KR20230096703A - Silica nano particles grafted with block isocyanate groups and coating composition containing thereof - Google Patents

Abstract

The present invention relates to a method for preparing silica nanoparticles grafted with block isocyanate groups capable of performing a heat-curing reaction with a coating binder that has hydroxyl groups on a surface of the silica nanoparticles in order to maintain the transparency of a coating film and at the same time improve hardness and wear resistance and to a coating composition containing the silica nanoparticles prepared by this method. The silica nanoparticles grafted with block isocyanate on the surface of the silica nanoparticles can induce chemical bonds on the surface of the silica nanoparticles through the heat-curing reaction with a binder containing the hydroxyl groups. These chemical bonds can efficiently transfer and absorb stress generated from external shocks to the nanoparticles such that the coating film with excellent hardness and wear resistance can be obtained. In addition, the silica nanoparticles grafted with the block isocyanate have a size ranging from several nanometers to tens of nanometers, thereby providing a highly transparent coating film without visible light interference effects.

Description

Silica nanoparticles grafted with a block isocyanate group and a coating composition containing the same

The present invention relates to a method for producing silica nanoparticles capable of undergoing a thermal curing reaction with a coating binder having a hydroxyl group, and to silica nanoparticles prepared by this method, and more particularly, while maintaining transparency in a coating film, hardness and wear resistance In order to improve, it relates to a method for preparing silica nanoparticles having a block isyanate group grafted on the surface and a coating composition comprising the same.

In general, a curing agent capable of inducing a chemical reaction in a coating composition is used to impart hardness and wear resistance to a coating film. At this time, the curing agent serves to increase the curing density of the material by inducing a three-dimensional network structure through a chemical reaction in the coating film by heat or ultraviolet rays.

In addition, when inorganic nanoparticles such as silicon oxide or zirconium oxide are included in the coating composition, hardness and wear resistance can be improved by serving as an inorganic filler in a coating film derived therefrom.

For example, Patent Registration No. 10-1183734 suggests that the hardness and wear resistance of a coating composition containing a curing agent and inorganic particles and a coating film derived therefrom can be improved. However, when the curing agent and the nanoparticle filler are included in the coating composition, the hardness increases to a certain level, but there is a limit to improving the curing density to a higher level.

In order to solve this problem, organic/inorganic coupling agent technology is known. For example, Patent Registration No. 10-2062385 reacts the surface of colloidal silica particles with a silane coupling agent (MPTMS: 3-methacryloxypropyltrimeyhoxysilane), includes it in a coating composition, and further increases the hardness and abrasion resistance of the coating film through UV curing. techniques to improve are presented.

However, nanoparticle application technology using such a conventional silane coupling agent is limited to UV curable coatings and cannot be applied to thermal curable coatings, so improvement is required.

Registered Patent No. 10-1183734 Registered Patent No. 10-2062385

The present invention has been made to solve the problems of the background art discussed above, and a method for producing silica nanoparticles grafted with a block isocyanate group by introducing a block isocyanate silane coupling agent that can be applied to a thermally curable coating to the surface, and this method It is to provide a high-hardness and wear-resistant coating composition containing silica nanoparticles made of.

A method for producing blocked isocyanate-grafted silica nanoparticles according to an embodiment of the present invention includes preparing a blocked silane coupling agent by reacting a blocking agent with 3-isocyanatepropyltrialkoxysilane; and reacting the blocked silane coupling agent with the silica organosol.

The blocking agent is at least one selected from the group consisting of 3,5-dimethylpyrazole (DMP), diethylmalonate (DEM), methylethylkeoxime (MEK) and caprolactone (ε-CAP), It is preferable that said 3-isocyanate propyl trialkoxysilane is 3-isocyanate propyl trimethoxysilane or 3-isocyanate propyl triethoxysilane.

In addition, the silica organosol may be a colloid in which silica particles having a particle size of several to several tens of nanometers are dispersed at 5 to 40 wt% in an alcohol dispersion medium, and the alcohol dispersion medium is methanol, ethanol, propanol, and butanol. It is preferably at least one or more selected from the group consisting of.

As another embodiment of the present invention, a thermosetting coating composition containing the blocked isyanate-grafted silica nanoparticles prepared by this manufacturing method at a concentration of 2 to 30 wt% may be mentioned.

Another embodiment of the present invention includes a coating film layer characterized by being formed of such a thermosetting coating composition.

Silica nanoparticles grafted with a block isocyanate group according to the present invention are included in a thermosetting coating composition and have an effect of improving the hardness and abrasion resistance of a coating film formed therefrom.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims and specification.

1 is a schematic diagram showing a manufacturing process of a silane coupling agent containing a block isocyanate group.
2 is a schematic diagram showing a manufacturing process of silica nanoparticles grafted with block isocyanate groups.

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. In the drawings showing the manufacturing process, the size and contents of the components in the shape and chemical structure may be exaggerated for clarity and convenience of description.

In addition, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, only the present embodiments make the disclosure of the present invention complete, and the common knowledge in the art to which the present invention belongs It is provided to fully inform the holder of the scope of the invention, and the present invention is only defined by the scope of the claims.

Meanwhile, the terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of a user or operator, so the definition of these terms should be made based on the contents throughout this specification. .

In addition, the following examples do not limit the scope of the present invention, but are merely illustrative of the components presented in the claims of the present invention, are included in the technical spirit throughout the specification of the present invention, and constitute the claims. Embodiments including elements that can be replaced as equivalents in elements may be included in the scope of the present invention.

Terminology used herein is for describing the embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms unless otherwise specified in the text. As used herein, "comprises" and/or "comprising" means that a stated component, step, operation, and/or element is present in the presence of one or more other components, steps, operations, and/or elements. or do not rule out additions.

Although first, second, etc. are used to describe various constituent elements, these constituent elements are, of course, not limited by these terms. These terms are only used to distinguish one component from another. Accordingly, it goes without saying that the first component mentioned below may also be the second component within the technical spirit of the present invention.

In order to solve the problems of the prior art described above and achieve the object of the present invention, a method for preparing silica nanoparticles grafted with a block isocyanate group is provided.

In addition, the silica nanoparticles grafted with block isocyanate groups prepared in this way can be used together with a thermosetting coating composition containing a conventional block isocyanate urethane curing agent to form a coating film having high hardness and high wear resistance. .

Block isocyanate group-grafted silica nanoparticles according to the present invention, which can be used to form a coating film of high hardness and high wear resistance, are prepared by preparing a silane coupling agent containing a block isocyanate group, and and forming silica nanoparticles grafted with block isocyanate groups obtained by performing a coupling reaction on the surface of the silica nanoparticles with a ringing agent.

The silane coupling agent containing the block isocyanate group is obtained through the reaction process shown in FIG. 1, and 3,5-dimethylpyrazole (DMP), diethylmalonate (DEM), methylethylkeoxime (MEK) and It can be obtained by chemically reacting at least one or more blocking agents selected from the group consisting of lactones (ε-CAP) with 3-isocyanate propyltrimethoxysilane or 3-isocyanate propyltriethoxysilane.

The obtained silane coupling agent containing a block isocyanate group is added to colloidal silica in which colloidal silica particles in the range of several nanometers to several tens of nanometers are dispersed in an alcohol dispersion medium, in a reaction vessel maintained at a temperature of 30 to 80 ° C. By carrying out the reaction for 2 to 10 hours, it is possible to prepare silica nanoparticles grafted with block isocyanate groups.

Colloidal silica dispersed in the alcohol dispersion medium may be prepared by a sol-gel process. For example, tetraethoxysilane (TEOS) is mixed with isopropanol at a molar ratio of 1: 1.7 to 3.5 to prepare a uniform mixed solution, and then a 1 M hydrochloric acid aqueous solution (pH 1.2) is mixed with 1 to 10 mol% based on TEOS. Silica nanoparticles having a particle size ranging from several nanometers to several tens of nanometers can be prepared by adding a small amount in the range of and stirring for several hours.

However, in addition to the manufacturing method of silica nanoparticles by the sol-gel process, it is also possible to use commercially available colloidal silica nanoparticles dispersed in alcohol, such as OSCAL, which is a commercially available product, and Renko's OPTISOL-LSE230N. do.

Silica nanoparticles grafted with block isocyanate groups have a structure in which block isocyanate groups are grafted onto the surface of the silica nanoparticles, as shown in FIG. 2 . By mixing and including the silica nanoparticles grafted with block isocyanate groups in the coating composition, the coating process is performed in the form of a coating film using the coating composition, and then when the thermal curing reaction is performed, the binder resin and the silica nanoparticles are chemically formed. Since bonding can be induced, there is an advantage in that much superior hardness and high wear resistance can be imparted to silica nanoparticles compared to the case of simple physical mixing.

The block isocyanate group used in the present invention is obtained by blocking the isocyanate group so that the reaction between the isocyanate group (-NCO) and the hydroxyl group (-OH) does not proceed at room temperature, and the blocking agent dissociates when a certain temperature is reached. As a result, the activated isocyanate and polyol react to form a urethane bond.

The dissociation temperature of these blocking agents is 100 to 120 ° C for 3,5-dimethylpyrazole (DMP) and diethyl malonate (DEM), 140 to 160 ° C for methyl ethyl keoxime (MEK), caprolactone ( ε-CAP) is 160 to 180°C.

The high-hardness and wear-resistant coating composition according to the present invention may include a curing agent in the range of 1 to 30 wt%, and preferably, considering the dissociation temperature of the blocking agent, a block isocyanate curing agent capable of thermal curing may be used as the curing agent. .

As such a block isocyanate curing agent. toluene diisocyanate, isophorone diisocyanate tri-monomer or hexamethylene diisocyanate tri-monomer and ε-caprolactone, 3,5-dimethyl pyrazole or methyl-ethyl keoxime reactants, etc., commercially available block isocyanate The curing agent may include BI 7960, BI 7981, and BI 7642 from Baxenden chemical.

When the block isocyanate curing agent is included in a polyacrylate resin, an epoxy resin, a polyurethane resin, an alkyd resin, etc. having a hydroxyl (-OH) group and performs a thermal curing reaction at the dissociation temperature of the blocking agent for a certain period of time, 3 By inducing a dimensional network structure, hardness and wear resistance of the coating film are imparted.

The coating composition according to the present invention may include 2 to 30 wt% of silica nanoparticles grafted with a block isocyanate group, 10 to 77 wt% of a binder resin, 1 to 30 wt% of a curing agent, and 20 to 60 wt% of a solvent.

The silica nanoparticle organosol to which the block isocyanate group is grafted is preferably a colloid in which silica particles having a particle size of several to several tens of nanometers are dispersed in an alcohol dispersion medium at 5 to 40 wt%, and the block isocyanate group is grafted The prepared silica nanoparticle organosol may include silica nanoparticles grafted with an organic solvent containing 50 to 80% by weight of an alcohol and 20 to 50% by weight of a block isocyanate group.

The coating composition is coated on a metal substrate using a conventional coating process selected from spray coating, immersion coating, spin coating, and the like, and is thermally cured in a temperature range and time suitable for the dissociation temperature of the blocking agent. The coating film thus obtained can obtain a coating film of high hardness and wear resistance.

Hereinafter, a method for forming silica nanoparticles grafted with a block isocyanate group according to the present invention and an effect when included in a coating composition will be described in detail through Examples and Comparative Examples. However, the protection scope of the present invention is not limited to the examples described below.

[Manufacture of coating composition]

Preparation Example 1: Preparation of block isocyanate silane coupling agent blocked by 3,5-dimethylpyrazole (DMP)

After putting 105 g of methoxypropyl acetate and 90.3 g of 3,5-dimethylpyrazole in a 1 liter reactor, the temperature was raised to 80° C. under a nitrogen atmosphere. Subsequently, 182.7 g of 3-isocyanate propyltrimethoxysilane was continuously added dropwise over 2 hours.

Additionally, after maintaining the reactant at 80° C. for 3 hours, using an infrared spectrometer, it was confirmed that the isocyanate group absorption peak disappeared at 2200 cm ⁻¹ , and then the reaction was terminated. The concentration of the synthesized silane coupling agent was 72.1 wt%.

Preparation Example 2: Preparation of Silica Nanoparticles Grafted with Block Isocyanate Groups

200 g of nano-silica (Optisol LSE230) dispersed in ethanol at 30 wt%, 90 g of the block isocyanate silane coupling agent of Preparation Example 1, and 50 g of methoxypropyl acetate were added to a 1 liter reactor, and the temperature was raised to 40 ° C. An aqueous phosphoric acid solution containing 0.05 g of phosphoric acid in 5.7 g of water was added and reacted by stirring at 40° C. for 16 hours.

The silica nanoparticles grafted with the block isocyanate group obtained at this time maintained a stable state for more than 6 months in a transparent state without precipitation in an organic solvent composed of ethanol and methoxypropyl acetate. The prepared block isocyanate grafted silica nanoparticles had a solid content of 36.4 wt% after being maintained in an oven at 160° C. for 1 hour. The particle size was measured as 21 nanometers as a result of analysis by a Horiba DLS nanoparticle size analyzer.

Preparation Example 3: Synthesis of Acrylic Binder Resin

After adding 191 g of methoxypropyl acetate to a 1 liter reactor, the temperature was raised to 80° C. under a nitrogen atmosphere. Subsequently, a mixture of 7 g of azobisisobutyronitrile dissolved in 95 g of 2-hydroxyethyl acrylate, 31 g of methyl methacrylate, 43 g of 2-ethylhexyl acrylate, 96 g of styrene, and 61 g of t-butyl acrylate was slowly stirred for 2 hours. Dropped. Additionally, 10 g of an initiator solution dissolved in methoxy propyl acetate at a concentration of 10% by weight was added dropwise for 10 minutes to increase the conversion rate of the polymerization reaction. After the initiator solution was completely injected, the reaction was maintained for an additional 2 hours while maintaining the reactor at 80° C., and the reaction was terminated. At this time, the solid concentration of the obtained acrylic binder resin was 61wt%, and the conversion rate of the input monomer was confirmed to be 96%. In addition, the mass average molecular weight (Mw) of the synthesized binder resin was 23,150 g/mol as a result of gel permeation chromatography (GPC) evaluation.

[Preparation of coating composition] (Preparation Examples 4 to 8)

40 g of the acrylic binder resin synthesized in Preparation Example 3 was mixed with 10 g of Baxenden chemical's BI 7960 and stirred, but as shown in [Table 1] below, the silica nanoparticles grafted with the block isocyanate group of Preparation Example 2 were included. The coating solution compositions of Preparation Examples 4 to 6 of the coated coating composition were prepared.

As a comparative example to confirm the effect of the present invention, a coating composition (same as Preparation Example 5) containing silica nanoparticles (Optisol LSE230) to which block isocyanate groups are not grafted was prepared in Preparation Example 7, and silica nanoparticles ( A coating composition not containing Optisol LSE230) was prepared in Preparation Example 8.

Production Example 4 Preparation Example 5 Preparation Example 6 Preparation Example 7 Preparation Example 8 Acrylic binder resin of Preparation Example 3 (g) 40 40 40 40 40 Silica nanoparticles grafted with block isocyanate groups of Preparation Example 2 (g) 20 5 0.1 - - nano silica
Optisol LSE230 (g) - - - 5 - Blocked isocyanate curing agent BI7960 (g) - 15 15 15 20 Urethane Curing Catalyst
(DBTDL) 0.2 0.2 0.2 0.2 0.2

[Formation of Coating Layer]

Using the coating solutions of Preparation Examples 4 to 8, bar coat No. Coat using 15 Then, the coated glass substrate was cured in an oven at 140° C. for 60 minutes to obtain a transparent coating film having a thickness of about 15 μm.

[Evaluation of physical properties of the coating layer]

The physical properties of the cured coating layers formed using the coating solutions of Preparation Examples 4 to 8 were measured in various ways, and the results are summarized in [Table 2].

(1) Visible light transmittance

The transmittance of the coated and heat-cured specimens was measured at a wavelength of 550 nm using a UV-Visible Spectrophometer (UV-2450, Shimadzu) to measure the transmittance change in the visible ray region.

(2) Pencil hardness

Insert a pencil for measuring pencil hardness into a hot pencil hardness tester (CT-PC1, Core Tech., Korea) at a 45° angle, apply a constant load (500 g), and push it 4 to 8 times to show the degree of scratches. did Mitsubishi pencils were used as pencils, and pencils showing strengths such as H-9H, F, HB, and B to 6B were used.

(3) adhesion

The adhesion of the coating film is measured by making a checkerboard-shaped groove with a cutter on the heat-cured coating film layer according to ASTM 3359, and then attaching 3M tape well on it and peeling it off several times with a constant force to observe the degree of adhesion between the coating layer and the substrate. did The surface of the coated support was cut crosswise in 11 × 11 at 1 mm intervals to make 100 squares, and a tape was attached thereon, followed by rapid pulling to evaluate the surface.

◎: Excellent, more than 100 extra eyes

○: Good, the number of remaining eyes is 95 or more

△: Normal, the number of extra eyes is 85 or more

×: Defective, the number of remaining eyes is less than 85

(4) Wear resistance

The initial gloss of the coated specimens was measured using a 20° Novo-Gloss 20 gloss meter available from Gardner Instruments. Using an Atlas AATCC Scratch Tester Model CM-5 obtained from Atlas Electrical Devices, Chicago, Illinois, the coated surface was linearly scratched with weighted abrasive paper for 10 times double-sided rubbing to obtain the results of Preparation Examples 4 to 8. Abrasion resistance test of the specimen was performed. The abrasive paper is a 3M 2819 wet or dry production 9 micron abrasive paper sheet available from 3M. The 20° gloss was measured on the scratched area of the test specimen. The reported value is the percentage of initial gloss retained after the scratch test, i.e. 100% x (gloss after scratch/initial gloss).

Production Example 4 Preparation Example 5 Preparation Example 6 Preparation Example 7 Preparation Example 8 Visible light transmittance (%) 93 95 96 93 96 pencil hardness 6H 5H 3H 3H 2H adhesion ○ ◎ ◎ ◎ ◎ 20° gloss retention rate after scratch test % (abrasion resistance) 86.7 82.1 35.9 36.4 25.7

As confirmed from the results of Table 2, the coating film obtained from the coating solution containing the blocked isocyanate grafted silica nanoparticles according to the present invention has excellent wear resistance and high hardness characteristics from the gloss retention and pencil hardness evaluation after the scratching test. Confirmed. In addition, since the block isocyanate-grafted silica nanoparticles had a size of 50 nm or less, there was no decrease in visible light transmittance. In the case of Preparation Example 6, a significant increase in abrasion resistance and hardness was not observed because too few block isyanate grafted silica nanoparticles were included.

On the other hand, in the case of Preparation Examples 7 and 9, which did not contain block isocyanate-grafted silica nanoparticles, the wear resistance and hardness characteristics were relatively poor from the results of 20 ° gloss retention after pencil hardness and scratching tests. did

Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art can realize that the present invention can be implemented in other specific forms without changing the technical spirit or essential features. you will be able to understand Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting.

Claims (7)

preparing a blocked silane coupling agent by reacting a blocking agent with 3-isocyanatepropyltrialkoxysilane; and
A method for producing blocked isocyanate-grafted silica nanoparticles, comprising: reacting the blocked silane coupling agent with silica organosol. The method of claim 1, wherein the blocking agent,
Block isocyanate, characterized in that at least one selected from the group consisting of 3,5-dimethylpyrazole (DMP), diethylmalonate (DEM), methylethylkeoxime (MEK) and caprolactone (ε-CAP) Method for preparing grafted silica nanoparticles. The method of claim 1, wherein the 3-isocyanate propyltrialkoxysilane,
A method for producing block isocyanate grafted silica nanoparticles, characterized in that 3-isocyanate propyltrimethoxysilane or 3-isocyanate propyltriethoxysilane. The method of claim 1, wherein the silica organosol,
A method for producing block isocyanate grafted silica nanoparticles, characterized in that silica particles having a particle size of several to several tens of nanometers are colloidal in which 5 to 40 wt% of silica particles are dispersed in an alcohol dispersion medium. The method of claim 4, wherein the alcohol dispersion medium,
Method for producing block isocyanate grafted silica nanoparticles, characterized in that at least one selected from the group consisting of methanol, ethanol, propanol and butanol. Claims 1 to 5, comprising a block isyanate grafted silica nanoparticles prepared by the manufacturing method according to any one of 2 to 30wt% concentration, a thermosetting coating composition. A coating film layer characterized by being formed from the thermosetting coating composition according to claim 6.

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