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CA1102040A - Polyethylene coating for ferrous metals - Google Patents

Polyethylene coating for ferrous metals

Info

Publication number
CA1102040A
CA1102040A CA270,219A CA270219A CA1102040A CA 1102040 A CA1102040 A CA 1102040A CA 270219 A CA270219 A CA 270219A CA 1102040 A CA1102040 A CA 1102040A
Authority
CA
Canada
Prior art keywords
coating
blend
high density
density polyethylene
low density
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA270,219A
Other languages
French (fr)
Inventor
Chester E. Feehan
Ernest F. Wagner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
United States Pipe and Foundry Co LLC
Original Assignee
United States Pipe and Foundry Co LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by United States Pipe and Foundry Co LLC filed Critical United States Pipe and Foundry Co LLC
Priority to CA270,219A priority Critical patent/CA1102040A/en
Application granted granted Critical
Publication of CA1102040A publication Critical patent/CA1102040A/en
Expired legal-status Critical Current

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  • Paints Or Removers (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)

Abstract

ABSTRACT

This invention provides a method of coating ferrous metal surfaces with a blend of high density and low density polyethylene powder wherein the coating is completed to the desired thickness in one application of the blended powder on a hot (400°F. to 550°F.) ferrous m tal surface. The coating may be cured or quenched after application depending on the amount of heat available from the coated object.

Description

1~2q~4~

The present invention is in the field of thermoplas-tic coatings, and, more specifically, is directed to a method of coating metal articles with a polyethylene coating.
~ lastics in the form of powder have been used for coating metal substrates to protect them from corrosion. Var-ious methods of application and curing are known such as pre-heating an object to a temperature ranging from 350F. to 600F. and dipping the object in a fluidized bed, spraying it by flock or electrostatic gun. No one type of polyethylene by itself has proven to be a satisfactory coating material due to poor adhesion to the metal substrate of low density types or the high cost and poor physical characteristics of the high density types. To obtain an acceptable adhesion level, primers were developed consisting of either special high density poly-ethylene or ethylene copolymers. These primers may be applied to the metal substrate in relatively thin films (2-4 mils), fused and subsequently covered with a finish coat of low den-sity polyethylene to develop the total thickness required.
This two-step application procedure requires close temperature control of both application steps with concomitant high capital cost for production equipment.
The use of primers as a full thickness coating has not proven satisfactory for several reasons. Pigmentation to provide resistance to ultra violet rays may adversely change adhesive characteristics. Cured physical properties are unsat-tisfactory in that the surface may be quite soft and rubbery or hard and brittle. Also, the high density primer is much more expensive than low density polyethylene.

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The present invention provides a method of coating a metal article with a polyethylene composition com-prising the steps of preparing a blend of high density and low density polyethylene powders, said blend containing a range by volume of from 1 part of high density polyethylene and 1 part of low density polyethylene to 1 part of high density poly-ethylene to 3 parts of low density polyethylene, heating a surface of said metal article to a temperature of between above 450F. to about 600F. applying said blend to powders over said heated surface of said metal article to a desired thickness, maintaining said surface at a temperature of be-tween over 450F. to about 600F. for a period of from about 5 to 15 minutes, and then cooling said metal article to am-bient temperature.
Due to the problems encountered with the prior art methods, it was conceived that the desired objectives of ten-acious adhesion, single-stage application and minimal cost might be obtained by blending plastic powders. A number of combinations were tried with minor success. However, a blend -of linear high density polyethylene and low density poly-ethylene produced results that were quite unexpected. The two ingredients were blended in ratios of from 1:1 to 1:3, high density polyethylene to low density polyethylene. The two materials may be mixed using conventional dry material mixing ~'. .

~2~3 equipment and techniques. Application may be by spray or dip methods where the metal surface to be coated is at 350Fo to 600F. After application, the coating should be kept in an at~
mosphere of from 4aooF. to 500F. for a period of from lO min-utes to 15 minutes. Satisfactory coatings are obtained from blends of high and low density polyethylene powders between and including the ratios of from l:1 to 1:3, such ratios being by volume of high density to low density p~lyethylene.
In order to test the adhesion of the coatings of the invention, the metal surfaces coated in accordance with the invention were small sections cut from a centrifugally cast pipe of gray iron which had been annealed. The customary oxide which forms on the surface during annealing had been en-tirely removed, to "white" metal by grit blasting, or eighty per cent of the oxide had been removed by grinding with an abrasive wheel, prior to coating.
Adhesio~of the coating was measured by making two razor blade cuts through the coating l/4 inch apart and at~
tempting to peel the l/4 inch strip of coating from the metal surface. If the coating could be lifted and peeled from the metal surface in one piece, the adhesion was said to be ''poor''0 If the coating could be lifted and peeled from the surface but broke into small pieces approximately l/8 inch long, the adhe-sion was said to be "good". If the coating could not be lifted to peel off small pieces, the adhesion was said to be "excel-lent".
Results of these tests are tabulated belowo Z~4~) Blend Ratio High Density to Metal Surface Temp. Surface Low DensityDegrees F.Preparation ~dhesion 1~1 400Grit Blast Poor 1:1 450 " " Good 1 1 500 " " Good 1:1 400 80% Grird Poor lol 450 " " Good lol 500 " " Good 102 400 Grit Blast Poor 1:2 450 " " Good 1:2 500 " " Excellent 1:2 400 80% Grind Poor 1:2 450 " " Good 1:2 500 " " Excellent 1:3 400Grit Blast Poor 1:3 45 ~ood 1:3 500 " " Excellent 1:3 ~0080~ Grind Poor 1:3 45 " " Good 1:3 500 " " Excellent The resulting coatings were compared with those ap-plied by prior art methods and found to adhere more tenaciou~
ly.
The prior art coatings used for comparative tests were prepared in the following manner. The object to be coat~
ed was grit-blast cleaned to white metal and heated to temper-atures of 550 to 600F. A-primer of high density linear poly-ethylene, density 0.95, was applied to a thic~ness of approxi mately 4 mils by means of air spray. This was allowed to fuse and a final coat of low density polyethylene, density 00916, was immediately applied to a thickness of 15-20 mils. The re- -sultant coating was cured by the residual heat in the object being coated. In other cases, the same temperature level and procedure was used except that the primer was ethyIene vinyl acetate copolymer, density 0.94, applied to a thickness of ap proximately 4 mils.
One test used to compare adhesion was to place the coated ferrous metal surface in boiling water. In such a test a coating applied by the above described prior art method ~1~2~40 failed in four and one-half hours while a coating applied ac-cording to the present invention had not failed after 410 5 hours in boiling water.
Applicant's blend consisted of high density linear polyethylene powders with the following range of propertieso 0.945 to 0.960 density, 6 ~o 18 melt index and 35 to 50 mesh particle size, such as U.S. Industrial Chemicals Company's "ML-713,' U.S. Industrial Chemicals Company's"MA-778"and Phillips Petroleum com ~ y'a"~MN TR-980,' and low density poly-ethylene powders with the following range of properties:
o.gl to 0.92 density, 16 to 25 melt index and 35 to 50 mesh particle size, such as U.S. Industrial Chemicals Company's "MC-91007,' U.S. Industrial Chemicals Company's"711-942,' or Union Carbide Corporation's"DNPA o408"
Blending may be accomplished by using a "V" shaped rotating drum type blender or other satisfactory dry powder blender. Such blenders are well known to those familiar with the art and include Patterson-Kelly Company's rotating drum blenders, as well as paddle or ribbon blenders.
Application was accomplished by entraining the de-sired amount of blended powder in an air stream and directing the air stream and the entrained powder onto the hot (400~
to 500F.) ferrous metal surface. The blend of powders fused together into a uniform coating covering the metal surface completely. Coatings of various thicknesses were applied to ferrous metal surfaces. The thickness was varied by simply applying more powder to the surface. Complete coverage of the ferrous metal surface with a coating of 15 mils thickness was found to be easily attainable. Thinner coatings tended to leave small uncoated areas. Thicker coatings up to 45 mils were also applied in the s~me manner with excellent results.

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Also coatings of the same blended powder were applied to fer-rous metal surface by the well-known fluidized bed methodO In these trials the ferrous metal surface to be coated was heated to between 400F. and 600F. and brought into contact with a fluidized bed of the blended powder. Coatings obtained from such a method were of the same appearance and quality as those obtained from entraining the blended powder in an air stream and directing the resulting stream onto the metal surface.
A series o~ tests was made using blends of a high density polyethylene obtained from U.S. Industrial Chemicals Company, MA 778, with melt index -6, density -0.949, 35 mesh powder and a low d~nsity polyethylene also obtained from U.S.
Industrial Chemicals Company, MC-91007, with melt index -22, density -0.916, 35 mesh powder. Grit blast cleaned ductile iron panels were heated to various temperature levels and coated in a fluidized bed. Each panel was tested for adhesion after four hours in boiling water with the following resultso Panel Blend Blend Temp. 1 Part - MA-778 1 Part - MA-778 F 3 Pa,rts - MC-91007 2 Parts - MC-91007 400 - Poor 450 Excellent Excellent 500 Excellent Excellent 525 Excellent Excellent 550 GoQd - Excellent 575 Fair Good 600 Fair Good A series of tests were made with blend ratios rang-ing from 1:1 to 1:3 linear high density polyethylene to low density polyethylene and evaluated f~r film characteristics.
The materials used were U.S. Industrial Chemicals Company's ML-713 and Union Carbid~ Corporation's DNPA o408. The re-sults were as follows:

llO~ L~) Blend Ratio Panel Temp. 4-Hour Boiling Water High:Low F. Adhesion 1:1 400 Poor 1:1 450 Good 1:1 500 Good 1:2 400 Poor 1:2 450 Good 1:2 500 Excellent 1:3 400 Poor 10 1:3 45 Good 1:3 500 Excellent When the blend of high density to low density poly-ethylene was increased above 1:1, e.gO, 1.25:1J the resultant coating was brittle and took on a dull, wrinkled finish rather than a smooth finish. Reducing the proportion of high density linear polyethylene below 1:3 was found to result in a loss in adhesion.
While the above description is of the preferred em-bodiment of the present invention, it will be understood that modifications will be apparent that will fall within the scope of the invention.

Claims (2)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:
1. A method of coating a metal article with a poly-ethylene composition comprising the steps of preparing a blend of high density and low density polyethylene powders, said blend containing a range by volume of from 1 part of high density polyethylene and 1 part of low density polyethylene to 1 part of high density polyethylene to 3 parts of low density poly-ethylene, heating a surface of said metal article to a tempera-ture of between 450°F. to 600°F. applying said blend of powders over said heated surface of said metal article to a desired thickness, maintaining said surface at a temperature of 450°F.
to 600°F. for a period of from 5 to 15 minutes, and then cooling said metal article to ambient temperature.
2. A method of coating a metal article with a poly-ethylene compound as recited in claim 1 in which said blend of powders is applied in a thickness of between 15 and 45 mils.
CA270,219A 1977-01-21 1977-01-21 Polyethylene coating for ferrous metals Expired CA1102040A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA270,219A CA1102040A (en) 1977-01-21 1977-01-21 Polyethylene coating for ferrous metals

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA270,219A CA1102040A (en) 1977-01-21 1977-01-21 Polyethylene coating for ferrous metals

Publications (1)

Publication Number Publication Date
CA1102040A true CA1102040A (en) 1981-05-26

Family

ID=4107789

Family Applications (1)

Application Number Title Priority Date Filing Date
CA270,219A Expired CA1102040A (en) 1977-01-21 1977-01-21 Polyethylene coating for ferrous metals

Country Status (1)

Country Link
CA (1) CA1102040A (en)

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