II and then
purifying the reaction mixture by fractional crystallization.
Accordingly, one starting product is a monofunctional cyanoacrylic
acid corresponding to formula III or an alkyl ester thereof. The alkyl group
should be selected so that the alcohol formed can be easily removed.
Suitable possibilities are known to the expert from the general
transesterification reaction. The alcohol is preferably removed by
distillation. Accordingly, R2 is a branched or unbranched alcohol radical
containing 1 to 6 carbon atoms, preferably 1 or 2 carbon atoms. The
monofunctional cyanoacrylate is stabilized in the usual way.
The diols (formula IV) are dihydric primary or secondary alcohols,
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preferably primary alcohols. The hydroxyl groups may be in any position to
one another, although they are preferably in the alpha/omega position.
The diols contain 2 to 18 carbon atoms and preferably 6 to 12 carbon
atoms. They may be in a linear, branched or cyclic arrangement. The
aliphatic radical may also contain an aromatic group or, besides the
hydrogen and carbon atoms, hetero atoms such as, for example, chlorine
or oxygen atoms, preferably in the form of polyethylene or polypropylene
glycol units. Hexane diol, octane diol, decane diol and dodecane diol are
specifically mentioned as diols.
The cyanoacrylate is used in excess. Accordingly, the molar ratio of
monofunctional cyanoacrylate to diol is at least 2.0:1.0, preferably 2.5:1.0
and, more preferably, 2.2:1Ø
The transesterification is catalyzed by strong acids, more especially
sulfonic acids and preferably aromatic sulfonic acids such as, for example,
p-toluene sulfonic acid. However, naphthalene sulfonic acid, benzene
sulfonic acid and acidic ion exchangers may also be used. The
concentration of the transesterification catalyst should be between 1 and
20% by weight, based on the monofunctional cyanoacrylate.
The transesterification reaction is carried out in solution, as is
normally the case. Suitable solvents are aromatic hydrocarbons and
halogenated hydrocarbons. Preferred solvents are toluene and xylene.
The concentration of the solution is 10 to 50% and preferably 10 to 20%.
The monohydric alcohol formed and the water formed are removed
in known manner and, preferably, distilled off with the solvent. The
conversion of the transesterification reaction is monitored, for example,
from NMR spectra. The reaction takes several hours, as is normally the
case. Where toluene is used as the solvent and p-toluene sulfonic acid as
the catalyst, the reaction is terminated after 10 to 15 hours when there is no
further separation of alcohol.
The working up of the reaction mixture is very important. Where
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acidic ion exchangers are used as the catalyst, they may be simply ~Itered
off. Where soluble sulfonic acids, for example p-toluene sulfonic acid, are
used as the catalyst, they are removed by solvent substitution: toluene is
replaced by~ a mixture of hexane, heptane or decane. Pure
biscyanoacrylate is obtained after two fractional crystallizations. According
to NMR spectra, it has a purity of more than 99%.
The biscyanoacrylate obtained is stable in storage with the usual
stabilizers and in the usual concentrations, i.e. there is hardly any change
in its melting point after storage for 6 months at 20°C.
However, the biscyanoacrylates obtained polymerize very quickly in
the presence of bases, preferably at substantially the same rate as the
corresponding monocyanoacrylates. As with the monofunctional cyano-
acrylates, traces of water are sufficient. A three-dimensionally crosslinked
polymer with relatively good thermal properties is formed.
According to the invention, therefore, it is used in known
cyanoacrylate adhesives in a quantity of 0.5 to 50% by weight, preferably 1
to 10% by weight and more preferably 2 to 5% by weight, based on the
cyanoacrylate composition as a whole.
It is known that cyanoacrylates are accessible both to anionic and to
radical chain polymerization so that it is advisable to protect the ester
compositions against both types of polymerization in order to prevent
premature hardening of the ester, thereby avoiding difficulties in storage.
In order to prevent anionic polymerization, an anionic polymerization
inhibitor may be added to the adhesives according to the invention. Any
anionic polymerization inhibitors of the type hitherto used in cyanoacrylate
adhesives are suitable for this purpose. For example, the anionic
polymerization inhibitor may be an acidic gas, a protonic acid or an
anhydride thereof. The preferred anionic polymerization inhibitor for the
adhesives according to the invention is sulfur dioxide, preferably in a
quantity of 0.001 to 0.5%, based on the adhesive. Other suitable anionic
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polymerization inhibitors are dinitrogen monoxide, hydrogen fluoride,
hydrochloric acid, sulfuric acid, phosphoric acid, organic sulfonic and
carboxylic acids and anhydrides thereof, phosphorus pentoxide and acid
chlorides. In a preferred embodiment, a radical chain polymerization
inhibitor is also added to the adhesives according to the invention in a
quantity of 0.01 to 0.05% by weight. This radical chain polymerization
inhibitor may be any one of the known radical chain polymerization
inhibitors for cyanoacrylate compositions. Phenolic compounds, for
example hydroquinone, t-butyl catequinone, pyrocatechol and p-
methoxyphenol, are normally used. The above-mentioned commercially
available ethyl 2-cyanoacrylate preparations are already stabilized. Should
it be necessary to adjust the concentration of stabilizer where these
commercially available preparations are used, this would present no
difficulties to the expert.
In another preferred embodiment, polymers are also added to the
cyanoacrylate compositions according to the invention, for example to
increase their viscosity (thickeners) or to vary the adhesive properties. The
polymers may be used in a quantity of 1 to 60% by weight, more
particularly 10 to 50% by weight and preferably 10 to 30% by weight, based
on the formulation as a whole. Suitable polymers are, above all, polymers
based on vinyl ethers, vinyl esters, esters of acrylic acid and methacrylic
acid containing 1 to 22 carbon atoms in the alcohol component, styrene or
styrene co- and terpolymers with ethene, butadiene. Vinyl chloride/vinyl
acetate copolymers with a vinyl chloride content of 50 to 95% by weight are
preferred. The polymers may be present in liquid, resin-like or even in solid
form. It is particularly important that the polymers contain no impurities
from the polymerization process which could inhibit curing of the
cyanoacrylate. If the polymers have too high a water content, they may
have to be dried. The molecular weight (Mw) of the polymers may be
scattered over a wide range but should be at least 1500 and at most
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1,000,000 because otherwise the final viscosity of the adhesive formulation
would be too high. Mixtures of the above-mentioned polymers may also be
used. More particularly, a combination of low molecular weight and high
molecular weight products has particular advantages in regard to the final
viscosity of the adhesive formulation. Examples of suitable polymers
based on vinyl acetate include Mowilith types 20, 30 and 60 and Vinnapas
types B1.5, B100, B17, B5, B500/20VL, B60, UW10, UW1, UW30, UW4
and UW50. Examples of suitable acrylate-based polymers are Acronal 4F
and Laromer types 8912, PE55F and P033F. Examples of suitable
methacrylate-based polymers include Elvacite 2042, Neocryl types B 724,
B999 731, B 735, B 811, B 813, B 817 and B722, Plexidon MW 134,
Plexigum types M 825, M 527, N 742, N 80, P 24, P28 and PQ 610. An
example of a suitable vinyl ether-based polymer is Lutonal A25. Cellulose
derivatives and silica gel may also be used for thickening. The addition of
polycyanoacrylates is particularly emphasized.
In addition, the cyanoacrylate composition according to the invention
may contain other auxiliaries to obtain certain effects commensurate with
the application envisaged. These other auxiliaries include above all the
polymerization accelerators described in DE 43 17 886, i.e. polyalkylene
oxides and derivatives thereof, particularly esters and ethers. Other
polymerization accelerators are CROWN ETHERS and derivatives thereof,
silica-crown compounds and cyclosulfur compounds. These polymerization
accelerators are known to be added in a quantity of 10 to 100,000 ppm and
more particularly in a quantity of 30 to 10,000 ppm, based on the
cyanoacrylate composition. Another accelerator is cyclodextrin.
The fatty derivatives described in DE 197 52 893 and in DE 43 17
886 may also be used as plasticizers. These are fats and fatty derivatives,
more particularly aliphatic alcohols, aliphatic carboxylic acid esters and
carboxylic acid esters of a carbocyclic compound. Further information can
be found in the patents cited above. The usual plasticizers, for example
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phthalates, citric acid esters, chloroparaffin and trimellitic acid esters,
may
of course also be used.
Solvents may also be added, in particular to increase the solubility of
the aldehyde or ketone condensation product or to enable this product to
be incorporated more easily in the form of a solution. Suitable organic
solvents are, for example, alcohols, ethers, ketones and alkyl esters of low
molecular weight. Particularly suitable organic solvents are isopropanol,
methoxypropanol, ethoxypropanol, ethoxyethanol, propoxyethanol, butoxy-
ethanol, methyl ethyl ketone and N-methyl-2-pyrrolidone. However, the
content of solvents in the cyanoacrylate composition should be low in order
not to jeopardize dimensional stability and is preferably less than 20% by
weight.
Other auxiliaries are activators, dyes, pigments, fragrances,
preservatives, antiseptics and fillers.
The cyanoacrylate composition according to the invention is
produced essentially by dissolving the cyanoacrylates and the aldehyde or
ketone condensation products with a polyol by heating and then hardening
the resulting solution by cooling. In general, a stabilized cyanoacrylate
composition is first prepared from an acrylate and an anionic
polymerization inhibitor under nitrogen as an inert gas and is then heated
to 50 to 90°C. The required components are then dissolved or suspended
with intensive stirring until a homogeneous mixture is obtained. The
condensation product is then added in portions at 80 to 95°C and
largely
dissolved at 90 to 95°C. The mixture is then cooled, preferably to ca.
80°C,
and poured into the required molds. After ca. 1 hour, the composition is
generally hard and, after ca. 24 hours, is dimensionally stable enough for
use as an adhesive stick. Despite its dimensional stability, the
cyanoacrylate composition can be rubbed under tight pressure onto a
substrate, for example paper.
By virtue of its dimensional stability, the cyanoacrylate composition
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is suitable for conversion into a geometric shape, above all into a stick.
Adhesive sticks are preferably produced in cylindrical form. The particular
shape is preferably adapted to the application envisaged. However, any
shapes are possible, 'particularly geometric shapes with at least one plane
or axis of symmetry, for example spheres, squares, pyramids, cones,
cylinders, sticks, tapes, flakes, films and "pillows". The shape is preferably
smaller in two dimensions than in the third. Such shapes are, for example,
sticks (hotmelt sticks) or "refills" in the form of wax sticks. The base or
the
geometric element may be angular, especially triangular, rectangular or
hexagonal, or round (for example circular or elliptical). The diameter may
be from 2 to 100 mm and the length up to 150 mm. Accordingly, the shape
and quantity of the cyanoacrylate compositions according to the invention
are highly variable and are largely determined by what is convenient for the
particular application envisaged.
Liquid cyanoacrylate compositions with highly thixotropic properties
can be produced by shearing of the ready-to-use cyanoacrylate
composition at high rotational speeds. The cyanoacrylate compositions
according to the invention are suitable for bonding, coating and sealing,
more particularly for bonding porous substrates such as, for example,
leather, textiles, paper, paperboard, cardboard, wood and skin. By virtue of
their stick form, the cyanoacrylate compositions according to the invention
may be used with particular advantage as an adhesive for repairing shoes,
for PVC pipes and for artificial finger nails. The "gluing" of wounds,
particularly where relatively long-chain cyanoacrylates are used, is also
possible. In conjunction with primers, for example aliphatic amines,
polyolefins can also be firmly bonded. The primers can also be converted
into stick form with the gel formers according to the invention. Coloring and
correcting sticks can also be produced by adding covering pigments and/or
dyes. Through the absence of solvents, such sticks are particularly
environment-friendly. In portioned form, the cyanoacrylate compositions
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according to the invention may also be used as filling material for filling
cracks and holes in various materials. Both substrates are preferably
coated with the adhesive, for example by rubbing with an adhesive stick.
Gap-filling bonds are also possible.
Where the cyanoacrylate compositions are used for sealing, their
rapid curing rate is worth mentioning.
Surprisingly, the cyanoacrylate composition according to the
invention is extremely stable in storage. For example, in conventional
adhesive stick tubes, it could be stored and handled for many weeks at
room temperature without any reduction in its adhesive strength.
Other advantages of the cyanoacrylate composition according to the
invention include simple application, safe handling (no spattering, for
example into the eyes or onto the skin), application over large areas,
bonding of vertical substrates.
The invention is illustrated by the following Examples.
After 6 months at 2 to 5°C, the adhesive sticks were still usable,
i.e.
their consistency and adhesive properties were good. After 9 months at
-18°C, the adhesive sticks were again still usable, i.e. no destruction
of the
gel structure and no polymer formation were observed. After heating to
20°C, the closure caps were easy to remove from the tubes. In tests
with
paper, the setting time and adhesive strength were virtually unchanged
(paper tears). The stability in storage at -18°C of more than 9 months
is
important above all for medical applications.
Examples
1. Production of cyanoacrylate compositions
The stabilized cyanoacrylate was introduced under nitrogen into a
three-necked flask and polymethacrylate was added in portions with
intensive stirring at 50°C. After 10 minutes, the solution was clear
and
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homogeneous.
To form a gel, the temperature was increased to 85°C and
dibenzylidene sorbital was added in portions to avoid the formation of
lumps. After 10 minutes, the gelling agent was largely dissolved. After
cooling to around 80°C, undissolved particles were removed by
filtration.
The solution was poured while still hot into conventional adhesive stick
tubes and then cooled. After ca. 1 hour, the consistency was solid. The
next day the adhesive stick was ready-to-use and remained stable for
several weeks despite repeated closing and opening.
2. Tests
a) To test stability in storage, a cyanoacrylate composition in an
adhesive stick tube was tested weekly for its adhesiveness on paper
at 23°C/50% relative air humidity.
b) To determine setting time, the cyanoacrylate composition was
applied to one side of a 30 cm long paper strip and, immediately
afterwards, a second strip of paper was applied and pressed down.
The time elapsing before the paper tore on separation of the
adhesive bond was measured.
c) To determine the tensile shear strength of longitudinal bonds, a) two
drops of the liquid adhesive were applied to a 10 x 25 mm area of
the substrate or b) a comparable quantity was applied to one side by
rubbing with the adhesive stick. Immediately afterwards, the second
substrate was lightly pressed on. After 2 days at 23°C/50% relative
air humidity, the beechwood and also the non-wood specimens were
tested for tensile shear strength (rate: 10 mm/min.) in accordance
with EN 205.
The results were expressed as the averages of 5 measurements.
The substrates were pretreated as follows:
- beechwood, untreated
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- PMMA: degreased
- ABS plastic: degreased
- PVC: degreased and
- Alu: sandblasted and degreased.
3. Results
The test results are set out in Table 1. They show that useful
strengths were obtained in every case, exceeding the strengths of
conventional cyanoacrylate adhesives in the case of beechwood.
Table 1. Composition (in parts by weight) and properties of
cyanoacrylate compositions
E1 E2
I
Compositions
1. Ethyl cyanoacrylate 100 100
2. S02
+ +
3. Phosphoric acid, methanesulfonic+ +
acid
4. Polymethacylate 5 5
5. Dibenzylidene sorbital 0 1.8
II
Properties
a) Storage stability [weeks] - >10
b) Setting time [seconds] No bond 20
c) Tensile shear strength [MPa]
- beechwood 7.33 TA 7.75
- PMMA 7.01 MF 6.11 MF
- ABS plastic 8.10 MF 6.21 part.
MF
- aluminium 14.75 7.08
- PVC 14.59 MF 4.90 MF
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TA = tearing of material
MF = material failure
part. MF = material failure in some test specimens
