Note: Descriptions are shown in the official language in which they were submitted.
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1 Zinc-rich electrostatic powders are employed as
2 coatings to protect iron or steel parts from corrosion.
3 The zinc in the coating acts as a sacrificial metal to protect
4 the iron base.
Coatings of this general type are known and even
6 zinc-containing electrostatic powders are known- U.S. Milla~ patent
7 3,770,482 describes one such heterogeneous powder. Millar employs
8~ a two layer system. Millar employs up to 30% of zinc, col. 5,
9 lines 13-40.
It is also known to make a free flowing powder for
11 fusion coating of metals including steel employing a mixture of
12 (A) an epoxide resin, a siloxane resin, and a polycarboxylic
13 acid anhydride and (B) a filler, U.S. Bo~d paten~ 3,170,890
14 Component (B) can be 25 to 70~ of the total of (A) and (B~,
col. 3, lines 40-55 and the claims. Boyd mentions zinc as a
16 filler on col. 3, line 55. ~e makes a heterogeneous mixture of
17 the powder which can then be applied to the mPtal substrate by
18 conventional procedures, e.g., fluidized bed techniques~
l9 U.S.Manasia patent 3,336,251 shows employing zinc dust as
a filler for an epoxy resin in an amount of 1 up to 150 parts
21 per lO0 parts of the resin. Manasia simply dry blends ~is
22 mixture and applies his mixture to a metal substrate, e.g.,
23 steel by a fluidized bed procedure.
24 U.S. Car~nanian patent 3,939,020 discloses applying a
coating containing an epoxy resin, powdered zinc, inorganic
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1 fibers and barium sulfate to a rotor, e.~., col. 1, lines 42-46.
2 U.S.Kenyon patent 3,518,221 discloses a molding composition
3 comprising an inorganic fiber enveloped in a first epoxy resin
4 and a second epoxy resin surrounding the enveloped fiber, eOg.,
claim 6. Powdery fillers can also be used, col. 9, lines 23-26.
It has now been found that homogeneous zinc-rich
7 powders/ e.g., electrostatic powders, can be prepared by
8 ~ incorporating zinc powder into an epoxy resin melt and thereby,
9 the zinc is uniformly distributed-without any density gradient
in the finished free-flowing powder.
11 The zinc powder can be blended with molten epoxy
12 resin in a conventional manner in a screw fed melt compounder
13 followed by cooling and grinding the solid to form a powder
14 compound or else the zinc powder and epoxy resin in powder form
can be mixed and the preblended powder homogenized on a heated
16 two-roll mill, at a temperature suficient to soften or melt the
17 resin, but insufficient to cure it during its working time on
18 the mill. Thus a temperature of 180F. can be used with PpOxy
19 resins that soften below this temperature. Alternatively, the
epoxy resin in powder, lump or flake form is added to the heated
21 two roll mill and after it is in softened or molten form, the zinc
2~ powder is added and milling continued until a homogeneous blend
23 is obtained. After removal of the homogeneous blend obtained
24 in either of the two milling procedures just described, the
product is al]owed to cool to solid form and ground to a powder.
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1 Normally the curing aid is added to the epoxy resin
2 prior to mixing with the æinc powder whether the mixing is
3 accomplished by using a screw fed mel-t compounder or by using
4 hot rolls~ In this manner there is obtained a high weight %
of zinc powder homogeneously blended with epoxy resin powder.
6 The zinc is 75 to 90%- of the total weight of the composition.
7 As stated, after incorporation of the zinc in the molten resin or
8 after milling the product is cooled to form a solid which is
9 then ground to a powder. The exact si2e of the powder is not
particularly critical, but it is usually small enough to pass
11 100 mesh (Tyler sieve series~. For fluid bed application to the
12 metal substrate, e.~., iron or steel, the composition is ground
13 to pass 60 mesh or to pass 200 mesh for spray or electrostatic
14 fluid bed application.
Any of the conventional solid epoxy resins or mixtures
16 o two or more such epoxy resins can be used. There can also
17 be used any of the conventional curing agents for the epoxy
18 resin. Thus, there can be used, for example, as curing agents
19 dicyandiamide, P-108~(a mixture of an imidazole and dicyandiamide
having a melting point range of 40-200C.~, solid cyclic carboxylic
21 acid anhydrides, e.g., trimellitic anhydride, phthalic anhydride,
22 cyclopentane dianhydride, tetrachlorophthalic anhydride and the
23 like.
24 Illustrative of suitable epoxy resins are Epirez S22F
(a bisphenol A-epichlorhydrin resin with a weight per epoxide
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1 (WPE) of 600, Durran's Melting Point of 80C. and supplied
2 by Celanese), DRH 201 (a linear solid bisphenol A-epichlorhydrin
3 resin having a WPE of about 750, a Durran's Melting Point of
4 90C. and supplied by Shell), DRH (an epoxy resin identical with
DRH 201, except DRH 203 also contains 5% of Modaflow, a flowaid
6 supplied by Monsanto), DER-667 (a solid bisphenol A-epichlor~
7 hydrin resin with a WPE of 1600-2000, a Durran's Melting Point
8 of 115-130C. and supplied by Dow), XU-21~(a solid bisphenol A-
9 epichlorhydrin resin with an average WPE of 700 and supplied
by Ciba-Geigy), Epon~1001 (bisphenol A-epichlorhydrin resin,
11 WPE 450-550, Durran's Melting Point 65-74C. and supplied by
12 Shell). There can be even used a small amount of liquid
13 bisphenol A-epichlorhydrin, e.g., Epon~828, having a WPE of
14 180-195 and a viscosity of 100-160 poises, supplied by Shell,
providing the overall epoxy resin in a solid.
16 The zinc-rich epoxy hot melt powder compositions of
17 the invention can replace conventional zinc
18 galvanizing/plating finishes for iron or steel and offer true
19 galvanic sacrificial protection.
The compositions of the invention have excellent
21 adhesion to iron and steel and when applied thereto, e.~., by
22 spray or electrostatic fluid bed technique, provide a continuous
23 film coating for iron or s~eel.
24 In a series of tests of formulations within the
invention, the formulation containing 90% zinc provided the best
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1 adhesion to steel and the formulatioll with 85% zinc had the best
2 visual appearance after the coated steel had been subjected
3 to salt attack.
4 Unless otherwise indicated all parts and percentages
are by weight.
6 The compositions preferably consist essentially of the
7 zinc dust and epoxy resin. As previously indicated there can, of
8 course, be included a curing agent for ~he epoxy resin to
9 improve the cured film properties and also a small amount of a
flow modifier can be included. Small amounts of silica aerogels
11 can be included, e.~., 0.2~ of Cab-O-Si~, ~ flame hydrated silica~
12 Examples of suitable formulations are the following:
13
14 Example 1
DRH-201 12.0
16 DRH-203 3.0%
17 Zinc Dust (finely ground
18 100~ zinc powder) 85.0~ ~
19 ~,
20 Example 2
21 Epirez 522F 20.0 parts
22 DRH-203 5.0 parts
23 Zinc Dust 75.0 parts
24 P-108~ 1.56 parts
101.56 parts
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1 Examples 3 and 4
2 Example 3 Example 4
3 Epirez 522F 11.22~ 7.48%
4 DRH-203 3.00~ 2.00%
Zinc Dust 85.00% 90.00%
6 P-108~ 0.7~% 0.52~
9 Examples 5, 6 and 7
Example 5 Example 6 Example 7
11 DRH-203 5.0~ 1~84% 3.00%
12 Zinc Dust 75.0~ 75~00% 85.00
13 P-108~ 1.3~ - 0.7
14 Modified Trimellitic
Anhydride Curing
Agent - 6.42%
16 DER-667 18.7~ - -
17 Epirez~522F - 16.74%
18 X~-214~ - _ 11.22%
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21 In tests on st~el panels both the compositions of
22 Examples 5 and 7 had good to excellent adhesion to steel and the
23 composition of Example 7 had 0-creepage from the scribe marks
24 and no blistering or rust spotting.
The compositions containing 85%-zinc (Example 7) and
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1 90% zinc (Example 4) had better anticorrosive results when
applied to the steel than the compositions of Example 5, thus
3 indicating superior sacrificial properties as shown by ~alt
4 fog exposure at times of 100, 200, 300, 400 and 500 hours.
In the above tests the homogeneous zinc-rich
6 compositions were applied to the steel by the conventional
7 fluidized bed procedure. Coatings of 2 mil, 4 mil, 6 mil,
8 8 mil, 9.4 mil and 12.0 mil thickness were applied to the steel.
9 The composition of Example 2 was cured on the steel
for 15 minutes at 180C. and in other tests was cured on the
11 steel for 7 minutes at 210C. The other compositions containing
12 curing agents were similarly cured at 180C. for 15 minutes
13 or at 210C. for 7 minutes. A cure cycle of 15 minutes at
14 180C. is preferred. Also it is preferred to form a film
build of 4-10 mils of the homogeneous zinc-epoxy composition
16 on the iron or steel, e.g., cold rolled steel strip or steel
17 rods-
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