WO1991015550A1 - Heat-curing melt adhesives - Google Patents

Abstract

The description relates to reactive heat-curing melt adhesives consisting of a resin component (I) which is solid at room temperature and a hardener component (II) which is insoluble in (I) and solid at applications temperature and is present in (I) in the form of discrete particles. The melt adhesives may be used in particular as a structural adhesive in coachbuilding and have the special feature that (I) contains polymers with on average 2 or more carboxyl groups and (II) contains higher-molecular multi-functional epoxides.

Description

 Thermally curing hot melt adhesives

The invention relates to reactive hot-curing hot melt adhesives consisting of a resin component (I) which is solid at room temperature and a hardener component (II) which is insoluble in (I) and is solid at the application temperature and is present in the form of discrete particles distributed in (I). Furthermore, the invention relates to a method for the flat connection of substrates with these hot melt adhesives and their use.

Reactive hot melt adhesives are a further development of conventional hot melt adhesives. In this case, the formerly thermoplastic material is converted into a thermosetting material by a crosslinking reaction which takes place after application. The post-crosslinked hotmelt adhesive now remains solid at temperatures at which it was previously applied. An important development in this area are the moisture-curing hotmelt adhesives, which are connected, for example, via terminal isocyanate or alkoxysilane groups Post-crosslink water. Another development of reactive hot melt adhesives led to thermosetting systems. Here, the hot melt adhesive is macroscopically 1-component, but consists of a resin and a hardener, the latter being present in solid form in the resin at room temperature and only reacting with it in the molten liquid state. Systems based on epoxy resins which contain reaction products of bisphenol A and epichlorohydrin are known to the person skilled in the art. A ines which have a higher melting point than the hardener component are used as hardeners. A preferred area of application for such reactive hot-curing hot melt adhesives is automotive engineering.

The object of the invention is to provide reactive hot-curing hotmelt adhesives on a new raw material basis for these systems. These should also meet the requirements of automotive engineering. In particular, they should adhere well to oiled sheet metal and withstand the relatively high temperatures of the paint drying ovens. In particular, they should be coordinated in such a way that they crosslink under the conditions prevailing in the paint drying ovens. In addition, they should also be sufficiently wash-resistant even in the uncured state.

The object was achieved according to the invention by reactive hot-curing hot melt adhesives consisting of a resin component (I) which is solid at room temperature and a hardener component (II) which is insoluble in (I) and is solid at application temperature and which is present in the form of discrete particles distributed in (I) characterized in that (I) contains polymers with an average of 2 or more carboxyl groups and (II) higher molecular weight multifunctional epoxides.

As already mentioned, reactive hot-curing hot melt adhesives consist of a resin component (I) and a hardener component (II). (I) is solid at room temperature, ie without external influences dimensionally stable. The softening or melting temperature is therefore above the usual room temperature. The application temperature is within a range which is limited at the bottom by the melting or softening temperature and within which the hot melt adhesive can be applied using conventional applicators. On the other hand, the application temperature should be below the melting point of the hardener component. This means that the hardener component is required to have a melting point above the melting or softening point of the resin component. (II) is present in the form of discrete particles distributed in (I), so that such hot melt adhesives macroscopically represent a 1-component system.

According to the invention, the resin component contains polymers with an average of 2 or more carboxyl groups and the hardener component contains higher molecular weight polyfunctional epoxides. The polymers from (I) preferably have a molecular weight of 2,000 to 10,000. A range which is particularly suitable with regard to the stated requirements for the melting or softening point of (I) is between 2000 and 5000. Polymers with a molecular weight of approximately 3000 give particularly good results, with fluctuations of 200 units within half of the tolerance limit. The ranges and values mentioned mean the average molecular weight.

Polyamides, polyesters, poly (eth) acrylates and / or polyurethanes are preferred as polymers according to the invention. The starting materials for polyamides and polyesters are multifunctional carboxylic acids. Here, for example, compounds such as adipic acid, phthalic acid, oxalic acid, maleic acid, succinic acid, glutaric acid, acelic acid, sebacic acid and dimerized fatty acids come into consideration. In addition to the dicarboxylic acids mentioned, tricarboxylic acids are also very suitable. To produce polyamides, carboxylic acids are reacted with functional amines. These can be both aliphatic, aromatic or cyclic amines. Dipri ary diamines such as ethylenediamino and the corresponding higher homologs or secondary amino groups-containing diamines with alkyl substituents or piperazine are examples of heterocyclic diamines.

Polyamides based on di-fatty acid are preferred. Such polyamides are known to the person skilled in the art, for example, from the published documents DE 3531 941, DE 35 35732 and DE 37 23941. Measures familiar to the person skilled in the art can be used to prepare corresponding polyamides in the molecular weight ranges preferred for the purposes of the present invention.

Polyesters are available as reaction products of polyfunctional carboxylic acids with polyfunctional hydroxy compounds. Low molecular weight multifunctional hydroxy compounds which can suitably be used are e.g. Ethylene glycol, propylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol and triols such as glycerin, trimethylolpropane, trimethylolethane and higher-functionality hydroxy compounds such as pentaerythritol. Higher molecular multifunctional hydroxy compounds can e.g. obtained by reacting the abovementioned low molecular weight hydroxy compounds with epoxides or tetrahydrofuran, the epoxide used being, for example, ethylene oxide, propylene oxide, butylene oxide, styrene oxide, cyclohexene oxide, trichlorobutylene oxide and epichlorohydrin. Suitable polyesters can also be prepared by ring-opening polymerization of, for example, epsilon-caprolactone or methyl-eps lon-caprolactone.

The polyesters, if they have several reactive OH groups, are just like the abovementioned low and high molecular weight Suitable hydroxy compounds as a polyol component for the production of polyurethanes. Natural substances, so-called oleochemical polyols or, for example, castor oil, can also be used as the polyol component.

j The polyol component is reacted with an isocyanate component.

Aromatic as well as aliphatic and / or cycloaliphatic isocyanates can be used as the isocyanate component. Suitable isocyanates with a functionality of 2 and larger are, for example, the isomers of tolylene diisocyanate, isophorone diisocyanate, dicyclohexyl ethane diisocyanate, tetraethylene diisocyanate, trimethylhexamethylene diisocyanate, triethyloxy1o1diisocyanate, hexamethylene diisocyanate and diphenyl triisocyanate and diphenyl triisocyanate and diisocyanate and diisocyanate triisocyanate as well. Diphenylmethane-4,4-diisocyanate (MDI) and tolylene di-isocyanate-2,4 (TDI) are of particular technical importance.

Suitable poly (meth) acrylates can be obtained by radical polymerization of (meth) acrylates. Examples of suitable (meth) acrylates are acrylic acid, methacrylic acid and their salts and esters. The alcohol component of these esters preferably contains 1 to 6 carbon atoms. Suitable polymers can also be copolymerized from mixtures of (meth) acrylates with other ethylenically unsaturated monomers known to the person skilled in the art, provided that these can be polymerized. A suitable comonomer is, for example, styrene.

The above-mentioned polyamides, polyesters, poly (meth) acrylates and polyurethanes or their starting materials are exemplary mentions. A large number of corresponding compounds which are suitable in the sense of the invention are known to the person skilled in the art from the technical and patent literature. A variety of suitable compounds are also commercially available. From this multitude Suitable polymers naturally result in an even greater number of possible suitable combinations.

For the purposes of the invention, the polymers have an average of 2 or more carboxyl groups. With the polyamides and polyesters mentioned, this can be achieved relatively simply by using an excess of multifunctional carboxylic acid in their preparation. In the case of the poly (meth) acrylates, carboxyl groups can be inserted into the polymer by, for example, polymerizing in a corresponding proportion of (meth) acrylic acid. Polyurethanes containing carboxyl groups can be obtained, for example, by polymerizing a polyol component with an additional carboxyl function. Such a suitable polyol component is, for example, dimethylol propionic acid. Such polyurethanes containing carboxyl groups are described, for example, in published patent application EP 354471.

According to the invention, preference is given to those polymers which have on average 2 to 4 carboxyl groups. Particularly good results are obtained with polymers which have 2 terminal carboxyl groups. This preferred variant can be obtained relatively easily if, for example, diamines or diols are reacted with an excess of dicarboxylic acids.

Higher molecular weight polyfunctional epoxides are contained in the hardener component in the hotmelt adhesives according to the invention. These preferably have 2 to 6 epoxy groups on average. If the person skilled in the art wants to ensure spatial networking, he will choose connections with a functionality greater than 2. Preferred epoxy compounds with 3 to 5 epoxy groups per molecule give particularly good results. As already mentioned, the melting or softening point of the epoxies should be above that of the resin component used in combination. It has proven particularly favorable if this value for the epoxides is above 70 ° C. With regard to the usual application temperatures for hot melt adhesives, which are partly also caused by the corresponding application devices, epoxides with a corresponding value above 90 ° C. are particularly preferred. However, it is also preferred that the value is less than 180 ° C. On the one hand, this is due to the fact that 180 ° C. is a preferred hardening temperature and, in the sense of the invention, the hardener component should have a melting or softening point less than the hardener temperature, and on the other hand there is a temperature above 180 ° C. increases the risk that the polymers will start to decompose.

There are a large number of epoxides which can be used according to the invention and which the person skilled in the art can see from the patent and specialist literature, reference works and relevant manuals. Ullmann, Encyclopedia of Industrial Chemistry, 4th Edition, Volume 10, Verlag Chemie, Weinheim 1974, page 563 ff. May be mentioned as a reference. The person skilled in the art will also find suitable epoxides on the market. With regard to the object according to the invention, however, epoxides of the formula have proven particularly suitable

(1)

und/oder

and or

proven. The compound of formula (1) is the main product from a condensation reaction of tetraphenylolethane with epichlorohydrin. Such suitable technical condensation products usually have an average molecular weight greater than 700 and a softening temperature of approximately 94 ° C. Multifunctional epoxides according to formula (2) can be prepared by reacting ortho-cresol formaldehyde novolac with epichlorohydrin. The molecular weight of the epoxy compound and thus also its melting point or softening point can also be controlled via the molecular weight of the novolac used. In formula (2), R can represent chlorohydrin, glycol and / or polyether. The average functionality of such suitable condensation products is usually 2.5 to 5.5. Suitable multifunctional epoxides are also compounds such as, for example, tetraglycidyldiaminodiphenylmethane.

The optimum quantitative ratio of (I) and (II) is determined, inter alia, by the molecular weight and the functionality of the carboxyl group-containing polymers and the multifunctional epoxy compounds. Good application results are obtained if the amounts of (I) and (II) are chosen so that the ratio of epoxy groups to carboxyl groups is in a preferred range ranges from 4: 1 to 1: 4. Within this range, particularly good results are not obtained (as might have been presumed) with a stoichiometric equilibrium, but with a clear excess of epoxy groups, namely in a preferred ratio range of 2: 1 to 1.5: 1.

The hot melt adhesives according to the invention can of course contain the additives customary for hot melt adhesives and / or epoxy adhesives. These are in particular stabilizers, fillers, anti-aging agents, pigments, dyes and / or catalysts or accelerators. Such additives or additives are known to the person skilled in the art or can be found in the relevant patent and technical literature.

The invention further relates to a method for the flat connection of substrates. In such a method, a hot melt adhesive as described above is applied to at least one of the substrates. The hot melt adhesive must have a temperature which is between the softening temperature of the resin component and the hardening component of the hot melt adhesive. The temperature at which the hot-melt adhesive is applied is also called the application temperature. At this temperature, the reactive hot melt adhesive initially behaves like a simple non-reactive hot melt adhesive, since only the resin component is in the molten state. Crosslinking of the hotmelt adhesive is therefore not yet taking place or has not yet taken place to any appreciable extent. After the hot melt adhesive has been applied to at least one of the substrates, these are then joined together. As in the case of non-reactive hot melt adhesives, these are adhesively bonded to one another by cooling the adhesive. This state can be maintained over any period of time. For hot curing, ie for post-crosslinking, the hot-melt adhesive is peeled on at least hardening points. brought. Since the hardening temperature is by definition above the melting or softening temperature of the hardener component, it melts - and thus the epoxy contained therein - and can react with the resin component. After this hardening has taken place, the hotmelt adhesive can no longer be melted at the application temperature, but remains solid.

The method is particularly suitable for the flat connection of metals, in particular steel sheets and / or struts. Also preferred is a method in which the curing is carried out at approximately 180 ° C., in particular over a period of approximately 30 minutes. The hotmelt adhesives according to the invention prove to be sufficiently stable in storage. This also applies to an elevated storage temperature. The hardened hot melt adhesives have good elongation and high strength at the same time. They include also suitable for the flat connection of oiled sheets. However, the quality of the bond deteriorates with increasing contamination of the parts to be joined.

The curing conditions of the reactive hot melt adhesives can be matched in a special embodiment to the conditions required in the automotive industry. For example, It is customary to bake the body paints at a temperature of approx. 180 ° C for a period of around 30 minutes. During this time, special embodiments of the hotmelt adhesive according to the invention can also harden. The hot melt adhesives are therefore particularly suitable for

Suitable for use as construction adhesive in body construction.

The hotmelt adhesives according to the invention can be thixotropic. This is particularly advantageous if the curing temperature is significantly higher than the melting temperature of the hot melt adhesive. The thixotropy then at least largely prevents the hot melt adhesive from running out of the adhesive joint. Physical thixotropy is particularly suitable for example with highly disperse silica. If the adhesive joint is exposed to a mechanical load, the corresponding joining parts should be fixed before heating to the curing temperature. As in the automotive industry, this can be done, for example, by additional spot welding. If the hotmelt adhesives according to the invention are used more as sealants than as adhesives, for example for sealing the lower door seam, additional fixing is generally not necessary.

The invention is illustrated by the examples below.

B e i s p i e l e

Carboxyl group-containing polyamides with different dimer fatty acid content were produced as resin components and are designated A to E in the following.

Polyamide A (acid number (SZ) = 40: MG = 2800):

62 parts by weight of dimer fatty acid 21 parts by weight of azelaic acid 17 parts by weight of piperazine

Polyamide B (SZ = 40: MG = 2800):

21 parts by weight of dimer fatty acid, 54 parts by weight of azelaic acid, 25 parts by weight of piperazine

Polyamide C (SZ = 50; MG = 2250):

63 parts by weight of dimer fatty acid

22 parts by weight of azelaic acid 15 parts by weight of piperazine

Polyamide D (SZ = 47; MW = 2390): 39 parts by weight of dimer fatty acid 39 parts by weight of azelaic acid 22 parts by weight of piperazine

Polyamide E (SZ = 34); 58 parts by weight of dimer fatty acid 20 parts by weight of azelaic acid 14 parts by weight of piperazine 8 parts by weight of polyoxypropylene-α, w-diamine MG 400 Abbreviations used in Table 1:

RF = tensile strength [MPa] according to DIN 93504

RD = elongation at break [%] according to DIN 93504

ZSF / \] = tensile shear strength [MPA] on sandblasted

Aluminum according to DIN 53283 = melt viscosity [Pas] according to ASTM D-3236 in an RVT viscometer from Brookfield MG = average molecular weight

GT = parts by weight

MPa = Mega Pascal

Pas = Pascal second

The polyamides were melted and epoxy compounds were added in the molten state and distributed homogeneously. The temperature of the melt was between 80 ° C and 120 ° C depending on the melting point of the polyamides. The epoxy compounds had previously been comminuted in a household mixer (Starmix) for about 1 min.

The following epoxy compounds were used:

X = condensation product of tetraphenylolethane and epichlorohydrin with an average molecular weight above 700 and a softening temperature of 94 ° C.

Y = condensation product of ortho-cresol formaldehyde novolac with epichlohydrin with an average molecular weight of 1170 and an average functionality of about 4

Z = condensation product of ortho-cresol formaldehyde novolac with epichlorohydrin with a molecular weight of 1270 and a functionality of about 4.5

Combinations of different polyamides with various epoxides are listed as examples in the following table: Table 1

MPa Pas Viskosität bei ange- qebenen BedingungenZSF _A1 25 ° C 100 ° C Viscosity Relative increase in

MPa Pas viscosity under specified conditions

1 2 0% (4.0 h, 90 ° C)

25% (2.0 h, 110 ° C)

0% (8.0 h, 90 ° C)

4

4-. 5 I 6 200% (0.5 h, 130 ° C) 7 8 9

10

11

2 , 2 12

2, 2

Table 1 (continued)

Example polyamide epoxy curing

GT GT min / ° C

In Examples 1 to 16 above, some hotmelt adhesives according to the invention were tested for certain performance properties. It becomes clear that the person skilled in the art can selectively control the application properties of the hot-melt adhesive by choosing and combining suitable polyamides and epoxides. A + X thus gave good strengths at high elongation values and very good stability at very high temperatures. The combination B + X gives excellent strengths, but with low elongation values. The melt stability is significantly lower. Hot melt adhesives made from C + X give comparable strengths with lower elongation than hot melt adhesives made from A + X. Better strengths are obtained with C + X than with D + X, but with lower melt stability. The combination E + X shows excellent elongation values with good tensile shear strength and reduced tear strength. In general, it can be said that as the proportion of dimer fatty acid in the polyamide increases, the stability of the melt of the hot-melt adhesive increases, but the strengths are in opposite directions. A comparison of Examples 3, 13 and 15 shows that the polyamide A with the epoxides X, Y or Z leads to hotmelt adhesives according to the invention, but in this case the best values can be achieved with the epoxy X. The combination of the polyamide B with the epoxides X, Y and Z in Examples 14, 16 and 5 to 7 shows that in this case the combination of B and Z has the best values for the tensile strength and the elongation at break results.

Claims

Patent claims 1. Reactive heat-curing hotmelt adhesives consisting of a resin component (I) which is solid at room temperature and a hardener component (II) which is insoluble in (I) and which is solid at the application temperature and is present in the form of discrete particles in (I), characterized in that in (I) Polymers with an average of 2 or more carboxyl groups and (II) higher molecular weight multifunctional epoxides are contained. 2. Hotmelt adhesives according to claim 1, characterized in that the polymers have an average molecular weight of from 2000 to 10,000, preferably from 2500 to 5000, but in particular from about 3000. 3. Hot melt adhesives according to one of the preceding claims, characterized in that the polymers polyamides, polyesters, poly (meth) acrylates and / or polyurethanes. 4. Hotmelt adhesives according to one of the preceding claims, characterized in that the polymers are polyamides based on dimer fatty acid. 5. Hotmelt adhesives according to one of the preceding claims, characterized in that the polymers have an average of 2 to 4 carboxyl groups, in particular 2 terminal carboxyl groups. 6. Hotmelt adhesives according to one of the preceding claims, characterized in that the higher molecular weight polyfunctional epoxides have on average 2 to 6 epoxy groups, preferably 3 to 5 epoxy groups, per molecule. 7. Hotmelt adhesives according to one of the preceding claims, characterized in that the melting or softening point of the epoxides has a value of greater than 70 ° C, preferably greater than 90 ° C, in particular less than 180 ° C. 8. Hot melt adhesives according to one of the preceding claims, characterized in that epoxides of the formula

and or

are included. Hot melt adhesives according to one of the preceding claims, characterized in that the amounts of (I) and (II) are chosen so that the ratio of the epoxy groups to the carboxyl groups in is in a range from 4: 1 to 1: 4, preferably in a range from 2: 1 to 1.5: 1. 10. Hotmelt adhesives according to one of the preceding claims, characterized in that it contains conventional additives for hotmelt adhesives and / or epoxy adhesives. 11. A method for the flat connection of substrates, characterized ge indicates that a hot melt adhesive according to one of the preceding claims is applied to at least one of the substrates at a temperature which is between the softening temperature of (I) and the curing temperature of the hot melt adhesive is then joined together and bonded to one another by cooling the adhesive, and after a period of time the hot melt adhesive is heated to at least the curing temperature. 12. The method according to claim 11, characterized in that as substrates preferably metals, in particular steel sheets and / or struts, are connected to one another. 13. The method according to claims 11 and 12, characterized in that the curing is carried out at about 180 ° C, in particular over a period of about 30 minutes. 14. Use of the hot melt adhesives according to claims 1 to 11 as construction adhesive in body construction.