How to set conditions for recoating water-repellent coatings

Abstract

To provide a technique that is able to continuously impart good water repellent performance to a vehicle exterior member for a long period of time.SOLUTION: A condition setting method for re-coating a vehicle exterior member with a water-repellent coating film includes: a peeling step of peeling off a water-repellent coating film formed on a surface of the vehicle exterior member; a re-coating step of forming a water-repellent coating film on the surface to obtain a vehicle exterior member having the coating film after the peeling step; and an evaluation step of applying a test liquid drop to the water-repellent coating film after the re-coating step and performing water repellent evaluation; wherein, when a falling angle of the test liquid drop is 20° or less in the evaluation step, the re-coating condition used in the peeling step and the re-coating step is evaluated as passing.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for setting conditions for recoating a water-repellent coating film on an exterior member for a vehicle. [Background technology]

[0002] There are cases where exterior members for vehicles are required to have water repellency. In recent years, vehicles are generally equipped with various radars to ensure driving safety, pedestrian protection, etc. For example, in a remote sensing technology called LiDAR (Light Detection and Ranging), a radar is used to measure the distance between an object and a vehicle. Specifically, the radar irradiates the object with near-infrared light, visible light, ultraviolet light, etc., and detects the reflected light. In addition, in a speed maintenance system for a traveling vehicle, known as cruise control or auto cruise, a radar is used to measure the distance between the vehicle ahead and the vehicle itself. The radar irradiates millimeter waves or laser waves ahead of the vehicle and detects the reflected light.

[0003] These radars are usually installed on the inner side (i.e., the vehicle body side) of the exterior member for a vehicle. In this case, if many water droplets adhere to the exterior member for a vehicle, it becomes difficult for the radar to perform sensing with high accuracy through the exterior member for a vehicle.

[0004] It is expected that these problems can be solved or alleviated by imparting water repellency to vehicle exterior members (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-187725 [Patent Document 2] Patent No. 4395628 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 introduces a technology for forming a protective coating on the paint film of a body shell of a vehicle, such as the bonnet, while Patent Document 2 introduces a technology for forming a water-repellent coating on the paint film of a body shell of a vehicle, such as the ceiling. It is believed that if the coatings introduced in Patent Documents 1 and 2 are formed on an exterior component for a vehicle that is to be placed on the front side of a radar, adhesion of water droplets to the exterior component for a vehicle can be suppressed.

[0007] However, general protective films and water-repellent films change in quality and deteriorate in performance as they are used. Therefore, even if the protective films and water-repellent films introduced in Patent Documents 1 and 2 are formed on vehicle exterior members, it is difficult to provide the vehicle exterior members with good water-repellent performance for a long period of time.

[0008] The present invention has been made in view of the above circumstances, and has an object to provide a technique that can continuously impart good water repellency to a vehicle exterior member for a long period of time. [Means for solving the problem]

[0009] The recoating condition setting method for a water-repellent coating film of the present invention, which solves the above problems, comprises the steps of: A method for setting conditions for recoating a water-repellent coating film on an exterior member for a vehicle, comprising: A peeling step of peeling off the water-repellent coating film formed on the surface of the vehicle exterior member; a recoating step of forming a water-repellent coating film on the surface after the peeling step to obtain a coated vehicle exterior member; and an evaluation step of attaching a test droplet to the water-repellent coating film after the recoating step to evaluate water repellency. This is a method for setting recoating conditions for a water-repellent coating film, in which if the falling angle of the test droplet in the evaluation step is 20° or less, the recoating conditions used in the peeling step and the recoating step are evaluated as passing. Effect of the Invention

[0010] According to the method of setting recoating conditions for a water-repellent coating film of the present invention, it is possible to continuously impart good water-repellent properties to exterior members for vehicles for a long period of time. [Brief description of the drawings]

[0011] [Figure 1] 1 is a graph showing the transition of the sliding angle and the contact angle for a coated exterior member for a vehicle after the first to fourth recoatings. [Diagram 2] 1 is a graph showing the transition of the sliding angle and the contact angle for a coated exterior member for a vehicle after the first to fourth recoatings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiment of the present invention will be described. Unless otherwise specified, the numerical range "a to b" described in this specification includes the lower limit a and the upper limit b. The numerical range can be formed by arbitrarily combining these upper and lower limit values, as well as the numerical values ​​listed in the examples. Furthermore, the numerical values ​​arbitrarily selected from within the numerical range can be the upper and lower limit numerical values.

[0013] The method for setting recoating conditions for a water-repellent coating film of the present invention is intended to provide a vehicle exterior member with good water-repellent performance for a long period of time by peeling off the durable water-repellent coating film and recoating, i.e., recoating, the water-repellent coating film, on the premise that the water-repellent coating film will deteriorate over time.The method is also intended to set the conditions for the peeling and recoating steps that enable suitable recoating of the water-repellent coating film on a vehicle exterior member with a coating film mounted on an actual vehicle, by evaluating in advance whether the recoated water-repellent coating film can have good water-repellent performance.

[0014] The detailed conditions for the stripping step and the recoating step vary depending on, for example, the shape and material of the vehicle exterior member, the composition of the paint used for the water-repellent coating film, and the like. Therefore, by carrying out the water-repellent coating film recoating condition setting method of the present invention in advance for each combination of paint and vehicle exterior part, and setting the optimal water-repellent coating film recoating conditions for that combination, it is possible to stably recoat the water-repellent coating film onto painted vehicle exterior parts mounted on actual vehicles at a constant level in a variety of situations, environments, or circumstances. In other words, by using the method for setting recoating conditions for a water-repellent coating film of the present invention, a water-repellent coating film recoating service can be provided with stable quality regardless of the type of business or store, such as a dealer, car accessory store, or gas station.

[0015] As a result, according to the method for setting recoating conditions for a water-repellent coating film of the present invention, it is possible to continue to impart good water-repellent performance to a coated vehicle exterior member mounted on an actual vehicle for a long period of time. Hereinafter, the method for setting recoating conditions for a water-repellent coating film of the present invention will be described step by step. In addition, hereinafter, the method for setting recoating conditions for a water-repellent coating film of the present invention may be referred to as the condition setting method of the present invention, as necessary.

[0016] The condition setting method of the present invention comprises a stripping step, a recoating step, and an evaluation step. The peeling step is a step of peeling off the water-repellent coating film formed on the surface of the vehicle exterior member.

[0017] The vehicle exterior component may be any component capable of forming a water-repellent coating film or suitable for forming a water-repellent coating film, and its use, shape, material, etc. are not particularly limited. However, it is preferable that the vehicle exterior component be disposed on the front side of the radar device as described above.

[0018] In the condition setting method of the present invention, the material of the vehicle exterior member is not limited, and examples thereof include resin materials such as polycarbonate (PC), acrylic, and acrylonitrile-butadiene-styrene copolymer synthetic resin (ABS). The vehicle exterior member may have various coating layers formed thereon. For example, a coating layer such as a hard coat may be formed on a base material made of the above-mentioned various resin materials.

[0019] The size of the exterior member for a vehicle is also not particularly limited, and may be small, such as an emblem, or large, such as a front grille.

[0020] The water-repellent coating film may be any film that has water repellency. The term "water repellency" used here means that the film repels water or has low compatibility with water. Since the water-repellent coating film is formed on the surface of an exterior member for a vehicle, it is preferable that the water-repellent coating film has excellent weather resistance.

[0021] Specifically, various types of water-repellent or hydrophobic paints can be used as paints for the water-repellent coating film, with fluorine-based paints being particularly suitable. In particular, as the paint for the water-repellent coating film, it is more preferable to use a paint in which a curing component such as a metal alkoxide and a silane coupling agent are dissolved in a solvent, as disclosed in JP 2016-147469 A. As the solvent, a solvent having either an alcohol group or a ketone group, or a solvent having a relatively high boiling point, such as a water-soluble solvent, is preferable.

[0022] The water-repellent coating film may be formed directly on the vehicle exterior member, or may be formed on a primer layer formed on the vehicle exterior member.

[0023] In the peeling step in the condition setting method of the present invention, the water-repellent coating film formed on the surface of the vehicle exterior member may be peeled off by any method. For example, the peeling step may be a chemical peeling method in which the water-repellent coating film is dissolved with an organic solvent such as methyl ethyl ketone (MEK) or ethanol, an alkali, a water-soluble solvent, or the like, or a physical peeling method in which the water-repellent coating film is scraped off with a file, a brush, a paper or nonwoven wiper, or the like, or these may be used in combination.

[0024] Here, in the above-mentioned peeling step, it is sufficient to peel off the water-repellent coating film, and the layer below the water-repellent coating film, such as the above-mentioned primer layer or hard coat layer, may remain on the vehicle exterior member without being peeled off even after the peeling step.

[0025] These underlayers and exterior components for vehicles may be damaged by the peeling process. Therefore, if excessive force is applied in the peeling process or if the peeling process is repeated, the smoothness of the underlayers and exterior components for vehicles may be impaired. In such cases, the water-repellent coating film after recoating may be relatively firmly integrated with the underlayer and exterior components for vehicles due to the anchor effect, and may be difficult to peel off sufficiently during the next recoating.

[0026] Therefore, the peeling step is preferably performed a sufficient number of times and with sufficient strength to sufficiently peel the water-repellent coating film from the vehicle exterior member. When any measurement area on the surface of the vehicle exterior member is taken as 100% by area, the water-repellent coating film remaining on the surface of the vehicle exterior member after the peeling step is preferably 10% by area or less, more preferably 5% by area or less, and particularly preferably 3% by area or less. The evaluation can be performed by processing images obtained under a microscope.

[0027] When the water-repellent coating film is peeled off to the above-mentioned extent, the surface of the exterior part for a vehicle appears smooth. Therefore, when the conditions set by the condition setting method of the present invention are used to recoat a water-repellent coating film on a painted exterior component for a vehicle mounted on an actual vehicle, whether or not the peeling step is complete may be determined by measuring the mass, by visual inspection by an operator, or by other methods such as image analysis.

[0028] The recoating process is a process for forming a water-repellent coating film on the surface of the vehicle exterior member after the peeling process. The water-repellent coating film formed in the recoating process may be the same as or different from the water-repellent coating film peeled off in the peeling process. When the water-repellent coating film remains after the peeling process, it is preferable that the water-repellent coating film formed in the recoating process is the same as the water-repellent coating film peeled off in the peeling process, taking into consideration the compatibility with the water-repellent coating film remaining after the peeling process.

[0029] The recoating step may be performed by a general painting method, such as a method of applying paint to the exterior member for a vehicle using a paint application tool such as a brush or a sponge, a method of spraying paint onto the exterior member for a vehicle using a sprayer, or a method of immersing the exterior member for a vehicle in paint.

[0030] Thereafter, if necessary, the solvent contained in the paint applied to the vehicle exterior member is removed by drying, heating, or the like, thereby recoating the vehicle exterior member to obtain a coated vehicle exterior member.

[0031] In the condition setting method of the present invention, an evaluation step is performed after the recoating step. Specifically, in the evaluation step, a test droplet is attached to the water-repellent coating film after the recoating step, and the water repellency is evaluated. If the falling angle of the test droplet is 20° or less, the recoating conditions, i.e., the recoating conditions used in the peeling step and the recoating step, are evaluated as acceptable.

[0032] If the evaluation is successful, it is possible to say that the water-repellent coating film has a sufficient water-repellent function, and it is also possible that the peeling step and the recoating step have been carried out suitably. In other words, if the evaluation obtained in the evaluation step is successful, it can be judged that the conditions are suitable for suitably recoating a vehicle exterior member and for obtaining a coated vehicle exterior member having a sufficient water-repellent function. Thus, according to the condition setting method of the present invention, it is possible to appropriately set the conditions for the peeling step and the recoating step that can suitably recoat the water-repellent coating film.

[0033] The falling angle here means an angle measured when the coated vehicle exterior member is tilted until the test droplet falls off the coated vehicle exterior member. More specifically, a test droplet is attached to the coated vehicle exterior member as a test specimen, and the sample stage on which the coated vehicle exterior member is placed or held is tilted while the test droplet is captured by a high-speed camera. The difference between the angle of the sample stage when the test droplet falls off the coated vehicle exterior member and the angle of the sample stage in the initial state is taken as the falling angle. The falling angle can be said to be a dynamic index of water repellency.

[0034] The liquid for forming the above-mentioned test droplets contains at least a liquid medium, and if necessary, an additive may be added to the liquid medium. The liquid medium may be aqueous or non-aqueous, but considering that the coating film is water-repellent, it is preferable that the liquid medium contains 50% or more by volume of water. As the water, common water such as tap water, ion-exchanged water, and distilled water may be used. Of course, the liquid for forming the test droplets may be made of only these waters, that is, it is preferable that the liquid contains 100% by volume of water.

[0035] The additives mentioned above are preferably ones that can reproduce a composition close to that of droplets that actually adhere to a coated vehicle exterior member mounted on an actual vehicle, such as rainwater or muddy water, and may be water-soluble or water-insoluble. Examples of water-soluble additives include glycerin and ethylene glycol. Examples of water-insoluble additives include oils such as mineral oil and silicone oil, and minerals such as talc, mica, zeolite, and smectite. These additives may be used alone or in combination.

[0036] The method for attaching the test droplets to the water-repellent coating film after the recoating step is not particularly limited, and any method may be used to apply a liquid to the water-repellent coating film of the coated vehicle exterior member. The liquid on the water-repellent coating film becomes the test droplets due to surface tension.

[0037] The method for attaching the test droplets to the water-repellent coating film after the recoating step may be, for example, to simply drip the above-mentioned liquid onto the water-repellent coating film, to paint it with a brush, or to spray it with a spray device. In any case, it is preferable to apply an amount of liquid onto the water-repellent coating film that drips off.

[0038] The method for evaluating the water repellency of a coated exterior member for a vehicle by measuring the sliding angle of the test droplet may be the method described in the Examples section below, or a method in which the coated exterior member for a vehicle to which the test droplet is attached is tilted to the same degree as in the above method and the state of the test droplet can be monitored. Alternatively, the sliding angle may be measured with reference to the water repellency evaluation method introduced in Surface Technology Vol. 60, No. 1, 2009, pages 21 to 26.

[0039] The water repellency evaluation of the coated vehicle exterior member may be performed alone, or may be performed while mounted on an actual vehicle. In order to perform the water repellency evaluation under realistic conditions, it is preferable to perform the water repellency evaluation of the coated vehicle exterior member while mounted on an actual vehicle. In order to perform the water repellency evaluation easily and efficiently, it is preferable to perform the water repellency evaluation of the coated vehicle exterior member alone.

[0040] The coated vehicle exterior member used for the water repellency evaluation may be of the same shape as that of the vehicle to be mounted on an actual vehicle, or may be a simple test piece. In order to evaluate the vehicle under conditions close to reality, it is preferable that the coated vehicle exterior member has the same shape as that of the vehicle to be mounted on an actual vehicle.

[0041] In the condition setting method of the present invention, the recoating conditions are evaluated as passing when the above-mentioned sliding angle is 20° or less. Considering that the smaller the sliding angle, the higher the water repellency, the sliding angle for passing is preferably 19.5° or less, and more preferably 19° or less.

[0042] It is expected that repeated recoating will increase the amount of water-repellent coating remaining after the peeling process, and the number and size of scratches formed in the lower layer of the water-repellent coating and on the vehicle exterior member by the peeling process, impairing the smoothness of the water-repellent coating formed on the upper layer. Therefore, if recoating is repeated too many times, the water-repellent performance of the water-repellent coating will decrease, and the sliding angle measured in the water-repellent evaluation will exceed 20°.

[0043] As will be explained in detail in the Examples section below, if recoating is performed appropriately, the falling angle of the test droplet in the evaluation step will be 20° or less if the number of recoating cycles is four or less. Therefore, in order to evaluate the recoating conditions more strictly, it is preferable to perform the evaluation step after four recoating cycles.

[0044] In addition, when recoating a painted exterior component for a vehicle mounted on an actual vehicle based on the conditions set by the condition setting method of the present invention, it is preferable to limit the number of recoatings to four or less. In other words, when recoating a painted exterior component for a vehicle mounted on an actual vehicle based on the conditions set by the condition setting method of the present invention, it is preferable to carry out recoating only if the number of recoatings up to that point is three or less.

[0045] As described above, the condition setting method of the present invention employs the sliding angle, which is a dynamic evaluation criterion, to evaluate the water repellency of the water repellent coating film. In the condition setting method of the present invention, in order to perform a more precise evaluation of the water repellency, in addition to the evaluation using the sliding angle, which is a dynamic evaluation criterion, evaluation using the contact angle, which is a static evaluation criterion, may be performed. Specifically, in the condition setting method of the present invention, when the contact angle of the test droplet is 100° or more in the evaluation step, it is preferable to evaluate the recoating conditions as excellent, which is a higher level of pass.

[0046] The contact angle here means so-called wettability, and can be measured based on JIS K6768:1999. The liquid used for the test droplet may be a mixed liquid disclosed in JIS K6768:1999, or the same liquid as that used for measuring the sliding angle may be used. If the contact angle of the test droplet is large, the angle between the surface of the coated vehicle exterior member and the test droplet is large, and it can be said that the coated vehicle exterior member has low wettability and is excellent in water repellency.

[0047] In the evaluation step, a contact angle of the test droplet of 102° or more is preferably evaluated as excellent, and a contact angle of 105° or more is more preferably evaluated as good.

[0048] The condition setting method of the present invention will be described below with a specific example.

[0049] Example 1 In the condition setting method of Example 1, a cover for covering a LiDAR mounted on a vehicle was adopted as the vehicle exterior member. The condition setting method of Example 1 is a method for setting conditions for recoating a water-repellent coating film formed on the surface of the cover.

[0050] The condition setting method of the first embodiment includes a preparation step, a stripping step, a recoating step, and an evaluation step.

[0051] [Preparation process] In the preparation step, a coated exterior member for a vehicle was prepared, in which a water-repellent coating film was formed on the surface of the exterior member for a vehicle. The vehicle exterior member used was made of polycarbonate and had a substantially flat base material and a hard coat layer formed on the surface of the base material. The hard coat layer was formed by applying an acrylic urethane paint onto the base material, and then drying and curing the paint.

[0052] A material for a water-repellent coating film disclosed in JP 2016-147469 A was further dipped onto the hard coat layer and dried to prepare a coating-film-attached exterior member for a vehicle having a water-repellent coating film formed on the surface of the exterior member for a vehicle. The water-repellent coating film formed at this time had a thickness of 200 nm.

[0053] [Peeling process] The water-repellent coating film of the above-mentioned coated exterior vehicle member was wiped off with paper soaked in a water-soluble solvent. New Super Clean manufactured by Penguin Wax Co., Ltd. was used as the water-soluble solvent, and a commercially available paper wiper was used as the paper. The wiping operation was continued until the worker visually confirmed that the water-repellent coating film had disappeared.

[0054] Thereafter, the surface of the vehicle exterior member was photographed under a microscope and the image was processed to measure the amount of the water-repellent coating film remaining on the surface of the vehicle exterior member. Since the amount of the water-repellent coating film remaining on the surface of the vehicle exterior member was 2 area % or less, it was determined that the water-repellent coating film had been sufficiently peeled off.

[0055] [Recoating process] A water-repellent coating film was formed on the vehicle exterior member after the peeling process in the same manner as in the preparation process, to obtain a vehicle exterior member with a first recoating film. The water-repellent coating film formed at this time is estimated to have a thickness of 200 nm, the same as in the preparation process.

[0056] [Evaluation process] The sliding angle and contact angle were measured for the vehicle exterior member with the first recoat film obtained in the recoating process. Water was used as the liquid for forming the test droplet in measuring the sliding angle. The contact angle was measured based on JIS K6768:1999, and the liquid mixture disclosed in JIS K6768:1999 was used as the liquid for the test droplet in measuring the contact angle.

[0057] The sliding angle was measured using a contact angle meter equipped with a sliding unit manufactured by Kyowa Interface Science Co., Ltd. The coated vehicle exterior component was attached to the sample stage, and a minute test droplet of about 20 μL was formed on the water-repellent coating using a dispenser containing ion-exchanged water. Then, while continuously capturing images of the test droplet with a high-speed CCD camera, the sample stage was tilted from the horizontal position, and the angle of the sample stage when the test droplet slid down was measured. The angle of the sample stage at this time was taken as the sliding angle.

[0058] The sliding angle and contact angle of the coated exterior member for a vehicle before the peeling step were also measured in advance. The first recoating was completed through the above steps.

[0059] The above-mentioned peeling step to evaluation step were repeated three times, and second to fourth recoatings were performed. The test was performed with n=2. The changes in the sliding angle and contact angle for the coated exterior member for a vehicle after the first to fourth recoatings are shown in FIG. 1 and FIG.

[0060] As shown in Figures 1 and 2, from the first to fourth recoatings, the sliding angle was maintained at 20° or less and the contact angle at 100° or more, and the water-repellent performance of the water-repellent coating was fully demonstrated. From these results, it is clear that a water-repellent coating film with sufficient water-repellent properties can be formed by recoating under recoating conditions that result in a sliding angle of 20° or less. It is also clear that if the recoating is repeated four times or less, the water-repellent coating film formed by recoating has sufficient water-repellent properties.

[0061] For reference, when the transmittance at 870 nm was measured for the vehicle exterior parts that had been recoated 1st to 4th times, the transmittance was 88% or more for all of the vehicle exterior parts that had been recoated 1st to 4th times, which was sufficient transmittance. These results show that if the recoating conditions are such that the fall angle is 20° or less, and the number of recoating cycles is four or less, then recoating can form a water-repellent coating that is sufficiently smooth and suitable for placement on the front side of a radar device.

[0062] The present invention is not limited to the embodiment described above and shown in the drawings, and can be modified and implemented as appropriate without departing from the scope of the present invention. Furthermore, each component shown in this specification, including the embodiment, can be arbitrarily extracted and combined for implementation.

Claims

1. A method for setting conditions for recoating a water-repellent coating film on an exterior member for a vehicle, comprising: A peeling step of peeling off the water-repellent coating film formed on the surface of the vehicle exterior member; a recoating step of forming a water-repellent coating film on the surface after the peeling step to obtain a coated vehicle exterior member; and an evaluation step of attaching a test droplet to the water-repellent coating film after the recoating step to evaluate water repellency. A method for setting conditions for recoating a water-repellent coating film on a coated vehicle exterior component that has a transmittance of 88% or more at 870 nm and is disposed on the front side of a radar device, the method evaluating the recoating conditions used in the peeling process and the recoating process as passing if the falling angle of the test droplet in the evaluation process is 20° or less.

2. 2. The method for setting recoating conditions for a water-repellent coating film on a vehicle exterior member having a transmittance of 88% or more at 870 nm and disposed on the front side of a radar device according to claim 1, wherein, when the contact angle of the test droplet in the evaluation step is 100° or more, the recoating conditions used in the peeling step and the recoating step are evaluated as excellent, which is the higher level of pass.

3. A method for setting conditions for recoating a water-repellent coating on a coated vehicle exterior component that has a transmittance of 88% or more at 870 nm and is positioned on the front side of a radar device, as described in claim 1 or claim 2, wherein the peeling process and the recoating process are repeated, and the evaluation process is performed after the fourth recoating process.

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