US2451785A - Method for making a lacquer enamel - Google Patents

Description

Patented Oct. 19, 1948 METHOD FOR MAKING A LACQUER ENAMEL Marcus Thau, New York, N. Y., assignor to Lacquer & Chemical Corporation, Brooklyn,

N. Y., a corporation of New York No Drawing. Application July 26, 1944, Serial No. 546,756

This invention relates to methods for makin lacquer enamels.

The term lacquer as used in the specification is a protective coating material or composition containing cellulose derivatives, solvents, diluents, '5 ing the speed of airplanes has its shortcomings thinners, and/or plasticizers and/or resins. The and drawbacks, which have militated against term lacquer enamel means a pigmented lactheir adoption on a large scale. For instance, quer; i. e. a lacquer containin pigments. waxing requires considerable amounts of mate- An important object is to provi e a lacquer rial and labor, and results in a specular gloss enamel, which is capable of producing a very finish, which is particularly undesirable in planes smooth, very durable, substantially waterproof used for military purposes. Much work has been protective film or coating, which is materially done during the war to render airplanes as inunaffected by exposure to sunlight and extreme conspicuous as possible, and conventional methatmospheric and weather conditions. ods for decreasing their Wind. resistance have had Another object of importance is to provide a just the opposite -eifect., Furthermore, the re-, lacquer enamel, which is substantially devoid of sults produced by conventional methods are gensettling and chalking tendencies, and which is erally very short-lived due to chalking of the laccapable of producing a non-specular gloss film quer film. chalking of the lacquer film decreases or coating. 7 surface smoothness, thereby increasing wind re- Another important object is to provide a lacsistance and consequently impairing the normal quer enamel particularly adapted for use in coatspeed characteristics of the airplane. ing the exterior of vehicles such as airplanes, The present invention has several important automobiles, trains and speed boats, whose servadvantages over suggested methodsfor enhancing ice requirements include exceptionally high the speed of vehicles. The speed is increased speeds and exposure to extreme atmospheric and without rendering the vehiclemore conspicuous. weather conditions. In fact, in the preferred embodiment of the in- Another important object is to provide a lacvention, the coated vehicle is rendered less conquer enamel which serves to enhance the speed spicuous or less visible as well as less windcharacteristics of vehicles such as airplanes, autoresistant, than had previously been considered mobiles, trains and speed boats. possible. Furthermore, the effect is permanent,

By enhancing the speed characteristics is due to the fact that the protective coating is dumeant rendering possible increased speed with rable and non-chalking. substantially unchanged power consumption or The invention is based in part upon the obdecreased D B consumption With bstantially servation that the smoothness of a lacquer enamunchanged speed. The term impairing the e1 film depends upon the following factors: speed characteristics has just the opposite (1) Particle size of the pigment. meaning. a 2) Uniformity of particles.

Another object of importance is to provide a (3) "Extent of dispersion of the pigment in the method for making a lacquer enamel having any vehicle. one or more of the aforementioned desirable 40 Pigments having coarse particles do not have as properties. effectual a hiding power as do finer pigments. The term speed vehicle will in the following Furthermore, because of the necessary thinness specification be used to denote a vehicle, whose of the finished film, coarse pigments have the service requirements include high speeds. tendency to produce an uneven surface. How- Prior to the present invention, it was suggested ever, within certain limits the uniformit of the that the speed characteristics of speed vehicles particles is a more important factor as far as might be improved by reducing the coefiicient of smoothness of surface is concerned than the friction between the vehicle and the medium particle size. In other words, the fact that the through which the vehicle moves. In the case maximum particle size of the pigment contained of airplanes, it was suggested that the wind rein a lacquer enamel is relatively small does not sistance might be considerably decreased and the necessarily mean that it will produce a smooth speed correspondingly increased or the power or even film. If there is a great variation in the consumption considerably decreased by. waxing particle size, the surface will nevertheless be unthe exterior surface of the airplane after the laceven. a quer had dried. It was also suggested that simi'-- 1 Claim. (01. 106-198) 2 lar results might be obtained by adding graphite or other solid lubricant to the lacquer with which the airplane was to be coated.

Each of the suggested procedures for enhanc- At this point, it is to be noted that specifications as a general rule limit the particle size to 44 microns. For instance, United States Army Navy Aircraft Specifications AN-TT-L51, M 485C (Camouflage Lacquer), and AN-L-Zl allow .1% to be retained on a 325 mesh screen; which corresponds to a particle size of 44 microns. The maximum size of particles in lacquer enamels made according to the invention is often less than 2 microns, the particle size in many cases being as low as /2 micronl More important than the particle size is the fact that the particles are substantially uniform in size and shape and that they are substantially uniformly dispersed or distributed through the vehicle.

Essentially the method of producing a lacquer enamel according to the present invention consists in grinding the pigment with part of the vehicle until the pigment is thoroughly dispersed in the vehicle, adding more vehicle to obtain the desired formulation, and finally separating out from the material the coarse particles of pigment.

In practice, it has been found that grinding of the pigment with the vehicle by conventional methods, i. e. in a roller or ball mill and to a lesser extent in a pebble mill, generally tends to develop a gloss in-the lacquer. This is undesirable in military airplanes, and hence in practicing the invention, I prefer to use pigments which readily disperse, and I preferably stop the grinding operation just short of the development of an appreciable gloss.

In practicing the invention, I have found it very important to omit from the lacquer enamel materials which have a tendency to cause chalking in the finished film. A film may be exceedingly smooth when first applied, and hence may initially enhance the speed characteristics of the airplane. Chalking will soon impair the smoothness of surface, with the inevitable result that the speed of the plane perceptibly drops and the power consumption correspondingly rises.

Many pigments, which are otherwise suitable, and most extenders have a decided chalking tendency. Hence, in the preferred embodiment of the invention I carefully select the pigment from those that do not have this undesired tendency. As examples of suitable pigments may be mentioned titanium dioxide of the non-chalking type, antimony trioxide (Timonox) iron blue (ferrocyanide), and lead chromate pigments of a type that disperse readily, such as lemon yellow. I also prefer to omit extenders. As above stated, most of the extenders have chalking tendencies, and also cause settling. In many cases films containing extenders are unduly porous and lack compactness.

At this point, it is to be noted that the pigments used in practicing the invention are of the low dispersion type, that is, they have been treated either mechanically, physically or chemically by the pigment manufacturer, so that they disperse very easily in the vehicle.

It is also to be noted that the pigments which have been found particularly suitable for use in practicing the teachings of this invention have in the prior art been used to produce very glossy finishes. It is therefore considered wholly unexpected that these same pigments can be used to obtain a very dull or flat finish. This unexpected result is due to the fact that I use pigments, which as above stated, have been especially processed by the pigment manufacturer to render them readily dispersible. Because of this fact, the pigments can be thoroughly and uniformly dispersed without the development of an appreciable gloss. The development of a gloss can be avoided by stopping the grinding operation when a test of a sample shows that the dispersion is substantially thorough and uniform.

The following examples are given to illustrate the method of this invention for making a lacquer enamel particularly adapted for airplanes:

Example I Three pounds of titanium dioxide N. C. (a brand of non-chalking pigment containing 99% 'IiOz and 1% Z1102) is ground in a ball or pebble mill with 2- pounds of a vehicle containing 14.21% dry sec. nitrocellulose, 8% alcohol from the cotton, 37.79% butyl acetate, 40% Solvesso #1, and 10% butyl alcohol for about 5 to 10 hours until a sample of the ground mixture, mixed in the proportion of about 57 72, of ground mixture to 42 /2% of additional vehicle does not leave more than .1% on a 325 mesh screen. The grinding is stopped immediately to avoid imparting an undue amount of gloss. The bulk ground mixture is then mixed with more vehicle (57 /z% of the paste to 42 of the vehicle) to make up the proper formulation corresponding with the formula of the given specification. The material is then centrifuged to remove the oversized particles of the pigment. This may be done with a suitable centrifuge such as a Sharples Super- Centrifuge. The separation of the undesired particles may be carried out at a speed of 7,500 R. P. M. or at the higher speed of 15,000 R. P. M.

Example II Three pounds of titanium oxide were ground together as in Example I with 2 pounds of vehicle corresponding to Army and Navy control formula AN-L-21, the viscosity being maintained around 2 cps.

The following is the control formula for the clear vehicle:

Ingredients Weight Paraplex RG-Z 000%) Amberlac 13-94 in xylen Aroclor 5460 (100%) Ethyl-Cellulose (3 to 4 seconds) (100%) Cellulose-Nitrate second R. S.) (65% in ethyl alcohol). Ethyl Alcohol. Ethyl Acetate. Butyl AlcohoL Butyl Acetate Amyl Acetate (Pentacetatc) Aromatic Petroleum Naptha Type 1, Grade B on a i zs ewweeew CHOiPDFCHUIUkWWQD- Reference is hereby made to the Condensed Chemical Dictionary, Third Edition, Reinhold Publishing Corp., New York, 1942, for definitions of Paraplex, etc.

The rest of the method is the same as in Example I.

Example III Antimony trioxide may be used to replace the titanium dioxide in whole or in part.

Eccample IV Example V Any of the examples using the Army and Navy Control formula may be varied by replacing of the butyl acetate with 10% of amyl acetate (Pentacetate) or other high-boiling or slow-evapcrating solvent or :thinner. The change prevents drying during the spraying operation as well as powdering of the lacquer. Powdering of the lacquer may produce a rough surface.

In practice, I have found it advantageous to centrifuge the vehicle itself before mixing with the other ingredients in order to remove jelled particles.

The coating compositions of the foregoing examples may be applied to the object (speed vehicle) to be lacquered in any way known to the art, 1. e. brush, spray, etc. However applied, the

coating when dry will present a very smooth or even, dull or non-specular gloss, substantially non-chalking, very durable, substantially waterproof protective film, which will be materially unaffected by exposure to sunlight and extreme atmospheric and weather conditions.

The utility and practicability of the invention have been demonstrated by actual flying tests. Such tests show that the normal speed of an airplane for a given power consumption may be increased more than ten miles per hour, or that the normal power consumption can be correspondingly decreased.

In conclusion, I wish it to be understood that the foregoing disclosure has been given by Way of illustration only, and that no limitations are to be imported into the claim which is not required by the state of the prior art.

I claim:

A method for making a lacquer enamel adapted to provide a particularly smooth, durable, nonchalking protective film or coating, which consists in providing a readily-dispersible pigment substantially free of materials having chalking tendencies, and a lacquer vehicle containing a cellulose derivative selected from the group consisting of nitro-cellulose and ethyl cellulose, grinding the pigment with a portion of the lacquer vehicle for a time just short of the time necessary to impart a gloss to the resultant coating, mixing the ground mixture with the rest of the lacquer vehicle, and screening the resultant mixture to remove conglomerates and particles larger than 2 microns.

MARCUS THAU.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,791,119 Cabot Feb. 3, 1931 1,860,532 Ensminger May 31, 1932 1,914,563 Gilbert June 20, 1933 1,948,580 Hucks Feb. 27, 1934 2,157,901 Hucks May 9, 1939 2,302,305 Farrell Nov. 17, 1942 2,304,754 Wainer Dec. 8, 1942 OTIHER REFERENCES Handbook of Plastics, Simonds et a1. (1943).

Van Nostrand Company, New York. Pages 240-