Two-Coat Zinc-Rich Polyurethane Primer/Aliphatic Polyurea Topcoat Coating System
COATING SYSTEM SSPC-PS 28.01
1. Scope
This specification contains performance requirements for a coating system for steel substrates that consists of a zinc-rich moisture-cure polyurethane primer (complying with SSPC-Paint 40) and an aliphatic polyurea topcoat (complying with SSPC-Paint 39, Type 2)
1.1 The coating system is generally suitable for exposures in SSPC Environmental Zones 1A (interior, normally dry), 1B (exterior, normally dry), 2A (frequently wet by fresh water, excluding immersion), 2B (frequently wet by salt water, excluding immersion), 3B (chemical exposure, neutral) and 3C (chemical exposure, alkaline). The primer/topcoat system shall meet the performance requirements of Sections 7 and 8 described in this standard.
2. Description
2.1 This coating system consists of a polyurethane zinc-rich primer and a two-component aliphatic (moderate-dry) polyurea topcoat. The prerequisite requirements of the primer and topcoat shall be in accord with those stipulated in SSPC-Paint 40 (primer) and SSPC-Paint 39 (topcoat). Individual products meeting minimum performance requirements of this standard may vary in formulation, raw materials, and application characteristics.
2.2 The primer is intended for spray application with allowance for small area touch-up by brush (see Notes 11.1 and 11.2). The polyurea topcoat is intended for application by single-component airless spray, electrostatic spray, or plural-component equipment, depending upon its formulation.
3. Referenced Standards
3.1 The latest issue, revision, or amendment of the referenced standards in effect at the time of the bid solicitation shall govern, unless otherwise specified. A standard marked with an asterisk (*) is referenced only in the Notes or the Appendix, which are not requirements of this standard.
3.2 If there is a conflict between the requirements of any of the cited reference standards and this standard, the requirements of this standard shall prevail.
3.3 SSPC STANDARDS AND JOINT STANDARDS:
Guide 13 Guide for the Identification and Use of Industrial Coating Materials in Computerized Product Databases
PA 2 Measurement of Dry Coating Thickness with Magnetic Gages
Paint 39 Two-Component Aliphatic Polyurea Topcoat, Performance-Based
Paint 40 Zinc-Rich Moisture Cure Polyurethane Primer, Performance Based
PS 12.00 Guide to Zinc-Rich Coatings
SP 1 Solvent Cleaning
SP 5/NACE No. 1 White Metal Blast Cleaning
3.4 ASTM INTERNATIONAL STANDARDS:
* D 512
* D 520 D 523
* D 562
D 714 D 1014
* D 1475 D 1640
D 1654
Standard Specification for High-Strength Low-Alloy Columbium-Vanadium Structural Steel Standard Test Methods for Chloride Ion in Water Standard Specification for Zinc Dust Pigment Standard Test Method for Specular Gloss Standard Test Method for Consistency of Paints Measuring Krebs Unit (KU) Viscosity Using a Stormer-Type Viscometer Standard Test Method for Evaluating Degree of Blistering of Paints Standard Practice for Conducting Exterior Exposure Tests of Paints on Metal Substrates Standard Test Method for Density of Liquid Coatings, Inks, and Related Products Standard Test Methods for Drying, Curing, or Film Formation of Organic Coatings at Room Temperature Standard Test Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments.
D 2244 Standard Test Method for Calculation of 4. Composition Requirements Color Tolerances and Color Differences from Instrumentally Measured Color 4.1 RESINS AND PIGMENTS Coordinates
D 2369 Standard Test Method for Volatile Content of Coatings
D 2371 Standard Test Method for Pigment Content of Solvent-Reducible Paints
D 2621 Standard Test Method for Infrared Identification of Vehicle Solids from Solvent-Reducible Paints
D 2794 Standard Test Method for Resistance of Organic Coatings to the Effects of Rapid Deformation (Impact)
D 4417 Standard Test Methods for Field Measurement of Surface Profile of Blast Cleaned Steel D 4541 Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers
D 4587 Standard Practice for Fluorescent UV-Condensation Exposures of Paint and Related Coatings
* D 4940 Standard Test Method for Conductimetric Analysis of Water Soluble Ionic Contamination of Blasting Abrasives
D 5402 Standard Practice for Assessing the Solvent Resistance of Organic Coatings Using Solvent Rubs
D 5894 Standard Practice for Cyclic Salt Fog/UV Exposure of Painted Metal, (Alternating Exposures in a Fog/Dry Cabinet and a UV/ Condensation Cabinet)
* G 101 Standard Guide for Estimating the Atmospheric Corrosion Resistance of Low-Alloy Steels
3.5 AMERICAN NATIONAL STANDARDS INSTITUTE (ANSI) STANDARDS:
ANSI Z129.1 Hazardous Industrial Chemicals– Precautionary Labeling ANSI B94.50 Basic Nomenclature and Definitions for Single-Point Cutting Tools
3.6 AMERICAN ASSOCIATION OF HIGHWAY AND TRANSPORTATION OFFICIALS (AASHTO) SPECIFICATION3
* Standard Specifications for Highway Bridges, Division1, Section 10.32.3.2.3, Appendix A, Testing Method to Determine the Slip Coefficient for Coatings Used in Bolted Joints
2 American National Standards Institute, 1819 L Street, NW, Suite 600, Washington, DC 20036. Standards available online at http://www.ansi.org.
3 American Association of State Highway and Transportation Officials, 444 North Capitol Street, NW, Suite 249, Washington DC 20001. Standards are available online at https://bookstore.transportation.org.
4.1.1 Primer: The resin used in the primer is characterized by the presence of free polyisocyanate groups capable of reacting with atmospheric moisture in order to form a film. The major pigment component is zinc dust. Composition requirements of the primer are described in SSPC-Paint 40 (see Notes 11.3, 11.4, and 11.5).
4.1.2 Topcoat: The resins used in the topcoat are comprised of a hindered polyamine and a polyisocyanate that react to form an aliphatic polyurea with a moderate dry time (to handle) of thirty minutes to two hours (see Note 11.6). Composition requirements of the topcoat are described in SSPC-Paint 39 (Type 2).
5. Standard Testing Conditions
5.1 TEST PANELS: Triplicate panels shall be used for each test. Unless otherwise specified (see Appendix A), the hot-rolled steel test panels shall conform to ASTM A572. Panel size shall be 100 mm x 150 mm x 6 mm (4 inch x 6 inch x ¼ inch). Test panels shall be solvent cleaned in accordance with SSPC-SP 1 prior to blast cleaning. The test panels shall be blast cleaned in accordance with SSPC-SP 5. The average blast profile for each test panel shall be between 44 to 57 micrometers (1.75 to 2.25 mils) as measured in accordance with ASTM D 4417, Method B. The average profile for each test panel shall be computed from 20 measurements.
5.2APPLICATION:The primer and topcoat shall be spray-applied in accordance with the manufacturer’s recommendations. The coatings shall show no streaking, running, sagging or other defects during application or while drying.
5.3 DRY FILM THICKNESS: The dry film thickness (DFT) for the primer and topcoat on the test panels shall meet the manufacturer’s written recommended range (see Note 11.7). The DFT of the primer alone and of the primer plus the topcoat (i.e. the complete system) shall be measured and recorded. The DFT shall be measured in accordance with SSPC-PA 2, Appendix 5.
5.4. CURE: The primer and the topcoat shall be dried and cured in accordance with manufacturer’s written recommendations. Unless otherwise specified (for example, for preparing panels for testing according to AASHTO R-31) all coated panels shall be aged for a minimum of 7 days in an environment with a minimum relative humidity of 50%, and at a temperature of 23 ± 2 °C (73.5 ± 3.5 °F), as described in paragraph 5.1 of ASTM D 1640.
5.5 SCRIBING: Scribe two parallel lines on the face of the coated panels so as to expose the underlying metal before testing. The lines shall be at least 2.5 cm (1 inch) from the edge, the top, and the bottom of each panel and at least 5 cm (2 inches) from each other. Each scribe shall be 6 cm (2.4 inches) long. The scribes shall run vertically across the face of the panel. Follow the scribe-making procedure described in ASTM D 1654 utilizing a straight-shank tungsten carbide tip, lathe-cutting tool (ANSI B94.50, Style E).
5.6 BACKS AND EDGES: Coat and seal all edges and the back of each panel with a coating or tape that will provide the necessary protection to these surfaces.
6. Requirements of Liquid Coatings
The liquid primer shall meet the requirements of Paint 41 and the liquid topcoat shall meet the requirements of Paint 39 (see Note 11.8).
7. Laboratory Physical Tests of Applied Films
7.1 PRIMER ADHESION TO SUBSTRATE: Apply the primer to three panels in accordance with Sections 5.1 through 5.4. Test adhesion according to ASTM D 4541, using an adhesion tester with a self-aligning pulling mechanism as described in ASTM D 4541. Report the type of adhesive and the adhesion tester employed. Perform three pulls on each of the three replicate panels. The minimum adhesion value of the primer to the substrate for each pull shall be 4.1 MPa (600 psi). In the case of adhesive failure below 4.1 MPa (600 psi), the pull test shall be repeated. The instrument used to verify compliance to this standard shall be of the same type used to perform the initial testing.
7.2 TOPCOAT ADHESION TO PRIMER: Prepare three panels according to Sections 5.1 through 5.4. Test adhesion according to ASTM D 4541, using an adhesion tester with a self-aligning pulling mechanism as described in ASTM D 4541. Report the type of adhesion tester employed. Perform three pulls on each of the three replicate panels. At least two of the pulls on each panel as well as the average of the three pulls on each panel shall be at least 4.1 MPa (600 psi). One pull on each panel may be as low as 3.4 MPa (500 psi).
7.2.1 Recoat Window: In order to obtain optimum adhesion, the coating manufacturer shall provide an acceptable time frame between the applications of coatings in a multi-coat system. Unless the purchaser specifically requests a variance, the maximum dry film thicknesses and minimum curing time (with reported conditions for temperature and humidity) as stated on the manufacturer’s product data sheets shall be used for coating application procedures prior to adhesion testing.
8. Weathering and Corrosion Resistance Requirements
8.1 Color and Gloss Weathering Resistance Test Procedures
8.1.1 Weathering:Test procedures with minimum color and gloss values as specified in SSPC-Paint 39, Section 8 are the basis of performance acceptance of the polyurea topcoat (see Note 11.9). It is left to the discretion of the specifier whether to accept outdoor data or to use UV-A data in lieu of outdoor weathering data. These test methods are specifically defined in SSPC-Paint 39, i.e., (1) three levels of accelerated testing and (2) two levels of natural exterior testing are provided with acceptance criteria shown in Table 1.
8.1.1.1 Level 1A: Products conforming to this performance level shall have a maximum gloss reduction of 20% and maximum color change of 2.0 ΔE* after a 500 h exposure.
8.1.1.2 Level 2A: Products conforming to this performance level shall have a maximum gloss reduction of 30% and maximum color change of 3.0 ΔE* after a 1000 h exposure.
8.1.1.3 Level 3A: Products conforming to this performance level shall have a maximum gloss change of 40% and a maximum color change of 3.0 ΔE* after a 2000 h exposure.
8.1.2 Outdoor Weathering: Triplicate test panels shall be prepared in accordance with Sections 5.1 through 5.4. Outdoor weathering shall be performed in accordance with ASTM D 1014 (45 degrees south exposure, washed with mild detergent). Sixty degree gloss shall be measured according to ASTM D 523 and tristimulus color measured according to ASTM D 2244 both initially and at the end of each level period. The coating shall meet the weathering test requirements both initially and at the end of each level period.
8.1.2.1 Level 1N: Products conforming to this performance level shall have a maximum gloss change 35% and a maximum color change of 2.0 ΔE* after a 12-month exposure.
8.1.2.2 Level 2N: Products conforming to this performance level shall have a maximum gloss change 50% and a maximum color change of 3.0 ΔE* after a 24-month exposure.
Note: Table 1 shows acceptable color retention values of the polyurea topcoat (per ASTM D 2244) that are in an approximate range of 2 to 3 ΔE* depending upon the type of exposure test selected. Maximum gloss reductions from original readings range from 20% to 50% (per ASTM D 523) depending upon the selected test exposure.
8.2 Cyclic Salt Spray/UV/Condensation Cabinet: The coating system shall be applied to triplicate panels prepared in accordance with Section 5 and shall be exposed in a cyclic test
TABLE 1 SUMMARY OF PERFORMANCE TESTING RESULTS TO BE REPORTED
(a) Smaller values of color change (less than 2.0 ΔE*) may be visible to the eye, but the noticeable change maximum of 3.0 ΔE* specified herein is deemed acceptable for most industrial and marine applications. More stringent gloss and color retention requirements should be specified as needed.
(b) These values do not apply to deep tones and safety colors.
(c) Either outdoor or accelerated testing will fulfill the requirements of this standard. The user stipulates the type of testing to be used. Data from both tests are not required unless specified.
(d) South Florida testing is ongoing. 24-month testing was completed in July 2003 and testing is continuing to obtain 48-month data.
Cabinet in accordance with ASTM D 5894 for 15 cycles (5040 hours). Performance acceptance criteria is as follows:
8.2.1 Rust Evaluation: After the specified exposure time, each replicate panel shall have no rusting of the coated portion (a rust rating of 10 per SSPC-VIS 2). Moderate rusting in the scribe mark is permissible and resulting staining shall be ignored. Strips 6 mm (1/4 inch) wide along the edges of the panel shall be ignored.
8.2.2 Blister Evaluation: After the specified exposure time, there shall be no blistering of the coated portion (a rating of 10 per ASTM D 714).
8.2.3 Scribe Evaluation: The coating shall be applied to triplicate panels prepared in accordance with Sections 5.1 through 5.5. Undercutting shall be measured after removing the coating along the scribe by scraping with a suitable instrument. Visible areas of corrosion along the scribe are measured. Measure 12 maximum undercutting values, one from each side of each scribe. Calculate the average of the 12 maximum values and the standard deviation. Compute the scribe undercutting test parameter, U, as the average plus two standard deviations (U = x’ + 2s). Report the number of data points, average undercutting, standard deviation, and scribe undercutting test parameter. The maximum U shall be 4 mm. The maximum x’ shall be 2 mm.
9. Labeling
9.1 Labeling shall conform to ANSI Z129.1.
9.2 Technical data shall be provided for at least all data elements categorized as “essential” in SSPC-Guide 13.
10. Disclaimer
10.1 While every precaution is taken to ensure that all information furnished in SSPC standards and specifications is as accurate, complete, and useful as possible, SSPC cannot assume responsibility nor incur any obligation resulting from the use of any materials, coatings, or methods specified herein, or of the specification or standard itself.
10.2 This coating system specification does not attempt to address problems concerning safety associated with its use. The user of this specification, as well as the user of all products or practices described herein, is responsible for instituting appropriate health and safety practices and for ensuring compliance with all governmental regulations.
11. Notes
Notes are not requirements of this standard.
11.1 The zinc-rich primer (SSPC-Paint 40) is preferably applied by spray, but may be brushed for small areas or to fill in irregularities. Brushing should be done with extreme caution to avoid zinc settlement. Zinc-rich coating system may settle, and care should be taken to ensure they are thoroughly mixed before and during application. Exercise caution during work stoppages to prevent settling of zinc in hoses and equipment.
11.2 VOC CONTENT: Local regulations regarding VOC content,VOC emissions, and container labeling may vary depending on project location. Federal limits for VOCs in industrial maintenance coatings were published in 1998 and may be found at:
<http://www.epa.gov/ttn/atw/183e/aim/aimpg.html#RULE> These limits apply to the coating at the time of application after thinning according to the manufacturer’s recommendations. However, many state and local governments and/or air quality management areas have more stringent VOC regulations than those in the federal rule. In the U.S., information on the VOC content of each component before mixing or thinning is found on the container label and in the manufacturer’s safety data sheet. The coating manufacturer’s product data sheet usually provides information on the total VOC content of a coating after mixing and any recommended thinning.
11.3 Typically, many organic zinc-rich primers contain at least 80% zinc dust pigment by weight in the dry film.
11.4 LEAD LEVEL IN ZINC DUST: ASTM D 520 specifies three types of zinc dust for use as a pigment in coatings. Type I is a general grade in which no maximum level of lead is specified. Type II is a high-purity grade with a maximum lead level of 0.01% by weight. Type III is the highest purity grade, with a maximum lead level of 0.002% by weight. Any grade of zinc dust can be used in the zinc coatings covered by this specification. However, it is important to note that if Type I zinc is used, it is possible to exceed the permissible exposure limit (PEL) for lead when the products are removed by abrasive blasting. For additional information relating the lead content of the coating to worker exposure to lead during blasting see Gary L. Tinklenberg and Denise M. Doezema,“Health Concerns for Workers Using Zinc-Rich Coatings,” Journal of Protective Coatings and Linings, Vol. 15, No. 5 [May 1998], pp 36-46.
In addition to lead, cadmium and other toxic metals may pose a health hazard. Placing overly restrictive requirements on some materials may result in the inability of manufacturers to produce products meeting this specification.
11.5 Other resins or modifiers in the zinc-rich primer are typically less than 10% of total resin content.
11.6 Hindered aliphatic polyureas (Type 2, Moderate Cure) have properties that include good color and gloss retention and controllable film builds, pot lives, and dry times with application advantages using either conventional or plural spray equipment. Typical dry times (to handle) range from 30 minutes to 2 hours with dry film thicknesses approaching 381 micrometers (15 mils) per coat. Variable pot lives range from 30 minutes to 90 minutes.
11.7 Typically, the zinc-rich polyurethane primer is applied at approximately 76 to 102 micrometers (3 to 4 mils) DFT and the polyurea topcoat is applied at approximately 152 to 229 micrometers (6 to 9 mils) DFT.
11.8 QUALITY ASSURANCE TESTS: If the user chooses, tests may be used to determine the acceptability of a lot or batch of a qualified coating system. The quality assurance tests are used to determine whether the supplied products are of the same type and quality as those originally tested and certified for acceptance. The selected tests should accurately and rapidly measure the physical and chemical characteristics of the coating necessary to verify that the supplied material is substantially the same as the previously accepted material. All of the quality assurance tests must be performed on the originally submitted qualification sample. The results of these tests are used to establish pass/fail criteria for quality assurance testing of supplied products.
11.8.1 Establishing Quality Assurance Acceptance Criteria: Many ASTM test methods contain precision and bias statements. Specification developers should be cognizant of the fact that these statements exist. Quality assurance test criteria should not be more stringent than the interlaboratory precision of the test methods used.
Where precision and bias data are not available for a given test method, determine the standard deviation of a minimum of five measurements taken on the originally tested and certified material. The pass/fail criterion is that the measurement of the test sample shall fall within two standard deviations of the target value. The contracting parties should agree on a target value.
11.8.2 Recommended Quality Assurance Tests: Recommended quality assurance tests include but are not limited to, infrared analysis (ASTM D 2621), viscosity (ASTM D 562), weight per gallon (ASTM D 1475), total solids (ASTM
D 2369), dry time (ASTM D 1640), and percent pigment (ASTM D 2371).
11.9 GLOSS LEVELS:Typically, 60-degrees pecular gloss levels are identified as follows: Low Gloss – less than 30 Medium Gloss – 30 to 70 High Gloss – higher than 70
Non-Mandatory Appendix A: Example of Test Panel Requirements:
Customers may impose specific requirements for steel test panels in order to compare the performance of various coatings and coating system on a standardized substrate,or to evaluate a coating’s performance on a specific type of steel. An example of one customer’s test panel requirements is shown below:
Steel test panels shall be fabricated from steel heats having certified mill test reports and an Atmospheric Corrosion Resistance Index of 5.5 ± 0.5. Certified mill test reports shall, at a minimum, state the elemental composition for each of the following elements; copper, nickel, chromium, silicon, and phosphorus. The Atmospheric Corrosion Resistance Index shall be calculated in accordance with ASTM G 101, subsections 6.3.1.1 and 6.3.1.2. Test panels shall be 100 mm x 150 mm with a minimum thickness of 6 mm (4 inch x 6 inch with a minimum thickness of 1/4 inch). Test panels shall be cleaned in accordance with SSPC-SP 5 using recyclable metallic abrasives. The abrasives shall have a maximum chloride content of 15 ppm determined in accordance with ASTM D 512 and a maximum conductivity of 150 micromhos per cm as determined in accordance with ASTM D 4940. The abrasive mixture shall be approximately 60 percent SAE shot number S230 and 40 percent SAE grit number G40. Both the shot and grit shall have a Rockwell hardness of C 45 ± 3. The surface profile of the cleaned test panels shall be 65 to 90 µm (2.5 to 3.5 mils) when determined in accordance with ASTM D 4417, Method C. Surface profile measurements shall be performed and documented for a minimum of 10% of the number of prepared test panels. The surface profile shall be clean, sharp and free of embedded friable material.
COATING SYSTEM SSPC-PS 28.01 – Two-Coat Zinc-Rich Polyurethane Primer/Aliphatic Polyurea Topcoat Coating System, Performance-Based
