NO138030B - STORAGE-RESISTANT, ZINC-RESISTANT PAINT, INCLUDING A BINDER ON THE BASIS OF ORGANIC SILICATES - Google Patents

Description

The present invention relates to a new type of paint, comprising a binder based on organic silicates and optionally containing an organic solvent and/or other pigments or fillers., and the characteristic of the paint is that the binder is produced by transesterification of 1

mol of an organic ortho- and/or polysilicate of a monohydric alcohol with 0.3-3 mol of an aliphatic polyol, and that the paint optionally contains a curing catalyst, preferably a soluble zinc salt, as known per se.

The transesterification reaction takes place during distillation of liberated alcohol, as the reaction is stopped before significant gel formation occurs. The degree of alcohol removal regulates the viscosity of the product. The resulting polymer product can be dissolved in an anhydrous, suitable organic solvent, and there-

a dry, finely divided, inorganic substance is added, so that a dispersion or slurry is formed which can be applied as a coating on a substrate.

The ratio between polyol and alkyl silicate regulates the properties of the polymer that makes up the binder. According to the invention, this ratio is between 0.5 and 3 mol polyol per moles of alkyl silicate.

From British patent no. 712,845 it is known per se to transesterify orthosilicates of lower alcohols with polyols. Preferably, a mixed ester of butanol and methanol (here called "dibutoxy dimethoxysilane") is used, and only methanol is distilled off. A viscous but water-soluble liquid is obtained which cannot be used for painting purposes.

The method described above is a batch type process. Continuous processes are, however, also applicable, and the alkyl silicate reactant is then added to the hot glycol reactant which contains traces of an acid catalyst, while at the same time the alcohol formed is distilled off. In the second step, an equilibrium is established between the tetraglycol silicate, -formed in this way, and excess glycol and -condensed ethyl silicate or ethyl silicate "40". -

"The reaction, which takes place during the production of the polymeric binder, is essentially carried out under alcohol-free conditions, so that it results in the formation of a polymer share with a new structure represented by:

where x is an integer. M is chosen from one of the following groups:

It should be noted that compounds other than the structures shown are formed with both diethanolamine and triethanolamine, depending on the charge ratio, alcohol removed and the reaction conditions,

and the groups R^, I^., R^, R 4 , R^ and. Rg can be the same or different organic compounds bound to the silicon atom by a - 0 bond.

The degree of polymerization, which occurs during the aforementioned reactions, is a function of the amount of alcohol removed by distillation. According to the invention, it is preferred to remove as much alcohol as possible, without, however, taking the polymerization so far that the polymer becomes insoluble. If the polymerization has progressed so far that the polymer is insoluble, heating with a small amount of -alcohol will solubilize it.

It has been found that the molar ratio between tetraalkyl silicate and glycol also plays a significant role in the type of polymer compound that is obtained. This will be explained in more detail later in this description.

The binder mentioned here is formed from what is called "the sump", i.e. the residual mass that is left in the reaction vessel when the glycol/alkyl silicate is formed. The sump may comprise, as part of the reaction mass, an organic solvent. According to the invention, the sump can be further diluted with a methyl ketone, a hydrocarbon solvent, preferably aromatic, or an organic ether or ester or another inert organic compound which is a solvent for the polymer, and which is essentially free of moisture.. To accelerate the hardening reaction, a catalyst, such as zinc chloride or zinc acetate, will occasionally be used, but other catalysts, such as sulfuric acid, can be used.

From US patent no. 3,056,684 it is known in and of itself to add zinc chloride to paints containing zinc dust on

basis of organic silicates.

The resulting zinc dust-containing paint remains stable against gel formation for a long time, if kept in a moisture-proof and airtight container, such as e.g. an ordinary paint can. However, after application to a surface with consequent exposure to the atmosphere, the paint cures to a hard, adherent coating that can be used under high temperature conditions. Gel formation in the paint can be produced quickly by introducing a small amount of water, or by exposing the paint to ammonia gas or certain amines. -

One of the advantages of the present paint preparations

is that they can be premixed in large batches and .^portioned out in unvarnished cans. The contents of the boxes can thus be applied without

to have to be mixed with some other component.. It only needs a simple stirring before use.

The paint according to the invention freezes, does not freeze, is not exposed to bacterial attack, can be used in the form of an aerosol and can be attractively pigmented for use as colored high-temperature measurements.

In the production of the binder for the paint according to the invention, ethylene glycol and/or propylene glycol is preferably used, but any of the following polyols can be used together with a main amount of ethylene or propylene glycol:

If di- or polyols with a higher molecular weight are used, a careful adjustment of the weight ratios and of the amount of alcohol to be distilled off is needed to prevent gel formation.

In the production of the binder according to the invention, a mixture of the reactants is heated under essentially anhydrous conditions, preferably in the presence of an acid-reacting catalyst, to 90-130°C, and the temperature is raised sufficiently to effect the desired polymerization together with the distillation of alcohol , as well as possibly organic solvents. A suitable catalyst is sulfuric acid.

Organic solvents that can be used to liquefy the polymer are hydrocarbons, ketones, esters and ethers, etc.

The use of organic solvents in zinc dust-containing paints based on organic silicates is known per se, see e.g. Norwegian patent document no. 115,084, especially the last paragraph of the description.

The paint according to the invention can suitably be used as a primer for one or more other coatings, especially a plastic coating.

The service life of the known zinc/silicate paints was often limited to 2-12 hours, and clogging of connection pipelines with solid silicate particles represented a serious problem, especially where such pipelines were exposed to high temperatures, such as on hot ship decks.

The new one-component, stable paint makes it possible to carry out the coating by dipping in large tanks, whereas this was previously impossible, as gel formation or degradation would occur within a few hours.

The new one-component paint preparation can be applied in many ways, such as spraying, including r high-pressure spraying, brushing, rolling or dipping.

Another advantage of the paint according to the invention is that it has excellent properties at high temperatures, so that a finished dry coating on a steel plate can be heated to a red-hot state and then quenched in cold water without any cracking or degradation of the coating. This thermal cycle of heating and quenching can be repeated many times without visible deterioration of the coating.

Maintaining an optimal ratio between the glycol/alkyl silicate and zinc dust and other particulate fillers, where other fillers are used, is very important in order to achieve a hard, strongly adherent, fast-setting coating. The ratio between zinc dust and silicate depends on the particle size in the zinc dust. Coatings containing as little as 10% zinc dust, calculated on the total amount of particulate fillers, provide some galvanic protection. The filler prevents a rapid breakdown of the zinc, especially if it is neutral and does not contain a metal which will produce an electro-chemical reaction with the zinc and thereby cause its breakdown. If the zinc dust content in the filler is low, the galvanic protection effect can be used up in some places.

For long-term protection, a minimum of 50% zinc dust in the filler is advisable.

Other features and advantages of the invention will be apparent from the following description.

The following table indicates the results obtained by reacting tetraethylorthosilicate with ethylene glycol.

As regards the boiling point of the glycol/alkyl silicates according to the invention, it should be noted that they should be distilled under reduced pressure to avoid thermal decomposition, or rearrangement, of the polymer structure, the latter of which can occur above 160°C.

As for the "physical form" of the polymers, they are all colorless and range from easily flowing to syrupy, and all the way to semi-solid substances that can no longer be made to flow.

Regarding their solubility, reference should be made to the following table. Polymer No. 1 is soluble in all hydrocarbon solvents and oxygen-containing organic solvents, but insoluble in water;

No. 2 is soluble in aromatic hydrocarbons, insoluble in paraffinic and naphthenic hydrocarbons, soluble in said oxygen-containing solvents, but insoluble in water;

No. 3-6 have the same solubilities as No. 2;

No. 7 is insoluble in aromatic hydrocarbons, soluble in ketones and insoluble in water;

No. 8 is insoluble in most organic solvents, except hot alcohol and compounds with active hydrogen.

The following table provides additional data regarding the above-mentioned polymers.

The molar ratio between ethylene glycol and tetraethyl silicate increases from 0.5 mol glycol per 1 mol in No. 1 to 3 mol 'glycol per moles of silicate in No. 8, and as the ratio increases, the structure changes drastically from a polymer of the main chain type

HH

(-Si-OCCO-Si-) - in which both hydroxyl groups in the glycol are bound

HH

to silicon atoms, to a predominance of the side chain type ("pendant" groups with only one hydroxyl group attached to silicon). In each case, enough alcohol was drawn off to achieve polymerization to a very viscous but not insoluble consistency.

It must be noted that the analyzes and the suggested structure in the data table are calculated on the average composition.

The missing absorption peaks in the IR spectrogram in the 2.7 pm region show no (OH) groups; thus all the glycol must be in the main chain in the first two examples. The silicon content of hydrogen, oxygen and carbon all confirm the suggested structure shown, as does the weight balance; and TR and NMR data indicate the relationship between main chain -and.side-chain glycols.-

NMR spectra of the -OH group in the side chain glycols show a peak in the range -3.25-3.45 dpm (6), which is the range for free OH groups. This peak is not present when there is a main-chain glycol structure. The r-OH groups in the unreacted glycol (which is not bound to any silicon atom) also do not give resonance absorption.

The solutions were in 15% denatured chloroform, and NEAT was used as a standard.

Example 1

Solvent for the binder Inorganic substance

1000 g of substantially anhydrous tetraethylorthosilicate, containing less than 3% by weight of dimer plus polymer, and 450 g of ethylene glycol, are mixed together in a suitable reaction vessel equipped with heating devices, an agitator and a cooler with outlet for condensate. The mixture is heated to around 100-110°C, and 1-3 drops of sulfuric acid (98% H2SO4) are added.

During the first few minutes after the addition of sulfuric acid, the mixture in the reaction container turns yellow, but becomes colorless again after approx. 3 minutes. The ester-yielded alcohol begins to distill jav. By regulating the speed of this distillation, one can regulate the reaction rate and prevent overheating. Evaporation of liquid in the reaction vessel cools the liquid. As a consequence of this . regulation of the distillation rate will to a certain extent regulate the temperature in the reaction mass. The viscosity and structure of the reaction mass depends on the amount of alcohol that is removed and collected.

Distillation can be finished under reduced pressure to remove the last traces of free alcohol. Collection of condensed alcohol (and all other distillate) is continued until 425-450 g of alcohol has been distilled. At about this point, the reaction mass in the container shows a tendency to form a gel or to become quite viscous. The mass can be diluted with a solvent such as toluene to form an azeotropic mixture. In this way, more alcohol can be removed at a lower temperature. The heating is then stopped, and a small amount of toluene, approx. 200 ml, is added to cool the reaction mixture and to dissolve the polymer. After the dilution with toluene, the resulting solution was poured out of the reactor. After the reaction had been carried out and a weight balance had been achieved, it was noted that the glycol used contained about 1% by weight of water, which, however, did not cause any problems, either with the product or the reaction.

The weight balance showed the following details.

Lost

Solids (at the bottom of the reactor) 41

The recovered polymer solution had the following characteristic features and components:

After the cooled solution was taken out of the reactor, 100 parts by weight of this solution, called "OP4", was used to make a mixture with the following composition:

0P4, MEK and zinc chloride were mixed thoroughly and the zinc dust added to the resulting mixture in a high shear mixer. The pigment suspension obtained in this way was applied to a metal surface, e.g. by brushing on a cold-rolled, non-sandblasted steel plate. The suspension was easy to apply and did not contain lumps and gave after 10 min. a very hard, strongly adhesive coating. After drying for a further 15 min. the coating, in tests against water and oil solubility, was found to be unaffected by both of these. By covering the coated sheet with a vinyl coating, excellent adhesion was achieved. Even after pickling, the coated plate showed excellent resistance to salt corrosion when subjected to spraying of a 5% salt solution at 35°C, even after 2000 hours.

The coating, which is from 0.05-0.075 mm in thickness, when dry, shows no cracking, good adhesion in the cross-scratch test, no loss of adhesion in the tear-off test with 1.6 mm deep incisions, and good heat resistance. There is almost no reduction in adhesion or toughness of the coating if heated to 371°C and then quenched in cold water, not even if heated for short periods to 593°C, although oxidation occurs upon prolonged heating to this temperature .

A bending test shows no loss of adhesion at 90° bending, and only a slight loss at 180° bending. Impact tests showed superior results compared to other known zinc/silicate coatings.

The reactions which occur when carrying out the method in the aforementioned example, in which the polymer is essentially not hydrolysed and where anhydrous conditions are maintained; leads to the formation of a polymer portion with the new main chain structure represented by the grouping:

where R is ethoxy or hydroxyethoxy (HO-C^H^-O-).

The exceptional heat resistance of this preparation is presumably due to the fact that all organic groups are driven off by evaporation upon exposure to air and moisture, so that the inorganic groups -SiC^, ZnO, SiC^- remain, which groups are stable up to temperatures, for red-hot .

Example 2

2500 g "condensed" ethyl silicate, containing 95.5% tetraethylorthosilicate monomer, 4% dimer and 0.5% trimer and somewhat higher polymer, is mixed with 1120 g ethylene glycol in a 5 liter flask equipped with a flask thermometer and a reflux thermometer, stirrer, a short packed column, distillation head, cooler and publisher. An immiscible dispersion occurs when this mixture is stirred, but when heated with continuous stirring to about 105°C (flask temperature), and by adding 3 drops of concentrated sulfuric acid (98% H2S04) as a catalyst, the solution becomes clear, and within After a few minutes, ethyl alcohol begins to distill off. A total of 11-24 g of alcohol was collected up to the point where the contents of the container began to thicken noticeably. The contents of the container were then cooled, and 100 g of xylene was added. The resulting liquid product is stable and effective as a binder.

The binder produced in this way is hereinafter called "Silicate No. 1". It remains stable and active as a binder for a period of at least six months, probably much longer.

Example - 3

500 g of "Silicate No. 1" is mixed with 500 g of methyl ethyl ketone and 2 g of zinc chloride, together with 2500 g of zinc dust and 200 g of dried

talc pads, and the resulting mixture is thoroughly mixed in a mixer with high shear. such as a "Waring Blender", The-" resulting product remains stable when stored in a sealed can and kept therein for a period of six months, and remains usable as a highly adhesive, galvanic _coating. The resulting paint is henceforth called "Paint let".

Example 4

"Paint la" is used in a system for continuous and automatic dip coating of cleaned steel parts. For this purpose, the parts are placed in a mesh container, and after they have been dipped in "Paint la", the excess liquid is removed with the help of a centrifuge, while at the same time the coating is spread evenly over the surface of the parts, especially in and around all holes and the adjacent areas. The parts/coated in this manner are then placed on a grid cloth equipped with spikes to minimize contact between the wet coated surfaces and the support surfaces of the screen. Rapid drying of the coating occurs by agitating the sieve-supported parts in circulated, warm, moist air under a hood. Hardening takes place within a few minutes. To accelerate the curing further, a small amount of zinc chloride or zinc acetate in methyl ketone solution can be added.

The coated parts were then subjected to various tests, with the following results:

When the described glycol/alkylsilicate binder was diluted with the same volume of -xylene instead of methyl ketone, and 2.5 parts by weight of zinc dust added per part diluted binder, the resulting paint was kept in perfect workable condition for a period of 1.5 years. The coatings from this binder provided an excellent hard, fast-setting and adhesive, highly protective coating for steel.

When the glycol/alkyl silicate binder was diluted with an equal volume of a high flash point aromatic solvent and 2.5 parts by weight of zinc dust and 0.5 parts by weight of flaky silica flour and 0.003 parts of triethylamine were added to the mixture and this was -applied to a clean steel substrate which coating, the coating dried quickly and was adhesive and protective (pencil hardness 3H - salt spray 5% salt at 35°C for more than 3,000 hours produced no rust). This paint mixture was kept for 1.5 years and was found to be perfectly suitable as a coating, and had not changed its character during this time, did not outgas and did not deposit a hard layer on the bottom.

Example 5

In the preparation of a paint called "Paint lb", 500 g of glycol/alkyl silicate binder from "Silicate No. 1" was mixed primer with 500 g of mesityl oxide, 4 g of zinc chloride, 2500 g of zinc dust and 200 g of talc, using a mixer. with high shear force. Preliminary tests similar to those described in Example 4 showed that excellent coatings with almost identical properties to that obtained with "Paint la" had been obtained.

Example 6

500 g of the glycol/alkyl silicate binder previously called "Silicate No. 1" is mixed with 500 g of methyl isobutyl ketone, 2 g of zinc chloride, 2500 g of zinc dust and 200 g of talc. When tested in the same way as the above-mentioned samples, the preparation, which is called "Paint lc", gave identical results, except that the coating was somewhat softer, but it passed all the tests that "Paint la" was (subjected..

Example 7

500 g of glycol/alkyl silicate binder "Silicate no. 1" is mixed with 50 g of methyl ethyl ketone and 450 g of xylene together with 2500 g

zinc dust, 10 g bentonite and 60 g talc. 4 g zinc chloride was added and the mixture was subjected to vigorous stirring in a Waring Blender. The resulting paint, herein called "Paint 13", turns out to be somewhat softer than "Paint la", but similar to the latter in all other respects.

In order to produce a harder coating than, for example, "Paint la", - and to improve the suspension - of zinc dust so that - it does not - settle, one can add different forms of "finely divided silicon dioxide, such as a finely divided, fumed silicon dioxide airgel, in an amount corresponding to about 5 g, to the other ingredients in this example, or an even harder coating is obtained by adding 100 g of SiC^ with an average particle size of 5 ym.

Example 8

1200 g of condensed ethyl silicate and 670 g of propylene glycol with 2 drops of concentrated sulfuric acid to catalyze the ester-alcohol yield, are mixed and heated, - as in ex. 1, to 110°C. 637 g of alcohol are removed before further polymerization is stopped by cooling the residual mass. The resulting mass is very viscous. Paints made from this viscous binder, which is called "Silicate binder no. 4", although smaller amounts of binder are used than shown in ex. 2 for "Silicate no. 1", gives a coating that is harder and somewhat less firm, but which nevertheless performed satisfactorily through all tests.

Aerosol cans of 200 ml are filled with 30 ml of "Silicate binder no. 4", 60 ml of trichlorofluoromethane and 60 ml of dichlorodifluoromethane with a steel rod as an agitator, so that a suitable mixture can be obtained by shaking. These jugs, in a sealed state, preserved their contents well, ready for use when refreshing galvanizing smaller surfaces.

Example 9

All the above-mentioned paints are suitable for application as a thin priming coating (primer) on steel objects to be formed into prefabricated constructions by welding, as you can weld straight through the coating. After it is welded, such as when erecting a building of such prefabricated constructions, the erected construction is coated again with a thicker coating of the same zinc/silicate coating preparation.

It is appropriate to carry out these operations in an automatic production line on cleaned and sandblasted construction pieces, which are then dried and either stored for later use or used immediately. They are finally given a thicker coating of the same ^zinc/silicate-containing preparation, without having to remove any rust that may have formed. During welding, the coating is converted into entirely through inorganic silicate, ZnO, SiO, which does not cause any "burnback" in automatic welding tests, and which does not impair the strength and other properties of the weld when the coating has a dry thickness of less than 0.018 mm.

Example 10

For the glycol/alkyl silicate polymer which has been produced, e.g. such as in ex. 1, before adding solvent, 200 g of 2-ethoxyethanol are added (to the reaction vessel), and heating is continued until 120 g of additional ethyl alcohol is driven off. At this point the contents of the container begin to thicken, the heating is stopped, and the reaction mass is cooled by adding 50 ml of xylene. The resulting product, which contains a mixture of glycol/ethyl and ethoxy/ethyl silicate polymer, is diluted with an equal volume of methyl ethyl ketone and 0.025% by weight (of the mixture) of zinc chloride is added. 200 g of the resulting liquid mass is vigorously mixed with 50 g of zinc dust with a particle size of 0.5-10 ym and 0.5 g of fine plate-shaped talc. The resulting mixture was stable in a paint can for several months without developing appreciable gas pressure and without hardening or thickening. Applied as a coating to a clean steel plate, the coating quickly hardened to a hardness of 4H within approx. 16 hours. Adhesion was excellent.

Example 11

In this example, a new glycol/alkyl silicate binder is produced by an equilibrium reaction between (1) the product of a. glycol/alkyl silicate in which the side chain groups are mainly glycol residues, and (2) condensed ethyl silicate.

In the first step to produce the glycol silicate

are the starting materials: 2805 g condensed ethyl silicate (containing 95% tetraethyl orthosilica.tmonomer and 5% dimer), <q>g 3340 g ethylene glycol. These substances are mixed and heated to 110°C in a three-necked flask equipped with a thermometer, a stirrer, a short column, downward-directed condenser and press. Two small drops of sulfuric acid were added, and the mixture became clear when the alcohol began to distill off. A total of 2,480 g of alcohol was collected. The residual content

in the flask was recovered as a very thick, semi-solid "bottom product" and believed to contain mainly tetraglycol silicate.

To 204 g or 0.78 mol of this bottom product (tetra-glycol orthosilicate) 249 g of ether 1.2 were added. moles of condensed ethyl silicate in a small, round-bottomed, three-necked flask equipped as mentioned above. By adding h drop of concentrated (98%-±g) sulfuric acid to the reaction mass when this had been heated to 110<O,>C, the mixture immediately became clear, and alcohol began to distill off. 67 g of alcohol was collected before the bottom product began to polymerize to a near solid state. Before total solidification, the polymerization reaction was stopped, and the bottom product was used for the production of zinc dust coating after dilution with the same volume amount of methyl isobutyl ketone (MIBK). To the diluted binder solution was added 2.5 parts by weight of zinc dust with a particle size essentially within the range of about 2-10 µm, and a zinc-containing coating preparation was obtained which provided galvanic protection for steel surfaces.

Example 12

i_" The reaction equation is as follows:

H H

Si(OEt)4 + HOCH2CH2NCH2CH2OH ■+ (RO) 3~Si-(OCH2CH2NCH2CH2OSif (OR) 3,

wherein R is an ethyl group and x is an integer. Compounds are also formed with both hydroxyl groups in the alkanolamine attached to the same silicon atom, as follows:

Carrying out this reaction: 150 g of diethanolamine and 230 g of tetraethylorthosilicate were charged to a 500 ml flask equipped as previously mentioned. On heating the charge to 110°C, the reaction started without the addition of catalyst, and the reaction continued until the reaction mass began to solidify, at which point the heat supply was stopped. Before this, 113 g of alcohol had been removed and collected. Since this amount of alcohol was equivalent to 2.46 moles, and because 1.43 moles of diethanolamine and 1.1 moles of ethyl silicate were charged, the logical conclusion was that nearly all of the diol is incorporated into the main chain grouping shown in the above equation. This indicates that a much larger amount of diethanolamine went -into the main chain structure than had ever been achieved" using glycol as a reactant. It is believed that in addition to the bridging compound* formed by the diol between two silicon atoms, a product was formed containing the amine diol with both hydroxyl groups attached to the same silicon atom.

Of the residue left in the reaction flask, here called the bottom product, 25 g was mixed with 25 g MEK and 170 g zinc dust, and the resulting dispersion was applied to a plate of cold-rolled steel. After drying for 2 min. was coated .cured within 1 hour.

Example 13

To 300 g of the product according to example 2 in the table, 490 g of butyl alcohol was added, and the product was heated to 110°C. Ethyl alcohol was distilled off until 300 g of distillate had been collected, at which point the reaction mass was cooled. The binder solution thus obtained had a flash point above 37.8°C by the "closed cup" method of Pensky Martin. Added zinc dust gave the product good protective coatings.

Example 14

200 g of tetraglycol silicate, prepared as in ex.

13, was mixed with -200 g of. a partially hydrolyzed ethyl/silicate binder which was prepared as follows: 473 g of anhydrous ethyl alcohol and 14 3 g of condensed ethyl silicate (28% silica) were mixed and heated to 65°C, and a solution of 0.14 g of hydrochloric acid (37 %) in 9.7 g of water was added to the above slowly over 1 hour. 25 g of the above-mentioned hydrolyzed binder was mixed with .25 g of tetraglycol silicate (prepared as in ex. 13), and 70 g of zinc dust was added. The resulting paint was applied to a sandblasted steel sheet as a 0.062 mm thick film. The coating quickly cured to a satisfactory coating, but was not nearly as tacky or hard as the new glycol/alkyl silicate coatings in methyl ketone solution, and produced less stable unit seals.

Example 15

.61 g of ethylene glycol and 30 g of 0-tetra (2-ethoxyethyl) silicate" were heated to .13-0°C, and to this was added a drop of concentrated sulfuric acid. 137 g of 2-ethoxyethanol was distilled therefrom. The resulting b-produced-bee mixed with the same volume of Tnet<y>lisoam<y>lketone, and-a coating preparation was pxerved as Jiolger: 1 part b landed b unproduct and ketone-containing methyl-ketones, 0.003 parts zinc chloride and 2.8 parts zinc dust.

The preparation indicated above was applied to a clean test plate made of steel. The coating hardened quickly and gave good protection. The flash point of the paint (Pensky-Martin) was above 37.8°C. Due to its high flash point, this paint is more usable when painting in closed narrow spaces.

Example 16

99.5 g of trimethylolpropane and 385 g of tetraethylorthosilicate were heated to 120°C and 1 drop of sulfuric acid was added. This caused a very violent reaction. After the alcohol had been removed, by distillation, the bottom product was cooled and diluted with

methyl isoamyl ketone and tried with zinc dust as paint and found to give acceptable coating.

Example 17

184 ml of condensed ethyl silicate and 100 g of triethanolamine were heated to 120°C. Alcohol began to distill off at 145°C, and 98 ml of alcohol was removed. With continued heating, a total of 165 ml of ethyl alcohol was removed. By cooling and dissolving the bottom product in the same volume of methyl isoamyl ketone and adding 2.5 parts zinc dust and 0.002 parts zinc acetate, a paint was obtained which gave a coating that dried slowly to a zinc/silicate type coating with good protective properties. The structure of triethanolamine (TEA) silicate is much more complex than the structure of glycol/alkyl silicate polymers. TEA alkyl silicate is possibly a mixture of compounds containing both TEA bridges and other compounds such as:

and mixed compounds. Which compounds are formed depends on the degree of reaction and removal of alcohol, as well as on the ratio between TEA and alkyl silicate. The zinc dust and TEA alkyl silicate coatings usually have less hardness, adhesion and protective value than glycol/alkyl silicate polymers.

Example 18

This example shows the production of tetraglycol silicate in an excess of glycol by heating condensed ethyl silicate and glycol to 110°C, adding a drop of sulfuric acid, removing all the ester yielded alcohol and then adding more condensed ethyl silicate so that by transesterification and equilibrium formation the desired glycol/ethyl silicate polymer with distillation removal of formed alcohol.

The apparatus of a .5 liter, three-necked, round-bottomed pyrex glass flask, equipped with stirrer, 2-plate column, distillation head, publisher and cooler. Charge: 1088.62 g ethylene glycol and 725.75 g condensed ethyl silicate (containing 95% monomer with the rest mainly dimer). The above-mentioned charge was heated to 115°C, and two drops of concentrated sulfuric acid were added and then distilled from 820 ml of ethyl alcohol. 1714.6 g of condensed ethyl silicate was then added and 4 drops of concentrated HCl were added as "catalyst. The alcohol liberated

in ester yield, was distilled from the mixture until it began to solidify, and then xylene, in the same amount by weight as the bottom products, was added to dilute the product to a usable binder. The solution was a non-viscous, pale straw-colored liquid. When this bee mixed with 1-4 parts by weight of zinc dust and applied as a coating to a steel substrate, the coating cured to finger dry condition within 8 min. and hardens to insolubility in organic solvents or water during 2.5 hours. The coating had no tendency to crack up to a thickness of 0.76 mm.

To another portion of the xylene solution of the binder was added 1/4 part "VM&P" high flash point naphtha and 2.5 parts by weight of a 50/50 mixture of noviculite and zinc dust, and this was applied to a clean steel substrate and tested against salt spray. After 2000 hours, the scratched 0.076 mm thick coating was perfect in all respects and the cracks were completely filled with zinc hydroxide products. This shows the galvanic and protective effect of this coating, even with a low zinc content. A .silicone rubber overcoat was placed over part of the zinc dust silicate base coat. The coating combination was completely superior in salt spray testing.

In a. second experiment, ..1 part by weight of particulate aluminum oxide (325 mesh and finer)... was added to 1/3_ part by weight of the binder specified above. This coating was pigmented with a small amount of TiO 2 and applied over the zinc/silicate coating to produce a coating which was permanent, attractive, white, porous and blister free, even after 3000 hours in salt spray.

To another portion of the xylene solution of the binder was added 0.001" part of triethylamine, 2.5 parts by weight of fine zinc dust, and the mixture was blended in a Waring Blender. The paint was kept in suspension for a period of 1.5 years, but still cured when applied as a single 0.05mm layer over steel to a hard protective galvanic coating It cured to a finger-dry condition in 10 min, and to a dry, hard, water- and solvent-insoluble coating in 2 hours The coating withstood more than 3,000 hours in the salt spray test.

To another part of the xylene solution of the binder

1 part by weight of zinc dust and 1 part by weight of noviculite silicon oxide flour of -3 25 mesh were added. The paint was held in suspension for several months and applied as a top coat over a zinc/silicate substrate and was found to cure hard and to have excellent protective properties in atmospheric exposure and salt spray. Another portion of this paint was applied to a clean steel substrate and gave excellent performance in all the above mentioned tests.

Example 19

To the reaction flask and the apparatus described in example 18, 1800 g of condensed ethyl silicate (containing 95% tetraethylorthosilicate and 5% higher silicate polymers) and 780 g of ethylene glycol and 100 g of diethanolamine were added. No catalyst was added, nor was this necessary as the ester exchange reaction occurred between 120 and 145°C flask temperature. 940 g of alcohol was removed and the mixture separated into two layers, neither layer being found usable as a coating. The bottom layer was insoluble in both xylene and methyl ethyl ketone. However, in an identical experiment, the alcohol removal was stopped just before splitting, and the product was found to be usable as a binder in zinc/silicate coatings.

Example 20

In this example, example 18 was repeated with the change that in the second equilibrium step (as previously mentioned), "Ethyl Silicate-40" - (a siloxane silicate polymer with an average of 5 Si/molecular weight) was used instead of the condensed ethyl silicate . 3.63 kg of "Ethyl Silicate 40" was used instead of 1.71 kg of condensed ethyl silicate, and this was used to prepare a copolymer of glycol/alkyl polysiloxane silicate. After removal of the alcohol and dilution, as in ex. 18, the product was evaluated and was found to provide excellent zinc/silicate coatings, and it had good storage properties in one-component packages. Example 21 2 mol of ethylene glycol monomethyl ether and 1 mol of condensed ethyl silicate were heated to 110°C in the presence of a trace of sulfuric acid, and ethyl alcohol was distilled off, so that a mixed ethyl/methoxyethyl silicate was obtained. One mole of this mixed ester was reacted with 1 mole of ethylene glycol in the presence of a trace of sulfuric acid at 100-130°C while distilling off the ethyl alcohol so that the polymeric "methoxy-ethylglycol-silicate" was formed. The alcohol distillation was stopped just before gel formation in the bottom product, and this was dissolved in aromatic naphtha with a high flash point (1 part product to \ part by weight of naphtha"). For each part diluted bottom product, 2 parts by weight of zinc dust and 0.01 part by weight of highly dispersed SiC> were added 2 and 1/4 parts by weight -3 25 mesh kaolin, and this was vigorously mixed into a homogeneous paint. The paint was applied to the inside of a steel tank in a water softener. The paint was dried for .16-18 hours before the salt solution used for quenching was added. The container was examined 1.5 years later and found to be rust free. The dry thickness of the film,

which was applied with a brush, was between 0.025 mm and 0.1 mm. The paint itself had a high flash point (over 35°C).

Example 22

In the presence of a trace of sulfuric acid, 3 moles of ethylene glycol monoethyl ether (2-ethoxyethanol) were heated with 1 mole of tetraethyl orthosilicate, and ethyl alcohol was liberated and removed by distillation. 1 mole of this mixed ester and 0.4 mole of tetraglycol silicate were heated to 110°C in the presence of a drop of sulfuric acid, and the remaining alcohol was removed by distillation. Before gelation, the alcohol distillation was stopped and the bottom product was diluted with half its weight with "high-flashpoint naphtha (aromatic), and for each" part of this solution 1.5 parts of zinc dust and .,0.5 parts of talc were added, this .was mixed -in a., strong, bl ander.. -The homogeneous paint was applied-to a basement-sewage collection well of steel, by spraying to a thickness of 0.76 mm, after which .it was. allowed to harden for a day before use. After 1.5 years, the coating was still perfect, with no rust, while an uncoated overflow well, after exposure to the same corrosive conditions, was completely corroded. The paint had a "Pensky-Martin" flash point of 41.1° C, and was particularly suitable for indoor use where vapor toxicity and the risk of explosion are problems.

Claims (2)

1. Storage-resistant, zinc dust-containing paint comprising a binder based on organic silicates and optionally containing an organic solvent and/or other pigments or fillers, characterized in that the binder is produced by transesterification of 1 mol of an organic ortho- and/or polysilicate of a monohydric alcohol with 0.5-3 mol of an aliphatic polyol, and that the paint optionally contains a curing catalyst, preferably a soluble zinc salt, which is known per se. 2. Paint according to claim 1, characterized in that the binder is produced by transesterification of 1 mol of the silicate with 1.0-1.7 mol of the polyol.