JP3480964B2 - Water-based coating material composition having blister preventing ability - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a latent cross-linking agent which prevents swelling and cracking of a film which is generated during heating and drying when line-coating a water-based undercoat material to be applied on the bottom surface of an automobile or the like, and a mixture thereof. And a water-based coating material composition.

More specifically, the present invention relates to the application of a water-based coating material composition containing a water-dispersible urethane resin emulsion as an undercoat material for coating automobile steel sheets such as galvanized steel sheets and cationic electrodeposition steel sheets. The present invention relates to an additive that prevents swelling and cracks that occur in a film in a heating and drying step, and an aqueous coating material composition containing the additive.

[0003] In particular, the use of the above-mentioned additives forms a dense film and exhibits strong adhesiveness to an adherend.
It is possible to form a film suitable for protecting the automobile body from the impact of flying stones from the road surface during traveling and for preventing corrosion due to salt such as calcium chloride sprayed as a snow melting agent.

[0004]

2. Description of the Related Art In recent years, the automobile industry has been confronted with global environmental problems, resource conservation, and high-performance problems, and is emitted during the recycling of volatile solvents and structures discharged during painting of paints and the like. It is required to review materials containing environmental pollutants. In particular, the problem of environmental pollution due to combustion of materials containing organic chlorine compounds has come to be highlighted.

Conventionally, a vinyl chloride plastisol composition has been widely used as an undercoat material for the purpose of rust prevention and chipping resistance of the bottom surface of automobiles and the like. The use of such a composition has led to the development of a polyamide-based or blocked isocyanate-based adhesion improver that improves the adhesion between galvanized steel sheet, cationic electrodeposition steel sheet and vinyl chloride plastisol, which results in chipping resistance. It was because of the dramatic improvement.

However, the vinyl chloride resin used in automobiles these days produces a large amount of harmful hydrogen chloride gas when it is incinerated after it is scrapped, which is regarded as a cause of environmental pollution such as acid rain and the atmosphere. This is the current situation.

Therefore, devinylation of the undercoat material is rapidly progressing, and various alternative coating materials are being devised. Among them, water-based coating materials, which emit a small amount of solvent and generate a toxic gas, are attracting attention.

However, the conventional vinyl chloride plastisol composition has no volatile component and does not lose its thickness during film formation.
Since the solid content of the water-based undercoat material is 70 to 80% and the volatile component is water with high latent heat of vaporization, swelling occurs when a film is formed in the same heating and drying process as the vinyl chloride plastisol-based undercoat material. There is a drawback that coating defects such as cracks and cracks tend to occur. Therefore, the use of various additives is indispensable for preventing this.

Examples of such additives include thickeners, dispersants, film-forming aids, anti-swelling agents, drying property modifiers, antiseptic / antifungal agents and the like.

As the binder resin for the water-based undercoat material, a water-dispersible resin having a good drying property is used because of the requirement for thickening the film. Generally, an acrylic resin emulsion, a urethane resin emulsion or an SBR resin is used alone or individually. Often used in combination.

Undercoat materials are classified into 1, 2, and 3 types according to the required performance, but cold resistance and
Strict physical properties such as chipping resistance are required 2
In types 3 and 3, urethane resins having good adhesiveness and film physical properties tend to be used in many cases.

However, the urethane resin has a drawback that it undergoes depolymerization in a high temperature atmosphere. Urethane resin generally varies depending on the materials that make it up, but is generally 120-130 ° C.
Depolymerization begins. In particular, a resin using a polyether polyol as a raw material tends to be decomposed at a low temperature due to cleavage of the urethane bond itself to cause softening of the film.

Therefore, when the water-based undercoat material based on the urethane resin emulsion is applied to an ordinary automobile manufacturing line or the like and forcedly dried in a high temperature baking oven, the coating film may be swollen or cracked. is there.

It has been conventionally known that these coating film defects can be prevented by adding a small amount of polyamine. However, when polyamine is added to the urethane resin emulsion undercoat material, the storage stability is remarkably increased. It had the drawback of making it worse. That is, when the undercoat material is used for a short time after preparation, it is good, but when it is stored for a long time, there is a drawback that viscosity or gelation occurs and the workability during spray coating deteriorates. Further, there is a defect that the coating film turns brown due to heating and drying, which significantly deteriorates the appearance.

[0015]

DISCLOSURE OF THE INVENTION The present invention provides a water-based coating material composition which prevents swelling and cracking during film formation under heating and drying, which is a drawback of the polyurethane resin, and which is excellent in storage stability. Especially.

[0016]

[Means for Solving the Problems] The inventors of the present invention have earnestly studied for the purpose of preventing swelling or cracking caused by cleavage of a polyurethane resin in a film forming process of an aqueous coating material composition containing a polyurethane resin. As a result, the inventors have found that the addition of a specific latent crosslinking agent prevents blistering and cracking without affecting storage stability, and has completed the present invention.

That is, these coating film defects are caused by carbon dioxide gas generated by thermal cleavage of the urethane bond of the water-dispersible urethane resin emulsion contained therein when the water-based undercoat material is baked at a high temperature in an automobile production line. It is considered that this occurs because the bubbles remain in the coating film. Generally, three types of thermal decomposition reaction of urethane bond are generally proposed as shown in the following equation (coloring material, 53 [1
1] 676-688.1980).

[0018]

[Chemical 1]

Cleavage of the urethane bond occurs at 120 to 200 ° C., but the reaction of (1) proceeds at a temperature of 175 ° C. or lower, and the amine-forming reactions of (2) and (3) occur at a high temperature of 175 ° C. or higher. It is believed that. The actual baking temperature of the water-based undercoat material when baking at high temperature in an automobile production line is 130 to 140 ° C, and it is considered that mainly the reaction (1) occurs. Therefore, it is considered that the dissociated isocyanate reacts with water to generate carbon dioxide gas, which causes these coating film defects. The present invention prevents the generation of carbon dioxide gas by trapping -N = C = O generated in this equilibrium state with a polyamine compound by adding a specific latent cross-linking agent, and forms a cross-linked structure by a urea bond. It is intended to form a tough film by removing.

That is, in the present invention, a polyamine [a] is added to a water-based coating material composition containing a water-dispersible urethane resin emulsion at a phenolic hydroxyl group equivalent of 130 to 1.
The latent cross-linking agent [c] blocked with the phenol resin [b] in the range of 000 is dispersed and blended in the form of powder having a maximum particle size of 50 μm or less to prevent swelling and cracking in the film forming process.

[0021] Conventionally, vinyl chloride plastisol has been applied by spray coating as an undercoat material for automobiles, and is simultaneously formed into a film during the baking and curing process of the aminoblast-based coating material for vehicle body outer panels.

The viscosity required for the water-based undercoat material is that it can be spray-coated and can be coated to a desired film thickness without dripping. For this purpose, an appropriate coating viscosity and thixotropic property are required. It must also have excellent storage stability. In the case of vinyl chloride plastisol, the storage stability at 35 ° C. for 10 days is suppressed within 30% in terms of viscosity change rate, and it is required that the water-based undercoat material also has a minimum value of less than that.

Generally, in order to prevent swelling and cracks during film formation in a water-based undercoat material using a water-dispersible urethane resin, a polyamine-based curing agent (for example, a trade name of curing agent P manufactured by Hodogaya Chemical Co., Ltd.) is used. It is possible to add an amine compound such as, but the storage stability is significantly deteriorated, the viscosity becomes thick even at room temperature storage, spray coating cannot be performed, and further gelation may occur.

It is considered that this is because the amino group of the curing agent breaks the dispersed particles of the water-dispersible urethane resin or causes a crosslinking reaction with the dissociated isocyanate to cause thickening or gelation. Therefore, it is necessary to prevent the free amine from eluting into water as a dispersion medium, and the present inventors have prepared a water-based coating material composition of a latent crosslinking agent in which an amino group is blocked with a phenol resin having a hydroxyl equivalent of 130 to 1000. It has been found that by adding finely dispersed powder to the product, a storage stability is good and a film without swelling or cracks can be obtained during film formation.

In order to improve storage stability, the powdery latent crosslinking agent of the present invention is set so that its melting temperature and the dissociation temperature of the urethane resin compounded in the water-based coating material composition are close to each other. It is effective.

The polyamine used in the latent crosslinking agent of the present invention may be aliphatic, alicyclic, or aromatic. Further, these polyamines can be mixed and used in the same or different groups.

As the aliphatic, ethylenediamine,
Diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,2-propylenediamine,
1,3-diaminopropane, 1,4-diaminobutane,
1,6-hexamethylenediamine, undecamethylenediamine, 2,2-dimethylpropane, 1,3-diamine and the like can be mentioned.

As the alicyclic group, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, 4,
4'-diamino-3,3'-dimethyldicyclohexylmethane, 4,4'-diamino-3,3'-dimethyldicyclohexyl and the like can be mentioned.

As the aromatic system, phenylenediamine, diaminodiphenylmethane, 4,6-dimethyl-m
-Phenylenediamine, 2,4-diaminomesitylene,
4,4'-methylene-2,6-diethylaniline, m-
Examples thereof include aminobenzylamine and xylenediamine.

The polyamine used in the present invention is not limited to the compounds exemplified here.

The ratio of the hydroxyl equivalent of the phenol resin used in the latent crosslinking agent of the present invention to the amine equivalent of the polyamine is 1:
The range of 0.5 to 1: 2.0 is preferable, and various properties as an undercoat material are excellent. When the equivalent ratio of the amine to the phenol resin is less than 0.5, a sufficient blistering prevention effect cannot be obtained, and when it is more than 2.0, the latent cross-linking agent according to the present invention easily dissolves in the solvent, This causes deterioration in storage stability of the water-based undercoat material composition, and further deteriorates workability in pulverizing the latent crosslinking agent according to the present invention.

As the phenol resin used in the latent crosslinking agent of the present invention, industrially used phenols,
For example, addition condensates of phenol, cresol, xylenol, resorcin and the like with formalin and the like, and either type of resol or novolac can be used. Also, p-
Dehydrogenation of ethylphenol, p-hydroxystyrene polymer which is a thermal polymer, and the like can also be used.

Any of the above-mentioned phenol resins alone or modified phenol resins modified with rosin, ester gum, drying oil, synthetic rubber or the like, or a mixture thereof having a hydroxyl equivalent of 130 to 1000 can be used. can do.

If the hydroxyl equivalent of the phenolic resin is less than 130, the water-solubility of the blocked product with amine becomes strong and elutes over time to deteriorate the storage stability. Also, 1000
The amount exceeding 10% has a small amount of blocked amine,
The amount of effective addition to the water-based coating material composition increases, which may impair the film physical properties such as chipping resistance.

The softening point of the phenol resin used in the present invention is 6 because the latent crosslinking agent is pulverized and added as a fine powder.
It is preferably in the range of 0 to 180 ° C. When the temperature is lower than 60 ° C, tackiness occurs in the blocked product with the amine to deteriorate the pulverizability, and when the temperature is higher than 180 ° C, the phenol resin itself may be condensed when melt-neutralizing the phenol resin and the polyamine, which is not preferable. .

The latent crosslinking agent used in the present invention is blended in the form of powder in consideration of the storage stability of the water-based coating material composition, but the particle diameter is preferably 50 μm or less at the maximum. When the particle size exceeds 50 μm, it is difficult to disperse the particles uniformly in the water-based undercoat material, and the effect of preventing swelling and cracks may not be sufficiently obtained when forced heating and drying.

The latent crosslinking agent can be pulverized by a hammer mill, a jet mill, a dry mill such as a media mill. Especially for those having a low softening point, a freeze pulverization method using liquid nitrogen or the like can be used.

The compounding amount of the latent crosslinking agent according to the present invention with respect to the aqueous coating material composition is preferably in the range of 0.3 to 2.0%. If the content is less than 0.3%, no sufficient effect can be expected, and if it exceeds 2.0%, the coating may turn yellow during baking depending on the type of polyurethane resin contained in the water-based coating material composition. It may come.

The water-dispersible urethane resin emulsion used in the present invention is not particularly limited, but its resin film strength is 3 kg / cm ² to 15 at 100% modulus.
Those of 0 Kg / cm ² are preferable because they have excellent physical properties as an aqueous undercoat material. For example, Aizerax S-1
020 (100% modulus, 6 kg / cm ² ), S-
1040 (100% modulus, 15 Kg / cm ² ),
S-2020 (100% modulus, 20Kg / cm
² ), S-5050L (100% modulus, 16Kg
/ Cm ² ), S-1085C (100% modulus, 1
5 Kg / cm ² ) (trade name, manufactured by Hodogaya Chemical Co., Ltd.), Hydran HW-111 (100% modulus, 32 Kg / cm ² ), HW-301 (100% modulus, 15 Kg / cm ² ), Bondik 1612NS
C (100% modulus, 15 Kg / cm ² ) (these are trade names, manufactured by Dainippon Ink and Chemicals, Inc.) and the like.

In addition, an ionic group such as a carboxyl group is introduced into a side chain or a terminal of a polyurethane resin polymer, or a polyol portion which is a main raw material of polyurethane has a hydrophilic group such as ethylene oxide or propylene oxide. It is also possible to use a self-emulsifying urethane resin which is emulsified and dispersed in water using.

The water-based coating material composition of the present invention includes an emulsion resin filler, a cosolvent, and various other additives. Heavy calcium carbonate is generally used as the filler, but kaolin,
Diatomaceous earth, talc and the like can also be used. Also,
In order to adjust the specific gravity of the water-based undercoat material itself in order to reduce the weight of automobiles and prevent sagging during coating and film formation, a filler for adjusting the specific gravity such as pulp fiber or hollow glass balloons can also be used. However, it is not preferable to use a large amount of these specific gravity adjusting fillers because they deteriorate the physical properties of the undercoat material.

Other optional additives include thickeners. To apply the prepared coating solution to a constant film thickness without dripping, 10,000mPa · s (E-type clay meter, 5r
The viscosity and thixotropy are required around pm, 20 ° C). For these purposes, hydroxyethyl cellulose, carboxymethyl cellulose, water-soluble polysaccharides (trade name, Kelzan, manufactured by Sansho Co., Ltd.), polyacrylates, associative thickeners, etc. as an organic system, and anhydrous as an inorganic system Silica, bentonite, synthetic mica, metal soap, etc. can be used.

As the wetting and dispersing agent, a surfactant, a polymer surfactant, a water-soluble polymer compound or the like can be used.

A film-forming agent and a film-forming auxiliary are also used in order to adjust the surface of the dried coating film and prevent small cracks such as cracks. For these additives, it is common to use alcohol or alcohol ether type solvent. In addition, an antifreeze agent for emulsion, an antiseptic and antifungal bactericidal agent are also added.

The coating method of the undercoat material for automobiles is as follows.
It has been conventionally performed by a spray method, and it is preferable that the coating method of the water-based coating material composition of the present invention is performed by an airless type spray coating machine as in the conventional method.

The heat-drying conditions for the water-based coating material composition of the present invention applied to an adherend are at least 90 ° C. and 1
After preheating for 0 minutes, it is preferable to heat-dry at 130 to 140 ° C. for 20 to 30 minutes.

When the water-based coating material composition of the present invention is applied to an adherend, the dry coating film has a thickness of 300 to 1000 μm.
To be applied. Generally, a plurality of robots are used for coating an undercoat material in an automobile manufacturing line or the like, and the film thickness of the overlapped portions of the robots reaches 2000 to 3000 μm. In those portions having a high film thickness, the water inside the coating film may not be sufficiently evaporated and swelling may occur in a short time forced drying. In order to prevent the swelling of such a portion, it is particularly effective to add a latex coagulant such as an inorganic salt or a polymer surfactant.

[0048]

EXAMPLES The present invention will be described below with reference to Synthesis Examples 1 to 10 and performance evaluation tests, but the present invention is not limited to these. The test method of the performance evaluation test will be described later.
Central part and% are weight.

[Synthesis of Latent Crosslinking Agent] Synthesis Example 1 A novolac type phenol resin (Super Beckasite 3011 Dainippon Ink and Chemicals, Inc.) Made, hydroxyl equivalent 560, softening point 129 ° C) 560
Parts are weighed and melted by heating under a nitrogen stream at 150 ° C. Next, 68 parts of xylylenediamine is gradually added while maintaining the same temperature to melt and mix, and the uniformly melted mixture is put into another container and cooled and solidified. Then SAMPLE MILL
(Fuji Paudal Co., Ltd.) Finely pulverized with a pulverizer, further sieve-filtered with a 300-mesh wire mesh to obtain a maximum particle size of 50.
A fine powder of latent crosslinking agent 1 having a particle size of less than or equal to μm was obtained. The particle size of the powder is measured by Microtrac particle size distribution meter (LEEDS & NO
RTHRUP INSTRUMENTS).

Synthesis Example 2 1 liter equipped with a reflux condenser, a stirrer and a thermometer 4
188 parts of phenol-neck flask, 250 parts of 37% aqueous formaldehyde, take the _{Ba (OH) 2 · 8H 2} O 9.4 parts, was heated at 70 ° C.. Then 10% for the reaction
The pH was adjusted to 7 by adding sulfuric acid. And 30 ~ 50mmHg
After water was distilled off under reduced pressure of 70 ° C. or lower to obtain a soluble brown solid, rosin was added to these and heated to obtain a rosin-modified phenol resin having a hydroxyl equivalent of 130. Furthermore, an equivalent amount (44 parts) of 1,4 diaminobutane was added to 130 parts of this rosin-modified phenolic resin and uniformly mixed, followed by cooling and fine pulverization to obtain a fine powdery latent crosslinking agent 2 having a maximum particle size of 50 μm or less. Obtained.

Synthetic Examples 3 to 7 In the same manner as in Synthetic Example 1, the latent crosslinking agents (3 to 7) were obtained according to the formulations shown in Table 1.

Synthesis Example 8 In a 1-liter 4-necked flask equipped with a stirrer, a thermometer, a nitrogen introducing tube, and a condenser, p-vinylphenol polymer (Maruka Linker M (S-2), Maruzen Petrochemical Co., Ltd., hydroxyl equivalent 120) was used. (Softening point 143 ° C.) 240 parts are weighed and heated to 150 ° C. under a nitrogen stream to melt. next,
While maintaining the same temperature, 116 parts of 1,6 hexamethylenediamine are gradually added and melt-mixed, and the uniformly melted mixture is taken in another container and cooled to solidify. In addition, it SA
The powder was pulverized with a MPLE MILL (Fuji Paudal Co., Ltd.) pulverizer and further sieve-filtered with a 300-mesh wire net to obtain a fine powder of the latent crosslinking agent 8 having a maximum particle diameter of 50 μm or less.

Synthesis Example 9 A rosin-modified phenol resin having a hydroxyl equivalent of 1200 was used as the phenol resin, and 1,4 diaminobutane 1.4
A latent crosslinking agent 9 was obtained in the same manner as in Synthesis Example 2 except that the equivalent amount (blending ratio) was blended.

Synthetic Example 10 A latent crosslinking agent 10 was obtained in the same manner as in Synthetic Example 9 except that the 1,4 diaminobutane of Synthetic Example 9 was changed to 1.2 equivalents of diethylenetriamine (blending ratio).

Table 1 shows the phenolic resin (resin name, OH group equivalent), amine (polyamine name, amine equivalent) and amine / phenol compounding ratio (equivalent) of the latent crosslinking agent synthesized by the above-mentioned Synthesis Examples 1-10. Shown in.

[0056]

[Table 1]

[Performance Evaluation Test] Examples in which the latent cross-linking agents 1 to 7 synthesized in the above-mentioned synthesis examples are added are shown in Examples 1 to 7 and those in which the latent cross-linking agents 8 to 10 are added or not added. Aqueous coating material compositions were prepared as Comparative Examples 1 to 4, and the effects of the evaluation items described below were confirmed.

(Preparation of water-based coating material composition) Table 2
Each emulsion resin, filler, other additive, and the latent crosslinking agent 1-10 synthesized in the above-mentioned synthesis example according to
Was charged into a kneader stirrer and kneaded at room temperature for 30 minutes, and then degassed under reduced pressure at room temperature to prepare an aqueous coating material composition. Next, the obtained water-based coating material composition was treated with an airless spray coating machine at 150 mm × 75 mm and a thickness of 8 mm.
mm cationic electrodeposited steel sheet to a dry film thickness of 1200 μm, and the coating film at 90 ° C for 10 minutes, then 130 ° C.
And dried by blowing air for 30 minutes.

[Evaluation items] Blisters and cracks: Blisters and cracks in the coating film are confirmed. Those without swelling and cracks are shown with a circle, and those with a crack are shown with a cross.

Adhesiveness: The heat-dried coating film is peeled off with a nail,
Check whether it corresponds to cohesive failure or interface failure. Cohesive failure is indicated by cf and interface failure is indicated by af.

Storage stability: Confirm the presence or absence of gelation at the beginning of the water-based coating material composition and after storage at 35 ° C. for 10 days. Those not gelled are indicated by a circle, and those gelled are indicated by a cross.

Chipping property: 2-3 layers of heat-dried coating film
Within an hour, at room temperature (20 ° C), air pressure 4.0 kg / c
After 500 m of crushed stone of m ² and 6 was damaged by flying stones 5 times, a salt spray test for 72 hours was performed to check for rust. It was shown by the score of rust in the central portion 50 mm × 120 mm of the test piece.

Examples 1 to 7 Table 2 shows the results of the compounding and performance evaluation tests of Comparative Examples 1 to 4.

[0064]

[Table 2]

[0065]

The water-based coating material composition of the present invention is
Since it is compounded as described above, the following effects are achieved.

The aqueous coating material composition of the present invention contains a urethane resin emulsion containing a latent cross-linking agent having a blistering-preventing ability to prevent blistering and cracking under forced heating and drying in the production line process. It is possible to form a coating film that is dense and has excellent chipping resistance.

Further, the aqueous coating material composition of the present invention can be prepared by adding the latent crosslinking agent in the form of finely dispersed powder,
It has excellent storage stability and can maintain good coating workability for a long time.

Further, the undercoat material for automobiles using the water-based coating material composition of the present invention is easy to handle like conventional vinyl chloride plastisol, and is less colored even during heat treatment during construction or after coating. No discoloration occurs even when a thin coating of topcoat paint is applied. Therefore, even when it is applied to an automobile manufacturing line or the like, it can be easily replaced without adding any improvement to existing equipment such as coating equipment and heating / drying equipment.

Front page continuation (72) Inventor Chihiro Masago 1,48-203, 5-1-1 Suzaku, Nara City, Nara Prefecture (56) Reference JP-A-1-287183 (JP, A) JP-A-58-83023 (JP) , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C09D 175/00 C09D 5/00

Claims (4)

(57) [Claims] 1. A water-based coating material composition comprising a water-dispersible urethane resin emulsion containing a latent cross-linking agent (c) having a blistering preventing ability, which is obtained by blocking polyamine (a) with phenol resin (b). , The phenol resin (b) has a phenolic hydroxyl group equivalent of 130
A water-based coating material composition having a value of ˜1000. 2. The polyamine (a) is an aliphatic, alicyclic,
The water-based coating material composition according to claim 1, which is an aromatic α, ω-primary-diamine type polyamine. 3. The latent crosslinking agent (c) has a maximum particle size of 5
The water-based coating material composition according to claim 1 or 2, which is in the form of powder having a particle size of 0 μm or less. 4. The compounding ratio of the hydroxyl equivalent of the phenol resin (b) and the amine equivalent of the polyamine (a) is 1: 0.5 to.
It is the range of 1: 2.0, It is characterized by the above-mentioned.
The water-based coating material composition according to any one of 1.