JP7519315B2 - Coating for dispense application and method for producing coated article - Google Patents

Description

The present invention relates to a paint for dispense application and a method for manufacturing a coated article.

Traditionally, automobile bodies and parts are spray painted. In spray painting, the paint is atomized and flows with the air, and then adheres to the object being painted. The coating efficiency of spray painting is low, generally said to be between 50% and 70%.

In light of recent environmental issues, efforts have been made to improve coating efficiency. For example, Patent Documents 1 and 2 disclose devices that can apply droplets of paint to automobile parts.

JP 2016-144805 A JP 2020-22965 A

However, when applying paint by methods other than spray painting, it is difficult to obtain a smooth coating.

The object of the present invention is to provide a paint for dispense application that can produce a smooth coating film. Another object of the present invention is to provide a method for producing a coated article using the above paint.

The present invention provides the following aspects [1] to [12].
[1]
A coating material for dispense application, comprising:
The shear viscosity at a shear rate of 1000/s is 0.01 Pa sec or more and 0.20 Pa sec or less,
A coating material for dispense application, wherein the coating material is stretched at an extension speed V of 0.5 m/sec or less using an extensional rheometer to measure the breaking length L (mm) of the coating material, and the L/V obtained by dividing the breaking length L (mm) by the extension speed V (m/sec) is 10 or more and 49 or less.

[2]
The coating material according to the above-mentioned [1], wherein the L/V is 15 or more and 45 or less.

[3]
Contains a solvent,
The paint according to the above [1] or [2], wherein the proportion of water in the solvent is 20 mass% or more.

[4]
Contains a solvent,
The coating material according to the above [1] or [2], wherein the ratio of the organic solvent in the solvent is 40 mass% or more.

[5]
The coating material according to any one of the above [1] to [4], which contains a coating film-forming resin.

[6]
The coating material according to any one of the above [1] to [5], having a surface tension of 20 mN/m or more and 33 mN/m or more.

[7]
The method includes a step of discharging paint from a nozzle of a dispenser toward a workpiece that moves relatively,
The shear viscosity of the coating material at a shear rate of 1000/s is 0.01 Pa sec or more and 0.20 Pa sec or less,
A method for producing a coated article, wherein the coating material is stretched using an extensional rheometer at an extension speed V of 0.5 m/sec or less to measure a breaking length L (mm) of the coating material, and the breaking length L (mm) is divided by the extension speed V (m/sec), so that L/V is 10 or more and 49 or less.

[8]
The coating material contains a film-forming resin,
The method for producing a coated article according to the above-mentioned [7], further comprising a curing step of curing the coating film-forming resin after the discharging step.

[9]
The method for producing a coated article according to the above-mentioned [7] or [8], wherein the diameter of the nozzle is 5 μm or more and 300 μm or less.

[10]
The method for producing a coated article according to any one of the above [7] to [9], wherein the distance between the object to be coated and the nozzle is 4 mm or more and 200 mm or less.

[11]
The method for producing a coated article according to any one of the above [7] to [10], wherein the substrate is a member for an automobile body.

[12]
The method for producing a coated article according to any one of the above [7] to [11], wherein in the discharging step, the paint is discharged in the form of droplets from the nozzle.

The present invention provides a paint for dispense application that can produce a smooth coating film. The present invention also provides a method for producing a coated article using the paint.

FIG. 2 is an explanatory diagram showing a schematic diagram of a method for measuring the breaking length using an extensional rheometer. FIG. 2 is an explanatory diagram showing a schematic diagram of a method for measuring the breaking length using an extensional rheometer. 1 is a flowchart illustrating a method for manufacturing a coated article according to one embodiment of the present invention. 1 is a surface photograph of a portion of the coating film produced in Example 1. 1 is a surface photograph of a portion of the coating film produced in Comparative Example 1. 1 is a surface photograph of a portion of the coating film produced in Comparative Example 2.

Dispense coating is a method in which a fixed amount of liquid coating material is dispensed onto the substrate. In dispense coating, the coating material is dispensed in liquid form, not as a mist. This results in high coating efficiency.

In dispense coating, paint is applied with shear stress to eject it from the nozzle. Paint is generally a non-Newtonian fluid. Non-Newtonian fluids such as paint, particularly thixotropic fluids, change in viscosity before and after ejection from the nozzle. In dispense coating, the viscosity of the paint has a significant effect on the smoothness of the coating film.

For example, paint with an excessively low viscosity when discharged is likely to break into multiple droplets between the time it is discharged and the time it lands, forming so-called satellites. The formation of satellites impairs the paint's ability to move in a straight line, so the paint is likely to land at a point other than the intended point. This causes the film thickness to decrease in parts, resulting in the formation of streaks. Satellites can also cause contamination of non-coated areas. Furthermore, paint with a low viscosity after discharge has an excessively low viscosity before discharge, and is likely to form a puddle at the tip of the nozzle. Therefore, the amount of liquid discharged and therefore the amount of liquid that lands is likely to vary, and streaks are likely to form. On the other hand, paint with an excessively high viscosity after discharge is discharged from the nozzle while drawing threads. Because the nozzle and the workpiece move relative to each other, it is not possible to land the specified amount of paint at the intended point, and streaks are also likely to form.

In order to control the amount of paint dispensed, the amount that lands, and even the point where it lands, we focused on the elongation of the paint after it is dispensed. By reproducing this elongation using an extensional rheometer, we found the elongation that is suitable for dispensing, in other words, the breaking length.

That is, in this embodiment, the shear viscosity at a shear rate of 1000/s (hereinafter sometimes referred to as high shear viscosity) is set within a specific range, and the paint break length L (mm) measured when stretched at an extension rate V of 0.5 m/s or less is divided by the extension rate V (m/s) to obtain L/V. The shear rate and extension rate V are set taking into account the shear stress applied to the paint during dispense application.

Specifically, the high shear viscosity is controlled to 0.01 Pa·s or more and 0.20 Pa·s or less, and the L/V is controlled to 10 or more and 49 or less. This makes it possible to obtain a paint suitable for dispense application, which is less likely to form satellites, puddles, or paint threads. This prevents streaks from forming, and a smooth coating is obtained. In particular, the ejected droplets tend to become spherical.

The breaking length L is measured using an extensional rheometer. An extensional rheometer is a device that measures the rheological properties of a liquid sample when it is stretched. In an extensional rheometer, a uniaxial (stretching direction) shear stress is applied to the paint. The paint is stretched into a thread-like shape and eventually breaks. The length of the paint thread when it breaks (breaking length L) divided by the speed V at which the paint is stretched is L/V.

Specifically, L/V is calculated as follows. First, the breaking length L is measured using an extensional rheometer. The extensional rheometer has two circular plates that face each other vertically. The two plates can be separated from each other. The paint is sandwiched between the two plates, and they are separated at a constant speed (extension speed V, 0.5 m/sec or less). At this time, the paint is stretched into a thread. When the plates are further separated from each other, the paint threads eventually break. This behavior of the paint is photographed, for example, with a high-speed camera. From this image, the distance between the plates when the thread breaks is measured and taken as the breaking length L. The extension speed V is changed within a range of 0.5 m/sec or less, and the breaking length L at each extension speed V is measured. The measurement results are plotted on a graph with the horizontal axis being the extension speed V (m/sec) and the vertical axis being the breaking length L (mm), and a straight line is drawn by linear regression analysis using the least squares method. The slope of this straight line is L/V.

Figures 1A and 1B are explanatory diagrams that show a typical method for measuring the breaking length using an extensional rheometer. In Figure 1A, paint 1 is sandwiched between circular plates 2A and 2B and is stretched into a thread. As circular plate 2A moves upward at a constant speed V, circular plates 2A and 2B move apart. Figure 1B shows the state in which circular plates 2A and 2B in Figure 1A are further apart, representing the time when the thread of paint 1 breaks. The length between circular plates 2A and 2B at this time is the breaking length L. For convenience, paint 1 is hatched.

[paint]
The coating material according to this embodiment is a coating material for dispense application, and has a high shear viscosity of 0.01 Pa·s or more and 0.20 Pa·s or less, and an L/V of 10 or more and 49 or less.

The high shear viscosity is preferably 0.012 Pa·s or more. The high shear viscosity is preferably 0.18 Pa·s or less, and more preferably 0.15 Pa·s or less.

L/V is preferably 15 or more, and more preferably 16.5 or more. L/V is preferably 45 or less, and more preferably 42 or less. Specifically, L/V is preferably 16.5 or more and 42 or less.

Dispense coating is a method of dispensing a fixed amount of liquid coating material (paint) onto the substrate. In dispense coating, the paint may be dispensed in the form of a liquid column or droplets. The method of dispensing in droplets is known as inkjet printing.

The surface tension of the paint can also affect the break length of the paint. The higher the surface tension, the smaller the break length is likely to be, and the lower the surface tension, the larger the break length is likely to be. In particular, the surface tension of water-based paint is preferably 20 mN/m or more and 33 mN/m or less. This makes it easier to control L/V within the above range. The surface tension of the paint is more preferably 22 mN/m or more, and particularly preferably 23 mN/m or more. The surface tension of the paint is more preferably 32 mN/m or less, and particularly preferably 31 mN/m or less.

Surface tension is measured by the pendant drop method. For example, a contact angle meter (DMo-701, manufactured by Kyowa Interface Science Co., Ltd.) is used to measure surface tension.

The paint according to this embodiment may be for a so-called undercoat coating, a base coat coating, or a clear coating. The paint may be a one-component paint, or a multi-component paint such as a two-component paint containing a base agent and a hardener. The base agent and hardener that make up the two-component paint may be mixed and then supplied to a nozzle, or may be supplied to the same nozzle and mixed while being discharged.

The paint may be a so-called water-based paint, which contains water as a solvent. In water-based paint, the proportion of water in the solvent is, for example, 20% by mass or more. The paint may also be a so-called solvent-based paint, which contains an organic solvent as a solvent. In solvent-based paint, the proportion of organic solvent in the solvent is, for example, 40% by mass or more.

The solid content of the paint is not particularly limited. The solid content of the paint is preferably 2% by mass or more and 70% by mass or less. The solid content of the paint is all components of the paint excluding volatile components (typically, the solvent).

From the viewpoint of preventing nozzle clogging, it is desirable that the paint does not contain particles (typically pigments) with an average particle diameter of 1/10 or more of the nozzle diameter. This improves the paint's dischargeability, making it easier to prevent streaks from appearing in the coating film. Prior to dispense application, it is desirable to filter the paint to remove particles with an average particle diameter of 1/10 or more of the nozzle diameter. The average particle diameter is the volume average particle diameter measured by laser light scattering (the same applies below).

The paint according to this embodiment contains, for example, a film-forming resin, a curing agent, a pigment, and a solvent. Each component is described in detail below.

(Film-forming resin)
The film-forming resin is a thermosetting or active energy ray-curable resin. In water-based paints, the film-forming resin is usually dispersed in a solvent. In solvent-based paints, the film-forming resin is usually dissolved in a solvent. After the paint is dispensed onto the substrate, it is cured by heating or exposure to active energy rays. The film-forming resin is formed by a crosslinkable functional group and a base resin.

Examples of crosslinkable functional groups include carboxy groups, hydroxyl groups, epoxy groups, silanol groups, and (meth)acryloyl groups.

Examples of base resins include acrylic resins, polyester resins, alkyd resins, polyurethane resins, epoxy resins, and fluororesins. The epoxy resin may be a urethane-modified epoxy resin. The polyester resin may be a urethane-modified polyester resin. The acrylic resin may be a urethane-modified acrylic resin. Each urethane-modified resin has a urethane bond in the resin skeleton. These may be used alone or in combination of two or more. Among these, acrylic resins and polyester resins are preferred in terms of improved chipping resistance.

The amount of the film-forming resin is not particularly limited. When a curing agent is included, the solid content of the film-forming resin is preferably 60% by mass or more and 90% by mass or less of the total solid content of the film-forming resin and the curing agent, and more preferably 70% by mass or more and 85% by mass or less.

As the film-forming resin contained in the water-based paint, an acrylic resin having a crosslinkable functional group is preferable. Among them, a hydroxyl-containing acrylic resin emulsion is preferable. The hydroxyl-containing acrylic resin emulsion is obtained, for example, by emulsion polymerization of an α,β-ethylenically unsaturated monomer mixture. The α,β-ethylenically unsaturated monomer mixture preferably contains 65% by mass or more of (meth)acrylic acid esters having 1 or 2 carbon atoms in the ester moiety. The acid value (solid acid value; the same applies below) of the α,β-ethylenically unsaturated monomer mixture is preferably 3 mgKOH/g or more and 50 mgKOH/g or less.

The average particle size of the acrylic resin emulsion is preferably 0.01 μm or more and 1.0 μm or less. When the average particle size of the acrylic resin emulsion is in the above range, the coating workability and appearance are likely to be improved. From the same viewpoint, the average particle size is more preferably 0.02 μm or more. The average particle size is more preferably 0.3 μm or less.

The acrylic resin emulsion is neutralized with a base as necessary. This allows it to be stably dispersed in the pH range of 5 to 10. Neutralization is carried out, for example, by adding a tertiary amine such as dimethylethanolamine or triethylamine to the polymerization system before or after emulsion polymerization.

As the film-forming resin contained in the solvent-based paint, an acrylic resin having a crosslinkable functional group is preferable. In particular, in the case of a solvent-based paint used for a clear coating, it is more preferable to contain an acid anhydride group-containing acrylic resin (a), a carboxyl group-containing polyester resin (b), and an acrylic resin having a hydroxyl group and an epoxy group (c). These three types of resins are preferably used together with a curing catalyst (d). This makes it easier for the three types of resins to react with each other, making it easier to increase the crosslink density.

The acid anhydride group-containing acrylic resin (a) preferably has an average of two or more acid anhydride groups per molecule. The hydroxyl group- and epoxy group-containing acrylic resin (c) preferably has an average of two or more epoxy groups per molecule. Examples of the curing catalyst (d) include phosphite compounds. Examples of the phosphite compounds include phosphite triesters and diphosphite esters.

For solvent-based paints used for base coat coatings, amide group-containing acrylic resins are preferred. The solids weight ratio of the amide group-containing acrylic resin to other film-forming resins may be 30/70 to 90/10.

(Hardening agent)
The curing agent is not particularly limited, and may be appropriately selected according to the coating film-forming resin. Examples of the curing agent include amino resins, urea resins, polyisocyanate compounds, epoxy group-containing compounds, carboxy group-containing compounds, carbodiimide group-containing compounds, hydrazide group-containing compounds, and semicarbazide group-containing compounds. The polyisocyanate compounds include blocked polyisocyanate compounds in which the isocyanate group is blocked with a blocking agent. These are used alone or in combination of two or more. Among them, amino resins and polyisocyanate compounds are preferred in terms of the performance and cost of the coating film obtained.

Amino resins are obtained, for example, by condensing an amino compound such as melamine, benzoguanamine, or urea with formaldehyde, and then etherifying the resulting mixture with a lower monohydric alcohol. The amino resins may be used alone or in combination of two or more.

The polyisocyanate compound has at least two isocyanate groups in one molecule. Examples of the polyisocyanate compound include aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates having aromatic rings in the molecule that are not bonded to isocyanate groups (araliphatic polyisocyanates), aromatic polyisocyanates, and derivatives of these polyisocyanates. As the polyisocyanate compound, a prepolymer of the above polyisocyanate or its derivative may be used. As the polyisocyanate compound, a blocked polyisocyanate compound may be used. The polyisocyanate compound may be used alone or in combination of two or more types.

The equivalent ratio (=OH/NCO) between the hydroxyl groups of the hydroxyl-containing resin and the isocyanate groups of the polyisocyanate compound is not particularly limited. From the viewpoint of the curability and scratch resistance of the coating film, the above equivalent ratio (=OH/NCO) is preferably 0.5 or more and 2.0 or less, and more preferably 0.8 or more and 1.5 or less.

The amount of the curing agent is not particularly limited. In terms of curability, the solid content of the curing agent is preferably 10% by mass or more and 40% by mass or less of the total solid content mass of the coating-forming resin and the solid content mass of the curing agent, more preferably 15% by mass or more and 30% by mass or less, and particularly preferably 15% by mass or more and 25% by mass or less.

(solvent)
The solvent is not particularly limited. As described above, the solvent may be water (deionized water), an organic solvent, or a combination thereof.

Examples of the organic solvent include ester-based solvents such as ethyl acetate, butyl acetate, isopropyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate;
Examples of the solvent include ether solvents such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, methyl methoxybutanol, ethoxypropanol, ethylene glycol isopropyl ether, ethylene glycol t-butyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, methoxybutanol, and propylene glycol monobutyl ether; alcohol solvents such as methanol, ethanol, butanol, and propyl alcohol; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as Swazol, Shellsol, and mineral spirits; and aromatic solvents such as xylene, toluene, Solvesso-100 (S-100), and Solvesso-150 (S-150). These may be used alone or in combination of two or more.

The amount of solvent is not particularly limited and is set appropriately depending on the solid content and high shear viscosity of the paint. For example, the solvent is added so that the solid content of the paint is 2% by mass or more and 70% by mass or less.

(Pigment)
The paint may contain a pigment. The pigment is not particularly limited and is appropriately selected according to the purpose. However, the average particle diameter of the pigment is preferably less than 1/10 of the diameter of the nozzle. This makes it easier to suppress clogging of the nozzle. The average particle diameter of the pigment is, for example, 30 μm or less, and preferably 25 μm or less. When a glittering material for the purpose of imparting design is used as the pigment, the average particle diameter of the pigment is preferably 5 μm or more in terms of ease of production or availability. The average particle diameter of the pigment may be measured using image processing software from an electron microscope image of the painted surface after the paint is applied to a substrate. For example, 10 pigments are arbitrarily selected from the above image, and the diameter of a circle (equivalent circle) having the same area as the area of the pigments is regarded as the diameter of the pigment. The diameters of the 10 pigments are calculated, and the average value of these is regarded as the average particle diameter of the pigment.

The mass ratio of pigment to resin solids (PWC) is not particularly limited and may be set appropriately taking into consideration the type and purpose of the pigment, as well as the breaking length L. The larger the PWC, the smaller the breaking length L tends to be.

The pigment may be at least one selected from the group consisting of a scaly pigment, a color pigment, and an extender pigment. Examples of the scaly pigment include metal flakes, metal oxide flakes, pearl pigments, glass flakes coated with metal or metal oxide, silica flakes coated with metal oxide, graphite, hologram pigments, and cholesteric liquid crystal polymers. These may be used alone or in combination of two or more. The scaly pigment may be colored. This further improves the design.

The content of the scaly pigment is not particularly limited. The PWC of the scaly pigment may be, for example, 1% by mass or more and 40% by mass or less. The PWC of the scaly pigment is preferably 5% by mass or more and 30% by mass or less.

Examples of color pigments include organic color pigments such as azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments; and inorganic color pigments such as yellow lead, yellow iron oxide, red iron oxide, carbon black, and titanium dioxide. These may be used alone or in combination of two or more.

Examples of extender pigments include calcium carbonate, barium sulfate, clay and talc. These may be used alone or in combination of two or more.

The content of color pigments and extender pigments is not particularly limited. The PWC of all pigments is appropriately adjusted within the range of 0.1% by mass to 50% by mass. The lower limit of PWC is preferably 0.5% by mass, more preferably 1.0% by mass. The upper limit of PWC is preferably 40% by mass, more preferably 30% by mass.

(Viscosity adjuster)
The coating preferably contains a viscosity modifier, which facilitates adjustment of the high shear viscosity and L/V of the coating to the desired range.

The viscosity modifier is not particularly limited. Examples of viscosity modifiers include silica-based fine powder, mineral-based viscosity modifier, polyamide-based viscosity modifier, urethane association type viscosity modifier, alkali swelling type viscosity modifier, cellulose-based viscosity modifier, aminoplast-based viscosity modifier, polyolefin-based viscosity modifier, polyurea-based viscosity modifier, barium sulfate fine powder, organic resin fine particle viscosity modifier, and polyacrylic acid-based viscosity modifier. These are used alone or in combination of two or more. Among them, from the viewpoint of controlling high shear viscosity and L/V, at least one selected from the group consisting of silica-based fine powder, mineral-based viscosity modifier, polyamide-based viscosity modifier, urethane association type viscosity modifier, alkali swelling type viscosity modifier, cellulose-based viscosity modifier, aminoplast-based viscosity modifier, polyolefin-based viscosity modifier, and polyurea-based viscosity modifier is preferred.

The silica-based fine powder is a powder containing SiO _2. Examples of the silica-based fine powder include clay, diatomaceous earth, white carbon, and colloidal silica. Among them, colloidal silica is preferable.

Examples of mineral viscosity adjusters include swellable layered silicates having a 2:1 crystal structure. Specific examples include smectite clay minerals such as natural or synthetic montmorillonite, saponite, hectorite, stevensite, beidellite, nontronite, bentonite, and laponite; swellable mica clay minerals such as Na-type tetrasilicic fluorine mica, Li-type tetrasilicic fluorine mica, Na-salt-type fluorine taeniolite, and Li-type fluorine taeniolite; vermiculite; and substitutes and derivatives thereof. Bentonite is particularly preferred.

Examples of polyamide viscosity modifiers include fatty acid amides, polyamides, acrylamides, long-chain polyaminoamides, aminoamides, and salts thereof (e.g., phosphates).

Examples of urethane association type viscosity modifiers include polyether polyol-based urethane prepolymers and urethane-modified polyether type viscosity modifiers.

Examples of alkali swelling viscosity modifiers include polycarboxylic acid viscosity modifiers, polysulfonic acid viscosity modifiers, and polyphosphoric acid viscosity modifiers. Of these, polycarboxylic acid viscosity modifiers are preferred. Examples of polycarboxylic acid viscosity modifiers include high molecular weight polycarboxylic acids, high molecular weight unsaturated acid polycarboxylic acids, and partially amidated products thereof.

Examples of cellulose-based viscosity modifiers include cellulose acetate butyrate (CAB), carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and cellulose nanofiber gel. These may be used alone or in combination of two or more. Of these, CAB is preferred.

Aminoplast viscosity modifiers are addition condensates of formaldehyde and compounds having an amino group, such as melamine or guanamine. Examples of aminoplast viscosity modifiers include hydrophobically modified ethoxylate aminoplast associative viscosity modifiers.

Examples of polyolefin viscosity modifiers include polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene oxide, polypropylene oxide, ethylene oxide-propylene copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-maleic anhydride copolymer, and propylene-maleic anhydride copolymer. Among these, polyethylene oxide or a colloidal dispersion thereof (polyethylene wax) is preferred.

Polyurea viscosity modifiers are reaction products of isocyanates and amines. Polyurea viscosity modifiers are also called sag control agents (SCAs).

The content of the viscosity modifier is preferably 0.01% by mass or more and 20% by mass or less of the solid content of the film-forming resin. When the content of the viscosity modifier is in this range, the high shear viscosity and L/V of the paint can be easily adjusted to the desired range. The content of the viscosity modifier is more preferably 0.05% by mass or more of the solid content of the film-forming resin, and particularly preferably 0.5% by mass or more. The content of the viscosity modifier is more preferably 10% by mass or less of the solid content of the film-forming resin, and particularly preferably 5% by mass or less.

(Surface conditioner)
The paint may contain a surface conditioner. The surface conditioner is added to control the surface tension of the paint. The surface conditioner makes it easier to adjust the high shear viscosity and L/V of the paint to the desired range.

The surface conditioner is not particularly limited. Examples of the surface conditioner include silicone-based, acrylic-based, vinyl-based, and fluorine-based surface conditioners. These may be used alone or in combination of two or more. Among them, from the viewpoint of controlling high shear viscosity and L/V, at least one of silicone-based and acrylic-based surface conditioners is preferred. Examples of silicone-based surface conditioners include polydimethylsiloxane and modified silicones obtained by modifying this. Examples of modified silicones include polyether-modified products, acrylic-modified products, and polyester-modified products. Examples of acrylic surface conditioners include acrylic copolymers.

The content of the surface conditioner is not particularly limited. The content of the surface conditioner is preferably 0.01% by mass or more and 10% by mass or less of the solid content of the paint. When the content of the surface conditioner is in this range, the high shear viscosity and L/V of the paint can be easily adjusted to the desired range. The content of the surface conditioner is more preferably 0.02% by mass or more of the solid content of the paint, and particularly preferably 0.04% by mass or more. The content of the surface conditioner is more preferably 8% by mass or less of the solid content of the paint, and particularly preferably 6% by mass or less.

(others)
The colored coating film may contain various additives as necessary, such as ultraviolet absorbers, antioxidants, antifoaming agents, dispersants, pinhole prevention agents, and interface control agents.

For example, a dispersant is added to increase the dispersibility of the pigment. There are no particular limitations on the dispersant, and it is selected appropriately depending on the type of solvent and pigment, etc.

In the case of water-based paints, examples of dispersants include inorganic dispersants such as phosphates and polyphosphates; polymeric dispersants such as polycarboxylic acid-based polyethylene glycol-based and naphthalenesulfonic acid-formaldehyde condensation-based; and low molecular weight dispersants such as alkylsulfonic acid-based, quaternary ammonium-based, and higher alcohol alkylene oxide-based. Examples of phosphates include sodium hexametaphosphate, sodium pyrophosphate, and sodium phosphate.

For solvent-based paints, polymeric dispersants such as polycarboxylic acid partial alkyl esters, polyethers, and polyalkylene polyamines are used as dispersants.

The amount of dispersant contained is not particularly limited. For example, the amount of dispersant contained may be 0.01% by mass or more and 3% by mass or less, or 0.1% by mass or more and 1.0% by mass or less, of the solid content of the paint.

[Method of manufacturing coated articles]
The coated article is manufactured by a method including a step of discharging paint from a nozzle of a dispenser toward a relatively moving substrate. The shear viscosity of the paint at a shear rate of 1000/s is 0.01 Pa·s or more and 0.20 Pa·s or less. The paint is stretched at an extension rate V of 0.5 m/s or less using an extensional rheometer, and the break length L (mm) of the paint is measured and divided by the extension rate V (m/s), giving a value of L/V of 10 to 49. When the paint contains a film-forming resin, the discharging step may be followed by a curing step of curing the film-forming resin.
FIG. 2 is a flowchart showing the method for producing a coated article according to this embodiment.

(1) Discharge process (S11)
First, an object to be painted is prepared.
(Substrate)
The shape of the object to be coated is not particularly limited. The object to be coated may be flat or may have a three-dimensional shape. According to this embodiment, the coating can be performed even on an object to be coated having a three-dimensional shape. The size of the object to be coated is not particularly limited. According to this embodiment, a smooth coating film can be formed even on a large object to be coated, such as an object exceeding 100 cm square. can do.

The material of the substrate is not particularly limited. Examples of the substrate material include metal, resin, and glass. Examples of metal include iron, copper, aluminum, tin, zinc, and alloys thereof.

The metallic substrate may be surface-treated. Examples of surface treatments include phosphate treatment, chromate treatment, zirconium conversion treatment, and composite oxide treatment. After surface treatment, the metallic substrate may be further coated with an electrocoating paint. The electrocoating paint may be of the cationic type or the anionic type.

Examples of resins include polypropylene resin, polycarbonate resin, urethane resin, polyester resin, polystyrene resin, ABS resin, polyvinyl chloride resin, and polyamide resin.

It is preferable that the resin substrate is degreased. After degreasing, the resin substrate may be further coated with a primer paint. There are no particular limitations on the primer paint, and it may be selected appropriately depending on the type of paint to be applied on top of it.

The method according to this embodiment is particularly suitable for manufacturing components for automobile bodies. Examples of automobile body components include roofs, doors, spoilers, bumpers, mirror covers, grills, doorknobs, and hoods. Specific examples of automobile bodies include passenger cars, trucks, motorcycles, and buses.

Next, the paint is dispensed from the nozzle of a dispenser (fixed-volume dispenser) toward the object to be coated, which is moving relative to the object. This forms a coating film containing the paint on the surface of the object to be coated. Since the paint is dispensed from the nozzle in liquid form, the coating efficiency is high. Furthermore, the paint adheres evenly to the object to be coated. As a result, the resulting coating film has excellent smoothness.

The workpiece is placed, for example, on a mounting table. The workpiece may be moved together with the mounting table, the dispenser may be moved, or both the mounting table and the dispenser may be moved.

The dispenser is not particularly limited as long as it has a nozzle capable of discharging a fixed amount of liquid paint. The dispenser may discharge paint from the nozzle in the form of a liquid column, or in the form of droplets. The paint discharge mechanism is also not particularly limited, and examples include pneumatic, piezoelectric, plunger, non-contact, and thermal valve types. The number of nozzles is also not particularly limited, and may be one or more, or two or more.

The nozzle diameter is preferably 5 μm or more and 300 μm or less. This helps to prevent nozzle clogging and makes it easier to perform highly accurate painting. The nozzle diameter is more preferably 10 μm or more, and particularly preferably 30 μm or more. The nozzle diameter is more preferably 250 μm or less, and particularly preferably 200 μm or less.

The distance between the substrate and the nozzle is, for example, 4 mm or more and 200 mm or less. With the paint according to this embodiment, it is possible to dispense and apply the coating to substrates that are so far away while suppressing streaks. The distance between the substrate and the nozzle may be 5 mm or more, or 10 mm or more. The distance between the substrate and the nozzle may be 100 mm or less, or 50 mm or less. The distance between the substrate and the nozzle is the average value of the distances between any number of points (e.g., five points) on the substrate and the nozzle that passes through each of the points and extends in the normal direction of the substrate.

The size of the substrate is not particularly limited and can be set arbitrarily. According to the coating material of this embodiment, it is possible to dispense and coat the substrate while suppressing streaks, regardless of the size of the substrate. The substrate may be, for example, a polygon (typically, a rectangle) with one side of 1 cm or more, or 3 cm or more. The length of one side of the substrate may be 50 cm or more, 90 cm or more, or 100 cm or more. The area of the substrate may be 2,500 cm ² or more, 8,100 cm ² or more, or 10,000 cm ² .

The size of the droplets or the diameter of the liquid column are not particularly limited. However, in order to easily suppress streaks, it is preferable that the maximum length D of the droplets or liquid column in the direction perpendicular to the normal direction of the substrate is smaller than 5 times the nozzle diameter Dn (D<Dn x 5). When the paint according to this embodiment is used, the maximum length D of the droplets/liquid column in the direction perpendicular to the normal direction of the substrate is easily controlled within the above range. The above maximum length D of the droplet is synonymous with the maximum diameter D2 described below.

The droplets are preferably spherical in that streaks are easily suppressed. When the paint according to this embodiment is used, the droplets tend to become spherical. A spherical droplet means that when the droplet is viewed from the side just before impact, the ratio D1/D2 between the maximum diameter D1 of the droplet in the normal direction to the workpiece and the maximum diameter D2 of the droplet in the direction perpendicular to the normal direction is 0.8 or more and 1.2 or less. Images captured by a high-speed camera, for example, can be used to measure each maximum diameter.

The amount of paint applied is not particularly limited. For example, the paint is applied so that the thickness of the coating film after curing is 7 μm or more and 50 μm or less.

The ejection process may be repeated multiple times. In this case, the composition of the paint used may be changed as long as the high shear viscosity is in the range of 0.01 Pa·s to 0.20 Pa·s and the L/V is in the range of 10 to 49.

After the ejection process, preliminary drying (also called preheating) may be performed before curing. This will prevent the solvent contained in the colored coating from bumping during the curing process, making it easier to prevent popping. This will make it easier to improve the appearance of the resulting coating.

There are no particular limitations on the conditions for pre-drying. Examples of pre-drying include leaving the material at a temperature of 20°C to 25°C for 15 to 30 minutes, or heating the material at a temperature of 50°C to 100°C for 30 seconds to 10 minutes.

(2) Curing process (S12)
The paint is cured. The paint can be cured by heating. The heating conditions are appropriately set according to the composition of the paint. The heating temperature is, for example, 70° C. or higher and 150° C. or lower, and preferably 80° C. or higher and 140° C. or lower. The heating time may be, for example, 10 minutes or more and 40 minutes or less, and may be 20 minutes or more and 30 minutes or less. The heating device may be, for example, a drying oven such as a hot air oven, an electric oven, or an infrared induction heating oven. Examples include:

Before or after the discharging step, or after the curing step, the substrate may be coated using a method other than dispense coating. Coating methods include, for example, air spray coating, airless spray coating, rotary atomization coating, and curtain coat coating. These methods may be combined with electrostatic coating. Among these, rotary atomization electrostatic coating is preferred from the viewpoint of coating efficiency. For rotary atomization electrostatic coating, a rotary atomization electrostatic coater, commonly known as "micro-microbell (μμbell)", "microbell (μbell)", or "metallicbell (metabell)", is used.

The present invention will be explained in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples. Note that "parts" and "%" are all based on mass.

[Example 1]
(I) Preparation of substrate A zinc phosphate-treated steel sheet (50 mm long, 50 mm wide) with a cured electrodeposition coating was prepared as a substrate. The cured electrodeposition coating was formed by electrodeposition coating the zinc phosphate-treated steel sheet with "Powernics", a cationic electrodeposition paint manufactured by Nippon Paint Automotive Coatings, to a dry film thickness of 20 μm, and then heating at 160° C. for 30 minutes.

(II) Preparation of paint Acrylic resin emulsion (manufactured by Nippon Paint Automotive Coatings, average particle size 150 nm, solid content concentration 30%, acid value 20 mg KOH / g, hydroxyl value 40 mg KOH / g) 93.4 parts, 10 parts of dimethylethanolamine 10% aqueous solution, 71.6 parts of water-soluble acrylic resin (manufactured by Nippon Paint Automotive Coatings, solid content concentration 30%, acid value 56 mg KOH / g, hydroxyl value 70 mg KOH / g), 42.9 parts of Cymel 250 (hardener, manufactured by Mitsui Cytec, methyl / butyl mixed alkylated melamine resin, solid content concentration 70%), and 48 parts of black pigment paste prepared as follows were mixed and adjusted with ion exchange water so that the solid content was 22.9 mass%, to obtain water-based paint X1. Water-based paint X1 is used, for example, to form a base coat coating film.

(Preparation of black pigment dispersion paste)
Disperbyk 190 (dispersant, manufactured by BYK-Chemie) 23.8 parts, Nippon Paint Automotive Coatings water-soluble acrylic resin (solid content concentration 30.0%, acid value 56 mgKOH/g, hydroxyl value 70 mgKOH/g) 35.2 parts, BYK-011 (defoamer, manufactured by BYK-Chemie) 0.5 parts, ion-exchanged water 36.8 parts, RAVEN 5000 (black pigment, manufactured by COLUMBIA) 10.57 parts were premixed. Then, using a paint conditioner and a glass bead medium, the mixture was mixed at room temperature until the average particle size of the pigment was 0.1 μm or less, to obtain a black pigment dispersion paste.

(III) Dispense Coating The above-mentioned water-based paint X1 was applied to the substrate using a micro-dispense system (Vermes, MDS 3200, nozzle diameter 100 μm). Then, the substrate was preheated at 80° C. for 5 minutes to obtain an uncured coating film A1 having a thickness of 15 μm after curing. The distance between the substrate and the nozzle was 5 mm.

When the droplets were photographed from the side using a high-speed camera during dispense application, they were found to be spherical (D1/D2 ≒ 1/1) with their maximum length D2 being less than five times the nozzle diameter.

(IV) Curing of Coating Film The uncured coating film A1 was heated at 140° C. for 20 minutes to obtain a coated article having a cured coating film A1. The thickness of the cured coating film A1 was 15 μm.

(V) Evaluation The above evaluations were carried out on the cured coating film A1. The results of evaluations (i) to (iv) are shown in Table 1.

(i) High Shear Viscosity Steady flow measurements were carried out under the following conditions using a stress-controlled rheometer (MCR301, manufactured by Anton Paar), and the measurement data 60 seconds after the start of the measurement was taken as the high shear viscosity.
Jig: 50mm cone plate Gap: 0.1mm
Shear rate: 1000/sec Measurement temperature: 23°C

(ii) L/V
Using an extensional rheometer (elongational shear rheometer HAAKE CaBER1 manufactured by Thermo Fisher Scientific) and a high-speed camera (FASTCAM Mini AX50 manufactured by Photoron), the breaking lengths were measured when the extension speed was changed to 0.1 m/s, 0.2 m/s, 0.3 m/s, 0.4 m/s, and 0.5 m/s. The measured values were plotted on a graph with the horizontal axis representing the extension speed V and the vertical axis representing the breaking length L, and a straight line was obtained by linear regression analysis using the least squares method. The slope of this straight line (=breaking length L (mm)/extension speed V (m/s)) was calculated.

(iii) Surface Tension The surface tension of the paint was measured by the pendant drop method using a contact angle meter (Kyowa Interface Science Co., Ltd., DMo-701).

(iv) Coating uniformity (streaks)
The surface of the resulting coating film was visually observed and evaluated according to the following criteria.
Good: No streaks, or streaks that are just barely visible can be seen in parts of the coating. Poor ^*1 : Streaks can be clearly seen in parts of the coating. Poor ^*2 : Streaks can be clearly seen over the entire coating.

[Example 2]
In the preparation of the paint (II), 3.3 parts of ADEKA NOL UH814N (urethane association type viscosity modifier, manufactured by ADEKA Corporation) were further mixed, and the same procedure as in Example 1 was used to prepare water-based paint X2 (solid content 23.1% by mass). The content of the viscosity modifier was 1% of the solid mass of the coating film-forming resin. Using the water-based paint X2, a coated object having a cured coating film A2 was prepared in the same manner as in Example 1, and evaluations (i) to (v) were performed. The results are shown in Table 1. In addition, when the droplets were photographed from the side using a high-speed camera during dispense coating, the droplets were spherical (D1/D2 ≒ 1/1), and their maximum length D2 was less than 5 times the nozzle diameter.

[Example 3]
A water-based paint X3 (solid content 20.5% by mass) was prepared in the same manner as in Example 1, except that 40.8 parts of ion-exchanged water was further mixed in the paint preparation (II). Using the water-based paint X3, a coated object having a cured coating film A3 was prepared in the same manner as in Example 1, and evaluations (i) to (v) were performed. The results are shown in Table 1. In addition, when the droplets were photographed from the side using a high-speed camera during dispense coating, the droplets were spherical (D1/D2 ≒ 1/1), and their maximum length D2 was less than 5 times the nozzle diameter.

[Comparative Example 1]
In the preparation of the paint (II), 245 parts of ion-exchanged water was further mixed, and the same procedure as in Example 1 was used to prepare the water-based paint Y1 (solid content: 13.5% by mass). Using the water-based paint Y1, a coated object having a cured coating film B1 was prepared in the same manner as in Example 1, and evaluations (i) to (v) were performed. The results are shown in Table 1. In addition, when the droplets were photographed from the side using a high-speed camera during dispense coating, the droplets were spherical (D1/D2 ≒ 1/1), but their maximum length D2 was 5 times or more the nozzle diameter. This is thought to be because the high-shear viscosity of the paint was excessively low, which resulted in the formation of a puddle at the tip of the nozzle, resulting in a large amount of liquid being discharged.

[Example 4]
In the preparation of the paint (II), the water-based paint X4 (solid content 46% by mass) was prepared as follows. The water-based paint X4 is used, for example, to form an intermediate coating film. Using the water-based paint X4, a coated object having a cured coating film A4 was prepared in the same manner as in Example 1, and evaluations (i) to (v) were performed. The results are shown in Table 1. In addition, when the droplets were photographed from the side using a high-speed camera during dispense coating, the droplets were spherical (D1/D2 ≒ 1/1), and their maximum length D2 was less than 5 times the nozzle diameter.

(II) Preparation of Paint 24.6 parts of hydroxyl-containing acrylic resin emulsion produced as described below, 99.9 parts of hydroxyl-containing polyester resin, 37.5 parts of Cymel 211 (hardener, manufactured by Mitsui Cytec Co., Ltd., imino-type melamine resin), 33.3 parts of carbodiimide composition A (interface control material), and 139 parts of white pigment dispersion paste were mixed to obtain a water-based paint X4.

(Production of Hydroxyl-Containing Acrylic Resin Emulsion)
In a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser and a nitrogen inlet tube, 445 parts of ion-exchanged water and 5 parts of Newcol 293 (dispersant, manufactured by Nippon Nyukazai Co., Ltd.) were charged and heated to 75°C while stirring. Separately, a monomer mixture consisting of 0.4 parts of methacrylic acid, 2.0 parts of 2-hydroxyethyl acrylate, 8.6 parts of styrene, 9.4 parts of n-butyl acrylate and 4.2 parts of ethyl acrylate, 240 parts of ion-exchanged water and 30 parts of Newcol 293 were mixed and emulsified by a homogenizer. The obtained monomer pre-emulsion was dropped into the reaction vessel over 3 hours while stirring. In parallel with the dropping of the monomer pre-emulsion, a certain amount of an aqueous solution in which 1 part of ammonium persulfate (polymerization initiator) was dissolved in 50 parts of ion-exchanged water was dropped into the reaction vessel. After the dropping of the monomer pre-emulsion was completed, the reaction was continued at 80°C for another 1 hour. After cooling, an aqueous solution of 2 parts of dimethylaminoethanol in 20 parts of water was added to the reaction vessel to obtain a hydroxyl-containing acrylic resin emulsion with a solid content concentration of 40.6%. The pH of the acrylic resin emulsion was adjusted to 7.2 using a 30% aqueous dimethylaminoethanol solution.

(Production of Hydroxyl-Containing Polyester Resin)
Into a reaction vessel, 25.6 parts of isophthalic acid, 22.8 parts of phthalic anhydride, 5.6 parts of adipic acid, 19.3 parts of trimethylolpropane, 26.7 parts of neopentyl glycol, 17.5 parts of ε-caprolactone and 0.1 parts of dibutyltin oxide were added, and the mixture was heated to 170°C while being mixed and stirred. Then, the mixture was heated to 220°C over 3 hours, and water generated by the condensation reaction was removed until the acid value was 8. Next, 7.9 parts of trimellitic anhydride were added to the reaction vessel, and the mixture was reacted at 150°C for 1 hour. This resulted in a polyester resin having an acid value of 403 mgKOH/g. Next, the reaction vessel was cooled to 100°C, and 11.2 parts of butyl cellosolve were added, and the mixture was stirred until it was homogeneous. Subsequently, the reaction vessel was cooled to 60°C, and 98.8 parts of ion-exchanged water and 5.9 parts of dimethylethanolamine were added to obtain a hydroxyl-containing polyester resin having a solids concentration of 50%, an acid value of 40 mgKOH/g, a hydroxyl value of 110 mgKOH/g, and a number average molecular weight of 2,870.

(Preparation of Carbodiimide Composition A)
2.5 parts of 3-methyl-1-phenyl-2-phospholene-1-oxide (carbodiimidization catalyst) was added to 250 parts of 4,4-dicyclohexylmethane diisocyanate, and the mixture was allowed to react at 170°C until the NCO equivalent reached 300. The resulting reaction product had an average of 2.8 carbodiimide groups per molecule. Furthermore, 106 parts of polyethylene glycol monomethyl ether having an average repeat number of 9, 295 parts of polypropylene glycol monobutyl ether having an average repeat number of 19, and 0.18 parts of dibutyltin dilaurate were added, and the mixture was allowed to react at 90°C until the absorption of NCO could no longer be confirmed by IR. As a result, a carbodiimide composition A was obtained.

(Preparation of White Pigment Dispersion Paste)
4.5 parts of Disperbyk190 (acidic dispersant, manufactured by BYK-Chemie), 0.5 parts of BYK-011 (defoamer, manufactured by BYK-Chemie), 22.9 parts of ion-exchanged water, and 72.1 parts of rutile-type titanium dioxide (white pigment) were premixed. Then, using a paint conditioner and a glass bead medium, the mixture was mixed at room temperature until the average particle size of the pigment became 0.3 μm or less, to obtain a white pigment dispersion paste.

[Example 5]
In the preparation of the paint (II), a solvent-based paint X5 (solid content 50.7% by mass) was prepared as follows. The solvent-based paint X5 is used, for example, to form a clear coating film. Using the solvent-based paint X5, a coated object having a cured coating film A5 was prepared in the same manner as in Example 1, and evaluations (i) to (v) were performed. The results are shown in Table 2. In addition, when the droplets were photographed from the side using a high-speed camera during dispense coating, the droplets were spherical (D1/D2 ≒ 1/1), and their maximum length D2 was less than 5 times the nozzle diameter.

(II) Preparation of paint: 57.7 parts of acid anhydride group-containing acrylic resin (a) (manufactured by Nippon Paint Automotive Coatings, solid content concentration 56%, acid value 140 mgKOH/g, number average molecular weight 3000), 20.0 parts of carboxyl group-containing polyester resin (b) (manufactured by Nippon Paint Automotive Coatings, solid content concentration 75%, acid value 124 mgKOH/g, number average molecular weight 2500), 75.3 parts of hydroxyl group- and epoxy group-containing acrylic resin (c) (manufactured by Nippon Paint Automotive Coatings, solid content concentration 70%, epoxy equivalent 400, hydroxyl value 50 mgKOH/g), 1 part of Tinuvin 928 (ultraviolet absorber, manufactured by BASF), 1 part of Tinuvin 123 (light stabilizer, manufactured by BASF), RESIFLOW LV (acrylic surface conditioner, manufactured by ESTRON CHEMICAL 0.3 parts (0.3% by mass of the solid content of the paint) manufactured by Epson Corporation (manufactured by Epson Corporation) and 1.0 parts of Disparlon OX-881 (anti-popping agent, manufactured by Kusumoto Chemical Industries, Ltd.) were mixed. Next, the mixture was diluted with a thinner consisting of ethyl 3-ethoxypropionate/Solvesso 150 to a viscosity of 28 seconds/20°C in a No. 4 Ford cup to obtain a solvent-based paint X5. The solvent-based paint X5 is used, for example, to form a clear coating film.

[Example 6]
In the preparation of the paint (II), a solvent-based paint X6 (solid content 35.6% by mass) was prepared as follows. The solvent-based paint X6 is used, for example, to form a base coat film. Using the solvent-based paint X6, a coated object having a cured coating film A6 was prepared in the same manner as in Example 1, and evaluations (i) to (v) were performed. The results are shown in Table 2. In addition, when the droplets were photographed from the side using a high-speed camera during dispense coating, the droplets were spherical (D1/D2 ≒ 1/1), and their maximum length D2 was less than 5 times the nozzle diameter.

(II) Preparation of paint 13.3 parts of crosslinkable resin particles produced as follows were mixed with 4.7 parts of toluene. Then, 19.4 parts of U-Ban 20N60 (butylated melamine resin, manufactured by Mitsui Toatsu Co., Ltd.) were added and mixed uniformly. Furthermore, 32.6 parts of amide group-containing acrylic resin and 16.4 parts of acrylic resin produced as follows were added and mixed uniformly. Next, 19.25 parts of black pigment dispersion paste prepared as follows, 0.04 parts (about 0.07% by mass of the solid content mass of the paint) of FLOWRENE AC-300 (manufactured by Kyoeisha Chemical Co., Ltd., acrylic-vinyl ether surface conditioner) were added, and then 31.7 parts of Solvent 150 (organic solvent, manufactured by Shoei Chemical Co., Ltd.) were added and mixed. In this way, a solvent-based paint X6 was obtained.

(Production of Crosslinked Resin Particles)
In a reaction vessel equipped with a thermometer, stirring blade, nitrogen inlet tube, cooling condenser and decanter, 213 parts of bishydroxyethyl taurine, 208 parts of neopentyl glycol, 296 parts of phthalic anhydride, 376 parts of azelaic acid and 30 parts of xylene were charged and heated. Water generated by the reaction was removed by azeotropy with xylene. The reaction liquid temperature was raised to 210°C over about 3 hours from the start of reflux, and stirring and dehydration were continued until the acid value equivalent to carboxylic acid reached 135 mgKOH/g. After cooling the reaction liquid temperature to 140°C, 500 parts of Cardura E10 (Versatic acid glycidyl ester, Shell) were dropped into the reaction vessel over 30 minutes. Then, stirring was continued for 2 hours to terminate the reaction. As a result, an amphoteric ion group-containing polyester resin with an acid value of 55 mgKOH/g, a hydroxyl value of 91 mgKOH/g and a number average molecular weight of 1250 was obtained.

10 parts of this amphoteric ion group-containing polyester resin, 140 parts of ion-exchanged water, 1 part of dimethylethanolamine, 50 parts of styrene and 50 parts of ethylene glycol dimethacrylate were vigorously stirred in a stainless steel beaker to prepare a monomer suspension.
Separately, 0.5 parts of azobiscyanovaleric acid, 40 parts of ion-exchanged water, and 0.32 parts of dimethylethanolamine were mixed to prepare an aqueous initiator solution.

5 parts of the above zwitterionic group-containing polyester resin, 280 parts of ion-exchanged water, and 0.5 parts of dimethylethanolamine were charged into a reaction vessel equipped with a thermometer, stirring blade, nitrogen inlet tube, cooling condenser, and dropping funnel, and the temperature was raised to 80°C. 251 parts of the above monomer suspension and 40.82 parts of the initiator aqueous solution were simultaneously dropped into the reaction vessel over 60 minutes. The reaction was then continued for 60 minutes and terminated. This resulted in an emulsion containing crosslinked resin particles. The particle diameter of the crosslinked resin particles measured by dynamic light scattering was 55 nm. Butyl acetate was added to this emulsion, and water was removed by azeotropic distillation under reduced pressure. The medium was then replaced with butyl acetate to obtain a crosslinked resin particle solution with a solids concentration of 20%.

(Production of Amide Group-Containing Acrylic Resin)
A reaction vessel equipped with a nitrogen inlet tube, a stirrer, a temperature controller, a cooling condenser and a dropping funnel was charged with 178 parts of xylene and 98 parts of butanol, and the temperature was raised to 108 ° C. Separately, 80.4 parts of styrene, 76.2 parts of methyl methacrylate, 74.3 parts of 2-ethylhexyl acrylate, 74.3 parts of butyl acrylate, 6.2 parts of acrylic acid, 6.2 parts of methacrylic acid, 47.8 parts of 2-hydroxyethyl acrylate, 19.3 parts of N-butoxymethylacrylamide, 9.7 parts of t-butylperoxy-2-ethylhexanoate and 28.9 parts of xylene were mixed to prepare a monomer solution. This monomer solution was added dropwise to the reaction vessel over 3 hours. After the dropwise addition, the mixture was reacted at 108° C. for 1 hour to obtain an amide group-containing acrylic resin having a number average molecular weight of 6,000, a hydroxyl value of 60 mgKOH/g, an acid value of 29.2 mgKOH/g and a resin solids content of 56.5%.

(Production of acrylic resin)
In a reaction vessel similar to the above, 280 parts of xylene and 80 parts of butyl acetate were charged and heated to 105 ° C. Separately, 20 parts of styrene, 120 parts of methyl methacrylate, 41.6 parts of 2-hydroxyethyl methacrylate, 177.6 parts of ethyl acrylate, 31.6 parts of ethyl methacrylate, 9.2 parts of methacrylic acid, 2.8 parts of t-butylperoxy-2-hexanoate, and 40 parts of xylene were mixed to prepare a monomer solution. This monomer solution was dropped into the reaction vessel over 3 hours under stirring. After dropping, the mixture was reacted at 105 ° C. for 1 hour to obtain an acrylic resin with a number average molecular weight of 21,000, a hydroxyl value of 45 KOH / g, an acid value of 15 mg KOH / g, and a solid content concentration of 50%.

(Preparation of black pigment dispersion paste)
21.5 parts of Disperbyk 182 (dispersant, manufactured by BYK-Chemie), 43 parts of the above amide group-containing acrylic resin, 15.8 parts of xylene, 15.8 parts of butyl acetate, and 10.25 parts of RAVEN 5000 (black pigment, manufactured by COLUMBIAN) were premixed. Then, using a paint conditioner and a glass bead medium, the mixture was mixed at room temperature until the average particle size of the pigment became 0.1 μm or less, to obtain a black pigment dispersion paste.

[Example 7]
Solvent-based paint X7 (solid content 28.9 mass%) was prepared in the same manner as in Example 6, except that the amount of Solvent 150 added was 63.4 parts. Using the solvent-based paint X7, a coated object having a cured coating film A7 was prepared in the same manner as in Example 1, and evaluations (i) to (v) were performed. The results are shown in Table 2. In addition, when the droplets were photographed from the side using a high-speed camera during dispense coating, the droplets were spherical (D1/D2 ≒ 1/1), and their maximum length D2 was less than 5 times the nozzle diameter.

[Comparative Example 2]
Solvent-based paint Y2 (solid content 46.2% by mass) was prepared in the same manner as in Example 6, except that Solvent 150 was not added. Using the solvent-based paint Y2, a coated object having a cured coating film B2 was prepared in the same manner as in Example 1, and evaluations (i) to (v) were performed. The results are shown in Table 2. In addition, when droplets were photographed from the side using a high-speed camera during dispense coating, the droplets were elliptical (D1/D2 ≒ 1/1.4) that were elongated in the discharge direction. This is thought to be because the paint was stretched into threads due to the excessively high high-shear viscosity of the paint.

[Comparative Example 3]
Solvent-based paint Y3 (solid content 27.2% by mass) was prepared in the same manner as in Example 6, except that the amount of Solvent 150 added was 74 parts. Using the solvent-based paint Y3, a coated object having a cured coating film B3 was prepared in the same manner as in Example 1, and evaluations (i) to (v) were performed. The results are shown in Table 2. In addition, when the droplets were photographed from the side using a high-speed camera during dispense coating, the droplets were spherical, but their maximum length D2 was more than 5 times the nozzle diameter.

Figure 3 is a photograph of the surface of a portion of the cured coating film A1 produced in Example 1. It can be seen that there are no noticeable defects or streaks on the surface.

Figure 4 is a photograph of the surface of a portion of the cured coating film B1 produced in Comparative Example 1. It can be seen that streaks have formed due to the fact that there are areas where no paint has adhered or where only a small amount of paint has adhered.

Figure 5 is a photograph of the surface of a portion of the cured coating film B2 produced in Comparative Example 2. It can be seen that there are more areas with no paint or only a small amount of paint attached than in Figure 4, and that numerous streaks have formed over the entire surface.

The coating material of the present invention is suitable for use in dispense applications.

1 Paint 2A, 2B Circular plate

Claims (10)

A coating material for dispense application, comprising:
The coating composition includes a film-forming resin formed from a crosslinkable functional group and a base resin including at least one of an acrylic resin and a polyester resin,
The shear viscosity at a shear rate of 1000/s is 0.01 Pa sec or more and 0.20 Pa sec or less,
A coating material for dispense application, wherein the coating material is stretched at an extension speed V of 0.5 m/sec or less using an extensional rheometer to measure the breaking length L (mm) of the coating material, and the L/V obtained by dividing the breaking length L (mm) by the extension speed V (m/sec) is 15 or more and 45 or less. Contains a solvent,
The paint according to claim 1 , wherein the ratio of water in the solvent is 20% by mass or more. Contains a solvent,
The coating material according to claim 1 , wherein the organic solvent accounts for 40% by mass or more of the solvent. The coating material according to any one of claims 1 to 3 , which has a surface tension of 20 mN/m or more and 33 mN/m or less. The method includes a step of discharging paint from a nozzle of a dispenser toward a workpiece that moves relatively,
The coating material contains a film-forming resin formed by a crosslinkable functional group and a base resin containing at least one of an acrylic resin and a polyester resin,
The shear viscosity of the coating material at a shear rate of 1000/s is 0.01 Pa sec or more and 0.20 Pa sec or less,
A method for producing a coated article, wherein the coating is stretched using an extensional rheometer at an extension speed V of 0.5 m/sec or less to measure a breaking length L (mm) of the coating, and the breaking length L (mm) is divided by the extension speed V (m/sec), so that L/V is 15 or more and 45 or less. The method for producing a coated article according to claim 5 , further comprising a curing step of curing the film-forming resin after the discharging step. The method for producing a coated article according to claim 5 or 6 , wherein the nozzle has a diameter of 5 μm or more and 300 μm or less. The method for producing a coated article according to any one of claims 5 to 7 , wherein a distance between the object to be coated and the nozzle is 4 mm or more and 200 mm or less. The method for producing a coated article according to any one of claims 5 to 8 , wherein the substrate is a member for an automobile body. The method for producing a coated article according to claim 5 , wherein in the discharging step, the coating material is discharged from the nozzle in the form of droplets.

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