JPH0366940B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method of applying a paint to a substrate to be painted for the purpose of beauty, corrosion protection, etc. [Prior Art] When painting metal materials and metal products for the purpose of preventing corrosion, etc., multiple coats are usually applied. For example, when painting metal materials,
The surface of the base material to be painted is subjected to surface treatment such as blasting and sanding to remove rust and surface deposits, and then an undercoat is applied with the main purpose of preventing corrosion.After this paint solidifies and dries, Then, if necessary, an intermediate coat is applied, and after this has solidified and dried, a top coat is applied mainly for aesthetic purposes. This is because paints that have excellent adhesion to the substrate and corrosion resistance do not necessarily satisfy aesthetic requirements, and paints that have excellent aesthetic properties and are resistant to the environment that comes into contact with the painted surface do not necessarily satisfy the aesthetic requirements. In many cases, it is difficult to say that it is the best in adhesion to other materials and corrosion resistance, and the aim is to complement these to obtain a coating film that is excellent in both. Also, remove defects such as pinholes that may occur with one coat of paint.
It is also meant to reduce the probability of remaining after multiple coats, and in some cases, the adhesion between the undercoat and top coat is not very good, or to improve corrosion resistance or add other coating properties. For this purpose, an intermediate coating that acts as a bridge between the two coatings is also applied. In each of these painting steps, it is common knowledge in the industry that the next coating is applied after the coating film formed by the undercoat has dried. However, in the following cases, a top coat has been applied while the undercoat is still uncured. That is, a baking-type phenolic resin-based or alkyd resin-based undercoat paint is applied, an intermediate coat or top coat is applied after the solvent has volatilized but not yet cured, and the undercoat and intermediate coat or top coat are applied in one baking process. A method of curing the coating film at the same time is being used. When spraying the same paint multiple times to increase the thickness of the paint film or to prevent the aforementioned pinholes from remaining, the spray gun is moved back and forth many times to form the desired thick paint film. Since the paint is the same, it is common practice to apply a topcoat while the undercoat is still wet. As disclosed in Special Publication No. 60-17588,
When the main components of the undercoat and topcoat are the same vehicle, the topcoat is usually applied before the undercoat is completely cured. This method shortens the process by curing the undercoat and topcoat at the same time in one baking, which normally requires two baking steps. Although the film is in an uncured state, the top coat is applied after it is dry to the touch, and the desired paint film is only formed by baking. It is not a paint that is applied when the paint film is wet, nor is it a room-temperature curing paint. In this case, since the paint is the same, there is no possibility of interaction due to two or more coats, and it is clear that there will be no problem even if the undercoat is wet and the topcoat is applied, so this is done. Unlike the present invention, different types of paint are not applied. In this case, the undercoat and topcoat are both epoxy resin or modified epoxy resin paints, and the main component vehicle is the same type of paint, so they are not strictly different types of paint. do not have. In this way, for the same type of paint, the top coat is applied while the base coat is still wet, but it is common practice to apply the top coat while the base coat is wet, but it is common practice to apply a top coat while the base coat is wet, but it is common practice to apply a top coat while the base coat is still wet, but it is common practice to apply a top coat while the base coat is still wet, but it is common practice to apply a top coat while the base coat is still wet. For resins, it is not practiced to apply a top coat while the base coat is still wet. JP-A No. 60-92365 proposes a top coat clear paint composition to be applied on a base coat by a wet-on-wet method.
The base coat paint is acrylic silver metallic paint, polyester white paint, or acrylic silver metallic paint, and the two-component reactive undercoat paint is only acrylic resin isocyanate curing paint. On top of this, add an acrylic polymer, a diluent, and a crosslinking agent with a particle size of 0.01 to
It is a top coat with a clear paint composition containing cross-linked polymer fine particles with a diameter of 10 μm.The base coat paint is mainly a one-component type, and if it is a two-component type, the top coat is also a two-component type, although it cannot be said that it is the same type. The same type of paint is used. Furthermore, the composition is intended for line painting of automobiles, and is not intended for large structures such as buildings, bridges, and tanks, as is the case with the present invention, and the composition itself is different. [Problems to be solved by the invention] In the conventional painting process, for example, in the drying process between the coating process and the intermediate coating process, or between the intermediate coating process and the top coating process, dirt and dust are removed. It is a well-known phenomenon that when foreign matter adheres to a painted surface, the adhesion between the respective paint film layers becomes insufficient, resulting in the problem of delamination. Furthermore, in the conventional process, the work period from surface preparation to topcoat painting is long, and there is a problem that the painting cost increases accordingly for water-type buildings and bridges. The present invention was devised in view of this point of view, and provides a coating film forming method different from conventional coating methods, which reduces coating costs by shortening the construction period, and reduces delamination due to dirt and dust. It also attempts to solve the problem of [Means for solving the problem] The present invention involves applying a two-component reactive undercoating paint based on urethane resin or epoxy resin to the substrate to be coated,
The coating is characterized in that, while the coating film is wet before touch dry, a one-component top coat, which is a room temperature drying coating selected from chlorinated rubber, alkyd resin, and acrylic resin, is applied. This is a film forming method. Epoxy resin or urethane resin paint is used as the two-component reactive paint. The two-component reactive paint may be a relatively low molecular weight resin that is liquid at room temperature, but a resin that is solid at room temperature is preferred. The resin used in the epoxy resin undercoat paint may be any ordinary epoxy resin obtained by the reaction of epichlorohydrin and bisphenol A, specifically Epicote (Ciel Chemical Registered Trademark) 828, 834. , 1001, 1004, 1007, 1009, etc., Araldite (Japan Ciba Geigy registered trademark) 6071,
General-purpose resins such as 7071, 6084, 7097, 6097, and Sumiepoxy (Sumitomo Chemical registered trademark) ESA-011, 014 may be used. The curing agent for epoxy resin used in this case is preferably a polyamide curing agent. Other ingredients include:
Extenders such as coumaron resin, petroleum resin, or white tar, extender pigments such as silica, talc, and calcium carbonate, coloring pigments such as Bengara, titanium oxide, and carbon black, and thixotropy such as organic bentonite and silicic anhydride fine powder. A coating agent and a solvent may be used as necessary. The resins used in urethane resin paints include regular polyester, hydroxyl group-containing epoxy resin,
Alternatively, a vehicle such as a modified epoxy resin in which the number of hydroxyl groups is increased by modifying an epoxy resin with an alkanolamine is used in combination with a resin containing active isocyanate groups for curing the resin.
Methylene isocyanate (MDI), tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), and the like are generally known as isocyanate group-containing resins, and any of them can be used. However, the use of MDI and TDI resins may cause them to stand out on the surface of the top coat and cause the paint film to change color over time, but if HMDI resins are used as a curing agent, this will not happen. No such phenomenon occurs. As other compounding materials, those used in the above-mentioned epoxy resin paints can be used as desired. However, if a bituminous material such as tar or asphalt or a tar oil resin having similar properties is added as an extender to an epoxy resin or urethane resin as an undercoat, When a top coat is applied, the above-mentioned bituminous material bleeds out immediately after painting, so it is good when emphasis is placed on corrosion resistance and aesthetics are not required, but such bituminous material is recommended when aesthetics are required. Alternatively, it is preferable not to use a paint containing tar oil resin or the like as an undercoat paint. The top coat is selected from chlorinated rubber paints, which are solvent-volatile synthetic resin paints, acrylic resin paints, and oxidation-polymerized alkyd resin paints. Other alkyd resin-containing chlorinated rubber paints can also be used. The main feature of the present invention is that after the two-component reactive type undercoat paint is applied, the topcoat paint is applied while the undercoat film is still wet. This wet state is defined in JIS K-5400-
This refers to the state before touch dry as described in the 1970 "General Test Methods for Paints 5.10". Traditionally, this type of painting method has not been used because of the preconception that layering different types of paint, such as undercoat and topcoat, will cause delamination, blistering, foaming, or disorder of the paint film. This is the actual situation. However, the present inventors thought that if this type of coating could be applied, the construction period would be considerably shortened and there would be significant economic benefits.As a result, the inventors deliberately researched recoating in wet conditions, which goes against common sense. The inventors have discovered that by employing the combination of undercoat and topcoat as in the present invention, a coating film with no defects in corrosion resistance can be formed, and the present invention has been completed. At first glance, this method of forming a coating film seems absurd, as if it goes beyond common sense, but the results are of a surprising level. Since the top coat is applied while the undercoat is still wet, a composite paint film is naturally formed in which the undercoat and topcoat components are mixed at the interface. Although it is unclear why good results are obtained,
This is thought to be because the components of the undercoat and topcoat do not mix together at once due to differences in the solvent composition in the paint or a type of solvent shock, and only the interface between the two exists as a mixed layer. Epoxy resin type or urethane resin type 2 for undercoat paint
It is thought that even better results can be obtained if a liquid reaction type is used and a chlorinated rubber, acrylic resin, or alkyd resin is applied as the top coat because the coating film curing mechanism is different. In this case, the paint vehicle used for the undercoat is preferably one that has a large molecular weight and is solid at room temperature. As for the painting method, it is best to use regular air spray or airless spray. Brush painting, roller painting, etc. are difficult to apply because the undercoat film is in a wet state. To achieve the present invention, one of the two painters should apply the undercoat and the other should immediately apply the topcoat, but painting on scaffolding involves work hazards, and Such coatings are often difficult. However, if two spray nozzles are installed in one coating machine, and the first spray nozzle applies the undercoat and the second spray nozzle applies the topcoat, the present invention can be applied in one operation of the coating machine. Since the desired coating film is formed, coating costs can be drastically reduced. If such a coating machine is equipped with a device that performs surface treatment, each step of the normal painting process, from base treatment to undercoating to topcoating, can be performed in one operation of the painting machine, making the work more efficient. This will further reduce costs. The coating film thickness is not particularly limited for this reason, and may be arbitrarily determined depending on the purpose;
Considering corrosion resistance, the dry film thickness of the undercoat should be
The dry film thickness of the top coat should be 10 to 50 μm, preferably 60 to 250 μm, preferably 100 to 120 μm.
Preferably, it may be applied to a thickness of 20 to 30 μm. After application, dry under normal conditions. This coating film is comparable in performance to a conventional coating in which a top coat is applied on top of a dried undercoat. Example 1 A test plate obtained by degreasing a 150 x 70 x 1 mm mild steel plate and subjecting it to shot blasting treatment was used as a substrate to be coated. The surface of this test plate was coated with a two-component reactive urethane resin paint (trade name: Nippon Steel Chemical Co., Ltd.).
NB coat 3000GW gray color) with thinner about 5
% and applied with an airless spray method so that the film thickness after drying is 100 to 120 μm, and then immediately coated with white chlorinated rubber synthetic resin paint (Nippon Steel Chemical Co., Ltd., product name: NB Coat CR-503). Chlorinated rubber topcoat) or alkyd resin paint (Nippon Steel Chemical Co., Ltd. product name: NB
Approximately 20% by weight of thinner on Coat FE-503 (overcoat)
It was added and applied by air spraying so that the film thickness after drying was 20 to 30 μm. 7 in a constant temperature and humidity chamber at a temperature of 20 ± 1°C and a humidity (RH) of 75 ± 5%.
I cured it for a day. Various tests were conducted on each composite coating film thus formed. The results are shown in Table 1. For comparison, the conventional painting interval (after undercoating)
After drying for 16 hours, the coatings applied with a topcoat were simultaneously tested.

【table】

[Table] ○ mark: Good △ mark: Slightly bad Example 2 The same test plate as in Example 1 was used, the same base treatment was applied, and a two-component reactive epoxy resin paint (Nippon Steel Co., Ltd.) was used as the undercoat. The same top coat as in Example 1 was applied, except that Kagaku Co., Ltd. (trade name: NB Coat EP Blue) was used, and the coating was cured in the same manner. The test results for the coating film are shown in Table 2.

【table】

[Table] ○ mark: Good △ mark: Fairly bad [Effect of the invention] Conventional surface treatment, undercoating, If it rained during each topcoat job, we had to wait until the surface became dry when the weather turned sunny, and during that time, dirt, dust, and foreign matter from birds stuck to the surface, which extended the construction period longer than planned, and during that time we had to set up scaffolding. It is necessary to leave the
In addition, there are many inconveniences such as the need for workers to be stationed in the construction area, which causes high painting costs. Subsequently, these can be done almost at the same time, which not only greatly reduces painting costs, but also prevents insufficient adhesion due to foreign matter adhering between the paint layers, and the formed paint film is It had corrosion resistance and aesthetics comparable to those formed by a conventional painting process that involved drying. This is a painting method with great practical value.

Claims (1)

[Claims] 1. Apply a urethane resin-based or epoxy resin-based two-component reactive undercoat paint to the substrate to be painted, and select from chlorinated rubber-based, alkyd resin-based, or acrylic resin-based, while the paint film is wet before drying to the touch. A coating film forming method characterized by applying a one-component top coat paint that dries at room temperature.