KR100478867B1 - Cathodic Electrocoating Compositions Containing Alkane Sulfonic Acid - Google Patents

Abstract

The aqueous cathode electrocoating composition of the present invention is a binder of an epoxy-amine adduct of an epoxy resin reacted with an amine, a blocked polyisocyanate crosslinker, and an epoxy amine adduct to provide an electrocoating composition with improved uniform electrodeposition. It contains alkanesulfonic acid as a neutralizing agent.

Description

Cathodic Electrocoating Compositions Containing Alkane Sulfonic Acid

The use of alkanesulfonic acids as neutralizing agents in electrocoating compositions provides compositions with improved uniform electrodeposition, low applied voltage, improved film thickness in recessed areas and small dispersed binder particles in the composition. The resulting electrocoating composition preferably has a pH of 5.5 to 8. Representative useful alkanesulfonic acids are methane sulfonic acid, ethane sulfonic acid, propane sulfonic acid, and methane sulfonic acid is preferred because of its relatively low cost and ease of availability. In addition, substituted alkanesulfonic acids may be used as neutralizing agents, giving results similar to alkanesulfonic acids, and typically useful substituted acids are hydroxy ethane sulfonic acid and hydroxy propane sulfonic acid.

Exemplary electrocoating compositions are aqueous compositions having a solids content of 5-50% by weight of base emulsions, additives, pigment dispersant resins, pigments, etc., with negative film forming resins and blocked polyisocyanate crosslinkers, and the compositions are usually organic copolymers. Solvents.

The negative electrode film forming binder of the basic emulsion used to prepare the negative electrode electrocoating composition is an epoxy amine adduct and a blocked polyisocyanate crosslinker and is dispersed in an aqueous medium. The epoxy amine adduct is preferably formed of an epoxy resin chain extended and then reacted with the amine. Representative aqueous cationic electrocoating compositions are disclosed in U.S. Pat. Described.

The epoxy resin used in the epoxy amine adduct is a polyepoxy hydroxy ether resin having an epoxy equivalent of 100-2000.

Epoxy equivalent is the weight in grams of resin comprising 1 g equivalent of epoxy.

These epoxy resins can be any epoxy hydroxy containing polymer having 1,2 epoxy equivalents of two or more epoxy groups per molecule. Preferred are polyglycidyl ethers of cyclic polyols. Especially preferred are polyglycidyl ethers of polyhydric phenols such as bisphenol A. These polyepoxides can be prepared by etherification of polyhydric phenols with epihalohydrin or dihalohydrin such as epichlorohydrin or dichlorohydrin in the presence of alkalis. Examples of polyhydric phenols include 2,2-bis- (4-hydroxyphenyl) ethane, 2-methyl-1,1-bis- (4-hydroxyphenyl) propane, 2,2-bis- (4-hydroxy 3-tertiarybutylphenyl) propane, 1,1-bis- (4-hydroxyphenol) ethane, bis- (2-hydroxynaphthyl) methane, 1,5-dihydroxy-3-naphthalene .

In addition to polyhydric phenols, other cyclic polyols may be used to prepare polyglycidyl ethers of cyclic polyol derivatives. Examples of other cyclic polyols are aliphatic ring compounds, especially 1,2-bis (hydroxymethyl) cyclohexane, 1,3-bis- (hydroxymethyl) cyclohexane, 1,2 cyclohexane diol, 1,4 cyclo Cycloaliphatic polyols such as hexane diol and hydrogenated bisphenol A.

Polyepoxide hydroxy ether resins can be chain extended by any of the polyhydric phenols described above, with preference being given to bisphenol A, polyether or polyester polyols which improve flowability and coalescence. Representative useful polyol chain extenders include polycaprolactone diols such as the series "Tone 200" available from Union Carbide, polyoxys such as the brand name "Jeffamine D-2000" having a molecular weight of about 2000 available from Texco Chemical Company. Ethoxylated bisphenol A, such as propylene diamine, and the trade name "SYNFAC 8009" available from Milliken Chemical Company.

Examples and conditions of polyether polyols for chain expansion are disclosed in US Pat. No. 4,468,307. Examples of polyester polyols for chain expansion are disclosed in US Pat. No. 4,148,772, issued to Marchetti et al. On April 10, 1979.

Representative catalysts used in the preparation of these polyepoxy hydroxy ether resins are tertiary amines such as dimethyl benzyl amine and organometallic complexes such as triphenyl phosphonium iodide.

Ketamine can be used in the present invention with epoxy amine adducts and is prepared from ketones and primary amines. The water formed is removed, for example, by azeotropic distillation. Useful ketones include dialkyl, diaryl and alkylaryl ketones having 3 to 13 carbon atoms. Specific examples include acetone, methyl ethyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, methyl isoamyl ketone, methyl aryl ketone, ethyl isoamyl ketone, ethyl amyl ketone, acetophenone and benzophenone. Suitable diamines are ethylene diamine, 1,3-diamopropane, 1,4-diaminobutane, 1,6-diaminohexane, 4,9-dioxadodecon, 1,12-diamine. One typically useful ketimine is diketamine, a ketimine of diethylene triamine and methyl isobutyl ketone.

Representative useful primary and secondary amines used to prepare epoxy amine adducts are diethyl amine, methyl ethyl amine, methyl ethanol amine, ethyl ethanol amine, mono ethanol amine, ethyl amine, dimethyl amine, diethyl amine, propyl Amines, dipropyl amines, isopropyl amines, diisopropyl amines, butyl amines, dibutyl amines. Preference is given to alkanol amines such as methyl ethanol amine.

Polyisocyanate crosslinkers used are well known in the art. These are aliphatic, cycloaliphatic and aromatic isocyanates such as hexamethylene diisocyanate, cyclohexamethylene diisocyanate, toluene diisocyanate, methylene diphenyl diisocyanate. Methylene diphenyl diisocyanate is preferred. These isocyanates are pre-reacted with blocking agents such as oximes, alcohols or caprolactams which block isocyanate functionality, ie crosslinking functionality. When the blocking agent is heated to separate it thereby provides a reactive isocyanate group and crosslinking takes place. Isocyanate crosslinkers and blockers are well known in the art and are disclosed in the above-mentioned US Pat. No. 4,419,467.

The binder of the electrocoating composition typically contains 20-80% by weight of epoxy amine adduct and 80-20% of blocked isocyanate and is the basic resin component in the electrocoating composition.

In addition to the binder resins described above, the electrocoating composition usually comprises a pigment incorporated into the composition in the form of a pigment paste. Pigment pastes are prepared by grinding the pigment and dispersing it in the grinding vehicle and optional ingredients such as wetting agents, surfactants and antifoaming agents. Any pigment grinding vehicle that is well known in the art can be used. After grinding, the particle size of the pigment should be practically small, and generally the particle size is 6-8 when using a Hegman grinding gauge.

Pigments that can be used in the present invention include titanium dioxide, basic lead silicate, strontium chromate, carbon black, iron oxide, zinc hydroxy phosphite, clay. Pigments with high surface area and oil absorbency should be used with discretion because they can adversely affect the coalescence and flow of the electrodeposited coating.

The weight ratio of pigment to binder is also important and should preferably be 0.5: 1 or less, more preferably 0.4: 1 or less, usually 0.2 to 0.4: 1. Higher weight ratios of pigment to binder have been found to adversely affect coalescence and flow.

The electrocoating composition of the present invention may contain optional ingredients such as wetting agents, surfactants, antifoaming agents. Examples of surfactants and wetting agents are alkyl imidazolines, such as those available as "Amine C" from Ciba-Geigy Industrial Chemicals, acetylene alcohols available as "Surfynol 104" from Air Products and Chemicals. . These optional ingredients, when present, comprise about 0.1-20% of the weight of the binder of the composition.

Optionally, plasticizers can be used to promote the flow. Examples of useful plasticizers are high boiling water immiscible materials such as ethylene or propylene oxide adducts of nonyl phenol or bisphenol A. Plasticizers are usually used in amounts of 0.1 to 15% by weight of the binder of the composition.

The electrocoating composition of the present invention is an aqueous dispersion. The term "dispersion" as used in the context of the present invention is considered to be a two-phase transparent or opaque aqueous resin binder system in which the binder is present in a dispersed phase and a continuous phase. The average particle size diameter of the binder phase is from 0.02 to 10 microns, preferably 1 micron or less. The concentration of the binder in the aqueous medium is generally not important, but usually most of the aqueous dispersion is water. Aqueous dispersions usually comprise 3 to 50%, preferably 5 to 40% by weight of the binder solids. Aqueous binder concentrates which will be further diluted with water when added to the electrocoating bath generally have 10 to 30% by weight binder solids.

The electrocoating composition of the present invention is used in a conventional cathode electrocoating method. The electrocoating tank comprises two electrically conductive electrodes, an anode which is part of the electrocoating tank and a cathode to be coated, such as an automobile body or an automotive part. When sufficient voltage is applied between the two electrodes, a tacky film is formed on the cathode. The voltage applied can vary depending on the type of coating and the coating thickness and uniform electrodeposition required, and can be as small as 1 volt or as high as thousands of volts. Typical voltages used are 50-500 volts. The current density is usually 0.5 to 5 A / ft ² and decreases during electrodeposition, indicating that an insulating film is formed. Various substrates can be electrocoated by the compositions of the present invention, such as steel, phosphorylated steel, galvanized steel, copper, aluminum, magnesium and various plastics with electrically conductive coatings.

After electrocoating, it is cured by baking for 1-40 minutes at elevated temperature, such as 90-160 ° C.

The electrocoating compositions of the present invention neutralized with alkanesulfonic acid form stable dispersions compared to the electrocoating compositions neutralized with other organic acids such as formic acid, acetic acid and glycolic acid, and have surprisingly good uniform electrodeposition and improved wedges. Have Uniform electrodeposition is a property of electrocoating compositions that coat a film on a target with a film of equal density at varying distances from the corresponding electrode. The wedge is the distance from the corresponding electrode on which a 0.5 mil (12.7 micron) thick film is coated at a given voltage. Tests to measure uniform electrodeposition and wedges are described in the following examples.

The following examples illustrate the invention. All parts and percentages are by weight unless otherwise indicated.

<Example>

Crosslinker Resin Solution

The following components were charged to a properly equipped reactor:

Part 1 Parts by weight

MDI (Methylene Diphenyl Diisocyanate) 1705.80

Methyl Isobutyl Ketone 402.30

Dibutyl Tin Dilaurate 0.40

Part 2

Alcohol Blend (72.5-73.5% Diethylene

Glycol Monobutyl Ether, 15.5-16.5% Ethanol

And 10.5-11.5% methanol) 1106.70

Part 3

Methyl Isobutyl Ketone 52.10

Part 4

Butyl Alcohol 9.40

Methyl Isobutyl Ketone 473.30

Total 3750.00

Part 1 was charged to the reactor and heated to 74-76 ° C. Part 3 was fed to the reactor at a constant rate over 120 minutes. The temperature of the reaction mixture was maintained at 107 ° C. and the reaction mixture was held at 107 ° C. for a further 3 hours. Part 3 was added and part 4 was added to cool the reaction mixture to room temperature.

The resulting crosslinker resin solution of blocked isocyanate had a 75% weight solids content and a Gardner Hholdt viscosity of R-U as measured at 25 ° C.

Electro Coating Resin Solution

Part 1 Parts by weight

EPON 828 (trade name, having an epoxy equivalent of 188)

Diglycidyl ether of bisphenol A) 2384.30

Synfac 8009 ™, having an epoxy equivalent of 247

Ethoxylated Bisphenol A) 850.40

Xylene 202.20

Bisphenol A 684.40

Part 2

Dimethyl Benzylamine 4.10

Part 3

Dimethyl Benzylamine 8.20

Part 4

Crosslinker Resin Solution (manufactured above) 3428.80

Part 5

Diketamine resin solution (in methyl isobutyl ketone

75% resin solids; Diketamine resin is 2 mol

Methyl isobutyl ketone and 1 mole diethylene

Reaction product of triamine,

Weight average molecular weight) 271.50

Part 6

N- (2 hydroxyethyl) -n-methyl amine 224.80

Part 7

Nonionic Surfactant (Aryl Polyoxyethyl Ether) 113.80

Part 8

Methyl Ethyl Ketone 1892.50

Total 10,065.00

Part 1 was charged to the reactor and heated to 145-147 ° C. Part 2 was added and the reaction mixture was maintained at 160-200 ° C. for 2 hours to prepare a polymer having an epoxy equivalent of 575-750. The reaction mixture was then cooled to 143-146 ° C. and part 3 was added to maintain the reaction mixture at this temperature until a polymer with an epoxy equivalent of 1030-1070 was formed. The resulting polymer solution is cooled to 106-108 ° C. and portion 4 is added with mixing. Add part 5 while mixing. Part 6 is added with mixing and the mixture is maintained at 120-122 ° C. for 1 hour. Part 7 is added and mixed for 30 minutes, then the mixture is cooled to 80 ° C. and part 8 is added and mixed.

The resulting electrocoated resin solution has a solids content of 70%.

The following ingredients were blended together to prepare Emulsion A.

Part 1 Parts by weight

Electrocoated Resin Solution (manufactured above)

Part 2

Methane sulfonic acid (MSA) solution (10% aqueous solution) 360.70

Part 3

Deionized Water 269.03

Surfactant blends (tetra descindiol, 2-butoxy

A mixture of ethanol, coconut imidazoline and acetic acid) 18.50

Part 4

Deionized Water 1974.00

 Total 4275.01

Part 1 is added to the mixing vessel, then part 2 is added and mixed for 10 minutes. Part 3 is added and mixed for 15 minutes, then part 4 is added and mixed to form an emulsion. The emulsion is stirred and kept at 50 ° C. for several hours to evaporate all organic solvents present in the emulsion. The solid weight of the emulsion was adjusted to 33% by the addition of water. The particle size of the emulsion measured as described below was 91 NM (nanometer).

Emulsion B was prepared as follows:

Part 1 Parts by weight

Emulsion A (prepared above) 3121.41

Part 2

Crater calibration additive 172.48

Part 3

Anticrater Additive 100.80

Part 4

Deionized Water 104.31

 Total 3500.00

Part 1 is added to the mixing vessel, then part 2 is added and mixed for 15 minutes. Add part 3 and mix for 15 minutes, then add part 4 and mix for 1 hour.

The following components were mixed to prepare an electrocoating bath:

Part 1 Parts by weight

Emulsion B (prepared above) 3472.19

Deionized Water 1516.44

Part 2

Pigment pastes (US Pat. No. 5,356,960)

Paragraph 6, lines 45-54) 776.23

Part 3

Deionized Water 1735.14

 Total 7500.00

Part 1 was charged to the mixing vessel and mixed for 15 minutes. Add Part 2 while mixing over 5 minutes and mix for an additional 15 minutes, then add Part 3 and mix. The resulting electrocoating bath composition had a solids content of 33% and a particle size of 91 NM (nanometer).

An electrocoating bath B-E was prepared in a similar manner, except that the following acid was used instead of methane sulfonic acid:

Bath B-Formic Acid

Bath C-Lactic Acid

Bath D-Glycolic Acid

Bath E-Acetic Acid

The following tests were performed for each bath and the results are shown in Table 1. Each panel was electrocoated and then baked at 163 ° C. for 30 minutes.

The particle size of the PS (particle size) -bath emulsion was measured by a Coulter Model LS 150 Automated Laser Based Particle Sizer Analyzer manufactured by Coulter Scientific Instruments.

pH-measured by pH meter.

COND (conductivity)-company [Yellow Springs Instrument Co. Inc., Yellow Springs, Ohio], measured in microsiemens units with a device manufactured by the USI Model 35 Conductivity Meter.

Vc (voltage)-voltage that achieves a 0.85 mil (21.6 micron) film thickness on the interior of the box used in the following uniform electrodeposition tests.

THROW-Homogeneous electrodeposition is Vc and 2 according to the Test Method [Ford Laboratory Test Method MJ BI 20-2C] using a box made of two 12 × 4 inch (30.48 × 10.16 cm) phosphorylated steel panels It was measured at an electrodeposition time of minutes. The distance at which the coating was deposited in the box, ie the zero film thickness, was measured in mm.

WEDGE—The distance in the box used in the above reach test, with a film thickness of 0.5 mils (12.7 microns) at Vc.

The results shown in Table 1 are summarized below:

Electrocoated composition A neutralized with methane sulfonic acid has a smaller particle size emulsion, lower Vc and higher reach, which exhibit a longer bath stability period compared to electrocoated composition B neutralized with formic acid.

Electrocoating composition A has smaller particle size, lower Vc, higher reach and higher wedge compared to electrocoating composition C neutralized with lactic acid.

Electrocoating composition A has smaller particle size, higher reach and higher wedges compared to electrocoating composition D neutralized with glycolic acid.

Electrocoating composition A has smaller particle size, higher reach and higher wedges compared to electrocoating composition E neutralized with acetic acid.

Electric coating bath mountain pH COND Vc THROW 0.5 mil WEDGE A MSA 6.04 1973 200 194 55 PS 91 NM B Formic acid 6.09 2540 210 184 62 PS 169 NM C Lactic acid 5.99 1738 210 181 41 PS 133 NM D Glycolic acid 6.03 1908 190 180 45 PS 129 NM E Acetic acid 6.07 1890 200 179 40 PS 135 NM

Background of the Invention

The present invention relates to a negative electrode electrocoating composition, in particular a negative electrode electrocoating composition containing an alkane sulfonic acid neutralizer.

Coating of electrically conductive substrates by electrodeposition, also called electrocoating, is a well known and important industrial technique. Electrodeposition of primers to automotive substrates is widely used in the automotive industry. In this process, conductive products, such as automotive bodies or automotive parts, are immersed in an aqueous emulsion coating composition bath of film forming polymers and function as electrodes in the electrodeposition process. Until the required coating is made on the product, a current is passed between the product in contact with the aqueous emulsion and the corresponding electrode. In the cathode electrocoating method, the product to be coated is a cathode and the corresponding electrode is an anode.

Resin compositions for use in typical cathode electrodeposition baths are also well known in the art. Typically these resins are made of polyepoxide resins that are chain expanded and then have an adduct formed to include amine groups in the resin. Typically amine groups are introduced through the reaction of a resin with an amine compound. These resins are blended with a crosslinker and then neutralized with acid to form a water emulsion, commonly referred to as a base emulsion.

The basic emulsion is combined with pigments, coalescing solvents, water and other additives to form an electrocoating bath. This electrocoating bath is located in an insulated tank containing an anode. The product to be coated is passed through a tank containing an electrodeposition bath as a cathode. The thickness of the coating made on the product to be electrocoated is a function of the bath's properties, electrical operating properties and soaking time.

The resulting coated product is removed from the bath after a set time and washed with deionized water. The coating on the product is typically cured in an oven at a temperature sufficient to produce a crosslinking finish on the product.

Cathodic electrocoating compositions, resin compositions, coating baths, and cathodic electrodeposition methods are described in US Patent No. 3,922,253, issued December 25, 1975 to Jarabek et al., Wismer on December 6, 1983. U.S. Patent No. 4,419,467 to U.S. Patent No. 4,419,467, U.S. Patent No. 4,137,140 to Belanger on January 30, 1979, and U.S. Patent No. 4,468,307 to Wizmer on August 25, 1984 It is.

Various acids such as sulfamic acid, toluene sulfonic acid, inorganic mineral acid, acetic acid, oxalic acid, formic acid, trichloro acetic acid and the like have been used to neutralize the polyepoxide amine adduct of the electrocoating bath. These acids are described in US Pat. No. 3,681,224, issued to Stromberg on August 1, 1972, US Pat. No. 4,467,604, issued to Kempter et al. On March 3, 1987, and June 1986. US Patent No. 4,594,403, issued to Kempter et al., Dated 10, and US Patent No. 4,933,056, issued to Corrigan et al., June 12, 1990, and European Patent Application No. 0,361,882. It is. Weak acids do not provide the increase in throw power required for many applications.

Uniform electrodeposition of the electrocoating composition continues to be a problem. Homogeneous electrodeposition is such that the electrodeposited membrane penetrates and coats the surface of the recessed interior region of the vehicle or truck body. Electrodeposition of the coating follows the force distribution line of the electric field present in the electrocoating bath between the cathode and anode. This force distribution line diminishes as it penetrates into the recessed areas of the car or truck body and will not be present when the recessed areas are too deep, and coating will not be applied to these areas.

As automotive and truck body designs change, there is a need for electrocoating compositions that increase uniform electrodeposition and penetrate and coat recessed areas. The improved compositions of the present invention have increased uniform electrodeposition with other desirable properties such as lower organic volatile compounds and smaller dispersed binder particles.

Summary of the Invention

The aqueous cathode electrocoating composition of the present invention is a binder of an epoxy-amine adduct of an epoxy resin reacted with an amine, a blocked polyisocyanate crosslinker, and an epoxy amine adduct to provide an electrocoating composition with improved uniform electrodeposition. It contains alkanesulfonic acid as a neutralizing agent.

Claims (6)

In an aqueous negative electrode electrocoating composition comprising an epoxy-amine adduct binder of an epoxy resin reacted with an amine, and a blocked polyisocyanate crosslinker, C ₁ -C ₃ alkanesulfonic acid is used as a neutralizing agent to improve uniform electrodeposition. An aqueous negative electrode electrocoating composition, characterized in that. The improved cathode electrocoating composition of claim 1, wherein said alkane sulfonic acid is methane sulfonic acid. 3. The improved negative electrode electrocoating composition of claim 2, wherein said methane sulfonic acid is included in an amount to provide a composition having a pH of about 5.5-8. 4. The improved negative electrode electrocoating composition of claim 3, wherein said epoxy amine adduct is expanded to a dihydric phenol and consists of a polyepoxy hydroxy ether resin reacted with an amine. (a) preparing an epoxy resin-amine adduct; (b) preparing a blocked polyisocyanate crosslinker; (c) blending the epoxy-amine adduct with the blocked polyisocyanate crosslinker; (d) neutralizing the epoxy-amine adduct with an organic acid to prepare an emulsion; (e) blending the emulsion with a pigment paste In the method for producing a negative electrode electrocoating composition comprising in any practicable order, A method for preparing a negative electrode electrocoating composition, comprising adding an organic acid composed of C ₁ -C ₃ alkanesulfonic acid to provide an electrocoating composition with improved uniform electrodeposition. A substrate coated with a dried and cured layer of the composition according to claim 1.