CROSS REFERENCE TO RELATED APPLICATIONS

[0001 ] This application claims priority to United States Provisional Application No. 62/540,368, filed August 2, 2017, the entire specification of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The present technology relates to a phosphate-ester adhesion promoter that can improve the adhesion of film-forming compositions to a substrate. The present technology also relates to the film-forming compositions that comprise the adhesion promoter. The film-forming compositions may be polyurethane, epoxy, thermosetting acrylic, or silicone compositions.

[0003] Film-forming compositions, such as polyurethane compositions, have been used in a wide variety of applications, such as in adhesives, in coatings such as paints, and in sealants. Adhesives can be used for bonding a variety of materials, including metals and plastics. Coatings can be applied to various substrates and allowed to dry or cure to form a protective or decorative film on the surface of the substrates. Suitable substrates include metals, plastics, composites, wood, and concrete. Sealants are applied to a variety of surfaces and allowed to dry or cure to form a watertight or airtight coating. In all of these applications, an important property of the film-forming composition is the ability to adhere to the substrate or surface to which it has been applied. With some substrates, such as metals or plastics, it is difficult to obtain good bond strength between the film-forming composition and the substrate without pretreating the substrate, such as by applying layers of primer compositions. However, pretreatment steps with a primer composition increase both manufacturing costs and production time.

[0004] Adhesion promoters have been developed to improve bond strength between coating, adhesive, and sealant compositions and different substrates. Known adhesion promoters include epoxy-functional silanes, amine-functional metal organic complexes, and amine-functional zircoaluminates. However, these adhesion promoters may not give satisfactory results on some substrates, such as untreated steel, untreated aluminum, composite materials, and plastics.

[0005] There is therefore a need in the art for an adhesion promoter that can improve the bonding strength and adhesion of film-forming compositions to substrates such as, for example, untreated aluminum, untreated steel, composite materials, and plastic substrates. There is also a need in the art for film-forming compositions that provide good adhesion to substrates, particularly low energy/difficult-to-stick-to substrates, such as untreated aluminum and plastics.

SUMMARY OF THE INVENTION

[0006] In one aspect, the disclosure provides an adhesion promoting agent for enhancing the adhesion of a film-forming composition to a substrate, wherein the adhesion promoting agent comprises a mixture of epichlorohydnn phosphate esters that is the reaction product of epichlorohydnn reacted with phosphoric acid in a molar ratio of greater than 1 :1 but less than 3:1 , such as about 2:1 or 2:1 .

[0007] In a further aspect, this disclosure provides a method for enhancing adhesion of a film-forming composition to a substrate comprising: (a) adding an adhesion promoting agent to at least one of the film-forming composition or the substrate, wherein the adhesion promoting agent comprises a mixture of epichlorohydrin phosphate esters that is the reaction product of epichlorohydrin reacted with phosphoric acid in a molar ratio of greater than 1 :1 but less than 3:1 , such as about 2:1 or 2:1 ;

(b) applying the film-forming composition to the substrate, and

(c) curing the film-forming composition.

[0008] In a still further aspect, the disclosure provides a system comprising:

(a) a substrate;

(b) a film-forming composition adhered to at least a portion of the substrate; and

(c) an adhesion promoting agent comprising a mixture of epichlorohydrin phosphate esters that is the reaction product of epichlorohydrin reacted with phosphoric acid in a molar ratio of greater than 1 :1 but less than 3:1 , such as about 2:1 or 2:1 ;

wherein the adhesion promoting agent is present in the system in an amount effective to provide an increased bond strength between the film-forming composition and the substrate compared to a similar system that does not contain the adhesion promoting agent.

[0009] In another aspect, the disclosure provides a polyurethane composition that comprises a polyester polyol; an activator for reacting with the polyester polyol to form a polyurethane film; and an adhesion promoting agent comprising a mixture of epichlorohydrin phosphate esters that is the reaction product of epichlorohydrin reacted with phosphoric acid in a molar ratio of greater than 1 :1 but less than 3:1 , such as about 2:1 or 2:1 .

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a graph comparing adhesion test results of an untreated aluminum substrate treated with a polyurethane coating having no adhesion promoting agent, and polyurethane coatings having different concentrations of the adhesion promoting agent of the present technology;

[001 1 ] Figure 2 is a graph comparing adhesion test results of a steel substrate treated with a polyurethane coating having no adhesion promoting agent, and polyurethane coatings having different concentrations of the adhesion promoting agent of the present technology;

[0012] Figure 3 is a graph comparing adhesion test results of an untreated aluminum substrate treated with a polyurethane coating having no adhesion promoting agent, polyurethane coatings containing known adhesion-promoting agents, and a polyurethane coating containing the adhesion promoting agent of the present technology;

[0013] Figure 4 is a graph comparing adhesion test results of a steel substrate treated with a polyurethane coating having no adhesion promoting agent, polyurethane coatings containing known adhesion-promoting agents, and a polyurethane coating containing the adhesion promoting agent of the present technology. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present technology encompasses an adhesion promoting agent that can enhance the adhesion of film-forming compositions, such as polyurethane, epoxy, thermosetting acrylic, or silicone compositions, to various substrates. The film-forming compositions may be in the form of coatings, adhesives, and sealants. The adhesion promoting agent is particularly useful for enhancing the adhesion of polyurethane compositions to untreated surfaces, such as untreated aluminum, untreated steel, composite materials, wood, and plastics that normally require primer layers to achieve adequate adhesion.

[0015] The adhesion promoting agent comprises a mixture of epichlorohydrin phosphate esters that can be prepared by reacting epichlorohydrin (EPI) with phosphoric acid in a molar ratio that is greater than 1 :1 but less than 3:1 . In some embodiments, the molar ratio of epichlorohydrin to phosphoric acid is preferably about 2:1 , such as 2:1 . In some embodiments, the molar ratio of epichlorohydrin to phosphoric acid may range from 1 .1 :1 to 2.9:1 , alternatively 1 .2:1 to 2.8:1 , alternatively 1 .4:1 to 2.6:1 ; alternatively 1 .5:1 to 2.5:1 , alternatively 1 .8:1 to 2.2:1 . In some other embodiments, the molar ratio of epichlorohydrin to phosphoric acid may be 1 .2:1 , 1 .3:1 , 1 .4:1 , 1 .5:1 , 1 .6:1 , 1 .7:1 , 1 .8:1 , 1 .9:1 , 2.1 :1 , 2.2:1 , 2.3:1 , 2.4:1 , 2.5:1 , 2.6:1 , 2.7:1 , 2.8:1 , or 2.9:1 . The reaction can be via a single-step procedure, in which the desired amounts of epichlorohydrin and phosphoric acid are introduced into a reactor. The reaction temperature can range from room temperature (for example, 25°C) up to 80°C. Preferred temperatures range from about 40°C to about 60°C. Since the reaction is exothermic, it is desirable to use a water bath or other cooling method to control the reaction temperature. It is also desirable to incrementally add the epichlorohydrin to the phosphoric acid in the reactor. The reaction proceeds for a time sufficient for all of the epichlorohydrin to react with the phosphoric acid. The reaction can be performed neat, or in a suitable solvent. Suitable solvents include acetates, such as n-butyl acetate, carbonates, such as propylene carbonate, hydrocarbon solvents, such as hexane, toluene, xylene, and terpenes, and certain oxygenated solvents, such as ketones, glycol ethers, glycol esters, and nitroparaffin.

[0016] The following is a reaction scheme showing the reaction between epichlorohydrin and phosphoric acid in a 2:1 molar ratio to obtain the epichlorohydrin phosphate ester adhesion promoting agent (sometimes referred to herein as EMPA):

Phosphoric Acid

Diester 1

additional EPT

[0017] As can be seen from the reaction scheme, the resulting reaction product is a mixture comprised of phosphoric acid monoesters and diesters along with residual phosphoric acid. Minor amounts of other compounds resulting from the reaction may also be present in the reaction product mixture. It should be appreciated by one skilled in the art that the amount of each component in the reaction product need not be exact, and that some variation in the particular amounts of the components in the reaction product will occur from batch to batch.

[0018] Phosphorous NMR analysis of one example of the epichlorohydrin phosphate ester reaction product mixture resulting from a batch reaction of a 2:1 molar ratio of epichlorohydrin and phosphoric acid showed the reaction product mixture for this particular batch comprised the following components:

[0019] The epichlorohydrin and phosphoric acid reaction product can be used as the adhesion promoting agent without further purification, and has an acid value ranging from about 200 to about 400 mg KOH/g. The adhesion promoting agent can be used as a 100% solids material. However, it may be desirable to dilute the adhesion promoting agent in a solvent to reduce its viscosity and improve its handling properties. Suitable solvents include acetates, such as n-butyl acetate, carbonates, such as propylene carbonate, hydrocarbon solvents, such as hexane, toluene, xylene, and terpenes, and certain oxygenated solvents, such as ketones, glycol ethers, glycol esters, and nitroparaffin. Mixtures of solvents may also be used. The solvent or mixture of solvents may comprise from about 5% to about 95% by weight based on the combined weight of the solvent and the adhesion promoter.

[0020] The adhesion promoting agent can be used as an additive in the film forming compositions for coatings, adhesives, and sealants. Alternatively, the adhesion promoting agent can be applied as is (either alone or in a solvent) directly to a substrate as a pretreatment to enhance the adhesion of the composition being applied to the substrate.

[0021 ] As an additive, the adhesion promoting agent can be added and blended into solvent borne or high solids type curable film-forming formulations to improve adhesion of the composition to different substrates. Such film-forming compositions include polyurethane compositions, epoxy compositions, thermosetting acrylic compositions, and silicone compositions.

[0022] Polyurethane formulations typically comprise one or more active hydrogen containing compounds, such as polyols, and at least one activator, such as isocyanates. The polyols can be aromatic, aliphatic, or a combination thereof, and include without limitation, polyester polyols, polyether polyols, polyether ester polyols, and/or polycaprolactones. Epoxy compositions typically comprise one or more resins having an epoxy functionality and at least one curing agent, such as amines. The one or more epoxy resins may be aromatic, aliphatic, cycloaliphatic, or mixtures thereof. Thermosetting acrylic compositions include hydroxyl functional (meth)acrylic resins that can be cross-linked with active nitrogen-containing resins, or carboxyl functional (meth)acrylic resins that can be cross-linked with epoxy resins. Silicone compositions can comprise moisture curing and/or thermal curing silicone resins.

[0023] The amount of adhesion promoting agent added will depend on the particular film-forming composition used and the particular substrate involved. An effective amount of adhesion promoting agent is about 10% by weight or less, based on the total weight of the film-forming composition. In some embodiments, the amount of the adhesion promoting agent is about 0.01 % to about 8% by weight, alternatively about 0.01 % to about 7% by weight, alternatively about 0.02% to about 5% by weight, alternatively about 0.03% to about 3% by weight, alternatively about 0.01 % to about 1 .5%, alternatively about 0.05% to about 1 .0%, alternatively about 0.05% to about 0.5%, alternatively about 0.06% to about 0.25%, based on the total weight of the film- forming composition.

[0024] When used as a pretreatment agent, the adhesion promoting agent can be applied directly to the substrate surface, and then the film-forming coating, adhesive, or sealant composition is applied over the pretreatment agent and substrate surface. When used in this manner, the adhesion promoting agent can be applied as is (100% solids), or dissolved or dispersed in a solvent. Suitable solvents are described above. The amount of solvent can be from about 5% to about 95% by weight.

[0025] The epichlorohydrin phosphate ester adhesion promoting agent described herein surprisingly provides enhanced adhesion of film-forming coatings, adhesives, and sealants to a variety of substrates, such as metal, wood, composite materials, glass, concrete, and plastic substrates. Even more surprising, dramatically improved adhesion is achieved with untreated or poorly treated surfaces, such as cold roll steel or untreated aluminum, even with small amounts (less than 0.2 wt. %) of the adhesion promoting agent. Typically, bonding to untreated metal such as cold roll steel and aluminum is difficult without some type of pretreatment in order to achieve proper bonding strength. However, adequate bond strengths to untreated metals can be obtained with the adhesion promoting agent of the present technology, without the need for a pretreatment step. Without being bound by theory, it is believed that the enhanced adhesion properties may be due to the mixture of the monoesters, diesters, and phosphoric acid resulting from the reaction of epichlorohydrin with phosphoric acid. A further benefit is that the adhesion promoting agent may reduce metal corrosion due to the phosphate ester structure. The adhesion promoting agent may also provide enhanced adhesion to concrete materials.

[0026] The polyurethane, epoxy, or other compositions comprising the epichlorohydrin phosphate ester adhesion promoting agent can be applied to the desired substrate by any standard method known in the art, such as rolling, brushing, spraying, or dipping. After application, the polyurethane composition is allowed to dry or cure for an appropriate length of time and curing conditions to form the coating, adhesive, or sealant on the substrate. Drying or curing can be at room temperature and/or at elevated temperatures, such as up to about 150°C depending on the formulation and/or the prescribed curing conditions.

[0027] The presently described technology and its advantages will be better understood by reference to the following examples. These examples are provided to describe specific embodiments of the present technology. By providing these examples, the inventors do not limit the scope and spirit of the present technology. [0028] The following test methods are used to determine properties and performance of polyurethane coating compositions comprising the epichlorohydrin phosphate ester adhesion promoter.

[0029] Adhesion of the coatings is measured by the cross-hatch tape test according to ADTM D 3359-95. Briefly, a lattice pattern with cuts in each direction is made in the film to the substrate. Pressure-sensitive tape is applied over the lattice and then removed. Test Method B is used to evaluate adhesion, wherein a rating of 5 indicates 0% of the coating is removed, and a rating of 0 indicates greater than 65% of the coating is removed.

Example 1 : Procedure for Synthesis of the Epichlorohydrin Phosphate Esters.

[0030] Orthophosphoric acid (198.0 g, 2.02 mol) was charged into a 2L four-necked round-bottomed flask equipped with a mechanical stirrer, thermometer probe, nitrogen inlet, and water-cooled condenser. The content of the flask was heated to ~60°C to get liquefied, and epichlorohydrin (370.0 g, 4.00 mol) was added dropwise over the period of 60 min maintaining the temperature at <60°C by ice/water. The temperature of the flask was maintained at 60°C and agitation was continued for 30 min followed by vacuuming for 10 min at <100 torr at the temperature. After cooling to ambient temperature, a highly-viscous paste was obtained, yielding 567 g (99.8%). Measured acid value of the product was 283 mg KOH/g.

Example 2: Adhesion Test for Different Additive Amounts

[0031 ] The epichlorohydrin phosphate ester adhesion promoter made according to Example 1 was blended into a commercial, two component polyurethane system (Rust- Oleum ^® 9400) at two different amount levels, and compared to the system without the addition of the adhesion promoter. The amount of epichlorohydrin phosphate ester used in the two formulations was 0.07% by weight and 0.12% by weight, based on the total weight of the formulation. The formulations prepared and tested are shown in Table 1 .

Table 1 - Coating Formulation

[0032] Coated metal panels for testing were prepared by first cleaning the metal panels with acetone before the coating formulation was applied. Rust-Oleum ^® 9400 polyol was mixed with Rust-Oleum ^® 9401 activator in the desired ratio for about 30 seconds and applied to the metal panels using a 150 mil drawn down rod. The coatings were allowed to cure at room temperature for seven days before cross hatch adhesion testing was done.

[0033] Figure 1 graphically illustrates the results of cross-hatch adhesion testing for the test formulations (Formulations B and C), and the control formulation (Formulation A) on an untreated aluminum panel. From Figure 1 it can be seen that the test formulations containing the epichlorohydrin phosphate ester adhesion promoting agent had ratings of 4 or 5, whereas the control had a rating of 2 (15-35% coating removed) for the untreated aluminum substrate. The results show a significant improvement in adhesion of the coating on untreated aluminum when the epichlorohydnn phosphate ester adhesion promoting agent is added to the formulation. Surprisingly, the test formulation containing epichlorohydnn phosphate ester in an amount of 0.07% by weight achieved a rating of 5 at both the 1 week and 2 week evaluations, showing that enhanced adhesion is obtained at very low levels of additive.

[0034] Figure 2 graphically illustrates the results of cross-hatch adhesion testing for the test formulations and the control formulation on an untreated steel panel. All the formulations had a rating of 5 for the untreated steel substrate.

Example 3: Adhesion Test Comparison of Different Adhesion Promoters

[0035] Test formulations were prepared by adding an adhesion promoter to the polyester urethane component of a commercial polyurethane system (Rustoleum ^® 9400) according to the following Table 2. The commercial polyurethane system without an added adhesion promoter served as a control (Formulation A).

Table 2 - Coating Formulation

[0036] The adhesion promoters added to the respective formulations were (1 ) the epichlorohydrin phosphate ester (EMPA) adhesion promoting agent of the present technology; (2) a silane-based adhesion promoter; (3) an amino functional metal complex; and (4) an amino functional zircoaluminate.

[0037] Coated metal panels for testing were prepared as described in Example 2, and the coatings were allowed to cure at room temperature for 7 days before cross- hatch adhesion testing was done.

[0038] Figure 3 graphically illustrates the results of cross-hatch adhesion testing for each of the test formulations and the control formulation on an untreated aluminum panel. From Figure 3 it can be seen that the test formulation containing the epichlorohydrin phosphate ester (EMPA) adhesion promoting agent had a rating of 5 (0% coating removed), whereas the other three test formulations each had a rating of 0 (greater than 65% coating removed). The control had a rating of 1 (35-65% coating removed). These results demonstrate that the adhesion promoting agent provides a dramatic improvement in adhesion of a polyurethane coating to untreated aluminum.

[0039] Figure 4 graphically illustrates the results of cross-hatch adhesion testing for each of the test formulations and the control formulation on an untreated steel panel. From Figure 4 it can be seen that each of the test formulations had a rating of 5. The Figure 3 and Figure 4 test results show that, although the test formulations containing the commercial adhesion promoters provided good adhesion of the polyurethane coating to untreated steel, they were not effective (and indeed were detrimental) for an untreated aluminum substrate. However, the epichlorohydrin phosphate ester adhesion promoting agent of the present technology provided good adhesion of the polyurethane coating to both metal substrates.

Example 4: Adhesion Test Using Adhesion Promoter with Different Adhesives and Substrates

[0040] In this example, the epichlorohydrin phosphate ester adhesion promoter of the present technology was added to different commercially available adhesives, and the adhesives with the adhesion promoter were compared to the same adhesives without the adhesion promoter for adhesive properties on different substrates. Test formulations were prepared by adding to the following commercial products an amount of 0.7% by weight based on the weight of the test formulation of a solution comprising 10% by weight of the epichlorohydrin phosphate ester adhesion promoter in n-butyl acetate solvent (0.07% epichlorohydrin phosphate ester active):

1 . Gorilla Glue - a one component moisture cure liquid polyurethane adhesive from Gorilla Glue Company

2. Goop - a styrene butadiene solvent adhesive, from Eclectic Products, Inc.

3. Liquid Nails (NL-150) - general purpose household adhesive from PPG Industries

4. Epoxy Glue - a five minute two component bisphenol A resin epoxy adhesive from JB Weld

5. Loctite PL Polyurethane Roof and Flashing sealant - a one component polyurethane sealant from Henkel

6. GE Metal Gray Silicone II - a silicone sealant from Momentive Amer. Ind. [0041 ] The epichlorohydrin phosphate ester adhesion promoter was hand blended into each test adhesive or sealant for one minute. The test formulations with the adhesion promoter and the adhesives or sealants without the adhesion promoter were each used as specified by the manufacturer label.

[0042] Wood-to-substrate lap sheer assemblies were made in sets of five by first making marks across the bonding faces of wood samples (0.125 inches thick, trimmed to 1 " x 4") to allow separate inch square overlaps between the wood and the test substrate materials. The test substrate materials were acrylonitrile-butadiene-styrene (ABS) (0.125 inches thick), polycarbonate (PC) (0.1 18 inches thick), aluminum (Al) (0.063 inches thick), thermoplastic olefin (TPO) (0.125 inches thick), and cold rolled steel (CRS) (0.0163 inches thick), each material trimmed to 1 " x 4" samples. Wood bonding surfaces were pretreated by first rubbing briefly with a moist paper towel prior to applying the adhesive or sealant to the wood surface. Goop applied to the wood surface was allowed to free-air dwell for about one minute before proceeding to bond to a test substrate. After application of the adhesive to the wood surface, 10 mil glass beads were deposited onto the adhesive surface to maintain a constant 10 mil gap between bonded materials. The test substrate material was placed on the treated wood sample to make a 1 -inch square bond between the two substrates and the substrates were clamped together to maintain pressure throughout the curing process.

[0043] After at least one week at ambient temperature, the lap shear samples were evaluated for bond strength by measuring the force required for normal separation at 0.057minute with an MTS testing machine. Bond destruction was obtained for each lap shear assembly tested, and the failure mechanism, adhesive, cohesive, or substrate, was noted for each sample. Adhesive failure occurs when the adhesive fails to adhere to one of the substrates and remains on the other substrate surface. Cohesive failure occurs when the adhesive comes apart at the adhesive line between substrates such that adhesive remains on each substrate surface. Substrate failure occurs when the adhesive bond strength between substrates is stronger than the substrate, and the substrate breaks but the adhesive bond remains intact. The results are shown in Table 3.

Table 3 - Lap Shear Bonding Results

Bond Type

Wood to:

Product Al CRS ABS PC TPO

Gorilla Glue CS.'S.C c.s/s.c C'CS A,S,C/A,S A/A,C

5 Epoxy S/S A.S/S.A A/A A.S/A A/A

Liquid Nails A.C/A.C S/A.C A/A

Goop A/A A/A S,A/S,C S,A/S,A

PU Sealant C,A/A A.S/A A.S/A A/A

Si Sealant A/A.S A/A A/A A/A,C

Shading Significantly greater bonding results with EM PA, 95% Key: confidence interval

Insignificant difference in bonding strength with & without EMPA, 95% confidence interval

Bond Failures: S = Substrate, C = Cohesive, A = Adhesive

Strike "/"Script: without/with EMPA

C,S = Cohesive (majority), Substrate (minority)

A,S/A = Mostly Adhesive failure, some substrate without

EMPA/Adhesive failure with EMPA [0044] Shading indicates statistically significant bonding improvement with the addition of EMPA. Significantly different results between the test adhesive with the epichlorohydrin adhesion promoter and without were assessed using the Student's t test: Two Sample Assuming Equal Variances analysis of the 2013 Excel Data Analysis platform. Significance was taken at the 95% level (one-tail distribution). The results in Table 3 show that the addition of the epichlorohydrin phosphate ester adhesion promoter provided significant bonding strength improvement to Gorilla Glue when bonded to aluminum and ABS, to Liquid Nails when bonded to ABS and TPO, to Goop when bonded to PTO, to polyurethane sealant when bonded to ABS, and to silicone sealant when bonded to CRS. These results demonstrate that the adhesion promoter of the present technology can improve the adhesion of some adhesives and sealants to different substrates, including difficult-to-stick-to substrates, such as plastics and untreated aluminum.

[0045] The present technology is now described in such full, clear and concise terms as to enable a person skilled in the art to which it pertains, to practice the same. It is to be understood that the foregoing describes preferred embodiments of the present technology and that modifications may be made therein without departing from the spirit or scope of the present technology as set forth in the appended claims. Further, the examples are provided to not be exhaustive but illustrative of several embodiments that fall within the scope of the claims.