CA1234824A - Stabilized adhesives - Google Patents

Abstract

A B S T R A C T

Stabilized adhesives This invention relates to stabilized adhesives, to which silyl esters are added for stabilization.

Le A 23 021

Description

82~

Stabilized adhesives This invention relates to stabilized adheslves, to which silyl esters are added for stabilization.
It is known that monomeric cyanacrylic acid esters can be stabilized with respect to polymerizatlon by addition of ~mall quantities of acidic gases, such as SO2 and radicalscavenqers, such as hydroquinone ~e.g. PS-PS 27 94 783 and 27 65 332).
However~ the use-of SO2 suffers from a series of disadvantages:
A concen~ration of from 0.001 to O.Ol ~ by weight has to be observed as the setting speed of the cyan-acrylates decreases with higher SO2 concentrations,and the cyanacrylates are not sufficiently stabilized with lower concentrations. The quantity can only be adjusted with difficulty owing to the gaseous state of the stabilizer and the low concentration.
The monomeric cyanacrylates are convent$onally obtained by depolymerisation of polycyanacrylates.
In this production method more of the acidic stabilizing gas is suitably added during the gas phase than is required for stabilization. After cooling, excess SO2 has to be removed by means of time-consuming operations in order to provide a product which has ~ufficient stability and cuning speed. Continual determination of the SO2 content is required. The monomer which has been stabilized in this manner yields SO2 under certain conditions.
The known non-gaseous stabilizers, such as sulphonic acids, have either only a moderately-stabilizing effect or theyseriously reduce the setting speed. Thus, for example, a cyanacrylate adhesive which can firmly bond two nitrile rubber sections Le A 23 021 d ~

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together in two seconds, can beso modified by the addition of only 0.5~ by weight of methane sulphonic acid that adhesion no longer takes place even withinl0 seconds.
It is also known to add sulphonic ac1d anhydrides to reduce the delay insetting ofcyanacrylates (e.g~
DAS 2 128 985). However, the rapid setting speed and good stability in storage desired in modern methods :
of adhesive productlon are not always achieved by using sulphonic acid ~nhydridesO Owing to thelr hydrolysis sensitivity, they almost always contasn ~ulphonicacids~ As traces of water can only be excluded with difficulty from the storage or use of an adh~sive, the proportion of sulphonic acids in the adhesive can be even higher.
Silicon compound-containing cyanacrylates are known and described,for example,in Japanese Patent no. 73 103 633. However, these Si compounds ~erve to make the cyanacrylates hydrophobic and do not contribute to the improvement of stability in storage.
It has now been found that cyanacrylate adhesives can be stabilized, while avoiding the above disadvantages, by the addition of silyl esters of strong mono- or poly-valent inorqanïc or organic mono~ or polyaclds.
The setting speed and stability in storage is ~arkedly greater than with hitherto known stabilized cyan-acrylate adhesives.
Thus, this invention relates to stabilized adhesives consisting of anionically polymeris~ble monomeric olefins corresponding to the formula (I) X
/

CH2=C (I), Y

Le ~ 23 021 ~234~2~

wherein X represents CN and COOR, and Y represents CN, halogen, such as chlorine and bromine, S03R and -COOR, and R represents a Cl-C20 alkyl or alkenyl group,a C5-C10 cycloalkyl group or an aryl group having 6 ~arbon atoms, such as phenyl, and asilyl ester of a ~trong acid and optionally other conventional additives.
Cyanacrylic acid esters corresponding to the formula (II) CH2=C-COOR ~II), wherein R is as defined in formula (I), methylene malodinitrile or compounds corresponding to formula (III~

CH2=C \ (III), CN
wherein R is also as defined in formula (I), can, for example, be used as anionically polymerisable monomer olefins.
Cyanacrylic acid esters corxesponding t~ formula ~II) are preferably used.
Silyl esters of strongmono- or poly valent inorganic or organic mono- or poly-acids, such as mono-, di- or tri-alkyl silyl esters of strong acids such as hydrohalic acids, mono-, di- or tri-sulphuric acid, mono-~ di- or poly-phosphoric acid, substituted or unsubstltuted alkyl-, cyclo-àlk~ aryl- or aralkyl-sulphonic acids, chlorosulphonic Le A 23 021 ~234~2~

acid, sulphinic acid esters, nitric acid or substituted or unsubstituted carboxylic acids are used acc~rding to the invention.
Examples of silyl esters of strong mono- or poly-basic inorganic or organic mono- or poly-acids are tetra-chlorosilane, methyl-, ethyl and butyltrichlorosilane, dimeth~l-, diethyl- or dibutyldichlorosilane, trimethyl~, triethyl- or tributylchlorosilane, bis-trimethylsilyl sulphuric acid, bis-triethylsilyl-disulphuric acid, bis-tributyltrisulphuric acid,dimeric dimethylsilylsulphate, tris-trimethyl~, tris-triethyl- or tris-tributylphosphate, 6-butyl-4,6-dimethyl-1,2,6-oxathiosilinane-2,2-dloxide, trimethylsilylchlorosulphonate, trimethylsilylmethane, sulphinate, trimethylsilylnitrate or trimethylsilyltri-fluoroacetateO

Bis trialkylsilyl esters of mono-, di- and tri-sulphuric acid corresponding to formula (IV) Rl R4 R -si_o ~o203--Si-R5 ~ IV), R3 n R6 wherein Rl to R6 are the same or different and represent a Cl-ClO alkyl-, aryl- or aralkyl group, and n represents an integer of from l to 3, are preferably used~
Bis-trialkylsilyl ester of monosulphuric acid, such as bis-trimethylsilyl sulphate are most preferably used.
The stabilizers for adhesives used according to the invention are produced by known methods. Their production is summarized in, for example, Houben-Weyl, Methoden der organischen Chemie, Yol 13/5, pages 163 to l75, 4th edition, Georg Thieme Verlag Stuttgart New York, 19800 Le A 23 021 1;~3~2~
.

The superiority of the stabilizers used according to the invention for anionically readily polymerisable monomers resides in the fact that they are straightforwaxd to produce and ~imple to handle and that the adhesives set more rapidly and have greater stability in storage than in the state of the art.
A further advantage of the stabilizers aaaording to the invention resides in the fact that they can be used as anionic inhibitors in the synthesis of anionically readily polymerising monomers, such as ~-eyanacrylates. This makes redundant the addition of known stabilizers in the production thereof so that they do not have to be trivially removed by costly methods.
The ~tabilizer us~d according to the invention~
such as the silyl esters of inorganic acids, such as phosphoric acid or sulphuric acid, also have the advantage that their decomposition products do not yield distillable acidic compounds under the effects of moisture, for example.
If, for example, cyanacrylates are stabilized with sulphonic acid anhydrides, this cyanacrylate can scarcely be freed by distillation from sulphonic acid which may be present. However, if a cyanacrylate contains bis-trimethylsilylsulphuric acid according to the invention, for example, sulphuric acid and hexame~hyldisiloxane are produced under the effects of moisture. If a cyanacrylate which has been stabilized in this manner is distilled, then only the stabilizer and the cyanacrylate distill off under ~uitable conditions. The hexamethyldisiloxane which incertain c~ses alsodistilLs offdoes nothavë a detrimental~ffect.
The quantity of stabilizer added to the monomeric olefin is from O.OOOS to 3~ by weight. The stabilizer content according to the present invention_~s preferably from 0.001 to 1~ by weight, most preferably from 0.001 to 0.1~ by weight, based on the quantity by Le A 23 021 ~23~32~
.

weight of olefin used.
In exceptional cases, further additives, such as stabilizers of anionic and radical polymerisation, such as SO2, sulphonic acids, sulphonic acid anhydrides, hydroquinone, p-methoxyphenol or quinone can be added to the anionically readily polymerisable monomers in addition to the stabilizers used according to the invention.
Furthermore, the ætabilized adhesives according to the invention can contain further conventional additives, which, for example, influence the viscosity or reduce the brittleness o~ the cured adhesive. These measures have already been described in the relevant literature. Thus, it is possible to add polymers, such as polymethyl meth-acrylate, fillers, such as highly-dispersed silica, or plasticisers, such as tricresylphosphate.
The stabilized anionically readily polymerisable monomers according to the invention, such as ~-cyanacrylates, are very suitable as rapid-setting single-component adhesives which are stable in storage. They set rapidly particularly when in the form of thin layers. The most varied substrates, such as pla6tics materials, metal, earthenware, wood or glass, can be bonded with the cyanacrylates which have been stabilized according to the present invention.

Example 1 100 g of the ~-cyanacrylic acid methyl ester produced by depolymerisation of polycyanacrylic acid methyl esters are mixed with the quantities of bis-trimethylsilyl sulphate (BTSS) gi~en in the followingTable. In order to test the stability in storage, the samples are poured into flasks of polyethylene and are stored in a heating chamber at 77~. The stability in storage is measured by cooling the samples at regular time intervals to room temperature and assessing their ~tate of aggregation.
Le A 23 021 1234~29~

In order to test the setting speed, single-row overlapped adhesives are produced with the cyanacrylate adhesives which have been stabilized as gi~Jen above, ~s described in VDI 229 ~5.1.1.), iron ~5T 1303) and SMC ~cross-linked unsaturated glass fibre-reinfor~ed polyester resin) being used as joining materials. The ~ample~ are produced and the adhesive strength is determined by the shear tension test accordlng to DIN 53 283. The combined tension and shear resistances are determined at various time intervals after the adhesive has been produced.

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comparative Example As in Example l, lO0 g of cyanacrylic acid methyl ester are mixed with the ~uantities given in the following Table of methane sulphonic acid anhydride(MSA) and the stahility in storage and setting speed are measured:

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The measured results given show that the adhesives which have been stabilized according to the invention have a very rapid setting speed and good ~tability in storage.

Le A 23 021

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A stabilized adhesive material consisting of an anionically polymerisable monomeric olefin as stabilizer correspon-ding to the formula (I) wherein X represents CN or COOR and Y represents CN halogen, SO3R and -COOR, and R represents a C1-C20 alkyl or alkenyl group, a C5-C10 cycloalkyl group or an aryl group, and a silyl ester of a strong acid as a stabilizer.

2. An adhesive according to claim 1, characterized in that an .alpha.-cyanacrylate is used as the anionically polymerisable monomeric olefin.

3. A stabilized adhesive according to claim 1, characterized in that a bis-trialkylsilyl ester of mono-, di- or tri-sulphuric acid corresponding to the general formula (IV) (IV), wherein R1 to R6 are the same or different and represent a C1-C10 alkyl, -aryl or -aralkyl group, and n represents an integer of from 1 to 3, is used as a sta-bilizer.

4. A stabilized adhesive according to claim 1, characterized in that the substituted olefin corresponding to the general formula I are produced in the presence of a stabilizer according to claim 1 or 3.

5. The use of the monomers which have been stabilized accor-ding to claim 1, 2 or 3 as adhesives.