JPH0354146B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to highly processable coating compositions suitable for precoated metal. Conventionally, light electrical appliances, building materials, and the like have been painted by forming unpainted metal plates using methods such as welding, and then painting them. However, such a post-coating method has a problem in that the coating process is complicated, and in the case of an object to be coated having a complicated shape, it is difficult to uniformly coat the entire surface. Therefore, plate-shaped or coil-shaped objects such as galvanized steel plates, cold-rolled steel plates, aluminum plates, and stainless steel plates are coated in advance and cut and processed when used.
It undergoes processing such as bending and squeezing.
The so-called pre-coated metal construction method is becoming widely adopted. However, there are still many unresolved problems with this pre-coated metal construction method.
For example, in order to improve the rust prevention properties of a cut surface of a material, the edges are bent and wrapped inside, or when a cylindrical product is made from a plate material, it is squeezed. Under severe conditions, such as when objects are bent at right angles, such as at the corners of objects, the paint film cannot follow the elongation and bending of the material, resulting in cracks in the paint film, exposure of the base, or peeling of the paint film from the material. As a result, defects such as a decrease in the antirust ability of the coating film and a loss of aesthetic appearance often occur. Therefore, there is currently a strong demand for a highly workable coating composition that can follow the elongation and bending of the material and is suitable for the precoat metal construction method due to the simplification of the coating process. The present invention was made in view of the above-mentioned current situation, and the present invention is capable of forming a coating film that not only has high processability but also has excellent physical and chemical properties such as weather resistance and solvent resistance. The object of the present invention is to provide a coating composition that can be obtained. That is, in the present invention, a main component consisting of a linear polyol resin having a hydroxyl value of 5 to 100 and a weight average molecular weight of 20,000 or more, and a curing agent component consisting of a blocked polyisocyanate resin having a weight average molecular weight of 1000 to 2000 are cured. The present invention relates to a highly workable coating composition for precoat metal, which is blended so that the equivalent ratio (NCO/OH) of the isocyanate group of the agent component to the hydroxyl group of the main component is (0.1 to 0.5/1.0). The present invention will be explained in detail below. The linear polyol resin as the main component used in the coating composition of the present invention has a molecular structure whose main chain is mainly linear, with short ester branches, aromatic rings, etc. emerging from the main chain. This includes those who are present. Specifically, polyester resins, acrylic resins, silicon resins, fluorine resins, etc. may be mentioned. These can be used alone or as a mixture of two or more. The linear polyol resin has a hydroxyl value of 5 to
100 (resin solid content) and a weight average molecular weight of 20,000 or more should be used. In the linear polyol resin, when the hydroxyl value is less than 5, the number of crosslinks with isocyanate groups in the coating film is too small, and the coating film does not have sufficient water resistance.
It is not preferable because it cannot impart solvent resistance and the number of polar groups remaining in the formed coating film decreases, resulting in insufficient adhesion to the material and deterioration of outdoor weather resistance. On the other hand, if the hydroxyl value exceeds 100, if all these hydroxyl groups are crosslinked with isocyanate groups, the number of crosslinks will be too large, resulting in a shortening of the molecular chain length between the crosslinks, which will be insufficient to withstand the stress during processing of the material. It becomes impossible to follow. However, in a linear polyol resin with a high number of hydroxyl groups, if only a small portion of the hydroxyl groups are crosslinked and the molecular chain length between the crosslinks is lengthened, elongation corresponding to stress can be expected. Since a large number of groups that are easily compatible with the paint remain, disadvantages such as the paint film being easily whitened by rainwater outdoors occur. In the present invention, the hydroxyl value of the linear polyol resin is particularly preferably 10 to 80. Further, the reason why the weight average molecular weight of the linear polyol resin used in the coating composition of the present invention is set to 20,000 or more is that the minimum value of the hydroxyl value, that is, the hydroxyl value 5
This is because the minimum weight average molecular weight for a compound to have at least two hydroxyl groups in one molecule on average is 22,400. In addition, the upper limit of the weight average molecular weight is preferably as high as possible as long as it does not interfere with painting workability such as ordinary knife coating or roll coating, but generally it is 15 to 20.
10,000, preferably 100,000 or less. As mentioned above, the linear polyol resin used in the present invention is not particularly limited other than that the hydroxyl value and weight average molecular weight are within specified ranges, but there are various performances such as weather resistance and solvent resistance of the coating film. From the viewpoint of the use of the material, the present invention particularly uses polyester resin,
Most preferred is one type or a mixture of two or more of acrylic resins, silicone resins, and fluorine resins. The linear polyol resin used in the present invention includes:
It is also possible to modify using linear or branched resins such as epoxy resins, alkyd resins, vinyl resins, amino resins, and phenol resins. On the other hand, the blocked polyisocyanate resin as a curing agent component used in the coating composition of the present invention includes, for example, hexamethylene diisocyanate,
Aliphatic or alicyclic diisocyanates such as tetramethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylene diisocyanate, hydrogenated xylylene diisocyanate, dimers, trimers, biuret structures thereof, or isocyanate compounds thereof The polyisocyanate compound obtained from the reaction product of an excess of ethylene glycol, glycerin, trimethylolpropane, pentaerythritol, etc. with a polyol such as ethylene glycol, glycerin, trimethylolpropane, pentaerythritol, etc., is treated with a blocking agent such as phenols, alcohols, oximes, lactams, amines, etc. A polyisocyanate resin whose isocyanate groups are blocked with a blocking agent such as an amide, and whose weight average molecular weight is 1,000 to 2,000. Note that some commercially available polyisocyanate resins have a molecular weight of 500 or less per isocyanate group, but in order to obtain polyisocyanate resins with higher molecular weights, including these, bifunctional polyol compounds or bifunctional polyisocyanate resins can be used. It can be made into a polymer by reacting with an amine or the like. As mentioned above, the purpose of the present invention is to obtain a coating film that has high processability and is also excellent in water resistance and chemical resistance by appropriately lengthening the molecular chain between crosslinks. The weight average molecular weight of the blocked polyisocyanate resin used is 1000.
~2000 are needed. Furthermore, in the coating composition of the present invention, the linear polyol resin and the blocked polyisocyanate resin as described above contain OH in the linear polyol resin.
group and in the blocked polyisocyanate resin.
Both must be blended so that the NCO group becomes NCO/OH=0.1 to 0.5/1.0. By setting the above specific range, it is possible to appropriately lengthen the molecular chain length between the crosslinks of the linear polyol resin and the blocked polyisocyanate resin, resulting in excellent processability and improved various performance characteristics. An excellent coating film can be obtained. In order to increase the processability of a coating film, it is considered necessary to increase the molecular structure in the coating film, especially the molecular weight between crosslinks, and to make the molecule itself flexible. This is because when external stress is applied to a paint film, the molecules in the resin are first stretched, but if there are no crosslinks between the molecules, each molecule slides unevenly, and only the areas where stress is concentrated are stretched. was torn,
Cracks occur in the appearance of the paint film. In order to prevent uneven sliding of only a portion of the molecules as described above, it seems necessary to crosslink the molecular chains so that the coating film as a whole is subjected to stress and stretches uniformly as a whole. However, when the number of crosslinks in the coating film is large, that is, when the molecular chain length between crosslinks is short, processability is significantly reduced. From this point of view, the above-mentioned NCO/
The OH ratio was established. By the way, an example of improving processability by increasing only the molecular weight of a resin is known, in which a non-crosslinked composition such as a vinyl chloride sol is applied onto a material. However, PVC sol has drawbacks such as stringiness during roll coating and low coating film gloss. On the other hand, when the composition of the present invention is dissolved in a solvent and applied, there is no difficulty in the application process, and since the composition is crosslinked and polymerized during coating film formation, it provides a coating film with excellent performance. can be formed. Coloring pigments, extender pigments, metal pigments, dyes, solvents, reaction catalysts, and various other additives used in ordinary coating compositions can be added to the coating composition of the present invention. The thus obtained coating composition of the present invention can be applied to various metals that require workability, or metals that have been subjected to appropriate surface treatment or primer coating, using a conventional coating machine such as a brush, roll coater, knife coater, or spray coating machine. Coat with a coating machine to a dry film thickness of about 5 to 50 μm, and apply at a temperature higher than the dissociation temperature of the blocking agent in the blocked isocyanate resin, usually 100 to 300°C.
By baking at a temperature of 0.5 to 40 minutes, a coating film with high workability and excellent physical and chemical properties is obtained. Hereinafter, the details of the present invention will be explained with reference to Examples.
"Part" or "%" indicates "part by weight" or "% by weight". First, prior to Examples, a linear polyol resin was manufactured as follows. Production example of linear polyol resin A mixture of the acrylic monomer and polymerization catalyst shown in Table 1 was placed in a dropping tank, and 50 parts of xylene and 51.5 parts of butyl acetate were placed in a reaction vessel at 78 to 80°C.
It was added dropwise over about 2 hours while stirring, polymerized, and then heated to 82℃.
After heating for 2 hours, the weight average molecular weight reached 21000.
~23000 and various resin solutions with non-volatile content of 50% were obtained.

【table】

[Table] Example 1 Blocked polyisocyanate resin solution [“Coronate DC2725” (trade name of Nippon Polyurethane Co., Ltd.),
Nonvolatile content: 80%, varnish NCO equivalent: 362, weight average molecular weight: approximately 1040] and the linear polyol resin solution (A
-G) were mixed in the proportions shown in Table 2. However, linear polyol resin solutions A, F, G and NCO/OH=
Cases of 0, 0.8, and 1.0 are outside the scope of the present invention. To 100 parts of the mixture of the linear polyol resin solution and blocked polyisocyanate resin solution, 0.2 parts of a dissociation catalyst for blocked isocyanate, 0.2 parts of a surface conditioner, and 0.6 parts of a silane coupling agent were added to form a paint, and then diluted with a solvent. The dry film thickness on stainless steel material (SUS#304-2D: plate thickness 0.5 mm)
It was applied to a thickness of 20μ. After drying by heating at 150°C for 30 minutes, it was subjected to various comparative performance tests. The results are shown in Tables 3-7.

【table】

【table】

【table】

【table】

【table】

[Table] ○: No abnormality △: Whitening or peeling of the paint film As is clear from the above results, the coating compositions of the present invention (polyol resins B, C, D, and E and sample No.
The coating films obtained from combinations 2 to 4) were excellent in processability and various physical and chemical properties. On the other hand, those using polyol resin with a hydroxyl value of less than 5 (A), those using polyol resin with a hydroxyl value of over 100 (F, G), and those using NCO/OH
Those with NCO/OH of less than 0.1 (Sample No. 1) and those with NCO/OH exceeding 0.5 (Samples No. 5 and 6) were tested for solvent resistance of the coating film.
In the bending test, pencil hardness test, impact deformation test, and corrosion resistance test, the performance was poor in any one of them, making it unsuitable as a paint for pre-coated metal. Example 2 A comparative test was conducted in the same manner as in Example 1, except that the blocked polyisocyanate resin solution was replaced with the following. Table 8 shows the paint formulation, and Tables 9 to 13 show the coating film performance. Indicated. <Preparation of blocked polyisocyanate resin solution> 27.94 parts of trimethylolpropane adduct type dimethylcyclohexane diisocyanate solution ["Takenate 120N" (trade name of Takeda Pharmaceutical Co., Ltd.), non-volatile content 75%] was reacted with 19.23 parts of methyl ethyl ketone. Add 4.25 parts of methyl ethyl ketone oxime and methyl ethyl ketone to a container and while stirring.
4.25 parts of the mixture was added dropwise, and 1
Allowed time to react. Furthermore, 0.001 part of a polymerization catalyst dissolved in 2.93 parts of methyl ethyl ketone was added to completely react the methyl ethyl ketone oxime. Next, a solution of 24.78 parts of polycaprolactone diol [PCP0240 (trade name of Chitsuso Chemical Industry Co., Ltd.)] dissolved in 16.52 parts of methyl ethyl ketone was added and reacted at a temperature of about 60°C to form a blocked polyisocyanate resin solution (weight average Molecular weight 1900, non-volatile content 50%,
NCO equivalent weight 2045) was prepared.

【table】

【table】

【table】

【table】

【table】

【table】

[Table] It is clear from the comparative test results that the coating composition of the present invention (polyol resins B, C, D and E and the sample
The coating films obtained from combinations No. 8 to 10 had high workability and excellent physical and chemical properties. On the other hand, those using a polyol resin with a hydroxyl value of less than 5 (A), those using a polyol resin with a hydroxyl value of over 100 (F, G), and those with an NCO/OH of 0.1
Those with NCO/OH of less than 0.5 (Sample No. 7) and those with NCO/OH exceeding 0.5 (Samples No. 11 and 12) were tested in the solvent resistance test, bending test, pencil hardness test, impact deformation test, and corrosion resistance test of the coating film. Its performance was poor and it was unsuitable as a paint for pre-coated metal. Example 3 Blocked polyisocyanate resin solution (same as Example 1), fluorine resin solution [Asahi Glass Co., Ltd.]
Product name Lumiflon: Non-volatile content 50%, hydroxyl value (solid content) 57, weight average molecular weight 70000], titanium white,
A coating composition was obtained by blending a surface conditioner, a curing catalyst, and a solvent as shown in Table 14. The coating composition was applied onto a chromate-treated aluminum material (1100H24: plate thickness 0.4 mm) using a knife coater to a dry film thickness of 20 μm, and then heated at 240°C for 1 hour.
It was baked for a minute and then subjected to a comparative test. The result is
15 as shown in Table 15.

【table】

【table】

[Table] From the above comparative test results, it is clear that the coating composition of the present invention exhibited very excellent coating film properties. On the other hand, NCO/OH is less than 0.1 (sample No. 13)
The solvent resistance and corrosion resistance of the coating film are poor, and
When NCO/OH exceeded 0.5, the processability of the coating film was poor.

Claims (1)

[Scope of Claims] 1. A main component consisting of a linear polyol resin having a hydroxyl value of 5 to 100 and a weight average molecular weight of 20,000 or more, and a curing agent component consisting of a blocked polyisocyanate resin having a weight average molecular weight of 1000 to 2000, A highly workable coating composition for precoated metal, which is blended so that the equivalent ratio (NCO/OH) of isocyanate groups in a curing agent component to hydroxyl groups in a main component is (0.1 to 0.5/1.0). 2 The linear polyol resin is a polyester resin,
The highly workable coating composition for precoated metal according to claim 1, which is an acrylic resin, a silicon resin, a fluorine resin, or a mixture of two or more thereof.