JPH083237A - Production of coating emulsion - Google Patents

Abstract

PURPOSE:To obtain a coating emulsion having controlled viscosity and giving a coating film of excellent appearance by adding a vinyl polymerizable monomer to a specified polysiloxane emulsion and subjecting the entire mixture to a graft copolymerization reaction. CONSTITUTION:To an emulsion prepared by dispersing a polysiloxane (A) comprising 50-99mol% (in terms of the amount of the Si atoms) dimethylsiloxane units, 1-50mol%, in total, polysiloxane containing 0.1-30mol% at least one kind siloxane unit selected from among vinyl polymerizable functional group- containing siloxane units and SH-containing siloxane units in water, a vinyl polymerizable monomer (B) in an amount 0.5-20 times as large as that of polysiloxane (A) is added. Vinyl monomer B is grafted into polysiloxane A in the presence of a radical polymerization initiator to obtain the objective emulsion. This emulsion has controlled viscosity and can give a coating film of excellent appearance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polysiloxane emulsion useful as a paint having a controlled viscosity, and more particularly, to a polysiloxane-containing paint having a controlled viscosity and providing a coating film having an excellent appearance. The present invention relates to a method for producing an emulsion.

[0002]

2. Description of the Related Art Polysiloxane resins are excellent in heat resistance, water repellency and weather resistance and are usefully used as paint resins. However, polysiloxane resin-based paints have the elastic modulus and strength of the polysiloxane resin itself. Since it is too low, it is difficult to obtain a tough coating film, and its use is limited to a narrow range. Therefore, conventionally, a combination of a polysiloxane resin and an acrylic resin, a polyester resin, or the like is used to make the best use of the characteristics and improve the difficulty of the polysiloxane resin.

Further, a resin component is emulsified and dispersed in water,
So-called emulsion paints have a much lower risk of ignition, poisoning and air pollution due to the solvent used than solvent-based paints, so various types of emulsion paints such as acrylic emulsions and urethane emulsions have been developed and widely used. It's being used. However, there are still some problems to be solved in the practical application of emulsion coatings containing a large amount of polysiloxane resin, and the present situation is that they have not been widely used for general coating applications. Among them, one of the most important issues is to secure the transparency and high appearance of the coating film formed from the polysiloxane-based emulsion, and to simultaneously control the viscosity of the emulsion. In the case of emulsion-based paints containing, it has not been developed an industrially advantageous manufacturing method capable of satisfying both of them.

Japanese Examined Patent Publication No. 63-23212 discloses a water-soluble coating material using a polysiloxane having a plurality of alcoholic hydroxyl groups introduced into its side chain. This polysiloxane is completely soluble in water. It is of a low molecular weight type, and the characteristics of the obtained coating film are not sufficient. If the polysiloxane is made to have a high molecular weight in order to enhance this characteristic, the viscosity of the obtained coating material will be too high, and the polysiloxane A large amount of hydrophilic functional groups remain in the coating film formed from the paint, which causes disadvantages such as difficulty in ensuring the water repellency of the coating film.

Japanese Unexamined Patent Publication No. 1-315451, and
In JP-A-2-92974, a vinyl-polymerizable functional group is introduced into the surface layer of a core of a crosslinked polysiloxane obtained by copolymerizing a vinyl-polymerizable functional group-containing polyfunctional alkoxysilane and a vinyl-polymerizable monomer, Further, a so-called core / shell type emulsion having a shell formed by graft-polymerizing an acrylic polymer having a hydrophilic group is disclosed. This core / shell type emulsion has excellent thixotropy, and it has been shown that the sagging property at the time of coating is improved. However, if an attempt is made to make an emulsion containing a large amount of polysiloxane by this method, it is necessary to use a large amount of an expensive graft crossing agent, which causes a problem that the raw material cost becomes high.

JP-A-4-202554 discloses a flexible coating by mixing dialkoxydimethylsilane during emulsion polymerization of a polyfunctional alkoxysilane containing a vinyl polymerizable functional group and a vinyl polymerizable monomer. An invention is shown for an emulsion paint for coating concrete exterior walls that is capable of forming a film. However, in this method, since a large amount of dialkoxydimethylsilane is used in the production of the coating material, in addition to the problem that the coating material manufacturing cost becomes high, a large amount of alcohol is produced as a by-product during the polycondensation of the alkoxysilane. There is.

In JP-A-1-168971 and JP-A-1-168972, an emulsion of radical-reactive group- or mercapto-group-containing polysiloxane is used to prepare an ethylenically unsaturated monomer containing an acid group or an amide group. Graft-polymerized to obtain a fiber treatment agent with excellent durability and flexibility against washing. However, the amount of the graft crossing agent used in the examples of the present invention was only 1.2% by weight (about 0.5 mol%) with respect to the polysiloxane component, and even if the fiber treating agent was used as it was as a paint. The problem of lack of transparency arises. This invention seeks to obtain a fiber treating agent and does not describe the amount of graft crossing agent needed to obtain the transparency required for common coatings.

In Japanese Patent Laid-Open No. 58-126378, there is SH
Although a method of graft-polymerizing a vinyl monomer onto a group-containing polysiloxane to prepare an emulsion coating is disclosed, nothing is mentioned about the viscosity of the emulsion obtained by this method.

[0009]

The present invention provides a coating film containing a polysiloxane and having a good appearance, and
It is an object of the present invention to provide a method for producing a polysiloxane emulsion which is an inexpensive water-dispersible emulsion and whose viscosity can be arbitrarily controlled. For more details,
The present invention contains a polysiloxane and a vinyl polymer,
It is an object of the present invention to provide a method for controlling the viscosity of an emulsion by a method other than changing the solid content in the emulsion when producing a water-dispersed emulsion paint that gives a coating film having an excellent appearance.

[0010]

The inventors of the present invention have made extensive studies to solve the above problems, and as a result, have found that the object can be achieved by adopting the following manufacturing method. That is, the gist of the present invention is that 50 mol% or more and 99 mol% or less of dimethylsiloxane units based on the amount of silicon atoms, and 1 mol% or more and 50 mol% or less of a vinyl-polymerizable functional group-containing siloxane unit in total. And SH
A polysiloxane (A) containing at least one siloxane unit selected from group-containing siloxane units, in which the content of SH group-containing siloxane units is 0.1 mol% or more and 30 mol% or less is dispersed in water. To the emulsion, 0.5 to 20 times the weight of the polysiloxane is added and mixed with the vinyl polymerizable monomer (B), and the vinyl monomer (B) is added to the polysiloxane (A) in the presence of a radical polymerization initiator. ) Is graft-copolymerized with a method for producing an emulsion for paints.

The present invention controls the viscosity of the emulsion without using the means of changing the solid content. By the method of the present invention, an emulsion having any thixotropy can be obtained. The addition of thixotropy to the emulsion is useful for preventing the sagging during the drying and curing of the coating film while ensuring the fluidity at the time of coating.

The SH group-containing polysiloxane (A) can be produced by a known silicone polymerization method such as bulk polymerization or emulsion polymerization. In order to prevent the deterioration of SH groups in the polysiloxane (A), it is preferable to use an emulsion polymerization method which can take relatively mild polymerization conditions. Emulsion polymerization of silicon can be suitably carried out, for example, by polycondensation of SH group-containing polysiloxane with cyclic silicon oligomer or alkoxysilane as a raw material using dodecylbenzenesulfonic acid as an emulsifier and polymerization catalyst.

When the SH group-containing polysiloxane (A) is obtained by emulsion polymerization, the polymerization temperature of the siloxane is not particularly limited, but it can be efficiently performed by subjecting it to a heat history of 60 ° C. or more at least once. More preferably, it is subjected to a heat history of 75 ° C. or higher. The particle size of the obtained siloxane polymer emulsion can be controlled by the degree of preliminary dispersion of the raw material, the amount of emulsifier used, the polymerization temperature and the method of supplying the raw material. An emulsion of polysiloxane (A) having a smaller particle size is
Preliminarily emulsify the raw materials used and water with a high shear generator such as a homogenizer in the presence of an emulsifier, drop these raw materials or their pre-emulsion into water, increase the emulsifier, or raise the polymerization temperature. It can be obtained by any one of these methods, or by appropriately combining these methods. The time required for siloxane polymerization varies depending on the polymerization conditions, but is usually 0.5 hour or more and 1 month or less.

As the radical polymerization initiator used in the emulsion graft polymerization of the vinyl polymerizable monomer (B), known ones used in the emulsion radical polymerization can be used. The method of charging the vinyl-polymerizable monomer (B) is not particularly limited, but in order to more efficiently promote the copolymerization of the siloxane polymer (A) with the grafting active site, the siloxane polymer should be previously prepared before the initiation of the polymerization. In some cases, it is preferable that the emulsion of (A) and at least a part of the vinyl polymerizable monomer (B) are well mixed to impregnate the siloxane polymer particles with the vinyl polymerizable monomer.

The total amount of at least one siloxane unit selected from the SH group-containing siloxane and the vinyl polymerizable functional group-containing siloxane unit contained in the polysiloxane (A) is from 1 mol% to 50% based on the silicon atom. Mol%
It is necessary that the content be the following, and the transparency of a coating film formed from an emulsion coating obtained by using a polysiloxane having a siloxane unit content of less than 1 mol% is poor. In addition to the drawback that when an emulsion paint is prepared using a polysiloxane having an SH group-containing siloxane or a total amount of vinyl-polymerizable functional group-containing siloxane units exceeding 50 mol%, the raw material cost thereof becomes high, By-products such as alcohol that are eliminated during siloxane condensation reduce the stability and handleability of the resulting latex, and further reduce the performance of the coating film formed from the emulsion. Preferably, the total amount of SH group-containing siloxane units or vinyl polymerizable functional group-containing siloxane units is 1 mol% or more and 30 mol% or less, and more preferably 2 mol% or more and less than 20 mol%. preferable. S
The transparency of a coating film formed from the emulsion coating composition of the present invention prepared by using the polysiloxane (A) in which the total amount of H group-containing siloxane units or vinyl polymerizable functional group-containing siloxane units is 2 mol% or more. When a latex of polysiloxane having an extremely good siloxane unit content of 20 mol% or less is used, the vinyl monomer is obtained by emulsion polymerization.
The latex stability during graft polymerization of (B) will be good.

The SH group-containing siloxane unit content in these polysiloxanes (A) must be 0.1 mol% or more and 30 mol% or less, and the siloxane unit content is 0.1 mol% or less.
Emulsions obtained with less than less than polysiloxane show less of its viscosity control. A polysiloxane having an SH group-containing siloxane component in excess of 30 mol% is disadvantageous in that the raw material cost is high, and by-products such as alcohol that is eliminated during siloxane condensation are obtained. The stability of the latex is deteriorated, and its handleability and the performance of the coating film formed from the obtained emulsion paint are impaired. further
A polysiloxane having a large amount of SH group-containing siloxane units exceeding 30 mol% causes a decrease in the polymerization rate during radical polymerization of the vinyl polymerizable monomer (B), and adverse effects such as a decrease in the molecular weight of the resulting polymer. . Preferably,
The content of SH group-containing siloxane units in the polysiloxane (A) is 0.5 mol% or more and 30 mol% or less, and more preferably. It is at least 1 mol% and less than 20 mol%. An emulsion prepared by using a polysiloxane (A) having an SH group-containing siloxane unit content of 1 mol% or more has a viscosity that can be significantly adjusted, and a coating film formed from the obtained emulsion paint. The transparency of is good. Also, SH
Polysiloxane containing 20 mol% or less of group-containing siloxane is
The latex stability during emulsion polymerization is improved, and the adverse effect of radical polymerization inhibition of the vinyl monomer (B) is further reduced.

One of the most preferable combinations of the SH group-containing siloxane unit and the vinyl-polymerizable functional group-containing siloxane unit in the polysiloxane (A) is such that the total amount thereof is in the range of 3 to 6 mol%, and , SH group-containing siloxane content is in the range of 0.1 to 3 mol%. The coating film formed from the emulsion obtained by using the polysiloxane (A) in this range has the great feature that the viscosity of the emulsion can be freely controlled while using the siloxane containing a functional group that is close to the minimum amount that can secure its transparency. have.

It is preferable that the polysiloxane (A) before grafting the vinyl polymerizable monomer (B) is not crosslinked. Emulsions obtained with cross-linked emulsions have limited viscosity control properties. Preferably, the amount of the siloxane cross-linking component due to the trifunctional or higher functional silane in the polysiloxane (A) is 5 mol% or less, and more preferably 1 mol% or less. The smaller the content of the tetrafunctional silane in the polysiloxane (A) used for preparing an emulsion having higher viscosity, the better, and the content is preferably 1 mol% or less, more preferably 0.2 mol% or less, Most preferably 0 mol%
Is.

The inactive substituent on the silicon atom introduced into the bifunctional or monofunctional silane compound used for preparing the polysiloxane (A) is generally an alkyl group, a phenyl group or derivatives thereof. It is preferably a methyl group or a phenyl group, and the total amount thereof is 1 in the case of a bifunctional silane and 2 in the case of a monofunctional silane.

The type of vinyl-polymerizable monomer (B) used in carrying out the present invention is not particularly limited, but preferable examples that can be used include alkyl methacrylate, alkyl acrylate, cycloalkyl methacrylate, cycloalkyl acrylate, and styrene. The
The vinyl monomer (B) containing 60% by weight or more of at least one vinyl monomer selected from the above is preferable. As the vinyl-polymerizable monomer (B), those having at least one functional group selected from a hydroxyl group and a carboxyl group can also be used. Using a functional vinyl monomer for this, the hydroxyl group or carboxyl group introduced into the polymer can be reacted with the following self-crosslinking side chain, and is formed from a polymer having such a polar functional group. The formed coating film has the effect of improving the adhesion to the substrate. Examples of such vinyl monomers include acrylic acid, methacrylic acid, hydroxyalkyl (meth) acrylate and the like.

Further, the emulsion of the present invention can be prepared by further using a vinyl polymerizable monomer having a self-crosslinking functional group. The self-crosslinkable functional group refers to a functional group that reacts with each other or with the above-mentioned hydroxyl group and carboxyl group by heating or evaporation of water to form a chemical bond between side chains. Examples of the vinyl polymerizable monomer having a self-crosslinkable functional group in the side chain include glycidyl acrylate, glycidyl methacrylate, N-alkoxymethyl acrylamide, diacetone acrylamide, γ.
-Methacryloxypropyltrimethoxysilane and the like. For example, an emulsion prepared by using N-butoxymethylacrylamide has good storage stability, but the coating film formed from this emulsion is heated. It is a preferred vinyl monomer because of its excellent balance of reactivity during crosslinking and curing.

The amounts of the polar functional group-containing vinyl monomer and the self-crosslinkable functional group-containing vinyl monomer used can be changed depending on the intended performance of the coating film formed from the emulsion of the present invention, If you want to obtain a cross-linkable curable coating,
The total amount of these functional group-containing vinyl monomers is preferably 2 mol% or more in the vinyl monomer (B). However, a coating film formed from an emulsion in which more than 20 mol% of a polar functional group-containing vinyl monomer is introduced into the vinyl monomer (B) tends to reduce its durability such as water resistance. Further, since the functional group-containing monomer tends to reduce latex stability during emulsion radical polymerization of the polysiloxane (A) and the vinyl monomer (B), the total amount of the functional group-containing monomer is It is preferably 20 mol% or less in the vinyl polymerizable monomer (B).

The glass transition temperature of the vinyl polymer contained in the emulsion of the present invention is one of the factors that determines the minimum film forming temperature of the latex. The preferred glass transition temperature of the vinyl polymer changes depending on the weight ratio with the polysiloxane component and the content of the graft crossing points on the polysiloxane component, but the content of the graft crossing points is
The amount of polysiloxane component is not so effective in lowering the glass transition temperature of the entire resin component as long as the amount of the coating film formed from the emulsion can ensure good transparency. Therefore, the glass transition temperature of the vinyl polymer is preferably in the range of -30 ° C to 70 ° C. A coating film formed from a latex containing a vinyl polymer having a glass transition temperature of less than −30 ° C. is required to have special physical properties such as flexibility because the flexibility thereof is improved but the strength tends to decrease. Except the case, the glass transition temperature of the vinyl polymer is preferably -30 ° C or higher. However, the preferred glass transition temperature of the vinyl polymer can also be changed by adding a film-forming aid such as an organic solvent to the emulsion.

The amount of the vinyl polymerizable monomer (B) used with respect to the weight of the polysiloxane (A) must be 0.5 times or more and 20 times or less. A coating film formed from an emulsion obtained by using a vinyl polymerizable monomer (B) in an amount of less than 0.5 times the amount of polysiloxane (A) has good flexibility, but the strength and surface hardness of the coating film are It tends to decrease. A coating film formed from an emulsion produced under the condition that the amount of vinyl polymerizable monomer (B) used with respect to polysiloxane (A) exceeds 20 times, and exhibits the water repellency and flexibility characteristic of silicone polymers. It becomes difficult to be played. In order to maintain a high balance of hardness and durability of the coating film, the amount of vinyl polymerizable monomer (B) used is preferably 2 times or more and 20 times or less with respect to the weight of polysiloxane (A). .

The obtained emulsion is used as it is, or after diluting with water, it is sprayed or applied on a plastic, metal plate or surface-treated substrate by another method, followed by drying and curing. It can be made into a coating film.

The emulsion obtained by the method of the present invention has good storage stability. The particle size of the emulsion obtained by the method of the present invention can be arbitrarily changed,
A usual average particle diameter is about 0.01 μm to 1 μm. The correlation between the particle size of the resin contained in the emulsion obtained by the method of the present invention and the transparency of the coating film formed from the emulsion is small.

The resin component content in the emulsion is usually 50
The content can be arbitrarily selected at a content rate of not more than%, but a higher concentration can be obtained by concentrating the emulsion.
When the emulsion of the present invention is subjected to ordinary spray coating, the resin component content is preferably 15 to 45% in consideration of coatability and performance of the resulting coating film. The emulsion obtained by the method of the present invention may optionally contain a pigment, a stabilizer, a co-curing agent, or a curing aid, and may further contain another emulsion resin, a water-soluble resin, or a viscosity control agent. You may mix and use it. However,
When the emulsion obtained by the method of the present invention contains a large amount of siloxane polymer, the refractive index of the obtained coating film decreases as the siloxane content increases. A coating film formed from an emulsion prepared by mixing and using another resin component that is difficult to dissolve will reduce the transparency thereof, and therefore sufficient care must be taken when mixing with other resins. Coatings made using the emulsions obtained by the method of the invention have smooth, good gloss and improved durability.

Hereinafter, the present invention will be described in more detail with reference to examples. All "parts" in the examples are parts by weight.

[0029]

Example 1 90 parts of dimethyl cyclics (mixture of cyclic dimethyl siloxane oligomer 3-7 mer), 10 parts of graft crossing agent (γ-mercaptopropylmethyldimethoxysilane), 300 parts of water, and dodecylbenzenesulfonic acid sodium salt 0.5 After premixing the parts with a homomixer, they were sheared with a homogenizer at a pressure of 200 kg / cm ² and forcibly emulsified to obtain a silicon raw material emulsion. Next, 100 parts of water and 10 parts of dodecylbenzenesulfonic acid were charged into a flask equipped with a stirrer, a condenser, a heating jacket and a dropping pump, and the temperature inside the flask was adjusted to 80
The above silicon raw material emulsion was added dropwise over 3 hours while maintaining the temperature at 88 ° C. After further heating and stirring for 1 hour, the obtained emulsion was cooled to room temperature and neutralized with sodium hydroxide to obtain an emulsion of polysiloxane (A). The obtained emulsion was placed in a flask equipped with a stirrer, a condenser, a heating jacket, and an inert gas inlet, and under a nitrogen atmosphere, an aqueous solution of EDTA, Rongalit, and ferrous oxide was added and the temperature was raised to 65 ° C. Next, 100 parts of methyl methacrylate (MMA), 100 parts of n-butyl methacrylate (BA), 10 parts of hydroxyethyl methacrylate (HEMA), methacrylic acid (MA
A) 10 parts, styrene (St) 10 parts, N-butoxymethyl acrylamide (N-BMAAm) 10 parts and t-butyl hydroperoxide (TBH) 1 part as an initiator were mixed and then added dropwise over 3 hours. . 2 at 65 ° C
After holding for a period of time, the reaction solution was cooled to room temperature to obtain a silicone-acrylic composite polymer emulsion. The obtained emulsion was diluted with water to obtain a resin solid content of 40%, and the viscosity was measured with a B type viscometer.
The viscosity at 6 revolutions was 40,000 cps (40 Pa · sec) and the viscosity at 60 revolutions was 5,500 cps (5.5 Pa · sec), and this emulsion was found to have extremely high viscosity and thixotropy. The obtained emulsion had properties suitable for coating, and when it was applied on a test steel plate by a bar coater and dried at room temperature, a smooth and transparent coating film was obtained. The viscosity and coatability of this emulsion did not change for at least one week. Furthermore, this coating film
When heated at 25 ° C for 25 minutes, a smooth, transparent and tough coating film was obtained, and the 60 ° gloss value of the coating film measured by a gloss meter was 90. When the obtained coating film was further kept at room temperature in the atmosphere for 2 weeks, no change was observed in the coating film appearance. Further, this heat-cured coating film was immersed in warm water at 80 ° C. for 1 hour and then measured, and the 60 ° gloss value was also 90, showing that the coating film had good water resistance.

[0030]

Example 2 The polysiloxane component was charged with methyl cyclics (cyclic dimethylsiloxane oligomers 3 to 7).
A silicone-acrylic emulsion was obtained in the same manner as in Example 1 except that 95 parts of the monomer mixture) and 5 parts of the graft crossing agent (γ-mercaptopropylmethyldimethoxysilane) were used. The viscosity of an emulsion with a solid content of 40% is 63,000 in 6 revolutions.
cps (63Pa ・ sec), 60 rpm 4,700cps (4.7Pa ・ se)
c), and it was found to have high thixotropy. Further, the coating film formed from this emulsion had good transparency, but had almost the same performance except that a slight haze was observed as compared with Example 1.

[0031]

Example 3 A polysiloxane component was charged with methyl cyclics (cyclic dimethylsiloxane oligomers 3 to 7).
Polymer mixture), 85 parts, graft crossing agent (γ-mercaptopropylmethyldimethoxysilane) 7.5 parts, graft crossing agent (γ-methacryloxypropylmethyldimethoxysilane) 7.5 parts An acrylic emulsion is obtained. The viscosity of an emulsion with a solid content of 40% is 1,600 cps (1.6 Pa · sec) in 6 revolutions.
), 1,000 cps (1.0 Pa · sec) at 60 rotations, and it was found that the viscosity as it is was suitable for bar coater coating. Further, the coating film formed from this emulsion had extremely good transparency, and the durability of the coating film was about the same as in Example 1.

[0032]

[Comparative Example 1] Methyl cyclics (cyclic dimethyl siloxane oligomer 3 to 7) was charged as a polysiloxane component.
A silicone-acrylic emulsion was obtained in the same manner as in Example 1 except that 85 parts of the monomer mixture) and 15 parts of the graft crossing agent (γ-methacryloxypropylmethyldimethoxysilane) were used. The viscosity of an emulsion with a solid content of 40% is 100 cps (0.1 Pa · sec) after 6 rotations and 100 cps even after 60 rotations.
It was (0.1 Pa · sec), and it was found that at this concentration, the viscosity was such that bar coater coating was a little difficult and thixotropy was extremely low.

[0033]

The emulsion obtained by the production method of the present invention can be used as a resin for water-based paint containing polysiloxane, and gives a coating film having good appearance and durability,
Moreover, it has a good storage stability and a controlled viscosity, and can be used for various coating applications. Further, the production method of the present invention is extremely useful as a method for producing a polysiloxane-containing emulsion for water-based paints stably and at low cost.

Claims (1)

[Claims] 1. 50 mol% to 99 mol% of dimethyl siloxane units based on the amount of silicon atoms, 1 mol% to 50 mol% of vinyl polymerizable functional group-containing siloxane units and SH group-containing siloxane units in total. Containing at least one siloxane unit selected from the group consisting of at least 0.1 mol% of SH group-containing siloxane units,
In an emulsion in which 30 mol% or less of polysiloxane (A) is dispersed in water, the weight of polysiloxane (A) is
Add 0.5 times to 20 times vinyl polymerizable monomer (B) and mix,
A method for producing a coating emulsion, which comprises graft-copolymerizing in the presence of a radical polymerization initiator.