CA1150889A - Process for preparing aminoplast resins - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Highly methylated methylolguanamines, such as a methylated tatramethylolbenzoguanamine or tetramethylolacetoguanamine, are advanced by heating under acid to neutral conditions with an advancement agent such as benzoguanamine, acetoguanamine, ethyleneures, 1,3-propyleneures, melamine, or urea. The products may be heated with resins containing at least two alcoholic hydroxyl, carboxylic acid, or carboxylic amide groups per molecule to form hard, crosslinked coatings. They are particularly useful in powder coatings.

Description

~15~)~89 BACKGROUND OF T~E INVENTlON

T~IS INVENTION relates ~o a novel process for preparingaminoplast resins, mQre particularly, advanced etherified methylolguanamine resins, to the resins made by the new process, snt to théir use in coating compositions.
Etherified methylolguanamine resins are, in general, well known, commercially available materials ant are used in numerous fields of application, especially iD liquid or powder coating compositions.
They are prepared by reacting a guanamine with formaldehyde or a formaldehyde donor such as paraform under neutral or basic conditions to form the methylolated guanamine and etherifying this with an alkanol under acid conditions ( see, for example, British Patent Specification No. 1 026 696). Such materials are often blended with an alcoholic hydroxyl group-containing resin, such as an alkyd, polyester, acrylic resin, or polyepoxide, and cured at elevated -~emperatures in the presence o an acid ca~alyst, or, when larger proportions of an acid catalyst are used, at room temperature.
Carboxyl-containing resins have also been used as the coreactant.
For certain applications, such as in the formulation of powder coatings, it is preferred that the etherifiet methylolguanamine resin is a non-sticky solid at room temperature or at slightly elevated temperatures. Many commercially available etherified methylolguanamine resins are sticky, high viscosity liquids at ordinary temperatures, and so cannot be used in powder coatings, Purther, it is known that while, when butanol is used as the etherifying alcohol, the resultant resin in fully compatible with a wide range of co-reactants and solvents, such compatibility '~

115{~889 i8 not always achieved when a lower alcohol is used. However, complete elimination of butanol from the resin is not easy to achieve, and its presence, either remaining after etherification or liberated by the curing process, makes the resin unpleasant to handle without very effective ventilation.
We have now found a novel method of making`etherified methylolguanamine resins which are solid at ambient and slightly elevated temperatures, which are fully compatible with a wide range of co-reactants and solvents, and which do not contain butanol or liberate it on curing.
It is known, from British Patent Specification Nb. 948 853, to prepare a modified aminoplast resinous composition by i. forming a partially polymerised aminotriazine resin comprising an aldehyde, especially formaldehyde, and an aminotriazine, which is usually melamine but may be a guanamine, ii. adding a small unt of an ~m;notriazine to the partially polymerised aminoplast resin ( which i8 unetherified), iii. heat-treating the resulting syrup for a short period, and iv. cooling the hot syrup, and then blending there*ith a small unt of one or more amines.
The product is used alone to form laminates from glasscloth.
British Patent Specification No. 1 048 710 describes the reaction of benzoguanamine and formaldehyde to form a monomeric reaction product which is then treated with melamine and a polymerisation catalyst i6 added. The product is likewise unetherified.
In the process now provided, a monomeric, highly methylated, methyl-olated guanamine i8 heated with an advancement agent, which may be an il5~889 Aminotriazine, urea, a cyclic urea, or a biscarbamate, under neutral or slightly acid conditions. The term "atvancement" is used herein in its conventional sense to mean a process iD which an essentially linear, i.e., not substantially crosslinked, product of higher molecular veight is produced. In the present process, part of the etherifying methanol is eliminated.
DETAILED DISCLOS~RE
Accordingly, this invention provides a process for the preparation of an advanced methylated, methylolated guanamine resin which comprises reaction of a methylatet methylolated guanamine of the formula RlOC~2 ~ N 20R

N ~ N ~ ~ N
R OCH2 ~ \ CH20R
where R represents an alkyl group of 1 to 16, and preferably 1 to 4, carbon atoms, a phenyl group, or a group of formula Rloc~ N ------ ~ CH ORl

2 \ ~ 2 II
N ~ N N
R10CH2~ \ C}120Rl each Rl represents a hydrogen atom or a methyl group with the proviso that, on average, at least 70% of the total number of groups R

on the methylated methylolated guanamine of formula I are methyl groups, and 115{)889 R represents an alkylene group of from 2 to 16, and preferably 2 to S, carbon atoms or a phenylene group, at a pH of from 2.5 to 7, with 0.1 to 1 mole, per gram equivalent of guanamine residue in the compound of formula I, of an advancement agent of gen-eral formula III

where either R represents a carbonyl group and R and R each represent a hydrogen atom or together represent an alkylene chain having from 2 to 4 carbon atoms which may be substituted by one or two hydroxyl groups, for example a group of the formula -fH-ICH- or -CH2-CHCH2-OH OH OH
or R represents a residue of formula -CO - O - R - O - CO - IV
or N =~=~55 ~ N
~ N
where R represents an alkylene group of 2 to 20 carbon atoms or an arylene group of 6 to 12 carbon atoms, and R represents an alkyl group of 1 to 16 carbon atoms, a phenyl group, or an amino group (NH2-), and R and R each represent a hydrogen atom.
This advancement may be effected in the presence or absence of . ~.

, j _~
~J ~.

115~)889 an acid catalyst, preferably at a pH of 4~to 7. Acids which may be used as the catalyst include formic acid, phosp~oric acid, and aromatic sulphonic acids, especially toluene~-sulphonic acid. The amount of the advancing agent of formula III, and thè reaction conditions, may be varied according to the physical properties sought in the final product, more advancement agent and a longer reaction time generally leading to higher molecular weight materials, these having higher melting temperature ranges. Preferably, the reaction is effected with 0.2 to 0.7 mole of advancing agent of formula III per gram equiYalent of guanamine residue in the compound of formula I, but as little as~e.g., 0.125 le may be used successfully.
Preferably, too, the mixture i8 heated in the presence or absence of an inert solvent at from 80 to 120C for from 2 to 6 hours. The product may be purified by removal of solvent if present and, if desired, by re val of the acid using conventional methods, including neutralisation. Often, however, it is not necessary to remove the acid, since it does not usually interfere with, and may indeed help, the later cùring reactions. The product preferably melts within the range 50 to 130C, especially w~thin the range 60 to 90C.
The etherified methylolated guanamines of formula I used as starting materials for the novel process are known materials, their prepsration baving been described in, for example, British Patent Specification No.1 026 696 and We~t German Offenlegungsschrift ~o. 2 03i 035, They are normally prepared by reaction of a guanamine of general formula llSV~89 N ~ N VI

2 N ~ ~ NH2 ~bere R8 represents an alkyl group of 1 to 16 carbon atoms, a phenyl group, or a group of formula N ~ N
NH2 ~ N J ~ NH2 VII

where R2 is as hereinbefore tefined, with at least 4 moles, and especially 4.5 to 7 moles, of formaldehyte per gram equivalent of guanamine residue in the guanamine of formula VI, under alkaline conditions, the methylolation being substantially complete after ~ to 4 bours at 50 to 100C.
The mixture is then treated with at least 4 les of methanol per gram equivalent of guanamine residue in the guanamine of formula VI and acidified. An exces6 of methanol is preferred, this excess serving as a solvent for the reaction. Acidification is effected using a strong acid, such as hydrochloric acid, which is preferably added in an amount sufficient to reduce the pH to within the range 1.5 to 4, and the reaction is carried out at any temperature from 20C to the boiling temperature of the mixture.
The reactant of formula I may, for example, be a methylated octamethylolatipoguanamine or a methylated octamethylolsuccino-~15(3`~89 guanamine, but preferably it is a methylated tetramethylol-benzoguanamine or a ~methylated tetramethylolacetoguanamine. As the advancement agent of formula III there may be used, for example, urea, melamine, ethylene dicarbamate, 1,4-butylene dicarbamate, and 1,2-dihydroxyethyleneurea ( i.e., 4,5-dihydroxyimidazolidin-2-one) but preferably benzoguanamine, acetoguanamine, ethyleneurea ( i.e., imidazolidin-2-one), or 1,3-propyleneurea (i.e., hexahydro-2H-pyrimidin-2-one).
The products of the present invention are suitable for use in a variety of coatings applications. They may, for example, be dissolved in an organic solvent or a mixture of organic solvents and blented with pigments, co-reactants, or other polymerisable materials as paints for application to woot or metals or as inks for application to paper or card. Alternatively, they may, if desired, be mixed with pigments, fillers, polymerisable materials, or co-reactants, ground to a fine powder, typically having a particle size within the range 0.015 to 500 ~m, and used as powder coatings.
Suitable co-reactants contain two or more free alcoholic hydroxyl groups per average molecule and may be any of those used conventionally with guanamine resins, including alkyds, polyesters, hydroxyl-containing epoxide resins, and hydroxyl-containing acrylic resins. There also may be used ( although in general they are less preferred~being less reactive towards the advanced methylated, methylolated resins of this invention) resins containing two or more free carboxylic acid groups per average molecule. Yet further suitable co-reactants comprise resins containing at least two amide groups (-CONH2) per average molecule, such as copolymers of styrene g and/or (meth)acrylic acid esters with minor proportions of (meth)acrylamide and (meth)acrylic acid as described in British Patent Specification No~ 1 026 696.
The coatings may be applied by means conventional for liquid or powder coating compositions and, after drying if necessary, they may be cured at room temperature or by heating, usually within the range 35 to 300C, especially from 100 to 200C or 225C, to give a coating having a very good gloss, colour, hardness, and resistance to grease, staining, and detergents.
This invention therefore also provides a process for coating a surface which comprises applying to the surface an advanced ~ethylated, methylolated guan~m;ne resin prepared by the novel process, optionally with a compound containing at least two alcoholic hydroxy groups or at least two carboxylic acid groups or amide groups per average lecule, and causing the resin to form a hard, cross-linked coating, usually by heating.
The invention will be further illustrated in the following Examples, in which all parts are by weight ( unless otherwise specified). Softening points are recorded as determined by means of a ~ofler bench.

~15~)~89 EXA~LE 1 A. Preparation of a methylated, methylolated guanamine resin Methanol (387.2g), paraformaldehyde (444.6g; 91% pure), benzoguanamine ~841.5g), and aqueous sodium hydroxide solution (54.0 ml; 20% w/w) were stirred and heated together for one hour at 70C. A further quantity of paraformaldehyde (444.6g) and of sodium hydroxide solution (54.0 ml; 20Z w/w) were adted, and heating was continued at 70C for one hour.
The mixture was cooled to 45-50C, and concentrated hydrochloric acid was added to bring the pH of the mixture to 8.6-8.8 (approximately 2.5 ml was required) Methanol (2475g) was added, and the ~ixture was cooled to 36C.
Concentratet .hyarochloric acid (67.5 ml) was added, and the mixture was stirred at 40C for 2 hours. The mixture was adjusted to pH 8.6-8.8 with 20% sodium hydroxide solution (approximately 117 ml) and the mixture was distilled under a water pump vacuum to remove aqueous methanol. When the temperature of the distillation residue reached 70C, water (100 ml) was added and distillation was continued until the residue reached a temperature of 100-110C.
This residue was then ~ooled to 90C and filtered to remove sodium chloride. The filtrate comprised a highly methylated tetramethylol-benzoguanamine resin (1550g), a colourless clear liquid having a refractive index n2 of 1.5700-1.5750 and a viscosity at 25C
of 20.-25 Pas. Its degree of methylation (i.e., the proportion of groups Rl which are methyl groups) was 82.5%~
B. Advancement This resin (104.54g) and benzoguanamine (27.81g, i.e., 0.51 115(i~9 mole per gram equivalent of guanamine resitue in the resin) were mixed and stirred at 100C for 15 minutes. Toluene~-sulphonic acid (0.4 ml of a 50% solution in methanol) was added and the mixture, which had a pH value of 5.0, was stirred at 100C for a further 2 hours, all volatile materials being removed as they formed. At the ent of this heating the residue hat a softening point of 60C.
The product was substantially of formula ~L~2--N ~N J~ N-CII2-NII--~N --~NI~

3 CH2 n N _ ~ N

N ~ N ~ ¦ CH2 VIII

where n represents an integer of average value 0.8, as determined by vapour pressure osmometry, and R9 and R10 each represent a phenyl group.

A. Preparation of a methylated, ~eth~lolated cuanamine resin_ Acetoguanamine (600g) and methanolic formaltehyde solution (939g;
44% methanol, 46% formaldehyte, 10% water) were mixet with 57.6 ml of 20% agueous sodium hydroxide solution ant heated to 70C. Ater 1 hour, paraformaldehyte (474.2g; 91Z formaldehyde) and 57.6 ml of 20~ aqueous sodium hydroxide solution were added and the reaction was continued for a further hour. The solution was neutralised with hydrochloric acid, then methanol (2640g) was added and the solution was cooled to 37C. Hydrochloric acid (72ml) was adted, and the reaction was continued for a further 2 hours. After neutralising the mixture with 20Z aqueous sodium hydroxide solution, excess of methanol and water were removed by distillation under reduced pressure. The product, a highly methylated tetramethylolacetoguanamine, which was filt~red to remove sodium chloride, was a viscous liquid.
Its degree of methylation was approximately 80%.
B. Advancement To 689 parts of the above liquid was added 1~2.5 parts of acetoguanamine (i.e., O.S mole per gram equivalent of guanamine residue in the resin) and the mixture was heated to 120C. After 15 minutes, 1.3 parts of toluene~-sulphonic acid solution (50%
in methanol) was added; reaction was continued at 120C until the product had a softening point of 75C. The catalyst was neutralised with N-benzyldimethylamine and the product was allowed to solidify in a tray.
The product was substantially of formula VIII, in which R9 and R10 each represent a methyl group and n has a calculsted average value of 1Ø

Example 2 was repeated but only 1~8 parts of acetoguanamine werç used, instead of 162.5 parts, in the advancement reaction, i.e., .llS~`889 0.33 mole per gram equivalent of guanamine residue in the resin.
Heating was continued~for lO hours at 120C, and the product then had a softening point of 7SC. This product is of formula VIII, in which R9 and R10 each represent a methyl group and- n has a calculated average value of 0.66.
E~A~LE 4 Example 2 was repeated, the 162.5 parts of acetoguanamine employed in the advancement reaction being replaced by 243 parts of benzoguanamine, i.e., 0.5 mole per gram equivalent of guanamine residue in the resin. The reaction was continued until the product had a softeniDg point of 60C.
This product is of formula VIII, in which R9 represents a methyl group, R10 represents a phenyl group, and n has a calculated average value of lØ

The product of each of Exæmples 1, 2, and 4 was mixed with an equal weight of either a solid~hydroxyl-containing polyester resin (hydroxyl content 3.4 equiv.lkg) prepared in a conventional manner from cyclohexanedimethanol, trimethylolpropane, neopentyl glycol, and dimethyl terephthalate, or a solid, hydroxyl-containing acrylic resin (hydroxyl content 1.91 equiv./kg) prepared in a conventional manner from 70% of methyl methacrylate and 30% of 2-hydroxyethyl methacrylate. ~br ease of application the mixtures were dissolved in xylene/n-butanol (1:1 by volume) to give a 50%
solution. The solutions were applied by means of a wire-wound rod to glass or metal plates to give a coating 37.5 ~m thickness. The coatings were cured for 15 minutes at 180 or 200C. After being llSU~389 conditioned overnight at 65% relative humidity and 15.5C their hsrdness (Persoz) was measured, and they were tested for acetone rub resistance by rubbing 20 times with a swab of cotton wool soaked in acetone. The results obtained are recorded in Table I.

TABLE I

Protuct Co-reactant Cure Hardness Acetone of Temp C (Persoz) Resistance Example ¦ _ 1 Polyester 180 312 no effect 1 Acrylic 180 274 no effect 1 Polyester 200 289 no effect 1 Acrylic 200 286 no effect 2 Polyester 180 270 slight softening 2 Acrylic 180 256 no effect 2 Polyester 200 255 slight softening 2 Acrylic 200 263 no effect

4 Polyester 180 289 softening 4 Acrylic 180 291 no effect 4 Polyester 200 301 slight softening 4 Acrylic 200 256 no effect A highly methylated tetra~ethylolbenzoguanamine resin was prepared as described in Part A of Example I. A 104.5g portion of this resin was advanced by stirring with 14.9g of 1,3-propyleneurea 115~9 (i.e., 0.50 mole per gram equivalent of guanamine residue in the resin) at 100C for 15 minutes, adding toluene~-sulphonic acid (0.4 ml of a 50% solution in methanol) to bring the pH to 5.2, and heating for a further 4 hours at 100C, all volatile materials being re ved as they formed. The product had a softening point of 65C. The catalyst was neutralised with N-benzyldimethylamine.

The procedure of FY~mple 6 was repeated, there being used 6.95g of benzoguanamine ( i.e., 0.125 mole per gram equivalent of guanamine resitue in the resin) in place of the propyleneurea. The softening point of the product was 67C.

Example 6 was repeated, there being used 14.2g of ethyleneurea (90% pure, the balance being water), i.e., 0.50 mole per gram equivalent of the guanamine residue in the resin, in place of the 1,3-propyleneurea. The softening point of the product wa~ 55C.

Example 6 was repeated, there being used 13.5 g of melamine, i.e., 0.36 mole per gram equivalent of the guanamine residue in the resin in place of the 1,3-propyleneurea. The softening point of the product, which was opaque, was 74C.

Example 6 was repeated, there -being used in place of the 1,3-propyleneurea, 8.9g of urea ( i.e., 0.50 mole per gram equivalent of the guanamine residue in the resin) The softening point of the product was 60C.

115~89 Example 6 was repeated, but in place of the 1,3-propyleneurea there was used 17.6 g of 1,2-dihydroxyethyleneurea (i.e., 0.50 mole per gram equivalent of the guanamine residue in the resin). The product had a softening point of 70C.

Powder coating compositions were made from the products of Example 6 and 7. The components of each composition are listed in Table II.

TABLE II

Component Parts in Mixture Product of Exa=ple 6 5~ _ C _ Product of Example 7 _ 50 _ 55 Polyester I 240 240 _ Polyester II _ 200 200 Polyacrylic resin (a commercially-available 5 5 5 5 flow additive) Benzoin (as flow 3 3 3 3 additive) Titanium dioxide 200 200 175 175 Polyester I denotes "Uralac P2115", an oil-free, hydrosyl group-115(J~89 containing branched polyester available from Synthetic Resins Ltt., Speke, Liverpool, England, which has the following properties:
acid value less than 10 mg KOH/g; hydroxyl value 30-40 mg KOH/g;
softening point ( measured according to ASTM E28-67 without stirrer) 110-120C.
*~ Polyester II tenotes BA 530, available from BIP Chemicals Ltd., Oldbury, Worley, ~orcestershire, England, which has an acid value of approximately 7.5 mg KO~/g, a hydroxyl value of 90-110 mg KOH/g, and a softening point, measured according to 8S 2782 Method 103A, of 90-97C.
Mixing was effected by dry blending, followed by hot-melt extrusion in a Buss Ko-Kneader using a barrel temperature of 95C
and a screw t~mperature of 40C. (Buss Ko-Kneader is a trademark).
The extrudate was cooled to ambient temperature, crushed, ant ground to a particle size below 75 ~m, the bulk of the msterial hsving a particle size between 20 and 75 ~m.
The gel time~ of these mixtures at 180C were:
Mixture A 9 mi~utes;
Mixture B 7 minutes;
Mixture C 8~ minutes;
Mixture D 7 minutes.
The mixtures were sprayed onto steel panels or onto chromate-treated aluminium panels using an electrostatic powder sprayer, and cured by heating for 20 minutes at 200C, giving costings 50 ~m thick. These coatings were then tested as follows:
~ EMK resistance" was determined by giving the panels 20 double rubs with a cotton wool swab soaked in ethyl methyl ketone "Fle~;bility" was detenmined by bending the panels around mandrels of decreasing diameter to find the smallest diameter around which the panels could be bent without cracking the coating.
"Gloss" was determined by the method of BS 3900 Part D2 (1967~ using a 60 angle of incidence, The result~ are given in Table III~

TABLE III

Misture EMK Flexibility Gloss Appearance resistance A Unaffected 3m~ 60% hard, glossy, . . . slight "orange B Unaffected 1.5 m~ 22Z even matt C Unaffected 12 ~ 40% hard, glossy, . slight "orange . D ~tfecce~ 20Z hard, s=ooth ? even .

Claims (11)

What is claimed is:

1. A process for the preparation of an advanced methylated, methylolated guanamine resin which comprises reaction of a methylated methylolated guanamine of the formula I

where R represents an alkyl group of 1 to 16 carbon atoms, a phenyl group, or a group of formula II

each R1 represents a hydrogen atom or a methyl group with the proviso that, on average, at least 70% of the total number of groups R1 on the methylated methylolated guanamine of formula I are methyl groups, and R2 represents an alkylene group of from 2 to 16 carbon atoms or a phenylene group, at a pH of from 2.5 to 7 with 0.1 to 1 mole, per gram equivalent of guanamine residue in the compound of formula I, of an advancement agent of general formula III

where either R3 represents a carbonyl group and R4 and R5 each both represent a hydrogen atom or together represent an alkylene hydrocarbon chain having from 2 to 4 carbon atoms, which may be substituted by one or two hydroxyl groups, or R3 represents a residue of formula or V

where R6 represents an alkylene group of 2 to 20 carbon atoms or an arylene group of 6 to 12 carbon atoms, R7 represents an alkyl group of 1 to 16 carbon atoms, a phenyl group, or a group -NH2, and R4 and R5 both each represent a hydrogen atom.

2. The process of claim 1, which is carried out at a pH in the range 4 to 7.

3. The process of claim 1, in which 0.2 to 0.7 mole of advancing agent of formula III is used per gram equivalent of guanamine residue in the compound of formula I.

4. The process of claim 1, in which the reaction mixture is heated at a temperature in the range 80° to 120°C for from 2 to 6 hours.

5. The process of claim 1, in which R in formula I represents an alkyl group of 1 to 4 carbon atoms.

6. The process of claim 1 or 5, wherein R and R in formula I together represent a group of the formula or -

7. The process of claim 1, in which the compound of formula I is a methyl-ated tetramethylolbenzoguanamine, a methylated tetramethylolacetoguanamine, a methylated octamethyloladipoguanamine, or a methylated tetramethylolsuccinoguana-mine.

8. The process of claim 1, in which the advancement agent of formula III
is urea, melamine, ethylene dicarbamate, 1,4-butylene dicarbamate, 1,2-dihydroxy-ethyleneurea, benzoguanamine, acetoguanamine, ethyleneurea, or 1,3-propyleneurea.

9. An advanced methylated, methylolated guanamine resin obtained by the process of claim 1 and melting within the range 60° to 130°C.

10. A process for coating a surface which comprises applying thereto an advanced resin obtained by the process of claim 1 and heating it to form a hard, crosslinked coating.

11. The process of claim 10, wherein the said advanced resin is heated in the presence of a co-reactant resin containing, per average molecule, at least two groups selected from alcoholic hydroxyl groups, carboxylic acid groups, and carboxylic amide groups.