WO2024000098A1

WO2024000098A1 - Aqueous composition for elastomeric roof coating

Info

Publication number: WO2024000098A1
Application number: PCT/CN2022/101463
Authority: WO
Inventors: Bo TONG; Jitao CHEN; Cheng Shen; Ling Zhong; Xiaohong Zhang
Original assignee: Dow Global Technologies Llc
Priority date: 2022-06-27
Filing date: 2022-06-27
Publication date: 2024-01-04
Also published as: CN119630752A

Abstract

The present disclosure relates to an elastomeric roof coating composition, which comprises: (1) an acrylic binder in the amount of 30.0 –50.0 %by weight, based on the total weight of the composition, comprising (i) 90 to 99.6 %an acrylic polymer by weight of the acrylic binder, wherein the acrylic polymer comprises at least 90%by weight of acrylic or methacrylic repeat units; and (ii) 0.4 to 10.0 %an (meth) acrylic acid monomer by weight of the acrylic binder; (2) zinc oxide in the amount of 1.5 -4.0%by weight, based on the total weight of the composition; (3) a silane coupling agent in the amount of 0.1-0.5 %by weight, based on the total weight of the composition; and (4) the balance being water. In the present invention, the elastomeric roof coating composition may exhibit excellent adhesion to the various substrates, particularly to the polyester coated steel, preferably also exhibits a low odor characteristic (e.g., low ammonia release), and/or good acid resistance.

Description

AQUEOUS COMPOSITION FOR ELASTOMERIC ROOF COATING

FIELD

The present disclosure relates to an aqueous composition for elastomeric roof coating, particularly a low odor, acid resistant elastomeric roof coating composition with adhesion to polyester coated steel.

BACKGROUND

The elastomeric roof coating (ERC) composition is generally used as a liquid applied, seamless, fully adhered flexible membrane formed on a low slope roof. The elastomeric roof coating offers the benefits of solar reflectance for cooling buildings, reducing energy demands to maintain a comfortable temperature and etc. Additionally, the solar reflectance can lessen the urban heat island effect. During use, water-based ERC formulations are preferred due to its low toxicity and lessened environmental impact, when compared with solvent-based systems. Further, all-acrylic latex binders have become the industry standard for ERCs due to enhanced UV and mechanical durability, relative to other commercial water-based binder technologies.

An ERC composition must balance the need of mechanical strength such as tensile strength with the need of elongation. In addition, the ERC composition should provide excellent durability, dirt pickup resistance and adhesion to the desired substrate. Also, under JG/T 375-2012 and JC-1066-2008, the ERC composition requires an ammonia release of 500 mg/kg or less, and must meet acid resistance requirements. The adhesion to low surface energy substrates, such as coated steel substrates is a challenge, and key pigments/fillers are required to achieve the balance between mechanical properties and application performance, especially high tensile strength, high adhesion to colored steel panel and acid resistance. Currently available ERC compositions are not satisfactory in one way or another.

Accordingly, there is a need to provide a novel aqueous composition for elastomeric roof coating which can offer at least one characteristic: low odor, an ammonia release of 500 mg/kg or less, good acid resistance and good adhesion to various substrates, particularly to the polyester coated steel.

SUMMARY

After persistent exploration, the inventors have surprisingly developed an aqueous composition for elastomeric roof coating, which exhibits excellent adhesion to the various substrates, particularly to the polyester coated steel, preferably also exhibits a low odor characteristic (e.g., low ammonia release) , and/or good acid resistance.

In a first aspect of the present disclosure, it provides an aqueous composition for elastomeric roof coating, which comprises:

(1) an acrylic binder in the amount of 30.0 –50.0 %by weight, based on the total weight of the composition, comprising

(i) 90 to 99.6 %an acrylic polymer by weight of the acrylic binder, wherein the acrylic polymer comprises at least 90%by weight of acrylic or methacrylic repeat units; and

(ii) 0.4 to 10.0 %an (meth) acrylic acid monomer by weight of the acrylic binder;

(2) zinc oxide in the amount of 1.5 -4.0%by weight, based on the total weight of the composition;

(3) a silane coupling agent in the amount of 0.1-0.5 %by weight, based on the total weight of the composition; and

(4) the balance being water.

In a second aspect of the present disclosure, the present disclosure provides an elastomeric roof coating comprising the aqueous composition according to claim 1 and ammonia post-added into the aqueous composition, wherein the ammonia is in the amount of 0-0.2 %by weight based on the total weight of the elastomeric roof coating. In a third aspect of the present disclosure, the present disclosure provides use of an acrylic binder in the elastomeric roof coating according to claim 6, wherein the acrylic binder comprising

(i) 90 to 99.6 %an acrylic polymer by weight of the acrylic binder, wherein the acrylic polymer comprises at least 90%by weight of acrylic or methacrylic repeat units;

(ii) 0.4 to 10.0 %by weight of an (meth) acrylic acid monomer; and

wherein the acrylic binder comprises less than 0.04%ammonia by weight of the acrylic binder.

In a forth aspect of the present disclosure, the present disclosure provides a process of preparing the elastomeric roof coating, comprising: (1) providing the aqueous composition for elastomeric roof coating; and then (2) mixing ammonia with the aqueous composition, wherein the ammonia is in the amount of 0～0.2%by weight based on the total weight of the elastomeric roof coating.

In the present disclosure, the elastomeric roof coating composition may exhibit excellent adhesion to the various substrates, particularly to the polyester coated steel. For example, the peel-off strength to colored steel panel is higher than 0.3 N/mm. For some elastomeric roof coating compositions, they may also exhibit a low odor characteristic, e.g., low ammonia release which is less than 500 mg/kg in total ammonia present. Furthermore, the elastomeric roof coating compositions may exhibit good acid resistance, i.e., the initial tensile strength of the elastomeric roof coating is higher than 2.0 MPa; the initial elongation of the elastomeric roof coating is higher than 200%; and the tensile strength retention and elongation after acid treatment are higher than 80%and 100%, respectively.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. As disclosed herein, “and/or” means “and, or as an alternative” or “additionally or alternatively” . All ranges include endpoints unless otherwise indicated.

Unless otherwise indicated, all temperature and pressure units are room temperature and standard pressure.

All phrases comprising parentheses denote either or both of the included parenthetical matter and its absence. For example, the phrase “ (meth) acrylate” includes, in the alternative, acrylate and methacrylate.

Unless otherwise indicated, as used herein, the term “glass transition temperature” or “Tg” refers to the mid-point glass transition temperature of a polymer as determined by differential scanning calorimetry, measured using a DSC Q2000 (TA Instruments, New Castle, Del. ) in accordance with ASTM E-1356 (1991) , wherein a given emulsion copolymer was dried over night at 60℃ and then cooled to a temperature of -70℃ before scanning from -70℃ to 130℃with a ramp rate of 20℃/minute. The results were averaged over two runs (original and a rescan run with a different sample of the same polymer) .

As used herein, unless otherwise indicated, the term “coating thickness/thickness” refers to an average of at least three measurements of a dried coating (e.g., a dry film having a thickness of 0.8-1.2mm) obtained by applying 3 wet films (e.g., with a thickness of about 1500 microns) on a release paper roofing substrate, as measured using an Ames Gage, Model 13C-B2600 (Ames Corporation Waltham Mass. ) .

As used herein, the term “ (meth) acrylate” means acrylate, methacrylate, and mixtures thereof.

As used herein, the term “polymer” refers, in the alternative, to a polymer made from one or more different monomers, such as a copolymer, a terpolymer, a tetrapolymer, a pentapolymer etc., and may be any of a random, block, graft, sequential or gradient polymer.

As used herein, the term “pigment volume concentration” or %PVC refers to the quantity calculated by the following formula:

%PVC = ( (volume of pigment (s) +volume extender (s) +volume of filler (s) ) /Total dry volume of coating) ×100

As used herein, the term “total composition solids” or “solids” refers to any and every material in the composition other than water, ammonia and volatile solvents, if any.

As used herein, unless otherwise indicated, the term “average particle size” means a weight average particle size as determined by light scattering (LS) using a BI-90 particle size analyzer (Brookhaven Instruments Corp. Holtsville, N.Y. ) .

As used herein, the term “weight average molecular weight” or “MW” refers to the weight average molecular weight as measured by aqueous gel permeation chromatography (GPC) , using, for aqueous solution polymers (e.g. polymeric polyacids) , polyacrylic acid (PAA) standards, and, for aqueous emulsion copolymers, polystyrene standards.

As used herein, the phrase “wt. %” stands for weight percent.

In accordance with the present invention, the aqueous composition for elastomeric roof coating comprises an acrylic binder in the amount of 30.0 –50.0 %by weight, 30.0 –45.0 %by weight, 30.0 –40.0 %by weight, 30.0 –35.0 %by weight, 35.0 –50.0 %by weight, 35.0 –45.0 %by weight, 35.0 –40.0 %by weight, 40.0 –50.0 %by weight, 40.0 –45.0 %by weight or 45.0 –50.0 %by weight, based on the total weight of the composition. The acrylic binder may comprises (i) 90 to 99.6 %, 92 to 99.6 %, 94 to 99.6 %, 96 to 99.6 %or 98 to 99.6 %, an acrylic polymer by weight of the acrylic binder, wherein the acrylic polymer comprises at least 90 wt. %, at least 92 wt. %, at least 94 wt. %, at least 96 wt. %or at least 98 wt. %of acrylic or methacrylic repeat units; and (ii) 0.4 to 10.0 wt. %, 0.4 to 8.0 wt. %, 0.4 to 6.0 wt. %, 0.4 to 4.0 wt. %, 0.4 to 2.0 wt. %of an (meth) acrylic acid monomer by weight of the acrylic binder.

In an embodiment of the present disclosure, the acrylic binder may have a pH in a range of 4.0 to 7.0, 4.0 to 6.0, 4.0 to 5.0, 5.0 to 7.0, 5.0 to 6.0 or 6.0 to 7.0; and a glass transition temperature (Tg) from -40 ℃ to -15 ℃; from -40 ℃ to -20 ℃; from -40 ℃ to -25 ℃; from -40 ℃ to -30 ℃; from -40 ℃ to -35 ℃; from -35 ℃ to -15 ℃; from -35 ℃ to -20 ℃; from -35 ℃ to -25 ℃; from -35 ℃ to -30 ℃; from -30 ℃ to -15 ℃; from -30 ℃ to -20 ℃; from -30 ℃ to -25 ℃; from -25 ℃ to -15 ℃; from -25 ℃ to -20 ℃ or from -20 ℃ to -15 ℃. In the present disclosure, the acrylic polymer has average molecular weight is from 50 kDa to 2000 kDa, from 50 kDa to 1500 kDa, from 50 kDa to 1000 kDa, from 50 kDa to 500 kDa, from 50 kDa to 200 kDa, from 200 kDa to 2000 kDa, from 200 kDa to 1500 kDa, from 200 kDa to 1000 kDa, from 200 kDa to 500 kDa, from 500 kDa to 2000 kDa, from 500 kDa to 1500 kDa, from 500 kDa to 1000 kDa, from 1000 kDa to 2000 kDa, from 1000 kDa to 1500 kDa or from 1500 kDa to 2000 kDa. In addition, use of acrylic polymer of such a molecular weight enable an increase in the %PVC of compositions containing them.

In an embodiment of the present disclosure, the (meth) acrylic acid monomer includes, but not limited to, (meth) acrylic acid, alkyl (meth) acrylate, and 2-hydroxyethyl (meth) acrylate phosphate.

In an embodiment of the present disclosure, the acrylic binder has an ammonia content of less than 0.04 %by weight. In an embodiment of the present disclosure, the acrylic binder is comprised in the aqueous composition as a sole binder. In an embodiment of the present disclosure, the aqueous composition further comprises at least one inert filler in the amount of 30 -35%by weight, based on the total weight of the composition. In an embodiment of the present disclosure, the inert filler is selected from BaSO ₄, kaolin, silica flour, talcum powder, aluminum trihydrate or combination of them.

Peel-off strength (adhesion) of commercially available ERC is a challenging performance for ERC when applying to certain substrates such as concrete, metal, asphalt, etc. Different primers can be deployed to enhance the adhesion to a select substrate, but these are often solvent based and cause an increase in the application complexity and add to the cost of materials and labor. Adhesion to select substrates, such as polyesters that are used to coat steel are a particular challenge due to that substrate’s inherently low surface energy. A key application of ERC is coating polyester coated steel (colored steel) metal roof systems. Surprisingly, the inventors of the present invention find that use of ZnO cross-linker, together with the acrylic binder and silane coupling agents, may enhance the film strength and adhesion to colored steel panel, achieve the balanced mechanical and application performance, especially the high tensile strength, high adhesion to colored steel panel and acid-resistance.

In accordance with the present invention, the aqueous composition for elastomeric roof coating comprises zinc oxide in the amount of 1.5 -4.0%by weight, 1.5 –3.8%by weight, 1.5 – 3.5 %by weight, 1.5 -3.0%by weight, 1.5 –2.5%by weight, 1.5 -2.0%by weight, 2.0 -4.0%by weight, 2.0 –3.8%by weight, 2.0 –3.5 %by weight, 2.0 -3.0%by weight, 2.0 –2.5%by weight, 2.5 -4.0%by weight, 2.5 –3.8%by weight, 2.5 –3.5 %by weight, 2.5 -3.0%by weight, 3.0 -4.0%by weight, 3.0 –3.8%by weight, 3.0 –3.5 %by weight, 3.5 -4.0%by weight, 3.5 –3.8%by weight or 3.8 -4.0%by weight, based on the total weight of the composition. In an embodiment of the present disclosure, the zinc oxide is used as acid reactive filler, which connects to the acids on neighboring polymer chains, creating a tightly knit polymer network in the coating with reduced water absorption, increased tensile strength and improved resistance to water.

In accordance with the present invention, the aqueous composition for elastomeric roof coating comprises a silane coupling agent in the amount of 0.1-0.5 %by weight, 0.1-0.4 %by weight, 0.1-0.3 %by weight, 0.1-0.2 %by weight, 0.2-0.5 %by weight, 0.2-0.4 %by weight, 0.2-0.3 %by weight, 0.3-0.5 %by weight, 0.3-0.4 %by weight or 0.4-0.5 %by weight, based on the total weight of the composition. In an embodiment of the present disclosure, the silane coupling agent includes, but not limited to, amino-silane, epoxy silane, vinyl silane, methacryloxy silane and etc. The silane coupling agent could bond the inorganic filler with polymers, increase the coating film strength and water-resistance. Zinc oxide, silane coupling agent and the acrylic binder of the present disclosure will promote the adhesion significantly to low-energy-surface substrate like colored steel panel.

In accordance with the present invention, the aqueous composition for elastomeric roof coating may be substantially free of organic solvent. In particular, the balance in the aqueous composition for elastomeric roof coating is water, e.g., deionized water.

In accordance with the present invention, the aqueous composition for elastomeric roof coating substantially comprises or consists of an acrylic binder, zinc oxide, a silane coupling agent and water. Alternatively, the acrylic binder is a sole binder in the aqueous composition. In accordance with the present invention, the aqueous composition for elastomeric roof coating has an ammonia content of less than 0.04 %by weight. Alternatively, the acrylic binder substantially comprises or consists of 90 to 99.6 %an acrylic polymer by weight of the acrylic binder, wherein the acrylic polymer comprises at least 90%by weight of acrylic or methacrylic repeat units and 0.4 to 10.0 %an (meth) acrylic acid monomer by weight of the acrylic binder. In a preferred embodiment of the present invention, the aqueous composition comprises a low ammonia acrylic binder latex (ammonia content being less than 0.035%, less than 0.033%, less than 0.028%or less than 0.02%) as sole binder. In the present disclosure, it also provides use of the acrylic binder, particularly low ammonia acrylic binder, in the elastomeric roof coating as sole latex binder.

In the present invention, acid resistance of ERC coating is mainly impacted by the extenders/fillers. In general, calcium carbonate, silica flour, talcum powder etc. are widely used in coating formulations but could react with acid to cause the strength failure. In accordance with the present invention, the aqueous composition for elastomeric roof coating may further comprises: (5) at least one inert filler in the amount of 30 -35%by weight or 30 -32%by weight, based on the total weight of the composition. According to the present invention, the commonly used extenders or fillers, e.g., calcium carbonate, are replaced with inert fillers such as kaolin, BaSO ₄ etc. so as to enhance the strength retention of coating film after acid treatment. In an embodiments, the inert filler is selected from BaSO ₄, kaolin, silica flour, talcum powder, aluminum hydroxide or combination of them.

In an embodiment of the present disclosure, the aqueous composition further comprises (5) at least one inert filler in the amount of 30 -35%by weight, based on the total weight of the composition. In an embodiment of the present disclosure, the inert filler is selected from BaSO ₄, kaolin, silica flour, talcum powder, aluminum hydroxide or combination of them.

In some embodiments of the present disclosure, the aqueous composition for elastomeric roof coating of the present invention may comprise conventional fillers and processing aids for elastomeric roof coatings, so long as the amount of ammonia is limited to within the desired levels. The aqueous composition for elastomeric roof coating is pigmented and also contain extenders or fillers. Suitable pigments may be opacifiers, for example, titanium dioxide, hollow sphere or void containing or polymer pigments; iron oxides, IR reflective pigments or zinc oxide. Suitable extenders may be, for example clay, mica, talc, alumina silicates, aluminum trihydrate, nepheline syenite or mixtures of any of these with other extenders. Fillers and extenders are considered the same thing. If desired, the aqueous composition of the present invention may further comprises one or more extenders, such as nepheline syenite, and one or more pigments, such as titanium dioxide, or iron oxide. Clear ERC compositions may be formulated with extenders and no pigments.

In an embodiment of the present disclosure, the aqueous composition for elastomeric roof coating may have a solid content in range of 65%to 70%by weight, based on the total weight of the composition. The solid content of the aqueous component of the present invention may range within 60%to 75%by weight or 65%to 70%by weight. The solids in the present invention include any fillers, extenders and pigments and any solid additive present in a coating or film made from the compositions.

The aqueous compositions for elastomeric roof coating of the present invention can have a pigment volume concentration (%PVC) of from 30 to 50, preferably from 30 to 45, or more preferably from 35 to 45. Total volumes of pigment, extender and/or opacifier in excess of 50 %PVC may generally impair elongation, whereas a lack of sufficient volume of such materials can impair tensile strength of a coating made from the aqueous compositions of the present invention.

In accordance with the present invention, the elastomeric roof coating composition is prepared by adding ammonia containing precursors (preferably ammonia water) , as neutralizer, to the aqueous composition, preferably that comprising a low ammonia acrylic binder. In the present disclosure, the acrylic binder has an ammonia content of less than 0.04 %by weight; or it removes any steps of post-adding ammonia in the acrylic binder, which may still maintain the mechanical and heat storage stability. Meanwhile, ammonia or ammonia water may then be added to the aqueous composition to neutralize and stabilize the ERC composition. This approach will reduce total ammonia release of the elastomeric roof coating as formed to less than 500 mg/kg and meanwhile shorten drying time for the ERC composition, which is critical for early rain resistance. The inventors surprisingly find that contrary to the present invention, use of commonly used acrylic binder comprising post-added ammonia, together with removal of adding ammonia or ammonia water to the aqueous composition, would not reduce total ammonia release of the elastomeric roof coating as formed to less than 500 mg/kg, as required according to JC-1066-2008 Limit of harmful substances of building waterproof coatings. The elastomeric roof coating composition comprise or consists of the aqueous composition, and ammonia in the amount of 0-0.2 %by weight, 0-0.15 %by weight, 0-0.1 %by weight, 0-0.05 %by weight, 0.05-0.2 %by weight, 0.05-0.15 %by weight, 0.05-0.1 %by weight, 0.1-0.2 %by weight, 0.1-0.15 %by weight or 0.15-0.2 %by weight, based on the total weight of the elastomeric roof coating composition.

In an embodiment of the present disclosure, the elastomeric roof coating may have a pH within a range of from 7.0 to 9.0, from 7.0 to 8.0 or from 8.0 to 9.0; and have a low ammonia release which is less than 500 mg/kg, less than 400 mg/kg, less than 300 mg/kg or less than 200 mg/kg in total ammonia present.

In accordance with the present invention, the elastomeric roof coating composition may exhibits excellent adhesion to the various substrates, particularly to the polyester coated steel. For example, the peel-off strength to colored steel panel is higher than 0.3 N/mm. Furthermore, the elastomeric roof coating compositions may exhibit good acid resistance, i.e., the initial tensile strength of the elastomeric roof coating is higher than 2.0 MPa; the initial elongation of the elastomeric roof coating is higher than 200%; and the tensile strength retention and elongation after acid treatment are higher than 80%and 100%, respectively.

EXAMPLES

Some embodiments of the invention will now be described in the following examples, wherein all parts and percentages are by weight unless otherwise specified.

The information of the raw materials used in Examples is listed in the following Table 1:

Table 1. Raw materials used in Examples

Inventive Examples 1-3 and Comparative Examples 1-2

In Inventive Examples 1-3 of the present disclosure, low-ammonia acrylic binder latex was synthesized based on above commercial Acrylic binder latex described in Table 1 with processing developments, which lowered the ammonia content in the acrylic binder latex and maintain stability. In Comparative Examples 1 and 2, they utilized DOW commercial products and 2-component blended latex, respectively.

Table 2. Formulations used in Examples

	Raw material	Weight/kg
GRIND
A	Deionized water	144.5
	Nopco NXZ	3
	Orotan ^TM 1850E	4
B	Titanium dioxide	72
	Inert Filler	330
	ZnO	20
LET-DOWN
C	Acrylic binder Latex	403
	Nopco NXZ	3
D	Texanol	6
E	Ammonia 28%	0.6
F	Natrosal ^TM 250 HBR	3.5
G	OFS-6040	1.5
	Total	991.1
	Solid%	65.70
	PVC%	39.37

The formulations in Inventive Examples 1-3 were prepared in according to below process:

(1) During GRIND process, the initial ingredients A of the GRIND were changed to the mixing kettle.

(2) While mixing at low speed, the pigments B were added to the kettle.

(3) Half of premix F (with DI water) was added to the kettle.

(4) After all the pigments were added in the kettle, the mixer was stopped and the sides and bottom of the kettle were scraped.

(5) The mixer was turned back on and the contents in the mixer were ground at high speed for 15-30 minutes, or until a good grind was obtained (Hegman reading of 4.5 to 5.0) .

(6) For the LETDOWN process, C the latex emulsion was added to the kettle. The defoamer was added “layer” on top of the Primal EC emulsion.

(7) The mixer was turned on and the contents in the mixer were blended together.

(8) While blending, ingredients D and E were added to the kettle.

(9) Remained half ingredients F was added as a premix, immediately after the NH ₄OH was added to the mix. Ingredients F was added within 5 minutes of the NH ₄OH or necessary thickening time drastically increased.

(10) Ingredient (G) was post-added.

Table 3: Acrylic Binder Latex properties:

Table 3 shows the Acrylic binder latex has good mechanical and heat storage stability, and less ammonia in the total formulation with 5～6 pH value.

Table 4: Formulations:

In Table 4, Inv. Ex 1/Ex 2 comprise low-ammonia latex, ZnO fillers (replacing CaCO ₃ in Comp Ex1 (DOW ARM-91-1) ) and silane; while Comp. Ex 2 uses 2-component binder latex and different filler/pigments.

Testing and Evaluation

The experimental binder was synthesized in Sanshui plant according to the formula listed in the above with the production of several commercial latex, removal of the post-added Ammonia and biocide package in the last processing step. Latex basic properties e.g. pH, viscosity, solid contents%, heat storage stability, mechanical stability were confirmed by standard testing protocols.

Sample preparation and tests are in accordance with JG/T 375-2012 Acrylic waterproof coating for metal roof. 1. JG/T 375-2012 Acrylic waterproof coating for metal roof is summarized in brief:

(1) Initial tensile strength≥1.5MPa (≥*2.0MPa) ;

(2) Initial elongation%≥150 (*≥200) ;

(3) water absorption≤15%;

(4) low temperature flexibility at -30℃;

(5) Tensile strength retention after acid treatment≥80%;

(6) Tensile elongation after acid treatment≥100%;

(7) Peel-off strength on colored steel≥0.3 N/mm etc. (*≥0.5)

*obtained in the present invention.

Sample preparation

The samples prepared according to the formulations in Table 2 were conditioned at (23 ± 2) ℃ and (50 ± 10) %relative humidity for more than 24 hrs before coating. They were stirred and poured into the prescribed mold for coating without mixing air bubbles. Coating films were prepared by applying 3 coats. Each coat was dried for maximum 24 hrs before the subsequent coat applied, to form an integrated film suitable to be released and not to be torn upon removal. The coating thickness of the total film was controlled to (1.0 ± 0.2) mm within 48 hrs drying. The films were allowed to thoroughly cure at 23℃ and 50%relative humidity for 96 hrs, then removed from the release paper and put into (40 ± 2) ℃ ovens for 48 hrs for a complete curing. The films should be conditioned at (23 ± 2) ℃ and (50 ± 10) %relative humidity for more than 4 hrs before testing.

Solid content

ERC Solid content was tested in accordance with JG/T 375-2012 with 0.6 g samples, 3 replicates were were dried in an oven at (105 ± 2) ℃ for (180 ± 15) min.

Initial tensile strength and percent elongation

Tensile strength measurements were made in accordance with GB/T 16777-2008 Test Method 9.2.1. The tensile speed is 200 mm/min. Chinese standard code JG/T 375-2012 requires the coating to have an initial tensile strength ≥ 1.5MPa and initial percent elongation ≥ 150%at 23℃, respectively.

Acid treatment &tensile strength and elongation after

Six rectangular specimens (120 *25) mm were put into 2%H ₂SO ₄ solution. The liquid level was kept 10 mm higher than the surface of the test pieces. They were taken out after continuous immersion for 168 ± 1 hrs, rinsed thoroughly with water and dried in an oven for 6 hrs ± 15min. Then they were placed under the standard testing conditions of 23 ± 2℃ and 50 ± 10%relative humidity for 18 ± 2 hrs and cut type I shape according to GB/T528-2009 requirements and tested in accordance with the test method specified in 9.2.4 of GB/T 16777-2008.

Peel-off strength on colored steel

According to GB/T 12754, three rectangular specimens 200mm X 200mm polyester coated colored steel was taken as substrate. Non-woven PET cloth ten tensile strength of MD ≥150N/50mm, rectangular 420 mm X 200mm, thickness is 0.3mm～0.5mm. Coating films were prepared by applying 3 coats. Each coat was dried for maximum 24 hrs before the subsequent coat applied, to form an integrated film suitable to be released and not to be torn upon removal. The nonwoven PET cloth was coated together with the second coating. The thickness of the total film was controlled to (1.5 ± 0.2) mm within 48 hrs drying. The films were allowed to thoroughly cure at 23℃ and 50%relative humidity for 96 hrs, then removed from the release paper and put into (40 ± 2) ℃ ovens for 48 hrs for a complete curing. The films should be conditioned at (23 ± 2) ℃ and (50 ± 10) %relative humidity for more than 4 hrs before testing. Cut the sample to 5 specimen and immerge it into water for 168 hrs. The peel-off speed is 50mm/min with minimum peel-off length 115mm in accordance with JG/T 375-2012 appendix A, and the requirement of peel-off strength ≥ 0.3 N/mm.

Ammonia release

Ammonia is distilled from an alkaline solution and absorbed with excess standard solution of sulfuric acid. Using the mixed indicator of methyl red -methylene blue, the excess sulfuric acid was titrated with sodium hydroxide standard titration solution according to JC-1066-2008 limit of harmful substances of building waterproof coatings, 4.1 class A requires ammonia ≤500 mg/kg. (JC-1066-2008 Limit of harmful substances of building waterproof coatings: class A, VOC≤80 g/L; Formaldehyde≤100 g/L; Benzene series ≤300 g/L; ammonia ≤ 500 mg/kg. )

Coating Film Drying Time (GB1728-1979 Testing Methods for the Drying Time of Coating Films and Skim Coat)

Coating films were liquid applied by 1000 um thickness applicator on top of standard experimental fiber cement panels. Below testing methods are adopted to test the surface dry time (touch dry) and full dry time within the area range at least 1 cm aside from the coating film edge.

Surface drying time (touch dry)

Carefully touch the coating surface using fingers. If it feels tacky for coating film but no coating left on fingers, it is considered as touch dry. Record the time as surface drying time.

Full drying time

Use knife to cut through the coating film to carefully observe the bottom and inside section of coating film. If there is no tacky phenomenon, it is considered as full dry. Record the time as full drying time.

Table 5: ERC properties:

Table 5 shows the coating properties, which indicate that the ammonia release of Inventive ERC formulation was significantly lowered from around 1000mg/kg to 160 mg/kg.

Table 6: Results for Tensile and Acid treated Tensile:

Table 6 shows the mechanical performance of strength/elongation before and after acid treatment. The ZnO filler (Inv Ex1/2 v. s. Comp Ex1) can significantly enhance the initial strength/elongation about 50～60%, and the inventive filler may also improve elongation%after acid treatment tremendously. The experimental results prove that the low-ammonia acrylic binder latex incorporated into the ERC matrix with inert fillers has better coverage, interaction and higher crosslinking density which contributes to the mechanical strength and acid resistance of ERC. Moverover, the tensile strength retention of Inv. Ex 3 using silica flour and BaSO ₄ dropped down to 54%.

Table 7: Summary Results for Heat Age and Adhesion

Table 5 shows the adhesion (peel-off strength) of inventive ERC formulation is much higher than Comp. Ex 2, which thanks to the coupling agent silane and the low-ammonia acrylic binder latex incorporated with ERC the coating formulation.

Based on all the above performance comparison, it was confirmed as follows:

1. The inventive low-ammonia acrylic binder latex enables the ERC composition to lower the ammonia release to less than 500 mg/kg and its incorporation with the ERC coating matrix help on the mechanical strength.

2. Comparing with prior art (e.g., DOW ARM-91-1 in Comp. Ex 1) , the inventive ERC composition may keep as much as the mechanical strength/elongation after acid treatments, and may show superior acid resistance properties.

3. Comparing with prior art (e.g., Comp. Ex 2) , the inventive ERC composition used a low-ammonia acrylic binder latex, instead of two-component blended acrylic latex, and meanwhile it used ZnO, inert fillers and silane coupling agents to balance the ERC mechanical strength, acid-resistance properties, and further significantly enhanced the adhesion to colored steel.

4. The low-ammonia latex ERC composition is a new composition of low odor, good acid resistant with higher adhesion to polyester coated steel, fulfill JC-1066-2008 limit of harmful substances of building waterproof coatings, class A and JG/T 375-2012 acrylic waterproof coating for metal roof.

Claims

An aqueous composition for elastomeric roof coating, which comprises:

(1) an acrylic binder in the amount of 30.0 –50.0 %by weight, based on the total weight of the composition, comprising

(i) 90 to 99.6 %an acrylic polymer by weight of the acrylic binder, wherein the acrylic polymer comprises at least 90%by weight of acrylic or methacrylic repeat units; and

(ii) 0.4 to 10.0 %an (meth) acrylic acid monomer by weight of the acrylic binder;

(2) zinc oxide in the amount of 1.5 -4.0%by weight, based on the total weight of the composition;

(3) a silane coupling agent in the amount of 0.1-0.5 %by weight, based on the total weight of the composition; and

(4) the balance being water.
The aqueous composition for elastomeric roof coating according to claim 1, wherein the acrylic binder comprises less than 0.04%ammonia by weight of the acrylic binder.
The aqueous composition for elastomeric roof coating according to claim 1, wherein the acrylic binder is a sole binder in the aqueous composition.
The aqueous composition for elastomeric roof coating according to claim 1, wherein the aqueous composition further comprises:

(5) at least one inert filler in the amount of 30 -35%by weight, based on the total weight of the composition.
The aqueous composition for elastomeric roof coating according to claim 4, wherein the inert filler is selected from BaSO ₄, kaolin, silica flour, talcum powder, aluminum hydroxide or combination of them.
An elastomeric roof coating comprising the aqueous composition according to claim 1 and ammonia post-added into the aqueous composition, wherein the ammonia is in the amount of 0-0.2 %by weight based on the total weight of the elastomeric roof coating.
The elastomeric roof coating according to claim 6, wherein the acrylic binder comprises less than 0.04%ammonia by weight of the acrylic binder; and total ammonia release of the elastomeric roof coating is less than 500 mg/kg.
The elastomeric roof coating according to claim 6, wherein the acrylic binder is a sole binder in the aqueous composition.
The elastomeric roof coating according to claim 6, wherein the aqueous composition further comprises:

(5) at least one inert filler in the amount of 30 -35%by weight, based on the total weight of the composition.
The elastomeric roof coating according to claim 6, wherein the inert filler is selected from BaSO ₄, kaolin, silica flour, talcum powder, aluminum hydroxide or combination of them.
Use of an acrylic binder in the elastomeric roof coating according to claim 6, wherein the acrylic binder comprising

(i) 90 to 99.6 %an acrylic polymer by weight of the acrylic binder, wherein the acrylic polymer comprises at least 90%by weight of acrylic or methacrylic repeat units;

(ii) 0.4 to 10.0 %by weight of an (meth) acrylic acid monomer; and wherein the acrylic binder comprises less than 0.04%ammonia by weight of the acrylic binder.
A process of preparing the elastomeric roof coating according to claim 6, comprising:

(1) providing the aqueous composition according to claim 1; and then

(2) mixing ammonia with the aqueous composition, wherein the ammonia is in the amount of 0～0.2% by weight based on the total weight of the elastomeric roof coating.
The process of claim 12, wherein the acrylic binder comprises less than 0.04%ammonia by weight of the acrylic binder; the acrylic binder is a sole binder in the aqueous composition;

and/or the aqueous composition further comprises at least one inert filler in the amount of 30 -35%by weight, based on the total weight of the composition.
The elastomeric roof coating according to claim 12, wherein the inert filler is selected from BaSO ₄, kaolin, silica flour, talcum powder, aluminum hydroxide or combination of them.