Note: Descriptions are shown in the official language in which they were submitted.
~SZ9~1
The subject of the present invention are contact
adhesives based on copolymers of compounds with ethylenical-
ly unsaturated groups, in which of the polymers incorporat-
ed by polymerlsation, at least one possesses a glass
transition temperature of <-20C and at least a second a
glass transition temperature of >+20C. The glass transi- -
tion temperatures of these known copolymers lie below 0C.
In German Patent Specification 1,964,~43 there
are described copolymers of acrylic acid esters and N-
vinyl lactams. These copolymers possess glass transition
temperatures below 0C and are suitable directly or aftersubsequent cross-linking as contact adhesives. They
contain wi~h the acrylic acid ester polymers a polymer
component with a glass transition temperature below -20C.
The polymers of N~vinyl lactams possess, in
contrast, glass transition temperatures above +20C. On
combination of these two pol.ymer components within the
there indicated range of quantities, copolymers are obtain-
ed with the glass transition temperatures belo~ 0C, which
are suitable for use as contact adhesives.
The cross-linking of these copolymers to form
contact adhesives can be carried out according to the dis-
closures in this patent specificati.on both by radiation
cross-linking and also with the aid of organic pero~ides.
With other known copolymers of compounds with
ethylenically unsaturated groups and glass transition
temperatures below 0C, which are likewise known as bonding
agents, the chemical cross-linking takes place, for example
with epoxide compounds or carbodiimides or metal chelates
or also by means of unsaturated alkylolamides, which are
polymerised into the copolymers. The chemical cross-
linking of these known copolymers has the clisadvantage
that it only takes place at elevated temperature. In a
few cases therefore a polymer componen-t with OH-gro~lps,
- 1 - ~1~'
52~i
preferably Erom unsaturated alkylolimides is present and
polymerlsed in. Moreover cross-linking also takes place
if the copolymers are present in solution. This operates
adve~sely on the stability Oll stor~ge when using this
product as adhesive.
The cross-linking by energy rich radiation can
indeed take place at room temperature. It is however
connected with a large expenditure on apparatus and is not
always complete; moreover the risk is encountered that,
not immediately recognisable radiation harm can occur with
the working personnel on use thereof.
Furthermore in U.~. Patent Specification
4,164,614 contact adhesives of the above-indicated type
are described which indeed can be employed without cross-
linking but possess the disadvantage that they are obtainedwith their shear streng-th resistances according to test
method 7 of the Pressure Sensitive Tape Council (PSTC)
which are not sufficient, with values of below 24 hours,
for a series o~ uses. Moreover they must be distributed
on the substrate from the melt.
- Therefore, it would be advantageous to have
contact adhesives based on copolymers formed from ethylen-
ically unsaturated polymers in which the cross-linking oE
the polymers ta]ses place at room temperature without large
expenditure on apparatus anci yields shear s-treng-ths which
lie above 48 hours according to PSTC-7. Furthermore the
desired contact adhesives should be able to be applied as
much as possible free from solvent or otherwise be applied
from those solutions which only make possible a cross-
linking after evaporation oE the solvent.
The present invention provides a contact adhesivebased on copolymers oE compounds ~ith ethylenically un-
saturated groups, in which, of the polymers incorporated
by polymer:isation at least one possesses a glass transi~.ion
-- 2 --
A. .
, . . .
-
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temperature of <-20C and at least a second a glass transi-
tion temperature of >-~20C, characterised in that in addl-
tion a vinyl alkoxysilane is incorporated into the copo-
lymers by copolymerisation in amounts between 0.5 and 10%
by weight related to the total weight oE the copolymers
and the glass transition temperature of the adheslve
obtained lies below 0C.
The contact adhesives according to the invention
may have molecular weights between 2000 and 150,000,
determined by ge] permeation chromatography (GPC). The
low molecular copolymer can be applied to a substrate at
room temperature without use of solvents and, after cross-
linking, yields high shear strength. The high molecular
copolymers are employed in suitable solvents such as for
15 ` example acetic acid esters. They are stable in these
solutions and practically not cross-linked provided that
the solutions are not too concentrated~ After application
to a substrate, these high polymers cross-iink to contact
adhesives with still better shear strength than the low
molecular contact adhesives according to the invention.
The vinyl alkoxy silane, which is employed as
cross-lin}cer can correspond to the general formula.
CH2 = ÇH - li (OR)3-a
R ' a
in which R' stands for a methyl or ethyl residue and R for
an alkyl residue with 1 to ~ C-atoms which can optionally
be interrupted by one or more ether oxygen atoms. The
residue a can be 0 or 1. Examples for such monomers, which
can be polymerised-in are: vinyltrimethoxy silane. ~inyl-
triethoxy silane, vinylmethyldimethoxy silane, vinyl-tris-
(~-methoxy-ethoxy)-silane.
The vinylalkoxy silane is polymerised into the
copolymers in proportions between 0.5 and 10% by weight.
The al]coYy groups of the vinylalkoxy silanes react wi-th
-- 3 --
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water with intermediate formation of vinyl silanols which
then react on cross-linking with the remaining constltuents
of the copolymers.
As starting monomers there are employed on the
one hand those acrylates which polymerise to polymers with
glass transition temperatures below -20C. For this pur-
pose there may be enumerated chiefly acrylic acid esters
whose ester components possess 4 to 12 C atoms, such as
for example n-octylacrylates, iso-octylacrylate, 2-ethyl-
hexylacrylate or decylacrylate. Also higher esters ofmethacrylic acid, whose ester components possess 16 to 24
C~atoms, may be employed, such as for example n-octadecyl-
methacrylate. Also vinyl esters of higher fatty acids
(with 12 or more C-atoms) for example vinyl laurate can be
employed. Mixes of these es-ters can also be employed.
The amount of these components in the contact adhesive
lies between 60 and 80~ by weight.
The second component of the copolymers into which
the vinylalkoxy silane is polymerisecl is a polymer of
compounds with ethylenically unsaturated groups which,
when polymerised alone, yields glass transition tempera-
tures above +20C. For this group of monomers there may
be enumerated for example the above-indicated vinyl lactams
such as for example N-vinyl pyrrolidone, vinyl esters, such
as vinyl acetate, vinyl propionate, styrene or acrylic
acid. It is sufficient if either of these compounds is
copolymerised with the above-indicated acrylic or metha-
crylic acid esters, provided that in so doing there results
a copolymer whose glass transition temperature lies be~low
0C. In general, however, at least two of the indicated
monomers are copolymerised with the remaining components
of the copolymers. On account of the presence of a poly-
merised vinylalkoxysilane, it is not necessary that the
copolymers accordlng to the lnventlon must contaln poly-
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merised-in or mixed in hitherto known cross-linkers, Eor
example unsaturated alkylolamides for the cross-linking
reaction. The cross linking and hardening of this contact
adhesive already takes place at room temperature by means
of atmospheric mois-ture. It can be accelerated if the
adhesive is treated during or after the application to a
substrate in known manner with water vapour-saturated
air. Also the addition of cross-linking catalysts known
~ se accelerates the cross-linking.
Suitable as the cross-linking catalysts are the
cross-linking catalysts known ~ se such as for example
dibutyl tin laurate or acids such as sulphonic acids or
phosphoric acids, especially hypophosphoric acid. If the
copolymers contain acrylic acids polymerised therewith,
the addition of such cross-linking catalysts is not
necessary.
The cross-linking catalysts are employed in
amounts between 0.1 and 2.0~ by weight, related to the
contact adhesive. The addi-tion takes place preferably
before the application of the contact adhesive to the
substrate; it can, however, also take place already a
longer time before the a~plication if the contact adhe-
sive is present in solution since the cross-linking takes
place in general only in concentrated solutions or with
substantially solvent-free polymers.
The preferred copolyrners are those which are
produced by copolymerisation of 60 to 80~ by wei~ht
acrylic acid esters whose ester components possess 6 to
lO C-atoms with 30 to 5% by weight N-vinylpyrrolidone, 5
to 15% by weight styrene or vinyl acetate and 4 to 6%
by weight vinyl trialkoxysilane.
The preparation of the new copolymers takes
place in known manner by radical polymerisation of the
indicated monomers. ~lso polymerisa-tion regulators such
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as for example aliphatic mercap-tans may be added to the
mixture, especially if produc-ts with relatively low
molecul~ wei(JIlt are desi~e~l.
The polymerisation can be carried out both with
and without solvents. The formex is then especially
preferred if products with low molecular weight are to be
ob-tained which then can be immediately applied to the
substrate, optionally after mixing in o~ the cross linking
catalysts.
If the polymerisation is to be carried out as a
solvent polymerisation, there are preferably employed as
solvents those compounds which are able to dissolve the
monomers and in particular the polymers. Such solvents
are known to the man skilled in the art. As examples,
there may be named alkyl esters of acetic acid and aro-
matic hydrocarbons liquid at room temperature. The copo-
lymers are soluble in these solvents on corresponding
dilution, without cross-linking. Before the application -
to the substrate, the solvent is largely evaporated,
~o after, if necessary, the cross-linking catalyst was mixed
in.
The contact adhesive only needs to be applied
in a thin layer - in general between 10 and 18 ,u - so that
already at normal atmospheric moisture, sufficient water
can ~iEEuse into -th~ polyme-l. In this way there occurs
cross-linking which, especially in the presence oE cata-
lysts, is accomplished prac-tically instantaneously.
EXAMPLES
A. Preparation of the copolymer
Example 1
A 500 ml three-necked flask with stirrer, reflux
condenser and N2-supply tube is used as reaction vessel.
There are emplaced in the three-necked flask: 140 g of
ethylhexylacryla-te, 40 g oE N-vinyl pyrrolidone, 20 g of
~Z~52~S
styrene and lO g of viny~ triethoxysilane as well as 200
ml of acetic acid hetyl ester and 0.75 g of Porofor N ~
(azoisobutyric acid dinitrile). The reaction mixture is
warmed to 65C with stirring. ~fter a reaction time of
two hours at 65C as well as after a further three hours
a further 0.75 g of Porofor N ~ are added to the mixture.
AEter a total polymerisation time of 7.5 hours, a copoly-
mer wi-th a molecular weight of 120,000 (according to GPC)
was obtained. The conversion amounted to 99%.
Example 2
The procedure of Example 1 was repeated with
the difference that instead of 20 g of styrene, 20 g of
vinyl acetate were used. 'I'he conversion amounted to 99
and the molecular weight 130,000.
Example 3
Example l was repeated with the difference that,
in addition, l2 g of dodecylmercaptan were added as the
regulator. The conversion amounted to 98% and the mole- -
cular weight 3200. After evaporation of the ester of
acetic acid, a brushable solvent-free copolymer was
obtained which, after mixing in of the catalyst was
employed directly for the testing of shear strength.
Example 4
The procedure of ~xample 1 was repeated with
the difference that there were employed as monomers: 160
g of ethylhexylacrylate, 20 g of acrylic acid, 20 g of
styrene and lO g of vinyl triethoxysilane.
B. Contact adhesive Example_
The copolymers of Examples 1, 2 and 4 were
applied from solution after mixing in oE 0.5~ H3PO2
(related to pure copolymer). For comparison they were
applied without catalyst. Example 4 is applied without
addition of H3PO2. The shear obtained are reproduced in
the following 't'able. The shear strengths were measured
as follows:
-- 7
~s~
The adheslve or the adhesive solution is applied
with a wiper blade to a Mylar foil (polyethylene tereph-
thal.ate foil) in a thickness of about 30,u. AEter apply-
ing the adhesive film, the Eoil is kept for 45 minutes a-t
- 5 50C in a vacuum. Afterwards the foil with an adhesive
surface of 25 x 12.5 mm is rolled onto an iron sheet and
loaded wi.th a weight of I kg. The time aEter which the
adhesive connection tears is designated as the shear
strength.
TA~LE -
Exam~le Shear strength
.
I 3.5 hours
I 3 2 > 3 months
II 6.0 hours
II + H3PO2 > 3 months
III 1.5 hours
III + H3PO2 2 months
IV > 3 months
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