WO2000038844A1

WO2000038844A1 - Method of improving adhesion to galvanized surfaces

Info

Publication number: WO2000038844A1
Application number: PCT/US1999/030978
Authority: WO
Inventors: Eric A. Mee; Wim J. Van Ooij
Original assignee: Senco Products, Inc.; University Of Cincinnati
Priority date: 1998-12-30
Filing date: 1999-12-23
Publication date: 2000-07-06
Also published as: AU2217300A; TW469178B; ES2363216T3

Abstract

The adhesion between a galvanized surface and a polymeric material is improved by coating the galvanized surface with an adhesion promoter. The adhesion promoter is a compound which includes at least two trialkoxysilyl groups which are bridged together by a compound which includes at least one reactive nitrogen atom. In certain embodiments the galvanized surface is treated with an alkaline cleaner prior to application of the adhesion promoter. The coating composition forms an adhesion promoting coating in either the hydrolyzed or unhydrolyzed form and can further be used on steel, aluminum or brass.

Description

METHOD OF IMPROVING ADHESION TO GALVANIZED SURFACES

Galvanized coatings (generally zinc or zinc alloy coatings)

are used to prevent rusting of ferrous metals. Galvanized steel is used

for a vaπety of different applications. Galvanized coatings are used on

articles which are subjected to moist and sometimes corrosive

environments.

In certain applications the galvanized article must be coated

with, for example, paints or adhesives. One example of adhesive coated

galvanized articles is galvanized collated fasteners such as staples, nails,

screws, tacks and the like. When fasteners are used with automatic tools,

the individual fasteners are formed and held together using either

adhesive or an adhesive tape. When fasteners are stored in a moist

environment, moisture can destroy the adhesion between the adhesive

and the galvanized surface. This may prevent the fasteners from loading

properly or may cause the tool to jam or leave a portion of the adhesive

tape on the discharged fastener. Summary of the Invention

The present invention is premised on the realization that the

adhesion between a polymeric coating and a galvanized surface can be

improved by coating the galvanized surface with a compound which

5 includes both a nitrogen functionality and a plurality of alkoxy silane

functionalities.

More particularly the present invention is premised on the

realization that a compound having two or more trialkoxysilyl groups

bridged together by a moiety which includes nitrogen, when coated onto

10 a galvanized surface, provides a surface onto which polymeric coatings will remain bonded regardless of humidity. The nitrogen can be a primary

or secondary amine, ureido group, an isocyanate or a cyanide group.

This compound can be applied either as an aqueous

solution after the galvanized surface has been treated with a base or can

15 be applied as a 100% liquid coating without pretreatment. Thus, the

compound can bind to the metal surface without hydrolysis. Further, this

compound also improves adhesion to other engineering metals i.e.,

stainless steel, carbon steel, brass and aluminum. The objects and

advantages of the present invention were further appreciated in light of

20 the following detailed description. Detailed Description

The present invention is a method of improving the

adhesion between a polymeric coating such as paint, an adhesive or an

adhesive tape and a galvanized metal surface.

Galvanized references a zinc or zinc alloy coating which is

applied to a metal surface generally a ferrous metal surface to prevent the

rusting of the metal. Galvanized includes both hot dipped and electro

galvanized surfaces. Although the present invention can be utilized to

improve the adhesion of any galvanized surface, it is at least in one

preferred embodiment used to hold together staples for use in an

automatic stapler.

The coating used to improve the adhesion to a galvanized

surface according to the present invention has the following general

formula.

R, R,

O O

R₁ O - Si - X - Si - O R₁

O O

R₁ R₁

Wherein R₁ represents the same or different lower alkyls, generally C to

ureido group, isocyanate or cyanide. Specific embodiments of X are as

follows: H H

1 1

- R₂ -N - R₂ - - N -

NH₂

1

R₂

1

- O - Si - O - H H

1 1 1

NH, H H

O

R,

R, - N - C - N - R,

- O - Si - O

O

R₄

NH₂ - R₂ - N - O - R₂ -

- R₃ - H

Wherein R₂ is a lower alkenyl, R₃ represents alkenyl and

substituted alkenyl wherein the substituents include acyl, amine, silyl,

urethane, and R₄ represents an alkoxysilyl group.

Preferred compounds include:

bis [(3-trimethoxysilylpropyl)] amine (A1170, OSI Specialties)

bis [(3-triethoxysilylpropyl)] amine (B2492, United Chemicals)

1 ,4 bis [3-(trimethoxysilyl)propyl] ethylenediamine (B2493, United Chemicals) As indicated, the coating of the present invention can be

applied to any galvanized surface. The galvanization process may leave

an oily residue on the galvanized metal surface and it is preferable to

remove this. This can be done using typical cleaners in particular caustic

cleaners such as Brent AC1055 cleaner available from Brent America

Inc., Lake Bluff, IL (about 7.5% by weight, pH 12.5). Aqueous solutions

of sodium hydroxide will also function.

The alkaline cleaner not only removes any oily residue but

also improves the adhesion between the coating and the zinc and

ultimately the polymer and the zinc. Generally the galvanized surface is

soaked or passed through the alkaline solution for a period of about 4

minutes or less with the bath temperature at 60° C.

The coating composition of the present invention can be

applied in a variety of different concentrations from as little as .5% up to

100% i.e. without any water added). Generally it is preferable to disperse

the coating composition into water or a water/alcohol blend. The

preferred concentration level is generally from about 1 % to about 5%.

Further the pH of the coating solution should be basic to

maximize adhesion between the coating composition and the zinc. But

the pH should not exceed 9.5, or the coating composition will fall out of

solution. Accordingly as the coating composition is mixed with water or

water/alcohol, glacial acetic acid can be added to establish the pH of 6.5

to 9.5. The adhesive promoting coating composition can be applied

by spraying, dipping or brushing the coating composition onto the surface.

With wire it is preferable to simply run the wire through a bath containing

the coating composition. The coating composition is then dried and the

surface is ready for application of the polymeric coating i.e., adhesive or

paint.

The amount of the coating composition that is applied can

vary widely. It generally will be about 100 angstroms in thickness

although this is not believed to be critical for practicing the invention. In

fact the coating composition does not have to be continuous in order to

significantly improve the adhesion to the galvanized surface.

The polymeric coating can be in a form of either a

thermoplastic or thermoset. Thermoplastic coatings particularly

adhesives that will function in the present invention include ethylene

acrylic acid copolymers, ethylene methacrylic acid copolymer and methyl

acrylate and copolymers of acrylic acid derivatives such as methyl

acrylate esters, ethyl acrylate and butyl acrylate esters, ethylene vinyl

acetate copolymers, ethylene acrylic acid or ethylene methacrylic acid

ionomers, maleic anhydride copolymers and derivatives, chlorinated

polyethylene polyvinylchloride, polycarbonates, styrene/acrylic acid or

methacrylic acid copolymers, acrylic and methacrylic resins, rubber

modified polystyrenes as well as others. Thermoset compositions that will adhere to the coated

galvanized surface include epoxies, enamels, polyurethanes. Generally

the more polar the polymer, the better the adhesion. However, even

nonpolar polymers can be made to adhere to the coated galvanized

surface by modification of the polymer with polar compatibilizing agents.

The present invention will be further appreciated in light of

the following examples. To test the adhesion promoting compositions of

the present invention, galvanized steel plates either electrogalvanized or

hot-dipped as specified in the examples were coated as explained and

subjected to either a 95% relative humidity test or a twenty minute rolling

boil test. In the 95% relative humidity test the panels with the adhesive

applied are subjected to 95% humidity for 72 hours. Generally two panels

are tested each with three sections of adhesive per panel. After the 72

hours these are then allowed to come to ambient conditions and

evaluated.

In the twenty minute rolling boil test, three cut specimens

1/4 to V2 inch wide with three sections of adhesive per specimen were

immersed in water which was at a rolling boil. After twenty minutes they

were removed, cooled for five minutes and evaluated.

The evaluation for both tests involved attempting to lift a

section of the adhesive with a razor blade and then use this section to

peel off the remaining adhesive. This was given a numerical value of

from 0 to 4, 0 representing no adhesion, 1 representing weak adhesion, 2 representing moderate adhesion, 3 representing sufficient adhesion to

cause the adhesive to break when pulled and 4 representing sufficient

adhesion as to prevent the adhesive from being removed. The results

were the averages of the number of sections of adhesives per specimen.

The panels tested were either cleaned or uncleaned panels.

The clean panels were prepared by immersing the panels for two minutes

in 7.5% by weight solution of Brent AC1055 cleaner heated to a

temperature of 60° C.

Different procedures were used to prepare the solutions of

silane compositions. The compositions tested included bis [3-

(trimethoxysilyl) propyl] amine which is referred to hereinafter by its trade

designation of A-1170, 3-amino propyltris (trimethylsiloxy) silane referred

to hereinafter as A-0805 and 1 , 4 bis [3-(trimethoxysilyl) propyl]

ethylenediamine referred to hereinafter as B-2492.

With respect to the A-1170 silane, this can be either used

in a diluted concentration or as 100%. When the diluted silane was used,

the percentage i.e., 3% would be added slowly to water adjusting the pH

with glacial acetic acid to maintain a pH range of 6.7 to 9.5.

The panels would be coated by dipping the panels into the

silane solution and holding them for thirty seconds. Excess coating at the

bottom of the panel is removed with a towel or dry compressed air i.e.,

"de-teared", dried at 100° C. for ten minutes and the adhesive applied. When 100% of the A-1170 silane was used, two to five

drops were simply placed on the surface of the panel and spread to

uniform thickness with a paper towel or other leveling device and heated

to 120° to 150° C. for ten minutes to dry.

The B-2492 is sold as an alcohol solution (62% actives).

This simply would be blended with about 3% water and the balance

methanol with a pH maintained at a 6.7 to 9.5 with glacial acetic acid.

The panels would be coated as described with respect to the diluted A-

1170. When 100% of B-2492 is used, it would be applied to the panels

as described above with respect to the undiluted A-1170.

Panels were tested to determine the effect of metal surface

pretreatment with a caustic solution i.e., Brent AC1055. The first series

of panels listed on Table 1 were not treated with Brent AC1055 whereas

the remaining four sets of panels were treated with Brent AC1055.

In all of these examples, the adhesive applied was ethylene

acrylic acid copolymer. Specifically Primacor 3460 brand sold by Dow

Chemical Company applied at 150° C and rolled on with pressure roller

with minimal pressure.

TABLE 1

Effect of Metal Surface Pretreatment on Silane Adhesion Promoter Effectiveness

Adhesion of EAA Hot Melt Tape at 150° C to EZG60 Electrogalvanized Panels

All Panels Degreased with Isopropanol pH of Aqueous Treatment = 7.5 - 8.5

72-Hour 20 Minute 95% RH Water Boil

Control 1

3% A-1170

No pretreatment

5% A-1170

No pretreatment 1.5

7.5% A-1170 No pretreatment

10% A-1170 No pretreatment

100% A-1170 No pretreatment

100% B2493 No pretreatment

Control Brent 1055

3% A-1170 Brent 1055

3% B2493 Brent 1055

100% A- 1170 Brent 1055

These tests indicate that the caustic pretreatment significantly improves

adhesion and thereby reduces the concentration of the silane required to improve adhesion. Without pretreatment excellent results were obtained

only using at least 10% and preferably 100% of the A-1170 or 100% of

the B2493. Whereas with the caustic pretreatment 3% of the A-1170 or

B2493 produced excellent results.

Table 2 shows the effect of the pH of the A-1170 solution.

The test panels were all cleaned with isopropanol and then treated with

the caustic Brent AC1055. Both electrogalvanized steel panels and hot-

dipped steel panels were tested. These tests demonstrate that the best

results are achieved between pH 6.7 and 8.5.

TABLE 2

3% Aqueous Silane Treatment Cleaned Isopropanol, Brent 1055, 7.5%, 60^e ' C. 95% RH, 40° C.

Electrogalvanized Hot-Dip

No Treatment 2.5 3.5

pH 4.0 2 2

pH 5.5 3 3.5

pH 6.7 4 3.5

pH 8.5 4 4

The silane coating composition can also be applied to the

metal surface in combination with a process lubricant. This would be

most useful for coating drawn metal such as drawn wire. In these tests

the process lubricant, which was primarily mineral oil with emulsifiers, was

combined with a 3% aqueous solution of the A-1170 silane. Panels that had been cleaned with the isopropanol and Brent 1055 at 7.5% for 60°

C. were tested. As shown below, excellent results are obtained at a

variety of concentrations of the process lubricant.

TABLE 3 3% Aqueous A-1170 Silane Formulated with Process Lubricant

EZG60 Electrogalvanized Panels Cleaned Isopropanol, Brent 1055, 7.5%, 60° C.

72-Hour

95% RH 20 Minute 40° C. Boil

Untreated 3 2

0% Process 4 4

Lubricant

5% Process 3.8 3 Lubricant

10% Process 4 4

Lubricant

20% Process 4 4

Lubricant

Thus the present invention has a wide variety of applications

and can be utilized to improve adhesion between a variety of adhesives

and not only galvanized metals but also steel, brass and aluminum as

well as either electroplated or hot dipped galvanized surfaces. It can be

utilized on flat metal surfaces as well as drawn wire. This basically

eliminates the effect of humidity on adhesion to galvanized surfaces.

This has been a description of the present invention along

with the preferred method of practicing the present invention. However, the invention itself should be defined only by the appended claims

wherein we claim:

Claims

1. A method of improving adhesion to a metal surface applying an

effective amount of an adhesion promoter onto said surface, said

adhesion promoter comprising a compound having at least two alkoxy

silyl groups bonded together by a bridging group said bridging group

having at least one reactive nitrogen.

2. The method claimed in claim 1 wherein said metal surface is a

galvanized metal surface.

3. The method claimed in claim 2 wherein said adhesion promoting

compound has the following general formula:

I I

R, O - Si - X - Si - O R₁

O O

4. The method claimed in claim 3 wherein X is selected from the

group consisting of:

H H i i

- R₂ -N - R₂ - - N -

NH₂

R,

O-Si-O H H

I I I

O R2, - N - R ^l 3, - N - R,

NH '2, H H

I O

R₂ i II I

I - R, - N - C - N - R,

-O-Si-O i

O

I

R₄ NH₂ - R₂ - N - O - R₂ - i i

- R₃ - H

wherein R₂ is a lower alkenyl, R₃ represents alkenyl and

substituted alkenyl and R₄ represents alkoxysilyl.

5. The method claimed in claim 2 wherein said adhesion promoting

compound is dissolved in the polar solvent selected from the group

consisting of water and a mixture of water and alkyl alcohol.

6. The method claimed in claim 4 wherein said adhesion promoting

compound is applied as a concentration of about 0.1 to about 100%.

7. The method claimed in claim 2 wherein said galvanized metal

surface is pretreated with an alkaline cleaner.

8. The method claimed in claim 2 wherein said adhesion promoter is

Bis [3-(trimethoxysilyl) propyl] amine.

9. The method claimed in claim 2 wherein said adhesion promoting

compound is 3 - aminopropyl tris (trimethylsilyl) silane.

10. The method claimed in claim 2 wherein said adhesion promoting

compound is Bis [3 - (triethoxysilyl) propyl] amine.

11. The method claimed in claim 3 wherein said surface is further

coated with a polymer.

12. The method claimed in claim 11 wherein said polymer is a

thermoplastic polymer.

13. The method claimed in claim 12 wherein said polymer is selected

from the group consisting of ethylene acrylic acid copolymers, ethylene

methacrylic acid copoiymer, methyl acrylate, methyl acrylate esters, ethyl

acrylate esters, butyl acrylate esters, ethylene vinyl acetate copolymers,

ethylene acrylic acid ionomer, ethylene methacrylic acid ionomer, maleic

anhydride copolymers, chlorinated polyethylene and polyvinylchloride.

14. A metal surface having an adhesion promoting coating, said

adhesion promoting coating comprising a compound having at least two

alkoxy silane groups bonded together by a bridging group said bridging

group including at least one reactive nitrogen.

15. The metal surface claimed in claim 14 wherein said surface is

galvanized.

16. The galvanized surface claimed in claim 15 wherein said adhesion

promoting compound has the following general formula:

R, R.,

O O l I

R_ϊO-Si-X-Si-OR_ϊ

O O

17. The galvanized surface claimed in claim 16 wherein X is selected

from the group consisting of:

H H i i

R₂. -N - R₂ - -N-

NH₂

R₂

^■O -Si-O H H

I I I

O R, - N - R, - N - R,

NNHH₂, H H

O

R₂

R₂ - N - C - N - R₂

-O -Si-O

I

O

I

R₄ NH₂ - R₂ - N - O - R₂ -

- R₃ - H wherein R₂ represents a lower alkenyl, R₃ represents alkenyl

and substitute alkenyl and R4 represents alkoxysilyl.

18. The galvanized surface claimed in claim 15 wherein said adhesion

promoter is Bis [3-(trimethoxysilyl) propyl] amine.

19. The galvanized surface claimed in claim 15 wherein said adhesion

promoting compound is 3 - aminopropyl tris (trimethylsiloxy) silane.

20. The galvanized surface claimed in claim 15 wherein said adhesion

promoting compound is Bis [3 - (triethoxysiiyl) propyl] amine.

21. The galvanized surface claimed in claim 15 wherein said surface

is further coated with a polymer.