Coating apparatus

Abstract

To provide a coating apparatus capable of forming a highly uniform coated surface even on a vertical surface, a coating apparatus is configured to apply a paint composition containing a coloring material, a resin, an organic solvent, and water by an inkjet method. The paint composition has a storage modulus of 0.1 Pa or greater and 85 Pa or less and a loss modulus of 1.0 Pa or greater and 30 Pa or less. The paint composition satisfies an expression (1) below, where A represents a static surface tension of the paint composition and B represents a loss tangent of the paint composition. A×B≦110---(1)

Description

COATING APPARATUS

[0001] The present invention relates to a coating apparatus.

[0002] The inkjet recording method is a method of causing a small amount of a liquid droplet of an ink (coloring liquid or paint) to fly from a minute nozzle and adhere to a recording medium such as paper to record letters and images. The method is widely used in home printers because of its low noisiness, simple process, and coloring ease.

[0003] In recent years, the inkjet recording method has been expanding its use to commercial printing as well, because of its advantages such as adaptability to variable data printing and to a wide range of media. In commercial printing, printing is performed on a wide variety of paper, and the wide variety of paper is roughly divided into plain paper and coated paper.

[0004] There are increasing opportunities of direct printing on films and metals, not only on paper, and the required functions are also different from those in the case of paper. In particular, it is very difficult for all required properties such as close adhesiveness, ink dripping (image drying property), scratch resistance, light resistance, bleeding, beading, and discharge stability to be satisfied on metals.

[0005] In order to solve the problems, such methods have been proposed, as previously applying a material for fixing a paint composition such as an ink on the surface of a recording medium when an image of the paint composition is formed on the surface of the recording medium, or heating the surface. However, these proposals are cost- and workload-consuming and require operation equipment, and have not been widely spread from the viewpoint of workload and cost.

[0006] In addition, since non-absorbent media such as metals exhibit a surface property different from that of paper, the paint composition may coalesce by remaining in the droplet form without spreading over the media by wetting, or may conversely drip due to excessively spreading over the media by wetting. Therefore, it is necessary to uniformly level the paint composition after it lands as droplets, but the measures taken to achieve this uniformity in turn leads to generation of a mist during discharging.

[0007] To cope with this, various paint compositions and coating apparatuses have been proposed. For example, from the viewpoint of improving discharge stability and fixing property, there is a technique of using an aqueous latex liquid composition using a hardly evaporative solvent and an apparatus configured to discharge a liquid containing the aqueous latex liquid composition (for example, PTL 1).

[0008] [PTL 1]　　Japanese Unexamined Patent Application Publication No. 2018-154696

[0009] Paint compositions used in existing printers, however, drip on vertical surfaces such as assembled vehicle bodies, base materials already assembled and standing upright, and the like (e.g., side surfaces of vehicles and trucks), and it is difficult to print such paint compositions in a manner qualifiable as images. In addition, when such a paint composition is discharged, droplets scatter and have difficulty coalescing to form well-defined dots. Therefore, it is difficult to form a uniform coated surface on a vertical surface with existing paint compositions or existing coating apparatuses.

[0010] An object of the present invention is to provide a coating apparatus capable of forming a coated surface having a high uniformity even on a vertical surface.

[0011] In order to solve the problem described above, an embodiment of the present invention is a coating apparatus for applying a paint composition containing a coloring material, a resin, an organic solvent, and water to a coating object by an inkjet method. The paint composition has a storage modulus of 0.1 Pa or greater and 85 Pa or less and a loss modulus of 1.0 Pa or greater and 30 Pa or less. The paint composition satisfies an expression (1) below, where A represents a static surface tension of the paint composition and B represents a loss tangent of the pain composition. A×B≦110 ---(1)Advantageous Effect of Invention

[0012] According to an embodiment of the present invention, it is possible to provide a coating apparatus that can form a coated surface having a high uniformity even on a vertical surface.

[0013] FIG. 1 is an oblique view of the appearance of a discharge head of a coating apparatus according to a first embodiment of the present invention.FIG. 2 is a cross-sectional view along a cross-section S1 of FIG. 1.FIG. 3 is a cross-sectional view of one discharge module of the discharge head.FIG. 4 is an enlarged cross-sectional view of a main part of a discharge module.FIG. 5 is an enlarged view of a holding member holding a discharge module.FIG. 6 is a view illustrating performing printing on an airplane, which is a printing object (coating object), using a coating apparatus according to a second embodiment of the present invention.FIG. 7 is an oblique view of a coating apparatus according to a second embodiment of the present invention.FIG. 8 is an oblique view of a coating apparatus according to a third embodiment of the present invention.FIG. 9 is an oblique view of a driver of the coating apparatus of FIG. 8.

[0014] <Coating Apparatus> Embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is an oblique view of the appearance of a discharge head of a coating apparatus according to a first embodiment, and FIG. 2 is a cross-sectional view along a cross-section S1 of FIG. 1. FIG. 3 is a cross-sectional view of one discharge module of the discharge head, and FIG. 4 is an enlarged cross-sectional view of a main part of the discharge module. FIG. 5 is an enlarged view of a holding member holding the discharge module.

[0015] The coating apparatus according to the present embodiment is a coating apparatus for applying a paint composition to a coating object by an ink jet method.

[0016] <Configuration of Coating Apparatus> The coating apparatus of this embodiment includes a discharge head 1. The discharge head 1 includes a nozzle 111, a valve element 113, and a piezoelectric element 114. The nozzle 111 discharges a paint composition described later. The valve element 113 opens and closes the nozzle 111. The piezoelectric element 114 drives the valve element 113.

[0017] Specifically, the discharge head 1 includes a plurality of discharge modules 100 disposed in a housing 10 side by side on one or more lines. A pressurized liquid (paint composition) is supplied to each discharge module 100 from the outside through a supply port 11, and the paint composition that has not been discharged is recovered externally through a recovery port 12. The housing 10 includes a connector 2.

[0018] The discharge module 100 includes a nozzle plate 101 in which the nozzle 111 for discharging a paint composition is formed, a flow path 112 with which the nozzle 111 communicates and to which a pressurized paint composition is supplied, the needle-shaped valve element 113 for opening and closing the nozzle 111, and the piezoelectric element 114 for driving the valve element 113.

[0019] The nozzle plate 101 and the housing 10 are joined with each other. The flow path 112 is a common flow path for a plurality of discharge modules 100 formed in the housing 10, and as described above, is supplied with a pressurized liquid (paint composition) through the supply port 11. The paint composition is recovered through the recovery port 12.

[0020] An elastic body 113a is provided at the tip of the valve element 113, and when pressed against the nozzle plate 101, securely closes the nozzle 111. A bearing part 121 is provided between the valve element 113 and the housing 10, and a seal member 122 such as an O-ring is provided between the bearing part 121 and the valve element 113.

[0021] The piezoelectric element 114 is contained in a piezoelectric element containing space 123 of the housing 10. The piezoelectric element 114 is held in a center space 115a of a holding member 115 also serving as a biasing member. The piezoelectric element 114 and the valve element 113 are coaxially coupled to each other via an end 115b of the holding member 115.

[0022] The holding member 115 has the center space 115a in which the piezoelectric element 114 is contained. Its end 115b is connected to the valve element 113, and its back end 115c is fixed by a piezoelectric element fixing shaft 124 attached to the housing 10.

[0023] The holding member 115 includes a holding plate spring 116 serving as a biasing member. The holding plate spring 116 includes elastically deformable spring parts 116a and 116b at both ends thereof in a longitudinal direction corresponding to the expansion and contraction direction of the piezoelectric element 114. The spring part 116a is on the end 115b side to which the valve element 113 is attached, and the spring part 116b is on the back end 115c side opposite to the end 115b side to which the valve element 113 is attached.

[0024] The spring parts 116a and 116b have a spring function by being provided with slits 115d alternately in the transverse direction orthogonal to the longitudinal direction such that the spring parts remain in a crank shape. In this embodiment, the spring parts 116a and 116b have substantially the same spring constant, or some of them have the same spring constant.

[0025] Here, the length of the center space 115a of the holding member 115 (the length in the direction of the axis of the valve element 113) is shorter than the length of the piezoelectric element 114. Therefore, when the piezoelectric element 114 is fitted into the center space 115a of the holding member 115, the spring parts 116a and 116b of the holding plate spring 116 are in an extended state.

[0026] Thus, when the piezoelectric element 114 contracts in the direction of an arrow a in FIG. 4, the holding plate spring 116 also contracts in the direction of an arrow b, and a biasing force pulling the valve element 113 in a direction of opening the nozzle 111 acts on the valve element 113.

[0027] Here, when a voltage is applied by a voltage applying part 200, the piezoelectric element 114 operates in a D31 mode to drive the valve element 113 in the direction of opening the nozzle 111. That is, when a voltage is applied to the piezoelectric element 114, the valve element 113 is driven in the direction of opening the nozzle 111.

[0028] Therefore, since the valve element 113 blocks the nozzle 111 when no voltage is applied to the piezoelectric element 114, the paint composition is not discharged from the nozzle 111 even if the pressurized liquid (paint composition) is supplied to the flow path 112.

[0029] When a voltage is applied to the piezoelectric element 114, the piezoelectric element 114 contracts and pulls the valve element 113 via the holding member 115, so that the valve element 113 separates from the nozzle 111 and opens the nozzle 111. Thus, the pressurized liquid (paint composition) supplied to the flow path 112 is discharged from the nozzle 111.

[0030] In the coating apparatus of the present embodiment, the distance between the nozzle 111 and the coating object is preferably 5 mm or more.

[0031] In the present embodiment, the piezoelectric element 114 is held by the holding member 115 having a biasing member (holding plate spring 116) parallel with the piezoelectric element 114. That is, a biasing member for biasing the valve element 113 in the direction of opening the nozzle 111 is provided in parallel with the piezoelectric element 114.

[0032] Thus, when a voltage is applied to the piezoelectric element 114 to contract the piezoelectric element 114 and move the valve element 113 in the direction of opening the nozzle 111, a shift of the valve element 113 to its open position is assisted by the contraction of the holding plate spring 116.

[0033] Therefore, the force for shifting the valve element 113 is increased, to improve the responsiveness of the valve element 113 in shifting toward opening the nozzle 111, to thereby reduce dispersion of the discharge performance.

[0034] On the other hand, when the biasing member such as a spiral spring is arranged in series with the piezoelectric element 114, the movement of the biasing member is independent of the movement of the piezoelectric element. Therefore, there is a disadvantage that when the spiral spring is experiencing free vibration, vibration in the direction of inhibiting the movement of the piezoelectric element may also occur.

[0035] In this embodiment, since the piezoelectric element and the biasing member are arranged in parallel, a spring force (biasing force) is generated by being controlled by the shape of the piezoelectric element, so that the movement (displacement) of the piezoelectric element can be perfectly synchronized with and assisted by the biasing force.

[0036] Next, a second embodiment of the present invention will be described with reference to FIGS. 6 and 7. FIG. 6 is a view illustrating performing printing on an airplane as a printing object (coating object), using the coating apparatus according to the embodiment, and FIG. 7 is an oblique view of the coating apparatus.

[0037] The coating apparatus 500 includes a linear rail 504 for linearly reciprocating a carriage, which is a moving body mounted with the discharge unit 501 including the discharge head 1 described above, and an articulated robot 505 for appropriately moving the linear rail 504 to a predetermined position and holding it at that position.

[0038] The articulated robot 505 includes a robot arm 505a capable of freely moving like a human arm by a plurality of joints, and can freely move the leading end of the robot arm 505a and position it at an intended position accurately.

[0039] As the articulated robot 505, for example, a 6-axiscontrolled industrial robot including six axes, that is, six joints can be used. By being previously taught information about the operations, the articulated robot of the 6-axis type can bring the linear rail 504 to face a predetermined position of the printing object 700 (airplane) very accurately and quickly. The robot 505 is not limited to the 6-axis type, and an articulated robot including an appropriate number of axes such as five axes and seven axes can be used. The printing object 700 is an example of the coating object.

[0040] A fork-shaped supporting member 524 branched in two is provided on the robot arm 505a of the robot 505, and a vertical linear rail 523a is attached to the leading end of a left branch 524a of the supporting member 524 and a vertical linear rail 523b is attached to the leading end of a right branch 524b so as to be parallel with the former vertical linear rail.

[0041] Both ends of the linear rail 504 holding the discharge unit 501 movably are supported by the two vertical linear rails 523a and 523b, respectively, as if the linear rail stretched across the vertical linear rails.

[0042] The discharge unit 501 includes, for example, a plurality of discharge heads 1 or a discharge head 1 having a plurality of nozzle rows, for discharging paint compositions of various colors, which will be described later. Paint compositions of corresponding colors are pressure-supplied from liquid tanks 530 to the discharge heads 1 or to the nozzle rows of the discharge head 1 of the discharge unit 501.

[0043] In the coating apparatus 500, the linear rail 504 is moved to a position facing a printing-required area of the printing object 700 by the robot 505. Then, while the discharge unit 501 is moved along the linear rail 504 according to the printing data, the piezoelectric elements 114 (or piezoelectric elements 134) of the discharge modules 100 of the discharge head 1 are driven to perform printing.

[0044] When printing for one line is completed, the vertical linear rails 523a and 523b are driven to move the discharge head 1 of the discharge unit 501 from one line to the next.

[0045] By repeating this operation, it is possible to apply printing to the printing-required area of the printing object 700.

[0046] Next, a third embodiment of the present invention will be described with reference to FIGS. 8 and 9. FIG. 8 is an oblique view of a coating apparatus according to this embodiment, and FIG. 9 is an oblique view of a driver of the coating apparatus.

[0047] The coating apparatus 500 includes a movable frame unit 802 that is mounted so as to face a printing object 700 having a curved surface such as a bonnet of a vehicle. A movable unit 813 is attached to left and right frame members 810 and 811, which are constituents of the frame unit 802, so as to stretch across the frame members 810 and 811 so as to be able to move up and down in the vertical direction (Y direction).

[0048] The movable unit 813 is mounted with: a driver 803 including a built-in motor and disposed so as to be movable reciprocally on the movable unit 813 in a horizontal direction (X direction); and a discharge unit 501 attached to the driver 803 and configured to discharge a paint composition toward the printing object 700.

[0049] The apparatus further includes a controller 805 for controlling discharging of the paint composition from the discharge unit 501, the reciprocating movement of the driver 803, and the upward or downward movement of the movable unit 813, and an information processing device 806 such as a PC (personal computer) for giving instructions to the controller 805. The information processing device 806 is connected to a database unit (DB unit) 807 for recording and storing information regarding the printing object 700 such as the shape and size.

[0050] The frame unit 802 includes upper, lower, left, and right frame members 808, 809, 810, and 811 formed of a metal columnar body or the like, and left and right leg members 812a and 812b that are attached to both sides of the lower frame member 809 at right angles and horizontally in order to make the frame unit 802 stand on its own.

[0051] The movable unit 813 stretching across the left and right frame members 810 and 811 is configured to be capable of moving up or down while supporting the driver 803.

[0052] The printing object 700 is disposed at right angles with respect to a discharge direction (Z direction) in which the paint composition is discharged, that is, so as to face a plane formed by the upper, lower, left, and right frame members 808, 809, 810, and 811 of the frame unit 802.

[0053] In this case, it is possible to bring a predetermined printing-required position of the printing object 700 into place, by, for example, attracting and holding the back side of that printing area of the printing object 700 by a chuck attached to the leading end of the arm of the articulated arm robot. By using the articulated arm robot, it is possible to dispose the printing object 700 accurately at the printing position, and to change the attitude of the printing object 700 appropriately.

[0054] As illustrated in FIG. 9, the driver 803 is disposed so as to be movable reciprocally on the movable unit 813 in a horizontal direction (X direction). The movable unit 813 includes a rail 830 provided horizontally so as to stretch across the left and right frame members 810 and 811 of the frame unit 802, a rack gear 831 provided so as to be parallel with the rail 830, a linear guide 832 externally fitted around a part of the rail 830 and configured to move by sliding, a pinion gear unit 833 connected to the linear guide 832 and engageable with the rack gear 831, a motor 834 with a reducer 836 for rotating and driving the pinion gear unit 833, and a rotary encoder 835 for detecting the printing point position.

[0055] By driving (forward or reversely) the motor 834, the discharge unit 501 is moved in the right or left direction along the movable unit 813. The driver 803 functions as a driving mechanism for the discharge unit 501 in the X direction. Limit switches 837a and 837b are mounted on both sides of the casing of the reducer 836.

[0056] The discharge unit 501 includes a plurality of discharge heads 1 or a discharge head 1 having a plurality of nozzle rows, for discharging paint compositions of various colors, which will be described later. The discharge heads 1 or the nozzle rows of the discharge heads 1 of the discharge unit 501 are pressure-supplied with paint compositions of corresponding colors from ink tanks.

[0057] The coating apparatus 500 prints a required image on the printing object 700 by moving the movable unit 813 in the Y direction and moving the discharge unit 501 in the X direction.

[0058] <<Coating Object>> The coating object is an object to be coated with a paint composition or a recording medium used for recording. The coating object is not particularly limited, and examples thereof include paper, film, cloth, metal, plastic material, and the like. The metal may have a surface subjected to surface treatment.

[0059] A coating film may further be formed on an object, which may or does not need to be subjected to surface treatment. For example, a coating object, which is a base material, may be subjected to surface treatment as required, and an undercoat film may be formed thereon, a middle coat film may be formed on the undercoat film, and a top coat film may be formed on the middle coat film. For example, when the coating object is an automobile body, these films may be formed using publicly-known undercoat, middle coat, and top coat painting materials commonly used in the painting of an automobile body.

[0060] <<Inkjet Method>> The inkjet method is a method of forming an image on the surface of a recording medium by discharging an ink (droplets) onto the recording medium. In this embodiment, a coating object is coated with a paint composition by the inkjet method. By applying paints by the inkjet method in this way, the discharged droplets of the paint composition can be minute, and the paint composition can be uniformly applied to the coating object.

[0061] <Paint composition> The paint composition contains a coloring material, a resin, an organic solvent, and water.

[0062] <<<Coloring Material>>> The coloring material is not particularly limited, and pigments and dyes can be used.

[0063] As the pigment, inorganic pigments or organic pigments can be used. One of these may be used alone, or two or more of these may be used in combination. The pigment may contain a mixed crystal.

[0064] As the pigment, for example, a black pigment, a yellow pigment, a magenta pigment, a cyan pigment, a white pigment, a green pigment, an orange pigment, a glossy color pigment such as gold or silver, a light interference pigment or a metallic pigment can be used.

[0065] As the inorganic pigment, in addition to clay, kaolin, titanium oxide, iron oxide, calcium carbonate, barium sulfate, talc, silica, alumina white, aluminum hydroxide, barium yellow, cadmium red, molybdenum red, chromium yellow, chromium oxide, Prussian blue, cobalt blue, and complex metal oxide pigments, carbon black produced by publicly-known methods such as contact method, furnace method, and thermal method can be used.

[0066] As the organic pigment, azo pigment, polycyclic pigment (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, thren pigments, diketopyrrolopyrrole pigments, and the like), dye chelate (e.g., basic dye chelate, acid dye chelate, and the like), nitro pigment, nitroso pigment, aniline black, and the like can be used.

[0067] Of these pigments, those having good affinity with solvents are suitable for use. Resin hollow particles and inorganic hollow particles can also be used.

[0068] Specific examples of the pigments for black include carbon black (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black, channel black and the like, metals such as copper, iron (C.I. Pigment Black 11), titanium oxide, and the like, and organic pigments such as aniline black (C.I. Pigment Black 1).

[0069] Further, examples of the pigments for color include C. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, 213, C. I. Pigment Orange 5, 13, 16, 17, 36, 43, 51, C. I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:2 (Permanent Red 2B (Ca)), 48:3, 48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101 (colcothar), 104, 105, 106, 108 (Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, 264, C. I. Pigment Violet 1 (rhodamine lake), 3, 5:1, 16, 19, 23, 38, C. I. Pigment Blue 1, 2, 15 (phthalocyanine blue), 15:1, 15:2, 15:3, 15:4 (phthalocyanine blue), 16, 17:1, 56, 60, 63, C. I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, and the like.

[0070] The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. One of these may be used alone or two or more of these may be used in combination.

[0071] Examples of the dye include C. I. Acid Yellow 17, 23, 42, 44, 79, 142, C. I. Acid Red 52, 80, 82, 249, 254, 289, C. I. Acid Blue 9, 45, 249, C. I. Acid Black 1, 2, 24, 94, C. I. Food Black 1, 2, C. I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C. I. Direct Red 1, 4, 9, 80, 81, 225, 227, C. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C. I. Direct Black 19, 38, 51, 71, 154, 168, 171, 195, C. I. Reactive Red 14, 32, 55, 79, 249, C. I. Reactive Black 3, 4, and 35.

[0072] <<<<Content in Paint Composition>>>> The content of the coloring material in the paint composition is preferably 1% by mass or greater and 70% by mass or less, and more preferably 5% by mass or greater and 60% by mass or less with respect to the total content of solids in the paint composition, from the viewpoints of improvement of color developing performance and image density, fixability and discharge stability, and the like.

[0073] <<<<Method for Dispersing Coloring Materials>>>> Examples of the method for dispersing the coloring material in the paint composition include a method of forming a self-dispersible coloring material by introducing a hydrophilic functional group into the coloring material, a method of dispersing the coloring material that is surface-coated with a resin, and a method of dispersing the coloring material by using a dispersant.

[0074] As the method of forming a self-dispersible coloring material by introducing a hydrophilic functional group into the coloring material, for example, a self-dispersible pigment obtained by adding a functional group such as a sulfone group or a carboxyl group to a pigment (for example, carbon) to make the pigment dispersible in water can be used.

[0075] As the method of dispersing the coloring material that is surface-coated with a resin, a coloring material that is microencapsulated to be able to disperse in water can be used. This can be paraphrased as a resin-coated coloring material. In this case, it is not necessary that all of the coloring material particles to be blended in the paint composition are coated with a resin, and uncoated coloring material particles or partially coated coloring material particles may be dispersed in the paint composition as long as the effect of the present invention is not impaired.

[0076] As the method of dispersing the coloring material using a dispersant, a publicly-known low-molecular-weight dispersant or a polymeric dispersant, a representative example of which is a surfactant, can be used.

[0077] As the dispersant, for example, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant or the like can be used depending on the coloring material. A nonionic surfactant (available from Takemoto Oil & Fat Co., Ltd, T-100) or a sodium naphthalene sulfonate formalin condensate can also be suitably used as the dispersant. One dispersant may be used alone or two or more dispersants may be used in combination.

[0078] <<<<Adjustment of Coloring Material>>>> A paint composition can be obtained by mixing a coloring material with materials such as water and an organic solvent. It is also possible to produce a paint composition by mixing a coloring material with water, a dispersant, and the like to form a coloring material dispersion, and mixing it with materials such as water, an organic solvent, and the like.

[0079] The coloring material dispersion is obtained by dispersing water, a coloring material, a coloring material dispersant and, if necessary, other components, and adjusting their particle diameter. It is preferable to use a disperser for the dispersion treatment.

[0080] The particle diameter of the coloring material in the coloring material dispersion is not particularly limited, and from the viewpoint of dispersion stability, discharge stability, and image density of the coloring material and the like, D50, which is the median diameter on a volume basis, is preferably 5 nm or greater and 800 nm or less, and more preferably 10 nm or greater and 300 nm or less. The particle diameter of the coloring material can be measured by a dynamic light scattering method using a particle size analyzer (Nanotrac Wave-UT151, available from Microtrac-Bel Corp.).

[0081] The content of the coloring material in the coloring material dispersion is not particularly limited and can be appropriately selected according to the purpose, and is preferably 10% by mass or greater and 98% by mass or less, and more preferably 20% by mass or greater and 95% by mass or less with respect to the total content of solids in the coloring material dispersion from the viewpoint of discharge stability, image density, and the like.

[0082] It is preferable to filter out coarse particles from the coloring material dispersion by a filter, a centrifuge, or the like, and degas the coloring material dispersion, as needed.

[0083] <<<Resin>>> The resin contributes to the viscoelasticity of the paint composition. The type of the resin to be contained in the paint composition is not particularly limited and can be suitably selected according to the purpose, and examples of the resin include polyurethane resins, polyester resins, acrylic resins, polyether resins, polycarbonate resins, acrylic-modified-urethane resins, polyester-modified-urethane resins, polyolefin resins, epoxy resins, vinyl acetate resins, styrene-based resins, butadiene-based resins, styrene-butadiene-based resins, vinyl chloride-based resins, acrylic styrene-based resins, acrylic silicone-based resins, and the like.

[0084] Resin particles made of these resins may be used. It is possible to obtain a paint composition by mixing the resin particles, which are in the form of a resin emulsion in which the resin particles are dispersed in water serving as a dispersion medium, with materials such as a coloring material, an organic solvent, and the like. The resin particles may be a suitably synthesized product or a commercially available product. One type of resin particles may be used alone, two or more types of resin particles may be used in combination.

[0085] It is preferable that the resin contains a reactive functional group-containing resin from the viewpoint of weather resistance and the like.

[0086] The reactive functional group-containing resin is not particularly limited as long as it contains a reactive functional group, and can be suitably selected according to the purpose. Examples include a hydroxyl group, an amino group, an epoxy group, a carboxyl group, an isocyanate group, an alkoxysilyl group, and the like. They may be used alone or in combination of two or more types.

[0087] It is preferable that the reactive functional group-containing resin contains a hydroxyl group-containing resin from the viewpoint of weather resistance and the like.

[0088] <<<<Hydroxyl Group-Containing Resin>>>> The hydroxyl group-containing resin is not particularly limited as long as it is a resin containing a hydroxyl group, and can be suitably selected according to the purpose. It is preferable that the hydroxyl group-containing resin contains any one selected from hydroxyl group-containing acrylic resins and hydroxyl group-containing polyester resins.

[0089] The hydroxyl group-containing acrylic resin can be produced by copolymerizing, for example, a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer by a method known itself, for example, a solution polymerization method in an organic solvent, an emulsion polymerization method in water, or the like.

[0090] <<<<Hydroxyl Group-Containing Acrylic Resin>>>> The hydroxyl group-containing polymerizable unsaturated monomer is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds in one molecule. Examples of the hydroxyl group-containing polymerizable unsaturated monomer include: mono-esterified product of (meth)acrylic acid and divalent alcohol containing 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone modified product of the mono-esterified product of (meth)acrylic acid and divalent alcohol containing 2 to 8 carbon atoms; N-hydroxymethyl (meth)acrylamide; allyl alcohol; (meth)acrylates having a polyoxyethylene chain having a hydroxyl group at a molecular terminal; and the like. It should be noted that, in the present invention, any monomers that fall within (xvii) polymerizable unsaturated monomers having an ultraviolet-absorbing-functional group described later should be defined as the another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer, and are excluded from among hydroxyl group-containing polymerizable unsaturated monomers. Those listed above can be used alone or in combination of two or more types.

[0091] As the another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer, for example, the following monomers (i) to (xx) can be used. These polymerizable unsaturated monomers can be used alone or in combination of two or more types.

[0092] (i) Alkyl or cycloalkyl (meth)acrylates: examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, tricyclodecanyl (meth)acrylate, and the like.

[0093] (ii) Polymerizable unsaturated monomers having an isobornyl group: examples thereof include isobornyl (meth)acrylate, and the like.

[0094] (iii) Polymerizable unsaturated monomers having an adamantyl group: examples thereof include adamantyl (meth)acrylate, and the like.

[0095] (iv) Polymerizable unsaturated monomers having a tricyclodecenyl group: examples thereof include tricyclodecenyl (meth)acrylate, and the like.

[0096] (v) Polymerizable unsaturated monomers having an aromatic ring: examples thereof include benzyl (meth)acrylate, styrene, α-methylstyrene, vinyl toluene, and like.

[0097] (vi) Polymerizable unsaturated monomers having an alkoxysilyl group: examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, vinyl tris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, and the like.

[0098] (vii) Polymerizable unsaturated monomers having a fluorinated alkyl group: examples thereof include perfluoroalkyl (meth)acrylates such as perfluorobutylethyl (meth)acrylate, perfluorooctylethyl (meth)acrylate, and the like; fluoroolefin; and the like.

[0099] (viii) Polymerizable unsaturated monomers having a photopolymerizable functional group such as a maleimide group.

[0100] (ix) Vinyl compounds: examples thereof include N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, and the like.

[0101] (x) Carboxyl group-containing polymerizable unsaturated monomers: examples thereof include (meth)acrylic acid, maleic acid, crotonic acid, β-carboxyethyl (meth)acrylate, and the like.

[0102] (xi) Nitrogen-containing polymerizable unsaturated monomers: examples thereof include (meth)acrylonitrile, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, methylene bis(meth)acrylamide, ethylene bis(meth)acrylamide, an adduct of glycidyl (meth)acrylate with an amine compound, and the like.

[0103] (xii) Polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule: examples thereof include allyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and the like.

[0104] (xiii) Epoxy group-containing polymerizable unsaturated monomers: examples thereof include glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, allyl glycidyl ether, and the like.

[0105] (xiv) (Meth)acrylates having a polyoxyethylene chain having an alkoxy group on a molecular terminal.

[0106] (xv) Polymerizable unsaturated monomers having a sulfonic group: examples thereof include 2-acrylamide-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, allyl sulfonic acid, 4-styrene sulfonic acid, and the like; and sodium salts and ammonium salts of these sulfonic acids; and the like.

[0107] (xvi) Polymerizable unsaturated monomers having a phosphoric group: examples thereof include acid phosphoxyethyl (meth)acrylate, acid phosphoxypropyl (meth)acrylate, acid phosphoxypoly(oxyethylene) glycol (meth)acrylate, acid phosphoxypoly(oxypropylene) glycol (meth)acrylate, and the like.

[0108] (xvii) Polymerizable unsaturated monomers having an ultraviolet-absorbing functional group: examples thereof include 2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2-hydroxy-4-(3-acryloyloxy-2-hydroxypropoxy) benzophenone, 2,2´-dihydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2,2´-dihydroxy-4-(3-acryloyloxy-2-hydroxypropoxy) benzophenone, 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole, and the like.

[0109] (xviii) Photostable polymerizable unsaturated monomers: examples thereof include 4-(meth)acryloyloxy 1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, and the like.

[0110] (xix) Polymerizable unsaturated monomers having a carbonyl group: examples thereof include acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formyl styrol, vinyl alkyl ketone having 4 to 7 carbon atoms (e.g., methyl vinyl ketone, vinyl ethyl ketone, vinyl butyl ketone), and the like.

[0111] (xx) Polymerizable unsaturated monomers having an acid anhydride group: examples thereof include maleic anhydride, itaconic anhydride, citraconic anhydride, and the like.

[0112] As used herein, the term "polymerizable unsaturated group" means a radical-polymerizable unsaturated group. Examples of such polymerizable unsaturated groups include vinyl group, (meth)acryloyl group, and the like.

[0113] As used herein, the term "(meth)acrylate" means acrylate or methacrylate. The term "(meth)acrylic acid" means acrylic acid or methacrylic acid. Further, the term "(meth)acryloyl" means acryloyl or methacryloyl. Further, the term "(meth)acrylamide" means acrylamide or methacrylamide.

[0114] The proportion of the hydroxyl group-containing polymerizable unsaturated monomer used in producing the hydroxyl group-containing acrylic resin is preferably in the range of 1% by mass to 50% by mass, more preferably in the range of 2% by mass to 40% by mass, and more preferably in the range of 3% by mass to 30% by mass relative to total amount of monomer components.

[0115] The hydroxyl group-containing acrylic resin has a hydroxyl value preferably in the range of 1 mgKOH / g to 150 mgKOH / g, more preferably in the range of 2 mgKOH / g to 120 mgKOH / g, and more preferably in the range of 5 mgKOH / g to 100 mgKOH / g from the viewpoint of weather resistance and the like.

[0116] The hydroxyl group-containing acrylic resin has an acid value preferably in the range of 1 mgKOH / g to 150 mgKOH / g, more preferably in the range of 5 mgKOH / g to 100 mgKOH / g, and more preferably in the range of 5 mgKOH / g to 80 mgKOH / g from the viewpoint of discharge stability, uniformity of the coated surface, liquid dripping, and the like.

[0117] When obtaining the hydroxyl group-containing acrylic resin by an emulsion polymerization method in water, it is possible to perform the emulsion polymerization by a method publicly-known so far. For example, emulsion polymerization of a polymerizable unsaturated monomer mixture using a polymerization initiator in the presence of an emulsifier can be performed. As the emulsifier, anionic emulsifiers and nonionic emulsifiers can be suitably used.

[0118] Examples of the anionic emulsifier include sodium salts and ammonium salts of alkyl sulfonic acids, alkyl benzene sulfonic acids, alkyl phosphoric acids, and the like.

[0119] Examples of the nonionic emulsifier include polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene phenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan trioleate, polyoxyethylene sorbitan monolaurate, and the like.

[0120] A polyoxyalkylene group-containing anionic emulsifier having an anionic group and a polyoxyalkylene group such as a polyoxyethylene group, a polyoxypropylene group, or the like in one molecule; a reactive anionic emulsifier having an anionic group and a radical-polymerizable unsaturated group in one molecule; and the like may also be used. Examples of the reactive anionic emulsifier include a sodium salt of a sulfonic acid compound having a radical-polymerizable unsaturated group such as an allyl group, a methallyl group, a (meth)acryloyl group, a propenyl group, a butenyl group, and the like; an ammonium salt of the sulfonic acid compound mentioned above, and the like.

[0121] The amount of the emulsifier used is preferably approximately 0.1% by mass to 15% by mass, more preferably approximately 0.5% by mass to 10% by mass, and more preferably approximately 1% by mass to 5% by mass relative to the total amount of all monomers used.

[0122] Examples of the polymerization initiator include: organic peroxides such as benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butyl peroxylaurate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, diisopropyl benzene hydroperoxide and the like; azo compounds such as azobisisobutyronitrile, azo bis(2,4-dimethylvaleronitrile), azo bis(2-methylpropionitrile), azo bis(2-methylbutyronitrile), 4,4´-azo bis(4-cyanobutanoic acid), dimethyl azo bis(2-methylpropionate), azo bis[2-methyl-N-(2-hydroxyethyl)-propionamide], azo bis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide}, and the like; and persulfate salts such as potassium persulfate, ammonium persulfate, sodium persulfate, and the like. These polymerization initiators can be used alone or in combination of two or more types.

[0123] If necessary, a reductant such as sugar, sodium formaldehyde sulfoxylate, iron complex, and the like can be used in combination with the polymerization initiator to obtain a redox initiator.

[0124] In general, the amount of the polymerization initiator used is preferably in the range of 0.1% by mass to 5% by mass, and more preferably in the range of 0.2% by mass to 3% by mass relative to the total amount of all monomers used. The method for adding the polymerization initiator is not particularly limited, and can be suitably selected in accordance with the type, the amount, and the like thereof. For example, the polymerization initiator may be added in a monomer mixture or an aqueous medium in advance, or may be added in a batch or dropwise during polymerization.

[0125] It is preferable that the hydroxyl group-containing acrylic resin contains a hydroxyl group-containing acrylic resin having a core / shell structure from the viewpoints of discharge stability, uniformity of a coated surface, liquid dripping, and the like.

[0126] Here, the term "shell part" means a polymer layer existing in the outermost layer of a resin particle, the term "core part" means a polymer layer in an inner layer of a resin particle excluding the shell part, and the term "core / shell-type structure" means a structure having the core and shell parts. The core / shell-type structure generally has a layer structure in which the core part is completely covered with the shell part, but depending on the mass ratio between the core part and the shell part, the monomer amount in the shell part may not be enough to form the layer structure.

[0127] In such a case, it is not necessary for the resin particles to have the perfect layer structure as described above, but the structure may be a structure in which a part of the core part is covered with the shell part, or a structure in which a polymerizable unsaturated monomer as a constituent of the shell part is graft-polymerized with a part of the core part. The concept of the multilayer structure in the core / shell-type structure is also applicable to the case where a multilayer structure is formed in the core part of the hydroxyl group-containing acrylic resin. The core / shell structure can be obtained, for example, by reacting monomer compositions that are compositionally different in multiple steps.

[0128] When the paint composition contains the hydroxyl group-containing acrylic resin having the core / shell structure, the content of the hydroxyl group-containing acrylic resin having the core / shell structure is preferably in the range of 30% by mass to 100% by mass, more preferably in the range of 40% by mass to 90% by mass, and more preferably in the range of 50% by mass to 80% by mass relative to the total amount of resin solids in the hydroxyl group-containing acrylic resin from the viewpoints of discharge stability, uniformity of the coated surface, liquid dripping, and the like.

[0129] When the paint composition contains the hydroxyl group-containing acrylic resin, the content of the hydroxyl group-containing acrylic resin is preferably in the range of 1% by mass to 70% by mass, more preferably in the range of 2% by mass to 60% by mass, and more preferably in the range of 3% by mass to 50% by mass relative to the total content of resin solids in the paint composition from the viewpoints of discharge stability, uniformity of the coated surface, liquid dripping, and the like.

[0130] In the present specification, the term "content of solids" means a non-volatile component, of a resin, a curing agent, or a coloring material, and the like, that remains through drying at 110℃ for 1 hour. The content of solids can be determined, for example, by weighing out a sample into a heat-resistant container such as an aluminum foil cup or the like, spreading the sample on the bottom surface of the container, then drying the sample at 110℃ for 1 hour, and weighing the mass of the component remaining through drying.

[0131] In the present specification, the term "solid concentration" means the mass ratio of the solids in the composition. Therefore, for example, the solid concentration of the composition can be calculated by weighing out the composition into a heat-resistant container such as an aluminum foil cup or the like, spreading the composition on the bottom surface of the container, then drying the composition at 110℃ for 1 hour, weighing the mass of the component of the composition remaining through drying, and determining the mass ratio of the component remaining through drying to the total mass of the composition before drying.

[0132] <<<<Hydroxyl Group-Containing Polyester Resin>>>> The hydroxyl group-containing polyester resin can be synthesized by allowing a polybasic acid and a polyvalent alcohol to undergo esterification reaction by a known method according to a routine method.

[0133] The polybasic acid is a compound having two or more carboxyl groups in one molecule, and examples include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexahydrophthalic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid and anhydrides thereof. The polyvalent alcohol is a compound having two or more hydroxyl groups in one molecule, and examples include: diols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-diethyl-1,3-propanediol, neopentyl glycol, 1,9-nonanediol, 1,4-cyclohexanediol, hydroxypivalic acid neopentyl glycol ester, 2 butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethylpentanediol, hydrogenated bisphenol A, and the like; trivalent or higher polyol components such as trimethylolpropane, trimethylolethane, glycerin, pentaerythritol, and the like; and hydroxycarboxylic acids such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolpentanoic acid, 2,2-dimethylolhexanoic acid, 2,2-dimethyloloctanoic acid, and the like.

[0134] Further, α-olefin epoxides such as propylene oxide, butylene oxide, and the like, monoepoxy compounds such as glycidyl ester of synthetic highly branched saturated fatty acid (CARDURA E10P available from HEXION Inc., "CARDURA" is a registered trademark), and the like may be reacted with acid to introduce these compounds into the polyester resin.

[0135] The hydroxyl group-containing polyester resin may be a fatty acid-modified polyester resin modified with a (semi)drying oil fatty acid, such as linseed oil fatty acid, coconut oil fatty acid, safflower oil fatty acid, soybean oil fatty acid, sesame oil fatty acid, perilla oil fatty acid, hemp oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, and the like. In general, the amount of modification with these fatty acids is suitably 30% by mass or less in terms of oil length. The hydroxyl group-containing polyester resin may be obtained by partially reacting a monobasic acid such as benzoic acid.

[0136] The hydroxyl group-containing polyester resin may be modified with a fatty acid, a monoepoxy compound, a polyisocyanate compound, an acrylic resin, or the like during or after preparation of the resin.

[0137] Examples of the fatty acid include coconut oil fatty acid, cottonseed oil fatty acid, hempseed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, tall oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, tung oil fatty acid, rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor oil fatty acid, safflower oil fatty acid, and the like.

[0138] As the monoepoxy compound, for example, glycidyl ester of a synthetic highly branched saturated fatty acid (available from HEXION Inc., CARDURA E10P) can be suitably used.

[0139] Examples of the polyisocyanate compound include: aliphatic diisocyanate compounds such as lysine diisocyanate, hexamethylene diisocyanate, trimethylhexane diisocyanate, and the like; alicyclic diisocyanate compounds such as hydrogenated xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2,4-diisocyanate, methylcyclohexane-2,6-diisocyanate, 4,4´-methylene bis(cyclohexyl isocyanate), 1,3-(isocyanatomethyl) cyclohexane, and the like; aromatic diisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, and the like; organic polyisocyanate itself such as trivalent or higher polyisocyanate such as lysine triisocyanate; adducts of these organic polyisocyanates with polyvalent alcohol, low-molecular-weight polyester resin, water, or the like; cyclized polymers (e.g., isocyanurates) and biuret-type adducts of these organic polyisocyanates themselves; and the like. These polyisocyanate compounds can be used alone or in a mixture of two or more types.

[0140] As a method for modifying the hydroxyl group-containing polyester resin with an acrylic resin, known methods can be used. Examples of the method include a method of polymerizing a mixture of a polymerizable unsaturated group-containing polyester resin and a polymerizable unsaturated monomer, a method of reacting a hydroxyl group-containing and carboxyl group-containing polyester resin with an acrylic resin, which is a method of reacting a resin with a resin, and the like.

[0141] The hydroxyl group-containing polyester resin has a hydroxyl value preferably in the range of 1 mgKOH / g to 250 mgKOH / g, more preferably in the range of 2 mgKOH / g to 200 mgKOH / g, and more preferably in the range of 5 mgKOH / g to 200 mgKOH / g from the viewpoint of weather resistance and the like.

[0142] The hydroxyl group-containing polyester resin has an acid value preferably in the range of 1 mgKOH / g to 150 mgKOH / g, more preferably in the range of 2 mgKOH / g to 100 mgKOH / g, and more preferably in the range of 2 mgKOH / g to 50 mgKOH / g from the viewpoint of discharge stability, uniformity of a coated surface, liquid dripping, and the like.

[0143] The number average molecular weight of the hydroxyl group-containing polyester resin is preferably in the range of 800 to 100,000, more preferably in the range of 1,000 to 50,000, and more preferably in the range of 1,200 to 10,000.

[0144] In this specification, the average molecular weight is a value calculated based on the molecular weight of standard polystyrene from a chromatogram measured by Gel Permeation Chromatography (GPC). Gel permeation chromatography (GPC) was performed using "HLC 8120GPC" (obtained from Tosoh Corporation).

[0145] As the columns, four columns, namely "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL" and "TSKgel G-2000HXL" (all obtained from Tosoh Corporation) were used, and the measurement was performed using, as conditions, tetrahydrofuran as a mobile phase, a measuring temperature of 40℃, a flow rate of 1 mL / min, and RI as a detector.

[0146] When the paint composition contains a hydroxyl group-containing polyester resin, the content of the hydroxyl group-containing polyester resin is preferably in the range of 1% by mass to 70% by mass, more preferably in the range of 2% by mass to 50% by mass, and more preferably in the range of 3% by mass to 30% by mass relative to the total amount of resin solids in the paint composition from the viewpoints of discharge stability, uniformity of a coated surface, liquid dripping, and the like.

[0147] <<<<Polyurethane Resin>>>> The polyurethane resin can be obtained by a routine method, for example, by reacting a polyol with a polyisocyanate compound. After the reaction, chain extension can be performed in the presence of a chain extender that is a low-molecular-weight compound having at least two active hydrogens in one molecule, such as a diol or a diamine. The resin can be modified with an acrylic resin or the like during or after preparation or the resin.

[0148] Examples of low-molecular-weight types of the polyol include divalent alcohols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, hexamethylene glycol, and the like; and trivalent alcohols such as trimethylolpropane, glycerin, pentaerythritol, and the like. Examples of high-molecular-weight types of the polyol include polyether polyols, polyester polyols, acrylic polyols, epoxy polyols, and the like. Examples of the polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. Examples of the polyester polyols include: polycondensates of alcohols such as divalent alcohols listed above, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and the like with dibasic acids such as adipic acid, azelaic acid, sebacic acid, and the like; lactone-based ring-opened polymer polyols such as polycaprolactone, and the like; polycarbonate diols; and the like. For example, carboxy group-containing polyols such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, and the like may also be used. The polyols may be used alone or in combination with two or more types.

[0149] Examples of the polyisocyanate compounds to be reacted with the polyols include: aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, lysine diisocyanate, and the like; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; alicyclic diisocyanates such as isophorone diisocyanate, 4,4´-methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4-(or -2,6-) diisocyanate, 1,3-(or 1,4-) di(isocyanatomethyl)cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate, and the like; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; aromatic diisocyanate compounds such as xylylene diisocyanate, meta-xylylene diisocyanate, tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4´-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4-toluidine diisocyanate, 4,4´-diphenyl ether diisocyanate, (m- or p-) phenylenediisocyanate, 4,4´-biphenylenediisocyanate, 3,3´-dimethyl-4,4´-biphenylenediisocyanate, bis(4-isocyanatophenyl)sulfone, isopropylidene bis(4-phenylisocyanate), and like; and biuret-type adducts and isocyanurate ring-adducts of these polyisocyanates; polyisocyanates having three or more isocyanate groups in one molecule, such as triphenylmethane-4,4´,4´´-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, 4,4´-dimethyldiphenylmethane-2,2´,5,5´-tetraisocyanate, and the like; and biuret-type adducts and isocyanurate ring-adducts of these polyisocyanate compounds; and the like.

[0150] Examples of diols as the chain extender include ethylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, cyclohexanediol, and the like. Examples of diamines include ethylenediamine, propylenediamine, xylylenediamine, N-(2-hydroxyethyl)ethylenediamine, and the like.

[0151] From the viewpoint of weather resistance, and the like, the polyurethane resin has a hydroxyl value preferably in the range of 0 mgKOH / g to 250 mgKOH / g, more preferably in the range of 0 mgKOH / g to 200 mgKOH / g, and more preferably in the range of 0 mgKOH / g to 150 mgKOH / g.

[0152] From the viewpoint of discharge stability, uniformity of a coated surface, liquid dripping, and the like, the polyurethane resin has an acid value preferably in the range of 1 mgKOH / g to 100 mgKOH / g, more preferably in the range of 2 mgKOH / g to 50 mgKOH / g, and more preferably in the range of 2 mgKOH / g to 30 mgKOH / g.

[0153] The weight average molecular weight of the polyurethane resin is preferably 3,000 or more, more preferably 5,000 or more, and more preferably 10,000 or more.

[0154] From the viewpoint of discharge stability, uniformity of a coated surface, liquid dripping, and the like, the content of the polyurethane resin in the paint composition is preferably in the range of 2% by mass to 70% by mass, more preferably in the range of 5% by mass to 50% by mass, and more preferably in the range of 10% by mass to 40% by mass relative to the total amount of resin solids in the paint composition.

[0155] <<<<Diameter of Resin Particles>>>> The volume average particle diameter of the resin particles is not particularly limited and can be appropriately selected according to the purpose, and is preferably 50 nm or greater and 3,000 nm or less, and more preferably 100 nm or greater and 2,500 nm or less, from the viewpoint of obtaining a good fixability and a high image hardness. The volume average particle diameter can be measured, for example, by a dynamic light scattering method using a particle size analyzer (Nanotrac Wave-UT151, available from Microtrac-Bel Corp.).

[0156] <<<<Resin Content>>>> The content of the resin is not particularly limited and can be appropriately selected according to the purpose, and is preferably 10% by mass or greater and 98% by mass or less, and more preferably 20% by mass or greater and 95% by mass or less relative to the total amount of solids in the paint composition, from the viewpoint of fixability and the like. For adjustment of viscoelasticity, it is possible to increase storage modulus and / or loss modulus by increasing the content, and reducing storage modulus and / or loss modulus by reducing the content.

[0157] <<<Organic Solvent>>> The organic solvent used in the embodiment of the present invention is not particularly limited, and examples thereof include alcohols, ethers such as polyvalent alcohol alkyl ethers and polyvalent alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.

[0158] Specific examples of the organic solvent include: alcohols such as methanol, ethanol, isopropanol, n-butanol, sec-butanol, isobutanol, 1-hexanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, 1-decanol, benzyl alcohol, ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, petriol, and the like; polyvalent alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol-n-butyl ether, and the like; polyvalent alcohol aryl ethers such as ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, and the like; ester-based solvents such as n-butyl acetate, isobutyl acetate, methylamyl acetate, ethylene glycol monobutyl ether acetate, n-butyl propionate, and the like; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, 2-heptanone, ethyl n-amyl ketone, diisobutyl ketone, isophorone, cyclohexanone, and the like; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, γ-butyrolactone, and the like; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, and the like; amines such as monoethanolamine, diethanolamine, and triethylamine, and the like; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, thiodiethanol, and the like; and propylene carbonate, ethylene carbonate, and the like.

[0159] As the organic solvent, it is preferable to use an organic solvent having a boiling point of 250℃ or lower because it not only functions as a wetting agent but also provides a good drying property.

[0160] It is preferable that the organic solvent contains at least one organic solvent selected from n-butanol, 2-ethyl-1-hexanol, ethylene glycol monobutyl ether, ethylene glycol mono-2-ethylhexyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol n-butyl ether from the viewpoint of uniformity of a coated surface and the like.

[0161] <<<<Content of Organic Solvent>>>> The content of the organic solvent in the paint composition is not particularly limited and can be appropriately selected according to the purpose, and is preferably 3% by mass or greater and 30% by mass or lower, and more preferably 5% by mass or greater and 20% by mass or less from the viewpoint of drying property, discharge stability, and the like.

[0162] <<<Other Components>>> Other components may be added to the paint composition as needed. Examples of the other components include a curing agent, an oligomer, a curing catalyst, a surfactant, a defoaming agent, an antiseptic fungicide, an antirust agent, a pH adjusting agent, a viscosity adjusting agent, a surface adjusting agent, an ultraviolet absorber, a light stabilizer, and the like.

[0163] <<<<Curing Agent>>>> The paint composition may contain a curing agent. The curing agent is a compound capable of reacting with a reactive functional group of a reactive functional group-containing resin when the resin includes the reactive functional group-containing resin, and is a compound capable of forming a crosslinked structure by the reaction. It is preferable that the reactive functional group in the resin is a hydroxyl group, and that the curing agent is a compound having reactivity with the hydroxyl group.

[0164] Specific examples of the curing agent include an amino resin, a polyisocyanate compound, a blocked polyisocyanate compound, and the like. In particular, it is preferable that the curing agent contains an amino resin from the viewpoint of hardness, weatherability, and the like of a coating film to be formed.

[0165] As the amino resin usable as the curing agent, a partially methylolated amino resin or a completely methylolated amino resin obtained by reaction of an amino component with an aldehyde component can be used.

[0166] Examples of the amino component include melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine, dicyandiamide, and the like. Examples of the aldehyde component include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde, and the like.

[0167] The methylolated amino resin, of which a methylol group is partially or completely etherified with an appropriate alcohol can also be used. Examples of the alcohol used for the etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethylbutanol, 2-ethylhexanol, and the like.

[0168] The amino resin is preferably a melamine resin. As the melamine resin, for example, an alkyl-etherified melamine resin obtained by partially or completely etherifying a methylol group of a partially or completely methylolated melamine resin with the alcohol listed above can be used.

[0169] As the alkyl etherified melamine resin, for example, a methyl-etherified melamine resin obtained by partially or completely etherifying a methylol group of the partially or completely methylolated melamine resin with methyl alcohol; a butyl-etherified melamine resin obtained by partially or completely etherifying a methylol group of the partially or completely methylolated melamine resin with butyl alcohol; a methyl / butyl mix-etherified melamine resin obtained by partially or completely etherifying a methylol group of the partially or completely methylolated melamine resin with methyl alcohol and butyl alcohol; and the like can be suitably used.

[0170] The melamine resin has a weight-average molecular weight preferably in the range of 400 to 6,000, more preferably in the range of 500 to 5,000, and yet more preferably in the range of 500 to 4,000 from the viewpoint of uniformity of a coated surface to be formed, and the like.

[0171] Commercially available products can be used as the melamine resin. Examples of commercially available products include "Cymel 202", "Cymel 203", "Cymel 238", "Cymel 251", "Cymel 303", "Cymel 323", "Cymel 324", "Cymel 325", "Cymel 327", "Cymel 350", "Cymel 385", "Cymel 1156", "Cymel 1158", "Cymel 1116", "Cymel 1130" (all available from Allnex Japan Inc., "Cymel" is a registered trademark), "Uban 120", "Uban 20HS", "Uban 20SE60", "Uban 2021", "Uban 2028", and "Uban 28-60" (all available from Mitsui Chemicals, Inc., "Uban" is a registered trademark), and the like.

[0172] The above-mentioned melamine resins can be used alone or in combination with two or more types.

[0173] When the paint composition contains the above amino resin as the curing agent, the content thereof is preferably in the range of 5% by mass to 60% by mass, more preferably 15% by mass to 50% by mass, and still more preferably 25% by mass to 45% by mass relative to the total amount of resin solids in the paint composition from the viewpoint of uniformity of a coated surface to be formed, and the like.

[0174] The polyisocyanate compound is a compound having at least two isocyanate groups in one molecule, and examples thereof include an aliphatic polyisocyanate compound, an alicyclic polyisocyanate compound, an aromatic-aliphatic polyisocyanate compound, an aromatic polyisocyanate compound, a derivative of the above polyisocyanate compounds, and the like.

[0175] Examples of the aliphatic polyisocyanate compound include aliphatic diisocyanate compounds such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, methyl 2,6-diisocyanatohexanoate (trivial name: lysine diisocyanate), and the like; aliphatic triisocyanate compounds such as 2-isocyanatoethyl 2,6-diisocyanatohexanoate, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyl octane, 1,3,6-triisocyanatohexane, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyl octane, and the like.

[0176] Examples of alicyclic polyisocyanate compounds include alicyclic diisocyanate compounds such as 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (trivial name: isophorone diisocyanate), 4-methyl-1,3-cyclohexylene diisocyanate (trivial name: hydrogenated TDI), 2-methyl-1,3-cyclohexylene diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl) cyclohexane (trivial name: hydrogenated xylylene diisocyanate) or mixtures thereof, methylene bis(4,1-cyclohexanediyl) diisocyanate (trivial name: hydrogenated MDI), norbornane diisocyanate, and the like; alicyclic triisocyanate compounds such as 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo (2.2.1) heptane, 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo (2.2.1) heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo (2.2.1) heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo (2.2.1) heptane, 6-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo (2.2.1) heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo (2.2.1)-heptane, 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo (2.2.1) heptane, and the like.

[0177] Examples of the aromatic aliphatic polyisocyanate compounds include: aromatic aliphatic diisocyanate compounds such as methylene bis(4,1-phenylene) diisocyanate (trivial name: MDI), 1,3- or 1,4-xylylene diisocyanate or mixtures thereof, ω,ω´-diisocyanate-1,4-diethylbenzene, 1,3- or 1,4-bis (1-isocyanato-1-methylethyl) benzene (trivial name: tetramethylxylylene diisocyanate) or mixtures thereof; aromatic aliphatic triisocyanate compounds such as 1,3,5-triisocyanatomethylbenzene and the like.

[0178] Examples of the aromatic polyisocyanate compound include aromatic diisocyanate compounds such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4´-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate (trivial name: 2,4-TDI) or 2,6-tolylene diisocyanate (trivial name: 2,6-TDI) or mixtures thereof, 4,4´-toluidine diisocyanate, 4,4´-diphenyl ether diisocyanate, and the like; aromatic triisocyanate compounds such as triphenylmethane-4,4´,4´´-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, and the like; and aromatic tetraisocyanate compounds such as 4,4´-diphenylmethane-2,2´,5,5´-tetraisocyanate, and the like.

[0179] Examples of the derivatives of the polyisocyanate compounds include dimers, trimers, biurets, allophanates, uretdiones, uretoimines, isocyanurates, oxadiazinetriones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like of the polyisocyanate compounds listed above.

[0180] The polyisocyanate compounds and their derivatives may be used alone or in combination or two or more types.

[0181] As the polyisocyanate compounds, it is preferable to use at least one selected from aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, and their derivatives, and it is more preferable to use aliphatic polyisocyanate compounds and / or their derivatives, from the viewpoint of uniformity of a coated surface to be formed, and the like.

[0182] As the aliphatic polyisocyanate compounds and / or their derivative, it is preferable to use an aliphatic diisocyanate compound and / or its isocyanurate body, and it is more preferable to use hexamethylene diisocyanate and / or its isocyanurate body.

[0183] The blocked polyisocyanate compound usable as the curing agent is a compound obtained by blocking the isocyanate group of the polyisocyanate compound described above with a blocking agent.

[0184] Examples of the blocking agent include: phenolic compounds such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, methyl hydroxybenzoate, and the like; lactams such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, β-propiolactam, and the like; aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol, and the like; ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, methoxymethanol, and the like; alcohols such as benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylolurea, methylolmelamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and the like; oximes such as formamide oxime, acetamide oxime, acetoxime, methylethylketoxime, diacetylmonoxime, benzophenone oxime, cyclohexane oxime, and the like; active methylenes such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone, and the like; mercaptans such as butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, ethylthiophenol, and the like; acid amides such as acetanilide, acetanisidide, acetotoluidide, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, benzamide, and the like; imides such as succinimide, phthalic acid imide, maleic acid imide, and the like; amines such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, butylphenylamine, and the like; imidazoles such as imidazole, 2-ethylimidazole, and the like; ureas such as urea, thiourea, ethyleneurea, ethylenethiourea, diphenylurea, and the like; carbamic esters such as phenyl N-phenylcarbamate, and the like; imines such as ethyleneimine, propyleneimine, and the like; sulfites such as sodium bisulfite, potassium bisulfite and the like; azole compounds; and the like. Examples of the azole compound include pyrazole or pyrazole derivatives such as pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, 3-methyl-5 phenylpyrazole, and the like; imidazole or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole, and the like; and imidazoline derivatives such as 2-methylimidazoline, 2-phenylimidazoline, and the like.

[0185] Examples of preferred blocking agents among those described above include oxime-based blocking agents, active methylene-based blocking agents, and pyrazoles or pyrazole derivatives.

[0186] Blocking (reacting the blocking agent) may be performed by, as needed, adding a solvent. The solvent used in the blocking reaction is preferably a solvent that is not reactive with an isocyanate group, and examples of such solvents include ketones such as acetone, methyl ethyl ketone, and the like, esters such as ethyl acetate and the like, and N-methyl-2 pyrrolidone (NMP).

[0187] When the paint composition contains the blocked polyisocyanate compound as a curing agent, the content of the blocked polyisocyanate compound is preferably in the range of 5% by mass to 60% by mass, more preferably in the range of 15% by mass to 50% by mass, and more preferably in the range of 25% by mass to 45% by mass relative to the total amount of resin solids in the paint composition from the viewpoint of uniformity of a coated surface to be formed, and the like.

[0188] The curing agents can be used alone or in combination of 2 or more types.

[0189] <<<<Oligomer>>>> The paint composition can contain an oligomer.

[0190] The weight average molecular weight of the oligomer is preferably in the range of 200 to 2,000, more preferably in the range of 300 to 1,600, and more preferably in the range of 350 to 1,500 from the viewpoint of uniformity of a coated surface to be formed, and the like.

[0191] Specific examples of the oligomer include polyoxyalkylene glycols such as polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, etherified products thereof, and the like.

[0192] Commercially available products may be used as the oligomer. Examples of commercially available products include "Sannix GP250", "Sannix GP400", "Sannix GP600", and "Sannix GP100" (all available from Sanyo Chemical Industries, Ltd., polyoxypropylene glyceryl ether, "Sannix" is a registered trademark), "Sannix PP200", " Sannix PP400", and "Sannix PP1000" (all available from Sanyo Chemical Industries, Ltd., polyoxypropylene glycol), and "PTMG250", "PTMG650", "PTMG1000", and "PTMG2000" (all available from Mitsubishi Chemical Group Corporation, polyoxytetramethylene glycol).

[0193] When the paint composition of the present invention contains the oligomer, the content of the oligomer is preferably in the range of 0.5% by mass to 30% by mass, more preferably in the range of 1.0% by mass to 20% by mass, and more preferably in the range of 2.0% by mass to 10% by mass relative to the total amount of resin solids in the paint composition from the viewpoint of uniformity of a coated surface to be formed, and the like.

[0194] <<<<Surfactant>>>> As the surfactant, any of silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, anionic surfactants, and cationic surfactants can be used.

[0195] The silicone-based surfactant is not particularly limited and can be appropriately selected according to the purpose. Among silicone-based surfactants, those that do not decompose even at high pH are preferable, and examples include side-chain-modified polydimethylsiloxane, both-end-modified polydimethylsiloxane, one-end-modified polydimethylsiloxane, side-chain-both-end-modified polydimethylsiloxane, and the like. Those having polyoxyethylene groups and polyoxyethylene-polyoxypropylene groups as the modifying groups are particularly preferable because they exhibit good properties as water-based surfactants.

[0196] A suitably synthesized surfactant or a commercially available surfactant may be used as the surfactant. Commercially available surfactants are available from, for example, Byk-Chemie GmbH, Shin-Etsu Chemical Co., Ltd., Dow Corning Toray Silicone Co., Ltd., Nihon Emulsion Co., Ltd., Kyoeisha Chemical Co., Ltd., and the like.

[0197] The above-mentioned polyether-modified silicone-based surfactants are not particularly limited and can be suitably selected according to the purpose. Examples thereof include those represented by the following general formulae (1) and (2) in which a polyalkylene oxide structure is introduced into the side chain of the Si moiety of dimethylpolysiloxane. (In the general formula (1), m, n, a, and b represent integers. In general formula (2), R and R´ represent an alkyl group or an alkylene group.)

[0198] As the polyether-modified silicone-based surfactants, commercially available products can be used, and examples include KF-618, KF-642, and KF-643 (all available from Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602 and SS-1906EX (both available from Nihon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, and FZ-2164 (available from Dow Corning Toray Silicone Co., Ltd.), BYK-33 and BYK-387 (both available from Byk-Chemie GmbH, "BYK" is a registered trademark), TSF4440, TSF4452, and TSF4453 (available from Toshiba Silicone Co., Ltd.), and the like.

[0199] As the fluorine-based surfactants, for example, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compound, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain are particularly preferred because of their low foaming properties.

[0200] Examples of the perfluoroalkyl sulfonic acid compounds include perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, and the like. Examples of the perfluoroalkyl carboxylic acid compounds include perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate.

[0201] Examples of the polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in the side chain include a sulfate ester salt of a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in the side chain, a salt of a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in the side chain, and the like.

[0202] Examples of counterions of the salts of these fluorine-based surfactants include Li, Na, K, NH4, NH3CH2CH2OH, NH2(CH2CH2OH)2, NH(CH2CH2OH)3, and the like.

[0203] As the fluorine-based surfactants, a compound in which the number of carbon atoms replaced with fluorine is 2 to 16 is preferable, and a compound in which the number of carbon atoms replaced with fluorine is 4 to 16 is more preferable.

[0204] Examples of the fluorine-based surfactants include a perfluoroalkyl phosphate ester compound, a perfluoroalkyl ethylene oxide adduct, and a polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in the side chain.

[0205] Among these, a polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in the side chain is preferable because of its low foaming property, and fluorine-based surfactants represented by general formulae (3) and (4) below are particularly preferable. In the compound represented by the above general formula (3), m is preferably an integer of 0 to 10 and n is preferably an integer of 0 to 40 in order to impart water solubility. In the compound represented by the above general formula (4), Y is H, or CnF2n+1where n is an integer of 1 to 6, or CH2CH (OH)CH2-CnF2n+1where n is an integer of 4 to 6, or CpH2p+1where p is an integer of 1 to 19, and "a" is an integer of 4 to 14.

[0206] Commercially available products may be used as the fluorine-based surfactant. Examples of such commercially available products include Surflon S-111, S-112, S-113, S-121, S-131, S-132, S-141, and S-145 (all available from AGC Seimi Chemical Co., Ltd., "Surflon" is a registered trademark); Fluorad FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, and FC-431 (available from Sumitomo 3M Limited); Megafac F-470, F-1405, and F-474 (all available from DIC Corporation, "Megafac" is a registered trademark); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, and UR (all available from DuPont Kabushiki Kaisha); FT-110, FT-250, FT-251, FT-400S, FT-150, and FT-400SW (all available from Neos Co., Ltd.), Polyfox PF-136A, PF-156A, PF-151N, PF-154, and PF-159 (all available from Omnova Solution Inc.), and Unidyne DSN-403N (available from Daikin Industries, Ltd., "Unidyne" is a registered trademark). Among these, FS-300 available from DuPont Kabushiki Kaisha, FT-110, FT-250, FT-251, FT-400S, FT-150, and FT-400SW available from Neos Co., Ltd., Polyfox PF-151N available from Omnova Solutions Inc., and Unidyne DSN-403N available from Daikin Industries Ltd. are particularly preferable from the viewpoint of good print qualities, and particularly because color developability, permeability to paper, wettability, and level dyeing property are remarkably improved.

[0207] Examples of the amphoteric surfactant include laurylaminopropionate, lauryldimethylbetaine, stearyldimethylbetaine, lauryldihydroxyethylbetaine, and the like.

[0208] Examples of the nonionic surfactant include polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkylamine, polyoxyethylene alkylamide, polyoxyethylene propylene block polymer, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, ethylene oxide adduct of acetylene alcohol, and the like.

[0209] Examples of the anionic surfactant include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, laurate, salt of polyoxyethylene alkyl ether sulfate, and the like.

[0210] Examples of the cationic surfactant include alkyltrimethylammonium chloride, polyoxyethylene alkylmethyl ammonium chloride, mono or dialkylmethylated ammonium chloride, alkylpentamethylpropylene diamine chloride, alkyldimethylbenzalkonium chloride, benzethonium chloride, and the like.

[0211] One of these surfactants may be used alone or two or more of them may be used in combination.

[0212] The content of the surfactant in the paint composition is not particularly limited and can be suitably selected according to the purpose, and from the viewpoint of wettability, discharge stability, uniformity of a coated surface, and the like, it is preferably 0.001% by mass or greater and 5% by mass or less, and more preferably 0.05% by mass or greater and 5% by mass or less relative to the total amount of solids in the paint composition.

[0213] <<<<Defoaming Agent>>>> The defoaming agent is not particularly limited and examples include a silicone-based defoaming agent, a polyether-based defoaming agent, a fatty acid ester-based defoaming agent, and the like. One of these may be used alone or two or more of these may be used in combination. Among these, a silicone defoaming agent is preferable from the viewpoint of excellent foam breaking effect.

[0214] <<<<Antiseptic Fungicide>>>> The antiseptic fungicide is not particularly limited, and examples include 1,2 benzisothiazolin-3-one and the like.

[0215] <<<<Antirust Agent>>>> The antirust agent is not particularly limited, and examples include acidic sulfite, sodium thiosulfate, and the like.

[0216] <<<<pH Adjusting Agent>>>> The pH adjusting agent is not particularly limited as long as pH can be adjusted to 7 or greater, and examples include amines such as diethanolamine, triethanolamine, and the like.

[0217] <<<<Viscosity Adjusting Agent>>>> The paint composition may include a viscosity adjusting agent.

[0218] Specific examples of the viscosity adjusting agent include: silica-based powder; mineral-based viscosity adjusting agents; barium sulfate powder; polyamide-based viscosity adjusting agents such as fatty acid amide, polyamide, acrylamide, long-chain polyaminoamide, aminoamide, salts thereof (e.g., phosphate), and the like; aminoplast-based viscosity adjusting agents such as hydrophobically-modified ethoxylate aminoplast and the like: organic resin particle viscosity adjusting agents; diurea-based viscosity adjusting agents; urethane-associated viscosity adjusting agent; polyacrylic acid-based viscosity adjusting agents (also referred to as alkali swelling-type viscosity adjusting agents); cellulose-based viscosity adjusting agents; and the like.

[0219] The viscosity adjusting agent is preferably a mineral-based viscosity adjusting agent, a polyacrylic acid-based viscosity adjusting agent, a cellulose-based viscosity adjusting agent, or a urethane-associated viscosity adjusting agent from the viewpoint of liquid dripping resistance and the like. It is more preferable that the viscosity adjusting agent include at least one selected from cellulose-based viscosity adjusting agents, polyacrylic acid-based viscosity adjusting agents, and urethane-associated viscosity adjusting agents, and the urethane-associated viscosity adjusting agent is particularly preferable. These viscosity adjusting agents may be used alone or in combination with two or more types.

[0220] Examples of the mineral-based viscosity adjusting agent include inorganic layered compound-based viscosity adjusting agents such as swellable layered silicates having a 2:1 crystal structure. Specific examples include: natural or synthetic smectite group clay minerals such as montmorillonite, saponite, hectorite, stevensite, beidellite, nontronite, bentonite, and laponite, and the like; swellable mica group clay minerals such as Na-type tetrasilicic fluorine mica, Li-type tetrasilicic fluorine mica, Na salt-type fluoroteniolite, Li-type fluoroteniolite, and the like; Vermiculite; replaced products or derivatives thereof; and mixtures thereof.

[0221] Examples of the urethane-associated viscosity adjusting agent include polyether-polyol-based urethane prepolymers, urethane-modified polyether-type viscosity adjusting agents, and the like.

[0222] Examples of commercially available products of the urethane-associated viscosity adjusting agent include: the Adekanol series such as "Adekanol UH-814N", "UH-752", "UH-756VF", "UH-420", "UH-462" and the like (all available from ADEKA Corporation, "Adekanol" is a registered trademark); "SN Thickener 621N" and "SN Thickener 623N" (both available from San Nopco Ltd.); "Rheolate 244" and "Rheolate 278 " (available from Elementis Japan KK.); and the like.

[0223] Examples of the polyacrylic acid-based viscosity adjusting agent include sodium polyacrylate, polyacrylic acid-(meth)acrylic acid ester copolymer, and the like.

[0224] Examples of commercially-available products of the polyacrylic acid-based viscosity adjusting agents include: "Primal ASE-60", "Primal TT615", and "Primal RM5" (all available from Dow Chemical Company, "Primal" is a registered trademark); "SN Thickener 613", "SN Thickener 618", "SN Thickener 630", "SN Thickener 634", and "SN Thickener 636" (available from San Nopco Ltd.); and the like.

[0225] The acid value of the solid of the polyacrylic acid-based viscosity adjusting agent is preferably 30 mgKOH / g or greater and 300 mgKOH / g or less, and more preferably 80 mgKOH / g or greater and 280 mgKOH / g or less.

[0226] Examples of the cellulose-based viscosity adjusting agent include carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, cellulose nanofibers, and the like. Among them, cellulose nanofibers are preferable from the viewpoint of liquid dripping resistance and the like.

[0227] The cellulose nanofibers are sometimes referred to as cellulose nanofibrils, fibrillated cellulose, or nanocellulose crystals.

[0228] The number average fiber diameter of the cellulose nanofiber is preferably 2 nm or greater and 500 nm or less, more preferably 2 nm or greater and 250 nm or less, and yet preferably 2 nm or greater and 150 nm or less, and the number average fiber length is preferably 0.1 μm or greater and 20 μm or less, more preferably 0.1 μm or greater and 15 μm or less, and yet more preferably 0.1 μm or greater and 10 μm or less.

[0229] The number average fiber diameter and the number average fiber length are measured and calculated, for example, from a Transmission Electron Microscope (TEM)-observed image of a sample of the cellulose nanofiber diluted with water, subjected to dispersion treatment, and cast over a hydrophilized carbon film-coated grid.

[0230] The cellulose nanofiber may be obtained by defibrating a cellulose raw material and stabilizing it in water. Here, the cellulosic raw material means various forms of materials mainly composed of cellulose, and specific examples include: pulp (wood pulp, pulp derived from herbaceous plants such as jute, manila hemp, kenaf, and the like); natural cellulose such as cellulose produced by microorganisms; regenerated cellulose obtained by dissolving cellulose in some solvent such as a copper ammonia solution, morpholine derivative, or the like, and then spinning the resulting product; fine cellulose obtained by depolymerizing cellulose by subjecting the cellulosic raw material listed above to hydrolysis, alkaline hydrolysis, enzymatic decomposition, blasting treatment, mechanical treatment such as vibration ball milling and the like; and the like.

[0231] Anion-modified cellulose nanofibers may also be used as the cellulose nanofibers. Examples of the anion-modified cellulose nanofibers include carboxylated cellulose nanofibers, carboxylmethylated cellulose nanofibers, sulfonic acid group-containing cellulose nanofibers, phosphoric acid group-containing cellulose nanofibers, and the like. The anion-modified cellulose nanofiber can be obtained, for example, by introducing a functional group such as a carboxyl group, a carboxylmethyl group, or the like into a cellulose raw material by a publicly-known method, washing the obtained modified cellulose to prepare a dispersion liquid of the modified cellulose, and then defibrating the dispersion liquid. The carboxylated cellulose is also referred to as oxidized cellulose.

[0232] The oxidized cellulose can be obtained, for example, by oxidizing the cellulose raw material in water with an oxidizing agent in the presence of a compound selected from the group consisting of an N-oxyl compound, bromides, and iodides or mixtures thereof.

[0233] Examples of commercially-available products of the cellulose nanofiber include Rheocrysta (registered trademark) available from DKS Co., Ltd., Auro Visco (registered trademark) available from Oji Holdings Corporation, and the like.

[0234] <<<Surface Adjusting Agent>>> The paint composition of the present invention may contain a surface adjusting agent.

[0235] Examples of the surface adjusting agent include surface adjusting agents such as a silicone-based surface adjusting agent, an acrylic-based surface adjusting agent, a vinyl-based surface adjusting agent, a fluorine-based surface adjusting agent, and the like. Among these, it is preferable that the surface adjusting agent includes a silicone-based surface adjusting agent from the viewpoint that wettability over a foundation when the paint composition is an undercoat paint composition, improvement of finish quality and coating film properties by adjustment of the leveling property of the paint composition, and an antifoaming or defoaming effect are expected. The surface adjusting agents can be used alone or in combination of two or more types.

[0236] Examples of the silicone-based surface adjusting agent include organopolysiloxane such as dimethyl polysiloxane, modified silicones obtained by modifying organopolysiloxane, and the like. Specific examples of modified silicones include alkyl-modified polysiloxane, phenyl-modified polysiloxane, polyether-modified polysiloxane, and the like. These can be used alone or in combination of two or more types.

[0237] Specific examples include: dimethylpolysiloxane; methylphenylpolysiloxane; polyether-modified siloxane such as polyether-modified polydimethylsiloxane, polyether-modified dimethylpolysiloxane, and the like; polyester-modified dimethylpolysiloxane, polyester-modified polyalkylsiloxane of polyester-modified polydimethylsiloxane, and the like; polymethylalkylsiloxane; aralkyl-modified polymethylalkylsiloxane; polyether-modified acrylic group-containing polydimethylsiloxane; polyester-modified acrylic group-containing polydimethylsiloxane; and the like. Among them, polyether-modified siloxane is preferable.

[0238] The weight average molecular weight of the polyether-modified siloxane is preferably in the range of 400 to 3,000, particularly in the range of 500 to 2,000. The weight average molecular weight is a value measured in terms of polystyrene by Gel Permeation Chromatography (GPC).

[0239] Commercially-available products can be used as the polyether-modified siloxane, and specific examples of commercial products include BYK-345, BYK-347, BYK-348, BYK-349, BYK-UV3500, BYK-3510, BYK-3530, and BYK-3570 (all available from Byk-Chemie Japan K.K.), TEGO Wet 245, TEGO Wet 250, TEGO Wet 260, TEGO Wet 270, and TEGO Wet 280 (all available from Evonik Degussa Corporation, "TEGO" is a registered trademark), and the like.

[0240] Examples of surface adjusting agents other than those listed above include silicone-based, acetylene-based, acrylic-based, fluorine-based, and vinyl-based surface adjusting agents and the like, other than the polyether-modified siloxane.

[0241] The content of the silicone-based surface adjusting agent in a case where the paint composition contains the silicone-based surface adjusting agent is preferably in the range of 0.01% by mass to 10% by mass, preferably 0.3% by mass to 2.0% by mass relative to the total amount of solids in the paint composition from the viewpoint of improvement of wettability and finish property of the paint composition.

[0242] <<<<Ultraviolet Absorber>>>> Examples of the ultraviolet absorber include benzotriazole-based absorbers, triazine-based absorbers, salicylic acid derivative-based absorbers, benzophenone-based absorbers, and the like.

[0243] <<<<Light Stabilizer>>>> Examples of the light stabilizer include hindered amine-based light stabilizers.

[0244] <<<Water>>> The water may be ion-exchanged water or the like. The content of the water in the paint composition is not particularly limited and can be suitably selected according to the purpose, and is preferably 10% by mass or greater and 90% by mass or less, and more preferably 20% by mass or greater and 60% by mass or less from the viewpoint of liquid dripping resistance, uniformity of a coated surface to be formed, and the like.

[0245] <<Solid Concentration of Paint composition>> The solid concentration in the paint composition is preferably 10% by mass or more, more preferably 12% by mass or more, and more preferably 15% by mass or more from the viewpoint of discharge stability, uniformity of a coated surface, liquid dripping, and the like. From the viewpoint of uniformity of a coated surface, discharge stability, and the like, the solid concentration in the paint composition is preferably 60% by mass or less, more preferably 55% by mass or less, and more preferably 40% by mass or less.

[0246] <<<Physical Properties of Paint composition>>> The paint composition has the following physical properties.

[0247] <<<<Storage Modulus>>>> The storage modulus of the paint composition is 0.1 Pa or greater and 85 Pa or less, preferably 0.3 Pa or greater and 60 Pa or less, and more preferably 1.5 Pa or greater and 40 Pa or less.

[0248] In the present specification, the storage modulus is a storage modulus obtained by measurement using a rheometer.

[0249] <<<<Loss Modulus>>>> The loss modulus of the paint composition is 1.0 Pa or greater and 30 Pa or less, preferably 2.0 Pa or greater and 25 Pa or less, and more preferably 3.0 Pa or greater and 20 Pa or less.

[0250] In the present specification, the loss modulus is a loss modulus obtained by measurement using a rheometer, as the storage modulus.

[0251] <<<<Static Surface Tension>>>> The static surface tension of the paint composition is a static surface tension obtained by measurement using a contact angle meter.

[0252] <<<<Loss Tangent>>>> The loss tangent of the paint composition is a loss tangent obtained by measurement using a rheometer, as the storage modulus.

[0253] <<<<A×B>>>> The paint composition satisfies the following expression (1), where A represents static surface tension and B represents loss tangent. A×B≦110---(1) It is preferable that the paint composition satisfies A×B≦95, and more preferably, A×B≦80.

[0254] <<<<Shear Viscosity>>>> The shear viscosity of the paint composition means a viscosity at a shear rate of 10 (1 / s) and a viscosity at a shear rate of 10,000 (1 / s).

[0255] <<<<C / D>>>> The paint composition satisfies the following expression (2), where C represents the viscosity at a shear rate of 10 (1 / s) and D represents the viscosity at a shear rate of 10,000 (1 / s). 7≦C / D≦155---(2) It is preferable that the pain composition satisfies 8≦C / D≦145, and more preferably 9≦C / D≦135.

[0256] <<<Other Physical Properties>>> Other physical properties of the paint composition are not particularly limited, and can be appropriately selected according to the purpose. For example, the pH of the paint composition is preferably 6 to 12 and more preferably 7 to 11 from the viewpoint of corrosion prevention of any metal member that may be in contact with the paint composition, stability of the paint composition, and the like.

[0257] In the coating apparatus according to the present embodiment, as described above, a paint composition that has a storage modulus of 0.1 Pa or greater and 85 Pa or less, a loss modulus of 1.0 Pa or greater and 30 Pa or less, and satisfies a relationship of A×B≦110 between the static surface tension A and the loss tangent B is used. Thus, by setting the ratio between the surface tension and the loss tangent of the paint composition to a prescribed range and maintaining the fluidity of the liquid, it is possible to form a coated surface having a high uniformity by droplet coating.

[0258] Furthermore, as described above, the paint composition, which has liquid properties even though the viscosity thereof is high, can easily move over the surface coated with the composition depending on the ratio between the surface tension and the loss tangent. Therefore, the composition can form a highly uniform coated surface even on a metal and a surface of a metal subjected to surface treatment.

[0259] In the coating apparatus according to the present embodiment, as described above, the paint composition satisfies the relationship of 7≦C / D≦155 where C represents the viscosity at a shear rate of 10 (1 / s) and D represents the viscosity at a shear rate of 10,000 (1 / s). Thus, it is possible to avoid generation of a scattering mist of the paint composition when the paint composition is discharged, and to avoid liquid dripping at the same time.

[0260] The coating apparatus according to the present embodiment has the discharge head 1 as described above. The discharge head 1 includes the nozzle 111 for discharging the paint composition, the valve element 113 for opening and closing the nozzle 111, and the piezoelectric element 114 for driving the valve element 113. The valve element 113 is driven in the direction of opening the nozzle 111 when a voltage is applied to the piezoelectric element 114. Thus, a coated surface having high uniformity can be reliably formed on a vertical surface.

[0261] Further, in the coating apparatus of the present embodiment, when the distance between the nozzle 111 and the coating object is 5 mm or more, it is possible to reliably avoid generation of a scattering mist of the paint composition when the paint composition is discharged, and to reliably avoid liquid dripping at the same time.

[0262] Hereinafter, the present invention will be described more specifically by way of Examples, but the present invention should not be construed as being limited to these Examples. In the following description, "part" and "%" are on a mass basis, unless otherwise particularly specified. Various tests and evaluations are performed according to the following methods.

[0263] <Production of Hydroxyl Group-Containing Acrylic Resin> <Production Example 1> A hundred parts of deionized water and 0.5 parts of polyoxyethylene alkyl ether sulfate ammonium salt (obtained from DKS Co., Ltd., Aqualon KH-10, 97% active ingredient) were added into a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a dropping device, and stirred and mixed in a stream of nitrogen, and raised to a temperature of 80℃. Next, 10.3 parts of ammonium persulfate aqueous solutions of 1% and 3% of the total amount of the following monomer emulsion 1 were introduced into the reaction vessel, and the materials were maintained at 80℃ for 15 minutes. Then, the remaining monomer emulsion 1 was dropped into the reaction vessel in 3 hours, and the materials were aged for 1 hour after the dropping was completed. Then, the following monomer emulsion 2 was dropped in 2 hours, and the materials were aged for 1 hour, then cooled to 30℃ while 42 parts of a 5.0% dimethylethanolamine aqueous solution was gradually added to the reaction vessel, and then drained while being filtered through a 100-mesh nylon cloth, to obtain a hydroxyl group-containing acrylic resin I having a core / shell structure having an average particle diameter of 100 nm, an acid value of 32 mgKOH / g, a hydroxyl value of 43 mgKOH / g, and an amount of solids of 30% by mass. The average particle diameter was measured in a state of being diluted with deionized water at 20℃ using a submicron particle size distribution measuring apparatus (obtained from Beckman Coulter, Inc., COULTER N4 type, "COULTER" is a registered trademark).

[0264] (Monomer Emulsion 1) The monomer emulsion 1 was obtained by mixing and stirring 70 parts of deionized water, 1 part of polyoxyethylene alkyl ether sulfate ammonium salt (obtained from DKS Co., Ltd., Aqualon KH-10, 97% active ingredient), 3 parts of methylenebisacrylamide, 4 parts of styrene, 13 parts of methyl methacrylate, 30 parts of ethyl acrylate, and 20 parts of n-butyl acrylate.

[0265] (Monomer Emulsion 2) The monomer emulsion 2 was obtained by mixing and stirring 10 parts of deionized water, 1 part of polyoxyethylene alkyl ether sulfate ammonium salt (obtained from DKS Co., Ltd., Aqualon KH-10, 97% active ingredient), 0.1 parts of ammonium persulfate, 3 parts of styrene, 6 parts of methyl methacrylate, 2 parts of ethyl acrylate, 4 parts of n-butyl acrylate, 10 parts of hydroxyethyl acrylate, and 5 parts of methacrylic acid.

[0266] <Production Example 2> A hundred parts of deionized water and 0.5 parts of polyoxyethylene alkyl ether sulfate ammonium salt (obtained from DKS Co., Ltd., Aqualon KH-10, 97% active ingredient) were added into a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a dropping device, stirred and mixed in a stream of nitrogen, and raised to a temperature of 80℃. Next, 10.3 parts of ammonium persulfate aqueous solutions of 1% and 3% of the total amount of the following monomer emulsion 3 were introduced into the reaction vessel and maintained at 80℃ for 15 minutes. Then, the remaining monomer emulsion 3 was dropped into the reaction vessel in 3 hours, and the materials were aged for 1 hour after the dropping was completed. Then, the following monomer emulsion 4 was dropped in 2 hours, and the materials were aged for 1 hour, cooled to 30℃ while 42 parts of a 5.0% dimethylethanolamine aqueous solution was gradually added to the reaction vessel, and drained while filtering through a 100-mesh nylon cloth, to obtain a hydroxyl group-containing acrylic resin II having a core / shell structure having an average particle diameter of 100 nm, an acid value of 19 mgKOH / g, a hydroxyl value of 22 mgKOH / g, and an amount of solids of 30% by mass. The average particle diameter was measured in a state of being diluted with deionized water at 20℃ using a submicron particle size distribution measuring apparatus (obtained from Beckman Coulter Inc., COULTER N4 type).

[0267] (Monomer Emulsion 3) The monomer emulsion 3 was obtained by mixing and stirring 70 parts of deionized water, 1 part of polyoxyethylene alkyl ether sulfate ammonium salt (obtained from DKS Co., Ltd., Aqualon KH-10, 97% active ingredient), 3 parts of acrylamide, 10 parts of styrene, 20 parts of methyl methacrylate, and 27 parts of n-butyl acrylate.

[0268] (Monomer Emulsion 4) The monomer emulsion 4 was obtained by mixing and stirring 10 parts of deionized water, 1 part of polyoxyethylene alkyl ether sulfate ammonium salt (obtained from DKS Co., Ltd., Aqualon KH-10, 97% active ingredient), 0.1 parts of ammonium persulfate, 10 parts of methyl methacrylate, 10 parts of ethyl acrylate, 12 parts of n-butyl acrylate, 5 parts of hydroxyethyl acrylate, and 3 parts of methacrylic acid.

[0269] <Production Example 3> Thirty five parts of propylene glycol monomethyl ether was added into a reaction vessel equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen introducing tube, and a dropping device and raised to a temperature of 85℃. Then, a mixture of 30 parts of methyl methacrylate, 20 parts of 2-ethylhexyl acrylate, 29 parts of n-butyl acrylate, 15 parts of 2-hydroxyethyl acrylate, 6 parts of acrylic acid, 15 parts of propylene glycol monomethyl ether, and 2.3 parts of 2,2´-azobis(2,4-dimethylvaleronitrile) was dropped in 4 hours, and the materials were aged for 1 hour after the dropping was completed. Then, a mixture of 10 parts of propylene glycol monomethyl ether and 1 part of 2,2´-azobis(2,4-dimethylvaleronitrile) was dropped in 1 hour, and the materials were aged for 1 hour after the dropping was completed. Further, 7.4 parts of diethanolamine and 13 parts of propylene glycol monomethyl ether were added, to obtain a hydroxyl group-containing acrylic resin III solution having an amount of solids of 55%. The obtained hydroxyl group-containing acrylic resin III solution had an acid value of 47 mgKOH / g, a hydroxyl value of 72 mgKOH / g, and a weight average molecular weight of 58,000.

[0270] <Production Example 4> Eighty two parts of deionized water and 1.0 part of α-sulfo-ω-(1-(alkoxy)methyl-2-(2-propenyloxy)ethoxy)-poly(oxy-1,2-ethanediyl) ammonium salt (obtained from Adeka Corporation, Adekaria Soap SR-1025, 25% active ingredient) were added into a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a dropping device, stirred and mixed in a stream of nitrogen, and raised to a temperature of 75℃. Next, 10 parts of an ammonium persulfate aqueous solutions of 3% and 0.5% of the total amount of the following monomer emulsion 5 were introduced into the reaction vessel, and the materials were maintained at 75℃ for 2 hours. Then, the remaining monomer and an initiator emulsion were dropped into the reaction vessel in 5 hours, and the materials were aged for 6 hours after the dropping was completed. Then, the materials were cooled to 30℃, and adjusted to an amount of solids of 40% and pH of 6.8, using a 5.0% dimethylethanolamine aqueous solution and deionized water. Next, the materials were drained while being filtered through a 200-mesh nylon cloth, to obtain a hydroxyl group-containing acrylic resin IV having an average particle diameter of 140 nm, an acid value of 11 mgKOH / g, a hydroxyl value of 24 mgKOH / g, a weight average molecular weight of 2,900,000, and an amount of solids of 40%. The average particle diameter was measured in a state of being diluted with deionized water at 20℃ using a submicron particle size distribution measuring apparatus (obtained from Beckman Coulter Inc., COULTER N4 type).

[0271] (Monomer Emulsion 5) The monomer emulsion 5 was obtained by mixing and stirring 55 parts of deionized water, 4 parts of sodium polyoxyethylene alkyl ether sulfate (obtained from Kao Corporation, Latemul E-118B, 26% active ingredient, "Latemul" is a registered trademark), 10 parts of styrene, 53.5 parts of methyl methacrylate, 30 parts of n-butyl acrylate, 5 parts of 2-hydroxyethyl acrylate, 1.5 parts of acrylic acid, and 0.2 parts of 2,2´-azobis[2-(2-imidazolin-2-yl)propane].

[0272] <Production of Hydroxyl Group-Containing Polyester Resin> <Production Example 5> Two hundred and thirty six parts of 1,6-hexanediol, 308 parts of hexahydrophthalic anhydride, and 490 parts of CARDURA E10P were added into a reactor equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a water separator, and reacted at 100℃ to 230℃ for 3 hours. Then, 230 parts of trimellitic anhydride was further added, and the materials were allowed to undergo a condensation reaction 180℃, and diluted with propylene glycol monomethyl ether, to obtain a hydroxyl group-containing polyester resin I solution having an amount of solids of 70%. The obtained hydroxyl group-containing polyester resin I had an acid value of 50 mgKOH / g, a hydroxy value of 69 mgKOH / g, and a number average molecular weight of 1,900.

[0273] <Production Example 6> A hundred and thirteen parts of trimethylolpropane, 131 parts of neopentyl glycol, 80 parts of 1,2-cyclohexanedicarboxylic anhydride, 93 parts of isophthalic acid, and 91 parts of adipic acid were added into a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a water separator, raised to a temperature of 160℃ to 230℃ in 3 hours, and then allowed to undergo a condensation reaction at 230℃ for 4 hours. Then, 33.5 parts of trimellitic anhydride was added, and the materials were reacted at 170℃ for 30 minutes, and then diluted with propylene glycol monomethyl ether, to obtain a hydroxyl group-containing polyester resin II solution having an amount of solids of 70%. The obtained hydroxyl group-containing polyester resin II had an acid value of 40 mgKOH / g, a hydroxyl value of 161 mgKOH / g, and a number average molecular weight of 1,300.

[0274] <Production of Hydroxyl Group-Containing Acrylic Urethane Complex Resin> <Production Example 7> Twenty four point three parts of 1,6-hexanediol-based polycarbonate diol (obtained from UBE Corporation, ETERNACOLL UH-100, having a molecular weight of approximately 1,000, "ETERNACOLL" is a registered trademark), 35 parts of 2-ethylhexyl acrylate, 0.008 parts of butylhydroxytoluene, and 0.03 parts of dibutyl tin laurate were added into a reaction vessel equipped with a thermometer, a thermostat, a stirrer, and a reflux condenser, and then raised to a temperature of 90℃. Then, 5.7 parts of hydrogenated MDI was added dropwise in 30 minutes. Then, while being maintained at 90℃, the materials were reacted until the NCO value became 1 mg / g or less. To this reaction product, 2 parts of n-butyl acrylate and 3 parts of allyl methacrylate were added, to obtain a hydroxyl group-containing polyurethane resin diluted with an acrylic monomer. The urethane resin component of the obtained polyurethane resin had a hydroxyl value of 10 mgKOH / g and a weight average molecular weight of 30,000. Then, the components specified below were put into a glass beaker and stirred in a disper at 2,000 rpm for 15 minutes to produce a pre-emulsified liquid, and the pre-emulsified liquid was subjected to a high-pressure treatment at 100 MPa in a high-pressure emulsification device, to obtain a polyurethane-containing acrylic monomer emulsion in which the dispersed particles had an average particle diameter of 290 nm.

[0275] <Composition of Polyurethane-Containing Acrylic Monomer Emulsion> -70 parts of the hydroxyl group-containing polyurethane resin diluted with the acrylic monomer -4.7 parts of an anionic emulsifier having a polyoxyethylene chain (obtained from Nippon Nyukazai Co., Ltd., NEWCOL 707SF, having a solid concentration of 30% by mass, "NEWCOL" is a registered trademark) -65.3 parts of deionized water

[0276] A hundred and forty parts of the polyurethane-containing acrylic monomer emulsion 1 was removed into a flask, diluted with 42.5 parts of deionized water, and raised to a temperature of 70℃ while being stirred. Then, an initiator solution obtained by dissolving 0.2 parts of a polymerization initiator for emulsion polymerization (obtained from Wako Pure Chemical Industries, Ltd., VA-057) in 10 parts of deionized water was added dropwise into the flask in 30 minutes, and the materials were stirred for 2 hours while being maintained at the temperature. Then, a product obtained by dissolving a monomer emulsion 6 having the composition specified below and 0.15 parts of "VA-057" in 7.5 parts of deionized water was added dropwise in 1.5 hours, and the materials were stirred for 1 hour while being maintained at the temperature. Then, an initiator solution obtained by dissolving 0.1 parts of "VA-057" in 5 parts of deionized water was added into the flask, and the materials were stirred for 2 hours while being maintained at the temperature, and then cooled, to obtain an aqueous dispersion of an acrylic urethane complex resin I.

[0277] (Monomer Emulsion 6) The monomer emulsion 6 was obtained by mixing and stirring 8 parts of 2-ethylhexyl acrylate, 3 parts of n-butyl acrylate, 14 parts of methyl methacrylate, 3.5 parts of 2-hydroxyethyl methacrylate, 0.5 parts of acrylic acid, 1 part of allyl methacrylate, 2.0 parts of an anionic emulsifier having a polyoxyethylene chain (obtained from Nippon Nyukazai Co., Ltd., NEWCOL 707SF, having a solid concentration of 30% by mass), and 18 parts of deionized water. The obtained aqueous dispersion of the acrylic urethane complex resin I had a mass concentration of solids of 40%, an average particle diameter of 210 nm, an acrylic resin component hydroxyl value of 21.6 mgKOH / g, and an acid value of 5.6 mgKOH / g. The average particle diameter was measured in a state of being diluted with deionized water at 20°C using a submicron particle size distribution measuring apparatus (obtained from Beckman Coulter Inc., "COULTER N4" type).

[0278] <Production of Viscosity Adjusting Agent> <Production Example 8> A hundred and twenty nine parts of deionized water and 0.8 parts of an anionic emulsifier having a polyoxyethylene chain (obtained from Nippon Nyukazai Co., Ltd., NEWCOL 707SF, having a solid concentration of 30% by mass) were added into a four-neck flask equipped with a stirrer, a thermometer, a reflux tube, and a nitrogen introduction tube, and after nitrogen purge, were maintained at 82℃ while being stirred. Into this, a mixture obtained by dissolving 5 parts of the following monomer emulsion 7 and 0.3 parts of ammonium persulfate in 3 parts of deionized water was added first, and then after 20 minutes, a product obtained by dissolving the remaining monomer emulsion 7 and 0.3 parts of ammonium persulfate in 3 parts of deionized water was added dropwise in 4 hours, to allow them to undergo emulsion polymerization. As a result, an emulsion of a viscosity adjusting agent I having an amount of solids of 30% was obtained. The average particle diameter of the viscosity adjusting agent I was 120 nm.

[0279] (Monomer Emulsion 7) The monomer emulsion 7 was obtained by stirring and emulsifying 100 parts of deionized water, 0.5 parts of an anionic emulsifier having a polyoxyethylene chain (obtained from Nippon Nyukazai Co., Ltd., NEWCOL 707SF, having a solid concentration of 30% by mass), 20 parts of styrene, 35 parts of methyl methacrylate, 39 parts of n-butyl acrylate, 5 parts of 1,6-hexanediol diacrylate, and 1 part of acrylic acid.

[0280] <Preparation of Coloring Material Dispersion Liquid> <Production Example 9> Eighteen point two parts of the hydroxyl group-containing acrylic resin III solution (having an amount of solids of 10 parts) obtained in Production Example 3, four parts of carbon black (obtained from Mitsubishi Chemical Group Corporation, carbon MA-100, having a solid concentration of 100% by mass), 5 parts of a barium sulfate pigment (obtained from Sakai Chemical Industry Co., Ltd., Barifine BF-20, having a solid concentration of 100% by mass), and 50 parts of deionized water were added into a container equipped with a stirrer, uniformly mixed to form a mixed solution, which was adjusted to pH of 7.5 by addition of 2-(dimethylamino)ethanol. Next, the pH-adjusted mixed solution was added into a wide-mouth glass bottle, glass beads having a diameter of approximately 1.3 mm were added as a dispersion medium, and the glass bottle was tightly sealed to be subjected to dispersion treatment in a paint shaker for 4 hours, to obtain a coloring material dispersion liquid (P-1).

[0281] <Production Examples 10 to 20> Coloring material dispersion liquids P-2 to P-12 were obtained in the same manner as in Production Example 9, except that the blend composition of Production Example 9 was changed as indicated in Table 1 below.

[0282] The values indicated in Table 1 denote an amount of solids.

[0283]

[0284] The components indicated in Table 1 are as follows. -"TITANIX JR-903": obtained from Tayca Corporation, titanium oxide, having a solid concentration of 100% by mass ("TITANIX" is a registered trademark) -"CHLORINATED COPPER CYANINE BLUE G-314": obtained from Sanyo Color Works, Ltd., a phthalocyanine blue pigment, having a solid concentration of 100% -"PERRIND MAROON179 229-6440": obtained from Sun Chemical Corporation, an organic perylene pigment, having a solid concentration of 100% -"YELLOW 2GLMA": obtained from Dominion Colour Corporation, a bismuth vanadate-based yellow pigment, having a solid concentration of 100% -"JR-806": obtained from Tayca Corporation, a rutile titanium dioxide, having a solid concentration of 100% -"BARIACE B-35": obtained from Sakai Chemical Industry Co., Ltd., a barium sulfate powder, having a solid concentration of 100% -"MICRO ACE S-3": obtained from Nippon Talc Co., Ltd., a talc powder, having a solid concentration of 100% -"STAPA IL Hydrolan 2153": obtained from Eckart Effect Pigments, an aluminum flake pigment, having a solid concentration of 65% -"XIRALLIC T60-10 SW Crystal Silver": obtained from Merck KGaA, a metal oxide-coated alumina flake pigment, having a solid concentration of 100% ("XIRALLIC" is a registered trademark) -"PALIOCROM ORANGE L2800": obtained from BASF GmbH, an iron oxide-coated scaly aluminum pigment, having a solid concentration of 65%

[0285] <Preparation of Paint Composition> <Example 1> In a stirring / mixing vessel, the coloring material dispersion liquid (P-1) obtained in Production Example 9 (77.2 parts, of which 19 parts was solid), the hydroxyl group-containing acrylic resin I having a core / shell structure obtained in Production Example 1 (33.3 parts, of which 10 parts was solid), the hydroxyl group-containing acrylic resin II having a core / shell structure obtained in Production Example 2 (66.7 parts, of which 20 parts was solid solid), the hydroxyl group-containing polyester resin I obtained in Production Example 5 (21.4 parts, of which 15 parts was solid), a urethane emulsion (obtained from Sanyo Chemical Industries, Ltd., U-Coat UX-8100, having a solid concentration of 35%, "U-Coat" is a registered trademark) (28.6 parts, of which 10 parts was solid), a polyether polyol (obtained from Sanyo Chemical Industries, Ltd., Sannix GP-1000, having a number average molecular weight of 1,000, and a solid concentration of 100%) (5 parts, of which 5 parts was solid), a methyl / butyl mix-etherified melamine resin (obtained from Allnex Japan Inc., Cymel 250, having a solid concentration of 70%) (42.9 parts, of which 30 parts was solid), a urethane-associated viscosity adjusting agent (obtained from ADEKA Corporation, Adekanol UH-756VF, having a solid concentration of 32%) (5.6 parts, of which 1.8 parts was solid), a polyacrylic acid-based thickener (obtained from Rohm & Haas Company, Primal ASE-60, having a solid concentration of 28%) (3.6 parts, of which 1.0 parts was solid), a silicone-based surface adjusting agent (obtained from Byk-Chemie GmbH, BYK348, having a solid concentration of 100%) (1 part, of which 1.0 part was solid), polyether phosphate (obtained from Kusumoto Chemicals, Ltd., Disparon AQ-330, having a solid concentration of 100%, "Disparon" is a registered trademark) (4.0 parts, of which 4.0 parts was solid), polyether-modified siloxane (obtained from Byk-Chemie Japan K.K., BYK015, having a solid concentration of 100%) (2.0 parts, of which 2.0 parts was solid), a benzotriazole-based ultraviolet absorber (obtained from BASF GmbH, TINUVIN 384-2, having a solid concentration of 95%, "TINUVIN" is a registered trademark) (1.1 parts, of which 1 part was solid), a light stabilizer (obtained from BASF GmbH, TINUVIN 123, having a solid concentration of 100%) (1.0 part, of which 1.0 part was solid), ethylene glycol monobutyl ether (7.5 parts), and n-butanol (7.5 parts) were uniformly mixed, and 2-(dimethylamino) ethanol and deionized water were added, to obtain a paint composition No. 1 having pH of 8.0 and a paint material solid concentration of 23.0%. The compositional proportions in the paint composition No. 1 are indicated in Table 2 below.

[0286] <Examples 2 to 31 and Comparative Examples 1 to 4> Paint compositions No. 2 to No. 35 were obtained in the same manner as in Example 1, except that the compositional proportions of Example 1 were changed as indicated in Table 2 to Table 5 below. The compositional compositions in the paint compositions No. 2 to No. 35 are indicated in Table 2 to Table 5 below.

[0287] The values indicated in Tables 2 to 5 denote an amount of solids.

[0288]

[0289]

[0290]

[0291] The components listed in Table 2 to Table 5 are as follows. -"CYMEL 303LF": obtained from Allnex Japan Inc., a melamine resin, having a solid concentration of 100% by mass -"BAYHYDUR VPLS2310": obtained from Sumika Covestro Urethane Co., Ltd., a blocked polyisocyanate compound, having a solid concentration of 38% by mass ("BAYHYDUR" is a registered trademark) -"RHEOCRYSTA I-2SX": obtained from DKS Co., Ltd., cellulose nanofiber, a viscosity adjusting agent, having a solid concentration of 2.0% by mass -"DISPARON AQ-600": obtained from Kusumoto Chemicals, Ltd., a polyamide amine salt, having a solid concentration of 20% by mass -"MEGAFAC F-444": obtained from DIC Corporation, a fluorine-based surface adjusting agent, having a solid concentration of 100% by mass

[0292] <Storage Modulus and Loss Modulus> The paint composition was left to stand still for one night, adjusted to a temperature of 23℃, and placed on a measuring table. After the plate was descended to be at a specified gap, trimming was performed, and storage modulus (Pa) and loss modulus (Pa) were measured using a rheometer under the following conditions. As the plate to be used with the rheometer, a cone plate having a diameter of 50 mm and an angle of 0.5° was used. Storage modulus and loss modulus at a stress of 0.1 Pa were measured based on the measurement data. The results are indicated in Tables 2 to 5.

[0293] <Measurement conditions> -Apparatus: Rheometer (obtained from Anton Paar GmbH, MCR302e) -Measurement: Dynamic viscoelasticity, stress-dependent control -Measurement range: at a stress from 0.1 Pa to 20 Pa (24 point data acquisition) -Measurement temperature: 23℃ -Measurement gap: 0.05 mm -Frequency: 0.5 Hz

[0294] <Loss tangent> The ratio (G'' / G') between storage modulus (G') and loss modulus (G'') was defined as loss tangent. The results are indicated in Tables 2 to 5.

[0295] <Static surface tension> The static surface tension (mJ / m2)of the paint composition was measured by the platinum ring method using a surface tensiometer under the following conditions. The results are indicated in Tables 2 to 5.

[0296] <Measurement conditions> -Apparatus: Surface tensiometer (obtained from EKO Instruments Co., Ltd., DCAT25) -Measurement: Du Nouy ring method -Measurement temperature: 23℃ -Measurement speed: 0.20 mm / s

[0297] <A×B> The value A×B was calculated, where A represents the static surface tension and B represents the loss tangent. The results are indicated in Tables 2 to 5.

[0298] <Shear viscosity> The paint composition was left to stand still for one night, adjusted to a temperature of 23℃, and placed on a measuring table. After the plate was descended to be at a specified gap, trimming was performed. The viscosity (mPa・s) of the paint composition at a shear rate of 10 (1 / s) and the viscosity (mPa・s) of the paint composition at a shear rate of 10,000 (1 / s) were measured using a rheometer under the following conditions. As the plate to be used with the rheometer, a cone plate having a diameter of 50 mm and an angle of 0.5° was used. The results are indicated in Tables 2 to 5.

[0299] <Measurement conditions> -Apparatus: Rheometer (obtained from Anton Paar GmbH, MCR302e) -Measurement: Shear rate dependency -Measurement range: at a shear rate from 0.01 (1 / s) to 10,000 (1 / s) -Measurement temperature: 23℃ -Measurement gap: 0.05 mm

[0300] <C / D> The value C / D was calculated, where C represents the viscosity at a shear rate of 10 (1 / s) and D represents the viscosity at a shear rate of 10,000 (1 / s). The results are indicated in Tables 2 to 5.

[0301] <Uniformity of coated surface> One-scan printing was performed on an aluminum composite panel, using an autobody printer. After coating, drying was performed, and roughness was observed visually. According to the following evaluation criteria, B or greater was determined as a pass level. The evaluation results are indicated in Tables 6 and 7.

[0302] <Evaluation criteria> A: A highly uniform coated surface was formed (no traces of dots were recognizable). B: Slight traces of dots were recognized (but could not recognized at a position 10 cm away). C: Traces of dots were recognized (but could not recognized at a position 30 cm away). D: Traces of dots were recognized (could be recognized at a position 30 cm or greater away)

[0303] <Scattering mist (mist generation rank)> Using an autobody printer, one-scan printing was performed on an aluminum composite panel at a hydraulic pressure of 0.4 MPa, to confirm any mist that would be scattered to anywhere except the coated surface. According to the following evaluation criteria, B or greater was determined as a pass level. The evaluation results are indicated in Tables 6 and 7.

[0304] <Evaluation criteria> A: No mist was generated. B: A slight mist was generated (but could not be recognized at a position 10 cm away) C: A mist was generated (but could not be recognized at a position 30 cm away) D: A mist was generated (and could be recognized even at a position 30 cm away)

[0305] <Liquid dripping> Line printing was performed on an aluminum composite panel using an autobody printer, and solid printing in a size of 5 cm in four directions was performed, to visually determine any occurrence of liquid dripping. According to the following evaluation criteria, B or greater was determined as a pass level. The evaluation results are indicated in Tables 6 and 7.

[0306] <Evaluation criteria> AA: None at all. A: Unevenness in a solid patch due to liquid dripping was recognized at a distance of 0.5 m. B: Unevenness in a solid patch due to liquid dripping was recognized at a distance of 1 m. C: Unevenness in a solid patch due to liquid dripping was recognized at a distance of 2 m. D: Liquid dripping to outside a patch occurred.

[0307]

[0308]

[0309] From Table 6 and Table 7, as exhibited in Examples 1 to 31, a paint composition having a storage modulus of 0.1 Pa or greater and 85 Pa or less and a loss modulus of 1.0 Pa or greater and 30 Pa or less, and satisfying the relationship of A×B≦110 between the static surface tension A and the loss tangent B was evaluated as being good in all of uniformity of a coated surface, scattering mist, and liquid dripping.

[0310] On the other hand, as exhibited in Comparative Examples 1 to 4, as indicated in Table 7, a paint composition having a storage modulus of 0.1 Pa or greater and 85 Pa or less and a loss modulus of 1.0 Pa or greater and 30 Pa or less, and failing to satisfy the relationship of A×B≦110 between the static surface tension A and the loss tangent B was evaluated as being faulty in at least any of uniformity of a coated surface, scattering mist, and liquid dripping.

[0311] The above-disclosed embodiments include, for example, the following aspects.

[0312] (Appendix 1) A coating apparatus for applying a paint composition containing a coloring material, a resin, an organic solvent, and water to a coating object by an inkjet method, wherein the paint composition has a storage modulus of 0.1 Pa or greater and 85 Pa or less, a loss modulus of 1.0 Pa or greater and 30 Pa or less, and the paint composition satisfies an expression (1) below, where A represents a static surface tension of the paint composition and B represents a loss tangent of the paint composition, A×B≦110---(1).

[0313] (Appendix 2) The coating apparatus according to Appendix 1, wherein the paint composition satisfies an expression (2) below, where C represents a viscosity of the paint composition at a shear rate of 10 (1 / s) and D represents a viscosity of the paint composition at a shear rate of 10,000 (1 / s), 7≦C / D≦155---(2).

[0314] (Appendix 3) The coating apparatus according to Appendix 1 or 2, wherein the coating object is a metal or a surface of a metal subjected to surface treatment.

[0315] (Appendix 4) The coating apparatus according to any one of Appendices 1 to 3, wherein the coating apparatus comprises: a discharge head, wherein the discharge head includes: a nozzle configured to discharge the paint composition; a valve element configured to open and close the nozzle; and a piezoelectric element configured to drive the valve element, and wherein the valve element is driven in a direction of opening the nozzle when a voltage is applied to the piezoelectric element.

[0316] (Appendix 5) The coating apparatus according to Appendix 4, wherein a distance between the nozzle and the coating object is 5 mm or greater.

[0317] Although embodiments of the present invention have been described above, the present invention is not limited to any particular embodiment, and various modifications and changes are applicable within the scope of the invention described in the claims.

[0318] This international application claims priority based on Japanese Patent Application No. 2024-012197 filed with the Japan Patent Office on January 30, 2024, the entire contents of which are incorporated in this international application.

[0319] 1 discharge head 10 housing 100 discharge module 101 nozzle plate 111 nozzle 113 valve element 114 piezoelectric element 115 holding member 116 holding plate spring (biasing member) 123 piezoelectric element containing space 200 voltage applying part 500 coating apparatus 501 discharge unit 700 printing object (coating object)

Claims

1. A coating apparatus for applying a paint composition containing a coloring material, a resin, an organic solvent, and water to a coating object by an inkjet method, wherein the paint composition has 　　a storage modulus of 0.1 Pa or greater and 85 Pa or less, and 　　a loss modulus of 1.0 Pa or greater and 30 Pa or less, and the paint composition satisfies an expression (1) below, where A represents a static surface tension of the paint composition and B represents a loss tangent of the paint composition, A×B≦110---(1).

2. The coating apparatus according to claim 1, wherein the paint composition satisfies an expression (2) below, where C represents a viscosity of the paint composition at a shear rate of 10 (1 / s) and D represents a viscosity of the paint composition at a shear rate of 10,000 (1 / s), 7≦C / D≦155---(2).

3. The coating apparatus according to claim 1, wherein the coating object is a metal or a surface of a metal subjected to surface treatment.

4. The coating apparatus according to any one of claims 1 to 3, wherein the coating apparatus comprises: a discharge head, wherein the discharge head includes: 　　a nozzle configured to discharge the paint composition; 　　a valve element configured to open and close the nozzle; and 　　a piezoelectric element configured to drive the valve element, and wherein the valve element is driven in a direction of opening the nozzle when a voltage is applied to the piezoelectric element.

5. The coating apparatus according to claim 4, wherein a distance between the nozzle and the coating object is 5 mm or greater.

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