US 2676932 A
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April 27, 1954 POLYETHYLENE AND A FLUXING AGENT Filed March 28, 1951 POLYET HYLE NE HIGH MELTING POINT wAx HEAT COMPONENTS To FORM INTIMATE DISPERSION POUR HEATED DISPERSION ON SMOOTH SURFACE BREAK FILM INTO DRY ICE FINE PARTICLES GRIND CHILLED PARTICLES SELECT PARTICLES 40 TO I00 MESH SPRAY PARTICLES A INVENTOR SELECTED SIZE BY GEORGE L. DENISTON mm W ATTORNEYS Patented Apr. 27, 1954 FLAME-SPRAYING COMPOSITIONS COM- PRISING POLYETHYLENE, AND A FLUX- ING AGENT George L. 'Deniston, Dayton, Ohio, assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio Application March 28, 1951, Serial No. 217,925
This invention relates to improvements in the coating of surfaces by the flame spraying method. More particularly the invention relates to compositions containing polyethylene as the organic thermoplastic coating material.
In the process of flame spraying it is essential that the sprayed surface receive a smooth continuous film free of pinholes and other surface defects, for such coatings are used in electrolytic processes, as electrical insulation, and more recently on food containers of both the metal and paper types. Therefore it is desirable that the material when sprayed flow evenly over the surface to which it is applied without developing checks or cracks upon hardening.
There is described in my co-pending application .Serial No. 186,267, filed September 22, 1950, a method of attaining a polyethylene composition which satisfies the above requirements. In that process the polyethylene, having a molecular weight of ten thousand or above, is first fluxed with a wax or resinous material having a rela tively low softening point, and thereafter the flux'ed material is ground to a, fine particle size in the presence of Dry Ice 01' other cooling medium, after which the finely ground particles are sprayed by the use of a flame gun. v
1 I have now discovered that a greater degree of control in the fiuxing operation and a finer film may be obtained on the finished article if the medium with which the fusible polyethylene is fluxed has a relatively high softening point. When such a material is used the composition containing the polyethylene and flux material may be permitted to attain a higher temperature, thus accelerating the fluxing action and increasing the fineness of the dispersion of the material, such as the flux or plasticizer in the polyethylene.
In the process of invention the polyethylene having a molecular weight of six thousand or above may be fluxed with a plasticizing material, wax or resin, having a softening point in the range of between about 200 to 250 degrees centigrade. The temperature of the composition should be slightly in excess of the softening point of the fluxing material during the combining so that the polyethylene and the flux blend together in fluid form to secure intimate mixing of the components. After fluxing, the polyethylene composition is preferably flowed onto a smooth surface, such as Pyrex glass or stainless steel plate, and cooled, whereafter the polyethylene film is cut and sheared into small pieces suitable for grinding.
The grinding operation is preferably carried out in a hammer mill or other suitable grinding 2' claims, (01. 260-23) medium using Dry Ice in the form of small pellets which surround the polyethylene material to render the same brittle to facilitate the grinding thereof. It is believed that the fluxed composition assists materially in the grinding operation, shortening the time over that required for the grinding of polyethylene itself. Further, the higher softening point of the fluxing material is beneficial over that of lower softening point organic materials as there is less tendency to clog the hammer mill when using the high softening point substance.
The ground material should attain a particle size in the range of 40 to mesh. Larger particle sizes may give rise to difficulty in the flame gun' due to failure to become thoroughly plastic, whereas the smaller particle sizes may be wholly consumed by the flame, resulting in the deposition of charred particles on the finished surface.
The invention will be more fully understood by reference to the following detailed description and accompanying flow sheet.
In the preferred embodiment of the invention 100 parts of fusible polyethylene having a molecular weight of six thousand or above was mixed .with approximately 15 parts of a high softening point wax 8-1184, produced by Glyco Products 00., Inc. of Brooklyn, New York, having a softening point between about 223 and 229 degrees centig-rade. This material is a tough hon-brittle brown-black wax, having a flash point of 313 0., a fire point of 332 C. and a specific gravity of about 0.96. This brown-black wax is insoluble in water and alcohol, partially soluble in hot toluol and soluble hot in naphtha and mineral oil, gelling when the same cools to room temperature.
The wax and polyethylene are heated toegther at a temperature sufficient to insure that the mass becomes molten, that is in the range of about 250 degrees centigrade, and the composition is agitated to insure of the thorough dispersal of the wax throughout the polyethylene.
Thereafter the composition while fluid is poured onto a'smooth surface plate to form a thin film thereon; This film may be peeled from the plate and broken into small fragments, whereafter they are placed in a hammer mill together with solid carbon dioxide and ground to a mesh of between about 40 to 100.
The Dry Ice which under proper insulating conditions will drop the temperature as low as minus 40 F. is necessary to render the material friable and to prevent the mix from becoming plastic in the hammer mill under the heat evolved by the grinding operation. It may be noted in this connection that the use of a high softening point wax is of particular assistance in this respect as the wax itself does not tend to soften under the thermal conditions imposed by the grinding. The Dry Ice of course sublimes during this grinding process and the carbon dioxide gas evolved passes off.
The particles obtained by grinding are screened to obtain particles greater than .40 mesh. The resultant material is then screened on a 100 mesh screen to prevent particles of extreme smallness from appearing in the resultant composition which is to be used in the flame gun. The particu lar range of particle size to be used in any given instance is, of course, dependent to some extent upon the type of flame gun and the length -of the channel therein and the speed at which the plastic particles are to be passed through the gun. general, I have found that a particle size from about 40 to about 100 mesh is most suitable, as hereinbefore noted.
The flame spray gun itself may be of any type known to the art and accordingly no description thereof will be given herein. However, it .should be noted that when using the composition .of invention the heat of the gun may assist to some extent in the smoothing of the applied film of polyethylene, since the flux'ing material will induce a degree of fluidity in the material as it strikes the base to which it is-applied.
The composition of invention may be applied to any type of base, that is, glass, metal, paper, and so forth; and in connection with the latter type of application it should :be noted that it is preferable to move the object during the application in order that the paper material itself will not be unduly subjected to the excessive heat of the flame.
Another material which is satisfactory for the practice of the invention is diethylene glycol stearate. This glycol ester has a considerably lower softening point than the wax referred to hereinbefore, and accordingly is somewhat inferior to the wax. However, it is sufiiciently high to be more suitable than the lower softening point waxes and resins which have been heretofore incorporated with polyethylene and cloes stiffen the polyethylene in a manner beyond that expected from a consideration of the softening point alone. Such a glycol ester is produced under the name Diglycol Stearate S, by the Glyco Products .00., Inc, and has a specific gravity of 0.96, a softening point of 55 to 59 degrees centigrade, an acid value of 95 to 105, and a saponification point of 170 to 180. The diglycol stearate is also used to the extent of about parts by weight to '100 parts by Weight of polyethylene.
The fluxing temperature most suitable for a given wax material is dependent toa considerable extent upon the degree of polymerization of the polyethylene. Thus polyethylene having a'mol'ecular weight of about six thousand softens at about 75 C., at a molecular weight of twelve thousand the softening point is about 100 C. and at sixteen 4 thousand about 112 C. Accordingly a temperature of about 100 C. will be satisfactory when using diethylene glycol stearate with a polyethylene of six thousand molecular weight, while about 125 C. is required when the polyethylene has a molecular weight-of about sixteen thousand.
While for most purposes, particularly where high chemical inertness is desired as in linings of foodstuff containers, I prefer to use polyethylene having .a molecular weight of ten thousand or more, the-process of invention i applicable, as indicated, to molecular weights of the polyethylene as low'as six thousand.
It will be understood that I do not wish to be limited to the exact proportions, ratios and other factors specifically set forth in the foregoing description and accompanying drawing, but desire to comprehend such changes thereof as may be further desirable to adapt my invention to different conditions and usages.
1. A particulate composition for application .to a base'by flame spraying and consisting essentially of a pro-fused intimate mixture of a polyethylene having a molecular weight of at least 6000 and,
as a fluxing aid for the polyethylene, diethylene glycol stearate having a softening point between about 55 C. and 59 0., a specific gravity of about 0.96, an acid value between about and 105, and a saponification point between about 170 and 1 80,
said polyethylene and diethylene glycol stearate being present in the proportions of about parts of the polyethylene to 15 parts of .the stearate,.and
the particles of thecompositionhaving a size be tween .40 and 100 mesh.
2. The method of making a particulate, flame sprayable composition which comprises heating polyethylene having a molecular Weight of at least 6000 with, as fluxing aid therefor, diethylene glycol stearate having a softening point between about 55 0., and 59 C., a specific gravity of about 0:96, 'anacid value between about 95 and 105., and a sapon-ification point between about and 180, in the proportions of about 100 parts .of the polyethylene to about 15 parts of the stearate, to obtain a molten intimate mixture of the two, de-
positing the molten mixture on a surface to .form
a film, removing the film from the surface, disrupting the film to obtain fragments, and grinding the fragments in the presence of solid carbon dioxide to obtain a ilame-sprayable mass of particles having a size between .40 and 'l00mesh.
References Gited in the file of this patent 'UNIIED'STATES PATENTS Number Name Date 23341464 Cuno Apr. 25, 1944 2,410,225 Macht et a1. Oct. 29, 1,946 --2, i48,7-99 Happoldt Sept. '7, 1948 3,499,486 Fuller Mar. 7, 1950 2;50 l,4 00 Erchak Apr. 18, 1950 2;52 5,691 Lee et a1 Oct. 10, 1950