US3069279A - Coating composition - Google Patents

Description

3,069,279 Patented Dec. 18, 1962 free 3,069,279 COATING COMPOSITEGN Robert A. Hartley, Mount Royal, Quebec, Alfred K.

Pester, Cartierville, Quebec, and James F. Hayes, Montreal West, Quebec, Canada, assignors to International Paints (Canada) Limited, Montreal, Quebec, Canada No Drawing. Filed Dec. 7, 1959, Ser. No. 857,583 6 Claims. (Cl. 106-128) This invention relates to coating compositions and to methods of their preparation.

It has particular application to compositions of the general type described in United States Patent 2,591,904 to John C. Zola dated April 8, 1952, the disclosure of which is hereby incorporated by reference. Compositions of this type comprise a dispersion of particles of viscous coating material in a water solution containing a colloidal suspension stabilizer in an amount sufficient to prevent appreciable coalescence but insufficient to cause emulsification of the particles. In the patented composition most of the particles are said to exceed 50 microns in size.

While compositions of this type have been found effective for application by spraying, difficulty has been experienced in applying them by painting roller coating. The applicants now provide compositions which are not fraught with this problem.

Fundamentally the applicants compositions have a consistency (viscosity) considerably higher than that of dispersions produced in accordance with the aforesaid patent with a correspondingly large particle size. The consistency of the applicants compositions is above 65 Krebs units and is preferably below about 95 Krebs units. A preferred range is from about 77 to about 85 Krebs units. Thickening the consistency also has the effect of rendering the composition stickier which is an advantage for application by roller. Raising the consistency without reducing the particle size and without forming a stable emulsion is effected according to a preferred phase of the present invention by incorporating with agitation over a short period of time enough additional protective colloid into the base dispersion to bring about the increased consistency. Preferably this agitation is equivalent to that brought about by mixing in a twoor three-bladed propeller-type mixer at about 150' to about 350- r.p-.m. for a time within the range from about l minute to about 3 minutes. This contrasts with the agitation usually employed during the preparation of the base dispersion in which agitation takes place equivalent to mixing for about 20 to about 30 minutes in a lightning type v trasted with lab scale mixing in which the mixing speed and time might differ.

Temperature also has a bearing on the resulting composition. Mixing can take place within a temperature range from about- 35' F. to about 100 F. Elongated particles'which are desirable are produced when the mixing is effected within the range from about 70 F. to about 80 F. A certain amount of particle size control can therefore be exercised by varying the temperature. The applicants have found that in their compositions most of the particles as in Zola are above 50 microns and many are above 100 microns, some go up to 5000 microns.

In the mixing, care should also be taken to' avoid blending of the respectivephases atthe outset and before agitationcommences. In this connection the applicants prefer to add the liquid phase to the lacquer phase in making the base composition by pouring it on in a layer and then to start the agitation. In other words, the lacquer is added to the aqueous phase one colour at a time and it is necessary to splash some of the aqueous phase over each colour to prevent amalgamation of the colours from occurring. If the lacquer phase is added during agitation,- then the particle size will vary considerably. When the additional colloid or other additive is added, this may be accomplished while agitation is taking place and the addition is done slowly. I

Thus, according to a preferred method of the invention, the base composition is made according to the teachings of United States Patent 2,591,904. Then, the protective colloid is added under the conditions above described. The applicants have also found that a still further improvement in the nature of the resulting composition can be brought about if the protective colloid is present in a synthetic resin emulsion or paint. Therefore, a preferred phase of the invention is to add, instead of a protective colloid alone, a synthetic resin emulsion or paint in which such colloid is present. If desired, a combination of protective colloid and synthetic resin emulsion or paint may be employed.

The applicants have found that contray to the experience with the base dispersion, a modified composition as above described can be applied by a painting roller as well as by spraying, preferably a painting roller having a coarse, tufted texture. The applicants have found it of decided advantage to use a roller which is covered by textile fabric being an 18 pick frieze, with a mohair-rayon blend face, and a cotton backing coated with neoprene latex. And, a .075 inch gaugepile wire is used in making the fabric. In using the roller it is desirable to keep it uniformly and fairly heavily loaded and to roll it gently but firmly on the surface. It is of advantage to work in a small area, for example 2-foot squares, applying the coating evenly in a vertical direction and then to roll the same area with horizontal strokes. The globules which appear after rolling will flatten as they dry. The composition may also be applied by conventional spray equipment or a vacuum cleaner spray attachment.

It is also desirable to first coat the surface with a sealer. This has the advantage of obliterating previously painted surfaces and producing a more pleasing effect. The colour of the sealer should be similar to the basic colour of the paint. The sealer also acts to provide a uniform suction over the entire surface and hence prevents shadows or highlights caused by joints, nailheads or other unevennesses.

ADDITIVES Effective additives are the materials usually classified under the heading of organic or synthetic hydrophilic or protective colloids. The applicants have found the following. hydrophilic colloids are effective and are preferably employed within the range of concentration stated,

by dry weight of the finished composition.

Percent Methyl cellulose (4000 centipoises) 0.7 to'2 Glue l to 2 Dextrine 6 to 16 Casein- 1 to2 Hydroxyet-hyl cellulose 0.3 to'0;6 Carooxymethyl cellulose 0.3 to 0.6

The hydrophilic colloid is first put into equeous solution and this solution is added to the base composition in the manner described-above.

The applicants have found that preferred results are achieved by adding thermoplastic synthetic resin emulsions or paints which contain the colloid. Polyvinyl acetate emulsions or paints are preferred, particularly the paints. Emulsions or paints of butadiene-styrene, polyacrylates and other polyvinyl esters, for example polyvinyl propionate may be employed.

The characteristics of these emulsions that are necessary in order that they function according to the invention are that the emulsion be stable. They can be an emulsion alone or pigmented so as to constitute pigmented emulsions or actual compositions which are known commercially as emulsion paints. Generally speaking these paints contain pigment in an amount which will give from about to about 40% by volume of pigment in the dry volume. This is generally an amount in excess of by weight in the paint. Generally speaking the solids in the emulsion will run from about to about 55% when it is not pigmented and from about 20% to about 40% in the case of a paint. The emulsion or emulsion paint type of additive should be added to the base composition in an amount within the range from about 3% to about 20% by weight with 5% to about 10% preferred.

The quality of the composition for use in roller coating can be tested by trying the composition with a roller. Compositions containing insutficient colloid will smear whereas in compositions containing an excess of colloid there is a tendency of the particles to break down prematurely due to shearing action.

The applicants have found that inorganic colloidal materials in the nature of fullers earth, talc, barium sulfate, calcium carbonate, calcium sulfate, magnesium carbonate and diatomaceous earth are not desirable for the purposes of the invention.

The presence or absence of other materials and the amounts of these materials will have a bearing on the properties of the composition. For example, the solvents used in the lacquer phase are preferably hydrophobic or there is a tendency of the emulsions to break down. Preferred solvents are methyl amyl acetate, amyl acetate and ethyl amyl ketone.

The proportions of solvents employed in the lacquer phase is preferably within the range from about 60% to 70% by weight of the total lacquer phase. The ratio of coating material to the aqueous is within the range 2.75:1 to 3.25:1. The specific gravity of the lacquer phase is preferably controlled to be Within the range from about 1.003 to about 1007 so that the above mentioned proportions hold true even if the lacquer phase is considered by weight instead of by volume.

The applicants can use the standard pigments as prescribed in the afore-mentioned Zola Patent. Pigments should be used which are insoluble in lacquer type solvent.

The applicants have generally described the invention and will now give examples of specific, preferred formulations and procedures in order that the invention be more fully understood.

Example I The following is an example of the preparation of a typical coating composition in accordance with the invention.

A base composition according to United States Patent 2,591,904, was prepared by mixing the following constituents:

These constituents were mixed together in a threebladed propeller type mixer at a mixing speed of 300 r.p.m. for minutes.

A polyvinyl acetate paint additive was prepared according to the following formulation. made of the following constituents:

The mixture was Rutile titanium dioxide (pigment) 252 Tributyl phosphate (anti-foaming agent) 1 /2 Polyvinyl acetate emulsion (CRC emulsion F 20) (plasticized with dibutylphthalate) 314 CRC emulsion F 60 (plasticized with dibutylphthalate) 314 Water (to adjust viscosity to between 72 to 76 Krebs units) 30 This mixture was ground on a Morehouse mill. The resulting additive was mixed with the base composition at 250 r.p.m. for 3 minutes. Most of the particles in the composition exceeded 50 microns in size and the composition was relatively stable.

The composition was applied using a roller of the characteristics described above. The resulting coating had excellent covering power and adhesion to the surface.

Example II Another composition was prepared in which the base composition contained the following constituents:

Pounds 1% methyl cellulose solution 74 Water 141 First coloured lacquer 108 Second coloured lacquer 615 These constituents were dispersed using a three-bladed propeller type mixer' operating at 250 r.p.m. for about 30 minutes. Then, 83 pounds of 2% methyl cellulose solution were added and the composition stirred for 3 minutes at 300 r.p.m.

An excellent coating composition resulted which was applicable with a roller to form good coatings.

Example III A base composition was prepared having the following constituents:

Pounds 1% methyl cellulose solution 74 Water 73 First coloured lacquer 72 Second coloured lacquer 217 Third coloured lacquer 434 The basic composition was prepared by dispersing the constituents with a three-bladed propeller type mixer operating at 350 r.p.m. for 20 minutes and then the following modifying substances were added while mixing at 300 r.p.m. for 2 minutes.

Pounds Polyvinyl propionate dispersion (Propiofan 5 D) 55 1% methyl cellulose solution 45 An excellent coating composition resulted which was applicable with a roller to form good coatings.

Example IV A base composition was prepared having the followmg constituents:

Pounds 1% methyl cellulose solution 74 Water 101 First coloured lacquer 687 Second coloured lacquer 36 These constituents were dispersed as in Example I and there was then added 122 pounds of a 37.5% dextrine solution and the mixture was stirred for 2 minutes at 300 r.p.m.

An excellent coating composition resulted which was applicable with a roller to form good coatings.

In all the examples the film has a mottled effect. The colours can be changed by varying the concentration of the coloured lacquers within the ranges stated. It is also possible to change the size and shape by varying the concentration of protective colloid and the viscosity of the lacquer phase within the limits given.

We claim:

I. A multiple step process for preparing an aqueous dispersion of a coating composition having a viscosity adapted for roller coating of surfaces which comprises:

as a first step, forming an aqueous dispersion of discrete large particles of a viscous hydrophobic coating material most of which are larger than 50 microns under strenuous dispersing conditions including vigorously agitating a viscous hydrophobic coating material over an extended period of time with a colloidal solution of a quantity of an organic hydrophilic protective colloid suflicient to maintain said large particles in the dispersed state Without substantial coalescence but insuflicien-t to substantially further reduce the sizes of said particles under the conditions aforesaid to provide thereby an aqueous dispersion having a viscosity consistency below 65 Krebs units; and as a second step, introducing into the formed aqueous dispersion additional quantities of an organic hydrophilic protective colloid suflicient to increase the viscosity of theresulting aqueous dispersion to between about 77 to 95 Krebs units under substantially less strenuous dispersing conditions including agitation tor a substantially shorter period of time sufiicient to term thereby a homogeneous dispersion of the additional colloid but insufi'icient to substantially reduce the sizes of said large particles; the total amount of protective colloid being sufiicient to substantially decrease the sizes of said large particles under the dispersing conditions of said first step.

2. The process of claim 1 wherein the dispersing conditions in the first step is equivalent to that of a lightning type mixer at a speed from about 250 to about 350 r.p.m. for a time from about to about 30 minutes and the dispersing conditions in the second step is equivalent to agitation with a lightning type mixer at a speed from about 150 to about 350 r.p.m. for a time from about 1 minute to about 3 minutes.

3. The process of claim 1 wherein the hydrophilic protective colloid is a resin.

4. The process of claim 1 wherein particles of a difierent color are dispersed in said first step.

5. The composition prepared according to the process of claim 1.

6. A multiple step process for preparing an aqueous dispersion of a coating composition having a viscosity adapted for roller coating of surfaces which comprises:

as a first step, forming an aqueous dispersion of discrete large particles of a viscous hydrophobic coating material most of which are larger than 50 microns under strenuous dispersing conditions includ ing vigorously agitating a viscous hydrophobic coating material under conditions equivalent to that of a lightning type mixer at a speed from about 250 to about 350 r.p.m. for a time from about 20 to about 30 minutes with a colloidal solution of a quantity of an organic hydrophilic protective colloid sutficient to maintain said large particles in the dispersed state without substantial coalescence but insufiicient to substantially further reduce the sizes of said particles under conditions aforesaid to provide thereby an aqueous dispersion having a viscosity consistency below Krebs units; and

as a second step, introducing into the formed aqueous dispersion additional quantities of an organic hydrophilic protective colloid sufiicient to increase the viscosity of the resulting aqueous dispersion to a viscosity substantially above 65 Krebs units under substantially less strenuous dispersing conditions including agitation equivalent to agitation with a lightning type mixer at a speed from about 4150 to about 350 r.p.m. for a time from about 1 minute to about 3 minutes to form thereby a homogeneous dispersion of the additional colloid without substantially reducing the sizes of said large particles;

the total amount of protective colloid being sufficient to substantially decrease the sizes of said large particles under the dispersing conditions of said first step.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A MULTIPLE STEP PROCESS FOR PREPARING AN AQUEOUS DISPERSION OF A COATING COMPOSITION HAVING A VISCOSITY ADAPTED FOR ROLLER COATING OF SURFACES WHICH COMPRISES: AS A FIRST STEP, FORMING AN AQUEOUS DISPERSION OF DISCRETE LARGE PARTICLES OF A VISCOUS HYDROPHOBIC COATING MATERIAL MOST OF WHICH ARE LARGER THAN 50 MICRONS UNDER STRENUOUS DISPERSING CONDITIONS INCLUDING VIGOROUSLY AGITATING A VISCOUS HYDROPHOBIC COATING MATERIAL OVER AN EXTENDED PERIOD OF TIME WITH A COLLOIDAL SOLUTION OF A QUANTITY OF AN ORGANIC HYDROPHILIC PROTECTIVE COLLOID SUFFICIENT TO MAINTAIN SAID LARGE PARTICLES IN THE DISPERSED STATE WITHOUT SUBSTANTIAL COALESENCE BUT INSUFFICIENT TO SUBSTANTIALLY FURTHER REDUCE THE SIZES OF SAID PARTICLES UNDER THE CONDITIONS AFORESAID TO PROVIDE THEREBY AN AQUEOUS DISPERSION HAVING A VISCOSITY CONSISTENCY BELOW 65 KREBS UNITS; AND AS A SECOND STEP, INTRODUCING INTO THE FORMED AQUEOUS DISPERSION ADDITIONAL QUANTITIES OF AN ORGANIC HYDROPHILIC PROTECTIVE COLLOID SUFFICIENT TO INCREASE THE VISCOSITY OF THE RESULTING AQUEOUS DISPERSION TO BETWEEN ABOUT 77 TO 95 KREBS UNITS UNDER SUBSTANTIALLY LESS STRENUOUS DISPERSING CONDITIONS INCLUDING AGITATION FOR A SUBSTANTIALLY SHORTER PERIOD OF TIME SUFFICIENT TO FORM THEREBY A HOMOGENOUS DISPERSION OF THE ADDITIONAL COLLOID BUT INSUFFICIENT TO SUBSTANTIALLY REDUCE THE SIZES OF SAID LARGE PARTICLES; THE TOTAL AMOUNT OF PROTECTIVE COLLOID BEING SUFFICIENT TO SUBSTANTIALLY DECREASE THE SIZE OF SAID LARGE PARTICLES UNDER THE DISPERSING CONDITIONS OF SAID FIRST STEP.