JP2012162717A - Modified epoxide primer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a primer composition that shows improved hardness, adhesion, and mechanical properties.SOLUTION: Telechelic resins with reactive end groups (e.g., epoxy phosphate and epoxy ester) are synthesized using bisphenol-A (BPA) epoxide. The bisphenol-A based epoxide and the telechelic resins are all modified with tetraethylorthosilicate (TEOS) oligomers to produce epoxide/polysilicate (organic/inorganic) hybrid systems. The modified epoxides are thermally cured with a melamine-formaldehyde resin, cast on steel substrates. Salt spray analysis has revealed that the inorganically modified epoxides provide improvement over unmodified epoxide resins with respect to both corrosion resistance and adhesion to steel substrates.

Description

REFERENCE TO RELATED APPLICATIONS This application claims priority from US Provisional Application No. 61 / 388,665, filed Oct. 1, 2010, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION This invention relates to modified epoxide primers, and in particular to such primers modified with tetraethylorthosilicate oligomers.

BACKGROUND OF THE INVENTION Organic / inorganic hybrid materials have received much attention for over two decades because hybrid materials synergistically combine the advantageous properties of both materials [1, 2]. Hybrid materials offer unique properties such as improved physical properties, mechanical properties, thermal properties, gas barrier properties and photon properties [3-7]. Various elastomers, thermoplastics and cross-linking systems have been modified in situ with inorganic materials [8-10]. Hybrid materials have the characteristics of inorganic materials, ie, hardness, durability and thermal stability, and the characteristics of organic materials, ie, flexibility and toughness. As a result, such hybrids are promising materials for various applications such as solid state lasers, silicon dioxide alternatives as insulating materials in the microelectronics industry, contact lenses or host materials for chemical sensors [11-14. ].

  In coating science, improvements in corrosion protection, impact, chemicals, tamper resistance, antifouling, appearance, flexibility and impermeability have also been made by applying inorganic / organic hybrid coating systems [15 ~ 18]. In hybrids, sol-gel technology of alkoxysilanes is one useful method for preparing inorganic / organic hybrid materials because the reaction can proceed in solution at ambient temperature. The general sol-gel reaction scheme is based on the hydrolysis of various alkoxides to form the respective silanols [19]. Thereafter, the condensation reaction that occurs between silanols or between silanols and alkoxides follows. The organic component of an inorganic-organic hybrid is generally the same as the synthesis of two independent (non-covalent) polymer networks (organic / inorganic) or of a matrix where the covalent bond binds the organic and inorganic components. Can be generated by any of the formations [20, 21]. Organic monomers or polymers modified with alkoxysilane groups are used as coupling agents that provide bonds to the in situ generated inorganic structures. Strong interactions between the organic and inorganic phases have been found to improve the mechanical properties of the hybrid [20, 22, 23].

  Silicon sol-gel technology has been widely used to prevent metal corrosion and improve coating adhesion [24-27]. Holmes-Farley and Yanyo [28] used tetraethoxysilane (TEOS) in combination with an aminosilane adhesion promoter to prevent corrosion on aluminum substrates. Soucek et al. [29, 30] studied polyurea and polyurethane organic / inorganic films using various sol-gel precursors such as organofunctional alkoxysilanes. Polyurethane / polysiloxanes were developed as “Unicoat” systems [31-33]. In this system, polyurethane provides general mechanical properties as both a primer and a topcoat, and polysiloxane functions as an adhesion promoter and corrosion inhibitor. The ceramer film exhibited improved adhesion and corrosion resistance due to a self-assembled phase separation mechanism. Corrosion resistance is comparable to chromate pretreatment systems, so a portion of the research body was directed to chromate replacement. For organic / inorganic hybrid coatings, the mixing of dry oil and sol-gel precursors using an approach developed by Soucek and its collaborators was also reported [34, 35]. The resulting hybrid coating showed improved hardness and adhesion with increasing sol-gel precursor content.

  There have been several reports so far on the preparation of epoxide resin / silica hybrids. Several researchers [36-38] have investigated the well-defined dimensions of epoxide resin-montmorillonite hybrids and clay layers using an intercalation process. Landry et al. [39] prepared a hybrid material from a very high molecular weight epoxide functionalized with γ-aminopropyltriethoxysilane and silica. Hussain et al. [40] reported the preparation of a hybrid material based on an epoxy resin / silica system using tetraglycidyl-meta-xylene-diamine as the resin. In their work, silica fillers were produced using a sol-gel method and then incorporated into an epoxy resin mixture to prepare hybrids. The epoxide-silica interpenetrating network (IPN) was investigated by Bauer et al. [41] and modeled by Matejka et al. [42, 43]. The hybrid system consists of an inorganic silica structure formed by a sol-gel process from an organic rubbery network and tetraethoxysilane.

  Epoxides, especially bisphenol-A (BPA) type epoxides, have been the choice of primers for metals since it was introduced into the commercial market. Epoxide primers have excellent adhesion to metals due to secondary hydroxyl groups within the repeat unit [44]. Epoxides are also notable for hardness, hydrophobicity and chemical resistance due to the BPA group. Overall properties, evaluation and comparison of corrosion performance and adhesion for low molecular weight epoxide derivative / tetraethoxysilane oligomer hybrid systems have not yet been reported.

SUMMARY OF THE INVENTION Telechelic resins (epoxy phosphates and epoxy esters) having reactive end groups were synthesized using bisphenol-A (BPA) epoxide. The epoxides, epoxy phosphates and epoxy esters based on Bosphenol-A were all modified with tetraethylorthosilicate (TEOS) oligomers, which were prepared by hydrolysis and condensation of TEOS monomers with water under acidic conditions. Epoxide / polysilicate (organic / inorganic) hybrid systems are Fourier Transform Infrared Spectroscopy (FTIR), ¹ H, ¹³ C, ³¹ P and ²⁹ Si Nuclear Magnetic Resonance (NMR) and Matrix Assisted Laser Desorption / Ionization-Time of Flight Characterization was comprehensively performed using scanning mass spectrometry (MALDI-TOF). The modified epoxide was heat cured with melamine-formaldehyde resin cast on a steel substrate. The coating properties of the modified epoxide were evaluated by pencil hardness, cross-hatch adhesion, reverse and direct impact resistance, mandrel bending and pull-off adhesion. The viscoelastic properties of the hybrid system were also evaluated as a function of polysilicate content. Corrosion performance was evaluated by a 264 hour salt spray (fog) test. Salt spray analysis showed that the inorganic modified epoxide was improved over the unmodified epoxide resin in terms of both corrosion resistance and adhesion to steel substrates.

Brief Description of Drawings
FIG. 1 is a schematic diagram of the chemical structure of a) an epoxide resin based on BPA, b) an epoxy phosphate and c) an epoxy ester.

FIG. 2 is a schematic diagram of the chemical structure shown in FIG. 1 of a) epoxide resin based on BPA, b) epoxy phosphate and c) epoxy ester modified with TEOS oligomer.

FIG. 3 is an FTIR spectrum of an epoxy phosphate based on bisphenol-A.

FIG. 4 is an FTIR spectrum of epoxides and epoxy esters based on bisphenol-A.

FIG. 5 is a mass spectrum of TEOS oligomer-modified epoxy phosphate.

FIG. 6 is a schematic view of a crosslinking reaction between a melamine formaldehyde resin and an —OH functional group of an epoxide resin.

FIG. 7 shows an epoxy / TEOS hybrid coating (0% (E0), 2.5% (E2.5), 5% (E5), 7.5% (E7.5) and 10% (E10) TEOS). FIG. 2 is a graph of viscoelastic properties as a function of temperature at: storage modulus (a) and tan δ (b).

FIG. 8 shows an epoxy phosphate / TEOS hybrid coating (0% (EP0), 2.5% (EO2.5), 5% (EP5), 7.5% (EP7.5) and 10% (EP10) TEOS. FIG. 2 is a graph of viscoelastic properties as a function of temperature in :) (a) storage modulus and (b) tan δ.

FIG. 9 shows epoxy ester / TEOS hybrid coatings (0% (EE0), 2.5% (EE2.5), 5% (EE5), 7.5% (EE7.5) and 10% (EE10) TEOS. Viscoelastic properties as a function of temperature in): storage elastic modulus (a) and tan δ.

FIG. 10 shows the epoxide / TEOS hybrid coating (E0 = 0%, E2.5 = 2.5%, E5 = 5%, E7.5 = 7.5% and 96 hours and 264 hours after salt spray exposure). FIG. 3 is a series of optical images of an untreated steel substrate coated with (E10 = 10% TEOS oligomer).

FIG. 11 shows the epoxy phosphate / TEOS hybrid coating (EP0 = 0%, EP2.5 = 2.5%, EP5 = 5%, EP7.5 = 7.5% after 96 and 264 hours salt spray exposure. And EP10 = 10% TEOS oligomer), a series of optical images of an untreated steel substrate.

FIG. 12 shows the epoxy ester / TEOS hybrid coating (EE0 = 0%, EE2.5 = 2.5%, EE5 = 5%, EE7.5 = 7.5% after 96 and 264 hours salt spray exposure. And EE10 = 10% TEOS oligomer), a series of optical images of an untreated steel substrate.

FIG. 13 is a schematic diagram of the proposed mechanism for interaction between a hybrid coating and a steel substrate according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention discloses a modified primer composition that provides improved corrosion resistance to a coated substrate and a method for making the modified primer composition. Thus, the present invention has utility as a primer and / or basecoat layer for protective coatings and aesthetically pleasing coatings.

  The modified primer composition can include a telechelic resin and an alkoxide oligomer. The telechelic resin can be an epoxide with reactive end groups and may or may not have at least two phenol functional groups. The epoxide can be a alicyclic epoxide such as bisphenol-A (BPA) epoxide or an acrylic alicyclic epoxide. The reactive end group can comprise at least one hydroxide group.

  In some cases, the telechelic resin having reactive end groups is an epoxy phosphate, an epoxy ester or an epoxy molybdate. Further, the alkoxide oligomer can be a metal alkoxide oligomer or an alkoxysilane oligomer, such as tetraethylorthosilicate oligomer (TEOS), tetramethylorthosilicate oligomer (TMOS), and the like.

  The modified primer can be used to coat metals and / or alloys, including illustratively uncoated steel, galvanized steel, aluminum alloys, and the like. Furthermore, the modified primer can be used as a base coat for a self-layered coating.

  To better illustrate, but without limiting the scope of the invention, exemplary modified primer compositions and methods of making modified primer compositions are provided below.

Materials Telechelic resins (epoxy phosphates and epoxy esters) with reactive end groups were synthesized using bisphenol-A (BPA) epoxide. Epoxides, epoxy phosphates and epoxy esters based on bisphenol-A have all been modified with tetraethylorthosilicate (TEOS) oligomers, which were prepared by hydrolysis and condensation of TEOS monomers with water under acidic conditions. Epoxide / polysilicate (organic / inorganic) hybrid systems are Fourier Transform Infrared Spectroscopy (FTIR), ¹ H, ¹³ C, ³¹ P and ²⁹ Si Nuclear Magnetic Resonance (NMR) and Matrix Assisted Laser Desorption / Ionization-Time of Flight Characterization was comprehensively performed using scanning mass spectrometry (MALDI-TOF). The modified epoxide was heat cured with melamine-formaldehyde resin cast on a steel substrate. The coating properties of the modified epoxide were evaluated by pencil hardness, cross-hatch adhesion, reverse and direct impact resistance, mandrel bending and pull-off adhesion. The viscoelastic properties of the hybrid system were also evaluated as a function of polysilicate content. Corrosion performance was evaluated by a 264 hour salt spray (fog) test. Salt spray analysis showed that the inorganic modified epoxide was improved over the unmodified epoxide in terms of both corrosion resistance and adhesion to steel substrates.

A liquid epoxide based on bisphenol-A (BPA) (trade name: DER317) was obtained from Dow Chemicals. A Pamolyn 380 mixture of fatty acids (70 wt% conjugated linoleic acid with the remainder being oleic acid and non-conjugated linoleic acid) was obtained from Eastman Chemical Company. Tetraethoxysilane (TEOS), phosphoric acid (ACS reagent, ≧ 99.0%), hydrochloric acid (37 wt% in water), ethanol, p-xylene (puriss.pa ≧ 99.0%), diethylene glycol butyl ether (puriss.pa ≧ 99.2%) and dibutyltin oxide were purchased from Aldrich Chemical Company. Methanol-etherified melamine formaldehyde resin (trade name: Luwipal 072) was obtained from BASF Corporation. Plain steel (0.020 inch thick) substrates were purchased from The Q-Panel Company. All materials were used as received. The chemical structure of the material is shown in Table 1.

Epoxide Equivalent Determination Epoxide equivalent weight was determined according to ASTM D1652-97. Liquid epoxide resin (DER317, 0.3 g) was placed in a 250 mL Erlenmeyer flask. Methylene chloride (30 mL) was also added to the flask to dissolve the resin. Tetraethylammonium bromide (3.75 g) was dissolved in glacial acetic acid (15 mL) and the solution was mixed with the epoxide using a magnetic stirrer. A few drops of phenolphthalein solution (0.1 wt% in methanol) was added as an indicator. Titration was performed with a perchloric acid solution (0.1N in glacial acetic acid). The epoxide equivalent weight was calculated using the following formula.
EEW = W × 1000 / V × N (1)
Where W is the mass (g) of epoxide, V is the amount of 0.1N perchloric acid solution (mL) used to titrate the sample, and N is the perchloric acid solution Normality). The equivalent of epoxide was calculated to be 192 g / eq. After EEW determination, n was calculated to be 0.155 based on the chemical structure of the liquid epoxide resin listed in Table 1.

Synthesis of Epoxyphosphate (EP) Based on BPA Based on the epoxide resin, 1 wt% phosphoric acid (1 g, 0.0102 mol) was dissolved in diethylene glycol butyl ether (9.67 g, 0.0596 mol, 10 mL). . The solution was added dropwise to a four neck round bottom flask (500 mL) containing epoxide resin (DER317, 100 g) while the mixture was mechanically stirred. The reaction was carried out at 150 ° C. for 1 hour. 2 wt% (based on epoxy resin) of distilled water (2.00 g, 0.111 mol) was then added to the hot mixture and stirred at 150 ° C. for 2 hours. The number average molecular weight (Mn) obtained by gel permeation chromatography (GPC) was 543, and the polydispersity was 1.48. ³¹ P NMR shows a singlet at 108.2 ppm assigned to the phosphorus of the C—O—P group. The ¹ H and ¹³ C NMR resonance assignments of the epoxy phosphate are shown in Table 2.

Fatty Acid Equivalent Determination Fatty acid (Pamolyn 380, 2 g) was dissolved in high purity grade acetone (39.25 g, 50 mL) in a 250 mL Erlenmeyer flask. 3-4 drops of phenolphthalein solution (0.1 wt% in methanol) was added as an indicator. The solution was then titrated with KOH solution (0.1N in methanol). Fatty acid equivalents were determined by the following formula:
E _FA = W × 1000 / (B−V) × N (2)
(W is the mass of fatty acid (g), B is the amount of 0.1N KOH solution used in the blank test (mL), and V is the amount used to titrate the sample. 1N KOH amount (mL) and N is the normality of the KOH solution). The equivalent weight of fatty acid was determined to be 321 g / eq.

Synthesis of BPA-based epoxy ester (EE) The esterification reaction was performed in a 500 mL four-necked round bottom flask placed in a heating mantle connected to a temperature controller. The reaction flask was equipped with a thermometer, mechanical stirrer, nitrogen gas inlet, Dean-Stark trap and reflux condenser. Liquid epoxide resin (DER317, Mn = 356, polydispersity 1.03, E _E = 192 g / eq), fatty acid (Pamolyn 380, E _FA = 321 g / eq) and 1: 1 epoxide group / fatty acid group The reaction was based on the equivalence ratio. Therefore, epoxide resin (100 g), fatty acid (167 g), xylene (10.68 g, 0.1008 mol, 4 wt% based on the total amount of epoxide and fatty acid) and catalyst dibutyltin oxide (0.8010 g, 0.0032 mol) , 0.3 wt% based on the total amount of epoxide and fatty acid) was charged to the reaction flask. The reaction mixture was slowly heated to 210 ° C. and maintained at that temperature for 6 hours until the acid number was 5 mg KOH / g (ASTM D1639-90). The number average molecular weight (Mn) was measured to be 1528 and the polydispersity was 1.42. The ¹ H and ¹³ C NMR resonance assignments of the epoxy esters are shown in Table 3.

Preparation of TEOS oligomer and TEOS oligomer modified epoxide Tetraethylorthosilicate (TEOS, 100 g, 0.48 mol) was dissolved in ethanol (88.32 g, 1.92 mol) in a round bottom flask (250 mL) and then distilled. Water (8.64 g, 0.48 mol) was added into the mixture. After the water was dispersed, hydrochloric acid (0.175 g, 0.0048 mol) was added dropwise while the mixture was mechanically stirred. The reaction was run at ambient temperature for 96 hours. Unreacted residue in the mixture was removed using a rotary evaporator at 50 ° C. to provide a TEOS oligomer (77.23% yield based on TEOS). The product was characterized by ¹ H and ²⁹ Si NMR, FTIR and ESI-MS. Later, commercially available epoxide, synthesized phosphorylated epoxy and synthesized epoxy ester were all mixed with TEOS oligomer solution in various mass ratios (2.5 wt%, 5 wt%, 7.5 wt% and 10 wt% based on total solution) And stirred for 72 hours under acidic conditions at 40 ° C. to produce the corresponding hybrid system before mixing with the crosslinker. The ¹ H and ¹³ C NMR resonance assignments of TEOS oligomer modified epoxy phosphates and epoxy esters are shown in Table 4.

Film Preparation and Coating Test Film formation was performed by crosslinking the epoxy derivative with a melamine formaldehyde (MF) resin based on a 2: 1 equivalent ratio of methoxy groups in MF resin / hydroxy groups in epoxide. The equivalent of MF resin was 80 g / eq and was obtained from the presence of dimers, trimers and higher oligomers [45]. P-Toluenesulfonic acid monohydrate, 1 wt% MF resin as a strong acid catalyst was added to the formulation. The mixture was stirred for 1 hour, after which a thin film was cast on a steel panel with a draw down bar at a wet thickness of 125 μm. The wet film was placed in a dry environment without dust for 24 hours at room temperature and heat cured at 120 ° C. for 1 hour. Film is used for salt spray (fog) test (ASTM B117), pencil hardness (ASTM D3363), crosshatch adhesion (ASTM D3359), pull-off adhesion (ASTM D4541), impact resistance (ASTM D2794), mandrel Used for coating tests such as bending test (ASTM D522-93) and solvent (MEK) resistance (ASTM D4752). The dry film thickness was usually 50-80 μm. All films were stored for 7 days prior to testing.

  The name developed to represent the hybrid system in this study focuses on the type of epoxide and the concentration of TEOS in the composition. Specifics consist of terms and numbers. The first term “E”, “EP” or “EE” defines epoxide, epoxide phosphate or epoxide ester, respectively. The second term (0, 2.5, 5, 7.5 or 10) specifies the alkoxysilane present in the coating. The number quantifies the mass fraction of TEOS relative to the total composition.

Instrument Fourier transform infrared (FTIR) spectroscopy was performed by scanning 32 times at 4000-400 cm ⁻¹ with a Thermo Scientific Nicolet 380 FTIR using diamond crystal UATR. ¹ H NMR, ¹³ C NMR and ³¹ P NMR spectra were recorded on a Gemini-300 MHz spectrometer (Varian) in chloroform-d as solvent. ²⁹ Si NMR spectra were recorded on a Gemini-400 MHz spectrometer (Varian) in chloroform-d as solvent. The chemical shift of the ²⁹ Si-NMR spectrum was determined relative to a tetramethylsilane (TMS) reference standard.

  Gel permeation chromatography was performed using a Waters Breeze GPC instrument consisting of a uniform concentration HPLC pump, a refractive index detector and three styragel HR series columns; a column set consisting of HR1, HR2 and HR3. The instrument was calibrated using polystyrene (PS) standards. Samples were prepared in distilled tetrahydrofuran (THF) to obtain a 1% (v / v) concentration. The solution was filtered over a 0.45 μm membrane syringe filter and 200 μL was injected into the chromatograph at room temperature with an effluent flow rate of 1.0 mL / min.

  Bruker REFLEX-III time-of-flight matrix-assisted laser desorption ionization mass spectrometer equipped with LSI model VSL-337ND pulsed nitrogen laser (337nm, 3nm pulse width), two-stage gridless reflector and single-stage pulsed ion extraction source (Bruker Using Daltonics, Bi11erica, MA), mass spectral experiments were conducted to help determine the chemical structure of the copolymer. Separate THF (amorphous, ≧ 99.9; Aldrich) solution of dithranol matrix (20 mg / mL) (> 97%; Alfa Aesar), sodium trifluoroacetate (10 mg / mL) (> 98%; Aldrich ) And copolymer (10 mg / mL) in a matrix: cationized salt: copolymer (10: 1: 2) ratio and 0.5 μL of the resulting mixture was introduced onto a MALDI target plate. Spectra were acquired in reflectron mode. The nitrogen laser attenuation was adjusted to minimize undesired copolymer fragmentation and maximize sensitivity. Mass scale calibration was performed externally using a poly (methyl methacrylate) standard (Fluka) having the same molecular weight as the sample.

Viscoelastic properties were measured with a dynamic mechanical thermal analyzer (Perkin Elmer Instruments, Pyris Diamond DMTA) using a frequency of 1 Hz in tensile mode and a heating rate of 3 ° C./min over a range of −50 to 200 ° C. During the measurement, it was circulated in the DMTA furnace with an N ₂ flow rate set at 40 psi. The gap distance was set at 2 mm for a rectangular test sample (length 15 mm, width 8 to 10 mm, and thickness 0.05 to 0.08 mm). The reproducibility of DMTA data was confirmed by scanning multiple times over a useful temperature range.

A pull-off adhesion test for the coating was performed using an Elcometer 106 adhesion tester. Three aluminum pull stubs (dolly) were bonded to each test panel using a commercially available two-part epoxy adhesive. The adhesive was cured for 24 hours before testing. The tester imposed a true axial tensile stress as the stub was pulled and measured quantitatively the bond strength between the coating and the test surface. The average bond strength obtained from the three dollies was reported as lbf / in ² .

  A salt spray test [46] was performed according to ASTM B117. The coated steel panel is scored through the coating in a standard fashion, exposing the bare substrate and suspended in a salt spray chamber where the panel is exposed to a 5% NaCl solution mist by an atomizer with a nozzle pressure of 10-12 psi. did. During the test, the chamber was hermetically sealed. The temperature and relative humidity inside the chamber was maintained at 35 ± 2 ° C. and 99 ± 1% over a test time of 264 hours. The condition of the coated panel was periodically examined closely by visual inspection for surface changes. Uncreased areas were examined for blistering, and the creased portion was observed to see how far away from the crease marks the coating was peeled off or lost adhesion. Digital images of the coated panels were taken at 96 and 264 hour intervals.

Commercially available BPA-based epoxides were chemically modified with three different chemical groups: fatty acids, phosphoric acid and TEOS oligomers. Tetraethylorthosilicate (TEOS) oligomers were prepared by hydrolysis and condensation of TEOS with water under acidic conditions. Organic / inorganic hybrid systems were characterized using FTIR spectroscopy, ¹ H, ¹³ C, ³¹ P and ²⁹ Si-NMR and mass spectroscopy. Corrosion resistance was determined by subjecting the coating to a salt spray (fog) test. Coating properties were evaluated prior to 264 hours salt spray exposure. The viscoelastic properties of the film were examined as a function of TEOS oligomer content.

Preparation and depiction of organic / inorganic hybrid systems Epoxide resins based on bisphenol-A were modified with phosphoric acid and fatty acids to give epoxy phosphates and epoxy esters, respectively. The chemical structure of the epoxy derivative is shown in FIG.

A covalent bond between the inorganic and organic networks can be formed by reaction of the silanol groups of the hydrolyzed tetraethoxysilane clusters with the pendant hydroxyl groups in the CH ₂ CH (OH) CH ₂ O segment of the epoxide. Inorganic structures grafted to epoxy derivatives can exist in different forms as cyclic and / or linear polysilicates. FIG. 2 shows an inorganic modified epoxide network structure.

Structural Properties of Epoxide Derivatives The room temperature FTIR transmission spectrum (FIG. 3) supports the structure of epoxy phosphate (EP) based on bisphenol-A in all respects. The very broad absorption peak in the range of 3200-3700 cm ⁻¹ is attributed to OH stretching resulting from pendant hydroxyl groups in the phosphorylated epoxide structure. All C—H stretch bands above 3000 cm ⁻¹ are caused by aromatic C—H stretch. For this reason, the two closely spaced absorption bands at 3057 and 3036 cm ⁻¹ are assigned to asymmetric and symmetric aromatic CH stretching vibrations in the oxirane ring (epoxide group) and the benzene ring of bisphenol-A. The three distinct bands occurring at 2967, 2928 and 2871 cm ⁻¹ are due to asymmetric and symmetric C—H stretching modes of several methyl (CH ₃ ) and methylene (CH ₂ ) groups in the structure. It is assigned to the double absorption band P—OH stretching vibration around 2350 cm ⁻¹ [47]. Weak combinations and overtone bands appear in the 1650-2100 cm ⁻¹ region (not shown, using axial breaks in FIG. 3).

Three strong bands at 1610, 1580 and 1506 cm ⁻¹ can be attributed to aromatic C═C and C—C stretching of the benzene ring in the structure. The absorption bands at 1454 and 1362 cm ⁻¹ are the out-of-phase (asymmetric) and in-phase (symmetric) bending vibrations of the C—H bond in the methyl (CH ₃ ) group, respectively. Is due to. The absorption band at 1383 cm ⁻¹ is attributed to the CH scissor vibration of the methylene (CH ₂ ) group. The intensity of the band produced by the symmetric bending of the methyl C—H bond is greater than that of the asymmetric methyl bending vibration or methylene scissor vibration. Methylene torsional vibration and longitudinal torsional vibration are observed in the 1350-1150 cm ⁻¹ region. Strong bands in the 1260-1200 cm ⁻¹ region are asymmetric C—O—C stretching vibrations in the 1,2-oxirane or benzene rings and P═O stretching of phosphate units. The shoulder at 1160 cm ⁻¹ is assigned to the vibration mode of PO bond [48].

The band at 1035 cm ⁻¹ is attributed to symmetrical C—O—C stretching vibrations in the epoxy and benzene rings. The two distinct bands that occur at 971 cm ⁻¹ and 914 cm ⁻¹ are due to out-of-plane C—H bending (torsion) vibrations of methyl and methylene groups in the structure. On the other hand, aromatic out-of-plane C—H bending vibrations in the structure appear at 831 cm ⁻¹ and 775 cm ⁻¹ . As a result, modification of BPA-based epoxides with phosphoric acid results in small vibrations and slightly increases the intensity and / or width of various bands associated with phosphorus atoms.

FIG. 4 shows the FTIR spectrum of the epoxide resin based on bisphenol-A and the synthesized epoxy ester. The OH stretch band in the 3200-3600 cm ⁻¹ range is much wider and sharper in the infrared spectrum of the epoxy ester than the corresponding band observed in the epoxide spectrum. The increase in strength and width is due to the higher hydroxyl functionalization in the epoxy ester structure. The two absorption bands at 3047 and 3029 cm ⁻¹ in the epoxide are assigned to the aromatic C—H stretching vibration. However, due to the fact that the 1,2-oxirane ring opens to react with fatty acids during the esterification reaction, a single absorption band appears around 3010 cm ^{−1 in} the spectrum of the epoxy ester. This can cause the epoxy ester to lose the strength of ring stretching vibration. The C—H stretching modes of the methyl (CH ₃ ) and methylene (CH ₂ ) groups appear as three distinct bands occurring at 2970, 2921 and 2867 cm ⁻¹ in the infrared spectrum of bisphenol A-based epoxides. On the other hand, the epoxy ester exhibits two absorption bands occurring at 2918 and 2852 cm ^{−1 in the} same region. 4, to avoid a large blank wave number region of 2500～1800Cm ^-1, and to extend the low wavenumber region 1800～500Cm ^-1, using a shaft fracture x- axis of the spectrum.

A strong C═O stretch absorption band has a high intensity at a relatively constant position at 1737 cm ⁻¹ and is easily recognized in the spectrum of epoxy esters. Three bands attributed to the aromatic C = C and C-C stretch are observed at 1608, 1581 and 1508 cm ⁻¹ for the epoxy ester. The positions of these stretch frequencies remain nearly constant for the epoxy resin and occur at 1604, 1579 and 1504 cm ⁻¹ . 1460,1377 in epoxy ester and 1359cm ^-1 and the absorption at 1452,1382 and 1361cm ^-1 in the epoxide resin, respectively, an asymmetrical vibration of C-H bond in the methyl group, C-H scissor vibration of methylene group And the symmetric vibration of the C—H bond of the methyl group.

A strong band generated by methylene shaking vibration in which all methylene groups in the epoxy ester structure are oscillated synchronously appears as a single term at 723 cm ⁻¹ . Symmetric expansion and contraction of the epoxy ring occurs around 1250 cm ⁻¹ . Another band attributed to asymmetric epoxy ring stretching in which the C—C bond extends during C—O bond contraction appears at 825 cm ⁻¹ [49]. A third band associated with the epoxy ring appears only in the spectrum of the epoxide resin around 750 cm ⁻¹ .

In the low wavenumber region (600-1500 cm ⁻¹ ) of the FTIR spectrum of the TEOS oligomer-modified epoxy derivative, the intensity of the absorption band at 1000-1110 cm ⁻¹ is due to Si—O—C (aliphatic) and Si—O—Si stretching. Increase [50]. Two strong absorption bands appear at 1107 and 1080 cm ⁻¹ in the FTIR spectrum of inorganic modified phosphorylated epoxides, and similarly, the two closely spaced absorption bands occurring at 1099 and 1081 cm ⁻¹ are of inorganic modified epoxy esters. Observed in the infrared spectrum. Further, the O—H stretching vibration of the Si—OH group is absorbed in the region 3700-3200 cm ⁻¹ . The absorption characteristics in that region depend on the degree of hydrogen bonding. Therefore, the intensity and width of the absorption band around 3500 cm ⁻¹ increase significantly after the epoxy derivative is modified with TEOS oligomers. As previously reported by Soucek et al. [29], spectroscopic characterization of TEOS oligomers was performed using ¹ H NMR, ²⁹ Si NMR and ESI-MS.

The chemical shifts of the ¹ H and ¹³ C NMR (CDCl ₃ ) spectra of the TEOS oligomer modified epoxy phosphate are summarized in Table 4. ²⁹ Si NMR showed a singlet at δ-81.6 ppm assigned to the Si—O—C (aliphatic) group and a doublet at −88.6 ppm. Resonance differences can be attributed to substitution of adjacent silicon atoms. Two singlets at δ-91.2 ppm and -96.0 ppm also appear in the spectrum and are attributed to the Si—O—Si bond in the linear or cyclic polysilicate attached to the epoxy phosphate.

The TEOS oligomer modified epoxy phosphate was further analyzed by MALDI-TOF spectroscopy shown in FIG. The observed ions are generated by sodium bound to the existing species. For example, the structure corresponding to 1141 Da results from sodium (23 Da) cationization of cyclic Si ₃ O ₃ (OEt) ₆ grafted epoxy phosphate. Cyclic Si ₃ O ₃ (OEt) ₆ ([M] = 134n) is 402 Da, and the inorganic modified epoxy phosphate loses cyclic trisilicate units from m / z = 1141 to m / z = 739. Another distribution corresponding to denaturation with linear trisilicate ([M] = 74 + 134n) also appears in the spectrum, showing a peak at 665 Da. The chemical species associated with 1195 Da ions and 1061 Da are correlated to each other by the monocyclic structure SiO (OEt) ₂ (134 Da) units. On the other hand, the peak at 987 Da correlates with the chemical species observed at 1195 Da due to the addition of linear Si (OEt) ₄ silicate (208 Da).

Preparation of Thermosetting Epoxy Derivatives The main cross-linking reaction between the unmodified epoxy resin and the melamine formaldehyde resin is described in FIG. 6 and shows how the hydroxyl groups in the epoxide repeat unit react with melamine. After the unmodified epoxy derivative and the chemically modified epoxy derivative were all crosslinked with a curing agent, general coating tests and dynamic mechanical thermal properties and corrosion resistance were evaluated.

Viscoelastic properties The viscoelastic properties of the hybrid network were investigated using a dynamic mechanical thermal analyzer (DMTA). 7a and 7b show the storage modulus and loss factor tan δ of the epoxy (E) hybrid network as a function of temperature, respectively. FIG. 7a is referred to as a semilogarithmic graph. Since the storage modulus data spans several orders of magnitude, the distribution of values in FIG. 7a is more clearly identified by replacing the linear y scale with a log y scale. In order to increase the rubber elastic flat area of the graph, axial breaks are placed along both axes without omitting any data points. The most noticeable decrease in tan δ maximum is observed with epoxide E10 containing 10% TEOS, while epoxide E2.5 containing 2.5% TEOS shows only a gradual decrease. The storage modulus (FIG. 7a) decreases slightly until the film reaches a temperature of 50 ° C. and decreases significantly at 50-110 ° C. Above 110 ° C., the storage modulus is minimal for all epoxy hybrid films. The height of the tan δ peak decreases with increasing degree of cure and the peak becomes broad.

  The storage modulus and loss factor tan δ of the epoxy phosphate-TEOS oligomer hybrid network are shown in FIGS. 8a and 8b, respectively. In FIG. 8a, the storage modulus (E ′) of the epoxy phosphate (EP) hybrid film again shows a downward trend until the temperature reaches 40 ° C. For the phosphorylated epoxy hybrid network, the value of E 'decreases dramatically at a temperature of 40-90 ° C and shows a minimum value at a temperature very close to 90 ° C or higher.

  9a and 9b show the storage modulus (E ′) and loss factor tan δ of the epoxy ester (EE) / TEOS hybrid system. In FIG. 9a, the storage elastic modulus (E ′) shows a slight decreasing tendency until the temperature reaches 0 ° C. From 0 ° C. to 60 ° C., E ′ decreases dramatically for epoxy ester (EE) / TEOS oligomer hybrid films. An increase in the storage modulus of the epoxy ester hybrid network is accompanied by a change in the loss factor tan δ. The tan δ α-transition, located at about 29 ° C., corresponds to the glass transition of the neat epoxy ester network, which decreases and broadens with the epoxy ester-TEOS oligomer hybrid, which is typical for most composite systems. [51].

  The reduction in loss maximum height shown in FIG. 9b is directly proportional to the TEOS concentration. The glass transition temperature of the cured film also increases with the TEOS content in the hybrid film. None of the hybrid systems show a new decay peak at higher temperatures, which is evidence that no macrophase separation has occurred in the epoxy derivative-TEOS hybrid system. In other words, it promotes a uniform system without major separation or clustering of inorganic regions in the film.

Figures 8a and 9a are also referred to as semi-logarithms. In both graphs, data points were not omitted, and for a clear comparison on the graph, axial breaks were placed on the x-axis and y-axis so that the difference between the minimum storage modulus of the film could be observed. . The crosslink density of the film was calculated by an equation derived from the theory of rubber elasticity [52]. Table 5 summarizes the viscoelastic properties of epoxy, epoxy ester and epoxy phosphate hybrid films: minimum storage modulus (E'min), crosslink density (γc), maximum tan δ, glass transition temperature (Tg) and tan δ transition width. To do.

In the epoxide (E) system, a significant increase in glass transition temperature from 84 ° C. to 91 ° C. is observed with 2.5% TEOS oligomer modification of the epoxy resin on a mass basis. As the inorganic content increases, the loss factor decreases while the crosslink density increases. For the epoxy ester (EE) series, the highest percentage (10%) inorganic content in the hybrid film showed the highest crosslink density, which was calculated to be 1180 mol / m ³ . A decrease in glass transition temperature is also observed in epoxy phosphate (EP) films (around Tg 60 ° C.).

Coating Properties and Corrosion Performance Table 6 shows the film properties of various TEOS modified epoxy hybrids cured with MF resin. Most coating formulations showed the same pencil height (5H) and crosshatch adhesion (5B) behavior. In order to obtain more accurate results with respect to adhesion properties, a pull-off adhesion test was performed. The TEOS modification of the epoxide resulted in an increase in pull-off adhesion from 50% with 2.5 wt% TEOS to> 100% with 10 wt% TEOS. The flexibility of the film was judged by a reverse impact test and showed that the flexibility was independent of TEOS loading (except for the unmodified epoxide E0).

  The corrosion performance of the film is shown in FIGS. FIG. 10 shows images after 96 hour and 264 hour salt spray exposure of an epoxy hybrid primer coated on an untreated steel substrate. No blistering or lifting of the coating was observed on any of the 24 hour salt spray exposed panels. However, after 48 hours of exposure, corrosion was observed for the unmodified epoxy derivative. Panels coated with inorganic modified epoxides (E5, E7.5 and E10) passed the salt spray test even after 264 hours exposure.

  The salt spray test results of the epoxy phosphate and epoxy ester hybrid primers are shown in FIGS. 11 and 12, respectively. The scored panels were evaluated with salt spray exposure for up to 264 hours. In FIGS. 10, 11 and 12, only 96 hour and 264 hour images were shown, but the examination was performed periodically. Buchheit et al. [53] used an inspection method in an attempt to quantify the corrosion damage due to pit formation that occurred during salt spray exposure. In that test, at each inspection interval, the panel was assigned a pass or fail grade. Based on that criterion, changes in pit formation damage versus time were evaluated against the panel. For example, blister formation in EP0 decreases dramatically with increasing inorganic content in the system, with no visible corrosion product stains or traces in EP10 after 96 hours exposure (see FIG. 11). ). Epoxy derivative coated panels modified with TEOS oligomer content greater than 5 wt% passed the corrosion performance test, did not have more than 5 isolated spots or pits, and had a diameter of 0.031 in. There was nothing exceeding (0.8 mm). Further improvements in the salt spray performance of the coated panels were observed by modifying the epoxide resin with phosphoric acid and unsaturated fatty acids.

  The sample coated with neat epoxy ester failed after 24 hours exposure to salt spray. On the other hand, the inorganically modified sample was resistant to exposure for more than about 200 hours. The best salt spray performance was always observed when the epoxy coating was inorganically modified with 10 wt% TEOS oligomer. Phosphorylated epoxies and epoxy esters have been found to provide substantial improvements to epoxy resins and significantly improved adhesion to metal substrates by significantly improving blister resistance ( See FIG. 6).

  Since unsaturated fatty acids have been selected in the epoxy ester system, it is appreciated that the grafting of fatty acids provides the ability of an auto-oxidative cure (thermoset) mechanism [15]. The glass transition temperature is very low compared to epoxy and epoxy phosphate counterparts due to improved flexibility. Flexibility arises from the conversion of epoxy end groups from 1,2-oxiranes to ester groups. A decrease in glass transition temperature is also observed in epoxy phosphate (EP) films (see Table 5). The same approach is effective and the 1,2-oxirane group can react with phosphoric acid and water to form a phosphate ester. Furthermore, unreacted low molecular weight species can also act as plasticizers, resulting in lower glass transition temperatures.

  Phosphate ester groups have been found to increase adhesion to metal substrates by reacting with the metal and thus creating a strong chemical bond between the coating polymer and the metal [25, 57]. This metal-phosphate bond is more resistant to water displacement than conventional coating hydrogen bonds to metal substrates and also contributes to improving the corrosion resistance of the coating (see FIG. 11). Inclusion of TEOS oligomers also increased adhesion, but leveled off with further increase in TEOS oligomer concentration (see Table 6). This behavior was also observed by Soucek et al. [29] in the polyurea / polysiloxane ceramer system. The increase in adhesion can be attributed to an increase in the number of Si—O—H bonds formed on the surface of the steel panel. Thus, epoxy resins modified with both phosphate ester groups and TEOS oligomers are expected to achieve better adhesion to metal substrates. The reason why TEOS oligomer-modified epoxy can obtain better adhesion to metal substrates is that silanol groups (Si-OH) in the modified resin are bonded to metal hydroxyl groups (M-OH) and condensed. This is because Si—OM bonds can be formed by the reaction.

  Without being bound by theory, and in part, based on images of the hybrid coating taken after salt spray exposure (see FIGS. 10, 11 and 12), a corrosion protection mechanism is proposed in FIG. In corrosion resistant coatings, the use of epoxide resins dominates other synthetic resins. This is because the bondability to the metal substrate and the long-term corrosion resistance are improved. However, the epoxy resin has a hydrophilic property, so the wet resistance is compromised. Better adhesion of the sol-gel layer on the steel substrate can block the transport of species of corrosion reactions, mainly water and oxygen, on the coating substrate interface and reduce the rate of corrosion. It can be limited.

  In view of the teachings presented herein, it should be understood that many modifications and variations of the present invention will be readily apparent to those skilled in the art. For example, although the present invention has been described with reference to liquid epoxide resins and tetraethylorthosilicates based primarily on bisphenol-A (BPA), other epoxide resins and alkoxysilane oligomers may be used in combination as well, Modified epoxy derivatives can be provided which are substantially improved over resins. Thus, while the above are exemplary of specific embodiments of the invention, they are not intended to limit its implementation. The claims, including all equivalents, define the scope of the invention.

References

Claims (21)

A telechelic resin having reactive end groups, and
Alkoxide oligomers,
A modified epoxide primer composition comprising:   The composition of claim 1, wherein the telechelic resin is an epoxide having a reactive end group.   The composition of claim 2, wherein the epoxide has at least two phenol functional groups.   4. The composition of claim 3, wherein the epoxide is a bisphenol-A (BPA) epoxide.   4. The composition of claim 3, wherein the epoxide is an alicyclic epoxide.   The composition of claim 1, wherein the reactive end group has at least one hydroxide group.   The composition of claim 1, wherein the telechelic resin having reactive end groups is epoxy phosphate.   The composition according to claim 1, wherein the telechelic resin having a reactive end group is an epoxy ester.   The composition of claim 1, wherein the telechelic resin having reactive end groups is epoxy molybdate.   The composition of claim 1, wherein the alkoxide oligomer is a metal alkoxide oligomer.   The composition of claim 1, wherein the alkoxide oligomer is an alkoxysilane oligomer.   The composition of claim 11, wherein the alkoxysilane oligomer is a tetraethylorthosilicate oligomer.   The composition according to claim 11, wherein the alkoxysilane oligomer is a tetramethylorthosilicate oligomer. Providing a telechelic resin having reactive end groups; and
A method for producing a modified epoxide primer, comprising contacting a telechelic resin having a reactive end group with an alkoxide oligomer.   15. The method of claim 14, wherein the telechelic resin having reactive end groups comprises an epoxide having reactive end groups.   The method of claim 15, wherein the epoxide comprises at least two phenol functional groups.   The method of claim 15, wherein the epoxide comprises bisphenol-A (BPA) epoxide.   The method of claim 15, wherein the epoxide comprises an alicyclic epoxide.   15. The method of claim 14, wherein the telechelic resin having reactive end groups is epoxy phosphate.   The method of claim 14, wherein the telechelic resin having a reactive end group is an epoxy ester.   The method of claim 14, wherein the alkoxide oligomer is an alkoxysilane oligomer.