One-component reactive adhesive based on polyurethane.

The invention relates to polyurethane reactive compositions and their use as one-pot adhesive systems.

Thermosetting one-component reactive adhesives based on solid, finely divided polyisocyanates stabilized by polyadduct coating and compounds which are reactive with isocyanates, such as polyols and polyamines, are well known in the patent literature (see, for example, EP-A-62 780, 100 508 and 153 579 and DE -A-31 12 054, 32 28 723 and 34 03 499).

There is a strong interest in the bonding of car body parts made of, for example, glass fiber reinforced polyester resin (SMC). Up to now, the usual adhesives that achieve the final strength through the application of heat are not real one-component adhesives, but two-component adhesives with a very long pot life or mixtures that react over more than one step.

When gluing SMC parts, the heat is usually transferred to the parts to be joined and thus also to the adhesive layer by means of metal heating jaws, which are adapted to the contour of the parts to be manufactured and through which heated thermal oil flows. Heating in the heating jaw process is much faster than heating in a convection oven, in which air, rather than metal, serves as the heat-transfer medium. This means that short cycle times are possible. Previously common two-component adhesives, in which at least the polyisocyanate is contained as a continuous phase, continue to react slowly after the first heat surge and the loss of heat even at room temperature until the final strength.

Heat-curable one-component adhesives of the type described, based on powdery solid polyisocyanates, require constant heat from the outside to react. A hitherto unsolved problem in the bonding of SMC parts with the heating jaw technology was therefore to use the one-component adhesive in the first setting step (e.g. 2nd min at 120 ° C) to the extent that good manageability is achieved (hand strength> 1N / mm²), and the bond in the course of the thermal aftertreatment (painting furnace) reaches its final strength.

The speed at which the adhesive mass is brought to the setting temperature is obviously very important for the build-up of cohesion (strength due to high molecular structure) and adhesion (physical and chemical interactions of the adhesive boundary layer with the surface of the part to be joined).

In the convection oven, the heat is supplied relatively slowly. The temperature in the adhesive film also rises relatively slowly and the reactants have enough time to react by diffusion and chemical reaction to a high-molecular substance with good adhesion to the surface of the part to be bonded, i.e. to a real adhesive.

In the heating baking process, the heating takes place so quickly that the adhesive solidifies but cannot develop any adhesion to the surface of the part to be joined. In such cases, a subsequent heat treatment can no longer bring about the adhesion that is required for an adhesive.

The object of the present invention was to provide improved adhesives, in particular for rapid heating systems.

The invention relates to polyurethane reactive compositions containing at least one polyisocyanate and at least one polyol B, characterized in that they contain<ul id="ul0001" list-style="none"><li>A) a polyisocyanate</li><li>B) a polyol mixture obtainable from the polyols B1, 92 and B3, each having at least three hydroxyl groups, where B1 a molecular weight of 800 to 6,000, B2 a molecular weight of 400 to 799 and B3 has a molecular weight of 92 to 399 and</li><li>C) a polyamine.</li></ul>

The molecular weight is defined as the number average of all molar masses occurring in the polyol in question. The number average M_n (as opposed to the weight average) the molecular weight is defined as<maths id="math0001" num=""><img file="EP0402728A2_D0001.tif" /></maths> that is the number n of molecules i with the molecular mass M divided by the total number of all molecules.

For 1 mole of component B2 there are preferably: Component B1: 0.03-3 mol, in particular 0.1-1.0 mol, Component B3: 0.03-5 mol, in particular 0.1-2 mol.

Preferred polyisocyanates A have a melting point above 40 ° C., preferably above 80 ° C., for example 1,5-naphthalene diisocyanate, dimeric 4,4'-diisocyanatodiphenylmethane, dimeric 2,4-diisocyanatotoluene, 3,3'-diisocyanato-4,4 ' -dimethyl-N, N'-diphenylurea and N, N'-bis- [4- (4- or 2-isocyanatophenylmethyl) phenyl] urea. Dimeric 2,4-diisocyanatotoluene is particularly preferred.

The polyisocyanates are preferably stabilized by the action of, for example, aliphatic polyamines with molecular weights of 32 to 399 and, if appropriate, by the action of aliphatic polyamines with molecular weights of 400 to 8000. Examples of such polyamines are: ethylenediamine, 1-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, diethylenetriamine, methylnonanediamine.

Other suitable stabilizers are, for example: hydrazine, mostly in the form of hydrazine hydrate, C₁-C₆-alkyl-substituted hydrazines, for example methylhydrazine, ethylhydrazine, hydroxyethylhydrazine or N, N′-dimethylhydrazine, compounds with hydrazide end groups such as, for example, carbodihydrazide, ethylene bis-carbazinester, β-semicarbazido-propionic acid hydrazide or isophorone-bis-semicarbazide. Further deactivating agents are listed in DE-A-3 230 757 and 3 112 054 and EP-A-103 325 and 62 780.

Open-chain, mono- or bicyclic amidines or guanidines which have no hydrogen atoms reactive towards isocyanates can also be used as stabilizers for the isocyanate component. Examples of such compounds are: tetramethylguanidine, pentamethylguanidine, 1,2-dimethyl-tetrahydropyrimidine, 1,8-diaza-bicyclo [5,4,0] -undec-7-ene, 1,5-diaza-bicyclo [4 , 3.0] non-5s. Further examples of such amidines are listed in DE-A-3 403 500.

Liquid or low-melting (&lt;80 ° C, preferably &lt;60 ° C) low and / or higher molecular weight polyols and / or polyamines are used as NCO-reactive suspending agents for the solid, stabilized polyisocyanates.

Preferred polyols B1 to B3 are polyesters, polythioethers, polyacetals, polycarbonates, polyesteramides and in particular glycols and polyethers. Examples of these are listed, for example, in DE-A-2 920 501, DE-A-2 854 384 and DE-A-3 230 757.

If appropriate, it is also possible to use polyhydroxyl compounds which contain high molecular weight polyadducts or polycondensates or polymers in finely dispersed or else dissolved form (filled polyols)

Polyhydroxy compounds containing polyadduct are obtained if polyaddition reactions (for example reactions between polyisocyanates and amino-functional compounds) or polycondensation reactions (for example between formaldehyde and phenols and / or amines) are carried out in situ in the abovementioned compounds containing hydroxyl groups.

Polyhydroxyl compounds modified by vinyl polymers, as obtained, for example, by polymerizing styrene and acrylonitrile in the presence of polyethers or polycarbonate polyols, are also suitable for the process according to the invention. Representatives of these compounds to be used according to the invention are, for example, in High Polymers, Vol. XVI, "Polyurethanes, Chemistry and Technology", written by Saunders-Frisch, Interscience Publishers, New York, London, Volume I, 1962, pages 32-42 and pages 44 and 54 and Volume II, 1964, pages 5-6 and 198 -199, as well as in the plastics manual, volume VII, Vieweg-Höchtlen, Carl-Hanser-Verlag, Munich, 1966, for example on pages 45 to 71, and in DE-2 854 384 and 2 920 501.

Suitable polyols are also hydroxyl-containing polymers, for example copolymers of olefinically unsaturated monomers and olefinically unsaturated monomers with active hydrogen. They are described, for example, in EP-A 62 780, page 5 and their examples. They are preferably used for sealing, filling, adhesive or underbody protection compounds.

Mixtures of the abovementioned compounds with at least two hydrogen atoms which are reactive toward isocyanates, for example mixtures of polyethers and polyesters, can be used within each of the three molecular weight ranges mentioned.

Low molecular weight chain extenders or crosslinkers are also suitable as polyols B3 which may be present in the suspensions. These chain extenders or crosslinkers are in particular at least three-functional compounds which have hydroxyl groups bonded to aliphatic and / or cycloaliphatic groups and have molecular weights between 92 and 399. Low molecular weight triols with hydroxyl groups of molecular weight range 92 to 399 bound to aliphatic or cycloaliphatic groups are preferred.

These compounds generally have 3 to 8, preferably 3 to 4, but particularly preferably 3, hydroxyl groups. Mixtures of different compounds can also be used, in particular trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, glycerol, pentaerythritol, quinite, mannitol, sorbitol, castor oil and formose or formite.

Also suitable are tertiary amine-containing polyols, for example triethanolamine.

Polyhydroxyl compounds already containing urethane or urea groups and optionally modified natural polyols, such as castor oil, carbohydrates or starch, can also be used. Addition products of alkylene oxides with phenol-formaldehyde resins or with urea-formaldehyde resins can also be used in the process according to the invention. In a particularly preferred embodiment, the polyol mixture B1 to B3 consists at least in part of prepolymers which can be obtained by reaction with at least one isocyanate. However, pre-extended mixtures cannot be used.

To prepare the prepolymers containing hydroxyl groups, the abovementioned low and high molecular weight polyols are modified by pre-reaction with a deficit of polyisocyanate.

Suitable polyisocyanates for the modification of the polyols B1 to B3 are aliphatic, cycloaliphatic, araliphatic, aromatic and / or heterocyclic polyisocyanates, as are listed, for example, in DE-A-2 920 501 (pages 12 to 16).

The technically easily accessible polyisocyanates, e.g. B. 2,4- and 2,6-tolylene diisocyanate as well as any mixtures of these isomers ["TDI"), polyphenyl-polymethylene polyisocyanates, such as those produced by aniline-formaldehyde condensation and subsequent phosgenation ("crude MDI"), 4, 4'- and / or 2,4'-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (IPDI), perhydro2,4'- and / or -4,4'-diphenylmethane diisocyanate.

Liquid, low and / or higher molecular weight, aromatic and / or aliphatic polyamines, in particular with a molecular weight of 700 to 4500, can be used as polyamine C. High molecular weight aliphatic polyamines are preferred, optionally with minor amounts of low molecular weight aliphatic polyamines.

In a preferred embodiment, higher molecular weight polyamino compounds with aliphatic amino groups with an equivalent weight range from 250 to 2000, preferably from 300 to 750, are used, as are obtained, for example, by reductive amination of polyoxyalkylene glycols with ammonia according to BE-PS 634741 and US Pat. No. 3,654,370. Further higher molecular weight polyoxyalkylene polyamines can be prepared by methods such as those listed in the company publication "Jeffamine, Polyoxypropylene Amines" by Texaco Chemical Co., 1978, for example by hydrogenation of cyanoethylated polyoxypropylene glycols (DE-A-1 193 671), by amination of polypropylene glycol sulfonic acid esters (US Pat. No. 3,236,895), by treating a polyoxyalkylene glycol with epichlorohydrin and a primary amine (FR-PS 1 466 708) or by reacting NCO prepolymers with hydroxyl-containing enamines, aldimines or ketimines and subsequent hydrolysis according to DE-A-2 546 536. Suitable higher molecular weight aliphatic di- and polyamines are also those according to DE-A-29 48 419, DE-A-3 039 600, DE-A-3 112 118, EP-A-61 627, EP-A-71 132 and EP-A-71 139 by alkaline hydrolysis of NCO prepolymers (with aliphatic diisocyanates) with bases via the polyamines accessible via the carbamate stage.

The process according to DE-A-2 948 419 and the other references cited are preferably polyether polyamines, but also polyester, polyacetal, polythioether or polycaprolactone polyamines, preferably 2- or 3-functional polyamines, which Contain urethane groups (from the reaction of the corresponding higher molecular weight polyhydroxyl compounds with the excess polyisocyanates) and carry the amino groups on the rest of the (former) polyisocyanate. However, the higher molecular weight polyamines can also be prepared by other processes, for example by reacting NCO prepolymers with excess amounts of diamines in accordance with DE-AS 1 694 152; FR-PS 1 415 317 describes another synthesis possibility by converting the NCO prepolymers with formic acid into the N-formyl derivatives and saponifying them.

These higher molecular weight, aliphatic polyamines can be used both as stabilizers for the polyisocyanate component and as a suspension medium and reactive component C component.

Very particularly preferred polyamines C are polyethers with polyalkylene oxide units which are added to aromatic starting molecules.

In addition, low molecular weight chain extenders D can be used, in particular low molecular weight aromatic diamines in the molecular weight range 108 to 399, which may also contain the amino groups bonded to heterocyclic radicals with an aromatic character.

The conventional polyurethane catalysts, with particularly good effect tertiary amines or metal catalysts, can optionally be used.

These are, for example, tertiary amines, such as triethylamine, tributylamine, N, N, N ′, N′-tetramethylethylenediamine, 1,4-diaza-bicyclo- (2,2,2) -octane, N, N-dimethylbenzylamine, N, N-dimethylcyclohexylamine.

In particular, organic tin compounds and lead compounds are suitable as catalysts as organic metal compounds. Suitable organic tin compounds are preferably tin (II) salts of carboxylic acids such as tin (II) ethylhexoate and tin (II) stearate and the dialkyltin salts of carboxylic acids, such as dibutyltin dilaurate or dioctyltin diacetate. Preferred organic lead compounds are lead (II) salts of carboxylic acids such as lead (II) naphthenate, lead (II) ethylhexoate, lead (II) stearate, but also, for example, lead (II) bis-diethyldithiocarbamate.

Further representatives of catalysts to be used according to the invention and details on the mode of action of the catalysts are in the plastics manual, volume VII, edited by Vieweg and Höchtlen, Carl-Hanser-Verlag, Munich 1966, for example on pages 96 to 102, and in DE -A 3 230 757.

The catalysts are generally used in an amount between about 0.001 and 10% by weight, based on the overall composition.

Auxiliaries and additives which may be mentioned are: dyes or pigments, fillers such as heavy spar, chalk, quartz powder, diatomaceous earth, silica gel, precipitated silicas, pyrogenic silicas, gypsum, talc, activated carbon, carbon black, metal powder.

It is also possible to use reaction retarders, for example acidic substances such as hydrochloric acid, organic acid halides or organic acids, further flame retardants of the type known per se, for example tris-chloroethylphosphate or ammonium phosphate and polyphosphate, and stabilizers against the effects of aging and weathering such as phenolic antioxidants and light stabilizers, Plasticizers and fungistatic and / or bacteriostatic substances are used.

Examples and details on the use and mode of action of these additives can be found in the Kunststoff-Handbuch, Volume VI, published by Vieweg and Höchtlen, Carl-Hanser-Verlag, Munich 1966, for example on pages 103 to 113 and in DE-A-2 854 384 and 2 920 501.

Depending on the viscosity and melting behavior of the starting components and on the type and amount of fillers added, more or less viscous PU reactive adhesive mixtures are obtained at room temperature. These reactive adhesive mixtures are suspensions of a solid polyisocyanate stabilized in the polyol and polyamine component by a polyadduct coating. These mixtures are solidified by the action of heat, for example by heating baked with thermal oil. The processing of the systems according to the invention depends on their nature and the technical task. You can, for example, by hand or using a suitable squeezing or conveying device, e.g. using a cartridge or a squeegee, on the materials to be bonded, e.g. items made of bare or pre-coated metal, glass, glazed ceramics, or plastics, which can also be made with glass fibers can be reinforced, applied.

Unless otherwise stated, the amounts in the examples relate to parts by weight.

example 1

Production of the OH prepolymer:

To a mixture of 60.5 parts of a 17.5% polyoxypropyleneoxyethylene ether triol. Ethylene oxide as the end block, the 0H number 34 and the molecular weight 4950, 35 parts of polyoxypropylene ether triol, the OH number 370 and the molecular weight 450, and 4.5 parts of trimethylolpropane (OH number 1254, molecular weight 134) are heated (80 ° C. ) 0.1 part of Pb octoate and 5 parts of isophorone diisocyanate (molecular weight 222) were slowly added dropwise with stirring. The mixture is subsequently stirred at 100 ° C. for 1 hour, finally with the application of a vacuum, and an OH prepolymer mixture having a viscosity of 8000 mPa.s is obtained at room temperature (25 ° C.).

To 63.36 parts of the OH prepolymer, 40 parts of a polyoxypropylene ether diamine of NH number 112, molecular weight 1000, which was obtained from a polyoxypropylene ether diol started on 2,2-bis (4-hydroxyphenyl) propane by pressure amination with NH₃, and a further 0.2 parts of Pb octoate, 0.2 parts of a 33% solution of DABCO in dipropylene glycol, 9 Parts of Aerosil R202 (hydrophobicized pyrogenic silica from DEGUSSA) and 0.10 parts of 4,4'-diamino-3,3'-dimethyldicyclohexylmethane were added, and finally 54.21 parts of dimeric 2,4-diisocyanatotoluene were suspended. A thixotropic suspension which is stable up to 50 ° C. and has a viscosity of approx. 70,000 mPa.s at room temperature is obtained. Thickening temperature: 84 ° C. Hardness after solidification at 120 ° C: 60 Shore D.

Testing the adhesive properties

Joining parts made of a 20 mm x 40 mm x 4 mm (SMC) polyester resin reinforced with 30% glass fibers serve as test material.

In addition to the glass fiber reinforced polyester, Makrolon (poly-hexanediol carbonate) and Duran glass were used as further test materials. After applying the adhesive, two strips of joint are put together in such a way that an overlapped area of ​​10 x 20 mm and an adhesive film thickness of approx. 0.2 mm are created. The test specimens are firmly bonded to one another (heat-bonded) under the conditions specified below.

After the test specimens had been stored for one hour at room temperature, the shear strength was determined in accordance with DIN 53 283 with a spindle feed of 100 mm per minute.

The results are shown in the following table. <tables id="tabl0001" num="0001"><table frame="topbot"><tgroup cols="4" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Parts to be joined</entry><entry namest="col2" nameend="col2" align="center">Tensile shear strength in N / mm²</entry><entry namest="col3" nameend="col3" align="center">Curing conditions</entry><entry namest="col4" nameend="col4" align="center">Test temperature</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">SMC / SMC</entry><entry namest="col2" nameend="col2" align="char" char=",">1,6</entry><entry namest="col3" nameend="col3" align="left">2nd min 120 ° C heating jaws</entry><entry namest="col4" nameend="col4" align="left">Room temperature</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">SMC / SMC</entry><entry namest="col2" nameend="col2" align="char" char=",">8,3</entry><entry namest="col3" nameend="col3" align="left">2nd min 120 ° C heating jaws + 30 min 140 ° C</entry><entry namest="col4" nameend="col4" align="left">Room temperature</entry></row><row><entry namest="col1" nameend="col1" align="left">Makrolon / Makrolon</entry><entry namest="col2" nameend="col2" align="char" char=",">4,8</entry><entry namest="col3" nameend="col3" align="left">5 min 120 ° C in the air circulation cabinet, fixation with letter clip</entry><entry namest="col4" nameend="col4" align="left">Room temperature</entry></row><row><entry namest="col1" nameend="col1" align="left">Makrolon / Makrolon</entry><entry namest="col2" nameend="col2" align="char" char=",">10,2</entry><entry namest="col3" nameend="col3" align="left">15 min 120 ° C, in the air circulation cabinet, fixation with a paper clip</entry><entry namest="col4" nameend="col4" align="left">Room temperature</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Makrolon / Makrolon</entry><entry namest="col2" nameend="col2" align="char" char=",">5,7</entry><entry namest="col3" nameend="col3" align="left">15 min 120 ° C, in the air circulation cabinet, fixation with a paper clip</entry><entry namest="col4" nameend="col4" align="left">85 ° C</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Duran glass macrolon</entry><entry namest="col2" nameend="col2" align="char" char=",">4,4</entry><entry namest="col3" nameend="col3" align="left">15 min 120 ° C, in the air circulation cabinet, fixation with a paper clip</entry><entry namest="col4" nameend="col4" align="left">Room temperature</entry></row></tbody></tgroup></table></tables>

Example 2

(Comparative example)

According to Example 1 of EP-A-153 579, a heat-curable one-pot adhesive mixture was produced and this was tested for its usability for the bonding of SMC parts in the heating jaw process. The test was carried out in exactly the same way as in Example 1 of this application.

In the following overview, the test results from comparative example 2 were directly compared with the corresponding results from example 1 of this application. <tables id="tabl0002" num="0002"><table frame="none"><tgroup cols="3" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center">Tensile shear strength [N / mm²] at room temperature</entry><entry namest="col3" nameend="col3" align="left">Curing conditions</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Example 1 of this application</entry><entry namest="col2" nameend="col2" align="left">8.3; Material failure</entry><entry namest="col3" nameend="col3" align="left">2nd min 120 ° C, heating jaws + 30 min 140 ° C, heating cabinet</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="left">Example 2 of this application = Example 1 from EPA 153579</entry><entry namest="col2" nameend="col2" align="left">5.3; Cohesive failure</entry><entry namest="col3" nameend="col3" align="left">5 min 120 ° C, heating jaws (not set after 2 min) + 30 min 140 ° C, heating jaws</entry></row></tbody></tgroup></table></tables>

The adhesive mixture from Example 2, which contains only 1 triol (MW 450), solidifies significantly more slowly than the mixture according to the invention from Example 1 and does not produce a satisfactory tensile shear strength even after prolonged exposure to the heating jaw.