GB1580506A - Aqueous coating agents and a process for their prepartion - Google Patents

Description

(54) AQUEOUS COATING AGENTS AND A PROCESS FOR THEIR PREPARATION (71) We, BAYER AKTIENGESELL SCHAFT, a body corporate organised under the laws of Federal Republic of Germany, of Leverkusen, Germany, and WOLFF WALS RODE A.G., a body corporate organised under the laws of Federal Republic of Germany, of D 3036, Bomlitz, 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:- Aqueous coating agents, for example lacquering furniture, have hitherto generally contained synthetic resins, such as acrylic polymers or cellulose esters, as the film-forming agents.

Methods for preparing aqueous emulsions of suitable cellulose derivatives are known and are described, for example, in German Auslegeschrift 1,286,672 and U.S. Patent 3,615,792.

Emulsions of cellulose esters, for example of nitrocellulose, cannot be used as the sole binders for coating agents, because they only produce brittle and fragile films. They must be combined with ketone resins or vinyl acetate copolymers in order to achieve glossy coatings with good mechanical properties.

Cellulose esters, for example nitrocellulose, usually combined with alkyd resins, are used for lacquering wood or similar materials. This combination leads to coatings of high gloss, adequate hardness, good elasticity and excellent flow, but it is not possible to work with aqueous emulsions; instead, these combinations have hitherto had to be processed from organic solutions. All attempts hitherto emulsify alkyd resins and cellulose esters lead either to emulsions of inadequate stability or to emulsions with particles which are too coarse and which do not permit levelling to give glossy coatings.

The present invention relates to aqueous dispersions of coating agents comprising 550 parts by weight of cellulose ester, 5-30 parts by weight of plasticiser, 5-50 parts by weight of alkyd resin, 30-1 35 parts by weight of water and 0.5-10 parts by weight of emulsifier, in which the emulsifier is a vinyl alcohol, homopolymer or copolymer and the alkyd resin is an alkyd resin containing 550% by weight of oil.

These dispersions are stable and can give coatings of substantially faultless gloss.

This invention further relates to a process for the preparation of such dispersions of coating agents, which is characterised in that a cellulose ester, an alkyd resin and a plasticiser are dissolved in an organic solvent, this solution is dispersed into a solution consisting of emulsifier and water and the organic solvent is removed by distillation.

The size of the dispered particles is particularly important for the stability of the dispersion and also for its behaviour in film formation. According to the invention it is preferably 0.1 to 0.5lla and it does not change substantially even on prolonged storage at 5 50"C.

Cellulose esters which can be used in accordance with the invention are, in particular, cellulose acetate, cellulose acetobutyrate, cellulose acetate-benzoate and cellulose sorbate-acetate and mixtures of these esters. Nitrocellulose, for example the customary collodion cotton qualities, that is to say cellulose nitric acid esters having a nitrogen content of 10.2 to 12.4% by weight, is more particularly suitable.

Plasticisers within the meaning of the invention are, in particular, esters, such as dibutyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, dibutyl adipate, benzylbutyl adipate, dioctyl adipate, phosphoric acid esters, such as tricresyl phosphate, triphenyl phosphate or trioctyl phosphate, and also benzenesulphonic acid N-methylamide.

Suitable alkyd resins are oil-modified or fatty acid-modified alkyd resins having the oil content specified above. Alkyd resins are understood as Dolyesters which are prepared from alcohols and carboxylic acids by polycondensation according to known processes and such as are defined, for example, in Ullmanns Enzyklonildie der Technischen Chemie (Ullmann's Encyclopaedia of Industrial Chemistry) or are describtd in D. H. Solomon, The Chemistry of Organic Filmformers, page 75-101. In general, the alcohols employed contain 1 to 15, preferably 2 to 6, C atoms and the acids used, or their esterforming derivatives, contain 2 to 14, preferably 4 to 12, C atoms. These alkyd resins can optionally be mixed with other polyesters, for example also with oil-free polyesters.

Examples of suitable alcohols are pentaerythritol, glycerol, trimethylolpropane, trimethylolethane, 1,2,4 - butane - triol, 1,2,6hexanetriol, ethylene glycol, propane - 1,2 diol, propane - 1,3 - diol, butane - 1,2 - diol, butane - 1,3 - diol and butane - 1,4 - diol, neopentylglycol, diethylene glycol, triethylene glycol, dipropylene glycol, hexane - 1,6 - diol, 1,2 - bis - (hydroxymethyl) - cyclohexane and 1,4 - bis - (hydroxymethyl) - cyclohexane, 2 - ethylpropane - 1,3 - diol, 2 ethylhexane - 1,3 - diol, cyclohexane - 1,2 diol, cyclohexane - 1,4 - diol and adipic acid bis-ethylene glycol ester; benzyl alcohol, cyclohexanol and other mono-alcohols having 1 to 6 C atoms. Preferred alcohols are glycerol, trimethylolpropane, neopentylglycol and pentaerythritol.

The following carboxylic acids, or their ester-forming derivatives, may be mentioned as examples of suitable acid components: phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid and hexahydro phthalic acid, endomethylenetetrahydrophthalic acid, succinic acid, adipic acid, sebacic acid, trimelltic acid, benzoic acid and their deriva tives, such as, for example, p-tert.-butyl benzoic acid and hexahydrobenzoic acid.

Phthalic acid is the most customary.

In the alkyl resins which are employed for the coating emulsions according to the inven tion, the proportion of oil can be 5 to 50% by weight, calculated as triglyceride and rela tive to the alkyd resin. The drying or non drying fatty acids, which generally contain 6 to 24 C atoms, can be employed either as such or in the form of their glycerol esters (triglycerides). Animal and vegetable oils, fats or fatty acids, such as, for example, coconut oil, groundnut oil, castor oil, olive oil, soya bean oil, linseed oil, cottonseed oil, safflower oil or safflower oil fatty acids, de hydrated castor oil or castor oil fatty acid, mono-unsaturated fatty acids, lard, tallow and train oils, tall oil fatty acid and synthetic fatty acids, may be mentioned as being suitable.

Suitable emulsifiers are homopolymers and copolymers of vinyl alcohol, for example poly vinyl alcohols which are formed by hydrolysis of polyvinyl acetate and which are available commercially, for example under the designation Polyviol W 25/240 and W 25/140.

Hydrolysed copolymers of vinyl-pyrrolidone and vinyl acetate are also suitable.

The dispersions of coating agents of the invention preferably contain alkyd resins having an oil content of 20 to 45%.

The coatings according to the invention can be produced by dissolving the alkyd resin, the cellulose ester and the plasticiser in a polar solvent which is not soluble in water, and which can be removed by distillation from the emulsion to be formed, combining the solution with an aqueous solution of the emulsifier and thus forming an oil-in-water emulsion by means of high shearing forces.

The organic solvent is then removed by distillation, on its own or in the form of an aqueous azeotrope. Solvents which are particularly suitable are alkyl acetates and alkyl propionates. The aqueous emulsion which remains can be diluted with more water or a suitable coalescing agent can be added to it.

In the following this will be designated a secondary emulsion.

One or more coalescing or aggregating agents can also be added to the dispersion in order to achieve a clear film of high gloss.

Coalescing agents which form an azeotrope with the water are preferred here. It is then necessary to add to the dispersion sufficient coalescing agent so that the azeotrope is first distilled off and, in addition, to add further coalescing agent which effects the aggregation of the particles. Possible coalescing agents are ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and ethylene glycol monobutyl ether-acetate, diethylene glycol, diethylene glycol monobutyl ether, diacetone alcohol methylglycol acetate, methyl amyl ketohe and diisobutyl ketone.

The primary emulsion consisting of cellulose ester, alkyd resin, emulsifier, plasticiser, water and organic solvent is produced in a commercially available device having an adequately high peripheral speed of 5 to 50 m/second, preferably 10/30 m/second.

Examples are: "Ultra-Turrax" (Trade Mark) type 45 and 10,000 revolutions per minute; Gaulin homogeniser, dissolver and bead mills.

The emulsification time in the Ultra-Turrax should not be more than 2 minutes, since otherwise too great an evolution of heat takes place. This time is adequate to produce small, spherical particles of 0.1-1.5 preferably 0.1 4 51y from the constituents of the ultimate emulsion.

In a preferred embodiment, the aqueous coating compositions contain additionally 440 parts by weight of an urea and/or melamine resin.

Urea and melamine resins in this context are art recognized condensation products of urea or melamine and formaldehyde which are made in an alkaline medium. They are soluble in water and are added to the dispersions in the form of aqueous solutions. Their effect is a crosslinking of the coatings obtained from the dispersions which improves their stability and gloss. Catalytic amounts of ptoluene sulfonic acid accelerate crosslinking.

Example 1.

A solution in ethyl acetate was prepared from: 100 g of nitrocellulose chips containing approximately 12% of nitrogen, Standard Specification 24 E in accordance with DIN 53,179, con sisting of 82% of collodion cotton and 18% of dibutyl phthalate, 100 g of groundnut oil fatty acid alkyl resin having an oil content of 41%, and 300 g of ethyl acetate.

500 g After stirring slowly for approximately 3 hours a clear solution was obtained which was combined with 300 g of a 3% strength aqueous solution of polyvinyl alcohol (Polyviol W 25/140), whilst stirring slowly. The mixture was then dispersed for 2 minutes in an Ultra-Turrax type 45 laboratory disperser by raising the speed of rotation continuously to 10,000 revolutions per minute. The solvent is distilled off under reduced pressure. A primary emulsion having a solids content of 40% and a flow viscosity of 34 seconds in the DIN cup No. 4 is thus obtained.

Comparison Example.

A dispersion was prepared as described in Example 1, except that instead of the polyvinyl alcohol 300 g of an aqueous solution of a non-ionic fatty acid ester (emulsifier "Emulphor" (Trade Mark) EL of BASF) were used. This gave an emulsion which was stable for a short time and which gave an average size of 13lss in a determination of particle pattern.

Example 2.

A dispersion was prepared from: 100 g of groundnut oil fatty acid alkyd resin having an oil content of 41%, 100 g of nitrocellulose chips as in Example 1, and 300 g of ethyl acetate.

500 g After stirring for 3 hours, a clear solution was obtained which is combined with 500 g of a 2.504 strength solution of polyvinyl alcohol (Polyviol W 25/140) in water. The procedure described under Dispersion 1 was then followed. A primary emulsion with a solids content of approximately 29% and a flow viscosity of 28 seconds in the DIN cup No. 4 is obtained.

USE EXAMPLES.

Example 1 (Comparison).

A lacquer of the following composition was prepared: Parts by weight Ground nut oil fatty acid alkyl resin with 41% of oil, 60% strength solution in xylene 152 Collodion cotton (cellulose nitric acid ester containing approx mately 12% of nitrogen), Standard Specification type 24 E, DIN 53,179, in the form of chips 111 Dibutyl phthalate 8 Ethylene glycol monoethyl ether 59 Butyl acetate 190 Ethyl acetate 140 Xylene 300 Ethylglycol acetate 40 The resulting lacquer exhibited a viscosity corresponding to a flow time of approximately 30 seconds, measured in accordance with DIN 53,211 (DIN cup No. 4). The curing to give films and the assessment are described in Table 1.

Example 2.

A dispersion of the following composition was prepared: Parts by weight Dispersion from Example 1, 40% strength in water 350 Dibutyl phthalate 10 Ethylene glycol monomethyl ether 124 Ethylglycol acetate 44 4-Methyl-4-hydroxypentan-2-one 32 Water 234 Levelling agent (alkylbenzene sulphonate) 6 The resulting dispersion exhibited a viscosity corresponding to a flow time of approximately 15 seconds, measured in accordance with DIN 53,211.

TABLE 1 Example 1 Example 2 Drying until free from tackiness, in minutes 30 35 Pendulum hardness by Albert-Koenig method, DIN 53,157 after 1 hour 80 seconds 30 seconds 3 hours 102 seconds 78 seconds 5 hours 112 seconds 100 seconds 24 hours 116 seconds 114 seconds Resistance to water') 0 1/2 Resistance to alcohols2 0/1 4 Gloss by Gardner's method 60 88 82 Retouchability, after storage at 500, with lacquer No result after No result after according to Example 1 25 days 25 days Service life, in hours Unlimited Unlimited " The test is caried out, after storing the specimen sheet at 200C for one week, by exposing it to cotton wool wadding impregnated with water. Time of exposure: 8 hours.

2) Corresponding to 1, but 50% strength aqueous ethyl alcohol solution instead of water.

WHAT WE CLAIM IS: 1. An aqueous dispersion of a coating agent comprising of 5 to 50 parts by weight of cellulose ester, 5 to 30 parts by weight of a plasticiser, 5 to 50 parts by weight of an alkyd resin, 30 to 135 parts by weight of water and 0.5 to 10 parts by weight of an emulsifier, in which the emulsifier is a vinyl alcohol homopolymer or copolymer and the alkyd resin is an alkyd resin containing 5 to 50% by weight of oil.

2. An aqueous dispersion according to claim 1 which contains additionally 4 to 40 parts by weight of an urea and/or melamine resign.

3. An aqueous dispersion according to -claim 1, in which the alkyd resin has been prepared by polycondensing any of those alcohols hereinbefore specifically mentioned with any of those carboxylic acids herein before specifically mentioned.

4. An aqueous dispersion according to any of the foregoing claims in which the alkyd resin contains 20 to 45% by weight of oil.

5. An aqueous dispersion according to any of the foregoing claims, in which the dispersed particles have a size from 0.1 to 0.5.u.

6. An aqueous dispersion according to any of the foregoing claims, in which the cellulose ester is any of those hereinbefore specifically mentioned.

7. An aqueous dispersion according to any of the foregoing claims, in which the cellulose ester is a nitrocellulose ester.

8. An aqueous dispersion according to any of the foregoing claims, in which the plasticiser is any of those hereinbefore specifically mentioned.

9. An aqueous dispersion according to claim 1, as hereinbefore specifically identified in Example 1 or 2.

10. A process for the preparation of an aqueous dispersion of coating agent as claimed in claim 1, in which the cellulose ester, alkyd resin and plasticiser are dissolved in an organic solvent, this solution is dispersed into a solution of the emulsifier in water and the organic solvent is removed by distillation.

11. A process according to claim 10, when carried out substantially as described in Example 1 or 2.

12. An aqueous dispersion of a coating agent when produced by the process of claim 10 or 11.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   The resulting dispersion exhibited a viscosity corresponding to a flow time of approximately 15 seconds, measured in accordance with DIN 53,211.

   TABLE 1 Example 1 Example 2 Drying until free from tackiness, in minutes 30 35 Pendulum hardness by Albert-Koenig method, DIN 53,157 after 1 hour 80 seconds 30 seconds

   3 hours 102 seconds 78 seconds

   5 hours 112 seconds 100 seconds

   24 hours 116 seconds 114 seconds Resistance to water') 0 1/2 Resistance to alcohols2 0/1 4 Gloss by Gardner's method 60 88 82 Retouchability, after storage at 500, with lacquer No result after No result after according to Example 1 25 days 25 days Service life, in hours Unlimited Unlimited " The test is caried out, after storing the specimen sheet at 200C for one week, by exposing it to cotton wool wadding impregnated with water. Time of exposure: 8 hours.

   2) Corresponding to 1, but 50% strength aqueous ethyl alcohol solution instead of water.

   WHAT WE CLAIM IS: 1. An aqueous dispersion of a coating agent comprising of 5 to 50 parts by weight of cellulose ester, 5 to 30 parts by weight of a plasticiser, 5 to 50 parts by weight of an alkyd resin, 30 to 135 parts by weight of water and 0.5 to 10 parts by weight of an emulsifier, in which the emulsifier is a vinyl alcohol homopolymer or copolymer and the alkyd resin is an alkyd resin containing 5 to 50% by weight of oil.
2. 2. An aqueous dispersion according to claim 1 which contains additionally 4 to 40 parts by weight of an urea and/or melamine resign.
3. 3. An aqueous dispersion according to -claim 1, in which the alkyd resin has been prepared by polycondensing any of those alcohols hereinbefore specifically mentioned with any of those carboxylic acids herein before specifically mentioned.
4. 4. An aqueous dispersion according to any of the foregoing claims in which the alkyd resin contains 20 to 45% by weight of oil.
5. 5. An aqueous dispersion according to any of the foregoing claims, in which the dispersed particles have a size from 0.1 to 0.5.u.
6. 6. An aqueous dispersion according to any of the foregoing claims, in which the cellulose ester is any of those hereinbefore specifically mentioned.
7. 7. An aqueous dispersion according to any of the foregoing claims, in which the cellulose ester is a nitrocellulose ester.
8. 8. An aqueous dispersion according to any of the foregoing claims, in which the plasticiser is any of those hereinbefore specifically mentioned.
9. 9. An aqueous dispersion according to claim 1, as hereinbefore specifically identified in Example 1 or 2.
10. 10. A process for the preparation of an aqueous dispersion of coating agent as claimed in claim 1, in which the cellulose ester, alkyd resin and plasticiser are dissolved in an organic solvent, this solution is dispersed into a solution of the emulsifier in water and the organic solvent is removed by distillation.
11. 11. A process according to claim 10, when carried out substantially as described in Example 1 or 2.
12. 12. An aqueous dispersion of a coating agent when produced by the process of claim 10 or 11.