JP2007039617A - Cationic electrodeposition coating composition and coated material produced therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cationic electrodeposition coating composition exhibiting high rust-prevention property even at an extremely thin film thickness (for example, film thickness of about 7μm) and having excellent various other film properties. <P>SOLUTION: The cationic electrodeposition coating composition contains silica particles having a pore volume of 0.44-1.8 ml/g and an average particle diameter of ≤10μm and has a coating film diffusion coefficient √Tc of ≥2.5 measured by solution diffusion method. The invention further provides a coated material produced by using the composition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cationic electrodeposition coating composition, in particular, a cationic electrodeposition coating composition having high corrosion resistance even when the coating film is thinned, and a coated product obtained therefrom.

  Electrodeposition coating can be applied to the details even if the object has a complicated shape, and it can be applied automatically and continuously. It is widely used as an undercoating method for objects to be coated that requires high rust prevention. Moreover, it is economical because the use efficiency of the paint is extremely high compared with other coating methods, and is widely used as an industrial coating method. Cationic electrodeposition coating is performed by immersing an object to be coated as a cathode in a cationic electrodeposition coating and applying a voltage.

  Patent Document 1 (Japanese Patent Laid-Open No. 2003-268315) discloses a lead-free cationic electrodeposition coating composition containing silica particles having a pore volume of 0.44 to 1.8 ml / g and an average particle diameter of 10 μm or less. It is disclosed. This cationic electrodeposition coating composition is intended for the surface smoothness of the coating film, and is not intended for high rust prevention at a film thickness of 10 μm or less, particularly a thin film thickness of about 7 μm.

Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-269627) discloses a lead-free cation containing an aqueous medium, a binder resin, a neutralizing acid, an organic solvent, a pigment, and a metal catalyst dispersed or dissolved in the aqueous medium. An electrodeposition coating composition, the film resistance of the electrodeposition coating film electrodeposited to a thickness of 20 μm with respect to the object to be coated is 1000-2500 kΩ · cm ² , and the conductivity of the coating composition is 1500-500. A lead-free cationic electrodeposition coating composition having 2000 μS / cm and a minimum deposition pH of 11.90 to 12.00 in electrodeposition coating is disclosed. Claim 3 of Patent Document 2 describes that the square root of the coating film diffusion coefficient by solution diffusion is 2.5 to 3.2, but this cationic electrodeposition coating composition has a very thin thickness of about 7 μm. The film thickness is not considered.
JP 2003-268315 A JP 2004-269627 A

  An object of the present invention is to provide a cationic electrodeposition coating composition that can ensure high rust prevention even at a very thin film thickness (for example, a film thickness of about 7 μm) and is excellent in other coating film performance.

  The present invention includes cationic electrodeposition containing silica particles having a pore volume of 0.44 to 1.8 ml / g and an average particle diameter of 10 μm or less, and a coating film diffusion coefficient √Tc = 2.5 or more by solution diffusion. A coating composition is provided, whereby the above object is achieved.

  The cationic electrodeposition coating composition further contains an amine-modified epoxy resin (A) and a blocked isocyanate curing agent (B), and the weight of the amine-modified epoxy resin (A) and the blocked isocyanate curing agent (B). The ratio (A / B) is 50/50 to 90/10, and the blocked isocyanate curing agent comprises a mixture of blocked aliphatic polyisocyanate and blocked aromatic polyisocyanate, and their weight ratio (blocked fat Group polyisocyanate / blocked aromatic polyisocyanate) is preferably 3/1 to 1/3.

  Further, the silica particles are contained in an amount of 1 to 30% by weight based on the total pigment.

  The present invention also provides a coated product electrodeposited with the cationic electrodeposition coating composition.

The present invention will be described in detail below.
In general, a cationic electrodeposition coating contains a cationic epoxy resin and a curing agent for the resin as basic components, and additionally contains a pigment and an additive and is dispersed in an aqueous medium.

Silica Particles The cationic electrodeposition paint of the present invention is characterized by containing specific silica particles as described above. The silica particles are porous, and the pore volume is 0.44 to 1.8 ml / g, preferably 0.8 to 1.6 ml / g. When the amount is less than 0.44 ml / g, the effect (corrosion resistance) is disadvantageously reduced, which becomes more conspicuous than when the amount is less. If it exceeds 1.6 ml / g, it will have the disadvantage of poor dispersion stability, and if it is more, it will become more dispersible. Here, the pore volume means the pore volume of the porous portion. The pore volume is measured by mercury porosimetry. The mercury intrusion method is a method for measuring specific surface area and pore distribution by injecting mercury into the pores of a powder and measuring the pressure required and the amount of mercury injected. These can be measured using a mercury intrusion pore distribution measuring device.

  The silica particles have an average particle size of 10 μm or less, preferably 5 to 0.1 μm. If it is smaller than 0.1 μm, it has a disadvantage of poor dispersion stability. When it exceeds 10 μm, the corrosion resistance decreases. Here, the “average particle size” is generally used to represent the particle size of the particles (whether the particle size is coarse or fine), and the median diameter, arithmetic average diameter, surface area average diameter corresponding to 50% by weight, A volume area average diameter or the like is used. The average particle diameter shown in the present specification is a value measured by a laser method. The laser method is a method of measuring an average particle size, a particle size distribution, and the like by dispersing particles in a solvent, applying a laser beam to the dispersion solvent, and capturing and calculating the obtained scattered light.

  In general, silica is a solid substance mainly composed of silicon dioxide, but the silica particles of the present invention are porous as described above, and have a pore volume of 0.44 to 1.8 ml / g and an average particle size of 10 μm. Must be: Silica particles having such characteristics are special, and are different from generally known silica gels and natural silica particles (for example, extender pigments such as kaolin). The silica particles used in the present invention can be obtained by mixing sodium silicate and acid using a so-called wet method. Examples of the special silica particles used in the present invention include silicia commercially available from Fuji Silysia Chemical Co., Ltd.

  In general, cathodic corrosion causes the pH of the corrosive environment to become alkaline, and corrosion proceeds, but when silica particles are present, a pH buffer action that suppresses alkalinity can be expected to have high rust prevention properties, I understand.

  The silica particles used in the present invention can be considered to constitute a part of a pigment described later with a solid substance. In that case, it can be considered that a part of the pigment described later is replaced with the silica particles of the present invention. Therefore, it is preferable that the compounding quantity of the said silica is 1-30 weight% with respect to a pigment, Furthermore, it is preferable that it is 10-25 weight%. Addition exceeding 30% lowers the smoothness of the coating film. On the contrary, if the amount is less than 1% by weight, the effect (corrosion resistance) due to the addition of silica particles becomes insufficient.

  As described above, the lead-free cationic electrodeposition coating composition of the present invention contains a cationic epoxy resin, a curing agent, and, if necessary, a pigment and an additive in addition to the specific silica particles. Hereinafter, each component will be described.

Amine-modified epoxy resin The amine-modified epoxy resin used in the present invention refers to an epoxy resin modified with an amine. The amine-modified epoxy resin may be a known resin described in Japanese Patent Publication Nos. 54-4978 and 56-34186.

  An amine-modified epoxy resin typically opens all of the epoxy rings of a bisphenol-type epoxy resin with an active hydrogen compound capable of introducing a cationic group, or some epoxy rings with other active hydrogen compounds. It is produced by opening the ring and opening the remaining epoxy ring with an active hydrogen compound capable of introducing a cationic group.

  A typical example of the bisphenol type epoxy resin is a bisphenol A type or bisphenol F type epoxy resin. As the former commercial product, there are Epicoat 828 (manufactured by Yuka Shell Epoxy Co., Epoxy Equivalent 180-190), Epicoat 1001 (Same, Epoxy Equivalent 450-500), Epicoat 1010 (Same, Epoxy Equivalent 3000-4000), Examples of the latter commercially available product include Epicoat 807 (same as above, epoxy equivalent 170).

  An oxazolidone ring-containing epoxy resin as described in the formula in the paragraph 0004 of JP-A-5-306327 and the chemical formula 3 may be used as the amine-modified epoxy resin. This is because a coating film having excellent heat resistance and corrosion resistance can be obtained.

  As a method for introducing an oxazolidone ring into an epoxy resin, for example, a block polyisocyanate blocked with a lower alcohol such as methanol and a polyepoxide are heated and kept in the presence of a basic catalyst, and a by-product lower alcohol is introduced from the system. Obtained by distilling off.

  Particularly preferred epoxy resins are oxazolidone ring-containing epoxy resins. This is because a coating film having excellent heat resistance and corrosion resistance and further excellent impact resistance can be obtained.

  It is known that an epoxy resin containing an oxazolidone ring can be obtained by reacting a bifunctional epoxy resin with a diisocyanate blocked with a monoalcohol (ie, bisurethane). Specific examples and production methods of this oxazolidone ring-containing epoxy resin are described, for example, in paragraphs 0012 to 0047 of JP-A No. 2000-128959.

  These epoxy resins may be modified with a polyester polyol, a polyether polyol, a suitable resin such as a carboxylic acid or a xylene resin, or a mercapto compound. In addition, the epoxy resin can be chain-extended using a reaction between an epoxy group and a diol or dicarboxylic acid.

  These epoxy resins are ring-opened with an active hydrogen compound so that an amine equivalent of 0.3 to 4.0 meq / g is obtained after ring opening, and more preferably 5 to 50% of them are occupied by primary amino groups. It is desirable to do.

  Active hydrogen compounds that can introduce a cationic group include primary amines, secondary amines, tertiary amine acid salts, sulfides and acid mixtures. In order to prepare the primary, secondary or / and tertiary amino group-containing epoxy resin of the present invention, an acid salt of a primary amine, secondary amine or tertiary amine is used as an active hydrogen compound capable of introducing a cationic group. Use.

  Specific examples include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, diethyl disulfide / acetic acid mixture, etc. In addition, there are secondary amines in which primary amines such as aminoethylethanolamine ketimine and diethylenetriamine diketimine are blocked. A plurality of amines may be used in combination.

Sulfonium-modified epoxy resin The cationic electrodeposition coating composition used in the present invention may contain a sulfonium-modified epoxy resin. The sulfonium-modified epoxy resin is a resin in which a sulfonium base is introduced at the same time as the epoxy group is opened by reacting an epoxy resin with a sulfide compound and a neutralizing acid. The sulfonium-modified epoxy resin may be a conventionally known one as described in, for example, JP-A-6-128351 and JP-A-7-206968. The sulfonium-modified epoxy resin is typically produced by opening the epoxy ring of a bisphenol type epoxy resin with a sulfide compound and a neutralizing acid.

  The sulfide compound to be reacted with the epoxy resin includes all sulfide compounds that react with the epoxy group and do not contain an interfering group. In addition, it is necessary to perform reaction of an epoxy resin and a sulfide compound in presence of a neutralizing acid, As a result, a sulfonium group is introduce | transduced into an epoxy resin.

  Specific examples of the sulfide compound may be aliphatic sulfide, mixed aliphatic-aromatic sulfide, aralkyl sulfide, or cyclic sulfide. Examples of sulfide compounds that can be used include diethyl sulfide, dipropyl sulfide, ethylphenyl sulfide, tetramethylene sulfide, pentamethylene sulfide and the like.

［式中、Ｒ及びＲ'はそれぞれ独立して炭素数２〜８の直鎖又は分枝鎖アルキレン基である。］
で表されるチオジアルコールである。かかるスルホニウム変性エポキシ樹脂は電着開始直後の短時間（約１０秒間）塗膜抵抗の形成を遅くする機能を有し、かつバインダー樹脂に水分散安定性を付与する。 Particularly preferred sulfide compounds are of the formula

[Wherein, R and R ′ each independently represents a linear or branched alkylene group having 2 to 8 carbon atoms. ]
It is a thiodialcohol represented by Such a sulfonium-modified epoxy resin has a function of delaying the formation of coating film resistance for a short time (about 10 seconds) immediately after the start of electrodeposition, and imparts water dispersion stability to the binder resin.

  Examples of thiodialcohols include thiodiethanol, thiodipropanol, thiodibutanol, 1- (2-hydroxyethylthio) -2-propanol, 1- (2-hydroxyethylthio) -2,3-propanediol, 1- (2-hydroxyethylthio) -2-butanol and 1- (2-hydroxyethylthio) -3-butoxy-1-propanol. Most preferably, the sulfide compound is 1- (2-hydroxyethylthio) -2-propanol.

Blocked Polyisocyanate Curing Agent The blocked isocyanate curing agent used in the present invention is preferably a blocked polyisocyanate obtained by blocking polyisocyanate with a blocking agent. Here, polyisocyanate has an isocyanate group in one molecule. A compound having two or more. The polyisocyanate may be, for example, any of aliphatic, alicyclic, aromatic and aromatic-aliphatic.

  Specific examples of polyisocyanates include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI), 2,2,4- C3-C12 aliphatic diisocyanates such as trimethylhexane diisocyanate and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI) , Methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4′-diisocyanate, and 1,3-diisocyanatomethylcyclo Carbon such as xane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate). Aliphatic diisocyanates having a number of 5 to 18; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); modified products of these diisocyanates (urethanes, carbodiimides, Uretdione, uretoimine, burette and / or isocyanurate modified product); These can be used alone or in combination of two or more.

  Adducts or prepolymers obtained by reacting polyisocyanates with polyhydric alcohols such as ethylene glycol, propylene glycol, trimethylolpropane and hexanetriol at an NCO / OH ratio of 2 or more may also be used as curing agents.

  The polyisocyanate is preferably a combination of an aliphatic polyisocyanate and an aromatic polyisocyanate. This is because the formed coating film is excellent in coating film smoothness and weather resistance. The mixing ratio of the aliphatic polyisocyanate and the aromatic polyisocyanate is 3/1 to 1/3, preferably 7/3 to 3/7, by weight ratio of aliphatic polyisocyanate / aromatic polyisocyanate. When this weight ratio is larger than 3/1, the smoothness of the coating film is lowered, and when it is smaller than 1/3, the weather resistance is inferior.

  Preferred specific examples of the aliphatic polyisocyanate include hexamethylene diisocyanate, hydrogenated TDI, hydrogenated MDI, hydrogenated XDI, IPDI, norbornane diisocyanate, their dimer (biuret), trimer (isocyanurate) and the like. Can be mentioned.

  Preferable specific examples of the aromatic polyisocyanate include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), xylylene diisocyanate and dimers, trimers and condensates thereof.

  The blocking agent is added to a polyisocyanate group and is stable at ordinary temperature, but can regenerate a free isocyanate group when heated to a temperature higher than the dissociation temperature.

  As a blocking agent, when low temperature curing (160 ° C. or lower) is desired, lactam blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam and β-propiolactam, and formaldoxime, acetoald It is preferable to use an oxime blocking agent such as oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, and cyclohexane oxime.

  The binder containing the amine-modified epoxy resin and the curing agent is generally contained in the electrodeposition coating composition in an amount that occupies 25 to 85% by weight, preferably 40 to 70% by weight of the total solid content of the electrodeposition coating composition. The

The pigment electrodeposition coating composition generally contains a pigment as a colorant. The electrodeposition coating composition of the present invention also contains a commonly used pigment. Examples of such pigments include colored pigments such as titanium white, carbon black and bengara; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica and clay; zinc phosphate, iron phosphate, phosphoric acid Rust prevention pigments such as aluminum, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphomolybdate, aluminum phosphomolybdate Can be mentioned.

  The pigment is generally contained in the electrodeposition coating composition in an amount occupying 1 to 35% by weight, preferably 10 to 30% by weight of the total solid content of the electrodeposition coating composition. As described above, the specific silica particles used in the present invention can be considered as a part of the pigment as a solid component, and in this case, a part of the blending amount of the pigment is made into silica particles. In the case where the silica particles are regarded as an additive, the amount of the pigment is reduced to 0.01 to 15% by weight, preferably 0.2 to 2% by weight, based on the solid content of the paint.

  Since the cationic electrodeposition coating composition of the present invention is preferably lead-free from the viewpoint of the environment, lead-containing corrosion resistance imparting agents such as basic lead silicate, basic lead sulfate, lead red, and cyanamide lead Such lead-based anticorrosive pigments should not be used, or should be used in such an amount that the lead ion concentration of the diluted paint (added to the electrodeposition bath) will be 100 ppm or less. If the lead ion concentration is high, it is harmful to the environment and smoothness may be reduced.

Pigment-dispersed paste When a pigment is used as a component of an electrodeposition paint, generally, the pigment is dispersed in an aqueous medium at a high concentration in advance together with a resin called a pigment-dispersing resin to form a paste. This is because the pigment is in a powder form, and it is difficult to disperse in a single step in a low concentration uniform state used in the electrodeposition coating composition. Such a paste is generally called a pigment dispersion paste.

  The pigment dispersion paste is prepared by dispersing a pigment together with a pigment dispersion resin in an aqueous medium. In the present invention, the silica particles are preferably formed into a dispersion paste together with the pigment. As the pigment dispersion resin, a cationic polymer such as a cationic or nonionic low molecular weight surfactant or a modified epoxy resin having a quaternary ammonium group and / or a tertiary sulfonium group is generally used. As the aqueous medium, ion-exchanged water or water containing a small amount of alcohol is used. Generally, the solid content ratio of the pigment dispersion resin and the pigment is used in a ratio of 1:10 to 1: 1.

Electrodeposition Paint Composition The electrodeposition paint composition of the present invention is prepared by dispersing a pigment dispersion paste containing an amine-modified epoxy resin, a curing agent, and silica particles in an aqueous medium. Further, the aqueous medium usually contains a neutralizing agent in order to improve the dispersibility of the amine-modified epoxy resin. Neutralizing agents are inorganic or organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid. The amount is that which achieves a neutralization rate of at least 20%, preferably 30-60%.

  The amount of the curing agent reacts with an active hydrogen-containing functional group such as a primary, secondary or / and tertiary amino group or hydroxyl group in an amine-modified epoxy resin (or sulfonium-modified epoxy resin) at the time of curing, and a good cured coating is obtained. Must be sufficient to give a membrane. The weight ratio (A / B) of the amine-modified epoxy resin (A) and the blocked polyisocyanate curing agent (B) is 50/50 to 90/10, preferably 55/45 to 80/20. When the weight ratio (A / B) of the amine-modified epoxy resin (A) and the blocked polyisocyanate curing agent (B) exceeds 50/50, the smoothness of the coating film is lowered. Corrosion resistance is not obtained.

  When the sulfonium-modified epoxy resin is added to the cationic resin, the mixing ratio of the sulfonium-modified epoxy resin and the amine-modified epoxy resin is 25/75 to 50/50, preferably 40/60 to 50/50, in mass ratio. Range. If the mass ratio of the sulfonium-modified epoxy resin is less than the mixing ratio 25/75, the gas pin resistance of the paint is inferior. If the mixing ratio exceeds 50/50, the appearance defect of the coating film is difficult to be solved.

  The electrodeposition paint can contain a tin compound such as dibutyltin dilaurate and dibutyltin oxide, and a usual urethane cleavage catalyst. Since lead is not substantially contained, the amount is preferably 0.1 to 5% by weight of the block polyisocyanate compound.

  The electrodeposition paint can contain conventional paint additives such as water-miscible organic solvents, surfactants, antioxidants, UV absorbers, and pigments.

  The electrodeposition coating composition of the present invention is electrodeposited onto an article by a method well known to those skilled in the art to form a cured coating film. The object to be coated when performing electrodeposition coating using this cationic electrodeposition coating composition is preferably a conductor that has been subjected to surface treatment such as zinc phosphate treatment in advance by dipping, spraying method, etc. The surface treatment may not be performed. In addition, the conductor is not particularly limited as long as it can become a cathode in performing electrodeposition coating, and a metal substrate is preferable.

  Examples of such a metal substrate include steel plates such as cold rolled steel plates and zinc nickel steel plates. Moreover, such a steel plate may be a structure used for a specific application, such as the automobile body described above. The structure means a product formed by forming the metal material into a concavo-convex shape so as to be used for automobiles or other applications. The coating object is preferably a structure using a zinc-nickel steel plate from the viewpoint of corrosion resistance, particularly when used for automobiles.

The conditions under which electrodeposition is performed are generally the same as those used for other types of electrodeposition coating. The applied voltage may vary greatly and may range from 1 volt to several hundred volts. The current density is usually about 10 amperes / m ^{2 to} 160 amperes / m ² and tends to decrease during electrodeposition.

  After electrodeposition, the coating is baked at an elevated temperature in the usual manner, for example, in a baking furnace, in a baking oven or with an infrared heat lamp. The baking temperature may vary but is usually about 140 ° C to 180 ° C.

  The electrodeposition process includes a process of immersing an object to be coated in a cationic electrodeposition coating composition, and a process of applying a voltage between the object to be coated as a cathode and an anode to deposit a film. Moreover, although the time which applies a voltage changes with electrodeposition conditions, generally it can be made into 2 to 4 minutes. In the present specification, the “electrodeposition coating film” refers to an uncured coating film after electrodeposition coating after the above-described process of depositing the coating film and before baking hardening.

  The film thickness of the electrodeposition coating film is preferably 5 to 30 μm, more preferably 7 to 25 μm. When the film thickness is less than 5 μm, the rust prevention property is insufficient, and when it exceeds 30 μm, the paint is wasted. In the present invention, as described above, even when the film thickness is thinner than 10 μm (specifically, a thin film of about 7 μm) of a conventional general thin film type electrodeposition paint, it has high anticorrosion properties (rust resistance). It is characterized by exhibiting.

  The electrodeposition coating film obtained as described above is cured by baking at 120 to 260 ° C., preferably 140 to 220 ° C. for 10 to 30 minutes after completion of the electrodeposition process or after washing with water. In this specification, the coating film after baking hardening is called "cured coating film".

  The square root (√Tc) of the diffusion coefficient of the cured coating film obtained with the cationic electrodeposition coating composition of the present invention is 2.5 or more, preferably 2.5 to 3.2, more preferably 2.7 to 3.0. It is. The diffusion coefficient (Tc) is an index indicating the degree to which the solution permeates and diffuses into the coating film, and is a characteristic value related to the crosslinking density of the cured coating film. When the crosslinking density of the cured coating film is high, the value of the diffusion coefficient (Tc) becomes large.

When the value of the diffusion coefficient (Tc) of the cured coating film is large, that is, when the crosslinking density of the cured coating film is high, the electrolytes such as Na ⁺ , Cl ⁻ , and SO ₄ ²⁻ contained in mud, dirt, etc. Diffusibility into the cured coating is reduced. That is, the cured coating film permeability of a substance that corrodes the coating object is lowered, and as a result, the cured coating film is highly effective in preventing the corrosion of the coating object due to adhesion of mud or the like.

  The diffusion coefficient (Tc) of the cured coating film is measured as follows. First, the paint film surface of the electrodeposition coated plate is immersed in the solution, and a DC voltage is applied between the painted plate and the solution. When the electrical resistance is measured over time, the resistance drops significantly at a certain point. This indicates that the solution is electrolyzed into ions, and the ions are diffused from the surface layer of the coating film through the coating film to the object to be coated. The time from when this voltage is applied until the resistance decreases is called the diffusion coefficient (Tc).

  The method of measuring the diffusion coefficient is described in Hitoshi Kawai, Takashi Yamamoto, Hiroshi Kyoko, “Color Material”, 47 (1974), page 396, left column, line 24 to line 398, left column, line 12. This part of this document is incorporated herein by reference.

  In the measurement of the diffusion coefficient, in the present invention, a galvanized steel plate is used as an object to be coated, and a coated plate that is electrodeposited to a thickness of 7 μm and dried at 150 ° C. for 25 minutes is used as a sample. Further, water / methanol mixed at a volume ratio of 1/3 is used as a solution.

As shown in FIG. 1, a platinum ring electrode 103 and a Teflon ^{(registered trademark)} ring 104 are fixed on a coating film 101 of a coating plate 100 through silicon rubber packings 102 and 102 ′. This apparatus is put into an air constant temperature layer, and the temperature is adjusted to 28 ° C. with an accuracy within ± 0.1 ° C.

  A DC voltage is applied between the workpiece 105 and the platinum electrode 103, water / methanol mixed in a volume ratio of 1/3 is placed in the ring, and the current change from this point is measured with a Keithley 610 ° C electrometer 106. Measure and record with recorder 107. The surface temperature of the coated plate is measured by attaching a copper-constantan thermocouple (PHILIPS, PR6452A) (not shown).

  In the plot showing the specific resistance (Ω · cm) of the coating film with respect to time (min), the time when the inclination first changes is Tc.

  By adding silica particles of a specific shape to the cationic electrodeposition coating composition and controlling the coating film diffusion coefficient, anticorrosion (rust prevention) can be achieved even with a film thickness thinner than the conventional common sense, for example, about 7 μm. Further, the surface smoothness of the coating film is improved. Further, when the cationic electrodeposition coating composition of the present invention is used, the corrosion resistance of the galvanized steel sheet is good also in the wet test and the dry / wet cycle test.

  The following preparation examples and examples are given by way of illustration only and not limitation. In these, “parts” and “%” are based on weight unless otherwise specified.

Production Example 1 (Synthesis of amine-modified epoxy resin)
752.0 parts bisphenol A type epoxy resin (epoxy equivalent 188), 77.0 parts methanol, 200.3 parts methyl isobutyl ketone and dilauric acid in a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel Charge 0.3 parts of dibutyltin, stir at room temperature to make a homogeneous solution, and drop 174.2 parts of a 2,4- / 2,6-tolylene diisocyanate 80/20 (mass ratio) mixture over 50 minutes. The temperature inside reached 70 ° C. The IR spectrum showed the disappearance of the absorption at 2280 cm ⁻¹ based on the isocyanate and the appearance of an absorption at 1730 cm ⁻¹ based on the carbonyl group of the urethane.

After adding 2.7 parts of N, N-dimethylbenzylamine, the temperature in the system was raised to 120 ° C., and the reaction was performed until the by-product methanol was distilled off using a decanter until the epoxy equivalent reached 463. . IR spectrum showed the appearance of absorption of 1750 cm ^-1 based on the carbonyl group of disappearance and oxazolidone rings in the absorption of 1730 cm ^-1 based on the carbonyl group of urethane.

  158.3 parts of octylic acid and 83.3 parts of methyl isobutyl ketone were added, and the reaction was continued until the epoxy equivalent reached 1146 while maintaining a temperature of 125 ° C. The system was cooled to 110 ° C., and 47.2 parts of aminoethylethanolamine ketimine (79% by weight methyl isobutyl ketone solution), 42.0 parts diethanolamine, 30.0 parts N-methylethanolamine and After adding 17.3 parts of methyl isobutyl ketone, the temperature was raised and reacted at 120 ° C. for 2 hours. In this way, an amino group-containing epoxy resin having a nonvolatile content of 80% was obtained.

Production Example 2 (Synthesis of blocked aliphatic polyisocyanate curing agent)
In a flask equipped with a stirrer, a cooler, a nitrogen inlet tube, a thermometer and a dropping funnel, 199 parts of hexamethylene diisocyanate isocyanurate type trimer (Coronate HX, manufactured by Nippon Polyurethane), 122.8 parts of methyl isobutyl ketone, And 0.2 part of dibutyltin dilaurate was weighed and heated to 50 ° C. 87 parts of methyl ethyl ketoxime was added dropwise over 2 hours while cooling from the outside and maintaining the temperature at 50 ° C. After completion of the dropwise addition, the temperature was raised to 70 ° C., and the reaction was carried out until the isocyanate group disappeared by IR analysis while maintaining this temperature to obtain an aliphatic block polyisocyanate curing agent.

Production Example 3 (Synthesis of blocked aromatic polyisocyanate curing agent)
To a flask similar to Production Example 1, 723 parts of diphenylmethane-4,4′-diisocyanate, 350 parts of methyl isobutyl ketone (MIBK) and 0.01 part of dibutyltin dilaurate were charged. The resulting reaction mixture was heated to 70 ° C., and the reaction mixture was uniformly dissolved. Then, ε-caprolactam (131 parts) was dissolved in 546 parts of butyl cellosolve, and the solution was added dropwise over 2 hours. After completion of the dropping, the reaction was continued until the absorption based on the isocyanate group disappeared in the measurement of IR spectrum while maintaining the reaction temperature at 90 ° C. to obtain a blocked aromatic polyisocyanate curing agent (resin solid content) 80%).

Production Example 4 (Production of pigment-dispersed resin)
In a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introduction tube and a thermometer, 222.0 parts of isophorone diisocyanate (hereinafter referred to as IPDI) was added, diluted with 39.1 parts of MIBK, and then 0.2 parts of dibutyltin laurate. Was added. Thereafter, the temperature was raised to 50 ° C., and then 131.5 parts of 2-ethylhexanol was added dropwise over 2 hours in a dry nitrogen atmosphere while stirring. The reaction temperature was maintained at 50 ° C. by cooling appropriately. As a result, 2-ethylhexanol half-blocked IPDI was obtained.

  Subsequently, 376.0 parts of Epicoat 828 (bisphenol A type epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd., epoxy equivalent 182-194), 114.0 parts of bisphenol A, and 29.2 parts of octyl acid were added to a stirrer, a cooling tube, and nitrogen introduced. A reaction vessel equipped with a tube and a thermometer was charged. The reaction mixture was heated to 130 ° C. in a nitrogen atmosphere, 0.15 part of dimethylbenzylamine was added, and the mixture was reacted at 170 ° C. for 1 hour under an exothermic reaction, whereby a bisphenol A type epoxy resin having an epoxy equivalent of 649 was obtained. Obtained.

  Subsequently, after cooling to 140 ° C., 396.8 parts of 2-ethylhexanol half-blocked IPDI prepared above was added, and the mixture was kept at 140 ° C. for 1 hour for reaction. Next, after diluting by adding 323.2 parts of ethylene glycol monobutyl ether, the reaction mixture was cooled to 100 ° C. Subsequently, 188.8 parts of a 78.3% MIBK solution of aminoethylethanolamine in methyl isobutyl monoketimine was added.

  The mixture was kept at 110 ° C. for 1 hour, then cooled to 90 ° C., 360.0 parts of ion-exchanged water was added, and stirring was continued for another 30 minutes, whereby the ketiminate portion in the epoxy resin was converted into a primary amino acid. Converted into a group. Excess water and MIBK were removed from this mixture under reduced pressure, and then diluted with 588.1 parts of ethylene glycol monobutyl ether to obtain a pigment dispersing resin having a primary amino group. (Resin solid content 50%)

Production Example 5 (Production of pigment dispersion paste)
In a sand grind mill, 60 parts by weight of the pigment-dispersed resin obtained in Production Example 4, 100.0 parts of the pigment described in Table 1, and 221.7 parts of ion-exchanged water are added to obtain a particle size of 10 μm or less. To obtain pigment dispersion pastes A to G.

Example 1
The amine-modified epoxy resin of Production Example 1 and the block polyisocyanate curing agent (mixture of Production Example 2 / Production Example 3 of Polyisocyanate Curing Agent 2 / Production Example 3 in a weight ratio of 1/1) were mixed at a solid content ratio of 60. : After uniformly mixing at 40, ethylene glycol mono-2-ethylhexyl ether was added to 3% based on the solid content. 90% acetic acid was added thereto for neutralization so that the neutralization rate was 43.0%, and ion-exchanged water was further added for dilution. The main emulsion was obtained by removing MIBK under reduced pressure so that the solid content was 36.0%. Using 1500.0 parts of this main emulsion and the pigment dispersion resin obtained in Production Example 4, 541.7 parts of Pigment Dispersion Paste A obtained in Production Example 5 were mixed with 1949.3 parts of ion-exchanged water and 9.0 parts of dibutyltin oxide. Thus, a cationic electrodeposition paint having a solid content of 20.0% was prepared.

  The thus prepared cationic electrodeposition paint was electrodeposited on a galvanized steel sheet to obtain a film thickness of 7 μm, and the corrosion resistance of the electrodeposition coating film obtained by baking with a dryer at 170 ° C. for 30 minutes was evaluated. The evaluation results are shown in Table 2.

Example 2
The amine-modified epoxy resin of Production Example 1 and the block polyisocyanate curing agent (mixture of Production Example 2 / Production Example 3 of Polyisocyanate Curing Agent of Production Example 2 and Production Example 3 at a weight ratio of 1/3) were mixed at a solid content ratio of 80. : After uniformly mixing at 20, ethylene glycol mono-2-ethylhexyl ether was added to 3% based on the solid content. 90% acetic acid was added thereto for neutralization so that the neutralization rate was 43.0%, and ion-exchanged water was further added for dilution. The main emulsion was obtained by removing MIBK under reduced pressure so that the solid content was 36.0%. Using 1500.0 parts of this main emulsion and the pigment dispersion resin obtained in Production Example 4, 541.7 parts of Pigment Dispersion Paste B obtained in Production Example 5 were mixed with 1949.3 parts of ion-exchanged water and 9.0 parts of dibutyltin oxide. Thus, a cationic electrodeposition paint having a solid content of 20.0% was prepared.

  The thus prepared cationic electrodeposition paint was electrodeposited on a galvanized steel sheet to obtain a film thickness of 7 μm, and the corrosion resistance of the electrodeposition coating film obtained by baking with a dryer at 170 ° C. for 30 minutes was evaluated. The evaluation results are shown in Table 2.

Example 3
The amine-modified epoxy resin of Production Example 1 and the block polyisocyanate curing agent (mixture of Production Example 2 / Production Example 3 of Polyisocyanate Curing Agent 2 / Production Example 3 in a weight ratio of 3/1) were mixed at a solid content ratio of 50. : After uniformly mixing at 50, ethylene glycol mono-2-ethylhexyl ether was added to 3% based on the solid content. 90% acetic acid was added thereto for neutralization so that the neutralization rate was 43.0%, and ion-exchanged water was further added for dilution. The main emulsion was obtained by removing MIBK under reduced pressure so that the solid content was 36.0%. Using 1500.0 parts of this main emulsion and the pigment dispersion resin obtained in Production Example 4, 541.7 parts of pigment dispersion paste C obtained in Production Example 5 were mixed with 1949.3 parts of ion-exchanged water and 9.0 parts of dibutyltin oxide. Thus, a cationic electrodeposition paint having a solid content of 20.0% was prepared.

  The thus prepared cationic electrodeposition paint was electrodeposited on a galvanized steel sheet to obtain a film thickness of 7 μm, and the corrosion resistance of the electrodeposition coating film obtained by baking with a dryer at 170 ° C. for 30 minutes was evaluated. The evaluation results are shown in Table 2.

Comparative Example 1
The amine-modified epoxy resin of Production Example 1 and the block polyisocyanate curing agent (mixture of Production Example 2 / Production Example 3 of Polyisocyanate Curing Agent 2 / Production Example 3 in a weight ratio of 9/1) were mixed at a solid content ratio of 80. : After uniformly mixing at 20, ethylene glycol mono-2-ethylhexyl ether was added to 3% based on the solid content. 90% acetic acid was added thereto for neutralization so that the neutralization rate was 43.0%, and ion-exchanged water was further added for dilution. The main emulsion was obtained by removing MIBK under reduced pressure so that the solid content was 36.0%. Using 1500.0 parts of this main emulsion and the pigment dispersion resin obtained in Production Example 4, 541.7 parts of pigment dispersion paste D obtained in Production Example 5 were mixed with 1949.3 parts of ion-exchanged water and 9.0 parts of dibutyltin oxide. Thus, a cationic electrodeposition paint having a solid content of 20.0% was prepared.

  The thus prepared cationic electrodeposition paint was electrodeposited on a galvanized steel sheet so that a film thickness of 10 μm was obtained, and the corrosion resistance of the electrodeposition coating film obtained by baking with a dryer at 170 ° C. for 30 minutes was evaluated. The evaluation results are shown in Table 2.

Comparative Example 2
The cation electrodeposition paint prepared in Comparative Example 1 was electrodeposited on a galvanized steel sheet so as to obtain a film thickness of 7 μm, and the corrosion resistance of the electrodeposition coating film obtained by baking with a dryer at 170 ° C. for 30 minutes was evaluated. . The evaluation results are shown in Table 2.

Comparative Example 3
The amine-modified epoxy resin of Production Example 1 and the block polyisocyanate curing agent (mixture of Production Example 2 / Production Example 3 of Polyisocyanate Curing Agent 2 / Production Example 3 in a weight ratio of 1/1) were mixed at a solid content ratio of 60. : After uniformly mixing at 40, ethylene glycol mono-2-ethylhexyl ether was added to 3% based on the solid content. 90% acetic acid was added thereto for neutralization so that the neutralization rate was 43.0%, and ion-exchanged water was further added for dilution. The main emulsion was obtained by removing MIBK under reduced pressure so that the solid content was 36.0%. Using 1500.0 parts of this main emulsion and the pigment dispersion resin obtained in Production Example 4, 541.7 parts of pigment dispersion paste E obtained in Production Example 5 were mixed with 1949.3 parts of ion-exchanged water and 9.0 parts of dibutyltin oxide. Thus, a cationic electrodeposition paint having a solid content of 20.0% was prepared.

  The thus prepared cationic electrodeposition paint was electrodeposited on a galvanized steel sheet to obtain a film thickness of 7 μm, and the corrosion resistance of the electrodeposition coating film obtained by baking with a dryer at 170 ° C. for 30 minutes was evaluated. The evaluation results are shown in Table 2.

Comparative Example 4
The amine-modified epoxy resin of Production Example 1 and the block polyisocyanate curing agent (mixture of Production Example 2 / Production Example 3 of Polyisocyanate Curing Agent 2 of Production Example 2 / Production Example 3 in a weight ratio of 9/1) were mixed at a solid content ratio of 95. : After uniformly mixing at 5, ethylene glycol mono-2-ethylhexyl ether was added to 3% based on the solid content. 90% acetic acid was added thereto for neutralization so that the neutralization rate was 43.0%, and ion-exchanged water was further added for dilution. The main emulsion was obtained by removing MIBK under reduced pressure so that the solid content was 36.0%. Using 1500.0 parts of this main emulsion and the pigment dispersion resin obtained in Production Example 4, 541.7 parts of Pigment Dispersion Paste F obtained in Production Example 5 were mixed with 1949.3 parts of ion-exchanged water and 9.0 parts of dibutyltin oxide. Thus, a cationic electrodeposition paint having a solid content of 20.0% was prepared.

  The thus prepared cationic electrodeposition paint was electrodeposited on a galvanized steel sheet to obtain a film thickness of 7 μm, and the corrosion resistance of the electrodeposition coating film obtained by baking with a dryer at 170 ° C. for 30 minutes was evaluated. The evaluation results are shown in Table 2.

  The electrodeposition coating film and the cured coating film obtained by electrodeposition coating the cationic electrodeposition coating compositions obtained in Examples and Comparative Examples were evaluated by the following methods.

<Coating diffusion coefficient>
It measured by the above-mentioned method using the zinc-phosphate processing steel plate (Surfdyne SD-2500 process of JIS G 3141 SPCC-SD). In this specification, it is described as the square root (√Tc) of the diffusion coefficient.

<Corrosion resistance test>
Evaluation was made in the cycle mode described in JP-A No. 2001-294816. The evaluation is as follows.
A: The generation area of blisters in 120 cycles is 30% or less.
A: The generation area of 120 cycles of blister is 50% or less
X: The generation area of 120 cycles of blisters is 80% or less.
XX: The generation area of 120 cycles of blisters is 80% or more.

It is a schematic cross section which shows one aspect | mode of the measuring method of the diffusion coefficient of a coating film.

Explanation of symbols

100 ... painted plate,
101 ... coating film,
102, 102 '... silicon rubber packing,
103 ... platinum ring electrode,
104 ... Teflon ^{(registered trademark)} ring,
105 ... Coating material,
106 ... Electrometer,
107: Recorder.

Claims (4)

  A cationic electrodeposition coating composition containing silica particles having an average particle diameter of 10 μm or less having a pore volume of 0.44 to 1.8 ml / g and a coating film diffusion coefficient √Tc = 2.5 or more by solution diffusion.   Furthermore, it contains an amine-modified epoxy resin (A) and a blocked isocyanate curing agent (B), and the weight ratio (A / B) of the amine-modified epoxy resin (A) and the blocked isocyanate curing agent (B) is 50/50. ~ 90/10, and the blocked isocyanate curing agent comprises a mixture of blocked aliphatic polyisocyanate and blocked aromatic polyisocyanate, and their weight ratio (blocked aliphatic polyisocyanate / blocked aromatic polyisocyanate) ) Is 3/1 to 1/3. The cationic electrodeposition coating composition according to claim 1.   The cationic electrodeposition coating composition according to claim 1, wherein the silica particles are contained in an amount of 1 to 30% by weight based on the total pigment. A coated article electrodeposited with the cationic electrodeposition coating composition according to claim 1.

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