CH630951A5 - Process for the preparation of powder lacquer coatings - Google Patents

Description

The invention therefore relates to a process for the preparation of powder coating materials using storage-stable powder coating materials with a grain size of less than 0.25 mm, preferably 0.02 to 0.06 mm, which are obtained by reacting 1,2-epoxide compounds with more than a 1,2-epoxy group in the molecule and a lower melting point of> 40 ° C. with he-35 terocyclic hardeners and paint additives at elevated temperature can be obtained by applying the powder coating obtained to an object to be coated and curing at elevated temperature, characterized in that that as a heterocyclic hardener compounds of the general formula

55

The electrostatic powder spray technology for painting 45 primarily metallic objects is one of the most important painting processes today. Seen worldwide, the powder coatings based on epoxy resins dominate. Apart from some special products, hardeners based on dicyandiamide are used. It is part of the prior art 50 that the reactivity of such powder resins can be varied over a comparatively large range. This also results in different application temperatures, which are in the range 140-200 ° C. However, all these products have in common that they react more or less slowly at room temperature or slightly elevated temperature. This leads to higher molecular proportions, which later become apparent in the application of the powder coating in a deterioration in the flow properties. An epoxy resin powder coating, depending on its history with regard to thermal stress, may have a very different appearance. This means that the reproducibility of the surface quality is not guaranteed.

Based on the crosslinking reaction that begins at a moderately elevated temperature, complications can arise in the production of such powder coatings. Powder coatings are known to be obtained by extrusion of physical mixtures of the resins with pigments and coating auxiliaries in which R is a -C--, -CH2 - CH- R '' - CH- CH2- -

OH

I.

OH

O

O

60

or -C— R "- C— grouping,

R 'is hydrogen or an alkyl radical, preferably C1-C5-,

and

R "is a divalent, optionally substituted, aliphatic, aromatic or heterocyclic radical.

The hardener is expediently used in such an amount that there is 0.5-1.1, preferably 0.75-1.0, amine hydrogen equivalents for a 1,2-epoxy equivalent. The molecular weights of the heterocyclic hardeners mentioned are in particular between 300 and 2300, preferably between 350 and 1300.

3 630 951

The mentioned “lower melting point” of a melted bileate and the 3,4-epoxycyclohexylmethyl ester of 3,4-epoxycy-

ren material is the temperature at which during the clohexane carboxylic acid.

Simultaneous and even heating of a sample die- Mixtures of solid polyepoxides can also be used with different material and another piece of material, e.g. a mixture of a polyepoxide, the difference between the sample and the other piece of material 5 melting point between 120 and 160 ° C and a poly begins to set, due to the beginning melting epoxy with a melting point between 60 and 80 ° C of the sample. With further heating, the temperature passes through (the melting point is determined according to the mercury method difference in the maximum and then becomes zero again, if von Durrans). Suitable mixtures contain between 30 and the sample is completely melted. (See RC Mackenzie: and 50% by weight of a solid polyglycidyl ether of 2,2-bis (4- "Differential Thermal Analysis", vol. 1, pages 7 and 8, Academic 10 hydroxyphenyI) propane with an epoxy equivalent weight of press , London and New York, 1970). between 1650 and 2050 and a melting point of 120 to

Another object of the invention is that after this 160 ° C, and between 50 and 70 wt .-% of a solid polyglycine

Processes obtained coatings. dyl polyether of 2,2-bis (4-hydroxyphenyl) propane with one

The advantages of these 1,2-epoxy resin powder coatings, whose hardening epoxy equivalent weight is between 450 and 525 and a component, as already mentioned, based on TAD, are 15 melting points from 60 to 80 ° C.

in the following predicates: If high epoxy functionality appears desirable, see above

1. Extremely good storage stability, even at higher ones, a preferred polyepoxide is the polyglycidyl ether of temperatures. l, l, 2,2-tetra (hydroxyphenyl) ethane.

2. Very good leveling properties, which are practically only otherwise As mentioned earlier, in addition to the so-called solvent-based paints are suitable. 2 (also called solid resins adduct hardeners for carrying out the

3. Unproblematic processing on extruders and similar process according to the invention. Such fixed adduct hardeners lent to working machines. can, for example, from liquid polyepoxides

4. Compared to the usual amine-curing epoxy resin-saturated hydrocarbons, such as vinylcyclohexene, dicyclostems, improved UV and weather stability. pentadiene and the like, epoxethers of polyhydric alcohols and phenols

To produce the finely divided mixtures, which are to be used as powder, etc., and aliphatic, cycloaliphatic and aromatic lacquers, diamines 1,2-epoxy compounds will be produced. A prerequisite for the properties with more than one 1,2-epoxy group in the molecule and such an adduct is that the lower lower melting point of> 40 ° C. is provided. Compound melting point is above 40 ° C.

ge, which correspond to these characteristics, are poly- To improve the flow properties of the varnish wer epoxy compounds, which are solid at 40 ° C and below, 30 added to the so-called flow control agents in the preparation, including higher molecular weight compounds (so-called solid resins) Agents can be chemical compounds (ze), and those which, owing to their symmetrical structure or mixtures thereof, of very different chemical types or the size of the carbon bound to the 1,2-epoxy group, for example polymeric or monomeric compounds, acetal systems are solid, and, on the other hand, those caused by oils such as polyvinyl formal, polyvinyl acetal, polyvinyl butyral, polyreaction of liquid 1,2-epoxy compounds with more than 35 vinyl acetobutyral or di-2-ethylhexyl-i- butyraldehyde, di-2-one epoxide group per molecule with primary or secondary ethylhexyl-n-butyraldehyde acet, diethyl-2-ethyIhexanoI-acetaI, amines have been prepared in such an amount that the ad-di-n-butyl-2- Ethylhexanol-acetal, di-i-butyl-2-ethylhexanol product at least on average still contains a 1,2-epoxy group acetal, di-2-ethyl-hexyI-acetaldehyde-acetal and the like, ether, such as that contained per molecule (so-called adduct hardener). polymeric polyethylene and polypropylene glycols, mixed poly-

The 1,2-epoxy compounds can be saturated as well as from n-butyl acrylate and vinyl isobutyl ether, ketone Al

also unsaturated and aliphatic, cycloaliphatic, aromatic dehyde condensation resins, solid silicone resins or mixtures

and be hetercyclic. They can also contain substitutes such as zinc soaps, fatty acids and aromatic acids, which are among the mixture or reaction conditions, carboxylic acid and the like. Also for this purpose, trade will not cause any troublesome side reactions. No products, such as Modaflow, are offered, whose chemical character

Side reactions call alkyl or aryl substituents, hydrates are unknown to consumers and of which only

oxyl groups, ether groups and the like. is known that it is a complex, polymeric, effective

Solid resins are used for this purpose liquid on the basis of polyacrylates. Such

1,2-epoxy compounds with more than one epoxy group in the leveling agent can be used in amounts of 0.2-5.0

Preferred molecule, the epoxy equivalent weight between wt .-%, based on the total amount of powder coating,

500-1000 lies. These are the solid, polymeric polyglycidyl 50 hold.

polyether of 2,2-bis (4-hydroxyphenyl) propane, e.g. The other components of the powder coating mixture, such as pig

are held by reaction of 2,2-bis (4-hydroxyphenyl) elements, dyes, fillers, etc. can, based on the

propane with epichlorohydrin in molar ratios of 1: 1.9-1.2 ge of 1,2-epoxy compounds, within a wide range

(in the presence of a ^ alkali hydroxide in an aqueous medium). vary.

Polymeric polyepoxides of this type can also be obtained. 55 After the powder coating has been applied to the

by reacting a polyglycidyl ether of 2,2-bis (4-hyden objects), these are hardened to temperature

droxyphenyl) propane with less than the equimolecular ren of in particular 130-210 ° C, preferably 140-180 ° C,

Amount of dihydric phenol, preferably heated in the presence. After that, the resulting coating has the described

a catalyst such as a tertiary amine, a tertiary ben benefits.

Phosphines or a quaternary phosphonium salt. The eo Before using it, the powder paint components

Polyepoxide can also be a solid epoxidized polyester that mixes intimately, extrudes and then mills. For those obtained, for example, by the implementation of a practical application, a particle size of alcohol and / or a polybasic carboxylic acid of> 100 [x] is preferably sought, the particle size maximum or its anhydride being combined with a low molecular weight polyepoxide. should be between 30 and 50 [x.

Examples of such low molecular weight polyepoxides 65 The application of the powder coating to the important to be coated is liquid diglycidyl ether of 2,2-bis (4-hydroxyphe body can be carried out by known methods,

nyl) propane, diglycidyl phthalate, diglycidyl adipate, diglycidylte- Z-B- by electrostatic powder spraying, fluidized bed sintering, elec-

trahydrophthalate. Diglycidyl hexahydrophthalate, diglycidyl matrostatic spinal sintering etc.

630 951

4th

The derivatives of 2.2.6.6-tetramethyl-4-aminopiperidine used according to the invention as hardeners can be prepared by known methods. For example,

O

II

prepare the compounds in which R is a —C— group by reacting 2 moles of TAD with one mole of urea, urea compounds, carbon dioxide or dicarbonic acid ester and, if appropriate, subsequent alkylation. Compounds with R = —CH2 - CH- R '' - C— CH2- grouping

OH OH can be by reacting 2 moles of TAD with one mole of an aliphatic, aromatic or heterocyclic diepoxide. When using triepoxides instead of 15 diepoxides while changing the molar ratios, hardeners are obtained which still contain a third TAD residue, i.e. are substituted in R ".

O O

II II 20

The —C— R— —C— grouping can be prepared by reacting 2 moles of TAD with one mole of, for example, a dicarboxylic acid - analogous to the triepoxides also tricarboxylic acid - or their mono- or diesters. When using esters as reaction partners It is expedient to use those with lower alcohol residues (Cj-Cy. The above list is only intended to give a general overview of possible production methods, but these are not the subject of the patent application.

The method according to the invention is illustrated by the following examples:

C. Property profile of the powder coating

Layer thickness: 60-70 | x

Hardness (DIN 53157): 180-190 sec.

Elasticity (DIN 53156): 8-10 mm

5 liability (DIN 53151): 0

Gloss (ASTM-D-523): 95

Course after storage very good

30 days at 40 ° C: no «orange peel effect>:

Free flowing after practically unchanged 10 storage 30 days at 40 ° C: very good Accelerated short weathering in the Xenotest device 450 LF (according to DIN 53231)

Loss of gloss after 500 h: 12%

Loss of gloss after 1000 h: 23%

Loss of gloss after 1500 h: 31%

Loss of gloss after 2000 h: 35%

Example 2:

A. Preparation of the hardener

To condense 2 mol of TAD (312 g) with 1 mol of urea (60 g), the starting materials were reacted at 150 ° C. for about 2 hours with stirring. After 2 hours, about 80% of the theoretical amount of NH3 had been split off. To complete the reaction, the mixture was condensed at 210-220 ° C. for a further hour and then heat-treated at 170 ° C. for 30 minutes under a vacuum of approx. 2 mm Hg.

The hardener so produced had an H-active equivalent weight of 167.

Example 1:

A. Preparation of the hardener

In a 3-neck glass flask, 624 g (4 mol) of TAD were heated to approx. 60 ° C and within 10 minutes with 760 g 35 of a diepoxide based on bisphenol A with an equivalent weight of approx. 190 g / val (epoxy ) mixed. After a homogeneous mixture had formed, the temperature in the swamp was raised to about 70 ° C. The addition reaction started at this temperature and the temperature of the reaction mixture rose to about 110 ° C. due to the exothermic reaction heat. An ice / water mixture was used for cooling during the reaction time. To complete the reaction, the mixture was kept at 80 ° C. for about 30 minutes.

After cooling to room temperature, a solid, brittle resin with a melting point of approx. 65 ° C. was obtained.

B. Production of an Epoxy Resin Powder Coating A powder coating of the following recipe was produced according to the procedure described in Example 1:

57.1% by weight bifunctional epoxy resin

Equivalent weight: 850-940 g / Val 5.4% by weight TAD adduct, see under 2A 37.0% by weight white pigment, rutile type 0.5% by weight leveling agent based on polyacrylate

After the electrostatic application on 1 mm steel sheets, the paint was cured at 220 ° C. for 15 minutes.

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B. Production of an Epoxy Resin Powder Coating A powder coating was formulated on the basis of a bifunctional, solid epoxy resin with the equivalent weight of 850-940 g / val (epoxy).

To this were added 252 g of the resin described under A., 1310 g of the solid epoxide with the equivalent weight of 850-940 g / Val (epoxy), 925 g of white pigment titanium dioxide (of the rutile type) and 12.5 g of a leveling agent based on 55 a polyacrylate intensively mixed in a solid mixer and then extruded in a single-screw extruder at a melt temperature of 95-100 ° C. The extruded, cooled melt was ground to a powder in a pin mill and the grain size fraction> 100 jx was sieved off. 60 The finished powder was applied electrostatically to 1 mm steel sheet in the usual manner and cured at 180 ° C. for 30 minutes.

C. Property profile of the powder coating

Layer thickness: 50-60 | x

Hardness (DIN 53157): 190-200 sec.

Elasticity (DIN 53156): 9 mm

Liability (DIN 53151): 0

Gloss (ASTM-D-523): 100

Course very well

Course after storage: no "orange peel effect"

30 days at 40 ° C: unchanged, very good

Free flowing after very good

Storage 30 days at 40 ° C: free-flowing Accelerated short weathering in the Xenotest device 450 LF (according to DIN 53231)

Loss of gloss after 500 h: 13%

Loss of gloss after 1000 h: 24%

Loss of gloss after 1500 h: 34%

Loss of gloss after 2000 h: 37%

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c

Claims (5)

630 951 2. The method according to claim 1, characterized in that for a 1,2-epoxy equivalent 0.5-1.1 hydrogen amine equivalents of the hardening compound. 2nd PATENT CLAIMS 1. Process for the production of powder coatings using storage-stable powder coatings with a grain size less than 0.25 mm, which are produced by reacting 1,2-epoxy compounds with more than one 1,2-epoxy group in the molecule and a lower one Melting point of> 40 ° C with heterocyclic hardeners and paint additives at elevated temperature can be obtained by applying the powder coating obtained to an object to be coated and curing at elevated temperature, characterized in that compounds of the general formula h3c - 3 are used as heterocyclic hardeners ch3 h3c HjC CH3 ch3 h3c o where R is -C- -, -CH2 - C H- R "- C H- CH2- - I I OH OH O O or -C- R "- C- grouping, R 'is hydrogen or an alkyl radical, and R "is a divalent, optionally substituted, aliphatic, aromatic or heterocyclic radical. 3. The method according to claim 1, characterized in that there are 0.75-1.0 amine hydrogen equivalents of the hardening compound for a 1,2-epoxy equivalent. 4. powder coating, produced by the method according to any one of claims 1-3. produced. Temperatures of 90-105 ° C are common for the melt temperature of the molten resins. Self, if the production extruder can be run consistently and reproducibly, there are always faulty batches, e.g. 5 due to mixing errors or deviations in the required color. After mixing with the additions necessary for correction, such an approach must be extruded again. This inevitably leads to a further, proportional reaction, which later has an effect in the hardened paint film due to poor leveling properties. Further problems arise when transporting or storing finished powder coatings. Even if a number of precautionary measures are taken, it cannot be avoided that powder coatings, especially in southern countries, are exposed to temperatures of around 40 ° C for days and weeks. There are also problems here due to the reproducibility and the surface properties. For the reasons mentioned above, transport and storage are often carried out in cooling units. 20 Surprisingly, hardeners have now been found that eliminate all these difficulties. These are derivatives of 2.2.6.6-tetramethyl-4-amino-piperidine, hereinafter referred to as TAD. These hardeners are distinguished primarily by the fact that the primary amino group 25 of the TAD is suitably converted by condensation or addition during the preparation of the hardener, ie is no longer available in this form for epoxy resin hardening.