JPH057433B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an alkyd resin coating composition that dries at room temperature by oxidative polymerization, and more particularly relates to an alkyd resin coating composition that can form a coating film with excellent coating hardness in the early stage of drying. [Prior Art] Paints using oxidation-polymerizable room-temperature curing alkyd resins have been widely used for coating automobiles, buildings, electrical equipment, and their parts. This paint hardens even at room temperature after being applied, but in order to improve productivity, it is common to force dry it in a drying oven to harden it in as short a time as possible. However, oxidative polymerization type paints are in a semi-cured state immediately after drying in a drying oven and have a low glass transition point (Tg). For this reason, there is a phenomenon in which stickiness remains on the surface of the coating film when the temperature is high immediately after it comes out of the drying oven. If the paint film remains sticky in this way, it becomes difficult to handle, resulting in loss of time and space until it cools down. Conventionally, as a means to improve this non-stick property, that is, tack-free property, measures such as changing the type of modified oil of alkyd resin or adding a metal chelate compound have been taken (Japanese Patent Laid-Open No. 52-69437). , Japanese Patent Publication No. 51-8324). However, even with these methods, the improvement in tack-free property was not necessarily sufficient. The reason for this can be explained as follows. That is,
Tack-free properties are closely related to the Tg of semi-cured resins, but the crosslinking reaction of oxidation-polymerized alkyd resins is inherently slow, and even if the type and amount of modified oil and dryer are changed, they can be cured quickly at low temperatures. A sufficient increase in Tg due to crosslinking cannot be expected only by heating for a period of time. Further, if a metal chelate compound is added, the tack-free property is improved to some extent, but other physical properties of the coating film such as impact resistance are deteriorated. [Problems to be Solved by the Invention] The present invention overcomes the above-mentioned drawbacks, and provides a coating film that is excellent in tack-free properties and initial coating film hardness, and that does not impair water resistance, corrosion resistance, and impact resistance. The purpose is to provide an alkyd resin coating composition. [Means for Solving the Problems] The alkyd resin coating composition of the present invention has a short oil length for 100 parts by weight of a cold-curing alkyd resin that is modified with a drying oil or a semi-drying oil and can be cured at room temperature by oxidative polymerization. Consisting of a base resin made of at least one of an alkyd resin and an acrylic resin, and a curing agent made of an amino resin crosslinkable with the base resin and mixed in an amount of 1 to 50 parts by weight per 100 parts by weight of the base resin. Heat-curable resin mixture is 11~
It is characterized by containing 150 parts by weight and 0.1 to 10 parts by weight of an acid catalyst. The room temperature curable alkyd resin refers to an alkyd resin that can be cured at room temperature by oxidative polymerization. Such alkyd resins include drying oils such as linseed oil, tung oil, dehydrated castor oil, or soybean oil,
Those modified with semi-drying oils such as safflower oil and tall oil are known. Furthermore, those modified with phenol resin, epoxy resin, acrylic resin, urethane resin, etc. can also be used. The greatest feature of the present invention is that this room temperature curing alkyd resin is mixed with a heat curing resin mixture consisting of a main resin and a curing agent and an acid catalyst. The main resin is a resin that can react with an amino resin as a curing agent, and either one of a short oil length alkyd resin and an acrylic resin, or a mixture of both can be used. However, in the case of acrylic resin,
It is necessary to select a material that has good compatibility with the room temperature curing alkyd resin. The curing agent is composed of an amino resin. Amino resin refers to a resin obtained by adding formaldehyde to melamine, urea, or benzoguanamine, and then condensing or etherifying the mixture. In order to improve the curability at low temperatures, it is desirable to have a high degree of methylolation, and methylolation melamine is particularly preferred. This curing agent is added in an amount of 1 part by weight per 100 parts by weight of the main resin.
It is used in a range of 50 parts by weight. If the amount of the curing agent is less than 1 part by weight, it is difficult to improve tack-free properties, and if it is more than 50 parts by weight, the coating film becomes too hard and other physical properties of the coating film deteriorate. Particularly preferred is
The amount is 3 to 20 parts by weight based on 100 parts by weight of the main resin. The heat-curable resin mixture containing the main resin and the curing agent in the above appropriate blending ratio is mixed in an amount of 11 to 150 parts by weight based on 100 parts by weight of the room-temperature curing alkyd resin. If the amount of the heat-curable resin mixture is less than 11 parts by weight, it will be difficult to improve tack-free properties, and if it exceeds 150 parts by weight, other physical properties of the coating film such as curability and water resistance at room temperature and low temperature will deteriorate. If the curing agent is in the optimal range of about 10 parts by weight based on 100 parts by weight of the main resin, the optimum amount of the heat-curing resin mixture is about 11 to 55 parts by weight based on 100 parts by weight of the room-temperature curing alkyd resin. be. In this case, as shown in the examples, the tack-free property and water resistance are particularly excellent. Although inorganic acids such as hydrochloric acid, phosphoric acid, and sulfuric acid may be used as the acid catalyst, it is preferable to use organic acids from the viewpoint of compatibility. Among these organic acids, para-toluenesulfonic acid is preferred, and block type para-toluenesulfonic acid is particularly preferred from the viewpoint of storage stability of the paint. This acid catalyst is a room temperature curing alkyd resin 100
It is blended in an amount of 0.1 to 10 parts by weight. 0.1
If it is less than 1 part by weight, the tack-free property after drying at a low temperature of about 70° C. will not be improved, and if it exceeds 10 parts by weight, the tack-free property will be improved, but storage stability and water resistance will decrease. The type and amount of the acid catalyst to be added are appropriately determined depending on the required drying conditions and the type of amino resin. Note that the coating composition of the present invention can contain not only the above-mentioned resin but also various pigments, additives, solvents, and the like. For example, as pigments, inorganic pigments such as carbon black, red iron oxide, and titanium white, organic pigments such as phthalocyanine and quinacridone, or extender pigments such as calcium carbonate, talc, clay, and barium sulfate can be used. Further, as additives, dryers, antifoaming agents, leveling agents, dispersants, color separation inhibitors, etc. can be used, and as solvents, various conventionally used organic solvents can be used. [Effects of the Invention] The alkyd resin coating composition of the present invention contains a heat-curable resin mixture in addition to the conventional room-temperature-curable alkyd resin. This thermosetting resin mixture has a higher crosslinking rate than a room temperature curing alkyd resin, and is rapidly crosslinked even at a low temperature of about 100°C or less. Therefore, the Tg of the semi-cured coating film is improved, the tack-free property is improved, and the initial hardness of the coating film is improved. Furthermore, since the coating composition of the present invention contains an acid catalyst, the reaction of the heat-curable resin mixture is accelerated, and low-temperature drying properties are further improved. Therefore, the tack-free property and initial hardness of the coating film after low-temperature drying are further improved. Thereafter, the room-temperature curing alkyd resin is gradually crosslinked by oxidative polymerization, ultimately forming a tough coating film with excellent coating properties. Therefore, according to the alkyd resin coating composition of the present invention, the coated article can be easily handled immediately after drying at a low temperature, and productivity is improved. [Example] Hereinafter, the present invention will be explained in detail with reference to Examples. Table 1 shows the compositions of the alkyd resin coating compositions in Examples 1-2 and Comparative Examples 1-4. Here, as the room temperature curing alkyd resin, except for Comparative Example 2, tall oil-modified alkyd resin (oil length 51%), which is a semi-drying oil, was used; %) was used. Carbon black was used as the coloring pigment, cobalt naphthenate was used as the metal dryer, calcium carbonate was used as the extender pigment, and toluene was used as the solvent. Moreover, as the metal chelate compound of Comparative Example 3, ethyl acetoacetate aluminum diisopropylate was used. In Examples 1 to 2 and Comparative Example 4, the short oil length alkyd resin constituting the main resin of the heat-curable resin mixture was a tall oil modified alkyd resin with an oil length of 33% ("Betsukosol ET330" manufactured by Dainippon Ink & Chemicals). Co., Ltd.), and as the amino resin constituting the curing agent, methylolated melamine ("Nikaratsuku MW12LF", manufactured by Sanwa Chemical Co., Ltd.) was used.
Further, as the acid catalyst in Examples 1 and 2, amine block type para-toluenesulfonic acid ("Kyatanit B" manufactured by Nitto Chemical Co., Ltd.) was used. In order to evaluate the performance of each of the above coating compositions, test panels were prepared from each of the coating compositions. First, degreased mild steel plate (“SPCC-SD” 70×
150 x 0.8 mm), coated with air spray so that the dry film thickness was 20 μm, and after setting for 5 minutes, heated at 70℃ for 20 minutes, 90℃ for 20 minutes, and 110℃.
It was dried in a hot air dryer under various drying conditions for 20 minutes. Each coating film was evaluated for tack-free property, corrosion resistance, water resistance, impact resistance, and storage stability, and the results are shown in Table 1. Tack-free property was evaluated by touch evaluation of the degree of stickiness of the coating film surface immediately after removal from the dryer. In Table 1, ◎ means hard and not sticky, ○ means soft but not sticky, ○ to △ means slightly sticky, and × means sticky. Corrosion resistance was evaluated by a salt spray test, and ○ means that the rust width was 3 mm or less after 96 hours of salt spray. Water resistance is evaluated by evaluating the state of the paint film after immersing it in 40℃ warm water for a specified time. ◎ indicates no abnormality, ○ indicates whitening but no blisters, △ to ○ indicates slight blisters, and × to △ indicates blisters. The occurrence of 1/4 or less, × means the occurrence of blisters on the entire surface. Impact resistance was evaluated by Dupont impact test, ◎ passed 500g x 30cm, ○ passed 500g x 20cm,
△ means passing 500g x 10cm. Storage stability is determined by keeping the coating composition in a sealed container.
Evaluation was made based on the change in viscosity after storage at 45°C for 7 days. ◯ means no thickening, △ means slight thickening but still usable.

Table 1 shows that the coating films formed from the coating compositions of Examples 1 to 2 and Comparative Example 4 have improved tack-free properties and impact resistance compared to Comparative Examples 1 to 3. This is clearly an effect of blending a heat-curable resin mixture consisting of a short oil length alkyd resin and methylolmelamine. However, in Comparative Example 4, the tack-free property under low temperature drying conditions of 70°C is inferior to Examples 1 and 2. Therefore, it is clear that the addition of an acid catalyst improves the tack-free property at low temperatures. From the above, according to the coating compositions of Examples 1 and 2, in which a thermosetting resin mixture and an acid catalyst were further added to the oxidative polymerization type room temperature curing alkyd resin,
It is clear that tack-free properties and impact resistance can be significantly improved with almost no loss in corrosion resistance, water resistance, and storage stability compared to the case where only the room temperature curing alkyd resin is added and no acid catalyst is added.

Claims (1)

[Claims] 1. Cold-curing alkyd resin 100 that is modified with drying oil or semi-drying oil and can be cured at room temperature by oxidative polymerization.
A main resin consisting of at least one of a short oil length alkyd resin and an acrylic resin, and an amino resin crosslinkable with the main resin, so that the amount is 1 to 50 parts by weight based on 100 parts by weight of the main resin. A thermosetting resin mixture consisting of a curing agent mixed with
An alkyd resin coating composition comprising 150 parts by weight and 0.1 to 10 parts by weight of an acid catalyst.