GB1568725A - Thermally hardenable compositions and production of shaped articles and coatings - Google Patents

Abstract

In these thermocurable compositions, the curing agent employed for 1,2-epoxide compounds containing more than one epoxide group in the molecule is 2,2,6,6-tetramethyl-4-aminopiperidine, known as TAD, alone or mixed with other epoxide curing agents. The compositions are used for the production of mouldings and coatings and are distinguished by long shelf-lives.

Description

(54) THERMALLY HARDENABLE COMPOSITIONS AND PRODUCTION OF SHAPED ARTICLES AND COATINGS (71) We, VEBACHEMIE AKTIEN GESELLSCHAFT, a German Body Corporate of 4660 Gelsenkirchen-Buer, Pawikerstrape 30, Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to thermally hardenable compositions and articles prepared from such compositions.

The compositions of the present invention incorporate a diamine of formula

This diamine, which in the usual nomenclature is called 2,2,6,6-tetramethyl4-amino-piperidine, is also referred to as TAD in this specification.

Very recently, numerous publications on the use of TAD derivatives as UV stabilisers have appeared.

The use of TAD itself as hardener for epoxy resins has, however, nowhere been mentioned in the literature, nor has it been suggested to one skilled in the art.

TAD and its production are described in the literature. It is usually produced in two steps in a first step, 3 moles of acetone are condensed with one mole of ammonia to give triacetonamine (i.e. 2,2,6,6tetramethyl-piperidone-4) (F.Asinger et al., Monatsh. Chemie, 99, (1968), pp. 1437 and 1444--1455) and in a second step this is then hydrogenated in aminating manner to give TAD.

In order to produce thermally hardenable mixtures consisting of amine hardeners and 1,2-epoxide compounds, aromatic polyamines are usually employed. Mixtures of epoxide compounds with aliphatic or cycloaliphatic polyamines have only slight stability in storage. Since aromatic polyamines are generally poisonous, it is desirable to avoid their use.

There is an interest in amines which will, when mixed with 1,2-epoxide compounds having more than one equivalent of epoxide groups per mole, give a longer stability in storage, especially in solvent-free mixtures, and at normal temperature preferably change their viscosity only slightly over months.

It has now been found that mixtures with high stability during storage are obtained when TAD is used as an amine hardener to form shaped articles and coatings and impregnations based on 1,2-epoxide compounds having more than one epoxide group per molecule.

According to the present invention there is provided a thermally hardenable composition for the production of shaped articles and coatings, which composition comprises: (a) at least one 1,2-epoxide compound having more than one epoxide group per molecule and (b) 2,2,6,6-tetramethyl-4-aminopiperidine, (a) and (b) being present in such amounts that for 1 epoxy equivalent, there are 0.- 1.3 equivalents of hydrogen atoms, bound to nitrogen, of the piperdine; and, if desired, 0.05-10% by weight, preferably 0.5-5% by weight, of a reaction accelerator, based on the weight of the 1,2-epoxide compound.

According to the present invention there is also provided a process for the production of shaped articles or coatings which process comprises heating in known manner a thermally hardenable composition including at least one 1 ,2-epoxide compound having more than one epoxide group per molecule and a cyclic diamine which is 2,2,6,6 - tetramethyl - 4 - amino - piperidine whereby a polyadduct of the 1,2-epoxide compound is formed.

Preferably in order to produce the hardenable composition of the invention there are present for each epoxide equivalent of component (a), 0.6-1.3 equivalents, more preferably about 1 equivalent, of hydrogen atoms of the TAD which are bound to nitrogen and are reactive.

Examples of suitable epoxide compounds having more than one 1,2-epoxide group per molecule (component (a)) are the epoxides of poly-unsaturated hydrocarbons (vinylcyclohexene, dicyclopentadiene, cyclohexadiene, cyclododecadiene, cyclododecatriene, isoprene, 1,5-hexadiene, butadiene, polybutadienes and divinylbenzenes) epoxy ethers of polyhydric alcohols (ethylene-, propylene- and butylene-glycols, polyglycols, thio-diglycols, glycerol, pentaerythritol, sorbitol, polyvinyl alcohol and polyallyl alcohol epoxy ethers of polyhydric phenols (resorcinol, hydroquinone, bis - (4-hydroxyphenyl) - methane, bis - (4-hydroxy-3methylphenyl) - methane, bis - (4-hydroxy3,5-dichlorophenyl) - methane, bis - (4hydroxy-3,5-dibromophenyl) - methane, bis - (4-hydroxy-3,5-difluorophenyl) - methane, 1,1 - bis - (4hydroxyphenyl)- ethane, 2,2-bis hydroxyphenyl)- propane, 2,2-bis - (4 hydroxy-3-methylphenyl) - propane, 2,2bis - (4-hydroxy-3-chlorophenyl) propane, 2,2-bis - (4-hydroxy-3,5,5dichlorophenyl)- propane, bis - (4hydroxyphenyl) - phenyl-methane, bis - (4hydroxyphenyl)- diphenylmethane, bis (4-hydroxyphenyl) - 4' - methylphenyl methane, 1,1,- is- - (4-hydroxyphenyl) - 2,2,2-trichloroethane, bis - (4hydroxyphenyl)- (4-chlorophenyl)methane, 1,1,-bis - (4-hydroxyphenyl) - cyclohexane, bis - (4-hydroxyphenyl) - cyclohexylmethane, 4,4'-dihydroxydiphenyl, 2,2'-dihydroxydiphenyl, 4,4'-dihydroxydiphenylsulphone and their hydroxyethyl ethers, of phenolformaldehyde condensation products, such as phenol alcohols and phenolaldehyde resins), S- and N-containing epoxides (N,Ndiglycidylaniline, N,N'-dimethyldiglycidyl4,4' - diaminodiphenylmethane, triglycidylisocyanurate) and epoxides which have been prepared according to customary processes from polyunsaturated carboxylic acids or mono-unsaturated carboxylic acid esters of unsaturated alcohols, glycidyl ester, polyglycidyl esters (which may be obtained by polymerisation or copolymerisation of glycidyl esters of unsaturated acids) or are obtainable from other acid compounds (diglycidyl sulphide, cyclic trimethylenetrisulphone or their derivatives).

As well as the above pure epoxides, their mixtures, and mixtures with mono-epoxides, where appropriate in the presence of solvents or plasticisers, may be used. Thus, for example the following mono-epoxides in admixture with the aforesaid epoxide compounds may be used: epoxidised mono-unsaturated hydrocarbons (butylene oxide, cyclohexene oxide and styrene oxide, halogen containing epoxides such as epichlorohydrin, epoxy ethers of monohydric alcohols (methyl, ethyl, butyl, 2-ethylhexyl, and dodecyl alcohol) epoxy ethers of monohydric phenols (phenol, cresol and other phenols substituted in the ortho or para position), glycidyl esters of unsaturated carboxylic acids, epoxidised esters of unsaturated alcohols or unsaturated carboxylic acids as well as the acetals of glycidaldehyde.

Particularly interesting for the production of the poly-adducts are those 1,2-epoxide compounds having more than one epoxide group per molecule and which are free from aromatic rings.

In order to produce the polyadducts according to the invention, a part of the cyclic diamine may also be replaced by other known "hardeners", e.g. polyamines, polyamides, aminoamides and polyamidoamines in stoichiometric proportion. However, the replacement should expediently not exceed 50% of the stoichiometric amount of the cyclic diamine.

The production of the polyadducts according to the invention is effected by mixing the amines with the 1,2-epoxy resins or 1,2-epoxide compounds and shaping according to known processes and is further explained in the Examples. Shaped articles as well as coatings and impregnations can be produced therewith.

The mixing of the hardener used in the compositions of the present invention with epoxide compounds presents no difficulties because of the prolonged pot lives. Mixing with solid epoxy resins can be effected by brief melting. However, the mixing may also be carried out in solvents, e.g. in alcohols, hydrocarbons or ketones.

A particularly preferred process for the production of the hardenable mixtures according to the invention comprises first mixing the TAD with a part of the epoxy resin to give a solid hardener which is then mixed with the remainder of the epoxy resin and the other components of the mixture, such as pigments, fillers, etc., by kneading which is best effected in an extruder.

TAD is a particularly effective heat hardener for epoxy resins, i.e. the actual hardening of the thermally hardenable mixtures according to the invention into shaped articles and the like is expediently effected at temperatures above 140"C, preferably from 150 to 2000C.

The hardening may also be effected in two or more steps; the first hardening step is effected for example at room temperature and the after-hardening at substantially higher temperature, i.e. at the temperatures mentioned above.

The hardening may, where appropriate, also be effected in two or more steps by first breaking off the hardening reaction prematurely or carrying out the first step at room temperature or a slightly elevated temperature, a still meltable and soluble, hardenable precondensate (so-called "B step") being obtained from the epoxide component (a) and the amine hardener (TAD). Such a precondensate can then be used for producing "prepegs", moulding powders and the like which are then hardened out at the temperatures stated.

The time for producing the shaped articles and coatings according to the invention can, where appropriate, be shortened by the addition to the hardenable composition of substances having an accelerating effect, e.g. a mono- or polyhydric phenol, in particular an aminophenol, a mono- or poly-hydric alcohol or by using compounds such as mercapto compounds, thioethers, dithioethers or compounds with nitrogencarbon-sulphur groupings or sulphoxide groups. Also suitable are salts of thiocyanic acid, where appropriate in the form of complex compounds.

By complex compounds of salts of thiocyanic acid are understood complex compounds of these with inorganic or organic components. Examples of such compounds are: NH4SCN, NaSCN, KSCN, Mg(SCN)2, Ca(SCN)2, Zn(SCN)2, Mn(SCN)2, pyridine. HSCN, quinoline. HSCN, aniline. HSCN, o- and p-toluidine- HSCN, guanidine. HSCN, Cd(SCN)2. 4NH3, Zn(SCN)2. 2N2H;, Mn(SCN)2. 2N2H4, 2 KSCN. (CH2)6N4, Zn(SCN)2. (pyridine)4, Mn(C5H5N)2. (SCN)2, NaSCN. (C3H6O) and (NH2)2CS3. KSCN.

The amount of the accelerator added may, depending on the reactivity of the amine components or epoxide components, be varied within a wide range.

As a rule, amounts of accelerator in the range of 0.05 to 10% by weight, preferably 0.5 to 5% by weight, with reference to the epoxide, are used, but sometimes smaller or larger additions may also be particularly advantageous.

The hardening accelerators may be added both to the mixture of (a) and (b) and to the epoxide (a) or the amine (b) in the form of a solid substance, dispersion or also in solution.

The use of TAD as hardener for 1,2epoxide compounds with more than one 1,2epoxide group per molecule possesses a number of advantages. Thus, for example the pot life of liquid mixtures consisting of TAD and the 1,2-epoxide compounds is considerably increased. In the case of the use of this hardener in moulding powders based on solid 1 ,2-epoxide compounds, the resulting products are distinguished by their outstanding creep resistance. The products are used in the electrical insulating sector.

In addition, the moulding powders based on TAD possess a surprisingly good stability during storage. In the case of known moulding powders based on solid 1,2epoxide compounds the stability in storage is, as is known, of limited duration; in most cases 34 months. Storage at lower temperatures is therefore often recommended. Moulding powders produced according to the invention are storable for at least 1--2 years.

The partial slowness in reaction of TAD compared to epoxides at room temperature makes it particularly interesting for the production of specific amine/epoxide moulding powders which can be processed on injection moulding machines.

According to this injection moulding process the hardener, the resin and the additives (fillers, mould release agents, etc.) are mixed in a screw-kneader, plasticised, transported and injected under pressure into a heated mould in which hardening takes place. The residence period in the intake zone is for example 10 minutes, the temperature of the screw is for example 7e-80"C, depending on the viscosity of the mixture.

It is necessary when carrying out this process to choose a screw temperature at which the epoxide-amine mixture does not harden in the screw.

To the hardenable mixtures according to the invention there may also be added, as already indicated, before hardening customary modifying agents such as extenders, fillers and reinforcing agents, pigments, dyestuffs, organic solvents, flame retardant substances, plasticisers or flexibilisers, flow-promoting agents, thixotropic agents and mould release agents.

As extenders, reinforcing agents, fillers (including those which already possess pigment character) which may be used in the hardenable mixtures according to the invention there are to be mentioned for example: coal tar, bitumen, glass fibres, textile fibres, asbestos fibres, boron fibres, carbon fibres, polyethylene powder, polypropylene powder, silica flour, asbestos flour, slate flour, kaolin, powdered chalk, gypsum, finely divided silicic acid, titanium dioxide, carbon black, graphite, oxide colours such as iron oxide and metal powders such as aluminium powder or iron powder.

As plasticisers for the modification of the hardenable mixtures there may be used for example phthalates, such as di-n-butyl, diiso-octyl and dinonyl phthalate and phosphates, such as tricresyl phosphate, trixylenyl phosphate and also polypropylene glycols.

As flow-promoting agents, especially when the hardenable mixtures are used for surface protection, there may be used for example silicones, cellulose acetobutyrate, polyvinyl butyrate, waxes, stearates, etc.

(which in part are also employed as mould release agents).

It is a particular advantage of the process according to the invention that, as a result of the prolonged processing period, there is enough time available for the intensive mixing in of the said additives.

The hardenable epoxy resin mixtures according to the invention are used above all in the fields of surface protection and electrical engineering as well as laminating technology. They may be used in formulations adapted for the specific intended application of the hardened mixtures. The formulations may be filled or unfilled and, as appropriate, may be in the form of solutions, lacquers, moulding powders, injection moulding formulations, casting resins or impregnating resins.

The epoxy resin films hardened with TAD show a surprisingly good UV stability for epoxy resins. This, however, is not surprising when it is borne in mind that TAD derivatives are already described as UV stabilisers for polyolefins, polyurethanes, polyamides. This is an additional advantage of the compositions according to the invention.

The present invention is illustrated by the following Examples; the term "epoxide index" used in the Examples means the number of epoxide equivalents per 100 grams of epoxide compounds or resin.

Example 1 156 parts by weight of TAD were mixed with 570 parts by weight of an epoxy resin, a diglycidyl ether of bisphenol-A (2,2-bis(4hydroxy-phenyl) - propane with an epoxide index of 0.52. After a duration of mixing of about 10 minutes, the mixture was heated briefly to 800C (5-10 minutes) and then mounted on metal sheets and for 10 minutes at 1800C.

The films obtained were resistant to solvents and showed a remarkably better UV stability than for example corresponding films of epoxide/amine mixtures with other cyclic amines, e.g. isophorone diamine.

The lacquer technology properties of these films were very good: Layer thickness (in microns) 3540 Pendulum hardness (in sec.) (according to Konig) 214 Rocker hardness (according to Sward) 30 Buchholz hardness (DIN (German Standard Specification) 53 153) 111 Lattice cut (DIN (German Standard Specification) 53 151) 0 Erichsen cupping (in mm) (DIN (German Standard Specification) 53 156) 10.2 Ball impact hardness test (inch pound) (according to Gardner) 70 Example 2 156 parts by weight of TAD were mixed well with 570 parts by weight of the epoxy resin used in Example 1. This mixture was then poured into moulds for standard small rods and hardened for 1 hour at 800C and then for 4 hours at 1 500C. Test specimens were obtained whose impact strength according to DIN (German Standard Specification) 53 453) was 25 kpcm/cm2. The dimensional stability in the heat (according to Martens) lay at 1320C. The pot life of the epoxide-hardener mixture was 8 hours.

Example 3 a. To 500 parts by weight of an epoxide, likewise, based on bisphenol A, whose epoxide index was 0.2, were added 156 parts by weight of TAD at 1300C with good stirring. The reaction mixture was kept for a further 5-10 minutes at this temperature and then rapidly cooled to room temperature. This "pre-adduct" thus prepared from TAD and the epoxide, whose epoxide index was 0.2, has a softening point, according to the ring and ball method, of 102"C.

b. 65.6 parts by weight of the "preadduct" thus prepared and 100 parts by weight of the epoxy resin used in (a) above were kneaded and extruded in a twin-screw extruder at 700C with a residence period of 7 minutes. The extruded product was stable in the "B state" at normal temperature for at least + year. When used as a moulding powder it hardened within 5 minutes at 1800C. The resultant shaped articles were colourless, transparent and very hard. The dimensional stability in the heat (according to Martens) lay at 1010C.

Example 4 65.6 parts by weight of the "pre-adduct" prepared in Example 3a were intensively mixed on a kneading roll at 80"C with 100 parts by weight of an epoxy resin based on bisphenol A, whose epoxy index was 0.2, 5U parts by weight of slate flour and 2.5 parts by weight of a wax with a saponification number of 140160 and a drip-point of 7681"C.

With this mixture, 4mm thick plates were then produced in an injection moulding machine.

The temperature in the screw was about 80"C; the residence period of the mixture in the screw was about 15 minutes. The temperature of the mould in which hardening out was effected was 1 800C; the hardening time was 2-3 minutes.

The dimensional stability (according to Martens) of these shaped articles which were hardened in this manner was 105 C.

They showed an excellent creep resistance (KA 3c according to DIN (German Standard Specification) 53 480).

WHAT WE CLAIM IS: 1. A thermally hardenable composition for the production of shaped articles and coatings, comprising (a) at least one 1 2-epoxide compound having more than one epoxide group per molecule and (b) 2,2,6,6-tetramethylXamino-piperidine, (a) and (b) being present in such amounts that for each epoxy equivalent there are 0.61.3 equivalents of the hydrogen atoms of the piperidine which are bound to nitrogen; and, if desired, 0.0l0% by weight, of a reaction accelerator, based on the weight of the 1,2-epoxide compound.

2. A composition according to Claim 1, wherein the 1,2-epoxide compound having more than one epoxide group per molecule is free from aromatic rings.

3. A composition according to Claim 1 or Claim 2, wherein 0.5 to 5% by weight, based on the weight of the 1 2-epoxide, of a reaction accelerator is used.

4. A composition according to Claim 1, 2 or 3, wherein a part of component (b) is replaced in stoichiometric proportion by other known epoxy resin hardeners selected from polyamines, polyamides, aminoamides and polyamidoamines.

5. A thermally hardenable composition according to Claim 1 substantially as described in any one of the foregoing Examples 1 to 4.

6. A process for the production of shaped articles or coatings which process comprises heating in known manner a thermally hardenable composition including at least one 1,2-epoxide compound having more than one epoxide group per molecule and a cyclic diamine which is 2,2,6,6-tetramethyl4-amino-piperidine whereby a polyadduct of the 1,2-epoxide compound is formed.

7. A process according to Claim 6, in which the 1,2-epoxide compound having more than one epoxide group per molecule is free from aromatic rings.

8. A process according to Claim 6 or 7, in which the heating is carried out in two steps, the temperature of the second step being considerably higher than the first.

9. A process according to Claim 6, 7 or 8, wherein a part of the cyclic diamine is replaced in stoichiometric proportion by other known epoxy resin hardeners selected from polyamines, polyamides, aminoamides and polyamidoamines.

10. A process according to any of Claims 6 to 9, wherein the rate of formation of the polyadduct is accelerated by the addition of a catalytic accelerator.

11. A process for the production of shaped articles or coatings according to Claim 6 substantially as described in any one of the foregoing Examples 1 to 4.

12. A coating or shaped article produced from a composition as claimed in any one of

Claims (1)

1. Claims 1 to 5.

   13. A coating or shaped article when produced by a process as claimed in any one of Claims 6 to 11.