POWDER COATING PRIMER

Abstract

A primer composition for coating a substrate prior to application thereon of an intumescent fire protecting coating composition, the primer composition being a powder coating composition consisting of an extruded and subsequently ground mixture of binding agents, hardening agents and optionally one or more of optional pigments, optional filler, and optional additives, and a porous material in a proportion of one to twelve percent by weight of the powder coating composition. The porous material is mesoporous or microporous.

Claims

1. A primer composition for coating a substrate prior to application thereon of an intumescent fire protecting coating composition, the primer composition being a powder coating composition consisting of: an extruded and subsequently ground mixture of binding agents, hardening agents and optionally one or more of optional pigments, optional filler, and optional additives; and a porous material in a proportion of one to twelve percent by weight of the powder coating composition, wherein the porous material is mesoporous or microporous.

2. The primer composition according to claim 1, wherein the proportion of the porous material is three to ten percent by weight of the powder coating composition.

3. The primer composition according to claim 1, wherein the proportion of the porous material is five to seven percent by weight of the powder coating composition.

4. The primer composition according to claim 1, wherein the porous material is blended into the extruded and subsequently ground mixture of binding agents.

5. The primer composition according to claim 1, wherein the porous material is bonded to powder coating particles of the extruded and subsequently ground mixture of binding agents.

6. The primer composition according to claim 1, wherein the porous material is diatomaceous earth or another natural or synthetic microporous material.

7. The primer composition according to claim 6, wherein the porous material is a zeolite or active alumina.

8. The primer composition according to claim 1, wherein the optional pigments comprise titanium dioxide, the optional filler comprises one or more of calcium carbonate, talc, and barium sulfate, and the optional additives comprise a levelling agent.

9. The primer composition according to claim 8, wherein the levelling agent comprises a polyacrylate, a degassing agent, or both the polyacrylate and the degassing agent.

10. The primer composition according to claim 9, wherein the leveling agent comprises benzoin.

11. A coating system, wherein the coating system comprises a primer composition according to claim 1 and an intumescent fire protecting coating composition configured to be applied onto the primer composition.

12. The coating system according to claim 11, wherein the intumescent fire protecting coating composition is liquid.

13. A method of coating a steel structural member with the coating system according to claim 8, the method comprising: applying the primer composition to the steel structural member and then applying the intumescent fire protecting coating composition on the primer composition.

14. A method for production of a powder coating composition as a primer for coating a substrate prior to application thereon of an intumescent fire protecting coating composition, the method comprising: processing binding agents and hardening agents in an extruder to form an extrudate; grinding the extrudate to form a ground extrudate; and blending the ground extrudate with a porous material with a proportion of one to twelve percent by weight of the powder coating composition, wherein the porous material is mesoporous or microporous.

15. The method according to claim 14, wherein the porous material is bonded in a mixer to powder coating particles of the ground mixture.

Description

DRAWINGS

[0054] In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

[0055] FIG. 1 shows a photograph illustrating a laboratory fire test of a coating system in accordance with the teachings of the present disclosure;

[0056] FIG. 2 shows a diagram representative of a measured microroughness of an exemplary liquid primer composition in accordance with the teachings of the present disclosure;

[0057] FIG. 3 shows a diagram representative of a measured microroughness of the primer composition according to the reference example in accordance with the teachings of the present disclosure;

[0058] FIG. 4 shows a scanning electron microscope (SEM) image of a diatomaceous earth in accordance with the teachings of the present disclosure;

[0059] FIGS. 5 to 7 show SEM images of a surface of the primer composition according to example 2 after application in accordance with the teachings of the present disclosure;

[0060] FIG. 8 shows a light optical microscope image of the surface of the primer composition according to example 2 after application in accordance with the teachings of the present disclosure;

[0061] FIG. 9 shows a photograph of the coating system including a primer composition according to the reference example after completion of the laboratory fire test in accordance with the teachings of the present disclosure;

[0062] FIG. 10 shows a photograph of a further coating system including the primer composition according to the reference example after completion of the laboratory fire test in accordance with the teachings of the present disclosure; and

[0063] FIG. 11 shows a photograph of a coating system including a primer composition according to example 2 after completion of the laboratory fire test in accordance with the teachings of the present disclosure.

[0064] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

[0065] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0066] In FIG. 1 a photograph of an exemplary laboratory fire test is shown. A substrate coated with an intumescent layer 1 is subjected to fire with a gas burner 2. For many applications in steel construction, powder coating provides high-quality corrosion protection and a decorative layer. For steel structures that have to be coated with an intumescent layer for improved fire resistance, however, liquid coating systems are used, which are applied manually, as commercially available powder primers do not provide the required and certified fire protection class. State of the art powder coatings as primers for fire protection coatings provide poor adhesion of the intumescent layer on powder coatings. Intumescent layers have a low binder content of typically below 10%, which is one reason for a weak dry adhesion.

[0067] However, the decisive factor for failure is the slipping of the foaming intumescent layer in a fire test. Foaming of the intumescent layer occurs at temperatures of 250-300 C. Whether the adhesion between the primer and the intumescent layer is sufficient is thus tested in fire tests.

[0068] Relevant mechanisms for adhesion between coating layers are the chemical valence bond between functional groups and the physical adherence of rough surfaces, which is referred to with regard to FIGS. 2 and 3 now. In FIG. 2, a diagram representative of a measured microroughness of a liquid primer composition approved for fire protection systems is shown. In FIG. 3, a diagram representative of a measured microroughness of the primer composition according to the reference example is shown. The respective ordinate axes 3, 4 represent a deviation of the respective surfaces from a nominal value of zero in m over a length dimension in m on the abscissae axes 5, 6. As can be seen in the curve 7, the deviations of the liquid primer surface are about twice as high as those of the smoother powder coating primer, represented by the curve 8. An increase in the microroughness of powder coatings, which improves the adhesion values, is advantageously achieved by blending in a porous material subsequently to grinding with a proportion of one to twelve percent by weight of the powder coating composition. Even more advantageously, capillary forces wielded by the porous material are effective in the molecular range. The narrower the capillary, the greater the effect. For example, the natural raw material diatomaceous earth, a deposit of the silicate shells of diatoms, is capable of absorbing up to three times its own weight in liquid and binding it.

[0069] In FIG. 4, a scanning electron microscope (SEM) image of diatomaceous earth is shown. To take advantage of the additional adhesion provided by the capillary forces, the diatomaceous earth particles should be present on the surface of the coating layer as unbroken as possible. This can be achieved by dry-blending the diatomaceous earth into the powder coating composition subsequent to grinding. This procedure has the additional advantage that the binder chemistry and formulation of the powder coating composition have little influence on the adhesion result.

[0070] In FIGS. 5 to 7, SEM images of a surface of the primer composition according to example 2 after application are shown. The SEM images of the primer layer illustrate that unchanged fragments 9 of diatomaceous earth are present on the surface.

[0071] In FIG. 8, a light optical microscope image of the surface of the primer composition according to example 2 after application is shown. The scale 10 has a length of 500 m. The light optical microscope image illustrates that the primer composition surface further provides sufficient roughness for a good mechanical adhesion.

[0072] The presence of unaltered, unbroken fragments of diatomaceous earth on the primer surface and the increased roughness provide enhanced adhesion properties of the primer to the intumescent layer. The capillary forces of the diatomaceous earth advantageously absorb solvents and binders of the foaming intumescent layer, thus maintaining the firm adhesion under the impact of heat and/or fire.

[0073] The desired amount of diatomaceous earth for safe adhesion may disturb the processing of the primer powder during electrostatic application. To enhance application behavior, even in automatic application systems, the diatomaceous earth can be blended into the powder coating composition subsequent to grinding by way of bonding the diatomaceous earth particles in a mixer to the powder coating particles of the ground mixture.

[0074] Experiment 1: X-cut test: To test the adhesion of intumescent layers to powder primers, three millimeter thick steel sheets were primed, once with the primer composition according to example 2 and as a reference with the primer composition according to the reference example. Subsequently, identical 500 m thick intumescent layers of Sika Pyroplast ST-100 were applied onto the primer layers. According to DIN EN ISO 16276-2, Corrosion protection of steel structures by protective paint systems Assessment of, and acceptance criteria for, the adhesion/cohesion (fracture strength) of a coatingPart 2: Cross-cut testing and X-cut testing, the X-cut testing is applicable for coatings over 250 m thickness. A cut in the form of an X (X-cut) is made into the coating, penetrating through to the substrate. X-cut test results are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Primer Top Coat Adhesion Thickness Thickness Result Code Surface () () X cut D002014 Trial 12 Tex. 60-95 Sika ~500 Perfect D002014 Trial 13 Tex. 55-80 100 ~500 Very good D002014 Trial 14 Tex. 55-70 ~500 Very good D002014 Trial 15 Tex. 50-75 ~500 Perfect D002014 Trial 16 Tex. 60-75 ~500 Good D002014 Trial 17 Tex. 50-90 ~500 Perfect

[0075] Table 1: D002014 Trial 12-17 denominate the primer composition according to example 2 with the given thickness, applied on steel sheets (Tex. means an increased surface roughness attained through additive). About 500 m thick layers of Sika Pyroplast ST-100 were applied onto the primer layers. Adhesion results of the X-cut test are given in the right column.

[0076] To test the adhesion of intumescent layers to powder primers, three millimeter thick steel sheets were primed, now with the primer composition according to the reference example and other primers according to the state of the art. Subsequently, again identical 500 m thick intumescent layers of Sika Pyroplast ST-100 were applied onto the primer layers. The X-cut test could not be executed correctly as the adhesion of the intumescent layer to the primer was too weak, cf. Table 2 below.

TABLE-US-00002 TABLE 2 Primer Top Coat Thickness Thickness Code (curing cond.) Surface & Type () Code (mm) Adhesion Result thermoset #1 (180 C. & 5) Tex. & EP-MATT 70-80 Sika 100 1.2-1.3 X (visually good adhesion but no bonding, bad) thermoset #1 (180 C. & 10) Tex. & EP-MATT 70-80 Sika 100 1.2-1.3 X (visually good adhesion but no bonding, bad) thermoset #2 (180 C. & 5) Smooth & PP-MAT 60-70 Sika 100 1.2-1.3 X (visually little adhesion, no bonding, bad) thermoset #2 (180 C. & 10) Smooth & PP-MAT 60-70 Sika 100 1.2-1.3 X (bad) thermoset #3 (180 C. & 5) Tex. & PP-MAT 60-70 Sika 100 1.2-1.3 X (bad) thermoset #3 (180 C. & 10) Tex. & PP-MAT 60-70 Sika 100 1.2-1.3 X (no adhesion) thermoset #4 (180 C. & 10) Smooth & EP-S.GLZ 60-70 Sika 100 1.2-1.3 X (no adhesion) thermoplastic smooth thicker Sika 100 thinner X (no adhesion)

[0077] Table 2: Four different thermoset primers, followed by the curing conditions temperature (180 C.) and time (5 or 10 minutes) and one thermoplastic primer are listed. The surface property of the steel plate is given (Tex. means an increased roughness attained through additive compared to a smooth surface), and the thermoset primer base (EPepoxy-based primer, PPpolyester-based primer, matt or glossy).

[0078] Experiment 2: fire test: As noted before, one further factor for failure is tested in a fire test, wherein foaming of the intumescent layer occurs at temperatures of 250-300 C. During the fire test the foaming intumescent layer must not slip of the primer layer.

[0079] In FIG. 9, a photograph of the coating system including a primer composition according to the reference example is shown, which was taken after completion of the laboratory fire test as described above. The intumescent layer slipped in the laboratory test, i.e., the coating system failed.

[0080] In FIG. 10, a photograph of a further coating system including the primer composition according to the reference example after completion of another laboratory fire test is depicted. For this laboratory fire test boards dimensioned 500 mm500 mm5 mm were coated as described above. A drop and/or slipping of the intumescent layer can be observed, which means that the tests according to EN 13381-8 are not passed.

[0081] In FIG. 11, a photograph of a coating system including a primer composition according to example 2 after completion of the laboratory fire test is depicted. If the intumescent layer remains closed, the test according to EN 13381-8 is passed. After completion of the laboratory fire test, the intumescent layer does not show any failure or slip. The powder primer composition according to example 2 with the intumescent layer fulfils the fire protection tests according to EN 13381-8 and EN 1363-1.

[0082] Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word about or approximately in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, material, manufacturing, and assembly tolerances, and testing capability.

[0083] As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean at least one of A, at least one of B, and at least one of C.

[0084] The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.