CA1339656C

CA1339656C - Polyurethane based multi-purpose household adhesive

Info

Publication number: CA1339656C
Application number: CA000607989A
Authority: CA
Inventors: Rainer Hoefer; Gerhard Gierenz; Wolfgang Klauck; Roland Gruetzmacher
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 1988-08-12
Filing date: 1989-08-10
Publication date: 1998-02-03
Anticipated expiration: 2015-02-03
Also published as: NO173703C; NO173703B; JPH04500083A; PT91404A; TR25089A; KR900701883A; NO910460L; IE63014B1; DE3827378A1; DK305190D0; ZA896159B; BR8907594A; EP0354471A1; CN1040386A; ATE76415T1; JP2892409B2; ES2037352T3; DE58901469D1; WO1990001508A1; PT91404B

Abstract

The invention relates to the use of a substantially clear and at least largely solventless, aqueous, one-component polyurethane dispersion based on - a polyol mixture consisting completely or partly of polytetrahydrofuran, - a difunctional or more than difunctional isocyanate component used in an OH:NCO ratio of 1:0.5 to 1:2.0, preferably 1:1.0 to 1:1.7 and more preferably 1:1.05 to 1:1.6 thereto, - a functional component capable of salt formation in aqueous solution and - optionally a chain-extending agent as a universal household adhesive.

Description

~3~!~6~6 Field of the Invention This invention relates to multi-purpose household adhesives, also known as universal household adhesives, which are used for bonding a number of substrates encountered in the home, such as paper, cardboard, photo-graphs, fabrics, leather, felt, bast, cork, films, metals such as aluminum and iron, china, ceramics, glass, wood, and various plastics, including for example polystyrene foams. These adhesives are expected to produce an adequate adhesive effect on these various substrates which differ chemically and physically in their surface structure and which are normally subjected to a special surface treatment before industrial bonding.
Statement of Related Art Compared with the large variety of classes and types of adhesive used in industry and workshops, there are only a few substances which are capable of meeting the stringent demands imposed on the versatility of a multi-purpose household adhesive. Among those substances, only polyvinyl acetate and its copolymers are widely used - normally in solution or, for gluing wood, in the form of a dispersion.
The demand for versatility represents a particularly difficult selection criterion for an adhesive. Ultimately, it means that the adhesive molecules must show high afffin-ity for both polar and apolar interfaces. Accordingly, thestatement that a certain substance is suitable as an adhe-sive does not indicate to one skilled in the art whether it can also be used as a multi-purpose household adhesive.
In addition to the versatility requirement, there has also recently been a demand for physiologically unobjectionable, transparent, aqueous multi-purpose household adhesives free from the odors associated with :~3~65~

common solvent-based adhesives. However, these adhesives are expected to produce dried films with substantial resistance to water. In addition, these water-based adhesives are also expected to be able to bond substrates that are difficult to bond, such as plastics.
This requirement profile has not heretofore been fully satisfied either by the binders hitherto preferred for multi-purpose adhesives, namely polyvinyl acetate and vinyl acetate copolymers, or by such alternatives as nitrocel-lulose. Although polyvinyl acetate can be produced withoutsolvents in the form of aqueous dispersions, the disper-sions obtained are not transparent, but milky white. They show good performance properties when used, for example, as wood glue. The acrylates and styrene acrylates widely used as dispersion adhesives are also not known commercially in the form of transparent household adhesives with the properties mentioned.
DE-OS 15 95 602, which goes back to the year 1966, broadly describes a process for the production of cati-onically modified polyurethane dispersions which containquaternary ammonium groups in a quantity of at least 0.21%
as an emulsifying component. The specification names numerous polyols, numerous isocyanate compounds, and numerous cationic salt-forming components as modifiers.
The usual chain-extending agents are also mentioned. It is possible by the process in question to produce optically almost clear colloidal dispersions of aggregates which give tack-free or tacky films. The use of the products as adhesives is also generally mentioned without any particulars.
The broad disclosure of DE 15 95 602 encompasses both polyurethane dispersions, in which polyesters are used as the OH-functional component, and also those in which poly-ethers or polyacetals are used. However, polyurethane dispersions based on polyurethanes synthesized from OH-functional polyesters are not suitable as multi-purpose h-ousehold adhesives because they undergo hydrolysis during 133965~

storage and hence do not have the required storage stability. Polyurethane dispersions based on polyethylene oxide and/or polypropylene oxide as OH-functional component are also not suitable as multi-purpose adhesives because they show poor adhesion to plastics and thus do not satisfy the versatility requirement.
Although DE 15 95 602 mentions polytetrahydrofuran as a possible polyol, there is no reference to the fact that this particular polyol is a suitable basis for polyurethane dispersions for multi-purpose household adhesives.
Published Japanese patent application No. 62(1987)-112676 published on 23 May 1987 describes an aqueous poly-urethane adhesive comprising a polyurethane which has been obtained by reaction of a polytetrahydrofuran diol with a polyfunctional isocyanate. More particularly, the published Japanese application teaches reacting polytetrahydrofuran diol (with a molecular weight of 400 to 2,000) with organic diisocyanates and a dimethylol alkanoic acid, subjecting the product of this reaction to chain extension with hydrazine and, after neutralization with a tertiary amine, reacting the product with a water-soluble epoxide or a water-soluble aziridine. Bonding is obtained by crosslinking of the carboxyl-terminated polyurethane with the polyepoxide or polyaziridine. There is no teaching in the Japanese patent application that polyure-thane dispersions of the type in question may be used, without any addition of epoxide or aziridine, as multi-purpose "single-part" household adhesives.
An object of the present invention is to provide aqueous, transparent materials that satisfy the complex and partly conflicting requirements mentioned above in regard to multi-purpose household adhesives.
Description of the Invention It has now surprisingly been found that specially selected aqueous polyurethane dispersions are excellent multi-purpose household adhesives. The polyurethane dispersions according to the invention consist of adducts 133~6~6 of polyfunctional isocyanates with selected polyfunctional hydroxy or amino compounds. The reaction products contain co-condensed units capable of salt formation in aqueous solution.
In particular, the adhesives useful in the present invention include products from reaction of:
- a polyol mixture consisting completely or partly of polytetrahydrofuran, - a difunctional or more than difunctional isocyanate component used in an OH:NCO ratio of 1:0.5 to 1:2.0, preferably 1:1.0 to 1:1.7 and more preferably 1:1.05 to 1:1.6 thereto, - a functional component capable of salt formation in aqueous solution and 15 - optionally a chain-extending agent as a universal household adhesive.
The polyurethanes forming the basis of the polyure-thane dispersions used in accordance with the invention are based on a polyol mixture consisting completely or partly of polytetrahydrofuran, in which the polytetrahydrofuran content, based on polyol mixtures, should be no less than 30% by weight and, preferably, no less than 70% by weight.
In the context of the invention, the term polytetrahydro-furan applies to polyethers which may be theoretically or actually prepared by ring-opening polymerization of tetra-hydrofuran and have a hydroxyl group at either end of the chain. Suitable products have a degree of oligomerization of from approximately 1.5 to 150 and preferably from 5 to 100 .
In addition to or instead of the polytetrahydrofuran diols, it is also possible to use the analogous compounds in which up to 50% of the tetrahydrofuran units involved in the synthesis of the polyols are replaced by ethylene oxide or propylene oxide. Among these compounds, preference is attributed to those which consist of 25 to 30 mol-% ethyl-ene oxide units and 75 to 70 mol-% tetrahydrofuran oxide units. In addition to the diols based on tetrahydrofuran, :~3396S~i the analogous diamines may also be used.
In addition, up to 70% by weight of the polytetra-hydrofuran polyols on which the polyurethane dispersions used in accordance with the invention are based may be replaced by other polyols typically used in preparations of the type in question. A general rule in this regard is that these other polyols must contain at least two reactive hydrogen atoms and should be substantially linear with a molecular weight in the range from 300 to 20,000 and pref-erably in the range from 500 to 6,000. Preferred other polyols are polyesters, polyacetals, polyethers, polythio-ethers, polyamides and/or polyester amides containing on average 2 to 4 hydroxyl groups.
Suitable polyethers are, for example, the polymeriza-tion products of ethylene oxide, propylene oxide, butyleneoxide and copolymerization and graft polymerization prod-ucts thereof and the polyethers obtained by condensation of polyhydric alcohols or mixtures thereof and the polyethers obtained by alkoxylation of polyhydric alcohols, amines, polyamines and aminoalcohols. Isotactic polypropylene glycol may also be used.
Suitable and preferred polyacetals include the compounds obtainable from glycols, such as diethylene glycol, triethylene glycol, hexanediol, and formaldehyde;
and polyacetals prepared by polymerization of cyclic acetals.
Among the polythioethers, the condensates of thiodi-glycol alone or with other glycols, dicarboxylic acids, formaldehyde, aminocarboxylic acids, or aminoalcohols are suitable and preferred. Depending on the co-components, the products are polythioethers, polythio mixed ethers, polythioether esters, or polythioether ester amides.
Hydroxyl terminated compounds such as these may also be used in alkylated form or in admixture with alkylating agents.
Suitable and preferred polyesters, polyester amides, and polyamides include the predominantly linear condensates ~3~96S6 , obtained from polybasic, saturated and unsaturated carboxylic acids or their anhydrides and polyhydric, saturated and unsaturated alcohols, aminoalcohols, diamines, polyamines, and mixtures thereof and also polyterephthalates or polycarbonates. Polyesters of lactones, for example caprolactone, or of hydroxycarboxylic acids may also be used. The polyesters may contain terminal hydroxyl or carboxyl groups. Relatively high molecular weight polymers or condensates such as, for example, polyethers, polyacetals, and polyoxymethylenes may also be used as alcohol component in the synthesis of the polyurethane dispersions used in this invention.
Hydroxyl terminated compounds and polymers already containing urethane or urea groups and modified natural polyols, such as castor oil, may also be used as part of the polyol mixture, as may other compounds containing basic nitrogen atoms such as, for example, polyalkoxylated primary amines or polyesters or polythioethers containing alkyl diethanolamine in co-condensed form. Polyols obtainable by complete or partial ring opening of epoxidized triglycerides with primary or secondary hydroxyl compounds, for example the reaction product of epoxidized soybean oil with methanol, are also suitable.
Suitable multifunctional isocyanates for reaction to make dispersions according to the invention include any aromatic and aliphatic diisocyanates such as, for example, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 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 tolylene diisocya-nate, 1-methyl-2,4-diisocyanatocyclohexane, 1,6-diisocyanato-2,2,4-trimethyl hexane, 1,6-diisocyanato-2,4,4-trimethyl hexane, 1-isocyanatomethyl-3-isocyanato-1,5,5-trimethyl cyclohexane, chlorinated and brominated diisocyanates, phosphorus-containing diisocyanates, 4,4'-diisocyanatophenyl perfluoroethane, tetramethoxy butane-~96~û

1,4-diisocyanate, butane-1,4-diisocyanate, hexane-1,6-diisocyanate, dicyclohexyl methane diisocyanate, cyclohexane-1,4-diisocyanate, ethylene diisocyanate, phthalic acid-bis-isocyanatoethyl ester, also polyisocya-S nates containing reactive halogen atoms, such as 1-chloro-methylphenyl-2,4-diisocyanate, 1-bromomethylphenyl-2,6-diisocyanate, 3,3-bis-chloromethylether-4,4'-diphenyl diisocyanate. Suitable sulfur-containing polyisocyanates may be obtained, for example, by reaction of 2 moles of hexamethylene diisocyanate with 1 mole of thiodiglycol or dihydroxydihexyl sulfide. Preferred diisocyanates include isophorone diisocyanate, which is most preferred, and trimethyl hexamethylene diisocyanate, m-and/or p-tetramethyl xylene diisocyanate, l,4-diisocyanatobutane, 1,2-diisocyanatododecane and dimer fatty acid diisocyanate.
The multifunctional isocyanates may be used individually or in mixtures. Cyclic or branched aliphatic diisocyanates, such as isophorone diisocyanate, are generally preferred.
Also suitable and of special interest are partly masked polyisocyanates which provide for the formation of self-crosslinking polyurethanes, for example dimeric tolylene diisocyanate, or polyisocyanates partly reacted, for example, with phenols, tertiary butanol, phthalimide, and/or caprolactam.
Suitable chain extending agents containing reactive hydrogen atoms include:
- saturated and unsaturated glycols, such as ethylene glycol or condensates of ethylene glycol, butane-1,3-diol, butane-1,4-diol, butenediol, propane-1,2-diol, propane-1,3-diol, neopentyl glycol, hexanediol, bis-hydroxymethyl cyclohexane, dioxyethoxy hydroquinone, terephthalic acid-bis-glycol ester, succinic acid di-2-hydroxyethyl amide, succinic acid di-N-methyl-(2-hydroxyethyl)-amide, 1,4-di-(2-hydroxymethylmercapto)-2,3,5,6-tetrachlorobenzene, 2-methylene propane-1,3-diol, 2-methylpropane-1,3-diol;
- aliphatic, cycloaliphatic and aromatic diamines, such 1~96~&

as ethylenediamine, hexamethylenediamine, 1,4-cyclo-hexylenediamine, piperazine, N-methyl propylenedi-amine, diaminodiphenylsulfone, diaminodiphenyl ether, diaminodiphenyl dimethylmethane, 2,4-diamino-6-phenyl triazine; and 3,3'-dibromo-4,4'-diaminodiphenyl methane (diamines known to be health hazards, such as for example hydrazine, diaminodiphenyl methane, the isomers of phenylenediamine, carbohydrazides, and hydrazides of dicarboxylic acids are not recommended;) 10 - aminoalcohols, such as ethanolamine, propanolamine, butanolamine, N-methyl ethanolamine, N-methyl isopropanolamine;
- aliphatic, cycloaliphatic, aromatic and heterocyclic mono- and diaminocarboxylic acids, such as glycine, 1-and 2-alanine, 6-aminocaproic acid, 4-aminobutyric acid, the isomeric mono- and diaminobenzoic acids, the isomeric mono- and diaminonaphthoic acids; and - water.
Suitable special chain-extending agents containing at least one basic nitrogen atom include, for example, mono-, bis- or polyalkoxylated aliphatic, cycloaliphatic, aromatic or heterocyclic primary amines, such as N-methyl diethanolamine, N-ethyl diethanolamine, N-propyl diethanolamine, N-isopropyl diethanolamine, N-butyl diethanolamine, N-isobutyl diethanolamine, N-oleyl diethanolamine, N-stearyl diethanolamine, ethoxylated coconut oil fatty amine, N-allyl diethanolamine, N-methyl diisopropanolamine, N-ethyl diisopropanolamine, N-propyl diisopropanolamine, N-butyl diisopropanolamine, N-cyclohexyl diisopropanolamine, N,N-diethoxylaniline, N,N-diethoxyl toluidine, N,N-diethoxyl-l-aminopyridine, N,N'-diethoxyl piperazine, dimethyl-bis-ethoxyl hydrazine, N,N'-bis-(2-hydroxyethyl)-N,N'-diethylhexahydro-p-phenylenediamine, N-12-hydroxyethyl piperazine, polyal-koxylated amines, such as propoxylated methyl diethanol-amine, also such compounds as N-methyl-N,N-bis-3-aminopro-pylamine, N-(3-aminopropyl)-N,N'-dimethyl ethylenediamine, ~3965~

N-(3-aminopropyl)-N-methyl ethanolamine, N,N'-bis-(3-aminopropyl)-N,N'-dimethyl ethylenediamine, N,N'-bis-(3-aminopropyl)-piperazine,N-(2-aminoethyl)-piperazine,N,N'-bisoxyethyl propylenediamine, 2,6-diaminopyridine, dieth-anolaminoacetamide, diethanolamidopropionamide, N,N-bis-oxyethylphenyl thiosemicarbazide, N,N-bis-oxyethylmethyl semicarbazide, p,p'-bis-aminomethyl dibenzyl methylamine, 2,6-diaminopyridine,2-dimethylaminomethyl-2-methylpropane-1,3-diol.
Suitable chain-extending agents containing R-S020-groups and/or halogen atoms capable of quaternization include, for example, glycerol-l-chlorohydrin, glycerol monotosylate, pentaerythritol-bis-benzenesulfonate, glycerol monomethanesulfonate, adducts of diethanolamine and chloromethylated aromatic isocyanates or aliphatic haloisocyanates, such as N,N-bis-hydroxyethyl-N'-m-chloromethyl phenylurea, N-hydroxyethyl-N'-chlorohexyl urea, glycerol monochloroethyl urethane, bromoacetyl dipropylene triamine, and chloroacetic acid diethanolamide.
The polyurethanes on which the polyurethane disper-sions used in accordance with the invention are based con-tain a functional component capable of salt formation in aqueous solution as a necessary constituent. This functional component may be a dihydroxy or a diamino compound containing an ionizable carboxylic acid, sulfonic acid, or ammonium group. These compounds may either be used as such or they may be prepared in situ. To introduce compounds bearing ionizable carboxylic acid groups into the polyurethane, one skilled in the art may add dihydroxycar-boxylic acids to the polyols. A preferred dihydroxycar-boxylic acid is dimethylolpropionic acid.
To introduce sulfonic acid groups capable of salt formation, a diaminosulfonic acid may be added to the polyols. Examples are 2,4-diaminobenzenesulfonic acid and also the N-(~-aminoalkane)-~-aminoalkanesulfonic acids described in DE 20 35 732.
To introduce ammonium groups capable of salt formation 13~6~6 into the polymer, it is also possible in accordance with DE
15 95 602 cited above to modify the polyurethane prepolymer with an aliphatic or aromatic diamine in such a way the chains are terminated by primary amino groups which may then be converted into quaternary ammonium compounds or into amine salts with standard alkylating agents.
It is preferred to make the polyurethane prepolymers to be used soluble in water by means of carboxylic acid or sulfonic acid groups because polyurethane dispersions containing anionic modifiers such as these can be removed under alkaline conditions, i.e. adhesives of the type in question can be removed from certain substrates, for example from fabrics, by washing under proper conditions.
The polymers are present at least partially in salt form in the polyurethane dispersions used in accordance with the invention. In the case of the preferred polymers modified with carboxylic acids or sulfonic acids, alkali metal salts, ammonia, or primary, secondary, or tertiary amines, are preferably present as counterions. In the cationically modified products, acid anions, for example chloride, sulfate, or the anions of organic carboxylic acids, are present as counterions. The groups capable of salt formation may be completely or partly neutralized by the counterions. An excess of neutralizing agent is also possible.
As already mentioned in the discussion of the chain extending agents to be used according to the invention, compounds which are known to be dangerous or detrimental to health are not desirable in the adhesives. This is especially important because the present invention provides a very versatile adhesive which is likely be used by types of people, such as children, the elderly, people with illnesses, and pregnant women, whose health is particularly at risk. Therefore in a particularly preferred embodiment, not only the chain extending agents but also the remaining components of the adhesive are selected in as far as possible to be physiologically unobjectionable. In this ~3~96~6 connection for example, the partial or, if possible, total absence of organic solvents is to be aimed at. In this connection also, it is worth noting that the much discussed danger to health of polyurethane adhesives containing free isocyanate or unreacted isocyanate groups of the polymers or prepolymers does not occur in the present invention, because the polyurethanes are dispersed in water and the isocyanate groups, as is known to those skilled in the art, react very rapidly with the water. Thus it can be guaranteed that the polyurethane dispersions according to the invention contain no physiologically offensive reactive NCO groups.
To produce the polyurethanes particularly suitable for the purposes of the invention, the polyols and an excess of diisocyanate are preferably reacted to form an isocyanate-terminated polymer, suitable reaction conditions including reaction times and temperatures being chosen for the par-ticular isocyanate(s) used. One skilled in the art knows that the reactivity of the constituents to be reacted necessitates maintenance of a suitable balance between reaction velocity and unwanted secondary reactions which lead to discoloration and a reduction in molecular weight.
The reaction is typically carried out with stirring over approximately 1 to 6 hours at approximately 50~C to approx-imately 120DC.
The preferred production process is the so-called acetone process described by D. Dietrich, Angew. Makromol.
Chem., 98, 133 (1981). The polyurethane dispersions used in accordance with the invention may also be produced by the process according to DE 15 95 602. A more recent suitable process for the production of polyurethane dispersions is described in DE 36 03 996 and in the prior art cited therein, namely: DE-PS 880 485, DE-AS 10 44 404, US-PS 3,036,998, DE-PS 11 78 586, DE-PS 1 184 946, DE-AS 12 37 306, DE-AS 14 95 745, DE-OS 15 95 602, DE-OS 17 70 068, DE-OS 20 19 324, DE-OS 20 35 732, DE-OS 24 46 440, DE-OS 23 45 256, DE-OS 24 27 274, US-PS 3,479,310 and Angewandte 6 5~ ~

Chemie 82, 53 (1970) and Angew. Makromol. Chem. 26, 85 et seq (1972).
Of the processes mentioned, the "acetone process"
according to DE-OS 14 95 745 (= US-PS 3,479,310) and DE-OS
14 95 847 (GB-PS 1,067,788) is of particular importance.
In this process, an NCO-terminated prepolymer is generally first prepared and then dissolved in an inert solvent, followed by chain extension in solution to form the high molecular weight polyurethane. The hydrophilic groups required for dispersion are preferably introduced either by the incorporation of diols bearing ionic and/or potentially ionic and, optionally, nonionic hydrophilic groups into the prepolymer or by the use of corresponding amines as chain-extending agents. Dispersion takes place continuously in tanks equipped with stirrers and, optionally, baffles. The solvent used is generally distilled off from the stirred tank immediately after dispersion in water.
Other processes for the production of polyurethane prepolymers, more especially for the continuous production of polyurethane prepolymers, are described in DE-OS 22 60 870, 23 11 635 and 23 44 135.
To obtain substantially clear, i.e. from water-clear and transparent to translucent, polyurethane dispersions according to the invention, it is important to maintain an appropriate ratio between the component(s) capable of salt formation and the other polyurethane-forming components.
Thus, it is preferred to use the component capable of salt formation, when it is dimethylolpropionic acid, in quantities of from 1 to 30~ by weight, more preferably in quantities of from 2 to 20% by weight, and most preferably in quantities of from 10 to 18% by weight, based on total polyol reacted to form the urethane. In addition, the transparency depends on the degree of neutralization. One skilled in the art is able, through a few preliminary tests, to determine what quantity of modifier capable of ion formation and what quantity of neutralizing agent produce an adequate degree of transparency. In general, as ~3396~

little of these components as possible to obtain the needed degree of transparency will be used, because they can adversely affect the water resistance of the adhesive film if used in excessive quantities.
The polyurethane dispersions according to the inven-tion are two-phase aqueous/polyurethane dispersions, pref-erably comprising the polyurethane phase as a colloid or sol, with a particle size of 10 to 100 nanometers. These dispersions are preferably optically translucent to transparent, and are to be distinguished from optically clear "true" solutions.
The solids content of the adhesive solutions according to the invention may be varied within wide limits. Solids contents of from 20 to 70% by weight and preferably from 30 to 50% by weight have proved effective in practice.
The practice of the invention may be further appreciated from the following operating examples and comparison examples.
E x a m p 1 e s General Synthesis Procedure The polyols are dissolved or dispersed in acetone.
The component capable of ion formation is then added with stirring. Diisocyanate is then added at temperatures of 50 to 70~ C until there is no further reduction in the NCO
content. The reaction mixture is then neutralized at 60~
C, for example with N-methyl morpholine. After about 30 minutes, water is added. After dispersion for 30 minutes, the acetone is distilled off, ultimately under a fairly high vacuum at temperatures of 55 to 60~ C.
The ingredients used in the Example according to the invention and in Comparison Example 1 are shown in Table 1.
Some results of adhesion tests with these adhesives and two other commercial types of household adhesives are shown in Table 2.

1~39~56 Table 1 Ingredient Parts by Weiqht (pbw) Used in:
Example Comparison ExamPle 1 -Polytetrahydrofuran 100 pbw Glycerol-started polyether - 100 pbw polyol, OH value 34 Oleochemical polyol - 82 pbw according to DE 37 04 350, OH value 160 Dimethylolpropionic acid lS.58 pbw 21.50 pbw Acetone 50 pbw 50 pbw Isophorone diisocyanate 48.9 pbw 98.05 pbw N-methyl morpholine 11.63 pbw 16.04 pbw Deionized water 233 pbw 450 pbw Table 2 Substrates Tensile Shear Strength in Newton-meters Bonded Per Square Meter of Bonded Surface*
Example Comparison Universal PVAc Example 1 adhesive, disper-solvent- sion based Wood/PVC 6.0 1.4 n.d. 1.6 Wood/wood 8.5 4.5 6-7 3.0 Wood/alu 6.0 4.9 1.4 2.0 Wood/ABS 5.0 1.4 5.5 with 1.5 swelling of the ABS

PVC = poly(vinyl chloride) plastic; alu = aluminum metal;
ABS = acrylonitrile-butadiene-styrene plastic; n.d. = not determined; * indicates measured according to DIN 53 254.

.~3~65~
Test of Speed of Bond Formation For this test, a 60 ~m thick adhesive film was applied to chromo paper with a wire wound coating bar. Immediately another piece of the same paper was pressed against the wet adhesive film. The two pieces of paper were slowly rubbed against one another until the development of an adhesive bond caused one of the pieces of paper to tear. The time to such tearing was found to be as shown in Table 3.

Table 3 Example Comparison Universal adhesive PVAc disper-Example 1 solvent-based sion 15 secs. 20 secs. 70 secs. 25 secs.

Additional comparison examples were prepared in the same general manner as indicated above for the preparation of the Example and Comparison Example 1, but using a polyester diol that is conventional for making polyurethanes, rather than a polyether diol as required for this invention, to be reacted to produce the polyurethane used in these comparison examples.
Additional information about the diol used and the amounts of various ingredients used to make the polymers is shown in Table 4, as are the results of the adhesion tests done with these products.
Storage Test Polyurethane dispersions made according to the Example and according to Comparison Example 1 to 4 were subjected to a storage test at temperatures of 50~C. The observed change in viscosity is shown in Table 5.
The results in Tables 4 and 5 show that with some of the comparative Examples, notably Comparative Example 4, one can initially obtain adhesive strengths about as good as with the Examples according to the invention. The Comparative Examples, however, have far less storage stability. On the other hand, Comparison Example 1 has 13396.56 o 0 ~ ~ ~ ~
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s ~I U ~ ~ C~
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Dispersion Made Initial y~scOsity after Accordinq to: viscosity, A 3 r~nth~, Pascal-seconds ~c,al-seconds ~)oS~1~3. ~_ Example 4.000 ~_L,~o-~~~
Comparison Example 1 4.000 3.700 Comparison Example 2 3.700 0.180 Comparison Example 3 3.500 0.120 Comparison Example 4 3.600 0.410 reasonably good storage stability but substantially poorer adhesion for all the substrates shown in Table 2. Thus the Example according to the present invention possesses a unique combination of properties: the ability to bond strongly a wide variety of materials, including paper, wood, metal, and several plastics; no loss in viscosity after three months storage; transparency; and freedom from any significant amount of organic solvents, with their associated nuisance of odor and hazard of fire.

Claims

1. A universal household adhesive which is a substantially clear and at least largely solventless, aqueous, one-part polyurethane dispersion based on the reaction products of - a polyol mixture consisting completely or partly of polytetrahydrofuran, - a difunctional or more than difunctional isocyanate component used in an OH:NCO ratio of 1:0.5 to 1:2.0, and -dimethylol propionic acid as a functional component capable of salt formation in aqueous solution, suitable for use as a universal household adhesive, wherein the amount of dimethylol propionic acid is from 10% to 18% by weight of the amount of the polyol mixture.

2. An adhesive as claimed in claim 1, wherein the OH:NCO
ratio is 1:1.0 to 1:1.7.

3. An adhesive as claimed in claim 2, wherein the OH:NCO
ratio is 1:1.05 to 1:1.6.

4. An adhesive as claimed in claim 1, containing a chain-extending agent.

5. An adhesive as claimed in claim 1, wherein 30 to 100%
by weight of the polyol mixtures on which the polyurethane dispersions are based consist of polytetrahydrofuran and 0 to 70% by weight of the polyol mixtures consist of other polyether polyol, polyacetal polyol and/or polyester polyol, all containing an average 2 to at most 4 OH groups.

6. An adhesive as claimed in claim 4, wherein 70 to 100%
by weight of the polyol mixtures on which the polyurethane dispersions are based consist of polytetrahydrofuran.

7. An adhesive as claimed in any of claims 1, 5, or 6, wherein the polyurethanes on which the polyurethane dispersions are based are synthesized from difunctional or more than difunctional aliphatic and/or aromatic diisocyanates.

8. An adhesive as claimed in any of claims 1, 5, or 6, the polyurethanes on which the polyurethane dispersions are based are synthesized from difunctional or more than difunctional branched and/or cyclic aliphatic diisocyanates.

9. An adhesive as claimed in any of claims 1, 5, or 6, the polyurethanes on which the polyurethane dispersions are based contain carboxylic acids, sulfonic acid or ammonium compounds containing 1 to 2 hydroxyl groups or isocyanate-reactive amino groups in co-condensed form as components capable of salt formation in aqueous solution.

10. An adhesive as claimed in any of claims 1, 5 or 6, wherein the polyurethanes on which the polyurethane dispersions are based contain co-condensed carboxylic acids or sulfonic acids present in the form of an alkali salt, ammonium salt or salt of primary, secondary or tertiary amines.

11. An adhesive as claimed in any of claims 1, 5 or 6, wherein the polyurethanes on which the polyurethane dispersions are based contain isocyanate-reactive diamines or dihydroxy compounds as chain-extending agents.

12. An adhesive as claimed in any of claims 1, 5 or 6 wherein the particle size responsible for the clear appearance of the polyurethane dispersions used is controlled through the quantity of groups capable of salt formation in aqueous solution.

13. An adhesive as claimed in any of claims 1, 5 or 6, wherein the quantity of the salt forming groups, expressed as dimethylolpropionic acid, is from 1 to 70% by weight, based on polyol.

14. An adhesive as claimed in any of claims 1, 5 or 6, wherein the quantity of the salt forming groups, expressed as dimethylolpropionic acid, is from 2 to 30% by weight, based on polyol.

15. An adhesive as claimed in any of claims 1, 5 or 6, wherein the quantity of the salt forming groups, expressed as dimethylolpropionic acid, is from 10 to 18% by weight, based on polyol.

16. An adhesive as claimed in any of claims 1, 5 or 6, wherein the particle size responsible for the clear appearance of the polyurethane dispersions used is adjusted through the quantity of neutralizing agent added for the functional groups capable of salt formation.

17. A process for the production of a substantially clear universal household adhesive wherein - an NCO-terminated prepolymer is initially prepared from - a polyol mixture consisting completely or partly of polytetrahydrofuran, - a difunctional or more than difunctional isocyanate component used in an OH:NCO ratio of 1:1.0 to 1:1.7, and - dimethylol propionic acid as a functional component capable of salt formation in aqueous solution, - and is then dissolved in an inert solvent, - dispersion is then carried out discontinuously in stirred tanks comprising stirrers and, optionally baffles, and - the solvent used is distilled off from the stirred tank, if desired immediately after dispersion in water.

18. A process for the production of the universal household adhesive according to claim 17, wherein the difunctional or more than difunctional isocyanate component in the preparation of the NCO-terminated prepolymer is used in an OH:NCO ratio of 1:1.05 to 1:1.6.

19. A process for the production of the universal household adhesive according to claim 17 or 18, wherein - the polyol component is diluted with acetone or is dissolved or dispersed therein, - the dimethylol propionic acid is added with stirring, - diisocyanate is added at temperatures of 50 to 70°C
until there is no further reduction in the NCO content, - the product is neutralized at 60°C, - water is added after about 30 minutes, and - after dispersion for 30 minutes, the acetone is distilled off, subsequently in a relatively high vacuum at temperatures of 55 to 60°C.