JP2011195633A - Hydrophilizing agent for water-based coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrophilizing agent for a water-based coating exhibiting enhanced floating functions by using a thermally responsive polymer compound making a sharp switch of phase transition from hydrophobic to hydrophilic around a phase transition temperature.SOLUTION: The hydrophilizing agent comprises a thermally responsive polymer compound carried on a silica particle, where the polymer compound is obtained by copolymerizing a hydrophobic monomer, which exhibits hydrophobicity when polymerized, and has a phase transition temperature where it switches reversibly between hydrophilicity and hydrophobicity. Thus, the hydrophilizing agent gives sharp phase transition from hydrophilic to hydrophobic to easily float up to the surface in a coating.

Description

  The present invention relates to a hydrophilizing agent used in water-based paints.

  In the coating film formed on the surface of the adherend by the paint, since the surface is usually hydrophobic, when used outdoors, hydrophobic dirt caused by exhaust gas etc. is likely to adhere, The dirt is difficult to remove with rainwater. In order to make it difficult for such hydrophobic stains to adhere to the surface of the coating film, and to make it easier to flow down with rainwater, etc., there is a hydrophilizing agent for paints that makes the coating surface hydrophilic and makes it easily wet. It is requested.

  In addition, due to increasing interest in global environmental issues in recent years and considerations for painters, organic solvents can be introduced into the atmosphere rather than solvent-based paints that release a relatively large amount of organic solvents into the atmosphere after application. There is a demand for paints such as water-based paints that are less likely to be released in large quantities and have performance equivalent to or better than solvent-based paints.

  On the other hand, conventionally, as a hydrophilizing agent for paint, for example, a silicate compound is known. This silicate compound can be blended with the solvent-based paint to make the surface of the coated film hydrophilic after coating. However, this silicate compound is highly reactive with water, and in order to use it in water-based paints, it is necessary to adjust the liquidity such as keeping the liquidity of the paint relatively strong alkaline. Aqueous paint containing a compound may be gelled depending on its temperature condition and humidity condition after storage or after application, which may cause problems such as non-uniform film formation.

  On the other hand, as described in Patent Document 1, the present applicant is a hydrophilizing agent for water-based paint using silica particles, and has a phase transition temperature at which hydrophilicity and hydrophobicity are reversibly changed. A hydrophilizing agent for water-based paints characterized in that a heat-sensitive polymer compound is supported on the silica particles has been proposed. This hydrophilizing agent can be dispersed in an aqueous paint under a temperature condition in which the heat-sensitive polymer compound is hydrophilic in a coating film formed by applying an aqueous paint containing the hydrophilizing agent. If the thermosensitive polymer compound becomes hydrophobic beyond the phase transition temperature, the thermosensitive polymer compound can move to the coating film surface with the silica particles. Subsequently, when the temperature is lowered after the coating film is cured, the polymer compound on the coating film surface becomes hydrophilic, and hydrophilic silica particles may exist on the coating film surface.

JP 2009-127028 A

  As a result of diligent research, the present applicant has determined that the hydrophilizing agent for water-based paints has an improved floating function by using a thermosensitive polymer compound that is sensitive to switching from a hydrophilic phase to a hydrophobic phase near the phase transition temperature. Was invented.

  In other words, the hydrophilizing agent for water-based paints according to the present invention comprises a thermosensitive polymer compound having a phase transition temperature at which hydrophilicity and hydrophobicity reversibly change, supported on the silica particles, and the thermosensitive polymer. The compound is characterized in that a hydrophobic monomer that exhibits hydrophobicity when polymerized is copolymerized.

  In the hydrophilizing agent for water-based paints according to the present invention, the polymerization ratio of the hydrophobic monomer in the thermosensitive polymer compound may be 10% or less.

  According to the present invention, since the thermosensitive polymer compound is copolymerized with a hydrophobic monomer that exhibits hydrophobicity when polymerized, the aqueous paint containing the hydrophilizing agent for aqueous paint of the present invention is applied. In the coating film formed in this way, it can be dispersed in the water-based paint because it can become hydrophilic below the phase transition temperature, and if it exceeds the phase transition temperature, the hydrophobicity of the copolymerized hydrophobic monomer is added. The degree of hydrophobicity increases rapidly, and the polymer compound can easily move to the surface of the coating film with the silica particles.

  Further, in the hydrophilizing agent for water-based paints according to the present invention, if the polymerization ratio of the hydrophobic monomer in the thermosensitive polymer compound is 10% or less, the hydrophilizing agent for water-based paints of the present invention. In a water-based paint containing water, the possibility of inhibiting the hydrophilicity of the polymer compound is reduced below the phase transition temperature, so that problems such as aggregation between the hydrophilizing agents are less likely to occur.

It is explanatory drawing which shows one Embodiment of the hydrophilizing agent for water-based paints which concerns on this invention.

  Next, the best mode for carrying out the present invention will be specifically described.

  The hydrophilizing agent for water-based paints of this embodiment is one in which a heat-sensitive polymer compound is supported on silica particles, and the polymer compound is copolymerized with a hydrophobic monomer that exhibits hydrophobicity when polymerized. It is what. The meaning of “support” in the present invention means physical adhesion to the surface of the silica particles, chemical bonding on the surface of the silica particles or chemical bonding by hydrogen bonding, or these physical adhesion and chemical bonding. A bond is a complex bond.

  Here, the water-based paint refers to a paint that can be diluted with water, and specifically refers to a paint in which water containing water or a water-soluble organic solvent is used as a dispersion medium or a solvent. More specifically, for example, an emulsion-based aqueous paint in which a water-insoluble resin or pigment is dispersed in the dispersion medium, a water-soluble resin-based aqueous paint in which a water-soluble resin is dissolved in the solvent, and the like. . Since water-based paints contain a relatively large amount of water as a dispersion medium or solvent, the amount of organic solvent released into the atmosphere when a water-based paint is applied to an object and a coating film is formed. Are relatively few.

  The silica particles are not particularly limited, and examples thereof include natural products and synthetic products, and crystalline and amorphous materials. The method for producing the silica particles is roughly classified into a wet method and a dry method, and the wet method is preferable in that the average particle size of the silica particles can be easily controlled. The wet method is classified into a precipitation method and a gel method. In the wet method, silica particles are generally synthesized by a neutralization reaction between sodium silicate and sulfuric acid. More preferable silica particles include, for example, colloidal silica synthesized by sol-gel method using alkoxysilane as a raw material. As the silica particles, those commercially available can be used.

  The average particle size of the silica particles is preferably 20 to 100 nm, and more preferably 20 to 50 nm. When the average particle diameter of the silica particles is 20 nm or more, there is an advantage that the thermosensitive polymer compound is easily supported on the silica particles, and when the average particle diameter is 100 nm or less, There is an advantage that the hydrophilizing agent for water-based paint becomes easier to move.

  The average particle diameter of the silica particles is measured by a dynamic light scattering method. Specifically, using a particle size distribution measuring device (trade name “Concentrated Particle Size Analyzer FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.), measurement was performed at a concentration of 0.05% by weight using pure water or isopropanol as a dispersion medium. A value obtained using the CONTIN method is used for distribution analysis.

  Next, a thermosensitive polymer compound generally changes its hydrophilicity and hydrophobicity reversibly at the boundary of the phase transition temperature, and is hydrophilic at a temperature lower than the phase transition temperature and hydrophobic at a temperature higher than the phase transition temperature. Is shown. Although the thermosensitive polymer compound according to the present embodiment is copolymerized with a hydrophobic monomer that exhibits hydrophobicity when polymerized, the degree of hydrophilicity at or below the phase transition temperature is reduced, but the polymer compound The silica particles carrying the polymer compound can be dispersed in the water-based paint.

  Specifically, the phase transition temperature is determined by preparing a 5% by weight aqueous solution of the polymer compound, raising the temperature of the aqueous solution in the range of 20 to 80 degrees, and measuring the transmittance at a wavelength of 700 nm. The temperature at which the temperature starts to rise rapidly is taken as the phase transition temperature. Since the polymer compound is used by being blended in an aqueous coating composition, the phase transition temperature of the polymer compound blended in the aqueous coating composition that may contain components other than water is as described above. It may be different from the phase transition temperature measured in.

  The phase transition temperature is preferably 30 to 70 degrees. When the phase transition temperature is 30 ° C. or more, there is an advantage that the stability of the aqueous coating composition is increased at room temperature and can be stored at room temperature for a longer period of time. Moreover, since the said phase transition temperature becomes lower than the boiling point of water because it is 70 degrees or less, when the coating-film drying temperature needs to be more than a phase transition temperature, there exists an advantage that the selection range of the drying temperature spreads.

  The weight molecular weight of the polymer compound is not particularly limited, and is usually 2,000 to 50,000, and preferably 2,000 to 10,000. When the molecular weight of the temperature-responsive portion is 2,000 or more, the heat-sensitive polymer compound is more easily supported on the silica particles, and moreover is less likely to be separated from the silica particles. Yes, by being 10,000 or less, the thermosensitive polymer compound is easily dissolved in a solvent that can be used when producing a hydrophilizing agent for water-based paints, and the production can be more easily performed. There are advantages. In addition, molecular weight shall convert the measured value obtained by GPC analysis by standard polystyrene.

  The polymer compound is obtained by copolymerizing a general thermosensitive polymer with a hydrophobic monomer that exhibits hydrophobicity when polymerized. Examples of the general thermosensitive polymer include poly N-isopropylacrylamide, polyethylene glycol, Examples include polypropylene glycol and polyvinyl methyl ether, and a mixture of these. Among these, poly N-isopropylacrylamide and polyvinyl methyl ether are preferable in that the phase transition temperature is around 35 degrees. Examples of hydrophobic monomers that exhibit hydrophobicity when polymerized include ethyl methacrylate, ethyl methacrylate, styrene, ethylene, propylene, and the like.

  The polymer compound may be prepared by first adjusting a thermosensitive polymer, and then copolymerizing the hydrophobic monomer with the thermosensitive polymer, and is a constituent unit of the thermosensitive polymer. A monomer and the hydrophobic monomer may be copolymerized. In particular, if N-isopropylacrylamide and methyl methacrylate are copolymerized, the chemical reaction for the copolymerization is only one step, and the reactivity of methyl methacrylate is lower than that of N-isopropylacrylamide. Utilizing the difference in reactivity, it becomes easier to adjust the polymerization ratio of N-isopropylacrylamide and methyl methacrylate in the polymer compound, which is more preferable.

  As the polymer compound, those polymerized by a general method, those obtained by further reacting commercially available compounds, and the like can be used.

  The hydrophilizing agent for water-based paint according to this embodiment is formed by supporting the polymer compound on the silica particles. Specific examples of the hydrophilizing agent for water-based paints include those in which the polymer compound is physically attached to the silica particles. Moreover, for example, a compound in which the thermosensitive polymer compound is chemically bonded to the silica particles can be used. Further, for example, the heat-sensitive polymer compound is chemically bonded to the silica particles, and the heat-sensitive polymer compound is physically attached.

  It is preferable that the hydrophilizing agent for water-based paint contains chemically modified silica particles obtained by chemically bonding the thermosensitive polymer compound and the silica particles. By including chemically modified silica particles in which the thermosensitive polymer compound and the silica particles are chemically bonded, the thermosensitive polymer compound is more reliably accompanied by the silica particles. There is an advantage that it moves to the surface of the coating film.

  Examples of the chemically modified silica particles formed by chemically bonding the polymer compound and the silica particles include, for example, a polymer silane coupling agent having an alkoxysilyl group as a part of the polymer compound and chemically treating the silica particles. What is combined with is mentioned. Also obtained by chemically bonding an alkoxysilane compound having a polymerization reactive group and the silica particles, and then polymerizing the polymerization reactive group and a monomer that is a constituent unit of the polymer compound. Can be mentioned.

The weight ratio of the silica particles to the polymer compound supported on the silica particles is not particularly limited, but covers the silica surface when the polymer compound becomes hydrophobic at the phase transition temperature. The hydrophilizing agent for water-based paints may be hydrophobic, and specifically, the polymer compound is preferably 0.1 to 1 part by weight with respect to 1 part by weight of silica particles.

  Next, the manufacturing method of the hydrophilizing agent for water-based paints of this embodiment is demonstrated.

  The hydrophilizing agent for water-based paints of the present embodiment can be produced in a state of a dispersion by, for example, mixing colloidal silica containing the silica particles and the polymer compound.

  Further, for example, by mixing colloidal silica containing the silica particles, a water-soluble organic solvent such as ethanol, and a silane compound having an alkoxysilane group or the like in a part of the thermosensitive polymer compound, Can be manufactured.

  Furthermore, for example, colloidal silica containing the silica particles, a water-soluble organic solvent such as ethanol, and a compound having a polymerizable group and a reactive group capable of chemically bonding to the silica particles are mixed, and polymerized to the silica particles. It is manufactured by introducing a functional group and further adding a constituent monomer of a thermosensitive polymer compound to make the silica particles chemically modified silica particles chemically modified with the thermosensitive polymer compound. be able to.

  As an aqueous paint using the hydrophilizing agent for water-based paints of the present embodiment, the hydrophilizing agent for aqueous paints is 0.5 to 10 wt. %, Preferably 1 to 5% by weight. By blending 0.5% by weight or more of the hydrophilizing agent for water-based paints, there is an advantage that the applied coating film becomes more hydrophilic, and by blending 10% by weight or less, the coating film There is an advantage that other coating properties such as strength and coating uniformity are more excellent.

The water-based paint composition of the present embodiment may contain, for example, a resin, a colorant and / or an extender pigment, an organic solvent, a surfactant, an antiseptic, an antifungal agent and the like. In addition, the water-based coating composition, if necessary, a crosslinking agent, an antiseptic, a rust inhibitor, an antifoaming agent, a plasticizer, a film-forming aid, an ultraviolet absorber, ordinarily used in general coating compositions, Antioxidants, viscosity modifiers, anti-gelling agents, light stabilizers, antistatic agents and the like may be included.
In addition, this invention is not limited to the hydrophilizing agent for water-based paints and water-based paint composition illustrated above. Moreover, various aspects used in a general water-repellent hydrophilizing agent and water-based paint composition can be employed as long as the effects of the present invention are not impaired.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these. In the examples and comparative examples described below, the relationship between the parts by weight and the capacity is the same as the relationship between 1 g and 1 ml.

<Preparation of thermosensitive polymer compound>
N-isopropylacrylamide (NIPAM) 1 part by weight, methyl methacrylate, 0.1 part by weight, polymerization initiator azobisisobutyronitrile 0.02 part by weight, γ-mercaptopropyl-removed methoxysilane 0.02 part by weight in the flask And 50 parts by volume of ethanol were added, and the mixture was stirred at 70 ° C. for 6 hours. Then, the solution after polymerization was reprecipitated with n-hexane, and the resulting crude polymer was washed with diethyl ether 8 times, and then dried under reduced pressure. Thus, an N-isopropylacrylamide-methyl methacrylate copolymer, which is a thermosensitive polymer, was prepared. In addition, the molecular weight by GPC measurement of the prepared polymer compound was 9800 (standard polystyrene conversion). The phase transition temperature was 30.0 degrees.

Example 1
In the following manner, chemically modified silica particles obtained by chemically bonding a hydrophilizing agent for water-based paints, specifically, an N-isopropylacrylamide-methyl methacrylate copolymer and silica particles, were produced. In a three-necked flask equipped with a reflux tube, a thermometer, and a dropping funnel, 0.25 parts by weight of colloidal silica (in terms of solid content) as in Example 1, 0.5 weight of N-isopropylacrylamide-methyl methacrylate copolymer And 50 parts by volume of ethanol were added to the flask and stirred at 70 ° C. for 6 hours. Then, the reaction solution was centrifuged and the supernatant was removed eight times. The residue after washing was dried under reduced pressure to produce 0.231 parts by weight of chemically modified silica particles in which an N-isopropylacrylamide-methyl methacrylate copolymer and silica particles were chemically bonded.

Comparative example

  To the flask was added 1 part by weight of N-isopropylacrylamide (NIPAM), 0.02 part by weight of a polymerization initiator azobisisobutyronitrile, 0.02 part by weight of γ-mercaptopropyltrimethoxysilane, and 50 parts by volume of ethanol. After stirring for 6 hours, the polymerized solution was reprecipitated with n-hexane, and the resulting crude polymer was washed 8 times with diethyl ether and then dried under reduced pressure to obtain a thermosensitive polymer compound. An N-isopropylacrylamide-methyl methacrylate copolymer was prepared. In addition, the molecular weight by GPC measurement of the prepared polymer compound was 9600 (standard polystyrene conversion). The phase transition temperature was 28.5 degrees.

(Comparative Example 1)
In the following manner, chemically modified silica particles obtained by chemically combining a hydrophilizing agent for water-based paints, specifically, poly N-isopropylacrylamide and silica particles were produced. In a three-necked flask equipped with a reflux tube, a thermometer, and a dropping funnel, 0.25 parts by weight of colloidal silica as in Example 1 (in terms of solid content), 0.5 parts by weight of poly N-isopropylacrylamide, and 50 parts by volume of ethanol Was added to the flask and stirred at 70 ° C. for 6 hours, and then the washing operation of centrifuging the reaction solution to remove the supernatant was performed 8 times. The residue after washing was dried under reduced pressure to produce 0.231 parts by weight of chemically modified silica particles in which poly N-isopropylacrylamide and silica particles were chemically bonded.

<Evaluation of hydrophilic and hydrophobic switching function>
FIG. 1 schematically shows changes in hydrophilicity when chemically modified silica particles produced in Examples and Comparative Examples are dispersed in water and the temperature is raised from 20 degrees to 80 degrees. In the temperature region lower than the phase transition temperature, the example retains hydrophilicity although the degree of hydrophilicity is lower than that of the comparative example. As the temperature rises and approaches the phase transition temperature, the decrease in hydrophilicity begins gradually. Furthermore, when the phase transition temperature is exceeded, the degree of hydrophobicity of the examples increases compared to the comparative example due to the copolymerized hydrophobic monomer.

  Further, in water, the portions exhibiting hydrophobicity of the polymer compound are gathered to further increase the degree of hydrophobicity. Therefore, in the state where the phase transition temperature shown above is exceeded, the hydrophobicity of the polymer compound is higher in the examples than in the examples. It can be said that the degree of sex is likely to increase. That is, in the chemically modified silica particles dispersed in water, the surface of the hydrophilizing agent for water-based paints of this example also rapidly increased in hydrophobicity due to the rapid increase in hydrophobicity in the example compared with the comparative example, and the early It can easily float on the water surface.

Claims (2)

  A thermosensitive polymer compound having a phase transition temperature that reversibly changes hydrophilicity and hydrophobicity is supported on the silica particles, and the thermosensitive polymer compound is a hydrophobic monomer that exhibits hydrophobicity when polymerized. A hydrophilizing agent for water-based paints, characterized by being copolymerized. The hydrophilizing agent for water-based paint according to claim 1, wherein the thermosensitive polymer compound has a polymerization ratio of the hydrophobic monomer of 10% or less.

Images