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l’atented Sept. 25, 1945 2,385,560 UNITED STATES PATENT oar-"ices 2,385,560 METHOD OF TESTING A PIGMENT John K. Wise, Chicago, n1., assignor to United States Gypsum ‘Company, Chicago, 111., a corporation of Illinois No Drawing. Application June 16, 1941, Serial No. 398,243 4 Claims. (01. 23-230) The present invention relates. to an improved forms of cellulose etherse-for example, methyl type of coating composition, suitable for use as ~ cellulose, and the like. a paint and the like, comprising a water-solu It has been proposed in the past to manufac ture water thinnable paints such as the well known casein paints of commerce, which are vble aminoplastic condensation product capable of becoming insoluble in an acid-reacting medi um, pigments nonreactive therewith, and a set ting accelerator which comprises a compound which is capable of hydrolyzing in the presence \ available in dry powdered form as well as in paste and liquid form, and the so-called resin emulsion paints which. generally consist of a pro of water to yield an acid-reacting solution, tein solution in which a suitable type of alkyd whereby the aminoplasticv condensation product 10 resin has been emulsi?ed. will, upon evaporation of the water contained in It is already well known that urea-formalde the coating composition, becomes insoluble in water so that the resulting coating composition ’ hyde condensation products can be prepared in water-soluble form and dried to form more or may, after a suitable period, be washed with wa less coherent ?lms merely upon the evaporation ter without becoming dissolved or dislodged from 15 of the water used to dissolve the condensation the surface to which it has been applied. product. Such ?lms, however, will again be One of the primary objects of the invention come dissolved or dispersed by water when it therefore is to provide a coating composition comes in contact therewith, so that'obviously no which may be either in dry form or in the form permanent paint could be produced thereby. It vof a solution or paste and in which the binder is 20 is known that insolubilization of these amino primarily an aminoplastic condensation product plastic condensation products can be effected by of the type which, while soluble in water in neu rendering the solution slightly acid. tral or slightly alkaline solutions, tends to become This insolubilization'can be eifected by means insoluble if the hydrogen-ion concentration of either of an acid or of a substance, for instance the solution is increased to a pH below 5. This 25 an ammonium salt, which su?iciently hydrolyzes may be accomplished, for example, by the addi to produce the required amount of free hydrogen tion of either all-acid or an acid-reacting sub ions in the solution. It has been found, how stance or of a salt which upon hydrolysis will ever, that there are certain limitations to the yield free hydrogen ions. If this composition is production of such a coating material, namely, to be kept in liquid or paste form for any length 30 the necessity of carefully selecting the pigments - of time, it becomes advisable to prevent the pre which are associated therewith. In the first mature insolubilization of the aminoplastic by the expedient of incorporating with the composi place, these pigments must be entirely nonreac tive with the aminoplastic condensation prod tion a small amount of a suitable volatile alkali uct; but they must also be of such a nature such as; for example, ammonium hydroxide, mor that they will not interfere with the develop pholine, or the like. ment of acidity in the solution as a result of the If such a composition is applied to a given surface, the water as well as presence of, or addition of, an accelerator capa the volatile alkali will evaporate, whereafter the ble of yielding hydrogen ions. Obviously, if the hydrolysis of the accelerator will take place, pigment reacts alkaline of itself or at least is yielding free hydrogen ions which serve to in 40 capable of binding the hydrogen ions which are solubilize the aminoplastic condensation prod depended upon to-insolubilize the aminoplastic uct. , condensation product, no such insolubilization In its broadest aspects, the invention is par can be effected. It therefore becomes necessary ticularly applicable to the manufacture of what ‘ to select such pigments as will not interfere with is known as water-thinnable paints, such as the insolubilization of the material. those which are designed for application to ma In general it may be stated that suitable com sonry, plaster, wood, fiber, or other porous sur positions may comprise a water-soluble amino faces, upon which the composition will dry to plastic resin, some form of pigment such as, for form a water resistant ?lm. Obviously, in or example, various types of lithopone, titanium ox der to impart the desired hiding power and color 50 ide, antimony oxide and the like, and a small ing power to the material, suitable pigments and quantity of an ammonium salt of a strong acid. , fillers are also admixed therewith. Suitable for this purpose are ammonium chloride, It is also within the scope of the invention to ammonium sulfate, and ammonium nitrate. add other ?lm-forming substances, such as, for In order to determine what pigments will be example, water-soluble gums, water-soluble 55 suitable for this purpose. the following test may 2, 2,386,580’ be used: 20 grams of the pigment or ?ller which is to be used in the paint is suspended in 50 c. c. of distilled water containing either 5 c. o, of 4% materials may be added as further binders, par ticularly to improve the resistance of the coat ing to crazing or check cracking. - Among the aminoplastic condensation products formalin or 14 gramsof a water-soluble urea formaldehyde resin, and the hydrogen-ion con are to be‘included the well-known types of urea centration of the thus formed suspension (that aldehyde condensation products, such for exam- '_ is, its pH) is measured by a suitable method-for ple as urea-formaldehyde condensation products, example, by means of a glass electrode and there thiourea aldehyde and formaldehyde. condensa with associated electronic devices. The suspen tion products, substituted thiourea aldehyde con sion should preferably be close to neutrality, hav 10 densation products, and the like, provided they ing a pH of, say, from 6 to 7. An ammonium are capable of insolubilization in the cold in an chloride solution of known concentration is then acid environment. By the term “urea-aldehyde gradually added to the suspension, using for this condensation produc ” it‘is intended to cover all purpose a su?icient amount of ‘ammonium chlo of these urea-aldehyde condensation products ride to be equivalent to about 5% of ammonium considered as a genus. This term has been ap chloride on the basis of the suspended pigment plied to these materials for some years past, and it is generally understood among chemists as meaning the condensation products of urea or carbamide and analogous compounds. For most or ?ller. The hydrogen-ion concentration of the solution should thereupon increase to the extent that the pH thereof drops, say, down to some where between 4 and 5. If the pigment will pre purposes the simple urea-aldehyde condensation vent the development of the acidity-that is, the product is suitable. This is now a commercially decrease in the pH-such pigment will be un suitable for the purposes of the present invention. It has also been discovered that the degree of development .of acidity, by for example an am monium salt, can be somewhatincreased by the presence in the ?nished product-that is, the paint-of a very small amount of free formalde available product that may be freely purchased on the open market. As actual examples of compositions which may be made within the scope of the presentinven tion may be mentioned the following: Example 1 Parts by weight hyde, this being particularly true in the presence of pigments. ~ If the composition of the present invention is Urea formaldehyde resin (water soluble) _..__ 392 30 Concentrated ammonium hydroxide ______ __ to be made up into paste form so that it may be sold in cans, ready for dilution by the user, two expedients may be employed to keep the mate rial from becoming insoluble in the can. The ?rst expedient is to keep the accelerator out of the composition and to furnish it in a separate con tainer so that it may be added to the paste by the user Just prior to application to the surface that is to be painted. The second expedient, and the one which is preferred, is to add to the paste a small amount of a volatile alkali such as am 25 Pigment, e. g., antimony oxide ____________ __ 400 Mica _ 40 Clay 360 Ammonium chloride ___; ________________ __ Water 3' 16 385 Example 2 Parts by weight Urea formaldehyde resin (water soluble) _____ 14 Pigment, such as lithopone or other zinc sul ?de pigment __________________________ __ 46 Water 25 monium hydroxide, or morpholine, whereafter Ammonium chloride _____________________ __ 3 the accelerator material is added. Usually this Both of these formulas are for stiff pastes. is an ammonium salt, preferably ammonium chlo 45 However, the second formula may be made up ride. It is, of course, obvious that a small amount in dry form merely by omitting the water and of sodium hydroxide could be employed together may be employed by the user by stirring the mix with the ammonium salt so as to liberate a small ture into water until it is dissolved. If it is de quantity of ammonia. In any event, the purpose sired to preserve the second composition for any is to keep the composition substantially neutral while in the can, before use. What happens when 50 length of time, it is desirable to add su?lcient ammonium hydroxide thereto to render it faintly such a composition is applied to the surface to alkaline. be coated is substantially as follows: The water In the above formulas, equivalent amounts of evaporates, carrying with it the still more vola thiourea-aldehyde condensation products may be tile ammonia which is evolved from the am monium hydroxide, so that at about the time the 55 substituted, and it is also possible to use dicy andiamid condensation products in lieu thereof. composition is nearly dry practically all the am However, as the ordinary urea-formaldehyde con monia has escaped. Thereafter, the residual am densation products are the least expensive of this monium salt will hydrolyze, yielding. free hydro group, they are generally preferred. gen ions which then will effect the desired insolu-. While all pigments are not necessarily adapted 60 bilization of the aminoplastic condensation prod uct. If desired, a small amount of free formal dehyde may also be present in the solution or paste, as already indicated hereinabove. The pigments, coloring matter, ?llers, and the like may be added to an aqueous dispersion or 65 solution of the aminoplastic condensation prod uct, or all of the ingredients may be introduced either conjointly or individually into the water, for use in connection with the coating composition of the present invention, their adaptability can readily be determined in'accordance with the tests hereinabove outlined. The methods of mixing and the proportions of ?llers and pigments are, of course, capable of wide variation, depending upon the color and hid ing power of the paint and also whether it is to be used as a ?nal coating or an initial or prim whereafter the mixture may be agitated, as in ing composition. 70 a mixing kettle Or the like, to obtain a uniform Saving for himself such modi?cations as fall mixture therewith. A very advantageous pro within the scope of the art to which this inven cedure is to follow the mixing by running the tion appertains, applicant claims: paint through an ordinary paint mill in order to 1. Process of determining the suitability of a remove lumps and undispersed particles. Other 75 pigment for use in a coating composition con 2,886,660 taining a water-soluble urea-formaldehyde con densation product capable of becoming water-in soluble in an acid-reacting medium which process comprises suspending a quantity ofv said pigment in an aqueous solution of a substance capable of 3 consisting of the chloride,'sulphate and nitrate, and after a short interval of time measuring the hydrogen-ion concentration of the suspension to determine whether it will be within the range of about pH 4 to pH 5; failure to attain such a de gree of acidity being indicative of the unsuit ability of the pigment because of its interference with the development of suiilclent acidity to effect the desired hardening of the said condensation furnishing free formaldehyde thereto, adding about 5% by weight (as calculated on the dry weight of said pigment) of a salt of ammonium capable of liberating free strong mineral acid, 10 product. said salt being selected from the group consist 3. The process of claim 2 in which the ammoni ing of ammonium chloride, ammonium sulphate um salt is the chloride. and ammonium nitrate, and measuring the hy 4. Process of testing a pigment as to its suit drogen-ion concentration of the suspension; ability for use in a urea-formaldehyde coating‘ whereby if the hydrogen-ion concentration of composition which comprises suspending the pig the suspension falls within the range of about ment in the relative proportions of about 20 parts pH 4 and pH 5, the suitability of the pigment by weight thereof in about 50 parts by weight for the intended use is established. 0! water containing about 5 parts of a 4% for 2. Process of testing a pigment for its poten malin solution, adding about 1 part by weight tial property of interfering with the hardening 20 of ammonium ‘chloride, and measuring the hydro of aqueous solutions of urea-formaldehyde con gen-ion concentration of the resulting mixture, densation products by the development of acidity which, if it falls within the range of about pH 4 therein which comprises suspending the pigment to about pH 5, indicates the suitability of the that it to be tested in an aqueous solution con taining formaldehyde, adding an acid-yielding 25 ammonium salt thereto selected from the group pigment. JOHN K. WISE.