How To Apply This Polyurethane Coating
PAINT SPECIFICATION NO. 41 – Moisture-Cured Polyurethane Coating/Primer or Intermediate Coat, Micaceous Iron Oxide Reinforced, Performance-Based
This specification contains performance requirements for a moisture cured aromatic polyurethane coating with a thermoset binder and micaceous iron oxide pigment reinforcement.
2.1 This coating is a single-package moisture-cured polyurethane coating characterized by the presence of free isocyanate groups capable of reacting with atmospheric moisture in order to form a solid film.
2.2 Coatings meeting the requirements of this specification are generally suitable for exposures in 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). Primer/intermediate coat systems described in this standard meet the performance requirements of Section 7.4 of SSPC-Paint 40 (including Environmental Zone 2C-Fresh Water Immersion).
2.3 This polyurethane coating is intended for spray application according to manufacturer’s instructions, with allowance for small area touch-up by brush (see Note 11.1) either directly to a steel substrate, or over itself or a compatible primer such as SSPC-Paint 40 or other primers recommended by the coating manufacturer.
3. Referenced Standards
3.1 The latest issue, revision, or amendment of the referenced documents in effect on the date of invitation to bid shall govern unless otherwise specified. Those documents marked with an asterisk (*) are referenced only in the Notes or the Appendix, which are not requirements of this specification.
3.2. If there is a conflict between the requirements of any of the cited reference documents and this specification, the requirements of this coating specification shall prevail.
3.3 SSPC Standards and Joint Standards:
SSPC Guide 13
Guide for the Identiﬁcation and Use of Industrial Coating Material in Computerized Product Databases
Measurement of Dry Coating Thickness with Magnetic Gages
Zinc-Rich Moisture Cure Polyurethane Primer, Performance Based
SP 5/NACE No. 1
White Metal Blast Cleaning
3.4 ASTM International Standards:
1 D 185 Standard Test Methods for Coarse Particles in Pigments
* D 562 Standard Test Method for Consistency of Paints Measuring Krebs Unit (KU) Viscosity Using a Stormer-Type Viscometer
D 714 Standard Test Method for Evaluating Degree of Blistering of Paints
* D 1475 Standard Test Method for Density of Liquid Coatings, Inks, and Related Products
D 1640 Standard Test Methods for Drying, Curing, or Film Formation of Organic Coatings at Room Temperature
D 1654 Standard Test Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments
D 2369 Standard Test Method for Volatile Content of Coatings
D 2371 Standard Test Method for Pigment Content of 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 5894 Standard Practice for Cyclic Salt Fog/UV Exposure of Painted Metal, (Alternating Exposures in a Fog/Dry Cabinet and a UV/Condensation Cabinet)
3.5 American National Standards Institute (ANSI) Standard:
2 ANSI Z129.1 Hazardous Industrial Chemicals– Precautionary Labeling
4. Composition Requirements
4.1 The manufacturer is given wide latitude in the selection of materials and manufacturing processes.
4.2 Pigment Requirement
4.2.1 Micaceous iron oxide is a required pigment component in this coating (see Note 11.2 for typical formulation percentage ranges). The manufacturer shall provide information on the micaceous iron oxide content on the product data sheet, or as required by the purchaser.
4.2.2 Optional pigment components include extenders, tinting colors and suspension control agents.
4.3 Resin Requirement: The resin used in polyurethane coating shall be a polyisocyanate-based product that cures through a chemical reaction with atmospheric moisture. Use of other resins or modifiers shall be limited to products necessary for formula ingredient compatibility and to improve re-coating properties. See Note 11.3 for information on VOC content, and Note 11.4 for information on modifying resins.
4.4 Analytical Test Data: If mutually agreed upon by purchaser and supplier, the coating manufacturer shall provide certificates of analysis for polyurethane coating batches qualified by independent testing to meet this standard, including petrographic analysis of the percentage of lamellar particles present in the micaceous iron oxide pigment.
5. Standard Testing Conditions
5.1 TEST PANELS: The hot rolled steel test panels shall conform to ASTM A 572. Panel size shall be 100 mm x 150 mm x 3.2 mm (4 inch x 6 inch x 1/8 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-SP5. The blast profile shall be 44 to 57 micrometers (1.75 to 2.25 mils) as measured in accordance with ASTM D 4417, Method C.
5.2 APPLICATION: The coating shall be spray applied as a single coat in accordance with recommendations on the manufacturer’s product data sheet. The polyurethane coating shall show no streaking, running, sagging, or other defects during application or while drying.
5.3 DRY FILM THICKNESS: The dry film thickness (DFT) on the test panels shall meet the manufacturer’s written recommended range. The DFT shall be measured in accordance with SSPC-PA 2, Appendix 5.
5.4 CURE: The primer shall be dried and cured in accordance with manufacturer’s written recommendations. Before any testing, 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 may run vertically or at an angle across the face of the panel. Follow the scribe-making procedure described in ASTM D 1654.
5.6 BACKS AND EDGES: Coat and seal all edges and the back side of each panel with a coating or tape that will provide the necessary protection to these surfaces.
6. Requirements of Liquid Coating
6.1 MIXING: The coating shall be mixed and dispersed to produce a product that is uniform, stable, free from grit, and in conformance with the requirements of this specification
6.1.1 The single-component coating shall be capable of being dispersed under mechanical agitation to a smooth, uniform consistency and shall not show any objectionable properties in the mix.
6.1.2 After mixing and filtering through a standard 60 mesh screen in accordance with ASTM D 185, the amount of coarse particles and skins retained shall not exceed 0.5% by weight (see Note 11.5).
6.2 STORAGE LIFE: The coating shall exhibit no curdling, gelling, gassing, or hard caking after being stored unmixed for a minimum of six months from date of delivery in a tightly sealed, unopened container at a temperature of 10 to 32 °C (50 to 90 °F).
6.3 WORKING PROPERTIES: The mixed coating shall spray easily and show no signs of streaking, running, sagging, or other objectionable features when applied according to the manufacturer’s product data sheets. Notes 11.6 and 11.7 provide additional information on adhesion testing and quality assurance tests.
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 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 per panel. 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 INTERMEDIATE COAT ADHESION TO PRIMER: If this polyurethane coating is to be used as an intermediate coat over itself or another primer, apply the intermediate coat to three primed panels prepared in accordance with Sections 5.1 through 5.4. Use only primers identified as compatible by the intermediate coat manufacturer. Test adhesion 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 per panel. The minimum adhesion value of the intermediate coat to the primer 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.
7.3 DIRECT IMPACT RESISTANCE: The minimum impact resistance when measured in accordance with ASTM D 2794, shall be 6.8 N•m (60 inch-lb).Table 1 provides a summary of performance requirements for laboratory and accelerated testing.
8. Accelerated Laboratory Weathering Requirements
8.1 Cyclic Salt Spray/UV/Condensation Cabinet: Triplicate panels prepared in accordance with Section 5 shall be exposed in a cyclic test cabinet in accordance with ASTM D 5894 for 1500 hours.
8.1.1 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.
8.1.2 Blister Evaluation: After the specified exposure time, there shall be no blistering of the coated portion (a rating of 10 per ASTM D 714).
8.1.3 Scribe Evaluation: After the specified exposure time, the undercutting from the center of the scribe, measured at any point along the scribe, shall be a maximum of 4 mm (3/16 inch), a rating of 5 per Table 1 of ASTM D 1654. Moderate rusting in the scribe mark is permissible and resulting staining should be ignored.
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.
10.1 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 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.
Notes are not requirements of this specification.
11.1 Application: Moisture-cure polyurethane coatings are preferably applied by spray directly to steel substrates, but may be brushed on small areas for touch-up or to fill in irregularities.
11.2 Pigment: The typical micaceous iron oxide content for these coatings ranges from 15 to 35% by weight of nonvolatile components.
11.2.1 Micaceous iron oxide pigment is incorporated into coatings for the purposes of improved film hardness,decreased film porosity and viscosity control. It may also provide improved adhesion to steel substrates, and superior inter-coat adhesion properties. Micaceous iron oxide can impart a measure of film reinforcement while relieving stresses that can be developed in the binder. Optimally, the pigment provides a better barrier to the effects of ultraviolet weathering exposure.
11.2.2 Blends of micaceous iron oxide and aluminum pigments are used in various coating formulations for reasons of improved ultraviolet light and water resistance where extended periods of exterior exposure are anticipated prior to application of topcoats.
11.3 VOC Content: 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.
Many state and local governments and/or air quality management areas have more stringent VOC regulations than those in the federal rule. Information on the VOC content of each container 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.
11.4 Modifying Resins: Other resins or modifiers are typically less than 15% of total resin content.
11.5 Sieve Sizes: While Section 6.1.2 requires use of standard 60-mesh screen, the contracting parties may agree upon alternate screen sizes for new technology coatings.
11.6 Topcoat Adhesion: If desired, an adhesion test may be performed to determine adhesion between this coating and a compatible topcoat. To test for adhesion, prepare three panels in accordance with Sections 5.1 through 5.3. Apply a compatible topcoat and cure as recommended by the topcoat manufacturer. The thickness of the topcoat shall conform to the manufacturer’s recommendations. Test adhesion 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 per panel. The minimum adhesion value of each pull shall be 4.1 MPa (600 psi). In the case of adhesive failure below 4.1 MPa (600 psi), repeat the pull test. The instrument used to verify compliance to this standard shall be of the same type used to perform the initial testing.
11.7 Quality Assurance Tests: If the user chooses, tests may be used to determine the acceptability of a lot or batch of a qualified coating. 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 polyurethane 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.
11.7.1 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 inter-laboratory 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.
11.7.2 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).
PAINT SPECIFICATION NO. 41 – Moisture-Cured Polyurethane Coating/Primer or Intermediate Coat, Micaceous Iron Oxide Reinforced, Performance-Based