Note: Descriptions are shown in the official language in which they were submitted.
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1
A Firm, Adhesive and Smooth-rubbing Paste
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to a firm, adhesive and smooth-rubbing paste
based on reaction products of polyisocyanates, to its production and to its
use.
DISCUSSION OF RELATED ART
Pastes of the type in question are known. Thus, DE 24 19 067
describes a stick of a gel-forming agent, water and an active component. The
gel-forming agent is a reaction product of an aromatic diisocyanate with
mono- and/or dialkanolamines containing 2 to 16 carbon atoms. The active
component can be an adhesive, for example polyacrylamide, polyvinyl
acetate, polyacrylate, polyvinyl alcohol, polyvinyl methyl ether and synthetic
or natural rubbers. There is no mention of a polyurethane as the adhesive
component. The stick has to be protected against drying out to remain
usable.
EP 405 329 describes firm, smooth-rubbing adhesive sticks based on
a soap gel as the gel-forming component and an aqueous polyurethane
dispersion as the adhesive component. The polyurethane is a reaction
product of a polyol or a polyol mixture, an isocyanate component with a
functionality of two or more, a component capable of salt formation in the
form
of an alkaline aqueous solution and/or a nonionic hydrophilic modifying agent
and, if desired, a chain-extending agent. The adhesive stick contains water
and has to be protected against drying out to remain usable.
WO 94/13726 describes a hydrophilic high molecular weight nonionic
polyurethane which may be used in water-free form as a hotmelt adhesive.
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The polyurethane is characterized by the following structural units:
a) -O-(CH2 CH2 O)~-,
where n = 8 to 500 and more particularly 20 to 300;
b) -CO-NH-X-NH-CO-,
where X is an aliphatic or cycloaliphatic radical, more particularly a
residue of m-tetramethyl xylene diisocyanate (TMXDI);
c) -O-Y-O,
where Y is a hydrophobic group, more particularly either
(-CH2 CH(CH3)-O)m CH2 CH(CH3)-,
(-CH2 CH(C2H5)-O)m-CH2 CH(C2H5)- and
(-CH2 CH2 CHa CHZ O)m CHZ CH2 CH2 CH2
where m = 8 to 500 and more particularly 20 to 300,
or alkylene or cycloalkylene groups containing 2 to 44 and, more
particularly, 6 to 36 carbon atoms,
c) making up 0 to 40% by weight, preferably 2 to 30% by weight and
more preferably 5 to 25% by weight, based on a)+c) in the
polyurethane.
There is no reference to bonding at room temperature in the water-free
state.
Earlier German patent application 195 19 391 describes a
polyurethane adhesive which may be used in water-free form as an adhesive
stick. The polyurethane may be prepared from the following components:
a) at least one aliphatic or aromatic diisocyanate, preferably from the
following group: MDI, TDI, HDI, IPDI and, above all, TMXDI,
b) at least one crystallizing polyester or polyether diol, more particularly
from the following group:
- polyethylene glycol with a molecular weight (number average) of
200 to 40,000,
- polytetrahydrofuran with a molecular weight of 200 to 4,000,
- copolymer of ethylene oxide and propylene oxide with a molecular
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3
weight of 200 to 40,000, preferably a block copolymer with the
structure PEG/PPG/PEG and with a PEG content of 10 to 80% by
weight, and
- a polyester diol, more particularly polycaprolactone with a
molecular weight of 200 to 50,000,
c) optionally at least one diol capable of forming ions, more particularly
for forming carboxylates, and
d) optionally at least one trihydric or higher polyol, such as glycerol and
TMP, and
e) optionally at least one hydrophobic diol, more particularly from the
following group:
- polypropylene glycol with a molecular weight of 200 to 4,000 and
- alkanediol containing 1 to 100, preferably 2 to 50 and more
preferably 5 to 30 carbon atoms,
the ratio of isocyanate groups to hydroxyl groups being variable from 0.5 to
1.2:1 and, more particularly, from 0.7 to 1:1.
The adhesive stick does not contain any free NCO groups.
The strengths of all adhesive sticks are high enough for paper, but not
for other substrates. In addition, the wet strengths of the adhesive pastes
mentioned are very poor. Accordingly, the problem addressed by the present
invention was to provide a firm smooth-rubbing adhesive paste which would
not have any of these disadvantages and which would be distinguished not
only by easy handling, but also by favorable performance properties. More
particularly, the adhesive paste would be easy to apply, would allow for early
correction of the bond and would still develop high ultimate strength and,
optionally, water resistance.
DESCRIPTION OF THE INVENTION
The present invention provides a firm, smooth-rubbing adhesive paste,
free of water, comprising a solid reaction product of a polyisocyanate
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component and a monofunctional fatty derivative component, wherein the
reaction product contains moisture reactive isocyanate groups.
The solution provided by the invention is defined in the claims and lies
essentially in a firm, smooth-rubbing adhesive paste based on reaction
products of a polyisocyanate, the paste being water-free and containing
moisture-reactive NCO groups.
A paste is regarded as "firm" when it is capable of forming dimension-
ally stable geometric objects on its own. In particular, it should have a
deformation load of 10 to 150 at 20°C as measured by the compressive
strength method described hereinafter.
A paste is regarded as "adhesive" when it is capable of attaching
lightweight materials at least, such as paper or paperboard, to flat surfaces
at room temperature, even without fixing.
A paste is regarded as "smooth-rubbing" when between 0.5 and 0.1
mm per m and, more particular, between 0.25 and 0.35 mm/m are rubbed off
at the application temperature, more particularly at 20 to 25°C, as
measured
by the rub-off method described hereinafter. According to the invention, the
application temperature may rise to 10°C below the melting point. It
may of
course also be above the melting point, in which case the paste is applied in
the same way as a normal hotmelt adhesive.
The isocyanate content of the paste according to the invention is in the
range from 0.5 to 20 g NCO/100 g of paste and, more particularly, in the
range from 1 to 15 g.
The polyisocyanates are reacted directly or indirectly with monofunc-
tional fatty derivatives. The monofunctional fatty derivatives are preferably
fatty alcohols, fatty amines and fatty acids. Fatty alcohols are linear
saturated
or unsaturated primary alcohols obtainable by reduction of triglycerides,
fatty
acids or fatty acid methyl esters. Specific examples are capryl alcohol, 1-
nonyl alcohol, capric alcohol, lauryl alcohol, myristyl alcohol, cetyl
alcohol,
stearyl alcohol, oleyl alcohol, erucyl alcohol, ricinol alcohol, linoleyl
alcohol,
linolenyl alcohol, arachidyl alcohol, gadoleyl alcohol, behenyl alcohol,
erucyl
' CA 02247023 1998-08-20
alcohol, brassidyl alcohol.
Fatty acids are aliphatic saturated carboxylic acids with, almost
exclusively, an unbranched carbon chain. They are normally prepared from
fats and oils. Specific examples of fatty acids are capric acid, undecanoic
acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid,
palmitic
acid, margaric acid, stearic acid, nonadecanoic acid, arachic acid, behenic
acid, palmitoleic acid, oleic acid and erucic acid.
The fatty amines are normally prepared from the fatty acids with
ammonia via the fatty acid amide and fatty acid nitride stage. However, the
nitrite may also be directly prepared from the fat with ammonia. By virtue of
these reactions, the fatty amines have the same number and the same
structure as the fatty alcohols and fatty acids mentioned above. The amino
groups may also be substituted by an R' group, where R' is an alkyl group
containing 1 to 30 carbon atoms and, more particularly, 1 to 18 carbon atoms.
Corresponding fatty derivatives containing SH groups instead of OH group
may also be used. The fatty derivatives may of course also be prepared by
petrochemical methods and may even have an odd number of carbon atoms.
The paste according to the invention may consist a) of a product of the
direct or indirect reaction of a polyisocyanate with a fatty derivative in
combination with a "liquid polyisocyanate" and b) solely of a reaction product
of a polyisocyanate. Mixtures of a) and b) are of course also possible.
Variant a) is a gel structure of at least two components, the solid gel-
forming component being a reaction product of a polyisocyanate containing
on average 1 to 10, preferably 1 to 5 and more preferably 1 to 4 terminal
groups of fatty derivatives and the dispersant being a "liquid polyisocyanate"
containing on average 1 to 6 and preferably 1 to 4 isocyanate groups per
molecule.
The polyisocyanates are, above all, compounds containing 1 to 10,
preferably 1 to 4 and more preferably 3 isocyanate groups per molecule. In
principle, any aliphatic and aromatic polyisocyanates may be used, although
aliphatic polyisocyanates are preferred.
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The following are mentioned as suitable polyisocyanates: phenyl
isocyanate, 1,5-naphthylene diisocyanate, 4,4'-diphenyl methane diisocyanate
(MDI), hydrogenated MDI (H,2MD1), xylylene diisocyanate (XDI), tetramethyl
xylylene diisocyanate (TMXDI), 4,4'-diphenyl dimethyl methane diisocyanate,
di- and tetraalkyl diphenyl methane diisocyanate, 4,4'-dibenzyl diisocyanate,
1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, the isomers of
toluene diisocyanate (TDI), optionally in the form of a mixture, 1-methyl-2,4-
diisocyanatocyclohexane, 1,6-diisocyanato-2,2,4-trimethyl hexane, 1,6-
diisocyanato-2,4,4-trimethylhexane, 1-isocyanatomethyl-3-isocyanato-1,5,5-
trimethyl cyclohexane (IPDI), chlorinated and brominated diisocyanates,
phosphorus-containing diisocyanates, 4,4'-diisocyanatophenyl perfluoro-
ethane, tetramethoxybutane-1,4-diisocyanate,butane-1,4-diisocyanate,hex-
ane-1,6-diisocyanate(HDI), dicyclohexyl methane diisocyanate, cyclohexane-
1,4-diisocyanate, ethylene diisocyanate, phthalic acid-bis-isocyanatoethyl
ester; polyisocyanates containing reactive halogen atoms, such as 1-
chloromethylphenyl-2,4-diisocyanate,1-bromomethylphenyl-2,6-diisocyanate,
3,3-bis-chloromethylether-4,4'-diphenyldiisocyanate. Sulfur-containingpoly-
isocyanates are obtained, for example, by reaction of 2 moles of hexamethy-
lene diisocyanate with 1 mole of thiodiglycol or dihydroxydihexyl sulfide.
Other important diisocyanates are trimethyl hexamethylene diisocyanate,1,4-
diisocyanatobutane, 1,12-diisocyanatododecane and dimer fatty acid diiso-
cyanate. Also of interest are partly masked polyisocyanates from which self
crosslinking polyurethanes can be formed, for example dimeric toluene
diisocyanate, or polyisocyanates partly or completely reacted, for example,
with phenols, tertiary butanol, phthalimide, caprolactam.
In one particular embodiment, the isocyanate component contains
dimer fatty acid isocyanate. Dimer fatty acid is a mixture of predominantly
C3s
dicarboxylic acids which is produced by thermal or catalytic dimerization of
unsaturated C,$ monocarboxylic acids, such as oleic acid, tall oil fatty acid
or
linoleic acid. Dimer fatty acids have long been known to the expert and are
commercially available. The dimer fatty acid may be reacted to form dimer
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fatty acid isocyanates. Technical dimer fatty acid diisocyanate contains on
average at least two and less than three isocyanate groups per molecule of
dimer fatty acid.
Diisocyanates trimerized to isocyanurates, for example the isocyanu-
rate of HDI and IPDI, are particularly suitable for the production of low-
diisocyanate one-component reactive PUR adhesives. It is known that the
trimerization reaction is carried out in the presence of suitable
trimerization
catalysts (see, for example, Kunststoff-Handbuch, Vol. 7, Polyurethane,
page 108). Mixtures of cyclotrimers of aliphatic and cycloaliphatic diisocya-
nates, especially mixed trimers thereof, are particularly advantageous. The
HDI biuret may also be used.
The higher homologs of MDI containing three or more isocyanate
groups per molecule (= polymer MDI) obtainable, for example, by removing
the difunctional isocyanate from the technical MDI by distillation (= crude
MDI)
are also suitable for the same purpose. The same applies to so-called tri-
MDI, the trifunctional homolog of MDI.
Higher homologs of MDI (polymer MDI) or aliphatic polyisocyanates,
more especially trimerized diisocyanates and, above all, trimerized HDI, are
preferably used as, quantitatively, the principal component of the polyisocya-
nates.
It may be appropriate to use oligomerized NCO-terminated adducts of
the above-mentioned isocyanates and polyols, polyamines or amino alcohols,
more especially adducts of aliphatic isocyanates. It is also appropriate to
use
polyisocyanates of high molecular weight, for example prepolymers of diols
or triols with an excess of diisocyanates. The diols or triols are polyesters
or
polyethers. The polyols are preferably 1 to 5 and more preferably 1 to 3 of
the:organic polyhydroxyl compounds known per se for the production of high
molecular weight compounds in PUR chemistry. Particularly suitable polyols
are the polyhydroxypolyethers known per se with molecular weights of 60 to
10,000 and preferably 70 to 6,000 which contain from 2 to 10 hydroxyl groups
per molecule. Polyhydroxypolyethers such as these are obtained in known
CA 02247023 1998-08-20
8
manner by alkoxylation of suitable starter molecules, for example water,
propylene glycol, glycerol, trimethylol propane, sorbitol, cane sugar, amino
alcohols, such as ethanolamine or diethanolamine, or aliphatic amines, such
as n-hexylamine or 1,6-diaminohexane, and mixtures of such starter
molecules. Suitable alkoxylating agents are, above all, propylene oxide and
optionally ethylene oxide.
The usual polyester polyols with molecular weights of 400 to 10,000
may also be used providing they contain 2 to 6 hydroxyl groups. Suitable
polyester polyols are the reaction products known per se of excess quantities
of polyhydric alcohols of the type already mentioned by way of example as
starter molecules with polybasic acids, for example succinic acid, adipic
acid,
phthalic acid, tetrahydrophthalic acid or mixtures of such acids.
Polycarbonate polyols may also be used.
It is also possible to use a) partial esters of saturated and unsaturated
fatty acids with polyhydroxy compounds and ethoxylated or propoxylated
derivatives thereof, b) saturated and unsaturated fatty alcohols, c) starch,
sugar and cellulose and derivatives thereof, d) ring-opening products of
epoxidized triglycerides or fatty acid esters with alcohols, carboxylic acids,
amines and water and corresponding alkoxylated derivatives and e) castor oil
or castor oil derivatives.
Instead of alcohols, polyfunctional primary or secondary amines may
also be used as chain constituents. The same also applies to aminocarboxy-
lic acids and low molecular weight protein compounds. Specific examples are
polyoxyethylene, polyoxypropylene and polyoxybutylene diamine - both the
homopolymers and copolymers based on these monomers - with molecular
weights of up to 5,000 (Jeffamine) and glycine, alanine, valine, leucine,
cysteine, cystine, aspartic acid, glutamic acid, tyrosine, tryptophane, eta-
amino caproic acid, 11-aminoundecanoic acid, 4-aminobutyric acid, mono-
and diaminonaphthoic acid. The percentage content of these substances
should be less than 20 mole-% and preferably 10 mole-%, based on the
polyols.
CA 02247023 1998-08-20
9
The relatively high molecular weight polyols are particularly appropriate
where a large excess of isocyanate groups is used.
The monofunctional fatty derivatives mentioned above are reacted with
the polyisocyanates likewise mentioned above in known manner.
The equivalence ratio of isocyanate groups to the reactive hydroxyl,
amino and carboxyl groups may be from 0.9:1 to 10:1 and is preferably in the
range from 1:1 to 5:1. In that case, the number of terminal groups of fatty
derivatives is on average at most 10, preferably at most 5 and more
preferably at most 4 per molecule.
Suitable "liquid polyisocyanates" are any of the polyisocyanates
mentioned above providing they have a viscosity of at most 30 Pas and
preferably at most 10 Pas at 20°C. In addition, the number of their NCO
groups should not exceed 6 and, in particular, 4 per molecule. On the other
hand, the "liquid polyisocyanate" should contain on average at least 2 and,
more particularly, 2 to 5 isocyanate groups per molecule. The polyisocya-
nates used as "liquid polyisocyanates" are preferably isocyanurates or NCO
prepolymers.
According to variant b, however, the paste according to the invention
may also be based on a single solid PUR component. In this case, it has an
average of 1 to 4 fatty derivatives and at least 1.5 and preferably 2 to 4
isocyanate groups per molecule.
Suitable fatty derivatives and polyisocyanates are, again, the
substances mentioned above. Preferred polyisocyanates are prepolymers
which contain an average of at least 1.5 and preferably 2 to 4 aliphatic
and/or
aromatic isocyanate groups.
The reaction of the isocyanate groups with the hydroxyl, amino and
carboxyl groups and later with water may be accelerated by addition of
catalysts. Preferred catalysts are tertiary amines which combine firmly with
the polymer chains. Their concentration may thus be increased several times
without any danger that they could migrate, for example like a plasticizer, or
give rise to toxicological disadvantages. Accordingly, the one-component
CA 02247023 1998-08-20
reactive PUR adhesive according to the invention preferably contains at least
one tertiary amine containing at least one functional group for incorporation
in the polymer chain as catalyst. The number of functional groups of the
tertiary amine is preferably two although there may also be three or one
functional groups) per tertiary amine. The number of these reactive tertiary
amines is at least and preferably one. However, two different tertiary amines
differing, for example, in their functionality could also be effectively used.
In
theory, there is no upper limit to the number of reactive tertiary amines
although, in practice, it should not be any greater than five. The tertiary
amine may be completely or partly replaced by a quaternary ammonium
compound. The reactive tertiary amines best contain the following functional
groups: -OH, -SH, -COOH, -NCO, -NH2 and -NHR, where R is an alkyl group
containing 1 to 25 carbon atoms. Hydroxyfunctional amines are preferably
used. Actual compounds are N,N-dimethyl ethanolamine, N,N-dimethyl
diaminoethane, N-methyl diethanolamine, N,N-dimethyl-2-(2-dimethylamino-
ethoxy)-ethanol, N,N,N-trimethyl-N-hydroxyethyl diaminoethane bis-amino-
ethyl ether, N,N-bis-(3-dimethylaminopropyl)-N-isopropanolamine,tetrameth-
ylimino-bis-propylamine and N-(3-dimethylaminopropyl)-N,N-diisopropanol-
amine. The reactive tertiary amine should best be used in a quantity of 1 to
30 g and preferably 2 to 10 g per 100 g of prepolymer. Outside these ranges,
disadvantages arise either because there is a distinct reduction in reactivity
or because the adhesive becomes brittle. By virtue of the high concentration
of catalyst, even aliphatic isocyanate groups react sufficiently quickly at
room
temperature and, in spite of this, are surprisingly stable in storage.
Besides these incorporable catalysts, the usual catalysts, more
particularly the following tertiary amines, may be used either on their own or
in conjunction with other catalysts: diazabicyclooctane (Dabco),
triethylamine,
dimethyl benzylamine (Desmorapid DB, BAYER AG), bis-dimethylaminoethyl
ether (Catalyst A I, UCC), tetramethyl guanidine, bis-dimethylaminomethyl
phenol, 2,2'-dimorpholinodiethylether, 2-(2-dimethylaminoethoxy)-ethanol,2-
dimethylaminoethyl-3-dimethylaminopropylether, bis-(2-diaminoethyl)-ether,
CA 02247023 1998-08-20
11
N,N-dimethyl piperazine, N-(2-hydroxyethoxyethyl)-2-azanorbornane, Tacat
DP-914 (Texaco Chemical), JeffcatJ, N,N,N,N-tetramethyl butane-1,3-
diamine, N,N,N,N-tetramethyl propane-1,3-diamine, N,N,N,N-tetramethyl
hexane-1,6-diamine.
The catalysts may even be present in oligomerized or polymerized
form, for example as N-methylated polyethylene imine.
Other suitable catalysts are 1-methyl imidazole, 2-methyl-1-vinyl
imidazole, 1-allyl imidazole, 1-phenyl imidazole, 1,2,4,5-tetramethyl
imidazole,
1-(3-aminopropyl)-imidazole, pyrimidazole, 4-dimethyl aminopyridine, 4-
pyrrolidinopyridine,4-morpholinopyridine,4-methyl pyridine and N-dodecyl-2-
methyl imidazole.
Besides the tertiary amines, other catalysts may be added, above all
organometallic compounds, such as tin(II) salts of carboxylic acids, strong
bases, such as alkali metal hydroxides, alcoholates and phenolates, for
example di-n-octyl tin mercaptide, dibutyl tin maleate, diacetate, dilaurate,
dichloride, bis-dodecyl mercaptide, tin(II) acetate, ethyl hexoate and diethyl
hexoate or lead phenyl ethyl dithiocarbamate. DABCO, TMR-2 etc. (Air
products), which are quaternary ammonium salts dissolved in ethyl glycol, are
mentioned as trimerization catalysts.
In addition, the paste according to the invention may contain additives.
Of particular importance in this regard are additives which improve tackiness
and which thus lead to good adhesion, even in cases where the substrates
are pressed briefly and lightly together. Suitable tackifiers are, above all,
resins. Resins in the present context are understood to be liquid to solid,
organic amorphous products with a broad molecular weight distribution and
hence with a broad softening range (see DIN 55958). The resins should not
react with the NCO groups under the storage conditions (mainly room
temperature, 12 months). Useful synthetic resins include hydrocarbon
(petroleum) resins and urea, alkyd, epoxy, melamine, phenolic, polyester,
unsaturated polyester, polyurethane, ketone, coumarone/indene, isocyanate,
polyamide and terpene/phenol resins. Useful natural resins are any of the
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non-NCO-reactive resins which are listed, for example, in I'<CARSTEN's
"Lackrohstoff-Tabellen", 9th Edition, 1992, Vincentz Verlag, Hannover
and in JORDAN's "Klebharze", Hinterwalder Verlag, Muenchen 1994.
Preferred resins include phenolic resins, hydrocarbon resins and rosin and its
derivatives, particularly the methyl esters of partly hydrogenated rosin, such
as diabietyl phthalate. The resins are used in a quantity of 0 to 80% by
weight and, more particularly, 1 to 50% by weight, based on the mixture as
a whole.
Other suitable tackifiers are polymers together with solvents, optionally
even together with resins. The polymers also should not react with the NCO
groups. Suitable polymers are, above all, natural and synthetic rubbers,
polyacrylates, styrene acrylates, polyesters, polychloroprenes, polyisobu-
tenes, polyvinyl esters (for example polyvinyl acetates), polyvinyl ethers and
polyurethanes. Among the radical-polymerizable monomers, monomer
combinations of any type are also capable of being converted into suitable
polymers. The polymers are used in a quantity of 0 to 80% by weight and,
more particularly, 2 to 25% by weight, based on the mixture as a whole.
Suitable solvents for these polymers are any inorganic and organic
substances which are liquid at 20°C and in which the polymer dissolves
in a
quantity of at least 2 g per 100 g of solvent at room temperature. Preferably,
the PU prepolymer should also dissolve in the solvent. Naturally, the solvents
also should not react with the NCO group.
If the molecular weight of the prepolymers increases, the smoothness
with which the paste rubs off onto the substrate may possibly be no longer
guaranteed. In that case, it is appropriate to add a solvent to the
prepolymer.
Suitable solvents are any inorganic or organic substances in which the PU
prepolymerdissolves in a quantity of at least 2 g per 100 g of solvent at
20°C.
Polar liquids, such as acetone, give transparent to opaque mixtures while
nonpolar liquids give white mixtures. The solvent is added in a quantity of 0
to 80% by weight and, more particularly, 2 to 45% by weight, based on the
mixture as a whole. Naturally, these solvents also should not react with the
CA 02247023 1998-08-20
13
NCO group. Solvents with a low evaporation index, more particularly below
3.0, based on diethyl ether, are preferred. One example of such a solvent is
acetone. Solvents are also particularly preferred if, in addition, they have a
high boiling point, more particularly a boiling point above 70°C at
normal
pressure. One example of such a solvent is isooctane. The addition of
solvents to the PU prepolymers affects not only the smoothness with which
the paste rubs off, but also its early adhesion.
In addition, the paste according to the invention may contain typical
additives such as, for example, fillers (particularly fine-particle silica,
chalk,
clays and fibers), pigments, soluble dyes (particularly fluorescent dyes),
defoamers, adhesion promoters, non-NCO-reactive plasticizers, antiagers and
C02 absorbing or adsorbing additives, for example molecular sieves and silica
gel. However, substances which react chemically with C02, for example CaO,
may also be added.
Other additives are typically added in the following quantities: filler 0
to 50% by weight, pigments and dyes 0 to 20% by weight, plasticizers 0 to
20% by weight and other additives 0 to 10% by weight, based on the paste
as a whole.
In its physical properties, the paste according to the invention is
reminiscent of waxes, particularly paraffin waxes. It is firm, but rubs off
onto
the substrate, at 20°C. It melts distinctly, i.e. within 5°C, in
the temperature
range from 40 to 100°C. The melt is clear. Even just above the melting
range, it has a relatively low viscosity and is only very slightly stringy.
After
cooling from the melt, the paste is opaque to transparent or has a color
brought about by the additives introduced.
The paste is also reminiscent of waxes in its rubbing behavior. When
the paste is rubbed onto a surface, it leaves a thin layer behind. This
rubbing
behavior distinguishes the paste according to the invention from typical solid
polyurethanes with their rubber-elastic properties which make rubbing off onto
a substrate impossible.
The paste according to the invention differs from waxes in the
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14
tackiness of the layer rubbed off. Early adhesive strength (after 1 minute) is
as high as that of hitherto known adhesive sticks. Accordingly, the bond can
still be corrected. After curing with moisture either from the air or from the
substrate, there is a drastic increase in adhesive strength which reaches
values that are clearly above those reached by known adhesive sticks. After
curing, the bond is relatively resistant to water and solvents in general. It
is
also relatively temperature-resistant.
To avoid premature curing, the adhesive has to be packed in moisture-
tight containers.
Since the paste according to the invention, although firm, rubs off
smoothly onto substrates, it is best used in geometric form, more particularly
cylindrical form. The cylinder may have a circular, oval or polygonal cross-
section. Its size will be determined by the application envisaged, for example
by the required width of area to be covered.
The paste according to the invention may be molded as follows: the
liquid melt is poured into corresponding containers or molds and cooled
therein. At the same time, it also solidifies. The paste may also be punched
out from hardened blocks.
By virtue of its properties, the paste according to the invention is
suitable for coating, filling, sealing and, in particular, for bonding. Where
it is
used for coating, the paste may be applied as a paint, as a conductive
coating, as a correcting layer, as a lacquer coat or as a repair layer. Where
it is used for bonding, the paste according to the invention may be applied as
a contact adhesive and, above all, as a one-component, moisture-reactive
broad-spectrum adhesive.
By virtue of these properties, the adhesive is suitable for the
production of adhesive sticks. Adhesive sticks are understood to be
adhesives in stick form which are mounted for displacement in a closable tube
and which leave behind a tacky film when rubbed onto a surface. The
compressive strength of such adhesive sticks with a diameter of 16 mm is of
the order of 30 to 70 N. By virtue of their handiness and their extremely high
- CA 02247023 1998-08-20
adhesive strength, adhesive sticks can be used for many purposes, for
example for bonding damaged furniture veneers, for repairing toys and
household goods, such as the straps of leather handbags, etc.
The invention is illustrated by the following Examples.
I. Starting materials for the Examples:
! Tris-(6-isocyanatohexyl)-isocyanatearade name Tolonate HDT-LV, as
polyisocyanate
! Octadecanol: trade name Lorol C 18, OH value 207; PEG 600:
polyethylene glycol, OH value 187.5, as polyols
Dibutyl tin dilaurate: trade name Stanclere DBTL; bis-(2-dimethyl-
aminoethyl)-ether: trade name Jeffcat ZF 20, as a catalysts
II. Production of the paste
Example 1
No. Name g/100 Molar Ratio
g
1 Tris-(6-isocyanatohexyl)-isocyanate50.0 1
2 Octadecanol 49.0 2
3 Dibutyl tin dilaurate 0.01
4 Bis-(2-dimethylaminoethyl)-ether1.0
NCO:OH ratio 1.5:1
The polyisocyanate (1) and the catalyst (3) were added to the
octadecanol (2) melted at 70°C and added for about 3 hours at
90°C until the
NCO content had reached its final value of 3.8%. The NCO content was
determined titrimetrically by Spiegelberger=s method in which dibutyl amine
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16
is reacted with the NCO-containing substance in ethyl acetate as solvent and
the excess is back-titrated with hydrochloric acid. At the end of the
reaction,
amine catalyst (4) was added. The end product was poured into a suitable
pack and, after cooling, formed a firm paste which could be rubbed under a
certain pressure onto various substrates to which it adhered after curing with
moisture from the air.
Example 2
No. Name g/100 Molar Ratio
g
1 Tris-(6-isocyanatohexyl)-isocyanate8.1 1
2 Octadecanol 11.9 3
3 Dibutyl tin dilaurate 0.01
NCO:OH ratio 1.0:1
The polyaddition was carried out as in Example 1 except that the
reaction was continued until an NCO content of 0% was reached.
Components 4 and 5 were then added to the melt, followed by stirring for 2
hours at 90°C.
No. Name g/100g Molar Ratio
4 Tris-(6-isocyanatohexyl)-isocyanate62.1 4
Polyethylene glycol 600 16.9 1
6 Bis-(2-dimethylaminoethyl)-ether1.0
After component (6) had been stirred in, followed by cooling, a firm,
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smooth-rubbing, moisture-reactive adhesive paste was obtained as in
Example 1 and had more internal strength than Example 2.
Example 3
Example 3 had the same composition as Example 2. However, the
procedure was different. Components (1 ) to (5) were weighed in together and
added for 5 hours at 90 to 100°C. After an NCO content of 11.9% had
been
reached, amine catalyst (6) was added. The paste obtained after cooling had
both a higher internal strength and better adhesive properties than Example
2.
Example 4
No. Name g/100g Molar Ratio
1 Tris-(6-isocyanatohexyl)-isocyanate29.4 2
2 Octadecanol 10.9 1.5
3 Polyester 230* 38.9 0.75
4 Bis-(2-dimethylaminoethyl)-ether0.8
Acetone 20.0
* Polyester 230 = polyester of isophthalic acid/adipic acid/diethylene glycol
NCO:OH ratio: 2.0:1
The starting materials listed above were reacted as in Example 3
except that the solvent was stirred in just before cooling. The reaction
products were firm but did rub ofF and contained NCO groups. Their adhesive
properties are apparent from the following Table.
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I I I . Tests
The strength of the paste was determined as compressive strength.
In addition, the rub-off behavior of the paste, which should enable it to be
easily applied as a uniform coating, and the ultimate strength of single-
overlap
bonds with beech plywood were determined.
The results are set out in the following Table'
Exam- Exam- ConventExam- Exam-
ple ple Tonal ple ple
1 2 3 4
Soap
Gel
Stick
Compressive strength [N] 200 10 50 30
Ultimate strength [MPa] 4.8 6.9 1.5 9.5
on wood
Ultimate strength [MPa] 2.9 4.0 0.8 7.6
on wood/
PMMA (Plexiglas)
Rub-off <0.2 0.41 0.3 0.38
Early adhesion - - +/- - +
The tests were based on the following methods:
Rub-off
In addition to a subjective evaluation, rub-off was measured using a
specially designed instrument (manufactured by BVI of Wuppertal).
Principle: a cylindrical stick of the paste to be rubbed off with a
diameter of 16 mm was clamped in a holder and pressed under a defined
pressure of 4.5 N onto a strip of paper (5.7 mm wide) running past at a
constant speed (1.8 m/minute). The cash register paper running past rubs
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19
the paste off, the reduction in the length of the cylinder per meter of paper
being determined as a measure of the rub-off. Evaluation is carried out on
the following scale:
The temperature is 20°C unless otherwise stated.
CA 02247023 1998-08-20
Rub-off [mm/m] Evaluation
# 0.1 Very hard
# 0.2 Hard
# 0.3 Optimal
# 0.4 Soft
# 0.5 Very soft
Compressive strength
Compressive strength is defined as the maximum load measured when
the stick collapses under pressure applied parallel to its longitudinal axis.
Compressive strength is measured with an Erichsen model 464L
(measuring head 709) compressive strength tester (manufacturer: Erichsen,
Simonschofchen 31, 56 Wuppertal 11 ).
The adhesive with a minimum length of 30 mm cut off immediately
above the plunger is placed between two holders in the form of disks of rigid
PVC which have a thickness of around 10 mm and a circular 3 mm deep
depression adapted to the particular stick diameters. The stick provided with
the holders is placed centrally on the table of the compressive strength
tester.
The height of the force measuring instrument above the table is adapted to
the height of the test specimen. The measuring head is then advanced
towards the stick to be tested at a rate of about 7 mm per minute. After the
highest compressive force has been reached, the value is read off from the
digital display.
Settin t~1-ime
To determine whether the adhesive properties of the sticks are
adequate for the purpose envisaged, test bondings are carried out by hand
under certain processing conditions and evaluated. The following procedure
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is adopted: A supply of white chromo paper (weight per unit area around 100
g/m5) coated on one side and adhesive sticks to be tested are conditioned for
at least 24 hours at 20°C/65% relative air humidity. The test paper is
cut into
strips 5 cm wide and around 30 cm long. An adhesive stick is longitudinally
rubbed twice under uniform pressure over the uncoated side of the paper strip
with the object of producing a uniform coating. Immediately afterwards, a
second strip of paper which has not been coated with adhesive is placed on
the coated strip with its uncoated side facing inwards and is then rubbed on
by hand. An attempt is then made to separate the paper strips slowly from
one another. The time at which the strips of paper will only separate where
they are bonded by tearing over their full width characterizes the setting
time.
Open time
The open time is the time after application of the adhesive within which
the materials to be bonded have to be fitted together to obtain complete
tearing of the paper after setting in the separation test. The method
corresponds to the setting time test except that the strips of paper are only
fitted together a certain after application of the adhesive. Beginning after
15
seconds, the open time may be graduated, for example, at further 15 second
intervals. In the case of slow-setting adhesives with a predictable longer
open
time, the intervals selected will be correspondingly longer.
Early holding
The test is carried out in a standard climate of 23°C/50% relative air
humidity in which the test specimens of beech plywood are stored for at least
3 days. Two test specimens measuring 80 mm x 25 mm x 4 mm are coated
with the particular adhesive with an overlap 20 mm in length, corresponding
to an overlap area of 500 mm5, pressed together for 5 seconds under a
pressure of 0.2 N/mm5 and immediately subjected to a shear force of 200 g.
The test is passed if the parts do not shift relative to one another after 1
hour.
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Ultimate stren_-qth
Tensile shear strength (TSS) was determined by bonding beech
plywood test specimens which had been stored at 23°C/50% relative air
humidity with an overlap on one side and measuring the tensile shear
strengths after 3 days with a tensile shear tester advancing at 50 mm/min.
Viscosity
Viscosity was measured with a Brookfield viscosimeter unless
otherwise indicated.
The invention may be varied in any number of ways as would be
apparent to a person skilled in the art and all obvious equivalents and the
like
are meant to fall within the scope of this description and claims. The
description is meant to serve as a guide to interpret the claims and not to
limit
them unnecessarily.
