JPH0678501B2 - Aqueous coating composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aqueous coating composition which forms a coating film having excellent film forming properties, durability, stain resistance and hardness.

(Problems to be Solved by Conventional Techniques and Inventions) Usually, water-based resins include water-soluble resins and water-dispersible resins,
Each has its own characteristics. For example, there are two types of water-soluble resins: an anion type that neutralizes and dissolves carboxyl groups with alkali such as ammonia or amine, and a cation type that neutralizes and dissolves tertiary amino groups with acid. Both types have excellent film forming properties. , Regardless of the glass transition temperature of the polymer, it forms a film when the water-soluble solvent flies, so it is excellent in stain resistance (contamination resistance by outdoor exposure, black heel mark resistance on floors, roads, etc.). A polymer coating is obtained.

However, in the case of a water-soluble resin, since many acids and amines are used for imparting hydrophilicity, there is a drawback that durability such as water resistance, alkali resistance, and acid resistance is poor. Also, if the molecular weight is increased, it is difficult to obtain a high-concentration and low-viscosity product, so the molecular weight must be lowered from the viewpoint of handling, but the low molecular weight is also one of the causes of poor durability. It was

On the other hand, in the case of a water-dispersible resin obtained by emulsion polymerization in the presence of an emulsifier or protective colloid or obtained by mechanical dispersion, a high-concentration, relatively low-viscosity resin can be obtained regardless of the molecular weight. Almost no organic solvent, amine, etc.,
Although it has the feature that there are few problems such as pollution, it has the drawback that the water resistance of the coating film and the adhesion to the substrate are poor due to the effects of the emulsifier and protective colloid used. In addition, the water-dispersible resin has a different film-forming mechanism from the water-soluble resin, and if fusion between resin particles does not occur, a continuous film is not formed, and if the glass transition temperature of the polymer is high or low, the MFT (minimum film-forming temperature) ) Is also high and low, so that it is difficult to obtain a hard polymer coating film having excellent stain resistance at room temperature. A hard polymer coating film can be obtained by heating and drying, but it lacks practical versatility. Therefore, it is known that a large amount of a film-forming aid such as a plasticizer or a water-soluble solvent is added to a water-dispersible resin of a hard polymer as a means for obtaining a hard polymer coating film by drying at room temperature. It takes a long time to restore the hardness of the coating film,
During that time, there is a drawback that water resistance and stain resistance are reduced.

As another means, it is already known to add colloidal silica to a water-dispersible resin of MFT at room temperature,
When the amount of colloidal silica added was increased, the film-forming property gradually decreased, and it was difficult to obtain a coating film with high hardness by normal drying.

(Means for Solving Problems) As a result of various studies on water-soluble resins and water-dispersible resins having the above advantages and disadvantages, the present inventors have solved the disadvantages of the respective resins and are excellent. The present invention has been completed by finding an aqueous coating composition having film forming property, durability, stain resistance, and hardness. That is, it is an aqueous coating composition comprising a water-dispersible resin composition [A] obtained by emulsion polymerization in the presence of colloidal silica and an aqueous urethane resin [B].

In the present invention, the water-dispersible composition obtained by emulsion polymerization in the presence of colloidal silica means one or more monomers selected from α, β-monoethylenically unsaturated carboxylic acid alkyl ester and alkenylbenzene. (Hereinafter, referred to as an acrylic comonomer), it is a water-dispersible composition obtained by emulsion polymerization of colloidal silica in an aqueous system. Preferably acrylic comonomer 10
0 to 5 parts by weight (in terms of solid content), colloidal silica 10 to 5
A water-dispersible composition obtained by emulsion polymerization of 00 parts by weight (in terms of solid content) in an aqueous system in the presence of an anionic surfactant and / or a nonionic surfactant is preferable.

Here, examples of the acrylic comonomer include esters of (meth) acrylic acid and alkanol having 1 to 18 carbon atoms, and among them, typical ones are methyl (meth) acrylate and (meth) acrylate. Ethyl acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate or 2- (meth) acrylate For example, hydroxyethyl.

Typical examples of the alkenylbenzene include styrene, α-methylstyrene and vinyltoluene.

In addition, α, β such as (meth) acrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid or itaconic acid which are monomers copolymerizable with these ester comonomers and / or alkenylbenzenes. It is also possible to use monoethylenically unsaturated carboxylic acids.

In addition, divinyldimethoxysilane, divinylbis-β-
Contains a polymerizable unsaturated bond and an alkoxysilane group such as a di- or trialkoxysilane compound such as methoxy-ethoxysilane, vinyltriethoxysilane, vinyltris-β-methoxy-ethoxysilane or γ-methacryloxypropyltrimethoxysilane. When the silane monomer is used together during emulsion polymerization, the compatibility between the organic polymer and the inorganic polymer is further improved, a more stable water-dispersible composition is obtained, and the durability of the coating film is further improved.

The colloidal silica is a dispersion in water containing SiO ₂ as a basic unit, and particularly refers to a dispersion having a particle size of 4 to 100 μm (μm). It can be used either on the side or the basic side, and can be appropriately selected according to various conditions during emulsion polymerization.

Of these, "Snowtex O" (a product of Nissan Chemical Industries, Ltd.) is representative of the colloidal silica on the acidic side, while "Snowtex 20, 30, 40" is the colloidal silica on the basic side. , C and N ”(products of the same company) are typical.

The aqueous polyurethane resin used in the present invention is a polyol such as polyester polyol or polyether polyol and a polyurethane prepolymer composed of aromatic or fat, alicyclic diisocyanate, and two or more active hydrogens such as diol and diamine. A stable polyurethane resin which is chain-extended with a low molecular weight compound is dispersed or dissolved in water. The following methods are known as dispersion or dissolution methods.

(1) A polymer in which the reaction is completed or a terminal isocyanate group is blocked with a blocking agent (oxime, alcohol, phenol, mercaptan, amine, sodium bisulfite, etc.) is forced into water by using an emulsifier and mechanical shearing force. How to disperse. Furthermore, a method in which a urethane prepolymer having a terminal isocyanate group is mixed with water / emulsifier / chain extender and the mechanical shearing force is used to simultaneously disperse and increase the molecular weight.

(2) A method of imparting hydrophilicity by introducing an ionic group such as a hydroxyl group, an amino group or a carboxyl group into a side chain or a terminal of a polyurethane polymer, and dispersing or dissolving in water by self-emulsification.

(3) A method in which a water-soluble polyol such as polyethylene glycol is used as a main raw material for polyurethane to obtain a water-soluble polyurethane resin, which is dispersed or dissolved in water.

The aqueous polyurethane resin used in the present invention is not limited to the above-mentioned single dispersion or dissolution method, and a mixture obtained by each method can also be used. From the viewpoint of mixing stability and water resistance when used by mixing with the aqueous polyester resin of the present invention, a nonionic aqueous dispersion type or anionic type aqueous polyurethane resin is particularly preferable. For example, as commercially available products, "Bondic" series, "Hydran" series (manufactured by Dainippon Ink and Chemicals, Inc.), "Implanyl" series (manufactured by Bayer), "Sofranate" series (manufactured by Japan Soflan Kako Co., Ltd.) ), "Poise" series (manufactured by Kao Corporation), "Neolets" series (manufactured by Polyvinyl Chemicals Co., Ltd.), "Sampren" series (manufactured by Sanyo Chemical Industry Co., Ltd.), "Resamine" series (Dainichi Seika Co., Ltd.) Made), "Aizerax" series (made by Hodogaya Chemical Co., Ltd.), "Superflex"
A series (made by Daiichi Kogyo Seiyaku Co., Ltd.) etc. can be mentioned.

It was confirmed that the aqueous coating composition obtained in the present invention had good film-forming property in normal drying and excellent durability, stain resistance and hardness. The reason why it may have the above features is not necessarily clear, during emulsion polymerization, the surface OH groups of the colloidal silica and acid monomers and silane monomers react and crosslink, resulting in It is believed that an organic-inorganic hybrid type water dispersible composition is formed.
Since it is a hybrid type, it is superior in flexibility, film-forming property and storage stability as compared with a simple mixture. Further, when the ratio of colloidal silica is high, shrinkage and cohesive force may act on the coating film itself during film formation and cracks may occur, but in the present invention, the contraction and cohesive force generated by the aqueous urethane resin are also absorbed. Therefore, it is considered that good film forming properties are exhibited.

When the colloidal silica is less than 10 parts by weight with respect to 100 parts by weight of the acrylic monomer, the effect of forming a strong organic-inorganic composite coating film is not exhibited, and durability, hardness, stain resistance of colloidal silica, etc. The features that it has are reduced. On the other hand, if the amount exceeds 500 parts by weight, the flexibility of the acrylic polymer decreases and the mixing stability with the aqueous urethane resin also decreases.

The solid content weight ratio of the water-dispersible resin composition [A] obtained by emulsion polymerization in the presence of colloidal silica and the aqueous urethane resin [B] is preferably in the range of 90:10 to 10:90. If the ratio [] exceeds 90, the film formability is deteriorated and a continuous coating film cannot be obtained. If the ratio of [B] exceeds 90,
Features such as hardness and durability of [A] are not expressed [B]
Only the characteristic of the is exhibited and a durable hard coating film cannot be obtained.

In the obtained aqueous coating composition, pigments (white pigments such as titanium dioxide, calcium carbonate, barium carbonate, kaolin etc., colored pigments such as red iron oxide, carbon, cyanine blue etc.) and plasticizers, which are usually used in paints, are optionally added. It is also possible to mix and use additives commonly used for coating compositions, such as solvents, dispersants, thickeners, defoamers and preservatives.

The aqueous coating composition of the present invention is useful as a paint, and also for papers, fibers and various coatings (for example, glass, asbestos, plastics, etc.).

(Effect) The composition of the present invention exhibits an excellent film-forming property when dried at room temperature, and can form a coating film having excellent durability, stain resistance and hardness.

(Examples) Next, the present invention will be specifically described with reference to Examples or Comparative Examples. In the following, all parts and% are based on weight unless otherwise specified.

Example 1. (1) Polymerizable monomers 2-ethylhexyl acrylate 43 parts Methyl methacrylate 55〃 acrylic acid 2〃 (2) Surfactants sodium lauryl sulfonate 3〃 (3) Colloidal silica "Snowtex 30" ( Solid content = 30%) 333〃 (4) Ion-exchanged water 145〃 (5) Polymerization initiator Ammonium persulfate 0.5〃 Sodium hydrogen sulfite 0.2〃 A four-necked flask is charged with surfactant, colloidal silica and ion-exchanged water. The temperature was raised to 60 ° C in a nitrogen stream, then the polymerization initiators were added, and the mixture of the polymerizable monomers was added dropwise over 3 hours. The reaction temperature at this time was in the range of 60 to 70 ° C. Adjusted to. After the dropping is completed, the reaction is continued under stirring while maintaining the same temperature range for 2 hours, then cooled and adjusted to pH 8-9 with 14% ammonia water to obtain stable target water with a solid content of 35%. A dispersible composition was obtained. To 100 parts of the water-dispersible composition obtained above, 15.6 parts of an aqueous urethane resin "Hydran HW-311" (solid content: 45%) was added to obtain an intended aqueous coating composition.

Example 2. (1) Polymerizable monomers 2-ethylhexyl acrylate 43 parts Methyl methacrylate 55〃 acrylic acid 2〃 (2) Surfactants sodium lauryl sulfonate 3〃 (3) Colloidal silica "Snowtex 30" ( Solid content = 30%) 667 〃 (4) Ion-exchanged water 97 〃 (5) Polymerization initiators Ammonium persulfate 0.5 〃 Sodium hydrogen sulfite 0.2 〃 Same as Example 1 with solid content 35% A stable target water-dispersible composition was obtained. This water dispersible composition 10
Water-based urethane resin "Bondic 1660" for 0 parts
35 parts (solid content: 40%) were added to obtain the desired aqueous coating composition.

Example 3 (Production Example of Aqueous Coating Composition) (1) Polymerizable Monomer 2-Ethylhexyl Acrylate 43 Parts Methyl Methacrylate 55〃 Acrylic Acid 2〃 (2) Surfactants Sodium Lauryl Sulfonate 3〃 (3) Colloidal silica "Snowtex 30" (solid content = 30%) 1667〃 (4) Ion-exchanged water 59〃 (5) Polymerization initiator Ammonium persulfate 0.5〃 Sodium hydrogen sulfite 0.2〃 Similarly, a stable water-dispersible composition having a solid content of 33% was obtained. To 100 parts of this water-dispersible composition, 60 parts of a water-based urethane resin "Neoretz R-960" (solid content: 33%) was added to obtain an intended water-based coating composition.

Comparative Example 1. Acrylic emulsion "Boncoat 40-418" (manufactured by Dainippon Ink and Chemicals, Inc.) (solid content: 55%, MFT: 15 ° C)
Was used as the aqueous coating composition.

Comparative Example 2. Water-based urethane resin "Hydran HW-311" (solid content: 45
%) Was used as the aqueous coating composition.

Comparative Example 3. (1) Polymerizable Monomers 2-Ethylhexyl Acrylate 43 Parts Methyl Methacrylate 55〃 Acrylic Acid 2〃 (2) Surfactants Sodium Lauryl Sulfonate 3〃 (3) Ion-exchanged Water 192.6〃 (4) Polymerization Initiators Ammonium persulfate 0.5 〃 Sodium hydrogen sulfite 0.2 〃 In the same manner as in Example 1, a stable water-dispersible composition having a solid content of 35% was obtained. This water dispersible composition 100
Water-based urethane resin "Hydran HW-311"
(Solid content: 45%) 15.6 parts was added to obtain an intended aqueous coating composition.

The aqueous coating compositions of Examples 1 to 3 and Comparative Examples 1 to 3 prepared as described above were applied, and the mixing stability of each of them was measured.
The film forming property, hardness, stain resistance, water resistance and alkali resistance were evaluated. The results are summarized in Table 1.

The evaluation method is as follows.

(1) Mixing stability Each aqueous coating composition was put in a 250 milliliter (ml) bottle, left in a dryer at 50 ° C., and visually observed for aggregation and precipitation.

(2) Film Formability Each aqueous coating composition was applied onto a glass plate with a 6 mm applicator and dried at 25 ° C. and 65% RH for 2 days, and the presence or absence of cracks was visually observed.

(3) Hardness The pencil hardness of a sample whose film formability was observed was measured (breaking hardness).

(4) Stain resistance (1) Commercially available carbon paper is placed on the sample prepared in the same manner as the sample for evaluating the film forming property, a glass plate is further placed thereon, and a 2 kg weight is placed on the glass plate. After standing still at 25 ° C and 65% RH for 5 minutes, peel off the carbon paper and visually observe the state of carbon adhesion to the film.

(5) Stain resistance (2) The same test as the stain resistance (1) was conducted in a dryer at 50 ° C. and observed.

(6) Water resistance A sample prepared in the same manner as the sample for evaluation of film forming property was immersed in water for 7 days, and the degree of whitening and swelling of the film was visually observed.

(7) Alkali resistance 3% of the sample prepared in the same manner as the film forming property evaluation sample.
Immerse the film in NaOH aqueous solution and visually observe the degree of whitening and swelling of the film.

Continuation of the front page (56) Reference JP-A-60-120750 (JP, A) JP-A-59-120650 (JP, A) JP-A-60-4551 (JP, A) JP-A-61-266 (JP , A) JP-A-60-90270 (JP, A)

Claims (1)

[Claims] 1. An aqueous coating composition comprising a water-dispersible resin composition [A] obtained by emulsion polymerization in the presence of colloidal silica and an aqueous urethane resin [B].