JP2839169B2 - Thermosetting aqueous coating composition - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel thermosetting aqueous coating composition.

[Prior art and its problems] Aqueous paints are widely used because they use water as a medium, and in particular, there is no risk of deteriorating the working environment and causing fire.

Conventionally, as an aqueous paint, a paint obtained by neutralizing a resin composition containing a hydroxyl group-containing polycarboxylic acid resin and an aminoaldehyde resin with an amine compound and then dispersing the same in water is known. However, this requires baking at a temperature of 180 ° C or higher, and the resulting coating film has resistance to impregnation,
There is a disadvantage that the chemical properties such as acid resistance are inferior. Further, in the above-mentioned conventional paints, those using bisphenol epichlorohydrin type epoxy resin in place of the aminoaldehyde resin thicken and gel the paint system during storage and do not give a practical water-based paint.

[Means for Solving the Problems] The present inventors have conducted intensive studies for the purpose of improving the storage stability of the water-based coating composition and the curability of the coating film in a well-balanced manner. An aqueous coating composition containing a thermosetting resin composition in which a specific epoxy resin as a cross-linking agent and a quaternary ammonium compound as a reaction catalyst are mixed with a resin having a group, can achieve the above object. And completed the present invention.

Thus, the present invention provides a resin (A) having a hydroxyl group and a carboxyl group (hereinafter referred to as “resin (A)”), an epoxy group and / or an alicyclic hydrocarbon on an alicyclic hydrocarbon ring. An epoxy resin (B) having an average of two or more epoxy groups directly bonded to carbon atoms forming a ring in one molecule (hereinafter referred to as "epoxy resin (B)") and a quaternary ammonium compound (C ) Is provided as an essential component.

In the aqueous coating composition of the present invention, a hydroxyl group in the resin (A) and an epoxy in the epoxy resin (B) in the presence of a carboxyl group in the resin (A) and a base in the quaternary ammonium compound (C). It is considered that the reaction similar to the functional group with the group hardly proceeds at a temperature of about room temperature, and that the reaction similar to the functional group proceeds rapidly when baked at a temperature of about 100 ° C. It is considered that the aqueous coating composition of (1) exhibits an effect of being particularly excellent in storage stability and low-temperature curability of a coating film.

Hereinafter, the thermosetting aqueous coating composition of the present invention will be described in more detail.

The resin (A) used in the coating composition of the present invention is not limited as long as it has a hydroxyl group and a carboxyl group. For example, conventional resins based on vinyl resins, polyester resins, polyether resins, etc. Any resin known in the coatings art can be used. The following are representatives of such resins.

(1) Examples of the vinyl resin include hydroxyethyl (meth) acrylate and hydroxypropyl (meth).
Hydroxyl-containing monomers such as acrylate, hydroxybutyl (meth) acrylate, polycaprolactone diol mono (meth) acrylate, and polyoxyethylene glycol mono (meth) acrylate; carboxyl-containing monomers such as (meth) acrylic acid, carboxyethyl acrylate, and itaconic acid Monomers; and, if necessary, methyl (meth) acrylate, ethyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, acrylonitrile, acrylamide, styrene, Functional groups that react with hydroxyl groups and carboxyl groups such as vinyl toluene, vinyl acetate, i-propyl vinyl ether, n-butyl vinyl ether, and methoxyethyl vinyl ether That the radically polymerizable unsaturated group-containing monomer were obtained by co-polymerizing the non like.

(2) Examples of polyester resins include polyol components such as trimethylolethane, trimethylolpropane, pentaerythritol, glycerin, ethylene glycol, propylene glycol, 1,3-butylene glycol, neopentyl glycol, and 1,6-hexanediol. And (anhydride) phthalic acid, isophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, adipic acid,
(Anhydride) A polyester resin obtained by polycondensation with a polycarboxylic acid component such as trimellitic acid; a product obtained by modifying the polyester resin with a fatty acid or an epoxy resin; and a modified polyester resin grafted with acryl; a bisphenol-epichlorohydrin type epoxy resin Modified polyester resins obtained by adding an acid anhydride such as maleic anhydride to an esterified product modified with a fatty acid or the like are exemplified.

(3) As the polyether resin, for example, a resin obtained by polymerizing a bisphenol / epichlorohydrin type epoxy resin in the presence of a catalyst and adding a polycarboxylic acid or the like can be suitably used.

Among the above-mentioned resins (A), a coating film having excellent aesthetics and weather resistance can be obtained, and thus can be obtained by copolymerizing a hydroxyl group-containing monomer, a carboxyl group-containing monomer, and if necessary, other monomers. Acrylic copolymers are particularly preferred.

Resin (A) generally has an acid number in the range of about 1 to about 100, preferably about 10 to about 80, and a hydroxyl value of about 10 to about 5,000.
It is desirably in the range of 0, preferably about 20 to about 2,000. When the acid value is less than about 1, it is difficult to make the composition aqueous, and when the acid value is more than about 100, the storage stability of the coating material is deteriorated. Also, the hydroxyl value is about
When the value is less than 10, the curability of the coating film decreases, and the coating film performance such as hardness and flex resistance tends to decrease.On the other hand, when the hydroxyl value exceeds about 5,000, the coating performance such as water resistance and corrosion resistance decreases. It is not so preferable because it lowers.

The resin (A) generally has a number average molecular weight of about 1,000 to
Preferably it is in the range of about 100,000, preferably in the range of about 2,000 to about 80,000, and has a softening point of less than 130C, preferably less than about 115C. If the number average molecular weight is less than about 1,000, the coating properties such as hardness, flex resistance, and corrosion resistance are likely to decrease,
On the other hand, when the number average molecular weight is more than about 100,000, the appearance of the coating film such as smoothness tends to be deteriorated. On the other hand, if the softening point is higher than about 130 ° C., the appearance of the coating film such as smoothness tends to deteriorate.

Resin (A) is, in addition to the above hydroxyl group and carboxyl group,
Functionalities such as a phenolic hydroxyl group and an alkoxysilane group (and a hydroxysilane group) can be introduced as necessary. The method for introducing these functional groups is not particularly limited, and a method known per se can be used,
For example, the introduction of a phenolic hydroxyl group uses bisphenol-modified (meth) acrylate as a monomer component of the vinyl resin, and the introduction of an alkoxysilane group (and a hydroxysilane group) uses γ-methacryloxypropyltrimethoxysilane and It can be carried out by using a compound such as a hydrolyzate as a monomer component of the vinyl resin and copolymerizing the same.

Epoxy resin (B) used in the coating composition of the present invention
Is at least two or more epoxy groups per molecule selected from an epoxy group on an alicyclic hydrocarbon ring and an epoxy group directly bonded to a carbon atom forming the alicyclic hydrocarbon ring. And the alicyclic hydrocarbon ring may be a member having a small member of 3 to 7 or more, and the ring may be monocyclic or polycyclic, Further, the ring may constitute a bridged hydrocarbon ring. As the epoxy group on the alicyclic hydrocarbon ring,
For example: The epoxy group directly bonded to a carbon atom forming an alicyclic hydrocarbon ring includes, for example, a group represented by the following formula: The group shown by these is mentioned.

As the epoxy resin (B), a commercially available epoxy resin can be used, and specific examples of such an epoxy resin include the following.

And other bifunctional epoxy resins.

In addition to the above [X in the above formula is Or -OR, wherein R is a C _1-36 hydrocarbon group, n is 0-100, m is 5-100, p
Is 2 to 100]. An epoxy resin containing a unit such as
9667)), [In the formula, k is an integer of 0 to 15.] It is also possible to use a trifunctional or higher functional epoxy resin.

In combination with the epoxy resin (B), other epoxy resins having an epoxy group such as a glycidyl ether type epoxy resin and an aliphatic internal epoxy resin can also be used. The other epoxy resin is desirably used at a ratio of about 25% by weight or less based on the total amount of both, from the viewpoints of storage stability of the paint and curability of the coating film.

The epoxy resin (B) generally has a number average molecular weight of about 100.
From about 100,000, preferably from about 110 to about 20,000, with an epoxy equivalent of from about 50 to about 2,000, preferably from about 55 to about 2,000.
Is in the range of about 1,000, and has a softening point of about 130 ° C. or less,
Preferably it is below about 115 ° C. Those having a number average molecular weight of less than about 100 are difficult to obtain, while those having a number average molecular weight of more than about 100,000 are not preferred because of poor coated surface smoothness. Those having an epoxy equivalent of less than about 50 are difficult to obtain, while
If the epoxy equivalent is greater than about 2,000, the curability of the coating tends to decrease. Further, when the softening point is higher than about 130 ° C., the smoothness of the coating film tends to deteriorate.

The resin (A) and the epoxy resin (B) are generally used in an amount of about 40 to about 97% by weight, preferably about 50 to about 95% by weight, and more preferably about 60 to about 90% by weight in terms of the total weight of both. %, About 3 to about 60% by weight, preferably about 5 to about 50% by weight, and more preferably about 10 to about 40% by weight. Less than about 40% by weight of resin (A) and about 60% by weight of epoxy resin (B)
The higher the amount, the lower the water dispersibility of the obtained coating composition, while the lower the amount of the resin (A) and the amount of the epoxy resin (B), the lower the water resistance and corrosion resistance. In addition, the coating film performance such as bending resistance is deteriorated. The epoxy resin (B) has a hydroxyl group in the resin (A) in an equivalent ratio (hydroxyl group / epoxy group) of about 0.3 or more, preferably about 0.5 to the epoxy group in the epoxy resin (B).
To about 5, more preferably about 0.7 to about 4, and the resin (A) is desirably blended with the resin (A). ) Components tend to increase, and the coating properties such as flex resistance, water resistance and corrosion resistance tend to decrease. The carboxyl group in the resin (A) is for stably dispersing the epoxy resin (B) in water. It is desirable that the equivalent ratio be in the range of about 0.1 to about 1, preferably about 0.1 to about 0.6.

 Quaternary ammonium used in the coating composition of the present invention
Compound C) has the general formula: [R¹R^TwoR^ThreeR^FourN ] X Indicated by
Can be used. In the above formula, R¹,
R^Two, R^ThreeAnd R^FourRepresents a hydrocarbon group, and these are
They may be the same or different. The above hydrocarbons
The groups may be substituted with hydroxy groups. X is haloge
Represents an anion or an anionic residue of an acid, such as Cl, Br,
F, I, SO_Four, HSO_Four, NO_Three, PO_Four, ClO_Four, HCOO, CH_ThreeCOO, O
H and the like.

Specific examples of the quaternary ammonium compound (C) include, for example, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride, methyltriethylammonium chloride, tetramethylammonium bromide, tetraethylammonium fluoride, tetraethylammonium Tetraalkylammonium halides such as iodide; tetraalkylammonium organic acid salts such as tetramethylammonium acetate and tetraethylammonium formate; tetramethylammonium hydrogen sulfate, tetraethylammonium hydrogensulfate, tetramethylammonium nitrate, tetraethylammonium nitrate, perchlorine Tetraethylammonium phosphate, tetraethylammonium phosphate, etc. Laalkylammonium inorganic acid salt; tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, tetraisoamylammonium hydroxide, tetradodecylammonium hydroxide, methyltriethyl Ammonium hydroxide, ethyltrimethylammonium hydroxide, decyltrimethylammonium hydroxide, monohydroxyethyltrimethylammonium hydroxide, monohydroxyethyltriethylammonium hydroxide, dihydroxyethyldimethylammonium hydroxide, dihydroxyethyldiethylammonium hydroxide, trihydroxy Quaternary ammonium hydroxides such as tylmonomethylammonium hydroxide, trihydroxyethylmonoethylammonium hydroxide, benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, benzylmethyldiethylammonium hydroxide and cyclohexyltrimethylammonium hydroxide; Can be

Among the above-mentioned quaternary ammonium compounds, quaternary ammonium hydroxide easily disperses the resin (A) and the epoxy resin (B) in water to give a coating composition having excellent storage stability, and It has the advantage that a coating film having excellent water resistance, corrosion resistance and the like can be formed, and can be used particularly preferably.

The quaternary ammonium compound (C) is generally used in an amount of about 0.01 to about generally based on the total weight of the resin (A), the epoxy resin (B) and the quaternary ammonium compound (C).
10% by weight, preferably about 0.1 to about 7% by weight, more preferably 0.1 to 5% by weight.

The coating composition of the present invention can be prepared, for example, by adding an epoxy resin (B) to a solution obtained by dissolving or dispersing the resin (A) in an organic solvent.
Or a solution obtained by dissolving or dispersing the epoxy resin (B) in an organic solvent, and then mixing the resulting mixture with a quaternary ammonium compound (C) and, if necessary, a neutralizing agent. Can be obtained. The organic solvent that can be used for dissolving or dispersing the resin (A) or the epoxy resin (B) is preferably an organic solvent that is substantially inert to the functional groups of these resins. Examples thereof include alcohol solvents, ether solvents, ketone solvents, ester solvents, and hydrocarbon solvents. Among these, it is particularly preferable to use a hydrophilic solvent such as an alcohol solvent or an ether solvent as a main solvent. On the other hand, examples of the neutralizing agent include ammonia, trimethylamine, triethylamine, tributylamine, dimethylethanolamine, diethylethanolamine, dimethylpropanolamine, methyldiethanolamine, ethyldiethanolamine, and triethanolamine. Further, as described above, when a quaternary ammonium hydroxide is used as the quaternary ammonium (C), the resin component can be dispersed in water without particularly using a neutralizing agent. If necessary, the quaternary ammonium compound (C) can be used in combination with the neutralizing agent.

In the coating composition of the present invention, for example, polytetramethylene glycol, bisphenol A
-Ethylene oxide adducts, polycaprolactone polyols, polycarbonate diols, polyurethane polyols, vinyl alcohol (co) polymers, styrene-allyl alcohol copolymers, and other polyol resins that do not contain carboxyl groups can also be blended. Further, for the purpose of curing the coating film at a lower temperature, a phenol compound (for example, catechol, etc.), a silanol compound (for example, diphenylsilanediol, etc.), a metal chelate compound (for example, Al, Ti, V, Fe, Zn, Zr) , A chelate of a metal such as Sn with a β-diketone such as ethyl acetoacetate, trifluoroacetylacetone or dibenzoylacetylacetone). The (co) catalyst is usually used in an amount of about 0.01 to 100 parts by weight of the total of the resin (A) and the epoxy resin (B).
It can be blended within a range of from about 10 parts by weight.

Further, the coating composition of the present invention may contain a coloring pigment (for example, titanium white, carbon black, red iron, etc.) and an extender (for example, clay, talc, silica, etc.) as necessary.
And other paint additives (for example, a pigment dispersant, an anti-cissing agent, a fluidity adjusting agent, etc.) and the like.

The method of forming a coating film using the coating composition of the present invention is not particularly limited. For example, electrodeposition coating, spray coating, dip coating, roller coating, coating on a substrate surface by means such as brush coating, and drying. Can be implemented. The coating film thickness is not particularly limited, but usually, a range of 10 to 100 μm seems to be sufficient. Drying of the coating is usually about 120 ° C
About 30 minutes, and at about 180 ° C. for about 10 minutes. The substrate to be applied is also not particularly limited, but preferably is steel, aluminum, alumite, copper, plated steel in which zinc, tin, chromium, aluminum, etc. are plated on the surface of steel, or chromic acid, phosphoric acid Can be applied to a wide range of metals such as those subjected to chemical treatment or electrolytic treatment.

[Examples] Next, the present invention will be described specifically with reference to examples, but the present invention is not limited thereto. “Parts” and “%” in Examples and Comparative Examples are based on weight.

Example 1 A four-necked flask was charged with 89 parts of methylpropanol.
Heat to 0 ° C. 3 parts of acrylic acid, 20 parts of hydroxyethyl acrylate, 57 parts of methyl methacrylate
20 parts of the mixture and 2,2'-azobisisobutylnitrile 1
And a mixture of 10 parts of methyl isobutyl ketone is added dropwise over 1 hour. Aged for another 1.5 hours, acid value 23, hydroxyl value 9
7. A resin having a number average molecular weight of about 20,000 and a solid content of 50% was obtained. 25 parts of EHPE-3150 (epoxidized polyvinyl cyclohexene oxide, epoxy equivalent 190, average molecular weight about 1500; trade name, manufactured by Daicel Chemical Industries, Ltd.) was added to methylpropanol.
31.3 parts of an 80% EHPE-3150 solution dissolved in 6.3 parts was added, and 19.5 parts of a 20% aqueous solution of tetraethylammonium hydroxide was further added. While stirring, 166 parts of deionized water was added to give a solid content of 30%, and an average particle diameter of 30%. An aqueous dispersion of 0.10 μm was obtained. The storage stability ^{(* 1)} of the obtained water-dispersed product was not abnormal with the paint state and the coating film performance. In addition, the water dispersion before storage test was applied to zinc phosphate treated steel sheet with a dry film thickness of about
It was spray-coated to 20 μm, dried at 80 ° C. for 10 minutes, and further dried at 120 ° C. for 20 minutes to obtain a coated product. The coated material has good coating smoothness ^{(* 2)} and salt spray resistance
^{(* 3)} pass, pencil hardness ^{(* 4)} 2H, flex resistance ^{(* 5)}
It passed. Further, the gel fraction ^{(* 6)} of the coating film was 90%.

Example 2 4 parts of methacrylic acid, 25 parts of hydroxyethyl methacrylate, 10 parts of 2-ethylhexyl methacrylate, 10 parts of methyl methacrylate under the same conditions as in Example 1 except that the monomer components were all replaced by the following. 51
Parts, styrene 10 parts of acrylic resin of monomer composition was synthesized, acid value 26, hydroxyl value 108, number average molecular weight 25000, solid content
200 parts of a 50% resin were obtained. To this, 18.8 parts of 80% EHPE3150 was added (15 parts in solid content), and 16.2 parts of a 10% aqueous solution of tetramethylammonium hydroxide was further added. While stirring, 148 parts of deionized water was added, and the solid content was 30%, averaged. Particle size 0.1
5 μm of an aqueous dispersion was obtained. The storage stability ^{(* 1)} of the obtained water-dispersed product was not abnormal in both the paint state and the coating film performance. The water dispersion before the storage test was painted in the same manner as in Example 1,
The coating was obtained by drying. The coating is smooth
^{(* 2)} good, salt spray ^{(* 3)} passed, pencil hardness ^{(* 4)} 2H, flex resistance ^{(* 5)} passed. Further, the gel fraction ^{(* 6)} of the coating film was 92%.

Example 3 200 parts of the 50% resin obtained in Example 1, 3,4-epoxycyclohexylcarboxymethylcyclohexene oxide 15
Parts, 10% tetrabutylammonium hydroxide aqueous solution
While stirring a mixture of 17.9 parts and 2 parts of triethylamine, 148 parts of deionized water was added thereto to give a solid content of 30% and an average particle size of 0.09.
A μm aqueous dispersion was obtained. The storage stability ^{(* 1)} of the obtained water-dispersed product was not abnormal in both the paint state and the coating film performance. Spray the water dispersion before storage test on a zinc phosphate treated steel sheet so that the dry film thickness is about 20 μm,
After drying for 10 minutes, the coating was further dried at 140 ° C. for 20 minutes to obtain a coated product. The coated material has good coating smoothness ^{(* 2)} , passed salt spray resistance ^{(* 3)} , pencil hardness ^{(* 4)} 2H, bending resistance
^{(* 5)} Passed. Furthermore, the gel fraction of the coating film
^{(* 6)} was 93%.

Comparative Example 1 In Example 1, 20 parts of hydroxyethyl acrylate and 57 parts of methyl methacrylate were added to 77 parts of methyl methacrylate to give a 20% aqueous solution of tetraethylammonium hydroxide.
A water dispersion having a solid content of 30% was obtained in the same manner as in Example 1 except that 19.5 parts was replaced with 3.4 parts of triethylamine and 166 parts of deionized water was replaced with 172 parts. The storage stability ^{(* 1)} of the obtained aqueous dispersion was not abnormal. The water-dispersed product before storage was coated and dried in the same manner as in Example 1 to obtain a coated product. The coated material has good coating smoothness ^{(* 2)} and salt spray resistance
^{(* 3)} reject, pencil hardness ^{(* 4)} 4B, bending resistance
^{(* 5)} Failed. Furthermore, the gel fraction of the coating film
^{(* 6)} was 55%.

( ^* 1) Storage stability: After standing at 30 ° C. for one month, the sedimentation and separation of the dispersion were visually observed. Further, the water-dispersed product after storage was painted and dried, and the initial appearance of the coating film and the presence or absence of a decrease in coating film performance (such as salt spray resistance, bending resistance, and pencil hardness) were examined.

( ^* 2) Coating smoothness: The unevenness of the coating film surface was visually observed.

( ^* 3) Salt spray resistance: Tested in accordance with JIS Z-2371, and those with a creep width within 2 mm on one side from the cut part of the coating film were accepted. The test time was 1000 hours.

( ^* 4) Pencil hardness: Tested in accordance with JISK-5400.

( ^* 5) Bending resistance: The test plate is bent at a right angle in 1 to 2 seconds in an atmosphere at a temperature of 20 ° C. Peeling of the coating film at the bent part,
Those that had no abnormalities such as cracks were accepted.

( ^* 6) Gel fraction: 300 peeled off dried coating film
After being placed in a mesh stainless steel mesh net-like container and extracted with a Soxhlet extractor at a reflux temperature for 6 hours using acetone / methanol = 1/1 solvent, the gel fraction was calculated according to the following equation.

Gel fraction (%) = (coating weight after extraction / coating weight before extraction)

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification symbol FI C09D 201/08 C09D 201/08 (58) Investigated field (Int.Cl. ⁶ , DB name) C09D 163/00-163/10 C09D 201/02-201/08 C09D 5/00 C08G 59/20 C08G 59/40

Claims (1)

(57) [Claims] 1. A resin (A) having a hydroxyl group and a carboxyl group, and one molecule of an epoxy group on an alicyclic hydrocarbon ring and / or an epoxy group directly bonded to a carbon atom forming an alicyclic hydrocarbon ring. A thermosetting aqueous coating composition comprising, as essential components, an epoxy resin (B) and a quaternary ammonium compound (C) having an average of two or more of them.