Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-01-24
2003-09-09
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S331700, C524S591000
Reexamination Certificate
active
06616797
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to processes for producing adhesive bonds by means of a dispersion D comprising a polyurethane (1) which comprises carbodiimide structural units of the formula (I)
—N═C═N— (I)
by
I. coating the surface of an article with the dispersion D,
II. drying the dispersion D with which the article is coated to give an essentially anhydrous coating (coating II), and
III. producing a coating III by subjecting the coating II to heat activation.
2. Discussion of the Background
Polyurethane dispersions having anionic groups and their use as adhesives are common knowledge (cf. D. G. Oertel “Kunststoff-Handbuch” Volume 7, 2nd edition, 1983, Carl Hanser Verlag, Munich, Vienna, pp. 24 to 25, pp. 571 to 574 and pp. 591 to 592).
Polyurethane dispersions are frequently employed as adhesives in a form in which they are applied as a film to the workpiece to be bonded, the water is evaporated, the dried film is heated (activated) briefly at temperatures from about 40 to 100° C., and this workpiece is bonded to another workpiece.
Using adhesive dispersions having a satisfactory level of properties it is possible in this way to form firm connections between workpieces composed of different materials, such as metal, wood, woodbase materials, glass and plastic. These composites possess both high shear strength and high peel strength.
Among adhesives processors there is an increasing desire for adhesive dispersions which despite a low activation temperature give rise to adhesive bonds which not only have a high load-bearing capacity at room temperature but which also withstand subsequent loading even at temperatures markedly above the activation temperature. This property is referred to in the art as heat resistance. Here, the maximum temperature at which the adhesive bond can still be subjected to loading without being destroyed in the process should be as far as possible above the temperature to which the adhesive film is heated to activate it prior to bonding (activation temperature). Moreover, the adhesive bonds should be capable of bearing high loads just a short time after bonding; in other words, they should have a high immediate strength.
The application PCT 98/04483 further generally discloses the use as adhesives of dispersions containing carbodiimide. Nothing, however, is stated therein regarding the method of heat activation.
SUMMARY OF THE INVENTION
It is an object of the invention to provide for improved bonding. We have found that this object is achieved by the bonding process specified at the outset.
The dispersions D that are used in the process of the invention contain carbodiimide structural units of the formula (I) preferably in amounts of from 5 to 200, with particularly preference in amounts of from 5 to 150 and, with very particular preference, in amounts of from 10 to 100 mmol per kg of polyurethane (1).
The carbodiimide structural units of the formula (I) can be incorporated into the polyurethane (1) with particular ease by synthesizing the polyurethane using, in whole or in part, diisocyanates (a1.1) which have on average from 1 to 10, preferably from 1 to 4, structural units of the formula (I).)
Examples of suitable diisocyanatocarbodiimides (a1.1) are those of the formula (Ia1.1)
OCN—(R
1
—N═C═N)
m
—R
1
—NCO (Ia1.1)
where R
1
is a divalent hydrocarbon radical with or without urethane, ester and/or ether groups, as is obtained by removing the isocyanate groups from a simple organic isocyanate or from a prepolymer containing urethane groups and, if desired, ether or ester groups and carrying terminal isocyanate groups, it being possible when there are two or more radicals R
1
in the same molecule for these radicals R
1
to have different meanings within the stated definition at the same time, and m being an integral or (on average) fractional number from 1 to 10, preferably from 1 to 4.
The radicals R
1
are preferably derived by abstracting the isocyanate groups from monomers (a1), which are the diisocyanates typically used in polyurethane chemistry.
As monomers (a1), particular mention may be made of diisocyanates X(NCO)
2
, where X is an aliphatic hydrocarbon radical having 4 to 12 carbon atoms, a cycloaliphatic or aromatic hydrocarbon radical having 6 to 15 carbon atoms, or an araliphatic hydrocarbon radical having 7 to 15 carbon atoms. Examples of such diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane, 1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 2,2-bis(4-isocyanatocyclohexyl)propane, trimethylhexane diisocyanate, 1,4-diisocyanatobenzene, 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, 4,4′-diisocyanatodiphenylmethane, 2,4′-diisocyanatodiphenylmethane, p-xylylene diisocyanate, tetramethylxylylene diisocyanate (TMXDI), the isomers of bis(4-isocyanatocyclohexyl)methane (HMDI) such as the trans/trans, the cis/cis and the cis/trans isomers, and mixtures of these compounds.
Examples of mixtures of these isocyanates are the mixtures of the respective structural isomers of diisocyanatotoluene and diisocyanatodiphenylmethane, with particular suitability being attached to the mixture comprising 80 mol % 2,4-diisocyanatotoluene and 20 mol % 2,6-diisocyanatotoluene. Further advantageous mixtures are those of aromatic isocyanates such as 2,4-diisocyanatotoluene and/or 2,6-diisocyanatotoluene with aliphatic or cycloaliphatic isocyanates such as hexamethylene diisocyanate, HMDI or IPDI, with the preferred ratio of aliphatic to aromatic isocyanates being from 4:1 to 1:4.
The radicals R
1
derive by abstracting the isocyanate groups from a prepolymer having urethane groups, ether or ester groups if desired, and terminal isocyanate groups are preferably those built up from the diols (b1) and the diisocyanates (a1.2).
The preparation of the monomers (a1.1) is known per se and is described, for example, in U.S. Pat. Nos. 2,840,589, 2,941,966 and EP-A-628 541 and by P. W. Campbell and K. C. Smeltz in Journal of Organic Chemistry, 28, 2069 (1963). Diisocyanatocarbodiimides can also be obtained in a particularly gentle manner, and free from byproducts, by heterogeneous catalysis in accordance with DE-A 2 504 400 and DE-A 2 552 350. The carbodiimidization of diisocyantes in the presence of very small amounts of phospholine oxide with subsequent blocking of the catalyst using acid chlorides is described in DE-A 2 653 120.
In general, the diisocyanates (a1.2) are used not only to prepare the diisocyanates (a1.1) but also-directly for the synthesis of the polyurethanes that are present in polyurethane dispersions of the invention, since the synthesis of the polyurethanes frequently requires more isocyanate than is necessary to inroduce the carbodiimide groups.
To synthesize the polyurethanes it is possible as compounds (a1.2) to use not only the abovementioned isocyanates but also isocyanates which in addition to the free isocyanate groups carry further blocked isocyanate groups, e.g., uretdione groups.
With a view to good filming and elasticity, compounds which are ideally suitable as diols (b1) are diols (b1.1) of relatively high molecular weight, this molecular weight being from about 500 to 5000, preferably from about 1000 to 3000 g/mol.
The diols (b1.1) are, in particular, polyester polyols which are known, for example, from Ullmanns Encyklopädie der technischen Chemie, 4th edition, Volume 19, pp. 62 to 65. It is preferred to use polyester polyols which are obtained by reacting dihydric alcohols with dibasic carboxylic acids. Instead of the free polycarboxylic acids it is also possible to use the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols or mixtures thereof to prepare the polyester polyols. The polycarboxylic acids can be aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic and can be unsubstituted or substituted, for example by halogens, and/or saturated or unsaturated. Examples are s
Licht Ulrike
Neumann Hans J.
Wistuba Eckehardt
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Yao Sam Chuan
LandOfFree
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