DE1770814C3 - Hardener for epoxy resins - Google Patents

Description

35

The mixtures of epoxy resins with acidic and basic hardeners are not stable in storage At normal temperature there is a continuous increase in viscosity and finally gelation Processes for increasing the storage stability are therefore the amino groups of the hardener by salt formation blocked In the course of the hardening reaction, which takes place on heating, the acid is released and must removed. The amine salt is a latent hardener.

Combinations of polyamines and polyaminoamides with epoxy resins that are more than the equivalent Amount of epoxy resin, can be stored if there is a sufficient excess of epoxy resin, for amine hardening but no longer capable. A hardening reaction taking place at high temperatures comes jo only with the participation of the OH groups of the epoxy resin.

The invention is now based on the object of finding hardeners for epoxy resins, the latent amine hardeners represent, which release amino groups when heated and which then act as amine hardeners with the epoxy groups can react without simultaneously forming non-reactive compounds that are removed Need to become.

It has now surprisingly been found that this object can be achieved by using polyureas with units of the general formula

[—NH-CO — NH-R—] "

in which n> 2 and R is the hydrocarbon radical of a bifunctional amine or a bifunctional low molecular weight polyamide, can dissolve for curing epoxy resins.

The use of the polyureas for curing epoxy resins results in epoxy resin-hardener combinations which are storable, thermoplastically processable , thermally-curing mixtures.

Polyureas of the above formula split when heated to higher temperatures, usually above 150 ° C, to the difunctional compounds

NH ₂

Polyurea
(according to the invention)

NH ₂
NCO

NCO

The resulting diamines, diisocyanates, amino isocyanates then react with the epoxy or OH groups of the epoxy resins,

The resulting epoxy resin-hardener combinations consist of two components, A, the Epoxy resin, and B, the (latent) hardener. Both can be in the form of a mixture. But you can also exist in the form of a prepolymer if R also has additional functional groups or NHr groups which allow the reaction with excess epoxy resin.

The mixing ratio of A: B can vary within wide limits. It is only made possible by the Desired crosslinking density determined If you want to have highly crosslinked, hard end products, then you lay the mixing ratio is so tight that there are two epoxy groups for each latent NH group. Should the If the crosslinking density is low, which is the case with highly elastic end products, then only one may be used when heating Fraction of the latent groups react. Accordingly, the weight ratio becomes A: B always be between 1:20 and 20: 1. These limits can however, it can also be exceeded and fallen short of.

The polyureas used according to the invention can be prepared by known processes, z. B. from diamines and CO2, diamines and phosgene, diamines and urea or diamines and diisocyanates. These processes are well known (see, for example, Houben-Weyl, Methods of Org. Chemistry, Vol. XIV / 2).

In principle, all polyureas are suitable for the use according to the invention insofar as they can be found in mix any shape with the epoxy resin. The mixture should be as homogeneous as possible best by melting them together or by dissolving in a solvent and distilling off the the latter achieved with initially existing intolerance of the two components A and B - with When the reaction begins, the intolerance disappears - make sure that the dispersion is as fine as possible.

The number of units of the type mentioned present in the molecule is important for the processing properties significant. At η = 3, preferably = 5, the viscosity of the melt increases to such an extent that it rises conventional machines for thermoplastic processing can be processed without difficulty can. That is why polyureas, in which next 3 is given preference.

Particularly advantageous resin-hardener combinations obtained with polyureas which are not crystalline or only to a small extent. Have this low softening temperatures and are in cheap solvents, e.g. B. in alcohols, readily soluble. she can easily be mixed with the epoxy resin in the form of their melts or their solution. the end for this reason, predominantly non-crystalline polyureas are preferred as curing components.

If one starts from aliphatic or cycloaliphatic diamines, one obtains the after hardening Polyureas made from them with epoxy resins End products with particularly high impact strength. The alkyl-substituted aliphatic and cycloaliphatic diamines, e.g. B. 2,2,4- and 2,4,4-trimethylhexamethylene diamine (TMD for short) and I -aminoO-aminomethyl-S.S.S-trimethylcyclohexane. That the latter is also known under the name isophoronediamine (IPD for short). Also mixtures of these diamines can be used.

The products made on this basis draw look after hardening by high dimensional stability in the heat with high impact strength at the same time,

A resin-hardener combination which is particularly advantageous in terms of processing technology is obtained with those according to the invention used polyureas because of the terminal NHr groups of the amino groups. These can be reacted with excess epoxy resin with a short reaction time and result in very stable, homogeneous resin-hardener combinations. The amount of excess epoxy resin depends on the Number of latent NH2 and NCO groups and according to the desired degree of crosslinking within the above mentioned limits.

Hardened plastics with particularly high impact strength are obtained from the resin-hardener combinations and low shrinkage, if one does not use the simple ones for the production of the polyureas Diamines, but instead low molecular weight polyamides with terminal amino groups This is obtained z. B. by condensation of dicarboxylic acids and / or aminocarboxylic acids or their lactams with diamines. The molecular weight of these polyamides with terminal NHr groups should between 200 and 5000. They are converted into polyureas using the methods mentioned above

There is no restriction on the epoxy resins. You can get both predominantly aromatic Epoxy resins based on phenyl glycidyl ethers as also aliphatic polyglycidyl ethers of polyalcohols or cycloaliphatic epoxides, such as l-epoxyethyl-3,4-epoxycyclohexane, use.

The resin-hardener combinations have the advantage that they are stable in storage. They have thermoplastic properties over a wide temperature range and can be processed like thermoplastics, e.g. B. in extruders and injection molding machines. Only when the temperature rises, usually above 150 ° C, do the thermoset properties predominate. For example, it is possible to preheat and plasticize the mixtures in an injection molding machine and ^{inject them into a closed mold preheated to temperatures above 150 °} C., in which the hardening reaction then takes place from the resins, e.g. B. by rolling or extruding, and then coated with a steel sheet or other materials. When this composite is subsequently heated, curing then takes place. The resin-hardener combinations can also be used as hot-melt adhesive or stoving varnish.

The use according to the invention of the special polyureas is illustrated by the examples below illustrated

example 1

250 parts by weight one for 158 kg of 2,2,4-trimethylhexamethylenediamine and 189 kg of 2,2,4-trimethylhexamethylene diisocyanate Polyurea produced by melt condensation, the average molecular weight of which is 2700 and which contained on average 18-20 of the units / mole described were 300 parts by weight. one Epoxy resin based on bisphenol A glycidyl ether, with an epoxy value of 0.52, mixed in a kneader at 80 ° C.

The kneading resistance in the Brabender plastograph

was at 70 ⁰ C 3.1 mkp / sec, after a storage period of 3 months at 20-22 ⁰ C, a value of 3.2 mkp / sec was measured.

Part of the mixture was injected on a piston injection molding machine in a heated at 150 ⁰ C shape for standard small bars. The shaped bodies were then heated ^{to 180 ° C. for a further hour}

Ball indentation hardness:
Limit bending stress:

I960 kgf / cm ²
1240kp / cm ²

Example 2

250 parts by weight one from 158 kg of 2,4,4-trimethylhexameihylenediamine, 28 kg of hexamethylenediamine and 256 kg

2, «T, 4-trimethylhexamethylene diisocyanate

Melt condensation produced polyurea, the average molecular weight of which was about 15,000 and the contained on average 80 units / mol, were in 250 parts by weight. Methanol dissolved The solution was with 57 parts by weight a 70% solution of the epoxy resin used in Example 1 and mixed in a vacuum evaporated to dryness

The kneading resistance in a Brabender plastograph was at 90 ⁰ C 2.7 mkp / sec. After three months of storage at 20-22 ° C, a value of 2.8 mkp / sec was measured.

Part of the mixture was ^{injected into a mold heated to 180 °} C. on a piston injection molding machine, elastic moldings being obtained.

Ball indentation hardness: 780 kp / cm ² Bending limit stress: 260 kp / cm ² Example 3

270 parts by weight a polyurea produced by melt condensation from 170 kg of l-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 158 kg of 2,2,4-trimethylhexamethylene diamine and 400 kg of 2,2,4-trimethylhexamethylene diisocyanate with an average molecular weight of 7000, which in the Agent contained 40 units / mol, were in 250 parts by weight. Methanol dissolved The solution was with 360 parts by weight. of a 70% solution of an aromatic epoxy resin having a Epoxiwert of 0.46, and mixed in vacuo to dryness, the viscosity in Brabender plastograph was at 90 ⁰ C 3.9 mkp / sec. After three months of storage at 20-22 ° C, a value of 4.0 mkp / sec was measured.

Part of the product was pressed in a die for sheets for 5 minutes at 190 ⁰ C and then heated for 1 hour at 170 ° C.

The Vicat temperature was 148 ° C.
No breakage occurred in the impact test according to DIN 53 453.

Example 4

One mole of a basic polyamide made from adipic acid and trimethylhexamethylenediamine (molecular weight 730)

ho was condensed with 1 mole of urea at 150-200 ° C. The average molecular weight of this polyamide polyurea was 12,000. One mole contained an average of 15 units.
250 parts by weight of polyamide polyurea

μ together with 50 parts by weight Methanol and 135 parts by weight. Epoxy resin with an epoxy value of 0.49, kneaded intensively, then the solvent is removed in vacuo. The kneading resistance in the Brabender Plastograph bc-

carried 2.0 mkp / sec at 100 "C, after a storage time of three months a value of 2.0 mkp / sec, measured.

A portion of the product was sprayed on a piston injection molding machine in a heated at 180 ⁰ C for form V Normkleiinstäbe and left for ₂ h at this temperature, the volume shrinkage was 1.2%.

No breakage was observed in the impact test according to DIN 53 453. The notched impact strength was 7.3 kp / cm ² .

Example 5

2.5 mol of a basic polyamide made from decanedi- _{) 5} carboxylic acid and 2Ä4-trimethylhexamethylenediamine with an average molecular weight of 935 and 1.5 mol of S-iso-yanatomethyl-SAS-trimethylcyclohexyl isocyanate became a basic polyamide polyurea with an average molecular weight of 2,650 by melt condensation produced This contained an average of 3 units / time.

250 parts by weight this Polyamidpolyhanvtoffes were together with 400 parts by weight Methanol and 215 parts by weight. an aromatic epoxy resin (epoxy value 0.53) 1 Boiled for 1 hour on the reflux condenser. The solvent was removed in vacuo, the resin residue was sharp dried

The kneading resistance in Brabender PIastographen at 90 ⁰ C was 2J> mkp / sec. After a storage time of 6 months, a value of 2.6 was measured.

A portion of the product was pressed in a sheet form at 180 ⁰ C and held for _V2 hour at this temperature.

Ball indentation hardness: Limit bending stress: Notched impact strength:

1330 kgf / cm ²
1010 kgf / cm ²
8.4 kgf / cm ²

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These properties of the hardening agents used according to the invention could not be foreseen, since the DE-AS 1,124 240, issued on Feb. 22, 62, already diureas of the general formula

H ₂ N-CO-NH-R'-NH-CO-NH ₂

in which R 'is an aliphatic, cycloaliphatic or aromatic divalent hydrocarbon radical with 2 to 25 carbon atoms, describes as a curing agent for epoxy resins. The reactive hydrogen, which reacts with the epoxy groups, comes exclusively from amide groups. About this diurea epoxy resin mixtures is further known that it can be, that is, cured to hard products already at a moderately elevated temperature of about 50 ⁰ C.

In order to demonstrate the advantages of the hardeners used according to the invention, 2 comparative tests were carried out

45

50 carried out The following substances were used as comparison substances:

Hardener A: H ₂ N-CO-NH-R'-NH-CO -NH ₂

(Diurea according to DE-AS11 24 240)
HardenerB: H ₂ NR ² -NH-CQ-NH-R ' _n

L-NH-CO-NH-R ² -NH ₂
(Polyurea according to the invention)

In the formula for hardeners A and B, R 'is the hydrocarbon radical of the TMD and R ^{2 is} the hydrocarbon radical of the IPD.

Comparative example 1
(according to DE-AS 11 24 240)

23 g of hardener A and 165 g of a polyglycidyl ether based on bisphenol A, with an epoxy value of 0.24, were dissolved in 282 g of a mixture of equal parts of isopropanol and toluene. After standing for 2 hours, the solution was applied to sheet steel with a lacquer dumbbell . The film was dried in the air for 1 hour ^{and baked at 180 °} C. for 30 minutes. The cured film exhibited numerous flow defects. The indentation hardness (according to Buchholz) was 105.

Resistance to acetone: A cotton ball soaked with acetone was placed on the film and with covered with a watch glass After 20 minutes, the film was completely destroyed at the stressed area

COMPARATIVE EXAMPLE 2
(according to the invention)

28 g of hardener B and 225 g of a polyglycidyl ether based on bisphenol A, with an epoxy value of 0.24, were dissolved in 380 g of a mixture of equal parts of isopropanol and toluene. After standing for 2 hours, the solution was applied to sheet steel with a lacquer dumbbell. The film was air-dried for 1 hour and ^{baked at 180 °} C. for 30 minutes

The cured film was smooth and glossy. The indented edge was 116.

The resistance to acetone was tested under the same conditions as in 1. After 20 min the film was slightly swollen at the point where it was claimed. The swelling went on after standing for 5 hours Air completely back again.

The different amounts of hardener and resin are due to the different equivalent weights of the Urea conditional

The comparative tests show that in addition to the thermoplastic processing possibilities described the polyureas used according to the invention also provide faster and more complete crosslinking effect under comparable conditions. The resistance to organic solvents.

Claims (1)

Claim: Use of polyureas with units of the general formula [- NH- CO — NH- R—] " in the nfe2 and R the hydrocarbon radical of a difunctional amine or a difunctional low molecular weight polyamide is used to harden epoxy resins.